WO1993009991A1

WO1993009991A1 - Power steering assembly and bush assembly therefor

Info

Publication number: WO1993009991A1
Application number: PCT/GB1992/002162
Authority: WO
Inventors: David Carrington Yates; Michael John Andrews
Original assignee: Hampton Industries Limited
Priority date: 1991-11-23
Filing date: 1992-11-23
Publication date: 1993-05-27
Also published as: AU2950692A

Abstract

A power steering assembly comprises a cylinder (10), a piston (14) slidable in the cylinder, and a piston rod (16) extending from the piston. At one end, the rod (16) passes through a lockstop support bush assembly (18) prior to connection of the rod (16) to a tie rod (22) of a vehicle wheel by a universal joint (10). The bush assembly comprises a housing (13) which may be moulded in two parts (130, 150; 230, 250; 330, 350) which are clipped together, the body carrying a retaining device (36, 136, 236, 334) operative to transmit axial loading on the bush assembly to the cylinder (10, 110, 210, 310).

Description

Title: Power steering assembly and bush assembly therefor Description of Invention

This invention is concerned with improvements relating to power steering assemblies. A power steering assembly conventionally comprises a cylinder disposed generally transversely of the vehicle, a piston in the cylinder, and a piston rod extending from the piston in opposite axial directions. The piston rod is connected at its opposite ends by tie rods to the wheels, and by admission of fluid under pressure to the cylinder, the wheels may be turned.

Conventionally at one end of the cylinder the piston rod passes through a bush, hereinafter referred to as being of the kind specified, commonly referred to as a "lock stop support bush", which provides a stop, against which a universal ball joint housing engages, to limit retractive movement of the piston rod and hence the turning movement of the wheels. Such a stop not only limits turning movement of the wheels under the operation of the steering wheel, but also absorbs the shock loading should (e.g.) the wheel be driven against a kerb. The bush is thus required to be located positively in relation to the cylinder by a means which resists such shock forces. Conventionally the end portion of the cylinder is swaged outwardly, and the bush is located in the portion of enlarged diameter. A circumferential groove is provided on the exterior face of the bush, and on the internal face of the cylinder, said grooves cooperating to provide a retaining passage within which a retaining wire is located. Conventionally the end of the retaining wire is inserted through an opening in the cylinder, and is hooked into engagement with an aperture in the bush, and by rotation of the bush the wire is drawn around the bush through the aperture, passing into the retaining passage.

Thus shock loading on the bush is restrained primarily by the retaining wire.

To ensure maximum strength, it is necessary for the bush to fit snugly into the swaged end portion of the cylinder, to ensure that sheer forces are restrained to the best advantage. This requires that, subsequent to being swaged, the end portion of the cylinder be machined, to ensure an absence of ovality of the cylinder, which adds to the expense of manufacture.

Additionally it is conventional for the bush to perform two other functions, namely to provide bearing support for the piston rod, and to support a seal for the cylinder against loss of hydraulic fluid.

Conventionally the bush is manufactured of a glass reinforced plastics material, which is difficult to mould, and is abrasive, and to avoid wear on the piston rod it is necessary for the bush to carry a sleeve to afford a bearing formation.

A further disadvantage is that, where different lock stop positions are required, it is necessary to provide bushes of different axial lengths.

A further problem is that, for the accommodation of a bellows seal between the cylinder and the universal joint, it is necessary and conventional to provide a rim on the end of the cylinder, behind which a retaining clip for the bellows may be located, and this further adds to the cost of manufacture.

It is one of the various objects of this invention to provide a bush of the kind specified, in which some at least of the problems and difficulties set out above are reduced or avoided.

According to this invention there is provided a power steering assembly comprising a cylinder, a piston on the cylinder, a piston rod extending from the piston, and a bush assembly in the cylinder providing a bearing support for the piston rod and to limit movement of the piston, the bush assembly comprising at least one channel extending transverse to the longitudinal axis of the bush assembly and a rigid retaining member located in the cylinder and which cooperates with the channel to transmit longitudinal forces applied to the bush assembly to the cylinder.

