Drive unit and vehicle

A drive unit that includes a solenoid device that includes: a solenoid section having a movable portion that abuts on a case to arrive at an initial state when de-energized; a pump section axially sliding in association with a movement of the movable portion by an electromagnetic force of the solenoid section and pumping a hydraulic fluid by reciprocation; and an elastic member biasing the pump section in a direction counter to the electromagnetic force of the solenoid section; and a control unit that controls the solenoid device so that a current applied to the solenoid section is repeatedly increased and decreased between an upper limit value and a lower limit value that is greater than 0.

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2008-196591 filed on Jul. 30, 2008 including the specification, drawings and abstract is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a drive unit, and particularly, to a drive unit for a power transmission apparatus that drives a power transmission apparatus in a vehicle provided with an internal combustion engine capable of being automatically stopped and automatically started and the power transmission apparatus having a clutch and being capable of establishing a connection and breaking the connection between an output shaft of the internal combustion engine and a shaft on an axle side by switching an engagement state of the clutch, and a vehicle having the drive unit installed thereon.

As a vehicle of this type in related art, a vehicle has been proposed that is provided with an engine capable of being automatically stopped and automatically started and an automatic transmission for transmitting power from the engine, and that includes, as pumps for generating hydraulic pressure for engaging hydraulically driven clutches or brakes in the automatic transmission, a mechanical oil pump driven by the power from the engine, and an electric oil pump driven by the supply of electric power from a battery (for example, refer to Japanese Patent Application Publication No. JP-A-2003-74689). In this mechanism, when the engine is automatically stopped as the vehicle is stopped, the electric oil pump is driven in place of the mechanical oil pump so that a clutch C1establishing the first forward speed is held in a state immediately before engagement. Thus, when starting off the vehicle by re-starting the engine and engaging the clutch C1based on a start-off request from the driver, delay of the engagement of the clutch C1can be prevented.

SUMMARY OF THE INVENTION

In a drive unit for an automatic transmission of the above-described type, the electric oil pump is typically arranged in parallel with the mechanical oil pump. A line pressure is generated by pumping oil from either one of the electric oil pump and the mechanical oil pump, and supplied to the entire hydraulic circuit. The line pressure in the hydraulic circuit is adjusted by a pressure adjusting valve and thereafter supplied to corresponding clutches and brakes. Accordingly, the electric oil pump is required to have relatively high pumping capacity, resulting in an increase in the volume of the electric oil pump and therefore in the size of the entire unit.

A main object of the present invention which provides a drive unit for a power transmission apparatus and a vehicle is to achieve downsizing of the unit, while achieving quick power transmission to the axle side when an internal combustion engine capable of being automatically stopped and automatically started is automatically started.

In order to achieve the aforementioned main object, the drive unit for a power transmission apparatus and the vehicle of the present invention have adopted the following means.

A drive unit according to a first aspect of the present invention includes a solenoid device and a control unit. The solenoid device includes: a solenoid section having a movable portion that abuts on a case to arrive at an initial state when de-energized; a pump section axially sliding in association with a movement of the movable portion by an electromagnetic force of the solenoid section and pumping a hydraulic fluid by reciprocation; and an elastic member biasing the pump section in a direction counter to the electromagnetic force of the solenoid section. The control unit controls the solenoid device so that a current applied to the solenoid section is repeatedly increased and decreased between an upper limit value and a lower limit value that is greater than 0.

In the drive unit according to the first aspect of the present invention, the solenoid device is controlled so that the current applied to the solenoid section having the movable portion that abuts on a case to arrive at an initial state when de-energized is repeatedly increased and decreased between an upper limit value and a lower limit value that is greater than 0. Accordingly, generation of any noise due to collision between the movable portion and the case can be suppressed. Further, by avoiding the collision between the movable portion and the case, abrasion powder which may be produced by the movable portion and the case worn by the collision can be reduced, and hence any possible malfunction arising from sticking, poor sliding, variations in the stroke volume and the like of the movable portion can be prevented. Still further, durability of the movable portion and the case can also be improved.

In the drive unit according to the first aspect of the present invention, the solenoid device may include a valve element that adjusts a fluid pressure from a fluid pressure source, and the pump section may pump the hydraulic fluid by reciprocation of the valve element sliding in association with the movement of the movable portion. Thus, the unit can be more compact. It is to be noted that the movable portion of the solenoid section includes, besides a movable portion formed separately from the valve element, a movable portion formed integrally with the valve element.

In the drive unit for a power transmission apparatus according to the first aspect of the present invention, which drives the power transmission apparatus in a vehicle provided with an internal combustion engine capable of being automatically stopped and automatically started and the power transmission apparatus having a friction engagement element and being capable of establishing a connection and breaking the connection between an output shaft of the internal combustion engine and a shaft on an axle side by switching an engagement state of the friction engagement element, the control unit may be a unit that, when the internal combustion engine is automatically stopped, repeatedly increases and decreases the current applied to the solenoid section between an upper limit value and a lower limit value that is set to a first predetermined current in preparation for causing the solenoid device to function as a pump while the solenoid device adjusts and supplies the fluid pressure from the fluid pressure source to the friction engagement element, and thereafter repeatedly increases and decreases the current applied to the solenoid section between the upper limit value and a lower limit value that is set to a second predetermined current smaller than the first predetermined current and greater than 0.

Alternatively, the drive unit for a power transmission apparatus according to the first aspect of the present invention, which drives a power transmission apparatus in a vehicle provided with an internal combustion engine capable of being automatically stopped and automatically started and the power transmission apparatus having a friction engagement element and being capable of establishing a connection and breaking the connection between an output shaft of the internal combustion engine and a shaft on an axle side by switching an engagement state of the friction engagement element, may further include a mechanical pump driven by power from the internal combustion engine to pump the hydraulic fluid, and, as the solenoid device, a hollow sleeve in which various ports are formed, a spool that is a shaft-like member inserted into the sleeve and capable of opening and closing the various ports by axially sliding, the elastic member axially biasing the spool, and the solenoid section generating a thrust force with respect to the spool in a direction opposite to the elastic member. An input port for inputting the hydraulic fluid pumped from the mechanical pump, an output port for outputting the hydraulic fluid to the friction engagement element, and a discharge port may be formed as the various ports. A pressure adjusting chamber may be formed between the sleeve and the spool to function as a pressure adjusting valve that adjusts, while discharging from the discharge port, a fluid pressure input from the input port by axial sliding of the spool and that outputs the adjusted fluid pressure to the output port. A suction port and a discharge port for discharging the hydraulic fluid to the friction engagement element may be formed as the various ports. A pump chamber may be formed between the sleeve and the spool as a space blocked from the pressure adjusting chamber to function as a pump that sucks the hydraulic fluid via the suction port by sliding of the spool caused by a biasing force of the elastic member when the thrust force of the solenoid section is released, and that discharges the sucked hydraulic fluid via the discharge port by sliding of the spool caused by the thrust force generated by the solenoid section. The control unit may be a unit that operates the internal combustion engine, and, when the internal combustion engine is automatically stopped by breaking the connection between the output shaft of the internal combustion engine and the shaft on the axle side by engaging the friction engagement element using the solenoid device caused to function as the pressure adjusting valve, repeatedly increases and decreases the current applied to the solenoid section between an upper limit value and a lower limit value that is set to a first predetermined current in preparation for causing the solenoid device to function as the pump while the pressure adjusting valve supplies the fluid pressure to the friction engagement element, and thereafter repeatedly increases and decreases the current applied to the solenoid section between the upper limit value and a lower limit value that is set to a second predetermined current smaller than the first predetermined current, so that, by causing the solenoid device to function as the pump, the friction engagement element is held under a low pressure condition that is lower than a pressure under which the friction engagement element fully engages. Thus, since the solenoid device is caused to function as a pump to directly pump the hydraulic fluid to the friction engagement element in order to hold the friction engagement element under the low pressure condition, as compared with a case where an electric pump is provided in parallel with a mechanical pump so that, when the internal combustion engine is automatically stopped, the electric pump supplies via a pressure adjusting valve the hydraulic fluid to the friction engagement element so as to maintain the low pressure condition, the required pump amount of the hydraulic fluid can be reduced, and hence the solenoid device of a small size can be used. Further, since the preparation for causing the solenoid device to function as a pump is carried out while the fluid pressure from the pressure adjusting valve of the solenoid device is supplied to the friction engagement element, the solenoid device functioning as a pressure adjusting valve can smoothly be switched to function as a pump. Since the friction engagement element is held under the low pressure condition while the internal combustion engine is automatically stopped, when thereafter the internal combustion engine is automatically started, the friction engagement element can quickly be engaged and hence the connection between the shafts can quickly be established. The foregoing achieves downsizing of the unit as well as quick power transmission to the axle side when the internal combustion engine capable of being automatically stopped and automatically started is automatically started. Here, the “friction engagement element” includes, besides a clutch for connecting two rotational systems, a brake for connecting a single rotation system to a fixing system such as a case.

