Abstract:
The disclosed vehicle, control method, and program lead to improved fuel consumption, durability, and stability. When the vehicle starts to move, a clutch control performs controls so as to set the clutch to a half clutch state, in which a part of the motive force is transmitted, and thereafter to a connected state, in which the entire motive power is transmitted. When the clutch is the half clutch state, an electric motor control unit controls an electric motor to generate an assist torque when the vehicle starts to move equal to the difference between the torque requested by the driver and the idling torque generated when the engine is idling. The disclosed invention can be applied to hybrid vehicles.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This is a U.S. national stage of application No. PCT/JP2011/074167, 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. 2010-237803, filed on Oct. 22, 2010, the disclosure of which are also incorporated herein by reference. 
     
    
     TECHNICAL FIELD  
       [0002]    The present invention relates to a vehicle, a control method, and a computer program. 
       BACKGROUND ART  
       [0003]    A so-called hybrid vehicle that is driven by an internal combustion engine and an electric motor has been focused. In the hybrid vehicle, the electric motor functions as a generator to regenerate electric power (hereinafter merely referred to as regenerate power), and store the electric power during deceleration. The stored electric power is utilized to generate driving force for accelerating the vehicle or driving the vehicle. 
         [0004]    Some hybrid vehicles have an automatic transmission. The automatic transmission is also referred to as a transmission below. 
         [0005]    In this case, a clutch that transmits power or cuts the transmission of power can be provided between the internal combustion engine and the electric motor. 
         [0006]    There has conventionally been proposed a vehicle including an internal combustion engine, an electric machine that can realize an electric - motor operation and a generator operation, a clutch, a variable ratio transmission, a power electronics, and an electric energy storage device, wherein the clutch is arranged between the internal combustion engine and the transmission so as to transmit driving torque to the transmission from the internal combustion engine, and from the electric machine to the internal combustion engine, via the clutch, and the electric machine is arranged between only clutch arranged between the internal combustion engine and the transmission, and the transmission so as to directly transmit positive or negative toque to the input shaft of the transmission (see, for example, patent literature PTL1). 
       CITATION LIST  
     Patent Literature  
       [0007]    PTL1: JP 2007-118943 A 
       SUMMARY OF INVENTION  
     Technical Problem  
       [0008]    However, when the driver starts the vehicle with the internal combustion engine with small displacement, torque upon the start is liable to be insufficient. Therefore, upon starting the vehicle, the internal combustion engine is sharply revved up, and retaining this state, the driving force is gradually transmitted with a partial clutch engagement, in order to increase the speed of the vehicle. 
         [0009]    In the method of starting the vehicle as described above, the internal combustion engine consumes large amount of fuel, and in addition, this method encourages the abrasion of the clutch, and causes a temperature rise of the electric motor. 
         [0010]    In view of the foregoing circumstance, the present invention aims to solve the above-mentioned problem, i.e., to provide a vehicle, a control method, and a computer program that can prevent the abrasion of the clutch and the temperature rise of the electric motor with less consumption of the fuel, in other words, that can improve fuel consumption rate, durability and stability. 
       Solution to Problem  
       [0011]    In order to solve the above-mentioned problem, according to an aspect of the present invention, a vehicle that is driven by an internal combustion engine and an electric motor, a shaft of the internal combustion engine and a shaft of the electric motor for transmitting power being connected by a clutch that transmits power or cuts the transmission of power includes a device having: a clutch control unit that controls the clutch to be in a partial engagement state for transmitting some power, and then, to be in an engagement state for transmitting the whole power, when the vehicle starts; and an electric motor control unit that controls the electric motor to generate torque assisting the start of the vehicle, when the clutch is in the partial engagement state. 
         [0012]    According to the aspect of the present invention, the vehicle described above further includes: a determination unit that determines whether the vehicle starts from an uphill having an inclination equal to or larger than a predetermined inclination; and a correction unit that corrects an upper limit value of torque generated by the electric motor to be smaller, when the determination unit determines that the vehicle starts from an uphill having the inclination equal to or larger than the predetermined inclination. 
         [0013]    According to the aspect of the present invention, in the vehicle described above, the electric motor control unit controls the electric motor to generate torque equal to a difference between torque requested by a driver and torque generated by the internal combustion engine. 
         [0014]    According to the aspect of the present invention, in the vehicle described above, the electric motor control unit controls the electric motor to generate torque equal to torque requested by the driver. 
