阅读说明：本技术 车辆的制动控制装置 (Vehicle brake control device ) 是由 山本勇作 于 2020-02-12 设计创作，主要内容包括：本发明提供车辆的制动控制装置。制动控制装置(50)具备：控制部(53),基于制动力分配和要求制动力控制前轮制动力以及后轮制动力；分配设定部(52),设定制动力分配；以及滑移判定部(54),判定是否为后轮先行滑移状态。分配设定部(52)在制动力分配为第一制动力分配的情况下进行了是后轮先行滑移状态的判定时,执行在规定的期间内使制动力分配转变为第二制动力分配的分配转变处理。第二制动力分配是与设定第一制动力分配作为制动力分配时相比减小后轮制动力的分配。(The invention provides a brake control device for a vehicle. A brake control device (50) is provided with: a control unit (53) that controls the front wheel braking force and the rear wheel braking force on the basis of the braking force distribution and the required braking force; a distribution setting unit (52) that sets the braking force distribution; and a slip determination unit (54) for determining whether the rear wheel is in a leading slip state. When the braking force distribution is the first braking force distribution, the distribution setting unit (52) executes a distribution transition process for transitioning the braking force distribution to the second braking force distribution for a predetermined period when the rear wheel pre-slip state is determined. The second braking force distribution is a distribution that reduces the rear wheel braking force as compared to when the first braking force distribution is set as the braking force distribution.)

1. A brake control device for a vehicle, comprising:

a control unit that controls the front wheel braking force and the rear wheel braking force, respectively, based on a braking force distribution that is a distribution of the front wheel braking force and the rear wheel braking force, which is a braking force applied to the front wheel, and a required braking force that is a required value of the braking force of the vehicle, the rear wheel braking force being a braking force applied to the rear wheel;

a distribution setting unit that sets the braking force distribution; and

a slip determination unit that determines a leading slip state of the rear wheel when the slip amount of the front wheel is smaller than a slip determination value and the slip amount of the rear wheel is equal to or greater than the slip determination value,

the distribution setting unit executes a distribution transition process of transitioning the braking force distribution to a second braking force distribution for a predetermined period of time when the braking force distribution is determined to be the rear wheel pre-slip state when the braking force distribution is the first braking force distribution,

the second braking force distribution is a distribution that reduces the rear wheel braking force as compared to when the first braking force distribution is set as the braking force distribution.

2. The brake control apparatus of a vehicle according to claim 1,

in the case where the above-described assignment transition processing is executed,

the control unit derives a rear wheel reference braking force that is a reference for the rear wheel braking force and a front wheel reference braking force that is a reference for the front wheel braking force, respectively, based on the braking force distribution and the required braking force that are being switched,

the rear wheel braking force is controlled so that the rear wheel braking force is equal to or less than the rear wheel reference braking force, and the front wheel braking force is controlled so that the front wheel braking force is equal to or more than the front wheel reference braking force.

3. The vehicle brake control device according to claim 1 or 2, comprising:

a μ value estimating unit that calculates an estimated road surface μ value based on a rear wheel load that is a load of a vertical component applied from a vehicle body to a road surface via the rear wheels and the rear wheel braking force, when it is determined that the rear wheel leading slip state is present when the braking force distribution is the first braking force distribution; and

a rear wheel locking line derivation unit that derives a rear wheel locking line that is a line indicating a relationship between the rear wheel braking force and the front wheel braking force when the rear wheel is locked, based on the calculated estimated road surface μ value,

the second braking force distribution is an ideal braking force distribution that is a braking force distribution in which the front wheel and the rear wheel are simultaneously locked,

when the required braking force is also increased during the execution of the distribution transition process,

deriving the rear wheel reference braking force and the front wheel reference braking force such that a point indicating a rear wheel reference braking force that is a reference of the rear wheel braking force and a front wheel reference braking force that is a reference of the front wheel braking force is located on the rear wheel locking line,

the rear wheel braking force is controlled so that the rear wheel braking force is equal to or less than the rear wheel reference braking force, and the front wheel braking force is controlled so that the front wheel braking force is equal to or more than the front wheel reference braking force.

4. The brake control apparatus of a vehicle according to claim 2 or 3,

in the case where the above-described assignment transition processing is executed,

the control unit executes a rear wheel slip suppression process for reducing the amount of slip of the rear wheel by varying the rear wheel braking force based on the rear wheel reference braking force,

when the rear wheel slip suppression process is executed, a front wheel brake correction process for making the front wheel braking force larger than the front wheel reference braking force is executed based on a value obtained by subtracting the rear wheel braking force from the rear wheel reference braking force.

5. The brake control apparatus of a vehicle according to claim 4,

the vehicle control device is provided with a parameter acquisition unit for acquiring a parameter indicating yaw motion of the vehicle,

in the front wheel brake correction process, the control unit may adjust the front wheel braking force such that a difference between the front wheel reference braking force and the front wheel braking force changes at a change speed corresponding to the parameter.

Technical Field

The present invention relates to a brake control device for a vehicle.

Background

Patent document 1 describes an example of a vehicle brake control device capable of adjusting the distribution of braking force to the front wheels and the rear wheels of the vehicle when the vehicle brakes. The braking force distribution is a distribution of a front wheel braking force, which is a braking force applied to the front wheels, and a rear wheel braking force, which is a braking force applied to the rear wheels. In this brake control device, when the vehicle is pitching toward the front end low head side by the vehicle braking, the pitch suppression control is performed so that the rear wheel braking force becomes larger than the magnitude based on the normal braking force distribution.

Patent document 1: japanese laid-open patent publication No. 2017-109664

When the pitch suppression control as described above is performed, the rear wheel braking force may be increased as compared to the case of braking the vehicle based on the ideal braking force distribution. The ideal brake force distribution is such that the front wheels and the rear wheels are locked at the same time. If the braking force distribution is increased as compared to the braking of the vehicle at the time of ideal braking force distribution due to the execution of the pitch suppression control, the rear wheel pre-slip state may be set. The rear wheel pre-slip state is a state in which the slip amount of the front wheel is smaller than the slip determination value and the slip amount of the rear wheel is equal to or larger than the slip determination value.

