GB2434622A

GB2434622A - Differential gear with staked pinion shaft

Info

Publication number: GB2434622A
Application number: GB0601715A
Authority: GB
Inventors: Roberto Gianone; Ugo Costelli
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: GB0601715D0

Abstract

A planetary gear of a vehicle differential assembly has a shaft (16,17,18) fixed in a casing (11). The shaft has a dished outer end (26) with a chamfer (27) around the periphery. A circular land (28) provides a ring of material adapted to be urged outwardly by a staking tool so as to fix the shaft (16,17,18) within the casing (11).

Description

1 2434622 P306382GB (05ARM0396) Improvements in Differential Gear

Assemblies This invention relates to an improved differential gear assembly of a motor vehicle, and particularly to a reduction of components therefor.

Differential gears are provided in the driven axles of vehicles to permit left and right driving wheels to rotate at different speeds whilst transmitting torque.

The most common kind of differential gear comprises a casing in which two opposite drive pinions are in mesh with two or four freely rotatable planetary gears. The casing is driven by a large input gear, and is itself supported for rotation within the vehicle axle casing.

The planetary gears are generally mounted on a respective rotatable shaft, and both the gear and shaft are hardened to resist wear thereof. Each planetary gear usually has a thrust washer to resist radially outward forces. The respective pins and thrust washers must be anchored against rotation relative to the relatively soft casing so as to prevent rapid wear thereof.

Furthermore the planetary gear shafts must be anchored against radially outward movement as the casing rotates in use, and in one prior art method, suitable pins or screws are provided to engage the head of each shaft after assembly into the casing.

This kind of retention solution requires additional machining of the casing and of the respective shafts, and may reduce the strength thereof. The number of separate components is also increased by the additional pins or screws.

What is required is an inexpensive solution which both retains the pinion shafts in axial position and against rotational movement.

According to a first aspect of the invention there is provided a differential gear assembly including a casing having a rotational axis and a shaft in a through hole of the casing and orthogonal to said axis, said shaft being adapted to support a planetary pinion for rotation thereon, and said shaft being substantially flush with the exterior of said casing, having a peripheral chamfer at the radially outer end thereof, a land immediately inboard of said chamfer, and a recess inboard of said land, wherein said land provides staking material adapted to be permanently deformed radially outwardly of the shaft to engage said casing and thereby retain said shaft against movement radially outwardly of the casing.

Such an arrangement permits an adequate retention force to be obtained without the requirement for additional retention means, such as pins or screws.

In one embodiment, four equispaced portions of said land are staked so as to permanently deform shaft material against the corresponding wall of said through hole.

Preferably said recess is circular and continuous, and may comprise a dished end of the shaft.

Said chamfer is preferably straight at e.g. 30-60 , most preferably 45 , and of constant width.

On one embodiment said land comprises a circular flat face extending generally radially of said shaft, and of substantially constant width. Preferably the width of said land and of said chamfer is substantially equal.

In a preferred embodiment said dished end is symmetrical and of substantially constant curvature; the maximum depth of the dish is preferably greater than the axial extent of said chamfer.

According to a second aspect of the invention, there is provided a staking tool for planetary gear shaft of a differential gear assembly, said shaft having a peripheral chamfer at one end, a land immediately inboard of said chamfer, and a recess inboard of said land, and said staking tool comprising a generally cylindrical body having a plurality of ball bearings mounted on one end thereof in a common plane orthogonal to the longitudinal axis of the body and substantially equispaced on a pitch circle substantially equivalent to a diameter of said land.

Such a tool can provide an adequate retention force against movement of said shaft axially thereof. Ball bearings are relatively hard, inexpensive, and thus suitable for use as the working elements.

Preferably four equispaced and identical ball bearings are provided, each ball bearing having a diameter greater than the width of said land, and preferably at least twice the width of said land. Preferably the pivot circle of said ball bearing is centred on said land and on the axis of said shaft.

Other features of the invention will be apparent from the following description of a preferred embodiment shown by way of example only in the accompanying drawings in which:-Fig. 1 is a schematic part cross-section through a differential gear assembly according to the invention, and including a staking tool.

Fig. 2 is a scrap section showing interlocking of pinion shafts.

Fig. 3 is an elevation of the inner end of a short pinion shaft.

Fig. 4 is an end view of the inner plate of a staking tool.

Fig. 5 is an end view of the assembled staking tool of Fig. 4.

Fig. 6 is a part sectional view on line 6-6 of Fig.4; and Fig. 7 is an enlarged end view of a pinion shaft when staked.

With reference to the drawings, a differential gear assembly comprises a half-casing 11 rotationally symmetrical about an axis 12 and defining bearing surfaces 13, 14 associated respectively with an output shaft and an axle housing. The casing has a radially extending circular flange 15 for mounting of a crown wheel drive gear. The casing is adapted to four equispaced planetary gears (not shown) which are rotatable about orthogonal axes in a common plane, and about respective pinion shafts 16, 17, 18. As described thus far, the assembly is of a conventional kind.

It will be well understood that a single pinion shaft 17 may be provided for one opposite pair of planetary gears, but two separate shafts 16, 18 are necessary for the other pair of gears because the shafts have crossing axes in a common plane.

One of the short shafts 16 will now be described in detail. As will become apparent the other short shaft 18 is identical, and the long shaft 17 comprises two short shaft portions with a central linking region 19.

The shaft 16 is rotationally symmetrical and has a mid-region 21 adapted to support a planetary gear pinion for rotation thereon. A radially outer portion 22 is a close fit in a corresponding aperture of the casing 11. The radially inner portion 23 bears on one side of the long pinion shaft 17, and the opposite identical shaft 18 bears on the other side as illustrated.

At its mid-portion 19, the long shaft 17 has opposite flats 24 machined thereon to support the respective ends of the short shafts 16, 18. Rotation of the long shaft 17 in the casing 12 is thereby prevented.

Each short shaft 16, 18 is also reduced in diameter at the sides, as illustrated in Figs. 2 and 3 so as to form shoulders 25 to fit against the sides of the flats 24, and this allows the long shaft to lock with the short shafts to prevent rotation of the short shafts.

The shafts 16, 17, 18 must be radially retained against the relatively small centripetal force which occurs when the casing is rotating in the axle. For this purpose, the outer end of each shaft has a circular dish 26 at the centre, and a circular chamfer 27 at the periphery. Between the dish and chamfer is provided a generally flat circular land 28 having a width of about 20% of the radius of the shaft.

A staking tool 30 is provided to deform regions of the land and chamfer so as to cause a locking force radially of the respective shaft which is sufficient to prevent shaft movement radially with respect to the axis 12.

The staking tool comprises a generally cylindrical body 31 having a head 32 attached thereto by countersunk screw 33. The head comprises an inner plate 34 and an outer plate 35. The inner plate 34 defines four circumferentially spaced recesses 36 for respective ball bearings 37, which are retained in place and protrude slightly through four respective apertures 38 of the outer plate 35. The recesses 36 are not strictly necessary since sufficient location and retention for the ball bearings 37 can be provided by the outer plate 35; however the recesses are an aid to assembly and can isolate the outer plate 35 from transverse forces. If required both the inner plate 34 and outer plate 35 can be dogged against relative rotation with each other and with the body 31, but the clamping force of the screw may be sufficient. One side of the tool 30 has a flat 39, which ensures clearance with the closely adjacent flange 15.

In use the shafts are supported 16, 17, 18 and the staking tool 30 pressed down on the land 28 to deform it into the region of the chamfer 27, and thereby induce a permanent deformation against the corresponding wall of the casing.

An example view of a deformed shaft 16, 17, 18 is illustrated in Fig. 7, the land 28 being indented in four locations 40, and material being squeezed into the region of the chamfer 27 in order to radially lock the shaft to the casing 11 by radial force.

The size of the ball bearing 37, the position and protrusion thereof, and the staking force can be selected empirically to give a desired indentation sufficient to lock the shafts in place.

On one example, the shafts 16, 17, 18 have an approximate diameter of 35mm, the other dimensions being in relative proportion, as illustrated in Fig. 1. Typically four equispaced ball bearings of 7mm diameter are used for staking, and generate axial retention loads according to the following table: r Axial Staking Load Force to Shift Staked Shaft 5OOOk 1180kg 10000kg 2520kg I 15000kg 3340kg Such forces are more than adequate to resist radially outward movement of the shafts in use.

Claims

Claims 1. A differential gear assembly including a casing having a

rotational axis and a shaft in a through hole orthogonal to said axis, said shaft being adapted to support a planetary pinion for rotation thereon, and said shaft being substantially flush with the exterior of said casing, having a peripheral chamfer at the radially outer end thereof, a land immediately inboard of said chamfer, and a recess inboard of said land, wherein said land provides staking material adapted to be permanently deformed radially outwardly of the shaft to engage said casing and thereby retain said shaft against movement radially outwardly of the casing.

2. An assembly according to claim 1 wherein four equispaced portions of said land are staked so as to permanently deform shaft material against the corresponding wall of said through hole.

3. An assembly according to claim I or claim 2 wherein said recess is circular and continuous.

4. An assembly according to claim 3 wherein said recess comprises a dished end of the shaft.

5. An assembly according to claim 4 wherein said dished end is symmetrical and of substantially constant curvature.

6. An assembly according to claim 5 wherein the maximum depth of the dish is greater than the axial extent of said chamfer.

7. An assembly according to any preceding claim wherein said chamfer is straight.

8. An assembly according to claim 7 wherein said chamfer is at 450 to said axis, and of constant width.

9. An assembly according to any preceding claim wherein said land comprises a circular flat face extending generally radially of said shaft, and of substantially constant width.

10. An assembly according to claim 9 wherein the width of said land and of said chamfer is substantially equal.