Fail-safe device for an electrical power assisted steering system including an in-line clutch mechanism

A power assisted steering system for a vehicle comprising:

• a direct current electric motor having an axially centered hollow armature shaft;
• at least one planetary gear ratio reduction unit including a hollow sun gear, planet gears mounted in a carrier and in circumferential mesh with the sun gear, and a mechanically grounded ring gear surrounding the planet gears and in circumferential mesh therewith;
• an operator controlled steering shaft, connected to at least one steerable wheel of the vehicle, extending axially through the sun gear and the armature shaft, the steering shaft operable to turn the wheel under control of the operator;
• a planet carrier connected between the planet gears and the steering shaft so that movement of the planet gears about the circumference of the sun gear produces a corresponding rotation of the steering shaft;
• a control circuit including a sensor for sensing rotational movement of the steering shaft by the operator and means for controlling the operation of the motor in response to the sensor so that the motor generates torque proportional to the velocity of the rotation of the steering shaft, the control circuit further including means to detect proper operation of the system and to generate an energization signal when the system is operating properly;
• a clutch, responsive to the energization signal, including a pair of coaxial clutch halves having a center axial opening for receiving the steering shaft therethrough, the first of said pair of clutch halves being axially mounted in a fixed rotational relationship on the armature shaft, the second of said pair of clutch halves being axially mounted in a fixed rotational relationship on the sun gear, at least one of said clutch halves being mounted for axial movement toward and away from the other of said clutch halves to thereby engage and disengage the clutch, and the clutch further including means for moving at least one of said clutch halves toward the other of said clutch halves when the energization signal is present so that torque from the motor is transmitted through the clutch to the planetary gear system and to the steering shaft thereby providing power assisted steering, and for moving at least one of said clutch halves away from the other of said clutch halves when the energization signal is not present so that the motor is effectively isolated from the steering shaft.

A power assisted steering system for a vehicle, the vehicle having an operator controlled steering wheel, at least one steerable wheel, and a steering shaft directly connecting the steering wheel to a steerable wheel, the system comprising:

• a DC electric motor;
• a multi-axis gear reduction unit coupled to the steering shaft so that rotation of the gears of the reduction unit produces a corresponding rotation of the steering shaft;
• a sensor for detecting rotation of the operator controlled steering wheel;
• control means, responsive to the sensor, for energizing the motor to turn at a speed and in a direction proportional to the speed and direction at which the steering wheel is turned, for monitoring the operational condition of the system, and for generating an energization signal when the system is operating properly;
• and
• a clutch, responsive to the control means, including a first clutch half and a coaxial second clutch half, each clutch half having a clutch face with angled teeth which interlock with the teeth from the other half when the clutch is engaged under conditions of normal torque, said first clutch half being axially mounted on the motor in a fixed rotational relationship therewith, said second clutch half being axially mounted on the reduction unit in a fixed rotation relationship therewith, at least one of said first or second clutch halves being mounted for axial sliding movement toward or away from other of said clutch halves to couple and decouple the motor to and from the reduction unit in the presence or absence of the energization signal, respectively.