control device

Abstract

Even when the electric vehicle is slipping, the motor rotation speed is precisely controlled by feedback. [Solution] The control device 10 controls the drive wheels W of the electric vehicle 1. D A control device 10 that measures the actual rotational speed of the motor 4 that drives the motor 1 and provides feedback control so that the motor 4 rotates at a target rotational speed, wherein the vehicle speed V of the electric vehicle 1 and the drive wheel W D Get the wheel speed Vw and drive wheel W D The system includes a calculation unit 11 that calculates the slip ratio λ, and a feedback control unit 12 that continuously decreases the proportional term gain Kp and integral term gain Ki of the feedback control as the slip ratio λ increases.

Description

[Technical Field]

[0001] This invention relates to a control device for electric vehicles. [Background technology]

[0002] Conventionally, control devices have been proposed for electric vehicles that include a motor for driving, which use feedback control to ensure that the motor's rotation angle and input current reach target control values ​​(see, for example, Patent Document 1). When controlling the motor rotation speed with such an electric vehicle control device, a gain calculated based on the equivalent moment of inertia of the motor's rotation axis is generally used. More specifically, the equivalent moment of inertia of the motor's rotation axis is calculated as the sum of the rotational inertia force of the motor's rotor itself and the inertia force obtained by converting the moment of inertia around the axle due to the vehicle weight and tires, etc., into a value equivalent to that around the motor's rotation axis. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2021-35146 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, in a slip state where the vehicle speed of the electric vehicle and the wheel speed of the drive wheels diverge, a difference arises between the calculated value of the axle inertia force and the actual value. For this reason, conventional control devices based on the moment of inertia as described above may not be able to accurately feedback control the motor rotation speed.

[0005] This invention has been made in view of these problems, and its objective is to provide a control device that can accurately feedback control the motor rotation speed even when the electric vehicle is in a slipping state. [Means for solving the problem]

[0006] To achieve the above object, a control device according to the present invention is a control device that measures an actual rotational speed of a motor that drives drive wheels of an electric vehicle and performs feedback control such that the motor rotates at a target rotational speed, comprising: a calculation unit that acquires a vehicle speed of the electric vehicle and a wheel speed of the drive wheels to calculate a slip ratio of the drive wheels; and a feedback control unit that continuously decreases a gain of the feedback control as the slip ratio increases. Effects of the Invention

[0007] In an electric vehicle driven by feedback control of a motor, the control device of the present invention calculates a slip ratio, which is a degree of deviation between a vehicle speed and a wheel speed, and continuously decreases the gain of feedback control in accordance with an increase in the slip ratio. Accordingly, even when an equivalent moment of inertia around a motor rotation shaft changes along with an increase in the slip ratio, the control device can continuously reduce motor torque so as to follow the change. Therefore, according to the control device of the present invention, the rotational speed of the motor can be accurately feedback-controlled even when the electric vehicle is in a slipped state. Brief Description of the Drawings

[0008] [Figure 1] It is a block diagram of an electric vehicle to which a control device according to the present disclosure is applied. [Figure 2] It is a flowchart showing a procedure of feedback control by a control device. [Figure 3] It is an example of a waveform representing a relationship between a slip ratio and a driving force of a drive wheel. [Figure 4] It is a conceptual diagram explaining dynamics around an axle in a procedure for calculating an equivalent inertia force. [Figure 5] It is a conceptual diagram explaining dynamics around a motor in a procedure for calculating an equivalent inertia force. [Figure 6] It is a control block diagram of feedback control for a motor. [Figure 7] It is a conceptual diagram explaining a procedure for calculating friction torque. [Modes for carrying out the invention]

[0009] The embodiments will be described in detail below with reference to the drawings. However, this disclosure is not limited to the content described below, and can be modified and implemented as such without altering its essence. Furthermore, the drawings used in describing the embodiments are schematic representations of the components, and may have been partially emphasized, enlarged, reduced, or omitted to enhance understanding, and may not accurately represent the scale or shape of the components.

[0010] Figure 1 is a block diagram of an electric vehicle 1 to which the control device 10 according to this disclosure is applied. The electric vehicle 1 has multiple wheels W, of which the drive wheels W D The electric vehicle (EV) is configured to provide driving force to the vehicle and drive it, and includes a battery 2, inverter 3, motor 4, reduction gear 5, differential gear 6, axle 7, wheel speed sensor 8, vehicle speed sensor 9, and control device 10. In addition to the configuration shown, the electric vehicle 1 is also equipped with various components that are known to be installed in electric vehicles.

[0011] Battery 2 is an energy storage device consisting of a lithium-ion battery or a nickel-metal hydride battery, which outputs the power necessary to drive the motor 4 and also supplies power to various electrical equipment (not shown) mounted on the electric vehicle 1.

