Patent Publication Number: US-8528711-B2

Title: Control system for a dual clutch transmission

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/285,483, filed on Dec. 10, 2009, which is hereby incorporated in its entirety herein by reference. 
    
    
     TECHNICAL FIELD 
     The invention relates to a control system for a dual clutch transmission, and more particularly to an electro-hydraulic control system having a plurality of solenoids and valves operable to actuate a plurality of actuators within the dual clutch transmission. 
     BACKGROUND 
     A typical multi-speed, dual clutch transmission uses a combination of two friction clutches and several dog clutch/synchronizers to achieve “power-on” or dynamic shifts by alternating between one friction clutch and the other, with the synchronizers being “pre-selected” for the oncoming ratio prior to actually making the dynamic shift. “Power-on” shifting means that torque flow from the engine need not be interrupted prior to making the shift. This concept typically uses countershaft gears with a different, dedicated gear pair or set to achieve each forward speed ratio. Typically an electronically controlled hydraulic control circuit or system is employed to control solenoids and valve assemblies. The solenoid and valve assemblies actuate clutches and synchronizers to achieve the forward and reverse gear ratios. 
     While previous hydraulic control systems are useful for their intended purpose, the need for new and improved hydraulic control system configurations within transmissions which exhibit improved performance, especially from the standpoints of efficiency, responsiveness and smoothness, is essentially constant. Accordingly, there is a need for an improved, cost-effective hydraulic control system for use in a dual clutch transmission. 
     SUMMARY 
     A hydraulic control system for a dual clutch transmission includes a plurality of pressure and flow control devices and logic valves in fluid communication with a plurality of clutch actuators and with a plurality of synchronizer actuators. The clutch actuators are operable to actuate a plurality of torque transmitting devices and the synchronizer actuators are operable to actuate a plurality of synchronizer assemblies. Selective activation of combinations of the pressure control solenoids and the flow control solenoids allows for a pressurized fluid to activate at least one of the clutch actuators and synchronizer actuators in order to shift the transmission into a desired gear ratio. 
     In one example of the hydraulic control system, the hydraulic control system includes an electric pump and an accumulator that provide a pressurized hydraulic fluid. 
     In another example of the hydraulic control system, the hydraulic control system includes two pressure control devices and two flow control devices used to actuate the dual clutch. 
     In yet another example of the hydraulic control system, the hydraulic control system includes two pressure control devices, two flow control devices, and two logic valves used to actuate the plurality of synchronizer assemblies. 
     Further features, 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. 
    
    
     
       BRIEF DESCRIPTION OF THE 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 exemplary dual clutch transmission having a hydraulic control system according to the principles of the present invention; and 
         FIGS. 2A-B  are schematic diagrams of an embodiment of a hydraulic control system for a dual clutch transmission according to the principles of the present invention. 
     
    
    
     DESCRIPTION 
     With reference to  FIG. 1 , an exemplary dual clutch automatic transmission incorporating the present invention is illustrated and generally designated by the reference number  10 . The dual clutch transmission  10  includes a typically cast, metal housing  12  which encloses and protects the various components of the transmission  10 . The housing  12  includes a variety of apertures, passageways, shoulders and flanges which position and support these components. While the housing  12  is illustrated as a typical rear wheel drive transmission, it should be appreciated that the transmission  10  may be a front wheel drive transmission or a rear wheel drive transmission without departing from the scope of the present invention. The transmission  10  includes an input shaft  14 , an output shaft  16 , a dual clutch assembly  18 , and a gear arrangement  20 . The input shaft  14  is connected with a prime mover (not shown) such as an internal combustion gas or Diesel engine or a hybrid power plant. The input shaft  14  receives input torque or power from the prime mover. The output shaft  16  is preferably connected with a final drive unit (not shown) which may include, for example, propshafts, differential assemblies, and drive axles. The input shaft  14  is coupled to and drives the dual clutch assembly  18 . The dual clutch assembly  18  preferably includes a pair of selectively engageable torque transmitting devices including a first torque transmitting device  22  and a second torque transmitting device  24 . The torque transmitting devices  22 ,  24  are preferably dry clutches. The torque transmitting devices  22 ,  24  are mutually exclusively engaged to provide drive torque to the gear arrangement  20 . 
     The gear arrangement  20  includes a plurality of gear sets, indicated generally by reference number  26 , and a plurality of shafts, indicated generally by reference number  28 . The plurality of gear sets  26  includes individual intermeshing gears that are connected to or selectively connectable to the plurality of shafts  28 . The plurality of shafts  28  may include layshafts, countershafts, sleeve and center shafts, reverse or idle shafts, or combinations thereof. It should be appreciated that the specific arrangement and number of the gear sets  26  and the specific arrangement and number of the shafts  28  within the transmission  10  may vary without departing from the scope of the present invention. In the example provided, the transmission  10  provides seven forward gears and a reverse gear. 
     The gear arrangement  20  further includes a first synchronizer assembly  30 A, a second synchronizer assembly  30 B, a third synchronizer assembly  30 C, and a fourth synchronizer assembly  30 D. The synchronizer assemblies  30 A-D are operable to selectively couple individual gears within the plurality of gear sets  26  to the plurality of shafts  28 . Each synchronizer assembly  30 A-D is disposed either adjacent certain single gears or between adjacent pairs of gears within adjacent gear sets  26 . Each synchronizer assembly  30 A-D, when activated, synchronizes the speed of a gear to that of a shaft and a positive clutch, such as a dog or face clutch. The clutch positively connects or couples the gear to the shaft. The clutch is bi-directionally translated by a shift rail and fork assembly (not shown) within each synchronizer assembly  30 A-D. 
