GB2557985A

GB2557985A - Differential gear assembly and method of assembly

Info

Publication number: GB2557985A
Application number: GB1621858.8A
Authority: GB
Inventors: Wheals Jonathan; Lewis Jackman Tobiasz
Original assignee: Ricardo UK Ltd
Current assignee: Ricardo UK Ltd
Priority date: 2016-12-21
Filing date: 2016-12-21
Publication date: 2018-07-04
Also published as: GB201621858D0

Abstract

A differential comprises a crown wheel assembly 300 mounted on a casing (200) within a crown wheel cavity (222) and includes an input opening for receiving a drive input. The crown wheel assembly 300 includes a crown gear 302 engaged with a plurality of pinion gears 602 and a crown wheel bearing 310, by means of which the crown gear 302 is rotatable relative to the casing (200). The casing (200) has first and second opposed side gear openings (218) in which side gears 500 are located. The side gears 500 are arranged to engage the pinion gears 602, and the differential is configured such that drive input to the crown gear 302 is transferred to the side gears 500 via the pinion gears 602. The bearing 310 is mounted in a support arrangement (400) comprising a stiffener bracket 402 which deflects such that the crown wheel is isolated. The stiffener bracket 402 includes upper and lower brackets 408, 410 which are fixed to the casing (200) by bolts after the crown gear has been inserted through the cavity (222).

Description

(71) Applicant(s):

Ricardo UK Ltd.

Shoreham Technical Centre, Bridgeworks, Shoreham by Sea, West Sussex, BN43 5FG, United Kingdom (72) Inventor(s):

Jonathan Wheals

Tobiasz Lewis Jackman (56) Documents Cited:

DE 102013016838 A1 US 6595085 B1 US 20140260789 A1 US 20130343691 A1 US 20050091823 A1

JP 2010223421 A US 5271294 A US 20140073471 A1 US 20080188343 A1 (58) Field of Search:

INT CLF16H

Other: ONLINE: EPODOC, WPI (74) Agent and/or Address for Service:

Withers 8t Rogers LLP

More London Riverside, LONDON, SE1 2AU, United Kingdom (54) Title ofthe Invention: Differential gear assembly and method of assembly Abstract Title: Differential gear assembly and method of assembly (57) A differential comprises a crown wheel assembly 300 mounted on a casing (200) within a crown wheel cavity (222) and includes an input opening for receiving a drive input. The crown wheel assembly 300 includes a crown gear 302 engaged with a plurality of pinion gears 602 and a crown wheel bearing 310, by means of which the crown gear 302 is rotatable relative to the casing (200). The casing (200) has first and second opposed side gear openings (218) in which side gears 500 are located. The side gears 500 are arranged to engage the pinion gears 602, and the differential is configured such that drive input to the crown gear 302 is transferred to the side gears 500 via the pinion gears 602. The bearing 310 is mounted in a support arrangement (400) comprising a stiffener bracket 402 which deflects such that the crown wheel is isolated. The stiffener bracket 402 includes upper and lower brackets 408, 410 which are fixed to the casing (200) by bolts after the crown gear has been inserted through the cavity (222).

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Differential gear assembly and method of assembly

BACKGROUND

The present invention relates to a differential gear assembly and a method of assembly therefore. In particular, the invention relates to a differential assembly having a compact and low mass construction as compared to known differentials. The invention also relates to a method of assembling such a differential

Differential gear assemblies are known and generally take the form of a housing having a crown wheel which is rotatably driven, for delivering drive to a pair of rotatable output shafts extending from the differential. Most commonly, drive is transferred from the crown wheel to the ouput shafts via a set of side gears. The differential allows power to be transferred to the rotatable output shafts, while allowing the output shafts to rotate at different speeds to one another (e.g. for going round a corner).

Such differential assemblies commonly include a carrier, generally fixed for rotation with the crown wheel. The carrier is arranged to receive pinion gears, mounted on rotatable shafts extending radially with respect to the axis of rotation of the crown wheel. The pinion gears engage the side gears, in order to deliver torque from the crown wheel to the side gears.

Assembly of pinion gears into the carrier can be a complex procedure requiring strength and dexterity. The procedure is also time-consuming. Moreover, conventional carriers represent a significant mass, adding weight to the differential and contributing to the moment of inertia of the differential, which can adversely affect its efficiency in use.

There is a need for improvements in differential gear assemblies.

The present invention provides an improved differential gear assembly, as well as a method of assembly of the same.

STATEMENTS OF INVENTION

The present invention provides a differential comprising a casing and a crown wheel assembly mounted on the casing. The casing defines a crown wheel cavity, within which the crown wheel assembly of the differential is located. The casing includes an input opening for receiving a drive input to the crown wheel assembly.

The crown wheel assembly includes a crown gear arranged for rotation relative to the casing. The crown wheel assembly includes a plurality of pinion gears, each pinion gear having an axis of rotation which is substantially radial with respect to the crown gear.

The differential includes a crown wheel bearing arrangement, by means of which the crown gear is rotatable relative to the casing.

The crown wheel assembly is mounted on the casing via a support arrangement located between the casing and crown wheel assembly.

