JPH07102804B2 - Anti-skid braking method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an anti-skid braking method suitably applied to a braking device of an automobile.

(Prior art and problems to be solved) When braking on a low μ road such as a road wet with rainwater, it is possible to prevent slipping of wheels and ensure steering stability, and to stop the vehicle at a short braking distance. There are known anti-skid braking methods that can be done. This braking method detects the rotation speed of each wheel, obtains each wheel speed, obtains the slip ratio of each wheel based on the deviation (slip amount) between the wheel speed and the vehicle body speed, and this slip ratio is The brake pressure of each wheel is controlled to be increased or decreased so that the friction coefficient of the wheel is maintained near the optimum slip ratio.

In such an anti-skid braking method,
It is extremely important to accurately detect the vehicle speed. For example, a method is known in which an ultrasonic sensor is attached to a vehicle, and the vehicle speed is obtained by detecting the moving speed of the vehicle with respect to the ground. This method can accurately detect the vehicle speed, but An ultrasonic sensor is required in addition to the speed sensor, and further maintenance of this sensor is required, which is a practical problem.

On the other hand, various methods of predicting the vehicle body speed from the detected wheel speeds have been proposed. When the slip ratio is kept at the optimum value, it is not always necessary to detect the actual vehicle body speed, but it is only necessary to be able to detect the reference vehicle speed (reference vehicle body speed) in place of this, but the predicted reference vehicle body speed is the road surface condition. In particular, at the beginning of braking (at the start of brake pressure control), it is affected by the degree of application of brake pressure, etc.
The road surface condition, for example, the road surface friction coefficient (road surface μ) is not sufficiently understood, which makes it difficult to predict the reference vehicle speed. For example, if the standard vehicle speed is predicted to be low,
Since the brake pressure is controlled to be strengthened, the locking tendency of the wheels becomes remarkable, and conversely, when the reference vehicle speed is predicted to be higher, the brake pressure is controlled to be weakened. Therefore, the tendency that the brake does not work (idle feeling) becomes remarkable.

The present invention has been made to solve such a problem, and even at the start of brake pressure control where the road surface condition is not yet understood, the wheels may be locked,
An object of the present invention is to provide an anti-skid braking method capable of predicting a reference vehicle speed to an appropriate value quickly without giving a feeling of idling.

(Means for Solving the Problems) According to the present invention in order to achieve the above-mentioned object, according to the present invention, a wheel speed is detected, a reference vehicle body speed is predicted from the detected wheel speed, and the wheel speed is estimated as the reference vehicle body speed. In the anti-skid braking method that controls the brake pressure of the wheels so that the slip ratio of the wheels is maintained near a predetermined value based on the deviation of
The deceleration of the wheel speed is obtained, and when the deceleration of the wheel speed becomes larger than the first predetermined value, it is predicted that the reference vehicle body speed will be decelerated by the second predetermined deceleration, and the deceleration of the wheel speed is the above-mentioned. When the deviation between the wheel speed and the reference vehicle body speed after a lapse of a predetermined time from the time when it becomes larger than the first predetermined value is larger than the predetermined value, the reference vehicle speed is smaller than the second predetermined deceleration.
The anti-skid braking method is characterized by predicting that the vehicle is decelerating at a predetermined deceleration of

(Operation) Immediately after the brake pressure control is started, the road surface condition is not sufficiently grasped. In such a case, according to the method of the present invention, the reference vehicle speed is first predicted on the assumption that the road surface is in the high μ condition. .
That is, it is predicted that the reference vehicle body speed is decelerated by the second predetermined deceleration after waiting for the deceleration of the wheel speed to become larger than the first predetermined value. Then, after a lapse of a predetermined time from the time when the deceleration of the wheel speed reaches the first predetermined value, it is determined whether the deviation between the wheel speed and the reference vehicle body speed is larger than the predetermined value. At this time, the road surface has a high μ
If the vehicle is in the state, since the wheel gripping force on the road surface is large, the deviation between the reference vehicle body speed decelerated at the second predetermined deceleration and the wheel speed becomes small, and the deviation becomes the predetermined value after the elapse of the predetermined time. It should be as follows. Therefore, according to the result of this determination, if the assumption is correct, it is sufficient to predict that the reference vehicle body speed will be decelerated by the second predetermined deceleration even after the above-mentioned predetermined time has elapsed. Immediately after the passage of, the reference vehicle speed may be predicted to be decelerated at a third predetermined deceleration smaller than the second predetermined deceleration.
Thus, the proper reference vehicle speed can be predicted quickly.

