Small-sized electric vehicle

Abstract

A small-sized electric vehicle (10) comprises: an electricity storage unit (71); and a plurality of drive devices (30) that respectively drive a plurality of drive wheels (12) of the small-sized electric vehicle. Each drive device comprises: a motor that generates power for rotating the drive wheel; an inverter that converts power supplied from the electricity storage unit and supplies the converted power to the motor; and a controller (40S, 40M) that controls the inverter. A main controller (40M) that is a controller for at least one drive device has at least a part of function of controlling the plurality of drive devices. The controllers for the plurality of drive devices control the inverters corresponding thereto on the basis of a command from the main controller.

Description

small electric vehicle CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on Japanese Application No. 2024-020238 filed on February 14, 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 drive unit that includes a first electric drive unit that drives the left rear wheel of an electric wheelchair and a second electric drive unit that drives the right rear wheel (see Patent Document 1). The electric drive unit described in Patent Document 1 includes a motor and a reduction gear, and the rotor, stator, and power converter are housed in a motor housing that is integrated with the reduction gear. Therefore, Patent Document 1 states that the wiring that electrically connects the stator winding and the power converter can also be housed in the motor housing, simplifying the configuration of the electric drive unit.

[0004] JP 2023-102121 A

[0005] Incidentally, a small electric vehicle equipped with multiple electric drive units is often provided with a host controller that controls the multiple electric drive units, a relay that collectively supplies and cuts off power to the multiple electric drive units, a rotational speed sensor that detects the rotational speed of each motor, etc. Therefore, in terms of simplifying the overall configuration of a small electric vehicle equipped with multiple electric drive units, the drive unit described in Patent Document 1 still has room for improvement.

[0006] The present disclosure has been made to solve the above-mentioned problems, and its main object is to simplify the overall configuration of a small electric vehicle equipped with multiple electric drive units.

[0007] A first means for solving the above problem is a small electric vehicle comprising a power storage unit and a plurality of drive devices that respectively drive a plurality of drive wheels of the small electric vehicle, each drive device comprising: a motor that generates power to rotate the drive wheels; an inverter that converts power supplied from the power storage unit and supplies it to the motor; and a controller that controls the inverter, wherein a main controller that is the controller of at least one of the drive devices has at least some of the functions of controlling the plurality of drive devices, and the controllers of the plurality of drive devices control the inverter corresponding to themselves based on instructions from the main controller.

[0008] According to the above configuration, the small electric vehicle includes a power storage unit and a plurality of drive devices that respectively drive a plurality of drive wheels of the small electric vehicle. Each drive device includes a motor that generates power to rotate the drive wheel, an inverter that converts power supplied from the power storage unit and supplies the converted power to the motor, and a controller that controls the inverter. Therefore, by each controller of each drive device controlling the corresponding inverter, each drive wheel is driven by the motor of each drive device, and the running state of the small electric vehicle can be controlled.

[0009] Here, if a host controller were to have all of the functions to control the multiple drive devices, the host controller would require a large number of functions and components, which could result in an excessive overall configuration of the small electric vehicle. In this regard, a main controller, which is the controller of at least one of the drive devices, has at least some of the functions to control the multiple drive devices. The controllers of the multiple drive devices then control their corresponding inverters based on commands from the main controller. This reduces the number of functions and components required for the host controller, or even eliminates the need for a host controller altogether. This simplifies the overall configuration of a small electric vehicle equipped with multiple electric drive devices.

[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 equipped with a sub-controller and its peripheral configuration, Fig. 3 is a block diagram showing an electric drive unit equipped with a main controller and its peripheral configuration, Fig. 4 is a block diagram showing an embodiment in which a speed command of the main controller is synchronously corrected, Fig. 5 is a block diagram showing an embodiment in which a speed command of the sub-controller is not corrected, Fig. 6 is a schematic diagram of a modified example of the automated guided vehicle, Fig. 7 is a schematic diagram of another modified example of the automated guided vehicle, Fig. 8 is a schematic diagram of another modified example of the automated guided vehicle, and Fig. 9 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, brakes 60, a battery 71, sensors 77, etc. Each set of electric drive devices 30 and brakes 60 corresponds to each set of drive wheels 12 and drive shafts 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 and, therefore, each drive wheel 12. 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 the battery 71 by a power supply line PL1. Each MCU is driven by the 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 rotational speed of the motor 31 (see FIG. 2) of the MCU and transmits the reduced rotational speed to the drive shaft 13.

