Vehicle braking control apparatus

Abstract

To provide a vehicle braking control apparatus capable of suppressing deterioration of a friction material of a friction braking device while ensuring regenerative energy.SOLUTION: A brake ECU 22 determines whether or not a road surface condition detected by a road surface condition detection sensor 36 is a dry condition. Then, in the case of determining the road surface condition to be the dry condition, when target braking force Vtb is larger than maximum regenerable braking force Vrbm applicable by a rear motor 12, the brake ECU 22 causes brake pads 40p of a friction brake mechanism 40 of front wheels 50F and rear wheels 50R to be pushed onto brake disks 40d so as to generate the target braking force Vtb in a vehicle 1.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a brake control device for a vehicle. [Background technology]

[0002] Conventionally, a vehicle brake control device, for example, disclosed in Patent Document 1, is known. The conventional vehicle brake control device is applied to a vehicle equipped with a regenerative brake device and a friction brake device that generate braking forces on each of a pair of left and right front and rear wheels. When the conventional vehicle brake control device determines that there is a deceleration request for the vehicle and that a break-in is required to bring the friction material of the friction brake device into contact with a rotating member such as a rotor, the conventional vehicle brake control device operates the friction brake device in priority to the regenerative brake device. In this way, the conventional vehicle brake control device performs the break-in of the friction brake device to realize early recovery of the effectiveness of the friction brake device. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-130367 Summary of the Invention [Problem to be solved by the invention]

[0004] In the conventional vehicle brake control device, when the vehicle is new or the friction material is replaced, the friction brake device is preferentially operated to bring the friction material into contact with the rotating member to generate frictional braking force while the vehicle is traveling a predetermined distance. Therefore, while the vehicle is traveling a predetermined distance, the friction brake device is operated more frequently, and a load that generates frictional heat and wear is applied to the friction material of the friction brake device. As a result, deterioration due to a decrease in the frequency of use of the friction material, for example, deterioration of the friction material due to water absorption, is suppressed while the friction material is being brought into contact. However, after the vehicle has traveled a predetermined distance, in other words, after the contact is completed, the regenerative braking force is preferentially applied by the regenerative brake device, so the friction brake device is operated less frequently. As a result, there is a risk that a load is not applied to the friction material, and deterioration of the friction material occurs or progresses.

[0005] Furthermore, while the vehicle is traveling a predetermined distance, the friction braking force of the friction brake device is applied preferentially; in other words, the frequency of operating the regenerative brake device is reduced. Therefore, while the vehicle is traveling a predetermined distance, the current recovered by regeneration of the regenerative brake device, i.e., the regenerative energy, is reduced. This affects the distance the vehicle can travel using the regenerative energy (current), which affects the so-called power consumption rate of the vehicle. In other words, in a situation where the friction brake device is applied, the conventional vehicle brake control device suppresses the deterioration of the friction material, but affects the power consumption rate.

[0006] An object of the present invention is to provide a brake control device for a vehicle that can suppress deterioration of the friction material of a friction brake device while ensuring regenerative energy. [Means for solving the problem]

[0007] The vehicle braking control device of the present invention is a vehicle braking control device applied to a vehicle equipped with a regenerative braking device that applies a regenerative braking force to at least one of the front and rear wheels, and a friction braking device that applies a friction braking force to the front and rear wheels, and is equipped with a road surface condition detection unit that detects the road surface conditions ahead of the vehicle's direction of travel, and a controller that performs cooperative control of the regenerative braking device and the friction braking device so as to generate a target braking force for braking the vehicle, and the controller determines whether the road surface conditions detected by the road surface condition detection unit are in a predetermined state that does not disrupt stability when the vehicle is braked, and if the road surface conditions are in the predetermined state, when the target braking force is greater than the regenerative braking force generated by the regenerative braking device, activates the friction brake devices of the front and rear wheels to generate a friction braking force so that the target braking force is generated in the vehicle. Effect of the Invention

[0008] According to the present invention, when a target braking force larger than the regenerative braking force is to be generated, the controller can activate the friction brake devices provided on the front and rear wheels of the vehicle to generate a friction braking force. This allows the vehicle to recover regenerative energy by the regenerative braking device while increasing the frequency of operation of the friction brake devices. As a result, an appropriate load can be applied to the friction material of the friction brake devices provided on the front and rear wheels. Therefore, the friction material to which the load is applied can be prevented from deteriorating due to a decrease in frequency of use. [Brief description of the drawings]

