Control device for electric vehicle

Abstract

The invention provides a control device for an electric vehicle, which can suppress the reduction delay of braking force and ensure the driving stability even when the road surface resistance is reduced during the operation of an ABS (Anti-lock Brake System). A control device for an electric vehicle executes an anti-lock control in which a braking force applied to wheels is controlled using a hydraulic braking force generated by a hydraulic brake device and a regenerative braking force generated by a motor to suppress lock of the wheels, when the anti-lock control is executed, the hydraulic pressure of the hydraulic brake device is set to be constant, and the regenerative braking force is controlled through speed feedback control of enabling the speed of the wheels to follow the target speed, and when the road surface resistance is determined to be lower than a preset value in the first state, the control is performed. Regenerative braking force is controlled by speed feedback control, and the hydraulic pressure of the hydraulic brake device is reduced.

Description

Technical Field

[0001] The present invention relates to a control device for an electric vehicle. Background Art

[0002] Patent Document 1 discloses an electric vehicle equipped with an antilock braking system (ABS) that performs antilock control using a hydraulic brake and a regenerative brake. In the structure described in Patent Document 1, when performing antilock control, while maintaining the braking force of the hydraulic brake, the braking force of the regenerative brake is reduced to a reduction limit. When the braking force of the regenerative brake is reduced to the reduction limit, the braking force of the hydraulic brake is then started to be reduced.

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Patent Laid-Open No. 06-171490 Summary of the Invention

[0006] Problems to be Solved by the Invention

[0007] When the ABS is operating, the road surface resistance changes due to the travel of the vehicle. Therefore, it is necessary to control the magnitude of the braking force according to the road surface resistance. For example, in the case where the road surface resistance decreases, it is necessary to increase the amount of reduction of the braking force. However, in the structure described in Patent Document 1, when the road surface resistance decreases, after the braking force of the regenerative brake reaches the reduction limit, the braking force of the hydraulic brake is then started to be reduced. Therefore, the reduction of the braking force is delayed, the amount of wheel lock-up becomes large, and the driving stability of the vehicle may deteriorate.

[0008] The present invention has been made in view of the above circumstances, and an object thereof is to provide a control device for an electric vehicle that can suppress the delay in the reduction of the braking force and ensure driving stability even when the road surface resistance decreases during ABS operation.

[0009] Means for Solving the Problems

[0010] The present invention relates to a control device for an electric vehicle. The electric vehicle performs anti-lock control, which uses hydraulic braking force generated by a hydraulic braking device and regenerative braking force generated by a motor to control the braking force applied to the wheels and suppress wheel lock-up. The control device for the electric vehicle is characterized in that when performing the anti-lock control, it controls to keep the hydraulic pressure of the hydraulic braking device constant and controls the regenerative braking force through speed feedback control to make the speed of the wheel follow a target speed in a first state. It determines whether the road surface resistance decreases below a predetermined value during the period of controlling to the first state. When it is determined that the road surface resistance decreases below the predetermined value in the first state, it controls the regenerative braking force through the speed feedback control and reduces the hydraulic pressure of the hydraulic braking device.

[0011] Advantages of the Invention

[0012] In the present invention, even when the road surface resistance decreases during ABS operation, it is possible to suppress the delay in the reduction of the braking force and ensure driving stability. Description of the Drawings

[0013] Figure 1 It schematically shows the electric vehicle in the embodiment.

[0014] Figure 2 It is a timing chart showing the case where the road surface resistance does not change during ABS operation.

[0015] Figure 3 It is a diagram for explaining the decompression reference speed.

[0016] Figure 4 It is a timing chart showing the case where the road surface resistance decreases during ABS operation.

[0017] Figure 5 It is a diagram for explaining the increase in the wheel lock-up amount.

[0018] Figure 6 It is a flowchart showing the wheel speed control.

[0019] Figure 7 It is a diagram for explaining the control state corresponding to the magnitude of the regenerative braking force.

[0020] Figure 8 It is a diagram for explaining the case where the maximum regenerative braking force is small.

[0021] Figure 9 It is a flowchart showing the wheel speed control in the modified example. Detailed Embodiment

[0022] Hereinafter, a control device for an electric vehicle in an embodiment of the present invention will be specifically described. In addition, the present invention is not limited to the embodiments described below.