In the prior art, it is known to mount the crown wheel or crown wheel bearing directly on the casing. If the casing deflects in use, the relative position of key meshing components of the differential can be changed (e.g. the relative position of the crown gear and an input pinion of the differential), leading to efficiency losses etc.

Use of the support assembly of the present invention advantageously provides an intermediate support for mounting of the crown wheel for rotation relative to the casing. By mounting the crown wheel on a support assembly intermediate the casing and the crown wheel assembly, deleterious effects of casing deflection can be reduced. The invention also provides for benefits in assembly and maintenance, as well as reductions in the overall mass of the differential.

Casing deflections can lead to inefficient loading or meshing between the crown gear and an input pinion of conventional differentials. By mounting the crown wheel on the support arrangement, the support arrangement can serve as a buffer which reduces the impact of such deflections, thereby making it possible to improve the efficiency of the differential.

In exemplary embodiments, the support arrangement is configured for reducing or preventing movement of the crown gear relative to a drive pinion of the differential, e.g.

as might otherwise occur due to external influences, in use, such as thermal expansion or loads from sources other than the crown wheel or drive pinion.

In exemplary embodiments, the support arrangement is configured to be capable of deflection during use of the differential, whilst maintaining support of the crown wheel assembly, e.g. such that a desired state of mesh between an input pinion of the differential and the crown gear, in use, can be maintained.

In exemplary embodiments, the support arrangement is configured to be capable of deflection during use of the differential, whilst maintaining support of the crown wheel assembly, such that the crown gear, in use, is isolated from substantial movement relative to the drive pinion.

In exemplary embodiments, the crown gear has a desired axis of rotation relative to the casing, and the support arrangement is configured to provide a buffer to substantially isolate the axis of rotation of the crown gear against the effects of thermal expansion/contraction of the casing, in use.

In exemplary embodiments, the crown gear has a desired axis of rotation relative to the casing, and the support arrangement is configured to prevent or minimise axial and radial deflection of the desired axis of rotation of the crown gear, in use.

In exemplary embodiments, the support arrangement comprises a plurality of brackets mounted on the casing, and wherein the crown wheel assembly is supported for rotation relative to the casing on said brackets.

In exemplary embodiments, each bracket includes flexible support arms, with at least one flexible support arm arranged at each end of the bracket. The flexible nature of the support arms contributes to reduce deleterious effects of casing deflection, for example.

In exemplary embodiments, the support arrangement is configured to define a desired fixed point, wherein each flexible support arm includes a web and, in use, a line extending through a respective web and said desired fixed point extends in a direction at least substantially perpendicular to said web. In exemplary embodiments, the desired fixed point may be intended to be coincident with a desired point of mesh between an input pinion of the differential and the crown gear, in use.

The invention has particular advantage if the casing is a structural unit of the differential (which may comprise a single unit or a composite unit assembled from multiple casing parts), configured to react loads generated between the crown wheel assembly, side gears and input opening when the differential is driven.

In exemplary embodiments, the casing defines a crown wheel cavity, and the crown gear extends from said cavity through a crown wheel aperture in the casing. Advantageously, the crown wheel aperture is sized so that the crown gear can be moved into/from said crown wheel cavity, for assembly/disassembly. In exemplary embodiments, said crown wheel aperture is formed in an upper or lower surface of the casing, and the differential is configured such that the crown gear can be moved in a substantially radial direction, with respect to the intended axis of rotation of the crown gear relative to the casing.

Others aspects and features of the invention will be apparent from the claims and following description of embodiments, made by way of example only, with reference to the following drawings, in which:

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 is an exploded perspective view of parts of an example differential assembly; Figure 2 is a perspective view of an example of support arrangement for a crown wheel assembly;

Figure 3 is a plan view from above an example of a bracket for use in a support arrangement of the kind shown in Figure 2;

Figures 4 to 12 show an example sequence of assembly for a differential of the kind shown in Figure 1;

Figures 13 and 14 show an example of a compact support and bearing arrangement for a 'bevelled gear' crown wheel, for use in a differential of the kind shown in Figure 1;

Figures 15 and 16 show an example of a compact support and bearing arrangement for a 'face gear' crown wheel, for use in a differential of the kind shown in Figure 1;

Figure 17 shows a cross-section through an example of a differential of the kind shown in

Figures 13 and 14, specifically with respect to an exemplary mounting of a drive pinion for the differential; and

Figure 18 shows a cross-section through an example of a differential of the kind shown in Figures 15 and 16, specifically with respect to an exemplary mounting of a drive pinion for the differential.

DETAILED DESCRIPTION OF EMBODIMENTS

Figure 1 shows an exploded view of part of a differential 100. The differential 100 includes a casing 200, into which a crown wheel assembly 300 is intended to be rotatably supported. In particular, the crown wheel assembly 300 is rotatably supported on a support arrangement 400, which is mounted directly onto the casing 200.

The casing 200 defines front and rear ends 202, 204, as well as opposing sides 206, 208, and upper and lower ends 210, 212.

The front end 202 defines an input aperture 216, through which an input shaft for an input pinion (not shown) extends in use. The input aperture 216 is offset (to the left as viewed) from a longitudinal axis of the casing 200, extending between the front and rear ends 202, 204. In other embodiments, the input aperture may be provided in the rear end 204.

