Fail-safe mechanism for an electrical power assisted steering system.

摘要

In a power assisted steering system for a vehicle, an operator controlled steering shaft (24) is connected directly to at least one steered wheel of the vehicle. An electric motor (12) is connected to the steering shaft (24) via a ratio reduction means (14). A clutch (28) is interposed between the motor (12) and the ratio reduction eans (14) to connect and disconnect the motor from the steering shaft (24). A control circuit (36) senses torque and direction of rotation of the steering shaft (24) by the operator and operates the motor (12) to provide power steering assistance. The control circuit (36) also monitors the operation of the system and, when the system is operating properly, keeps the clutch (28) in engagement to transmit torque from the motor (12) to the steering shaft (24). When the system is diagnosed to be operating improperly, the clutch (28) is rapidly disengaged and the motor (12) is effectively isolated from the steering shaft (24).