Patent Publication Number: US-2015088353-A1

Title: Electric vehicle

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an electric vehicle that uses electric power as motive power. 
     2. Description of the Related Art 
     In an electric vehicle, an operation amount of an accelerator device such as an accelerator grip is detected by an accelerator position sensor. The electric power supplied from a battery to a motor is adjusted based on the detection result. Thus, a torque generated by the motor is adjusted. In this manner, a rider operates the accelerator device so that a speed of the electric vehicle is adjusted. 
     When a problem occurs at the accelerator position sensor, however, the operation amount of the accelerator device may be inaccurately detected. In that case, the electric vehicle may perform an operation that differs from the intention of the rider. Therefore, it is necessary to stop the travelling of the electric vehicle in order to repair or exchange the accelerator position sensor. 
     In a two-wheel electric vehicle described in JP 2013-6468 A, if a brake device is operated during travelling, energy supplied to the motor is stopped. Therefore, even if a problem occurs at the accelerator position sensor, the two-wheel electric vehicle is easily decelerated and stopped by the operation of the brake device. 
     When the energy supplied to the motor is stopped, however, the torque of the motor rapidly decreases. Therefore, the rider may have an uncomfortable feeling at the time of operating the brake device. For example, the rider may operate the brake device while turning the two-wheel electric vehicle. In that case, the torque of the motor rapidly decreases, and the rider has an uncomfortable feeling. 
     On the other hand, in the two-wheel electric vehicle, if the operation of the brake device is released while the accelerator device is operated, the torque of the motor rapidly increases. Also in this case, the rider has an uncomfortable feeling. 
     SUMMARY OF THE INVENTION 
     Preferred embodiments of the present invention provide an electric vehicle in which a rider is unlikely to have or prevented from having an uncomfortable feeling at the time of operating a braking device or at the time of releasing operation of the braking device. 
     According to a preferred embodiment of the present invention, an electric vehicle includes a main body including a drive wheel, a motor configured to generate a torque to rotate the drive wheel, an accelerator device configured to be operated by a rider in order to adjust the torque of the motor, an operation amount detector configured to detect an operation amount of the accelerator device, a braking device configured to be operated by the rider in order to brake the main body, and a controller programmed to control the motor based on the operation amount detected by the operation amount detector and the operation of the braking device by the rider, wherein the controller is programmed to control the motor such that the torque of the motor gradually decreases when the braking device switches from a non-operation state to an operation state with the torque being generated by the motor. 
     In the electric vehicle, the operation amount of the accelerator device by the rider is detected by the operation amount detector. The torque that corresponds to the detected operation amount is generated by the motor. The drive wheel is rotated by the torque of the motor so that the main body is moved. On the other hand, the rider operates the braking device so that the main body is braked. 
     When the braking device is switched from the non-operation state to the operation state with the torque being generated by the motor, the torque of the motor gradually decreases. Thus, even in a state in which the operation amount of the accelerator device is inaccurately detected, the main body is easily decelerated and stopped. Further, because the torque of the motor does not rapidly decrease but gradually decreases, the rider is unlikely to have or prevented from having an uncomfortable feeling. 
     The controller is programmed to store first torque information and second torque information that respectively indicate the torque to be generated by the motor according to a movement speed of the main body, to control the motor based on the first torque information with the braking device not being operated, and to control the motor based on the second torque information with the braking device being operated. The first and second torque information are preferably set such that a value indicated by the second torque information with regard to each movement speed is smaller than a value indicated by the first torque information, and the controller is preferably programmed to control the motor such that the torque of the motor gradually changes from the value indicated by the first torque information to the value indicated by the second torque information when the braking device switches from the non-operation state to the operation state with the torque being generated by the motor. 
     In this case, because the value indicated by the second torque information is smaller than the value indicated by the first torque information with regard to each movement speed, the torque of the motor obtained when the braking device is operated is smaller than the torque of the motor obtained when the braking device is not operated. Therefore, the main body is easily decelerated and stopped by the operation of the braking device. 
     Further, at the time of the operation of the braking device, because the torque of the motor gradually changes from the value indicated by the first torque information to the value indicated by the second torque information, the rider is unlikely to have or prevented from having an uncomfortable feeling. 
     According to another preferred embodiment of the present invention, an electric vehicle includes a main body including a drive wheel, a motor configured to generate a torque to rotate the drive wheel, an accelerator device configured to be operated by a rider in order to adjust the torque of the motor, an operation amount detector configured to detect an operation amount of the accelerator device, a braking device configured to be operated by the rider in order to brake the main body, and a controller programmed to control the motor based on an operation amount of the accelerator device and the braking device by the rider, wherein the controller is programmed to control the motor such that the torque of the motor gradually increases when the braking device switches from an operation state to a non-operation state with the accelerator device being operated. 