     The transmission also includes a transmission control module  32 . The transmission control module  32  is preferably an electronic control 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. The transmission control module  32  controls the actuation of the dual clutch assembly  18  and the synchronizer assemblies  30 A-D via a hydraulic control system  100  according to the principles of the present invention. 
     Turning to  FIGS. 2A-B , the hydraulic control system  100  of the present invention is operable to selectively engage the dual clutch assembly  18  and the synchronizer assemblies  30 A-D by selectively communicating a hydraulic fluid  102  from a sump  104  to a plurality of shift actuating devices, as will be described in greater detail below. The sump  104  is a tank or reservoir preferably disposed at the bottom of the transmission housing  12  to which the hydraulic fluid  104  returns and collects from various components and regions of the automatic transmission  10 . The hydraulic fluid  102  is forced from the sump  104  via a pump  106 . The pump  106  is preferably driven by an electric engine (not shown) or any other type of prime mover and may be, for example, a gear pump, a vane pump, a gerotor pump, or any other positive displacement pump. The pump  106  includes an inlet port  108  and an outlet port  110 . The inlet port  108  communicates with the sump  104  via a suction line  112 . The outlet port  110  communicates pressurized hydraulic fluid  102  to a supply line  114 . The supply line  114  is in communication with a spring biased blow-off safety valve  116 , a pressure side filter  118 , and a spring biased check valve  120 . The spring biased blow-off safety valve  116  communicates with the sump  104 . The spring biased blow-off safety valve  116  is set at a relatively high predetermined pressure and if the pressure of the hydraulic fluid  102  in the supply line  114  exceeds this pressure, the safety valve  116  opens momentarily to relieve and reduce the pressure of the hydraulic fluid  102 . The pressure side filter  118  is disposed in parallel with the spring biased check valve  120 . If the pressure side filter  118  becomes blocked or partially blocked, pressure within supply line  114  increases and opens the spring biased check valve  120  in order to allow the hydraulic fluid  102  to bypass the pressure side filter  118 . 
     The pressure side filter  118  and the spring biased check valve  120  each communicate with an outlet line  122 . The outlet line  122  is in communication with a second check valve  124 . The second check valve  124  is in communication with a main supply line  126  and is configured to maintain hydraulic pressure within the main supply line  126 . The main supply line  126  supplies pressurized hydraulic fluid to an accumulator  130  and a main pressure sensor  132 . The accumulator  130  is an energy storage device in which the non-compressible hydraulic fluid  102  is held under pressure by an external source. In the example provided, the accumulator  130  is a spring type or gas filled type accumulator having a spring or compressible gas that provides a compressive force on the hydraulic fluid  102  within the accumulator  130 . However, it should be appreciated that the accumulator  130  may be of other types, such as a gas-charged type, without departing from the scope of the present invention. Accordingly, the accumulator  130  is operable to supply pressurized hydraulic fluid  102  back to the main supply line  126 . However, upon discharge of the accumulator  130 , the second check valve  124  prevents the pressurized hydraulic fluid  102  from returning to the pump  106 . The accumulator  130 , when charged, effectively replaces the pump  106  as the source of pressurized hydraulic fluid  102 , thereby eliminating the need for the pump  106  to run continuously. The main pressure sensor  132  reads the pressure of the hydraulic fluid  102  within the main supply line  126  in real time and provides this data to the transmission control module  32 . 
     The main supply line  126  is channeled through a heat sink  134  used to cool the controller  32 , though it should be appreciated that the heat sink  134  may be located elsewhere or removed from the hydraulic control system  100  without departing from the scope of the present invention. The main supply line  126  supplies pressurized hydraulic fluid  102  to four pressure control devices including a first clutch pressure control device  136 , a second clutch pressure control device  138 , and a first actuator pressure control device  140 , and a second actuator pressure control device  141 . 
     The first clutch pressure control device  136  is preferably an electrically controlled variable force solenoid having an internal closed loop pressure control. Various makes, types, and models of solenoids may be employed with the present invention so long as the first clutch pressure control device  136  is operable to control the pressure of the hydraulic fluid  102 . The first clutch pressure control device  136  includes an inlet port  136 A that communicates with an outlet port  136 B when the first clutch pressure control device  136  is activated or energized and includes an exhaust port  136 C that communicates with the outlet port  136 B when the first clutch pressure control device  136  is inactive or de-energized. Variable activation of the first clutch pressure control device  136  regulates or controls the pressure of the hydraulic fluid  102  as the hydraulic fluid  102  communicates from the inlet port  136 A to the outlet port  136 B. The internal closed loop pressure control provides pressure feedback within the solenoid to adjust the amount of flow to the outlet port  1368  based on a particular current command from the controller  32 , thereby controlling pressure. The inlet port  136 A is in communication with the main supply line  126 . The outlet port  136 B is in communication with an intermediate line  142 . The exhaust port  136 C is in communication with the sump  104 . 