The drive unit according to the first aspect of the present invention in the mode for use in driving a power transmission apparatus may further include a switching valve for selectively switching a connection of a flow passage formed between the pressure adjusting section of the solenoid device and the friction engagement element and a connection of a flow passage formed between the pump section of the solenoid device and the friction engagement element using the hydraulic fluid pumped from the mechanical pump. Thus, the flow passages can smoothly be switched. In this case, the switching valve may be a valve that discharges the hydraulic fluid in the pump chamber in association with blocking of the flow passage formed between the discharge port of the pump section and the friction engagement element. Thus, the hydraulic fluid remaining in the pump chamber can be prevented from disturbing the movement of the spool when the solenoid device is caused to function as a pressure adjusting valve.

In the drive unit according to the first aspect of the present invention in the mode for use in driving a power transmission apparatus, the power transmission apparatus may be an automatic transmission, and the friction engagement element may be a friction engagement element for starting off a vehicle. Thus, the gear ratio for starting off the vehicle can quickly be established when the internal combustion engine is automatically started, allowing the vehicle to be started off smoothly.

A vehicle according to a second aspect of the present invention includes: an internal combustion engine capable of being automatically stopped and automatically started; a power transmission apparatus having a friction engagement element and being capable of establishing a connection and breaking the connection between an output shaft of the internal combustion engine and a shaft on an axle side by switching an engagement state of the friction engagement element; and the drive unit for a power transmission apparatus according to the first aspect of the present invention in the mode for use in driving the power transmission apparatus. Specifically, the drive unit basically drives a power transmission apparatus in a vehicle provided with an internal combustion engine capable of being automatically stopped and automatically started and the power transmission apparatus having a friction engagement element and being capable of establishing a connection and breaking the connection between an output shaft of the internal combustion engine and a shaft on an axle side by switching an engagement state of the friction engagement element, that further includes a mechanical pump driven by power from the internal combustion engine to pump the hydraulic fluid, and, as the solenoid device, a hollow sleeve in which various ports are formed, a spool that is a shaft-like member inserted into the sleeve and capable of opening and closing the various ports by axially sliding, the elastic member axially biasing the spool, and the solenoid section generating a thrust force with respect to the spool in a direction opposite to the elastic member. An input port for inputting the hydraulic fluid pumped from the mechanical pump, an output port for outputting the hydraulic fluid to the friction engagement element, and a discharge port are formed as the various ports. A pressure adjusting chamber is formed between the sleeve and the spool to function as a pressure adjusting valve that adjusts, while discharging from the discharge port, a fluid pressure input from the input port by axial sliding of the spool and that outputs the adjusted fluid pressure to the output port. A suction port and a discharge port for discharging the hydraulic fluid to the friction engagement element are formed as the various ports. A pump chamber is formed between the sleeve and the spool as a space blocked from the pressure adjusting chamber to function as a pump that sucks the hydraulic fluid via the suction port by sliding of the spool caused by a biasing force of the elastic member when the thrust force of the solenoid section is released, and that discharges the sucked hydraulic fluid via the discharge port by sliding of the spool caused by the thrust force generated by the solenoid section. The control unit is a unit that operates the internal combustion engine, and, when the internal combustion engine is automatically stopped by breaking the connection between the output shaft of the internal combustion engine and the shaft on the axle side by engaging the friction engagement element using the solenoid device caused to function as the pressure adjusting valve, repeatedly increases and decreases the current applied to the solenoid section between an upper limit value and a lower limit value that is set to a first predetermined current in preparation for causing the solenoid device to function as the pump while the pressure adjusting valve supplies the fluid pressure to the friction engagement element, and thereafter repeatedly increases and decreases the current applied to the solenoid section between the upper limit value and a lower limit value that is set to a second predetermined current smaller than the first predetermined current, so that, by causing the solenoid device to function as the pump, the friction engagement element is held under a low pressure condition that is lower than a pressure under which the friction engagement element fully engages.

Since the vehicle according to the second aspect of the present invention has the above-described drive unit according to the first aspect the present invention installed thereon, the advantageous effects similar to that achieved by the drive unit of the present invention, for example, downsizing of the unit together with quick power transmission to the axle side when the internal combustion engine capable of being automatically stopped and automatically started is automatically started, can be achieved.

DETAILED DESCRIPTION OF THE EMBODIMENT

Next, an embodiment of the present invention will be described.

FIG. 1is a schematic diagram showing the configuration of a motor vehicle20in which a drive unit for a power transmission apparatus according to an embodiment of the present invention is installed.FIG. 2is a schematic diagram showing the configuration of an automatic transmission30.FIG. 3is an operation table of the automatic transmission30.FIG. 4is a schematic diagram showing the configuration of a hydraulic circuit40. The motor vehicle20is provided, as shown inFIG. 1, with an engine22as an internal combustion engine that outputs power by hydrocarbon fuels such as gasoline or diesel oil, a starter motor23for cranking the engine22to start up, an automatic transmission30having an input shaft36connected to a crankshaft26of the engine22via a torque converter28and an output shaft38connected to driving wheels74aand74bvia a differential gear72for transmitting power input from the input shaft36to the output shaft38, a hydraulic circuit40serving as an actuator for driving the automatic transmission30, and a main electronic control unit (hereinafter referred to as a main ECU)60for controlling the whole vehicle.

The operation of the engine22is controlled by an engine electronic control unit (hereinafter referred to as an engine ECU)24. The engine ECU24is structured, although not shown in details, as a microprocessor centering on a CPU, and is provided with, besides the CPU, a ROM for storing processing programs, a RAM for temporarily storing data, an I/O port, and a communication port. The engine ECU24is fed via the input port with signals required for controlling the operation of the engine22from various sensors, such as an engine speed sensor25installed on the crankshaft26. The engine ECU24outputs via the output port a drive signal to a throttle motor for adjusting a throttle opening, a control signal to a fuel injector, an ignition signal to spark plugs, a drive signal to the starter motor23and the like. The engine ECU24communicates with the main ECU60to control the engine22by the control signal from the main ECU60and to output data relating to operating condition of the engine22to the main ECU60as required.

