Patent Publication Number: US-8118704-B2

Title: Vehicle and control method of vehicle

Description:
This is a 371 national phase application of PCT/JP2008/050899 filed 23 Jan. 2008, claiming priority to Japanese Patent Application No. JP 2007-015485 filed 25 Jan. 2007, the contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to a vehicle and a control method of the vehicle. 
     BACKGROUND ART 
     A proposed configuration of a vehicle includes an engine, a planetary gear mechanism constructed to have a carrier linked with an crankshaft of the engine and a ring gear linked with drive wheels, a first motor linked with a sun gear of the planetary gear mechanism, a second motor linked with the ring gear, and a battery arranged to transfer electric power to and from the first motor and the second motor (see, for example, Patent Document 1). According to the vehicle, in response to a starting demand of the engine when the vehicle is parked, a lock position is first set based on a rotational position of the rotor of the second motor, for example, is selected as one of six. The ring gear is locked by the flow of electric current through two, phases corresponding to the set lock position among three phases to form the fixed magnetic field on a stator of the second motor. After locking the ring gear, the engine is motored by means of the first motor and started. This arrangement prevents occurrence of a shock or a tremor when the engine is started. 
     Patent Document 1: Japanese Patent Laid-Open No. 2006-81324 
     DISCLOSURE OF THE INVENTION 
     In a vehicle equipped with a multistage transmission located between the ring gear of the planetary gear mechanism and an axle of the vehicle in addition to the above hardware configuration, at a gearshift position set to a parking position, the ring gear is generally disconnected from the axle by means of the multistage transmission, while the axle is locked. In this state, restriction of rotation of the ring gear is demanded for reduction of the shock when the ring gear is connected to the drive wheels by means of the multistage transmission in response to the setting of the gearshift position of a gearshift lever from the parking position to a driving position, and for cancellation of a torque applied to the ring gear while the engine is motored by means of the first motor to be started or stopped or while the engine is operated. The ring gear may be unable to be locked with a sufficient level due to insufficient flow of the electric current through the second motor depending on a state of the second motor or a state of the battery. It is, however, demanded to prevent the rotation of the ring gear in this occasion. 
     In a vehicle of the invention equipped with an internal combustion engine, a motoring structure, and a transmission unit configured to allow and prohibit a transmission of power with a change in speed between a rotating shaft connected with a motor and an axle of the vehicle, and a control method of such the vehicle, the object of the invention is to enable restriction of rotation of the rotating shaft while engine is motored and started at a gearshift position set to a parking position. In the vehicle of the invention equipped with the transmission and the control method of such the vehicle, the another object of the invention is to enable restriction of rotation of the rotating shaft in consideration of at least one of a state of the motor and a state of the accumulator unit . 
     At least part of the above and the other related demands is attained by a vehicle of the invention and a control method of the vehicle having the configurations discussed below. 
     According to one aspect, the present invention is directed to a vehicle. The vehicle comprises: an internal combustion engine; a motoring structure connected with an output shaft of the internal combustion engine and a rotating shaft and configured to perform a motoring of the internal combustion engine while outputting power to the rotating shaft; a motor that has a rotor connected with the rotating shaft and drives and rotates the rotor by a rotating magnetic field formed on a stator to input and output the power from and to the rotating shaft; an accumulator unit that transfers electric power to and from the motoring structure and the motor; a transmission unit configured to allow and prohibit transmission of power with a change in speed between the rotating shaft and an axle of the vehicle; and a control module configured to, in response to a starting instruction of the internal combustion engine at a gearshift position set to a parking position, control the motor to fix a direction of a magnetic field formed on the stator with a level that is capable of restricting rotation of the rotating shaft against a shaft driving force defined as driving force applied to the rotating shaft within a driving force range set based on at least one of a state of a motor system including the motor and a state of the accumulator unit, control the motoring structure to perform a motoring of the internal combustion engine while outputting driving force that makes the shaft driving force within the driving force range, and control the internal combustion engine to be started with the motoring by the motoring structure. 
     In response to a starting instruction of the internal combustion engine at a gearshift position set to a parking position, the vehicle according to this aspect of the invention controls the motor to fix a direction of a magnetic field formed on the stator with a level that is capable of restricting rotation of the rotating shaft against a shaft driving force defined as driving force applied to the rotating shaft within a driving force range set based on at least one of a state of a motor system including the motor and a state of the accumulator unit, controls the motoring structure to perform a motoring of the internal combustion engine while outputting driving force that makes the shaft driving force within the driving force range, and controls the internal combustion engine to be started with the motoring by the motoring structure. At the gearshift position set to the parking position, an axle of the vehicle is generally locked and the transmission unit separates the rotating shaft from the axle of the vehicle. In response to a starting instruction of the internal combustion engine at a state that the rotating shaft is separated from the axle, the vehicle of this aspect of the invention performs the motoring of the engine and starts the engine while the motoring structure outputs the driving force that makes the shaft driving force within the driving force range that enables restriction of rotation of the rotating shaft by means of the motor. This arrangement effectively prevents rotation of the rotating shaft. Additionally, the vehicle of this aspect of the invention sets the driving force range based on the at least one of the state of the motor system and the state of the accumulator unit. This arrangement effectively prevents rotation of the rotating shaft based on the driving force range set in consideration of these states. The terminology ‘motoring system’ in specification hereof includes a drive circuit for driving the motor, as well as the motor. 
     In one preferable application of the vehicle of the invention, the driving force range is set to a narrower range when a temperature of the motor system is more than a preset temperature than a range that is set when the temperature of the motor system is less than or equal to the preset temperature. An electric current flowing through the motor is comparatively small when the temperature of the motor system is relatively high, in the case of applying an increasing electric current through the motor with an increase of the driving force range. Therefore, the vehicle of the application enables suppression of an excessive increase of the temperature of the motor system. Additionally, the vehicle performs the motoring of the engine while the motoring structure outputs the driving force that makes the shaft driving force within the driving force range. The vehicle of the application effectively prevents rotation of the rotating shaft even when the electric current flowing through the motor is relatively decreased. In this application, the vehicle further has: a temperature rise estimating module configured to estimate that the temperature of the motor system may rise over the preset temperature. The driving force range is set to a narrower range when the temperature rise estimating module estimates the temperature of the motor system may rise over the preset temperature than a range that is set when the temperature rise estimating module does not estimate that the temperature of the motor system may rise over the preset temperature. The vehicle of this application more effectively enables suppression of the excessive increase of the temperature of the motor system. 
