Patent Publication Number: US-2022233377-A1

Title: Small electric vehicle

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application claims priority of Japanese Patent Application No. 2021-012217 filed Jan. 28, 2021. The entire contents of which are hereby incorporated by reference. 
     TECHNICAL FIELD 
     The present invention relates to a small electric vehicle. 
     BACKGROUND 
     Small electric vehicles including cart-type electric rollators and electric wheelchairs for users having difficulty in walking, such as the elderly, have been publicly known. For example, JP 2014-064620 discloses a small electric vehicle (electric wheelchair) that includes left and right motors that individually drive respective left and right driving wheels, and is configured such that the numbers of revolutions of left and right motors are determined from an operation position of joystick-type operation means, the vehicle goes forward when an operation element is tilted forward, it turns when the piece is tilted obliquely forward, it turns about a fixed position when the piece is tilted obliquely backward, and it stops when the piece is tilted straight backward. 
     SUMMARY 
     As for the small electric vehicle as described above, the speed (speed difference between left and right) is determined by the operation position of the joystick-type operation element. Accordingly, in a case of turning at a slow speed, the operation element is required to be held at an intermediate operation position, which leads to a problem for a user to drive at an intended speed on a route. 
     The present invention has been made in view of the circumstances in the prior art described above, and it has as an object to provide a small electric vehicle that can achieve turning characteristics depending on the driving state, through intuitive operation on the joystick-type operation element. 
     To solve the problems, a small electric vehicle according to the present invention includes: 
     a vehicle body that has a forward and backward direction, and a width direction; 
     left and right driving wheels provided apart in the width direction of the vehicle body; 
     free wheels provided apart from the left and right driving wheels in the forward and backward direction of the vehicle body; 
     left and right motors connected so as to respectively transmit power to the left and right driving wheels; 
     left and right rotation speed sensors for detecting rotation speeds of the left and right motors; 
     an operation unit that includes a joystick-type operation element; and 
     a control unit that controls the left and right motors according to an amount of operation on the operation element, 
     wherein the control unit is configured to calculate target rotation speeds of the left and right motors, based on a target vehicle speed provided by an operation position of the operation element, and on a target vehicle angular velocity provided by the operation position of the operation element and by the actual speed of the vehicle, and control the left and right motors such that actual rotation speeds of the left and right motors follow the respective target rotation speeds. 
     As described above, the small electric vehicle according to the present invention is configured to calculate the target rotation speeds of the left and right motors, based on the target vehicle speed provided by the operation position of the joystick-type operation element, and on the target vehicle angular velocity provided by the operation position and the actual speed of the vehicle, and control the left and right motors such that the actual rotation speeds of the left and right motors follow the target rotation speeds. Accordingly, the turning characteristics can be changed so as to support the actual speed. Appropriate turning characteristics supporting the travel state can be obtained merely through intuitive operations on the joystick-type operation element. It is thus advantageous in operation simplicity, usability, and improvement in safety. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view showing a small electric vehicle. 
         FIG. 2  is a block diagram showing a control system of the small electric vehicle. 
         FIG. 3  is a block diagram showing left and right motor control. 
         FIG. 4  shows a target vehicle speed map through a joystick operation. 
         FIG. 5  shows a target angular velocity map for low speed (a), and a target angular velocity map for high speed (b), through joystick operations. 
         FIG. 6  is a schematic plan view showing a limiter plate of the joystick. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, embodiments of the present invention are described in detail with reference to the drawings. 
     In  FIG. 1 , an electric vehicle  1  according to an embodiment of the present invention includes a vehicle body  2  made up of a mobile base  21  (lower traveling body), and an upper frame  22  provided to stand from a rear part (rear-side base  24 ) of the mobile base  21 , and is usable in a small electric vehicle mode (riding mode  1 ) indicated by solid lines in the diagram, and in a rollator mode ( 1 ′) indicated by chain double-dashed lines in the diagram. 
     The mobile base  21  includes: the rear-side base  24  (main body part) provided with left and right driving wheels  4  (rear wheels), and the upper frame  22 ; and a front-side base  25  provided with left and right driven wheels  5  (front wheels). The front-side base  25  is joined to the front side of the rear-side base  24  slidably in the front and rear direction. The mobile base  21  is configured such that the wheelbase is expandable and contractible. 
