Electric vehicle traction control system and vehicle behavior control unit

Abstract

According to the present invention, in a system in which a motor control device has a traction control function that carries out a feedback control applying the rotation speed of drive wheels or a drive motor to a target rotation speed, execution of traction control can be stopped quickly once slip of the drive wheels has been eliminated. A vehicle behavior control unit 40 used in a traction control system 10 of an electric vehicle sets and outputs a target rotation speed v_tgt for traction control on the basis of a driving state of the electric vehicle 1, determines whether or not the behavior of the electric vehicle 1 is an unstable state while a motor control unit 50 is executing the traction control, and, when the behavior is not determined to be an unstable state and the elapsed time T_st since the behavior was no longer determined to be an unstable state has become equal to or greater than a prescribed threshold T_st_thr, outputs a stop command to stop execution of the traction control.

Description

[0001] [Document name] Statement

[0002] [Title of invention] Traction control system and vehicle behavior control unit for electric vehicles

[0003] [Technical Field]

[0004]

[001] The present invention relates to a traction control system and a vehicle behavior control unit for an electric vehicle.

[0005] [Background technology]

[0006]

[002] Various traction control devices that suppress slippage of a vehicle's drive wheels have been known. For example, Patent Document 1 discloses a traction control device in which a motor control unit, which controls a drive motor that outputs drive force to the drive wheels of an electric vehicle, sets a target rotation speed that can reduce slippage of the drive wheels when it detects that the drive wheels are slipping, and controls the output torque of the electric motor by executing feedback control based on the deviation between the actual rotation speed of the drive motor and the target rotation speed.

[0007] [Prior art documents]

[0008] [Patent documents]

[0009]

〇 0 0 3

[0010] [Patent Document 1] Japanese Patent Application Laid-Open No. 2021-164354

[0011] Summary of the Invention

[0012] [Problem to be solved by the invention]

[0013]

[0004] The traction control device described in the above Patent Document 1 does not convert the target torque for traction control set by the vehicle behavior control unit, also known as ESP (Electronic Stability Program), into the target rotation speed of the drive motor in the motor control device, but has a configuration in which the motor control device executes feedback control based on the deviation between the actual rotation speed of the drive motor and the target rotation speed for traction control. As a result, there is no time lag required for the process of converting the target torque into the target rotation speed, and quick traction control is possible by taking advantage of the characteristics of the drive motor, which can generate maximum torque from a low rotation speed range.

[0014]

[0005] However, motor control devices are generally not configured to directly acquire sensor signals capable of detecting vehicle behavior. Therefore, if the motor control device is equipped with a traction control function that feedback-controls the rotational speed of the drive motor, there is a risk that the execution of traction control will not be stopped even if the drive wheel slip has been resolved. For example, if the vehicle behavior control unit increases the target rotational speed from the target rotational speed for traction control after the understeer state is resolved, there is a risk that the rotational speed of the drive motor will be maintained at a value close to the target rotational speed for traction control. In this case, the motor control device will not be able to determine whether to stop traction control, and there is a risk that the rotational speed of the drive motor will be limited even if the driver subsequently depresses the accelerator pedal.

[0015]

[0006] The present invention has been made in consideration of the above problems, and provides a traction control system and a vehicle behavior control unit that can quickly stop the execution of traction control when slippage of the drive wheels is eliminated in a system in which a motor control device has a traction control function that feedback controls the rotational speed of a drive wheel or a drive motor to a target rotational speed.

[0016] [Means for solving the problem]

[0017]

[0007] In order to solve the above problem, according to one aspect of the present invention, a traction control system for an electric vehicle, in which drive wheels are driven by a drive motor, suppresses slip of the drive wheels by controlling the output of the drive motor when the drive wheels slip, comprises: a vehicle behavior control unit that performs the following: - setting a target rotation speed obtained by adding a predetermined target slip amount to a reference rotation speed of the drive wheels or the drive motor based on an operating state of the electric vehicle, and outputting information on the target rotation speed; and a motor control unit that performs the following: - starting execution of traction control to control the output of the drive motor by executing rotation speed feedback control to make the rotation speed of the drive wheels or the drive motor follow the target rotation speed when slip of the drive wheels is detected; and - stopping execution of the traction control when the rotation speed falls below the target rotation speed and a difference between the rotation speed and the target rotation speed exceeds a predetermined threshold, wherein the vehicle behavior control unit: The traction control system for an electric vehicle is characterized in that, while the motor control unit is executing the traction control, it determines whether or not the behavior of the electric vehicle is unstable, and when it is determined that the behavior is not unstable and the elapsed time since the behavior is no longer determined to be unstable reaches or exceeds a predetermined minimum value, it outputs a stop command to stop the execution of the traction control.

[0018]

[0008] To solve the above problem, according to another aspect of the present invention, a vehicle behavior control unit used in a traction control system for an electric vehicle, in which drive wheels are driven by a drive motor, suppresses slip of the drive wheels by controlling the output torque of the drive motor when the drive wheels slip, comprises: - setting a target rotation speed for traction control by adding a predetermined target slip amount to a reference rotation speed of the drive wheels or the drive motor based on an operating state of the electric vehicle, and outputting information on the target rotation speed;

[0019] -While the motor control unit is executing traction control, it determines whether the behavior of the electric vehicle is unstable, and when it is determined that the behavior is not unstable and the elapsed time since the behavior is no longer determined to be unstable exceeds a predetermined minimum value, it outputs a stop command to stop the execution of the traction control.

