JP3157191B2 - Vehicle slip control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle for preventing a wheel from being locked when traveling on a road having a low friction coefficient such as an icy road by controlling a brake pressure in accordance with a wheel slip ratio or the like. The present invention relates to a slip control device.

[0002]

2. Description of the Related Art Conventionally, as disclosed in Japanese Patent Publication No. 41333/1988, by controlling a brake pressure in accordance with a running state of a vehicle, locking of wheels and generation of skid during braking are prevented. A vehicle slip control device having an anti-skid brake system configured as described above is known. In the above anti-skid brake system, in order to effectively prevent the wheels from locking, the deceleration of the wheels tends to sharply decrease, and the wheel speed is set to a value corresponding to a preset reference slip ratio. Control means is provided for rapidly reducing the brake pressure when it is confirmed that the brake pressure has fallen below the threshold.

[0003]

In the case where the control means for rapidly reducing the brake pressure according to the running state of the vehicle is provided as described above, the control is quickly performed when the wheels tend to lock suddenly. Although it has the advantage of being able to perform the rapid decompression control according to the wheel deceleration and the slip ratio regardless of the magnitude of the friction coefficient of the road surface,
There is a problem that it is not possible to execute appropriate control of the brake pressure according to the road surface condition.

For example, when traveling on a low μ road, the recovery of the wheel speed is delayed as compared with traveling on a high μ road, so that the rapid pressure reduction control is started at the same timing as when traveling on a high μ road. The rapid decompression time becomes longer, and the brake pressure tends to decrease too much. On the other hand, if the start timing of the rapid pressure reduction control when traveling on the high μ road is set in accordance with the traveling on the low μ road, the effect of preventing the locking of the wheels during traveling on the high μ road becomes insufficient. There is a problem that a tendency occurs.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and it is possible to effectively prevent the wheels from being locked during braking by executing rapid pressure reduction control in accordance with the condition of the traveling road surface. It is an object of the present invention to provide a wheel slip control device that can be used.

[0006]

The invention according to claim 1 is
A vehicle slip having detection means for detecting the running state of the vehicle and brake pressure adjusting means for adjusting the brake pressure, wherein the brake pressure is adjusted according to the running state of the vehicle to prevent wheels from locking. In the control device, when it is confirmed that the wheels have a sharp locking tendency according to the detection signal of the detection means, the control means controls the brake pressure adjustment means so as to rapidly reduce the brake pressure; Threshold value storage means for storing various threshold values as a criterion for determining whether or not to start the rapid pressure reduction control; road surface state estimating means for estimating a friction coefficient of a traveling road surface in accordance with a detection signal of the detection means; When it is confirmed that the traveling road surface is on a low μ road according to the output signal of the state estimating means, a threshold set to delay the start timing of the rapid pressure reduction control compared to when traveling on a high μ road. A threshold reading means for reading a value from the threshold storage means is provided.

According to a second aspect of the present invention, there is provided a vehicle speed calculating means for calculating a running speed of the vehicle. Thus, a threshold value set to advance the start time of the rapid pressure reduction control is read.

[0008]

According to the first aspect of the present invention, when the road surface condition estimating means confirms that the traveling road surface is a low μ road, it becomes a criterion for determining whether to start the rapid pressure reduction control. The threshold value, that is, the value of the wheel slip rate or the like is set so as to delay the start timing as compared to when traveling on a high μ road, and the rapid pressure reduction control is not started until the wheel slip rate decreases beyond the threshold value. Become.

According to the second aspect of the present invention, when the vehicle is running at a low speed, unnecessary rapid pressure reduction control is prevented from being executed, and when the vehicle is running at a high speed. That is, the rapid pressure reduction control is executed at an early stage, and the locking of the wheels is effectively suppressed.

[0010]

FIG. 2 shows a vehicle provided with a slip control device according to the present invention. This vehicle includes left and right front wheels 1 and 2 serving as driven wheels and left and right rear wheels 3 and 4 serving as driving wheels. The driving force of an engine 5 is controlled by an automatic transmission 6, a propeller shaft 7, a differential 8, and left and right. Axles 9,10
Are transmitted to the rear wheels 3, 4 via the. Each of the wheels 1 to 4 is provided with a brake device 11 to 14 including a disk 11 a to 14 a that rotates integrally with the wheel and a caliper 11 that receives a brake pressure and controls the rotation of the disk 11 a to 14 a. The driving of these brake devices 11 to 14 is controlled by a brake control system 15.