     In another preferable application of the vehicle of the invention, the driving force range is set to a narrower range when a discharge power from the accumulator unit is over a preset electric power based on an output limit of the accumulator unit than a range that is set when the discharge power from the accumulator unit is less than or equal to the preset electric power. An electric current flowing through the motor is comparatively small when the discharge power from the accumulator unit is over the preset electric power, in the case of applying an increasing electric current through the motor with an increase of the driving force range. Therefore, the vehicle of the application enables suppression of an excessive increase of the discharge power from the accumulator unit. Additionally, the vehicle performs the motoring of the engine while the motoring structure outputs the driving force that makes the shaft driving force within the driving force range. The vehicle of the application effectively prevents rotation of the rotating shaft even when the electric current flowing through the motor is relatively decreased. In this application, the vehicle further has: an electric power excess estimating module configured to estimate that the discharge power from the accumulator unit may exceed the preset electric power. The driving force range is set to a narrower range when the electric power excess estimating module estimates that the discharge power from the accumulator unit may exceed the preset electric power than a range that is set when the electric power excess estimating module does not estimate that the discharge power from the accumulator unit may exceed the preset electric power. The vehicle of this application more effectively enables suppression of the excessive increase of the discharge power from the accumulator unit. 
     In one preferable embodiment of the vehicle of the invention, the control module sets a target driving force to be output from the motoring structure, calculates an estimated shaft driving force estimated to be applied to the rotating shaft based on the target driving force, and sets the driving force range based on the estimated shaft driving force and at least one of the state of the motor system and the state of the accumulator unit. 
     In another preferable embodiment of the vehicle of the invention, the control module controls the motoring structure to output the driving force that makes the driving force applied to the rotating shaft within a second driving force range that is narrower than the driving force range. The vehicle of this application more effectively enables restriction of rotation of the rotating shaft. 
     In one preferable structure of the vehicle of the invention, the motoring structure is an electric power-mechanical power input output structure that is connected with the rotating shaft and with the output shaft of the internal combustion engine to enable rotation independently of the rotating shaft and inputs and outputs power into and from the output shaft and the rotating .shaft through input and output of electric power and mechanical power. In this structure, the electric power-mechanical power input output structure includes: a three shaft-type power input output assembly connected with three shafts, the rotating shaft, the output shaft and a third shaft and designed to input and output power to a residual shaft based on powers input from and output to any two shafts among the three shafts; and a generator configured to input and output power from and to the third shaft. 
     According to another aspect, the present invention is directed to a control method of a vehicle. The vehicle comprises: an internal combustion engine; a motoring structure connected with an output shaft of the internal combustion engine and a rotating shaft and configured to perform a motoring of the internal combustion engine while outputting power to the rotating shaft; a motor that has a rotor connected with the rotating shaft and drives and rotates the rotor by a rotating magnetic field formed on a stator to input and output the power from and to the rotating shaft; an accumulator unit that transfers electric power to and from the motoring structure and the motor; and a transmission unit configured to allow and prohibit transmission of power with a change in speed between the rotating shaft and an axle of the vehicle. In response to a starting instruction of the internal combustion engine at a gearshift position set to a parking position, the control method controls the motor to fix a direction of a magnetic field formed on the stator with a level that is capable of restricting rotation of the rotating shaft against a shaft driving force defined as driving force applied to the rotating shaft within a driving force range set based on at least one of a state of a motor system including the motor and a state of the accumulator unit, controls the motoring structure to perform a motoring of the internal combustion engine while outputting driving force that makes the shaft driving force within the driving force range, and controls the internal combustion engine to be started with the motoring by the motoring structure. 
     In response to a starting instruction of the internal combustion engine at a gearshift position set to a parking position, the control method of the vehicle according to this aspect of the invention controls the motor to fix a direction of a magnetic field formed on the stator with a level that is capable of restricting rotation of the rotating shaft against a shaft driving force defined as driving force applied to the rotating shaft within a driving force range set based on at least one of a state of a motor system including the motor and a state of the accumulator unit, controls the motoring structure to perform a motoring of the internal combustion engine while outputting driving force that makes the shaft driving force within the driving force range, and controls the internal combustion engine to be started with the motoring by the motoring structure. At the gearshift position set to the parking position, axle is generally locked and the transmission unit separates the rotating shaft from the axle of the vehicle. In response to a starting instruction of the internal combustion engine at a state that the rotating shaft is separated from the axle, the control method of the vehicle of this aspect of the invention performs the motoring of the engine and starts the engine while the motoring structure outputs the driving force that makes the shaft driving force within the driving force range that enables restriction of rotation of the rotating shaft by means of the motor. This arrangement effectively prevents rotation of the rotating shaft. Additionally, the control method of the vehicle of this aspect of the invention sets the driving force range based on the at least one of the state of the motor system and the state of the accumulator unit. This arrangement effectively prevents rotation of the rotating shaft based on the driving force range set in consideration of these. The terminology ‘motoring system’ in specification hereof includes a drive circuit for driving the motor, as well as the motor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  schematically illustrates the configuration of a hybrid vehicle  20  in a first embodiment of the invention; 
         FIG. 2  schematically shows the structure of an electric driving system centered on motors MG 1  and MG 2  and battery  50 ; 
         FIG. 3  is a flowchart showing a parking position start control routine executed by the hybrid electronic control unit  70 ; 
         FIG. 4  is a flowchart showing a torque command setting routine; 
         FIG. 5  is an alignment chart showing torque-rotation speed dynamics of the rotational elements included in the power distribution integration mechanism  30 ; 
         FIG. 6  shows the rotation restriction control; 
         FIG. 7  shows one example of a correction coefficient setting map; 
         FIG. 8  shows one example of a correction coefficient setting map; 
         FIG. 9  is a flowchart showing a rotation restriction control torque reception second motor control routine; 
         FIG. 10  schematically illustrates the configuration of another hybrid vehicle  120  in one modified example. 
     
