GB2218762A

GB2218762A - Self-aligning bevel gear differential assembly

Info

Publication number: GB2218762A
Application number: GB8909017A
Authority: GB
Inventors: Herbert Taureg
Original assignee: Viscodrive GmbH
Current assignee: GKN Viscodrive GmbH
Priority date: 1988-04-27
Filing date: 1989-04-20
Publication date: 1989-11-22
Anticipated expiration: 2009-04-20
Also published as: DE3814205A1; FR2630799B1; DE3814205C2; JPH01307546A; IT8905152A0; GB2218762B; IT1233041B; FR2630799A1; GB8909017D0

Description

2218762 1 I GMD/87105GB1 BEVEL GEAR DIFFERENTIAL ASSEMBLY This invention

relates to a bevel gear differential assembly of the type including a housing, a carrier rotatable in the housing about an axis, first and second side gears mounted within the carrier for rotation about the axis and a planet gear pin support comprising planet gear pins on which planet gears are rotatably mounted to mesh with the side gears, the support being mounted in the carrier so as to be non-rotatable relative thereto about said axis.

Normally, the support has two or four pins on each of which is mounted a planet gear. Where only two planet gears are provided such a differential cannot be used for high torques otherwise there is unacceptable wear on the gear tooth flanks. If four planet gears are used, the tooth flank loads are not balanced, i.e. the planet gears are subjected to uneven loads. This occurs with the unavoidable non-concentricity of the planet gears and if the support is received in the carrier to be axially slidable.

Even if only three planet gears were mounted on a support which was fixed, or slidable relative to the carrier the above problems would not be overcome.

It has been proposed to provide a differential assembly in which the support comprises two parts connected to each other, each part having three planet pins. Each planet pin carries two planet gears. The two parts of the support together comprise a support having six planet gear pins and thus behaves and has the same 2 disadvantages as a support having four gears, i.e. unequal loads occur on the planet gear teeth. This prior art differential assembly is intended primarily for trucks and its object is to permit a double reduction ratio by virtue of having two planet gears on each pin and two sets of side gears.

It is an object of the present invention to provide a bevel gear differential assembly in which the load on the planet gears is distributed automatically and evenly.

In accordance with the invention we provide a bevel gear differential assembly comprising: a housing; a carrier rotatable in the housing about an axis; first and second side gears mounted within the carrier for rotation about said axis; a planet gear pin support comprising three only planet gear pins and mounted within the carrier so as to be rotatable relative thereto about said axis; three only planet gears each rotatably mounted on a respective said pin and each meshing with the first and second side gears, the axes of rotation of said planet gears lying in a plane; and cooperating mounting means on the pins and the carrier to mount the support within the carrier for limited pivotal movement about the point of intersection of said axis and said plane from a rest position in which the plane is perpendicular to the axis.

The invention ensures that the support, together with the planet gears, can be self-adjusting so that any lack of concentricity of the planet gears as well as any resulting uneven tooth loads are compensated for. One of the advantages is that there is less wear on the gear S Z 3 tooth flanks. The invention results in an improved load distribution within the differential assembly because only three planet gears are used and the support takes up its position as determined by the static loads on it.

Preferably, the planet gear pins are equi-angularlyspaced about said axis although they may be unevenly spaced.

The means mounting the support in the carrier may be formed by the radially-outer ends of the planet gear pins and grooves in the carrier extending parallel to the axis and in which said ends are received.

To reduce point loads on the pins the outer end of each pin may be formed with flats lying in planes which are parallel to said axis and parallel to the longitudinal axis of the pin, the flats engaging the sides of one of said grooves.

In addition, to enable the necessary adjustment of the support to take place, in the rest position of the support there may be a clearance between the said ends the pins and the bases of the grooves. Alternatively, the end faces of the pins may be formed as part of the surface of a cylinder whose longitudinal axis lies in said plane and passes through said point of intersection.

A differential assembly embodying the invention may be designed as a limited-slip differential and may be combined with a two- part coupling located at one side of the assembly and arranged to restrict the differential action, one part of the coupling being connected to the first side gear and the other part of the coupling being 4 connected to the second side gear by a shaft which passes with clearance through a bore in the support.

Preferably, the coupling is a viscous shear coupling.

The invention will be described in detail by way of example with reference to the accompanying drawings in which:- Figure 1 is a section through a differential assembly embodying the invention on the line 1-1 of Figure 2; Figure 2 is a transverse section of the differential of Figure 1 with the housing omitted; Figure 3 is a section similar to Figure 1 but showing a limi-ted slip differential in which the differential action is restricted by a viscous shear coupling; and Figure 4 is a diagram illustrating the position in which a differential assembly embodying the invention can be located.

