Abstract:
A valve section that functions as a solenoid valve device that includes a pressure adjusting section that adjusts fluid pressure supplied from a fluid pressure source; a pump section that sucks and discharges working fluid in a reservoir; and a single solenoid section that drives the pressure adjusting section and the pump section.

Description:
INCORPORATION BY REFERENCE 
     The disclosure of Japanese Patent Applications No. 2008-141148 filed on May 29, 2008, No. 2008-179928 filed on Jul. 10, 2008, and No. 2009-070666 filed on Mar. 23, 2009, including the specification, drawings and abstract are incorporated herein by reference in its entirety. 
     BACKGROUND 
     The present invention relates to a solenoid valve device. 
     As a solenoid valve of this type in related art, there is one proposed that includes a sleeve having a cylindrical valve chamber formed therein with various ports of an input port, an output port, a drain port, and a feedback port for introducing and draining hydraulic oil, a spool that is a shaft-like member inserted into the valve chamber and includes a plurality of cylindrical lands having an outer diameter of about the same size as the inner diameter of the valve chamber and a cylindrical communicating portion that has an outer diameter smaller than the outer diameter of the lands and communicates between the ports, and a solenoid for moving the spool in an axial direction (for example, refer to Japanese Patent Application Publication No. JP-A-2004-176895). 
     Further, there is also proposed a solenoid pump which pumps fluid by repeating excitation and de-excitation of an electromagnetic coil (for example, refer to Japanese Patent Application Publication No. JP-A-2007-126974). This solenoid pump is provided with a spring member assembled for bouncing back a piston that forms a pump chamber by the bounce force of the spring member and disposed with an electromagnetic coil for generating attractive force in an opposite direction to the bouncing force of the spring member. De-excitation (switching off) of the electromagnetic coil moves the piston by the bouncing force of the spring member to suck fluid, and excitation (switching on) of the electromagnetic coil moves the piston by the attractive force of the electromagnetic coil to discharge the fluid sucked. 
     SUMMARY 
     In a device combined with a pump other than a solenoid valve, for example, a device in which a hydraulic circuit for activating clutches (brakes) of a vehicle automatic transmission on and off is combined with a solenoid valve (linear solenoid) for adjusting clutch pressure and a pump for generating fluid pressure, the space for mounting the device may be limited, and therefore miniaturization of device is required as much as possible. 
     It is a main object of the present invention to achieve miniaturization of a solenoid valve device as a whole, combining the function as a pump. 
     In order to achieve the aforementioned main object, the solenoid valve device of the present invention has adapted the following means. 
     A solenoid valve device according to a first aspect of the present invention includes: a pressure adjusting section that adjusts fluid pressure supplied from a fluid pressure source; a pump section that sucks and discharging working fluid in a reservoir; and a single solenoid section that drives the pressure adjusting section and the pump section. 
     In the solenoid valve device according to the first aspect of the present invention, the pressure adjusting section that adjusts the fluid pressure supplied from the fluid pressure source and the pump section that sucks and discharging the working fluid in the reservoir are driven by the single solenoid section. Accordingly, comparing to the case where a pressure adjusting valve and a solenoid pump are separately provided, the device as a whole can be miniaturized. 
     The solenoid valve device according to the first aspect of the present invention may further include a valve element. In the solenoid valve device, the pressure adjusting section is operated by electromagnetic force of the solenoid section, and the valve element selectively operates to compress and expand a pump chamber in the pump section and to adjust fluid pressure supplied from the fluid pressure source. 
     In the solenoid valve device according to an aspect of the present invention, the pressure adjusting section may include an elastic member that generates a thrust force in a direction opposite to a sliding direction of the valve element when driven by a thrust force of the solenoid section and an elastic member chamber that houses the elastic member. In the solenoid valve device, the elastic member chamber is commonly used as at least a part of the pump chamber. Here, the “elastic member” includes a spring. In the solenoid valve device according to the first aspect of the present invention, the working fluid may be sucked as the valve element slides by an elastic force of the elastic member when the thrust force of the solenoid section is released, and the working fluid sucked may be discharged as the valve element slides by the thrust force generated by the solenoid section. In the solenoid valve device according to the first aspect of the present invention, the pressure adjusting section may have a feedback port and be structured as a normal-closed type solenoid valve that is closed when the solenoid section is not being energized. Consequently, as the load of the elastic member (spring) can be reduced comparing to a normal-open type solenoid valve which is opened when the solenoid section is being energized, the thrust force required for the solenoid section when functioning as a pump can be reduced, thereby achieving miniaturization of the solenoid section. This is based on that the feedback pressure in a normal-closed type solenoid valve acts in the same direction as the thrust force of the solenoid section, while the feedback pressure in a normal-open type solenoid valve acts in an opposite direction to the thrust force of the solenoid section. 
     Further, in the solenoid valve device according to the first aspect of the present invention, the pump section may be provided with a suction/discharge mechanism that sucks the working fluid from the reservoir and discharges the working fluid sucked to an operation target. 
     In the solenoid valve device according to an aspect of the present invention in which the solenoid valve device is provided with the suction/discharge mechanism, the suction/discharge mechanism may be structured with a suction check valve that allows the working fluid to flow from the reservoir to the pump chamber in the pump section and a discharge check valve that allows the working fluid to flow from the pump chamber to the operation target. In the solenoid valve device according to the first aspect of the present invention, the suction check valve may be closed when inside the pump chamber is under a positive pressure and opened when inside the pump chamber is under a negative pressure, and the discharge check valve may be closed when inside the pump chamber is under a negative pressure and opened when inside the pump chamber is under a positive pressure. 
     The solenoid valve device according to an aspect of the present invention in which the pressure adjusting section is provided with the valve element, the elastic member, and the elastic member chamber may further include a suction check valve that allows the working fluid to flow from the reservoir to the pump chamber in the pump section and a discharge check valve that allows the working fluid to flow from the pump chamber to the operation target, and in the solenoid valve device, the suction check valve and the discharge check valve may be disposed external to the pressure adjusting section, or the suction check valve may be built into the pressure adjusting section. In the latter case, as the suction check valve which is considered to greatly contribute to volumetric efficiency can be structured in relatively high precision, the volumetric efficiency can be improved. Further, in the latter case, the discharge check valve may be built into the pressure adjusting section. As a consequence, the volumetric efficiency can further be improved. 
     Further, the solenoid valve device according to the first aspect of the present invention may further include a switching device that switches between a first state in which the working fluid in the pump chamber in the pump section is drained and a second state in which the working fluid in the pump chamber is inhibited to be drained. In the solenoid valve device according to the first aspect of the present invention, the switching device may have a spool being slidable in a hollow portion connected to the pump chamber through a flow passage, and may be a switching valve forming the first state when the spool is at a first position and forming the second state when the spool is at a second position. In the solenoid valve device according to the first aspect of the present invention, the pump section may be built in the pressure adjusting section, the pressure adjusting section may have a suction port, a discharge port, and a drain port that is connected to the hollow portion of the switching valve through the flow passage, and the working fluid may be sucked through the suction port and the working fluid sucked may be discharged through the discharge port. 
     Further, in the solenoid valve device according to the first aspect of the present invention, the pressure adjusting section may be provided with a hollow sleeve in which an input port and an output port are formed and a spool that forms a pressure adjusting chamber with the sleeve such that the fluid pressure input from the input port is adjusted and output to the output port by sliding inside the sleeve, and the pump chamber in the pump section may be formed as a space blocked from the pressure adjusting chamber. Consequently, the function as a pressure adjusting valve and the function as a pump can be provided for a single set of the sleeve and the spool, and therefore, the device can further be miniaturized. 
