Patent Publication Number: US-7896775-B2

Title: Control system for electronic range selection in a dual clutch transmission

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/893,882, filed on Mar. 8, 2007. The disclosure of the above application is incorporated herein by reference. 
    
    
     FIELD 
     The invention relates generally to a control system in a transmission, and more particularly to a control system for electronic transmission range selection in a dual clutch transmission. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art. 
     A typical multi-speed, dual clutch transmission uses a combination of two friction clutches and several dog clutch/synchronizers to achieve a plurality of forward and reverse gear or speed ratios, a Neutral, and a Park. Selection of speed ratios is typically accomplished by engaging a shift lever or other driver interface device that is connected by a shifting cable or other mechanical connection to the transmission. Alternatively, the selection of speed ratios may be controlled by an electronic transmission range selection (ETRS) system, also known as a “shift by wire” system. In an ETRS system, selection of speed ratios is accomplished through electronic signals communicated between the driver interface device and the transmission. The ETRS system reduces mechanical components, increases instrument panel space, enhances styling options, and eliminates the possibility of shifter cable misalignment with the transmission range selection levers. Accordingly, there is room in the art for a hydraulic control system having an internal ETRS system to control out-of-Park and return to Park functions in a dual clutch transmission. 
     SUMMARY 
     The present invention provides a system for shifting or controlling a dual clutch transmission where the transmission may operate in at least a first mode of operation and a second mode of operation. The system includes a controller, a plurality of solenoids, and a valve assembly. 
     An embodiment of a shift control system of the present invention includes a controller for providing a first control signal and a second control signal, a first solenoid in communication with the controller and having a first port for receiving a first fluid flow and a second port in communication with the first port for selectively receiving the first fluid flow, a second solenoid in communication with the controller and having a first port for receiving a second fluid flow and a second port in communication with the first port for selectively receiving the second fluid flow, and a valve assembly having a valve movably disposed within a valve body. The valve body includes a first inlet port in communication with the second port of the first solenoid, a second inlet port in communication with second port of the second solenoid, a third inlet port for receiving a third fluid flow, a first outlet port in communication with the third inlet port for selectively receiving the third fluid flow, and a second outlet port in communication with the third inlet port for selectively receiving the third fluid flow. The first control signal activates the first solenoid to open such that the second port of the first solenoid receives the first fluid flow and communicates the first fluid flow to the first inlet port of the valve assembly wherein the first fluid flow moves the valve to a first position. The second control signal activates the second solenoid to open such that the second port of the second solenoid receives the second fluid flow and communicates the second fluid flow to the second inlet port of the valve assembly wherein the second fluid flow moves the valve to a second position. The first position of the valve directs the third fluid flow to the first outlet port to shift the transmission to the first mode of operation and the second position of the valve directs the third fluid flow to the second outlet port to shift the transmission to the second mode of operation. 
     In one aspect of the embodiment of the present invention, the shift control system further includes a third solenoid in communication with the controller and having a first port for receiving a fourth fluid flow and a second port in communication with the first port for selectively receiving the fourth fluid flow, the second port in communication with a fourth inlet port located in the valve body, wherein a third control signal from the controller activates the third solenoid to open such that the second port of the third solenoid receives the fourth fluid flow and communicates the fourth fluid flow to the fourth inlet port of the valve assembly wherein the fourth fluid flow moves the valve to the first position. 
     In another aspect of the embodiment of the present invention, the third control signal is provided by the controller if the first solenoid does not open when activated by the first control signal. 
     In yet another aspect of the embodiment of the present invention, the third solenoid is located in a torque converter control subsystem within the transmission. 
     In yet another aspect of the embodiment of the present invention, the third solenoid is a variable bleed solenoid. 
     In yet another aspect of the embodiment of the present invention, the first solenoid is an on/off normally low solenoid. 
     In yet another aspect of the embodiment of the present invention, the second solenoid is an on/off normally low solenoid. 
     In yet another aspect of the embodiment of the present invention, the system includes an actuating assembly for initiating the first mode of operation and the second mode of operation, the actuating assembly in communication with the first outlet port and the second outlet port, wherein the third fluid flow received from the first outlet port activates the actuating assembly to initiate the first mode of operation and the third fluid flow received from the second outlet port activates the actuating assembly to initiate the second mode of operation. 