         [0015]    According to the aspect of the present invention, in the vehicle described above, the electric motor control unit controls the electric motor to increase the rotational speed of the electric motor and to generate torque assisting the start of the vehicle, when the clutch is in a partial engagement state. 
         [0016]    According to the aspect of the present invention, in the vehicle described above, the determination unit determines whether or not the difference between the torque requested by the driver and the torque generated from the internal combustion engine exceeds the corrected upper limit value of the torque, when determining that the vehicle starts from the uphill having the inclination equal to or larger than the predetermined inclination, and the electric motor control unit controls the electric motor to generate torque not more than the corrected upper limit value of the torque, when the clutch is in the partial engagement state in the case where the vehicle is determined to start from the uphill having the inclination equal to or larger than the predetermined inclination. 
         [0017]    According to another aspect of the present invention, a control method for a vehicle that is driven by an internal combustion engine and an electric motor, a shaft of the internal combustion engine and a shaft of the electric motor for transmitting power being connected by a clutch that transmits power or cuts the transmission of power includes: a clutch control step for controlling the clutch to be in a partial engagement state for transmitting some power, and then, to be in an engagement state for transmitting the whole power, when the vehicle starts; and an electric motor control step for controlling the electric motor to generate torque assisting the start of the vehicle, when the clutch is in the partial engagement state. 
         [0018]    According to still another aspect of the present invention, a computer program causes computer, which controls a vehicle that is driven by an internal combustion engine and an electric motor, a shaft of the internal combustion engine and a shaft of the electric motor for transmitting power being connected by a clutch that transmits power or cuts the transmission of power, to execute: a clutch control step for controlling the clutch to be in a partial engagement state for transmitting some power, and then, to be in an engagement state for transmitting the whole power, when the vehicle starts; and an electric motor control step for controlling the electric motor to generate torque assisting the start of the vehicle, when the clutch is in the partial engagement state. 
       Advantageous Effects of Invention  
       [0019]    According to one aspect of the present invention, a vehicle, a control method, and a computer program that can improve fuel consumption rate, durability, and stability can be provided. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS  
         [0020]      FIG. 1  is a block diagram illustrating an example of a configuration of a hybrid vehicle  1 . 
           [0021]      FIG. 2  is a block diagram illustrating an example of a configuration of functions realized in a hybrid ECU  18 . 
           [0022]      FIG. 3  is a view illustrating examples of vehicle full torque, assist start torque in normal state, assist start torque for starting the vehicle, and assist full torque. 
           [0023]      FIG. 4  is a time chart for describing an example of an assist start control. 
           [0024]      FIG. 5  is a flowchart illustrating an example of a process of the assist start control. 
           [0025]      FIG. 6  is a time chart for describing another example of the assist start control. 
           [0026]      FIG. 7  is a flowchart illustrating another example of the process of the assist start control. 
           [0027]      FIG. 8  is a view illustrating examples of vehicle full torque, assist start torque, and assist full torque. 
           [0028]      FIG. 9  is a flowchart illustrating still another example of the process of the assist start control. 
       
    
    
     DESCRIPTION OF EMBODIMENTS  
       [0029]    A hybrid vehicle according to one embodiment of the present invention will be described below with reference to  FIGS. 1 to 9 . 
         [0030]      FIG. 1  is a block diagram illustrating an example of a configuration of a hybrid vehicle  1 . The hybrid vehicle  1  is one example of a vehicle. The hybrid vehicle  1  is driven by an internal combustion engine and/or an electric motor via an automatic transmission, and for example, when the vehicle  1  reduces its speed, electric power can be regenerated by the electric motor. The automatic transmission is referred to as a semiautomatic transmission. It has the same configuration as a manual transmission, but can realize an automatic shift operation. 
         [0031]    The hybrid vehicle  1  includes an engine  10 , an engine ECU (Electronic Control Unit)  11 , a clutch  12 , an electric motor  13 , an inverter  14 , a battery  15 , a transmission  16 , a motor ECU  17 , a hybrid ECU  18 , a wheel  19 , and a shift unit  20 . Note that the transmission  16  has the above-mentioned semiautomatic transmission, and is operated by the shift unit  20  having a drive range (hereinafter referred to as D (Drive) range). 
