Abstract:
A vehicle drive train for transferring torque to first and second sets of wheels includes a first driveline adapted to transfer torque to the first set of wheels and a synchronizing clutch. A second driveline is adapted to transfer torque to the second set of wheels and includes a power disconnection device and a friction clutch. A hypoid gearset is positioned within the second driveline in a power path between the synchronizing clutch and the power disconnection device. The friction clutch and the power disconnection device are positioned on opposite sides of the hypoid gearset. The hypoid gearset is selectively disconnected from being driven by the first driveline, the second driveline or the wheels when the synchronizing clutch and the power disconnection device are operated in disconnected, non-torque transferring, modes.

Description:
[0001]    This application claims the benefit to U.S. Application Ser. No. 61/145,985, filed Jan. 21, 2009. 
     
    
     FIELD 
       [0002]    The present disclosure relates to a driveline for a motor vehicle having a system for disconnecting a hypoid ring gear from rotating at driveline speed. In particular, a power take-off unit includes a coupling for ceasing the transfer of torque from a power source to a rear driveline while another disconnect selectively interrupts the flow of power from a vehicle wheel to a hypoid ring gear of the rear driveline. A torque coupling selectively connects a portion of rear driveline with an input to the hypoid ring gear. 
       BACKGROUND 
       [0003]    Typical power take-off units transfer power from a transaxle in receipt of torque from a vehicle power source. The power take-off unit transfers power to a propeller shaft through a gear arrangement that typically includes a hypoid cross-axis gearset. Other gear arrangements such as parallel axis gears may be provided within the power take-off unit to provide additional torque reduction. 
         [0004]    Power take-off units have traditionally been connected to the transaxle output differential. Accordingly, at least some of the components of the power take-off unit rotate at the transaxle differential output speed. Power losses occur through the hypoid gear churning through a lubricating fluid. Efficiency losses due to bearing preload and gear mesh conditions are also incurred while the components of the power take-off unit are rotated. 
         [0005]    Similar energy losses occur when other driveline components are rotated. For example, many rear driven axles include hypoid gearsets having a ring gear at least partially immersed in a lubricating fluid. In at least some full-time all-wheel drive configurations, the rear drive axle hypoid gearset continuously rotates during all modes of operation and transmits a certain level of torque. In other applications, the rear axle hypoid gearset still rotates but with out the transmission of torque whenever the vehicle is moving. Regardless of the particular configuration, churning losses convert energy that could have been transferred to the wheels into heat energy that is not beneficially captured by the vehicle. As such, an opportunity may exist to provide a more energy efficient vehicle driveline. 
       SUMMARY 
       [0006]    A vehicle drive train for transferring torque to first and second sets of wheels includes a first driveline adapted to transfer torque to the first set of wheels and a synchronizing clutch. A second driveline is adapted to transfer torque to the second set of wheels and includes a power disconnection device and a friction clutch. A hypoid gearset is positioned within the second driveline in a power path between the synchronizing clutch and the power disconnection device. The friction clutch and the power disconnection device are positioned on opposite sides of the hypoid gearset. The hypoid gearset is selectively disconnected from being driven by the first driveline, the second driveline or the wheels when the synchronizing clutch and the power disconnection device are operated in disconnected, non-torque transferring, modes. 
         [0007]    Furthermore, a vehicle drive train for transferring torque from a power source to first and second sets of wheels includes a first driveline adapted to transfer torque from the power source to the first set of wheels and includes a power take-off unit. The first driveline includes a differential, a first hypoid gearset and a synchronizer positioned between the differential and the first hypoid gearset to selectively transfer or cease the transfer of torque from the power source to the first hypoid gearset. A second driveline is in receipt of torque from the first hypoid gearset and transfers torque to the second set of wheels. The second driveline includes a power disconnection device selectively interrupting the transfer of torque from the second set of wheels to the first hypoid gearset. The second driveline also includes a friction clutch for transferring torque between the first hypoid gearset and a second hypoid gearset associated with the second driveline. 
