Control device for electric vehicle

Abstract

Provided is a control device for an electric vehicle, the control device being capable of appropriately controlling the output torque of a plurality of motors and improving travel stability and steering stability for an electric vehicle in which the output torque of each of the plurality of motors is controlled and the driving force of a plurality of wheels is independently controlled. This electric vehicle control device is provided with a plurality of motors for independently driving a plurality of wheels, and controls the driving force generated by the wheels corresponding to the motors by controlling the motor torques output by the respective motors in accordance with predetermined motor characteristics. A predetermined parameter estimation method is used to calculate an estimated parameter related to motor characteristics, any one of the plurality of motors is selected as a reference motor, and a relative difference between the estimated parameter of the reference motor and the estimated parameters of other motors other than the reference motor is calculated as a characteristic difference. The difference in motor torque caused by the characteristic difference is reduced (step S3).

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] In Patent Document 1, there is described a control device for a motor, the object of which is to obtain an output torque accurately corresponding to a torque command even when the temperature rises. The control device for the motor described in Patent Document 1 presumes a temperature-dependent magnetic flux change (demagnetization characteristic) of the interlinkage magnetic flux in the permanent magnet of a permanent magnet synchronous motor (PM motor). And, it is configured to correct a torque current command value based on the presumed result of this magnetic flux change, thereby obtaining an output torque compensated for the demagnetization amount caused by temperature. Specifically, the following technique is described in Patent Document 1: calculating a magnetic flux estimated value (estimated value of interlinkage magnetic flux) based on a voltage equation in the rotating coordinate (dq coordinate) system of a PM motor, and using this magnetic flux estimated value and a motor model (a simulator that analogously realizes a motor equivalent to a PM motor), etc., to correct a magnetization current command value and a torque current command value.

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Patent No. 3467961 Gazette Summary of the Invention

[0006] Problems to be Solved by the Invention

[0007] The electric vehicle targeted in the present invention is equipped with at least two motors as driving power sources for generating driving force for traveling. For example, two motors for front-wheel drive and rear-wheel drive are provided, and these two drive motors are individually controlled, so that the driving force of the front wheels and the driving force of the rear wheels can be independently controlled. Or, two motors for driving the left wheels and the right wheels are provided, and these two drive motors are individually controlled, so that the driving force of the left wheels and the driving force of the right wheels can be independently controlled. Further, it may also be an electric vehicle in which drive motors are provided for all four wheels in the front, rear, left, and right, and these four drive motors are individually controlled, and the driving forces of all four wheels can be independently controlled.

[0008] In such an electric vehicle that independently drives the front and rear or left and right two wheels, or the four wheels of the front, rear, left, and right, in order to stabilize the straight running performance or improve the turning performance, it is necessary to simultaneously and independently control multiple motors with good precision. On the other hand, for example, temperature changes caused by the heat generation of the motor itself result in changes in the magnetic flux (magnetic flux density) of the magnets of the drive motor (synchronous motor) using the permanent magnets as described above. Moreover, due to the change in the magnetic flux of the magnets, the output characteristics of the motor will vary. There are inevitable individual differences in such changes in the output characteristics of the motors among the motors. There are also inevitable absolute errors when controlling the output torque of the motor. Therefore, for example, when the electric vehicle is running, if there are differences in the output characteristics between the left and right motors, it will pose an obstacle to the straight running stability of the electric vehicle. In addition, when the electric vehicle is turning, if there are differences (characteristic differences) 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 are differences in the output characteristics of each motor, the running stability and handling stability of the electric vehicle will decrease. Therefore, by applying the technique of using the voltage equation as described in the above Patent Document 1 to estimate the change in the magnetic flux of the magnet depending on the temperature, it is possible to obtain the characteristic differences of the motors and reflect them in the driving force control based on the output of the motors. In addition, in addition to the estimation technique using the voltage equation as described in the above Patent Document 1, for example, regression analysis using the least squares method, or parameter estimation methods such as sequential estimation using the sequential least squares method, the Kalman filter, etc. can also be applied to obtain the characteristic differences of the motors as described above. Thereby, it is possible to suppress the reduction of the running stability and handling stability of the electric vehicle as described above.

