Control device for electric vehicles

Abstract

To provide a control device for an electric vehicle, capable of improving torque control accuracy while suppressing an increase in energy loss.SOLUTION: A control device for an electric vehicle includes a controller for finding a d-axis current and q-axis current in a dq coordinate system on the basis of a torque command value of one of motors, and outputting the d-axis current and q-axis current which have been found to one of inverters which is connected to the one of the motors. The controller outputs, to the other of the inverters, a command signal for outputting braking torque from the other of the motors (Step S4). When vehicle speed-maintaining torque obtained by adding together driving torque required for the electric vehicle and the braking torque from the other of the motors is less than prescribed torque, the controller outputs, to the one of the inverters, a command signal of the d-axis current and a command signal of the q-axis current which are based on a torque control map (Step S7). When the torque command value is equal to or greater than the prescribed torque, the controller outputs a command signal of the d-axis current and a command signal of the q-axis current which are based on a maximum torque map (Step S6).SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a control device for an electric vehicle including a motor as a driving force source, and particularly to a control device for an electric vehicle including at least two motors, namely a motor for driving the front wheels and a motor for driving the rear wheels.

Background Art

[0002] Patent Document 1 describes a control device for an electric vehicle including a front motor for driving the front wheels and a rear motor for driving the rear wheels, the power consumption efficiency characteristics of which are different from those of the front motor. When the driving torque required for the vehicle is less than or equal to a predetermined threshold value, this control device determines the torque distribution between the motors by referring to a motor loss minimization torque distribution map that defines the torque distribution between the motors so that the loss of the drive device, which is the sum of the losses of each motor, is minimized, and determines the output torque of each motor. When the driving torque required for the vehicle is greater than the above threshold value, this control device determines the output torque of each motor by referring to a motor temperature rise minimization torque distribution map that defines the torque distribution so that the temperature rise rate of the drive device, which is the sum of the temperature rise rates of each motor, is minimized.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The control device described in Patent Document 1 is configured to determine the torque distribution between the motors based on a motor loss minimization torque distribution map that minimizes the loss of the drive device when the driving torque required for the vehicle is less than or equal to the threshold value. That is, the control device controls each motor so that the ratio of the output torque to the current value to be energized is good.

[0005] On the other hand, if the torque of each motor is controlled so that the ratio of output torque to the current supplied is good, as described above, the change in the motor's output torque becomes larger in relation to the change in the current supplied. In other words, the torque sensitivity improves. Therefore, in driving environments and conditions where precise control of the driving torque of an electric vehicle is required, it may not be possible to control the driving torque to an appropriate level, or it may be necessary to perform high-precision current control in order to control it to the required driving torque.

[0006] In contrast, if each motor is controlled at an operating point where the ratio of output torque to the current supplied is small, the driving torque of the electric vehicle can be precisely controlled. However, the losses of each motor become large, so if a relatively large driving torque is required, energy loss will increase, and the power consumption of the electric vehicle may increase excessively.

[0007] This invention was made in view of the above-mentioned technical problems, and aims to provide a control device for electric vehicles that can improve torque control accuracy while suppressing an increase in energy loss. [Means for solving the problem]

[0008] To achieve the above objective, this invention relates to a control device for an electric vehicle comprising a front motor having a multi-phase coil for driving the front wheels, a rear motor having a multi-phase coil for driving the rear wheels, a front inverter connected to the multi-phase coil in the front motor, and a rear inverter connected to the multi-phase coil in the rear motor, wherein the controller determines the d-axis current and q-axis current in a dq coordinate system based on the torque command value of one of the motors, the front motor and the front rear motor, converts the determined d-axis current and q-axis current into the multi-phase command values ​​and outputs them to one of the inverters, the front inverter and the rear inverter, connected to the one motor, and the controller includes a maximum torque map that defines the d-axis current and q-axis current so that the output torque with respect to the current supplied to the one motor is maximized, and the d-axis current and The system includes a torque control map that defines the d-axis current and the q-axis current such that the change in torque of one of the motors in response to the change in the q-axis current is smaller than that of the maximum torque map. The system outputs a command signal to the other of the front inverter and the rear inverter to output braking torque from the other of the front motor and the front rear motor. The system calculates the torque command value of one of the motors by adding the drive torque required for the electric vehicle and the braking torque of the other motor. If the torque command value of one of the motors is less than a predetermined torque, the system outputs a command signal for the d-axis current and a command signal for the q-axis current based on the torque control map to the one of the inverters. If the torque command value is equal to or greater than the predetermined torque, the system outputs a command signal for the d-axis current and a command signal for the q-axis current based on the maximum torque map.

