Hybrid vehicles integrate an internal combustion engine, electric motor with accompanying battery pack and generator, and potentially fuel cells to realize greater fuel economy and reduced emission levels. An attractive advantage of multiple energy sources is the increased travel range, reduced stationary recharging times, and availability of greater power for acceleration and payloads. A variety of operating scenarios exist for hybrid vehicle powertrains including engine (and belt driven generator), electric motor using battery back and/or fuel cell, and finally, engine and electric motor. Therefore, automotive subsystems such as hydraulic power steering cannot be consistently powered by a conventional belt driven hydraulic pump since the engine may be frequently turned-off to conserve energy. A need exists to investigate the dynamic behavior of various steering systems for hybrid vehicles in terms of platform steering characteristics, power consumption, and identification of performance requirements for a servo-motor steering system. In this paper, empirical and analytical mathematical models will be presented for power (e.g., hydraulic, electric, and steer-by-wire) rack and pinion steering units. The influence of vehicle and steering system nonlinearities will be introduced for greater accuracy in predicting the vehicle’s transient response. Representative results will be presented and discussed to investigate the response of the vehicle to different driver inputs as the steering system configurations are adjusted. An analysis of the numerical results will ultimately allow the prediction of vehicle trajectory, feedback torque, and power consumption during the driving maneuvers.

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