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Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
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2
Development of Vehicle Subsystems

CANDIDATE SYSTEMS

The ultimate success of the PNGV program will be measured by its ability to integrate R&D programs that collectively improve the fuel efficiency of automobiles within the very stringent boundary conditions of size, reliability, durability, safety, and affordability of today's cars. At the same time, the vehicles must meet even more stringent emission and recycling levels and must use components that can be mass produced and maintained in a manner similar to current automotive products.

In order to achieve a Goal 3 fuel economy that approaches the 80 mpg target (80 mpg is about three times the fuel efficiency of today's comparable vehicles), the energy conversion efficiency of the chemical conversion system (e.g., a power plant, such as a CIDI engine, a gas turbine, a Stirling engine, or a fuel cell) averaged over a driving cycle will have to be at least 40 percent, approximately double today's efficiency. This is an extremely challenging goal and will require assessing many possible concepts for improving efficiency. For example, the PNGV high fuel economy level of 80 mpg will require the integration of the primary power plant with energy storage devices, as well as the use of lightweight materials for the vehicle structure to reduce vehicle weight.

Despite concerted efforts in the last year to develop and evaluate the various candidate systems, none of the energy conversion power trains being considered meets all of the constraints. Therefore, R&D programs on both the selected and nonselected candidate systems have to be continued after the 1997 technology selection for the first concept vehicles, with the objective of attaining the breakthroughs that would make one or more of the technologies viable for meeting Goal 3 requirements. In 1997, the PNGV identified a stretch research objective of

Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
×

0.01 g/mile for emissions of particulate matter for the CIDI engine. The current target is 0.04 g/mile. Meeting the stretch research objective presents new challenges to the candidate CIDI engine, which would require expanded technology development to meet the PNGV goals. PNGV would also need to reevaluate other power plants relative to CIDI engines.

The hybrid electric vehicle (HEV), which is the PNGV power train of choice, uses an energy storage device to decrease the fluctuations in the demands on the primary power plant. This reduction allows for a decrease in the peak power output required from the primary energy conversion system and an opportunity to improve efficiency both by restricting the power fluctuations and by recovering a significant fraction of the vehicle's kinetic energy during braking operations. The PNGV is sponsoring research on batteries, flywheels, and ultracapacitors as energy storage devices.

Achieving the high fuel economy levels for the Goal 3 vehicle will require more than improving the energy conversion efficiency of the power train (including energy converters and transmissions) and reducing other energy losses in the vehicle. Vehicle weight reduction through the use of new vehicle designs and lightweight materials will be extremely important in achieving the very ambitious fuel economy targets.

The committee re-evaluated the candidate energy conversion and energy storage technologies, as well as candidate electrical and electronic systems, that were considered last year and addresses them in this chapter. This chapter also reviews progress on advanced structural materials for the vehicle body, a subject that was not addressed by the committee in its third review. The technologies evaluated in this chapter are listed below:

  • four-stroke CIDI engines

  • continuous combustion systems

  • fuel cells

  • electrochemical storage systems

  • electro-mechanical storage systems

  • electrical and electronic power-conversion devices

  • materials

The committee reviewed R&D programs on each of these technologies to assess the progress that has been made and the developments required for the future. The PNGV Technical Roadmap, which has been updated for most of these technologies, provided a good summary of the program goals (PNGV, 1997). In the committee's opinion, the PNGV has made substantial progress in assessing the potential of most candidate systems and identifying critical technologies that must be addressed to make each system viable. A few exceptions are noted in the sections describing specific technologies.

The committee has also described some international developments in the various technology areas, based both on its own knowledge and experience and

Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
×

on selected information gathering activities, but an extensive review of worldwide developments was not part of its task. Nevertheless, the issue of global competitiveness of the U.S. automotive industry is a key consideration in the development of advanced automotive technologies.

INTERNAL COMBUSTION RECIPROCATING ENGINES

The research team on the four-stroke direct injection (4SDI) engine has evaluated four engine configurations as candidate power plants: the CIDI engine, the homogeneous charge compression ignition engine, the gasoline direct injection (GDI) engine, and the homogeneous charge spark ignition engine. The PNGV has indicated that at this time the CIDI engine has the potential for the highest fuel conversion efficiency. Furthermore, because of the increased penetration of automotive diesel engines into the European market and a technical and manufacturing maturity that falls within the PNGV program schedule, there is a high level of confidence in the assessments of future improvements in CIDI engine performance.

In addition to better fuel economy, the performance of the CIDI engine is superior to other engine types in terms of evaporative, cold start, and hydrocarbon and carbon monoxide (CO) emissions. However, there are still significant challenges facing the development of CIDI engines that can meet the PNGV targets. The challenges include reducing the emissions of nitrogen oxides (NOx) and particulates, reducing the weight of the power plant, and reducing costs.

The CIDI engine is being considered as a possible stand-alone power plant, as well as part of either a series or parallel HEV. The trade-off of fuel economy and weight involved in adding energy conversion devices with a hybrid vehicle design must be carefully evaluated because an increase in vehicle weight results in a decrease in fuel economy.

Program Status and Progress

The 4SDI team was very active this past year. A five-year comprehensive plan was developed, and the technical developments required for each component of a CIDI engine for a PNGV vehicle were identified. Technologies that would enable an advanced CIDI engine to meet Goal 3 objectives would include four valves per cylinder; a common rail, electronically controlled fuel injection system; a variable-geometry turbocharger; exhaust-gas after-treatment for NOx and particulates; electric actuators; and an aluminum block. It would be fueled with a very low-sulfur diesel or alternative fuel. This engine would be significantly different from current diesel engines, which typically have two valves per cylinder; rotary pump fuel injection systems; fixed-geometry turbochargers; oxidation catalysts in the exhaust; pneumatic actuators; cast-iron structures; and use conventional diesel fuel. Technical developments are expected to reduce NOx

Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
×

and particulate emissions; reduce noise vibration and harshness (NVH); improve power density; and improve fuel economy.

Last year, the 4SDI team identified five high-priority areas for research: lightweight engine architectures; dimethyl ether (DME) as an alternative fuel for CIDI engines; combustion-related processes; lean NOx catalysis; and alternative fuels for CIDI engines. The 4SDI team has been active in all five areas in the last year.

Lightweight engine structures are being investigated to reduce vehicle weight. Ford, for example, is testing the DIATA (direct-injection, aluminum-block, through-bolt assembly) engine, a 1.2-liter displacement engine designed to produce 45 kW/l. The design is a lightweight engine that achieves state of the art NVH.

Under a contract with the U.S. Department of Defense Tank Automotive Command, Ricardo, Inc., has developed a preliminary design for an all new, three-cylinder, lightweight, high speed, direct injection engine. The main objective of this program was to establish an engine architecture compatible with lightweight materials. The key challenge is placing the lightweight materials under compression, and through-bolt assembly was considered the most promising way to accomplish this. Key aspects of this engine architecture are expected to be used in the Chrysler-U.S. Department of Energy HEV program.

One of the critical challenges to the CIDI engine is the so-called trade-off between emissions of soot (particulates) and NOx. In current diesel engines, methods used to reduce NOx (typically increased exhaust-gas recirculation and retarded injection timing) result in increased soot emissions and vise versa. It is usual to display the diesel emission characteristics on a graph of soot versus NOx. Obtaining a net benefit in emissions requires decreasing overall emissions toward the origin of the operating curve, rather than along the soot-NO x trade-off curve. The CIDI engine technology under development is targeted to achieve a 0.04 g/mile particulate emissions level or better by (1) limiting the application of engine controls that reduce NOx (e.g., exhaust gas recirculation) in order to minimize energy-out particulate emissions and (2) lowering NOx emissions to target levels using catalytic after-treatment. There is some leeway in implementing in-cylinder NOx reduction strategies, at the expense of increasing particulate emissions, while still meeting the total emission design target. Meeting the stretch research objective of 0.01 g/mile particulate emissions will require simultaneous reductions of soot and NOx and cannot be met by manipulating the soot-NOx trade-off relationship. Therefore, breakthrough improvements in engine controls to reduce emissions and for exhaust-gas after-treatment for both NOx and particulates will be required, as well as significant changes in fuels.

The research objective for particulate emissions, therefore, will require fundamental investigations of the in-cylinder combustion process with the objective of altering the interaction between soot and NOx emissions. To this end, PNGV has begun research on combustion fundamentals, such as combustion control through electronic control of the fuel-injection process and assessing the interaction

Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
×

between the combustion chamber geometry, the fuel injection, and fuel-air mixing. Ford and FEV have also been pursuing new technologies in fuel injection rate-shaping using piezoelectric techniques.

Many collaborative programs have been put in place in the past year. The 4SDI technical team participated in Vice President Gore's Technical Symposium Number 6 on 4SDI engines, which consisted of five sessions held over two days in the summer of 1997. The PNGV has established a Fuels Working Group and an Aftertreatment Working Group to develop PNGV strategy and plans. Cross-cutting teams were established to promote interchanges between the light-duty CIDI engine researchers and the heavy-duty diesel engine industry. For example, Chrysler is working cooperatively with Detroit Diesel Corporation to integrate a three-cylinder, 1.5-liter displacement, direct-injection, turbocharged, intercooled engine with hot and cold exhaust gas recirculation into an HEV. A DME fuel system has been designed and a follow-on program established.

Efforts to develop combustion systems are being augmented by experimental work at Sandia National Laboratories (SNL) and Wayne State University with computational support from the University of Wisconsin, Madison. SNL, Oak Ridge National Laboratory (ORNL), and Los Alamos National Laboratory (LANL) are pursuing improved lean NOx catalysts, and Pacific Northwest National Laboratory (PNL) and Lawrence Livermore National Laboratory (LLNL) are investigating plasma-assisted NOx reduction catalysis. A reformulated diesel fuel testing program is under way at EPA, and a USCAR-supported auto/energy fuel testing plan is being developed.

