Abstract:
An electric-powered vehicle includes electric-powered drivers for driving wheels, a controller for controlling the electric-powered drivers to generate an assisting driving force in accordance with a vehicle operating force by an operator, and a brake-operation unit for applying braking forces on the wheels. The vehicle also includes a brake-operation detector for detecting a brake operation performed by the brake-operation unit. When the brake-operation detector detects the brake operation, the controller controls the drivers to reduce the assisting driving force. This structure solves a problem caused by simultaneous generation of the braking forces and the assisting driving force.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an electric-powered vehicle such as an electric-powered wheelchair. 
   2. Description of the Related Art 
   Electric-powered wheelchairs of the related art include a type of wheelchair in which a motor generates an assisting driving force in accordance with an operating force generated when a caregiver pushes or pulls the wheelchair body while holding operation handles. The operating force generated by pushing or pulling the wheelchair body is detected by using a sensor to detect a force applied on the operation handles. 
   The wheelchair in which the assisting driving force is generated can be moved by the resultant of the operating force generated when the caregiver pushes or pulls the wheelchair body and the assisting driving force. This can reduce the load on the caregiver. 
   In the vicinity of the operation handles, brake levers are provided. The brake levers are connected to wheel brake mechanisms by control wires. By manually operating the brake levers, wheels can be mechanically braked. 
   In the electric-powered wheelchair of the related art, the braking force by the brake operation and the assisting driving force may be simultaneously generated. 
   By way of example, when the caregiver as an operator pushes the electric-powered wheelchair on an upslope, an assisting driving force is generated in accordance with the pushing operating force. The operator may apply the brake if needed while the wheelchair is moving on the upslope. In this case, the assisting driving force by a motor and the braking force by the brake lever are simultaneously generated. 
   In this case, the assisting driving force is generated against the braking force. This causes an unnecessary current to flow in the motor in the wheelchair, so that efficiency deteriorates. 
   For the amount of the assisting driving force generated in the wheelchair, the operator must generate a greater braking force, thus increasing the load of the brake operation. 
   When the operator deactivates the brake operation while the wheelchair is being brought to standstill by the brake, an assisting driving force which is being generated at the time may suddenly move the wheelchair. This causes instability of operation. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to eliminate the above problems by providing a vehicle in which a driving force for driving the vehicle is reduced when a braking force is generated. 
   The present invention provides an electric-powered vehicle supplied with a propulsive force based on a vehicle operating force applied by an operator of said electric-powered vehicle and an assisting driving force. The electric-powered vehicle includes wheels, at least one operation-force detector for detecting the vehicle operating force applied by the operator, at least one electric-powered driver for driving the wheels, at least one brake-operation unit for applying braking forces on the wheels, and at least one brake-operation detector for detecting the brake operation performed by the brake-operation unit, and a controller for controlling the electric-powered driver. The controller controls the electric-powered driver to generate the assisting driving force in accordance with the vehicle operating force detected by the operation-force detector, and controls the electric-powered driver to reduce the generated assisting driving force when the brake operation is detected by the brake-operation detector. 
   According to the electric-powered vehicle, in its structure in which the electric-powered driver can generate the assisting driving force in accordance with the vehicle operating force of the operator, when the brake-operation detector detects the brake operation performed by the brake-operation unit, the controller reduces the assisting driving force. Therefore, an unnecessary assisting driving force that is generated when the brake operation is performed is reduced. Since the assisting driving force on the vehicle is reduced, a small braking force is only needed. This facilitates the brake operation. In addition, the reduction in the assisting driving force also reduces sudden acceleration of the vehicle which occurs when the brake operation is deactivated. 
   Preferably, the assisting driving force obtained when the brake operation is performed is reduced to zero. In this case, the reduction of the assisting driving force to zero eliminates a problem caused by simultaneous generation of the assisting driving force and the braking force can be solved. 