[0023] Figure 1 FIG. is a diagram schematically showing an electric vehicle in the embodiment. The electric vehicle 1 includes a motor 2, a differential gear 3, front wheels 4, rear wheels 5, an inverter 6, a wheel speed sensor 7, a motor control device 10, and a brake control device 20. The control device of the electric vehicle 1 is configured to include the motor control device 10 and the brake control device 20. The electric vehicle 1 is a front-wheel drive vehicle equipped with the motor 2 as a power source, the front wheels 4 are drive wheels, and the rear wheels 5 are driven wheels. The motor 2 is connected to the front wheels 4 via the differential gear 3 in a manner capable of transmitting power.

[0024] The motor 2 is an electric generator that can function as an electric motor and a generator. When the electric vehicle 1 is running, the power output from the motor 2 is transmitted to the left and right front wheels 4 via the differential gear 3. During regenerative braking, the regenerative braking force of the motor 2 acts on the left and right front wheels 4. The motor 2 is electrically connected to the storage battery via the inverter 6.

[0025] The motor control device 10 is an electronic control device that controls the motor 2. The motor control device 10 is configured to include a microcomputer having a CPU, a RAM, a ROM, and an input / output interface. The motor control device 10 performs signal processing according to a program stored in the ROM in advance. Signals from various sensors mounted on the electric vehicle 1 are input to the motor control device 10. For example, signals from a motor speed sensor of the electric vehicle 1, the wheel speed sensor 7 that detects the speed of the wheels, etc. are input to the motor control device 10. The motor control device 10 executes various controls based on the signals input from the various sensors. The motor control device 10 executes speed feedback control. The motor control device 10 outputs a control signal for controlling the motor 2 through speed feedback control to the inverter 6. The motor control device 10 controls the torque of the motor 2 so that the rotational speed of the motor 2 follows the target speed.

[0026] Braking devices are provided on each wheel of the electric vehicle 1. The braking device is a hydraulic friction brake, and the braking force varies according to the hydraulic pressure. The braking force of the braking device (hereinafter, referred to as the hydraulic braking force) is controlled by the brake control device 20. In addition, in this description, the braking device constituted by the hydraulic friction brake is referred to as a hydraulic brake.

[0027] The brake control device 20 is an electronic control device that controls the braking force of the electric vehicle 1. The brake control device 20 is the same as the motor control device 10 in terms of hardware. Signals from various sensors mounted on the electric vehicle 1 are input to the brake control device 20. For example, signals from wheel speed sensors 7 provided on each wheel are input to the brake control device 20. The brake control device 20 performs various controls based on the input signals.

[0028] The brake control device 20 controls the hydraulic braking force of the hydraulic brake device and also controls the regenerative braking force of the motor 2. Control signals for controlling the hydraulic brake devices of each wheel are output from the brake control device 20 to the respective hydraulic brake devices. During regenerative braking, a control signal for controlling the motor 2 is output from the brake control device 20 to the motor control device 10. When controlling the motor 2, the brake control device 20 outputs a control signal to the motor control device 10. The motor control device 10 controls the torque and rotational speed of the motor 2 based on the control signal input from the brake control device 20. The brake control device 20 controls not only the hydraulic braking force of each hydraulic brake device but also the regenerative braking force of the motor 2.

[0029] When braking the electric vehicle 1 using the regenerative braking force of the motor 2 and the hydraulic braking force of the hydraulic brake device, the brake control device 20 performs anti-lock control for avoiding wheel lock-up. The brake control device 20 performs anti-lock control during braking, and controls the braking force applied to the wheels using the hydraulic braking force of the hydraulic brake device and the regenerative braking force of the motor 2, thereby suppressing wheel lock-up. The brake control device 20 has a function as an anti-lock braking system (ABS). In addition, when the ABS operates, it is synonymous with when anti-lock control is performed.

[0030] The brake control device 20 detects the tendency of wheel lock-up based on the wheel speed and determines whether to operate the ABS. When performing anti-lock control, the brake control device 20 controls the wheels with a tendency of lock-up so that their wheel speeds follow the target wheel speed.