     In this electric vehicle, the operation amount of the accelerator device by the rider is detected by the operation amount detector. The torque that corresponds to the detected operation amount is generated by the motor. The drive wheel is rotated by the torque of the motor, and the main body is moved. On the other hand, the rider operates the braking device so that the main body is braked. 
     If the operation of the braking device is released while the accelerator device is operated, the torque of the motor does not rapidly increase but gradually increases. Therefore, the rider is unlikely to have or prevented from having an uncomfortable feeling, and sudden acceleration and a rapid increase in speed of the main body are prevented. 
     The controller is programmed to store first torque information and second torque information that respectively indicate the torque to be generated by the motor according to a movement speed of the main body, to control the motor based on the first torque information with the braking device not being operated, and to control the motor based on the second torque information with the braking device being operated. The first and second torque information are preferably set such that a value indicated by the second torque information with regard to each movement speed is smaller than a value indicated by the first torque information, and the controller is programmed to control the motor such that the torque of the motor gradually changes from the value indicated by the second torque information to the value indicated by the first torque information when the braking device switches from the operation state to the non-operation state with the torque being generated by the motor. 
     In this case, because the value indicated by the second torque information is smaller than the value indicated by the first torque information with regard to each movement speed, the torque of the motor obtained when the braking device is operated is smaller than the torque of the motor obtained when the braking device is not operated. Therefore, the main body is easily decelerated and stopped by the operation of the braking device. 
     Further, at the time of releasing the operation of the braking device, because the torque of the motor gradually changes from the value indicated by the second torque information to the value indicated by the first torque information, the rider is unlikely to have or prevented from having an uncomfortable feeling. 
     The electric vehicle may further include a speed detector configured to detect a movement speed of the main body, wherein the first and second torque information preferably respectively indicate a relationship among the movement speed of the main body, the operation amount of the accelerator device, and the torque to be generated by the motor, and the controller is programmed to control the motor based on the movement speed detected by the speed detector, the operation amount detected by the operation amount detector, and the first and second torque information. 
     In this case, in the operation state of the braking device, the motor is controlled according to the movement speed of the main body, the operation amount of the accelerator device, and the first torque information. On the other hand, in the non-operation state of the braking device, the motor is controlled according to the movement speed of the main body, the operation amount of the accelerator device, and the second torque information. Thus, the torque of the motor is appropriately adjusted in either one of the operation state and the non-operation state of the braking device. 
     The second torque information is preferably set to indicate a value larger than 0 when the operation amount of the accelerator device is larger than 0 and the movement speed of the main body is larger than 0 and is in a first range that is smaller than a predetermined value, and to indicate 0 when the operation amount of the accelerator device is larger than 0 and the movement speed of the main body is in a second range that is more than the predetermined value. 
     In this case, when the main body is stopped and is moved at a low speed, if the operation amount of the accelerator device is larger than 0, the torque of the motor does not become 0 even if the braking device is operated. Thus, the main body is reliably stopped and started while climbing. On the other hand, the torque of the motor becomes 0 if the braking device is operated during a period in which the main body is moved at an intermediate or high speed. Therefore, the main body is easily decelerated and stopped by the operation of the braking device. 
     The second torque information is preferably set to indicate a value that decreases from a maximum value to 0 as the movement speed increases in the first range. 
     In this case, in a state in which the accelerator device is operated and the braking device is operated, the lower the movement speed of the main body is, the larger the torque of the motor is. Therefore, the torque of the motor is appropriately adjusted according to the movement speed of the main body. 
     The electric vehicle may further include a battery, wherein the controller is preferably programmed to adjust the torque of the motor by adjusting electric power supplied from the battery to the motor. 
     In this case, the torque of the motor is easily adjusted. 
     The preferred embodiments of the present invention make it unlikely or not possible for the rider to have an uncomfortable feeling at the time of operating the braking device or releasing the operation of the braking device. 
     The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic side view showing the schematic configuration of an electric vehicle according to a preferred embodiment of the present preferred embodiment. 
         FIG. 2  is an external perspective view showing the configuration of a handle. 
         FIG. 3  is a block diagram showing the configuration of the control system of the electric vehicle. 
         FIG. 4  is a diagram showing one example of a normal torque map. 
         FIG. 5  is a diagram showing one example of a brake torque map. 
         FIGS. 6A to 6C  are diagrams for explaining the change of the actual torque obtained when the electric vehicle switches from a brake-off state to a brake-on state. 
         FIGS. 7A to 7C  are diagrams for explaining the change of the actual torque obtained when the electric vehicle switches from the brake-on state to the brake-off state. 
         FIGS. 8A to 8C  are diagrams for explaining the change of the actual torque obtained when the electric vehicle switches from the brake-off state to the brake-on state, and returns to the brake-off state. 
         FIG. 9  is a flow chart of a torque adjustment process performed by a CPU of  FIG. 3 . 