The device described in patent document 1 is configured to increase the front wheel braking force when a determination is made that the rear wheel is in a leading slip state. When the determination of the leading slip state of the rear wheel is made during turning of the vehicle, the lateral force of the front wheel is rapidly reduced when the increase speed of the front wheel braking force is large, and the change speed of the difference between the lateral slip force of the front wheel and the lateral slip force of the rear wheel of the vehicle becomes high. If the difference between the sideslip force of the front wheels and the sideslip force of the rear wheels changes abruptly when the vehicle turns, there is a concern that the stability of the turning behavior of the vehicle may be degraded.

Disclosure of Invention

The vehicle brake control device for solving the above problems includes: a control unit that controls the front wheel braking force and the rear wheel braking force, respectively, based on a braking force distribution that is a distribution of the front wheel braking force and the rear wheel braking force, which is a braking force applied to the front wheel, and a required braking force that is a required value of a braking force of the vehicle; a distribution setting unit that sets the braking force distribution; and a slip determination unit configured to determine that the rear wheel is in the leading slip state when the slip amount of the front wheel is smaller than a slip determination value and the slip amount of the rear wheel is equal to or greater than the slip determination value. In the brake control device, the distribution setting unit may execute a distribution transition process of transitioning the braking force distribution to a second braking force distribution for a predetermined period when the determination that the rear wheel is in the pre-slip state is made when the braking force distribution is the first braking force distribution. The second braking force distribution is a distribution that reduces the rear wheel braking force as compared to when the first braking force distribution is set as the braking force distribution.

According to the above configuration, when it is determined that the rear wheel pre-slip state is present in a situation where the first braking force distribution is set as the braking force distribution at the time of braking the vehicle, the braking force distribution is shifted to the second braking force distribution by executing the distribution shift processing. Even in the process of shifting the braking force distribution in this way, the front wheel braking force and the rear wheel braking force are controlled individually based on the braking force distribution and the required braking force at that time. That is, the front wheel braking force can be increased while considering the braking force distribution. Therefore, even when the determination is made that the rear-wheel preceding slip state is present during turning of the vehicle, a sudden decrease in the lateral force of the front wheels due to an increase in the front-wheel braking force can be suppressed. This can suppress an excessively high change speed of the difference between the side slip force of the front wheels and the side slip force of the rear wheels. Therefore, it is possible to suppress deviation of the vehicle deceleration from the target deceleration during the change of the braking force distribution while ensuring stability of the vehicle behavior.

Drawings

Fig. 1 is a diagram showing a functional configuration of an embodiment of a brake control device for a vehicle and a schematic configuration of a vehicle including the brake control device.

Fig. 2 is a flowchart illustrating a flow of a series of processes executed by the brake control apparatus when the vehicle brakes.

Fig. 3 is a graph showing an example of transition of the front wheel reference braking force and the rear wheel reference braking force.

Fig. 4(a) and 4(b) are timing charts of an example of the case where the allocation transition processing is executed at the time of vehicle braking.

Fig. 5 is a graph showing an example of transition of the front wheel reference braking force and the rear wheel reference braking force.

Fig. 6(a) and 6(b) are timing charts of an example of the case where the allocation transition processing is executed at the time of vehicle braking.

Fig. 7 is a graph showing an example of transition of the front wheel reference braking force and the rear wheel reference braking force.

Detailed Description

Hereinafter, an embodiment of a vehicle brake control device will be described with reference to fig. 1 to 7.

Fig. 1 shows a part of a vehicle including a brake control device 50 according to the present embodiment. The vehicle includes a brake device 30 controlled by a brake control device 50, a front wheel brake mechanism 20F that applies a braking force to the front wheel 11F, and a rear wheel brake mechanism 20R that applies a braking force to the rear wheel 11R. The braking force applied to the front wheels 11F is referred to as "front wheel braking force", and the braking force applied to the rear wheels 11R is referred to as "rear wheel braking force".

Each of the brake mechanisms 20F and 20R is configured such that the higher the WC pressure, which is the hydraulic pressure in the wheel cylinder 21, the greater the force that presses the friction member 23 against the rotating body 22 that rotates integrally with the wheels 11F and 11R. That is, the higher the WC pressure is, the larger the braking force can be applied to the wheels 11F and 11R by the brake mechanisms 20F and 20R.

The brake device 30 has a brake operating member 31 operated by a driver of the vehicle, and a brake actuator 32. The brake operating member 31 may be, for example, a brake pedal. Each wheel cylinder 21 is connected to the brake actuator 32. Further, the brake actuator 32 can independently adjust the WC pressure in each wheel cylinder 21.

The brake control device 50 receives detection signals from various sensors. In fig. 1, an operation amount sensor 101, a yaw rate sensor 102, a lateral acceleration sensor 103, a wheel speed sensor 104, and a steering angle sensor 105 are illustrated as sensors. The operation amount sensor 101 detects a brake operation amount INP which is an amount of operation of the brake operation member 31 by the driver, and outputs a signal corresponding to the detected brake operation amount INP as a detection signal. The yaw rate sensor 102 detects the yaw rate YR of the vehicle, and outputs a signal corresponding to the detected yaw rate YR as a detection signal. The wheel speed sensors 104 are provided in the same number as the wheels 11F, 11R. The wheel speed sensor 104 detects a wheel speed VW of the corresponding wheel, and outputs a signal corresponding to the detected wheel speed VW as a detection signal. The steering angle sensor 105 detects a steering angle STR, which is a rotation angle of a steering wheel operated by a driver, and outputs a signal corresponding to the detected steering angle STR as a detection signal. The brake control device 50 controls the brake actuator 32 based on detection signals of the various sensors 101 to 105.

The brake control device 50 transmits and receives various kinds of information to and from other control devices. For example, when the vehicle travels by automatic driving, the required braking force BPCR, which is the required value of the braking force of the vehicle, is transmitted from the control device 60 for automatic driving to the brake control device 50. In this case, the brake control device 50 controls the brake actuator 32 based on the received required braking force BPCR.

The brake control device 50 includes, as functional units for operating the brake actuator 32, a required braking force acquisition unit 51, a distribution setting unit 52, a control unit 53, a slip determination unit 54, a μ value estimation unit 55, a rear wheel lock line derivation unit 56, and a parameter acquisition unit 57.

