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Review of the Research Program of the Partnership for a New Generation of Vehicles: Third Report 4 Powertrain Developments CANDIDATE SYSTEMS A key measure of the ultimate success of the PNGV will be its ability to integrate R&D programs that collectively improve the efficiency of converting fuel into motive power for automobiles. This improvement must take place within the very stringent boundary conditions of size, reliability, durability, safety, and affordability of today's cars. At the same time, it must meet even more stringent emissions and recyclability levels and use components capable of being mass produced and maintained in a manner similar to current powertrains. In order to achieve the Goal 3 fuel economy target (up to three times the fuel efficiency of today's comparable vehicles), the efficiency of the combustion engine (e.g., a CIDI, Stirling engine, or gas-turbine engine) or fuel cell, averaged over a driving cycle, will have to be approximately double today's efficiency to achieve at least 40 percent thermal efficiency (see Appendix E). This is a very challenging goal, considering all of the constraints noted above. The candidate systems and subsystems have not changed during the past year. They are as follows: four-stroke CIDI engines gas turbines Stirling engines fuel cells reversible energy-storage devices1 electrical and electronic power-conversion devices 1 Reversible in this context means that the device can both accept and provide energy, not that it is reversible in a thermodynamic sense.
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Review of the Research Program of the Partnership for a New Generation of Vehicles: Third Report HEVs use an energy storage device to modify the fluctuating demands on the primary power plant. This modification allows the engine or fuel-cell peak power output to be reduced and provides an opportunity for improved efficiency by both restricting the power fluctuations and recovering some of the vehicle's kinetic energy during braking operations. The PNGV is sponsoring research on batteries, flywheels, and ultracapacitors for this purpose. Committee members reviewed each of these R&D programs in considerable depth to assess the status of each, the progress that has been made, and the developments required for the future. The PNGV Technical Roadmap has been updated for most of these technologies, and it provides a good summary of the program goals. However, following in-depth reviews, the committee members almost all reported that the people in charge of performing the technical work had very limited information about the detailed requirements that would be imposed by a vehicle installation. This lack of information reflected a major concern for all of the candidate technologies, with the possible exception of the CIDI engine; namely, the systems analysis work and packaging studies that would provide this information have fallen significantly behind schedule. This lack of direction to the individual technical teams makes it difficult for them to focus their efforts. This basic flaw in the program cannot help but reduce R&D effectiveness and efficiency. FOUR-STROKE COMPRESSION IGNITION DIRECT INJECTION ENGINES Traditional passenger car diesel engines exhibit 15 percent to 30 percent better fuel economy, 10 percent to 20 percent lower carbon dioxide (CO2) emissions, nearly zero evaporative emissions, and very low cold-start emissions when compared with similar gasoline engines. However, CIDI engines also suffer from size, weight, noise, and cost penalties that have limited their market acceptance in passenger cars unless their purchase is encouraged by a substantial fuel cost differential. Eliminating these disadvantages, while retaining or increasing the superior fuel economy of these engines, represents major challenges on several fronts. Program Status and Progress During the past year, the CIDI engine has been selected as the most promising of the four-stroke, direct-injection PNGV engine candidates for either stand-alone or hybrid vehicle use, and a technology road map applicable to CIDI engines has been completed. Research priorities have been established, and five high priority areas are being addressed through dedicated research programs. A workshop was held in which individuals from industry, academia, and government discussed and prioritized the critical technologies necessary for CIDI engines to meet the PNGV objectives. Also, the PNGV USCAR participants and
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Review of the Research Program of the Partnership for a New Generation of Vehicles: Third Report the U.S. heavy-duty diesel-engine industry have established communications and agree that there are several areas of common interest including: understanding combustion fundamentals combustion gas after-treatment fuel-composition effects on engine performance The five high priority CIDI research areas identified by the CIDI technical group are: lightweight engine architectures dimethyl ether (DME) as an alternate fuel for CIDI engines combustion-related processes lean NOx catalysis alternative CIDI fuels assessment (including diesel reformulation) The focus on combustion and DME is related to concerns about particulate emissions from CIDI engines. New cooperative programs, initiated in 1996, address critical aspects of each area. Other programs, most notably those involving fuel injection technology and lean NOx catalysis, were already in place. The OEMs are supporting several in-house CIDI development programs, primarily through their European subsidiaries, but also in the United States. These projects involve both development of subsystems (fuel delivery, turbochargers, and engine- and emission-control strategies) and prototype vehicles through the HEV programs, which will serve as a test bed for the new technologies. CIDI hybrids are under contract at both Ford and Chrysler, with different delivery schedules. Because the HEV programs preceded PNGV, these hybrid vehicles are required to double fuel economy rather than meeting the PNGV Goal 3 vehicle target of tripling fuel economy. Technical Targets The critical characteristics of a CIDI engine, suitable for application to a Goal 3 vehicle, are shown as a function of PNGV milestone targets in Table 4-1. The last column shows that the 1995 targets have been met or exceeded in both test engines and some production engines. Passenger car diesel engines typically weigh 20 percent to 40 percent more than their gasoline counterparts. Table 4-1 shows a need to reduce the engine specific weight (usually referred to as specific power) by 26 percent and increase the displacement specific power (power density) by 29 percent in the 1995 to 2004 time frame. A production Volkswagen engine, which includes a variable geometry turbocharger and intercooler, is within 5 percent of the specific power goal but has made no progress toward the power specific weight goal. This indicates the need for radically new materials or construction techniques that can reduce the weight of CIDI engines. Using a turbo-charger and intercooler also adds to the packaging challenge. Compared to the