[0009] [Figure 1] 1 is a schematic configuration diagram of a vehicle and a vehicle brake control device according to an embodiment of the present invention; [Diagram 2] 11 is a graph for explaining a frictional braking force when a regenerative braking force is increased. [Diagram 3] 4 is a flowchart of a braking control program. [Figure 4] 4 is a graph illustrating a regenerative braking force on a rear wheel side and frictional braking forces on the rear wheel side and the front wheel side in the embodiment. [Diagram 5]11 is a graph illustrating a regenerative braking force on the rear wheel side and frictional braking forces on the rear wheel side and front wheel side, which involves switching, according to a first modified example. [Figure 6] 13 is a graph illustrating a regenerative braking force on the front wheel side and frictional braking forces on the front wheel side and the rear wheel side, which involves switching, according to a second modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, a vehicle brake control device according to an embodiment of the present invention will be described in detail with reference to the drawings. In addition to the embodiment described below, the present invention can be embodied in various forms with various modifications and improvements based on the knowledge of those skilled in the art.

[0011] As shown in FIG. 1, the vehicle 1 to which the vehicle brake control device of the present embodiment is applied includes a front motor 11 that drives a left front wheel 50FL and a right front wheel 50FR, and a rear motor 12 that drives a left rear wheel 50RL and a right rear wheel 50RR. Hereinafter, the left front wheel 50FL and the right front wheel 50FR may be collectively referred to as "front wheels 50F", and the left rear wheel 50RL and the right rear wheel 50RR may be collectively referred to as "rear wheels 50R". In addition, when it is not necessary to distinguish between the front wheels 50F and the rear wheels 50R, they may be simply referred to as "wheels 50". The vehicle 1 is a typical front-wheel steering vehicle in which the front wheels 50F are steered, but illustration and description of the steering mechanism are omitted.

[0012] In the vehicle 1, the rotation of the output shaft of the front motor 11 is transmitted to the left and right front wheel axles 14L, 14R via a differential gear 13 (including a reduction gear). As a result, the left front wheel 50FL and the right front wheel 50FR are rotationally driven in the vehicle 1. Also, in the vehicle 1, the rotation of the output shaft of the rear motor 12 is transmitted to the left and right rear wheel axles 16L, 16R via a differential gear 15 (including a reduction gear). As a result, the left rear wheel 50RL and the right rear wheel 50RR are rotationally driven in the vehicle 1. In other words, the vehicle 1 is a four-wheel drive electric vehicle.

[0013] The front motor 11 and the rear motor 12 are configured to be able to independently rotate forward in the forward direction of the vehicle 1 and reverse in the backward direction of the vehicle 1 by controlling the energization of the inverter 17. Furthermore, in the vehicle 1 of this embodiment, the inverter 17 also has the function of converting AC generated by the rear motor 12 into DC and charging the battery 19 via the DC / DC converter 18, i.e., storing regenerative energy.

[0014] As a result, in the vehicle 1 of this embodiment, the rear motor 12 generates a braking torque and applies a regenerative braking force to the rear wheels 50R. That is, in this embodiment, the rear motor 12 functions as a motor generator. Note that in the vehicle 1 of this embodiment, the front motor 11 does not have the function of regenerating power to the battery 19, unlike the rear motor 12, and cannot apply a regenerative braking force to the front wheels 50F.

[0015] The operation of the front motor 11 and the rear motor 12 is controlled by a drive ECU 21 constituting the controller 20. The drive ECU 21 is an electronic control unit having a microcomputer as its main component. The microcomputer includes a CPU and storage devices such as a ROM and a RAM, and the CPU realizes various functions by executing programs (instructions) stored in the ROM.

[0016] The drive ECU 21 receives a detection signal from an accelerator sensor 31, which detects an accelerator operation amount, among the sensor group 30, and calculates a driver requested driving force according to the accelerator operation amount. The drive ECU 21 then controls the front motor 11 and the rear motor 12 so that the front wheel target driving force and the rear wheel target driving force, which are obtained by distributing the calculated driver requested driving force to the front wheels 50F and the rear wheels 50R, are transmitted to the front wheels 50F and the rear wheels 50R, respectively. For example, the drive ECU 21 receives a detection signal output from a control sensor 32 of the front motor 11, and controls the operation of the inverter 17 to control the energization of the front motor 11. Similarly, the drive ECU 21 receives a detection signal output from a control sensor 33 of the rear motor 12, and controls the operation of the inverter 17 to control the energization of the rear motor 12.