[0017] Each brake 60 (braking device) brakes each drive shaft 13. Each brake 60 is fixed to the vehicle body 11. Each brake 60 is connected to a battery 71 by a power supply line PL2. Each brake 60 is driven by power supplied from the battery 71. Each brake 60 is, for example, a non-excitation actuated electromagnetic brake that brakes each drive shaft 13 when no power is supplied. The supply and cut-off of power to each brake 60 is controlled, for example, by each MCU. Note that the braking force applied to each drive shaft 13 by each brake 60 can also be controlled by each MCU.

[0018] The four MCUs are connected to each other via signal lines SL. The signal lines SL comply with, for example, the CAN (Controller Area Network) communication standard (a serial communication standard among digital communication standards). The four MCUs transmit and receive information to each other through the signal lines SL. One of the four MCUs (e.g., the MCU corresponding to the right rear wheel) includes a controller called a main controller 40M that controls the four MCUs (electric drive units 30). The main controller 40M is the controller that minimizes the total length of the signal lines SL connecting the four MCUs (four electric drive units 30). For example, if the controller included in the MCU corresponding to the left front wheel is selected as the main controller 40M, the total length of the signal lines SL will be longer than if the controller included in the MCU corresponding to the right rear wheel is selected as the main controller 40M. The controllers included in the MCUs other than the MCU corresponding to the right rear wheel are sub-controllers 40S that are controlled based on commands from the main controller 40M. The main controller 40M controls the three MCUs corresponding to the three sub-controllers 40S and the MCU corresponding to the main controller 40M in an integrated manner by inputting commands to the sub-controllers 40S via the signal line SL.

[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 main controller 40M.

[0020] 2 is a block diagram showing an electric drive unit 30 equipped with a sub-controller 40S and its peripheral configuration. Since the three electric drive units 30 equipped with the sub-controller 40S have the same configuration, one electric drive unit 30 will be described here 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. Each electric drive unit 30 includes one motor 31, a reducer 59, and a sub-controller 40S.

[0022] The inverter 34 of each system is connected to the battery 71 via a power supply line relay 32 and a 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 sub-controller 40S.

[0027] The sub-controller 40S includes a microcomputer and an ASIC (Application Specific Integrated Circuit). The microcomputer is configured with an ECU (Electronic Control Unit) including, for example, a CPU, memory (ROM, RAM, etc.), an input / output interface, etc. The ASIC is an IC optimized for controlling the motor 31, etc. The sub-controller 40S switches the power line relays 32 and battery reverse connection prevention relays 33 of each system between an on state and an off state. Specifically, the sub-controller 40S maintains the power line relays 32 and battery reverse connection prevention relays 33 in an on state while the MCU (electric drive device 30) is operating.

[0028] The sub-controller 40S executes a program stored in its memory to implement the functions of the motor control unit 40a. The motor control unit 40a controls the inverters 34 of each system based on commands from the main controller 40M and the detection results of the current sensors 41 and angle sensors 42 of each system. Specifically, the motor control unit 40a calculates the rotational speed of the motor 31, and therefore the rotational speed of the drive wheels 12, based on the detection results of the angle sensors 42. The motor control unit 40a then controls the inverters 34 of each system so that the rotational speed of the drive wheels 12 matches (approaches) the rotational speed command value.

[0029] Figure 3 is a block diagram showing an electric drive unit 30 equipped with a main controller 40M and its peripheral configuration. The configurations in Figures 2 and 3 are the same except that the sub-controller 40S in Figure 2 is replaced with the main controller 40M, and the main controller 40M in Figure 2 is replaced with the sub-controller 40S. Here, the differences between Figures 2 and 3 will be mainly described.

[0030] 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 main controller 40M.

[0031] The main controller 40M includes a microcomputer and an ASIC. The microcomputer is configured, for example, by an ECU including a CPU, memory (ROM, RAM, etc.), an input / output interface, etc. The main controller 40M switches the power line relays 32 and battery reverse connection prevention relays 33 of each system between the on state and the off state. Specifically, the main controller 40M maintains the power line relays 32 and battery reverse connection prevention relays 33 in the on state while the MCU (electric drive unit 30) is operating.

[0032] The main controller 40M executes the programs stored in the memory to realize the functions of the motor control unit 40a and the general control unit 40b.

