GB2162477A - Valve assembly for a power assisted steering gear - Google Patents

Abstract

A valve assembly for a power assisted steering gear has a housing 1 within a bearing 10 and shaft seal 11 in which is rotatably mounted a shaft 9. The shaft 9 controls rotation of a rotor 8 relative to a sleeve 7 to adjust control ports 14, 15, 16 to control fluid flow for power assistance. Pressure fluid is supplied by way of a chamber 19 formed between the seal 11 and a sleeve end face 22. To protect the seal 11 and bearing 10 from pressure of fluid in the chamber 19, a sealing plate 21 is provided which partly defines the chamber 19 and within which the shaft 9 is rotatable. The plate 21 engages with the housing through a seal 23 and, if required, a further seal can be provided between the plate and the shaft 9. <IMAGE>

Description

SPECIFICATION A valve assembly for and a power assisted steering gear with such an assembly TECHNICAL FIELD AND BACKGROUND ART This invention relates to a valve assembly for controlling fluid flow to servo motor means of a power assisted steering gear and to a steering gear which includes such an assembly.

In power assisted vehicle steering gears such as a conventional rack and pinion type gear with a double acting piston and cylinder type servo motor, valve assemblies for controlling fluid flow to the piston and cylinder device to provide power assistance in response to a steering manoeuvre have hitherto been proposed as comprising a housing within which is rotatably mounted a shaft rotated in response to the steering manoeuvre. Also rotatably mounted within the housing co-axial with the input shaft is a sleeve and a rotor received therein; one of the sleeve and rotor is coupled to provide a steering drive or output from the steering gear while the other is coupled to the shaft.The sleeve and rotor are rotationally spring biased with respect to each other (usually by a torsion bar or other spring component) and are rotatable relative to each other in response to rotation of the shaft to adjust control ports within the assembly and control fluid flow as required for power assistance.

It has also been proposed for convenience of design and/or manufacture (see for example Figure 16 of G.B. Patent No.

2,047,1 83B) to rotatably mount the shaft in a fluid seal which extends between itself and the housing and to provide between this seal and an end face of the sleeve adjacent thereto, a chamber which is subjected to fluid pressure--either constant pressure which may be derived directly from the fluid pressure input to the assembly or alternating pressure as may be derived from actuation of the control ports in effecting the alternate expansion and contraction of one side of the double acting piston and cylinder servo motor.This arrangement of a chamber which is subjected to fluid pressure and located at an end of the sleeve is also particularly advantageous as providing a means whereby the sleeve can have a short axial length to permit a reduction in the overall size of the valve assembly as discussed in our co-pending Patent Application No. 83 21 219 Conventionally power assisted steering gears usually operate with fluid pressure in the order of 500 Ibs. per square inch or greater so it will be appreciated that the chamber seal on the shaft as above described is subjected to considerable pressure; consequently, these seals can rapidly deteriorate and may require frequent replacement.It is an object of the present invention to provide a valve assembly which incorporates a shaft seal as above and the structure of which alleviates the aforementioned difficulties to permit a relative increase in seal life.

STATEMENTS OF INVENTION AND ADVAN TAGES According to the present invention there is provided a valve assembly for controlling fluid flow to servo motor means of a power assisted steering gear comprising a housing; a shaft extending from said housing and rotatable in response to a steering manoeuvre; seal means between said shaft and said housing; a sleeve and a rotor received therein which are co-axial with said shaft and are rotatable relative to each other in response to rotation of the shaft to adjust control ports and control fluid flow for power assistance; said housing having a chamber which is subjected to fluid pressure and is located between the seal means and an end face of the sleeve adjacent to said seal means, and wherein said shaft extends through sealing plate means located in said housing between the sleeve and the seal means, the sealing plate means partly defining the chamber remote from the end face of the sleeve and alleviating pressure on the seal means from fluid in the chamber.

Further according to the present invention there is provided a power assisted steering gear having servo motor means fluid flow to which is controlled by a valve assembly as specified in the immediately preceding paragraph.