[0017] The vehicle 1 also includes a brake ECU 22 constituting the controller 20. The vehicle 1 also includes friction brake mechanisms 40FL, 40FR, 40RL, and 40RR (hereinafter also simply referred to as “friction brake mechanism 40”) provided on a left front wheel 50FL, a right front wheel 50FR, a left rear wheel 50RL, and a right rear wheel 50RR, and a brake actuator 41 electrically connected to the brake ECU 22.

[0018] The friction brake mechanism 40 includes brake discs 40dFL, 40dFR, 40dRL, and 40dRR (hereinafter simply referred to as "brake discs 40d") fixed to the wheels 50, and brake calipers 40cFL, 40cFR, 40cRL, and 40cRR (hereinafter simply referred to as "brake calipers 40c") fixed to the vehicle body. The friction brake mechanism 40 operates a wheel cylinder (not shown) built into the brake caliper 40c by the hydraulic pressure of the hydraulic oil supplied from a brake actuator 41. As a result, the friction brake mechanism 40 applies frictional braking force by pressing brake pads 40pFL, 40pFR, 40pRL, and 40pRR (hereinafter simply referred to as "brake pads 40p") as friction materials against the brake disc 40d.

[0019] The brake actuator 41 is an actuator provided between the friction brake mechanism 40 and a master cylinder (not shown) that pressurizes hydraulic oil by the depression force of the brake pedal (not shown), and controls the hydraulic pressure of the brake hydraulic oil supplied to wheel cylinders (not shown) built into each brake caliper 40c. Here, the brake actuator 41 can apply a frictional braking force to the wheels 50 by controlling the hydraulic pressure of the wheel cylinders (not shown) independently for the front wheels 50F and the rear wheels 50R, for example. The brake actuator 41 can also apply a frictional braking force to the wheels 50 by controlling the hydraulic pressure of the wheel cylinders (not shown) independently for each of the four wheels.

[0020] The operation of the brake actuator 41 is controlled by the electrically connected brake ECU 22. The brake ECU 22 is an electronic control unit having a microcomputer as a main part. The brake ECU 22 is connected to the drive ECU 21 via a controller area network (CAN) (not shown) so as to be able to transmit and receive signals to and from the drive ECU 21.

[0021] The brake ECU 22 is connected to a hydraulic sensor, various control valves, and a pump (not shown) that are provided in a brake actuator 41. Also connected to the brake ECU 22 are, among the sensor group 30, a brake sensor 34 that detects the amount of braking operation by the driver from the amount of depression (or angle, pressure, etc.) of a brake pedal (not shown), and four wheel speed sensors 35 that detect the wheel speeds of the four wheels, respectively.

[0022] In addition, the brake ECU 22 is connected to a road surface condition detection sensor 36 out of the sensor group 30. The road surface condition detection sensor 36 includes, for example, a stereo camera or a LiDAR, and detects the condition of the road surface ahead in the traveling direction of the vehicle 1. Here, the road surface condition detection sensor 36 can detect a road surface condition that may cause a decrease in braking force, specifically, a condition in which the friction coefficient μ of the road surface decreases, such as a wet road surface (puddles) due to rainfall or snow accumulation or ice on the road surface due to snowfall. In other words, the road surface condition detection sensor 36 can detect a dry road surface in which the friction coefficient μ of the road surface is high, as the road surface condition.

[0023] The brake ECU 22 executes a process of calculating a friction braking force (corresponding to a hydraulic braking force) to be generated by the friction brake mechanism 40 and a regenerative braking force to be generated by the rear motor 12 so as to realize a target braking force Vtb required by brake pedal operation. The brake ECU 22 also executes a process of transmitting information (regenerative brake command) representing the calculated (or determined) regenerative braking force to the drive ECU 21. The brake ECU 22 also executes a process of controlling the operation of the brake actuator 41 based on the friction braking force (hydraulic braking force). Furthermore, the brake ECU 22 also executes a process of calculating a vehicle speed (vehicle body speed) based on the wheel speeds of the four wheels detected by the wheel speed sensor 35, and transmitting vehicle speed information representing the calculated vehicle speed to a plurality of on-board ECUs including the drive ECU 21 via a communication network (not shown).

