Abstract:
An apparatus for automatically controlling the number of drive wheels to which power is applied in accordance with the range in which the transfer case is operated. In the low range of operation, including reverse, the drive power is supplied solely to the rear wheels. In the higher range, the number of drive wheels to which drive power is applied is in accordance with the operator settings. A pair of, for example, locking hubs that are actuated by vacuum, air or hydraulic power appropriately routed to the wheels and controlled by an electrically driven valve is operated, in conjunction with the transmission or transfer case shifting mechanism. The arrangement provides a means for automatically reducing the stress on the transmission and transfer case when the vehicle is operated in the four wheel drive mode.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates generally to an apparatus for disconnecting two of the drive wheels of a four wheel drive vehicle, and is specifically related to an apparatus for automatically disconnecting two of the drive wheels of a four wheel drive vehicle in response to certain predetermined conditions.  
         STATEMENT OF THE PRIOR ART  
         [0002]    The present invention relates to a power transfer system for controlling the application of drive power between the front and rear wheels of a four-wheel drive vehicle as a function of predetermined operator-initiated inputs.  
           [0003]    With the increased popularity of four-wheel drive vehicles, a plethora of power transfer systems are currently being utilized in vehicular drivetrain applications for selectively directing drive power (i.e., drive torque) to the non-driven wheels of the vehicle. In many power transfer systems, a part-time transfer case is incorporated into the drivetrain and is normally operable in a two-wheel drive mode for delivering drive torque to the driven wheels. Such part-time transfer cases usually include a mechanical “mode” shift mechanism which can be selectively actuated by the vehicle operator for rigidly coupling the non-driven wheels to the driven wheels for establishing a part-time four-wheel drive mode. As will be appreciated, a motor vehicle equipped with a part-time transfer case offers the vehicle operator the option of selectively shifting between the two-wheel drive mode during normal road conditions and the part-time four-wheel drive mode for operation under adverse road conditions or for off road operation of the vehicle.  
           [0004]    One problem with these automatic systems is that when power is applied to the front wheels and the transfer case is in the low range, i.e., the transmission is in first, second, or reverse, excessive wear occurs on the running gear which may lead to premature failure of the running gear components. While prior art systems allow the user to manually shift out of four wheel drive, they usually only shift automatically in response to road conditions or other stimuli.  
           [0005]    U.S. Pat. No. 4,625,846 issued to Gomez discloses a device for disconnecting two drive wheels from an optional drive mechanism. The device does not disclose any means for discerning when the transmission is in the low range and does not shift in response to this stimuli.  
           [0006]    U.S. Pat. No. 5,605,201 issued to McGinn discloses a system for converting from two wheel drive to four wheel drive based upon certain sensed conditions. By contrast, the present invention contemplates a system which converts from four wheel drive to two wheel drive when the transfer case is in the low range.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention provides an apparatus for automatically controlling the number of drive wheels to which power is applied in accordance with the range in which the transfer case is operated. In the low range of operation, including reverse, the drive power is supplied solely to the rear wheels. In the higher range, the number of drive wheels to which drive power is applied is in accordance with the operator settings. A pair of, for example, locking hubs that are actuated by vacuum, air or hydraulic power appropriately routed to the wheels and controlled by an electrically driven valve is operated, in conjunction with the transmission or transfer case shifting mechanism.  
           [0008]    Accordingly, it is a principal object of the invention to provide an automatic front axle disconnect.  
           [0009]    It is another object of the invention to provide an automatic front axle disconnect which disengages the front drive wheels in accordance with the range in which the transfer case is operated.  
           [0010]    It is another object of the invention to provide an automatic front axle disconnect which uses an electrically controlled valve to disconnect a source of fluid pressure from locking hubs or other front wheel engaging mechanisms.  
           [0011]    These and other objects of the present invention will become readily apparent upon further review of the following specification and drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    Various other objects, features, and attendant advantages of the present invention will become more fully appreciated as the same becomes better understood when considered in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the several views, and wherein:  
         [0013]    [0013]FIG. 1 is a schematic representation of an exemplary four-wheel drive vehicle having a power transfer system within which the present invention may be incorporated.  