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Review of the Research Program of the Partnership for a New Generation of Vehicles: Third Report TABLE 4-1 CIDI Engine Critical Characteristics versus PNGV Milestone Targets Characteristics Units 1995 Target 1997 Target 2000 Target 2004 Target 1996 Best brake thermal efficiency % 41.5 43 44 45 42.5a Displacement specific powerd kW/L 35 40 42 45 42.6a 45b Power specific weightd kW/kg 0.50 0.53 0.59 0.63 0.49a Cost per kW $/kW 30 30 30 30 30 Durability 1,000 miles 150 150 150 150 150 NVH (reduction in one meter noise) dBA -10 -10 -10 -10 -10c FTP 75 NOx Emissions in 2,500-lb ETW vehicle g/mile 0.6 0.4 0.3 0.2 0.6 0.4b FTP 75 PM Emissions in 2,500-lb ETW vehicle g/mile 0.08 0.06 0.05 0.04 0.08 0.04b Note: Based on data in Table III. F-1 in PNGV (1996). Acronyms: NVH (noise, vibration and harshness); FTP (federal test procedure); PM (particulate matter); ETW (emissions test weight) a Volkswagen production engine. b Prototype single-cylinder. c Current estimate for prototype hybrid. d Displacement specific power is also referred to as power density; power specific weight is more commonly referred to as specific power. gasoline engine, these components suggest an initial cost penalty of perhaps $800 to $1,200 in addition to the undetermined added cost of a sophisticated electronic fuel-injection system. The need for these added components makes keeping the cost to $30/kW (shown in Table 4-1) a major challenge. Fuel economy targets for the CIDI engine have been moderated in recognition of the likelihood of having to meet the increasingly stringent emissions standards shown in Table 4-2. The CIDI team believes that the most technically challenging aspect of the CIDI program will be meeting the NOx emission standards; however, possible stringent fine-particulate standards could also become a significant barrier for diesels. (Note that recently EPA issued a proposed rule for an atmospheric air-quality standard for fine particulates.) The PNGV should discuss with the EPA the likelihood of more restrictive particulate emission standards and their potential effect on the PNGV program. Intensive development of both in-cylinder combustion control and exhaust-gas after-treatment will be required
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Review of the Research Program of the Partnership for a New Generation of Vehicles: Third Report TABLE 4-2 PNGV Emission Targets and Standards Species g/mile 1997 Target 2000 Target 2004 Target Tier 1 Tier 2 LEV ULEV NOx 0.4 0.3 0.2 1.25a 0.2 0.3 0.3 Particulate matter (PM) 0.06 0.05 0.04 0.1a — 0.08 0.04 Carbon monoxide (CO) 1.7 4.2 1.7 4.2 2.1 Hydrocarbons 0.125 0.31 0.125 0.09 0.055 Note: LEV (low emission vehicle); ULEV (ultra-low-emission vehicle). Tier 1 and Tier 2 refer to standards for 10 years or 100,000 miles under the Clean Air Act Amendments of 1990. a For California, the NOx standard is 1.0 g/mile, and PM is 0.08 g/mile. The European standards for PM, which are based on a different driving cycle than U.S. standards, are (or are proposed to be) Euro II, 0.10 g/mile; Euro III, 0.04 g/mile; and Euro IV, 0.025 g/mile. reduce emissions from the CIDI engine, including reducing NOx emissions. In-cylinder combustion control will require a sophisticated, high-pressure, fuel-injection system that is matched to the engine's in-cylinder flow field over the entire operating range of the engine. Exhaust-gas after-treatment will require the development of lean NOx catalysts, NOx traps, or plasma-aided catalysts. Current Program Elements Emissions After-Treatment Two types of reductants have been considered for lean catalysis: urea (or ammonia) and hydrocarbons. Urea reduction of NOx is a well-known technology developed for treatment of exhaust from stationary sources. However, the technology has not been tested under highly variable vehicle operating conditions, which would require a sophisticated control system to avoid ammonia in the exhaust as a result of incomplete conversion of injected urea. The possible formation of ammonium sulfate particulates and the need to refill a reservoir tank of urea solution also may hamper consumer acceptance of this technology. Diesel fuel can also be used as a hydrocarbon reductant for NOx; it can be injected into the exhaust stream. Like the use of urea, the injection technology must be developed for optimal operation with minimal fuel consumption. At present, noble metal (e.g., platinum [Pt], and rhodium [Rh] catalysts are the most promising, but control of nitrous oxide (N2O) emissions, formation of metal sulfates, and prevention of emission of unburned hydrocarbons are still significant issues. Laboratory data suggest that the Tier II target could be met by matching the operating temperature window of the catalyst and the exhaust-gas temperature, but at a 1 percent fuel penalty. NOx trap technology uses an alkaline earth oxide to trap NOx by reacting
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Review of the Research Program of the Partnership for a New Generation of Vehicles: Third Report with it to form metal nitrate when the engine is running lean. Periodically, the engine runs fuel-rich, and the temperature of the exhaust increases. Then the metal nitrate is decomposed to release NOx, which is treated by a catalyst, such as the proven three-way catalyst. The long-term stability of such a system has yet to be demonstrated. The formation of stable metal sulfate and carbonate could cause severe degradation of the performance of such a device. Plasma-assisted catalytic removal of NOx is a new technology that has the potential to remove NOx and particulate matter (PM) simultaneously. The technology has not been tested commercially. In the PNGV CIDI Workshop of May 22–23, 1996, in Detroit, Michigan, it was reported that for this technology to be successful the required power must be reduced. It was also reported that the NOx removal rate needs to be increased while restraining the formation of nitric acid, ozone, and other atmospheric contaminants. Many of the research results have not been reported; therefore, the current status of and progress made with this technology is not clear. Laboratory test data presented to the committee by USCAR for the newest Volkswagen engine indicate that the Tier 0, and possibly the low-emission vehicle (LEV) PM standard can be met without exhaust after-treatment. However, the more stringent ultra-low-emission vehicle (ULEV), or Euro III standard, will probably require an oxidation catalyst. Because of the trade-off between PM and NOx, it is unlikely that these standards can be met by engine modification alone; an after-treatment device will be necessary. Catalytic oxidation devices to reduce PM emissions are currently used successfully on some heavy-duty trucks. A lean NOx cooperative research and development agreement (CRADA) was formed in 1994 involving the USCAR partners and five government laboratories, supported by the Department of Defense (DOD) and the U.S. Department of Energy (DOE). The government budget for Fiscal Year 1996 was $293,000 from the DOE Office of Defense Programs technology transfer initiative, and $950,000 from DOE. Unfortunately, because of late appropriation of the DOE funds, there was a nine-month stoppage of research at Sandia National Laboratories and Lawrence Livermore National Laboratory. The Fiscal Year 1997 request from DOE is for $840,000 and the emphasis of the research will be on methods to coat catalysts onto a monolith support and on production of full-size converters for testing and optimizing the reductant. No PNGV funds have been allocated for catalyst R&D because there are strong business incentives for companies to pursue proprietary research in this area. Catalyst suppliers worldwide, as well as Ford, General Motors, Cummins, and other engine manufacturers, both in the United States and abroad, are supporting intensive R&D of lean NOx reduction technology. High-Pressure Fuel-Injection Systems and Combustion Fundamentals Significant advancements in the fuel-injection system's ability to control the fuel injection rate to match it to in-cylinder combustion processes are required for