The automatic transmission30is provided, as shown inFIG. 2, with a planetary gear mechanism30aof a double pinion type, two sets of planetary gear mechanisms30band30cof a single pinion type, three sets of clutches C1, C2and C3, four sets of brakes B1, B2, B3and B4, and three sets of one-way clutches F1, F2and F3. The double pinion type planetary gear mechanism30ais provided with a sun gear31aas an external gear, a ring gear32aas an internal gear concentrically disposed with the sun gear31a, a plurality of first pinion gears33ameshing with the sun gear31a, a plurality of second pinion gears34ameshing with the first pinion gears33aand the ring gear32a, and a carrier35afor coupling the plurality of first pinion gears33aand the plurality of second pinion gears34awith one another and holding the pinion gears to freely rotate and revolve. The sun gear31ais coupled with the input shaft36via the clutch C3and is adapted to rotate freely or in one direction restricted by switching on/off the brake B3which is coupled via the one-way clutch F2. The ring gear32ais adapted to rotate freely or be held stationary by switching on/off the brake B2. The carrier35ais adapted to rotate in one direction restricted by the one-way clutch F1and to rotate freely or be held stationary by switching on/off the brake B1. The single pinion type planetary gear mechanism30bis provided with a sun gear31bas an external gear, a ring gear32bas an internal gear concentrically disposed with the sun gear31b, a plurality of pinion gears33bmeshing with the sun gear31band the ring gear32b, and a carrier35bholding the plurality of pinion gears33bto freely rotate and revolute. The sun gear31bis coupled with the input shaft36via the clutch C1. The ring gear32bis coupled with the ring gear32aof the double pinion type planetary gear mechanism30aand is adapted to rotate freely or be held stationary by switching on/off the brake B2. The carrier35bis coupled with the input shaft36via the clutch C2and is adapted to rotate in one direction restricted by the one-way clutch F3. Further, the single pinion type planetary gear mechanism30cis provided with a sun gear31cas an external gear, a ring gear32cas an internal gear concentrically disposed with the sun gear31c, a plurality of pinion gears33cmeshing with the sun gear31cand the ring gear32c, and a carrier35cholding the plurality of pinion gears33cto freely rotate and revolve. The sun gear31cis coupled with the sun gear31bof the single pinion type planetary gear mechanism30b. The ring gear32cis coupled with the carrier35bof the single pinion type planetary gear mechanism30band is adapted to rotate freely or be held stationary by switching on/off the brake B4. The carrier35cis coupled with the output shaft38.

The automatic transmission30is adapted, as shown inFIG. 3, to switch positions of between first to fifth forward speeds, a reverse speed and neutral by switching on/off the clutches C1to C3, and switching on/off the brakes B1to B4. The first forward speed, more specifically, the state where the rotation of the input shaft36is transmitted to the output shaft38decelerated at the largest reduction ratio, can be established by switching on the clutch C1and switching off the clutches C2and C3and the brakes B1to B4. In this state, as the ring gear32cof the single pinion type planetary gear mechanism30cis fixed to rotate in one direction by the one-way clutch F3, the power input from the input shaft36to the sun gear31cvia the clutch C1is decelerated at a large reduction ratio and is output to the carrier35c, i.e., the output shaft38. In the first forward speed, when engine brake is in operation, by switching on the brake B4, in place of the one-way clutch F3, the ring gear32cis held stationary. The second forward speed can be established by switching on the clutch C1and the brake B3and switching off the clutches C2and C3and the brakes B1, B2and B4. In this state, as the sun gear31aof the double pinion type planetary gear mechanism30ais fixed to rotate in one direction by the one-way clutch F2and the carrier35ais fixed to rotate in one direction by the one-way clutch F1, the ring gear32aand the ring gear32bof the single pinion type planetary gear mechanism30bare also fixed to rotate in one direction and the power input from the input shaft36to the sun gear31bvia the clutch C1is decelerated by the ring gear32bbeing fixed and is output to the carrier35band the ring gear32cof the single pinion type planetary gear mechanism30c. The power input from the input shaft36to the sun gear31cvia the clutch C1is decelerated at a slightly smaller reduction ratio than the first forward speed corresponding to the rotating condition of the ring gear32cand is output to the carrier35c, i.e., the output shaft38. In the second forward speed, when the engine brake is in operation, by switching on the brake B2, in place of the one-way clutch F1and the one-way clutch F2, the ring gear32aand the ring gear32bare held stationary. The third forward speed is established by switching on the clutches C1and C3and the brake B3and switching off the clutch C2and the brakes B1, B2and B4. In this state, as the carrier35aof the double pinion type planetary gear mechanism30ais fixed to rotate in one direction by the one-way clutch F1, the power input from the input shaft36to the sun gear31avia the clutch C3is decelerated and is output to the ring gear32aand the ring gear32bof the single pinion type planetary gear mechanism30b. The power input from the input shaft36to the sun gear31bvia the clutch C1is decelerated corresponding to the rotating condition of the ring gear32band is output to the carrier35band the ring gear32cof the single pinion type planetary gear mechanism30c. The power input from the input shaft36to the sun gear31cvia the clutch C1is decelerated at a slightly smaller reduction ratio than the second forward speed corresponding to the rotating condition of the ring gear32cand is output to the carrier35c, i.e., the output shaft38. In the third forward speed, when the engine brake is in operation, by switching on the brake B1, in place of the one-way clutch F1, the carrier35ais held stationary. The fourth forward speed can be established by switching on the clutches C1to C3and the brake B3and switching off the brakes B1, B2and B4. In this state, as the input shaft36is connected to the sun gear31bof the single pinion type planetary gear mechanism30band the sun gear31cof the single pinion type planetary gear mechanism30cvia the clutch C1and is connected to the carrier35band the ring gear32cvia the clutch C2, all the rotating elements of the single pinion type planetary gear mechanisms30band30crotate as a unit, and the input shaft36and the output shaft38are directly connected, whereby the power input from the input shaft36is transmitted at a value of 1.0 reduction ratio. In the fifth forward speed, more specifically, the state where the rotation of the input shaft36is transmitted to the output shaft38, with the rotation decelerated at the smallest reduction ratio (acceleration), can be established by switching on the clutches C2and C3and the brakes B1and B3and switching off the clutch C1and the brakes B2and B4. In this state, as the carrier35aof the double pinion type planetary gear mechanism30ais held stationary by the brake B1, the power input from the input shaft36to the sun gear31avia the clutch C3is decelerated and is output to the ring gear32aand the ring gear32bof the single pinion type planetary gear mechanism30b. The power input from the input shaft36to the carrier35bvia the clutch C2is accelerated corresponding to the rotating condition of the ring gear32band is output to the sun gear31band the sun gear31cof the single pinion type planetary gear mechanism30c. The power input from the input shaft36to the ring gear32cvia the clutch C2is accelerated at the smallest reduction ratio corresponding to the rotating condition of the sun gear31cand is output to the carrier35c, i.e., the output shaft38.

