JP2903888B2 - Anti-skid braking method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an anti-skid braking method suitably applied to a brake device of an automobile.

[0002]

2. Description of the Related Art (1) Anti-skid brake capable of preventing wheel slip, ensuring steering stability, and stopping a vehicle within a short braking distance during braking on a low μ road such as a running road wet with rainwater. Is known. This braking method detects the rotational speed of each wheel to determine the respective wheel speed, determines the slip rate of each wheel based on the deviation between the wheel speed and the reference vehicle speed, and changes the wheel speed over time, that is, Determines wheel acceleration, and controls the brake pressure of each wheel according to the determined slip rate and wheel acceleration so that the slip rate is maintained near the optimal slip rate at which the friction coefficient of the wheel is maximized. It is.

[0003] The wheel acceleration is controlled by a brake pressure increasing / decreasing control so that the wheels are controlled toward a locked state (locking tendency) or controlled toward a brake releasing state (brake releasing tendency). ) Is used as a control parameter for determining

[0004]

When the vehicle enters a high μ road such as an asphalt road from a low μ road having a small coefficient of friction, the conventional brake fluid pressure increase / decrease control has a slow rise in longitudinal acceleration. However, since it is difficult to accurately detect the entry into the high μ road from the wheel acceleration, there is a problem that the pressure increase immediately after the entry is delayed, and the braking effect is delayed accordingly. Further, in such a case, since the rise of the longitudinal acceleration is slow, the driver feels that the brake does not work, so-called “free running feeling”, which is not preferable.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and when entering from a low μ road to a high μ road,
It is an object of the present invention to provide an anti-skid braking method that detects this approach early to prevent a control delay and improve braking performance.

[0006]

In order to achieve the above-mentioned object, in the present invention, a slip ratio of a wheel is calculated from a deviation between a reference vehicle speed and a wheel speed of a wheel, and a wheel cylinder of each wheel of a brake device is calculated. In the anti-skid braking method of controlling pressure increase / reduction according to at least the calculated slip rate and wheel acceleration, a difference obtained by subtracting a predetermined value from the calculated slip rate every time the slip rate is calculated. When it is determined that there is almost no change in the wheel speed detected from the wheel acceleration, and when it is determined that the state in which the slip ratio is small is continued by the integrated value, the value is supplied to the wheel cylinder. An anti-skid braking method characterized by increasing the hydraulic pressure to be applied is provided.

Preferably, a plurality of fuzzy rules are set by using at least a slip ratio, a wheel acceleration and an integrated value of a slip ratio as input variables and a control value corresponding to a pressure increase / decrease value of a hydraulic pressure supplied to a wheel cylinder as an output. A membership function for determining the degree of conformity of the fuzzy rule is set, and the degree of conformity of each fuzzy rule is calculated according to the input variables of the slip rate, the wheel acceleration and the integrated value of the slip rate, and from the calculated degree of conformity, The control value may be calculated, and the pressure increase / decrease control may be performed.

As a method of obtaining the integrated value of the slip ratio, upper and lower limits are set for the slip ratio, and when the calculated slip ratio is larger than the upper limit, the difference obtained by subtracting the upper limit from the calculated slip ratio is used. If the calculated slip rate is smaller than the lower limit, the integrated value is calculated from the difference obtained by subtracting the lower limit from the calculated slip rate. When it is between, the calculation method of setting the integrated value to 0 is preferable.

[0009]

The integrated value of the slip ratio represents a period in which the hydraulic pressure supplied to the wheel cylinder is controlled out of the preferable control range of the slip ratio, and the integrated value is negative and its absolute value is large. In this case, it means that the state where the slip ratio is small is long and continuous. Therefore, when it is determined that there is almost no change in the wheel speed detected from the wheel acceleration, and when it is determined that the state in which the slip ratio is small is continued based on the integrated value of the slip ratio, the wheel cylinder is supplied. By increasing the hydraulic pressure, control delay is prevented.

