Drive system for vehicle

A drive system for a vehicle includes an engine, a transmission, a clutch mechanism including first and second clutch portions, the clutch mechanism being switchable between connected and disconnected states, and a clutch operation mechanism switching the clutch mechanism between the connected and disconnected states, the clutch operation mechanism including a clutch drum forming a drum chamber, a piston dividing the drum chamber into a spring chamber and a pressurizing chamber, a control valve, a biasing member arranged in the spring chamber and exerting a biasing force in a direction in which the first and second clutch portions are engaged with each other, and a bore formed in the clutch drum, the bore discharging oil of the spring chamber to an outer side of the spring chamber in a state where a counteracting force against a centrifugal force acting in the pressurizing chamber is generated in the spring chamber.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 U.S.C. §119 to Japanese Patent Application 2010-246864, filed on Nov. 2, 2010, the entire content of which is incorporated herein by reference.

TECHNICAL FIELD

This disclosure relates to a drive system for a vehicle.

BACKGROUND DISCUSSION

A known drive system for a vehicle disclosed in each of JP2009-101730A, JP2006-137406A, and JP2010-6190A (hereinafter referred to as References 1, 2, and 3) includes a transmission to which a driving force of an engine is transmitted from an output shaft of the engine, and a clutch mechanism arranged between the output shaft of the engine and an input shaft of the transmission. According to the drive system disclosed in each of References 1, 2, and 3, the clutch mechanism includes a first clutch portion arranged at the output shaft of the engine, and a second clutch portion arranged at the input shaft of the transmission. The clutch mechanism is switchable between a connected state where the first and second clutch portions are engaged with each other to thereby transmit the driving force of the engine to the transmission and a disconnected state where the first and second clutch portions are disengaged from each other to thereby block the transmission of the driving force of the engine to the transmission.

According to the drive system disclosed in each of References 1, 2, and 3, when the clutch mechanism is brought into the connected state or into the disconnected state under a condition where the input shaft of the transmission is in rotation, a hydraulic pressure caused by a centrifugal force due to the rotation (hereinafter, the hydraulic pressure caused by the centrifugal force due to the rotation will be referred to as a centrifugal hydraulic pressure) may influence operational responsiveness of the clutch mechanism when the clutch mechanism shifts between the connected and disconnected states. As a result, improvement of the operational responsiveness of the clutch mechanism may be limited. In addition, the centrifugal hydraulic pressure due to the rotation is influenced by a rotating speed of the input shaft. Accordingly, the operational responsiveness of the clutch mechanism may be influenced by a moving speed of the vehicle, therefore limiting the improvement of the operational responsiveness of the clutch mechanism.

A need thus exists for a drive system for a vehicle, which is not susceptible to the drawback mentioned above.

SUMMARY

According to an aspect of this disclosure, a drive system for a vehicle includes an engine having an output shaft, a transmission including an input shaft to which a driving force of the output shaft of the engine is transmitted, the transmission transmitting the driving force to driving wheels of the vehicle, a clutch mechanism including a first clutch portion arranged between the output shaft of the engine and the input shaft of the transmission and positioned at the output shaft, and a second clutch portion arranged at the input shaft, the clutch mechanism being switchable between a connected state where the first clutch portion and the second clutch portion are engaged with each other to transmit the driving force of the engine to the transmission and a disconnected state where the first clutch portion and the second clutch portion are disengaged from each other to block the transmission of the driving force of the engine to the transmission, and a clutch operation mechanism switching the clutch mechanism between the connected state and the disconnected state by supply and discharge of oil to and from the clutch mechanism, the clutch operation mechanism including a clutch drum supported by the input shaft or the output shaft and having a cylindrical shape to form a drum chamber, a piston dividing the drum chamber of the clutch drum into a spring chamber generating a driving force for engaging the first clutch portion and the second clutch portion with each other, and a pressurizing chamber generating a driving force for disengaging the first clutch portion and the second clutch portion from each other, a control valve being switchable between a first position allowing the supply of the oil to the spring chamber and a second position allowing the supply of the oil to the pressurizing chamber, a biasing member arranged in the spring chamber and exerting a biasing force in a direction in which the first clutch portion and the second clutch portion are engaged with each other, and a bore formed in the clutch drum to establish a connection between inner and outer sides of the spring chamber, the bore discharging the oil of the spring chamber from the inner side to the outer side in a state where a counteracting force against a centrifugal force acting in the pressurizing chamber is generated in the spring chamber.

According to another aspect of the disclosure, a drive system for a vehicle includes an input member rotatably connected to a drive source, a shaft member arranged coaxially with the input member along a rotational axis of the input member and connected to a transmission, first clutch portions movably engaged with one of the input member and the shaft member along the rotational axis, second clutch portions arranged in an alternating manner with the first clutch portions and being engageable with and disengageable from the first clutch portions, the second clutch portions being movably engaged with the other one of the input member and the shaft member along the rotational axis, a clutch drum supported by the input member or the shaft member and including a bore positioned away from the rotational axis by a predetermined length in a radial direction, the clutch drum connecting to an outer side via the bore, a piston slidably fitted to the clutch drum along the rotational axis and including a pressing portion pressing the first clutch portions and the second clutch portions, a biasing member arranged between the piston and the clutch drum and biasing the piston toward the first clutch portions and the second clutch portions, the biasing member firmly pressing the first clutch portions and the second clutch portions against one another by the pressing portion, a pressurizing chamber defined between the clutch drum and a first axial end surface of the piston, and a spring chamber defined between the clutch drum and a second axial end surface of the piston, the piston separating from the first clutch portions and the second clutch portions against a biasing force of the biasing member by a hydraulic pressure of oil supplied to the pressurizing chamber, the oil being supplied to the spring chamber and discharged therefrom through the bore of the clutch drum to an outer side of the spring chamber.

DETAILED DESCRIPTION

A first embodiment of this disclosure is applied to a hybrid vehicle, for example, a hybrid passenger vehicle, a large-sized hybrid vehicle, and the like. The first embodiment of the disclosure will be explained with reference to the attached drawings.FIG. 1is a cross sectional view illustrating an upper half portion of a drive system for a vehicle, according to the first embodiment.FIG. 2is a cross sectional view illustrating a portion in the vicinity of a clutch mechanism2of the drive system according to the first embodiment. Each ofFIGS. 3 and 4is an enlarged view illustrating a main portion of a lower half portion of the drive system according to the first embodiment.FIG. 5is a block diagram of the drive system according to the first embodiment. As illustrated inFIG. 5, the drive system includes an engine1serving as a drive source, the clutch mechanism2, and a drive motor8(hereinafter referred to as a motor) formed by an electric motor for driving the vehicle, a transmission6, and a control unit7(hereinafter referred to as an ECU). The ECU7controls the engine1, the motor8, the transmission6, a control valve70, and an oil pump78. The motor8functions as a generator regenerating electric power when the vehicle decelerates or in other cases. According to the first embodiment, various configurations to increase an electric power regeneration efficiency of the motor8are adapted to the drive system. The oil pump78serving as an oil supply source is an electric pump, therefore supplying oil (lubricant) to the clutch mechanism2and the transmission6even in a case where the engine1is not in operation. InFIG. 5, solid arrows indicate hydraulic passages connecting to the oil pump and dashed arrows indicate signal lines connecting to ECU7.

