Abstract:
Provided are a vehicle, control method, and computer program with which reliable starting is possible without modifying hardware. When a clutch is disconnected, an inverter determines whether the time period in which the absolute value of the rotational speed of a motor becomes a predetermined first threshold or less and the torque of the motor becomes a predetermined second threshold or greater has continuously equaled or exceeded a predetermined third threshold. When the clutch is disconnected and it is determined that the time period in which the absolute value of the rotational speed of the motor becomes the predetermined first threshold or less and the torque of the motor becomes the predetermined second threshold or greater has continuously equaled or exceeded the predetermined third threshold, an HV-ECU controls the motor to restrict the torque of the motor and also controls the clutch to connect the clutch.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a U.S. national stage of application No. PCT/JP2011/074190, filed on Oct. 20, 2011. Priority under 35 U.S.C.§119(a) and 35 U.S.C.§365(b) is claimed from Japanese Patent Application No. 2010-237800, filed on Oct. 22, 2010, the disclosure of which are also incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to a vehicle, a control method, and a computer program. 
     BACKGROUND ART 
     A so-called hybrid vehicle that is driven by an internal combustion engine and an electric motor receives attention. When the hybrid vehicle decelerates, the electric motor functions as an electric generator in order to perform an electric power regeneration (hereinafter, also simply referred to as a regeneration) and store the electric power. The stored electric power is used for generating driving force, for example, when the vehicle accelerates or runs. 
     Some hybrid vehicles have a gear box configured to automatically shift gears. Hereinafter, the gear box is also referred to as a transmission. 
     In such cases, a clutch that connects the power or cuts the connection of the power can be provided between the internal combustion engine and the electric motor. 
     Some conventional vehicles include an internal combustion engine, an electric machine capable of operating as an electric motor and as an electric generator, a clutch, a gear box of which transfer ratio is variable, a power electronics, and an electric energy storage device. The clutch is provided between the internal combustion engine and the gear box. The driving torque can be led through the clutch from the internal combustion engine to the gear box and from the electric machine to the internal combustion engine. The electric machine is provided between the only clutch placed between the internal combustion engine and the gear box, and the gear box so that the electric machine can directly transfer positive torque or negative torque to the gear box input shaft of the gear box (for example, see patent literature PTL1). 
     CITATION LIST 
     Patent Literature 
     PTL1: JP 2007-118943 A 
     SUMMARY OF INVENTION 
     Technical Problem 
     However, when the hybrid vehicle starts moving only by the electric motor and then the electric motor stops although generating torque, for example, when the vehicle surmounts a steep upgrade or an obstacle, the vehicle sometimes cannot start moving because the current is concentrated in the element of an inverter that drives the electric motor and heat is generated. 
     In order to solve the problem, enhancing the heat-resistance or cooling performance of the element can be considered. However, it is concerned that this increases the cost. 
     In light of the foregoing, an objective of the present invention is to solve the problem or, in other words, to provide a vehicle, a control method, and a computer program that enable the vehicle to certainly start moving without changing the hardware. 
     Solution to Problem 
     To solve the above-mentioned problem, an aspect of the present invention is directed to a vehicle driven by an internal combustion engine and an electric motor that are connected to shafts configured to transfer power through a clutch configured to connect the power or disconnect the connection of the power, the vehicle includes an apparatus comprising: determination means for determining, while the clutch is disengaged, whether a condition, where an absolute value of a rotational speed of the electric motor is equal to or less than a predetermined first threshold and where torque of the electric motor is equal to or more than a predetermined second threshold, lasts for a predetermined third threshold or more; and control means for controlling the electric motor to limit the torque of the electric motor and controlling the clutch to be engaged when it is determined, while the clutch is disengaged, that the condition where the absolute value of the rotational speed of the electric motor is equal to or less than the first threshold and where the torque of the electric motor is equal to or more than the second threshold lasts for the third threshold or more. 