By use of a channel as distinct from a circumferential groove, the shear forces on the bush assembly may be spread over a wider area than is conventionally practical, reducing tendency for shear forces to occur. Preferably two such channels are provided on opposite sides of the bush, and two retaining members, or two retaining portions of one member, are utilised, one in conjunction with each channel.

Thus the retaimng member may be of C-shape or U-shape in general, having parallel limbs affording the retaining portions, and a curved bridging portion.

Preferably the or each channel is provided by a through-extending aperture in a body portion of the bush assembly.

In this manner not only is the strength of the bush and resistance to fracture increased, but it is increased to an extent sufficient to enable the bush to be moulded from non-reinforced plastics, and a material such as nylon or polyurethane may be used conveniently, allowing the bush to serve as a bearing support for the piston rod directly.

If desired a strengthening member may be moulded into the bush, preferably downstream, in the direction of shear forces, of the channels, further to spread load, such strengthening member conveniently being in the form of a washer.

Advantageously the bush assembly comprises two body parts which are secured together to provide the bush assembly, and advantageously the or each channel is provided between the body parts, the retaining member being located in position in relation to the bush body by locating the retaining member between said body parts during assembly thereof.

Preferably means is provided to resist movement of the retaining member, which may be afforded by interlocking formations on the bush and retaining formations, or by a strap joining to two retaining portions on the other side of the bush.

According to this invention there is also provided a bush of the kind specified, wherein there is incorporated into the moulding a washer to distribute shock loading applied to the bush, and to reduce tendency to shear. According to this invention there is also provided, in or for a power steering assembly of the kind comprising a cylinder, a piston in the cylinder, a piston rod extending from the piston, a bush assembly in the cylinder providing a bearing support for the piston rod and to limit movement of the piston, said bush assembly comprising two parts, one part cooperating with a retaining means of the bush assembly to retain the bush assembly in position in relation to the cylinder, the other part affording a bearing for the piston rod and a seal for hydraulic fluid, said parts being provided with cooperating formations to enable them to be secured together.

In this manner only a part of the assembly will require to be changed when it is desired to vary the position of the lock stop. Further, different materials having different physical properties may be selected and combined in a particularly advantageous manner.

In such a construction, a retaining device of the kind hereinbefore described, comprising two generally parallel retaining formations joined by a bridging piece, may be engaged with one of said parts, restraining the bush as a whole against movement from a desired position.

Preferably the load transmission member extends into an internal circumferential groove in the cylinder wall. The load transmission member may be located in said groove subsequent to a positioning of one part of the lockstop support bush within the cyhnder, and prior to a location of the second part in the cylinder, but preferably the lockstop support bush is inserted into the cylinder in pre-assembled form.

In this manner a more convenient mechanism for the transmission of the axial load from the bush to the cylinder may be obtained than was previously possible.

Preferably the load transmission member is afforded by a part-circular member capable of being deformed against its inherent resilience into a state of reduced diameter. Thus, preferably said load transmission member is afforded by a "circlip" or the like, which may be inserted into the cylinder in the axial direction in the state of reduced diameter, being allowed to expand to enter the internal circumferential groove of the cylinder when in a desired position.

Advantageously said first part also comprises a portion extending axially on the opposite side of the circlip.

Conveniently said first part affords a seal carrier and a bearing sleeve.

Advantageously the second part may be snap-fitted into engagement with said first part, and preferably a load-spreading means is interposed between said two parts on assembly thereof together, such load-spreading means conveniently being afforded by a metal washer.

In this manner a greater load-spreading between the load transmission member and one or both parts of said bush may be obtained, without utilisation of a load transmission member having a large radial depth.

According to this invention there is also provided a bush assembly for a power steering assembly of the kind comprising a cylinder, a piston in the cylinder, and a piston rod extending from the piston, the bush assembly providing a bearing support for the piston rod and being operative to limit movement of the piston, characterised in that the bush assembly comprises two parts, said parts being provided with cooperating formations to enable them to be secured together, and a low transmission member located in an annular space between the two parts, axial load on the bush assembly being transmitted to the load transmission member and thence to the cylinder.

Preferably load is transmitted from the load transmission member to the cylinder through a further member located in an internal groove in the cylinder wall.

There will now be given a detailed description, to be read with reference to the accompany drawings, of four lock stop support bushes which are preferred embodiments of this invention, having been selected for the purposes of illustrating the invention by way of example.

In the accompanying drawings: FIGURE 1 is a perspective view showing a conventional lock stop support bush;

FIGURE 2 is a longitudinal sectional view of bush which is the first embodiment of this invention, in position in the steering system; FIGURE 3 is a sectional view of the bush;

FIGURE 4 is a sectional view of the lock stop support bush which is the second embodiment of this invention;

FIGURE 5 is a longitudinal sectional view of part of the second embodiment, in exploded form;

FIGURE 6 is a longitudinal sectional view showing part of the lock stop support bush which is the third embodiment of the invention;

FIGURE 7 is a longitudinal sectional view, on the line 7-7 of Figure 8, of the lockstop support bush which is the fourth embodiment of the invention; FIGURE 8 is an axial sectional view thereof on the Line 8-8 of Figure 1; and

FIGURE 9 is a view of an element of the assembly. Figure 1 illustrates a conventional power steering assembly, showing a power steering cylinder or tube 10 having ports 12, 13 whereby hydraulic fluid may be caused to act on a piston 14, in the movement of a piston rod 16 during a steering operation of the vehicle. At one end, the right-hand side shown in Figure 1, the rod 16 passes through a lock stop support bush assembly 18, prior to connection of the rod 16 to a universal joint 10, connected by a tie rod 22 to the vehicle wheel.

During operation of the power steering system, fluid may be admitted or vented from the ports 12, 13 to move the piston 14, and hence the rod 16 back and forth. Alternatively the rod may be moved by the action of force to the vehicle wheels.

The bush 18 is of the kind specified, being generally cylindrical, and being retained in position by a retaining wire located in a circumferential channel 24, afforded by semi-circular grooves in the outer face of the bush 18 and the inner face of the cylinder 10. It will be appreciated that movement of the rod 16 to the left in Figure 1 be limited by engagement of the universal joint housing 20 with the bush 18, such force being taken on the bush 18.

The bush which is the first embodiment of the invention, shown in Figure 2, comprises a housing 30 moulded conveniently from polyurethane, provided with spaced apertures 32 which in the use of the bush are aligned with upper and lower apertures 33a. and 33b on opposite sides of the cylinder 10. The body 30 is located in position by retaining device in the form of a C-clip 36, comprising parallel legs 38, affording retaining formations, joined by abridging portion 39, said legs 38 each being inserted through one of the upper apertures 33a, through one of the channels 32, and through the lower aperture 33b_. of the cylinder. A re-entrant hook formation 40 on the leading end of the leg 38 engages behind a projection 42 of the body 30, to prevent the clip 36 readily from being withdrawn from its located position.

Thus on movement of the piston rod 16 to the left, and movement of the housing 20 of the universal joint 10 into its lock stop position, said housing 20 engages the body 30, and shock loading is transmitted by the device 36 direct to the cylinder 10, tendency for shear forces to damage the body 30 being minimal.

Conveniently the bush is strengthened by the location of a reinforcing member 44, conveniently afforded by a metal washer, within the moulded body 30.

If desired protrusions 46 may be provided on the face of the body 30 initially engaged by the housing 20, to reduce shock impact.

The bush 28 which is the first embodiment of this invention also comprises a low friction bearing/seal carrier 50, conveniently moulded from nylon, preferably releasably secured to the body 30, by interfitting formations 52. In turn, the seal carrier 50 has secured to a leading face thereof an oil seal 54, similarly conveniently by interfitting formations 56.

In this manner a compound bush comprising lock stop support, bearing support for the piston rod 16, and a seal for hydraulic fluid, may be manufactured relatively economically, and may be located easily in position with significantly reduced risk on failure occurring.

Further, conveniently on the inner circumference of the body 30 a circumferential rib 31 is provided, serving as a wiper to prevent passage of material into a position between the seal carrier and the piston rod 16.

The projection of the device 36 circumferentially outwardly of the cylinder 10 at the three positions shown, namely the bridge portion 39, and the terminal portions of the legs 38, allows one end of a bellows seal to be located over the end of the cylinder 10, and located in position by a circlip, the other end of the bellows seal being secured to the housing 20 of the universal joint in conventional manner.

