Electric vehicles

Abstract

To provide an electric vehicle capable of suppressing discrepancy between outputs a plurality of motors, with rotation speeds of output shaft thereof mutually restrained.SOLUTION: An electric vehicle comprises: first and second motors; a drive force combining section which combines drive force of the first and second motors with rotation speeds of output shafts of the first and second motors mutually restrained; a first rotation speed sensor 13 which detects the rotation speed of the first motor; a main control section which generates a rotation speed command signal on the basis of a target rotation speed; and first and second motor drivers 20 and 30 which are respectively provided for the first and second motors. The main control section transmits the rotation speed command signal to the first motor driver 20 and does not transmit the rotation speed command signal to the second motor driver 30. The second motor driver 30 generates a second motor command signal to be transmitted to the second motor on the basis of a processing result of the rotation speed command signal received by the first motor driver 20.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an electric vehicle. [Background technology]

[0002] Conventionally, a vehicle described in Patent Document 1 is known as a technology relating to an electric vehicle. The vehicle described in Patent Document 1 is a battery-powered vehicle that includes an AC conversion circuit that converts the battery's output voltage into an AC voltage, two AC motors that are connected in parallel to the battery and receive voltage from the AC conversion circuit, and a driving force transmission member that engages with the output shafts of the two AC motors and transmits the driving force obtained from the two AC motors to the wheels. An AC conversion circuit is provided corresponding to each of the two AC motors. At least one of the AC motors is provided with a detection means for detecting the rotation speed of the AC motor. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-327004 Summary of the Invention [Problem to be solved by the invention]

[0004] In the above-described conventional technology, a control means generates a common rotation speed control signal that controls the rotation speeds of two AC motors to a target speed. The control means inputs the generated common rotation speed control signal to each of two orthogonal transform circuits. However, due to a small delay that may occur during the rotation speed control process or a communication delay between the control means and the orthogonal transform circuit, the actual outputs of the two AC motors may not match. If the outputs of the two AC motors do not match, the AC motor with the smaller output acts as a load on the AC motor with the larger output because the two AC motors are connected by a driving force transmission member. This can result in excess heat generation and a decrease in the efficiency of the AC motors.

[0005] An object of the present invention is to provide an electric vehicle that can suppress discrepancies in the outputs of a plurality of motors whose output shaft rotation speeds are mutually restricted. [Means for solving the problem]

[0006] An electric vehicle according to one aspect of the present invention comprises a plurality of motors, a driving force combining unit that combines the driving forces of the plurality of motors while the rotation speeds of the output shafts of the plurality of motors are constrained relative to one another, a rotation detection unit that detects the rotation speed of a target motor that is one of the plurality of motors, a main control unit that generates a rotation speed command signal based on a target rotation speed, and a plurality of command units that are provided corresponding to each of the plurality of motors and transmit motor command signals to the corresponding motor, wherein the main control unit transmits the rotation speed command signal to a first command unit that is the command unit corresponding to the target motor, but does not transmit the rotation speed command signal to a second command unit that is the command unit corresponding to motors other than the target motor, and the second command unit generates a second motor command signal to be transmitted to the motor corresponding to the second command unit based on the processing result of the rotation speed command signal received by the first command unit.

[0007] In an electric vehicle according to one aspect of the present invention, a rotation speed command signal is transmitted from the main control unit to the first command unit, while the main control unit does not transmit the rotation speed command signal to the second command unit. If the main control unit transmits rotation speed command signals separately and independently to the first command unit and the second command unit, and each unit processes the rotation speed command signal separately and independently, calculation errors may accumulate before the processing result of the rotation speed command signal is obtained. In contrast to this case, the second command unit generates a second motor command signal based on the processing result of the rotation speed command signal received by the first command unit, thereby preventing the outputs of multiple motors from becoming inconsistent due to the influence of calculation errors. Therefore, the electric vehicle according to one aspect of the present invention makes it possible to suppress inconsistencies in the outputs of multiple motors whose output shafts are constrained from each other in rotation speed.

[0008] In one embodiment, the first command unit may generate a torque command signal based on the received rotation speed command signal, generate a first motor command signal to be transmitted to the target motor based on the generated torque command signal, and transmit the generated torque command signal to the second command unit, and the second command unit may generate a second motor command signal based on the torque command signal received from the first command unit. In this case, the first motor command signal and the second motor command signal can be generated so that the torques output by the multiple motors are equal.