Technical Targets

The critical characteristics of a CIDI engine that can meet the PNGV performance targets are shown as a function of milestone targets in Table 2-1. All of the USCAR partners have made good progress towards meeting these targets.

A comprehensive evaluation of the Chrysler Generation I 1.46-liter, three-cylinder engine has revealed general conformance with the 1997 targets with respect to part load brake thermal efficiency, exhaust emissions of NOx and particulates, based on a 14-mode test protocol. The one-meter noise assessment is in conformance with the 1997 target. Peak thermal efficiency is 2.5 percentage points below the 1997 target; however, improvements are expected in both the Generation I and II versions. Both displacement and weight-specific power are below target for 1997 by 5 and 13 percent, respectively. The latter shortfalls will be addressed by the Generation II design, which will incorporate more lightweight materials than the Generation I version. Mount vibration measurements have not yet been made.

Initial engine dynamometer tests have been made on the Ford Research 1.2-liter, four-cylinder engine. Displacement-specific power and engine noise results compare favorably to the 1997 PNGV targets. The part-load thermal

Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
×

TABLE 2-1 Critical Characteristics of the CIDI Engine vs. PNGV Milestone Targets

 

 

1995

1997

2000

2004

Characteristic

Units

Target

Target

Target

Target

Best brake thermal efficiency

%

41.5

43

44

45

Displacement specific power

kW/L

35

40

42

45

Power specific weight

kW/kg

0.50

0.53

0.59

0.63

Cost per kW

$/kW

30

30

30

30

Durability

1,000 miles

150

150

150

150

NVH (one meter noise)

dBA

100

97

94

90

Engine-out NOx emissionsa

g/kW-hr

3.4

2.7

2.0

1.4

Engine-out particulatesa

g/kW-hr

0.3

0.25

0.20

0.15

FTP 75 NOx emissions in 2,500 lb ETW vehicle

g/mile

0.6

0.4

0.3

0.2

FTP 75 particulate emissions in 2,500 lb ETW vehicle

g/mile

0.08

0.06

0.04

0.04b

Source: Based on Table III. F-1 in PNGV (1997).

Acronyms: NVH = noise, vibration, and harshness; FTP = federal test procedure; ETW = emissions test weight.

aRepresentative values for operation over the FTP cycle

bIn 1997, PNGV identified a stretch research objective for particulate emissions of 0.01 g/mile.

efficiency and emissions levels are very calibration-specific and are under development, making comparisons with existing engines difficult. Peak thermal efficiency is below the 1997 target but is also under development. The weight-specific power and package volume PNGV targets were established assuming a three-cylinder engine. This four-cylinder engine is still below the weight-specific power targets and the package volume targets.

Based on testing of GM's single-cylinder CIDI research engine, projected emissions data meet the 1997 PNGV targets. Other targets cannot be assessed from tests on a single-cylinder engine.

Because of the soot-NOx trade-off inherent in CIDI engines, the more restrictive research objective for particulate emissions would alter the basis on which the CIDI engine has been evaluated as a potential PNGV power plant. To achieve the stretch objective, technological breakthroughs will be necessary for the CIDI engine to meet the PNGV milestones. A consequence of the more ambitious 0.01 g/mile research objective for particulate emissions is that fuel characteristics are now more important for meeting the PNGV goals. For example, the 0.01 g/mile particulate research objective corresponds to an emission of sulfates for a fuel with approximately 50 ppm of sulfur and a vehicle with a fuel economy of 80 mpg. Therefore, at a minimum, sulfur levels in the fuel will have to be drastically reduced from the current limit of approximately 500 ppm to about 50 ppm.

Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
×

The stretch objective would make the CIDI engine a high-risk candidate for meeting the PNGV goals.

Meeting the stretch research objective for particulate emissions increases the overall challenge of meeting the exhaust emission standards. Reducing NOx emissions is still one of the biggest challenges for the CIDI engine. Engine-out emissions appear to be 0.5 g/mile or greater, whereas the current emission target is the Tier 2 federal NOx limit of 0.2 g/mile. Meeting these limits will require after-treatment of NOx, with a NOx conversion efficiency of 60 to 90 percent. Demonstrated after-treatment efficiencies are currently less than 40 percent, and many technologies under development require near sulfur-free fuel. Clearly, a high-efficiency, sulfur-tolerant after-treatment device for NOx must be developed for the CIDI engine to be a viable option.

In addition to the higher priority of fuels technology, which should include investigating alternative fuels, such as DME and Fischer-Tropsch diesel fuel, the development of exhaust-gas after-treatment technologies must also be expanded to include methods for reducing particulate emissions.

Current Program Elements

Advances in engine combustion, exhaust-gas after-treatment and fuels technology will be necessary to meet the stringent PNGV emission requirements. The current program includes work on some aspects of all three of these technologies.

High-Pressure Fuel Injection Systems and Combustion Fundamentals

Significant advancements in combustion control will be necessary to meet the low emission targets without sacrificing fuel economy. The in-house research programs of all the USCAR partners on the fundamentals of combustion and emissions formation are being augmented by work at the national laboratories and universities.

The use of electronically controlled, high-pressure fuel injection systems as a means of combustion control is being investigated by the heavy-duty diesel engine industry. Next-generation electronic fuel injectors may allow for dynamic rate-of-injection profiling, in addition to multiple injections per cycle. NOx, particulates, and fuel economy can be significantly affected in heavy-duty diesel engines by manipulating fuel injection. The extent to which these advanced technologies can be used to improve combustion in small CIDI engines, such as those that would be used in a PNGV concept car, is not known. The smaller CIDI engine will be operating at a higher speed than the typical heavy-duty diesel engine, the quantity of fuel injected will be smaller, and the combustion chamber will be smaller, so that surfaces will be closer together and fuel jets from the injectors will impinge on those surfaces; the injector holes, however, will be approximately the same size. As a consequence, the smaller high-speed CIDI

Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
×

engines have a shorter injection duration and less time available for mixing, so that controlling combustion through injection manipulation is uncertain. This is a serious technical challenge for the 4SDI team. Interaction between the PNGV and the heavy-duty diesel engine industry via the crosscutting team is an appropriate way for PNGV to address this issue.

Exhaust-Gas After-treatment

Exhaust-gas after-treatment represents one of the most challenging aspects of the 4SDI program. The treatment of exhaust gas, both of NOx and of particulates, will be required to meet the program goals. Cooperative programs with Argonne National Laboratory (ANL), SNL, LANL, LLNL, ORNL, and PNL are already established. Both lean-NOx catalysis and plasma-assisted after-treatment approaches are being investigated. Yet progress in this area has been slow. In addition, the performance of those technologies at the present state of development is adversely affected by sulfur in the fuel. The best ''full brick" catalyst1 with diesel engine exhaust, with diesel fuel added as a reductant, reduces NOx by up to 37 percent at steady state over a narrow temperature range. Other reductants provide a higher efficiency but would require an auxiliary source of reductants onboard the vehicle. The fuel economy penalty of using a reductant is approximately 1 percent.

Plasma-assisted catalysis, a process in which an electrical potential difference generates nitrogen ions that combine with NO to form molecular nitrogen and atomic oxygen, shows promise of reducing both NOx and particulate emissions. The current state of the art of plasma exhaust treatment technology requires that a catalyst also be used to maximize the reduction of the NOx emissions. The results of early laboratory tests have been encouraging, but the technology must still be demonstrated on an engine. Estimates of the fuel economy penalty for plasma systems are in the range of 2 to 5 percent.

Particulate and NOx traps are also being considered. Issues of cost, durability, and regeneration capacity remain for particulate traps, and the engine control systems for momentary fuel enrichment to release the NOx from the trap and subsequent catalytic reduction are complex challenges that must still be met.

Despite the challenges, the emphasis on exhaust-gas after-treatment of NOx and particulate matter will continue. Breakthroughs will be necessary for the development of a sulfur-tolerant, long-life, effective, passive NOx removal device. In September 1997, PNGV representatives met with four major catalyst suppliers to discuss cooperative development.

1  

In the vast majority of laboratory catalyst tests, the catalyst is in the form of a powder. However, in current commercial catalytic converters, most of the catalysts are in the form of a coating on a monolithic structure. "Full brick" means that the catalyst test was conducted with a monolithic structure.

Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
×
Fuels Technology

The relationship between the physical and chemical characteristics of a fuel and the emissions from an engine is the basis for government regulations on fuel properties. In diesel fuel, for example, the cetane number, aromatic content, and sulfur levels are all subject to regulation. However, the relationships between the chemical characteristics of a fuel and its physical properties, such as viscosity, lubricity, and cetane number, are extremely complex. For example, the cetane number of a fuel can be increased either by decreasing the aromatic content in favor of longer-chain paraffins or by adding cetane improvers. Both fuels will have similar overall combustion and emissions characteristics as assessed by today's metrics. In an engine designed to meet PNGV goals, slight differences in the composition and properties of fuels may also have a significant effect on the performance of after-treatment devices, such as NOx catalysts.

Fuels containing oxygen generally produce less soot, which might be a basis for reducing emissions. However, the incremental costs and the effects on the infrastructure of this change in fuel composition have to be considered. Certain components in fuel, such as sulfur, can affect both combustion and exhaust-gas after-treatment systems. Sulfur in the fuel can contribute to soot emissions by forming sulfates; sulfur can also deactivate the exhaust catalyst.

Indeed the PNGV recognizes the importance of the interactions between fuel and engine performance and is involved in programs to reduce emissions through fuel changes. These programs are all based on the target of 0.04 g/mile for particulate emissions. The stretch research objective of 0.01 g/mile requires PNGV to change its research goals accordingly and concentrate on alternative fuels. PNGV should establish a cooperative program with the U.S. transportation fuels industry (see Chapter 5).