In the second embodiment, in which similar numerals increased by 100 have been utilised to indicate parts similar to those of the first embodiment, the seal carrier 150 is provided with diametrically opposed legs 151 which protrude through diametrically spaced apertures 131 of the housing 130, projecting as abutments into the apertures 132 and which may be engaged behind interior formations 141 of the legs 138, further to prevent undesired withdrawal movement of the clip 136.

In the second embodiment, a seal (not shown) will be secured to the seal carrier in the manner of the first embodiment.

In the third embodiment, in which similar numerals increased by 200 have been utilised to indicate parts similar to those of the first and second embodiments, the seal carrier 250 is provided with an internal sleeve 260, which engages within the inner diameter of the housing 230, providing an elongate smooth bearing formation for engagement with the piston rod 216, the bush being provided at its end with a hook formation 262 which engages within a re-entrant channel 231 of the housing 230, to prevent relative movement between the housing and the seal carrier 250. In this manner the aperture 232 for the retaining device (not shown) is provided between the two parts 230, 250 which provide the bush, allowing in addition the reinforcing washer 244 to be located between the two parts 230, 250 on assembly thereof, rather than being moulded in situ.

The seal carrier 250 is provided with diametrically opposed slots 271, bounding on three sides a formation 251 which projects into the channel 232 on diametrically opposite sides, functioning in a manner similar to the legs 151 of the second embodiment, in providing additional restraint to retractive movement of the retaining device.

Further slots 281 are provided in the seal carrier 250, allowing the right hand end portion of the seal carrier 250 to be compressed radially inwardly during assembly.

As with the first and second embodiments, a seal (not shown) will be mounted on the left hand end of the seal carrier 250.

The lockstop support bush assembly which is the fourth embodiment of this invention, shown in Figures 4-6, in which similar numerals increased by 300 have been utilised to indicate parts similar to those of the first embodiment, comprises a first part 350, conveniently of nylon to afford a low friction bearing surface, a second part 330 conveniently of glass-filled nylon for compressive rigidity, and a load transmission member 336 in the form of a metal circlip, shown in Figure 3. The second part 330 is a good push-fit in the cylinder 310.

The first part 350 comprises a forward portion carrying a seal 354, and a pair of rearwardly-extending legs 360 providing respective parts of an extensive cylindrical bearing surface afforded by the axial bore of the part 350, said legs 360 being separated from the remainder of said bearing surface along their longitudinal edges, and terminating at their free ends in hook-formations 362.

The second part 330 comprises diametrically opposed and axially- extending channels 331 which extend forwardly through and slightly beyond an otherwise slightly reduced internal diameter rear portion of the part 330 and which on assembly are capable of engaging with the respective hook formations 362. In the assembly of the lockstop support bush, a circlip 336 is located behind the first part 350, and a load spreading member afforded by a metal washer 334 is located behind the circlip, the washer 334 having a diameter similar to the outside diameter of the parts 350 and 330, whilst the circlip at rest has a larger diameter. The second part is then mounted on the first part, the legs 360 being inserted into the axial bore of the part 330 until the hook formations 362 snap-fittingly engage with part-annular shoulders afforded at the forward ends of the channels 331, the circlip and washer being loosely held between said first and second parts.

The assembled lockstop support bush is then inserted into the cylinder 310, over the piston rod 316 (and prior to mounting of the joint 320), by the use pf a conical assembly dolly, causing the circlip to be annularly pressed and allowing the assembly as a whole to enter the cylinder into a position in which the circlip expands into an internal circumferential groove 324 in the wall of the cylinder, holding the assembly in the desired position shown in Figure 7.

The piston rod 316 and the internal wall of the cylinder 310 are each sealingly engaged by the seal 354.

The distance X may be checked, to verify the bush is in a correct position prior to testing of the assembly.

In use, on wheel impact with a kerb, for example, the ball joint 320 will engage the bush, the load being transmitted through the washer 334 to the circlip 336, and thence to the cylinder 310.

If desired, the distance X may be checked periodically, any small variation in said distance indicating the possibility of damage having been caused to the circlip, and a need for replacement of the bush.

