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Patent Searching and Data


Title:
STEERING YOKE
Document Type and Number:
WIPO Patent Application WO/2009/097648
Kind Code:
A1
Abstract:
A yoke for supporting a Y-rack in engagement with a pinion in a steering gear housing. The yoke is adapted to be located in a bore in the housing, and the yoke comprises a first and a second rack support member. The rack support members are movable with respect to each other. Each rack support member has a radial support surface adapted to be supported by the bore, and each rack support member has a non- concave rack support surface adapted to support the Y-rack. The rack support members are connected to each other by various means.

Inventors:
BELONOGOFF NICKOLAI (AU)
Application Number:
PCT/AU2009/000123
Publication Date:
August 13, 2009
Filing Date:
February 03, 2009
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
BISHOP INNOVATION LTD (AU)
BELONOGOFF NICKOLAI (AU)
International Classes:
B62D3/12; F16H19/04; F16H55/28
Domestic Patent References:
WO2001096167A12001-12-20
Foreign References:
GB1324322A1973-07-25
US3572158A1971-03-23
US5937703A1999-08-17
US4116085A1978-09-26
DE1605911A11970-07-16
Attorney, Agent or Firm:
HASSETT, Andrew (P.O. Box 635Chester Hill, NSW 2162, AU)
Download PDF:
Claims:

CLAIMS

1. A yoke for supporting a Y-rack in engagement with a pinion in a steering gear housing, the yoke being adapted to be located in a bore in the housing, the yoke comprising a first and a second rack support member, the rack support members being movable with respect to each other, each rack support member having a radial support surface adapted to be supported by the bore, and each rack support member having a non-concave rack support surface adapted to support the Y-rack, characterised in that the rack support members are connected to each other.

2. A yoke as claimed in claim 1 , wherein the rack support members are connected to each other by means of at least one flexible element.

3. A yoke as claimed in claim 2, wherein the flexible element allows the rack support members to be pushed together.

4. A yoke as claimed in claim 2, wherein the flexible element is located between the rack support members.

5. A yoke as claimed in claim 2, wherein the flexible element is wave shaped.

6. A yoke as claimed in claim 2, wherein the flexible element is straight and the flexible element is stretchable.

7. A yoke as claimed in claim 2, wherein the rack support members and the flexible element are moulded as a single piece.

8. A yoke as claimed in claim 2, wherein each flexible element is attached to both rack support members.

9. A yoke as claimed in claim 2, wherein the yoke further comprises a central member and each flexible element is attached to the central member and to one of the rack support members.

10. A yoke as claimed in claim 9, wherein the central member is a spigot and the yoke is assembled with a base member to form a yoke assembly by means of the spigot being pushed into a hole in the base member.

11. A yoke as claimed in claim 9, wherein the central member is a ring and the yoke , is assembled with a base member to form a yoke assembly by means of a boss on the base member being pushed into the ring.

12. A yoke as claimed in claim 2, wherein the flexible elements extend below the rack support members and at least one protrusion extends from the underside of each rack support member, the yoke being assembled with a base member to form a yoke assembly, the base member being located centrally to the yoke by the protrusions and the base member being retained to the yoke by the flexible elements overlapping the base member.

13. A yoke as claimed in claim 1 , wherein the yoke further comprises a base member adapted to be located between the rack support members and a spring, the spring biasing the yoke into contact with the Y-rack.

14. A yoke as claimed in claim 13, wherein the base member is a disc.

15. A yoke as claimed in claim 13, wherein the rack support members are connected to each other by means of the rack support members being retained to the base member.

16. A yoke as claimed in claim 15, wherein each rack support member has at least one barbed protrusion, and the rack support members are retained to the base member by pushing each barbed protrusions through a hole in the base member.

17. A yoke as claimed in claim 1, wherein the Y-rack passes through an opening in the housing, the opening intersecting the bore, and each rack support surface is adapted to extend radially outside of the bore, into the opening, when the yoke is supporting the Y-rack.

18. A yoke as claimed in claim 17, wherein each rack support member is sized to pass through the bore during assembly of the yoke into the housing.

19. A yoke as claimed in claim 18, wherein the rack support members are sized such that they can both pass through the bore together, when they are pushed towards each other, during assembly of the yoke into the housing.

20. A yoke as claimed in claim 1 , wherein the rack support members are made from a polymer.

21. A yoke as claimed in claim 1, wherein the rack support surface of each rack support member comprises a separate element.