The PNGV already has some programs in place to evaluate alternative fuels. Under a contract issued in cooperation with the of U.S. Department of Defense Tank Automotive Command, AVL List GmbH conducted an assessment of DME as an alternative fuel for diesel engines, and DME is a candidate for further investigation. Because the physical characteristics of DME are much like those of propane, significant infrastructure changes would have to be made if DME were chosen. EPA is also evaluating reformulated and alternative fuels. The committee believes that all of these programs should be continued and that all alternative fuels should be investigated.

However, it appears that none of the operating regimes for any of the candidate engines will meet the design targets with the research objective (0.01 g/mile) for particulate emissions. Therefore, the potential for altering the soot-NOx trade-off by manipulating the fuel formulation and the subsequent impact of fuel composition on exhaust-gas after-treatment devices is a critical issue for the 4SDI program, which must now investigate the engine and fuel as an integrated system. The fuels industry should be involved in this important area of development and

Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
×

research, just as it is in the European Auto Oil program and the Japan Clean Air Program (see Chapter 5 and Jones, 1997).

International Developments

Automotive Diesel Engines

The small direct-injection diesel engine is widely used in automobiles in Europe. Currently about half of all new cars sold in Europe are diesel powered, and it is estimated that as much as 30 percent of the entire fleet could be diesel powered by the year 2000. This market shift is being motivated by a combination of tax policies favoring the use of diesel fuel over gasoline, the high cost of fuel, and the consequent consumer demand for fuel-efficient vehicles. Diesel-powered automobiles are not as prevalent in Japan as they are in Europe, but they have a higher market penetration than in the United States, where less than 1 percent of the automobiles are diesel powered. Because there is little market demand for automotive diesel engines in the United States, domestic industries have little incentive to pursue critical technologies in this area. Therefore, it is not surprising that technical leadership in the critical areas of fuel injection and electronic control is outside the United States. The world leaders in automotive diesel engine injection and control technologies are probably Bosch (in Germany), Denso (in Japan), and Lucas CAV (in the United Kingdom). However, some important work is being done in the United States by Caterpillar and Navistar on automotive applications of electronically controlled, common rail, hydraulically amplified injection systems.

The partners in PNGV are well aware of the advancing state of the art in automotive diesel engines. In fact, through their foreign affiliates, they are participating in the development of these engines. GM has developed the Ecotec engine, and Ford has developed the DIATA engine in their respective European operations. Chrysler is involved in developing a state-of-the-art automotive-size diesel engine through working agreements with both a domestic and an international company. Although the United States cannot claim technical leadership in the general area of automotive-size diesel engines, the PNGV is well aware of the current state of the art and directions in development of this power plant. The USCAR partners are fully capable of utilizing this technology worldwide through their foreign affiliates and international agreements.

Gasoline Direct Injection Engines

In Japan, Mitsubishi, Toyota, and Nissan have introduced GDI engines to their domestic markets, claiming fuel efficiency improvements of 20 to 30 percent over the conventional spark-ignition engine vehicles. The PNGV partners have been following developments closely but have concluded that GDI engines

Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
×

would have a lower fuel conversion efficiency than CIDI engines and, like CIDI engines, they would not meet the U.S. emission standards (see Appendix B).2 The belief that the maximum fuel economy of the GDI engine would be less than that of a CIDI engine was reported to the committee during the Phase 3 review by Dr. Peter Herzog of AVL (Herzog, 1996). Hence, the GDI spark-ignition engine was not listed as a candidate power plant for the PNGV concept vehicles.

As part of the Phase 4 review, Dr. Ando of Mitsubishi Motors presented impressive results of recent developments on their GDI engines (Ando, 1997 a,b; Iwamoto et al., 1997; Kume et al., 1996). Mitsubishi claims that significant improvements have been made in the total performance of the engine by changing the intake manifold design, altering the in-cylinder flow pattern, maximizing the distance between the fuel injector and the spark plug, carefully matching the fuel injector characteristics to the cylinder flow at different loads, and taking full advantage of the capabilities of advanced electronic controls. At this time Mitsubishi Motors believes the new design of the GDI engines will be able to meet the stringent European and U.S. low-emission vehicle (LEV) standards with fuel conversion efficiencies within 1 percent of CIDI engines. Mitsubishi estimates that by the year 2000 85 percent of the engines they produce will be GDI engines.

The advancements of the GDI engine claimed by Mitsubishi represent technical strides for this power plant. If these claims of improved performance can be realized, the GDI engine would be a viable competitor to the CIDI engine. However, even if the GDI engine meets the LEV standards at a fuel conversion efficiency within 1 percent of the CIDI engine, it is not known if it will meet the PNGV emission targets, which are the ultra low emission vehicle (ULEV) standards. The PNGV partners are aware of the GDI programs in Japan and are assessing the potential of the GDI as a power plant for a PNGV vehicle. The committee feels that this assessment should continue.

Assessment of the Program

Excellent progress has been made in the past year in all aspects of the 4SDI program. However, the identification of a stretch research objective for particulate emissions of 0.01 g/mile presents significant additional challenges to the 4SDI program in developing the CIDI engine as a PNGV power plant. The prospect of developing a CIDI engine that can meet this research objective is high risk and would make a reevaluation of other candidate engines and system configurations necessary. To maximize the probability of success, the 4SDI program may have to be augmented and redirected. The 4SDI team must determine if the new stretch research objective can be met by operating the engine in previously

2  

This view is detailed in Figure III.F-1 of the 1997 update of the PNGV Technical Roadmap (PNGV, 1997).

Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
×

unattainable regimes or through new fuel formulations or alternative fuels. Cooperative programs with the transportation fuels industry would be a logical way to address this new challenge.

Recommendations

Recommendation. The PNGV should devote considerably more effort and resources to exhaust-gas after-treatment of NOx and particulates. PNGV should consider greatly expanding its efforts to involve catalyst manufacturers.

Recommendation. A broad cooperative effort between the PNGV and the transportation fuels industry should be established to assess the potential for enhancing the performance of CIDI engines through fuel reformulation or alternative fuels. The PNGV should also assess the effects of fuel changes on the fuel production and distribution infrastructure.

Recommendation. In light of the published improvements in gasoline direct-injection engines, it would be prudent for the PNGV partners to continue to assess developments in this technology against PNGV targets and the CIDI engine, whether or not the gasoline direct-injection engine is chosen as a potential PNGV power plant.

CONTINUOUS COMBUSTION ENGINES

As the committee anticipated, continuous combustion engines—gas turbines and Stirling cycle engines—have not reached a state of development suitable for use in the year 2000 concept vehicles. Therefore, they now fall into the category of post-PNGV technology development. The committee concurs with this PNGV decision. However, continuous combustion, which can be controlled more easily than intermittent combustion, may require reevaluation if continuous combustion engines can be shown to meet the 0.01 g/mile stretch research objective more easily than internal combustion reciprocating engines.

Gas Turbines

The requirements established by the PNGV for an automotive gas turbine (AGT) engine in a series hybrid vehicle include a power level of approximately 50 kW, a thermal efficiency of 40 percent, a factory cost of $1,500 ($30/kW), and a weight of 60 kg (0.8 kW/kg). Because no candidate AGT engines approach the thermal efficiency goal, and in light of progress made with other candidate power plants, the PNGV has dropped the gas turbine engine from its list of promising technologies in 1997. As a consequence, the committee understands that the U.S. Department of Energy (DOE) will reduce support for research on AGT engines in fiscal years 1998 and 1999.

Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
×
Program Status and Progress

The development of AGT engines has been supported by the government and private sector since the 1950s. To achieve high thermal efficiency and the necessary high operating temperatures, a number of development programs have focused on ceramic AGTs. Programs funded, or partly funded, by the DOE to develop ceramic AGTs have been conducted primarily by GM/Allison and Allied Signal with major contributions by ceramic suppliers. In the past decade, progress has been made toward achieving the desired properties and quality of the ceramic materials. Improvements have also been made in critical technologies associated with air bearings, low-emission ceramic combustors,3 ceramic rotary regenerators/ low-leakage seals, ceramic axial and radial turbine rotors, ceramic stator/static structures, and insulation systems. By the end of 1996, component tests had been run on ceramic turbine rotors, combustors, and regenerators, but no fully integrated AGT engine with high performance had been demonstrated, and the long-term reliability of the ceramic components had not been proven.

AlliedSignal has focused on placing ceramic stator vanes into existing products—notably airborne auxiliary power units and military ground carts—and has undertaken the task of bringing a new material system into production in these applications. Allison has continued its efforts to demonstrate operation at turbine temperatures of 1,370°C (2,500°F) on turbine stages that can withstand abusive operating cycles and impacts by foreign objects. In 1997, the DOE-sponsored programs were reduced in scope and now emphasize only the development of ceramic components. No new DOE-sponsored automotive ceramic AGT program contracts are planned after 1997. Phaseouts of existing contracts will continue into fiscal year 1998 and possibly fiscal year 1999. Development of gas turbines for stationary power applications will continue in other DOE programs.

Although most AGT development programs had been focused on free turbine, prime propulsion engines, in the past few years interest has shifted to turbogenerator use in HEVs. Metal turbogenerators have been purchased by the auto companies for use in the DOE HEV programs and other hybrid demonstrations, including a 30-kW engine designed by Capstone Turbines, a 60-kW engine designed by AlliedSignal, and a 40-kW engine designed by Williams Research. With a best thermal efficiency potential of only about 32 percent, these engines have provided useful HEV demonstrations, but no production program is expected. With the metal AGT as an energy converter, there is no real potential for achieving the PNGV fuel economy target of 80 mpg.

Programs to develop ceramic turbogenerators were briefly initiated with Allison (under GM's HEV Program) and Teledyne (under contract to Ford), but

3  

Two main approaches to ceramic combustors are the rich/quench/lean combustor, which is designed to avoid stoichiometric fuel-air conditions and associated temperatures to reduce the formation of NOx, and the catalytic combustor, which uses catalysts to promote combustion at reduced temperatures and consequently reduce the formation of Nox.

Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
×

both were canceled before they could produce meaningful results. Thus, no serious future effort or investment is being planned in the United States to produce an AGT that can meet the PNGV targets. Gas turbine manufacturers have indicated that they could develop small turbogenerators approaching 40 percent efficiency, but development is unlikely because the estimated development cost is about $75 million. Even with this expenditure, there would be substantial technical risk with regard to the cost and durability of ceramic components, as well as uncertainty about the market.

Cost Issues

Informal discussions between committee members and gas turbine experts indicated that small (50-kW class) AGTs could be manufactured in large quantities at a factory cost of around the target value of $1,500; however, the committee did not verify this claim. The greatest uncertainty pertains to the cost of ceramic components, which are based on low-cost raw materials and do not have the high costs of superalloys but are unproven in terms of net shape process yields, forming, and inspection costs. Because the gas turbine is radically different from the current reciprocating engines, massive infrastructure costs would be entailed—both in manufacturing plants and in maintenance training and facilities—if gas turbines were to be adopted into production automobiles.

International Developments

In 1997, Japanese programs reportedly demonstrated ceramic turbo-generators, one of which was directed toward automotive use and demonstrated 32.3 percent thermal efficiency at 92 kW (Nakazawa et al., 1997). A second, which was directed toward industrial and truck/bus applications, demonstrated 37 percent thermal efficiency at 240 kW (Nakazawa et al., 1997). Both engines were operated for more than 100 hours with ceramic components, including regenerators, combustors, turbine rotors, and static structure.

Assessment of the Program

Program Direction. If internal combustion engines can ultimately achieve close to 45 percent thermal efficiency and can economically meet the stringent emission regulations, or if fuel cells using gasoline reformate can be developed with similar efficiencies and lower or equal system costs, then the development of ceramic gas turbines by PNGV should be terminated. If not, the AGT, which has low emissions, 4 the potential to provide a thermal efficiency approaching

4  

NOx problems become worse at higher temperatures. At the temperatures necessary to achieve high efficiencies in gas turbines, NOx generation could be a significant problem.

Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
×

40 percent, and small size and weight, should be re-evaluated. Considering the risks inherent in developing a CIDI engine or a fuel cell that can meet all requirements, it may be premature to eliminate all PNGV-sponsored AGT technology development.

Ceramic Components. In spite of significant progress and successful production and durability testing of individual ceramic components, they have not been demonstrated to the point of acceptable risk for the development of a ceramic gas turbine for automotive application.

Recommendation

Recommendation. In view of the stringent emissions targets, the PNGV and DOE should continue to support the development of ceramic component manufacturing and durability demonstrations on a limited basis.

Stirling Engines

Although the Stirling-cycle engine has not been within the scope of the PNGV/USCAR joint activities, GM has a program to install a 30-kW engine in a series hybrid vehicle as part of DOE's HEV program. The engine technology is proprietary to Stirling Thermal Motors of Ann Arbor, Michigan. It is believed that a thermal efficiency of about 30 percent has been achieved by this automotive power plant and that many technical problems have been overcome. One exception may be the long-term containment and retention of the hydrogen working fluid used in this closed-cycle engine. Emission levels and other performance data have not been published.

GM has projected a potential for 36 percent thermal efficiency for the Stirling-cycle engine, which would fall somewhat short of the performance projections for other energy converters. Most observers believe that the continuous flow, external combustor has the potential for excellent emission levels, a principal advantage of the Stirling engine; however, the large size and complexity of this engine, which imply higher cost, are considered competitive disadvantages. The current demonstration under DOE's HEV contract has essentially been concluded.

Recommendation

Recommendation. The PNGV should continue to monitor the nonautomotive development of Stirling-cycle engines but should consider further development only if warranted by NOx and particulate emissions considerations.

Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
×

FUEL CELLS

Of all of the technologies being considered in the PNGV program to convert fuel energy into useful power, fuel cells still offer the best long-term potential for high efficiency and low emissions.5 A fuel-cell vehicle does not have to be a hybrid system if gaseous hydrogen is the fuel. However, most liquid hydrocarbon-fueled fuel cell systems are hybrid systems because they have faster startups (initial driving can be powered by a battery), better transient operation (a battery can be used to augment fuel cell power during rapid demand changes), and regenerative energy recovery. All of the PNGV fuel cell systems presented to the committee thus far have been hybrid systems. However, in spite of considerable, even impressive, progress, fuel cells still face substantial obstacles to reaching performance and cost goals in the PNGV 2000 to 2004 time frame.

It has become very clear that the development of a successful automotive fuel-cell system is intimately connected to the choice of fuel. Hydrogen, which combines electrochemically with oxygen to produce electric energy, namely, an electrical current and a potential (voltage), is the only part of the fuel that is utilized in the fuel-cell stack. However, pure hydrogen, which is an excellent fuel for fuel cells, is much more difficult to store onboard a vehicle than liquid hydrogen-containing hydrocarbon fuels. Vehicle studies have shown that it is very difficult to store enough compressed hydrogen gas on board a PNGV-type vehicle to travel more than 100 miles. Furthermore, even this range requires high pressures (3,000 to 6,000 psi) with correspondingly heavy (and expensive) storage tanks and the energy losses associated with compressing hydrogen. Transportation of hydrogen fuel from production plants is also expensive, and present projections show unit energy costs to be several times those of petroleum-based fuels. Furthermore, there is virtually no infrastructure for making hydrogen gas available to consumers. Thus, until onboard storage, unit energy costs, and infrastructure problems are resolved, gaseous hydrogen fuel will probably be practical only for certain commercial and vehicle fleets.

Most of the performance obstacles and many of the cost hurdles of fuel-cell systems are associated with the necessity of storing and using liquid hydrocarbon fuel onboard the vehicle. In fact, the PNGV program seems to consider the use of gasoline as a basic requirement because of the virtual absence of infrastructure for alternative fuels (e.g., hydrogen, ethanol, and methanol). This requirement solves the near-term fuel infrastructure problem but aggravates the near-term performance efficiency and cost problems.

5  

A well designed and properly operating system integrating a reformer with a fuel cell should have virtually no emissions of oxides of nitrogen, hydrocarbons, or carbon monoxide, although this has not yet been demonstrated on automotive-compatible reformer systems. However, there may be emissions during cold start. After-treatment of exhaust emissions may be required, but the technology for removing hydrocarbons and carbon monoxide, once the catalyst is warm, would be simpler than three-way catalysts since no NOx removal would be necessary.

Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
×

In the past, the technical teams paid little attention to fuel issues, but fuel strategy has now become a major issue. One result of this change is that DME is now considered a fuel potentially suitable for both diesel engines and fuel cells. Until fuel cells can be introduced in large numbers, alternative fuels may be an attractive option. Before fuel cells can become prevalent, however, the difficulties and inefficiencies of processing fuels onboard the vehicle related to transients, small size units, and the temperature mismatch between gasoline reformation (about 700°C) and the proton-exchange-membrane (PEM) stack (less than 100°C) must be overcome. Furthermore, if the reduction or elimination of carbon dioxide (CO2) emissions becomes a dominant consideration, off-board fuel processing to produce hydrogen and sequester CO2 or carbon could be another factor in favor of alternative fuels.

Providing hydrogen from a hydrocarbon fuel like gasoline requires an onboard fuel processor, which adds weight, volume, and cost to the system. It also adds start-up delays, slows transient response times, and reduces fuel conversion efficiency. It decreases stack performance, complicates system integration, and has the potential to produce some (very low level) emissions. Indeed, many performance aspects of fuel-cell stacks would be adversely affected, including (1) cell voltage at a given current density (mA/cm2), a measure of cell efficiency; (2) maximum values of current density for a given minimum voltage, a measure of cell surface area required to produce a given power; (3) catalyst loading of precious metal (mg/cm2), an important cost factor; and (4) specific power (kW/kg), a measure of stack weight for a given design power. Not surprisingly, then, a substantial part of the DOE-sponsored PNGV fuel-cell development (about 30 percent) has been directed toward reformers.

Significant attention has also been directed toward making stacks more tolerant to CO (produced by reformers) and toward improving the post-reformer CO cleanup. The CO cleanup utilizes preferential oxidation techniques to reduce the amount of CO that goes from the reformer to the stack. In short, PNGV's efforts have been directed both toward reducing the amount of CO reaching the stack and increasing the amount of CO the stack is able to tolerate. Because heavy precious metal loadings are required to improve CO tolerance, efforts are also under way to find alloy catalysts, which are less expensive alternatives to pure platinum.

Program Status and Progress

Stacks and Stack Systems

Significant progress has been made in the development of fuel-cell stack systems. An International Fuel Cells 50 kW hydrogen-fueled PEM system was operated at near atmospheric pressure (1 to 2 psig, i.e., about 1.07 to 1.14 atm) with 50 percent PEM system efficiency (hydrogen-to-electricity conversion) at 100 percent power, and with 57 percent system efficiency at 25 percent power.

Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
×

This system provided a specific power of about 0.37 kW/kg. Up to this point, it had been generally assumed that it would be necessary to pressurize the stack to at least 2 or 3 atmospheres. Pressurization does improve stack performance, but it requires adding a compressor and expander to the system, with accompanying costs and complexities. Thus, if acceptable performance can be demonstrated with little or no pressurization, it could ease operational problems and reduce costs.

A Ballard 30 kW PEM system operating on methanol reformate was also demonstrated. It showed a steady-state efficiency (at constant output level, methanol fuel-to-electric [direct current] power conversion) of 42 to 44 percent and a CO tolerance of 40 ppm. The fuel processor was integrated with the stack.

A small-scale cell (50 cm2) configuration with increased tolerance to CO (up to 100 ppm) and durability of at least 1,400 hours was demonstrated at LANL. However, the tests were conducted with hydrogen fuel (as opposed to reformate), and the catalyst loading was 0.9 mg/cm2, far above levels compatible with PNGV cost goals. Additional life tests are planned using 40 percent hydrogen in a simulated reformate. Short-term tests of cell performance on partial oxidation reformate (40 percent hydrogen) showed about 15 percent performance degradation compared to pure hydrogen.