[0020] [Effects of the Invention]

[0021]

[0009] As described above, according to the present invention, in a system in which a motor control device has a traction control function that feedback-controls the rotational speed of a drive wheel or a drive motor to a target rotational speed, when slippage of the drive wheel is eliminated, the execution of traction control can be quickly stopped.

[0022] BRIEF DESCRIPTION OF THE DRAWINGS

[0023] [ 0 0 1 0 ]

[0024] [Figure 1] An explanatory diagram showing an example of the configuration of a vehicle equipped with a traction control system according to an embodiment of the present invention.

[0025] [Figure 2] An explanatory diagram showing the configuration of the traction control system according to this embodiment in functional blocks.

[0026] [Figure 3] A flowchart showing an example of the processing operation of the vehicle behavior control unit according to this embodiment.

[0027] [Figure 4] A flowchart showing an example of the processing operation of the motor control unit according to this embodiment.

[0028] [Figure 5] An explanatory diagram showing the operation of the traction control system of this embodiment.

[0029] [Figure 6] An explanatory diagram showing the operation of the traction control system of this embodiment.

[0030] [Figure 7] A flowchart showing an example of the processing operation of a vehicle behavior control unit in another embodiment.

[0031] [Figure 8] A flowchart showing an example of the processing operation of a motor control unit according to another embodiment.

[0032] DETAILED DESCRIPTION OF THE INVENTION

[0033]

[0011] Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. In this specification and drawings, components having substantially the same functional configurations are designated by the same reference numerals, and redundant explanations will be omitted.

[0034]

[0012] <Basic configuration of vehicle> First, the basic configuration of a vehicle equipped with the traction control device of this embodiment will be described.

[0035]

[0013] Figure 1 shows an electric vehicle 1 equipped with a traction control system. The electric vehicle 1 is equipped with a drive motor 30, an inverter device 31, a battery 32, and a differential device 29. The electric vehicle 1 is an electric vehicle that runs using the output torque output from the drive motor 30. The electric vehicle 1 shown in Figure 1 is a front-wheel drive electric vehicle in which the output torque output from the drive motor 30 is distributed to the left and right front wheels via the differential device 29.

[0036]

[0014] The inverter device 31 is driven by the motor control unit 50, converts DC power supplied from the battery 32 into three-phase AC power, and supplies the converted three-phase AC power to the traction motor 30. The traction motor 30 operates as an electric motor that outputs drive torque for the drive wheels, and as a generator that generates electricity (regenerative power) using the rotational torque of the drive wheels. When operating as an electric motor, the traction motor 30 is driven by the three-phase AC power supplied from the inverter device 31. The output torque output from the traction motor 30 is transmitted to the right front wheel 11 and left front wheel 12 of the electric vehicle 1 via the differential device 29 and the drive shaft 19, thereby driving the right front wheel 11 and left front wheel 12 to rotate, and the electric vehicle 1 runs. Hereinafter, the right front wheel 11 and the left front wheel 12 will also be referred to as the drive wheels 11, 12.

[0037]

[0015] The drive motor 30 operates as a generator when braking the electric vehicle 1. Specifically, when braking the electric vehicle 1, braking torque applied to the right front wheel 11 and the left front wheel 12 is input to the drive motor 30 via the drive shaft 19 and the differential device 29. The drive motor 30 generates electricity using the braking torque input from the right front wheel 11 and the left front wheel 12. The three-phase AC power generated by the drive motor 30 is converted to DC power by the inverter device 31 and charged into the battery 32.

[0038]

[0016] When a difference in rotation speed occurs between the right front wheel 11 and the left front wheel 12, the differential 29 absorbs the difference in rotation speed and distributes the output torque output from the drive motor 30 to the right front wheel 11 and the left front wheel 12. The differential 29 may be provided with a differential limiting device that mechanically limits the differential rotation between the right front wheel 11 and the left front wheel 12 when the difference in rotation speed between the right front wheel 11 and the left front wheel 12 becomes equal to or exceeds a predetermined rotation speed.

[0039]

[0017] Friction brake devices 15-18 are provided on the wheels 11-14 of the electric vehicle 1, respectively. The friction brake devices 15-18 apply braking force to each wheel 11-14 by applying friction force to a rotating body that rotates integrally with each wheel 11-14. The friction brake devices 15-18 are, for example, hydraulic brake devices, and braking force is applied to each wheel 11-14 by supplying brake fluid pressure to each friction brake device 15-18 via a fluid pressure control device.

[0040] [ 0 0 1 8 ]

[0041] <Traction Control System> Next, we will explain the configuration of the traction control system of the electric vehicle 1. The traction control of the present invention may be performed using the rotation speed of the drive wheels 11, 12 as a parameter, or may be performed using the rotation speed of the drive motor 30 as a parameter. In this embodiment, we will explain an example in which traction control is performed using the rotation speed of the drive wheels 11, 12 as a parameter.

[0042]

[0019] Fig. 2 is an explanatory diagram showing the configuration of a traction control system 10 according to this embodiment in functional blocks. The electric vehicle 1 includes wheel speed sensors 21 to 24, an acceleration sensor 25, a yaw rate sensor 26, an accelerator opening sensor 27, a hydraulic pressure control device 28, a vehicle behavior control unit 40, a vehicle control unit 60, and a motor control unit 50.