[0009] In this invention, the invention further comprises a power storage device which is the power source for the front motor and the rear motor, and the other inverter is connected to the positive terminal of the power storage device and the front The other side Multiple upper arm switches are provided between the motor and the negative terminal of the energy storage device. The other sideThe inverter has a plurality of lower arm switches provided between it and the motor, and the command signal output to the other inverter may include a signal that keeps all of the switches of either the plurality of upper arm switches or the plurality of lower arm switches energized.

[0010] In this invention, the other motor may include the motor with the larger maximum output braking torque among the front motor and the rear motor.

[0011] In this invention, the maximum torque map may be defined such that the amount of change in the torque of the one motor decreases as the output torque of the one motor increases, in relation to the amount of change in the d-axis current or the q-axis current. [Effects of the Invention]

[0012] The electric vehicle control device in this invention includes a maximum torque map and a torque control map for determining the d-axis current and q-axis current of one of the motors, either a front motor or a rear motor. The other motor is controlled to output a braking torque, and the first motor is controlled to generate a torque that is the sum of the braking torque from the other motor and the torque required for the electric vehicle. The d-axis current and q-axis current are determined based on the torque control map when the torque command value is less than a predetermined torque, and based on the maximum torque map when it is greater than or equal to the predetermined torque. In other words, by controlling the other motor to output a braking torque, the torque required for the first motor is increased. By increasing the torque required for the first motor in this way, the d-axis current and q-axis current can be determined based on the maximum torque map. The maximum torque map is configured to determine the d-axis current and q-axis current so that the output torque for the current supplied to the first motor is maximized. Therefore, by outputting a braking torque from the other motor and increasing the torque required for the first motor, the energy loss of the first motor can be reduced. Furthermore, by increasing the motor's output torque, the change in output torque in relation to the change in the current supplied becomes smaller, thus improving the accuracy of torque control. As a result, the motor's drive torque can be precisely controlled without having to precisely control the d-axis current and q-axis current supplied to the motor that outputs the drive torque. [Brief explanation of the drawing]

[0013] [Figure 1] This figure schematically shows an example of the configuration of an electric vehicle in an embodiment of this invention. [Figure 2] This is an electrical circuit diagram illustrating an example of a configuration connecting a power storage device and a front motor. [Figure 3] This is a control block diagram illustrating an example of control for defining the switch signal of an inverter. [Figure 4] This diagram shows the maximum torque map and torque control map. [Figure 5] This flowchart illustrates an example of control for determining the current command value for each motor. [Figure 6] This figure shows the magnitude of the braking torque when three-phase ON control is performed. [Modes for carrying out the invention]

[0014] An example of the configuration of an electric vehicle in an embodiment of this invention is schematically shown in Figure 1. The electric vehicle Ve shown in Figure 1 (hereinafter simply referred to as "vehicle") is equipped with a front motor 2f for driving a pair of front wheels 1fr, 1fl and a rear motor 2r for driving a pair of rear wheels 1rr, 1rl.

[0015] The front motor 2f and rear motor 2r can be configured in the same way as motors used as power sources in conventional electric vehicles and hybrid vehicles. That is, in addition to functioning as motors that output driving torque by receiving power from the energy storage device 3, which is the power source for each motor 2f, 2r, they also function as generators that convert at least a portion of the power into electricity to charge the energy storage device 3 as the output shafts 4f, 4r are rotated together. Specifically, they are configured as synchronous motors with permanent magnets on the rotor. The front motor 2f and rear motor 2r may be the same motor, or they may be motors with different maximum output torque and energy conversion efficiency (ratio of output to input power).

[0016] In the example shown in FIG. 1, a pair of front wheels 1fr, 1fl are connected to the output shaft 4f of the front motor 2f via a front drive train 5f including a reduction mechanism, a differential unit, etc. not shown in the figure, and a pair of front drive shafts 6fr, 6fl. Similarly, a pair of rear wheels 1rr, 1rl are connected to the output shaft 4r of the rear motor 2r via a rear drive train 5r including a reduction mechanism, a differential unit, etc. not shown in the figure, and a pair of rear drive shafts 6rr, 6rl. Note that the mechanisms constituting the front drive train 5f and the mechanisms constituting the rear drive train 5r may be different.