[0031] Specifically, the brake control device 20 controls in the following manner: When the ABS operates, it calculates the target speed, and makes the wheel speed accurately follow the target speed only through the regenerative speed feedback control of the motor control device 10, and the pressure reduction of the hydraulic brake device does not operate. The regenerative speed feedback control is the feedback control of the motor rotational speed, and controls the regenerative braking force in such a way that the motor rotational speed follows the target speed. The only regenerative speed feedback control means that when changing the braking force of the wheels during the operation of the ABS, the hydraulic braking force is set to be constant and only the regenerative braking force is changed, and the change of the regenerative braking force is performed through the feedback control of the motor rotational speed.

[0032] When the road surface resistance is constant during ABS operation, the braking control device 20 keeps the hydraulic pressure of the hydraulic braking device constant and controls the regenerative braking force through regenerative speed feedback control to make the wheel speed follow the target speed. In contrast, when the road surface resistance decreases during ABS operation, although it is necessary to reduce the braking force of the wheels, wheel lock-up may sometimes occur only by reducing the regenerative braking force. Therefore, it is necessary to perform a pressure reduction operation of the hydraulic braking device. Therefore, the braking control device 20 sets a reference speed (hereinafter referred to as the pressure reduction reference speed) for performing the pressure reduction of the hydraulic braking device during ABS operation. The braking control device 20 sets the pressure reduction reference speed to a speed smaller than the target wheel speed toward the wheel lock-up side. When the wheel speed becomes equal to or lower than the pressure reduction reference speed during ABS operation, the braking control device 20 performs the pressure reduction of the hydraulic braking device. The braking control device 20 is configured to cause the pressure reduction of the hydraulic braking device to work without delay only when the road surface resistance decreases and the wheel slip increases.

[0033] Figure 2 is a timing chart showing the case where the road surface resistance does not change during ABS operation. As Figure 2 shown, the braking control device 20 makes the wheel speed follow the target speed through regenerative speed feedback control. During ABS operation, the braking control device 20 tries not to generate an increase or decrease in the hydraulic pressure of the hydraulic braking device and controls the hydraulic pressure of the hydraulic braking device to a constant hydraulic pressure that compensates for the insufficient amount of regenerative braking force. The control value of this hydraulic pressure (the value of the constant hydraulic pressure) is set according to the road surface resistance and is determined to be a value proportional to the magnitude of the road surface resistance. When the regenerative braking force is smaller than the maximum regenerative braking force that can be output during ABS operation, the braking control device 20 stops the pressure increase of the hydraulic braking device and uses the motor speed control of the motor control device 10 to accurately control the wheel slip to the target speed near the maximum of the road surface resistance.

[0034] As Figure 3 shown, the target speed of the wheel speed is set near the peak of the road surface resistance. The pressure reduction reference speed is set to a speed shifted from the target speed toward the wheel slip side. The offset amount is a predetermined value α. The predetermined value α is set to a value greater than or equal to the variation amount of the wheel speed when the road surface resistance does not change during ABS operation. The braking control device 20 sets the pressure reduction reference speed to a speed shifted from the target speed of the motor speed toward the wheel lock-up side. The offset amount is the predetermined value α, which is greater than or equal to the speed variation amount in the motor speed control. The braking control device 20 sets the pressure reduction reference speed to be smaller than the target speed of the regenerative control. In this way, since the pressure reduction reference speed is set to be closer to the wheel lock-up side than the variation of the motor speed, the wheel speed does not decrease to the pressure reduction reference speed and the pressure reduction of the hydraulic braking device does not occur when the road surface resistance does not change. As a result, the hydraulic braking force of the hydraulic braking device does not change, and the controllability of the wheel slip of the motor 2 is not deteriorated.

[0035] The braking control device 20 presets a desired slip ratio in advance. The slip ratio of the wheel is obtained based on the wheel speed and the vehicle body speed. The braking control device 20 can preset the slip ratio that is presumed to be near the maximum of the road surface resistance. The braking control device 20 controls the wheel such that the slip ratio of the wheel where the ABS operates is within the range of the preset slip ratio. The braking control device 20 calculates the target speed of the wheel based on the vehicle body speed and the slip ratio. In order to achieve the target speed of the wheel, the braking control device 20 sets the target speed of the motor 2 using the target speed of the wheel. The motor control device 10 can make the wheel speed follow the target speed by making the motor speed follow the target speed using the motor speed control based on the target speed from the braking control device 20.