As illustrated inFIG. 1, the engine1includes an output shaft10and a flywheel14. The output shaft10is rotated by a driving force of the engine1around a rotational axis P1of an input member20of the clutch mechanism2that will be described below (the rotational axis P1of the input member20corresponds to a rotational axis of an input shaft60of the transmission6). The flywheel14formed in a ring shape is coaxially connected to the output shaft10by means of an attachment member10w. A ring gear12formed at an outer circumferential portion of the flywheel14engages with a drive shaft of a starter motor. The starter motor is brought in operation, thereby rotating the flywheel14. A torque converter61arranged at the transmission6includes the input shaft60serving as a shaft member rotated by the driving force of the output shaft10of the engine1. The input shaft60is mechanically connected via a transmission gear mechanism of the transmission6to driving wheels of the vehicle, thereby rotating the driving wheels.

The clutch mechanism2will be explained as follows. The clutch mechanism2configuring a wet multiplate clutch includes the input member20, a clutch drum22, friction plates23supported by the input member20and serving as first clutch portions, and separate plates24supported by the clutch drum22and serving as second clutch portions. The friction plates23and the separate plates24are arranged in an alternating manner so as to face one another in the direction of the rotational axis P1. The friction plates23and the separate plates24may be firmly pressed against one another so as to be brought into an engaged state (connected state). In addition, the friction plates23and the separate plates24that are in the engaged state are separated from one another so as to be brought into a disengaged state (disconnected state).

The friction plates23, the separate plates24, the input member20, and the clutch drum22are coaxially arranged with one another around the rotational axis P1. The input member20is connected by a damper13to the flywheel14. The engine1is brought into operation, therefore integrally rotating the output shaft10, the flywheel14, the damper13, the input member20, and the friction plates23with one another around the rotational axis P1.

As illustrated inFIG. 1, the input member20includes a shaft portion201, an extending portion202, and a supporting portion203. The shaft portion201is arranged coaxially with the output shaft10. The extending portion202having a ring shape formed around the rotational axis P1extends radially outwardly from an axial end of the shaft portion201, which axial end is in the vicinity of the transmission6. The supporting portion203supports the friction plates23and has a ring shape formed around the rotational axis P1. The plural friction plates23are fitted to an outer circumferential portion of the supporting portion203so as to be restricted from rotating relative to one another and so as to move relative to one another along the rotational axis P1.

As illustrated inFIG. 1, the clutch drum22includes a fixed cylindrical portion220, a first extending portion221, a radially-inward cylindrical portion222, a second extending portion223, and a radially-outward cylindrical portion224. The fixed cylindrical portion220spline-fitted to an outer circumferential portion of the input shaft60of the transmission60integrally rotates with the input shaft60. The first extending portion221extends radially outwardly from an axial end of the fixed cylindrical portion220, which axial end is in the vicinity of the engine1. The radially-inward cylindrical portion222extends from a radially outward end of the first extending portion221toward the transmission6along the rotational axis P1. The second extending portion223extends radially outwardly from an axial end of the radially-inward cylindrical portion222, which axial end is in the vicinity of the transmission6. The radially-outward cylindrical portion224extends from a radially outward end of the second extending portion223toward the clutch mechanism2along the rotational axis P1. The plural separate plates24are fitted to an end of the radially-outward cylindrical portion224so as to be restricted from rotating relative to one another and so as to move relative to one another along the rotational axis P1. A drum chamber230is formed by the radially-inward cylindrical portion222, the second extending portion223, and the radially-outward cylindrical portion224. Here, the fixed cylindrical portion220, the radially-inward cylindrical portion222, the radially-outward cylindrical portion224, and the drum chamber230that form the clutch drum22are formed so as to surround the rotational axis P1. A piston32of a clutch operation mechanism3that will be described below is slidably or movably arranged in the drum chamber230so as to make contact with a piston stopper229of the clutch drum22. The piston32divides the drum chamber230into a pressurizing chamber34and a spring chamber38. Bores250connecting inner and outer sides of the spring chamber38to each other are formed in the second extending portion223so as to be arranged in the vicinity of the transmission6relative to the clutch mechanism2. Each of the bores250functions to reduce a flow rate of the oil. As illustrated inFIG. 2, a length between the rotational axis P1and an axial center of the bore250in a radial direction of the clutch drum22is defined as a length L (predetermined length).

The clutch mechanism2is switchable between the connected state where the driving force of the engine1is being transmitted to the input shaft60of the transmission6and the disconnected state where the transmission of the driving force of the engine1to the input shaft60is blocked. Under a condition where the clutch mechanism2is in the connected state, the friction plates23adjoining the separate plates24are firmly pressed against one another so as to be engaged with one another, thereby transmitting the driving force of the engine1to the input shaft60of the transmission6. Meanwhile, under a condition where the clutch mechanism2is in the disconnected state, the friction plates23and the separate plates24are released from the engaged state, thereby blocking the transmission of the driving force of the engine1to the transmission6. The clutch mechanism2is a normally closed clutch. Under a condition where the clutch mechanism2is in a normal state where the driving force of the engine1is being transmitted to the transmission6, the piston32moves by biasing forces of biasing members33of the clutch operation mechanism3toward the engine1along the rotational axis P1. Accordingly, the friction plates23and the separate plates24are firmly pressed against one another so as to be maintained in the engaged state. Consequently, in the case that the clutch mechanism2is in the normal state, a hydraulic pressure of the oil for firmly pressing the friction plates23and the separate plates24against one another is not needed, therefore effectively saving energy. Additionally, for example, even in a case where any defect occurs in a hydraulic system, the friction plates23and the separate plates24that form the clutch mechanism2are firmly pressed against one another so as to be in the connected state. As a result, the driving force of the engine1may be transmitted to the transmission6, thereby bringing the vehicle into motion.

The clutch operation mechanism3for operating the clutch mechanism2will be described as follows. As illustrated inFIG. 3, the clutch operation mechanism3includes a fixed plate31, the piston32, the biasing members33, the pressurizing chamber34, and an oil passage35that connects to the pressurizing chamber34. The fixed plate31is fixed to a fixing groove of an outer circumferential side of the radially-inward cylindrical portion222of the clutch drum22by a fixing member31xhaving a C-ring shape. The fixed plate31has a surface310facing an opposite direction to the clutch mechanism2. The piston32is movably or slidably fitted in the drum chamber230along the rotational axis P1. The piston32has a pressure surface325facing the clutch mechanism2and corresponding to a first axial end surface. The biasing members33formed by biasing members including coils are arranged between the piston32and the second extending portion223of the clutch drum22. The pressurizing chamber34is formed between the surface310of the fixing plate31and the pressure surface325of the piston32. In particular, the pressurizing chamber34is defined between the clutch drum22and the pressure surface325(first axial end surface) of the piston32. The pressurizing chamber34, the piston32, and the drum chamber230are formed to have ring shapes around the rotational axis P1. The plural biasing members33are circumferentially arranged at substantially equal intervals around the rotational axis P1in the drum chamber230. The fixed plate31constitutes a portion of the clutch drum22.