     The solenoid valve device incorporated in a drive unit that drives an automatic transmission provided with a plurality of fluid pressure servos for friction engagement elements according to the first aspect of the present invention may be structured to function as a pressure adjusting valve that adjusts fluid pressure acting on one of the plurality of fluid pressure servos for the friction engagement elements and to function as a solenoid pump that generates fluid pressure acting on the other one of the plurality of fluid pressure servos for the friction engagement elements, or may be structured to function as a pressure adjusting valve that adjusts fluid pressure acting on one of the plurality of fluid pressure servos for the friction engagement elements and to function as a solenoid pump that generates fluid pressure acting on the one of the plurality of fluid pressure servos for the friction engagement elements. Here, the “friction engagement elements” include, in addition to a clutch for connecting two rotational systems, a brake for connecting a single rotation system to a fixing system, such as a case. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram showing the configuration of a solenoid valve  20  according to an embodiment of the present invention; 
         FIGS. 2A and 2B  are schematic diagrams showing the configuration of a drain valve  100 ; 
         FIG. 3  is a schematic diagram showing the configuration of a motor vehicle  120  in which a drive unit for an automatic transmission is installed; 
         FIG. 4  is a schematic diagram showing the configuration of an automatic transmission  130 ; 
         FIG. 5  is an operating table of the automatic transmission  130 ; 
         FIG. 6  is a schematic diagram showing the configuration of a hydraulic circuit  140 ; 
         FIGS. 7A and 7B  are diagrams explaining the operation of a switching valve  148 ; 
         FIG. 8  is a flowchart showing an example of an auto-stop control routine; 
         FIG. 9  is a explanatory chart showing the changes in time for a vehicle speed V, an engine speed Ne, an accelerator opening Acc, a brake switch signal BSW, a shift position SP, a line pressure PL, hydraulic pressure for a clutch C 1 , current command for a linear solenoid SLC 1  and current command for a solenoid pump; 
         FIG. 10  is a schematic diagram showing the configuration of a solenoid valve  20 B according to a modification example; 
         FIG. 11  is a schematic diagram showing the configuration of a solenoid valve  20 C according to a modification example; 
         FIG. 12  is a schematic diagram showing the configuration of a solenoid valve  20 D according to a modification example; 
         FIG. 13  is a schematic diagram showing the configuration of a hydraulic circuit  240  according to a modification example; 
         FIGS. 14A and 14B  are diagrams explaining the operation of a switching valve  250 ; 
         FIG. 15  is a schematic diagram showing the configuration of a solenoid valve  20 E according to a modification example; 
         FIG. 16  is a schematic diagram showing the configuration of a hydraulic circuit  340 ; and 
         FIGS. 17A and 17B  are diagrams explaining the operation of a switching valve  350 . 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Next, an embodiment of the present invention will be described with an embodiment of the present invention. 
       FIG. 1  is a schematic diagram showing the configuration of a solenoid valve  20  according to the embodiment of the present invention. The solenoid valve  20  of the present embodiment is used, for example, for hydraulic control of clutches incorporated in an automatic transmission, and is structured to function as a linear solenoid valve for directly controlling the clutches by generating optimum clutch pressure from a line pressure and to function as a solenoid pump for generating hydraulic pressure. The solenoid valve  20  is provided with a solenoid section  30 , a pressure adjusting valve section  40  driven by the solenoid section  30  for inputting the line pressure, adjusting the line pressure input, and outputting the adjusted line pressure, and a pump section  60  also driven by the solenoid section  30  for pumping hydraulic oil in a reservoir  30   a  ( FIG. 6 ). 
     The solenoid section  30  is provided with: a case  31  as a cylindrical member having an open end and a closed bottom end; a coil (solenoid coil)  32  that is disposed on an inner periphery of the case  31  with an insulated electrical conductor wound around an insulating bobbin; a first core  34  composed of a flange portion  34   a  that has a flange outer peripheral portion fixed to the open end of the case  31  and a cylindrical portion  34   b  axially extending from the flange portion  34   a  along an inner peripheral surface of the coil  32 ; a cylindrical second core  35  that abuts an inner peripheral surface of a recessed portion formed at the bottom end of the case  31  and axially extending along the inner peripheral surface of the coil  32  to a position from which the cylindrical portion  34   b  of the first core  34  is separated by a predetermined gap; a plunger  36  that is inserted in the second core  35  and is axially slidable on inner peripheral surfaces of the first core  34  and the second core  35 ; and a shaft  38  that is inserted in the cylindrical portion  34   b  of the first core  34  abutting the tip of the plunger  36 , and axially slidable on an inner peripheral surface of the cylindrical portion  34   b . Further, in the solenoid section  30 , terminals from the coil  32  are connected to a connector portion  39  formed on an outer peripheral portion of the case  31 , and the coil  32  is energized through these terminals. The case  31 , the first core  34 , the second core  35 , and the plunger  36  are all composed of a ferromagnetic material such as highly pure iron, and a space between an end face of the cylindrical portion  34   b  of the first core  34  and an end face of the second core  35  are formed to serve as a non-magnetic body. As this space is to serve as a non-magnetic body, a non-magnetic material such as stainless steel or brass may be provided. 
     In the solenoid section  30 , when the coil  32  is energized, a magnetic circuit is formed such that magnetic flux flows around the coil  32  in the order of the case  31 , the second core  35 , the plunger  36 , the first core  34 , and the case  31 . Consequently, an attractive force is acted on between the first core  34  and the plunger  36  to attract the plunger  36 . As described above, since the tip of the plunger  36  abuts on the shaft  38  that is axially slidable on the inner peripheral surface of the first core  34 , the shaft  38  is pushed forward (leftward in the drawing) as the plunger  36  is attracted. 
     The pressure adjusting valve section  40  and the pump section  60  are provided with, as common members thereof, a nearly cylindrical sleeve  22  that is incorporated in a valve body  10  and has one end attached to the first core  34  by the case  31  of the solenoid section  30 , a spool  24  that is inserted in the internal space formed in the sleeve  22  and that has one end abutting on the tip of the shaft  38  of the solenoid section  30 , an end plate  26  screwed onto the other end of the sleeve  22 , and a spring  28  provided between the end plate  26  and the other end of the spool  24  for biasing the spool  24  towards the solenoid section  30 . 
     The sleeve  22  is formed, as openings formed in a portion that constitutes the pressure adjusting valve section  40 , with an input port  42  for inputting hydraulic oil, an output port  44  for discharging the hydraulic oil input to a clutch C 2 , a drain port  46  for draining the hydraulic oil input, and a feedback port  48  for causing a feedback force to be acted on the spool  24  by inputting the hydraulic oil output from the output port  44  through an oil passage  48   a  formed by the inner surface of the valve body  10  and the outer surface of the sleeve  22 . Further, at the end of the sleeve  22  on the solenoid section  30  side, a drain hole  49  for draining the hydraulic oil leaked from between the inner peripheral surface of the sleeve  22  and the outer peripheral surface of the spool  24  as the spool  24  slides. 
     The sleeve  22  is formed, as openings formed in a portion that constitutes of the pump section  60 , with a suction port  62  for sucking hydraulic oil, a discharging port  64  for discharging the hydraulic oil sucked, and a drain port  66  for draining the hydraulic oil remaining when the function of the pump section  60  is stopped. The drain port  66  is adapted to drain hydraulic oil through a drain valve  100 .  FIGS. 2A and 2B  are schematic diagrams showing the configuration of the drain valve  100 . The drain valve  100  is inserted, as shown in the drawing, with a spool  102 . The spool  102  is disposed with an upper land  102   a  having an outer diameter of a value L 1  at an upper portion of the spool  102  and a lower land  102   b  having an outer diameter of a value L 2 , which is larger than the value L 1 , at a lower portion of the spool  102 . The drain valve  100  is provided with a spring  104  for biasing the spool  102  upward in the drawing at a lower end of the drain valve  100 . There is also formed, sequentially from top to bottom of the drawing, a signal pressure port  106   a  for inputting line pressure PL as a signal pressure, an input port  106   b  communicating with the drain port  66  of the pump section  60 , and an output port  106   c  for draining. In the drain valve  100 , when the line pressure PL is off, the biasing force of the spring  104  moves the spool  102  upward in the drawing, blocking off the communication between the input port  106   b  and the output port  106   c  by the land  102   b  having the outer diameter of value L 2  (refer to  FIG. 2A ). When the line pressure PL is acted on, the signal pressure overcomes the biasing force of the spring  104  and moves the spool  102  downward in the drawing, communicating the input port  106   b  with the output port  106   c  through a clearance of the land  102   a  having the outer diameter of the value L 1 , which is smaller than the value L 2 , to drain the remaining hydraulic oil (refer to  FIG. 2B ). 
