CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 62/222,917 filed on September 24, 2015; U.S. Provisional Patent Application No. 62/261 ,497 filed on December 1 , 2015; U.S. Provisional Patent Application No. 62/301 ,086 filed February 29, 2016; and Indian Patent Application No. 201611014792 filed on April 28, 2016. The disclosures of the above applications are incorporated herein by reference.

FIELD

[0002] The present disclosure relates generally to a vehicle differential and, more particularly, to an electro-hydraulic limited slip differential.

BACKGROUND

[0003] Differentials are provided on vehicles to permit an outer drive wheel to rotate faster than an inner drive wheel during cornering as both drive wheels continue to receive power from the engine. While differentials are useful in cornering, they can allow vehicles to lose traction, for example, in snow or mud or other slick mediums. If either of the drive wheels loses traction, it will spin at a high rate of speed and the other wheel may not spin at all. To overcome this situation, limited slip differentials were developed to shift power from the drive wheel that has lost traction and is spinning to the drive wheel that is not spinning.

[0004] Electronically controlled, limited slip differentials can include a hydraulically actuated clutch to limit differential rotation between output shafts of the differential. However, some vehicles may experience trailer sway or oversteer during cornering. While such known systems function for their intended purposes, it is desirable to provide improved differential systems to counteract or mitigate trailer sway.

[0005] The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.

SUMMARY

[0006] In one aspect, an electro-hydraulic limited slip differential system for a vehicle is provided. The system includes an axle assembly having an axle housing having an aperture formed therein, and an electro-hydraulic limited slip differential assembly disposed within the axle housing. The limited slip differential assembly includes a differential case, a differential gear assembly disposed in the differential case, a clutch assembly having a clutch pack and a clutch actuator assembly, and a hydraulic fitting disposed at least partially within the aperture. The hydraulic fitting is coupled to a hydraulic port of the clutch actuator assembly.

[0007] In addition to the foregoing, the described system may include one or more of the following features: a hydraulic control unit configured to be coupled to a portion of the vehicle remote from the axle assembly, the hydraulic control unit coupled to the hydraulic fitting and configured to supply a hydraulic fluid to the clutch actuator assembly to selectively actuate the clutch assembly; wherein the hydraulic control unit is configured to couple to a cross-member of the vehicle underbody; wherein the hydraulic control unit includes an integrated accumulator and sump; wherein the hydraulic control unit further includes a motor, a hydraulic pump, and at least one sensor; wherein the hydraulic fitting is a dual O-ring seal configured to fluidly seal the clutch actuator assembly and a sump of the axle assembly; a plurality of force transfer rods that couple the clutch pack and the clutch actuator assembly; wherein the clutch pack is disposed inside the differential case, and the clutch actuator assembly is disposed outside of the differential case; wherein the clutch actuator assembly is rotatably coupled to a hub protruding from the differential case; a plurality of transfer rods coupled between the clutch pack and the clutch actuator assembly; wherein the clutch pack further comprises a first transfer plate and the clutch actuator assembly further comprises a second transfer plate, wherein the plurality of transfer rods is coupled between the first and second transfer plates; wherein the clutch actuator assembly includes a piston received in a piston housing, the actuator assembly configured to actuate the clutch pack.

[0008] In another aspect, a vehicle is provided. The vehicle includes an underbody support member and an electro-hydraulic limited slip differential system. The system includes an axle assembly including an axle housing having an aperture formed therein, a hydraulic control unit coupled to the underbody support member at a location remote from the axle assembly, and an electro-hydraulic limited slip differential assembly disposed within the axle housing. The differential assembly includes a differential case, a differential gear assembly disposed in the differential case, and a clutch assembly having a clutch pack and a clutch actuator assembly. A hydraulic fitting is disposed at least partially within the aperture and is coupled to a hydraulic port of the clutch actuator assembly and to the hydraulic control unit. The hydraulic control unit is configured to supply a hydraulic fluid to the clutch actuator assembly to selectively actuate the clutch assembly.

[0009] In addition to the foregoing, the described vehicle may include one or more of the following features: wherein the underbody support member is a cross- member of the vehicle underbody; wherein the hydraulic control unit includes an integrated accumulator and sump; wherein the hydraulic control unit further includes a motor, a hydraulic pump, a control valve, and at least one sensor; wherein the hydraulic control unit includes a first electrical conduit coupled to the control valve, a second electrical conduit coupled to the motor and hydraulic pump, and a third electrical conduit coupled to the at least one sensor, the first, second, and third electrical conduits electrically coupled to an electronic control module; a hydraulic conduit fluidly coupled between the hydraulic control unit and the hydraulic fitting; an electronic control unit disposed within the vehicle and in signal communication with the hydraulic control unit; and a selector box in signal communication with the hydraulic control unit, the selector box configured to switch the electro-hydraulic limited slip differential system on and off. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein:

[0011] FIG. 1 is a side view of an example electro-hydraulic limited slip differential system in accordance with the principles of the present disclosure;

[0012] FIG. 2 is another side view of the electronic limited slip differential system with an example hydraulic control unit removed in accordance with the principles of the present disclosure;

[0013] FIG. 3 is a cross-sectionai view of the limited slip differential system shown in FIGS. 1 and 2;

[0014] FIG. 4 is a perspective view of an example limited slip differential assembly that may be used in the system shown in FIGS. 1-3 in accordance with the principles of the present disclosure;

[0015] FIG. 5 is an exploded view of the limited slip differential assembly shown in FIG. 4;

[0016] FIG. 6 is a perspective view of an example hydraulic control unit shown in FIG. 1 in accordance with the principles of the present disclosure;

[0017] FIG. 7 is perspective view of the hydraulic control unit shown in FIG. 1 secured to a vehicle underbody;

[0018] FIG. 8 is a perspective view of an example wiring harness and cab pass-through that may be used with the system shown in FIG. 1 in accordance with the principles of the present disclosure;

[0019] FIG. 9 is a perspective view of an example electronic control unit that may be used in signal communication with the system shown in FIG. 1 in accordance with the principles of the present disclosure; and

[0020] FIG. 10 is a perspective view of an example selector box that may be used in signal communication with the system shown in FIG. 1 in accordance with the principles of the present disclosure. DETAILED DESCRIPTION

[0021] With initial reference to FIGS. 1-3, an example electro-hydraulic limited slip differential (LSD) system 10 is shown. In the illustrated example, the electro- hydraulic LSD system 10 generally includes an axle assembly 12, an electro-hydraulic limited slip differential assembly 14 (FIGS. 3-5), and a hydraulic control unit 16.

[0022] With reference to FIGS. 3-5, the electronic limited differential assembly 14 can generally include a differential gear assembly or mechanism 18 arranged in a differential case 20, and a clutch assembly 22. The limited slip differential assembly 14 can be received in a housing 26 of the axle assembly 12 and operates to drive a pair of axle shafts (not shown) received through axle shaft openings 28, 30 and connected to drive wheels (not shown). In general, the limited slip differential assembly 14 functions as a traditional open differential during normal operating conditions until an event occurs where a bias torque is required. For example, when a loss in traction is detected or anticipated, the clutch assembly 22 can be selectively actuated in order to generate the optimum bias ratio for the situation.

[0023] With continued reference to FIGS. 4 and 5, the differential gear assembly 18 can include a pair of side gears 32, 34 that are mounted for rotation with the axle shafts (and first and second drive wheels). The side gears 32, 34 define first and second axle shaft openings 36, 38 (FIG. 3). A cross pin or pinion gear shaft 40 can be fixedly mounted to the differential case 20 for rotation therewith. A corresponding set of pinion gears 42 (e.g., three pinion gears 42) are mounted for rotation with the pinion gear shaft 40 and are in meshing relationship with both of the side gears 32, 34. In an open configuration, described more fully below, the differential gear assembly 18 acts to allow the axle shafts to rotate at different speeds.

[0024] The clutch assembly 22 couples an input of the limited slip differential assembly 14 with the differential gear assembly 18. In some examples, the input can comprise a ring gear fixedly arranged around the differential case 20 that is driven by a pinion gear. The clutch assembly 22 can generally comprises a clutch pack 24 and a piston/plenum or clutch actuator assembly 44. [0025] The clutch pack 24 includes a plurality of annular plates 46 interleaved between a plurality of annular friction disks 48. The plurality of annular plates 46 can be coupled for rotation with one of the differential case 20 and the differential gear assembly 18. The plurality of annular friction disks 48 can be coupled for rotation with the other one of the differential case 20 and the differential gear assembly 18.

[0026] In the illustrated example, the plurality of annular plates 46 are coupled for rotation to the differential case 20 (e.g., splined to an inner diameter of the differential case 20) and the plurality of annular friction disks 48 are coupled for rotation with the differential gear assembly 18 (e.g., splined to an outer diameter of the side gear 32). It will be appreciated that the annular friction disks 48 may be supported for rotation by either of the side gears 32 or 34, or both. A first transfer plate 50 can be arranged as part of the clutch pack 24.

[0027] The plurality of annular plates 46 and annular friction disks 48 are interleaved between one another and act to rotate past one another in substantially non- contacting relationship when the clutch assembly 22 is in its open position. However, it will be appreciated by those skilled in the art that the term "non-contacting" as used herein is relative and is not meant to necessarily indicate that the annular plates 46 and annular friction disks 48 have absolutely no contact when the clutch assembly 22 is in the open condition. The annular plates 46 and annular friction disks 48 are axially movable into frictional engagement relative to one another, thereby reducing relative rotation between the annular plates 46 and annular friction disks 48 when the clutch assembly 22 is in the closed or partially closed configurations. In this manner, when the clutch assembly 22 is in its closed position, the side gears 32, 34, as well as the axle shafts and the drive wheels rotate together.

[0028] The clutch assembly 22 can operate in an open configuration to allow the side gears 32, 34 to rotate independently from each other, e.g., at different speeds. The clutch assembly 22 can also operate in a closed or partially closed configuration where the side gears 32, 34 rotate together or partially together (that is, not independently), e.g., at substantially the same speed. The clutch assembly 22 can, for example, be a hydraulic clutch assembly 22 that utilizes pressurized hydraulic fluid that can act on the clutch actuator assembly 44 to selectively actuate the clutch pack 24 between the open, closed and partially closed configurations.

[0029] With particular reference now to FIGS. 3-5, the clutch actuator assembly 44 will be further described. The clutch actuator assembly 44 is arranged on an opposite end of the differential case 20 as the clutch pack 24. Moreover, the clutch actuator assembly 44 can be disposed on an outside of the differential case 20, and the clutch pack 24 can be disposed inside the differential case 20. As shown in FIG. 4, the clutch actuator assembly 44 can be rotatably mounted to a hub 52 extending from the differential case 20. As a result, a number of advantages are realized. For example, the resulting package size of the electronic limited slip differential assembly 14 is reduced, the cross-shaft 40 is centered between bearing races, and stock axle shafts having standard lengths can be used. Moreover, the clutch pack 24 can be constructed larger to provide greater torque capacity, and the electronic limited slip differential assembly 14 can be replaced with an "open" differential on the same assembly line.

[0030] The clutch actuator assembly 44 can generally include a retainer 60, a first needle roller 62, a bearing race 64, a piston housing 66, a piston 68, a series of O- rings 70, a second needle roller 72, and a second transfer plate 74. The second transfer plate 74 can act as a bearing race for the second needle roller 72. The piston housing 66 can generally define an annular pocket 76. The piston 68 is configured to ride within the annular pocket 76 upon introduction of hydraulic fluid between the piston 68 and the piston housing 66. The O-rings 70 sealingly engage the piston housing 66. During operation, the piston housing 66 does not rotate.

[0031] A plurality of force transfer rods 78 are disposed between the second transfer plate 74 of the clutch actuator assembly 44 and the first transfer plate 50 of the clutch pack 24. The transfer rods 78 can be spaced equally around the differential case 20 and various quantities of transfer rods are contemplated. Furthermore, other structures may be used to transfer force between the first and second transfer plates 50, 74.

[0032] During operation, movement of the piston 68 leftward (as viewed in FIGS. 3-5) causes the force transfer rods 78 to push the first transfer plate 50 leftward causing the clutch pack 24 to close. Similarly, when pressure is released from the piston 68, the force transfer rods 78 move in an axial direction rightward (as viewed in FIGS. 3- 5) causing the clutch pack 24 to open. A hydraulic port 80 can extend from an outer diameter of the piston housing 66 and can be configured to fluidly couple to the hydraulic control unit 16, as described herein in more detail.

[0033] As shown in FIGS. 2 and 3, axle assembly 12 can include a cover 82 that forms part of the axle housing 26, and the cover 82 can include a boss or aperture 84 formed therein disposed proximate to the hydraulic port 80. The aperture 84 is configured to receive a dual O-ring seal hydraulic fitting 86 (FIG. 1) for fluidly coupling to the hydraulic port 80 of the clutch actuator assembly 44. The hydraulic fitting 86 is configured to seal both the hydraulic circuit (FIG. 1) and a sump of the axle assembly 12.

[0034] As shown in FIGS. 1 and 7, the hydraulic control unit 16 is coupled to a vehicle underbody 88 in a location remote from the axle assembly 12 and the electro- hydraulic limited slip differential assembly 14. In the illustrated example, the hydraulic control unit 16 is coupled to a vehicle component that is stationary or generally stationary during movement of the vehicle, for example, a cross-member 90 (FIG. 7) of the vehicle frame. A hydraulic conduit 92 (FIG. 1) can be fluidly coupled between the hydraulic control unit 16 and the hydraulic fitting 86. As such, the hydraulic control unit 16 is configured to supply hydraulic fluid to the clutch actuator assembly 44 for selective actuation thereof.

[0035] As shown in FIGS. 6 and 7, the hydraulic control unit 16 can generally include an integrated accumulator and sump 94, a control valve 96, a motor and hydraulic pump 98, and one or more sensors 100. As illustrated in FIG. 7, electrical conduits 102 can be coupled to each of control valve 96, motor and hydraulic pump 98, and the one or more sensors 100.

[0036] As shown in FIGS. 8-10, the plurality of electrical conduits 102 can be routed through a wire harness and cab pass-through 104 (FIG. 8) and electrically coupled to an Electronic Control Unit (ECU) 106 (FIG. 9). In the illustrated example, ECU 106 can be disposed within a cab 108 of the vehicle. A selector box 110 (FIG. 10) can be disposed inside the vehicle (e.g. on a dashboard) and is configured for signal communication with the ECU 106 to automatically or manually switch the electronic limited slip differential capability of the electronic LSD system 10 on and off. [0037] The foregoing description of the examples has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular example are generally not limited to that particular example, but, where applicable, are interchangeable and can be used in a selected example, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.