JP2001191907A - Brake controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a brake controller having a front and rear brake force distribution device capable of improving safety of a vehicle during braking by preventing unnecessary ABS control to rear wheels without reducing brake efficiency. SOLUTION: In this controller, when at least one front wheel is under ABS control, a rear wheel boosting speed calculation part 28 changes brake hydraulic pressure boosting speed to the rear wheels under EBD control according to an estimation road surface μ calculated in a road surface state detection part 26. When none of the front wheels are under the ABS control, the calculation part 28 sets the brake hydraulic pressure boosting speed to the rear wheels under the EBD control to a prescribed value smaller than the value in the case that at least one front wheel is under the ABS control.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brake control device for a vehicle, and more particularly to a front-rear braking force distribution device that adjusts a distribution of a braking force of a front wheel and a braking force of a rear wheel.

[0002]

2. Description of the Related Art When a vehicle is braked, the load applied to the front wheels is larger than the load applied to the rear wheels. Therefore, the rear wheels tend to lock more easily during braking than the front wheels. Therefore, conventionally, a proportioning valve (hereinafter, referred to as a P valve) is provided so that the wheel cylinder hydraulic pressure of the rear wheel during braking is lower than the wheel cylinder hydraulic pressure of the front wheel. On the other hand, with the development of electronic control, the function of the P-valve, that is, the distribution of braking force between the front wheels and the rear wheels, has been performed by a front-rear braking force distribution device using electronic control. If the deceleration or a certain speed difference between the front wheel and the rear wheel is detected, the increase in the brake fluid pressure of the rear wheel is limited, and the function of the P valve is substituted.

FIG. 7 is a diagram showing an example of a braking state of a vehicle when a braking force distribution control (hereinafter, referred to as EBD control) by a conventional longitudinal braking force distribution device is performed.
As can be seen from FIG. 7, when the brake pedal is operated and the brake switch is turned on during braking, the vehicle body deceleration VC
When EL increases and exceeds a predetermined threshold value, the EBD control is started, and an increase in the wheel cylinder hydraulic pressure of the rear wheel is limited to avoid skid of the rear wheel.

[0004]

However, when the EBD control is started, the rate of increase in the brake fluid pressure for the rear wheels is constant regardless of whether the ABS control is performed for the front wheels. . For this reason, the front wheel skids and A
Even though the BS control has been started, the ABS control for the rear wheels may not be performed by the EBD control. For this reason, it takes too much time for the brake fluid pressure to increase until the rear wheels skid, and the braking efficiency is degraded, even though the driver performs the brake operation enough to skid the front wheels. was there.

On the other hand, when the EBD control is started while the brake operation is being performed to the extent that the front wheel skids or not, the brake fluid pressure of the rear wheel gradually increases,
Since the rising speed is constant, the brake fluid pressure may increase as the rear wheels skid, and the ABS control for the rear wheels may be started. But in such a case,
Even though the front wheels are not skid, the ABS control is started only for the rear wheels. Therefore, it is determined that the ABS control is malfunctioning and unnecessary ABS control is performed, and a predetermined error process is performed. There was a problem.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem. When a skid is generated in the front wheels, the speed of increasing the brake fluid pressure with respect to the rear wheels during the EBD control is estimated on a road surface. Since the friction coefficient is changed according to the friction coefficient, unnecessary ABS control for the rear wheels is not performed without lowering the braking efficiency, so that the stability of the vehicle during braking can be improved. It is an object to obtain a brake control device provided with a power distribution device.

Although different from the present invention, Japanese Patent Application Laid-Open No.
Japanese Patent No. 92659 discloses a braking force distribution method and a braking force distribution method in which, when a rear wheel tends to lock, a brake fluid pressure of the rear wheel is reduced and held until the front wheel shows a tendency to lock. ing.

[0008]

SUMMARY OF THE INVENTION A brake control device according to the present invention is a brake control device for a vehicle having an anti-skid control device for performing ABS control. And brake fluid pressure limiting means for limiting an increase in brake fluid pressure on the rear wheels so that the braking force on the rear wheels has a predetermined relationship with the braking force on the front wheels. The brake fluid pressure increasing speed of the rear wheels during the brake fluid pressure increase restriction is changed according to the ABS control execution determination of the ABS control execution determination means for the front wheels.