[0009] In one embodiment, the multiple motors are each provided with a rotation detector, and when the rotation detector of a target motor fails, the main control unit may designate one of the multiple motors that does not have the failed rotation detector as a new target motor, and transmit a rotation speed command signal to a new first command unit corresponding to the new target motor, without transmitting a rotation speed command signal to new second command units corresponding to motors other than the new target motor. In this case, even if the rotation detector of the motor that was designated as the target motor fails, it is possible to avoid the outputs of the multiple motors from continuing to be inconsistent. [Effects of the Invention]

[0010] According to the present invention, it is possible to suppress discrepancies in the outputs of a plurality of motors whose output shafts have mutually restricted rotational speeds. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic configuration diagram showing an electric vehicle according to an embodiment; [Figure 2] FIG. 2 is a block diagram showing the functional configuration of each motor driver in FIG. [Figure 3] 2 is a flowchart showing an example of processing by the first motor driver of FIG. 1. [Figure 4] 10 is a flowchart showing an example of processing by the second motor driver of FIG. [Figure 5] FIG. 2 is a schematic diagram showing the functional configuration of each motor driver of an electric vehicle according to a comparative example. [Figure 6] FIG. 6 is a diagram illustrating an example of an operation simulation of the electric vehicle of FIG. 5. [Figure 7] FIG. 7 is an enlarged view of the rising portion of FIG. 6. [Figure 8] FIG. 3 is a block diagram showing a modified example in which the target motor is different from that shown in FIG. 2. [Figure 9] FIG. 3 is a block diagram showing a modified example of the second motor driver in FIG. 2. DETAILED DESCRIPTION OF THE INVENTION

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, the same or equivalent elements will be designated by the same reference numerals, and redundant description will be omitted.

[0013] FIG. 1 is a schematic diagram showing the configuration of an electric vehicle according to one embodiment. The electric vehicle 10 is, for example, an industrial vehicle such as a forklift. The electric vehicle 10 is equipped with a first motor 1 and a second motor 2. The first motor 1 and the second motor 2 are, for example, induction motors that operate on three-phase AC. The first motor 1 and the second motor 2 are, for example, the same type of motor.

[0014] In the first motor 1 and the second motor 2, the rotation speeds of the output shafts 3 and 4 are constrained to each other. Specifically, as shown in FIG. 1 , a gear 5 attached to the output shaft 3 of the first motor 1 and a gear 6 attached to the output shaft 4 of the second motor 2 mesh with a common gear 7. The gears 5 and 6 have the same number of teeth. The driving forces of the first motor 1 and the second motor 2 are joined by the gears 5 and 6 and the gear 7 and transmitted to a running load L (e.g., the wheels of an electric vehicle 10) via a transmission shaft 8. The output shafts 3 and 4, the gears 5 and 6, the gear 7, and the transmission shaft 8 constitute a driving force joining unit 9. The driving force joining unit 9 joins the driving forces of the first motor 1 and the second motor 2 while the rotation speeds of the output shafts 3 and 4 of the first motor 1 and the second motor 2 are constrained to each other. The driving force joining unit 9 is, for example, a gear box. In this way, the first motor 1 and the second motor 2 are physically configured to have the same rotation speed via the gear 7. The first motor 1 and the second motor 2 are in a so-called direct connection state.

[0015] Fig. 2 is a block diagram showing the functional configuration of each motor driver in Fig. 1. As shown in Fig. 1 and Fig. 2, electric vehicle 10 includes battery 11, main control unit 12, first rotation speed sensor (rotation detection unit) 13, second rotation speed sensor (rotation detection unit) 14, first motor driver (command unit) 20, and second motor driver (command unit) 30.

[0016] The battery 11 is a DC power supply that drives the first motor 1 and the second motor 2. The battery 11 may be, for example, a lead-acid battery or a lithium battery. A first motor driver 20 and a second motor driver 30 are connected in parallel to the output terminal of the battery 11. The first motor 1 and the second motor 2 are connected in parallel to the battery 11.

[0017] The main control unit 12 is a controller including, for example, a microcomputer, and performs overall control of the electric vehicle 10. The main control unit 12 is an electronic control unit having, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), a CAN (Controller Area Network) communication circuit, etc. The main control unit 12 loads programs stored in the ROM into the RAM and executes the programs loaded into the RAM with the CPU, thereby realizing various functions. The main control unit 12 may be composed of multiple electronic control units.

[0018] The main control unit 12 calculates a target rotation speed. The target rotation speed is the rotation speed of the first motor 1 and the second motor 2 that corresponds to the target vehicle speed of the electric vehicle 10. The main control unit 12 calculates the target vehicle speed according to, for example, the operation amount of an accelerator pedal (not shown) of the electric vehicle 10.

[0019] The main control unit 12 generates a rotation speed command signal based on the target rotation speed. The rotation speed command signal is a command signal to the first motor driver 20 or the second motor driver 30 for performing rotation speed control to bring the rotation speeds of the first motor 1 and the second motor 2 closer to the target rotation speeds.