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Review of the Research Program of the Partnership for a New Generation of Vehicles: Third Report the CIDI power plant to be successful in the PNGV concept car and prototype. The concept engine will probably use more sophisticated electronically controlled injectors than are currently used. Two high-pressure fuel-injection configurations are under consideration: a hydraulically actuated common rail and a hydraulically intensified fuel injection system. They are referred to as the common rail and the hydraulic electronic unit injector (HEUI) types. Both are capable of providing an injection pressure independent of engine speed. This characteristic yields engines with relatively high low-end torque, which results in very good driving characteristics. Using a very high pressure common-rail injection system and large amounts (35 percent) of exhaust-gas recirculation (EGR), led a European contractor, AVL, to conclude that engine emissions eventually may be able to achieve the ULEV NOx standard (Meurer, 1996). The injection system must be capable of optimizing the injection rate shape and increasing the tolerance for EGR. A small pilot injection at varying times prior to the main injection has shown promise both for controlling combustion and reducing noise. However, as the EGR tolerance of the engine is increased, through increased injection-pressure and injection-rate-shape control, the carbon monoxide (CO) and unburned hydrocarbon emissions are also increased. These emissions are not a problem in current CIDI designs, but they may become a problem as regulations become more stringent and engine operation is extended into the operating range projected for the PNGV concept vehicles. The development of these injection systems for a concept engine is being pursued cooperatively between the USCAR participants and injection system manufacturers. Both types of injection system are being aggressively developed, and the prognosis is good for successful deployment to an engine in the required time frame. In 1996 the PNGV program established a 4-year combustion CRADA, with an initial allocation of $700,000/yr, plus matching funds from industry, to address the in-cylinder combustion processes of fuel injection, air-fuel mixing, combustion, and emission formation. The CRADA objective is to provide ''the technological understanding required to develop a new CIDI diesel engine which meets the efficiency and emissions standards of a PNGV vehicle." Participants are Sandia National Laboratories, Wayne State University, and the Engine Research Center of the University of Wisconsin, Madison. Optical diagnostics will be performed on a single-cylinder engine at Sandia; engine bench testing will be performed at Wayne State University; and modeling will be done at the Engine Research Center at the University of Wisconsin, Madison. The CRADA is just starting, and initial results are expected by the second half of the 1998 calendar year. Structural Engine Design and Manufacturing The Tank Automotive Command (TACOM) of DOD and USCAR initiated a program to investigate alternative engine architectures and lightweight materials
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Review of the Research Program of the Partnership for a New Generation of Vehicles: Third Report leading to procurement, development, and pre-prototype engine testing in 1997. The requested funding of $2.44 million for 1997 is not yet firm, and if it is held at a carryover level of $450,000, such lack of funding would seriously hamper progress. Concept designs being developed by Ricardo Engineering Ltd. are now focused on the possible use of magnesium for the engine block (Talwar, 1996). A specific manufacturing issue has surfaced related to the need for extremely close tolerances within the injection system; namely, the capability to make 0.10 mm diameter fuel injector holes consistently, compared to today's limit of 0.15 mm. A number of design and manufacturing approaches, for both affordability and weight reduction, are suggested throughout the program status documents. However, the benefits projected for these actions are not quantified with respect to their contribution to the cost or weight objectives, nor are these elements visible in the PNGV work plans. Assessment Of The Program The relatively advanced small-displacement CIDI engines in production in Europe, together with programs put in place through the PNGV and by individual companies to improve these engines, make the PNGV CIDI performance goals seem potentially achievable.2 The highest technology risk appears to be the ability to develop a combustion system and after-treatment system to meet an uncertain set of exhaust emission requirements in 2004. The PNGV program has put in place a modest effort to address both engine-out emissions reduction and after-treatment, but the funds are minimal, and results to date are insufficient to assess a rate of progress. However, substantial commercial programs are under way to address these issues. The cost and weight objectives of a CIDI engine that will meet the challenging goals for 2004 appear to be major obstacles. Ideas have been proposed for novel engine architectures, systems integration, reduced parts count, and manufacturing improvements to address these problems. However, it seems likely that the sophisticated high pressure injection system, variable geometry turbocharger, and high cylinder pressures, combined with the need for lightweight, high strength materials will continue to bring a substantial cost premium for this engine. It also 2 A presentation to the committee by AVL indicated a significant increase in fuel economy afforded by CIDI diesel engines (Herzog, 1996). Using data from production engines, by normalizing the weights of several vehicles to 1,000 kg (2,200 lb), AVL showed a CIDI fuel economy of 57.4 mpg as compared to 31.4 mpg for the multi-port fuel injection (MPFI) spark-ignited gasoline engine. This is an 83 percent increase in fuel economy as compared to state-of-the-art fuel injection gasoline engines. It should be noted, however, that these fuel economies are for the "1/3 Euromix" driving cycle, which is said to be less severe than the American federal urban driving cycle used for EPA fuel-economy estimates. They do not properly express efficiency differences, since the higher heating value of diesel fuel is not reflected in the normalization process; also the process may not properly reflect other vehicle differences.