    
    
     BEST MODES OF CARRYING OUT THE INVENTION 
     One mode of carrying out the invention is described below as a preferred embodiment. 
       FIG. 1  schematically illustrates the configuration of a hybrid vehicle  20  in one embodiment of the invention. As illustrated, the hybrid vehicle  20  of the embodiment includes an engine  22 , a three shaft-type power distribution integration mechanism  30  that is linked to a crankshaft  26  or an output shaft of the engine  22  via a damper  28 , a motor MG 1  that is linked to the power distribution integration mechanism  30  and has power generation capability, a motor MG 2  that is linked to a ring gear shaft  32   a  or a rotating shaft connected to the power distribution integration mechanism  30 , a transmission  60  that converts power of the ring gear shaft  32   a  and outputs the converted power to a driveshaft  36  connected to drive wheels  39   a  and  39   b , a parking lock mechanism  90  that locks the drive wheels  39   a  and  39   b , and a hybrid electronic control unit  70  that controls the operations of the whole hybrid vehicle  20 . 
     The engine  22  is an internal combustion engine that uses a hydrocarbon fuel, such as gasoline or light oil, to output power. An engine electronic control unit (hereafter referred to as engine ECU)  24  receives signals from diverse sensors that detect operating conditions of the engine  22 , and takes charge of operation control of the engine  22 , for example, fuel injection control, ignition control, and intake air flow regulation. The engine ECU  24  communicates with the hybrid electronic control unit  70  to control operations of the engine  22  in response to control signals transmitted from the hybrid electronic control unit  70  while outputting data relating to the operating conditions of the engine  22  to the hybrid electronic control unit  70  according to the requirements. 
     The power distribution and integration mechanism  30  has a sun gear  31  that is an external gear, a ring gear  32  that is an internal gear and is arranged concentrically with the sun gear  31 , multiple pinion gears  33  that engage with the sun gear  31  and with the ring gear  32 , and a carrier  34  that holds the multiple pinion gears  33  in such a manner as to allow free revolution thereof and free rotation thereof on the respective axes. Namely the power distribution and integration mechanism  30  is constructed as a planetary gear mechanism that allows for differential motions of the sun gear  31 , the ring gear  32 , and the carrier  34  as rotational elements. The carrier  34 , the sun gear  31 , and the ring gear  32  in the power distribution and integration mechanism  30  are respectively coupled with the crankshaft  26  of the engine  22 , the motor MG 1 , and the ring gear shaft  32   a  as the rotating shaft. While the motor MG 1  functions as a generator, the power output from the engine  22  and input through the carrier  34  is distributed into the sun gear  31  and the ring gear  32  according to the gear ratio. While the motor MG 1  functions as a motor, on the other hand, the power output from the engine  22  and input through the carrier  34  is combined with the power output from the motor MG 1  and input through the sun gear  31  and the composite power is output to the ring gear  32 . The power output to the ring gear  32  is thus finally transmitted to the drive wheels  39   a  and  39   b  via the transmission  60 , the driveshaft  36 , and the differential gear  38  from ring gear shaft  32   a.    
       FIG. 2  shows the schematic structure of an electric drive system including the motors MG 1  and MG 2  and battery  50  on the hybrid vehicle  20 . As shown in  FIGS. 1 and 2 , the motors MG 1  and MG 2  respectively have rotors  45   a  and  46   a  with permanent magnets attached thereto and stators  45   b  and  46   b  with three phase coils wound thereon. The motors MG 1  and MG 2  are constructed as known synchronous motor generators that may be actuated both as a generator and as a motor. The motors MG 1  and MG 2  transmit electric power to and from a battery  50  via inverters  41  and  42 . Each of the inverters  41  and  42  includes six transistors T 1  to T 6  or T 7  to T 12  and six diodes D 1  to D 6  or D 7  to D 12  connected in inverse parallel with the transistors T 1  to T 6  or T 7  to T 12 . The six transistors T 1  to T 6  or T 7  to T 12  are arranged in pairs to function as the source and the sink to a positive bus connecting with a cathode of the battery  50  and to a negative bus connecting with an anode of the battery  50 . Three phase coils (U phase, V phase, and W phase) of the motor MG 1  or MG 2  are connected to the connection points of the respective pairs of transistors T 1  to T 6  or T 7  to T 12 . Regulation of the ratio of ON time of the respective pairs of the transistors T 1  to T 6  or T 7  to T 12  forms a rotating magnetic field in the three phase coils to drive and rotate the motor MG 1  or MG 2 . Power lines  54  connecting the battery  50  with the inverters  41  and  42  are structured as common positive bus and negative bus shared by the inverters  41  and  42 . 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  50  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  50  is neither charged nor discharged upon the balance of the input and output of electric powers between the motors MG 1  and MG 2 . The operations of both the motors MG 1  and MG 2  are controlled by a motor electronic control unit (hereafter referred to as motor ECU)  40 . The motor ECU  40  is constructed as a microprocessor including a CPU  40   a , a ROM  40   b  for storage of processing programs, a RAM  40   c  for temporary storage of data, an input port, an output port, and a communication port (not shown). The motor ECU  40  inputs signals required for driving and controlling the motors MG 1  and MG 2 , for example, signals representing rotational positions θm 1  and θm 2  of the rotors  45   a  and  46   a  in the motors MG 1  and MG 2  from rotational position detection sensors  43  and  44  and phase currents Iu 1 , Iv 1 , Iu 2  and Iv 2  flowing through U phases and V phases of the three phase coils in the motors MG 1  and MG 2  from current sensors  45 U,  45 V,  46 U and  46 V. The motor ECU  40  outputs switching control signals to the transistors T 1  to T 6  included in the inverter  41  and to the transistors T 7  to T 12  included in the inverter  42 . The motor ECU  40  establishes communication with the hybrid electronic control unit  70  to drive and control the motors MG 1  and MG 2  in response to control signals received from the hybrid electronic control unit  70  and to output data regarding the operating conditions of the motors MG 1  and MG 2  to the hybrid electronic control unit  70  according to the requirements. 
     The transmission  60  has brakes and clutches (not shown) and is constructed to couple and decouple the ring gear shaft  32   a  or the rotating shaft with and from the driveshaft  36  and to change the rotation speed of the ring gear shaft  32   a  at four speeds in the coupled state of the two shafts and transmit the changed speed to the driveshaft  36 . 
     The parking lock mechanism  90  has a parking gear  92  attached to the driveshaft  36  and a parking lock pole  94  engaging with the parking gear  92  to lock the parking gear  92  in its rotation stop state. The parking lock pole  94  is actuated by an actuator (not shown), which is driven and controlled by the hybrid electronic control unit  70  in response to input of a gearshift signal from another gear position to a parking position or a gearshift signal from the parking position to another gear position. The parking lock pole  94  is engaged with and disengaged from the parking gear  92  to enable and release the parking lock. The driveshaft  36  is mechanically linked to the drive wheels  39   a  and  39   b . The parking lock mechanism  90  thus indirectly locks the drive wheels  39   a  and  39   b.    
     The battery  50  is under control of a battery electronic control unit (hereafter referred to as battery ECU)  52 . The battery ECU  52  receives diverse signals required for control of the battery  50 , for example, an inter-terminal voltage Vb measured by a voltage sensor  51   a  disposed between terminals of the battery  50 , a charge-discharge current Ib measured by a current sensor  51   b  attached to the power line  54  connected with the output terminal of the battery  50 , and a battery temperature Tb measured by a temperature sensor  51   c  attached to the battery  50 . The battery ECU  52  outputs data relating to the state of the battery  50  to the hybrid electronic control unit  70  via communication according to the requirements. The battery ECU  52  calculates a state of charge SOC of the battery  50 , based on the accumulated charge-discharge current measured by the current sensor, for control of the battery  50 . 