[0043]

[0020] The vehicle behavior control unit 40, the vehicle control unit 60, and the motor control unit 50 each include a microcomputer having an arithmetic processing unit such as a CPU (Central Processing Unit) and a storage element such as a RAM (Random Access Memory) or a ROM (Read Only Memory). Some or all of these control units may be configured with updatable firmware or the like, or may be program modules executed by commands from the CPU or the like.

[0044]

[0021] As shown in Fig. 1, wheel speed sensors 21 to 24 are provided on wheels 11 to 14, respectively. Wheel speed sensors 21 to 24 detect the wheel speed, which is the rotational speed of each wheel 11 to 14, and output a signal corresponding to the detected wheel speed to vehicle behavior control unit 40. Acceleration sensor 25 detects the lateral acceleration of electric vehicle 1 and outputs a signal corresponding to the detected lateral acceleration to vehicle behavior control unit 40. Yaw rate sensor 26 detects the yaw rate, which is the angular velocity of electric vehicle 1 about the vertical axis, and outputs a signal corresponding to the detected yaw rate to vehicle behavior control unit 40.

[0045]

[0022] The accelerator opening sensor 27 detects the accelerator opening corresponding to the amount of depression of the accelerator pedal of the electric vehicle 1, and outputs a signal corresponding to the detected accelerator opening to the vehicle control unit 60.

[0046]

[0023] The hydraulic pressure control device 28 includes an oil pump and an electronically controlled valve (not shown), and is driven by the vehicle behavior control unit 40 to adjust the brake hydraulic pressure supplied to the friction brake devices 15-18 of each wheel 11-14.

[0047] [ 0 0 2 4 ]

[0048] (Vehicle behavior control unit) The vehicle behavior control unit 40 has the function of executing a computer program to perform control to stabilize the behavior of the electric vehicle 1. The control to stabilize the vehicle behavior is, for example, anti-skid control to suppress understeer or oversteer of the vehicle body, but other control may also be used.

[0049]

[0025] The vehicle behavior control unit 40 includes a processing unit 41 and a memory unit 47. The processing unit 41 includes an arithmetic processing device such as a CPU. The memory unit 47 includes one or more memory devices such as memory elements such as RAM and ROM, SSD (Solid State Drive) or HDD (Hard Disk Drive).

[0050]

[0026] The processing unit 41 includes a slip detection unit 42, a brake control unit 43, a target rotational speed setting unit 44, and a forced stop determination unit 45. The slip detection unit 42, the brake control unit 43, the target rotational speed setting unit 44, and the forced stop determination unit 45 are functions realized by the execution of a program by a processing device. However, part of the slip detection unit 42, the brake control unit 43, the target rotational speed setting unit 44, and the forced stop determination unit 45 may be configured by hardware such as an analog circuit.

[0051]

[0027] The slip detection unit 42 detects whether the vehicle behavior is unstable. For example, the slip detection unit 42 determines whether the electric vehicle 1 is oversteered or understeered, as an example of an unstable vehicle behavior. Specifically, the slip detection unit 42 determines whether the electric vehicle 1 is oversteered or understeered, based on the lateral acceleration of the electric vehicle 1 detected by the acceleration sensor 25 and the yaw rate of the electric vehicle 1 detected by the yaw rate sensor 26.

[0052]

[0028] When the slip detection unit 42 detects oversteer or understeer, the brake control unit 43 drives the hydraulic control device 28 to apply braking force to each wheel 11 to 14 using the friction brake devices 15 to 18, thereby automatically controlling the attitude of the electric vehicle 1 to bring it closer to an ideal driving state.

[0053]

[0029] The target rotational speed setting unit 44 sets a target rotational speed v-tgt by adding a predetermined target slip amount to the reference rotational speed v-ref of the drive wheels 11, 12 based on the operating state of the electric vehicle 1. The target rotational speed setting unit 44 also outputs information about the set target rotational speed v-tgt. In this embodiment, the target rotational speed setting unit 44 outputs information about the set target rotational speed v-tgt to the vehicle control unit 60. The target rotational speed setting unit 44 may also output information about the set target rotational speed v-tgt to the motor control unit 50.

[0054]

[0030] The reference rotational speed v_ref is the rotational speed of the drive wheels 11, 12 calculated using a predetermined calculation formula based on the operating state of the electric vehicle 1. For example, the reference rotational speed v_ref is the rotational speed of the drive wheels 11, 12 estimated based on the rotational speed v_m_t of the drive motor 30, the gear ratio of the torque transmission path from the drive motor 30 to the drive wheels 11, 12, and the brake fluid pressure of the friction brake devices 15, 16.

[0055]

[0031] The target rotational speed v_tgt is the target rotational speed v_tgt of the drive wheels 11, 12 while traction control is being executed, and is the target rotational speed v_tgt that allows the drive wheels 11, 12 to be driven while slipping to an extent that does not cause the behavior of the electric vehicle 1 to become unstable. The target slip amount to be added to the reference rotational speed v_ref is set to an appropriate value according to the vehicle behavior (slip state, understeer state, oversteer state, etc.) or the friction coefficient of the road surface estimated from the measurement results of sensors that detect weather and road surface conditions.