     The spool  24  is formed as a shaft-like member to be inserted inside the sleeve  22 , and is provided with: three cylindrical lands  52 ,  54  and  56  slidable on an inner wall of the sleeve  22 ; a communicating portion  58  that is formed to couple the land  52  with the land  54 , has an outer diameter smaller than the outer diameters of the lands  52  and  54  in a tapered shape such that the outer diameter becomes smaller towards the center from each of the lands  52  and  54 , and communicates between each of the input port  42 , the output port  44 , and the drain port  46 ; a coupling portion  59  that couples the land  54  with the land  56  having an outer diameter smaller than that of the land  54  and forms a feedback chamber together with the inner wall of the sleeve  22  for causing the feedback force to be acted on the spool  24  towards the solenoid section  30 ; and a suction check valve  80  connected to the land  56 . The sleeve  22 , the communicating portion  58  of the spool  24 , and the lands  52  and  54  form a pressure adjusting chamber  50 , and the sleeve  22 , the suction check valve  80  of the spool  24 , and the end plate  26  form a pump chamber  70 . 
     The suction check valve  80  is provided with: a cylindrical body  82  that is coupled with the land  56  and formed with an opening  82   a  in the center thereof for communicating the pump chamber  70  with the suction port  62 ; a ball  84 ; and a spring  86  with the end plate  26  as a spring holder for urging the ball  84  to be pressed against the opening  82   a  of the body  82 . The suction check valve  80  is closed by the biasing force of the spring  86  when inside the pump chamber  70  is under a positive pressure, and is opened when inside the pump chamber  70  is under a negative pressure. 
     Further, the valve body  10  is provided with a discharge check valve  90  that is a counterpart of the suction check valve  80 , and the discharge check valve  90  is structured to be closed when inside the pump chamber  70  is under a negative pressure and to be opened when inside the pump chamber  70  is under a positive pressure. 
     The operation of the solenoid valve  20  of the present embodiment thus structured, particularly when functioning as a linear solenoid valve and as a solenoid pump, will be described. First, the operation when functioning as a linear solenoid valve will be described. Now, the coil  32  is not being energized. In this case, as the spool  24  is moved towards the solenoid section  30  by the biasing force of the spring  28 , the input port  42  is blocked by the land  54 , and the output port  44  and the drain port  46  are placed in communication with each other through the communicating portion  58 . Accordingly, no hydraulic pressure is acted on the clutch C 2 . When the coil  32  is energized, the plunger  36  is attracted to the first core  34  by the attractive force corresponding to the amount of current applied to the coil  32  causing the shaft  38  to be pushed out and thus the spool  24  that abuts on the tip of the shaft  38  is moved towards the end plate  26 . Consequently, the input port  42 , the output port  44 , and the drain port  46  are placed in communication with one another, and a part of the hydraulic oil input from the input port  42  is output to the output port  44  and the rest of the hydraulic oil is output to the drain port  46 . Additionally, the hydraulic oil is supplied to the feedback chamber through the feedback port  48  and the feedback force corresponding to the output pressure of the output port  44  is act on the spool  24  towards the solenoid section  30 . Accordingly, the spool  24  stops at the position where the thrust force (attractive force) of the plunger  36 , the spring force of the spring  28 , and the feedback force just balance out. In this case, the larger the amount of current applied to the coil  32 , more specifically, the larger the thrust force of the plunger  36 , the more the spool  24  moves towards the end plate  26 , thereby expanding the opening area of the input port  42  and reducing the opening area of the drain port  46 . When the energization of the coil  32  is maximized, the spool  24  is moved to the position that is closest to the end plate  26  within the range of movement of the plunger  36 , and thus the input port  42  and the output port  44  are placed in communication with each other through the communicating portion  58  and the drain port  46  is blocked by the land  52 , cutting off the communication of the output port  44  with the drain port  46 . Consequently, the maximum hydraulic pressure is acted on the clutch C 2 . As described in the foregoing, in the solenoid valve  20  of the present embodiment, as the input port  42  is blocked and the output port  44  is placed in communication with the drain port  46  in the state where the coil  32  is de-energized, it is apparent that the solenoid valve  20  of the present embodiment functions as a normal-closed type solenoid valve. 
     Secondly, the operation of the solenoid valve  20  of the present embodiment when functioning as a solenoid pump will be described. Now, the coil  32  is just de-energized after being energized. In this case, as the spool  24  is moved from the end plate  26  side to the solenoid section  30  side, the pressure inside the pump chamber  70  becomes negative, thereby opening the suction check valve  80  and closing the discharge check valve  90  so that the hydraulic oil is sucked into the pump chamber  70  from the suction port  62  through the suction check valve  80 . When the coil  32  is energized from this state, the spool  24  is moved from the solenoid section  30  side to the end plate  26  side, and therefore the pressure inside the pump chamber  70  becomes positive, thereby closing the suction check valve  80  and opening the discharge check valve  90  so that the hydraulic oil sucked in the pump chamber  70  is discharged from the discharge port  64  through the discharge check valve  90 . Consequently, by repeatedly energizing and de-energizing the coil  32 , the solenoid valve  20  of the present embodiment can be made to function as a solenoid pump for pumping hydraulic oil. 
     Next, the configuration in which the solenoid valve  20  thus structured is incorporated in a drive unit of an automatic transmission installed in a motor vehicle will be described.  FIG. 3  is a schematic diagram showing the configuration of a motor vehicle  120  in which a drive unit of an automatic transmission is installed,  FIG. 4  is a schematic diagram showing the configuration of an automatic transmission  130 .  FIG. 5  is an operation table of the automatic transmission  130 , and  FIG. 6  is a schematic diagram showing the configuration of a hydraulic circuit  140 . As shown in  FIG. 3 , the motor vehicle  120  is provided with: an engine  122  as an internal combustion engine; a starter motor  123  for cranking the engine  122  to start up; an automatic transmission  130  in which an input shaft  136  is coupled with a crank shaft  126  of the engine  122  via a torque converter  128  and an output shaft  138  is coupled with driving wheels  174   a  and  174   b  via a differential gear  172  so as to transmit power input from the input shaft  136  to the output shaft  138 ; a hydraulic circuit  140  serving as an actuator for driving the automatic transmission  130 ; and a main electronic control unit (hereinafter referred to as main ECU)  150  for controlling the whole motor vehicle. 
     The operation of the engine  122  is controlled by an engine electronic control unit (hereinafter referred to as engine ECU)  124 . The engine ECU  124  is structured, although not shown in details, as a microprocessor centering on a CPU, and is provided with, other than the CPU, a ROM for storing processing programs, a RAM for temporarily storing data, an I/O port, and a communication port. The engine ECU  124  is fed with signals required for controlling the operation of the engine  122  from various sensors such as a rotation sensor  125  installed on the crank shaft  126  via the input port. The engine ECU  124  outputs a drive signal to a throttle motor for adjusting throttle openings, a control signal to a fuel injection valve, an ignition signal to spark plugs, a drive signal to the starter motor  123  and the like via the output port. The engine ECU  124  communicates with the main ECU  150  to control the engine  122  based on the control signal from the main ECU  150  and to output data relating to operating condition of the engine  122  to the main ECU  150  as required. 
