Patent Publication Number: US-8978500-B2

Title: Hydraulic pressure supply apparatus for transmission

Description:
BACKGROUND 
     1. Technical Field 
     An embodiment of the invention relates to a hydraulic pressure supply apparatus for a transmission, particularly to a hydraulic pressure supply apparatus for a vehicle transmission that can disengage (release) a lockup clutch of a torque converter with the simple structure. 
     2. Background Art 
     When a transmission has a torque converter equipped with a lockup clutch, under a predetermined vehicle driving condition, unless the lockup clutch is promptly disengaged, a prime mover such as an engine stalls. To cope with it, a conventional technique is configured to install a special device for releasing the lockup clutch, as taught, for example, by Japanese Laid-Open Patent Application No. 2009-92213 (&#39;213). 
     SUMMARY 
     The technique of the reference is configured as above to promptly disengage the lockup clutch under the predetermined vehicle driving condition, yet it requires the special device, the cost rises disadvantageously. 
     Further, in the reference, the manual valve is installed for switching a hydraulic passage in response to the operation of a range selector manipulated by the operator. However, the manual valve needs to be set with at least four positions of D, P, R and N and it leads to the increase in its valve length, while, since it is connected with a lever installed in a vehicle interior, it degrades the layout of components in a transmission case. Thus, due to the installment of the manual valve, the transmission can not have the compact structure. 
     An object of an embodiment of the invention is therefore to overcome the foregoing drawbacks by providing a hydraulic pressure supply apparatus for a transmission that can disengage a lockup clutch of a torque converter promptly and easily, while enabling the transmission to operate in a range selected by the operator without the manual valve. 
     In order to achieve the object, this invention provides an hydraulic pressure supply apparatus for a transmission having an input shaft connected to a drive shaft of a prime mover mounted on a vehicle through a torque converter with a lockup clutch, first and second secondary input shafts installed in parallel with the input shaft, an output shaft connected to a wheel, first and second clutches connect the input shaft to the first and second secondary input shafts upon being supplied with hydraulic pressure, a plurality of pairs of gear groups installed at the first or second secondary input shaft, and a gear selecting mechanism adapted to select one of the plurality of the pairs of the gear groups upon being supplied with hydraulic pressure to establish an odd-numbered speed or even-numbered speed, the transmission changing an output of the prime mover in speed through the established speed and transmitting it to the wheel through the output shaft, comprising: a hydraulic pump adapted to be driven by the prime mover and to draw up operating oil from a hydraulic pressure source and discharge the operating oil; a regulator valve adapted to regulate discharged pressure discharged from the hydraulic pump to a line pressure; first and second switching valves adapted to supply hydraulic pressure to the first and second clutches; a first hydraulic control valve adapted to supply the regulated line pressure to the lockup clutch; a third switching valve connected to an output port of the first hydraulic control valve; and first and second electromagnetic valves connected to operating ports of the first, second and third switching valves and adapted to switch among the first, second and third switching valves upon being energized and deenergized. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects and advantages of an embodiment of the invention will be more apparent from the following description and drawings in which: 
         FIG. 1  is an overall schematic view of a hydraulic pressure supply apparatus for a transmission according to an embodiment of this invention; 
         FIG. 2  is a hydraulic pressure circuit diagram showing details of a hydraulic pressure supply unit shown in  FIG. 1 ; 
         FIG. 3  is an enlarged view partially showing the hydraulic pressure circuit diagram of  FIG. 2 ; 
         FIG. 4  is a table showing operation modes of the transmission shown in  FIG. 1 ; 
         FIG. 5  is a set of explanatory views showing the characteristics of outputs relative to supply current of a hydraulic control valve shown in  FIG. 2  and the like; and 
         FIG. 6  is a set of explanatory views similarly showing the characteristics of outputs relative to supply current of the hydraulic control valve shown in  FIG. 2  and the like. 
     
    
    
     DESCRIPTION OF EMBODIMENT 
     A hydraulic pressure supply apparatus for a transmission according to an embodiment of the present invention will now be explained with reference to the attached drawings. 
       FIG. 1  is an overall schematic view of a hydraulic pressure supply apparatus for a transmission according to an embodiment of this invention,  FIG. 2  is a hydraulic pressure circuit diagram showing details of the apparatus shown in  FIG. 1 ,  FIG. 3  is an enlarged view partially showing the hydraulic pressure circuit diagram of  FIG. 2  and  FIG. 4  is a table showing operation modes of the transmission shown in  FIG. 1 . 
     In  FIG. 1 , symbol T indicates the transmission. The transmission T comprises a dual (twin) clutch type automatic transmission mounted on a vehicle (not shown) and having gear positions (gear ratios) of 8 forward speeds and 1 reverse speed. The transmission T has ranges of D, P, R and N. 
     The transmission T is installed with an even-numbered speed input shaft (hereinafter called “even input shaft”)  14  connected via a torque converter  12  to a drive shaft  10   a  connected to a crankshaft of an engine (prime mover)  10 , and an odd-numbered speed input shaft (hereinafter called “odd input shaft”)  16  in parallel with the even input shaft  14 . The engine  10  comprises, for example, a spark-ignition, gasoline internal combustion engine. 
     The torque converter  12  has a pump impeller  12   b  fixed to a drive plate  12   a  that is directly connected to the drive shaft  10   a  of the engine  10 , a turbine runner  12   c  fixed to the even input shaft  14 , and a lockup clutch  12   d , so that the driving force (rotation) of the engine  10  is transmitted to the even input shaft  14  through the torque converter  12 . 
