Control device for electric vehicles

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 decrease limit while maintaining the braking force of the hydraulic brake, and when the braking force of the regenerative brake decreases to the decrease limit, the braking force of the hydraulic brake starts 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 decrease limit and then the braking force of the hydraulic brake starts to decrease, so the decrease in the braking force is delayed, the locking amount of the wheels 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 the delay in the decrease of the braking force and ensure the running stability even when the road surface resistance decreases during the operation of the ABS.

Means for Solving the Problems

[0006] The present invention is a control device for an electric vehicle that performs anti-lock control to suppress wheel locking by controlling the braking force applied to the wheels using hydraulic braking force from a hydraulic brake system and regenerative braking force from a motor, characterized in that, when the anti-lock control is performed, the hydraulic pressure of the hydraulic brake system is kept constant, and the regenerative braking force is controlled by speed feedback control to make the speed of the wheels follow a target speed, and it is determined whether the road resistance has fallen below a predetermined value while in the first state, and if it is determined that the road resistance has fallen below a predetermined value in the first state, the hydraulic pressure of the hydraulic brake system is reduced while controlling the regenerative braking force by speed feedback control. [Effects of the Invention]

[0007] In this invention, even when road resistance decreases during ABS operation, the decrease in braking force is suppressed, thereby ensuring driving stability. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic diagram showing an electric vehicle in an embodiment. [Figure 2] This is a time chart showing the case where road resistance does not change when ABS is activated. [Figure 3] This is a diagram illustrating the standard rate of decompression. [Figure 4] This is a time chart showing the decrease in road resistance when ABS is activated. [Figure 5] This diagram illustrates the increased degree of wheel lock-up. [Figure 6] This is a flowchart illustrating wheel speed control. [Figure 7] This diagram illustrates the control state in relation to the magnitude of the regenerative braking force. [Figure 8] This diagram illustrates the case where maximum regeneration is small. [Figure 9] This is a flowchart illustrating wheel speed control in a modified example. [Modes for carrying out the invention]

[0009] The following describes in detail the control device for an electric vehicle in an embodiment of the present invention. However, the present invention is not limited to the embodiments described below.

[0010] Figure 1 is a schematic diagram showing an electric vehicle in an embodiment. The electric vehicle 1 comprises 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 a motor 2 as a power source, with the front wheels 4 being the drive wheels and the rear wheels 5 being the driven wheels. The motor 2 is connected to the front wheels 4 via the differential gear 3 so as to be able to transmit power.

[0011] Motor 2 is a motor-generator capable of functioning as both an electric motor and a generator. When the electric vehicle 1 is running, the power output from motor 2 is transmitted to the left and right front wheels 4 via the differential gear 3. During regenerative braking, the regenerative braking force from motor 2 acts on the left and right front wheels 4. Motor 2 is electrically connected to the battery via an inverter 6.

[0012] The motor control device 10 is an electronic control device that controls the motor 2. The motor control device 10 consists of a microcomputer equipped with a CPU, RAM, ROM, and input / output interfaces. The motor control device 10 performs signal processing according to a program pre-stored in the ROM. The motor control device 10 receives signals from various sensors mounted on the electric vehicle 1. For example, signals from the motor rotation speed sensor of the electric vehicle 1 and the wheel speed sensor 7 that detects the speed of the wheels are input to the motor control device 10. The motor control device 10 performs various controls based on the signals input from the various sensors. The motor control device 10 performs speed feedback control. The motor control device 10 outputs a control signal to the inverter 6 to control the motor 2 using speed feedback control. 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] Each wheel of the electric vehicle 1 is equipped with a brake device. The brake devices are hydraulic friction brakes, and the braking force changes according to the hydraulic pressure. The braking force provided by the brake devices (hereinafter referred to as hydraulic braking force) is controlled by the brake control device 20. In this explanation, a brake device composed of hydraulic friction brakes will be referred to 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 brake control device 20 is hardware-based and is the same as 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 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.