[0024] When the drive ECU 21 receives a regenerative braking command transmitted from the brake ECU 22, the drive ECU 21 outputs a control signal generated so that a regenerative braking force requested as information included in the regenerative braking command is applied to the rear wheel 50R to the inverter 17. This controls the duty ratio of the switching elements of the inverter 17, and a current corresponding to the regenerative braking force flows from the rear motor 12 to the battery 19 via the DC / DC converter 18, i.e., the regenerative energy is recovered and a braking force is applied to the rear wheel 50R.

[0025] The configuration consisting of the friction brake mechanism 40, brake actuator 41, brake pedal (not shown), and master cylinder (not shown) corresponds to the friction brake device of the present invention. Moreover, the configuration consisting of the rear motor 12 (or the front motor 11 as described below), inverter 17, DC / DC converter 18, and battery 19 corresponds to the regenerative brake device of the present invention. And the controller 20 consisting of the drive ECU 21 and brake ECU 22 executes cooperative control of the regenerative brake device and the friction brake device. Furthermore, the wheel speed sensor 35 and the road surface condition detection sensor 36 correspond to the road surface condition detection unit of the present invention.

[0026] Next, the braking control of this embodiment will be described. When regenerative braking force is applied only to the rear wheels 50R by the rear motor 12, the current generated by the rear motor 12 functioning as a generator is charged and recovered in the battery 19 via the DC / DC converter 18. The recovered current, i.e., regenerative energy, is then supplied to the front motor 11 and the rear motor 12, for example, when the vehicle 1 is traveling, to drive the front wheels 50F and the rear wheels 50R. Therefore, the more efficiently and the more regenerative energy is recovered, the longer the distance that can be traveled by driving the front wheels 50F and the rear wheels 50R, that is, the more the power consumption rate can be improved.

[0027] Therefore, when regenerative braking force is generated only on the rear wheels 50R in the vehicle 1, the brake ECU 22 outputs a regenerative brake command representing the regenerative braking force to the drive ECU 21 so that the maximum regenerative energy can be recovered during braking. Specifically, as shown in Fig. 2, the brake ECU 22 sets the maximum regenerative braking force Vrbm determined based on the maximum regenerative energy that can be recovered during braking of the vehicle 1 as the regenerative braking force of the rear wheels 50R, and outputs a regenerative brake command including the maximum regenerative braking force Vrbm.

[0028] Then, the brake ECU 22 sets the braking force that is insufficient when the drive ECU 21 applies the maximum regenerative braking force Vrbm to the rear wheel 50R relative to the target braking force Vtb (shown by a black circle in FIG. 2) required of the vehicle 1 by the driver as the friction braking force of the front wheel 50F, and operates the friction brake mechanism 40 of the front wheel 50F to generate a braking force that coincides with the target braking force Vtb on the vehicle 1. Note that in FIG. 2 and FIGS. 4, 5 and 6 described below, the area shown by dots indicates the normal braking range of the vehicle 1.

[0029] In this way, when the regenerative braking force of the rear wheels 50R is set to the maximum regenerative braking force Vrbm so as to recover more regenerative energy, that is, to improve the power consumption rate, only the friction brake mechanism 40 of the front wheels 50F operates and friction braking force is applied to the front wheels 50F without following the actual braking force distribution line, as shown in Fig. 2. That is, in a vehicle 1 that applies regenerative braking force only to the rear wheels 50R, when the maximum regenerative braking force Vrbm is set, the frequency with which the friction brake mechanism 40 of the rear wheels 50R operates becomes extremely low.

[0030] Therefore, the brake pads 40pRL, 40pRR constituting the friction brake mechanism 40 of the rear wheel 50R are pressed against and contact the brake discs 40dRL, 40dRR less frequently. As a result, the brake pads 40pRL, 40pRR are less frequently subjected to loads that cause frictional heat generation and surface wear, and for example, there is a risk that deterioration due to water absorption will occur or that existing deterioration will progress with the decrease in frequency of use.

