GB1580532A

GB1580532A - Power assisted rack and pinion gear

Info

Publication number: GB1580532A
Application number: GB2823776A
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: FR2357413A1; IT1083884B; DE2730135A1

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 powerassisted rack and pinion gear, and particularly to a power-assisted rack and pinion steering gear for a vehicle.

Power-assistance can be imparted to the rack of a rack and pinion steering gear from a piston which is slidably 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 movement 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 rack and pinion steering gear, the piston is mounted on the rack bar so as to be slidably movable in the rack bar housing which acts as the cylinder. In certain rack and pinion constructions, such as for example when the pinion is disposed on or near the centre line of the vehicle, difficulties can arise in providing a piston arrangement which can operate in the available length of the rack bar. In order to overcome this difficulty the piston has been mounted for slidable movement in a cylinder distinct from the rack bar housing. It will be appreciated that in order to provide the required power-assistance it is necessary to couple the piston to the rack bar.

Accordingly there is provided a rack and pinion gear including a rack bar movably mounted in a rack bar housing, and hydraulic means comprising a piston and a cylinder which are relatively movable to provide power-assistance to movement of the rack bar, the cylinder being distinct from the rack bar housing, in which resilient coupling means is provided between the hydraulic means and the rack bar.

The coupling means may include a resilient intermediate means located between two members which are connected to respective ones of the hydraulic means and the rack bar.

Said two members may for example comprise an eyelet and a rod portion, with the eyelet mounted on the said rod portion. The resilient means may be a resilient bush located on the rod portion between adjacent surfaces of the said portion and the eyelet, and the bush may comprise two bush portions each having a radially outwardly extending end flange to receive a respective end surface of the eyelet.

In one gear of the invention, the rod portion may be a part of a piston rod on which the piston is mounted, and the eyelet may be located on an arm extending from the rack bar. In another gear of the invention, the eyelet may be located on an arm extending from the cylinder, and the rod portion may pass through arms extending from the rack bar and the cylinder respectively. In both the aforementioned gears, the piston and the rack bar are operable to move parallel to one another.

Two power-assisted rack and pinion gears of the invention will now be described by way of example with reference to the accompanying drawings in which: FIGURE 1 is a plan view partly in section of part of one vehicle steering gear; FIGURE la is a plan view partly in section on an enlarged scale of part of the steering gear of Figure 1; FIGURE 2 is a plan view partly in section of part of another vehicle steering gear; and FIGURE 3 is a plan view partly in section on an enlarged scale of part of the steering gear of Figure 2.

Referring to Figures 1 and la, a vehicle 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 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 member 16 is extendable to accommodate movement of the rack bar 2 in the housing 8.

The steering gear includes a powerassistance piston 18 slidably 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 screwthreaded 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 wheei actuates a control valve 48 to pass oil intro either one of the chambers 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.

FIGURES 2 and 3 illustrate another power-assisted rack and pinion gear of the invention, and for clarity corresponding components of the two gears performing the same function will be given the same reference numerals.

Referring to Figures 2 and 3, a vehicle steering gear includes a rack bar 2 engaging a centrally mounted pinion 4 coupled by a connector (not shown) to a steering column.

The rack bar 2 is slidably mounted in an open ended housing 50 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.

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 50. Each sealing member 16 has one end coupled to an end of the rack bar housing 50, its intermediate section coupled to the ball joint 14, and its other end coupled to the linkage. The sealing member 16 is extendable to accommodate movement of the rack bar 2 in the housing 50.

The steering gear includes a powerassistance piston 52 which makes a sliding fit in a closed cylinder 54 parallel to the rack bar housing 50 to divide the cylinder 54 into two chambers 22 and 24 one on either side of the piston 52. A piston rod 56 extends through the cylinder 54 and makes a sliding oil-tight fit through the two end walls of the cylinder 54. The piston 52 is mounted on the central portion of the piston rod 56, and the two ends of the piston rod 56 are secured to respective mounting bars 58 and 60 which extend trans- versely from the rack bar housing 50. Each end of the piston rod 56 is screw-threaded, and is secured to its respective mounting bar by two nuts 62 and 64. The parts of the piston rod 56 between the ends of the cylinder 54 and the mounting bars 58 and 60 are housed in corrugated bellows 61.

Each bearing carrier sleeve 12 includes an integral connecting arm 66 extending radially outwards through an elongate slot 32 in the rack bar housing 50. Each arm 66 is resiliently coupled to the cylinder 54 in a manner which will now be described with reference to Figure 3.

The end of each arm 66 remote from the sleeve 12 is forked to provide two parallel spaced side walls 68 having co-axial tubular bores of equal diameter extending through them. Two arms 70 project transversely from the cylinder 54, and each arm 70 is dimensioned to make a clearance fit between the side walls 68 of its respective connecting arm 66. Each arm 70 has a tubular bore extending through it of greater diameter than the bores in the side walls 68.

To connect the arm 70 to its respective connecting arm 66, firstly the arm 70 is withdrawn from between the walls 68. Two tubular rubber bushes 38 each having a radially outwardly extending end flange 40 are positioned in the bore in the arm 70 with their end flanges 40 abutting opposite sides of the arm 70. 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 arm 70 with its assembled coupling components is located between the side walls 68 with the bore of the spacer 42 aligned with the bores through the walls 68. A rod 72, which is screw-threaded at each end, is pushed through the aligned bores, and two nuts 74 and 76 are screwed onto the ends of the rod 72 so that the assembly is held firmly between the arms 66 and 70. The assembly is dimensioned so that the tab washer 44 makes a firm fit between the side walls 68 and bush flanges 40, and so that the bore of the spacer 42 and the holes in the washer 44 are of slightly greater diameter than that of the rod 72.