     The intermediate line  142  communicates the hydraulic fluid  102  from the first clutch pressure control device  136  to a first clutch flow control device  144 , to a first pressure limit control valve  146 , and a three way ball check valve  147 . The first clutch flow control device  144  is preferably an electrically controlled variable force solenoid that is operable to control a flow of the hydraulic fluid  102  from the first clutch flow control device  144  in order to actuate the first torque transmitting device  22 , as will be described in greater detail below. The first clutch flow control device  144  includes an inlet port  144 A that communicates with an outlet port  144 B when the first clutch flow control device  144  is activated or energized and includes an exhaust port  144 C that communicates with the outlet port  144 B when the first clutch flow control device  144  is inactive or de-energized. Variable activation of the first clutch flow control device  144  regulates or controls the flow of the hydraulic fluid  102  as the hydraulic fluid  102  communicates from the inlet port  144 A to the outlet port  144 B. The inlet port  144 A is in communication with the intermediate line  142 . The outlet port  144 B is in communication with a first clutch supply line  148  and a flow restriction orifice  150 . The exhaust port  144 C is in communication with the sump  104 . The first pressure limit control valve  146  is disposed in parallel with the first clutch flow control solenoid  144  and is in communication with the first clutch supply line  148 . If pressure within the first clutch supply line  148  exceeds a predetermined value, the first pressure limit control valve  146  opens to relieve and reduce the pressure. 
     The first clutch supply line  148  is in fluid communication with an inlet/outlet port  152 A in a first clutch piston assembly  152 . The first clutch piston assembly  152  includes a single acting piston  154  slidably disposed in a cylinder  156 . The piston  154  translates under hydraulic pressure to engage the first torque transmitting device  22 , shown in  FIG. 1 . When the first clutch flow control device  144  is activated or energized, a flow of pressurized hydraulic fluid  102  is provided to the first clutch supply line  148 . The flow of pressurized hydraulic fluid  102  is communicated from the first clutch supply line  148  to the first clutch piston assembly  152  where the pressurized hydraulic fluid  102  translates the piston  154 , thereby engaging the first torque transmitting device  22 . When the first clutch flow control solenoid  144  is de-energized, the inlet port  144 A is closed and hydraulic fluid from the cylinder  156  passes from the outlet port  144 B to the exhaust port  144 C and into the sump  104 , thereby disengaging the first torque transmitting device  22 . 
     The second clutch pressure control device  138  is preferably an electrically controlled variable force solenoid having an internal closed loop pressure control. Various makes, types, and models of solenoids may be employed with the present invention so long as the second clutch pressure control device  138  is operable to control the pressure of the hydraulic fluid  102 . The second clutch pressure control device  138  includes an inlet port  138 A that communicates with an outlet port  138 B when the second clutch pressure control device  138  is activated or energized and includes an exhaust port  138 C that communicates with the outlet port  138 B when the second clutch pressure control device  138  is inactive or de-energized. Variable activation of the second clutch pressure control device  138  regulates or controls the pressure of the hydraulic fluid  102  as the hydraulic fluid  102  communicates from the inlet port  138 A to the outlet port  138 B. The internal closed loop pressure control provides pressure feedback within the solenoid to adjust the amount of flow to the outlet port  1388  based on a particular current command from the controller  32 , thereby controlling pressure. The inlet port  138 A is in communication with the main supply line  126 . The outlet port  138 B is in communication with an intermediate line  158 . The exhaust port  138 C is in communication with the sump  104 . 
     The intermediate line  158  communicates the hydraulic fluid  102  from the second clutch pressure control device  138  to a second clutch flow control device  160 , to a second pressure limit control valve  162 , and to the three-way ball check valve  147 . The second clutch flow control device  160  is preferably an electrically controlled variable force solenoid that is operable to control a flow of the hydraulic fluid  102  from the second clutch flow control device  160  in order to actuate the second torque transmitting device  24 , as will be described in greater detail below. The second clutch flow control device  160  includes an inlet port  160 A that communicates with an outlet port  160 B when the second clutch flow control device  160  is activated or energized and includes an exhaust port  160 C that communicates with the outlet port  160 B when the second clutch flow control device  160  is inactive or de-energized. Variable activation of the second clutch flow control device  160  regulates or controls the flow of the hydraulic fluid  102  as the hydraulic fluid  102  communicates from the inlet port  160 A to the outlet port  160 B. The inlet port  160 A is in communication with the intermediate line  158 . The outlet port  160 B is in communication with a second clutch supply line  164  and a flow restriction orifice  166 . The exhaust port  160 C is in communication with the sump  104 . The second pressure limit control valve  162  is disposed in parallel with the second clutch flow control solenoid  160  and is in communication with the second clutch supply line  164 . If pressure within the second clutch supply line  164  exceeds a predetermined value, the second pressure limit control valve  162  opens to relieve and reduce the pressure. 
     The second clutch supply line  164  is in fluid communication with an inlet/outlet port  168 A in a second clutch piston assembly  168 . The second clutch piston assembly  168  includes a single acting piston  170  slidably disposed in a cylinder  172 . The piston  170  translates under hydraulic pressure to engage the second torque transmitting device  24 , shown in  FIG. 1 . When the second clutch flow control device  160  is activated or energized, a flow of pressurized hydraulic fluid  102  is provided to the second clutch supply line  164 . The flow of pressurized hydraulic fluid  102  is communicated from the second clutch supply line  164  to the second clutch piston assembly  168  where the pressurized hydraulic fluid  102  translates the piston  170 , thereby engaging the second torque transmitting device  24 . When the second clutch flow control solenoid  160  is de-energized, the inlet port  160 A is closed and hydraulic fluid from the cylinder  172  passes from the outlet port  160 B to the exhaust port  160 C and into the sump  104 , thereby disengaging the second torque transmitting device  24 . 