[0009] However, when estimating the magnetic flux of the magnet in the drive motor as described above, for example, there are inevitably individual differences in the motors, modeling errors other than the estimation object, etc., so it is difficult to accurately estimate the characteristic differences of the motors. In the technique of estimating the change in the magnetic flux of the magnet described in the above Patent Document 1 and other existing techniques, when estimating the magnetic flux of the magnet and the error of the current sensor, the voltage equation, equipment model, etc. in parameter estimation are used, and the parameters are estimated based on 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 equation or model of parameter estimation, the difference between the above equation or model and the actual measurement value or command value cannot be calculated appropriately. Such a deviation of the value is directly related to the estimation error of the magnetic flux as described above.

[0010] For example,

[0011] For y = ax + b (where y is the target variable and x is the independent variable), when calculating the error Δa of the constant a based on the measurable x, y, and the nominal values of the known constants a and b,

[0012] Transforming from y=(a + Δa)x + b to Δa=(y - ax - b) / x,

[0013] the error Δa can be obtained. However, when there is an unmeasurable (inevitable) modeling error e in the above calculation formula, assuming "y→y + e", when calculating the estimated value Δa of the error Δa _est it becomes

[0014] Δa _est =(y + e - ax - b) / x = Δa + e / x.

[0015] That is, Δa _est ≠Δa, and the error Δa or the model parameter (a + Δa) cannot be accurately calculated.

[0016] Therefore, in an electric vehicle that independently controls the driving forces of multiple wheels by separately controlling the output torques of multiple motors, as described above, due to the inevitable change in the magnetic flux of the magnet depending on the temperature change, there will be a difference in the characteristics of the motors. And due to this characteristic difference, the output torque of the motor cannot be properly controlled. As a result, it may lead to a decrease in the driving stability and handling stability of the electric vehicle.

[0017] The present invention is conceived in view of the above technical problems, and its purpose is to provide a control device for an electric vehicle, which is targeted at an electric vehicle that uses multiple motors as driving power sources and independently controls the driving forces of multiple wheels by separately controlling the output torques of these multiple motors, and can properly control the output torque of the motor and improve the driving stability and handling stability.

[0018] Solution to the problem

[0019] To achieve the above object, the present invention is a control device for an electric vehicle. The control device for the electric vehicle includes multiple motors that separately and independently drive multiple wheels, and separately controls the motor torque output according to a predetermined motor characteristic of each of the motors, so as to control the driving force generated on the wheels corresponding to the motors. The control device for the electric vehicle is characterized in that it includes a control unit that controls the electric vehicle and separately controls each of the motors. The control unit has: a parameter estimation unit that calculates an estimated parameter related to the motor characteristic using a predetermined parameter estimation method; a reference motor selection unit that selects any one of the multiple 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 the characteristic difference; and a motor torque control unit that reduces the difference in the motor torque caused by the characteristic difference.

[0020] Alternatively, it may be configured such that the parameter estimation unit in the present invention calculates at least any one of the estimated motor torques (estimated values of actual motor torques) of the respective motors, the estimated input powers of the respective motors, or the estimated torque constants of the respective motors as the estimated parameters, and the motor torque control unit in the present invention corrects a predetermined control target value in such a way as to reduce the difference in the motor torque caused by any one of the differences in the estimated motor torques, the differences in the estimated input powers, or the differences in the estimated torque constants.

[0021] Also, it may be configured such that the motors in the present invention are all synchronous motors constituted by using permanent magnets, the parameter estimation unit in the present invention calculates the magnetic flux of the permanent magnets as the estimated parameter, the characteristic difference calculation unit in the present invention calculates the difference in the magnetic flux as the characteristic difference, and the motor torque control unit in the present invention corrects the current value of the motor in such a way as to cancel the difference in the magnetic flux and thereby reduce the difference in the motor torque caused by the difference in the magnetic flux.