[0033] The motor control unit 40a controls the inverters 34 of each system based on commands to control the four electric drive devices 30 (commands to the three sub-controllers 40S and commands to the main controller 40M itself) and the detection results of the current sensors 41 and angle sensors 42 of each system. More specifically, the motor control unit 40a calculates the rotational speed of the motor 31, and therefore the rotational speed of the drive wheels 12, based on the detection results of the angle sensor 42. The motor control unit 40a then controls the inverters 34 of each system so that the rotational speed of the drive wheels 12 matches (approaches) the rotational speed command value.

[0034] When the overall control unit 40b (main controller 40M) determines that the unmanned guided vehicle 10 has been instructed to travel straight ahead, it sends a rotational speed command value to each sub-controller 40S and each motor control unit 40a of the main controller 40M so that the left and right drive wheels 12 are rotated in the same direction and at the same rotational speed.

[0035] When the integrated control unit 40b determines that braking of the automated guided vehicle 10 has been instructed, it transmits torque command values ​​to the motor control units 40a of the sub-controllers 40S and the main controller 40M so as to generate braking torque in each motor 31. This applies a braking force to the automated guided vehicle 10, and the automated guided vehicle 10 then stops. The integrated control unit 40b can also control the braking force acting on each drive shaft 13 by controlling each brake 60.

[0036] When the overall control unit 40b determines that the unmanned guided vehicle 10 has been instructed to turn, it rotates the left and right drive wheels 12 in the same direction and sends a rotational speed command value to each motor control unit 40a of each sub-controller 40S and the main controller 40M so that the rotational speed of the drive wheel 12 in the instructed turning direction is lower than the rotational speed of the remaining drive wheels 12.

[0037] That is, the overall control unit 40b of the main controller 40M has all the functions for controlling the four electric drive units 30. For this reason, in this embodiment, the automated guided vehicle 10 does not have a host controller that controls the four electric drive units 30 in an integrated manner.

[0038] The main controller 40M can also transmit rotational speed command values ​​to the sub-controllers 40S and the motor control units 40a of the main controller 40M so as to rotate the left and right drive wheels 12 in opposite directions. In this case, the automated guided vehicle 10 makes a pivot turn.

[0039] 4 is a block diagram showing a manner in which a phase delay is corrected for a speed command of the main controller 40M. The speed command is, for example, a rotational speed command value for the drive wheels 12. Here, a difference due to a communication delay occurs between the timing at which the motor control unit 40a of the main controller 40M receives the rotational speed command value from the overall control unit 40b of the main controller 40M and the timing at which the motor control unit 40a of the sub-controller 40S receives the rotational speed command value. Specifically, a communication delay occurs between the time when the overall control unit 40b of the main controller 40M transmits the rotational speed command value and the time when the motor control unit 40a of the sub-controller 40S receives the rotational speed command value.

[0040] To correct this communication delay and synchronize the rotation of the motor 31 corresponding to the main controller 40M and the motor 31 corresponding to the sub-controller 40S, the motor control unit 40a of the main controller 40M is equipped with a delay circuit 40d. The delay circuit 40d (synchronization corrector) is a circuit that delays the timing at which the speed control unit 40e inputs a rotational speed command value relative to the timing at which the motor control unit 40a inputs a rotational speed command value (command). The speed control unit 40e controls the inverters 34 of each system so that the rotational speed of the drive wheels 12 matches (approaches) the rotational speed command value. Specifically, the speed control unit 40e controls the rotational speed of the motor 31 corresponding to the main controller 40M, taking into account the reduction ratio of the reducer 59. On the other hand, as shown in FIG. 5, the motor control unit 40a of the sub-controller 40S does not include the delay circuit 40d, and the rotational speed command value input by the motor control unit 40a is immediately input to the speed control unit 40e. That is, the delay circuit 40d corrects the rotational speed command value input by the motor control unit 40a of the main controller 40M so as to correct the difference between the timing at which the main controller 40M transmits the rotational speed command value and the timing at which the sub-controller 40S receives the rotational speed command value.

[0041] The present embodiment described above in detail has the following advantages.

[0042] If a host controller were to have all the functions to control the four electric drive units 30, the host controller would require many more functions and components, potentially resulting in an excessive overall configuration of the automated guided vehicle 10. In this regard, the main controller 40M, which controls one electric drive unit 30, has all the functions to control the four electric drive units 30. The controllers 40S, 40M of the four electric drive units 30 control their corresponding inverters 34 based on commands from the main controller 40M. This eliminates the need for a host controller, and the host controller itself can be eliminated. This reduces the number of wirings and the number of assembly and inspection steps. Therefore, the overall configuration of the automated guided vehicle 10 equipped with four electric drive units 30 can be simplified.

[0043] The main controller 40M and the sub-controller 40S communicate via digital communication (specifically, serial communication). This reduces the number of signal lines SL connecting the main controller 40M and the sub-controller 40S. Furthermore, because CAN, a communication protocol for automobiles, is used for communication between the main controller 40M and the sub-controller 40S, the electric drive unit 30 for automobiles and its communication protocol can be used as is.

[0044] Each electric drive unit 30 is equipped with a power supply line relay 32 and a battery reverse connection prevention relay 33 that 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 power is cut off. With this configuration, if, for example, one electric drive unit 30 fails, the motor 31 of the failed electric drive unit 30 can be allowed to rotate freely by switching the power supply line relay 32 or battery reverse connection prevention relay 33 of the failed electric drive unit 30 to the OFF state. Therefore, even if, for example, one electric drive unit 30 fails, it becomes easier to continue driving the automatic guided vehicle 10 using the normal electric drive unit 30.

[0045] Each electric drive unit 30 is equipped with an angle sensor 42 that detects the rotation angle of the motor 31, and the controllers 40S, 40M calculate the rotation speed of the motor 31 based on the rotation angle detected by the angle sensor 42. With this configuration, the rotation speed of the motor 31 can be calculated using the angle sensor 42 that is generally equipped in each electric drive unit 30. Therefore, the automated guided vehicle 10 does not need to be equipped with an additional rotation speed sensor that detects the rotation speed of each motor 31, and the overall configuration can be simplified.

[0046] When the automated guided vehicle 10 has four electric drive units 30 and only one main controller 40M, the total length of the signal lines SL connecting the four electric drive units 30 to each other may be long or short depending on which controller is selected as the main controller 40M. In this regard, the main controller 40M is the controller that has the shortest total length of the signal lines SL connecting the four electric drive units 30 to each other. Therefore, the cost of the signal lines SL can be reduced and the effects of noise on the signal lines SL can be suppressed. Note that a controller other than the controller that has the shortest total length of the signal lines SL connecting the four electric drive units 30 to each other can also be selected as the main controller 40M.

[0047] The automated guided vehicle 10 includes a delay circuit 40d that corrects the rotational speed command value to compensate for the difference between the timing when the main controller 40M transmits the rotational speed command value (command) and the timing when the sub-controller 40S receives the rotational speed command value. Specifically, the delay circuit 40d of the main controller 40M delays the timing when the speed control unit 40e inputs the rotational speed command value relative to the timing when the motor control unit 40a inputs the rotational speed command value. This configuration allows the rotational speed command value (the rotational speed command value used by the speed control unit 40e relative to the rotational speed command value input by the motor control unit 40a) to be corrected taking into account communication delays between the main controller 40M and the sub-controller 40S, making it easier to synchronize the rotations of the motors 31 of the four electric drive units 30. This improves the running stability of the automated guided vehicle 10.

[0048] The automated guided vehicle 10 has front and rear wheels as drive wheels 12, and the main controller 40M is a controller for the electric drive unit 30 that drives the rear wheels. With this configuration, if the front of the automated guided vehicle 10 collides with an obstacle or the like, damage to the main controller 40M can be suppressed. Note that the controller for the electric drive unit 30 that drives the front wheels can also be the main controller 40M.

[0049] 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.

[0050] The automated guided vehicle 10 can dynamically switch the controller that serves as the main controller 40M depending on the specifications of the automated guided vehicle 10 and the external environment. For example, a program for the integrated control unit 40b that is compatible with the standard specifications (first specifications) of the automated guided vehicle 10 is stored in the memory of the main controller 40M of the right rear electric drive unit 30. A program for the integrated control unit 40b that is compatible with the special specifications (second specifications) of the automated guided vehicle 10 is stored in the memory of the main controller 40M of the left rear electric drive unit 30. Then, when the automated guided vehicle 10 is of the standard specifications, the controller of the right rear electric drive unit 30 is the main controller 40M, and when the automated guided vehicle 10 is of the special specifications, the controller of the left rear electric drive unit 30 is the main controller 40M. With this configuration, even if the memory capacity of the controllers is limited, functions that are compatible with the specifications of the automated guided vehicle 10 can be shared by the controllers of the multiple electric drive units 30. In addition, the program of the overall control unit 40b that is adapted to the external environment of the automated guided vehicle 10 can be stored in the memory of the controllers of multiple electric drive units 30, and the main controller 40M can be switched depending on the external environment of the automated guided vehicle 10.

[0051] If there is no substantial problem with the rotational synchronization of the motors 31 of the four electric drive units 30, the synchronization corrector that corrects the difference between the timing at which the main controller 40M sends the rotational speed command value and the timing at which the sub-controller 40S receives the rotational speed command value can be omitted.

[0052] Each electric drive device 30 may include a rotation speed sensor that detects the rotation speed of each motor 31 .

[0053] The main controller 40M and the sub-controller 40S may communicate with each other using digital communication of a serial communication method other than CAN (for example, LIN (Local Interconnect Network)). The main controller 40M and the sub-controller 40S may also communicate with each other using digital communication of a parallel communication method.

[0054] As shown in FIG. 6 , the automated guided vehicle 10 includes at least two main controllers 40M (two in FIG. 6 ), and the at least two main controllers 40M can determine commands for the controllers 40S, 40M of the four electric drive units 30 based on the results of mutually monitoring each other's rotational speed command values ​​(commands). For example, if the automated guided vehicle 10 includes two main controllers 40M on the rear wheel side, each main controller 40M can calculate commands for the controllers 40S, 40M and issue commands only if the commands are approximately consistent. In this case, the two front electric drive units 30 and the two rear electric drive units 30 can be controlled separately (independently). This configuration improves the safety of commands issued to the controllers 40S, 40M of the four electric drive units 30. If the commands from the two main controllers 40M do not approximately match, the automated guided vehicle 10 can be stopped, for example. Furthermore, for example, if the automated guided vehicle 10 is equipped with three main controllers 40M, a command can be determined by majority vote of the three commands. In this case, too, the two front electric drive units 30 and the two rear electric drive units 30 can be controlled separately (independently). With this configuration, even if, for example, one main controller 40M breaks down, the automated guided vehicle 10 can continue to be driven by the two normal main controllers 40M.

[0055] 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.

[0056] As shown in FIG. 7 , the automated guided vehicle 10 may include an MCU relay 73 and a brake relay 75. The 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 is cut off to the four MCUs. When the MCU relay 73 is in the ON state, each MCU is driven by power supplied from the battery 71. A brake relay 75 is provided on the power supply line PL2 between the battery 71 and the four brakes 60. The brake relay 75 (braking unit relay) is switched between an ON state, in which power is supplied from the battery 71 to the four brakes 60, and an OFF state, in which power is cut off to the four brakes 60. When the brake relay 75 is in the ON state, each brake 60 is driven by power supplied from the battery 71. The main controller 40M then switches the MCU relay 73 and the brake relay 75 between the on state and the off state. The main controller 40M maintains the MCU relay 73 and the brake relay 75 in the on state while the drive unit 20 is operating. With the above configuration, if any of the electric drive devices 30 fails, the main controller 40M can switch the MCU relay 73 and the brake relay 75 to the off state and stop the drive unit 20 (automated guided vehicle 10).

[0057] As shown in FIG. 8 , the automated guided vehicle 10 can also include a host controller 70. In this case, for example, the host controller 70 receives driving state commands via communication from a management device that manages multiple automated guided vehicles 10. The main controller 40M controls four (multiple) electric drive units 30 based on the driving state commands input from the host controller 70. In other words, the main controller 40M has at least some of the functions for controlling the four electric drive units 30. With this configuration, the number of functions and components required for the host controller 70 can be reduced compared to when the host controller 70 has all the functions for controlling the four electric drive units 30. Therefore, the overall configuration of the automated guided vehicle 10 equipped with four electric drive units 30 can be simplified.

[0058] When the automatic guided vehicle 10 includes the MCU relay 73, the power supply line relay 32 may be omitted from each electric drive unit 30. With this configuration, the configuration of each electric drive unit 30 can be simplified.

[0059] 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.

[0060] As shown in FIG. 9 , an electric wheelchair 110 can be employed 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 main controller 40M, which controls the electric drive unit 30 that drives the left rear wheel, has all or part (at least part) of the functions to drive the two electric drive units 30. The controllers 40S, 40M of the two electric drive units 30 control their corresponding inverters 34 (not shown) based on commands from the main controller 40M. This configuration also eliminates the need for a host controller, and the host controller itself can be dispensed with. Therefore, the overall configuration of the electric wheelchair 110 equipped with two electric drive units 30 can be simplified. In addition, small electric vehicles equipped with multiple electric drive units 30 may also be used, for example, as 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, or an inspection robot.

[0061] The above-described embodiment and modifications may be combined within the scope of possible combinations.