[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 performs antilock control to avoid wheel lock. The brake control device 20 performs 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 performs antilock control, for the wheels having 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 implementing 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 lower than the pressure reduction reference speed during ABS operation, the brake control device 20 implements 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] Figure 2 is a time chart showing the case where road resistance does not change when ABS is activated. As shown in Figure 2, the brake control device 20 makes the wheel speed follow the target speed by regenerative speed feedback control. When ABS is activated, the brake control device 20 minimizes the increase or decrease in hydraulic pressure of the hydraulic brake system and controls the hydraulic pressure of the hydraulic brake system to a constant hydraulic pressure that compensates for the deficiency of regenerative braking force. This hydraulic pressure control value (value of constant hydraulic pressure) is set according to the road resistance and is determined to a value proportional to the magnitude of the road resistance. When ABS is activated, if the regenerative braking force is less than the maximum regeneration that can be output, the brake control device 20 stops increasing the pressure of the hydraulic brake system and uses the motor speed control of the motor control device 10 to control the wheel slip with high precision to a target speed near the maximum road resistance.

[0021] As shown in Figure 3, the target wheel speed is set near the peak of road resistance. The pressure reduction reference speed is set to a speed offset from the target speed towards 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 amount of wheel speed fluctuation when road resistance does not change during ABS operation. The brake control device 20 sets the pressure reduction reference speed to a speed offset towards the wheel lock side relative to the target motor rotation speed. The amount of offset is the predetermined value α, which is greater than or equal to the speed fluctuation amount during motor speed control. The brake control device 20 sets the pressure reduction reference speed to be smaller than the target speed for regenerative control. In this way, since the pressure reduction reference speed is set towards the wheel lock side relative to the fluctuation of motor rotation speed, if road resistance does not change, the wheel speed does not decrease to the pressure reduction reference speed and no pressure reduction occurs in the hydraulic brake system. As a result, the hydraulic braking force by the hydraulic brake system does not fluctuate and the controllability of wheel slip by the motor 2 does not deteriorate.

[0022] The brake control device 20 has a desired slip ratio set in advance. The slip ratio of the wheel is determined based on the wheel speed and the vehicle speed. The brake control device 20 can set in advance a slip ratio that is estimated to be near the maximum road resistance. The brake control device 20 controls the slip ratio of the wheel for which ABS is activated so that it falls within the range of the preset slip ratio. The brake control device 20 calculates the target speed of the wheel based on the vehicle speed and the slip ratio. In order to achieve the target speed of the wheel, the brake control device 20 sets the target speed of the motor 2 using this 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 motor 2 using the wheel speed of the front wheel 4 to which 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 motor target speed to the average of the control target values ​​of the left and right front wheels 4. The brake control device 20 outputs the motor target speed, and the motor control device 10 controls the torque of motor 2 to achieve the motor target speed.

[0024] Figure 4 is a time chart showing the case where road resistance decreases when ABS is activated. As shown in Figure 4, a large fluctuation in wheel speed occurs due to the decrease in road resistance, and the wheel speed reaches the decompression reference speed on the wheel lock side. As shown in Figure 5, when the amount of fluctuation in wheel speed becomes large due to a large wheel slip and the wheel speed reaches the decompression reference speed, the brake control device 20 starts decompressing the hydraulic brake system. The amount of fluctuation in the slipping wheel speed relative to the target speed represents the amount of wheel lock. Since the brake control device 20 starts decompressing the hydraulic brake system when the wheel speed falls below the decompression reference speed, it starts decompressing the hydraulic brake system before the regenerative braking force becomes zero (reduction limit).

[0025] When the brake control device 20 reduces the pressure of the hydraulic brake system due to a decrease in road resistance, it readjusts the hydraulic pressure control value to maintain a constant hydraulic pressure. Since the hydraulic pressure control value is set to a value proportional to the magnitude of road resistance, the hydraulic pressure control value set after the decrease in road resistance will be lower than the hydraulic pressure control value set before the decrease in road resistance. When the ABS is activated and the road resistance decreases, the brake control device 20 makes the hydraulic pressure constant based on the readjusted hydraulic pressure control value, and the motor control device 10 uses regenerative speed feedback control to precisely track the wheel speed to the target speed.

[0026] In this way, when road resistance decreases during ABS operation, the recovery from wheel lock can be accelerated by starting to depressurize the hydraulic brake system before the regenerative braking force reaches its limit. This allows for a smaller amount of wheel lock compared to depressurizing the hydraulic pressure of the hydraulic brake system after the regenerative braking force has reached its limit.

[0027] Figure 6 is a flowchart illustrating wheel speed control. The control shown in Figure 6 is performed by the motor control device 10 and the brake control device 20 while ABS is operating. In the explanation of Figure 6, the ABS operating wheel is referred to as the front wheel 4.

