JP2002264790A - Antiskid controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an erroneous estimate of a road surface μ estimate on a wet road and improve estimate accuracy of a road surface μ. SOLUTION: In this antiskid controller constituted such that antiskid control is changed by a low friction coefficient road surface and a non-low friction coefficient road surface in accordance with the results of estimate by a road surface friction coefficient estimate means when a control unit 12 performs antiskid control, the road surface friction coefficient estimate means cancels low friction coefficient road surface judgement and performs return acceleration judgement for judging that a road surface is the non-low friction coefficient road surface if wheel acceleration exceeds μ judgement acceleration set in advance based on wheel acceleration after determining that the road surface is the low friction coefficient road surface based on pressure reduction time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an anti-skid control device for performing so-called anti-skid control for controlling brake fluid pressure in order to prevent wheels from locking during braking.

[0002]

2. Description of the Related Art An anti-skid control device controls a wheel cylinder pressure (braking fluid pressure) so as to prevent wheel lock during braking and to stabilize vehicle body behavior. Such an anti-skid control device generally includes a pressure increase control for increasing the brake fluid pressure, a pressure reduction control for decreasing the brake fluid pressure, and a brake fluid pressure in accordance with the relative relationship between the vehicle speed and the wheel speed (so-called slip ratio). It is configured to appropriately execute a holding control for keeping the pressure constant, a gradual pressure increase control for gradually increasing the brake fluid pressure, and the like.

In a conventional anti-skid control device, a road surface friction coefficient (hereinafter, referred to as friction coefficient μ) is estimated, and control for high μ control and low μ control is performed according to the road surface μ. What switches is known. In other words, on a low μ road (an ice road or a snow-covered road), since the locking tendency becomes strong even when the braking pressure is low, the control for the low μ road is executed and the pressure reduction amount is increased as compared with the control for the high μ road. The amount of pressure increase was reduced. When the control for the low μ road is executed, a predetermined time (for example, about several seconds to one second) is determined for a predetermined time (for example, about several seconds to one second) after it is determined that the road is a low μ road in order to prevent occurrence of control hunting. It was configured to execute control for a low μ road. As means for estimating the road surface μ, there is known a means for judging a low μ when the vehicle deceleration is equal to or less than a predetermined value based on the vehicle deceleration during braking using an acceleration sensor. However, since the acceleration sensor is expensive, an inexpensive conventional technique for estimating without using the acceleration sensor is also known.

As such a prior art, there is known a means for judging a low μ when the decompression time exceeds a predetermined time based on the decompression time during anti-skid control. That is, when the road surface μ is high, the friction coefficient between the wheel and the road surface is high, so that when the brake fluid pressure is reduced, the speed of the wheel is relatively quickly recovered (increased), and the pressure reduction which is a determination threshold for executing the pressure reduction is performed. Exceeds threshold. On the other hand, when the road surface μ is low,
Since the coefficient of friction between the wheels and the road surface is low, the recovery of the wheel speed is slow even if the brake fluid pressure is reduced, and it takes time for the wheel speed to recover until the wheel speed exceeds the pressure reduction threshold, during which time the pressure reduction control continues to be executed Will be. As described above, since the decompression time is relatively long on the low μ road, it is possible to estimate whether or not the road is the low μ road by monitoring the decompression time.

[0005]

In the prior art for estimating the road surface μ based on the decompression time without using the acceleration sensor described above, in the case of heavy rainfall or a wet road surface such as a road surface with a puddle, (Hereinafter referred to as a wet road)), there is a possibility that the following problems may occur. When traveling on a wet road, the wheels may float on the water. Therefore, when the wheels float on the water during the execution of the anti-skid control, the slip amount of the wheels may temporarily increase (this is expressed as a deeper slip amount). is there. When the slip amount is deepened in this way, the decompression time is lengthened similarly to the low μ road described above. When the decompression time becomes long in this way, the road surface μ determining means estimates that the μ is low, and the anti-skid control means performs the control for the low μ road for a predetermined time despite the non-low μ road (wet road). For example, there is a possibility that the control according to the road surface μ may not be performed.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and has as its object to prevent erroneous estimation of the road surface μ on a wet road or the like and improve the estimation accuracy of the road surface μ.

[0007]

In order to achieve the above object, the invention according to claim 1 comprises a wheel speed detecting means for detecting a wheel speed, a vehicle speed detecting means for detecting a vehicle speed, and A brake fluid pressure adjusting means capable of reducing and increasing the brake fluid pressure of the wheels, a vehicle speed and a wheel speed are compared to determine the slip state of the wheels, and the brake fluid pressure adjusting means reduces and increases the brake fluid pressure as necessary. Anti-skid control means for performing anti-skid control for performing braking while pressing to prevent locking of the wheels; and a μ provided in the anti-skid control means, wherein a decompression time is set in advance based on a decompression time by the anti-skid control. Road friction coefficient estimating means for estimating a low friction coefficient road surface when the determined pressure reduction value is exceeded, and estimating a non-low friction coefficient road surface when the μ determination pressure reduction value is not exceeded, The anti-skid control device is configured to change the control between the low-friction-coefficient road surface and the non-low-friction-coefficient road surface according to an estimation result by the road surface friction coefficient estimation device when performing the anti-skid control, The road surface friction coefficient estimating means determines the low friction coefficient road surface based on the wheel acceleration, and then determines the low friction coefficient road surface if the wheel acceleration exceeds a predetermined μ determination acceleration based on the wheel acceleration. A means for determining a return acceleration for canceling and determining a non-low friction coefficient road surface is provided. Anti-skid control device.