Reformers

Delphi has demonstrated a 30-kW methanol reformer integrated with a preferential oxidation (PrOx) system. This reformer provided about 20 ppm of CO at 100 percent load and 40 ppm at 25 percent load and a reported reformer system efficiency (methanol-to-hydrogen conversion) of 85 percent at 100 percent load.6 The PrOx CO cleanup system accounted for about 20 percent of the system weight and volume.

One of the most visible accomplishments in the past year was the successful operation of a partial oxidation reformer, designed by AD Little, integrated with a PrOx system designed by LANL. Tests utilizing low-sulfur gasoline showed an output of about 40 percent hydrogen and 50 ppm of CO at an oxygen stoichiometry of about 1.25.7 In another test, an AD Little Gen-2 50-kW fuel processor was integrated with a LANL three-stage PrOx CO-cleanup system. The resulting reformate (6 to 40 ppm of CO) was fed into Plug Power and Ballard PEM stacks (0.5 kW to 5 kW). Perhaps the most impressive part of this test was switching from ethanol fuel to gasoline while the system was in operation. This test appeared to demonstrate multifuel capability, although the hardware was far from

6  

Conversion efficiencies refer to a lower heating value of hydrogen fuel out relative to a lower heating value of hydrogen fuel in.

7  

An oxygen stoichiometry of 1.25 implies 25 percent more oxygen than necessary to oxidize all carbon to carbon dioxide.

Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
×

acceptable for automotive applications. An issue that must still be addressed is the sensitivity of the catalytic system to the sulfur content in the fuel. Either a sulfur-removal device or a low-sulfur fuel will be necessary for durable operation.

Progress on fuel processors was also demonstrated with a ''microscale" version of an autothermal reformer that showed high efficiency (about 87 to 93 percent) in producing hydrogen from methanol, ethanol, and gasoline. GM is currently validating this reformer for methanol for a 50-kW fuel processor.

Fuel Flexibility

Substantial improvements have been made in matching the CO level produced by the fuel processor (20 to 40 ppm) and the CO level that can be tolerated by the fuel-cell stack (perhaps 100 ppm with an air bleed), suggesting that the choice of fuels could be flexible; it may be possible to use gasoline, methanol, ethanol, or methane. However, a clear picture of the efficiency trade-offs is necessary to achieve this match. The overall projected efficiency (direct current electrical energy out relative to fuel energy in) of the fuel-cell system must also be compared with other technologies, including losses that might occur during fuel processing before the fuel gets to the vehicle (methanol, DME, hydrogen).

Gasoline is a blend of hydrocarbon fuels and small quantities of other substances, including sulfur. The relative amounts of the hydrocarbon fuels and the other substances vary across fuel manufacturers and their retail outlets, and composition can change over time. Thus, it may be difficult to optimize fuel processor performance, and the sulfur in gasoline could have adverse effects on catalysts in the fuel processor or PrOx system and in the stack.

Cost Issues

Cost projections for gasoline-fueled fuel-cell systems have decreased dramatically but are still very high at $500/kW, nearly double the 1997 goal of $300/kW and about an order of magnitude higher than the 2004 PNGV goal of $50/kW. However, for the first time, rigorous cost analyses are being conducted by Directed Technologies, Inc., for stacks, fuel processors, and ancillary systems. These analyses could help determine ways to lower costs for high-volume manufacture (e.g., manufacturing techniques, materials selection, etc.). Until low-cost membrane-electrode assemblies, low-cost bipolar plates, lower catalyst loadings, and low-cost reformer/cleanup systems are developed, the cost of reformers will remain a major issue.

International Developments

The most visible foreign developments are associated with Ballard Power Systems, Inc., of Canada, and Daimler Benz of Germany. Ballard is forming

Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
×

strategic partnerships and receiving orders for PEM systems from automobile manufacturers worldwide. Probably, the activities with the greatest potential for a long-term effect on automotive fuel-cell development are Ballard's $450 million (Canadian) joint venture with Daimler Benz and Daimler's apparent commitment to fuel-cell vehicles. Daimler introduced two prototype fuel-cell vehicles in 1997 and acquired a 25 percent stake in Ballard in the joint venture. One of the vehicles was a 250-kW PEM hydrogen-fueled bus; the other was a hydrogen-fueled minivan, NECAR III. Daimler is also expected to introduce a prototype methanol-powered subcompact car based on the new A-class vehicle. Meanwhile, Ballard is supplying fuel cells to Delphi, Chrysler, and Nissan and has joined the Ford P2000 project. Ballard is also expected to deliver three more fuel-cell powered buses to Chicago and three to Vancouver for testing and evaluation. In addition, they are providing a methanol-fueled PEM system for the Georgetown University (in Washington, D.C.) 40-ft bus program. Ford has announced that it will join Ballard and Daimler Benz with an investment of $420 million in cash, technology, and assets in the development of fuel-cell technologies for vehicles (Ford, 1997).

A European program is under way to develop and test a 30-kW fuel-cell powered Peugeot van in partnership with PSA (a French company) and Deltona and Ansaldo (Italian companies). In Japan, Nissan and Mitsubishi are working on government-sponsored R&D, and Honda and Toyota appear to be making major corporate investments to develop their in-house capabilities. The combined government-industry investments in transportation fuel-cell technologies in Europe, Japan, and Canada are significant, and individual USCAR partners have responded with ambitious investments and programs of their own.

Assessment of the Program

Tests of fuel processors, stacks, and complete systems to date have not included emissions and energy efficiencies for cold start-ups, shutdowns, or even rapid transient operation. The same is true of tests of component models and system simulation studies.

Even though PNGV is committed to the development of systems that will utilize gasoline for fuel, the committee is not aware of any efforts by PNGV to determine the sulfur tolerance of the stack platinum catalyst or the catalysts in the fuel processor or PrOx cleanup system. A requirement for sulfur-free gasoline could be a challenge for gasoline manufacturers.

In general, research on automotive fuel-cell systems has focused on systems that require pressurization to 2 or 3 atmospheres, which will require a small, high-efficiency, low-cost compressor, as well as a companion expander (turbine), to recover part of the stack air discharge energy. Because the compressor for these pressurized systems could consume 25 percent (or more) of the stack gross power output, the importance of high efficiency is obvious. DOE currently has contracts for the development of compressors with three firms: AlliedSignal

Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
×

(turbo compressor-expander), AD Little (scroll compressor-expander), and Vairex (variable displacement compressor). All three contracts have completed Phase I and are going into Phase II. However, viable solutions to meet efficiency, performance, and cost requirements compatible with PNGV fuel-cell system goals have not been demonstrated.

Progress has been made in the development of models of fuel-cell systems, primarily by ANL and LANL, which have delivered fuel-cell/fuel-processor simulations to the PNGV systems analysis team. However, these models appear to be very modest compared to the models required for full performance-range simulations. In spite of the likelihood that effective modeling and simulation could dramatically improve the development of appropriate systems and subsystems, modeling is still a low priority for PNGV.

In spite of significant reductions of estimated cost for the stack and other subsystems, cost is still a major uncertainty for fuel-cell viability. The costs associated with several critical (and expensive) subsystems, such as the compressor, turbine, fuel processor, reformate cleanup, and control, are all but unknown.

Recommendations

Recommendation. The PNGV should place a very high priority on additional modeling and system analyses for fuel-cell systems. Analyses of emissions and the overall efficiency of gasoline-fueled systems over the full range of operations, from cold start-up to shutdown, should be done, as well as trade-off studies for alternative fuels, such as methanol versus gasoline.

Recommendation. The PNGV should attempt to determine the sulfur and carbon monoxide tolerance of the fuel-cell stack platinum catalyst and the catalysts in the fuel processor and preferential oxidation cleanup system.

Recommendation. The PNGV should expand and accelerate its cost studies to include critical items, such as compressor expanders, fuel-flexible reformers, and carbon monoxide cleanup systems.

Recommendation. Because of their high efficiency and low emission potential, fuel-cell systems for transportation systems could become vitally important to the United States. U.S. government and industry investments in research and development should, therefore, be continued at current levels or even increased for an extended period.

ELECTROCHEMICAL ENERGY STORAGE

HEVs use energy storage systems to recover and to store braking energy, thereby enhancing overall vehicle system efficiency. Energy storage devices also provide some power during transient and peak power periods, allowing a smaller

Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
×

engine to operate at more constant power, improving efficiency and reducing emissions. Among electrochemical energy storage technologies, batteries are at a considerably more advanced state of development than ultracapacitors. Because commercial lead-acid and nickel-cadmium rechargeable batteries do not meet the PNGV performance and cost criteria, attention has been focused on lithium-ion and nickel metal hydride batteries.

HEVs require a higher-value battery power-to-energy ratio than battery-powered electric vehicles because relatively little energy has to be stored onboard hybrid vehicles, as compared with electric vehicles. Two types of power plants have been assumed in the PNGV analysis, fast-response and slow-response power plants. A fast-response power plant, such as a reciprocating internal combustion engine, is capable of reaching its maximum power in a fraction of a second. Fast-response power plants place lower demands on the energy storage device than power plants that take several seconds to develop full power. For slow-response power plants (such as reformer fuel-cell systems), the energy storage device must deliver the difference between the power demanded for rapid vehicle acceleration and the power available from the power plant, and it must deliver this power for a longer period of time. This increases the peak power demand, as well as the energy required from the storage device. Table 2-2 shows the PNGV power, energy, and other design targets for short-term energy storage.

TABLE 2-2 PNGV Design Targets for Short-Term Energy Storage

Characteristic

Units

Fast Response

Slow Response

Discharge pulse power (18 s)

kW

25

65

Peak regenerative power (10 s)

kW

30

70

Available energy

kWh

0.3

3

Discharge power density

kW/L

0.78

1.6

Minimum round-trip efficiency on the FUDS/HWFTET cycle

%

90

95

Discharge-specific power

kW/kg

0.63

1.0

Cost

$/kW

12

7.7

Durability (100 Wh)

cycles

50,000

120,000

Lifetime

yr

10

10

Operating temperature

°C

-40 to +52

-40 to +52

Source: PNGV (1997).