The required braking force acquisition unit 51 acquires the required braking force BPCR received from the control device 60 for automatic driving when the vehicle is traveling by automatic driving. The required braking force acquisition unit 51 calculates and acquires a value corresponding to the brake operation amount INP as the required braking force BPCR when the vehicle is running by the operation of the driver.

The distribution setting unit 52 sets the braking force distribution of the vehicle based on the traveling state of the vehicle, the posture during traveling, and the like. The braking force distribution refers to the distribution of the front wheel braking force BPF and the rear wheel braking force BPR. In the present embodiment, the distribution setting portion 52 sets the braking force distribution by setting the braking force distribution ratio X. The braking force distribution ratio X is a target value of the ratio of the proportion of the rear wheel braking force BPR in the required braking force BPCR. Therefore, "1" is set as the braking force distribution ratio X in the case where the rear wheel braking force BPR and the required braking force BPCR are made equal. In contrast, "0 (zero)" is set as the braking force distribution ratio X in the case where the front wheel braking force BPF and the required braking force BPCR are made equal. The braking force distribution ratio X is set as follows.

The control unit 53 controls the brake actuator 32 during braking of the vehicle based on the required braking force BPCR acquired by the required braking force acquisition unit 51 and the braking force distribution ratio X, i.e., the braking force distribution, set by the distribution setting unit 52.

In a situation where the braking force is applied to the front wheels 11F and the rear wheels 11R as described above, the control unit 53 executes a rear wheel slip suppression process for suppressing the deceleration slip of the rear wheels 11R when the wheel speed VW of the rear wheels 11R is lower than the vehicle body speed VS of the vehicle and the predetermined deceleration slip occurs in the rear wheels 11R due to the application of the braking force. When the rear wheel slip suppression process is performed on the rear wheel 11R, the control unit 53 performs a front wheel brake correction process for adjusting the front wheel braking force BPF. The contents of the rear wheel slip suppression process and the front wheel brake correction process will be described later.

The slip determination unit 54 determines whether or not the rear wheel is in the leading slip state. The rear wheel leading slip state is a state in which a predetermined deceleration slip is not generated in the front wheel 11F and a predetermined deceleration slip is generated in the rear wheel 11R. The slip determination unit 54 calculates a value obtained by subtracting the wheel speed VW of the front wheels 11F from the vehicle body speed VS of the vehicle as the slip amount SLPF of the front wheels 11F. The slip determination unit 54 calculates a value obtained by subtracting the wheel speed VW of the rear wheel 11R from the vehicle body speed VS of the vehicle as the slip amount SLPR of the rear wheel 11R. The vehicle body speed VS is calculated based on the wheel speed VW of each wheel 11F, 11R. The slip determination unit 54 determines that the predetermined deceleration slip is generated in the front wheel 11F when the slip amount SLPF of the front wheel 11F is equal to or greater than the determination slip amount SLPTh, and does not determine that the predetermined deceleration slip is generated in the front wheel 11F when the slip amount SLPF is smaller than the determination slip amount SLPTh. The slip determination unit 54 determines that the predetermined deceleration slip is generated in the rear wheel 11R when the slip amount SLPR of the rear wheel 11R is equal to or greater than the determination slip amount SLPTh, and does not determine that the predetermined deceleration slip is generated in the rear wheel 11R when the slip amount SLPR is smaller than the determination slip amount SLPTh. In other words, the slip amount SLPTh is a criterion for determining whether or not a predetermined deceleration slip is generated in the wheels 11F and 11R.

The μ value estimating unit 55 calculates an estimated road surface μ value RS, which is an estimated value of the μ value of the road surface on which the vehicle travels. That is, the μ value estimating unit 55 calculates the estimated road surface μ value RS based on the rear wheel braking force BPR at the time when the slip determining unit 54 determines that the rear wheel is in the rear-wheel leading slip state, and the rear wheel load MR, which is the load input from the vehicle body to the road surface via the rear wheels 11R. The rear wheel load MR is, for example, a value obtained according to the specifications of the vehicle. A specific calculation method of the estimated road surface μ value RS will be described later.

The rear wheel locking line derivation section 56 derives the rear wheel locking line LRR based on the estimated road surface μ value RS calculated by the μ value estimation section 55 when the slip determination section 54 determines that the rear wheel is in the forward slip state. The rear wheel locking line LRR is a line indicating a relationship between the rear wheel braking force BPR and the front wheel braking force BPF when the rear wheel 11R is locked. That is, in the graph shown in fig. 3 in which the front wheel braking force BPF is taken on the horizontal axis and the rear wheel braking force BPR is taken on the vertical axis, the set of points representing the rear wheel braking force BPR and the front wheel braking force BPF when the rear wheel 11R is locked for each braking force BPC of the vehicle corresponds to the rear wheel locking line LRR. Further, the lower the μ value of the road surface, the lower the rear wheel locking line LRR is located in the graph.

The parameter acquiring unit 57 acquires a parameter indicating yaw motion of the vehicle. The parameter mentioned here is a parameter that affects the yaw motion of the vehicle. Examples of the parameters include a steering angle STR, a steering angle of the front wheels 11F, a lateral acceleration GY, a yaw rate YR, a vehicle slip angle ASL, and a vehicle speed VS.

Next, a flow of processing in a case where the vehicle braking is started will be described with reference to fig. 2. Here, a flow of processing until the allocation transition processing described later is completed will be described.

In initial step S11, a first braking force distribution ratio X1, which is a target value of the braking force distribution ratio at the start of vehicle braking, is determined. The first braking force distribution ratio X1 is a braking force distribution ratio corresponding to the "first braking force distribution". In the present embodiment, the first braking force distribution ratio X1 is greater than the ideal braking force distribution ratio XID at the start of vehicle braking. The ideal braking force distribution ratio XID is the braking force distribution ratio when the front wheel 11F and the rear wheel 11R are simultaneously locked. That is, the ideal braking force distribution ratio XID is a braking force distribution ratio corresponding to "ideal braking force distribution". Even if the required braking force BPCR is the same, in the case where the front wheel braking force BPF and the rear wheel braking force BPR are controlled based on the first braking force distribution ratio X1, the rear wheel braking force BPR is larger than in the case where the front wheel braking force BPF and the rear wheel braking force BPR are controlled based on the ideal braking force distribution ratio XID.