[0009] Specifically, the brake fluid pressure restricting means is arranged so that, when the ABS control is performed on at least one of the front wheels, the brake fluid pressure limiting means is provided after the ABS control is not performed on all the front wheels. The brake fluid pressure increasing speed for the wheels is increased.

On the other hand, a brake control device according to the present invention includes a road surface μ calculating means for calculating an estimated value of a road surface μ, which is a friction coefficient of the road surface.
When the ABS control is performed on at least one of the front wheels, the brake fluid of the rear wheels during the brake fluid pressure increase restriction on the rear wheels is determined according to the estimated value of the road surface μ calculated by the road surface μ calculating means. The pressure raising speed was changed.

More specifically, the brake fluid pressure limiting means increases the brake fluid pressure increasing speed of the rear wheels during the limitation of the brake fluid pressure increase for the rear wheels as the estimated value of the road surface μ calculated by the road surface μ calculating means increases. Was made larger.

Further, in the brake control device according to the present invention, specifically, the brake fluid pressure limiting means sets a brake fluid pressure increasing speed for the rear wheels to a predetermined value when ABS control is not performed for all front wheels. Value.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described in detail based on an embodiment shown in the drawings. FIG. 1 is a schematic control system diagram showing an example of a brake control device according to an embodiment of the present invention, and shows a diagonal two-system brake system as an example. In FIG. 1, the right front wheel (FR) and the left rear wheel (R
L) only is shown.

In FIG. 1, a master cylinder 1 and wheel cylinders 2 corresponding to left and right front wheels and left and right rear wheels, respectively.
While the inlet valves 3A to 3D made of ON / OFF type electromagnetic valves are arranged between A to 2D, the outlet valves 4A to 4D made of ON / OFF type electromagnetic valves and the pump 5 are connected to the wheel cylinders 2A to 2D. A recirculation line 6 for recirculating the brake fluid is provided in the master cylinder 1 through the intermediary. A buffer chamber 7 is disposed between the outlet valves 4A to 4D of the reflux line 6 and the pump 5. In addition, A of the code | symbol which shows a wheel cylinder, an inlet valve, and an outlet valve
ＤD respectively indicate left and right front wheels and left and right rear wheels of the vehicle.

The wheel speed sensors S0 to S3 are connected to a signal processing device 8 to be described later.
S3 detects the respective wheel speeds of the corresponding left and right front wheels and right and left rear wheels, and outputs the detected wheel speeds to the signal processing device 8 as wheel speed signals.

FIG. 2 is a schematic block diagram showing an example of the brake control device according to the embodiment of the present invention. In FIG. 2, a brake control device 10 includes wheel speed sensors S0 to S3 provided for each wheel, and a signal processing device 8 shown in FIG. 1 including a microcomputer or the like. Is connected to a hydraulic control device 12 for controlling the pressure. The hydraulic pressure control device 12 shows the wheel cylinders 2A to 2D, the inlet valves 3A to 3D, the outlet valves 4A to 4D, the pump 5, and the buffer chamber 7 in FIG.

The signal processing device 8 includes a wheel speed and wheel deceleration calculating unit 21, an estimated vehicle speed calculating unit 22, a wheel state detecting unit 23, and a hydraulic pressure control unit driving unit 24. Further, the signal processing device 8 includes a vehicle deceleration calculating unit 25.
A road surface state detecting unit 26 for detecting a road surface state;
A D control determining unit 27 and a rear wheel boost speed calculating unit 28 that variably sets the rear wheel boost speed are provided.

The wheel speed sensors S0 to S3, the wheel speed and wheel deceleration calculating unit 21, the estimated vehicle speed calculating unit 22, the wheel state detecting unit 23, and the hydraulic pressure control unit driving unit 24 are anti-skid control units for performing ABS control. The vehicle body deceleration calculating unit 25, the road surface state detecting unit 26, the EBD control determining unit 27, the rear wheel boosting speed setting unit 28, and the hydraulic pressure control device driving unit 24 are configured to distribute the braking force before and after performing the EBD control. Forming device. Strictly speaking, the wheel speed sensors S0 to S3,
The front-rear braking force distribution device includes the wheel speed and wheel deceleration calculation unit 21 and the estimated vehicle speed calculation unit 22.