Further, in the automatic transmission30, the neutral state, more specifically, the input shaft36and the output shaft38can be separated by switching off all the clutches C1to C3and the brakes B1to B4. Furthermore, the reverse state can be established by switching on the clutch C3and the brake B4and switching off the clutches C1and C2and the brakes B1to B3. In this state, as the carrier35aof the double pinion type planetary gear mechanism30ais fixed to rotate in one direction by the one-way clutch F1, the power input from the input shaft36to the sun gear31avia the clutch C3is decelerated and is output to the ring gear32aand the ring gear32bof the single pinion type planetary gear mechanism30b. As the carrier35bof the single pinion type planetary gear mechanism30band the ring gear32cof the single pinion type planetary gear mechanism30care held stationary by the brake B4, the power output to the ring gear32aresults in reverse rotation and is output to the carrier35c, i.e., the output shaft38. In the reverse state, when the engine brake is in operation, by switching on the brake B1, in place of the one-way clutch F1, the carrier35ais held stationary.

The hydraulic circuit40is structured, as shown inFIG. 4, with the elements such as: a mechanical oil pump41for pumping hydraulic oil by the power from the engine22; a regulator valve42for adjusting the pressure of the hydraulic oil (line pressure PL) pumped from the mechanical oil pump41; a linear solenoid43for adjusting the line pressure PL fed through a not-shown modulator valve and outputting the adjusted line pressure PL as a signal pressure so as to drive the regulator valve42; a solenoid valve120provided with a pressure adjusting valve section140for receiving an input of the line pressure PL through a manual valve44, adjusting the received line pressure PL, and outputting the adjusted line pressure PL to the clutch C1side, and a pump section160for sucking hydraulic oil using an electromagnetic force and pumping the sucked hydraulic oil to the clutch C1side; an accumulator45for accumulating the line pressure PL supplied to the pressure adjusting valve section140of the solenoid valve120; a switching valve50for selectively switching the connections of the flow passage formed between the pressure adjusting valve section140and the clutch C1and the flow passage formed between the pump section160and the clutch C1; an on/off solenoid46providing on/off output according to the line pressure PL as the signal pressure that is input through the not-shown modulator valve so as to drive the switching valve50; and a linear solenoid valve (hereinafter referred to as a linear solenoid) SLC2for receiving an input of the line pressure PL through the manual valve44, adjusting the received line pressure PL, and outputting the adjusted line pressure PL to the clutch C2side. InFIG. 4, while the hydraulic system for the clutches C1and C2is shown, the hydraulic systems for, other than the clutches C1and C2, the clutch C3and the brakes B1to B4may also be similarly structured. In the following, the solenoid valve120incorporated in the hydraulic circuit40will be described in detail.FIG. 5is a schematic diagram showing the configuration of the solenoid valve120.

The solenoid valve120is structured to function as a direct control pressure adjusting valve for directly controlling the clutches by generating optimum clutch pressure from the line pressure and to function as a solenoid pump for generating hydraulic pressure, and is provided with, as shown inFIG. 5, a solenoid section130, the pressure adjusting valve section140driven by the solenoid section130for receiving the input of the line pressure, adjusting the received line pressure, and outputting the adjusted line pressure, and the pump section160also driven by the solenoid section130for pumping hydraulic oil.

The solenoid section130is provided with: a case131as a cylindrical member having an open end and a closed bottom end; a coil (solenoid coil)132that is disposed on an inner periphery of the case131with an insulated electrical conductor wound around an insulating bobbin; a first core134including a flange portion134ahaving a flange outer peripheral portion fixed to the open end of the case131and a cylindrical portion134baxially extending from the flange portion134aalong an inner peripheral surface of the coil132; a cylindrical second core135that abuts on the inner peripheral surface of a recessed portion formed at the bottom of the case131and axially extends along the inner peripheral surface of the coil132to a position from which the cylindrical portion134bof the first core134is separated by a predetermined gap; a plunger136that is inserted in the second core135and axially slidable on inner peripheral surfaces of the first core134and the second core135; and a shaft138that is inserted in the cylindrical portion134bof the first core134, abuts on the tip of the plunger136, and is axially slidable on an inner peripheral surface of the cylindrical portion134b. Further, in the solenoid section130, terminals from the coil132are connected to a connector portion139formed on an outer peripheral surface of the case131, and the coil132is energized through these terminals. The case131, the first core134, the second core135, and the plunger136are all composed of a ferromagnetic material such as highly pure iron, and a space between an end face of the cylindrical portion134bof the first core134and an end face of the second core135is 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 space.

In the solenoid section130, when the coil132is energized, a magnetic circuit is formed where magnetic flux flows around the circumference of the coil132in the order of the case131, the second core135, the plunger136, the first core134, and the case131. Consequently, an attractive force is acted on between the first core134and the plunger136to attract the plunger136. As described above, since the tip of the plunger136abuts on the shaft138that is axially slidable on the inner peripheral surface of the first core134, the shaft138is pushed forward (leftward in the drawing) by the attraction of the plunger136.

The pressure adjusting valve section140and the pump section160are provided with, as common materials, a nearly cylindrical sleeve122that is incorporated in a valve body110and has one end attached to the first core134by the case131of the solenoid section130, a spool124that is inserted in the internal space formed in the sleeve122and has one end abutting on the tip of the shaft138of the solenoid section130, an end plate126screwed onto the other end of the sleeve122, and springs128and196that are provided between the end plate126and the other end of the spool124and bias the spool124towards the solenoid section130.

The sleeve122includes, as openings in a region that forms the pressure adjusting valve section140, an input port142for inputting hydraulic oil, an output port144for discharging the hydraulic oil input to the clutch C2side, a drain port146for draining the hydraulic oil input, and a feedback port148for causing feedback force to act on the spool124by inputting the hydraulic oil output from the output port144through an oil passage148aformed by the inner surface of the valve body110and the outer surface of the sleeve122in a portion of the sleeve122that forms the pressure adjusting valve portion140. Further, also formed at the end of the sleeve122on the solenoid section130side is a drain hole149for draining the hydraulic oil leaked from between the inner peripheral surface of the sleeve122and the outer peripheral surface of the spool124in association with sliding of the spool124.

The sleeve122is formed, as openings in a region that forms the pump section160, a suction port162for sucking hydraulic oil, a discharging port164for discharging the hydraulic oil sucked, and a drain port166for draining the hydraulic oil remaining when the function of the pump section160is stopped. The drain port166is adapted to drain hydraulic oil through the switching valve50.

The spool124is formed as a shaft-like member to be inserted inside the sleeve122, and is provided with: three columnar lands152,154and156slidable on inner walls of the sleeve122; a communicating portion158that is formed to couple the land152with the land154, has an outer diameter smaller than the outer diameters of the lands152and154, is formed in a tapered shape such that the outer diameter of the communication portion158becomes smaller towards the center from each of the lands152and154, and communicates between each of the input port142, the output port144, and the drain port146; and a coupling portion159that couples the land154with the land156having an outer diameter smaller than that of the land154and forms a feedback chamber together with an inner wall of the sleeve122such that the feedback force is acted on the spool124towards the solenoid section130. The sleeve122, the communicating portion158of the spool124, and the lands152and154form a pressure adjusting chamber150.

