Electric vehicle and vehicular electric assistance device

Abstract

An electric wheelchair (1) comprises: a vehicle body (2) having casters (2c) and main wheels (2b); a bracket (18) fixed to the vehicle body (2); an arm (20) supported so as to be swingable in the vertical direction by the bracket (18); a drive wheel (14) provided to the leading end section (21a) of the arm (20); an actuator (16) for driving the drive wheel (14); and an elastic member (58) which is provided between the bracket (18) and the arm (20) and biases the arm (20) in the downward direction.

Description

Electric vehicle and electric assist device for vehicle

[0001] The present invention relates to an electric vehicle and an electric assist device for a vehicle.

[0002] Patent Document 1 discloses an electric assist device for use with wheelchairs. This electric assist device comprises a main body including a battery, an electric motor, and drive wheels, and an attachment bar. The electric motor drives the drive wheels. The attachment bar is a member for mounting the main body to the body of the wheelchair. The position of the main body mounted to the body via the attachment bar can be switched between a standby position and a drive position. In the standby position, the drive wheels are raised above the road surface. In the drive position, the drive wheels are in contact with the road surface. By driving the drive wheels when in the drive position, the electric assist device assists the wheelchair in traveling.

[0003] Japanese Patent Application Laid-Open No. 2016-150077

[0004] Wheelchairs equipped with the above-mentioned conventional power-assisted devices travel with the main body fixed in the drive position. As a result, shocks and vibrations from the road surface are directly transmitted to the main body via the drive wheels. These shocks and vibrations can cause damage to the electric motor mounted on the main body and peripheral devices used to drive the drive wheels.

[0005] One possible solution is to mount the main body so that it can move up and down to cushion the vibrations from the drive wheels. However, in this case, the drive wheels would be pressed against the road surface only by the weight of the main body, which would not ensure sufficient contact pressure on the drive wheels, resulting in reduced traction and the risk of impeding stable driving.

[0006] (1) An electric vehicle according to an embodiment includes a vehicle body having wheels, a bracket fixed to the vehicle body, an arm supported on the bracket so as to be swingable in the vertical direction, a drive wheel provided at the tip of the arm, an actuator that drives the drive wheel, and an elastic member provided between the bracket and the arm that urges the arm downward.

[0007] (7) From another perspective, the present embodiment is an electric assist device for a vehicle mounted on a vehicle, the electric assist device for a vehicle includes a bracket fixed to the vehicle, an arm mounted on the bracket so as to be able to swing up and down, a drive wheel mounted at the tip of the arm, an actuator that drives the drive wheel, and an elastic member that is mounted between the bracket and the arm and that urges the arm downward.

[0008] According to the present disclosure, it is possible to increase the contact surface pressure of the drive wheels while damping vibrations from the drive wheels.

[0009] FIG. 1 is a perspective view of an electric wheelchair according to an embodiment. FIG. 2 is a diagram showing the main parts of the electric wheelchair as seen from the rear. FIG. 3 is an enlarged view of the main parts of FIG. 1. FIG. 4 is an enlarged perspective view showing a bracket and arm of a drive unit. FIG. 5 is a cross-sectional view of the bracket and arm. FIG. 6A is a diagram showing the relationship between the drive wheels and the main wheels when the arm main body is in the lower swing position. FIG. 6B is a diagram showing the relationship between the drive wheels and the main wheels when the vehicle body is placed on the road surface. FIG. 7A is a diagram showing the force acting on the arm when the brakes are applied to the drive wheels of an electric wheelchair in which a line passing through the swing center of the arm and the rotation center of the drive wheels is not parallel to the road surface. FIG. 7B is a diagram showing the force acting on the arm when the brakes are applied to the drive wheels of the electric wheelchair according to this embodiment. FIG. 8 is a diagram showing the bracket of a drive unit according to another embodiment.

[0010] First, the contents of the embodiments will be listed and explained. [Outline of the Embodiments] (1) An electric vehicle according to the embodiments includes a vehicle body having wheels, a bracket fixed to the vehicle body, an arm supported by the bracket so as to be swingable in the up and down direction, a drive wheel provided at the tip of the arm, an actuator that drives the drive wheel, and an elastic member that is provided between the bracket and the arm and that urges the arm downward.

