Control apparatus for motor-driven power steering system in which power suppy to an electric clutch is reduced upon detection of a malfunction

摘要

A control apparatus for a motor-driven power steering system of a motor vehicle for preventing generation of actuation noise of a clutch without sacrificing reliability of the steering system. A current calculating/driving means 91 calculates a motor current command value I0 on the basis of a vehicle speed V and a steering torque T for driving a motor 13. An abnormal torque decision reference value arithmetic means 901 calculates an abnormal torque decision reference value T0 and a reference time t0 in dependence on the vehicle speed V, while a load torque calculating means 902 calculates a load torque TL on the basis of the steering torque T and the motor current command value I0. A motor rotation decision means 907 estimates a rotation number NM of the motor 13 from a motor regeneration voltage. When the load torque TL is greater than the abnormal torque decision reference value T0 and when a duration tL thereof is greater than the reference time t0, power supply to the motor 13 is interrupted under the control of a motor fault monitor/control means 904, provided that the rotation number NM is not greater than a motor stop decision reference rotation number N0. A clutch control means 92B is also so controlled that the steering torque T becomes equal to a preset torque limitation triggering value T1 so that the steering can be performed without encountering any appreciable obstacle.