As illustrated inFIG. 4, the piston32includes a radially-inward cylindrical movable portion321, a radially-outward cylindrical movable portion322, and a pressure portion323that connects the radially-inward cylindrical movable portion321to the radially-outward cylindrical movable portion322along a radial direction of the piston32. The radially-inward cylindrical movable portion321and the radially-outward cylindrical movable portion322are formed coaxially with each other. For example, the piston32moves in a direction indicated by an arrow F1seen inFIG. 3(the direction of the arrow F1will be hereinafter referred to as the direction F1and the direction F1corresponds to an engagement direction to bring the clutch mechanism2into the connected state). As a result, a pressing portion32kof the radially-outward cylindrical movable portion322of the piston32moves the separate plates24toward the friction plates23, thereby firmly pressing the separate plates24against the friction plates23(see inFIG. 3). On the other hand, for example, the piston32moves in a direction indicated by an arrow F2seen inFIG. 3(the direction of the arrow F2will be hereinafter referred to as the direction F2and the direction F2corresponds to a disengagement direction to release the clutch mechanism2from the engaged state). As a result, the radially-outward cylindrical movable portion322of the piston32separates from the separate plates24, thereby releasing the frictional plates23and the separate plates24from the engaged state.

As illustrated inFIG. 3, first ends of the biasing members33are seated at the second extending portion223of the clutch drum22and second ends of the biasing members33are seated at a biasing member supporting a recessed portion36formed at an axial end surface (second axial end surface) of the piston32, which axial end surface faces the transmission6along the rotational axis P1. Thus, the biasing members33are inhibited from loosening from the clutch drum22. As seen fromFIG. 3, the biasing members33bias the piston32toward the fixing plate31in the direction F1. Accordingly, when the hydraulic pressure is not applied to the pressurizing chamber34, the piston32moves toward the clutch mechanism2in the direction F1(in the engagement direction to bring the clutch mechanism2into the connected state). Consequently, the frictional plates23and the separate plates24are firmly pressed against one another, therefore bringing the clutch mechanism2into the connected state. According to the drive system of the first embodiment, in the case of the electric power regeneration by the motor8, the clutch mechanism2is shifted from the connected state to the disconnected state to therefore block the transmission of the driving force of the engine1to the transmission6. As a result, the electric power regeneration efficiency of the motor8may be increased.

As illustrated inFIG. 3, the oil passage35and an oil passage39are formed in the clutch operation mechanism3. The clutch operation mechanism3is further provided with the control valve70. The oil is supplied/discharged from/to the pressurizing chamber34through the oil passage35connecting to the pressurizing chamber34. The oil is supplied/discharged to/from the spring chamber33through the oil passage39connecting to the spring chamber38. The oil passage35is formed within a fixing cylindrical portion94of a second case92constituting a portion of a case9that will be described below. The oil passage35includes an annular groove352and a through hole353. The annular groove352is formed at a first end of the oil passage35so as to have an opening relative to an outer circumferential surface of the fixing cylindrical portion94. The through hole353penetrates through the radially-inward cylindrical portion222in a thickness direction of the clutch drum22and has an opening relative to the annular groove352. The oil passage39is formed within the fixing cylindrical portion94of the second case92of the case9. The oil passage39includes an annular groove392and a through hole393. The annular groove392is formed at a first end of the oil passage39so as to have an opening relative to the outer circumferential surface of the fixing cylindrical portion94. The through hole393penetrates through the radially-inward cylindrical portion222in the thickness direction of the clutch drum22and has an opening relative to the annular groove392. As illustrated inFIG. 3, respective second ends of the oil passage35and the oil passage39are connected via the control valve70to the oil pump78. The control valve70is switchable between first and second positions71and72by a solenoid70aand a biasing member70c.

The first position71is a position to bring the clutch mechanism2into the connected state. The first position71includes a passage73aconnecting a discharge port78aof the oil pump78to the oil passage39, and a passage73bconnecting the oil passage35to an oil storing portion79. The second position72is a position to bring the clutch mechanism2into the disconnected state. The second position72includes a passage73cconnecting the discharge port78aof the oil pump78to the oil passage35, and closing ports73hand73i. In a case where the control valve70is shifted to the first position71by the ECU7when the oil pump78is in operation, the oil is supplied from the discharge port78athrough the passage73a, the oil passage39, the annular groove392, and the through hole393to the spring chamber38, thereby increasing the hydraulic pressure in the spring chamber38. Consequently, the piston82is moved by the hydraulic pressure of the spring chamber38in the direction F1(seeFIG. 3), therefore bringing the clutch mechanism2into the connected state. In such case, the oil in the pressurizing chamber34is discharged therefrom through the passage73bto the oil storing portion79.

Meanwhile, in a case where the control valve70is shifted to the second position72by the ECU7, the pressurizing chamber34establishes a connection via the oil passage35and the passage73cto the discharge port78aof the oil pump78. Accordingly, the oil of the oil pump78is supplied through the discharge port78a, the passage73c, the oil passage35, the annular groove352, and the through hole353to the pressurizing chamber34, thereby increasing the hydraulic pressure in the pressurizing chamber34. Consequently, the piston32is moved by the hydraulic pressure of the pressurizing chamber34in the direction F2(seeFIG. 3), therefore bringing the clutch mechanism2into the disconnected state. In such case, the oil passage39connecting to the spring chamber38is closed by the closing port73h. Therefore, the oil in the spring chamber38does not flow to the control valve70. Then, the oil of the spring chamber38is discharged therefrom through each of the bores250in a direction indicated by an arrow X seen inFIG. 3(the direction will be hereinafter referred to as the direction X), thereafter being stored in the oil storing portion79(seeFIG. 2). As illustrated inFIG. 2, an opening diameter of the bore250and the length L (seeFIG. 2) affect a discharge rate of the oil being discharged from the spring chamber38. The opening diameter of the bore250and the length L further affect a centrifugal hydraulic pressure in the spring chamber38, operational responsiveness of the clutch mechanism2when the clutch mechanism2shifts from the connected state to the disconnected state, and the electric power regeneration efficiency of the motor8. In addition, the oil pump78is the electric pump as described above, therefore supplying the oil to the pressurizing chamber34regardless of whether the engine1is in operation. Moreover, according to the drive system of the first embodiment, the control valve70may be accommodated in the case9. Alternatively, the control valve70may be arranged at an outer side of the case9.

As described above, the clutch mechanism2is the normally closed clutch. In the case that the clutch mechanism2is in the normal state, the friction plates23adjoining the separate plates24are firmly pressed against one another by the biasing forces of the biasing members33and are engaged with one another, therefore bringing the clutch mechanism2into the connected state. Accordingly, the output shaft10of the engine1is connected to the input shaft60of the transmission6by the clutch mechanism2. In such case, for example, the engine1is in operation to therefore rotate the output shaft10. Accordingly, the input member20, and the friction plates23and the separate plates24that are in the engaged state rotate about the rotational axis P1. In addition, the clutch drum22rotates together with a rotor82of the motor8and a rotating force of the rotor82is transmitted to the input shaft60to thereby rotate the input shaft60of the transmission6, therefore rotating the driving wheels of the vehicle.