     An idle shaft  18  is installed in parallel with the even and odd input shafts  14 ,  16 . The even input shaft  14  is connected to the idle shaft  18  via gears  14   a ,  18   a  and the odd input shaft  16  to the idle shaft  18  via gears  16   a ,  18   a , whereby the even and odd input shafts  14 ,  16  and idle shaft  18  are rotated by the rotation of the engine  10 . 
     Further, a first secondary input shaft  20  and second secondary input shaft  22  are installed on outer peripheries of the odd and even input shafts  16 ,  14  to be coaxially therewith and rotated relative thereto, respectively. 
     The odd input shaft  16  and the first secondary input shaft  20  are interconnected by a first clutch  24 , while the even input shaft  14  and the second secondary input shaft  22  by a second clutch  26 . The first and second clutches  24 ,  26  comprise hydraulically-operated multi-plate wet clutches. 
     An output shaft  28  is disposed between the even and odd input shafts  14 ,  16  in parallel therewith. The even and odd input shafts  14 ,  16 , idle shaft  18  and output shaft  28  are rotatably supported by bearings  30 . 
     The first secondary input shaft  20  on the odd-numbered speed side is fixed with a first-speed drive gear  32 , third-speed drive gear  34 , fifth-speed drive gear  36  and seventh-speed drive gear  38 , while the second secondary input shaft  22  on the even-numbered speed side with a second-speed drive gear  40 , fourth-speed drive gear  42 , sixth-speed drive gear  44  and eighth-speed drive gear  46 . 
     The output shaft  28  is fixed with a first-second speed driven gear  48  to be meshed with the first-speed and second-speed drive gears  32 ,  40 , a third-fourth speed driven gear  50  to be meshed with the third-speed and fourth-speed drive gears  34 ,  42 , fifth-sixth speed driven gear  52  to be meshed with the fifth-speed and sixth-speed drive gears  36 ,  44 , and a seventh-eighth speed driven gear  54  to be meshed with the seventh-speed and eighth-speed drive gears  38 ,  46 . 
     The idle shaft  18  rotatably supports an RVS (reverse) idle gear  56  that is to be meshed with the first-second speed driven gear  48  fixed at the output shaft  48 . The idle shaft  18  is connected with the RVS idle gear  56  through an RVS clutch  58 . 
     The RVS clutch  58  comprises a hydraulically-operated multi-plate wet clutch similarly to the first and second clutches  24 ,  26 , but the diameter and the number of friction plates of the RVS clutch  58  are smaller than those of the clutches  24 ,  26 . In the operation mode table in  FIG. 4 , the first and second clutches  24 ,  26  are indicated by “CL 1 ” and “CL 2 ” and the RVS clutch  50  by “RVS” in the “CLUTCH” column. 
     The odd input shaft  16  is disposed with a first-third speed synch (synchronizing) mechanism  60  that selectively engages the first-speed drive gear  32  or third-speed drive gear  34  with the first secondary input shaft  20  and with a fifth-seventh speed synch (synchronizing) mechanism  62  that selectively engages the fifth-speed drive gear  36  or seventh-speed drive gear  38  with the first secondary input shaft  20 . 
     The even input shaft  14  is disposed with a second-fourth speed synch (synchronizing) mechanism  64  that selectively engages the second-speed drive gear  40  or fourth-speed drive gear  42  with the second secondary input shaft  22  and with a sixth-eighth speed synch (synchronizing) mechanism  66  that selectively engages the sixth-speed drive gear  44  or eighth-speed drive gear  46  with the second secondary input shaft  22 . The synch mechanisms  60 ,  62 ,  64 ,  66  engage the gears with the shafts while synchronizing the rotation therebetween. 
     When the first clutch  24  or the second clutch  26  is engaged, the driving force of the engine  10  is transmitted via the odd input shaft  16  to the first secondary input shaft  16  or via the even input shaft  14  to the second secondary input shaft  22 , and then transmitted to the output shaft  28  through relevant ones of the aforementioned drive gears and driven gears. 
     When the vehicle is to be moved backward, the driving force of the engine  10  is transmitted to the output shaft  28  through the even input shaft  14 , gear  14   a , gear  18   a , RVS clutch  58 , idle shaft  18 , RVS idle gear  56  and first-second speed driven gear  48 . 
     The output shaft  28  is connected to a differential mechanism  72  through a gear  70  and the differential mechanism  72  is connected to wheels  76  through drive shafts  74 . 
     The synch mechanisms  60 ,  62 ,  64 ,  66  are operated upon being supplied with hydraulic pressure. A hydraulic pressure supply unit  80  is provided to supply hydraulic pressure to the above synch mechanisms  60 ,  62 ,  64 ,  66 , first and second clutches  24 ,  26  and RVS clutch  58 . 
     The hydraulic pressure supply unit  80  will be explained with reference to  FIG. 2 . 
     In the hydraulic pressure supply unit  80 , discharged pressure (hydraulic pressure) of operating oil ATF that is pumped up (drawn) from a reservoir  80   a  through a strainer  80   b  by a hydraulic pump (oil transfer pump)  80   c , is regulated (decreased) to a line pressure by a regulator valve  80   d.    
     Although not illustrated, the hydraulic pump  80   c  is connected to the pump impeller  12   b  of the torque converter  12  through a gear so that the hydraulic pump  80   c  is driven by the engine  10 . 
     The regulated line pressure is sent to input ports of first, second, third and fourth linear solenoid valves (hydraulic control valves (electromagnetic control valves))  80   f ,  80   g ,  80   h ,  80   i  through a hydraulic passage  80   e . In a CLUTCH column and SERVO column of the operation mode table in  FIG. 4 , the first to fourth linear solenoid valves  80   f ,  80   g ,  80   h ,  80   i  are indicated by A, B, C and D, respectively. 