     The three-way ball check valve  147  includes three ports  147 A,  147 B, and  147 C. The ball check valve  147  closes off whichever of the ports  147 A and  147 B that is delivering the lower hydraulic pressure and provides communication between whichever of the ports  147 A and  147 B having or delivering the higher hydraulic pressure with the outlet port  147 C. The ports  147 A and  147 B each communicate with the pressure control devices  136  and  138 , respectively. The outlet port  147 C is in communication with a control device feed line  173 . The control device feed line  173  communicates with a valve control device  174 . Accordingly, activation of either clutch pressure control devices  136  and  138  provides a flow of pressurized hydraulic fluid  102  to the valve control device  174  via the control device feed line  173  without allowing a flow of pressurized hydraulic fluid  102  into the circuit of the inactivated clutch pressure control device  136 ,  138 . 
     The first and second pressure control devices  140  and  141  are operable to selectively provide flows of pressurized hydraulic fluid  102  through first and second flow control devices  178 ,  180  and through first and second valve assemblies  182 ,  184  in order to selectively actuate a plurality of synchronizer shift actuators. The synchronizer actuators include a first synchronizer actuator  186 A, a second synchronizer actuator  186 B, a third synchronizer actuator  186 C, and a fourth synchronizer actuator  186 D. 
     For example, the first actuator pressure control device  140  is preferably an electrically controlled variable force solenoid having an internal closed loop pressure control. Various makes, types, and models of solenoids may be employed with the present invention so long as the first actuator pressure control device  140  is operable to control the pressure of the hydraulic fluid  102 . The first actuator pressure control device  140  includes an inlet port  140 A that communicates with an outlet port  140 B when the first actuator pressure control device  140  is activated or energized and includes an exhaust port  140 C that communicates with the outlet port  140 B when the first actuator pressure control device  140  is inactive or de-energized. Variable activation of the first actuator pressure control device  140  regulates or controls the pressure of the hydraulic fluid  102  as the hydraulic fluid  102  communicates from the inlet port  140 A to the outlet port  140 B. The internal closed loop pressure control provides pressure feedback within the solenoid to adjust the amount of flow to the outlet port  140 B based on a particular current command from the controller  32 , thereby controlling pressure. The inlet port  140 A is in communication with the main supply line  126 . The outlet port  140 B is in communication with an intermediate line  188 . The exhaust port  140 C is in communication with the sump  104 . 
     The intermediate line  188  communicates pressurized hydraulic fluid  102  from the first actuator pressure control device  140  to a first flow control device  178  and the first valve assembly  182 . The first flow control device  178  is preferably an electrically controlled variable force solenoid. Various makes, types, and models of solenoids may be employed with the present invention so long as the first flow control device  178  is operable to control the flow of the hydraulic fluid  102 . The first flow control device  178  includes an inlet port  178 A that communicates through an adjustable hydraulic orifice or restriction with an outlet port  178 B when the first flow control device  178  is activated or energized and includes an exhaust port  178 C that communicates with the outlet port  178 B when the first flow control device  178  is inactive or de-energized. Variable activation of the first flow control device  178  regulates or controls the flow of the hydraulic fluid  102  as the hydraulic fluid  102  communicates from the inlet port  178 A to the outlet port  178 B. The inlet port  178 A is in communication with the intermediate line  188 . The outlet port  178 B is in communication with an intermediate line  190  which communicates with the first valve assembly  182 . The exhaust port  178 C is in communication with the sump  104 . 
     The first valve assembly  182  is operable to selectively direct the pressurized hydraulic fluid  102  flows from the first pressure control device  140  and the first actuator flow control device  178  to the first synchronizer actuator  186 A and to the second synchronizer actuator  186 B, as will be described in greater detail below. The first valve assembly  182  includes a first inlet port  182 A, a second inlet port  182 B, a first outlet port  182 C, a second outlet port  182 D, a third outlet port  182 E, a fourth outlet port  182 F, a plurality of exhaust ports  182 G, and a control port  182 H. The first inlet port  182 A is in communication with the intermediate line  190 . The second inlet port  182 B is in communication with the intermediate line  188 . The first outlet port  182 C is in communication with a synchronizer supply line  192 . The second outlet port  182 D is in communication with a synchronizer supply line  194 . The third outlet port  182 E is in communication with a synchronizer supply line  196 . The fourth outlet port  182 F is in communication with a synchronizer supply line  198 . The exhaust ports  182 G are in communication with the sump  104 . The control port  182 H is in communication with a control line  200  that communicates with the control device  174 . 
     The first valve assembly  182  further includes a valve  202  slidably disposed within a bore  204 . The valve  202  is movable between at least two positions by a biasing member  206  and the valve control device  174 . The biasing member  206  is preferably a spring and acts on an end of the valve  202  to bias the valve  202  to the first position or de-stroked position. The valve control device  174  is preferably an on-off solenoid that is normally closed. However, it should be appreciated that other types of solenoids and other control devices may be employed without departing from the scope of the present invention. For example, the valve control device  174  may be a direct acting solenoid. The valve control device  174  includes an inlet port  174 A in fluid communication with the control device feed line  173  and an outlet port  174 B in fluid communication with the control line  200 . The valve control device  174  is electrically actuated by the controller  32  between a closed state and an open state. In the closed state, the inlet port  174 A is prevented from communicating with the outlet port  174 B. In the open state, the inlet port  174 A is allowed to communicate with the outlet port  174 B. Accordingly, the valve control device  174 , when energized to the open state, allows hydraulic fluid  102  to communicate from the inlet port  174 A to the outlet port  174 B and from the outlet port  174 B to the control port  182 H via the control line  200 . Then, the hydraulic fluid  102  acts on an end of the valve  202  to move the valve  202  to the second position or stroked position against the bias of the basing member  206 . When the valve control device  174  is de-energized or in the closed state, the flow of hydraulic fluid  102  acting against the valve  202  is cut off and the biasing member  206  moves the valve  202  to the de-stroked position. 