[0020] The main control unit 12 transmits a rotation speed command signal to a first command unit, which is a command unit corresponding to the target motor, and does not transmit a rotation speed command signal to a second command unit, which is a command unit corresponding to motors other than the target motor. The target motor is one of multiple motors (here, first motor 1 and second motor 2), and is a motor whose rotation speed is controlled using a rotation speed command signal from the main control unit 12. In the example of FIG. 2, the target motor is first motor 1, and the first command unit, which is a command unit corresponding to the target motor, is first motor driver 20. The second command unit, which is a command unit corresponding to motors other than the target motor, is second motor driver 30.

[0021] A first rotation speed sensor 13 is attached to the first motor 1. A temperature sensor (not shown) may be attached to the first motor 1 and the inverter of the first motor driver 20. The first rotation speed sensor 13 of the first motor 1 is connected to the first motor driver 20 and transmits a detection signal to the first motor driver 20. A second rotation speed sensor 14 is attached to the second motor 2. A temperature sensor (not shown) may be attached to the inverter of the second motor 2 and the second motor driver 30. The second rotation speed sensor 14 of the second motor 2 is connected to the second motor driver 30 and transmits a detection signal to the second motor driver 30. As the first rotation speed sensor 13 and the second rotation speed sensor 14, for example, known sensors such as an optical encoder or a tachometer using a magnetic sensor can be used.

[0022] The first motor driver 20 and the second motor driver 30 include a controller including, for example, a microcomputer, and inverters that drive the first motor 1 and the second motor 2, respectively. The power supply terminals of the first motor 1 are connected to the output terminals of the first motor driver 20 (e.g., U, V, and W terminals). The first motor driver 20 is provided corresponding to the first motor 1 and transmits motor command signals to the first motor 1. The power supply terminals of the second motor 2 are connected to the output terminals of the second motor driver 30. The second motor driver 30 is provided corresponding to the second motor 2 and transmits motor command signals to the second motor 2. In other words, the first motor driver 20 and the second motor driver 30 are multiple command units that transmit motor command signals to the corresponding first motor 1 and second motor 2.

[0023] In this embodiment, the rotation speed of one of the first motor 1 and the second motor 2 (in the example of FIG. 2, the rotation speed of the first motor 1 detected by the first rotation speed sensor 13) is used to perform rotation speed control to bring the detected rotation speed closer to the target rotation speed. In the example of FIG. 2, the first motor 1 is the target motor, and the first rotation speed sensor 13 functions as a rotation detection unit that detects the rotation speed of the target motor. In the example of FIG. 2, rotation speed control is performed on the first motor 1, and torque control is performed on the second motor 2 to make the output torque equal to that of the first motor 1 (details will be described later).

[0024] The first motor driver 20 includes, as functional components, a first rotation speed control unit 21, a first current calculation unit 22, a first output limiting unit 23, and a first voltage output unit 24. The second motor driver 30 includes, as functional components, a second rotation speed control unit 31, a second current calculation unit 32, a second output limiting unit 33, and a second voltage output unit 34.

[0025] The first rotation speed control unit 21 receives a rotation speed command from the main control unit 12 via the CAN communication circuit, for example. The first rotation speed control unit 21 obtains the first rotation speed based on the detection result of the first rotation speed sensor 13.

[0026] The first rotation speed control unit 21 generates a torque command signal based on the received rotation speed command signal. The torque command signal here refers to an output command generated by rotation speed control and is calculated as a torque value. The first rotation speed control unit 21 calculates, for example, an output command corresponding to an output according to the deviation between the first rotation speed and the target rotation speed so as to perform rotation speed control such that the first rotation speed of the first motor 1 (the target motor here) detected by the first rotation speed sensor 13 approaches the target rotation speed. Note that in the example of FIG. 2, no rotation speed command is sent from the main control unit 12 to the second motor driver 30. Therefore, the second rotation speed control unit 31 has the same function as the first rotation speed control unit 21, but does not calculate an output command.

[0027] The first current calculation unit 22 calculates a current command based on the torque command signal generated by the first rotation speed control unit 21. For example, the first current calculation unit 22 converts the output command calculated by the first rotation speed control unit 21 into a current value equivalent to the output command so that the first motor 1 outputs a torque corresponding to the output command, and calculates the current command. Note that in the example of FIG. 2, in the second motor driver 30, the second rotation speed control unit 31 does not generate an output command. The second current calculation unit 32 has the same function as the first current calculation unit 22, but does not calculate a current command.

