NHTSA Modeling and Technology Projections Underlying the Proposed CAFE Target of 34.1 mpg by MY 2016
|Three of the NHTSA scenarios for penetration of technologies for passenger cars for MY 2016. Shown are slow growth (3%), the preferred proposed alternative, and the maximum potential. Data: Preliminary Regulatory Impact Analysis. Click to enlarge.|
On 15 Sep, NHTSA and the US EPA proposed a joint rulemaking on fuel economy and greenhouse gas emissions for light duty vehicles: an average new car 34.1 mpg and 250 g CO2/mile for model year 2016. (The 250 g/mile of CO2 equivalent emissions limit by EPA is equivalent to 35.5 mpg if the automotive industry were to meet this CO2 level just through fuel economy improvements.) (Earlier post.)
Behind the targets is a significant amount of modeling, including revisions to certain aspects of the Volpe modeling process, such as the inputs, data, modeling techniques, and the constraints used in assessing appropriate stringency for future CAFE standards. In developing the proposed preferred alternative for the rulemaking, NHTSA also projected technology penetration and associated costs for the vehicle fleet. NHTSA details the modeling and the projections in the “Preliminary Regulatory Impact Analysis”, and the NHTSA/EPA “Draft Joint Technical Support Document”.
|Three of the NHTSA scenarios for penetration of technologies for light trucks for MY 2016. Shown are slow growth (3%), the preferred proposed alternative, and the maximum potential. Data: Preliminary Regulatory Impact Analysis. Click to enlarge.|
In an earlier rulemaking, NHTSA reformed the corporate average fuel economy (CAFE) standards with a size-based standard based on footprint. (Earlier post.) The new proposed rulemaking continues this approach; a continuous mathematical function provides a separate fuel economy target for each footprint. Individual manufacturers will be required to comply with a single fuel economy level that is based on the distribution of its production among the footprints of its vehicles.
Although the same reformed CAFE scheme is required for both passenger cars and light trucks, they are established with different continuous mathematical functions specific to the vehicles’ design capabilities.
The baseline assumptions for the NHTSA proposed rulemaking differ from previous analyses. In the past, the baseline was the manufacturers’ confidential plans for each model year; in the new analysis, the baseline is each manufacturer’s MY 2008 fleet. NHTSA assumes that similar vehicles will be produced through MY 2016 and technologies are added to this baseline fleet to determine what mpg levels could be achieved with technologies. This approach, said the agency, is more transparent than relying on manufacturers’ confidential plans.
NHTSA examined eight scenarios examined include five alternatives that are annual percentage improvements over the baseline. The “Preferred Alternative” proposed in the rulemaking would require fuel economy levels that are between the 4 and 5% annual increase alternatives.
Technologies. In developing technology inputs for MY 2012-2016 standards, NHTSA and EPA reviewed, as requested by President Obama in his January 26 memorandum, the technology assumptions that NHTSA used in setting the MY 2011 standards and the comments that NHTSA received in response to its May 2008 NPRM.
The agencies also reviewed the technology input assumptions identified in EPA’s July 2008 Advanced Notice of Proposed Rulemaking and 2008 Staff Technical Report and supplemented their review with updated information from more current literature, new product plans and from EPA certification testing. The two agencies are continuing with their analysis, and will incorporate the upcoming National Academies update of the 2002 NAS Report, which presents technology effectiveness estimates.
The technologies considered by the NHTSA and EPA fall under the five broad categories of engine, transmission, vehicle, electrification/accessory, and hybrid technologies. The agencies did not consider technologies in the research stage because their effectiveness and/or costs are presently only known with greater levels of uncertainty.
Low-friction lubricants: low viscosity and advanced low friction lubricants oils are now available with improved performance and better lubrication.
Reduction of engine friction losses: can be achieved through low-tension piston rings, roller cam followers, improved material coatings, more optimal thermal management, piston surface treatments, and other improvements in the design of engine components and subsystems that improve engine operation.
Conversion to dual overhead cam with dual cam phasing: as applied to overhead valves designed to increase the air flow with more than two valves per cylinder and reduce pumping losses.
Cylinder deactivation: deactivates the intake and exhaust valves and prevents fuel injection into some cylinders during light-load operation. The engine runs temporarily as though it were a smaller engine which substantially reduces pumping losses.