[0010]

Embodiments of the present invention will be described below with reference to the accompanying drawings. System Overview Figure 1 is an anti-skid braking system for a vehicle (hereinafter "AB
S ”), the front, rear, left and right wheels 1L, 1L,
A motor direct-acting hydraulic unit (HU) 10 is interposed between each of the R, 2L, and 2R brake devices 3 to 6 and a master cylinder 9 driven by a brake pedal 8, and each wheel 1L, 1R , 2L, 2R, wheel speed sensors 21, 22, 23, 24, the steering wheel 7 has a steering wheel angle sensor 25, and the vehicle body has an acceleration sensor (front and rear G sensor) 26 for detecting longitudinal acceleration. Is provided. The sensors 21 to 26 and the hydraulic unit 10 are connected to the electronic control unit 30.
(ECU). The ABS of the present embodiment
Applies to front-wheel drive vehicles, and the rear wheels are non-drive wheels.

As shown in FIG. 2, the hydraulic unit 10 has a housing 11 having a cylinder 12 formed in a housing 11. A piston 13 is slidably fitted in the cylinder 12. In the upper part of the housing 11, the cylinder 1
2, passages 11 a to 11 c are provided, an ABS check valve 14 is provided between the passages 11 a and 11 c, and a passage 11 b juxtaposed to the check valve 14 is provided.
Is provided with an ABS cut valve 15. The check valve 14 allows the flow of brake fluid from the passage 11c to the passage 11a, and the cut valve 15 opens and closes the passage 11b. When the piston 13 reaches the upper limit position, the check valve 14 is opened against a spring force by a projection 13a provided on the upper end surface of the piston 13.

The housing 11 is provided with a motor 16, and the driving force of the motor 16 is transmitted to the piston 13 via a gear mechanism 17 and a feed mechanism 18 to drive the piston 13. When the motor 16 rotates forward, the feed mechanism 18 is rotated via the gear mechanism 17 to rotate the piston 1.
3 is moved upward, and when the rotation is reversed, the piston 13 is moved downward. The passage 11a of the housing 11 is connected to the master cylinder 9, and the passage 11c is connected to the wheel cylinder 3a of the brake device 3. The hydraulic unit 10 is shown only between the brake device 3 of the front wheel 1L on one side and the master cylinder 9.

The electronic control unit 30 takes in signals from the wheel speed sensors 21 to 24, the steering wheel angle sensor 25, and the front and rear G sensor 26 at the time of braking, and outputs signals from the wheels 1L, 1R,
The slip conditions of 2L and 2R are predicted, the ABS cut valve 15 and the motor 16 are controlled so that these wheels are not locked, and the braking forces of the brake devices 3 to 6 are controlled. That is, when the wheels are in the locking direction, the piston 13 is moved downward, the brake fluid pressure is reduced to avoid wheel lock, and when the risk of wheel lock is avoided, the piston 13 is moved upward to increase the brake fluid pressure. Is increased again, and such control is repeated to control the brake fluid pressure applied to the wheel cylinder. ABS control procedure Next, ABS control executed by the electronic control unit 30 of the ABS is performed.
The BS control procedure will be described.

FIGS. 3 and 4 show functional block diagrams corresponding to the ABS control executed by the electronic control unit 30, which will be described with reference to the flowchart of the ABS main routine shown in FIG. ABS Main Routine First, input signals detected by various sensors are processed by the sensor signal processing means shown in FIG. 3 (step S).
1). The wheel speed signals from the wheel speed sensors 21 to 24 are amplified, waveform processed, sampled,
After the processing such as A / D conversion is completed, the high frequency component is cut by the filter means 31a and output from the sensor signal processing means as the wheel speed FVx of each wheel. The output from the filter means 31 a calculates the wheel acceleration of each wheel by the differentiating circuit 32, and the high-frequency components of these values are cut by the low-pass filter means 33. The correction signal is corrected by the longitudinal acceleration FGS detected by the longitudinal G sensor 26 described later, and output from the sensor signal processing means as the wheel acceleration FGx of each wheel. Here, the suffix "x" when representing the wheel speed FVx and the wheel acceleration FGx (the same applies to the slip ratio Sx of each wheel described later).
Represents each of the right front wheel 1R, the left front wheel 1L, the right rear wheel 2R, and the left rear wheel 2L. When the wheel speeds and the like are indicated with a suffix “x”, the value of each wheel is individually Is calculated.