[0017] The above-described power storage device 3 is configured in the same manner as the power storage devices provided in conventional electric vehicles and hybrid vehicles. That is, it is constituted by a secondary battery such as a lithium-ion battery or a nickel-hydrogen battery, or a capacitor. Note that the power storage device 3 may be constituted by a battery pack in which secondary batteries or capacitors are connected in series.

[0018] Since the above-described power storage device 3 outputs DC power or charges DC power, in the vehicle Ve, a front inverter 7f that converts the DC power output from the power storage device 3 into AC power and outputs it to the front motor 2f, and converts the AC power generated by the front motor 2f into DC power and outputs it to the power storage device 3, and a rear inverter 7r that converts the DC power output from the power storage device 3 into AC power and outputs it to the rear motor 2r, and converts the AC power generated by the rear motor 2r into DC power and outputs it to the power storage device 3 are provided.

[0019] FIG. 2 schematically shows an electrical circuit diagram for explaining an example of the configuration connecting the power storage device 3 and the front motor 2f. Since the configuration connecting the power storage device 3 and the rear motor 2r can also be configured in the same manner as the example shown in FIG. 2, in the following description, without distinguishing between the front motor 2f and the rear motor 2r, it is simply denoted as the motor 2, and without distinguishing between the front inverter 7f and the rear inverter 7r, it is simply denoted as the inverter 7 for explanation.

[0020] In the example shown in FIG. 2, the power storage device 3 and its internal resistance 8 are shown in series. A reactor 9 is connected to the positive electrode terminal side of the power storage device 3, and the power storage device 3 and the reactor 9 are housed in one battery pack 10. Further, the motor 2 is constituted by a star-connected three-phase AC motor provided with three-phase coils 2u, 2v, and 2w of U-phase, V-phase, and W-phase.

[0021] A positive electrode bus bar 11 is connected to the positive electrode of the power storage device 3, and a negative electrode bus bar 12 is connected to the negative electrode of the power storage device 3. A capacitor 13 for suppressing fluctuations in the input voltage of the inverter 7 is connected between the positive electrode bus bar 11 and the negative electrode bus bar 12. Specifically, one terminal (positive electrode side terminal) of the capacitor 13 is connected to the positive electrode bus bar 11, and the other terminal (negative electrode side terminal) is connected to the negative electrode bus bar 12.

[0022] Also, an upper arm switch (switching element) 14 and a lower arm switch (switching element) 15 are provided between the positive electrode bus bar 11 and the negative electrode bus bar 12. Specifically, the collector, which is the high-potential side terminal of the upper arm switch 14, is connected to the positive electrode bus bar 11, the emitter, which is the low-potential side terminal, is connected to the collector, which is the high-potential side terminal of the lower arm switch 15, and the emitter, which is the low-potential side terminal of the lower arm switch 15, is connected to the negative electrode bus bar 12. That is, the upper arm switch 14 and the lower arm switch 15 are connected in series.

[0023] As described above, the motor 2 shown in Figure 2 is a three-phase AC motor, so the upper arm switch 14 and the lower arm switch 15 are each composed of three switches. Specifically, the upper arm switch 14 is composed of a first switch Q1 connected to the U-phase coil 2u, a third switch Q3 connected to the V-phase coil 2v, and a fifth switch Q5 connected to the W-phase coil 2w. The lower arm switch 15 is composed of a second switch Q2 connected to the U-phase coil 2u, a fourth switch Q4 connected to the V-phase coil 2v, and a sixth switch Q6 connected to the W-phase coil 2w.

[0024] Each of these switches Q1 to Q6 is composed of a conventionally known insulated-gate bipolar transistor (IGBT), and each of these IGBTs is connected in antiparallel to a flyhole diode D1 to D6.