     In addition, in the vehicle according to the aspect of the present invention, the control means may control the electric motor to cause the torque of the electric motor to be equal to or less than a predetermined fourth threshold within a predetermined period. 
     In addition, in the vehicle according to the aspect of the present invention, the control means may control the electric motor to cancel the limitation of the torque of the electric motor after a predetermined period elapses after the torque of the electric motor is limited. 
     According to another aspect of the present invention, a control method for controlling a vehicle driven by an internal combustion engine and an electric motor that are connected to shafts configured to transfer power through a clutch configured to connect the power or disconnect the connection of the power includes the steps of: determining, while the clutch is disengaged, whether a condition, where an absolute value of a rotational speed of the electric motor is equal to or less than a predetermined first threshold and where torque of the electric motor is equal to or more than a predetermined second threshold, lasts for a predetermined third threshold or more; and controlling the electric motor to limit the torque of the electric motor and controlling the clutch to be engaged when it is determined, while the clutch is disengaged, the condition where the absolute value of the rotational speed of the electric motor is equal to or less than the first threshold and where the torque of the electric motor is equal to or more than the second threshold lasts for the third threshold or more. 
     According to still another aspect of the present invention, a computer program causes a computer for controlling a vehicle driven by an internal combustion engine and an electric motor that are connected to shafts configured to transfer power through a clutch configured to connect the power or disconnect the connection of the power to perform a process including the steps of: determining, while the clutch is disengaged, whether a condition, where an absolute value of a rotational speed of the electric motor is equal to or less than a predetermined first threshold and where torque of the electric motor is equal to or more than a predetermined second threshold, lasts for a predetermined third threshold or more; and controlling the electric motor to limit the torque of the electric motor and controlling the clutch to be engaged when it is determined, while the clutch is disengaged, that the condition where the absolute value of the rotational speed of the electric motor is equal to or less than the first threshold and the time when the torque of the electric motor is equal to or more than the second threshold lasts for the third threshold or more. 
     Advantageous Effects of Invention 
     According to an aspect of the present invention, a vehicle, a control method, and a computer program that enable the vehicle to certainly start moving without changing the hardware can be provided. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram for illustrating an exemplary structure of a hybrid vehicle  1 . 
         FIG. 2  is a block diagram for illustrating an exemplary configuration of a function implemented in an HV-ECU  21 . 
         FIGS. 3A to 3C  are time charts for describing a process for limiting the torque of an electric motor  14 . 
         FIG. 4  is a flowchart for describing a process for limiting the torque of the electric motor  14 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, a hybrid vehicle according to an embodiment of the present invention will be described with reference to  FIGS. 1 to 4 . 
       FIG. 1  is a block diagram for illustrating an exemplary structure of a hybrid vehicle  1 . The hybrid vehicle  1  is an example of a vehicle. The hybrid vehicle  1  is driven by an internal combustion engine and/or an electric motor through a gear box configured to automatically shift gears. For example, when the vehicle decelerates, the electric power can be regenerated by the electric motor. The gear box configured to automatically shift gears is, for example, referred to as an automated mechanical/manual transmission. The transmission can automatically shift the gears while having the same structure as a manual transmission. 
     The hybrid vehicle  1  includes an internal combustion engine  11 , a clutch  12 , a hybrid device  13 , an electric motor  14 , an inverter  15 , a Hybrid Vehicle (HV) battery  16 , a gear box  17 , an output shaft  18 , a differential gear  19 , a wheel  20 , and an HV-Electronic Control Unit (ECU)  21 . Note that the hybrid device  13  includes the electric motor  14 , the inverter  15 , the HV battery  16 , and the HV-ECU  21 . Note that the gear box  17  includes the above-mentioned automated mechanical/manual transmission and is operated by a shift unit (not shown in the drawings) including a drive range (hereinafter, referred to as a D (Drive) range). 
     The internal combustion engine  11  internally combusts gasoline, light oil, Compressed Natural Gas (CNG), Liquefied Petroleum Gas (LPG), alternative fuel, or the like in order to generate power for rotating a shaft and transfer the generated power to the clutch  12 . 
