The U.S. Environmental Protection Agency (EPA) and the U.S. Department of Transportation National Highway Traffic Safety Administration (DOT/NHTSA) issued proposed greenhouse gas emissions standards and fuel efficiency standards for medium- and heavy-duty engines in a notice of proposed rulemaking (NPRM) on October 26, 2010 (EPA/NHTSA, 2010a,b). On September 15, 2011, the EPA and NHTSA issued final greenhouse gas emissions standards and fuel efficiency standards for medium- and heavy-duty engines and vehicles that are tailored to each of three regulatory categories of heavy-duty vehicles: (1) Heavy-Duty Pickup Trucks and Vans, (2) Vocational Vehicles, and (3) Combination Tractors (EPA/NHTSA, 2011a). The agencies are providing credits for the use of hybrid powertrain technology as an incentive (EPA/NHTSA 2011a,b). The approach to account for the use of a hybrid powertrain when evaluating compliance with the standards is described below.
HEAVY-DUTY PICKUP AND VAN HYBRIDS
For the heavy-duty pickup truck and van hybrid class of vehicles with gross vehicle weight ratings [GVWRs] between 8,500 and 14,000 lb (that are not already covered under the Model Year 2012-2016 light-duty truck and medium-duty passenger vehicle greenhouse gas [GHG] standards), the agencies have proposed that testing would be done using adjustments to the test procedures developed for light-duty hybrids, using the light-duty Federal Test Procedure (FTP) and the Highway Fuel Economy Test (HWFET), but extending the requirement for chassis certification for CO2 emissions to diesel-powered vehicles. Currently, chassis certification is a gasoline requirement and a diesel option. Manufacturers would be allowed to continue to certify engines for criteria pollutant (non-GHG) requirements as they do today.
The EPA and NHTSA fuel-consumption standards are expressed on a gal/100 mile basis, and that would apply to a manufacturer’s fleet of heavy-duty pickup trucks and vans with a GVWR from 8,500 to 14,000 lb. The credits for the hybrid vehicle would be calculated according to the Averaging, Banking, and Trading (ABT) program described by an equation for fuel consumption credits given later in this section.
A manufacturer’s credit or debit balance will be determined by calculating its fleet average performance using the data from the FTP and HWFET tests and comparing this data to the manufacturer’s fuel-consumption standards, as determined by its fleet mix, for a given model year. A target standard is determined for each vehicle with a unique payload, towing capacity, and drive configuration (two-wheel versus four-wheel drive). These unique targets, weighted by their associated production volumes, are summed at the end of the model year to derive the production volume-weighted manufacturer annual fleet average standard. A manufacturer would generate credits if its fleet average fuel-consumption level were lower than its standard and would generate debits if its fleet average fuel-consumption level were above that standard.
In addition to production weighting, the credit calculations include a factor for the useful life, in miles, in order to allow the expression of credits in gallons. The following equation is used to calculate credits (debits) and account for the amount that the family limit is below (above) the standard, the payload tons, the sales volume, and the useful life.
Fuel Consumption Credits (gallons) = (FC Std - FC Act) × Volume × UL × 100,
FC Std = Fleet average fuel-consumption standard (gal/100 mile)
FC Act = Fleet average actual fuel-consumption value (gal/100 mile)
Volume = Total production of vehicles in the regulatory category
UL = Useful life for the regulatory category (miles)
VOCATIONAL VEHICLE AND TRACTOR HYBRIDS
For vocational vehicles and combination tractors incorporating hybrid powertrains, the agencies specify two methods for establishing credits. The first method uses chassis dynamometer evaluation of the vehicle, and the second method uses engine dynamometer evaluation with the powerpack in either a (1) pre-transmission format or a (2) post-transmission format. Each method requires a comparison test of the actual physical product, because the agencies are not aware of analytical models that can assess the technology.
Chassis Dynamometer Evaluation
Similar to heavy-duty pickup and van hybrids, to generate credits for hybrid vocational vehicles, full vehicle chassis dynamometer testing is a straightforward basis for comparing fuel consumption performance of hybrid vehicles to conventional vehicles. The agencies specify two sets of duty cycles for vocational trucks to evaluate the benefit depending on the vehicle application. The key difference between the two sets is that one does not include operation of a power take-off (PTO) unit while the other does. For example, delivery trucks do not operate a PTO while bucket and refuse trucks do.
The duty cycles that apply to hybrid powertrains without a PTO system are shown in Table F-1 .