[0031] Therefore, in this embodiment, the brake ECU 22 executes the braking control program shown in Fig. 3 every time a predetermined short time has elapsed. In this embodiment, the brake ECU 22 executes the braking control program, thereby actively operating the friction brake mechanism 40 of the rear wheel 50R without affecting the power consumption rate, in other words, without reducing the regenerative energy that can be recovered by the rear motor 12. As a result, in this embodiment, the frequency of operation of the friction brake mechanism 40 of the rear wheel 50R is increased, and a load is applied to the brake pads 40pRL, 40pRR, thereby suppressing deterioration of the brake pads 40p. The braking control program will be specifically described below.

[0032] The brake ECU 22 (more specifically, the CPU of the microcomputer constituting the brake ECU 22) starts executing a braking control program in step S10. In the following step S11, the brake ECU 22 acquires road surface condition information, such as an image showing the road surface condition detected by the road surface condition detection sensor 36, and / or wheel speed information detected by the wheel speed sensors 35 of each wheel 50.

[0033] In the next step S12, the brake ECU 22 determines whether the road surface condition is a predetermined condition that does not disturb the stability of the vehicle 1 when braking, specifically, a dry road surface with a high friction coefficient μ, based on the acquired road surface information and / or wheel speed information. That is, the brake ECU 22 determines whether the road surface is dry so as to prevent the stability of the vehicle 1 from being impaired even when the vehicle 1 is braked, as described later. Therefore, if the road surface is dry, the brake ECU 22 determines "Yes" and executes each step processing from step S13 onwards. On the other hand, if the road surface is not dry, for example, if it is a wet road surface with a low friction coefficient μ due to rainfall or snowfall, the brake ECU 22 determines "No" and ends execution of the program in step S16.

[0034] In step S13, the brake ECU 22 determines whether or not the target braking force Vtb requested by the driver is greater than the maximum regenerative braking force Vrbm of the rear wheel 50R by the rear motor 12. That is, if the target braking force Vtb is greater than the maximum regenerative braking force Vrbm, the brake ECU 22 determines "Yes" and executes the process of step S14.

[0035] In step S14, the brake ECU 22 cooperates with the drive ECU 21 to cause the rear motor 12 to generate the maximum regenerative braking force Vrbm as a regenerative braking force. That is, the rear motor 12 generates the maximum regenerative braking force Vrbm as a rear wheel braking force on the rear wheel 50R as shown by the dashed arrow in Fig. 4. This allows the rear motor 12, as a generator, to recover a current equivalent to the maximum regenerative braking force Vrbm, i.e., regenerative energy, to the maximum extent possible.

[0036] On the other hand, the brake ECU 22 sets a braking force equivalent to the difference between the target braking force Vtb and the maximum regenerative braking force Vrbm as a friction braking force. Then, the brake ECU 22 activates the friction brake mechanism 40 of the front wheel 50F and the friction brake mechanism 40 of the rear wheel 50R to generate the set friction braking force. Specifically, the brake ECU 22 activates the friction brake mechanisms 40 of the front wheel 50F and the rear wheel 50R as shown by the thick circle in FIG. 4. As a result, in the friction brake mechanism 40 of the rear wheel 50R, the brake pads 40pRL and 40pRR are pressed against the brake discs 40dRL and 40dRR to apply a friction braking force. Next, the brake ECU 22 stops the operation of the friction brake mechanism 40 of the rear wheel 50R, that is, activates only the friction brake mechanism 40 of the front wheel 50F, and finally generates the target braking force Vtb set on the constant deceleration line on the vehicle 1. This allows the vehicle 1 to stop.

[0037] Here, the friction braking force applied by the friction brake mechanism 40 of the rear wheel 50R is smaller than the friction braking force applied by the friction brake mechanism 40 of the front wheel 50F. This is to prevent the stability of the vehicle 1 from being impaired even if a further friction braking force is applied to the rear wheel 50R to which the rear motor 12 is applying the maximum regenerative braking force Vrbm as described above. Therefore, the brake ECU 22 controls the operation of the friction brake mechanism 40 of the rear wheel 50R via the brake actuator 41 based on, for example, wheel speed information detected by the wheel speed sensor 35 so that an appropriate braking force is generated on the rear wheel 50R.

