Abstract:
In at least one embodiment, a hydraulic clutch assembly for a motor vehicle driveline is provided. The clutch assembly comprises an input member, and output member and a friction clutch pack operably disposed therebetween for controlling torque transfer. A first fluid circuit contains hydraulic based fluid at a first pressure and is in fluid communication with the friction clutch pack for lubrication thereof. A second fluid circuit is in fluid communication with the first fluid circuit for replenishing the second fluid circuit with the hydraulic based fluid at a second pressure that is less than the first pressure. The clutch assembly further comprises a motor and a gear train. The gear train has an input force driven by the motor and an output force. A first piston is in fluid communication with the second fluid circuit for delivering the hydraulic based fluid thereto and is operatively driven by the output force to displace the hydraulic based fluid. A second piston is translated by the hydraulic based fluid displaced by the first piston to actuate the friction clutch pack.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is related to and claims all available benefit of U.S. provisional patent application 61/116,308 filed Nov. 20, 2008, the entire contents of which are herein incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    This invention relates generally to a hydraulic clutch and more particularly, to a hydraulic clutch assembly that includes a multiple plate friction clutch pack for use in a motor vehicle driveline. 
         [0004]    2. Background 
         [0005]    Hydraulically actuated clutches are common components that are used in rotary powered transmission systems, such as for example, transfer cases, rear differentials and front differentials. These clutches are controlled through a hydraulic fluid circuit. Conventional hydraulic fluid circuits for clutch actuation are closed systems, which include a fluid reservoir within the driveline assembly to accommodate a loss of fluid due to leakage, and changes in the system due to thermal effects and etc. Over a period of time and from usage of the clutch system, the driveline assembly may lose some of the hydraulic fluid from the hydraulic fluid circuit, such as for example, via leakage of the hydraulic fluid through the seals. Accordingly, the reservoir may need to be accessed externally by a technician or otherwise for replenishing the hydraulic fluid circuit with hydraulic fluid. For many vehicles, however, access to the reservoir which is located within the driveline assembly is difficult because of the tight packaging of driveline components surrounding the reservoir and the corresponding tortuous pathway to the reservoir. Thus, further improvements and enhancements in hydraulic clutch systems for motor vehicle drivelines may be desirable. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    In one embodiment of the present invention, a hydraulic clutch assembly for a motor vehicle driveline is provided. The clutch assembly comprises an input member and an output member. A friction clutch pack is operably disposed between the input and output members for controlling torque transfer between the two members. A first fluid circuit contains a hydraulic based fluid at a first pressure and is in fluid communication with the friction clutch pack for lubricating the clutch pack. In fluid communication with the first fluid circuit is a second fluid circuit which has a reservoir. The first fluid circuit replenishes the reservoir with the hydraulic based fluid at a second pressure that is less than the first pressure. A motor and a gear train are also included. The gear train has an input force, which is driven by the motor, and an output force. In fluid communication with the second fluid circuit is a first piston. The second fluid circuit is for delivering the hydraulic based fluid from the reservoir to the first piston. The first piston is driven by the output force to displace the hydraulic based fluid. A second piston is translated by the displaced hydraulic based fluid to actuate the friction clutch pack. 
         [0007]    In one aspect, the second fluid circuit has a compensation port that is in fluid communication with the reservoir. The motor is a bi-directional electric motor, which includes a rotor, and the gear train has the input force that is driven by the electric motor. An electric brake is for selectively inhibiting rotation of the rotor. A ball screw is driven by the output force. The first piston is in fluid communication with the reservoir via the compensation port for delivery of the hydraulic based fluid and is driven by the ball screw to displace the hydraulic based fluid. 