     The clutch  12  transfers the shaft output from the internal combustion engine  11  to the wheel  20  through the electric motor  14 , the gear box  17 , the output shaft  18 , and the differential gear  19 . In other words, the clutch  12  mechanically connects (hereinafter, simply referred to as connects) the rotating shaft of the internal combustion engine  11  to the rotating shaft of the electric motor  14  by the control of the HV-ECU  21  in order to transfer the shaft output of the internal combustion engine  11  to the electric motor  14 . On the other hand, the clutch  12  cuts (hereinafter, simply referred to as cuts or disconnects) the mechanical connection between the rotating shaft of the internal combustion engine  11  and the rotating shaft of the electric motor  14  so that the rotating shaft of the internal combustion engine  11  and the rotating shaft of the electric motor  14  can rotate at different rotational speeds from each other. 
     For example, the clutch  12  mechanically connects the rotating shaft of the internal combustion engine  11  to the rotating shaft of the electric motor  14 , for example, when the hybrid vehicle  1  runs by the power of the internal combustion engine  11  and this causes the electric motor  14  to generate electric power, when the driving force of the electric motor  14  assists the internal combustion engine  11 , and when the electric motor  14  starts the internal combustion engine  11 . 
     Alternatively, for example, the clutch  12  cuts the mechanical connection between the rotating shaft of the internal combustion engine  11  and the rotating shaft of the electric motor  14  when the internal combustion engine  11  stops or is in an idling state and the hybrid vehicle  1  runs by the driving force of the electric motor  14 , and when the hybrid vehicle  1  decelerates or runs on the down grade and the electric motor  14  generates electric power (regenerates electric power) while the internal combustion engine  11  stops or is in an idling state. 
     Note that the clutch  12  differs from the clutch operated by the driver&#39;s operation of a clutch pedal, and is operated by the control of the HV-ECU  21 . 
     The electric motor  14  is a so-called motor generator that supplies a shaft output to the gear box  17  by generating the power for rotating the shaft using the electric power supplied from the inverter  15 , or that supplies electric power to the inverter  15  by generating the electric power using the power for rotating the shaft supplied from the gear box  17 . For example, when the hybrid vehicle  1  accelerates or runs at a constant speed, the electric motor  14  generates the power for rotating the shaft to supply the shaft output to the gear box  17  in order to cause the hybrid vehicle  1  to run in cooperation with the internal combustion engine  11 . Further, the electric motor  14  works as an electric generator, for example, when the electric motor  14  is driven by the internal combustion engine  11 , or when the hybrid vehicle  1  runs without power, for example, the hybrid vehicle  1  decelerates or runs on the down grade. In that case, electric power is generated by the power for rotating the shaft supplied from the gear box  17  and is supplied to the inverter  15  in order to charge the HV battery  16 . 
     The inverter  15  is controlled by the HV-ECU  21 , and converts the direct voltage from the HV battery  16  into an alternating voltage or converts the alternating voltage from the electric motor  14  into a direct voltage. When the electric motor  14  generates power, the inverter  15  converts the direct voltage of the HV battery  16  into an alternating voltage and supplies the electric power to the electric motor  14 . When the electric motor  14  generates electric power, the inverter  15  converts the alternating voltage from the electric motor  14  into a direct voltage. In other words, in that case, the inverter  15  works as a rectifier and a voltage regulator for supplying a direct voltage to the HV battery  16 . 
     Further, the inverter  15  determines, for example, whether a condition, where the absolute value of the rotational speed of the electric motor  14  is equal to or less than a predetermined rotational speed A and where the torque of the electric motor  14  is equal to or more than a predetermined torque B, lasts for a predetermined period C or more. When it is determined that the condition where the absolute value of the rotational speed of the electric motor  14  is equal to or less than the predetermined rotational speed A and the torque of the electric motor  14  is equal to or more than the predetermined torque B lasts for the predetermined period C or more, the inverter  15  transmits a current concentration determination flag to the HV-ECU  21 . 
