Controller of electric vehicle

Abstract

To provide a controller of an electric vehicle controlling each output torque of a plurality of motors to independently control driving force of a plurality of wheels which adequately controls the output torque of the motor to be capable of improving traveling stability and steering stability.SOLUTION: There is provided a controller of an electric vehicle with a plurality of motors independently driving a plurality of wheels respectively controls motor torque outputted according to prescribed motor characteristics of respective motors to control driving forces generated in the wheels corresponding to the motors. The controller of the electric vehicle calculates an estimation parameter regarding the motor characteristics through a prescribed parameter estimation method, selects one of the plurality of motors as a reference motor, calculates a relative difference between an estimation parameter of the reference motor and the estimation parameter of the other motor other than the reference motor as a characteristic difference, and decreases the difference of the motor torques due to the characteristic difference (step S3).SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a control device for an electric vehicle equipped with a plurality of motors as driving power sources.

Background Art

[0002] Patent Document 1 describes a control device for a motor aimed at obtaining an output torque that accurately corresponds to a torque command even when the temperature rises. The motor control device described in this Patent Document 1 estimates a magnetic flux change (demagnetization characteristic) that depends on the temperature of the interlinkage magnetic flux in the permanent magnet of a synchronous motor (PM motor). Then, based on the estimation result of the magnetic flux change, the torque current command value is corrected to obtain an output torque that compensates for the demagnetization due to temperature. Specifically, this Patent Document 1 calculates an estimated magnetic flux value (estimated value of the interlinkage magnetic flux) based on the voltage equation in the rotating coordinate (dq coordinate) system of the PM motor, and uses the estimated magnetic flux value, a motor model (a simulator that simulates an equivalent motor to the PM motor), etc. to correct the magnetization current command value and the torque current command value.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The electric vehicle targeted by this invention is equipped with at least two motors as a driving force source for generating driving force for traveling. For example, two motors for front-wheel drive and rear-wheel drive are provided, and by individually controlling these two driving motors, it is possible to independently control the driving force of the front wheels and the driving force of the rear wheels. Alternatively, two motors for driving the left wheels and two motors for driving the right wheels are provided, and by individually controlling these two driving motors, it is possible to independently control the driving force of the left wheels and the driving force of the right wheels. Furthermore, it may be an electric vehicle in which driving motors are provided for all four wheels, front, rear, left, and right, and by individually controlling these four driving motors, it is possible to independently control all of the driving forces of the four wheels.

[0005] In such an electric vehicle that independently drives two wheels in the front and rear or left and right, or four wheels in the front, rear, left, and right, in order to stabilize straight running performance or improve turning performance, it is necessary to control a plurality of motors simultaneously, independently, and with high precision. On the other hand, in a drive motor (synchronous motor) using a permanent magnet as described above, for example, the magnetic flux (magnetic flux density) of the magnet changes due to temperature changes caused by heat generation of the motor itself. And when the magnetic flux of the magnet changes, the output characteristics of the motor fluctuate. Such fluctuations in the output characteristics of the motor are inevitable individual differences among the motors. An inevitable absolute error also occurs when controlling the output torque of the motor. Therefore, for example, when the electric vehicle is running, if a difference occurs in the output characteristics between the left and right motors, it will interfere with the straight running stability of the electric vehicle. Also, when the electric vehicle is turning, if a difference (characteristic difference) occurs in the output characteristics between the left and right or front and rear motors, the turning performance and handling performance of the electric vehicle will deteriorate. That is, if there is a difference in the output characteristics of each motor, the running stability and handling stability of the electric vehicle will deteriorate. Therefore, by applying the technique of estimating the magnetic flux change of the magnet depending on temperature using the voltage equation as described in Patent Document 1 above, the characteristic difference of the motor can be obtained and reflected in the driving force control by the output of the motor. Also, in addition to the estimation technique using the voltage equation as described in Patent Document 1 above, for example, regression analysis using the least squares method, or parameter estimation methods such as sequential estimation using the sequential least squares method or the Kalman filter can be applied to obtain the characteristic difference of the motor as described above. Thereby, it is possible to suppress the deterioration of the running stability and handling stability of the electric vehicle as described above.