Embodiment An embodiment of the present invention will be described in detail below with reference to the drawings.

First, the structure of an anti-skid brake device in which the method of the present invention is implemented will be described with reference to FIGS. 1 and 2.

Hydraulic circuit of anti-skid brake device Fig. 1 is a hydraulic circuit diagram of the anti-skid brake device. Front wheels 1L and 1R that are driving wheels and rear wheels 1L and 2R that are non-driving wheels are respectively drums or desk brakes. Three
6 are attached, and the braking force is adjusted by controlling the brake pressure supplied to the wheel cylinders 3a to 6a of each brake.

The so-called diagonal split system is used to supply the brake pressure to the wheel cylinders 3a to 6a, and the master cylinder 10 is connected to the left front wheel 1L, the right rear wheel 2R, and the right front wheel 1R via the two hydraulic circuits 12 and 14. The left rear wheel 2L is performed separately.

The hydraulic circuit 12 branches into oil passages 12a and 12b, and an oil passage 12a toward the wheel cylinder 3a of the left front wheel and an oil passage 12b toward the wheel cylinder 6a of the right rear wheel are provided with hydraulic control valves 16,
20 are arranged respectively. On the other hand, the hydraulic circuit 14 is an oil passage.
Hydraulic control valves 18 and 22 are respectively provided in the middle of the oil passage 14a branched to 14a and 14b and directed to the right front wheel wheel cylinder 4a, and the oil passage 14b directed to the left rear wheel wheel cylinder 5a. . Further, proportioning valves (PV) 24, 26 are respectively arranged on the oil passage 12b and the oil passage 14b on the master cylinder 10 side of the hydraulic control valve. The proportioning valves 24 and 26 have a function of increasing the brake pressure generated in the master cylinder 10 in the high pressure region with respect to the front brake pressure while increasing the rear brake pressure while maintaining a constant reduction rate. This prevents the vehicle from swinging back and forth when a normal brake operation is performed.

As shown in detail in FIG. 2A, the hydraulic control valve 16 includes an expander piston 161 slidably fitted in a piston chamber 16a, two cutoff valves 162, 163 accommodated in a valve chamber 16b, and the like. The piston chamber 16a is partitioned by the one end surface of the expander piston 161, and the port 16c
A pressure chamber 165 is formed to open. A piston-shaped cut-off valve 162 is slidably fitted in the valve chamber 16b and is partitioned by one end surface of the valve 162,
A pressure chamber 166 is formed to open the port 16d.

The cut-off valve 162 is formed such that the other end surface thereof can project into the piston chamber 16a, and the cut-off valve 163 is housed inside the cut-off valve 162, and the valve chamber 1 is opened at the other end surface.
62a is formed. An outer peripheral wall of the cutoff valve 162, one half of the pressure chamber 166 side is in liquid-tight contact with the inner peripheral wall of the valve chamber 16b, and the other half of the expander piston 161 side is formed to have a smaller diameter than the one half. An oil passage 167 is formed between the inner peripheral walls of the valve chamber 16b. The oil passage 167 is always connected to the master cylinder 10 via the port 16e and the oil passage 12a. Then, as will be described later, the other end surface of the cutoff valve 162 and the other end surface of the expander piston 161 contact each other, and the expander piston 161 opposes the hydraulic pressure of the pressure chamber 166 to valve the protruding end surface of the cutoff valve 162. When pushed back to the chamber 16b side, the cutoff valve 162 is opened, and the port 16e communicates with the port 16f provided on the piston chamber 16a side via the oil passage 167. This port 16f is connected to the wheel cylinder 3a, so
The 10 side and the wheel cylinder 3a side are in communication.

The cutoff valve 163 housed in the valve chamber 162a is constantly urged in the valve closing direction by the spring 164, and when the cutoff valve 163 is closed, the integrally formed rod 163a projects toward the piston chamber 16a side. And this protrusion amount is
It is larger than the protrusion amount of the other end surface of the cutoff valve 162. The oil passage 167 communicates with the valve chamber 162a through a hole formed in the peripheral wall of the cutoff valve 162. As will be described later, when the oil pressure in the pressure chamber 165 increases and the expander piston 16a pushes down the rod 163a toward the valve chamber 16b side, the cutoff valve 163 opens and the port 16e opens the oil passage 167 and the valve chamber 162. Through the port 16f via the master cylinder 10
The side and the wheel cylinder 3b side are communicated with each other.

