Patent Publication Number: US-2010116615-A1

Title: Power transmitting apparatus

Description:
TECHNICAL FIELD 
     The present invention relates to a power transmitting apparatus that has a plurality of elements including at least two rotating elements and is capable of transmitting power between the two rotating elements. 
     BACKGROUND ART 
     There is known a conventional two-speed power transmitting unit for an electric scooter as an electric vehicle, that includes a dog clutch having a cylindrical clutch moving portion on which a permanent magnet is mounted and a cylindrical clutch driving portion on which an excitation coil is mounted, and an excitation circuit that reverses an acting force in response to a movement of the clutch moving portion by excitation of the clutch driving portion (see, Patent Document 1). In the power transmitting unit, thicknesses in both ends of a yoke of the clutch driving portion are larger than those in both ends of a yoke of the clutch moving portion. Accordingly, an attraction force acts between the permanent magnet of the clutch moving portion and the yoke of the clutch driving portion so as to generate force in an engagement direction of the clutch moving portion when the clutch moving portion is positioned in an end of a movement stroke. Further, there is known a conventional two/four wheel drive switching device for a part-time four-wheel drive vehicle, that includes a front wheel propeller shaft for driving front wheels and a rear wheel propeller shaft for driving rear wheels (see, Patent Document 2). The switching device interlockingly connects one of the propeller shafts with an output shaft of a transmission in a full-time connection state. The other of the propeller shafts is interlockingly and intermittently connected with the one propeller shaft with a clutch member movable between a connection position and a disconnection position. In the two/four wheel drive switching device, a hydraulic actuator for moving the clutch member is disposed in a lower portion within a crankcase. 
     [Patent Document 1] Japanese Patent Laid-Open No. 2003-235115 
     [Patent Document 2] Japanese Patent Laid-Open No. H11-151947 
     DISCLOSURE OF THE INVENTION 
     According to the above power transmitting unit, a position of the clutch moving portion can be fixed when the clutch moving portion reaches the end of the movement stroke even if the excitation coil of the clutch driving portion is in a non-excitation state. However, outer diameters of the clutch moving portion and the clutch driving portion should be enlarged to some extent in order to satisfactorily ensure the attraction force when the clutch moving portion and the clutch driving portion are formed in a cylindrical shape as described above. Thus, the power transmitting unit may be upsized. Further, in a dog clutch driven by an electromagnetic actuator as described above, the challenge is to reduce noise resulted from a magnetic coupling between the magnet and another member. 
     The present invention has an object to provide a power transmitting apparatus that can be configured to be compact and is capable of reducing operating noise of an electromagnetic actuator. 
     The present invention accomplishes the demands mentioned above by the following configurations applied to a power transmitting apparatus. 
     A power transmitting apparatus according to the present invention is a power transmitting apparatus that has a plurality of elements including at least two rotating elements and is capable of transmitting power between the two rotating elements. The power transmitting apparatus includes a casing that houses the plurality of elements, a lubricating medium reservoir defined in a lower portion within the casing, the lubricating medium reservoir storing a lubricating medium capable at least of lubricating the plurality of elements, and a connecting unit including a movable engagement member capable of engaging with at least two elements among the plurality of elements, and an electromagnetic actuator disposed in the lubricating medium reservoir and connected with the movable engagement member, the electromagnetic actuator moving the movable engagement member to allow a connection between at least the two elements among the plurality of elements and a release of the connection. 
     The power output apparatus includes the casing that houses the plurality of elements including at least two rotating elements, the lubricating medium reservoir defined in the lower portion within the casing and storing the lubricating medium capable at least of lubricating the plurality of elements, and the connecting unit that allows the connection between at least the two elements among the plurality of elements and the release of the connection. The connecting unit includes the movable engagement member capable of engaging with at least two elements among the plurality of elements, and the electromagnetic actuator disposed in the lubricating medium reservoir and connected with the movable engagement member. The electromagnetic actuator moves the movable engagement member to allow the connection between at least the two elements among the plurality of elements and the release of the connection. As described above, the movable engagement member capable of engaging with at least the two elements is connected with the electromagnetic actuator disposed in the lower portion within the casing. Thus, the whole of the power transmitting apparatus can be configured to be compact in comparison with an apparatus including an electromagnetic actuator having a cylindrical shape. Further, lubricating function and shock absorbing function of the lubricating medium ensure smooth operation of the electromagnetic actuator and reduce operation noise of the electromagnetic actuator by disposing the electromagnetic actuator in place within the lubricating medium reservoir. 
     The electromagnetic actuator may include an actuator shaft connected with the movable engagement member and, movable in a predetermined direction, a permanent magnet secured to the actuator shaft, a couple of fixed magnetic poles arranged so that the permanent magnet is positioned between the fixed magnetic poles, and a polarity changing device capable of changing a polarity of each of the fixed magnetic poles. According to the electromagnetic actuator, it is possible to release a magnetic coupling between the permanent magnet and one of the fixed magnetic poles and to move the actuator shaft together with the movable engagement member by changing the polarity of each of the fixed magnetic poles. After a magnetic coupling between the permanent magnet and the other of the fixed magnetic poles, it is possible to readily and reliably retain a connection or a disconnection between at least the two elements by means of the movable engagement member even if a setting of the polarity of each of the fixed magnetic poles is released. Further, the shock absorbing function of the lubricating medium favorably reduces noise due to the permanent magnet and the fixed magnetic pole by disposing the electromagnetic actuator in the lubricating medium reservoir. 
     The power transmitting apparatus may further include a bearing that supports one end portion of the actuator shaft. The one end portion may be further than the other end of the actuator shaft from the permanent magnet. Thus, it is possible to prevent the actuator shaft from inclining and to smoothly move the actuator shaft or the movable engagement member. 
     The movable engagement member and the actuator shaft may be connected with each other via a connecting member. The connecting member may be formed so that a size of a portion secured to the actuator shaft is larger than a size of a portion secured to the movable engagement member. Thus, rigidity of a securing portion between the actuator shaft and the connecting member can be increased, thereby preventing the actuator shaft from inclining and smoothly moving the actuator shaft. In this structure, particularly, the movable engagement member is advantageously formed as a relatively thin ring-shaped member. 
     The power transmitting apparatus may further include a movable shaft secured to the movable engagement member and connected with the actuator shaft. The actuator shaft and the movable shaft may be arranged offset from each other. Thus, the electromagnetic actuator can be flexibly disposed within the lubricating medium reservoir, so that the whole of the power transmitting apparatus can be configured to be compact. In this structure, particularly, the power transmitting apparatus advantageously includes a plurality of sets of the movable engagement member and the electromagnetic actuator. 
     In the power transmitting apparatus, the actuator shaft and the movable shaft may be respectively movable in a moving direction of the movable engagement member. The actuator shaft and the movable shaft may be offset from each other in a direction orthogonal to the moving direction of the movable engagement member. Thus, it is possible to smoothly move the movable engagement member and to flexibly dispose the electromagnetic actuator within the lubricating medium reservoir. 
     The power transmitting apparatus may further include bearings that supports both end portions of the movable shaft. Thus, it is possible to prevent the actuator shaft from inclining and to smoothly move the actuator shaft or the movable engagement member. 
     The movable engagement member and the movable shaft may be connected with each other via a connecting member. The connecting member may be formed so that a size of a portion secured to the movable shaft is larger than a size of a portion secured to the movable engagement member. Thus, rigidity of a securing portion between the movable shaft and the connecting member can be increased, thereby preventing the movable shaft from inclining and smoothly moving the movable shaft. In this structure, particularly, the movable engagement member is advantageously formed as a relatively thin ring-shaped member. 
     In the power transmitting apparatus, the elements may include two power input elements and one power output element. The power from the two power input elements may be selectively transmitted to the power output element. The power transmitting apparatus may be a transmission capable of selectively transmitting power from the two power input elements at predetermined respective speed ratios to the power output element. For example, such a transmission may includes a first change-speed differential rotation mechanism configured to have an input element connected with a first power output source, an output element connected with the power output element, and a fixable element and to allow differential rotations of the three elements, a second change-speed differential rotation mechanism configured to have an input element connected with a second power output source, an output element connected with the power output element, and a fixable element and to allow differential rotations of the three elements. The transmission may further includes a first fixation device configured to fix the fixable element of the first change-speed differential rotation mechanism in a non-rotatable manner, and a second fixation device configured to fix the fixable element of the second change-speed differential rotation mechanism in a non-rotatable manner. The transmission may further include a change-speed connecting-disconnecting device configured to allow a connection between the output element and the fixable element in either one of the first change-speed differential rotation mechanism and the second change-speed differential rotation mechanism and a release of the connection. Further, the power transmitting apparatus may includes two power input elements, one power output element, a first movable engagement member capable of engaging with both one of the two power input elements and the power output element, a second movable engagement member capable of engaging with both the other of the two power input elements and the power output element, an electromagnetic actuator connected with the first movable engagement member, and a second electromagnetic actuator connected with the second movable engagement member. 
