GB2030093A

GB2030093A - Control valve for a power steering system

Info

Publication number: GB2030093A
Application number: GB7915870A
Authority: GB
Original assignee: Jidosha Kiki Co Ltd
Current assignee: Jidosha Kiki Co Ltd
Priority date: 1978-09-11
Filing date: 1979-05-08
Publication date: 1980-04-02
Also published as: ES480864A0; GB2030093B; JPS5541941U; ES8203297A1; DE2922253A1

Abstract

The damper/seal is made of resilient material, such as rubber or synthetic resin, and has an outer peripheral surface (33a) backed with tetrafluoroethylene to form a thin surface layer. The surface layer of the damper slidingly engages the inner peripheral surface of the outer sleeve of a control valve of a power steering system and prevents vibration of the control valve. Four different embodiments of the seal are described with reference to Figs. 5, 6, 7 and 9. <IMAGE>

Description

SPECIFICATION Control valve for a power steering system This invention relates to an anti-vibration device in a control valve for use in a power steering system of the kind in which a power cylinder is integrally provided with a rotary control valve adapted to control an hydraulic circuit. The control valve controls an hydraulic circuit connected between an hydraulic pressure source and fluid chambers disposed one at each end of a power cylinder by the rotational differential of a pair of valve elements, comprising inner and outer sleeves.

The inner sleeve is connected to a steering shaft, and the outer sleeve is connected to a ball-thread shaft screw threadedly engaged with the power piston.

However, the fluid flow in the interior of the control valve is violently changed at the transition stage when the hydraulic source is about to communicate one of the fluid chambers of the power cylinder. The dynamic pressure of the violently changed flow may be applied to the pair of valve elements in a complex manner thereby causing the valve element to vibrate, which in turn causes the cross-sectional area of fluid passages in the control valve to be varied. This results in deteriorating desirable hydraulic flow, and generating an odd noise sounding like guu . . '' in the control valve. In this condition, chattering may occur in the steered wheel, thus degrading comfortable steering operation.Such phenomena may be conspicuous or noticeable, especially when the steering wheel is slowly rotated, i.e., when the rotational differential between the valve elements in the control valve is delicate or subtle.

The "guu..." noise due to the pulsation of the hydraulic pressure is transmitted to the interior of the vehicle through the steering shaft or the like, and becomes an audiable, unusual noise, and therefore the driver may entertain some undesirable apprehension about the safety of the vehicle or the condition of some components.

Further during the "guu..." noise generating period, the steered wheels may be subject to chattering, which is transmitted to the steering wheel to thus impair steering feeling of the driver. This also tends to raise suspicion about the operability of the vehicle.

In order to overcome these drawbacks, conventionally an annular groove 43 having a relatively large depth and having a rectangular cross section is formed in an outer peripheral surface of the inner sleeve 2 as shown in Fig.

1 of the accompanying drawings, which will be hereinafter defined. An O-ring 42 having a circular cross section and made of rubber is fitted in the bottom portion of the groove 43 and then an annular damper 41 having a rectangular cross section is fitted around the O-ring 42 in the groove 43. The damper 41 has a relatively large radial width, and is made of tetrafluoroethylene having a low coefficient of friction with the material of an outer sleeve 19. Upon fitting the damper 41, the 0ring 42 is slightly deformed, and the outer peripheral surface of the damper 41 is in surface engagement with an inner peripheral surface of the outer sleeve 19, whereby relative vibration between the inner and outer sleeves 2 and 1 9 is prevented by the oppositely urging forces between the damper 41 and the O-ring 42 as shown by the arrows.

However, according to the above-mentioned conventional structure, the different members, that is, the damper 41 which is adapted to prevent vibration mainly because of its frictional resistance, and the O-ring 42 which is adapted to provide a resilient force in the radial direction of the interface between the damper 41 and the outer sleeve 19, because of the deformation of the ring 42, are both press-fitted in opposite directions with approximate line-contact therebetween. Slippage may occur between the O-ring and damper over a long period of use, so that as shown in Fig. 2 inner and side peripheral surfaces 45, 44 of the damper 41, and the outer side surface of the O-ring 42, which confronts the inner surface 45, may wear out.This tends to reduce the radially outward urging force of the O-ring 42 because of its deformation whereby the anti-vibration force of the damper 41 against the outer sleeve 1 9 may be decreased. This in turn generates vibration of the control valve to generate the above mentioned "guu..." noise, and to generate chattering of the steered wheel.

It should be noted that a high pressure circuit exists at the left side of the damper as seen in the drawings, and a low pressure circuit (connected to a liquid reservoir) exists at the right side thereof. The reason for wear of the side surface 44 of the damper 41 is due to the fact that since the damper 41 is urged towards the side wall of the annular groove 43 and the outer sleeve 1 9 by the high fluid pressure, relative sliding engagement occurs between the O-ring 42 and the damper 41 and also between the damper 41 and the side wall of the annular groove 43, thereby causing the side surface 44 to wear out.

Within the prior art, rod seals are generally known having tetrafluoroethylene (Teflon) surfaces bearing against a moving rod. For example U.S. Patent Specification No. 3,300,225 discloses a typical type of rod seal. The purpose of such seals is to prevent leakage of pressurized fluid in a cavity. By forming the seal with three actions, an inner Teflon ring 23, an outer rubber ring 25 and a back-up cast iron ring 29 a compression seal is defined. This structure is unsuitable for use in vibrating control of sleeve type valves but is cited to show a rod seal using a Teflon bearing surface.

Additionally, a typical prior art power steer ing system is shown in U.S. Patent Specification No. 3,033,051. This type of system uses a series of annular pressure grooves and seals 118 in the fluid control valve portion of the system shown in Fig. 2. Also shown, but not referred to is an O-ring as discussed with respect to Figs. 1 and 2 herein. This ring together with a similar element 36 provide seals for the ends of the axial passages in the valve body. Elimination of vibration is not a consideration.

Given the deficiencies of the prior art it is an object of this invention to provide for a power steering control valve, an improved anti-vibration arrangement which inhibits the generation of unusual noises and meander in steered wheels, and which maintains its effectiveness over a long service life.

In accordance with the invention, a control valve for use in a power steering system, the valve including a pair of valve elements comprising inner and outer sleeves both concentri cally fitted in a valve chamber integrally provided with a power cylinder, the outer sleeve being connected to a ball-thread shaft and the inner sleeve being connected to a steering shaft, and the ball-thread shaft and steering shaft being connected to each other by a torsion bar to allow a relative rotational differential between the valve elements; and a piston disposed in the power cylinder and screw threadedly engaged with the ball-thread shaft is characterised by an annular groove formed in the inner sleeve at a sliding portion between the valve elements, and a resilient damper fitted in the groove, the damper being composed of a resilient material, such as rubber synthetic resin, and having an outer peripheral surface provided with a layer of tetrafluoroethylene which slidingly engages an inner peripheral surface of the outer sleeve whereby vibration of the control valve is inhibited.

Such examples of control valves constructed in accordance with the invention and a comparison with the prior art are illustrated in the accompanying drawings, in which: Figure 1 is a cross-sectional view of a conventional composite damper of an antivibration means in a control valve; Figure 2 is a cross-sectional view of the conventional damper showing the condition after a long period of use; Figure 3 is a cross-sectional view of a control valve in a power steering mechanism according to this invention; Figure 4 is a cross-sectional view of an antivibration device of the control valve of Fig. 3; Figure 5 is a cross-sectional view of one damper; Figure 6 is a cross-sectional view of a second damper; Figure 7 is a cross-sectional view of a third damper; Figure 8 is a transverse cross-sectional view of the damper shown in Fig. 7; and, Figure 9 is a cross-sectional view of a fourth damper.

