Abstract:
Hydraulic control systems for a dual clutch transmission include a regulated source of pressurized hydraulic fluid including an electric pump, a filter and an accumulator, a pair of pressure control valves and a branching hydraulic circuit including pressure or flow control valves, spool or logic valves and two position valves which collectively supply and exhaust hydraulic fluid from a plurality of shift actuators. The actuators are connected to shift rails which include shift forks and are slidable to engage synchronizers and positive clutches associated with the various gear ratios.

Description:
FIELD 
     The present disclosure relates to hydraulic control systems and more particularly to hydraulic control systems and their components for dual clutch transmissions. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art. 
     In automotive transmission art, the dual clutch transmission (DCT) is a relatively new concept. A typical dual clutch transmission configuration includes a pair of mutually exclusively operating input clutches which drive a pair of input shafts. The input shafts may be disposed on opposite sides of an output shaft or may be disposed concentrically between spaced-apart output shafts. One of each of a plurality of pairs of constantly meshing gears which provide the various forward and reverse gear ratios is freely rotatably disposed on one of the shafts and the other of each pair of gears is coupled to one of the other shafts. A plurality of synchronizer clutches selectively couple the freely rotatable gears to the associated shaft to achieve forward and reverse gear ratios. After the synchronizer clutch is engaged, the input clutch associated with the input shaft having the engaged synchronizer clutch is applied to transmit power through the transmission. Reverse gear is similarly achieved except that it includes an additional (idler) gear to provide torque reversal. 
     Dual clutch transmissions are known for their sporty, performance oriented operating characteristics which mimic those of a conventional (manual) transmission. They also typically exhibit good fuel economy due to their good gear mesh efficiency, ratio selection flexibility, reduced clutch losses and the lack of a torque converter. 
     There are several design considerations unique to dual clutch transmissions, for example, the input clutches must be of relatively large size because of heat generated during clutch slip. Furthermore, such heat generation typically requires correspondingly larger and more complex cooling components capable of dissipating relatively large quantities of heat. Finally, because such transmissions typically have many sets of axially aligned, meshing gears, their overall length may limit their use to certain vehicle designs. 
     Control of the input clutches and selection and engagement of a particular gear by translation of a synchronizer and associated positive clutch is typically achieved by a hydraulic control system. Such a system, itself under the control of an electronic transmission control module (TCM), includes hydraulic valves and actuators which engage the synchronizers and gear clutches. Optimum operating efficiency and thus fuel efficiency and minimal heat generation can be achieved by designing such hydraulic control systems to exhibit low leakage and positive control characteristics. The present invention is so directed. 
     SUMMARY 
     The present invention comprehends two embodiments of a hydraulic control system for a dual clutch transmission having three countershafts, a third, idler shaft and five shift rails and hydraulic actuators. The hydraulic control systems include a regulated source of pressurized hydraulic fluid including a pump, a filter and an accumulator, a pair of pressure control valves and a branching hydraulic circuit including pressure or flow control valves, spool or logic valves and two position valves which collectively supply and exhaust hydraulic fluid from a plurality of shift actuators. The actuators are connected to shift rails which include shift forks and are slidable to engage synchronizers and positive clutches associated with the various gear ratios. 
     The embodiments incorporate two essentially independent control systems supplied with hydraulic fluid through two independently operating valves. The two independent control systems are associated with the input clutch operators and the gear shift logic valves and actuators. When the transmission is operating in a normal ascending or descending gear selection sequence, this configuration permits pre-staging or pre-selection of a gear associated with one countershaft while a gear associated with the other countershaft is engaged and transmitting torque. Furthermore, if a component or components associated with one countershaft fail, the other countershaft and the alternating (i.e., first, third, fifth) selection of gear ratios it provides will still be fully operational—a highly desirable failure mode. 