         [0032]    The engine  10  is one example of the internal combustion engine. It is controlled by the engine ECU  11  to burn gasoline, light gas oil, CNG (Compressed Natural Gas), LPG (Liquefied Petroleum Gas), or alternate fuel therein, thereby generating power for rotating a shaft. It then transmits the generated power to the clutch  12 . 
         [0033]    The engine ECU  11  is a computer that works in conjunction with the motor ECU  17  in accordance with an instruction from the hybrid ECU  18 . It controls the engine  10 , i.e., controls the fuel injection amount or valve timing. For example, the engine ECU  11  is composed of a CPU (Central Processing Unit), ASIC (Application Specific Integrated Circuit), microprocessor (microcomputer), and DSP (Digital Signal Processor), and includes a calculation unit, a memory, and an I/O (Input/Output) port. 
         [0034]    The clutch  12  is controlled by the hybrid ECU  18 , and transmits a shaft output from the engine  10  to the wheel  19  via the electric motor  13  and the transmission  16 . Specifically, the clutch  12  mechanically connects (hereinafter merely referred to as connection) the rotation shaft of the engine  10  and the rotation shaft of the electric motor  13  to transmit the shaft output of the engine  10  to the electric motor  13 , or cuts the mechanical connection between the rotation shaft of the engine  10  and the rotation shaft of the electric motor  13  (hereinafter merely referred to as cut) to allow the rotation shaft of the engine  10  and the rotation shaft of the electric motor  13  to rotate with a different rotational speed, under the control of the hybrid ECU  18 . 
         [0035]    For example, the clutch  12  mechanically connects the rotation shaft of the engine  10  and the rotation shaft of the electric motor  13 , when the hybrid vehicle  1  runs by the power from the engine  10 , by which the electric motor  13  generates electric power; when the engine  10  is assisted by the driving force of the electric motor  13 ; and when the engine  10  is started by the electric motor  13 . 
         [0036]    For example, the clutch  12  cuts the mechanical connection between the rotation shaft of the engine  10  and the rotation shaft of the electric motor  13 , when the engine  10  is stopped or in an idling condition, and the hybrid vehicle  1  runs with the driving force of the electric motor  13 , or when the engine  10  is stopped or in an idling condition, the hybrid vehicle  1  reduces its speed, or runs on a downhill, and the electric motor  13  generates electric power (regenerates electric power). 
         [0037]    The clutch  12  is different from a clutch that is operated by the driver&#39;s operation on a clutch pedal, and the clutch  12  is operated by the control of the hybrid ECU  18 . 
         [0038]    The electric motor  13  is a so-called motor generator, and it generates power for rotating a shaft by electric power supplied from the inverter  14 , and supplies the shaft output to the transmission  16 . Alternatively, the electric motor  13  generates electric power by the power for rotating the shaft supplied from the transmission  16 , and supplies the electric power to the inverter  14 . For example, when the hybrid vehicle  1  increases its speed, or runs with a constant speed, the electric motor  13  generates power for rotating the shaft, and supplies the shaft output to the transmission  16 , thereby allowing the hybrid vehicle  1  to run in cooperation with the engine  10 . For example, when the electric motor  13  is driven by the engine  10 , or when the hybrid vehicle  1  runs without using power, such as in the case where the hybrid vehicle  1  reduces its speed or runs on a downhill, the electric motor  13  operates as a motor generator. In this case, the electric motor  13  generates electric power by the power for rotating the shaft supplied from the transmission  16 , and supplies the electric power to the inverter  14 , whereby the battery  15  is charged. 
         [0039]    The inverter  14  is controlled by the motor ECU  17 , and it converts DC voltage from the battery  15  into AC voltage, or converts AC voltage from the electric motor  13  to DC voltage. When the electric motor  13  generates power, the inverter  14  converts the DC voltage from the battery  15  into AC voltage so as to supply the electric power to the electric motor  13 . When the electric motor  13  generates electric power, the inverter  14  converts the AC voltage from the electric motor  13  into DC voltage. In other words, in this case, the inverter  14  functions as a rectifier or a voltage regulation device for feeding DC voltage to the battery  15 . 
         [0040]    The battery  15  is a secondary cell capable of being charged and discharged. It feeds electric power to the electric motor  13  through the inverter  14  when the electric motor  13  generates power, or it is charged by the electric power generated from the electric motor  13  when the electric motor  13  generates electric power. 