         [0008]    Furthermore, a method for transferring torque from a power source to a first pair and a second pair of wheels in a vehicle drive train is disclosed. The method includes transferring torque from the power source to the first pair of wheels through a first transmission device. A synchronizing clutch, within the first power transmission device, is actuated to transfer torque to a driveline interconnecting the first pair and second pair of wheels. A friction clutch is subsequently actuated to transfer torque from the driveline to a rear drive axle to initiate rotation of a gearset within the rear drive axle. The method further includes actuating a disconnect to drivingly interconnect a shaft coupled to one wheel of the second pair of wheels and a rotatable member of the rear drive axle once speed synchronization between the components coupled by the disconnect is achieved. 
         [0009]    Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples 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 illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
           [0011]      FIG. 1  is a schematic of an exemplary vehicle equipped with a vehicle drive train of the present disclosure; 
           [0012]      FIG. 2  is an enlarged schematic depicting a portion of the drive train shown in  FIG. 1 ; 
           [0013]      FIG. 3  is an enlarged schematic depicting another portion of the drive train shown in  FIG. 1 ; 
           [0014]      FIG. 3A  is an enlarged schematic depicting an alternate portion of the drive train shown in  FIG. 1 ; 
           [0015]      FIG. 4  is a schematic of another exemplary vehicle equipped with another alternate drive train; and 
           [0016]      FIG. 5  is an enlarged schematic depicting a portion of the drive train depicted in  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. 
         [0018]    In general, the present disclosure relates to a coupling and hypoid disconnect system for a driveline of a motor vehicle. A power take-off unit may be equipped with a synchronizer to disconnect the power source from a portion of the driveline and to reconnect through synchronization of the driveline. A dog or roller-type clutch may be provided to disconnect a portion of the driveline from one or more of the vehicle wheels. Additionally, a friction coupling may be positioned in series within the driveline to provide speed synchronization between front and rear driveline components when a power reconnection is desired. The hypoid gearing of the vehicle driveline may be separated from the driving source of power to reduce churning losses and other mechanical inefficiencies. 
         [0019]    With particular reference to  FIGS. 1-3  of the drawings, a drive train  10  of a four-wheel drive vehicle is shown. Drive train  10  includes a front driveline  12  and a rear driveline  14  both drivable from a source of power, such as an engine  16  through a transmission  18  which may be of either the manual or automatic type. In the particular embodiment shown, drive train  10  is a four-wheel system incorporating a power transmission device  20  for transmitting drive torque from engine  16  and transmission  18  to front driveline  12  and rear driveline  14 . Power transmission device  20  is shown as a power take-off unit. 
         [0020]    Front driveline  12  is shown to include a pair of front wheels  24  individually driven by a first axle shaft  26  and a second axle shaft  28 , as well as a differential assembly  32 . Power take-off unit  20  includes a reduction speed gearset  30 , a synchronizer clutch  34 , an output gearset  35  and a right-angled drive assembly  36 . 
         [0021]    Rear driveline  14  includes a propeller shaft  38  connected at a first end to right-angled drive assembly  36  and at an opposite end to one side of a friction coupling  39 . The opposite side of friction coupling  39  is connected to a rear axle assembly  40 . Rear driveline  14  also includes a pair of rear wheels  42  individually driven by a first rear axle shaft  44  and a second rear axle shaft  46 . Rear axle assembly  40  also includes a hypoid ring and pinion gearset  48  driving a differential assembly  50 . A disconnect  52  selectively drivingly disconnects second rear axle shaft  46  from ring and pinion gearset  48  and differential assembly  50 . 
         [0022]    Reduction speed gearset  30  of power take-off unit  20  includes a drive gear  56  fixed for rotation with an output shaft of transmission  18 . A driven gear  58  is in constant meshed engagement with drive gear  56  and is also fixed for rotation with a carrier  60  of differential assembly  32 . Differential assembly  32  includes a first side gear  62  fixed for rotation with first axle shaft  26  and a second side gear  64  fixed for rotation with second axle shaft  28 . Each of first and second side gears  62 ,  64  are in meshed engagement with pinion gears  66 ,  68 . 