On the other hand, in the case of blocking of the transmission of the driving force of the engine1to the transmission6, the oil is supplied to the pressurizing chamber34by the operation of the oil pump78. Then, the hydraulic pressure of the pressurizing chamber34for blocking the transmission of the driving force of the engine1to the transmission6(the hydraulic pressure of the pressurizing chamber34corresponds to a driving force for bringing the friction plates23and the separate plates24into the disengaged state) becomes larger than the sum of the biasing forces of the biasing members33and the hydraulic pressure of the spring chamber38; therefore, the piston32moves in the direction F2. In such case, the separate plates24are movable in the direction F2. Accordingly, the friction plates23and the separate plates24configuring the clutch mechanism2and adjoining one another separate from one another, therefore being brought into the disengaged state (disconnected state). As a result, the clutch mechanism2is shifted from the connected state to the disconnected state. Thus, the connection between the engine1and the transmission6is blocked; therefore, the driving force of the output shaft10of the engine1is not transmitted to the input shaft60of the transmission6. Here, as illustrated inFIG. 4, a centrifugal hydraulic pressure FA1in the pressurizing chamber34and a centrifugal hydraulic pressure FA2(corresponding to a counteracting force against a centrifugal force acting in the pressurizing chamber34) in the spring chamber38act in opposite directions from each other and offset each other or decrease. In such case, the oil is supplied to the pressurizing chamber34by the control valve70, thereby smoothly moving the piston32in the direction F2. Consequently, the clutch mechanism2is promptly shifted from the connected state to the disconnected state in reaction to the hydraulic pressure from the pressurizing chamber34. At this time, the engine1may be quickly disconnected from the motor8, therefore increasing the electric power regeneration efficiency of the motor8.

As illustrated inFIGS. 1 and 2, in the case that the clutch mechanism2is maintained in the connected state, a distance of an inner space of the pressurizing chamber34along the rotational axis P1is designed to be short and a radial distance of the inner space of the pressurizing chamber34is designed to be long, that is, the pressurizing chamber34is thinned so as to have a flattened shape. Accordingly, a capacity of the pressurizing chamber34may be minimized and a large area of the pressure surface325of the piston32may be obtained. Therefore, an operating force of the piston32for blocking the transmission of the driving force of the engine1to the transmission6is increased. Consequently, the oil is supplied to the pressurizing chamber34; thereby, the operational responsiveness of the clutch mechanism2when the clutch mechanism2shifts from the connected state to the disconnected state may be increased. As a result, in the case where the motor8is utilized as the generator so as to regenerate the electric power, the clutch mechanism2may be quickly shifted from the connected state to the disconnected state and the motor8driving the vehicle may promptly shifts to the generator generating the electric power. Therefore, a volume of the electric power being stored in an electric storage device may be increased, resulting in improvement of fuel efficiency of the vehicle.

According to the drive system of the first embodiment, each of the biasing members33biasing the piston32may be formed by a plate or disk shaped biasing member. However, the plate or disk shaped biasing member is easily deformed; therefore, a load of the plate or disk shaped biasing member tends to vary in a substantially quadratic curve form. In such case, a torque capacity of the clutch mechanism2may not be secured, for example, in an occurrence of aging deteriorations or abrasions of the friction plates23and the separate plates24configuring the clutch mechanism2. Further, in a case where the load of the plate or disk shaped biasing member drastically varies, torque being transmitted from the output shaft10to the clutch mechanism2may not be easily controlled by supplying the oil to the pressurizing chamber84to therein control the hydraulic pressure. On the other hand, the biasing member33formed by the biasing member including the coil is deformed; thereafter, a load of the biasing member33linearly varies compared to the plate or disk shaped biasing member. In such case, the torque being transmitted from the output shaft10to the clutch mechanism2may be precisely controlled by controlling the hydraulic pressure of the pressurizing chamber34. In addition, the biasing member33including the coil may be easily arranged in a small space and the plural biasing members33may be arranged in the drum chamber230of the clutch mechanism2. Accordingly, the sum of the loads of the biasing members33increases; therefore, the clutch mechanism2may be maintained in the connected state by the large loads of the biasing members33. As described above, although the biasing members33are formed by the biasing members including the coils in the drive system according to the first embodiment, the biasing members33may be formed by the plate or disk shaped biasing members according to needs.

As illustrated inFIG. 1, the motor8is arranged in a drive-train connecting the clutch mechanism2to the transmission6. The motor8includes a stator80and the rotor82. The stator80fixed to an inner circumferential portion of the second case92includes an excitation wiring80cwound around an iron core. The rotor82is coaxially arranged with the stator80in a state where a clearance80xis generated between the stator80and the rotor82at a radially inward side of the stator80. The rotor82is fixed to an outer circumferential portion of the radially-outward cylindrical portion224of the clutch drum22by means of attachment members89aand a bracket89c, thereby integrally rotating with the clutch drum22around the rotational axis P1. An excitation current is applied to the excitation wiring80c; therefore, a rotating magnetic field is generated around the rotational axis P1. As a result, the rotor82, the clutch drum22, and the input shaft60of the transmission6rotate, therefore rotating the driving wheels via the transmission6.

As illustrated inFIG. 1, the case9accommodates the clutch mechanism2, the clutch operation mechanism3, the motor8, the torque converter61, and the like. The case9includes a first case91, the second case92connected to the first case91, a third case93connected to the second case92in the mentioned order as seen from the engine1to the transmission6along the rotational axis P1. The first case91includes a first wall910extending radially inwardly. The second case92includes a second wall920extending radially inwardly and the fixing cylindrical portion94formed at a radially inward portion of the second wall920so as to extend along the rotational axis P1. As illustrated inFIG. 1, the clutch drum22is arranged in the case9so as to be fixed therein by the fixing cylindrical portion94. A bearing96asupporting the clutch drum22so that the clutch drum22is rotatable is arranged between the fixing cylindrical portion94and the clutch drum22, thereby smoothly rotating the clutch drum22. The bearing96ais provided at a position corresponding a position in which the piston32is arranged in the direction of the rotational axis P1(seeFIGS. 1 and 2); thereby, an axial length of the case9may be reduced. Additionally, the oil passages35and39that shift the clutch mechanism2between the connected and disconnected states are formed in the fixing cylindrical portion94, thereby reducing the size and cost of the drive system.

As illustrated inFIG. 1, the stator80of the motor8is fixed to an inner circumferential portion of an outer-circumferential-wall cylindrical portion92xof the second case92. The first wall910and the second wall920face each other along the rotational axis P1. The bearing96ais arranged between the fixing cylindrical portion94of the second wall920and the input shaft60of the transmission6; thereby, the clutch drum22may integrally rotate with the input shaft60relative to the fixing cylindrical portion94around the rotational axis P1. A bearing96cis arranged between the input member20and a radially inward portion of the first wall910of the first case91; thereby, the input member20integrally rotates with the clutch drum22relative to the first ease91around the rotational axis P1. A bearing96eis arranged between the output shaft10and the shaft portion201. The clutch mechanism2and the clutch operation mechanism3are coaxially arranged with each other at an inner circumferential side of the motor8in the case9described above. Thus, an axial length of the motor8is effectively utilized and the clutch mechanism2and the clutch operation mechanism3may be arranged at the inner circumferential side of the motor8. As a result, the size of the drive system in the direction of the rotational axis P1may be reduced.