     In the power transmitting apparatus, the elements may include one power input element and two power output elements. The power from the power input element may be selectively transmitted to the two power output elements. The power transmitting apparatus may includes one power input element, two power output elements, a first movable engagement member capable of engaging with both the power input element and one of the two power output elements, a second movable engagement member capable of engaging with both the power input elements and the other of two power output elements, an electromagnetic actuator connected with the first movable engagement member, and a second electromagnetic actuator connected with the second movable engagement member. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic block diagram of a hybrid vehicle  20  including a transmission  60  that is a power transmitting apparatus according to one embodiment of the invention; 
         FIG. 2  is a schematic block diagram of the transmission  60 ; 
         FIG. 3  is an explanatory view exemplifying a state of torques and rotational speeds of primary elements included in a power distribution integration mechanism  40  and the transmission  60  when a change speed state of the transmission  60  is changed in accordance with a vehicle speed change during a drive of the hybrid vehicle  20  with an engagement of a clutch C 0  and an operation of an engine  22 ; 
         FIG. 4  is a similar explanatory view to  FIG. 3 ; 
         FIG. 5  is a similar explanatory view to  FIG. 3 ; 
         FIG. 6  is a similar explanatory view to  FIG. 3 ; 
         FIG. 7  is a similar explanatory view to  FIG. 3 ; 
         FIG. 8  is a similar explanatory view to  FIG. 3 ; 
         FIG. 9  is an explanatory view exemplifying an alignment chart showing a state of torques and rotational speeds of elements included in the power distribution integration mechanism  40  and a reduction gear mechanism  50  when a motor MG 1  is operated as a generator and a motor MG 2  is operated as a motor; 
         FIG. 10  is an explanatory view exemplifying an alignment chart showing a state of torques and rotational speeds of elements included in the power distribution integration mechanism  40  and a reduction gear mechanism  50  when a motor MG 1  is operated as the motor and a motor MG 2  is operated as the generator; 
         FIG. 11  is an explanatory view for explaining a motor drive mode of the hybrid vehicle  20 ; 
         FIG. 12  is a schematic block diagram of a transmission  60 A according to a modified example; 
         FIG. 13  is a schematic block diagram of an electromagnetic actuator  101 A according to a modified example; 
         FIG. 14  is a schematic block diagram of a clutch  200  in a modified example of the power transmitting apparatus according to the invention; and 
         FIG. 15  is a schematic block diagram of a clutch  300  in a modified example of the power transmitting apparatus according to the invention. 
     
    
    
     BEST MODES OF CARRYING OUT THE INVENTION 
     One mode of carrying out the invention is discussed below as a preferred embodiment. 
       FIG. 1  is a schematic block diagram of a hybrid vehicle  20  including a transmission  60  that is a power transmitting apparatus according to one embodiment of the invention. The hybrid vehicle  20  shown in  FIG. 1  is constructed as, for example, a rear-wheel drive vehicle and includes an engine  22  located in a front portion of the vehicle body, a power distribution integration mechanism  40  connected to a crankshaft (engine shaft)  26  of the engine  22 , a motor MG 1  having power generation capability and linked with the power distribution integration mechanism  40 , a motor MG 2  having power generation capability and linked with the power distribution integration mechanism  40  via a reduction gear mechanism  50  to be coaxial with the motor MG 1 , a transmission  60  that transmits power from the power distribution integration mechanism  40  to a driveshaft while changing a rotational speed, and a hybrid electronic control unit (hereafter referred to as ‘hybrid ECU’)  70  configured to control operations of the whole hybrid vehicle  20 . 
     The engine  22  is an internal combustion engine that receives a supply of a hydrocarbon fuel, such as gasoline or light oil, and outputs power. The engine  22  is under control of an engine electronic control unit (hereafter referred to as ‘engine ECU’)  24  and is subjected to, for example, a fuel injection control, an ignition control, and an intake air control. The engine ECU  24  inputs diverse signals from various sensors that are provided for the engine  22  to measure and detect operating states of the engine  22 , for example, a crank position sensor (not shown) mounted on the crankshaft  26 . The engine ECU  24  establishes communication with the hybrid ECU  70  to drive and control the engine  22  in response to control signals from the hybrid ECU  70  and with reference to the diverse signals from the various sensors and to output data regarding the operating states of the engine  22  to the hybrid ECU  70  according to the requirements. 
     The motors MG 1  and MG 2  are constructed as synchronous motor generators of an identical specification that can be operated both as a generator and as a motor. The motors MG 1  and MG 2  receive and supply electric power to a battery  35  or a secondary cell via inverters  31  and  32 . Power lines  39  connecting the battery  35  with the inverters  31  and  32  are structured as a common positive bus and a negative bus shared by the inverters  31  and  32 . Such connection enables electric power generated by one of the motors MG 1  and MG 2  to be consumed by the other motor MG 2  or MG 1 . The battery  35  may thus be charged with surplus electric power generated by either of the motors MG 1  and MG 2 , while being discharged to supplement insufficient electric power. The battery  35  is neither charged nor discharged upon the balance of the input and output of electric powers between the motors MG 1  and MG 2 . Both the motors MG 1  and MG 2  are driven and controlled by a motor electronic control unit (hereafter referred to as ‘motor ECU’)  30 . The motor ECU  30  inputs various signals required for driving and controlling the motors MG 1  and MG 2 , for example, signals representing rotational positions of rotors in the motors MG 1  and MG 2  from rotational position detection sensors  33  and  34  and signals representing phase currents to be applied to the motors MG 1  and MG 2  from current sensors (not shown). The motor ECU  30  outputs switching control signals to the inverters  31  and  32 . The motor ECU  30  executes a rotational speed computation routine (not shown) to compute rotational speeds Nm 1  and Nm 2  of the rotors of the motors MG 1  and MG 2  from the signals output from the rotational position detection sensors  33  and  34 . The motor ECU  30  establishes communication with the hybrid ECU  70  to drive and control the motors MG 1  and MG 2  in response to control signals received from the hybrid ECU  70  and to output data regarding operating states of the motors MG 1  and MG 2  to the hybrid ECU  70  according to the requirements. 
     The battery  35  is under control and management of a battery electronic control unit (hereafter referred to as ‘battery ECU’)  36 . The battery ECU  36  inputs various signals required for management and control of the battery  35 , for example, an inter-terminal voltage from a voltage sensor (not shown) located between terminals of the battery  35 , a charge-discharge current from a current sensor (not shown) located in the power line  39  connecting with an output terminal of the battery  35 , and a battery temperature Tb from a temperature sensor  37  attached to the battery  35 . The battery ECU  36  outputs data regarding operating states of the battery  35  by communication to the hybrid ECU  70  and to the engine ECU  24  according to the requirements. In the embodiment, the battery ECU  36  calculates a remaining charge amount or a state of charge SOC of the battery  35  based on an integrating value the charge-discharge current measured by the current sensor and calculates a charge-discharge power demand Pb* of the battery  35  based on the computed state of charge SOC. The battery ECU  36  also sets an input limit Win as an allowable charging power to be charged into the battery  35  and an output limit Wout as an allowable discharging power to be discharged from the battery  35 , based on the computed state of charge SOC and the measured battery temperature Tb. The input and output limits Win and Wout of the battery  35  are set by setting base values depending on the battery temperature Tb and setting an input limit correction coefficient and an output limit correction coefficient based on the state of charge SOC of the battery  50 , and then multiplying the set base value of the input and output limits Win and Wout by the set correction coefficient. 
     The power distribution integration mechanism  40  is housed in a non-illustrated transmission case (casing) together with the motors MG 1  and MG 2 , the reduction gear mechanism  50  and the transmission  60 . The power distribution integration mechanism  40  is arranged apart from the engine  22  by a predetermined distance to be coaxial with the crankshaft  26 . The power distribution integration mechanism  40  of the embodiment is a double pinion planetary gear mechanism and includes a sun gear  41  that is an external gear, a ring gear  42  that is an internal gear arranged concentrically with the sun gear  41 , and a carrier  45  that supports at least one set of two pinion gears  43  and  44  intermeshing with each other so as to allow both their revolutions and their rotations on their axes. One of the two pinion gears  43  and  44  engages with the sun gear  41  and the other engages with the ring gear  42 . In this power distribution integration mechanism  40 , the sun gear  41  (second element), the ring gear  42  (third element), and the carrier  45  (first element) are designed as elements of differential rotations. In the embodiment, the power distribution integration mechanism  40  is constructed to have a gear ratio ρ (quotient of the number of teeth of the sun gear  41  divided by the number of teeth of the ring gear  42 ) satisfying a relation of ρ&lt;0.5. The sun gear  41  or the second element of the power distribution integration mechanism  40  is connected with the motor MG 1  (more specifically with its hollow rotor) or a second motor via a hollow sun gear shaft  41   a  extended from the sun gear  41  in a direction opposite to the engine  22  (that is, toward a rear portion of the vehicle body) and a hollow first motor shaft  46 . The carrier  45  or the first element is connected with the motor MG 2  (more specifically with its hollow rotor) or a first motor via the reduction gear mechanism  50  located between the power distribution integration mechanism  40  and the engine  22  and a hollow second motor shaft  55  extended from the reduction gear mechanism  50  (more specially from its sun gear  51 ) toward the engine  22 . The ring gear  42  or the third element is connected with the crankshaft  26  of the engine  22  via a ring gear shaft  42   a  extended to pass through the second motor shaft  55  and the motor MG 2 , as well as a damper  28 . 
     As shown in  FIG. 1 , a clutch C 0  (connecting-disconnecting device) is disposed between the sun gear shaft  41   a  and the first motor shaft  46 . The clutch C 0  is configured to allow a connection (drive source-element connection) between the sun gear shaft  41   a  and the first motor shaft  46  and a release of the connection. The clutch C 0  of the embodiment is a dog clutch driven by an electromagnetic actuator  100 . When the connection between the sun gear shaft  41   a  and the first motor shaft  46  is released by the clutch C 0 , connection between the motor MG 1  or the second motor and the sun gear  41  or the second element of the power distribution integration mechanism  40 , so that the engine  22  can be substantially separated from the motors MG 1  and MG 2  and the transmission  60  by the function of the power distribution integration mechanism  40 . The first motor shaft  46  that can be connected with the sun gear  41  of the power distribution integration mechanism  40  via the clutch C 0  is further extended from the motor MG 1  in the direction opposite to the engine  22  (toward the rear portion of the vehicle body) and is connected with the transmission  60 . A carrier shaft (coupling shaft)  45   a  is extended from the carrier  45  of the power distribution integration mechanism  40  in the direction opposite to the engine  22  (toward the rear portion of the vehicle body). The carrier shaft  45   a  passes through the hollow sun gear shaft  41   a  and the hollow first motor shaft  46 , and is connected with the transmission  60 . Thus, in the embodiment, the power distribution integration mechanism  40  is arranged coaxially with the motors MG 1  and MG 2  and is located between the motors MG 1  and MG 2  coaxially arranged with each other. Further, the engine  22  is arranged coaxially with the motor MG 2  and is located to oppose the transmission  60  across the power distribution integration mechanism  40 . The engine  22 , the motor MG 2 , (the reduction gear mechanism  50 ), the power distribution integration mechanism  40 , the motor MG 1 , and the transmission  60  as the constituents of the power output apparatus are thus arranged in this sequence from the forward to the rearward of the vehicle body. This arrangement reduces the size of the power output apparatus to be suitable for mounting on the rear-wheel drive hybrid vehicle  20 . 