Note: A fast-response power plant is assumed to react very much like a conventional automotive engine, which responds very quickly to vehicle power demands. A slow-response power plant puts a much greater demand on the energy storage system for the instantaneous delivery of high power. Each cycle is about one minute long and includes a discharge pulse during acceleration, a smaller discharge current at cruising speed, a strong charge pulse during braking, and a rest period. Superimposed on this is a charging current, which has the net effect of restoring the battery to the same state of charge at the end of the cycle as the beginning.

FUDS = federal urban drive cycle; HWFTET = highway fuel economy test.

Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
×

In the third report, the committee documented significant progress, especially in the development of high-power batteries (NRC, 1997). Since then, further progress has been made in lithium-ion and nickel metal hydride battery technology, and in all likelihood target design and performance goals can be approached. As a result, the year 2000 concept vehicle will not be unduly compromised. However, meeting the cost goals is still a major challenge.

Program Status and Progress

Lithium-Ion Batteries

SAFT is the principal contractor for the development of lithium-ion batteries for HEVs. In the past year, SAFT has designed and constructed 10 6-Ah cells. The specific energy of these cells has not reached the target, but the cycle life is close to the goals shown in Table 2-2. AFT has also conducted some abuse-tolerance tests for 6-Ah cells, including nail penetration and mechanical shocks. Abuse-tolerance tests on 12-Ah cells were completed by the end of January 1998. Facilities for fabricating full-size cells (12 Ah) have been installed, and preliminary designs have been completed for the 50-volt module. The modeling and trade-off analyses are somewhat behind schedule; the results to date are insufficient to predict the optimized design, performance, and costs of the 50-volt modules. Costs remain significantly higher than the targets.

New exploratory projects have been initiated at PolyStor and VASTA to assess alternative baseline technologies. Both of these are six-month contracts that started in July 1997. A second program to develop 50-volt modules may be initiated at VARTA.

Nickel Metal Hydride Batteries

Nickel metal hydride batteries have reached the manufacturing stage for applications in electric vehicles commercialized by GM, Toyota, and Honda. VARTA, the principal contractor to DOE for development of a hybrid vehicle application, was able to meet its performance goals for 10-Ah nickel metal hydride cells. The specific energy is still below the target value of 60 Wh/kg with a power-to-energy ratio of 25 W/Wh. Tests of VARTA cells at Idaho National Engineering and Environmental Laboratory included determinations of (1) capacity and discharge/regenerative pulse power vs. rates at different temperatures, and (2) efficiency loss due to cycling at very low charge/discharge rates. Cycle life tests are in progress.

Like the modeling studies for lithium-ion batteries, modeling for nickel metal hydride batteries is in the preliminary stage, and the projected costs are high by a factor of about four. A Phase 2 program was initiated at VARTA in August 1997 to design, construct, and test a 50-volt module. The contract is for an 18-month period.

Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
×
Ultracapacitors

The exploratory R&D on ultracapacitors has been completed. The technology is too immature for the PNGV time frame, although it is being considered for use in the control of the power-electronics system. The committee agrees with the PNGV assessment that breakthroughs will be necessary to increase the specific energy of ultracapacitors significantly and to lower the costs before they can be considered as primary HEV energy storage devices.

Assessment of the Program

Considerable progress has been made in the development of full-size cells of lithium-ion batteries and of nickel/metal hydride batteries. However, specific power and energy must still be improved, and the degradation in performance associated with cycling, particularly in the case of lithium-ion batteries, must be minimized.

PNGV should undertake fundamental investigations to elucidate the increased cell resistance and decreased capacity and power associated with cycling of lithium-ion batteries. For PNGV's purposes, the energy efficiency of the battery will have to remain high throughout the life of the battery. Test results should indicate energy efficiency, as well as the usual specific energy and power and cycle life.

PNGV recognizes the uncertainties of choosing the best battery and has opted instead to continue working on two main systems and monitoring progress on lead-acid and nickel-cadmium batteries. Of the two main systems, the lithium-ion system promises higher performance, but the nickel metal hydride system is more likely to meet the goals for 2000 and 2004. In general, the battery program is well directed, with proper emphasis on overcoming the obstacles to meeting the program goals.

Modeling analysis is still in its infancy and appears not to be coordinated well with modeling by the vehicle systems analysis team. Systems analysis (see Chapter 3) involves going back and forth between the requirements of the vehicle mission and the capabilities of the various subsystems and requires better models for the electrochemical energy storage systems so that realistic goals and targets can be set. The PNGV did not inform the committee of progress toward certain targets, such as the energy efficiency of the energy storage device, which is essential to a hybrid system achieving high mileage. For a better understanding, the committee would need to know the test protocols in more detail, as well as the test results.

Safety, particularly for the lithium-ion system and the 50-volt modules, is closely related to the need for efficient thermal management and electronic control of individual cells during cycling. The performance of the batteries and their safety over the temperature range indicated in Table 2-2 has not been reported.

Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
×

Previous studies have suggested that performance, including cycle life and safety, is compromised at higher temperatures. Safety is generally considered a key issue even for small batteries in consumer electronics. Safety issues must be addressed and reported thoroughly in the PNGV program, which involves much larger batteries and fewer opportunities for controls on individual cells. Methods for controlling and monitoring cell level currents must be investigated further.

At the present time, the costs of all the battery systems under consideration are sufficiently high that it seems unlikely that the cost goals can be realized within the PNGV time frame. A detailed cost analysis with a complete breakdown would shed some light on ways to reduce costs.

International Developments

Several international battery developers (Matsushita-Panasonic, SONY, Japan Storage Battery, VARTA, and SAFT) are exploring high-power batteries for HEV applications. Matsushita-Panasonic is developing a 20-Ah capacity battery. SONY uses lithium cobalt oxide for the positive electrode material. Japan Storage Battery is investigating an alternative material, lithium manganese oxide. Honda and Mazda plan to utilize an ultracapacitor for regenerative braking in an HEV. The committee was encouraged that the U.S. PNGV contractors appear to be well ahead in energy storage technology for HEV applications.

Recommendations

Recommendation. The PNGV should expand its programs to include safety issues, such as temperature limits for lithium-ion batteries and preventing the generation of potentially explosive gases (e.g., hydrogen) in nickel metal hydride batteries.

Recommendation. The PNGV should conduct a detailed cost analysis to identify major contributors to high cost and establish strategies for reaching the cost goals.

Recommendation. The PNGV should update the storage requirements and goals by means of subsystem models integrated with the overall system analysis. In addition to specific energy, test results should be reported on energy efficiency and specific power over well defined test protocols and compared to the refined goals.

FLYWHEELS

Because of their attractive power-to-weight and power-to-volume characteristics, flywheels continue to be considered for energy capture and delivery in support of the efficiency of the "core power system" for PNGV vehicles. Flywheels

Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
×

excel in accepting the high power generated during engine and vehicle braking and delivering it to meet vehicle system peak power needs. The issues of safety, cost, and size are still serious but are yielding to development programs.

Work continues at ORNL to develop more specific flywheel design guidelines to support fast-response power-plant systems. A fast-response power plant, which has a similar response time to a conventional engine, places a much lower requirement on the power output of the flywheel than a slow-response power plant. A vehicle system model is now available that can be used for simulations to optimize the performance of the flywheel and to update the PNGV technical targets, which have been unchanged since 1996 (see Table 2-2). Flywheel designs will not be pursued for slow-response power plants because the much greater energy demands would require a larger and more costly flywheel system.

Program Status, Progress, and Plans

The PNGV flywheel technical term is now confident that it is possible to design and build a practical prototype energy storage flywheel system for automotive applications. A significant amount of work on failure containment has provided more confidence that the system can be designed to comply with the established safety criteria. Furthermore, improved containment designs have reduced cost and weight, which lends further support to the expectation that a practical system can be designed.

A key technology development is the design of an adequate containment mechanism in case of failure. The flywheel technical team has followed several strategies and has essentially overcome this significant barrier. Perhaps the most important advance is the growing evidence that flywheels (or portions thereof) that fail at low stress-to-strength ratios do not "burst" but remain intact. This knowledge dictates that the rotating parts have a high ultimate strength-to-maximum operating stress ratio (about 4:1).

Retaining "loose flywheels" is significantly easier than containing fragments because of the increased time for energy dissipation. The new design strategy for flywheel housings are designed to retain loose flywheels and contain fragments from partial flywheel failures instead of containing a complete burst and disintegration of a flywheel. This design strategy also attempts to manage energy as it dissipates. Limiting the use of flywheels to fast-response power plants reduces the energy storage requirement and permits the design to meet the safety goal for strength-to-stress ratio with a manageable increase in weight.

A variety of flywheel containment tests have been run in the Trinity/LLNL project, which led to a lightweight stainless steel/aluminum honeycomb structure that has so far been tested 41 times in sample form and has demonstrated consistent retention of test projectiles.

The current overall state of development for a flywheel system with a power level of 30 kW and an energy storage of 300 Wh indicates that, although the

Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
×

projected cost and weight are still well above PNGV targets, substantial improvements have been made in the last year. The assumptions in the projections include a cost of $5/lb for carbon fiber material, a containment-to-rotor weight ratio of 2:1, and a cost of $4/kW for power electronics. The first two projections appear to be achievable by 2004, but the $4/kW target is $3/kW lower than the $7/kW target set for the power electronics overall, which is already considered an extremely ambitious cost target. The relative simplicity of the flywheel electronic controls might justify these lower cost estimates and target, but the committee is not convinced of this. The cost for the flywheel, including the containment housing and motor generator, is substantially higher than the target; the weight is also significantly over its target. The amount of effort that will be required to achieve the desired targets is clearly much less than was projected a year ago but is still sizable. The flywheel technical team noted that if the power plant system required a flywheel with a capability of 15 kW power and 200 Wh energy-storage, current estimates of cost and weight would practically meet the targets.