[0011] According to the above configuration, since the arm that can swing up and down has an elastic member that biases it downward, the drive wheel can be pressed against the road surface when the wheel is in contact with the ground, thereby increasing the contact pressure of the drive wheel while damping vibrations from the drive wheel.

[0012] (2) When the electric vehicle is traveling in a direction from the center of rotation of the drive wheel toward the center of swing of the arm, if the drive wheel is braked, a force pulling the tip of the arm in the direction opposite to the direction of travel may be applied by the drive wheel. When this pulling force by the drive wheel acts on the arm, a force may be generated in the arm that rotates the arm upward. When this force is generated, the contact pressure of the drive wheel on the ground is reduced and vertical vibration of the drive wheel may occur.

[0013] In contrast, in this embodiment, when the wheel and the drive wheel are in contact with the road surface, a line passing through the swing center of the arm and the rotation center of the drive wheel is parallel to the road surface. This makes it possible to suppress the generation of a force that would rotate the arm upward, even if a pulling force from the drive wheel acts on the arm. As a result, it is possible to suppress a decrease in the contact pressure of the drive wheel and vertical vibrations that occur in the drive wheel.

[0014] (3) The electric vehicle may further include a low-friction member interposed between the bracket and the arm. In this case, even if a simple configuration is adopted in which the arm and the bracket are clamped with fastening members such as bolts and nuts, the frictional force between the arm and the bracket can be appropriately reduced, and the arm can be provided to be swingable relative to the bracket. Furthermore, by clamping the arm and the bracket with the low-friction member interposed therebetween, an appropriate frictional force can be applied between the arm and the bracket, and even if a force in a direction that would rotate the arm upward is generated, the force can be suppressed. Furthermore, the frictional force between the arm and the bracket can suppress vibrations occurring in the arm and the drive wheel.

[0015] (4) In the above-described electric vehicle, it is preferable that the bracket has a support member including a support shaft that supports the arm so that it can swing, and the low-friction member includes a low-friction washer that is provided on the outer periphery of the support shaft and is interposed between the arm and the support member.

[0016] (5) In the electric vehicle described above, the arm may have a protrusion protruding from a base end of the arm along the longitudinal direction of the arm, and the bracket may have an upper wall portion provided above the protrusion and against which the protrusion abuts when the arm swings, and a lower wall portion provided below the protrusion and against which the protrusion abuts when the arm swings. In this case, the upper wall portion and the lower wall portion can limit the swing range of the protrusion. This can limit the swing range of the arm. As a result, the arm can be prevented from swinging beyond a necessary range.

[0017] (6) In the electric vehicle, the vehicle body may include a wheelchair.

[0018] (7) From another perspective, the present embodiment is an electric assist device for a vehicle mounted on a vehicle, the electric assist device for a vehicle includes a bracket fixed to the vehicle, an arm mounted on the bracket so as to be able to swing up and down, a drive wheel mounted at the tip of the arm, an actuator that drives the drive wheel, and an elastic member that is mounted between the bracket and the arm and that urges the arm downward.

[0019] According to the above configuration, since the bracket has an elastic member that biases the arm downward, the bracket can be fixed to the vehicle body so that the drive wheel is pressed against the road surface when the vehicle wheel is in contact with the road. As a result, the drive wheel is pressed against the road surface by the elastic member. As a result, it is possible to increase the contact pressure of the drive wheel while damping vibrations from the drive wheel.

[0020] (8) In the above-described electric assist device for a vehicle, the bracket includes a main body on which the arm is mounted and a fixing part that fixes the main body at a predetermined height on the vehicle. The predetermined height is preferably a position where, when the wheels of the vehicle to which the electric assist device for a vehicle is mounted and the drive wheels are in contact with the road surface, a line passing through the center of swing of the arm and the center of rotation of the drive wheels is parallel to the road surface. In this case, it is possible to suppress a decrease in contact pressure of the drive wheels and vertical vibrations occurring in the drive wheels.

[0021] (9) In the above-described electric assist device for a vehicle, the bracket may include a main body to which the arm is attached and a fixing portion that allows the height position of the main body on the vehicle to be adjusted. In this case, the height position of the main body can be adjusted so that when the wheels of the vehicle to which the electric assist device for a vehicle is attached and the drive wheels are in contact with the road surface, a line passing through the center of swing of the arm and the center of rotation of the drive wheels is parallel to the road surface. As a result, it is possible to reduce the contact pressure of the drive wheels and suppress vertical vibrations occurring in the drive wheels.

[0022] [Details of the embodiment] A preferred embodiment will now be described with reference to the drawings. [Overall configuration] Fig. 1 is a perspective view of an electric wheelchair according to the embodiment. Fig. 2 is a diagram showing the main parts of the electric wheelchair as seen from behind. This electric wheelchair 1 has a function of driving the drive wheels of the electric wheelchair 1 when pushed from behind by an operator, thereby assisting the operator.

[0023] The electric wheelchair 1 is an electric vehicle equipped with a vehicle body 2 and a vehicle power assist device 4. The vehicle body 2 is a typical wheelchair, and includes a frame 2a mainly made of metal pipes, a pair of main wheels 2b, and a pair of casters 2c. The frame 2a includes a pair of rear tubes 2a1, a pair of front tubes 2a2, a pair of upper tubes 2a3, and a pair of lower tubes 2a4.

[0024] The pair of rear tubes 2a1 extend in the up-down direction. The pair of rear tubes 2a1 are arranged parallel to each other with a fixed gap in the left-right direction. The pair of lower tubes 2a4 are connected to the lower ends of the pair of rear tubes 2a1. The pair of upper tubes 2a3 are connected to the pair of rear tubes 2a1. The portion of the pair of rear tubes 2a1 where the pair of upper tubes 2a3 are connected is higher than the lower ends. The pair of upper tubes 2a3 and the pair of lower tubes 2a4 extend in the front-rear direction. The pair of upper tubes 2a3 and the pair of lower tubes 2a4 are arranged substantially parallel to each other with a fixed gap in the left-right direction. The portion of the pair of lower tubes 2a4 rearward of the rear tubes 2a1 is a tipping bar 2t. The tipping bar 2t is a member that is stepped on by the operator's foot. When the operator steps on the tipping bar 2t, the caster 2c is lifted upward with the main wheel 2b as a fulcrum.

[0025] The pair of front tubes 2a2 extend in the vertical direction and connect the ends of the pair of upper tubes 2a3 and the pair of lower tubes 2a4. Therefore, the pair of front tubes 2a2 are shorter than the pair of rear tubes 2a1.

[0026] A pair of casters 2c are provided at the lower end of the front tube 2a2. A pair of main wheels 2b are provided at the lower end of the rear tube 2a1. The pair of main wheels 2b are provided behind the pair of casters 2c. The pair of main wheels 2b are rear wheels. The pair of casters 2c are front wheels. The vehicle body 2 further has a seat 2d on which a passenger sits, and a backrest 2e. The seat 2d is fixed to the pair of upper tubes 2a3. The backrest 2e is fixed to the pair of rear tubes 2a1. The electric wheelchair 1 is constructed by attaching a vehicle electric assist device 4 to a vehicle body 2 that can be used as a wheelchair.

[0027] In the following description, the direction in which the rider faces when riding in the electric wheelchair 1 (the direction in which the backrest 2e faces forward) is referred to as the forward direction, and the opposite direction as the rearward direction. Therefore, the rider rides facing the front of the electric wheelchair 1. Also, the direction facing left from the rider's perspective is referred to as the leftward direction, and the direction facing right from the rider's perspective is referred to as the rightward direction.

[0028] The vehicle electric assist device 4 includes a pair of drive units 8 and a pair of operating devices 10. As shown in FIG. 1 , a pair of protrusions 2a5 are provided at the upper ends of the pair of rear tubes 2a1. The pair of protrusions 2a5 protrude further rearward than the backrest 2e. The pair of operating devices 10 are provided on the pair of protrusions 2a5. Thus, the pair of operating devices 10 are disposed above the left and right sides of the backrest 2e. Each of the pair of operating devices 10 has a grip 12. The grip 12 is movable in the front-rear direction relative to the protrusions 2a5. The operating device 10 further has a potentiometer (not shown). The potentiometer detects the amount of displacement of the grip 12 in the front-rear direction. The operating device 10 provides an output indicating the amount of displacement of the grip 12 to a control device (described later).

[0029] The pair of drive units 8 are fixed to the left and right sides of the frame 2a. The pair of drive units 8 are arranged on the vehicle inboard side of the pair of main wheels 2b. Each of the pair of drive units 8 includes a drive wheel 14 and an actuator 16. The actuator 16 drives the drive wheel 14. The actuator 16 is an in-wheel motor and is provided inside the drive wheel 14. The drive unit 8 will be described in detail later.

[0030] The vehicle electric assist device 4 further includes a control box (not shown) that houses a battery and a control device that controls each component. The battery stores power supplied to the pair of drive units 8 (actuators 16) and each component. The control device has a function of controlling the pair of actuators 16 based on outputs from the pair of operation units 10. As described above, the outputs from the pair of operation units 10 indicate the amount of displacement of the pair of grips 12. The control device controls the pair of actuators 16 based on the amount of displacement of the pair of grips 12 so as to maintain the relative position between the grips 12 and the frame 2a (vehicle body 2). The control device can cause the actuators 16 to drive the drive wheels 14, thereby accelerating or maintaining the speed of the vehicle body 2. The control device can also cause the actuators 16 to perform regenerative braking, short-circuit braking, or the like, thereby braking the drive wheels 14 and decelerating the vehicle body 2.

[0031] For example, when the operator pushes the grip 12 forward, the grip 12 is displaced forward. The control device moves the vehicle body 2 forward based on the output of the pair of operating units 10 so as to return the grip 12 to its original position. Conversely, when the operator pulls the grip 12 rearward, the grip 12 is displaced rearward. The control device moves the vehicle body 2 backward so as to return the grip 12 to its original position. In this way, the control device adjusts the amount of operation of the actuator 16 in response to the operator pushing or pulling the grip 12. In this way, the control device controls the pair of actuators 16 so as to maintain the relative position between the grip 12 and the vehicle body 2.

[0032] [Configuration of the Drive Unit] Figure 3 is an enlarged view of the main parts of Figure 1. For ease of understanding, Figure 3 omits the right main wheel 2b, the left drive wheel 14, and the actuator 16. The drive unit 8 further includes a bracket 18 and an arm 20. The bracket 18 is a plate-shaped member. The bracket 18 is fixed to the lower tube 2a4 and the rear tube 2a1. The arm 20 is supported by the bracket 18 so as to be swingable in the up and down direction. The arm 20 includes an arm body 21 and a protrusion 22 integrally formed with the arm body 21. A notch 21a1 is formed in the tip end 21a of the arm body 21. The axle 14a extending from the drive wheel 14 is fixed to the notch 21a1. As a result, the drive wheel 14 and the actuator 16 are provided at the tip end 21a of the arm body 21. Therefore, when the arm body 21 swings up and down, the drive wheel 14 and the actuator 16 move up and down.

[0033] A rotor (not shown) of the actuator 16 can rotate integrally with the drive wheel 14. A stator (not shown) of the actuator 16 is fixed to the arm 20. As a result, the actuator 16 drives the drive wheel 14 to rotate.

[0034] Fig. 4 is an enlarged perspective view showing the bracket 18 and arm 20 of the drive unit 8. Fig. 4 shows the bracket 18 and arm 20 of the left drive unit 8. The left and right drive units 8 have the same configuration. Therefore, only the left drive unit 8 will be described here.

[0035] The bracket 18 has a main body portion 24 and a fixing portion 26. The main body portion 24 is provided with an arm 20. The fixing portion 26 is provided on the upper side of the main body portion 24. The fixing portion 26 fixes the main body portion 24 at a predetermined height position on the vehicle main body 2. The fixing portion 26 includes a front fixing portion 28 and a rear fixing portion 30. The front fixing portion 28 has a rectangular plate-shaped portion 28a connected to the main body portion 24 and a semi-cylindrical member 28b. One end of the semi-cylindrical member 28b is inserted into a slit 28c provided in the plate-shaped portion 28a and fixed to the plate-shaped portion 28a. The other end of the semi-cylindrical member 28b is fixed to the plate-shaped portion 28a by a bolt 28d. The lower tube 2a4 passes between the plate-shaped portion 28a and the semi-cylindrical member 28b (see FIG. 3). The lower tube 2a4 is sandwiched between the plate-shaped portion 28a and the semi-cylindrical member 28b. As a result, the front fixing portion 28 is fixed to the lower tube 2a4.

[0036] The rear fixing part 30 has a protruding part 30a that protrudes from the edge of the main body part 24 toward the inside of the vehicle, and a pillar part 30b that extends upward from the tip of the protruding part 30a. The upper surface of the protruding part 30a abuts against the lower tube 2a4 (see FIG. 3). A notch part 30b1 is provided at the tip of the pillar part 30b. A threaded part 3a protruding from the hub 3 of the main wheel 2b fixed to the rear tube 2a1 is fixed to the notch part 30b1 (see FIG. 3). The pillar part 30b is sandwiched between the hub 3 and a nut 3b that threads onto the threaded part 3a. In this way, the rear fixing part 30 is fixed to the rear tube 2a1. The fixing part 26 is fixed to the lower tube 2a4 and the rear tube 2a1. In this way, the fixing part 26 fixes the main body part 24 to the frame 2a.

[0037] As shown in Fig. 4, the arm body 21 of the arm 20 provided on the main body 24 swings around the central axis C1. In other words, the central axis C1 is the swing center of the arm body 21. Fig. 5 is a cross-sectional view of the bracket 18 and the arm 20. Fig. 5 shows a cross section along the vertical direction including the central axis C1.

[0038] As shown in FIG. 5 , the bracket 18 further includes a support member 34. The support member 34 is a member that supports the arm 20 so that the arm 20 can swing. The support member 34 includes a support shaft 36, a spacer 38, a washer 44, and a nut 42. The support member 34 is fixed to a support hole 24a provided in the main body 24. The support hole 24a is a hole centered on the central axis C1. The support shaft 36 includes a shaft portion 36a, a head portion 36b, and a threaded portion 36c. The head portion 36b is provided at one end of the shaft portion 36a. The threaded portion 36c is provided at the other end of the shaft portion 36a. A nut 42 is threaded onto the threaded portion 36c.

[0039] The support member 34 is configured by arranging the arm 20, a spacer 38, and a washer 44 on the outer periphery of the support shaft 36. A pair of low-friction washers 40 is also incorporated into the support member 34. The pair of low-friction washers 40 are arranged on both sides of the arm 20. On the outer periphery of the support shaft 36, from the head 36b toward the threaded portion 36c, the washer 44, the low-friction washer 40, the arm 20, the low-friction washer 40, the spacer 38, and the main body 24 are arranged in this order.

[0040] The washer 44 is a member that prevents each component from falling off the support shaft 36. The spacer 38 is a cylindrical member. The shaft portion 36a is inserted into the inner periphery of the spacer 38. The spacer 38 is a member that ensures a gap between the main body 24 and the arm 20. A hole 21b1 is provided on the base end 21b side of the arm main body 21. The shaft portion 36a is inserted into the hole 21b1. A plain bearing 46 is interposed between the hole 21b1 and the shaft portion 36a. The pair of low-friction washers 40 are washers with low coefficients of friction on their front and back surfaces. The low-friction washers 40 are interposed between the arm 20 and the spacer 38, and between the arm 20 and the washer 44. Examples of low-friction washers 40 include ordinary washers whose front and back surfaces are coated with a low-friction material, such as fluororesin, that reduces the friction coefficient, and washers made of a low-friction material. Furthermore, spring washers and wave washers can also be used as the low-friction washer 40. Spring washers and wave washers can appropriately reduce the coefficient of friction by reducing the contact area between them and the member that comes into contact with them.

[0041] The washer 44, the low-friction washer 40, the arm 20, the low-friction washer 40, the spacer 38, and the main body 24 are fastened between the head 36b and the nut 42. In other words, the arm 20, the main body 24, and other members are clamped between the support shaft 36 and the nut 42, which are fastening members.

[0042] The arm 20 is disposed between the pair of low-friction washers 40, which makes it possible to appropriately reduce the frictional force between the arm 20 and the support member 34. That is, even if a simple configuration is adopted in which the arm 20 and the main body 24 are sandwiched between fastening members, as in this embodiment, it is possible to appropriately reduce the frictional force between the arm 20 and the support member 34, and it is possible to provide the arm 20 so that it can swing relative to the support member 34 (bracket 18).

[0043] As shown in Figures 4 and 5, the protrusion 22 of the arm 20 is provided on the base end 21b side of the arm main body 21. The protrusion 22 has a radial portion 50 and a longitudinal portion 52. The radial portion 50 protrudes from the side surface 21c of the arm main body 21. The radial portion 50 extends along a radial direction perpendicular to the central axis C1. The radial portion 50 also extends from the base end 21b in a direction intersecting the longitudinal direction of the arm main body 21. The longitudinal portion 52 extends from the side surface 50a of the radial portion 50. The longitudinal portion 52 extends in the opposite direction to the extension direction of the arm main body 21. The longitudinal portion 52 extends approximately parallel to the longitudinal direction of the arm main body 21.

[0044] As shown in Figure 4, the bracket 18 has a bent portion 54 that protrudes toward the inside of the vehicle along the side edge of the main body portion 24. The bent portion 54 has a recess 55. The recess 55 is formed by cutting out the edge of the bent portion 54. The recess 55 has an upper wall portion 55a and a lower wall portion 55b. The upper wall portion 55a and the lower wall portion 55b face each other.

[0045] The longitudinal portion 52 is inserted into the recess 55. Therefore, the upper wall portion 55a is provided above the longitudinal portion 52. The lower wall portion 55b is provided below the longitudinal portion 52. Furthermore, the longitudinal portion 52 (protrusion 22) is provided integrally with the arm main body 21. Therefore, the longitudinal portion 52 swings together with the swing of the arm main body 21. When the arm main body 21 swings downward by a predetermined angle, the longitudinal portion 52 swings upward and abuts against the upper wall portion 55a. In this case, further upward swing of the longitudinal portion 52 is restricted. Furthermore, when the arm main body 21 swings upward by a predetermined angle, the longitudinal portion 52 swings downward and abuts against the lower wall portion 55b. In this case, further downward swing of the longitudinal portion 52 is restricted.

[0046] Therefore, the upper wall portion 55a and the lower wall portion 55b limit the swing range of the longitudinal portion 52 (protrusion 22), thereby limiting the swing range of the arm 20 (arm main body 21). As a result, it is possible to prevent the arm main body 21 from swinging beyond a necessary range.

[0047] In other words, the swing range of the arm main body 21 is limited to the range from the position of the arm main body 21 where the longitudinal portion 52 and the upper wall portion 55a abut against each other to the position of the arm main body 21 where the longitudinal portion 52 and the lower wall portion 55b abut against each other. In the following description, the position of the arm main body 21 where the longitudinal portion 52 and the upper wall portion 55a abut against each other is referred to as the lower swing position, and the position of the arm main body 21 where the longitudinal portion 52 and the lower wall portion 55b abut against each other is referred to as the upper swing position.

[0048] 4, the drive unit 8 further includes an elastic member 58. The elastic member 58 is provided between the bracket 18 and the arm 20. The elastic member 58 biases the arm 20 (arm body 21) downward. The elastic member 58 is, for example, a tension coil spring.

[0049] An L-shaped spring hook portion 24b is provided at the rear end of the main body portion 24. A spring hook bolt 60 is provided at the radial portion 50 of the protrusion 22. The spring hook bolt 60 is inserted into a hole 50b in the radial portion 50 (see FIG. 5). The spring hook bolt 60 tightens the radial portion 50 by threading into a nut 62. This fixes the spring hook bolt 60 to the radial portion 50.

[0050] One end of the elastic member 58 is hooked on the spring hook portion 24b. The other end of the elastic member 58 is hooked on the groove portion 60a at the tip of the spring hook bolt 60. When the longitudinal portion 52 abuts against the upper wall portion 55a, the elastic member 58 applies a tensile force between the spring hook portion 24b and the spring hook bolt 60. Therefore, when no force is applied to swing the arm main body 21 upward, the position of the arm main body 21 is in the lower swing position. When the arm main body 21 is in the lower swing position, the elastic member 58 applies a tensile force between the spring hook portion 24b and the spring hook bolt 60. Therefore, when the arm main body 21 is located between the lower swing position and the upper swing position, the elastic member 58 biases the arm 20 (arm main body 21) downward.

[0051] 6A is a diagram showing the relationship between the drive wheels 14 and the main wheels 2b when the arm main body 21 is in the lower swing position. As shown in Fig. 6A, when the main wheels 2b and drive wheels 14 of the vehicle main body 2 are not in contact with the road surface R, no force from the road surface R acts on the arm main body 21. Therefore, the position of the arm main body 21 is in the lower swing position. When the position of the arm main body 21 is in the lower swing position, the lowest part of the drive wheels 14 is lower than the lowest part of the main wheels 2b.

[0052] 6B is a diagram showing the relationship between the drive wheels 14 and the main wheels 2b when the vehicle body 2 is placed on a road surface R. In this case, the casters 2c, the main wheels 2b, and the drive wheels 14 are in contact with the road surface R. Therefore, the position of the arm body 21 is between the lower swing position and the upper swing position. At this time, the elastic member 58 biases the arm body 21, which can swing up and down, downward, so that the drive wheels 14 are pressed against the road surface R by the tensile force of the elastic member 58. As a result, it is possible to increase the contact pressure of the drive wheels 14 while damping vibrations transmitted from the drive wheels 14 to the vehicle body 2.

[0053] In this embodiment, when the caster 2 c, the main wheel 2 b, and the drive wheel 14 are in contact with the road surface R, the line L is configured to be parallel to the road surface R. The line L is a line passing through the central axis C1, which is the swing center of the arm main body 21, and the rotation center C2 of the drive wheel 14.

[0054] In this embodiment, "the straight line L is parallel to the road surface R" includes not only the case where the straight line L is parallel to the road surface R, but also the case where the straight line L is approximately parallel to the road surface R. "The straight line L is parallel to the road surface R" refers to the case where the acute angle θ between the straight line L and a line along the road surface R is equal to or greater than 0 degrees and equal to or less than 8 degrees. In this embodiment, between the lower swing position and the upper swing position, there is a position of the arm main body 21 where the straight line L is approximately parallel to the road surface R.

[0055] Here, we will explain the case where the brakes are applied to the drive wheels when an electric wheelchair, whose line L is not parallel to the road surface R, moves forward. FIG. 7A is a diagram showing the forces acting on the arm when the brakes are applied to the drive wheels 114 while the electric wheelchair, whose line L is not parallel to the road surface R, is moving. FIG. 7A shows the case where the electric wheelchair moves forward (forward) from the center of rotation C2 of the drive wheels 114 toward the central axis C1 of the arm 120. In this case, the brakes are applied to the drive wheels 114 (regenerative braking or short-circuit braking), and a force F1 is applied to the tip end 120A of the arm 120, pulling it in the direction opposite to the direction of travel by the drive wheels 114. At this time, because the line L is not parallel to the road surface R, a force F2 may be generated in the arm 120 in a direction that rotates the arm 120 upward. When such force F2 is generated in the arm 120, the ground contact pressure of the drive wheels 114 is reduced and vertical vibrations may occur in the drive wheels 114.

[0056] 7B is a diagram showing the force acting on the arm when the brakes are applied to the drive wheels while the electric wheelchair of this embodiment is moving. As shown in FIG. 7B, when the line L is parallel to the road surface R, even if a pulling force from the drive wheels 14 acts on the arm 20, it is possible to prevent the arm 20 from being rotated upward. As a result, it is possible to prevent a decrease in the contact pressure of the drive wheels 14 and vertical vibrations occurring in the drive wheels.

[0057] In addition, in this embodiment, by sandwiching the arm 20 and the support member 34 (bracket 18) with the low-friction washer 40 interposed therebetween, it is possible to apply an appropriate frictional force between the arm 20 and the support member 34, and even if a force is generated in a direction that rotates the arm 20 upward, this force can be suppressed. In addition, the frictional force between the arm 20 and the support member 34 can suppress vibrations that occur in the arm 20 and the drive wheel 14.

[0058] 8 is a diagram showing the bracket 18 of the drive unit 8 according to another embodiment. This embodiment differs from the above embodiment in that the notch 30b1 provided in the column 30b is longer in the height direction, and that the slits 28c and the bolt holes 28b1 are arranged in multiple rows along the height direction.

