WO2007085845A1

WO2007085845A1 - Differential gear casing

Info

Publication number: WO2007085845A1
Application number: PCT/GB2007/000270
Authority: WO
Inventors: Roberto Gianone
Original assignee: Meritor Heavy Vehicule Systems Cameri Spa
Priority date: 2006-01-27
Filing date: 2007-01-26
Publication date: 2007-08-02
Also published as: GB0601717D0

Abstract

A plug (12) for a bowl-like body (11) of a differential gear casing comprises an annular disc having a bearing sleeve (32, 33, 34) . The plug (12) is preferably a press flush fit in the body and is positioned by an internal shoulder (29) . The plug (12) and body (11) may be permanently connected by high energy beam welding at the interface A. The plug (12) can support an integral toothed member (35) of a differential lock.

Description

Differential Gear Casing

This invention relates to a differential gear assembly of a motor vehicle, and particularly to the differential gear casing and method of manufacture 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, hi 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 accurate, and that for example the bearing surfaces are correctly aligned; this latter requirement can be problematic in casings assembled from two major components.

Yet another difficulty is that the casing design must permit ready assembly thereof. For this purpose the casing may include windows to permit insertion of pinions, thrust washers and other components. However such windows inevitably weaken the casing wall, which must be correspondingly stiffened. They also result increased churning losses as the casing rotates in oil.

EP-A-0979960 discloses a differential casing comprising two major components, one each defining a journal of a drive shaft, and each component being in the form of a bowl. To form the casing one bowl is fitted within a flange defined by the other bowl, and each bowl defines a semicircular recess for each planetary gear pinion shaft. The respective semi-circular recesses fit together in register to define circular support surfaces for the pinion shaft(s).

A disadvantage of this arrangement is that extremely accurate machining of the semi-circular recesses is required in order to ensure that, on assembly, the two bowls define circular and concentric bearing surfaces of the required diameter.

What is required is a simplified construction which is both straightforward to manufacture and relatively easy to assemble.

According to a first aspect of the invention, there is provided a plug for a differential casing, the casing comprising a bowl having a rotational axis and defining apertures in the wall thereof for planetary gear shafts, and wherein the plug comprises an annular disc adapted to the mouth of the bowl and defining a circular sleeve on the rotational axis thereof, said sleeve defining on the inside a bearing support surface for a drive gear of a drive shaft, and on the outside a bearing support surface for an axle housing.

Such a plug is relatively easy to machine with concentricity of the critical bearing and location surfaces, and is preferably a press-fit in the circular mouth of said bowl.

The plug may be affixed in said mouth by a continuous circular weld at the interface, and in the preferred embodiment the plug is pressed flush into said bowl so as to provide a flat annular surface across said interface.

Preferably said plug includes on the sleeve side a concentric circular array of castellations adapted to provide one component of a differential lock whereby the plug is anchored on demand against rotation relative to an axle housing. Such an array is relatively easily formed, by e.g. forging, prior to machining of bearing and location surfaces, and preferably comprises curvic teeth directed parallel to the axle of rotation of the differential and on the radially inner border of said sleeve.

According to a second aspect of the present invention there is provided a casing of a differential gear, said casing comprising a main body and a cover, wherein said main body comprises a bowl having a rotational axis, a peripheral flange at the outer circumference of the mouth of the bowl, and a first bearing aperture in the base of the bowl and on said axis, and wherein said cover comprises a disc having a second bearing aperture therein, said main body and cover further include registration means to permit insertion of said disc into the mouth of said bowl so that said first and second apertures are aligned on said axis.

Such an arrangement permits the control surfaces for the drive shafts of the differential casing to be readily aligned thus ensuring that critical machining can be performed without difficulty since the registration means can be produced at the same time as the bearing apertures. The cover can be a relatively simple component since it defines only a common control surface, namely the bearing surfaces of one side of the differential assembly.

The cover is preferably a press-fit within the main body.

