GB2154299A

GB2154299A - A rack bar housing assembly

Info

Publication number: GB2154299A
Application number: GB08404004A
Authority: GB
Inventors: Frederick John Adams
Original assignee: TRW Steering Systems Ltd
Current assignee: TRW Steering Systems Ltd
Priority date: 1984-02-15
Filing date: 1984-02-15
Publication date: 1985-09-04
Also published as: GB2154299B; GB8404004D0

Abstract

A rack bar housing assembly and a method of manufacturing such an assembly. The assembly has a pinion housing 1 to which is secured a longitudinally extending tube 2. The tube 2 communicates a chamber 3 in the housing within which a pinion is to engage with a rack bar displaceable through the chamber 3 and tube 2. The tube is of composite construction having a relatively rigid structure comprising one or more spiral windings of fibrous material such as filament, staple fibre or formed on a mandrel and bonded with cured resin. The fibrous material is preferably glass, carbon, asbestos or P.T.F.E. The wall thickness and profile of the tube can be determined by the number and location of the windings applied to the mandrel. <IMAGE>

Description

SPECIFICATION A rack bar housing assembly and a method of manufacturing such an assembly TECHNICAL FIELD AND BACKGROUND ART This invention relates to rack bar housing assemblies of the type which are predominantly incorporated in rack and pinion steering gears for motor vehicles. Conventionally an assembly of the aforementioned type comprises a pinion housing having a chamber within which is rotatably mounted a pinion.

The teeth of the pinion drivingly engage a rack bar which is slidably mounted in the housing to be longitudinally displaceable by rotation of the pinion. Conventionally the rack bar extends longitudinally within a tube extending from the pinion housing. This tube, inter alia, serves to carry a bearing or bush within which the rack bar is slidably supported at or towards the end of the tube remote from the pinion housing. Desirably the rack bar housing assembly is of a structure which lends itself to inexpensive manufacture, is light in weight, has sufficient strength and rigidity to meet the necessary safety standards required of vehicle steering gears and permits smooth running of the rack bar during a steering manoeuvre. In an attempt to satisfy the requirements of lightness in weight and inexpensive manufacture it has hitherto been proposed, for example in our G.B.Patents Nos. 1,340,882 and 1,422,122, to form the rack bar housing assembly and components thereof as injection mouldings in plastics.

However, a difficulty encountered with previously proposed plastics structures particularly for the extension tube of the pinion housing, is that the saving in weight is achived at the expense of a loss in rigidity (as compared with conventional rack bar housing assemblies of metal). This loss in rigidity if encountered in the extension tube may permit the rack bar bearing or bush which that tube carries to be moved out of alignment during flexing of the tube in use (to such an extent that the free running of the rack bar through the assembly is impaired).It is an object of the present invention to provide a rack bar housing assembly and a method of constructing such an assembly by which the above mentioned desirable characteristics can be achieved and by which sufficient rigidity can be provided for the extension tube of the housing to ensure that a rack bar bearing or bush carried thereby will be maintained in alignment to permit free running of the rack bar therethrough.

STATEMENT OF INVENTION AND ADVAN TAGES According to the present invention there is provided a rack bar housing assembly comprising a pinion housing having a pinion chamber communicating with a longitudinally extending tube secured to the pinion housing and within which chamber and tube a rack bar is to be received to be longitudinally displaceable relative to the assembly and wherein said tube comprises spiral winding of fibrous material reinforcement bonded with cured resin to provide a relatively rigid structure.

Further according to the present invention there is provided a method for manufacturing a rack bar housing assembly which comprises spirally winding fibrous material into tubular form on a mandrel and applying resinous fluid to said material; curing the resin to provide a relatively rigid tubular structure reinforced with said fibrous material, removing the tube from the mandrel and securing the tube to a pinion housing with said tube communicating with a pinion chamber in the housing for the reception, within the tube and chamber of a rack bar which is to be longitudinally displaceable relative thereto.

Still further according to the present invention there is provided a rack and pinion steering gear which incorporates a rack bar housing assembly as specified above or as manufactured by the above specified method.

By incorporating in the rack bar housing assembly the resin bonded tube reinforced with its spiral winding of fibrous material it has been found that the tube can have a rigidity comparable with that of a metal tube (as conventionally used for a similar purpose) while its cost of manufacture and weight characteristics may be favourably compared with the previously proposed plastics moulded tubes (and possibly even an improvement upon such plastics tubes).

