Control device for electric vehicle

Abstract

To ensure running stability by suppressing a delay in reduction in braking force even when a road surface resistance drops during ABS operation.SOLUTION: A control device for an electric vehicle executes anti-lock control such that locking of a wheel is suppressed by controlling braking force applied to the wheel using hydraulic braking force by a hydraulic brake device and regenerative braking force by a motor. The control device executes control to set a first state where the regenerative braking force is controlled by speed feedback control such that a hydraulic pressure of the hydraulic brake device is kept constant during execution of the anti-lock control, and that a speed of the wheel is caused to follow a target speed. When it is determined that a road surface resistance has become lower than a predetermined value in the first state, the control device reduces the hydraulic pressure of the hydraulic brake device while controlling the regenerative braking force by the speed feedback control.SELECTED DRAWING: Figure 6

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 brake system (ABS) that performs antilock control using a hydraulic brake and a regenerative brake. In the configuration described in Patent Document 1, when performing antilock control, the braking force of the regenerative brake is decreased to the limit of decrease while maintaining the braking force of the hydraulic brake, and when the braking force of the regenerative brake decreases to the limit of decrease, the braking force of the hydraulic brake begins to decrease.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When the ABS is operating, the road surface resistance changes due to the progress of the vehicle, so it is necessary to control the magnitude of the braking force according to the road surface resistance. For example, when the road surface resistance decreases, it is necessary to increase the amount of decrease in the braking force. However, in the configuration described in Patent Document 1, when the road surface resistance decreases, the braking force of the regenerative brake reaches the limit of decrease and then the braking force of the hydraulic brake begins to decrease, so the decrease in the braking force is delayed, the amount of wheel lock increases, and there is a risk that the running stability of the vehicle deteriorates.

[0005] 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 a delay in the decrease of the braking force and ensure the running stability even when the road surface resistance decreases during ABS operation.

Means for Solving the Problems

[0006] The present invention is a control device for an electric vehicle that executes antilock control for suppressing wheel lock by controlling the braking force applied to a wheel using hydraulic braking force by a hydraulic brake device and regenerative braking force by a motor. When executing the antilock control, the hydraulic pressure of the hydraulic brake device is made constant, and it is controlled to a first state in which the regenerative braking force is controlled by speed feedback control that causes the speed of the wheel to follow a target speed. It is determined whether the road surface resistance has decreased from a predetermined value during the control in the first state. When it is determined that the road surface resistance has decreased from the predetermined value in the first state, while controlling the regenerative braking force by the speed feedback control, the hydraulic pressure of the hydraulic brake device is reduced.

Effects of the Invention

[0007] In the present invention, it is possible to suppress a delay in the decrease of the braking force even when the road surface resistance decreases during ABS operation, and to ensure driving stability.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Best Mode for Carrying Out the Invention

[0009] Hereinafter, the control device for an electric vehicle in an embodiment of the present invention will be specifically described. Note that the present invention is not limited to the embodiments described below.

[0010] FIG. 1 is a diagram schematically showing an electric vehicle in an 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 for 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 a motor 2 as a power source, and 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 a differential gear 3 so as to be capable of power transmission.

[0011] The motor 2 is a motor generator capable of functioning as an electric motor and a generator. When the electric vehicle 1 travels, 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 by the motor 2 acts on the left and right front wheels 4. The motor 2 is electrically connected to a battery via the inverter 6.

[0012] 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 advance in the ROM. Signals from various sensors mounted on the electric vehicle 1 are input to the motor control device 10. For example, signals from a motor rotation speed sensor of the electric vehicle 1 and a wheel speed sensor 7 that detects the speed of the wheels 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 in speed feedback control to the inverter 6. The motor control device 10 controls the torque of the motor 2 so that the rotation speed of the motor 2 follows the target speed.

[0013] A brake device is provided on each wheel of the electric vehicle 1. The brake device is a hydraulic friction brake, and the braking force changes according to the hydraulic pressure. The braking force by the brake device (hereinafter referred to as the hydraulic braking force) is controlled by the brake control device 20. In this description, the brake device constituted by the hydraulic friction brake is described as a hydraulic brake.

