Compact electric vehicle

Abstract

This compact electric vehicle (10) is provided with a left drive wheel (12) and a right drive wheel (12), and executes differential wheel speed control for causing a rotational speed difference between the rotational speed of the left drive wheel and the rotational speed of the right drive wheel during cornering. The compact electric vehicle varies a parameter for setting the rotation speed difference in the differential wheel speed control according to the vehicle speed of the compact electric vehicle.

Description

small electric vehicle CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on Japanese Application No. 2024-032172 filed on March 4, 2024, the contents of which are incorporated herein by reference.

[0002] The present disclosure relates to small electric vehicles.

[0003] For example, there is a traveling vehicle that drives a traveling motor with an inverter, and that is provided with means for storing a target speed pattern of the traveling vehicle, means for storing a control gain of the traveling motor for each speed, and means for controlling the inverter based on the stored target speed and the control gain for each speed (see Patent Document 1).The traveling vehicle described in Patent Document 1 can travel at the target speed by controlling with a gain that changes depending on the traveling vehicle speed.

[0004] JP 2011-93676 A

[0005] Meanwhile, vehicles (small electric vehicles) often travel around curves using wheel speed difference control, which creates a difference between the rotational speeds of the left and right drive wheels. In wheel speed difference control when traveling around a curve, if the difference between the rotational speeds of the left and right drive wheels is not appropriately set, the vehicle may sway left or right or deviate from a target trajectory. The vehicle described in Patent Document 1 does not take into account traveling around a curve using wheel speed difference control, and there is still room for improvement.

[0006] The present disclosure has been made to solve the above-mentioned problems, and its main purpose is to appropriately set the difference in rotational speed between the left drive wheel and the right drive wheel in a small electric vehicle that performs wheel speed difference control when traveling around a curve.

[0007] The first means for solving the above problem is a small electric vehicle that has a left drive wheel and a right drive wheel and executes wheel speed difference control to generate a rotational speed difference between the rotational speed of the left drive wheel and the rotational speed of the right drive wheel when traveling around a curve, and a parameter that sets the rotational speed difference in the wheel speed difference control is made variable depending on the vehicle speed of the small electric vehicle.

[0008] According to the above configuration, the small electric vehicle has a left drive wheel and a right drive wheel, and executes wheel speed difference control to generate a rotational speed difference between the rotational speed of the left drive wheel and the rotational speed of the right drive wheel when traveling around a curve. Therefore, for example, when the target trajectory is turning left, the small electric vehicle can turn left by making the rotational speed of the left drive wheel slower than the rotational speed of the right drive wheel.

[0009] Here, in the wheel speed difference control, if the rotational speed difference between the left drive wheel and the right drive wheel (hereinafter referred to as the "rotational speed difference between the left and right drive wheels") is not appropriately set, the small electric vehicle may sway left or right when traveling around a curve, or the small electric vehicle may deviate from the target trajectory. For example, if the rate of change in the rotational speed difference between the left and right drive wheels in the wheel speed difference control is too large compared to the vehicle speed, the small electric vehicle may sway left or right. On the other hand, if the rate of change in the rotational speed difference between the left and right drive wheels in the wheel speed difference control is too small compared to the vehicle speed, the small electric vehicle may deviate from the target trajectory. In this regard, in the small electric vehicle, the parameter for setting the rotational speed difference in the wheel speed difference control is variable depending on the vehicle speed of the small electric vehicle. Therefore, it becomes easier to appropriately set the rotational speed difference between the left and right drive wheels in the wheel speed difference control, and ultimately the small electric vehicle's ability to follow the target trajectory when traveling around a curve can be improved.

[0010] The above and other objects, features, and advantages of the present disclosure will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which Fig. 1 is a schematic diagram of an automated guided vehicle, Fig. 2 is a block diagram showing an electric drive unit and its peripheral configuration, Fig. 3 is a schematic diagram showing a curve running at high vehicle speed when the rotational speed difference between the left and right drive wheels is appropriate, Fig. 4 is a schematic diagram showing a front view of the automated guided vehicle, Fig. 5 is a schematic diagram showing a curve running at low vehicle speed when the rotational speed difference between the left and right drive wheels is excessive, Fig. 6 is a schematic diagram showing a curve running at high vehicle speed when the rotational speed difference between the left and right drive wheels is insufficient, and Fig. 7 is a schematic diagram showing a curve running at high vehicle speed when the rotational speed difference between the left and right drive wheels is appropriate. FIG. 10 is a graph showing an example of changing the relationship between vehicle speed and gain; FIG. 11 is a block diagram showing another example of changing the gain in wheel speed difference control; FIG. 12 is a map showing the relationship between vehicle speed, object weight, and gain; FIG. 13 is a map showing the relationship between vehicle speed, curve curvature, and gain; and FIG. 14 is a schematic diagram of an electric wheelchair.

[0011] An embodiment of the present invention will be described below with reference to the drawings. The automatic guided vehicle is an AGV (Automatic Guided Vehicle) that is guided by a magnetic tape (magnetic line) in a factory, warehouse, or the like.

[0012] 1 , the automated guided vehicle 10 includes a vehicle body 11, four (multiple) sets of drive wheels 12 and drive shafts 13, and a drive unit 20. Each drive wheel 12 is connected to a corresponding drive shaft 13 and rotates around the corresponding drive shaft 13. The four drive wheels 12 are the left and right front wheels and the left and right rear wheels of the automated guided vehicle 10.