         FIG. 10  is a diagram showing another example of a normal torque map. 
         FIG. 11  is a diagram showing another example of a brake torque map. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An electric vehicle according to preferred embodiments of the present invention will be described below. 
       FIG. 1  is a schematic side view showing the schematic configuration of the electric vehicle according to a preferred embodiment of the present preferred embodiment. The electric vehicle according to the present preferred embodiment is preferably a motorcycle, for example. 
     The electric vehicle  100  of  FIG. 1  includes a main body  1 . The main body  1  includes a main frame  11  and a front fork  12 . The front fork  12  is attached to a head pipe  11   a  that is provided at the front end of the main frame  11  to be swingable to the right and the left. A front wheel  2  is supported at the lower end of the front fork  12  to be rotatable. A handle  13  is provided at the upper end of the front fork  12 . 
     A battery storage  11   b  is provided at the center or substantially the center of the main frame  11 . A battery  5  is stored in the battery storage  11   b . A rear arm cover  7  is provided behind the battery storage  11   b . A rear arm (not shown) and a motor  8  are provided in the rear arm cover  7 . A rear wheel  3  is supported by the rear arm to be rotatable. The motor  8  is driven by the electric power of the battery  5 , and generates a torque to rotate the rear wheel  3 . The torque of the motor  8  is transmitted to the rear wheel  3  via a chain or the like. A seat  9  is provided above the rear arm cover  7 , and a controller  10  is provided at a position between the rear arm cover  7  and the seat  9 . 
     A brake  2   a  is provided at the front wheel  2 , and a brake  3   a  is provided at the rear wheel  3 . The front wheel  2  is braked by the brake  2   a , and the rear wheel  3  is braked by the brake  3   a . The brake  2   a  is preferably a disc brake, for example, and the brake  3   a  is preferably a drum brake, for example. Further, a vehicle speed sensor SS is provided at the front wheel  2 . The vehicle speed sensor SS detects the rotation speed of the front wheel  2 . The movement speed (the vehicle speed) of the main body  1  is calculated from the detected rotation speed. 
       FIG. 2  is an external perspective view showing the configuration of the handle  13 . In  FIG. 2 , the appearance of the handle  13  is shown as viewed from a rider who is seated on the seat  9 . As shown in  FIG. 2 , the handle  13  includes a handle bar  40  that extends to the right and the left. A grip  41  is provided at the left end of the handle bar  40 , and an accelerator grip  42  is provided at the right end of the handle bar  40 . The accelerator grip  42  is provided to be rotatable in a predetermined rotation angular range with respect to the handle bar  40 . The accelerator grip  42  is an example of an accelerator device. The accelerator device is operated by the rider in order to adjust the torque of the motor  8 . In the present example, the accelerator grip  42  is operated so that the torque generated by the motor  8  of  FIG. 1  is adjusted. 
     A brake lever  43  to operate the brake  3   a  of the rear wheel  3  of  FIG. 1  is arranged in front of the grip  41 , and a brake lever  44  to operate the brake  2   a  of the front wheel  2  of  FIG. 1  is arranged in front of the accelerator grip  42 . The brake levers  43 ,  44  are examples of a braking device. The braking device is operated by the rider in order to brake the main body  1 . In the present example, when the brake lever  43  is operated, the rear wheel  3  is braked by the brake  3   a . When the brake lever  44  is operated, the front wheel  2  is braked by the brake  2   a . Therefore, one or both of the brake levers  43 ,  44  is operated so that the front body  1  is braked. 
     A main switch (not shown) is provided below the handle  13 . When the main switch is turned on, electric power is supplied from the battery  5  to the controller  10  of  FIG. 1 . 
       FIG. 3  is a block diagram showing the configuration of the control system of the electric vehicle  100 . As shown in  FIG. 3 , the electric vehicle  100  includes brake sensors BS 1 , BS 2  and an accelerator sensor AS. 
     The brake sensors BS 1 , BS 2  respectively detect the presence or absence of the operation of the brake levers  43 ,  44 . Specifically, when an operation amount of the brake lever  43  exceeds a threshold value, the operation of the brake lever  43  is detected by the brake sensor BS 1 . Similarly, when the operation amount of the brake lever  44  exceeds the threshold value, the operation of the brake lever  44  is detected by the brake sensor BS 2 . For example, a minimum value of the necessary operation amount of the brake levers  43 ,  44  in order to cause the brakes  2   a ,  3   a  to operate the front wheel  2  and the rear wheel  3  is set to the above-mentioned threshold value. The accelerator sensor AS detects the operation amount (the accelerator opening) of the accelerator grip  42 . 
     The controller  10  includes a CPU (Central Processing Unit)  51 , a ROM (Read Only Memory)  52 , a RAM (Random Access Memory)  53  and an inverter  54 . The detection results obtained by the brake sensors BS 1 , BS 2 , the vehicle speed sensor SS, and the accelerator sensor AS are supplied to the CPU  51 . 