[0014] The brake control device 20 is an electronic control device that controls the braking force of the electric vehicle 1. The hardware of the brake control device 20 is the same as that of the motor control device 10. Signals from various sensors mounted on the electric vehicle 1 are input to the brake control device 20. For example, signals from the wheel speed sensors 7 provided on each wheel are input to the brake control device 20. The brake control device 20 executes various controls based on the input signals.

[0015] The brake control device 20 controls the hydraulic braking force by the hydraulic brake device and also controls the regenerative braking force by the motor 2. A control signal for controlling the hydraulic brake device of each wheel is output from the brake control device 20 to each hydraulic brake device. 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 the brake control device 20 controls the motor 2, it 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 the regenerative braking force by the motor 2 in addition to the hydraulic braking force by each hydraulic brake device.

[0016] When the brake control device 20 brakes the electric vehicle 1 using the regenerative braking force of the motor 2 and the hydraulic braking force of the hydraulic brake device, it executes antilock control to avoid wheel lock. The brake control device 20 executes antilock control during braking and suppresses wheel lock by controlling the braking force applied to the wheels using the hydraulic braking force by the hydraulic brake device and the regenerative braking force by the motor 2. The brake control device 20 has a function as an antilock brake system (ABS). Note that the operation of the ABS and the execution of antilock control are synonymous.

[0017] The brake control device 20 detects the wheel lock tendency based on the wheel speed and determines whether to operate the ABS. When the brake control device 20 executes antilock control, for the wheels with a lock tendency, it controls the wheel speed to follow the target wheel speed.

[0018] Specifically, when the ABS is activated, the brake control device 20 calculates the target speed, and makes the wheel speed accurately follow the target speed only by the regenerative speed feedback control of the motor control device 10, and controls so that the pressure reduction of the hydraulic brake device does not operate. The regenerative speed feedback control is the feedback control of the motor rotation speed, and controls the regenerative braking force so that the motor rotation speed follows the target speed. The phrase "only the regenerative speed feedback control" means that when changing the braking force of the wheel during ABS operation, the hydraulic braking force is kept constant and only the regenerative braking force is varied, and the variation of the regenerative braking force is performed by the feedback control of the motor rotation speed.

[0019] When the road surface resistance is constant during ABS operation, the brake control device 20 keeps the hydraulic pressure of the hydraulic brake device constant, and controls the regenerative braking force by the regenerative speed feedback control to make the wheel speed follow the target speed. On the other hand, when the road surface resistance decreases during ABS operation, although it is necessary to reduce the braking force of the wheel, wheel lock may occur only by reducing the regenerative braking force, so it is necessary to operate the pressure reduction of the hydraulic brake device. Therefore, the brake control device 20 sets a reference speed (hereinafter referred to as the pressure reduction reference speed) for performing the pressure reduction of the hydraulic brake device during ABS operation. The brake control device 20 sets the pressure reduction reference speed to a speed slightly on the wheel lock side with respect to the target wheel speed. When the wheel speed becomes equal to or lower than the pressure reduction reference speed during ABS operation, the brake control device 20 performs the pressure reduction of the hydraulic brake device. The brake control device 20 is configured to operate the pressure reduction of the hydraulic brake device without delay only when the road surface resistance decreases and the wheel slip increases.

[0020] FIG. 2 is a time chart showing the case where the road surface resistance does not change during ABS operation. As shown in FIG. 2, the brake control device 20 causes the wheel speed to follow the target speed by regenerative speed feedback control. During ABS operation, the brake control device 20 does not generate an increase or decrease in the hydraulic pressure of the hydraulic brake device as much as possible, and controls the hydraulic pressure of the hydraulic brake device to a constant hydraulic pressure that compensates for the shortage of the 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 less than the maximum regeneration that can be output during ABS operation, the brake control device 20 stops increasing the pressure of the hydraulic brake 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.

