GB2037931A

GB2037931A - Rack-and-pinion Gearing

Info

Publication number: GB2037931A
Application number: GB7935742A
Authority: GB
Original assignee: TRW Steering Systems Ltd
Current assignee: TRW Steering Systems Ltd
Priority date: 1978-11-23
Filing date: 1979-10-15
Publication date: 1980-07-16
Also published as: GB2037931B; FR2442385A1

Abstract

A rack and pinion gear has a rack bar (5) which is longitudinally displaceable in a housing (4) by rotation of a pinion (1) which engages with a rack on the rack bar. A yoke (8) straddles the rack bar (5) and supports it for engagement of its rack with the pinion. The yoke has a tubular portion within which is located a slipper (15) which is rotatable about an axis (10) relative to the yoke. Opposed helical ramp surfaces 14 and 16 engage in face-to-face engagement between the slipper and yoke which causes the yoke (8) to be displaced into engagement with the rack bar (5) when the slipper 15 is rotated about axis (10) by the biasing effect of spring (19) one end of which is anchored to the slipper and the other end to the yoke (8). The spring 19 can be a tension, torsion or a blade spring. During rotation of the slipper (15) the slipper reacts against a plate (11) on the housing to bias the yoke (8) into supporting engagement with the rack bar (5) through the ramp surfaces (14 and 16). <IMAGE>

Description

SPECIFICATION Improvements in or Relating to Rack and Pinion Gears This invention relates to a rack and pinion gear.

More particularly the invention concerns a rack and pinion gear comprising a longitudinally extending rack member which is longitudinally displaceable relative to a housing; a pinion rotatably mounted in the housing and engaging with a rack on the rack member so that rotation of the pinion effects said longitudinal displacement of the rack member; a yoke member which engages with the rack member on the side thereof remote from the rack slidably to support the rack member with its rack in engagement with the pinion, and in which the.yoke member is biased laterally into engagement with the rack member by a slipper which is spring biased relative to the yoke member and through slidably co-operating and opposed ramp surfaces which are inclined relative to the direction in which the yoke member is biased.Such a rack and pinion gear will hereinafter be referred to as "of the kind specified".

A rack and pinion gear of the kind specified is disclosed in our U.K. Patent No. 1,181,738 in which the slipper is a wedge shaped component having one of the ramp surfaces and is spring loaded relative to the housing to be displaced laterally or longitudinally in the manner of a wedge so that its ramp surface slides over a ramp surface on the yoke to bias the yoke relative to the housing for supporting the rack member. The spring biasing arrangements in the prior proposals may prove inconvenient on assembly of the gear.

Furthermore, the displacement of the wedge shaped slipper can result in assymmetric biasing forces being subjected to the yoke member since as the components wear in use the wedge shaped slipper is displaced laterally further from its optimum thrusting position (which is preferably in lateral alignment with, and on the side of the rack member remote from, the position of engagement between the rack and pinion teeth); such assymmetric forces on the yoke member may cause excessive wear on one or more parts of the yoke member which engage with the rack member and therefore afford support for the rack member. It is therefore an object of the present invention to provide a rack and pinion gear of the kind specified by which the aforementioned disadvantages can be alleviated.

According to the present invention there is provided a rack and pinion gear of the kind specified in which the slipper is rotatable about an axis which extends in a direction in which the rack member is biased; and wherein spring means is provided which biases the slipper relative to the rack member and for rotation about said axis to cause, during said rotation, one of the ramp surfaces to rotate with the slipper and to slide relative to the other ramp surface in a sense which urges the yoke member into engagement with, and provides said support for, the rack member.

By the present invention the slipper member merely rotates about an axis which extends in the direction in which the rack member is biased so that as the components of the gear wear and the spring means reacts to accommodate for that wear, the biasing force to which the yoke member is subjected from the slipper is maintained in a direction along the said axis. Preferably this latter axis is perpendicular to the longitudinal axis along which the rack member is displaceable and extends through the position of engagement between the rack and pinion teeth while the yoke member is located on the side of the rack member remote from such position of engagement.

Furthermore, the spring means which rotatably biases the slipper relative to the yoke member can be of a form which is easily accessible for assembly of the gear.