     When the valve  202  is in the de-stroked position, the first inlet port  182 A is in communication with the second outlet port  182 D, the second inlet port  182 B is in communication with the fourth outlet port  182 F, and the first and third outlet ports  182 C,  182 E are in communication with the exhaust ports  182 G. When the valve  202  is in the stroked position, as shown in  FIG. 2B , the first inlet port  182 A is in communication with the first outlet port  182 C, the second inlet port  182 B is in communication with the third outlet port  182 E, and the second and fourth outlet ports  182 D,  182 F are in communication with the exhaust ports  182 G. Accordingly, when the valve control device  174  is opened, pressurized hydraulic fluid  102  flows from the first pressure control device  140  and a variable flow of hydraulic fluid  102  flows from the first flow control device  178  to the second synchronizer actuator  186 B. When the valve control device  174  is closed, pressurized hydraulic fluid  102  flows from the first pressure control device  140  and a variable flow of hydraulic fluid  102  flows from the first flow control device  178  to the first synchronizer actuator  186 A. 
     The second actuator pressure control device  141  is preferably an electrically controlled variable force solenoid having an internal closed loop pressure control. Various makes, types, and models of solenoids may be employed with the present invention so long as the second actuator pressure control device  141  is operable to control the pressure of the hydraulic fluid  102 . The second actuator pressure control device  141  includes an inlet port  141 A that communicates with an outlet port  141 B when the second actuator pressure control device  141  is activated or energized and includes an exhaust port  141 C that communicates with the outlet port  141 B when the second actuator pressure control device  141  is inactive or de-energized. Variable activation of the second actuator pressure control device  141  regulates or controls the pressure of the hydraulic fluid  102  as the hydraulic fluid  102  communicates from the inlet port  141 A to the outlet port  141 B. The internal closed loop pressure control provides pressure feedback within the solenoid to adjust the amount of flow to the outlet port  141 B based on a particular current command from the controller  32 , thereby controlling pressure. The inlet port  141 A is in communication with the main supply line  126 . The outlet port  141 B is in communication with an intermediate line  210 . The exhaust port  141 C is in communication with the sump  104 . 
     The intermediate line  210  communicates pressurized hydraulic fluid  102  from the second actuator pressure control device  141  to the second flow control device  180  and the second valve assembly  184 . The second flow control device  180  is preferably an electrically controlled variable force solenoid. Various makes, types, and models of solenoids may be employed with the present invention so long as the second flow control device  180  is operable to control the flow of the hydraulic fluid  102 . The second flow control device  180  includes an inlet port  180 A that communicates through an adjustable hydraulic orifice or restriction with an outlet port  180 B when the second flow control device  180  is activated or energized and includes an exhaust port  180 C that communicates with the outlet port  180 B when the second flow control device  180  is inactive or de-energized. Variable activation of the second flow control device  180  regulates or controls the flow of the hydraulic fluid  102  as the hydraulic fluid  102  communicates from the inlet port  180 A to the outlet port  180 B. The inlet port  180 A is in communication with the intermediate line  210 . The outlet port  180 B is in communication with an intermediate line  212  which communicates with the second valve assembly  184 . The exhaust port  180 C is in communication with the sump  104 . 
     The second valve assembly  184  is operable to selectively direct the pressurized hydraulic fluid  102  flows from the second pressure control device  141  and the second actuator flow control device  180  to the third synchronizer actuator  186 C and to the fourth synchronizer actuator  186 D, as will be described in greater detail below. The second valve assembly  184  includes a first inlet port  184 A, a second inlet port  184 B, a first outlet port  184 C, a second outlet port  184 D, a third outlet port  184 E, a fourth outlet port  184 F, a plurality of exhaust ports  184 G, and a control port  184 H. The first inlet port  184 A is in communication with the intermediate line  212 . The second inlet port  184 B is in communication with the intermediate line  210 . The first outlet port  184 C is in communication with a synchronizer supply line  214 . The second outlet port  184 D is in communication with a synchronizer supply line  216 . The third outlet port  184 E is in communication with a synchronizer supply line  218 . The fourth outlet port  184 F is in communication with a synchronizer supply line  220 . The exhaust ports  184 G are in communication with the sump  104 . The control port  184 H is in communication with the control line  200  that communicates with the control device  174 . 