         [0041]    The transmission  16  has a semiautomatic transmission (not illustrated in the drawings) for selecting any one of plural gear ratios (transmission gear ratios) in accordance with a instruction signal to shift from the hybrid ECU  18 . The transmission  16  changes the transmission gear ratio, and transmits the shifted power of the engine  10  and/or the shifted power of the electric motor  13  to the wheel  19 . When the vehicle reduces its speed, or runs on the downhill, the transmission  16  transmits power from the wheel  19  to the electric motor  13 . The transmission  16  changes gear to bring the vehicle  1  into a driving state in which power is transmitted, into a so-called neutral state in which the transmission of power is cut, or into a reverse state, by the driver&#39;s operation on the shift unit  20  for selecting a drive range (D range), a neutral range, or a reverse range. In the semiautomatic transmission, the driver can manually change the gear position to an arbitrary gear number by operating the shift unit  20 . 
         [0042]    The motor ECU  17  is a computer that works in conjunction with the engine ECU  11  in accordance with an instruction from the hybrid ECU  18 . It controls the electric motor  13  by controlling the inverter  14 . For example, the motor ECU  17  is composed of a CPU, ASIC, microprocessor (microcomputer), and DSP, and includes a calculation unit, a memory, and an I/O port. 
         [0043]    The hybrid ECU  18  is one example of a computer. It acquires accelerator opening amount information, brake operation information, vehicle speed information, inclination information that is acquired from a three-dimensional force sensor (e.g., triaxial gyro) or a three-dimensional acceleration sensor (not illustrated in the drawings) and that indicates an inclination of a road surface, and engine rotational speed information and engine torque information acquired from the engine ECU  11 , and an electric-motor rotational speed information and electric-motor torque information acquired from the motor ECU  17 , and controls the engine  10 , the clutch  12 , and the electric motor  13  by referring to the acquired information. 
         [0044]    More specifically, the hybrid ECU  18  issues an instruction to the clutch  12  to control the same. The hybrid ECU  18  issues an instruction to control the electric motor  13  and the inverter  14  to the motor ECU  17 , thereby controlling the electric motor  13 . The hybrid ECU  18  also issues an instruction to control the engine  10  to the engine ECU  11 , thereby controlling the engine  10 . For example, the hybrid ECU  18  is composed of a CPU, ASIC, microprocessor (microcomputer), and DSP, and includes a calculation unit, a memory, and an I/O port. 
         [0045]    A computer program executed by the hybrid ECU  18  is stored beforehand into a non-volatile memory in the hybrid ECU  18 , whereby the computer program can preliminarily be installed to the hybrid ECU  18  that is a computer. 
         [0046]    The engine ECU  11 , the motor ECU  17 , and the hybrid ECU  18  are interconnected with a bus in accordance with a standard such as CAN (Control Area Network). 
         [0047]    The wheel  19  is a driving wheel that transmits driving force to a road surface. Although  FIG. 1  illustrates only one wheel  19 , the hybrid vehicle  1  actually includes plural wheels  19 . 
         [0048]      FIG. 2  is a block diagram illustrating an example of a configuration of functions realized in the hybrid ECU  18 . Specifically, when the hybrid ECU  18  executes the computer program, a determination unit  31 , a clutch control unit  32 , an electric motor control unit  33 , an engine control unit  34 , and a correction unit  35  can be realized. The determination unit  31  performs various determinations, such as a determination as to whether a condition for an assist start in which the  1371687 . 1  vehicle starts with the electric motor  13  assisting the engine  10  is established or not, or a determination as to whether a condition for engaging the clutch  12  is established or not. 
         [0049]    The clutch control unit  32  issues an instruction to the clutch  12  so as to control the clutch  12  to be in an engagement state, in a disengagement state, or in a partial engagement state for transmitting some power. 
         [0050]    The electric motor control unit  33  issues an instruction to the motor ECU  17  to control the electric motor  13  and the inverter  14 , thereby controls the electric motor  13  to rotate with a desired rotational speed so as to generate desired torque. 
         [0051]    The engine control unit  34  issues an instruction to the engine ECU  11  to control the engine  10 , thereby controls the engine  10  to rotate with a desired rotational speed so as to generate desired torque. 