The first braking force distribution ratio X1 may be the same value regardless of whether the vehicle is braked by the driver's braking operation or by the automated driving. Further, the first braking force distribution ratio X1 at the time of vehicle braking accompanying the driver's braking operation may be made different from the first braking force distribution ratio X1 at the time of vehicle braking by automated driving.

In the next step S12, the slip determination unit 54 determines whether or not the rear wheel is in the leading slip state. If the determination of the rear wheel leading slip state is not made (no in S12), the process proceeds to the next step S13. In step S13, the first braking force distribution ratio X1 is set as the braking force distribution ratio X by the distribution setting portion 52. That is, the first braking force distribution is set as the braking force distribution. Next, in step S14, the control unit 53 derives the target front wheel braking force BPFTr and the target rear wheel braking force BPRTr based on the braking force distribution ratio X and the required braking force BPCR. The target front wheel braking force BPFTr refers to a target of the front wheel braking force BPF, and the target rear wheel braking force BPRTr refers to a target of the rear wheel braking force BPR. For example, the control unit 53 calculates the target front wheel braking force BPFTr using the following relational expression (expression 1), and calculates the target rear wheel braking force BPRTr using the following relational expression (expression 2). Therefore, the larger the braking force distribution ratio X, the smaller the target front wheel braking force BPFTr. The larger the braking force distribution ratio X, the larger the target rear wheel braking force BPRTr.

[ number 1]

BPFTr ═ BPCR × (1-X) … (formula 1)

BPRTr ═ BPCR-BPFTr … (formula 2)

Then, in the next step S15, the brake actuator 32 is controlled by the control portion 53 such that the front wheel braking force BPF follows the target front wheel braking force BPFTr and the rear wheel braking force BPR follows the target rear wheel braking force BPRTr. Then, the process proceeds to step S11 described above. That is, while the determination that the rear-wheel preceding slip state is not being made, the front-wheel braking force BPF and the rear-wheel braking force BPR are respectively adjusted so that the actual braking-force distribution ratio XR becomes the first braking-force distribution ratio X1, that is, the actual braking-force distribution becomes the first braking-force distribution.

On the other hand, if it is determined that the rear wheel is in the forward-drive slip state in step S12 (yes), the process proceeds to step S16. In step S16, the μ value estimating unit 55 calculates an estimated road surface μ value RS. When the slip amount SLPR of the rear wheel 11R becomes equal to or larger than the determination slip amount SLPTh and the determination of the rear wheel leading slip state is performed, the relationship in which the product of the actual road surface μ value RSR, which is the actual road surface μ value, and the actual rear wheel load MRR, which is the actual rear wheel load, approaches the rear wheel braking force BPR is present. Therefore, the μ value estimating unit 55 derives the estimated road surface μ value RS by dividing the rear wheel braking force BPR by the rear wheel load MR. In the next step S17, the rear wheel locking line estimated based on the estimated road surface μ value RS is derived as the rear wheel locking line LRR by the rear wheel locking line deriving unit 56. Next, in step S18, the control unit 53 starts the rear wheel slip suppression process.

In the next step S19, the assignment setting unit 52 starts the assignment transition process. In the distribution transition process, the braking force distribution ratio X is transitioned from the first braking force distribution ratio X1 to the second braking force distribution ratio X2 for a prescribed period. The second braking force distribution ratio X2 is a braking force distribution ratio corresponding to "second braking force distribution". The second braking force distribution ratio X2 is smaller than the first braking force distribution ratio X1. In the present embodiment, the ideal braking force distribution ratio XID is set as the second braking force distribution ratio X2. For example, in the distribution transition process, the braking force distribution ratio X is transitioned to the second braking force distribution ratio X2 within the prescribed time TMA. That is, the braking force distribution is changed from the first braking force distribution to the second braking force distribution within the predetermined time TMA. The specific processing contents of the assignment transition processing will be described later. If the assignment transition processing is started, the processing moves to the next step S20.

In step S20, the front wheel reference braking force BPFB and the rear wheel reference braking force BPRB are derived by the control portion 53 based on the braking force distribution ratio X and the required braking force BPCR that are shifted by the execution of the distribution shift process, respectively. The front wheel reference braking force BPFB is a reference for the front wheel braking force, and is calculated based on the current braking force distribution ratio X and the required braking force BPCR. The rear wheel reference braking force BPRB is a reference of the rear wheel braking force, and is calculated based on the current braking force distribution ratio X and the required braking force BPCR. The derivation of the front wheel reference braking force BPFB and the rear wheel reference braking force BPRB described later.

In the next step S21, the parameter acquisition unit 57 acquires various parameters.

Then, in step S22, the control unit 53 derives the limit value Δ BPFLm for the rate of increase of the front wheel braking force BPF based on the parameters acquired in step S21. The derivation of the limit value Δ BPFLm is included in the front wheel braking correction processing. The limit value Δ BPFLm is an upper limit of the amount of increase in the front wheel braking force BPF per unit time. When the yaw moment applied to the vehicle is large, if the front wheel braking force BPF is rapidly increased, the lateral force of the front wheels 11F is rapidly decreased, and the difference between the front wheel side slip force and the rear wheel side slip force of the vehicle, that is, the difference between the lateral slip forces, is significantly changed. The front wheel side slip force is the side slip force of the front wheel 11F, and the rear wheel side slip force is the side slip force of the rear wheel 11R. If the change speed of the side slip difference is high during turning of the vehicle, the stability of the turning behavior of the vehicle may be lowered. On the other hand, when the yaw moment is small or the lateral acceleration GY is low, the generated side slip force itself of the wheels 11F, 11R is small, and the change in the front wheel side slip force is not so large even if the front wheel braking force BPF is sharply increased. Therefore, the variation in the side slip difference is small, and the stability of the turning behavior of the vehicle is hardly lowered. Therefore, the control unit 53 derives the limit value Δ BPFLm as a value corresponding to at least one of the steering angle STR, the steering angle of the front wheels 11F, the lateral acceleration GY, the yaw rate YR, the vehicle body slip angle ASL, and the vehicle body speed VS, which are acquired as parameters. That is, the control unit 53 decreases the limit value Δ BPFLm as the yaw moment estimated from the parameter increases. For example, the control unit 53 decreases the limit value Δ BPFLm as the absolute value of the yaw rate YR increases. For example, the control unit 53 decreases the limit value Δ BPFLm as the vehicle body speed VS of the vehicle increases. For example, the control unit 53 decreases the limit value Δ BPFLm as the absolute value of the steering angle STR increases.