The detection signal from the longitudinal G sensor 26 is subjected to processing such as amplification, waveform processing and sampling by an input processing means 35 and output as raw data GS of longitudinal acceleration, while high-frequency components are cut by a low-pass filter means 36. Is output as the filtered filter value FGS.
The detection signal from the handle angle sensor 25 is subjected to filtering processing by a low-pass filter means 38 after processing such as amplification, waveform processing, and sampling by an input processing means 37, and is output as a handle angle Fθh.
Further, the steering wheel angle Fθh is time-differentiated by the differentiating circuit 39, and then filtered by the low-pass filter means 40, and is output as the steering speed FDθh.

Next, the wheel speed FVx, the wheel acceleration FGx and the steering wheel angle Fθh, which have been processed as described above, are used.
Is supplied to the reference vehicle speed calculating means 41 shown in FIG. 4, and the reference vehicle speed Vref is calculated (step S2). At this time, at the time of a sharp turn in which the absolute value of the steering wheel angle Fθh is large, the inner wheel difference is corrected, and the reference vehicle speed Vrefo of the outer wheel and the reference vehicle speed Vrefi of the inner wheel are calculated. The vehicle speed on the outer wheel side and the vehicle speed on the inner wheel side differ depending on the inner wheel difference, and the slip ratio of each wheel can be accurately obtained by correcting the inner wheel difference in vehicle speed.

The reference vehicle speed Vref (Vrefo and Vrefi) calculated by the reference vehicle speed calculating means 41 is supplied to the slip ratio calculating means 42, and the wheel speed FVx of each wheel and the reference vehicle speed Vref are used for each wheel. The slip ratio Sx is calculated based on the following equation (S1) (step S3). Sx = (Vref−FVx) / Vref × 100 (S1) The slip ratio correcting means 44 is composed of an initial correcting means 44a, a rough road correcting means 44b, a steering correcting means 44c, and an adding means 44d. Correction means 44a-44
The correction value calculated in step c is added by the adding means 44d, and the above-mentioned slip ratio Sx is corrected using the added value HSR (step S4). These corrections are performed in order to prevent the operation of the ABS due to riding over a protrusion, improve the braking force and directional stability on a rough road, and improve the maneuverability at the time of sudden steering.

The increase / decrease determination means 46 includes a slip rate SRx corrected by the slip rate correction means, an integrated value ISRx of the slip rate SRx, and a wheel acceleration FGx of each wheel.
, And its differential value Jx are supplied, and a brake pressure increase / decrease determination is executed by fuzzy inference (step S5). The calculation of the integrated value ISRx is performed by the slip rate integrating means 4.
According to 8, the operation of the differential value Jx is executed by the differentiating means 49, respectively.

FIG. 6 shows the relationship between the slip ratio S and the friction coefficient μ. As a general method of the ABS control, the relationship between the slip ratio S and the friction coefficient μ, and the wheel acceleration FGx
From equation (1), the slip ratio S becomes the value S1 at which the friction coefficient μ becomes maximum.
If the value is smaller or smaller than the value S1, the brake fluid pressure is increased. If the value is larger than the value S1 or larger than the value S1, the pressure is reduced. However, with only the wheel acceleration FGx, the termination of the pressure reduction control may be delayed due to the phase delay of the sensor filter system. To prevent this, the recovery tendency of the wheel speed is determined by the differential value (jerk) Jx of the wheel acceleration FGx. We try to detect it early. Further, the extremely low μ road is detected by the integrated value ISRx of the slip ratio SRx, and the transition from the low μ road to the high μ road is detected at an early stage to optimize the brake fluid pressure.