[0021] As shown in FIG. 3, 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 offset toward the wheel slip side from the target speed. The offset amount is a predetermined value α. The predetermined value α is set to a value equal to or greater than the amount of variation in the wheel speed when the road surface resistance does not change during ABS operation. The brake control device 20 sets the pressure reduction reference speed to a speed offset toward the wheel lock side with respect to the target speed of the motor rotation speed. The amount of offset is the predetermined value α and is greater than the amount of speed variation during motor speed control. The brake control device 20 sets the pressure reduction reference speed to be lower than the target speed of the regenerative control. Since the pressure reduction reference speed is set closer to the wheel lock side than the variation in the motor rotation speed in this way, the wheel speed does not decrease to the pressure reduction reference speed and the pressure reduction of the hydraulic brake device does not occur when the road surface resistance does not change. As a result, the hydraulic braking force by the hydraulic brake device does not fluctuate, and the controllability of the wheel slip by the motor 2 is not deteriorated.

[0022] The brake control device 20 presets a desired slip ratio. The slip ratio of the wheel is obtained based on the wheel speed and the vehicle body speed. The brake control device 20 can preset the slip ratio at which the road surface resistance is estimated to be near the maximum. The brake control device 20 controls so that the slip ratio of the wheel where the ABS operates falls within the preset slip ratio range. The brake control device 20 calculates the target speed of the wheel based on the vehicle body speed and the slip ratio. The brake control device 20 sets the target speed of the motor 2 using this target speed of the wheel in order to achieve the target speed of the wheel. The motor control device 10 can make the wheel speed follow the target speed by making the motor rotation speed follow the target speed using motor speed control based on the target speed from the brake control device 20.

[0023] The brake 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 brake 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 brake 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 brake control device 20 outputs the motor target speed, and the motor control device 10 controls the torque of the motor 2 in order to achieve the motor target speed.

[0024] FIG. 4 is a time chart showing the case where the road surface resistance decreases when the ABS operates. As shown in FIG. 4, a large fluctuation occurs in the wheel speed due to the decrease in the road surface resistance, and the wheel speed reaches the pressure reduction reference speed on the wheel lock side. As shown in FIG. 5, when the amount of fluctuation of the wheel speed increases due to a large slip of the wheel and the wheel speed reaches the pressure reduction reference speed, the brake control device 20 starts to reduce the pressure of the hydraulic brake device. The amount of fluctuation of the wheel speed on the slip side with respect to the target speed represents the amount of wheel lock. Since the brake control device 20 starts to reduce the pressure of the hydraulic brake device when the wheel speed becomes equal to or lower than the pressure reduction reference speed, it starts to reduce the pressure of the hydraulic brake device before the regenerative braking force becomes zero (reduction limit).

[0025] When the brake control device 20 performs pressure reduction of the hydraulic brake device due to a decrease in road surface resistance, it newly sets a control value of the hydraulic pressure for controlling it to a 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 decrease in the road surface resistance becomes lower than the control value of the hydraulic pressure set before the decrease in the road surface resistance. After the decrease in the road surface resistance during ABS operation, the brake control device 20 makes the hydraulic pressure constant based on the newly set control value of the hydraulic pressure, and causes the wheel speed to accurately follow the target speed by the regenerative speed feedback control by the motor control device 10.

[0026] In this way, when the road surface resistance decreases during ABS operation, it is possible to accelerate the recovery from wheel lock by starting the pressure reduction of the hydraulic brake device before the regenerative braking force reaches the decrease limit. Thereby, the amount of wheel lock can be suppressed to be smaller than when the hydraulic pressure of the hydraulic brake device is reduced after the regenerative braking force reaches the decrease limit.

[0027] FIG. 6 is a flowchart showing wheel speed control. The control shown in FIG. 6 is performed by the motor control device 10 and the brake control device 20 during ABS operation. In the description of FIG. 6, the ABS operating wheel is described as the front wheel 4.

[0028] The brake control device 20 sets the target speed of the motor 2 during ABS operation (step S1). In step S1, the target speed of the motor 2 is set based on the wheel speed of the wheel that is power-transmittably connected to the motor 2.

[0029] 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 motor speed control based on the 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.

[0030] The motor control device 10 outputs a command value for the regenerative braking force (step S3). In step S3, the regenerative braking force calculated in step S2 is output as the command value from the motor control device 10.