[0006] However, when estimating the magnetic flux of the magnet in the drive motor as described above, for example, due to inevitable individual differences in the motor and modeling errors other than the estimation target, it is difficult to accurately estimate the characteristic differences of the motor. In the technology for estimating the change in the magnetic flux of the magnet described in Patent Document 1 above and other conventional technologies, when estimating the magnetic flux of the magnet and the error of the current sensor, the voltage equation and the plant model in parameter estimation are used, and the parameters are estimated from the difference between the equation or model and the actual measurement value or command value. Therefore, if there are errors other than the parameters to be estimated in the parameter estimation equation or model, the difference between the equation or model and the actual measurement value or command value cannot be calculated appropriately. Such numerical deviations are directly linked to the estimation error of the magnetic flux as described above.

[0007] For example, y = ax + b (where x is an independent variable with respect to the target variable y) When calculating the error Δa of the constant a from the measurable x, y, and the nominal values of the known constants a and b, y = (a + Δa)x + b From this, Δa = (y - ax - b) / x and it can be transformed to obtain the error Δa. However, when there is an unmeasurable (inevitable) modeling error e in the above calculation formula, by setting "y → y + e", the estimated value Δa of the error Δa _est is calculated as Δa _est = (y + e - ax - b) / x = Δa + e / x That is, Δa _est ≠ Δa and the error Δa or the model parameter (a + Δa) cannot be accurately calculated.

[0008] Therefore, in an electric vehicle that controls the output torque of a plurality of motors to independently control the driving forces of a plurality of wheels, as described above, due to the magnetic flux change of the magnets that inevitably occurs depending on the temperature change, a characteristic difference between the motors occurs. Then, due to this characteristic difference, it becomes impossible to appropriately control the output torque of the motors. As a result, there is a risk of causing a decrease in the running stability and handling stability of the electric vehicle.

[0009] This invention was conceived by paying attention to the above technical problems. It is directed to an electric vehicle equipped with a plurality of motors as driving power sources and controlling the output torques of these plurality of motors to independently control the driving forces of a plurality of wheels, and aims to provide a control device for an electric vehicle that can appropriately control the output torque of the motors and improve the running stability and handling stability.

Means for Solving the Problems

[0010] To achieve the above object, this invention provides a control device for an electric vehicle comprising a plurality of motors that independently drive a plurality of wheels, and controlling the motor torque output according to the predetermined motor characteristics of each of the motors to control the driving force generated by the wheels corresponding to the motors. The control device includes a control unit that controls the electric vehicle and controls each of the motors. The control unit has a parameter estimation unit that calculates an estimated parameter related to the motor characteristics using a predetermined parameter estimation method, a reference motor selection unit that selects any one of the plurality of motors as a reference motor, a characteristic difference calculation unit that calculates the relative difference between the estimated parameter of the reference motor and the estimated parameters of the other motors other than the reference motor as a characteristic difference, and a motor torque control unit that reduces the difference in the motor torque caused by the characteristic difference.

[0011] In addition, the parameter estimation unit in the present invention calculates, as the estimated parameter, at least any one of the estimated motor torque (estimated value of the actual motor torque) of each motor, the estimated input power of each motor, or the estimated torque constant of each motor. The motor torque control unit in the present invention may be configured to correct a predetermined control target value so that the difference in the motor torque caused by any one of the difference in the estimated motor torque, the difference in the estimated input power, or the difference in the estimated torque constant decreases.

[0012] Moreover, each of the motors in the present invention is a synchronous motor configured using a permanent magnet. The parameter estimation unit in the present invention calculates the magnetic flux of the permanent magnet as the estimated parameter. The characteristic difference calculation unit in the present invention calculates the difference in the magnetic flux as the characteristic difference. The motor torque control unit in the present invention may be configured to correct the current value of the motor so as to cancel the difference in the magnetic flux and reduce the difference in the motor torque caused by the difference in the magnetic flux.