     The reduction gear mechanism  50  is a single pinion planetary gear mechanism and includes a sun gear  51  that is an external gear, a ring gear  52  that is an internal gear arranged concentrically with the sun gear  51 , multiple pinion gears  53  arranged to engage with the sun gear  51  and with the ring gear  52 , and a carrier  54  arranged to support the multiple pinion gears  53  so as to allow both their revolutions and their rotations on their axes. The sun gear  51  of the reduction gear mechanism  50  is connected with the rotor of the motor MG 2  via the second motor shaft  55 . The ring gear  52  of the reduction gear mechanism  50  is secured to the carrier  45  of the power distribution integration mechanism  40 , so that the reduction gear mechanism  50  is substantially integrated with the power distribution integration mechanism  40 . The carrier  54  of the reduction gear mechanism  50  is fixed to the transmission case of the transmission  60 . The function of the reduction gear mechanism  50  reduces the speed of power from the motor MG 2  to be input into the carrier  45  of the power distribution integration mechanism  40 , while increasing the speed of the output power from the carrier  45  to be input into the motor MG 2 . In the power distribution integration mechanism  40  or the double pinion planetary gear mechanism having the gear ratio ρ of less than 0.5, the engine  22  has a large torque distribution rate to the carrier  45  in comparison with the sun gear  41 . The arrangement of the reduction gear mechanism  50  between the carrier  45  of the power distribution integration mechanism  40  and the motor MG 2  downsizes the motor MG 2  and reduces a power loss of the motor MG 2 . The arrangement of the reduction gear mechanism  50  between the motor MG 2  and the power distribution integration mechanism  40  to be integrated with the power distribution integration mechanism  40  enables further size reduction of the power output apparatus. In the embodiment, the reduction gear mechanism  50  is constructed to have a reduction gear ratio (number of teeth of the sun gear  51 /number of teeth of the ring gear  52 ) set to a value close to ρ/(1−ρ), where ρ represents the gear ratio of the power distribution integration mechanism  40 . The motors MG 1  and MG 2  can thus be constructed to have substantially identical specifications. This arrangement effectively improves the productivity of the hybrid vehicle  20  and the power output apparatus and reduces the manufacturing cost of the hybrid vehicle  20  and the power output apparatus. 
     The transmission  60  is a planetary gear-type automatic transmission capable of setting its speed ratio at multiple different stages. The transmission  60  includes a first change speed planetary gear mechanism PG 1  (first change speed differential rotation mechanism) connected via the carrier shaft  45   a  with the carrier  45  or the first element of the power distribution integration mechanism  40 , a second change speed planetary gear mechanism PG 2  (second change speed differential rotation mechanism) connected with the first motor shaft  46  connectable via the clutch C 0  with the sun gear  41  or the second element of the power distribution integration mechanism  40 , a brake B 1  (first fixation device) corresponding to the first change speed planetary gear mechanism PG 1 , a brake B 2  (second fixation device) corresponding to the second change speed planetary gear mechanism PG 2 , a brake B 3  (third fixation device) and a clutch C 1  (change-speed connecting-disconnecting device). 
     As shown in  FIGS. 1 and 2 , the first change speed planetary gear mechanism PG 1  is a single pinion planetary gear mechanism and includes a sun gear  61  connected with the carrier shaft  45   a , a ring gear  62  that is an internal gear arranged coaxially with the sun gear  61 , and a carrier  64  arranged to hold multiple pinion gears  63  engaging with both the sun gear  61  and the ring gear  62  and connected with the driveshaft  69 . The sun gear  61  (input element), the ring gear  62  (fixable element), and the carrier  64  (output element) are designed as elements of differential rotations. The second change speed planetary gear mechanism PG 2  is also a single pinion planetary gear mechanism and includes a sun gear  65  connected with the first motor shaft  46 , a ring gear  66  that is an internal gear arranged coaxially with the sun gear  65 , and the common carrier  64  that is shared with the first change speed planetary gear mechanism PG 1  and holds multiple pinion gears  67  engaging with both the sun gear  65  and the ring gear  66 . The sun gear  65  (input element), the ring gear  66  (fixable element), and the carrier  64  (output element) are designed as elements of differential rotations. In the embodiment, the second change speed planetary gear mechanism PG 2  is arranged to be coaxial with and ahead of the first change speed planetary gear mechanism PG 1  in the vehicle body. A gear ratio ρ 2  (number of teeth of the sun gear  65 /number of teeth of the ring gear  66 ) of the second change speed planetary gear mechanism PG 2  is set to be slightly larger than a gear ratio ρ 1  (number of teeth of the sun gear  61 /number of teeth of the ring gear  62 ) of the first change speed planetary gear mechanism PG 1  (See  FIG. 3 ). Constituents of the first change speed planetary gear mechanism PG 1 , the second change speed planetary gear mechanism PG 2 , the brakes B 1 -B 3  and the clutch C 1  are housed in the transmission case (casing)  600  of the transmission  60 . The power transmitted from the carrier of the transmission  60  to the driveshaft  69  is eventually output through a differential gear DF to rear wheels RWa and RWb or drive wheels. The transmission  60  of the above structure enables significant size reduction both in the axial direction and in a radial direction in comparison with the parallel shaft-type transmission. The first and second change speed planetary gear mechanisms PG 1  and PG 2  can be arranged coaxially with and in the downstream of the engine  22 , the motors MG 1  and MG 2 , the reduction gear mechanism  50 , and the power distribution integration mechanism  40 . The transmission  60  constructed as described above desirably simplifies the bearing structure and reduces the number of bearings. 
     The brake B 1  is a dog clutch including a movable engagement member  151  and an electromagnetic actuator  101  to move the movable engagement member  151  back and forth in the axial direction of the carrier shaft  45   a  and the first motor shaft  46 . The brake B 1  is capable of fixing the ring gear  62  of the first change speed planetary gear mechanism PG 1  to the transmission case  600  in a non-rotatable manner and releasing the ring gear  62  in a rotatable manner. In the embodiment, the movable engagement member  151  is a relatively thin ring-shaped member having tooth portions  151   a  capable of engaging with both splines  62   a  formed on an outer periphery of the ring gear  62  and splines  601   a  formed on a tip of a locking member  601  having a ring-shape in the embodiment and secured to an inner surface of the transmission case  600 . The brake B 2  is a dog clutch including a movable engagement member  152  and an electromagnetic actuator  102  to move the movable engagement member  152  back and forth in the axial direction of the carrier shaft  45   a  and the first motor shaft  46 . The brake B 2  is capable of fixing the ring gear  66  of the second change speed planetary gear mechanism PG 2  to the transmission case  600  in a non-rotatable manner and releasing the ring gear  66  in a rotatable manner. In the embodiment, the movable engagement member  152  is a relatively thin ring-shaped member having tooth portions  152   a  capable of engaging with both splines  66   a  formed on an outer periphery of the ring gear  66  and splines  602   a  formed on a tip of a locking member  602  having a ring-shape in the embodiment and secured to the inner surface of the transmission case  600 . The brake B 3  is a dog clutch including a movable engagement member  153  and an electromagnetic actuator  103  to move the movable engagement member  153  back and forth in the axial direction of the carrier shaft  45   a  and the first motor shaft  46 . The brake B 3  is capable of fixing the first motor shaft  46  or the sun gear  41  that is the second element of the power distribution integration mechanism  40  to the transmission case  600  in a non-rotatable manner via a fixing member  68  secured to the first motor shaft  46  and releasing the fixing member  68  so as to allow the first motor shaft  46  to rotate. In the embodiment, the movable engagement member  153  is a relatively thin ring-shaped member having tooth portions  153   a  capable of engaging with both splines  68   a  formed on an outer periphery of the fixing member  68  and splines  603   a  formed on a tip of a locking member  603  having a ring-shape in the embodiment and secured to an inner surface of the transmission case  600 . The clutch C 1  is a dog clutch including a movable engagement member  154  and an electromagnetic actuator  104  to move the movable engagement member  154  back and forth in the axial direction of the carrier shaft  45   a  and the first motor shaft  46 . The clutch C 1  is capable of a connection between the carrier  64  or the output element of the first and second change speed planetary gear mechanisms PG 1  and PG 2  the ring gear  62  or the fixable element of the planetary gear mechanisms PG 1  and PG 2  and a release of the connection. In the embodiment, the movable engagement member  154  is a relatively thin ring-shaped member having tooth portions  154   a  capable of engaging with both splines  62   a  formed on the outer periphery of the ring gear  62  and splines  64   a  formed on an outer periphery of the carrier  64 . Although a detailed description thereof is omitted, the above clutch C 0  is a dog clutch similar to the clutch C 1 . 