Two fluid feed conduits 78 and 80 pass along their respective sections 82 and 84 of the piston rod 56. Each conduit extends from its respective end of the piston rod along its piston rod section and has an outlet which communicates with its appropriate cylinder chamber 22 and 24 just short of the piston 52.

In operation, rotation of the vehicle steering wheel actuates a control valve (not shown) to pass oil along the appropriate feed conduit to either one of the chambers 22 or 24 to move the cylinder 54 to assist the movement of the rack bar 2. This movement of the cylinder 54 is transmitted to the rack bar 2 by the arms 70, the spacer bush assemblies, the connecting arms 66 and the carrier sleeves 12.

Reference is hereby made to the Applicant's co-pending Application No. 28236/76 Serial No. 1 580 531 which discloses similar subject matter.

WHAT WE CLAIM IS: 1. A rack and pinion gear including a rack bar movably mounted in a rack bar housing, and hydraulic means comprising a piston and a cylinder which are relatively movable to provide power-assistance to movement of the rack bar, the cylinder being distinct from the rack bar housing, in which resilient coupling means is provided between the hydraulic means and the rack bar.

2. A rack and pinion gear as claimed in Claim 1, in which the coupling means includes a resilient intermediate means located between two members which are connected to respective ones of the hydraulic means and the rack bar.

3. A rack and pinion gear as claimed in Claim 2, in which said two members comprise an eyelet and a rod portion, the eyelet being mounted on the said rod portion.

4. A rack and pinion gear as claimed in Claim 3, in which the resilient means is a resilient bush located on the rod portion between adjacent surfaces of the said portion and the eyelet.

5. A rack and pinion gear as claimed in Claim 4, in which the bush comprises two bush portions each having a radially outwardly extending end flange to receive a respective end surface of the eyelet.

6. A rack and pinion gear as claimed in Claim 5, in which the bush portions are made of rubber.

7. A rack and pinion gear as claimed in Claim 5 or Claim 6, further including a tubular spacer located between the bush portions and the rod portion.

8. A rack and pinion gear as claimed in any one of Claims 3 to 7, further including a U-shaped tab washer located on the said rod portion to receive the bush-spacer assembly.

9. A rack and pinion gear as claimed in any one of Claims 3 to 8, in which the rod portion is a part of a piston rod on which the piston is mounted.

10. A rack and pinion gear as claimed in any one of Claims 3 to 9 in which the eyelet is located on an arm extending from the rack bar.

11. A rack and pinion gear as claimed in any preceding Claim, in which the piston is resiliently coupled to the rack bar.

12. A rack and pinion gear as claimed in any one of Claims 1 to 8 in which the cylinder is resiliently coupled to the rack bar.

13. A rack and pinion gear substantially as herein described and shown in Figures 2 and 3 of the accompanying drawings.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. The end of each arm 66 remote from the sleeve 12 is forked to provide two parallel spaced side walls 68 having co-axial tubular bores of equal diameter extending through them. Two arms 70 project transversely from the cylinder 54, and each arm 70 is dimensioned to make a clearance fit between the side walls 68 of its respective connecting arm 66. Each arm 70 has a tubular bore extending through it of greater diameter than the bores in the side walls 68. To connect the arm 70 to its respective connecting arm 66, firstly the arm 70 is withdrawn from between the walls 68. Two tubular rubber bushes 38 each having a radially outwardly extending end flange 40 are positioned in the bore in the arm 70 with their end flanges 40 abutting opposite sides of the arm 70. 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 arm 70 with its assembled coupling components is located between the side walls 68 with the bore of the spacer 42 aligned with the bores through the walls 68. A rod 72, which is screw-threaded at each end, is pushed through the aligned bores, and two nuts 74 and 76 are screwed onto the ends of the rod 72 so that the assembly is held firmly between the arms 66 and 70. The assembly is dimensioned so that the tab washer 44 makes a firm fit between the side walls 68 and bush flanges 40, and so that the bore of the spacer 42 and the holes in the washer 44 are of slightly greater diameter than that of the rod 72. Two fluid feed conduits 78 and 80 pass along their respective sections 82 and 84 of the piston rod 56. Each conduit extends from its respective end of the piston rod along its piston rod section and has an outlet which communicates with its appropriate cylinder chamber 22 and 24 just short of the piston 52. In operation, rotation of the vehicle steering wheel actuates a control valve (not shown) to pass oil along the appropriate feed conduit to either one of the chambers 22 or 24 to move the cylinder 54 to assist the movement of the rack bar 2. This movement of the cylinder 54 is transmitted to the rack bar 2 by the arms 70, the spacer bush assemblies, the connecting arms 66 and the carrier sleeves 12. Reference is hereby made to the Applicant's co-pending Application No. 28236/76 Serial No. 1 580 531 which discloses similar subject matter. WHAT WE CLAIM IS:

1. A rack and pinion gear including a rack bar movably mounted in a rack bar housing, and hydraulic means comprising a piston and a cylinder which are relatively movable to provide power-assistance to movement of the rack bar, the cylinder being distinct from the rack bar housing, in which resilient coupling means is provided between the hydraulic means and the rack bar.