     The left and right driving wheels  4  are independently driven respectively by left and right motor units  40  ( 40 L and  40 R) mounted on the rear-side base  24 . The left and right driven wheels  5  is made up of free wheels (omni wheels, or omnidirectional wheels) including many rotatable rollers  50  at grounding parts around axes in circumferential directions. As described later, the electric vehicle  1  can be steered, braked, and driven only by controlling the left and right motor units  40 L and  40 R. 
     The upper frame  22  have an inverted U form or a gate shape formed by joining upper ends of a pair of left and right side frames provided to stand upward from both the left and right sides of the rear-side base  24 , with an upper end frame extending in the vehicle width direction. A lower end part of a stem  31  of a rear handle  3  is rigidly coupled to a coupling part  23  at the center of the upper end frame in the vehicle width direction, and a seat backrest  6  is supported at the coupling part  23 . 
     The rear handle  3  is formed in a T-bar shape that has a pair of grip parts extending left and right from a connection portion  32  with the upper end of the stem  31 . At the left and right grip parts of the rear handle  3 , grip sensors  30  that detect a state of gripping (hands on) by a user (or a helper) are provided. Touch sensors, such as capacitance sensors or pressure-sensitive sensors, can be used as the grip sensors  30 . The left and right grip parts of the rear handle  3  serve as an operation unit in a case of use by the user himself or herself in the rollator mode ( 1 ′), and in a case in which the helper or the like operates the electric vehicle in a case in which the user is seated on the seat  7 . Note that although omitted in  FIG. 1 , an electromagnetic brake release switch  34 , and a speaker  35  are provided on the connection portion  32  at the center of the rear handle  3 . 
     Base parts of support frames  81  for armrests  82  are fixed at bent parts at the middle of the upper frame  22  (side frames) in the height direction. A joystick  83 , which constitutes a riding mode operation unit  8 , is provided at a front end part of the armrest  82  on the right side, which is a deeper side in the  FIG. 1 . A display unit  80  and a travel permission switch  84  are provided on an upper surface of the grip part having the same shape at a front end part of the armrest  82  on the left side, which is a near side in  FIG. 1 . 
     A two-axis joystick that can be tilted to the front, rear, left, and right, and allows an output to be obtained depending on a tilted angle, or a multi-axis joystick involving this function may be used as the joystick  83 . A non-contact joystick that uses a Hall sensor is preferable. The joystick  83  is configured such that an urging force (a restoring force or an operational reaction force) toward a neutral position depending on the tilted angle is applied, by an urging member (spring, etc.), not shown. In a state in which no operational force is applied, that is, a state in which the hand of the user is off the joystick  83 , the joystick returns by itself to the neutral position. Control of the left and right motor units  40  ( 40 L and  40 R) through an operation on the joystick  83  is described later. 
     At a pivot support part  27  that protrudes forward from the bent parts of the upper frame  22  (side frames), support frames  71  for the seat  7  (seat cushion) are pivotably supported by a shaft  7   a  in the vehicle width direction. In addition, the lower ends of the support frames  71  are rotatably and slidably joined to the front-side base  25  (pins) via the joining parts  7   b  (slots). 
     According to the configuration described above, when the seat  7  at a seating position is turned downward ahead from the riding mode ( 1 ), indicated by the solid lines in the diagram, to a folded position ( 7 ′) as indicated by chain double-dashed lines in the diagram, the front-side base  25  is slid backward in an interlocking manner, the mobile base  21  is shortened, and the mode becomes a rollator mode ( 1 ′), which allows user operation while standing and walking with the rear handle  3  being gripped. 
     Conversely, when the seat ( 7 ′) at the folded position is moved from the rollator mode ( 1 ′) to the seating position  7  by turning upward behind, the front-side base  25  slides forward, the mobile base  21  is elongated, and the mode becomes the riding mode ( 1 ). In this state, an upper surface  25   b  of the front-side base  25  moved ahead of a tray  24   b  can be used as a footrest for a passenger. 