The other hydraulic control valves 18, 20, 22 are also configured in the same manner as the hydraulic control valve 16, and thus detailed description thereof will be omitted.

Returning to FIG. 1, the pressure chambers 165 and 185 of the front hydraulic control valves 16 and 18 are connected to the reserve tank 36 via the solenoid valves 30 and 32, respectively, and to the accumulator 46 via the solenoid valves 40 and 42. It is connected. On the other hand, the pressure chambers 205, 225 of the respective hydraulic control valves 20, 22 on the rear side are connected to the reserve tank 36 via a common solenoid valve 34, and also connected to the accumulator 46 via a common solenoid valve 44. ing.
The accumulator 46 has hydraulic chambers 162, 182, 20 for each hydraulic control valve.
It is directly connected to 2,222, and a high-pressure liquid pressure (for example, 200 to 220 kg / cm ² ) is constantly supplied from this accumulator 46. This hydraulic pressure is generated by the pump 47, and the pressure required for anti-skid brake control is constantly stored. The pump 47 is driven by the motor 48, and the motor 48 is electrically connected to the output side of the electronic control unit (ECU) 50.

On the input side of the electronic control unit 50, a hydraulic pressure sensor 56 for detecting the hydraulic pressure accumulated in the accumulator 46 is electrically connected, and the electronic control unit 50 controls the hydraulic pressure in the accumulator 48 to the hydraulic pressure. Monitored by the sensor 56, the motor 48 is turned on when the hydraulic pressure in the accumulator 48 is below the lower limit allowable value of the pressure required for control, and is turned off when the upper limit allowable value is exceeded to maintain the above hydraulic pressure. ing.

The solenoid valve (40) that supplies the hydraulic pressure of the accumulator 46 to the pressure chamber (165) of each hydraulic control valve (16) closes its valve when an ON signal is supplied from the electronic control unit 50. , The passage between the accumulator 46 and the pressure chamber (165) is shut off. On the other hand, when the solenoid valve (40) is off, the valve moves in the closing direction due to the spring, but because the hydraulic pressure of the accumulator 46 is high, the spring force is overcome and the valve is opened.

On the other hand, the solenoid valve (30) on the side for releasing the hydraulic pressure to the reserve tank 36 opens when the ON signal is supplied from the electronic control unit 50, and the solenoid valve (30) opens and the reserve tank 36 and the pressure chamber (16
The passage between 5) is opened, and the hydraulic pressure in the pressure chamber (165) is discharged to the reserve tank 36 side. On the other hand, when the solenoid valve (30) is not energized, the valve is closed by the spring and the passage between the reserve tank 36 and the pressure chamber (165) is shut off. In this case, the normal accumulator pressure cannot overcome the spring force to open the passage.

On the input side of the electronic control unit 50, in addition to the above-mentioned sensors, wheel speed sensors 52 to 55 that detect the wheel speed of each wheel, a brake switch 58 that detects the depression of the brake petal, etc. are electrically connected and output. Electromagnetic valves 30 to 44 and the like are electrically connected to the side.

Operation of Hydraulic Control Valve Next, the operation of the above hydraulic control valve will be described. Since the operation of each hydraulic control valve is substantially the same, only the operation of the hydraulic control valve 16 with respect to the left front wheel 1L will be described with reference to FIGS. 2A to 2D, and the others will be omitted. .

FIG. 2A shows the state of the hydraulic control valve in the case where the solenoid valves 30 and 40 are not energized from the electronic control unit 50 and the anti-skid brake device is inactive.

Since the solenoid valves 30 and 40 are not energized by the electronic control unit 50, they are closed by spring force. However, since a high hydraulic pressure is stored in the accumulator 46, the accumulator pressure pushes open the valve of the solenoid valve 40 and opens the pressure chamber 165.
Then, the expander piston 161 is pushed downward in the drawing. On the other hand, the hydraulic pressure of the accumulator 46 is also supplied to the pressure chamber 166 through the port 16d and pushes the cutoff valve 163 and the cutoff valve 162 upward. However, expander piston 161 and cutoff valve 1
Expander piston 161 due to different pressure receiving area of 62
Presses the other end surface of the cutoff valve 162 projecting into the piston chamber 16a and the rod 163a of the cutoff valve 163 to open these valves. Therefore, when the brake petal 10a is stepped on, the hydraulic pressure of the master cylinder 10 reaches the wheel cylinder 3a via the route of the port 16e → the oil passage 167 → the port 16f and the route of the port 16e → the valve chamber 162a → the port 16f. , The brake is activated. When the brake petal 10a is opened, the hydraulic pressure in the master cylinder 10 drops, so the wheel cylinder pressure returns to the reserve tank via a return port (not shown) of the master cylinder 10.