[0008] The invention described in claim 2 is the first invention.
In the anti-skid control device described in the above, the anti-skid control means has a decompression threshold setting means for setting a predetermined decompression threshold lower than the vehicle speed, when determining the wheel slip state, when the wheel speed is reduced When the vehicle speed falls below the threshold value, the pressure reduction control is performed assuming that there is excessive slip, and the road surface friction coefficient estimating means calculates a time period from when the wheel speed falls below the pressure reduction threshold value to when the wheel speed recovers to a predetermined slip state. Based on a certain slip time,
The present invention is characterized in that there is provided a μ judgment acceleration setting means for using a larger value as the μ judgment acceleration as the slip time becomes longer.

[0009] The invention described in claim 3 is the first invention.
In the anti-skid control device described in the above, the road surface friction coefficient estimating means cancels at least the determination of the return acceleration when the wheel lock occurs, and the wheel speed has returned to the vehicle body speed after the pressure reduction in the previous control cycle. The time differential value of the spin-up vehicle speed, which is the vehicle speed at the time of departure from the vehicle speed at the time or after returning, and the spin-up vehicle speed in the current control cycle are obtained, and this time differential value is set to a predetermined μ judgment differential. If the value is less than the value, it is determined that the road surface has a low friction coefficient.
When the differential value exceeds the μ judgment differential value, a vehicle body deceleration judgment for judging that the road surface has a non-low friction coefficient is executed.

[0010] The invention described in claim 4 is the first invention.
4. The anti-skid control device according to any one of Items 3 to 3, wherein the reduced pressure value for μ determination is a value within a range of 30 msec to 200 msec. According to a fifth aspect of the present invention, in the anti-skid control device of the first to fourth aspects, the μ judgment acceleration is 3 g to 15 g.
Is a value in the range of According to a sixth aspect of the present invention, in the anti-skid control device according to the first to fifth aspects, the μ judgment acceleration setting means is means for setting the μ judgment acceleration with reference to a map. And According to a seventh aspect of the present invention, in the anti-skid control device according to the first to sixth aspects,
The μ judgment differential value is a value in a range of 0.3 g to 0.6 g.

[0011]

According to the present invention, in an anti-skid control device for determining a road surface μ based on a depressurization time, when braking is performed on a wet road that is not a low μ road, the wheel If the vehicle temporarily floats on the water and a slip condition occurs, the slip condition will be deep, that is, the wheel speed will greatly decrease from the vehicle speed, and when the wheel speed is reduced based on the anti-skid control, the wheel speed will increase. Speed may not be easily restored, and the decompression time may be long.
If the pressure reduction time exceeds the μ determination pressure reduction value, the road surface μ estimating means determines that the road is a low μ road surface even though the road is not a low μ road but a wet road. However, when traveling on such a non-low μ road surface, the return acceleration at which the wheel speed returns to the vehicle body speed when the pressure reduction by the above-described anti-skid control is performed is the return acceleration when traveling on the low μ road. This is a higher value than. Therefore, in the present invention, the road surface μ estimating means:
The return acceleration determination is executed, and when the return acceleration exceeds the μ determination acceleration, the determination of the low μ road surface is canceled and the non-low μ road surface is determined. As described above, the present invention can prevent the erroneous determination on the wet road caused by the road surface μ estimation based only on the decompression time, improve the accuracy of the road surface μ estimation, and control the low μ road based on the erroneous estimation Is executed, and control accuracy can be improved. On the low μ road, when the decompression time becomes longer, the wheel cylinder pressure becomes lower, the brake torque decreases, and the wheel return acceleration may show a large value. Therefore, if the road surface μ is to be estimated only by the return acceleration, an erroneous determination may be made on a low μ road. On the other hand, in the present invention, first, the road surface μ is estimated based on the decompression time, and then, based on the return acceleration of the wheels, the risk of the erroneous μ estimation on a wet road as described above is removed. Therefore, erroneous determination on the low μ road can be prevented, and high estimation accuracy can be obtained.

Next, in the inventions according to the second to seventh aspects, the μ judgment acceleration setting means changes the μ judgment acceleration used for the above-mentioned return acceleration judgment according to the wheel slip state. That is, the value of the wheel return acceleration increases as the wheel slip state increases. Therefore, even on a low μ road, the deeper the slip condition, the greater the wheel return acceleration becomes.Therefore, when a constant value is used as the μ determination acceleration, even if the return acceleration becomes large on the low μ road as described above, It is necessary to set a value that does not exceed the value. In this case, it is difficult to set a high balance with the determination accuracy on the non-low μ road. On the other hand, in the present invention, the μ determination acceleration setting means sets the wheel speed to be lower than the pressure reduction threshold value and causes excessive slip, and thereafter returns to, for example, the pseudo vehicle speed and eliminates the slip state. Based on the slip time, which is the time required to recover to a predetermined slip state, the longer the slip time, the larger the value of the μ judgment acceleration is used, and the μ judgment acceleration is made variable. Therefore, on a low μ road, it is possible to prevent an erroneous determination due to an increase in the wheel return acceleration after the slip is deepened, thereby obtaining an effect of obtaining a high road surface μ estimation accuracy.

Further, according to the present invention, if the wheels are locked during braking on a wet road, at least the determination of the return acceleration is canceled.
In other words, when the wheel is locked, the return acceleration of the wheel may increase even on a low μ road, and there is a possibility that the road surface μ determination based on the return acceleration cannot be performed with high accuracy. In this case, in the present invention, the spin-up speed, which is the vehicle speed at the time when the wheel speed returns to the vehicle speed due to the pressure reduction in the previous control cycle or when the wheel speed departs from the vehicle speed after the return, is the same as that in the current control cycle. Find the time derivative with the spin-up speed. This time differential value corresponds to the deceleration of the vehicle. If the time differential value falls below the μ judgment differential value, it is determined that the road is a low μ road, and if the time derivative value exceeds the μ determination differential value, the road is a non-low μ road. As described above, when the wheel lock occurs, the determination of the return acceleration is canceled, and the road surface μ is estimated based on the vehicle body deceleration, which is a change in the vehicle body speed when the wheel speed and the vehicle body speed substantially match. By increasing the wheel return acceleration after the wheel lock occurs, it is possible to prevent erroneous determination as a non-low μ road even though it is a low μ road, and to increase the road surface μ.
The effect that the estimation accuracy can be obtained is obtained.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. It is assumed that the anti-skid control device according to the embodiment is mounted on a two-wheel drive vehicle.