     In yet another aspect of the embodiment of the present invention, the actuating assembly includes a servo mechanism having a piston disposed within a servo body, the servo body having a first inlet port in communication with the first outlet port of the valve assembly and an optional second inlet port in communication with the second outlet port of the valve assembly, wherein the third fluid flow moves the piston within the servo body to a first position when the third fluid flow is communicated from the first outlet port of the valve assembly to the first inlet port of the servo mechanism, and wherein the third fluid flow moves the piston within the servo body to a second position when the third fluid flow is communicated from the second outlet port of the valve assembly to the second inlet port of the servo mechanism, and wherein the first position of the piston initiates the first mode of operation and the second position of the piston initiates the second mode of operation. If the optional second inlet port is not utilized, an exhaust port is connected to the second inlet port of the servo. 
     In yet another aspect of the embodiment of the present invention, the first mode of operation is an out-of-Park mode and the second mode of operation is a Park mode. 
     In yet another aspect of the embodiment of the present invention, the system includes a driver interface device in communication with the controller and operable to provide a Park control signal indicative of activating the Park mode and an out-of-Park control signal indicative of activating the out-of-Park mode, and wherein the controller provides the second control signal to initiate the Park mode when the controller receives the Park control signal and wherein the controller provides the first control signal to initiate the out-of-Park mode when the controller receives the out-of-Park control signal. 
     In yet another aspect of the embodiment of the present invention, the Park control signal, the out-of-Park control signal, the first control signal, and the second control signal are electrical signals. 
     Another embodiment of a shift control system of the present invention includes a controller for providing a first control signal and a second control signal, a first solenoid in communication with the controller and having a first port for receiving a first fluid flow and a second port in communication with the first port for selectively receiving the first fluid flow, a second solenoid in communication with the controller and having a first port for receiving a second fluid flow and a second port in communication with the first port for selectively receiving the second fluid flow, and a valve assembly having a valve movably disposed within a valve body. The valve body includes a first inlet port in communication with the second port of the first solenoid, a second inlet port in communication with second port of the second solenoid, a third inlet port for receiving a third fluid flow, and an outlet port in communication with the third inlet port for selectively receiving the third fluid flow. The first control signal activates the first solenoid to open such that the second port of the first solenoid receives the first fluid flow and communicates the first fluid flow to the first inlet port of the valve assembly wherein the first fluid flow moves the valve to a first position. The second control signal activates the second solenoid to open such that the second port of the second solenoid receives the second fluid flow and communicates the second fluid flow to the second inlet port of the valve assembly wherein the second fluid flow moves the valve to a second position. The first position of the valve allows the outlet port to receive the third fluid flow to shift the transmission to the first mode of operation and wherein the second position of the valve prevents the outlet port from receiving the third fluid flow to shift the transmission to the second mode of operation. 
     In one aspect of the embodiment of the present invention, the system includes an actuating assembly in communication with the outlet port of the valve assembly for initiating the first mode of operation and having a biasing member for initiating the second mode of operation, wherein the third fluid flow received from the outlet port activates the actuating assembly to initiate the first mode of operation and wherein the biasing member initiates the second mode of operation when the third fluid flow is not received from the outlet port of the valve assembly. 
     In another aspect of the embodiment of the present invention, the actuating assembly includes a servo mechanism having a piston engaged by the biasing member and disposed within a servo body and/or attached to the manual shaft, the servo body having an inlet port in communication with the outlet port of the valve assembly, wherein the third fluid flow moves the piston within the servo body to a first position when the third fluid flow is communicated from the outlet port of the valve assembly to the inlet port of the servo mechanism, and wherein the biasing member moves the piston within the servo body to a second position when the third fluid flow is not communicated from the outlet port of the valve assembly to the inlet port of the servo mechanism, and wherein the first position of the piston initiates the first mode of operation and the second position of the piston initiates the second mode of operation. 