     The HV battery  16  is a secondary cell capable of being charged and discharged. The HV battery  16  supplies electric power to the electric motor  14  through the inverter  15  when the electric motor  14  generates power. Alternatively, the HV battery  16  is charged with the electric power generated by the electric motor  14  when the electric motor  14  generates electric power. 
     The gear box  17  includes an automated mechanical/manual transmission (not shown in the drawings) that selects one of a plurality of gear ratios (change gear ratios) according to the instruction signal to shift gears from the HV-ECU  21  in order to shift the change gear ratios and transfer the gear-shifted power of the internal combustion engine  11  and/or of the electric motor  14  to the wheel  20  through the output shaft  18  and the differential gear  19 . Alternatively, the gear box  17  transfers the power from the wheel  20  through the output shaft  18  and the differential gear  19  to the electric motor  14 , for example, when the vehicle decelerates or runs on the down grade. Note that the automated mechanical/manual transmission can also shift the gear position to a given gear number by the driver&#39;s hand operation of the shift unit. 
     The output shaft  18  is a so-called propeller shaft or drive shaft. The output shaft  18  transfers the power output from the gear box  17  to the differential gear  19 . The differential gear  19  transfers the power to the right and left wheels  20  and absorbs the difference between the rotations of the right and left wheels  20 . 
     The HV-ECU  21  is an example of a computer, and controls the electric motor  14  by controlling the inverter  15 . When receiving the current concentration determination flag transmitted from the inverter  15 , the HV-ECU  21  determines that the condition where the absolute value of the rotational speed of the electric motor  14  is equal to or less than the predetermined rotational speed A and the torque of the electric motor  14  is equal to or more than the predetermined torque B lasts for the predetermined period C or more. 
     For example, the HV-ECU  21  includes a Central Processing Unit (CPU), an Application Specific Integrated Circuit (ASIC), a microprocessor (micro-computer), a Digital Signal Processor (DSP), and the like, and internally has an operation unit, a memory, an Input/Output (I/O) port, and the like. 
     Note that a computer program to be executed by the HV-ECU  21  can be installed on the HV-ECU  21  that is a computer in advance by being stored in a non-volatile memory inside the HV-ECU  21  in advance. 
     The wheel  20  is a drive wheel for transferring the driving force to the road surface. Note that, although only a wheel  20  is illustrated in  FIG. 1 , the hybrid vehicle  1  actually includes a plurality of the wheels  20 . 
       FIG. 2  is a block diagram for illustrating an exemplary configuration of a function implemented in the HV-ECU  21  executing a predetermined computer program. In other words, when the HV-ECU  21  executes the computer program, a determination unit  51 , a torque control unit  52 , and a clutch control unit  53  are implemented. 
     The determination unit  51  determines whether a condition, where the absolute value of the rotational speed of the electric motor  14  is equal to or less than the predetermined rotational speed A and where the torque of the electric motor  14  is equal to or more than the predetermined torque B, lasts for the predetermined period C or more, and determines whether a predetermined period F has elapsed after the torque of the electric motor  14  has been limited. The determination unit  51  includes a current concentration determination unit  61 , a period elapse determination unit  62 , and a threshold storage unit  63 . 
     According to whether the current concentration determination unit  61  has received a current concentration determination flag transmitted from the inverter  15 , the current concentration determination unit  61  determines whether the condition where the absolute value of the rotational speed of the electric motor  14  is equal to or less than the predetermined rotational speed A and the torque of the electric motor  14  is equal to or more than the predetermined torque B lasts for the predetermined period C or more. Note that, in order to determine whether the condition where the absolute value of the rotational speed of the electric motor  14  is equal to or less than the predetermined rotational speed A and the torque of the electric motor  14  is equal to or more than the predetermined torque B lasts for the predetermined period C or more, the current concentration determination unit  61  can also obtain, in real time, the data indicating the rotational speed and the torque of the electric motor  14  from the inverter  15 , and read a threshold A indicating the rotational speed A, a threshold B indicating the torque B, and a threshold C indicating the period C from the threshold storage unit  63  that stores the thresholds in advance. In that case, the current concentration determination unit  61  can internally maintain the thresholds A, B, and C, for example, as constant numbers. 