[0038] 3, when the brake ECU 22 stops the vehicle 1 in step S14, the brake ECU 22 executes the process of step S16. The brake ECU 22 temporarily ends the execution of the braking control program in step S16. Then, after a predetermined short time has elapsed, the brake ECU 22 starts the execution of the braking control program again in step S10.

[0039] On the other hand, in step S13, if the target braking force Vtb is equal to or less than the maximum regenerative braking force Vrbm, for example, within the normal braking range indicated by dots in Fig. 4, the brake ECU 22 determines "No" and executes the process of step S15. In step S15, the brake ECU 22 cooperates with the drive ECU 21 to brake the vehicle 1 by normal control that mainly generates regenerative braking force.

[0040] That is, the brake ECU 22 outputs a regenerative brake command to the drive ECU 21 to generate a regenerative braking force, for example, equal to the maximum regenerative braking force Vrbm, on the rear wheel 50R in accordance with the target braking force Vtb set by the driver. As a result, the drive ECU 21 outputs a control signal to the inverter 17, with the maximum regenerative braking force Vrbm being the regenerative braking force. As a result, a braking force of the maximum regenerative braking force Vrbm is applied to the rear wheel 50R, and the vehicle 1 is decelerated to an extremely slow speed. Then, when the vehicle 1 is in an extremely slow speed state, the brake ECU 22 activates, for example, the friction brake mechanism 40 of the front wheel 50F to generate a friction braking force on the front wheel 50F, thereby completely stopping the vehicle 1.

[0041] Then, when the brake ECU 22 stops the vehicle 1 in step S15, the brake ECU 22 executes the process of step S16. The brake ECU 22 temporarily ends the execution of the braking control program in step S16. Then, after a predetermined short time has elapsed, the brake ECU 22 starts the execution of the braking control program again in step S10.

[0042] As can be understood from the above description, according to the vehicle brake control device of this embodiment, when generating a target braking force Vtb larger than the maximum regenerative braking force Vrbm, the brake ECU 22 constituting the controller 20 activates the friction brake mechanism 40 constituting the friction brake device provided on the front wheels 50F and the rear wheels 50R of the vehicle 1 to generate a friction braking force. This increases the operation frequency of the friction brake mechanism 40 constituting the friction brake device, and as a result, an appropriate load is applied to the brake pads 40p, which are friction materials of the friction brake mechanism 40 provided on the front wheels 50F and the rear wheels 50R, to cause, for example, generation of friction heat and surface wear. Therefore, the brake pads 40p to which the load is applied can be suppressed from deteriorating due to a decrease in frequency of use, specifically, from deteriorating due to water absorption.

[0043] Next, a first modification of the above-described embodiment will be described. In the first modification, braking control is executed when a target braking force Vtb larger than the target braking force Vtb in the above-described embodiment is required.

[0044] Specifically, as shown in Fig. 5, in the first modified example, the target braking force Vtb indicated by the black circle is required to be a value larger than the target braking force Vtb of the above embodiment indicated by the black circle in Fig. 4. In this case, in step S14 of the braking control program shown in Fig. 3, the brake ECU 22 first generates the maximum regenerative braking force Vrbm by the rear motor 12, thereby braking the vehicle 1 while recovering regenerative energy, as in the above embodiment.

[0045] In the first modified example, in order to generate a larger target braking force Vtb, the brake ECU 22 cooperates with the drive ECU 21 to execute braking control by coordinating the friction brake device and the regenerative brake device. That is, the brake ECU 22 and the drive ECU 21 switch between the regenerative braking force and the friction braking force so as to reduce at least a part of the maximum regenerative braking force Vrbm, i.e., the regenerative braking force, applied by the rear motor 12, and increase the friction braking force applied by the friction brake mechanism 40 of the front wheel 50F and the friction brake mechanism 40 of the rear wheel 50R.

[0046] Specifically, the drive ECU 21 gradually reduces the regenerative braking force by the rear motor 12 from the maximum regenerative braking force Vrbm, as shown by the thick circle in Fig. 5, in accordance with the regenerative braking command from the brake ECU 22. On the other hand, the brake ECU 22 activates the friction brake mechanism 40 of the front wheel 50F and the friction brake mechanism 40 of the rear wheel 50R via the brake actuator 41 in accordance with the reduction in the regenerative braking force by the rear motor 12.