     Each of the first to fourth linear solenoid valves  80   f ,  80   g ,  80   h ,  80   i  is configured to have the characteristics in which a spool is displaced in proportion to supplied current so as to change output hydraulic pressure to be outputted from its output port linear, and is of N/C (normally-closed) type in which the spool is displaced to the open position upon being supplied with current (being energized). 
     The output port of the first linear solenoid valve  80   f  is connected to the first clutch  24  of the odd input shaft  16  through a first clutch shift valve  80   j , while the output port of the second linear solenoid valve  80   g  is connected to a piston chamber of the second clutch  26  of the even input shaft  14  through a second clutch shift valve  80   k.    
     When the first or second clutch  24 ,  26  is engaged (made ON) upon being supplied with hydraulic pressure, the first or second secondary input shaft  20  or  22  is fastened to the odd or even input shaft  16  or  14 . In contrast, when hydraulic pressure is discharged so that the first or second clutch  24 ,  26  is disengaged (made OFF), the connection between the first or second secondary input shaft  20  or  22  and the odd or even input shaft  16  or  14  is cut off. 
     The output port of the third linear solenoid valve  80   h  is connected to a fifth-speed piston chamber  62   a  and seventh-speed piston chamber  62   b  of the fifth-seventh speed synch mechanism  62  and also to a second-speed piston chamber  64   a  and fourth-speed piston chamber  64   b  of the second-fourth speed synch mechanism  64  through the first clutch shift valve  80   j  and first and second servo shift valves  80   n ,  80   o.    
     The output port of the fourth linear solenoid valve  80   i  is connected to a first-speed piston chamber  60   a  and third-speed piston chamber  60   b  of the first-third speed synch mechanism  60  and also to a sixth-speed piston chamber  66   a  and eighth-speed piston chamber  66   b  of the sixth-eighth speed synch mechanism  66  through the second clutch shift valve  80   k , the first servo shift valve  80   n  and a third servo shift valve  80   p.    
     In the synch mechanisms, the above piston chambers  60   a  and  60   b ,  62   a  and  62   b ,  64   a  and  64   b  and  66   a  and  66   b  are arranged to face each other, and pistons of each pair are interconnected by a shared piston rod. The piston rod of each pair is connected to a shift folk  60   c ,  62   c ,  64   c ,  66   c.    
     The shift folk  60   c ,  62   c ,  64   c ,  66   c  is fixed on a folk shaft (not shown). Detents (not shown) are provided at the folk shaft at positions corresponding to the neutral position and right and left gear-in (engaging) positions. When the shift folk  60   c ,  62   c ,  64   c ,  66   c  is at the neutral or gear-in position, the position is retained by the detent, thereby making hydraulic pressure supply unnecessary. 
     In the synch mechanism  60 ,  62 ,  64 ,  66 , as shown in  FIG. 2 , the shift folk  60   c ,  62   c ,  64   c ,  66   c  is connected to a circular sleeve  60   d ,  62   d ,  64   d ,  66   d . The inner periphery of the sleeve  60   d ,  62   d ,  64   d ,  66   d  accommodates a hub  60   e ,  62   e ,  64   e ,  66   e  that is spline-coupled to the first or second secondary input shaft  20 ,  22  to be movable in the axial direction. 
     The first-speed and third-speed drive gears  32 ,  34  are installed on either side of the hub  60   e  through a blocking ring  60   f , the fifth-speed and seventh-speed drive gears  36 ,  38  on either side of the hub  62   e  through a blocking ring  62   f , the second-speed and fourth-speed drive gears  40 ,  42  on either side of the hub  64   e  through a blocking ring  64   f , and the sixth-speed and eighth-speed drive gears  44 ,  46  on either side of the hub  66   e  through a blocking ring  66   f . Springs are each provided near the blocking rings  60   f ,  62   f ,  64   f ,  66   f.    
     The blocking rings  60   f ,  62   f ,  64   f ,  66   f  are formed with splines while the associated drive gears are formed with dog teeth. Further, the blocking rings  60   f ,  62   f ,  64   f ,  66   f  are formed with tapered cones while the associated drive gears are formed with corresponding tapered cones. 
     Further explanation will be made taking the synch mechanism  60  as an example. Since it is configured as described above, when hydraulic pressure is supplied to one of the piston chambers, e.g., the third-speed piston chamber  60   b  so that the first-speed piston chamber  60   a  facing thereto and the piston rod connected to the piston chamber  60   a  are moved forward right in  FIG. 2 , the sleeve  60   d  connected to the piston rod through the shift folk  60   c  is moved in the same direction and contacts the spring to urge the blocking ring  60   f  toward the first-speed drive gear  32  through the spring. 
     When the sleeve  60   d  is moved further forward, the spline of the sleeve  60   d  contacts the spline of the blocking ring  60   f  and the tapered cone of the blocking ring  60   d  contacts the tapered cone of the gear  32 , whereby torque is induced by the frictional force. 
     When the sleeve  60   d  is still further moved, the rotation of the sleeve  60   d  and that of gear  32  are synchronized due to the torque and the sleeve  60   d  is moved forward with its spline pushing the spline of the blocking ring  60   f . Subsequently, when the torque disappears due to the synchronized rotation, the sleeve  60   d  is moved still further forward so that its spline is integrally engaged with the spline of the blocking ring  60   f , and moved still further forward to be integrally engaged with the dog teeth of the gear  32 . Thus the gear-in (engaging) condition is established. 
     The other synch mechanisms  62 ,  64 ,  66  are configured in the same manner. Specifically, when the sleeve  62   d ,  64   d ,  66   d  is axially moved (shifted) from the center (corresponding to the neutral position) to the in-gear position, it is engaged with the dog teeth of corresponding one of the drive gears  36 ,  38 ,  40 ,  42 ,  44 ,  46  as synchronizing their rotation, so as to connect the drive gear  36 , etc., to the first or second secondary input shaft  20 ,  22 . 
