MODULAR ASSEMBLY OF A POWER TRANSMISSION UNIT FOR A VEHICLE

Abstract

Assembly of a power transmission unit (38, 138, 238, 338) for transmitting torque from a differential carrier (24) of a front differential (26) to a cardan shaft (40) of a vehicle (10); wherein the differential carrier (24) rotates about a first axis of rotation (36) and the cardan shaft (40) rotates about a second axis of rotation (42) which is perpendicular to the first axis of rotation (36), wherein the assembly of a power transmission unit (38, 138, 238, 338) comprises: an input shaft (44) which is designed to be driven rotatably about a first axis of rotation (36) by the differential carrier (24); a first bevel gear (46); a second bevel gear (48) which engages with the first bevel gear (46); wherein the first bevel gear (46) has an annular shaft section (56) and concentrically surrounds the input shaft (44); wherein the second bevel gear (48) is designed to drive the cardan shaft (40) rotatably about the second axis of rotation (42); a compound planetary gear set (70) which is concentric with the first axis of rotation (36) and is designed to transmit torque from the input shaft (44) to the first bevel gear (46) such that the torque of the first bevel gear (46) is less than the torque of the input shaft (44) and a rotational speed of the first bevel gear (46) is greater than a rotational speed of the input shaft (44); a stationary element adjacent to the compound planetary gear set (70), wherein the compound planetary gear set (70) comprises: a first sun wheel (72) which can be functionally connected to the stationary element; a second sun gear (74) which is attached to the annular shaft section (56) of the first bevel gear (46) in order to rotate in harmony with it; a support (76) which is attached to the input shaft (44) to rotate in accordance with it; a first set of pinion gears (77) and a second set of pinion gears (78), both of which are rotatably mounted on the carrier (76); wherein the first set of pinion gears (77) meshes with the first sun gear (72); and wherein the second set of pinion gears (78) meshes with the first set of pinion gears (77) and with the second sun gear (74); and A disconnecting clutch (80) that selectively functionally connects the first sun gear (72) to the stationary element to allow torque transmission from the input shaft (44) to the first bevel gear (46) through the compound planetary gear set (70), wherein the disconnecting clutch (80) is selectively disengageable to disconnect the first sun gear (72) from the stationary element, thereby preventing torque transmission from the input shaft (44) to the first bevel gear (46) through the compound planetary gear set (70), and wherein the disconnecting clutch (80) comprises the following plates: a rotating plate (81) that is mounted to rotate with the first sun gear (72); a stationary plate (82) that is mounted to the stationary element; and a selector plate (83) that is moved by an actuator (A) into contact with the rotating plate (81) to lock the rotating plate (81) to the stationary plate (82).

Description

TECHNICAL AREA

[0001] The teachings presented here generally comprise an assembly of a power transmission unit for an all-wheel drive vehicle. BACKGROUND

[0002] Power transfer units (PTUs) are used in some vehicles to distribute drive torque supplied by an engine and transmission to the right front wheel and both rear wheels. In some other arrangements, the right-hand half-shaft passes through the PTU and is not considered part of it. For example, some power transfer units simply transfer torque from a transverse transmission differential to a driveshaft, which then drives rear half-shafts through a rear differential. A hypoid gear set is often used to reverse the direction of the drive by 90 degrees between the axis of rotation of the front differential carrier and the axis of rotation of the driveshaft. The torque ratio that the hypoid gear set can deliver depends on the relative number of teeth on the hypoid ring gear and pinion gear.The diameters of these gears are limited by the available installation space.

[0003] German patent DE 39 11 118 A1 discloses an all-wheel drive system for a vehicle in which power transmission is achieved via a drivetrain consisting of a bevel gear, a driveshaft, and a reduction stage. JP H03-54 030 A discloses an all-wheel drive vehicle with torque distribution, wherein the torque distribution is achieved via a differential device with a compound planetary gear set. US patent 5,547,430 A describes a drive unit with a viscous coupling for an all-wheel drive vehicle. German patent DE 10 2006 038 358 A1 discloses an axle drive unit with a bevel gear for a drivetrain. US patent 2012 / 0 073 929 A1 discloses a vehicle drivetrain with a power transmission unit that includes a coupling. SUMMARY

[0004] A power transmission assembly for transmitting torque from the differential carrier of a front differential to a driveshaft of a vehicle. The differential carrier rotates about a first axis of rotation, and the driveshaft rotates about a second axis of rotation perpendicular to the first axis. The assembly includes an input shaft designed to be driven by the differential carrier so as to rotate about the first axis of rotation. The power transmission assembly also includes a first bevel gear and a second bevel gear, the second bevel gear meshing with the first bevel gear. The first bevel gear has an annular shaft section and surrounds the input shaft concentrically. The second bevel gear is designed to drive the driveshaft so as to rotate about a second axis of rotation.The assembly of a power transmission unit comprises a composite planetary gear set concentric with the first axis of rotation. The composite planetary gear set is designed to transmit torque from the input shaft to the first bevel gear such that the torque of the first bevel gear is less than the torque of the input shaft and the rotational speed of the first bevel gear is greater than the rotational speed of the input shaft. Furthermore, the assembly of a power transmission unit includes a stationary element located adjacent to the composite planetary gear set. The composite planetary gear set comprises a first sun gear, a second sun gear, a carrier, and first and second sets of pinions. The first sun gear is functionally connected to the stationary element. The second sun gear is attached to the annular shaft section of the first bevel gear to rotate in sync with the first bevel gear.The carrier is attached to the input shaft to rotate in unison with it. The first set of pinions and the second set of pinions are both rotatably mounted on the carrier. The first set of pinions meshes with the first sun gear, and the second set of pinions meshes with both the first set of pinions and the second sun gear. The power transmission assembly also includes a disengaging clutch that selectively connects the first sun gear to the stationary element to allow torque transmission from the input shaft to the first bevel gear through the combined planetary gear set. The disengaging clutch can be selectively disengaged to disconnect the first sun gear from the stationary element, thereby preventing torque transmission from the input shaft to the first bevel gear through the combined planetary gear set.The disconnecting coupling has the following plates: a rotating plate which is attached to rotate with the first sun gear; a stationary plate which is attached to the stationary element; and a selector plate which is moved by an actuator into contact with the rotating plate in order to attach the rotating plate to the stationary plate.

[0005] When the disconnect clutch is disengaged, no torque is delivered to the cardan shaft and the vehicle operates in a front-wheel drive mode.

[0006] The first sun gear is functionally connected to a fixed element, such as a cover for a power transmission unit assembly, to lock the first sun gear in place. The first sun gear can be permanently locked or selectively disengageable from the fixed element.

[0007] As used herein, when two components are attached to each other, they rotate “in unison” to rotate as a single unit at the same speed.

[0008] The uniaxial design of the compound planetary gear set (i.e., the concentricity of the compound planetary gear set with the first axis of rotation) saves installation space compared to power transmission units that require multiaxial gear arrangements between the input element and the hypoid ring gear in order to reduce the overall torque ratio of the assembly of a power transmission unit.Additionally, the single-axis design of the compound planetary gear set enables modularity, as common components can be used with different sets of additional components, such as the compound planetary gear set and / or the disconnect clutch, to meet the requirements of a specific vehicle platform. This is achieved while maintaining a constant relative position of the first axis of rotation of the input shaft and the first bevel gear to the second axis of rotation of the second bevel gear, as well as a constant direction of rotation and a constant torque level of the driveshaft. Thus, different modular assemblies of power transmission units can be implemented across different vehicle lines, all sharing a fixed orientation of the power transmission unit's input axis relative to the driveshaft's axis of rotation.The torque reduction ratio of the compound planetary gear set can be specifically designed to provide a common torque at the driveshaft, regardless of whether the compound planetary gear set is included in the power transmission unit assembly or not. This ensures that a higher input shaft torque, such as in a vehicle with a high-performance engine, or a lower input shaft torque, such as in a vehicle with a lower-power engine, will result in the same torque at the driveshaft. The driveshaft speed will be higher with a modular power transmission unit assembly that incorporates the compound planetary gear set. Therefore, the torque-carrying capacity of the hypoid ring gear and pinion gear does not need to be increased for use with the high-performance engine.

[0009] Since a second axis is not required for the torque reduction achieved by the planetary gear set, a reduction in the overall packing diameter is achieved by using the single-axis power transmission unit assembly disclosed herein. The overall weight and number of components are also reduced, as dual-axis power transmission units require a second transmission shaft between the input shaft and the first bevel gear, necessitating two additional sets of bearings. Furthermore, dual-axis power transmission units use helical gear sets, which create high gear separation forces between the axes, requiring a more robust and therefore heavier housing to counteract these forces.

[0010] The above features and advantages, and further features and advantages of the present teachings, will become readily apparent from the following detailed description of the best ways of carrying out the present teachings when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a schematic and fragmentary view in partial section of a vehicle having a drive train with a first embodiment of a power transmission unit assembly surrounding the front half-shaft. Fig. Figure 2 is a schematic perspective representation of a section of the assembly of a power transmission unit. Fig. 1, which surrounds the front half-shaft. Fig. Figure 3 is a schematic and fragmentary view in partial section of a section of the assembly of a power transmission unit. Fig. 1, which surrounds the front half-shaft. Fig. Figure 4 is a schematic and fragmentary partial section view of a section of a second embodiment of a power transmission unit assembly surrounding the front half-shaft, for use in the drive train of Fig. 1. Fig. Figure 5 is a schematic and fragmentary partial section view of a third embodiment of a power transmission unit assembly surrounding the front half-shaft, for use in the drive train of Fig. 1. Fig. Figure 6 is a schematic and fragmentary partial section view of a section of a fourth embodiment of a power transmission unit assembly surrounding the front half-shaft, for use in the drive train of Fig. 1. DETAILED DESCRIPTION

[0011] Referring to the drawings, in which the same reference symbols refer to the same components throughout the different views, shows Fig. 1. A section of a vehicle 10 comprising a drivetrain 12. The drivetrain 12 includes a power unit 14 which drives a multi-speed transmission 16. The power unit 14 has an engine block 15. A crankshaft 17 extends from within the engine block 15 to connect with a transmission input element (not shown), as understood by a person skilled in the art. The transmission 16 may comprise a gear assembly and a plurality of electrically engaged clutches which supply torque to a transmission output element 20. Alternatively, a continuously variable transmission (CVT) may be used instead of a gear assembly and clutches. The transmission 16 has a transmission housing 18.

[0012] The transmission output element 20 meshes with a helical gear 22, which is mounted on a carrier 24 of a front differential 26 to rotate in harmony with the carrier 24, or may be connected to the carrier 24 via a chain drive. The front differential 26 is also referred to herein as a transmission differential 26. A differential housing 28 surrounds the front differential 26 and is mounted to the transmission housing 18. The differential 26 comprises connected pinion gears 30A, 30B, which rotate in harmony with the differential carrier 24. The pinion gears 30A, 30B mesh with side gears 32A, 32B. Side gear 32A is mounted to rotate with a first half-shaft 34A, which is connected such that it rotates with a left front wheel (not shown). Side wheel 32B is mounted to rotate with a second half-shaft 34B, which is connected in such a way that it rotates with a right front wheel (also not shown).The helical differential gear 22, differential carrier 24, side gears 32a, 32B and half shafts 34A, 34B all rotate about a first axis of rotation 36. The gear differential 26 is designed to allow a variation in wheel speeds from side to side, and the differential carrier 24 rotates at the mean of these speeds.

[0013] A first embodiment of a power transmission unit 38 is configured to functionally connect the differential carrier 24 to a cardan shaft 40, which in turn is connected to the rear wheels by a rear differential (not shown). The cardan shaft 40 is arranged such that it rotates about a second axis of rotation 42, which is essentially perpendicular to the first axis of rotation 36, but offset from the first axis of rotation 36 and does not intersect it. That is to say, in Fig. 1 the second axis of rotation 42 lies above or below the plane of the cross-section containing the first axis of rotation 36.

[0014] Accordingly, the assembly of a power transmission unit 38 enables drive torque from the power engine 14 to be delivered to the front wheels via the front differential 26, and also to the rear wheels via the cardan shaft 40, as in an all-wheel drive operating mode.

[0015] As will be discussed further herein, the assembly of a power transmission unit 38 is one of four different assemblies of power transmission units 38, 138, 238, 338 which are described in the Fig. Figures 3-6 show that the components share some common elements, such as an input shaft 44, a bevel gear set comprising a first bevel gear 46 and a second bevel gear 48, and a stationary housing 50 that surrounds and supports the bevel gears 46 and 48. The bevel gears 46 and 48 may be hypoid spiral gears, but are not limited to this. As used herein, the first bevel gear 46 is referred to as a hypoid ring gear 46, and the second bevel gear 48 is referred to as a pinion gear 48.

[0016] The four power transmission unit assemblies 38, 138, 238, 338 are thus modular, as they share a common base of components that can be supplemented with additional components (such as a disconnect clutch, a composite planetary gear set, or both) to achieve different architectures suitable for different vehicle platforms. Each of the power transmission unit assemblies 38, 138, 238, 338 can be selected for use in a vehicle with the same differential 26 and the same cardan shaft 40, or with a different differential and a different cardan shaft, but still be arranged along the same first axis of rotation 36 and second axis of rotation 42. The four power transmission unit assemblies 38, 138, 238, 338 are each arranged with torque transmission components that are concentrically and rotatably connected to, respectively, the first axis of rotation 36 and the second axis of rotation 42.about a single axis of rotation (the first axis of rotation 36). Because the components are arranged about a single axis of rotation 36, the overall radial dimension of each of the power transmission unit assemblies 38, 138, 238, 338 is kept relatively small, which allows them to be packed into a fixed available installation space adjacent to the power engine block 15. Specifically, the power transmission unit assemblies 38, 138, 238, 338 can be used across vehicle platforms that have different distances from an effective axis of rotation 52 of the crankshaft 17 to a first axis of rotation 36 of the hypoid ring gear 46.

[0017] With reference to the Fig. Figures 1-3 show the first assembly of a power transmission unit 38, the input shaft 44, which is designed such that it is driven by the differential carrier 24 so as to rotate about the first axis of rotation 36. The input shaft 44 is connected in such a way that it rotates in sync with the transmission differential carrier 24, as shown in Fig. 1 is shown schematically. Fig. Figure 2 shows a splined section 54 of the input shaft 44, which is designed to fit a splined opening of the differential carrier 24. The half-shaft 34B extends through the input shaft 44. A splined section 55 of the half-shaft 34B is designed to mesh with the side gear 32B.

[0018] The hypoid ring gear 46 is ring-shaped and surrounds the input shaft 44 concentrically. As shown in Fig. As best shown in Figure 3, the hypoid ring gear 46 has a first annular shaft section 56, a second annular shaft section 58, and a tooth section 60. The hypoid ring gear 46 is supported by only two ring bearings 62A and 62B. Bearing 62A supports the shaft section 56 for rotation relative to a central support element 64, which is connected to a stationary housing 66 that surrounds and supports the hypoid ring gear 46 and the pinion gear 48. The support element 64 has an opening 65 through which the shaft section 56, the input element 44, and the half-shaft 34B extend. Bearing 62B supports the shaft section 58 for rotation relative to the stationary housing 66. Fig. 2 is the case 66 away.

[0019] The hypoid ring gear 46 engages with (i.e., meshes with) the pinion gear 48. In each of the Fig. 1 - 6 The pinion gear 48 meshes with the hypoid ring gear 46 in a different plane than the cross-section through the center of the hypoid ring gear 46. In other words, the pinion gear 48 is offset from the hypoid ring gear 46, so that the second axis of rotation 42 does not intersect the first axis of rotation 36. In the Fig. In sections 1-6, the pinion gear 48 is located above the cross-section shown. The pinion gear 48 drives the cardan shaft 40 around the second axis of rotation 42 and is connected to the cardan shaft 40 by a universal joint 68, which is located in Fig. 1 is shown, or connected by another suitable connection. The ability of the pinion gear 48 to engage with the hypoid ring gear 46 at an offset allows the position of the pinion gear 48, and thus the cardan shaft 40, to be higher or lower relative to the front half-shafts 34A, 34B, as required to accommodate vehicle floor height, ground clearance, or another vehicle component, such as the steering gear or engine mount.

[0020] The assembly of a power transmission unit 38 comprises a compound planetary gear set 70, which is arranged to be concentric with the first axis of rotation 36 and is configured to transmit torque from the input shaft 44 to the hypoid ring gear 46 with a torque reduction ratio. The power transmission unit 38 has a first sun gear 72, which is functionally connectable to a stationary element, namely a cover 73. The cover 73 is screwed to the housing 66 with the support element 64 between the housing 66 and the cover 73, as shown in Fig. Figure 3 shows only a section of cover 73 above the first axis of rotation 36. Fig. 3 shown. Cover 73 is in Fig. 2 removed. A second sun gear 74 is attached to the annular shaft section 56 of the hypoid ring gear 46 to rotate in unison with it. A carrier 76 is attached to the input shaft 44 to rotate in unison with it. The carrier 76 is a rotating, web-like structure and is designed to rotatably support a first set of pinions 77 and a second set of pinions 78, both of which are attached to the carrier 76 by pins around which they rotate, as a person skilled in the art understands. The first set of pinions 77 meshes with the first sun gear 72. The second set of pinions 78 meshes with the first set of pinions 77 and with the second sun gear 74. The compound planetary gear set 70 has no ring gear or other elements. Fig. 3. The sets of pinion wheels 77 and 78 are not shown in the lower section of the view in order to make the carrier 76 visible, and the carrier 76 is not shown in the upper section in order to make the sets of pinion wheels 77, 78 visible. Fig. Figure 2 shows that the support 76 actually surrounds the first axis of rotation 36 concentrically. In the Fig. Figures 1 and 3-6 show only a section of the housing 76, the planetary gear set 70, and the clutch 80 above the first axis of rotation 36. Only the second sun gear 74 and the carrier 76 below the first axis of rotation 36 are shown. It should be noted that the housing 66 and the planetary gear set 70 are symmetrical about the first axis of rotation 36, and components have been omitted from the drawings for clarity.

[0021] The assembly of a power transmission unit 38 includes a disengaging clutch 80 that selectively connects the first sun gear 72 to the cover 73. When the disengaging clutch 80 is engaged, the first sun gear 72 is attached to the cover 73 and thus held in a fixed position. With the first sun gear 72 stationary, the combined planetary gear set 70 is active, as it can transmit torque from the input shaft 44 to the hypoid ring gear 46 with a torque reduction ratio. That is, the torque at the hypoid ring gear 46 is lower than the torque at the input shaft 44, while the rotational speed from the input shaft 44 to the hypoid ring gear 46 is significantly increased.

[0022] In the assemblies of power transmission units 38 or 138 of the Fig. 3 and Fig. 4, which have a compound planetary gear set 70, a higher torque can be applied to the input shaft 44 when the disconnect clutch 80 is engaged and the compound planetary gear set 70 is active, and yet a similarly low torque results at the pinion gear 48 and the attached cardan shaft 40 than when a lower torque is applied to the input shaft 44 in the assemblies of power transmission units 238 and 338 of the Fig. 5 and Fig. 6 is applied, in which only the reduction ratio of the hypoid ring gear 46 to the pinion gear 48 affects the torque at the cardan shaft 40. Additionally, the double pinion design causes the hypoid ring gear 46 to rotate in the same direction as the input shaft 44. The direction of rotation of the pinion gear 48 and the cardan shaft 40 is the same as in a lower-ratio, lower-force power transmission assembly, such as 238 or 338. Furthermore, the disengaging clutch 80 engages to connect a rotating component (the first sun gear 72) to a stationary component (the cover 73), allowing for a simpler and less expensive coupling than would be required to connect two rotating components.

[0023] The assembly of a power transmission unit 38 offers an all-wheel drive mode in the vehicle 10 of Fig. 1, when the disconnect clutch 80 is engaged, and provides a front-wheel drive mode when the disconnect clutch 80 is disengaged, as the sun gear 72 will be free-running and no torque will be transmitted to the hypoid ring gear 46.

[0024] The disconnect clutch 80 can be any suitable type of selectively engaging clutch, such as a friction plate clutch, a band clutch, or a mechanical diode clutch, and can be engaged electrically or hydraulically by an actuator A under the control of a controller (not shown) that determines the operating conditions under which a four-wheel drive mode is established. To engage the disconnect clutch 80 and thus transition into a four-wheel drive mode, the cardan shaft 40 can first be brought to a speed that would produce associated speeds of the hypoid ring gear 46 and the planetary gear set components. This will slow the rotation of the sun gear 72, for example, from a speed in the range of 700 to 900 revolutions per minute (rpm) to approximately 100 rpm to allow nearly synchronous engagement of the sun gear 72 with the stationary cover 73 by the disconnect clutch 80.This can be accomplished if a clutch can be engaged between the cardan shaft 40 and a rear differential to rotate the cardan shaft 40.

[0025] In one embodiment, the disengaging clutch 80 has a rotating plate 81, which is mounted to rotate with the first sun gear 72, a stationary plate 82, which is mounted on the cover 73, and a selector plate 83, which is moved by the actuator A into contact with the rotating plate 81 to engage the rotating plate 81 with the stationary plate 82. This type of clutch can be described as a mechanical diode. The selector plate 83 can be designed to engage regardless of the direction of rotation of the rotating plate, in which case the clutch 80 is a two-way brake clutch, or it can be designed as a one-way brake clutch that can only be engaged when the rotating plate 81 is rotating in a direction corresponding to a forward gear, so that four-wheel drive capability is only available in forward motion.

[0026] Spacing errors of the planetary gear due to tolerance addition during manufacturing can be mitigated by designing the first sun gear 72 such that it has a certain radial float or play relative to the first axis of rotation 36 through a serrated interface with the plate 81 or with the cover 73A in the assembly of a power transmission unit 138. Fig. 4 without a disengaging clutch. Additionally, the carrier 86 is constrained only by axial thrust bearings or disks 86 (one is shown) to resist the axial load due to flank angles of the helical pinion gear. The carrier 76 has no radial bearings (i.e., the outermost radial face of the carrier 76 is not constrained), and thus both the carrier 76 and the input shaft 44 are centered at a point that depends on the meshing of the first sun gear 72 with the first set of pinions 77 and the meshing of the second sun gear 74 with the second set of pinions 78, since the sets of pinions 74, 78 circumscribe the sun gears 72, 74. The second sun gear 74 can be attached to the ring-shaped shaft section 56 of the hypoid ring gear 46 with an involute or square splined toothing and can therefore also self-center on the basis of the meshing with the second set of pinion gears 78.

[0027] Only two sets of tapered or roller bearings 62A, 62B are required to center the hypoid ring gear 46 so that it rotates around the first axis of rotation 36. Another set of tapered or roller bearings 62C centers the pinion gear 48 so that it rotates around the second axis of rotation 42. The roller bearings 62C are located between the pinion gear 48 and a pinion gear cover 63 (in Fig. 2 shown), which is connected to the housing 66, which is in Fig. 2 is removed. Rolling bearings 62D support the front half-shaft 34B rotatably relative to the cover 73 and center the front half-shaft 34B for rotation around the first axis of rotation 36. A lip seal 67 seals the half-shaft 34B against the cover 73.

[0028] The central support 64 provides a local fixation for an annular double-lip seal 88A, which seals between the shaft section 56 of the hypoid ring gear 46 and the central support 64. Another annular double-lip seal 88B seals between the shaft section 58 of the hypoid ring gear 46 and the housing 66. A passage 90A is provided in the central support 64 in conjunction with the lip seal 88A. One end of the passage 90A can be located at a point on the underside of the assembly of a power transmission unit 38 that is easily accessible for maintenance. The passage 90A can be referred to as a leakage hole, since it provides an indication of leakage past the lip seal 88A if fluid leaks through the passage 90A. A similar passage 90B is provided in the housing 66 in conjunction with the lip seal 88B to provide an indication of leakage past the lip seal 88B.

[0029] The housing 66 and the central support 64 define a first cavity 62A, which contains the hypoid ring gear 46 and the pinion gear 48. The cover 73 and the central support 64 define a second cavity 92B, which contains the compound planetary gear set 70. The central support 64 and the lip seals 88A, 88B essentially isolate the first cavity 92A from the second cavity 92B. This allows the use of different fluids in the two cavities. For example, the first cavity 92A can be filled with a hypoid gear lubricating fluid, which has a relatively high viscosity.A lower viscosity fluid, such as automatic transmission fluid (ATF), can be supplied from the transmission 16 and the differential housing 28 to the second cavity 92B through an annular passage 94A between the hypoid ring gear 46 and the input shaft 44, and through an annular passage 94B between the input shaft 44 and the half-shaft 34B. The carrier 76 can immerse itself in any fluid that settles in the lower section of the cavity 92B to distribute the fluid over the rotating components of the planetary gear set 70 in both front-wheel drive and all-wheel drive modes. By using lower viscosity transmission fluid in the second cavity 92B and isolating the higher viscosity gear lubricant in the first cavity 92A, circulation losses are reduced.The lip seals 88A, 88B have the additional function of increasing the resistance on the rotating hypoid ring gear 46 to keep it stationary around the first axis of rotation 36 when the front-wheel drive mode is engaged. The lip seal 67 seals between the cover and the half-shaft 34B and is the only seal that experiences relative movement when the disengaging clutch 80 is disengaged. An alternative method for separating the two cavities 92A, 92B would be to place seals between the rotating hypoid ring gear 46 and the input shaft 44, and between the input shaft 44 and the half-shaft 34B. In such an embodiment, the housing 66 would include an opening with a drain and fill plug to allow the cavity 92B to be filled with fluid.

[0030] Fig. Figure 4 shows an assembly of a power transmission unit 138, which is similar in all aspects to the assembly of a power transmission unit 38, except that instead of the cover 73, a cover 73A is used, which has a serrated opening 96 that receives an external serration of the first sun gear 72 in order to permanently fix the sun gear 72 to the cover 73A without a disengaging clutch. The power transmission unit 138 thus operates only in an all-wheel drive mode with torque reduction.

[0031] Fig. Figure 5 shows an assembly of a power transmission unit 238, which shares many of the same components as the assemblies of power transmission units 38 and 138, but without a torque-reducing compound planetary gear set. Instead of cover 73 or 73A, a cover 73B is used, which can potentially be smaller since it does not need to contain a compound planetary gear set. The power transmission unit 238 has a disconnect capability because a disconnect clutch 280 is provided. Thus, both front-wheel drive and all-wheel drive capability are available in a vehicle that incorporates the assembly of a power transmission unit 238. The disconnect clutch 280 is a jaw clutch with a sleeve 283 that can be moved by an actuator A1 to slide axially on the shaft section 56, on which it is splined, in order to engage with the gear 285 on an outer circumference of the input shaft 44.When the clutch 280 is disengaged (i.e., not engaged), the hypoid ring gear 46 is not driven by the input shaft 44 and remains stationary. The assembly of a power transmission unit 238 is a single-axis power transmission unit capable of sharing the same first and second axes of rotation 36, 42 and the same hypoid ring gear 46 and pinion gear 48 as the assemblies of power transmission units 38 and 138, but the input element 44 is only capable of transmitting torque to the cardan shaft 40. Fig. 1 to transmit with a torque reduction ratio that is provided only by the hypoid ring gear 46 and pinion gear 48.

[0032] Fig. Figure 6 shows an assembly of a power transmission unit 338, which shares many of the same components as the assemblies of power transmission units 38, 138, and 238, but is a lower-ratio unit that, like the assembly of a power transmission unit 238, provides only the torque reduction of the hypoid ring gear 46 and pinion gear 48. The hypoid ring gear 46 of the assembly of a power transmission unit 338 is permanently attached to the input shaft 44. Thus, torque is always transmitted to the cardan shaft 40 when the power machine 14 delivers torque. The hypoid ring gear 46 can be integral with the input shaft 44 or attached to the input shaft 44 by any number of means, including but not limited to welding, shrink-fitting, splined connections, or a permanently installed sleeve. Additionally, a cover 72C, which is integral with the central support element 64C, is used.Cover 73C requires less radial installation space than cover 73 because it does not need to contain a planetary gear set. The cavity 92D, defined by cover 73C, can be smaller than cavity 92B.

[0033] Accordingly, the assemblies of power transmission units 38, 138, 238, and 338 are modular, as each has a base consisting of a housing 46, an input shaft 44, a hypoid ring gear 46, and a pinion gear 48. To meet the needs of different vehicle applications while maintaining a constant relative position of the first axis of rotation 36 and the second axis of rotation 42, either a direct torque unit or a torque reduction unit is added to the basic components, either with or without disengagement capability via a disconnect clutch, such as clutch 80 or 280.The use of common components, such as the hypoid ring gear 46 and pinion gear 48, and holding the components that accomplish the additional torque reduction concentric with a first axis (the first axis of rotation 36) can reduce the weight, cost and installation space requirements compared with a two-axis torque reduction arrangement.

[0034] Since the compound planetary gear set 70 provides a torque reduction on the input side of the bevel gear set (i.e., between the input shaft 44 and the hypoid ring gear 46), similar torque (but at increased speed) can be achieved at the cardan shaft 40 with a torque reduction unit ( Fig. 3 and Fig. 4) as with a direct torque unit ( Fig. 5 and Fig. 6) can be achieved. An application of the torque reduction unit ( Fig. 3 or Fig. 4) A relatively high-powered engine can ensure the same torque at the cardan shaft 40 as a direct drive application ( Fig. 5 or Fig. 6) with a relatively low-powered motor. For example, if a torque of 2900 Nm is applied to the input shaft 44 of the power transmission unit 38 or 138, and the torque ratio (torque of the input element 44 to torque of the pinion shaft 48) is 2.9 : 1.0, the torque at the cardan shaft 40 will be 1000 Nm. If a lower-powered motor is used and 1700 Nm of torque is applied to the input shaft 44 of the power transmission unit 238 or 338, and the torque ratio is 1.7 : 1.0 (torque of the input element 44 to torque of the pinion shaft 48 without a composite planetary gear set), then the torque at the cardan shaft 40 will also be 1000 Nm.

[0035] Although the best ways of carrying out the many aspects of the present invention have been described in detail, those skilled in the field relating to these teachings will recognize various alternative aspects for the practical implementation of the present teachings which are within the scope of the appended claims.

Claims

[1] Assembly of a power transmission unit (38, 138, 238, 338) for transmitting torque from a differential carrier (24) of a front differential (26) to a cardan shaft (40) of a vehicle (10); wherein the differential carrier (24) rotates about a first axis of rotation (36) and the cardan shaft (40) rotates about a second axis of rotation (42) perpendicular to the first axis of rotation (36), wherein the assembly of a power transmission unit (38, 138, 238, 338) comprises: an input shaft (44) which is designed to be driven rotatably about a first axis of rotation (36) by the differential carrier (24); a first bevel gear (46); a second bevel gear (48) which engages with the first bevel gear (46); wherein the first bevel gear (46) has an annular shaft section (56) and concentrically surrounds the input shaft (44); wherein the second bevel gear (48) is designed to drive the cardan shaft (40) rotatably about the second axis of rotation (42); a compound planetary gear set (70) which is concentric with the first axis of rotation (36) and is designed to transmit torque from the input shaft (44) to the first bevel gear (46) such that the torque of the first bevel gear (46) is less than the torque of the input shaft (44) and a rotational speed of the first bevel gear (46) is greater than a rotational speed of the input shaft (44); a stationary element adjacent to the compound planetary gear set (70), wherein the compound planetary gear set (70) comprises: a first sun wheel (72) which can be functionally connected to the stationary element; a second sun gear (74) which is attached to the annular shaft section (56) of the first bevel gear (46) in order to rotate in harmony with it; a support (76) which is attached to the input shaft (44) to rotate in accordance with it; a first set of pinion gears (77) and a second set of pinion gears (78), both of which are rotatably mounted on the carrier (76); wherein the first set of pinion gears (77) meshes with the first sun gear (72); and wherein the second set of pinion gears (78) meshes with the first set of pinion gears (77) and with the second sun gear (74); and A disconnecting clutch (80) that selectively functionally connects the first sun gear (72) to the stationary element to allow torque transmission from the input shaft (44) to the first bevel gear (46) through the compound planetary gear set (70), wherein the disconnecting clutch (80) is selectively disengageable to disconnect the first sun gear (72) from the stationary element, thereby preventing torque transmission from the input shaft (44) to the first bevel gear (46) through the compound planetary gear set (70), and wherein the disconnecting clutch (80) comprises the following plates: a rotating plate (81) that is mounted to rotate with the first sun gear (72); a stationary plate (82) that is mounted to the stationary element; and a selector plate (83) that is moved by an actuator (A) into contact with the rotating plate (81) to lock the rotating plate (81) to the stationary plate (82). [2] Power transmission assembly according to claim 1, further comprising: a stationary element adjacent to the compound planetary gear set (70); a disconnecting clutch (80) that selectively and functionally connects the compound planetary gear set (70) to the stationary element to enable torque transmission from the input shaft (44) to the first bevel gear (46) through the compound planetary gear set (70); and wherein the disconnecting clutch (80) can be selectively disengaged to disconnect the compound planetary gear set (70) from the stationary element, thereby preventing torque transmission from the input shaft (44) to the first bevel gear (46) through the compound planetary gear set (70). [3] Power transmission assembly according to claim 1, wherein the first sun gear (72) is serrated on the stationary element. [4] Modular assembly of a power transmission unit (38, 138, 238, 338) for a vehicle (10); wherein the vehicle (10) has a front differential (26) with a differential carrier (24) defining a first axis of rotation (36) and a cardan shaft (40) defining a second axis of rotation (42) perpendicular to the first axis of rotation (36), wherein the modular assembly of a power transmission unit (38, 138, 238, 338) comprises: an input shaft (44) designed in such a way that it is driven rotatably about the first axis of rotation (36) by the differential carrier (24) when the modular assembly of a power transmission unit (38, 138, 238, 338) is installed in a vehicle (10); a bevel gear set comprising a first bevel gear (46) and a second bevel gear (48); wherein the first bevel gear (46) is annular and concentrically surrounds the input shaft (44); wherein the second bevel gear (48) engages with the first bevel gear (46) and is rotatably driven by the first bevel gear (46) such that it rotates about the second axis of rotation (42); wherein the second bevel gear (48) is configured to rotatably drive the cardan shaft (40) when the modular assembly of a power transmission unit (38, 138, 238, 338) is installed in the vehicle (10); a stationary housing (66) that surrounds and supports the first and second bevel gears (46, 48) and is designed such that it can alternatively be connected to one of the following selected elements: a torque reduction unit which is concentric with the first axis of rotation (36) and is designed to transmit torque with a reduction ratio from the input shaft (44) to the first bevel gear (46); or a direct torque unit which is concentric with the first axis of rotation (36) and is designed to transmit torque at a ratio of one from the input shaft (44) to the first bevel gear (46); wherein the cardan shaft (40) rotates in the same direction in response to a forward rotation of the input shaft (44) in an all-wheel drive mode when either the torque reduction unit or the direct torque unit is installed in the vehicle (10). [5] Modular power transmission unit (38, 138, 238, 338) according to claim 4, wherein the torque reduction unit comprises: a compound planetary gear set (70) concentric with the first axis of rotation (36); and a fixed cover (73) attached to the fixed housing (66) and surrounding the composite planetary gear set (70); wherein the composite planetary gear set (70) comprises: a first sun wheel (72) which is attached to the stationary cover (73); a second sun wheel (74) which is attached to the first bevel wheel (46) to rotate in harmony with it; a support (76) which is attached to the input shaft (44) to rotate in accordance with it; a first set of pinion gears (77) and a second set of pinion gears (78), both of which are rotatably mounted by the carrier (76); wherein the first set of pinion gears (77) meshes with the first sun gear (72); and wherein the second set of pinion gears (78) meshes with the first set of pinion gears (77) and with the second sun gear (74). [6] Modular power transmission unit (38, 138, 238, 338) according to claim 4, wherein the torque reduction unit comprises: a compound planetary gear set (70) concentric with the first axis of rotation (36); and a fixed cover (73) attached to the fixed housing (66) and surrounding the composite planetary gear set (70); wherein the composite planetary gear set (70) comprises: a first sun wheel (72) which can be selectively functionally connected to the fixed cover (73); a second sun wheel (74) which is attached to the first bevel wheel (46) to rotate in harmony with it; a support (76) which is attached to the input shaft (44) to rotate in accordance with it; a first set of pinion gears (77) and a second set of pinion gears (78), both of which are rotatably mounted on the carrier (76); wherein the first set of pinion gears (77) meshes with the first sun gear (72); wherein the second set of pinion gears (78) meshes with the first set of pinion gears (77) and with the second sun gear (74); and a disengaging clutch (80) that can be selectively engaged to secure the first sun gear element (72) to the stationary cover (73), thereby allowing torque transmission from the input shaft (44) to the first bevel gear (46) through the combined planetary gear set (70), and that can be selectively disengaged to disconnect the first sun gear (72) from the stationary cover (73), thereby preventing torque transmission from the input shaft (44) to the first bevel gear (46) through the combined planetary gear set (70). [7] Modular power transmission unit (38, 138, 238, 338) according to claim 4, wherein the unit for direct torque is concentric with the first axis of rotation (36); and wherein the input shaft (44) is permanently attached to the first bevel gear (46) to transmit torque at a ratio of one from the input shaft (44) to the first bevel gear (46). [8] Modular power transmission unit (38, 138, 238, 338) according to claim 4, wherein the unit for direct torque is concentric with the first axis of rotation (36); and further comprising: a disconnecting clutch (80) which can be engaged to secure the input shaft (44) to the first bevel gear (46) and thus allow torque transmission from the input shaft (44) to the first bevel gear (46), and which can be selectively disengaged to disconnect the input shaft (44) from the first bevel gear (46), thereby preventing torque transmission from the input shaft (44) to the first bevel gear (46).

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