22. A yoke as claimed in claim 21 , wherein each rack support member has a curved recess that the corresponding rack support surface sits in, and the back of each rack support surface is curved to match the curved recess such that each rack support surface is rotatable with respect to its corresponding rack support member.

23. A yoke as claimed in claim 22, wherein each rack support member has two rack support surfaces, the back of each rack support surface having a spherical curvature, and the recess that each rack support surface sits in has a spherical curvature.

24. A yoke as claimed in claim 21 , wherein the rack support surfaces are made from a different material than the rack support members.

25. A yoke as claimed in claim 1 , wherein the non-concave rack support surface is a flat rack support surface.

26. A yoke as claimed in claim 1, wherein the non-concave rack support surface is a convex rack support surface.

Description:

STEERING YOKE

TECHNICAL FIELD

The present invention relates to yokes for rack and pinion steering gears for land vehicles.

BACKGROUND

A conventional rack and pinion steering gear comprises a housing, a rack, a pinion, and a yoke. The steering gear may also comprise various components to provide power assistance. The rack is movable along its longitudinal axis through an opening in the housing. The pinion is supported for rotation in the housing and it has teeth that mesh with teeth on the rack. The yoke supports the rack to keep it in backlash free engagement with the pinion .

Steering racks can be categorised by the cross sectional shape of the toothed region of the rack. Most racks are "D-racks", which have a 'D' shaped cross section. Another common type of rack is a "Y-rack", which has a υ' shaped cross section. US Patents 4,571 ,982 (Bishop et al) and 5,862,701 (Bishop et al) disclose die apparatus for flashless warm forging racks having a toothed region with a "Y" shaped cross section.

A conventional yoke is constructed as a single, solid piece with one or more support surfaces that contact the rack. The support surfaces are shaped to suit the shape of the rack. For a D-rack, the support surface is typically a single curved surface to match the diameter of the rack. For a Y-rack, the support surfaces typically comprise two spaced apart flat surfaces angled to each other. A conventional yoke may be made entirely from a low friction material or the support surfaces may be separate inserts made from low friction material. A conventional yoke is a sliding fit in a bore in the housing. Typically, a cap is screwed into the housing bore, and spring positioned between the yoke and the cap urges the yoke into contact with the rack. There is typically only a small clearance between the yoke and the cap to limit the movement of the yoke.

Various yokes comprising two support members are known. The support members are movable with respect to each other, and each one supports one side of the rack. This arrangement can eliminate the clearance between the yoke and the bore in the housing. WO 2005/113318 A1 (Daimler Chrysler AG) discloses such a yoke for a Y- rack. US Patent 3,747,429 (Cass) and US Patent 5,746,285 (Yonezawa) disclose this type of yoke for D-racks. US Patent 5,937,703 (Engler) discloses a yoke for a D-rack having two support members where the support members are connected to each other by flexible elements that urge the support members apart. The prior art does not disclose any yokes suitable for a Y-rack having two support members that are connected together.

It is desirable for the support surfaces of a yoke to be as large as possible to minimise friction and wear. To make the support surfaces of a conventional yoke, or of a known yoke having two support members, larger it is necessary to increase the overall size of the yoke and of the bore in the housing that locates it. This is undesirable because it increases the size of the steering gear. This is particularly a problem for steering gears having Y-racks because conventional yokes for Y-racks tend to be larger than yokes for D-racks.

It is an object of the present invention to provide a yoke assembly that ameliorates at least some of the problems of the prior art.

SUMMARY OF INVENTION

The present invention consists of a yoke for supporting a Y-rack in engagement with a pinion in a steering gear housing, the yoke being adapted to be located in a bore in the housing, the yoke comprising a first and a second rack support member, the rack support members being movable with respect to each other, each rack support member having a radial support surface adapted to be supported by the bore, and each rack support member having a non-concave rack support surface adapted to support the Y-rack, characterised in that the rack support members are connected to each other. The non-concave rack support surfaces are either flat or convex.

In one preferred embodiment, the rack support members are connected to each other by means of at least one flexible element. Preferably, the flexible element allows the rack support members to be pushed together. Preferably, the flexible element is located between the rack support members. In one preferred embodiment, the flexible element is wave shaped. In another preferred embodiment, the flexible element is straight and the flexible element is stretchable. Preferably, the rack support members and the flexible element are moulded as a single piece.