     The period elapse determination unit  62  reads a threshold F indicating the period F from the threshold storage unit  63  that stores the threshold in advance, and compares the elapsed time shown by a real time clock housed in the HV-ECU  21  with the threshold F in order to determine whether the predetermined period F has elapsed after the torque of the electric motor  14  has been limited. 
     The threshold storage unit  63  stores the predetermined thresholds A, B, C, and F. 
     Note that the period elapse determination unit  62  can internally maintain the threshold F, for example, as a constant number. 
     The torque control unit  52  controls the electric motor  14  to increase and decrease the torque generated by the electric motor  14  by controlling the inverter  15 . 
     The clutch control unit  53  controls the clutch  12  to be engaged, be in a so-called half-engaged clutch state, or be disengaged by transmitting a control signal. 
       FIGS. 3A to 3C  are time charts for describing a process for limiting the torque of the electric motor  14 . The horizontal axes in  FIGS. 3A to 3C  show a time.  FIG. 3A  is a time chart in which the rotational speed of the electric motor  14  corresponding to the time shown as the horizontal axis is shown as the vertical axis.  FIG. 3B  is a time chart in which the torque of the electric motor  14  corresponding to the time shown as the horizontal axis is shown as the vertical axis.  FIG. 3C  is a time chart in which the torque of the internal combustion engine  11  corresponding to the time shown as the horizontal axis is shown as the vertical axis. 
     As illustrated in  FIGS. 3A and 3B , when the condition, where the absolute value of the rotational speed (r.p.m.) of the electric motor  14  is equal to or less than the predetermined rotational speed A and where the torque (Nm) of the electric motor  14  is equal to or more than the predetermined torque B, lasts for the predetermined period C (sec) or more before a time t 1 , it is determined that the current is concentrated in the inverter  15  and the inverter  15  transmits, to the HV-ECU  21 , the current concentration determination flag indicating that the current is concentrated. 
     Note that the internal combustion engine  11  stops or is in the idling state, the hybrid vehicle  1  runs by the driving force of the electric motor  14 , and the clutch  12  is disengaged at the period C. 
     When the current concentration determination flag has been transmitted to the HV-ECU  21 , the torque control unit  52  controls the inverter  15  by transmitting a command to the inverter  15  in order to limit the torque of the electric motor  14  and then linearly narrow the torque of the electric motor  14  to a predetermined torque E during a period D (sec) from the time t 1  to a time t 3 . In other words, the torque of the electric motor  14  is limited to the torque E. In that case, at the timing when a predetermined time has elapsed from the time t 1 , the clutch  12  gets in the so-called half-engaged clutch state in which the torque of the internal combustion engine  11  is partially transmitted to the electric motor  14 , and the clutch  12  is engaged at the timing when the rotational speed of the electric motor  14  and the rotational speed of the internal combustion engine  11  synchronize with each other. 
     Accordingly, as illustrated in  FIG. 3A , the rotational speed of the electric motor  14  increases from a time t 2 . Further, as illustrated in  FIG. 3C , the torque of the internal combustion engine  11  rises during the period D (sec) from the time t 1  to the time t 3 . 
     The torque of the electric motor  14  that has been limited to the torque E is added to the torque of the internal combustion engine  11  after the time t 3 . This causes the vehicle to start moving with assistance. When the vehicle starts moving with assistance, the electric motor  14  assists the internal combustion engine  11 . 
