Brake control device and brake control method

Abstract

The present invention relates to a brake control device and a brake control method, the brake control device comprising: a derivation unit that derives a slip rate of a wheel on the basis of a detected wheel speed and a vehicle speed; a brake processing unit that determines the amount of brake applied to the regenerative braking device and the friction braking device on the basis of the accelerator operation amount and the brake operation amount; and a control unit that controls the regenerative braking device and the friction braking device on the basis of the determined braking amount. When the amount of operation of the accelerator is reduced and the slip rate is equal to or greater than a predetermined threshold value, the control unit executes target slip control for adjusting the slip rate by controlling the torque of the motor of the regenerative braking device on the basis of a predetermined target slip rate, and executes the target slip control when the target slip control is executed and the brake operation is executed. The friction brake device generates a brake amount corresponding to the brake operation amount.

Description

Technical Field

[0001] The present invention relates to brake control using a friction brake device capable of applying frictional force to wheels and a regenerative brake device including a motor. Background Art

[0002] Japanese Unexamined Patent Application Publication No. 2014-73709 discloses a brake control device as follows: When the vehicle control unit performs coasting regenerative braking in a coasting driving state and slip exceeding a set value occurs in the drive wheels, the vehicle control unit executes coasting regenerative brake control to reduce the coasting regenerative brake torque.

[0003] In the technology disclosed in Japanese Unexamined Patent Application Publication No. 2014-73709, since the coasting regenerative brake torque is reduced when slip exceeding a set value occurs in the wheels, there is a concern that the amount of recovered regenerative power may decrease. On the other hand, an increase in wheel slip is not preferable. Summary of the Invention

[0004] An object of the present invention is to provide a technology capable of ensuring the amount of recovered regenerative power while suppressing wheel slip.

[0005] To solve the above problems, a certain aspect of the present invention is a brake control device that controls a regenerative brake device provided for a regenerative brake wheel of either the front wheels or the rear wheels and a friction brake device capable of independently controlling the frictional braking forces applied to the front wheels and the rear wheels, and includes: an acquisition unit that acquires the detection result of the accelerator operation amount for detecting the accelerator pedal, the detection result of the brake operation amount for detecting the brake pedal, the detection result of the wheel speeds of the front wheels and the rear wheels, and the detection result of the vehicle speed; a derivation unit that derives the wheel slip ratio based on the detected wheel speeds and the vehicle speed; a brake processing unit that determines the braking amounts applied to the regenerative brake device and the friction brake device based on the accelerator operation amount and the brake operation amount; and a control unit that controls the regenerative brake device and the friction brake device based on the determined braking amounts. When the slip ratio becomes equal to or more than a specified threshold value when the accelerator operation amount decreases, the control unit executes target slip control for adjusting the slip ratio by controlling the torque of the motor of the regenerative brake device based on the specified target slip, and when the target slip control is executed and a brake operation is performed, causes the friction brake device to generate a braking amount corresponding to the brake operation amount.

[0006] Another aspect of the present invention is a braking control method. This method is a braking control method in which each step is executed by a braking control device. The braking control device controls a regenerative braking device provided for a regenerative braking wheel of either the front wheels or the rear wheels and a friction braking device capable of independently controlling the frictional braking force applied to the front wheels and the rear wheels respectively. The braking control method includes: steps of obtaining detection results of an accelerator operation amount for detecting an accelerator pedal, a brake operation amount for detecting a brake pedal, wheel speeds of the front wheels and the rear wheels, and a vehicle speed; a step of deriving a slip ratio of the wheels based on the detected wheel speeds and the vehicle speed; a step of determining braking amounts to be applied to the regenerative braking device and the friction braking device based on the accelerator operation amount and the brake operation amount; and a step of controlling the regenerative braking device and the friction braking device based on the determined braking amounts. In the control step, when the slip ratio becomes equal to or greater than a specified threshold value when the accelerator operation amount decreases, target slip control is performed to control the torque of the motor of the regenerative braking device based on a specified target slip ratio to adjust the slip ratio. When the target slip control is executed and a brake operation is performed, the friction braking device generates a braking amount corresponding to the brake operation amount.