     The line pressure of a hydraulic passage  80   q  regulated by controlling an amount of operating oil discharged from a pressure regulation port  80   d   1  of the regulator valve  80   d , is sent to input ports of first to fifth solenoid valves (hydraulic control valves (electromagnetic valves))  80   r ,  80   s ,  80   t ,  80   u ,  80   v.    
     Those solenoid valves  80   r ,  80   s ,  80   t ,  80   u ,  80   v  are N/C type ON/OFF solenoid valves in each of which a spool is displaced to the open position upon being supplied with current (being energized). In an SH-SOL column of the operation mode table in  FIG. 4 , the first to fifth solenoid valves  80   r ,  80   s ,  80   t ,  80   u ,  80   v  are indicated by A, B, C, D and E, respectively. 
     An output port of the first solenoid valve  80   r  is connected to an operating port  80   j   1  of the first clutch shift valve  80   j  to urge a spool  80   j   2  rightward (in the drawing) against urging force of a spring. An output port of the second solenoid valve  80   s  is connected to an operating port  80   k   1  of the second clutch shift valve  80   k  to urge a spool  80   k   2  rightward against urging force of a spring. 
     An output port of the third solenoid valve  80   t  is connected to an operating port  80   n   1  of the first servo shift valve  80   n  to urge a spool  80   n   2  rightward against urging force of a spring. 
     Similarly, an output port of the fourth solenoid valve  80   u  is connected to an operating port  80   o   1  of the second servo shift valve  80   o  to urge a spool  80   o   2  rightward, while an output port of the fifth solenoid valve  80   v  is connected to an operating port  80   p   1  of the third servo shift valve  80   p  to urge a spool  80   p   2  rightward. 
     The hydraulic pressure supply unit  80  is further provided with a fifth linear solenoid valve (second hydraulic control valve (electromagnetic control valve))  80   w , sixth linear solenoid valve (first hydraulic control valve (electromagnetic control valve))  80   x  and LC shift valve (switching valve)  80   y.    
     The fifth linear solenoid valve  80   w  is of N/C type in which a spool is displaced to the open position upon being supplied with current (being energized), while the sixth linear solenoid valve  80   x  is of N/O (normally-opened) type in which a spool is displaced to the closed position upon being supplied with current. 
     In an LC column of the operation mode table in  FIG. 4 , the fifth linear solenoid valve  80   w  is indicated by E and in a PL column thereof, the sixth linear solenoid valve  80   x  by F. In  FIG. 4 , the “LC” means the pressure supplied to the lockup clutch  12   d  of the torque converter  12  and the “PL” means the line pressure. 
     Returning to the explanation on  FIG. 2 , an input port  80   w   1  of the fifth linear solenoid valve  80   w  is connected to the aforementioned line pressure, while a first output port  80   w   2  thereof is connected to an input port  80   y   1  of the LC shift valve  80   y  and then, through the input port  80   y   1  and an output port  80   y   2 , connected to an input side of the lockup clutch  12   d  of the torque converter  12 . 
     Internal pressure of the torque converter  12  is connected to a feedback port of the fifth linear solenoid valve  80   w . Engagement and disengagement of the lockup clutch  12   d  is controlled by the LC shift valve  80   y  and degree of engagement (engagement pressure) thereof is regulated through output pressure of the fifth linear solenoid valve  80   w.    
     The output ports of the first and second solenoid valves  80   r ,  80   s  are connected not only to the first and second clutch shift valves  80   j ,  80   k  but also to operating ports  80   y   3 ,  80   y   4  of the LC shift valve  80   y , respectively, and it makes possible to urge a spool  80   y   5  leftward (in the drawing) against urging force of a spring. 
     Accordingly, when the first and second solenoid valves  80   r ,  80   s  are deenergized (demagnetized), the spool  80   y   5  of the LC shift valve  80   y  is positioned as illustrated so that the input port  80   y   1  and output port  80   y   2  are communicated with each other. 
     As a result, LC control pressure outputted from the fifth linear solenoid valve  80   w  is supplied to the lockup clutch  12   d  of the torque converter  12  through the input port  80   y   1  and output port  80   y   2 , thereby engaging the lockup clutch  12   d.    
     On the other hand, when at least one of the first and second solenoid valves  80   r ,  80   s  is energized (magnetized), the spool  80   y   5  of the LC shift valve  80   y  is displaced leftward in the drawing and, as shown in  FIG. 3 , the input port  80   y   1  is communicated with an output port  80   y   6 . Consequently, the hydraulic pressure supply to the torque converter  12  (i.e., a piston chamber of the lockup clutch  12   d ) is stopped and, since the output port  80   y   2  is connected to a drain port, the operating oil in the piston chamber of the lockup clutch  12   d  is discharged through the drain port. 
     An input port  80   x   1  of the sixth linear solenoid valve  80   x  is connected to the line pressure and an output port  80   x   2  thereof is, on the one hand, connected to a second input port  80   y   7  of the LC shift valve  80   y  and then, through the input port  80   y   7  and an output port  80   y   8 , connected to a lubricating system (or a connecting section which is described later). 
     On the other, the output port  80   x   2  of the sixth linear solenoid valve  80   x  is connected to the pressure regulation port  80   d   1  of the regulator valve  80   d  through a hydraulic passage  80   a , as clearly shown in  FIG. 3 . As a result, the line pressure supplied through the sixth linear solenoid valve  80   x  supplies hydraulic pressure (signal pressure) to one end of a pool  80   d   2  of the regulator valve  80   d  through the pressure regulation port  80   d   1 . 