[0059] The fixing portion 26 of this embodiment has the above-described configuration, and thus the height position of the main body portion 24 on the vehicle body 2 can be adjusted. Therefore, the height position of the main body portion 24 can be adjusted so that the straight line L is parallel to the road surface. As a result, it is possible to reduce the contact pressure of the drive wheels 14 and suppress vertical vibrations occurring in the drive wheels 14.

[0060] [Others] The embodiments disclosed herein are illustrative in all respects and are not limiting. In the above embodiment, a tension coil spring is used as the elastic member 58, but an annular rubber or the like may be used instead of the tension coil spring.

[0061] Furthermore, in the above embodiment, the case where the position of the arm main body 21 where the straight line L is approximately parallel to the road surface R is included between the lower swing position and the upper swing position has been exemplified, but the lower swing position and the upper swing position may be included within the range of positions of the arm main body 21 where the straight line L is approximately parallel to the road surface R. In this case, the swing range of the arm main body 21 can be limited to the range where the straight line L is approximately parallel to the road surface R.

[0062] In the above embodiment, the vehicle body 2 has front and rear wheels (casters 2c and main wheels 2b), but the vehicle body 2 may have at least one of the front and rear wheels. Also, in the above embodiment, the vehicle body 2 is a general wheelchair to which the vehicle power assist device 4 is attached, but the vehicle body 2 may be a dolly, wagon, or the like other than a wheelchair. The scope of the present invention is not limited to the above embodiment, and includes all modifications within the scope of equivalents to the configurations set forth in the claims.

[0063] 2 Vehicle body 4 Vehicle electric assist device 14 Drive wheel 16 Actuator 18 Bracket 20 Arm 21a Tip end 21b Base end 22 Projection 24 Main body 26 Fixing portion 34 Support member 36 Support shaft 40 Low-friction washer (low-friction member) 55a Upper wall 55b Lower wall 58 Elastic member

Claims

1. A vehicle body having wheels; A bracket fixed to the vehicle body; an arm supported by the bracket so as to be swingable in the vertical direction; A drive wheel provided at a tip end of the arm; An actuator that drives the drive wheels; an elastic member provided between the bracket and the arm and biasing the arm downward, the arm has a protrusion protruding along a longitudinal direction of the arm on a base end side of the arm, The bracket has an upper wall portion that is provided above the protrusion and against which the protrusion abuts when the arm swings, and a lower wall portion that is provided below the protrusion and against which the protrusion abuts when the arm swings. Electric vehicle.

2. When the wheel and the drive wheel are in contact with a road surface, a straight line passing through the swing center of the arm and the rotation center of the drive wheel is parallel to the road surface. The electric vehicle according to claim 1 .

3. The bracket further includes a low-friction member interposed between the bracket and the arm. The electric vehicle according to claim 2 .

4. the bracket has a support member including a support shaft that swingably supports the arm, The electric vehicle according to claim 3 , wherein the low-friction member includes a low-friction washer provided on an outer circumferential side of the support shaft and interposed between the arm and the support member.

5. The vehicle body includes a wheelchair. The electric vehicle according to claim 1 .

6. An electric assist device for a vehicle that is mounted on a vehicle, A bracket fixed to the vehicle; an arm provided on the bracket so as to be swingable in the up and down direction; A drive wheel provided at a tip end of the arm; An actuator that drives the drive wheels; an elastic member provided between the bracket and the arm and biasing the arm downward, the arm has a protrusion protruding along a longitudinal direction of the arm on a base end side of the arm, The bracket has an upper wall portion that is provided above the protrusion and against which the protrusion abuts when the arm swings, and a lower wall portion that is provided below the protrusion and against which the protrusion abuts when the arm swings. An electric assist device for vehicles.

7. The bracket is a main body portion on which the arm is provided; a fixing portion that fixes the main body portion at a predetermined height position in the vehicle, The predetermined height position is When the wheels of the vehicle to which the vehicle electric assist device is attached and the drive wheels are in contact with the road surface, a straight line passing through the swing center of the arm and the rotation center of the drive wheels is parallel to the road surface. The electric assist device for a vehicle according to claim 6.

8. The bracket is a main body portion on which the arm is provided; a fixing portion capable of adjusting a height position of the main body portion in the vehicle; The electric assist device for a vehicle according to claim 6.