         [0052]    The correction unit  35  acquires an inclination of a road from the inclination information acquired from the inclination sensor which is not illustrated in the drawings. When the road is uphill with an inclination equal to or larger than a predetermined inclination, the correction unit  35  corrects the assist start torque to increase the assist start torque, which is a threshold value for determining whether the engine  10  is assisted or not by the driving force of the electric motor  13 , according to the inclination. When the road is uphill with an inclination equal to or larger than a predetermined inclination, the correction unit  35  corrects the assist full torque to decrease the assist full torque, which is an upper limit value of the torque of the electric motor  13  when the engine  10  is assisted by the driving force of the electric motor  13 , according to the inclination. 
         [0053]    The assist start torque can be used when the driver starts the vehicle or when the driver drives the vehicle, and it can be classified into assist start torque for starting used for starting the vehicle and assist start torque in normal state used for driving the vehicle. 
         [0054]      FIG. 3  is a view illustrating examples of vehicle full torque that is the maximum torque generated by the engine  10 , the assist start torque in normal state, the assist start torque for starting the vehicle, and assist full torque that is the maximum torque generated by the electric motor  13 . In  FIG. 3 , a vertical axis indicates torque, and a horizontal axis indicates a rotational speed. In  FIG. 3 , a solid line indicates the vehicle full torque, a dotted line indicates the assist start torque in normal state, a chain line indicates the assist start torque for starting the vehicle, and a two-dot chain line indicates the assist full torque. 
         [0055]    As illustrated in  FIG. 3 , the assist start torque for starting is set to have the value equal to the assist start torque in normal state, excluding a low-rotation area, and is set to have a value smaller than the assist start torque in normal state in the low - rotation area. 
         [0056]    As illustrated in  FIG. 3 , the assist full torque has a constant maximum value in the low-rotation area, and gradually decreases with the increase in the rotational speed. 
         [0057]      FIG. 4  is a time chart for describing an example of the assist start control for starting the vehicle with the engine  10  being assisted by the driving force of the electric motor  13 . 
         [0058]    In  FIG. 4 , a dotted line indicates the rotational speed of the engine  10 , and a chain line indicates the rotational speed of the electric motor  13 . A solid line indicates driver request torque that is the torque required by the driver according to the depression amount of the accelerator pedal depressed by the driver, and a two-dot chain line indicates engine torque that is torque generated by the engine  10 . 
         [0059]    In  FIG. 4 , the vehicle starts moving from a time t 1 . The clutch  12  is in a partial engagement state from the time t 1 . When the driver intends to drive the vehicle, the driver depresses the accelerator pedal. Therefore, the driver request torque increases, and the driver request torque is almost constant until the vehicle starts moving (the speed reaches initial rate). 
         [0060]    Then, the rotational speed of the engine  10  rises from the idling state, so that the engine  10  generates predetermined torque. With this, the electric motor  13  increases the rotational speed to generate the torque assisting the starting. 
         [0061]    On a time t 2 , the rotational speed of the engine  10  and the rotational speed of the electric motor  13  become almost the same, and the clutch  12  is engaged. 
         [0062]    After the time t 2 , the vehicle is in the normal assist state in which the driving force of the electric motor  13  assists the driving of the vehicle. 
         [0063]      FIG. 5  is a flowchart illustrating an example of a process of the assist start control. In step S 11 , the electric motor control unit  33  calculates an assist torque for starting the vehicle that is equal to the difference between the driver request torque according to the depression amount of the accelerator pedal depressed by the driver and the idling torque that is generated when the engine  10  is in the idling state. 
         [0064]    In step S 12 , the determination unit  31  determines whether the driver request torque exceeds the assist start torque for starting or not. When it is determined that the driver request torque exceeds the assist start torque for starting in step S 12 , the vehicle starts moving with the torque (driving force) of the electric motor  13  assisting the torque of the engine  10 . Therefore, the process proceeds to step S 13  where the clutch control unit  32  issues an instruction to the clutch  12  in order to control the clutch  12  to be in the partial engagement state. 
         [0065]    In step S 14 , the electric motor control unit  33  issues an instruction to the motor ECU  17  to control the electric motor  13  and the inverter  14 , thereby increasing the rotational speed of the electric motor  13 , and allowing the electric motor  13  to generate the assist start torque for starting. In step S 15 , the engine control unit  34  issues an instruction to the engine ECU  11  to control the engine  10 , thereby increasing the rotational speed of the engine  10 , and allowing the engine  10  to generate torque. 
