Electrohydraulic torque transfer device with integrated clutch and actuator unit

A power transmission device includes a housing, a rotatable input member and a rotatable output member supported in the housing by a pair of bearings. A friction clutch is operable to selectively transmit a requested magnitude of torque between the input member and the output member. The clutch is axially positioned between the bearings. An actuator is operable to provide an actuation force to the friction clutch to generate the requested magnitude of torque.

BACKGROUND

The present disclosure relates generally to a power transmission device operable to selectively transfer torque between first and second sets of drivable wheels of a vehicle. More particularly, the present disclosure describes a torque transfer device including a clutch integrally associated with driving axle components.

Due to increased demand for four-wheel drive vehicles, many power transmission systems are typically being incorporated into vehicle driveline applications for transferring drive torque to the wheels. Many vehicles include a power transmission device operably installed between the primary and secondary drivelines. Such power transmission devices are typically equipped with a torque transfer mechanism for selectively transferring drive torque from the primary driveline to the secondary driveline to establish a four-wheel drive mode of operation. At least one known torque transfer mechanism includes a dog-type lock-up clutch that may be selectively engaged for rigidly coupling the secondary driveline to the primary driveline when the vehicle is operated in four-wheel drive mode. Drive torque is delivered only to the primary driveline when the lock-up clutch is released and the vehicle operates in a two-wheel drive mode.

Another type of power transmission device is operable for automatically directing drive torque to the secondary wheels without any input or action on the part of a vehicle operator. When traction is lost at the primary wheels, the four-wheel drive mode is entered. Some transfer cases are equipped with an electrically-controlled clutch actuator operable to regulate the amount of drive torque transferred to a secondary output shaft as a function of changes in vehicle operating characteristics such as vehicle speed, throttle position and steering angle. Typically, the power transfer device includes a clutch positioned within the transfer case housing.

While many power transfer devices are currently used in four-wheel drive vehicles, a need exists to advance the technology and recognize the system limitations. For example, the size, weight and packaging requirements of the power transmission device may make such system costs prohibitive in some four-wheel drive applications.

SUMMARY

A power transmission device includes a housing, a rotatable input member and a rotatable output member supported in the housing by a pair of bearings. A friction clutch is operable to selectively transmit a requested magnitude of torque between the input member and the output member. The clutch is axially positioned between the bearings. An actuator is operable to provide an actuation force to the friction clutch to generate the requested magnitude of torque.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the disclosure, its application, or uses.

The present disclosure is directed to a power transmission device that may be adaptively controlled for modulating the torque transferred between a rotatable input member and a rotatable output member. The torque transfer mechanism may be useful within motor vehicle drivelines as a stand-alone device that may be easily incorporated between sections of propeller shafts, directly coupled to a driving axle assembly, or other in-line torque coupling applications. Accordingly, while the power transmission device is hereinafter described in association with a specific structural embodiment for use in a driveline application, it should be understood that the arrangement shown and described is merely exemplary.

With reference toFIG. 1of the drawings, a drive train10for a four-wheel vehicle is shown. Drive train10includes a first axle assembly12, a second axle assembly14and a power transmission16for delivering drive torque to the axle assemblies. In the particular arrangement shown, first axle12is the front driveline while second axle14is the rear driveline. Power transmission16includes an engine18and a multi-speed transmission20having an integrated front differential unit22for driving front wheels24via axle shafts26. A transfer unit28is also driven by transmission20for delivering torque to an input member29of a coupling30via a driveshaft32. The input member29of the coupling30is coupled to driveshaft32while its output member is coupled to a drive component of a rear differential36. Second axle assembly14also includes a pair of rear wheels38connected to rear differential36via rear axle shafts40.

Drive train10is shown to include an electronically-controlled power transfer system42including coupling30. Power transfer system42is operable to selectively provide drive torque in a two-wheel drive mode or a four-wheel drive mode. In the two-wheel drive mode, torque is not transferred via coupling30. Accordingly, 100% of the drive torque delivered by transmission20is provided to front wheels24. In the four-wheel drive mode, power is transferred through coupling30to supply torque to rear wheels38. The power transfer system42further includes a controller50in communication with vehicle sensors52for detecting dynamic and operational characteristics of the motor vehicle. The controller is operable to control actuation of coupling30in response to signals from vehicle sensors52. The controller50may be programmed with a predetermined target torque split between the first and second sets of wheels. Alternatively, controller50may function to determine the desired torque to be transferred through coupling30via other methods. Regardless of the method used for determining the magnitude of torque to transfer, controller50operates coupling30to maintain the desired torque magnitude.

FIGS. 2-4depict coupling30in greater detail. Coupling30includes an input shaft70selectively drivingly coupled to an output shaft or pinion72via a friction clutch74. An input flange76is mounted on one end of input shaft70to provide a mounting provision for a driveline component such as driveshaft32.

Coupling30includes a housing80fixed to a rear axle housing82. Rear axle housing82rotatably supports a differential case84of rear differential36. A ring gear86is fixed to differential case84. Pinion72includes a pinion gear88integrally formed thereon and positioned in meshed engagement with ring gear86. To achieve the appropriate gear mesh, a height setting shim90is positioned between housing80and rear axle housing82.

Pinion72is rotatably supported by a pinion head bearing92and an inner tail bearing94. Pinion head bearing92is pressed into housing80. A clip95retains inner tail bearing94within a pocket formed within input shaft70. A nut97retains inner tail bearing94on pinion72. Input shaft70is rotatably supported within housing80by an outer tail bearing96. A nut98retains outer tail bearing96on input shaft70. Axial movement of pinion72and input shaft70is restricted by this arrangement.

As previously mentioned, friction clutch74may be selectively actuated to drivingly interconnect input shaft70and pinion72. Friction clutch74includes a plurality of inner clutch plates100fixed for rotation with pinion72via involute splines. A plurality of outer clutch plates102are fixed for rotation with a drum104via another set of involute splines. Drum104is fixed to input shaft70. A laser welding technique may be employed to accomplish this task. Alternatively, the two-piece assembly of input shaft70and drum104may be replaced by a one-piece shaft having splines generated by a shaping operation.

A piston106is slidably positioned within a piston cavity108formed in housing80. Piston106may be acted on by a pressurized fluid to selectively apply a clutch actuation force to inner clutch plates100and outer clutch plates102to transfer torque through friction clutch74. A thrust bearing110is positioned between piston106and friction clutch74to allow relative rotation therebetween.

Input flange76is coupled for rotation with input shaft70via an involute spline. A snap ring116axially retains input flange76on input shaft70. A bushing118rotatably supports input flange76on pinion72allowing relative rotation therebetween. A seal120is positioned to prevent egress of oil and ingress of contamination between input flange76and housing80. A cap122and o-ring124seal a bore126extending through input flange76. A flinger128is coupled to input flange76to encourage debris away from seal120. Bearing preload is achieved by measuring the components and selecting an appropriately sized spacer130against which outer tail bearing96is tightened. During normal driving conditions, outer tail bearing96rotates and inner tail bearing94is static. Inner tail bearing94rotates only when there is a differential speed between front wheels24and rear wheels38.

Furthermore it should be appreciated that friction clutch74is axially positioned between pinion head bearing92and inner tail bearing94. This configuration provides a number of design benefits. In particular, a minimized packaging envelope is required due to the length of the rear axle assembly and coupling combination being greatly reduced compared to competitive designs. Competitive couplings are typically not integrated into the rear axle but instead may be bolted to an axle housing that rotatably supports the pinion. The known axle housings have a predetermined length in order to maintain an adequate spacing between the pinion head bearing and the pinion tail bearing to support the pinion adequately. The present disclosure utilizes the space between pinion head bearing92and inner tail bearing94by positioning friction clutch74at this location. This packaging feat allows a vehicle manufacturer to utilize the vehicle under body space for other challenges such as maximizing fuel tank volume.

Positioning friction clutch74between pinion head bearing92and inner tail bearing94encourages maintaining at least a minimum distance between pinion head bearing92and inner tail bearing94. It should be appreciated that an increase in gear life, an increase in bearing life, and a decrease in noise generated by the bearings and gear mesh may result from increasing the spacing between the pinion bearings.

Coupling30also provides a unique bearing loading arrangement. In a standard rear axle equipped with hypoid gearing, a thrust load encountered by the hypoid pinion reciprocates between drive and over-run modes of operation. In the drive mode, the thrust of the gear forces acts in a first direction132toward input flange76. In an over-run or coast mode, the thrust is in an opposite direction134. Oftentimes, steep angle tapered roller bearings are required at the pinion head and pinion tail positions to react the reciprocating loads. The pinion head bearing reacts gear thrust loads in the drive mode while the pinion tail bearing reacts the thrust loads in the over-run mode of operation. Furthermore, a relatively high pre-load is required between the pinion head and pinion tail bearings to reduce the likelihood of noise caused by the reciprocating load. A high bearing preload increases drag and therefore reduces the mechanical efficiency of the power transmission device.

The torque transfer device of the present disclosure provides a solution to issues arising from the reciprocating loads. When coupling30transfers torque, a thrust load is generated on input shaft70in first direction132toward input flange76. The load is transferred through inner tail bearing94and nut97into pinion72. In the drive mode of operation, a gear thrust load is generated in pinion72also acting in first direction132. Accordingly, a net thrust load is in the same direction132. This thrust load is reacted through pinion head bearing92into housing80.

In the over-run mode of operation, the thrust load generated by friction clutch74continues to act in first direction132and is transferred to pinion72as previously described. However, thrust loads input through pinion72are now in the opposite direction134. The pinion gear thrust loads generated during the over-run mode are of a lesser magnitude than the clutch thrust loads. Therefore, the net thrust load on pinion72is in first direction132and is reacted into housing80through pinion head bearing92as previously described. It should be appreciated that the net pinion thrust loads experienced by pinion72consistently act in first direction132. This predictable loading allows for a reduced preload in the bearing arrangement which also reduces drag and therefore increases mechanical efficiency. Because the thrust loading is uni-directional, higher efficiency bearings may be used at the constantly rotating outer tail bearing96position.

FIG. 4presents a schematic of a hydraulic circuit200in communication with coupling30. Hydraulic circuit200includes an accumulator202for storing pressurized hydraulic fluid provided by a hydraulic pump204driven by an electric motor206. An inlet208of pump204is in communication with a low pressure filter210. Fluid may be drawn from a sump212through low pressure filter210and pump204. Highly pressurized fluid exits pump204and passes through a high pressure filter214. Pressurized fluid continues to flow through a check valve216to charge accumulator202. Check valve216restricts fluid from flowing in a reverse direction toward pump204.

A pressure switch218controls motor206and pump204to maintain a desired fluid pressure within accumulator202. If the pressure within accumulator202drops below a predetermined value, pressure switch218closes to cause motor206to drive pump204and provide pressurized fluid to accumulator202. A proportional pressure reducing valve220is in communication with the pressurized fluid within accumulator202. Proportional pressure reducing valve220includes a solenoid222that may be selectively actuated to allow pressurized fluid to act on piston106. In one arrangement, controller50provides a pulse width modulated signal to solenoid222to accurately control the pressure applied to piston106. As pressure is applied to piston106, a compressive force acts on friction clutch74. The output torque of friction clutch74is controlled by varying the pressure applied to piston106via proportional pressure reducing valve220. When solenoid222is not actuated, fluid within piston cavity108returns to sump212and torque is not transferred through friction clutch74. A pressure relief valve224is positioned between accumulator202and proportional pressure reducing valve220to relieve pressure within accumulator202if a predetermined value is exceeded.

Coupling30also incorporates a lubrication and actuation system using a single lubricant from sump212to lubricate the rear axle, lubricate and cool friction clutch74and also act as the actuation fluid stored in accumulator202acting on piston106. A GL5 synthetic oil with friction modifier additives or an automatic transmission fluid may exhibit desirable properties for this application. Because a common hydraulic fluid is being used throughout the system, friction clutch74may include carbon fiber friction linings. By using a single lubricant, the risk of cross-contamination of lubricants is eliminated.

Motor206and pump204may also be used to provide a low pressure output of lubrication spraying onto pinion gear88and ring gear86. A fluid level within sump212may be maintained below a lower extremity of ring gear86. Mechanical efficiency of rear axle14may be increased due to a reduction in churning losses. Alternatively, ring gear86may extend into the fluid contained within sump212by a reduced amount compared to a standard rear axle assembly to reduce energy loss.

Furthermore, the foregoing discussion discloses and describes merely exemplary embodiments of the present invention. One skilled in the art will readily recognize from such discussion, and from the accompanying drawings and claims, that various changes, modifications and variations may be made therein without department from the spirit and scope of the invention as defined in the following claims.