[0025] One end of the U-phase coil 2u is connected to the connection point between the first switch Q1 and the second switch Q2, one end of the V-phase coil 2v is connected to the connection point between the third switch Q3 and the fourth switch Q4, and one end of the W-phase coil 2w is connected to the connection point between the fifth switch Q5 and the sixth switch Q6. In other words, the first switch Q1, the third switch Q3, and the fifth switch Q5 are provided between the positive terminal of the energy storage device 3 and the motor 2, and the second switch Q2, the fourth switch Q4, and the sixth switch Q6 are provided between the negative terminal of the energy storage device 3 and the motor 2. The other ends of the U-phase coil 2u, the V-phase coil 2v, and the W-phase coil 2w are connected, and the point where each of these coils 2u, 2v, and 2w is connected is the neutral point 16.

[0026] Furthermore, in the example shown in Figure 2, an ammeter 17v is provided to detect the current flowing through the V-phase coil 2v, an ammeter 17w is provided to detect the current flowing through the W-phase coil 2w, a resolver 18 is provided to detect the rotation angle of the motor 2, a cell detection sensor (not shown) is provided to detect the remaining charge (SOC), state of health (SOH), voltage, etc. of the energy storage device 3, and a temperature sensor is provided to detect the temperature of each switch Q1 to Q6 and the temperature of each coil 2u, 2v, 2w. A control device (controller) 19 is provided to control each switch Q1 to Q6 based on the data detected by the ammeters 17v, 17w and resolver 18.

[0027] This control device 19, like control devices installed in conventional vehicles, is mainly composed of a microcomputer and is configured to output signals to each switch Q1 to Q6 based on signals input from the ammeter 17V, 17W and resolver 18, as well as pre-stored calculation formulas and maps.

[0028] Figure 3 shows a control block diagram illustrating an example of control for determining the switch signals of each switch Q1 to Q6. The control device 19 shown in Figure 3 includes a command conversion unit 20, a data conversion unit 21, PI controllers 22d and 22q, a rotation speed calculation unit 23, a non-interference term calculation unit 24, a voltage command conversion unit 25, a PWM generation unit 26, and a modulation rate calculation unit 27.

[0029] The command conversion unit 20 is configured to determine the d-axis current command value Idcom and the q-axis current command value Iqcom in the dq coordinate system based on the torque command value of the motor 2. This torque command value of the motor 2 is calculated by the system controller 28. The system controller 28 receives signals from an accelerator pedal position sensor 29 (not shown) that detects the amount the accelerator pedal is pressed, and a vehicle speed sensor 30 that detects the vehicle speed. The system controller 28 then calculates a target driving force based on the signal input from the accelerator pedal position sensor 29, determines the torque command value of the motor 2 based on that target driving force, or calculates the difference between a predetermined target vehicle speed and the actual vehicle speed based on the signal input from the vehicle speed sensor 30, and calculates the torque command value of the motor 2 by feeding back that difference.

[0030] The dq coordinate system is a coordinate system used for current control of conventional synchronous motors. It defines the direction of the magnetic flux of the permanent magnets on the rotor as the d-axis, and the axis advanced 90 degrees from the d-axis as the q-axis. The conversion from three-phase current values ​​to current values ​​in the dq coordinate system, and the conversion from voltage values ​​in the dq coordinate system to three-phase voltage values, are well-known techniques, so their explanation will be omitted here.

[0031] The command conversion unit 20 stores two maps: a maximum torque map and a torque control map, which determine the d-axis current command value Idcom and the q-axis current command value Iqcom in the dq coordinate system based on the torque command value of the motor 2. The map referenced when determining the d-axis current command value Idcom and the q-axis current command value Iqcom is switched based on the control example shown in Figure 5.

[0032] Figure 4 shows examples of a maximum torque map and a torque control map, with the d-axis representing the current command value Idcom and the q-axis representing the current command value Iqcom. In Figure 4, the solid line shows an example of a maximum torque map, the dashed line shows an example of a torque control map, the dashed line shows the current command value Ia supplying power to motor 2, and the thin lines show isotorque lines connecting identical torques. Note that the current command value Ia is √(Id2 +Iq 2 )

[0033] As shown in Figure 4, the maximum torque map is determined by the MTPA (Maximum Torque Per Ampere) line, which is formed by plotting and connecting the points where the torque is maximum for a given current command value (current) Ia. This is determined based on the characteristics of motor 2 and is determined in advance through experiments and simulations. Also, as shown in Figure 4, the spacing between the equitorque lines on the maximum torque map gradually increases as the output torque of motor 2 increases. In other words, the change in output torque in response to changes in the d-axis current and q-axis current becomes smaller.