         [0008]    Further aspects, features, and advantages of the present invention will become apparent from consideration of the following description and the appended claims when taken in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a plan view of a motor vehicle driveline including a transfer case in accordance with an embodiment of the present invention; 
           [0010]      FIG. 2  is a sectional view of a motor vehicle transfer case in accordance with one embodiment of the present invention; 
           [0011]      FIG. 3  is a schematic representation of a lubrication fluid circuit in accordance with one embodiment of the present invention; 
           [0012]      FIG. 4  is a schematic representation of a hydraulic clutch assembly including a hydraulic fluid circuit in accordance with one embodiment of the present invention; and 
           [0013]      FIG. 5  is a side sectional view of a fluid reservoir for fluid communication between the lubrication and hydraulic fluid circuits in accordance with one embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    Detailed embodiments of the present invention are disclosed herein. It is understood, however, that the disclosed embodiments are merely exemplary of the invention and may be embodied in various and alternative forms. The Figures are not necessarily to scale; some figures may be configured to show the details of a particular component. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting but merely as a representative bases for the claims and for teaching one skilled in the art to practice the present invention. 
         [0015]    Referring to  FIG. 1 , a vehicle driveline system incorporating at least one embodiment of the present invention is illustrated and generally designated by the reference numeral  10 . The vehicle drive system  10  includes an engine  12  which drives a transmission  14 . The transmission  14  may be a manual transmission with a clutch or an automatic transmission. The output of the transmission  14  drives a transfer case assembly  16 . In turn, the transfer case assembly  16  is operably coupled to and drives a rear or primary driveline assembly  20 . The primary driveline  20  has a rear or primary drive shaft  22  which is operably coupled to and drives a rear or primary differential  24 . The primary differential  24  drives a pair of aligned primary or rear axles  26  which are each coupled to a primary or rear tire and wheel assembly  28 . 
         [0016]    The transfer case assembly  16  also provides torque to a front or secondary driveline assembly  30 . The secondary driveline  30  includes a front or secondary drive shaft  32  which in turn drives the front or secondary differential  34 . The secondary differential  34  provides drive torque through a pair of aligned front or secondary axles  36  which are each coupled to a front or secondary tire and wheel assembly  38 . 
         [0017]    In one embodiment, locking hubs  42  are operably disposed between the front or secondary pair of axles  36  and the front tire and wheel assemblies  38 . The locking hubs  42  may be either remotely operated and thus include electrical or pneumatic operators or may be manually activated. Alternatively, front axle disconnects (not illustrated) may be housed within the secondary differential  34  and may be activated or deactivated to couple or uncouple the secondary axles  36  from the output of the secondary differential  34 . 
         [0018]    Both the primary driveline  20  and the secondary driveline  30  include suitable and appropriately disposed universal joints  44  which may be of conventional type or so-called “constant velocity” joints. The universal joints may function in a convention fashion to allow static and dynamic offsets and misalignments between the various shafts and components. 
         [0019]    The system  10  also includes a microcontroller  46  having various programs and sub-routines which receive data from various vehicle sensors. The microcontroller in response to the data provides a control output to achieve the design goals of the present invention which will be more fully described below. 
         [0020]      FIG. 2  is a cross-sectional view of the transfer case assembly  16  incorporating at least one embodiment of the present invention. It should be noted, however, that although various embodiments of the present invention are described herein as being incorporated within the transfer case assembly  16 , it will be readily appreciated by those skilled in the art that various other embodiments of the present invention may be incorporated into other vehicle driveline assemblies, such as for example, the primary and/or secondary differential assemblies  20  and  30 . 
         [0021]    The output drive power from the transmission  14  is provided to the transfer case  16  by an input shaft  18 . The input shaft  18 , the rear output shaft  31  and the front output shaft  33  extend from an outer housing  62  of the transfer case  16 . The rear and front output shafts  31  and  33  are correspondingly coupled to the primary and secondary drive shafts  22  and  32 , e.g. via universal joints  44 . 
         [0022]    In one embodiment, the housing  62  includes two housing halves  64  and  66  secured together by bolts  68 . The housing  62  includes various seals  70  and  71 , recesses, shoulders, flanges, bores, etc. that receive and position the various components and parts of the transfer case  16  discussed herein. The input shaft  18  is coupled to the rear output shaft  31  for AWD and 2-wheel drive. The rear output shaft  31  is rotably mounted on bearings  78  and  79  at opposite ends. 
         [0023]    The front output shaft  33  is rotably mounted within the housing  62  on bearings  80 . The input gear  84  is selectively driven through a clutch  94  by the rear output shaft  31  and is concentric therewith. A front output gear  86  is coupled to the front output shaft  33  and rotates therewith. An idler gear  90  is coupled to the input gear  84  and the front output gear  86 . When the transfer case  16  is in the two-wheel drive mode, the input gear  84  rotates freely on the rear output shaft  31  and thus, no output drive power is applied to the front output shaft  33 . 
         [0024]    To initiate the AWD or 4-WD mode, the clutch  94  is activated to controllably and selectively provide rotational energy to the input gear  84  so that it will provide rotational energy as needed or selected to the front wheels  38  through a series of rotationally coupled parts. In this mode, shafts  22  and  32  ( FIG. 1 ) may be allowed to rotate at different speeds for smooth vehicle handling. When the clutch  94  is fully in the AWD mode, the clutch  94  and the input gear  84  will be more fully coupled and will rotate at the same speed or nearly the same speed with only some slippage. In this mode, the rear and front drive shafts  22  and  32  rotate at or closer to the same speed. 
         [0025]    Referring also to  FIG. 4  is one embodiment of a hydraulic clutch assembly  48 , which includes the clutch  94 , in accordance with the present invention. The hydraulic clutch assembly  48  is located within the housing  62  and is operable to actuate the clutch  94 . The clutch assembly  48  includes a hydraulic fluid circuit  49  containing a hydraulic based fluid or hydraulic fluid, e.g., hydrocarbon based oil, synthetic oil, silicone fluid or any other suitable fluid for hydraulic actuation. 
         [0026]    Operating the hydraulic clutch assembly  48  is a bi-directional, fractional horsepower electric motor  50  which is disposed within a suitably sized region of the housing  62 . The electric motor  50  includes an output shaft  52  that may optionally be supported upon suitable bearings (not shown). The drive shaft  52  is coupled with a spur gear  54  and an electric brake  56 . When electric power is provided to the electric motor  50 , the electric motor  50  rotates the output shaft  52  and the spur gear  54 . When electric power to the electric motor  50  is terminated, system forces may attempt to back drive the electric motor  50 . The electric brake  56  inhibits further reverse rotation of the output shaft  52  and thus the spur gear  54 . 
         [0027]    In one embodiment, the spur gear  54  is in constant mesh with a second spur gear  58 . The second spur gear  58  is secured to a second drive shaft  60  that is support by anti-friction bearings such as a roller bearing assembly  72 . The second drive shaft  60  includes a ball screw portion  74 . Between the drive shaft  60  and the ball screw portion  74  is mounted at least one spring or washer  76  that functions as a resilient stop. Disposed about the ball screw portion  74  is a re-circulating ball nut  78 . The re-circulating ball nut  78  includes at least one ball or roller bearing  80  which will re-circulate about a complimentary configured groove  88  in the ball screw  74  and thus, provides a low friction interconnection between the ball screw  74  and the nut  78 . As the shaft  60  bi-directionally rotates in response to bi-directional rotation of the output shaft  52  of the electric motor  50 , the re-circulating ball nut  78  translates to the left and right. The ball screw portion  74  and the re-circulating ball nut  78  thus function as a rotary to linear motion actuator. 
         [0028]    The re-circulating ball nut  78  is coupled to a source piston  92  (e.g. master piston) which translates axially between a retracted position  93  and an extended position  95  within an elongated cylinder  96 . The source piston  92  includes a pair of high-pressure seals  98  which are received in suitable configured circumferential grooves  100  near each end of the piston  92 . The piston  92  in  FIG. 4  is shown in a partially retracted position (e.g. between the fully retracted position  93  and the fully extended position  95 ). As the piston  92  is retracted by rotation of the ball screw nut  78 , it passes a compensation port  102  which is in fluid communication with a fluid reservoir  104 . The fluid reservoir  104  is preferably maintained substantially full of the hydraulic based fluid. In the retracted position  93 , the compensation portion  102  is unobstructed by the source piston  92  to advance the hydraulic based fluid into the elongated cylinder  96 . 