     The ROM  52  is preferably a nonvolatile memory, for example, and stores computer programs such as a system program of the CPU  51 , the below-mentioned torque adjustment processing program, and the like. Further, the ROM  52  stores the below-mentioned torque map. The RAM  53  is preferably a volatile memory, for example, and is used as a processing area of the CPU  51  and temporarily stores each type of data. The CPU  51  performs the below-mentioned torque adjustment process by executing the torque adjustment processing program stored in the ROM  52  on the RAM  53 . 
     The inverter  54  is connected between the battery  5  and the motor  8 . The electric power of the battery  5  is supplied to the motor  8  via the inverter  54 . In this case, DC/AC (Direct Current/Alternate Current) conversion is performed by the inverter  54 . Further, the electric power generated by the motor  8  is supplied to the battery  5  via the inverter  54  so that regenerative charging of the battery  5  is performed. In this case, AC/DC (Alternate Current/Direct Current) conversion is performed by the inverter  54 . 
     The CPU  51  controls the inverter  54  based on the detection results obtained by the brake sensors BS 1 , BS 2 , the vehicle speed sensor SS, and the accelerator sensor AS. Thus, the electric power supplied from the battery  5  to the motor  8  is adjusted, and the torque of the motor  8  is adjusted. 
     A torque map shows the relationship between the vehicle speed and the torque (hereinafter referred to as a target torque) to be generated by the motor  8 . The CPU  51  determines the target torque using the torque map stored in the ROM  52 , and controls the inverter  54  such that the determined target torque is generated by the motor  8 . 
     In the present preferred embodiment, different torque maps are used between a case in which neither one of the brake levers  43 ,  44  is operated, and a case in which one or both of the brake levers  43 ,  44  is operated. Hereinafter, a state in which neither one of the brake levers  43 ,  44  is used is referred to as a brake-off state, and a state in which one or both of the brake levers  43 ,  44  is used is referred to as a brake-on state. The torque map used in the brake-off state is referred to as a normal torque map, and the torque map used in the brake-on state is referred to as a brake torque map. 
       FIG. 4  is a diagram showing one example of the normal torque map.  FIG. 5  is a diagram showing one example of the brake torque map. In  FIGS. 4 and 5 , the abscissas indicate the vehicle speed, and the ordinates indicate the target torque. The target torques differ depending on the accelerator opening, and the larger the accelerator opening is, the larger the target torque is. The solid line L 1  of  FIG. 4  and the solid line L 2  of  FIG. 5  respectively indicate the target torque (hereinafter referred to as a maximum target torque) obtained when the accelerator opening is at a maximum. 
     In the normal torque map of  FIG. 4 , in a case in which the vehicle speed is 0, the maximum target torque is T 1 , and the maximum target torque gradually decreases as the vehicle speed increases. 
     In the brake-off state, the target torque is calculated based on the vehicle speed detected by the vehicle speed sensor SS, the accelerator opening detected by the accelerator sensor AS, and the normal torque map of  FIG. 4 . 
     First, the maximum target torque that corresponds to the detected vehicle speed is obtained from the normal torque map. For example, when the detected vehicle speed is S 11 , the maximum target torque T 11  is obtained from the normal torque map. Subsequently, the obtained maximum target torque is multiplied by a value that corresponds to the detected accelerator opening. For example, when the detected accelerator opening is n percent (n is a value not less than 0 and not more than 100) with respect to the maximum value of the accelerator opening, the maximum target torque T 11  is multiplied by n/100. Thus, a target torque T 11 A is calculated. 
     In the brake torque map of  FIG. 5 , in a case in which the vehicle speed is 0, the maximum target torque is T 2 , and when the vehicle speed is not less than 0 and is in a range of less than S 1 , the maximum target torque gradually decreases as the vehicle speed increases. The value T 2  is smaller than the value T 1  of  FIG. 4 . When the vehicle speed is in a range of not less than S 1 , the maximum target torque is 0. S 1  is a value of not less than about 10 km/h, for example, and not more than about 30 km/h, for example. In the present example, the value S 1  preferably is about 22 km/h, for example. With regard to each vehicle speed, a value of the maximum target torque of the brake torque map is set to be smaller than a value of the maximum target torque of the normal torque map. 
     In the brake-on state, the target torque is calculated based on the vehicle speed detected by the vehicle speed sensor SS, the accelerator opening detected by the accelerator sensor AS, and the brake torque map of  FIG. 5 . 
