Abstract:
A control system is provided for a multiple clutch transmission ( 10 ) having at least three synchronizers ( 74, 76, 78, 80 ) with opposed acting alpha and beta pressure chambers ( 106, 104 ) to selectively synchronize alpha or beta gears with a rotating shaft. The control system includes a pressure source ( 124 ), a sump ( 120 ), a first multiplex valve ( 160 ) having a first position allowing fluid communication of alpha and beta chambers for two synchronizers ( 74, 76 ) with the pressure source ( 122 ) and diverting alpha and beta pressure chambers ( 106, 104 ) of remaining synchronizers ( 80, 78 ) to sump ( 120 ). The first multiplex valve ( 160 ) has a second position reversing the above action. A second multiplex valve ( 164 ) connected with the first multiplex valve ( 160 ) having a first position connecting alpha and beta chambers ( 106, 104 ) of a given synchronizer with the pressure source ( 122 ) and alpha and beta chambers ( 106, 104 ) of the other synchronizer with the sump ( 120 ). The second multiplex valve ( 164 ) has a second position reversing the action. A first regulator valve ( 170 ) is connected with the second multiplex valve ( 164 ) for selectively connecting the alpha chamber ( 106 ) with one of a set of the pressure source ( 122 ) and the sump ( 120 ). A second regulator valve is provided connected with the second multiplex valve ( 164 ) for selectively connecting the beta chamber ( 104 ) with one of a set of the pressure source ( 122 ) and the (sump  120 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/904,698, filed 2 Mar. 2007. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to control systems for dual clutch transmissions. 
     BACKGROUND OF THE INVENTION 
     Examples of dual clutch transmissions are described in U.S. Pat. Nos. 5,711,409; 6,996,989; 6,887,184; 6,909,955; 2006/0101933A1; and 2006/0207655A1. A control system for a dual clutch transmission is shown in Koenig et al., U.S. Pat. No. 6,898,992 (commonly assigned). It is desirable that a control system for a dual clutch transmission prevent simultaneous engagement of synchronized gears. It is also desirable that the control system for a dual clutch transmission offer as much operational capacity as possible when a given component of the control system is non operational. 
     SUMMARY OF THE INVENTION 
     To make manifest the above noted and other desires, a revelation of the present invention is brought forth. The present invention in a preferred embodiment provides a control system for a multiple clutch transmission, the transmission having at least three synchronizers with opposed acting alpha and beta pressure chambers to alternately selectively synchronize alpha or beta gears with a rotating shaft. The control system includes a pressure source, a sump, a first multiplex valve having a first position allowing fluid communication of alpha and beta chambers for two synchronizers with the pressure source and diverting alpha and beta pressure chambers of remaining synchronizers to the sump. The first multiplex valve also has a second position reversing the above noted action. A second multiplex valve is included fluidly connected with the first multiplex valve having a first position connecting alpha and beta chambers of a given synchronizer with the pressure source and alpha and beta chambers of the other synchronizer with the sump. The second multiplex valve also has a second position reversing the above noted action. A first actuator regulator valve is included fluidly connected with the second multiplex valve for selectively connecting said alpha chamber with one of a set including the pressure source and the sump. A second actuator regulator valve is included fluidly connected with the second multiplex valve for selectively connecting said beta chamber with one of a set including the pressure source and the sump. 
     Other features of the invention will become more apparent to those skilled in the art as the invention is further revealed in the accompanying drawings and Detailed Description of the Invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is schematic view of a dual clutch transmission. 
         FIG. 2  is a sectioned view of an actuator for a synchronizer utilized in the dual clutch transmission of  FIG. 1 . 
         FIG. 3  is a hydraulic schematic of a control system of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A representative dual clutch transmission that may be controlled by the present invention is generally indicated at  10  in the schematic illustrated in  FIG. 1 . Specifically, as shown in  FIG. 1 , the dual clutch transmission  10  includes a dual, coaxial clutch assembly generally indicated at  12 , a first input shaft, generally indicated at  14 , a second input shaft, generally indicated at  16 , that is coaxial to the first, a counter shaft, generally indicated at  18 , an output shaft  20 , a reverse counter shaft  22 , a plurality of synchronizers, generally indicated at  24 , and a plurality of shift actuators generally indicated at  26  ( FIG. 2 ). 
