JPH11152026A - Road surface friction coefficient estimating device and braking control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To instantaneously and precisely find a road surface without a phase delay by providing an estimating means for estimating a road surface friction coefficient according to the wheel increased acceleration determined by an increased acceleration arithmetic means such that the fiction coefficient is lower as the increased acceleration is larger, and the friction coefficient is higher as the increased acceleration is smaller. SOLUTION: A control unit 12 provided with a wheel speed sensor 13 for detecting the rotating speed of each wheel FR, FL, RR, RL and front and rear acceleration sensors or brake switches as input means to execute an ABS control for preventing a wheel lock in braking. The value of the coefficient of a polynomial showing a change of wheel speed from the past value and present value of wheel speed is determined to determine the increased acceleration of wheel speed, and the estimation of a road surface μ is performed on the basis of this increased acceleration. This determination of the increased acceleration is hardly influenced by a phase delay or noise, compared with the determination by differential, and the estimation of the road surface μ can be thus performed with a high precision.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention is applied to a brake control device which executes a so-called ABS control for controlling a wheel cylinder pressure so as to obtain a maximum braking force while preventing a wheel from locking during braking. The present invention relates to a suitable road surface friction coefficient determining device and a braking control device using the device.

[0002]

2. Description of the Related Art Conventionally, it has been known that in a braking control device that executes ABS control, control is changed according to a road surface friction coefficient (hereinafter, the friction coefficient is simply expressed as μ). That is, on a high μ road, the wheel cylinder pressure when the wheels are locked or tends to lock at the time of braking is high, and the hydraulic pressure difference from the reservoir side (atmospheric pressure) increases. When the control valve is opened, the brake fluid in the wheel cylinder flows into the reservoir instantaneously by opening the valve for a short time to reduce the pressure. On the other hand, on a low μ road, the wheel cylinder pressure when the wheels are locked or tend to lock during braking is low,
Since the pressure difference with the reservoir is small,
It is necessary to open the hydraulic pressure control valve for a longer time than on the high μ road. Therefore, conventionally, it has been proposed to perform the ABS control by changing the pressure reduction time (pressure reduction amount) according to the difference in the road surface μ.

In order to accurately execute the ABS control for changing the decompression time according to the road surface μ, it is necessary to instantaneously and accurately detect the road surface μ. As a device for detecting (estimating) the road surface μ, a conventional device is disclosed in
No. 59 is publicly known, and this conventional device calculates the sum of the slip ratios of the respective wheels, further integrates a plurality of the sums, and similarly calculates the road surface μ from the relationship with the integrated vehicle acceleration. It is configured to estimate.

[0004]

However, in the above-mentioned prior art, noise is removed by obtaining the sum of the slip ratios of the respective wheels and then integrating the sum, but this integrated number is As the number increases, the phase delay increases and the control accuracy decreases. In order to prevent the phase delay from increasing, it is necessary to reduce the number of integrated signals. In this case, noise as intended cannot be removed. Further, in the prior art, the acceleration of the vehicle body is integrated, but when the acceleration is obtained, the acceleration is obtained by differentiating the vehicle speed by applying a low-pass filter. A phase delay occurs. And
When the road surface μ is estimated based on a value where the above-mentioned phase delay occurs or the noise is not sufficiently removed, and the ABS control is executed based on the estimation result, the execution timing of the increase and decrease of the wheel cylinder pressure and The amount of increase or decrease is different from the optimal value for control, and in such a case, there is a problem that control deficiency such as wheel lock may occur. SUMMARY OF THE INVENTION The present invention has been made in view of the above-described conventional problem, and has as its first object to provide a road surface μ estimating device capable of instantaneously and accurately obtaining a road surface μ without a phase delay. A second object is to provide a braking control device that executes ABS control based on the estimation result of the μ estimation device.

