GB2461749A

GB2461749A - A differential having a symmetrical housing which can be fixed in different orientations

Info

Publication number: GB2461749A
Application number: GB0812846A
Authority: GB
Inventors: Valerian Dare-Bryan
Original assignee: Lockheed Corp; Lockheed Martin Corp
Current assignee: Lockheed Martin Corp
Priority date: 2008-07-14
Filing date: 2008-07-14
Publication date: 2010-01-20
Anticipated expiration: 2028-07-14
Also published as: GB0812846D0; GB2461749B

Abstract

A differential comprises a housing (49, fig 4) having attachment points 46, (48) whereby it can be attached to a structure of a number of vehicles. The housing (49) has a first symmetry under rotation about axis (41) of output half shafts 22, 23 and a second symmetry under rotation about axis (45) of propeller shaft 39. The first and second symmetry provides the housing with two rotational orientations so that the attachment points 46 or attachment points (48) are always used to attach the differential to the structure of the vehicle. The differential may be interchanged between a fleet of vehicle and/or it may be fixed in different positions on a vehicle depending on transmission layout of the vehicle. Propeller shaft 39 has a pinion (31) which meshes with a crown wheel (32) that drives a differential gear arrangement having sun wheels (34) and planet wheels (35) which rotate half shafts 22, 23.

Description

I

VEHICLE TRANSMISSION

This invention relates to transmissions for vehicles.

Figure 1 shows one layout for the transmission of a four-wheel-drive vehicle. For the purpose of this description either end could be the front of the vehicle. The engine 1 drives a gearbox 2, which drives a T-box 3. The T-box splits the drive between the front and rear wheels. The drive to one pair of wheels 6 runs from the T-box through a differential 4 and along half shafts 5 to that pair of wheels.

The drive to the other set of wheels 11 runs from the T-box along a propeller shaft 7, through a cross-box 8 and a differential 9 and along half shafts 10 to that pair of wheels 11.

It is highly desirable to reduce the number of parts needed to manufacture or maintain a vehicle or a fleet of similar vehicles, even if those vehicles have different transmission layouts. This is especially significant for military vehicles, since they may have to be maintained in remote locations to which it is difficult to supply components. In that situation it might even be desired to requisition parts from a vehicle of one transmission layout in order to repair a vehicle of another transmission layout.

For example, it may be desirable to have front-engined and rear-engined versions of the vehicle shown in figure 1, and for those vehicles to have some components in common. One way to do this would be to exchange the forwards direction of the vehicle. If wheels 6 were the front wheels, then the vehicle of figure 1 would be front-engined. In that case the transmission would have to be arranged to turn the half shafts 5 such that the wheels 6 rotated clockwise when viewed from the point illustrated at 12 when the gearbox was in a forwards gear. Alternatively, if the forwards direction were to be exchanged then wheels 11 would be the front wheels, in which case the vehicle would be rear-engined, and then the transmission would have to be arranged to turn the half shafts 5 such that the wheels 6 rotated anti-clockwise when the gearbox was in a forwards gear.

Hence, adapting the vehicle from being front-engined to being rear-engined would not simply be a matter of reconfiguring the bodywork relative to the transmission: the sense of the drive would also have to be changed.

One way to do this would be to have equal numbers of forward and reverse gears.

Another way would be to introduce an additional component to swap the direction of rotation at the output of the engine or at the output of the gearbox. Both of these solutions introduce additional weight and complexity.

More generally, figure 2 shows some of the transmission layouts that might be present in a fleet of vehicles. The forwards direction is shown by the arrow next to each layout, the engine is shown at 14 and the wheels at 13. The layouts are: (a) rear-engined four-wheel-drive, (b) front-engined four-wheel-drive, (c) rear-engined six-wheel drive. It would be advantageous to be able to construct all of these layouts -and others -using as few parts as possible. As explained above, adapting a set of common transmission components for both layout (a) and layout (b) of figure 2 is not straightforward because the sense of the drive is different in each case. Adapting a set of common transmission components for both layout (a) and layout (c) of figure 2 is not straightforward because the layout of figure (c) has to provide drive to an additional set of wheels.

There is a need for a transmission arrangement that allows the number of parts needed to manufacture or maintain a vehicle or fleet of vehicles to be reduced.

Some vehicles have beam axles. In this design a rigid axle extends through the differential from wheel to wheel. The axle is surrounded by a casing which is permanently attached to the differential's housing, usually by heat shrink fitting, and the differential housing has a dedicated input port for attachment to a propeller shaft. The casing is asymmetrical about the axle, with a bell housing extending to one side for connection to the propeller shaft, and optionally a removable cover opposite the bell housing through which a take-off can be provided to drive an additional set of wheels.

