Variable ratio steering gear

• US 20040040779A1
• Filed: 07/01/2003
• Published: 03/04/2004
• Est. Priority Date: 11/01/2000
• Status: Active Grant

• Current Assignee: Bishop Steering Technology Limited (Georgsmarienhütte Holding GmbH)
• Original Assignee: Bishop Steering Technology Limited (Georgsmarienhütte Holding GmbH)
• Inventors: Bishop, Arthur Ernest
• Granted Patent: US 6,945,353 B2
• Time in Patent Office: Days
• US Class Current: 180/443
• CPC Class Codes: B62D 1/166 Means changing the transfer ratio between steering wheel and steering gear
• CPC Class Codes: B62D 3/12 of rack-and-pinion type
• CPC Class Codes: B62D 6/02 responsive only to vehicle speed

Abstract

A rack (1) and pinion (4) steering gear for a vehicle in which the steering angle ratio varies as a function of at least both the steering wheel angle input by the driver and vehicle speed. The steering gear comprising a rack (1) laterally displaceable with respect to a steering gear housing and a pinion (4) laterally moveable within the housing substantially in a direction of travel of the rack (1) whilst engaged with the rack (1). The steering angle ratio is increased in a central region of travel of the rack (1) when compared to regions either side thereof, and steering angle ratio is further increased in the central region as vehicle speed increases.

Claims

1. A rack and pinion steering gear for a vehicle in which the steering angle ratio varies as a function of at least both the steering wheel angle input provided by the driver and vehicle speed, said steering gear comprising a rack laterally displaceable with respect to a steering gear housing, characterised in that said steering gear further comprises a pinion laterally moveable within said housing substantially in a direction of travel of said rack whilst engaged with said rack, and said steering angle ratio is increased in a central region of travel of said rack when compared to regions either side thereof, and said steering angle ratio is further increased in said central region as vehicle speed increases.

2. A rack and pinion steering gear as claimed in claim 1, in which said pinion is journalled for rotation within a pinion housing laterally movable within said steering gear housing substantially in the direction of travel of said rack, so subtracting from the travel of said rack and so minimising the travel ratio therebetween by a variable amount, said amount decreasing with rotation of the pinion from the centre straight ahead position and also decreasing with the speed of the vehicle.

3. A rack and pinion steering gear as claimed in claim 1, comprising a first mechanical linkage means connected to said pinion to move said pinion in said housing in accordance with a predetermined transmission pattern operable in said central region of travel of said rack and disconnected therefrom in said regions either side thereof, and a second mechanical linkage means connected to said first mechanical linkage means adapted to multiply said transmission pattern as a function of vehicle speed to further increase said steering angle ratio in said central region.

4. A rack and pinion steering gear as claimed in claim 3, comprising a by-pass means connected to said second mechanical linkage means adapted to limit loads transmitted through said first and second mechanical linkage means when the load being transmitted from the pinion to the rack or vice versa exceeds a predetermined value, said loads thereafter being carried solely by said rack and said pinion.

6. A rack and pinion steering gear for a vehicle as claimed in claims 3 to 5 wherein said first mechanical linkage means comprises a Geneva mechanism, having a first shaft rotatable with said pinion carrying a first pin offset from the axis of said first shaft, said first pin operarable to engage a first radial slot in a member carried by a second shaft whose axis is parallel with and offset from the axis of the first shaft, a second radial slot in said member rotatable with said second shaft, and a second pin engaged in said second slot, fixed laterally with respect to said housing at a distance with respect to the axis of said second shaft variable in accordance with vehicle speed.

7. A rack and pinion steering gear for a vehicle as claimed in claim 6 further comprising a lever pivoted with respect to said housing, said second pin being secured to said lever.

8. A rack and pinion steering gear for a vehicle as claimed in claim 6 wherein said vehicle includes a detection means for detecting the departure of the vehicle from the directional course as indicated by the driver'"'"'s position of the steering wheel and in respect to the vehicle speed, said detection means providing an output signal to an actuator means in order to move said second pin laterally in said housing in response said output signal.

9. A rack and pinion steering gear as claimed in claims 3 to 5 wherein said first mechanical linkage means comprises a pair of desmodromic cams.

5. A rack and pinion steering gear for a vehicle as claimed in 4 wherein said bypass means comprises a detent mechanism connected to said housing.

10. A rack and pinion steering gear for controlling the road wheel steering angle of a vehicle as a function of at least the steering wheel angle input provided by the driver and vehicle speed, the steering gear comprising a rack laterally displaceable in a fixed rack housing, and a pinion journalled for rotation in a pinion housing, the displacement of the rack in the rack housing determining the road, wheel angle and the rotation of the pinion in the pinion housing determined by the steering wheel angle, the instantaneous ratio between changes in steering wheel angle and changes in road wheel angle defining a steering ratio characteristic which varies as a function of steering wheel angle and vehicle speed, wherein the pinion housing is journalled for lateral displacement relative to the rack housing, and an actuation means determines the lateral displacement of the pinion housing relative to the rack housing as a function of the magnitude of at least steering wheel angle and vehicle speed, thereby determining the steering ratio characteristic.

11. A rack and pinion steering gear as claimed in claim 10 wherein the actuation means comprises a mechanical linkage, such that, when displacement inputs relating to the magnitude of steering wheel angle and vehicle speed are applied to said linkage, and said linkage has a kinematic characteristic output to the rack which therefore varies with the magnitude of said displacement inputs.

12. A rack and pinion steering gear as claimed in claim 11 wherein one or both of the displacement inputs are provided by an electric or hydraulic actuator.

13. A rack and pinion steering gear as claimed in claim 11 wherein the mechanical linkage means comprises a pin-and-slot mechanism.

14. A rack and pinion steering gear as claimed in claim 11 wherein the mechanical linkage means comprises a cam-and-follower mechanism.

15. A rack and pinion steering gear as claimed in claim 11 wherein the mechanical linkage means comprises a spring loaded element which provides compliance to the linkage during high load conditions, and thereby protecting the mechanism from damage during these conditions.

16. A rack and pinion steering gear as claimed in claim 11 wherein the actuation means determines the lateral displacement of the pinion housing relative to the rack housing also as a function of an additional input which is independent of the steering wheel angle input provided by the driver.

17. A rack and pinion steering gear as claimed in claim 10 wherein the actuation means is a hydraulic or electric actuator.

18. A rack and pinion steering gear as claimed in claim 10 wherein the steering ratio characteristic provides a steering ratio in the centre operating region of the steering gear associated with on-centre driving which is greater, by a given maximum increment, than the steering ratio provided in the other operating regions of the steering gear either side of this centre operating region.

19. A rack and pinion steering gear as claimed in claim 18 wherein the increment is larger in magnitude for higher vehicle speeds.

20. A rack and pinion steering gear as claimed in claim 18 wherein the increment is zero or negative for low vehicle speeds.