[0036] The braking control device 20 calculates the target speed of the motor 2 using the wheel speed of the front wheel 4 to which the motor 2 is connected. The braking control device 20 detects the wheel speed of the front wheel 4 based on the signal input from the wheel speed sensor 7. For example, the braking control device 20 sets the average value of the control target values of the left and right front wheels 4 as the motor target speed. The motor target speed is output from the braking control device 20, and the motor control device 10 controls the torque of the motor 2 in order to achieve the motor target speed.

[0037] Figure 4 It is a timing chart showing the case where the road surface resistance decreases when the ABS operates. As Figure 4 shown, due to the decrease in the road surface resistance, the wheel speed fluctuates greatly, and the wheel speed reaches the decompression reference speed on the wheel lock side. As Figure 5 shown, in the case where the amount of change in the wheel speed becomes large due to the large slip of the wheel and the wheel speed reaches the decompression reference speed, the braking control device 20 starts the decompression of the hydraulic braking device. The amount of change in the wheel speed on the slip side with respect to the target speed represents the amount of wheel lock. The braking control device 20 starts the decompression of the hydraulic braking device when the wheel speed becomes below the decompression reference speed, and thus starts the decompression of the hydraulic braking device before the regenerative braking force becomes zero (reduction limit).

[0038] When the braking control device 20 performs the decompression of the hydraulic braking device due to the decrease in the road surface resistance, it resets the control value of the hydraulic pressure for controlling the constant hydraulic pressure. Since the control value of the hydraulic pressure is set to a value proportional to the magnitude of the road surface resistance, the control value of the hydraulic pressure set after the road surface resistance decreases becomes a value lower than the control value of the hydraulic pressure set before the road surface resistance decreases. After the road surface resistance decreases during the ABS operation, the braking control device 20 makes the hydraulic pressure constant based on the reset control value of the hydraulic pressure, and makes the wheel speed accurately follow the target speed through the regenerative speed feedback control of the motor control device 10.

[0039] In this way, when the road surface resistance decreases during the operation of the ABS, by starting the pressure reduction of the hydraulic braking device before the regenerative braking force reaches the reduction limit, the recovery from wheel lock-up can be accelerated. As a result, compared with the case where the hydraulic pressure of the hydraulic braking device is reduced after the regenerative braking force reaches the reduction limit, the amount of wheel lock-up can be suppressed to a smaller value.

[0040] Figure 6 It is a flowchart showing the wheel speed control. Figure 6 The control shown is implemented by the motor control device 10 and the brake control device 20 during the operation of the ABS. In addition, in Figure 6 the description, the ABS operating wheel is described as the front wheel 4.

[0041] The brake control device 20 sets the target speed of the motor 2 during the operation of the ABS (step S1). In step S1, the target speed of the motor 2 is set based on the wheel speed of the wheel connected to the motor 2 in a power-transmitting manner.

[0042] The brake control device 20 outputs the target speed to the motor control device 10, and the motor control device 10 calculates the regenerative braking force for the motor speed control based on this target speed (step S2). In step S2, the regenerative braking force required to make the rotational speed of the motor 2 follow the target speed is calculated. This target speed is the value calculated in step S1.

[0043] The motor control device 10 outputs the command value of the regenerative braking force (step S3). In step S3, the regenerative braking force calculated in step S2 is output from the motor control device 10 as the command value.

[0044] The brake control device 20 sets the pressure reduction reference speed (step S4). In step S4, the speed obtained by subtracting a predetermined value α from the motor target speed is set as the pressure reduction reference speed. The pressure reduction reference speed becomes a value smaller than the motor target speed by the predetermined value α. In step S4, the brake control device 20 uses the motor target speed calculated in step S1 and the preset predetermined value α to set the pressure reduction reference speed. The predetermined value α is the offset amount toward the wheel lock-up side with respect to the target speed.

[0045] The brake control device 20 determines whether the wheel speed is greater than the pressure reduction reference speed (step S5). In step S5, it is determined whether the wheel speed of the front wheel 4 detected by the wheel speed sensor 7 is greater than the pressure reduction reference speed set in step S4. The brake control device 20 determines whether the hydraulic braking device has pressure reduction by comparing the wheel speed and the pressure reduction reference speed.

