Abstract:
A servo valve for shifting a transmission between a park and out of park position includes a valve housing and a park servo. A first and second solenoid is disposed in the valve housing for transmitting a respective first or second signal to shift the transmission to the respective first or second state of operation. The park servo is fluidly connected to the transmission and is responsive to the first and second signals to shift the transmission to the respective positions. Fluid pressure within the valve housing moves a valve member therein to move a piston within the park servo to shift the transmission to the corresponding position. A third solenoid transmits a third signal in combination with the second signal to latch and hold the valve member in the corresponding position.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The subject patent application claims priority to and all the benefits of U.S. Provisional Patent Application Ser. No. 61/042,375, filed on Apr. 4, 2008, which is expressly incorporated herein by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to a system and method for controlling park positions in a park by wire system for a hybrid transmission. 
       BACKGROUND OF THE INVENTION 
       [0003]    A typical vehicle includes a transmission which is shiftable between a park position, for parking the vehicle, and various out of park positions, for allowing the vehicle to move. A cable extends between the transmission and a lever, inside the vehicle. A user of the vehicle physically moves the lever to pull or push the cable and physically shift the transmission between the park position and the out of park position. 
       SUMMARY OF THE INVENTION 
       [0004]    A servo assembly is configured to shift a hybrid transmission between a first state of operation and a second state of operation. The servo assembly includes a valve housing that extends between a first end and a second end. The valve housing defines a valve chamber that extends between the ends. A relay valve is slidably disposed within the valve chamber between a first position and a second position. A park servo is in fluid communication with the valve chamber and is movable between a first condition, to move the hybrid transmission to the first state of operation, and a second condition, to move the transmission to the second state of operation. A pressure supply port is defined in the valve housing and opens to the valve chamber. The pressure supply port is configured to selectively open to allow fluid to enter the valve housing through the pressure supply port and move the park servo to the second condition. The park servo is configured to move the hybrid transmission to the second state of operation when the park servo moves to the second condition. 
         [0005]    A method of shifting a hybrid transmission between a first state of operation and a second state of operation with a servo assembly having a valve housing and a park servo includes directing fluid through a pressure supply line to a valve chamber of the valve housing to apply a fluid pressure to a relay valve. A relay valve is slid to one of a first position, corresponding to the first state of operation, and a second position, corresponding to the second state of operation. Fluid is directed from one of the valve chamber and the park servo to the other one of the valve chamber and the park servo as a function of the relay valve being in one of the second position and the first position, respectively. 
         [0006]    A servo assembly is configured to shift a hybrid transmission between a park position and an out of park position. The servo assembly includes a valve housing that extends between a first end and a second end and defines a valve chamber that extends between the ends. A relay valve is slidably disposed within the valve chamber between a first position and a second position. A first solenoid is disposed in the first end of the valve housing and is configured to transmit fluid into the valve chamber at a first solenoid pressure to move the relay valve to a first position. A second solenoid is disposed in the second end of the valve housing and is configured to transmit fluid into the valve chamber at a second solenoid pressure to move the relay valve to a second position. A park servo is in fluid communication with the valve chamber and is movable between a first condition and a second condition. A pressure supply port is defined in the valve housing and opens to the valve chamber. The pressure supply port is configured to selectively open and allow fluid to enter the valve housing through the pressure supply port and move the park servo from the first condition to the second condition. The park servo is configured to move the hybrid transmission from the park position to the out of park position when the park servo moves from the first condition to the second condition. 
         [0007]    The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    Referring now to the figures, which are exemplary embodiments and wherein like elements are numbered alike: 
           [0009]      FIG. 1  is a schematic view depicting a hydraulic mechanism for controlling a hybrid transmission with the mechanism in a park position; and 
           [0010]      FIG. 2  is a schematic view depicting the hydraulic mechanism of  FIG. 1  with the mechanism in an out of park position. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0011]    Referring to the drawings, wherein like reference numbers refer to like components,  FIG. 1  shows a servo assembly or “park by wire mechanism”  10  for shifting a transmission  12  between a first position and a second position. In the embodiment shown in the Figures, the first position is a park position, shown in  FIG. 1 , and the second position is an out of park position, shown in  FIG. 2 , in a park by wire system for a vehicle. It should be appreciated, however, that the first position and the second position are not limited to being the positions shown and described herein as other positions may also be used as known to those skilled in the art. The servo assembly  10  includes a valve assembly  14  and a park servo  15 . A plurality of solenoids  20 ,  22 ,  28  are configured for setting the park position. The park servo  15  is configured for moving between a park position and an out of park position. The solenoids  20 ,  22 ,  28  are in operative communication with a shifter (not shown), e.g., a switch, etc., for selecting between the park position and the out of park position for the transmission  12 . Therefore, by using the shifter to select the desired position of the transmission  12 , the shifter sends a series of signals to one of the solenoids  20 ,  22 ,  28  for moving the park servo  15  to the corresponding desired transmission  12  position. 