     The second valve assembly  184  further includes a valve  222  slidably disposed within a bore  224 . The valve  222  is movable between at least two positions by a biasing member  226  and the valve control device  174 . The biasing member  226  is preferably a spring and acts on an end of the valve  222  to bias the valve  222  to the first position or de-stroked position. The valve control device  174  when energized to the open state allows hydraulic fluid  102  to communicate from the inlet port  174 A to the outlet port  174 B and from the outlet port  174 B to the control port  184 H via the control line  200 . Then, the hydraulic fluid  102  acts on an end of the valve  222  to move the valve  222  to the second position or stroked position against the bias of the basing member  226 . When the valve control device  174  is de-energized or in the closed state, the flow of hydraulic fluid  102  acting against the valve  222  is cut off and the biasing member  226  moves the valve  222  to the de-stroked position. It should be appreciated that the valve control device  174  actuates both valve assemblies  182  and  184  when in the open condition via the control line  200 . 
     When the valve  222  is in the de-stroked position, the first inlet port  184 A is in communication with the second outlet port  184 D, the second inlet port  184 B is in communication with the fourth outlet port  184 F, and the first and third outlet ports  184 C,  184 E are in communication with the exhaust ports  184 G. When the valve  222  is in the stroked position, as shown in  FIG. 2B , the first inlet port  184 A is in communication with the first outlet port  184 C, the second inlet port  184 B is in communication with the third outlet port  184 E, and the second and fourth outlet ports  184 D,  184 F are in communication with the exhaust ports  184 G. Accordingly, when the valve control device  174  is opened, pressurized hydraulic fluid  102  flows from the second pressure control device  141  and a variable flow of hydraulic fluid  102  flows from the second flow control device  180  to the fourth synchronizer actuator  186 D. When the valve control device  174  is closed, pressurized hydraulic fluid  102  flows from the second pressure control device  141  and a variable flow of hydraulic fluid  102  flows from the second flow control device  180  to the third synchronizer actuator  186 C. 
     The synchronizer actuators  186 A-D are preferably two-area piston assemblies operable to each engage or actuate a shift rail in a synchronizer assembly, but can be three-area piston assemblies without departing from the scope of the present invention. For example, the first synchronizer actuator  186 A is operable to actuate the first synchronizer assembly  30 A, the second synchronizer actuator  186 B is operable to actuate the second synchronizer assembly  30 B, the third synchronizer actuator  186 C is operable to actuate the third synchronizer assembly  30 C, and the fourth synchronizer actuator  186 D is operable to actuate the fourth synchronizer assembly  30 D. 
     The first synchronizer actuator  186 A includes a piston  230 A slidably disposed within a piston housing or cylinder  232 A. The piston  230 A presents two separate areas for pressurized hydraulic fluid to act upon. The piston  230 A engages or contacts a finger lever, shift fork, or other shift rail component  233 A of the first synchronizer assembly  30 A. The first synchronizer actuator  186 A includes a fluid port  234 A that communicates with a first end  235 A of the piston  230 A and a fluid port  236 A that communicates with an opposite second end  237 A of the piston  230 A having a smaller contact area than the first end  235 A. Fluid port  234 A is in communication with the synchronizer supply line  194  and fluid port  236 A is in communication with the synchronizer supply line  198 . Accordingly, the pressurized hydraulic fluid  102  communicated from the first actuator pressure control device  140  enters the first synchronizer actuator  186 A through the fluid port  236 A and contacts the second end  237 A of the piston  230 A and the flow of hydraulic fluid  102  from the first flow control device  178  enters the first synchronizer actuator  186 A through the fluid port  234 A and contacts the first end  235 A of the piston  230 A. The difference in force between the hydraulic fluid  102  delivered to fluid port  236 A from the first actuator pressure control device  140  and the hydraulic fluid  102  delivered to fluid port  234 A from the first flow control device  178  moves the piston  230 A between various positions. By controlling the flow of hydraulic fluid  102  from the first flow control device  178 , the piston  230 A is actuated between the various positions. Each position in turn corresponds to a position of the shift rail of the first synchronizer assembly  30 A (i.e., engaged left, engaged right, and neutral). A fork position sensor  240 A may be included to communicate to the controller  32  the position of the shift fork  233 A. 
     The second synchronizer actuator  186 B includes a piston  230 B slidably disposed within a piston housing or cylinder  232 B. The piston  230 B presents two separate areas for pressurized hydraulic fluid to act upon. The piston  230 B engages or contacts a finger lever, shift fork, or other shift rail component  233 B of the second synchronizer assembly  30 B. The second synchronizer actuator  186 B includes a fluid port  234 B that communicates with a first end  235 B of the piston  230 B and a fluid port  236 B that communicates with an opposite second end  237 B of the piston  230 B having a smaller contact area than the first end  235 B. Fluid port  234 B is in communication with the synchronizer supply line  192  and fluid port  236 B is in communication with the synchronizer supply line  196 . Accordingly, the pressurized hydraulic fluid  102  communicated from the first actuator pressure control device  140  enters the second synchronizer actuator  186 B through the fluid port  236 B and contacts the second end  237 B of the piston  230 B and the flow of hydraulic fluid  102  from the first flow control device  178  enters the second synchronizer actuator  186 B through the fluid port  234 B and contacts the first end  235 B of the piston  230 B. The difference in force between the hydraulic fluid  102  delivered to fluid port  236 B from the first actuator pressure control device  140  and the hydraulic fluid  102  delivered to fluid port  234 B from the first flow control device  178  moves the piston  230 B between various positions. By controlling the flow of hydraulic fluid  102  from the first flow control device  178 , the piston  230 B is actuated between the various positions. Each position in turn corresponds to a position of the shift rail of the second synchronizer assembly  30 B (i.e., engaged left, engaged right, and neutral). A fork position sensor  240 B may be included to communicate to the controller  32  the position of the shift fork  233 B. 