A power steering system is shown in Fig. 3, wherein a piston 1 5 formed with a rack at the outer peripheral surface portion thereof is fitted in a cylinder 1 7. The rack is engaged with a gear shaft adapted to transmit steering power to the steered wheel. A hollow ballthreaded shaft 5 is screw threadedly engaged with a central portion of the piston 1 5 through a ball 23. A torsion bar 1 4 extends through the ball-thread shaft 5 and the bar is connected to an end portion of a steering shaft 10 by a pin 24. The ends of the ballthread shaft 5 and the torsion bar 14 are connected with each other by a pin (not shown).By the rotation of the steering shaft 10, the torsion bar 14 is distorted by a steering reaction force applied to the ballthread shaft 5, so that a pair of valve elements of a control valve generate rotational differential to thus provide a hydraulic pressure circuit to one of two chambers 1 6 in the cylinder 17, one on each side of the piston 1 5 to provide rotational power of the ballthread shaft 5.

The control valve includes outer and inner sleeves 1 9,2 concentrically disposed with each other in housing 1 8 connected to the cylinder 17, The outer sleeve 1 9 is rotationally connected to a base portion of the ballthread shaft 5 by a pin 7. The inner sleeve 2 is rotationally connected to the steering shaft 10 by a pin 3. The ball-thread shaft 5 is supported by a thrust bearing 6 disposed at an inner end wall of the housing 18 and a thrust bearing 25 together with a spacer 20 formed with a fluid passage 20a communicating with a fluid recirculation port 1 2. The thrust bearing 25 and the spacer 20 are disposed at an end plate 21 which closes the housing 18.The steering shaft 10 is supported by a bearing 4 disposed in a cylindrical portion of the ball-thread shaft 5 and a bearing 1 disposed at the end plate 21.

The outer end of the bearing 1 is sealed by an oil seal 11 fitted in a shaft hole of the end plate 21 and supported by a stopper ring 22.

An inner peripheral surface of the housing 18 is formed with the fluid recirculation port 1 2 and fluid supply port (not shown) connected to a hydraulic pump. The port 1 2 is positioned at a different circumferential position from the supply port. One of the ports is selectively connected to one of the fluid chambers 1 6 in the power cylinder through a fluid passage 8 formed in the housing 1 8. The other port is selectively connected to the other of the fluid chambers through a fluid passage 1 3 by means of a valve groove provided at a rotational sliding portion defined between the resistance and a low-friction coefficient with the material of the outer sleeve, the durability of the damper 33 is excellent.

In a second embodiment shown in Fig. 6, an inner peripheral surface of the damper 33 is in the form of an arcuate shape in cross section, and the most radially inward portion is resiliently supported by the bottom surface 31 a of the annular groove 31 to distribute the resilient force uniformly along the entire surface of the surface layer 33a. Generally, the damper with a rectangular cross-section may provide distortion after moulding, so that a uniformly distributed resilient force may not be applied to the entire surface layer 33a. The arcuately shaped inner peripheral surface as shown in Fig. 6 can avoid uneven resilience of the damper 33 due to moulding error or distortion after moulding thereof.

In the third embodiment shown in Figs. 7 and 8, a plurality of notched grooves 35 are formed in the inner peripheral surface of the damper 33 along the axial direction thereof at certain intervals with respect to the inner surface. These grooves 35 serve to urge the damper 33 uniformly radially outwardly, to maintain excellent contact between the surface layer 33a and the outer sleeve 19. The pressurized fluid in the clearance 38 is intro duced into spaces each defined between the bottom surface 31 a of the annular groove 31 and notched groove 35, so that the surface layer 33a is urged towards the outer sleeve 1 9 in response to the fluid pressure variation.

Therefore, an uneven resilient pressure by the surface layer 33a due to uneven moulding can be further minimized.

In a fourth embodiment shown in Fig. 9, a damper 33 has an outer diameter larger than the inner diameter of the outer sleeve 1 9 prior to assembly, and no crushed portion is produced during assembly, since an annular space 39 is provided between the damper and the bottom surface of the annular groove 31.

Pressurized fluid in the clearance space 38 is introduced into the annular space 39 and the introduced pressurized fluid urges the surface layer 33a radially outwardly, to increase surface contact pressure with the outer sleeve 19. According to this embodiment, resistance between the outer sleeve 1 9 and the surface layer 33a of the damper 33 is changed in response to the pressure of the fluid, and the damper 33 functions to push against the outer sleeve 1 9 from the inner sleeve 2.

