GB1580531A

GB1580531A - Power assisted rack and pinion gear

Info

Publication number: GB1580531A
Application number: GB2823676A
Authority: GB
Original assignee: TRW Steering Systems Ltd
Current assignee: TRW Steering Systems Ltd
Priority date: 1976-07-07
Filing date: 1976-07-07
Publication date: 1980-12-03
Also published as: IT1083885B; FR2357414A1; DE2730167A1

Description

(54) A POWER ASSISTED RACK AND PINION GEAR (71) We, CAM GEARS LIMITED, a British Company, of 45 Wilbury Way, Hitchin, Hertfordshire SG4 OTU, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to a power assisted rack and pinion gear and particularly to a power assisted rack and pinion steering gear for a vehicle.

A conventional technique for providing power assistance for a rack and pinion steering gear is to have a piston slideably mounted in a cylinder to provide two chambers one on either side of the piston. Rotation of the vehicle steering wheel actuates a control valve to pass oil into either one of the chambers to move the piston along the cylinder in the direction of the rack bar movement. The piston is coupled to the rack bar so that the motion of the piston under the action of the oil pressure assists the movement of the rack bar and hence the steering movement of the vehicle road wheels.

In a conventional power assisted steering gear, the piston may be mounted on the rack bar so as to be slideably moveable in the rack bar housing which acts as the cylinder.

With certain rack and pinion constructions, such as for example when the pinion is disposed on or near the centreline of the vehicle, difficulties can arise in providing a piston arrangement in the available length of the rack bar. In order to overcome this difficulty, the piston has been mounted on a piston rod for slideable movement in a cylinder distinct from the rack bar housing, and the piston rod is coupled to the rack bar at or near one of its ends. Because the power assistance is imparted at or near one end of the rack bar, there is a tendency for this arrangement to apply offset forces to the rack bar. These offset forces may produce bending of the rack bar and consequent inaccuracy in the applied steering.

It is an aim of the invention to alleviate this tendency, and according to the invention there is provided a rack and pinion gear including a rack bar slidably mounted in a rack bar housing by at least one bearing mounted on the bar, and a piston hydraulically operable in a cylinder distinct from the rack bar housing to provide power-assistance to movement of the rack bar, in which the piston is coupled to the said one bearing.

The coupling between the piston and the bearing may include an arm extending from the bearing through the rack bar housing.

This arm may extend through an elongate slot in the rack bar housing, and the end of the arm remote from the bearing may be coupled to a piston rod which is connected to the piston.

The bearing may include a cylindrical carrier sleeve to which the arm is connected, and a tubular bush suitably mounted on the sleeve. In a preferred construction, the piston and the rack bar are operable to move parallel to one another, with the arm extend mg radially from the rack bar.

One power-assisted rack and pinion gear of the invention will be now be described by way of example with reference to the accompanying drawing in which: FIGURE 1 is a plan view partly in section of part of a vehicle steering gear; and FIGURE la is a plan view partly in section on an enlarged scale of part of the steering gear of Figure 1.

Referring to the drawing, the steering gear includes a rack bar 2 engaging a centrally mounted pinion 4 coupled by a connector 6 to a steering column. The rack bar 2 is slidably mounted in an open ended housing 8 by means of two bearing assemblies, one on either side of the pinion 4. Each assembly comprises a tubular bush 10 mounted on a bearing carrier sleeve 12 which is itself mounted on the rack bar 2. Each bush 10 is located in a recess in its respective sleeve 12 by a circlip 13.

Each end of the rack bar 2 is coupled by a ball joint 14 to a linkage for providing steering movement of a respective road wheel. A sealing member 16 is located at each end of the rack bar housing 8. Each sealing member 16 has one end coupled to an end of the rack bar housing 8, its intermediate section coupled to the ball joint 14, and its other end coupled to the linkage. The sealing members 16 are extendible to accommodate movement of the rack bar 2 in the housing 8.

The steering gear includes a power assistance piston 18 slideably mounted in a closed cylinder 20, parallel to the rack housing 8, to divide the cylinder 20 into two chambers 22 and 24, one on either side of the piston 18. A piston rod 26 makes a sliding oil-tight fit through the left hand end wall of the cylinder 20. One end of the piston rod 26 is secured to the piston 18, and the other end is outside the cylinder 20 and has a screw threaded end portion 28.

The left hand illustrated carrier sleeve 12 includes an integral connecting arm 30 extending radially outwards through an elongate slot 32 in the rack housing 8. The end of the arm 30 remote from the sleeve 12 constitutes an eyelet 34 of tubular internal cross section, greater than the external cross section of the piston rod end portion 28. To connect the arm 30 to the piston rod 26, a positioning nut 36 is screwed onto the end portion 28. Two tubular rubber bushes 38 each having a radially outwardly extending end flange 40 are positioned in the eyelet 34 with their end flanges 40 abutting opposite sides of the connecting arm 30. A tubular steel spacer 42 is slid into the bushes 38 and a U-shaped tab washer 44 is fitted over the bush-spacer assembly. The tab washer 44 has two co-axial holes which align with the bore of the spacer 42. The assembly is dimensioned so that the bore of the spacer 42 and the holes in the washer 44 are of slightly greater diameter than that of the piston rod end 28. The assembly is pushed onto the end 28 to abut the positioning nut 36, and a second nut 46 is screwed onto the end 28 so that the assembly is held firmly on the end 28 between the nuts 36 and 46.