[0056]

[0032] While the motor control unit 50 is performing traction control, the forced stop determination unit 45 outputs a stop command to stop the execution of traction control when the slip detection unit 42 does not determine that the behavior of the electric vehicle 1 is unstable and the elapsed time T_st since the behavior was no longer determined to be unstable becomes equal to or greater than a predetermined threshold T_st_thr. In this embodiment, the forced stop determination unit 45 outputs the stop command to the vehicle control unit 60. Note that the forced stop determination unit 45 may also output the stop command to the motor control unit 50.

[0057]

[0033] In this embodiment, the forced stop determination unit 45 outputs an offset signal to the vehicle control unit 60 as a stop command, which increases the target rotational speed v_tgt for a short period of time. For example, the forced stop determination unit 45 generates a command to send a square wave offset signal. This offset signal is converted into a waveform that does not result in a sudden increase via a filter and sent to the vehicle control unit 60. The elapsed time threshold T_st_thr may be set to any value, but is set to an appropriate value so that traction control is not released due to the behavior of the electric vehicle 1 becoming stable for a moment.

[0058] [ 0 0 3 4 ]

[0059] (Vehicle Control Unit) The vehicle control unit 60 has the function of comprehensively controlling the traveling of the electric vehicle 1 by executing a computer program. The vehicle control unit 60 is configured with a processing unit 61 and a memory unit 63. The memory unit 63 is configured with memory elements such as RAM and ROM, and one or more memory devices such as SSDs or HDDs.

[0060]

[0035] The processing unit 61 sets a torque command value, which is a command value for the output torque of the drive motor 30, based on, for example, the accelerator opening detected by the accelerator opening sensor 27. When the electric vehicle 1 is in the autonomous driving control mode, the processing unit 61 calculates the torque command value by a predetermined calculation. The vehicle control unit 60 transmits the set torque command value to the motor control unit 50.

[0061]

[0036] Furthermore, when the processing unit 61 acquires information on the target rotational speed v_tgt and a stop command output from the vehicle behavior control unit 40, it outputs the information on the target rotational speed v_tgt and a stop command to the motor control unit 50.

[0062] (Motor control unit) The motor control unit 50 has the function of controlling the drive motor 30 by executing a computer program. The motor control unit 50 is configured with a processing unit 51 and a memory unit 54. The memory unit 54 is configured with memory elements such as RAM and ROM, and one or more storage devices such as SSDs or HDDs.

[0063]

[0037] The drive motor 30 is provided with a rotational speed sensor 30a that detects the rotational speed of the drive motor 30. The rotational speed sensor 30a detects the rotational speed of the drive motor 30 and outputs a signal corresponding to the detected rotational speed to the motor control unit 50. The motor control unit 50 acquires information about the rotational speed of the drive motor 30 based on the output signal of the rotational speed sensor 30a.

[0064]

[0038] The motor control unit 52 controls the driving of the drive motor 30 by driving the inverter device 31 based on the torque command value of the drive motor 30 input from the vehicle control unit 60. When the motor control unit 52 receives the torque command value from the vehicle control unit 60, it drives the inverter device 31 so that an output torque corresponding to the torque command value is output from the drive motor 30. Through control of the drive motor 30 based on the torque command value (torque control), the electric vehicle 1 is able to travel in accordance with the acceleration request of the driver or automatic driving control. Torque control is basically feedforward control.

[0065]

[0039] The motor control unit 52 stops torque control while the traction control unit 53 performs traction control. Furthermore, when braking the electric vehicle 1, the motor control unit 50 drives the inverter device 31 so that the power generated by regenerative power generation of the drive motor 30 is charged into the battery 32.

[0066]

[0040] The traction control unit 53 detects slippage of the drive wheels 11, 12 and performs traction control. The traction control unit 53 determines whether the drive wheels 11, 12 are slipping. For example, the traction control unit 53 converts the rotational speed of the drive motor 30 input from the rotational speed sensor 30a using the gear ratio of the power transmission system from the drive motor 30 to the drive wheels 11, 12, and calculates the rotational speed v_axl of the drive wheels 11, 12. The traction control unit 53 determines that the drive wheels 11, 12 are slipping when the calculated rotational speed V-ax1 of the drive wheels 11, 12 exceeds the target rotational speed v_tgt input from the vehicle control unit 60.

[0067]

[0041] Furthermore, the traction control unit 53 starts executing traction control when slippage of the drive wheels 11, 12 is detected. When starting to execute traction control, the traction control unit 53 outputs a signal indicating the start of execution of traction control to the vehicle control unit 60 and the vehicle behavior control unit 40. During execution of traction control, the traction control unit 53 controls the output of the drive motor 30 by executing rotational speed feedback control that causes the rotational speed v_ax1 of the drive wheels 11, 12 to follow the target rotational speed v_tgt input from the vehicle control unit 60.

[0068]

[0042] The traction control unit 53 stops the execution of traction control when the rotational speed v_axl of the drive wheels 11, 12 falls below the target rotational speed V_tgt and the difference Δv between the rotational speed V_ax1 and the target rotational speed V_tgt exceeds a predetermined threshold value Av_thr. The predetermined threshold value Δv_thr is a threshold value that is set in advance to determine whether the drive wheels 11, 12 have recovered from a slipping state, and is set to any appropriate value.