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Review of the Research Program of the Partnership for a New Generation of Vehicles: Third Report appears that the proof-of-concept demonstration of lightweight structures and cost-reduction features for the CIDI are lagging the year 2000 concept vehicle schedule by a year or more. Obviously, further delays will be incurred unless funding is significantly increased from the 1996 level. In spite of the significant risks of not meeting the PNGV goals as noted above, it is clear that CIDI technology is, by far, the best understood and most highly developed of any power plant technology being considered in the program. Because it is almost certain to be one of the final candidates for use in the year 2000 concept vehicles, the CIDI technology program needs to be more focused and needs a substantial increase in financial support. Recommendations Based on its review of the program status and progress for CIDI engines, the committee makes the following recommendations. Recommendation. The PNGV should expand efforts to devise lightweight, low-cost alternative CIDI engine structures, and additional resources should be made available. Recommendation. The PNGV should immediately assess the possible effect of regulatory actions aimed at reducing the atmospheric levels of fine PM on the viability of passenger car CIDI engines, and the research and development program should be modified, if necessary. To help the EPA make decisions based on the best possible information, the EPA should be continually informed of decisions made by the PNGV during the downselect process. Furthermore, the PNGV and EPA should work together to determine the trade-offs between vehicle performance and environmental standards and associated impacts on social benefits and costs. GAS TURBINES Gas turbine engines have some attributes that make them potentially successful as a Goal 3 vehicle engine and other attributes that will make realizing this potential very difficult. The low-pressure, excess-air, continuous-flow combustion provides very low levels of untreated emissions and a broad multifuel capability. The all-rotating machinery leads to low levels of vibrations and noise. The continuous flow, annular flow path, and high rotational speeds result in high power-to-weight and power-to-volume ratios for the "core" of the engine. Furthermore, the dominance of the gas turbine engine in commercial and military aircraft has generated an enormous amount of R&D, which has resulted in significant technological advances. However, for more than 40 years, substantial efforts to develop the gas turbine for automotive applications have been unsuccessful for several reasons. Most notable are (1) achieving sufficiently efficient
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Review of the Research Program of the Partnership for a New Generation of Vehicles: Third Report aerodynamic turbomachinery components, which becomes more difficult as their size is reduced; (2) attaining high enough turbine inlet temperatures; (3) developing efficient means to recover a portion of the turbine exit thermal energy; and (4) developing materials, manufacturing techniques, and designs capable of meeting cost requirements. The "core" of the gas turbine engine generates hot, high-pressure gas that is expanded through one or more turbines to produce work. These engines lose efficiency very rapidly if the main shaft speed is allowed to decrease in partial-power operations. A single-shaft turbine engine can attain a relatively high efficiency over a very limited speed range. Therefore, automotive gas-turbine engines have generally required at least two turbines operating on separate shafts, which make the engine bulkier and more expensive. However, for a series hybrid vehicle, the engine speed is independent of the vehicle speed, the engine-speed range can be reduced, and the single-shaft arrangement may be adequate, depending on the hybrid-vehicle control strategy. Idle fuel consumption of gas-turbine engines is much higher than for similar-output reciprocating engines, so systems optimization is critical. High temperature gas at the turbine exit in an automotive gas turbine represents lost thermal energy, making regenerators or recuperators essential for efficient operation. These devices are heat exchangers that transfer some of the turbine exit thermal energy to the compressor discharge flow. However, they are large and heavy and thus detract from the power-to-weight and power-to-volume advantages of the engine "core." Turbine-engine size can be reduced and thermal efficiency improved dramatically by increasing turbine inlet temperatures. Cycle studies have shown that to approach the thermal efficiencies required for a Goal 3 vehicle it is necessary for this temperature to approach 2,500¹F, although there is some indication that it may have to be limited to less than 2,300¹F to limit NOx emissions. These temperatures exceed, by several hundred degrees, those possible with even the most exotic uncooled metal turbines. Even if they did not, the cost of these exotic materials and their fabrication would prohibit automotive usage. The alternative is to develop a ceramic material with the potential to meet both the cost and high temperature objectives. Program Status and Progress Previously Identified Barriers In its second report, the committee reported that gas turbines represent a promising technology for hybrid vehicles and that considerable progress had been made in the previous year, especially in turbo-alternator design, bearings, combustors, heat recovery, and controls. However, the committee also reported that progress was behind schedule and there were major technical roadblocks (NRC,
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Review of the Research Program of the Partnership for a New Generation of Vehicles: Third Report 1996). Foremost among the roadblocks was the lack of a turbine material that could withstand high temperatures, that was capable of being precision-formed to provide efficient aerodynamics, and that could be mass produced at low cost. It also appeared that little had been accomplished with respect to systems studies at the vehicle or power plant levels. To some extent, this clouded the actual magnitude of the technical barriers because the requirements and trade-offs were largely unknown. Progress toward Removing Barriers Some completed systems studies give better indications of the more desirable configurations and the projected performance parameters. The single shaft, turbo-generator configuration has been chosen, thereby limiting the vehicle application to a series hybrid. This configuration uses an all-electric drive system, in contrast to the parallel hybrid, where there is a direct mechanical link between the engine and the drive wheels. Some systems studies have projected better drivetrain efficiency for the parallel hybrid. If this is confirmed, the challenge of enhancing gas turbine efficiency will be increased. The systems studies presented to the committee were very preliminary, and there was no evidence that systems trade-offs had been made. The Allison engine design is complete, and the Teledyne Ryan design is well under way. Both designs appeared reasonable, although probably optimistic, in their projected goals. The designs have different target characteristics based upon two different hybrid-vehicle performance and control strategies. The Teledyne design power is 55 kW to 60 kW and its efficiency at one-third power, required to meet the Goal 3 vehicle fuel economy target, is 43 percent. Comparable values for the Allison design are 40 kW and 38 percent. The most optimistic projections would put attainable efficiencies at least several points lower than these values. Although many component tests have been run supporting the plausibility of the projections, the necessary resources have not been applied to iterative component and subsystem developments to indicate that these levels of performance can be maintained for the complete engine system. Ceramic Turbine Progress The single most critical component yet to be demonstrated is a suitably sized, efficient ceramic turbine, capable of being mass produced. The committee found the significant progress has been made by Kyocera-Vancouver and AlliedSignal Ceramics in making high-quality ceramic components with complex shapes and using processes with high potential for scale-up to automotive volumes and cost. Extruded regenerator rotors, integral turbine rotors, and scrolls have all shown new capabilities which, although beset by tooling and startup yield problems, have produced quality engine parts and have supported successful component