         [0066]    In step S 16 , the determination unit  31  determines whether the rotational speed of the electric motor  13  becomes equal to a target engine rotational speed for starting that is determined beforehand. When it is determined that the rotational speed of the electric motor  13  does not become equal to the rotational speed of the target engine rotational speed for starting, the determination unit  31  repeats the determination process, until the rotational speed of the electric motor  13  becomes equal to the target engine rotational speed for starting. 
         [0067]    When it is determined that the rotational speed of the electric motor  13  becomes equal to the target engine rotational speed for starting in step S 16 , the process proceeds to step S 17  where the clutch control unit  32  issues an instruction to the clutch  12  in order to control the clutch  12  to be in the engagement state. 
         [0068]    In step S 18 , the electric motor control unit  33  issues an instruction to the motor ECU  17  to control the electric motor  13  and the inverter  14 , thereby controls the electric motor  13  to generate an assist torque in normal state. Then, the process of the assist start control is ended. 
         [0069]    When it is determined that the driver request torque does not exceed the assist start torque for starting in step S 12 , the assist by the electric motor  13  is unnecessary for starting the vehicle. Therefore, the assist by the electric motor  13  is not carried out, so that the assist start control is ended, and the vehicle starts moving only by the driving force of the engine  10 . 
         [0070]    As described above, the driving force (torque) of the electric motor  13  assists the engine  10  when the vehicle starts. Therefore, it is unnecessary to rapidly increase the rotational speed of the engine  10 . Accordingly, the fuel consumption is improved, and the rotational speed of the engine  10  can be kept down, whereby the abrasion of the clutch  12  can be prevented. It is only necessary that the electric motor  13  generates necessary torque during a short period in which the clutch  12  is in the partial engagement state, whereby the temperature rise of the electric motor  13  and the inverter  14  can be prevented. 
         [0071]    As described above, the fuel consumption can be reduced, and the abrasion of the clutch and the temperature rise of the electric motor can be prevented. In other words, the present embodiment can enhance fuel consumption, durability, and stability. 
         [0072]    When the SOC (state of charge) of the battery  15  is low (when the amount of charge is low), the assist starting is not carried out, and the vehicle starts only with the driving force of the engine  10 , even if the assist torque for starting exceeds the assist start torque for starting. 
         [0073]    Upon the start of the vehicle, the electric motor  13  may generate whole driver request torque according to the depression amount of the accelerator pedal depressed by the driver. 
         [0074]      FIG. 6  is a time chart for describing the assist start control, when the electric motor  13  generates the driver request torque upon the start of the vehicle. 
         [0075]    In  FIG. 6 , a dotted line indicates the rotational speed of the engine  10 , and a chain line indicates the rotational speed of the electric motor  13 . A solid line indicates the driver request torque, and a two-dot chain line indicates engine torque. 
         [0076]    In  FIG. 6 , the vehicle starts running from a time t 1 . The clutch  12  is in a partial engagement state from the time t 1 . When the driver intends to drive the vehicle, the driver depresses the accelerator pedal. Therefore, the driver request torque increases, and the driver request torque is almost constant until the vehicle starts moving (the speed reaches initial rate). 
         [0077]    In this case, the engine  10  keeps an idling rotational speed. Simultaneously, the electric motor  13  increases the rotational speed, and generates the driver request torque necessary for starting the vehicle. 
         [0078]    On a time t 2 , the rotational speed of the engine  10  and the rotational speed of the electric motor  13  become almost the same, and the clutch  12  is engaged. 
         [0079]    Specifically, during the period from the time t 1  to time t 2  when the clutch is in the partial engagement state, the hybrid vehicle  1  is driven to start only by the driving force of the electric motor  13 . 
         [0080]    After the time t 2 , the vehicle is in the normal assist state in which the driving force of the electric motor  13  assists the driving of the vehicle. 
         [0081]      FIG. 7  is a flowchart for describing another example of the process of the assist start control, when the electric motor  13  generates the driver request torque upon the start of the vehicle. In step S 31 , the electric motor control unit  33  calculates an assist torque for starting equal to the driver request torque according to the depression amount of the accelerator pedal depressed by the driver. 
         [0082]    The processes in steps S 32  to S 34  are the same as those in steps S 12  to S 14  in  FIG. 5 , and the description thereof will not be repeated. The processes in steps S 35  to S 37  are the same as those in steps S 16  to S 18  in  FIG. 5 , and the description thereof will not be repeated. 
