Patent Publication Number: US-2022233376-A1

Title: Small electric vehicle

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application claims priority of Japanese Patent Application No. 2021-012216 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) configured such that when an operation piece of joystick-type operation means is tilted straight backward, the vehicle is stopped, and when the piece is tilted left or right backward, the vehicle turns at a fixed position. 
     SUMMARY 
     The electric vehicle in Patent Document 1 is normally prohibited from moving backward. To move backward, it is required to operate a separate switch to switch to backward travel, and in this case, forward travel is prohibited. Accordingly, there is a problem in operability in a case in which the stop position is to be adjusted by repeating forward travel and backward travel. Furthermore, no function is provided to rapidly stop in case of urgency, thereby causing a problem in safety. 
     The present invention has been made in view of the above points in the conventional art, and has an object to provide a small electric vehicle that can perform operations including forward travel, backward travel, turning, stopping, and rapid stopping, only with a joystick-type operation piece, without using a separately provided switch. 
     To solve the above 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; 
     left and right motors connected so as to respectively transmit power to the left and right driving wheels; 
     an operation unit that includes a joystick-type operation piece; and 
     a control unit for controlling the left and right motors according to an amount of operation on the operation piece, 
     wherein the control unit is configured to execute deceleration and stop control when the operation piece is returned to the neutral position during travel, and execute rapid stop control irrespective of an amount of operation in left and right directions when the operation piece is tilted backward during forward travel at a speed equal to or greater than a predetermined threshold. 
     As described above, the small electric vehicle according to the present invention is configured to execute deceleration and stop control when the operation piece is returned to the neutral position during travel, and to execute rapid stop control irrespective of the amount of operation in left and right directions when the operation piece is tilted backward during forward travel at a speed equal to or greater than a predetermined threshold. Accordingly, the vehicle can perform operations including forward travel, backward travel, turning, stopping, and rapid stopping, depending on the situation, only with a joystick-type operation piece, without using a switch or a brake lever. It is advantageous to improve operational simplicity, usability and safety, simplify the structure, and reduce the number of components. 
    
    
     
       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. 3A, 3B  show joystick control maps for normal control, and for rapid stop control. 
         FIG. 4  is a deceleration map showing target deceleration for the normal control and the rapid stop control. 
         FIG. 5  is a flowchart showing the normal control and the rapid stop control for the small electric vehicle. 
     
    
    
