GB2466008A

GB2466008A - Differential gear with a friction reducing sliding coating

Info

Publication number: GB2466008A
Application number: GB0822218A
Authority: GB
Inventors: Mikael Westerberg; Anders Karlsson
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2008-12-05
Filing date: 2008-12-05
Publication date: 2010-06-09
Anticipated expiration: 2028-12-05
Also published as: GB2466008B; GB0822218D0

Abstract

A differential gear 10, for a motor vehicle, comprises a plurality of gear wheels 22, 24 for transferring torque and a carrier housing 12 the plurality of gear wheels 22, 24. Between the carrier housing 12 and at least one of the gear wheels 22, 24 there is a friction reducing sliding coating. Since axial thrust washers (28, fig 1) of the differential gear 10 may be replaced by the sliding coating, the size of the differential gear (10) may be reduced and/or the size of the gear wheels 22, 24 may be increased for transmitting a higher maximum transferrable torque, wherein wear is not increased and the life time of the differential gear 10 is increased. The surface coating may be applied by sputtering or roll bonding and may comprise of aluminium, copper, tin, lead or nickel. The carrier housing 12 may be split into a first carrier part and a second carrier part wherein a ratio of an inner surface of the first carrier part with respect to an overall inner surface of the carrier housing 12 is greater or equal to 25% and less than or equal to 75%.

Description

Differential gear

Description

The invention relates to differential gears, which may be used for transferring a torque provided by an engine of a motor vehicle to different wheels, particularly rear wheels, of the motor vehicle.

A typical differential gear comprises a carrier, which is turned by an applied torque. The carrier houses a plurality of gearwheels for transferring torque.

Between an inner surface of the carrier and each gear wheel an axial thrust washer, like an annular washer, is provided for reducing friction and wear.

It is a disadvantage of such kind of a differential gear that the maximum transferrable torque is low in comparison to the size of the differential gear. There is a permanent need that the size of a differential gear should be reduced and/or the maximum transferrable torque is increased without reducing the life time of the differential gear.

It is the object of the invention to provide a differential gear, which is able to provide a reduced size and/or an increased maximum transferrable torque without reducing the life time.

The solution of the object is achieved by the features of claim 1. Preferred embodiments are given by the dependent claims.

The differential gear according to the invention, which may be used for a motor vehicle, comprises a plurality of gear wheels for transferring torque and a carrier housing the plurality of gear wheels. According to the invention between the carrier and at least one of the gear wheels a sliding coating is provided.

Due to the sliding coating an axial thrust washer, like an annular washer, can be omitted. The sealing by means of a washer or the like can be replaced by the sliding coating. Since the sliding coating comprises a significantly reduced thickness in comparison to the axial thrust washer the size of the differential gear may be reduced by the difference of the thicknesses of the axial thrust washer and the sliding coating. Further the size of the gear wheel assigned to the sliding coating may be increased by the difference of the thicknesses of the axial thrust washer and the sliding coating. Due to the increased size the gear wheel is more stable and may transfer an increased maximum transferrable torque. Since the sliding coating provides a low friction, a low wear is maintained leading to a high life time. Due to the sliding coating a reduction of the life time of the differential gear is prevented.

Particularly the at least one gear wheel is only via the sliding coating in relative moving contact to the carrier. Since only the sliding coating provides a bearing between an inner surface of the carrier and the at least one gear wheel, further bearings are not necessary. Only the thickness of the sliding bearing is relevant for defining the distance of the at least one gear wheel to the inner surface of the carrier.

Particularly the sliding coating may be provided by a surface treatment, so that the thickness of the sliding coating may be mainly zero.

Preferably the at least one sliding coating is the only bearing member between the plurality of gear wheels and an inner surface of the carrier. Particularly all gear wheels are only via the sliding coating in contact to the inner surface of the carrier. All axial thrust washers are omitted. This leads to a high amount by which the size of the differential can be reduced and/or by which the size of the gear wheels may be increased.

Particularly the carrier and/or the at least one gear wheel comprises the sliding coating. The sliding coating may be provided on the inner surface of the carrier and/or on an outer surface of the at least one gear wheel. A material combination is particularly chosen by means of the at least one sliding coating with respect to a low friction and a high durability at preferably low costs.

In a preferred embodiment the plurality of gear wheels comprises at least one planet gear supported by the carrier and at least two side gears in meshing contact with the planet gear, wherein the side gears are only via the sliding coating in contact to the carrier.

Each of the side gears may be connected via an axle to a wheel, particularly rear wheel of a motor vehicle. The planet gear may be rotatably supported by the carrier for instance by means of a pin-like support axle protruding from the carrier. The only contact between the carrier as a whole and the side gears is only via the sliding coating. Since the side gears may be connected to an axle for a rear wheel or a front wheel, further support between the side gears to the carrier is, if so at all, only provided by the axle, which may be guided by the carrier by means of a bearing or the like. Since this guidance of the axle is provided outside the space provided by the carrier for housing the gear wheels, the bearings for the axles do not increase the size of the carrier.

Particularly the sliding coating is provided by sputtering or roll bonding. This leads to a cost efficient coating of the carrier and/or the gear wheels.

It is particularly possible to coat only a part of a surface, for instance where a direct contact between the carrier and the gear wheels is expected. Thus, only a few amount of coating material is necessary for providing the sliding coating.

In a preferred embodiment the sliding coating comprises at least one of the elements aluminum, copper, tin, lead, nickel. Such kind of a coating material comprises a good plasticity and provides particularly in the presence of nickel a high durability mainly without the risk of migrating copper. Further suitable coatings are known from the technical field of coating light alloy cylinder bores of an engine of a motor vehicle.

Most preferred the carrier is made from a light alloy, particularly mainly aluminum. This leads to a low weight without impairing the stability and the durability of the carrier. Further the light alloy is a suitable substrate for providing a suitable sliding coating.

Particularly the carrier is split into at least a first carrier part and a second carrier part, wherein the first carrier part comprises an inner surface A1 pointing to the plurality of gear wheels, wherein the ratio of the inner surface A1 with respect to the overall inner surface A of the carrier is 25% �= A1/A �= 75%, particularly 30% �= A1/A �= 70%, preferably 35% �= A1!A �= 65% and most preferred 40% �= A1/A �= 60%. Due to this size the at least two carrier parts comprises an inner surface, which is well accessible for providing the sliding coating. Particularly the carrier parts may be split in axial direction with respect to a pivoting axis of the carrier or perpendicular to the pivoting axis of the carrier.

Preferably the ratio of the inner surface A1 of the first carrier part with respect to the overall inner surface A of the carrier is A1/A �= 55%, particularly A1/A �= 60%. Since the carrier part is not exactly cut into two mainly synuttetrical parts, the first carrier parts is better suitable for assembling the gear wheels one by one into the first carrier part. The second carrier part may be used as cap for enclosing the assembled gear wheels into the carrier.

The invention further relates to a motor vehicle comprising an engine for providing torque and a differential gear, which may be designed as previously described, for transmitting the torque to at least to different wheels, wherein the engine comprises an output shaft connected to the carrier of the differential gear.

Since axial thrust washers of the differential gear may be replaced by sliding coatings, the size of the differential gear may be reduced and/or the size of the gear wheels may be increased for transmitting a higher maximum transferrable torque, wherein the wear is not increased, so that the life time of the differential gear is not increased.

These and other aspects of the invention will be apparent from and elucidated with reference to a preferred embodiment described hereinafter.

In the drawings: Fig. 1 is a schematic sectional view of a differential gear according to the state of the art and Fig. 2 is a schematic sectional view of a differential gear according to the invention.

The differential gear 10 as illustrated in Fig. 1 comprises a carrier 12, which is split into a first carrier part 14 and a second carrier part 16. The carrier is rotatably supported around a pivot axis 18 by means of bearings 20. The carrier houses a plurality of gear wheels, which comprises two planet gears 22 rotatably supported by the carrier 20 and two side gears 24 in meshing contact with the planet gears 22. The side gears 24 may be connected to not illustrated axles particularly for a left and right rear wheel or a left and right front wheel of a motor vehicle, respectively. Between an inner surface 26 of the carrier 12 and the planet gears 22 as well as the side gears 24 axial thrust washers 28 in the form of annular washers are provided for reducing friction and wear.

In comparison to the differential gear 10 as illustrated in Fig. 1 the differential gear 10 as illustrated in Fig. 2 comprises sliding coatings instead of axial thrust washers 28. Due to the omitted axial thrust washers 28 the size of the differential 10 may reduced and/or the size of the gear wheels 22, 24 may be increased for transmitting a higher maximum transferrable torque, wherein due to the sliding coating the life time of the differential gear 10 is not reduced.

Referencesigns differential gear 12 carrier 14 first carrier part 16 second carrier part 18 pivot axis bearing 22 planet gear 24 side gear 26 inner surface 28 axial thrust washer

Claims

Claims 1. Differential gear for a motor vehicle, comprising a plurality of gear wheels (22, 24) for transferring torque and a carrier (12) housing the plurality of gear wheels (22, 24) characterized in that between the carrier (12) and at least one of the gear wheels (22, 24) a sliding coating is provided.
2. Differential gear according to claim 1 whereby the at least one gear wheel (22, 24) is only via the sliding coating in relative moving contact to the carrier (12).
3. Differential gear according to claim 1 or 2 whereby the at least one sliding coating is the only bearing member between the plurality of gear wheels (22, 24) and an inner surface (26) of the carrier (12)
4. Differential gear according to anyone of claims 1 to 3 whereby the carrier (12) and/or the at least one gear wheel (22, 24) comprises the sliding coating.
5. Differential gear according to anyone of claims 1 to 4 whereby the plurality of gear wheels (22, 24) comprises at least one planet gear (22) supported by the carrier (12) and at least two side gears (24) in meshing contact with the planet gear (22), wherein the side gears (24) are only via the sliding coating in contact to the carrier (12).
6. Differential gear according to anyone of claims 1 to whereby the sliding coating is provided by sputtering or roll bonding.
7. Differential gear according to anyone of claims 1 to 6 whereby the sliding coating comprises at least one of the elements aluminum, copper, tin, lead, nickel.
8. Differential gear according to anyone of claims 1 to 7 whereby the carrier(12) is made from a light alloy, particularly mainly aluminum.
9. Differential gear according to anyone of claims 1 to 8 whereby the carrier (12) is split into at least a first carrier part (14) and a second carrier part (16), wherein the first carrier part (14) comprises an inner surface A1 pointing to the plurality of gear wheels (22, 24), wherein the ratio of the inner surface A1 with respect to the overall inner surface A of the carrier (12) is 25% �= A1/A �= 75%, particularly 30% �= A1/A �= 70%, preferably 35% �= A1/A �= 65% and most preferred 40% �= A1/A �= 60%.
10. Differential gear according to claim 9 whereby the ratio of the inner surface A1 of the first carrier part (14) with respect to the overall inner surface A of the carrier (12) is A1/A �= 55%, particularly A1/A �= 60%.
11. Motor vehicle comprising an engine for providing torque and a differential gear (10) according to anyone of claims 1 to 10 for transmitting the torque to at least to different wheels, wherein the engine comprises an output shaft connected to the carrier (12) of the differential gear (10).