     The hydraulic control systems according to the present invention are less complex and expensive relative to competing systems, provide improved control through interconnected logic valves which reduce the likelihood of engaging a wrong or multiple gears and provide reduced energy consumption by allowing shut-down of portions of the control system during steady state operation. Certain embodiments of the control system utilize pairs of pressure or flow control valves to control pressure on both sides of shift actuator pistons which provides better control and improved shifts. 
     Thus it is an object of the present invention to provide a hydraulic control system for a dual clutch automatic transmission. 
     It is a further object of the present invention to provide a hydraulic control system for a dual clutch transmission having a plurality of spool or logic valves and hydraulic actuators. 
     It is a still further object of the present invention to provide a hydraulic control system for a dual clutch transmission having a plurality of two position solenoid valves (on-offs), spool valves and hydraulic actuators. 
     It is a still further object of the present invention to provide a hydraulic control system for a dual clutch transmission having a plurality of flow or pressure control valves, two position solenoid valves, logic or spool valves and hydraulic actuators. 
     It is a still further object of the present invention to provide a hydraulic control system for a dual clutch transmission comprising two essentially independent hydraulic systems, one associated with clutch operation and the other associated with gear selection. 
     It is a still further object of the present invention to provide a hydraulic control system for a dual clutch transmission having a pair of input clutches associated with a pair of concentric input shafts and a pair of countershafts. 
     Further objects, advantages and areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       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 pictorial view of an exemplary dual clutch automatic transmission with portions broken away incorporating a hydraulic control system according to the present invention having five shift actuator assemblies; 
         FIGS. 2A ,  2 B and  2 C are schematic flow diagrams of a first embodiment of a hydraulic control system according to the present invention for a dual clutch automatic transmission; and 
         FIGS. 3A ,  3 B and  3 C are schematic flow diagrams of a second embodiment of a hydraulic control system according to the present invention for a dual clutch automatic transmission. 
     
    
    
     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 , an exemplary dual clutch automatic transmission incorporating the present invention is illustrated and generally designated by the reference number  60 . The dual clutch transmission  60  includes a typically cast, metal housing  12  which encloses and protects the various components of the transmission  60 . The housing  12  includes a variety of apertures, passageways, shoulders and flanges (not illustrated) which position and support the components of the transmission  60 . The transmission  60  includes an input shaft  14  which receives motive power from a prime mover (not illustrated) such as an internal combustion gas or Diesel engine or a hybrid or electric power plant and a single or double output shaft  16  which drives a final drive assembly  18  which may include a propshaft, a differential and drive axles. The input shaft  14  is coupled to and drives a clutch housing  62 . The clutch housing  62 , in turn, drives a pair of concentrically disposed dry input clutches, a first input clutch  64 A and a second input clutch  64 B which are mutually exclusively engaged to provide drive torque to a respective pair of concentric input members, a first or inner input shaft  66 A and a second or outer hollow input shaft or quill  66 B. 
     Secured to and rotating with each of the input members  66 A and  66 B are a plurality of helical or spur gears (not illustrated) which are in constant mesh with helical or spur gears which are freely rotatably disposed on a first layshaft or countershaft  68 A and a parallel, second layshaft or countershaft  68 B. Adjacent and parallel to the second countershaft is a third layshaft or countershaft  68 C. A first drive gear meshes with a first driven gear  70 A on the first countershaft  68 A. A second drive gear meshes with a second driven gear  72 A on the first countershaft  68 A. A third drive gear meshes with a third driven gear  74 A on the first countershaft  68 A. A fourth drive gear meshes with a fourth driven gear  76 A on the first countershaft  68 A. A fifth driven gear  70 B on the second countershaft  68 B meshes with a fifth drive gear  70 C on the third countershaft  68 C. The second drive gear also meshes with a sixth driven gear  72 B on the second countershaft  68 B which meshes with a seventh driven gear  72 C on the third countershaft  68 C. An eighth drive gear meshes with an eighth driven gear  74 B on the second countershaft  68 B. 
