Clark Hochgraf at the Rochester Institute of Technology (RIT) presented a paper at this week’s SAE 2011 World Congress that examined the powertrain and braking efficiency (PABE) of a wide spectrum of light duty vehicles to create a list of the ten most efficient powertrains, and the ten vehicles with the lowest vehicle limited fuel consumption (VLFC).
Hochgraf found that in 2010, the top 10 most efficient powertrains on the city cycle all had CVTs and were hybrids. Three of the top te most efficient powertrains in the highway cycle did not use CVTs or hybrid powertrains. The most efficient powertrains were not necessarily matched to the lowest energy consumption chassis, although, he noted, there was some overlap.
VLFC represents the minimum amount of fuel a vehicle consumes to complete a given drive cycle; in computing VLFC, the powertrain is assumed to have 100% efficiency and the braking system is considered lossless.
PABE characterizes the powertrain for the effect of powertrain energy conversion efficiency and for regenerative braking efficiency
The powertrain and braking efficiency metric characterizes the powertrain system, for both forward propulsion characteristics and for braking characteristics. PABE is affected by hybridization, by engine efficiency, by accessory loads (e.g., air conditioning, lighting) and by powertrain operating strategies including non-hybrid strategies.
The advantage of defining VLFC as done here, is that it provides a figure of merit for the vehicle’s energy consumption characteristics, completely separate from the powertrain’s characteristics and performance. Thus, the VLFC is independent of the degree of hybridization or non-hybridization. However, VLFC does play a key role in the measured fuel consumption.Hochgraf 2011
The lowest energy consumption chassis of the 2010 passenger vehicle fleet by the VLFC method is the Toyota Prius, followed by the Suzuki SX4 chassis, the Yaris, and then the Civic Hybrid and the Kia Rio.
The most efficient powertrains on the UDDS city cycle by PAGE analysis are (1) Toyota Highlander Hybrid 4WD); Mercury Milan; Mercury Mariner HEV 4x4; and the Ford Escape HEV 4x2.
The most efficient powertrains on the highway cycle by PABE analysis are: Toyota Highlander Hybrid 4WD; Ford Taurus AWD; Mercury Mariner HEV 4x4; and the Ford Escape HEV 4x2.
Clark Hochgraf (2011) 2010 North American Light DUty Vehicle Assessment: The Ten Most Efficient Powertrains, The Ten Lowest Energy Consumption Chassis (SAE 2011-01-0889)