     Thus, it is configured such that, in accordance with a position of the spool  80   d   2  that can be displaced in response to the signal pressure sent after being regulated by the sixth linear solenoid valve  80   x , the regulator valve  80   d  regulates (decreases) discharged pressure of the hydraulic pump  80   c  to further regulate the line pressure. 
     The hydraulic passage  80 α connecting the output port  80   x   2  of the sixth linear solenoid valve  80   x  and the pressure regulation port  80   d   1  of the regulator valve  80   d  is connected via the connecting section (now assigned by  80 γ) with a hydraulic passage  80 β connected to the first output port  80   w   2  of the fifth linear solenoid valve  80   w  through the LC shift valve  80   y . The connecting section  80 γ is installed with a selecting mechanism  80 δ. 
     As shown in  FIG. 3 , the selecting mechanism  80 δ has a ball valve  80 δ 1  that is movably housed in an oil chamber having a larger diameter than inner diameters of the hydraulic passages  80 α,  80 β. 
     The ball valve  80 δ 1  functions to select the higher-pressure one between the output pressure of the fifth linear solenoid valve  80   w  and that of the sixth linear solenoid valve  80   x  such that the selected one acts on the pressure regulation port  80   d   1  of the regulator valve  80   d.    
     To be more specific, in the selecting mechanism  80 δ, the oil chamber is connected with the hydraulic passages  80 α,  80 β so that they face to each other, while the ball valve  80 δ 1  is movably housed in the oil chamber. Owing to the configuration, upon being pressed by the higher-pressure output between the output pressures of the fifth and sixth linear solenoid valves  80   w ,  80   x  supplied through the hydraulic passages  80 α,  80 β, the ball valve  80 δ 1  can be moved to obstruct the lower-pressure output side (that faces the higher-pressure output side). Thus, it is configured to select the higher-pressure output between the output pressures of the fifth and sixth linear solenoid valves  80   w ,  80   x , such that the selected one acts on the pressure regulation port  80   d   1  of the regulator valve  80   d.    
     Hence, the output ports of the first and second solenoid valves  80   r ,  80   s  are connected not only to the first and second clutch shift valves  80   j ,  80   k  but also to one end of the spool  80   y   5  through the operating ports  80   y   3 ,  80   y   4  of the LC shift valve  80   y , so that the spool  80   y   5  is urged leftward (in the drawing) against urging force of a spring. 
     As mentioned above concerning the explanation about the hydraulic pressure supply to the lockup clutch  12   d  of the torque converter  12 , when the first and second solenoid valves  80   r ,  80   s  are both deenergized, the spool  80   y   5  of the LC shift valve  80   y  is positioned as illustrated so that the input port  80   y   1  and output port  80   y   5  are communicated with each other, whereby the line pressure outputted through the fifth linear solenoid valve  80   w  is supplied to the lockup clutch  12   d  of the torque converter  12  through the input port  80   y   1  and output port  80   y   2 . 
     On the other hand, when at least one (or both) of the first and second solenoid valves  80   r ,  80   s  is energized, the spool  80   y   5  of the LC shift valve  80   y  is displaced leftward in  FIG. 3  so that the input port  80   y   1  is communicated with the output port  80   y   6 , whereby, as shown in the drawing, the line pressure transmitted through the fifth linear solenoid valve  80   w  is sent from the output port  80   y   6  to the connecting section  80 γ through the hydraulic passage  80 β. 
     The explanation on  FIG. 1  will be resumed. The transmission T has a shift controller  84 . The shift controller  84  is constituted as an Electronic Control Unit (ECU) having a microcomputer. Further, an engine controller  86  similarly constituted as an ECU having a microcomputer is provided to control the operation of the engine  10 . 
     The shift controller  84  is able to communicate with the engine controller  86  to acquire information including an engine speed, throttle opening, AP (Accelerator Pedal) opening, etc., therefrom. 
     A first rotational speed sensor  90  is installed near the even input shaft  14  to produce an output or signal indicative of an input rotational speed NM of the transmission T, while second, third and fourth rotational speed sensors  92 ,  94 ,  96  are installed at the first and second secondary input shafts  20 ,  22  and the output shaft  28 , respectively, and each produces an output or signal indicative of a rotational speed of the associated shaft. A fifth rotational speed  100  is installed near the drive shaft  74  to produce an output or signal indicative of a vehicle speed V. 
     First and second pressure sensors  102 ,  104  are installed at hydraulic passages connected to the first and second clutches  24 ,  26  of the hydraulic pressure supply unit  80  to produce outputs or signals indicative of pressure (hydraulic pressure) of the operating oil ATF to be supplied to the first and second clutches  24 ,  26 , respectively. 
     A range selector position sensor  106  is provided near a range selector (not shown) installed at the operator&#39;s seat of the vehicle and produces an output or signal indicative of a range selected from among D, P, R and N through manipulation by the operator. 
     The outputs of the above sensors are all sent to the shift controller  84 . Based on the sensor outputs and information acquired by communicating with the engine controller  86 , the shift controller  84  energizes and deenergizes the first linear solenoid valve  80   f , etc., in accordance with the operation mode table in  FIG. 4 , thereby controlling the operation of the transmission T. 
     As shown in the operation mode table in  FIG. 4 , in this embodiment, the transmission T has four operation modes of A, B, C and D, as follows: 
     A: Normal driving (running) in the D range 
     B: Driving (running) only with odd-numbered speed in the D range 
     C: Driving (running) only with even-numbered speed in the D range 
     D: Driving (running) in the R range or parked in the P or N range 
     In the foregoing, the modes B and C are given as fail safe modes to be applied when a failure (abnormality) occurs at the first or second clutch  24 ,  26 , or the like. 