[0028] The first output limiting unit 23 may implement a first output limit to protect the first motor 1 based on the detection result of the temperature sensor of the first motor 1. For example, if the first motor 1 or the inverter is in an overheated state, the first output limiting unit 23 outputs a current command limited to a predetermined limited current value as the first output limit. For example, if the first motor 1 is not in an overheated state, the first output limiting unit 23 outputs the current command as is without limiting it.

[0029] The first voltage output unit 24 generates a first motor command signal to be transmitted to the first motor 1 (the target motor in this case). The first motor command signal is a command signal for a first voltage for powering the first motor 1. As the first motor command signal, the first voltage output unit 24 calculates a first voltage having a predetermined phase as a three-phase AC sine wave, for example, by turning on or off a plurality of MOSFETs of an inverter based on the current command from the first output limiting unit 23 and the first rotation speed. The first voltage output unit 24 issues an output command for the calculated first voltage to the first motor 1.

[0030] Here, the first motor driver 20 transmits the generated torque command signal to the second motor driver 30. The generated torque command signal represents the processing result of the rotation speed control by the first rotation speed control unit 21, and may be a command signal downstream of the first rotation speed control unit 21 in the processing flow. In the example of FIG. 2 , the first motor driver 20 transmits a current command calculated by the first current calculation unit 22 to the second motor driver 30. The torque command signal transmitted to the second motor driver 30 is, for example, the current command calculated by the first current calculation unit 22.

[0031] The second output limiting unit 33 may implement a second output limit to protect the second motor 2 based on the detection result of the temperature sensor of the second motor 2. For example, when the second motor 2 or the inverter is in an overheated state, the second output limiting unit 33 outputs a current command limited to a predetermined limited current value as the second output limit. For example, when the second motor 2 is not in an overheated state, the second output limiting unit 33 outputs the current command as is without limiting it.

[0032] The second motor driver 30 generates a second motor command signal to be transmitted to the second motor 2 corresponding to the second motor driver 30 based on the processing result of the rotation speed command signal transmitted from the main control unit 12 and received by the first motor driver 20. The second motor driver 30 generates the second motor command signal based on the torque command signal received from the first motor driver 20. The second motor command signal is a second voltage command signal for powering the second motor 2. The second voltage output unit 34 calculates a second voltage having a predetermined phase as a three-phase AC sine wave based on, for example, the current command from the second output limiting unit 33 and the second rotation speed by, for example, turning on or off multiple MOSFETs of the inverter. The second voltage output unit 34 outputs the calculated second voltage to the second motor 2. The second voltage output unit 34 may also obtain the second rotation speed based on the detection result of the second rotation speed sensor 14.

[0033] With the above configuration, the second motor 2 is combined with torque control that makes the output torque equal to that of the first motor 1. This ensures that the outputs of the first motor 1 and the second motor 2 match, and prevents the outputs of the first motor 1 and the second motor 2 from becoming inconsistent due to the influence of calculation errors.

[0034] [An example of motor driver processing] Next, an example of the processing of each motor driver will be described. Fig. 3 is a flowchart showing an example of the processing of the first motor driver of Fig. 1. The processing shown in Fig. 3 is repeatedly executed at predetermined calculation intervals while the electric vehicle 10 is in operation, for example.

[0035] 3, in S11, the first motor driver 20 receives a rotation speed command from the first rotation speed control unit 21. The first rotation speed control unit 21 receives the rotation speed command transmitted from the main control unit 12 via the CAN communication circuit, for example. Here, the second motor driver 30 does not receive a rotation speed command transmitted from the main control unit 12.

[0036] In S12, the first motor driver 20 acquires the first rotation speed using the first rotation speed control unit 21. The first rotation speed control unit 21 acquires the first rotation speed based on the detection result of the first rotation speed sensor 13. Here, in the second motor driver 30, the second rotation speed control unit 31 does not acquire the first rotation speed or the second rotation speed.

[0037] In S13, the first motor driver 20 calculates an output command for rotation speed control using the first rotation speed control unit 21. The first rotation speed control unit 21 calculates an output command corresponding to an output according to, for example, the deviation between the first rotation speed and the target rotation speed, so as to perform rotation speed control that brings the first rotation speed of the first motor 1 (target motor here) detected by the first rotation speed sensor 13 closer to the target rotation speed.

[0038] In S14, the first motor driver 20 calculates a current command using the first current calculation unit 22. The first current calculation unit 22 calculates a current command of a current value equivalent to the output command calculated by the first rotation speed control unit 21 so that the first motor 1 outputs a torque corresponding to the output command, for example.

[0039] In S15, the first motor driver 20 transmits a current command to the second motor driver 30. The first motor driver 20 transmits to the second motor driver 30, for example, the latest current command calculated by the first current calculation unit 22 in the current process of FIG.