[0069]

[0043] When traction control unit 53 stops the execution of traction control, it outputs a signal indicating the end of traction control to vehicle control unit 60 and vehicle behavior control unit 40. In this case, traction control unit 53 determines that drive wheels 11, 12 have recovered from the slip state and that electric vehicle 1 has returned to a stable, drivable state, and stops the execution of traction control. Accordingly, torque control by motor control unit 52 is resumed.

[0070] [ 0 0 4 4 ]

[0071] <Processing Operation of Traction Control System> Up to this point, the configuration of the traction control system 10 according to this embodiment has been explained. Next, the processing operation related to traction control of the traction control system 10 according to this embodiment will be specifically explained. Below, the processing operation of the vehicle behavior control unit 40 and the processing operation of the motor control unit 50 will be explained respectively.

[0072] [ 0 0 4 5 ]

[0073] (Processing Operation of Vehicle Behavior Control Unit) Fig. 3 shows a flowchart of the processing operation of the vehicle behavior control unit 40. First, the target rotational speed setting unit 44 acquires information on the driving state of the electric vehicle 1, and sets a target rotational speed v-tgt by adding a predetermined target slip amount to the reference rotational speed v-ref of the drive wheels 11, 12 based on the acquired information on the driving state (step S11). For example, the target rotational speed setting unit 44 acquires information such as the rotational speed v_m_t of the drive motor 30, the gear ratio of the torque transmission path from the drive motor 30 to the drive wheels 11, 12, and the brake fluid pressure of the friction brake devices 15, 16, and calculates the expected rotational speed of the drive wheels 11, 12. In addition, the target rotational speed setting unit 44 adds a predetermined target slip amount to the calculated reference rotational speed v_ref to set the target rotational speed v_tgt.

[0074]

[0046] Next, the slip detection unit 42 detects the rotational speed v_ax1 of the drive wheels 11, 12 based on the output signals of the wheel speed sensors 21, 22, and determines whether the rotational speed v_ax1 exceeds the target rotational speed v_tgt (step S13). If the slip detection unit 42 determines that the rotational speed v_ax1 exceeds the target rotational speed v_tgt (S13 / Yes), the target rotational speed setting unit 44 outputs information about the set target rotational speed v_tgt to the vehicle control unit 6 (step S15).

[0075]

[0047] On the other hand, if the flip detection unit 42 does not determine that the rotational speed v-ax1 exceeds the target rotational speed v-tgt (S13 / N), the target rotational speed setting unit 44 determines whether the motor control unit 50 is executing traction control (step S17). For example, if the target rotational speed setting unit 44 receives a signal indicating the start of traction control from the motor control unit 50 and then does not receive a signal indicating the end of the execution, the target rotational speed setting unit 44 determines that the motor control unit 50 is executing traction control.

[0076]

[0048] If the target rotational speed setting unit 44 determines that the motor control unit 50 is not executing traction control (S17 / NO), it outputs information about the set target rotational speed v_tgt to the vehicle control unit 60 (step S15). In this case, although the execution of traction control is stopped, the motor control unit 50 outputs information about the set target rotational speed v_tgt to the vehicle control unit 60 in order to determine whether to start or stop the execution of traction control.

[0077]

[0049] On the other hand, if the target rotational speed setting unit 44 determines that the motor control unit 50 is executing traction control (S17 / Yes), the forced stop determination unit 45 determines whether the slip detection unit 42 has detected that the vehicle behavior is unstable (step S19). In other words, the forced stop determination unit 45 determines whether either the drive wheels 11, 12 are slipping, or whether the electric vehicle 1 is in an understeer or oversteer state. If the slip detection unit 42 detects that the vehicle behavior is unstable (S19 / Yes), it is necessary to continue traction control by the motor control unit 50, so the target rotational speed setting unit 44 outputs information about the set target rotational speed v_tgt to the vehicle control unit 60 (step S15).

[0078]

[0050] On the other hand, if the slip detection unit 42 does not detect that the vehicle behavior is unstable (S19 / N), the forced stop determination unit 45 counts up the forced stop counter of the traction control (step S21). The forced stop counter is a counter that counts the elapsed time st from when the slip detection unit 42 no longer determines that the behavior of the electric vehicle 1 is unstable.

[0079]

[0051] Next, the forced stop determination unit 45 determines whether the counter value (elapsed time T_st) of the forced stop counter has reached a predetermined threshold T_st_thr (step S23). If the counter value (elapsed time T_st) of the forced stop counter has not reached the predetermined threshold T_st_thr (S23 / N), the target rotational speed setting unit 44 outputs information about the set target rotational speed vtgt to the vehicle control unit 60 (step S15). In this case, traction control by the motor control unit 50 continues.

[0080]

[0052] On the other hand, if the counter value (elapsed time T_st) of the forced stop counter reaches a predetermined threshold T_st_thr (S23 / Yes), the forced stop determination unit 45 sets an offset signal as a stop command to increase the target rotational speed v_tgt for a short period of time (step S25). Next, the forced stop determination unit 45 adds the offset signal to the target rotational speed v_tgt set by the target rotational speed setting unit 44 and outputs the result to the vehicle control unit 6 (step S27). As a result, the motor control unit 50 that receives the offset signal stops the execution of traction control even if it has not itself determined to stop the execution of traction control.

[0081]

[0053] The vehicle behavior control unit 40 repeatedly executes the above-described steps S11 to S27 while the traction control system 10 is activated.