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Review of the Research Program of the Partnership for a New Generation of Vehicles: Third Report meaningful scale of technology could be carried out with a modest budget. These actions should considerably enhance the program focus and the probability of success in Phase 2. Assuring a high probability that the most promising battery systems are selected and production prototypes are developed that meet the PNGV performance, cycle life, safety, and cost goals will require substantially higher funding levels in the future. It seems likely that a meaningful share of the funding required for each system (on the order of $60 million to $150 million for the critical prototype and pilot-plant phases) will have to be provided by PNGV over the next five to seven years. Recommendations Based on its review of battery-development programs, the committee makes the following recommendations. Recommendation. Development of the high-power lithium-ion battery should continue until the prototype module level is reached, with early emphasis on ensuring safety under all foreseeable conditions. The control requirements for safe operation of modules and batteries in the hybrid mode should be determined, and development of potentially low-cost electric and thermal control systems should be initiated. Recommendation. The ongoing exploration of high-power nickel metal hydride batteries should be completed. Based on data and test data from promising nickel metal hydride batteries available from other sources, the PNGV should determine whether this technology offers advantages over lithium-ion batteries in hybrid applications and how these advantages might be captured for the PNGV Goal 3 vehicle. Recommendation. Modest efforts should be supported to explore the potential of other battery systems (such as the SRI concept) that show promise of providing superior performance, safety, enhanced cycle life, and/or lower cost. This support should be provided at least until the capabilities of the lithium-ion and/or nickel metal hydride batteries to meet PNGV goals can be predicted with confidence. Recommendation. Continued efforts should be supported to (1) develop storage subsystem and vehicle subsystem models that provide realistic performance, cycle life, and cost targets that establish a capability for conducting trade-off analyses; and (2) establish a testing methodology and a physical capability for evaluating high power batteries for hybrid electric vehicles both from within the PNGV program and externally.
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Review of the Research Program of the Partnership for a New Generation of Vehicles: Third Report FLYWHEELS Flywheels have very attractive power-to-weight and power-to-volume characteristics of the "core" system (compared to batteries) both in delivering power and in accepting the high power developed during vehicle braking. However, serious problems related to safety, cost, and size must still be solved. Technical Targets A detailed vehicle systems analysis, with appropriate vehicle subsystem trade-offs, has not been performed to define flywheel requirements for a PNGV hybrid vehicle. Nevertheless, the PNGV flywheel technical team has assumed parameters in order to specify its application to vehicles designed with either a fast-response or slow-response power plant. The fast-response power plant is assumed to react very much like a conventional automotive engine, responding very quickly to vehicle power demands. This type of power plant places the least demand on the flywheel system. The slow-response engine puts a much greater demand on the flywheel for the delivery of instant high power. This demand requires a much larger and more costly flywheel system. The flywheel objectives metrics for both types of power plants are shown in Table 4-4. Program Status and Progress There is a high probability that the design performance objectives shown in Table 4-4 can be achieved for the basic flywheel system because material specifications and performance characteristics are well known. However, because of the potential for catastrophic flywheel failure, safety considerations require that a containment structure be included. Requirements for this structure have not yet been determined; therefore, the ultimate cost, volume, and overall system weight cannot be determined at this time. Progress during 1996 The PNGV flywheel technical team has put together a mission statement and a technical plan. Objectives of the technical plan include developing automotive-applications requirement guidelines and action plans for testing, identifying high-leverage issues, developing a scalable model, and reviewing the feasibility of other mechanical energy storage systems (e.g., hydraulic) and progress documentation. The team is also monitoring flywheel design and testing efforts being pursued for other applications. For example, the University of Texas Center for Electromechanics at Austin is developing a flywheel system for a bus with AlliedSignal and another project, funded by the Advanced Research Projects
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Review of the Research Program of the Partnership for a New Generation of Vehicles: Third Report Agency (ARPA) and the Houston Metropolitan Transit Authority, to develop a safety containment system. Plans for 1997 Program guidelines and vehicle test data are not expected to be available until the end of 1997. The action plan for the test protocol is scheduled for completion by May 1997. The University of Texas Center for Electromechanics plans to mount a flywheel system on an advanced technology transit bus by the end of 1997, and they will complete a substantial number of flywheel burst-containment tests by May of 1997. The Federal Railroad Administration is testing composite flywheels that are one-third of the full design size making them comparable to the bus requirements. The ARPA flywheel safety program will provide a fundamental understanding of composite flywheel behavior and will develop rational means for developing safe designs. Containment of failures will be pursued through (1) careful design to avoid flywheel failure, (2) detection of initial failure potential and shutdown of the flywheel system to minimize failure loads, and (3) barriers to contain and mitigate potential damage. Assessment of the Program The PNGV flywheel technical team believes it is unlikely that flywheel subsystems will be able to support the first PNGV concept vehicles; but, if estimated funding of $1.3 million for Fiscal Year 1997 is made available, they should have a laboratory-scale subsystem by the end of 1997. The committee concurs with the team's assessment, while noting that other activities have produced significant data on flywheels systems that can assist in the downselect decision. These activities include the Trinity model flywheel from Lawrence Livermore National Laboratory, the Unique Mobility flywheel contracted by Ford Motor Company, and the Satcon work on the flywheel for the Patriot Vehicle at Chrysler. Containment cost and weight remain significant issues that are, as yet, undefined in terms of total vehicle system requirements. Recommendations Based on its review of the program and progress for flywheel development, the committee makes the following recommendations. Recommendation. After appropriate vehicle system trade-off studies have been conducted, performance objectives should be created that satisfy the requirements of the fast-response power plant vehicle system, and a plan should be developed for evaluating and integrating a flywheel subsystem in post-2000 concept vehicles.