     Yet another embodiment of a shift control system of the present invention includes a controller for providing a first control signal, a second control signal, and a third control signal, a first solenoid in communication with the controller and having a first port for receiving a first fluid flow and a second port in communication with the first port for selectively receiving the first fluid flow, a second solenoid in communication with the controller and having a first port for receiving a second fluid flow and a second port in communication with the first port for selectively receiving the second fluid flow, a third solenoid in communication with the controller and having a first port for receiving a third fluid flow and a second port in communication with the first port for selectively receiving the third fluid flow, and a valve assembly having a valve movably disposed within a valve body. The valve body includes a first inlet port in communication with the second port of the first solenoid, a second inlet port in communication with second port of the second solenoid, a third inlet port in communication with the second port of the third solenoid, and a fourth inlet port for receiving a fourth fluid flow, a first outlet port in communication with the fourth inlet port for selectively receiving the fourth fluid flow, and a second outlet port in communication with the fourth inlet port for selectively receiving the fourth fluid flow. The first control signal activates the first solenoid to open such that the second port of the first solenoid receives the first fluid flow and communicates the first fluid flow to the first inlet port of the valve assembly wherein the first fluid flow moves the valve to a first position. The second control signal activates the second solenoid to open such that the second port of the second solenoid receives the second fluid flow and communicates the second fluid flow to the second inlet port of the valve assembly wherein the second fluid flow moves the valve to a second position. The third control signal activates the third solenoid to open if the first solenoid does not open such that the second port of the third solenoid receives the third fluid flow and communicates the third fluid flow to the third inlet port of the valve assembly wherein the third fluid flow moves the valve to the first position. The first position of the valve directs the fourth fluid flow to the first outlet port to shift the transmission to the first mode of operation and the second position of the valve directs the fourth fluid flow to the second outlet port to shift the transmission to the second mode of operation. 
     In one aspect of the embodiment of the present invention, the third solenoid is located in a torque converter control subsystem within the transmission. 
     Further objects, aspects and advantages of the present invention will become apparent by reference to the following description and appended drawings wherein like reference numbers refer to the same component, element or feature. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
         FIG. 1  is a schematic diagram of an embodiment of a hydraulic control system for a dual clutch transmission having an internal electronic transmission range selection subsystem according to the principles of the present invention; 
         FIG. 2  is a diagrammatic view of an embodiment of the internal electronic range selection subsystem according to the present invention in a cold start park position; 
         FIG. 3  is a diagrammatic view of an embodiment of the internal electronic range selection subsystem according to the present invention in a out of park command position; 
         FIG. 4  is a diagrammatic view of an embodiment of the internal electronic range selection subsystem according to the present invention in an out of park position; 
         FIG. 5  is a diagrammatic view of an embodiment of the internal electronic range selection subsystem according to the present invention in a return to park command position; and 
         FIG. 6  is a diagrammatic view of an embodiment of the internal electronic range selection subsystem according to the present invention in a park position. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. 
     With reference to  FIG. 1 , a hydraulic control system for use in a dual clutch transmission in a motor vehicle is illustrated schematically and generally indicated by reference number  10 . The hydraulic control system  10  includes a plurality of subsystems including a line pressure subsystem  12 , an actuator control subsystem  14 , a torque converter clutch (TCC) control subsystem  16 , a lubrication control subsystem  18 , a clutch control subsystem  20 , and an electronic transmission range selection (ETRS) subsystem  22 . The hydraulic control system  10  is operable to control the dual clutch transmission, as will be described in greater detail below. 
     The line pressure subsystem  12  is operable to provide and regulate pressurized hydraulic fluid, such as oil, throughout the hydraulic control system  10 . Accordingly, the line pressure subsystem  12  may include various components (not shown) such as a hydraulic pump, a fluid source, a line pressure blow-off valve, a line pressure regulator valve, and/or a filter. In the example provided, the line pressure subsystem  12  includes a fluid communication channel or line passage, indicated by reference number  28 , which directly provides pressurized hydraulic fluid to the actuator control subsystem  14 , the ETRS subsystem  22 , the TCC control subsystem  16 , and the clutch control subsystem  20 . The line passage  28  is illustrated schematically in  FIG. 1  as a plurality of separate lines, however it should be appreciated that the line passage  28  may be a single continuous passage or a plurality of linked passages in series or in parallel without departing from the scope of the present invention. 
     The actuator control subsystem  14  controls the actuation of a plurality of actuators  30  such as synchronizers, clutches, and/or brakes. The actuators  30  are operable to selectively engage a plurality of gear sets (not shown) within the dual clutch transmission to provide a plurality of forward and reverse speed ratios and a Neutral. Accordingly, the actuator control subsystem  14  may include various components (not shown) such as solenoids and valves to actuate or control the actuators  30 . 
     The TCC control subsystem  16  controls the operation of a torque converter (not shown) in the dual clutch transmission. The TCC control subsystem  16  is in direct hydraulic communication with the ETRS subsystem  22  through a fluid passage  34  and with the lubrication control subsystem  18  through a fluid passage  36 . The fluid passages  34 ,  36  may be single channels or a plurality of linked channels in series or in parallel without departing from the scope of the present invention. 