In a preferred embodiment, each flexible element is attached to both rack support members. In another preferred embodiment, the yoke further comprises a central member and each flexible element is attached to the central member and to one of the rack support members. The central member may be a spigot and the yoke is assembled with a base member to form a yoke assembly by means of the spigot being pushed into a hole in the base member. Alternatively, the central member may be a ring and the yoke is assembled with a base member to form a yoke assembly by means of a boss on the base member being pushed into the ring.

In another preferred embodiment, the flexible elements extend below the rack support members and at least one protrusion extends from the underside of each rack support member, the yoke being assembled with a base member to form a yoke assembly, the base member being located centrally to the yoke by the protrusions and the base member being retained to the yoke by the flexible elements overlapping the base member.

In another preferred embodiment, the yoke further comprises a base member adapted to be located between the rack support members and a spring, the spring biasing the yoke into contact with the Y-rack. Preferably, the base member is a disc. Preferably, the rack support members are connected to each other by means of the rack support members being retained to the base member. Preferably, each rack support member has at least one barbed protrusion, and the rack support members are retained to the base member by pushing each barbed protrusions through a hole in the base member.

In another preferred embodiment, the Y-rack passes through an opening in the housing, the opening intersecting the bore, and each rack support surface is adapted to extend radially outside of the bore, into the opening, when the yoke is supporting the Y-rack. Preferably, each rack support member is sized to pass through the bore during assembly of the yoke into the housing. Preferably, the rack support members are sized such that they can both pass through the bore together, when they are pushed towards each other, during assembly of the yoke into the housing.

Preferably, the rack support members are made from a polymer. In one preferred embodiment, the rack support surface of each rack support member comprises a separate element. Preferably, each rack support member has a curved recess that the corresponding rack support surface sits in, and the back of each rack support surface is curved to match the curved recess such that each rack support surface is rotatable with respect to its corresponding rack support member. In one preferred embodiment, each rack support member has two rack support surfaces, the back of each rack support surface having a spherical curvature, and the recess that each rack support surface sits in has a spherical curvature. Preferably, the rack support surfaces are made from a different material than the rack support members.

BRIEF DESCRIPTION OF DRAWINGS

Fig. 1 is a sectional view of a typical prior art steering gear having a typical prior art yoke.

Fig. 2 is a plan view of the yoke of the steering gear shown in Fig. 1.

Fig. 3 is a sectional view of a steering gear having a first embodiment of a yoke in accordance with the present invention.

Fig. 4 is a plan view of the yoke of the steering gear shown in Fig. 3.

Fig. 5 is a sectional view of a steering gear having a second embodiment of a yoke in accordance with the present invention.

Fig. 6 is a plan view of the yoke of the steering gear shown in Fig. 5.

Fig. 7 is a sectional view of a steering gear having a third embodiment of a yoke in accordance with the present invention.

Fig. 8 is an elevation view of the yoke of the steering gear shown in Fig. 7.

Fig. 9 is an end view of the yoke shown in Fig. 8.

Fig. 10 is a side view of one of the support members of the yoke shown in Fig. 8.

Fig. 11 is a sectional view of a steering gear having a fourth embodiment of a yoke in accordance with the present invention.

Fig. 12 is an elevation view of the yoke of the steering gear shown in Fig. 11.

Fig. 13 is a plan view of the yoke shown in Fig. 12.

Fig. 14 shows the yoke of Fig. 12 being assembled into the steering gear of Fig. 11.

Fig. 15 is a sectional view of a steering gear having a fifth embodiment of a yoke in accordance with the present invention.

Fig. 16 is an elevation view of the yoke of the steering gear shown in Fig. 15.

Fig. 17 is a plan view of the yoke shown in Fig. 16.

Fig. 18 is a sectional view of a steering gear having a sixth embodiment of a yoke in accordance with the present invention.

Fig. 19 is an elevation view of the yoke of the steering gear shown in Fig. 18.

Fig. 20 is a plan view of the yoke shown in Fig. 19.

Fig. 21 is an elevation view of a seventh embodiment of a yoke in accordance with the present invention.

Fig. 22 is a plan view of the yoke shown in Fig. 21.

Fig. 23 is an elevation view of an eighth embodiment of a yoke in accordance with the present invention.

Fig. 24 is a plan view of the yoke shown in Fig. 23.