[0007] According to the present invention, a technique capable of ensuring the amount of regenerative power recovered while suppressing wheel slip can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Hereinafter, the features, advantages, techniques and industrial importance of exemplary embodiments of the present invention will be described with reference to the drawings. In the drawings, the same reference numerals denote the same components, where:

[0009] Figure 1 is a diagram showing the functional configuration of the braking system.

[0010] Figure 2A is a diagram for explaining the braking control when target slip control is executed.

[0011] Figure 2B is a diagram for explaining the braking control when target slip control is executed.

[0012] Figure 2C is a diagram for explaining the braking control when target slip control is executed.

[0013] Figure 2D is a diagram for explaining the braking control when target slip control is executed.

[0014] Figure 3A is a diagram for explaining the braking control when target slip control is not executed.

[0015] Figure 3B This is a diagram for explaining the braking control when the target slip control is not executed.

[0016] Figure 3C This is a diagram for explaining the braking control when the target slip control is not executed.

[0017] Figure 3D This is a diagram for explaining the braking control when the target slip control is not executed.

[0018] Figure 4 This is a diagram showing the relationship between the front wheel deceleration and the rear wheel deceleration when the regenerative braking wheel is the rear wheel.

[0019] Figure 5 is a flowchart of the brake control method of the embodiment. DETAILED DESCRIPTION

[0020] Figure 1 : is a diagram showing the functional configuration of the brake system 1. The functions of the brake system 1 can be configured by a circuit module, a memory, and other LSIs in hardware, and can be implemented by system software loaded into the memory, an application program, etc. in software. Therefore, those skilled in the art can understand that the functions of the brake system 1 can be implemented in various forms by hardware only, software only, or a combination thereof, and are not limited to any one. The brake system 1 can be provided in a vehicle that can drive automatically.

[0021] The brake system 1 includes a brake control device 10 , an accelerator pedal sensor 12 , a brake pedal sensor 14 , a vehicle speed sensor 16 , a wheel speed sensor 18 , a friction brake device 20 , and a regenerative brake device 22 .

[0022] The accelerator pedal sensor 12 detects the amount of operation of the accelerator pedal and sends the detection result to the brake control device 10. The brake pedal sensor 14 detects the amount of operation of the brake pedal and sends the detection result to the brake control device 10. The accelerator pedal sensor 12 and the brake pedal sensor 14 are, for example, stroke sensors that detect the amount of pedal depression. In addition, even if a sensor that detects the master cylinder pressure is used instead of the brake pedal sensor 14, the amount of operation of the brake pedal can be detected.

[0023] The vehicle speed sensor 16 detects the vehicle speed and sends the detection result to the brake control device 10. The wheel speed sensor 18 is provided for each wheel, detects the wheel speed of each wheel, and sends the detection result to the brake control device 10. The vehicle is provided with other on-board sensors used for brake control. For example, a sensor for detecting the deceleration of the vehicle, a sensor for detecting the torque of the motor provided in the regenerative brake device 22, etc. are provided.

[0024] The friction braking device 20 is respectively provided on each wheel and can independently control the friction braking force applied to the front wheels and the rear wheels. The friction braking device 20 moves a piston forward and backward by hydraulic pressure, and by the forward movement of this piston, a brake pad is pressed against a brake disc, thereby applying a braking force to the wheel.

[0025] A regenerative braking device 22 is provided for the regenerative braking wheel of either the front wheels or the rear wheels. The regenerative braking wheel can be, for example, the rear wheels. The regenerative braking device 22 includes a motor, an inverter, and a battery. The motor can generate a driving torque that rotates the wheel and can apply a regenerative torque to the rotation of the regenerative braking wheel when the vehicle decelerates. The regenerative power generated by the regenerative torque of the motor is charged to the battery. The regenerative torque can be adjusted by the control of the inverter.