The opposing sides 206, 208 of the casing 200 each include a side gear aperture 218, for supporting a side gear of the differential (not shown), so as to be closer to one side 206 of the casing than the other side 208. The side gear apertures 218 directly oppose one another, and are aligned with a transverse axis of the casing 200. In use, the alignment of the side gear apertures 218 defines an output axis of rotation of the differential 100.

The upper and lower ends 210, 212 each include a crown wheel aperture 220, forming part of a crown wheel cavity 222 of the casing 200.

The crown wheel assembly 300 will be described in more detail below, but includes a toothed crown gear 302 formed on a crown wheel portion 304 of the crown wheel assembly 300. The crown wheel assembly 300 also includes a planetary gear assembly 600 located radially inboard of the crown gear 302. The planetary gear assembly 600 is carried on the crown wheel assembly, and is configured for cooperation with side gears (not shown) of the differential. More specifically, the differential is configured such that such that drive input to the crown gear 302 is transferred to side gears of the differential via the planetary gear assembly 600.

In use, the crown gear 302 projects through the crown wheel aperture 220 in each of the upper and lower ends 210, 212 of the casing 200. One or more separate covers (not shown, but indicated at 250 in later Figures) may be provided to cover the crown wheel apertures 220, to seal the crown wheel cavity 222. Each cover is ideally substantially non-structural, and configured to cover the crown wheel assembly 300 and support arrangement 400 at the respective upper or lower end 210, 212 of the casing 200. Advantageously, such covers may be of lightweight, flexible construction (e.g. of an elastomer or plastics material).

Although not visible in Figure 1, the crown wheel assembly 300 further includes a crown wheel bearing arrangement (indicated generally at 310 in later Figures), by means of which the crown wheel assembly 300 is mounted for rotation relative to the casing 200. As will be described below, the support arrangement 400 supports the crown wheel assembly 300, via the crown wheel bearing 310.

As will be described below, by mounting the crown wheel assembly 300 on a support assembly 400 intermediate the casing 200 and the crown wheel assembly 300, deleterious effects of casing deflection can be reduced. This configuration also provides for benefits in assembly and maintenance, as well as reductions in the overall mass of the differential. Casing deflections can lead to inefficient loading or meshing between the crown gear and an input pinion of conventional differentials. By mounting the crown wheel assembly 300 on the support arrangement 400, the support arrangement 400 can serve as a buffer which reduces the impact of such deflections, thereby making it possible to improve the efficiency of the differential. More particularly, the support arrangement 400 can be configured for reducing or preventing movement of the crown gear relative to a drive pinion of the differential, e.g. as might otherwise occur due to external influences, in use, such as thermal expansion or loads from sources other than the crown wheel or drive pinion.

As will be described below, the support arrangement 400 can be configured to be capable of deflection during use of the differential, whilst maintaining support of the crown wheel assembly 300, e.g. such that a desired state of mesh between an input pinion of the differential and the crown gear, in use, can be maintained. The support arrangement 400 can be configured to be capable of deflection during use of the differential, whilst maintaining support of the crown wheel assembly 300, such that the crown gear, in use, is isolated from substantial movement relative to the drive pinion. In exemplary embodiments, the crown gear has a desired axis of rotation relative to the casing 200, and the support arrangement 400 is configured to provide a buffer to substantially isolate the axis of rotation of the crown gear against the effects of thermal expansion/contraction of the casing 200, in use, and/or to prevent or minimise axial and radial deflection of the desired axis of rotation of the crown gear, in use.

Referring also to Figure 2, it can be seen that the support arrangement 400 takes the form of a plurality of stiffener brackets 402, intended to be secured onto the casing 200 (e.g. via bolts 404). As mentioned above, the brackets 402 provide a support for rotation of the crown gear 302 with respect to the casing 200, via the crown wheel bearing 310. In the illustrated embodiment, the support arrangement 400 includes upper and lower brackets 402 (associated with a respective upper or lower end 212, 214 of the casing 200).

Each bracket 402 is intended to define a bridge, which extends over the crown wheel cavity 222 in a direction between the front and rear ends 202, 204 (e.g. in a direction substantially parallel with longitudinal axis of the casing 200, more preferably in a direction perpendicular to the transverse axis of the casing 200), in use.

Each bracket 402 defines first and second ends 408, 410, with a central portion 412 extending therebetween.

Each stiffener bracket 402 is configured for supporting the crown wheel bearing 310, more particularly an outer race (not shown) of the crown wheel bearing 310. IN the illustrated embodiment, the central portion 412 is configured for receiving a portion of the crown wheel bearing 310. More particularly, each stiffener bracket 402 includes channel 406, intended for receiving an outer race (not shown) of the crown wheel bearing 310. In the illustrated embodiment, each channel 406 is provided on an internal surface of the bracket 402, and defines an arc. As such, the crown wheel bearing 310 is arranged radially inboard of the brackets 402, in use.