     When the detected vehicle speed is less than S 1 , the target torque is calculated using the brake torque map of  FIG. 5  similarly to a case in which the normal torque map of  FIG. 4  is used. For example, when the detected vehicle speed is S 12 , the maximum target torque T 12  is obtained from the brake torque map. The obtained maximum target torque T 12  is multiplied by a value that corresponds to the accelerator opening (n/100, for example). Thus, the target torque T 12 A is calculated. On the other hand, when the detected vehicle speed is not less than S 1 , the target torque is 0. 
     When the accelerator openings are the same, a value indicated by the brake torque map is smaller than a value indicated by the normal torque map with regard to each vehicle speed. 
     The inverter  54  ( FIG. 3 ) is controlled based on the calculated target torque. Thus, in the brake-off state, the torque of the motor  8  is adjusted to a value indicated by the normal torque map. Further, in the brake-on state, the torque of the motor  8  is adjusted to a value indicated by the brake torque map. 
     In the present preferred embodiment, when the electric vehicle  100  switches from the brake-off state to the brake-on state, the torque of the motor  8  does not rapidly change but gradually changes from a value indicated by the normal torque map to a value indicated by the brake torque map. Further, when the electric vehicle  100  switches from the brake-on state to the brake-off state, the torque of the motor  8  does not rapidly change but gradually changes from a value indicated by the brake torque map to a value indicated by the normal torque map. Hereinafter, the torque actually generated by the motor  8  is referred to as an actual torque. 
       FIGS. 6A to 6C  are diagrams for explaining the change of the actual torque obtained when the electric vehicle  100  switches from the brake-off state to the brake-on state.  FIGS. 7A to 7C  are diagrams for explaining the change of the actual torque obtained when the electric vehicle  100  switches from the brake-on state to the brake-off state. In  FIGS. 6A to 7C , the abscissas indicate the vehicle speed, and the ordinates indicate the actual torque. 
     In  FIGS. 6A to 7C , the solid line L 1  of  FIG. 4  and the solid line L 2  of  FIG. 5  that indicate the maximum target torques are shown, and the one-dot and dash lines L 3 , L 4  that indicate the target torques obtained when the accelerator opening is smaller than the maximum value by a certain ratio are shown. The target torques indicated by the one-dot dash lines L 3  of  FIGS. 6A to 6C  are smaller than the maximum target torques indicated by the solid line L 1  by the certain ratio, and the target torques indicated by the one-dot dash lines L 4  of  FIGS. 7A to 7C  are smaller than the maximum target torques indicated by the solid lines L 2  by the certain ratio. 
     The change of the actual torque obtained when the electric vehicle  100  switches from the brake-off state to the brake-on state will be described with reference to  FIGS. 6A to 6C . In the example of  FIGS. 6A to 6C , the accelerator opening is kept at a value that corresponds to the one-dot dash lines L 3 , L 4 . The accelerator opening that corresponds to the one-dot dash line L 3  and the accelerator opening that corresponds to the one-dot dash line L 4  are equal to each other. 
     As shown in  FIG. 6A , in the brake-off state, the actual torque is adjusted based on the normal torque map to match a value on the one-dot dash line L 3 . In the present example, the actual torque is adjusted to T 21  when the vehicle speed is S 21 . When the electric vehicle  100  switches to the brake-on state, the vehicle speed gradually decreases, and the actual torque gradually decreases as shown in  FIGS. 6B and 6C . In this case, the actual torque decreases with a predetermined time constant, for example. In the present example, the vehicle speed gradually decreases from the value S 21  of  FIG. 6A  to a value S 22  of  FIG. 6B  and then a value S 23  of  FIG. 6C , and the actual torque gradually decreases from the value T 21  of  FIG. 6A  to a value T 22  of  FIG. 6B  and then a value T 23  of  FIG. 6C . The value T 23  is a value on the one-dot dash line L 4 . When the actual torque reaches a value on the one-dot dash line L 4 , the actual torque is thereafter adjusted based on the brake torque map to match a value on the one-dot dash line L 4 . 
     In this manner, when the electric vehicle  100  switches from the brake-off state to the brake-on state, the actual torque gradually decreases from a value indicated by the normal torque map to a value indicated by the brake torque map. Thereafter, the actual torque is adjusted to match a value indicated by the brake torque map. 
     The change of the actual torque obtained when the electric vehicle  100  switches from the brake-on state to the brake-off state with reference to  FIGS. 7A to 7C  will be described. In the example of  FIGS. 7A to 7C , the accelerator opening is kept at a value that corresponds to the one-dot dash lines L 3 , L 4 . 
