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 A calculation unit 11 calculates the slip ratio λ of the drive wheel W, and based on the slip ratio λ, D Slip condition where the drive wheel W slips D A determination unit 12 determines one of the grip states in which the drive wheel W grips the road surface, and D The system includes a feedback control unit 13 that, when it is determined that the system is in a slip state, reduces the proportional term gain Kp and the integral term gain Ki of the feedback control compared to when it is determined that the system is in a grip state.

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 vehicle's weight inertial 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 of the present invention is a control device that measures an actual rotational speed of a motor that drives driving wheels of an electric vehicle and performs feedback control so 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 driving wheels to calculate a slip ratio of the driving wheels; a determination unit that determines, based on the slip ratio, whether the driving wheels are in a slip state where the driving wheels slip or a grip state where the driving wheels grip a road surface; and a feedback control unit that reduces a gain of the feedback control when it is determined that the driving wheels are in the slip state, compared to when it is determined that the driving wheels are in the grip state. [Effect of the Invention]

[0007] The control device of the present invention determines whether the driving wheels are in the slip state or the grip state based on the slip ratio calculated from the vehicle speed and the wheel speed of the electric vehicle, and reduces the gain of feedback control for the motor in the slip state compared to that in the grip state. Accordingly, the control device can control the motor with an appropriate feedback gain even in the slip state where the influence of vehicle weight inertia force is reduced. 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 the slip state. [Brief Description of the Drawings]

[0008] [Figure 1] FIG. 1 is a block diagram of an electric vehicle to which the control device according to the present disclosure is applied. [Figure 2] FIG. 2 is a flowchart showing a procedure of feedback control by the control device. [Figure 3] FIG. 3 is an example of a waveform representing a relationship between a slip ratio and a driving force of the driving wheels. [Figure 4] FIG. 4 is a conceptual diagram explaining a calculation procedure of a required inertia force in the grip state. [Figure 5] FIG. 5 is a control block diagram of feedback control for the motor. [Figure 6]It is a conceptual diagram explaining the calculation procedure of friction torque in a slip state. MODE FOR CARRYING OUT THE INVENTION

[0009] Hereinafter, embodiments will be described in detail with reference to the drawings. The present disclosure is not limited to the content described below, and can be arbitrarily modified and implemented without changing the gist of the present disclosure. In addition, all drawings used for describing the embodiments schematically show constituent members, and are partially emphasized, enlarged, reduced or omitted to facilitate understanding, and may not accurately represent the scale, shape, etc. of the constituent members.

[0010] FIG. 1 is a block diagram of an electric vehicle 1 to which the control device 10 according to the present disclosure is applied. Among the plurality of wheels W of the electric vehicle 1, drive wheels W D is an electric vehicle (EV) including a battery 2, an inverter 3, a motor 4, a reduction gear 5, a differential gear 6, an axle 7, a wheel speed sensor 8, a vehicle speed sensor 9, and the control device 10 as a configuration for applying a driving force to travel and drive the vehicle. The electric vehicle 1 is equipped with various components mounted on known electric vehicles in addition to the illustrated configuration.

[0011] The battery 2 is a power storage device formed of a lithium-ion battery or a nickel-metal hydride battery, and outputs electric power necessary for driving the motor 4, and also supplies electric power to various unillustrated electrical devices mounted on the electric vehicle 1.

[0012] The inverter 3 is a power conversion device that converts between direct-current power and alternating-current power. It converts the direct-current power output by the battery 2 into alternating-current power and supplies it to the motor 4, thereby rotating and driving the motor 4. In addition, when the motor 4 performs regenerative power generation, the inverter 3 can convert the alternating-current power of the motor 4 into direct-current power and supply the direct-current power to the battery 2, thereby charging 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 is a mechanism that increases torque by reducing the rotational driving force (torque) output from the motor 4 by a reduction 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, a determination unit 12, and a feedback control unit 13 as functional blocks for controlling the drive torque τ. The calculation unit 11 acquires the vehicle speed V of the electric vehicle 1 and the drive wheels W D and the wheel speed Vw of the drive wheels W D to calculate the slip ratio λ.

[0021] The determination unit 12 determines, based on the slip ratio λ, whether the drive wheels W D are in a slipping state where they idle or the drive wheels W D are in a gripped state where they grip the road surface.