[0082] [ 0 0 5 4 ]

[0083] (Processing Operation of Motor Control Unit) Figure 4 shows a flowchart of the processing operation of the motor control unit 50. First, the traction control unit 53 calculates the rotational speed v_ax1 of the drive wheels 11, 12 (step S31). For example, the traction control unit 53 converts the rotational speed of the drive motor 30 input from the rotational speed sensor 30a using the gear ratio of the power transmission system from the drive motor 30 to the drive wheels 11, 12, and calculates the rotational speed v_ax1 of the drive wheels 11, 12.

[0084]

[0055] Next, the traction control unit 53 acquires information on the target rotational speed v-tgt output from the vehicle behavior control unit 40 from the vehicle control unit 6 (step S33).

[0085]

[0056] Next, the traction control unit 53 determines whether the rotational speed v_axl of the drive wheels 11, 12 exceeds the target rotational speed v_tgt (step S35). If the rotational speed v_axl of the drive wheels 11, 12 exceeds the target rotational speed v_tgt, the traction control unit 53 executes torque control based on the torque command input from the vehicle control unit 60 (step S37). On the other hand, if the traction control unit 53 determines that the rotational speed v_axl of the drive wheels 11, 12 exceeds the target rotational speed v_tgt (S35 / Yes), it starts executing traction control (step S39). After starting to execute traction control, the traction control unit 53 acquires the rotational speed v_axl of the drive wheels 11, 12 and the target rotational speed v_tgt (steps S41 to S43), similar to steps S31 to S43.

[0086]

[0058] Next, the traction control unit 53 determines whether the rotational speed v_axl of the drive wheels 11, 12 is lower than the target rotational speed V_tgt and whether the difference Δv between the rotational speed v_ax1 and the target rotational speed V_tgt exceeds a predetermined threshold value Av_thr (step S45). For example, the traction control unit 53 determines whether the difference Av obtained by subtracting the rotational speed v_ax1 from the target rotational speed v_tgt exceeds a predetermined threshold value Δv_thr.

[0087] In this embodiment, even if the rotational speed V_ax1 of the drive wheels 11, 12 has been below the target rotational speed V_tgt for a predetermined time, when the difference Av between the rotational speed V_ax1 and the target rotational speed vtgt is equal to or less than a predetermined threshold Av_thr, an offset signal is added to the target rotational speed v_tgt output from the vehicle behavior control unit 40. Therefore, the traction control unit 53 can make a positive determination in step S45 even in such a case.

[0088]

[0060] If the result of step S45 is negative (S45 / NO), the traction control unit 53 executes rotational speed feedback control to make the rotational speed V-ax1 of the driving wheels 11, 12 follow the target rotational speed V-tgt (step S47). The traction control unit 53 repeats steps S41 to S47 while the result of step S45 is negative.

[0089]

[0061] On the other hand, if the result of step S45 is affirmative (S45 / Yes), the traction control unit 53 stops the execution of traction control (step S49) and resumes torque control (step S51).

[0090]

[0062] The motor control unit 50 repeatedly executes the above-described steps S31 to S51 while the traction control system ! is activated.

[0091] [ 0 0 6 3 ]

[0092] (Operation of Traction Control System) Next, the operation of the traction control system 10 according to this embodiment will be explained. Below, the operation of the traction control system 10 will be explained separately for when the electric vehicle 1 accelerates and travels straight ahead, and when it enters an understeer state while turning.

[0093]

[0064] Figure 5 shows the time-dependent changes in the rotational speed v_a x 1, reference rotational speed v_ref, and target rotational speed v_tgt of the drive wheels 11 and 12 when the electric vehicle 1 accelerates and travels straight ahead.

[0094]

[0065] As the electric vehicle 1 accelerates and the drive wheels 11 and 12 begin to slip, at time t11, the rotational speed V_axl of the drive wheels 11 and 12 exceeds the target rotational speed V_tgt. The motor control unit 50 then starts to perform traction control (denoted as "TCS" in FIG. 5). Thereafter, the rotational speed V_axl of the drive wheels 11 and 12 changes to follow the target rotational speed V_tgt.

[0095]

[0066] Then, at time t12, the rotational speed v_ax1 of the drive wheels 11, 12 falls below the target rotational speed v_tgt, and at time t13, when the difference v between the rotational speed v_ax1 of the drive wheels 11, 12 and the target rotational speed v-tgt exceeds a threshold v-thr, the motor control unit 50 stops executing traction control and resumes torque control.

[0096]

[0067] When the electric vehicle 1 is traveling straight, when the drive wheels 11, 12 recover from a slipping state, the rotational speed v-ax1 of the drive wheels 11, 12 approaches the reference rotational speed v-ref, and the motor control unit 50 can determine by itself whether to stop the execution of traction control.

[0097]

[0068] Figure 6 shows the time-dependent changes in the rotational speed v_axl, reference rotational speed v_ref, target rotational speed v_tgt, and understeer state US of the drive wheels 11 and 12 when an understeer state occurs during cornering.

[0098]

[0069] As the electric vehicle 1 turns, the understeer condition US increases, causing the drive wheels 11 and 12 to begin slipping. At time t21, when the rotational speed v_ax1 of the drive wheels 11 and 12 exceeds the target rotational speed v_tgt, the motor control unit 50 begins to execute traction control. If the understeer condition US is large, the target slip amount added to the reference rotational speed v_ref is gradually reduced. Thereafter, the rotational speed v_ax1 of the drive wheels 11 and 12 is controlled to follow the target rotational speed v_tgt, but because the understeer condition US is large, the rotational speed v_ax1 remains above the target rotational speed v_tgt.