     The above electromagnetic actuators  100 - 104  of the brakes B 1 -B 3 , the clutches C 0  and C 1  have basically same construction and are disposed within an oil pan  605  that is defined in a lower portion of the transmission case  600  and stores a transmission oil for lubricating and cooling the constituents of the transmission  60 . The construction of the electromagnetic actuators  100 - 104  will be explained as follow while taking the electromagnetic actuator  102  as an example. As shown in  FIG. 2 , the electromagnetic actuator  102  includes an actuator shaft  110  connected with the movable engagement member  152  and movable in a predetermined direction, a permanent magnet  111  secured to the actuator shaft  110 , a couple of fixed magnetic poles  112  and  113  arranged so that the permanent magnet  111  is positioned between the fixed magnetic poles  112  and  113 , a coil  114  connected with the fixed magnetic poles  112 , and a coil  115  connected with the fixed magnetic poles  113 . The actuator shaft  110  is inserted into hole portions of the fixed magnetic poles  112  and  113 . Both ends of the actuator shaft  110  are slidably supported by bearings  116  and  117  that are disposed on the outside of the fixed magnetic poles  112  and the coil  114  or the outside of the fixed magnetic poles  113  and the coil  115 . The actuator shaft  110  extends in parallel with the carrier shaft  45   a  and the first shaft  46 . In the embodiment, the bearing  116  on the left side in  FIG. 2  is held by a base end portion of the locking member  602  and the bearing  117  on the right side in  FIG. 2  is secured to a surface of the oil pan  605 . It may be possible to provide a function of the bearing to one of the fixed magnetic poles  112  and  113  and the coils  114  and  115  and the bearing  117  on the right side in  FIG. 2 , for example, may be omitted. The permanent magnet  111  is formed in a disk-shape for example. The permanent magnet  11  is secured to the actuator shaft  110  so that it is positioned between the fixed magnetic poles  112  and  113  and a polarity of the permanent magnet  111  in the side of the fixed magnetic pole  112  and that in the side of the fixed magnetic pole  113  are opposite with respect to each other (hereafter, for simplicity, the polarity of the permanent magnet  111  in the side of the fixed magnetic pole  112  is supposed to be the north pole and that in the side of the fixed magnetic pole  113  is supposed to be the south pole). The fixed magnetic poles  112  and  113  and the coils  114  and  115  are mounted on a base plate  118  that is secured to the surface of the oil pan  605 . The coils  114  and  115  are electrically connected to a drive circuit  105  (see  FIG. 1 ) that is configured to individually apply voltage to the coils  114  and  115  of the electromagnetic actuators  100 - 104  so as to change polarities of each of the coils  114  and  115 . An movable shaft  120  is connected to one end (left end in the figure) of the actuator shaft  110  via a connecting rod  119 . As shown in  FIG. 2 , both ends of the movable shaft  120  are slidably supported by a bearing  121  that is held by the locking member  602  to be positioned over the bearing  116  and a bearing  122  that is secured to an upper portion of the bearing  117 . Thus, the actuator shaft  110  and the movable shaft  120  are arranged offset from each other in a top to bottom direction in the figure that is a direction orthogonal to a moving direction of the movable engagement member  152 , that is, an axial direction of the carrier shaft  45   a  and the first motor shaft  46 . The movable shaft  120  is secured to the movable engagement member  152  via a connecting member  125 . In the embodiment, the connecting member  125  has a trapezoid-shaped cross-section in which a lower base length is longer than an upper base length. The connecting member  125  is secured to the movable engagement member  152  in the side of the upper base and is secured to the movable shaft  120  in the side of the lower length. That is, the connecting member  125  is formed so that a size of a portion secured to the movable shaft  120  is larger than a size of a portion secured to the movable engagement member  152 . 
     According to the electromagnetic actuators  100 - 104 , it is possible to release a magnetic coupling between the permanent magnet  111  and one of the fixed magnetic poles  112  and  113  and to move the actuator shaft  110  and the movable shaft  120  together with the movable engagement member  152  by changing the polarities of the fixed magnetic poles  112  and  113  by means of the drive circuit  105 , the coils  114  and  115 , thereby capable of a connection between two elements corresponding to the brakes B 1 -B 3  and clutches C 1  and C 0  and a release of the connection. When the permanent magnet  111  magnetically couples with the other of the fixed magnetic poles  112  and  113 , it is possible to readily and reliably retain the connection between the two elements by means of the movable engagement member  152  even if a setting of the polarity of each of the fixed magnetic poles  112  and  113  by means of the drive circuit  105 , the coils  114  and  115  is released. For example, repulsive force releases a magnetic coupling between the permanent magnet  111  and the fixed magnetic pole  112  on the left side by applying voltage to the coils  114  and  115  of the electromagnetic actuator  102  from the drive circuit  150  so as to set both polarities of the fixed magnetic poles  112  and  113  to the north pole when the permanent magnet  111  magnetically couples with the fixed magnetic pole  112  as shown in  FIG. 2  and the ring gear  66  is fixed to the transmission case  600  in the non-rotatable manner via the locking member  602  by the brake B 2 . Then, the permanent magnet  111  and the fixed magnetic pole  113  attract each other, so that the actuator shaft  110  and the movable shaft  120  moves on the right side in the figure and the permanent magnet  111  magnetically couples with the fixed magnetic pole  113 . The permanent magnet  111  keeps on magnetically coupling with the fixed magnetic pole  113  by magnetic force thereof even if an application of the voltage from the drive circuit  105  to the coils  114  and  115  is released. The movable engagement member  152  moves on the right side in the figure in response to the movement of the movable shaft  120  that is secured to the movable engagement member  152 , so that the ring gear  66  is released from the locking member  602  to be rotatable and a release state of the ring gear  66  is retained by the magnetic coupling between the permanent magnet  111  and the fixed magnetic pole  113 . Repulsive force releases a magnetic coupling between the permanent magnet  111  and the fixed magnetic pole  113  on the right side by applying voltage to the coils  114  and  115  of the electromagnetic actuator  102  from the drive circuit  150  so as to set both polarities of the fixed magnetic poles  112  and  113  to the south pole when an engagement between the ring gear  66  and the locking member  602 . Then, the permanent magnet  111  and the fixed magnetic pole  112  attract each other, so that the actuator shaft  110  and the movable shaft  120  moves on the left side in the figure and the permanent magnet  111  magnetically couples with the fixed magnetic pole  112 . Thus, the movable engagement member  152  moves on the left side in the figure in response to the movement of the movable shaft  120  that is secured to the movable engagement member  152 , so that the ring gear  66  engages with the locking member  602  to be non-rotatable and a non-rotatable state of the ring gear  66  is retained by the magnetic coupling between the permanent magnet  111  and the fixed magnetic pole  112 . It is possible to operate the brakes B 1 , B 2 , clutches C 0  and C 1  as described above by actuating the electromagnetic actuator  100 ,  101 ,  103  and  104  in accordance with procedure similar to the above described one. 
     The hybrid ECU  70  is constructed as a microprocessor including a CPU  72 , a ROM  74  that stores processing programs, a RAM  76  that temporarily stores data, a non-illustrated input-output port, and a non-illustrated communication port. The hybrid ECU  70  receives various inputs via the input port: an ignition signal from an ignition switch (start switch)  80 , a shift position SP from a shift position sensor  82  that detects the current position of a shift lever  81 , an accelerator opening Acc from an accelerator pedal position sensor  84  that measures a depression amount of an accelerator pedal  83 , a brake pedal position BP from a brake pedal position sensor  86  that measures a depression amount of a brake pedal  85 , and a vehicle speed V from a vehicle speed sensor  87 . The hybrid ECU  70  communicates with the engine ECU  24 , the motor ECU  30 , and the battery ECU  36  via the communication port to transmit diverse control signals and data to and from the engine ECU  24 , the motor ECU  30 , and the battery ECU  36 , as mentioned previously. The hybrid ECU  70  also controls the drive circuit  105  that applies voltage to the coils  114  and  115  of the electromagnetic actuators  100 - 104  of the clutch C 0 , the brakes B 1 -B 3  and the clutch C 1  includes in the transmission  60 . 
     Operations of the hybrid vehicle  20  are described below with reference to  FIGS. 3 through 11 . During a drive of the hybrid vehicle  20  in respective change speed states of  FIGS. 3 to 9 , under comprehensive control of the hybrid ECU  70  based on the driver&#39;s depression amount of an accelerator pedal  83  and the vehicle speed V, the engine  22  is controlled by the engine ECU  24 , the motors MG 1  and MG 2  are controlled by the motor ECU  30 , and the electromagnetic actuators  100  to  104  (the clutch C 0 , the brakes B 1 -B 3  and the clutch C 1  of the transmission  60 ) are directly controlled by the hybrid ECU  70 . In  FIGS. 3 through 8 , an S-axis represents a rotational speed of the sun gear  41  in the power distribution integration mechanism  40  (equivalent to a rotational speed Nm 1  of the motor MG 1  or the first motor shaft  46 ). An R-axis represents a rotational speed of the ring gear  42  in the power distribution integration mechanism  40  (equivalent to a rotational speed Ne of the engine  22 ). A C-axis represents a rotational speed of the carrier  45  in the power distribution integration mechanism  40  (equivalent to a rotational speed of the carrier shaft  45   a  and the ring gear  52  of the reduction gear mechanism  50 ). A 54-axis represents a rotational speed of the carrier  54  of the reduction gear mechanism  50 , and a 51-axis represents a rotational speed of the sun gear  51  of the reduction gear mechanism  50  (equivalent to a rotational speed Nm 2  of the motor MG 2  or the second motor shaft  55 ). A 61, 65-axis represents a rotational speed of the sun gear  61  in the first change speed planetary gear mechanism PG 1  and a rotational speed of the sun gear  65  in the second change speed planetary gear mechanism PG 2  in the transmission  60 . A 64-axis represents a rotational speed of the carrier  64  in the transmission  60  (equivalent to a rotational speed of the driveshaft  69 ). A 62-axis represents a rotational speed of the ring gear  62  in the first change speed planetary gear mechanism PG 1 . A 66-axis represents a rotational speed of the ring gear  66  in the second change speed planetary gear mechanism PG 2 . 