     Note that locking mechanisms (locking pins or the like urged by urging members, such as springs) that lock the front-side base  25  at each of an elongated position and a shortened position are provided in the mobile base  21 , where a vehicle state detection sensor  28  (mechanical switch etc.) that detects the locked state in each position is attached. Furthermore, urging members (springs, etc.) for urging toward the intermediate position (in a release direction) at each of the elongated position and the shortened position are provided. Release tags  26  joined to the locking mechanisms through Bowden cables are provided at upper end portions of the support frames  71 . 
     Accordingly, the configuration is made such that when the release tags  26  are pulled at either of the elongated position and the shortened position, the locking mechanisms are released, the vehicle body  2  is at the intermediate position by being urged by the urging members, and when from this state the seat  7  (support frames  71 ) is turned forward or backward from the intermediate position against urging by the urging members, and the locking mechanisms are locked at either of the elongated position and the shortened position of the front-side base  25 . 
       FIG. 2  is a block diagram showing a control system of the electric vehicle  1 . The electric vehicle  1  includes a battery  9  that supplies power to the left and right motor units  40  ( 40 L and  40 R), and a control unit  10  that controls the left and right motor units  40  ( 40 L and  40 R). The control unit  10  has an interlock function of executing control for each of the riding mode ( 1 ) and the rollator mode ( 1 ′) in the locked state at the corresponding position detected by the vehicle state detection sensor  28 . 
     In the riding mode ( 1 ), the grip sensors  30  are disabled, the control unit  10  is configured to control the speeds of the left and right motor units  40  ( 40 L and  40 R) on the basis of a control map, described later, in response to an operation (the amount of operation, and operation direction) on the joystick  83 , which constitutes the riding mode operation unit  8 , when the travel permission switch  84  is turned on, and allow drive operations that include going forward, backward, turning, and braking and stopping of the electric vehicle  1 . Note that when an inclination equal to or greater than a predetermined threshold is detected by an inclination sensor  20 , the target speed is corrected in consideration of the gravity (load) applied depending on the inclination. 
     On the other hand, in the rollator mode ( 1 ′), the riding mode operation unit  8  is disabled, the control unit  10  controls the torques of the left and right motor units  40  ( 40 L and  40 R) on the basis of detection information from the inclination sensor  20 , the left and right rotation speed sensors  43  and the like and of a predetermined control map. Note that when an inclination equal to or greater than a predetermined threshold is detected by the inclination sensor  20 , a compensation torque for compensating for the gravity (load), which is applied depending on the inclination, is superimposed on the torque command value. The grip sensor  30  only detects a grip (hands on/off) on the rear handle  3  by the user, and is not involved in the torque control of the motor units  40 . 
     The control unit  10  includes: a computer (microcomputer) made up of a ROM that stores a program and data for executing control in each of the modes, a RAM that temporarily stores a computation processing result, a CPU that performs computation processes and the like; and a power source circuit that includes drive circuits (motor drivers) for the left and right motors  41 , and a relay that turns the power of the battery  9  on and off 
     The left and right motor units  40  ( 40 L and  40 R) each include a motor  41 , an electromagnetic brake  42  that locks the rotor of the corresponding motor  41 , and a rotational position sensor ( 43 ) that detects the rotational position of the corresponding motor  41 . Drive shafts of the motors  41  are connected to the respective driving wheels  4  ( 4 L and  4 R) via reduction gears, not shown, in a power-transmissible manner. 
     The left and right motors  41  are made up of brushless DC motors that switch the currents in coils in corresponding phases in the drive circuits to support the phases of rotors detected by the rotational position sensors ( 43 ). In the riding mode ( 1 ), the rotational position sensors (Hall sensors) are used as vehicle speed sensors ( 43 ) that detect the actual speed of the electric vehicle  1 . In the rollator mode ( 1 ′), the rotational position sensors are used as the rotation speed sensors  43 . 
     The drive circuits for the left and right motors  41  include current sensors that detect coil currents. The coil currents correspond to the torques of the left and right motors  41 . The control unit  10  executes the torque control of the left and right motors  41  by controlling the coil currents through PWM control (pulse width modulation control) or the like. 