[0099]

[0070] Thereafter, as the understeer condition US is alleviated and the target slip amount gradually increases, at time t22 the rotational speed V-aX1 of the drive wheels 11, 12 falls below the target rotational speed V-tgt. However, as the target slip amount gradually increases and the difference between the target rotational speed v-tgt and the reference rotational speed v-ref gradually increases, the rotational speed v-ax1 of the drive wheels 11, 12 remains close to the target rotational speed v-tgt. Therefore, even though the rotational speed v_ax1 of the drive wheels 11 and 12 falls below the target rotational speed v_tgt and the understeer state is resolved, the difference v between the rotational speed v_ax1 of the drive wheels 11 and 12 and the target rotational speed v_tgt remains below the minimum value v_thr.

[0100] In this embodiment, when the elapsed time st from the time t23 when the understeer state is resolved reaches the minimum value st_thr, the vehicle behavior control unit 40 adds an offset signal to the target rotational speed v_tgt as a stop command and outputs the result. As a result, at time t24, the difference v between the rotational speed V_ax1 of the drive wheels 11, 12 and the target rotational speed V_tgt exceeds the minimum value Av_thr, and the motor control unit 50 can stop the execution of traction control and resume torque control.

[0101]

[0072] <Effects> According to the traction control system 10 of this embodiment described above, while the motor control unit 50 is executing traction control, the vehicle behavior control unit 40 determines whether the behavior of the electric vehicle 1 is unstable, and outputs a stop command to stop the execution of traction control when it is determined that the behavior is not unstable and the elapsed time T_st since the behavior was no longer determined to be unstable is equal to or greater than a predetermined threshold T_st_thr. Therefore, even when the vehicle behavior control unit 40 adjusts the target rotational speed v_tgt to resolve the unstable state of the vehicle behavior and suppresses a decrease in the rotational speed v_ax1 of the drive wheels 11, 12, the motor control unit 50 can determine to stop the execution of traction control. This prevents traction control from limiting acceleration when a request for acceleration is subsequently made by the driver or automatic driving control.

[0102]

[0073] In the traction control system i0 according to the above embodiment, the vehicle behavior control unit 40 outputs an offset signal as a stop command by adding it to the target rotational speed v-tgt. Therefore, the motor control unit 50 can stop the execution of traction control in response to the stop command output from the vehicle behavior control unit 40 without changing the traction control stop determination logic of the motor control unit 50.

[0103] [ 0 0 7 4 ]

[0104] <Other Embodiments> In the above embodiment, the vehicle behavior control unit 40 generated an offset signal to be added to the target rotational speed v-tgt as a stop command, but the stop command is not limited to this offset signal.

[0105] For example, the stop command may be a message signal instructing the execution of traction control to be stopped. In this case, the vehicle behavior control unit 40 outputs the target rotational speed v-tgt set by the target rotational speed setting unit 44 without adjusting it, and outputs the message signal generated by the forced stop determination unit 45 instructing the execution of traction control to be stopped.

[0106]

[0076] Furthermore, when the traction control unit 53 of the motor control unit 50 receives the message signal output from the vehicle behavior control unit 40 via the vehicle control unit 60, it forcibly stops the execution of traction control. In this case, too, the traction control unit 53 outputs a signal indicating the end of the execution of traction control to the vehicle control unit 60 and the vehicle behavior control unit 40.

[0107]

[0077] Fig. 7 shows a flowchart of the processing operation of the vehicle behavior control unit 40 according to another embodiment. The processing of steps S11 to S23 of the flowchart shown in Fig. 7 is executed in the same manner as steps S11 to S23 of the flowchart shown in Fig. 3. In another embodiment, when the slip detection unit 42 determines that the rotational speed v-ax1 exceeds the target rotational speed v-tgt (S13 / Yes), the target rotational speed setting unit 44 outputs a message signal permitting the execution of traction control (step S14), and further outputs information on the set target rotational speed v-tgt to the vehicle control unit 60 (step S15).

[0108]

[0078] In another embodiment, when the counter value (elapsed time T_st) of the forced stop counter reaches a predetermined threshold value T_st_thr (S23 / Yes), the forced stop determination unit 45 outputs a message signal to stop the execution of traction control as a stop command (step S26), and further outputs information on the set target rotation speed v_tgt to the vehicle control unit 6 (step S15).

[0109]

[0079] Fig. 8 shows a flowchart of the processing operation of the motor control unit 50 according to another embodiment. The flowchart shown in Fig. 8 differs from the flowchart shown in Fig. 4 in that step S

[0110] In another embodiment, the traction control unit 53 is

[0111] If the result of step S45 is negative (S45 / No), it is determined whether a message signal has been input as a stop command output from the vehicle behavior control unit 40 (step S46).

[0112] 〇 This prevents traction control from limiting acceleration.

[0113]

[0082] In the traction control system 10 according to another embodiment, the vehicle behavior control unit 40 outputs a message signal as a stop command to instruct the execution of traction control to be stopped. Therefore, when the message signal is input to the motor control unit 50, the traction control can be reliably stopped.