   According to a procedure for reducing the assisting driving force, as soon as the brake operation is detected, the assisting driving force can be reduced to zero or a predetermined value. Alternatively, it is preferable that, when the brake operation is detected, the assisting driving force be gradually reduced, because the operability improves. In other words, when the assisting driving force is immediately reduced to zero by performing the brake operation when the vehicle is on an upslope, the weight of the vehicle acts on the operator at a time, thus causing a load on the operator. However, by gradually reducing the assisting driving force, such a situation can be prevented from occurring. 
   It is preferable that the brake-operation detector be provided on the brake-operation unit. By providing the brake-operation detector on the brake-operation unit, it is ensured that the brake operation can be detected. 
   In addition, it is preferable that the brake-operation unit include a brake-operation-unit body and a movable portion provided on the brake-operation-unit body so as to be moved, and it is preferable that the brake-operation detector be provided on the brake-operation-unit body, and detects a movement of the movable portion. This case improves handling of the brake-operation detector in the case of assembling the vehicle since the brake-operation detector is provided on the brake-operation-unit body. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side view of an electric-powered wheelchair; 
       FIG. 2  is a back view of the electric-powered wheelchair shown in  FIG. 1 ; 
       FIG. 3  is an enlarged side view of a vehicle operation portion; 
       FIG. 4  is a section view taken on the line IV—IV shown in  FIG. 6 ; 
       FIG. 5  is a section view taken on the line V—V shown in  FIG. 1 ; 
       FIG. 6  is a bottom view of a battery container; 
       FIG. 7  is a control block diagram of the electric-powered wheelchair in  FIG. 1 ; and 
       FIG. 8  is a graph showing a state in which an assisting driving force decreases. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   A preferred embodiment of the present invention is described below with reference to the accompanying drawings. 
     FIGS. 1 and 2  are a side view and back view of an electric-powered wheelchair  1  as an example of an electric-powered vehicle. The electric-powered wheelchair  1  has a wheelchair body  2  and right and left wheels (driving wheels)  3  provided on the right and left sides of the wheelchair body  2 . The wheelchair body  2  includes wheelchair frames  4  and a pair of right and left electric-powered drivers  5  which each include a motor and a speed-reducing mechanism in a housing  5   a.    
   The right and left wheels  3  as the driving wheels are attached to the electric-powered drivers  5 . The wheels  3  are rotated by driving forces generated by the electric-powered drivers  5 , and the driving forces are used as part of propulsion for the electric-powered wheelchair  1 . Each driving force is called the “assisting driving force”. The wheelchair body  2  has, in its front part, a pair of right and left casters  6 . The wheelchair body  2  has a power-supply battery  7  disposed therein. 
   The wheelchair frames  4  consist of a left frame  8  and a right frame  9 . Each of the wheelchair frames  4  is constituted by connecting a plurality of pipe members, etc. Between the right frame  9  and the left frame  8 , a seat  11  and a back  12  are tightly stretched. 
   The wheelchair body  2  (wheelchair frames  4 ) has vehicle operation portions  14  at the top rear thereof. The vehicle operation portions  14  are manually held by the operator such as a caregiver when he or she pushes or pulls the electric-powered wheelchair  1 . The vehicle operation portions  14  include operation grips  15 . The operation grips  15  are almost horizontally provided from the tops to rear portions of the right and left frames  9  and  8 . A vehicle operating force is used as part of a propulsive force of the electric-powered wheelchair  1 . 
   The vehicle operation portions  14  each have, for example, a potentiometer as an operation-force detector. The potentiometer is provided in each vehicle operation portion  14 . The potentiometer can detect a vehicle operating force of the operator which pushes or pulls the electric-powered wheelchair  1 . A signal representing the detected vehicle operating force is supplied to a controller (described later). Instead of the potentiometer, a bridge circuit including a strain gauge may be used. 
   In a type of electric-powered wheelchair that can perform electric-powered assisting without any caregiver, the operation-force detector can be provided in a push rim  17  of each wheel  3 . By providing the push rim  17  with the operation-force detector, a vehicle-operating force applied on the push rim  17  by a passenger as an operator can be detected. 