         [0023]    Power take-off unit  20  also includes an input shaft  76  supported for rotation within a housing. A drive gear  78  is supported for rotation on input shaft  76 . A driven gear  80  is in meshed engagement with drive gear  78  and fixed for rotation with a ring gear  82  of right-angled drive assembly  36 . Driven gear  80  and ring gear  82  are fixed for rotation with a countershaft  84 . Synchronizer clutch  34  selectively drivingly interconnects input shaft  76  and drive gear  78 . Synchronizer clutch  34  includes a hub  86  fixed for rotation with input shaft  76 . An axially moveable sleeve  88  is in splined engagement with hub  86 . A second hub  90  is fixed for rotation with drive gear  78  and includes an external spline  92 . Synchronizer clutch  34  also includes a blocker ring  94  positioned between hub  86  and second hub  90 . Blocker ring  94  functions to assure that the rotational speed of input shaft  76  is substantially the same as drive gear  78  prior to allowing a driving connection between hub  86  and second hub  90  via sleeve  88 . It should be appreciated that an alternate synchronizer (not shown) may not require a blocker ring to function properly. 
         [0024]    A synchronizer clutch actuation mechanism  96  includes a shift fork  98  slidingly positioned with a groove  100  formed in sleeve  88 . An actuator  102  is operable to move fork  98  and sleeve  88  from a first position where sleeve  88  is disengaged from spline  92  and a second position where sleeve  88  concurrently drivingly engages hub  86  and second hub  90 . 
         [0025]    Right-angled drive assembly  36  includes ring gear  82  and a pinion gear  108  in meshed engagement with ring gear  82 . Pinion gear  108  may be integrally formed with a pinion shaft  110 . Pinion shaft  110  is fixed for rotation with propeller shaft  38  via a flange  112 . Synchronizer clutch  34  may be placed in an activated mode where torque is transferred between input shaft  76  and drive gear  78 . Synchronizer clutch  34  is also operable in a deactivated mode where no torque is transferred to rear driveline  14 . Power from engine  16  is not transferred to right-angled drive assembly  36  when synchronizer clutch  34  is in the deactivated mode. 
         [0026]    Friction coupling  39  is depicted as a friction clutch fixed to a rear axle assembly  113 . Rear axle assembly  113  includes differential assembly  50 , rear axle shaft  44 , rear axle shaft  46  and disconnect  52 . Differential  50  includes a carrier housing  114  fixed for rotation with a ring gear  115  of ring and pinion gearset  48 . Differential assembly  50  also includes first and second side gears  116 ,  117  fixed for rotation with rear axle shafts  44 ,  46 , respectively. A pair of pinion gears  118  are positioned within carrier housing  114  and placed in constant meshed engagement with side gears  116 ,  117 . Friction coupling  39  includes a drum  120  fixed for rotation with propeller shaft  38 . A hub  122  is fixed for rotation with a pinion shaft  124 . A pinion gear  126  of pinion gearset  48  may be integrally formed with pinion shaft  124 . Outer clutch plates  128  are splined for rotation with drum  120 . A plurality of inner clutch plates  130  are splined for rotation with hub  122  and interleaved with outer clutch plates  128 . An actuator  134  is operable to apply a clutch actuation force to clutch plates  128 ,  130  and transfer torque through friction coupling  39 . In one example, an axially moveable piston may be in receipt of pressurized fluid to provide the actuation force. Alternatively, an electric motor may cooperate with a force multiplication mechanism. In yet another embodiment described below in greater detail, the friction clutch may be actuated based on wheel slip or a difference in rotational speed across the friction clutch. 
