Abstract:
The object of this invention is directed to an improved control system and actuator for a transfer case. More particularly, this invention is directed to a hydraulic actuator and control system for a transfer case. One aspect of the present invention provides a hydraulic control system for a transfer case that includes an actuator for generating fluid pressure. The system also includes an isolation valve and a control valve in fluid communication with the actuator. The isolation valve is in a normally closed position and the control valve is in a normally open position. The system further includes a piston for applying fluid pressure to a device of the transfer case. The invention further provides a method for controlling the hydraulic pressure to a transfer case.

Description:
RELATED APPLICATION  
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/287,915, filed May 1, 2001, entitled System and Method for Actuating and Controlling a Vehicle Drivetrain Transfer Case by Schuyler S. Shaw and John B. Hageman. 
     
    
     
       TECHNICAL FIELD  
         [0002]    The present invention relates generally to transfer cases for use in four-wheel drive vehicles. More particularly, the present invention relates to a system to provide a clutch pack slip control mode and range selector shift function to a transfer case clutch and range selector.  
         BACKGROUND OF THE INVENTION  
         [0003]    The drivetrain in many light-duty and sport-utility vehicles includes a transfer case for transmitting drive torque for the engine and transmission to all four of the wheels, thereby establishing a four-wheel-drive mode of operation. To accommodate differing road surfaces and conditions, many transfer cases are equipped with a gear reduction unit that can be selectively shifted by the vehicle operator to establish four-wheel high range and low range drive modes.  
           [0004]    In addition, current control of transfer case clutch packs allows high slip conditions to occur. After a short period, approximately 10 seconds, the motor actuator locks up the clutch pack using a brake to prevent the motor and clutch pack from overheating. At full lock, speed differential on the clutch pack is zero, thereby generating no heat. This mode of operation is not always appropriate in certain situations.  
           [0005]    It would be desirable to provide an electrohydraulic actuator system for a drivetrain transfer case that overcomes these and other disadvantages  
         SUMMARY OF THE INVENTION  
         [0006]    The object of this invention is directed to an improved control system and actuator for a transfer case. More particularly, this invention is directed to an electrohydraulic actuator and control system for a transfer case.  
           [0007]    One aspect of the present invention provides an electrohydraulic control system for a vehicle drivetrain transfer case that includes an actuator for generating fluid pressure. The system also includes an isolation valve and a control valve in fluid communication with the actuator and a clutch pack. The isolation valve is in a normally closed position and the control valve is in a normally open position. The system further includes a piston for applying fluid pressure to the clutch pack of the transfer case.  
           [0008]    Another aspect of the invention provides a hydraulic control system for a vehicle drivetrain transfer case that includes an actuator for generating fluid pressure. The system also includes a first piston for applying fluid pressure to a first device, a selector piston for applying fluid pressure to a second device, and a shuttle valve positioned between the actuator and the second piston. The shuttle valve is in fluid communication with the actuator via a first and a second selector fluid line and in fluid communication with the second piston via a second and a third fluid line.  
           [0009]    The invention further provides a method of generating hydraulic pressure for a vehicle drivetrain transfer case that includes generating fluid pressure, applying the fluid pressure to at least one piston, and controlling the fluid pressure to the at least one piston.  
           [0010]    Yet another aspect of the invention provides a system for a vehicle drivetrain transfer case comprising means for generating fluid pressure, means for isolating an at least one device from the pressurized fluid, means for applying fluid pressure to the at least one device, means for controlling the pressurized fluid, and means for sensing fluid pressure.  