     During a drive of the hybrid vehicle  20  with an engagement of the clutch C 0  and an operation of the engine  22 , the transmission  60  can be set in a first change speed state (first speed) by fixing the ring gear  62  of the first change speed planetary gear mechanism PG 1  to the transmission case  600  in the non-rotatable manner by the brake B 1  as shown in  FIG. 3 . In the first change speed state, the power from the carrier shaft  45   a  (the carrier  45 ) is subjected to speed change at a speed ratio (=ρ 1 /(1+ρ 1 )) based on the gear ratio ρ 1  of the first change speed planetary gear mechanism PG 1  and is transmitted to the driveshaft  69 . When the rotational speed of the ring gear  66  in the second change speed planetary gear mechanism PG 2  changes from a negative value to almost 0 in response to a decrease of the rotational speed Nm 1  of the motor MG 1  (the sun gear  41  and the first motor shaft  46 ) in the first change speed state of  FIG. 3 , the ring gear  66  or the fixable element of the second change speed planetary gear mechanism PG 2  may be fixed in the non-rotatable manner as shown in  FIG. 4  while fixing the ring gear  62  of the first change speed planetary gear mechanism PG 1  in the non-rotatable manner. Hereafter, a mode of fixing both the ring gear  62  in the first change speed planetary gear mechanism PG 1  and the ring gear  66  in the second change speed planetary gear mechanism PG 2  in the non-rotatable manner by means of the brakes B 1  and B 2  is referred to as ‘simultaneous engagement mode’. The state of  FIG. 4  is specifically called ‘1 st  speed-2 nd  speed simultaneous engagement state’. Setting torque commands of the motors MG 1  and MG 2  to 0 in the 1 st  speed-2 nd  speed simultaneous engagement state causes the motors MG 1  and MG 2  to run idle without performing either power operation or regenerative operation. Power (torque) from the engine  22  is thus mechanically (directly) transmitted at a fixed (constant) speed ratio (a value between the speed ratio of the first change speed state and the speed ratio of a second change speed state) to the driveshaft  69  without conversion into electrical energy. When the brake B 2  is released so that the ring gear  62  of the first change speed planetary gear mechanism PG 1  is in the rotatable manner while non-rotatably fixing the ring gear  66  of the second change speed planetary gear mechanism PG 2  in the 1 st  speed-2 nd  speed simultaneous engagement state of  FIG. 4 , the transmission  60  is set in a second change speed state (second speed) as shown in  FIG. 5 . In the second change speed state, power from the first motor shaft  46  is subjected to speed change at a speed ratio (=ρ 2 /(1+ρ 2 )) based on the gear ratio ρ 2  of the second change speed planetary gear mechanism PG 2  and is transmitted to the driveshaft  69 . 
     When the rotational speeds of the sun gear  61 , the ring gear  62 , and the carrier  64  of the first change speed planetary gear mechanism PG 1  are almost equal to one another to allow substantially integral rotation of these elements  61 ,  62 , and  64  in the second change speed state of  FIG. 5 , the ring gear  62  of the first change speed planetary gear mechanism PG 1  may be coupled with the carrier  64  by the clutch C 1  as shown in  FIG. 6 . Hereafter, a mode of coupling the ring gear  62  of the first change speed planetary gear mechanism PG 1  with the carrier  64  by means of the clutch C 1  while fixing the ring gear  66  of the second change speed planetary gear mechanism PG 2  in the non-rotatable manner by means of the brake B 2  is also referred to as the ‘simultaneous engagement mode’. The state of  FIG. 6  is specifically called ‘2 nd  speed-3 rd  speed simultaneous engagement state’. Setting torque commands of the motors MG 1  and MG 2  to  0  in the 2 nd  speed-3 rd  speed simultaneous engagement state causes the motors MG 1  and MG 2  to run idle without performing either power operation or regenerative operation. Power (torque) from the engine  22  is thus mechanically (directly) transmitted at a fixed (constant) speed ratio (a value between the speed ratio of the second change speed state and the speed ratio of a third change speed state) to the driveshaft  69  without conversion into electrical energy. When the brake B 2  is released so that the ring gear  66  of the second change speed planetary gear mechanism PG 2  is in the rotatable manner in the 2 nd  speed-3 rd  speed simultaneous engagement state of  FIG. 6 , the transmission  60  is set in a third change speed state (third speed). In the third change speed state shown in  FIG. 7 , the clutch C 1  substantially locks the sun gear  61 , the ring gear  62 , and the carrier  64  of the first change speed planetary gear mechanism PG 1  to allow integral rotation of these elements  61 ,  62 , and  64 . Power from the carrier  45  of the power distribution integration mechanism  40  is thus directly transmitted at a speed ratio of “1” to the driveshaft  69  via the carrier shaft  45   a  and the integrally rotating elements of the first change speed planetary gear mechanism PG 1  as shown in  FIG. 7 . In the third change speed state, a ratio of the rotational speed of the engine  22  to a rotational speed of the driveshaft  69  directly linked with the carrier  45  or the output element is varied continuously in a stepless manner by controlling the rotational speed of the motor MG 1 . 
     When the rotational speeds of the motor MG 1 , the first motor shaft  46 , the sun gear  41  and the sun gear  61  of the first change speed planetary gear mechanism PG 1  approach to 0 in the third change speed state of  FIG. 7 , the sun gear  41  or the second element of the power distribution integration mechanism  40  may be fixed in the non-rotatable manner by the brake B 3  via the fixing member  68  and the first motor shaft  46  as shown in  FIG. 8 . Hereafter, a mode of fixing the first motor shaft  46  (the motor MG 1 ) in the non-rotatable manner by means of the brake B 3  while keeping the ring gear  62  coupled with the carrier  64  by means of the clutch C 1  to substantially lock the first change speed planetary gear mechanism PG 1  of the transmission  60  is also referred to as the ‘simultaneous engagement mode’. The state of  FIG. 9  is specifically called ‘3 rd  speed fixing state’. Setting the torque commands of the motors MG 1  and MG 2  to 0 in the 3 rd  speed fixing state causes the motors MG 1  and MG 2  to run idle without performing either power operation or regenerative operation. Power (torque) from the engine  22  is thus directly transmitted to the driveshaft  69  at a fixed (constant) speed ratio (a value in an increasing speed side compared to the speed ratio of, the third change speed state) to the driveshaft  69  without conversion into electrical energy. The speed ratio of the transmission  60  may be shifted down in accordance with a procedure reverse to the above description. 
     When the transmission  60  is set to either the first change speed state or the third change speed state during the drive of the hybrid vehicle  20  with the operation of the engine  22 , the motors MG 1  and MG 2  may be driven and controlled to make the motor MG 2 , which is connected with the carrier  45  of the power distribution integration mechanism  40  working as the output element, function as the motor and to make the motor MG 1 , which is connected with the sun gear  41  working as the reactive element, function as the generator. In this state, the power distribution integration mechanism  40  distributes the power from the engine  22  input via the ring gear  42  at its gear ratio ρ into the sun gear  41  and the carrier  45 , while integrating the power from the engine  22  with the power from the motor MG 2  functioning as the motor and outputting the integrated power to the carrier  45 . Hereafter, a mode of making the motor MG 1  function as the generator and making the motor MG 2  function as the motor is referred to as ‘first torque conversion mode’. In the first torque conversion mode, the power from the engine  22  goes through torque conversion by means of the power distribution integration mechanism  40  and the motors MG 1  and MG 2  and is then output to the carrier  45 . The ratio of the rotational speed Ne of the engine  22  to the rotational speed of the carrier  45  or the output element is varied continuously in a stepless manner by controlling the rotational speed of the motor MG 1 .  FIG. 9  is an explanatory view exemplifying an alignment chart showing a state of torques and rotational speeds of elements included in the power distribution integration mechanism  40  and the reduction gear mechanism  50  in the first torque conversion mode. The S-axis, the R-axis, and the C-axis in  FIG. 9  represent the same meanings as those in  FIGS. 3 through 8 . The 54-axis represents the rotational speed of the carrier  54  in the reduction gear mechanism  50 , and the 51-axis represents the rotational speed of the sun gear  51  in the reduction gear mechanism  50  (equivalent to the rotational speed Nm 2  of the motor MG 2  or the second motor shaft  55 ). In the alignment chart of  FIG. 9 , ρ denotes the gear ratio of the power distribution integration mechanism  40  (number of teeth of the sun gear  41 /number of teeth of the ring gear  42 ), and pr denotes the reduction gear ratio of the reduction gear mechanism  50  (number of teeth of the sun gear  51 /number of teeth of the ring gear  52 ). In  FIG. 9 , values above a O-axis (horizontal axis) and values below the O-axis respectively show positive rotational speeds and negative rotational speeds on the S-axis, the R-axis, the C-axis, and the 51-axis. Thick arrows on the axes represent torques applied to the corresponding elements; upward arrows show application of positive torques and downward arrows show application of negative torques. These definitions are similarly applied to the alignment charts of  FIGS. 3 through 8  explained above and the alignment charts of  FIGS. 10 and 11  explained later. 
     When the transmission  60  is set to the second change speed state during the drive of the hybrid vehicle  20  with operation of the engine  22 , the motors MG 1  and MG 2  may be driven and controlled to make the motor MG 1 , which is connected with the sun gear  41  of the power distribution integration mechanism  40  working as the output element, function as the motor and to make the motor MG 2 , which is connected with the carrier  45  working as the reactive element, function as the generator. In this state, the power distribution integration mechanism  40  distributes the power from the engine  22  input via the ring gear  42  at its gear ratio ρ into the sun gear  41  and the carrier  45 , while integrating the power from the engine  22  with the power from the motor MG 1  functioning as the motor and outputting the integrated power to the sun gear  41 . Hereafter, a mode of making the motor MG 2  function as the generator and making the motor MG 1  function as the motor is referred to as ‘second torque conversion mode’. In the second torque conversion mode, the power from the engine  22  goes through torque conversion by means of the power distribution integration mechanism  40  and the motors MG 1  and MG 2  and is then output to the sun gear  41 . The ratio of the rotational speed Ne of the engine  22  to the rotational speed of the sun gear  41  as the output element is varied continuously in a stepless manner by controlling the rotational speed of the motor MG 2 .  FIG. 10  is an explanatory view exemplifying an alignment chart showing a state of torques and rotational speeds of elements included in the power distribution integration mechanism  40  and the reduction gear mechanism  50  in the second torque conversion mode. 
