Assessment of Technologies for Improving Light-Duty Vehicle Fuel Economy Letter Report (2008) / Chapter Skim
Currently Skimming:
Letter Report
Letter Report
Pages 1-16
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 1... ...
20590 Dear Administrator Nason: The National Highway Traffic Safety Administration requested that the National Academies provide an objective and independent update of the 2001 National Research Council report Effectiveness and Impact of Corporate Average Fuel Economy (CAFE) Standards and add to its assessment other technologies that have emerged since that report was prepared.
|
From page 2... ...
The current study focuses on technology and will not consider CAFE issues related to safety, economic effects on industry, or the structure of fuel-economy standards; these issues were addressed in the earlier report. It will look at lowering fuel consumption by reducing power requirements through such measures as reduced vehicle weight, lower tire rolling resistance, or improved vehicle aerodynamics and accessories; by reducing the amount of fuel needed to produce the required power through improved engine and transmission technologies; by recovering some of the exhaust thermal energy with turbochargers and other technologies; and by improving engine performance and recovering energy through regenerative braking in hybrid vehicles.
|
From page 3... ...
FIGURE 1 Relationship of fuel consumption to fuel economy. FUEL-ECONOMY TECHNOLOGIES On the basis of a preliminary analysis of sales information on light-duty vehicles, the committee selected the vehicle classes shown in Table 1 for use in assessing the costs and fuel-economy benefits of engine, transmission, and vehicle technologies.
|
From page 4... ...
Turbocharging with downsizing is another technique for raising fuel economy. The improved size-to-output efficiency of a turbocharged engine allows a smaller displacement engine to be used for the same power output and thus reduces fuel consumption.
|
From page 5... ...
pumping-loss Goal is to shorten intake-valve-lift duration; short "throttling"; reduction durations may reduce pumping losses; reduced implementations valve lift is simply a consequence of shorter include analogue or durations stepwise control (an Manufacturing tolerance control is critical alternative to As intake-manifold vacuum decreases, alternative conventional pressure means must be found to implement power throttling) brakes and positive crankcase-ventilation valves Benefit will vary with engine size Other valve events: Independently, relatively small Timing of exhaust-valve closing is important for exhaust-valve closing, effects outside the aforementioned maintaining peak power exhaust-valve opening, intake-valve opening Friction reduction 0.3-1% owing to reduced-viscosity Roller-follower valve trains and piston-kit friction lubricants; other approaches require reduction measures were nearly universally further investigation implemented in the middle 1980s Parasitic-loss reduction Electric coolant pump To be determined Camless valve actuation To be determined Variable charge motion To be determined Homogeneous-charge To be determined compression ignition a Improvements are over a 2007 naturally aspirated gasoline vehicle engine of similar performance characteristics.
|
From page 6... ...
At the time of that report, the technology available could not overcome the tradeoff between NOx and particulate emissions typical of light-duty diesel engines. The motivation for including light-duty diesel technology in the new report stems from the fact that the light-duty diesel vehicles in production and in widespread use in Europe have already demonstrated a 30-40% reduction in fuel consumption, depending on engine size, compared with 2007 model-year gasoline engines.
|
From page 7... ...
TABLE 4 Transmission Technologies for Reducing Fuel Consumptiona Fuel-Consumption Technology Reduction Comments Five-speed automatic transmissions 2-3% Technology can also improve vehicle performance Six-speed automatic transmissions 3-5% Seven-speed automatic transmissions 5-7% Eight-speed automatic transmissions 6-8% Automated manual transmissions (six- 6-8% speed) Continuously variable transmissions 1-8% Some issues related to differences in feel and engine noise; improvements depend on engine size Early torque converter lockup 0.5% NVH issues Aggressive shift logic 1-5%b Potential effects on drivability a Improvements are over a 2007 naturally aspirated gasoline vehicle engine of similar performance characteristics.
|
From page 8... ...
Two measures that can improve fuel economy, early lock-up and aggressive shift logic, can be implemented by the ETC through the ECU; both measures can also increase NVH and affect drivability. Vehicle Technologies for Improving Fuel Economy Vehicle technologies focus on nonpowertrain methods of reducing fuel consumption.
|
From page 9... ...
The associated effect on fuel consumption and fuel economy could be 1-2%. A report on tires and fuel economy estimates that a 10% reduction in rolling resistance will improve fuel economy by 1-2% (NRC, 2006)
|
From page 10... ...
That enables some energy recovery through regenerative braking, which results in a reduction in fuel consumption of 11-17% in the city driving cycle. Generally, these vehicles use a larger battery (such as a 42-V battery)
|
From page 11... ...
Of particular importance is the prospect for the newer lithium-ion batteries, which, it is predicted, will substantially reduce safety problems and have longer cycle lives and considerably higher energy densities than the NiMH batteries now installed in all type III hybrids. Both all-electric and fuel-cell vehicles have the potential to reduce energy use and emissions (depending on how electricity and hydrogen are produced)
|
From page 12... ...
. With the ability to simulate the interactions of vehicle subsystems directly, this approach has the potential to provide useful information about applying combinations of technologies to a given vehicle, to account for the nonlinear effects on overall vehicle performance that can result from the combinations, and to evaluate whether the estimated benefits of the individual technologies applied to vehicle subsystems are realized at the vehicle system level when technologies are combined.
|
From page 13... ...
The challenges related to the PDA approach lie in the difficulty of inferring specific details about the synergies among subsystem technologies from the input data used to generate the summary. As opposed to the FSS approach, in which these interactions are represented in the formulation of the model, in the PDA approach synergies are approximated by using simple lumped-parameter models, are embedded in the available vehicle data, or are introduced by means of engineering judgment.
|
From page 14... ...
The rationale for assessing vehicle technologies incrementally is that when the fuel economy of a particular vehicle is estimated with the FSS approach, the probability that the final estimate will be consistent with the actual value is reduced because of the accumulation of modeling errors for each component in the system. Often, the modeling errors are multiplicative; even if the component models represent the physics of the process accurately, the multiplicative effect at the system level can produce large estimation errors.
|
From page 15... ...
reduces thermodynamic losses that are affected by gas temperatures and pressures and thus reduces engine fuel consumption. Such effects would be highlighted directly by analysis based on the second law of thermodynamics.
|
From page 16... ...
Sincerely, Trevor O Jones, Chair Committee on Assessment of Technologies for Improving Light-Duty Vehicle Fuel Economy 16
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.