[0046] When it is determined that the wheel speed is below the decompression reference speed (step S5: No), the braking control device 20 determines that the wheel lock-up amount is large and performs decompression of the hydraulic braking device (step S6). In step S6, it is determined that the road surface resistance decreases during ABS operation, and decompression of the hydraulic braking device is started. The braking control device 20 outputs a command signal for decompressing the hydraulic pressure of the hydraulic braking device to the hydraulic braking device. After the process of step S6 is performed, this control routine ends.

[0047] When it is determined that the wheel speed is greater than the decompression reference speed (step S5: Yes), the braking control device 20 determines whether the regenerative braking force is less than the maximum regenerative braking force that can be output (step S7). In step S7, it is determined whether there is room for increasing the regenerative braking force before the maximum regenerative braking force. The braking control device 20 calculates the maximum regenerative braking force that can be output from the motor 2 based on the driving state of the electric vehicle 1 and the charging state of the storage battery. The calculation method of the maximum regenerative braking force that can be output from the motor 2 can be a well-known method. The braking control device 20 compares the maximum regenerative braking force that can be output from the motor 2 with the regenerative braking force calculated in step S2, and determines whether the regenerative braking force is less than the maximum regenerative braking force. The motor control device 10 can output the regenerative braking force calculated in step S2 to the braking control device 20.

[0048] When it is determined that the regenerative braking force is less than the maximum regenerative braking force that can be output (step S7: Yes), the braking control device 20 stops the pressurization of the hydraulic braking device (step S8). In step S8, it is determined that the increase in the braking force can be provided by the increase in the regenerative braking force, and the pressurization of the hydraulic braking device is stopped. The braking control device 20 stops the pressurization of the hydraulic braking device by keeping the hydraulic pressure of the hydraulic braking device constant. In this case, the braking control device 20 keeps the hydraulic braking force constant and only changes the regenerative braking force. After the process of step S8 is performed, this control routine ends.

[0049] When it is determined that the regenerative braking force is not less than the maximum regenerative braking force that can be output (step S7: No), the braking control device 20 performs pressurization of the hydraulic braking device (step S9). In step S9, the regenerative braking force reaches the maximum regenerative braking force that can be output, and it is determined that the regenerative braking force cannot be further increased, so pressurization of the hydraulic braking device is performed. The braking control device 20 outputs a command signal for increasing the hydraulic pressure of the hydraulic braking device to the hydraulic braking device. After the process of step S9 is performed, this control routine ends.

[0050] As described above, according to the embodiment, when the ABS operates, the wheel can be accurately controlled to an appropriate slip ratio by the regenerative braking force, and when the road surface resistance decreases, an increase in the wheel lock-up amount caused by the switching delay of the hydraulic control can be prevented. Thereby, the deterioration of the running stability, steering performance, and deceleration feeling of the electric vehicle 1 can be prevented.

[0051] In addition, the electric vehicle 1 is not limited to a front-wheel drive vehicle, and may also be a rear-wheel drive vehicle. The electric vehicle 1 only needs to be a vehicle equipped with a motor that generates regenerative braking force on either the front wheels 4 or the rear wheels 5.

[0052] Further, the braking control device 20 may also set the pressure reduction reference speed to the motor target speed when the regenerative braking force enters a range close to the reduction limit during ABS operation. Moreover, the braking control device 20 may also stop the pressurization of the hydraulic braking device when the regenerative braking force is smaller than the range close to the maximum regenerative braking force that can be output during ABS operation. In this way, as a modified example of the braking control device 20, it can be configured to switch the control state according to the relationship between the regenerative braking force and the maximum regenerative braking force that can be output and the relationship between the regenerative braking force and the reduction limit during ABS operation. Refer to Figures 7 - 9 A description will be given of the modified example of the braking control device 20.

[0053] As Figure 7 shown, when the maximum regenerative braking force of the regenerative braking force during ABS operation is large, it is assumed that the range between the maximum regenerative braking force and zero is divided into ranges X, Y, and Z. In this case, the regenerative braking force enters one of the ranges X close to the maximum regenerative braking force, the intermediate range Y, and the range Z close to the reduction limit. In addition, the range X includes the case where the regenerative braking force reaches the maximum regenerative braking force, and the range Z includes the case where the regenerative braking force reaches the reduction limit.