         [0029]    Additionally, a secondary port  103  may be provided which is in fluid communication with both the reservoir  104  and the source piston  92  and is positioned along the elongated cylinder  96  to provide lubrication between the source piston  92  and the elongated cylinder  96  with the hydraulic based fluid. In at least one embodiment, the hydraulic based fluid is suitable as both a lubrication fluid and a hydraulic fluid. In one embodiment, a flexible diaphragm/separator  106  within the reservoir  104  may be used to accommodate any changes in volume of the hydraulic based fluid and a metal plate or cap  108  may be used to secure the flexible diaphragm/separator  106  in position. In an alternative embodiment, the reservoir  104  does not include a diaphragm/separator  106 . 
         [0030]    The elongated cylinder  96  narrows to a first fluid passageway  110 . The first fluid passageway  110  communicates with an annular cylinder  126  which includes a pressure plate  128  (e.g. slave or apply piston). In one embodiment, the pressure plate is in the form of a bonded piston with rubber seals bonded onto a monolithic base metal. When the source piston  92  is in the extended position  95 , the hydraulic based fluid is displaced from the elongated cylinder  96  through the first fluid passageway  110  into the annular cylinder  126 . The pressure plate  128  transfers axial motion from the displaced hydraulic based fluid to the clutch  94 , thereby activating or engaging the clutch  94 . 
         [0031]    In one embodiment, a second fluid passageway  130  provides fluid communication between the elongated cylinder  96  and a fluid pressure sensor or transducer  132 . The pressure fluid sensor  132  is preferably a piezoelectric device which provides a signal in a single or multiple conductor cable to a microprocessor  134  regarding the real time hydraulic pressure within the elongated cylinder  96 . Electrical energy is provided to the electric motor  50  through a single or multiple conductor cable to control actuation of the source piston  92 . 
         [0032]    In at least one embodiment of the present invention, the clutch  94  is in the form of a multiple plate friction clutch pack assembly. In the activated or engaged condition, the friction clutch pack assembly  94  is driven by a plurality of male or external splines or teeth  112  disposed on the rear output shaft  31  (e.g. providing input torque) which engages complimentarily configured female splines  114  on the first plurality of smaller diameter friction clutch plates or discs  116 . The first plurality of friction clutch plates or discs  116  are interleaved with a second plurality of larger diameter friction clutch plates or discs  118 . The friction clutch plates or discs  116  and  118  may include suitable clutch paper or friction material in accordance with convention practice. 
         [0033]    Each of the second plurality of larger diameter friction clutch plates or discs  118  include male or external splines  120  which engage and drive complimentary configured female or internal splines  122  formed on the interior of a cylindrical portion of a clutch drum  124  (e.g. receiving output torque). The clutch drum  124  is engaged with the input gear  84  and receives torque from the hydraulic clutch assembly  48  to drive the input gear  84 . Suitable oil seals prevent the ingress of foreign materials and maintain a fluid tight seal between the housing  62 , the rear output shaft  31  and the clutch drum  124 . 
         [0034]    Also referring to  FIG. 3 , a lubrication fluid circuit  140  is in fluid communication with the reservoir  104 . The lubrication fluid circuit  140  is provided within the housing  62  and contains the hydraulic based fluid. The hydraulic fluid circuit  49  is open to and receives hydraulic based fluid from the lubrication fluid circuit  140 . Accordingly, any hydraulic based fluid that may have escaped from the hydraulic fluid circuit  49 , e.g., weeping through seals, etc., is preferably replenished by the oil base fluid from the lubrication fluid circuit  140 , thereby minimizing or eliminating the need to externally access the reservoir  104  for replenishing with the hydraulic based fluid. 
         [0035]    In one embodiment, the lubrication fluid circuit  140  is in fluid communication with the clutch assembly  94  (forming a “wet clutch assembly”) and provides a lubricating interface for the clutch assembly  94  and between the clutch assembly  94  and the rear output shaft  31  and/or the clutch drum  124 , e.g., via the clutch lube port  142 . 