         [0083]    As described above, the driver request torque can be generated by the electric motor  13  upon the start of the vehicle. 
         [0084]    When the vehicle  1  starts with the engine  10  being assisted by the driving force of the electric motor  13  on an uphill having a sharp inclination, the period in which the clutch is in the partial engagement state becomes long. In this case, the discharge amount of the battery  15  is excessive, so that the balance of the SOC of the battery  15  might be disrupted. 
         [0085]    In view of this, the assist start torque is rather increased, when the inclination sensor detects that the uphill has a sharp inclination. Thus, the electric motor  13  compensates only the torque corresponding to an amount that cannot be supplied as the power performance from the engine  10  with small displacement, and the basic power is fed by the engine  10 . The control described above can reduce a fear that the balance of the SOC of the battery  15  is disrupted because of the excessive assist by the electric motor  13 , and can shorten the period in which the clutch is in the partial engagement state. 
         [0086]    On a flat road, the electric motor  13  can generate most of the driver request torque, whereby the vehicle speed is promptly increased to a speed by which the period of the partial engagement state of the clutch is ended. This can shorten the period of the partial engagement state of the clutch, and prevent the engine  10  from revving up upon the start of the vehicle, whereby the fuel consumption can be improved with less power consumption. 
         [0087]      FIG. 8  is a view illustrating examples of the vehicle full torque, assist start torque, and assist full torque. In  FIG. 8 , a vertical axis indicates torque, and a horizontal axis indicates a rotational speed. In  FIG. 8 , a solid line indicates the vehicle full torque, a chain line indicates the assist start torque on a flat road, and a double chain line indicates the assist start torque on an uphill having sharp inclination. A two-dot chain line indicates the assist full torque on the flat road, and a double two-dot chain line indicates the assist full torque on the uphill having sharp inclination. 
         [0088]    As illustrated in  FIG. 8 , the assist start torque on the uphill having sharp inclination has a value larger than the assist start torque on the flat road. The assist full torque on the uphill having sharp inclination has a value smaller than the assist full torque on the flat road. 
         [0089]      FIG. 9  is a flowchart illustrating still another example of the process of the assist start control. In step S 71 , the electric motor control unit  33  calculates an assist torque for starting the vehicle that is equal to the difference between the driver request torque according to the depression amount of the accelerator pedal depressed by the driver and the idling torque that is generated when the engine  10  is in the idling state. 
         [0090]    In step S 72 , the determination unit  31  acquires the inclination information indicating the inclination of the road surface, thereby detecting the inclination of the road surface. The inclination information is also fed to the correction unit  35 . In step S 73 , the determination unit  31  determines whether or not the uphill has an inclination equal to or larger than a predetermined inclination by referring to the inclination information. When the determination unit  31  determines that the uphill has the inclination equal to or larger than the predetermined inclination in step S 73 , the correction unit  35  increases the assist start torque according to the inclination indicated by the inclination information in step S 74 . In this case, the correction unit  35  may increase the assist start torque in proportion to the inclination, may non-linearly increase the assist start torque with respect to the inclination, or may increase the assist start torque in a stepwise manner. 
         [0091]    In step S 75 , the correction unit  35  decreases the assist full torque according to the inclination indicated by the inclination information. In this case, the correction unit  35  may linearly decrease the assist full torque with respect to the inclination, may non-linearly decrease the assist full torque with respect to the inclination, or may decrease the assist full torque in a stepwise manner. After step S 75 , the process proceeds to step S 76 . 
         [0092]    When the determination unit  31  determines that the uphill does not have the inclination equal to or larger than the predetermined inclination in step S 73 , the processes in step S 74  and step S 75  are skipped, so that the assist start torque and the assist full torque are not corrected. 
         [0093]    In step S 76 , the determination unit  31  determines whether the driver request torque exceeds the assist start torque or not. When it is determined that the driver request torque exceeds the assist start torque in step S 76 , the process proceeds to step S 77  where the determination unit  31  determines whether the assist torque for starting exceeds the assist full torque or not. 
         [0094]    When it is determined that the assist torque for starting exceeds the assist full torque in step S 77 , the process proceeds to step S 78  where the correction unit  35  specifies the assist torque for starting as the assist full torque. In other words, the value of the assist torque for starting becomes equal to the value of the assist full torque. After step S 78 , the process proceeds to step S 79 . 