[0013] The drive unit 20 is housed in the vehicle body 11. The drive unit 20 includes four (multiple) sets of electric drive devices 30 and brakes 60, a host controller 70, a battery 71, an MCU relay 73, a brake relay 75, and sensors 77. Each set of electric drive devices 30 and brakes 60 corresponds to each set of drive wheels 12 and drive axles 13. In Fig. 1, power supply lines PL1 and PL2 are indicated by solid lines, and the signal line SL is indicated by a dashed line.

[0014] Each electric drive unit 30 (drive unit) drives each drive shaft 13. Each electric drive unit 30 is fixed to the vehicle body 11. Each electric drive unit 30 includes an MCU (Motor Control Unit) and a reducer 59.

[0015] Each MCU (each electric drive unit 30) is connected to a battery 71 via a power supply line PL1. An MCU relay 73 is provided on the power supply line PL1 between the battery 71 and the four MCUs. The MCU relay 73 (high-order relay) is switched between an ON state, in which power is supplied from the battery 71 to the four MCUs (electric drive units 30), and an OFF state, in which power to the four MCUs is cut off. When the MCU relay 73 is in the ON state, each MCU is driven by power supplied from the battery 71.

[0016] The reducer 59 is, for example, a planetary gear mechanism, a cycloid gear mechanism, etc. The reducer 59 reduces the rotation speed of the motor 31 (see FIG. 2) of the MCU and transmits the reduced rotation speed to the drive shaft 13.

[0017] Each brake 60 (brake device) brakes each drive axle 13. Each brake 60 is fixed to the vehicle body 11. Each brake 60 is connected to a battery 71 via a power supply line PL2. A brake relay 75 is provided on the power supply line PL2 between the battery 71 and each of the four brakes 60. The brake relay 75 (brake device relay) is switched between an ON state, in which power is supplied from the battery 71 to each of the four brakes 60, and an OFF state, in which power is cut off from each of the four brakes 60. When the brake relay 75 is in the ON state, each of the brakes 60 is driven by power supplied from the battery 71. Each of the brakes 60 is, for example, a non-excitation actuated electromagnetic brake that brakes each of the drive axles 13 when no power is supplied. The braking force applied by each of the brakes 60 to each of the drive axles 13 can also be controlled by each of the MCUs or the host controller 70.

[0018] The host controller 70 (control unit) is composed of an ECU (Electronic Control Unit) equipped with, for example, a CPU, ROM, RAM, an input / output interface, etc. The host controller 70 and the four MCUs are connected to each other via a signal line SL. The signal line SL is a signal line that meets, for example, the CAN (Controller Area Network) communication standard. The host controller 70 and the four MCUs transmit and receive information to each other via the signal line SL. The host controller 70 controls the four MCUs (electric drive devices 30) by inputting commands to each MCU via the signal line SL. The host controller 70 switches the MCU relay 73 and the brake relay 75 between the on state and the off state. The host controller 70 maintains the MCU relay 73 and the brake relay 75 in the on state while the drive unit 20 is operating.

[0019] The sensors 77 include, for example, an abnormality stop button, a collision detection switch, a magnetic sensor that detects the magnetism of the magnetic tape, a position information sensor that reads floor position information, a human presence sensor that detects people, etc. The detection results of the sensors 77 are input to the upper controller 70.

[0020] 2 is a block diagram showing the electric drive unit 30 and its peripheral configuration. Since the four electric drive units 30 have the same configuration, one electric drive unit 30 will be described as an example.

[0021] The electric drive unit 30 includes two systems each of a power supply line relay 32, a battery reverse connection prevention relay 33, an inverter 34, a current sensor 41, and an angle sensor 42. The electric drive unit 30 includes one motor 31, a reducer 59, and a controller 40.

[0022] The inverter 34 of each system is connected to the MCU relay 73 (battery 71 ) via the power supply line relay 32 and the battery reverse connection prevention relay 33 .

[0023] The power supply line relay 32 (predetermined relay) is switchable between an ON state in which power is supplied from the battery 71 to the inverter 34 and an OFF state in which the power is cut off. The reverse battery connection prevention relay 33 corrects reverse connection when the battery 71 is connected with reverse polarity (reverse connection). The reverse battery connection prevention relay 33 (predetermined relay) can be switched between an ON state in which power is supplied from the battery 71 to the inverter 34 and an OFF state in which the power is cut off.

[0024] The inverter 34 is, for example, a three-phase inverter, and includes a plurality of switching elements corresponding to the respective phases, and converts the supplied DC power into AC power. The inverter 34 inputs (supplies) the AC power to the motor 31.

[0025] The motor 31 is, for example, a three-phase motor, and includes one rotor (not shown) and two systems of stator windings 31 a. AC power is input to the stator windings 31 a of each system from the inverter 34 of each system.

[0026] The current sensor 41 of each system detects the current flowing through the stator winding 31 a of the corresponding system. The angle sensor 42 of each system detects the electrical angle (angle) of the rotor. The current sensor 41 and the angle sensor 42 input the detection results to the controller 40.

[0027] The controller 40 includes a microcomputer and an ASIC (Application Specific Integrated Circuit). The microcomputer is configured, for example, by an ECU including a CPU, memory (ROM, RAM, etc.), an input / output interface, etc. The ASIC is an IC optimized for controlling the motor 31, etc. The controller 40 switches the power line relay 32 and the reverse battery connection prevention relay 33 of each system between an on state and an off state. Specifically, the controller 40 maintains the power line relay 32 and the reverse battery connection prevention relay 33 in an on state while the MCU (electric drive device 30) is operating. The controller 40 executes a program stored in the memory to realize the function of the motor control unit 40a. The motor control unit 40a controls the inverter 34 of each system based on commands from the upper controller 70 and detection results of the current sensor 41 and the angle sensor 42 of each system. The motor control unit 40a then controls the inverter 34 of each system so that the rotational speed of the corresponding drive wheel 12 matches (approaches) the rotational speed command value received from the upper controller 70.