[0005]

As a result of research conducted by the present inventor to achieve the above object, the present inventor has found that the wheel jerk has a very high correlation with the road surface μ. It was decided to. Further, the inventor of the present application
In determining a wheel jerk for estimating a road surface μ, the present invention invents a device in which a phase delay hardly occurs and hardly includes noise, and applies a road surface estimating means to a braking control device which performs ABS control, thereby performing ABS control. This is to improve performance. That is, the road surface friction coefficient estimating device according to claim 1 includes a wheel speed detecting means f for obtaining a wheel speed of each wheel of the vehicle, and a detection value of the wheel speed detecting means f, as shown in the claim correspondence diagram of FIG. Jerk calculating means g for calculating the wheel jerk based on the following formulas. According to the wheel jerk determined by the jerk calculating means g, the larger the jerk, the lower the friction coefficient, and the smaller the jerk, the higher the friction coefficient. And estimating means h for estimating the road surface friction coefficient. According to a second aspect of the present invention, in the road surface friction coefficient estimating apparatus according to the first aspect, the jerk calculating means g represents a change in wheel speed by a quadratic or higher order polynomial which is a function of time,
It is characterized in that the jerk is obtained from the value of the coefficient of the polynomial. According to a third aspect of the present invention, in the road surface friction coefficient estimating apparatus according to the second aspect, the polynomial is a quadratic equation as a function of time, and the jerk calculating means g calculates a coefficient of a square term as The present invention is characterized in that it is configured to be obtained based on the sum of past wheel speeds and the present detected wheel speed. According to a fourth aspect of the present invention, in the road surface friction coefficient estimating apparatus according to the third aspect, the polynomial is represented by y = ax ² + bx + c where y is a wheel speed and x is a time. Based on the least squares method, the coefficient a of the squared term is calculated as a = (＝ x ² y + 4Σxy + 2Σy) /
When the value of the coefficient a is larger than a predetermined first threshold value, the estimating means h estimates that the road has a low friction coefficient, and the value of the coefficient a is equal to the first threshold. When the value is smaller than the value and larger than the second threshold value, the road is estimated to be a medium friction coefficient road, and when the value of the coefficient a is equal to or less than the second threshold value, the road is estimated to be the high friction coefficient road. It is characterized by being.

According to a fifth aspect of the present invention, a master cylinder j
Circuit m for connecting the wheel cylinder k with the master cylinder j; a drain circuit p for releasing the brake fluid of the wheel cylinder k to the reservoir n;
Side, a pressure-reducing state in which the wheel cylinder k is connected to the reservoir n side, and a holding state in which the wheel cylinder k is shut off to both the master cylinder j side and the reservoir n side. And a recirculation circuit r connecting the reservoir n to a position closer to the master cylinder j than the hydraulic pressure control valve q of the brake circuit m, and the recirculation circuit r stores the recirculation circuit r. A pump s for discharging the brake fluid toward the brake circuit m; and a control unit t for controlling the operation of the pump s and the hydraulic pressure control valve q. The control unit t obtains a pressure reduction threshold from the vehicle speed, When the wheel speed drops below the pressure reduction threshold, the hydraulic pressure control valve q is set in a pressure reduction state and the wheel cylinder k
Is released to the reservoir n, and thereafter, when the wheels recover from the locking tendency, the operation of supplying the brake fluid to the wheel cylinder k with the hydraulic pressure control valve q in a pressure-increasing state is repeated, and the pump s is operated to activate the reservoir n. In a brake control device configured to execute ABS control for returning brake fluid in the brake circuit m to the brake circuit m, the control unit t inputs an estimation result by the road surface friction coefficient estimation device according to any one of claims 1 to 4, At the time of the ABS control, the pressure reduction time is corrected so as to increase the pressure reduction time as the road surface friction coefficient decreases.