     Disposed either adjacent certain single gears or between adjacent pairs of gears on the countershafts  68 A,  68 B and  68 C are synchronizer clutch assemblies. Each synchronizer clutch assembly, in accordance with conventional practice, includes a synchronizer assembly which, when activated, synchronizes the speed of a gear to that of the associated countershaft and a positive clutch, such as a dog or face clutch, which positively connects the gear to the shaft. Thus, between the driven gears  70 A and  72 A on the first countershaft  68 A is a first shift actuator and synchronizer clutch assembly  80 A having a double, i.e., back-to-back, first synchronizer clutch  82 A which selectively and exclusively synchronizes and engages one of the gears  70 A and  72 A to the first countershaft  68 A. The first synchronizer clutch  82 A is bi-directionally translated by a first shift rail and fork assembly  84 A which, in turn, is translated by a first shift actuator assembly  86 A. The real time position of the first synchronizer clutch  82 A and the first shift rail and fork assembly  84 A is sensed by a first linear position sensor  88 A which preferably provides a continuous, i.e., proportional, output signal to a transmission control module TCM indicating the position of the first synchronizer clutch  82 A. 
     Between the fifth driven gear  70 B and the sixth driven gear  72 B on the second countershaft  68 B is a second shift actuator and synchronizer clutch assembly  80 B having a single synchronizer clutch  82 B which synchronizes and couples the driven gears  70 B and  72 B together. The second synchronizer clutch  82 B is bi-directionally translated by a second shift rail and fork assembly  84 B which, in turn, is translated by a second shift actuator assembly  86 B. The real time position of the second synchronizer clutch  82 B and the second shift rail and fork assembly  84 B is sensed by a second linear position sensor  88 B which preferably provides a continuous, i.e., proportional, output signal to the transmission control module TCM indicating the position of the second synchronizer clutch  82 B. 
     Between the driven gears  74 A and  76 A on the first countershaft  68 A is a third shift actuator and synchronizer clutch assembly  90 A having a double, i.e., back-to-back, third synchronizer clutch  92 A which selectively and exclusively synchronizes and engages one of the gears  74 A and  76 A to the first countershaft  68 A. The third synchronizer clutch  92 A is bi-directionally translated by a third shift rail and fork assembly  94 A which, in turn, is translated by a third shift actuator assembly  96 A. The real time position of the third synchronizer clutch  92 A and the third shift rail and fork assembly  94 A is sensed by a third linear position sensor  98 A which preferably provides a continuous, i.e., proportional, output signal to the transmission control module TCM indicating the position of the third synchronizer clutch  92 A. 
     Adjacent the eighth driven gear  74 B on the second countershaft  68 B is a fourth shift actuator and synchronizer clutch assembly  90 B having a single synchronizer clutch  92 B which synchronizes and couples the eighth driven gear  74 B to the second countershaft  68 B. The fourth synchronizer clutch  92 B is bi-directionally translated by a fourth shift rail and fork assembly  94 B which, in turn, is translated by a fourth shift actuator assembly  96 B. The real time position of the fourth synchronizer clutch  92 B and the fourth shift rail and fork assembly  94 B is sensed by a fourth linear position sensor  98 B which preferably provides a continuous, i.e., proportional, output signal to the transmission control module TCM indicating the position of the fourth synchronizer clutch  92 B. 
     Finally, between the fifth drive gear  70 C and the seventh driven gear  72 C on the third countershaft  68 C is a fifth shift actuator and synchronizer clutch assembly  90 C having a double, i.e., back-to-back, synchronizer clutch  92 C which selectively and exclusively synchronizes and engages one of the gears  72 C to the third countershaft  68 C or couples the driven gear  72 C to the drive gear  70 C. The fifth synchronizer clutch  92 C is bi-directionally translated by a fifth shift rail and fork assembly  94 C which, in turn, is translated by a fifth shift actuator assembly  96 C. The real time position of the fifth synchronizer clutch  92 C and the fifth shift rail and fork assembly  94 C is sensed by a fifth linear position sensor  98 C which preferably provides a continuous, i.e., proportional, output signal to the transmission control module TCM indicating the position of the fifth synchronizer clutch  92 C. It should be appreciated that the linear position sensors  88 A,  88 B,  98 A,  98 B and  98 C may be replaced with other sensors such as two or three position switches or open loop control with system characterization. 