Operation of the drive system according to the first embodiment will be explained as follows. A driver of the vehicle turns on an ignition switch and presses an accelerator pedal (when the driver presses the accelerator pedal, an opening angle of a throttle valve is small). Then, the oil pump78serving as the electric pump powered by a battery is brought into operation and the hydraulic pressure is supplied to the pressurizing chamber34. Thereafter, the clutch mechanism2is brought in the disconnected state and the excitation current is applied to the excitation wiring80cof the motor8to therefore rotate the rotor82. Further, the clutch drum22connected to the rotor82rotates in accordance with the rotation of the rotor82and the driving wheels are rotated by the transmission6, therefore bringing the vehicle into motion. When the vehicle is brought into motion as described above, the engine1may not start and therefore remains in a non-operational state. In such case, the vehicle is brought into motion only by a driving force of the motor8. At this time, the ECU7commands the oil pump78to start moving to generate the hydraulic pressure. In addition, the control valve70is shifted to the second position72. Accordingly, the oil is discharged from the oil pump78through the discharge port78ato the passage73cof the second position72, therefore being supplied through the oil passage35to the pressurizing chamber34. Consequently, the hydraulic pressure of the pressurizing chamber34increases, therefore moving the piston32in the direction F2. As a result, the clutch mechanism2corresponding to the normally closed clutch is shifted from the connected state to the disconnected state. Thus, in the case that the vehicle is brought into motion only by the motor8, the engine1, the flywheel14, and the like are disconnected from the transmission6, thereby improving startablity of the vehicle.

For example, in a state where the engine1is operating under a low or extremely low load, that is, in a state where the engine1is in a region where efficiency of the engine1is insufficient, it is appropriate that the operation of the engine1is stopped. In other words, in the case that the vehicle is under the low or extremely low load, it is recommended that the vehicle is driven into motion only by the motor8. As described above, in the case that the operation of the engine1is stopped, the clutch mechanism2corresponding to the normally closed clutch is shifted from the connected state to the disconnected state. In such case, the oil is supplied from the passage73cof the control valve70through the oil passage35to the pressurizing chamber34in accordance with the operation of the oil pump78. Thereafter, the hydraulic pressure of the pressurizing chamber34becomes larger than the biasing forces of the biasing members33, therefore moving the piston32in the direction F2(seeFIG. 3). Consequently, the friction plates23and the separate plates24adjoining one another to configure the clutch mechanism2separate from one another, therefore being brought into the disengaged state.

On the other hand, in a case where the vehicle accelerates or is driven on a climbing road surface, it is appropriate for the engine1to be brought into operation. For example, the driver presses the accelerator pedal in order for the vehicle to accelerate or to move on the climbing road surface and the opening angle of the throttle valve becomes larger than a predetermined opening angle. Then, a fuel injection device is brought into operation and a spark plug is ignited. In addition, the driven shaft of the starter motor is driven; thereby, the ring gear12of the flywheel14engaging with the driven shaft of the starter motor is rotated along with the flywheel14and the output shaft10. Consequently, the engine1is brought into operation. When the engine1is driven as described above, the clutch mechanism2is maintained in the connected state. In such case, the control valve70is shifted to the first position71. Accordingly, the oil of the oil pump78is supplied through the passage73aof the control valve7and the oil passage39to the spring chamber38, therefore increasing the hydraulic pressure of the spring chamber38. In addition, the oil of the pressurizing chamber34is discharged from the oil passage35through the passage73bof the control valve70to the oil storing portion79. Accordingly, the biasing forces of the biasing members33formed by the biasing members including the coils become larger than the hydraulic pressure of the pressurizing chamber34, and the piston32and the separate plates24move in the direction F1(seeFIG. 3). Consequently, the separate plates24are firmly pressed against the friction plates23so as to be engaged therewith. As a result, the driving force of the output shaft10of the engine1is transmitted by the clutch mechanism2to the input shaft60of the transmission6. Thus, the driving force of the engine1and the driving force of the motor8are increased, thereby bringing the vehicle into motion by means of the large driving forces. For example, in a case where the vehicle is in a normal moving state, the efficiency of the engine1is high. Therefore, it is recommended that power feeding to the motor8is stopped in order to idle the motor8. In the case that the power feeding to the motor8is stopped, the clutch mechanism2is maintained in the connected state and the driving force of the output shaft10of the engine1is transmitted by the clutch mechanism2to the input shaft60of the transmission6, therefore bringing the vehicle1into motion by the driving force of the engine1.

In the case of the electric power regeneration by the motor8, for example, when the vehicle decelerates or in other cases, power feeding to the excitation wiring80cof the motor8is stopped. In addition, a load applied to the rotor82is reduced in order that the clutch mechanism2is shifted from the connected state to the disconnected state for the purpose of disconnecting the output shaft10of the engine1from the input member20of the clutch mechanism2. Therefore, the electric power regeneration efficiency of the motor8may be increased. In such case, the oil is supplied by the oil pump78to the pressurizing chamber34; thereafter, the hydraulic pressure of the pressurizing chamber84becomes larger than the biasing forces of the biasing members33. Accordingly, the piston32moves in the direction F2(seeFIG. 3), therefore separating the separate plates24from the friction plates23to bring the friction plates23and the separate plates24in the disconnected state. As described above, in the case of the electric power regeneration by the motor8, the motor8functions as the generator and generates the electric power. The electric power generated by the motor8is stored in the battery.

According to the drive system of the first embodiment, in a state where the vehicle is in motion, the clutch drum22rotates along with the rotor82around the rotational axis P1and receives a centrifugal force. Accordingly, when the clutch mechanism2is in the connected and disconnected states, the oil may remain in the pressurizing chamber34and the spring chamber38. For example, in a case where the oil remains in either one of the pressurizing chamber34and the spring chamber38, a centrifugal hydraulic pressure generated by a centrifugal force caused by the rotation of the input shaft60may affect the operational responsiveness and operational controllability of the clutch mechanism2. In particular, in a condition where the input shaft60rotates at high speed, the centrifugal force increases. Accordingly, in a case where the vehicle is driven at high speed, the centrifugal force may further affect the operational responsiveness and operational controllability of the clutch mechanism2.

According to the drive system of the first embodiment, in a state where the input shaft60is in rotation, the oil of the spring chamber38remains therein while being discharged through the bores250to the outer side of the spring chamber38. Accordingly, the centrifugal hydraulic pressure FA1generated by the centrifugal force caused by the oil remaining in the pressurizing chamber34may counteract the centrifugal hydraulic pressure FA2generated by the centrifugal force caused by the oil remaining in the spring chamber38(seeFIG. 4). In other words, the centrifugal hydraulic pressure FA1and the centrifugal hydraulic pressure FA2act in opposite directions from each other. Consequently, for example, in a case where the centrifugal hydraulic pressure FA1is equal to the centrifugal hydraulic pressure FA2, the centrifugal hydraulic pressure FA1and the centrifugal hydraulic pressure FA2offset each other. In addition, even in a case where the centrifugal hydraulic pressure FA1is not equal to the centrifugal hydraulic pressure FA2, the centrifugal hydraulic pressure FA1and the centrifugal hydraulic pressure FA2act in the opposite directions from each other. Accordingly, influences of the centrifugal hydraulic pressure FA1and the centrifugal hydraulic pressure FA2on the operational controllability of the clutch mechanism2may be further reduced. Consequently, even in the case where the centrifugal hydraulic pressure FA1and the centrifugal hydraulic pressure FA2are generated, mechanical influences of the biasing forces of the biasing members33arranged in the spring chamber38are greater than the influences of the centrifugal hydraulic pressure FA1and the centrifugal hydraulic pressure FA2. Therefore, the influences of the centrifugal hydraulic pressure FA1and the centrifugal hydraulic pressure FA2may be minimized. As a result, a delay in the operational responsiveness of the clutch mechanism2due to the centrifugal hydraulic pressures FA1and FA2may be decreased, thereby improving the operational controllability of the clutch mechanism2. Moreover, the both centrifugal hydraulic pressures FA1and FA2increase as a rotating speed of the input shaft60increases. On the other hand, the both centrifugal hydraulic pressures FA1and FA2decrease as the rotating speed of the input shaft GO decreases. Thus, even when the rotating speed of the input shaft60varies, the influences of the centrifugal hydraulic pressures FA1and FA2on the operational controllability of the clutch mechanism2may be appropriately cancelled, therefore increasing the operational controllability of the clutch mechanism2. In addition, the drive system according to the first embodiment is adapted to the hybrid vehicle. Accordingly, the operational responsiveness of the clutch mechanism2when the clutch mechanism2shifts from the connected state to the disconnected state is improved in the case of the electric power regeneration by the motor8. Consequently, the clutch mechanism2is promptly shifted from the connected state to the disconnected state and the engine1is therefore disconnected from the motor8, thereby increasing the electric power regeneration efficiency of the motor8.