Advantages of the Invention

[0013] The vehicle to be controlled in this invention is an electric vehicle that uses at least two motors as drive power sources. In particular, it is an electric vehicle capable of driving the left and right or front and rear wheels, or the four wheels on all sides (front, rear, left, and right) with independent multiple motors respectively. With such an electric vehicle as the control target, in the control device of the electric vehicle of this invention, motor characteristics such as the output characteristics, torque characteristics, or thermal characteristics of each motor are used as estimated parameters, and predetermined parameter estimation is carried out. For example, using general parameter estimation methods such as the least squares method or the maximum likelihood method, estimated parameters related to the motor characteristics are calculated. At the same time, a reference motor is arbitrarily selected from all the motors to be controlled, and the relative difference between the estimated parameters of the reference motor and the estimated parameters of other motors is calculated as the characteristic difference. Then, based on the characteristic difference, the output torque of each motor, that is, the motor torque, is controlled. Specifically, each motor is controlled so that the difference in motor torque generated due to the characteristic difference decreases. The above-mentioned estimated parameters include inevitable estimation errors caused by measurement errors, modeling errors, etc. On the contrary, by obtaining the relative characteristic difference as described above, the influence of the estimation errors included in the estimated parameters can be eliminated or reduced. Therefore, each motor can be accurately controlled in a state where the influence of the estimation errors is removed. As a result, the driving force of the electric vehicle can be appropriately controlled.

[0014] In addition, in the control device for an electric vehicle of the present invention, as the above-described estimated parameters, for example, estimated values of each motor torque (i.e., estimated motor torque), estimated values of the power supplied to each motor (i.e., estimated input power of each motor), or estimated values of the torque constants of each motor (i.e., estimated torque constants of each motor) are calculated. Then, each motor is controlled based on the characteristic differences calculated from the estimated parameters regarding the estimated motor torque, estimated input power, and estimated torque constant. For example, the control target value of each motor torque is corrected so that the difference in the estimated motor torque becomes a desired value. Alternatively, the control target value of each motor torque is corrected so that the difference in the estimated input power becomes a desired value. Alternatively, the actual torque constant of each motor is corrected so that the difference in the estimated torque constant becomes a desired value. Therefore, each motor can be accurately controlled in a state where the influence of the estimation error is appropriately removed.

[0015] And, in the control device for an electric vehicle of the present invention, particularly when a synchronous motor using a permanent magnet is the control target, as the above-described estimated parameters, the magnetic flux of the permanent magnet of each motor is calculated. Then, each motor is controlled based on the characteristic differences calculated from the estimated parameters regarding the magnetic flux of each motor. Specifically, the current value of each motor is corrected so as to cancel the difference in magnetic flux and reduce the difference in motor torque caused by the difference in magnetic flux. Therefore, each motor can be controlled more accurately in a state where the influence of the estimation error is appropriately removed.

[0016] Therefore, according to the control device for an electric vehicle of the present invention, for an electric vehicle that controls a plurality of motors mounted as drive power sources to independently control the driving forces of a plurality of wheels, the motor torque output by each motor is appropriately controlled, and the running stability and handling stability of the electric vehicle can be improved.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

[0018] Embodiments of the present invention will be described with reference to the drawings. Note that the embodiments shown below are merely examples of the case where the present invention is embodied, and do not limit the present invention.

[0019] The vehicle to be controlled in the embodiments of the present invention is an electric vehicle equipped with a plurality of motors as driving power sources. A hybrid vehicle equipped with an engine (internal combustion engine) together with the plurality of motors may also be used. At least the driving torques of the left and right front wheels can be independently controlled by the plurality of motors of the driving power source. Alternatively, the driving torques of the left and right rear wheels can be independently controlled. Or, the driving torques of the four wheels on the front, rear, left, and right can be independently controlled. In the following examples, an example is shown in which four motors (first motor 1, second motor 2, third motor 3, and fourth motor 4) capable of independently controlling the driving torques of the four wheels on the front, rear, left, and right are mounted.