     The third synchronizer actuator  186 C includes a piston  230 C slidably disposed within a piston housing or cylinder  232 C. The piston  230 C presents two separate areas for pressurized hydraulic fluid to act upon. The piston  230 C engages or contacts a finger lever, shift fork, or other shift rail component  233 C of the third synchronizer assembly  30 C. The third synchronizer actuator  186 C includes a fluid port  234 C that communicates with a first end  235 C of the piston  230 C and a fluid port  236 C that communicates with an opposite second end  237 C of the piston  230 C having a smaller contact area than the first end  235 C. Fluid port  234 C is in communication with the synchronizer supply line  216  and fluid port  236 C is in communication with the synchronizer supply line  220 . Accordingly, the pressurized hydraulic fluid  102  communicated from the second actuator pressure control device  141  enters the third synchronizer actuator  186 C through the fluid port  236 C and contacts the second end  237 C of the piston  230 C and the flow of hydraulic fluid  102  from the second flow control device  180  enters the third synchronizer actuator  186 C through the fluid port  234 C and contacts the first end  235 C of the piston  230 C. The difference in force between the hydraulic fluid  102  delivered to fluid port  236 C from the second actuator pressure control device  141  and the hydraulic fluid  102  delivered to fluid port  234 C from the second flow control device  180  moves the piston  230 C between various positions. By controlling the flow of hydraulic fluid  102  from the second flow control device  180 , the piston  230 C is actuated between the various positions. Each position in turn corresponds to a position of the shift rail of the third synchronizer assembly  30 C (i.e., engaged left, engaged right, and neutral). A fork position sensor  240 C may be included to communicate to the controller  32  the position of the shift fork  233 C. 
     The fourth synchronizer actuator  186 D includes a piston  230 D slidably disposed within a piston housing or cylinder  232 D. The piston  230 D presents two separate areas for pressurized hydraulic fluid to act upon. The piston  230 D engages or contacts a finger lever, shift fork, or other shift rail component  233 D of the fourth synchronizer assembly  30 D. The fourth synchronizer actuator  186 D includes a fluid port  234 D that communicates with a first end  235 D of the piston  230 D and a fluid port  236 D that communicates with an opposite second end  237 D of the piston  230 D having a smaller contact area than the first end  235 D. Fluid port  234 D is in communication with the synchronizer supply line  214  and fluid port  236 D is in communication with the synchronizer supply line  218 . Accordingly, the pressurized hydraulic fluid  102  communicated from the second actuator pressure control device  141  enters the fourth synchronizer actuator  186 D through the fluid port  236 D and contacts the second end  237 D of the piston  230 D and the flow of hydraulic fluid  102  from the second flow control device  180  enters the fourth synchronizer actuator  186 D through the fluid port  234 D and contacts the first end  235 D of the piston  230 D. The difference in force between the hydraulic fluid  102  delivered to fluid port  236 D from the second actuator pressure control device  141  and the hydraulic fluid  102  delivered to fluid port  234 D from the second flow control device  180  moves the piston  230 D between various positions. By controlling the flow of hydraulic fluid  102  from the second flow control device  180 , the piston  230 D is actuated between the various positions. Each position in turn corresponds to a position of the shift rail of the fourth synchronizer assembly  30 D (i.e., engaged left, engaged right, and neutral). A fork position sensor  240 D may be included to communicate to the controller  32  the position of the shift fork  233 D. 
     *During general operation of the hydraulic control system  100 , the accumulator  130  provides the pressurized hydraulic fluid  102  throughout the system and the pump  106  is employed to charge the accumulator  130 . Selection of a particular forward or reverse gear ratio is achieved by first selectively actuating one of the synchronizer assemblies  30 A-D and then selectively actuating one of the torque transmitting devices  22 ,  24 . It should be appreciated that which actuator assembly  30 A-D and which torque transmitting device  22 ,  24  provide which forward or reverse gear ratio may vary without departing from the scope of the present invention. 
     Generally, the first actuator pressure control device  140  provides pressurized hydraulic fluid  102  to each of the synchronizer actuators  186 A-B and the first flow control device  178  and the second actuator pressure control device  141  provides pressurized hydraulic fluid  102  to each of the synchronizer actuators  186 C-D and the second flow control device  180 . Individual synchronizer actuators  186 A-D are actuated by controlling a flow from one of the flow control devices  178  and  180  based upon positioning of the first and second valve assemblies  182  and  184 . 
     For example, to actuate the first synchronizer assembly  30 A, the first pressure control device  140  is energized and the valve control device  174  is opened to move the first valve assembly  182  to the stroked position. The first pressure control device  140  provides a steady pressure on the piston  230 A and provides a flow of pressurized hydraulic fluid  102  to the first flow control device  178 . Bi-directional translation of the first synchronizer assembly  30 A is then achieved by selectively energizing the first flow control device  178 . For example, energizing the first flow control device  178  to provide a flow of hydraulic fluid  102  to the synchronizer actuator  186 A which provides a pressure acting on the piston  230 A that is sufficient to overcome the pressure acting on the piston  230 A from the first actuator pressure control device  140  moves the piston  230 A to a first engaged position. Energizing the first flow control device  178  to provide a flow of hydraulic fluid  102  to the synchronizer actuator  186 A which provides a pressure acting on the piston  230 A that is balanced with the pressure acting on the piston  230 A from the first actuator pressure control device  140  moves the piston  230 A to a neutral or unengaged position. Energizing or de-energizing the first flow control device  178  to provide a flow of hydraulic fluid  102  to the synchronizer actuator  186 A which provides a pressure acting on the piston  230 A that is insufficient to overcome the pressure acting on the piston  230 A from the first actuator pressure control device  140  moves the piston  230 A to a second engaged position. 