   As  FIG. 3  shows, in the vicinity of each vehicle operation portion  14 , a brake-operation unit  19  is provided. The brake-operation unit  19  is used to apply a braking force on each wheel  3  when being operated by the operator. The brake-operation unit  19  is connected by a control wire  21  to a brake mechanism  20  that mechanically brakes the rotation of the wheel  3 . The brake-operation unit  19  includes a movable portion  24  so that it can be moved with respect to a brake-operating-portion body  23  provided in the vicinity of the operation grip  15 . Specifically, the movable portion  24  is a brake lever supported so as to swingablely pivot around a horizontal axis  23   a  with respect to the brake-operating-portion body  23 . The brake lever is disposed below each of the right and left operation grips  15 . 
   When the operator performs, by holding the brake lever  24  as well as the operation grip  15 , a brake operation so that the brake lever  24  is close to the operation grip  15 , as indicated by the chain double-dashed line shown in  FIG. 3 , the control wire  21  (its inner wire  21   a ) is pulled to operate the brake mechanism  20  to which the control wire  21  is connected, whereby each wheel  3  is braked. 
   A state in which the above brake operation is performed or not performed is detected by a brake-operation detector  26  provided on the brake-operating-portion body  23  in the brake-operation unit  19 . The brake-operation detector  26  is provided in a lower portion of the brake-operating-portion body  23 , and is formed by a limit switch whose ON/OFF state can be changed over in accordance with the movable operating portion (brake lever)  24 . Specifically, the limit switch  26  is set so that, when the brake-operation unit  19  is not operated, a movable member  26   a  of the limit switch  26  touches the brake lever  24 , and when the brake-operation unit  19  is operated, that is, when the brake lever  24  is in the position indicated by the chain double-dashed line in  FIG. 3 , the movable member  26   a  of the limit switch  26  does not touch the brake lever  24 . Implementation of the brake operation allows the limit switch  26  to output a brake-operation signal, and the brake-operation signal is supplied to the controller (described later). 
   The battery  7  is set in a battery container (battery case)  28 . The battery container  28  is provided on the right side of the rear portion of the wheelchair body  2 . The position of the battery container  28  is not limited. In other words, the battery  7  as a power supply can be disposed in an arbitrary position of the wheelchair body  2 . 
   The battery  7  is removably set in the battery container  28 . As  FIGS. 4 and 5  show, the battery container  28  has an opening  29  from which the battery  7  is inserted. In this embodiment, the opening  29  is formed on the top of the battery container  28 . Accordingly, to set the battery  7 , the battery  7  may be inserted downward from the opening  29  into the battery container  28 . After the battery  7  is inserted into the battery container  28 , the battery  7  and the battery container  28  are engaged with each other by an engaging unit (not shown), so that the battery  7  is accommodated in the battery container  28 . conversely, to remove the battery  7 , it may be pulled upward. As described above, the battery  7  can be easily set or removed by insertion or pulling. 
   The battery container  28  has therein a battery accommodating portion  30  whose depth, which specifically corresponds to a length in which the battery  7  is inserted and which corresponds to the vertical length of the battery accommodating portion  30  in  FIGS. 1 ,  4 , and  5 , is shorter than a length in which the battery  7  is inserted. In a state in which the battery  7  is fitted into the battery container  28 , part (the top) of the battery  7  is positioned outside the battery accommodating portion  30 , and another part (the bottom) of the battery  7  is positioned in the battery accommodating portion  30 . 