[0026] The braking control device 10 controls the friction braking device 20 and the regenerative braking device 22 based on the detection results of various in-vehicle sensors. The braking control device 10 includes an acquisition unit 24, a derivation unit 26, a braking processing unit 28, and a control unit 30.

[0027] The acquisition unit 24 acquires the detection results of the accelerator operation amount that detects the accelerator pedal, the braking operation amount that detects the brake pedal, the detection results of the wheel speeds of the front wheels and the rear wheels, and the detection result of the vehicle speed. In addition, the acquisition unit 24 acquires the detection results from a sensor that detects the torque of the regenerative braking device 22 and a sensor that detects the deceleration of the vehicle.

[0028] The derivation unit 26 derives the slip ratio of each wheel based on the detected wheel speed and vehicle speed. The slip ratio of the wheel refers to the ratio of the difference between the vehicle speed and the wheel speed to the vehicle speed.

[0029] The braking processing unit 28 has a braking amount calculation unit 32, a target slip processing unit 34, and a distribution unit 36. The braking amount calculation unit 32 determines the braking amounts applied to the regenerative braking device 22 and the friction braking device 20 based on the accelerator operation amount and the braking operation amount. The braking amount calculation unit 32 can respectively determine the braking amount corresponding to the accelerator operation amount and the braking amount corresponding to the braking operation amount. The braking amount can be a torque or a deceleration.

[0030] When the accelerator operation amount decreases, that is, during coasting driving, the braking amount calculation unit 32 determines the regenerative torque generated by the regenerative braking device 22 as the braking amount corresponding to the accelerator operation amount. When the accelerator operation amount decreases, the regenerative braking device 22 generates a regenerative torque to obtain regenerative power.

[0031] The target slip processing unit 34 determines to execute target slip control. The target slip control is a control that adjusts the slip rate by controlling the torque of the motor of the regenerative braking device 22 based on a prescribed target slip rate. When the accelerator operation amount decreases, that is, when the slip rate of the wheels during coasting driving becomes equal to or greater than a prescribed threshold value, the target slip processing unit 34 determines to execute target slip control. The situation where the slip rate of the wheels becomes equal to or greater than the prescribed threshold value may be a situation where the average value of the slip rates of the respective wheels becomes equal to or greater than the prescribed threshold value, or a situation where the slip rate of any one wheel becomes equal to or greater than the prescribed threshold value. The prescribed threshold value is set to a value smaller than the slip rate at which the ABS (Anti-lock Brake System) starts to operate. For example, the slip rate at which the ABS starts to operate is about 12%, and the target slip control is executed before the ABS starts to operate, and the control is to maintain a target slip rate smaller than 12%. The control unit 30 controls the torque of the motor of the regenerative braking device 22 so that the slip rate of the wheels maintains the prescribed target slip rate. The target slip rate may be a predetermined fixed value, or may change according to vehicle state quantities such as vehicle speed and yaw rate, and driver operation quantities such as steering operation.

[0032] In the target slip control, the control unit 30 adjusts the regenerative torque of the regenerative braking device 22, and can obtain regenerative power while allowing the slip rate of the wheels at a certain ratio. Since the target slip control is executed when the slip rate of the wheels is equal to or greater than the prescribed threshold value, it is executed in a situation where slipping is likely to occur due to the influence of rain, snow, etc. By the target slip control, it becomes difficult for the ABS to execute and the driving becomes stable, and regenerative power can be ensured. If a series of braking controls end, the target slip control ends. A series of braking controls refers to the period from when the accelerator pedal is released and the accelerator operation amount starts to decrease until the brake pedal is depressed and the brake operation amount increases, and finally the brake pedal is released and the brake operation amount becomes zero.