According to the drive system of the first embodiment, as illustrated inFIG. 2, minimum and maximum diameters of the spring chamber38formed between the clutch drum22and the axial surface (second axial end surface) of the piston32are defined as minimum and maximum diameters D1and D2. Each of the bores250is arranged between the minimum and maximum diameters D1and D2in the radial direction of the clutch drum22. Accordingly, the oil of the spring chamber38may remain in a radially outward portion of the spring chamber38by the centrifugal force while being discharged through the bores250to the outer side of the spring chamber38. Consequently, the centrifugal hydraulic pressure FA2may be obtained in the spring chamber38. As a result, the centrifugal hydraulic pressure FA1generated by the centrifugal force caused by the oil remaining in the pressurizing chamber34may be offset or reduced by the centrifugal hydraulic pressure FA2generated by the centrifugal force caused by the oil remaining in the spring chamber38. In other words, the centrifugal hydraulic pressure FA1may be cancelled by the centrifugal hydraulic pressure FA2. Ability of the bore250to discharge the oil (the ability will be hereinafter referred to as the oil discharge ability) is basically determined by the opening diameter of the bore250and the length L between the rotational axis P1and the axial center of the bore250in the radial direction of the clutch drum22. Accordingly, the opening diameter of the bore250and the length L are adjusted; thereby, the oil discharge ability of the bore250may be adjusted. Further, the centrifugal hydraulic pressure FA2in the spring chamber38may be adjusted. In addition, the operational responsiveness of the clutch mechanism2when the clutch mechanism2shifts between the connected and disconnected states may be adjusted.

Further, according to the drive system of the first embodiment, as illustrated inFIG. 2, the clutch drum22includes the fixed cylindrical portion220fixed to the outer circumferential portion of the input shaft60, the first extending portion221extending radially outwardly from the fixed cylindrical portion220, the radially-inward cylindrical portion222extending from the first extending portion221toward the transmission6along the rotational axis P1, the second extending portion223extending radially outwardly from the radially-inward cylindrical portion222, and the radially-outward cylindrical portion224extending from the second extending portion223toward the clutch mechanism2along the rotational axis P1. The clutch drum22forms the spring chamber38in which the biasing members33and the piston82are accommodated. Further, the clutch drum22includes the drum chamber230in which the biasing members33, the piston32, the fixed plate31, and the separate plates24are accommodated in the mentioned order and are fixed by means of a fixing member238formed by a snap ring. Thus, the size (axial length) of the clutch drum22particularly in the direction of the rotational axis P1may be reduced.

Furthermore, according to the drive system of the first embodiment, the biasing members33face the bores250in the spring chamber38. The oil in the vicinity of the biasing members33is discharged through the bores250from the spring chamber38. Accordingly, an influence of the oil remaining in the spring chamber38on operations of the biasing members33may be minimized. Consequently, the centrifugal hydraulic pressure FA2generated by the centrifugal force caused by the oil remaining in the spring chamber38may be inhibited from affecting the operational controllability of the clutch mechanism2. In addition, as described above, in the case that the oil remains in the pressurizing chamber34, the centrifugal hydraulic pressure FA1is generated by the centrifugal force caused by the oil remaining in the pressurizing chamber34, thereby pressing the piston32in the direction F2(see inFIG. 4). In such case, the clutch mechanism2maintained in the connected state may be released therefrom depending on circumstances. Therefore, a check valve may be arranged at the fixed plate31configuring a wall consisting a portion of the pressurizing chamber34; thereby, the oil remaining in the pressurizing chamber34may be discharged therefrom through the check valve. The check valve includes an orifice having an opening to an outer side of the pressurizing chamber34, and a valve member closing the orifice. The valve member of the check valve opens the orifice when the centrifugal force FA1of the pressurizing chamber34increases. However, capability of the valve member to close the orifice is not stable; therefore, the operational controllability of the clutch mechanism2may not be surely obtained. In addition, in the case where the oil is supplied to the pressurizing chamber34to thereby bring the clutch mechanism2into the disconnected state, the orifice of the check valve opens and the oil supplied in the pressurizing chamber34may therefore leak from the orifice to the outer side of the pressurizing chamber34. Therefore, a leakage volume of the oil from the pressurizing chamber34needs to be considered so that a volume of the oil to be supplied to the pressurizing chamber34may be increased. In such case, the size of the oil pump78may be inhibited from being increased.

Therefore, according to the drive system of the first embodiment, the check valve is not arranged at the fixed plate31. Accordingly, the oil may not be discharged through the orifice of the check valve and therefore remains in the pressurizing chamber34. As a result, the centrifugal hydraulic pressure FA1may be generated in accordance with the rotation of the input shaft60. However, according to the drive system of the first embodiment, in a state where the input shaft60is in rotation, the oil of the spring chamber38is allowed to remain therein while being discharged through the bores250to the outer side of the spring chamber38as described above. Accordingly, the centrifugal hydraulic pressure FA2generated by the centrifugal force caused by the oil remaining in the spring chamber38may be generated so as to counteract the centrifugal hydraulic pressure FA1generated by the centrifugal force caused by to the oil remaining in the pressurizing chamber34. Consequently, the centrifugal hydraulic pressure FA1in the pressurizing chamber34and the centrifugal hydraulic pressure FA2in the spring chamber38may offset each other or reduce. As a result, the check valve may be inhibited from being arranged at the fixed plate31in the drive system according to the first embodiment and the influence of the centrifugal hydraulic pressure FA1caused by the oil remaining in the pressurizing chamber34on the operational controllability of the clutch mechanism2may be reduced or cancelled. In addition, the check valve is not arranged at the fixed plate31in the drive system according to the first embodiment, therefore reducing the cost of the drive system. Moreover, since the check valve is not arranged at the fixed plate31in the drive system according to the first embodiment, the oil filled in the pressurizing chamber34in order to bring the clutch mechanism2into the disconnected state may not leak from the orifice of the check valve. Accordingly, the volume of the oil being supplied to the pressurizing chamber34may be appropriately adjusted. As a result, the size of the oil pump78may be inhibited from being increased, thereby increasing installability of the drive system relative to the vehicle.

In addition, according to the drive system of the first embodiment, as illustrated inFIG. 4, an outer circumferential portion38pof the spring chamber38is positioned further outward than an outer circumferential portion34pof the pressurizing chamber34in the radial direction of the clutch drum22. Accordingly, a centrifugal hydraulic pressure caused by the oil in the vicinity of the outer circumferential portion38pof the spring chamber38is larger than a centrifugal hydraulic pressure caused by the oil in the vicinity of the outer circumferential portion34pof the pressurizing chamber34. In such case, a driving force for moving the clutch mechanism2in the engagement direction may be effectively increased, thereby promptly bringing the clutch mechanism2into the connected state.