     The automatic transmission  130  is provided, as shown in  FIG. 4 , with a planetary gear mechanism  130   a  of a double pinion type, two sets of planetary gear mechanisms  130   b  and  130   c  of a single pinion type, three sets of clutches C 1 , C 2  and C 3 , four sets of brakes B 1 , B 2 , B 3  and B 4 , and three sets of one-way clutches F 1 , F 2  and F 3 . The double pinion type planetary gear mechanism  130   a  is provided with: a sun gear  131   a  as an external gear; a ring gear  132   a  as an internal gear concentrically disposed with the sun gear  131   a ; a plurality of first pinion gears  133   a  meshing with the sun gear  131   a ; a plurality of second pinion gears  134   a  meshing with the first pinion gears  133   a  and the ring gear  132   a ; and a carrier  135   a  for coupling the plurality of first pinion gears  133   a  and the plurality of second pinion gears  134   a  with one another and holding the first pinion gears  133   a  and the second pinion gears  134   a  in a rotatable and revolvable manner. The sun gear  131   a  is coupled with the input shaft  136  via the clutch C 3 , and is adapted to rotate freely or is restricted to rotate in one direction by switching the brake B 3 , which is coupled via the one-way clutch F 2 , on and off. The ring gear  132   a  is adapted to rotate freely or be fixed by switching the brake B 2  on and off. The carrier  135   a  is adapted to rotate in one direction restricted by the one-way clutch F 1  and to rotate freely or be fixed by switching the brake B 1  on and off. The single pinion type planetary gear mechanism  130   b  is provided with a sun gear  131   b  as an external gear, a ring gear  132   b  as an internal gear concentrically disposed with the sun gear  131   b , a plurality of pinion gears  133   b  meshing with the sun gear  131   b  and the ring gear  132   b , and a carrier  135   b  holding the plurality of pinion gears  133   b  in a rotatable and revolvable manner. The sun gear  131   b  is coupled with the input shaft  136  via the clutch C 1 . The ring gear  132   b  is coupled with the ring gear  132   a  of the double pinion type planetary gear mechanism  130   a  and is adapted to rotate freely or be fixed by switching the brake B 2  on and off. The carrier  135   b  is coupled with the input shaft  136  via the clutch C 2  and is adapted to rotate in one direction restricted by the one-way clutch F 3 . Further, the single pinion type planetary gear mechanism  130   c  is provided with: a sun gear  131   c  as an external gear; a ring gear  132   c  as an internal gear concentrically disposed with the sun gear  131   c ; a plurality of pinion gears  133   c  meshing with the sun gear  131   c  and the ring gear  132   c , and a carrier  135   c  holding the plurality of pinion gears  133   c  in a rotatable and revolvable manner. The sun gear  131   c  is coupled with the sun gear  131   b  of the single pinion type planetary gear mechanism  130   b . The ring gear  132   c  is coupled with the carrier  135   b  of the single pinion type planetary gear mechanism  130   b  and is adapted to rotate freely or be fixed by switching the brake B 4  on and off. The carrier  135   c  is coupled with the output shaft  138 . 
     The automatic transmission  130  is adapted, as shown in  FIG. 5 , to switch among first to fifth forward speeds, a reverse speed and neutral by switching the clutches C 1  to C 3  on and off, and switching the brakes B 1  to B 4  on and off. The first forward speed stage, more specifically, the state where the rotation of the input shaft  136  is transmitted to the output shaft  138  at a speed reduced by the largest reduction ratio, can be established by switching on the clutch C 1  and switching off the clutches C 2  and C 3  and the brakes B 1  to B 4 . In this state, as the ring gear  132   c  of the single pinion type planetary gear mechanism  130   c  is fixed to rotate in one direction by the one-way clutch F 3 , the power input from the input shaft  136  to the sun gear  131   c  via the clutch C 1  is output to the carrier  135   c , i.e., the output shaft  138 , at a speed reduced by the large reduction ratio. In the first speed stage, when an engine brake is in operation, by switching on the brake B 4  in place of the one-way clutch F 3 , the rotation of the ring gear  132   c  is fixed. The second forward speed stage can be established by switching on the clutch C 1  and the brake B 3  and switching off the clutches C 2  and C 3  and the brakes B 1 , B 2  and B 4 . In this state, as the sun gear  131   a  of the double pinion type planetary gear mechanism  130   a  is fixed to rotate in one direction by the one-way clutch F 2  and the carrier  135   a  is fixed to rotate in one direction by the one-way clutch F 1 , the ring gear  132   a  and the ring gear  132   b  of the single pinion type planetary gear mechanism  130   b  are also fixed to rotate in one direction and the power input from the input shaft  136  to the sun gear  131   b  via the clutch C 1  is output to the carrier  135   b  and the ring gear  132   c  of the single pinion type planetary gear mechanism  130   c  at a speed reduced by the ring gear  132   b  that is fixed. The power input from the input shaft  136  to the sun gear  131   c  via the clutch C 1  is output to the carrier  135   c , i.e., the output shaft  138  at a speed reduced by a slightly smaller reduction ratio than that of the first forward speed stage corresponding to the rotating condition of the ring gear  132   c . In the second speed stage, when the engine brake is in operation, by switching on the brake B 2  in place of the one-way clutch F 1  and the one-way clutch F 2 , the rotations of the ring gear  132   a  and the ring gear  132   b  are fixed. The third forward speed stage is established by switching on the clutches C 1  and C 3  and the brake B 3  and switching off the clutch C 2  and the brakes B 1 , B 2  and B 4 . In this state, as the carrier  135   a  of the double pinion type planetary gear mechanism  130   a  is fixed to rotate in one direction by the one-way clutch F 1 , the power input from the input shaft  136  to the sun gear  131   a  via the clutch C 3  is output to the ring gear  132   a  and the ring gear  132   b  of the single pinion type planetary gear mechanism  130   b  at a reduced speed. The power input from the input shaft  136  to the sun gear  131   b  via the clutch C 1  is output to the carrier  135   b  and the ring gear  132   c  of the single pinion type planetary gear mechanism  130   c  at a speed reduced corresponding to the rotating condition of the ring gear  132   b . The power input from the input shaft  136  to the sun gear  131   c  via the clutch C 1  is output to the carrier  135   c , i.e., the output shaft  138  at a speed reduced by a slightly smaller reduction ratio than that of the second forward speed stage corresponding to the rotating condition of the ring gear  132   c . In the third speed stage, when the engine brake is in operation, by switching on the brake B 1  in place of the one-way clutch F 1 , the rotation of the carrier  135   a  is fixed. The fourth forward speed stage can be established by switching on the clutches C 1  to C 3  and the brake B 3  and switching off the brakes B 1 , B 2  and B 4 . In this state, as the input shaft  136  is connected to the sun gear  131   b  of the single pinion type planetary gear mechanism  130   b  and the sun gear  131   c  of the single pinion type planetary gear mechanism  130   c  via the clutch C 1  and is connected to the carrier  135   b  and the ring gear  132   c  via the clutch C 2 , all the rotating elements of the single pinion type planetary gear mechanisms  130   b  and  130   c  rotate as a unit, and the input shaft  136  and the output shaft  138  are directly connected. Thus, the power input from the input shaft  136  is transmitted at a value of 1.0 reduction ratio. In the fifth forward speed stage, more specifically, the state where the rotation of the input shaft  136  is transmitted to the output shaft  138  at a speed reduced by the smallest reduction ratio (at an increased speed) can be established by switching on the clutches C 2  and C 3  and the brakes B 1  and B 3  and switching off the clutch C 1  and the brakes B 2  and B 4 . In this state, as the carrier  135   a  of the double pinion type planetary gear mechanism  130   a  is fixed to rotate in one direction by the one-way clutch F 1 , the power input from the input shaft  136  to the sun gear  131   a  via the clutch C 3  is output to the ring gear  132   a  and the ring gear  132   b  of the single pinion type planetary gear mechanism  130   b  at a reduced speed. The power input from the input shaft  136  to the carrier  135   b  via the clutch C 2  is output to the sun gear  131   b  and the sun gear  131   c  of the single pinion type planetary gear mechanism  130   c  at a speed increased corresponding to the rotating condition of the ring gear  132   b . The power input from the input shaft  136  to the ring gear  132   c  via the clutch C 2  is output to the carrier  135   c , i.e., the output shaft  138  at a speed increased by the smallest reduction ratio corresponding to the rotating condition of the sun gear  131   c.    
     Further, in the automatic transmission  130 , the neutral state, more specifically, disengaging the input shaft  136  from the output shaft  138  can be carried out by switching off all the clutches C 1  to C 3  and the brakes B 1  to B 4 . Furthermore, the reverse state can be established by switching on the clutch C 3  and the brake B 4  and switching off the clutches C 1  and C 2  and the brakes B 1  to B 3 . In this state, as the carrier  135   a  of the double pinion type planetary gear mechanism  130   a  is fixed to rotate in one direction by the one-way clutch F 1 , the power input from the input shaft  136  to the sun gear  131   a  via the clutch C 3  is output to the ring gear  132   a  and the ring gear  132   b  of the single pinion type planetary gear mechanism  130   b  at a reduced speed. As the rotations of the carrier  135   b  of the single pinion type planetary gear mechanism  130   b  and the ring gear  132   c  of the single pinion type planetary gear mechanism  130   c  are fixed by the brake B 4 , the power output to the ring gear  132   a  results in reverse rotation and is output to the carrier  135   c , i.e., the output shaft  138 . In the reverse state, when the engine brake is in operation, by switching on the brake B 1  in place of the one-way clutch F 1 , the rotation of the carrier  135   a  is fixed. 