         [0036]    A pump  144  (e.g. gerotor pump), which is illustrated in this example as being an off-axis pump, is in fluid communication with the lubrication fluid circuit  140  and is used to pressurize and drive the oil base fluid through the lubrication fluid circuit  140 . In one embodiment, the pressure of the hydraulic based fluid in the lubrication fluid circuit  140  is greater than about 100 psig. 
         [0037]    In the illustrated example, the lubrication fluid circuit  140  is in fluid communication with the hydraulic fluid circuit  49  via an inlet port  146 . The hydraulic based fluid is advanced from the lubrication fluid circuit  140  through the inlet port  146  and into the reservoir  104  for replenishing the hydraulic fluid circuit  49  with the hydraulic based fluid. 
         [0038]    The relatively high pressure of the hydraulic based fluid from the lubrication fluid circuit  140  is reduced prior to being introduced into the reservoir  104 . In one example, the hydraulic based fluid in the reservoir  104  has a pressure that is less than about 20 psig. As illustrated in  FIG. 3 , an inlet check valve  148  may be disposed in the inlet port  146  for reducing the pressure of the hydraulic based fluid being advanced into the reservoir  104 . Additionally, a filter  150  may be disposed within the inlet port  146  for removing debris from the hydraulic based fluid, providing a relative clean stream of hydraulic based fluid for replenishing the reservoir  104 . In one example, the filter  150  reduces the pressure of the hydraulic based fluid being delivered to the reservoir  104 . 
         [0039]    Any excess hydraulic based fluid from the reservoir  104  is returned to the lubrication fluid circuit  140  via a return port  154 . A return check valve  156  may be positioned in the return port  154  for controlling the amount of hydraulic based fluid returning to the lubrication fluid circuit  140 . Alternatively, the return port  154  may be open (e.g. without a valve) for returning any excess hydraulic fluid to the lubrication fluid circuit  140 . 
         [0040]    The lubrication fluid circuit  140  includes a sump  158  that is preferably upstream from the pump  144  and is for containing a supply of the hydraulic based fluid. The sump  158  has a filter  160  for capturing any debris in the hydraulic based fluid prior to being advanced through the pump  144 . 
         [0041]    Referring to  FIG. 5  is an alternative configuration for replenishing the hydraulic fluid circuit  49  with the hydraulic based fluid from the lubrication fluid circuit  140 . An orifice plug  162  is positioned within the inlet port  146  that feeds the reservoir  104 . A restricted opening  164  (e.g. narrow opening), which is formed through the orifice plug  162 , reduces the pressure of the hydraulic based fluid being delivered to the reservoir  104 . In one example, the hydraulic based fluid is delivered continuously to the reservoir through the restricted opening  154  keeping the reservoir substantially full of the fluid. 
         [0042]    The filter  166  (e.g. a micron filter) is positioned above the main chamber  168  of the reservoir  104  for capturing any debris in the hydraulic based fluid. The main chamber  168  provides the hydraulic based fluid to the source piston  92  via the compensation port  102  and the secondary port  103  as described earlier. 
         [0043]    The return port  154  and the inlet port  146  are preferably positioned adjacent to the diaphragm-filter  106  and  166  and opposite the main chamber  168 . It is believed that this configuration will facilitate removing any excess hydraulic based fluid from the reservoir  104 . That is, the excess hydraulic based fluid may flow directly from the inlet port  146  across the diaphragm-filter  106  and  166  to the return port  154  without descending into the main chamber  168  when the main chamber  168  is substantially full of the hydraulic based fluid. An outlet valve  170  may also be disposed in the return port  154  for controlling the outflow of the hydraulic based fluid from the reservoir  104 . The return port  154  provides a fluid pathway for returning the excess hydraulic based fluid to the lubrication circuit  140 . 
         [0044]    As a person skilled in the art will readily appreciate, the above description is meant as an illustration of the implementation of the principles of this invention. This description is not intended to limit the scope or application of this invention in that the invention is susceptible to modification, variation, and change, without departing from the spirit of this invention as defined in the following claims.