     The hybrid electronic control unit  70  is constructed as a microprocessor including a CPU  72 , a ROM  74  that stores processing programs, a RAM  76  that temporarily stores data, and a non-illustrated input-output port, and a non-illustrated communication port. The hybrid electronic control unit  70  receives various inputs via the input port: a temperature αm 2  of the motor MG 2  from a temperature sensor  47  that measures a temperature of the motor MG 2 , an ignition signal from an ignition switch  80 , a gearshift position SP from a gearshift position sensor  82  that detects the current position of a gearshift lever  81 , an accelerator opening Acc from an accelerator pedal position sensor  84  that measures a step-on amount of an accelerator pedal  83 , a brake pedal position BP from a brake pedal position sensor  86  that measures a step-on amount of a brake pedal  85 , and a vehicle speed V from a vehicle speed sensor  88 . The hybrid electronic control unit  70  outputs, via its output port, driving signals to the actuator for the brakes and clutches (not shown) of the transmission  60  and driving signals to the actuator (not shown) for the parking lock mechanism  90 . The hybrid electronic control unit  70  communicates with the engine ECU  24 , the motor ECU  40 , and the battery ECU  52  via the communication port to transmit diverse control signals and data to and from the engine ECU  24 , the motor ECU  40 , and the battery ECU  52 , as mentioned previously. 
     In the hybrid vehicle  20  of the embodiment, the gearshift position SP of the gearshift lever  81  detected by the gearshift position sensor  82  has multiple different options: parking position (P position), neutral position (N position), drive position (D position) for forward drive of the vehicle, and reverse position (R position) for reverse drive of the vehicle. At the gearshift position of the gearshift lever  81  set to the parking position, the brakes and clutches (not shown) of the transmission  60  are released to disconnect the ring gear shaft  32   a  or the rotating shaft from the driveshaft  36 . 
     The hybrid vehicle  20  of the embodiment thus constructed calculates a torque demand to be output to the ring gear shaft  32   a  functioning as the rotating shaft, based on observed values of a vehicle speed V and an accelerator opening Acc, which corresponds to a driver&#39; s step-on amount of an accelerator pedal  83 . The engine  22  and the motors MG 1  and MG 2  are subjected to operation control to output a required level of power corresponding to the calculated torque demand to the ring gear shaft  32   a . The operation control of the engine  22  and the motors MG 1  and MG 2  selectively effectuates one of a torque conversion drive mode, a charge-discharge drive mode, and a motor drive mode. The torque conversion drive mode controls the operations of the engine  22  to output a quantity of power equivalent to the required level of power, while driving and controlling the motors MG 1  and MG 2  to cause all the power output from the engine  22  to be subjected to torque conversion by means of the power distribution integration mechanism  30  and the motors MG 1  and MG 2  and output to the ring gear shaft  32   a . The charge-discharge drive mode controls the operations of the engine  22  to output a quantity of power equivalent to the sum of the required level of power and a quantity of electric power consumed by charging the battery  50  or supplied by discharging the battery  50 , while driving and controlling the motors MG 1  and MG 2  to cause all or part of the power output from the engine  22  equivalent to the required level of power to be subjected to torque conversion by means of the power distribution integration mechanism  30  and the motors MG 1  and MG 2  and output to the ring gear shaft  32   a , simultaneously with charge or discharge of the battery  50 . The motor drive mode stops the operations of the engine  22  and drives and controls the motor MG 2  to output a quantity of power equivalent to the required level of power to the ring gear shaft  32   a.    
     The description regards the operations of the hybrid vehicle  20  of the embodiment having the configuration discussed above, especially a series of operation control at the gearshift position of the gearshift lever  81  set to the parking position.  FIG. 3  is a flowchart showing a parking position start control routine executed by the hybrid electronic control unit  70 . This routine is triggered by a starting instruction of the engine  22  at the gearshift position of the gearshift lever  81  set to the parking position. 
     In the parking position start control routine, the CPU  72  of the hybrid electronic control unit  70  first inputs various data required for control, that is, the temperature αm 2  of the motor MG 2  from the temperature sensor  47 , a rotation speed Ne of the engine  22 , a discharge power Pb from the battery  50  and an output limit Wout of the battery  50  (step S 100 ). The rotation speed Ne of the engine  22  is computed from a signal output from a crank position sensor (not shown) attached to the crankshaft  26  and is input from the engine ECU  24  by communication. The discharge power Pb is calculated as the product of the inter-terminal voltage Vb measured by the voltage sensor  51   a  and the charge-discharge current Ib measured by the current sensor  51   b  and is input from the battery ECU  52  by communication. The output limit Wout of the battery  50  is set based on the battery temperature Tb measured by the temperature sensor  51   c  and the state of charge SOC of the battery  50  and is input from the battery ECU  52  by communication. 
     After the data input, the CPU  72  sets a torque command Tm 1 * of the motor MG 1  or a motoring torque for performing a motoring of the engine  22  (step S 110 ). This torque command Tm 1 * of the motor MG 1  in this embodiment is set by means of a torque command setting routine. This routine is shown in the flowchart of  FIG. 4  and executed by the hybrid electronic control unit  70  in parallel with the parking position start control routine of  FIG. 3 . The details of the torque command setting routine of  FIG. 4  is described with suspension of the description of the parking position start control routine of  FIG. 3 . 
     In the torque command setting routine, the CPU  72  first sets the torque command Tm 1 * of the motor MG 1  to 0 (step S 300 ). The CPU  72  then performs the processing of setting the torque command Tm 1 * with an increase of the torque command Tm 1 * by an increasing rate Tup until the torque command Tm 1 * of the motor MG 1  reaches a maximum torque Tm 1 max (steps S 310  and S 320 ). When the torque command Tm 1 * of the motor MG 1  reaches more than or equal to the maximum torque Tm 1 max, the CPU  72  sets the torque command Tm 1 * of the motor MG 1  to the maximum torque Tm 1 max (step S 330 ), inputs the rotation speed Ne of the engine  22  (step S 335 ), waits for the rotation speed Ne of the engine  22  to reach more than or equal to a predetermined reference value Nref (step S 340 ). The increasing rate Tup is the extent of increasing the torque command Tm 1 * and is determined according to a time interval at which the processing of increasing the torque command Tm 1 * by the increasing rate Tup is repeatedly executed. The maximum torque Tm 1 max is set as a torque that is capable of performing the motoring of the engine  22  to the rotation speed more than or equal to the predetermined reference value Nref, and is determined according to the characteristics of the engine  22  and the motor MG 1 . The predetermined reference value Nref is the rotation speed that fuel injection control and ignition control is started. When the rotation speed Ne of the engine  22  reaches the predetermined reference value Nref (step S 340 ), the CPU  72  performs the processing of setting the torque command Tm 1 * with a decrease of the torque command Tm 1 * by a decreasing rate Tdown until the torque command Tm 1 * of the motor MG 1  reaches less than or equal to 0 (steps S 350  and S 360 ). When the torque command reaches less than or equal to 0, the CPU  72  sets the torque command Tm 1 * of the motor MG 1  to 0 (step S 370 ), waits for complete explosive combustion of the engine  22  (step  380 ). Upon complete explosive combustion of the engine  22 , the torque command setting routine is terminated. The decreasing rate Tdown is the extent of decreasing the torque command Tm 1 * and is determined according to a time interval at which the processing of decreasing the torque command Tm 1 * by the decreasing rate Tdown is repeatedly executed. 
     The explanation of the parking position start control routine of  FIG. 3  is resumed. After setting the torque command Tm 1 * of the motor MG 1  at step S 110 , the CPU  72  calculates a estimated shaft torque Trest, that is, a torque estimated to be applied to the ring gear shaft  32   a  or the rotating shaft when a torque corresponding to the torque command Tm 1 * is output from the motor MG 1 , from the torque command Tm 1 * and a gear ratio ρ of the power distribution integration mechanism  30  according to Equation (1) given below (step S 120 ):
 