[0062] The following describes characteristic configurations extracted from the above-mentioned embodiments and modified examples. [Configuration 1] A small electric vehicle (10, 110) including a power storage unit (71) and multiple drive devices (30) that respectively drive multiple drive wheels (12) of the small electric vehicle (10, 110), wherein each drive device includes a motor (31) that generates power to rotate the drive wheels, an inverter (34) that converts power supplied from the power storage unit and supplies the converted power to the motor, and a controller (40S, 40M) that controls the inverter, wherein a main controller (40M) that is the controller of at least one of the drive devices has at least a portion of the function of controlling the multiple drive devices, and the controllers of the multiple drive devices control the inverters corresponding to the main controller based on commands from the main controller. [Configuration 2] The small electric vehicle according to Configuration 1, wherein the main controller (40M) and the controllers (40S) other than the main controller communicate via digital communication. [Configuration 3] The small electric vehicle according to Configuration 1 or 2, wherein each drive device includes a predetermined relay (32, 33) switchable between an ON state for supplying power from the power storage unit to the inverter and an OFF state for cutting off the power. [Configuration 4] The small electric vehicle according to any one of Configurations 1 to 3, wherein each drive device includes an angle sensor (42) for detecting a rotation angle of the motor, and wherein the controller calculates the rotation speed of the motor based on the rotation angle detected by the angle sensor. [Configuration 5] The small electric vehicle according to any one of Configurations 1 to 4, wherein the small electric vehicle includes at least two main controllers, and the at least two main controllers determine the commands to the controllers of the plurality of drive devices based on a result of mutually monitoring each other's commands. [Configuration 6] The small electric vehicle according to any one of Configurations 1 to 4, wherein the small electric vehicle includes only one main controller, and the main controller has all the functions of controlling the plurality of drive devices. [Configuration 7] The small electric vehicle according to Configuration 6, wherein the small electric vehicle includes at least four drive devices, and the main controller is the controller that has the shortest total length of signal lines connecting the plurality of drive devices to each other.[Configuration 8] The small electric vehicle according to any one of Configurations 1 to 7, comprising a synchronization corrector (40d) that corrects the command so as to correct a difference between the timing when the main controller transmits the command and the timing when the controller other than the main controller receives the command. [Configuration 9] The small electric vehicle according to any one of Configurations 1 to 8, wherein the small electric vehicle has front wheels and rear wheels as the drive wheels, and the main controller is the controller of the drive device that drives the rear wheels.

[0063] 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 comprising a power storage unit (71) and a plurality of drive devices (30) that respectively drive a plurality of drive wheels (12) of the small electric vehicle (10, 110), wherein each drive device comprises: a motor (31) that generates power to rotate the drive wheel; an inverter (34) that converts power supplied from the power storage unit and supplies it to the motor; and a controller (40S, 40M) that controls the inverter, wherein a main controller (40M) that is the controller of at least one of the drive devices has at least part of the function of controlling the plurality of drive devices, and the controllers of the plurality of drive devices control the inverter corresponding to themselves based on instructions from the main controller.

2. The small electric vehicle according to claim 1, wherein the main controller (40M) and the controller (40S) other than the main controller communicate with each other by digital communication.

3. A small electric vehicle as described in claim 1 or 2, wherein each drive device is provided with a predetermined relay (32, 33) that can be switched between an on state in which power is supplied from the storage unit to the inverter and an off state in which the power is cut off.

4. A small electric vehicle as described in claim 1 or 2, wherein each drive device is provided with an angle sensor (42) that detects the rotation angle of the motor, and the controller calculates the rotation speed of the motor based on the rotation angle detected by the angle sensor.

5. A small electric vehicle as described in claim 1 or 2, comprising at least two main controllers, wherein the at least two main controllers determine the commands to the controllers of the plurality of drive devices based on the results of mutual monitoring of each other's commands.

6. The small electric vehicle according to claim 1 or 2, comprising only one main controller, the main controller having all of the functions of controlling the plurality of drive devices.

7. A small electric vehicle according to claim 6, comprising at least four drive devices, wherein the main controller is the controller that has the shortest total length of signal lines connecting the plurality of drive devices to each other.

8. A small electric vehicle as described in claim 1 or 2, further comprising a synchronization corrector (40d) that corrects the command to correct the difference between the timing when the main controller sends the command and the timing when the controller other than the main controller receives the command.

9. The small electric vehicle according to claim 1 or 2, wherein the small electric vehicle has front wheels and rear wheels as the drive wheels, and the main controller is the controller of the drive device that drives the rear wheels.

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