     Preferably, the electromagnetic brakes  42  are negative actuated type electromagnetic brakes that lock the drive shafts of the motors  41  in an unexcited state, and release the locking in an excited state. By adopting the negative actuated type electromagnetic brakes, the electric vehicle  1  can be securely stopped when the key is turned off or at a stop without consuming power. 
     On the other hand, to cause the locks of the electromagnetic brakes  42  to be released and allow the electric vehicle  1  to be movable in case of urgency or emergency, for example, in a case in which it is intended to move the electric vehicle  1  without using the power of the motors  41 , or in an undrivable case due to reduction in remaining battery charge, the electromagnetic brake release switch  34  is provided as forcible release means for the electromagnetic brakes  42 . The electromagnetic brake release switch  34  is provided adjacent to the grip part of the rear handle  3 , but is operable irrespective of detection of gripping of the grip sensor  30 . 
     The inclination sensor  20  is implemented on a circuit board of the control unit  10  mounted in the mobile base  21  (rear-side base  24 ) of the vehicle body  2 . A two-axis inclination sensor or an acceleration sensor that detects the inclinations in the front and rear direction and the lateral direction of the vehicle body  2 , or a multi-axis inertial sensor in which the acceleration sensor and an angular acceleration sensor (gyroscope sensor) are integrated is usable. 
     (Travel Control in Riding Mode) 
     According to the electric vehicle  1  configured as described above, in the riding mode ( 1 ), the rotation speeds of the left and right motors  41  ( 40 L and  40 R) are controlled based on an operation (an amount of operation and an operation direction) of the joystick  83  by the user. However, the target rotation speeds of the left and right motors  41  ( 40 L and  40 R) are not immediately determined from the operation position of the joystick  83 . Instead, the target vehicle speed (straight travel speed) based on the operation position of the joystick  83 , and the target vehicle angular velocity based on the left and right direction components of the operation position of the joystick  83  are separately calculated. Based on these, the target rotation speeds of the left and right motors  41  ( 40 L and  40 R) corresponding to the rotation speeds of the left and right driving wheels  4  ( 4 L and  4 R) are calculated. 
     That is, as shown in the block diagram of  FIG. 3 , for the target vehicle speed calculation block  110 , not only inputs in the front and rear direction through the joystick  83  but also inputs in the left and right direction are used. Accordingly, speed control during turning, for example, deceleration traveling, which is different from that during straight traveling, can be executed without particular consideration. Not only left and right direction inputs on the joystick  83 , but also the vehicle actual speed during operation is reflected in a target vehicle angular velocity calculation block  120 . Accordingly, the turning characteristics can be changed depending on the traveling speed of the electric vehicle  1 . 
     In the block diagram of  FIG. 3 , based on the target rotation speeds of the left and right motors  41  ( 40 L and  40 R) corresponding to the target vehicle speed v calculated by the target vehicle speed calculation block  110 , and on the difference between the target rotation speeds of the left and right motors  41  ( 40 L and  40 R) corresponding to the target vehicle angular velocity ω calculated by the target vehicle angular velocity calculation block  120 , the target rotation speeds of the left and right motors  41  ( 40 L and  40 R) are calculated in a left and right motor target rotation speed calculation block  130 . 
     Furthermore, in the left and right motor required torque calculation block  150 , based on the actual rotation speeds of the left and right motors  41  ( 40 L and  40 R) detected by the left and right rotation speed sensors  43 , and on the target rotation speeds of the left and right motors  41  ( 40 L and  40 R), the required left and right motor torques are calculated by feedback control (e.g., PID control) that causes the actual rotation speeds of the left and right motors  41  ( 40 L and  40 R) to follow the respective target rotation speeds. Based on these, current control for the left and right motors  41  ( 40 L and  40 R) is executed. 
     When the inclination sensor  20  detects a vehicle inclination (the pitch angle P and the roll angle R) equal to or greater than a predetermined threshold, a compensation torque calculation block  140  calculates a compensation torque in a direction of compensating for the climbing/traveling downhill load applied depending on the pitch angle P and/or the lateral direction load applied depending on the roll angle R, and superimposes the torque on the left and right motor required torques calculated by the left and right motor required torque calculation block  150 . 
