Abstract:
A power transmission device constructed in accordance to one example of the present teachings includes a torque transfer device and a differential. The torque transfer device includes a housing. The torque transfer device selectively communicates rotatable motion from an input member to an output member. A frictional clutch is disposed in the housing that actuates to selectively transfer torque between the input member and the output member. A first and a second axle shaft selectively drives a first and a second drive wheel, respectively. The differential selectively transfers drive torque from the output member to at least one of the first and second axle shafts. A fluid distribution system distributes a common fluid for actuating the frictional clutch and for lubricating select components of the differential.

Description:
FIELD 
       [0001]    The present disclosure relates generally to power transmission devices having a torque transfer device and a differential. More particularly, the present disclosure is directed to a fluid distribution system configured to utilize a common fluid for creating hydraulic pressure in the torque transfer device as well as for target lubricating select components of the differential. 
       BACKGROUND 
       [0002]    This section provides background information related to the present disclosure which is not necessarily prior art. 
         [0003]    Due to increased demand for four-wheel drive and all-wheel drive vehicles, many power transmission systems are 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 device for selectively transferring drive torque from the primary driveline to the secondary driveline to establish a four-wheel drive mode of operation. In many examples, a differential is incorporated on the secondary driveline that receives an input from the torque transfer mechanism. The differential selectively transmits the drive torque to a pair of axle shafts. 
         [0004]    Proper lubrication is one of the most important aspects of a vehicle driveline. A primary function of lubrication is to reduce friction between moving parts, increase corrosion resistance and dissipate heat from the moving components in the driveline. Traditional drivelines use the rotation of a ring gear, pinion, and other masses to transfer the lubrication throughout the driveline. As the masses rotate, they pick up the lubricant and distribute it around the inside of the assembly. Traditional drivelines have oil channels built into the assemblies to allow for the lubrication to reach other key internal areas. This form of lubrication requires a portion of the ring gear, or other rotating mass, to be submerged in the lubricant. If the lubricant level is too low, the lubricant will not be dispersed sufficiently around the inside of the driveline. 
       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]    A power transmission device constructed in accordance to one example of the present teachings includes a torque transfer device and a differential. The torque transfer device includes a housing. The torque transfer device selectively communicates rotatable motion from an input member to an output member. A frictional clutch is disposed in the housing that actuates to selectively transfer torque between the input member and the output member. A first and a second axle shaft selectively drives a first and a second drive wheel, respectively. The differential selectively transfers drive torque from the output member to at least one of the first and second axle shafts. A fluid distribution system distributes a common fluid for actuating the frictional clutch and for lubricating select components of the differential. 
         [0007]    According to additional features, the select components include a first and a second differential bearing associated with the first and second axle shafts. These select components further include a head and a tail bearing associated with the output member. The fluid distribution system also distributes fluid to an interface between the output member and ring gear of the differential. The fluid distribution system comprises a hydraulic power pack that distributes the fluid to the components through at least one fluid line. According to one example, the hydraulic power pack comprises a fluid pump. 
         [0008]    According to other features of the present disclosure, the fluid distribution system further comprises a conduit that communicates the fluid from the hydraulic power pack to a piston that responsively regulates an engagement force applied to the frictional clutch. A return fluid line communicates the fluid from the differential to the hydraulic power pack. According to one configuration, the differential is a rear differential and the first and second axle shafts are first and second rear axle shafts. 
         [0009]    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 
         [0010]    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. 
           [0011]    The present invention will become more fully understood from the detailed description and the accompanying drawings wherein: 
           [0012]      FIG. 1  is a schematic of a four-wheel drive vehicle equipped with a power transmission device incorporating a lubrication distribution system in accordance to one example of the present teachings; 
           [0013]      FIG. 2  is a schematic of the power transmission device of  FIG. 1 ; 
           [0014]      FIG. 3  is a perspective view of the power transmission device of  FIG. 2  incorporating the lubrication distribution system and having external fluid lines according to one implementation of the present teachings; 
           [0015]      FIG. 4  is a partial sectional view of the power transmission device of  FIG. 3  illustrating an exemplary fluid distribution path according to one example of the present teachings; and 
           [0016]      FIG. 5  is a partial sectional view of the power transmission device of  FIG. 3  and illustrating an exemplary return fluid path according to one example of the present teachings. 