As explained above, as an anti-vibration device for a control valve in a power steering mechanism, at the sliding interface of a pair of valve elements having outer and inner sleeves, a damper is fitted in its compressed state in an annular groove formed in the inner sleeve. The damper is made of a resilient material such as rubber or the like. The radial thickness of the damper is larger than the depth of the annular groove of alternatively, the outer diameter of the dampering is larger than the inner diameter of the outer sleeve.

The damper has an outer peripheral surface baked with a tetrafluoroethylene layer to provide a surface which is strongly urged toward the inner peripheral surface of the outer sleeve.

Therefore, the vibration of the vale elements due to pressurized fluid turbulence and the change of dynamic pressure of the fluid caused by the rotational differential between the valve elements can be prevented by the resilient of the damper per se which functions to urge the inner and outer sleeves in opposite directions, and by the resistance of the surface layer of the damper exerted on the outer sleeve because of the resiliency of the damper and the fluid pressure applied thereto.

Further, since the damper disposed in the groove of the inner sleeve is frictionally engaged with one of the side walls of the groove by the fluid pressure, the damper does not slide relative to the groove to obviate its wear.

Therefore the damper can maintain a constant resilient force to be applied via the surface layer 33a. Furthermore, since the surface layer 33a provides small sliding resistance relatively to the outer sleeve, a stabilizing force is exerted to the outer sleeve for a long period of use. With this structure smooth rotational sliding between the valve elements, so that excellent effect is obtainable, that is, vibration and noise generated at the control valve and chattering of the steered wheels due to variation of the output of the power cylinder can be prevented.

Claims

1. A control valve for use in a power steering system, the valve including a pair of valve elements comprising inner and outer sleeves both concentrically fitted in a valve chamber integrally provided with a power cylinder, the outer sleeve being connected to a ball-thread shaft and the inner sleeve being connected to a steering shaft, and the ballthread shaft and steering shaft being connected to each other by a torsion bar to allow a relative rotational differential between the valve elements; and a piston disposed in the power cylinder and screw threadedly engaged with the ball-thread shaft; an annular groove formed in the inner sleeve at a sliding portion between the vale elements, and a resilient damper fitted in the groove, the damper being composed of a resilient material and having an outer peripheral surface provided with a layer of tetrafluoroethylene which slidingly engages an inner peripheral surface of the outer sleeve, whereby vibration of the control valve is inhibited.

2. A valve according to claim 1, wherein the damper has an axial width smaller than the axial width of the annular groove and radial thickness when unstressed larger than inner and outer sleeves 2,1 9 of the control valve. These fluid communications can be reversed. The structure of such valve elements has been known and does not directly concern the subject matter of this invention, and therefore further explanation is omitted.

Relative vibration of the valve elements is prevented by fitting a damper 33 at the sliding interface defined between the inner and outer sleeves 2,1 9 as shown in Fig. 4. To be more specific, an annular groove 31 is formed at the outer peripheral end portion of the inner sleeve 2 and the damper 33 is fitted in the groove. The damper 33 is made of a resilient material such as rubber or synthetic resin. Preferably, the damper 33 has an axial width smaller than that of the annular groove 31, and a radial thickness larger than the depth of the annular groove 31. Also, the damper 33 has a rectangular cross-section and an outer peripheral surface baked with tetrafluoroethylene to provide a thin anti-friction surface layer 33a.In the embodiment shown in the drawings, a closing ring 30 is force-fitted in the inner peripheral end surface of the outer sleeve 1 9 in order to close the end portion of the valve groove extending along the axial direction of the outer sleeve 19. The layer 33a is in surface engagement with an inner peripheral surface of the closing ring 30.

The right hand end portion of the inner and outer sleeves 2,1 9 continuously communicates with the fluid recirculation port 1 2 by the fluid passage 20a formed in the spacer 20, while the central portion of the sliding interface between the inner and outer sleeves 2 and 1 9 is formed with the valve groove communicating with the fluid supply port. A clearance 38 defined between the damper 33 and the left hand side wall of the groove 31 communicates with the valve groove 40 formed in the inner sleeve 2 through a minute clearance space 37 defined between the inner and outer sleeves 2,1 9. Fluid pressure supplied from the fluid supply port is applied to the clearance 37 during the operation state of the control valve (when the valve is displaced from its neutral position, see Fig. 5).