     Additionally, a detent mechanism may be employed with each of the shift assemblies to assist obtaining and maintaining a gear or speed ratio once it is selected and to assist obtaining and maintaining the synchronizer clutch in neutral, i.e., an unengaged position. Thus, a first detent assembly  89 A may be operatively associated with the first shift actuator and synchronizer clutch assembly  80 A. A second detent assembly  89 B may be operatively associated with the second shift actuator and synchronizer clutch assembly  80 B. A third detent assembly  99 A may be operatively associated with the third shift actuator and synchronizer clutch assembly  90 A. A fourth detent assembly  99 B may be operatively associated with the fourth shift actuator and synchronizer clutch assembly  90 B and a fifth detent assembly  99 C may be operatively associated with the fifth shift actuator and synchronizer clutch assembly  90 C. 
     It will be appreciated that the transmission  60  illustrated and described above is laid out with four forward gears on one countershaft and the remaining (three) forward gears and reverse on two other countershafts. It is thus capable of providing seven forward speeds and reverse. Similar configurations, all deemed to be within the scope of this invention may, for example, include six forward speeds (or gears) and one or two reverse speeds (or gears) or five forward speeds and one or two reverse speeds. 
     It should be understood that while the present invention is directed to hydraulic control systems for dual clutch transmissions, such systems are typically controlled by sensor signals and memory, software and one or more microprocessors contained in a transmission control module TCM. Thus, the transmission control module TCM includes a plurality of inputs which receive data from, for example, the linear position sensors, the speed sensors and the pressure sensor, and a plurality of outputs which control and modulate, for example, the positions of the clutches, pressure and flow control valves, logic solenoid valves and shift rails. 
     Referring now to  FIGS. 1 ,  2 A,  2 B and  2 C, a first embodiment of a hydraulic control system for the dual clutch automatic transmission  60  described above is illustrated and designated by the reference number  2000 . The hydraulic control system  2000  includes a sump  102  to which hydraulic fluid returns and collects from various components and regions of the automatic transmission  60 . A suction line  104  which may include a filter  106  communicates with the inlet port  108  of an engine driven or electric pump  110  which may be, for example, a gear pump, a vane pump, a gerotor pump or other positive displacement pump. An outlet port  112  of the pump  110  provides hydraulic fluid under pressure in a supply line  114  to a spring biased blow-off safety valve  116  and to a pressure side filter  118  which is disposed in parallel with a spring biased check valve  120 . The safety valve  116  is set at a relatively high predetermined pressure and if the pressure in the supply line  114  exceeds this pressure, the safety valve  116  opens momentarily to relieve and reduce it. If pressure ahead of the filter  118  rises to a predetermined differential pressure, indicating a partial blockage or flow restriction when cold of the filter  118  and the possibility that insufficient hydraulic fluid may be provided in an outlet line  122  to the remainder of the control system  2000 , the check valve  120  opens to allow hydraulic fluid to bypass the filter  118 . 
     A second check valve  124 , in the outlet line  122 , is configured to maintain hydraulic pressure in a main supply line  126  and to prevent backflow through the pump  110 . The main supply line  126  supplies pressurized hydraulic fluid to an accumulator  130  having a piston  132  and a biasing compression spring  134 . The accumulator  130  may be one of many other designs such as gas charged. The accumulator  130  stores pressurized hydraulic fluid and supplies it to the main supply line  126 , to a main or system pressure sensor  136  and to the other components of the control system  2000  thereby eliminating the need for the engine driven or electric pump  110  to run continuously. The main pressure sensor  136  reads the delivered hydraulic system pressure in real time and provides this data to the transmission control module TCM. 