[0033] The braking amount calculation unit 32 calculates the braking amount corresponding to the brake operation amount. The distribution unit 36 distributes the braking amount generated by the friction braking device 20 and the regenerative braking device 22 for the determined braking amount. When the driving state and driving environment of the vehicle are good, the regenerative braking device 22 is preferentially distributed compared to the friction braking device 20. In the control of preferentially distributing the regenerative braking device 22, the distribution unit 36 distributes the braking amount to the maximum regenerative amount of the regenerative braking device 22, and the friction braking device 20 supplements the insufficient braking amount. The control unit 30 controls the regenerative braking device 22 and the friction braking device 20 based on the braking amount determined by the braking processing unit 28.

[0034] When the brake operation amount increases during the execution of the target slip control, the distribution unit 36 causes only the friction braking device 20 to generate a braking amount corresponding to the brake operation amount. When this brake operation is ON, the regenerative torque obtained in the target slip control can be maintained or reduced, but an increase in the regenerative torque is restricted. Thereby, the brake control can be stabilized. The operation during the execution of the target slip control will be described with reference to new drawings.

[0035] Figure 2A 、 Figure 2B 、 Figure 2C 、 Figure 2D is a diagram for explaining the brake control when the target slip control is executed. Figures 2A - 2D The horizontal axis of is time, and the times t1 to t4 are the same times.

[0036] Figure 2A The vertical axis of is speed, showing the vehicle speed 40 and the wheel speed 42. Figure 2B The vertical axis of is the operation amount, showing the accelerator operation amount 44 and the brake operation amount 46. Figure 2C The vertical axis of is the regenerative torque, showing the accelerator regenerative torque 48 and the brake regenerative torque 50. Figure 2D The vertical axis of is the friction amount, showing the front wheel friction amount 52 and the rear wheel friction amount 54.

[0037] Figure 2B shows that the accelerator operation amount 44 starts to decrease from time t1, Figure 2C shows that the accelerator regenerative torque 48 starts to increase from time t1. At this time, as shown in Figure 2D , the friction braking device 20 is not operating. In Figure 2A , from time t1, the wheel speed 42 starts to deviate from the vehicle speed 40, and at time t2, the slip ratio becomes equal to or greater than the specified threshold, and the target slip control starts.

[0038] In Figure 2C , since the target slip control starts during the period from time t2 to time t3, the accelerator regenerative torque 48 increases and decreases within a certain range and shows a waveform. In Figure 2A , since the target slip control starts, the wheel speed 42 decreases along the target slip value 43, and the difference from the vehicle speed 40 is ensured to be constant. During the target slip control from time t2 to time t3, the friction braking device 20 is not executed. During the period from time t2 to time t3, there is an idle time from the accelerator to the brake, Figure 2B shows the case where the brake operation amount 46 starts to increase from time t3.

[0039] In Figure 2DIn this case, from time t3, as the brake operation amount 46 increases, the front wheel friction amount 52 and the rear wheel friction amount 54 increase. On the other hand, in Figure 2C the accelerator regeneration torque 48 does not increase, and the brake regeneration torque 50 does not increase either. The accelerator regeneration torque 48 corresponds to the accelerator operation amount, and the brake regeneration torque 50 corresponds to the brake operation amount. From time t3, the accelerator regeneration torque 48 is constant, and the target slip control ends. Thus, when the target slip control is executed, for the subsequent brake operation, only the friction brake device 20 is used to additionally apply a braking force. Thereby, the regeneration torque can be controlled to be continuous within a certain range starting from the target slip control, and in the case of generating slip, the friction brake device 20 can be used for braking to suppress the increase in the slip ratio.

[0040] The front wheel friction amount 52 from time t3 is greater than the rear wheel friction amount 54, but the hydraulic pressure executed by the front wheel friction brake device 20 and the rear wheel friction brake device 20 is executed at an equal pressure. Thereby, the brake control can be simplified.

[0041] From time t3, the front wheel friction amount 52 and the rear wheel friction amount 54 start to increase simultaneously, but the control unit 30 may also cause the front wheel friction amount 52 to start increasing earlier than the rear wheel friction amount 54 and cause the rear wheel friction amount 54 to increase with a slight delay. Among them, the rear wheel is a regenerative braking wheel, and the front wheel is a non-regenerative braking wheel.

