Rear wheel steering apparatus

• US 4,884,647 A
• Filed: 11/30/1987
• Issued: 12/05/1989
• Est. Priority Date: 02/28/1984
• Status: Expired due to Fees

• Current Assignee: Mitsubishi Jidosha Kogyo Kabushiki Kaisha
• Original Assignee: Mitsubishi Jidosha Kogyo Kabushiki Kaisha
• Inventors: Honda, Masahiro, Mimuro, Tetsushi, Mitsui, Takeshi, Abe, Hiroki
• Primary Examiner(s): HILL, MITCHELL
• Application Number:
  US07/127,618
• Time in Patent Office: 736 Days
• Field of Search: 180/140, 180/141, 180/142, 180/143, 180/79, 180/79.1, 280/91, 364/424.05, 364/404.1, 74/388 PS, 60/385, 60/386, 91/536, 92/117 R, 92/117 A
• US Class Current: 180/415
• CPC Class Codes: B62D 7/1581 characterised by comprising an electrical interconnecting system between the steering control means of the different axles
• CPC Class Codes: B62D 7/159 characterised by computing methods or stabilisation processes or systems, e.g. responding to yaw rate, lateral wind, load, road condition

Abstract

A rear wheel steering hydraulic cylinder is arranged in a rear wheel steering apparatus to steer rear wheels to the right and left. When a front wheel steering angle detected by a front wheel steering angle sensor exceeds a predetermined value, the hydraulic cylinder is actuated to steer the rear wheels in a direction opposite to that of the front wheels. When the rear wheel steering angle detected by a rear wheel steering angle sensor is changed in response to the front wheel steering angle, the hydraulic cylinder is not activated, thereby not steering the rear wheels.

Claims

1. A rear wheel steering apparatus for a vehicle having steerable front and rear wheels comprising:

driving condition detecting means including,

front wheel steering angle detecting means for detecting a front wheel steering angle of said vehicle and generating a signal corresponding to the front wheel steering angle, and

rear wheel steering angle detecting means for detecting a rear wheel steering angle of the vehicle and generating a signal corresponding to the rear wheel steering angle;

rear wheel steering control means for steering said rear wheels, including,

a first cylinder housing,

a first piston member adapted to reciprocate within said cylinder housing and coupled to the rear wheels,

a selector control valve for selectively causing a pressure source and a tank to communicate with two chambers defined in said first cylinder housing by said piston member, and

a steering mechanism which is arranged between said selector control valve and said two chambers and which has check valves allowing a flow-in operation for one of said two chambers and simultaneously a flow-out operation for the other of said two chambers, said steering control means being adapted to control said steering mechanism; and

rear wheel steering control means including,

discriminating means for discriminating a difference between said front and rear wheel steering angle signals from said front and rear wheel steering angle detecting means, and

steering control means, responsive to said decriminating means, for supplying a steering signal to said rear wheel steering means to eliminate the difference between said front and rear wheel steering angles when the difference exceeds a predetermined value.

2. An apparatus according to claim 1, wherein said driving condition detecting means further comprises velocity detecting means for detecting a velocity of the vehicle and providing a signal corresponding thereto, and said rear wheel steering control means further comprises enabling means for enabling the rear wheels to be steered in response to a signal within a predetermined velocity range from said velocity detecting means, and for inhibiting the rear wheel steering angle to be increased from a neutral position and enabling the rear wheels to return to the neutral position in response to a signal outside said predetermined velocity range, said steering control means generating an enabling signal to enable said rear wheel steering means to steer the rear wheels.

3. An apparatus according to claim 2, wherein said steering control means includes means for causing said rear wheel steering means to steer the rear wheels in a direction opposite to that of the front wheels in response to a velocity signal from said velocity detecting means which is below a preset velocity.

4. An apparatus according to claim 3, wherein said driving condition detecting means further comprises lever position detecting means for detecting a position of an operation lever of a gear transmission unit of the vehicle, said enabling means inhibiting the rear wheel steering angle to be increased from the neutral position and enabling the rear wheels to be steered to the neutral that said operation lever is set in a high velocity mode.

5. An apparatus according to claim 2, wherein said steering control means includes means for causing said rear wheel steering means to steer the rear wheels in the same direction as that of the front wheels in response to a velocity signal from said velocity detecting means which is above a preset velocity.

6. An apparatus according to claim 5, wherein said steering control means further includes means for causing said rear wheel steering means to steer the rear wheels in a direction opposite to that of the front wheels in response a velocity signal from said velocity detecting means which is below said preset velocity.