Next, in step S23, the control unit 53 derives the target front wheel braking force BPFTr and the target rear wheel braking force BPRTr. The derivation of the target rear wheel braking force BPRTr here is included in the rear wheel slip suppression process. The derivation of the target front wheel braking force BPFTr here is included in the front wheel braking correction process.

The control unit 53 derives the target rear wheel braking force BPRTr to be equal to or less than the rear wheel reference braking force BPRB. When the anti-lock braking control is performed on the rear wheel 11R as the rear wheel slip suppression process, the control unit 53 derives the target rear wheel braking force BPRTr based on the transition of the slip amount SLPR of the rear wheel 11R. Further, another control different from the antilock brake control may be performed on the rear wheel 11R as the rear wheel slip suppression process. Another example of the control is a control for temporarily decreasing the rear wheel braking force BPR to a magnitude corresponding to the ideal braking force distribution ratio XID and then increasing the rear wheel braking force BPR toward the rear wheel reference braking force BPRB. When such control is performed as the rear wheel slip suppression process, the control unit 53 temporarily decreases the target rear wheel braking force BPRTr to a magnitude corresponding to the ideal braking force distribution ratio XID and then increases it to the rear wheel reference braking force BPRB.

Further, the control unit 53 derives the target front wheel braking force BPFTr to be equal to or greater than the front wheel reference braking force BPFB. For example, the control unit 53 derives the target front wheel braking force BPFTr based on a value obtained by subtracting the target rear wheel braking force BPRTr from the rear wheel reference braking force BPRB, the limit value Δ BPFLm, and the front wheel reference braking force BPFB. That is, the control unit 53 increases the latest value of the target front wheel braking force BPFTr as the value obtained by subtracting the target rear wheel braking force BPRTr from the rear wheel reference braking force BPRB increases within the range in which the difference between the latest value of the target front wheel braking force BPFTr and the last value of the target front wheel braking force BPFTr does not exceed the limit value Δ BPFLm.

Then, if the target rear wheel braking force BPRTr and the target front wheel braking force BPFTr are derived, the process proceeds to the next step S24.

In step S24, the control unit 53 operates the brake actuator 32 such that the rear wheel braking force BPR follows the target rear wheel braking force BPRTr and the front wheel braking force BPF follows the target front wheel braking force BPFTr. The control of the operation of the brake actuator 32 to cause the rear wheel braking force BPR to follow the target rear wheel braking force BPRTr is included in the rear wheel slip suppression process. The control of the operation of the brake actuator 32 to cause the front wheel braking force BPF to follow the target front wheel braking force BPFTr is included in the front wheel brake correction processing. Then, in the next step S25, it is determined whether or not the assignment transition processing is ended. For example, when the elapsed time from the start of the distribution transition process reaches the predetermined time TMA, the transition of the braking force distribution to the second braking force distribution is completed, and therefore it can be determined that the distribution transition process is finished. When it is determined that the assignment transition process is completed (yes in S25), the series of processes shown in fig. 2 is completed. On the other hand, if it is not determined that the assignment transition processing is ended (no in S25), the process proceeds to step S20 described above.

Next, the distribution transition process and the derivation of the front wheel reference braking force BPFB and the rear wheel reference braking force BPRB during execution of the distribution transition process will be described.

First, with reference to fig. 3, the distribution transition process in the case where the required braking force BPCR is increased before the determination that the rear-wheel preceding slip state is achieved is made, but the required braking force BPCR is maintained after the determination is made, and the derivation of the front-wheel reference braking force BPFB and the rear-wheel reference braking force BPRB during execution of the distribution transition process will be described.

In the case where the required braking force BPCR is increased in the state where the braking force distribution ratio X is the first braking force distribution ratio X1, the target front wheel braking force BPFTr and the target rear wheel braking force BPRTr are increased in accordance with the first braking force distribution ratio X1, respectively. In this case, in the graph of fig. 3, the points indicating the target front wheel braking force BPFTr and the target rear wheel braking force BPRTr are located on the dashed line indicating the first braking force distribution ratio X1. That is, as indicated by the thick solid line arrows in fig. 3, the target front wheel braking force BPFTr and the target rear wheel braking force BPRTr increase as the required braking force BPCR increases. Then, when the target front wheel braking force BPFTr becomes the first front wheel braking force BPF1 and the target rear wheel braking force BPRTr becomes the first rear wheel braking force BPR1, it is determined that the rear wheel is in the forward slip state, and therefore the distribution transition process is started.

The two-dot chain line in fig. 3 is an equal braking force line LEB that is an aggregate of points of the front wheel braking force BPF and the rear wheel braking force BPR when the braking force of the vehicle (i.e., the vehicle body acceleration of the vehicle) is equal in magnitude. A first equivalent braking force line LEB1 of the plurality of equivalent braking force lines LEB shown in fig. 3 is an equivalent braking force line corresponding to the required braking force BPCR at the time when the determination of the rear wheel advanced slip state is made.

When the distribution transition process is executed, the divided front wheel reference braking force BPFB and the divided rear wheel reference braking force BPRB are changed as indicated by arrows of thick solid lines in fig. 3. In this case, the front wheel reference braking force BPFB increases with the passage of time, while the rear wheel reference braking force BPRB decreases with the passage of time. Then, at the time when the predetermined period has elapsed, the target front wheel braking force BPFTr becomes the second front wheel braking force BPF2, and the target rear wheel braking force BPRTr becomes the second rear wheel braking force BPR 2. The front wheel braking force BPF at the intersection of the line representing the second braking force distribution ratio X2 and the first equal braking force line LEB1 is the second front wheel braking force BPF2, and the rear wheel braking force BPR at this intersection is the second rear wheel braking force BPR2, so the distribution transition process ends. Thereafter, in the case where the required braking force BPCR is changed, since the second braking force distribution ratio X2 is set as the braking force distribution ratio X, the front wheel reference braking force BPFB and the rear wheel reference braking force BPRB are adjusted in accordance with the second braking force distribution ratio X2, respectively.