The result of the pressure increase / decrease determination by the pressure increase / decrease determination means 46 is output to the motor current command value calculation means 50 as a motor drive target value II, and the calculation means 50 calculates the motor drive current IMTR by a predetermined procedure. Further, the motor drive processing means 52 outputs a drive current IOUT of the motor 16 of the hydraulic unit (HU) 10 based on the calculated value IMTR (step S6). The motor drive processing means 52 controls the current value IOUT to be supplied to the motor 16 to an optimum value according to the change of the calculated value IMTR and the sign. Next, the method of determining whether to increase or decrease the pressure (step S5 in FIG. 5) according to the present invention will be described in detail.

The determination of the increase or decrease of the brake fluid pressure in this embodiment is basically performed by fuzzy inference using the slip ratio SRx and the wheel acceleration FGx as inputs. First, the basic fuzzy inference will be described. The storage device of the electronic control unit 30 stores three sets of membership functions shown in FIGS. FIG. 7 shows a membership function for each wheel wheel acceleration FGx of the fuzzy input, and FIG. 8 shows each wheel slip ratio SR of the fuzzy input.
FIG. 9 shows a membership function that outputs a target pressure increase / decrease amount (control value) II. In these functions, PB is positive big (positive), PM is positive medium (middle), PS
Represents positive small (positive and small), Z0 represents zero, NB represents negative big (negative large), and NS represents negative small (negative small), respectively.

The storage device of the electronic control unit 30 includes:
20 basic rules shown in Table 1 are stored.

[0023]

[Table 1]

Some of the basic fuzzy rules shown in Table 1 are exemplified below. IF FGx = NB and SRx = PB, THE
N II = NB. (If the wheel acceleration FGx is NB and the slip ratio SRx is PB, the target pressure increase / decrease amount II is N
B) IF FGx = ZO and SRx = PS, THE
N II = PS. (If the wheel acceleration FGx is ZO and the slip ratio SRx is PS, the target pressure increase / decrease amount II is P
S) The rule in the above table is the wheel jerk J described later.
x is not PB and the slip ratio integrated value ISRx is P
This rule is satisfied when the value is not B and the slip ratio integrated value ISRx is not NB.

The electronic control unit 30 is, for example, a known MA
A target pressure increase / decrease amount II corresponding to the calculated wheel acceleration FGx and slip ratio SRx is calculated for each wheel by the X-MIN method and the center of gravity method. That is, for one rule, each degree of conformity is obtained from FIGS. 7 and 8 according to the calculated wheel acceleration FGx and slip ratio SRx of each wheel.
The smaller of the two determined degrees of fitness (MIN method)
Is determined from FIG. 9. Then, similarly, the target pressure increase / decrease amount II is obtained for all of the 20 rules, and the target pressure increase / decrease amount I obtained for each rule is obtained.
The outline is obtained by superimposing 20 I (MAX method),
The target pressure increase / decrease amount II is finally obtained from the center of gravity of the figure surrounded by the obtained contour (centroid method).

In the above-described fuzzy inference, the target pressure increase / decrease amount II is obtained in accordance with the two inputs, the wheel acceleration FGx and the slip ratio SRx. Not only the two inputs but also many inputs, that is, judgment conditions can be set, and fine-grained pressure increase / decrease control can be performed. Therefore, control accuracy is improved, and hydraulic pressure fluctuation of brake fluid pressure is reduced. Therefore, vibration and noise can be reduced and riding comfort can be improved.

For example, with only the wheel acceleration FGx, the determination of the end point of the pressure reduction control may be delayed due to the phase delay of the filter system in the input signal processing. In order to prevent this, a differential value of the acceleration FGx whose phase is ahead of the wheel acceleration FGx, that is, the wheel jerk Jx is added to the fuzzy input variable, so that the recovery tendency of the wheel speed can be detected at an early stage. .