As can be seen most clearly in Figure 2, the upper and lower brackets 402 of the illustrated embodiment are configured to cooperate with one another, e.g. to define an internal circle. In use, the brackets 402 cooperate to clamp the outer race of the crown wheel bearing 310. The upper and lower brackets 402 of the illustrated embodiment are intended to be secured to one another, in order to bring about the necessary clamping action for the crown wheel bearing 310. In the illustrated embodiment, the brackets 402 are bolted to one another, e.g. using bolts 414.

Referring also to Figure 3, each bracket 402 includes flexible support arms 416, arranged at each of said first and second ends 408, 410 of each bracket 402. Each support arm 416 includes a fixing portion 418 at a distal end thereof, by means of which the brackets 402 are secured to the casing 200, e.g. via the bolts 404. Bolt holes 420 also visible in this view, e.g. for use with bolts 414, for securing the upper and lower brackets 402 together.

In the illustrated embodiment, each bracket 402 includes first and second support arms 416 at a respective first and second end 408, 410. The first and second support arms 416 extend on opposing sides of the bracket 402. Each support arm 416 includes a web 422 extending between the central portion 412 and the fixing portion 418.

The support arrangement 400 is configured to define a desired fixed point 424, wherein, in use, a line extending through the web 422 of a respective support arm 416 and said fixed point 424 extends in a direction at least substantially perpendicular to said web 422. This concept is illustrated, by way of example, in Figure 3. The desired fixed point 424 is intended to be coincident with a desired point of mesh between an input pinion of the differential and the crown gear 302, in use. When the brackets 402 are secured onto the casing 200 and the crown wheel assembly 300 is rotatably supported on the support arrangement 400, the configuration of the flexible support arms 416 is intended to ensure that support arrangement 400 serves to be capable of deflection during use of the differential 100, whilst maintaining support of the crown wheel assembly 300, such that the crown gear 302, in use, is isolated from substantial movement relative to a drive pinion of the differential 100. In this way, the support arrangement 400 ensures that a desired state of mesh between an input pinion of the differential 100 and the crown gear 302, in use, is maintained.

It will be understood that it is advantageous for the support arrangement to be stiff enough to provide rigidity for supporting the crown wheel assembly in use, whilst the flexible arm components of the support assembly are sufficiently flexible in a desired direction (whilst remaining stiff in all other directions), to isolate the crown gear against significant deflection.

The casing 200 will typically be of aluminium construction, whereas the brackets 402 will be produced from steel. In exemplary embodiments, the casing is a structural unit of the differential 100 (which may comprise a single unit or a composite unit assembled from multiple casing parts), configured to react loads generated between the crown wheel assembly 300, side gears and input opening when the differential 100 is being driven.

Figures 4 to 12 show exemplary and advantageous stages of assembly of the differential 100.

Firstly, by comparing Figures 4 and 5, it can be seen that the crown wheel assembly 300 is moved into the crown wheel cavity 222 through the crown wheel aperture 220 in the upper end 210 of the casing 200. The configuration of the casing 200 is such that the crown wheel assembly 300 may be moved in a direction which is at least substantially radial with respect to the output axis of rotation of the casing 200, when locating the crown wheel assembly 300 in the crown wheel cavity 222. It will be understood that this radial direction of entry could also be achieved through the lower end of the casing 200. Moreover, it will be understood that entry of the crown wheel assembly into the casing 200 is not possible other than through the crown wheel aperture 220 in either the upper or lower ends of the casing 200.

By comparing Figures 5 and 6, it can be seen that the upper and lower brackets 402 are located with respect to one another to engage the outer race of the crown wheel bearing 310, and then secured to one another (e.g. using bolts 414), in order to clamp the crown wheel bearing 310 in place on the support arrangement, such that the outer race of the crown wheel bearing 310 is fixed, yet the crown gear 302 is capable of rotation, relative to the support assembly 400.

The brackets 402 are then secured onto the casing 200 (e.g. using bolts 404 - see Figure 7), which has the effect of setting the fixed point 424 of the brackets 402 at the desired point of mesh for the crown gear 302 and an input pinion of the differential 100 (to be introduced via input aperture 216).

Side gears 500 of the differential 100 are then introduced into the casing 200, via the side gear apertures 218 (see Figure 8). In exemplary embodiments, the side gears 500 define respective cavities 580, into which output shafts (not shown) can be received to deliver drive from the differential 100 to those output shafts.

As will be described below, the side gears 500 are configured for engagement with the planetary gear arrangement 600 of the crown wheel assembly 300. A central shaft 522 is introduced through one of the side gears 500 (see Figure 9), in order to extend through the planetary gear arrangement 600 and into the opposing side gear 500. A locking nut 524 is introduced through the opposing side gear 500, and engaged with the free end of the shaft 522. As will be described below, this arrangement serves to lock the side gears against axial movement with respect to one another.

Finally, an input pinion 550 is introduced through the input aperture 216 of the casing 200 (see Figure 10), and secured in place on the casing 200, to provide meshing engagement with the crown gear 302. Finally, covers 250 are fitted (see Figures 11 and 12), in order to seal the crown wheel assembly 300 and support arrangement 400 on the casing 200.