[0042] The case where the regenerative braking wheel is not limited to the rear wheel is as follows. When the target slip control is executed and the brake operation is performed, the control unit 30 causes the friction brake device 20 corresponding to the front wheel and the rear wheel and not corresponding to the regenerative braking wheel to generate a braking amount earlier than the friction brake device 20 corresponding to the regenerative braking wheel. Since the regenerative braking wheel is given a braking force by the regenerative braking device 22, for the brake operation, by first applying a braking force to the non-regenerative braking wheel, the imbalance between the braking forces of the front wheel and the rear wheel can be suppressed at the initial stage of the brake operation.

[0043] In a poor road surface condition, if the brake control device 10 wants to obtain the maximum regeneration torque, the slip ratio increases, and there is a concern that the ABS may work in advance. Although the difference between the wheel speed 42 and the vehicle speed 40 becomes slightly larger due to the brake operation from time t3, since the regeneration torque does not increase, the increase in the slip ratio can be suppressed.

[0044] Return to Figure 1When the target slip control is not executed when the accelerator operation amount is decreased, and then when the brake operation amount is increased later, if the absolute value of the difference in slip ratio between the front wheels and the rear wheels becomes equal to or greater than a specified value, the distribution unit 36 executes control to limit the braking amount generated by the regenerative braking device 22. A description will be given of the control of a situation where slipping occurs due to brake operation even without executing the target slip control with reference to a new drawing.

[0045] Figure 3A 、 Figure 3B 、 Figure 3C 、 Figure 3D is a diagram for explaining the braking control when the target slip control is not executed. Figures 3A - 3D The horizontal axis of is time, and the times t1 to t5 are the same times.

[0046] Figure 3A The vertical axis of is speed, showing the vehicle speed 60 and the wheel speed 62. Figure 3B The vertical axis of is the operation amount, showing the accelerator operation amount 64 and the brake operation amount 66. Figure 3C The vertical axis of is the regenerative torque, showing the accelerator regenerative torque 68 and the brake regenerative torque 70. Figure 3D The vertical axis of is the friction amount, showing the front wheel friction amount 72 and the rear wheel friction amount 74.

[0047] At Figure 3B it is shown that the accelerator operation amount 64 starts to decrease from time t1, Figure 3C it is shown that the accelerator regenerative torque 68 starts to increase from time t1. At this time, as Figure 3D shows, the friction braking device 20 is not operating. At Figure 3A since the wheel speed 62 slightly deviates from the vehicle speed 60 but the slip ratio is small from time t1, the target slip control is not executed.

[0048] At time t2, the accelerator operation stops (OFF). At Figure 3C the accelerator regenerative torque 68 increases during the period from time t1 to time t2 and becomes a constant value after time t2. The period from time t2 to time t3 is the idle time when switching from the accelerator to the brake, and a constant accelerator regenerative torque 68 is given, and the vehicle speed 60 and the wheel speed 62 decrease.

[0049] From time t3, Figure 3B the brake operation amount 66 of starts to increase, Figure 3C the brake regenerative torque 70 of starts to increase, Figure 3D the front wheel friction amount 72 and the rear wheel friction amount 74 of do not increase. This is because the regenerative braking of the regenerative braking device 22 is preferentially executed over the friction braking device 20.

[0050] At Figure 3AIn this case, starting from time t3, the wheel speed 62 begins to deviate from the vehicle speed 60. If the absolute value of the difference in slip ratios between the front wheels and the rear wheels becomes greater than or equal to a specified value at time t4, the braking processing unit 28 determines to limit the braking amount generated by the regenerative braking device 22. Therefore, starting from time t4, the brake regenerative torque 70 begins to decrease, and the front wheel friction amount 72 begins to increase.