 T rest=− Tm 1*/ρ  (1)
 
The alignment chart of  FIG. 5  shows torque-rotation speed dynamics of the rotational elements included in the power distribution integration mechanism  30  at the time when the motoring of the engine  22  is performed by means of the motor MG 1 . The left axis ‘S’ represents a rotation speed of the sun gear  31  that is equivalent to the rotation speed Nm 1  of the motor MG 1 . The middle axis ‘C’ represents a rotation speed of the carrier  34  that is equivalent to the rotation speed Ne of the engine  22 . The right axis ‘R’ represents a rotation speed of ring gear  32  (ring gear shaft  32   a ) that is equivalent to the rotation speed Nm 2  of the motor MG 2 . A thick arrow on the axis ‘R’ respectively shows a torque applied to the ring gear shaft  32   a  by the torque Tm 1  output from the motor MG 1 . Equation (1) is readily introduced from the alignment chart.
 
     Then the CPU  72  sets a rotation restriction control torque Tm 2  to the sum of the absolute value of the estimated shaft torque Trest and a predetermined torque ΔT (step S 130 ). The rotation restriction control torque Tm 2  is a torque that is used for setting the value of the electric current required to flow through three phase coils of the motor MG 2  while the CPU  72  performs control for restricting rotation of the rotor  46   a  (the ring gear shaft  32   a  or the rotating shaft) of the motor MG 2  by fixing a direction of a magnetic field formed on the stator  46   b  (hereafter referred to as rotation restriction control). This rotation restriction control torque Tm 2  in the embodiment is set more than or equal to 0. As the predetermined torque ΔT, it is possible to use magnitude equal to or slightly more than magnitude of a torque, which might be applied to the ring gear shaft  32   a  by means of an inertia of a rotating system comprising the engine  22  and the motor MG 1  or by means of disturbances when the engine  22  is motored and started by means of the motor MG 1 . The predetermined torque ΔT is experimentally determined.  FIG. 6  shows the rotation restriction control. When the motor MG 2  is controlled, as shown in  FIG. 6 , a composite magnetic field (shown by the thick arrow of solid line) is formed on the stator  46   b  of the motor MG 2  as combination of the magnetic fields formed respectively on the U phase, the V phase, and the W phase with application of electric currents. In the rotation restriction control, the motor MG 2  is controlled to prohibit rotation of this composite magnetic field. This composite magnetic field that does not rotate is hereafter referred to as fixed magnetic field. When the direction of the fixed magnetic field is identical with the direction of the magnetic field formed by the permanent magnets on the rotor  46   a  of the motor MG 2  (that is, the direction of the axis ‘d’ in the d-q coordinate system), no torque is output from the motor MG 2  to the ring gear shaft  32   a  or the rotating shaft. The torque applied to the ring gear shaft  32   a  rotates the rotor  46   a  to deviate the current direction of the magnetic field of the rotor  46   a  (the direction of the axis ‘d’) from the direction of the fixed magnetic field formed on the stator  46   b . A torque depending on the deviation of the current direction of the magnetic field of the rotor  46   a  from the fixed magnetic field formed on the stator  46   b  is then applied to the rotor  46   a  to make the current direction of the magnetic field of the rotor  46   a  substantially match with the fixed magnetic field formed on the stator  46   b  (hereafter this torque is referred to as suction torque). The rotor  46   a  stops at the position where the torque applied to the ring gear shaft  32   a  is balanced with the suction torque. The suction torque increases with an increase of the deviation of the current direction of the magnetic field of the rotor  46   a  from the direction of the fixed magnetic field within a range of an electric angle of π/2, and increases with an increase of the electric current flowing through three phase coils of the stator  46   b  to form the fixed magnetic field. The rotation restriction control torque Tm 2  is used to determine the value of an electric current required to flow through three phase coils. In the embodiment, the value of the electric current is set to increase with an increase of the rotation restriction control torque Tm 2  and is set to be capable of preventing rotation of the ring gear shaft  32   a  against the torque applied to the ring gear shaft  32   a  at magnitude that is less than or equal to the rotation restriction control torque Tm 2  (within the range of a torque −Tm 2  to a torque Tm 2 ). When the torque corresponding to the torque command Tm 1 * is output from the motor MG 1 , the torque applied to the ring gear shaft  32   a  is within the range of the torque −Tm 2  to the torque Tm 2 . Therefore, applying the electric current corresponding to such set electric current through the three phase coils of the stator  46   b  of the motor MG 2  enables restriction of rotation of the ring gear shaft  32   a . The details of such control of the motor MG 2  will be described later. In the d-q coordinate system, the axis ‘d’ represents the direction of the magnetic field formed by the permanent magnets attached to the rotor  46   a , and the axis ‘q’ represents the direction advanced from the axis ‘d’ by an electrical angle of π/2. 
     The CPU  72  sets a rotation restriction control torque limit Tm 2 lim based on the temperature αm 2  of the motor MG 2  and the discharge power Pb from the battery  50  (step S 140 ). The rotation restriction control torque limit Tm 2 lim in this embodiment is set as the product of a basic value Tm 2 limtmp, a correction coefficient k 1  based on the temperature αm 2  of the motor MG 2 , and a correction coefficient k 2  based on the discharge power Pb from the battery  50 . The relation between the temperature αm 2  of the motor MG 2  and the correction coefficient k 1  is shown in  FIG. 7 . The relation between the discharge power Pb and the correction coefficient k 2  is shown in  FIG. 8 . The correction coefficient k 1  in  FIG. 7  is set to 1 when the temperature αm 2  of the motor MG 2  is not higher than a predetermined temperature αm 2 ref, and is set to decrease to 0 with an increase of the temperature αm 2  when the temperature αm 2  is higher than the predetermined temperature αm 2 ref. As the predetermined temperature αm 2 ref, it is possible to use a temperature equal to or slightly less than a predetermined allowable temperature of the motor MG 2 . The correction efficient k 2  in  FIG. 8  is set to 1 when the discharge power Pb from the battery  50  is equal to or less than a predetermined electric power Pbref, and is set to decrease to 0 with an increase of excess of the discharge power Pb over the predetermined power Pbref when the discharge power Pb is more than the predetermined electric power Pbref. As the determined power Pbref, it is possible to use the power corresponding to or slightly less than the output limit Wout of the battery  50 . By such the setting of the correction coefficient k 1  and the correction coefficient k 2 , the rotation restriction control torque limit Tm 2 lim is set to the basic value Tm 2 limtmp when the temperature αm 2  of the motor MG 2  is not higher than the predetermined temperature αm 2 ref and the discharge power Pb is equal to or less than the predetermined electric power Pbref, and is set to the value, depending on the temperature αm 2  of the motor MG 2  and the discharge power Pb from the battery  50 , less than the basic value Tm 2 limtmp when the temperature αm 2  of the motor MG 2  is higher than the predetermined temperature or when the discharge power Pb is more than the predetermined electric power pbref. The reason why the rotation restriction control torque limit Tm 2 lim is set in such the way will be described later. 
     After setting the rotation restriction control torque limit Tm 2 lim, the CPU  72  compares the rotation restriction control torque Tm 2  with the rotation restriction control torque limit Tm 2 lim (step S 150 ). The comparison of the rotation restriction control torque Tm 2  with the rotation restriction control torque limit Tm 2 lim is the processing for determining whether execution of the rotation restriction control with the use of the rotation restriction control torque Tm 2  set at step S 130  is permitted or not, in consideration of the temperature αm 2  of the motor MG 2  and the discharge power Pb from the battery  50  when the torque corresponding to the torque command Tm 1 * is output from the motor MG 1 . When the rotation restriction control torque Tm 2  is equal to or less than, the rotation restriction control torque limit Tm 2 lim, it is determined that executing the rotation restriction control with the use of the rotation restriction control torque Tm 2  set at step S 130  is permitted. The CPU  72  then sends the torque command Tm 1 * of the motor MG 1  and the rotation restriction control torque Tm 2  to the motor ECU  40  (step s 190 ). The motor ECU  40  receives the settings of the torque command Tm 1 * and the rotation restriction control torque Tm 2 , performs switching control of switching elements included in the inverter  41  to drive the motor MG 1  with the torque command Tm 1 *, executes a rotation restriction control torque reception second motor control routine shown in  FIG. 9  described below. The motor MG 1  is controlled to output the torque corresponding to the torque command Tm 1 *, that is, the torque that makes the torque (−Tm 1 */ρ) applied to the ring gear shaft  32   a  within the range of the torque −Tm 2  to the torque Tm 2 . The motor MG 2  is controlled to enable to prevent rotation of the ring gear shaft  32   a  against the torque applied to the ring gear shaft  32   a  within the range of the torque −Tm 2  to the torque Tm 2 . This arrangement effectively prevents rotation of the ring gear shaft  32   a  when the engine  22  is motored and started by means of the motor MG 1 . 
     When the rotation restriction control torque Tm 2  is more than the rotation restriction control torque limit Tm 2 lim, on the other hand, the CPU  72  sets the rotation restriction control torque limit Tm 2 lim as the rotation restriction control torque Tm 2  again (step S 160 ). The CPU  72  subsequently calculates a torque limit Tm 1 lim of the motor MG 1  from the set rotation restriction control torque Tm 2 , the predetermined torque ΔT and the gear ratio ρ of the power distribution integration mechanism  30  according to Equation (2) given below (step S 170 ):
 