Next, the operation and effect of the case where the front wheel reference braking force BPFB and the rear wheel reference braking force BPRB are changed as described above will be described with reference to fig. 4. The chain line in fig. 4(b) indicates the transition of each of the WC pressures PWCF and PWCR when the brake control is performed in a state where the WC pressure in the wheel cylinder 21 for the front wheel 11F, that is, the front wheel WC pressure PWCF is equal to the WC pressure in the wheel cylinder 21 for the rear wheel 11R, that is, the rear wheel WC pressure PWCR.

As shown in fig. 4(a) and (b), when the vehicle braking is started at the timing T11, the front wheel WC pressure PWCF and the rear wheel WC pressure PWCR are increased based on the first braking force distribution ratio X1, respectively. Thus, the front wheel braking force BPF increases following an increase in the target front wheel braking force BPFTr, and the rear wheel braking force BPR increases following an increase in the target rear wheel braking force BPRTr. Then, when it is determined that the rear wheel is in the front wheel slip state at the timing T12, the distribution shift processing is started. Then, as explained in fig. 3, the rear wheel reference braking force BPRB decreases and the front wheel reference braking force BPFB increases.

In the example shown in fig. 4, another control other than the antilock brake control is performed as the rear wheel slip suppression process. Therefore, the target rear wheel braking force BPRTr decreases so that its deviation from the rear wheel reference braking force BPRB increases, and thereafter, the target rear wheel braking force BPRTr increases so that the deviation becomes smaller. Then, at the end of the distribution transition process, the target rear wheel braking force BPRTr is the same magnitude as the rear wheel reference braking force BPRB at that time. On the other hand, when the rear wheel slip suppression process is executed, the front wheel brake correction process is executed. Therefore, the target front wheel braking force BPFTr increases so that its deviation from the front wheel reference braking force BPFB increases, and thereafter, the target front wheel braking force BPFTr decreases so that the deviation becomes smaller. Then, at the end of the distribution transition process, the target front wheel braking force BPFTr becomes the same magnitude as the front wheel reference braking force BPFB at that time.

As shown in fig. 4(b), the rear wheel WC pressure PWCR fluctuates in conjunction with the change in the target rear wheel braking force BPRTr during the period from the timing T12 to the timing T13 at which the distribution transition process is executed. The front wheel WC pressure PWCF fluctuates in conjunction with the change in the target front wheel braking force BPFTr. In fig. 4(b), the front wheel reference WC pressure PWCFB is the WC pressure of the front wheel 11F corresponding to the front wheel reference braking force BPFB, and the rear wheel reference WC pressure PWCRB is the WC pressure of the rear wheel 11R corresponding to the rear wheel reference braking force BPRB. During execution of the distribution transition process, the rear wheel WC pressure PWCR varies in a range below the rear wheel reference WC pressure PWCRB. The front wheel WC pressure PWCF varies in a range equal to or higher than the front wheel reference WC pressure PWCFB. By varying the rear wheel WC pressure PWCR in this manner, the slip amount SLPR of the rear wheel 11R can be reduced. During execution of the distribution transition process, the front wheel braking force BPF fluctuates in conjunction with the fluctuation of the rear wheel braking force BPR as described above. For example, when a value obtained by subtracting the target rear wheel braking force BPRTr from the rear wheel reference braking force BPRB is used as the calculated value, the sum of the calculated value and the front wheel reference braking force BPFB is set as the target front wheel braking force BPFTr when the calculated value does not exceed the limit value Δ BPFLm for the rate of increase of the front wheel braking force BPF. On the other hand, when the calculated value exceeds the limit value Δ BPFLm, the sum of the previous value of the target front wheel braking force BPFTr and the limit value Δ BPFLm is set as the target front wheel braking force BPFTr. Therefore, the vehicle body acceleration DVS of the vehicle can be suppressed from deviating from the target vehicle body acceleration DVSTr in the transition of the braking force distribution.

Then, if the second braking force distribution ratio X2 is set as the braking force distribution ratio X at the timing T13, the distribution transition process ends. That is, if the ideal braking force distribution ratio XID is set as the braking force distribution ratio X, the distribution transition process ends. In the present embodiment, the braking force distribution gradually approaches the second braking force distribution. Therefore, an abrupt change in the lateral force of the front wheels 11F caused by the change in the braking force distribution can be suppressed. As a result, the above-described excessively high change speed of the sideslip force difference can be suppressed. Therefore, the stability of the behavior of the vehicle in the rear wheel leading slip state can be ensured.

In the example shown in fig. 4, the target vehicle body acceleration DVSTr, that is, the required braking force BPCR is maintained after the timing T12. Therefore, after the timing T13 at which the allocation transition processing ends, the WC voltages PWCF and PWCR are held. That is, the front wheel braking force BPF and the rear wheel braking force BPR are respectively maintained. Therefore, the change in the vehicle body acceleration DVS during the change of the braking force distribution ratio X can be suppressed while ensuring the stability of the vehicle behavior.

Next, with reference to fig. 5, the distribution transition process in the case where the increase in the required braking force BPCR is continued even after the determination that the rear-wheel leading slip state is achieved, and the derivation of the front-wheel reference braking force BPFB and the rear-wheel reference braking force BPRB during execution of the distribution transition process will be described.

When the rear wheel leading slip state is determined, the distribution transition process is started. When the required braking force BPCR also increases during execution of the distribution transition process, the front wheel reference braking force BPFB and the rear wheel reference braking force BPRB are derived based on the rear wheel locking line LRR derived by the rear wheel locking line deriving unit 56 and the braking force distribution ratio X at that time. For example, in the graph of fig. 5, the front wheel braking force BPF and the rear wheel braking force BPR at the intersection of the line representing the braking force distribution ratio X at that time and the rear wheel locking line LRR are derived as the front wheel reference braking force BPFB and the rear wheel reference braking force BPRB, respectively. That is, as indicated by the thick solid line arrows in fig. 3, the target front wheel braking force BPFTr and the target rear wheel braking force BPRTr are changed. In this graph, the rear wheel locking line LRR is a line inclined downward to the right. Therefore, in the distribution transition process in this case, the front wheel reference braking force BPFB increases with the passage of time, while the rear wheel reference braking force BPRB decreases with the passage of time. At the time when the predetermined period has elapsed, the target front wheel braking force BPFTr becomes the third front wheel braking force BPF3, and the target rear wheel braking force BPRTr becomes the third rear wheel braking force BPR 3. The front wheel braking force BPF at the intersection of the line representing the second braking force distribution ratio X2 and the rear wheel locking line LRR is the third front wheel braking force BPF3, and the rear wheel braking force BPR at this intersection is the third rear wheel braking force BPR3, so the distribution transition process ends.

In the graph of fig. 5, the thin solid line is the front wheel locking line LFR. The front wheel lock line LFR is a line indicating the relationship between the rear wheel braking force BPR and the front wheel braking force BPF when the front wheel 11F is locked. In the graph, the front wheel locking line LFR passes through the intersection of the line representing the ideal braking force distribution ratio XID and the rear wheel locking line LRR.

Next, the operation and effect of the case where the front wheel reference braking force BPFB and the rear wheel reference braking force BPRB are changed as described above will be described with reference to fig. 6. The chain line in fig. 6(b) indicates the transition of each of the WC pressures PWCF and PWCR when the brake control is performed in a state where the front wheel WC pressure PWCF and the rear wheel WC pressure PWCR are equal to each other.

As shown in fig. 6(a) and (b), when the vehicle braking is started at the timing T21, the front wheel WC pressure PWCF and the rear wheel WC pressure PWCR are increased based on the first braking force distribution ratio X1, respectively. Then, when it is determined that the rear wheel is in the front wheel slip state at the timing T22, the distribution shift processing is started. Then, as described with reference to fig. 5, since the rear wheel reference braking force BPRB and the front wheel reference braking force BPFB are changed according to the rear wheel locking line LRR, the rear wheel reference braking force BPRB decreases while the front wheel reference braking force BPFB increases.

In the example shown in fig. 6, from the timing T22, the anti-lock brake control is performed as the rear wheel slip suppression process for the rear wheel 11R. When the antilock brake control is performed, a value obtained by subtracting a control amount of the antilock brake control from the rear wheel reference brake force BPRB is derived as the target rear wheel brake force BPRTr. That is, the target rear wheel braking force BPRTr is set to a magnitude equal to or smaller than the rear wheel reference braking force BPRB. The rear wheel WC pressure PWCR is changed so as to be interlocked with the fluctuation of the target rear wheel braking force BPRTr. At this time, the rear wheel WC pressure PWCR is not higher than the rear wheel reference WC pressure PWCRB.

In the present embodiment, when the anti-lock brake control is performed as the rear wheel slip suppression process for the rear wheels 11R, the front wheel brake correction process is performed to suppress a decrease in the braking force BPC of the vehicle due to the execution of the rear wheel slip suppression process. If the front wheel brake correction processing is executed, the target front wheel braking force BPFTr is larger than the front wheel reference braking force BPFB. That is, in the execution of the antilock brake control, when the target rear wheel braking force BPRTr decreases, the target front wheel braking force BPFTr increases at a higher speed than when the target rear wheel braking force BPRTr does not decrease. As a result, as shown in fig. 6(b), when the rear wheel WC pressure PWCR is decreased, the front wheel WC pressure PWCF is abruptly increased during the execution of the antilock brake control. At this time, the front wheel WC pressure PWCF increases so that the value thereof increases as the value obtained by subtracting the rear wheel braking force BPR from the rear wheel reference braking force BPRB increases, that is, the target front wheel braking force BPFTr increases in this manner.

Fig. 6(a) shows, by a chain line, a transition of the vehicle body acceleration DVS in the comparative example in which the anti-lock brake control is performed on the rear wheel 11R while the target front wheel braking force BPFTr, that is, the front wheel WC pressure PWCF is maintained at the time when the determination of the rear wheel leading slip state is made. In the case of the comparative example, the absolute value of the vehicle body acceleration DVS is smaller than the absolute value of the target vehicle body acceleration DVSTr because the deviation between the rear wheel braking force BPR and the rear wheel reference braking force BPRB is not compensated for on the front wheel 11F side.

In contrast, in the present embodiment, the deviation between the rear wheel braking force BPR and the rear wheel reference braking force BPRB can be compensated to some extent on the front wheel 11F side by executing the front wheel braking correction process. As a result, it is possible to suppress a deviation between the vehicle body acceleration DVS and the target vehicle body acceleration DVSTr when the anti-lock brake control is performed on the rear wheels 11R due to the determination that the rear wheel is in the leading slip state.

However, when the braking forces BPF, BPR of the wheels 11F, 11R increase during the turning of the vehicle, the lateral force of the wheels 11F, 11R decreases. On the other hand, when the braking forces BPF, BPR of the wheels 11F, 11R decrease, the lateral force of the wheels 11F, 11R increases. Therefore, when the rear wheel braking force BPR is decreased by the execution of the rear wheel slip suppression process and the front wheel braking force BPF is increased by the execution of the front wheel brake correction process, the lateral force of the rear wheel 11R is increased and the lateral force of the front wheel 11F is decreased. Further, since the yaw moment of the vehicle changes rapidly when the change speed of the lateral force of the front wheels 11F is high, there is a concern that the stability of the turning behavior of the vehicle may be degraded by the front wheel braking correction processing.

In this regard, in the present embodiment, the limit value Δ BPFLm of the increase speed of the front wheel braking force BPF during the period in which the rear wheel braking force BPR is decreased by the antilock brake control is derived based on the parameter acquired by the parameter acquisition unit 57. Specifically, the greater the yaw moment applied to the vehicle, the smaller the limit value Δ BPFLm. In the front wheel brake correction process, the target front wheel braking force BPFTr is derived such that the amount of increase per unit time of the target front wheel braking force BPFTr does not exceed the limit value Δ BPFLm. Then, the front wheel braking force BPF is adjusted to follow the target front wheel braking force BPFTr. Therefore, even if the vehicle body acceleration DVS deviates from the target vehicle body acceleration DVSTr during the execution of the front wheel brake correction process, a sudden change in the yaw moment applied to the vehicle can be suppressed, and therefore, the stability of the turning behavior of the vehicle can be ensured.

The above embodiment can be modified as follows. The above-described embodiments and the following modifications can be combined and implemented within a range not technically contradictory to each other.

In the above-described embodiment, the derivation of the front wheel reference braking force BPFB and the rear wheel reference braking force BPRB when the required braking force BPCR is also increased after the determination that the rear wheel is in the leading slip state is made will be described with reference to fig. 5. However, there is also a case where the required braking force BPCR is not increased until the second braking force distribution ratio X2 is set as the braking force distribution ratio X by execution of the distribution changeover process. In this case, after the determination that the rear wheel is in the leading slip state is made, the front wheel reference braking force BPFB and the rear wheel reference braking force BPRB are derived so that the points indicating the front wheel reference braking force BPFB and the rear wheel reference braking force BPRB are located on the rear wheel locking line LRR as described in the above embodiment while the required braking force BPCR is increasing. In the period from the holding of the required braking force BPCR to the completion of the distribution transition process, the front wheel reference braking force BPFB and the rear wheel reference braking force BPRB are derived based on the equal braking force line LEB corresponding to the braking force BPC of the vehicle at the start time of the period. Specifically, the front wheel reference braking force BPFB and the rear wheel reference braking force BPRB are respectively derived so that points indicating the front wheel reference braking force BPFB and the rear wheel reference braking force BPRB are located on the braking lines LEB.

Even when the required braking force BPCR is increased after the determination that the rear wheel is in the leading slip state is made, the front wheel reference braking force BPFB and the rear wheel reference braking force BPRB may be derived in a manner different from that described in the above embodiment, as long as the point at which the front wheel reference braking force BPFB and the rear wheel reference braking force BPRB are indicated in the graph of fig. 5 is not increased toward the rear wheel braking force BPR as compared with the rear wheel lock line LRR. That is, when the intersection of the line indicating the braking force distribution ratio X that is being changed by the distribution change process and the equal braking force line LEB of the requested braking force BPCR at that time is located on the side where the rear wheel braking force BPR is increased as compared with the rear wheel locking line LRR, the front wheel braking force BPF and the rear wheel braking force BPR at the intersection of the line indicating the braking force distribution ratio X and the rear wheel locking line LRR are derived as the front wheel reference braking force BPFB and the rear wheel reference braking force BPRB, respectively. On the other hand, when the intersection of the line indicating the braking force distribution ratio X and the equal braking force line LEB of the requested braking force BPCR at that time is on the rear wheel lock line LRR or is located on the side where the rear wheel braking force BPR is reduced from the rear wheel lock line LRR, the front wheel braking force BPF and the rear wheel braking force BPR at that intersection are derived as the front wheel reference braking force BPFB and the rear wheel reference braking force BPRB, respectively.

In the above embodiment, the predetermined time TMA, which is a criterion for determining whether or not the predetermined period has ended, is fixed to a predetermined time, but the predetermined time TMA may be variable. For example, the predetermined time TMA may be required to be longer as the increase rate of the braking force BPCR is lower. For example, the predetermined time TMA may be extended as the yaw moment applied to the vehicle estimated based on the parameters is increased.

The limit value Δ BPFLm may not be variable based on the above parameters.

The second braking force distribution may be a distribution different from the ideal braking force distribution as long as it is a distribution that can reduce the rear wheel braking force BPR as compared to the vehicle braking at the first braking force distribution. That is, the second braking force distribution ratio X2 may be a value different from the ideal braking force distribution ratio XID as long as it is a value smaller than the first braking force distribution ratio X1. Fig. 7 illustrates an example in the case where a value smaller than the ideal braking force distribution ratio XID is set as the second braking force distribution ratio X2. As shown in fig. 7, when the required braking force BPCR increases even after the determination that the rear wheel is in the leading slip state is made, the rear wheel locking line LRR is derived as in the above-described embodiment. In the example shown in fig. 7, the intersection of the line indicating the second braking force distribution ratio X2 and the rear wheel locking line LRR is located on the side where the front wheel braking force BPF is greater than the front wheel locking line LFR. The front wheel locking line LFR passes through the intersection of the line representing the ideal braking force distribution ratio XID and the rear wheel locking line LRR. That is, the front wheel locking line LFR can be derived based on the rear wheel locking line LRR and the ideal braking force distribution ratio XID. Then, an intersection of a line indicating the second braking force distribution ratio X2 and the front wheel lock line LFR is derived, and a line connecting the intersection and a point indicating the front wheel braking force BPF and the rear wheel braking force BPR at the time when the rear wheel pre-slip state is determined is derived as a reference braking force line LBB. In this way, in the distribution transition process, the front wheel reference braking force BPFB and the rear wheel reference braking force BPRB are derived so that the points indicating the front wheel reference braking force BPFB and the rear wheel reference braking force BPRB are located on the reference braking force line LBB.

In the above embodiment, the first braking force distribution ratio X1 is set so that braking force can be applied to both the front wheels 11F and the rear wheels 11R even when the first braking force distribution ratio X1 is set as the braking force distribution ratio X. However, the first braking force distribution ratio X1 may be a braking force distribution ratio such that the front wheel braking force BPF is "0".

The braking device may have any configuration as long as it can independently control the braking force applied to each of the wheels 11F and 11R. For example, the brake device may be an electric brake device that can apply frictional braking force to the wheels 11F and 11R in ancient language without using brake fluid.

The front wheel braking force BPF may be the sum of the friction braking force applied to the front wheel 11F by the operation of the front wheel braking mechanism 20F and the regenerative braking force applied to the front wheel 11F by the power generation of the generator.

The rear wheel braking force BPR may be the sum of the friction braking force applied to the rear wheel 11R by the operation of the rear wheel braking mechanism 20R and the regenerative braking force applied to the rear wheel 11R by the power generation of the generator.