     The lubrication control subsystem  18  provides lubrication and cooling to a variety of components throughout the dual clutch transmission. For example, the lubrication control subsystem  18  may direct hydraulic fluid through a plurality of fluid passages (not shown) to components that generate heat. 
     The clutch control subsystem  20  is operable to control a dual clutch assembly that includes a first clutch  38  and a second clutch  40 . The clutches  38 ,  40  may be used to engage one or more countershafts (not shown) within the dual clutch transmission and provide dynamic or “power-on” shifts by alternating engagement between the clutches  38 ,  40  and the actuator control sub-system  14 . 
     The ETRS subsystem  22  is operable to control a park system  42  upon receipt of electronic control signals, as will be described in further detail below. The park system  42  is operable to provide at least two modes of transmission operation including a first mode or out-of-Park mode and a second mode or Park mode. While in Park mode, the park system  42  prevents the transmission from moving the vehicle by preferably locking an output shaft (not shown) of the transmission. While in out-of-Park mode, the park system  42  is disengaged and the transmission may move the vehicle by engaging any of the forward or reverse speed ratios. 
     Turning to  FIG. 2 , the ETRS subsystem  22  will now be described in further detail. The ETRS subsystem  22  generally includes a valve assembly  50 , a first solenoid  52 , a second solenoid  54 , a servo mechanism  56 , and a park release actuator  58  that all cooperate to control the park system  42 . The valve assembly  50  includes a valve  60  located within a valve body  62 . More specifically, the valve body  62  includes a bore  64  that defines a valve chamber  66  and the valve  60  is slidably supported within the valve chamber  66 . The valve body  62  is preferably formed as an integral component of the transmission. The valve  60  includes a central body  68  that extends along a length of the valve chamber  66 . A plurality of lands  70  extend from the central body  68  and engage the bore  64  of the valve chamber  66 . The lands  70  are spaced along the length of the central body  68  and cooperate with the bore  64  of the valve chamber  66  to define a plurality of fluid chambers  72 . The valve  60  is moveable within the valve chamber  66  between a Park position, as illustrated in  FIG. 2 , and an out-of-Park position, as illustrated in  FIG. 3 . A biasing member  74 , such as a spring, is located within the valve chamber  66  between the valve  60  and a seat  76 . The seat  76  is fixed relative to the valve body  62 . The biasing member  74  biases the valve  60  to the Park position. 
     The valve body  62  further defines a plurality of ports that connect with a plurality of fluid communication channels or passages. In the example provided, the valve body  62  includes a first inlet port  75  that communicates with the valve chamber  66  at an end of the valve  60  opposite the end of the valve  60  engaged by the biasing member  74 . The first inlet port  75  communicates with a first fluid communication channel  80 . A second inlet port  77  communicates with the valve chamber  66  at an end of the valve  60  engaged by the biasing member  74 . The second inlet port  77  communicates with a second fluid communication  82  channel. A third inlet port  79  communicates with the valve chamber  66  on an end of the valve  60  proximate or near the first inlet port  75 . The third inlet port  79  communicates with a third fluid communication channel  84 . A first outlet port  81  communicates with the valve chamber  66  between the second and third inlet ports  77 ,  79 . The first outlet port  81  communicates with a fourth fluid communication channel  86 . A second outlet port  83  communicates with the valve chamber  66  between the third inlet port  79  and the first outlet port  81 . The second outlet port  83  communicates a fifth fluid communication channel  88 . The valve body  62  also defines a fourth inlet port  85  located between the outlet ports  81 ,  83  that communicates with the line channel  28 . As described in  FIG. 1 , the line channel  28  is in communication with the line pressure control subsystem  12  and provides a third fluid flow to the fourth inlet port  85 . Finally, a plurality of exhaust channels  90  communicate with the valve chamber  66  at various locations along the length of the valve chamber  66 . It should be appreciated that various other arrangements of fluid communication channels and ports may be employed without departing from the scope of the present invention. 