[0040] In S16, the first motor driver 20 implements the first output limitation using the first output limiting unit 23. For example, based on the detection result of the temperature sensor of the first motor 1, the first output limiting unit 23 outputs a current command limited to a predetermined limit current value as the first output limitation if the first motor 1 or the inverter is in an overheated state, and outputs the current command without limiting it if the first motor 1 is not in an overheated state.

[0041] In S17, the first motor driver 20 issues a command to output a first voltage via the first voltage output unit 24. The first voltage output unit 24 calculates a first voltage having a predetermined phase as a three-phase AC sine wave based on, for example, the current command from the first output limiting unit 23 and the first rotation speed. The first voltage output unit 24 issues a command to output the calculated first voltage to the first motor 1. Thereafter, the first motor driver 20 ends the processing of FIG. 3.

[0042] Fig. 4 is a flowchart showing an example of the processing of the second motor driver of Fig. 1. The processing shown in Fig. 4 is repeatedly executed at predetermined calculation intervals while the electric vehicle 10 is in operation, for example.

[0043] 4, in S21, the second motor driver 30 receives a current command from the first motor driver 20. The second motor driver 30 receives from the first motor driver 20, for example, the latest current command calculated by the first current calculation unit 22 of the first motor driver 20 in the current process of FIG.

[0044] In S22, the second motor driver 30 implements the second output limitation using the second output limiting unit 33. For example, based on the detection result of the temperature sensor of the second motor 2, the second output limiting unit 33 outputs a current command limited to a predetermined limit current value as the second output limitation if the second motor 2 or the inverter is in an overheated state, and outputs the current command without limiting it if the second motor 2 is not in an overheated state.

[0045] In S23, the second motor driver 30 acquires the second rotation speed by the second voltage output unit 34. The second voltage output unit 34 acquires the second rotation speed based on the detection result of the second rotation speed sensor 14, for example.

[0046] In S24, the second motor driver 30 issues a command to output a second voltage via the second voltage output unit 34. The second voltage output unit 34 calculates a second voltage having a predetermined phase as a three-phase AC sine wave based on, for example, the current command from the second output limiting unit 33 and the second rotation speed. The second voltage output unit 34 issues a command to output the calculated second voltage to the second motor 2. Thereafter, the second motor driver 30 ends the processing of FIG. 4.

[0047] [Actions and effects of the electric vehicle 10] FIG. 5 is a schematic diagram showing the functional configuration of each motor driver of an electric vehicle according to a comparative example. As shown in FIG. 5, in the electric vehicle according to the comparative example, a rotation speed command signal is sent separately and independently from the main control unit 12 to each of the first motor driver 120 and the second motor driver 130. The first motor driver 120 is basically configured similarly to the first motor driver 20. However, it differs from the first motor driver 20 in that the command signal output from any of the first rotation speed control unit 121, the first current calculation unit 122, the first output limiting unit 123, and the first voltage output unit 124 is not sent to the second motor driver 130. The second motor driver 130 is basically configured similarly to the second motor driver 30. However, it differs from the second motor driver 30 in that the second rotation speed control unit 131 receives a rotation speed command from the main control unit 12 via a CAN communication circuit and generates a torque command signal.

[0048] The first motor driver 120 and the second motor driver 130 process the rotation speed command signal separately and independently. In such a configuration, calculation errors may accumulate before an output command, which is the result of processing the rotation speed command signal, is obtained.

[0049] The calculation error can be caused by a small delay that can occur during the rotation speed control process using the rotation speed command received by each motor driver (e.g., a delay in reception timing due to variations in the CAN communication period from the main control unit 12). The calculation error can also be caused by a small difference in the rotation speed recognized by each motor driver (e.g., differences in the rotation speed itself due to variations in each rotation speed sensor itself, or differences in the recognized rotation speed caused by variations in the integration period when counting up pulse signals from each rotation speed sensor due to variations in the calculation period, etc.). Because such internal calculation errors are one cause, calculation errors can occur even if the first rotation speed of the first rotation speed sensor 13 is input to the first rotation speed control unit 21 and the second rotation speed control unit 31. As a result, the accumulated calculation errors can cause the actual outputs of the first motor 1 and the second motor 2 to not match.