First, an anti-skid control device according to an embodiment will be described. FIG. 2 shows a hydraulic circuit of a brake device to which the anti-skid control device according to the embodiment is applied. In the drawing, reference numeral 1 denotes 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 pipe 2
And is connected to the wheel cylinder 3 via. In the middle of the brake pipe 2, the upstream (master cylinder 1 side) and downstream (wheel cylinder 3
Side), a pressure reduction state in which the brake fluid of the wheel cylinder 3 is released to the drain circuit 4, and a holding state in which the brake pipe 2 is shut off to maintain the brake fluid pressure of the wheel cylinder 3. A control valve 5 is provided as a suitable braking fluid pressure adjusting means. That is, the brake fluid pressure in the wheel cylinder 3 can be arbitrarily controlled based on the switching of the control valve 5. The control valve 5
May be constituted by two solenoid valves, a pressure increasing valve for switching the brake pipe 2 between a communicating state and a shut-off state, and a pressure reducing valve for switching the drain circuit 4 between a communicating state and a shut-off state.

The drain circuit 4 is provided with a reservoir 6 capable of storing brake fluid. A recirculation circuit 8 is provided for connecting the reservoir 6 to a position upstream of the control valve 5 of the brake pipe 2, and the recirculation circuit 8 supplies the brake fluid stored in the reservoir 6 to the brake pipe 2. Is provided with a pump 7 for reflux.

In FIG. 2 described above, the configuration of the area surrounded by the dashed line is combined as one brake unit 11. Although FIG. 2 illustrates the configuration of one wheel, the overall configuration is as shown in FIG. 1, and the brake unit 11 includes four wheels FR, FL, R
The brake fluid pressure of each of the R and RL wheel cylinders 3 (not shown in FIG. 1) can be controlled.

The operation of the control valve 5 and the pump 7 of the brake unit 11 is controlled by a control unit 12. The control unit 12 corresponds to the anti-skid control means in the claims.
As input means, there are provided wheel speed sensors 13, 13, 13, 13 for detecting rotation speeds of the wheels FR, FL, RR, RL as wheel speed detecting means in the claims. The wheel speed sensor 13 has a well-known configuration in which the pulse of the output signal changes according to the rotation speed of the wheel. Further, in the present embodiment, an expensive longitudinal acceleration sensor is not provided as a detecting means.

Next, the anti-skid control of this embodiment will be described. FIG. 3 shows the overall flow of the anti-skid control for controlling the brake fluid pressure for each wheel in order to prevent the wheels from locking during braking. It corresponds to a means.

The brake control is performed at a cycle of 10 msec. First, at step 101, a sensor frequency is obtained from the number and the cycle of the sensor pulses of each wheel speed sensor 13 generated every 10 msec, and the wheel speed Vw and the wheel acceleration are obtained. Calculate ΔVw. In step 102, a pseudo vehicle body speed VI is calculated based on the wheel speed Vw. The part for performing the processing for obtaining the pseudo vehicle body speed VI corresponds to the vehicle body speed detecting means in the claims, and the details of the calculation will be described later. In step 103, the vehicle body deceleration VIK is calculated based on the change rate of the pseudo vehicle speed VI. The details of this calculation will be described later. In step 104, calculation is performed to obtain a pressure reduction threshold value λ, which is a threshold value for determining the start of pressure reduction control. The part for calculating the pressure reduction threshold value λ corresponds to the pressure reduction threshold value setting means in the claims, and the details of the calculation will be described later.

In step 105, it is determined whether or not the wheel speed Vw is lower than the pressure reduction threshold value λ. If the wheel speed Vw is lower than the pressure reduction threshold value λ, it is determined that the wheel slip ratio indicates a lock tendency and steps 106 to 108 are performed. Thus, the pressure reduction control is executed. That is, in step 106, the anti-skid timer AS is set to 150. Next step 10
At 7, it is determined whether or not the wheel acceleration △ Vw is greater than a predetermined value of 0.8 g, and NO, that is, △ Vw ≧ 0.8 g
In step 108, the routine proceeds to step 108, where the control valve 5 is switched to a reduced pressure state to execute a pressure reduction control for reducing the wheel cylinder pressure.

If NO in step 105 (if Vw ≧ λ), the routine proceeds to step 109, where it is determined whether or not the wheel acceleration ΔVw is less than a preset normal holding threshold. That is, when the wheel speed Vw is larger than the normal holding threshold value, it is determined that the wheel speed Vw has returned to step 110, and the pressure increase control (switching of the control valve 5 to the pressure increase state) is performed. Lock flag LOCKF indicating lock
= 0. On the other hand, if the wheel acceleration ΔVw is smaller than the normal holding threshold in step 109, the process proceeds to step 111 to perform holding control (switch the control valve 5 to the holding state). Steps 108, 116, 11
After executing the control of No. 1, the process proceeds to step 112, where 1
It is determined whether 0 ms has elapsed. If 10 ms has elapsed, the process proceeds to step 113, where the anti-skid timer A
After subtracting S by 1 (decrement), step 11
In step 4, it is determined whether or not the anti-skid timer AS is equal to or less than 0. If AS ≦ 0, AS = 0 in step 115, and the process returns to step 101. Therefore,
The anti-skid timer AS is reset to 0 until the first pressure reduction control of the anti-skid control is performed. Thereafter, each time the pressure reduction control is executed, the ABS timer AS is set to 150 and once. Every time the control flow is executed, the count is reduced from 150, and when the anti-skid timer AS becomes 0 or less, AS = 0.