Moreover, according to the drive system of the first embodiment, as illustrated inFIG. 2, the rotor82is fixed to the outer circumferential portion of the radially-outward cylindrical portion224of the clutch drum22by means of the bracket89cand the attachment members89a. The attachment members89aare attached to attachment bores89kformed in the clutch drum22. The attachment bores89kface the spring chamber38in which the centrifugal hydraulic pressure FA2is generated. Boundary portions between the attachment bores89kand the attachment members89aare sealed by a seal adhesive in order to obtain the centrifugal hydraulic pressure FA2; thereby, the oil in the spring chamber38is inhibited from leaking therefrom.

Additionally, according to the drive system of the first embodiment, as illustrated inFIG. 2, the oil storing portion79for storing the oil is formed at bottom portions (at a lower side seen inFIG. 2) of the first case91and the second case92. The oil storing portion79serves as a reservoir for storing the oil of the oil pump78. A level of the oil in a vertical direction inFIG. 2is shown as an oil level79x. A lower portion of the stator80, a lower portion of the excitation wiring80c, and a lower portion of the rotor82are immersed in the oil so as to be located under the oil level79xin the vertical direction seen inFIG. 2. Accordingly, the stator80, the excitation wiring80c, and the rotor82may be cooled by the oil, thereby increasing operational and power generation efficiencies of the motor8. As illustrated inFIG. 2, the oil level79xis positioned slightly closer to an inner side in the radial direction of the clutch drum22than an outer circumferential side of the rotor82, thereby inhibiting the rotor82from being excessively immersed in the oil. Accordingly, in a case where the rotor82is brought in rotation, rotational resistance of the rotor82is inhibited from excessively increasing, resulting in the improvement of the fuel efficiency of the vehicle. For example, the motor8is brought in operation, therefore rotating the rotor82to thereby splash a portion of the oil stored in the oil storing portion79over the friction plates23and the separate plates24of the clutch mechanism2that are in the connected and disconnected states. In addition, the rotor82allows a portion of the oil of the oil storing portion79to splash over the bearings96a,96c, and96e, and the like. Thus, the friction plates23, the separate plates24, and the bearings96a,96c, and96e, and the like may be cooled and lubricated by the oil. As a result, the operational and power generation efficiencies of the motor8are increased and durability of the drive system according to the first embodiment may be further increased.

A second embodiment of the disclosure will be illustrated inFIG. 8. The drive system according to the second embodiment has substantially the same configuration and operational effects as those of the drive system according to the first embodiment. As shown inFIG. 6, the drive system according to the second embodiment differs from the drive system according to the first embodiment in that a relief valve400including a passage410is arranged between the discharge port78aand a suction port780of the oil pump78. The relief valve400is switchable between a first position403including a passage401and a closing port402and a second position405including a passage404. The hydraulic pressure of the passage410connecting to the passages73aand73ccounteracts a biasing force of a biasing member420of the relief valve400. In a normal state, the biasing force of the biasing member420is larger than the hydraulic pressure of the passage410, therefore setting the relief valve400in the first position403. Meanwhile, in a case where the hydraulic pressure of the passage410connecting to the passages73aand73cexcessively increases and therefore is larger than the biasing force of the biasing member420, the relief valve400is shifted from the first position403to the second position405. As a result, the oil in the passage410is discharged from the passage404of the second position405to the oil storing portion79, thereby further increasing durability of the oil pump78.

The drive system according to the first embodiment may be modified as follows. The drive system according to the first embodiment is arranged in the hybrid vehicle provided with the both engine1and the motor8. Alternatively, the drive system according to the first embodiment may be arranged in a vehicle provided with the engine1but not provided with the motor8. The configuration of the clutch operation mechanism3may be configured in a different manner from the configuration described in the first embodiment as long as the clutch operation mechanism3is configured to shift the clutch mechanism2between the connected and disconnected states. Further, according to the first embodiment, the first and second clutch portions (friction plates and separate plates)23and24of the clutch mechanism2have plate shapes. Alternatively, the first and second clutch portions may be formed in different shapes as long as the clutch mechanism2is configured so as to transfer the driving force of the engine1to the transmission6and so as to block the transmission of the driving force of the engine1to the transmission6. As described above, according to the first embodiment, the friction plates23and the separate plates24that correspond to the first and second clutch portions, respectively, are adapted to the clutch mechanism2. Alternatively, other members may be adapted to the clutch mechanism2instead of the first and second clutch portions (friction and separate plates)23and24. Moreover, according to the first embodiment, the oil pump78serves as the electric pump. Alternatively, the oil pump78may be a pump mechanically driven by the engine1and the like. In addition, according to the first embodiment, in a case where the vehicle is started, the clutch mechanism2is shifted from the connected state to the disconnected state and the vehicle is brought into motion by the motor8. Alternatively, the vehicle may be driven by the driving force of the engine1in addition to the driving force of the motor8. The drive system of the disclosure is not limited to the first and second embodiments illustrated in the attached drawings and may be modified as required without departing from the scope of the disclosure.

As described above, according to each of the first and second embodiments, the drive system includes the engine1having the output shaft10, the transmission6including the input shaft60to which the driving force of the output shaft10of the engine1is transmitted, the transmission6transmitting the driving force to the driving wheels of the vehicle, the clutch mechanism2including the friction plates23arranged between the output shaft10of the engine1and the input shaft60of the transmission6and positioned at the output shaft10, and the separate plates24arranged at the input shaft60, the clutch mechanism2being switchable between the connected state where the friction plates23and the separate plates24are engaged with one another to transmit the driving force of the engine1to the transmission6and the disconnected state where the friction plates23and the separate plates24are disengaged from one another to block the transmission of the driving force of the engine1to the transmission6, and the clutch operation mechanism3switching the clutch mechanism2between the connected state and the disconnected state by the supply and discharge of the oil to and from the clutch mechanism2, the clutch operation mechanism3including the clutch drum22supported by the input shaft60or the output shaft10and having the cylindrical shape to form the drum chamber230, the piston32dividing the drum chamber230of the clutch drum22into the spring chamber38generating the driving force for engaging the friction plates23and the separate plates24with one another, and the pressurizing chamber34generating the driving force for disengaging the friction plates23and the separate plates24from one another, the control valve70being switchable between the first position71allowing the supply of the oil to the spring chamber38and the second position72allowing the supply of the oil to the pressurizing chamber34, the biasing members33arranged in the spring chamber38and exerting the biasing force in the direction in which the friction plates23and the separate plates24are engaged with one another, and the bores250formed in the clutch drum22to establish a connection between the inner and outer sides of the spring chamber38, the bores250discharging the oil of the spring chamber38from the inner side to the outer side in a state where the counteracting force against the centrifugal force acting in the pressurizing chamber34is generated in the spring chamber38.

According to the aforementioned configuration of the drive system of each of the first and second embodiments, the biasing members33exerting the biasing force in the direction in which the friction plates23and the separate plates24are engaged with (connected to) one another are arranged in the spring chamber38. For example, in a state where the input shaft60of the transmission6is in rotation, the oil is supplied to the spring chamber38. Consequently, the hydraulic pressure of the spring chamber38and the mechanical biasing forces of the biasing members33may serve as the driving forces for bringing the friction plates23and the separate plates24into the connected state. As a result, the friction plates23and the separate plates24are promptly engaged with one another, therefore increasing the operational responsiveness of the clutch mechanism2when the clutch mechanism2shifts from the disconnected state to the connected state.