FIG. 2B shows the state of the hydraulic control valve when the anti-skid brake device operates and the hydraulic pressure in the wheel cylinder 3a decreases.

When the hydraulic pressure to the wheel cylinder 3a increases due to the braking action, the wheel speed decreases. When the electronic control unit 50 determines from the signal from the wheel speed sensor 52 that the wheel 1L is about to lock, it outputs a signal for reducing the hydraulic pressure, that is, an ON signal, to the solenoid valves 30, 40. As a result, the solenoid valve 40 is closed to shut off the accumulator pressure, the solenoid valve 30 opens its valve, and the oil passage to the reserve tank 36 is opened. Therefore, the cutoff valve 162 is at the accumulator pressure, and the cutoff valve 163 is closed by the master cylinder pressure and the spring 164, so that the master cylinder 10 and the wheel cylinder 3a are shut off from each other. As a result, the wheel cylinder pressure pushes the expander piston 161 upward to reduce the pressure. The hydraulic pressure acting on the expander piston 161 until now is controlled according to the wheel cylinder pressure, and the port 16c
Is returned to the reserve tank 36 via the solenoid valve 30.

FIG. 2C shows the state of the hydraulic control valve when the hydraulic pressure of the wheel cylinder 3a is maintained during the operation of the anti-skid brake device.

When the hydraulic pressure in the wheel cylinder 3a is reduced to an optimum value, the electronic control unit 50 stops energizing the solenoid valve 30 and closes the solenoid valve 30. This allows the expander piston 161
The hydraulic pressures acting on both end surfaces of the wheel are balanced and the wheel cylinder pressure is maintained.

FIG. 2D shows the state of the hydraulic control valve when the hydraulic pressure of the wheel cylinder 3a is increased during the operation of the anti-skid brake device.

When the electronic control unit 50 determines that the hydraulic pressure of the wheel cylinder 3a needs to be increased, the solenoid valve 40 is deenergized and the solenoid valve 40 is stopped.
The pressure of the pressure chamber 165 is increased by pushing 40 open by the hydraulic pressure of the accumulator 46. This allows the expander piston 161
Moves downward and pushes out the hydraulic oil in the piston chamber 16a to increase the wheel cylinder pressure. When the expander piston 161 moves to the lowest end of the piston chamber 16a, the 2A
Returning to the state of the figure, the cutoff valves 162 and 163 are opened, the master cylinder 10 and the wheel cylinder 3a are communicated with each other, and the normal brake (the non-operation state of the anti-skid brake device) is restored.

Brake Pressure Increase / Decrease Control Method Next, a brake pressure increase / decrease control method of the antiskid brake device by the electronic control unit 50 will be described in detail with reference to the ABS main flow chart shown in FIG. The electronic control unit 50 executes the program shown in this flowchart in a predetermined cycle (for example, every 8 msec).

Calculation of Wheel Speed VW and Wheel Acceleration GVW First, the electronic control unit 50, based on the input signals from the wheel speed sensors 52 to 55 attached to each wheel, the wheel speed VW of each wheel and the acceleration / deceleration GVW of each wheel. Calculate (Step S
1).

Each wheel speed sensor has, for example, a large number of protrusions at equal intervals on its outer circumference, a gear-shaped rotating disc that rotates with the wheel, and a pickup mounted on the fixed side, facing the protrusions of this disc. The pickup coil supplies a pulse signal to the electronic control unit 50 each time the pickup coil detects a protrusion. The electronic control unit 50 calculates the angular velocity of the wheel from the time interval at which this pulse signal is generated, and multiplies this by the wheel radius to calculate the wheel speed VW. Calculated wheel speed VW
Are stored in a storage device (not shown) of the electronic control unit 50.
And, this time the calculated wheel speed VW _n and the wheel speed V which was previously calculated
W _n-1 Metropolitan from the wheel acceleration _{GVW (= VW n -VW n-} 1) is calculated.