[0050] If the actual outputs of the first motor 1 and the second motor 2 do not match, excess heat may be generated in the first motor 1 and the second motor 2, potentially reducing motor efficiency. For example, the first motor driver 120, while receiving the discrepancy in the outputs of the first motor 1 and the second motor 2 as a disturbance, calculates an output command using the first rotation speed control unit 121 such that the first rotation speed becomes the target rotation speed. The second motor driver 130, while receiving the discrepancy in the outputs of the first motor 1 and the second motor 2 as a disturbance, calculates an output command using the second rotation speed control unit 131 such that the second rotation speed becomes the target rotation speed. In other words, in the electric vehicle according to the comparative example, the rotation speed control is not configured to feed back the discrepancy in the outputs of the first motor 1 and the second motor 2. Therefore, rather than reducing the discrepancy in the outputs of the first motor 1 and the second motor 2, rotation speed control may be performed while maintaining the discrepancy in the outputs.

[0051] Specifically, FIG. 6 is a diagram illustrating an operation simulation of the electric vehicle of FIG. 5. FIG. 7 is an enlarged view of the rising portion of FIG. 6. The horizontal axis of FIGS. 6 and 7 represents time, and the vertical axis represents torque, current, and rotation speed. In FIGS. 6 and 7, the "rotation speed command" is the rotation speed command from the main control unit 12. The "internal rotation speed command" is the target rotation speed when processing the rotation speed control of each motor driver. The internal rotation speed command may be, for example, a rotation speed command received from the main control unit 12 that has been subjected to a predetermined filter process or the like. The "first rotation speed" is the rotation speed of the first motor 1 based on the detection result of the first rotation speed sensor 13. The "second rotation speed" is the rotation speed of the second motor 2 based on the detection result of the second rotation speed sensor 14. The "torque 1" is the output torque of the first motor 1. The "torque 2" is the output torque of the second motor 2.

[0052] 6 and 7 show simulation results of the outputs of the first motor 1 and the second motor 2 when the rotation speed command, indicated by the dashed-dotted line, is increased in steps from 0 and then decreased in steps to 0 after a predetermined time has elapsed. To simulate the accumulation of calculation errors described above, in this simulation, a fixed time delay is intentionally added to the second rotation speed from the first rotation speed immediately after the rotation speed command is increased in steps from 0, as shown in FIG. 7. The fixed time delay corresponds to the portion of the graph in FIG. 7 where the apparent second rotation speed does not follow the internal rotation speed command, while the rotation speed of the output shafts of the first motor 1 and the second motor 2 is constrained by each other. However, the physical rotation speed of the second motor 2 is assumed to match the rotation speed of the first motor 1.

[0053] The first rotation speed without this fixed time delay increases in accordance with the internal rotation speed command. but The second rotation speed is unable to follow the internal rotation speed command in the delay portion compared to the first rotation speed. Therefore, torque 2 increases significantly more than torque 1 in accordance with the difference between the internal rotation speed command and the second rotation speed. Here, because the rotation speeds of the output shafts of the first motor 1 and the second motor 2 are constrained relative to each other, the output shaft of the first motor 1 is twisted by torque 2 of the second motor 2, and torque 1 is reduced to resist torque 2 as a disturbance. As a result, torque 1 increases more slowly than torque 2. However, because the mismatch between the outputs of the first motor 1 and the second motor 2 is not reduced, the mismatch between torque 1 and torque 2 remains unchanged, resulting in the state shown in Figure 6.

[0054] As a result, as shown in FIG. 6, when the rotation speed command is increased stepwise from 0 and the first and second rotation speeds converge to the rotation speed command, torque 1 and torque 2 do not match and are nearly line-symmetrical about the horizontal axis (torque = 0). This state is nearly line-symmetrical because not only is there a load required for rotation while the first and second rotation speeds are constrained relative to one another, but the mismatch between torque 1 and torque 2 is added to this load as a disturbance torque. In other words, first motor 1 and second motor 2 generate excess heat by the amount of disturbance torque corresponding to the mismatch between torque 1 and torque 2, resulting in a deterioration in motor efficiency. Note that, in reality, there is no such addition, and only the load required for rotation while the first and second rotation speeds are constrained relative to one another is present, and torque 1 and torque 2 have the same sign.

[0055] In contrast to this comparative example, in electric vehicle 10, a rotation speed command signal is sent from main control unit 12 to first motor driver 20, but the rotation speed command signal is not sent from main control unit 12 to second motor driver 30. Second motor driver 30 generates a second motor command signal based on the processing result of the rotation speed command signal received by first motor driver 20. This makes it possible to avoid discrepancies between the outputs of first motor 1 and second motor 2 due to the influence of calculation errors. Therefore, electric vehicle 10 makes it possible to suppress discrepancies between the outputs of first motor 1 and second motor 2, in which the first rotation speed and the second rotation speed, which are the rotation speeds of output shafts 3 and 4, are constrained from each other.

[0056] In electric vehicle 10, first motor driver 20 generates a torque command signal using first rotation speed control unit 21 based on the rotation speed command signal received from main control unit 12. First motor driver 20 generates a first motor command signal using first voltage output unit 24 to be sent to first motor 1, which is a target motor, based on the torque command signal generated by first rotation speed control unit 21. First motor driver 20 sends the torque command signal generated by first rotation speed control unit 21 to second motor driver 30. Second motor driver 30 generates a second motor command signal using second voltage output unit 34 based on the torque command signal received from first motor driver 20. In this way, the first motor command signal and the second motor command signal can be generated so that the torques output by first motor 1 and second motor 2 are equal.

[0057] [Variations] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments. The present invention can be embodied in various forms, including the above-described embodiments, with various modifications and improvements made based on the knowledge of those skilled in the art.

[0058] 2, the first motor 1 is the target motor, the first rotation speed sensor 13 functions as a rotation detection unit that detects the rotation speed of the target motor, and the first motor 1 is subjected to rotation speed control, while the second motor 2 is subjected to torque control that makes the output torque equal to that of the first motor 1. However, this is not limiting. For example, as shown in FIG. 2, if the first motor driver 20 and the second motor driver 30 have similar functional configurations, the first motor driver 20 and the second motor driver 30 may be reversed from the example in FIG. 2.

[0059] FIG. 8 is a block diagram showing a modified example of FIG. 2 in which the target motor is different. As shown in FIG. 8, the second motor 2 is the target motor, and the second rotation speed sensor 14 functions as a rotation detection unit that detects the rotation speed of the target motor. The second motor 2 is subjected to rotation speed control, while the first motor 1 is subjected to torque control that equalizes the output torque of the second motor 2. In this case, the first command unit corresponding to the target motor is the second motor driver 30. The second command unit corresponding to the motor other than the target motor is the first motor driver 20. Furthermore, when issuing a command to output the first voltage by the first voltage output unit 24, the first voltage output unit 24 may acquire the detection result of the second rotation speed sensor 14 instead of the detection result of the first rotation speed sensor 13.

[0060] 8 may be configured to switch as a fail-safe if the first rotation speed sensor 13 fails when the target motor is the first motor 1 and the motor is operating in the state shown in FIG. 2. If the first rotation speed sensor 13 of the first motor 1, which is the target motor, fails, the main control unit 12 may designate the second motor 2 (any one of the motors not equipped with the failed rotation speed sensor 13) as the new target motor. In this case, the main control unit 12 transmits a rotation speed command signal to the second motor driver 30 (new first command unit) corresponding to the second motor 2, which is the new target motor. The main control unit 12 does not transmit a rotation speed command signal to the first motor driver 20 (new second command unit) corresponding to the first motor 1, which is a motor other than the new target motor. This prevents the outputs of the first motor 1 and the second motor 2 from continuing to differ even if the first rotation speed sensor 13 of the first motor 1, which was previously the target motor, fails.

[0061] 2, the torque command signal transmitted from the first motor driver 20 to the second motor driver 30 is a current command between the first current calculation unit 22 and the first output limiting unit 23, but is not limited to this. The torque command signal may be an output command between the first rotation speed control unit 21 and the first current calculation unit 22, a current command between the first output limiting unit 23 and the first voltage output unit 24, or a voltage command output from the first voltage output unit 24.

[0062] In the above embodiment, as shown in FIG. 2, the first motor driver 20 and the second motor driver 30 have similar functional configurations. However, this is not limiting. Part of the functional configuration of the second motor driver 30 corresponding to the second motor 2, which is a motor other than the target motor, may be omitted. For example, FIG. 9 is a block diagram showing a modified example of the second motor driver of FIG. 2. As shown in FIG. 9, for example, the second rotation speed control unit 31 and the second current calculation unit 32 may be omitted. The functional configuration to be omitted may be determined based on the torque command signal transmitted from the first motor driver 20 to the second motor driver 30. For example, when the first motor driver 20 transmits an output command between the first rotation speed control unit 21 and the first current calculation unit 22 as a torque command signal to the second motor driver 30, the second current calculation unit 32 is required to calculate the current command, and therefore only the second rotation speed control unit 31 may be omitted.

[0063] In the above embodiment, the second voltage output unit 34 calculates the second motor command signal (second voltage) based on the second rotation speed, but if the first motor 1 and the second motor 2 are induction motors, the second voltage may be calculated based on the first rotation speed. Note that if the first motor 1 and the second motor 2 are permanent magnet motors, the second voltage output unit 34 may calculate the second voltage based on the second rotation speed.