For example, in a case where the oil remains in either one of the pressurizing chamber34and the spring chamber38, the centrifugal force caused by the rotation of the input shaft60may affect the operational responsiveness and operational controllability of the clutch mechanism2. In particular, in a condition where the input shaft60rotates at high speed, the centrifugal force increases. Accordingly, in a case where the vehicle is driven at high speed, the centrifugal force may further affect the operational responsiveness and operational controllability of the clutch mechanism2. According to the configuration of the drive system of each of the first and second embodiments, in a state where the input shaft60is in rotation, the oil of the spring chamber38is allowed to remain therein while being discharged through the bores250to the outer side of the spring chamber38. Accordingly, the centrifugal hydraulic pressure FA2generated by the centrifugal force caused by the oil remaining in the spring chamber38may counteract the centrifugal hydraulic pressure FA1generated by the centrifugal force caused by the oil remaining in the pressurizing chamber34. In particular, the centrifugal hydraulic pressures FA1and FA2act in the opposite directions from each other. Accordingly, in a case where the centrifugal hydraulic pressure FA1is equal to the centrifugal hydraulic pressure FA2, the centrifugal hydraulic pressure FA1and the centrifugal hydraulic pressure FA2offset each other. On the other hand, in a case where the centrifugal hydraulic pressure FA1is not equal to the centrifugal hydraulic pressure FA2, the centrifugal hydraulic pressure FA1and the centrifugal hydraulic pressure FA2act in the opposite directions from each other as described above. Accordingly, the influences of the centrifugal hydraulic pressure FA1and the centrifugal hydraulic pressure FA2on the operational controllability of the clutch mechanism2may be reduced. Consequently, the influence of the biasing forces of the biasing members33arranged in the spring chamber38become larger than the influences of the centrifugal hydraulic pressure FA1and the centrifugal hydraulic pressure FA2. Therefore, the influences of the centrifugal hydraulic pressure FA1and the centrifugal hydraulic pressure FA2are minimized, therefore improving the operational responsiveness of the clutch mechanism2when the clutch mechanism2shifts between the connected and disconnected states. Moreover, the both centrifugal hydraulic pressures FA1and FA2increase as the rotating speed of the input shaft60increases. However, as described above, the centrifugal hydraulic pressures FA1and FA2act in the opposite directions from each other and offset each other or decrease. Accordingly, even when the input shaft60rotates at high speed, the appropriate operational responsiveness and operational controllability of the clutch mechanism2may be secured.

In addition, the check valve for discharging the oil remaining in the pressurizing chamber34therefrom may be arranged at the wall consisting a portion of the pressurizing chamber34. However, the operation of the check valve is not stable; therefore, the operational controllability of the clutch mechanism2may not be surely obtained. As described above, according to drive system of the first embodiment, the centrifugal hydraulic pressure FA2counteracting the centrifugal hydraulic pressure FA1of the pressurizing chamber34may be generated. Accordingly, the check valve does not need to be arranged at the wall of the pressurizing chamber34in the drive system according to the first embodiment. Moreover, for example, in a case where the drive system according to the first embodiment is adapted to the hybrid vehicle, the operational responsiveness of the clutch mechanism2when the clutch mechanism2shifts from the connected state to the disconnected state is increased at the time of the electric power regeneration by the motor8. As a result, the engine1is promptly disconnected from the transmission6, thereby increasing the electric power regeneration efficiency of the motor8.

According to each of the aforementioned first and second embodiments, the spring chamber38has the minimum diameter D1and the maximum diameter D2, and each of the bores250is arranged between the minimum diameter D1and the maximum diameter D2in the radial direction of the clutch drum22.

According to the aforementioned configuration of the drive system of each of the first and second embodiments, the oil of the spring chamber38is allowed to remain therein while being discharged through the bores250to the outer side of the spring chamber38. Accordingly, the centrifugal hydraulic pressure FA2may be obtained in the spring chamber38. Consequently, the centrifugal hydraulic pressure FA1generated by the centrifugal force caused by to the oil remaining in the pressurizing chamber34may be offset or reduced by the centrifugal hydraulic pressure FA2in the spring chamber38.

According to each of the aforementioned first and second embodiments, the clutch drum22includes the fixed cylindrical portion220fitted to the outer circumferential portion of the input shaft60, the first extending portion221extending radially outwardly from the fixed cylindrical portion220, the radially-inward cylindrical portion222formed to extend along the rotational axis P1, the second extending portion223extending radially outwardly from the radially-inward cylindrical portion222, and the radially-outward cylindrical portion224formed to extend along the rotational axis P1. Further, the radially-inward cylindrical portion222, the second extending portion223, and the radially-outward cylindrical portion224form the drum chamber230in which the biasing members33and the piston32are accommodated.

As described above, the piston32, the biasing members33, and the like are accommodated in the drum chamber230of the clutch drum22, thereby reducing the size of the drive system in the direction of the rotational axis P1.

According to each of the aforementioned first and second embodiments, the motor8functioning to drive the vehicle and serving as the generator is arranged in the drive-train connecting the friction plates23and the separate plates24to the transmission6. The motor8includes the stator80and the rotor82. The rotor82rotating relative to the stator80and outputting the rotating force. The rotating force is transmitted to the input shaft60of the transmission6. The stator80and the rotor82are coaxially arranged with each other at the outer circumferential side of the friction plates23and the separate plates24.

As described above, the motor8functioning to drive the vehicle and serving as the generator is arranged in the drive-train connecting the clutch mechanism2to the transmission6. Accordingly, even in a case where the clutch mechanism2is shifted from the connected state to the disconnected state to block the transmission of the driving force of the engine1to the transmission6, the driving force of the motor8is transferred to the input shaft60of the transmission6, thereby rotating the input shaft60. As a result, the vehicle may be brought into motion by the driving force of the motor8in a state where the operation of the engine1is stopped.

According to each of the aforementioned first and second embodiments, the biasing members33face the bores250in the spring chamber38.

Accordingly, the oil in the vicinity of the biasing members33in the spring chamber38is discharged through the bores250to the outer side of the spring chamber38; thereby, the operation of the biasing members33is inhibited from being influenced by the oil remaining in the spring chamber38. Consequently, the operational controllability of the clutch mechanism2may be increased.

According to the configuration of the drive system of each of the aforementioned first and second embodiments, for example, in a state where the input shaft60of the transmission6is in rotation, the oil of the spring chamber38remains therein while being discharged therefrom through the bores250. As a result, the centrifugal hydraulic pressure FA2(the counteracting force) counteracting the centrifugal force acting in the pressurizing chamber34may be obtained in the spring chamber38. Here, in a case where the centrifugal hydraulic pressure FA1is equal to the centrifugal hydraulic pressure FA2, the centrifugal hydraulic pressure FA1and the centrifugal hydraulic pressure FA2offset each other. Meanwhile, even in a case where the centrifugal hydraulic pressure FA1is not equal to the centrifugal hydraulic pressure FA2, the centrifugal hydraulic pressure FA1and the centrifugal hydraulic pressure FA2act in the opposite directions from each other. Accordingly, the influences of the centrifugal hydraulic pressure FA1and the centrifugal hydraulic pressure FA2on the operational controllability of the clutch mechanism2may be further reduced.