RACK AND PINION GEARS, HOUSINGS THEREFOR AND A METHOD OF MANUFACTURING SUCH HOUSINGS

Abstract: A rack and pinion gear, a housing for such gear, and a method of manufacturing such a housing. The housing is an assembly of two tubular members (1) and (2); member (1) is for receiving the rack bar of the gear and member (2) is for receiving the pinion. Each of the members (1), (2) has in its side wall an aperture and these members are mated and secured (by welding, brazing, bonding or otherwise) one with the other with the two apertures communicating with each other. The communicating apertures provide an opening through which the rack and pinion can co-operate. The tubular members (1, 2) can be formed by shaping from sheet material and during such shaping a projection (4) can be erected from the sheet material to form a chamber communicating with the bore of its tubular member; the chamber can be used to locate a bearing yoke or other support means for the rack bar.

Description: DESCRIPTION This invention relates to rack and pinion gears, to housings therefor and to a method of manufacturing such housing. More particularly the invention concerns a rack and pinion gear of the kind (hereinafter referred to as "the kind specified") comprising a housing; a rack bar in the housing and longitudinally displaceable relative thereto, and a pinion rotatably mounted in the housing and having its teeth engaging with the teeth of a rack carried by the rack bar so that upon rotation of the pinion the rack bar is displaced longitudinally through the housing. Gear assemblies of the kind specified are well known, particularly in the art of vehicle steering, and ever increasing attempts are being made to reduce the cost of manufacture of such gears without detracting from their performance or reliability. An appreciable proportion of the cost of the gear can be attributed to the cost of manufacture of the housing - especially with conventional housings formed by machined castings or mouldings. To alleviate the high cost of housing manufacture it has hitherto been proposed, for example in our U.K. Specification No. 1,422,122, to form the housing as an assembly of two or more pre-formed shell-like components which are assembled around the gear components and secured together to constitute a unitary housing. An object of the present invention is to provide a novel structure of housing for a rack and pinion gear of the kind specified by which the housing is susceptible to relatively inexpensive manufacture. According to the present invention there is provided a housing for a rack and pinion gear of the kind specified, said housing being an assembly comprising a first tubular member for receiving the rack bar and a second tubular member for receiving the pinion, each of said tubular members having an aperture in its side wall, and wherein said tubular members are mated and secured one with the other with the apertures communicating with each other to provide an opening within the housing through which the rack and pinion are intended to co-operate. Further according to the present invention there is provided a method of manufacturing a housing for a rack and pinion gear of the kind specified which comprises providing a first tubular member with an aperture in its side wall, said member being intended to receive the rack bar; providing a second tubular member with an aperture in its side wall, said second tubular member being intended to receive the pinion; mating said tubular members one with the other and with the apertures communicating with each other to provide an opening within the housing through which the rack and pinion are intended to co-operate, and securing the mated tubular members one to the other. Still further according to the present invention there is provided a housing when manufactured by the method specified in the immediately preceding paragraph. The invention also provides a rack and pinion gear of the kind specified and incorporating a housing as specified as being in accordance with the present invention, and in which the rack bar of the gear is received in the first tubular member relative to which it is longitudinally displaceable and the pinion is rotatably mounted within the second tubular member, and wherein the pinion engages with the rack of the rack bar through the opening in the housing proied by the communicating apertures. Preferably the tubular members are mated and secured one with the other at an angular relationship which is consistant with the desired angular relationship which is to be provided between the rack bar and the pinion. The tubular members can be of any desired cross sectional shape and are not necessarily of the same cross sectional shape, for example in a preferred embodiment the first tubular member is of substantially triangular cross section and the second tubular member is substantially circular section. Furthermore, the tubular members can be made in various, and not necessarily the same, materials, although it is envisaged that they will usually be made in an engineering plastics material (which material is discussed together with examples in our Specification No. 1,422,122) or in an appropriate metal. The tubular members can be secured together in the desired angular relationship by use of an adhesive, a bonding agent, welding techniques or otherwise as is appropriate for the particular materials employed. The tubular members can be formed by conventional means such as extrusion or drawing techniques and thereafter the apertures formed by cutting or otherwise to provide the appropriate mating relationship between the tubular members. Preferably however one or each of the tubular members is formed from sheet material which is rolled or otherwise shaped into the appropriate tubular form and thereafter welded or otherwise secured along one or more seams of the tube. By this latter technique of tube formation the sheet can be cut to size as appropriate and also provided with one or more apertures or recesses which are so located and shaped that the desired aperture is provided in the tubular member when formed from the sheet. It is also possible by forming the tubular member from sheet material as aforementioned to provide a tubular member with one or more lateral projections or extensions on its side wall which form chambers communicating with the bore of the tube for the reception and/or location of component parts associated with a rack and pinion gear. By way of example, in a conventional rack and pinion gear there is frequently provided a spring or resiliently located yoke or similar component which is located oppositely to the pinion on the side of the rack bar remote from the pinion and which serves to bias the rack bar to maintain its teeth in engagement with those of the pinion; such a yoke is usually mounted in a chamber formed by an extension of the housing and by forming the first tubular member by shaping sheet material such sheet can be profiled and cut as necessary so that in the forming of the tubular member a laterally extending projection can be erected on its side wall to define the chamber for reception of the yoke. Desirably the apertures in the side walls of the tubular members are profiled to provide close mating engagement between those members when the apertures are in communication (so that the appearance of the housing is that of two tubes partially intersecting each other). It will be realised however that it is not essential for the peripheral edges of the two apertures to coincide with each other provided that the opening which is formed between the tubular members enables co-operation to be maintained between the rack and pinion teeth of the assembled gear. Furthermore, fairly wide mating tolerances may be permissible between the two tubular members (particularly, if, for example, those members are to be welded or brazed together with a filler material) provided that the desired angular relationship, orientation and other positioning of those two tubular members is maintained (for example, by mounting the tubular members in a jig) whilst they are being secured together. The pinion will usually be mounted within the second tubular member in bearings and that tubular member can be shaped, for example by nipping, pressing or otherwise to provide seatings for such bearings (the latter usually being located one at each end of the second tubular member). It will also be usual for the rack bar to be longitudinally displaceable through the first tubular member while mounted in bearings and the wall of the second tubular member can also be appropriately shaped to provide seatings for such bearings. One embodiment of a housing constructed in accordance with the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is an end view of the housing; Figure 2 illustrates a metal sheet from which the first tubular member in the housing of Figure 1 is shaped; Figure 3 diagrammatically illustrates a perspective view of the first tubular member formed from the metal sheet in Figure 2; Figure 4 illustrates a metal sheet from which the second tubular member in the housing of Figure 1 is shaped, and Figure 5 is a side elevation of the housing in Figure 1 and in which the first tubular member is provided with an extension portion. The housing in Figure 1 for a rack and pinion gear of the kind specified comprises a first tubular member 1 which is secured by welding in mated relationship with a second tubular member 2. The tubular member 1 has a tubular portion 3 of substantially triangular cross section and a laterally outwardly extending box-like projection 4 on the wall of the portion 3 which forms a yoke chamber opening into the bore of the tubular portion. The tubular portion 3 is intended to receive the rack bar (not shown) of the gear so that rack bar is displaceable longitudinally through the tube and tubular member 1 is intended to receive the pinion (not shown) of the gear so that the pinion is rotatably mounted in the bore of the member 2. The yoke chamber formed by the box-like projection 4 is intended to receive a yoke (not shown) for example of resilient material, which supports the rack bar with the teeth of its rack in engagement with those of the pinion. The tubular member 1 is formed from a steel sheet 1a (see Figure 2) which is of generally rectangular shape except for a pair of projections 5 and 5' extending from opposed side edges 15 of the sheet. The tubular member 2 is of substantially circular cross section and is formed by rolling a substantially rectangular steel sheet 2a (see Figure 4). Prior to formic the tubular member 1 an aperture 6 having parallel and opposed edge portions 7 connected by opposed concave edge portions 8 is cut into the sheet la. In addition the projections 5 and 5' (each of which is substantially in the shape of an isosceles trapezium) are cut or slit into "T" formations. The head of the "T" formation for projection 5 being provided by a central rectangular portion 9 and triangular ears 10 and the stem of that "T" being provided at 11 so that the sheet is cut along the lines indicated at x. Projection 5' is similarly cut at x' to provide the "T" formation, the head of which has a central rectangular portion 9' and a pair of ears 10' and the stem of which is shown at 11'. The tubular portion 3 is constructed from the sheet la by folding the sheet about longitudinally extending lines 12 so that the opposed edges 15 are in abutment and the tube has a base 13 and opposed side walls 14. The sheet 1a is retained in its tubular form by welding together the abutting edges 15 to form seams on the longitudinally opposed sides of the stems 11 and 11'. The box-like projection 4 is erected from the "T" formations by displacing those portions of the sheet from the planes of the respective side walls 14 and thereafter folding them about fold line 16, 17 and 18 (and also 16', 17' and 18') into the box-like shape as shown in Figure 3. Following erection of the projection 4, the abutting edges 19 and 19' are welded together to form a seam which is continuous with the seams 15 and the free edges of the triangular ears 10 and 10' are welded to the respectively adjacent edges of the stems 11 and 11' and of the side walls 14 to provide a rigid structure. It will be seen from Figures 2 and 3 that the aperture 6 extends- > across the full width of the base 13 and part way into opposed side walls 14 so that the curved edge portions 8 of the aperture are located in the side walls 14. The sheet 2a has an aperture 20 with opposed edge portions 21 which are parallel to opposed side edges 22 of the sheet. The edge portions 21 are joined by opposed dog-legged edge portions 23. The tubular member 2 is formed by rolling sheet 2a into cylindrical form where the edges 22 are in abutment and the cylindrical form is retained by welding a seam along the abutting side edges 22. After their formation, the tubular members 1 and 2 are mated as shown in Figure 1 so that the member 1 sits in saddle-like manner on the member 2 with the apertures 6 and 20 communicating with each other. In particular the aperture 6 is shaped to mate with the tubular member 2 in substantially complimentary relationship whereby the concave edge portions 8 follow the substantially circular or elliptical profile presented by the cylindrical surface of member 2 while the straight edge portions 7 extend adjacent and parallel to the edge portions 21. Desirably the peripheral edge of the aperture 6 coincides with the peripheral edge of the aperture 20. In this mated condition the tubular members 1 and 2 present the appearance of intersecting tubes and they are secured together as such by welding around the edges of the communicating apertures 6 and 20. In a rack and pinion gear of the kind specified the axis of the pinion is usually off-set at an oblique angle to the longitudinal direction along which the rack bar is displaced to ensure that the rack and pinion teeth mate in correct manner. Consequently the tubular members 1 and 2 are arranged to mate at an angular relationship consistant with the desired angular relationship which is to be provided between the rack bar and the pinion, such typical relationship is indicated at K in Figure 5. To provide the correct angular elationship between the tubular members 1 and 2 the apertures 6 and 20 are appropriately obliquely off-set with respect to the longitudinal extending side edges 15 and 22 of the respective sheets 1a and 2a (this is particularly evident from the aperture 6 in the Figure 2). After the housing in Figure 1 has been formed by welding together the tubular members 1 and 2 any burrs or flashes are removed from the inside of the housing and the rack and pinion gear can be assembled. To assemble the gear the pinion is inserted into the bore of the member 2 and rotatably mounted in bearings (not shown) within the member 2. Seatings can be provided for such bearings at opposite ends of the tubular member 2 by nipping or otherwise shaping those ends to form annular inwardly directed ribs 24 which serve to locate the bearings. The pinion and its bearings are enclosed within the member 2 by appropriate end caps (not shown) through one of which a shaft from the pinion projects for coupling to a steering column. After insertion of a yoke (not shown) into the yoke chamber formed by the projection 4, the rack bar can be fed into the tubular portion 3 so that its rack is engaged with the pinion. Such engagement of the rack and pinion teeth is effected through the opening which is provided within the housing by the communicating apertures 6 and 20 and it will be realised that the shape and configuration of this opening should permit such engagement to be maintained throughout the operative stroke of the rack bar. It is frequently necessary, particularly in vehicle steering assemblies which include rack and pinion gears of the kind specified, for the rack bar to be enclosed by the housing for the whole or a major part of its longitudinal extent. If required therefore the tubular portion 3 of the housing can be extended by a tubular portion 3a which is of complimentary size and cross sectional shape to the portion 3 and is butt welded to an end of the portion 3 as indicated at 25 in Figure 5. The extension portion 3a can be formed from a steel sheet similarly to the portion 3 and is conveniently provided with a bracket 26 for mounting the gear. In a modification of the housing (not shown) the box-like projection 4 is omitted and the tubular member 1 is formed from a steel sheet which is similar to that shown in Figure 2 except that the sheet is of rectangular shape (i.e. the projections 5 and 5' are omitted) and a continuous welded seam is provided along the whole length of the abutting edges 15. If required the tubular portion 3 can be nipped or otherwise shaped to provide one or more seats (for example similarly to the shapings 24 for the tubular member 2) to locate bearing means by which the rack bar is displaceably supported in the tubular member 1.