         [0012]    The valve assembly  14  includes a valve housing  16  which extends between opposing ends  24 ,  26  and defines a valve chamber  18  that extends between the ends  24 ,  26 . A return to park solenoid (RTP solenoid)  20 , which produces a RTP signal pressure, is disposed at the first end  24  of the valve housing  16  and an out of park solenoid (OOP solenoid)  22 , which produces an OOP signal pressure, is disposed at the second end  26  of the valve housing  16 , opposite the first end  24  of the valve housing  16 . Therefore, the RTP and the OOP solenoids  20 ,  22  are in fluid communication with the valve chamber  18  of the valve housing  16 . 
         [0013]    A Y solenoid  28 , which produces a Y signal pressure, is operatively connected to the valve assembly  14 . A Y signal port  31  is defined by the valve housing  16 . A Y signal line  29  is disposed between the Y solenoid  28  and the Y signal port  31  such that the Y solenoid  28  is in fluid communication with the valve chamber  18  of the valve housing  16 . The Y solenoid  28  supplies a Y signal pressure to the valve housing  16  through the Y signal port  31 . 
         [0014]    A solenoid pressure supply line  32  is in fluid communication with the RTP solenoid  20 , via a RTP control port  34  that opens to the valve chamber  18 , and the OOP solenoid  22 , via an OOP control port  36  that opens to the valve chamber  18 . The solenoid pressure supply line  32  is also in fluid communication with the Y solenoid  28 . Therefore, the solenoid pressure supply line  32  supplies a solenoid pressure to the RTP solenoid  20 , the OOP solenoid  22 , and the Y solenoid  28 . An inlet pressure supply line  38  is in fluid communication with a pressure supply port  40  defined in the valve housing  16  to supply an inlet pressure to the valve chamber  18  within the valve housing  16 . The pressure supply port  40  may be defined in the valve housing  16  between the Y signal port  31  and the RTP solenoid  20 . The inlet pressure is typically at a higher pressure than the solenoid pressure moving through the solenoid pressure supply line  32 . Therefore, each solenoid  20 ,  22 ,  28  is in fluid communication with the valve chamber  18  of the valve assembly  14 . 
         [0015]    A sleeve  42  may be disposed within the valve chamber  18  of the valve housing  16 , adjacent the RTP solenoid  20 . The sleeve  42  defines a hollow interior  44 . A return spring  30 , which may be a coil spring, is disposed within the sleeve  42  between the RTP solenoid  20  and the retainer  46 . An actuator  48  may be slidably disposed within the sleeve  42  between the return spring  30  and the retainer  46 . The retainer  46  keeps the actuator  48  contained within the sleeve  42  during assembly only. The actuator  48  is generally cylindrical, but may be any shape known to those skilled in the art. A relay valve  50  is slidably disposed within the valve chamber  18 , adjacent the OOP solenoid  22 . Therefore, the relay valve  50  is slidably disposed between the OOP solenoid  22  and the actuator  48 . The return spring  30  biases the actuator  48  away from the RTP solenoid  20 , which pushes the relay valve  50  away from the RTP solenoid  20 . 
         [0016]    The relay valve  50  includes a first section  51 , a second section  53 , and an intermediate section  55 . A connector  57  extends between the first section  51  and the intermediate section  55 . The intermediate section  55  extends between the connector  57  and the second section  53 . The first section  51  is disposed in the valve chamber  18  adjacent the actuator  48 . The second section  53  is disposed in the valve chamber  18  adjacent the OOP solenoid  22 . The intermediate section  55  is disposed in the valve chamber  18  such that an intermediate chamber  59  is defined between the first section  51  and the intermediate section  55 . A nose  61  may extend from the first section  51 , opposite the connector  57 , such that the nose  61  keeps the actuator  48  spaced from the first section  51 . The surface area presented by the first section  51  within the valve chamber  18  is larger than the surface area presented by the second section  53  within the valve chamber  18 . 
         [0017]    Prior to the OOP solenoid  22  receiving the OOP pressure signal to activate and open, the valve chamber  18  must first be exhausted. When the OOP solenoid  22  receives the signal to shift the transmission  12  out of the park position, the OOP solenoid  22  opens and fluid F moves through the OOP solenoid  22  and into the valve chamber  18  between the relay valve  50  and the OOP solenoid  22  to apply the OOP signal pressure to the area on the second side of the second section  53 . If the OOP solenoid  22  is open, then the RTP solenoid  20  is de-energized such that the RTP solenoid  20  is closed. The OOP signal pressure of fluid F that enters the valve chamber  18  and is acting on the second side of the second section  53  causes the relay valve  50  to move toward the sleeve  42 . Eventually, the relay valve  50  pushes the actuator  48  and the actuator  48  compresses the return spring  30 . The pressure that moves the relay valve  50  needs to be great enough to not only slide the relay valve  50  and the actuator  48  toward the RTP solenoid  20 , but also great enough to compress the return spring  30 . As long as the OOP solenoid  22  is actuated, fluid F remains in the valve chamber  18  between the second side of the second section  53  and the OOP solenoid  22 , keeping the return spring  30  compressed by the actuator  48  and the relay valve  50 . 
         [0018]    If the RTP solenoid  20  receives the signal to shift the transmission  12  to the park position, the RTP solenoid  20  opens and fluid F moves through the return to park solenoid  20  and into the valve chamber  18  between the actuator  48  and the RTP solenoid  20 . If the RTP solenoid  20  is open, the OOP solenoid  22  is de-energized such that the OOP solenoid  22  is closed. The pressure of fluid F that enters the valve chamber  18  from the RTP solenoid  20  acts on an area on the actuator  48  which causes the actuator  48  and the relay valve  50  to slide away from the RTP solenoid  20 , toward the OOP solenoid  22 . The pressure that moves the actuator  48  needs to be great enough to also slide the relay valve  50 . 
         [0019]    The park servo  15  is operatively connected between the valve housing  16  of the isolator valve  14  and the transmission  12  for shifting into and out of the park position based on whether the RTP or the OOP solenoid  20 ,  22  is energized. The out of park and the return to park positions are based solely on the position of the relay valve  50 . The park servo  15  is slidably disposed within a servo housing  52 . The servo housing  52  defines a hollow core  54  and extends to an end. A retainer  56 , which is disposed at the end of the servo housing  52 , extends to partially cover the end for retaining the park servo  15  within the servo housing  52  when the servo slides toward the retainer  56 . A neck  58  is formed on the servo housing  52 , opposite the retainer  56 . The neck  58  is a hollow portion of the servo housing  52  and the neck  58  receives a portion of the park servo  15 . The park servo  15  is slidably disposed within the neck  58  and a seal is formed between the neck  58  and the park servo  15 , as the park servo  15  slides within the neck  58 . A piston  60  extends about a portion of the park servo  15 . The piston  60  moves with the park servo  15  and is therefore slidably disposed within the servo housing  52 , while sealing therebetween. A servo chamber  62  is defined within the servo housing  52 , between the neck  58  of the servo chamber  62  and the piston  60  of the park servo  15 . The servo chamber  62  changes volume based on the position of the piston  60  within the housing. A servo supply line  64  extends between the servo housing  52  and the valve housing  16  and supplies a fluid pressure to the servo chamber  62  within the servo housing  52 . The servo supply line  64  extends to a servo supply port  66  that opens to the intermediate chamber  59  defined between the first section  51  and the intermediate section  55 . The servo supply port  66  is defined in the valve housing  16  between the pressure supply port  40  and the Y signal port  31 . An exhaust port  33  is defined by the valve housing  16  between the servo supply port  66  and the Y signal port  31 . Both the servo supply port  66  and the exhaust port  33  are in fluid communication with the intermediate chamber  59  when the RTP solenoid  20  is actuated such that the RTP signal pressure is acting on the actuator  48  to move the relay valve  50  toward the OOP solenoid  22 . When the relay valve  50  is in this position, fluid F from the servo chamber  62  exits the servo chamber  62  via the servo supply line  64  and enters the intermediate chamber  59  and is exhausted from the intermediate chamber  59  and relay valve via the exhaust port  33 . Both the servo supply port  66  and the pressure supply port  40  open to the intermediate chamber  59  when the OOP solenoid  22  is actuated such that the OOP signal pressure is acting on the second side of the second section  53  of the relay valve  50  to move the relay valve  50  and the actuator  48  toward the RTP solenoid  20 . Fluid F enters the pressure supply port  40  and flows into the intermediate chamber  59  at a latch pressure. Fluid F acts against the area of the second side of the first section  51  to hold the relay valve  50  and the actuation  48  toward the RTP solenoid. The latch pressure is sufficient to overcome the spring force of the return spring  30  and hold the relay valve  50  in this position. Pressurizing the park servo  15  pulls the transmission  12  out of the park position, as shown in  FIG. 2 , and depressurizing, or exhausting, the park servo  15  shifts the transmission  12  into the park position, as shown in  FIG. 1 . 