Fig. 25 is a sectional view of a steering gear having a ninth embodiment of a yoke in accordance with the present invention.

Fig. 26 is an elevation view of the yoke of the steering gear shown in Fig. 25.

Fig. 27 is a plan view of the yoke shown in Fig. 26.

Fig. 28 is a sectional view of a steering gear having a tenth embodiment of a yoke in accordance with the present invention.

Fig. 29 is a plan view of the yoke of the steering gear shown in Fig. 28.

Fig. 30 is an elevation view of the yoke shown in Fig. 29.

Fig. 31 is a plan view of the base member of the yoke assembly of the steering gear shown in Fig. 28.

Fig. 32 is an elevation view of the yoke assembly of the steering gear shown in Fig. 28.

Fig. 33 is a sectional view of a steering gear having an eleventh embodiment of a yoke in accordance with the present invention.

Fig. 34 is a plan view of the yoke of the steering gear shown in Fig. 33.

Fig. 35 is an elevation view of the yoke shown in Fig. 34.

Fig. 36 is a plan view of the base member of the yoke assembly of the steering gear shown in Fig. 33.

Fig. 37 is an elevation view of the yoke assembly of the steering gear shown in Fig. 33.

Fig. 38 is a sectional view of a steering gear having a twelfth embodiment of a yoke in accordance with the present invention.

Fig. 39 is an end view of the yoke of the steering gear shown in Fig. 38.

Fig. 40 is an elevation view of the yoke shown in Fig. 39.

Fig. 41 is an end view of the yoke assembly of the steering gear shown in Fig. 38.

Fig. 42 is an elevation view of the yoke assembly shown in Fig. 41.

BEST MODE OF CARRYING OUT THE INVENTION

Fig. 1 shows an example of a typical prior art steering gear 1 having a typical prior art yoke 5. Steering gear 1 comprises a housing 2, and a Y-rack 3 meshing with a pinion 4. Steering gear 1 is a manual steering gear but the yoke 5 is also typical of yokes used for power assisted steering gears. The pinion 4 is supported for rotation in the housing 2 by bearings 12 and 13. A retainer 14 retains bearing 13 and a seal 15 seals on the shaft of the pinion 4. The rack 3 is movable along its longitudinal axis 18 through an opening 17 in the housing 2.

Referring to Figs. 1 and 2, the yoke 5 has two flat rack support surfaces 20, angled to each other, that contact the Y-rack 3. In this example, the yoke 5 is moulded as a single rigid piece from a low friction polymer. However, other not shown prior art yokes are made from metal with separate inserts for the rack support surfaces. The yoke 5 is a sliding fit in a bore 21 in the housing 2. A cap 9 is screwed into the end of bore the 21, and is locked in position by a lock nut 10. A coil spring 8 positioned between the yoke 5 and the cap 9 urges the yoke 5 into contact with the Y-rack 3 to maintain backlash free engagement between the teeth of the Y-rack 3 and the pinion 4. There is a small clearance 22 between the yoke 5 and the cap 9 to limit the movement of the yoke 5 in the bore 21. In this example, an o-ring 7 is located in a circumferential groove around the yoke 5 to dampen the movement of the yoke 5 in the bore 21.

Fig. 3 shows a steering gear 1a having a first embodiment of a yoke 6 in accordance with the present invention. The housing 2, Y-rack 3, and pinion 4 are the same as the steering gear 1 shown in Fig. 1. Referring to Figs. 3 and 4, the yoke 6 comprises two rack support members 24. The rack support members 24 are connected to each other by two wave shaped flexible elements 25 located between the rack support members 24. The flexibility of the flexible elements 25 allows the rack support members 24 to be moved with respect to each other, and in particular wave shape of the flexible elements 25 allows the rack support members 24 to be pushed towards each other. In this embodiment, when the rack support members 24 are pushed together, the

flexible elements 25 act as a spring that tends to urge the rack support members 24 apart.

Each rack support member 24 has a flat rack support surface 20a that contacts the Y- rack 3 to support it. Each rack support member 24 also has a radial support surface 26 that contacts the bore 21 of the housing 2. The bore 21 supports rack support members 24 through the radial support surfaces 26 to maintain the spacing between the rack support members 24. The radial support surfaces 26 have a curvature that matches the bore 21.