[0064] In the above embodiment, the first motor 1 and the second motor 2 in the electric vehicle 10 are provided with the first rotation speed sensor 13 and the second rotation speed sensor 14, respectively, but this is not limited to this. For example, if the target motor is fixed to the first motor 1, the second rotation speed sensor 14 may be omitted and only the detection result of the first rotation speed sensor 13 may be used.

[0065] In the above embodiment, the first motor driver 20 has the first output limiting unit 23, but the first output limiting unit 23 is not essential. The second motor driver 30 has the second output limiting unit 33, but the second output limiting unit 33 is not essential.

[0066] In the above embodiment, the output shafts 3 and 4, gears 5 and 6, gear 7, and transmission shaft 8 constitute the driving force joining unit 9, but this configuration is not limiting. The driving force joining unit 9 may be any other known driving force transmission mechanism as long as it joins the driving forces of the first motor 1 and the second motor 2 while the rotation speeds of the output shafts 3 and 4 of the first motor 1 and the second motor 2 are constrained from each other. For example, the rotation speeds of the output shafts 3 and 4 of the first motor 1 and the second motor 2 may be constrained from each other via planetary gears, the gears may be configured in multiple stages, or the rotational force may be transmitted by a belt or the like.

[0067] In the above embodiment, the electric vehicle 10 is an industrial vehicle such as a forklift, but it may be any other vehicle as long as the motor is driven by a battery 11 as a power source. Also, the first motor 1 and the second motor 2 are three-phase AC motors, but this is not limiting. In short, as long as the torque of multiple motors is controlled using the same output command as the processing result of the rotation speed control, they may be two-phase AC motors or DC motors. [Explanation of symbols]

[0068] 1...first motor (target motor), 2...second motor (new target motor), 3, 4...output shaft, 9...driving force joining section, 10...electric vehicle, 12...main control section, 13...first rotation speed sensor (rotation detection section), 14...second rotation speed sensor (rotation detection section), 20...first motor driver (command section, first command section, new second command section), 30...second motor driver (command section, second command section, new first command section).

Claims

1. A plurality of motors; a driving force combining unit that combines driving forces of the plurality of motors while restricting the rotational speeds of the output shafts of the plurality of motors with each other; a rotation detection unit that detects the rotation speed of a target motor that is any one of the plurality of motors; a main control unit that generates a rotation speed command signal, which is a command signal to the target motor, for performing rotation speed control to bring the rotation speed of the target motor closer to the target rotation speed, based on the target rotation speed; a plurality of command units provided corresponding to the plurality of motors, each command unit transmitting a motor command signal to the corresponding motor; Equipped with the main control unit transmits the rotation speed command signal to a first command unit that is the command unit corresponding to the target motor, and does not transmit the rotation speed command signal to a second command unit that is the command unit corresponding to the motor other than the target motor; the second command unit generates a second motor command signal to be transmitted to the motor corresponding to the second command unit based on a processing result of the rotation speed command signal received by the first command unit; the first command unit has a first rotation speed control unit that generates a torque command signal based on the received rotation speed command signal, the main control unit transmits the rotation speed command signal to the first rotation speed control unit of the first command unit, The first command unit generating a first motor command signal to be transmitted to the target motor based on the torque command signal generated by the first rotation speed control unit; transmitting the torque command signal generated by the first rotation speed control unit to the second command unit; The second command unit generating the second motor command signal based on the torque command signal received from the first command unit as a result of processing the rotation speed command signal received by the first command unit; an electric vehicle in which, with the rotation speeds of the output shafts mutually constrained by the driving force joining section, the rotation speed control is performed for the target motor, and torque control is combined for the motors other than the target motor so that the output torque is equal to that of the target motor.

2. The first command unit a first current calculation unit that calculates a current command based on the torque command signal generated by the first rotation speed control unit; transmitting the current command generated by the first current calculation unit to the second command unit; The second command unit The electric vehicle according to claim 1 , wherein the second motor command signal is generated based on the current command received from the first command unit.

3. The plurality of motors are each provided with the rotation detection unit, The main control unit When the rotation detection unit of the target motor fails, any one of the plurality of motors that is not provided with the failed rotation detection unit is set as a new target motor; transmit the rotation speed command signal to a new first command unit corresponding to the new target motor, and do not transmit the rotation speed command signal to a new second command unit corresponding to a motor other than the new target motor; 3. The electric vehicle according to claim 1, wherein the rotation speed control is performed for the new target motor while the rotation speeds of the output shafts are mutually constrained by the driving force joining portion, and the torque control is combined with the motors other than the new target motor so that their output torques are equal to that of the new target motor.

4. An electric vehicle as described in claim 1 or 2, wherein the second command unit has a second rotation speed control unit that does not receive the rotation speed command signal and does not generate the torque command signal.

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