Claims: CLAIMS 1. A housing for a rack and pinion gear of the kind specified, said housing being an assembly comprising a first tubular member (1) for receiving the rack bar and a second tubular member (2) for receiving the pinion, each of said tubular members (1, 2) having an aperture (6, 20) in its side wall, and wherein said tubular members are mated and secured one with the other with the apertures (6, 20) communicating with each other to provide an opening within the housing through which the rack and pinion are intended to co-operate. 2. A housing as claimed in claim 1 wherein said tubular members (1, 2) are mated and secured one with the other at an angular relationship (S) consistant with the desired angular relationship to be provided between the rack bar and the pinion. 3. A housing as claimed in either claim 1 or claim 2 in which at least one of the tubular members (1,2) is formed from sheet material (la, 2a) shaped and secured in the tubular form. 4. A housing as claimed in claim 3 in which at least one of the tubular members (1, 2) formed from sheet material (1a, 2a) has a lateral projection or extension (4) formed in its side wall by shaping said sheet material and which projection or extension (4) forms a chamber communicating with the bore of that tubular member for receiving a component part associated with the rack and pinion gear. 5. A housing as claimed in claim 4 in which the lateral projection or extension (4) is provided in the side wall of the first tubular member (1) and provides a chamber for receiving bearing means by which the rack bar is to be supported in the first tubular member. 6. A housing as claimed in claim 5 in which the lateral projection or extension (4) is located in the side wall of the first tubular member (1) so that the chamber provided thereby is located substantially laterally opposite to the opening through which the rack and pinion are intended to co-operate and said chamber is for receiving bearing means for biasing the rack bar into engagement with the pinion. 7. A housing as claimed in any one of the preceding claims in which the second tubular member (2) has in its side wall seatings (24) for bearing means by which the pinion is to be rotatably mounted in the housing. 8. A housing as claimed in any one of the preceding claims in which the first tubular member (1) is of substantially triangular cross-section. 9. A housing as claimed in claim 8 when appendant to claim 4 in which the first tubular member (1) has a box-like lateral projection or extension (4) formed in its side wall. 10. A housing as claimed in any one of the preceding claims in which the second tubular member (2) is of substantially circular cross-section. 11. A method of manufacturing a housing for a rack and pinion gear of the kind specified which comprises providing a first tubular member (1) with an aperture (6) in its side wall, said member (1) being intended to receive the rack bar; providing a second tubular member (2) with an aperture (20) in its side wall, said second tubular member (2) being intended to receive the pinion; mating said tubular members (1, 2) one with the other and with the apertures (6, 20) communicating with each other to provide an opening within the housing through which the rack and pinion are intended to co-operate, and securing the mated tubular members (1, 2) one to the other. 12. A method as claimed in claim 11 which comprises mating said tubular members (1, 2) one with the other at an angular relationship ( < ) consistant with the desired angular relationship to be provided between the rack bar and the pinion. 13. A method as claimed in either claim 11 or claim 12 which comprises shaping at least one of the tubular members (1, 2) from sheet material (la, 2a) and securing the sheet material in tubular form. 14. A method as claimed in claim 13 which comprises forming the aperture or apertures (6, 20) in the sheet material (lea, 2a) prior to shaping said material into its tubular form. 15. A method as claimed in either claim 13 or claim 14 which comprises shaping the sheet material (la, 2a) during the manufacture of the or a tubular member therefrom to form in the side wall of that member (1, 2) a lateral projection or extension (4) which forms a chamber communicating with the bore of that tubular member for receiving a component part associated with the rack and pinion gear. 16. A method as claimed in claim 15 which comprises forming the first tubular member (1) by shaping from sheet material (1a) and erecting from said sheet material during said shaping a box-like projection (4) for the reception of bearing means by which the rack bar is to be supported in that tubular member (1). 17. A housing when manufactured by the method as claimed in any one of claims 11 to 16. 18. A rack and pinion gear of the kind specified and incorporating a housing as claimed in any one of claims 1 to 10 and 17 in which the rack bar of the gear is received in the first tubular member (1) relative to which it is longitudinally displaceable and the pinion is rotatably mounted within the second tubular member (2), and wherein the pinion engages with the rack of the rack bar through the opening in the housing provided by the communicating apertures (6, 20).

Inventors: WHITNEY, JOHN
Applicants: CAM GEARS LIMITED
Application year: 1979
Main classification: F16H57
IPC codes: F16H57, B62D3, F16H19