GB2508202A

GB2508202A - A differential testing device and method

Info

Publication number: GB2508202A
Application number: GB201221128A
Authority: GB
Inventors: Nicholas John Peter Wirth
Original assignee: Wirth Research Ltd
Current assignee: Wirth Research Ltd
Priority date: 2012-11-23
Filing date: 2012-11-23
Publication date: 2014-05-28
Anticipated expiration: 2032-11-23
Also published as: GB201221128D0; GB2508202B

Abstract

A differential testing device (10) and method for testing a differential (4), the device comprising: a drive torque applicator (50) configured to be coupled to the differential and to apply a drive torque to the differential; a first restraining member (20a) adapted to couple with a first output shaft of the differential; and a second restraining member (20b) adapted to couple with a second output shaft of the differential; wherein the first and second restraining members (20a, 20b) are configured to prevent rotation of the first and second output shafts in the same direction in response to the drive torque and to force rotation of the first and second output shafts in opposite directions. The apparatus and method may be used to measure the threshold locking torque of an automatic locking differential by measuring the maximum torque difference as the torque difference exceeds the threshold locking torque and the differential enters the unlocked configuration.

Description

A DIFFERENTIAL TESTING DEVICE AND METHOD

The present invention relates to a differential testing device and method, and particularly but not exclusively to a device and method which characterises the properties of an automatic locking differential.

It is common for automobiles to have a plurality of wheels (usually 2014) which are driven by a single engine. Ordinarily, the driven wheels are constrained to rotate at the same speed which is related to the speed of the drive shaft.

As a vehicle turns a corner the wheel that is on the outside of the corner must cover a longer path and thus travel faster than the wheel that is on the inside of the curve.

A differential may be used to allow the wheels to rotate at different speeds and thus to achieve this effect. For an engine running at a constant speed, the rotational speed of each driving wheel can vary, but the sum (or average) of the speeds of the two wheels is maintained at a fixed value. Consequently, an increase in the speed of one wheel must be balanced by an equal decrease in the speed of the other.

Standard "open" differentials always provide the same torque to each of the two wheels. This can be problematic since if one wheel loses traction, the torque required to rotate this wheel becomes very low. Consequently, since an open differential splits torque equally to each side, the torque that is applied to the other wheel is limited to this amount and thus minimal drive is provided.

Locking differentials are used to overcome this disadvantage by locking both wheels together as if on a common shaft.

There are various types of locking differentials. For example, automatic locking differentials, such as limited-slip differentials, are designed to lock and unlock automatically. Such differentials are commonly used in race cars where loss of traction is common due to the high torque supplied by the engine.

Automatic locking differentials are commonly configured to operate in a locked configuration under normal conditions and will unlock only when a torque difference between the first and second wheels exceeds a locking torque. These arrangements typically use a multi-plate clutch pack between each side gear and the differential case to lock and unlock the differential. The clutch arrangement may be modified to set the locking torque.

It is desirable, particularly for differentials used in race cars, to fully understand how the differential performs under different conditions. Various testing rigs are known which provide this information. These aie typically large scale units which analyze the dynamic behaviour of the differential by rotating the diffeiential at opelating speeds. Howevei, these units are not easily transported due to their laige scale.

This is particularly important for teams and manufacturers who are travelling from race circuit to race circuit. Further, these testing rigs are very complex and expensive systems. Accordingly, they are not suitable as a final build check tool at the point of assembly (possibly following modification of the clutch arrangement).

It is therefore desirable to provide a less complex differential testing device which is compact and thus easily transported.

According to an aspect of the invention there is provided a differential testing device for testing a differential, the device comprising: a drive torque applicator configured to be coupled to the diffeiential and to apply a drive torque to the differential; a first restraining member adapted to couple with a first output shaft of the differential; and a second restraining member adapted to couple with a second output shaft of the differential; wherein the first and second restraining members are configured to prevent rotation of the first and second output shafts in the same diiection in response to the drive torque and to force rotation of the first and second output shafts in opposite directions.

The torque applicator may apply a drive torque in first and second directions corresponding to drive and overrun operation.

The differential testing device may be used for testing an automatic locking diffeiential which is adapted to operate in a locked configuration when a toique difference between the first and second output shafts is below or equal to a threshold locking torque and to operate in an unlocked configuration when the torque difference exceeds the threshold locking torque which allows the first and second output shafts to rotate at different velocities.