It will be understood that the differential 100 described above has multiple benefits, in terms of assembly and construction. The use of radial entry of the crown wheel assembly through the upper or lower ends of the casing is of particular benefit, in terms of ease of access etc. Moreover, the use of non-structural covers to seal the crown wheel and support arrangement can significantly reduce the mass of the differential.

Figures 13 and 14 relate to an example of a first embodiment of crown wheel assembly

300 for use in the differential 100 of Figures 1 to 12. In this embodiment, as in the embodiment of Figures 1 to 12, the crown gear 302 has a bevelled gear configuration.

The crown wheel assembly 300 includes a crown gear 302 intended for rotation relative to the casing 200. The crown wheel assembly 300 includes a planetary gear arrangement 600 having plurality of pinion gears 602 located radially within an inner radius of the crown gear 302. It will be understood that each pinion gear 602 has an axis of rotation which is substantially radial with respect to the crown gear 302. In exemplary embodiments, four pinion gears 602 are arranged radially within the inner diameter of the teeth of the crown gear (only two being visible in Figures 13 and 14), although other numbers of pinion gears such as 2, 3, 5, 6 or more, can be beneficial in certain arrangements.

Figures 13 and 14 also show a crown wheel bearing arrangement 310, by means of which the crown gear 302 is rotatable relative to the casing 200.

As in the embodiment of Figures 1 to 12, opposing side gears 500 are located in side gear openings 218 of the casing 200. It will be understood that the crown gear 302 is arranged for rotation relative to the casing 200, substantially coaxially with the side gear openings 218 of the casing 200. Moreover, the side gears 500 are arranged to engage the pinion gears 602, such that drive input to the crown gear 302 is transferred to the side gears 500, via the pinion gears 602.

As can be seen, each side gear 500 has a configuration having first and second sections 502, 504. The first section 502 is axially inboard of the second section 504, relative to the crown wheel assembly 300. Side gear teeth 506 are provided at one end of the first section 502. The first section 502 extends in an axial direction through the respective side gear opening 218 with a first diameter. The second section 504 is located distal said side gear teeth 506 and extends in an axial direction outside the casing 200 with a second diameter. The first diameter is smaller than the second diameter.

Advantageously, such a configuration allows for a more compact design of differential.

Moreover, as will be described below, such a configuration makes it possible to reduce seal and bearing diameters, which has a direct impact on the reduction of drag losses associated with conventional joint bearing and sealing arrangements.

As can be seen, each side gear 500 defines a stepped configuration between said first and second sections 502, 504. In exemplary embodiments, the second section 504 forms part of a CV joint track (e.g. an outer race thereof). CV joint tracks have a standard configuration. However, the modified configuration of side gears 500 allows seal diameters (outer diameter and running diameter) and bearing diameters to be reduced.

Each side gear 500 is configured to rotate within a side gear bearing 508. In this embodiment, the side gear bearing 508 is mounted in the side gear opening 218. Accordingly, the side gear bearing 508 has an outer diameter smaller than the diameter of the second section 504. The side gear bearing 508 is located on the first section 502. In this embodiment, the side gear bearing 508 takes the form of a deep groove ball bearing

A side gear seal 510 is located on said casing 200, between the first section 502 and said casing 200, e.g. between the outer surface of said first section 502 and an internal surface of the respective side gear opening 218.

The above described configuration provides a compact bearing and seal arrangement for the side gears 500.

The pinion gears 602 have teeth which engage the side gear teeth 506 at a location radially inboard of the first section 502. The teeth of the pinion gears 602 engage the side gear teeth 506 at a radial distance from the axis of rotation of the side gears 500 which is less than the first diameter of the first section 502. Again, this configuration provides a compact arrangement.

Advantageously, the side gear teeth 506 and teeth on the pinion gears 602 are of bevel gear configuration. Such a configuration is easier to locate for active mesh (without clash) than, say, teeth of 'face gear' configuration. It also makes it possible to reduce the height of the pinion gears, thereby allowing a more compact arrangement.

In this embodiment, a central locking arrangement 520 is provided, for preventing significant axial separation of the opposing side gears 500 in a direction towards the pinion gears, to ensure engagement of the side gear teeth with the pinion gears. The central locking arrangement includes a shaft 522 extending between the first and second side gears 500, and passing through a pinion mount 620 for the pinion gears 602. In exemplary embodiments, the shaft 522 is fixedly connected to and extends from a first side gear 500 and is rotatably connected to the opposing side gear 500 (via a locking nut 524 and thrust washer 526, for example), so as to axially retain the first and second side gears 500 in engagement with the pinion gears 602, while allowing relative rotation of the side gear members 500.

As can be seen, the outer diameter of the pinion mount 620 is smaller than the inner diameter of the crown wheel teeth on the crown gear 302.

In exemplary embodiments, the pinion mount 620 takes the form of a spider or cross-pin, having a plurality of radial members configured for supporting a respective pinion gear 602. The radial members may be mounted to or integrally formed with a central portion of the pinion mount 620. The pinion gears may be rotatably mounted on the radial members, e.g. via respective thrust washers or thrust bearings.

The radially inner diameter of the side gear teeth 506 and teeth on the pinion gears 602 is proximal said shaft 522. Locating these components close to the shaft 522, and thereby closer to the output axis of rotation, allows for a more compact arrangement.