     In the hybrid vehicle  20  of the embodiment, the first torque conversion mode and the second torque conversion mode are alternately switched over with a change of the change speed state (speed ratio) in the transmission  60 . Such switchover prevents the rotational speed Nm 1  or Nm 2  of the motor MG 1  or MG 2  functioning as the generator from having a negative value with an increase in rotational speed Nm 2  or Nm 1  of the motor MG 2  or MG 1  functioning as the motor. This effectively prevents the occurrence of power circulation in the first torque conversion mode, as well as the occurrence of power circulation in the second torque conversion mode. The power circulation in the first torque conversion mode is triggered by the negative rotational speed of the motor MG 1  and causes the motor MG 2  to consume part of the power output to the carrier shaft  45   a  and generate electric power, while causing the motor MG 1  to consume the electric power generated by the motor MG 2  and output driving power. The power circulation in the second torque conversion mode is triggered by the negative rotational speed of the motor MG 2  and causes the motor MG 1  to consume part of the power output to the first motor shaft  46  and generate electric power, while causing the motor MG 2  to consume the electric power generated by the motor MG 1  and output driving power. Such prevention of the power circulation desirably improves the power transmission efficiency in a wider drive range. The prevention of the power circulation also reduces the maximum required rotational speeds of the motors MG 1  and MG 2  and thereby enables size reduction of the motors MG 1  and MG 2 . In the hybrid vehicle  20  of the embodiment, the output power of the engine  22  can be mechanically (directly) transmitted to the driveshaft  69  at the fixed speed ratios uniquely set for the 1 st  speed-2 nd  speed simultaneous engagement state, the 2 nd  speed-3 rd  speed simultaneous engagement state, and the 3 rd  speed fixing state. This desirably increases the potential for mechanical output of the power from the engine  22  to the driveshaft  69  without conversion into electrical energy and thereby further enhances the power transmission efficiency in the wider drive range. In a general power output apparatus equipped with an engine, two motors, and a differential rotation mechanism such as a planetary gear mechanism, the relatively large reduction gear ratio between the engine and a driveshaft increases the potential for conversion of the engine output power into electrical energy. This undesirably decreases the power transmission efficiency and tends to cause heat generation in the motors MG 1  and MG 2 . The simultaneous engagement mode described above is thus especially advantageous for the relatively large reduction gear ratio between the engine  22  and the driveshaft  69 . 
     Next, a motor drive mode of the hybrid vehicle  20  will be described with reference to  FIG. 11 . In, the motor drive mode, at least one of the motors MG 1  and MG 2  is driven with supply of electric power from the battery  35  to output driving power while the engine  22  is stopped. In the hybrid vehicle  20  of the embodiment, the motor drive mode includes a clutch engagement one-motor drive mode, a clutch release one-motor drive mode, and a two-motor drive mode. In the clutch engagement one-motor drive mode, the clutch C 0  is engaged, and the transmission  60  is set in the first change speed state or the third change speed state to allow the power output from only the motor MG 2  or is set in the second change speed state to allow the power output from only the motor MG 1 . In the clutch engagement one-motor drive mode, the clutch C 0  is set to connect the sun gear  41  of the power distribution integration mechanism  40  with the first motor shaft  46 . Accordingly, the motor MG 1  or MG 2  in the state of no power output thus follows the motor MG 2  or MG 1  in the state of power output to run idle as shown by the broken line in  FIG. 11 . In the clutch release one-motor drive mode, the clutch C 0  is released, and the transmission  60  is set in the first change speed state or the third change speed state to allow the power output from only the motor MG 2  or is set in the second change speed state to allow the power output from only the motor MG 1 . In the clutch release one-motor drive mode, the clutch C 0  is released to disconnect the sun gear  41  from the first motor shaft  46 . As shown by the one-dot chain line and the two-dot chain line in  FIG. 11 , such disconnection effectively avoids a following rotation of the crankshaft  26  of the engine  22  that is stopped, as well as a following rotation of the motor MG 1  or MG 2  in the state of no power output, thereby preventing a decrease in power transmission efficiency. In the two-motor drive mode, the clutch C 0  is released, and at least one of the motors MG 1  and MG 2  is driven and controlled while the transmission  60  is set in the 1 st  speed-2 nd  speed simultaneous engagement state or the 2 nd  speed-3 rd  speed simultaneous engagement state by means of the brakes B 1  and B 2  and the clutch C 1 . Such setting and drive control effectively avoids the following rotation of the engine  22  and enables the power output from both the motors MG 1  and MG 2  and transmission of a large driving power to the driveshaft  69  in the motor drive mode. This two-motor drive mode is especially suitable for a hill start and ensures the favorable towing performance during the motor drive of the hybrid vehicle  20 . 
     In the hybrid vehicle  20  of the embodiment, the change speed state (speed ratio) of the transmission  60  can be readily changed to enable the efficient power transmission to the driveshaft  69  when the clutch release one-motor drive mode is selected. When the clutch C 0  is released and the transmission  60  is set in the first change speed state to allow the power output from only the motor MG 2  while fixing the ring gear  62  of the first change speed planetary gear mechanism PG 1  to the transmission case by means of the brake B 1 , for example, the motor MG 1  may be driven and controlled to make the rotational speed of the ring gear  66  of the second change speed planetary gear mechanism PG 2  approach to 0 so as to shift up the speed ratio of the transmission  60 . Then, the brake B 2  may be set to fix the ring gear  66  of the second change speed planetary gear mechanism PG 2  to the transmission case so as to set the transmission  60  in the above 1 st  speed-2 nd  speed simultaneous engagement state. Further, the brake B 1  may be released so as to release the ring gear  62  of the first change speed planetary gear mechanism PG 1  in the rotatable manner and to allow the power output from only the motor MG 1 , so that the transmission  60  can be set in the second change speed state to change the speed ratio in the shift up side (second speed). In order to shift up the speed ratio of the transmission  60  while the clutch C 0  is released and the transmission  60  is set in the second change speed state to allow the power output from only the motor MG 1 , the motor MG 2  is driven and controlled to synchronize the rotational speed of the ring gear  62  of the first change speed planetary gear mechanism PG 1  with the rotational speed of the carrier  64  (the driveshaft  69 ). Then, the clutch C 1  may be controlled to couple the ring gear  62  with the carrier  64  of the first change speed planetary gear mechanism PG 1  so as to shift the transmission  60  from the second change speed state to the 2 nd  speed-3 rd  speed simultaneous engagement state. Further, the brake B 2  may be released to release the ring gear  66  of the second change speed planetary gear mechanism PG 2  in the rotatable manner and to allow the power output from only the motor MG 2 , so that the transmission  60  can be set in the third change speed state to change the speed ratio in the shift up side (third speed). In the hybrid vehicle  20  of the embodiment, the transmission  60  is used to change the rotational speed of the carrier shaft  45   a  and the first motor shaft  46  and amplify the torque in the motor drive mode, thereby desirably reducing the maximum required torques of the motors MG 1  and MG 2  and enabling size reduction of the motors MG 1  and MG 2 . In the hybrid vehicle  20 , the simultaneous engagement mode or the two-motor drive mode is once performed when the speed ratio of the transmission  60  is changed during the motor drive. Accordingly, it is possible to prevent a torque loss upon the change of the speed ratio and to ensure an extremely smooth change of the speed ratio with causing no significant shock. 
     The speed ratio of the transmission  60  may be shifted down in the motor drive mode according to the procedure basically reverse to the above description. In response to an increase of a driving force demand or a decrease of the state of charge SOC of the battery  35  in the clutch engagement one-motor drive mode, the motor MG 1  or MG 2  to be made into the state of no power output corresponding to the setting of the speed ratio in the transmission  60  is driven and controlled to crank and start up the engine  22 . In response to the increase of the driving force demand or the decrease of the state of charge SOC of the battery  35  in the clutch release one-motor drive mode, on the other hand, the motor MG 1  or MG 2  in the state of no power output is driven and controlled to synchronize its rotational speed Nm 1  or Nm 2  with the rotational speed of the sun gear  41  or with the rotational speed of the carrier  45  in the power distribution integration mechanism  40 . After the clutch C 0  is engaged, the motor MG 1  or MG 2  is subsequently driven and controlled to crank and start up the engine  22 . The engine  22  can thus be started up with smooth power transmission to the driveshaft  69 . At the startup of the engine  22  in the two-motor drive mode, after selection of one of the motors MG 1  and MG 2  as a motor of continuously outputting power corresponding to a target speed ratio set in the transmission  60 , power conversion is performed to transmit the power of the other motor MG 2  or MG 1  of not continuously outputting power to the one motor MG 1  or MG 2  of continuously outputting power. On completion of the power conversion, the brake B 2  or the brake B 1  is released to disconnect the other motor MG 2  or MG 1  of not continuously outputting power from the transmission  60 . Then, the other motor MG 2  or MG 1  is driven and controlled to synchronize its rotational speed Nm 2  or Nm 1  with the rotational speed of the carrier  45  or with the rotational speed of the sun gear  41  in the power distribution integration mechanism  40 . Further, the clutch C 0  is engaged and the other motor MG 2  or MG 1  is driven and controlled to motor and start up the engine  22 . The engine  22  can thus be started up with smooth power transmission to the driveshaft  69 . 
     As has been described above, the hybrid vehicle  20  of the embodiment includes the transmission  60  equipped with the sun gear  61  connected with the carrier shaft  45   a  and the sun gear  65  connected with the first motor shaft  46  as the power input elements, and the carrier  64  connected with the driveshaft  69  as the power input element. The transmission  60  is capable of selectively transmitting power from the sun gears  61  and at predetermined respective speed ratios to the carrier  64  (driveshaft  69 ). The transmission  60  includes the transmission case  600  that houses the plurality of elements including the sun gears  61  and  65 , the carrier  64  and the like, the oil pan  605  defined in the lower portion within the transmission case  600  and storing the transmission oil capable at least of lubricating the constituents of the transmission  60 , the electromagnetic actuator  101  that is connected with the movable engagement member  151  and allows the connection between the ring gear  62  of the first change speed planetary gear mechanism PG 1  and the locking member  601  and the release of the connection, the electromagnetic actuator  102  that is connected with the movable engagement member  152  and allows the connection between the ring gear  66  of the second change speed planetary gear mechanism PG 2  and the locking member  602  and the release of the connection, the electromagnetic actuator  103  that is connected with the movable engagement member  153  and allows the connection between the fixing member  68  secured to the first motor shaft  46  and the locking member  603  and the release of the connection, and the electromagnetic actuator  104  that is connected with the movable engagement member  154  and allows the connection between the carrier  64  or the output element of the first change speed planetary gear mechanism PG 1  and the ring gear  62  or the fixable element of the mechanism PG 1  and the release of the connection. These electromagnetic actuators  101 - 104  are disposed in the oil pan  605  defined in the lower portion within the transmission case  600 . 
