| 摘要 |
An electric power steering system (60) for vehicles has an electromagnetic servo device (1) including a drive control circuit (30, 40) for feeding a drive signal (Va) to an electric motor (14) for producing auxiliary torque to be supplied to an output shaft (6) in accordance with a steering torque signal (S1, S2) from a steering torque detection mechanism (32) which detects steering torque (Ts) acting on an input shaft (5) and a vehicle speed signal (S5) from a vehicle speed detection mechanism (50) which detects the speed (Vs) of the vehicle. The drive control circuit is adapted to determine, of the motor drive signal, a component (D(F)) corresponding to the load due to friction elements of the servo device and a component (D(L)) corresponding to the load from the road surface side, depending on the steering torque signal, and to determine a vehicle speed factor (K(V)), depending on the vehicle speed signal. The magnitude of the motor drive signal is determined as the sum of the frictional load component and a corrected road surface side load component (D'(L)) obtained by multiplying the road surface side load component by the vehicle speed factor. The drive control circuit includes a microcomputer unit (30) for determining the frictional load component and the road surface side load component in an address designation manner in dependence on the steering torque signal and the vehicle speed factor in an address designation manner in dependence on the vehicle speed signal.
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