     In  FIG. 4 , numbers of 1 to 8 labeled beside A, B, C and D in a vertical row under the “MODE” (operation mode) indicate forward gears of first to eighth speeds. Letters of A, B, C, D and E in a lateral row under the “SH-SOL” indicate the first to fifth solenoid valves  80   r ,  80   s ,  80   t ,  80   u ,  80   v  as mentioned above, and when a circle (o) is given, it means to be energized while when a cross (x) is given, it means to be deenergized, so that the corresponding gear is established. 
     In the same manner, letters of A, B, C, D, E and F under the “CLUTCH,” “SERVO,” “LC” and “PL” indicate the first to sixth linear solenoid valves  80   f ,  80   g ,  80   h ,  80   i ,  80   w ,  80   x . When one of the letters of A to F is given, it means that the corresponding valve is energized. 
     The fifth and sixth linear solenoid valves  80   w ,  80   x  are indicated by E and F in the LC column and PL column. In the PL column, “F or E” means that the higher-pressure one between the output pressure of the fifth linear solenoid valve  80   x  (F) and that of the sixth linear solenoid valve  80   w  (E) is applied. 
     As for the reverse gear, in the mode A, since it is established when hydraulic pressure is supplied to the RVS clutch  58  to engage it, no indication is given. In the modes B, C and D, the reverse gear is not established when a cross (x) is given and is established when one of the valves corresponding to the indicated letter, e.g., the second linear solenoid valve  80   g  indicated by B is energized. 
     As can be clearly seen in  FIG. 4 , this embodiment is characterized in that the lockup clutch  12   d  of the torque converter  12  can be disengaged with simple structure, while the operation of the transmission T can be changed among the above four operation modes. 
     The change in the operation mode is first explained. When both of the first and second solenoid valves  80   r ,  80   s  are deenergized, the mode A is established. When the first solenoid valve  80   r  is deenergized and the second solenoid valve  80   s  is energized, the mode B is established, while in the opposite case thereof, the mode C is established. When both of the first and second solenoid valves  80   r ,  80   s  are energized, the mode D is established. 
     In the mode A, the first and second clutches  24 ,  26  and the lockup clutch  12   d  are all engageable; in the mode B, only the first clutch  24  is engageable; in the mode C, only the second clutch  26  is engageable; and in the mode D, none of the three clutches  24 ,  26 ,  12   d  are engageable. 
     Based on the output of the range selector position sensor  106 , when a failure does not occur at the first and second clutches  24 ,  26 , the shift controller  84  energizes and deenergizes the first and second solenoid valves  80   r ,  80   s  to establish the mode A or D, while when a failure occurs, controlling the valves  80   r ,  80   s  to establish the mode C or D in accordance with the table of  FIG. 4 . 
     In the mode A, the first-third speed synch mechanism  60  is moved rightward in  FIGS. 1 and 2  to connect the first-speed drive gear  32  to the first secondary input shaft  20  to engage the first clutch  24 , so that the first speed gear is established. 
     When the second-fourth speed synch mechanism  64  is moved rightward in  FIGS. 1 and 2  to connect the second-speed drive gear  40  to the second secondary input shaft  22  to engage the second clutch  26 , the second speed gear is established. The gear is shifted up and down among the first to eighth speeds by repeating the similar process. 
     At this time, a so-called “pre-shift” operation in which, while a present gear is established, hydraulic pressure is supplied to the synch mechanism corresponding to the next (target) gear, is carried out. With this, it becomes possible to shift the gear with uninterrupted driving force and good response. 
     This embodiment is configured to be able to change (select) the operation mode among the four modes through magnetization and demagnetization of the first and second solenoid valves  80   r ,  80   s . Owing to this configuration, it becomes possible to change or select the operation mode with simple structure, i.e., without the manual valve that is generally used in this type of hydraulic pressure supply apparatus to switch a hydraulic passage in response to the operation of a range selector. Further, since driving of the vehicle in either one of the mode B and C is possible even when a failure occurs, the required minimum driving can be ensured. 
     Next, the configuration that the lockup clutch  12   d  of the torque converter  12  can be disengaged with simple structure will be explained. In this embodiment, in order to achieve this configuration, the first output port  80   w   2  of the fifth linear solenoid valve  80   w  that controls the line pressure and supplies it to the lockup clutch  12   d  of the torque converter  12  is connected to the LC shift valve  80   y , and the operating ports  80   y   3 ,  80   y   4  of the LC shift valve  80   y  are connected to at least one (more exactly, both) of the first and second solenoid valves  80   r ,  80   s  with which the operation mode can be changed. 
     Specifically, since some components double as other devices, it becomes possible to suppress increase in the number of components. Further, when a failure occurs, the foregoing configuration simply connects the output port  80   y   2  of the LC shift valve  80   y  to the drain port, so that hydraulic pressure supply to the lockup clutch  12   d  of the torque converter  12  can be promptly stopped to disengage the lockup clutch  12   d , thereby reliably avoiding a stall of the engine  10 . 
     This embodiment is further characterized in that, as explained with reference to  FIG. 3 , the hydraulic passage  80 α connecting the output port  80   x   2  of the sixth linear solenoid valve  80   x  and the pressure regulation port  80   d   1  of the regulator valve  80   d  is connected via the connecting section  80 γ with the hydraulic passage  80 β connected to the first output port  80   w   2  of the fifth linear solenoid valve  80   w  through the LC shift valve  80   y , and the connecting section  80 γ is installed with the selecting mechanism  80 δ in which the higher pressure output is selected to act on the pressure regulation port  80   d   1  of the regulator valve  80   d.    
     This will be further explained with reference to  FIG. 5  onward. 
       FIG. 5  is a set of explanatory views showing the characteristics of outputs relative to supply current to the valves. 