[0054] When the regenerative braking force enters the range X near the maximum regenerative braking force during the operation of the ABS, the braking control device 20 shifts the pressure reduction reference speed by a predetermined value α toward the wheel slip side from the target speed and performs pressure increase of the hydraulic braking device. If the regenerative braking force enters the range X close to the maximum regenerative braking force during the motor speed control, the pressure increase of the hydraulic braking device is started. As the hydraulic braking device is pressurized, the regenerative braking force decreases and becomes outside the range X (within the range Y). When the regenerative braking force changes from the range X to the range Y, the braking control device 20 stops the pressure increase of the hydraulic brake again and makes the wheel speed follow the target speed only by the motor speed control (only the speed feedback control of regeneration). Thus, a state where the regenerative braking force cannot be increased does not occur during the operation of the ABS, so it is possible to prevent controlling the wheel speed only by the hydraulic control of the hydraulic braking device in a state where the regenerative braking force cannot be increased. Therefore, the regenerative braking force increases to near the maximum regenerative braking force, and the wheel slip control based on the motor 2 continues even in a region where the regeneration increase is insufficient, so the controllability of the wheel slip is not deteriorated.

[0055] When the regenerative braking force enters the intermediate range Y during the operation of the ABS, the braking control device 20 shifts the pressure reduction reference speed toward the wheel slip side by a predetermined value α and stops the pressure increase of the hydraulic braking device.

[0056] When the regenerative braking force enters the range Z near the reduction limit during the operation of the ABS, the braking control device 20 makes the pressure reduction reference speed coincide with the target speed and stops the pressure increase of the hydraulic braking device. Since the motor target speed and the pressure reduction reference speed become the same speed, pressure reduction of the hydraulic braking device occurs during the motor speed control. If the regenerative braking force enters the range Z near the reduction limit during the motor control, the pressure reduction of the hydraulic braking device is started. Along with the pressure reduction of the hydraulic braking device, the regenerative braking force increases and becomes outside the range Z (within the range Y). When the regenerative braking force changes from the range Z to the range Y, the braking control device 20 sets the pressure reduction reference speed to a speed shifted toward the wheel lock side from the motor target speed and makes the wheel speed follow the target speed only by the motor speed control (only the speed feedback control of regeneration). Thus, a state where the regenerative braking force cannot be reduced does not occur during the operation of the ABS, so it is possible to prevent controlling the wheel speed only by the hydraulic control of the hydraulic braking device in a state where the regenerative braking force cannot be reduced. Therefore, even in a region where the regenerative braking force is reduced to near the reduction limit and the regeneration reduction is insufficient, the wheel slip control based on the motor 2 continues, so the controllability of the wheel slip is not deteriorated.

[0057] As Figure 8As shown, when the maximum regenerative braking force of the regenerative braking force during ABS operation is small, it is assumed that the range is only the range X and the range Z between the maximum regenerative braking force and zero. In this case, there is no intermediate range Y, and the regenerative braking force only enters the ranges of range X and range Z. When the battery of the electric vehicle 1 is fully charged and the electric vehicle 1 is traveling at a high speed, as Figure 8 shown, the maximum regenerative braking force of the regenerative braking force becomes smaller.

[0058] When the maximum regenerative braking force is small during ABS operation and the regenerative braking force always enters the range close to the maximum regenerative braking force and the reduction limit, the braking control device 20 makes the pressure reduction reference speed coincide with the target speed and implements the boosting of the hydraulic braking device. If the maximum regenerative braking force becomes smaller due to the state of the battery and the high rotational speed of the motor 2, the change range of the regenerative braking force becomes smaller, and sometimes the regenerative braking force enters both the range X close to the maximum regenerative braking force and the range Z close to the reduction limit. In this case, the change amount of the regenerative braking force is insufficient, and the wheel slip cannot be controlled only by the motor speed control, but the boosting and pressure reduction of the hydraulic brake are implemented, and the hydraulic brake control can also control the wheel slip together.

[0059] Figure 9 It is a flowchart showing the wheel speed control in the modified example. Figure 9 The control shown is implemented by the motor control device 10 and the braking control device 20 during the ABS operation. In addition, Figure 9 The steps S11 to S13 shown are the same processes as Figure 6 the steps S1 to S3 shown, so the description is omitted.