[0007]

According to the road friction coefficient estimating apparatus of the present invention, the jerk calculating means g determines the jerk of the wheel speed. The wheel jerk corresponds to the slip state between the wheel and the road surface when the acceleration / deceleration of the wheel changes during acceleration or braking, and is correlated with the road surface μ. Since jerk is more sensitive than acceleration, jerk and road μ
Is larger than the correlation between the acceleration and the road surface μ. Therefore, the estimating means h estimates the road surface μ based on the wheel jerk. According to the second aspect of the present invention, when the jerk calculating means g calculates the wheel jerk, the jerk is calculated from the values of the coefficients of the quadratic or higher order polynomial indicating the change in the wheel speed. That is, the jerk is a value obtained by differentiating the wheel speed twice, and the value obtained by differentiating twice is correlated with the coefficient of the quadratic term. Therefore, the jerk can be obtained by obtaining the coefficient of the polynomial representing the change in the wheel speed. That is, when the polynomial is a quadratic expression as in the third aspect of the present invention, the jerk can be obtained by calculating the coefficient of at least the square term. More specifically, assuming that the wheel speed is y and the time is x as in the invention of claim 4, the wheel speed y can be expressed by an equation of y = ax ² + bx + c. To find the coefficient a of the squared term based on the least squares method, a = (＝ x ² y + 4Σxy +
2Σy) / 14. As described above, according to the second to fourth aspects of the present invention, in obtaining the jerk, means for obtaining the differential by a method of generating a phase delay or including noise (for example, the wheel acceleration detected last time and the wheel detected this time) Instead of dividing the acceleration difference by the detection time to determine the jerk), instead of using a means for determining the coefficients of the polynomial, a phase lag is less likely to occur and noise is less likely to be included. The estimating means h estimates the road surface μ in accordance with the wheel jerk (coefficient value) obtained in this way. When the value is larger than the first threshold value, it is estimated that the road is a low μ road, and when the coefficient a is between the first threshold value and the second threshold value, it is estimated that the road is a medium μ road, and the coefficient a is If it is equal to or smaller than the second threshold value, it is estimated that the road is a high μ road. Therefore, the estimation of the road surface μ can be performed with high accuracy.

In the brake control device according to the fifth aspect, the ABS
At the time of control, since the decompression time is corrected based on the estimation result of the road surface friction estimating device according to the first to fourth aspects of the present invention, the ABS control is performed based on the highly accurate estimation of the road surface μ. Can be.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is a configuration diagram showing a main part of the braking control device according to the embodiment, in which 1 is a master cylinder. The master cylinder 1 is configured to generate a hydraulic pressure when a driver operates a brake pedal (not shown).

The master cylinder 1 includes a brake circuit 2
Through the wheel cylinder 3. In addition, a drain circuit 4 for releasing the brake fluid of the wheel cylinder 3 to the reservoir 6 is provided.

In the middle of the brake circuit 2, a pressure increasing state in which the wheel cylinder 3 communicates with the master cylinder 1 side, a pressure reducing state in which the wheel cylinder 3 communicates with the reservoir 6 side, and a state in which the wheel cylinder 3 A switching valve (hydraulic pressure control valve) 5 is provided which can be switched between a holding state in which both the cylinder 1 side and the reservoir 6 side are shut off. Therefore, the hydraulic pressure of the wheel cylinder 3 can be arbitrarily controlled based on the switching of the switching valve 5. The switching valve 5
Is maintained in the illustrated pressure-increasing state by the force of a spring (not shown) when not operating.

The drain circuit 4 and the brake circuit 2
Is connected to a position upstream of the switching valve 5 by a return circuit 8, and a pump 7 for returning the brake fluid stored in the reservoir 6 to the brake circuit 2 is provided in the middle of the return circuit 8. .

In FIG. 2 described above, the configuration in the range surrounded by the dashed line is provided as a brake unit 11 in one unit. Although FIG. 2 illustrates the configuration of one wheel, the overall configuration is as shown in FIG. 3, and the brake unit 11 includes four wheels F
The brake fluid pressure of each of the wheel cylinders 3 (not shown in FIG. 3) of R, FL, RR, RL is configured to be arbitrarily controllable.

The operation of the switching valve 5 of the brake unit 11 and the operation of the pump 7 are controlled by a control unit 12. The control unit 12 is provided with, as input means, wheel speed sensors 13, 13, 13, 13 for detecting rotation speeds of the wheels FR, FL, RR, RL, and a longitudinal acceleration sensor or a brake switch (not shown). And executes ABS control for preventing wheel lock during braking.