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Review of the Research Program of the Partnership for a New Generation of Vehicles: Third Report Recommendation. The ARPA comprehensive flywheel failure containment plan should be pursued, including collecting burst/collision failure test data from all available sources. ULTRACAPACITORS Technical Targets Ultracapacitors are in the same category as flywheels—they are compatible only with the power-assist (fast-response engine) type of HEV configuration. The technical targets for ultracapacitors are essentially the same as those of the flywheel. The goal of the projects, sponsored mainly by DOE, is to develop high-power ultracapacitors that meet or exceed the energy storage requirements for fast-response engines. Program Status and Progress Several laboratories in the United States and other countries are examining the prospects for using ultracapacitors to provide pulse power for military applications, but there is little evidence of R&D abroad of ultracapacitors for use in the HEV. However, carbon-based, aqueous electrolyte ultracapacitors have been developed and commercialized in Japan for other applications, such as providing instantaneous power to high-speed computers during power failure. The ultracapacitors being developed for the HEV are of the electrochemical type, the active material being high-surface-area carbon, a noble metal oxide, or a conducting polymer. Of these types, ultracapacitors using carbon in an aqueous electrolyte are the most highly developed. However, the cell potential for this type of device is only 1 V, compared with 3 V for a cell with an organic electrolyte. General Electric Company is developing ultracapacitors of the latter type for the Ford HEV program. Based on the testing of unpackaged single cells, they project the following performance characteristics at 2.75 V: specific energy of 4.1 Wh/kg, energy density of 5 Wh/L to 7 Wh/L, specific power (to half maximum voltage) of 1,100 W/kg, and power density of 1,500 W/L. Maxwell Laboratory, Inc. is developing this same type of cell and has built 24-V modules and determined temperature effects and cycle life performance. At a constant power (1,100 W/kg) the performance was found to be better at a higher temperature, but there was a problem with an increased self-discharge rate. There is also some loss in energy after about 60,000 charge/discharge cycles. Sixteen cell modules (electrode area 200 cm2) are being built. Ultracapacitors using noble metal oxides and conducting polymers have the advantage of achieving a high specific power (2,000 W/kg to 4,000 W/kg); their drawback is having lower values of specific energy. Ultracapacitors with p-doped and n-doped conducting polymers, have demonstrated a value of 10 Wh/kg (the
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Review of the Research Program of the Partnership for a New Generation of Vehicles: Third Report PNGV goal for 2004 is 15 Wh/kg) for the specific energy. Los Alamos National Laboratory has demonstrated a very high specific power (about 10 kW/kg) with devices of this type. The Army Research Laboratory at Fort Monmouth, New Jersey, has obtained promising results with a new electrolyte, which is benign and exhibits a high specific conductivity, high solubility, high electrochemical stability, and the ability to work satisfactorily over a wide range of temperature and Small (-40¹C to 70¹C). In addition, Small Business Technology Transfer and Small Business Innovation Research Phase I awards were made in 1996 for innovative research on electrode structures, "wet" electrochemical ultracapacitors, and solid-state ultracapacitors, including thin-film dielectrics. Assessment of the Program Ultracapacitor projects are in an early stage of research and development. Their only potential applicability in the PNGV program is in conjunction with fast-response engines. The current programs are behind schedule, and the milestones for 1996 have not been reached. Developing ultracapacitors for energy storage in an HEV is a high risk, high payoff project. It is unlikely that the ongoing projects will be able to meet the PNGV timing, performance, and cost goals for the following reasons: Even though the specific power and power density could reach high values, the energy density is likely to remain low. For this application, the ultracapacitors must have a time constant of less than 100 ms. The high capacity needed for a high specific power and a relatively high energy density makes it very difficult to have such a low time constant because the equivalent series resistance will have to be of the order of a few ohms. The current costs of materials and fabrication processes are very high; to meet the PNGV cost goal for this energy storage device ($150/kWh), these costs will have to be reduced by two orders of magnitude. Self-discharge rates, particularly of the carbon ultracapacitors, are relatively high; although 100,000 to 200,000 cycles have been demonstrated in small cells, there is a significant loss in capacity after about 50,000 cycles. The prospects for developing batteries (particularly the high performance nickel metal hydride and lithium-ion batteries) that meet the PNGV technical goals for energy storage, both for the slow-response and fast-response engines, are excellent. The ultracapacitor technology will require at least 10 times the current level of financial support for a period of 10 to 15 years to reach the same state of development. A considerable amount of research is needed just to identify the type of ultracapacitor that might attain the performance level required for an energy-storage device for the HEV. It is premature to carry out scale-up and
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Review of the Research Program of the Partnership for a New Generation of Vehicles: Third Report cell-stacking tasks for the HEV application. Because ultracapacitors may be used in other applications, for which there are ongoing investigations, the PNGV should follow the progress of these programs and then analyze the needed research, development, and demonstration for the HEV at a later date. Recommendations Based on its review of ultracapacitor programs and progress, the committee makes the following recommendations. Recommendation. PNGV should conduct appropriate systems studies to determine the prospects for ultracapacitors in HEV applications in comparison with high power batteries and other energy storage devices, such as flywheels. Recommendation. Work on ultracapacitors for HEV applications should be limited to basic and applied research studies at universities, national laboratories, and industrial R&D centers and should be directed toward making fundamental advances and breakthroughs. ELECTRICAL AND ELECTRONIC POWER-CONVERSION DEVICES Program Description and Requirements All of the PNGV vehicle configurations involving electric motor drives, energy recovery, flywheels, or fuel cells require electric motors/alternators, power electronic inverters, and sophisticated electronic controllers. There are other vehicle subsystems and accessories, such as power steering and heating, ventilation, and air conditioning (HVAC) systems, that also require electric power control. During its second review, the committee noted that the PNGV Technical Roadmap demonstrated a good awareness of the state of the art for these devices and had established appropriate and challenging targets for performance, efficiency, weight, and cost. The milestones in the PNGV Technical Roadmap show the overall electric driveline efficiency improving from today's estimated 70 percent to 80 percent in 10 years, and the weight decreasing by 47 percent. The cost of the electronic converter/controller must be reduced by 85 percent, and the cost of the electric motor must be reduced by 80 percent. The committee commented that these are very ambitious goals. The committee did not conduct an in-depth review of the technologies during its second review and did not make specific recommendations. Current Status The following assessment is based on presentations on October 10, 1996, by the PNGV electrical and electronics power conversion devices team to the committee