FIG. 10 shows an example of a membership function set for the wheel jerk Jx of the added fuzzy input variable. Table 2 shows rules added when the wheel jerk Jx is PB.

[0029]

[Table 2]

A fuzzy rule for performing fuzzy inference by adding the wheel jerk Jx is as follows, for example. IF FGx = NB, SRx = PB and Jx @ PB,
THEN II = NB. (If the wheel acceleration FGx is NB, the slip ratio SRx is PB, and the wheel jerk Jx is not PB, the target pressure increase / decrease amount II is NB from Table 1.) IF FGx = NB, SRx = PB and Jx = PB,
THEN II = ZO. (If the wheel acceleration FGx is NB, the slip ratio SRx is PB, and the wheel jerk Jx is PB, the target pressure increase / decrease amount II is as shown in Table 2.
When the wheel jerk Jx is added to the fuzzy inference, the increasing tendency of the wheel acceleration FGx can be detected earlier by 1/4 phase by the wheel jerk Jx as shown in FIG. 11 (FIG. 11). (Refer to (a)), the brake fluid pressure can be prevented from being excessively reduced (overshoot).

The integrated value ISRx of the slip ratio SRx
Is added to the fuzzy input variable, traveling on an extremely low μ road or transition from a low μ road to a high μ road can be detected at an early stage. For this purpose, a procedure for calculating the integral value ISRx will be described with reference to FIGS. Electronic control unit 3
First, in step S50, the slip ratio SRx of each wheel is set to a predetermined value range XS12 to XS20 (for example, 12
〜20%) is determined. If the slip ratio SRx is a value within the predetermined value range XS12 to XS20, it means that the brake fluid pressure for generating the maximum friction is supplied to the wheel cylinder of the relevant wheel. It is not necessary to detect the traveling on the extremely low μ road or the transition from the low μ road to the high μ road.
Proceeding to 1, the integral value ISRx is reset to 0, and the routine ends. As long as the determination result in step S50 is affirmative (from t1 to t2, from t5 to t6, and from t7 in FIG. 13).
Step S51 is repeatedly executed, and the integrated value ISRx is held at 0.

On the other hand, if the decision result in the step S50 is negative, the process proceeds to a step S52, in which it is determined whether or not the slip ratio SRx is equal to or less than the predetermined value XS12. If the determination result is positive, the process proceeds to step S53, where
The integral value ISRx is calculated by (SS1). ISRx = ISRx + (SRx-XS12) dt (SS1) At this time, the integrated value ISRx calculated at this time becomes a negative value as apparent from FIG. 13 (before t1 and t6 in FIG. 13).
~ T7).

When the SRx value is equal to or greater than a predetermined value XS20, and
If the value is equal to or smaller than the predetermined value XS30 (for example, 30%), the determination result in step S54 becomes affirmative. In such a case, step S55 is executed, and the integral value ISRx is calculated by the following equation (SS2). ISRx = ISRx + (SRx-XS20) dt (SS2) At this time, the calculated integrated value ISRx becomes a positive value as is clear from FIG. 13 (from t2 to t3 in FIG.
(between t4 and t5, between t8 and t9). If the SRx value is equal to or more than the predetermined value XS30 (30%), step S54 is executed.
Is negative, and in such a case, step S56 is executed, and the integral value IS is calculated by the following equation (SS3).
Calculate Rx.

ISRx = ISRx + (XS30−XS20) dt (SS3) At this time, the integrated value ISRx calculated becomes a positive value as is clear from FIG. 13, but a constant value (XS30−XS20)
20) dt is added (t3 in FIG. 13)
To t4). This calculation prevents the integral value ISRx from becoming too large. When traveling on an extremely low μ road, the wheel may move toward the locked state while the wheel acceleration FGx is kept low (ZO).
The detection is to be performed depending on whether or not Rx is PB (positive).