     To actuate the second synchronizer assembly  30 B, the first pressure control device  140  is energized and the valve control device  174  is closed to move the first valve assembly  182  to the de-stroked position. The first pressure control device  140  provides a steady pressure on the piston  230 B and provides a flow of pressurized hydraulic fluid  102  to the first flow control device  178 . Bi-directional translation of the second synchronizer assembly  30 B is then achieved by selectively energizing the first flow control device  178 . For example, energizing the first flow control device  178  to provide a flow of hydraulic fluid  102  to the synchronizer actuator  186 B which provides a pressure acting on the piston  230 B that is sufficient to overcome the pressure acting on the piston  230 B from the first actuator pressure control device  140  moves the piston  230 B to a first engaged position. Energizing the first flow control device  178  to provide a flow of hydraulic fluid  102  to the synchronizer actuator  186 B which provides a pressure acting on the piston  230 B that is balanced with the pressure acting on the piston  230 B from the first actuator pressure control device  140  moves the piston  230 B to a neutral or unengaged position. Energizing or de-energizing the first flow control device  178  to provide a flow of hydraulic fluid  102  to the synchronizer actuator  186 B which provides a pressure acting on the piston  230 B that is insufficient to overcome the pressure acting on the piston  230 B from the first actuator pressure control device  140  moves the piston  230 B to a second engaged position. 
     To actuate the third synchronizer assembly  30 C, the second pressure control device  141  is energized and the valve control device  174  is closed to move the second valve assembly  184  to the de-stroked position. The second pressure control device  141  provides a steady pressure on the piston  230 C and provides a flow of pressurized hydraulic fluid  102  to the second flow control device  180 . Bi-directional translation of the third synchronizer assembly  30 C is then achieved by selectively energizing the second flow control device  180 . For example, energizing the second flow control device  180  to provide a flow of hydraulic fluid  102  to the synchronizer actuator  186 C which provides a pressure acting on the piston  230 C that is sufficient to overcome the pressure acting on the piston  230 C from the second actuator pressure control device  141  moves the piston  230 C to a first engaged position. Energizing the second flow control device  180  to provide a flow of hydraulic fluid  102  to the synchronizer actuator  186 C which provides a pressure acting on the piston  230 C that is balanced with the pressure acting on the piston  230 C from the second actuator pressure control device  141  moves the piston  230 C to a neutral or unengaged position. Energizing or de-energizing the second flow control device  180  to provide a flow of hydraulic fluid  102  to the synchronizer actuator  186 C which provides a pressure acting on the piston  230 C that is insufficient to overcome the pressure acting on the piston  230 C from the second actuator pressure control device  141  moves the piston  230 C to a second engaged position. 
     To actuate the fourth synchronizer assembly  30 D, the second pressure control device  141  is energized and the valve control device  174  is opened to move the second valve assembly  184  to the stroked position. The second pressure control device  141  provides a steady pressure on the piston  230 D and provides a flow of pressurized hydraulic fluid  102  to the second flow control device  180 . Bi-directional translation of the third synchronizer assembly  30 D is then achieved by selectively energizing the second flow control device  180 . For example, energizing the second flow control device  180  to provide a flow of hydraulic fluid  102  to the synchronizer actuator  186 D which provides a pressure acting on the piston  230 D that is sufficient to overcome the pressure acting on the piston  230 D from the second actuator pressure control device  141  moves the piston  230 D to a first engaged position. Energizing the second flow control device  180  to provide a flow of hydraulic fluid  102  to the synchronizer actuator  186 D which provides a pressure acting on the piston  230 D that is balanced with the pressure acting on the piston  230 D from the second actuator pressure control device  141  moves the piston  230 D to a neutral or unengaged position. Energizing or de-energizing the second flow control device  180  to provide a flow of hydraulic fluid  102  to the synchronizer actuator  186 D which provides a pressure acting on the piston  230 D that is insufficient to overcome the pressure acting on the piston  230 D from the second actuator pressure control device  141  moves the piston  230 D to a second engaged position. 
     To engage or actuate the first torque transmitting device  22 , the first clutch pressure control device  136  and the first clutch flow control device  144  are energized or opened. To engage or actuate the second torque transmitting device  24 , the second clutch pressure control device  138  and the second clutch flow control device  160  are energized or opened. 
     By providing flow control of the clutches  22  and  24  and/or the synchronizer assemblies  30 A-D, the hydraulic control system  100  is operable to provide direct clutch position control, direct synchronizer actuator position control, and variable clutch and synchronizer actuator position control. At the same time, quick clutch response times are enabled, spin losses are reduced, and packaging space of the hydraulic control system  100  is reduced, all of which contributes to improved fuel economy and performance. The hydraulic control system  100  is also compatible with BAS/BAS+ hybrid systems. Finally, failure mode protection is enabled through pre-staged position control of the control devices  136 ,  138 ,  140 ,  141 ,  144 ,  160 ,  178 ,  180 , and the valves  182  and  184 . 
     The description of the invention is merely exemplary in nature and variations that do not depart from the general essence 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.