[0028] The power supply line relay 32, the battery reverse connection prevention relay 33, the controller 40, the current sensor 41, and the angle sensor 42 constitute a control circuit that controls the inverter 34.

[0029] When the upper controller 70 determines that the automatic guided vehicle 10 has been instructed to travel straight ahead, it sends a rotational speed command value to the controller 40 of each MCU so that the left and right drive wheels 12 are rotated in the same direction and at the same rotational speed.

[0030] When the host controller 70 determines that braking of the automated guided vehicle 10 has been instructed, it transmits a torque command value to the controller 40 of each MCU so as to cause each motor 31 to generate a braking torque. This applies a braking force to the automated guided vehicle 10, and the automated guided vehicle 10 then stops. The host controller 70 can also control the braking force acting on each drive shaft 13 by controlling each brake 60.

[0031] When the upper controller 70 determines that the unmanned guided vehicle 10 has been instructed to curve (turn) the left and right electric drive units 30 at the front and the left and right electric drive units 30 at the rear as follows:

[0032] For example, as shown in Figure 3, the magnetic tape M extends so as to curve to the left, thereby instructing the automatic guided vehicle 10 to travel around a curve. The left and right front electric drive units 30 are integrated and supported rotatably about the front swing arm shaft C1. A sensor unit 45 is attached to the integrated left and right front electric drive units 30. For convenience, the sensor unit 45 is shown shortened in Figure 3.

[0033] As shown in the front view of FIG. 4 , the front sensor unit 45 includes, for example, 16 magnetic sensors S1 to S16. The magnetic sensors S1 to S16 are arranged horizontally in a direction perpendicular to the forward movement direction of the automatic guided vehicle 10. That is, the magnetic sensors S1 to S16 are arranged in the left-right direction of the automatic guided vehicle 10. The magnetic sensors S1 to S16 are arranged at equal intervals from the right end to the left end of the automatic guided vehicle 10. The magnetic sensors S1 to S16 turn on when a magnetic tape M is present directly below them, and turn off when a magnetic tape M is not present directly below them. That is, the magnetic sensors S1 to S16 detect only the magnetic tape M directly below them (the magnetic tape M directly below them). The detection results of the magnetic sensors S1 to S16 are input to the host controller 70.

[0034] The left-right positions of magnetic sensors S1 to S16 are referred to as positions 1 to 16, respectively. The left-right center position of magnetic sensors S1 to S16 is midway between position 8 of magnetic sensor S8 and position 9 of magnetic sensor S9, and is position 8.5 (hereinafter also referred to as "center position 8.5"). The left-right center position of the automated guided vehicle 10 and the left-right center position 8.5 of the sensor unit 45 coincide with each other.

[0035] The AGV 10 controls each of the front drive wheels 12 of the AGV 10 so that the left-right center (e.g., position 12) of the detection range (e.g., S10 to S14) in which the magnetic tape M is detected coincides with (approaches) the left-right center of the AGV 10 (center position 8.5). That is, the AGV 10 executes wheel speed difference control for the front left and right drive wheels 12 when traveling around a curve, which generates a rotational speed difference between the rotational speed of the left drive wheel 12 and the rotational speed of the right drive wheel 12. The AGV 10 rotates the left and right drive wheels 12 in the same direction, and transmits a rotational speed command value to the controller 40 of each MCU so that the rotational speed of the drive wheel 12 in the commanded turning direction is lower than the rotational speed of the remaining drive wheels 12. Details of the wheel speed difference control will be described later.

[0036] Returning to FIG. 3 , the left and right rear electric drive units 30 are integrated and supported rotatably around the rear swing arm shaft C2. A sensor unit 45 is attached to the integrated left and right rear electric drive units 30. The rear sensor unit 45 has a configuration similar to that of the front sensor unit 45. The AGV 10 controls the rear drive wheels 12 of the AGV 10 so that the left-right center of the detection range in which the magnetic tape M is detected coincides (approaches) with the left-right center of the AGV 10. That is, when traveling around a curve, the AGV 10 performs wheel speed difference control on the left and right rear drive wheels 12, causing a rotational speed difference between the left drive wheel 12 and the right drive wheel 12. The AGV 10 separately (independently) performs wheel speed difference control on the front left and right drive wheels 12 and wheel speed difference control on the rear left and right drive wheels 12.

[0037] Here, in the wheel speed difference control, if the rotational speed difference between the left drive wheel 12 and the right drive wheel 12 (hereinafter referred to as the "rotational speed difference between the left and right drive wheels") is not set appropriately, there is a risk that the automated guided vehicle 10 will sway left and right when traveling around a curve, or that the automated guided vehicle 10 will deviate from the target trajectory.

[0038] 3 shows the state of traveling around a curve at high vehicle speed when the rotational speed difference between the left and right drive wheels is appropriate. In the wheel speed difference control, the rate of change of the rotational speed difference between the left and right drive wheels is increased in response to high vehicle speeds. Therefore, the rotational speed difference between the left and right drive wheels is set to a value appropriate for the high vehicle speed and the curvature of the curve. As a result, the lateral center of the detection range of the sensor unit 45 coincides with the lateral center of the AGV 10, and the AGV 10 travels along the magnetic tape M.

[0039] 5 shows the behavior of a vehicle traveling around a curve at low vehicle speed when the difference in rotational speed between the left and right drive wheels is excessive. In the wheel speed difference control, the rate of change in the difference in rotational speed between the left and right drive wheels is set large in a manner that does not correspond to the low vehicle speed. Therefore, the difference in rotational speed between the left and right drive wheels is set larger than the difference in rotational speed appropriate for the low vehicle speed and the curvature of the curve. As a result, the lateral center of the detection range of the sensor unit 45 and the lateral center of the AGV 10 repeatedly coincide and overshoot, causing the AGV 10 to travel while swaying left and right relative to the magnetic tape M.

[0040] 6 shows a curved road at high vehicle speed when the difference in rotational speed between the left and right drive wheels is insufficient. In the wheel speed difference control, the rate of change in the difference in rotational speed between the left and right drive wheels is set small and does not correspond to the high vehicle speed. Therefore, the difference in rotational speed between the left and right drive wheels is set smaller than the difference in rotational speed appropriate for the high vehicle speed and the curvature of the curve. As a result, the lateral center of the detection range of the sensor unit 45 does not coincide with the lateral center of the AGV 10, and the AGV 10 is located outside the magnetic tape M.

[0041] 7 shows the state of traveling around a curve at low vehicle speed when the rotational speed difference between the left and right drive wheels is appropriate. In the wheel speed difference control, the rate of change in the rotational speed difference between the left and right drive wheels is reduced in response to low vehicle speeds. Therefore, the rotational speed difference between the left and right drive wheels is set to a value appropriate for the low vehicle speed and the curvature of the curve. As a result, the lateral center of the detection range of the sensor unit 45 coincides with the lateral center of the AGV 10, and the AGV 10 travels along the magnetic tape M.

[0042] Based on these considerations, the host controller 70 varies gains G1 and G2 (parameters) that amplify (set) the difference in rotational speed between the left and right drive wheels in the wheel speed difference control, as shown in Fig. 8. Specifically, the host controller 70 includes a subtractor 70a, a wheel speed difference control unit 70b, a gain adjuster 70c, and adders 70d and 70e.

[0043] The subtractor 70a calculates the difference between the travel position sensor signal indicating the center in the left-right direction of the detection range of the sensor unit 45 and the center position 8.5 in the left-right direction of the automatic guided vehicle 10 as the amount of deviation from the center. For example, the amount of deviation from the center is calculated to be a positive value when the center in the left-right direction of the detection range is to the left of the center position 8.5, and is calculated to be a negative value when the center in the left-right direction of the detection range is to the right of the center position 8.5.

[0044] The wheel speed difference control unit 70b calculates the rotational speed difference between the left and right drive wheels based on the amount of deviation from the center. The rotational speed difference between the left and right drive wheels is calculated as a positive value when the amount of deviation from the center is positive, and as a negative value when the amount of deviation from the center is negative. The wheel speed difference control unit 70b then increases the absolute value of the rotational speed difference between the left and right drive wheels as the absolute value of the amount of deviation from the center increases.

[0045] The gain adjuster 70c changes a first gain G1 that determines the rotational speed of the right drive wheel 12 and a second gain G2 that determines the rotational speed of the left drive wheel 12 in accordance with the vehicle speed of the automatic guided vehicle 10. The vehicle speed of the automatic guided vehicle 10 may be detected by a vehicle speed sensor that detects the vehicle speed, may be calculated based on the detection results of a rotational speed sensor that detects the rotational speed of the drive wheels 12, or may be calculated by calculating the rotational speed of the motor 31 based on the detection results of the angle sensor 42, and then calculating the rotational speed of the drive wheels 12 based on the rotational speed of the motor 31 and the reduction ratio of the reducer 59. The gain adjuster 70c can change the first gain G1 and the second gain G2 individually (independently). However, here, a case where the first gain G1 and the second gain G2 are changed to the same value will be described as an example. As shown in FIG. 9 , the gain adjuster 70c increases the gains G1 and G2 as the vehicle speed increases. Specifically, the gains G1 and G2 increase linearly (continuously) from 0 to a predetermined vehicle speed, and become constant when the vehicle speed exceeds the predetermined vehicle speed. The gain adjuster 70c multiplies the difference in rotational speed between the left and right drive wheels by the gains G1 and G2 to amplify the difference in rotational speed between the left and right drive wheels.

[0046] The adder 70d adds the rotational speed difference between the left and right drive wheels, amplified by the first gain G1 (parameter), to a rotational speed conversion value obtained by converting the base vehicle speed into the rotational speed of the drive wheels 12. The following description will be given taking as an example a case where the automated guided vehicle 10 is traveling at a constant speed (constant vehicle speed) and the base vehicle speed matches the current vehicle speed (constant vehicle speed) of the automated guided vehicle 10. The adder 70d adds the amplified rotational speed difference between the left and right drive wheels to the rotational speed conversion value without changing its sign, thereby calculating a rotational speed command value for the right drive wheel 12. For example, if the center of the detection range of the sensor unit 45 in the lateral direction is to the left of the center position 8.5, the sign of the amplified rotational speed difference between the left and right drive wheels will be positive, and the rotational speed command value for the right drive wheel 12 will be a rotational speed higher than the rotational speed conversion value.