[0031] The brake control device 20 sets a decompression reference speed (step S4). In step S4, a speed obtained by subtracting a predetermined value α from the motor target speed is set as the decompression reference speed. The decompression reference speed is a value smaller than the motor target speed by a predetermined value α. In step S4, the brake control device 20 sets the decompression reference speed using the motor target speed calculated in step S1 and a preset predetermined value α. The predetermined value α is an offset amount toward the wheel lock side with respect to the target speed.

[0032] The brake control device 20 determines whether the wheel speed is greater than the decompression 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 decompression reference speed set in step S4. The brake control device 20 determines the presence or absence of decompression of the hydraulic brake device by comparing the wheel speed with the decompression reference speed.

[0033] When it is determined that the wheel speed is less than or equal to the decompression reference speed (step S5: No), the brake control device 20 determines that the wheel lock amount is large and performs decompression of the hydraulic brake device (step S6). In step S6, it is determined that the road surface resistance has decreased during ABS operation, and decompression of the hydraulic brake device is started. The brake control device 20 outputs a command signal for decompressing the hydraulic pressure of the hydraulic brake device to the hydraulic brake device. When the process of step S6 is performed, this control routine ends.

[0034] When it is determined that the wheel speed is greater than the decompression reference speed (step S5: Yes), the brake control device 20 determines whether the regenerative braking force is less than the maximum regeneration that can be output (step S7). In step S7, it is determined whether there is any remaining capacity up to the maximum regeneration for the regenerative braking force. The brake control device 20 calculates the maximum regeneration that can be output from the motor 2 based on the running state of the electric vehicle 1 and the charging state of the battery. The method for calculating the maximum regeneration that can be output from the motor 2 may be a known method. The brake control device 20 compares the maximum regeneration 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 regeneration. The motor control device 10 can output the regenerative braking force calculated in step S2 to the brake control device 20.

[0035] When it is determined that the regenerative braking force is less than the maximum regeneration that can be output (step S7: Yes), the brake control device 20 stops the pressure increase of the hydraulic brake device (step S8). In step S8, it is determined that the increase in the braking force can be covered by the increase in the regenerative braking force, and the pressure increase of the hydraulic brake device is stopped. The brake control device 20 stops the pressure increase of the hydraulic brake device by making the hydraulic pressure of the hydraulic brake device constant. In this case, the brake control device 20 keeps the hydraulic braking force constant and only varies the regenerative braking force. When the process of step S8 is carried out, this control routine ends.

[0036] When it is determined that the regenerative braking force is not less than the maximum regeneration that can be output (step S7: No), the brake control device 20 performs the pressure increase of the hydraulic brake device (step S9). In step S9, since it is determined that the regenerative braking force has reached the maximum regeneration that can be output and the regenerative braking force cannot be increased further, the pressure increase of the hydraulic brake device is carried out. The brake control device 20 outputs a command signal for increasing the hydraulic pressure of the hydraulic brake device to the hydraulic brake device. When the process of step S9 is carried out, this control routine ends.

[0037] As described above, according to the embodiment, when the ABS is operating, the regenerative braking force can accurately control the wheels to an appropriate slip amount, and when the road surface resistance decreases, it is possible to prevent an increase in the wheel lock amount due to the switching delay of the hydraulic control. Thereby, it is possible to prevent deterioration of the running stability, steerability, and deceleration feeling of the electric vehicle 1.

[0038] Note that the electric vehicle 1 is not limited to a front-wheel drive vehicle and may be a rear-wheel drive vehicle. The electric vehicle 1 may be any vehicle equipped with a motor that generates regenerative braking force on either the front wheels 4 or the rear wheels 5.

[0039] Also, when the regenerative braking force enters a range close to the decrease limit during ABS operation, the brake control device 20 may set the pressure reduction reference speed to the motor target speed. Further, when the regenerative braking force is smaller than the range close to the maximum regenerative force that can be output during ABS operation, the brake control device 20 may stop increasing the pressure of the hydraulic brake device. Thus, as a modification of the brake 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 force that can be output and the relationship between the regenerative braking force and the decrease limit during ABS operation. The modified brake control device 20 will be described with reference to FIGS. 7 to 9.