[0012] The inverter 3 is a power conversion device that converts DC power to AC power. It converts the DC power output by the battery 2 into AC power and supplies it to the motor 4, thereby driving the motor 4 to rotate. In addition, when the motor 4 is generating regenerative power, the inverter 3 can charge the battery 2 by converting that AC power back into DC power and supplying it to the battery 2.

[0013] Motor 4 is a traction motor that generates driving force to propel the electric vehicle 1 when power is supplied from inverter 3, and is also a motor generator that can regenerate power when the electric vehicle 1 is decelerating.

[0014] The reduction gear 5 receives the rotational driving force (motor torque τ) output from the motor 4. m This mechanism increases torque by reducing the gear ratio N. The reduction ratio of the reduction gear 5 is set appropriately according to the output characteristics and performance of the motor 4.

[0015] The differential gear 6 transmits torque from the reduction gear 5 to the left and right drive wheels W according to the driving conditions of the electric vehicle 1. D It is a mechanism for distribution.

[0016] Axle 7 controls the torque transmitted from differential gear 6 to the left and right drive wheels W D This is a drive shaft for rotating and driving the device.

[0017] The wheel speed sensor 8 controls the drive wheel W D This is a sensor for measuring the rotational speed, or wheel speed Vw.

[0018] The vehicle speed sensor 9 is a sensor for measuring the vehicle speed V, which is the driving speed of the electric vehicle 1.

[0019] The control device 10 is an electronic control unit that performs overall control of the electric vehicle 1, and is composed of input / output devices, memory devices (ROM, RAM, non-volatile RAM, etc.), a central processing unit (CPU), etc. In this embodiment, the control device 10 controls the drive wheels W via the wheel speed sensor 8. D The control device 10 acquires the wheel speed Vw and the vehicle speed V of the electric vehicle 1 via the vehicle speed sensor 9. Furthermore, as will be described in detail later, the control device 10 calculates the slip ratio λ of the electric vehicle 1 based on the wheel speed Vw and vehicle speed V, and controls the drive torque τ of the motor 4 so that the wheel speed Vw becomes appropriate according to the slip ratio λ.

[0020] The control device 10 includes a calculation unit 11 and a feedback control unit 12 as functional blocks for controlling the drive torque τ. The calculation unit 11 calculates the vehicle speed V of the electric vehicle 1 and the drive wheel WD and wheel speed Vw to calculate the slip ratio λ of drive wheels W D . As will be described in detail later, the feedback control unit 12 calculates a feedback gain from a moment of inertia adjusted based on the difference between the target rotational speed ωt and the actual rotational speed ω of the motor 4 and the slip ratio λ, and controls the motor 4 with the driving torque τ calculated based on the feedback gain.

[0021] Next, feedback control executed by the control device 10 will be described. Figure 2 is a flowchart showing the procedure of feedback control by the control device 10. The control device 10 repeatedly executes the procedure of the flowchart while the ignition of the electric vehicle 1 is ON, thereby controlling the motor 4 in accordance with the traveling state of the electric vehicle 1.

[0022] When the procedure of feedback control is started, the control device 10 causes the calculation unit 11 to calculate the slip ratio λ (step S1). Figure 3 shows the relationship between the slip ratio λ and the driving force of drive wheels W D as an example of a waveform. The control device 10 acquires the vehicle speed V of the electric vehicle 1 and the wheel speed Vw of drive wheels W D and can calculate the slip ratio λ, which is the degree of deviation between the two, using the calculation formula shown in Figure 3. In addition, as shown in the calculation formula, the slip ratio λ can also be expressed by the tire radius r of drive wheels W D and the wheel rotational speed ω W .

[0023] Here, the drive wheels W DAs shown in Figure 3, the driving force increases in proportion to the slip ratio λ in the region where the slip ratio λ is close to 0, but then decreases after peaking at a value corresponding to the friction force f = Mgμpeak. μpeak represents the maximum friction coefficient. Here, since the equivalent inertial force of the motor rotation shaft changes as the slip ratio λ increases, if the motor 4 were controlled based on the equivalent inertial force as in the conventional method, there was a risk that the motor rotation speed could not be accurately feedback controlled. Therefore, the control device 10 according to this disclosure controls the motor 4 with a feedback gain using the equivalent inertial force I(λ) with the slip ratio λ as a variable, in accordance with the procedure described below, thereby controlling the drive wheel W D The motor 4 is controlled with appropriate torque that follows the state.

[0024] The control device 10 calculates the slip ratio λ and then calculates the equivalent inertial force I(λ) (step S2). Figure 4 is a conceptual diagram illustrating the mechanics around the axle in the calculation procedure for the equivalent inertial force I(λ). As shown in Figure 4, the equation of motion around the rotation axis of the axle 7 is given by the wheel rotational acceleration and the drive wheel W D Axle inertia force J around the axle, such as brake rotors. DS , axle torque τ DS , drive wheel W D The equation of motion for the electric vehicle 1 itself is expressed as shown in equation (1), using the vehicle's driving force F.

[0025] Here, the vehicle speed V of electric vehicle 1 is calculated from the slip ratio λ calculation formula in Figure 3, and the drive wheel W D The tire radius r and wheel rotation speed ω W It can be expressed as in equation (3) using and . Then, by differentiating both sides of equation (3) with respect to time, and substituting the new equation obtained and equation (2) into equation (1), the relationship shown in equation (4) is derived.

[0026] Next, the axle torque τ DSThis is converted to torque around the rotation axis of motor 4, and the equation of motion around the motor axis is derived by adding it to the motor inertial force Jm. Figure 5 is a conceptual diagram illustrating the mechanics around the motor in the procedure for calculating the equivalent inertial force I(λ). As shown in Figure 5, the equation of motion around the rotation axis of motor 4 is the motor torque τm output by motor 4 and the above axle torque τ DS The value obtained by dividing this by the gear ratio can be expressed as shown in equation (5).

[0027] Here, axle torque τ DS Regarding this, by rearranging equation (4) above, it can be expressed as in equation (6). Also, the motor rotation speed ωm and the wheel rotation speed ω W In relation to the torsional resonance frequency, in the low-frequency region below the torsional resonance frequency, the relationship can be approximated as shown in equation (7). Therefore, by differentiating both sides of equation (7) and substituting them into equation (5) along with equation (6), the motor torque τm can be expressed by equation (8).

[0028] Then, the equivalent inertial force I(λ) can be expressed by equation (9) from the relationship between the motor torque τm around the motor shaft and the motor rotational acceleration in equation (8). This gives the axle inertial force J due to the vehicle weight M of the electric vehicle 1. DS The converted axle inertia force Ji(λ), obtained by converting it to a value around the motor, can be expressed as shown in equation (10). In other words, the control device 10 can calculate the equivalent inertia force I(λ) by calculating the converted axle inertia force Ji(λ) according to the slip ratio λ using equation (10) and adding it with the motor inertia force Jm obtained from the motor 4.

[0029] Returning to Figure 2, the control device 10 calculates a gain for feedback control of the motor 4 based on the calculated equivalent inertial force I(λ) (step S3). Figure 6 is a control block diagram of the feedback control for the motor 4. As shown in Figure 6, the control device 10 obtains the actual rotational speed ω of the motor 4 via the feedback circuit and adjusts the drive torque τ to the motor 4 by PI control so that the actual rotational speed ω becomes the target rotational speed ωt.

[0030] Here, PI control is represented by the transfer function shown in equation (11) using the proportional term gain Kp and the integral term gain Ki. Each gain is expressed as shown in equation (12) using the pole p of the transfer function. Therefore, the control device 10 calculates the pole p from the characteristic equation of the transfer function and calculates the proportional term gain Kp and the integral term gain Ki by substituting the equivalent inertial force I(λ) calculated in step S2 and the pole p into equation (12).

[0031] Furthermore, the control device 10 calculates the drive torque τ required for the motor 4 by PI control using the calculated proportional term gain Kp and integral term gain Ki (step S4). Also, the control device 10 controls the drive wheel W D The accuracy of the feedback control may be further improved by correcting the drive torque τ calculated by PI control, taking into account the effect of friction.

[0032] Figure 7 is a conceptual diagram illustrating the procedure for calculating friction torque. As shown in Figure 7, the drive wheel W D A frictional force f acts on the drive wheel W, which is expressed by equation (13) using the vehicle weight M, the coefficient of friction μ, and the acceleration due to gravity g. D As a result of the frictional force f acting on the axle, the axle torque τ, represented by equation (14), is applied to the axle 7. DS This will result in the motor 4 working separately from the drive torque τ mentioned above, as well as the axle torque τ. DS The friction torque τ is expressed by equation (15), which is obtained by converting it to the motor shaft. f An equivalent torque will be required separately.

[0033] Therefore, the control device 10 controls the friction torque τ mentioned above. f The friction torque τ is calculated and the drive torque τ calculated in step S4 is added to the friction torque τ. f The effect of friction is compensated for by adding (step S5).

[0034] Furthermore, friction torque τ f The value of is calculated using the theoretical formula shown in Figure 7. Also, the friction torque τ fThe value of may be calculated by substituting the measured output torque and rotational acceleration of the motor 4 into equation (16). In this case, the calculation based on the measured values ​​will provide a more accurate friction torque τ corresponding to the driving conditions of the electric vehicle 1 compared to the calculation using the theoretical formula. f This allows for correction of the drive torque τ.