According to one aspect of the present invention there is provided a differential having: a housing having attachment points whereby it can be attached to the structure of a vehicle; a crown wheel rotatably mounted within the housing for meshing with another gear to receive drive from outside the housing; a pair of transversely-directed output shafts; and a differential gear arrangement mounted within the housing and configured to take drive from the crown wheel and transmit it to the output shafts; the housing being configured such that in each of two rotational orientations of the housing about a longitudinal axis the attachment points present an identical attachment interface for attachment to the structure of a vehicle.

The attachment points could, for example, be through-holes or tapped holes for receiving bolts, or threaded rods for insertion into holes in the structure of the vehicle. The attachment points are preferably suitable for mounting of the differential in use as a vehicle drive differential.

Preferably the rotational orientations differ by 1800.

The output shafts may have a common axis of rotation. The longitudinal axis may be perpendicular to the axis of rotation of the or each output shaft. The longitudinal axis may be coplanar with the axis of rotation of the crown wheel.

The crown wheel may have bevelled teeth that facilitate its being driven by a pinion rotating about an axis parallel with or coincident with the said longitudinal axis.

The housing may define a port through which the crown wheel is exposed for receiving drive from outside the housing.

The housing may have two ports whereby the crown wheel is exposed for receiving drive from outside the housing. Either port may have peripheral mounts whereby a cover may be attached over it. The longitudinal axis may pass through the two ports.

The or each port may have second attachment points whereby it can be attached to a transmission component of a vehicle. In each of the two rotational orientations the second attachment points may present an identical mounting interface for attachment to a transmission component.

The output shafts may terminate at their distal ends in mounts whereby they can be releasably attached to drive shafts. The mounts may be equidistant from the longitudinal axis. The mounts may be flexible mounts. The mounts may be located adjacent to the housing.

According to a second aspect of the invention there is provided a fleet of vehicles including a first vehicle having a first transmission layout in which an engine is coupled to wheels via a differential configured to cause drive wheels of the vehicle to rotate in a first sense in response to forward drive from the engine, and a second vehicle having a second transmission layout in which an engine is coupled to wheels via an identical differential configured to cause the wheels to rotate in the opposite sense in response to forward drive from the engine.

The vehicles may each have a gearbox, and forward drive from the engine may be when the vehicles are in forward gears. The gearboxes of the vehicles may be the same.

The differentials of the vehicles may be differentials of the type as set out above.

The present invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows a transmission system; Figure 2 shows engine layouts; Figure 3 shows a schematic view of part of a vehicle's transmission including a differential; Figure 4 shows the differential of figure 3 in more detail; and Figures 5 and 6 show vehicle transmission systems.

Figure 3 shows part of a vehicle transmission. The transmission has a differential which is driven by a propeller shaft 39 and two half shafts 22, 23 which are driven by the differential and which drive road wheels via hubs 24, 25. (For clarity the wheels are not shown in figure 3). The half shafts are not enclosed, as would be the case with a typical beam axle configuration. The differential is configured with a certain symmetry so that it can be coupled to the propeller shaft in two orientations. When the differential is disconnected from the half shafts (and from any connection to the vehicle's frame) the differential can be rotated about the axis of the propeller shaft without the differential having been disconnected from the propeller shaft. The differential can then be re-connected to the half shafts.

The differential will drive the half shafts in one direction when the propeller shaft is connected in one orientation, and in the other direction when the propeller shaft is connected in the other orientation. This allows the differential to be used in a wide range of vehicle configurations and in a range of locations in a given vehicle.

The differential of figure 3 is shown in more detail in figure 4. Further components indicated in figure 3 will be discussed below with reference to figure 4, in which like components are numbered as for figure 3.

The differential comprises a casing 30 which encloses a pinion 31 and a crown wheel 32. In addition to enclosing the internal components of the differential, the casing supports bearings for some of those components and thereby maintains them in the appropriate spatial relationships. The pinion is driven by a propeller shaft 39, to which it is attached. The crown wheel 32 meshes with the pinion 31, and is attached to a differential cage 33 which rotates with the crown wheel. The crown wheel and the differential cage are mounted by bearings 36 to the housing 30. A differential gear arrangement comprising sun wheels 34 and planet wheels is mounted on and rotatable relative to the differential cage. As is normal in a differential, the driven cage can transmit rotation to both sun wheels, and different rates of rotation of the sun wheels can be accommodated through rotation of the planet wheels. Output shafts 37 are coupled by splines to the sun wheels. The output shafts are mounted to the casing 30 by bearings 38. The outer ends of the output shafts terminate in flexible mounts 40, by which the output shafts are attached to half shafts 22, 23. The half shafts are coupled to driven road wheels.

The flexible mounts 40 permit movement of each half shaft about axes perpendicular to the rotation axis of the respective output shaft 37. This allows the half shafts to flex independently of the differential and thereby accommodate the action of the vehicle's suspension. The mounts 40 could, for example, take the form of constant velocity joints, universal joints or flexible splined couplings.

Alternatively, the mounts could simply be inflexible plates or splines formed in or attached to the stub shafts. The half shafts could be attached to such mounts directly or via flexible couplings The casing has two pinion ports, shown generally at 42 and 43. In the differential shown in figure 4 port 42 is open and receives the pinion 31 and propeller shaft 39, and port 43 is closed and covered with a sealing plate 44. Either port can be covered by a sealing plate when not in use. The pinion ports are of a matching design, so that both can be connected to a structure of a similar shape by an identical attachment interface. In figure 4, a housing 49 is shown attached to port 42 by fixing points 48. That housing could, for example, be part of a T-case or of a cross box or a housing for protecting a prop shaft. The housing is preferably releasably attached, for instance by bolts passing through some of holes 48, to the casing 30. Bolts passing through others of holes 48 in an identical configuration attach the sealing plate 44 over port 43.

The differential preferably has symmetry in two ways: (a) under a rotation about the axis 41 of the output shafts and/or (b) under a rotation about a second, longitudinal axis 45 perpendicular to the output shafts and that passes through the pinion ports. In each case, the symmetry preferably preserves the mounting points 40 relative to the casing 30; preserves the shape of the periphery of the casing around the pinion ports, particularly its attachment points; preserves a circumferential meshing point of the crown wheel 32 where a pinion 31 can be engaged with it; and preserves the locations of fixing points (e.g. points 46 in figure 3) of the differential for attachment to the frame/chassis/body of a vehicle.

Those fixing points could be through-holes or threaded holes for receiving bolts, threaded bars for insertion into holes in the vehicle's structure. Alternatively they could be clips or clamps of a type that is suitable for holding a drive differential of a vehicle to the vehicle's structure. Alternatively they could be attachment structures for mating with such clips or clamps.

Whichever mounting points are active are located in the same place relative to each other and to the transmission interfaces of the differential in two positions of the differential. In addition, the configuration of the differential's surface -especially its upper surface -is preferably the same in each orientation since then it can interface properly with the vehicle in either orientation.

Symmetry (a). The differential of figure 4 has symmetry under a 1800 rotation of the casing about the axis 41 of the output shafts 37. Under such a rotation the locations of the mounts 40 and the crown wheel 32 remain constant. Therefore, the points at which the differential couples to the half shafts and meshes with a pinion 31 remain unchanged. As can be seen from figure 4, the peripheries of the pinion ports 42, 43, and their mounting points 48 are symmetrical and preserved under such a rotation. Preferably any mounts 46 to the vehicle's structure are also symmetrical and preserved under such a rotation. This means that -without modification of the other components -the differential casing 30 can be coupled interchangeably to a propeller shaft, to a structure that links to the periphery of the pinion port, to the half shafts and to the vehicle's structure irrespective of whether its casing is in the orientation shown in figure 4 or in an orientation rotated 1800 about the axis of the output shafts 37. Under this rotation the direction in which the half shafts are driven for a given drive direction of the pinion is unchanged.

Symmetry (b). The differential of figure 4 also has symmetry under a 180° rotation about the second axis 45. Under such a rotation the mounts 40 are interchanged in location, so the differential can readily be coupled to the half shafts in either orientation. The axis of the crown wheel 32 is perpendicular to the second axis 45, so in both rotational positions it will mesh with a pinion that remains in the same location. The peripheries of the pinion ports 42, 43, and their mounting points 48 are symmetrical and preserved under such a rotation.

Preferably any mounts 46 to the vehicle's structure are also symmetrical and preserved under such a rotation. This means that -without modification of the other components -the differential casing 30 can be coupled interchangeably to a propeller shaft, to structures that link to the pinion port(s), to the half shafts and to the vehicle's structure irrespective of whether its casing is in the orientation shown in figure 4 or in an orientation rotated 180° about the axis 45. Under this rotation the direction in which the half shafts are driven for a given drive direction of the pinion is reversed.

In the differential of figure 4 the pinion drives the crown wheel 32 directly, and the shafts 37 are coaxial with the sun wheels 34. Similar symmetry could be achieved with more a complex internal mechanical arrangement of the differential.

A second pinion can engage the crown wheel 32 through the other of the pinion ports 43. This feature allows drive to be passed from one pinion to the second; and additionally, via the differential, to wheels attached to the half shafts 22, 23.

The symmetry of the differential allows it to be configured in numerous configurations with little if any variation of the components with which it interacts.

Some example configurations will be described below.

1. The configuration shown in figure 4, in which only a single pinion is present, and drives the driven gear; and in which the half shafts turn in a first sense relative to motion of the pinion.

2. A configuration in which the casing is rotated by 1800 about axis 45 relative to the configuration shown in figure 4, and in which one pinion is present and drives the driven gear. In this configuration the half shafts turn in the opposite sense relative to motion of the pinion.

3. A configuration equivalent to configuration 1, but in which a second pinion opposite the first engages and is driven by the driven gear.

4. A configuration equivalent to configuration 2, but in which a second pinion opposite the first engages and is driven by the driven gear.

Examples of the vehicle layouts in which the differential can advantageously be used will now be described.

Figure 5 shows a four-wheel-drive vehicle layout, in which like components are numbered as for figure 1. In this layout there are front and rear differentials 50a, 50b which can be identical to each other except for the way in which they are configured. These connect to wheels 6 and 11 by half shafts 5 and 10. In this vehicle, those half shafts may all be identical. The crown wheels of the differentials are each driven by pinions, and the pinions are fixed to the output shafts of the cross-box 3 and the T-case 4 respectively, rather than being fixed directly to propeller shafts as illustrated in figure 4.

The engine 1, gearbox 2, T-case 3 and cross-box 4 will be such that when the engine is running and the gearbox is in a forward gear the direction of rotation of the output shaft of the T-case to differential 50b will be fixed, as will the direction of rotation of the output shaft from cross-box 8 to differential 50a. Those directions will not necessarily be the same. The differentials 50a and 50b attach to the cross-box 8 and the T-case 3 respectively by the mounting points at the periphery of their pinion ports. Due to the symmetry of the differentials, they can be mounted in two rotational orientations with respect to the longitudinal axis of the vehicle; making use of their symmetry of the type (b) described above. The direction in which each pair of wheels will rotate when the vehicle is in a forwards gear depends on which of those orientations the respective differential is connected in. This flexibility in the differentials' usage has a number of advantages.

1. The same differentials can be used irrespective of the internal details of the other components of the transmission. It does not matter which way the final drive from the T-box rotates relative to the final drive from the cross-box since each differential can simply be connected in the appropriate way to cause the wheels to rotate in the same direction when viewed from the side (location 12).

2. The same transmission components can be used whether the vehicle is to go forwards to the left or to the right when viewed from 12. To change the direction of motion in a forward gear the differentials can both be rotated 180° about the longitudinal axis of the vehicle. In the example of figure 5, this flexibility allows a front-engined or rear-engined vehicle to be constructed using the same transmission components, and with no change to the points by which, for example, the engine and the gearbox are attached to the frame of the vehicle.

The orientation of the differentials can be decided at the design or production stage. Alternatively, the forwards drive direction of an existing vehicle could even be altered. Since the differential does not use a beam axle, and the half-shafts mount symmetrically and detachably to the differential, the differentials of an existing vehicle could be uncoupled from the half shafts and the vehicle's body, rotated 180° about their input shafts and then reattached.

It is advantageous if the differential is mounted mid-way laterally between the wheels to which the half shafts from the differential connect. This means that those half shafts can be of equal length. This reduces the number of parts required for the vehicle's transmission, since both half shafts can be identical.

Figure 6 illustrates another feature of the differential of figure 4. Figure 6 shows a six-wheel-drive vehicle. Differentials 50c and 50d are the same as the differentials in the vehicle of figure 5. As described above, those differentials could be configured so that the vehicle goes either way in forwards gear. In figure 6 an additional propeller shaft 51 carries drive from differential 50d to a further differential 50e. Differential 50e can be the same as the other differentials and can drive wheels 53 via half shafts 52. For this configuration the cover is removed from the second pinion port of differential 50d. The propeller shaft 51 has pinions at both of its ends, which mesh with the respective drive wheels of differentials 50d and 50e. In this way the differential of figure 4 can be used to provide drive to an additional set of wheels. Further sets of wheels could be driven from differential 50c and/or from differential 50e. By suitable rotation of the differentials about the longitudinal axis of the vehicle, the vehicle can be made to drive in either direction in forwards gear.

The differential of figure 4 allows great flexibility in the design of vehicles, and especially in the selection of transmission components for a fleet of vehicles that have different drive layouts. Identical transmission components, with identical mounts to the vehicles' bodies can be used for four-wheel-drive vehicles irrespective of the desired forwards drive direction. Thus a single chassis and a single set of transmission components can be used for front-engined and rear-engined vehicles. With the addition of a propeller shaft and an additional differential, half shafts and wheels, the transmission can give an additional set of drive wheels without the need to modify any of the components and from either end of the vehicle. Thus a fleet or range of vehicles including two-wheel drive, front-engined and rear-engined four-wheel drive, various layouts of six-wheeled-drive including front-engined, mid-engined and rear-engined; and layouts driven by eight or more than eight wheels can use the same components. This can reduce production costs and parts inventories, and allow the parts of one vehicle to be re-used to repair a vehicle of a different layout.

The layout shown in figures 5 and 6 is also advantageous because, with the propeller shaft 7 running beside rather than below the engine, the engine can be mounted relatively low, for example in line with the half shaft. This can improve the vehicle's dynamics.

Any of the components of the transmission can be coupled together by prop shafts rather than by a direct coupling. This allows additional flexibility in the configuration of the transmission. For example, the engine can be spaced from the gearbox to allow the engine to be located at the point along the vehicle at which it is dynamically best or at which it fits best with other structures on the vehicle.

The applicant hereby discloses in isolation each individual feature described herein and any combination of two or more such features, to the extent that such features or combinations are capable of being carried out based on the present specification as a whole in the light of the common general knowledge of a person skilled in the art, irrespective of whether such features or combinations of features solve any problems disclosed herein, and without limitation to the scope of the claims. The applicant indicates that aspects of the present invention may consist of any such individual feature or combination of features. In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention.

Claims

CLAIMS1. A differential having: a housing having attachment points whereby it can be attached to the structure of a vehicle; a crown wheel rotatably mounted within the housing for meshing with another gear to receive drive from outside the housing; a pair of transversely-directed output shafts; and a differential gear arrangement mounted within the housing and configured to take drive from the crown wheel and transmit it to the output shafts; the housing being configured such that in each of two rotational orientations of the housing about a longitudinal axis the attachment points present an identical attachment interface for attachment to the structure of a vehicle.
2. A differential as claimed in claim 1, wherein the rotational orientations differ by 1800.
3. A differential as claimed in claim 1, wherein the output shafts have a common axis of rotation.
4. A differential as claimed in claim 3, wherein the longitudinal axis is perpendicular to the common axis of rotation.
5. A differential as claimed in any preceding claim, wherein the longitudinal axis is coplanar with the axis of rotation of the crown wheel.
6. A differential as claimed in any preceding claim, wherein the housing defines a port through which the crown wheel is exposed for receiving drive from outside the housing.
7. A differential as claimed in any preceding claim, wherein the housing has two ports whereby the crown wheel is exposed for receiving drive from outside the housing.
8. A differential as claimed in claim 7, wherein the longitudinal axis passes through the two ports.
9. A differential as claimed in any of claims 6 to 8, wherein the or each port has second attachment points whereby it can be attached to a transmission component of a vehicle, and in each of the two rotational orientations the second attachment points present an identical mounting interface for attachment to a transmission component.
10. A differential as claimed in any preceding claim, wherein the output shafts terminate at their distal ends in mounts whereby they can be releasably attached to drive shafts.
11. A differential as claimed in claim 10, wherein the mounts are equidistant from the longitudinal axis.
12. A differential as claimed in claim 10 or 11, wherein the mounts are flexible mounts.
13. A differential as claimed in any of claims 10 to 12, wherein the mounts are located adjacent to the housing.
14. A fleet of vehicles including a first vehicle having a first transmission layout in which an engine is coupled to wheels via a differential configured to cause drive wheels of the vehicle to rotate in a first sense in response to forward drive from the engine, and a second vehicle having a second transmission layout in which an engine is coupled to wheels via an identical differential configured to cause the wheels to rotate in the opposite sense in response to forward drive from the engine.
15. A fleet of vehicles as claimed in claim 14, wherein the differentials are differentials as claimed in any of claims I to 13.