[0022] Effects of the Invention

[0023] In the present invention, the vehicle to be controlled is an electric vehicle having at least two motors as driving power sources, particularly an electric vehicle capable of driving the left and right or front and rear wheels, or the four wheels on the front, rear, left, and right, respectively, by independent multiple motors. Taking such an electric vehicle as the control object, in the control device of the electric vehicle of the present invention, motor characteristics such as the output characteristics, torque characteristics, or thermal characteristics of the respective motors are used as estimated parameters, and predetermined parameter estimation is performed. For example, general parameter estimation methods such as the least squares method and the maximum likelihood method are used to calculate the estimated parameters related to the motor characteristics. At the same time, a reference motor is arbitrarily selected from all the motors of the control object, and the relative difference between the estimated parameter of the reference motor and the estimated parameters of other motors is calculated as the characteristic difference. Then, based on this characteristic difference, the output torque of each motor, that is, the motor torque, is controlled. Specifically, each motor is controlled in such a way as to reduce the difference in the motor torque caused by the characteristic difference. Among the above-mentioned estimated parameters, there are inevitable estimation errors caused by measurement errors, modeling errors, etc. In contrast, by obtaining the relative characteristic difference as described above, the influence of the estimation errors included in the estimated parameters can be excluded or reduced. Therefore, each motor can be accurately controlled in a state where the influence of the estimation errors is removed. Furthermore, the driving force of the electric vehicle can be appropriately controlled.

[0024] In addition, in the control device of the electric vehicle according to the present invention, as the above-mentioned estimated parameters, for example, an estimated value of each motor torque (i.e., estimated motor torque), an estimated value of the power supplied to each motor (i.e., estimated input power of each motor), or an estimated value of the torque constant of each motor (i.e., estimated torque constant of each motor) is calculated. Then, based on the characteristic difference calculated according to the estimated parameters related to these estimated motor torques, estimated input powers, and estimated torque constants, each motor is controlled. 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. Or, the control target value of each motor torque is corrected so that the difference in the estimated input power becomes a desired value. Or, 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.

[0025] Moreover, in the control device of the electric vehicle according to the present invention, particularly when a synchronous motor using a permanent magnet is used as a control target, the magnetic flux of the permanent magnet of each motor is calculated as the above-mentioned estimated parameter. Then, based on the characteristic difference calculated according to the estimated parameter related to the magnetic flux of each motor, each motor is controlled. Specifically, the current value of each motor is corrected in such a way as to cancel the difference in the magnetic flux, thereby reducing the difference in the motor torque caused by the difference in the magnetic flux. Therefore, each motor can be more accurately controlled in a state where the influence of the estimation error is appropriately removed.

[0026] Thus, according to the control device of the electric vehicle of the present invention, for an electric vehicle that independently controls the driving forces of a plurality of wheels by separately controlling a plurality of motors mounted as driving force sources, the motor torque output by each motor can be appropriately controlled, and the driving stability and handling stability of the electric vehicle can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a diagram for explaining the structure of the electric vehicle that is the object of control in the present invention, and is a diagram schematically showing the drive system and the control system.

[0028] Figure 2 It is a diagram for explaining the structure of the electric vehicle that is the object of control in the present invention, and is a block diagram showing the specific structure of the control unit (ECU) that executes the control.

[0029] Figure 3 It is a flowchart for explaining an example of the control executed by the control device of the electric vehicle according to the present invention.

[0030] Figure 4This is a diagram for explaining an example of the control executed by the control device of the electric vehicle of the present invention, and is a timing diagram showing an image of the difference (flux error) in the estimated flux between two motors.

[0031] Description of Reference Numerals

[0032] 1. First motor (driving force source: MG1); 2. Second motor (driving force source: MG2); 3. Third motor (driving force source: MG3); 4. Fourth motor (driving force source: MG4); 5. Detection unit; 5a. Wheel speed sensor (of the detection unit); 5b. Motor 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 left wheel; 12. Front right wheel; 13. Rear left wheel; 14. Rear right wheel; Ve. Vehicle (electric vehicle). Detailed Embodiment

[0033] The embodiments of the present invention will be described with reference to the accompanying drawings. It should be noted that the following-described embodiments are merely examples of the cases where the present invention is embodied, and do not limit the present invention.