   The battery  7  can be inserted or pulled by using a handle  32  ( FIG. 1 ) on the battery  7 . The handle  32  is provided on the top of the battery  7  which is positioned outside the battery accommodating portion  30  when the battery  7  is set. The handle  32  has (therein) a release-operation portion (lock releasing trigger)  33  ( FIG. 1 ) for releasing the engagement between the battery  7  and the battery container  28 . By upwardly pushing the release-operation portion  33 , the engagement by the engaging unit is released. By upwardly pulling the handle  32  while gripping it and the release-operation portion  33 , the engagement by the engaging unit is released, enabling the battery  7  to be pulled out. Accordingly, the battery  7  can be easily removed since a direction in which the release-operation portion  33  is operated for operation release corresponds to a direction in which the battery  7  is pulled. 
   The battery  7  has a lower portion (a portion of the battery  7  which is positioned in the battery accommodating portion  30  when the battery  7  is set) provided with output terminals (not shown). Inside the battery accommodating portion  30  is provided battery connecting terminals  34  ( FIGS. 4 and 5 ) corresponding to the-output terminals. When the battery  7  is set in the battery container  28 , the output terminals of the battery  7  are connected to the battery connecting terminals  34 . 
   In addition to the battery accommodating portion  30 , the battery container  28  includes a circuit board container  37  for containing circuit boards  36  such as the controller. The battery container  28  is not only a container for the battery  7  but also a container for the circuit boards  36  (controller). 
   In the battery container  28 , the battery accommodating portion  30  and the circuit board container  37  are separated by a separator  28   a . The separator  28   a  separates the inside of the battery container  28  in the direction (vertical direction) in which the battery  7  is inserted. The part of the battery container  28  above the separator  28   a  is used as the battery accommodating portion  30 , and the part of the battery container  28  below the separator  28   a  is used as the circuit board container  37 . In other words, the circuit board container  37  is disposed to the battery accommodating portion  30  in the innermost (bottom of the battery container  28 ) of the direction in which the battery  7  is inserted. By arranging the battery accommodating portion  30  and the circuit board container  37  in parallel, the required space for arrangement is reduced. Also, the battery container  28  contains both the battery  7  and the circuit boards  36 , whereby both  7  and  36  are close in position to each other, and wires connecting both  7  and  36  are shortened, thus achieving efficiency of wiring. 
   In the battery container  28 , the circuit board container  37  also has an opening  38 . The opening  38  is formed on the bottom of the battery container  28 , having a downward opening shape. The battery container  28  is provided with a cover  39  so that the opening  38  is covered. The cover  39  is removably provided on the battery container  28 . Specifically, the cover  39  is fixed to the battery container  28  by screws  40 . The circuit boards  36  can be put from the opening  38  and can be disposed in the circuit board container  37 . Thus, assembly, etc., is facilitated, even if the circuit board container  37  is positioned in the innermost of the direction in which the battery  7  is inserted. 
   The circuit boards  36 . (controller) consist of a plurality of boards (two boards in this embodiment). A first circuit board  36   a  and a second circuit board  36   b  are arranged in parallel, opposing each other. The area required for this arrangement can be reduced compared with the case of using a single board to form a controller circuit board, etc. Since the first circuit board  36   a  and the second circuit board  36   b  are arranged in parallel in the direction (vertical direction) in which the battery  7  is inserted, their dimension in the direction (cross-direction or horizontal direction) orthogonal to the battery-inserted direction is prevented from increasing. This downsizes the battery container  28 . 
   Referring to  FIG. 7 , electronic circuits formed on the circuit boards  36   a  and  36   b  are divided broadly into a controller (control circuit)  43 , a power-supply circuit  44 , and a motor-drive circuit  45 . Among the circuit boards  36   a  and  36   b , the motor-drive circuit  45  is provided on the second circuit board  36   b  (on the bottom) closest to the cover  39 . The motor-drive circuit  45  includes field effect transistors (FETS) as circuit components  47 . The number of FETs  47  on the motor-drive circuit  45  is plural (twelve in this embodiment). The FETs  47  generate large amounts of heat because relatively large currents flow in the FETs  47 . 