         [0014]    [0014]FIG. 2 shows a plan view of the affected components of an exemplary vehicle incorporating the front axle disconnect of the present invention.  
         [0015]    [0015]FIG. 3 shows a detailed diagrammatic view of the hardware components of the present invention.  
     
    
     DETAILED DESCRIPTION  
       [0016]    In general, the present invention is directed to a power transfer system which is operably installed between the driven and non-driven wheels of a four-wheel drive vehicle and which includes means for permitting a vehicle operator to select between a two-wheel drive mode, and a part-time four-wheel drive mode. When actuated, the inventive apparatus automatically causes the power transfer system to operate in the two-wheel drive mode, regardless of the status of the drive mode selection means.  
         [0017]    Referring to FIG. 1 of the drawings, a drivetrain for a four-wheel drive vehicle is schematically shown interactively associated with a power transfer system  10  which incorporates the novel principles of the present invention. The motor vehicle drivetrain has a pair of front wheels  12  and rear wheels  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, the drivetrain is a rear wheel drive system which incorporates a transfer case  20  operable to receive drive torque from engine  16  and transmission  18  for normally driving rear wheels  14  (i.e., the “driven” wheels) in the two-wheel drive mode of operation. However, it is to be understood that the specific orientation of the drivetrain is merely exemplary in nature and that the drivetrain could be reversed for normally driving front wheels  12  in the two-wheel drive mode.  
         [0018]    Front wheels  12  and rear wheels  14  are shown connected at opposite ends of front and rear axle assemblies  22  and  24 , respectively. As is known, a rear differential  26  is interconnected between rear axle assembly  24  and one end of a rear drive shaft  28 , the opposite end of which is interconnected to a first output member  30  of transfer case  20 . Similarly, front axle assembly  22  includes a front differential  32  that is coupled to one end of a front drive shaft  34 , the opposite end of which is coupled to a second output member  36  of transfer case  20 . Transfer case  20  may be equipped with an electronically-controlled torque transfer arrangement for transferring drive torque to front wheels  12  (i.e., the “non-driven” wheels) in addition to rear wheels  14  for establishing the part-time four-wheel drive mode and the “on-demand” drive mode.  
         [0019]    Referring now to FIGS. 2 and 3, there is shown a portion of an exemplary vehicle having a front axle assembly  22  which is pertinent to understanding the incorporation of axle disconnect system  360  into power transfer system  10  of the present invention. However, it is to be understood that the particular front axle assembly shown is merely illustrative in nature and is not intended to limit the present invention. The vehicle has a shift selector switch  31  for selecting the drive gear for the transmission (not shown) as well as a drive selector switch  33  for selecting the number of wheels, or axles to which drive power is applied.  
         [0020]    In general, front axle assembly  22  includes front differential  32 , axle connect mechanism  364 , a shaft assembly  370  and front wheels  12 . In particular, shaft assembly  370  has a first shaft  372  and that is coupled to drive or be driven by front differential  32 , and a second shaft  374  that is coaxially aligned on a common longitudinal axis with first shaft  372  and rotatably connected to one of front wheels  12  in a conventional manner. As is also conventional, the other one of front wheels  12  is rigidly coupled by shaft  375  to drive or be driven by front differential  32  in a well known manner. Finally, a first clutch gear  376  is mounted for rotation with first shaft  372  while a second clutch gear  378  is mounted for rotation with second shaft  374 .  
         [0021]    Front axle disconnect system  360  has a first operating mode that is associated with two-wheel drive operation of the motor vehicle wherein first and second shafts  372  and  374 , respectively, are not coupled together but rather are free to rotate independently of one another. In this first operating mode, rolling movement of front wheels  12  does not drive front differential  32 . Thus, no rotary motion is transferred from front wheels  12  through differential  32  to front drive shaft  34  and front output  36 , during motive operation of the motor vehicle. In addition, axle disconnect system  360  also has a second operating mode wherein shafts  372  and  374  are rigidly coupled for co-rotation such that front wheels  12  are coupled to front output  36  via front differential  32  and drive shaft  34 . This second mode of operation is preferably associated with four-wheel drive operation of the motor vehicle.  