           [0011]    The foregoing and other features and advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention rather than limiting, the scope of the invention being defined by the appended claims and equivalents thereof. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 is a schematic illustration of one embodiment of the drivetrain actuator system of the present invention;  
         [0013]    [0013]FIG. 2 is a schematic illustration of another embodiment of the drivetrain actuator system of the present invention; and  
         [0014]    [0014]FIG. 3 is a schematic illustration of another embodiment of the drivetrain actuator system of the present invention.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0015]    Referring to FIG. 1, a vehicle hydraulic control and drivetrain actuator system incorporating the present invention is illustrated and generally designated by the reference numeral  10 . The system includes an actuator  12 . The function of actuator  12  is to provide and control a pressurized brake fluid supply to remote brake cylinders associated with wheel assemblies  16 ,  18 ,  20  and  22 . In one embodiment, actuator  12  may be an antilock brake system (ABS) modulator. The actuator  12  typically includes, or has associated therewith, a pump or like source of pressurized fluid  14 .  
         [0016]    The modulator  12 , as an element of the control and drivetrain actuator system of this embodiment of the present invention, also provides pressurized fluid to a piston  24 . Piston  24  is positioned to act on a clutch pack  26  of a transfer case  28 . An outlet line  30  of the modulator  12  provides pressurized fluid to an isolation valve  32 . The line  30  is an outlet line from the pump  14  of the modulator. Isolation valve  32  is a normally closed valve that isolates clutch pack  26  from the ABS function. The isolation valve  32  at rest prohibits flow-through of fluid to piston  24  of clutch pack  26 . When opened, for example by a solenoid, valve  32  allows pressurized fluid to act on piston  24 . The opening and modulation of the isolation valve  32  can be performed in response to a demand or control signal from control device  36 .  
         [0017]    Between valve  32  and piston  24 , a pressure sensor  34  can be provided. The pressure sensor  34  senses the pressure in the output fluid line between the valve  32  and the piston  24 . The sensor  34  can provide a pressure signal to a control device  36  that operates to control functions of system  10  as described above and explained more fully below.  
         [0018]    Piston  24  is positioned to act against the torque management clutch pack  26  in such a manner as to increase the contact friction between the plates of the clutch pack. In other words, an increase of the fluid pressure acting on the piston  24  causes a linear movement of the piston against the clutch pack  26 . The compression of the clutch pack  26  increases the transfer of torque therethrough.  
         [0019]    An inlet fluid line  38  extends from the piston to the pump  14 . A normally open valve  40  is positioned along the inlet line. The normally open valve  40  is maintained in an open condition at rest permitting flow through of fluid. Closing valve  40  permits buildup of fluid pressure at piston  24 . The closing and modulation of the valve  40  can be performed in response to a demand or control signal from control device  36 .  
         [0020]    A check valve  42  may be provided between the valve  40  and the modulator  12 . The check valve  42  operates to prohibit backflow of fluid in inlet line  38  toward piston  24 .  
         [0021]    In one embodiment, fluid pressure to piston  24  is gradually applied by fully opening isolation valve  32  and gradually closing valve  40 . Pressure to piston  24  may then be increased, decreased or maintained by the opening or closing of valve  40 . In another embodiment, fluid pressure to piston  24  may be gradually applied by closing valve  40  and gradually opening isolation valve  32 .  
         [0022]    Referring now to FIG. 2, a vehicle hydraulic control and drivetrain actuator system incorporating the present invention is illustrated and generally designated by the reference numeral  100 .  
         [0023]    The system includes a source of pressurized fluid  144 . Pressurized fluid is generated by an actuator  144 , which can include electric motor  146 . Motor  146  can be a DC motor. The electric motor can be coupled to a ball screw  148  by a transmission  150 . The transmission  150  may be any suitable arrangement of intermeshed gears, belt driven pulleys and the like. It will be understood by one with skill in the art that any suitable mechanism can be used to transfer power from the motor  146 , including direct connection with the ball screw and further including belts, toothed belts, sprockets, pulleys, chain, chain belts, gears and the like.  