The yoke 6 may be moulded as single piece from a high strength, low friction polymer such as "Ertalyte TX", which is the trade name of an engineering plastic supplied by Quadrant Engineering Plastic Products. In other not shown embodiments of the invention, the rack support members 24 and the flexible elements 25 may be moulded separately then joined together prior to assembling the yoke into the housing.

A flat, disc shaped base member 27 is located between the underside of the rack support members 24 and a coil spring 8. Preferably the base member 27 is made from steel. The rack support members 24 can slide on the base member 27. The base member 27 transmits load from the spring 8 to the rack support members 24 to bias the yoke 6 into contact with the Y-rack 3 and maintain backlash free engagement between the teeth of the Y-rack 3 and the pinion 4. In a similar manner to the steering gear 1 shown in Fig. 1 , a cap 9a is screwed into the end of bore the 21 to locate the spring 8, and the cap 9a is locked in position by a lock nut 10. There is a small clearance 22 between the base member 27 and the cap 9a to limit the movement of the yoke 6 in the bore 21.

The load of the spring 8 and the angled orientation of the rack support surfaces 20a push the rack support members 24 apart and into contact with the bore 21. Unlike a conventional single piece yoke 5, this eliminates the clearance between the yoke 6 and the bore 21 and provides a degree of friction between the yoke 6 and the bore 21 that advantageously provides damping on the movement of the yoke 6 in the bore 21. As such, the o-ring 7 typically used on conventional yoke 5 to reduce clearance and

provide damping may not be required. However, an o-ring may be added to yokes in accordance with the present invention if additional damping is required.

An advantage of connecting the rack support members 24 together by the flexible elements 25 is that the yoke 6 is easier to assemble into the housing 2 than yokes having separate support members that are not connected to each other.

Fig. 5 shows a steering gear 1b having a second embodiment of a yoke 6b in accordance with the present invention. Referring to Figs. 5 and 6, yoke 6b is the same as the yoke 6 shown in Figs. 3 and 4 except that the rack support surfaces 20b of yoke 6b comprise separate elements made from a different material than the bodies of the rack support members 24b. The rack support surfaces 20b are flat, thin pieces located in recesses moulded into the rack support members 24b. An advantage of making the rack support surfaces 20b from a different material is that the entire yoke does not need to be made from a material that has both suitable structural properties and suitable friction and wear properties. For example, the rack support surfaces 20b may be made from steel with a low friction coating or from a low friction polymer, and the remainder of the yoke 6 may be moulded from a cheaper polymer with suitable structural properties that does not necessarily have good friction or wear properties.

Fig. 7 shows a steering gear 1c having a third embodiment of a yoke 6c in accordance with the present invention. Referring to Figs. 7, 8, 9 and 10, yoke 6c is similar to yoke 6 shown in Figs. 3 and 4 except that the rack support members 24c of yoke 6c are connected to each other by being retained to a base member 27c. The base member 27c is a disc with four elongated holes 28. Each rack support member 24c has two barbed protrusions 29 extending from its underside. In this example, the support members 24c are integrally moulded with the barbed protrusions 29 from a polymer such that the barbed protrusions 29 are flexible. The rack support members 24c are retained to the base member 27c by pushing the barbed protrusions 29 through the holes 28. The holes 28 are longer than the width of the barbed protrusions 29 to enable the rack support members 24c to be movable with respect to

each other. The yoke 6c, comprising the support members 24c and the base member 27c, is assembled prior to inserting the yoke 6c into the housing bore 21.

Fig. 11 shows a steering gear 1d having a fourth embodiment of a yoke 6d in accordance with the present invention. Referring to Figs. 11 , 12 and 13, yoke 6d is similar to yoke 6b shown in Figs. 5 and 6 except that the rack support surfaces 2Od of yoke 6d extend radially outside the housing bore 21 into the housing opening 17 when the yoke 6d is supporting the Y-rack 3, as shown in Fig. 11. The rack support surfaces of yoke 6d are larger than those of yoke 6b and conventional yokes, such as yoke 5, which improves to friction properties and wear resistance of the yoke. Like yoke 6b, rack support surfaces 2Od are separate elements. However, in other not shown embodiments of the invention rack support surfaces that extend radially outside of the bore 21 may be integrally formed with the yoke, in a similar manner to the support surfaces 20a of yoke 6 shown in Figs. 3 and 4.