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Review of the Research Program of the Partnership for a New Generation of Vehicles: Third Report subgroup on electrical and systems analysis. The PNGV-USCAR partners have varying degrees of experience in developing and producing power electronic converters and controls, and electrical motors and alternators of the type necessary for a Goal 3 vehicle. They are actively exploring various types of electric motor configurations, including induction, permanent magnet, switched reluctance, and synchronous reluctance. It was stated to the committee that power electronic converters available for demonstration today are approximately twice the weight required to meet the needs of a Goal 3 vehicle. Members of the team have some recent experience working with qualified semiconductor manufacturers in the development and fabrication of insulated-gate bipolar transistors (IGBTs) for high-power applications and a very preliminary understanding of the producibility of IGBT power converters and their associated production costs. PNGV-USCAR recognizes the importance of reducing vehicle accessory loads, such as HVAC loads, to reduce overall vehicle electrical loads. Moreover, they believe that the trend toward higher accessory loads in response to consumer demand will continue. This will make the challenge of reducing accessory loads even greater by the year 2004. PNGV needs to develop plans and allocate resources to address this issue. The PNGV-USCAR partners have made progress in understanding the effect of system requirements on the system architecture and primary components. The PNGV vehicle-defined need for 0.5-g vehicle acceleration will determine the configuration and size of the electric drive motors. The vehicle requirements for this subsystem have not been adequately defined for all vehicle configurations under consideration. The interface with the vehicle engineering team and the system analysis team has not been effectively established. It appears to the committee that this team is relying heavily on other electric-vehicle and HEV programs to guide their efforts in developing technology for the Goal 3 Vehicle. Chrysler is using its experience with the Patriot concept HEV; General Motors is using its experience from the Impact concept electric vehicle and the production of the EV-1; and Ford is using experience from the Ecostar and other advanced vehicle studies. Chrysler, Ford, and General Motors also have government-sponsored contracts to demonstrate HEV technology in concept vehicles. These programs provide the technology base for collaboration on electric motors, power converters, and other related components. It must be pointed out that these applications can provide background, but the PNGV requirements demand very specific design and development considerations in order to meet the performance targets. The DOE-funded HEV programs require the three OEMs to explore alternative HEV architectures. These include both parallel and series hybrid vehicles. Two of the partners (Ford and General Motors) selected parallel architectures for their HEV assumptions; the other partner (Chrysler) selected a series configuration. Chrysler received its HEV contract during the past year while General Motors and Ford have had contracts for a longer period. The partners have organized
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Review of the Research Program of the Partnership for a New Generation of Vehicles: Third Report technical steering groups that share information generated from the individual HEV programs. DOE and PNGV should make sure that detailed data developed in the HEV program is universally and uniformly shared with USCAR partners on a periodic basis. The technical steering groups have identified responsibilities, and members have collaborated on identifying cost, weight, and size targets for components. The steering groups have also developed various technical performance measures for the high-priority components, and they are assessing the state of existing technology. Analytic results are emerging, and limited test data are available from the partners' electric-vehicle and HEV efforts. The Chrysler Patriot program was targeted at a racing-technology vehicle; therefore, its requirements were quite different from those of a passenger vehicle. What was learned during development of the Patriot vehicle is useful to the PNGV program, especially in the design of the power controller. It must be noted, however, that manufacturability and cost were not major considerations in the Patriot vehicle program. The committee also reviewed an Office of Naval Research and DOE program, known as the Power Electronic Building Block (PEBB). This program is dedicated to developing new technologies to advance the state of the art in power electronics control. The goal of the program is to reduce the cost and weight of electric-propulsion systems while achieving a high degree of functional integration, efficiency, and reliability. Semiconductor development is a major part of this program. The committee questions the direct applicability of this program to PNGV requirements. The focus is on large packages containing multiple die, which are very expensive from both a device and system-manufacturing point of view. The cost constraints for automotive design will require optimum design for manufacturing and assembly where both weight and space must be minimized. In the course of the committee's review of this program, very little data on component and subsystem performance relative to PNGV requirements were presented. Both Ford and General Motors have made good progress in developing components that could contribute to the PNGV in their HEV programs. The new General Motors drive-motor design is an advance over currently available components, and the packaging density is impressive. These advances should lead to some design baselines and should provide needed cost and reliability data. General Motors' Impact vehicle could also provide basic cost data for a production vehicle. The PNGV-USCAR partners identified and ranked the highest priority areas for component technology development. These include electric motors and alternators, power control electronics, HVAC, and electric/electrohydraulic power steering. High performance efficiency for these subsystems and components is vital and a high priority because they greatly affect the overall efficiency of an HEV configuration. If the HEV configuration is selected for a Goal 3 vehicle, overall system performance will be significantly affected by the design and integration of the power electronics and electrical subsystems.