     The limitation of the torque of the electric motor  14  is cancelled at the time t 4  when the period F (sec) has elapsed from the time t 3  when the torque of the electric motor  14  has been limited to the torque E. At the time t 4 , the electric motor  14  can generate torque exceeding the torque E. 
     Next, the process for limiting the torque of the electric motor  14  will be described with reference to the flowchart in  FIG. 4 . In step S 11 , the inverter  15  determines whether the condition, where the absolute value of the rotational speed of the electric motor  14  is equal to or less than the predetermined rotational speed A and where the torque of the electric motor  14  is equal to or more than the predetermined torque B, lasts for the predetermined period C or more. 
     When it is determined in step S 11  that the condition where the absolute value of the rotational speed of the electric motor  14  is equal to or less than the predetermined rotational speed A and the torque of the electric motor  14  is equal to or more than the predetermined torque B lasts for the predetermined period C or more, the process goes to step S 12  and the inverter  15  transmits the current concentration determination flag to the HV-ECU  21 . 
     In step S 13 , when receiving the current concentration determination flag, the current concentration determination unit  61  in the determination unit  51  determines that the condition where the absolute value of the rotational speed of the electric motor  14  is equal to or less than the predetermined rotational speed A and the time when the torque of the electric motor  14  is equal to or more than the predetermined torque B lasts for the predetermined period C or more. Then, the torque control unit  52  controls the inverter  15  by transmitting a command to the inverter  15  in order to limit the torque of the electric motor  14  and then narrow the torque of the electric motor  14  to the predetermined torque E during the period D after the current concentration determination flag has been received. 
     In step S 14 , the clutch control unit  53  engages the clutch  12  by transmitting a control signal in order to switch the start of the vehicle to the start with assistance using the power of the internal combustion engine  11  and the power of the electric motor  14 . In more detail, during the period D after the current concentration determination flag has been received, the clutch control unit  53  controls the clutch  12  to get in the so-called half-engaged clutch state in order to partially transmit the torque of the internal combustion engine  11  to the electric motor  14 . After the period D has elapsed, the clutch control unit  53  controls the clutch  12  to get in a so-called engaged state in order to transmit all of the torque of the internal combustion engine  11  to the electric motor  14 . 
     In step S 15 , the period elapse determination unit  62  in the determination unit  51  reads the threshold F indicating the period F from the threshold storage unit  63  that stores the threshold in advance, and compares the elapsed time with the threshold F in order to determine whether the predetermined period F has elapsed after the torque of the electric motor  14  has been limited (after the torque of the electric motor  14  has become the torque E). When it is determined that the period F has not elapsed, the process goes back to step S 15  and the process of the determination is repeated until the period F has elapsed. 
     When it is determined in step S 15  that the period F has elapsed, the process goes to step S 16 . Then, the torque control unit  52  cancels the limitation of the torque of the electric motor  14  and the process for limiting the torque of the electric motor is completed. 
     When it is determined in step S 11  that the condition where the absolute value of the rotational speed of the electric motor  14  is equal to or less than the predetermined rotational speed A and the time when the torque of the electric motor  14  is equal to or more than the predetermined torque B does not last for the predetermined period C or more, the process for limiting the torque of the electric motor is completed without limiting the torque of the electric motor  14  because it is not necessary to limit the torque of the electric motor  14 . 
     Note that, in step S 11 , the current concentration determination unit  61  can also obtain, in real time, the data indicating the rotational speed and the torque of the electric motor  14  from the inverter  15 , and read the threshold A indicating the rotational speed A, the threshold B indicating the torque B, and the threshold C indicating the period C from the threshold storage unit  63  in order to determine whether the condition where the absolute value of the rotational speed of the electric motor  14  is equal to or less than the predetermined rotational speed A and the time when the torque of the electric motor  14  is equal to or more than the predetermined torque B lasts for the predetermined period C or more. 
     As described above, when the current is concentrated in the inverter  15 , the torque of the electric motor  14  is limited and the start of the vehicle is switched to the start with assistance. Thus, the inverter  15  is prevented from excessively generating heat. Accordingly, even when the hybrid vehicle  1  stops, for example, when the vehicle  1  surmounts a steep upgrade or an obstacle, constant torque can continuously be generated so that the vehicle  1  can certainly start moving. 
     Further, it is not necessary to enhance the heat-resistance or cooling performance of the element and it is not necessary to change the hardware. 
     As described above, the vehicle can certainly start moving without changing the hardware. 
     Further, while the computer program executed by the HV-ECU  21  is installed on the HV-ECU  21  in advance in the description above, the computer program can be installed on the HV-ECU  21  as a computer by attaching removable media recording the computer program (storing the computer program), for example, to a drive (not shown in the drawings) and storing the computer program read from the removable media in a non-volatile memory inside the HV-ECU  21 , or receiving, by a communication unit (not shown in the drawings), a computer program transmitted through a wired or wireless transmission medium and storing the computer program in a non-volatile memory inside the HV-ECU  21 . 
     Note that the computer program executed by the computer can be for performing the process in chronological order according to the order described herein or can be for performing the process in parallel or at the necessary timing, for example, when the computer program is invoked. 
     Further, the embodiments of the present invention are not limited to the above-mentioned embodiment, and can be variously modified without departing from the gist of the invention. 
     Although the threshold F is fixedly set in the above-mentioned embodiment, the threshold F can variably be set. For example, the A is set as the threshold of the rotational speed of the electric motor. However, a threshold A 1  lower than the A is provided. When the rotational speed of the electric motor is equal to or less than the threshold A 1  and the process reaches step S 14 , the period F can be controlled to be extended. The B is set as the threshold of the torque of the electric motor. However, a threshold B 1  higher than the B is provided. When the torque of the electric motor is equal to or more than the threshold B 1  and the process reaches step S 14 , the period F can be controlled to be extended. In such cases, one of the thresholds A 1  and B 1  can be adopted, or both of the thresholds A 1  and B 1  can be adopted. In other words, for example, (1) when the rotational speed of the electric motor is equal to or less than the threshold A 1 , the period F is extended. (2) when the torque of the electric motor is equal to or more than the threshold B 1 , the period F is extended. (3) when the rotational speed of the electric motor is equal to or less than the threshold A 1  and the torque the electric motor is equal to or more than the threshold B 1 , the period F is extended. Alternatively, the period F can be extended even longer in the case (3) than in the cases (1) and (2). 
     As another method to variably set the threshold F, the inclination of the road surface on which the hybrid vehicle  1  runs can be taken into consideration. For example, even though the limitation of the torque of the electric motor  13  has been cancelled, the torque is possibly limited again soon when the hybrid vehicle  1  runs on a steep upgrade. In light of the foregoing, a threshold is provided for the angle of the upgrade surface during the period F so that the period F is controlled to be extended when the angle of the upgrade exceeds the threshold. In that case, the period F is preferably extended until the angle of the upgrade is equal to or less than the threshold. 
     Further, when the weight of the load on the hybrid vehicle  1  is large even though the angle of the upgrade is equal to or less than the threshold, the torque of the electric motor  13  is possibly limited again soon even once the limitation of the torque has been released. In light of the foregoing, the threshold of the angle of the upgrade surface during the period F can be changed according to the weight of the load on the hybrid vehicle  1 . For example, when the load is relatively heavy, the threshold of the angle of the upgrade is changed to a smaller threshold. On the other hand, when the load is relatively light, the threshold of the angle of the upgrade is changed to a larger threshold. 
     Note that the quantity of the load on the hybrid vehicle  1  can be found by measuring the load of the carrier, for example, using an axle load sensor provided on the axle. Alternatively, the gross weight of the hybrid vehicle  1  can also be estimated by checking the behavior of the running hybrid vehicle  1  (for example, see JP 2004-025956 A). Further, the inclination of the road surface on which the hybrid vehicle  1  runs can be found, for example, using an inclination sensor or the like.