Each of the wheel speed sensors S0 to S3 is connected to a wheel speed and wheel deceleration calculating unit 21, respectively.
The respective wheel speeds and wheel decelerations are calculated from the signals from the third and third wheels. The wheel speed and wheel deceleration calculating unit 21 is connected to the estimated vehicle speed calculating unit 22, and the estimated vehicle speed calculating unit 2
2 calculates an estimated vehicle body speed VREF from the wheel speeds and the respective wheel speeds calculated by the wheel deceleration calculation unit 21.

Further, a wheel speed and wheel deceleration calculating section 21
The estimated vehicle speed calculating unit 22 includes a wheel state detecting unit 23
The wheel state detection unit 23 calculates the wheel speed based on the wheel speed and the wheel deceleration calculated by the wheel speed and wheel deceleration calculation unit 21 and the estimated vehicle speed VREF calculated by the estimated vehicle speed calculation unit 22. The lock and skid states of are detected. The wheel state detection unit 23 is connected to a hydraulic pressure control device drive unit 24 that drives and controls the hydraulic pressure control device 12 that increases or decreases or maintains the brake hydraulic pressure of each wheel.

On the other hand, the estimated vehicle speed calculation unit 22 is connected to a vehicle deceleration calculation unit 25, and the vehicle deceleration calculation unit 25
Estimated vehicle speed VR calculated by estimated vehicle speed calculator 22
The vehicle body deceleration VCEL is calculated from EF. The road surface state detection unit 26 is connected to the wheel state detection unit 23, and calculates an estimated value of a road surface friction coefficient (hereinafter, referred to as road surface μ) by a predetermined method from the wheel state detected by the wheel state detection unit 23. Calculate and detect the road surface condition.

An EBD control determining section 27 connected to the estimated vehicle speed calculating section 22 and the vehicle body deceleration calculating section 25, respectively.
Determines whether to perform the EBD control from the estimated vehicle speed VREF calculated by the estimated vehicle speed calculation unit 22 and the vehicle deceleration VCEL calculated by the vehicle deceleration calculation unit 25. On the other hand, the rear wheel step-up speed calculation unit 28 includes the wheel state detection unit 23,
When connected to the road surface state detection unit 26 and the EBD control determination unit 27, respectively, and the EBD control determination unit 27 determines to start the EBD control, it is determined whether one or both front wheels are under ABS control. The rear wheel brake pressure increasing speed is changed accordingly. Further, the rear wheel boost speed calculating unit 28
When one or both front wheels are under the ABS control, the brake fluid pressure increase of the rear wheels according to the estimated value of the road surface μ calculated by the road surface state detection unit 26 (hereinafter, referred to as the estimated road surface μ). Calculate the speed.

The EBD control judging section 27 and the rear wheel boosting speed calculating section 28 are further connected to a hydraulic pressure control device driving section 24, respectively.
Based on the command input from the control unit 3 and the determination of the EBD control determination unit 27, the hydraulic pressure control device 12 that controls the hydraulic pressure of each wheel to increase or decrease or maintain the hydraulic pressure is controlled. At this time, the hydraulic pressure control device drive unit 24 sends the EBD control determination unit 27
When the determination to execute the control is input, the hydraulic pressure control device 12 increases the brake fluid pressure of each rear wheel according to the brake fluid pressure increasing speed of the rear wheel input from the rear wheel pressure increasing speed calculation unit 28. Drive control.

In such a configuration, the EBD control performed by the front / rear braking force distribution device, particularly the EBD control
A method of setting the brake fluid pressure increasing speed of the rear wheels after the control is started will be described. Since the ABS control by the anti-skid control device is known, its description is omitted. The EBD control determination unit 27 includes the vehicle deceleration calculation unit 2
When the vehicle body deceleration VCEL calculated in 5 exceeds the predetermined value Th1 and the estimated vehicle speed VREF calculated in the estimated vehicle speed calculation unit 22 exceeds the predetermined value γ, it is determined that the EBD control is started, and the EBD control is performed. Is not established, a determination is made to prohibit the EBD control.

On the other hand, the road surface condition detecting section 26 calculates the estimated road surface μ by a predetermined method. The method of calculating the estimated road surface μ is well-known, and detailed description thereof is omitted here. However, for example, the magnitude of slip at each front wheel, that is, the estimated vehicle speed VREF and the wheel of each front wheel, obtained from the wheel state detection unit 23, for example, The estimated road surface μ is calculated from the difference from the speed and the skid time at each front wheel. Specifically, the road surface state detection unit 26 calculates a value obtained by multiplying the slip magnitude and the skid time obtained from the wheel state detection unit 23 for each front wheel, and is set in advance according to the calculated value. FIG. 3
The calculation of the road surface μ is performed using the relationship as described above. For each calculated road surface μ, the road surface state detection unit 26 sets the smaller value as the estimated road surface μ.

When the EBD control determining unit 27 determines that the EBD control is to be performed, the rear wheel boosting speed calculating unit 28 applies a brake to each rear wheel when ABS control is being performed on at least one front wheel. The hydraulic pressure increasing speed is changed in a predetermined relationship according to the estimated road surface μ calculated by the road surface state detection unit 26. Therefore, the brake fluid pressure increasing speed for each rear wheel can be expressed as a function f (μ) of the estimated road surface μ. For example, as shown in FIG. The smaller the value, the smaller the brake fluid pressure increasing speed for each rear wheel is calculated, and the calculated value is output to the fluid pressure control device drive unit 24.

When the ABS control is not performed for all the front wheels, the rear wheel boosting speed calculating section 28 sets the brake hydraulic pressure boosting speed to a predetermined value. At this time, the rear wheel boosting speed calculation unit 28 sets the brake hydraulic pressure boosting speed to a predetermined value smaller than when the ABS control for the front wheels is being performed.

When the EBD control determining section 27 determines to start the EBD control, the EBD control determining section 27 controls the hydraulic pressure control device driving section 24 to independently or independently adjust the pressurizing rates of the brake hydraulic pressures of the right and left rear wheels. The brake fluid pressure is adjusted so as to be smaller than the front wheel brake fluid pressure, and the brake fluid pressure of each rear wheel is increased according to the brake fluid pressure increasing speed calculated by the rear wheel pressure increasing speed calculation unit 28. The hydraulic pressure control device drive unit 24, based on a command from the EBD control determination unit 27,
The drive control of the hydraulic pressure control device 12 is performed.

Next, the flow of the operation of the longitudinal braking force distribution device will be described in more detail with reference to FIG. FIG.
5 is a flowchart showing an operation example of the front and rear braking force distribution device in FIG. 2, and FIG. 5 shows an operation when a driver performs a brake operation during braking.

In FIG. 5, first, the wheel speed and wheel deceleration calculating section 21 calculates the wheel speed SPEED of each wheel.
0 to SPEED3 (step S1), and the estimated vehicle speed calculating unit 22 calculates the calculated wheel speeds SPEED3.
An estimated vehicle speed VREF, which is an estimated value of the vehicle speed, is calculated from ED0 to SPEED3, and the calculated estimated vehicle speed VREF is output to the vehicle deceleration calculating unit 25 and the EBD control determining unit 27 (step S2). Since a method of calculating the estimated vehicle speed from each wheel speed is known, its description is omitted.

Next, the vehicle deceleration calculating section 25 calculates the vehicle deceleration VCEL from the estimated vehicle speed VREF calculated by the estimated vehicle speed calculating section 22 (step S3).
The BD control determination unit 27 checks whether the vehicle body deceleration VCEL exceeds a predetermined threshold Th1 (Th1> 0) (step S4). The EBD control determination unit 27 determines that the vehicle body deceleration VCEL exceeds the threshold value Th1 (YE
S), it is checked whether or not the estimated vehicle speed VREF exceeds a predetermined value γ (γ> 0) (step S5). When the estimated vehicle speed VREF exceeds the predetermined value γ (YES), the EBD control determination unit 27 determines whether to start the EBD control (step S6).

Next, the rear wheel boosting speed calculating section 28 calculates the EBD
With the start determination of the EBD control by the control determination unit 27,
The rear wheel brake fluid pressure increasing speed is calculated. The rear wheel boosting speed calculation unit 28 checks whether or not the front wheels are under ABS control based on the information from the wheel state detection unit 23 (step S7), and one or both of the front wheels are under ABS control. If there is (YES), the brake hydraulic pressure boosting speed of the rear wheels is set to a boosting speed corresponding to the estimated road surface μ calculated by the road surface state detecting unit 26 (step S8). After that, the EBD control determining unit 27 sends the E
A command to execute the BD control is output, and the hydraulic pressure control device driving unit 24 is output.
Performs the drive control of the hydraulic pressure control device 12 using the rear wheel brake hydraulic pressure boosting speed set by the rear wheel boosting speed calculating unit 28 (step S9), and this flow ends.