Further, built into the sleeve122are a suction check valve180and a discharge check valve190. The sleeve122, the suction check valve180, and the discharge check valve190form a pump chamber170. The suction check valve180is provided with a cylindrical body182that is coupled with the land156and formed with an opening182ain the axial center for communicating the pump chamber170with the suction port162, a ball184, and a spring186for pressing the ball184against the opening182aof the body182. The suction check valve180is closed by the biasing force of the spring186when inside the pump chamber170is under a positive pressure, and is opened when inside the pump chamber170is under a negative pressure. On the other hand, the discharge check valve190is provided with a cylindrical body192that functions as a spring holder for receiving the spring128and the spring186of the suction check valve180and is formed with an opening192ain the axial center thereof for communicating the pump chamber170with the discharge port164, a ball194, and a spring196with the end plate126as a spring holder for pressing the ball194against the opening192aof the body192. The discharge check valve190is closed by the biasing force of the spring196when inside the pump chamber170is under a negative pressure, and is opened when inside the pump chamber170is under a positive pressure. Accordingly, when the coil132of the solenoid section130is de-energized from an energized state, the spool124is moved towards the solenoid section130by the biasing force of the spring128, thereby sucking hydraulic oil from the suction port162into the pump chamber170through the suction check valve180. When the coil132of the solenoid section130is energized from a de-energized state, the spool124is moved towards the end plate126by the thrust force of the solenoid section130, thereby discharging the sucked hydraulic oil from the discharge port164through the discharge check valve190.

The operation of the solenoid valve120of the present embodiment thus structured, particularly when functioning as a pressure adjusting valve and as a solenoid pump, will be described. First, the operation of the solenoid valve120when functioning as a pressure adjusting valve will be described. Now, the coil132is not energized. In this case, as the spool124is moved towards the solenoid section130by the biasing force of the spring128, the input port142is blocked by the land154while the output port144and the drain port146are placed in communication with each other through the communicating portion158. Accordingly, no hydraulic pressure is acted on the clutch C1. When the coil132is energized, the plunger136is attracted to the first core134by the attractive force corresponding to the amount of current applied to the coil132causing the shaft138to be pushed out and thus the spool124abutting on the tip of the shaft138is moved towards the end plate126. Consequently, the input port142, the output port144, and the drain port146are placed in communication with one another, and a part of the hydraulic oil input from the input port142is output to the output port144and the rest of the hydraulic oil is output to the drain port146. Additionally, the hydraulic oil is supplied to the feedback chamber through the feedback port148, and the feedback force corresponding to the output pressure of the output port144is acted on the spool24in the direction towards the solenoid section130. Accordingly, the spool124stops at the position where the thrust force (attractive force) of the plunger136, the spring force of the spring128, and the feedback force just balance out. In this case, the larger the amount of current applied to the coil132, more specifically, the larger the thrust force of the plunger136, the more the spool124moves towards the end plate126, thereby expanding the opening area of the input port142and reducing the opening area of the drain port146. When the current applied to the coil132is maximized, the spool124is moved to the position that is closest to the end plate126within the range of movement of the plunger136, and thus the input port142and the output port144are placed in communication with each other through the communicating portion158while the drain port146is blocked by the land152, thereby cutting off the communication of the output port144and the drain port146. Consequently, the maximum hydraulic pressure is acted on the clutch C1. As described in the foregoing, when the coil132is not being energized, as the input port142is blocked while the output port144is placed in communication with the drain port146, it is apparent that the solenoid valve120functions as a normal-closed type solenoid valve.

Secondly, the operation of the solenoid valve120when functioning as a solenoid pump will be described. Now, the coil132is just de-energized after being energized. In this case, as the spool124is moved from the end plate126side towards the solenoid section130side, the pressure inside the pump chamber170becomes a negative pressure, opening the suction check valve180and closing the discharge check valve190so that the hydraulic oil is sucked into the pump chamber170from the suction port162through the suction check valve180. When the coil132is energized from this state, as the spool124is moved from the solenoid section130side towards the end plate126side, the pressure inside the pump chamber170becomes under a positive pressure, closing the suction check valve180and opening the discharge check valve190so that the hydraulic oil sucked in the pump chamber170is discharged from the discharge port164through the discharge check valve190. Consequently, by repeatedly energizing and de-energizing the coil132, the solenoid valve120can be made to function as a solenoid pump for pumping hydraulic oil. This concludes the description of solenoid valve120.

The switching valve50, as shown in operational schematic diagrams inFIGS. 6A and 6B, is provided with a spring54at the lower part thereof for biasing a spool52upward in the drawing, and an input port56for inputting the signal pressure from the on/off solenoid46at the upper part thereof. When the signal pressure is input from the on/off solenoid46, the signal pressure overcomes the biasing force of the spring54and thus the spool52is moved downward in the drawing, thereby connecting the flow passage formed between the output port144of the pressure adjusting valve section140and the clutch C1, blocking the flow passage formed between the discharge port164of the pump section160and the clutch C1, and connecting the flow passage formed between the drain port166of the pump section160and a drain port58(refer toFIG. 6A). When the signal pressure is not input from the on/off solenoid46, the spool52is moved upward in the drawing by the biasing force of the spring54, thereby blocking the flow passage formed between the output port144of the pressure adjusting valve section140and the clutch C1, connecting the flow passage formed between the discharge port164of the pump section160and the clutch C1, and blocking the flow passage formed between the drain port166of the pump section160and the drain port58(refer toFIG. 6B).

The hydraulic circuit40is drive controlled by an automatic transmission electronic control unit (hereinafter referred to as an ATECU)39. The ATECU39is structured, although not shown in details, as a microprocessor centering on a CPU and is provided with, besides the CPU, a ROM for storing processing programs, a RAM for temporarily storing data, an I/O port, and a communication port. The ATECU39outputs drive signals to the linear solenoid43, the solenoid valve120, the linear solenoid SLC2, and the on/off solenoid46, or the like, via the output port. The ATECU39communicates with the main ECU60to control the automatic transmission30(hydraulic circuit40) by control signals from the main ECU60and to output the data relating to the status of the automatic transmission30to the main ECU60as required.

The main ECU60is structured, although not shown in details, as a microprocessor centering on a CPU, and is provided with, besides the CPU, a ROM for storing processing programs, a RAM for temporarily storing data, an I/O port, and a communication port. The main ECU60is fed with an ignition signal from an ignition switch61, a shift position SP from a shift position sensor63which detects an operating position of a shift lever62, an accelerator opening Acc from an accelerator pedal position sensor65which detects the amount of depression of an accelerator pedal64, a brake switch signal BSW from a brake switch67which detects the depression of a brake pedal66, and a vehicle speed V from a vehicle speed sensor68via the input port. The main ECU60is connected with the engine ECU24and the ATECU39via the communication port to exchange various control signals and data to and from the engine ECU24and the ATECU39.

In the motor vehicle20of the present embodiment thus structured, while running with the shift lever62at the driving position of D (drive) after the engine22is started up, when all of predetermined auto-stop conditions as the value of the vehicle speed V is 0, the accelerator pedal is off, and the brake switch signal BSW is on, are satisfied, the engine22is automatically stopped. After the engine22is automatically stopped, when predetermined auto-start conditions as the brake switch signal BSW is off and the accelerator pedal is on are subsequently satisfied, the engine22that has been automatically stopped is then automatically started.

