Force and position control for active front steering

摘要

A steering system (100, 150, 175, 200, 201, 250, 251, 300, 301) with reduced coupling between a position overlay unit (102, 152, 180, 208, 262, 306) and a torque overlay unit (108, 154, 176, 202, 252, 310) may include a remote valve assembly (204) for controlling a hydraulic assist force (212, 260, 308) or an electric motor (178) for providing torque overlay and electric assist (182, 245, 295, 345) to a rack (116) of a rack (116) and pinion steering system (150, 175, 200, 201, 250, 251, 300, 301). In one embodiment, the position overlay unit (306) may provide the assist force (308, 345) and the torque overlay unit (310) may provide a motor command signal (318) to the motor (128) of a differential (106) positioned on a steering shaft. In another embodiment, the position overlay unit (180, 208, 262) may provide the motor command signal (130) and the torque overlay unit (176, 202, 252) may provide the assist force (182, 212, 245, 260, 295). In either embodiment, the position overlay unit (180, 208, 262, 306) may include variable ratio gain (122) that uses a position signal (190, 254, 314) to output a variable ratio command.