Next, details of an example of the pseudo vehicle speed calculation in step 102 will be described with reference to the flowchart of FIG. First, in step 201, the highest wheel speed among the four wheel speeds is determined as the control wheel speed VFS.
And Next, in step 202, it is determined whether or not the anti-skid timer AS = 0, that is, before or after the first pressure reduction is performed. 0, that is, after decompression, the process proceeds to step 204. In step 203, the control wheel speed VFS is set to the maximum value of the driven wheel speed Vw, and the low μ flag LoμF indicating the low μ road is reset to 0.

In step 204, it is determined whether or not the pseudo vehicle speed VI is equal to or higher than the control wheel speed VFS, that is, whether or not the wheel speed has returned to the vehicle speed after the pressure reduction.
If VI ≧ VFS, the process proceeds to step 205, where VI = VFS
The pseudo vehicle speed VI is calculated based on the formula VI- (VIK + 0.3 g) × k. In addition, as k, for example, (0.
353 km / h) / g, but this value is arbitrary. On the other hand, in step 204, NO, that is, VI
In the case of <VFS, the pseudo vehicle speed VI is calculated by the processing of steps 206 to 209. That is, step 2
In step 06, a constant x used in a formula for calculating the pseudo vehicle speed VI in step 209 described later is set to 2 km / h. In the following step 207, it is determined whether or not the first depressurization is being executed (during anti-skid control) based on whether or not AS = 0.
After resetting the constant x to 0.143 km / h, the routine goes to step 209. If AS ≠ 0, the routine goes to step 209 as it is. In step 209, the pseudo vehicle speed VI is determined by VI = VI-x. That is,
In the present embodiment, the control wheel speed VFS is compared with the pseudo vehicle speed VI, and a return point at which the wheel speed Vw returns to the pseudo vehicle speed VI after the pressure reduction, or thereafter, the wheel speed Vw leaves the pseudo vehicle speed VI again. It is determined whether the vehicle speed exceeds the spin-up vehicle speed Vp which is the pseudo vehicle speed VI at the separation point. If VFS> VI and the vehicle speed exceeds the spin-up vehicle speed Vp, the process proceeds to steps 206 to 209, where VI = VI− In the case where VFS ≦ VI and before the return point or the separation point is reached, the routine proceeds to step 205, where VI = VI− (VIK + 0.3g) × k. The spin-up vehicle speed Vp is equal to the wheel speed Vw.
Is not limited to the vehicle speed VI at the return or departure point returning to the pseudo vehicle speed VI, but may be the pseudo vehicle speed VI near the return or departure point.

Next, an example of the vehicle body deceleration calculation process in step 103 of FIG. 3 will be described with reference to the flowchart of FIG. In step 301, it is determined whether or not the anti-skid timer AS has changed from the state of AS = 0 to the state of AS ≠ 0, that is, whether or not the state of not performing pressure reduction control has changed to the state of executing pressure reduction control. Then, if there is no change, the process directly proceeds to step 303.
If this change has occurred, the routine proceeds to step 302, where the calculation speed V0 used for calculating the vehicle body deceleration VIK is calculated.
= VI and the same calculation time T0 = 0. In step 303, the calculation time T0 and the deceleration calculation time VpT up to the spin-up vehicle speed Vp are incremented by one (1 is added, where 1 is 10 m).
sec). Note that the calculation time T0 is a time measured from the time when the pressure reduction is started.

In step 304, it is determined whether or not the state has reached the spin-up vehicle speed Vp from the state that has reached the spin-up vehicle velocity Vp, by determining whether or not VI <VFS has changed to VI ≧ VFS. If it does not exceed the return point or the point of departure, the process proceeds directly to step 308;
307 is executed. In step 305, VIK
= (V0−VI) / T0, and the vehicle body deceleration VIK
Is calculated. In the subsequent step 306, the current spin-up vehicle speed VpB, which is the current (up to one control cycle before), is set as VpA, which is the previous spin-up vehicle speed.
And the pseudo body speed VI at the current return point or the departure point is changed to the current spin-up body speed V
updated as pB, and the latest vehicle deceleration VIKB
Is calculated by the equation VIKB = (VpA-VpB) / VpT. The latest vehicle deceleration VIKB is used for road surface μ determination when the wheels are locked. Further, step 307
, The deceleration calculation time VpT, a slip time LμT described later, and a high μ flag HμF are reset to 0, respectively. The deceleration calculation time VpT is a time measured from when the spin-up vehicle speed Vp is obtained this time to when the next spin-up vehicle speed Vp is obtained.

In step 308, the slip time LμT
It is determined whether ≠ 0 or the wheel speed Vw has fallen below the pressure reduction threshold λ. If neither LμT ≠ 0 nor Vw <λ, the process directly proceeds to step 310, and any one of LμT ≠ 0 and Vw <λ In the case of, the process proceeds to step 309 to increment the slip time LμT (add 1 only).
Then, the process proceeds to step 310. In step 310,
It is determined whether or not the wheel speed Vw = 0 km / h, that is, whether or not the wheels are completely locked, and Vw ≠ 0 km / h
In the case of h, the process directly proceeds to step 312, and Vw = 0k
In the case of m / h, the process proceeds to step 311 and the lock flag L
After setting OCKF = 1, the process proceeds to step 312.
That is, when the wheels are locked, the lock flag LOCKF
Is set. Here, the wheel speed, which is a criterion for determining wheel lock, is not necessarily limited to 0 km / h, and may be slightly higher than 0 km / h as long as wheel lock can be determined.