Next, the operation of the drive unit for a power transmission apparatus in the present embodiment installed on the motor vehicle20thus structured, particularly the operation while the engine22is automatically stopped, will be described. The drive unit for a power transmission apparatus in the present embodiment corresponds to the hydraulic circuit40and the ATECU39.FIG. 7is a flowchart showing an example of an auto-stop control routine carried out by the ATECU39. This routine is carried out when the auto-stop conditions for the engine22are satisfied while running with the shift lever62at the D position. In this running condition, the signal pressure is output from the on/off solenoid46, and the switching valve50is in the state blocking the flow passage formed between the discharge port164of the pump section160and the clutch C1and connecting the flow passage formed between the output port144of the pressure adjusting valve section140and the clutch C1.

When the auto-stop control routine is carried out, the CPU of the ATECU39first applies current Iset to the solenoid section130so that the clutch C1engages with an engagement pressure corresponding to idling speed Nidle while the engine22is in an idling operation before fuel supply to the engine22is cut off following the satisfaction of the auto-stop conditions for the engine22(step S100), waits for a lapse of a predetermined time T1from the satisfaction of the auto-stop conditions (step S110), and applies to the solenoid section130a rectangular wave current of a predetermined cycle F having the maximum current Imax applicable to the solenoid section130as the high value Ihi and the current Iset as the low value Ilo (step S120). Thus, the spool124reciprocates between a stroke position Shi corresponding to the high value Ihi and a stroke position Slo corresponding to the low value Ilo. Therefore, while the supply of hydraulic pressure to the clutch C1from the pressure adjusting valve section140corresponding to the stroke position Slo of the spool124is ensured, hydraulic oil is introduced into the pump chamber170of the pump section160by the pumping effect attained by the reciprocation of the spool124so that the solenoid valve120is prepared to function as a solenoid pump. Accordingly, the predetermined time T1may be set as a period obtained by subtracting the time required for the above-described preparation for causing the solenoid valve120to function as a solenoid pump from the time required from the satisfaction of the auto-stop conditions until the mechanical oil pump41ceases pumping of hydraulic oil as the engine22is stopped. The predetermined cycle F, in the present embodiment, has empirically been obtained as the cycle with which the solenoid valve120can fully exhibit performance as a solenoid pump.

Then, the engine speed Ne of the engine22is input (step S130). The process is repeated returning to step S120until the input engine speed Ne of the engine22becomes not greater than a threshold value Nref determined as the engine speed immediately before the engine22is stopped (e.g., 100 rpm) (step S140). When the engine speed Ne becomes not greater than the threshold value Nref, the on-off solenoid46is controlled so that the switching valve50blocks the flow passage formed between the output port144of the pressure adjusting valve section140and the clutch C1and connects the flow passage formed between the discharge port164of the pump section160and the clutch C1, thereby switching the solenoid valve120functioning as a pressure adjusting valve to function as a solenoid pump (step S150). A rectangular wave current of the predetermined cycle F having the maximum current Imax as the high value Ihi and a minimum current Imin as the low value Ilo is applied to the solenoid section130(step S160), awaiting for a lapse of a predetermined time T2(which is immediately before start-up of the engine22is finished) from the subsequent satisfaction of the auto-start conditions (step S170). Here, the minimum current Imin is determined to be a value smaller than the current Iset and greater than 0. This is based on the following consideration. It is desirable to ensure the maximum stroke volume of the spool124employing the maximum current Imax as the high value Ihi and the value of 0 as the low value Ilo in order to maximize the pumping capacity of the solenoid valve120when the solenoid valve12functions as a solenoid pump. However, in this case, when the current applied to the solenoid section130is switched from on to off, the spring force of the springs128and196may cause the plunger136to collide with the case131, producing noise which may discomfort the driver. Accordingly, the minimum current Imin is determined as a value that is as close to 0 as possible in the range where the plunger136does not collide with the case131by the reciprocation of the spool124. By the processing above, the clutch C1establishing the first forward speed is adapted to be replenished with hydraulic oil from the pump section160using a solenoid valve of low pumping capacity, for example, by the amount leaked from the seal ring or the like provided between the clutch piston and the drum, and to stand by under a low pressure Plo condition which is just enough for the clutch piston to be held at the stroke end position. In the present embodiment, the pump section160(the pumping capacity) of the solenoid valve120has been so designed that the low pressure Plo condition becomes the condition where the clutch C1has a torque capacity capable of transmitting a torque slightly larger than a cranking torque by the starter motor23to the engine22.

After a lapse of the predetermined time T2from the satisfaction of the auto-stop conditions, the current Iset is applied to the solenoid section130(step S180). The on-off solenoid46is controlled so that the switching valve50connects the flow passage formed between the discharge port164of the pump section160and the clutch C1and blocks the flow passage formed between the output port144of the pressure adjusting valve section140and the clutch C1, whereby the solenoid valve120functioning as a solenoid valve is switched to function as a pressure adjusting valve (step S190). When the engine22comes to be in complete explosion (step S200), the current applied to the solenoid section130is increased so as to establish full engagement of the clutch C1(step S210), and the routine is ended. Thus, the clutch C1is fully engaged, and the power from the engine22can be transmitted to the driving wheels74aand74bthrough the automatic transmission30at the first forward speed so as to start off the vehicle. It is to be noted that, as described above, when the switching valve50connects the flow passage formed between the discharge port164of the pump section160and the clutch C1and blocks the flow passage formed between the output port144of the pressure adjusting valve section140and the clutch C1, the drain port166of the pump section160and the drain port58of the switching valve50accordingly communicate with each other, thereby draining the hydraulic oil remaining in the pump chamber170. Therefore, the solenoid valve120will not be disturbed by the hydraulic oil remaining in the pump chamber170in functioning as a pressure adjusting pump.

FIG. 8is a timing 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 C1, current command for the solenoid section130of the solenoid valve120and the valve stroke of the solenoid valve120. As shown in the timing chart, after a lapse of the predetermined time T1from the satisfaction of the auto-stop conditions for the engine22at time point t1, the rectangular wave current of the predetermined cycle F having the maximum current Imax as the high value Ihi and the current Iset as the low value Ilo is applied to the solenoid section130, in preparation for switching the solenoid valve120functioning as a pressure adjusting valve to function as a solenoid pump. At time point t3, the fuel supply to the engine22is cut off. At time point t4, when the engine speed Ne of the engine22becomes not greater than the engine speed immediately before the engine22is stopped (threshold value Nref), the switching valve50switches the function of the solenoid valve120from that as a pressure adjusting valve to that as a solenoid pump, and the rectangular wave current of the predetermined cycle F having the maximum current Imax as the high value Ihi and the minimum current Imin, which is smaller than the current Iset and greater than 0, as the low value Ilo is applied to the solenoid section130, whereby the clutch C1is held under the low pressure Plo condition. Here, since the low pressure Plo condition can be maintained by replenishing the hydraulic oil just by the amount leaked from the seal ring or the like, the required pumping performance can be met by a solenoid pump which has relatively low pumping capacity. When the auto-start conditions for the engine22are then satisfied as the brake is switched off at the time point t5and the accelerator pedal is switched on at the time point t6, the engine22is cranked up by the starter motor23. Here, as the hydraulic pressure of the clutch C1is maintained under the low pressure Plo condition having a slightly larger torque capacity than the cranking torque, the cranking torque of the engine22is transmitted to the driving wheels74aand74bas creep torque through the clutch C1. When the cranking of the engine22is started, the switching valve50connects the flow passage formed between the discharge port164of the pump section160and the clutch C1and blocks the flow passage formed between the output port144of the pressure adjusting valve section140and the clutch C1, thereby switching the solenoid valve120to function as a pressure adjusting valve. When the engine22comes to be in complete explosion at time point t7, the current applied to the solenoid section130is increased so that the clutch C1is fully engaged.