[0047] The adder 70e reverses the sign of the rotational speed difference between the left and right drive wheels amplified by the second gain G2 (parameter) and adds it to a rotational speed conversion value obtained by converting the base vehicle speed into the rotational speed of the drive wheels 12. The adder 70e reverses the sign of the amplified rotational speed difference between the left and right drive wheels and adds it to the rotational speed conversion value, thereby calculating a rotational speed command value for the left drive wheel 12. For example, if the center of the detection range of the sensor unit 45 in the lateral direction is to the left of the center position 8.5, the sign of the amplified rotational speed difference between the left and right drive wheels will be negative, and the rotational speed command value for the left drive wheel 12 will be a rotational speed lower than the rotational speed conversion value.

[0048] The controller 40 of each electric drive unit 30 controls the inverter 34 of each system so that the rotational speed of the corresponding drive wheel 12 matches (approaches) the rotational speed command value received from the host controller 70. As a result, as wheel speed difference control, the rotational speed of the right drive wheel 12 and the rotational speed of the left drive wheel 12 are controlled based on the rotational speed difference between the left and right drive wheels amplified by the gains G1 and G2. The host controller 70 varies the gains G1 and G2 separately for the front and rear of the automatic guided vehicle 10 in accordance with the vehicle speed of the automatic guided vehicle 10.

[0049] The present embodiment described above in detail has the following advantages.

[0050] In the automatic guided vehicle 10, the parameter for setting the rotational speed difference between the left and right drive wheels in wheel speed difference control is variable according to the vehicle speed of the automatic guided vehicle 10. This makes it easier to appropriately set the rotational speed difference between the left and right drive wheels in wheel speed difference control, thereby improving the ability of the automatic guided vehicle 10 to follow the target trajectory when traveling around a curve.

[0051] The higher the vehicle speed, the more difficult it is for the automated guided vehicle 10 to turn. In this regard, the parameters are gains G1 and G2 that amplify the difference in rotational speed, and the higher the vehicle speed of the host controller 70, the larger the gains G1 and G2 are set. With this configuration, the higher the vehicle speed in the wheel speed difference control, the larger the difference in rotational speed between the left and right drive wheels can be, and the difference in rotational speed between the left and right drive wheels can be set appropriately according to the vehicle speed.

[0052] The gain adjuster 70c sets the first gain G1 and the second gain G2 to the same value, so that the left and right drive wheels 12 can have the same acceleration and deceleration rates. Therefore, the vehicle speed of the automatic guided vehicle 10 can be kept constant when traveling around a curve, and power consumption can be kept constant.

[0053] The gain adjuster 70c of the host controller 70 continuously (more specifically, linearly) increases the gains G1 and G2 as the vehicle speed increases. This configuration can prevent discontinuous changes in the rotational speed difference between the left and right drive wheels, further improving the ability of the automated guided vehicle 10 to track the target trajectory when traveling around a curve. Furthermore, because the gains G1 and G2 become constant values ​​when the vehicle speed exceeds a predetermined vehicle speed, it is possible to prevent the gains G1 and G2 from becoming excessively large. Note that even if the vehicle speed exceeds the predetermined vehicle speed, the gains G1 and G2 can be continuously increased as the vehicle speed increases.

[0054] The gains that amplify the rotational speed difference between the left and right drive wheels include a first gain G1 that determines the rotational speed of the right drive wheel 12 and a second gain G2 that determines the rotational speed of the left drive wheel 12. The gain adjuster 70c of the host controller 70 can individually vary the first gain G1 and the second gain G2. For example, when the automated guided vehicle 10 turns left at a low vehicle speed, the second gain G2 may be set to 0 to make the rotational speed command value for the left drive wheel 12 equal to the rotational speed conversion value. Alternatively, when the automated guided vehicle 10 turns left at a low vehicle speed, the first gain G1 may be set to 0 to make the rotational speed command value for the right drive wheel 12 equal to the rotational speed conversion value. These configurations allow the rotational speed difference between the left and right drive wheels to be flexibly set, making it easier to more appropriately set the rotational speed difference between the left and right drive wheels in wheel speed difference control.

[0055] The AGV 10 is provided with a left drive wheel 12 and a right drive wheel 12, respectively at the front and rear of the AGV 10, and executes wheel speed difference control for the front and rear, respectively. Therefore, the AGV 10 can travel around curves by executing wheel speed difference control for the front left and right drive wheels 12 and wheel speed difference control for the rear left and right drive wheels 12. Furthermore, the AGV 10 varies parameters (more specifically, gains G1 and G2) that set the rotational speed difference in the wheel speed difference control for the front and rear, respectively, depending on the vehicle speed of the AGV 10. Therefore, the AGV 10 can easily flexibly set the rotational speed difference between the left and right drive wheels in the wheel speed difference control for the front left and right drive wheels 12 and the wheel speed difference control for the rear left and right drive wheels 12. It is also possible to change the rear wheels of the automatic guided vehicle 10 to driven wheels, and have the automatic guided vehicle 10 only perform wheel speed difference control of the front left and right drive wheels 12.

[0056] The above embodiment can be modified as follows: The same parts as those in the above embodiment are denoted by the same reference numerals and the description thereof will be incorporated herein.

[0057] The gain adjuster 70c may increase the gains G1 and G2 in a curved line (continuously) when increasing the gains G1 and G2 as the vehicle speed increases. This configuration also makes it possible to prevent discontinuous changes in the rotational speed difference between the left and right drive wheels, thereby further improving the ability of the automated guided vehicle 10 to follow the target trajectory when traveling around a curve.