     As shown in  FIG. 6 , the hydraulic circuit  140  is structured with: a mechanical oil pump  141  for pumping oil by the power from the engine  122 ; a regulator valve  142  for adjusting the pressure of the oil (line pressure PL) pumped from the mechanical oil pump  141 ; a linear solenoid  143  for driving the regulator valve  142 ; a linear solenoid valve (hereinafter referred to as linear solenoid) SLC 1  for inputting the line pressure PL through a manual valve  144 , adjusting the line pressure PL input, and outputting the adjusted line pressure PL to the clutch C 1 ; an accumulator  145  for accumulating the line pressure PL supplied to the linear solenoid SLC 1 ; the solenoid valve  20  of the present embodiment as described in the foregoing which serves as a linear solenoid valve for inputting the line pressure PL through the manual valve  144 , adjusting the line pressure PL input, and outputting the adjusted line pressure PL to the clutch C 2 , and also serves as a solenoid pump while suspending the function as the linear solenoid valve; a switching valve  148  for selectively switching the connections of the flow passage formed between the linear solenoid SLC 1  and the clutch C 1  and the flow passage formed between the solenoid pump of the solenoid valve  20  and the clutch C 1 ; an on/off solenoid  149  for driving the switching valve  148 ; and a drain valve  100  for draining hydraulic oil in the pump chamber  70  when suspending the function of the solenoid valve  20  of the present embodiment as a solenoid pump. In  FIG. 6 , the hydraulic system for the clutches C 1  and C 2  are shown. However, the hydraulic systems for, other than the clutches C 1  and C 2 , the clutch C 3  and the brakes B 1  to B 4  may also be similarly structured using the linear solenoid valves. 
     The switching valve  148 , as shown in operational schematic diagrams in  FIGS. 7A and 7B , is provided with a spring  148   b  for biasing a spool  148   a  upward in the drawing at the lower portion of the switching valve  148 , and an input port  148   c  for inputting the signal pressure from the on/off solenoid  149  at the upper portion of the switching valve  148 . When the signal pressure is input from the on/off solenoid  149 , the signal pressure overcomes the biasing force of the spring  148   b  and thus the spool  148   a  is moved downward in the drawing, blocking the flow passage formed between the pump section  60  of the solenoid valve  20  and the clutch C 1  and connecting the flow passage formed between the linear solenoid SLC 1  and the clutch C 1  (refer to  FIG. 7A ). When the signal pressure is not input from the on/off solenoid  149 , the spool  148   a  is moved upward in the drawing by the biasing force of the spring  148   b , connecting the flow passage formed between the pump section  60  of the solenoid valve  20  and the clutch C 1  and blocking the flow passage formed between the linear solenoid SLC 1  and the clutch C 1  (refer to  FIG. 7B ). 
     The hydraulic circuit  140  is drive controlled by an automatic transmission electronic control unit (hereinafter referred to as ATECU)  139 . The ATECU  139  is structured, although not shown in details, as a microprocessor centering on a CPU and is provided with, other than the CPU, a ROM for storing processing programs, a RAM for temporarily storing data, an I/O port, and a communication port. The ATECU  139  outputs drive signals to the linear solenoid  143 , the linear solenoid SLC 1 , the solenoid valve  20  of the present embodiment, and the on/off solenoid  149  via the output port. The ATECU  139  communicates with the main ECU  150  to control the automatic transmission  130  (hydraulic circuit  140 ) based on the control signal from the main ECU  150  and to output the data relating to status of the automatic transmission  130  to the main ECU  150  as required. 
     The main ECU  150  is structured, although not shown in details, as a microprocessor centering on a CPU, and is provided with, other than the CPU, a ROM for storing processing programs, a RAM for temporarily storing data, an I/O port, and a communication port. The main ECU  150  is fed with an ignition signal from an ignition switch  160 , a shift position SP from a shift position sensor  162  which detects an operating position of a shift lever  161 , an accelerator opening Acc from an accelerator pedal position sensor  164  which detects the amount of depression of an accelerator pedal  163 , a brake switch signal BSW from a brake switch  166  which detects the depression of a brake pedal  165 , and a vehicle speed V from a vehicle speed sensor  168  via the input port. The main ECU  150  is connected with the engine ECU  124  and the ATECU  139  via the communication port to exchange various control signals and data to and from the engine ECU  124  and the ATECU  139 . 
     In the motor vehicle  120  of the present embodiment thus structured, while running with the shift lever  161  at its driving position of D (drive) after the engine  122  is started up, when all the conditions predetermined for an auto-stop operation, such as the conditions in which the value of the vehicle speed V is 0, the accelerator pedal is off, the brake switch signal BSW is on, are met, the engine  122  is automatically stopped. After the engine  122  is automatically stopped, when conditions predetermined for an auto-start operation, such as the condition in which the brake switch signal BSW is off and the accelerator pedal is on, are subsequently met, the engine  122  that has been automatically stopped is automatically started. 
     Next, the operation of the drive unit for the automatic transmission installed in the motor vehicle  120  thus structured, particularly the operation while the engine  122  is being automatically stopped, will be described. The drive unit for the automatic transmission corresponds to the hydraulic circuit  140  and the ATECU  139 .  FIG. 8  is a flowchart showing an example of an auto-stop control routine carried out by the ATECU  139 . This routine is carried out, while running with the shift lever  161  at the D position, when the auto-stop condition for the engine  122  is met. In this running condition, the signal pressure is output from the on/off solenoid  149 , and the switching valve  148  is placed in the state where the flow passage formed between the pump section  60  of the solenoid valve  20  and the clutch C 1  is blocked and the flow passage formed between the linear solenoid SLC 1  and the clutch C 1  is connected. 
     When the auto-stop control routine is carried out, since the fuel supplied to the engine  122  is cut off as the auto-stop condition for the engine  122  is met (step S 100 ), the CPU of the ATECU  139  first controls the linear solenoid SLC 1  to gradually reduce the hydraulic pressure acting on the clutch C 1  down to the value of 0 (step S 110 ) and waits for the engine speed Ne of the engine  122  comes close to the value of 0, i.e., stopping of the rotation of the engine  122  (steps S 120  and S 130 ). Note that the engine speed Ne of the engine  122  which is detected by the engine speed sensor  125  is to be input from the engine ECU  124  via the main ECU  150 . 
     When the rotation of the engine  122  is stopped, the on/off solenoid  149  is drive controlled so that the switching valve  148  connects the flow passage formed between the pump section  60  of the solenoid valve  20  of the present embodiment and the clutch C 1  and blocks off the flow passage formed between the linear solenoid SLC 1  and the clutch C 1  (step S 140 ), and the driving of the pump section  60  of the solenoid valve  20  is started (step S 150 ), waiting for the auto-start condition to be subsequently met (step S 160 ). While the pumping power of the pump section  60  of the solenoid valve  20  is less powerful comparing to an electric oil pump driven by an electric motor, in the present embodiment, it has been designed to have a pumping power sufficient enough to stroke a clutch piston under a low pressure condition having a slightly larger torque capacity than a cranking torque by the starter motor  123  to the engine  122  and to hold that state, although the clutch C 1  is not fully engaged. 
     When the auto-start condition for the engine  122  is met, as the engine  122  is cranked up by the starter motor  123 , the on/off solenoid  149  is drive controlled so that the switching valve  148  blocks the flow passage formed between the pump section  60  of the solenoid valve  20  and the clutch C 1  and connects the flow passage formed between the linear solenoid SLC 1  and the clutch C 1  (step S 170 ), the linear solenoid SLC 1  is drive controlled so as to increase the hydraulic pressure acting on the clutch C 1  (step S 180 ), and, when the engine  122  is in complete explosion (step S 190 ), the pump section  60  of the solenoid valve  20  is then stopped driving (step S 200 ). This completes the auto-stop control routine. When the engine  122  is in complete explosion, the line pressure PL is generated by the mechanical oil pump  141  driven by the power from the engine  122 , and the above described drain valve  100  is activated by the line pressure PL to drain the remaining hydraulic oil in the pump chamber  70  of the pump section  60  of the solenoid valve  20  of the present embodiment. Accordingly, no difficulty occurs when the solenoid valve  20  of the present embodiment is made to function as a linear solenoid valve for adjusting the clutch pressure for the clutch C 2 . 
