US4953652A — Four-wheel steering system for motor vehicle

Claim 1

Independent Claim 211 words

A four-wheel steering system for motor vehicle including a front wheel steering mechanism for steering front wheels in response to an operation of a steering wheel, a rear wheel steering mechanism for steering rear wheels in accordance with the steered movement of the front wheels, control means having driving condition detecting means for detecting a vehicle driving condition and controlling the rear wheel steering mechanism in accordance with the vehicle driving condition, fail judging means for judging of a failure of the control means and producing a failure signal denoting the failure, and fail-safe means for receiving the failure signal from the fail judging means and controlling the rear wheel steering mechanism independently from the control means when the control means is in an unusual condition, wherein the fail judging means being provided with first fail judging means and second fail judging means adapted to be actuated independently for judging different fail conditions, the control means being provided with a control unit for receiving signals from said driving condition detecting means and producing control signals to the rear wheel steering mechanism, the first fail judging means being provided in the control unit, and the second fail judging means being provided in a back up control unit independent from the control unit.

Claim 2

Dependent Claim 211 words

A four-wheel steering system for motor vehicle including a front wheel steering mechanism for steering front wheels in response to an operation of a steering wheel, a rear wheel steering mechanism for steering rear wheels in accordance with the steered movement of the front wheels, control means having driving condition detecting means for detecting a vehicle driving condition and controlling the rear wheel steering mechanism in accordance with the vehicle driving condition, fail judging means for judging of a failure of the control means and producing a failure signal denoting the failure, and fail-safe means for receiving the failure signal from the fail judging means and controlling the rear wheel steering mechanism independently from the control means when the control means is in an unusual condition, wherein the fail judging means being provided with first fail judging means and second fail judging means adapted to be actuated independently for judging different fail conditions, the control means being provided with a control unit for receiving signals from said driving condition detecting means and producing control signals to the rear wheel steering mechanism, the first fail judging means being provided in the control unit, and the second fail judging means being provided in a back up control unit independent from the control unit.

Claim 3

Dependent Claim 152 words

A four-wheel steering system in accordance with claim 1 in which the driving condition detecting means includes a vehicle speed sensor and a rear wheel steering amount sensor, the control unit being adapted to receive signals from the vehicle speed sensor and produce steering signals for steering the rear wheels in a direction opposite to the direction in which the front wheels are steered when the vehicle speed is low and in the same direction as a direction in which the front wheels are steered when the vehicle speed is high, and the second fail judging means being adapted to receive signals from the vehicle speed sensor and a rear steering amount sensor and to product failure signals of the control means when it is detected that the rear wheels are steered in a direction opposite to a direction in which the front wheels are steered in a high vehicle speed condition.

Claim 4

Dependent Claim 65 words

A four-wheel steering system in accordance with claim 2 in which the second fail judging means is provided with timer means for producing failure signals of the control means when it is detected for more than a predetermined period that the rear wheels are steered in a direction opposite to a direction in which the front wheels are steered in a high vehicle speed condition.

Claim 5

Dependent Claim 63 words

A four-wheel steering system in accordance with claim 2 in which the rear wheel steering mechanism includes a steering ratio changing mechanism for changing a steering ratio of a steering amount of the rear wheels to a steering amount of the front wheels, the rear wheel steering amount sensor being constituted by a steering ratio sensor provided in the steering ratio changing mechanism.

Claim 6

Dependent Claim 45 words

A four-wheel steering mechanism in accordance with claim 1 in which the fail-safe means prevent the rear wheels from steering in a negative position wherein the rear wheels is angularly positioned in a direction opposite to a direction in which the front wheels is positioned.

Claim 7

Dependent Claim 25 words

A four-wheel steering system in accordance with claim 5 in which the fail-safe means is actuated to position the rear wheel at a neutral position.

Claim 8

Dependent Claim 32 words

A four-wheel steering system in accordance with claim 1 wherein the fail-safe means is provided with first fail-safe means and second fail-safe means adapted to be actuated independently for different fail-safe controls.

Claim 9

Dependent Claim 208 words

A four-wheel steering system for motor vehicle including a front wheel steering mechanism for steering front wheels in response to an operation of a steering wheel, a rear wheel steering mechanism for steering rear wheels in accordance with the steered movement of the front wheels, control means having driving condition detecting means for detecting a vehicle driving condition and controlling the rear wheel steering mechanism in accordance with the vehicle driving condition, fail judging means for judging of a failure of the control means and producing a failure signal denoting the failure, and fail-safe means for receiving the failure signal from the fail judging means and controlling the rear wheel steering mechanism independently from the control means when the control means is in an unusual condition, wherein the fail-safe means is provided with first fail-safe means and second fail-safe means adapted to be actuated independently for different controls, the control means including steering ratio setting means for setting a steering ratio of a steering amount of the rear wheels to a steering amount of the front wheels, the first fail-safe means being adapted to change the steering ratio set by the steering ratio setting means, and the second fail-safe means being provided in the rear wheel steering mechanism.

Claim 10

Dependent Claim 208 words

A four-wheel steering system for motor vehicle including a front wheel steering mechanism for steering front wheels in response to an operation of a steering wheel, a rear wheel steering mechanism for steering rear wheels in accordance with the steered movement of the front wheels, control means having driving condition detecting means for detecting a vehicle driving condition and controlling the rear wheel steering mechanism in accordance with the vehicle driving condition, fail judging means for judging of a failure of the control means and producing a failure signal denoting the failure, and fail-safe means for receiving the failure signal from the fail judging means and controlling the rear wheel steering mechanism independently from the control means when the control means is in an unusual condition, wherein the fail-safe means is provided with first fail-safe means and second fail-safe means adapted to be actuated independently for different controls, the control means including steering ratio setting means for setting a steering ratio of a steering amount of the rear wheels to a steering amount of the front wheels, the first fail-safe means being adapted to change the steering ratio set by the steering ratio setting means, and the second fail-safe means being provided in the rear wheel steering mechanism.

Claim 11

Dependent Claim 88 words

A four-wheel steering system in accordance with claim 8 in which the rear wheel steering mechanism includes a steering ratio changing mechanism for changing the steering ratio, and a hydraulic cylinder for producing a steering force for the rear wheels by a hydraulic pressure which is generated by a hydraulic pump, the first fail-safe means being adapted to drive the steering ratio changing mechanism and the second fail-safe means being constituted by relief valve means provided in a hydraulic system between the hydraulic pump and the hydraulic cylinder.

Claim 12

Dependent Claim 29 words

A four-wheel steering system in accordance with claim 9 in which the second fail-safe means is provided with a pair of relief valve means in parallel with each other.

Claim 13

Dependent Claim 31 words

A four-wheel steering system in accordance with claim 9 in which the rear wheel steering mechanism is provided with a centering spring for positioning the rear wheels at a neutral position.

Claim 14

Dependent Claim 135 words

A four-wheel steering system in accordance with claim 9 in which the rear wheel steering mechanism is provided with a stepping motor for driving the steering ratio changing mechanism, the control means being adapted to speculate the present stepped position of the stepping motor based on information memorized in the control means when the control means cannot grasp the correct stepped portion of the stepping motor and to cause the first fail-safe means to drive the stepping motor when it is judged that the rear wheels are steered at a negative steering condition wherein the rear wheels is angularly positioned in a direction opposite to the front wheels through the speculation of the control means so that the steering changing mechanism is driven so as to escape the negative steering condition of the rear wheels.

Claim 15

Dependent Claim 35 words

A four-wheel steering system in accordance with claim 12 in which the first fail-safe means drives the stepping motor to position the steering ratio changing mechanism at a position where the steering ratio is zero.

Claim 16

Dependent Claim 37 words

A four-wheel steering system in accordance with claim 12 in which the fail judging means is provided with a plurality of actuating means, and each of the actuating means being able to actuating the fail judging means.

Claim 17

Dependent Claim 79 words

A four-wheel steering system in accordance with claim 14 in which the control means is provided with a driving condition detecting sensor, a control unit for receiving signals from the sensor and producing control signals to the rear wheel steering mechanism, a first fail judging means provided in the control unit, and a second fail judging means provided independent of the control unit for judging an unusual condition of the control means based on the signals from the sensor.

Claim 18

Dependent Claim 153 words

A four-wheel steering system in accordance with claim 15 in which the driving condition detecting means includes a vehicle speed sensor and a rear wheel steering amount sensor, the control unit being adapted to receive signals from the vehicle speed sensor and to produce steering signals for steering the rear wheels in a direction opposite to the direction in which the front wheels are steered when the vehicle speed is low and in the same direction as the direction in which the front wheels are steered when the vehicle speed is high, and the second fail judging means being adapted to receive signals from the vehicle speed sensor and the rear steering amount sensor and to produce failure signals of the control means when it is detected that the rear wheels are steered in a direction opposite to a direction in which the front wheels are steered in a high vehicle speed condition.