In operation, rotation of the vehicle steering wheel actuates a control valve 48 to pass oil into either one of the chamber 22 or 24 to move the piston 18 to assist the movement of the rack bar 2. This movement of the piston 18 is transmitted to the rack bar 2 by the piston rod 26, the spacer-bush assembly, the connecting arm 30 and the left hand carrier sleeve 12. Because the power assistance is transmitted to the rack bar 2 at the region of the bearing carrier sleeve 12, the side forces created by the offset piston rod are contained by the bush 10 in the housing 8, thereby eliminating the possibility of bending the rack bar 2.

Reference is hereby made to the Applicant's co-pending Application 28237/76, Serial No. 1580532, which discloses similar subject matter.

WHAT WE CLAIM IS: 1. A rack and pinion gear including a rack bar slidably mounted in a rack bar housing by at least one bearing mounted on the bar, and a piston hydraulically operable in a cylinder distinct from the rack bar housing to provide power assistance to movement of the rack bar, in which the piston is coupled to the said one bearing.

2. A rack and pinion gear as claimed in Claim 1, in which the coupling between the piston and the bearing includes an arm extending from the bearing through the rack bar housing.

3. A rack and pinion gear as claimed in Claim 2, in which the arm extends through an elongate slot in the rack bar housing.

4. A rack and pinion gear as claimed in Claim 2 or Claim 3, in which the end of the arm remote from the bearing is coupled to a piston rod connected to the piston.

5. A rack and pinion gear as claimed in any one of Claims 2 to 4 in which the bearing includes a cylindrical carrier sleeve to which the arm is connected.

6. A rack and pinion gear as claimed in Claim 5, in which the bearing includes a tubular bush mounted on the sleeve.

7. A rack and pinion gear as claimed in Claim 6, in which the bush is located in a recess in the sleeve.

8. A rack and pinion gear as claimed in any one of Claims 2 to 7, in which the arm extends radially outwards from the rack bar.

9. A rack and pinion gear as claimed in any preceding Claim, in which the piston and rack bar are operable to move parallel to one another.

10. A rack and pinion gear substantially as herein described and shown in the accom panying drawin$ ~ ~~~

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. mounted on the rack bar 2. Each bush 10 is located in a recess in its respective sleeve 12 by a circlip 13. Each end of the rack bar 2 is coupled by a ball joint 14 to a linkage for providing steering movement of a respective road wheel. A sealing member 16 is located at each end of the rack bar housing 8. Each sealing member 16 has one end coupled to an end of the rack bar housing 8, its intermediate section coupled to the ball joint 14, and its other end coupled to the linkage. The sealing members 16 are extendible to accommodate movement of the rack bar 2 in the housing 8. The steering gear includes a power assistance piston 18 slideably mounted in a closed cylinder 20, parallel to the rack housing 8, to divide the cylinder 20 into two chambers 22 and 24, one on either side of the piston 18. A piston rod 26 makes a sliding oil-tight fit through the left hand end wall of the cylinder 20. One end of the piston rod 26 is secured to the piston 18, and the other end is outside the cylinder 20 and has a screw threaded end portion 28. The left hand illustrated carrier sleeve 12 includes an integral connecting arm 30 extending radially outwards through an elongate slot 32 in the rack housing 8. The end of the arm 30 remote from the sleeve 12 constitutes an eyelet 34 of tubular internal cross section, greater than the external cross section of the piston rod end portion 28. To connect the arm 30 to the piston rod 26, a positioning nut 36 is screwed onto the end portion 28. Two tubular rubber bushes 38 each having a radially outwardly extending end flange 40 are positioned in the eyelet 34 with their end flanges 40 abutting opposite sides of the connecting arm 30. A tubular steel spacer 42 is slid into the bushes 38 and a U-shaped tab washer 44 is fitted over the bush-spacer assembly. The tab washer 44 has two co-axial holes which align with the bore of the spacer 42. The assembly is dimensioned so that the bore of the spacer 42 and the holes in the washer 44 are of slightly greater diameter than that of the piston rod end 28. The assembly is pushed onto the end 28 to abut the positioning nut 36, and a second nut 46 is screwed onto the end 28 so that the assembly is held firmly on the end 28 between the nuts 36 and 46. In operation, rotation of the vehicle steering wheel actuates a control valve 48 to pass oil into either one of the chamber 22 or 24 to move the piston 18 to assist the movement of the rack bar 2. This movement of the piston 18 is transmitted to the rack bar 2 by the piston rod 26, the spacer-bush assembly, the connecting arm 30 and the left hand carrier sleeve 12. Because the power assistance is transmitted to the rack bar 2 at the region of the bearing carrier sleeve 12, the side forces created by the offset piston rod are contained by the bush 10 in the housing 8, thereby eliminating the possibility of bending the rack bar 2. Reference is hereby made to the Applicant's co-pending Application 28237/76, Serial No. 1580532, which discloses similar subject matter. WHAT WE CLAIM IS:

1. A rack and pinion gear including a rack bar slidably mounted in a rack bar housing by at least one bearing mounted on the bar, and a piston hydraulically operable in a cylinder distinct from the rack bar housing to provide power assistance to movement of the rack bar, in which the piston is coupled to the said one bearing.