[0034] In the embodiment of the present invention, the vehicle to be controlled is an electric vehicle equipped with a plurality of motors as driving force sources. It can also be a hybrid vehicle equipped with an engine (internal combustion engine) together with a plurality of motors. At least the plurality of motors of the driving force source can independently control the driving torques of the left and right front wheels respectively. Or, it can independently control the driving torques of the left and right rear wheels respectively. Or, it can independently control the driving torques of the four wheels on the front, rear, left, and right. In the following embodiments, an example of a vehicle equipped with 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 is shown.

[0035] Figure 1 The shown electric vehicle (hereinafter, vehicle) Ve is equipped with a first motor (MG1) 1, a second motor (MG2) 2, a third motor (MG3) 3, and a fourth motor (MG4) 4 as driving force sources. And, the vehicle Ve is equipped with a detection unit 5 and a control unit (ECU) 6 for executing various controls.

[0036] Each of the motors 1, 2, 3, and 4 is constituted by, for example, a permanent magnet synchronous motor (PM motor). Each of the motors 1, 2, 3, and 4 has at least the function of a prime mover that outputs torque by being driven by supplied electric power. In addition, each of the motors 1, 2, 3, and 4 can also 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 can be a so-called motor generator that has both the function of a prime mover and the function of 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 function as a prime mover to output a driving torque. In addition, each of the motors 1, 2, 3, and 4 is driven by the torque transmitted from the wheels 11, 12, 13, and 14 described later. At this time, each of the motors 1, 2, 3, and 4 can also function as a generator, and the generated electric power can be used to charge the battery.

[0037] It should be noted that each of the motors 1, 2, 3, and 4 can also be constituted by, for example, an induction motor that does not use a permanent magnet. However, in the embodiment of the present invention, by using each of the motors 1, 2, 3, and 4 constituted by the permanent magnet synchronous motor (PM motor) as described above as a control object, as will be described later, the effect of the control device of the electric vehicle in the embodiment of the present invention can be obtained more effectively.

[0038] The first motor 1 drives the left front wheel 11. For example, the first motor 1 and the front wheel 11 are connected via a predetermined transmission mechanism such as a reduction gear (not shown) so as to be able to transmit power. Alternatively, as a so-called "in-wheel motor", the first motor 1 can be disposed inside the wheel (not shown) of the front wheel 11, and the first motor 1 can be directly connected to the front wheel 11.

[0039] The second motor 2 drives the right front wheel 12. For example, the second motor 2 and the front wheel 12 are connected via a predetermined transmission mechanism such as a reduction gear (not shown) so as to be able to transmit power. Alternatively, as a so-called "in-wheel motor", the second motor 2 can be disposed inside the wheel (not shown) of the front wheel 12, and the second motor 2 can be directly connected to the front wheel 12.

[0040] The third motor 3 drives the left rear wheel 13. For example, the third motor 3 and the rear wheel 13 are connected via a predetermined transmission mechanism such as a reduction gear (not shown) so as to be able to transmit power. Alternatively, as a so-called "in-wheel motor", the third motor 3 can be disposed inside the wheel (not shown) of the rear wheel 13, and the third motor 3 can be directly connected to the rear wheel 13.

[0041] The fourth motor 4 drives the right rear wheel 14. For example, the fourth motor 4 and the rear wheel 14 are connected via a predetermined transmission mechanism such as a reduction gear (not shown) in a manner capable of transmitting power. Alternatively, as a so-called "hub motor", the fourth motor 4 may be disposed inside the wheel (not shown) of the rear wheel 14, and the fourth motor 4 may be directly connected to the rear wheel 14.

[0042] The detection unit 5 is a device or apparatus for acquiring various data and information required for controlling the vehicle Ve, and includes, for example, a power supply unit, a microcomputer, sensors, and an input / output interface. In particular, in the embodiment of the present invention, the detection unit 5 respectively detects the running 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 torques (output torques of the motors 1, 2, 3, 4).