[0051] At time t5, the increase in the brake operation amount 66 stops, the decrease in the brake regenerative torque 70 stops, and the increase in the front wheel friction amount 72 stops. In Figure 3A this case, starting from time t4, the wheel speed 62 deviates from the vehicle speed 60 and the slip ratio increases. However, by increasing the proportion of friction braking compared to regenerative braking, the slip ratio is thereby reduced, and at time t5, the slip ratio converges to an allowable value. In this way, without performing target slip control, if the slip ratio becomes large due to brake operation, the proportion of regenerative braking can be reduced to decrease the slip ratio.

[0052] By determining the condition for restricting regenerative braking at time t4 based on the absolute value of the difference in slip ratios between the front wheels and the rear wheels, it is difficult to perform the restriction of regenerative braking, and the restriction of regenerative braking can be started at the timing when slip has reliably occurred. In addition, the condition for restricting regenerative braking at time t4 can be satisfied when the slip ratio of the wheel is greater than or equal to a specified threshold value. That is, after target slip control is not performed, when a specified condition indicating that the slip ratio of the wheel is greater than or equal to a set value is satisfied, the braking processing unit 28 determines to limit the braking amount generated by the regenerative braking device 22.

[0053] Starting from time t4, the braking processing unit 28 sets a limit value for the braking amount of the regenerative braking device 22, and the control unit 30 controls the brake regenerative torque 70 to be below the limit value. The limit value for the braking amount of the regenerative braking device 22 is set based on the slip ratio of the regenerative braking wheel. The slip ratio of the regenerative braking wheel can be the average of the slip ratios of the left and right wheels, or the slip ratio of either the left or right wheel. As the slip ratio of the regenerative braking wheel increases, the limit value for the braking amount of the regenerative braking device 22 decreases. If the slip ratio of the regenerative braking wheel becomes greater than or equal to a specified threshold value, the limit value for the regenerative braking device 22 is limited to zero, and the brake regenerative torque 70 is zero.

[0054] In addition, as Figure 3C shown, starting from time t4, even if the brake regenerative torque 70 is restricted, the accelerator regenerative torque 68 remains a constant value. Thereby, a sudden change in the regenerative torque can be suppressed. When the brake regenerative torque 70 is restricted, the accelerator regenerative torque 68 can also gradually decrease. Here, the amount by which the accelerator regenerative torque 68 decreases may not be filled by the friction braking device 20.

[0055] At time t4, the limitation of the braking amount of the regenerative braking device 22 starts. However, if the increase in the slip ratio since time t3 is rapid, the operation of the ABS may sometimes not be suppressed by the limitation of the braking amount of the regenerative braking device 22. In view of this, in the brake operation after the target slip control is not executed, the brake processing unit 28 limits the increase amount per unit time of the brake regenerative torque 70 according to the increase speed of the brake operation amount 66 and the slip ratio.

[0056] Return to Figure 1 The braking amount calculation unit 32 distributes the braking amounts of the front wheels and the rear wheels according to a preset distribution ratio. The distribution unit 36 distributes the braking amount allocated to the regenerative braking wheels to the friction braking device 20 and the regenerative braking device 22.

[0057] The brake control device 10 can make the braking stable by distributing more braking force to the front wheels than to the rear wheels. When the rear wheels are regenerative braking wheels, since the accelerator regenerative torque is first applied to the rear wheels, and then the braking force caused by the brake operation is applied to the rear wheels, the braking force of the rear wheels is greater than that of the front wheels at the initial stage of braking. Depending on the driving state and driving environment of the vehicle, there is a concern that the slip ratio of the rear wheels increases. In view of this, at the initial stage of the brake operation, the brake processing unit 28 changes the distribution of the braking amounts of the front wheels and the rear wheels, and distributes more braking force to the front wheels than to the rear wheels. This process will be described with reference to a new drawing.