The shaft 522 defines a central region 528 having a diameter smaller than the diameter at the ends of the shaft 522. More particularly, the central region 528 defines an arcuate depression or reduction in thickness in the wall of the shaft 522. This arrangement allows for the use of a more compact pinion mount 620, which increases the strength of this component. The diameter for the majority of the length of the shaft 522 must be small enough to pass through a central aperture of the pinion mount 620, e.g. (advantageously) with minimal working clearance. In use, the end regions of the shaft 522 are under greater stress than the central region 528, which makes it possible to reduce the outer diameter or wall thickness in that area, without compromising stiffness. Advantageously, the shaft 522 is a hollow member, thereby reducing mass.

Other features of the illustrated configuration provide for additional advantages related to the compact nature of the differential into which they are intended to be installed.

For example, the plane of rotation of the pinion gears 602 is radially inboard of the diameter of the first section 502 of the side gear 500, or is at least substantially aligned with the first diameter. In this embodiment, the teeth on the crown gear 302 are axially located within the width of the pinion gears 602. In this embodiment, the axis of rotation of the pinion gears 602 is located within the width of the crown gear teeth.

Advantageously, the ratio of the diameter of the first section 502 of the side gear 500 to the diameter of the second section 504 of the side gear 500 is in the range 0.6 to 0.8, e.g. 0.7.

The ratio of the diameter of the first portion 502 of the side gears 500 to the maximum diameter of the pinion gears 602 is less than or equal to 2, in exemplary embodiments (e.g. in the region of 1.2 for the illustrated embodiment). This arrangement allows for a very compact design, whilst avoiding gear clash.

As can be seen, the crown wheel bearing 310 is axially off-set from the pinion mount 620, e.g. to the left as viewed in Figure 13. In this embodiment, the crown gear 302 is rotatably supported on a single bearing 310, which is located adjacent a rear surface of the crown gear 302 (as opposed to the front 'toothed' surface of the crown gear) 302. This has the advantage that the pinion mount 620 does not have to be small enough to fit through the inner diameter of the crown wheel bearing. Moreover, the overall diameter of the bearing can be reduced, which means less cost, less mass and better efficiency.

The crown gear 302 (i.e teeth portion of the crown wheel assembly) is axially located within the width of the pinion gears 602. Moreover, the axis of rotation of the pinion gears 602 is located within the axial width of the crown gear teeth. This creates an advantageously compact assembly.

The outer diameter of the pinion mount 620 is smaller than the inner diameter of the crown wheel teeth, and is located in a recess 630 on a front face of the crown wheel portion 304. The pinion mount 620 is held in place in the recess via an annular plate 632.

The crown wheel assembly 300 includes a projection 320, extending axially from a rear portion of the crown gear 302. The crown wheel bearing 310 is supported on a radially outer side of the projection 320. Moreover, the radially inner side of the projection 320 is coincident with an inner radius of the crown gear 302. Furthermore, axial projection 320 extends in an axial direction at a radial distance inboard or coincident with an outer diameter of the side gears 500, contributing further to the compact nature of the differential 100.

A portion of the crown wheel bearing 310 extends into a space envelope corresponding the width of the pinion gears 602, at a radial distance greater than the maximum radial extent of the pinion gears 602 in use. This provides a particularly compact arrangement. The radially outer diameter of the side gear teeth 506 is smaller than the inner diameter of the crown wheel bearing, which also provides for a compact arrangement.

An inner race of the crown wheel bearing 310 is mounted on the axial projection 320. The inner race has first and second portions 314, 314', which are separate from one another in an axial direction. In this embodiment, the first portion 314 of the inner race is adjacent the crown gear 302 and is an integral part of said axial projection 320, which means there are fewer components to manufacture. In other embodiments, the first portion 314 is supported on the radially outer side of the axial projection 320. The second portion 314' of the inner race 312 is supported on the radially outer side of the axial projection 320.

The ratio of the inner diameter of the crown wheel portion 304 (e.g. the inner diameter of the axial projection 320 on which the inner race 312 of the crown wheel bearing 310 is mounted) to the first diameter of the side gears is in the range 1.1 to 1.5, e.g. 1.25 in the illustrated embodiment. This configuration contributes to the compact arrangement of the crown wheel assembly 300 and differential 100.

Rolling elements 316 are located between inner and outer races 312, 318 of the bearing 310. The central axis of the rolling elements 316 is located at a radial distance greater than the inner diameter of the crown gear 302 but smaller than the outer diameter of the crown gear 302, more particularly between the inner and outer diameter of the teeth on the crown gear 302.

The rolling elements 316 of the bearing 310 are provided as first and second rows or arrays of rolling elements 316, said first and second rows spaced apart axially from one another. The size (e.g. diameter) of the rolling elements 316 of the first row (e.g. closest to the crown gear 302) is greater than the size (e.g. diameter) of the rolling elements 316 in the second row. The rolling elements closest to the crown wheel take the greatest proportion of the mesh load, and so making them larger strengthens the arrangement. The rolling elements 316 in each row define a central axis, and the central axes of the rows are offset from one another in a radial direction, yet the radial distance (from the axis of rotation of the side gears 500) of the outer diameter of both rows of roller elements 316 is the same. A central portion of the bearing outer race 318 is located at a radial distance between the inner and outer diameter of the crown gear 302, more particularly between the inner and outer diameter of the teeth on the crown gear 302.