       
    
    
       [0017]    Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
       DETAILED DESCRIPTION 
       [0018]    Example embodiments will now be described more fully with reference to the accompanying drawings. 
         [0019]    The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
         [0020]    The present invention is directed to a power transmission device including a torque transfer device and a rear differential that may be adaptively controlled for modulating the torque transferred between a rotatable input member and a rotatable output member. The power transmission device described herein is specific to a rear drive module, however other applications such as transmission devices incorporated on a front drive module are contemplated. Accordingly, while the present invention is hereinafter described in association with a specific structural embodiment for use as a rear drive module in a driveline application, it should be understood that the arrangement shown and described is merely intended to illustrate an exemplary embodiment of the present invention. 
         [0021]    With initial reference to  FIGS. 1 and 2  of the drawings, a drive train  10  for a four-wheel vehicle is shown. The drive train  10  includes a first axle assembly  12 , a second axle assembly  14 , and a powertrain assembly  16  for generating and delivering drive torque to the axle assemblies  12  and  14 , respectively. In the particular arrangement shown, the first axle assembly  12  is the front axle while the second axle assembly  14  is the rear axle. The powertrain assembly  16  includes an engine  18  and a multi-speed transmission  20  having an integrated front differential unit  22  for driving front wheels  24  via front axle shafts  26 . The powertrain assembly  16  further includes a transfer unit  28  driven by the transmission  20  for delivering torque to an input member  29  of a power transmission device  30  via a drive shaft assembly  32 . The power transmission device  30  generally includes a torque transfer device  33  and a rear differential  34 . The input member  29  of the power transmission device  30  corresponds to an input member  35  of the torque transfer device  33  and is coupled to the drive shaft assembly  32 . An output member  36  ( FIG. 2 ) of the torque transfer device  33  is arranged to drive the rear differential  34 . The second axle assembly  14  also includes a pair of wheels  38  that are connected to the rear differential  34  via rear axle shafts  40 . 
         [0022]    The drive train  10  is shown to include an electronically-controlled power transfer system  42  that includes the power transmission device  30 . The power transfer system  42  is 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 the torque transfer device  33  of the power transmission device  30 . Accordingly, one hundred percent of the drive torque delivered by the transmission  20  is provided to the front wheels  24 . In the four-wheel drive mode, power is transferred through the torque transfer device  33  of the power transmission device  30  to supply drive torque to the rear wheels  38 . The power transfer system  42  further includes a controller  50  that is in communication with vehicle sensors  52  for detecting dynamic and operational characteristics of the motor vehicle. The vehicle sensors  52  can include, but are not limited to, sensors that can determine wheel speed, wheel slip, steering wheel angle, yaw rate, throttle position, engine/transmission torque, vehicle speed, stability control, etc. 
         [0023]    The controller  50  is operable to control actuation of the torque transfer device  34  in response to signals from the vehicle sensors  52 . The controller  50  may be programmed with a predetermined target torque split between the first and second set of wheels  24  and  38 , respectively. Alternatively, the controller  50  may function to determine the desired torque to be transferred through the torque transfer device  33  via other methods. Regardless of the method used for determining the magnitude of torque to transfer, the controller  50  operates the torque transfer device  33  to maintain the desired torque magnitude. 