[0034] On the other hand, the torque control map is a curve (self-propelled transport current command line) that is determined such that the ratio of the change in the torque generated by the motor 2 to the change in the d-axis current command value Idcom and the q-axis current command value Iqcom (hereinafter referred to as torque sensitivity) is smaller than the torque sensitivity in the maximum torque map, taking into consideration, for example, the characteristics of the motor 2, the power that can be pre-charged in the energy storage device 3 (i.e., the output voltage), and the temperature rise of the motor 2 and the energy storage device 3 due to power loss. This curve is determined through experiments and simulations.

[0035] The command conversion unit 20 then determines the d-axis current command value Idcom and the q-axis current command value Iqcom based on the input torque command value and the maximum torque map or torque control map, and outputs the corresponding signals.

[0036] The data conversion unit 21 is configured to calculate the dq-converted values ​​id and iq of the inverter output from the V-phase current iv and W-phase current iw detected by the ammeters 17V and 17W, and the rotor rotation angle θ detected by the resolver 18. Specifically, the data conversion unit 21 obtains the three-phase UVW current values ​​Iu, Iv, and Iw output by the inverter 7 from the V-phase current iv and W-phase current iw and the rotor rotation angle θ, and then performs a dq conversion on these current values ​​Iu, Iv, and Iw. Finally, it outputs signals of the dq-converted values ​​id and iq of the inverter output.

[0037] The PI controllers 22d and 22q are configured to convert the difference ΔId and ΔIq between the current command values ​​Idcom and Iqcom and the measured current values ​​id and iq into corresponding voltage values. Specifically, the difference ΔId and ΔIq between the d-axis current command value Idcom and q-axis current command value Iqcom determined by the command conversion unit 20 and the dq-converted values ​​id and iq converted by the data conversion unit 21 is input to the PI controllers 22d and 22q. Similar to conventional PI controllers, the voltage values ​​corresponding to the difference ΔId and ΔIq are calculated using proportional and integral control. The calculated voltage values ​​are then output as signals.

[0038] On the other hand, the rotational speed calculation unit 23 is configured to calculate the rotor's rotational speed ω by taking the time derivative of the rotor's rotation angle θ detected by the resolver 18, and this rotational speed ω signal is input to the non-interference term calculation unit 24.

[0039] This control device 19 is configured to calculate the three-phase voltage command values ​​Vu, Vv, and Vw using conventional voltage equations. Therefore, the non-interference term calculation unit 24 is configured to calculate a non-interference term that indicates the degree of q-axis voltage acting on the d-axis current and the degree of d-axis voltage acting on the q-axis current in order to determine the number of flux links of the phase winding corresponding to the d-axis and the number of flux links of the phase winding corresponding to the q-axis. Specifically, the non-interference term calculation unit 24 receives signals of the d-axis current command value Idcom and the q-axis current command value Iqcom from the command conversion unit 20, as well as a signal of the rotor rotation speed ω from the rotation speed calculation unit 23, and calculates the non-interference term based on these signals. The result of this calculation is then added to the voltage values ​​obtained by the PI controllers 22d and 22q.

[0040] As described above, the voltage command values ​​Vd and Vq, obtained by adding a non-interference term to the voltage values ​​obtained by the PI controllers 22d and 22q, and the signal of the rotor rotation angle θ detected by the resolver 18 are input to the voltage command conversion unit 25. The voltage command conversion unit 25 then calculates the three-phase voltage command values ​​Vu, Vv, and Vw using the conventional voltage equation based on the voltage command values ​​Vd and Vq and the rotor rotation angle θ.

[0041] Next, the three-phase voltage command values ​​Vu, Vv, and Vw calculated by the voltage command conversion unit 25 are input to the PWM generation unit 26. The PWM generation unit 26 calculates a PWM command value (pulse width modulation command value) to be output to the switch of the inverter 7 according to the three-phase voltage command values ​​Vu, Vv, and Vw and the voltage level VINV input to the inverter 7, and outputs a signal of that pulse width modulation command value to the inverter 7. Then, the inverter 7 performs a switching operation according to the PWM command value, and a three-phase AC current is supplied to the motor 2.

[0042] The voltage VINV input to the inverter 7, the voltage command value Vd for the d axis, and the voltage command value Vq for the q axis are input to the modulation rate calculation unit 27, which calculates the modulation rate to be used for other controls based on these signals.