 Tm 1 lim =( Tm 2−Δ T )·ρ  (2)
 
     The CPU  72  then limits the torque command Tm 1 * of the motor MG 1  set at step S 110  to the range between the lower torque limit −Tm 1 lim and the upper torque limit Tm 1 lim to set the torque command Tm 1 * again (step S 180 ). The CPU  72  sends the set torque command Tm 1 * and the set rotation restriction control torque Tm 2  to the motor ECU  40  (step S 190 ). The CPU  72  sets the rotation restriction control torque Tm 2  to the rotation restriction control torque limit Tm 2 lim reflecting the temperature αm 2  of the motor MG 2  and the discharge power Pb from the battery  50 , at step  160  again. Such setting enables suppression of an excessive increase of the temperature αm 2  of the motor MG 2  and an excessive increase of the discharge power Pb from the battery  50 . The CPU  72  also sets the torque command Tm 1 * that makes a torque applied to the ring gear shaft  32   a  or the rotating shaft within the range (the range of a torque (−Tm 2 +ΔT) to a torque (Tm 2 −ΔT)), which is narrower than the range (the range of the torque −Tm 2  to the torque Tm 2 ) corresponding to the rotation restriction control torque Tm 2  equal to the rotation restriction control torque limit Tm 2 lim, at the steps S 170  and S 180  again. Such setting enables restriction of rotation of the ring gear shaft  32   a  at the time when the engine  22  is motored by means of the motor MG 1 . 
     The CPU  72  compares the rotation speed Ne of the engine  22  with the predetermined reference value Nref (step S 200 ). When the rotation speed Ne of the engine  22  has not yet reached the predetermined reference value Nref, the parking position start control routine goes back to step S 100 . When the rotation speed Ne of the engine  22  has reached the predetermined reference value Nref by the motoring of the engine  22  with the torque output from the motor MG 1  (step S 200 ), the CPU  72  sends the instruction of fuel injection control and ignition control to the engine ECU  24  (step S 210 ). The engine ECU  24  receives the instruction and performs the fuel injection control and the ignition control of the engine  22 . The CPU  72  identifies complete or incomplete explosive combustion of the engine  22  (step S 220 ). Upon identification of incomplete explosive combustion of the engine  22 , the parking position start control routine goes back to step S 100 . Upon identification of complete explosive combustion of the engine  22 , the parking position start control routine is then terminated. 
     The description regards the rotation restriction control torque reception second motor control routine that is executed by the motor ECU  40  and is shown in  FIG. 9 . This routine is triggered by receiving the rotation restriction control torque Tm 2  from the hybrid electronic control unit  70 . In the rotation restriction control torque reception second motor control routine, the CPU  40   a  of the motor ECU  40  first inputs various data required for control, that is, the phase currents Iu 2  and Iv 2  flowing through the U phase and the V phase of the three-phase coils from the current sensors  46 U and  46 V, and the rotation restriction control torque Tm 2  (step S 400 ). The rotation restriction control torque Tm 2  is set at the parking position start control and is input from the hybrid electronic control unit  70 . 
     The CPU  40   a  identifies the value of the flag G (step S 410 ). Upon identification of the flag G equal to 0, the CPU  40   a  inputs the rotational position θm 2  of the rotor  46   a  in the motor MG 2  from the rotational position detection sensor  44  (step S 420 ). Then The CPU  40   a  calculates an electric angle θe 2  based on the rotational position θm 2  of the rotor  46   a  in the motor MG 2  (step S 430 ), sets the calculated electric angle as the control electric angle θeset (step S 440 ), sets flag G to 1 (step S 250 ). After setting flag G to 1, the processing of step S 420  to S 450  is skipped. Flag G is set to 0 as initial value and is set to 1 in response to the setting of the control electric angle θeset. The processing of step S 420  to S 450  sets the control electric angle θeset from the rotational position θm 2  of the rotor  46   a  in the motor MG 2  at the time when this routine is first executed by a starting instruction of the engine  22  at the gearshift position SP set to the parking position. 
     The input phase currents Iu 2  and Iv 2  are converted to electric currents Id 2  and Iq 2  on an axis ‘d’ and an axis ‘q’ by coordinate conversion (three phase-to-two phase conversion) according to Equation (3) given below with the control electric angle θeset upon assumption that the sum of the phase currents Iu 2 , Iv 2 , and Iw 2  flowing through the U phase, the V phase, and the W phase of the three-phase coils in the motor MG 2  is equal to 0 (step S 460 ): 
     
       
         
           
             
               
                 
                   
                     [ 
                     
                       
                         
                           
                             Id 
                             ⁢ 
                             
                                 
                             
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                             ⁢ 
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                   = 
                   
                     
                       
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                                 sin 
                                 ⁡ 
                                 
                                   ( 
                                   
                                     
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                                 sin 
                                 ⁡ 
                                 
                                   ( 
                                   
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                                 cos 
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                       [ 
                       
                         
                           
                             
                               Iu 
                               ⁢ 
                               
                                   
                               
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     The CPU  40   a  then sets the electric current command Id 2 * of the axis ‘d’ at the control electric angle θeset based on the rotation restriction control torque Tm 2  and sets the electric current command Iq 2 * of the axis ‘q’ to 0 (step S 470 ). The electric current command Id 2 * in this embodiment is set to increase with an increase of the rotation restriction control torque Tm 2 , and is set to be capable of preventing rotation of the ring gear shaft  32   a  against the torque applied to the ring gear shaft  32   a  at magnitude that is less than or equal to the rotation restriction control torque Tm 2  (within the range of the torque −Tm 2  to the torque Tm 2 ). 
     After setting the electric current commands Id 2 * and Iq 2 *, the CPU 40   a  calculates a voltage commands Vd 2 * and Vq 2 * of the axis ‘d’ and the axis ‘q’ in the motor MG 2  from the set electric current commands Id 2 * and Iq 2 * and the phase currents Id 2  and Iv 2  according to Equations (4) and (5) given below (step S 480 ):
 
 Vd 2*= k 1( Id 2*− Id 2)+Σ k 2( Id 2*− Id 2)  (4)
 
 Vq 2*= k 3( Iq 2*− Iq 2)+Σ k 4( Iq 2*− Iq 2)  (5)
 