Usually retaining means will be provided by which the slipper and yoke member are retained in the housing and against which retaining means the slipper reacts during its rotation to bias the yoke member into supporting engagement with the rack member. Conveniently the retaining means is a plate which is secured to the housing to close a yoke chamber in the housing. For convenience of assembly of the gear it is preferred for the slipper to be arranged so that upon initial assembly of the slipper in the housing the spring means in energised by the reaction which is imparted to such means as a result of rotation of the slipper effected by the reaction between the ramp surfaces with the retaining means as assembled with the housing.If required the slipper can include means such as a slot for temporary engagement of a screwdriver or other tool by which the slipper can be directly rotated manually about its axis to energise the spring means during assembly of the gear whereby when the tool is removed a spring means reacts to bias the yoke member in the appropriate direction through the opposed ramp surfaces.

The spring means preferably reacts between the slipper and the yoke member which latter is appropriately restrained from rotation about the aforementioned axis of the slipper (such restraint being conveniently effected by the yoke member being of a form which straddles the rack member to restrain displacement of the rack member in a direction parallel to the axis about which the pinion rotates). Alternatively however the spring means can react between the slipper and either the housing or the aforementioned retaining means. To facilitate assembly of the gear it is preferred that the slipper is located in a tubular portion of the yoke member and the spring means is located in a peripheral cavity formed between the slipper and that tubular portion.Spring means can be of any convenient form, for example they may be of resilient material which is bonded to both the slipper and yoke member. Preferably, and more usually however, the spring means will be a mechanical spring such as a helical tension spring, a helical torsion spring or a blade spring.

In a modification, the gear can include an assembly of two slippers which are rotatable relative to each other and to the yoke member and which slippers co-operate with each other through the ramp surfaces. These slippers are coupled together by the spring means which is arranged to bias one slipper for rotation relative to the other slipper and thereby cause relative sliding movement between the ramp surfaces to urge the yoke member into supporting engagement with the rack member. Preferably the ramp surfaces are located one on each slipper and have ratchet or saw toothed profiles which are substantially in complementary engagement with each other.

One embodiment of a rack and pinion gear of the kind specified and 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 shows the gear in part section taken in a plane which includes the axis about which the pinion rotates and which is perpendicular to the direction in which the rack member is longitudinally displaceable; Figure 2 is an enlarged view of the arrangement for biasing the yoke member into engagement with the rack member by a slipper under the biasing effect of a helical torsion spring; Figure 3 is a section of the assembly shown in Figure 2 with the spring illustrated in section along the successive lines A1-A2-A3;; Figure 4 is a similar view to that shown in Figure 3 and illustrates a modification in which the spring means is in the form of a blade spring, and Figure 5 is a similar view of the gear to that shown in Figure 2 and illustrates a further modification comprising an assembly of two slippers for biasing the yoke member into engagement with the rack member.

The gear as shown in Figure 1 has a pinion 1 which is mounted for rotation about its axis 1 a by a ball race 2 and needle bearings 3 in a housing 4.

Longitudinally displaceable relative to the housing 4 is a rack bar 5 having a rack 6 the teeth of which engage with pinion 1 so that upon rotation of the latter the rack bar 5 is displaced longitudinally in the direction of its axis 5a through the housing.

The rack bar 5 has a part cylindrical surface 6a which slidably engages the substantially complementary part cylindrical recess 7 in a yoke 8. The yoke 8 is located on the side of the rack bar 5 remote from the position of engagement between the rack and pinion teeth (and preferably directly opposite position of engagement) and is mounted in a yoke chamber 9 formed by a tubular extension 4a of the housing.

The yoke chamber 9 is substantially cylindrical and the peripheral surface of the yoke is cylindrical to be a substantially complementary and sliding fit within the yoke chamber. With this arrangement the yoke 8 straddles the surface 6a and thereby restrains displacement of the rack bar 5 in the direction of the pinion axis 1 a; it is also preferred that the yoke 8 and its chamber 9 are co-axial with an axis 10 which extends through, and is substantially perpendicular to, the rack bar axis 5a. The yoke 8 is retained in its chamber 9 by a plate 11 which is secured by bolts 1 2 to the housing 4 to close the chamber 9.

As is best seen from Figure 1 the yoke 8 has a cylindrical tubular portion co-axial with the axis 10, one end of the bore 1 3 of which is open to the plate 11 while the other end is formed as a ramp surface 14 of substantially helical formation about the axis 10. Mounted within the bore 13 of the tubular portion and between the ramp surface 1 4 and closure plate 11 is a slipper 1 5 of generally cylindrical form to be substantially complementary to and a sliding fit within the bore 13. The slipper 1 5 has a ramp surface 16 which is of helical formation substantially complementary to the ramp surface 14 of the yoke. The helical ramp surfaces 14 and 1 6 oppose each other and are in substantially face-to-face contract.

The slipper 1 5 has an annular recess 17 which is concentric with the axis 10 and forms with the bore 13 an annular cavity 18 within which is located a helical torsion spring 1 9. The spring 1 9 substantially encircles the slipper 1 5 within the cavity 18 (see Figure 3) and one end 1 spa of the spring is anchored in a socket 20 to the slipper while the other end 1 Sb of the spring is anchored in a slot 21 in the tubular wall of the yoke 8.The slot 21 restrains the end 1 9b of the spring from circumferential movement relative to the yoke 8 about the axis 10 but permits that end of the spring restricted movement relative to the yoke 8 in a direction parallel to the axis 1 0. When the slipper 1 5 is initially inserted into the yoke 8 and the ends 1 spa and 1 Sb of the spring are anchored as aforementioned, with the spring 19 in an untensioned condition and the ramp surfaces 14 and 1 6 in abutment with each other the slipper will initially protrude from the yoke 8 as indicated at 15' in Figure 2.Upon assembly of the yoke, slipper and spring (arranged as aforementioned) in the gear, as the closure plate 11 is secured to the housing 9, the yoke 8 straddles and abuts the rack bar 5 and the slipper 1 5 is forced in the direction of axis 10 into the bore 1 3. As a result of this latter effect the ramp surface 1 6 is slidably displaced over the ramp surface 14 whilst maintaining face-to-face contact therewith thereby causing the slipper 1 5 to rotate about axis 10 relative to the bore 13. The yoke 8 is restrained from rotation about the axis 10 (conveniently by its straddling engagement with the rack bar) and as a consequence the relative rotation between the slipper and yoke subjects the spring 1 9 to torque so that the spring is effectively wound up. During securing of the closure plate 11 to the housing the spring end 1 9b will likely be displaced axially along the slot 21; more importantly however when the plate is finally positioned the energy in spring 1 9 acts in a sense to rotate the slipper about the axis 10 and relative to the yoke 8 so that the yoke 8 is subjected to a biasing force in the direction of axis 10 through the co-operating helical ramp surfaces 14 and 1 6. This latter biasing force urges the yoke into engagement with the rack bar 5 to support the rack 6 in meshing engagement with the pinion 10. If required the spring 19 can be energised during assembly of the gear by rotation of the slipper 1 5 about axis 10 with a screwdriver or similar tool which is inserted into a slot 22 provided in the slipper.An aperture 23 is provided in the closure plate 11 for the purpose of locating the screwdriver in the slot 22 so that the slipper can be retained in a position in which the spring 19 is energised until the plate 11 has been secured to the housing extension 4a; upon removal of the screwdriver the slipper 1 5 will rotate under its spring biasing to urge the yoke into engagement with the rack bar.

By appropriate selection of the characteristics for the spring 19 and the angle a (see Figure 2) which the ramp surfaces 14 and 1 6 subtend relative to the axis 10 a desired force (say in the order of 1 5 kilogramms) can be exerted on the yoke 8 to urge it in the direction of axis 10 towards the rack bar. It will be appreciated that the angle a can be selected to alleviate movement of the yoke 8 away from the rack bar 5 in the direction of axis 10 and which movement would otherwise result from shock loads on the rack bar-thus tending to alleviate rattle in the gear.It will also be appreciated that if the angle a is greater than 450 the force necessary to rotate the slipper 15 about axis 10 and in a sense to energise the spring 19 will be greater than the force produced by the spring 19 and which is exerted in a sense to displace the yoke 8 into engagement with the rack bar 5 along the axis 10.

If required the spring 1 9 can extend around the periphery of the slipper 1 5 to an extent which is less than that shown in Figure 3 or can have more than one coil which encircles the slipper 1 5.

Further the spring end 1 9b can be anchored in either the closure plate 11 or the wall of the housing extension 4a.

In the modification shown in Figure 4 the spring means by which the slipper 1 5 is biased for rotation about axis 10 relative to both the yoke 8 and housing extension 4a is in the form of a blade spring 24. The blade spring 24 extends diametrically through the slipper 1 5 (conveniently being embedded therein) and the diametrically opposed ends of the blade are anchored to the yoke 8. Conveniently the ends of the blade 24 are received in slots in the wall of the yoke 8 which slots extend substantially parallel to the axis 1 0.

In its un-stressed condition the blade spring 24 is substantially straight as shown in Figure 4 and when energised upon assembly of the gear and in a similar manner to that previously described with reference to Figures 1 to 3 the blade deforms to bias the slipper 1 5 for rotation about the axis 10 with a similar effect to that in the previous embodiment.

In a further modification not illustrated the spring means is in the form of a small diameter helical coil extension spring which is located within the annular cavity 1 8 to extend wholly or partly around the slipper 1 5 while one end of the helical spring is anchored to the slipper 1 5 and the other end is anchored to the yoke 8, housing extension 4a or plate 11; conveniently the anchorages are by pegs which engage with the respective ends of the spring.

In the modification shown in Figure 5 the slipper arrangement shown generally at 15a is in the form of an assembly comprising two generally cylindrical and tubular slippers 25 and 26 which are slidably received in the bore 1 3 coaxial with the axis 10. The slippers 25 and 26 provide substantially flat and opposed end faces 25a and 26a which respectively abut, in face-to-face contact and in planes which extend perpendicularly relative to the axis 10, a blind end face 27 of the bore 13 and the closure plate 11.

The end face 25b of the slipper 25 remote from its face 25a is in abutting engagement with the end face 26b of the slipper 26 remote from its face 26a; these end faces 25b and 26b provide ramp surfaces which each have a substantially ratchet or saw toothed profile extending around the annular extent of the respective end faces and these profiles engage with each other in substantially complementary manner (as indicated at 28). By the ratchet or saw toothed profile engagement between the slippers it will be appreciated that when one of those slippers is rotated about the axis 10 and relative to the other slipper, the spacing between the opposed end faces 25a and 26a along the axis 10 will vary to an extent determined by the characteristics of the saw toothed profile.

Coupling the slippers 25 and 26 together is a helical torsion spring 29. The spring 29 substantially encircles the slippers 25 and 26 within an annular cavity 30 formed between the bore 13 and an annular recess 31 on the slippers.

One end 32 of the spring 29 is anchored to the slipper 25 (by location of that end in a lateral socket in the cylindrical wall of the slipper 25) while the other end 33 of the spring 29 is anchored to the slipper 26 (by location of the end 33 in a lateral socket in the cylindrical wall of the slipper 26). The spring 29 provides a biasing effect between the slippers 25 and 26 to cause them to rotate relative to each other about the axis 10 and in a sense which urges the end face 25a axially away from the end face 26a through the action of the co-operating saw toothed or ratchet ramp surfaces 25b and 26b as above described. This biasing force results in a reaction on the closure plate 11 and the yoke 8 causing the latter to be urged into supporting engagement with the rack bar 5. Similarly to the previously described arrangements, the spring 29 is conveniently energised automatically during assembly of the gear, for example as a result of the attachment of the closure plate 11 to the housing part 4a to displace the slippers 25 and 26 axially towards each other (by their reaction against the yoke 8) and thereby cause the spring 29 to be "wound up" by the relative rotation which is imparted between the slippers through the saw toothed or ratchet engagement 28. It will be realised that the slippers 25 and 26 can be biased for rotation relative to each other by means other than the torsion spring 29, for example by use of a blade spring or helical tension spring as previously mentioned.

Claims

1. A rack and pinion gear of the kind specified in which the slipper is rotatable about an axis which extends in a direction in which the rack member is biased; and wherein spring means is provided which biases the slipper relative to the rack member and for rotation about said axis to cause, during said rotation, one of the ramp surfaces to rotate with the slipper and to slide relative to the other ramp surface in a sense which urges the yoke member into engagement with, and provides said support for, the rack member.