[0040] As shown in FIG. 7, assume a case where, when the maximum regenerative force of the regenerative braking force during ABS operation is large, the range from the maximum regenerative force to zero is divided into ranges X, Y, and Z. In this case, the regenerative braking force will fall into any one of the range X close to the maximum regenerative force, the intermediate range Y, and the range Z close to the decrease limit. Note that the range X includes the case where the regenerative braking force reaches the maximum regenerative force, and the range Z includes the case where the regenerative braking force reaches the decrease limit.

[0041] When the regenerative braking force enters the range X near the maximum regeneration during ABS operation, the brake control device 20 offsets the decompression reference speed by a predetermined value α toward the wheel slip side from the target speed and increases the pressure of the hydraulic brake device. When the regenerative braking force enters the range X close to the maximum regeneration during motor speed control, the pressure increase of the hydraulic brake device is started. As the pressure of the hydraulic brake device increases, the regenerative braking force decreases and goes outside the range X (inside the range Y). When the regenerative braking force changes from the range X to the range Y, the brake control device 20 stops the pressure increase of the hydraulic brake again and makes the wheel speed follow the target speed only by motor speed control (only the speed feedback control of regeneration). As a result, a state where the regenerative braking force cannot be increased during ABS operation does not occur, and it is possible to prevent controlling the wheel speed only by the hydraulic pressure control of the hydraulic brake device in a state where the regenerative braking force cannot be increased. Therefore, even when the regenerative braking force increases up to near the maximum regeneration and it is a region where the increase in regeneration is insufficient, the wheel slip control by the motor 2 continues, so the controllability of the wheel slip is not deteriorated.

[0042] When the regenerative braking force enters the intermediate range Y during ABS operation, the brake control device 20 offsets the decompression reference speed by a predetermined value α toward the wheel slip side and stops the pressure increase of the hydraulic brake device.

[0043] When the regenerative braking force enters the range Z where it is close to the reduction limit during ABS operation, the brake control device 20 adjusts the pressure reduction reference speed to match the target speed and stops increasing the pressure of the hydraulic brake device. Since the motor target speed and the pressure reduction reference speed become the same speed, pressure reduction of the hydraulic brake device occurs during motor speed control. When the regenerative braking force enters the range Z where it is close to the reduction limit during motor control, the pressure reduction of the hydraulic brake device is started. Along with the pressure reduction of the hydraulic brake device, the regenerative braking force increases and goes outside the range Z (inside the range Y). When the regenerative braking force changes from the range Z to the range Y, the brake control device 20 sets the pressure reduction reference speed to a speed offset toward the wheel lock side from the motor target speed, and causes the wheel speed to follow the target speed only by motor speed control (only by regenerative speed feedback control). As a result, a state where the regenerative braking force cannot be reduced during ABS operation does not occur, so that it is possible to prevent controlling the wheel speed only by hydraulic pressure control of the hydraulic brake device in a state where the regenerative braking force cannot be reduced. Therefore, even when the regenerative braking force drops to near the reduction limit and it is a region where regenerative reduction is insufficient, the wheel slip control by the motor 2 continues, so that the controllability of the wheel slip is not deteriorated.

[0044] As shown in FIG. 8, assume a case where, when the maximum regeneration of the regenerative braking force during ABS operation is small, only the range that is the range X and the range Z exists between the maximum regeneration and zero. In this case, there is no intermediate range Y, and the regenerative braking force enters only the range that is the range X and the range Z. When the battery of the electric vehicle 1 is fully charged or when the electric vehicle 1 is traveling at a high vehicle speed, the maximum regeneration of the regenerative braking force becomes small as shown in FIG. 8.

[0045] When the maximum regeneration is small during ABS operation and the regenerative braking force is always within a range close to the maximum regeneration and the decrease limit, the brake control device 20 adjusts the decompression reference speed to match the target speed and increases the hydraulic pressure of the hydraulic brake device. When the state of the battery and the high rotational speed of the motor 2 result in a small maximum regeneration, the change range of the regenerative braking force becomes small, and the regenerative braking force may enter both the range X close to the maximum regeneration and the range Z close to the decrease limit. In this case, although the change amount of the regenerative braking force is insufficient and the wheel slip cannot be controlled only by motor speed control, the increase and decrease of the hydraulic brake are implemented, and the wheel slip can also be controlled in combination with the hydraulic brake control.