By the present invention the sealing plate means which is a component separate from both the sleeve and the shaft effectively provides a partition or barrier between the shaft seal and the pressurised chamber adjacent thereto to protect the seal from the high pressure to which the chamber is subjected (thereby enabling the shaft seal to have a relatively long working life and possibly permit the use of less expensive shaft seals).

Although the sealing plate means is intended to provide the seal between the pressurised chamber and the seal means it is possible that some fluid leakage will occur from the chamber to the seal meanshowever the pressure on the seal means will be considerably less than in the absence of the sealing plate means. The sealing plate means preferably carries a fluid seal which engages between the outer periphery of the plate and the valve housing and, if required can carry an internal seal which engages with the surface of the shaft. Preferably the shaft rotates relative to and within the sealing plate means-the latter conveniently being restrained from rotation by frictional engagement with the housing.Although the shaft may be arranged to rotate relative to and within the sealing plate, it is preferred that the shaft is rotatably mounted in a bearing and that this bearing is located in the housing on the side of the sealing plate means remote from the pressurised chamber and between the sealing plate means and the seal means (thereby alleviating the bearing from fluid pressure in the chamber).

The sealing plate means is preferably in the form of a simple annular plate which is received on the shaft and in sealed manner within a bore of the housing and is axially retained in the bore against displacement under the pressure of fluid in the chamber. The means of plate retention is conveniently by the location of an abutment or stop against the sealing plate.

It will be realised that the shaft, sleeve and rotor arrangement can be of conventional form, for example either the sleeve or rotor can be secured for rotation with (and may be an integral part of)the shaft; the chamber can be pressurised continuously during operation of the gear bv direct communication with the fluid pressure inlet port in the housing or may be pressurised and exhausted alternately where the chamber communicates with one side of a double acting piston and cylinder device servo motor.

DRAWING One embodiment of a power assisted steering gear incorporated in a valve assembly constructed in accordance with the present invention will now be described, by way of example only, with reference to the accompanying illustrative drawing which shows an axial section through the assembly.

DETAILED DESCRIPTION OF DRAWING The power assisted steering gear is of the rack and pinion type having a housing 1 within which is rotatably mounted aa pinion 2, the teeth of which engage a rack bar 3 so that rotation of the pinion drives the rack bar in conventional manner. Associated with the gear, conveniently on the rack bar 3 in conventional manner, is a servo motor (not shown) in the form of a double acting piston and cylinder device, fluid pressure flow to and exhausting of opposite sides of which device is effected through ports 4 and 5 in the housing, again in conventional manner to provide power assistance for a steering manoeuvre.

The pinion shaft 2 extends into a bore 6 in the housing and is pinned for rotation with a co-axial sleeve 7. Received within the sleeve 7 is a rotor 8 integrally formed with a steering input shaft 9 that extends through the bore 6 from a side of the housing 1. The shaft 9 is rotatably mounted in the housing co-axial with the sleeve 7 by a bearing 10 which bearing is retained seated in an annular rebate 10a in the bore 6 by a shaft seal 11 extending between the shaft and the housing. The seal 11 is retained by a circlip 1 2 (although other forms of retention such as a screw threaded end cap can be provided).

A lost motion coupling indicated at 1 3 is provided between the rotor 8 and the pinion shaft 2 which permits relative rotation between the rotor 8 and sleeve 7 in response to a steering manoeuvre and it is this relative rotation (which is conventionally resiliently restrained by a torsion rod or bar or other spring device between the shafts 2 and 9) which adjusts control ports between the rotor 8 and sleeve 7 to control fluid flow to and from the servo motor to provide the required power assistance.In the present example the control ports comprise a circumferentially spaced array of recesses 14 in the rotor, axially extending grooves 1 5 and 1 6 in the bore of the sleeve and passages 1 7 extending through the sleeve which are in constant communication with one or other of the ports 4 and 5.

The axially extending grooves 1 5 and 1 6 each have one end blind while the other end opens into an end face of the sleeve 7; in the case of grooves 15, their open ends are in constant communication with an exhaust chamber 1 7 which is in constant communication with an exhaust port 1 8 in the housing. In the case of grooves 1 6 their open ends are in constant communication with a fluid pressure chamber 1 9 which is in constant communication with a fluid pressure inlet port 20 in the housing 1.

By this control port arrangement the grooves 16 are always pressurised and when the rotor 8 is rotated relative to the sleeve 7 in response to a steering manoeuvre fluid under pressure will be directed by the recesses 14 to one or other of the ports 4 and 5 while the other of the ports 4 and 5 is open to communication through different recesses 14 to the grooves 1 5 and thereby to the exhaust port 18 so that the servo motor will operate as appropriate to provide the power assistance to the steering manoeuvre.

The pressure chamber 1 9 is intended to be subjected constantly to pressure fluid supplied to the inlet port 20 and to alleviate pressure of this fluid on the bearing 10 and on the shaft seal 11 ,an annular sealing plate 21 is provided between the bearing 10 and the adjacent end face 22 of the sleeve 7. The plate 21 is received on the shaft 9 as a close sliding fit for the shaft to be rotatable therein and carries an annular seal 23 which seals against the bore 6 of the housing. The plate 21 consequently partly defines the pressure chamber 1 9 and substantially protects both the bearing 10 and the shaft seal 11 from the fluid pressure inlet chamber 11. The plate 21 is restrained against axial displacement over the shaft 9 by the pressure of fluid in the chamber 1 9 by abutment of the plate against the bearing 10.

As the plate 21 is a close sliding fit on the shaft 9, an effective seal is thereby provided to alleviate substantial pressure of fluid on the bearing 10 and shaft seal 11. However, if required, the plate 21 can be provided with an internal annular seal against a shaft 9.

Claims (14)

1. A valve assembly for controlling fluid flow to servo motor means of a power assisted steering gear comprising a housing; a shaft extending from said housing and rotatable in response to a steering manoeuvre; seal means between said shaft and said housing; a sleeve and a rotor received therein which are co-axial with said shaft and are rotatable relative to each other in response to rotation of the shaft to adjust control ports and control fluid flow for power assistance; said housing having a chamber which is subjected to fluid pressure and is located between the seal means and an end face of the sleeve adjacent to said seal means, and wherein said shaft extends through sealing plate means located in said housing between the sleeve and the seal means, the sealing plate means partly defining the chamber remote from the end face of the sleeve and alleviating pressure on the seal means from fluid in the chamber.

2. An assembly as claimed in claim 1 in which the sealing plate means carries a fluid seal which engages between the outer periphery of the plate means and the valve housing.

3. An assembly as claimed in either claim 1 or claim 2 in which the sealing plate means carries a fluid seal which engages with the surface of the shaft.

4. An assembly as claimed in any one of the preceding claims in which the shaft rotates relative to and within the sealing plate means.

5. An assembly as claimed in claim 4 in which the sealing plate means is restrained from rotation with the shaft by its engagement with the housing.

6. An assembly as claimed in any one of the preceding claims in which the shaft is coaxially mounted in a bore in the housing and the sealing plate means comprises an annular plate through which the shaft extends and which annular plate is a close fit within said bore.

7. An assembly as claimed in any one of the preceding claims in which the sealing plate means is axially retained in said housing against displacement under the pressure of fluid in the chamber by an abutment or stop means.

8. An assembly as claimed in any one of the preceding claims in which the shaft is rotatably mounted in a bearing, which bearing is located in the housing on the side of the sealing plate means remote from the chamber.

9. An assembly as claimed in claim 8 in which the bearing is located between the sealing plate means and the seal means.

10. An assembly as claimed in claim 9 when appendant to claim 7 in which the sealing plate means is retained against said displacement by abutment with the bearing.

11. An assembly as claimed in claim 10 in which the bearing is retained in a seating in the housing by abutment with the seal means and means is provided which engages with the housing to retain the seal means.

1 2. An assembly as claimed in any one of the preceding claims in which the chamber is in constant communication with the fluid pressure inlet port in the housing.

1 3. A valve assembly as claimed in claim 1 and substantially as herein described with reference to the accompanying illustrative drawing.

14. A power assisted steering gear having servo motor means, fluid flow to which is controlled by a valve assembly as claimed in any one of the preceding claims.