Calculation of Reference Vehicle Speed Next, the electronic control unit 50 proceeds to step S2 to calculate the reference vehicle speed VREF. Details of this operation are shown in Figures 4A through 4C.
It is shown in the figures and will be explained with reference to FIGS. 5A and 5B. The electronic control unit 50 first determines whether or not the anti-skid brake control (ABS control) is being performed (step S20).
1). This ABS control is performed when the reference vehicle body speed VREF described later is set to a predetermined value (for example, 10 km / h) or more and the pressure reduction command value ΔP is set to a predetermined value (for example, -3.1 kg / cm ² ) or less,
It is first started with this as a control start condition, and once ABS control is started, it is continued until a predetermined control end condition is satisfied.

If it is determined that the ABS control is not in progress (if the determination result is negative (N)), the lower wheel speed of the wheel speeds detected by the rear wheel speed sensor 54 or 55 is used for the reference vehicle speed calculation. Therefore, the vehicle speed (reference wheel speed) SVW selected is used.
If the wheel is a driving wheel, the wheel may slip and may be detected at a speed higher than the actual vehicle speed. However, in the case of the embodiment, the rear wheel is a non-driving wheel and there is no such possibility as described above. However,
When the selected reference wheel speed SVW is the lowest value among the four wheels, a detection error due to a bump overriding the wheel, etc. may be considered. Therefore, it is determined whether or not the vehicle speed SVW selected in step S203 is the lowest among the four wheels. If it is not the lowest, the process proceeds to step S208 described later, and if it is the lowest, the selected reference wheel speed
The SVW is replaced with the average value of the vehicle speed detected by the rear vehicle speed sensors 54 and 55 (step S204), and the process proceeds to step S208.

In step S201, when it is determined that the ABS control is in progress (when affirmative (Y) is determined), the second wheel speed from the top among the four wheels is the reference wheel speed selected for the reference vehicle speed calculation. SVW. During ABS control, the wheels tend to lock due to brake operation, and the reference vehicle body speed VREF calculated when the vehicle speed on the lower side is selected becomes a value that is significantly smaller than the actual vehicle body speed. If the brake pressure is controlled to increase or decrease using the speed VREF, the wheels may be further locked. Therefore, the second vehicle speed from the top is selected in consideration of the detection error.

Then, the filtering process of the selected reference wheel speed SVW, the reference wheel acceleration, and the road surface μ value are calculated (step
S208). Since the selected reference wheel speed SVW contains a noise component, it is necessary to eliminate this noise component, which is actually filtered by the following equation (R1).

FSVW = FSVW + K1 (FSVW-SVW) (R1) where FSVW is the time average value of the reference wheel speed and K1 is a constant smaller than 1.0.

The current value of the reference wheel speed FSVW (FSV
Based on W _n ) and the previous value (FSVW _n-1 ), the reference wheel acceleration GSVW is calculated by the following formula (R2).

_{GSVW = FSVW n -FSVW n-1} ...... (R2) and, calculates the estimated road μ from the calculated acceleration GSVW by the following formula (R3).

MU1 = MU1 + K2 (MU1-GSVW) (R3) where MU1 is the estimated road surface μ value and K2 is the constant K1 mentioned above.
Is a smaller constant. The initial value of MU1 at the start of ABS control is set to a predetermined value corresponding to a typical high μ road.

In the present embodiment, the road surface μ is calculated using the reference wheel speed SVW detected by the wheel speed sensor, but a G sensor may be separately provided and calculated from the vehicle body acceleration detected by this G sensor. .

When the calculation of the acceleration GSVW or the like of the reference wheel speed is completed, the electronic control unit 50 again determines whether or not the ABS control is in progress (step S
210). Immediately after depressing the brake petal 10a (see Fig. 5A
Before the time t1), the pressure reduction control of the brake pressure has not been started yet, so the determination result is negative and the process proceeds to step S230 shown in FIG. 4C. In this step S230, it is determined whether or not the flag FGH is set.

This flag FGH is a program control flag for instructing the calculation of the reference vehicle speed for high μ roads.If this flag is not set yet, the process proceeds to step S232, and the above-mentioned reference wheel acceleration GSVW is the predetermined value X. _G2 (for example, -1.4g)
It is determined whether or not it is larger. If large, ie
When the deceleration of the wheel speed is smaller than the first predetermined value, the reference vehicle body speed VREF is set to a value equal to the reference wheel speed FSVW, and
The flag FGH is cleared (step S234), and the routine ends.