[0022] As will be described in detail later, the feedback control unit 13 calculates a feedback gain from the 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 drive torque τ calculated based on the feedback gain.

[0023] Next, feedback control executed by the control device 10 will be described. FIG. 2 is a flowchart showing the procedure of feedback control by the control device 10. The control device 10 controls the motor 4 in accordance with the traveling state of the electric vehicle 1 by repeatedly executing the procedure of this flowchart while the ignition of the electric vehicle 1 is ON.

[0024] When the feedback control procedure is started, the control device 10 calculates the slip ratio λ in the calculation unit 11 (step S1). FIG. 3 is an example of a waveform representing the relationship between the slip ratio λ and the driving force of the drive wheels W D The control device 10 acquires the vehicle speed V of the electric vehicle 1 and the wheel speed Vw of the drive wheels W D and calculates the slip ratio λ, which is the degree of deviation between the two, using the calculation formula shown in FIG. 3.

[0025] 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. The control device 10 controls the drive wheel W D To determine whether the drive wheel W is in a slipping or gripping state, D The slip ratio λ at which the driving force is maximum is stored in advance as λpeak.

[0026] In this case, if the control device 10 determines whether the vehicle is in a slip state or a grip state using λpeak as a single threshold, the control may become unstable due to continuous switching between the slip state and the grip state. Therefore, in order to introduce hysteresis into the determination of the slip state and the grip state, the control device 10 sets a first slip ratio λ1 that is slightly larger than λpeak and a second slip ratio λ2 that is slightly smaller than λpeak (step S2).

[0027] More specifically, the control device 10 determines that a state transition has occurred from a grip state to a slip state when the calculated slip ratio λ exceeds the state where it is greater than the first slip ratio λ1. Furthermore, the control device 10 determines that a state transition has occurred from a slip state to a grip state when the calculated slip ratio λ falls below the state where it is less than the second slip ratio λ2.

[0028] Furthermore, the control device 10 can reduce the possibility of frequent state transitions between slip and grip states occurring in a short period of time, even when the vehicle speed V of the electric vehicle 1 is relatively high, by setting a larger difference between the first slip ratio λ1 and the second slip ratio λ2 as the vehicle speed V of the electric vehicle 1 increases.

[0029] Furthermore, the determination of slip and grip states is not limited to determination based on the first slip ratio λ1 and the second slip ratio λ2. For example, the control device 10 can reduce the risk of frequent state transitions in a short period by determining the state transition between slip and grip states using λpeak and then prohibiting the determination of state transitions for a predetermined period. In addition, the control device 10 can effectively suppress frequent state transitions even when the vehicle speed V is relatively high by setting the predetermined period to be longer the faster the vehicle speed V of the electric vehicle 1 is.

[0030] Next, in this embodiment, the control device 10 determines whether the electric vehicle 1 is in a slipping state or a gripping state based on the calculated slip ratio λ and the first slip ratio λ1 or the second slip ratio λ2 (step S3).

[0031] If the control device 10 determines that there is no slipping condition (No in step S3), it calculates the required inertial force I required for the motor 4 in preparation for performing motor control according to the grip condition (step S4). The required inertial force I is calculated from the dynamics acting on the electric vehicle 1 as follows.

[0032] Figure 4 is a conceptual diagram illustrating the procedure for calculating the required inertial force I in the grip state. As shown in Figure 4, the drive wheel W in the grip state D The vehicle driving force f acting on the vehicle is expressed by equation (1) from the vehicle weight m and vehicle acceleration a. In this case, the vehicle acceleration a is the time derivative of the vehicle speed V acquired by the vehicle speed sensor 9, and the drive wheel W D It can be expressed as equation (2) as the product of the tire radius r and the wheel angular acceleration, which is the time derivative of the wheel speed Vw.

[0033] Furthermore, the axle torque τ applied to the axle 7 DS Since it is expressed as the product of the vehicle driving force f and the tire radius r, it can be expressed as equation (3) by substituting equation (2) into equation (1). Furthermore, the axle torque τ DSThis is expressed as shown in equation (4) using the vehicle weight inertial force Ji, which is the moment of inertia around the axle due to the vehicle weight. Therefore, the vehicle weight inertial force Ji can be calculated from equations (3) and (4) using the vehicle weight m and the tire radius r as shown in equation (5).