       FIG. 9  is a explanatory chart showing the changes in time for the vehicle speed V, the engine speed Ne, the accelerator opening Acc, the brake switch signal BSW, the shift position SP, the line pressure PL, the hydraulic pressure for the clutch C 1 , the current command for the linear solenoid SLC 1 , and the current command for the solenoid pump. As shown in the chart, when the auto-stop condition for the engine  122  is met at the time t 1  and the fuel supply to the engine  122  is cut off at the time t 2 , the linear solenoid SLC 1  is driven by the current command which is set such that the hydraulic pressure acting on the clutch C 1  forming the first forward speed stage is to be gradually reduced. After the rotation of the engine  122  is stopped, the flow passage formed between the pump section  60  of the solenoid valve  20  and the clutch C 1  is connected by the switching valve  148  and the hydraulic pressure acting on the clutch C 1  is made to be under a low pressure having a slightly larger torque capacity than a cranking torque by the pump section  60  driven by the solenoid section  30  (time t 3 ). In this case, as the pump section  60  can pump oil directly to the clutch C 1  without the linear solenoid SLC 1  intervening therebetween, and the hydraulic pressure to be act on the clutch C 1  can be in a low pressure state, the pump section  60  functioning as a solenoid pump does not cause the shortage of the required pumping power. When the auto-start condition for the engine  122  is then met by switching off the brake at the time t 4  and by switching on the accelerator pedal at the time t 5 , the engine  122  is cranked up by the starter motor  123 . In this case, as the hydraulic pressure of the clutch C 1  is held in a low pressure state having a slightly larger torque capacity than the cranking torque, the cranking torque of the engine  122  is transferred to the driving wheels  174   a  and  174   b  as creep torque through the clutch C 1 . When the cranking of the engine  122  is started, the switching valve  148  connects the flow passage formed between the linear solenoid SLC 1  and the clutch C 1  and drives the linear solenoid SLC 1  to increase the hydraulic pressure acting on the clutch C 1 . When the engine  122  comes to be in complete explosion, driving of the pump section  60  of the solenoid valve  20  is stopped (time t 6 ). 
     According to the solenoid valve  20  of the present embodiment described in the foregoing, the pressure adjusting valve section  40 , which functions as a linear solenoid valve for adjusting the clutch pressure of the clutch C 2 , and the pump section  60 , which functions as a solenoid pump for pumping hydraulic oil to the clutch C 1 , are formed by the sleeve  22  and the spool  24 , and the pressure adjusting valve section  40  and the pump section  60  are driven by the single solenoid section  30 . Therefore, comparing to the case where a solenoid valve and a solenoid pump are separately provided, miniaturization can be achieved. Furthermore, since the suction check valve  80  is built into the sleeve  22 , the suction check valve  80  can be formed in relatively high precision, thereby improving the volumetric efficiency when functioning as a solenoid pump. 
     The solenoid valve  20  of the present embodiment is structured as a direct control linear solenoid valve for directly controlling the clutch C 2  by generating an optimal clutch pressure from the line pressure PL when functioning as a linear solenoid valve. However, the linear solenoid valve may be used as a pilot linear solenoid valve driving a separate control valve, thereby controlling the clutch C 2  using the clutch pressure generated by the control valve. In addition, the clutch C 1  and the brakes B 1  to B 4  may be similarly structured. 
     In the solenoid valve  20  of the present embodiment, the suction check valve  80  is built into the sleeve  22  and the discharge check valve  90  is incorporated in the valve body  10  external to the sleeve  22 . However, as a solenoid valve  20 B of a modification example shown in  FIG. 10 , both a suction check valve  80 B and a discharge check valve  90 B may be incorporated in the valve body  10  external to the sleeve  22 . In the solenoid valve  20 B of the modification example, the solenoid section  30  and pressure adjusting valve section  40  are structured identical to the solenoid valve  20  of the present embodiment. In the pump section  60 B of the solenoid valve  20 B, as shown in  FIG. 10 , a pump chamber  70 B is formed by the sleeve  22 , land  56  of the spool  24 , and the end plate  26 . When the coil  32  of the solenoid section  30  is de-energized from energized state, the spool  24  (land  56 ) is moved towards the solenoid section  30  by the biasing force of the spring  28 , thereby sucking hydraulic oil from a suction port  62 B into the pump chamber  70 B through the suction check valve  80 B incorporated in the valve body  10 . When the coil  32  of the solenoid section  30  is energized from de-energized state, the spool  24  is moved towards the end plate  26  by the thrust force of the solenoid section  30 , thereby discharging the sucked hydraulic oil from a discharge port  64 B through the discharge check valve  90 B incorporated in the valve body  10 . 
     In the solenoid valve  20  of the present embodiment, the suction check valve  80  is built into the sleeve  22  and the discharge check valve  90  is incorporated in the valve body  10  external to the sleeve  22 . However, as a solenoid valve  20 C of a modification example shown in  FIG. 11 , both the suction check valve and the discharge check valve may be built into the sleeve  22 . In the solenoid valve  20 C of the modification example, the solenoid section  30  and the pressure adjusting valve section  40  are structured identical to the solenoid valve  20  of the present embodiment. In the pump section  60 C of the solenoid valve  20 C, as shown in  FIG. 11 , a suction check valve  80 C and a discharge check valve  90 C are both built into the sleeve  22 , and the sleeve  22 , the suction check valve  80 C, and the discharge check valve  90 C form a pump chamber  70 C. The suction check valve  80 C is structured identical to the suction check valve  80  of the solenoid valve  20  of the present embodiment. Meanwhile, the discharge check valve  90 C is provided with: a cylindrical body  92 C which functions as a spring holder for holding a spring  28  and a spring  86  of the suction check valve  80 C and is formed with an opening  92   a  in the center thereof for communicating the pump chamber  70 C with the discharge port  64 C; a ball  94 C; and a spring  96 C for urging the ball  94 C to be pressed against the opening  92   a  of the body  92 C with the end plate  26  as the spring holder. The discharge check valve  90 C is closed by the biasing force of the spring  96 C when inside the pump chamber  70  is under a negative pressure, and is opened when inside the pump chamber  70  is under a positive pressure. Accordingly, when the coil  32  of the solenoid section  30  is de-energized from energized state, the spool  24  is moved towards the solenoid section  30  by the biasing force of the spring  96 C and the spring  28 , thereby sucking hydraulic oil from the suction port  62 C into the pump chamber  70 C through the suction check valve  80 C. When the coil  32  of the solenoid section  30  is energized from de-energized state, the spool  24  is moved towards the end plate  26  by the thrust force of the solenoid section  30 , thereby discharging the sucked hydraulic oil from the discharge port  64 C through the discharge check valve  90 C. 
     Further, in the solenoid valve  20  of the present embodiment, the suction check valve  80  is built into the sleeve  22  and the discharge check valve  90  is incorporated in the valve body  10  external to the sleeve  22 . However, the suction check valve  80  may be incorporated in the valve body  10  external to the sleeve  22  and the discharge check valve  90  may be built into the sleeve  22 . 