[0043] Figure 5 shows a flowchart illustrating an example of control for determining the current command values ​​for each motor 2f, 2r. This control example is configured to determine the current command values ​​when the vehicle self-propels along an assembly line in a factory where doors, bodies, and other components are assembled. Specifically, the motors 2f, 2r, inverters 7f, 7r, energy storage device 3, ECU 19, a pair of front wheels 1fr, 1fl, and a pair of rear wheels 1rr, 1rl necessary for self-propulsion are assembled onto a monocoque. In this state, the system is configured to determine the current command values ​​for driving at a target vehicle speed of extremely low speed, which is determined for each process of assembling doors and bodies, or for the entire assembly line. This type of control for self-propulsion within a factory can be started by providing a switch on the electric vehicle to set the factory self-propulsion transport mode, and then using the on / off signal of that switch.

[0044] Therefore, in the control example shown in Figure 5, first, the travel mode is detected (step S1), and it is determined whether the travel mode is the factory self-propelled transport mode or not (step S2). Specifically, the signal from the switch for setting the factory self-propelled transport mode is detected, and it is determined whether the signal from that switch is ON or OFF.

[0045] If the driving mode is determined to be not the factory self-propelled transport mode in step S2, then the routine is terminated by performing current control on each motor 2f, 2r, or only one of the motors 2f (2r) using a normal current command (step S3). Specifically, the command conversion unit 20 sets the d-axis current command value Idcom and the q-axis current command value Iqcom by referring to the maximum torque map. Specifically, the system controller 28 calculates the target torque to be transmitted to the pair of front wheels 1fr, 1fl and the pair of rear wheels 1rr, 1rl based on the difference between the target vehicle speed and the actual vehicle speed in the section on which the electric vehicle Ve is traveling, as well as the required driving force, and calculates the torque command value for each motor 2f, 2r based on that target torque. Then, the d-axis current command value Idcom and the q-axis current command value Iqcom for each motor 2f, 2r are obtained from the torque command value of each motor 2f, 2r and the maximum torque map, and the obtained signals are output from the command conversion unit 20.

[0046] Conversely, if the driving mode is determined to be factory self-propelled transport mode in step S2, then regenerative control is performed on either the front motor 2f or the rear motor 2r (step S4). Specifically, a command signal is output to keep all switches Q1, Q3, Q5 (Q2, Q4, Q6) of either the upper arm switch 14 or the lower arm switch 15 of the inverter 7f (7r) connected to one of the motors 2f (2r) turned ON, thereby maintaining a powered state. This control is called three-phase ON control.

[0047] By implementing this three-phase ON control, a back electromotive force is generated corresponding to the characteristics of the motor 2f (2r) and inverters 7f and 7r, such as the magnetic flux of the magnets on the rotor and the inductances of the d-axis and q-axis. As a result, braking torque is generated, and a portion of the rotor's kinetic energy is converted into electricity.

[0048] Figure 6 shows the magnitude of the braking torque when three-phase ON control is performed. The horizontal axis represents the rotational speed of motor 2f (2r), and the vertical axis represents the magnitude of the braking torque. Note that the braking torque is shown as a negative value, indicating that the lower the value in Figure 6, the greater the braking torque.

[0049] As shown in Figure 6, by performing three-phase ON control, in the region where the rotational speed of motor 2f(2r) is below a predetermined rotational speed N1, the braking torque increases with increasing rotational speed, and in the region where the rotational speed of motor 2f(2r) is higher than the predetermined rotational speed N1, the braking torque gradually decreases with increasing rotational speed.

[0050] In step S4, it is preferable to regenerate control the motor that can output a larger braking torque by controlling the three phases. Alternatively, the motor to be regenerated may be selected based on, for example, whether the temperature of each switch Q1 to Q6 constituting one inverter 7f (7r) has reached a predetermined temperature, or whether the temperature of each coil 2u, 2v, 2w constituting one motor 2f (2r) has reached a predetermined temperature, or the motor to be regenerated may be switched during driving.