The part for performing the processing after step 312 is as follows:
It corresponds to a road surface friction coefficient estimating means in the claims, and performs road surface μ estimation. First, in step 312, it is determined whether or not the lock flag LOCKF = 1 has been set. If LOCKF = 1, the process proceeds to step 313,
314 and 320 are executed. On the other hand, if the lock flag LOCKF ≠ 1 in step 312, that is, if the wheels are not locked,
The road surface μ estimation is performed based on the processing of steps 315 to 319. In the present embodiment, the road surface μ estimation is performed based on whether or not the wheels are locked.

Step 31 to proceed when the wheels are locked
In 3, it is determined whether or not the latest vehicle deceleration VIKB is less than 0.5 μ, which is the μ determination differential value, and VIKB ≧ 0.5 g
, The process proceeds to step 320, where the low μ flag LμF =
Reset to 0, and if VIKB <0.5 g, proceed to step 314 to set the low μ flag Lμ flag LμF = 1. As the μ judgment differential value, 0.5 g is used in the embodiment, but this value is different from the optimum value depending on the vehicle specifications.
It is preferable to select an optimum value from a value within the range of 0.6 g. The part that performs the processing of steps 313, 314, and 320 is the part that executes the vehicle body deceleration determination described in the claims.

On the other hand, if the wheel lock has not occurred, first, at step 315, the pressure reduction counter DECT for counting the time during which the pressure reduction output described later is being performed becomes 100 msec or more, which is the predetermined μ judgment pressure reduction value. If DECT <100 msec, the process directly proceeds to step 417, but DECT ≧ 100 msec
In the case of, the routine proceeds to step 316, where the low μ flag LoμF = 1 indicating that the road is a low μ road surface is set. That is, when the decompression time exceeds the μ judgment decompression value, it is estimated that the road is a low μ road. The μ judgment pressure reduction value is a value for estimating the road surface μ based on the pressure reduction time. For example, the pressure reduction control is performed on a high μ or middle μ road, and the pressure reduction time when the brake fluid pressure becomes 0 mpa is calculated as μ. It can be set as a judgment pressure reduction value. Since the μ judgment pressure reduction value differs depending on the vehicle specifications, it is preferable to set an optimum value for each vehicle type by conducting an experiment, and the value is preferably in a range of, for example, 30 msec to 200 msec.
In step 317, the μ judgment acceleration αmax is obtained with reference to a preset acceleration map, and the part that performs this processing corresponds to the μ judgment acceleration setting means in the claims. As shown in FIG. 9, the acceleration map used here is based on the slip time L.mu.
This map is set so that the value of the μ judgment acceleration αmax becomes larger as μT becomes longer.
The setting range of ax is 3 g to 1 in the illustrated map.
The range is 5 g. In the present embodiment, since it is determined whether or not the road is a low μ road, the μ determination acceleration α is determined based on a value on a characteristic line separating low μ and middle μ in the drawing.
Although max is determined, when it is determined to be low μ / medium μ / high μ, the two characteristic lines in the figure are used. Further, it is possible to increase the estimated types of μ and to set a plurality of characteristic lines of three or more. Further, the routine proceeds to step 318, where it is determined whether or not the wheel return acceleration VWD30 has exceeded the μ determination acceleration αmax. The wheel return acceleration VWD30 is
This is the rate of change of the wheel speed Vw at the latest 30 msec. In this step 318, NO, that is, VWD
If 30 ≦ αmax, the process directly proceeds to step 321. If YES, that is, if VWD> αmax, the low μ flag LμF is reset in step 319.

Further, steps 314 and 31 described above are performed.
8, 319, 320, step 3
The program proceeds to 21 to determine whether or not the anti-skid timer AS is 0. If AS = 0, the program proceeds to step 322, where the vehicle body deceleration VIK is set to 1.3 g. That is, the vehicle body deceleration VIK is set to 1.3 g corresponding to a high μ road until the pressure reduction by the ABS control is executed, and thereafter, a spin-up vehicle speed is generated, and the calculation of the vehicle body deceleration VIK in step 306 is performed. Is calculated, the calculated value is updated.

Therefore, in this embodiment, when the wheels are locked, if VIKB <0.5 g based on the latest vehicle deceleration VIKB, it is determined that the road is a low μ road and the low μ flag LμF = 1 is set. (Step 312 → 313 → 3
14), if VIKB ≧ 0.5 g, it is determined to be high μ. When the wheels are not locked, first, as a first step, the pressure reduction counter DECT is set to μ.
If the determined pressure reduction value is 100 msec or more, the road is determined to be a low μ road, and the low μ flag LμF = 1 is set (steps 315 → 3).
16). Further, even if the low μ flag LμF is set to 1, the wheel return acceleration VWD30 (the wheel return acceleration that is the acceleration at which the wheel speed Vw returns toward the vehicle speed due to the pressure reduction) is determined as μ in the second stage. If it exceeds the judgment acceleration αmax, it is determined that the road is a high μ road, and the low μ flag LμF is reset to 0 (step 4).
17 → 418 → 419).