[0035] Furthermore, the control device 10 can continuously decrease the proportional term gain Kp and integral term gain Ki of the PI control via the equivalent inertial force I(λ) in response to an increase in the slip ratio λ of the electric vehicle 1 by repeating the procedure shown in Figure 2 during the period in which the electric vehicle 1 continues to run, thereby enabling accurate feedback control of the motor rotation speed.

[0036] As described above, the control device 10 according to this disclosure calculates the slip ratio λ, which is the degree of deviation between the vehicle speed V and the wheel speed Vw, in an electric vehicle 1 driven by feedback control of the motor 4, and continuously decreases the proportional term gain Kp and integral term gain Ki of the feedback control in accordance with the increase in the slip ratio λ. As a result, even when the equivalent inertial force I(λ) around the motor rotation axis changes due to the increase in the slip ratio λ, the control device 10 can continuously reduce the motor torque τm in accordance with the change. Therefore, with the control device 10 according to this disclosure, the motor rotation speed can be feedback controlled with high accuracy even when the electric vehicle 1 is in a slipping state. Furthermore, with the control device 10 according to this disclosure, since each feedback gain is continuously controlled in accordance with the slip ratio λ, the risk of sudden gain fluctuations can be reduced, and the control can be stabilized.

[0037] Furthermore, the control device 10 detects the axle inertia force J due to the vehicle weight M of the electric vehicle 1. DSThe converted axle inertia force Ji(λ), obtained by converting the value around the motor, is calculated based on the slip ratio λ, and each gain is calculated based on the sum of the converted axle inertia force Ji(λ) and the motor inertia force Jm of motor 4. As a result, the control device 10 can calculate each gain in accordance with the actual value of the converted axle inertia force Ji(λ) affected by the slip ratio λ, thereby enabling more accurate feedback control.

[0038] Furthermore, the control device 10 calculates the converted axle inertia force Ji(λ) as shown in equation (10) of Figure 5, thereby determining not only the slip ratio λ but also the axle inertia force around the axle J DS , drive wheel W D By considering the tire radius r, vehicle weight M, and gear ratio N, the torque can be calculated accurately.

[0039] Furthermore, the control device 10 calculates the drive torque τ based on the proportional term gain Kp and the integral term gain Ki, and the drive wheel W D The frictional force is converted to a value equivalent to the frictional torque τ around the motor. f The motor 4 is driven by the sum of and . This allows the control device 10 to compensate for the effect of friction in controlling the motor 4. At this time, the control device 10 controls the friction torque τ f By calculating the value of from the measured output torque and rotational acceleration of motor 4, a more accurate friction torque τ can be obtained according to the driving conditions of the electric vehicle 1. f This allows for correction of the drive torque τ.

[0040] This concludes the description of the embodiments, but this disclosure is not limited to the embodiments described above. For example, in the embodiments described above, the control device 10 according to this disclosure is applied to an electric vehicle (EV), but it can also be applied to a hybrid electric vehicle (HEV) or a plug-in hybrid electric vehicle (PHEV) capable of external charging or external power supply, when the vehicle is driven by an electric motor (EV mode). [Explanation of symbols]

[0041] 1 electric car 2 batteries 3 Inverter 4 motors 5 reduction gear 6 Differential Gear 7 axles 8. Wheel speed sensor 9. Vehicle speed sensor 10 Control device 11 Calculation Section 12 Feedback control unit W D Drive wheels V Vehicle speed vw wheel speed λ slip ratio τ Drive Torque N gear ratio Kp proportional term gain Ki integral term gain I(λ) equivalent inertia force Ji(λ) Converted axle inertia force Jm motor inertia force

Claims

1. A control device that measures the actual rotational speed of a motor that drives the drive wheels of an electric vehicle and provides feedback control to ensure that the motor rotates at a target rotational speed, A calculation unit that obtains the vehicle speed of the electric vehicle and the wheel speed of the drive wheel and calculates the slip ratio of the drive wheel, A control device comprising a feedback control unit that continuously reduces the gain of the feedback control as the slip ratio increases.

2. The control device according to claim 1, wherein the feedback control unit calculates a converted axle inertia force obtained by converting the axle inertia force due to the weight of the electric vehicle into a converted value around the motor, based on the slip ratio, and calculates the gain based on the sum of the converted axle inertia force and the motor torque of the motor.

3. The aforementioned converted axle inertia force is calculated by using the slip ratio as λ and the axle inertia force around the axle as J. ＤＳ The control device according to claim 2, wherein the following formula is used to calculate the tire radius of the drive wheel, the vehicle weight is M, and the gear ratio between the motor and the axle is N. [Math 1]

4. The control device according to any one of claims 1 to 3, wherein the feedback control unit drives the motor with the sum of the drive torque calculated based on the gain and the friction torque obtained by converting the friction force of the drive wheel into a value equivalent to that around the motor.

5. The control device according to claim 4, wherein the value of the friction torque is calculated from the measured values ​​of the output torque and rotational acceleration of the motor.

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