GB2434623A

GB2434623A - Non-circular thrust washer in a differential gear

Info

Publication number: GB2434623A
Application number: GB0601718A
Authority: GB
Inventors: Roberto Gianone; Clive Harrup
Original assignee: Meritor Heavy Vehicle Systems Cameri SpA
Current assignee: Meritor Heavy Vehicle Systems Cameri SpA
Priority date: 2006-01-27
Filing date: 2006-01-27
Publication date: 2007-08-01
Also published as: GB0601718D0

Abstract

A thrust washer of a planetary gear of a differential assembly has an anti-rotation feature. In one embodiment washer (21) has flats (24). In another embodiment a washer (31) has protruding ribs (34). In each case the anti-rotation feature engages an abutment provided by a differential casing. The washers (21,31) are preferably sintered and have different profiles on the opposite faces thereof.

Description

1 2434623 P306374GB (05ARM0394) Improvements in Differential Gears This

invention relates to a differential gear assembly of a motor vehicle, and particularly the improvements in thrust bearing arrangements thereof.

Differential gears are provided in driven axles of vehicles to permit left and right driven wheels to rotate at different speeds whilst transmitting torque; as is well known, such an arrangement is required to permit a vehicle to turn from a straight line.

Many different kinds of differential gear have been proposed, but the most common consists of a casing in which two or four freely rotatable planetary gears are arranged in mesh with opposite pinion gears of the vehicle drive shafts. The casing carries an annular crown wheel which is driven by a pinion of an input shaft which is itself driven from the vehicle engine.

Casings for differential gears have a number of exacting requirements. They must of course have sufficient strength to adequately resist distortion underload. In particular the casing must be stiff enough to ensure that the teeth of the internal gears remain in accurate mesh so as to avoid unnecessary wear and noise. Furthermore the casing must be capable of being accurately machined to ensure that initial placement of components is precise, and that for example the bearing surfaces are correctly aligned.

A particular requirement in differential gear assemblies is to provide a thrust washer for each of the planetary gears, so as to prevent the hardened planetary gear from wearing away the relatively soft surface of the differential casing. Such wear is particularly important to avoid, since it alters the radial position of the respective gear(s) and hence affects correct meshing with the gear neighbours. Incorrect meshing may result in further wear, and excessive noise.

The bearing surface of the differential gears may be flat or part-spherical, and corresponding thrust surfaces are required in the differential casing. Spherical and flat thrust surfaces are however difficult to machine directly in the casing. The most easily manufactured thrust surface for the casing is cylindrical, but such a surface does not provide a matching face for either kind of planetary gear thrust face.

Hitherto, thrust washers for interposition between the respective planetary gears and differential casing have been formed from flat sheet metal, and for example spherically pressed to match corresponding surfaces of the gear and casing.

A further difficulty with such thrust washers is that rotation thereof with respect to the casing is preferably avoided since such rotation may result in wear of the casing thrust surface. Most advantageously this relative rotation should be between the respective thrust washer and planetary gear. In this way the thrust washer can be a relatively inexpensive service item which can be replaced if wear occurs.

The present invention aims to overcome these problems by providing an improved thrust washer, and differential gear assembly.

According to a first aspect of the invention there is provided an annular thrust washer of a planetary gear of a differential gear assembly, the thrust washer having a non-circular periphery adapted to engage a corresponding shoulder of a differential casing.

The non-circular periphery provides an asymmetry which can assure against relative rotation if in abutment with the corresponding shoulder. Preferably the asymmetry comprises a radially inwardly directed portion, such as a flat. A plurality of flats, may be provided in order to give multiple installation positions.

According to a second aspect of the invention there is provided an annular thrust washer of a planetary gear of a differential gear assembly, the thrust washer having a projection on one thrust face thereof adapted to engage a corresponding recess of a differential casing.

Such a thrust washer can also be latched against rotation relative to the casing. A suitable casing recess may be machined, and into which the projection is dogged. The projection may comprise two identical radial ribs aligned on a diameter of the thrust washer so as to give multiple installation positions. The ribs preferably extend over the full annular width of the thrust washer.

According to a third aspect of the invention there is provided a differential gear assembly having one of the aforesaid thrust washers in engagement with a corresponding shoulder or recess thereof.

In a preferred embodiment lubrication pathways are provided on the differential pinion side so as to permit oil to pass to the face of the thrust washer which is subjected to the relative rotation.

Preferably the thrust washer is sintered. This arrangement permits the two faces of the thrust washer to have different profiles formed in a single manufacturing step, with or without lubrication pathways. The differential casing side is preferably part-cylindrical, whereas the planetary gear side is flat.

In a preferred embodiment the thrust washer has four flat edges symmetrically arranged at right angles so as to have a square' appearance. The edges are preferably radiused at the corners of the washer. Such a washer is not sensitive to a single installation orientation. Preferably four lubrication pathways are provided extending radially through the respective corners of the washers.

Other features of the invention will be apparent from the following description of preferred embodiments of the invention shown by way of example only in the accompanying drawings in which:-Fig. 1 is an isometric view of one side of a thrust washer according to the invention.

Fig. 2 corresponds to Fig. 1 and shows the other side.

Fig. 3 is a transverse section through the washer of Fig. 1 on line 3-3.

Fig. 4 is a part-section through a differential gear assembly.

Fig. 5 is an isometric view of an alternative thrust washer according to the invention. i0

With reference to Fig. 4, a typical differential gear assembly 10 includes drive pinions 11,12 for connection to respective drive shafts, and planetary gears 13,14 therebetween.

Two or four identical planetary gears may be provided, according to the required capabilities of the assembly 10.

The pinions 11,12 and gears 13,14 are supported for rotation in a differential casing 15, the gears rotating on respective shafts 16,17. The gears 13,14 have respective thrust washers 18 to resist the inevitable radially outward thrust.

A thrust washer 21 according to the invention is illustrated in Figs. 1-3.

The washer 21 is formed of an annulus of sintered material and has a part cylindrical casing face 22, and a flat gear face 23. The four edges 24 are substantially straight, generally at right angles, and merge at somewhat rounded corners 25. Lubrication grooves 26 extend radially from the central aperture 27 to the rounded corners 25 as illustrated; these grooves are in straight line pairs at an included angle to 60 .

A sintered washer permits the faces 22,23 to be of different shapes so as to permit convenient and easy machining of the casing thrust face as part cylindrical surfaces wherein the gear thrust faces may be flat, or in the alternative part spherical. In the latter case, the washer face 23 could also be part-spherical, but flat faces are preferred.

The cylindrical thrust face 22 has the effect of giving two opposite thin edges 24, and two opposite thick edges 24, as clearly illustrated in Figs. 1-3.

In use the differential casing is provided with a shoulder 19 or other suitable projection which can closely engage a side of the washer 21 so as to prevent rotation thereof by virtue of the greater radial dimension at the corners 25.

It will be understood that the edges of the thrust washer need not be straight, so long as the radial dimension at the corner 25 is largest. Furthermore the shoulder 19 may be a corresponding straight edge or some other suitable shape. Straight edges are however preferred.

Fig. 5 illustrates an alternative embodiment in which a circular thrust washer 31 has a flat face 32 for contact with a planetary gear, and a part cylindrical face 33 for contact with a differential casing. Suitable oil grooves (not shown) are provided in the flat face in the manner illustrated in Fig. 2. The washer 31 is preferably sintered to form opposite faces of different shape in one manufacturing step.

The part cylindrical face 33 has two protruding radial ribs 34 arranged on a diameter and extending across the full width of the annulus. Each rib is of generally rectangular section and adapted to engage a part-circular square-sided recess of the differential casing. Such a recess can be machined relatively easily, e.g. by a wheel-type milling cutter.

Engagement of the recess and ribs 34 ensures anti-rotation. Furthermore the ribs 34 tend to self-locate, thus facilitating assembly of the differential gear.

Claims

Claims 1. An annular thrust washer of a planetary gear of a

differential gear assembly, the thrust washer having a non-circular periphery adapted to engage a corresponding shoulder of a differential casing.

2. A washer according to claim 1 wherein said periphery comprises a radially inwardly directed portion.

3. A washer according to claim 2 wherein said radially inwardly directed portion is a flat.

4. A washer according to claim 3 wherein said periphery comprises a plurality of equispaced flats.

5. A washer according to claim 4 and having four flats.

6. An annular thrust washer of a planetary gear of a differential gear assembly, the thrust washer having a projection on one thrust face thereof adapted to engage a corresponding recess of a differential casing.

7. A washer according to claim 6 wherein said projection comprises two identical radial ribs aligned on a diameter of the thrust washer.

8. A washer according to claim 7 wherein said ribs extend over the full annular width of the thrust washer.

9. A washer according to any preceding claim and having lubrication pathways on the differential pinion side.

10. A washer according to any preceding claim and being sintered, one face of the thrust washer being substantially part-cylindrical, and the other face being substantially flat.