TECHNICAL FIELD

The present disclosure relates generally to a vehicle drivetrain and more particularly to a final drive unit for a vehicle.

BACKGROUND

In general, vehicle drivetrains transmit torque from a vehicle's engine to its wheels. Automotive drivetrains conventionally include a differential assembly equipped between sideshafts of a front axle, between sideshafts of a rear axle, or between sideshafts of both axles. Each axle typically includes a left sideshaft and a right sideshaft. The differential assembly allows wheels on one sideshaft to spin faster or slower than wheels on the other sideshaft. This occurs, for instance, when an automobile is turning a corner. The differential assembly also apportions driven torque between the sideshafts. All-wheel drive (A WD) drivetrains conventionally include an additional differential assembly between its front and rear axles to perform similar functions— this is frequently referred to as a center differential. Furthermore, some automotive drivetrains are equipped with disconnect capabilities in which disconnected components are no longer driven to transmit torque between them when torque transmission is not needed. In some vehicles, the front wheels may be positively driven and the rear wheels selectively driven when all-wheel drive performance is desired.

SUMMARY

In at least some implementations, a vehicle final drive unit (FDU) assembly, includes a differential and a torque distribution device. The differential includes a differential case and a differential gear set carried within the differential case. The torque distribution device transfers torque between the differential gear set and a side shaft of the vehicle, and may include a clutch and an actuator assembly. The actuator assembly includes an actuator and a coupler driven by the actuator. The coupler is selectively moved by the actuator to a first position wherein the side shaft is disconnected from the differential and not actively driven, a second position wherein the side shaft is coupled to the differential gear set, a third position wherein the side shaft is coupled to the differential case and a fourth position wherein the coupler actuates the clutch to couple the side shaft to the differential gear set.

In at least some implementations, a vehicle FDU assembly includes a differential including a differential case and a differential gear set carried within said differential case, and a torque distribution device transferring torque between the differential gear set and a side shaft of the vehicle. The torque distribution device may include a clutch and an actuator assembly, where the actuator assembly includes an actuator and a coupler driven by the actuator. The coupler is selectively moved by the actuator to multiple positions wherein in one position of the coupler the side shaft is disconnected from the differential and in another position of the coupler the side shaft is coupled to the differential gear set. The actuator is coupled to the coupler to positively drive the coupler in opposed directions as the actuator moves in opposed directions. This may improve control of the coupler as it is moved back-and-forth among its positions.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings, illustrative embodiments are shown in detail. Although the drawings represent some embodiments, the drawings are not necessarily to scale and certain features may be exaggerated, removed, or partially sectioned to better illustrate and explain the present invention. Further, the embodiments set forth herein are exemplary and are not intended to be exhaustive or otherwise limit or restrict the claims to the precise forms and configurations shown in the drawings and disclosed in the following detailed description.

FIG. 1 is a schematic depiction of a vehicle drivetrain system; FIG. 2 is a cross-sectional view of a differential that may be used in the drivetrain system of FIG. 1 ;

FIG. 3 is a cross-sectional view of a portion of the differential of FIG. 2 showing an actuator and coupler in a first position; FIG. 4 is a cross-sectional view of a portion of the differential showing an actuator and coupler in a second position;

FIG. 5 is a cross-sectional view of a portion of the differential showing an actuator and coupler in a third position;

FIGS. 6 and 7 are cross-sectional views of a portion of the actuator and coupler shown in two different positions; and

FIGS. 8-10 are perspective plan views of a ball-ramp actuator shown in three different positions.

DETAILED DESCRIPTION

Referring in more detail to the drawings, FIG. 1 illustrates a vehicle drivetrain assembly 10 such as one suitable for an automobile. The drivetrain assembly 10 has a transversely mounted engine 12 the power from which is transmitted via a transmission 14, and a plurality of shafts 16, 18, 20, 22 and corresponding articulating torque transfer joints, which are illustrated as constant velocity joints 24. However, other types of joints may be used, such as, but not limited to universal, tripod, cardan, double cardan, and plunging constant velocity joints. The shafts 16, 18, 20, 22, and joints 24, may be used to transmit torque from both a primary power transfer unit (PTU) 26 and the transmission 14 to a plurality of wheels 28. Generally, the engine 12 may be coupled to the transmission 14 through an engine crankshaft (not shown) that is fixed to a transmission input shaft (not shown) to provide torque to the transmission 14. The torque may be transmitted through a series of gears within the transmission 14 and ultimately to a transmission output shaft 30. The engine may also be coupled to the transmission through an electric motor, such as in a hybrid vehicle, and other vehicle drive configurations are possible.

At the transmission output, the transmission 14 may be coupled directly to the PTU 26, or a differential 32 may be utilized between the transmission 14 and the PTU 26 — this may depend on the architecture and position of the transmission 14. The PTU 26 may be rotatably connected to the transmission output shaft 30 through an input shaft 34. The first front shaft 16 is generally configured to extend from the transmission 14, which may include the differential 32, or it may be positioned within the input shaft 34 to extend exteriorly from one end of the PTU 26. And the second front shaft 18 may extend from an opposite end at a front output side 36 of the PTU 26. Additionally, the PTU 26 may include an output to transmit torque to a rear drive unit (RDU) 38 to drive the rear wheels 28 through a propeller shaft 40. The RDU 38 may include an input 42, a first output 44 configured to transmit torque to one of the wheels 28 through the first rear shaft 20, and a second output 46 configured to transmit torque to another wheel 28 through the second rear shaft 22.

The vehicle drivetrain 10 is merely an example and the RDU 38 is not limited to any particular drivetrain arrangement. Indeed, the RDU 38 may be employed in other, alternative drivetrain arrangements. The RDU 38 may be installed and utilized as a final drive unit (FDU) in the front or rear, and can hence be used with a front differential or a rear differential in a vehicle drivetrain.

Referring to FIG. 2, details of the RDU 38 will now be described. In one sense, the RDU 38 constitutes a side-shaft disconnect device since it is capable of disconnecting torque transfer at either of the rear shafts 20, 22. The RDU 38 can make up one part of a larger all wheel drive (A WD) disconnect system that may include other disconnect devices at other locations in the accompanying vehicle drivetrain and driveline. These types of AWD disconnect systems are employed for fuel efficiency gains and other improvements. But of course the RDU 38 need not necessarily be part of an AWD disconnect system and can be used for other functionality and other purposes in a particular vehicle drivetrain. FIG. 2 illustrates a cross section through the RDU 38. The RDU 38 includes an axle case 50 that may include first and second case members 52, 54 that may be discrete pieces mounted together in assembly. An axle cover 55 may be connected to the axle case 50 and may enclose at least part of the RDU 38. The first rear shaft 20 may extend through the cover 55 and the second rear shaft 22 may extend through the second axle case member 54. The first and second rear shafts 20, 22 may be journalled for rotation by suitable bearings 57. As will be set forth in more detail later, the first rear shaft is selectively coupled to the differential 32 in different manners by the RDU 38.

Within a differential case 59, a differential gear set 60 is rotatably arranged and supported. The differential gear set 60 generally includes two pinion gears 62, 64 that are rotatably arranged on a pinion shaft 66. The pinion shaft 66 has an axis that forms a rotational axis 67 for the pinion gears 62, 64. First and second differential side gears 68, 70 are arranged around a rotational axis 71 so as to be rotatable relative to the differential case 59. The rotational axis for the pinion gears 62, 64 intersects the rotational axis for the differential side gears 68, 70 within the differential case 59. The propeller shaft or drive shaft 40 (FIG. 1) engages the differential case 59 via the input 42, when then engages a driving gear 74. The driving gear 74 may be any suitable drive gear, such as, for example, one of a hypoid, spiral bevel, or helical gear, and is shown as being annular. In this embodiment, a torque distribution device is located within the axle case 50 and engages the differential gear set 60. More specifically, the torque distribution device will connect one of the differential side gears 68, 70 with one of the rear side shafts 20, 22. The torque distribution device can function to transfer torque to the first and second rear side shafts 20, 22 for accommodating various automotive driving situations such as cornering, reducing drag, and increasing tractive effort. The functionality is typically managed by an electronic control unit (ECU) or another type of controller. The torque distribution device can have different designs and constructions depending upon, among other possible influences, the design and construction of the RDU in which the torque distribution device is installed. In the implementation shown in the figures, the torque distribution device includes a clutch mechanism 75 with a friction plate pack 76 containing a varying number of clutch plates depending on the required torque transfer. The plate pack 76 may be, and as shown is, located in a larger radial diameter section of the differential case 59. This section is larger and has a greater diametric extent than an opposite side of the differential case 59 because the section accommodates the drive ring gear 74 which is typically mounted at an outside of the differential case 59 and has a larger diameter than most, if not all, portions of the differential case 59. Because of this location, the overall diameter of the plate pack 76 can be maximized, if desired, and hence the associated transmitted torque can also be maximized— these enhancements may be beneficial in some applications. Of course, the clutch mechanism 75 and actuator may be located at the opposite side of the differential, as desired.

The clutch mechanism 75 in this embodiment includes a clutch reaction member 78, clutch outer carrier 80 and a clutch hub or inner carrier 82. The clutch reaction member 78 may include a radially extending end plate 84 on one side (e.g. an axially facing end) of the clutch plate pack 76, and a stub shaft 86 to which the side gear 68 is connected via a splined connection. The stub shaft 86 may extend into an opening 88 in and be supported by the second axle case member 54. A recess 90 in the clutch reaction member 78 may receive a bearing 57 that journals for rotation one end of the side shaft 20. A bearing 92 may also be received between the first axle case member 52 and the end plate 84. The outer clutch carrier 80 may be annular, generally cylindrical, coupled to the end plate 84 and disposed surrounding the clutch plate pack 76. The inner clutch carrier 82 may be annular, disposed radially inwardly from the clutch plate pack 76 and coupled to the side shaft 20 for rotation with the side shaft 20, such as by a splined connection or any other means of fixing two components together. The inner clutch carrier 82 and side shaft 20 may also be combined into a single piece. When the clutch plate pack 76 is engaged, the side shaft 20 and clutch reaction member 78 are coupled together and rotation of the clutch reaction member 78 through the differential gear set 60 is transferred to the side shaft 20. When the clutch plate pack 76 is not engaged, the side shaft 20 is not driven for rotation by the differential 32, and the side shaft 20 rotates with the wheel 28 to which it is coupled without being positively driven.

Referring now to FIGS. 3-5, an actuator assembly 100 is coupled to the differential case 59. The actuator assembly 100 is shown diagrammatically in FIG. 2, and FIGS. 3-5 show the assembly 100 and RDU 38 with fragments of surrounding components to illustrate just one possible arrangement and to facilitate discussion of the RDU 38. In this embodiment, the actuator assembly 100 includes an actuator plate 102 and two reaction collars 104, 106 that are located on opposite sides of the actuator plate 102. The plate 102 and/or collars 104, 106 are configured with one or more ball ramp tracks 107 that cooperate with one or more balls 108 and/or a ball cage (not shown). The actuator plate 102 and collars 104, 106 may be annular and disposed surrounding the side shaft 20 and between the clutch plate pack 76 and the cover 55. The actuator assembly 100 can also include an electric motor drive 109 that rotates the actuator plate 102, or can include another mechanism and/or technique known to skilled artisans for imparting rotation to the actuator plate 102. As the actuator plate 102 is rotated, it is driven axially relative to the cover 55 and clutch plate pack 76 due to the engagement of the balls 108 within ball tracks 107, which have a varying axial depth and are formed within one or both of the actuator plate 102 and the collars 104, 106. The reaction collars 104, 106 may be fixed to the cover 55, or to another suitable component as desired. The reaction collars 104, 106 do not rotate and do not move linearly in operation, and instead, provide reaction surfaces for axial movement of the actuator plate 102 as it is rotated. Rotation of the actuator plate 102 in one direction moves the actuator plate 102 in a first axial direction and rotation of the actuator plate 102 in the opposite direction moves the actuator plate 102 in a second axial direction that is opposite to the first direction. In this way, the actuator plate 102 may be positively driven in opposed directions between multiple axial positions. In at least some implementations, the actuator plate is connected to a coupler 1 16 that controls the interconnection of the side shaft 20 with the differential 32. Movement of the actuator plate 102 moves the coupler 116 to control the interaction between the differential 32 and side shaft 20. Referring now to FIGS. 6 and 7, in at least some non-limiting implementations, so that the coupler 1 16 is responsive to axial movement of the actuator plate 102, the coupler may include opposed shoulders 115, 117 engaged by the actuator plate 102 to move the coupler 116 axially, back and forth, as the actuator plate 102 is driven in opposed directions. One shoulder 1 15 may be defined by a retainer 1 19 held on the coupler 1 16 by a clip 121 and the other shoulder 1 17 may be defined by a surface of the coupler 116. Of course, other constructions and features may be used. Bearings 123 may be provided between the shoulders 1 15, 1 17, and the actuator plate 102 to facilitate relative rotation between the plate 102 and coupler 1 16.

Referring again to FIGS. 3-5, the coupler 1 16 may be connected to the outer carrier 80 for co-rotation with the outer carrier, and hence, with the stub shaft 86 and side gear 68. The coupler 1 16 may be selectively coupled to one or both of the inner carrier 82 and the differential case 59 when the coupler 116 is driven by the actuator assembly 100. In the implementation shown, the coupler 116 is generally annular and includes an axially extending wall 118 and a radially inwardly extending flange 120. One or more direct mechanical engagement regions may be provided between the coupler and adjacent components to selectively couple the components and the coupler. In the non-limiting example shown in the drawings, the coupler includes three separate engagement regions with a first region adapted to engage a portion of the outer carrier, a second region adapted to engage a portion of the inner carrier and a third region adapted to engage a portion of the differential case or a component fixed to the differential case. In one example, the engagement regions includes splines. One or more splines 122 are provided along an inside surface of the wall 118 to engage complementary splines 124 on the outer carrier 80 to permit relative axial movement of these components as they co-rotate. Further, the flange 120 may include one or more splines 126 arranged to selectively engage complementary splines 128 on the inner carrier 82. The splines 128 on the inner carrier 82 may include a gap 130 in which the splines 126 of the flange 120 may be received in at least one position of the coupler 116 so that the coupler 116 and inner carrier 82 do not rotate together. As shown in FIG. 3, to selectively couple the coupler 116 to the differential case 50, the wall 118 may include a separate spline region 132 adapted to selectively engage splines 134 on the differential case 59 or on a connector 136 that is carried by or otherwise connected to the differential case 59. In the implementation shown, the connector 136 includes a generally cylindrical axial portion 138 that overlies and is connected by splines to a portion of the differential case 59 and an annular radial region 140 adjacent to the clutch end plate 84. The radial region 140 includes the splined end 134 located adjacent to the coupler 116. Suitable bearings may be provided adjacent to the connector 136, such as bearing 92 between the connector 136 and the clutch end plate 84, and bearing 144 overlying the axial portion 138 to journal for rotation the connector 136 and the second axle case member 54. Of course, there are other ways to couple the components together as desired, and the illustrated and described coupler 116, connector 136 and other components may be formed and arranged differently while still performing the same or similar functions.

FIGS. 3-5 illustrate different positions of the coupler 116, which provide different operating characteristics for the vehicle. In more detail, in FIG. 3, the coupler 116 is in a first position. In the first position, the coupler 116 is engaged with both the inner carrier 82 (via splines 126 and 128) and with the differential case 59, via the connector 136 (and splines 132 and 134). Hence, the side shaft 20 is coupled directly to the differential case 50 and this essentially provides a locked differential and the system effectively behaves like it has a solid rear axle, which may be useful or desirable in off-road driving conditions. The inner carrier 82 also is coupled to the outer carrier 80 via splines 122 and 124. The coupler 116 does not engage the clutch 75 in this position and the clutch 75 is not actuated so overheating or other issues that may occur in the clutch do not effect vehicle operation in this position.

In FIG. 4, the coupler 116 is in a second position wherein the coupler 116 engages both the inner and outer carriers 80, 82 via splines 122, 124 and 126, 128, while splines 132 and 134 are not engaged with each other. This couples the side shaft 20 to the side gear 68 in the differential 32, and provides an open differential. This may also be useful or desirable in certain off-road driving conditions as the rear axle is "locked" to the front axle in a manner similar to a vehicle with a transfer case having a locking center differential. In this position the coupler 116 does not engage the clutch 75 in this position, and the clutch 75 is not actuated so overheating or other issues that may occur in the clutch do not effect vehicle operation in this position.

In FIG. 5, the coupler 116 is in a third position wherein the coupler 116 is not coupled to either the inner carrier 82 or the differential case 59. That is, splines 126 are in gap 130 and not engaged with splines 128, and splines 132 and 134 also are not engaged. This position also provides an open differential and in this position, the side shaft 20 is not positively driven. This position may be called the disconnected position because the side shaft is essentially disconnected from the differential and is not positively driven. In one common example, with the coupler in the third position, the front wheels of a four wheel vehicle would be positively driven and the rear wheels would not, providing a front-wheel drive vehicle operating mode.

The coupler 116 may also be moved to a fourth position wherein the coupler 116 engages and actuates the clutch 75. In this position, the side shaft 20 is coupled to the side gear 68 via the clutch 75. The amount of torque that can be driven to the rear wheels is limited by the operational characteristics of the clutch 75, which characteristics may include, but are not limited to, the thermal capacity of the clutch. During extensive all-wheel drive excursions, the clutch plate pack 76 can overheat, causing the clutch 75 to slip interfering with or preventing operation as an all-wheel drive system. The vehicle would unintentionally become two-wheel drive in this situation.

While not normally a problem, the unavailable all-wheel drive vehicle operation may be a problem in certain situations, such as when operating the vehicle in off-road conditions wherein loss of torque to one or more wheels is undesirable. In these situations, the coupler 116 can move to, for example, the first position or second position, shown in FIGS. 3 and 4. Choice between the first and second position may be based on whether a locked or open differential is needed or desired. This decision and the attendant movement of the coupler 1 16 could be commanded by an operator of the vehicle, or by an electronic controller using feedback from various vehicle sensors to determine a preferred operating mode. Further, some systems lack a position wherein the differential is locked and open differential operation may be undesirable in certain situations, such as more extreme off-road driving. Using a brake controller to brake a spinning wheel in order to transfer torque to a non or less spinning wheel can be inefficient in some implementations and limits the amount of effective torque because the torque at the clutch pack is split between the brakes and the non or less spinning wheel. Desirably, in at least some implementations, the coupler 116 can be positively moved and positioned in any of the noted positions by the actuator 100, which provides controlled, two-way axial displacement of the coupler 1 16 on command. Further, the system need not rely entirely on a biasing mechanism (e.g. a spring) to provide movement in one direction as a positively driven system can more easily provide feedback that a particular position has been achieved, and can provide more force for engagement of the components in the different coupler positions. A spring or other biasing mechanism still may be provided to maintain pressure on the clutch plate pack in the disconnected position, and to provide a desired movement of the coupler if power is lost to the actuator. In that regard, in at least one implementation, the actuator assembly 100 may include a biasing member 150 that drives the actuator plate 102 to one position, to drive the coupler 116 to a corresponding position, should power to the actuator assembly 100 be interrupted or lost (e.g. loss of electrical power to a motor that rotates the actuator plate). As shown in FIGS. 8 and 9, one or more biasing members 150 are disposed within pockets 152 defined between opposed stop surfaces 154, 156. One of the stop surfaces 154 is defined on the actuator plate 102 and hence, moves within the pocket 152 when the actuator plate 102 rotates. The other stop surface 156 is defined in an adjacent reaction collar 104 or 106 and hence, is stationary relative to the actuator plate 102. Accordingly, when the actuator plate 102 is rotated, the gap between the two stop surfaces 154, 156 increases or decreases, as shown by comparison of FIGS. 8-10, depending upon the direction of rotation of the actuator plate 102. In the example where one or more springs 150 are used to bias the actuator assembly 100, the springs 150 may be compressed when the actuator plate 102 is rotated in one direction, and allowed to expand when the actuator plate 102 is rotated in the opposite direction. In at least one implementation, the spring or springs 150 bias the actuator plate 102 to a rotary position wherein the coupler 116 is in its third position and the side shaft 20 is not positively driven for rotation (e.g. by a motor or other actuator instead of by a biasing member or other passive member). In this example, the springs 150 are compressed when the actuator plate 102 is rotated to move the coupler 116 to the first position, wherein the differential is locked. And absent a force on the actuator 100 (e.g. from a motor), the springs 150 will displace the actuator plate 102 to move the coupler 116 from its first position, and in at least some implementations, to the third or disconnected position. This prevents or inhibits the system remaining in the first position, if for example, electrical power is lost in the system. This prevents the system from remaining in a position in which the differential is locked, which may, for example, make certain types of towing undesirable. The system may also be arranged so that the actuator plate 102 is rotated to the third position if power to the motor is lost when the coupler is in the fourth position in which the clutch 75 is engaged. Of course, the system could be configured in other ways and the examples noted herein are intended to be illustrative and not limiting.

The preceding description has been presented only to illustrate and describe exemplary embodiments of the methods and systems of the present invention. It is not intended to be exhaustive or to limit the invention to any precise form disclosed. It will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the scope. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the claims. The invention may be practiced otherwise than is specifically explained and illustrated without departing from its spirit or scope. The scope of the invention is limited solely by the following claims.

Reference in the specification to "one example," "an example," "one embodiment," or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the example is included in at least one example. The phrase "in one example" or "in one implementation", or "in at least some implementations" in various places in the specification does not necessarily refer to the same example each time it appears.

All terms used in the claims are intended to be given their broadest reasonable constructions and their ordinary meanings as understood by those skilled in the art unless an explicit indication to the contrary in made herein. In particular, use of the singular articles such as "a," "the," "the," etc. should be read to recite one or more of the indicated elements unless a claim recites an explicit limitation to the contrary.