   The FETs  47  are mounted on the second circuit board  36   b  so as to be positioned between the second circuit board  36   b  and the cover  39 . The FETs  47  are provided with component stays  49  composed of highly thermal conductive material (e.g., metal). The component stays  49  are provided on the FETs  47  so that surface contact is established, and heat generated by the FETs  47  is efficiently conducted to the component stays  49 . In other words, the component stays  49  have a heat radiating function for the FETs  47 . When heat-generating circuit components other than the FETs  47  are provided, they can be also provided with the component stays  49  for heat radiation. 
   Referring further to the FETs  47  and the component stays  49 , the FETs  47  are two rows of a plurality of (six) FETs provided on the second circuit board  36   b . The component stays  49  have abutting side walls  49   a  and  49   b  which are fixed to the rows of the FETs  47  so that surface contact is established, and a connecting face portion  49   c  which connects the side walls  49   a  and  49   b . The side walls  49   a  and  49   b , and the connecting face portion  49   c , are formed so that a formed section is almost U-shaped as a whole. 
   The component stays  49  are provided in contact with the cover  39 . Specifically, the component stays  49  are provided so that the connecting face portion  49   c  touches an inner surface  39   a  of the cover  39 . The component stays  49  and the cover  39  can be separated. Specifically, the component stays  49  and the cover  39  are joined by screws  51 . Accordingly, by unscrewing the screws  51  and the screws  40 , the cover  39  can be removed from the battery container  28 , with the component stays  49  mounted on the FETs  47 . 
   The cover  39  is composed of highly thermal conductive material (e.g., metal), and is provided so as to touch the component stays  49 . Thus, the heat generated by the FETs  47  as heat-generating components are conducted to the cover  39  through the component stays  49 , so that heat radiation is performed from the battery container  28  to its exterior. In other words, the cover  39  also has a heat radiator function. 
   The cover  39  has an outer surface  39   b  provided with a radiator  53 . The radiator  53  is L-shaped, and is provided projecting from the cover  39 , with its base portion  53   a  brought in surface contact with the outer surface  39   b  of the cover  39 . The radiator  53  is fixed to the cover  39  by spot-welding the base portion  53   a  to the cover  39 . 
   The heat generated by the FETs  47  as heat-generating components is conducted to the radiator  53  through the component stays  49  and the cover  39 , and the radiator  53  efficiently radiates the heat. 
   The radiator  53  is also used as a mounting stay for mounting the battery container  28  on the wheelchair body  2 . Specifically, the radiator  53  as the stay has screw holes  54  for mounting the battery container  28  on the wheelchair body  2 . Specifically, the radiator  53  as the stay is provided on a housing  5   a  for one of the electric-powered drivers  5 . That is, the battery container  28  is provided on the housing  5   a  for either electric-powered driver  5 . The battery container  28  is provided only for either one of the electric-powered drivers  5 . 
   As  FIG. 6  shows, the cover  39  has through-holes  56   a ,  56   b , and  56   c  which are continuous from the circuit board container  37  to the exterior of the battery container  28 . The through-holes  56   a ,  56   b , and  56   c  are cable-inserted holes into which electric cables connected to the circuit boards  36  are inserted. Electric cables led from portions of the electric-powered wheelchair  1  pass through the through-holes  56   a ,  56   b , and  56   c , and are connected to the circuit boards  36 . In  FIG. 6 , the through-holes  56   a  and  56   b  are used as motor-cable-inserted holes into which cables connected to the motors of the electric-powered drivers  5  are inserted, and the through hole  56   c  is used as a cable-inserted hole into which cables  59  connected to operation-force detectors  58 , cables  60  connected to brake-operation detectors  26 , and a cable connected to a power-supply-switch/battery-level-indicator unit are together inserted. The power-supply-switch/battery-level-indicator unit is provided in the vicinity of either operation grip  15 . 
   As the block diagram in  FIG. 7  shows, the operation-force detectors  58  and the brake-operation detectors  26  are connected to the controller  43 . A signal representing a vehicle operating force detected by the operation-force detector  58  in either operation grip  15 , and a brake-operation signal detected by either brake-operation detector  26  are input to the controller  43 . 