A failure mode and effects analysis for the vehicle system incorporating a flywheel was conducted at ORNL, and a flywheel simulation model has been provided to the systems analysis team by LLNL. Assumptions for the current flywheel system are that life-cycle tests will demonstrate that the vacuum in the flywheel chamber will be maintained and that the sealed bearings will continue to operate with acceptable characteristics. The flywheel technical team and ORNL have yet to confirm the basic shape of the flywheel system, which may have implications for gyroscopic effects and containment costs.

The development of analytical models will continue at ORNL and LLNL in 1998 to support design assumptions and containment design and development. The flywheel design assumptions will be written to support performance of a design level failure model and effects analysis, which in turn will be used to support requests for quotes for the flywheel system in 1999. With further refinements of the vehicle system model with iterations of flywheel system capabilities, estimates for the targets, which are currently considered rough projections, will be improved. The Trinity/LLNL project will continue testing the containment with a full-size housing subjected to overspeed burst.

Assessment of the Program

The flywheel technical team is confident that it is now possible to design and build practical energy storage flywheel systems for automotive applications. The team, working with a number of outside agencies, all of whom are providing corroborating data of various kinds, has a firm grasp on the key technology barrier, namely, containment of failure. The committee suggests, however, that an out-of-balance sensor be considered to shut off electrical power during flywheel run-up if a significant amount of out-of-balance vibration is detected. The committee believes the flywheel system should be included in second-generation

Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
×

concept vehicles to help clarify how the vehicle system and power plant will incorporate the energy captured by the flywheel and enable the development of a delivery system that optimizes overall cost, size, performance, and efficiency.

Lowering the cost and reducing the weight of the flywheel system are still necessary, but with a smaller flywheel system, the tasks will be easier to accomplish because the power and energy storage requirements will be lower. The committee believes that the relatively large cost penalty of $300 for the flywheel system will be extremely difficult to offset by reductions elsewhere in the vehicle system.

Recommendation

Recommendation. If vehicle systems modeling indicates an acceptable level of performance and cost for the flywheel, the PNGV should plan for the physical installation of flywheel hardware in a post-2000 concept vehicle.

POWER ELECTRONICS AND ELECTRICAL SYSTEMS

All three USCAR partners have elected to pursue HEV designs for the 2000 concept vehicle (Malcolm, 1997). Fuel cells for energy generation and flywheels for energy storage could very well be practical within the PNGV time frame. Electrification of major auxiliary functions, e.g., air conditioning and power steering, is attractive for ease of control and improved energy management and efficiency. Success depends on the development of efficient and economically acceptable actuators, motors, and power electronic converters.

Program Status and Progress

The electrical and electronics power conversion devices team (EE technical team) has made considerable progress in organizing and coordinating its efforts. The committee had noted in the third review that this team lacked leadership and had recommended that a full-time leader be appointed (NRC, 1997). Not only has this been done, but two technical subteams have also been established to address power electronics enablers and electric motor enablers. The subteams appear to be effectively setting priorities and addressing the important issues in their areas. Both have made designing and manufacturing for low cost their highest priority.

The progress of the EE technical team since the committee's last review is evident in the team's performance as measured against the targets for specific power, volumetric power density, cost, and efficiency. Except for motor efficiency, the 1997 targets for both the motor and electronics are reported to have been either met or exceeded (Malcolm, 1997). The reported cost of $15/kW for the power electronics module is particularly impressive in comparison to the 1997 target of $25/kW and is extraordinary in comparison to the interim technical

Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
×

target of $100/kW by 1997 that was indicated in the PNGV Technical Roadmap (PNGV, 1997).

The EE technical team has also made progress in leveraging the activities of other organizations, especially the Office of Naval Research (ONR), Wright-Patterson Air Force Base, and the National Renewable Energy Laboratory. The success of the PNGV power electronics developments appears to rely heavily on ONR's Power Electronic Building Block (PEBB) program. The EE technical team has established a liaison with the PEBB researchers and has been working with the PEBB program management to focus attention on PEBB specifications that are applicable to the PNGV program.

Although the EE team has made considerable progress in working more closely with the systems analysis team, some necessary models have still not been provided to the systems analysis team, including models for motor/generators, power electronic converters, and control algorithms for both the series and parallel hybrid drive configurations. The EE technical team is currently working on providing them.

Accessory loads, heating, ventilation, and air conditioning (HVAC), and regenerative braking were identified by the EE technical team as priorities for technology development. Work is being done on starting/charging and accessory loads by both the USCAR partners and their suppliers. In the committee's third review, regenerative braking efficiency was identified as an area of concern (NRC, 1997). Because this topic was not addressed in presentations for this (fourth) review, the committee has concluded that regenerative braking efficiency is still an outstanding issue. The EE technical team is aware of HVAC-related work being done at the national laboratories and is coordinating the electrical requirements of the HVAC system with developments as they are evaluated and adopted by the systems analysis team and the systems engineering team.

The USCAR partners have independently chosen HEV designs for the year 2000 concept vehicle. This means that each company may have different electrical system architectures and requirements.

Assessment of the Program

Both motor and power electronics technology will meet PNGV functional requirements. The remaining challenge for the EE technical team, as the team has clearly stated, is meeting the cost targets for these components. The 2004 target cost for motors is $4/kW, which the team recognizes as the approximate cost of materials in state-of-the-art motors. Although the team apparently already has achieved the very low cost of $15/kW for power electronics, the PNGV Technical Roadmap target for 2004 requires a further reduction of more than 50 percent to $7/kW. In the committee's opinion, the impact of the cost of power electronics on other vehicle systems has either not been recognized or has been considerably underestimated. Although the EE technical team has tried to provide models to

Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
×

the systems analysis team, coordination with other program teams could still be improved.

The committee was not made aware of assessments of foreign technology by the EE technical team. However, given the introduction of commercial HEVs by foreign manufacturers (e.g., the Toyota Prius) in the past year, the committee believes that the USCAR partners are aware of these developments and have been conducting independent evaluations of foreign technology.

The hybrid designs chosen independently by the USCAR partners will make a more comprehensive evaluation of competing technologies possible in an application where no single correct approach is obvious, especially for the electrical and electronic subsystems. However, the committee has not seen any evidence that the cost target of $7/kW for electronic power modules can be achieved in any of the designs. Given that the cost of less sophisticated computer power supplies produced in high volume is about $100/kW, the committee is concerned that the cost goals established by the EE technical team are too aggressive. The committee is also concerned that the EE technical team's reliance on the ONR's PEBB program will jeopardize the cost targets if the PEBB program changes direction, loses funding, or cannot meet its goals.

Recommendations

Recommendation. The PNGV should perform a thorough and convincing verification of the reported 1997 cost of power electronics in conjunction with a reevaluation of the 2004 cost goal. The reevaluation should include identifying developments that support the assumption that the cost target can be met.

Recommendation. The PNGV electronics and electrical systems team's reliance on the Navy's Power Electronic Building Block (PEBB) program should be mitigated by the initiation of a PNGV-specific cost reduction program.

Recommendation. Given the critical importance of electrical and electronic systems to the success of the PNGV program, the electrical and electronic systems technical team should provide cost models to the systems analysis team as soon as possible to ensure that cost assumptions for other subsystems that rely on power electronics are consistent with the projections and targets.

MATERIALS

The reduction of vehicle mass through the use of lightweight materials is one of the key elements in meeting the fuel economy goal of the PNGV program. Because the leading candidate materials are currently more costly than the steel used today, the requirement that there should be no increase in the overall cost of vehicle ownership presents a major hurdle to meeting the fuel economy goal.

Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
×

PNGV personnel are working closely with materials suppliers to develop less costly manufacturing processes and new design practices that utilize materials more efficiently. Each lightweight material alternative also offers a different weight reduction, has different costs, and raises different issues in terms of manufacturing feasibility, design experience and confidence, infrastructure needs, new failure modes, repairability, and recyclability.

To meet the 80 mpg vehicle fuel economy objective of Goal 3 while maintaining vehicle performance, size, utility, and cost of ownership, vehicle curb weight will have to be reduced by 40 percent from 3,240 to 1,960 lb. Table 2–3 shows the breakdown of the weight reduction targets by major vehicle subsystem.

Program Status

The major alternatives under consideration in 1997 for reducing vehicle weight were: more efficient design of the current steel-intensive vehicle, which is being led by the American Iron and Steel Institute; aluminum sheet and castings; fiber-reinforced composites; magnesium; matrix composites; titanium; and lightweight glazing (thinner glass and polymers).

More Efficient Steel Design

The approach of the American Iron and Steel Institute program has the potential of a 20 percent weight reduction for the body-in-white (BIW) structure (bolt-on panels, such as the hood, doors, front fenders, and deck lids are not included in the BIW). Based on efficient steel design technology, the weight of the baseline PNGV vehicle BIW could be reduced from 598 to 478 lbs; the cost could be reduced by $154. The PNGV material team also studied the possibility of using a stainless steel space frame but found that it would generate a cost penalty of $200 for a weight saving of only 22 percent, which is half of the savings needed for the Goal 3 vehicle.

Aluminum and Magnesium

The total potential vehicle weight savings with aluminum sheets and castings is 600 lbs; the total potential weight savings with magnesium castings alone is 150 lbs. Note that the weight saving potentials for the alternative materials are not additive because certain parts, wheels for example, have been targeted for both materials in the individual computations. On a part-by-part basis, the weight saved by substituting steel sheet with aluminum sheet is typically more than 50 percent. This number does not include secondary weight savings that result from reducing the size of other components, such as brakes, wheels, and suspensions. The total vehicle must be redesigned around the primary weight saving to assess accurately potential secondary savings.

Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
×

TABLE 2–3 Vehicle Weight Reduction Targets for the Goal 3 Vehicle

Subsystem

Current Vehicle

(lbs)

PNGV Vehicle Target

(lbs)

% Mass

Reduction

Body

1,134

566

50

Chassis

1,101

550

50

Power train

868

781

10

Fuel/other

137

63

55

Curb Weight

3240

1960

40

 

Source: Stuef (1997).

The automotive industry has considerable production experience with aluminum in the form of stamped body panels. The procedures and processes for recycling aluminum are also in place today, and much of the material is returned to high value automotive applications. As a matter of public record, several aluminum-intensive prototype vehicles have been built outside the PNGV program by the USCAR partners and evaluated for ride, handling, NVH, crashworthiness, joining, and painting (Jewett, 1997). Thus, the change to an aluminum-intensive vehicle would not be a major technology challenge because the USCAR partners already have extensive design and manufacturing expertise with this material. The challenge is to develop new processing methods so that an aluminum-intensive vehicle can be made as inexpensively as a steel vehicle. Based on a price for aluminum of $1.60/lb, the cost penalty of an aluminum BIW is estimated at $400.

Cast aluminum and magnesium would be used in the chassis, the body, and the power train subsystems. Major efforts to reduce the costs of feedstock and improve the casting processes of both materials are under way. Studies to improve the machinability of magnesium castings and to develop a lower cost high-temperature alloy are also under way. Improved processes for recycling magnesium will have to be developed.

Fiber-Reinforced Plastic

In 1997, a number of serious obstacles were identified that will limit the use of graphite fiber-reinforced plastic composite material (GrFRP) in meeting Goal 3. First, not enough is known about the consistency of the mechanical properties of GrFRP when produced in large volumes. Second, the criteria and methods for reliably designing GrFRPs for fatigue resistance and crashworthiness in the complex loading environment presented by the automotive body structure are far from production-ready. Third, methods for recycling the material into high-value applications to take advantage of its intrinsic properties, as opposed to using it only as filler, must still be developed.

Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
×

According to the latest PNGV/USCAR studies, the potential BIW weight reductions with GrFRPs are only a few percentage points better than for aluminum, 59 percent versus 55 percent. The committee was surprised at the reportedly small margin of improvement of GrFRPs over aluminum. PNGV/USCAR explained that the small margin reflected a combination of two factors. Manufacturing considerations and the need for sufficient structural strength to accommodate multi-axial loads required more material than the committee had expected.

The major barriers to the intensive use of GrFRPs for a Goal 3 vehicle, however, are the high cost of the graphite fibers and the lack of a suitable high-volume manufacturing process for the material. Currently, the cost penalty of a GrFRP BIW is higher than a steel BIW, and there is no feasible high-volume manufacturing process for the thin sections.

Glass fiber-reinforced plastic composites (FRPs) offer weight savings in the 25 to 35 percent range. FRPs that incorporate thermoset resins have been used extensively in noncritical stressed structures, such as hoods, deck lids, doors, and fenders. One drawback of using thermoset materials is the substantial investment in tooling because of the relatively slow cycle times. Chrysler is investigating low-cycle-time injection molding for glass-reinforced thermoplastic resins, which has additives for improving crashworthiness and weather resistance. Chrysler is considering using them in both body panels and body structures. Computer simulation and hardware tests are being used to test the crashworthiness of these materials.

Metal Matrix Composites

The applications for metal matrix composites are in the chassis and power train subsystems. The total potential weight savings of using metal matrix composites is only 30 to 50 lbs. The major hurdles to developing applications of this material are feedstock costs and the development of a reliable process for compositing the materials.

Titanium

The applications for titanium are in the chassis (40 lbs potential savings) and power train (10 lbs potential savings). The components of interest are springs, piston pins, connecting rods, and valves. The major barrier to the use of this material is its high feedstock cost.

Lightweight Glazing

New glazing materials—thin glass and polymers—are being considered for weight reduction. The potential weight saving is 50 lbs. The major concerns for polymers are abrasion/scratch resistance and cost.

Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
×

Program Progress and Plans

Steel

The American Iron and Steel Institute efficient steel vehicle design program, which will be completed in 1998, offers near-term weight and cost savings that can be implemented in goal 1 and 2 applications, once the USCAR partners have verified the findings. However, the intensive use of steel is not feasible for meeting the Goal 3 weight reduction targets unless there is a major breakthrough in power train efficiency.

Aluminum Sheet

In the past year, aluminum has become a leading structural material candidate for the Goal 3 vehicle technology selection process because (1) it offers a much larger percentage weight reduction than steel, (2) it is much less costly than GrFRP, (3) the knowledge base for the design and manufacture of this material is extensive, and (4) existing stamping facilities for steel can be used for aluminum without major modifications.

Because of aluminum's importance to weight reduction and high fuel economy, a major cooperative research and development agreement (CRADA) has been initiated between Reynolds Metals, LANL, and the USCAR United States Automotive Materials Partnership to reduce the cost of aluminum sheet through the development of a thin-slab (less than 1 in thick) continuous-casting process to replace the more costly ingot-based process used today. The preliminary results of this program are very promising. Another program to develop low-cost, non-heat-treatable alloys competitive with the 6000 series aluminum alloys is also under way, as well as studies on improving the formability of aluminum stampings and making the walls of aluminum extrusions thinner. The goal of all of these programs is to reduce the cost of an aluminum-intensive vehicle.

Graphite-Fiber-Reinforced Plastic Composite Material

The weight saving of GrFRPs compared to aluminum is not sufficiently attractive for this material to be the leading candidate in the Goal 3 technology selection process. Cost and thin-section manufacturing are major issues that cannot be resolved in time to support Goal 3 year 2000 concept vehicles. The development of GrFRPs should be continued with applications targeted beyond Goal 3. R&D should concentrate on reducing the fiber cost to $ 3/lb, developing a process for mass producing components in thin sections, acquiring a deeper understanding of reliable design for complex loading conditions, and developing high-value applications for the recycled material.

The injection molding of FRPs (glass-reinforced thermoplastics) being

Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
×

investigated by Chrysler looks much more promising at this juncture. Although the potential weight saving of 25 to 35 percent is not as great as it would be with GrFRPs, FRP may compete effectively with aluminum for body panels and certain structural applications because the processing technology could integrate two or more parts that are currently made with steel or aluminum into a single part. Nevertheless, the extensive design and production experience with aluminum for body panels and structural applications gives FRPs an edge in the near term.

Aluminum and Magnesium Castings

Several important R&D studies were conducted in 1997 to reduce the costs and improve the properties of aluminum and magnesium castings, including sand casting, semi-permanent mold casting, squeeze casting, and high-pressure die casting. Simulation models of the casting flow and solidification processes are being developed to predict microporosity as a function of the part and casting process design. Improved nondestructive evaluation techniques are being developed to support the use of aluminum and magnesium in more demanding applications. The development of rapid tooling processes for die-casting applications is under way. Methods and materials for improving the die-casting dies are also being studied to reduce the overall cost of using these materials.

Plans for 1998

The plans for 1998 are to continue the major material initiatives already under way. The committee agrees that the focus should be on following through on the cost-reduction initiatives begun in 1997, especially for the continuous casting of aluminum sheet.

Assessment of the Program

In 1997, the PNGV materials technology team and the vehicle engineering team made a thorough joint evaluation of the lightweight material candidates for the Goal 3 technology selection process. The criteria included potential weight savings, feedstock cost, manufacturing cost and feasibility, design and manufacturing experience, and the ability to recycle the material into high-value applications. The committee agrees with the criteria for selection used by the PNGV teams and with their conclusion that aluminum is the lightweight material of choice for intensive use in support of Goal 3 objectives, along with the selective use of FRPs, magnesium, GrFRPs, and titanium. The committee also agrees with PNGV/USCAR's assessment that intensive use of GrFRPs should be a longer range goal.

The manufacture of an aluminum-intensive vehicle would not meet the Goal 3 cost objectives if the aluminum were produced with today's mill practice

Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
×

technology. Consequently, the CRADA to develop continuous casting of aluminum sheet for automotive applications is critical to eliminating the cost penalty and, therefore, critical to meeting the overall objectives of Goal 3. Finding ways to improve the physical properties and reduce the cost of cast aluminum and magnesium is also important to meeting Goal 3 objectives. PNGV/USCAR should monitor these projects closely and ensure that they have adequate resources to meet these critical objectives.

Recommendations

Recommendation. The development of the continuous casting process of aluminum sheet should be given the highest priority in terms of resources and technical support. This includes support of the work already under way to characterize the material in terms of its microstructure, strength, ductility, formability, and weldability in parallel with the development of mill processing techniques.

Recommendation. The development program for low-cost graphite fiber should be continued for longer-term applications beyond Goal 3. A new program for manufacturing graphite-fiber-reinforced plastic composite materials in thin sections should be initiated to take advantage of the unique properties of this material.

Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
×
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Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
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Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
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Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
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Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
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Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
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Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
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Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
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Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
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Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
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Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
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Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
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Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
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Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
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Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
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Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
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Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
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Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
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Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
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Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
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Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
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Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
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Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
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Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
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Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
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Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
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Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
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Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
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Page 49
Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
×
Page 50
Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
×
Page 51
Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
×
Page 52
Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
×
Page 53
Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
×
Page 54
Suggested Citation:"2 Development of Vehicle Subsystems." National Research Council. 1998. Review of the Research Program of the Partnership for a New Generation of Vehicles: Fourth Report. Washington, DC: The National Academies Press. doi: 10.17226/6127.
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Page 55
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This book examines the state of development and research progress of technologies being considered for a new generation of vehicles that could achieve up to three times the fuel economy of comparable 1994 family sedans. It addresses advanced automotive technologies including engines, fuel cells, batteries, flywheels, power electronics, and lightweight materials being developed by the Partnership for a New Generation of Vehicles—a cooperative research and development program between the U.S. government and the U.S. Council for Automotive Research. The book assesses the relevance of the ongoing research to PNGV's goals and schedule, the program's adequacy and balance, and addresses several issues such as the benefits of hybrid versus nonhybrid vehicles and the importance of the sports utility vehicle market.

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