Simulated Performance of Alternative Hybrid-Electric Powertrains in Vehicles on Various Driving Cycles

In this paper, various alternative hybrid vehicle powertrains that are being considered by auto companies are evaluated based on simulation studies performed at the Institute of Transportation Studies, University of California-Davis. The following hybrid powertrain arrangements have been considered: a. Single-shift, parallel (Honda) b. Single-planetary, dual-mode (Toyota/Prius) c. Multiple-planetary, dual-mode (GM) d. Multiple-shaft, dual-clutch transmission (VW and Borg-Warner) e. Series – range extended EV (GM Volt) The primary strategy in all the options considered was to operate the engine only in the high efficiency part of its map and to lose as little as possible of the gain by losses in the energy storage unit and the electric machines. The simulations indicated that there are in general not large differences in the fuel economies predicted using the various powertrains for the same vehicle and battery. The fuel economy improvements were large in all case – 80-100% for the FUDS cycle, 40-60% for the Highway cycle, and 30-50% for the US06 cycle – using lithium-ion batteries and a 25-35 kW electric driveline. Limited simulations were also performed for a series hybrid that could be operated as a plug-in hybrid with a range of about 30 miles. In the charge depleting mode, the vehicles operate as full-function EVs. The simulations indicated that the series hybrids will have large fuel economy improvements compared to ICE vehicles of the same size and performance in the charge sustaining mode. Hence a key issue is the economics of the series vs. the parallel plug-in hybrids and not vehicle performance and fuel economy