     The voltage commands Vd 2 * and Vq 2 * of the axis ‘ d’ and the axis ‘ q’ are converted to voltage commands Vu 2 *, Vv 2 *, and Vw 2 * to be applied to the U phase, the V phase, and the W phase of the three-phase coils in the motor MG 2  by coordinate conversion (two phase-to-three phase conversion) according to Equations (6) and (7) given below (step S 490 ): 
                     [           Vu   ⁢           ⁢     2   *                 Vv   ⁢           ⁢     2   2             ]     =           2   3       ⁡     [           cos   ⁡     (     θ   ⁢           ⁢   eset     )             -     sin   ⁡     (     θ   ⁢           ⁢   eset     )                   cos   ⁡     (       θ   ⁢           ⁢   eset     -       2   ⁢           ⁢   π     3       )             -     sin   ⁡     (       θ   ⁢           ⁢   eset     -       2   ⁢           ⁢   π     3       )               ]       ⁡     [           Vd   ⁢           ⁢     2   *                 Vq   ⁢           ⁢     2   *             ]               (   6   )                 Vw   ⁢           ⁢     2   *       =       Vu   ⁢           ⁢     2   *       -     Vv   ⁢           ⁢     2   *                 (   7   )               
The CPU  40   a  converts the voltage commands Vu 2 *, Vv 2 *, and Vw 2 * after the coordinate conversion into a PWM signal for switching transistors T 7  to T 12  of the inverter  42  (step S 500 ), and outputs the converted PWM signal to transistors T 7  to T 12  of the inverter  42  to control the operations of the motor MG 2  (step S 510 ). The rotation restriction control reception second motor control routine is then terminated. In Equations (4) and (5), ‘k 1 ’ and ‘k 3  ’ represent proportionality coefficients, and ‘k 2 ’ and ‘k 4 ’ represent integral coefficients.
 
     As described above, in response to a starting instruction of the engine  22  at the gearshift position SP set to the parking position, the hybrid vehicle  20  of the embodiment controls the motor MG 2  to form the fixed magnetic field on the stator  46   b  of the motor MG 2  with a level that is capable of restricting rotation of the ring gear shaft  32   a  or the rotating shaft against the torque applied to the ring gear shaft  32   a  at magnitude that is less than or equal to the rotation restriction control torque Tm 2  based on the temperature αm 2  of the motor MG 2  and the discharge power Pb from the battery  50  (within the range of the torque −Tm 2  to the torque Tm 2 ), controls the motor MG 1  to perform the motoring of the engine  22  while outputting the torque that makes magnitude of the torque applied to the ring gear shaft  32   a  to magnitude less than or equal to magnitude of a torque (Tm 2 −ΔT), and controls the engine  22  to be started with the motoring by means of the motor MG 1 . This arrangement effectively prevents rotation of the ring gear shaft  32   a . Additionally, when the temperature αm 2  of the motor MG 2  is higher than the predetermined temperature αm 2 ref and when the discharge power Pb from the battery  50  is more than the predetermined electric power Pbref, the rotation restriction control torque Tm 2  is set to be smaller than the rotation restriction control torque Tm 2  that is set when the temperature αm 2  of the motor MG 2  is not higher than the predetermined temperature αm 2 ref and the discharge power Pb is not more than the predetermined electric power Pbref. This arrangement enables suppression of an excessive increase of the temperature αm 2  of the motor MG 2  and an excessive increase of the discharge power Pb from the battery  50 . 
     In the hybrid vehicle  20  of the embodiment, the rotation restriction control torque Tm 2  is set within the range less than or equal to the rotation restriction control torque limit Tm 2 lim that is set based on the temperature αm 2  of the motor MG 2  and the discharge power Pb from the battery  50 . The rotation restriction control torque Tm 2  may be set within the range less than or equal to the rotation restriction control torque limit Tm 2 lim that is set based on either the temperature αm 2  of the motor MG 2  or the discharge power Pb from the battery  50 . The rotation restriction control torque Tm 2  may be directly set based on at least one of the temperature αm 2  of the motor MG 2  and the discharge power Pb from the battery  50 . 
     In the hybrid vehicle  20  of the embodiment, when the temperature αm 2  of the motor MG 2  is higher than the predetermined temperature αm 2 ref, the correction coefficient k 1  is set to linearly decrease to 0 with the increase of the temperature αm 2  of the motor MG 2 . The correction coefficient k 1  may be set to a specific value (for example, 0.5) or to decrease step by step to 0 with the increase of the temperature αm 2  of the motor MG 2  when the temperature αm 2  of the motor MG 2  is higher than the predetermined temperature αm 2 ref. In the hybrid vehicle  20  of the embodiment, when the discharge power Pb from the battery  50  is more than the predetermined electric power Pbref, the correction efficient k 2  is set to linearly decrease to 0 with an increase of the discharge power Pb from the battery  50 . The correction coefficient k 2  may be set to a specific value (for example, 0.5) or to decrease step by step to 0 with the increase of the discharge power Pb from the battery  50  when the discharge power Pb is more than the predetermined electric power Pbref. 
     In the hybrid vehicle  20  of the embodiment, the rotation restriction control torque limit Tm 2 lim is set to based on the temperature αm 2  of the motor MG 2 . The rotation restriction control torque limit Tm 2 lim may alternatively be set based on a temperature of the inverter  42  or a temperature of the cooling water for cooling the motor MG 2  and the inverter  42 . 
     In the hybrid vehicle  20  of the embodiment, when the temperature αm 2  of the motor MG 2  is higher than the predetermined temperature αm 2 ref or when the discharge power Pb from the battery  50  is more than the predetermined power Pbref, the rotation restriction control torque Tm 2  is set to be smaller than the rotation restriction control torque Tm 2  that is set when the temperature αm 2  of the motor MG 2  is not higher than the predetermined temperature αm 2 ref and the discharge power Pb is not more than the predetermined electric power Pbref. When the CPU  72  estimates that the temperature αm 2  of the motor MG 2  may rise over the predetermined temperature αm 2 ref or when the CPU  72  estimates that the discharge power Pb from the battery  50  may exceed the predetermined electric power Pbref, even when the temperature αm 2  of the motor MG 2  is not higher than the predetermined temperature αm 2 ref and the discharge power Pb is not more than the predetermined electric power Pbref, the rotation restriction control torque Tm 2  may be set be smaller than the rotation restriction control torque Tm 2  that is set when the CPU  72  does not estimate these. This arrangement more effectively enables suppression of the excessive increase of the temperature αm 2  of the motor MG 2  and suppression of the excessive increase of the discharge power Pb from the battery  50 , because the rotation restriction control torque Tm 2  has been set to be relatively small from before the temperature αm 2  of the motor MG 2  rises over the predetermined temperature αm 2 ref or from before the discharge power Pb from the battery  50  exceeds the predetermined electric power Pbref. Whether the temperature αm 2  of the motor MG 2  may rise over the predetermined temperature αm 2 ref, for example, may be estimated based on the change of the temperature αm 2  of the motor MG 2  or the electric current flowing through the three phase coils of the stator  46   b  of the motor MG 2 . Whether the discharge power Pb from the battery  50  may exceed the predetermined electric power, for example, may be estimated based on the torque command Tm 1 * of the motor MG 1  or the rotation restriction control torque Tm 2 . 
     In the hybrid vehicle  20  of the embodiment, at step S 130  in the parking position start control shown in  FIG. 3 , the rotation restriction control torque Tm 2  is set to the torque that is higher by the predetermined torque ΔT than the estimated shaft torque Trest that is estimated to be applied to the ring gear shaft  32   a  or the rotating shaft at the time when the motor MG 1  outputs the torque corresponding to the torque command Tm 1 *. At steps S 170  and S 180  in  FIG. 3 , the torque command Tm 1 * of the motor MG 1  is set to the torque that magnitude of the torque applied to the ring gear shaft  32   a  is smaller by the predetermined torque ΔT than the rotation restriction control torque Tm 2 . At step S 130 , the rotation restriction control torque Tm 2  may be set to a torque equal to magnitude of the estimated shaft torque Trset. At steps S 170  and S 180 , the torque command Tm 1 * of the motor MG 1  may be set to a torque that makes a torque applied to the ring gear shaft  32   a  equal to the rotation restriction control torque Tm 2 . At steps S 170  and S 180 , the torque command Tm 1 * of the motor MG 1  may be set by using the torque limit Tm 1 lim of the motor MG 1  calculated from the rotation restriction control torque Tm 2 , the predetermined torque ΔT and the gear ratio ρ of the power distribution integration mechanism  30  according to Equation (8) given below, in place of Equation (2) above. In this case, the estimated torque Trest is within the range of a torque (−Tm 2 +ΔT 2 /ρ) to a torque (Tm 2 −ΔT 2 /ρ). Therefore, this arrangement effectively prevents rotation of the ring gear shaft  32   a . The value ‘ΔT 2 /ρ’ may be a value corresponding to the predetermined torque ΔT above.
 