[0046] Figure 9 is a flowchart showing wheel speed control in a modified example. The control shown in Figure 9 is implemented by the motor control device 10 and the brake control device 20 during ABS operation. Note that steps S11 to S13 shown in Figure 9 are the same processes as steps S1 to S3 shown in Figure 6, and thus the description thereof is omitted.

[0047] After performing the process of step S13, the brake control device 20 determines whether the regenerative braking force is smaller than the value obtained by adding a predetermined value A to the decrease limit of the regenerative braking force (step S14). As shown in Figure 7, the predetermined value A is a value that defines the range Z close to the decrease limit of the regenerative braking force. In step S14, it is determined whether the regenerative braking force is within the range Z shown in Figure 7.

[0048] When it is determined that the regenerative braking force is smaller than the value obtained by adding the predetermined value A to the decrease limit of the regenerative braking force (step S14: Yes), the brake control device 20 sets the decompression reference speed to the same value as the motor target speed (step S15). In step S15, it is determined that the decrease of the regenerative braking force is impossible in a short time, and the motor target speed is set to the decompression reference speed. The brake control device 20 determines that the regenerative braking force is within the range Z shown in Figure 7 and adjusts the decompression reference speed to match the target speed.

[0049] When it is determined that the regenerative braking force is equal to or greater than a value obtained by adding a predetermined value A to the reduction limit of the regenerative braking force (step S14: No), the brake control device 20 sets the pressure reduction reference speed to a value obtained by subtracting a predetermined value α from the motor target speed (step S16). In step S16, it is determined that the increase in the braking force can be achieved 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 brake control device 20 determines that the regenerative braking force is within the range X or range Y shown in FIG. 7, and offsets the pressure reduction reference speed by the predetermined value α toward the wheel slip side from the target speed.

[0050] After performing the process of step S15 or S16, the brake control device 20 determines whether the wheel speed is greater than the pressure reduction reference speed (step S17). When proceeding from step S15 to step S17, it is determined whether the wheel speed is greater than the pressure reduction reference speed (= motor target speed) set in step S15. When proceeding from step S16 to step S17, it is determined whether the wheel speed is greater than the pressure reduction reference speed (= motor target speed - α) set in step S16.

[0051] When it is determined that the wheel speed is equal to or less than the pressure reduction reference speed (step S17: No), the brake control device 20 determines that the wheel lock amount is large and performs pressure reduction of the hydraulic brake device (step S18). When step S18 is performed after step S15 is performed, the pressure reduction of the hydraulic brake device is started in a state where the regenerative braking force enters the range Z shown in FIG. 7. When step S18 is performed after step S16 is performed, the pressure reduction of the hydraulic brake device is started in a state where the regenerative braking force enters the range X or range Y shown in FIG. 7. When the process of step S18 is performed, this control routine ends.

[0052] When it is determined that the wheel speed is greater than the decompression reference speed (step S17: Yes), the brake control device 20 determines whether the regenerative braking force is less than a value obtained by subtracting a predetermined value B from the maximum regenerative braking force that can be output (step S19). As shown in FIG. 7, the predetermined value B is a value that defines a range X close to the maximum regeneration. In step S19, it is determined whether the regenerative braking force is outside the range X shown in FIG. 7.

[0053] When it is determined that the regenerative braking force is less than a value obtained by subtracting the predetermined value B from the maximum regenerative braking force that can be output (step S19: Yes), the brake control device 20 stops increasing the pressure of the hydraulic brake device (step S20). In step S20, it is determined that the increase in braking force can be covered by the increase in regenerative braking force, and the pressure increase of the hydraulic brake device is stopped. The brake control device 20 determines that the regenerative braking force has entered the range Y or range Z shown in FIG. 7, and stops increasing the pressure of the hydraulic brake device. When step S20 is performed after step S15 is performed, the pressure increase of the hydraulic brake device is stopped in a state where the regenerative braking force has entered the range Z shown in FIG. 7. When step S20 is performed after step S16 is performed, the pressure increase of the hydraulic brake device is stopped in a state where the regenerative braking force has entered the range Y shown in FIG. 7. When the process of step S20 is performed, this control routine ends.

[0054] When it is determined that the regenerative braking force is equal to or greater than a value obtained by subtracting the predetermined value B from the maximum regenerative braking force that can be output (step S19: No), the brake control device 20 increases the pressure of the hydraulic brake device (step S21). In step S21, it is determined that the increase in regenerative braking force is not possible in a short time, and the pressure of the hydraulic brake device is increased. The brake control device 20 determines that the regenerative braking force has entered the range X shown in FIG. 7, releases the pressure increase stop of the hydraulic brake device, and increases the pressure. When the process of step S21 is performed, this control routine ends.

[0055] According to the modified example, the hydraulic brake device can be operated minimally according to the regenerative braking force, and motor speed control can be used more. When the change amount of the braking force is insufficient only by the motor speed control, the hydraulic control of the hydraulic brake device can be operated. Thereby, while controlling the appropriate slip amount with high precision by the regenerative braking force, it is possible to cope with the switching delay to the hydraulic control of the hydraulic brake device. 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.

[0056] Note that the decrease limit of the regenerative braking force is not limited to zero. For example, a value near zero can be set as the decrease limit of the regenerative braking force.

Explanation of Signs

[0057] 1 Electric vehicle 2 Motor 3 Differential gear 4 Front wheel 5 Rear wheel 6 Inverter 7 Wheel speed sensor 10 Motor control device 20 Brake control device

Claims

1. A control device for an electric vehicle that executes antilock control to suppress wheel lock by controlling the braking force applied to the wheels using hydraulic braking force by a hydraulic brake device and regenerative braking force by a motor, controls the hydraulic pressure of the hydraulic brake device to be constant during execution of the antilock control, and controls the regenerative braking force by speed feedback control to make the speed of the wheel follow a target speed, and controls to a first state, determines whether the road surface resistance has decreased below a predetermined value during control in the first state, when it is determined in the first state that the road surface resistance has decreased below a predetermined value, while controlling the regenerative braking force by the speed feedback control, reduces the hydraulic pressure of the hydraulic brake device characterized by a control device for an electric vehicle.

2. sets a pressure reduction reference speed for reducing the hydraulic pressure of the hydraulic brake device in the first state, determines whether the rotational speed of the wheel is greater than the pressure reduction reference speed during control in the first state, when it is determined in the first state that the rotational speed of the wheel has become equal to or less than the pressure reduction reference speed, determines that the road surface resistance has decreased below a predetermined value during control in the first state, and starts reducing the pressure of the hydraulic brake device before the regenerative braking force reaches the reduction limit characterized by the control device for an electric vehicle according to claim 1.

3. sets the pressure reduction reference speed to a value obtained by subtracting a predetermined value from the target speed of the motor, sets a control value of the hydraulic pressure of the hydraulic brake device according to the magnitude of the road surface resistance, controls in the first state so that the hydraulic pressure of the hydraulic brake device becomes constant at the control value of the hydraulic pressure, when it is determined in the first state that the rotational speed of the wheel has become equal to or less than the pressure reduction reference speed, re-sets the control value of the hydraulic pressure according to the decreased road surface resistance, and continues to control the regenerative braking force by the speed feedback control characterized by the control device for an electric vehicle according to claim 2.

4. determines whether the regenerative braking force has entered a range close to the reduction limit of the regenerative braking force during control in the first state, when it is determined in the first state that the regenerative braking force has entered a range close to the reduction limit, sets the pressure reduction reference speed to the same value as the target speed of the motor characterized by the control device for an electric vehicle according to claim 2 or 3.

5. determines whether the regenerative braking force has entered a range close to the maximum regenerative power that can be output during control in the first state, When it is determined that the regenerative braking force has entered a range close to the maximum regeneration in the first state, the hydraulic pressure of the hydraulic brake device is increased. The control device for an electric vehicle according to claim 4, characterized in that.

Images