[0034] The required inertial force I for motor 4 is calculated as the motor inertial force Jm of motor 4 itself, plus the vehicle weight inertial force Ji around the axle due to the vehicle weight m, which is converted to a motor-related value using the reduction ratio N of the reduction gear 5, resulting in the converted vehicle weight inertial force Ji / N. 2 It can be expressed as the sum of and as shown in equation (6).

[0035] Next, the control device 10 calculates a gain for feedback control of the motor 4 based on the calculated required inertial force I (step S5). Figure 5 is a control block diagram of the feedback control for the motor 4. As shown in Figure 5, the control device 10 obtains the actual rotational speed ω of the motor 4 via a 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.

[0036] Here, PI control is represented by the transfer function shown in equation (7) using the proportional term gain Kp and the integral term gain Ki. Each gain is expressed as shown in equation (8) 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 required inertial force I calculated in step S4 and the pole p into equation (8).

[0037] 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 S6), and controls the motor 4 with the drive torque τ corresponding to the grip state (step S7).

[0038] Meanwhile, in step S3, the control device 10 controls the drive wheel W DIf it is determined that the vehicle is in a slip state (Yes in step S3), the required inertial force I for motor control according to the slip state is calculated (step S8). Here, the vehicle weight inertial force Ji, as in the grip state described above, does not act in the slip state. Therefore, the required inertial force I is only the motor inertial force Jm of the motor 4 itself.

[0039] Then, the control device 10 calculates the proportional term gain Kp and the integral term gain Ki by substituting the required inertial force I into equation (8) shown in Figure 5 (step S9), and also calculates the drive torque τ required for the motor 4 by PI control (step S10). In other words, the control of the motor 4 in the slip state has a lower feedback control gain compared to the control in the grip state. As a result, the control device 10 controls the drive wheel W D Even when the motor is in a slipping state, the motor rotation speed can be precisely controlled by feedback.

[0040] Furthermore, in a slipping state, 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.

[0041] Figure 6 is a conceptual diagram illustrating the procedure for calculating friction torque in a slipping state. The drive wheel W in a slipping state. D As shown in Figure 6, a frictional force f, expressed by equation (9) using the vehicle weight m, the coefficient of friction μ, and the acceleration due to gravity g, acts on the drive wheel W. D As a result of the frictional force f acting on the axle, the axle torque τ, represented by equation (10), is applied to the axle 7. DS This is activated. As a result, in addition to the above-mentioned drive torque τ, the motor 4 also uses the axle torque τ. DS The friction torque τ is expressed by equation (11), which is converted to the motor shaft. F This will require a torque equivalent to that.

[0042] Therefore, the control device 10 controls the friction torque τ mentioned above. FIn addition to calculating the friction torque τ calculated in step S10, the friction torque τ is added to the drive torque τ calculated in step S10. F The effect of friction is compensated for by adding (step S11).

[0043] Furthermore, friction torque τ F The value of is calculated using the theoretical formula shown in Figure 6. Also, the friction torque τ F The value of may be calculated by substituting the measured output torque and rotational acceleration of the motor 4 into equation (12). 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.

[0044] Furthermore, the control device 10 controls the friction torque τ in the slip state. F The motor 4 is controlled by the corrected drive torque τ (step S7). The control device 10 then repeats the procedure in Figure 2 for the duration that the electric vehicle 1 continues to travel, thereby accurately feedback-controlling the motor rotation speed regardless of whether the electric vehicle 1 is in a grip state or a slip state.

[0045] As described above, the control device 10 according to this disclosure drives the drive wheels W based on the slip ratio λ calculated from the vehicle speed V and wheel speed Vw of the electric vehicle 1. D The control device 10 determines whether the vehicle is in a slipping or gripping state and reduces the proportional term gain Kp and integral term gain Ki of the feedback control for the motor 4 in the slipping state compared to the gripping state. As a result, the control device 10 can control the motor 4 with appropriate feedback gains even in the slipping state, where the influence of the vehicle weight inertial force Ji is reduced. Therefore, according to the control device 10 of this disclosure, the motor rotation speed can be feedback-controlled with high accuracy even when the electric vehicle 1 is in a slipping state.