     (Target Vehicle Speed Map) 
       FIG. 4  shows a target vehicle speed map for target vehicle speed calculation ( 110 ) through joystick operations. The target vehicle speed map is stored as a look-up table in the ROM area of the control unit  10 . 
     In  FIG. 4 , when the operation position of the joystick  83  is in a forward region F 1  including the front end in the operation range, a target forward speed va is designated. When the position in a backward region B 1  including the rear end, a target backward speed vb is designated. When the operation position of the joystick  83  is in any of left and right side regions F 2  including the left and right ends, a target forward speed vc is designated. When the position in a center region n including the center (neutral position), stopping (a target speed of zero) is designated. 
     As indicated in maps on the right side and the lower side in  FIG. 4 , the target forward speed va in the forward region F 1  is higher than the target forward speed vc in the left and right side regions F 2 . The target forward speed vc in the left and right side regions F 2  has a greater (or equal) absolute value than the target backward speed vb in the backward region B 1  has. For example, the target forward speed va can be 3 to 5 km/h, the target forward speed vc can be 1 to 2 km/h, and the target backward speed vb can be 1 km/h. 
     Furthermore, in  FIG. 4 , transition regions F 3  and F 4  in which the target forward speed increases from the center region n toward the forward region F 1  and the left and right side regions F 2  are provided between the center region n and the forward region F 1 , and between the center region n and the left and right side regions F 2 . A transition region B 2  in which the target backward speed increases from the center region n toward the backward region B 1  is provided between the center region n and the backward region B 1 . When the operation position of the joystick  83  is in the transition region F 3  or the transition region B 2 , an intermediate target forward speed or an intermediate target backward speed is designated. 
     Consequently, not only when the joystick  83  is operated to the forward region F 1  (and its transition region F 3 ) but also when the joystick  83  is operated to any of the left and right side regions F 2  (and its transition region F 4 ), the target forward speed vc is designated, thereby allowing the forward rotation to be output even when a target vehicle angular velocity ±ω from a target vehicle angular velocity calculation  120  block, described later, is input. 
     This is because the lateral movement of free wheels  5  made up of omni wheels is achieved by the rotation of the rollers  50 , and the start performance and the step traveling performance are lower than those during straight traveling, and accordingly, the load on the system is reduced by preventing pivot turn (spin turn) due to an intuitive turning operation. Note that when the joystick  83  is operated obliquely backward FB, the target speed is zero at the middle between the left and right side regions F 2  and the backward region B 1 . Pivot turn (spin turn) can be achieved at a narrow place, such as in a room or an elevator entrance. 
     (Target Vehicle Angular Velocity Map) 
     Next,  FIG. 5  shows a target angular velocity map for target vehicle angular velocity calculation ( 120 ) through joystick operations. The target angular velocity map includes: a target angular velocity map for low speed (a) that defines the target vehicle angular velocity when the actual speed is in a low speed region or a speed of zero; and a target angular velocity map for high speed (b) that defines the target vehicle angular velocity when the actual speed is the maximum speed or in a predetermined high speed region in the setting speed region for the vehicle. These target angular velocity maps are also stored as look-up tables in the ROM area of the control unit  10 . 
     According to the target angular velocity map for low speed (a), the target vehicle angular velocity ω 1  is designated when the operation position of the joystick  83  is in left and right side regions T 1  including the left and right ends in the operation range, and the target vehicle angular velocity of zero is designated when the position is in a center region n 1  including the center (neutral position). Transition regions T 3  in which the target angular velocity co gradually increases from the center region n toward the left and right side regions T 1  are provided between the center region n 1  and the left and right side regions T 1 . 
     Similarly, according to the target angular velocity map for high speed (b), the target vehicle angular velocity ω 2  is designated when the operation position of the joystick  83  is in left and right side regions T 2  including the left and right ends in the operation range, and the target vehicle angular velocity of zero is designated when the position is in a center region n 2  including the center (neutral position). Transition regions T 4  in which the target angular velocity co gradually increases from the center region n 2  toward the left and right side regions T 2  are provided between the center region n 2  and the left and right side regions T 2 . 