Variable valve timing: alters the timing or phase of the intake valve, exhaust valve, or both, primarily to reduce pumping losses, increase specific power, and control residual gases.
Discrete variable valve lift: increases efficiency by optimizing air flow over a broader range of engine operation which reduces pumping losses. Accomplished by controlled switching between two or more cam profile lobe heights.
Continuous variable valve lift: is an electromechanically controlled system in which cam period and phasing is changed as lift height is controlled. This yields a wide range of performance optimization and volumetric efficiency, including enabling the engine to be valve throttled.
Stoichiometric gasoline direct-injection technology: injects fuel at high pressure directly into the combustion chamber to improve cooling of the air/fuel charge within the cylinder, which allows for higher compression ratios and increased thermodynamic efficiency.
Combustion restart (CBRST): can be used in conjunction with gasoline direct-injection systems to enable idle-off or start-stop functionality. Similar to other start-stop technologies, additional enablers, such as electric power steering, accessory drive components, and auxiliary oil pump, might be required.
Turbocharging and downsizing (TRBDS): increases the available airflow and specific power level, allowing a reduced engine size while maintaining performance. This reduces pumping losses at lighter loads in comparison to a larger engine.
Exhaust-gas recirculation boost: increases the exhaust-gas recirculation used in the combustion process to increase thermal efficiency and reduce pumping losses.
Diesel engines: have several characteristics that give superior fuel efficiency, including reduced pumping losses due to lack of (or greatly reduced) throttling, and a combustion cycle that operates at a higher compression ratio, with a very lean air/fuel mixture, than an equivalent-performance gasoline engine. This technology requires additional enablers, such as NOx trap catalyst after-treatment or selective catalytic reduction NOx after-treatment.
Improved automatic transmission controls: optimizes shift schedule to maximize fuel efficiency under wide ranging conditions, and minimizes losses associated with torque converter slip through lock-up or modulation.
Six-, seven-, and eight-speed automatic transmissions: the gear ratio spacing and transmission ratio are optimized for a broader range of engine operating conditions.
Dual clutch or automated shift manual transmissions: are similar to manual transmissions, but the vehicle controls shifting and launch functions. A dual clutch automated shift manual transmission uses separate clutches for even numbered and odd-numbered gears, so the next expected gear is pre-selected, which allows for faster and smoother shifting.
Continuously variable transmission: commonly uses V-shaped pulleys connected by a metal belt rather than gears to provide ratios for operation. Unlike manual and automatic transmissions with fixed transmission ratios, continuously variable transmissions can provide fully variable transmission ratios with an infinite number of gears, enabling finer optimization of transmission torque multiplication under different operating conditions so that the powertrain can operate at its optimum efficiency.
Manual 6-speed transmission: offers an additional gear ratio, often with a higher overdrive gear ratio, than a 5-speed manual transmission.
Low-rolling-resistance tires: have characteristics that reduce frictional losses associated with the energy dissipated in the deformation of the tires under load, therefore reducing the energy needed to move the vehicle.
Low-drag brakes: reduce the sliding friction of disc brake pads on rotors when the brakes are not engaged because the brake pads are pulled away from the rotors.
Front or secondary axle disconnect for four-wheel drive systems: provides a torque distribution disconnect between front and rear axles when torque is not required for the non-driving axle. This results in the reduction of associated parasitic energy losses.
Aerodynamic drag reduction: is achieved by changing vehicle shape or reducing frontal area, including skirts, air dams, underbody covers, and more aerodynamic side view mirrors.
Mass reduction and material substitution: Mass reduction encompasses a variety of techniques ranging from improved design and better component integration to application of lighter and higher-strength materials. Mass reduction is further compounded by reductions in engine power and ancillary systems (transmission, steering, brakes, suspension, etc.).
Electrification/accessory and hybrid technology
Electric power steering (EPS): is an electrically-assisted steering system that has advantages over traditional hydraulic power steering because it replaces a continuously operated hydraulic pump, thereby reducing parasitic losses from the accessory drive.
Improved accessories (IACC): may include high efficiency alternators, electrically driven (i.e., on-demand) water pumps and cooling fans. This excludes other electrical accessories such as electric oil pumps and electrically driven air conditioner compressors.
