Penalty for Fuel Economy— System Level Perspectives on the Reliability of Hybrid Electric Vehicles During Normal and Graceful Degradation Operation

Generally people tend to think only in terms of fuel economy and additional cost premium on vehicle price while discussing about hybrid electric vehicles (HEV). This paper tries to emphasize that the overall acceptability of a vehicle also has to do with its system level reliability. It discusses the issue of system level reliability in hybrid electric vehicles from a quantitative point of view. It also introduces a quantitative meaning to the concept of graceful degradation and mode of operation under graceful degradation condition. All these are discussed in stages, starting from a regular internal combustion engine based vehicle, and later transition of those to hybrid electric vehicles. This paper intends to drive the point that in HEV, one of the penalties for fuel economy that has to be paid comes in terms of reliability.