     The first solenoid  52 , or out-of-Park solenoid, is employed to initiate the park system  42  to move to the out-of-Park mode, as will be described in further detail below. The first solenoid  52  generally includes a first fluid port  93  in fluid communication with the pressure regulated line channel  92  and a second fluid port  95  in fluid communication with the first fluid communication channel  80 . The pressure regulated line channel  92  delivers pressurized hydraulic fluid from the line pressure subsystem  12  ( FIG. 1 ) to the first solenoid  52 . The first solenoid  52  is operable to selectively open to allow a first fluid flow from the pressure regulated line channel  92  to pass from the first fluid port  93  through the first solenoid  52  to the second fluid port  95  and to enter the first fluid communication channel  80 . The first solenoid  52  is preferably an on/off solenoid that either fully opens or closes and that is normally low or closed when not energized by a power source. 
     The second solenoid  54 , or return-to-Park solenoid, is employed to initiate the park system  42  to move to the Park mode, as will be described in further detail below. The second solenoid  54  generally includes a first fluid port  97  in fluid communication with the pressure regulated line channel  92  and a second fluid port  101  in fluid communication with the second fluid communication channel  82 . The pressure regulated line channel  92  delivers pressurized hydraulic fluid from the pump system  12  to the second solenoid  54 . The second solenoid  54  is operable to selectively open to allow a second fluid flow from the pressure regulated line channel  92  to pass from the first fluid port  97  through the second solenoid  54  to the second fluid port  101  and to enter the second fluid communication channel  82 . The second solenoid  54  is preferably an on/off solenoid that either fully opens or closes and that is normally low or closed when not energized by a power source. 
     The servo mechanism  56  is operable to translate hydraulic fluid pressure communicated through the valve assembly  50  into mechanical movement or translation of the park release actuator  58 . Accordingly, the servo mechanism  56  in the example provided is located within a cylinder  100  defined by a bore  103  of a servo body  105 . The servo mechanism  56  preferably includes a servo pin  102  coupled to a piston head  104  slidably supported within the cylinder  100 . The piston head  104  is sealingly engaged with the bore  103  of the servo body  105 . The piston head  104  cooperates with the bore  103  to define a first fluid chamber  106  and to define a second fluid chamber  108  located on an opposite side of the piston head  104  than the first fluid chamber  106 . The servo body  105  defines an inlet port  107  that communicates with the first fluid chamber  106  and an inlet port  109  that communicates with the second fluid chamber  108 . The inlet port  107  communicates with the fifth fluid communication channel  88  and the inlet port  109  communicates with the fourth fluid communication channel  86 . The piston head  104  and the servo pin  102  are slidable between a Park position, as illustrated in  FIG. 2 , and an out-of-Park position, as illustrated in  FIG. 4 . A biasing mechanism  110 , such as a spring, engages the piston head  104  and biases the piston head  104  and servo pin  102  into the Park position. 
     The park release actuator  58  is coupled to the servo pin  102  of the servo mechanism  56  and is operable to engage the park system  42 . Movement of the servo pin  102  of the servo mechanism  56  in turn actuates the park release actuator  58 , as will be described in further detail below. The park release actuator  58  may include switches and sensors employed to determine the operating mode of the park system  42  and may be in communication with the controller  120 . 
     The ETRS subsystem  22  further includes a fail-safe feature using a third solenoid  114  that generally includes a first fluid port  111  in fluid communication with the pressure regulated line channel  92  and a second fluid port  113  in fluid communication with the third fluid communication channel  84 . The pressure regulated line channel  92  delivers pressurized hydraulic fluid from the pump system  12  to the third solenoid  114 . The third solenoid  114  is operable to selectively open to allow a fourth fluid flow from the pressure regulated line channel  92  to pass from the first fluid port  111  through the third solenoid  114  to the second fluid port  113  and to enter the third fluid communication channel  84 . The third solenoid  114  is preferably a variable bleed, normally low or closed, torque converter clutch regulator solenoid that is part of the TCC control subsystem  16 . 
     A controller  120  is in electronic communication with various components of the hydraulic control system  10  including the solenoids  52 ,  54 ,  114  and the park release actuator  58 . The controller  120  may be a transmission control module or an engine control module and is preferably an electronic device having a preprogrammed digital computer or processor, control logic, memory used to store data, and at least one I/O peripheral. The control logic includes a plurality of logic routines for monitoring, manipulating, and generating data. However, various other types of controllers may be employed without departing from the scope of the present invention. The controller  120  receives input signals from a driver interface device  122  such as a shift lever. The input signals are indicative of the desired operating mode of the transmission. In the example of an automatic transmission, the desired operating modes may be Drive, Neutral, Reverse, Park, etc, or Park and out-of-Park. The controller  120  then electronically communicates with the hydraulic control system  10 , including the solenoids  52 ,  54 ,  114 , using a plurality of control signals to initiate the desired transmission operating mode according to the signals communicated from the driver interface device  122 . 