In the preferred embodiment, the main body comprises a circular recess adjacent the mouth thereof and adapted to receive a circular cover as a close fitting insert thereof, the recess also defining a shoulder to limit insertion of said cover to the desired depth, hi a preferred embodiment the shoulder is substantially radial and circular, and the periphery of the cover is substantially flush with the edge of said recess on assembly thereof. Thus the cover fits within the main body in the manner of a plug.

The cover may be adapted for permanent attachment to the main body by for example circular laser welding at the interface. The peripheral flange of the main body is, in the preferred embodiment continuous, substantially radial, and of substantially constant diameter. The side thereof adjacent the base of the bowl preferably includes a circular shoulder adapted to locate an annular crown wheel thereon. The crown wheel may be fixed to the flange by any suitable means, such as by circular laser welding from the mouth side of the main body.

The apertures of both main body and cover are preferably constituted by circular cylindrical projections so as to define internal bearing surfaces for opposed drive shafts, and external bearing surfaces for the usual rolling element support bearings.

According to a third aspect of the invention, there is provided a method of connecting a main body of a differential gear casing, a cover of a differential gear casing, and an annular crown wheel, the main body comprising a circular bowl-like casting having a peripheral circular flange at the mouth thereof, the cover comprising a disc insertable in said mouth, and the crown wheel being adapted to fit against said flange on the opposite side to said mouth, the method comprising the steps of welding said cover to the main body, and welding said main body to the crown wheel by concentric side by side circular welds at the radially inner and outer edges of said flange.

Such a method permits welding from one side, generally perpendicular to plane of the flange. The concentric welds may be made simultaneously and are for example electron beam or laser welds. The arrangement ensures that position and concentricity of components can be maintained during the welding operation.

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 an axial cross-section through a differential gear assembly incorporating the plug of the present invention. Fig. 2 is an isometric view of the main body of the casing of the invention from one side.

Fig. 3 corresponds to Fig. 2, and is a view from the other side.

Fig. 4 corresponds to Fig. 1 and shows an alternative means of retaining a pinion shaft.

With reference to the drawings, a differential gear assembly 10 has a casing comprising a main body 11 and a plug 12.

The main body 11 comprises a unitary symmetrical bowl-like casting having a major axis of rotation 13.

The main body has at its mouth 14 a generally radial continuous flange 15, which on the side opposite the mouth 14 defines a circular shoulder 16 adapted to receive a close-fitting, bevel gear crown wheel 17. As illustrated in Fig. 1, the flange has a circular recess 18 for a corresponding circular projection of the crown wheel, and a circular projection 19 for engagement in a corresponding recess of the crown wheel. On the side adjacent the mouth 14, the flange 15 is substantially plain (Fig. 3). The flange 15 and projection 19 ensure support for the crown wheel substantially on the thrust centreline thereof.

At the base, the main body 11 defines a circular cylindrical projection 21 concentric with the axis 13 and having an inner bearing support surface 22 for one drive shaft, and an outer bearing support surface 23 for the necessary rolling element bearing provided to mount the differential assembly in the axle housing.

The side wall of the main body 11 is of substantially constant radius adjacent the flange 15 and provides four equispaced holes 24 in a common plane at right angles to the axis

13. These holes 24 support the shafts on which the usual differential planetary gears rotate, a common shaft and two opposed gears being illustrated in Fig. 1. The other pair of opposed gears have respective shafts which may bear upon a respective flat pads on either side of the common shaft, to prevent rotation thereof.

At the periphery of each hole 24, the main body is thickened at the outside, and at the inside. Thickening 25 at the outside provides a locally greater depth of support for the planetary gear shafts. Thickening at the inside also increases the depth of support whilst providing a pad 26 which supports each planetary gear against radially outward thrust. It will be appreciated that such pads may be machined together concentric about axis 13, thus ensuring accuracy of manufacture.

Oil drain apertures 27 are provided around the main body 11 in the circular portion between the projection 21 and the pads 26.