     As shown in  FIG. 7A , in the brake-off state, the actual torque is adjusted based on the brake torque map to match a value indicated by the one-dot dash line L 4 . In the present example, when the vehicle speed is S 31 , the actual torque is adjusted to T 31 . When the electric vehicle  100  switches to the brake-off state, the vehicle speed gradually increases, and the actual torque gradually increases as shown in  FIGS. 7B and 7C . In this case, the actual torque increases at a predetermined time constant, for example. In the present example, the vehicle speed gradually increases from the value S 31  of  FIG. 7A  to a value S 32  of  FIG. 7B  and then to a value S 33  of  FIG. 7C , and the actual torque gradually increases from the value T 31  of  FIG. 7A  to a value T 32  of  FIG. 7B  and then a value T 33  of  FIG. 7C . The value T 33  is a value indicated by the one-dot dash line L 3 . In this manner, when the actual torque reaches a value indicated by the one-dot dash line L 3 , the actual torque is thereafter adjusted based on the normal torque map to match a value indicated by the one-dot dash line L 3 . 
     In this manner, when the electric vehicle  100  switches from the brake-on state to the brake-off state, the actual torque gradually increases from a value indicated by the brake torque map to a value indicated by the normal torque map. Thereafter, the actual torque is adjusted to match a value indicated by the normal torque map. 
     Next, difference from the examples of  FIGS. 6A to 6C  with regard to the change of the actual torque obtained when the electric vehicle  100  returns to the brake-off state after switching from the brake-off state to the brake-on state will be described. 
       FIGS. 8A to 8C  are diagrams for explaining the change of the actual torque obtained when the electric vehicle  100  switches from the brake-off state to the brake-on state, and then returns to the brake-off state. In  FIGS. 8A to 8C , the abscissas indicate the vehicle speed, and the ordinates indicate the actual torque. In  FIGS. 8A to 8C , the solid lines L 1 , L 2  and the one-dot dash lines L 3 , L 4  are shown similarly to  FIGS. 6A to 7C . Even in the examples of  FIGS. 8A to 8C , the accelerator opening is kept at a value that corresponds to the one-dot dash line L 3 , L 4 . 
     In the examples of  FIGS. 8A to 8C , the electric vehicle  100  switches from the brake-on state to the brake-off state before the actual torque reaches a value on the one-dot dash line L 4  after the electric vehicle  100  switches from the brake-off state to the brake-on state. Specifically, as shown in  FIG. 8B , when the actual torque reaches the value T 22  between the one-dot dash line L 3  and the one-dot dash line L 4 , the electronic vehicle  100  switches from the brake-on state to the brake-off state. As shown in  FIGS. 8A and 8B , at the time of switching from the brake-off state to the brake-on state, the vehicle speed gradually decreases from the value S 21  to the value S 22 , and the actual torque gradually decreases from the value T 21  to the value T 22 . As shown in  FIGS. 8B and 8C , at the time of switching from the brake-on state to the brake-off state, the vehicle speed gradually increases from the value S 22  to the value S 21 , and the actual torque gradually increases from the value T 22  to the value T 21 . 
       FIG. 9  is a flow chart of the torque adjustment process performed by the CPU  51  of  FIG. 3 . The torque adjustment process of  FIG. 9  is periodically performed by the execution of the torque adjustment processing program stored in the ROM  52  by the CPU  51 . 
     As shown in  FIG. 9 , the CPU  51  determines whether or not the electric vehicle  100  is in the brake-on state at that time point based on the detection result obtained by the brake sensors BS 1 , BS 2  (step S 1 ). When the electric vehicle  100  is in the brake-on state, the CPU  51  calculates the target torque using the brake torque map of  FIG. 5  (step S 2 ). On the other hand, when the electric vehicle  100  is in the brake-off state, the CPU  51  calculates the target torque using the normal torque map of  FIG. 4  (step S 3 ). 
     Next, the CPU  51  determines whether or not the difference between the actual torque (hereinafter referred to as a current torque) at that time point and the target torque calculated in step S 2  or step S 3  is larger than a predetermined threshold value (step S 4 ). The current torque corresponds to the electric power supplied to the motor  8  at that time point. Therefore, the current torque is calculated based on the electric power supplied to the motor  8  at that time point. When the electric vehicle  100  switches from the brake-off state to the brake-on state, or switches from the brake-on state to the brake-off state, the difference between the current torque and the target torque is likely to be large. Therefore, when the difference between the current torque and the target torque is larger than the threshold value, the CPU  51  corrects the target torque calculated in step S 2  or step S 3  such that the difference between the target torque and the current torque is a predetermined difference value (step S 5 ). Thus, the target torque decreases or increases at a time constant. The difference value may be the same as the threshold value of step S 4 , or may be smaller than the threshold value of step S 4 . Thereafter, the CPU  51  controls the inverter  54  such that the corrected target torque is generated by the motor  8  (step S 6 ), and terminates the torque adjustment process. 
     In this manner, because the target torque is corrected such that the difference between the target torque and the current torque is not larger than the threshold value, the actual torque is prevented from rapidly changing at the time of switching from the brake-off state to the brake-on state or at the time of switching from the brake-on state to the brake-off state. 