     For example,  FIG. 2  illustrates the ETRS subsystem  22  in a cold start Park mode or condition wherein the driver interface device  122  is in a Park condition, the park system  42  is in the Park mode, and the motor vehicle has just been started. In this condition, the valve  60  is in the Park position, and the third fluid flow from the line channel  28  pumped from the line pressure control subsystem  12  is directed through a fluid chamber  72  in the valve assembly  50 , into the fifth fluid communication channel  88 , and on into the first fluid chamber  106 . The third fluid flow in the first fluid chamber  106  acts against the piston  104  along with the biasing member  110  to position the servo mechanism  56  to the Park position. The Park position of the servo mechanism  56  in turn mechanically positions the park release actuator  58  to keep the park system  42  in the Park mode. 
     When the driver interface device  122  signals to the controller  120  to move out-of-Park, the controller  120  electronically communicates with the out-of-Park solenoid  52  and signals the out-of-Park solenoid  52  to open. The return to park solenoid  54  remains closed. The first fluid flow passes through the out-of-Park solenoid  52  and into the first fluid communication channel  80  and into the valve assembly  50 . The first fluid flow acts against the valve  60  and moves the valve  60  into the out-of-Park position, as is illustrated in  FIG. 3 . The third fluid flow from the line channel  28  is diverted by a land  70  in the valve assembly  50  from the fifth fluid communication channel  88  to the fourth fluid communication channel  86 . The third fluid flow travels through the fourth fluid communication channel  86  to the second fluid chamber  108  in the servo mechanism  56 . Additionally, hydraulic fluid remaining in the fifth fluid communication channel  88  exits the ETRS subsystem  22  through one of the exhaust channels  90 . 
     The third fluid flow in the second fluid chamber  108  acts against the piston  104  and moves the servo mechanism  56  into the out-of-Park position, as illustrated in  FIG. 4 . The servo mechanism  56  mechanically engages the park release actuator  58  which mechanically actuates the park system  42  and moves the park system  42  from the Park mode to the out-of-Park mode. This allows the transmission to provide forward gear ratios, neutral, and/or reverse. 
     When the driver interface device  122  signals to the controller  120  to return to park, the controller  120  electronically communicates with the out-of-Park solenoid  52  and signals the out-of-Park solenoid  52  to close and electronically communicates with the return to Park solenoid  54  and signals the return to Park solenoid  54  to open. Accordingly, the second fluid flow passes from the pressure regulated line channel  92  through the return to Park solenoid  54  and into the second fluid communication channel  82  and into the valve assembly  50 . The second fluid flow acts against the valve  60  and moves the valve  60  back into the Park position, as illustrated in  FIG. 5 . The third fluid flow from the line channel  28  is diverted by a land  70  in the valve assembly  50  from the fourth fluid communication channel  86  back to the fifth fluid communication channel  88 . The third fluid flow travels through the fifth fluid communication channel  88  to the first fluid chamber  106  in the servo mechanism  56 . Additionally, hydraulic fluid remaining in the fourth fluid communication channel  86  exits the ETRS subsystem  22  through one of the exhaust channels  90 . 
     The third fluid flow in the first fluid chamber  106  acts against the piston  104  and moves the servo mechanism  56  back into the Park position, as illustrated in  FIG. 6 . The servo mechanism  56  mechanically engages the park release actuator  58  which mechanically actuates the park system  42  and moves the park system  42  from the out-of-Park mode to the Park mode. This prevents the transmission from providing forward gear ratios, neutral, and/or reverse. 
     In the event of a failure of the out-of-Park solenoid  52 , the controller  120  may signal the TCC regulator solenoid  114  to open such that the fourth fluid flow passes from the pressure regulated line channel  92  through the TCC regulator solenoid  114  and into the third fluid communication channel  84  and into the valve assembly  50 . The fourth fluid flow acts against the valve  60  and is operable to move the valve  60  into the out-of-Park position. 
     In an alternate embodiment of the ETRS subsystem  22 , the servo mechanism does not contain the two fluid chambers  106  and  108 , and instead utilizes a single fluid chamber  108 . In this case, the inlet port  107  is connected directly to an exhaust thereby eliminating fluid communication channel  88 . Accordingly, a shorter valve  60  may be employed. 
     The description of the invention is merely exemplary in nature and variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.