     It should be appreciated that the other embodiment of the hydraulic control system according to the present invention preferably includes the same hydraulic supply, filtration and control components just described. Accordingly, these components will be only briefly described in connection with the subsequent figures and embodiment, it being understood that the above description may be referenced to provide details of these components. 
     The first embodiment  2000  of the hydraulic control system is divided into a clutch operating portion and gear selection portion. As such, the first main supply line  126 A communicates with the inlet port  140 A of a first pressure control solenoid valve  140 . An outlet port  140 B of the first pressure control solenoid valve  140  connects to a supply line  2002  and a first manifold  2004 . The first manifold  2004  has a first branch  2004 A which communicates with an inlet port  154 A of a first electric pressure or flow clutch control solenoid valve  154 . The first clutch control solenoid valve  154  also includes an outlet port  154 B and an exhaust port  154 C which communicates with the sump  102 . The outlet port  154 B provides hydraulic fluid through an orifice  156  to the first clutch piston and cylinder assembly  160  having the cylinder  162  and the piston  164  slidably disposed therein. It should be appreciated that the orifice  156  and other orifices can be added or omitted without departing from the scope of this invention. A check valve  166  is connected between the first piston and cylinder assembly  160  and a second branch  20048  of the first manifold  2004 . 
     A third branch  2004 C of the first manifold  2004  communicates with an inlet port  204 A of the second electric pressure or flow clutch control solenoid valve  204 . The second clutch control solenoid valve  204  also includes an outlet port  204 B and an exhaust port  204 C which communicates with the sump  102 . The outlet port  204 B of the second clutch control solenoid valve  204  provides hydraulic fluid through an orifice  206  to a second clutch piston and cylinder assembly  210  having a cylinder  212  and a piston  214  slidably disposed therein. A check valve  216  is connected between the second piston and cylinder assembly  210  and a fourth branch  2004 D of the manifold  2004 . It should be noted the check valves  166  and  216  could be eliminated depending upon the system requirements. 
     The second main supply line  126 B communicates with an inlet port  190 A of a second pressure control solenoid valve  190 . An outlet port  190 B connects to a second manifold  2012 . A first branch  2012 A of the second manifold  2012  communicates with an inlet port  2018 A of a first two position (on-off) solenoid valve  2018 . An outlet port  2018 B of the first two position solenoid valve  2018  communicates with a first inlet port  2020 A of a first spool or logic valve  2020  and an exhaust port  2018 C of the first two position (on-off) solenoid valve  2018  communicates with the sump  102 . 
     A second branch  2012 B of the second manifold  2012  communicates with an inlet port  2022 A of a first pressure or flow control solenoid valve  2022 . The first pressure or flow control solenoid valve  2022  has an outlet port  2022 B which communicates with a second inlet port  2020 B of the first spool or logic valve  2020 . An exhaust port  2022 C of the first pressure or flow control solenoid valve  2022  communicates with the sump  102 . A third branch  2012 C of the second manifold  2012  communicates with an inlet port  2026 A of a second pressure or flow control solenoid valve  2026  having an outlet port  2026 B which communicates with a third inlet port  2020 C of the first spool or logic valve  2020 . An exhaust port is associated with each of the inlet ports  2020 A,  2020 B and  2020 C which communicates with the sump  102 . An exhaust port  2026 C of the second pressure or flow control solenoid valve  2026  also communicates with the sump  102 . 
     A fourth branch  2012 D of the second manifold  2012  communicates with an inlet port  2028 A of a second two position solenoid valve  2028 . An outlet port  2028 B of the second two position (on-off) solenoid valve  2028  is connected to a control port  2020 D of the first logic valve  2020  and an exhaust port  2028 C of the second two-position solenoid valve  2028  is connected to the sump  102 . A fifth branch  2012 E of the second manifold  2012  communicates with an inlet port  2032 A of a third two position (on-off) solenoid valve  2032 . 