     On the other hand, if the electric vehicle  100  is kept in the brake-off state or the brake-on state for more than a predetermined time period, the difference between the current torque and the target torque is not likely to be large. Therefore, in step S 4 , when the difference between the current torque and the target torque is not more than the threshold value, the CPU  51  controls the inverter  54  such that the target torque calculated in step S 2  or step S 3  is generated by the motor  8  (step S 5 ), and terminates the torque adjustment process. 
     In the electric vehicle  100  according to the present preferred embodiment, if at least one of the brake levers  43 ,  44  is operated with the detected accelerator opening being larger than 0, the actual torque generated by the motor  8  gradually decreases. Thus, even when the accelerator opening is inaccurately detected due to a problem at the accelerator sensor AS, the main body  1  is easily decelerated and stopped. Further, the actual torque does not rapidly decrease at the time of operating the brake lever  43 ,  44 . Therefore, even if the brake lever  43 ,  44  is operated at the time of turning the electric vehicle  100  or the like, the rider is unlikely to have or prevented from having an uncomfortable feeling. 
     On the other hand, when the operation of the brake lever  43 ,  44  is released while the accelerator grip  42  is operated, the actual torque generated by the motor  8  gradually increases. Thus, because the actual torque does not rapidly increase, the rider is unlikely to have or prevented from having an uncomfortable feeling, and sudden acceleration of the main body  1  and a sudden increase in speed are prevented. 
     Further, in the present preferred embodiment, the target torque is calculated in the brake-off state based on the vehicle speed, the accelerator opening, and the normal torque map; and the target torque is calculated in the brake-on state based on the vehicle speed, the accelerator opening, and the brake torque map. In this manner, because different torque maps are used in the brake-off state and the brake-on state, the torque of the motor  8  is appropriately adjusted in either one of the brake-off state and the brake-on state. 
     Further, in the present preferred embodiment, the actual torque gradually changes from a value indicated by the normal torque map to a value indicated by the brake torque map at the time of switching from the brake-off state to the brake-on state, and the actual torque gradually changes from a value indicated by the brake torque map to a value indicated by the normal torque map at the time of switching from the brake-on state to the brake-off state. Thus, it is possible to easily perform acceleration or deceleration without giving the rider an uncomfortable feeling. 
     Further, in the present preferred embodiment, in a case in which the maximum target torque obtained when the vehicle speed is 0 is a positive value and the vehicle speed is in a range of not less than 0 and less than S 1 , the brake torque map is set such that the maximum target torque gradually decreases as the vehicle speed increases. Thus, during a period in which the main body  1  is stopped or is moving at a low speed, if the accelerator grip  42  is operated, the torque of motor  8  does not become 0 even if the brake lever  43 ,  44  is operated. Thus, in a case in which the main body  1  is stopped or started during climbing, the main body  1  is prevented from retreating due to the inclination on the road. Therefore, the main body  1  is reliably stopped or started. 
     On the other hand, when the vehicle speed is not less than S 1 , the brake torque map is set such that the maximum target torque is 0. Therefore, during a period in which the main body  1  is moving at an intermediate or a high speed, if the brake lever  43 ,  44  is operated, the torque of the motor  8  becomes 0. Thus, the main body  1  is easily decelerated and stopped by the operation of the brake lever  43 ,  44 . 
       FIG. 10  is a diagram showing another example of the normal torque map.  FIG. 11  is a diagram showing another example of the brake torque map. In  FIGS. 10 and 11 , the abscissas indicate the vehicle speed, and the ordinates indicate the target torque. With regard to the normal torque map of  FIG. 10  and the brake torque map of  FIG. 11 , differences from the normal torque map of  FIG. 4  and the brake torque map of  FIG. 5  will be described. 
     The solid line L 1  of  FIG. 10  indicates the relationship between the vehicle speed and the maximum target torque similarly to the example of  FIG. 4 , and a plurality of two-dot dash lines L 1   a  of  FIG. 10  indicate the relationship between the vehicle speed and the target torque at the accelerator openings that differ in steps. In  FIG. 10 , only the two-dot dash line L 1   a  that corresponds to the accelerator opening in a partial range is shown, and the two-dot dash line L 1   a  that corresponds to the accelerator opening in another range is not shown. A plurality of black dots of  FIG. 10  mean that the two-dot dash lines L 1   a  are not shown. In the brake-off state, the relationship indicated by the solid line L 1  or the one two-dot dash line L 1   a  is selected based on the accelerator opening detected by the accelerator sensor AS. The target torque that corresponds to the vehicle speed detected by the vehicle speed sensor SS is obtained based on the selected relation. 