     The dual clutch transmission  10  forms a portion of a vehicle powertrain and is responsible for taking a torque input from a prime mover, such as an internal combustion engine, and transmitting the torque through selectable gear ratios to the vehicle drive wheels. The dual clutch transmission  10  operatively routes the applied torque from the engine through the dual, coaxial clutch assembly  12  to either the first input shaft  14  or the second input shaft  16 . The input shafts  14  and  16  include a first series of gears, which are in constant mesh with a second series of gears disposed on the counter shaft  18 . Each one of the first series of gears interacts with one of the second series of gears to provide the different gear ratios sets used for transferring torque. The counter shaft  18  also includes a first output gear that is in constant mesh with a second output gear disposed on the output shaft  20 . The plurality of synchronizers  24  are disposed on the two input shafts  14 ,  16  and on the counter shaft  18  and are operatively controlled by the plurality of shift actuators  26  to selectively engage one of the alternate gear ratio sets. Thus, torque is transferred from the engine to the dual, coaxial clutch assembly  12 , to one of the input shafts  14  or  16 , to the counter shaft  18  through one of the gear ratio sets, and to the output shaft  20 . The output shaft  20  further provides the output torque to the remainder of the powertrain. Additionally, the reverse counter shaft  22  includes an intermediate gear that is disposed between one of the first series of gears and one of the second series of gears, which allows for a reverse rotation of the counter shaft  18  and the output shaft  20 . Each of these components will be discussed in greater detail below. 
     Specifically, the dual, coaxial clutch assembly  12  includes a first clutch mechanism  32  and a second clutch mechanism  34 . The first clutch mechanism  32  is, in part, physically connected to a portion of the engine flywheel (not shown) and is, in part, physically attached to the first input shaft  14 , such that the first clutch mechanism  32  can operatively and selectively engage or disengage the first input shaft  14  to and from the flywheel. Similarly, the second clutch mechanism  34  is, in part, physically connected to a portion of the flywheel and is, in part, physically attached to the second input shaft  16 , such that the second clutch mechanism  34  can operatively and selectively engage or disengage the second input shaft  16  to and from the flywheel. As can be seen from  FIG. 1 , the first and second clutch mechanisms  32 ,  34  are coaxial and co-centric such that the outer case  28  of the first clutch mechanism  32  fits inside of the outer case  36  of the second clutch mechanism  34 . Similarly, the first and second input shafts  14 ,  16  are also coaxial and co-centric such that the second input shaft  16  is hollow having an inside diameter sufficient to allow the first input shaft  14  to pass through and be partially supported by the second input shaft  16 . The first input shaft  14  includes a first input gear  38  and a third input gear  42 . The first input shaft  14  is longer in length than the second input shaft  16  so that the first input gear  38  and a third input gear  42  are disposed on the portion of the first input shaft  14  that extends beyond the second input shaft  16 . The second input shaft  16  includes a sixth input gear  40 , a fourth input gear  44 , a second input gear  46 , and a reverse input gear  48 . As shown in  FIG. 1 , the sixth input gear  40  and the reverse input gear  48  are fixedly supported on the second input shaft  16  and the fourth input gear  44  and second input gear  46  are rotatably supported about the second input shaft  16  upon bearing assemblies  50  so that their rotation is unrestrained unless the accompanying synchronizer is engaged, as will be discussed in greater detail below. 
     In the preferred embodiment, the counter shaft  18  is a single, one-piece shaft that includes the opposing, or counter, gears to those on the inputs shafts  14 ,  16 . As shown in  FIG. 1 , the counter shaft  18  includes a first counter gear  52 , a sixth counter gear  54 , a third counter gear  56 , a fourth counter gear  58 , a second counter gear  60 , and a reverse counter gear  62 . The counter shaft  18  fixedly retains the fourth counter gear  58  and second counter gear  60 , while first, sixth, third, and reverse counter gears  52 ,  54 ,  56 ,  62  are supported about the counter shaft  18  by bearing assemblies  50  so that their rotation is unrestrained unless the accompanying synchronizer is engaged as will be discussed in greater detail below. The counter shaft  18  also fixedly retains a first drive gear  64  that meshingly engages the corresponding second driven gear  66  on the output shaft  20 . The second driven gear  66  is fixedly mounted on the output shaft  20 . The output shaft  20  extends outward from the transmission  10  to provide an attachment for the remainder of the powertrain. 
     In a preferred embodiment, the reverse counter shaft  22  is a relatively short shaft having a single reverse intermediate gear  72  that is disposed between, and meshingly engaged with, the reverse input gear  48  on the second input shaft  16  and the reverse counter gear  62  on the counter shaft  18 . Thus, when the reverse gears  48 ,  62 , and  72  are engaged, the reverse intermediate gear  72  on the reverse counter shaft  22  causes the counter shaft  18  to turn in the opposite rotational direction from the forward gears thereby providing a reverse rotation of the output shaft  20 . It should be appreciated that all of the shafts of the dual clutch transmission  10  are disposed and rotationally secured within the transmission  10  by some manner of bearing assembly such as roller bearings, for example, shown at  68  in  FIG. 1 . 