The fibrous reinforcing material can take many forms but will usually be of single filament, multiple filament, staple fibre or tape, the nature of which permits it to be wound spirally on to the mandrel. Examples of suitable fibrous materials are glass, carbon, asbestos, and polytetrafluoroethylene and it will be appreciated that combinations of these materials may be employed. Similarly many resins (usually with appropriate hardeners) can be used and which may be cured at ambient temperature or by the application of heat; suitable resins such as epoxy resin or phenolic resin will be apparent to persons skilled in the art and having an understanding of the present invention.

The mandrel, which may be collapsible to facilitate removal of the tube therefrom, will usually be coated with a release agent to ease its removal from the tube. It will be appreciated that the profile of the mandrel will conform, substantially, to the internal profile required of the tube, particularly in so far as the latter may require variations in diameter over its length, longitudinal or annular recesses and seatings to faciliate location of compo nents (such as the previously mentioned rack bar bearing or bush) within the tube. The internal profile having been determined by the mandrel, the external profile of the tube and its wall thickness may be determined by the application of the spirally wound fibrous material and resin.During the spiral winding the wall thickness can be varied locally, for example by increasing or decreasing the pitch of the spiral winding or by varying the number of layers of fibrous material which are applied. Consequently, the external profile of the tube can be formed with annular flanges, ribs or the like by varying the wall thickness of the tube as aforementioned or by maintaining the wall thickness substantially constant and following an undulating profile which is presented by the surface of the mandrel. The exterior of the tube can accordingly be provided with appropriately positioned profile characteristics which faciliate the attachment of components such as mounting brackets, bellows and the like to the tube in a similar manner to conventional rack bar housing assemblies or which facilitate the attachment of the tube to the pinion housing.The capability to vary the wall thickness of the tube during the winding process has the advantage that stresses in the tube can be alleviated particularly as compared with the stresses which may be formed at a step in the will thickness of previously proposed injection moulded plastics tubes.

Conveniently the tube is attached to the pinion housing by an end of the tube being received in and secured to a complementary socket provided in the pinion housing. The pinion housing may be of a conventional metal structure, moulded in plastics or of other form but if of metal it will be appreciated that the spirally wound resin bonded tube can provide a significant weight reduction for the assembly as compared with a comparable conventional metal tube.

Desirably the fibrous material is impregnated with the resinous fluid, such impregnation may be achieved by painting or dipping the material following the spiral winding. Preferably however the resinous fluid is applied to the fibrous material as it is being wound into its spiral tubular form.

The resin bonded and fibrous reinforced tube in the assembly of the present invention may be drilled, slotted or otherwise apertured for connecting to components, mounting purposes or otherwise and if required components can be securely attached to the tube by providing a resin bond therewith.

An important consideration in modern manufacturing techniques is that of energy conservation and it is believed that the manufacture of the fibrous reinforced and resin bonded rack tube for the assembly in accordance with the present invention (especially if the resin is cold cured) will provide a considerable saving in energy (as compared with the energy requirements of conventional metal working and plastics injection moulding techniques), particularly when the tubes are mass produced.

DRAWINGS One embodiment of a rack bar housing assembly constructed in accordance with the present invention will now be described, by way of example only, with reference to the accompanying illustrative drawings, in which: Figure 1 is a longitudinal section through the assembly; Figure 2 shows an end of the tube incorporated in the assembly of Fig. 1, that end being remote from the pinion housing and having secured thereto a mounting bracket; Figures 3 and 4 show longitudinal sections through part lengths of tubes suitable for incorporation in the assembly of Fig. 1 and illustrate possible modifications to the ends of the tubes remote from the pinion hosing, and Figure 5 shows an end view of the tube in Fig. 4 and illustrate an alternative form of mounting bracket which the tube carries.

DETAILED DESCRIPTION OF DRAWINGS The rack bar housing assembly comprises a pinion housing 1 and an extension tube 2.

