Fail-safe mechanism for an electrical power assisted steering system

Claim 2

A power assisted steering system for a vehicle, the vehicle having an operator controlled steering mechanism (27), at least one steered wheel and a steering shaft (24) directly connecting the steering mechanism (27) to the wheel, the system comprising: a bidirectional electric motor (12); control means (36) for energizing the motor (12) to turn in a first direction when the steering mechanism (27) is moved in one direction by the operator, for energizing the motor (12) to turn in a direction opposite said first direction when the steering mechanism (27) is moved in a direction opposite said one direction by the operator, for monitoring the operational condition of the system to detect malfunctions, and for generating a signal indicative of the operational condition system; clutch means (28,30,32,38,39,40,42,44,46,48), responsive to the control means, for coupling the motor (12) to the steering shaft (24) when the system is operating properly, and for isolating the motor (12) from the steering shaft (24) when the system is not operating properly; and a ratio reduction means (14) connected between the motor (12) and the steering shaft (24) for increasing the torque delivered to the steering shaft by the motor, the ratio reduction means (14) including a planetary gear system comprising a sun gear (16), a plurality of planet gears (20) in circumferential mesh with the sun gear, a ring gear (25) surrounding and in mesh with the planet gears, and planet carriers (22) connecting the planet gears to the steering shaft so that revolution of the planet gears about the sun gear produces a corresponding rotation of the steering shaft.

Claim 3

The power assisted steering system of Claim 1 wherein the clutch means includes a clutch pad (28) mechanically grounded relative to the rotational movement of the sun gear (16), the planet gears (20) and the ring gear (25), said clutch pad (28) being biased radially away from the ring gear; and wherein the clutch means further includes means (38,39) for radially displacing the clutch pad toward and into frictional contact with the ring gear when the system is operating properly.

Claim 4

The power assisted steering system of Claim 1 wherein the clutch means includes a first clutch half (40) and a coaxial second clutch half (42), the first clutch half (40) being axially mounted on the armature (18) of the motor (12) for rotation therewith, the second clutch half (42) being mounted on the sun gear (16) for axial movement with respect thereto, the second clutch half (42) being mounted in a fixed rotational relationship with the sun gear (16), the clutch means further including means (38), responsive to the control means, for moving one of said first or second clutch halves (40,42) into frictional contact with the other of said clutch halves when the system is operating properly.

Claim 5

The power assisted steering system of Claim 3 wherein the first and second clutch halves (40,42) have interlocking angled teeth (50) on the contacting portions of each half so that the contacting portions of the clutch halves ratchet when excessive torque is applied to the clutch.

Claim 6

A power assisted steering system for a vehicle comprising: a bidirectional electric motor (12) having an axially centered hollow armature shaft (18); at least one planetary gear ratio reduction unit (14) including a hollow sun gear (16), planet gears (20) in circumferential mesh with the sun gear, and a ring gear (25) surrounding the planet gears and in circumferential mesh therewith; an operator controlled steering shaft (24), connected to at least one steerable wheel of the vehicle, extending axially through the sun gear (16) and the armature shaft (18), the steering shaft (24) operable to turn the wheel under the control of the operator; planet carriers (22) connected between the planet gears (20) and the steering shaft (24) so that movement of the planet gears around the circumference of the sun gear (16) produces a corresponding rotation of the steering shaft; a control circuit (36) including a sensor (34) for sensing the rotational movement of and input torque to the steering shaft (24) by the operator and means (52,54) for controlling the operation of the motor in response to the sensor so that the motor generates torque proportional to the input torque to the steering shaft, the control circuit further including means (56) to detect proper operation of the system and to generate an energization signal when the system is operating properly; and a clutch (28) including means (38,39) responsive to the energization signal such that, when the energization signal is present, said means operates to engage the clutch so that torque from the motor is transmitted through the planetary gear system (14) to the steering shaft (24) thereby providing power assisted steering and, when the energization signal is not present, said means operates to disengage the clutch so that the motor is effectively isolated from the steering shaft.