     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 walking assisting vehicle 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 frames  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, and braked and driven only by controlling the left and right motor units  40 L and  40 R. 
     The upper frames  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 the case of use by the user alone in the walking assisting vehicle mode ( 1 ′), and in the 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 frames  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, or a multi-axis joystick including the function thereof can be adopted as the joystick  83 , which 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. 
     At a pivot support part  27  that protrudes forward from the bent parts of the upper frames  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 walking assisting vehicle 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 walking assisting vehicle 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 , in which 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 any of the elongated position and the shortened position and 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, the locking mechanisms are locked at any 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 walking assisting vehicle 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  performs speed control (and rapid stop control, described later) for the left and right motor units  40  ( 40 L and  40 R) on the basis of a predetermined control map and 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. 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 walking assisting vehicle 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 on 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 on and off the power of the battery  9 . 
     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 speed of the electric vehicle  1 . In the walking assisting vehicle 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. 
     Preferably, the electromagnetic brakes  42  are negative actuation 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 actuation 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 an 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 . 
     A momentary operation release switch (e.g., a push button switch) is suitable for the electromagnetic brake release switch  34  such that in a state in which the user is in operation, the contact is closed and the locking of the electromagnetic brakes  42  is released, and when the user releases the touch on the electromagnetic brake release switch  34 , the contact is opened and the electromagnetic brakes  42  are locked. 
     Accordingly, if the electromagnetic brakes  42  are released to allow the electric vehicle  1  to travel and then the user&#39;s hand lets go of the electromagnetic brake release switch  34 , the electromagnetic brakes  42  are immediately locked, which prevents the electric vehicle  1  from running idle. Note that when the electromagnetic brakes  42  are released on an inclined ground, the vehicle may possibly run idle by its own weight until the user&#39;s hand is off the electromagnetic brake release switch  34 . Accordingly, a condition of releasing the electromagnetic brakes  42  is set depending on the inclination of the vehicle body  2  detected by the inclination sensor  20 . 
     The control unit  10  disables the operation on the electromagnetic brake release switch  34  during driving of the motors  41 . Only when the motors  41  are stopped and each of the rotation speeds detected by the rotation speed sensors  43  is less than a predetermined threshold value, that is, when the vehicle speed can be substantially assumed to be zero, does the unit enable the operation on the electromagnetic brake release switch  34 . 
     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. 
     According to the electric vehicle  1  configured as described above, in the riding mode ( 1 ), based on the operation (the amount of operation, and operation direction) on the joystick  83  by the user, the rotation speeds of the left and right motor units  40  ( 40 L and  40 R) are controlled, and normal control including forward travel, backward travel, turning, and deceleration and stop, and rapid stop control are executed. 
     (Normal Control in Riding Mode) 
     That is, in  FIG. 3A , when the joystick  83  is tilted forward FW from the neutral position, the rotation speeds of the left and right motor units  40  ( 40 L and  40 R) are controlled so as to achieve the target speed (target vehicle speed) in the forward traveling direction in response to the amount of operation (tilted angle) on the joystick  83 , and the electric vehicle  1  travels forward. 
     In this case, when the operation on the joystick  83  includes any of the left and right direction components (L and R), different target speeds are set in the left and right motor units  40  ( 40 L and  40 R), and the electric vehicle  1  travels forward and turns in the operation direction (L/R) of the joystick  83 . 
     On the other hand, when the joystick  83  is tilted backward RW from the neutral position, the target speed in the backward traveling direction is set in response to the amount of operation (tilted angle) of the joystick  83 , and the electric vehicle  1  travels backward. Also in backward travel, when the operation of the joystick  83  includes any of the left and right direction components (L and R), different target speeds are set in the left and right motor units  40  ( 40 L and  40 R), and the electric vehicle  1  travels backward and turns in the operation direction (L/R) of the joystick  83 . Note that the target speed and the maximum target speed in the backward traveling direction RW is set to have a smaller value than that in the forward traveling direction FW. 
     In a state in which the joystick  83  is operated in any of the forward, backward, and left and right directions, and the vehicle is traveling forward or backward, or turning as described above, returning the joystick  83  to the neutral position or returning the joystick  83  by itself to the neutral position decelerates and stops the electric vehicle  1  according to a predetermined deceleration. 
     (Rapid Stop Control in Riding Mode) 
     In a state in which the joystick  83  is operated forward FW and the vehicle is traveling forward or turning forward with a vehicle speed equal to or greater than the predetermined threshold, a reverse operation backward RW′ on the joystick  83  from the neutral position as shown in  FIG. 3B  executes rapid stop control irrespective of the left and right direction components. 
     That is, the target deceleration greater than that in the deceleration and stop case is set to the left and right motor units  40  ( 40 L and  40 R). Regenerative braking by the left and right motor units  40  is executed. In a state in which the electric vehicle  1  has a predetermined low speed or lower, the left and right motor units  40  are locked by the respective electromagnetic brakes  42 , and the electric vehicle  1  is completely stopped. 
     When the joystick  83  is operated forward FW or to the neutral position during the above rapid stop control (or when being returned by itself), or when a predetermined time period (e.g., four seconds) elapses after the vehicle is stopped by the rapid stop control, the rapid stop control is finished, and the control transitions to normal control in response to the operation position of the joystick  83  at the time. 