         [0020]    The Y solenoid  28  may operate to send the Y signal to the valve chamber  18  of the valve housing  16  through the Y supply line  29 . If the out of park position is desired and the RTP solenoid  20  does not de-energize, the Y solenoid  28  can be energized and the pressure of the Y signal will combine with the pressure from the OOP solenoid  22  and the latch pressure and act on the second side of the intermediate section  55  of the relay valve  50  to overcome the pressure from the RTP solenoid  20  and spring force of the return spring  30 . Additionally, if the OOP solenoid  22  does not energize, the Y signal can operate to overcome the spring force of the return spring  30  to shift from the park position to the out of park position. These features provide two redundant methods for shifting from the park position to the out of park position. 
         [0021]    When the OOP solenoid  22  is activated, as shown in  FIG. 2 , the OOP solenoid  22  opens and fluid F enters the valve chamber  18  through the OOP solenoid  22  at the OOP signal pressure to apply a force on the second side of the second section  53  of the relay valve  50  to slidably move the relay valve  50  and the actuation toward the RTP solenoid  20 . The relay valve  50  pushes the actuator  48  to slide the actuator  48  against the return spring  30 , to compress the return spring  30 . When the valve assembly  14  is acted upon by the OOP signal pressure, the relay valve  50  strokes and opens the servo supply port  66  to supply fluid to the servo chamber  62  of the park servo  15 . In the out of park position, pressure at the servo supply port  66  acts upon the differential area of the second side of the first section  51  of the relay valve  50  to latch the valve assembly  14  in the out of park position. To return to park, the RTP solenoid  20  and the spring  30  combine to overcome the latch force acting on the relay valve  50  and move the relay valve  50  to a position where fluid F is exhausted from the servo chamber  62  through the servo supply line  64  and into the intermediate chamber  59 . From the intermediate chamber  59 , fluid F is exhausted through the exhaust port  33 . 
         [0022]    To keep the transmission  12  in the park position, the RTP solenoid  20  is energized, as shown in  FIG. 1 , and the RTP signal output pressure from the RTP solenoid  20  acts on the actuator  48  of the valve assembly  14 . The RTP signal pressure from the RTP solenoid  20  combines with the spring force of the return spring  30  toward the OOP solenoid  22  to hold the valve assembly  14  in the park position. Even if the OOP solenoid  22  comes on, or is energized, the valve assembly  14  will remain in the park position because the output pressure, and the resultant force, applied by the OOP solenoid  22  to the second section  53  of the relay valve  50  cannot overcome the force applied by the RTP solenoid  20  when combined with the spring force of the return spring  30 . The RTP solenoid  20  must first de-energize to allow the system to shift from the park position to the out of park position. This feature prevents unexpected shifts from the park position to the out of park position. 
         [0023]    Once the transmission  12  is out of the park position, the force provided by the OOP signal pressure from the OOP solenoid  22  combines with the latch force from a servo latch pressure that is created when the high pressure from the inlet pressure supply line  38  is routed through the pressure supply port  40  and into the servo supply line  64  to maintain the valve assembly  14  in the out of park position. These two forces are greater than the forces of the RTP solenoid  20  when combined with the spring force of the return spring  30 . Therefore, the forces of the OOP solenoid  22  and the servo latch pressure provide a redundant method to prevent the transmission  12  from unexpectedly returning to the park position. To typically return to the park position, the OOP solenoid  22  is de-energized and the RTP solenoid  20  is energized. The force of the RTP signal pressure from the RTP solenoid  20  combines with the spring force of the return spring  30  to overcome the force of the servo latch and return to the park position. In the event that the OOP solenoid  22  does not release, i.e., is not de-energized, and the servo latch cannot be broken, the hybrid system allows the engine to stop until the park position is achieved. As the system hydraulic pressure is lost, the valve assembly  14  destrokes under the spring force of the return spring  30 , allowing the park servo  15  to exhaust and return to the park position. 
         [0024]    While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.