         [0024]    With specific attention now to  FIG. 2 , the torque transfer device  33  of the power transmission device  30  will be described in greater detail. The input member  35  of the torque transfer device  33  is shown to include an input shaft  70  while the output member  36  is shown to include an output shaft  72 . The output shaft  72  is preferably a pinion shaft supported by head and tail bearings  74  and  76 , respectively. The output shaft  72  has a pinion gear  78  that is meshed for rotation with a ring gear  80  on the rear differential  34 . The power transmission device  30  also includes a friction clutch  84  that is operably dispersed between the input shaft  70  and the output shaft  72 . The friction clutch  84  can comprise a first clutch plate  86  and a second clutch plate  88 . In one configuration, the input shaft  70  includes a clutch hub (not specifically shown) that is drivingly coupled to the first friction plate  86 . Similarly, the second clutch plate  88  is arranged in a splined engagement with a clutch drum (not specifically shown). The drum is drivingly coupled to the output shaft  72 . The friction clutch  84  is a wet clutch. While the first and second clutch plates  86  and  88 , respectively, are both represented as a single clutch plate, a set of clutch plates including multiple first and second clutch plates can be provided in an interleaved configuration. 
         [0025]    A piston  100  is slidably positioned within a cavity that is formed within a housing  102  of the torque transfer device  33 . The piston  100  is axially movable in response to pressurized fluid that flows through a conduit  112  formed in the housing  102  to control actuation of the friction clutch  84 . Other configurations are contemplated. When pressurized fluid builds on the face of the piston  100 , the piston  100  translates and applies a force such as through a thrust bearing and apply plate (not specifically shown) to the clutch plates  86  and  88 . Torque is transferred between the input shaft  70  and the output shaft  72  when the friction plates  86  and  88  are forced into contact with one another. A hydraulic power pack  116  is arranged to provide a controllable source of pressurized fluid to the conduit  112 . Regulation of the fluid pressure in the conduit  112  acts to proportionally regulate the clutch engagement force applied by the piston  100  which, in turn, regulates the drive torque transferred from the input shaft  70  to the output shaft  72 . While not limited thereto, the power pack  116  can include a motor-driven fluid pump and valving for controlling the fluid pressure delivered to the conduit  112 . 
         [0026]    With reference now to  FIGS. 2-5 , a fluid distribution system  120  constructed in accordance to one example of the present teachings will be described. In general, the fluid distribution system  120  includes the hydraulic power pack  116  that communicates pressurized fluid through the conduit  112  to the piston  100 . The fluid distribution system  120  also includes a plurality of lubrication delivery lines collectively identified at reference numeral  130  that deliver the pressurized fluid from the hydraulic power pack  116  to various components of the rear differential  34 . While the term “line” is used herein to denote the structure used to transport the fluid from the hydraulic power pack  116  to the various components of the rear differential  34 , it will be appreciated that the term encompasses other structures such as pipes, tubes, channels or other forms of enclosed spaces. 
         [0027]    In the particular example shown, the lubrication delivery lines  130  include first and second fluid delivery lines  132  and  134  that communicate fluid from the hydraulic power pack  116  to first and second differential bearings  136  and  138 , respectively. The lubrication delivery lines  130  further comprise a third fluid delivery line  142  and fourth fluid delivery line  144 . The third fluid delivery line  142  communicates fluid from the hydraulic power pack  116  to the head bearing  74 . The fourth fluid delivery line  144  communicates fluid from the hydraulic power pack  116  to the tail bearing  76 . A fifth fluid delivery line  146  communicates fluid from the hydraulic power pack  116  to an interface between the pinion  78  and the ring gear  80 . The lubrication delivery lines  130  of the fluid distribution system  120  therefore communicate fluid from the hydraulic power pack  116  to specific components of the rear differential  34 . Once the fluid is dispersed onto the identified components, the fluid then collects in a housing  150  of the differential  34  where a return line  152  routes the fluid back to the hydraulic power pack  116  where the process is repeated. 