         [0027]    Disconnect  52  is depicted in  FIGS. 1 and 3  as a dog clutch. Disconnect  52  includes a first hub  140  fixed for rotation with a shaft  142  drivingly engaged with a side gear  144  of differential assembly  50 . An external spline  146  is formed on first hub  140 . An axially translatable sleeve  148  is in splined engagement with first hub  140 . A second hub  150  is fixed for rotation with rear axle shaft  46 . A spline  152  is formed on an outer periphery of second hub  150 . 
         [0028]    A dog clutch actuation system  156  includes a fork  158  slidably positioned within a groove  160  formed in sleeve  148 . An actuator  162  is operable to translate fork  158  and sleeve  148  between a first position where sleeve  148  is engaged only with first hub  140  and a second position where sleeve  148  simultaneously engages splines  146  and  152  to drivingly interconnect shaft  142  with rear axle shaft  46 . 
         [0029]      FIG. 3A  depicts an alternate rear driveline  14 A and rear axle assembly  40 A. Rear axle assembly  40 A is substantially similar to rear axle assembly  40 , previously described. Accordingly, like elements will retain their previously introduced reference numerals. Rear axle assembly  40 A includes another disconnect identified as disconnect  52 A. The elements of disconnect  52 A are identified in similar fashion to the components of disconnect  52  except that the suffix “A” has been added. Disconnect  52 A may selectively drivingly connect and disconnect rear axle shaft  44  with an axle portion  142 A that is fixed for rotation with side gear  116 . During operation, ring and pinion gearset  48  and differential assembly  50  may be entirely disconnected from rear axle shaft  44  and rear axle shaft  46 . Accordingly, even the internal components of differential assembly  50  will not be rotated due to input from rear wheels  42 . To return to the all wheel drive mode of operation, actuator  162 A is controlled at substantially the same time as actuator  162  to reconnect shaft  142 A and rear axle shaft  44  in the same manner as shaft  142  is coupled to rear axle shaft  46 . 
         [0030]      FIGS. 4 and 5  depict an alternate drive train  10 ′. Drive train  10 ′ is substantially similar to drive train  10 . As such, like elements will be identified with the previously introduced reference numerals including a prime suffix. Drive train  10 ′ includes a power take-off unit  20 ′ that differs from power take-off unit  20  by being a single axis power transmission device that does not include countershaft  84 , previously described. On the contrary, power take-off unit  20 ′ includes a concentric shaft  166  having ring gear  82 ′ fixed thereto. Ring gear  82 ′ is in meshed engagement with pinion gear  108 ′ to drive propeller shaft  38 ′. 
         [0031]      FIGS. 4 and 5  also show that disconnect  52  may be alternatively formed as a roller clutch identified as reference numeral  52 ′. The driveline depicted in  FIGS. 1 and 4  may include either a dog clutch, a roller clutch or one of a number of other power transmission devices operable to selectively transfer torque and cease the transfer of torque between rotary shafts. In the example depicted, roller clutch  52 ′ includes an inner member  170  fixed for rotation with rear axle shaft  46 ′ and an outer member  172  fixed for rotation with shaft  142 ′. Inner member  170  includes a surface  174  having a plurality of curved recesses. Each recess is in receipt of a roller  176 . A split ring  178  is positioned between rollers  176  and outer member  172 . Split ring  178  also includes a plurality of curved recesses facing the recesses of inner member  170  and in receipt of rollers  176 . A control arm  180  cooperates with split ring  178  to restrict or permit relative rotation between inner member  170  and split ring  178 . When relative rotation is permitted, rollers  176  are forced radially outwardly to radially outwardly expand split ring  178  into engagement with outer member  172  to transfer torque across roller clutch  52 ′. When relative rotation between inner member  170  and split ring  178  is restricted, rollers  176  are not displaced, the rollers are not wedged between split ring  178  and inner member  170  and torque is not transferred across disconnect  52 ′. An actuator  182  may move control arm  180  to operate disconnect  52 ′. 