The first and second restraining members may be configured to force rotation of the first and second output shafts in opposite directions so as to apply a torque difference which exceeds the threshold locking torque, such that the differential enters the unlocked configuration.

The differential testing device may further comprise: a first torque meter coupled to the first and second restraining members, the first torque meter being configured to measure the torque difference applied by the first and second restraining members.

The first torque meter may be configured to measure the maximum torque difference applied by the first and second restraining members, the maximum torque difference corresponding to the threshold locking torque.

The first torque meter may be configured to measure the threshold locking torque at one or more drive torques applied by the drive torque applicator.

The differential testing device may further comprise: a second torque meter coupled to the drive torque applicator, the second torque meter being configured to measure a drive torque applied to the differential by the drive torque applicator.

The second torque meter may be a load cell. The load cell may be a compression and/or tension load cell.

The drive torque applicator may comprise a loading arm which is configured to be connected to the differential at or toward a first end of the loading arm, with a second opposing end of the loading arm being coupled to a load applicator which is configured to apply a force to the loading arm.

The first restraining member may comprise a first torque arm configured to be connected to the first output shaft at or towards a first end of the first torque arm; and the second restraining member may comprise a second link arm configured to be connected to the second output shaft at or towards a first end of the second torque arm.

The longitudinal axes of the first and second torque arms may be arranged to be perpendicular to rotational axes of the first and second output shafts.

The first restraining means may further comprise a first torque shaft (i.e. a stub axle) which is connected to the first torque arm, a longitudinal axis of the first torque shaft being perpendicular to the longitudinal axis of the fiist torque aim and parallel with the rotational axis of the first output shaft. The second restraining means may further comprise a second torque shaft (i.e. a stub axle) which is connected to the second toique aim, a longitudinal axis of the second torque shaft being perpendiculai to the longitudinal axis of the second torque aim and paiallel with the rotational axis of the second output shaft.

Second opposing ends of the first and second torque arms may be coupled to one anothei such that they aie airanged to move in concert in opposing diiections.

The second ends of the first and second torque arms may be each connected to a linking member, the linking member having a pivot point positioned midway between the fiist and second toique aims.

The differential testing device may further comprise a torque difference applicator connected to the linking member and configured to rotate the linking member about the pivot point.

The torque difference applicator may comprise a torque multiplier having a torque input for manual rotation of the linking member, the torque multiplier being configured to multiply the torque applied thiough the torque input.

The torque multiplier may be coupled to the linking member via the first torque nietei.

The differential testing device may further comprise: a base plate comprising one or nioie mounts for connecting the diffeiential to the base plate; the base plate having a male or female T-slot element extending in a direction which is parallel to the rotational axes of the fiist and second output shafts. At least one of the fiist and second restraining members may comprise a mounting bracket having the other of a male or female T-slot element which is configured to be slidably received in the T-slot element of the base plate.

This arrangement may allow the mounts to be moved and located in appropriate positions for the differential to be tested.

According to an aspect of the invention there is provided a method of testing a differential comprising: applying a drive torque to the differential; restraining first and second output shafts of the differential so as to prevent rotation of the first and second output shafts in the same direction in response to the drive torque; and forcing rotation of the first and second output shafts in opposite directions.

The differential may be an automatic locking differential which is adapted to operate in a locked configuration when a torque difference between the first and second output shafts is below or equal to a threshold locking torque and to operate in an unlocked configuration when the torque difference exceeds the threshold locking torque which allows the first and second output shafts to rotate at different velocities.

The method may further comprise: forcing rotation of the first and second output shafts in opposite directions so as to apply a torque difference which exceeds the threshold locking torque, such that the differential enters the unlocked configuration.

The method may further comprise: measuring the torque difference applied to the first and second output shafts.

The maximum torque difference applied to the first and second output shafts may be measured, the maximum torque difference corresponding to the threshold locking torque.

The method may further comprise: measuring the drive torque applied to the differential.

The maximum torque difference may be measured for a plurality of different drive torques.

For a better understanding of the present disclosure, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:-Figure 1 is a perspective view of a differential testing device according to an embodiment of the invention; Figure 2 is a top cross-sectional view of the differential testing device; Figure 3 is rear cross-sectional view of the differential testing device; Figure 4 is an enlarged perspective view of an input torque section of the differential testing device; Figures 5 to 9 are perspective views of the differential testing device depicting the stages of assembling the device; and Figure 10 is an exemplary graph produced by the differential testing device.

With reference first to Figure 1, a differential testing device 10 according to an embodiment of the invention is shown. The differential testing device 10 may be used to test a differential 4.

The differential 4 comprises an outer casing 6 having a first output portion 6a, a second output portion 6b and a central portion 6c.

The differential to be tested may be an automatic locking differential which is adapted to operate in a locked configuration when a torque difference between its first and second output shafts is below or equal to a threshold locking torque and to operate in an unlocked configuration when the torque difference exceeds the threshold locking torque which allows the first and second output shafts to rotate at different velocities.

The differential testing device 10 comprises a base plate 12. The base plate 12 comprises a first portion 12a and a second portion 12b arranged in a T-shape such that longitudinal axes of the first and second portions 1 2a, 1 2b are perpendicular to one another.

The first portion 12a comprises a plurality of slotted passages 14a which extend along the longitudinal axis of the first portion 12a. The plurality of slotted passages 14a are spaced across the first portion 12a and are parallel to one another. The slotted passages 14a extend along the entire longitudinal extent of the first portion 12a. Alternatively, slotted passages 14a may extend toward the centre of the first portion 12a from each end of the first portion 12a, but not meet at the centre.

Likewise, the second portion 12b comprises a plurality of slotted passages 14b which extend along the longitudinal axis of the second portion 12b. The plurality of slotted passages 14b are spaced across the second portion 12b and are parallel to one another. The slotted passages 14b extend along only a section of the second portion 12b which is spaced from the first portion 12a. Accordingly, the slotted passages 14b are provided at only a distal end of the first portion 12a. Alternatively! the slotted passages 14b may extend along the entire longitudinal extent of the second portion 12b.

The slotted passages 14a of the first portion 12a extend in a direction which is perpendicular to that of the slotted passages 14b of the second portion 14b.

The slotted passages 14a, 14b of the first and second portions 12a, 12b have a generally T-shaped cross-section. The term T-shaped cross-section encompasses other suitable cross-sections for retaining a complementary member and is not limited to strictly T-shapes. For example, the slotted passages 14a, 14b may have any form which is narrower at the surface of the base plate 12.

In the embodiment shown, the slotted passages 14a, 14b are defined by a plurality of grooves formed in the surface of base plate 12. A plurality of cover plates are affixed to the surface of the base plate 12 with their longitudinal axes aligned parallel to the grooves. The cover plates are spaced apart from one another but extend partially over the grooves to define a slot which is narrower than the groove.

The slotted passages 14a of the first portion 12a receive a pair of differential mounting brackets 16 each having a circular opening therethrough. The differential mounting brackets 16 are each formed by a lower section 1 6a and an upper section 16b. The lower section 16a and the upper section 16b each define a semicircular recess which together define the circular opening.

The lower section 16a is connected to the first portion 12a of the plate 12 by a complementary T-shaped retaining nut (not shown) which is received within and retained by the slotted passages 14a. This arrangement allows the differential mounting brackets 16 to translate along the slotted passages 14a (along the longitudinal axes of the first portion 12a) but restricts movement of the differential mounting brackets 16 in directions which are perpendicular to the longitudinal axis of the first portion 12a. However, once in the desired position, the differential mounting brackets 16 can be locked in position by tightening the retaining nuts.

The upper section 16b of each differential mounting bracket 16 is detachably connected to the lower section 16a by a pair of thumb nuts 18 which are each received on a threaded rod 19 (see Figure 5) that projects from the lower section 16a.

In use, the differential mounting brackets 16 receive and restrain the differential 4 to be tested by the differential testing device 2. The first and second output portions 6a, 6b of the casing 6 of the differential 4 are held between the lower and upper portions 16a, 16b of the differential mounting brackets 16.

The first portion 12a of the plate 12 also receives a first restraining member 20a and a second restraining member 20b.

The first and second restraining members 20a, 2Db comprise first and second mounting portions 22a, 22b respectively. The first and second mounting portions 22a, 22b are received by the slotted passages 14a of the first portion 12a. The first and second mounting portions 22a, 22b each comprise a pair of locking levers 24 which affix the first and second mounting portions 22a, 22b to the first portion 12a of the plate 12.

Referring now also to Figures 2 and 3, the first and second mounting portions 22a, 22b receive first and second stub axles 26a, 26b respectively. The first and second stub axles 26a, 26b are located within first and second sleeves 27a, 27b which pass through the first and second mounting portions 22a, 22b and are supported by annular bearings to allow rotation of the first and second stub axles 26a, 26b relative to the first and second mounting portions 22a, 22b.

As shown in Figure 3, each of the differential mounting brackets 16 is provided with a limit screw 23 which projects from the side of the lower section 1 6a thereof in a direction which is parallel to the slotted passages 14a of the first portion 12a of the base plate 12. Each limit screw 23 is provided with a nut 25 which is received on a threaded shaft of the limit screw 23 and limits the depth to which the threaded shaft can be received by the lower section 16a of the differential mounting bracket 16.

Accordingly, a head of each limit screw 23 is spaced from the lower section 16a of the differential mounting bracket 16 by a portion of the threaded shaft. The heads of the limit screws 23 abut the first and second mounting portions 22a, 22b. Each limit screw 23 therefore dictates the minimum distance between the differential mounting bracket 16 and the adjacent first or second mounting portion 22a, 22b. The limit screws 23 therefore allow the first and second mounting portions 22a, 22b to be quickly assembled. The position of the nut 25 on each limit screw 23 can be altered to suit the differential 4 being tested.

In use, inner ends of the first and second stub axles 26a, 26b are received within the first and second output portions 6a, 6b of the differential 4 and are coupled with first and second output shafts of the differential 4. The rotational axes of the first and second stub axles 26a, 26b are aligned with the rotational axes of the first and second output shafts of the differential 4.

Outer ends of the first and second stub axles 26a, 26b are connected to first and second elongate torque arms 28a, 28b respectively via flanged portions of the first and second sleeves 27a, 27b. The flanged portions of the first and second sleeves 27a, 27b are attached to the first and second torque arms 28a, 28b toward one end of the first and second torque arms 28a, 28b. The first and second torque arms 28a, 28b extend perpendicularly from the stub axles 26a, 26b with their longitudinal axes parallel to the longitudinal axis of the second portion 12b of the plate 12. At a distal end of each of the first and second torque arms 28a, 28b an aperture 30 is formed.

The aperture 30 of the first torque arm 28a receives a first end of a link rod 32 and the aperture 30 of the second torque arm 28b receives a second end of the link rod 32. The link rod 32 is coupled to the first and second torque arms 28a, 28b by spherical bearings which allow the orientation of the first and second torque arms 23a, 23b to be altered relative to the link rod 32. The link rod 32 couples the first and second torque arms 28a, 28b to one another.

The link rod 32 is connected at its centre to an input shaft 34 (see Figure 2). The link rod 32 and the input shaft 34 are perpendicular to one another such that the link rod 32 extends parallel to the first and second torque arms 28a, 28b (when level) and to the longitudinal axis of the second portion 12b of the base plate 12.

The link rod 32 is coupled to the input shaft 34 by a cylindrical sleeve 36 disposed at the end of the input shaft 34. The link rod 32 passes through the cylindrical sleeve 36 and is supported within the cylindrical sleeve 36 by low friction bearings, such as needle roller bearings, which allow the link rod 32 to rotate within the cylindrical sleeve 34.

The cylindrical sleeve 36 is connected to the input shaft 34 by a diaphragm coupling 38. The diaphragm coupling 38 allows the orientation of the cylindrical sleeve 36 (and thus the link rod 32) to vary by a small amount relative to the input shaft 34.

The diaphragm coupling 38 thus accommodates minor misalignments or small differences in the length of the first and second torque arms 28a, 28b.

The input shaft 34 is rotatably connected to the second portion 12b of the base plate 12 by a first supporting bracket 40. The first supporting bracket 40 is affixed to the second portion 12b of the base plate 12 in a desired position via the slotted passages 14b using complementary T-shaped retaining nuts. The input shaft 34 passes through an opening in the first supporting bracket 40 where it is supported by low friction bearings, such as ball bearings, which allow the input shaft 34 to rotate relative to the first supporting bracket 40.

The link rod 32 is therefore arranged to pivot about the rotational axis of the input shaft 34 which is positioned midway between the first and second torque arms 28a, 28b.

Consequently, the first and second torque arms 28a, 28b are coupled to one another by the link rod 32 such that they are arranged to move in concert in opposing directions.

The input shaft 34 is connected to a torque multiplier 42 via a first torque sensor 44 (or meter) which is coaxial with the input shaft 34.

The torque multiplier 42 and first torque sensor 44 are supported by a second supporting bracket 46. As per the first supporting bracket 40, the second supporting bracket 46 is affixed to the second portion 12b of the base plate 12 in a desired position via the slotted passages 14b using complementary T-shaped retaining nuts.

As shown particularly in Figure 4, the torque multiplier 42 comprises an input connection in the form of a socket 48. The socket 48 is configured to receive an Allen key or other suitable tool for providing an input torque to the torque multiplier 42 by hand. The torque multiplier is configured to multiply the input torque provided via the socket 48 and to provide a much larger output torque at the output connection of the torque multipliei 42. The output connection of the torque multiplier 42 is connected to the input shaft 34 via the first torque sensor 44.

The diffeiential testing device 10 fuither comprises a loading aim 50 (or torque applicator). The loading arm 50 has an opening 51 at one end of the loading aim 50 which receives the diffeiential to be tested 4 and couples the loading aim 50 to the central portion 6c of the outer casing 6. The loading arm 50 may be coupled to the central portion 6c of the outer casing 6 through a final drive of the differential 4 or through any other suitable connection which allows a drive toique to be applied to the differential 4. By acting in two diffeient directions, the loading arm 50 is able to test the differential 4 in drive and overrun conditions, as will be described below.

A distal end of the loading aim 50 is disposed within a channel formed in a guide plate 54 which is attached to the first supporting bracket 40. The guide plate 54 is provided to prevent damage or incorrect use, and to assist with assembly.

The othei distal end of the loading arm 50 is connected to a load application device 52, such as a lead screw or jack. The load application device 52 is connected to the second portion 12b of the base plate 12 via the slotted passages 14b. The load application device 52 is configured to apply a drive torque to the differential which acts to raise the loading arm 50 away from the base plate 12 oi lower the loading arm 50 towards the base plate 12.

The load application device 52 comprises a second torque sensor 55 (or meter) which is configured to measure the torque applied to the differential by the load application device 52 via the loading arm 50. The second torque sensor 55 compiises a load cell which is able to measuie cornpiession and/or tension loads.

The loading arm 50 tapers from the end at the differential 4 to the end at the load application device 52. The tapered nature of the loading arm 50 allows the loading arm to be lowered without coming into contact with the base plate 12. However, the loading arm 50 need not taper, if so desired.

The load application device 52 and the guide plate 54 are configured so as to allow the loading arm 50 to be offset from the centre of base plate 12. This may be utilised based on the differential being tested and the mechanism by which the loading arm 50 is connected to the differential.

The assembly of the differential testing device 10 will now be described with reference to the different stages of assembly shown in Figures 5 to 9.

As shown in Figure 5, the lower sections 16a of the differential mounting brackets 16 are attached to the first portion 12a of the base plate 12. The lower sections 16a of the differential mounting brackets 16 may, at first, be attached to the first portion 12a of the base plate l2so that they are able to translate along the slotted passages 14a. Once the lower sections 16a are in the desired position (corresponding to the dimensions of the differential 4), they may be locked in position. The differential mounting brackets 16 are preferably able to accommodate differentials ranging from approximately 10cm to 40cm in width, although smaller or larger designs may be implemented. In addition, it is worth noting that differentials need not be symmetrical about the torque application point. The differential mounting brackets 16 can also be arranged to accommodate such differentials.

The differential 4 with the loading arm 50 already attached to the outer casing 6 is then lowered onto the lower sections 16a of the differential mounting brackets 16, as shown in Figure 6. The first and second output portions 6a, 6b of the casing 6 of the differential 4 are seated on the lower sections 16a of the differential mounting brackets 16.

The load application device 52 is connected to the second portion 12b of the base plate 12 via the slotted passages 14b. Again, the load application device 52 may, at first, be slidably connected to the second portion 12b of the base plate 12 and then later locked in position.

As shown in Figure 7, the upper sections 16b of the differential mounting brackets 16 are then received over the first and second output portions 6a, 6b and fastened to the lower sections 1 6a. The upper sections 1 6b receive the threaded rods 19 which project from the lower sections 1 6a and are fastened to the lower sections 16a using the thumb nuts 18.

The first and second supporting brackets 40, 46 carrying the link rod 32, input shaft 34, torque multiplier 42 and first torque sensor 44 are also attached to the second portion 12b of the base plate 12 via the slotted passages 14b. The channel of the guide plate 54 is received around the end of the loading arm 50 and load application device 52.

As shown in Figures 8 and 9, the first and second restraining members 20a, 20b are then attached to the differential testing device 10.

The first and second mounting portions 22a, 22b are slidably received by the slotted passages 14a of the first portion 12a of the base plate 12. The first and second mounting portions 22a, 22b are translated such that the inner ends of the first and second stub axles 26a, 26b are received within the first and second output portions 6a, 6b of the differential 4 and are coupled with the first and second output shafts of the differential 4.

The first and second mounting portions 22a, 22b are then locked in position on the first portion 12a of the plate 12 using the locking levers 24.

As the first and second mounting portions 22a, 22b are slid into position on the first portion 1 2a of the base plate 12, the apertures 30 at the distal ends of the first and second torque arms 28a, 28b receive the ends of the link rod 32.

Figure 9 shows the fully assembled differential testing device 10 which is ready to test the differential 4. The operation of the differential testing device 10 will now be described in detail.

In the following description, the differential to be tested is an automatic locking differential which is adapted to operate in a locked configuration when a torque difference between its first and second output shafts is below or equal to a threshold locking torque and to operate in an unlocked configuration when the torque difference exceeds the threshold locking torque which allows the first and second output shafts to rotate at different velocities.

The loading arm 50 is configured to apply a drive torque to the differential 4. This is achieved by applying a load to the loading arm 50 using the load application device 52 (i.e. applying a force to the loading arm 50 acting either upwards or downwards).

This may be achieved by rotating the load application device using an Allen key or

other suitable tool.

The drive torque applied by the loading arm 50 acts to rotate the differential 4. This acts to cause the fiist and second output shafts to rotate in the same direction. As described above, the first and second output shafts are connected to the first and second torque arms 28a, 28b via the first and second stub axles 26a, 26b. The first and second toique arms 28a, 28b are coupled to one another by the link iod 32 such that they aie arianged to move in conceit in opposing directions and are not able to rotate in the same direction. Consequently, the first and second torque arms 28a, 28b prevent the first and second output shafts from rotating in the same direction in response to the drive torque applied by the loading arm 50. This creates a static load across the differential 4.

The drive torque applied to the differential 4 is measured by the second torque sensor 55 which (possibly, following subsequent manipulation) outputs a calibrated torque value.

The first and second torque arms 28a, 28b are prevented from rotating in opposite directions by the locking mechanism (when in the locked configuration) of the differential 4. In order to rotate the first and second torque arms 28a, 28b in opposite directions it is necessary to supply a sufficient torque difference between the first and second output shafts of the differential 4 to exceed the threshold locking torque.

Once the differential 4 is in the unlocked configuration, the first and second output shafts are able to rotate at different velocities. In the static frame of reference implemented by the differential testing device 10, the different velocities of the first and second outputs shafts are seen through the rotation of the first and second output shafts in opposite directions.

The first and second torque arms 28a, 28b can therefore be used to measure the threshold locking torque of the differential 4.

This is achieved by applying an input torque to the torque multiplier 42 using an Allen key or other similar tool. The multiplied input torque is transmitted to the input shaft 34 via the first torque sensor 44. The torque acts to rotate the link rod 32 and thus to rotate the first and second torque arms 28a, 28b in opposite directions.

As described above, the locking mechanism of the differential 4 withstands the movement of the first and second torque arms 28a, 28b until the applied torque exceeds the threshold locking torque.

The first torque sensor 44 measures the torque applied across the differential by the opposite movement of the first and second torque arms 28a, 28b. The maximum torque measured by the first torque sensor 44 corresponds to the threshold locking torque of the differential 4 at that drive torque. The torque measured by the first torque sensor 44 is calibrated to represent the torque across the differential and is nota direct measure of torque applied at the link rod 32.

It is important that the link rod 32 is not rotated past the maximum deflection point where it locks out as this will create a large torque and thus invalidate the reading of the first torque sensor 44. An additional sensor may be provided to indicate if the link rod 32 has been rotated past the maximum deflection point and thus to allow the reading from the first torque sensor 44 to be disregarded.

This process can be repeated for a plurality of different drive torques by adjusting the load applied through the loading arm 50 using the load application device 52.

Similarly, the loading arm 50 can be rotated in the opposite direction in order to produce data for both drive and overrun.

Figure 10 shows an exemplary graph of the data points produced by the differential testing device 10. The graph shows the input torque (in Nm) applied by the loading arm 50 along the x-axis and the threshold locking torque (in Nm) along the y-axis.

As shown, the differential 4 may have a relatively low threshold locking torque at low input torque values (both in drive and overrun), but have a relatively high threshold locking torque at high input torque values.

The differential testing device 10 thus allows the locking mechanism of the differential 4 to be characterised. The differential testing device 10 also allows the differential gain to be determined and provides information regarding the symmetry and friction of the differential 4.

The differential testing device 10 can be used to test the differential 4 immediately prior to the final build. The differential testing device 10 is particularly suited to investigating the change in the characteristics of the differential 4 following modifications to the differential 4. For example, the clutch arrangement of the diffeiential 4 may be modified and the differential testing device 10 used to understand how this has affected the characteristics of the differential 4.

The dimensions of the diffeiential testing device 10 aie approximately 100cm in length and 60cm in width. The differential testing device 10 is therefore a very compact design which is easily transported.

The differential testing device 10 only uses two torque sensors and thus has a very simple design. This means that the diffeiential testing device 10 is robust and relatively inexpensive to manufactuie.

The differential testing device 10 creates a static load across the differential.

Accordingly, it is not necessary to rotate the differential at high speeds in order to characterise its performance.

Although the invention has been described with reference to testing of an automatic locking differential which is noimally in the locked configuration, it may find applications in other types of differential. For example, the differential testing device may be used with automatic locking differentials which are normally unlocked.

Moreover, the differential testing device may be used to determine the differential gain and friction of a nornial open diffeiential.

Further, although the differential testing device has been described as comprising the first and second toique aims and the loading arm, it is cleai that the inventive concept may be applied using alternative arrangements. For example, the drive torque may be applied using a suitable rotary device. Likewise, the output shafts of the differential may be restiained using appropriate rotaiy devices which are coupled either mechanically or electronically so that they synchronously rotate the output shafts in opposite directions.

In addition, the input torque to the link rod need not be applied by hand and could instead arise fiom a suitable actuator.

Claims

Claims 1. A differential testing device for testing a differential, the device comprising: a drive torque applicator configured to be coupled to the differential and to apply a drive torque to the differential; a first restraining member adapted to couple with a first output shaft of the differential; and a second restraining member adapted to couple with a second output shaft of the differential; wherein the first and second restraining members are configured to prevent rotation of the first and second output shafts in the same direction in response to the drive torque and to force rotation of the first and second output shafts in opposite directions.
2. A differential testing device as claimed in claim 1, wherein the device is used for testing an automatic locking differential which is adapted to operate in a locked configuration when a torque difference between the first and second output shafts is below or equal to a threshold locking torque and to operate in an unlocked configuration when the torque difference exceeds the threshold locking torque which allows the first and second output shafts to rotate at different velocities; and wherein the first and second restraining members are configured to force rotation of the first and second output shafts in opposite directions so as to apply a torque difference which exceeds the threshold locking torque, such that the differential enters the unlocked configuration.
3. A differential testing device as claimed in claim 1, the device further comprising: a first torque meter coupled to the first and second restraining members, the first torque meter being configured to measure the torque difference applied by the first and second restraining members.
4. A differential testing device as claimed in claim 3, wherein the first torque meter is configured to measure the maximum torque difference applied by the first and second restraining members, the maximum torque difference corresponding to the threshold locking torque.
5. A differential testing device as claimed in claim 4, wherein the first torque meter is configured to measure the threshold locking torque at one or more drive torques applied by the drive torque applicator.
6. A differential testing device as claimed in any preceding claim, the device further comprising: a second torque meter coupled to the drive torque applicator, the second torque meter being configured to measure a drive torque applied to the differential by the drive torque applicator.
7. A differential testing device as claimed in claim 6, wherein the second torque meter is a load cell.
8. A differential testing device as claimed in any preceding claim, wherein the drive torque applicator comprises a loading arm, wherein the loading arm is configured to be connected to the differential at or toward a first end of the loading arm, with a second opposing end of the loading arm being coupled to a load applicator which is configured to apply a force to the loading arm.
9. A differential testing device as claimed in any preceding claim, wherein the first restraining member comprises a first torque arm configured to be connected to the first output shaft at or towards a first end of the first torque arm; and wherein the second restraining member comprises a second torque arm configured to be connected to the second output shaft at or towards a first end of the second torque arm.
10. A differential testing device as claimed in claim 9, wherein longitudinal axes of the first and second torque arms are arranged to be perpendicular to rotational axes of the first and second output shafts.
11. A differential testing device as claimed in claim 10, wherein the first restraining means further comprises a first torque shaft which is connected to the first torque arm, a longitudinal axis of the first torque shaft being perpendicular to the longitudinal axis of the first torque arm and parallel with the rotational axis of the first output shaft; and wherein the second restraining means further comprises a second torque shaft which is connected to the second torque arm, a longitudinal axis of the second torque shaft being perpendicular to the longitudinal axis of the second torque arm and parallel with the rotational axis of the second output shaft.
12. A differential testing device as claimed in any of claims 9 to 11, wherein second opposing ends of the first and second torque arms are coupled to one another such that they are arranged to move in concert in opposing directions.
13. A differential testing device as claimed in claim 12, wherein the second ends of the first and second torque arms are each connected to a linking member, the linking member having a pivot point positioned midway between the first and second torque arms.
14. A differential testing device as claimed in claim 13, further comprising a torque difference applicator connected to the linking member and configured to rotate the linking member about the pivot point.
15. A differential testing device as claimed in claim 14, wherein the torque difference applicator comprises a torque multiplier having a torque input for manual rotation of the linking member, the torque multiplier being configured to multiply the torque applied through the torque input.
16. A differential testing device as claimed in claim 15 when dependent on any of claims 3 to 5, wherein the torque multiplier is coupled to the linking member via the first torque meter.
17. A differential testing device as claimed in any preceding claim, the device further comprising: a base plate comprising one or more mounts for connecting the differential to the base plate; the base plate having a male or female T-slot element extending in a direction which is parallel to the rotational axes of the first and second output shafts; wherein at least one of the first and second restraining members comprises a mounting bracket having the other of a male or female T-slot element which is configured to be slidably received in the T-slot element of the base plate.
18. A differential testing device substantially as disclosed herein with reference to and as shown in the accompanying drawings.
19. A method of testing a differential comprising: applying a drive torque to the differential; restraining first and second output shafts of the differential so as to prevent rotation of the first and second output shafts in the same direction in response to the drive torque; and forcing rotation of the first and second output shafts in opposite directions.
20. A method of testing a differential as claimed in claim 19, wherein the differential is an automatic locking differential which is adapted to operate in a locked configuration when a torque difference between the first and second output shafts is below or equal to a threshold locking torque and to operate in an unlocked configuration when the torque difference exceeds the threshold locking torque which allows the first and second output shafts to rotate at different velocities; the method further comprising: forcing rotation of the first and second output shafts in opposite directions so as to apply a torque difference which exceeds the threshold locking torque, such that the differential enters the unlocked configuration.
21. A method of testing a differential as claimed in claim 20, further comprising: measuring the torque difference applied to the first and second output shafts.
22. A method of testing a differential as claimed in claim 21, wherein the maximum torque difference applied to the first and second output shafts is measured, the maximum torque difference corresponding to the threshold locking torque.
23. A method of testing a differential as claimed in claim 22, further comprising: measuring the drive torque applied to the differential.
24. A method of testing a differential as claimed in claim 23, wherein the maximum torque difference is measured for a plurality of different drive torques.
25. A method of testing a differential substantially as disclosed herein.