     In the solenoid valve  20  of the present embodiment, a so-called normal-closed type linear solenoid valve is combined with the function of a solenoid pump. However, as a solenoid valve  20 D of a modification example shown in  FIG. 12 , the function as a solenoid pump may be integrated into a so-called normal-open type linear solenoid valve. The solenoid section  30  is structured identical to the solenoid valve  20  of the present embodiment. In the pressure adjusting valve section  40 D of the solenoid valve  20 D of a modification example, when the coil  32  is de-energized, a spool  24 D is moved towards the solenoid section  30  by the biasing force of the spring  28 . Therefore, an input port  42 D and an output port  44 D formed in a sleeve  22 D are placed in communication with each other through a communicating portion  58 D of the spool  24 D, and a drain port  46 D is blocked by a land  56 D of the spool  24 D. Accordingly, the maximum hydraulic pressure is acted on the clutch C 2 . When the coil  32  is energized, the plunger  36  is attracted to the first core  34  by the attractive force corresponding to the amount of current applied to the coil  32  and the shaft  38  is then pushed out, and the spool  24 D in abutment with the tip of the shaft  38  is moved towards the end plate  26 . Accordingly, the input port  42 D, the output port  44 D, and the drain port  46 D are placed in communication with one another, and a part of the hydraulic oil input from the input port  42 D is output to the output port  44 D and the rest of the hydraulic oil is output to the drain port  46 D. Further, the hydraulic oil is supplied to a feedback chamber through a feedback port  48 D, and the feedback force corresponding to the output pressure of the output port  44 D is acted on the spool  24 D towards the end plate  26 . Consequently, the spool  24 D stops at the position where the thrust force (attractive force) of the plunger  36 , the spring force of the spring  28 , and the feedback force just balance out. In this case, the larger the amount of current applied to the coil  32 , more specifically, the larger the thrust force of the plunger  36 , the more the spool  24 D moves towards the end plate  26 , reducing the opening area of the input port  42 D and expanding the opening area of the drain port  46 D. When the energization of the coil  32  is maximized, the spool  24 D is moved to the position that is closest to the end plate  26  within the range of movement of the plunger  36 , and thus the input port  42 D is blocked by the land  54 D and the output port  44 D and the drain port  46 D are placed in communication with each other through the communicating portion  58 D. Accordingly, no hydraulic pressure is acted on the clutch C 2 . As described above, in the solenoid valve  20 D of the modification example, when the coil  32  is not being energized, as the input port  42 D and the output port  44 D are placed in communication with each other while the drain port  46 D is blocked, it is apparent that the solenoid valve  20 D of the modification example functions as a normal-open type solenoid valve. In a pump section  60 D of the solenoid valve  20 D of the modification example, both a suction check valve  80 D and a discharge check valve  90 D are incorporated into the valve body  10  external to the sleeve  22 . Further, the pump section  60 D of the solenoid valve  20 D is adapted such that, when the solenoid section  30  is de-energized from being energized, the spool  24 D is moved towards the solenoid section  30  by the biasing force of the spring  28 , making inside the pump chamber  70  under a negative pressure, thereby sucking hydraulic oil from the suction port  62 D. The pump section  60 D of the solenoid valve  20 D is also adapted such that, when the solenoid section  30  is energized from being de-energized, the spool  24 D is moved towards the end plate  26  by the thrust force of the solenoid section  30 , making inside the pump chamber  70  under a positive pressure, thereby discharging the sucked hydraulic oil from the discharge port  64 D. Naturally, both the suction check valve  80 D and the discharge check valve  90 D are not limited to be incorporated into the valve body  10  external to the sleeve  22 D, and only the suction check valve  80 D may be built into the sleeve  22 , only the discharge check valve  90 D may be built into the sleeve  22 , or both the suction check valve  80 D and the discharge check valve  90 D may be built into the sleeve  22 . 
     In the solenoid valve  20 D of the modification example described above, the solenoid section  30  tends to become larger comparing to the case where the solenoid section  30  is applied to a normal-closed type linear solenoid valve. This is because of that, while the direction of feedback force acting on the spool  24  is in an opposite direction to the thrust force of the solenoid section  30  in a normal-closed type linear solenoid valve, the direction of feedback force acting on the spool  24  is the same as that of the thrust force of the solenoid section  30  in a normal-open type linear solenoid valve. Accordingly, as the spring load of the spring  28  needs to be large when functioning as a solenoid pump, the thrust force required for the solenoid section  30  becomes large in that respect. 
     In the present embodiment, by selectively using the function as a linear solenoid and the function as a solenoid pump, the hydraulic pressure is acted on the clutch C 1  for starting off when functioning as a solenoid pump and the hydraulic pressure is acted on the clutch C 2  different from the clutch C 1  for starting off when functioning as a solenoid pump. However, when using either one of the function as a linear solenoid valve and the function as a solenoid pump, the hydraulic pressure may be acted on the same clutch C 1 .  FIG. 13  shows a hydraulic circuit  240  of such a modification example. In the hydraulic circuit  240  of the modification example, the same constituent elements as those of the hydraulic circuit  140  of the present embodiment will be denoted by the same reference numerals, and repeated descriptions thereof will be omitted. As shown in the drawing, the hydraulic circuit  240  of the modification example is provided, in place of the solenoid valve  20 , the drain valve  100 , linear solenoid SLC 1 , and the switching valve  148  provided in the hydraulic circuit  140  of the present embodiment, with the solenoid valve  20 C of the modification example shown in  FIG. 11 , a linear solenoid SLC 2  for inputting the line pressure PL through the manual valve  144 , adjusting the line pressure PL input, and supplying the adjusted line pressure PL to the clutch C 2 , and a switching valve  250  for selectively switching the connections of the flow passage formed between the pressure adjusting valve section  40  of the solenoid valve  20 C (output port  44 ) and the clutch C 1  and the flow passage formed between the pump section  60 C of the solenoid valve  20 C (discharge port  64 C) and the clutch C 1 , and for connecting the flow passage formed between the pressure adjusting valve section  40  of the solenoid valve  20 C and the clutch C 1  to drain hydraulic oil from the pump chamber  70 C when the function of the pump section  60 C is suspended (see  FIG. 11 ). The switching valve  250  is provided, as shown in operational schematic diagrams in  FIGS. 14A and 14B , with a spring  254  for biasing a spool  252  upward in the drawing at a lower portion of the switching valve  250  and with an input port  256  for inputting the signal pressure from the on/off solenoid  149  at an upper portion of the switching valve  250 . When the signal pressure is input from the on/off solenoid  149 , the signal pressure overcomes the biasing force of the spring  254  and thus the spool  252  is moved downward in the drawing, connecting the flow passage formed between the output port  44  of the pressure adjusting valve section  40  and the clutch C 1 , blocking the flow passage formed between the discharge port  64 C of the pump section  60 C and the clutch C 1 , and connecting the flow passage formed between the drain port  66 C of the pump section  60 C and a drain port  258  (refer to  FIG. 14A ). When the signal pressure is not input from the on/off solenoid  149 , the spool  252  is moved upward in the drawing by the biasing force of the spring  254 , blocking the flow passage formed between the output port  44  of the pressure adjusting valve section  40 C and the clutch C 1 , connecting the flow passage formed between the discharge port  64 C of the pump section  60 C and the clutch C 1 , and blocking the flow passage formed between the drain port  66 C of the pump section  60 C and the discharge port  258  (refer to  FIG. 14B ). In this modification example, the solenoid valve  20 C shown in  FIG. 11  is used, but the present invention is not limited as such. In place of the solenoid valve  20 C, the solenoid valve  20  shown in  FIG. 1 , the solenoid valve  20 B shown in  FIG. 10 , or the solenoid valve  20 D shown in  FIG. 12  may be used. 
     In the present embodiment, the solenoid valve  20  is structured combining a linear solenoid for adjusting hydraulic pressure of the clutch C 1  with a solenoid pump, but the present invention is not limited as such. For example, the linear solenoid  143  for driving the regulator valve  142  and a solenoid pump may be combined, or an on/off solenoid valve, in place of a linear solenoid, and a solenoid pump may be combined. 
     In the present embodiment, a portion of a pressure adjusting section composed of such as the sleeve  22  and the spool  24  is formed as a pump section  60 , but the present invention is not limited as such, and the pressure adjusting section and the pump section  60  may be separately made. More specifically, in the solenoid valve device of the present embodiment, a pump chamber may be separately formed from a spring chamber housing the spring  28  for adjusting pressure.  FIG. 15  is a schematic diagram showing the configuration of such a solenoid valve  20 E of a modification example. As shown in the drawing, the solenoid valve  20 E of the modification example is structured as a normal-open type linear solenoid provided with a spring chamber housing the spring  28 , a pressure adjusting chamber  50 E (a space connected with an input port  42 E, an output port  44 E, and a drain port  46 E), and a feedback chamber  48 E. A pump chamber  70 E is formed adjacent to the feedback chamber  48 E by a sleeve  22 E and a land  52 E of a spool  24 E on the solenoid section  30  side opposite to a land  56 E pressed against the spring  28 . In the solenoid valve  20 E, when functioning as a solenoid pump, as the coil  32  of the solenoid section  30  is energized from being de-energized, the spool  24 E is moved towards the end plate  26  by the thrust force of the solenoid section  30 , making inside the pump chamber  70 E under a negative pressure, thereby sucking hydraulic oil into the pump chamber  70 E through a suction check valve  360 , which will be described later. When the coil  32  of the solenoid section  30  is de-energized from being energized, the spool  24 E is moved towards the solenoid section  30  by the biasing force of the spring  28 , making inside the pump chamber  70 E under a positive pressure, thereby discharging the sucked hydraulic oil through a discharge check valve  370 , which will be described later. 