As described with reference to Figures 1 to 12, the brackets 402 of the support arrangement 400 may serve as a clamp, into which the outer race 318 is mounted. As shown in the Figures, brackets 402 are axially off-set from the axis of rotation of the crown gear 302.

The configuration shown in Figures 13 and 14 also provides other beneficial features, with respect to the compact nature of the arrangement. For example, the crown wheel bearing 310 is located at a position which is radially outboard of the pinion gears 602 and radially inboard of the outer diameter of the crown gear 302. As can be seen, a portion of the crown wheel bearing 310 is located within a space envelope defined by the axial width of the pinion gears 602. Moreover, at least a portion of the crown wheel bearing 310 (proximal the crown gear 302) is in axial alignment, yet is located radially outboard of, a zone of mesh between the pinion gears 602 and the side gear teeth 506. In addition, the outer diameter of the side gear teeth 506 is smaller than the inner diameter of the crown wheel bearing 310.

Figures 15 and 16 relate to an example of a second embodiment of crown wheel assembly

300 for use in the differential 100 of Figures 1 to 12. In this embodiment, the crown gear has a face gear configuration, but in many other respects is the same or substantially similar to the embodiment of Figures 13 and 14. As such, the same reference numerals are used for corresponding components etc.

The use of a stepped side gear configuration in combination with the illustrated arrangements of bevel pinion gears has an added benefit of creating space proximal the crown gear, into which it is possible to mount a bearing for an end of a drive pinion for the differential. In particular it is possible to provide multiple bearings, one on either side of a zone of mesh between the drive pinion and the crown gear.

Figure 17 shows an example of a drive pinion bearing arrangement for the embodiment of Figures 13 and 14 (i.e. in which the crown gear has a bevel gear configuration), whereas Figure 18 shows an example of a drive pinion bearing arrangement for the embodiment of Figures 15 and 16 (i.e. in which the crown gear has a face gear configuration). In many other respects, the embodiments of Figures 17 and 18 are the same or substantially similar, such that the same reference numerals are used for corresponding components etc.

In the example of Figure 17, the drive pinion bearing arrangement 700 has first and second bearings 702, 704. The bearing 702 is radially innermost with respect to the crown gear 302, and takes for form of a needle roller bearing, whereas the bearing 704 is radially outermost and takes the form of a pair of pair of opposed angular contact ball bearings. The axial position of the teeth of the drive pinion relative to the toothed portion of the crown gear is important for bevel gears, and so the use of multiple angular contact ball bearings at the radially outermost side of the straddled drive pinion bearing arrangement 700 provides a desirable level of clamping force to prevent undue displacement of the drive pinion relative to the crown gear along the axis of rotation of the drive pinion. The same degree of axial certainty is not as critical for face gear configurations. As such, the radially innermost bearing 702 is a needle roller bearing (as in the embodiment of Figure 17), but the radially outermost bearing 704 is a single deep groove ball bearing. This allows for a shorter length of drive pinion shaft than is achievable in the embodiment of Figure 18, thereby reducing material costs and mass.

Claims

1. A differential comprising a casing and a crown wheel assembly mounted on the casing, wherein:

the casing defines a crown wheel cavity, within which the crown wheel assembly of the differential is located; and the casing includes an input opening for receiving a drive input to the crown wheel assembly;

further wherein:

the crown wheel assembly includes a crown gear arranged for rotation relative to the casing; and the crown wheel assembly includes a plurality of pinion gears, each pinion gear having an axis of rotation which is substantially radial with respect to the crown gear; and wherein the differential includes a crown wheel bearing arrangement, by means of which the crown gear is rotatable relative to the casing;

further wherein the crown wheel assembly is mounted on the casing via a support arrangement located between the casing and crown wheel assembly.

2. A differential according to claim 1, wherein the crown gear has a desired axis of rotation relative to the casing, and the support arrangement is configured to provide a buffer to substantially isolate the axis of rotation of the crown gear against the effects of thermal expansion/contraction of the casing, in use.

3. A differential according to claim 1 or claim 2, wherein the crown gear has a desired axis of rotation relative to the casing, and the support arrangement is configured to prevent or minimise axial and radial deflection of the desired axis of rotation of the crown gear, in use.

4. A differential according to any of claims 1 to 3, wherein the support arrangement comprises a plurality of brackets mounted on the casing, and the crown wheel assembly is supported for rotation relative to the casing on said brackets.

5. A differential according to claim 4, wherein each bracket is configured for supporting the crown wheel bearing.

6. A differential according to claim 4 or claim 5, wherein the crown wheel bearing defines and inner race and an outer race, and wherein the outer race is directly is supported by said plurality of brackets.

7. A differential according to claim 6, wherein each bracket is configured for receiving a portion of the outer race of the crown wheel bearing.

8. A differential according to claim 7, wherein each bracket includes channel, intended for receiving a portion of the outer race of the crown wheel bearing.