[0114]

[0083] Although the preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to such examples. It is clear that a person skilled in the art to which the present invention pertains can conceive of various modifications or alterations within the scope of the technical ideas described in the claims, and it is understood that these also naturally fall within the technical scope of the present invention.

[0115]

[0084] For example, as described above, in the above embodiment, an example in which the rotational speed of the drive wheels is used as a parameter for traction control has been described, but the rotational speed of the drive motor may be used as a parameter for traction control. The rotational speed of the drive motor and the rotational speed of the drive wheels can be converted to each other using the gear ratio of the power transmission system from the drive motor to the drive wheels. Therefore, the technology of the present disclosure can be applied by converting the rotational speed, target rotational speed, and reference rotational speed of the drive wheels in the above embodiment into the rotational speed, target rotational speed, and reference rotational speed of the drive motor.

[0116]

[0085] In addition, although the above embodiment has been described using an example of a front-wheel drive vehicle in which the front wheels are driven by one drive motor, the technology of the present disclosure can also be applied to electric vehicles of other configurations. For example, the present disclosure can be applied to a rear-wheel drive vehicle in which the rear wheels are driven by one drive motor, an all-wheel drive vehicle in which all four wheels are driven by two drive motors, an all-wheel drive vehicle in which all four wheels are driven by a front-wheel drive motor and a rear-wheel drive motor, and a front-wheel drive vehicle, rear-wheel drive vehicle, or all-wheel drive vehicle in which each drive wheel is driven by a separate drive motor.

[0117] [Explanation of symbols]

[0118]

. 0 8 6

[0119] 1 Electric vehicles

[0120] 1. Traction control system

[0121] 3. Drive motor

[0122] 3 0 a Rotational speed sensor

[0123] 3 1 Inverter device

[0124] 3 2 Battery

[0125] 4 Vehicle behavior control unit

[0126] 4 1 Processing section

[0127] 4 2 Slip detection section

[0128] 4 3 Brake control unit

[0129] 4 4 Target rotation speed setting section

[0130] 4 5 Forced stop judgment section

[0131] 4 7 Storage section

[0132] 5 Motor control unit

[0133] 5 1 Processing section

[0134] 5 2 Motor control unit

[0135] 5 3 Traction control unit

[0136] 5 4 Storage section

[0137] T — st elapsed time

[0138] T — st — thr Negative value US Understeer state v — ax 1 rotation speed v — m〇 t rotation speed v — ref reference rotation speed v — tgt target rotation speed

[0139] A v difference

[0140] A v — thr value

Claims

[Document name] Scope of claims

1. A traction control system (10) for an electric vehicle (1) that drives drive wheels (11, 12) by a drive motor (30) to suppress slip of the drive wheels (11, 12) by controlling an output of the drive motor (30) when the drive wheels (11, 12) slip, comprising: a vehicle behavior control unit (40) that executes the following operations based on an operating state of the electric vehicle (1): setting a target rotation speed (vtgt) obtained by adding a predetermined target slip amount to a reference rotation speed (v-ref) of the drive wheels (11, 12) or the drive motor (30), and outputting information on the target rotation speed (v-tgt); and a vehicle behavior control unit (40) that executes the following operations based on an operating state of the electric vehicle (1): and a motor control unit (50) which executes the following: starting execution of a traction control for controlling an output of the drive motor (30) by executing a rotational speed feedback control for making the rotational speed (v-axl) of the drive motor (30) follow the target rotational speed (v_tgt), and stopping execution of the traction control when the rotational speed (v-ax1) falls below the target rotational speed (v-tgt) and a difference (Av) between the rotational speed (v-ax1) and the target rotational speed (v-tgt) exceeds a predetermined threshold value (△v_thr), and the vehicle behavior control unit (40) determines whether or not a behavior of the electric vehicle (1) is in an unstable state while the motor control unit (50) is executing the traction control, and when it is determined that the behavior is not in an unstable state, and when the elapsed time (T_st) from when the behavior is no longer determined to be unstable reaches or exceeds a predetermined threshold (T-st-thr), a stop command is output to stop the execution of the traction control.

2. The traction control system for an electric vehicle as described in claim 1, characterized in that the stop command is an offset signal that increases the target rotational speed (V-TGT) for a short period of time.

3. The traction control system for an electric vehicle as described in claim 1, wherein the vehicle behavior control unit (40) is configured such that the stop command is a message signal instructing the stopping of execution of the traction control.

4. A vehicle behavior control unit (40) used in an electric vehicle traction control system (10) for suppressing slip of drive wheels (11, 12) of an electric vehicle (1) that drives drive wheels (11, 12) by a drive motor (30) by controlling an output of the drive motor (30) when the drive wheels (11, 12) slip, comprises: - setting a target rotation speed (v-tgt) for traction control obtained by adding a predetermined target slip amount to a reference rotation speed (v-ref) of the drive wheels (11, 12) or the drive motor (30) based on an operating state of the electric vehicle (1), and outputting information on the target rotation speed (v-tgt); - controlling the electric vehicle (1) while a motor control unit (50) is executing traction control. a vehicle behavior control unit which determines whether the behavior of the vehicle is in an unstable state, and when the behavior is not determined to be in an unstable state and an elapsed time (T_st) since the behavior is no longer determined to be in an unstable state becomes equal to or longer than a predetermined threshold value (T-st-thr), outputs a stop command to stop the execution of the traction control.

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