     The first spool or logic valve  2020  also includes a first outlet port  2020 E which is connected by a hydraulic line  2036  to a control port  2040 B of a second spool or logic valve  2040  as well as a second port  2050 B of a second piston and cylinder assembly  2050 . A third outlet port  2020 G is connected by a line  2038  to a first inlet port  2040 A of the second logic valve  2040 . The second logic valve  2040  includes a pair of exhaust ports  2040 C and  2040 D and a first outlet port  2040 E that communicates through a line  2042  with a first port  2044 A of a first, preferably dual area piston and cylinder assembly  2044  which translates the first shift rail and fork assembly  84 A. A second port  2044 B at the other end of the first piston and cylinder assembly  2044  communicates with the fifth outlet port  20201  of the first logic valve  2020  through a line  2046 . A second outlet port  2040 F of the second logic valve  2040  communicates through a line  2048  to a first port  2050 A at the other end of the second piston and cylinder assembly  2050  which translates the second shift rail and fork assembly  84 B. 
     A second outlet port  2020 F of the first logic valve  2020  is connected through a line  2052  to a control port  2054 C of a third spool or logic valve  2054  and a port  2060 B at one end of a third, preferably dual area piston and cylinder assembly  2060  which translates the third shift rail and fork assembly  94 A. The sixth outlet port  2020 J of the first logic valve  2020  is connected through a line  2056  to a first inlet port  2054 A of the third logic valve  2054  which also includes a pair of exhaust ports. A first outlet port  2054 D of the third logic valve  2054  communicates through a line  2062  to a second inlet port  2064 B of a fourth spool or logic valve  2064 . A second outlet port  2054 E communicates through a line  2058  to a port  2060 A at the other end of the third piston and cylinder assembly  2060 . A fourth outlet port  2020 H of the first logic valve  2020  is connected by a line  2066  with a first inlet port  2064 A of the fourth logic valve  2064 . The fourth logic valve  2064  includes a control port  2064 C which is connected by a line  2068  to the outlet port  2032 B of the third two position solenoid valve  2032 . 
     The fourth logic valve  2064  includes three exhaust ports  2064 D,  2064 E and  2064 F alternating with the inlet ports  2064 A and  2064 B which communicate with the sump  102  and a first outlet port  2064 G which is connected to a port  2070 A one end of a fourth piston and cylinder assembly  2070  by a line  2072 . A port  2070 B at the other end of the fourth piston and cylinder assembly  2070  is connected to a third outlet port  2064 H by a line  2074 . The fourth piston and cylinder assembly  2070  translates the fourth shift rail and fork assembly  94 B. A second outlet port  20641  of the fourth logic valve  2064  is connected by a line  2078  to a port  2080 A at one end of a fifth, preferably dual area piston and cylinder assembly  2080 . A port  2080 B at the other end of the fifth piston and cylinder assembly  2080  is connected by a line  2082  to a fourth outlet port  2064 J of the fourth logic valve  2064 . The fifth piston and cylinder assembly  2080  translates the fifth shift rail and fork assembly  94 C. It will be appreciated that all of the piston and cylinder assemblies  2044 ,  2050 ,  2060 ,  2070  and  2080  may include dual area pistons, if desired, or that such assemblies may include single area pistons with associated feedback and control assemblies or combinations thereof, as illustrated. 