[0020] An electric vehicle (hereinafter referred to as vehicle) Ve shown in FIG. 1 includes a first motor (MG1) 1, a second motor (MG2) 2, a third motor (MG3) 3, and a fourth motor (MG4) 4 as driving power sources. And the vehicle Ve includes a detection unit 5 and a control unit (ECU) 6 for executing various controls.

[0021] Each of the motors 1, 2, 3, and 4 is configured by, for example, a permanent magnet type synchronous motor (PM motor). Each of the motors 1, 2, 3, and 4 has at least a function as a prime mover that is driven by being supplied with power to output torque. Further, each of the motors 1, 2, 3, and 4 may function as a generator that generates electric power by being driven by receiving torque from the outside. That is, each of the motors 1, 2, 3, and 4 may be a so-called motor generator having both a function as a prime mover and a function as a generator. A battery (not shown) is connected to each of the motors 1, 2, 3, and 4 via an inverter (not shown). Therefore, the electric power stored in the battery can be supplied to each of the motors 1, 2, 3, and 4, and each of the motors 1, 2, 3, and 4 can be made to function as a prime mover to output driving torque. Further, each of the motors 1, 2, 3, and 4 can be driven by the torque transmitted from the wheels 11, 12, 13, and 14 described later, and at that time, each of the motors 1, 2, 3, and 4 can be made to function as a generator to charge the battery with the generated electric power.

[0022] Note that each of the motors 1, 2, 3, and 4 can also be configured by, for example, an induction motor that does not use a permanent magnet. However, in the embodiment of the present invention, by controlling each of the motors 1, 2, 3, and 4 configured by the synchronous motor (PM motor) using a permanent magnet as described above, the effects of the control device of the electric vehicle in the embodiment of the present invention can be obtained more effectively as described later.

[0023] The first motor 1 drives the left front wheel 11. For example, the first motor 1 and the front wheel 11 are connected so as to be able to transmit power via a predetermined transmission mechanism such as a reduction gear (not shown). Alternatively, as a so-called "in-wheel motor", the first motor 1 may be disposed inside a wheel (not shown) of the front wheel 11, and the first motor 1 and the front wheel 11 may be directly connected.

[0024] The second motor 2 drives the right front wheel 12. For example, the second motor 2 and the front wheel 12 are connected so that power can be transmitted therebetween via a predetermined transmission mechanism such as a reduction gear (not shown). Alternatively, as a so-called "in-wheel motor", the second motor 2 may be disposed inside a wheel (not shown) of the front wheel 12, and the second motor 2 and the front wheel 12 may be directly connected.

[0025] The third motor 3 drives the left rear wheel 13. For example, the third motor 3 and the rear wheel 13 are connected so that power can be transmitted therebetween via a predetermined transmission mechanism such as a reduction gear (not shown). Alternatively, as a so-called "in-wheel motor", the third motor 3 may be disposed inside a wheel (not shown) of the rear wheel 13, and the third motor 3 and the rear wheel 13 may be directly connected.

[0026] The fourth motor 4 drives the right rear wheel 14. For example, the fourth motor 4 and the rear wheel 14 are connected so that power can be transmitted therebetween via a predetermined transmission mechanism such as a reduction gear (not shown). Alternatively, as a so-called "in-wheel motor", the fourth motor 4 may be disposed inside a wheel (not shown) of the rear wheel 14, and the fourth motor 4 and the rear wheel 14 may be directly connected.

[0027] The detection unit 5 is a device or apparatus for acquiring various data and information necessary when controlling the vehicle Ve. For example, the detection unit 5 includes a power supply unit, a microcomputer, sensors, an input / output interface, and the like. In particular, the detection unit 5 in the embodiment of the present invention respectively detects the traveling state of the vehicle Ve and the operating states of the motors 1, 2, 3, 4 for driving the vehicle. At the same time, the detection unit 5 detects various data for detecting and estimating the motor characteristics and motor torque (output torque of each of the motors 1, 2, 3, 4) of the motors 1, 2, 3, 4.