     The engagement and disengagement of the various forward and reverse gears is accomplished by the actuation of the synchronizers  24  within the transmission. As shown in  FIG. 1  in this example of a dual clutch transmission  10 , four synchronizers  74 ,  76 ,  78 , and  80  are utilized to shift through the six forward gears and reverse. It should be appreciated that there are a variety of known types of synchronizers that are capable of engaging a gear to a shaft and that the particular type employed for the purposes of this discussion is beyond the scope of the present invention. Generally speaking, any type of synchronizer that is movable by a shift fork or like device may be employed. As shown in the representative example of  FIG. 1 , the synchronizers are two sided, dual actuated synchronizers, such that they engage one gear to its respective shaft when moved off a center neutralized position to the right and engage another gear to its respective shaft when moved to the left. Specifically with reference to  FIG. 1 , synchronizer  78  can be actuated to the left to engage the first counter gear  52  on the counter shaft  18  or actuated to the right to engage the third counter gear  56 . Synchronizer  80  can be actuated to the left to engage the reverse counter gear  62  or actuated to the right to engage the sixth counter gear  54 . Likewise, synchronizer  74  can be actuated to the left to engage the fourth input gear  44  or actuated to the right to engage the second input gear  46 . Synchronizer  76  is actuated to the right to directly engage the end of the first input shaft  14  to the output shaft  20  thereby providing a direct 1:1 (one to one) drive ratio for fifth gear. There is no gear set to engage to the left of synchronizer  76 . 
     To actuate the synchronizers  74 ,  76 ,  78 , and  80 , this representative example of a dual clutch transmission  10  utilizes hydraulically driven shift actuators  26  with attached shift forks to selectively move the synchronizers so that they engage or disengage (neutralize) the desired gears. As shown in  FIG. 2 , the shift actuators  26  are essentially two way or dual hydraulic valve assemblies that are driven back and forth linearly, in parallel to one of the input shafts  14 ,  16  or the counter shaft  18 , to move a shift fork  96 , and ultimately one of the plurality of synchronizers  24  in and out of engagement. It should be appreciated from the description that follows that other types of actuators that are capable of driving a shift fork back and forth to move a synchronizer may also be employed with the method of the present invention. These include mechanical actuators, hydro-mechanical actuators, electromechanical actuators, electrical actuators, and the like. 
     Referring to  FIG. 2 , the hydraulically operated shift actuators  26  include an outer case  86  that includes a main bore  88  having two cylindrically shaped ends  90 ,  92 . A piston  98  is slidably disposed within the main bore  88  of the case  86 . The piston  98  includes two opposing sealed heads  82  and  84 . The interaction of each piston head  82  and  84  within its respective cylinder end  90 ,  92  forms alpha and beta pressure or expansion chambers  106 ,  104 . 
     Between the piston heads  82  and  84  is a gap. Positioned within the gap  95  is the shift fork  96 . To actuate the synchronize  74  to the right to actuate the second gear ratio, fluid is injected into alpha expansion chamber  106  through inlet-outlet  100  to move the piston and shift fork  96  to the right causing synchronizer  80  to engage the second input gear  46  to the shaft  16 . A detent mechanism (not shown) connected with the linkage with the shift fork  96  holds the shift fork  96  in to hold its actuated position. To release the second input gear  46  from its shaft  16 , the beta expansion chamber  104  is pressurized through inlet  102  and the piston  98  and shift fork  96  are shifted back to a detented neutral position. A slight pressurization of the expansion chamber  106  is temporarily maintained to prevent overtravel of the piston  98  and inadvertent engagement of fourth input gear  44  to the shaft  16 . 
       FIG. 3  illustrates a hydraulic control system for the first and second clutches  32 ,  34  and for synchronizers  74 ,  76 ,  78  and  80 . The control system  7  has an oil sump  120 . To provide a source of pressurize oil or fluid, a pump  122  is connected to the sump  120  via a suction filter  124 . The pump  122  delivers pressurized fluid to lines  126  and  128 . A pump relief valve  127  connected to line  126  prevents over pressurization in line  126 . Fluid in line  128  passes through pressure filter  130  into lines  132  and  134 . The line  134  is connected with a variable bleed solenoid (VBS.)  136 . The VBS  136  controls operation of a main line pressure regulator valve  140 . When at least partially actuated by VBS  136 , the valve  140  connects line  126  with a lube regulator valve  142 . A VBS  144  controls valve  142  to control lubrication of the clutches  32 ,  34  via a clutch lube line  146 . Clutch lube line  146  is connected with the clutch lubrication system. Valve  140  is also fluidly connected with an oil cooler limit valve  148 . An outlet of the valve  148  is looped back to in inlet side of the pump  122 . Valve  142  additionally delivers fluid to oil cooler  150 . Variable force solenoids (VFS)  152 ,  154  control the pressure within their respective clutches  32  and  34  by selectively communicating to the clutches with the line  134  or with the sump  120 . 