[0060] After performing the process of step S13, the braking control device 20 determines whether the regenerative braking force is less than the value obtained by adding a predetermined value A to the reduction limit of the regenerative braking force (step S14). As Figure 7 shown, the predetermined value A is a value that defines the range Z close to the reduction limit of the regenerative braking force. In step S14, it is determined whether the regenerative braking force enters Figure 7 the range Z shown.

[0061] When it is determined that the regenerative braking force is less than the value obtained by adding the predetermined value A to the reduction limit of the regenerative braking force (step S14: YES), the braking control device 20 sets the pressure reduction reference speed to the same value as the motor target speed (step S15). In step S15, it is determined that the regenerative braking force cannot be reduced in a short time, and the motor target speed is set to the pressure reduction reference speed. The braking control device 20 determines that the regenerative braking force enters Figure 7 the range Z shown, and makes the pressure reduction reference speed coincide with the target speed.

[0062] When it is determined that the regenerative braking force is equal to or greater than the value obtained by adding a predetermined value A to the minimum limit of the regenerative braking force (step S14: No), the braking control device 20 sets the pressure reduction reference speed to the value obtained by subtracting a predetermined value α from the motor target speed (step S16). In step S16, it is determined that the braking force can be increased by the regenerative braking force, and the value obtained by subtracting the predetermined value α from the motor target speed is set as the pressure reduction reference speed. The braking control device 20 determines that the regenerative braking force enters Figure 7 the range X or range Y shown in the figure, and shifts the pressure reduction reference speed from the target speed toward the wheel slip side by a predetermined value α.

[0063] After performing the process of step S15 or S16, the braking control device 20 determines whether the wheel speed is greater than the pressure reduction reference speed (step S17). When entering step S17 from step S15, it is determined whether the wheel speed is greater than the pressure reduction reference speed set in step S15 (= motor target speed). When entering step S17 from step S16, it is determined whether the wheel speed is greater than the pressure reduction reference speed set in step S16 (= motor target speed - α).

[0064] When it is determined that the wheel speed is equal to or less than the pressure reduction reference speed (step S17: No), the braking control device 20 determines that the wheel lock-up amount is large and performs pressure reduction of the hydraulic braking device (step S18). When performing step S18 after performing step S15, the pressure reduction of the hydraulic braking device starts in a state where the regenerative braking force enters Figure 7 the range Z shown in the figure. When performing step S18 after performing step S16, the pressure reduction of the hydraulic braking device starts in a state where the regenerative braking force enters Figure 7 the range X or range Y shown in the figure. When the process of step S18 is performed, this control routine ends.

[0065] When it is determined that the wheel speed is greater than the pressure reduction reference speed (step S17: Yes), the braking control device 20 determines whether the regenerative braking force is less than the value obtained by subtracting a predetermined value B from the maximum regenerative braking force that can be output (step S19). As Figure 7 shown in the figure, the predetermined value B is a value that defines the range X close to the maximum regenerative braking force. In step S19, it is determined whether the regenerative braking force is outside the Figure 7 range X shown in the figure.

[0066] When it is determined that the regenerative braking force is less than the value obtained by subtracting a predetermined value B from the maximum regenerative braking force that can be output (step S19: YES), the braking control device 20 stops the pressure increase of the hydraulic braking device (step S20). In step S20, it is determined that the increase in the braking force can be provided by increasing the regenerative braking force, and the pressure increase of the hydraulic braking device is stopped. The braking control device 20 determines that the regenerative braking force enters Figure 7 the shown range Y or range Z, and stops the pressure increase of the hydraulic braking device. When step S20 is implemented after step S15, the pressure increase of the hydraulic braking device is stopped in a state where the regenerative braking force enters Figure 7 the shown range Z. When step S20 is implemented after step S16, the pressure increase of the hydraulic braking device is stopped in a state where the regenerative braking force enters Figure 7 the shown range Y. After the process of step S20 is performed, this control routine ends.