2. A gear as claimed in claim 1 in which retaining means is provided by which the slipper and yoke member are retained in the housing and against which retaining means the slipper reacts during said rotation to bias the yoke member into supporting engagement with the rack member.

3. A gear as claimed in claim 2 in which the retaining means comprises a plate which is secured to the housing to close a yoke chamber in the housing.

4. A gear as claimed in either claim 2 or claim 3 in which initial assembly of the slipper in the housing energises the spring means by reaction imparted to said spring means as a result of rotation of the slipper effected by the reaction between the ramp surfaces by the assembly of the retaining means with the housing.

5. A gear as claimed in any one of the preceding claims in which the slipper includes means for direct manual rotation thereto about its axis to energise the spring means during assembly of the gear.

6. A gear as claimed in any one of the preceding claims in which the yoke member straddles the rack member to restrain displacement of the rack member in a direction which is parallel to the direction of the axis about which the pinion rotates and said straddling engagement between the rack and yoke members restrains rotation of the yoke member about the axis of the slipper.

7. A gear as claimed in any one of the preceding claims in which the slipper is mounted in a tubular portion of the yoke member and within which tubular portion the slipper is rotatable about said axis.

8. A gear as claimed in claim 7 in which the tubular portion has a substantially cylindrical bore co-axial with the axis about which the slipper is rotatable and the slipper is rotatable as a substantially complementary sliding fit in said bore.

9. A gear as claimed in either claim 7 or claim 8 in which a cavity is provided between the tubular portion of the yoke member and the slipper which cavity extends peripherally around the slipper and within which the spring means is located.

10. A gear as claimed in claim 8 in which the spring means is located in an annular peripheral cavity formed between the cylindrical bore of the tubular portion and an annular recess in the slipper.

11. A gear as claimed in any one of the preceding claims in which the spring means engages to react between the slipper and the yoke member.

12. A gear as claimed in any one of claims 1 to 10 in which the spring means engages to react between the slipper and the housing.

13. A gear as claimed in either claim 2 or claim 3 or in any one of claims 4 to 10 when appendant thereto in which the spring means engages to react between the slipper and the retaining means.

14. A gear as claimed in any one of claims 1 to 10 comprising an assembly of two slippers which are rotatable relative to each other and to the yoke member and which slippers co-operate with each other through said ramp surfaces, and wherein said slippers are coupled together by said spring means which biases one slipper to rotate relative to the other slipper to cause relative sliding movement between the ramp surfaces and urge the yoke member into supporting engagement with the rack member.

15. A gear as claimed in claim 14 in which the ramp surfaces have ratchet or saw toothed profiles and are located one on each slipper in substantially complementary engagement with each other.

16. A gear as claimed in any one of the preceding claims in which the spring means comprises a helical torsion spring which extends over the periphery of, and is anchored at one end to, the or a slipper and is anchored at its other end to provide, when energised, said rotatable biasing for the or a slipper.

17. A gear as claimed in any one of claims 1 to 1 5 in which the spring means comprises a helical tension spring which extends over the periphery of, and is anchored at one end to, the or a slipper and is anchored at its other end to provide, when energised, said rotatable biasing for the or a slipper.

18. A gear as claimed in any one of claims 1 to 1 5 in which the spring means comprises a blade spring which mounted in the or a slipper to extend therefrom to an anchorage which provides, when the blade spring is energised, said rotatable biasing for the or a slipper.

19. A gear as claimed in any one of claims 16 to 18 when appendant to any one of claims 1 to 1 3 in which the anchorage of the spring means remote from the slipper is restrained from displacement in a direction which extends circumferentially about the axis of the slipper but is capable of displacement in the direction of that axis.

20. A gear as claimed in any one of claims 1 to 13 in which the opposed ramp surfaces are of substantially helical formation concentric with the axis about which the slipper is rotatable.

21. A gear as claimed in any one of claims 1 to 1 3 in which the other of the opposed ramp surfaces is formed on the yoke member.

22. A gear as claimed in any one of the preceding claims in which the axis about which the or a slipper is rotatable is substantially perpendicular to a longitudinal axis along which the rack member is displaceable and substantially extends through the position of engagement between the rack and pinion teeth.

23. A rack and pinion gear of the kind specified and substantially as herein described with reference to the accompanying illustrative drawings.