Next, the ABS control of this embodiment will be described. FIG. 4 is a flowchart showing a basic flow of the known ABS control. This control is executed when it is detected that a braking operation is performed by a longitudinal acceleration sensor or a brake switch (not shown). , But the control is omitted.

In step S1, a signal is read from each wheel speed sensor 13 to calculate each control wheel speed. The right front wheel control wheel speed is VwFR, the left front wheel control wheel speed is VwFL, the right rear wheel control wheel speed is VwRR, and the left rear wheel control wheel speed is VwR.
L.

In the following step S2, each wheel acceleration / deceleration (hereinafter simply referred to as acceleration) △ Vw is calculated. In addition,
In the present embodiment, the calculation of the acceleration △ Vw is performed in road surface μ estimation control described later.
2, the acceleration ΔVw calculated in the road surface μ estimation control
Just read.

In step S3, a pseudo vehicle speed Vi is determined. In order to obtain the pseudo vehicle speed Vi, first, the larger value (ViF = max (VwFR, VwFL)) of the control wheel speeds VwFR and VwFL of the front left and right wheels is extracted, and then the wheel speeds of the left and right rear wheels are obtained. The larger value (ViR = max (VwRR, VwRR) of (VwRR, VwRL)
RL)) and the larger value of the value (ViF).

In step S4, a pressure reduction threshold value λ1 is calculated for each wheel. The decompression threshold λ1 is, for example, λ1 =
It is determined by the equation of Vi × Kx. Here, K is a constant, for example, a value of about 0.95. Further, x has a value different according to a road surface μ estimation result described later. For example, a value of about 8 is used for high μ road estimation, a value of about 4 is used for low μ road estimation, and an intermediate value is used for medium μ road estimation. Is used.

In step S5, each control wheel speed VwF
It is determined whether or not R, VwFL, VwRR, and VwRL are equal to or smaller than the pressure reduction threshold λ1, and if the pressure is equal to or smaller than the pressure reduction threshold λ1, the process proceeds to step S8, and if it is larger than the pressure reduction threshold λ1, the process proceeds to step S6.

In step S6, the acceleration of each wheel ΔVw
Is determined to be less than a positive predetermined value B, and if it is less than the predetermined value B, it is determined that the wheels are in a state equal to the pseudo vehicle speed, and the process proceeds to step S7 to increase the pressure, that is, the switching valve A process is performed to set 5 to a pressure increasing state. On the other hand, if the acceleration ΔVw is equal to or greater than the predetermined value B, it is determined that the wheel speed is about to return to the pseudo vehicle body speed, and the process proceeds to step S10 to perform a holding process, that is, a process of switching the switching valve 5 to the holding state. .

In step S8, it is determined whether or not the acceleration △ Vw of each wheel is less than a predetermined negative value A including 0. If the acceleration 所 定 Vw is less than the predetermined value A, the wheel is in the locking direction. Then, the process proceeds to step S9 to perform a pressure reducing process, that is, a process of setting the switching valve 5 to a reduced pressure state. On the other hand, if the value is equal to or more than the predetermined value A, the wheel is determined to be in the unlocking direction and the process proceeds to step S10. Performs the holding process. In the present embodiment, when performing the decompression process in step S9, the decompression time is changed according to the road surface μ. That is, the road surface μ estimation control is executed in parallel with the ABS control shown by the flowchart in FIG. 4, the road surface μ flag FRM is set according to the estimation result in the road surface μ control, and according to the road surface μ flag FRM, On the basis of the estimation of the medium μ road, the decompression time is made longer when estimating the low μ road than when estimating the middle μ road, while the decompression time is made shorter when estimating the high μ road than when estimating the middle μ road.