FIG. 14 shows an example of a membership function set for the slip ratio integral value ISRx of the added fuzzy input variable. Table 3 shows rules added when the slip ratio integrated value ISRx is PB.

[0036]

[Table 3]

The fuzzy rule when the slip ratio integral value ISRx is PB is as follows, for example. IF FGx = ZO, SRx = PM, ISRx ≠ NB a
nd ISRx ≠ PB, THEN II = Z0 (Wheel acceleration FGx is ZO and slip ratio SRx is PM
And the slip rate integral value ISRx is PB even if it is NB
If not, the target pressure increase / decrease amount II is ZO from Table 1) IF FGx = ZO, SRx = PM and ISRx = P
B, THEN II = NS (If the wheel acceleration FGx is ZO, the slip ratio SRx is PM, and the slip ratio integrated value ISRx is PB, the target pressure increase / decrease amount I
I is NS from Table 3) When the slip rate integral value ISRx is added to the fuzzy inference,
As shown in FIG. 15, even if the time change of the slip ratio SRx is small, a large change of the slip ratio integrated value ISRx with time is detected. Further, the slip ratio integrated value ISRx represents the length of the period in which the slip ratio SRx is controlled out of the above-described preferred range, and from the change in the slip ratio integrated value ISRx, the state where the slip ratio is large is determined. If it is determined that the brake fluid pressure has continued for a long time, the brake fluid pressure is controlled to reduce the pressure.

On the other hand, Table 4 shows the slip ratio integrated value ISRx
Shows a rule added when is an NB.

[0039]

[Table 4]

The fuzzy rule when the slip ratio integrated value ISRx is NB is as follows, for example. IF FGx = ZO, SRx = PM, ISRx ≠ NB a
nd ISRx ≠ PB, THEN II = Z0 (Wheel acceleration FGx is ZO and slip ratio SRx is PM
And the slip rate integral value ISRx is PB even if it is NB
If not, the target pressure increase / decrease amount II is ZO from Table 1) IF FGx = ZO, SRx = PM and ISRx = N
B, THEN II = PB (If the wheel acceleration FGx is ZO, the slip ratio SRx is PM, and the slip ratio integrated value ISRx is NB, the target pressure increase / decrease amount I
I is PB from Table 4) When the slip rate integral value ISRx is added to the fuzzy inference,
As shown in FIG. 16, when shifting from a low μ road to a high μ road,
Since the state where the slip ratio SRx is small continues for a long time and the slip ratio integrated value ISRx << 0, it is possible to detect a transition from a low μ road to a high μ road, and this detection allows the brake fluid pressure to rise. , And the feeling of idle running can be prevented.

In this embodiment, a motor direct-acting hydraulic unit (HU) 10 is provided in the oil passage between the wheel cylinder and the master cylinder, and the brake fluid pressure is controlled by this unit 10. However, the application of the present invention is not limited to the hydraulic unit (HU) 10 as a matter of course.

[0042]

As is apparent from the above description, according to the anti-skid braking method of the present invention, every time the slip ratio is calculated, a difference value obtained by subtracting a predetermined value from the calculated slip ratio is integrated. When it is determined that there is almost no change in the wheel speed detected from the wheel acceleration, and when it is determined that the state in which the slip ratio is small is continued by the integrated value, the hydraulic pressure supplied to the wheel cylinder Is increased, it is possible to detect at the time of entry from a low μ road to a high μ road at an early stage, to prevent a control delay of the pressure increase control, and to improve the braking performance.

[Brief description of the drawings]

FIG. 1 is a block diagram schematically showing an overall configuration of an ABS device to which a method of the present invention is applied.

FIG. 2 shows a hydraulic unit (HU) 1 shown in FIG.
FIG. 3 is a hydraulic circuit diagram showing a more detailed configuration of a hydraulic circuit.