     In the solenoid valve  20 E of the modification example, the suction check valve  360  and the discharge check valve  370  are built into a switching valve  350 .  FIG. 16  is a schematic diagram showing the configuration of a hydraulic circuit  340  provided with the solenoid valve  20 E and the switching valve  350 , and  FIGS. 17A and 17B  are diagrams explaining the operation of the switching valve  350 . The switching valve  350  is structured, as shown in the drawings, with a sleeve  352  formed with: a signal pressure input port  352   a  for inputting the line pressure as a signal pressure; an input port  352   b  connected to an output port  44 E of the solenoid valve  20 E; an output port  352   c  connected to the clutch C 1  through a check valve  380 ; two output ports  352   d  and  352   e  connected to the clutch C 1  without intervening the check valve  380 ; an input port  352   f  and an output port  352   g  connected to a pump chamber port  62 E of the pump chamber  70 E of the solenoid valve  20 E; an input port  352   h  connected to a suction hydraulic passage  342  formed between a mechanical oil pump  141  and a strainer  141   a ; and two drain ports  352   i  and  352   j . The switching valve  350  is also structured with a spool  354  that is slidable inside the sleeve  352  and in which the discharge check valve  370  is integrally formed, and a spring  356  for axially biasing the spool  354 , and the suction check valve  360  built into the sleeve  352 . 
     The suction check valve  360  is structured with: a hollow cylindrical body  362  formed with a central hole  362   a  in the axial center thereof in which a step is formed between a large diameter portion and a small diameter portion of the central hole  362   a ; a spring  366  inserted in the central hole  362   a  from the large diameter side with the step in the central hole  362   a  as a spring holder; a ball  364  inserted in the central hole  362   a  from the large diameter side after inserting the spring  366 ; a hollow cylindrical ball holder  368  inserted in the central hole  362   a  for holding the ball  364 ; and a snap ring  369  for fixing the ball holder  368  to the body  362 . Meanwhile, the discharge check valve  370  is structured with: a body  372  that is integrally formed with the spool  354  and formed with a recessed central hole  372   a  in the axial center thereof and a through hole  372   b  penetrating the central hole  372   a  in a radial direction thereof; a spring  376  inserted in the central hole  372   a  with a bottom of the central hole  372   a  as a spring holder; a ball  374  inserted in the central hole  372   a  after inserting the spring  376 ; a hollow cylindrical ball holder  378  inserted in the central hole  372   a  for holding the ball  374 ; and a snap ring  379  for fixing the ball holder  378  to the body  372 . Further, in the body  372  of the discharge check valve  370 , a narrow diameter portion  372   c , which is a portion where the outer diameter of the body  372  is made smaller, is formed. 
     In the switching valve  350  thus structured, as shown in  FIG. 17A , when the line pressure PL is being applied to the signal pressure input port  352   a , the spool  354  is moved downward in the drawing as the spring  356  compresses by the line pressure PL, making the input port  352   b  communicate with the output port  352   d  and making the input port  352   f  communicate with the drain port  352   j  through the narrow diameter portion  372   c . By making the solenoid valve  20 E function as a pressure adjusting valve, the hydraulic pressure from the output port  44 E can be acted on the clutch C 1 . In this case, as the hydraulic oil remaining in the pump chamber  70 E and the flow passage connected to the pump chamber  70 E is drained through the input port  352   f , the narrow diameter portion  372   c , and the drain port  352   j  in that order, the accuracy of pressure adjustment of the solenoid valve  20 E is not adversely affected. Further, a through hole  362   b  is formed in the body  362  of the suction check valve  360  at a position where the body  362  of the suction check valve  360  abuts on the body  372  of the discharge check valve  370 , and therefore the hydraulic oil remaining in a space between the suction check valve  360  and the discharge check valve  370  is also drained through the output port  352   g , the input port  352   f , the narrow diameter portion  372   c , and the drain port  352   j  in that order. Furthermore, as shown in  FIG. 17B , when the line pressure PL is not input to the signal pressure input port  352   a , the spool  354  is moved upward in the drawing as the spring  356  extends by the biasing force of the spring  356 , blocking the communication of the input port  352   b  with the output port  352   d , making the input port  352   h  communicate with the output port  352   g  through the suction check valve  360  (central hole  362   a ), making the input port  352   f  communicate with the output port  352   e  through the discharge check valve  370  (central hole  372   a  and through hole  372   b ), and blocking the communication of the input port  352   f  with the drain ports  352   i  and  352   j . By making the solenoid valve  20 E function as a solenoid pump, the hydraulic oil can be sucked into the pump chamber  70 E through the input port  352   h  of the switching valve  350 , the suction check valve  360 , and the output port  352   g  in that order, and the hydraulic oil sucked can be supplied to the clutch C 1  through the input port  352   f , the discharge check valve  370 , and the output port  352   e  in that order. 
     As described above, when functioning as a pressure adjusting valve, the hydraulic oil in the pump chamber  70 E or the flow passage connected thereto is drained into air, if the air enters therein when subsequently functioning as a pump, the hydraulic oil cannot be sufficiently pressurized and the pump performance may deteriorate. In the solenoid valve  20 E of the modification example, the pump chamber  70 E is formed adjacent to the feedback chamber  48 E, and therefore, when functioning as a pressure adjusting valve, inside the feedback chamber  48 E is under a high pressure and thus the hydraulic oil leaks out from the feedback chamber  48 E to the pump chamber  70 E. This leak of hydraulic oil is used to generate the flow of hydraulic oil from the pump chamber  70 E towards the drain, and the air entered is also drained together with the hydraulic oil. Consequently, when the solenoid valve  20 E is switched from the state where the solenoid valve  20 E functions as a pressure adjusting valve to the state where the solenoid valve  20 E functions as a solenoid pump, the performance of the pump can be promptly exercised. 
     In the present embodiment, it has been described that the solenoid valve  20  is incorporated in the drive unit of the automatic transmission. However, the present invention is not limited as such. The solenoid valve  20  may be applied to any device in which a solenoid valve is combined with a solenoid pump. 
     Here, the correspondence relation of the major elements of the present embodiment with respect to the major elements of the present invention described in Disclosure of the Invention will be described. In the present embodiment, the solenoid section  30  corresponds to the “solenoid section”, the pressure adjusting valve section  40  and the pump section  60  correspond to the “pressure adjusting section”, and the pump section  60 , the suction check valve  80 , and the discharge check valve  90  correspond to the “pump section”. Further, the suction check valve  80  and the discharge check valve  90  correspond to the “suction/discharge mechanism”. The spool  24  and  24 E correspond to the “valve element”. Furthermore, the automatic transmission  130  corresponds to the “automatic transmission”, and the hydraulic circuit  140  and the ATECU  139  correspond to the “drive unit”. Since the correspondence relation of the major elements of the present embodiment with respect to the major elements of the present invention described in Summary of the Invention is an example for explaining the embodiment of the present invention and is not intended to limit in any way the elements of the invention described in Summary of the Invention. More specifically, the present invention described in Summary of the Invention should be interpreted based on the description thereof, and the embodiment of the present invention is merely a specific example of the present invention described in the Summary of the Invention. 
     While the preferred embodiment of the present invention is described in details above, the present invention is not limited to the specific embodiment, and the present invention may be embodied in various modifications without departing from the spirit and scope of the present invention. 
     INDUSTRIAL APPLICABILITY 
     The present invention can be utilized in automotive industry.