Abstract:
An assembly selectively disconnecting a road wheel from a power source, includes a differential mechanism transmitting rotating power between the power source and an output shaft, a halfshaft, and a disconnect mechanism releasably secured mechanically to the differential mechanism and alternately opening and closing a drive connection between the output shaft and the halfshaft.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates generally to a motor vehicle driveline, particularly to disconnecting a half shaft or axle shaft from a differential mechanism. 
         [0003]    2. Description of the Prior Art 
         [0004]    Driveline disconnect devices have long been used on rear-wheel drive (RWD) based four wheel drive (4WD) vehicles to provide significant improvement in fuel economy while operating in two wheel drive (2WD) mode. In a RWD-based 4WD vehicle, the transfer case provides a natural location to disconnect torque input to the secondary axle, i.e. the front axle, of a RWD-based 4WD vehicle driveline. 
         [0005]    To maximize fuel economy, vehicle manufacturers have used wheel end disconnect devices, such as hub locks and integrated wheel end disconnects, which effectively eliminate spin losses from the entire secondary driveline. Alternate means, such as center axle disconnects, decouple one halfshaft from the differential, leaving the other halfshaft to back-drive the side gears. These alternate means are far simpler to execute, but only produce about one-half to two-thirds the fuel economy improvement potential attainable with wheel end disconnects. 
         [0006]    To maximize fuel economy, it is desirable to disconnect both halfshafts from the differential mechanism. Unfortunately, integrated wheel end disconnects (IWEs) require a purposed-designed wheel end to accommodate them. Wheel ends not designed for IWEs and center axle disconnect devices require a large retooling investment to retrofit them later. 
       SUMMARY OF THE INVENTION 
       [0007]    An assembly selectively disconnecting a road wheel from a power source, includes a differential mechanism transmitting rotating power between the power source and an output shaft, a halfshaft, and a disconnect mechanism releasably secured mechanically to the differential mechanism and alternately opening and closing a drive connection between the output shaft and the halfshaft. 
         [0008]    The modular nature of the mechanism permits it to be connected mechanically to existing structure, thereby significantly improving investment efficiency. 
         [0009]    The dual disconnect mechanism provides significantly better vehicle fuel economy compared to conventional axle disconnects. 
         [0010]    The mechanism avoids the large investment expense associated with retooling wheel ends for IWEs by moving the disconnect devices inboard such that they mount on the axle. 
         [0011]    The mechanism enables a running change wherein the same axle can be used with or without the disconnect function, providing a significant improvement in investment efficiency compared to purpose-built designs. 
         [0012]    The scope of applicability of the preferred embodiment will become apparent from the following detailed description, claims and drawings. It should be understood, that the description and specific examples, although indicating preferred embodiments of the invention, are given by way of illustration only. Various changes and modifications to the described embodiments and examples will become apparent to those skilled in the art. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0013]    The invention will be more readily understood by reference to the following description, taken with the accompanying drawings, in which: 
           [0014]      FIG. 1  is a cross sectional top view taken at a diametric plane through the drive unit of a motor vehicle. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0015]      FIG. 1  illustrates the drive unit  10  for the secondary wheels of a motor vehicle. A driveshaft  12  transmits rotating power from a power source, such as an engine or electric motor, through a bevel pinion  14 , and a bevel gear  16 , which meshes with the pinion and is secured to the carrier  18  of an interwheel differential mechanism  20 . The secondary wheels of the vehicle are driven by the differential  20  through output shafts  22 ,  24 . 
         [0016]    The differential  20  includes a pinion shaft  26 , secured to the carrier  18  for rotation with the carrier; bevel pinions  28 ,  30  supported on shaft  26  for rotation about axis  32  and revolution about axis  34 ; side bevel gears  36 ,  38 , meshing with pinions  28 ,  30  and secured to output shafts  24 ,  22 , respectively. Output shaft  22  is connected by a right-hand halfshaft  40  and to the right-hand secondary road wheel. Output shafts  24 ,  22  are supported on bearings  50 ,  51 , respectively. 
         [0017]    A casing  42 , which encloses a disconnect mechanism  44 , is secured at a bolt circle by a series of bolts  46  to a housing  48 , on which bevel pinion  14  is supported by a bearing  77 . A modified halfshaft assembly  52  is supported on left-hand output shaft  24 , which is driveably connected to the left-hand road wheel. Bearings  54 ,  55  support halfshaft assembly  52  on output shaft  24 . 
         [0018]    The disconnect mechanism  44  includes a locking collar  56 , which is continually secured by meshing axial spline teeth  58  formed on halfshaft assembly  52  and is selectively secured by meshing axial spline teeth  60  formed on output shaft  24 . Locking collar  56  is secured to an actuator piston  62 , which is biased by a compression spring  64  that continually urges the locking collar toward the connected position shown in the FIGURE above the axis  34 . 
         [0019]    A rotary seal  66 , located between surfaces of the modified halfshaft assembly  52  and the casing  42  of the disconnect mechanism  44 , seals the volume within casing. An outer diaphragm seal  68  is located between and is secured to surfaces of the housing  48  and actuator piston  62 . An inner diaphragm seal  70  is located between and is secured to surfaces of the actuator piston  62  and the casing  42  of the disconnect mechanism  44 . 
         [0020]    A vacuum passage  72  is connected to a vacuum source or a source of low pressure. A lube passage  74  carries lubricant to a sump in the lower elevation of the differential housing  48 . Internal passages  76  carry lubricant to the bearings  54 ,  55 . 
         [0021]    In operation, when differential pressure is applied across piston  62 , a pressure force due to the differential pressure acting on the piston in opposition to the force of spring  64  causes locking collar  56  to slide on the spline teeth  58  of halfshaft  52  leftward along axis  34  to the disconnect position shown below axis  34 , thereby disengaging the locking collar from the spline teeth  60  of output shaft  24  and disconnecting output shaft  24  from the left-hand halfshaft  52  and the left-hand road wheel. 
         [0022]    When differential pressure across piston  62  is removed, spring  64  forces piston  62  rightward causing locking collar  56  to slide on the spline teeth  58  of halfshaft  52  rightward along axis  34  to the connect position shown above axis  34 , thereby reengaging the locking collar with the spline teeth  60  of output shaft  24  and reconnecting output shaft  24  with the left-hand halfshaft  52  and the left-hand road wheel. 
         [0023]    Although the disconnect mechanism  44  is described as being actuated by vacuum pressure, the disconnect mechanism may be actuated pneumatically or hydraulically, either by a positive pressure applied to the inboard side of piston  62 , or by a negative pressure applied to the outboard side of piston  62 . Similarly, electro-mechanical energy can also be used to act directly upon locking collar  56 . 
         [0024]    Another drive unit  10  may be installed at the right-hand side of the differential  20  substantially as described with respect to the left-hand side, such that rotating inertial and frictional drag associated with the driveline components that transmit power to the right-side wheel is eliminated when the right-hand drive unit is disconnected from differential output shaft  22 . 
         [0025]    In accordance with the provisions of the patent statutes, the preferred embodiment has been described. However, it should be noted that the alternate embodiments can be practiced otherwise than as specifically illustrated and described.