[0051] Following step S4 described above, step S5 determines whether the torque required by the other motor 2r(2f) to maintain vehicle speed (vehicle speed maintenance torque) is less than a predetermined torque. As a result of step S4 described above, one of the motors 2f(2r) is regenerated and generates braking torque. Therefore, the vehicle speed maintenance torque in step S5 is the sum of the torque counteracting the braking torque generated by one of the motors 2f(2r) and the driving torque that balances the driving resistance based on the vehicle's own weight.

[0052] Then, in step S5, it is determined whether the vehicle speed maintenance torque is suitable for setting the d-axis current command value Idcom and the q-axis current command value Iqcom based on the torque control map. Therefore, the predetermined torque can be set to, for example, less than or equal to the upper limit torque when the d-axis current command value Idcom and the q-axis current command value Iqcom are set based on the torque control map. The upper limit torque may be the upper limit torque that can be output based on the characteristics of the other motor 2r (2f) or the predetermined charging power of the energy storage device 3, or an upper limit torque determined based on energy efficiency.

[0053] As described above, the factory self-propelled transport mode is a driving mode that maintains a target vehicle speed, and therefore the torque command value of motor 2 is determined by feeding back the difference between the target vehicle speed and the actual vehicle speed. On the other hand, as the amount of loaded material increases from the early to the later stages of the assembly process, the amount of load increases and the vehicle's weight increases, so the maintenance torque required for steady-state driving (vehicle speed maintenance torque) gradually increases. Therefore, in the early stages of the assembly process, the vehicle speed maintenance torque is less than the predetermined torque, resulting in a positive judgment in step S5, while conversely, in the later stages of the assembly process, the vehicle speed maintenance torque is greater than or equal to the predetermined torque, resulting in a negative judgment in step S5.

[0054] If it is determined positively in step S5 that the vehicle speed maintenance torque is less than a predetermined torque, then one motor 2f(2r) is controlled by three-phase ON control, and the other motor 2r(2f) is controlled by a low vehicle speed maintenance current command (step S6), and this routine is terminated. That is, based on the vehicle speed maintenance torque and the torque control map, the d-axis current command value Idcom and the q-axis current command value Iqcom of the other motor 2r(2f) are determined, and the determined command signals are output.

[0055] If it is determined negatively in step S5 because the vehicle speed maintenance torque is greater than or equal to a predetermined torque, a normal current command is issued (step S7) and this routine is terminated. That is, the d-axis current command value Idcom and the q-axis current command value Iqcom of the other motor 2r (2f) are determined based on the vehicle speed maintenance torque and the maximum torque map, and the determined command signals are output. In addition, during the transition period when changing from the d-axis current command value Idcom and q-axis current command value Iqcom according to the torque control map to the d-axis current command value Idcom and q-axis current command value Iqcom according to the maximum torque map, such as immediately after the vehicle speed maintenance torque becomes greater than or equal to a predetermined torque, it is preferable to gradually change the d-axis current command value Idcom and q-axis current command value Iqcom at a predetermined rate of change.

[0056] As described above, by regenerative control of either the front motor 2f or the rear motor 2r, the vehicle speed maintenance torque required of the other motor can be increased. By increasing the vehicle speed maintenance torque required of the other motor in this way, even if the d-axis current command value Idcom and the q-axis current command value Iqcom are determined based on the maximum torque map, the amount of change in output torque in response to the amount of change in current can be reduced. As a result, the drive torque of the motor can be precisely controlled without having to precisely control the d-axis current and q-axis current supplied to the motor that outputs the drive torque.

[0057] Furthermore, the motor that outputs the drive torque will output a higher torque than when one of the motors does not perform regenerative control, and although power consumption will increase, the regenerative control of one of the motors will generate electricity, so the input and output power of the energy storage device 3 will not increase substantially. Therefore, as described above, it is possible to suppress the increase in energy loss caused by reducing the controllability required of the other motor by regenerative control of one motor.

[0058] Furthermore, even when one motor performs regenerative control, if the torque for maintaining vehicle speed is small, the torque required for the vehicle is extremely low. Therefore, even if the d-axis current and q-axis current are determined based on the torque control map, power consumption can be kept low, the increase in energy loss can be suppressed, and the accuracy of torque control can be improved.

[0059] In other words, by improving the torque control accuracy, it becomes possible to switch maps to appropriately determine the d-axis current and q-axis current when power consumption becomes excessively high, or to determine the d-axis current and q-axis current of the other motor according to the maximum torque map across the entire assembly line. In short, it is possible to improve the torque control accuracy while reducing the overall energy loss of the vehicle.

[0060] Furthermore, the electric vehicle in this embodiment of the invention is not limited to a vehicle equipped with two motors, a front motor that drives a pair of front wheels and a rear motor that drives a pair of rear wheels. For example, it may be a hybrid vehicle configured to drive a pair of front wheels with an engine and a front motor, and a pair of rear wheels with a rear motor, and to be configured to allow setting an EV driving mode that is driven only by the front motor and the rear motor. It may also be an in-wheel motor vehicle in which a motor is mounted on each wheel.

[0061] Furthermore, the control device in this embodiment of the invention may be configured to switch between a maximum torque map and a torque control map when determining the d-axis current and q-axis current, depending on the driving environment and driving conditions, not only when the vehicle is self-propelled on an assembly line within a factory as described above, but also when a finished product with doors, a body, etc., is assembled. For example, if there is a need to warm up a motor or inverter, the control device may be configured to regenerate control one motor and determine the d-axis current and q-axis current based on either the maximum torque map or the torque control map, depending on the magnitude of the torque required for the other motor. [Explanation of Symbols]

[0062] 1fr,1fl front wheel 1rr,1rl Rear wheel 2 motors 2F Front Motor 2r Rear Motor 2u, 2v, 2w coil 3. Energy storage device 7 Inverter 7f Front Inverter 7r Rear Inverter 11 Positive busbar 12 Negative bus bar 14 Upper arm switch 15. Lower arm switch 19 Control device 20 Command conversion unit 21 Data Conversion Unit 22d,22q PI controller 23. Rotational speed calculation unit 24 Non-interference term calculation unit 25 Voltage command conversion unit 26 PWM generation unit 27 Modulation Rate Calculation Unit 28 System Controllers D1~D6 Flyhole Diodes Q1-Q6 Switch Ve electric vehicle

Claims

1. A control device for an electric vehicle comprising: a front motor having multiple phase coils for driving the front wheels; a rear motor having multiple phase coils for driving the rear wheels; a front inverter connected to the multiple phase coils in the front motor; and a rear inverter connected to the multiple phase coils in the rear motor, The system includes a controller that determines the d-axis current and q-axis current in the dq coordinate system based on the torque command value of one of the front motors and the front rear motor, converts the determined d-axis current and q-axis current into the multi-phase command values, and outputs them to one of the inverters, the front inverter and the rear inverter, which are connected to the one motor. The aforementioned controller, The system includes a maximum torque map in which the d-axis current and the q-axis current are defined such that the output torque for a given current supplied to one of the motors is maximized, and a torque control map in which the d-axis current and the q-axis current are defined such that the change in torque of the one of the motors for a given change in the d-axis current or the q-axis current is smaller than that in the maximum torque map. A command signal is output to the other inverter of the front inverter and the rear inverter, which outputs braking torque from the other motor of the front motor and the front rear motor. The torque command value for the one motor is obtained by adding the driving torque required for the electric vehicle and the braking torque of the other motor. If the torque command value of one of the motors is less than a predetermined torque, the inverter outputs a command signal for the d-axis current and a command signal for the q-axis current based on the torque control map. If the torque command value is equal to or greater than the predetermined torque, the inverter outputs a command signal for the d-axis current and a command signal for the q-axis current based on the maximum torque map. A control device for electric vehicles characterized by the following features.

2. A control device for an electric vehicle according to claim 1, The system further includes an energy storage device that provides power to the front motor and the rear motor. The other inverter has a plurality of upper arm switches provided between the positive terminal of the energy storage device and the other motor, and a plurality of lower arm switches provided between the negative terminal of the energy storage device and the other motor. The command signal output to the other inverter includes a signal that maintains all of the switches of either the plurality of upper arm switches or the plurality of lower arm switches in an energized state. A control device for electric vehicles characterized by the following features.

3. A control device for an electric vehicle according to claim 2, The other motor includes the motor with the larger maximum output braking torque among the front motor and the rear motor. A control device for electric vehicles characterized by the following features.

4. A control device for an electric vehicle according to any one of claims 1 to 3, The maximum torque map is defined such that as the output torque of one of the motors increases, the change in the torque of the one motor decreases in response to the change in the d-axis current or the q-axis current. A control device for electric vehicles characterized by the following features.

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