[0046] Furthermore, the feedback control unit 13 of the control device 10 calculates the converted vehicle weight inertial force Ji / N in the grip state. 2Based on the sum of the drive wheel W and the motor inertia force Jm, and in the slip state based on the motor inertia force Jm, the proportional term gain Kp and the integral term gain Ki are calculated. As a result, the control device 10 calculates the drive wheel W in both the slip state and the grip state. D The required inertial force I of the motor 4 can be set according to the state.

[0047] Furthermore, when a slip condition is determined, the feedback control unit 13 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.

[0048] Furthermore, the determination unit 12 of the control device 10 determines that a state transition has occurred from a grip state to a slip state when the slip ratio λ exceeds a predetermined first slip ratio λ1, and determines that a state transition has occurred from a slip state to a grip state when the slip ratio λ falls below a predetermined second slip ratio λ2 which is smaller than the first slip ratio λ1. This allows the control device 10 to have hysteresis in determining the slip state and grip state, reducing the risk of the control becoming unstable due to frequent state transition determinations in a short period of time. In this case, by setting a larger difference between the first slip ratio λ1 and the second slip ratio λ2 as the vehicle speed V of the electric vehicle 1 increases, the frequent occurrence of state transitions can be effectively suppressed even when the vehicle speed V is relatively high.

[0049] Furthermore, the determination unit 12 of the control device 10 can achieve the same effect as the hysteresis described above by prohibiting the determination of state transitions for a predetermined time after the state transition between the slip state and the grip state, thereby reducing the risk of control instability due to frequent state transition determinations in a short period of time. In this case, by setting a longer predetermined time the faster the vehicle speed V of the electric vehicle 1, frequent state transitions can be effectively suppressed even when the vehicle speed V is relatively fast.

[0050] This concludes the description of the embodiments, but this disclosure is not limited to the embodiments described above. For example, although the above embodiments are applied to electric vehicles (EVs), they can also be applied to hybrid electric vehicles (HEVs) or plug-in hybrid electric vehicles (PHEVs) that can be externally charged or supplied with external power, when the vehicle is driven by an electric motor (EV mode). [Explanation of Symbols]

[0051] 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 Judgment section 13 Feedback Control Unit W D Drive wheels V Vehicle speed vw wheel speed λ slip ratio λ1 First slip ratio λ2 Second slip ratio τ Drive Torque N Reduction ratio Kp proportional term gain Ki integral term gain

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 determination unit that determines, based on the slip ratio, either a slip state in which the drive wheel slips or a grip state in which the drive wheel grips the road surface, A control device comprising: a feedback control unit that, when it is determined that the drive wheel is in a slipping state, reduces the gain of the feedback control compared to when it is determined that the drive wheel is in a gripping state.

2. The feedback control unit, If the drive wheel is determined to be in the grip state, the gain is calculated based on the sum of the converted vehicle weight inertial force, which is obtained by converting the vehicle weight inertial force due to the vehicle's weight into a converted value around the motor, and the motor inertial force of the motor. The control device according to claim 1, wherein if the drive wheel is determined to be in the slip state, the gain is calculated based on the motor inertia force.

3. The control device according to claim 2, wherein when the drive wheel is determined to be in the slip state, 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.

4. The control device according to claim 3, wherein the value of the friction torque is calculated from the measured values ​​of the output torque and rotational angular acceleration of the motor.

5. The determination unit, When the slip ratio exceeds a predetermined first slip ratio, it is determined that a state transition has occurred from the grip state to the slip state. A control device according to any one of claims 1 to 4, wherein it is determined that a state transition has occurred from the slip state to the grip state when the slip ratio falls below a predetermined second slip ratio which is smaller than the first slip ratio.

6. The control device according to claim 5, wherein the determination unit sets the difference between the first slip ratio and the second slip ratio to be larger as the vehicle speed increases.

7. The control device according to any one of claims 1 to 4, wherein the determination unit prohibits determination of state transitions for a predetermined period of time after the state transition between the slip state and the grip state.

8. The control device according to claim 7, wherein the determination unit sets the predetermined time to be longer the faster the vehicle speed.

Images