         [0022]    Axle disconnect system  360  is shown to also include a vacuum motor  380  that is in fluid communication with a vacuum source  382 , such as the vacuum from the intake manifold of engine  16 . In the embodiment shown, front axle actuator  368  is an electronically-controlled solenoid valve  384  that can be selectively controlled for opening and closing a communication circuit between vacuum source  382  and vacuum motor  380 . Axle connect mechanism  364  is shown to include a shift fork assembly  386  that is coupled to an axially movable output shaft  388  of vacuum motor  380  for axially shifting a clutch collar  390  between positions corresponding to the first and second operating modes of axle disconnect system  360 . As seen, clutch collar  390  is retained for rotation with and axial sliding movement on first clutch gear  376 . Thus, the axial position of shift fork assembly  386  and clutch collar  390  are controlled by the actuated condition of vacuum motor  380 . In the first operating mode, clutch collar  390  is, as shown, located in a first or “de-coupled” position in engagement only with first clutch gear  376 . In this position, shafts  372  and  374  are disconnected and front differential  32  is disconnected from front wheels  12 . In the second operating mode, clutch collar  390  shifted to a second or “coupled” position (shown in phantom) for coupling first clutch gear  376  for rotation with second clutch gear  378 , thereby connecting shafts  372  and  374  for common rotation. In this position, front differential  32  is capable of transferring power from the transfer case through the connected shafts to front wheels  12 . In operation, control module  184  generates an output signal for selectively actuating solenoid control valve  384  for shifting vacuum motor shaft  388  between its retracted and extended positions which, in turn, causes corresponding movement of clutch collar  390  between its de-coupled and coupled positions. In accordance with a preferred embodiment of the invention, a 12 volt switch  392  is operated by control module  184  in response to the transfer case being operated in the low range.  
         [0023]    Referring specifically to FIG. 2, a simplified arrangement of the vacuum lines in a typical vehicle having optional four wheel drive is shown. Line  186 , commonly designated the red vacuum line, may be operatively connected to a main drive wheel engaging mechanism (not shown) for selectively disengaging the main drive wheels. Line  188 , commonly designated the black vacuum line, is operatively connected to vacuum motor  380  for disengaging the front drive wheels as has been previously explained. Switch  392 , which may be a solenoid switch or relay, allows for selective application of electrical power to electrically controlled valve  384  which may be a solenoid valve. As has been previously mentioned, a control module  184  sends control signals to switch  392  in response to the operation of the transfer case in the low range. Control module  184  is electrically connected to sensors or switches (not shown) associated with both shift selector  31  and drive selector  33 . Alternatively, valve  384  may be operated in accordance with the position of the transmission shift selector  31  without the use of a control module. In this scenario, a pair of contacts (not shown) connected to the shift selector  31  close a circuit when the transmission, and therefor the transfer case, is operating in the low range, e.g., reverse, second or first. The circuit is connected between the battery  44  and the switch  392 . Thus, the completion of the circuit between the shift selector contacts and the switch  392  takes the place of the control signal generated by control module  184 . This arrangement obviates the need for a control module and increases overall system reliability.  
         [0024]    In operation, when the shift selector  31  is in reverse, second, or first, the valve  384 , either by virtue of control module  284  sensing the position of the shift selector  31  and sending the appropriate control signal to switch  392 , or the closure of a switch connected to shift selector  31  which applies an activating voltage to switch  392  (from battery  44 ), disconnects the black vacuum line  188  from the vacuum motor  380  thereby disengaging the front drive wheels  12 , regardless of the position of the drive selector  33  switch.  
         [0025]    From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions. For example, the invention may be employed with four-wheel drive vehicles where selection of the number of drive wheels is a function of predetermined operator-initiated inputs. In this scenario, when the drive selector is in “conditional” 4 wheel drive mode, connection of the second pair of drive wheels would be prevented even when the predetermined inputs are sensed  
         [0026]    It is to be understood that the present invention is not limited to the sole embodiment described above, but encompasses any and all embodiments within the scope of the following claims: