Vehicle braking control system

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 braking control device for a vehicle.

Background Art

[0002] Conventionally, for example, a braking control device for a vehicle disclosed in Patent Document 1 is known. The conventional braking control device for a vehicle is applied to a vehicle equipped with a regenerative brake device and a friction brake device that generate braking force for each of a pair of left and right front wheels and rear wheels. And when there is a deceleration request for the vehicle and it is determined that it is necessary to perform a contact (a so-called bedding-in) of the friction material of the friction brake device with a rotating member such as a rotor, the conventional braking control device for a vehicle operates the friction brake device preferentially over the regenerative brake device. Thereby, the conventional braking control device for a vehicle executes the bedding-in of the friction brake device to realize an early recovery of the effectiveness of the friction brake device.

Prior Art Documents

Patent Documents

[0003]

Patent Document Ⅰ

Summary of the Invention

Problems to be Solved by the Invention

[0004] In conventional vehicle braking control systems, when a vehicle is new or after the friction material has been replaced, the friction brake system is preferentially activated to break in the friction material, bringing it into contact with the rotating member and generating frictional braking force. Therefore, while the vehicle is traveling a predetermined distance, the friction brake system is activated more frequently, and a load is placed on the friction material of the friction brake system that generates frictional heat and wear. As a result, deterioration of the friction material due to reduced usage, such as deterioration of the friction material due to water absorption, is suppressed during the break-in period. However, after the vehicle has traveled a predetermined distance, in other words, after the break-in period is complete, regenerative braking force from the regenerative braking system is preferentially applied, so the frequency of activation of the friction brake system decreases. As a result, the friction material is not subjected to load, and there is a risk that deterioration of the friction material will occur or accelerate.

[0005] Furthermore, while the vehicle travels a predetermined distance, frictional braking force from the friction brake system is preferentially applied; in other words, the frequency of activation of the regenerative braking system decreases. As a result, while the vehicle travels a predetermined distance, the current recovered by regeneration from the regenerative braking system, i.e., the regenerative energy, decreases. This affects the range the vehicle can travel using regenerative energy (current), and thus affects the vehicle's power consumption rate. In short, with conventional vehicle braking control systems, while the deterioration of the friction material is suppressed when the friction brake system is being broken in, a situation arises where the power consumption rate is affected.

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

[0007] The present invention relates to a vehicle braking control device applicable to a vehicle that includes a regenerative brake device that applies regenerative braking force to at least one of the front wheels and rear wheels, and a friction brake device that applies friction braking force to the front wheels and rear wheels. The vehicle braking control device comprises a road surface condition detection unit that detects the road surface condition in front of the vehicle in the direction of travel, and a controller that performs coordinated control of the regenerative brake device and the friction brake device to generate a target braking force for the vehicle. The controller determines whether the road surface condition detected by the road surface condition detection unit is a predetermined state that does not disrupt the stability of the vehicle when it is braking, and if it is a predetermined state, and the target braking force is greater than the regenerative braking force from the regenerative brake device, the controller operates the friction brake devices of the front wheels and rear wheels to generate friction braking force so that the target braking force is generated in the vehicle. [Effects of the Invention]

[0008] According to the present invention, when the controller generates a target braking force greater than the regenerative braking force, it can activate the friction brake devices provided on the front and rear wheels of the vehicle to generate friction braking force. As a result, the vehicle can recover regenerative energy with the regenerative braking device while increasing the frequency of operation of the friction brake devices. Consequently, an appropriate load can be applied to the friction material of the friction brake devices provided on the front and rear wheels. Therefore, deterioration of the friction material due to reduced usage frequency can be suppressed. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic diagram of the vehicle and vehicle braking control device according to this embodiment. [Figure 2] This graph illustrates the frictional braking force when regenerative braking force is increased. [Figure 3] This is a flowchart of the braking control program. [Figure 4] This graph illustrates the regenerative braking force on the rear wheels and the frictional braking forces on both the rear and front wheels in relation to the embodiment. [Figure 5]This graph illustrates the regenerative braking force on the rear wheels and the frictional braking forces on both the rear and front wheels in the first modified case, which involves substitution. [Figure 6] This graph illustrates the regenerative braking force on the front wheels and the frictional braking forces on both the front and rear wheels in the second variation, which involves a substitution. [Modes for carrying out the invention]

[0010] Hereinafter, a vehicle braking control device, which is one embodiment of the present invention, will be described in detail with reference to the drawings. It should be noted that, in addition to the embodiments described below, the present invention can be implemented in various forms with various modifications and improvements based on the knowledge of those skilled in the art.

[0011] Vehicle 1 to which the vehicle braking control device of this embodiment is applied includes, as shown in Figure 1, a front motor 11 that drives the left front wheel 50FL and the right front wheel 50FR, and a rear motor 12 that drives the left rear wheel 50RL and the right rear wheel 50RR. Hereinafter, the left front wheel 50FL and the right front wheel 50FR may be collectively referred to as "front wheel 50F," and the left rear wheel 50RL and the right rear wheel 50RR may be collectively referred to as "rear wheel 50R." Furthermore, when there is no need to distinguish between the front wheel 50F and the rear wheel 50R, they may simply be referred to as "wheel 50." Although vehicle 1 is a general front-wheel steering vehicle with the front wheel 50F as the steering wheel, the steering mechanism is not shown or described.

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

[0013] The front motor 11 and the rear motor 12 are configured to be independently driven in the forward rotation direction and the reverse rotation direction of the vehicle 1 by the power supply control of the inverter 17. Furthermore, in the vehicle 1 of this embodiment, the inverter 17 also has the function of storing regenerative energy by converting the alternating current generated by the rear motor 12 into direct current and charging the battery 19 via the DC / DC converter 18.

[0014] As a result, in the vehicle 1 of this embodiment, the rear motor 12 generates braking torque and applies regenerative braking force to the rear wheels 50R. In other words, in this embodiment, the rear motor 12 functions as a motor-generator. However, in the vehicle 1 of this embodiment, the front motor 11 does not have the function of regenerating power to the battery 19 like the rear motor 12, and therefore cannot apply regenerative braking force to the front wheels 50F.

[0015] The front motor 11 and rear motor 12 are controlled by a drive ECU 21 that constitutes the controller 20. The drive ECU 21 is an electronic control unit (ECU) that primarily consists of a microcomputer. The microcomputer includes a CPU and memory devices such as ROM and RAM, and the CPU implements various functions by executing programs (instructions) stored in the ROM.

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

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

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

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

[0020] The operation of the brake actuator 41 is controlled by a brake ECU 22 that is electrically connected. The brake ECU 22 is an electronic control unit (Electric Control Unit) having a microcomputer as a main part. The brake ECU 22 is connected to be able to mutually transmit and receive with the drive ECU 21 via a CAN (Controller Area Network), the illustration of which is omitted.

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

[0022] Furthermore, the brake ECU 22 is connected to a road surface condition detection sensor 36, which is part of the sensor group 30. The road surface condition detection sensor 36 is equipped with, for example, a stereo camera or LiDAR, and detects the condition of the road surface in front of the vehicle 1 in the direction of travel. The road surface condition detection sensor 36 can detect road surface conditions that may cause a decrease in braking force, specifically, conditions that reduce the friction coefficient μ of the road surface, such as wet roads (puddles) due to rainfall, or snow accumulation or freezing of the road surface due to snowfall. In other words, the road surface condition detection sensor 36 can detect a dry road surface, which is a road surface condition with a high friction coefficient μ.

[0023] The brake ECU 22 performs processing to calculate the friction braking force (equivalent to hydraulic braking force) generated by the friction brake mechanism 40 and the regenerative braking force generated by the rear motor 12 in order to achieve the target braking force Vtb required by the brake pedal operation. The brake ECU 22 also performs processing to transmit information (regenerative brake command) representing the calculated (or determined) regenerative braking force to the drive ECU 21. The brake ECU 22 also performs processing to control the operation of the brake actuator 41 based on the friction braking force (hydraulic braking force). Furthermore, the brake ECU 22 also calculates the vehicle speed (vehicle body speed) based on the wheel speeds of the four wheels detected by the wheel speed sensor 35 and performs processing to transmit the calculated vehicle speed information to multiple 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, it outputs a control signal to the inverter 17 that generates such a regenerative braking force as required by the regenerative braking command to be applied to the rear wheel 50R. This controls the duty cycle of the switching elements in the inverter 17, causing a current corresponding to the regenerative braking force to flow from the rear motor 12 through the DC / DC converter 18 to the battery 19, thereby recovering regenerative energy and applying braking force to the rear wheel 50R.

[0025] The friction brake system of the present invention consists of a friction brake mechanism 40, a brake actuator 41, a brake pedal (not shown), and a master cylinder (not shown). The regenerative brake system of the present invention consists of a rear motor 12 (or, as described later, a front motor 11), an inverter 17, a DC / DC converter 18, and a battery 19. The controller 20, consisting of a drive ECU 21 and a brake ECU 22, performs coordinated control of the regenerative brake system and the friction brake system. 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 recovered and charged to 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 running, to drive the front wheels 50F and the rear wheels 50R. Therefore, the more efficiently and in the amount of regenerative energy is recovered, the longer the distance that can be driven by driving the front wheels 50F and the rear wheels 50R, that is, the power consumption rate can be improved.

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

[0028] The brake ECU 22 then sets the amount of braking force that is insufficient when the drive ECU 21 applies the maximum regenerative braking force Vrbm to the rear wheels 50R in relation to the target braking force Vtb (shown as a black circle in Figure 2) requested by the driver to the vehicle 1, as the friction braking force of the front wheels 50F, and activates the friction brake mechanism 40 of the front wheels 50F to generate a braking force for the vehicle 1 that matches the target braking force Vtb. In Figure 2 and Figures 4, 5, and 6 described later, the areas shown by dots represent the normal braking range of the vehicle 1.

[0029] Thus, when the regenerative braking force of the rear wheel 50R is set to the maximum regenerative braking force Vrbm in order to recover more regenerative energy, that is, to improve the power consumption rate, as shown in Figure 2, only the friction brake mechanism 40 of the front wheel 50F operates without following the actual braking force distribution wiring, and friction braking force is applied to the front wheel 50F. In other words, in vehicle 1, which applies regenerative braking force only to the rear wheel 50R, when the maximum regenerative braking force Vrbm is set, the frequency in which the friction brake mechanism 40 of the rear wheel 50R operates becomes extremely low.

[0030] Therefore, the frequency with which the brake pads 40pRL and 40pRR, which constitute the friction brake mechanism 40 of the rear wheel 50R, are pressed against and in contact with the brake discs 40dRL and 40dRR decreases. As a result, the frequency with which the brake pads 40pRL and 40pRR are subjected to loads that cause frictional heat generation and surface wear decreases, and for example, deterioration due to water absorption may occur as the frequency of use decreases, or any deterioration that has occurred may progress.

[0031] Therefore, in this embodiment, the brake ECU 22 executes the braking control program shown in Figure 3 at predetermined short intervals. In this embodiment, by executing the braking control program, the brake ECU 22 actively operates 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 operating frequency of the friction brake mechanism 40 of the rear wheel 50R is increased, and by applying a load to the brake pads 40pRL and 40pRR, deterioration of the brake pad 40p is suppressed. The braking control program will be described in detail below.

[0032] In step S10, the brake ECU 22 (more specifically, the CPU of the microcomputer that constitutes the brake ECU 22) starts executing the braking control program. In the following step S11, the brake ECU 22 acquires road surface condition information, such as an image representing 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 subsequent step S12, the brake ECU 22 determines, based on the acquired road surface information and / or wheel speed information, whether the road surface is in a predetermined state that does not disrupt the stability of vehicle 1 when it is braked, specifically, whether it is a dry road surface with a high coefficient of friction μ. That is, the brake ECU 22 determines whether the road surface is dry so as to prevent the stability of vehicle 1 from being compromised even when vehicle 1 is braked, as will be described later. Therefore, if the road surface is dry, the brake ECU 22 determines "Yes" and executes the processing of each step 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 coefficient of friction μ due to rain or snow, the brake ECU 22 determines "No" and terminates the execution of the program in step S16.

[0034] In step S13, the brake ECU 22 determines whether the target braking force Vtb requested by the driver is greater than the maximum regenerative braking force Vrbm produced by the rear motor 12 of the rear wheel 50R. 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 in step S14.

[0035] In step S14, the brake ECU 22 works in cooperation with the drive ECU 21 to generate the maximum regenerative braking force Vrbm as regenerative braking force in the rear motor 12. That is, as shown by the dashed arrow in Figure 4, the rear motor 12 generates the maximum regenerative braking force Vrbm in the rear wheel 50R as rear wheel braking force. As a result, the rear motor 12, as a generator, can recover the maximum amount of regenerative energy, i.e., a current equivalent to the maximum regenerative braking force Vrbm.

[0036] Meanwhile, the brake ECU 22 sets a friction braking force equivalent to the difference between the target braking force Vtb and the maximum regenerative braking force Vrbm. The brake ECU 22 then operates the friction brake mechanisms 40 of the front wheel 50F and the rear wheel 50R to generate the set friction braking force. Specifically, the brake ECU 22 operates the friction brake mechanisms 40 of the front wheel 50F and the rear wheel 50R, as shown by the thick circles in Figure 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, applying friction braking force. Subsequently, the brake ECU 22 stops the operation of the friction brake mechanism 40 of the rear wheel 50R, that is, operates only the friction brake mechanism 40 of the front wheel 50F, and finally generates the target braking force Vtb set on the equal deceleration line for the vehicle 1. This allows vehicle 1 to come to a 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 ensure that the stability of the vehicle 1 is not compromised even if further friction braking force is applied to the rear wheel 50R, to which the rear motor 12 is already 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, for example, based on wheel speed information detected by the wheel speed sensor 35, so that appropriate braking force is generated on the rear wheel 50R.

[0038] Returning to the flowchart in Figure 3, when the brake ECU 22 stops vehicle 1 in step S14, it executes the process in step S16. In step S16, the brake ECU 22 temporarily terminates the execution of the braking control program. Then, after a predetermined short period of time has elapsed, the brake ECU 22 restarts the execution of the braking control program in step S10.

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

[0040] In other words, the brake ECU 22 outputs a regenerative braking command to the drive ECU 21 to generate a regenerative braking force on the rear wheels 50R that matches, for example, the maximum regenerative braking force Vrbm, according to the target braking force Vtb set by the driver. As a result, the drive ECU 21 outputs a control signal to the inverter 17 that sets the maximum regenerative braking force Vrbm as the regenerative braking force. This applies a braking force of the maximum regenerative braking force Vrbm to the rear wheels 50R, and the vehicle 1 is decelerated to an extremely slow speed. Then, with the vehicle 1 at an extremely slow speed, the brake ECU 22 activates, for example, the friction brake mechanism 40 of the front wheels 50F, generating a friction braking force on the front wheels 50F, thereby bringing the vehicle 1 to a complete stop.

[0041] Then, when the vehicle 1 is brought to a stop in step S15, the brake ECU 22 executes the process in step S16. In step S16, the brake ECU 22 temporarily terminates the execution of the braking control program. After a predetermined short period of time has elapsed, the brake ECU 22 restarts the execution of the braking control program in step S10.

[0042] As can be understood from the above explanation, according to the vehicle braking control device of this embodiment, when the brake ECU 22 constituting the controller 20 generates a target braking force Vtb that is greater than the maximum regenerative braking force Vrbm, it activates the friction brake mechanism 40 that constitutes the friction brake device provided on the front wheels 50F and rear wheels 50R of the vehicle 1 to generate friction braking force. This increases the operating frequency of the friction brake mechanism 40 that constitutes the friction brake device, and as a result, an appropriate load is applied to the brake pads 40p, which are the friction material of the friction brake mechanism 40 provided on the front wheels 50F and rear wheels 50R, causing, for example, the generation of frictional heat and surface wear. Therefore, the brake pads 40p that are subjected to a load can suppress deterioration due to decreased usage frequency, specifically deterioration due to water absorption.

[0043] Next, a first modified example of the above-described embodiment will be explained. In the first modified example, braking control is performed when a target braking force Vtb greater than the target braking force Vtb in the above embodiment is required.

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

[0045] In the first modified example, in order to generate a larger target braking force Vtb, the brake ECU 22 works in cooperation with the drive ECU 21 to coordinate the friction brake system and the regenerative brake system to perform braking control. Specifically, the brake ECU 22 and the drive ECU 21 swap the regenerative braking force with the friction braking force so as to reduce at least a portion 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, in accordance with the regenerative braking command from the brake ECU 22, gradually reduces the regenerative braking force from the rear motor 12 from the maximum regenerative braking force Vrbm, as shown by the thick circle in Figure 5. On the other hand, the brake ECU 22, in accordance with the decrease in regenerative braking force from the rear motor 12, 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.

[0047] As a result, the brake ECU 22 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 wiring, while increasing the frictional braking force of the friction brake mechanism 40 of the front wheel 50F and rear wheel 50R, as shown by the white arrows in Figure 5. The brake ECU 22 then operates the friction brake mechanism 40 of the front wheel 50F and rear wheel 50R via the brake actuator 41 in accordance with the actual braking force distribution wiring, generating frictional braking force on the front wheel 50F and rear wheel 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 and 40pRR that constitute the brake mechanism 40 of the rear wheel 50R are subjected to loads that cause frictional heat generation and surface wear more frequently. As a result, even in the first modified example, regenerative energy can be recovered while suppressing the deterioration of the brake pads 40pRL and 40pRR.

[0049] Next, a second modified example of the above-described embodiment will be explained. In the second modified example, braking control is performed when the vehicle 1 generates regenerative braking force only with the front motor 11, instead of the rear motor 12 generating regenerative braking force.

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

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

[0052] In the second modified configuration, in order to generate a larger target braking force Vtb, the brake ECU 22 works in cooperation with the drive ECU 21 to coordinate the friction brake system and the regenerative brake system to perform braking control. Specifically, the brake ECU 22 and the drive ECU 21 swap the regenerative braking force with the friction braking force so as to reduce at least a portion of the maximum regenerative braking force Vrbm, i.e., the regenerative braking force, applied by the front motor 11, while increasing the friction braking force applied by the friction brake mechanisms 40 of the front wheels 50F and the rear wheels 50R.

[0053] Specifically, the drive ECU 21, in accordance with the regenerative braking command from the brake ECU 22, gradually reduces the regenerative braking force from the front motor 11 from the maximum regenerative braking force Vrbm, as shown by the thick circle in Figure 6. On the other hand, the brake ECU 22, in accordance with the decrease in regenerative braking force from the front motor 11, 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.

[0054] As a result, the brake ECU 22 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 wiring, while increasing the frictional braking force of the friction brake mechanism 40 of the front wheel 50F and rear wheel 50R, as shown by the white arrows in Figure 6. The brake ECU 22 then operates the friction brake mechanism 40 of the front wheel 50F and rear wheel 50R via the brake actuator 41 in accordance with the actual braking force distribution wiring, generating frictional braking force on the front wheel 50F and rear wheel 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 configuration, regenerative energy can be recovered at the front wheel 50F where regenerative braking force is generated by the front motor 11. Furthermore, in the second modified configuration, the frequency of contact between the brake pads 40pFL and 40pFR, which constitute the friction brake mechanism 40, and the brake discs 40dFL and 40dFR can be increased at the front wheel 50F. Consequently, although the brake pads 40pFL and 40pFR, which constitute the brake mechanism 40 of the front wheel 50F, have opportunities to operate in the extremely low-speed range by the normal control described above, for example, they are subjected to a greater frequency of loads that cause greater frictional heat generation and surface wear. As a result, the deterioration of the brake pads 40pFL and 40pFR can be suppressed.

[0056] Furthermore, in implementing the present invention, various modifications are possible, not limited to the above embodiments, first modification, and second modification. For example, the above embodiments and the first modification illustrate a case where only the rear motor 12 of the rear wheel 50R provides regenerative braking force, while the second modification illustrates a case where only the front motor 11 of the front wheel 50F provides 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 provide regenerative braking force. Moreover, 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 also be a hybrid vehicle (HEV, PHEV) equipped with an internal combustion engine. [Explanation of Symbols]

[0057] 1...Vehicle, 11...Front motor (regenerative braking system), 12...Rear motor (regenerative braking system), 17...Inverter (regenerative braking system), 18...DC / DC converter (regenerative braking system), 19...Battery (regenerative braking system), 20...Controller, 21...Drive ECU, 22...Brake ECU, 40...Friction brake mechanism (friction braking system), 40p...Brake pad (friction material), 41...Brake actuator (friction braking system), 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 system that applies regenerative braking force to at least one of the front wheels and rear wheels, A vehicle braking control device applicable to a vehicle equipped with a friction brake device that applies frictional braking force to the front wheels and the rear wheels, A road surface condition detection unit that detects the road surface condition in front of the vehicle in the direction of travel, The system includes a controller that performs coordinated control between the regenerative braking system and the friction braking system to generate a target braking force in the vehicle, The aforementioned controller, The road surface condition detection unit determines whether the road surface condition detected is a predetermined condition that does not disrupt the stability of the vehicle during braking. In the predetermined state described above, when the target braking force is greater than the regenerative braking force from the regenerative braking device, the friction brake devices of the front and rear wheels are activated to generate the friction braking force so that the target braking force is generated in the vehicle. The regenerative braking system applies the regenerative braking force to the rear wheels. The aforementioned controller, When the predetermined state is met and the target braking force is greater than the regenerative braking force, A vehicle braking control device that replaces at least a portion of the regenerative braking force applied by the regenerative braking device to the rear wheel with the friction braking force applied by the friction brake device of the rear wheel and the friction brake device of the front wheel, and operates the friction brake device of the rear wheel and the friction brake device of the front wheel to generate the friction braking force so that the target braking force is generated in the vehicle.

2. The controller is When the predetermined state is met and the target braking force is greater than the regenerative braking force, The vehicle braking control device according to claim 1, wherein the friction brake device of the rear wheel is operated to generate the friction braking force such that it is smaller than the friction braking force generated by operating the friction brake device of the front wheel.

3. A regenerative braking system that applies regenerative braking force to at least one of the front wheels and rear wheels, A vehicle braking control device applicable to a vehicle equipped with a friction brake device that applies frictional braking force to the front wheels and the rear wheels, A road surface condition detection unit that detects the road surface condition in front of the vehicle in the direction of travel, The system includes a controller that performs coordinated control between the regenerative braking system and the friction braking system to generate a target braking force in the vehicle, The aforementioned controller, The road surface condition detection unit determines whether the road surface condition detected is a predetermined condition that does not disrupt the stability of the vehicle during braking. In the predetermined state described above, when the target braking force is greater than the regenerative braking force from the regenerative braking device, the friction brake devices of the front and rear wheels are activated to generate the friction braking force so that the target braking force is generated in the vehicle. The regenerative braking device applies the regenerative braking force to the front wheels. The aforementioned controller, When the predetermined state is met and the target braking force is greater than the regenerative braking force, A vehicle braking control device that replaces at least a portion of the regenerative braking force applied by the regenerative braking device to the front wheel with the friction braking force applied by the friction brake device of the front wheel and the friction brake device of the rear wheel, and operates the friction brake device of the front wheel and the friction brake device of the rear wheel to generate the friction braking force so that the target braking force is generated in the vehicle.

4. The vehicle braking control device according to any one of claims 1 to 3, wherein the regenerative braking force applied by the regenerative braking device is determined based on the maximum amount of regenerative energy that can be recovered when the vehicle is being braked.

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