Next, an example of the pressure reduction threshold value calculation processing in step 104 in FIG. 3 will be described with reference to the flowchart in FIG. First, in step 401, the constant xx is set to 8k
Set to m / h. Next, at step 402, it is determined whether or not the vehicle body deceleration VIK is smaller than a predetermined value 0.4 g, or whether the low μ flag LμF is set to 1, that is, whether or not it is low μ. In the case of YES, it is determined that it is low μ, the constant xx is set again to 4 km / h, and the routine proceeds to step 404. On the other hand, if NO in step 402, that is, if it is determined to be high μ, the constant xx is set to 8 k
The process proceeds to step 404 while keeping m / h. Then, in step 404, the decompression threshold λ is set to λ = VI × 0.
It is obtained by the calculation of 95-xx. Therefore, the pressure reduction threshold λ has a larger value (deeper value) with respect to the pseudo vehicle speed VI on the high μ road than on the low μ road.

Next, an example of the pressure reduction control in step 108 of FIG. 3 will be described in detail with reference to the flowchart of FIG. First, in step 701, a pressure increase counter INCT, which counts during execution of pressure increase output described later, is reset to 0. In step 702, a pressure reduction time GAW, which is a time for performing pressure reduction in the current pressure reduction control, is set to GAW.
= | VWD | 30 × α / VIK. Next, in step 703, it is determined whether or not the low-μ road is determined in the first cycle of the ABS control based on whether or not the vehicle body deceleration VIK is 0.4 g or more and the low-μ flag LμF = 1 is set. If NO, that is, if the low μ road determination is not made in the first cycle, the process proceeds directly to step 705, but YES, ie, VIK ≧ 0.4g and LμF = 1, and the low μ road is determined in the first cycle. If it is determined, the process proceeds to step 704, where the decompression time GAW is set to GAW.
= | Vw30 | × α / 0.1 g, and the routine proceeds to step 705. Incidentally, in the first control cycle, the vehicle body deceleration VIK is equal to the set value (1.3 for the high μ road).
Since g) is used, it is possible to determine that the state is the low μ determination state in the first control cycle by VIK ≧ 0.4g. Further, in the first cycle of the control, since a calculation value based on the change in the wheel speed has not been obtained, the decompression formula for calculating the pressure reduction time GAW is set to 0.
A small value of 1 g is used, and the decompression time GA
W is set to a large value. In the present embodiment,
The vehicle deceleration VIK is 1.3 g in the first cycle of control.
Is set in the vehicle body deceleration VI in step 703 for determining whether or not the cycle is the first cycle.
The value to be compared with K may be a value larger than the illustrated 0.4 g as long as the value is smaller than 1.3 g.
The setting is made according to the vehicle body deceleration VIK used in the first cycle of control.

In step 705, a pressure reduction output for setting the control valve 5 to a pressure reduction state is performed, and a pressure reduction counter DECT.
Is incremented (added by 1). Step 706
Then, it is determined whether or not the pressure reduction counter DECT has become equal to or longer than the pressure reduction time GAW set in step 702 or 704.
That is, it is determined whether or not the pressure reduction output has been performed only for the pressure reduction time GAW.
The decompression counter DECT is decremented (subtracted by 1).

Next, an example of the pressure increase control in step 110 of FIG. 3 will be described in detail with reference to the flowchart of FIG. First, in step 801, the decompression counter DE
CT is reset to 0, and in the following step 802,
A pressure increase time ZAW, which is a time for performing pressure increase in the current pressure increase control, is obtained by ZAW = │VWD30│ × β × VIK. Next, at step 803, the vehicle body deceleration VIK
Is not less than 0.4 g and the low μ flag LμF = 1 is set, it is determined whether or not the low μ road determination is made in the first cycle of the ABS control. If the μ road decision is not made,
Proceed directly to step 805, but YES, ie, VI
If K ≧ 0.4 g and LμF = 1 and it is determined that the road is a low μ road in the first cycle, the routine proceeds to step 804, where the pressure increase time ZAW is set to ZAW = | Vw30 | × β × 0.1 g. The process proceeds to step 805. That is, when the low μ road is determined in the first cycle of the control, the vehicle deceleration VIK corresponding to the actual wheel speed has not been obtained at that time. A small value of 0.1 g for the low μ road is used, so that the pressure increase time ZAW is set to a small value.

In step 805, a pressure-intensifying output for setting the control valve 5 to a pressure-increasing state is performed, and a pressure-increasing counter INCT
Is incremented (added by 1). Step 806
It is determined whether the pressure increase counter INCT has exceeded the pressure increase time ZAW set in step 802 or 804,
That is, it is determined whether or not the pressure increase output has been performed for the pressure increase time ZAW. If INCT ≧ ZAW, the process proceeds to step 807 and the hold output for holding the control valve 5 is performed.
The pressure increase counter INCT is decremented (subtracted by 1).

Next, the operation of the embodiment will be described with reference to time charts shown in FIGS. First, FIG. 10 is a time chart showing an operation example when traveling on a low μ road. In the example of this figure, braking is started at time t1, and at time t2, the wheel speed Vw falls below the pressure reduction threshold λ, and pressure reduction control is started. At this time t2, the anti-skid counter AS becomes 0 to 15
Set to 0. In the example of this figure, the wheels slip deeply due to braking on the low μ road, so that the wheel speed Vw easily returns to the pseudo vehicle body speed VI even though the pressure reduction control is executed for the time t3. do not do. As described above, when the decompression time becomes longer and exceeds the μ judgment decompression value of 100 msec (t4 in FIG. 10).
5), in the present embodiment, the flow of steps 312 → 315 → 316 in the flowchart of FIG. 5 is set, and the low μ flag LμF = 1 is set. In this case, since the slip time LμT, which is the time from when the pressure reduction is started until the wheel speed Vw returns to the pseudo vehicle body speed VI, becomes longer, the μ judgment acceleration αmax is set in step 317 by referring to the map. Where μ
The value of the judgment acceleration αmax increases. Therefore, even if the maximum wheel return acceleration VWD30max of the wheel return acceleration VWD30 is generated as shown in the figure, it does not exceed the μ judgment acceleration αmax, and therefore, the process proceeds from step 318 to step 319 in the flowchart of FIG. And the low μ decision is maintained. That is, the low μ flag LμF = 1 is maintained.