The drive unit for a power transmission apparatus installed on the motor vehicle20of the present embodiment described in the foregoing includes the solenoid valve120that functions as a pressure adjusting valve for supplying the line pressure through the pressure adjusting valve section140to the clutch C1establishing the first forward speed for starting off the vehicle, and also functions as a solenoid pump for directly supplying the hydraulic pressure from the pump section160to the identical clutch C1, so that, when the engine22is automatically stopped, the solenoid valve120is caused to function as a solenoid pump to directly pump the hydraulic oil to the clutch C1without having a pressure adjusting valve interposed to hold the clutch C1under the low pressure Plo condition. Therefore, the volume of the pump can drastically be reduced, as compared with the case where an electric oil pump is provided in parallel with the mechanical oil pump41so that, when the engine22is automatically stopped, the electric oil pump is driven to hold the clutch C1under the low pressure Plo condition through a pressure adjusting valve. Additionally, since the sleeve122and the spool124form the pressure adjusting valve section140which functions as a pressure adjusting valve for adjusting the clutch pressure of the clutch C1, as well as the pump section160which functions as a solenoid pump for directly pumping hydraulic oil to the identical clutch C1, and the pressure adjusting valve section140and the pump section160are driven by the single solenoid section130, downsizing of the unit can be achieved as compared with the case where the pressure adjusting valve and the solenoid pump are separately provided. Furthermore, in the present embodiment, when the auto-stop conditions for the engine22are satisfied, the rectangular wave current of the predetermined cycle F having the maximum current Imax as the high value Ihi and the current Iset as the low value Ilo is applied to the solenoid section130of the solenoid valve120, and, while the supply of hydraulic pressure from the pressure adjusting valve section140to the clutch C1is ensured, hydraulic oil is introduced into the pump chamber170of the pump section160due to the pumping effect by the reciprocation of the spool124, whereby the solenoid valve120is prepared to function as a solenoid pump. When the engine22is stopped and the line pressure is off, the switching valve50blocks the flow passage formed between the output port144of the pressure adjusting valve section140and the clutch C1and connects the flow passage formed between the discharge port164of the pump section160and the clutch C1, and the rectangular wave current of the predetermined cycle F having the maximum current Imax as the high value Ihi and a minimum current Imin smaller than the current Iset as the low value Ilo is applied to the solenoid section130, whereby the clutch C1is held under the low pressure Plo condition. Therefore, the solenoid valve120functioning as a pressure adjusting valve can be smoothly switched to function as a solenoid pump. As a matter of course, by causing the clutch C1establishing the first forward speed for starting off the vehicle to stand by under the low pressure Plo condition during the auto-stop of the engine22, the clutch C1can quickly be fully engaged when the accelerator pedal63is depressed, and the vehicle can be started off smoothly.

In the drive unit for a power transmission apparatus installed on the motor vehicle20of the present embodiment, the rectangular wave current having the maximum current Imax as the high value Ihi and the minimum current Imin greater than 0 as the low value Ilo is applied to the solenoid section130during the auto-stop of the engine22to hold the clutch C1establishing the first forward speed under the low pressure Plo condition. Alternatively, a rectangular wave current having the maximum current Imax as the high value Ihi and 0 as the low value Ilo may be applied to the solenoid section130to hold the clutch C1under the low pressure Plo condition, although some noise may be produced in this case.

While the drive unit for a power transmission apparatus installed on the motor vehicle20of the present embodiment is structured as a linear solenoid valve for directly controlling the clutch C1by generating an optimal clutch pressure from the line pressure PL when functioning as a pressure adjusting valve, the linear solenoid valve may be used as a pilot linear solenoid valve to drive a separate control valve, thereby controlling the clutch C1with the clutch pressure generated by the control valve. In addition, the clutch C2and the brakes B1to B4may be similarly structured.

In the drive unit for a power transmission apparatus installed on the motor vehicle20of the present embodiment, the clutch C1stands by during the auto-stop of the engine22under the low pressure Plo condition with the torque capacity capable of transmitting a slightly larger torque than a cranking torque by the starter motor23to the engine22. Alternatively, the clutch C1may stand by under a low pressure condition immediately before engagement without a torque capacity. In this case, the pump section160of the solenoid valve120may be designed to have pumping capacity just enough to hold the clutch C1under the low pressure condition where the clutch C1should stand by. Additionally, the pump section160may be provided with a margin of pumping capacity, and the current applied to the solenoid section130may be controlled so as to maintain the low pressure condition of the clutch C1.

In the drive unit for a power transmission apparatus installed on the motor vehicle20of the present embodiment, the on-off solenoid46turns on/off the signal pressure (the line pressure PL) supplied to the input port56to drive the switching valve50. Alternatively, the line pressure PL may be output directly (or via a modulator valve) to the input port56. In this case, steps S150and S190in the auto-stop control routine shown inFIG. 7are not necessary. In this case, since the line pressure PL is generated by the mechanical oil pump41when the engine22is in operation, the switching valve50blocks the flow passage formed between the discharge port164of the pump section160and the clutch C1and connects the flow passage formed between the output port144of the pressure adjusting valve section140and the clutch C1. Further, since the line pressure PL is off when the engine22is stopped and therefore the mechanical oil pump41is stopped, the switching valve50connects the flow passage formed between the discharge port164of the pump section160and the clutch C1and blocks the flow passage formed between the output port144of the pressure adjusting valve section140and the clutch C1.

In the drive unit for a power transmission apparatus installed on the motor vehicle20of the present embodiment, the suction check valve180and the discharge check valve190are built into the sleeve122. Alternatively, as a solenoid valve120B of a modification example shown inFIG. 9, both a suction check valve180B and a discharge check valve190B may be incorporated in the valve body110external to the sleeve122. In the solenoid valve120B of the modification example, the solenoid section130and the pressure adjusting valve section140are structured identical to those in the solenoid valve120of the present embodiment. In a pump section160B of the solenoid valve120B, as shown inFIG. 9, a pump chamber170B is formed by the sleeve122, the land156of the spool124, and the end plate126. When the coil132of the solenoid section130is de-energized from the energized state, the spool124(land156) is moved towards the solenoid section130by the biasing force of the spring128, thereby sucking hydraulic oil from a suction port162B into the pump chamber170B through the suction check valve180B incorporated in the valve body110. When the coil132of the solenoid section130is energized from the de-energized state, the spool124is moved towards the end plate126by the thrust force of the solenoid section130, thereby discharging the sucked hydraulic oil from a discharge port164B through the discharge check valve190B incorporated in the valve body110.

In the drive unit for a power transmission apparatus installed on the motor vehicle20of the present embodiment, the suction check valve180and the discharge check valve190are built into the sleeve122. Alternatively, as a solenoid valve120C of a modification example shown inFIG. 10, only the suction check valve180may be built into the sleeve122and a discharge check valve190C may be incorporated in the valve body110external to the sleeve122. In the solenoid valve120C of the modification example, the solenoid section130, the pressure adjusting valve section140, the suction check valve180of a pump section160C are structured identical to those in the solenoid valve120of the present embodiment. In the pump section160C of the solenoid valve120C, as shown inFIG. 10, when the coil132of the solenoid section130is de-energized from the energized state, the spool124is moved towards the solenoid section130by the biasing force of the spring128, thereby sucking hydraulic oil from a suction port162C into the pump chamber170C through the opening182aof the suction check valve180. When the coil132of the solenoid section130is energized from the de-energized state, the spool124is moved towards the end plate126by the thrust force of the solenoid section130, thereby discharging the sucked hydraulic oil from a discharge port164C through the discharge check valve190C incorporated in the valve body110.