7. An apparatus according to claim 5, wherein said driving condition detecting means further comprises lever position detecting means for detecting a position of an operation lever of a gear transmission unit of the vehicle, said enabling means inhibiting the rear wheel steering angle to be increased from the neutral position and enabling steering of the rear wheels to neutral position when said lever position detecting means detects that said operation lever is set in a high velocity mode.

8. An apparatus according to claim 2, wherein said driving condition detecting means further comprises velocity detecting means for detecting a velocity of the vehicle and providing a signal corresponding thereto, and said rear wheel steering control means further comprises means for inhibiting steering of the rear wheels when a front wheel steering angle signal from said front wheel steering angle detecting means falls within a preset steering angle range from a neutral position, and switching means for switching the preset steering range in response to the signal from said velocity detecting means.

9. An apparatus according to claim 8, wherein said switching means is arranged such that the preset steering angle range is wider when said velocity signal is below a preset velocity that when said velocity signal is above said preset velocity.

10. An apparatus according to claim 1, wherein said rear wheel steering control means further comprises front wheel steering direction detecting means for detecting a steering direction of the front wheels in response to a signal front wheel steering angle detecting means, said steering control means operating said rear wheel steering control means in response to outputs from said discriminating means and said front wheel steering direction detecting means.

11. An apparatus according to claim 2, wherein said apparatus further comprises:

front wheel steering direction detecting means for detecting a steering direction of the front wheels in response to a signal from said front wheel steering angle detecting means;

front wheel steering direction detecting means for detecting a steering direction of the front wheels in response to a signal from said front wheel steering angle detecting means; and

steering signal generating means for generating a steering signal for steering the rear wheels so as to eliminate said difference between said front and rear wheels steering angles in response to outputs from aid front wheel steering position detecting means and said discriminating means and for generating an overrun signal when the rear wheels are steered through an angle exceeding said difference, said steering control means operating said rear wheel steering means in response to a direction signal from said front wheel steering direction detecting means, said steering signal, and said overrun signal.

12. An apparatus according to claim 6, wherein said rear wheel steering angle detecting means further comprises signal switching means for switching an output signal in response to a change in an output signal from said front wheel steering angle detecting means when the velocity signal from said velocity detecting means is below said preset velocity and the rear wheels are steered in a direction opposite to that of the front wheels, and when the velocity signal is above said preset velocity and the rear wheels are steered in the same direction as that of the front wheels.

13. An apparatus according to claim 2, wherein the difference between the front and rear steering angles is detected by overshoot detecting means for detecting whether the difference is larger than a preset value, which preset value is larger than said predetermined value, and said enabling means inhibits the rear wheel steering angle from being increased when said overshoot detecting means detects that the difference exceeds the preset value.

14. An apparatus according to claim 2, wherein said rear wheel steering control means further comprises:

output comparing means for comparing whether a signal from said rear wheel steering angle detecting means is outside a range defined by a preset upper limit and a preset lower limit and providing a signal corresponding thereto; and

inhibiting means for inhibiting the operation of said rear wheel steering means in response to said signal from said output comparing means.

15. A apparatus according to claim 1, wherein said rear wheel steering means comprises a steering mechanism coupled to the rear wheels and a lock mechanism for inhibiting the operation of said steering mechanism to hold the rear wheels in the neutral position.

16. An apparatus according to claim 15, wherein said rear wheel steering control means further comprises:

lock detecting means for detecting that the lock mechanism is in an inhibiting mode and providing a signal corresponding thereto;

front wheel steering position detecting means for detecting a steering position of the front wheels in response to a signal from said front wheel steering angle detecting means; and

inhibiting means for generating a steering inhibiting signal to said steering control means when a signal is not received from said lock detecting means within a predetermined period of time after a signal representing that the front wheels are located in the neutral position is generating from said front wheel steering angle detecting means.

17. An apparatus according to claim 15, wherein said rear wheel steering control means further comprises:

front wheel steering position detecting means for detecting the steering position of the front wheels in response to a signal from said front wheel steering angle detecting means;

rear wheel steering position detecting means for detecting the steering position of the rear wheels in response to a signal from said rear wheel steering angle detecting means; and

lock control means for actuating and setting said lock mechanism in a lock enabling state when the steering angle detected by said front wheel steering position detecting means exceeds a preset value and the steering angle detected by said rear wheel steering position detecting means is smaller than said predetermined value.

18. An apparatus according to claim 1, further comprising:

a second cylinder housing;

a second piston member adapted to reciprocate within said second cylinder housing and coupled to the rear wheels;

a biasing member, movable within said second cylinder housing, for biasing said second piston member at a neutral position;

a lock member, arranged in said second cylinder housing, for engaging with said second piston member when said second piston member is located at the neutral position; and

a lock mechanism having an actuating control valve operated in a state wherein a pressure from said pressure source is applied to said biasing member and in a state wherein the pressure is applied to said lock member to separate said lock member from said piston member, said steering control means being adapted to control said lock mechanism and said steering mechanism to steer the rear wheels.

19. An apparatus according to claim 18, wherein said check valves are operated to cause said selector control valve to communicate with said two chambers when said actuating control valve applies pressure from said pressure source on said biasing member.

20. An apparatus according to claim 1, further comprising:

a second cylinder housing;

a second piston member adapted to reciprocate within said second cylinder housing and coupled to the rear wheels;

a biasing member, movable within said second cylinder housing, for biasing said second piston member at a neutral position;

a lock member, arranged in said second cylinder housing, for engaging with said second piston member when said second piston member is located at the neutral position; and

a lock mechanism having an actuating control valve operated to apply the pressure from said pressure source to said second cylinder housing so as to urge said biasing member against a biasing force thereof and separate said lock member from said piston member, said steering control means being adapted to control said lock mechanism and said steering mechanism to steer the rear wheels.

21. An apparatus according to claim 20, wherein said actuating control valve is operated to apply pressure from said pressure source to said check valves to cause said selector control valve to communicate with said two chambers when said actuating control valve is inactive.

22. An apparatus according to claim 2, wherein said rear wheel steering means comprises

a first cylinder housing:

a first piston member adapted to reciprocate within said first cylinder housing and coupled to the rear wheels;

a selector control valve for selectively causing a pressure source and a tank to communicate with two chambers defined in said first cylinder housing by said first piston member;

and a steering mechanism which is arranged between said selector control valve and said two chambers and which has check valves for allowing a flow-in operation for one of said two chambers and simultaneously a flow-out operation for the other of said two chambers, said driving condition detecting means further comprises lever position detecting means for detecting a position of an operation lever of a gear transmission means of the vehicle; and

said rear wheel steering control means further comprises pressure generation actuating means for actuating the pressure generating means of said pressure source in response to a position signal from said lever position detecting means, the predetermined velocity range signal from said velocity detecting means, and a low pressure signal which is supplied from said pressure source and which represents a pressure lower than a preset pressure.

23. An apparatus according to claim 1, wherein said rear wheel steering control means actuates said rear wheel steering means to steer the fear wheels at a preset angle when the difference detected by said discriminating means exceeds said predetermined value.

24. An apparatus according to claim 1, wherein said driving condition detecting means further comprises velocity detecting means for detecting the velocity of the vehicle, and said rear wheel steering control means comprises switching means for switching a ratio of the rear wheel steering angle to the front wheel steering angle in response to the velocity signal from said velocity detecting means.

25. A rear wheel steering apparatus for a vehicle having steerable front and rear wheels comprising:

driving condition detecting means including

front wheel steering angle detecting means for detecting a front wheel steering angle of said vehicle and generating a signal corresponding to the front wheel steering angle, and

rear wheel steering angle detecting means for detecting a rear wheel steering angle of the vehicle and generating a signal corresponding to the rear wheel steering angle;

preset steering angle range means for developing a plurality of preset steering angle ranges;

discriminating means for discriminating if the front wheel steering angle detecting by said front wheel steering angle detecting means is within one of said plurality of preset steering angle ranges and developing a specific steering angle range corresponding to one of said plurality of preset steering angle ranges having the front wheel steering angle detected therein; and

rear wheel steering control means for steering the rear wheels to a predetermined steering angle corresponding to the specific steering angle range developed by said discriminating means.

26. An apparatus according to claim 25, further comprising:

a motor for driving an output shaft of said rear wheel steering control means which is coupled to the rear wheels so as to steer the rear wheels;

braking means for braking the rotation of said output shaft; and

a lock mechanism for engaging with said output shaft to hold the rear wheels in the neutral position.

27. An apparatus according to claim 26, wherein said rear wheel steering control means operates said braking means to restrict the rotation of said output shaft when the difference between said rear wheel steering angle and said predetermined steering angle is substantially zero.