         [0024]    The ball or nut portion  152  of the ball screw  148  can be held in housing  154  to prohibit rotation of the nut. The screw portion  156  of the ball screw  148  is operably connected to a piston  158 , which is slidably disposed in a bore  160  of the housing  154 . A reservoir  162  provides hydraulic fluid, (oil or the like) to chamber  164  of actuator  144 . Chamber  164  is formed by piston  158  and bore  160 . Movement of the piston  158  in the bore  160  provides pressurized fluid to the system  100 .  
         [0025]    System  100  may also include a mode selector  215  operably connected to motor  146 . Mode selector  215  may send a signal to motor  146  to generate pressurized fluid in response to a signal sent to mode selector  215  by a vehicle operator (not shown) choosing to engage or disengage the range selector  178 .  
         [0026]    In the illustrated embodiment, pressurized fluid from actuator  144  can be provided to one or more devices. It will also be understood that actuator  144 , in other embodiments of the present invention, can be other devices well known in the art for providing pressurized fluid, for example, an ABS modulator, as described above and further described below in relation to FIG. 3.  
         [0027]    A first device can be a clutch pack  166  of a vehicle transfer case. The actuator  144  provides pressurized fluid via outlet line  168  through a normally open valve or solenoid  170 . The pressurized fluid acts on piston  172  to compress the torque management clutch pack  166  and thereby transfer torque therethrough.  
         [0028]    A pressure sensor  174  can be provided between valve  170  and piston  172 . The pressure sensor  174  senses the pressure in the output line  168  between the valve  170  and the piston  172 . The sensor  174  may then provide a pressure signal to a control device  176 . Control device  176  then operates to control functions of system  100  through a connection to motor  146 . The amount of pressure that acts on piston  172  may be controlled by varying the pressure generated by actuator  144 . In this manner, the fluid pressure to piston  172  may be infinitely varied.  
         [0029]    A second device included with system  100  may be a transfer case range selector  178 . The range selector typically operates to provide a low and high range of operating gearing for the vehicle. Pressurized fluid from the actuator  144  can be provided to a shuttle valve  180  to provide directional flow to the selector  178 .  
         [0030]    The shuttle valve  180  can be in fluid communication with a first and second fluid reservoir  182 ,  184 . A piston  186  is slidably disposed in the housing of the shuttle valve  180 . A spring  188  is positioned within the shuttle valve  180  to bias the piston  186  in a first direction, (to the right with respect to the illustration).  
         [0031]    A first selector line  190  provides pressurized fluid from the actuator  144  to the shuttle valve  180 . The first selector line  190  can include a normally open valve or solenoid  192 . When the valve  192  is open, and actuator  144  provides pressurized fluid to the shuttle valve  180 , the piston  186  of the shuttle valve is moved to a first position (as shown in FIG. 2) overcoming the bias of the spring  188 .  
         [0032]    A second selector line  193  can be provided in parallel fluid communication with first line  190  between actuator  144  and shuttle valve  180 .  
         [0033]    Pressurized fluid from the shuttle valve  180  is provided to a selector piston  194 . Selector piston  194  is slidably disposed within housing  196  defining left and right chambers  198 ,  200 . Left and right chambers  198 ,  200  are in fluid communication with shuttle valve  180  by left and right fluid lines  202 ,  204 . Selector piston  194  is operably connected to range selector  178 .  
         [0034]    In operation, when valve  192  is maintained in the open position fluid pressure in lines  190  and  193  are substantially equal. As shown in the illustration, fluid pressure within shuttle valve first chamber  206  moves piston  186  to a left position in valve  180 . Pressurized fluid in line  193  is then allowed to move through valve  180  out through left line  202  into left chamber  198 . Due to the build-up of fluid pressure in left chamber  198 , piston  194  is urged toward the right with respect to the illustration. At this time, fluid in chamber  200  is forced through right fluid line  204  and valve  180  into reservoir  184 .  
         [0035]    When the vehicle operator wishes to switch the range selector  178  mode to low a signal may be sent to motor  146  via mode selector  215  to retract piston  158 . The decrease in fluid pressure causes piston  186  to be urged toward the right by spring  188 . Movement of piston  186  to the right forces fluid to flow from chamber  206  passed valve  192  and into reservoir  162 . The movement of piston  186  cause piston seals  208 ,  210  to move past fluid lines  202 ,  204 .  
         [0036]    Once piston  186  has moved to the right, valve  192  is closed. Closing valve  192  allows pressurized fluid to flow through line  193 . Pressurized fluid in line  193  is then directed through right line  204  into chamber  200 . Due to the increase of fluid in chamber  200 , piston  194  is urged in the left direction. The fluid in chamber  198  can then flow past valve  180  into reservoir  182 . In this manner, reciprocation of the piston  194  actuates the transfer case range selector  178 .  
         [0037]    In one embodiment, valve  170  may be closed during the actuation of range selector  178  to isolate clutch pack  166 . Clutch pack  166  maybe isolated so that the actuation of range selector  178  does not affect the operation of clutch pack  166 .  
         [0038]    Referring now to FIG. 3, where like elements have like reference numbers as those of FIGS. 1 and 2, a vehicle hydraulic control and drivetrain actuator system incorporating the present invention is illustrated and generally designated by the reference numeral  250 .  
         [0039]    The system includes an actuator  12 . The function of actuator  12  is to provide and control a pressurized brake fluid supply to remote brake cylinders associated with wheel assemblies  16 ,  18 ,  20  and  22 . In one embodiment, actuator  12  may be an antilock brake system (ABS) modulator. The actuator  12  typically includes, or has associated therewith, a pump or like source of pressurized fluid  14 .  
         [0040]    In the illustrated embodiment, pressurized fluid from actuator  12  can also be provided to one or more devices.  
         [0041]    A first device can be clutch pack  166  of a vehicle transfer case. The actuator  12 , provides pressurized fluid to a piston  172 . Piston  172  is positioned to act on clutch pack  166  of a transfer case. An outlet line  30  of the actuator  12  provides pressurized fluid to an isolation valve  32 . The line  30  is an outlet line from the pump  14  of the actuator  12 . Isolation valve  32  is a normally closed valve that isolates clutch pack  166  from the ABS function. The isolation valve  32  at rest prohibits flow-through of fluid to piston  172  of clutch pack  166 . When opened, for example by a solenoid, valve  32  allows pressurized fluid to act on piston  172  through fluid line  168 . The opening and modulation of the isolation valve  32  can be performed in response to a demand or control signal from control device  36 .  
         [0042]    Between valve  32  and piston  172 , a pressure sensor  174  can be provided. The pressure sensor  174  senses the pressure in the fluid line  168  between the valve  32  and the piston  172 . The sensor  174  can provide a pressure signal to a control device  36  that operates to control functions of system  250 .  
         [0043]    Piston  172  is positioned to act against the torque management clutch pack  166  in the same manner as described above for clutch pack  26  of FIG. 1.  
         [0044]    An inlet fluid line  38  extends from the piston to the pump  14 . A normally open valve  40  is positioned along the inlet line. The normally open valve  40  is maintained in an open condition at rest permitting flow through of fluid. Closing valve  40  permits buildup of fluid pressure at piston  172 . . The closing and modulation of the valve  40  can be performed in response to a demand or control signal from control device  36 .  
         [0045]    A check valve  42  may be provided between the valve  40  and the modulator  12 . The check valve  42  operates to prohibit backflow of fluid in inlet line  38  toward piston  172 .  
         [0046]    In one embodiment, fluid pressure to piston  172  is gradually applied by fully opening isolation valve  32  and gradually closing valve  40 . Pressure to piston  172  may then be increased, decreased or maintained by the opening or closing of valve  40 . In another embodiment, fluid pressure to piston  172  may be gradually applied by closing valve  40  and gradually opening isolation valve  32 .  
         [0047]    A second device included with system  250  may be a transfer case range selector  178 . Pressurized fluid from the actuator  12  can be provided to a shuttle valve  180  to provide directional flow to range selector  178 . Flow of pressurized fluid is provided to range selector  178  in the same manner as fluid to clutch pack  166  by fully opening isolation valve  32  and gradually closing valve  40 .  
         [0048]    Between valve  32  and shuttle valve  180 , a pressure sensor  34  can be provided. The pressure sensor  34  senses the pressure in the fluid line  196  between the valve  32  and the shuttle valve  180 . The sensor  34  can provide a pressure signal to a control device  36  that operates to control functions of system  250 .  
         [0049]    The shuttle valve  180  can be in fluid communication with a first and second fluid reservoir  182 ,  184 . A piston  186  is slidably disposed in the housing of the shuttle valve  180 . A spring  188  is positioned within the shuttle valve  180  to bias the piston  186  in a first direction, (to the right with respect to the illustration).  
         [0050]    A first selector line  190  provides pressurized fluid from the actuator  12  to the shuttle valve  180 . The first selector line  190  can include a normally open valve or solenoid  192 . When the valve  192  is open, and actuator  12  provides pressurized fluid to the shuttle valve  180 , the piston  186  of the shuttle valve is moved to a first position (as shown in FIG. 3) overcoming the bias of the spring  188 .  
         [0051]    A second selector line  193  can be provided in parallel fluid communication with first line  190  between actuator  12  and shuttle valve  180 .  
         [0052]    Pressurized fluid from the shuttle valve  180  is provided to a selector piston  194 . Selector piston  194  is slidably disposed within housing  196  defining left and right chambers  198 ,  200 . Left and right chambers  198 ,  200  are in fluid communication with shuttle valve  180  by left and right fluid lines  202 ,  204 . Selector piston  194  is operably connected to range selector  178 .  
         [0053]    In operation, when valve  192  is maintained in the open position fluid pressure in lines  190  and  193  are substantially equal. As shown in the illustration, fluid pressure within shuttle valve first chamber  206  moves piston  186  to a left position in valve  180 . Pressurized fluid in line  193  is then allowed to move through valve  180  out through left line  202  into left chamber  198 . Due to the build-up of fluid pressure in left chamber  198 , piston  194  is urged toward the right with respect to the illustration. At this time, fluid in chamber  200  is forced through right fluid line  204  and valve  180  into reservoir  184 .  
         [0054]    When the vehicle operator wishes to switch the range selector  178  mode to low, a signal may be sent from control device  36  to isolation valve  32  to close valve  32  and open valve  40 . The decrease in fluid pressure causes piston  186  to be urged toward the right by spring  188 . Movement of piston  186  to the right forces fluid to flow from chamber  206  passed valve  192  and into pump  14  via inlet line  38 . The movement of piston  186  cause piston seals  208 ,  210  to move past fluid lines  202 ,  204 .  
         [0055]    Once piston  186  has moved to the right, a signal may be sent to close valve  192 , open valve  32  and close valve  40 . Closing valve  192  allows pressurized fluid to flow through line  193 . Pressurized fluid in line  193  is then directed through right line  204  into chamber  200 . Due to the increase of fluid in chamber  200 , piston  194  is urged in the left direction. The fluid in chamber  198  can then flow past valve  180  into reservoir  182 . In this manner, reciprocation of the piston  194  actuates the transfer case range selector  178 .  
         [0056]    In one embodiment, valve  170  may be closed during the actuation of range selector  178  to isolate clutch pack  166 . Clutch pack  166  may be isolated so that the actuation of range selector  178  does not affect the operation of clutch pack  166 .  
         [0057]    While the embodiments of the invention disclosed herein are presently considered to be preferred, various changes and modifications can be made without departing from the spirit and scope of the invention. The scope of the invention is indicated in the appended claims, and all changes that come within the meaning and range of equivalents are intended to be embraced therein.