     That is, if the joystick  83  is tilted forward FW when the rapid stop control is finished, the electromagnetic brakes  42  are released to start forward travel or forward turning. If the joystick  83  is tilted backward RW, the electromagnetic brakes  42  are released, and backward travel or backward turning is started. If the joystick  83  is at the neutral position, only releasing of the electromagnetic brakes  42  is performed. Note that in this case, when an inclination equal to or greater than the predetermined threshold is detected by the inclination sensor  20 , a compensation torque in the direction of compensating the gravity (load) applied depending on the inclination may be superimposed on the holding torque in the stop state. 
       FIG. 4  shows a setting example (deceleration map) of the target deceleration during deceleration and stop in normal control, and during rapid stop control. In  FIG. 4 , during deceleration and stop in normal control, the target deceleration is set such that depending on the vehicle speed v at the start of deceleration control, the speed gradually decreases from the target deceleration da at the maximum forward speed va, or the target deceleration db at the maximum backward speed −vb, to the target deceleration speed d 0 . According to such setting, smooth and secure deceleration and stop can be performed. 
     Note that with respect to the maximum forward speed va (e.g., 4.5 km/h), the maximum backward speed −vb (e.g., −1 km/h) is set to be smaller. Accordingly, the target deceleration db (e.g., 7 km/h/s) during backward travel is set to have a greater value than the target deceleration da (e.g., 5 km/h/s) during forward travel, but may be equivalent to that during forward travel. 
     On the other hand, during rapid stop control, depending on the vehicle speed v at the start of rapid stop control, the target deceleration is set from the target decelerations da′ (e.g., 15 km/h/s) sufficiently greater than that during normal control, to the target deceleration dl (e.g., 5 km/h/s) with the vehicle speed threshold val during rapid stop control, in order to securely achieve braking and stopping in a short time as much as possible. 
     Note that the target decelerations during deceleration and stopping in normal control and during rapid stop control may have fixed values corresponding to the respective cases. In such cases, the intermediate target deceleration may be, for example, target deceleration 4 km/h/s during deceleration and stopping in normal control, and target deceleration 8 km/h/s during rapid stop control. 
     (Basic Control Flow in Riding Mode) 
     When the power is turned on by an operation on a key  11  and the system is activated, the electric vehicle  1  configured as described above is set to the riding mode ( 1 ) or the walking assisting vehicle mode ( 1 ′) depending on the frame style at the activation. Note that as already described above, in the stop state of the electric vehicle  1 , the electromagnetic brakes  42  are in a locked state. 
     Hereinafter, control in a case of the riding mode ( 1 ) at the activation, or a case in which the riding mode ( 1 ) is set by an operation by the user in the stop state after activation is described with reference to a flowchart in  FIG. 4 . 
     First, in the state of the riding mode ( 1 ) being set (step  100 ), the user is seated on the seat  7  and turns on the travel permission switch  84 , normal control is executed, and the joystick  83  is in a standby state at the neutral position, and when the joystick  83  is operated to the front, rear, left or right, forward travel, backward travel, or left or right turning can be achieved (step  101 ). 
     During such normal control, in a state in which the joystick  83  is operated forward and the vehicle is traveling forward or turning forward with a vehicle speed equal to or greater than the predetermined threshold (e.g., 0.5 km/h) (step  102 ), the joystick  83  is reversely operated backward (step  103 ); in this case, rapid stop control is executed irrespective of the left and right direction components (step  104 ). 
     When the joystick  83  is operated forward or to the neutral position (or returns by itself) during rapid stop control (step  105 ), the rapid stop control is terminated, and the control transitions to normal control (step  101 ) in response to the operation position (forward or the neutral position) of the joystick  83 . 
     On the other hand, when, while the joystick  83  is maintained in the backward reverse operation state, the electric vehicle  1  is rapidly stopped and the vehicle speed of the electric vehicle  1  becomes 0 km/h (at a time when the electromagnetic brakes  42  are locked), measurement of the predetermined time period is started and the predetermined time period (e.g., four seconds) elapses; in this case, the control transitions to the normal control (step  101 ). 
     As described above in detail, the electric vehicle  1  according to the present invention is configured to execute relatively gradual deceleration and stop control when the joystick  83  is returned to the neutral position during travel, and execute rapid stop control irrespective of the amount of operation in the left and right directions when the joystick  83  is reversely operated backward during forward travel at a speed equal to or greater than the predetermined threshold. Accordingly, operations including forward travel, backward travel, turning, stopping, and in addition thereto, rapid stopping can be executed depending on the travel state of the electric vehicle  1 , only with the operation on the joystick  83 , without using a separately provided switch or the brake lever. 
     In particular, rapid stopping through the reverse backward operation on the joystick  83  conforms to an operation naturally performed by a person in situations with an intention of emergency stop of the electric vehicle  1 , and is advantageous to improvement in operational simplicity, usability, and safety. The switch, the brake lever, and the rapid stop button are not required to be mounted. Accordingly, it is advantageous to simplify the structure and reduce the number of components. 
     In the rapid stop control, the speed is reduced by regenerative braking by the left and right motor units  40  to a predetermined low speed, and then the electromagnetic brakes  42  are locked. Accordingly, the shock due to locking of the electromagnetic brakes  42  is small, and the vehicle can be securely stopped. 
     Furthermore, when the joystick  83  is operated forward or to the neutral position during the rapid stop control, or when a predetermined time period elapses after the vehicle is stopped by the rapid stop control, the rapid stop control is finished, and the control transitions to normal control in response to the operation position of the joystick  83 . Accordingly, when the need for a rapid stop is negated, the control can be easily returned to the normal control. 
     The embodiments of the present invention have been described above. However, the present invention is not limited to the embodiments. Based on the technical thought 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 walking assisting vehicle mode has been described. However, the present invention can be implemented as a small electric vehicle and an electric wheelchair that have no walking assisting vehicle 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.