     Operation of the first embodiment of the hydraulic control system  2000  essentially involves the selection of a desired gear ratio in the transmission  60  by the transmission control module TCM and selection and activation of the pressure control solenoid valves  140  and  190  to independently provide pressurized hydraulic fluid to the input clutch side or the gear shift side of the hydraulic control system  2000 , activation of the pressure or flow control solenoid valves  2022  and  2026  to provide controlled flow and pressure of hydraulic fluid to the logic valves  2020 ,  2040 ,  2054  and  2064  and activation of the two position solenoid valves  2018 ,  2028  and  2032  to position the logic valve spools to direct pressurized hydraulic fluid flow to the correct sides of the piston and cylinder assemblies  2044 ,  2050 ,  2060 ,  2070  and  2080  to translate the shift rails  84 A,  84 B,  94 A,  94 B and  94 C to engage the desired gear. Once this has occurred, the input clutch  64 A or  64 B associated with the countershaft  68 A,  68 B or  68 C of the selected gear is engaged by activation of one of the two piston and cylinder assemblies  160  or  210 . 
     A convenient example of operation may be presented by describing same with the spools of the logic valves  2020 ,  2040 ,  2054  and  2064  in the positions illustrated in  FIGS. 2B and 2C . Activation of the first pressure or flow control solenoid valve  2022  provides hydraulic fluid to the second inlet port  2020 B of the first logic valve  2020 , through the line  2038  to the second logic valve  2040  and through the line  2042  to one end of the first piston and cylinder assembly  2044 . The first shift rail  84 A will then translate to the right (to the left in  FIG. 1 ) and engage, for example, sixth gear. The shift is completed by engaging the appropriate input clutch. If, on the other hand, the second pressure or flow control solenoid valve  2026  is activated, hydraulic fluid flow occurs through the third inlet port  2020 C of the first logic valve  2020  and the line  2046 , either returning the first shift rail  84 A to neutral or moving the shift rail  84 A all the way to the left to the position illustrated in  FIG. 2B  to engage, for example, second gear. The choice of the center (neutral) or left position is commanded by the transmission control module TCM with linear position information from, for example, the first linear position sensor  88 A illustrated in  FIG. 1 . A similar pattern of valve activation and logic valve spool translation provides the seven forward and reverse gears of the transmission  60 . For example, if the second two position solenoid valve  2028  is energized, the spool of the first logic valve  2020  translates to the left in  FIG. 2B , shifting its hydraulic fluid outputs to the outlet ports  2020 F,  2020 H and  2020 J and the hydraulic circuitry illustrated in  FIG. 2C . 
     Referring now to  FIGS. 1 ,  3 A,  3 B and  3 C, a second embodiment of a hydraulic control system according to the present invention is illustrated and generally designated by the reference number  2100 . The second embodiment  2100  of the hydraulic control system, as stated above, includes, in common with the other embodiment, the sump  102 , the pump  110 , the filters  106  and  118 , the accumulator  130  and the other components of the hydraulic fluid supply and thus they will not be further described. It should be noted that the filters  106  and or  118  can be omitted without departing from the scope of this invention. 
     Additionally, the portion of the second embodiment  2100  associated with independent operation of the two sides or sections of the transmission  60  and associated clutches  64 A and  64 B includes the main supply line  126  which bifurcates into the first main supply line  126 A and the second main supply line  126 B. The first main supply line  126 A communicates with the inlet port  140 A of the first pressure control solenoid valve  140  and the second main supply line  126 B communicates with the inlet port  190 A of the second pressure control solenoid valve  190 . The outlet port  140 B of the first pressure control solenoid valve  140  communicates with a first supply manifold  1002  and the outlet port  190 B of the second pressure control solenoid valve  190  communicates with a second supply manifold  1004 . The exhaust ports  140 C and  190 C communicate with the sump  102 . 