         [0032]    During vehicle operation, it may be advantageous to reduce the churning losses associated with driving ring and pinion gearset  48  as well as right-angled drive assembly  36 . With reference to  FIG. 1 , a controller  190  is in communication with a variety of vehicle sensors  192  providing data indicative of parameters such as vehicle speed, four-wheel drive mode, wheel slip, vehicle acceleration and the like. One sensor  192  may be positioned at a location proximate ring and pinion gearset  48  to provide a signal indicating the rotational speed of a ring and pinion gearset component. At the appropriate time, controller  190  may output a signal to control actuator  96  and place synchronizer clutch  34  in the deactuated mode where torque is not transferred from engine  16  to rear driveline  14 . Controller  190  may also signal actuator  162 , associated with disconnect  52 , to place fork  158  in a position to cease torque transfer across disconnect  52  such that the energy associated with one of rotating rear wheels  42  will not be transferred to ring and pinion gearset  48  or differential assembly  50 . Accordingly, the hypoid gearsets  36 ,  48  will not be driven by differential assembly  32 . Furthermore, because side gear  144  is not restricted from rotation, input torque provided by rear axle shaft  44  will only cause the internal gears within differential assembly  50  to rotate. Ring and pinion gearset  48  is not driven. It should be appreciated that friction coupling  39  may be operated in either of an open mode or a torque transferring mode when synchronizer clutch  34  and disconnect  52  do not transfer torque because rear driveline  14  is not rotating at this time. 
         [0033]    When controller  190  determines that a four wheel drive mode of operation is to commence, controller  190  signals actuator  102  to slide sleeve  88  toward hub  90 . During this operation, speed synchronization between input shaft  76  and drive gear  78  occurs. Once the speeds are matched, sleeve  88  drivingly interconnects hub  86  and second hub  90 . At this time, right-angled drive assembly  36  is also driven by engine  16 . Once the front driveline components and the right-angled drive components are up to speed, controller  190  provides a signal to actuator  134  to begin speed synchronization of ring and pinion gearset  48  as well as differential assembly  50 . This sequence of operations will cause the speed of shaft  142  to match the speed of rear axle shaft  46 . At this time, controller  190  provides a signal to actuator  162  to place disconnect  52  in a torque transferring mode by axially translating sleeve  148 . At the end of this sequence, drive train  10  is operable in an all wheel drive mode. It should be appreciated that the procedure previously described may be performed while the vehicle is moving. 
         [0034]    It is contemplated that friction coupling  39  may be alternatively configured as a passive device having an actuation system operable in response to a speed differential between propeller shaft  38  and pinion shaft  124 . In particular,  FIG. 4  depicts friction coupling  39 ′ including a pump  202  driven by propeller shaft  38  when a speed differential exists between propeller shaft  38 ′ and pinion shaft  124 . Pressurized fluid from pump  202  is provided to a piston  204  for applying a compressive force to inner clutch plates  130 ′ and outer clutch plates  128 ′. In this arrangement, control of synchronizer clutch  34 ′ also provides control of friction coupling  39 ′ because rotation of propeller shaft  38 ′ relative to pinion shaft  124 ′ will cause pressurized fluid to cause torque transfer across friction coupling  39 ′ thereby quickly achieving speed synchronization of the front driveline and rear driveline components. Furthermore, the inclusion of friction coupling  39  or  39 ′ allows synchronizer clutch  34  or  34 ′ to be relatively minimally sized because only some of the components of power transmission device  20  and propeller shaft  38  are speed synchronized through actuation of synchronizer clutch  34 . The relatively large rotating masses within rear axle assembly  40  are accelerated through actuation of friction coupling  39 . 
         [0035]    While a number of vehicle drivelines have been previously described, it should be appreciated that the particular configurations discussed are merely exemplary. As such, it is contemplated that other combinations of the components shown in the Figures may be arranged with one another to construct a drive train not explicitly shown but within the scope of the present disclosure.