Hydraulically controlled torque coupling device

A hydraulically actuated torque coupling device is provided for transmitting a drive torque from an input to at least one output. The torque coupling device comprises a rotatable hydraulic manifold block having a plurality of cylinder bores defined therein, a multi-lobed cam ring rotatable coaxially with the manifold block, a plurality of pistons each disposed within corresponding one of the plurality of cylinder bores in the manifold block for reciprocating therewithin upon relative rotational movement between the manifold block and the cam ring and defining a plurality of pressure chambers within the corresponding cylinder bores, and restrictor device in fluid communication with each of the plurality of pressure chambers such that the restrictor device controls a discharge pressure attainable within each of the plurality of pressure chambers during discharge strokes. Each of the plurality of pistons rotably engages the at least one cam ring at distal ends thereof.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to torque coupling devices in general, and more particularly to a hydraulically actuated torque coupling device provided for transmitting a drive torque at from an input to at least one output.

2. Description of the Prior Art

Conventionally, torque coupling devices well known in the prior art, and are used in various applications, such as vehicular drivetrains, to limit slip and transfer drive torque between a pair of rotary members. In all-wheel drive applications, torque coupling devices are used to automatically control the drive torque transferred from a driven member to a non-driven member in response to speed differentiation therebetween. In limited slip applications, couplings are used in association with a differential to automatically limit slip and bias the torque distribution between a pair of rotary members.

Such torque coupling devices conventionally use a frictional clutch between the rotary members. The frictional clutch may be selectively actuated by various hydraulic actuator assemblies, which are constructed of elements disposed inside a casing. The hydraulic actuator assemblies internal to the casing often include displacement pumps disposed inside the casing and actuated in response to a relative rotation between the differential case and the output shaft. The displacement pumps are usually in the form of internal gear pumps, such as gerotor pumps adapted to convert rotational work to hydraulic work. The hydraulic actuator assemblies further include a hydraulic piston member for frictionally loading the friction clutch.

While known torque coupling devices, including but not limited to those discussed above, have proven to be acceptable for various vehicular driveline applications, such devices are nevertheless susceptible to improvements that may enhance their performance and reduce cost. With this in mind, a need exists to develop improved torque coupling devices that advance the art.

SUMMARY OF THE INVENTION

The present invention provides a novel hydraulically actuated torque coupling device provided for transmitting a drive torque from an input to at least one output.

The torque coupling device in accordance with the present invention comprises a rotatable hydraulic manifold block having at least one plurality of cylinder bores defined therein, at least one multi-lobed cam ring rotatable relative to and coaxially with the hydraulic manifold block, at least one plurality of pistons each disposed within corresponding one of the at least one plurality of cylinder bores in the manifold block for reciprocating therewithin upon relative rotational movement between the manifold block and the at least one cam ring. The at least one plurality of first pistons defines a corresponding plurality of variable displacement pressure chambers within the corresponding one of the at least one plurality of the cylinder bores.

The torque coupling device in accordance with the present invention further includes at least one restrictor device in fluid communication with each of the at least one plurality of pressure chambers such that the at least one restrictor device controls a discharge pressure attainable within each of the at least one plurality of pressure chambers during discharge strokes of the at least one plurality of pistons. Each of the at least one plurality of pistons engages the at least one cam ring at distal ends thereof.

Preferably, the at least one restrictor device is provided to selectively set the discharge pressure attainable within each of the at least one plurality of pressure chambers between a maximum pressure value and a minimum pressure value, wherein the minimum pressure value is at a level that prevents actuation of the torque coupling device and the maximum pressure value is at a level that enables complete actuation of the torque coupling device. When the at least one restrictor device is adjusted to set the discharge pressure attainable in each of the at least one plurality of pressure chambers is adjustable between the minimum pressure value and the maximum pressure value so as to the torque coupling device is partially actuated. The at least one restrictor device is selectively and variably controlled by an electronic controller in response to at least one vehicle parameter, such as input and output speed sensors, vehicle wheel speed sensors, an ABS activation sensor that detects the activation of the anti-lock braking system, a yaw rate sensor, a steering angle sensor, etc.

The torque coupling device in accordance with the present invention further includes at least one fluid reservoir for storing a supply of a hydraulic fluid. The at least one fluid reservoir is in fluid communication with both the plurality of pressure chambers and the at least one restrictor device, and is, preferably, disposed within the hydraulic manifold block.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The preferred embodiments of the present invention will now be described with the reference to accompanying drawings.

FIGS. 1-3depict a selectively operable torque coupling device10in accordance with the first exemplary embodiment of the present invention. The torque coupling device10comprises a substantially cylindrical housing12rotatably supporting therewithin a hydraulic manifold block14rotatable about an axis of rotation15and a multi-lobed cam ring26coaxial to the hydraulic manifold block14. The hydraulic manifold block14and the multi-lobed cam ring26are rotatably supported within the housing12by appropriate anti-friction bearings, such as roller bearings. Preferably, the cylindrical housing12includes two halves12aand12bsecured to each other in a manner known to those skilled in the art, such as by threaded fasteners, welding, riveting, etc.

In accordance with the first exemplary embodiment of the present invention, the hydraulic manifold block14is drivingly coupled to an input shaft (not shown), while the multi-lobed cam ring26is drivingly coupled to an output shaft (not shown). Correspondingly, an input torque TINis applied to the hydraulic manifold block14from the input shaft, while an output torque TOUTis transmitted to the output shaft through the cam ring26, as shown inFIG. 3. The torque coupling device10of the first exemplary embodiment of the present invention is capable to vary a torque transfer rate, i.e. the TIN/TOUTratio, transmitted from the input shaft to the output shaft by the torque coupling device10. It will be appreciated that alternatively, the hydraulic manifold block14may be drivingly coupled to the output shaft, while the multi-lobed cam ring26is drivingly coupled to the input shaft.

As further illustrated inFIGS. 1-3, the hydraulic manifold block14is substantially cylindrical in shape and includes a plurality of axially extending open cylinder bores16formed therein. Preferably, the cylinder bores16are equidistantly circumferentially spaced about the axis of rotation15. The cam ring26is formed with a cam surface28having a plurality of alternating cam crests (or lobes) and cam valleys at regular intervals. The cam surface26faces the cylinder bores16of the hydraulic manifold block14.

The torque coupling device10further includes a plurality of pistons20. The number of the pistons20corresponds to the number of the cylinder bores16in the hydraulic manifold block14so that each of the pistons20is slideably disposed within corresponding one of the plurality of the cylinder bores16in the hydraulic manifold block14for reciprocating therewithin upon relative rotational movement between the hydraulic manifold block14and the multi-lobed cam ring26. Each of the pistons20defines a variable displacement pressure chamber18within the corresponding one of the plurality of cylinder bores16. The cylinder bores16and the pistons20are preferably ring-shaped. However, alternatively, the cylinder bores16and the pistons20may have other suitable shapes. An intake/discharge hole19is formed in a bottom portion of each of the pressure chamber18. Distal ends22of the pistons20extend from the cylinder bores16as the pistons20are biased toward the cam surfaces28of the cam ring26by coil springs24disposed within the pressure chambers18. The distal ends22of the pistons20rotateably and slideably engage the cam surface28the multi-lobed cam ring26due to biasing forces of the coil springs24. Preferably, the distal ends22of the pistons20are semi-spherical in shape.

As further illustrated inFIG. 3, each of the pressure chambers18is in fluid communication with a fluid reservoir30storing a supply of an appropriate hydraulic fluid, such as oil, through a supply passageway32and a discharge passageway34. Preferably, the fluid reservoir30is integrally formed within the hydraulic manifold block14.

As the pressure chambers18are in fluid communication with the fluid reservoir30, the reciprocating movement of the pistons20within the cylinder bores16in the hydraulic manifold block14upon relative rotational movement between the hydraulic manifold block14and the cam ring26provides a pumping action including alternating suction and discharge strokes.

During the suction stroke when the pistons18extend from the cylinder bores16of the hydraulic manifold block14, volumes of the pressure chambers18increase and the hydraulic fluid is drawn into the pressure chambers18from the fluid reservoir30through the supply passageway32. Accordingly, during the discharge stroke when the pistons18retract into the cylinder bores16, volumes of the pressure chambers18decrease and the hydraulic fluid is discharged under pressure from the pressure chambers18back to the fluid reservoir30through the discharge passageway34. In other words, the pressure chambers18function to cooperate with the pistons20to pressurize the hydraulic fluid during the discharge stroke of the pistons20.

Preferably, as shown inFIGS. 1-3, the hydraulic manifold block14of the torque coupling device10in accordance with the first exemplary embodiment of the present invention comprises seven cylinder bores16and seven associated pistons20, while the multi-lobed cam ring26has six lobes. This arrangement provides at least three pistons20in the discharge stroke and at least three pistons in the suction stroke. It will be appreciated that more or less cylinder bores/pistons and cam lobes may be employed depending upon the relative dimensions and proportions of the particular arrangement of the torque coupling device.

In order to control the fluid pressure in the pressure chambers18and, subsequently, the torque transfer through the torque coupling device10, a variable restrictor device40is provided, as illustrated inFIG. 3. The variable restrictor device40according to the present invention, is provided to selectively control the hydraulic pressure in the pressure chamber18during the discharge stroke. More specifically, the variable restrictor device40is adapted to provide a variable resistance to the hydraulic fluid flow in the discharge passageway34, thud controlling the hydraulic pressure in the pressure chamber18during the discharge stroke. Obviously, the bigger the resistance, the higher the hydraulic pressure in the pressure chamber18during the discharge stroke.

The variable restrictor device40is located in the discharge passageway34so that the hydraulic fluid is discharged from any of the pressure chambers18back to the fluid reservoir30during the discharge stroke through the restrictor device40. As further illustrated inFIG. 3, the variable restrictor device40is operated by an electronic controller45, which may be in the form of a CPU or a computer. The electronic controller45operates the variable restrictor device40based on the information from a number of sensors including, but not limited, an input speed sensor46and an output speed sensor48. It will be appreciated by those skilled in the art that any other appropriate sensors, may be employed. For instance, if the torque coupling device10is used in a drivetrain of a four-wheel drive (4WD) motor vehicle to selectively engage an auxiliary drive axle assembly, vehicle wheel speed sensors50, a yaw rate sensor52, a steering angle sensor54, etc., also may be employed. Moreover, the electronic controller45may be connected to an electronic control network56of the motor vehicle.

Preferably, as illustrated inFIG. 3, the variable restrictor device40is in the form of a variable check valve operated by an electromagnetic (preferably, solenoid) actuator, electronically controlled by the controller45. The check valve40of the preferred embodiment of the present invention includes a valve closure member (not shown) biased against a valve seat (not shown) by an axial force of a magnetic flux generated by an electro-magnetic device (preferably, solenoid) (not shown). When energized, solenoid-operated check valve40is capable of modulating a retaining force of the valve closure member against the valve seat depending on an electrical current supplied to the solenoid, thus, variably adjusting a discharge pressure of the hydraulic fluid from the pressure chambers18in a variable range from a minimum pressure to a maximum pressure.

When a maximum current is applied to the solenoid, the retaining force of the check valve40is at its maximum, thus the hydraulic pressure attainable within the pressure chamber18during the discharge stroke of the piston20is at its maximum value. In this configuration, the torque coupling device10is in the fully “ON” condition in that the maximum discharge pressure which can be obtained in the piston pressure chamber18is sufficient to fully actuate the torque coupling device10, i.e. to transfer all the torque from the input shaft to the output shaft, thus providing a 100% torque transfer rate through the torque coupling device10.

As the less current is applied to the solenoid, the less axial retaining force is exerted to the check valve40, thus the less is the discharge pressure attainable within the pressure chamber18during the discharge stroke of the piston20.

When a minimum current is applied to the solenoid, the retaining force of the check valve40is at its minimum, thus the hydraulic discharge pressure attainable within the pressure chamber18during the discharge stroke of the piston20is at its minimum value. In this configuration, the torque coupling device10is in the fully “OFF” condition in that the maximum discharge pressure which can be obtained in the piston pressure chamber18is not high enough to transfer any torque through the torque coupling device10from the input shaft to the output shaft.

In between the “ON” and “OFF” conditions of the torque coupling device10, the variable check valve40may be set at any value between these limits by modulating the current applied to the solenoid. This provides the torque coupling device10with an infinitely variable torque transfer rate to match various operating conditions of apparatuses or machines employing the torque coupling device10of the present invention, such as motor vehicles.

Alternatively, the variable restrictor device40includes a variable valve opening adapted to selectively control a fluid flow through the variable restrictor device40by selectively varying the valve opening therein between a fully closed position providing a minim flow through the variable restrictor device40and a fully open position providing a maximum flow through the variable restrictor device40. It will understood by those skilled in the art that when the valve opening in the variable restrictor device40is fully closed, the hydraulic discharge pressure attainable within the pressure chamber18during the discharge stroke of the piston20is of a maximum value. Correspondingly, when the valve opening in the variable restrictor device40is fully open, the hydraulic discharge pressure attainable within the pressure chamber18during the discharge stroke of the piston20is of a minimum value. It will be appreciated, that varying the opening of the variable restrictor device40, the hydraulic discharge pressure attainable within the pressure chamber18during the discharge stroke may be set at any value by modulating the control signal applied to the variable restrictor device40by the electronic controller45.

The operation of the first exemplary embodiment of the present invention depicted inFIGS. 1-3will now be described.

When no rotational speed difference occurs between the hydraulic manifold block14and the cam ring26, the pistons20do not reciprocate in the cylinder bores16and the pistons20do not pump the hydraulic fluid into the pressure chamber18. Thus, the torque is not transferred through the torque coupling device10from the input shaft to the output shaft. Therefore, if the torque coupling device10is used in the drivetrain of the 4WD motor vehicle, the driving torque from an engine is not transferred to the auxiliary drive axle assembly. At this time, the pistons26are pressed against the cam surface28of the cam ring26by the coil springs24.

When, however, the rotational speed differential between the output shaft and the input shaft occurs (i.e., when there is relative rotational movement of the manifold block14and the cam ring26), the rotational speed differential between the manifold block14and the cam ring26causes the pistons20to reciprocate in the cylinder bores16since they slide on the crests and cam valleys of the cam surface28. When the pistons20reciprocate, the hydraulic fluid is alternately drawn into the pressure chambers18from the fluid reservoir30through the supply passageway32and the intake/discharge hole19(during the suction stroke), and is discharged under pressure from the pressure chambers18back to the fluid reservoir30through the intake/discharge hole19, the discharge passageway34and through the flow restriction provided by the variable restrictor device40(the discharge stroke).

Owing to the flow restriction provided by the variable restrictor device40, a pressure increase occurs in each of the pressure chambers18on the discharge strokes of the pistons20. If the pressure in the pressure chamber18is sufficient to resist axial movement of the associated pistons20and to urge the pistons20into firm engagement the crests and valleys of the cam surface28of the cam ring26, the torque coupling device10will resist relative rotational movement of the manifold block14and the cam ring26. As a result, the torque is transmitted from the manifold block14and the cam ring26.

Those skilled in the art would appreciate that depending on the specific adjustment of the variable restrictor device40by the electronic controller45various modes of operation of the torque coupling device10could be realized. More specifically, if the variable restrictor device40is adjusted to provide the minimum value of the discharge pressure attainable within the pressure chamber18during the discharge stroke of the piston20(the fully “OFF” condition), no torque is transmitted through the torque coupling device10despite the relative rotation between the input shaft and the output shaft (i.e. between the hydraulic manifold block14and the multi-lobed cam ring26). In other words, the torque transfer rate of the torque coupling device10when the variable restrictor device40is in the fully “OFF” condition is zero.

On the other hand, if the variable restrictor device40is adjusted to provide the maximum value of the discharge pressure attainable within the pressure chamber18during the discharge stroke of the piston20(the fully “ON” condition), all the torque from the input shaft to the output shaft is transmitted through the torque coupling device10(i.e. from the hydraulic manifold block14and the multi-lobed cam ring26). In other words, the torque transfer rate of the torque coupling device10when the variable restrictor device40is in the fully “ON” condition is 100%.

Evidently, by adjusting the variable restrictor device40to provide the value of the hydraulic pressure attainable within the pressure chamber18during the discharge stroke of the piston20between the “ON” and “OFF” conditions, the torque transfer rate of the torque coupling device10may be continuously varied in the 0-100% range by the electronic controller45based on the information from the sensors46,48,50,52and54. This provides the torque coupling device10with an opportunity to dynamically control the torque coupling device10of the present invention to match various operating conditions of apparatuses or machines employing the torque coupling device10of the present invention, such as motor vehicles.

FIGS. 4-6of the drawings illustrate a second exemplary embodiment of a torque coupling device in accordance with the present invention. Components, which are unchanged from, or function in the same way as in the first exemplary embodiment depicted inFIGS. 1-3are labeled with the same reference numerals, sometimes without describing detail since similarities between the corresponding parts in the two embodiments will be readily perceived by the reader.

FIGS. 4 and 5depict a torque coupling device of the second exemplary embodiment of the present invention in the form of a differential assembly110. As schematically illustrated inFIG. 6, the differential assembly110is provided for selectively actuate a drive axle unit100of a motor vehicle and to selectively distribute an input torque TINfrom a prime mover, such as an internal combustion engine, between right and left output axle shafts102aand102boutwardly extending from the differential assembly110and drivingly coupled to right and left wheels104aand104b, respectively.

As illustrated inFIGS. 4 and 5, the differential assembly110includes a hollow differential case112rotatably supported within an axle housing (not shown) and driven by a final drive pinion gear (not shown) transmitting an input torque from the prime mover to the differential case112. Preferably, the differential case112includes two halves112aand112bsecured to each other in a manner known to those skilled in the art, such as by threaded fasteners, welding, riveting, etc.

The differential assembly110further comprises a hydraulic manifold block114disposed within the differential case112for rotation about an axis of rotation115, and a first multi-lobed cam ring126aand a second multi-lobed cam ring126bboth disposed within the differential case112adjacent to opposite sides of the hydraulic manifold block114coaxially thereto. It will be appreciated that the first and second cam rings126aand126bare rotatably supported within the differential case112by appropriate anti-friction bearings, such as roller bearings, while the hydraulic manifold block114is drivingly coupled to the differential case112. Thus, the first and second cam rings126aand126bcan rotate relative to the hydraulic manifold block114.

In accordance with the second exemplary embodiment of the present invention, the hydraulic manifold block114is drivingly coupled to the differential case112, while the first and second multi-lobed cam rings126aand126bare operatively coupled to the right and left output axle shafts102aand102b, respectively, as shown inFIG. 6. Correspondingly, the input torque TINis applied to the hydraulic manifold block114from the final drive pinion gear through the differential case112. The differential assembly110then transmits and distributes the input torque TINfrom the hydraulic manifold block114to the first and second cam rings126aand126b. The first cam ring126aoperatively coupled to the output axle shaft102atransmits an output torque TRto the right wheel104a, while the second cam ring126boperatively coupled to the output axle shaft102btransmits an output torque TLto the left wheel104b, as shown inFIG. 6. The differential assembly110of the second exemplary embodiment of the present invention is capable to vary transfer rates of torque transmitted from the input shaft to the right and left output shafts of the differential assembly110, i.e. TIN/TRand TIN/TLratios. It will be appreciated that alternatively, the differential assembly110of the second exemplary embodiment of the present invention may comprise two hydraulic manifold block drivingly coupled to the output axle shafts102aand102b, and a single multi-lobed cam ring is drivingly coupled to the differential case112.

As further illustrated inFIGS. 4-6, the first cam ring126ais formed with a first cam surface128ahaving a plurality of alternating cam crests (or lobes) and cam valleys at regular intervals, while the second cam ring126bis formed with a second cam surface128balso having a plurality of alternating cam crests (or lobes) and cam valleys at regular intervals. Preferably, the first and second cam rings126aand126bare substantially identical.

Furthermore, the hydraulic manifold block114is substantially cylindrical in shape and has two opposite end faces115aand115bso that the end face115afaces the first cam surface128aof the first cam ring126a, while the end face115bfaces the second cam surface128bof the second cam ring126b.

The hydraulic manifold block114also includes two sets of open cylinder bores formed therein: a plurality of first cylinder bores116aand a plurality of second cylinder bores116b. Preferably, both the first cylinder bores116aand the second cylinder bores116bare axially extending in the direction of the axis115so that the first cylinder bores116aare open at the end face115a, while the second cylinder bores116bare open at the end face115b. Further preferably, the cylinder bores116aand116bare equidistantly circumferentially spaced about the axis of rotation115.

The differential assembly110further includes two sets of pistons: a plurality of first pistons120aand a plurality of second pistons120b.

The number of the first pistons120acorresponds to the number of the first cylinder bores116ain the hydraulic manifold block114so that each of the first pistons120ais slideably disposed within corresponding one of the plurality of the first cylinder bores116ain the hydraulic manifold block114for reciprocating therewithin upon relative rotational movement between the hydraulic manifold block114and the first multi-lobed cam ring126a. Each of the first pistons120adefines a first variable displacement pressure chamber118awithin the corresponding one of the plurality of the first cylinder bores116a. Distal ends122aof the first pistons120aextend from the first cylinder bores116aas the first pistons120aare biased toward the first cam surfaces128aof the first cam ring126aby coil springs24disposed within the first pressure chambers118a. The distal ends122aof the first pistons120arotateably engage the first cam surface128athe first multi-lobed cam ring126adue to biasing forces of the coil springs24. Also, an intake/discharge hole119ais formed in a bottom portion of each of the first pressure chambers118a.

Accordingly, the number of the second pistons120bcorresponds to the number of the second cylinder bores116bin the hydraulic manifold block114so that each of the second pistons120bis slideably disposed within corresponding one of the plurality of the second cylinder bores116bin the hydraulic manifold block114for reciprocating therewithin upon relative rotational movement between the hydraulic manifold block114and the second multi-lobed cam ring126b. Each of the second pistons120bdefines a second variable displacement pressure chamber118bwithin the corresponding one of the plurality of the second cylinder bores116b. Distal ends122bof the second pistons120bextend from the second cylinder bores116bas the second pistons120bare biased toward the second cam surfaces128bof the second cam ring126bby coil springs24disposed within the second pressure chambers118b. The distal ends122bof the second pistons120arotateably engage the second cam surface128bthe second multi-lobed cam ring126bdue to biasing forces of the coil springs24. An intake/discharge hole119bis formed in a bottom portion of each of the second pressure chambers118b.

Preferably, the first pistons120aand the corresponding first cylinder bores116aare substantially identical to the second pistons120band the corresponding second cylinder bores116b. The cylinder bores116aand116band the pistons120aand120bare preferably ring-shaped. However, alternatively, they may alternatively have other suitable shapes. Preferably, the distal ends122aand122bof the pistons120aand120bare semi-spherical in shape.

As further illustrated inFIG. 6, each of the first pressure chambers118ais in fluid communication with a first fluid reservoir130astoring a supply of an appropriate hydraulic fluid, such as oil, through a first supply passageway132aand a first discharge passageway134a. Accordingly, each of the second pressure chambers118bis in fluid communication with a second fluid reservoir130bstoring a supply of an appropriate hydraulic fluid, such as oil, through a second supply passageway132band a second discharge passageway134b. Preferably, the both first fluid reservoir130aand the second fluid reservoir130bare integrally formed within the hydraulic manifold block114. As the first and second pressure chambers118aand118bare in fluid communication with the corresponding fluid reservoirs130aand130b, the reciprocating movement of the first and second pistons120aand120bwithin the first and second cylinder bores116aand116bin the hydraulic manifold block14upon relative rotational movement between the hydraulic manifold block14and the first and second cam rings126aand126bprovides a pumping action including alternating suction and discharge strokes.

During the suction stroke when the pistons118aand118bextend from the cylinder bores116aand116bof the hydraulic manifold block114, volumes of the pressure chambers118aand118bincrease and the hydraulic fluid is drawn into the pressure chambers118aand118bfrom the fluid reservoirs130aand130b, respectively, through the corresponding supply passageways132aand132b. Consequently, during the discharge stroke when the pistons118aand118bretract into the cylinder bores116aand116b, volumes of the pressure chambers118aand118bdecrease and the hydraulic fluid is discharged under pressure from the pressure chambers118aand118bback to the fluid reservoirs130aand130b, respectively, through the corresponding discharge passageways134aand134b. In other words, the pressure chambers118aand118bfunction to cooperate with the pistons120aand120bto pressurize the hydraulic fluid during the discharge stroke of the pistons120aand120b.

Preferably, as shown inFIGS. 4-6, the hydraulic manifold block114of the differential assembly110in accordance with the second exemplary embodiment of the present invention comprises seven first cylinder bores116aand seven second cylinder bores116b, and seven associated first pistons120aand seven second pistons120b, while each of the multi-lobed cam rings126aand126bhas six lobes. It will be appreciated that more or less first and second cylinder bores/pistons and cam lobes may be employed depending upon the relative dimensions and proportions of the particular arrangement of the torque coupling device.

In order to control the torque transfer through the differential assembly110, two variable restrictor devices are provided: a first variable restrictor device140aand a second variable restrictor device140a, as illustrated inFIG. 6. The first variable restrictor device140ais provided to selectively control the hydraulic pressure in the first pressure chambers118aduring the discharge stroke of the first pistons120a, while the second variable restrictor device140bis provided to selectively control the hydraulic pressure in the second pressure chambers118bduring the discharge stroke of the second pistons120b.

Preferably, the first and second variable restrictor devices140aand140bare substantially identical to the variable restrictor device40of the first exemplary embodiment of the present invention. The first variable restrictor device140ais located in the discharge passageway134ain fluid communication with both the first reservoir130aand the first pressure chambers118aso that the hydraulic fluid is discharged from any of the pressure chambers118aback to the first fluid reservoir130aduring the discharge stroke through the first restrictor device140a. Similarly, the second variable restrictor device130bis located in the discharge passageway134bin fluid communication with both the second reservoir130aand the second pressure chambers118bso that the hydraulic fluid is discharged from any of the pressure chambers118bback to the fluid reservoir130bduring the discharge stroke through the second restrictor device140b.

As further illustrated inFIG. 6, the first and second variable restrictor devices140aand140bare operated by an electronic controller145, which may be in the form of a CPU or a computer. The electronic controller145operates each of the first and second variable restrictor devices140aand140bindependently based on the information from a number of sensors including, but not limited, an input speed sensor146and output speed sensors148aand148b. It will be appreciated by those skilled in the art that any other appropriate sensors, may be employed. For instance, if the differential assembly110is used in the drive axle unit100of the motor vehicle, a number of sensors sensing various vehicle parameter, such as vehicle wheel speed sensors150, an engine torque sensor152, a steering angle sensor154, a yaw rate sensor156, a longitudinal acceleration sensor158, a lateral acceleration sensor160, an ABS activation sensor that detects the activation of the anti-lock braking system, etc., also may be employed. Moreover, the electronic controller45may be connected to an electronic control network162of the motor vehicle.

The operation of the first exemplary embodiment of the present invention depicted inFIGS. 4-6will now be described.

When no rotational speed difference occurs between the hydraulic manifold block114and any of the cam ring126aand126b, the pistons120aand120bdo not reciprocate in the cylinder bores116aand116b, respectively, and the pistons120aand120bdo not pump the hydraulic fluid into the pressure chamber118aand118b, respectively. Thus, the torque is not transferred through the differential assembly110from the housing112to the output shafts102aand102b. Therefore, the driving torque from an engine is not transferred to the drive axle unit100.

When, however, the rotational speed differential between the output shafts102aand102band the input shaft occurs (i.e., when there is relative rotational movement of the manifold block114and the cam rings126aand126b), the rotational speed differential between the manifold block114and the cam rings126aand126bcauses the pistons120aand120bto reciprocate in the cylinder bores116aand116bsince they slide on the crests and cam valleys of the cam surface128aand128b. When the pistons120aand120breciprocate, the hydraulic fluid is alternately drawn into the pressure chambers118aand118bfrom the corresponding fluid reservoirs130aand130bthrough the supply passageways132aand132band the intake/discharge holes119aand119b(during the suction stroke), and is discharged under pressure from the pressure chambers118aand118bback to the fluid reservoirs130aand130bthrough the intake/discharge holes119aand119b, the discharge passageways134aand134band through the flow restriction provided by the variable restrictor devices140aand140b(the discharge stroke).

Those skilled in the art would appreciate that depending on the specific adjustment of each of the variable restrictor devices140aand140bby the electronic controller145various modes of operation of the differential assembly110could be realized. More specifically, if both of the variable restrictor devices140aand140bare adjusted to provide the minimum value of the hydraulic pressure attainable within the pressure chambers118aand118bduring the discharge stroke (the fully “OFF” condition), no torque is transmitted through the drive axle unit100despite the relative rotation between the input and the output shafts102a,102b. In other words, the torque transfer rate of the differential assembly110when the variable restrictor devices140aand140bare in the fully “OFF” condition is zero.

On the other hand, if both of the variable restrictor devices140aand140bare adjusted to provide the maximum value of the hydraulic pressure attainable within the pressure chambers118aand118bduring the discharge stroke (the fully “ON” condition), all the torque from the housing112to the output shafts102a,102bis transmitted through the differential assembly110(i.e. from the hydraulic manifold block114and the cam rings126a,126b), and the differential assembly110is locked. In other words, the torque transfer rate of the differential assembly110when the variable restrictor devices140aand140bare in the fully “ON” condition is 100%.

Evidently, by independently adjusting the variable restrictor devices140aand140bto provide the value of the hydraulic pressure attainable within the pressure chambers118aand118bduring the discharge stroke of the pistons120aand120bbetween the “ON” and “OFF” conditions, the torque transfer rate of the differential assembly110from the drive pinion to any of the output shafts102a,102bmay be continuously and selectively varied in the 0-100% range by the electronic controller145based on the information from the sensors146,148a,148b,150,152,154,156,158and160. The increase in pressure available may be a function of the speed difference. This will result in an optimized amount of limited slip between the fully “ON” and “OFF” conditions. Thus, the amount of the limited slip available to the differential assembly110can be limited and optimized to match various vehicle operating conditions. For instance, the differential assembly110allows 100% of the available drive torque to be delivered to one of the wheels104a,104b, while no torque is delivered to the other one of the wheels104a,104b. Moreover, by variably adjusting the restrictor devices140aand140b, the necessary speed differential between the left and right wheels104aand104bmay be achieved. The independent control the first and second restrictor devices140aand140ballows the torque distribution to and between each of the side wheels104aand104bof the same axle unit100to be tailored independently and to be infinitely adjustable.

Therefore, the present invention represents a novel arrangement of the electronically controlled torque coupling device comprising at least one restrictor device in fluid communication with pressure chambers within a rotatable hydraulic manifold block s such that the at least one restrictor device controls a hydraulic pressure in the pressure chambers. The torque coupling device of the present invention provides an opportunity to be dynamically controlled to match various operating conditions of apparatuses or machines employing the differential assembly of the present invention, such as motor vehicles. Moreover, no electrical power is necessary to activate the torque coupling device of the present invention, only minimum electrical power is required to power the electronic controller.

The foregoing description of the preferred exemplary embodiments of the present invention has been presented for the purpose of illustration in accordance with the provisions of the Patent Statutes. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiments disclosed hereinabove were chosen in order to best illustrate the principles of the present invention and its practical application to thereby enable those of ordinary skill in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated, as long as the principles described herein are followed. Thus, changes can be made in the above-described invention without departing from the intent and scope thereof. It is also intended that the scope of the present invention be defined by the claims appended thereto.