 Tm 1 lim=Tm 2·ρ−Δ T 2  (8)
 
     In the hybrid vehicle  20  of the embodiment, the motor MG 2  is constructed as a three phase alternating current motor. The motor MG 2  may be constructed a multiphase (not three phase) alternating current motor. 
     In the hybrid vehicle  20  of the embodiment, the motor ECU  40  sets the electric angle θe 2  calculated at the time starting the motoring of the engine  22  as the control electric angle θeset. The control electric angle θeset is, however, not restrictively the electric angle θe 2  calculated at the time starting the motoring of the engine  22 . For example, the motor ECU  40  may sets the electric angle θe 2  calculated before starting the motoring of the engine  22  as the control electric angle θeset. 
     In the hybrid vehicle  20  of the embodiment, the CPU  40   a  sets the electric current command Id 2 * of the axis ‘d’ at the control electric angle θeset based on the rotation restriction control torque Tm 2  and sets the electric current command Iq 2 * of the axis ‘q’ to 0. The technique of the invention is applicable to fixing the direction of the magnetic field of the stator  46   b  of the motor by means of applying an electric current based on the rotation restriction control torque, to the motor MG 2 . The CPU  40   a  may control the motor MG 2  without three phase-to-two phase conversion. 
     The hybrid vehicle  20  of the embodiment adopts the transmission  60  that has four speeds for the gear change. The number of speeds for the gear change is, however, not restricted to the four speeds. The transmission may have any number of speeds that is not less than 2 for the gear change. 
     In the hybrid vehicle  20  of the embodiment, the power of the engine  22  is output via the power distribution integration mechanism  30  to the ring gear shaft  32   a  or the rotating shaft connected via the transmission  60  to the driveshaft  36  linked with the drive wheels  39   a  and  39   b . The technique of the invention is also applicable to a hybrid vehicle  120  of another modified structure shown in  FIG. 10 , which is equipped with a pair-rotor motor  130 . The pair-rotor motor  130  includes an inner rotor  132  connected to a crankshaft  26  of an engine  22  and an outer rotor  134  connected to a rotating shaft  32   b  that is linked via a transmission  60  to a driveshaft  36  for outputting power to drive wheels  39   a  and  39   b . The pair-rotor motor  130  transmits part of the output power of the engine  22  to the drive wheels  39   a  and  39   b  via the rotating shaft  32   b , the transmission  60 , and the driveshaft  36 , while converting the residual engine output power into electric power. 
     The embodiment regards application of the invention to the hybrid vehicle. This application is, however, only illustrative and not restrictive in any sense. The technique of the invention may be actualized by diversity of other applications, for example, various vehicles including automobiles and other vehicles as well as control methods of such various vehicles. 
     The primary elements in the embodiment and its modified examples are mapped to the primary constituents in the claims of the invention as described below. The engine  22  of the embodiment corresponds to the ‘internal combustion engine’ of the invention. The power distribution integration mechanism  30  and the motor MG 1  of the embodiment corresponds to the ‘motoring structure’ of the invention. The power distribution integration mechanism  30  includes the carrier  34  linked to the crankshaft  26  of the engine  22 , and the ring gear  32  linked to the ring gear shaft  32   a  or the rotating shaft. The motor MG 1  is connected to the sun gear  31  of the power distribution integration mechanism  30 . The motor MG 2  of the embodiment corresponds to the ‘motor’ of the invention. The motor MG 2  has a rotor  46   a  connected to the ring gear shaft  32   a  or the rotating shaft and drives and rotates the rotor  46   a  by the rotating magnetic field formed on the stator  46   b  to input and output the power from and to ring gear shaft  32   a . The battery  50  of the embodiment corresponds to the ‘accumulator unit’ of the invention. The battery  50  transfers electric power to and from the motors MG 1  and MG 2 . The transmission  60  of the embodiment corresponds to the ‘transmission unit’ of the invention. The transmission  60  allows and prohibits a transmission of power with a change in speed between the ring gear shaft  32   a  and the drive shaft  36  linked to the drive wheels  39   a  and  39   b . The motor ECU  40 , the hybrid electronic control unit  70  and the engine ECU  24  of the embodiment correspond to the ‘control module’ of the invention. In response to a starting instruction of the engine  22  at the gearshift position SP set to the parking position, the hybrid electronic control unit  70  executes the processing of setting the rotation restriction control torque Tm 2  based on the temperature αm 2  of the motor MG 2  and the discharge power Pb from the battery  50 , the processing of setting the torque command Tm 1 * of the motor MG 1  within the range at which magnitude of the torque applied to the ring gear shaft  32   a  is less than or equal to the rotation restriction control torque Tm 2 , and the processing of instructing fuel injection control and ignition control when the rotation speed Ne of the engine  22  has reached the predetermined reference Nref with the motoring of the engine  22 . The motor ECU  40  receives the rotation restriction control torque Tm 2  from the hybrid electronic control unit  70  and controls the motor MG 2  by applying the electric current, which is capable of preventing rotation of the ring gear shaft  32   a  against a torque applied to the ring gear shaft  32   a  at magnitude more than or equal to magnitude of the rotation restriction control torque Tm 2  (a torque within the range of the torque −Tm 2  to the torque Tm 2 ), through the motor MG 2 . The motor ECU  40  controls the motor MG 1  based on the motor command Tm 1 *. The engine ECU  24  performs fuel the injection control and the ignition control according to the instruction from the hybrid electronic control unit  70 . This mapping of the primary elements in the embodiment and its modified examples to the primary constituents in the claims of the invention are not restrictive in any sense but are only illustrative for concretely describing some modes of carrying out the invention. Namely the embodiment and its modified examples discussed above are to be considered in all aspects as illustrative and not restrictive. The scope and spirit of the present invention are indicated by the appended claims, rather than by the foregoing description. 
     The embodiment and its modified examples discussed above are to be considered in all aspects as illustrative and not restrictive. There may be many other modifications, changes, and alterations without departing from the scope or spirit of the main characteristics of the present invention. 
     Industrial Applicability 
     The principle of the present invention is preferably applied to the manufacturing industries of vehicles.