To enable the yoke 6d to be assembled into the housing 2, the rack support members 24d are sized to pass through the housing bore 21. To achieve this, the length 30 of the rack support surfaces 2Od is less than the diameter of the housing bore 21. To assemble the yoke 6d into the housing 2, the rack support members 24d are pushed towards each and passed through the housing bore 21, as shown in Fig. 14. The flexible elements 25 connecting the rack support members 24d bend and compress to enable the rack support members 24d to be pushed towards each other.

Fig. 15 shows a steering gear 1e having a fifth embodiment of a yoke 6e in accordance with the present invention. Referring to Figs. 15, 16 and 17, yoke 6e is the same as the yoke 6 shown in Figs. 3 and 4 except that the rack support surfaces 2Oe of yoke 6e are convex rather than flat. The rack support surfaces 2Oe have a radius 31 as shown in Fig. 16. The advantage of convex rack support surfaces 2Oe is that the Y-rack 3 can rotate a small amount about its axis 18 to take up any misalignment that may occur due to manufacturing tolerances. However, a disadvantage is that the contact area is less than flat rack support surfaces 20a, which may lead to increased wear. Convex rack support surfaces may also be applied to the other rack yoke embodiments described herein.

The flat rack support surfaces 20a of yoke 6a and the convex rack support surfaces 2Oe of yoke 6e are both non-concave in that neither of them is concave. A yoke with concave rack support surfaces would not be suitable for supporting the flat, angled surfaces of a Y-rack.

Fig. 18 shows a steering gear 1f having a sixth embodiment of a yoke 6f in accordance with the present invention. Referring to Figs. 18, 19 and 20, yoke 6f is similar to yoke 6b shown in Figs. 5 and 6 except that the rack support surfaces 2Of of yoke 6f have a curved back 33. The rack support surfaces 2Of sit in corresponding curved recesses 32 in the rack support members 24f. The arrangement is such that the rack support surfaces 2Of can rotate about an axis parallel to the rack axis 18 with respect to the rack support members 24f. This enables the flat surfaces of the rack support surfaces 2Of to align themselves correctly to the Y-rack 3 to overcome any misalignment that may occur due to manufacturing tolerances. An advantage of this arrangement compared with convex rack support surfaces 2Oe as shown in Figs. 15, 16 and 17 is that the contact area of the rack support surfaces 2Of is not reduced. In the embodiment shown, the curved backs 33 of the rack support surfaces 2Of are convex and the curved recesses 32 are concave. However, in other not shown embodiments the curvature on the back of the rack support surfaces may be concave and the curvature on the curved recesses may be convex.

Figs. 21 and 22 show a seventh embodiment of a yoke 6g in accordance with the present invention. Yoke 6g is the same as yoke 6 shown in Fig. 4 except that yoke 6g has a single straight flexible element 25g, instead of the two wave shaped flexible elements 25 of yoke 6. The flexible element 25g can bend to allow the rack support members 24 of yoke 6g to be pushed together. The flexible element 25g is also stretchable to allow the rack support members 24 to be pushed apart.

Figs. 23 and 24 show an eighth embodiment of a yoke 6h in accordance with the present invention. Yoke 6h is the same as yoke 6 shown in Fig. 4 except that yoke 6h has flexible elements 25h that are wave shaped in plan view, compared with the flexible elements 25 of yoke 6 that are wave shaped in elevation view. An advantage

of the flexible elements 25h being wave shaped in plan view is that the mould for making the yoke 6h may be simpler. The variations in shape of the flexible elements shown in Figs. 21 , 22, 23 and 24 may be applied to the other embodiments of yoke described herein.

Fig. 25 shows a steering gear 1i having a ninth embodiment of a yoke 6i in accordance with the present invention. Referring to Figs. 25, 26 and 27, yoke 6i is the same as yoke 6f shown in Figs. 18, 19 and 20 except that each rack support member 24i of yoke 6i has two rack support surfaces 2Oi, and each rack support surface 2Oi has a spherically curved back 33i rather than a cylindrically curved back. Each rack support surface 2Oi sits in a corresponding spherically curved recess 32i in the rack support members 24i. The button like rack support surfaces 2Oi can rotate to accommodate both rotational and axial misalignment of the Y-rack 3.