Referring firstly to Figures 1 and 2, the differential assembly comprises a housing 10 in which is rotatably mounted a carrier 11. The carrier is mounted in bearings 12 which in turn are carried by flanged sleeves 13 inserted into the ends of the housing. The carrier carries a crown wheel 14 which meshes with a pinion 15. The pinion 15 is driven by a pinion shaft 16 received in a pinion bearing 17. Rotatably mounted in the carrier are two bevel side gears 18 and 19 which are 1 4 i internally splined at 20 and 21 respectively and which receive the splined ends of drive shafts 22 and 23. The drive shafts 22 and 23, the side gears 18 and 19 and the carrier 11 all rotate about an axis 24.

As clearly shown in Figure 2, three planet gears indicated at 25, 26 and 27 mesh with the side gears 18 and 19. These three planet gears are mounted on a planet-gear support which is indicated generally at 28. The support comprises a ring 29 on which are mounted three planet pins 30, 31 and 32 on which are rotatably mounted the planet gears 25, 26 and 27 respectively. The longitudinal axes of the pins 30, 31, 32 which are indicated at 30a, 31a, 32a respectively lie in a plane as. is apparent from Figure 1 and are equiangularly spaced about the axis 24. The plane is indicated in Figure 1 by the chain-dotted line 33. The plane 33 intersects the axis 24 at a point 34 and as is clear from Figure 2 the axes 30a, 31a, 32a intersect on the axis 24 in the position of the support 28 shown in Figures 1 and 2 which is a rest position.

The radially outer ends of each of the planet pins 30, 31 and 32 is formed with a pair of opposed flats indicated, for the planet pin 30, at 35. These flats lie perpendicular to the plane 33 and parallel to the axis 24. The flats on the planet pin 32 are indicated at 36.

The carrier 11 is formed with three longitudinal grooves 37, 38 and 39. As shown in Figures 1 and 2 the radially outer ends of the planet pins engage in the grooves thus the outer ends of the planet pin 30 engage in the groove 37 with the flats 35 engaging the sides of the groove. Similarly the flats 36 on the planet pin 32 6 engage the sides of the groove 39 and the flats on the end of-the planet pin 31 engage the sides of the groove 38.

Moreover, as clearly shown in Figure 2, there is, in the rest position of the support shown in that figure, a clearance between the radially outer end 40 of the planet pin 30 and the base 41 of the groove 37. Similarly there is a clearance between the radially outer end 42 of the pin 32 and the base 43 of the groove 36. There is also a radial clearance between the radially outer end 44 of the pin 31 and the base 45 of the groove 38.

Bearing plates are provided between the outer surfaces of the planet gears and the carrier to support the planet gears and these bearing plates are indicated at 46, 47 and 48.

The planet gear support is shown in its rest position in Figure 1 in which the plane 33 is perpendicular to the axis 24. Due to the mounting of the planet gear support with the ends of the pins in the grooves of the carrier, the support can pivot to a limited degree about tle point 34 from the rest position shown and can also slide to a limited extent by virtue of the ends of the planet pins sliding in the grooves in the carrier.

Due to this arrangement, the planet gear support is self-adjusting so that an even load distribution on the planet gears is obtained when the differential assembly is in use.

The differential gear assembly shown in Figures 1 30 and 2 is not restricted in its differential action.

W1 7 1 Figure 3, however, shows a limited slip differential assembly having essentially the same features as the assembly of Figures 1 and 2 but being associated with a viscous shear coupling which acts to restrict the differential action of the assembly.

Referring now to Figure 3, the differential assembly is shown without its housing and comprises a carrier 50 in which are rotatably mounted bevel side gears 51 and 52. Three planet bevel gears, one of which is shown at 53 mesh with the side gears and are supported by bearing plates 54 as described above. The planet gear support is indicated generally at 55 and comprises a ring 56 from which extend three equiangularly spaced planet gear pins, one of which is shown at 57. The carrier is provided with three longitudinal grooves, one of which is indicated at 58 into which the end portions of the pins are received. As before each pin is provided with flats such as 59 and there is a clearance between the end 60 of each pin and the base 61 of the groove in which it is received. As thus far described, therefore, the differential assembly is similar to that shown in Figures 1 and 2.

However, also mounted within the carrier 50 is a viscous shear coupling which is indicated generally at 62. The coupling comprises a housing 63 having a right hand end wall 64 in Figure 3 which is either formed integrally with or rigidly connected to the side gear 51. The left hand wall of the housing is indicated at 65 and is provided with an internally splined flange 66. The coupling includes a hub 67 which is rotatably mounted on the flange 66 and sealed thereto by a seal 68 and which also has an internally splined flange 69 mounted within the side gear 51 and sealed thereto by a seal 70.

8 Within the coupling housing are two sets of interleaved plates, plates of the outer set are indicated at 71 and are splined at 72 to the housing. Plates of the inner set are indicated at 73 and are splined at 74 to the hub. Adjacent plates 71 are spaced apart by rings which are inserted between each adjacent pair of outer plates. The interior of the housing not occupied by the plates contains a viscous medium, e.g. a silicone oil.

The differential assembly is driven by a crown wheel, not shown, which is connected to a flanged portion 76 of the carrier. The output from the assembly is taken by two drive shafts 77 and 78. The drive shaft 77 passes with clearance through a bore 79 in the ring 56 of the planet gear support and has a splined end 80 which engages the splines in the flange 69 of the coupling hub 67. The drive shaft 78 has a splined end 81 which engages in the internal splines of the flange 66 of the coupling housing. The drive shaft 77 is also engaged with internal splines 82 in the side gear 52.

The differential assembly of Figure 3 has the advantages of the assembly of Figures 1 and 2 in that the planet gears are self-adjusting to equalise the load and reduce tooth wear and in addition a limited slip capability is obtained because the viscous shear coupling 62 is connected between the side gears 51 and 52. This is so because the side gear 51 is connected to the housing of the viscous shear coupling which in turn is connected to the drive shaft 78 and the hub 67 of the viscous shear coupling is connected_by the drive shaft 77 to the side gear 52. The viscous shear coupling thus acts across the side gears to restrict differential action. The operation of the viscous shear coupling itself is conventional. The fact that there is a 9 1 clearance between the bore 79 of the planet pin support and the drive shaft 77 allows the support to pivot as described in-relation to Figures 1 and 2 to obtain the self-adjusting of the planet gears.

Figure 4 shows an application of the differential assembly described above to a vehicle. Thus the vehicle is indicated generally at 90 and comprises a prime mover 91 and a gearbox 92 which drives a differential assembly 93. The drive shafts of the differential assembly are indicated at 94 and 95 and drive road wheels 96 and 97.

Additional non-driven road wheels 98 are provided. The differential assembly 93 may be either the construction as shown in Figures 1 and 2 or of the limited slip type shown in Figure 3.

Although in the embodiment described the planet gear pins are equi-angularly spaced about the axis 24 in Figures 1 and 2 they may be be un-equi-angularly spaced if desired. They may also be unequally spaced in the embodiment of Figure 3.

In an alternative arrangement, not illustrated, instead of the planet pin ends having flats they may be formed to be part cylindrical, the axis of the cylinder lying in the plane containing the pin axes and passing through the point 34.

Claims

A bevel gear differential assembly comprising:

housing; carrier rotatable in the housing about an axis; first and second side bevel gears mounted within the carrier for rotation about said axis; a planet gear pin support comprising three only planet gear pins and mounted within the carrier so as to be rotatable relative thereto about said axis; three only planet bevel gears each rotatably mounted on a respective said pin and each meshing with the first and second side gears, the axes of rotation of said planet gears lying in a plane; and cooperating mounting means on the pins and the carrier mounting the support within the carrier for is limited pivotal movement about the point of intersection of said axis and said plane from a rest position in which the plane is perpendicular to the axis.
2. An assembly according to Claim 1, wherein the mounting means is formed by the radially outer ends of the planet gear pins and grooves in the carrier extending parallel to said axis and in which said ends are received.
3. An assembly according to Claim 2 wherein each said end of each said planet gear pin is formed-with flats lying in planes parallel to said axis and parallel to the longitudinal axis of the pin, said flats engaging the sides of one of said grooves.
4. An assembly according to Claim 2 or Claim 3 wherein in the rest position of the support, there is a clearance t.

between the said ends of the pins and the bases of the grooves.
5. An assembly according to Claim 2 or Claim 3 wherein the said end of each pin is formed as part of the surface of a cylinder whose longitudinal axis lies in said plane and passes through said point of intersection.
6. An assembly according to any preceding claim wherein the planet gear pins are unequi-angularly spaced about said axis.
7. An assembly according to any preceding claim in combination with a twopart coupling located at one side of the assembly and arranged to restrict differential action, one part of the coupling being connected to one side gear and the other part of the coupling being connected to the other side gear by a shaft which passes with clearance through a bore in the support.
8. An assembly according to Claim 7 wherein the coupling is a viscous shear coupling.
9. A motor vehicle having a prime mover, driven road wheels and a drive transmission between the prime mover and said road wheels, the drive transmission comprising an assembly according to any preceding claim wherein the carrier is driven by the prime mover and the first and second side gears are connected to respective driven road wheels.
10. A bevel gear differential assembly substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.

4 12
11. A bevel gear differential assembly substantially as hereinbefore described with reference to Figure 3 of the accompanying drawings.
12. A motor vehicle having a differential assembly substantially as hereinbefore described with reference to the accompanying drawings.

Published 1989 at The Patent Office, State House. 66171 High Holborn. London WClR 4TP Further copies maybe obtained from The Patent Office. Wes Branch, St Mary Cray, Orpington, Kent BR5 3RD. Printed by Multiplex techniques ltd, St Mazy Cray, Kent, Cori. 1/87 i j