[0058] As shown in FIG. 10 , the gains G1 and G2 can be increased in stages as the vehicle speed increases. Specifically, the gains G1 and G2 increase in stages from 0 to a predetermined vehicle speed, and become constant when the vehicle speed exceeds the predetermined vehicle speed. This configuration can reduce the amount of data for the gains G1 and G2 that amplify the difference in rotational speed between the left and right drive wheels. The magnitude of each step by which the gains G1 and G2 are increased as the vehicle speed increases may be constant or may vary depending on the vehicle speed. Furthermore, the gains G1 and G2 can be increased in stages as the vehicle speed increases, even when the vehicle speed exceeds the predetermined vehicle speed.

[0059] As shown in FIG. 11 , the host controller 70 may include a wheel speed difference control unit 170b instead of the wheel speed difference control unit 70b and the gain adjuster 70c of FIG. 8 . The wheel speed difference control unit 170b has a gain adjuster 170c and receives the vehicle speed of the automated guided vehicle 10 as an input. Like the wheel speed difference control unit 70b, the wheel speed difference control unit 170b calculates the difference in rotational speed between the left and right drive wheels 12 based on the deviation from the center. The gain adjuster 170c changes the gain G, which determines the rotational speeds of the left and right drive wheels 12, in accordance with the vehicle speed of the automated guided vehicle 10. In other words, the function of the gain adjuster 170c is the same as the function of the gain adjuster 70c of FIG. 8 when the first gain G1 and the second gain G2 are set equal. This configuration can simplify the configuration of the gain adjuster 170c and, ultimately, the configuration of the host controller 70.

[0060] The heavier the object being transported by the automated guided vehicle 10, the more difficult it is for the automated guided vehicle 10 to turn. Therefore, as shown in FIG. 12 , the gain adjuster 70c, 170c of the host controller 70 may vary the gains G1, G2, and G (parameters) in accordance with the weight of the object being transported by the automated guided vehicle 10. Specifically, the relationship between the vehicle speed, the weight of the object, and the gains G1, G2, and G is defined in a map. The gain adjuster 70c, 170c then determines the gains G1, G2, and G by applying the vehicle speed and the weight of the object to this map. This configuration makes it easier to appropriately set the rotational speed difference between the left and right drive wheels in the wheel speed difference control in accordance with the weight of the object being transported by the automated guided vehicle 10.

[0061] Furthermore, the gain adjusters 70c, 170c increase the gains G1, G2, G as the weight of the object increases. With this configuration, the difference in rotational speed between the left and right drive wheels can be increased as the weight of the object being transported by the automatic guided vehicle 10 increases in the wheel speed difference control, and the difference in rotational speed between the left and right drive wheels can be set appropriately depending on the weight of the object being transported. Note that the gains G1, G2, G may be increased continuously or in steps depending on the weight of the object.

[0062] Methods for the AGV 10 to transport an object include loading an object onto the AGV 10 (hereinafter referred to as "loading an object") and towing a towing vehicle loaded with an object (hereinafter referred to as "tow an object"). In the case of loading an object, the weight of the object is added to the AGV 10. On the other hand, in the case of towing an object, the weight of the object is added to the towing vehicle. Therefore, the AGV 10 is less likely to turn when loading an object than when towing an object. Therefore, the gain adjusters 70c, 170c of the host controller 70 may vary the gains G1, G2, and G (parameters) depending on whether the object is loaded or towed. Specifically, the gains G1, G2, and G when loading an object may be larger than the gains G1, G2, and G when towing an object. This configuration makes it easier to appropriately set the rotational speed difference between the left and right drive wheels in wheel speed difference control depending on whether the object is loaded or towed.

[0063] The greater the curvature of the curve on which the automated guided vehicle 10 travels, the more likely the automated guided vehicle 10 deviates from the target trajectory. Therefore, as shown in FIG. 13 , the gain adjuster 70c, 170c of the host controller 70 may vary the gains G1, G2, and G (parameters) according to the curvature of the curve on which the automated guided vehicle 10 travels. Specifically, the relationship between the vehicle speed, the curvature of the curve, and the gains G1, G2, and G is defined in a map. The gain adjuster 70c, 170c then determines the gains G1, G2, and G by applying the vehicle speed and the curvature of the curve to this map. This configuration makes it easier to appropriately set the rotational speed difference between the left and right drive wheels in the wheel speed difference control according to the curvature of the curve on which the automated guided vehicle 10 travels.

[0064] Furthermore, the gain adjusters 70c, 170c increase the gains G1, G2, G as the curvature of the curve increases. With this configuration, the wheel speed difference control can increase the difference in rotational speed between the left and right drive wheels as the curvature of the curve on which the automated guided vehicle 10 travels increases, and the difference in rotational speed between the left and right drive wheels can be set appropriately according to the curvature of the curve. Note that the gains G1, G2, G may be increased continuously or in steps according to the curvature of the curve.

[0065] Furthermore, the gain adjuster 70c of the host controller 70 can individually vary the first gain G1 and the second gain G2 depending on the curvature of the curve. For example, when the automated guided vehicle 10 turns left around a curve with a small curvature, the second gain G2 may be set to 0, making the rotational speed command value for the left drive wheel 12 equal to the rotational speed conversion value. Also, when the automated guided vehicle 10 turns left around a curve with a small curvature, the first gain G1 may be set to 0, making the rotational speed command value for the right drive wheel 12 equal to the rotational speed conversion value. These configurations allow the rotational speed difference between the left and right drive wheels to be flexibly set, making it easier to more appropriately set the rotational speed difference between the left and right drive wheels in wheel speed difference control. The gain adjuster 70c of the host controller 70 can also individually vary the first gain G1 and the second gain G2 depending on the weight of the object to be transported.