Fig. 28 shows a steering gear 1j having a tenth embodiment of a yoke 6j in accordance with the present invention. Referring to Figs. 28 to 32, the yoke 6j is similar to the yoke 6 shown in Figs. 3 and 4 except that the flexible elements 25j of the yoke 6j connect the rack support members 24j to each other via a central ring 36. The flexible elements 25j are curved in plan view and two flexible elements 25j connect each rack support member 24j to the central ring 36. In this embodiment, the rack support members 24j, the flexible elements 25j, and the central ring 36 are integrally moulded as a single piece. As with the yoke 6, the flexible elements 25j of yoke 6j act as springs that allow the rack support members 24j to be moved towards or away from each other.

The base member 27j of the steering gear 1 j is similar to the base member 27 shown in Figs. 3 and 4 except that the base member 27j has a circular boss 37 protruding from its top surface. The base member 27j and the yoke 6j are designed to be assembled together outside of the steering gear 1j to form a yoke assembly 38j as shown in Fig. 32. The yoke assembly 38j is designed to be inserted into the housing bore 21 as single unit. To assemble the yoke 6j to the base member 27j, the boss 37 is pushed into the central ring 36. The central ring 36 elastically stretches to fit over the boss 37 thereby retaining the yoke 6j to the base member 27j.

Fig. 33 shows a steering gear 1k having an eleventh embodiment of a yoke 6k in accordance with the present invention. Referring to Figs. 33 to 37, the yoke 6k is similar to the yoke 6j shown in Figs. 28 to 30 except that the flexible elements 25k of the yoke 6k connect the rack support members 24k to each other via a central spigot 40, instead of via the central ring 36 of yoke 6j. Two flexible elements 25k connect each rack support member 24k to the central spigot 40. In this embodiment, the rack support members 24k, the flexible elements 25k, and the central spigot 40 are integrally moulded as a single piece. As with the yoke 6, the flexible elements 25k of yoke 6k act as springs that allow the rack support members 24k to be moved towards or away from each other.

The base member 27k of the steering gear 1 k is similar to the base member 27 shown in Figs. 3 and 4 except that the base member 27k has a circular hole 41 through its centre. In a similar manner to the yoke assembly 38j shown in Fig. 32, the base member 27k and the yoke 6k are designed to be assembled together outside of the steering gear 1k to form a yoke assembly 38k as shown in Fig. 37. To assemble the yoke 6k to the base member 27k, the central spigot 40 is pushed into the hole 41. The central spigot 40 is designed to be an interference fit in the hole 41 thereby retaining the yoke 6k to the base member 27k.

Fig. 38 shows a steering gear 1m having a twelfth embodiment of a yoke 6m in accordance with the present invention. Referring to Figs. 38 to 42, the yoke 6m is similar to the yoke 6 shown in Figs. 3 and 4 except that the flexible elements 25m of yoke 6m extend below the rack support members 24m, as shown in Fig. 40. The flexible elements 25m are wave shaped, as shown in Fig. 39, such that they act as springs that allow the rack support members 24m to be moved towards or away from each other. Each rack support member 24m has three circularly spaced protrusions 43 extending from its underside.

The base member 27m of the steering gear 1m is a circular disc. The diameter of the base member 27m sized such that the base member 27m loosely fits inside the circle of protrusions 43, as shown in Fig. 41. The base member 27m and the yoke 6m are

designed to be assembled together outside of the steering gear 1m to form a yoke assembly 38m as shown in Fig. 42. To assemble the yoke 6m to the base member 27m, the flexible elements 25m are pushed temporarily away from each other and held in this position whilst the base member 27m is placed inside the circle of protrusions. The base member 27m is retained to the yoke 6m by means of the wave shape of the flexible elements 25m overlapping the underside of the base member 27m, as shown in Fig. 41 , and by the protrusions 43 centrally locating the base member 27m.

Unlike the steering gear 1a shown in Fig. 3, the small clearance 22 of the steering gear 1m, which limits the movement of the yoke 6m in the bore 21, is directly between the underside of the rack support members 24m and the cap 9m.

In other not shown embodiments of the invention, the spring 8 may contact the underside of the rack support members 24 directly, instead of having a base member 27 between the spring 8 and the rack support members 24. Furthermore, spring types other than coil springs may be used, such as leaf springs.

Although the embodiments of the invention described in detail are shown in relation to manual steering gears, the invention is equally applicable to power assisted steering gears.

The term "comprising" as used herein is used in the inclusive sense of "including" or "having" and not in the exclusive sense of "consisting only of.