The transient cycle, derived from the California Air Resources Board (CARB) Heavy-Duty Truck 5 Mode Cycle, is 668 seconds long and travels 2.84 miles. The cycle contains 5 stops and contains 112 seconds of idling. The maximum speed of the cycle is 47.5 mph with an average speed of 15.3 mph. The High Speed and Low Speed Cruise modes reflect constant speed cycles at 65 mph and 55 mph, respectively, which are representative of drivers using cruise control whenever possible. The final rules include a new optional PTO test cycle in addition to the standard set of test cycles in order for manufacturers of advanced PTO systems to demonstrate in the laboratory environment fuel consumption reductions that would be realized from their systems in the real world. The composite PTO test cycle for utility and refuse trucks is described in greater detail in EPA/NHTSA (2011b, see Table 3-23).
|Vehicle Category||Transient||55 mph||65 mph|
|Day cab tractor||19||17||64|
|Sleeper cab tractor||5||9||86|
Engine Dynamometer Evaluation
The engine test procedure involves exercising the conventional engine and the hybrid-engine system based on an engine testing strategy. Real-world functionality would need to be accurately represented. The testing would also need to recover vehicle kinetic energy. The agencies specify the use of the Heavy-Duty Engine FTP cycle for evaluation of hybrid vehicles, which is the same test cycle specified for engines used in vocational vehicles. Engine dynamometer evaluation may be undertaken in one of two ways:
1. Pre-transmission power-pack testing, which includes the engine and hybrid systems in a pre-transmission format, could utilize existing engine certification duty cycles. Changes to how the engine certification would be conducted to address energy capture and idle operation would need to be evaluated as a complete protocol is developed.
2. Post-transmission power-pack testing, which includes the transmission, would require a vehicle-like duty cycle, which provides the appropriate speeds and torques to match field operation.
Heavy-duty hybrid vehicles and hybrid powertrains can be certified using an A to B test method. This concept entails testing the conventional vehicle or powertrain, identified as “A,” and the hybrid version of the vehicle or powertrain, identified as “B.” The benefit associated with the hybrid system for fuel consumption would be determined from the weighted fuel-consumption results from the tests of each vehicle or hybrid powertrain, as described below:
1. Improvement Factor = (Fuel Cons_A - Fuel Cons_B)/(Fuel Cons_A)
2. Gallons/1,000 ton-mile benefit = Improvement Factor × GEM Fuel Cons Result_B
Note in the above equations that the GEM (Greenhouse Gas Emissions Model) result would be calculated for the base vehicle or powertrain without hybridization, and the Improvement Factor would account for hybridization of the vehicle or powertrain.
The following equation for the credits (debits) accounts for the amount that the family emission limit is below (above) the standard, the payload tons, the production volume, and the useful life:
Fuel Consumption credit (deficit)(gallons) = (Std-FEL) × (Payload Tons) × (Volume) × (UL) × 103,
Std = Standard associated with the regulatory category (gallons/1,000 ton-mile) (fuel consumption: Gallons/1,000 ton-mile)
Payload tons = Prescribed payload for each subcategory (12.5 tons for Class 7 tractors, 19 tons for Class 8 tractors, 2.85 tons for light heavy-duty [LHD] vocational, 5.6 tons for medium heavy-duty [MHD] vocational, 7.5 tons for heavy heavy-duty [HHD] vocational vehicles)
FEL = Family emission or fuel-consumption limit for the vehicle family (gallons/1,000 ton miles)
Volume = (Projected or actual) production volume of the vehicle family
UL = Useful life of the vehicle (435,000 miles for HHD, 185,000 miles for MHD, and 110,000 miles for LHD)
The final rules include an option for a manufacturer to obtain early credits by certifying a subcategory of vehicles at fuel-consumption levels below the standard prior to the model year the standard becomes effective. A 1.5 multiplier will be applied to early credits earned in model year 2013. Early credits provide an incentive for manufacturers to introduce more efficient engines and vehicles earlier than required by the standards.
Advanced Technology Credits
The final rules include a provision for obtaining credits for introducing advanced technologies to provide an incentive for their introduction. A 1.5 multiplier will be applied to these credits, but the total credits are capped in any model year. Hybrid powertrain designs that include energy storage systems are one of the advanced technologies defined by the agencies.
EPA/NHTSA (Environmental Protection Agency [Office of Transportation and Air Quality]/National Highway Traffic Safety Administration [Department of Transportation]). 2010a. Greenhouse Gas Emissions Standards and Fuel Efficiency Standards for Medium- and Heavy-Duty Engines and Vehicles. Dockets No. EPA-HQ-OAR-2010-0162 and No. NHTSA-2010-0079, October 25, 2010. Available at http://www.regulations.gov.
EPA/NHTSA. 2010b. Draft Regulatory Impact Analysis, Proposed Rulemaking to Establish Greenhouse Gas Emissions Standards and Fuel Efficiency Standards for Medium- and Heavy-Duty Engines and Vehicles. EPA-420-D-10-901. October.
EPA/NHTSA. 2011a. Greenhouse Gas Emissions Standards and Fuel Efficiency Standards for Medium- and Heavy-Duty Engines and Vehicles, Final Rules. August 9.
EPA/NHTSA. 2011b. Final Rulemaking to Establish Greenhouse Gas Emissions Standards and Fuel Efficiency Standards for Medium- and Heavy-Duty Engines and Vehicles, Regulatory Impact Analysis. EPA- 420-R-11-901. August.