     The solid line L 2  of  FIG. 11  indicates the relationship between the vehicle speed and the maximum target torque similarly to the example of  FIG. 5 , and the plurality of two-dot dash lines L 2   a  of  FIG. 11  indicate the relationship between the vehicle speed and the target torque at the accelerator openings that differ in steps. In  FIG. 11 , only the two-dot dash line L 2   a  that corresponds to the accelerator opening in a partial range is shown, and the two-dot dash line L 2   a  that corresponds to the accelerator opening in another range is not shown. A plurality of black dots of  FIG. 11  mean that the two-dot dash lines L 2   a  are not shown. In the brake-on state, the relationship indicated by the solid line L 2  or the one two-dot dash line L 2   a  is selected based on the accelerator opening detected by the accelerator sensor AS. The target torque that corresponds to the vehicle speed detected by the vehicle speed sensor SS is obtained based on the selected relationship. 
     When the torque maps of  FIGS. 4 and 5  are used, the target torque that corresponds to the accelerator opening is calculated from the maximum target torque. Whereas, when the torque maps of  FIGS. 10 and 11  are used, the target torque that corresponds to the accelerator opening is obtained without such calculation. Thus, the processing load of the CPU  51  ( FIG. 3 ) is reduced, so that a quick process is possible. 
     While the motor  8  preferably is controlled such that the actual torque changes at a predetermined time constant at the time of switching from the brake-off state to the brake-on state, or at the time of switching from the brake-on state to the brake-off state in the above-mentioned preferred embodiments, the control of the motor  8  at the time of switching from the brake-off state to the brake-on state, or at the time of switching from the brake-on state to the brake-off state is not limited to this. For example, a plurality of torque maps that indicate values of the target torque in steps between a value indicated by the normal torque map and a value indicated by the brake torque map are stored in the ROM  52 . The target torque is calculated sequentially using the plurality of torque maps as the time elapses, and the motor  8  is controlled based on the calculated target torque. Even in this case, the actual torque is gradually changed between a value indicated by the brake torque map and a value indicated by a normal torque map. 
     While the motor  8  is preferably controlled such that the torque of the motor  8  matches a value indicated by the brake torque map in the brake-on state in the above-mentioned preferred embodiments, the present invention is not limited to this. In the brake-on state, the motor  8  may be controlled such that the torque of the motor  8  becomes 0 regardless of the movement speed of the main body  1 . In this case, when the electric vehicle  100  is switched from the brake-off state to the brake-on state, the torque of the motor  8  gradually decreases until the torque of the motor  8  is 0. Note that, when the torque of the motor  8  is 0, the energy supplied to the motor  8  may be stopped. 
     While the target torque is preferably determined using the torque map in the above-mentioned preferred embodiments, the present invention is not limited to this. For example, the target torque may be determined by the calculation using each type of detection value. 
     While the switching between the brake-off state and the brake-on state is preferably performed according to the operation of at least one of the brake levers  43 ,  44  in the above-mentioned preferred embodiments, the present invention is not limited to this. The switching between the brake-off state and the brake-on state may be performed according to the operation of predetermined one (the brake lever  43  for braking the rear wheel  3 , for example) of the brake levers  43 ,  44 . 
     While the rear wheel  3  is preferably driven by the motor  8  in the above-mentioned preferred embodiments, the present invention is not limited to this. The front wheel  2  may be driven by the motor  8 . 
     While the movement speed (the vehicle speed) of the main body  1  is preferably detected by the vehicle speed sensor SS provided at the front wheel  2  in the above-mentioned preferred embodiments, the present invention is not limited to this. For example, the rotation speed of the motor  8  may be detected, and the vehicle speed may be calculated based on the detection result. The rotation speed of the motor  8  may be detected by a rotation sensor such as an encoder that is incorporated in the motor  8 , for example, or may be detected by another sensor. 
     While the above-mentioned preferred embodiments are examples in which the present invention is applied to the motorcycle, the present invention is not limited to this. The present invention may be applied to another electric vehicle such as a motor tricycle, an automobile (a four-wheeled automobile), or the like. 
     In the following paragraphs, non-limiting examples of correspondences between various elements recited in the claims below and those described above with respect to various preferred embodiments of the present invention are explained. 
     In the above-mentioned preferred embodiments, the electric vehicle  100  is an example of an electric vehicle, the main body  1  is an example of a main body, the rear wheel  3  is an example of a drive wheel, the motor  8  is an example of a motor, the accelerator grip  42  is an example of an accelerator device, the brake levers  43 ,  44  are examples of a braking device, and the controller  10  is an example of a controller. 
     Further, the normal torque map is an example of first torque information, the brake torque map is an example of second torque information, the vehicle speed sensor SS is an example of a speed detector, the accelerator sensor AS is an example of an operation amount detector, a range not less than 0 and less than 51 is an example of a first range, a range not less than 51 is an example of a second range and the battery  5  is an example of a battery. 
     As each of various elements recited in the claims, various other elements having configurations or functions described in the claims can be also used. 
     Preferred embodiments of the present invention can be effectively utilized for various types of electric vehicles, for example. 
     While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.