[0043] Specifically, the detection unit 5 has, for example: wheel speed sensors 5a that respectively detect the rotational speeds of the wheels 11, 12, 13, 14; motor 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 has, for example, a 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). Moreover, 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 / or apparatuses as described above to the control unit 6 as detection data.

[0044] The control unit 6 is an electronic control device mainly composed of a microcomputer. In the embodiment of the present invention, the control unit 6 respectively controls the motors 1, 2, 3, 4 for driving the vehicle, and controls the driving force of the vehicle Ve. Various data detected or calculated by the detection unit 5 are input to the control unit 6. The control unit 6 performs operations using the input various data and pre-stored data, calculation formulas, etc. And the control unit 6 is configured to output the operation result as a control command signal. As described above, it mainly executes the driving force control of the vehicle Ve based on the outputs of the motors 1, 2, 3, 4.

[0045] Specifically, in order to control each of the motors 1, 2, 3, and 4 for driving the vehicle, the control unit 6 in the embodiment of the present invention performs appropriate driving force control of the vehicle Ve. For example, as Figure 2 shown, 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.

[0046] 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 methods such as sequential least squares method and 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 (i.e., the estimated motor torque), the estimated value of the power supplied to each of the motors 1, 2, 3, and 4 (i.e., 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 (i.e., the estimated torque constant of each of the motors 1, 2, 3, and 4), or the magnetic flux of the permanent magnets (not shown) of each of the motors 1, 2, 3, and 4 are calculated as the estimated parameters of each of the motors 1, 2, 3, and 4.

[0047] 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 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 one of the "motors" fixedly selected in advance can also be selected as the "reference motor".

[0048] 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 the "other motors" other than the "reference motor" as the "characteristic difference". Among the estimated parameters calculated using the predetermined parameter estimation method as described above, there are inevitable estimation errors caused by measurement errors, modeling errors, etc. Therefore, in the characteristic difference calculation unit 6c, by calculating the relative difference from the estimated parameters of the "reference motor" as the "characteristic difference", the influence of the estimation errors included in the estimated parameters can be excluded or reduced.

[0049] The motor torque control unit 6d corrects a predetermined control target value in such a way as to reduce the difference in motor torque caused by the above-mentioned "characteristic difference", and controls the motor torques of the respective motors 1, 2, 3, and 4 (motor torque control). For example, the control target values of the motor torques of the respective motors 1, 2, 3, and 4 are corrected in such a way that the difference in the estimated motor torque (characteristic difference) becomes a desired value. Alternatively, the control target values of the motor torques of the respective motors 1, 2, 3, and 4 are corrected in such a way that the difference in the estimated input power becomes a desired value. Alternatively, the actual torque constants of the respective motors 1, 2, 3, and 4 are corrected in such a way that the difference in the estimated torque constants of the respective motors 1, 2, 3, and 4 becomes a desired value. Alternatively, the current values of the respective motors 1, 2, 3, and 4 are corrected in such a way as to cancel the difference in the magnetic fluxes of the permanent magnets in the respective motors 1, 2, 3, and 4 and reduce the difference in motor torque caused by the difference in the magnetic fluxes. Therefore, by calculating the above-mentioned "characteristic difference", it is possible to accurately control the respective motors 1, 2, 3, and 4 with high precision in a state where the influence of the estimation error is appropriately removed.

[0050] It should be noted that, in the above Figure 1 , Figure 2 , an example in which one control unit 6 is provided is shown, but the control unit 6 in the embodiment of the present invention may also be provided in plural for each controlled device, equipment, or for each control content. In addition, Figure 2 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 are named for explaining the structure and functions of the control unit 6 in the embodiment of the present invention. As the control unit 6, it is sufficient to have the structures and functions of the respective arithmetic units 6a, 6b, 6c, and 6d described above.

[0051] As described above, the control device for an electric vehicle in the embodiment of the present invention targets a vehicle Ve that can independently control the driving forces of "a plurality of wheels" (for example, wheels 11, 12, 13, and 14) by separately controlling the output torques of "a plurality of motors" (for example, motors 1, 2, 3, and 4). 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, and 4 to improve the driving stability and handling stability of the vehicle Ve. Therefore, Figure 3 An example of the control executed by the control unit 6 is shown in the flowchart of

[0052] This Figure 3The control shown in the flowchart is executed while the vehicle Ve is running. For example, it is executed when the main switch (not shown), ignition switch (not shown), or equivalent power switch (not shown) of the vehicle Ve is turned on. First, in step S1, parameter estimation is performed for each of the motors 1, 2, 3, and 4. As described above, using a predetermined parameter estimation method, for example, the estimated motor torque, the estimated input power, the estimated torque constant, or the estimated value of the magnetic flux of the permanent magnet in 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. The estimated parameters calculated here can also be any one of the above-mentioned motor characteristics. Alternatively, multiple motor characteristics can be used from the motor characteristics.

[0053] Next, in step S2, comparison with the estimated parameters of the "reference motor" is performed. That is, the "characteristic difference" in the embodiment of the present invention is calculated. Specifically, first, the "reference motor" is selected. As described above, the "reference motor" is arbitrarily selected from each of the motors 1, 2, 3, and 4. For example, the "motor" having the estimated parameter closest to the average value of the estimated parameters calculated in the above step S1 is selected as the "reference motor". Alternatively, any one of the "motors" selected in advance and fixed is selected as the "reference motor". In addition, the "reference motor" can also be switched according to predetermined conditions and situations. For example, the temperatures of the motors 1, 2, 3, and 4 can be compared, and the "motor" showing the most average temperature can be selected as the "reference motor" at any time. In addition, the magnetic fluxes of the motors 1, 2, 3, and 4 can be compared, and the "motor" showing the most average magnetic flux can be selected as the "reference motor" at any time. Alternatively, the degrees of change in the magnetic fluxes of the motors 1, 2, 3, and 4 can be compared, and the "motor" showing the most stable degree of change in the magnetic flux can be selected as the "reference motor" at any time. Or, according to the running state of the vehicle Ve, the "motor" in an appropriate position at that time can be selected as the "reference motor" at any time. In the following embodiments, an example of the case where the motor 1 is selected as the "reference motor" is described.

[0054] Then, the relative difference between the estimated parameters of the "reference motor" (motor 1) selected as described above and the "other motors" (motors 2, 3, and 4) other than the "reference motor" is calculated as the "characteristic difference".

[0055] For example, if the estimated parameter related to the magnetic flux of the nth "motor" (MGn) is set to and its true value is then due to the inevitable error e in the estimation model, mathematical formula (for example, voltage equation, motion equation), etc. used in the parameter estimation n , it becomes

[0056]

[0057] The absolute accuracy of parameter estimation reduces the error e n amount.

[0058] Then, the estimated parameters of the "reference motor" (motor 1) are carried out and the estimated parameters of each of the other motors 2, 3, 4 (n = 2, 3, 4) are compared, and the characteristic difference is calculated as their relative difference. For example, as shown in Figure 4 the timing chart of, the estimated parameters of the "reference motor" (motor 1) at a predetermined time t1 are calculated and the relative difference between the estimated parameters of motor 2 is used as the characteristic difference

[0059] Estimated parameter The estimation error e1 included in is an inevitable error of the estimation model and mathematical formula as described above. If the characteristics not reflected in the estimation model and mathematical formula (for example, the dead time of each of the motors 1, 2, 3, 4, the resistance of the wire, etc.) 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, the estimation error e1 in this case becomes

[0060] e1 = e2 = e3 = … = e n

[0061] Therefore, the relative difference from the estimated parameters of the "reference motor" (motor 1), that is, the characteristic difference is

[0062]

[0063] From this characteristic difference the influence of the estimation error e1 (= e n ) is removed.

[0064] Next, in step S3, the process using the relative difference (characteristic difference) of the estimated parameters is implemented. That is, the motor torque control in the embodiment of the present invention is executed. Specifically, each of the motors 1, 2, 3, 4 is controlled in such a way that the difference in motor torque caused by the characteristic difference calculated as described above is reduced.

[0065] As an example, the current values of each of the motors 1, 2, 3, and 4 are corrected in such a way as to cancel out the difference in the magnetic fluxes of the permanent magnets in the motors 1, 2, 3, and 4, thereby reducing the difference in the motor torques caused by the difference in the magnetic fluxes. For example, if the difference in the magnetic flux between the "reference motor" (motor 1) and the magnetic flux of motor 2 (i.e., the characteristic difference) is set to then the difference in the motor torque (torque difference) ΔT caused by this magnetic flux difference becomes

[0066] (n p is the number of motor poles, and i q2 is the q-axis current of motor 2)

[0067] Then, the current command value of motor 2 is corrected in such a way that this torque difference ΔT becomes 0, and the motor torque of motor 2 is controlled.

[0068] In step S4, an end determination of the control shown in the flowchart of this Figure 3 is performed. 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 has ended. Therefore, when it is determined as "No" in this step S4 because the end determination of the control has not been made yet, the process returns to the aforementioned step S1, and the same control as before is repeated.

[0069] Then, when it is determined as "Yes" in this step S4 because there is an end determination of the control, the routine shown in the flowchart of this Figure 3 is ended.

[0070] In this way, the vehicle Ve that is the control object in the embodiment of the present invention is an "electric vehicle (including a hybrid vehicle)" that can use at least two "motors" as driving force sources and drive "multiple wheels" by independent "multiple motors" respectively. Taking such a vehicle Ve as the control object, in the control device of the 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 the estimated parameters related to the motor characteristics such as the output characteristics, torque characteristics, or thermal characteristics of each of the motors 1, 2, 3, and 4. At the same time, a "reference motor" (motor 1 in the above embodiment) is arbitrarily selected from all of the motors 1, 2, 3, and 4 that are the control objects, and the relative difference between the estimated parameter of this "reference motor" and the estimated parameters of the "other motors" (motors 2, 3, and 4 in the above embodiment) is calculated as the "characteristic difference". Then, each of the motors 1, 2, 3, and 4 is controlled in such a way that the difference in the motor torques caused by this "characteristic difference" is reduced. As a result, the influence of the estimation error included in the estimated parameters can be eliminated or reduced, and each of the motors 1, 2, 3, and 4 can be accurately controlled. Furthermore, the driving force of the vehicle Ve can be appropriately controlled.

[0071] Therefore, for an electric vehicle Ve that controls the driving forces of a plurality of wheels 11, 12, 13, and 14 independently by controlling a plurality of motors 1, 2, 3, and 4 mounted as driving force sources respectively, the control device of the electric vehicle according to an embodiment of the present invention can appropriately control the motor torques output by the respective motors 1, 2, 3, and 4, and improve the driving stability and handling stability of the electric vehicle Ve.

Claims

1. A control device for an electric vehicle, the electric vehicle comprising a plurality of motors for independently driving a plurality of wheels, wherein the motor torque output by each of the motors is controlled according to a predetermined motor characteristic, thereby controlling the driving force generated at the wheels corresponding to the motors, characterized in that: The control device for the electric vehicle includes a control unit that controls the electric vehicle and controls each of the motors. The control unit has: a parameter estimating unit that calculates an estimated parameter related to the motor characteristic using a predetermined parameter estimating method; a reference motor selecting 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 parameter of the other motors other than the reference motor as a characteristic difference; as well as The motor torque control unit reduces the difference in the motor torque caused by the characteristic difference.

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

3. The control device for an electric vehicle according to claim 1 or 2, characterized in that: The motors are all synchronous motors using permanent magnets. The parameter estimating unit calculates the magnetic flux of the permanent magnet as the estimated parameter, The characteristic difference calculation unit calculates the difference in the magnetic flux as the characteristic difference, The motor torque control unit corrects 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.

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