[0066] The relationship between the vehicle speed, the weight of the object, the curvature of the curve, and the gains G1, G2, and G can also be defined in a map. The gain adjusters 70c and 170c can then determine the gains G1, G2, and G by applying the vehicle speed, the weight of the object, and the curvature of the curve to this map.

[0067] The route along which the AGV 10 travels and the target vehicle speed for each section included in the route may be preset in the AGV 10. The AGV 10 then travels through each section at the target vehicle speed for that section. In this case, when the target vehicle speed changes while the AGV 10 is traveling, the AGV 10 may change the gains G1, G2, and G (parameters) in accordance with the changed target vehicle speed. With this configuration, even when the target vehicle speed of the AGV 10 changes between sections of the route, it becomes easier to appropriately set the rotational speed difference between the left and right drive wheels in the wheel speed difference control. Note that the current vehicle speed of the AGV 10 may be detected, and when the vehicle speed changes while the AGV 10 is traveling, the gains G1, G2, and G may be changed in accordance with the detected current vehicle speed.

[0068] The AGV 10 may receive, from a management device or the like, setting information about the route along which the AGV 10 travels, the target vehicle speed of the AGV 10 for each section included in the route, and the gains G1, G2, and G (parameters) corresponding to the target vehicle speed for each section. The setting information about the gains G1, G2, and G is, for example, a number (e.g., 1 to 10) that selects the value of the gains G1, G2, and G to be used in wheel speed difference control. The AGV 10 travels through each section at the received target vehicle speed for that section. The AGV 10 then receives setting information about the gains G1, G2, and G corresponding to the target vehicle speed from the management device or the like, and uses the value of the gains G1, G2, and G selected by the setting information for wheel speed difference control. With this configuration, even when setting information about the route, each section, and the gains G1, G2, and G is received, it becomes easier to appropriately set the rotational speed difference between the left and right drive wheels in wheel speed difference control. The automated guided vehicle 10 can also receive, from a management device or the like, values ​​of the gains G1, G2, and G corresponding to the vehicle speed, and use the received values ​​of the gains G1, G2, and G for wheel speed difference control.Also, it is possible to receive setting information for the gains G1, G2, and G (parameters) for a certain section all at once from a management device or the like, and then not receive any more setting information until the travel of that certain section is completed, and to execute wheel speed difference control based on the setting information that has already been received.

[0069] The automated guided vehicle 10 may also be provided with a map that sets the rotational speed difference between the left and right drive wheels in accordance with the deviation from the center and the vehicle speed of the automated guided vehicle 10 as a parameter for setting the rotational speed difference between the left and right drive wheels in wheel speed difference control. The wheel speed difference control unit 70b can then determine the rotational speed difference between the left and right drive wheels by applying the deviation from the center and the vehicle speed to this map. This configuration also makes it easier to appropriately set the rotational speed difference between the left and right drive wheels in wheel speed difference control, thereby improving the ability of the automated guided vehicle 10 to follow the target trajectory when traveling around a curve. The map may also apply the curvature of the curve and the weight of the object being transported.

[0070] The electric drive device 30 may be configured to include only one system of the inverter 34, the stator winding 31a of the motor 31, the current sensor 41, and the angle sensor 42.

[0071] In a configuration in which the drive shaft 13 (drive wheels 12) is braked by causing each motor 31 to generate a braking torque, the brake 60 and the brake relay 75 may be omitted.

[0072] As shown in FIG. 14 , an electric wheelchair 110 can be used as a small electric vehicle equipped with multiple electric drive units 30. The drive unit 20 in the electric wheelchair 110 includes an electric drive unit 30 that drives the left rear wheel of the electric wheelchair 110 and an electric drive unit 30 that drives the right rear wheel. The electric wheelchair 110 varies the parameter for setting the rotational speed difference between the left and right drive wheels in wheel speed difference control for the rear wheels according to the vehicle speed of the electric wheelchair 110. This makes it easier to appropriately set the rotational speed difference between the left and right drive wheels in wheel speed difference control, thereby improving the ability of the electric wheelchair 110 to track a target trajectory when traveling around a curve. Note that an AMR (Autonomous Mobile Robot) used in warehouses, etc., an unmanned transport robot, an agricultural robot, a construction site robot, a factory robot, a food delivery robot, a cleaning robot, an inspection robot, etc. can also be used as a small electric vehicle equipped with left and right drive wheels 12.

[0073] The above-described embodiment and modifications may be combined within the scope of possible combinations.

[0074] Characteristic configurations extracted from the above-described embodiments and modified examples are described below. [Configuration 1] A small electric vehicle (10, 110) including a left drive wheel (12) and a right drive wheel (12), which executes wheel speed difference control to generate a rotational speed difference between the rotational speed of the left drive wheel and the rotational speed of the right drive wheel when traveling around a curve, wherein a parameter for setting the rotational speed difference in the wheel speed difference control is variable according to the vehicle speed of the small electric vehicle. [Configuration 2] The small electric vehicle according to Configuration 1, wherein the parameter is a gain for amplifying the rotational speed difference, and wherein the gain is increased as the vehicle speed increases. [Configuration 3] The small electric vehicle according to Configuration 2, wherein the gain is increased continuously as the vehicle speed increases. [Configuration 4] The small electric vehicle according to Configuration 2, wherein the gain is increased stepwise as the vehicle speed increases. [Configuration 5] The small electric vehicle according to any one of Configurations 1 to 4, wherein the parameter is variable according to the weight of an object being transported by the small electric vehicle. [Configuration 6] The small electric vehicle according to configuration 5, wherein the parameter is a gain that amplifies the rotational speed difference, and the gain is increased as the weight of the object increases. [Configuration 7] The small electric vehicle according to configuration 5 or 6, wherein the parameter is variable between when the object is loaded on the small electric vehicle and when the small electric vehicle is towing a towing vehicle loaded with the object. [Configuration 8] The small electric vehicle according to any one of configurations 1 to 7, wherein the parameter is variable according to the curvature of a curve on which the small electric vehicle is traveling. [Configuration 9] The small electric vehicle according to configuration 8, wherein the parameter is a gain that amplifies the rotational speed difference, and the gain is increased as the curvature of the curve increases. [Configuration 10] The small electric vehicle according to any one of configurations 1 to 9, wherein the parameter is a gain that amplifies the rotational speed difference, and the gain includes a first gain that determines the rotational speed of the right drive wheel and a second gain that determines the rotational speed of the left drive wheel, and the first gain and the second gain are individually variable.[Configuration 11] The small electric vehicle according to any one of configurations 1 to 10, wherein the left drive wheel and the right drive wheel are provided at the front and rear of the small electric vehicle, the wheel speed difference control is executed at the front and rear, and a parameter for setting the rotational speed difference in the wheel speed difference control is made variable depending on the vehicle speed of the small electric vehicle, separately for the front and rear. [Configuration 12] The small electric vehicle according to any one of configurations 1 to 11, wherein a target vehicle speed for the small electric vehicle for a route along which the small electric vehicle travels and for each section included in the route is set in advance, the small electric vehicle travels through each section at the target vehicle speed for each section, and when the target vehicle speed changes while the small electric vehicle is traveling, the parameter is changed depending on the target vehicle speed after the change. [Configuration 13] A small electric vehicle according to any one of configurations 1 to 11, which receives setting information of a route to be traveled by the small electric vehicle, a target vehicle speed for the small electric vehicle in each section included in the route, and the parameters corresponding to the target vehicle speed in each section, travels through each section at the received target vehicle speed for each section, and when the received setting information changes while the small electric vehicle is traveling, changes the parameters in accordance with the changed setting information.

[0075] Although the present disclosure has been described with reference to the embodiments, it is understood that the present disclosure is not limited to the embodiments or structures. The present disclosure also encompasses various modifications and equivalent modifications. In addition, various combinations and forms, including only one element, more than one element, or less than one element, are also within the scope and spirit of the present disclosure.

Claims

1. A small electric vehicle (10, 110) equipped with a left drive wheel (12) and a right drive wheel (12), which executes wheel speed difference control to generate a rotational speed difference between the rotational speed of the left drive wheel and the rotational speed of the right drive wheel when traveling around a curve, wherein a parameter for setting the rotational speed difference in the wheel speed difference control is variable according to the vehicle speed of the small electric vehicle.

2. The small electric vehicle according to claim 1, wherein the parameter is a gain that amplifies the rotational speed difference, and the higher the vehicle speed, the larger the gain is set.

3. The small electric vehicle according to claim 2, wherein the gain is continuously increased as the vehicle speed increases.

4. The small electric vehicle according to claim 2, wherein the gain is increased in stages as the vehicle speed increases.

5. A small electric vehicle according to any one of claims 1 to 4, wherein the parameter is variable depending on the weight of an object being transported by the small electric vehicle.

6. The small electric vehicle according to claim 5, wherein the parameter is a gain that amplifies the rotational speed difference, and the greater the weight of the object, the greater the gain.

7. A small electric vehicle according to claim 5, wherein the parameter is variable depending on whether the object is loaded onto the small electric vehicle or whether the small electric vehicle is towing a towing vehicle carrying the object.

8. A small electric vehicle according to any one of claims 1 to 4, wherein the parameter is variable according to the curvature of a curve on which the small electric vehicle is traveling.

9. The small electric vehicle according to claim 8, wherein the parameter is a gain that amplifies the rotational speed difference, and the greater the curvature of the curve, the greater the gain is made to be.

10. A small electric vehicle according to any one of claims 1 to 4, wherein the parameter is a gain that amplifies the rotational speed difference, the gain includes a first gain that determines the rotational speed of the right drive wheel and a second gain that determines the rotational speed of the left drive wheel, and the first gain and the second gain are individually variable.

11. A small electric vehicle as claimed in any one of claims 1 to 4, wherein the left drive wheel and the right drive wheel are provided at the front and rear of the small electric vehicle, respectively, the wheel speed difference control is executed at the front and rear, respectively, and a parameter for setting the rotational speed difference in the wheel speed difference control is made variable separately for the front and rear in accordance with the vehicle speed of the small electric vehicle.

12. A small electric vehicle as claimed in any one of claims 1 to 4, wherein a route along which the small electric vehicle travels and a target vehicle speed for the small electric vehicle in each section included in the route are set in advance, the small electric vehicle travels through each section at the target vehicle speed for that section, and when the target vehicle speed changes while the small electric vehicle is traveling, the parameters are changed in accordance with the changed target vehicle speed.

13. A small electric vehicle as claimed in any one of claims 1 to 4, which receives setting information on a route travelled by the small electric vehicle, a target vehicle speed for the small electric vehicle in each section included in the route, and the parameters corresponding to the target vehicle speed in each section, travels through each section at the received target vehicle speed for each section, and when the received setting information changes while the small electric vehicle is travelling, changes the parameters in accordance with the changed setting information.

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