Transfer case with active clutch on front output and pass-thru rear output

A transfer case for use in a four-wheel drive vehicle and having a clutch assembly disposed on a front output and a pass-through rear output arrangement. The front output is a front output shall. The rear output is established by directly interconnecting a transmission output shaft to an end segment of a rear propshaft. A transfer assembly is driven by the transmission output shaft and can be selectively coupled to the front output shaft via the clutch assembly.

FIELD

The present disclosure relates generally to power transfer systems for controlling the distribution of drive torque from a powertrain to front and rear drivelines of a four-wheel drive motor vehicle. More particularly, the present disclosure is directed to a compact transfer case having an actively-controlled clutch assembly operably associated with a front output drivingly interconnected to the front driveline and a pass-through rear output directly interconnecting the powertrain to the rear driveline

BACKGROUND

In view of increased consumer interest in four-wheel drive vehicles, a plethora of power transfer systems are currently being utilized in vehicular applications for selectively directing rotary tractive power (i.e., drive torque) from the powertrain to all four wheels of the vehicle. In many power transfer systems, a transfer case is used for delivering drive torque from the powertrain to one or both of the front and rear drivelines. Some conventional transfer cases are equipped with a mode clutch, typically a positive-locking type of dog clutch, that can be selectively actuated via operation of a mode shift mechanism to shift between a two-wheel drive mode and a part-time (i.e. locked) four-wheel drive mode. In addition, many transfer cases also include a two-speed reduction unit and a range clutch which can be selectively actuated via operation of a range shift mechanism for shifting between four-wheel high-range and low-range drive modes.

It is also known to use “on-demand” power transfer systems for automatically distributing the drive torque generated by the powertrain between the front and rear drivelines, without any input or action on the part of the vehicle operator, when traction is lost at either the front or rear wheels. Modernly, it is known to incorporate the “on-demand” feature into a transfer case by replacing the mechanically-actuated mode clutch with a multi-plate clutch assembly and a power-operated clutch actuator that is interactively associated with an electronic control system and a plurality of vehicle sensors. Such transfer cases configured to permit electronic control over the drive torque distribution between the front and rear drivelines are commonly referred to as “active” transfer cases. During normal road conditions, the multi-plate clutch assembly is typically maintained in a release condition such that drive torque is only delivered to the rear wheels. However, when the sensors detect a low traction condition, the power-operated clutch actuator is operated for engaging the multi-plate clutch assembly to deliver drive torque automatically to the front wheels. Moreover, the amount of drive torque transferred through the multi-plate clutch assembly to the front wheels can be varied as a function of specific vehicle operating characteristics and/or road conditions, as detected by the sensors. This adaptive clutch control system can also be used in full-time transfer cases to automatically bias the torque distribution ratio across an interaxle differential.

A majority of current active transfer cases include a rear output shaft interconnecting the transmission output to the rear driveline, a front output shaft interconnected to the front driveline, a transfer assembly driven by the front output shaft, and a power-operated clutch assembly arranged to selectively/automatically couple the transfer assembly to the rear output shaft for transmitting drive torque to the front driveline. Typically, the transfer assembly includes a first sprocket rotatably supported on the rear output shaft, a second sprocket fixed for rotation with the front output shaft, and a chain encircling and drivingly interconnecting the first sprocket for rotation with the second sprocket. The clutch assembly and various components of the power-operated clutch actuator are typically disposed to surround the rear output shaft and function to selectively/automatically couple the first sprocket to the rear output shaft.

Such active transfer cases also require lubrication of the clutch assembly and other rotary components. A sump of lubricant is maintained in a lower portion of the transfer case so as to typically submerge at least the second sprocket. A passive lubrication system utilizes lubricant splashed throughout the transfer case upon rotation of the sprockets to lubricate the rotary components and to cool the clutch assembly. As alternative, a shaft-driven gear or gerotor lube pump can be operably associated with the rear output shaft to pump lubricant from the sump and distribute such lubricant in response to rotation of the rear output shaft. Finally, an actively-controlled or “on-demand” lube pump can be installed with the transfer case to provide optimal lubricant flow in a manner that is independent of the rotational characteristics of the rear output shaft.