     As mentioned earlier, as a technique described in &#39;213, in order to supply a predetermined maximum pressure when a solenoid valve used to control line pressure fails, the solenoid valve is configured to be an N/O type linear solenoid valve that is opened when a failure occurs so as to supply the predetermined maximum pressure. Since manufacturing variance exists in this type of solenoid valve that controls line pressure, a value covering the variance (called the “variance coverage value”) is always added to a current value to be supplied. Under this condition, when the maximum value of supply line pressure is increased, a gain of the line pressure relative to the current value is increased and fluctuation in hydraulic pressure is also increased, so that the variance coverage value is needed to be increased. 
     In  FIG. 5A , solid lines indicate the characteristics of output pressure (maximum pressure) of the sixth linear solenoid valve  80   x  and imaginary lines indicate that when it is assumed that the output pressure is increased. As illustrated, when the output pressure is increased, a gain of the output relative to current supplied to a valve is increased and, consequently, fluctuation in hydraulic pressure becomes larger relative to current fluctuation in the same current value (command value), so that control accuracy deteriorates. 
     Further, as shown in  FIG. 5B , when the output pressure of the sixth linear solenoid valve  80   x  is increased, consumption current is increased in a low line pressure range that is often used when the vehicle cruises. 
     In view of the above facts, this embodiment is configured to ensure driving of the vehicle without a special device even when the sixth linear solenoid valve  80   x  that controls the line pressure fails, and suppress the increase in control margin of the line pressure and in consumption current. 
       FIG. 6A  is an explanatory view showing output pressure characteristics relative to supply current characteristics of the fifth and sixth linear solenoid valve  80   w ,  80   x.    
     Since the fifth linear solenoid valve  80   w  needs to output engagement pressure to the lockup clutch  12   d  of the torque converter  12 , the output pressure thereof is set higher than the maximum output pressure of the sixth linear solenoid valve  80   x  used to control the line pressure. 
     Note that the sixth linear solenoid valve  80   x  should preferably be of N/O type because it needs to output necessary hydraulic pressure when failed, while the fifth linear solenoid valve  80   w  should preferably be of N/C type so as not to output hydraulic pressure when failed. 
     This embodiment is configured to select the higher-pressure one between the output pressures of the fifth and sixth linear solenoid valves  80   w ,  80   x , as shown in  FIG. 6B . 
     Specifically, in a normal range, since the input port  80   y   1  and output port  80   y   2  of the LC shift valve  80   y  are communicated with each other, the output pressure of the fifth linear solenoid valve  80   w  is not supplied to the selecting mechanism  80 δ. However, in the case where hydraulic pressure is supplied to at least one of the operating ports  80   y   3 ,  80   y   4  of the LC shift valve  80   y  so that the output port  80   y   2  and output port  80   y   6  are communicated with each other, the output pressures of the fifth and sixth linear solenoid valves  80   w ,  80   x  are sent to the selecting mechanism  80 δ and the higher-pressure one therebetween is outputted from the selecting mechanism  80 δ. 
     Therefore, as mentioned in the foregoing, it is configured such that the selecting mechanism  80 δ (ball valve  80 δ 1 ) is provided at the connecting section  80 γ at which the hydraulic passage  80 α connecting the sixth linear solenoid valve  80   x  and the pressure regulation port  80   d   1  of the regulator valve  80   d  and the hydraulic passage  80 β connected to the first output port  80   w   2  of the fifth linear solenoid valve  80   w  are interconnected. 
     Further, it is configured such that the fifth linear solenoid valve  80   w  is connected to the LC shift valve  80   y , the operating ports  80   y   3 ,  80   y   4  are connected to the output ports of the first and second solenoid valves  80   r ,  80   s , and the second output port  80   y   6  of the LC shift valve  80   y  is connected to the connecting section  80 γ, whereby, at the connecting section  80 γ, the higher-pressure one between the output pressures of the fifth and sixth linear solenoid valves  80   w ,  80   x  is selected to act on the pressure regulation port  80   d   1 . 
     Here, when hydraulic pressure is not supplied from one or any of the first and second solenoid valves  80   r ,  80   s , the spool  80   y   5  of the LC shift valve  80   y  is positioned as illustrated, so that hydraulic pressure supplied from the output port  80   y   6  of the LC shift valve  80   y  to the oil chamber of the selecting mechanism  80 δ of the connecting section  80 γ through the hydraulic passage  80 β is zero. 
     As a result, the ball valve  80 δ 1  is positioned in the oil chamber of the selecting mechanism  80 δ as illustrated and accordingly, the output pressure of the sixth linear solenoid valve  80   x  is selected and supplied to the regulator valve  80   d.    
     In contrast, when hydraulic pressure is supplied from at least one of the first and second solenoid valves  80   r ,  80   s , the spool  80   y   5  of the LC shift valve  80   y  is displaced so that, as shown in  FIG. 3 , the input port  80   y   1  is communicated with the output port  80   y   6  while the output port  80   y   2  is connected to the drain port. Accordingly, the higher-pressure one between the output pressures of the fifth and sixth linear solenoid valves  80   w ,  80   x  is selected and supplied to the regulator valve  80   d.    
     Hence, driving of the vehicle can be ensured without a special device even when the sixth linear solenoid valve  80   x  that controls the line pressure fails. 
     Further, when the vehicle is moved backward (reverse), since the lockup clutch  12   d  is generally disengaged, it is not necessary to use the fifth linear solenoid valve  80   w  for engaging the lockup clutch  12   d . Consequently, when it is desired to make the line pressure high in a limited range such as a reverse range, the fifth linear solenoid valve  80   w  is utilized for that purpose, so that it becomes possible to reliably establish the reverse gear and suppress the variance coverage value, thereby preventing the increase in consumption current. 
     To be more specific, since the RVS clutch  58  is smaller in diameter and the number of friction plates than the first and second clutches  24 ,  26 , the higher line pressure is necessary compared to the first and second clutches  24 ,  26 . However, since it is configured as above, the reverse gear can be reliably established. 
     As stated above, the embodiment is configured to have an hydraulic pressure supply apparatus (hydraulic pressure supply unit  80 ) for a transmission (T) having an input shaft ( 12 ) connected to a drive shaft ( 10   a ) of a prime mover (engine  10 ) mounted on a vehicle through a torque converter ( 12 ) with a lockup clutch ( 12   a ), first and second secondary input shafts ( 20 ,  22 ) installed in parallel with the input shaft, an output shaft ( 28 ) connected to a wheel ( 76 ), first and second clutches ( 24 ,  26 ) connect the input shaft to the first and second secondary input shafts upon being supplied with hydraulic pressure, a plurality of pairs of gear groups (drive gears  32 ,  34 ,  36 ,  38 ,  40 ,  42 ,  44 ,  46 ) installed at the first or second secondary input shaft, and a gear selecting mechanism (synchronizing mechanisms  60 ,  62 ,  64 ,  66 ) adapted to select one of the plurality of the pairs of the gear groups upon being supplied with hydraulic pressure to establish an odd-numbered speed or even-numbered speed, the transmission changing an output of the prime mover in speed through the established speed and transmitting it to the wheel through the output shaft, comprising: a hydraulic pump ( 80   c ) adapted to be driven by the prime mover and to draw up operating oil (ATF) from a hydraulic pressure source (reservoir  80   a ) and discharge the operating oil; a regulator valve ( 80   d ) adapted to regulate discharged pressure discharged from the hydraulic pump to a line pressure; first and second switching valves (first and second clutch shift valves  80   j ,  80   k ) adapted to supply hydraulic pressure to the first and second clutches; a first hydraulic control valve (fifth linear solenoid valve  80   w ) adapted to supply the regulated line pressure to the lockup clutch; a third switching valve (LC shift valve  80   y ) connected to an output port of the first hydraulic control valve; and first and second electromagnetic valves (first and second solenoid valves  80   r ,  80   s ) connected to operating ports of the first, second and third switching valves and adapted to switch among the first, second and third switching valves upon being energized and deenergized. 
     With this, it becomes possible to promptly and easily disengage the lockup clutch  12   d  of the torque converter  12  with simple structure, i.e., without a special device, in other words, with the structure that does not result in high cost. Further, it becomes possible to operate the transmission T in a range selected by the operator without the manual valve. 
     In the apparatus, one of the first and second electromagnetic valves is energized and deenergized to change an operation mode of the transmission among a first operation mode (mode A) in which shifting is possible with the odd-numbered speed and the even-numbered speed in a forward range (D), a second operation mode (mode B or C) in which shifting is possible with the odd-numbered speed or the even-numbered speed in the forward range, and a third operation mode (mode D) in which the vehicle is driven in a range (NP, R, N) other than the forward range. 
     With this, in addition to the above effects, the operation of the transmission T can be changed among the three (more precisely, four) modes only by magnetizing and demagnetizing the first and second electromagnetic valves (first and second solenoid valves)  80   r ,  80   s.    
     In the apparatus, one of the first and second electromagnetic valves is energized and deenergized to supply hydraulic pressure to the lockup clutch through the first hydraulic control valve and stop the supply. With this, in addition to the above effects, the lockup clutch  12   d  can be easily and promptly disengaged only by magnetizing and demagnetizing the first and second electromagnetic valves (first and second solenoid valves)  80   r ,  80   s.    
     In the apparatus, the input shaft includes first and second input shafts (odd-numbered speed input shaft  16  and first secondary input shaft  20 ; even-numbered speed input shaft  14  and second secondary input shaft  22 ) connected to the drive shaft of the prime mover through first and second clutches, respectively, and the output shaft includes at least one output shaft installed in parallel with the first and second input shafts, and the transmission includes a dual clutch type automatic transmission having: a plurality of speeds (first-speed drive gear  32  to seventh-eighth speed driven gear  54 ) to be established through gears installed between the first and second input shafts and the output shaft, the plurality of the speeds being constituted by at least four sets; a synchronizing mechanism ( 60 ,  62 ,  64 ,  66 ) corresponding to each of the four sets, adapted to be operated upon being supplied with hydraulic pressure to move from a neutral position to select one of the speeds that constitutes a corresponding one of the four sets so as to engage a corresponding one of the gears to one of the first and second input shafts and the output shaft; and a hydraulic pressure supply control unit including first and second pressure regulators (fourth and third linear solenoid valves  80   i ,  80   h ) interposed at a hydraulic pressure circuit connecting the hydraulic pressure source and the synchronizing mechanism, each adapted to selectively supply hydraulic pressure to the synchronizing mechanism to move such that the output of the prime mover is outputted from one of the first and second input shafts to the output shaft through the selected speed. 
     With this, in addition to the above effects, in the dual clutch type automatic transmission, it becomes possible to promptly and easily disengage the lockup clutch  12   d  of the torque converter  12  with simple structure, i.e., without a special device. Further, it becomes possible to operate the transmission T in a range selected by the operator without the manual valve. 
     It should be noted that, in the foregoing, although the dual clutch type automatic transmission is explained, it is not limited to the exemplification above and any configuration can be applied. 
     It should also be noted that, although the engine (internal combustion engine) is exemplified as the prime mover, it may be hybrid combining the engine and an electric motor, or only the motor may be used. 
     Japanese Patent Application No. 2011-121641 filed on May 31, 2011 is incorporated by reference herein in its entirety. 
     While the invention has thus been shown and described with reference to specific embodiments, it should be noted that the invention is in no way limited to the details of the described arrangements; changes and modifications may be made without departing from the scope of the appended claims.