Therefore, the road surface μ estimation control according to the present embodiment will be described with reference to the flowchart of FIG. In step S101, the current value of the wheel speed Vw and the previous four values are summed up for each wheel, and the values are summed. That is, SY = Vw + Vw_1 + Vw_2 + Vw
_3 + Vw_4 is calculated. Incidentally, Vw indicates the current wheel speed, Vw_1 indicates the wheel speed one time before, Vw_2 indicates the wheel speed two times before, Vw_3 indicates the wheel speed three times before, and Vw_4 indicates the wheel speed four times before. One example is shown in FIG. At this time, the wheel speed Vw may be traced back to a value of three or more times in the past, and is not limited to the above four times.

In step S102, SXY =-(Vw
_1 + 2 * Vw_2 + 3 * Vw_3 + 4 * Vw_4).

In step S103, SX2Y = Vw_
The calculation of 1 + 4 * Vw_2 + 9 * Vw_3 + 16 * Vw_4 is performed.

In step S104, A = (SX2Y + 4 * SXY +) based on the values obtained in the above steps.
2 * SY) / 14.

That is, steps S101 to S104
Is to calculate the equation of a quadratic curve approximating the wheel speed change shown in FIG. Explaining this, the wheel speed in the L section of FIG. 6 can be represented by the following polynomial (1).

Y = ax ² + bx + c (1) Then, the least squares method is used to add the error e term to the above equation (1), and to minimize the square error at all sample points of the following equation (2), a, b, c Find each coefficient.

[0029] ^{_{Σe n 2 = Σ {y n}} - (ax n 2 + bx n + c)} 2 ... (3) (3) formula at a, b, and 0 to partial derivatives with partially differentiated respectively c, A, b, and c can be obtained by the following Expression 4.

[0030]

(Equation 4) In the present embodiment, when N = 5 and the sampling time is 1, a, b, and c are represented by the following (5-
1) It can be represented by the formulas (5-2) and (5-3).

A = (Σx ² y + 4Σxy + 2Σy) / 14 (5-1) b = (20Σx ² y + 87Σxy + 54Σy) / 70 (5-2) c = (5Σx ² y + 27Σxy + 31Σy) / 35 (5-3) The above equation (1) represents a change in the wheel speed, and the acceleration and jerk are represented by the following equations (6) and (7), respectively.

(Dy / dx) = 2ax + b (6) (d ² y / dx ² ) = 2a (7) As described above, the present inventor has determined that jerk corresponds to road surface μ more than acceleration. I found that. And
As shown in the above equation (7), the coefficient a represents jerk. Therefore, in the present embodiment, the jerk is obtained by calculating the coefficient a without performing differentiation (without using a low-pass filter).
Step S104 of this flowchart is performed in the above (5-
The coefficient a of the quadratic term in the above equation (1) is obtained by the equation (1). Then, steps S101 to S103 are performed to calculate the integrated values Σx ² y, Σxy, Σy necessary to obtain the coefficient a.
Is what you want.

In step S105, B = (20 * SX)
2Y + 87 * SXY + 54 * SY) / 70 is executed. This is to obtain the coefficient b of the first order term of the above equation (1) by the above equation (5-2). The value “B” of the coefficient b is the wheel acceleration ΔVw itself, and this value is read in step S2 in FIG. 4 described above. Note that the wheel acceleration △ Vw can be obtained by a differential calculation of (Vw ₀ −Vw ₋₁ ) / T. However, since noise becomes large in the differential calculation, the wheel acceleration ΔVw is secondarily obtained in obtaining the jerk. Noise can be reduced by using the coefficient b (used for the ABS control in FIG. 4).

In step S106, it is determined whether or not the value of A is greater than a first threshold value M1, and if A> M1, it is estimated that the road is a low μ road, and the flow advances to step S108 to set a road surface μ flag FRM. The value is set to “2”, which is a value representing a low μ road, while if A ≦ M1, the process proceeds to step S107.

In step S107, the value of A is
It is determined whether or not it is larger than a threshold value M2, and M1 ≧ A>
If M2, the road is estimated to be a medium μ road, and the process proceeds to step S109 to set the road surface μ flag FRM to “1”, which is a value indicating the medium μ road. Proceeding to S110, the road surface μ flag FRM is set to “0” which is a value indicating a high μ road.