[0028] The brake control device 20 sets the target speed of the motor 2 when ABS is activated (step S1). In step S1, the target speed of the motor 2 is set based on the wheel speed of the wheel to which the motor 2 is connected in a power-transmitting manner.

[0029] The brake control device 20 outputs a 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 that 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 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 a command value.

[0031] The brake control device 20 sets the depressurization 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 depressurization reference speed. The depressurization reference speed is a value that is smaller than the motor target speed by the predetermined value α. In step S4, the brake control device 20 sets the depressurization reference speed using the motor target speed calculated in step S1 and the predetermined value α that has been set in advance. The predetermined value α is the amount of offset toward the wheel lock side relative to the target speed.

[0032] 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 there is pressure reduction in the hydraulic brake system by comparing the wheel speed with the pressure reduction reference speed.

[0033] If the wheel speed is determined to be below the pressure reduction reference speed (step S5: No), the brake control device 20 determines that the wheel lock amount is large and performs pressure reduction of the hydraulic brake system (step S6). In step S6, it is determined that the road resistance has decreased when the ABS is activated, and pressure reduction of the hydraulic brake system is started. The brake control device 20 outputs a command signal to the hydraulic brake system to reduce the hydraulic pressure of the hydraulic brake system. After the processing in step S6 is completed, this control routine ends.

[0034] If the wheel speed is determined to be greater than the pressure reduction reference speed (Step S5: Yes), the brake control device 20 determines whether the regenerative braking force is less than the maximum regenerative force that can be output (Step S7). In Step S7, it is determined whether there is still capacity left to reach the maximum regenerative force. The brake control device 20 calculates the maximum regenerative force that can be output from the motor 2 based on the driving state of the electric vehicle 1 and the battery charge state. The method for calculating the maximum regenerative force that can be output from the motor 2 may be a known method. The brake control device 20 compares the maximum regenerative 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 force. The motor control device 10 can output the regenerative braking force calculated in Step S2 to the brake control device 20.

[0035] If it is determined that the regenerative braking force is less than the maximum regenerative force that can be output (Step S7: Yes), the brake control device 20 stops increasing the pressure of the hydraulic brake system (Step S8). In Step S8, 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 system is stopped. The brake control device 20 stops increasing the pressure of the hydraulic brake system by keeping the hydraulic pressure of the hydraulic brake system constant. In this case, the brake control device 20 keeps the hydraulic braking force constant and only varies the regenerative braking force. After the process in Step S8 is completed, this control routine ends.

[0036] If it is determined that the regenerative braking force is not less than the maximum regenerative force that can be output (step S7: No), the brake control device 20 increases the pressure of the hydraulic brake system (step S9). In step S9, it is determined that the regenerative braking force has reached the maximum regenerative force that can be output and that it is not possible to increase the regenerative braking force any further, so the pressure of the hydraulic brake system is increased. The brake control device 20 outputs a command signal to the hydraulic brake system to increase the hydraulic pressure of the hydraulic brake system. After the processing in step S9 is completed, this control routine ends.

[0037] As described above, according to the embodiment, when ABS is activated, the regenerative braking force can be used to control the wheels to an appropriate amount of slip with high precision, while preventing an increase in the amount of wheel lock due to a delay in switching hydraulic control when road resistance decreases. This prevents deterioration of the driving stability, steering performance, and deceleration feel of the electric vehicle 1.

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

[0039] Furthermore, the brake control device 20 may set the decompression reference speed to the motor target speed when the regenerative braking force enters a range close to the reduction limit during ABS operation. In addition, the brake control device 20 may stop boosting the hydraulic brake system when the regenerative braking force is smaller than the range close to the maximum regeneration that can be output during ABS operation. Thus, as a modified example of the brake control device 20, it can be configured to switch the control state according to the relationship between the regenerative braking force during ABS operation and the maximum regeneration that can be output, and the relationship between the regenerative braking force and the reduction limit. The modified brake control device 20 will be explained with reference to Figures 7 to 9.

[0040] As shown in Figure 7, when the regenerative braking force during ABS operation is large, we can assume that the range from the maximum regeneration to zero can be divided into ranges X, Y, and Z. In this case, the regenerative braking force will fall within one of the following ranges: range X, which is close to the maximum regeneration; range Y, which is in the middle; and range Z, which is close to the reduction limit. Range X includes the case where the regenerative braking force reaches the maximum regeneration, and range Z includes the case where the regenerative braking force reaches the reduction limit.