     As described above, each of the movable engagement members  151 - 154  capable of engaging with at least two corresponding elements is connected with a corresponding one of the electromagnetic actuators  101 - 104  disposed in the lower portion within the transmission case  600 . Thus, the whole of the transmission  60  can be configured to be compact in comparison with an apparatus including an electromagnetic actuator having a cylindrical shape. Further, lubricating function and shock absorbing function of the transmission oil ensure smooth operation of the electromagnetic actuators  101 - 104  and reduce operation noise of the electromagnetic actuators  101 - 104  by disposing the electromagnetic actuators  101 - 104  in place within the oil pan  605 . The whole body of the electromagnetic actuators  101 - 104  may be positioned below a fluid level of the transmission oil. A part of the body of the electromagnetic actuators  101 - 104  may be positioned above the fluid level of the transmission oil. That is, locations of the electromagnetic actuators  101 - 104  in the oil pan  605  may be selected in accordance with characteristics of the transmission oil so as to ensure smooth operation of the electromagnetic actuators  101 - 104  and reduce operation noise of the electromagnetic actuators  101 - 104 . 
     The electromagnetic actuators  101 - 104  include the actuator shaft  110  connected with a corresponding one of the movable engagement members  151 - 154  and movable in the predetermined direction, the permanent magnet  111  secured to the actuator shaft  110 , the couple of fixed magnetic poles  112  and  113  arranged so that the permanent magnet  111  is positioned between the fixed magnetic poles  112  and  113 , and the drive circuit  105  that changes the polarity of each of the fixed magnetic poles  112  and  113 . According to the electromagnetic actuators  101 - 104 , it is possible to release the magnetic coupling between the permanent magnet  111  and one of the fixed magnetic poles  112  and  113  and to move the actuator shaft  110  together with the movable engagement members  151 - 154  by changing the polarity of each of the fixed magnetic poles  112  and  113 . After the magnetic coupling between the permanent magnet  11  and the other of the fixed magnetic poles  112  and  113 , it is possible to readily and reliably retain the connection or the disconnection between the two elements by means of the movable engagement members  151 - 154  even if the setting of the polarity of each of the fixed magnetic poles  112  and  113  is released. Further, the shock absorbing function of the transmission oil favorably reduces noise due to a collision between the permanent magnetic  111  and the fixed magnetic pole  112  or  113  by disposing the electromagnetic actuator  101 - 104  in the oil chamber. 
     The transmission  60  includes the movable shaft  120  secured to the corresponding one of the movable engagement members  151 - 154  and connected with the actuator shaft  110 . In the embodiment, the actuator shaft  110  and the movable shaft  120  are arranged offset from each other. Thus, the electromagnetic actuators  101 - 104  can be flexibly disposed within the oil pan  605 , so that the whole of the transmission  60  including a plurality of sets of the movable engagement members  151 - 154  and the electromagnetic actuators  101 - 104  can be configured to be compact. In the embodiment, the actuator shaft  110  and the movable shaft  120  are respectively movable in the moving direction of the movable engagement members  151 - 154 . Further, the actuator shaft  110  and the movable shaft  120  are offset from each other in the direction orthogonal to the moving direction of the movable engagement members  151 - 154 . Thus, it is possible to smoothly move the movable engagement members  151 - 154  and to flexibly dispose the electromagnetic actuators  101 - 104  within the oil pan  605 . In the embodiment, the actuator shaft  110  and the movable shaft  120  are arranged offset from each other in the top to bottom direction in the figure that is the direction orthogonal to the moving direction (axial direction of the carrier shaft  45   a  and the first motor shaft  46 ) of the movable engagement member  151  (− 154 ). However, the present invention is not limited to this. As transmission  60 A shown in  FIG. 12 , the actuator shaft  110  and the movable shaft  120  may be arranged offset from each other in a width direction of the transmission case  600  (direction orthogonal to the sheet) that is the direction orthogonal to the moving direction of the movable engagement members  151 - 154  (axial direction of the carrier shaft  45   a  and the first motor shaft  46 ). Further, the both ends of the movable shaft  120  may be slidably supported by bearings  116 A and  117 A, thereby preventing the movable shaft  120  from inclining and smoothly moving the movable shaft  120  or the movable engagement member  151 - 154 . In the transmission  60  of the embodiment, the actuator shaft  120  and the corresponding one of the movable engagement members  151 - 154  are connected with each other via the connecting member  125 . Further, the connecting member  125  is formed so that the size of the portion secured to the movable shaft  120  is larger than the size of the portion secured to the movable engagement members  151 - 154 . Thus, rigidity of the securing portion between the movable shaft  120  and the connecting member  125  can be increased, thereby preventing the movable shaft  120  from inclining and smoothly moving the movable shaft  120  even if the movable engagement members  151 - 154  are formed as the relatively thin ring-shaped member. 
     In the transmission  60  of the embodiment, the actuator shaft  110  and the corresponding one of the movable engagement members  151 - 154  are connected each other via the movable shaft  120 . However, the present invention is not limited to this. As an electromagnetic actuator  101 A shown in  FIG. 13 , the actuator shaft  110  may be connected with the movable engagement member  151 (- 154 ) via the connecting member  125  without the movable shaft. In this configuration, as shown in  FIG. 13 , the bearing  117 A supports one end portion of the actuator shaft  110 . The one end portion is farther than the other end of the actuator shaft  110  from the permanent magnet  111 . Thus, it is possible to prevent the actuator shaft  110  from inclining and to smoothly move the actuator shaft  110  or the movable engagement members  151 - 154 . Further, in such a configuration, it may be possible to provide the function of the bearing to one of the fixed magnetic poles  112  and  113  and the coils  114  and  115 . In the electromagnetic actuator  101 A, the connecting member  125  may be formed so that so that the size of the portion secured to the actuator shaft  110  is larger than the size of the portion secured to the movable engagement members  151 - 154 . Thus, rigidity of the securing portion between the actuator shaft  110  and the connecting member  125  can be increased, thereby preventing the actuator shaft  110  from inclining and smoothly moving the actuator shaft  110  even if the movable engagement members  151 - 154  are formed as the relatively thin ring-shaped member. 
     The transmission  60  includes the three element-type first change speed planetary gear mechanism PG 1  and the three element-type second change speed planetary gear mechanism PG 2 . The transmission  60  can be arranged coaxially with and in the downstream (in the rear portion of the vehicle body) of the engine  22 , the motors MG 1  and MG 2 , and the power distribution integration mechanism  40 . The transmission  60  enables significant size reduction both in the axial direction and in the radial direction in comparison with the parallel shaft-type transmission. The power output apparatus of the embodiment including the engine  22 , the motors MG 1  and MG 2 , the power distribution integration mechanism  40 , and the transmission  60  is thus space-saving to be especially suitable for mounting on the rear-wheel drive hybrid vehicle  20 . In the hybrid vehicle  20 , the power distribution integration mechanism  40  is arranged coaxially with the motors MG 1  and MG 2  and is located between the motors MG 1  and MG 2  coaxially arranged with each other, thereby enabling size reduction of the motors MG 1  and MG 2  in the radial direction. Thus, the power output apparatus is accordingly small-sized and is specifically suitable for being mounted on the hybrid vehicle  20  of the rear-wheel drive-based system. The power distribution integration mechanism  40  constructed as the three element-type planetary gear mechanism allows the further size reduction and causes the power output apparatus to be small-size and suitable for being mounted on the vehicle. According to the transmission  60 , when the brake B 1  or the first fixation device fixes the ring gear  62  of the first change speed planetary gear mechanism PG 1  in the non-rotatable manner, the carrier  45  or the first element of the power distribution integration mechanism  40  works as the output element, the motor MG 2  connected with the carrier  45  works as the motor, and the motor MG 1  connected with the sun gear  41  or the second element of the power distribution integration mechanism  40  working as the reactive element works as the generator. Further, when the brake B 2  or the second fixation device fixes the ring gear  66  of the second change speed planetary gear mechanism PG 2  in the non-rotatable manner, the sun gear  41  or the second element of the power distribution integration mechanism  40  works as the output element, the motor MG 1  connected with the sun gear  41  works as the motor, and the motor MG 2  connected with the carrier  45  or the first element of the power distribution integration, mechanism  40  working as the reactive element works as the generator. The hybrid vehicle  20  adequately controlled to change the fixation of the ring gear  62  of the first change speed planetary gear mechanism PG 1  and the fixation of the ring gear  66  of the second change speed planetary gear mechanism PG 2 . Accordingly, the hybrid vehicle  20  effectively prevents the occurrence of the power circulation by retaining the rotational speed Nm 1  or Nm 2  of the motor MG 1  or MG 2  functioning as the generator at a positive value in response to the increase in rotational speed Nm 2  or Nm 1  of the motor MG 2  or MG 1  functioning as the motor. Further, when the brakes B 1  and B 2  of the transmission  60  fix the ring gear  62  and  66  of the first and second change speed planetary gear mechanism PG 1  and PG 2 , the power from the engine  22  can be mechanically transmitted to the driveshaft  69  at the fixed speed ratio. Accordingly, the hybrid vehicle  20  has the improved power transmission efficiency in a wider drive range, thereby ensuring the enhanced fuel efficiency and the improved driving performance. 