         [0028]    It is appreciated that while the schematic representation of the fluid distribution system  120  shown in  FIG. 2  identifies dedicated or distinct fluid distribution lines  130  used to route the fluid to the identified components, other configurations are contemplated. For example, some or all of the lubrication delivery lines  130  may be shared for delivering fluid from the hydraulic power pack  116  to more than one component. It will also be understood that the lubrication lines  130  can be routed externally to the power transfer device  30  as illustrated in  FIG. 3 . Alternatively, the lubrication lines  130  may be formed at least partially within the sidewall  102  of the torque transfer device  33  and/or the housing  150  of the differential  34  such as during a casting process. Other configurations are contemplated. For example, as illustrated in the cross-sectional representation of  FIG. 4 , lubrication lines  150  constructed in accordance to another example of the present disclosure are shown that incorporate partially shared fluid line paths to the dedicated components of the differential  34 . Specifically, the lubrication lines  150  include a first fluid line portion  153  that initiates at the hydraulic power pack  116  and connects with a second fluid line portion  154 , a third fluid line portion  156 , a fourth fluid line portion  158 , a fifth fluid line portion  160  and a sixth fluid line portion  162 . The second fluid line portion  154  has an outlet  164  that is proximate the differential bearing  136  for dispersement of fluid thereon. The third fluid line portion  156  includes an outlet  166  that is aligned for dispersing fluid onto the tail bearing  76 . The fourth fluid line portion  158  includes an outlet  168  that is aligned to disperse fluid onto the differential bearing  138 . The fifth fluid line portion  160  includes an outlet  170  that is aligned to disperse fluid onto the head bearing  74 . The sixth fluid line portion  162  includes an outlet  172  that is aligned to disperse fluid onto an interface between the pinion  78  and ring gear  80 . The outlets  164 ,  166 ,  168 ,  170  and  172  may comprise an orifice and/or nozzle sized to accommodate an optimal line pressure, exit diameter, flow rate, etc. 
         [0029]    While the return line  152  has been described above as collecting the dispersed fluid from the identified components in the housing  150  and returning the fluid to the hydraulic power pack  116  through a single line, it is contemplated that multiple return lines may be incorporated. Again, the return lines may be provided externally to the power transmission device  30  or alternatively may be formed as part of the housing  102  of the torque transfer device  33  and/or the housing  150  of the rear differential  34 . 
         [0030]    Turning now to  FIG. 5 , a return line configuration is shown according to another example and generally identified at reference numeral  180 . The return line  180  can collectively be formed by a first return line portion  182 , a second return line portion  184 , a third return line portion  186 , a fourth return line portion  188 , and a fifth return line portion  190  and a sixth return line portion  192 . The first return line portion  182  is generally located downstream of the other return line portions and is configured to route the fluid back to the hydraulic power pack  116 . The second return line portion  184  has an inlet  194  proximate the differential bearing  136 . The third return line portion  186  has an inlet  196  proximate the tail bearing  76 . The fourth return line portion  188  has an inlet  198  proximate the head bearing  74 . The fifth return line portion  190  has an inlet  200  generally proximate the rear differential bearing  138 . The sixth return line portion  192  has an inlet  202  generally proximate the pinion  78  and ring gear  80 . Again, it will be appreciated that other configurations may be provided. Nevertheless, the return line  180  communicates the fluid that was distributed through the lubrication delivery lines  130  back to the hydraulic power pack  116 . 
         [0031]    The power transmission device  30  of the present disclosure allows for a single lubrication to be used to apply the friction clutch  84  as well as lubricate dedicated components of the rear differential  34 . In this regard, it is not necessary to include multiple fluids of different viscosity and/or other properties for the power transmission device  30 . It will be appreciated that while the above description has been made with respect to the lubrication lines  130  providing directed lubrication onto the head bearing  74 , the tail bearing  76 , the differential bearings  136  and  138  as well as the interface between the pinion  78  and the ring gear  80 , the lubrication lines  130  may include other lines that are routed elsewhere to specifically target lubrication onto other components of the differential  34 . 
         [0032]    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.