[0041] When the regenerative braking force is within 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 system. During motor speed control, when the regenerative braking force enters range X close to the maximum regeneration, the hydraulic brake system starts increasing pressure. As the hydraulic brake system increases pressure, the regenerative braking force decreases and moves outside range X (within range Y). When the regenerative braking force changes from range X to range Y, the brake control device 20 stops increasing the hydraulic brake pressure again and makes the wheel speed follow the target speed using only motor speed control (only regenerative speed feedback control). This prevents a situation where the regenerative braking force cannot be increased during ABS operation, thus preventing the wheel speed from being controlled solely by hydraulic control of the hydraulic brake system when the regenerative braking force cannot be increased. Therefore, even when the regenerative braking force increases to near the maximum regeneration and is in a region where the regeneration increase is insufficient, wheel slip control by motor 2 continues, so the controllability of wheel slip is not deteriorated.

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

[0043] When the regenerative braking force enters range Z, which is close to the reduction limit, during ABS operation, the brake control device 20 adjusts the decompression reference speed to the target speed and stops increasing the pressure of the hydraulic brake system. Since the motor target speed and the decompression reference speed become the same speed, decompression of the hydraulic brake system occurs during motor speed control. When the regenerative braking force enters range Z, which is close to the reduction limit, during motor control, decompression of the hydraulic brake system begins. As the hydraulic brake system decompresses, the regenerative braking force increases and moves outside range Z (within range Y). When the regenerative braking force changes from range Z to range Y, the brake control device 20 sets the decompression reference speed to a speed offset towards the wheel lock side from the motor target speed, and makes the wheel speed follow the target speed using only motor speed control (only regenerative speed feedback control). This prevents a situation where the regenerative braking force cannot be reduced during ABS operation, thus preventing the wheel speed from being controlled solely by hydraulic control of the hydraulic brake system when the regenerative braking force cannot be reduced. Therefore, even when the regenerative braking force decreases to near its reduction limit and regenerative braking becomes insufficient, the wheel slip control by motor 2 continues, thus preventing a deterioration in the controllability of wheel slip.

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

[0045] When ABS is activated, if the maximum regeneration is small and the regenerative braking force is always close to the range between the maximum regeneration and the reduction limit, the brake control device 20 adjusts the pressure reduction reference speed to the target speed and increases the pressure of the hydraulic brake system. If the maximum regeneration is small due to the battery condition or the rotation speed of the motor 2 is high, the range of change in regenerative braking force becomes small, and the regenerative braking force may be in both the range X close to the maximum regeneration and the range Z close to the reduction limit. In this case, the amount of change in regenerative braking force is insufficient, and wheel slip cannot be controlled by motor speed control alone, but the hydraulic brake pressure is increased and decreased, and wheel slip can be controlled by hydraulic brake control as well.

[0046] Figure 9 is a flowchart illustrating wheel speed control in a modified example. The control shown in Figure 9 is performed by the motor control device 10 and the brake control device 20 while the ABS is operating. Steps S11 to S13 shown in Figure 9 are the same processes as steps S1 to S3 shown in Figure 6, so their explanation is omitted.

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

[0048] If it is determined that the regenerative braking force is less than the value obtained by adding a predetermined value A to the limit of the reduction 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 a reduction in the regenerative braking force is not possible 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 the target speed.

[0049] If it is determined that the regenerative braking force is greater than or equal to the value obtained by adding a predetermined value A to the limit of the reduction of the regenerative braking force (Step S14: No), the brake control device 20 sets the decompression 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 an increase in braking force is possible with regenerative braking force, and the decompression reference speed is set to a value obtained by subtracting a predetermined value α from the motor target speed. The brake control device 20 determines that the regenerative braking force is within the range X or range Y shown in Figure 7, and offsets the decompression reference speed by a predetermined value α towards the wheel slip side from the target speed.

[0050] After performing the process in step S15 or S16, the brake control device 20 determines whether the wheel speed is greater than the pressure reduction reference speed (step S17). If the process proceeds 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. If the process proceeds 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] If the wheel speed is determined to be below 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 system (step S18). If step S18 is performed after step S15, pressure reduction of the hydraulic brake system starts with the regenerative braking force in range Z shown in Figure 7. If step S18 is performed after step S16, pressure reduction of the hydraulic brake system starts with the regenerative braking force in range X or range Y shown in Figure 7. After the processing of step S18 is performed, this control routine ends.

[0052] If the wheel speed is determined to be greater than the pressure reduction reference speed (Step S17: Yes), the brake 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 force that can be output (Step S19). The predetermined value B is a value that defines a range X close to the maximum regenerative force, as shown in Figure 7. In Step S19, it is determined whether the regenerative braking force is outside the range X shown in Figure 7.

[0053] If it is determined that the regenerative braking force is less than the value obtained by subtracting a predetermined value B from the maximum regenerative force that can be output (step S19: Yes), the brake control device 20 stops increasing the pressure of the hydraulic brake system (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 system is stopped. The brake control device 20 determines that the regenerative braking force is within the range Y or range Z shown in Figure 7, and stops increasing the pressure of the hydraulic brake system. If step S20 is performed after step S15, the pressure increase of the hydraulic brake system is stopped when the regenerative braking force is within the range Z shown in Figure 7. If step S20 is performed after step S16, the pressure increase of the hydraulic brake system is stopped when the regenerative braking force is within the range Y shown in Figure 7. After the processing of step S20 is completed, this control routine ends.

[0054] If 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 force that can be output (step S19: No), the brake control device 20 increases the pressure of the hydraulic brake system (step S21). In step S21, it is determined that it is not possible to increase the regenerative braking force in a short time, and the hydraulic brake system is increased in pressure. The brake control device 20 determines that the regenerative braking force is within the range X shown in Figure 7, and releases the stop of the hydraulic brake system's pressure increase and performs the pressure increase. After the process in step S21 is completed, this control routine ends.

[0055] In the modified configuration, the hydraulic brake system can be activated minimally in response to regenerative braking force, allowing for greater use of motor speed control. Furthermore, if the amount of change in braking force is insufficient with motor speed control alone, the hydraulic control of the hydraulic brake system can be activated. This allows for high-precision control of the appropriate slip amount using regenerative braking force, while also compensating for any delay in switching to the hydraulic control of the hydraulic brake system. As a result, a decrease in the driving stability, steering response, and deceleration sensation of the electric vehicle 1 can be prevented.

[0056] Note that the limit of reduction in regenerative braking force is not limited to zero. For example, a value close to zero can be set as the limit of reduction in regenerative braking force. [Explanation of Symbols]

[0057] 1. Electric Vehicle 2 motors 3 Differential gear 4 Front wheels 5 Rear wheels 6 Inverters 7. Wheel speed sensor 10 Motor control device 20 Brake control device

Claims

1. A control device for an electric vehicle that performs anti-lock control to suppress wheel locking by controlling the braking force applied to the wheels using hydraulic braking force from a hydraulic brake system and regenerative braking force from a motor, During the execution of the anti-lock control, the hydraulic pressure of the hydraulic brake system is kept constant, and the regenerative braking force is controlled by speed feedback control that makes the wheel speed follow the target speed, in a first state. During control to the first state, it is determined whether the road surface resistance has decreased to a predetermined value. If it is determined that the road surface resistance has decreased 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 system is reduced. In the first state, a pressure reduction reference speed is set to reduce the hydraulic pressure of the hydraulic brake device. The aforementioned pressure reduction reference speed is set to a value obtained by subtracting a predetermined value from the target speed of the motor. The hydraulic control value of the hydraulic brake device is set according to the magnitude of the road surface resistance. In the first state, the hydraulic pressure of the hydraulic brake device is controlled to remain constant at the control value of the hydraulic pressure. While the control is in the first state, it is determined whether the rotational speed of the wheel is greater than the pressure reduction reference speed. If it is determined that the rotational speed of the wheel in the first state has fallen below the pressure reduction reference speed, it is determined that the road resistance has decreased below a predetermined value during control in the first state, and the pressure reduction of the hydraulic brake system is started before the regenerative braking force reaches its reduction limit, and the control value of the hydraulic pressure is reset according to the reduced road resistance, and the control of the regenerative braking force by speed feedback control is continued. A control device for electric vehicles characterized by the following features.

2. While the system is controlled to the first state, it is determined whether the regenerative braking force has entered a range close to the limit of reduction of the regenerative braking force. If it is determined that the regenerative braking force has entered a range close to the reduction limit in the first state, the pressure reduction reference speed is set to the same value as the motor's target speed. The control device for an electric vehicle according to feature 1.

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