Parametric Simulation of the Fuel Consumption Effects of Engine Design Variation with Advanced Transmission Powertrains

A generic simulation study examines the fuel economy interrelationship between basic engine design parameters and the choice of transmission, emphasizing the implications on engine design of the use of optimally shifted, advanced transmissions. A new engine model and a vehicle simulation package were combined to assess, with both conventional and optimal shifting, the fuel economy effects, without octane or emissions constraints, of variation in bore-to-stroke ratio, compression ratio, cam timing, displacement, and friction level. The fuel economy interaction between the engine technology and the type of transmission was also assessed, using measured fuel flow information on a series of diesel and PROCO engines. In the course of this work, the fundamental factors which determine the fuel economy improvement associated with optimal shifting were identified. The fuel economy effects of engine changes were, in general, quantitatively similar for both conventionally and optimally shifted transmissions.