The general purpose of the assembly is conventional for a vehicle steering gear whereby it is to receive a rack bar that extends longitudinally through the bore of the tube 1 and through a pinion chamber 3 in the housing 1 with which that bore communicates. A pinion is to be rotatably mounted in the housing 1 (partly within a seating 4) with its teeth in engagement with those of the rack bar so that the rack bar is displaced longitudinally through the assembly by rotation of the pinion. The pinion housing 1 is conveniently formed as a casting in metal (such as a light aluminium alloy), by injection moulding in plastics, or as a moulding in reinforced plastics (such as polyester resin reinforced with glass fibre). During its manufacture the pinion housing is provided with a tubular flange 5 coaxial with the tube 2 and to which is intended to be secured one end of a bellows (the other end of which will be secured to the rack bar in conventional manner), with a screw threaded counterbore 6 which is intended to receive a bearing (such as a saddle or yoke) which slidably engages the rack bar and biases the rack bar laterally into engagement with the pinion, and with a socket 7 within which an end of the tube 2 is received and secured, conveniently by bonding or adhesive. A major part length of the tube 2 from its end in the pinion housing 1 is of substantially constant external diameter and wall thickness (other than for a slight diametral enlargement to the end of the bore where an internal annular rebate 8 is provided).The end part length 9 of the tube remote from the pinion housing is diametrally enlarged (but has a wall thickness substantially the same as that of the adjacent smaller diameter part length) and is intended to provide a seating for a bush or bearing (not shown) within which the rack bar is to be borne to be longitudinally displaceable therethrough. For the purpose of mounting the bearing or bush the tube is provided with a circumferentially spaced array of slots 10 with which the bearing or bush can engage to be secured against longitudinal and rotational displacement relative to the tube.

To ensure that the rack bar is capable of relatively free running through the bearing or bush, the alignment between the bearing and the rack bar (having been set during fitting of the rack to the housing assembly) should be maintained during operational use of the rack and pinion in a vehicle steering gear. With this in mind the tube 2 should be of a relatively rigid structure and have other desirable characteristics of being light in weight, easily manufactured and reliable to comply with the safety requirements necessary in a vehicle steering gear. In accordance with the present invention the tube 2 is formed by a spiral winding 11 of fibrous reinforcing material bonded with cured resin.

In the formation of the tube 2 a mandrel (not shown) is provided the external profile of which corresponds to the internal profile required of the tube. Such a mandrel may be collapsible or partable to facilitate its removal from a tube which is formed thereon (bearing in mind the internal diametral enlargements provided at the ends 8 and 9 of the tube).

Prior to the formation of the tube the mandrel may be coated with a suitable release agent, again to facilitate removal of the tube. In a preferred structure the tube has glass fibre or carbon fibre reinforcement whereby a continuous filament of the fibre is spirally wound on to the mandrel as indicated at 11. Preferably the spiral winding is applied in two or more layers by reciprocating the winding process longitudinally and so that the windings 11 of one layer cross-over the windings 11 a of an adjacent underlying layer.

As the filament is wound on to the mandrel it is coated with an appropriate resinous fluid or alternatively such fluid may be applied to impregnate the windingson the mandrel. The resinous fluid, which may be hot or cold curing, may be a polyester resin having an appropriate hardener as will be well known for the type of resin employed.

If it is required that the wall thicknes of the tube is thickened locally, this can be achieved by additional layers of fibre windings and/or by varying the pitch of the windings. An example of such local wall thickening is indicated in Fig. 1 where annular ribs 1 2 and 1 3 are formed on the exterior of the tube. The rib 1 2 serves to limit the insertion of the tube end into the socket 7 while the rib 1 3 can serve to facilitate the location of bellows which may be attached at one end to the tube (over the rib 13) and at the other end to the rack bar in conventional manner.

Since the resin impregnated fibrous material closely follows the profile of the mandrel, the mandrel can, if required, be provided with localised protrusions so that such protrusions will be developed through the wall thickness of the tube to present correspondings protrusions on the exterior of the tube.

When the resin has cured to a sufficient hardness the tube is removed from the mandrel following which the slots 10 can be cut by a machining operation.

The enlarged diameter end part 9 of the tube 2 provides a convenient location for a bracket 14 (see Fig. 2) by which that end of the rack bar housing assembly may be fitted to a vehicle. The bracket 1 4 has feet 1 4a which are resin bonded to the surface of the tube to form a rigid attachment.

In the modified forms of tube 2 shown in Figs. 3 to 5 the profile of the mandrel permits differend shaped end part lengths 9 to be formed, primarily to provide differently shaped seatings to suit different forms of bearings or bushes and a different external profile to which a mounting bracket can be attached. In particular, it will be noted that in Fig. 3 the resin bonded fibrous material forms an inwardly directed end flange 1 5 against which a bearing bush can be seated and that in both Figs. 3 and 4 the tube wall is thickened locally at 1 6 to provide external annular ribs which serve as locations for the attachment of components to the tube.In Fig. 3 an external annular recess 1 7 is provided between a rib 1 6 and a shoulder 1 8 (formed by different diameter parts of the tube) while in Fig. 4 an external annular recess 1 9 is provided between two longitudinally spaced annular ribs 16. Each of the recesses 17 and 19 is intended to provide a location for a saddleshaped mounting bracket 20 by which the assembly is to be secured at one end to a vehicle. For this latter purpose a rubber collar 21 may be fitted into the recess 1 9 (or 17) and thereafter the bracket 20 is fitted to straddle the collar 21 and secure the end of the assembly to the vehicle.