The brake control system 15 has a booster 17 for increasing the stepping force of a brake pedal 16 and a master cylinder 18 for generating a brake pressure in accordance with the stepping force increased by the booster 17. And
The front-wheel brake pressure line 19 led from the master cylinder 18 is branched into two paths, and these front-wheel branch paths 19a, 19b form calipers 11a, 12a of the brake devices 11, 12 in the left and right front wheels 1, 2. One of the front-wheel branch passages 19a that communicates with the brake 11 of the left front wheel 1 has an electromagnetic on-off valve 2
0a and an electromagnetic relief valve 20b are arranged, and the other front wheel branch braking pressure line 19 communicating with the brake device 12 of the right front wheel 2 is provided.
Also in b, a second valve unit 21 composed of an electromagnetic on-off valve 21 similarly to the first valve unit 20 and an electromagnetic relief valve 21b is installed.

On the other hand, the first and second brake pressure lines 22 for the rear wheels led from the master cylinder 18 are provided.
Electromagnetic on-off valve 23 as well as valve units 20 and 21
a and a solenoid-operated relief valve 23b.
A valve unit 23 is installed, and the brake pressure line 22 is branched into two paths on the downstream side of the third valve unit 23, and these branch paths 2
2a, 22b are connected to the calipers 13b, 14b of the brake devices 13, 14 in the left and right rear wheels 2, 3, respectively.

The electromagnetic relief valves 20b, 21
The brake oil discharged from b and 23b is returned to the reservoir tank 18a of the master cylinder 18 via a drain line (not shown).

The first to third valve units 2
The drive units 0, 21 and 23 are independently driven and controlled by the control unit UTR, and the brake devices 11 of the left front wheel 1 are operated by the operation of the first and second valve units 20 and 21.
And the braking force of the braking device 12 of the right front wheel 2 is variably controlled, and the braking force of the braking devices 13 and 14 of the left and right rear wheels 3 and 4 is simultaneously variably controlled by the operation of the third valve unit 23. ing.

To the control unit UTR, a detection signal of a brake switch 25 for detecting the presence / absence of depression of the brake pedal 16 and detection signals of wheel speed sensors 26 to 29 for detecting the rotation speed of each wheel are inputted. The control unit UTR generates a control signal for anti-skid brake control based on these detection signals, and transmits the control signal to the first to third valve units 2.
0, 21 and 23 to control the braking of the left and right front wheels 1 and 2 and the rear wheels 3 and 4 from slipping.
Perform in parallel for each valve unit.

The control unit UTR is shown in FIG.
The vehicle speed calculating means 30 calculates the running speed of the vehicle according to the detection signals of the wheel speed sensors 26 to 29, and the slip rate calculating means 3 calculates the slip rate of the wheels 1 to 4, as shown in FIG.
1, acceleration / deceleration calculating means 32 for calculating the acceleration / deceleration of each of the wheels 1-4, road surface state estimating means 33 for estimating the friction coefficient of the road surface, and threshold storage means for storing various slip control thresholds as a map. And threshold reading means 35 for reading a threshold suitable for the current running state of the vehicle from the map.
And a control means 36 for controlling the brake pressure adjusting means composed of the brake control system 15.

The vehicle speed calculating means 30 is configured to calculate the pseudo vehicle speed Vr based on the wheel speed Vw obtained from the detection signals of the wheel speed sensors 26 to 29 by a conventionally known method. . The slip control device 31 calculates the wheel speed Vw and the pseudo vehicle speed V as shown in the following equation.
The slip ratio S, which is a ratio with respect to r, is calculated for each of the wheels 1 to 4.

Slip ratio (S1) = (wheel speed Vw / pseudo-vehicle Vr) × 100 [%] The acceleration / deceleration calculating means 32 calculates the acceleration or deceleration of the wheel speed Vw. The acceleration or deceleration is calculated by converting the difference between the previous value and the current value of Vw by the sampling period Δt (for example, 7 ms) into a gravitational acceleration. The road surface state estimating means 33 is configured to estimate the friction coefficient of the road surface from the acceleration AW or the deceleration DW of the wheel speed Vw obtained by the acceleration / deceleration calculating means 32 according to the flowchart shown in FIG.