[0028] Specifically, the detection unit 5 includes, for example, wheel speed sensors 5a that respectively detect the rotational speeds of the wheels 11, 12, 13, 14, motor rotation speed sensors (or resolvers) 5b that respectively detect the rotational speeds of the motors 1, 2, 3, 4, motor torque sensors 5c that respectively detect the torques of the motors 1, 2, 3, 4, motor current sensors 5d that respectively detect the current values of the motors 1, 2, 3, 4, motor power sensors 5e that respectively detect the input powers of the motors 1, 2, 3, 4, and motor temperature sensors 5f that detect the temperatures of the motors 1, 2, 3, 4. In addition, the detection unit 5 includes, for example, an SOC sensor (not shown) that detects the state of charge (SOC) of a battery (not shown), a battery temperature sensor (not shown) that detects the temperature of the battery, and an inverter temperature sensor (not shown) that detects the temperature of an inverter (not shown). The detection unit 5 is electrically connected to a control unit 6 described later, and outputs an electrical signal corresponding to the detection values or calculated values of the various sensors, devices, and apparatuses as described above to the control unit 6 as detection data.

[0029] The control unit 6 is an electronic control device mainly composed of, for example, a microcomputer. The control unit 6 in the embodiment of the present invention controls each of the motors 1, 2, 3, 4 for vehicle drive to control the driving force of the vehicle Ve. Various data detected or calculated by the detection unit 5 described above are input to the control unit 6. The control unit 6 performs calculations using the input various data and data and calculation formulas stored in advance. Then, the control unit 6 outputs the calculation result as a control command signal, and as described above, is configured to mainly execute the driving force control of the vehicle Ve by the outputs of the motors 1, 2, 3, 4.

[0030] Specifically, the control unit 6 in the embodiment of the present invention controls each of the motors 1, 2, 3, and 4 for vehicle drive, and in order to execute appropriate drive force control of the vehicle Ve, for example, as shown in FIG. 2, it has a parameter estimation unit 6a, a reference motor selection unit 6b, a characteristic difference calculation unit 6c, and a motor torque control unit 6d.

[0031] The parameter estimation unit 6a calculates the estimated parameters of each of the motors 1, 2, 3, and 4 using a predetermined parameter estimation method. For example, any parameter estimation method such as regression analysis using the least squares method, maximum likelihood estimation method, or sequential estimation method using the sequential least squares method or Kalman filter can be applied. Then, using such a predetermined parameter estimation method, for example, estimated parameters related to the motor characteristics of each of the motors 1, 2, 3, and 4 such as output characteristics, torque characteristics, thermal characteristics, or magnetic flux change are calculated. Specifically, the estimated value of the motor torque of the motors 1, 2, 3, and 4 (that is, the estimated motor torque), the estimated value of the power supplied to each of the motors 1, 2, 3, and 4 (that is, the estimated input power of each of the motors 1, 2, 3, and 4), the estimated value of the torque constant of each of the motors 1, 2, 3, and 4 (that is, the estimated torque constant of each of the motors 1, 2, 3, and 4), or the magnetic flux of the permanent magnet (not shown) of each of the motors 1, 2, 3, and 4 is calculated as the estimated parameter of each of the motors 1, 2, 3, and 4.

[0032] The reference motor selection unit 6b selects any one of the motors 1, 2, 3, and 4 as the "reference motor". The "reference motor" in this case is arbitrarily selected from among the motors 1, 2, 3, and 4. For example, the "motor" with the estimated parameter closest to the average value of the estimated parameters calculated by the parameter estimation unit 6a is selected as the "reference motor". Alternatively, any "motor" that is fixedly selected in advance may be selected as the "reference motor".

[0033] The characteristic difference calculation unit 6c calculates the relative difference between the estimated parameters of the above-mentioned "reference motor" and the estimated parameters of "other motors" other than the "reference motor" as the "characteristic difference". The estimated parameters calculated using a predetermined parameter estimation method as described above include inevitable estimation errors caused by measurement errors, modeling errors, and the like. Therefore, in this characteristic difference calculation unit 6c, by calculating the difference relative to the estimated parameters of the "reference motor" as the "characteristic difference", the influence of the estimation error included in the estimated parameters can be eliminated or reduced.

[0034] The motor torque control unit 6d corrects a predetermined control target value so that the difference in motor torque caused by the above-mentioned "characteristic difference" decreases, and controls the motor torque of each of the motors 1, 2, 3, and 4 (motor torque control). For example, the control target values of the motor torques of each of the motors 1, 2, 3, and 4 are corrected so that the difference in estimated motor torque (characteristic difference) becomes a desired value. Alternatively, the control target values of the motor torques of each of the motors 1, 2, 3, and 4 are corrected so that the difference in estimated input power becomes a desired value. Alternatively, the actual torque constants of each of the motors 1, 2, 3, and 4 are corrected so that the difference in estimated torque constants of each of the motors 1, 2, 3, and 4 becomes a desired value. Alternatively, the current values of each of the motors 1, 2, 3, and 4 are corrected to cancel out the difference in the magnetic flux of the permanent magnets in each of the motors 1, 2, 3, and 4 and reduce the difference in motor torque caused by the difference in the magnetic flux. Therefore, by calculating the "characteristic difference" as described above, each of the motors 1, 2, 3, and 4 can be accurately controlled in a state where the influence of the estimation error is appropriately removed.

[0035] In addition, in FIGS. 1 and 2 described above, an example in which one control unit 6 is provided is shown. However, in the embodiment of the present invention, a plurality of control units 6 may be provided for each device or equipment to be controlled, or for each control content. Further, the parameter estimation unit 6a, the reference motor selection unit 6b, the characteristic difference calculation unit 6c, and the motor torque control unit 6d shown in FIG. 2 are named for explaining the configuration and function of the control unit 6 in the embodiment of the present invention. As the control unit 6, it suffices to have the configuration and function of each arithmetic unit 6a, 6b, 6c, 6d described above.

[0036] As described above, the control device for an electric vehicle in the embodiment of the present invention controls a vehicle Ve that can independently control the driving forces of "a plurality of wheels" (for example, wheels 11, 12, 13, 14) by controlling the output torques of "a plurality of motors" (for example, motors 1, 2, 3, 4) respectively. And the control device for an electric vehicle in the embodiment of the present invention is configured for the purpose of appropriately controlling the output torques (motor torques) of the respective motors 1, 2, 3, 4 to improve the running stability and handling stability of the vehicle Ve. For this purpose, an example of the control executed by the control unit 6 is shown in the flowchart of FIG. 3.

[0037] The control shown in the flowchart of FIG. 3 is executed when the vehicle Ve is running. For example, it is executed when the main switch (not shown) of the vehicle Ve, or the ignition switch (not shown) or a corresponding power switch (not shown) is turned on. First, in step S1, parameter estimation is performed for each of the motors 1, 2, 3, 4. As described above, using a predetermined parameter estimation method, for example, the estimated motor torque of each of the motors 1, 2, 3, 4, the estimated input power of each of the motors 1, 2, 3, 4, the estimated torque constant of each of the motors 1, 2, 3, 4, or the estimated magnetic flux value of the permanent magnet in each of the motors 1, 2, 3, 4 is calculated as the estimated parameter of each of the motors 1, 2, 3, 4. The estimated parameter calculated here may be any one of the above motor characteristics. Or, a plurality of motor characteristics may be used from among the motor characteristics.

[0038] Next, in step S2, an estimated parameter comparison with the "reference motor" is performed. That is, the "characteristic difference" in the embodiment of this invention is calculated. Specifically, first, the "reference motor" is selected. As described above, the "reference motor" is arbitrarily selected from among the motors 1, 2, 3, and 4. For example, the "motor" with the estimated parameter closest to the average value of each estimated parameter calculated in step S1 above is selected as the "reference motor". Alternatively, any "motor" that is to be fixedly selected in advance is selected as the "reference motor". Also, the "reference motor" may be switched according to predetermined conditions or situations. For example, by comparing the temperatures of the motors 1, 2, 3, and 4, the "motor" showing the most average temperature may be selected as the "reference motor" at any time. Also, by comparing the magnet fluxes of the motors 1, 2, 3, and 4, the "motor" showing the most average magnet flux may be selected as the "reference motor" at any time. Alternatively, by comparing the degrees of change in the magnet fluxes of the motors 1, 2, 3, and 4, the "motor" showing the most stable degree of change in magnet flux may be selected as the "reference motor" at any time. Alternatively, according to the driving state of the vehicle Ve, the "motor" at an appropriate position at that time may be selected as the "reference motor" at any time. In the following examples, an example in the case where motor 1 is selected as the "reference motor" will be described.

[0039] Then, the relative difference between the estimated parameters of the "reference motor" (motor 1) selected as described above and the estimated parameters of the "other motors" (motors 2, 3, and 4) other than the "reference motor" is calculated as the "characteristic difference".

[0040] For example, let the estimated parameter regarding the magnetic flux of the nth "motor" (MGn) be φ n _est, and its true value be φ n . Then, due to inevitable errors e n in the estimation model and mathematical formulas (such as the voltage equation and the motion equation) used in parameter estimation, φ n _est = φ n + e n As a result, the absolute accuracy of parameter estimation decreases by the amount of the error e n .

[0041] Then, a comparison is made between the estimated parameter φ1_est of the "reference motor" (motor 1) and the estimated parameters φ n _est (n = 2, 3, 4) of the other motors 2, 3, 4, and as their relative difference, a characteristic difference Δφ 1·n is calculated. For example, as shown in the time chart of FIG. 4, the relative difference between the estimated parameter φ1_est of the "reference motor" (motor 1) and the estimated parameter φ2_est of motor 2 at a predetermined time t1 is the characteristic difference Δφ 1·2 is calculated as such.

[0042] The estimation error e1 included in the estimated parameter φ1_est is an inevitable error of the estimation model and mathematical formula as described above. If the characteristics (for example, dead time of each motor 1, 2, 3, 4, resistance of the electric wire, etc.) not reflected in the estimation model and mathematical formula are the same among all the "motors" (motors 1, 2, 3, 4) including the "reference motor" (motor 1), it can be assumed that the influence on the estimation result in parameter estimation is also the same. Therefore, in this case, the estimation error e1 is e1 = e2 = e3 = … = e n Thus, the relative difference of the estimated parameter from the "reference motor" (motor 1), that is, the characteristic difference Δφ 1·n is Δφ 1·n = φ1_est - φ n _est and from the characteristic difference Δφ 1·n , the influence of the estimation error e1 (= e n ) is removed.

[0043] Next, in step S3, processing using the relative difference (characteristic difference) of the estimated parameters is performed. That is, motor torque control in the embodiment of this invention is executed. Specifically, the characteristic difference Δφ 1·nEach motor 1, 2, 3, 4 is controlled so that the difference in motor torque caused thereby decreases.

[0044] As an example, the current values of each of the motors 1, 2, 3, 4 are corrected so as to cancel out the difference in magnetic flux of the permanent magnets in each of the motors 1, 2, 3, 4 and so that the difference in motor torque caused by the difference in magnetic flux decreases. For example, the difference in magnetic flux (i.e., characteristic difference) between the magnetic flux in the “reference motor” (motor 1) and the magnetic flux in motor 2 is Δφ d1·2 Then, the difference in motor torque (torque difference) ΔT caused by the magnetic flux difference Δφ d1·2 is ΔT = n p ×Δφ d1·2 ×i q2 (n p is the number of motor poles, i q2 is the q-axis current of motor 2) becomes. Then, the current command value of motor 2 is corrected so that this torque difference ΔT becomes 0, and the motor torque of motor 2 is controlled.

[0045] In step S4, an end determination of the control shown in this flowchart of FIG. 3 is made. For example, when the main switch of the vehicle Ve, or the ignition switch or a power switch equivalent thereto is turned OFF, it is determined that the control ends. Therefore, if it is determined as “No” in this step S4 because there is still no determination of the end of control, the process returns to step S1 described above, and the same control as before is repeated.

[0046] And, if it is determined as “Yes” in this step S4 because there is a determination of the end of control, the routine shown in this flowchart of FIG. 3 is ended.

[0047] As described above, the vehicle Ve to be controlled in the embodiment of the present invention is an "electric vehicle (including a hybrid vehicle)" that uses at least two "motors" as driving power sources and can drive "a plurality of wheels" with independent "a plurality of motors", respectively. Taking such a vehicle Ve as the control target, in the control device for an electric vehicle in the embodiment of the present invention, for example, general parameter estimation methods such as the least squares method and the maximum likelihood method are used to calculate estimation parameters related to motor characteristics such as the output characteristics, torque characteristics, or heat characteristics of each of the motors 1, 2, 3, and 4. At the same time, an "reference motor" (in the above embodiment, motor 1) is arbitrarily selected from all of the motors 1, 2, 3, and 4 that are the control targets, and the relative difference between the estimation parameters of the "reference motor" and the estimation parameters of the "other motors" (in the above embodiment, motors 2, 3, and 4) is calculated as the "characteristic difference". Then, each of the motors 1, 2, 3, and 4 is controlled so that the difference in motor torque generated due to the "characteristic difference" is reduced. Thereby, the influence of the estimation error included in the estimation parameters can be eliminated or reduced, and each of the motors 1, 2, 3, and 4 can be accurately controlled. As a result, the driving force of the vehicle Ve can be appropriately controlled.

[0048] Therefore, according to the control device for an electric vehicle in the embodiment of the present invention, for an electric vehicle Ve that controls a plurality of motors 1, 2, 3, and 4 mounted as driving power sources to independently control the driving forces of a plurality of wheels 11, 12, 13, and 14, the motor torques output by each of the motors 1, 2, 3, and 4 can be appropriately controlled, and the running stability and handling stability of the electric vehicle Ve can be improved.

Explanation of Reference Signs

[0049] 1 First motor (driving power source: MG1) 2 Second motor (driving power source: MG2) 3 Third motor (driving power source: MG3) 4 Fourth motor (driving power source: MG4) 5 Detection unit 5a Wheel speed sensor (of the detection unit) 5b Motor rotation speed sensor (or resolver) of the detection unit 5c Motor torque sensor of the detection unit 5d Motor current sensor of the detection unit 5e Motor power sensor of the detection unit 5f Motor temperature sensor of the detection unit 6 Control unit (ECU) 11 Front wheel (left side) 12 Front wheel (right side) 13 Rear wheel (left side) 14 Rear wheel (right side) Ve Vehicle (electric vehicle)

Claims

1. A control device for an electric vehicle, comprising a plurality of motors that independently drive a plurality of wheels, and controlling the driving force generated by the wheels corresponding to the motors by controlling the motor torque output according to predetermined motor characteristics of the individual motors, comprising a control unit that controls the electric vehicle and controls each of the motors, wherein the control unit comprises a parameter estimation unit that calculates an estimated parameter related to the motor characteristics using a predetermined parameter estimation method, a reference motor selection unit that selects any one of the plurality of motors as a reference motor, a characteristic difference calculation unit that calculates a relative difference between the estimated parameter of the reference motor and the estimated parameters of the other motors other than the reference motor as a characteristic difference, and a motor torque control unit that reduces the difference in motor torque caused by the characteristic difference. A control device for an electric vehicle, characterized by the above.

2. The control device for an electric vehicle according to claim 1, wherein the parameter estimation unit calculates at least any one of the estimated motor torque, the estimated input power, or the estimated torque constant of each motor as the estimated parameter, and the motor torque control unit corrects a predetermined control target value so that the difference in motor torque caused by any one of the difference in the estimated motor torque, the difference in the estimated input power, or the difference in the estimated torque constant is reduced. A control device for an electric vehicle, characterized by the above.

3. The control device for an electric vehicle according to claim 1 or 2, wherein all of the motors are synchronous motors configured using permanent magnets, the parameter estimation unit calculates the magnetic flux of the permanent magnet as the estimated parameter, the characteristic difference calculation unit calculates the difference in magnetic flux as the characteristic difference, and the motor torque control unit corrects the current value of the motor so as to cancel the difference in magnetic flux and reduce the difference in motor torque caused by the difference in magnetic flux. A control device for an electric vehicle, characterized by the above.

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