Variable ratio steering gear

• US 6,945,353 B2
• Filed: 10/30/2001
• Issued: 09/20/2005
• Est. Priority Date: 11/01/2000
• Status: Expired due to Fees

• Current Assignee: Bishop Steering Technology Limited (Georgsmarienhütte Holding GmbH)
• Original Assignee: Bishop Steering Technology Limited (Georgsmarienhütte Holding GmbH)
• Inventors: Bishop, Arthur Ernest
• Primary Examiner(s): WINNER, TONY H
• Application Number:
  US10/415,573
• Publication Number:
  US 20040040779A1
• Time in Patent Office: 1,421 Days
• Field of Search: 180/446, 180/443, 180/444, 701/41, 743/88.PS, 744/97
• US Class Current: 180/446
• 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 displacable with respect to a steering gear housing and a pinion (4) laterally movable 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, said vehicle having a variable speed and said steering gear having a steering angle ratio that varies as a function of at least both a steering wheel angle input provided by a driver and the speed of said vehicle, said steering gear comprising:

a rack laterally displaceable with respect to a steering gear housing; and

a pinion laterally moveable within said steering gear 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 the speed of said vehicle increases.

2. A rack and pinion steering gear as claimed in claim 1, wherein 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 minimizing the travel ratio therebetween by a variable amount, said amount decreasing with rotation of said pinion from a center straight ahead position and also decreasing with the speed of said vehicle.

3. A rack and pinion steering gear as claimed in claim 1, further comprising:

first mechanical linkage means connected to said pinion to move said pinion in said steering gear 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

second mechanical linkage means connected to said first mechanical linkage means adapted to multiply said transmission pattern as a function of the speed of said vehicle to further increase said steering angle ratio in said central region.

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

5. A rack and pinion steering gear as claimed in claim 4, wherein said by-pass means comprises a detent mechanism connected to said steering gear housing.

6. A rack and pinion steering gear for a vehicle as claimed in claim 3, wherein said first mechanical linkage means comprises:

a Geneva mechanism, having a first shaft rotatable with said pinion carrying a first pin of set from the axis of said first shaft, said first pin operable 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 steering gear housing at a distance, with respect to the axis of said second shaft, that is variable in accordance with the speed of said vehicle.

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

8. A rack and pinion steering gear as claimed in claim 6, wherein said vehicle includes:

detection means for detecting the departure of said vehicle from the directional course as indicated by said steering wheel angle input and in respect to the speed of said vehicle, said detection means providing an output signal to an actuator means in order to move said second pin laterally in said steering gear housing in response said output signal.

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

10. A rack and pinion steering gear for a vehicle, said vehicle having variable speed and at least one steerable road wheel having a road wheel angle, the steering gear controlling the road wheel angle as a function of at least a steering wheel angle input provided by a driver and the speed of the vehicle, 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 the steering wheel angle and changes in the road wheel angle defining a steering ratio characteristic which varies as a function of the steering wheel angle and the speed of the vehicle,

wherein the pinion housing is journalled for lateral displacement relative to the rack housing, and

actuation means determines the lateral displacement of the pinion housing relative to the rack housing as a function of the magnitudes of at least the steering wheel angle and the speed of the vehicle, thereby determining the steering ratio characteristic.

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

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

15. A rack and pinion steering gear as claimed in claim 11, wherein mechanical linkage comprises a spring loaded element which provides compliance to the mechanical linkage during high load conditions, thereby protecting the mechanical linkage 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 a center operating region of the steering gear associated with on-center 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 the center operating region.

19. A rack and pinion steering gear as claimed in claim 18, wherein the increment increases in magnitude as the speed of the vehicle increases.

20. A rack and pinion steering gear as claimed in claim 18, wherein the increment is zero or negative when the speed of the vehicle is low.