That is, when the control operation for estimating the friction coefficient starts, first, in step S1, various data are read, and then in step S2, according to the flag Fabs indicating that the anti-skid brake control is being executed. It is determined whether the anti-skid brake control is currently being executed. If the result of this determination is NO
If it is confirmed that the anti-skid brake control is not currently being executed, in step S3, “3” indicating a high μ road is set to the friction coefficient value MU.

Meanwhile, if it is being executed currently antiskid brake control in step S2 is confirmed, in step S4 to S6, the previous control value, i.e. the deceleration DW or acceleration of the wheel speed V _W AW
It is determined whether the road surface state is a high μ road, a medium μ road, or a low μ road based on the road conditions, and a friction coefficient value MU corresponding to each road surface state is set.

That is, in step S4, it is determined whether or not the deceleration DW is smaller than a preset reference deceleration "-20G".
In 6, it is determined whether or not the acceleration AW is greater than a preset first reference acceleration “10G” and a second reference acceleration “20G”. If it is determined that the deceleration DW is equal to or less than “−20 G” as a result of the above determination, “1” indicating a low μ road is set to the friction coefficient value MU in step S7, and the acceleration AW is reduced. If it is confirmed that the friction coefficient is larger than “20G”, in step S8, “3” indicating the high μ road is set to the friction coefficient value MU, and the acceleration AW is within the range of “10 to 20G”. Is confirmed, in step S9, "2" indicating the medium μ road is set to the friction coefficient value MU.

The threshold reading means 35 calculates the deceleration of the wheel speed corresponding to the current running state from the map stored in the threshold storing means 34 based on the output signals of the vehicle speed calculating means 30 and the road surface state estimating means 33. And the threshold value of the slip ratio is read out to the control means 36. In this control means 36, the start timing of anti-skid brake control described later is determined, and the timing of holding, reducing and increasing the brake pressure is determined. A control signal is output to the system 15.

The map of the wheel deceleration threshold is high μ
Road, medium μ road and low μ road, in each road surface state,
4 is obtained in advance by experiment or the like as a value at which locking occurs. In the present embodiment, for example, (high μ road threshold, middle μ road threshold, low μ road threshold) = (− 3.0 G, −2. 0G,
-1.5G).

The slip ratio threshold map is composed of various threshold values for setting the timing of decreasing or increasing the brake pressure, as will be described later. The threshold values corresponding to the vehicle speed and the road surface condition are read and the brake control is performed. It is configured to be output to the system 15 as a control signal.

The control means 36 controls the deceleration D of the wheel immediately after the start of braking in accordance with the depression operation of the brake pedal 6.
W is compared with the deceleration threshold read out by the threshold reading means 35, and when the deceleration DW of the wheels 1 to 4 falls below the threshold, a control signal for holding the brake pressure after the pressure increase is generated. . Also, the wheel 1 after increasing and holding the brake pressure
The slip rate S of the wheels 1-4 is compared with the threshold value of the slip rate read by the threshold reading means 35. When the slip rate S of the wheels 1-4 decreases below the threshold value, a control signal for reducing the brake pressure is issued. Generate. This control signal is input to the brake control system 15, where the first to third valve units 20,
The electromagnetic on / off valves 20a, 21a, 23a and the electromagnetic relief valves 20b, 21b, 23b are controlled to open and close by duty control, respectively, whereby the braking force corresponding to the slip state is reduced by the front wheels 1, 2 and the rear wheels 3. , 4.

When the anti-skid brake control is not being performed, the first to third valve units 2 are not used.
The braking pressure control signal is not output to 0, 21 and 23,
The electromagnetic on-off valves 20a, 21a, 23a are kept open while the electromagnetic relief valves 20b, 21b, 23
b is kept closed. This allows the brake pedal 1
The brake pressure generated in the master cylinder 18 in response to the stepping force of the brake pedal 6 is supplied to the brake devices 11 to 14 of the left and right front wheels 1 and 2 and the rear wheels 3 and 4 via the brake pressure lines 19 and 22, and the brake pedal 16 Is applied directly to the wheels 1-4.

Next, the control operation of the slip control device according to the present invention will be described with reference to FIG. The brake pressure increase / decrease control is performed by the first to third valve units 20, 21, 23.
The first valve unit 20 for the left front wheel 1 will be described here as an example.

When the brake pedal 16 is depressed at time point To in FIG. 4, the brake pressure generated by the master cylinder 18 gradually increases, and the braking force decreases the wheel speed Vw1 of the left front wheel 1. The deceleration DW of the wheel speed Vw is calculated by the acceleration / deceleration calculation means 32, and is read by the threshold reading means 34.
G ". When the deceleration DW of the wheel speed Vw falls below the threshold value “−3 G”, the phase shifts from the phase 0 in the non-control state of the anti-skid brake control to the phase 2
The anti-skid brake control in the first cycle is started.

As described above, in the first cycle of the anti-skid brake control, the threshold value of the high μ road is read as the threshold value of the deceleration of the wheel 1. This is because the friction coefficient of the road surface cannot be estimated during the control in the first cycle, and the threshold “−1.
If 5G ”is used, a situation may occur where the deceleration of the wheel is slightly lower than the threshold value even when the deceleration of the wheel is slightly reduced, so that the anti-skid control is frequently started.

The anti-skid brake control is started from the phase 2 for holding the brake pressure after the pressure increase, and the control in the phase 3 for reducing the brake pressure after the pressure increase / hold at the time Tb is executed. After the phase 4 for maintaining the reduced brake pressure at the time Tc is executed, the anti-skid brake control in the first cycle ends at the time Td. Next, from the time point Td, the control of the phase 1 for increasing the brake pressure again is executed, the anti-skid brake control of the second cycle is started, and when the second cycle is completed through the phases 2 to 4, the third cycle is completed. The anti-skid brake control after the cycle is repeatedly executed.

At the time of executing the holding control in the above phase 2,
From the wheel speed Vw, the wheel 1
Is calculated, and the threshold value of the slip rate serving as a criterion for determining whether to start the pressure reduction control in accordance with the vehicle speed Vr and the road surface friction coefficient is determined by the threshold reading means 3
5 and the threshold value is compared with the slip ratio S in the control means 36. For example, when a threshold value of 90% at high speed on a high μ road is read as the threshold value of the slip ratio, the time T at which the slip ratio S decreases to 90% or less.
The phase shifts from phase 2 to phase 3 in b, and the pressure reduction control of the brake pressure is started. That is, the relief valve 20b of the first valve unit 20 is turned on / off in accordance with a predetermined duty ratio, whereby the brake pressure is reduced at a predetermined gradient, the braking force is gradually reduced, and the rotational force of the left front wheel 1 is reduced. Recover.

When the deceleration DW or the acceleration AW of the wheel speed Vw of the left front wheel 1 becomes 0 at time Tc, the phase shifts from phase 3 to phase 4, and the brake pressure is maintained at the decelerated level. During four, the wheel speed Vw
Rise again. Then, at time Td, the wheel speed Vw recovers,
When the slip ratio S exceeds the slip ratio threshold value 90% again, the phase shifts from phase 4 to phase 1, and the anti-skid brake control in the second cycle is started.

During the execution of the pressure reduction control in the phase 2, the slip ratio S of the wheel 1 is compared with the threshold value for starting the rapid pressure reduction control read out by the threshold value reading means 35. For example, at the time Tf shown in FIG. If it is confirmed that the rate S has dropped below the threshold value, rapid pressure reduction control is performed to reduce the brake pressure more rapidly than usual. Then, during the execution of the rapid decompression control, the deceleration DW of the wheel 1 is compared with the threshold for ending the rapid decompression control read out by the threshold value reading means 35. For example, at the time Tg, the deceleration DW exceeds the threshold. When it is confirmed that the pressure has risen, the rapid pressure reduction control is terminated.

The rapid pressure reduction control will be described with reference to the flowchart shown in FIG. When the control operation diagram starts, first, in step S11, after inputting various data, in step S12, the slip ratio serving as a criterion for determining whether to start the rapid pressure reduction control from the map stored in the threshold value storage means 34 or not. Read the threshold. As shown in FIG. 6, the slip ratio threshold value for the start of the rapid pressure reduction is the vehicle speed Vr.
And the friction coefficient μ of the road surface are set as parameters,
When the friction coefficient μ of the road surface is low, it is set to a smaller value than when it is high, and when the vehicle speed Vr is low, it is set to a smaller value than when it is high.
As a result, when traveling on a low μ road, rapid decompression control is not executed until the slip ratio S of the wheel is significantly reduced compared to when traveling on a high μ road, and the timing of entering the rapid decompression control is delayed.
Also, at low speed traveling, the rapid pressure reduction control is not performed until the slip ratio S of the wheels is significantly reduced as compared with high speed traveling,
The timing for entering the rapid pressure reduction control is delayed.

The threshold value read in step S12,
The slip ratio S calculated based on the wheel speed Vw is compared to determine whether the slip ratio S is equal to or less than the threshold. If this determination result is YES and it is confirmed that the slip ratio S is equal to or less than the slip ratio threshold for starting rapid pressure reduction, in step S14, whether the deceleration DW of the wheel 1 is smaller than 0 or not. Is determined. That is, it is determined whether or not the rotation speed Vw of the wheel 1 is currently decreasing. If the result of this determination is YES, the flow shifts to step S15 to execute rapid pressure reduction control for rapidly reducing the brake pressure.

Next, in step S16, it is determined whether or not the point in time when the control state of the rapid pressure reduction is the high μ road. As a result of this determination, when it is confirmed that the vehicle has entered the rapid decompression state while traveling on the high μ road, it is determined in step S17 from the map stored in the threshold value storage means 34 whether the rapid decompression control is to be terminated. First reference deceleration threshold G1
Is read, and the first deceleration threshold G1 is compared with the deceleration DW of the wheel 1 to determine whether the deceleration is greater than the threshold G1.

The first deceleration threshold value G1 for terminating the rapid decompression.
As shown in FIG. 7, the friction coefficient of the traveling road surface at the present time, that is, at the time of determining whether or not to terminate the rapid pressure reduction control, is set as a parameter. When the friction coefficient μ of the road surface is high, It is set to a larger value than. As a result, when traveling on a low μ road, the timing of ending the rapid pressure reduction control is later than when traveling on a high μ road. Then, YES is determined in the above step S17,
When it is confirmed that the deceleration DW of the wheel 1 is equal to or greater than the threshold, the rapid pressure reduction control is ended in step S18.

If the determination in step S16 is NO, and it is confirmed that the vehicle has entered a rapid pressure reduction state while traveling on a low μ road, then in step S19 the threshold storage unit 3
The second deceleration threshold value G2 serving as a criterion for determining whether or not to terminate the rapid decompression control is read from the map stored in No. 4 and the second deceleration threshold value G2 is compared with the deceleration DW of the wheel 1. By determining whether or not this deceleration is greater than the threshold value G2, it is determined whether or not to terminate the rapid pressure reduction control. If the result of this determination is YES, the process moves to step S18 and the rapid pressure reduction control ends.

A second deceleration threshold value G for ending the rapid pressure reduction control
2, as shown in FIG. 8, the friction coefficient μ at the time of execution of the rapid pressure reduction control is set as a parameter, and when the friction coefficient μ at the time of execution of this rapid pressure reduction control is high,
The absolute value of the deceleration is set to a larger value than in the case of a low speed, and the absolute value of the deceleration is set to a larger value as a whole than the first deceleration threshold value G1. As a result, when the vehicle is in the control state of rapid decompression when traveling on the high μ road, compared with the case where the vehicle is in the control state of rapid decompression when traveling on the low μ road,
The timing to end the rapid pressure reduction control is delayed.

In the vehicle slip control device configured to rapidly reduce the brake pressure when it is confirmed that the wheels tend to lock rapidly as described above, the vehicle speed Vr and the friction coefficient μ are set as parameters. By providing a map of the slip ratio threshold value for the sudden decompression start, and reading out the slip ratio threshold value according to the running state of the vehicle from the map, when the friction coefficient μ of the road is low, the friction coefficient μ Since the timing for entering the rapid pressure reduction control is delayed as compared with the case where the pressure is high, there is an advantage that the brake pressure can be prevented from being excessively reduced due to the rapid pressure reduction control being executed earlier during low-μ travel. That is, when traveling on a low μ road, the rotational speed of the wheels is difficult to recover even if the pressure is suddenly reduced, and if the rapid pressure reduction control is performed early, the brake pressure tends to decrease too much. By selecting the slip ratio threshold value read from the map according to the coefficient μ and delaying the timing of entering the rapid pressure reduction control, it is possible to prevent the brake pressure from excessively decreasing.

Further, as described above, the slip ratio threshold value for the rapid decompression control read out according to the vehicle speed is selected, and the timing for entering the rapid decompression control during low-speed traveling is compared with that during high-speed traveling. This has the advantage that excessive locking of the wheels, which tends to occur during high-speed running, can be quickly and effectively prevented while preventing unnecessary anti-skid control from being performed during low-speed running.

Further, as in the above embodiment, the deceleration threshold value as a criterion for determining whether or not to terminate the rapid pressure reduction control is set as a map using the friction coefficient μ of the traveling road as a parameter.
When running on a low μ road, a threshold value set to delay the end timing of the rapid pressure reduction control as compared with when traveling on a high μ road is read from the map.
Advantageously, the wheels can be effectively prevented from being locked on a low μ road without causing a situation in which the rapid decompression control is executed for a long time during running on the road and the braking force is insufficient. There is.

In the above embodiment, a plurality of maps corresponding to the road surface friction coefficient μ at the time of executing the rapid pressure reduction control are provided, and the map to be used is selected according to the road surface friction coefficient μ at the time. When the control state of the rapid pressure reduction during traveling on the high μ road is configured to delay the timing of ending the rapid pressure reduction control as compared with the case where the control state of the rapid pressure reduction during the traveling on the low μ road is used, There is an advantage that the brake pressure which has been high in the traveling state on the high μ road is sufficiently reduced to effectively prevent the wheels from being locked.

[0044]

As described above, the present invention relates to a vehicle slip control device configured to rapidly reduce the brake pressure when it is confirmed that the wheels tend to lock rapidly. By selecting the threshold value for the start of rapid pressure reduction read out according to the friction coefficient of the road, the timing for entering the rapid pressure reduction control when traveling on a low μ road is delayed compared to when traveling on a high μ road. Excessive reduction in brake pressure due to early execution of rapid pressure reduction control during traveling of μ can be prevented, and appropriate anti-skid control can be performed.

Further, as described above, the slip rate threshold value for the rapid pressure reduction control read out according to the vehicle speed is selected, and the timing for entering the rapid pressure reduction control at low speed traveling is compared with that at high speed traveling. This has the advantage that excessive locking of the wheels, which tends to occur during high-speed running, can be quickly and effectively prevented while preventing unnecessary anti-skid control from being performed during low-speed running.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a slip control device according to the present invention.

FIG. 2 is an overall configuration diagram of a vehicle including the slip control device.

FIG. 3 is a flowchart showing an operation of estimating a friction coefficient in the slip control device.

FIG. 4 is a time chart showing a control operation of the slip control device.

FIG. 5 is a flowchart showing a rapid pressure reduction control operation in the slip control device.

FIG. 6 is a map showing a slip ratio threshold for the rapid pressure reduction control.

FIG. 7 is a map showing a first deceleration threshold value for the rapid pressure reduction control.

FIG. 8 is a map showing a second deceleration threshold value for the rapid pressure reduction control.

[Explanation of symbols]

 1-4 wheels 15 brake control system (brake pressure adjusting means) 33 road surface state estimating means 34 threshold storing means 35 threshold reading means

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Haruki Okazaki 3-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture Inside Mazda Co., Ltd. (56) References JP-A-56-95746 (JP, A) JP-A-64 JP-A-44564 (JP, A) JP-A-1-12764 (JP, A) JP-A-55-15381 (JP, A) JP-A-62-149546 (JP, A) JP-A-3-167059 (JP, A) (Japanese) Sho 63-45367 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) B60T 8/58

Claims (2)

(57) [Claims] 1. detecting means for detecting a running state of a vehicle;
A brake pressure adjusting means for adjusting a brake pressure, wherein the brake pressure is adjusted in accordance with a running state of the vehicle to prevent wheels from being locked. Accordingly, when it is confirmed that the wheels tend to lock suddenly, control means for controlling the brake pressure adjusting means so as to rapidly reduce the brake pressure, and determination as to whether or not to start the rapid pressure reduction control Threshold value storing means for storing various threshold values serving as references; road surface condition estimating means for estimating the friction coefficient of the traveling road surface in accordance with the detection signal of the detecting means; and traveling road surface in accordance with an output signal of the road surface estimating means. Is a low μ road,
A slip control device for a vehicle, comprising: threshold reading means for reading, from the threshold storage means, a threshold set to delay the start time of the rapid pressure reduction control as compared to when traveling on a high μ road. 2. A vehicle speed calculating means for calculating a running speed of a vehicle, wherein when the vehicle speed calculating device confirms that the vehicle is in a low-speed running state, the control unit starts the rapid pressure reduction control as compared with the high-speed running. 2. The vehicle slip control device according to claim 1, wherein a threshold value set to delay the timing is read.