In step S7, all the front wheels are AB.
If the S control is not being performed (NO), the rear wheel boosting speed calculation unit 28
Sets the brake fluid pressure increasing speed of the rear wheels to a predetermined value (step S10), and thereafter performs the process of step S9, and ends this flow. In step S4, the vehicle deceleration V
If CEL does not exceed threshold value Th1 (NO),
Alternatively, if the estimated vehicle speed VREF does not exceed the predetermined value γ in step S5 (NO), the EBD control determination unit 27
Commands the hydraulic pressure control device drive unit 24 to prohibit the EBD control (step S11), and this flow ends.

FIG. 6 is a diagram showing a braking state of the vehicle when the EBD control is performed by the front-rear braking force distribution device shown in FIGS. 2 to 5, and FIG. 6 (b) shows the time of the forcible movement on the high μ road where the road surface is high, and FIG. 6 (b) shows the time of the gentle braking on the low μ road where the estimated road surface μ is low.
As can be seen from FIG. 6, as the value of the estimated road surface μ increases, the brake fluid pressure increasing speed of the rear wheels increases, and the high μ
At the time of forcible movement on the road, it is possible to quickly reach the brake fluid pressure at which the rear wheels lock. Also, during slow braking on a low μ road, as shown by the portion A, the low μ μ
It is determined that the vehicle is on a road, and the brake fluid pressure increasing speed of the rear wheels is low. As described above, the rear end lock of each rear wheel is prevented and a high deceleration is obtained not only at the time of gentle braking but also at the time of sudden braking.

As described above, in the brake control device according to the present embodiment, the rear wheel boosting speed calculating unit 28 determines that at least one of the front wheels is under the ABS control, the brake fluid pressure increase for the rear wheel during the EBD control is performed. The speed is changed in accordance with the estimated road surface μ calculated by the road surface state detection unit 26. If all the front wheels are not under the ABS control, the brake fluid pressure increasing speed with respect to the rear wheels during the EBD control is determined. It is set to a predetermined value smaller than that during control. Therefore, when the front wheels are under the ABS control during the EBD control, the braking force of the rear wheels can be increased, and unnecessary ABS control for the rear wheels is not performed without reducing the braking efficiency. Therefore, the reliability at the time of braking and the stability of the vehicle can be improved.

In the above-described embodiment, the estimated road surface μ is calculated from the slip size and the skid time obtained from the wheel state detector 23. However, when the G sensor (acceleration sensor) is mounted. May calculate the estimated road surface μ according to the deceleration of the vehicle obtained from the G sensor. In this case, a G sensor is connected to the road surface state detection unit 26 instead of the wheel state detection unit 23, and the road surface state detection unit 26 estimates the estimated road surface μ as the deceleration of the vehicle detected by the G sensor increases. Of the estimated road surface μ is calculated so that the value of.

In the above-described embodiment, the case where the vehicle body deceleration VCEL is used for the determination of the start of the EBD control has been described as an example. However, the occurrence of the slip of the rear wheel is detected to determine the start of the EBD control. You may. In this case, the EBD control determination unit 27 calculates E from the wheel speed of each rear wheel calculated by the wheel speed and wheel deceleration calculation unit 21 and the estimated vehicle speed VREF calculated by the estimated vehicle speed calculation unit 22.
A BD control start determination is made. That is, the EBD control determination unit 27 determines to start the EBD control when the difference between the estimated vehicle body speed VREF and the wheel speed of the rear wheels exceeds the predetermined threshold Thy.

The EBD is calculated from the difference between the front wheel speed and the rear wheel speed.
Control start determination may be performed. In such a case, the EBD control determination unit 27 performs the EBD control start determination based on a speed difference between at least one of the front wheel speeds and the rear wheel speed corresponding to the front wheel. That is, the EBD control determination unit 27 determines to start the EBD control when the speed difference between the wheel speed of one of the front wheels and the wheel speed of the rear wheel corresponding to the front wheel exceeds the predetermined threshold Thz. I do.

[0039]

As is apparent from the above description, according to the brake control system of the present invention, the rear wheel at the time of limiting the brake fluid pressure on the rear wheel depends on whether the ABS control is performed on the front wheel. Changed the brake fluid pressure increase speed. From this, at the time of EBD control,
Since the rear wheels can be braked in accordance with the braking state of the front wheels, the braking efficiency can be increased, and unnecessary ABS control for the rear wheels can be prevented from being performed. In addition, the stability of the vehicle can be improved.

Specifically, when the ABS control is performed on at least one of the front wheels, the A / B control is performed on all the front wheels.
The brake fluid pressure increasing speed for the rear wheels is set to be higher than when the BS control is not performed. Thus, during the EBD control, the rear wheels can be braked in accordance with the braking state of the front wheels, and the braking efficiency during braking can be increased.

More specifically, a road surface μ calculating means for calculating an estimated value of the road surface μ is provided, and when the ABS control is performed on at least one of the front wheels, the road surface μ calculating means calculates the road surface μ. The brake fluid pressure increasing speed of the rear wheels is changed in accordance with the estimated value of the road surface μ. From this,
During the EBD control, the rear wheels can be braked according to the road surface μ, so that the braking efficiency can be further increased, and the reliability during braking and the stability of the vehicle can be further improved.

More specifically, the larger the estimated value of the road surface μ, the higher the brake fluid pressure increasing speed of the rear wheels.
Thus, the rear wheels can be braked according to the road surface μ, and the braking efficiency can be further increased.

On the other hand, when the ABS control is not performed on all the front wheels, the brake fluid pressure increasing speed for the rear wheels is set to a predetermined value. From this, the predetermined value is
By setting the value to a value smaller than when the ABS control for the front wheels is performed, unnecessary ABS control for the rear wheels can be prevented from being performed during the EBD control. The stability of the vehicle can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic control system diagram showing an example of a brake control device according to an embodiment of the present invention.

FIG. 2 is a schematic block diagram illustrating an example of a brake control device according to the embodiment of the present invention.

FIG. 3 is a diagram showing an example of a relationship between a value obtained by multiplying a front wheel slip magnitude and a front wheel skid time and an estimated road surface μ;

FIG. 4 is a diagram illustrating an example of a relationship between an estimated road surface μ and a brake fluid pressure increasing speed for a rear wheel.

FIG. 5 is a flowchart illustrating an operation example of a front-rear braking force distribution device in the brake control device of FIG. 2;

FIG. 6 is a diagram illustrating a braking state of the vehicle when EBD control is performed by the front and rear braking force distribution device illustrated in FIGS. 2 to 5;

FIG. 7 is a diagram illustrating a braking state of a vehicle when EBD control is performed during sudden braking by a conventional longitudinal braking force distribution device.

[Explanation of symbols]

 Reference Signs List 8 signal processing device 10 brake control device 12 hydraulic pressure control device 21 wheel speed and wheel deceleration calculation unit 22 estimated vehicle speed calculation unit 24 hydraulic pressure control device drive unit 25 vehicle body deceleration calculation unit 26 road surface state detection unit 27 EBD control determination Part 28 Rear wheel boost speed calculation unit

Claims (5)

[Claims] 1. A brake control device for a vehicle having an anti-skid control device for performing ABS control, wherein ABS control execution determining means for determining whether to perform ABS control for each wheel; Brake fluid pressure limiting means for limiting a rise in brake fluid pressure to the rear wheels so as to have a predetermined relationship with respect to the rear wheels. A brake control device, wherein a brake fluid pressure increasing speed is changed in accordance with ABS control execution determination of ABS control execution determination means for a front wheel. 2. The brake fluid pressure limiting means according to claim 1, wherein when at least one of the front wheels is subjected to the ABS control, the brake fluid pressure limiting means is adapted to brake the rear wheels more than when the ABS control is not performed to all the front wheels. The brake control device according to claim 1, wherein the hydraulic pressure increasing speed is increased. 3. A road surface μ calculating means for calculating an estimated value of a road surface μ, which is a coefficient of friction of the road surface, wherein the brake fluid pressure limiting means is provided when ABS control is performed on at least one of the front wheels. 2. The brake fluid pressure increasing speed of the rear wheel during the restriction of the brake fluid pressure increase on the rear wheel is changed according to the estimated value of the road surface μ calculated by the road surface μ calculating means. Brake control device. 4. The brake fluid pressure limiting means increases the brake fluid pressure increasing speed of the rear wheels during the brake fluid pressure increase limitation on the rear wheels as the estimated value of the road surface μ calculated by the road surface μ calculating means increases. The brake control device according to claim 3, wherein: 5. The brake fluid pressure limiting means sets a brake fluid pressure increasing speed for a rear wheel to a predetermined value when ABS control is not performed on all front wheels. Item 6. The brake control device according to any one of Items 4.