     The transmission  60  includes the clutch C 1  or the change-speed connecting-disconnecting device configured to allow the connection between the carrier  64  or the output element and the ring gear  62  or the fixable element of the first change speed planetary gear mechanism PG 1  and the release of the connection. Accordingly, when the carrier  64  and the ring gear  62  of the first change speed planetary gear mechanism PG 1  are connected with each other while fixing the ring gear  66  or the fixable element of the second change speed planetary gear mechanism PG 2  in the non-rotatable manner by the brake B 2 , the transmission  60  is set in the 2 nd  speed-3 rd  speed simultaneous engagement state. In the 2 nd  speed-3 rd  speed simultaneous engagement state, the power from the engine  22  can be mechanically transmitted to the driveshaft  69  at the fixed speed ratio different from the speed ratio of the 1 st  speed-2 nd  speed simultaneous engagement state of fixing both the ring gear  62  of the first change speed planetary gear mechanism PG 1  and the ring gear  66  of the second change speed planetary gear mechanism PG 2  in the non-rotatable manner by the brake B 1  and B 2 . When the brake B 2  is released to release the ring gear  66  of the second change speed planetary gear mechanism PG 2  in the rotatable manner in the 2 nd  speed-3 rd  speed simultaneous engagement state, the elements of the first change speed planetary gear mechanism PG 1  is substantially locked and integrally rotate, so that the power from the carrier  45  or the first element of the power distribution integration mechanism  40  can be directly transmitted to the driveshaft  69 . Thus, the hybrid vehicle  20  has the improved power transmission efficiency in a wider drive range. The transmission  60  may include a clutch capable of a connection between the carrier  64  or the output element and the ring gear  66  or the fixable element of the second change speed planetary gear mechanism PG 2  and a release of the connection. 
     In the hybrid vehicle of the embodiment, the transmission  60  includes the brake B 3  or the third fixation device capable of fixing the sun gear  41  or the second element of the power distribution integration mechanism  40 . The sun gear  41  (reactive element) or the second element of the power distribution integration mechanism  40  that connected with the motor MG 1  working as the generator may be fixed when the transmission  60  is set in the third change speed state by connecting the carrier  64  or the output element with the ring gear  62  or the fixable element of the first change speed planetary gear mechanism PG 1 . Thus, the power from the engine  22  can be mechanically transmitted to the driveshaft  69  at the fixed speed ratio different from the fixed speed ratio of the 1 st  speed-2 nd  speed simultaneous engagement state of fixing both the ring gear  62  of the first change speed planetary gear mechanism PG 1  and the ring gear  66  of the second change speed planetary gear mechanism PG 2  in the non-rotatable manner by the brakes B 1  and B 2  and from the fixed speed ratio of the 2 nd  speed-3 rd  speed simultaneous engagement state of coupling the ring gear  62  of the first change speed planetary gear mechanism PG 1  with the carrier  64 . Accordingly, the hybrid vehicle  20  has the improved power transmission efficiency in a wider drive range. The brake B 3  or the third fixation device may be configured to fix the carrier  45  or the first element of the power distribution integration mechanism  40  when the transmission  60  includes the clutch capable of the connection between the carrier  64  or the output element and the ring gear  66  or the fixable element of the second change speed planetary gear mechanism PG 2  and a release of the connection. The brake  83  may be separated from the transmission  60 . 
     The hybrid vehicle  20  of the embodiment includes the clutch C 0  that connects and disconnects the sun gear shaft  41   a  with and from the first motor shaft  46 , that is, connects and disconnects the sun gear  41  with and from the motor MG 1 . When the clutch C 0  is released to disconnect the sun gear shaft  41   a  from the first motor shaft  46 , the function of the power distribution integration mechanism  40  causes the engine  22  to be substantially separated from the motors MG 1  and MG 2  and the transmission  60 . Thus, the power from at least one of the motors MG 1  and MG 2  can be transmitted to the driveshaft  69  with high efficiency with the change of the speed ratio of the transmission  60  when the clutch C 0  is release and the engine  22  is stopped in the hybrid vehicle  20 . Accordingly, the hybrid vehicle  20  desirably decreases the maximum torques required for the motors MG 1  and MG 2  and thereby allows size reduction of the motors MG 1  and MG 2 . The clutch C 0  is not restricted to the structure of connecting and disconnecting the sun gear  41  with and from the motor MG 1 . The clutch C 0  may be configured to connect and disconnect the carrier  45  (first element) with and from the carrier shaft  45   a  (motor MG 2 ) or may be configured to connect and disconnect the crankshaft  26  of the engine  22  with and from the ring gear  42  (third element). 
     The hybrid vehicle  20  of the embodiment is equipped with the power output apparatus that includes the engine  22 , the motors MG 1  and MG 2 , the power distribution integration mechanism  40 , and the transmission  60  and is configured to drive the rear wheels RWa and RWb with the power from the driveshaft  69 . This power output apparatus is small-sized and is especially suitable for the hybrid vehicle  20  of the rear-wheel drive-based system, while improving the power transmission efficiency in the wider driving range. The hybrid vehicle  20  of the above configuration accordingly has both the high fuel consumption and the good driving performance. The first and second change speed planetary gear mechanism PG 1  and PG 2  may be a double pinion planetary gear mechanism. The hybrid vehicle  20  of the embodiment may be constructed as a rear wheel drive-based four wheel drive vehicle. In the embodiment, the power output apparatus is mounted on the hybrid vehicle  20 . The power output apparatus of the invention is, however, not restrictively mounted on the hybrid vehicle, but may be mounted on diversity of moving bodies including various automobiles and other vehicles, boats and ships, and air craft or may be built in stationary equipment including construction machinery. 
       FIG. 14  is a schematic block diagram of a clutch  200  in a modified example of the power transmitting apparatus according to the invention. The clutch  200  shown in  FIG. 14  is configured to selectively connect a first rotating shaft (first rotating element)  201  and a second rotating shaft (second rotating element)  202  coaxial with the first rotating shaft  201  to a third rotating shaft (third rotating element)  203 . The clutch  200  is a dog clutch that includes a first engagement portion  210  provided in the first rotating shaft  201 , a second engagement portion  220  provided in the second rotating shaft  202  to be spaced from the first engagement portion  210 , a third engagement portion  230  provided in the third rotating shaft  203  to be located around the first and second engagement portions  210  and  220 , a first movable engagement member  251  capable of engaging with both the first and third engagement portions  210  and  230  and moving in an axial direction thereof, a second movable engagement member  252  capable of engaging with both the second and third engagement portions  220  and  230  and moving in an axial direction thereof, a first electromagnetic actuator  101 A connected with the first engagement member  251  via a connecting member  125 , and a second electromagnetic actuator  102 A connected with the second engagement member  252  via a connecting member  125 . In the above clutch  200 , the movable engagement members  251  and  252  are connected with a corresponding one of the electromagnetic actuators  101 A and  102 A which are respectively disposed in the lower portion within the transmission case  600 , so that the whole of the apparatus can be configured to be compact in comparison with the apparatus including the electromagnetic actuator having the cylindrical shape. Further, lubricating function and shock absorbing function of the transmission oil ensure smooth operation of the electromagnetic actuators  101 A and  102 A and reduce operation noise of the electromagnetic actuators  101 A and  102 A by disposing the electromagnetic actuators  101 A and  102 A in place within the oil pan  605 . In the clutch  200 , the first and second rotating shafts  201  and  202  may be defined as the power input elements and the third rotating shaft  203  may be defined as the power output element. Further, in the clutch  200 , the third rotating shaft  203  may be defined as the power input element and the first and second rotating shafts  201  and  202  may be defined as the power output elements. 
       FIG. 15  is a schematic block diagram of a clutch  300  in a modified example of the power transmitting apparatus according to the invention. The clutch  300  shown in  FIG. 15  is also configured to selectively connect a first rotating shaft (first rotating element)  301  and a second rotating shaft (second rotating element)  302  coaxial with the first rotating shaft  301  to a third rotating shaft (third rotating element)  303 . The clutch  300  is a dog clutch that includes a first engagement portion  310  provided in the first rotating shaft  301 , a second engagement portion  320  provided in the second rotating shaft  302 , a third engagement portion  330  provided in the third rotating shaft  303  and having a flange portion  331  that faces with the second engagement portion  320 , a first movable engagement member  351  capable of engaging with both the first and third engagement portions  310  and  330 , a second movable engagement member  352 , a first electromagnetic actuator  101 A connected with the first engagement member  351  via a connecting member  125 , and a second electromagnetic actuator  102 A connected with the second engagement member  352  via a connecting member  125 . The movable engagement portion  352  includes a sliding portion  354  slidably supported by the third rotating shaft  303 , an engagement portion  356  engaging with the second engagement portion  320  at a side near to the rotating shaft  302  rather than the flange portion  331 , and connecting portion  358  connecting the siding portion  354  with the engagement portion  356  and having a projection  358   b  that is inserted into a hole portion  332  of the flange portion  331 . In the above clutch  300 , the movable engagement members  351  and  352  are also connected with a corresponding one of the electromagnetic actuators  101 A and  102 A which are respectively disposed in the lower portion within the transmission case  600 , so that the whole of the apparatus can be configured to be compact in comparison with the apparatus including the electromagnetic actuator having the cylindrical shape. Further, lubricating function and shock absorbing function of the transmission oil ensure smooth operation of the electromagnetic actuators  101 A and  102 A and reduce operation noise of the electromagnetic actuators  101 A and  102 A by disposing the electromagnetic actuators  101 A and  102 A in place within the oil pan  605 . In the clutch  300 , the first and second rotating shafts  301  and  302  may be defined as the power input elements and the third rotating shaft  303  may be defined as the power output element. Further, in the clutch  300 , the third rotating shaft  303  may be defined as the power input element and the first and second rotating shafts  301  and  302  may be defined as the power output elements. 
     There may be many modifications, changes, and alterations without departing from the scope or spirit of the main characteristics of the present invention. The scope and spirit of the present invention are indicated by the appended claims, rather than by the foregoing description. 
     INDUSTRIAL APPLICABILITY 
     The technique of the invention is preferably applied to the manufacturing industries of a power transmitting apparatus.