In the drive unit for a power transmission apparatus installed on the motor vehicle20of the present embodiment, the suction check valve180and the discharge check valve190are both built into the sleeve122. Alternatively, the suction check valve180may be incorporated in the valve body110external to the sleeve122and the discharge check valve190may be built into the sleeve122.

In the solenoid valve120of the present embodiment, the function as a solenoid pump is integrated into a so-called normal-closed type linear solenoid valve. Alternatively, as a solenoid valve120D of a modification example shown inFIG. 11, the function as a solenoid pump may be integrated into a so-called normal-open type linear solenoid valve. The solenoid section130is structured identical to that in the solenoid valve120of the present embodiment. In a pressure adjusting valve section140D of the solenoid valve120D of the modification example, while the coil132is de-energized, as a spool124D is moved towards the solenoid section130by the biasing force of the spring128, an input port142D and an output port144D formed in a sleeve122D are placed in communication with each other through a communicating portion158D of the spool124D while a drain port146D is blocked by a land156D of the spool124D. Accordingly, the maximum hydraulic pressure is acted on the clutch C2. When the coil132is energized, the plunger136is attracted to the first core134by the attractive force corresponding to the amount of current applied to the coil132and the shaft138is then pushed out, and the spool124D in abutment on the tip of the shaft138is moved towards the end plate126. Accordingly, the input port142D, the output port144D, and the drain port146D are placed in communication with one another, and a part of the hydraulic oil input from the input port142D is output to the output port144D and the rest of the hydraulic oil is output to the drain port146D. Further, the hydraulic oil is supplied to a feedback chamber through a feedback port148D, and the feedback force corresponding to the output pressure of the output port144D is acted on the spool124D in the direction towards the end plate126. Consequently, the spool124D stops at the position where the thrust force (attractive force) of the plunger136, the spring force of the spring128, and the feedback force just balance out. In this case, the larger the amount of current applied to the coil132, more specifically, the larger the thrust force of the plunger136, the more the spool124D moves towards the end plate126, thereby reducing the opening area of the input port142D and expanding the opening area of the drain port146D. When the current applied to the coil132is maximized, the spool124D is moved to the position that is closest to the end plate126within the range of movement of the plunger136, and thus the input port142D is blocked by the land154D while the output port144D and the drain port146D are placed in communication with each other through the communicating portion158D. Accordingly, no hydraulic pressure is acted on the clutch C2. As described above, in the solenoid valve120D of the modification example, when the coil132is not being energized, as the input port142D and the output port144D are placed in communication with each other while the drain port146D is blocked, it is apparent that the solenoid valve120D of the modification example functions as a normal-open type solenoid valve. In a pump section160D of the solenoid valve120D of the modification example, both a suction check valve180D and a discharge check valve190D are to be incorporated into the valve body110external to the sleeve122D. The pump section160D of the solenoid valve120D is adapted such that, when the solenoid section130is de-energized from the energized state, the spool124D is moved towards the solenoid section130by the biasing force of the spring128making inside the pump chamber170D under a negative pressure, thereby sucking hydraulic oil from the suction port162D and, when the solenoid section130is energized from the de-energized state, the spool124D is moved towards the end plate126by the thrust force of the solenoid section130making inside the pump chamber170D under a positive pressure, thereby discharging the sucked hydraulic oil from the discharge port164D. Naturally, both the suction check valve180D and the discharge check valve190D are not limited to be incorporated into the valve body110external to the sleeve122D, and only the suction check valve180D may be built into the sleeve122D, only the discharge check valve190D may be built into the sleeve122D, or both the suction check valve180D and the discharge check valve190D may be built into the sleeve122D.

In the solenoid valve120D of the modification example described above, the solenoid section130tends to become larger than when applied to a normal-closed type linear solenoid valve. This is because, while the direction of feedback force acting on the spool124is in an opposite direction to the thrust force of the solenoid section130in a normal-closed type linear solenoid valve, the direction of feedback force acting on the spool124is the same as that of the thrust force of the solenoid section130in a normal-open type linear solenoid valve. Accordingly, as the spring load of the spring128needs to be large, the thrust force required for the solenoid section130becomes large in that respect when functioning as 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 Detailed Description of the Embodiment will be described. In the present embodiment, the solenoid valve120corresponds to the “solenoid device”, and the ATECU39for carrying out the auto-stop control routine shown inFIG. 7corresponds to the “control unit”. Further, the solenoid section130corresponds to the “solenoid section”, and the spring128corresponds to the “elastic member”. Still further, the spool124corresponds to the “valve element”. The engine22corresponds to the “internal combustion engine”, and the automatic transmission30corresponds to the “power transmission apparatus”. The mechanical oil pump41corresponds to the “mechanical pump”, and the switching valve50corresponds to the “switching valve”. It is to be noted that, the “internal combustion engine” is not limited to an internal combustion engine that outputs power by hydrocarbon fuels such as gasoline or diesel oil, and it may be an engine of any type including a hydrogen engine. The “power transmission apparatus” is not limited to the automatic transmission30of five speeds, i.e., first to fifth forward speeds, and may be an automatic transmission of any speeds including four speeds, six speeds, eight speeds and the like. The “power transmission apparatus” is not limited to an automatic transmission. For example, the “power transmission apparatus” may be connected directly to the crankshaft26of the engine22(i.e., to the torque converter28) with a clutch and connected to the driving wheels74aand74bvia the differential gear72and thus, may be anything so long as the “power transmission apparatus” is provided with any clutch and is capable of establishing a connection and breaking the connection between an output shaft of the internal combustion engine and a shaft on an axle side by switching an engagement state of the clutch. The “solenoid pressure adjusting pumping unit” is not limited to the unit for pumping hydraulic fluid to the clutch C1establishing the first forward speed. For example, when any speed other than the first forward speed (e.g., second forward speed) is set as the speed for starting off the vehicle according to an instruction of the driver or the running state, the “solenoid pressure adjusting pumping unit” may pump hydraulic oil to the clutch or brake establishing that speed. The “auto-stop control unit” is not limited to the ATECU39, and the ATECU39, the engine ECU24and the main ECU60may be integrated, or the ATECU39may be realized by a plurality of electronic control units. Since the correspondence relation of the major elements of the present embodiment with respect to the major elements of the present invention described in Detailed Description of the Embodiment is an example for specifically explaining the embodiment of the present invention, it is not intended to limit in any way the elements of the present invention described in Detailed Description of the Embodiment. More specifically, the aspects of the present invention described in Detailed Description of the Embodiment should be interpreted based on the description thereof, as the embodiment of the present invention is merely a specific example of the present invention described in the Detailed Description of the Embodiment.

While the preferred embodiment of the present invention is described in details above, the present invention is not limited to the specific embodiment and, within the spirit and scope of the present invention, various modifications and alternations may be made.

The present application is based upon and claims the benefit of priority from the Japanese Patent Application No. 2008-196591, filed on Jul. 30, 2008; the entire contents of which are incorporated herein by reference.

The present invention can be utilized in the automotive industry.