The first and second threshold values M1 and M2 are
It is configured to change according to the vehicle speed. FIG.
7 shows the change in the value of “A” according to the vehicle speed for each road surface μ, and sets the threshold values M1 and M2 to “A” for each road surface μ in FIG.
Is set between the three lines shown in the change in the value of
When estimating the road surface μ in 06 and S107,
Referring to a map as shown in FIG.
1, M2.

In steps S111 to S114, the wheel speeds Vwn are sequentially fed one by one and stored for the next calculation.

FIG. 8 shows a high μ value when the vehicle is running at 80 km / h.
7 is a time chart showing a change of “A” (coefficient a) during an ABS operation on a road and a low μ road, where FIG. 7A shows a case of a high μ road, and FIG. Is shown. As shown in the figure, it can be seen that the value of the jerk in the negative direction tends to be larger on the low μ road.

In the present embodiment described above, the wheel speed V
The jerk of the wheel speed Vw is obtained by calculating the value “A” of the coefficient a of the polynomial representing the change in the wheel speed from the past value and the present value of w, and the road surface μ is estimated based on the jerk. , The road surface μ can be estimated with higher accuracy than the estimation of the road surface μ by the wheel acceleration, and the jerk is more affected by the phase lag and the noise than that obtained by differentiation. Therefore, it is possible to obtain an effect that the road surface μ can be estimated with high accuracy. The accuracy of the ABS control can be improved by executing the ABS control according to the road surface μ estimation result based on the jerk obtained without the influence of the phase delay and the noise as described above. However, the present invention is not limited to this embodiment. For example, in the embodiment, the road surface friction coefficient estimating device is applied to the braking control device. The present invention can also be applied to a braking control device that executes a control for generating a braking force to prevent idling, or a control device that controls the driving force of a prime mover to prevent such idling.
Further, in the embodiment, the hydraulic pressure control valve is constituted by one three-position switching valve. However, a two-position switching inflow valve for connecting or disconnecting the wheel cylinder and the master cylinder, and a wheel It may be constituted by a two-position switching outflow valve that connects or disconnects the cylinder and the reservoir.

[0040]

According to a first aspect of the present invention, there is provided a road friction coefficient estimating apparatus, wherein jerk calculating means obtains a wheel jerk having a greater correlation with a road friction coefficient than wheel acceleration, and the estimating means calculates a wheel jerk based on the wheel jerk. Since the configuration is such that the road surface friction coefficient is estimated, the accuracy of estimating the road surface friction coefficient can be improved. The road friction coefficient estimating device according to claim 2 is configured such that, when the jerk calculating means obtains the wheel jerk, the jerk is obtained from a value of a quadratic or higher-order polynomial coefficient indicating a change in wheel speed.
Compared with the case where the wheel jerk is obtained by differentiating the wheel speed twice, there is an effect that the phase delay is less likely to occur and the influence of the noise is less, and the estimation accuracy of the road surface friction coefficient can be improved. In the road surface friction coefficient estimating device according to the third or fourth aspect, the wheel jerk is obtained by obtaining the coefficient of the square term using a polynomial as a quadratic expression. In addition, the present invention is excellent in terms of noise influence and can improve the estimation accuracy of the road surface friction coefficient.

In the brake control device according to the fifth aspect, the ABS
At the time of control, the pressure reduction time is corrected based on the estimation result of the road surface friction estimating apparatus according to the above-described invention. Therefore, ABS control is performed based on highly accurate road surface μ estimation. As a result, the execution timing and the amount of increase / decrease of the wheel cylinder pressure can be made closer to the optimum than before, and the effect that the ABS control performance can be improved can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram corresponding to claims showing a road surface friction coefficient estimating device and a braking control device of the present invention.

FIG. 2 is a brake circuit diagram of the brake control device according to the embodiment;

FIG. 3 is an overall view of an embodiment.

FIG. 4 is a flowchart of ABS control according to the embodiment.

FIG. 5 is a flowchart for estimating a road surface friction coefficient according to the embodiment;

FIG. 6 is an explanatory diagram of road surface friction coefficient estimation according to the embodiment.

FIG. 7 is a diagram showing a road surface friction coefficient and a relationship between the coefficient and a vehicle speed.

FIG. 8 is a time chart showing an operation example of the embodiment.

[Explanation of symbols]

 f Wheel speed detecting means g jerk calculating means h estimating means j master cylinder k wheel cylinder m brake circuit n reservoir p drain circuit q hydraulic pressure control valve r return circuit s pump t control unit 1 master cylinder 2 brake circuit 3 wheel cylinder 4 Drain circuit 5 Switching valve (hydraulic pressure control valve) 6 Reservoir 7 Pump 8 Recirculation circuit 11 Brake unit 12 Control unit

Claims (5)

[Claims] 1. A wheel speed detecting means for obtaining a wheel speed of each wheel of a vehicle; a jerk calculating means for obtaining a wheel jerk based on a detection value of the wheel speed detecting means; According to the wheel jerk,
A road friction coefficient estimating device, comprising: estimating means for estimating a low friction coefficient for a larger jerk and a high friction coefficient and a road friction coefficient for a smaller jerk. 2. A method according to claim 1, wherein said jerk calculating means expresses the change in wheel speed by a quadratic or higher order polynomial which is a function of time, and obtains jerk by a coefficient value of said polynomial. The road surface friction coefficient estimating device according to claim 1, wherein 3. The polynomial is a quadratic equation as a function of time, and the jerk calculating means calculates a coefficient of a square term based on a sum of past wheel speeds and a current detected wheel speed. The road surface friction coefficient estimating apparatus according to claim 2, wherein the apparatus is configured to obtain the coefficient. 4. The polynomial expression is represented by y = ax ² + bx + c, where y is a wheel speed and x is a time, and the jerk calculating means calculates a coefficient a of a squared term as a = ( {X2y + 4 @ xy + ² @ y) / 1
4, the estimating means estimates the low friction coefficient path when the value of the coefficient a is larger than a predetermined first threshold value, and sets the coefficient a to the first threshold value. When the value is smaller than the second threshold value, the road is estimated to be a medium friction coefficient road, and when the value of the coefficient a is equal to or less than the second threshold value, the road is estimated to be a high friction coefficient road. The road surface friction coefficient estimating apparatus according to claim 3, wherein: 5. A brake circuit for connecting a master cylinder and a wheel cylinder, a drain circuit for releasing brake fluid of the wheel cylinder to a reservoir, a pressure-increasing state in which the wheel cylinder is connected to a master cylinder, and a wheel cylinder. A hydraulic pressure control valve capable of forming a pressure-reduced state in which the wheel cylinder is connected to the reservoir side and a holding state in which the wheel cylinder is shut off to both the master cylinder side and the reservoir side; and a hydraulic pressure control valve for the reservoir and the brake circuit. Recirculation circuit connecting the position to the master cylinder side, a pump for discharging the brake fluid stored in the reservoir toward the brake circuit via the recirculation circuit, and a control for controlling the operation of the pump and the hydraulic pressure control valve A control unit that determines a decompression threshold from the vehicle speed, If the value falls below the value, the hydraulic pressure control valve is set to the depressurized state, and the brake fluid of the wheel cylinder is released to the reservoir. Thereafter, when the wheels recover from the locking tendency, the hydraulic pressure control valve is set to the increased pressure state to supply the brake fluid to the wheel cylinder. ABS that repeats the operation and activates the pump to return the brake fluid in the reservoir to the brake circuit
In a braking control device configured to execute control, the control unit inputs an estimation result by the road surface friction coefficient estimating device according to any one of claims 1 to 4, and performs a pressure reduction time and a road surface friction coefficient during the ABS control. A braking control device configured to perform a decompression time correction that is longer as the pressure is smaller.