Air Conditioner Systems: These technologies include improved hoses, connectors and seals for leakage control. They also include improved compressors, expansion valves, heat exchangers and the control of these components for the purposes of improving tailpipe CO2 emissions as a result of A/C use. These technologies are covered separately in the EPA RIA.
12-volt micro-hybrid (MHEV): also known as idle-stop or start stop and commonly implemented as a 12-volt belt-driven integrated starter-generator, this is the most basic hybrid system that facilitates idle-stop capability. Along with other enablers, this system replaces a common alternator with an enhanced power starter-alternator, both belt driven, and a revised accessory drive system.
Higher Voltage Stop-Start/Belt Integrated Starter Generator (BISG): provides idle-stop capability and uses a high voltage battery with increased energy capacity over typical automotive batteries. The higher system voltage allows the use of a smaller, more powerful electric motor and reduces the weight of the motor, inverter, and battery wiring harnesses. This system replaces a standard alternator with an enhanced power, higher voltage, higher efficiency starter-alternator, that is belt driven and that can recover braking energy while the vehicle slows down (regenerative braking).
Integrated Motor Assist (IMA)/Crank integrated starter generator (CISG): provides idle-stop capability and uses a high voltage battery with increased energy capacity over typical automotive batteries. The higher system voltage allows the use of a smaller, more powerful electric motor and reduces the weight of the motor, inverter, and battery wiring harnesses. This system replaces a standard alternator with an enhanced power, higher voltage, higher efficiency starter-alternator that is crankshaft mounted and can recover braking energy while the vehicle slows down (regenerative braking).
2-mode hybrid (2MHEV): is a hybrid electric drive system that uses an adaptation of a conventional stepped-ratio automatic transmission by replacing some of the transmission clutches with two electric motors that control the ratio of engine speed to vehicle speed, while clutches allow the motors to be bypassed. This improves both the transmission torque capacity for heavy-duty applications and reduces fuel consumption and CO2 emissions at highway speeds relative to other types of hybrid electric drive systems.
Power-split hybrid (PSHEV): a hybrid electric drive system that replaces the traditional transmission with a single planetary gearset and a motor/generator. This motor/generator uses the engine to either charge the battery or supply additional power to the drive motor. A second, more powerful motor/generator is permanently connected to the vehicle’s final drive and always turns with the wheels. The planetary gear splits engine power between the first motor/generator and the drive motor to either charge the battery or supply power to the wheels.
Plug-in hybrid electric vehicles (PHEV): are hybrid electric vehicles with the means to charge their battery packs from an outside source of electricity (usually the electric grid). These vehicles have larger battery packs with more energy storage and a greater capability to be discharged. They also use a control system that allows the battery pack to be substantially depleted under electric-only or blended mechanical/electric operation.
Electric vehicles (EV): are vehicles with all-electric drive and with vehicle systems powered by energy-optimized batteries charged primarily from grid electricity.
Projected technology penetrations for the preferred alternative. EPA and NHTSA expect that automobile manufacturers will meet the proposed standards by utilizing technologies that are mainly available today, but with more widespread use across the light-duty vehicle fleet. With commercialization of electric vehicles and plug-in hybrids just beginning within the rulemaking period, their penetration in the modeled scenarios is negligible—0%, even by MY 2016, and even in the most aggressive scenario.
Among the results of the MY 2016 technology penetration projections under the preferred alternative scenario—i.e., the basis for the proposed CAFE rulemaking—based on total sales of 16.6 million units of MY 2016 vehicles are:
- Dual cam phasing: 61% for cars, 52% for trucks
- Stoichiometric Gasoline Direct Injection (GDI): 44% for cars, 56% for trucks
- Discrete variable valve lift on DOHC: 34% for cars, 33% for trucks
- Turbocharging and downsizing: 26% for cars, 15% for trucks
- Dual Clutch or Automated Manual Transmission: 61% for cars, 92% for trucks
- Electric Power Steering: 86% for cars, 96% for trucks
- Belt mounted Integrated Starter Generator: 33% for cars, 27% for trucks
- Power Split Hybrid: 5% for cars, 2% for trucks
- 2-mode hybrid and plug-in hybrid: 0% for both cars and trucks
- Mass Reduction (1.5%): 73% for cars, 71% for trucks
- Mass Reduction (3.5% to 8.5%): 32% for cars, 31% for trucks