With the above-mentioned structure of the power steering mechanism, when the steering shaft 10 is rotated about its axis by rotating a steering wheel or handle, a rotational differential is generated between the shaft 10 and the ball-thread shaft 5 distorting the torsion bar

14. That is, rotational differential occurs between the inner and outer sleeves 2 and 19, to change the connecting state and opening angle of the valve groove defined between the sliding surfaces of the inner and outer sleeves.

Hence communication of one of the passages 8 and 1 3 with the hydraulic pressure source and of the other of the passages with the fluid recirculation port 12, i.e. the fluid reservoir, is established. During the period of the rotational differential generation between the inner and outer sleeves 2 and 19, the surface layer 33a of the damper 33 is slidingly and sealingly rotated with respect to the outer sleeve 19, since the damper 33 is fitted under pressurised deformation from its normal shape 36 as shown by a chain line in Fig. 5. That is, the inner peripheral surface of the damper 33 is frictionally engaged with a bottom 31 a of the annular groove 31 so as not to slide thereon, by the resilient force.Furthermore, the damper 33 is urged toward the right hand side wall 31 b of the groove 31 to maintain frictional engagement by the hydraulic pressure in the clearance 38, and therefore, the damper 33 is integrally moved with the inner sleeve 2.

In the transition period of the switching of communication between the valve groove 31 of the inner and outer sleeves 2 and 19, working fluid flows in a complex manner along valve groove 31 and fluid passages communicated therewith, so that the flow speed and fluid pressure is locally varied violently. This causes the inner and outer sleeves to vibrate as above mentioned. However, since the vibration of the valve elements is absorbed by the damper 33, the pressurised fluid in the control valve is immediately stabilized to eliminate noise generation. Therefore, the piston 1 5 is smoothly moved in the cylinder 1 7 to prevent the steered wheels from chattering.

Furthermore, since resistance is applied between the surface layer 33a and the outer sleeve 1 9 because of the resilient deformation of the damper 33 in the radial direction thereof, the vibration of the valve elements is prevented. The resilient force due to the deformation of the damper 33 is received at the bottom 31 a of the annular groove 31, while the entire surface of the layer 33a is uniformly urged toward the inner peripheral surface of the outer sleeve 1 9 to contact the same. This blocks fluid communication between the clearance 37 of the valve groove side and a clearance 1 2a which is a fluid recirculation passage at the sliding interface defined between the inner and outer sleeves 2 and 1 9.

The fluid pressure in the clearance 38 of the groove 31 urges the damper 33 toward the right hand side wall of the groove 31 to prevent fluid from being leaked from the valve groove 40 to the clearance 1 2a through the bottom portion of the annular groove 31, as well as to prevent the damper 33 from being slidingly rotated in the annular groove 31.

Since the damper 33 which performs the anti-vibration function is not slidingly rotated relative to the annular groove 31 but is stationarily disposed with respect thereto, wear of the damper does not occur. Furthermore, since the rotational sliding portion of the damper, formed by the layer 33a, is formed with tetrafluoroethylene resin having a high wear the depth of the annular groove.

3. A valve according to claim 1 or claim 2, further comprising a closing ring disposed at the inner periphery of the outer sleeve, the surface layer of the damper engaging an inner peripheral surface of the closing ring.

4. A valve according to claim 1, wherein the damper defines a radial clearance space within the annular groove, the radial space being in fluid communication with a clearance between the valve elements whereby hydraulic pressure is supplied to the damper.

5. A valve according to any one of the preceding claims, wherein the damper has an arcuate inner peripheral surface whereby the bottom surface of the annular groove resiliently supports the arcuate inner peripheral surface.

6. A valve according to any one of claims 1 to 4, wherein the damper has an inner peripheral surface comprises a series of axially extending notches.

7. A valve according to claim 1 or claim 4, wherein the damper has an inner diameter larger than the inner diameter of the annular groove, whereby an annular space is created between the bottom of the annular groove and the damper.

8. A valve according to claim 1, substantially as described with reference to any one of the examples illustrated in the accompanying drawings.