FIG. 3 is a functional block diagram of input signal processing of the electronic control device 30 shown in FIG.

FIG. 4 is a functional block diagram of ABS control of the electronic control device 30 shown in FIG.

FIG. 5 is a flowchart of a main routine showing a control procedure of ABS control executed by electronic control device 30 shown in FIG.

FIG. 6 is a graph showing a relationship between a slip ratio S and a friction coefficient μ.

FIG. 7 is a graph of a membership function with respect to a wheel acceleration FGx, which is used by the electronic control device 30 to determine whether to increase or decrease the pressure.

FIG. 8 is a graph of a membership function with respect to a slip ratio SRx, which is used by the electronic control device 30 for pressure increase / decrease determination.

FIG. 9 is a graph of a membership function with respect to a target pressure increase / decrease amount II used by the electronic control device 30 for pressure increase / decrease determination.

FIG. 10 is used by the electronic control unit 30 to determine whether to increase or decrease the pressure.
It is a graph of the membership function with respect to the wheel jerk Jx.

FIG. 11 is a graph showing changes over time in wheel acceleration FGx, wheel jerk Jx, reference vehicle speed Vref, wheel speed FVx, and brake fluid pressure.

FIG. 12 is a flowchart of a slip ratio integration routine executed by the electronic control unit 30.

FIG. 13 is a graph showing a time change of a slip ratio SRx and a slip ratio integrated value ISRx obtained by integrating the slip ratio SRx.

FIG. 14 is a flowchart of a slip rate integration routine executed by the electronic control unit 30.

FIG. 15 shows a slip ratio SRx and a slip ratio integrated value ISR.
6 is a graph showing time changes of x, reference vehicle speed Vref, and wheel speed FVx.

FIG. 16 shows a slip rate integrated value ISRx and a reference vehicle speed Vre.
It is a graph which shows each time change of f, wheel speed FVx, and brake fluid pressure.

[Explanation of symbols]

 3-6 Brake device 7 Handle 8 Brake pedal 9 Master cylinder 10 Motor direct-acting hydraulic unit 21-24 Wheel speed sensor 25 Handle angle sensor 26 Acceleration sensor 30 Electronic control device

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B60T 8/58

Claims (3)

(57) [Claims] A wheel slip ratio is calculated from a difference between a reference vehicle speed and a wheel speed of a wheel, and a hydraulic pressure supplied to a wheel cylinder of each wheel of a brake device is determined at least according to the calculated slip ratio and wheel acceleration. In the anti-skid braking method of increasing / decreasing pressure control, every time the slip rate is calculated, a difference value obtained by subtracting a predetermined value from the calculated slip rate is integrated, and there is almost no change in the wheel speed detected from the wheel acceleration. When it is determined that the state where the slip ratio is small is continued by the integrated value, the hydraulic pressure supplied to the wheel cylinder is increased. 2. A plurality of fuzzy rules are set using at least a slip rate, a wheel acceleration and an integrated value of a slip rate as input variables, and a control value corresponding to a pressure increase / decrease value of a hydraulic pressure supplied to a wheel cylinder as an output. A membership function for determining the degree of conformity of the rule is set, and the degree of conformity of each fuzzy rule is calculated according to the input variables of the slip rate, the wheel acceleration, and the integrated value of the slip rate. The anti-skid braking method according to claim 1, wherein a control value is calculated, and the pressure increase / decrease control is performed. 3. An upper limit value and a lower limit value are set for the slip ratio, and when the calculated slip ratio is larger than the upper limit value, an integrated value is obtained from a difference value obtained by subtracting the upper limit value from the calculated slip ratio. When the calculated slip rate is smaller than the lower limit value, an integrated value is obtained by a difference value obtained by subtracting the lower limit value from the calculated slip rate, and when the calculated slip rate is between the upper limit value and the lower limit value. 3. The anti-skid braking method according to claim 1, wherein the integrated value is set to 0.