Claim 7

A power assisted steering system for a vehicle comprising: a bidirectional electric motor (12) having an axially centered hollow armature shaft (18); at least one planetary gear ratio reduction unit (14) including a hollow sun gear (16), planet gears (20) in circumferential mesh with the sun gear, and a ring gear (25) surrounding the planet gears and in circumferential mesh therewith; an operator controlled steering shaft (24), connected to at least one steerable wheel of the vehicle, extending axially through the sun gear (16) and the armature shaft (18), the steering shaft (24) operable to turn the wheel under the control of the operator; planet carriers (22) connected between the planet gears (20) and the steering shaft (24) so that movement of the planet gears around the circumference of the sun gear (16) produces a corresponding rotation of the steering shaft; a control circuit (36) including a sensor (34) for sensing the rotational movement of and input torque to the steering shaft (24) by the operator and means (52,54) for controlling the operation of the motor in response to the sensor so that the motor generates torque proportional to the input torque to the steering shaft, the control circuit further including means (56) to detect proper operation of the system and to generate an energization signal when the system is operating properly; and a clutch (28) including means (38,39) responsive to the energization signal such that, when the energization signal is present, said means operates to engage the clutch so that torque from the motor is transmitted through the planetary gear system (14) to the steering shaft (24) thereby providing power assisted steering and, when the energization signal is not present, said means operates to disengage the clutch so that the motor is effectively isolated from the steering shaft.

Claim 8

The power assisted steering system of Claim 5 wherein the means (38,39) responsive to the energization signal is a solenoid which includes a spring (30,32) to bias the clutch (28) into its disengaged state when the energization signal is not present.

Claim 9

The power assisted steering system of Claim 5 wherein the clutch (28) is mechanically grounded relative to the rotational movement of the ring gear (25) and biased radially away therefrom, said ring gear being free to rotate about its axis while the clutch is disengaged, said clutch, upon operation of said means (38,39) responsive to the energization signal, moving radially into circumferential frictional contact with the ring gear thereby preventing the ring gear from rotating about its axis.

Claim 10

The power assisted steering system of Claim 5 wherein the clutch (28) comprises a pair of coaxial clutch halves (40,42), each having a center axial opening for receiving the steering shaft (24) therethrough, the first of said pair of clutch halves (40,42) being axially mounted in a fixed rotational relationship with the armature shaft (18), the second of said pair of clutch halves being axially mounted in a fixed rotational relationship on the sun gear (16), at least one of said clutch halves (40,42) being mounted for axial movement toward and away from the other of said halves to thereby engage and disengage the clutch (28).

Claim 11

The power assisted steering system of Claim 8 wherein the face of each clutch half (40,42) includes a set of angled teeth (50), the teeth of one half interlocking with the teeth of the other half when the clutch is engaged to provide positive transfer of the torque from the first half to the second half under conditions of normal torque, and for permitting the clutch halves to rotate independently of one another when the clutch is engaged under conditions of excessively high torque.

Claim 12

A power assisted steering system for a vehicle, the vehicle having an operator controlled steering wheel (27), at least one steerable wheel, and a steering shaft (24) directly connecting the steering wheel to the steerable wheel, the system comprising: a bidirectional electric motor (12); a multi-axis gear reduction unit (14) coupled to the steering shaft (24) so that rotation of the gears of the reduction unit produce a corresponding rotation of the steering shaft, the reduction unit mounted for rotation independent from the rotation of the motor; a sensor (34) for detecting rotation of the operator controlled steering wheel (27); control means (36) responsive to the sensor (34), for energizing the motor (12) to turn in the direction in which the steering wheel (27) is turned and to provide torque proportional to the operator's input, for monitoring the operational condition of the system, and for generating an energization signal when the system is operating properly; and a clutch (28), responsive to the control means between the motor (12) and the reduction unit (14) for coupling the motor to the reduction unit when the energization signal is present and for decoupling the motor from the reduction unit when the energization signal is not present.

Claim 13

A power assisted steering system for a vehicle, the vehicle having an operator controlled steering wheel (27), at least one steerable wheel, and a steering shaft (24) directly connecting the steering wheel to the steerable wheel, the system comprising: a bidirectional electric motor (12); a multi-axis gear reduction unit (14) coupled to the steering shaft (24) so that rotation of the gears of the reduction unit produce a corresponding rotation of the steering shaft, the reduction unit mounted for rotation independent from the rotation of the motor; a sensor (34) for detecting rotation of the operator controlled steering wheel (27); control means (36) responsive to the sensor (34), for energizing the motor (12) to turn in the direction in which the steering wheel (27) is turned and to provide torque proportional to the operator's input, for monitoring the operational condition of the system, and for generating an energization signal when the system is operating properly; and a clutch (28), responsive to the control means between the motor (12) and the reduction unit (14) for coupling the motor to the reduction unit when the energization signal is present and for decoupling the motor from the reduction unit when the energization signal is not present.

Claim 14

ll. The power assisted steering system of Claim 10 wherein the clutch (28) includes a first clutch half (40) and a coaxial second clutch half (42), each clutch half having a clutch face with angled teeth (50) which interlock with the teeth from the other half when the clutch couples the motor (12) to the reduction unit (14) 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 rotational relationship therewith, at least one of said first or second clutch halves being mounted for axial sliding movement toward or away from the other of said clutch halves in the presence or absence of the energization signal, respectively.