   The controller  43  includes a central processing unit, a memory, and an analog-to-digital converter. In response to the input signal of the vehicle operating force, the controller  43  generates a driving-force signal for generating an assisting driving force that assists propulsive force of the electric-powered wheelchair  1 . The driving-force signal is supplied to each motor-drive circuit  45 , and operates its electric-powered unit  5  (motor) for generating an assisting driving force based on the driving-force signal. Control of the electric-powered unit  5  (motor) is performed by PWM control. 
   While the assisting driving force is being generated by pushing the electric-powered wheelchair  1  (the vehicle operation portions  14 ) on an upslope or the like by the caregiver, when the caregiver operates the brake levers  24  in the brake operating portions  19  for braking, the brake mechanisms  20  operate and the brake is applied. The brake operation is detected by either brake-operation detector  26 , and a brake-operation signal is input to the controller  43 . 
   Detection of the brake operation causes the controller  43  to perform control so that the assisting driving force is forcibly reduced, even if the vehicle operating force (pushing force) is applied by operating either vehicle operation portion  14 . As a result, the assisting driving force is reduced regardless of the vehicle operating force. Control of the assisting driving force to be reduced is performed for both electric-powered drivers  5  on the right and left sides when either brake-operation unit  19  is operated. In other words, only by operating either brake-operation unit  19 , the driving forces of both wheels  3  are reduced, so that improved operability is obtained. 
   According to this embodiment, an assisting driving force operating against a braking force is reduced, by eliminating or reducing the assisting driving force generated simultaneously with the braking force. In addition, an unnecessary assisting driving force generated when a brake operation is performed is reduced. The absence of the unnecessary assisting driving force only needs a small braking force, thus facilitating the brake operation. 
   As  FIG. 8  shows, after the brake operation is detected, the assisting driving force gradually decreases and finally decreases to zero (driving-force decreasing period). A state (zero-driving-force period) in which the assisting driving force is zero continues while the brake operation is being performed, that is, the brake lever  24  is being gripped. After the assisting driving force decreases to zero, a force that moves the electric-powered wheelchair  1  against the braking force is not generated. This facilitates braking, and good brake operability can be obtained. 
   After the brake operation is detected, the assisting driving force is gradually reduced instead of immediately reducing the assisting driving force. Thus, if the brake operation is performed when the electric-powered wheelchair  1  is on an upslope, the weight of the electric-powered wheelchair  1  is prevented from acting on the operator at a time. 
   After the brake operation is deactivated, the controller  43  performs control again so that a driving force in accordance with a vehicle operating force is generated, thus enabling a normal movement. 
   In this embodiment, while the brake operation is being detected, the controller  43  ignores the vehicle-operating-force signal. Instead, by setting a virtual vehicle-operating-force signal (zero or a small value close to zero), the controller  43  calculates an assisting driving force. This reduces the assisting driving force. In the calculation of the assisting driving force, regardless of detection of the brake operation, the controller  43  performs arithmetic processing so that an abrupt change of the assisting driving force is prevented, or so that a rate of change of the assisting driving force is limited so as not to exceed a predetermined range. The use of the arithmetic processing enables a reduction in the assisting driving force just after the brake operation starts, and a gradual increase in the assisting driving force just after the brake operation ends, as shown in FIG.  8 . Moreover, the assisting driving force can be also gradually changed, together with a gradual change in the setting of the virtual vehicle-operating-force signal. 
   The present invention is not limited to the above embodiment. For example, when the brake operation is detected, the driving force does not need to decrease to zero, but the driving force only needs to decrease to a level at which braking is not substantially hindered. In addition, each brake-operation detectors  26  does not need to be provided in each brake operation portion  19 , but may be provided in another portion of the electric-powered wheelchair  1 , such as the brake mechanism  20 . The brake-operation detectors  26  are not limited to limit switches, but various sensors such as optical sensors may be employed.