     Similarly, the second embodiment  2100  includes the components associated with activation of the first clutch  64 A, such as the electric pressure or flow clutch control solenoid valve  154 , which receives hydraulic fluid from a first branch  1002 A of the first supply manifold  1002 , the orifice  156 , the first clutch piston and cylinder assembly  160  and the first clutch pressure limit control valve  166  which communicates with a second branch  1002 B of the first supply manifold  1002 . The second embodiment  2100  also includes the components associated with activation of the second clutch  64 B, such as the second electric pressure or flow clutch control solenoid valve  204  which receives hydraulic fluid from a first branch  1004 A of the second supply manifold  1004 , the orifice  206 , the second clutch piston and cylinder assembly  210  and the second clutch pressure limit control valve  216  which communicates with a second branch  1004 B of the second supply manifold  1004 . It should be noted that the pressure control valves  166  and  216  can be eliminated depending upon the system requirements. 
     The second embodiment  2100  also includes a two inlet check valve  1510  disposed between and communicating with the first supply manifold  1002  and the second supply manifold  1004 . The first supply manifold  1002  or the second supply manifold  1004  having the higher pressure causes the check ball to close off the lower pressure supply manifold and allow communication between the higher pressure supply manifold and the second, main manifold  2012 . This achieves lower hydraulic fluid consumption rates and permits independent gear and clutch actuator control. However, it should be noted that instead of feeding the main manifold  2012  through the two inlet check valve  1510 , it could be connected to the higher pressure main supply line  126  without loss of functionality. 
     The portion of the second embodiment  2100  associated with gear selection and engagement is the same as the corresponding portion of the first embodiment  2000  illustrated in  FIGS. 2B and 2C . Thus, the second embodiment  2100  also includes the first two position (on-off) solenoid valve  2018 , the first pressure or flow control solenoid valve  2022 , the second pressure or flow control solenoid valve  2026 , the first spool or logic valve  2020 , the second two position (on-off) solenoid valve  2028 , the third two position (on-off) solenoid valve  2032 , the second spool or logic valve  2040 , the third spool or logic valve  2054  and the fourth spool of logic valve  2064 . 
     Similarly, the first, preferably dual area piston and cylinder assembly  2044  is connected to the first outlet port  2040 E of the second logic valve  2040  by the line  2042  and to the fifth outlet port  20201  of the first logic valve  2020  by the line  2046 ; the second piston and cylinder assembly  2050  is connected to the second outlet port  2040 F of the second logic valve  2040  by the line  2048  and to the control port  2040 B of the second logic valve  2040  by the line  2036 . The third, preferably dual area piston and cylinder assembly  2060  is connected to the second outlet port  2054 E of the third logic valve  2054  by the line  2058  and to the control port  2054 C of the third logic valve  2054  by the line  2052 . The fourth piston and cylinder assembly  2070  is connected to the first outlet port  2064 G of the fourth logic valve  2064  by the line  2072  and the third outlet port  2064 H by the line  2074 . The fifth, preferably dual area piston and cylinder assembly  2080  is connected to the second outlet port  20641  of the fourth logic valve  2064  by the line  2078  and the fourth outlet port  2064 J by the line  2082 . 
     It will be appreciated that the hydraulic control systems according to the two embodiments of the present invention achieve significant improvements in reduced energy consumption and shift performance not only because of the incorporation of the dedicated pump and accumulator but also because of the use of pressure and flow control solenoid valves which allow the majority of the hydraulic system components to be turned off in normal, steady-state, operation. It should also be appreciated that slight variations in logic valve connections and alternate piston and shift rail connections are possible in order to adapt to different five actuator transmissions. 
     Additionally, these solenoid valves and the linear position sensors on each piston and cylinder shift actuator assembly which provide real time data to the transmission control module regarding the instantaneous positions of the actuators, shift rails and clutches, achieve gear selection and clutch operation that is rapid, positive and efficient without overshoot and wasted energy. 
     Similarly, the configurations of the two embodiments and the position feedback provided by the linear position sensors permits and facilitates rapid gear sequencing and improved, i.e., reduced, shift times. 
     Finally, the separation of hydraulic fluid supply and control functions into two regions or sections relating to the input clutches and the gear selection components, allows precise and independent control of engagement and operating pressures of the clutches and shift actuators. 
     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.