At the inside of the mouth, a circular recess 28 is provided having a generally radial shoulder 29 axially outward of the pads 26. This recess 28 and shoulder 29 co-operate to provide axial location of a close fitting plug 12, which has a cylindrical projection 32 corresponding to projection 21 and for the opposite drive shaft/support bearing. The annular surface 30 immediately adjacent the recess 28 at the outside is orthogonal to the axis 13.

It will be readily appreciated that the majority of the major machined surface of differential gear are provided on the main body. These surfaces include inner and outer diameters of the projection 21; the shoulder 18 and projection 19; the recess 28 and shoulder 29. As a consequence these surfaces are more likely to be in the correct relative position with each other, and most importantly concentric about the major axis 13.

A threaded pin 36 may be used to retain each of the pinion shafts 40, as illustrated in Fig. 1.

Fig. 4 illustrates an alternative to the threaded stop pins 33. The pinion shafts 40 include a circular groove 41 adjacent the outer end, and an axial through hole 42 is formed in the casing 11 at the base of the recess 28 on the shoulder 29. A pin 43 may be dropped into the hole 42, and is of sufficient length to engage the groove 41 whilst being retained in place by the cover 12. If desired the pin 43 may be a push fit, for example a roll pin.

Concentricity of the recess 28 can be assured with ease during machining, and the corresponding diameter of the plug 12 is also easy to machine concentrically to size. Accordingly the plug 12 will be easily made concentric so that major axis 13 is straight after assembly.

The plug 12 has various circular surfaces concentric with the major axis 13 including an external surface 33 for a support bearing and an internal surface 34 for a half shaft drive gear, as illustrated.

The main body 11, plug 12 and crown wheel 17 may be permanently attached by welding. The arrangement of the invention is particularly advantageous because a double ring of concentric welds can be applied simultaneously from the same side, at locations identified by arrows A & B in Fig. 1. In particular the weld A is axial.

Also illustrated in Fig.1 is a concentric array of axially directed teeth 35 comprising one part of a differential lock whereby the differential assembly can be locked against relative rotation in the axle casing. The teeth 35 comprise a curvic coupling adapted to meet with another curvic coupling (not shown) anchored with respect to the axle housing and movable into engagement on demand by a suitable actuator. The teeth can conveniently be formed by forging and prior to machining of the control and location surfaces of the plug 12.

The plug 12 may be hardened with respect to the main body 11, and thus better able to provide bearing surfaces and the teeth 35. Furthermore, as illustrated, the plug may project axially on the inside to define a circular thrust face for the left side (as viewed) half shaft drive gear. No thrust washer is required, as compared with the right side.

Claims

1. A plug for a differential casing, the casing comprising a bowl having a rotational axis and defining apertures in the wall thereof for planetary gear shafts, and wherein the plug comprises an annular disc adapted to the mouth of the bowl and defining a circular sleeve on the rotational axis thereof, said sleeve defining on the inside a bearing support surface for a drive gear of a drive shaft, and on the outside a bearing support surface for an axle housing.

2. A plug according to claim 1 and having a circular outer periphery.

3. A plug according to claim 2 wherein said outer periphery comprises a continuous axially directed surface.

4. A plug according to claim 3 wherein on the sleeve side said outer periphery is immediately adjacent an annular radially directed surface.

5. A plug according to any preceding claim and including on the sleeve side a concentric circular array of castellations adapted to provide one component of a differential lock whereby in use the plug is anchored on demand against rotation relative to an axle housing.

6. A plug according to any preceding claim in combination with said bowl.

7. A plug and bowl combination according to claim 6 wherein said plug is a press-fit in the mouth of said bowl.

8. A plug and bowl combination according to claim 7 wherein said bowl includes a circular recess at the mouth thereof, said recess also defining a shoulder to limit insertion of said plug to the desired depth.

9. A plug and bowl combination according to claim 8 wherein said shoulder is substantially radial and circular.

10. A plug and bowl combination according to any of claims 6-9 and wherein said plug is permanently attached to the bowl by a circular high energy weld at the interface.