Claim 19

Dependent Claim 65 words

A four-wheel steering mechanism in accordance with claim 16 in which the second fail judging means is provided with timer means for producing failure signals of the control means when it is detected for more than a predetermined period that the rear wheels are steered in a direction opposite to a direction in which the front wheels are steered in a high vehicle speed condition.

Claim 20

Dependent Claim 31 words

A four-wheel steering system in accordance with claim 8 in which the first fail-safe means changes a value of the steering ratio set by the steering ratio setting means to zero.

Claim 21

Dependent Claim 36 words

A four-wheel steering system in accordance with claim 8 wherein the fail judging means is provided with first fail judging means and second fail judging means adapted to be actuated independently for judging different fail conditions.

Claim 22

Dependent Claim 169 words

A four-wheel steering system for motor vehicle including a front wheel steering mechanism for steering front wheels in response to an operation of a steering wheel, a rear wheel steering mechanism for steering rear wheels in accordance with the steered movement of the front wheels, control means having driving condition detecting means for detecting a vehicle driving condition and controlling the rear wheel steering mechanism in accordance with the vehicle driving condition, fail judging means for judging of a failure of the control means and producing a failure signal denoting the failure, and fail-safe means for receiving the failure signal from the fail judging means and controlling the rear wheel steering mechanism independently from the control means when the control means is in an unusual condition, wherein the fail-safe means being provided with first fail-safe means and second fail-safe means adapted to be actuated independently for different fail-safe controls, the first and second fail safe means including means for providing a steering angle for the rear wheels with zero.

Claim 23

Dependent Claim 169 words

A four-wheel steering system for motor vehicle including a front wheel steering mechanism for steering front wheels in response to an operation of a steering wheel, a rear wheel steering mechanism for steering rear wheels in accordance with the steered movement of the front wheels, control means having driving condition detecting means for detecting a vehicle driving condition and controlling the rear wheel steering mechanism in accordance with the vehicle driving condition, fail judging means for judging of a failure of the control means and producing a failure signal denoting the failure, and fail-safe means for receiving the failure signal from the fail judging means and controlling the rear wheel steering mechanism independently from the control means when the control means is in an unusual condition, wherein the fail-safe means being provided with first fail-safe means and second fail-safe means adapted to be actuated independently for different fail-safe controls, the first and second fail safe means including means for providing a steering angle for the rear wheels with zero.

Claim 24

Dependent Claim 36 words

A four-wheel steering system in accordance with claim 20 wherein the fail judging means is provided with first fail judging means and second fail judging means adapted to be actuated independently for judging different fail conditions.

Claim 25

Dependent Claim 81 words

A four-wheel steering system in accordance with claim 6 in which the rear wheel steering mechanism includes a steering ratio changing mechanism for changing the steering ratio, and a hydraulic cylinder for producing a steering force for the rear wheels by a hydraulic pump, the first fail-safe means being adapted to drive the steering ratio changing mechanism and the second fail-safe means being constituted by relief valve means provided in a hydraulic system between the hydraulic pump and the hydraulic cylinder.

Claim 26

Dependent Claim 31 words

A four-wheel steering system in accordance with claim 22 in which the rear wheel steering mechanism is provided with a centering spring for positioning the rear wheels at a neutral position.

Claim 27

Dependent Claim 135 words

A four-wheel steering system in accordance with claim 22 in which the rear wheel steering mechanism is provided with a stepping motor for driving the steering ratio changing mechanism, the control means being adapted to speculate the present stepped position of the stepping motor based on information memorized in the control means when the control means cannot grasp the correct stepped portion of the stepping motor and to cause the first fail-safe means to drive the stepping motor when it is judged that the rear wheels are steered at a negative steering condition wherein the rear wheels is angularly positioned in a direction opposite to the front wheels through the speculation of the control means so that the steering changing mechanism is driven so as to escape the negative steering condition of the rear wheels.

Claim 28

Dependent Claim 35 words

A four-wheel steering system in accordance with claim 24 in which the first fail-safe means drives the stepping motor to position the steering ratio changing mechanism at a position where the steering ratio is zero.

Annuity Stage	Window Opens	Payment Deadline	Surcharge Period Until	Estimated Fee	Status
3.5 Years (Year 4)	1993-09-03	1994-03-05	1994-09-04	$2000.00	Window Closed / Lapsed
7.5 Years (Year 8)	1997-09-03	1998-03-05	1998-09-04	$3760.00	Window Closed / Lapsed
11.5 Years (Year 12)	2001-09-03	2002-03-05	2002-09-04	$7700.00	Window Closed / Lapsed

Four-wheel steering system for motor vehicle

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