     Here, the maximum target angular velocity ω 2  in the left and right side regions T 2  in the target angular velocity map for high speed (b) is greater than the maximum target angular velocity ω 1  in the left and right side regions T 1  in the target angular velocity map for low speed (a), and the center region n 2  in the target angular velocity map for high speed (b) is narrower than the center region n 1  in the target angular velocity map for low speed (a). The transition regions T 4  in the target angular velocity map for high speed (b) are wider than the transition regions T 3  in the target angular velocity map for low speed (a). 
     According to a preferable embodiment, the target angular velocity map for low speed (a) corresponds to a case in which the actual speed of the vehicle is equal to or less than 0.5 km/h, which can be substantially considered to be zero. The target angular velocity map for high speed (b) corresponds to a case in which the actual speed of the vehicle is 4.5 km/h. The maximum target angular velocity ω 1  in the left and right side regions T 1  in the target angular velocity map for low speed (a) is 30 degrees per second (0.52 rad/s). The maximum target angular velocity ω 2  in the left and right side regions T 2  in the target angular velocity map for high speed (b) is 60 degrees per second (1.05 rad/s) to 120 degrees per second (2.09 rad/s). 
     Note that instead of setting of the transition regions T 4 , in which the target angular velocity continuously changes depending on the operation position of the joystick  83 , between the left and right side regions T 2  and the center region n 2 , a region with an intermediate target angular velocity of, for example, 90 degrees per second (1.57 rad/s) may be set. 
     The control unit  10  calculates the actual speed of the electric vehicle  1  on the basis of the actual rotation speeds of the left and right motor units  40  ( 40 L and  40 R) detected by the respective rotation speed sensors  43 . Depending on the vehicle actual speed, the target angular velocity map for low speed (a) or the target angular velocity map for high speed (b) is selectively applied. Alternatively, when the actual speed is in an intermediate speed region between the low speed region and the high speed region, the target angular velocity corresponding to the actual speed is calculated from the target angular velocity map for low speed (a) and the target angular velocity map for high speed (b). 
     For example, first and second, two-step, speed thresholds are configured. If during the application of the target angular velocity map for low speed (a) the actual speed becomes equal to or greater than the second speed threshold (e.g., 2.5 km/h) from the low speed region, the map is switched to the target angular velocity map for high speed (b). If during the application of the target angular velocity map for high speed (b) the actual speed becomes lower than the first speed threshold (e.g., 1.5 km/h) lower than the second speed threshold, the map is switched to the target angular velocity map for low speed (a). Such switching can reduce the map switching frequency, and perform stable control. 
     It may be configured such that to calculate the target angular velocity corresponding to the actual speed from the target angular velocity map for low speed (a) and the target angular velocity map for high speed (b), a target angular velocity may be designated to which target angular velocity designation values in the target angular velocity map for low speed (a) and the target angular velocity map for high speed (b) are proportionally distributed depending on the velocity of the current actual speed to the actual speed corresponding to the target angular velocity map for high speed (b). 
     According to the configuration of applying the target angular velocity map for low speed (a) and the target angular velocity map for high speed (b) depending on the actual speed as described above, the following turning characteristics can be obtained. 
     That is, when the electric vehicle  1  is substantially in a stop state (the actual speed is in the low speed region or the speed of zero), the relatively large center region n 1  (insensitive zone) is set on both the left and right sides of the neutral position of the joystick  83 . Even if the user operates the joystick  83  to the left or right in this range, the electric vehicle  1  does not start to move. Accordingly, as described above, immediate transition from the substantially stop state to the turning motion is prevented, and only when the user clearly intentionally operates the joystick  83  to any of the left and right side regions T 1 , forward traveling or turning is started. 
     On the other hand, when the actual speed of the electric vehicle  1  is in a high speed region, for example, when the user operates the joystick  83  forward and the vehicle is in a forward travelling state, the transition regions T 4  are set adjacent to the left and right sides of the neutral position. By the user operating the joystick  83  from the forward tilted position to the left or right, traveling in a desired direction can be achieved while finely adjusting course, and the steerable performance fairly corresponding to the straight travel speed of the electric vehicle  1  can be obtained. 
     Embodiment of Joystick 
     Next,  FIG. 6  shows an embodiment of a joystick and a limiter plate  304  in a riding mode operation unit  308  suitable for the operation of the electric vehicle  1  as described above. The limiter plate  304  has a function of mechanically limiting the operation region (movable range) of a shaft part  383  of the joystick. As shown in  FIG. 6 , the limiter plate  304  includes an opening part ( 304 ) having a basic shape that is a regular-octagonal shape. Eight moderation parts  341  to  348  are formed on the edge portion of the opening part. 
     Among them, the moderation parts  341  and  342  positioned forward and backward with respect to the traveling direction are formed over predetermined angle ranges  341   a  and  342   a  so as to have an arc shape or a curved-line shape having a larger radius of curvature than the shaft part  383  has, and are continuous to adjoining edge portions. 
     According to this configuration, as indicated by chain double-dashed lines in the diagram, in a state of traveling forward with the joystick ( 383 ′) being tilted immediately forward, the joystick ( 383 ″) is moved to the left and right along the moderation part  341 , and the operation for forward travel can be easily performed while the course is finely adjusted. Likewise, in a state of backward travel with the joystick ( 383 ) being operated backward, i.e., to the near side, the joystick is moved to the left and right along the moderation part  342 , which advantageously allows the course to be easily, finely adjusted. 
     In addition, the other moderation parts  343  to  348  are corner portions having a smaller radius of curvature than the shaft part  383  has. Accordingly, a definitive moderating sense can be achieved at each of the moderation parts  343  to  348 , and the joystick ( 383 ) is advantageously allowed to definitively move to the adjacent moderation part. 
     For example, the joystick ( 383 ) is operated from the forward moderation part  341  to any of the obliquely left and right forward moderation parts  345  and  346  to thereby allow transition to forward turning, is operated from the neutral position in the stop state to any of the left and right moderation parts  343  and  344  to thereby allow transition to forward turning, and is operated to the obliquely backward moderation parts  347  and  348  to thereby allow execution of pivot turn (spin turn). 
     In the electric vehicle  1  with the maximum speed being limited to a walking speed region (e.g., 6 km/h) or less, the user tends to perform a simple and definitive operation such that they tilt the joystick to the front end in the case of forward travel, and tilt it to the rear end in the case of backward travel. There is an advantage that while fine adjustment of the course using the forward and backward moderation parts  341  and  342  is allowed, the turning range can be limited (prevent excessive turning) using the obliquely forward moderation parts  345  and  346  smoothly continuous to the forward moderation part  341 . 
     When the forward travel ( 341 ; the forward region F 1  in  FIG. 4 ) transitions to the forward turning ( 345  and  346 ; the transition region F 3  in  FIG. 4 ), deceleration is performed according to the target vehicle speed map. Accordingly, even without particular consideration, speed control in response to the steering operation can be executed, and turning characteristics supporting the traveling speed can be obtained. 
     As described in detail above, the electric vehicle  1  according to the present invention is configured to calculate the target rotation speeds of the left and right driving wheels  4  ( 4 L and  4 R), based on the target vehicle speed v provided by the operation position of the joystick  83 , and on the target vehicle angular velocity ω provided by the operation position of the joystick  83  and the actual speed of the vehicle, and control the left and right motors  41  ( 40 L and  40 R) such that the actual rotation speeds of the left and right driving wheels  4  ( 4 L and  4 R) follow the target rotation speeds. Accordingly, the turning characteristics can be changed so as to support the actual speed. Appropriate turning characteristics supporting the travel state can be obtained only through intuitive operations on the joystick  83 . It is thus advantageous in operation simplicity, usability, and improvement in safety. 
     In particular, the control unit  10  includes a target speed map that defines the relationship between the operation position of the joystick  83  and the target vehicle speed, and a target angular velocity map that defines the relationship between the operation position of the joystick  83  and the target vehicle angular velocity depending on the actual speed, and is configured to calculate the target rotation speeds of the left and right driving wheels  4  ( 4 L and  4 R). Accordingly, a stable small electric vehicle can be configured while avoiding complication of control. 
     Furthermore, the target speed map has the forward region F 1  that includes the front end in the operation range of the joystick  83 , the backward region B 1  that includes the rear end, the left and right side regions F 2  that include the left and right ends, and the center region n that includes the center. The forward region F 1  indicates a first target forward speed (va). The backward region B 1  indicates a target backward speed (vb). The left and right side regions F 2  indicate a second target forward speed (vc). The center region n indicates stopping. The first target forward speed (va) is greater than the second target forward speed (vc), and the second target forward speed (vc) has an absolute value greater than or equal to that of the target backward speed (vb). Accordingly, there are advantages that even when the joystick  83  is operated to any of the left and right side regions F 2  to turn, the forward speed can be obtained, the load on the system of the small electric vehicle  1  including the left and right driving wheels  4  ( 4 L and  4 R) and the free wheels (omni wheels)  5  is reduced, and a practical and lightweight system can be configured with a motor having a relatively lower output. 
     Between the center region n, and the forward region F 1 , the backward region B 1  and the left and right side regions F 2 , the target speed map has the transition regions F 3 , F 4  and B 2  in which a target speed increases from the center region n to each of the regions F 1 , F 2  and B 1 . Accordingly, the target speed can be input depending on the amount of operation on the joystick  83 . Continuous and smooth control can be achieved while reducing the load on the motors. 
     In addition, the target angular velocity map includes the target angular velocity map for high speed (b) that defines the target vehicle angular velocity when the actual speed is at the maximum speed or in the predetermined high speed region in the setting speed region of the electric vehicle  1 , and the target angular velocity map for low speed (a) that defines the target vehicle angular velocity when the actual speed is in the low speed region or the speed of zero. Each map has the left and right side regions (T 1  and T 2 ) including the left and right ends in the operation range of the joystick  83 , and the center region (n 1  and n 2 ) including the center. The left and right side regions indicate the maximum target angular velocities (ω 1  and ω 2 ). The center region indicates the target angular velocity of zero. The maximum target angular velocity ω 2  of the target angular velocity map for high speed (b) is greater than the maximum target angular velocity ω 1  of the target angular velocity map for low speed (a). The control unit  10  selectively applies the target angular velocity map for high speed (b) or the target angular velocity map for low speed (a) depending on the actual speed of the electric vehicle  1 . Accordingly, by simple control of applying the control map depending on the actual speed, the turning characteristics and steerable performance in conformity with the operational intention of the user and the traveling speed of the electric vehicle  1  can be obtained. 
     The target angular velocity map for high speed (b) and the target angular velocity map for low speed (a) each have the transition regions T 3  and T 4  in which the target angular velocity increases from the center region toward the left and right side regions, between the center regions n 1  and n 2  and the left and right side regions T 1  and T 2 . Accordingly, abrupt turning motion can be suppressed. Continuous and smooth control can be achieved while reducing the loads on the motors. The straight traveling can smoothly transition to forward turning, and pivot turn. 
     In particular, by the configuration in which the center region n 2  of the target angular velocity map for high speed is configured to be narrower than the center region n 1  of the target angular velocity map for low speed, the sensitivity of the steering operation through the joystick  83  is high during forward travel in the high speed region, and traveling in a desired direction while finely adjusting the course through the joystick  83  can be achieved. In addition, in the low speed region and at a stop, the insensitive zone of the operation on the joystick  83  can be sufficiently secured. It is advantageous that a start of motion and an erroneous operation due to a behavior of the user placing a hand on the joystick  83  and the like can be prevented. 
     The embodiments of the present invention have been described above. However, the present invention is not limited to the embodiments. Based on the technical concept of the present invention, various modifications and changes can further be made. 
     For example, in the embodiments described above, the case in which the electric vehicle  1  has the rollator mode has been described. However, the present invention can be implemented as a small electric vehicle or an electric wheelchair that has no rollator mode. 
     In the embodiments described above, the case of including the omni wheels as driven wheels  5  has been described. Alternatively, caster type free wheels may be included.