When the low μ flag LμF is set, the steps 703 → 7 in the pressure reduction control shown in FIG.
Based on the flow in step S04, the pressure reduction time GAW is set to be longer than that when the high μ road is determined, and in the pressure increase control shown in FIG. The pressure reduction amount is set shorter than that at the time of determination, whereby the pressure reduction amount is controlled to be larger and the pressure increase amount smaller than that of the high μ road.

Next, a case where the wheels are locked during braking on a wet road (medium μ road) will be described with reference to FIG. As described above, when the wheels float on the water and the wheels are deeply slipped and locked on the wet road, the decompression time becomes long as in the above-described example. In the related art, when the decompression time becomes long, it is estimated that the value is low μ, and the control for the low μ is executed for a predetermined time (for example, about 0.6 to 1 second) from that time. In contrast, in the present embodiment,
When the wheel lock occurs, the flow of steps 312 → 313 → 320 in the flowchart of FIG. 5 is performed, and the road surface μ is estimated based on the latest vehicle body deceleration VIKB obtained based on the illustrated VpA, VpB, and VpT. . In this case, since the vehicle is traveling on a wet road, that is, on a medium μ road, the latest vehicle body deceleration VIKB becomes larger than when traveling on a low μ road, LμF = 0, and it is determined that the vehicle is on a non-low μ road.

If the wheel lock does not occur as shown in FIG.
When the decompression time exceeds 100 msec, the low μ flag is set as shown by the dotted line in the figure, similarly to the example of FIG. However, in this case, the acceleration VWD3 when the wheel speed Vw is restored by executing the pressure reduction control.
The maximum wheel return acceleration VWD30max of 0 exceeds the μ judgment acceleration αmax. Therefore, in the flowchart of FIG. 5, steps 317 → 318 → 3
Step 19 is performed, the low μ flag LμF is reset to 0, and the high μ road control is executed from that point. Therefore, there is no problem that the control for the low μ road is executed while the vehicle is traveling on a wet road. In the case of a wet road, the slip time LμT is shorter than that of a low μ road as shown in the figure. As a result, μ obtained based on the map of FIG.
The judgment acceleration αmax has a smaller value than the case of the low μ road shown in FIG. Therefore, the maximum wheel return acceleration VW
Even if D30max is a relatively small value, the road is determined to be a non-low μ road.

Next, a case where a wheel lock occurs during braking on a low μ road will be described with reference to FIG. When the wheels are locked on a low μ road, the wheel return acceleration VWD30 takes a relatively large value as shown in the figure, even on a low μ road. Therefore, step 315 of FIG.
319, there is a possibility that the road surface μ is determined to be non-low μ in the road surface μ determination based on the wheel return acceleration VWD30. That is, FIG. 13 shows the relationship between the slip time LμT when the wheels are locked on the low μ road and the wheel return acceleration VWD30. As shown in FIG. Since there is a region where the wheel return acceleration VWD30 is common to the case of, an erroneous determination may occur in this region.

Therefore, when the wheel lock occurs in this way, as described in FIG.
13, the road surface μ determination based on the latest vehicle deceleration VIKB, that is, the latest vehicle deceleration VIKB is obtained by dividing the speed difference between the spin-up vehicle speeds VpA and VpB by the elapsed time, and the value is a μ determination differential value. It is determined whether it is low μ or non-low μ compared to 0.5 g. This FIG.
In the example, the latest vehicle deceleration VIKB becomes a relatively low value (the slope of the line connecting the spin-up vehicle speeds VpA and VpB is gentle), and it is determined that the road is a low μ road. That is, after the wheels are locked, the maximum wheel return acceleration VWD30max becomes a relatively large value even on a low μ road, and if the μ determination is performed based on the wheel return acceleration VWD30, there is a risk that the μ will be erroneously determined to be high μ. . Therefore, when the wheels are locked, μ is determined based on the spin-up vehicle speed Vp,
This erroneous determination can be prevented.

As described above, in the present embodiment, the inexpensive means for judging the road surface μ based on the decompression time without using the longitudinal acceleration sensor for estimating the road surface μ is adopted. Even on a non-low μ road such as a wet road, even if the slip state is temporarily deepened and the decompression time becomes longer, the decompression time becomes longer and the low μ
After determining that the wheel return acceleration VWD and the μ determination acceleration αmax have been determined, if the wheel return acceleration VWD exceeds the μ determination acceleration αmax, the determination of a low μ road is canceled. Is determined to be a non-low μ road surface, it is possible to prevent erroneous determination on a wet road caused by the road surface μ estimation based only on the decompression time, improve the accuracy of the road surface μ estimation, and reduce the low- An effect is obtained in that the problem that the μ road control is executed is prevented, and the control accuracy can be improved.
Further, in the present embodiment, the μ judgment acceleration αma
x is set to a larger value as the μ judgment acceleration αmax as the slip time is longer in accordance with the slip time based on the map. Therefore, even when the slip is deeper even on a low μ road, the wheel return acceleration becomes larger. It is possible to prevent the erroneous determination that the road value becomes a large value and determine that the road is a high μ road, and to obtain a high road surface μ estimation accuracy.

In addition, in this embodiment, when a wheel lock occurs during braking, the determination of the road surface μ by the pressure reduction counter DECT and the above-described determination of the return acceleration are canceled, and the spin-up vehicle speed VpA in the previous control cycle is canceled. The latest vehicle deceleration V based on the time derivative of the spin-up vehicle speed VpB in this control cycle
Since the IKB is obtained and the latest vehicle body deceleration VIKB is compared with a predetermined μ judgment differential value of 0.5 g to perform the road surface μ judgment, the wheel return acceleration becomes large after the wheel lock occurs. As a result, it is possible to prevent an erroneous determination as a non-low μ road even though the road is a low μ road, and obtain an effect that a high estimation accuracy can be obtained.

Although the embodiment has been described with reference to the drawings, the present invention is not limited to this embodiment. In the embodiment, the low μ flag LμF is switched between the low μ determination and the non-low μ determination,
Although the control is switched between the low-μ control and the non-low-μ control based on the low-μ flag LμF, the control may be directly switched instead of switching the flag in this manner. In the present embodiment, the slip time L
In determining μT, the wheel speed Vw becomes equal to the pressure reduction threshold value λ.
The count is started from the time when the value falls below the threshold value. However, when the execution of the anti-skid control is started from the holding control, the counting of the slip time LμT may be started from the time when the holding control is started. .

[Brief description of the drawings]

FIG. 1 is an overall view showing an anti-skid control device according to an embodiment.

FIG. 2 is a hydraulic circuit diagram showing a main part of the embodiment.

FIG. 3 is a flowchart showing a flow of anti-skid control in the embodiment.

FIG. 4 is a flowchart showing a flow of calculating a pseudo vehicle body speed in the embodiment.

FIG. 5 is a flowchart showing a flow of a vehicle body deceleration calculation in the embodiment.

FIG. 6 is a flowchart showing a flow of a pressure reduction threshold value calculation process in the embodiment.

FIG. 7 is a flowchart showing a flow of pressure reduction control in the embodiment.

FIG. 8 is a flowchart showing a flow of pressure increase control in the embodiment.

FIG. 9 is a characteristic diagram showing a μ judgment acceleration map in the embodiment.

FIG. 10 is a time chart showing an operation example when traveling on a low μ road in the embodiment.

FIG. 11 is a time chart showing an operation example when a wheel lock occurs during running on a wet road in the embodiment.

FIG. 12 is a time chart showing an operation example when a wheel lock occurs during traveling on a low μ road in the embodiment.

FIG. 13 shows a wheel return acceleration and a road surface μ when a wheel lock occurs.
FIG. 4 is a characteristic diagram showing the relationship of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Master cylinder 2 Brake piping 3 Wheel cylinder 4 Drain circuit 5 Control valve 6 Reservoir 7 Pump 8 Recirculation circuit 11 Brake unit 12 Control unit 13 Wheel speed sensor

Claims (7)

[Claims] 1. A wheel speed detecting means for detecting a wheel speed, a vehicle speed detecting means for detecting a vehicle speed, a brake fluid pressure adjusting means capable of reducing and increasing a brake fluid pressure of each wheel, Anti-skid control means for determining the slip state of the wheel by comparing the wheel speed with the wheel speed and executing anti-skid control for braking while preventing and locking the wheel by reducing and increasing the pressure as required by the brake fluid pressure adjusting means The anti-skid control means is provided to estimate a low friction coefficient road surface when the decompression time exceeds a preset μ judgment pressure reduction value based on the pressure reduction time by the anti-skid control, while the μ judgment pressure reduction value is Road surface friction coefficient estimating means for estimating the road surface as a non-low friction coefficient when the road surface does not exceed the anti-skid control means. An anti-skid control device configured to change control between a low friction coefficient road surface and a non-low friction coefficient road surface according to the estimation result by the coefficient estimation unit, wherein the road surface friction coefficient estimation unit includes a low friction coefficient based on a pressure reduction time. If the wheel acceleration exceeds a predetermined μ judgment acceleration based on the wheel acceleration after judging the road surface, a return acceleration judgment for canceling the low friction coefficient road surface judgment and judging a non-low friction coefficient road surface is performed. An anti-skid control device having a configuration. 2. The anti-skid control means includes pressure reduction threshold value setting means for setting a predetermined pressure reduction threshold value lower than the vehicle speed. When judging a slip state of a wheel, when the wheel speed falls below the pressure reduction threshold value. The road surface frictional coefficient estimating means is configured to execute a pressure reduction control assuming that there is excessive slip, and the road surface friction coefficient estimating means performs a slip time that is a time from when the wheel speed falls below a pressure reduction threshold to when a predetermined slip state is restored. 2. The anti-skid control device according to claim 1, further comprising a μ judgment acceleration setting unit that uses a larger value as the μ judgment acceleration based on a longer slip time. 3. The road surface friction coefficient estimating means cancels at least the determination of the return acceleration when the wheel is locked, and at the time when the wheel speed returns to the vehicle body speed after the pressure reduction in the previous control cycle or after the return. The time differential value of the spin-up vehicle speed, which is the vehicle speed at the time when the vehicle speed departs from the vehicle speed, and the spin-up vehicle speed in the current control cycle is obtained, and the time differential value falls below a preset μ judgment differential value. 2. The vehicle body deceleration determination of determining that the road surface has a low friction coefficient in the case, and conversely determining that the road surface has a non-low friction coefficient when the differential value exceeds the μ determination differential value. Anti-skid control device. 4. The pressure reduction value for μ judgment is 30 msec to 2 msec.
4. The anti-skid control device according to claim 1, wherein the control value is within a range of 00 msec. 5. The anti-skid control device according to claim 1, wherein the μ judgment acceleration has a value in a range of 3 g to 15 g. 6. The anti-skid control device according to claim 1, wherein the μ judgment acceleration setting means is means for setting the μ judgment acceleration with reference to a map. 7. The μ judgment differential value is from 0.3 g to 0.6.
7. A value in the range of g.
3. The anti-skid control device according to claim 1.