9. A differential according to any of claims 4 to 8, wherein the crown wheel bearing is arranged radially inboard of the brackets, in use.

10. A differential according to any of claims 4 to 9, wherein each bracket defines a bridge, which extends over the crown wheel cavity in a direction between front and rear ends of the casing (e.g. in a direction perpendicular to a transverse axis of the casing, or in a direction substantially parallel with a longitudinal axis of the casing).

11. A differential according to any of claims 4 to 10, wherein each bracket defines first and second ends, with a central portion extending therebetween.

12. A differential according to claim 11, wherein the central portion is configured for receiving a portion of the crown wheel bearing.

13. A differential according to any of claims 4 to 12, wherein the support arrangement includes upper and lower brackets (e.g. associated with a respective upper or lower end of the casing).

14. A differential according to claim 13, wherein the upper and lower brackets are configured to cooperate with one another to clamp the crown wheel bearing, in use.

15. A differential according to claim 14, wherein the upper and lower brackets are configured to define an internal circle, for supporting the crown wheel bearing.

16. A differential according to any of claims 13 to 15, wherein the upper and lower brackets are secured to one another, in use.

17. A differential according to any of claims 4 to 16, wherein each bracket includes flexible support arms, with at least one arranged at each end of the bracket.

18. A differential according to claim 17, wherein each arm includes a fixing portion at a distal end thereof, for use in securing the bracket to the casing.

19. A differential according to claim 17 or claim 18, wherein each bracket includes first and second support arms at a respective first and second end of the bracket.

20. A differential according to claim 19, wherein the first and second support arms extend from opposing sides of the bracket.

21. A differential according to claim 19 or claim 20, each support arm includes a web and the support arrangement is configured to define a desired fixed point, further wherein, in use, a line extending through said web and said fixed point extends in a direction at least substantially perpendicular to said web.

22. A differential according to claim 21, wherein the desired fixed point is intended to be coincident with a desired point of mesh between an input pinion of the differential and the crown gear, in use.

23. A differential according to any preceding claim, wherein the support arrangement is configured to be capable of deflection during use of the differential, whilst maintaining support of the crown wheel assembly, such that a desired state of mesh between an input pinion of the differential and the crown gear, in use, is maintained.

24. A differential according to any preceding claim, wherein the support arrangement is configured to be capable of deflection during use of the differential, whilst maintaining support of the crown wheel assembly, such that the crown gear, in use, is isolated from substantial movement relative to the drive pinion.

25. A differential according to any preceding claim, wherein the casing defines front and rear ends, first and second opposing sides, and upper and lower ends, and wherein the crown gear projects through an aperture in each of the upper and lower ends of the casing.

26. A differential assembly according to claim 25, wherein the front end or rear end includes the input aperture for a drive pinion, and wherein the first and second opposing sides include side apertures through which output members may extend.

27. A differential according to any preceding claim, wherein the input aperture is offset from a longitudinal axis of the casing extending between the front and rear ends.

28. A differential according to any preceding claim, wherein the casing has first and second opposed side gear openings in which side gear members are located, and wherein the side gears are arranged to engage the pinion gears, wherein the differential is configured such that drive input to the crown gear is transferred to the side gears via the pinion gears.

29. A differential according to claim 28, wherein the crown gear is arranged for rotation relative to the casing substantially coaxially with the side gear openings of the casing.

30. A differential according to any preceding claim, wherein the crown wheel assembly is supported for rotation relative to the casing on said support arrangement.

31. A differential according to any preceding claim, wherein the casing is a structural unit of the differential (which may comprise a single unit or a composite unit assembled from multiple casing parts), configured to react loads generated between the crown wheel assembly, side gears and input opening when the differential is driven.

32. A differential according to any preceding claim, wherein the support arrangement defines a plurality of fixing portions, and the casing includes a plurality of discrete location points (e.g. sockets) configured for receiving a respective fixing portion of the support arrangement.

33. A differential according to any preceding claim, wherein the support arrangement is produced from steel.

34. A differential according to any preceding claim, comprising at least one substantially non-structural cover mounted on the casing and arranged to seal the crown wheel cavity and crown wheel assembly located therein.

35. A differential according to claim 34, wherein at least one substantially nonstructural cover is configured to cover and the support arrangement.

36. A differential according to claim 34 or claim 35, wherein the substantially nonstructural cover is flexible, e.g. made of an elastomer or flexible plastics material.

37. A differential according to any preceding claim, wherein the casing defines a crown wheel cavity, and the crown gear extends from said cavity through a crown wheel aperture in the casing, wherein the crown wheel aperture is sized so that the crown gear can be moved into/from said crown wheel cavity, for assembly/disassembly; and further wherein said crown wheel aperture is formed in an upper or lower surface of the casing, and the differential is configured such that the crown gear can be moved in a substantially radial direction, with respect to the intended axis of rotation of the crown gear relative to the casing.

38. A differential according to claim 37, wherein at least a portion of the support arrangement also extends beyond the crown wheel cavity through said crown wheel aperture.

39. A differential according to any preceding claim, wherein the crown wheel assembly is radially supported by a single crown wheel bearing.

Intellectual

Property

Office

Application No: GB1621858.8