         [0095]    When the determination unit  31  determines that the assist torque for starting does not exceed the assist full torque in step S 77 , the process in step S 78  is skipped, so that the assist torque for starting is not corrected, and the process proceeds to step S 79 . 
         [0096]    In step S 79 , the clutch control unit  32  issues an instruction to the clutch  12  to control the clutch  12 , whereby the clutch  12  is in the partial engagement state. 
         [0097]    In step S 80 , the electric motor control unit  33  issues an instruction to the motor ECU  17  to control the electric motor  13  and the inverter  14 , thereby controlling the electric motor  13  to increase the rotational speed of the electric motor  13 , and allowing the electric motor  13  to generate the assist torque for starting. 
         [0098]    In step S 81 , the engine control unit  34  issues an instruction to the engine ECU  11  to control the engine  10 , thereby controlling the engine  10 , whereby the engine  10  generates the torque equal to the difference between the driver request torque and the assist torque for starting. 
         [0099]    In step S 82 , the determination unit  31  determines whether the rotational speed of the electric motor  13  becomes equal to the target engine rotational speed for starting the vehicle that is determined beforehand. When it is determined that the rotational speed of the electric motor  13  does not become equal to the rotational speed of the target engine rotational speed for starting, the determination unit  31  repeats the determination process, until the rotational speed of the electric motor  13  becomes equal to the target engine rotational speed for starting. 
         [0100]    When it is determined that the rotational speed of the electric motor  13  becomes equal to the target engine rotational speed for starting in step S 82 , the process proceeds to step S 83  where the clutch control unit  32  issues an instruction to the clutch  12  in order to control the clutch  12  to be in the engagement state. 
         [0101]    In step S 84 , the electric motor control unit  33  issues an instruction to the motor ECU  17  to control the electric motor  13  and the inverter  14 , thereby controls the electric motor  13  to set the torque of the electric motor  13  as  0 . In step S 85 , the electric motor control unit  33  issues an instruction to the motor ECU  17  to control the electric motor  13  and the inverter  14 , thereby controls the electric motor  13  to generate the assist torque in normal state. Then, the process of the assist start control is ended. 
         [0102]    When it is determined that the driver request torque does not exceed the assist start torque in step S 76 , the assist by the electric motor  13  is unnecessary for starting the vehicle. Therefore, the vehicle starts normally without the assist by the electric motor  13 , so that the assist start control is ended. 
         [0103]    When the inclination of the uphill is sharp, the assist start torque is rather increased to compensate only the insufficient torque of the engine  10  by the electric motor  13 , and the basic power (torque) is generated by the engine  10 . Accordingly, the excessive discharge of the battery  15  can be prevented, and the period of the partial engagement state of the clutch can be shortened. 
         [0104]    Most of the driver request torque is generated by the electric motor  13  on the flat road. Therefore, the vehicle speed can promptly be increased to a speed by which the period of the partial engagement state of the clutch is ended. Accordingly, this can shorten the period of the partial engagement state of the clutch, and can prevent the engine  10  from revving up upon the start of the vehicle, and can improve fuel consumption with less power consumption. 
         [0105]    It is described above that the engine  10  is the internal combustion engine. However, the engine  10  may be a thermal engine including an external combustion engine. 
         [0106]    The computer program executed by the hybrid ECU  18  is installed beforehand in the hybrid ECU  18  in the above description. However, a removable media on which the computer program is stored (that stores the computer program) may be attached to a drive not illustrated, and the computer program read from the removable media may be stored on the non-volatile memory in the hybrid ECU  18 , or the computer program sent via a wired or wireless transfer medium may be received by a communication unit not illustrated, and stored in the non-volatile memory in the hybrid ECU  18 , whereby the computer program may be installed to the hybrid ECU  18  that is a computer. 
         [0107]    The respective ECUs may be realized by an ECU having some of these functions or all of these functions. Alternatively, an ECU having classified functions of each ECU may newly be provided. 
         [0108]    The computer program executed by the computer may be a computer program by which the process is executed in a time-series manner according to the order described in the present specification, or may be a computer program by which the process is executed simultaneously, or on a necessary timing when called. 
         [0109]    The embodiment of the present invention is not limited to the above-mentioned embodiment, and various modifications are possible without departing from the gist of the present invention.