In the past, the vehicle ride height and suspension configuration of many trucks and sport utility vehicles provided sufficient packaging volume for such traditional active transfer cases equipped with a pair of offset output shafts. However, in view of increased demand for smaller four-wheel drive vehicles, the packaging volume allocated to the powertrain and the transfer case has been greatly reduced. To accommodate reduced packaging space, commonly-owned U.S. Pat. No. 8,316,738 discloses an active transfer case having a traditional rear output shaft and clutch assembly configuration in association with a beveloid gearset type of transfer assembly and an angulated front output shaft. Alternatively, some active transfer cases have been developed which position the clutch assembly and power-operated clutch actuator on the front output shaft as shown, for example, in U.S. Pat. No. 8,157,072.

While such alternative transfer case configurations attempt to address the need for reduced packaging requirements, a need still exists to advance the technology and structure of active transfer cases to provide enhanced configurations that improve upon the prior art.

SUMMARY

This section provides a general summary of the disclosure and is not intended to be interpreted as a complete and comprehensive disclosure of all of its features, advantages, objectives and aspects.

It is an aspect of the present disclosure to provide a transfer case for use in a four-wheel drive vehicle that is configured to transmit drive torque directly from the transmission output to the rear driveline.

It is a related aspect of the present disclosure to provide a transfer case configured to eliminate the conventional rear output shaft by interconnecting the transmission output to a rear propshaft associated with the rear driveline.

It is another related aspect of the present disclosure to provide a transfer case including a front output shaft adapted for interconnection to the front driveline, a transfer assembly having a first transfer component fixed for rotation with the transmission output and a second transfer component drivingly connected to the first transfer component and which is rotatably supported on the front output shaft, and a clutch assembly operable for selectively coupling and uncoupling the second transfer component with the front output shaft. The transmission output extends at least partially through the transfer case and is configured to be drivingly coupled to the rear propshaft of the rear driveline.

It is another related aspect of the present disclosure to provide an active transfer case having a transfer assembly directly coupled to the transmission output, a multi-plate friction clutch assembly operably installed on the front output shaft, and a power-operated clutch actuator for selectively/automatically transferring drive torque from the transmission output through the transfer assembly to the front output shaft.

In accordance with these and other aspects of the present disclosure, an active transfer case is disclosed for use in a four-wheel drive vehicle having front and rear drivelines. The active transfer case is configured for interconnecting an output shaft of the transmission to a first end of a rear propshaft, the opposite end of which is drivingly coupled to a rear differential of a rear axle assembly associated with the rear driveline. The active transfer case of the present disclosure includes: a t-case housing adapted to be attached to a transmission housing of the transmission; a front output shaft rotatably supported by the t-case housing and which is adapted for connection to a first end of a front propshaft, the opposite end of which is drivingly coupled to a front differential of a front axle assembly associated with the front driveline; a transfer assembly having a first sprocket drivingly coupled to the transmission output shaft and rotatably supported in the t-case housing, a second sprocket rotatably supported on the front output shaft, and a chain drivingly intermeshed with both of the first and second sprockets; a multi-plate friction clutch assembly operably disposed between the second sprocket and the front output shaft; and a power-operated clutch actuator for adaptively regulating the magnitude of a clutch engagement force applied to the multi-plate friction clutch assembly.

In accordance with an alternative embodiment, the active transfer case of the present disclosure includes: a t-case housing adapted to be secured to the transmission housing of the transmission; a front output shaft rotatably supported by the t-case housing and adapted for connection to the front driveline; a transfer assembly having a first gear coupled for rotation with the transmission output, a second gear rotatably supported on the front output shaft, and a third gear meshed with the first and second gears; a multi-plate friction clutch assembly operably disposed between the second gear and the front output shaft; and a power-operated clutch actuator for adaptively regulating a clutch engagement force applied to the multi-plate friction clutch assembly for controlling the drive torque transferred from the transmission output to the front output shaft through the transfer assembly.

DETAILED DESCRIPTION

Referring initially toFIG. 1of the drawings, an example of a four-wheel drive motor vehicle10is shown schematically to include a powertrain11operable for generating rotary power (i.e., drive torque) which is transmitted through a transfer case16to a first or rear driveline18and a second or front driveline20. Powertrain11is shown, in this non-limiting example, to include an internal combustion engine12and a multi-speed transmission14. In the particular arrangement shown, rear driveline18includes a pair of ground-engaging rear wheels22drivingly connected via a pair of rear axle shafts23to a rear differential assembly24associated with a rear axle assembly26. A rear propshaft28interconnects a rotary input29of rear differential assembly24to a rotary output30of transmission14which is shown to extend through transfer case16. A pair of rear joint units31are shown to interconnect opposite ends of rear propshaft28to rotary input29of rear differential assembly24and rotary output30of transmission14and which function to transmit drive torque while permitting angular and/or translational movement therebetween.

Front driveline20is shown inFIG. 1to include a pair of ground-engaging front wheels32drivingly connected via a pair of front axle shafts33to a front differential assembly34associated with a front axle assembly36. A front propshaft38interconnects a rotary input39of front differential assembly34to a front output shaft40associated with transfer case16. A pair of front joint units41are shown to interconnect opposite ends of front propshaft38to rotary input39of front differential assembly34and front output shaft40of transfer case16to transmit drive torque while permitting angular and/or translational movement therebetween. A disconnect coupling43is shown associated with one of front axle shafts33and is operable in a connected mode to drivingly couple front wheels32to the remainder of front driveline20and is operable in a disconnected mode to uncouple front wheels32from driven connection with the remainder of front driveline20.

Powertrain11is shown in association with a powertrain control system42generally and schematically shown to include an array of vehicle sensors44and a mode selector46, both of which provide signals which communicate with a vehicle controller48. Vehicle controller48can be interpreted to include one or more individual controllers associated with engine12, transmission14, transfer case16, and disconnect coupling43which are configured and arranged to control operation of vehicle10.

Referring toFIG. 2of the drawings, the interaction of components associated with transmission14and transfer case16will now be described to provide a better understanding of the pass-through rear output and clutched front output concepts associated with the present disclosure. In this regard, transmission output30is an otherwise conventional transmission output shaft adapted to extend outwardly from a transmission housing60. Transfer case16includes a t-case housing62adapted to be secured to transmission housing60and which defines an internal chamber64. An end segment30A of transmission output shaft30is shown schematically to be directly coupled to an end segment28A of rear propshaft28via a coupling interface66. Alternatively, end segment30A of transmission output shaft30can be directly coupled to a shaft component of joint unit31which, in turn, is coupled to end segment28A of rear propshaft28. Based on these arrangements, a common transmission shaft30and a common rear propshaft28can be used with two-wheel/rear wheel drive (2WD/RWD) versions of motor vehicle10as well as with four-wheel drive (4WD) versions of motor vehicle10.

Transfer case16is further shown inFIG. 2to generally include a transfer assembly68, a clutch assembly70, and a power-operated clutch actuator72. Transfer assembly68can be configured as a geared drive assembly or as a chain drive assembly. In the particular example disclosed, transfer assembly68is a chain and sprocket drive assembly having a first sprocket74drivingly coupled directly to transmission shaft30, a second sprocket76rotatably supported on front output shaft40, and a continuous power chain78encircling and meshing with both first sprocket74and second sprocket76. A coupling interface79is schematically shown for indicating the direct coupling of first sprocket74with transmission shaft30. Clutch assembly70is shown, in this non-limiting embodiment, as a multi-plate friction clutch having a first clutch member80coupled for common rotation with second sprocket76, a second clutch member82coupled for common rotation with front output shaft40, and a multi-plate clutch pack84comprised of a plurality of interleaved inner and outer clutch plates. Power-operated clutch actuator72includes an axially moveable apply device88capable of applying a compressive clutch engagement force on clutch pack84, and a powered driver unit90operable for controlling the axial position of apply device88relative to clutch pack84.

The magnitude of the clutch engagement force exerted on clutch pack84by apply device88is proportional to the amount of drive torque transmitted from transmission shaft30through transfer assembly68to front output shaft40. Accordingly, when a predetermined minimum clutch engagement force is applied to clutch pack84, a minimum drive torque is transmitted to front driveline20. In contrast, when a predetermined maximum clutch engagement force is applied to clutch pack84, a maximum drive torque is transmitted to front driveline20. As such, adaptive control over the front/rear drive torque distribution ratio can be provided by active transfer case16to establish a two-wheel drive (2WD) mode and an on-demand four-wheel drive (4WD) mode.FIG. 2illustrates a transfer case controller48A associated with vehicle controller48ofFIG. 1that is operable for controlling actuation of powered driver unit90which, in turn, controls the axial position of apply device88relative to clutch pack84.

Referring now toFIG. 3, a sectional view of an embodiment of transfer case16constructed in accordance with the present disclosure will be described in detail with common reference numerals from the schematic illustration ofFIG. 2used again to identify similar components. In general, transfer case16is a single-speed active transfer case with its clutch assembly and apply device arranged on the front output shaft so as to allow the rear propshaft (or a joint unit associated with the rear propshaft) to be directly connected to the transmission output shaft. This compact arrangement permits use of a common rear propshaft in a motor vehicle having 2WD and 4WD variants. This arrangement improves overall system weight and costs by eliminating the rear output shaft and concomitantly reduces vehicle assembly complexity.

Transfer case16ofFIG. 3is shown to have an axially-extending stubshaft segment100of first sprocket74fixed via a splined connection79with tubular end segment30A of transmission shaft30. Specifically, external splines formed on end segment30A of transmission shaft30are meshed with internal splines formed on stubshaft segment100of first sprocket74. A pair of laterally-spaced bearing assemblies102,104are provided to support stubshaft segment100for rotation within t-case housing62. First and second rotary seals106,108are also disposed between stubshaft segment100of first sprocket74and t-case housing62. As also shown in this non-limiting example, a sliding-type splined connection66is provided between tubular end segment30A of transmission shaft30and end segment28A of rear propshaft28. As noted, in an alternative arrangement, an end segment of a shaft portion of joint unit31could be coupled via sliding spline connection66to end segment30A of transmission shaft30, with another portion of joint unit31being coupled to end segment28A of rear propshaft28. Thus, the present disclosure considers the term “rear propshaft28” to be stand-alone arrangement or a rear propshaft assembly having joints31associated therewith. Regardless of the configuration, an end segment of transmission shaft30extends through t-case housing62and is directly connected to a component of rear driveline18so as to eliminate the use of a mainshaft/rear output in transfer case16. A bellow-type boot cover107is shown between stubshaft segment100of first sprocket74and end segment28A of rear output shaft28. A deflector plate109is also mounted to stubshaft segment100and is located between rotary seal108and boot cover107.

Front output shaft40is rotatably supported in t-case housing62by a pair of laterally-spaced bearing assemblies110,112. A rotary seal114and a deflector plate116are also attached to front output shaft40. Second sprocket76is supported by a suitable bearing assembly118for rotation relative to front output shaft40. A radial thrust bearing120and a retainer ring122delineate an edge of second sprocket76. In the non-limiting embodiment shown, first clutch member80of clutch assembly70is a clutch drum that is fixed for common rotation with second sprocket76. Likewise, second clutch member82of clutch assembly70is a clutch hub that is fixed for common rotation with front output shaft40. Clutch pack84includes a set of outer clutch plates splined to clutch drum80and a set of inner clutch plates splined to clutch hub82. The apply device88of clutch actuator72is shown, in this non-limiting embodiment, to include a ballramp unit130and an apply plate132. Ballramp unit130includes a stationary first cam or support ring134that is non-moveably fixed to t-case housing62, a rotatable and axially moveable second cam or adjustment ring136, and a plurality of circumferentially-spaced balls138that are retained in aligned cam grooves formed in each of the first and second cam rings. Adjustment ring136includes a radially-extending sector flange140having gear teeth142formed at its peripheral edge. Powered drive unit90is best shown inFIGS. 4 and 5to include an electric motor144having a rotary output145with a worm146having threads148meshingly engaged with gear teeth142on sector flange140of adjustment ring136. Rotation of worm146in a first direction causes rotation of adjustment ring136due to engagement of threads148with gear teeth142in a first direction which, in turn, causes axial translation of adjustment ring136in a first or “clutch engage” direction toward clutch pack84. Apply plate132is axially moveable with adjustment ring136in this clutch engage direction to apply the clutch engagement force to clutch pack84. Obviously, rotation of worm146in a second direction causes axial translation of adjustment ring136and apply plate132an opposite second or “clutch release” direction away from clutch pack84. A thrust bearing150is disposed between apply plate132and adjustment ring136to facilitate relative rotation therebetween. A return spring (not shown) acts to normally bias apply plate132and adjustment ring136in the clutch release direction.

To be able to bring about the explained rotary and axial movement of the adjustment ring136, it is drive-operationally coupled to electric motor144via a step-down transmission160. This is shown in the plan view in accordance withFIG. 4. In accordance withFIG. 4, powered driver unit90includes the reduction gear unit160formed by the worm gearset having helical threads148of worm146meshing with spur gear teeth142formed on sector flange140. The worm146is rotationally fixedly coupled with output shaft145of the electric motor144. The spur gear flange section140can be made in one piece with the adjustment ring136.

The axis of rotation S of worm146is inclined by an oblique position angle α with respect to the rotational plane R of spur gear flange section140of adjustment ring136. This oblique position angle α corresponds to the pitch angle β of threads148on worm146. The pitch angle β of worm146is shown inFIG. 5which shows a detailed view of the engagement region between helical threads148of worm146and spur gear teeth142on flange section140. The pitch angle β can be recognized here as the angle which the worm thread148adopts relative to a normal plane of the worm axis S. As can furthermore be seen inFIG. 4, spur gear section140of the adjustment ring136has a straight toothed arrangement. Spur gear section140is made as a peripheral section of a cylindrical spur gear, that is not, for instance, as an enveloping gear. Worm146is made as a cylinder worm, with worm146and spur gear section140being in engagement in the manner of a bevel gear toothed arrangement. Alternatively, worm146can, however, also be made as an enveloping worm to mesh with spur gear section140in the manner of a spur gear worm toothed arrangement.

Thread148of worm146hereby extends in the engagement region between worm146and spur gear flange section140substantially parallel to the axis of rotation A of adjustment ring136. Adjustment ring136can thus move freely, i.e. without a superimposed rotary movement, in the axial direction and the rotary drive of adjustment ring136by means of worm140does not result in any additional axial forces and tilting moments, or only in slight additional axial forces and tilting moments, which act on adjustment ring136. A precise control of power-operated clutch actuator72and a precise actuation of multi-plate friction clutch70are hereby possible. This applies in particular if the control of the actuator is based on a monitoring of the motor current of electric motor144.

Those skilled in the art will appreciate that apply device88can include any device capable of applying a clutch engagement force and may include, without limitation, linear actuators, leadscrew drives, pivot actuators, EM actuators, hydraulic actuators and the like having movement controlled by a powered driver unit90which may include, without limitations, electric motors, hydraulic power packs, EM actuators and the like. Those alternative devices and units are intended to be sufficiently disclosed based on the schematic illustrations thereof provided inFIG. 2to define alternative embodiments to the devices and unit associated with the power-operated clutch actuator72shown inFIGS. 3-5.

Referring now toFIG. 6, a one-speed transfer case16A is shown and which is generally an alternative version of transfer case16shown inFIG. 2having a positive-locking type of mode clutch70A replacing multi-plate friction clutch70. As seen, mode clutch70A includes a first clutch member80A fixed for common rotation with second sprocket76of transfer assembly68, a second clutch member82A fixed for common rotation with first output shaft40, and an apply component88A operable for coupling second clutch member82A for common rotation with first clutch member80A so as to transmit drive torque from transmission shaft30to front output shaft40through transfer assembly68. In this non-limiting embodiment, first clutch member80A is a clutch ring, second clutch member82A is a clutch hub, and apply member88A is a sliding mode sleeve. The mode sleeve is splined for common rotation with the clutch hub (and first output shaft40) and is axially moveable between a first or 2WD mode position (shown) and a second or 4WD mode position. A mode shift mechanism85interconnects mode sleeve88A to powered drive unit90which, in turn, control movement of mode sleeve88A between its first and second mode positions. In the first mode position, first output shaft40is uncoupled from driven connection with transmission shaft30. In contrast, movement of mode sleeve88A into its second mode position results in establishment of a drive connection between transmission shaft30and front output shaft40through transfer assembly68. Thus, transfer case16A illustrates a pass-through rear drive arrangement in combination with a positive locking type of mode clutch arrangement on the front output shaft.

Referring now toFIG. 7, one-speed active transfer case16B is shown which is generally an alternative version of transfer case16ofFIG. 2having a geared transfer assembly68B instead of chain and sprocket transfer assembly68. As seen, geared transfer assembly68B includes a first gear74B fixed via connection interface79for common rotation with transmission shaft30, a second gear76B rotatably supported on first output shaft40, and a third gear77in constant mesh with first gear74B and second gear76B. Third gear77is shown to be rotatably supported on an idler shaft81mounted in t-case housing62and functions to maintain the desired rotational direction relationship between transmission shaft30and front output shaft40. The operation and function of multi-plate friction clutch70and power-operated clutch actuator72being the same as previously disclosed in relationship to transfer case16.