In the majority of cases the extension tube will be of circular form in lateral section; it will be appreciated however that the tube can comprise other forms of lateral section depending upon the external profile presented by the mandrel.

Claims

1. A rock bar housing assembly comprising a pinion housing having a pinion chamber communicating with a longitudinally extending tube secured to the pinion housing and within which chamber and tube a rack bar is to be received to be longitudinally displaceable relative to the assembly and wherein said tube comprises spiral winding of fibrous material reinforcement bonded with cured resin to provide a relatively rigid structure.

2. An assembly as claimed in claim 1 in which the fibrous material is in at least one of the forms of multiple filament, staple fibre, monofilament and tape.

3. An assembly as claimed in either claim 1 or claim 2 in which the fibrous material is at least one of the materials selected from glass, carbon, asbestos and polytetrafluoroethylene.

4. An assembly as claimed in any one of the preceding claims in which the fibrous material is wound in at least two layers with the fibres of one layer crossing over the fibres of an adjacent layer.

5. An assembly as claimed in any one of the preceding claims in which the pinion housing comprises a metal or plastics structure.

6. An assembly as claimed in any one of the preceding claims in which an end of the tube is received and secured within a socket provided in the pinion housing.

7. An assembly as claimed in claim 6 in which the tube end is bonded or adhesively secured in said socket.

8. An assembly as claimed in any one of the preceding claims in which the external profile of the tube is determined by the spiral winding of the fibrous material and the resin applied thereto.

9. An essembly as claimed in any one of the preceding claims in which the wall thickness of the tube is determined by the spiral winding of the fibrous material and the resin applied thereto.

10. An assembly as claimed in claim 1 and substantially as herein described with reference to the accompanying illustrative drawings.

11. A method for manufacturing a rack bar housing assembly which comprises spirally winding fibrous material into tubular form on a mandrel and applying resinous fluid to said material; curing the resin to provide a relatively rigid tubular structure reinforced with said fibrous material, removing the tube from the mandrel and securing the tube to a pinion housing with said tube communicating with a pinion chamber in the housing for the reception, within the tube and chamber, of a rack bar which is to be longitudinally displaceable relative thereto.

12. A method as claimed in claim 11 in which the internal contour of the tube is determined by the external profile of the mandrel.

1 3. A method as claimed in either claim 11 or claim 1 2 which comprises spirally winding the fibrous material in at least two layers with the fibres of one layer crossing over the fibres of an adjacent layer.

1 4. A method as claimed in any one of claims 11 to 13 which comprises locally varying the spiral winding of the fibrous material to provide local variations in the wall thickness of the tube.

1 5. A method as claimed in any one of claims 11 to 1 4 which comprises locally varing the spiral winding of the fibrous material to provide local variations in the external profile of the tube.

1 6. A method as claimed in any one of claims 11 to 1 5 which comprises adhesively securing or bonding the tube to the pinion housing.

1 7. A method as claimed in any one of claims 11 to 1 6 in which the fibrous material is in at least one of the forms of multiple filament, staple fibre, monofilament and tape.

1 8. A method as claimed in any one of claims 11 to 1 7 in which the fibrous material is at least one of glass, carbon, asbestos and polytetrafluorethylene.

1 9. A method as claimed in any one of claims 11 to 1 8 which comprises coating the mandrel with a release agent prior to the spiral winding of the fibrous material.

20. A method as claimed in any one of claims 11 to 1 9 which comprises collapsing the mandrel to facilitate its removal from the tube.

21. A method as claimed in any one of claims 11 to 20 which comprises completely enclosing the fibrous material in the resin.

22. A method as claimed in claim 11 and substantially as herein described.

23. A rack and pinion steering gear which incorporates a rack bar housing assembly as claimed in any one of claims 1 to 10 or when manufactured by the method as claimed in any one of claims 11 to 22.

24. A gear as claimed in claim 23 in which the exterior of the tube carries gear assembly means or mounting means by which the gear is intended to be assembled or to be fitted in a vehicle and said tube is profiled externally to provide a seating or location for said gear assembly or mounting means.

25. A gear as claimed in claim 23 in which the mounting means is bonded to the tube.

26. A gear as claimed in any one of claims 23 to 25 in which the interior of the tube carries a rack bar mounting or bearing and the tube is profiled internally to provide a seating or location for said rack bar mounting or bearing.

27. A gear as claimed in claim 23 and substantially as herein described.