     The control system for the synchronizers includes a first multiplex valve  160 . The first multiplex valve  160  has a first position allowing delivery of pressurize fluid to synchronizers  74  and  76 . Synchronizers  78  and  80  are diverted to the sump  120 . In a second position of the first multiplex valve  160  the reverse occurs allowing delivery of pressurize fluid to synchronizers  78  and  80  with synchronizers  74  and  76  being diverted to the sump. An on/off solenoid valve  162  controls operation of the first multiplex valve  160 . 
     A second multiplex valve  164  is fluidly connected with the first multiplex valve  160 . The second multiplex valve  164  has a first position allowing pressurized fluid connection of alpha and beta chambers of the synchronizer  74  (when the first multiplex valve  160  is in the first position). The alpha and beta chambers of synchronizer  76  are diverted to the sump  120 . When the second multiplex valve  164  is placed in the second position by an on/off solenoid  166 , the fluid connections of the second multiplex valve  164  are reversed. The alpha chambers for the synchronizers  74 ,  76 ,  78 , and  80  include pressure chambers for odd and even gear ratios. 
     To actuate the alpha chamber there is provided a first actuator regulator valve  170 . First actuator regulator valve  170  has a biased position connecting the alpha chamber to the sump  120 . In a second position, the first actuator regulator valve  170  connects the alpha chamber with the line  132 . A proportional solenoid valve provided by VBS solenoid valve  174  controls the first actuator regulator valve  170 . In like manner, VBS  176  controls the second actuator regulator valve  180  for the beta chamber of the synchronizer  74 . 
     To control the synchronizer  76  the first multiplex valve  160  is in the first position and the second multiplex valve is placed in the second position. To control synchronizer  80  or synchronizer  78  the first multiplex valve  160  is placed in the second position. For synchronizer  80 , the second multiplex valve  164  is in the first position. For control of the synchronizer  78 , the second multiplex valve  164  is placed in the second position. 
     To place the second input gear  46  into engagement with the shaft  16 , the first multiplex valve  160  and second multiplex valve  162  are placed in the first position. The first regulator valve  170  is turned on to pressurize the alpha expansion chamber  106  moving the piston  98  and shift fork  96  to the right. A position sensor  97  is used to inform or confirm the fact to the transmission electronic controller (not shown) that the transmission  10  is in the second gear. A major advantage of the present control system for the synchronizers is that no two gears of the transmission can be actuated at the same time. If the second input gear  46  is being actuated, all of the pressure chambers of the synchronizers  80 ,  78  and  76  are diverted to the sump. If a control system failure causes the second actuator regulator valve  180  to pressurize the beta expansion chamber  104  of the shift actuator  26  for synchronizer  74 , the pressure within the opposing beta  104  and alpha  106  expansion chambers act against each preventing any simultaneous gear activation (however when the alpha chamber  106  is depressurized the above noted failure causes the gear (fourth input gear  44 ) associated with the beta chamber to be stuck on). Another advantage of the present control system is that most valve failures allow at least one odd gear and at least one even gear to still operate. Failure of the first multiplex valve  160  in the first position allows operation of synchronizer  74  providing second and fourth gears. Additionally, fifth and neutral gears of synchronizer  76  are available. Upon such a failure, the transmission controller programs the transmission  10  to operate in second, fourth and fifth gear ratios dependent upon vehicle speed in a “limp” home mode of operation. 
     A failure of the first multiplex valve  160  in the second position still allows for operation of the reverse, six gear, third gear and first. Failure of the second multiplex valve  164  in the first position will still allow operation of the second, fourth, sixth and reverse gears. Failure of any one given actuator valve still allows for partial gear operation. Failure of the actuator regulator valve  170  in the on position will freeze (be detented) second input gear  46  with the shaft  16 . To get another gear for “limp” home operation, the transmission controller opens the clutch  34 . Engaged clutch  32  is utilized to rotate the shaft  14 . The controller of the transmission then picks a gear ratio from a set of gear ratios associated with the shafts  14  or  20  (first, third or fifth) gear to be utilized for “limp” home mode of operation. The transmission controller then alternates between second and one gear from the set of first, third or fifth gear. As long as a forward travel gear is engaged when one of the actuator regulator valves  170 ,  180  fails, the transmission will have two gear ratios of forward operation in the “limp” home mode of operation. 
     Still another advantage of the present invention over other control systems as shown in Koenig et al. U.S. Pat. No. 6,898,992 (commonly assigned) is that only two high flow rate solenoid actuator regulator valves  170 ,  180  are required. 
     While preferred embodiments of the present invention have been disclosed, it is to be understood it has been described by way of example only, and various modifications can be made without departing from the spirit and scope of the invention as it is encompassed in the following claims.