[0058] Figure 4 is a diagram showing the relationship between the front wheel deceleration and the rear wheel deceleration when the regenerative braking wheel is the rear wheel. Figure 4 The vertical axis represents the rear wheel deceleration, and the horizontal axis represents the front wheel deceleration. When the brake control device 10 applies the braking force, it is preferably close to the ideal distribution line 80 or the isobaric braking distribution line 82. The ideal distribution line 80 represents the ideal distribution of the deceleration, and the isobaric braking distribution line 82 represents the distribution when the friction braking devices 20 of the front wheels and the rear wheels are controlled isobarically respectively.

[0059] In Figure 4 In the case where the regenerative braking wheel shown is the rear wheel, in the deceleration distribution transition 84 of the comparative example, the deceleration of the rear wheel increases due to the accelerator regenerative torque and transfers to be close to the ideal distribution line 80 by starting the brake operation.

[0060] In the braking force distribution transition 86 of the embodiment, if the deceleration of the rear wheels starts the brake operation due to an increase in the accelerator regeneration torque, braking force is applied to the front wheels and the rear wheels. At this time, when the brake operation amount, the accelerator regeneration torque, and the vehicle deceleration satisfy the specified conditions, the brake processing unit 28 sets the deceleration of the rear wheels to the specified deceleration and supplements the shortage amount with the front wheels. The control unit 30 gradually reduces the deceleration of the rear wheels to the specified deceleration, stops the gradual reduction when the specified deceleration is reached, and maintains the deceleration of the rear wheels. If the brake operation amount and the accelerator regeneration torque are equal to or greater than the specified torque, the vehicle deceleration is equal to or greater than the specified torque, and the brake regeneration torque is equal to or greater than the specified value, the specified conditions are satisfied. For example, the specified conditions are satisfied when the vehicle is traveling on a highway. In this way, when the brake operation amount is large and a large deceleration is applied to the vehicle, the deceleration of the rear wheels can be reduced.

[0061] Figure 5 is a flowchart of the braking control method of the embodiment. The acquisition unit 24 acquires the detection results of the accelerator pedal sensor 12 and the brake pedal sensor 14, and acquires the pedal operation amount of the driver (S10). The brake processing unit 28 determines whether there is no brake operation (S12).

[0062] In the case of no brake operation (Yes in S12), the brake processing unit 28 determines whether the accelerator operation amount is decreasing (S14). If there is no brake operation and the accelerator operation amount is not decreasing (No in S14), no braking is performed and this process ends.

[0063] If the accelerator operation amount is decreasing (Yes in S14), the derivation unit 26 derives the slip ratio of the wheels based on the vehicle speed and the wheel speed (S16). The brake processing unit 28 determines whether the slip ratio of the wheels is equal to or greater than the specified threshold (S18). If the slip ratio of the wheels is equal to or greater than the specified threshold (Yes in S18), target slip control is started to apply the adjusted accelerator regeneration torque (S20).

[0064] If the slip ratio of the wheels is not equal to or greater than the specified threshold (No in S18), a constant accelerator regeneration torque is applied by the regenerative braking device 22 (S22), and the vehicle travels in a so-called coasting state.

[0065] If there is a brake operation (No in S12), the brake processing unit 28 determines whether target slip control is being executed in a series of braking controls (S24). When target slip control is being executed in a series of braking controls (Yes in S24), the braking corresponding to the brake operation is performed only by the friction braking device 20 (S26).

[0066] When the target slip control is not being executed in a series of braking controls (No in S24), the derivation unit 26 calculates the slip ratio of the wheel (S28). The braking processing unit 28 determines whether the slip ratio of the wheel satisfies a specified condition (S30). The specified condition may be satisfied if the absolute value of the difference in slip ratio between the front wheel and the rear wheel is equal to or greater than a specified value, or may be satisfied if the slip ratio of the wheel is equal to or greater than a specified threshold value.

[0067] When the slip ratio of the wheel satisfies the specified condition (Yes in S30), the braking processing unit 28 determines to limit the braking amount of the regenerative braking device 22, and the control unit 30 controls the braking amount of the regenerative braking device 22 to be equal to or less than a limit value (S32).

[0068] When the slip ratio of the wheel does not satisfy the specified condition (No in S30), that is, when the wheel hardly slips, the braking processing unit 28 preferentially allocates the regenerative braking device 22, and if it exceeds the maximum braking amount of the regenerative braking device 22, it controls the friction braking device 20 to supplement the shortage (S34).

[0069] As described above, the present disclosure has been described based on the embodiments. The present disclosure is not limited to the above-described embodiments, and various design changes and the like can be made based on the knowledge of those skilled in the art.

Claims

1. A brake control device for controlling a regenerative brake device provided for a regenerative brake wheel of either a front wheel or a rear wheel and a friction brake device capable of independently controlling the friction braking force applied to the front wheel and the rear wheel, characterized in that: have: an acquisition unit that acquires a detection result of an accelerator operation amount of an accelerator pedal, a detection result of a brake operation amount of a brake pedal, a detection result of wheel speeds of the front wheels and the rear wheels, and a detection result of a vehicle speed; a deriving unit for deriving a slip ratio of the wheel based on the detected wheel speed and vehicle speed; a brake processing unit that determines a braking amount to be applied to the regenerative brake device and the friction brake device based on an accelerator operation amount and a brake operation amount; and a control unit that controls the regenerative braking device and the friction braking device based on the determined braking amount, When the slip ratio becomes greater than a specified threshold value when the accelerator operation amount decreases, the control unit performs target slip control to adjust the slip ratio by controlling the torque of the motor of the regenerative braking device based on a specified target slip ratio, and when the target slip control is performed and the brake operation is performed, the friction braking device generates a braking amount corresponding to the brake operation amount.

2. The brake control device according to claim 1, characterized in that: When the target slip control is not executed when the accelerator operation amount is reduced and the brake operation is subsequently executed, the brake processing unit causes the regenerative brake device to be executed with priority over the friction brake device for a braking amount corresponding to the brake operation amount. When the target slip control is not executed when the accelerator operation amount is reduced and the brake operation is subsequently executed, the brake processing unit executes control to limit the braking amount to be generated by the regenerative brake device if the slip ratio satisfies a predetermined condition.

3. The brake control device according to claim 1 or 2, characterized in that: When the target slip control is executed and the brake operation is performed, the control unit causes the friction brake device that does not correspond to the regenerative brake wheel among the friction brake devices corresponding to the front wheels and the rear wheels to generate a braking amount before the friction brake device corresponding to the regenerative brake wheel.

4. The brake control device according to claim 2, characterized in that: In the control for limiting the braking amount to be generated by the regenerative braking device, the braking processing unit sets a value for limiting the braking amount based on a slip ratio of the regenerative braking wheel.

5. A braking control method, wherein each step is performed by a braking control device, wherein the braking control device controls a regenerative braking device provided for a regenerative braking wheel of either a front wheel or a rear wheel and a friction braking device capable of independently controlling the friction braking force applied to the front wheel and the rear wheel, The braking control method is characterized by comprising: The step of acquiring a detection result of detecting an accelerator operation amount of an accelerator pedal, a detection result of detecting a brake operation amount of a brake pedal, a detection result of detecting wheel speeds of the front wheels and the rear wheels, and a detection result of detecting a vehicle speed; a step of deriving a wheel slip ratio based on the detected wheel speed and vehicle speed; a step of determining a braking amount applied to the regenerative braking device and the friction braking device based on an accelerator operation amount and a brake operation amount; as well as a step of controlling the regenerative braking device and the friction braking device based on the determined braking amount, In the control step, when the slip ratio becomes above a specified threshold value when the accelerator operation amount decreases, a target slip control is performed to adjust the slip ratio by controlling the torque of the motor of the regenerative braking device based on a specified target slip ratio, and when the target slip control is performed and the brake operation is performed, the friction braking device generates a braking amount corresponding to the brake operation amount.

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