[0047] 5, the brake ECU 22 increases the friction braking force applied by the friction brake mechanisms 40 of the front wheels 50F and the rear wheels 50R, and controls the vehicle 1 to generate a braking force that coincides with the intersection of the equal deceleration line and the actual braking force distribution line. Then, the brake ECU 22 activates the friction brake mechanisms 40 of the front wheels 50F and the rear wheels 50R via the brake actuator 41 so as to follow the actual braking force distribution line, and generates a friction braking force on the front wheels 50F and the rear wheels 50R while ensuring the stability of the vehicle 1 until the target braking force Vtb is reached.

[0048] As a result, even in the first modified example, regenerative energy can be recovered at the rear wheel 50R where regenerative braking force is generated by the rear motor 12, and the frequency of operation of the friction brake mechanism 40 can be increased. Therefore, even in the first modified example, the brake pads 40pRL, 40pRR constituting the brake mechanism 40 of the rear wheel 50R are frequently subjected to loads that cause generation of frictional heat, surface wear, and the like. As a result, even in the first modified example, it is possible to suppress the progression of deterioration of the brake pads 40pRL, 40pRR while recovering regenerative energy.

[0049] Next, a second modification of the above-described embodiment will be described. In the second modification, braking control is executed in a case where the vehicle 1 generates a regenerative braking force only by the front motor 11, instead of by the rear motor 12.

[0050] In the second modified example, the front motor 11 of the vehicle 1 generates a braking torque and applies a regenerative braking force to the front wheels 50F. That is, in the second modified example, the front motor 11 functions as a motor generator. Therefore, in the second modified example, unlike the above-described embodiment and the first modified example, the rear motor 12 does not have a function of regenerating power to the battery 19 and cannot apply a regenerative braking force to the rear wheels 50R.

[0051] Also in the second modified example, as shown in Fig. 6, the target braking force Vtb indicated by the black circle is required to be a value larger than the target braking force Vtb of the above embodiment indicated by the black circle in Fig. 4. In this case, in step S14 of the braking control program shown in Fig. 3, the brake ECU 22 first applies the maximum regenerative braking force Vrbm to the front wheels 50F by the front motor 11, thereby braking the vehicle 1 while recovering regenerative energy.

[0052] In the second modified example, in order to generate a larger target braking force Vtb, the brake ECU 22 cooperates with the drive ECU 21 to execute braking control by coordinating the friction brake device and the regenerative brake device. That is, the brake ECU 22 and the drive ECU 21 switch between the regenerative braking force and the friction braking force so as to reduce at least a part of the maximum regenerative braking force Vrbm, i.e., the regenerative braking force, applied by the front motor 11, and increase the friction braking force applied by the friction brake mechanism 40 of the front wheel 50F and the friction brake mechanism 40 of the rear wheel 50R.

[0053] Specifically, the drive ECU 21 gradually reduces the regenerative braking force of the front motor 11 from the maximum regenerative braking force Vrbm, as shown by the thick circle in Fig. 6, in accordance with the regenerative braking command from the brake ECU 22. On the other hand, the brake ECU 22 activates the friction brake mechanism 40 of the front wheel 50F and the friction brake mechanism 40 of the rear wheel 50R via the brake actuator 41 in accordance with the reduction in the regenerative braking force of the front motor 11.

[0054] 6, the brake ECU 22 increases the friction braking force by the friction brake mechanisms 40 of the front wheels 50F and the rear wheels 50R, and controls the vehicle 1 to generate a braking force that coincides with the intersection of the equal deceleration line and the actual braking force distribution line. Then, the brake ECU 22 activates the friction brake mechanisms 40 of the front wheels 50F and the rear wheels 50R via the brake actuator 41 so as to follow the actual braking force distribution line, and generates a friction braking force on the front wheels 50F and the rear wheels 50R while ensuring the stability of the vehicle 1 until the target braking force Vtb is reached.

[0055] As a result, in the second modified example, regenerative energy can be recovered at the front wheel 50F where regenerative braking force is generated by the front motor 11. In the second modified example, the frequency of the brake pads 40pFL, 40pFR constituting the friction brake mechanism 40 being pressed against and contacting the brake discs 40dFL, 40dFR can be increased at the front wheel 50F. Therefore, although the brake pads 40pFL, 40pFR constituting the brake mechanism 40 of the front wheel 50F have a chance to operate in the extremely slow speed range by the above-mentioned normal control, the frequency of the loads that cause larger generation of frictional heat and surface wear, etc. is increased. As a result, the deterioration of the brake pads 40pFL, 40pFR can be suppressed.

[0056] In addition, the present invention is not limited to the above embodiment, the first modification, and the second modification, and various modifications are possible. For example, the above embodiment and the first modification illustrate a case where only the rear motor 12 of the rear wheel 50R applies a regenerative braking force, and the second modification illustrates a case where only the front motor 11 of the front wheel 50F applies a regenerative braking force. However, it is also possible for both the front motor 11 of the front wheel 50F and the rear motor 12 of the rear wheel 50R to apply a regenerative braking force. Furthermore, the vehicle 1 is not limited to an electric vehicle (EV) equipped with at least one of the front motor 11 and the rear motor 12, but may be a hybrid vehicle (HEV, PHEV) equipped with an internal combustion engine. [Explanation of symbols]

[0057] 1...vehicle, 11...front motor (regenerative braking device), 12...rear motor (regenerative braking device), 17...inverter (regenerative braking device), 18...DC / DC converter (regenerative braking device), 19...battery (regenerative braking device), 20...controller, 21...drive ECU, 22...brake ECU, 40...friction brake mechanism (friction brake device), 40p...brake pad (friction material), 41...brake actuator (friction brake device), 30...sensor group, 34...brake sensor, 35...wheel speed sensor (road surface condition detection unit), 36...road surface condition detection sensor (road surface condition detection unit), 50...wheel, Vtb...target braking force, Vrbm...maximum regenerative braking force (regenerative braking force).

Claims

1. A regenerative braking device that applies a regenerative braking force to at least one of the front wheels and the rear wheels; A vehicle brake control device that is applied to a vehicle equipped with a friction brake device that applies a friction braking force to the front wheels and the rear wheels, a road surface condition detection unit that detects a road surface condition ahead in a traveling direction of the vehicle; a controller that executes cooperative control of the regenerative brake device and the friction brake device so as to generate a target braking force for braking the vehicle, The controller: determining whether the road surface condition detected by the road surface condition detection unit is a predetermined state that does not disturb stability when braking the vehicle; A vehicle braking control device that, when the specified state is present, operates the friction brake devices of the front wheels and the rear wheels to generate the friction braking force when the target braking force is greater than the regenerative braking force generated by the regenerative braking device, so that the target braking force is generated in the vehicle.

2. the regenerative braking device applies the regenerative braking force to the rear wheels, The controller: When the vehicle is in the predetermined state and the target braking force is greater than the regenerative braking force, 2. The vehicle brake control device according to claim 1, wherein the friction braking force generated by activating the friction brake device of the rear wheels is smaller than the friction braking force generated by activating the friction brake device of the front wheels.

3. the regenerative braking device applies the regenerative braking force to the rear wheels, The controller: When the vehicle is in the predetermined state and the target braking force is greater than the regenerative braking force, 2. The brake control device for a vehicle according to claim 1, wherein at least a portion of the regenerative braking force applied to the rear wheels by the regenerative braking device is replaced with the friction braking force applied by the friction brake device of the rear wheels and the friction brake device of the front wheels, and the friction braking force is generated by activating the friction brake device of the rear wheels and the friction brake device of the front wheels so that the target braking force is generated in the vehicle.

4. The regenerative braking device applies the regenerative braking force to the front wheels, The controller: When the vehicle is in the predetermined state and the target braking force is greater than the regenerative braking force, 2. The vehicle brake control device according to claim 1, wherein at least a portion of the regenerative braking force applied to the front wheels by the regenerative braking device is replaced with the friction braking force applied by the friction brake device of the front wheels and the friction brake device of the rear wheels, and the friction braking force is generated by activating the friction brake device of the front wheels and the friction brake device of the rear wheels so that the target braking force is generated in the vehicle.

5. 5. The vehicle brake control device according to claim 1, wherein the regenerative braking force applied by the regenerative brake device is determined based on a maximum recoverable regenerative energy during braking of the vehicle.

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