[0067] When it is determined that the regenerative braking force is greater than or equal to the value obtained by subtracting a predetermined value B from the maximum regenerative braking force that can be output (step S19: NO), the braking control device 20 performs the pressure increase of the hydraulic braking device (step S21). In step S21, it is determined that the regenerative braking force cannot be increased in a short period of time, and the pressure increase of the hydraulic braking device is performed. The braking control device 20 determines that the regenerative braking force enters Figure 7 the shown range X, releases the stop of the pressure increase of the hydraulic braking device, and performs the pressure increase. After the process of step S21 is performed, this control routine ends.

[0068] According to the modification example, the hydraulic braking device can be made to operate minimally according to the regenerative braking force, and the motor speed control can be used more. Also, when the change amount of the braking force is insufficient only by the motor speed control, the hydraulic control of the hydraulic braking device can be made to operate. Thus, it is possible to accurately control to an appropriate slip amount by the regenerative braking force, and it is also possible to cope with the switching delay of the hydraulic braking device to the hydraulic control. Therefore, it is possible to prevent a decrease in the running stability, a decrease in the steering response, and a decrease in the deceleration feeling of the electric vehicle 1.

[0069] In addition, the reduction limit of the regenerative braking force is not limited to zero. For example, a value near zero can be set as the reduction limit of the regenerative braking force.

[0070] Explanation of Reference Numerals

[0071] 1 Electric vehicle

[0072] 2 Motor

[0073] 3 Differential gear

[0074] 4 Front wheels

[0075] 5 Rear wheels

[0076] 6 Converter

[0077] 7 Wheel speed sensor

[0078] 10 Motor control device

[0079] 20 Brake control device

Claims

1. A control device for an electric vehicle, which performs anti-lock control, wherein the anti-lock control uses a hydraulic braking force generated by a hydraulic brake device and a regenerative braking force generated by a motor to control the braking force applied to the wheels to suppress the locking of the wheels, wherein the control device for an electric vehicle is characterized in that: The control device of the electric vehicle is configured as follows: The first state of the regenerative braking force is controlled by controlling the hydraulic pressure of the hydraulic brake device to be constant and making the speed of the wheel follow the target speed through speed feedback control when the anti-lock control is executed, determining whether the road surface resistance has decreased to a value lower than a predetermined value during control in the first state, When it is determined that the road surface resistance has dropped below a predetermined value in the first state, the regenerative braking force is controlled by the speed feedback control, and the hydraulic pressure of the hydraulic brake device is reduced.

2. The control device for an electric vehicle according to claim 1, characterized in that: The control device of the electric vehicle is configured as follows: setting a pressure reducing reference speed for reducing the hydraulic pressure of the hydraulic brake device in the first state, determining whether the rotation speed of the wheel is greater than the decompression reference speed during control in the first state, When it is determined that the rotation speed of the wheel in the first state has become lower than the decompression reference speed, it is determined that the road resistance has dropped to lower than a predetermined value during control in the first state, and decompression of the hydraulic brake device is started before the regenerative braking force reaches the reduction limit.

3. The control device for an electric vehicle according to claim 2, characterized in that: The control device of the electric vehicle is configured as follows: The decompression reference speed is set to a value obtained by subtracting a predetermined value from the target speed of the motor, The hydraulic pressure control value of the hydraulic brake device is set according to the magnitude of the road resistance. The hydraulic brake device is controlled so that the hydraulic pressure is constant at the control value of the hydraulic pressure in the first state. When it is determined that the rotation speed of the wheel has become equal to or lower than the pressure reduction reference speed in the first state, the control value of the hydraulic pressure corresponding to the reduced road surface resistance is reset, and the regenerative braking force is continuously controlled by the speed feedback control.

4. The control device for an electric vehicle according to claim 2 or 3, characterized in that: The control device of the electric vehicle is configured as follows: determining whether the regenerative braking force has entered a predetermined range including a reduction limit of the regenerative braking force during control in the first state, When it is determined that the regenerative braking force has entered the predetermined range including the reduction limit in the first state, the decompression reference speed is set to the same value as the target speed of the motor.

5. The control device for an electric vehicle according to claim 4, characterized in that: The control device of the electric vehicle is configured as follows: determining whether the regenerative braking force has entered a predetermined range including a maximum regenerative braking force that can be output during control in the first state, When it is determined that the regenerative braking force has entered the predetermined range including the maximum regenerative braking force in the first state, the hydraulic pressure of the hydraulic brake device is increased.

Images