Also, during manufacture, pressure testing may sometimes reveal incomplete sealing by the seal 354, necessitating bush replacement.

In order to replace the bush, the second part 330 may be withdrawn, conveniently by rotating the second part 330 to cause the hook formations 362 to ride up chamfered side faces of the channels 331, to disengage the formations from the shoulders. A pair of circlip pliers may be inserted into the cylinder to be engaged with the circlip, the nose extremities of the pliers being accommodated within a peripheral recess 337 (Figure 8) of the portion 350, permitting the circlip to be radially collapsed and withdrawn from the circumferential groove 324, prior to axial removal from the cylinder.

Of course, the chamfered faces may if desired be provided on the side faces of the hook formations 362.

The first portion 350, together with the seal 354, may then be withdrawn, to be replaced by a new bush.

It will of course be appreciated that the washer 334, whilst being desirable, is not necessary, and that alternatively the axial loading on the bush may be transmitted to the cylinder by the circlip alone.

The part 350 illustrated comprises, adjacent to the front end of its axial bore, an integrally formed annular anti-extrusion flange, to assist retention of the seal 354.

Claims

1. A Power steering assembly comprising

(a) a cylinder (10);

(b) a piston in the cylinder (14);

(c) a piston rod extending from the piston; and

(d) a bush assembly (18) in the cyhnder (10) providing a bearing support for the piston rod and to limit movement of the piston, . the bush assembly comprising at least one channel (32; 132; 232; 332) extending transverse to the longitudinal axis of the bush assembly and a rigid retaining member (36; 136; 236; 334) located in the cylinder and which cooperates with the channel to transmit longitudinal forces applied to the bush assembly to the cylinder (10).

2. A power steering assembly according to Claim 1 wherein two channels (32; 132) are provided which extend through the bush assembly in a plane extending at right angles to the longitudinal axis thereof, the retaining member (36; 136) having parallel limbs (38, 138) located in said channels and a bridge section connecting said limbs.

3. A power steering assembly according to Claims 1 and 2 wherein the or each channel (32; 132) is provided in a body portion of the bush assembly.

4. A power steering assembly according to one of Claims 1 and 2 wherein the bush assembly comprises two body parts (130, 150; 230, 250; 330, 350) which are secured together to provide the bush assembly.

5. A power steering assembly according to Claim 4 wherein the channel (232, 332) is provided between the body parts, and is afforded by a circumferential channel.

6. A power steering assembly according to Claim 5 wherein the construction and arrangement is such that the retaining member (236, 334) is located in position in relation to the bush body by locating the retaining member between said body parts (230, 250; 330, 350) during assembly thereof.

7. In or for a power steering assembly of the kind comprising a cylinder (10), a piston (14) in the cylinder, a piston rod (16) extending from the piston, a bush assembly (18) in the cylinder providing a bearing support for the piston rod and to limit movement of the piston, said bush assembly comprising two parts (30, 50; 130, 150; 230, 250), one part (30, 130, 230, 330) cooperating with retaining means (36, 136, 236, 334) of the bush assembly to retain the bush assembly in position in relation to the cylinder, the other part (50, 150, 250, 350) affording a bearing for the piston rod (16) and a seal for hydraulic fluid, said parts being provided with cooperating formations (52; 260, 262; 360, 362) to enable them to be secured together.

8. A bush assembly according to Claim 7 wherein said parts are secured together around the retaining means (236, 334).

9. A bush assembly for a power steering assembly of the kind comprising a cylinder (10), a piston (14) in the cylinder, and a piston rod (16) extending from the piston, the bush assembly (18) providing a bearing support for the piston rod and being operative to limit movement of the piston, characterised in that the bush assembly comprises two parts (30, 50; 130, 150; 230, 250; 330, 350), said parts being provided with cooperating formations (52; 260, 262; 360, 362) to enable them to be secured together, and a load transmission member (36, 136, 236, 334) located in an annular space (132, 232, 332) between the two parts, axial load on the bush assembly being transmitted to the load transmission member and thence to the cylinder.

10. A bush assembly according to Claim 9 wherein load is transmitted from the load transmission member (334) to the cylinder through a further member (336) located in an internal groove in the cylinder wall.