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Review of the Research Program of the Partnership for a New Generation of Vehicles: Third Report Typically, accessory loads, such as HVAC, power steering, wipers, cooling pumps, instrumentation, and the antilock braking system, can increase the demand for engine power by approximately 30 percent (Malcolm, 1996). Although the team presented limited descriptive material on these systems and their impact on fuel economy, it is clear that the power required by these loads must be reduced, and this will require a well-directed active effort by the PNGV team to achieve maximum efficiency. An aggressive cost-reduction program is also mandatory. For example, the electric or electrohydraulic steering subsystem cost must be reduced by a factor of three to meet the vehicle cost objectives (Piccinato, 1996). The group working on regenerative braking has identified a number of barriers to the development of a practical system. Of these, the efficiency of the energy storage device is critical. The battery technology now available cannot accept a high charging current efficiently. Questions concerning over-charging and depleting batteries as a storage device remain unaddressed. The efficiency goal for regenerative braking is 75 percent, without considering energy storage efficiency; current efficiency is estimated at 35 percent. There are many constraints to efficient braking energy regeneration, and recovering the energy at low vehicle speeds is a significant challenge. The team did not review or discuss the awareness of global technology. In Japan and Europe, for example there are several electric-vehicle and HEV programs in various stages of development. The team should make an effort to capitalize on all applicable technology. Assessment of the Program The committee concluded that very little was accomplished overall by the electrical and electronics power conversion devices team during the past year. The report given to the committee subgroup in October 1996 was virtually the same as the status reported at Vice President Gore's symposium in the spring of 1996. It should be noted that the team did not have an appointed leader for most of the year, and the committee believes the team lacks on overall sense of urgency. The PNGV Technical Roadman details four PEBB milestones. The first PEBB milestone, scheduled for 1995, has been missed. At the current rate of accomplishment, the second milestone, established for 1997, probably will be missed. The third and fourth milestone are scheduled for 2000 and 2002. Many tasks described in the PNGV Technical Roadmap are not being addressed. For example, no trade-off format with well defined requirements has been established to support the downselect process in 1997. The committee was informed at its November 11–13, 1996, meeting that a part-time team leader had been selected. The question of adequate funding was not addressed by the team. The committee had requested that this be reviewed and can only assume that it is not an issue.
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Review of the Research Program of the Partnership for a New Generation of Vehicles: Third Report Although the team did not specifically identify barriers to progress, the committee concluded that the following major issues could constitute barriers: Overall driveline efficiency is currently estimated to be 70 percent. The PNGV goal is 80 percent. No data were presented to establish a confidence factor in achieving the goal. Today's electric/electronic subsystems, such as power steering and HVAC, and accessories, such as wipers, cooling pumps, instrumentation, and antilock braking systems, require electric power equal to approximately 30 percent of the PNGV vehicle drive power. This level of power must be reduced. Sufficient, directed technical effort is necessary to achieve the required efficiency. Costs of motors and alternators, the power controller, vehicle electrical subsystems, and accessories are estimated at from 50 percent to 300 percent above the individual subsystem targets. No plan of action to achieve these targets was presented. The committee has a major concern about the overall process of assigning attribute targets to individual components without the benefit of a top-down, overall system definition supported by a systems analysis. Optimization of overall vehicle performance can be achieved only by this approach. Evaluation of the differences among the power plants is especially important. Recommendations Based on its review of electrical and electronic power conversion device programs and progress, the committee makes the following recommendations: Recommendation. The new electrical and electronic power conversion devices team leader should function full time and should determine how to make up for lost time and establish a schedule for the team. The team leader should identify the staff necessary for effective team performance and should commit them to the team's activities. One of the highest priorities for the new team leader should be developing interfaces with the vehicle engineering and the systems analysis teams. Recommendation. The impact of the team's schedule slippage on the technology downselect process should be reviewed immediately by the PNGV, and plans should be made to meet schedules that support the overall PNGV effort. REFERENCES Herzog, P. Future High Speed Diesel Engines for Passenger Cars. Presentation to the Standing Committee to Review the Research Program of the PNGV, National Academy of Sciences, Washington, D.C., November 12, 1996.
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Review of the Research Program of the Partnership for a New Generation of Vehicles: Third Report Kizer, T. 1996. Performance and Cost Metrics. Presentation to the Committee Subgroup on Non-electrochemical Storage Devices, University of Texas Center for Electromechanics, Austin, Texas, October 7, 1996. Malcolm, R. 1996. HVAC Status and General Requirements. Presentation to the Committee Subgroup on Electrical Systems and Systems Analysis, the Chrysler Technology Center, Auburn Hills, Michigan, October 10, 1996. Meurer, P. 1996. Fuel Injection Systems. Presentation to the Committee Subgroup on CIDI Engines, Ford Scientific Research Laboratory, October 22, 1996. NRC (National Research Council). 1996. Review of the Research Program of the Partnership for a New Generation of Vehicles, Second Report. Board on Energy and Environmental Systems and the Transportation Research Board. Washington, D.C.: National Academy of Sciences. Piccinato, P. 1996. Electrical Steering Review. Presentation to the Committee Subgroup on Electrical Systems and Systems Analysis, the Chrysler Technology Center, Auburn Hills, Michigan, October 10, 1996. PNGV (Partnership for a New Generation of Vehicles). 1996. Technical Roadmap (draft). Dearborn, Michigan: PNGV. Talwar, C. 1996. Lightweight Engine Structures. Presentation to the Committee Subgroup on CIDI Engines, Ford Scientific Research Laboratory, October 22, 1996.
Representative terms from entire chapter: