Abstract:
A vehicle driveline component having a dual friction clutch differential assembly and a hydraulic circuit for operating the friction clutches. The hydraulic circuit includes a pair of normally open, solenoid operated valves that are selectively closed to control the fluid pressure that acts on the friction clutches. The hydraulic circuit provides a simplified and cost-effective means for providing disconnecting and/or torque vectoring capabilities to the vehicle driveline component.

Description:
FIELD 
       [0001]    The present disclosure relates to a dual clutch drive module with a single servo hydraulic pump and normally-open valve actuation. 
       BACKGROUND 
       [0002]    This section provides background information related to the present disclosure which is not necessarily prior art. 
         [0003]    One trend in automotive drivelines relates to an all-wheel drive driveline with an axle assembly having disconnecting and/or torque vectoring capabilities. Disconnecting capabilities permit the driveline to be selectively operated in a two-wheel drive mode as a means for improving fuel economy. Torque vectoring capabilities permit the driveline to alter the torque that would otherwise be applied to a pair of vehicle wheels that are driven by the axle to correct for understeer or oversteer in some situations. 
         [0004]    One type of axle assembly that is capable of providing disconnecting and/or torque-vectoring capabilities is an axle assembly that employs a pair of friction clutches to provide speed differentiation between a pair of vehicle wheels. The known dual friction clutch differential arrangements, however, require complex mechanisms and/or hydraulic circuits to control the operation of the friction clutches. Accordingly, there is a need in the art for an axle assembly having a dual friction clutch differential arrangement with a simplified actuation means for operating the friction clutches. 
       SUMMARY 
       [0005]    This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
         [0006]    In one form, the present disclosure provides a vehicle driveline component that includes a housing, an input pinion received in the housing and rotatably disposed about a first axis, a ring gear received in the housing and rotatably disposed about a second axis, a differential assembly mounted in the housing for rotation about the second axis, and a hydraulic circuit. The differential assembly has a differential case, a first friction clutch and a second friction clutch. The differential case is coupled to the ring gear for common rotation. The first friction clutch has a first input portion, which is coupled to the differential case for common rotation, and a first output portion. The second friction clutch has a second input portion, which is coupled to the differential case for common rotation, and a second output portion. The hydraulic circuit includes a reservoir, a first cylinder assembly, a second cylinder assembly, a first valve, a second valve, an electric motor, a pump, a first flow control device and a second flow control device. The reservoir is configured to hold a hydraulic fluid. The first cylinder assembly is configured to selectively actuate the first friction clutch and includes a first piston that is received in a first chamber. The second cylinder assembly is configured to selectively actuate the second friction clutch and includes a second piston that is received in a second chamber. The first valve is a solenoid operated, normally open two-way valve with a first outlet port, which is in fluid communication with the first chamber, and a first inlet port. The second valve is a solenoid operated, normally open two-way valve with a second outlet port, which is in fluid communication with the second chamber, and a second inlet port. The electric motor is selectively operable for driving the pump. The pump is configured to draw hydraulic fluid from the reservoir and provide pressurized hydraulic fluid to the first and second inlet ports. The first flow control device is in fluid communication with the first chamber and the reservoir. The second flow control device is in fluid communication with the second chamber and the reservoir. 
         [0007]    In another form, the present disclosure provides a method for operating a driveline component having a housing, an input pinion received in the housing and rotatably disposed about a first axis, a ring gear received in the housing and rotatably disposed about a second axis, and a differential assembly mounted in the housing for rotation about the second axis. The differential assembly has a differential case, a first friction clutch and a second friction clutch. The differential case is coupled to the ring gear for common rotation. The first friction clutch has a first input portion, which is coupled to the differential case for common rotation, a first output portion, and a first clutch cylinder assembly that is configured to output a force to selectively engage the first output portion and the first input portion. The second friction clutch has a second input portion, which is coupled to the differential case for common rotation, a second output portion and a second clutch cylinder assembly that is configured to output a force to selectively engage the second output portion and the second input portion. The method includes: operating a pump to provide pressurized hydraulic fluid to a first normally open valve and a second normally open valve, the first normally open valve being in fluid communication with the first clutch cylinder assembly, the second normally open valve being in fluid communication with the second clutch cylinder assembly; providing first and second flow control devices, the first flow control device being configured to vent fluid from the first clutch cylinder assembly, the second flow control device being configured to vent fluid from the second clutch cylinder assembly; sensing a first parameter indicative of the force output by the first clutch cylinder assembly; sensing a second parameter indicative of the force output by the second clutch cylinder assembly; operating the first normally open valve based in part on the first parameter; and operating the second normally open valve based in part on the second parameter. The first and second normally open valves are operated independently of one another. 
         [0008]    Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     
    
     
       DRAWINGS 
         [0009]    The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
           [0010]      FIG. 1  is a schematic illustration of an exemplary vehicle having a vehicle driveline constructed in accordance with the teachings of the present disclosure; 
           [0011]      FIG. 2  is an enlarged portion of  FIG. 1  illustrating the vehicle driveline component in more detail; 
           [0012]      FIG. 3  is a section view of a portion of the vehicle driveline component; and 
           [0013]      FIG. 4  is a schematic illustration of the vehicle driveline component. 
       
    
    
       [0014]    Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
       DETAILED DESCRIPTION 
       [0015]    Example embodiments will now be described more fully with reference to the accompanying drawings. 
         [0016]    With reference to  FIG. 1  of the drawings, an exemplary vehicle having a vehicle driveline component constructed in accordance with the teachings of the present disclosure is generally indicated by reference numeral  10 . The vehicle  10  can have a power train  12  and a drive line or drive train  14 . The power train  12  can be conventionally constructed and can comprise a power source  16  and a transmission  18 . The power source  16  can be configured to provide propulsive power and can comprise an internal combustion engine and/or an electric motor, for example. The transmission  18  can receive propulsive power from the power source  16  and can output power to the drive train  14 . The transmission  18  can have a plurality of automatically or manually-selected gear ratios. The drive train  14  in the particular example provided is of an all-wheel drive configuration, but those of skill in the art will appreciate that the teachings of the present disclosure are applicable to other drive train configurations, including four-wheel drive configurations, rear-wheel drive configurations, and front-wheel drive configurations. 
         [0017]    The drive train  14  can include a front axle assembly  20 , a power take-off unit (PTU)  22 , a prop shaft  24  and a rear axle assembly  26 . In the particular example provided, the vehicle driveline component is the rear axle axle assembly  26 , but those of skill in the art will appreciate that the teachings of the present disclosure have application to other types of driveline components, including front axle assemblies and interaxle differential devices (e.g., transfer cases, center differentials). An output of the transmission  18  can be coupled to an input of the front axle assembly  20  to drive an input member  30  of the front axle assembly  20 . The PTU  22  can have a PTU input member  32 , which can receive rotary power from the input member  30  of the front axle assembly  20 , and a PTU output member  34  that can transmit rotary power to the prop shaft  24 . The prop shaft  24  can couple the PTU output member  34  to the rear axle assembly  26  such that rotary power output by the PTU  22  is received by the rear axle assembly  26 . The front axle assembly  20  and the rear axle assembly  26  could be driven on a full-time basis to drive front and rear vehicle wheels  36  and  38 , respectively. It will be appreciated, however, that the drive train  14  could include one or more clutches to interrupt the transmission of rotary power through a part of the drive train  14 . In the particular example provided, the drive train  14  include a first clutch  40 , which can be configured to interrupt the transmission of rotary power into or through the PTU  22 . 
         [0018]    The front axle assembly can be configured in a manner that is generally similar to that which is described in copending, commonly assigned U.S. patent application Ser. No. 13/785,425 filed Mar. 5, 2013, the disclosure of which is incorporated by reference as if fully set forth in detail herein. Briefly, the input member  30  of the front axle assembly  20  can drive a first differential assembly  21 , which can provide rotary power to the front vehicle wheels  36 . 
         [0019]    With reference to  FIG. 2 , the rear axle assembly  26  can include a housing  398 , an input pinion  400 , a bevel ring gear  402 , a second differential assembly  404 , a pair of shafts  406 , a hydraulic circuit  408  and a control system  410 . The input pinion  400  can be housed in the housing  398  for rotation about a first axis. The input pinion  400  can be coupled to an end of the propshaft  24  for rotation therewith. The second bevel ring gear  402  being meshed with the input pinion  400  and can be rotatable about a second axis that can be transverse or perpendicular to the first axis. In the example provided, the input pinion  400  and the bevel ring gear  402  form a hypoid gear set. 
         [0020]    The second differential assembly  404  can be configured to receive rotary power transmitted through the second bevel ring gear  402  and can have a spool or differential case  410 , a pair of output members  412 , a first friction clutch  414  and a second friction clutch  416 . The differential case  410  can comprise a generally tubular structure that can be coupled to the second bevel ring gear  402  for common rotation about the second axis. Each of the output members  412  can be drivingly coupled to a corresponding one of the shafts  406 . The shafts  406  are configured to transmit rotary power between the output members  412  and the rear vehicle wheels  38 . 
         [0021]    In the particular example provided, each of the first and second friction clutches  414  and  416  has an outer clutch basket  420 , which is coupled for rotation with the differential case  410 , an inner clutch basket  422 , which is coupled for rotation with a corresponding one of the output members  412 , a plurality or set of first clutch or friction plates  424  and a plurality or set of second clutch or friction plates  426 . Each set of the first friction plates  424  can be non-rotatably coupled but axially slidably mounted on a corresponding one of the outer clutch baskets  420 . Each set of the second friction plates  426  can be non-rotatably coupled but axially slidably mounted on a corresponding one of the inner clutch baskets  422 . The second friction plates  426  can be interleaved with the first friction plates  424 . With brief reference to  FIG. 3 , the first and second friction plates  424  and  426  can comprise one or more springs  430  that can be configured to urge the first and second friction plates  424  and  426  apart from one another. In the example provided, the first and second friction plates  424  and  426  are formed as Belleville spring washers, but it will be appreciated that one or more springs could be integrated into the first friction plates  424  and/or the second friction plates  426  in a desired manner (e.g., one or more tabs that are integrally formed with the body of the friction plates that form leaf spring(s), discrete coil or leaf springs that are coupled to the first and/or second friction plates). Returning to  FIG. 2 , each of the inner clutch baskets  422  is drivingly coupled to an associated one of the output members  412  for common rotation about the second axis. 
         [0022]    With reference to  FIG. 4 , the hydraulic circuit  408  can comprise a first cylinder assembly  500 , a second cylinder assembly  502 , a pump  504 , a first valve  506 , a second valve  508 , a first flow control device  510  and a second flow control device  512 . The first cylinder assembly  500  is configured to selectively activate the first friction clutch  414  ( FIG. 2 ) and can include a first cylinder  520  and a first piston  522 . The first cylinder  520  can be fixedly coupled to the housing  398  ( FIG. 2 ) and can define a first chamber or cavity  524  having an annular shape. The first piston  522  can be received in the first cavity  524  and is configured to output a force that causes the first and second friction plates  424  and  426  ( FIG. 2 ) in the first friction clutch  414  ( FIG. 2 ) to engage one another. The second cylinder assembly  502  can be similarly configured to selectively activate the second friction clutch  416  ( FIG. 2 ) and can include a second cylinder  530  and a second piston  532 . The second cylinder  530  can be fixedly coupled to the housing  398  ( FIG. 2 ) and can define a second chamber or cavity  534  having an annular shape. The second piston  532  can be received in the second cavity  534  and is configured to output a force that causes the first and second friction plates  424  and  426  ( FIG. 2 ) in the second friction clutch  416  ( FIG. 2 ) to engage one another. 
         [0023]    The pump  504  can be any type of pump, such as a gerotor pump, and is configured to be driven by an appropriate power source, such as an electric motor  538 . The pump  504  is configured to draw a hydraulic fluid from a reservoir  540  and to provide pressurized hydraulic fluid to the first and second valves  506  and  508 . In the particular example shown, the first and second valves  506  and  508  are hydraulically coupled to the pump  504  in a parallel manner, but it will be appreciated that pressurized hydraulic fluid could be provided to the first and second valves  506  and  508  in a different manner, such as in series. 
         [0024]    The first valve  506  can be a two-way, normally open solenoid-operated valve having an inlet port  550 , which receives pressurized hydraulic fluid from the pump  504 , an outlet port  552 , which is coupled in fluid communication with an inlet of the first cylinder assembly  500 , a valve element  554  and a solenoid  556 . The valve element  554  is biased into a first position (e.g., via a return spring) that permits fluid communication between the inlet port  550  and the outlet port  552 . The solenoid  556  can be selectively operated to move the valve element  554  into a second position that inhibits fluid communication between the inlet port  550  and the outlet port  552 . The second valve  508  can be a two-way, normally open solenoid-operated valve having an inlet port  560 , which receives pressurized hydraulic fluid from the pump  504 , an outlet port  562 , which is coupled in fluid communication with an inlet of the second cylinder assembly  502 , a valve element  564  and a solenoid  566 . The valve element  564  is biased into a first position that permit fluid communication between the inlet port  560  and the outlet port  562 . The solenoid  566  can be selectively operated to move the valve element  564  into a second position that inhibits fluid communication between the inlet port  560  and the outlet port  562 . In the particular example provided, the first and second valves  506  and  508  are ball seat valves of the type that is disclosed in copending, commonly assigned U.S. patent application Ser. No. 14/153,175 filed Jan. 13, 2014, the disclosure of which is incorporated by reference as if fully set forth in detail herein. 
         [0025]    The first flow control device  510  can be coupled in fluid communication with the first cavity  524  and can be configured to bleed or vent hydraulic fluid from the first cylinder  520  to the reservoir  540 . Similarly, the second flow control device  512  can be coupled in fluid communication with the second cavity  534  and can be configured to bleed or vent hydraulic fluid from the second cylinder  530  to the reservoir  540 . The first and second flow control devices  510  and  512  can be any type of flow control device but in the particular example provided, each comprises an orifice of a predetermined diameter. Each orifice can be a discrete component that can be coupled to fluid conduits coupled to the reservoir  540  and the first cylinder  520  or the second cylinder  530 , but in the particular example provided, the orifices are formed in a part of the housings (not specifically shown) that house the first and second friction clutches  414  and  416  ( FIG. 2 ). 
         [0026]    With reference to  FIGS. 2 and 4 , the hydraulic fluid in the reservoir  540  can be a fluid that is solely configured for use in the hydraulic circuit  408 . Alternatively, the hydraulic fluid could be employed to lubricate the first and second clutch plates  424  and  426  of the first and second clutches  414  and  416 , and optionally to also lubricate the input pinion  400 , the ring gear  402 , and any bearings that support the input pinion  400  or the ring gear  402  for rotation relative to the housing  398 . 
         [0027]    The control system  410  can comprise a first sensor  570 , a second sensor  572  and a controller  574 . The first sensor  570  can be configured to sense a parameter that is indicative of a force that is applied by the first piston  522  to the first friction clutch  414  and to responsively produce a first sensor signal. The second sensor  572  can be configured to sense a parameter that is indicative of a force that is applied by the second piston  532  to the second friction clutch  416  and to responsively produce a second sensor signal. In the particular example provided, the first and second sensors  570  and  572  are pressure sensors that are configured to sense the pressure of the hydraulic fluid in the first and second cavities  524  and  534 , respectively. The controller  574  can be coupled to the first and second sensors  570  and  572 , the first and second valves  506  and  508 , the electric motor  538 , and a vehicle network or data bus  580 . The controller  574  can be configured to receive data from the vehicle network  580  and the first and second sensor signals and can responsively control the electric motor  538 , for example via operation of a relay (not shown) that can be disposed in the vehicle junction box, as well as produce first and second control signals for operation of the first and second valves  506  and  508 , respectively. 
         [0028]    The first and second control signals can be modulated signals that can control the first and second solenoids  556  and  566  to move the first and second valve elements  554  and  564  to selectively close the first and second valves  506  and  508 . In the particular example provided, the first and second control signals are pulse-width modulated signals that are configured to operate the first and second solenoids  556  and  566  (to thereby close the first and second valves  506  and  508 ) over a duration that is associated with duty cycles that are associated with the first and second control signals. It will be appreciated that the first and second valves  506  and  508  can be controlled independently of one another, which renders the operation of the rear axle assembly  26  relatively insensitive to internal leakage within the hydraulic circuit  408 . Moreover, the force exerted by the first and second pistons  522  and  532  onto the first and second friction clutches  414  and  416  can be tailored so that more torque can be applied to one of the rear vehicle wheels  38  to aid in steering or stabilizing the vehicle. 
         [0029]    The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.