The minimum value of the reference vehicle body acceleration during deceleration is theoretically -1.
Although it is 0 g, it is below the theoretical value when considering the detection accuracy of the reference vehicle speed and the adhesiveness of the tire on the high μ road (-1.
Since it may be a value smaller than 0 g), the predetermined value X _G2 is smaller than -1.0 g (-
It is preferably set to 1.4g).

In step S232, the reference wheel acceleration GSVW is the predetermined value X
If it is smaller than _G2 (time t1 in FIG. 5A), that is, if the deceleration of the wheel speed is larger than the first predetermined value, the process proceeds to step S236, the flag FGH is set, and the timer variable TM Is reset to the value 0 and the process proceeds to step S238. In step S238, the timer variable TM is set to a predetermined value X _TM (for example, 80 mse
(value corresponding to c) is larger than t1.
It is determined whether or not a predetermined time corresponding to the predetermined value X _TM has elapsed from the time point. Then, if the predetermined time has not elapsed, step S240 is skipped and the process proceeds to step S242.

In step S242, the reference vehicle speed VREF is calculated by the following equation (R4).

VREF = VREF-C2-Δt (R4) Here, C2 is a constant (for example, 1.4 g), and Δt is a minute time (here, a value corresponding to a program execution period of 8 msec). As is clear from the above formula (R4), the reference vehicle body speed VREF is set by predicting that the vehicle will decelerate at a predetermined deceleration (second deceleration C2 × Δt).

Then, in step S246, the set reference vehicle speed VR
After determining whether EF is smaller than the reference wheel speed FSVW, the timer variable value TM is incremented (step S248),
The routine is finished.

When the ABS control is started, as described above, step S20
6 is executed and the second vehicle speed from the top among the four wheels is the reference wheel speed S
It is selected as VW, the determination result of step S210 becomes affirmative, and step S212 is executed. In step S212, it is determined whether or not the road μ is low using the predicted road surface μ value MU1 calculated in step S208, that is, whether or not the absolute value of the MU1 value is larger than a predetermined value X _MU (for example, 0.45 g). To determine. Immediately after the ABS control is started, the calculated road surface μ value MU1 is
Since the value is close to the initial value which is a high μ value, step S212
The determination result of No is negative, and the above-described steps after step S230 are repeatedly executed.

In step S230, the flag FGH has already been set, so the determination result is affirmative, and immediately step S238.
Is executed. Then, step S242 is repeatedly executed until the timer variable TM reaches a predetermined value X _TM (between t1 time and t2 time in FIG. 5A), and the reference vehicle body speed VREF is decelerated at a predetermined deceleration (C2 × Δt). Is predicted.

In step S238 that is executed immediately after the predetermined time X _TM (80 msec) has elapsed, the determination result is affirmative, and the step
In S240, it is determined whether the deviation between the reference vehicle body speed VREF and the reference wheel speed FSVW is larger than a predetermined value X _KM (for example, 4 km / h). Immediately after the ABS control was started, the road surface μ could not be accurately predicted, and the reference vehicle speed VREF was predicted on the assumption that the road μ was high.However, if the road surface μ is close to the predicted value, that is, high If it is a μ road, the reference wheel speed FSVW recovers quickly by the brake pressure reduction control described later, and
When X _TM (80 msec) has elapsed, the deviation between the reference vehicle body speed VREF and the reference wheel speed FSVW should be smaller than the predetermined value X _KM . Therefore, the magnitude of the road surface μ can be determined by determining whether or not the deviation is larger than the predetermined value X _KM .

If the determination result of step S240 is affirmative, step S244
Then, the reference vehicle speed VREF is calculated by the following equation (R5).

VREF = VREF−C3 × Δt (R5) Here, C3 is a constant smaller than the above constant C2 (for example,
0.4 g). Therefore, the reference vehicle speed VREF is predicted to be decelerated at the predetermined deceleration (third deceleration C3 × Δt) on the low μ road (between the time points t2 and t3 in FIG. 5A).

The reference wheel speed FSVW is recovered by the brake pressure reduction control described later, and if the determination result in the above step S240 is negative, step S242 is executed and the reference vehicle body speed VREF is
Again on the high μ road, the predetermined deceleration (second deceleration C2 × Δ
It is predicted that the vehicle will decelerate at t) (from time t3 in Fig. 5A).
between t4).

When the reference vehicle body speed VREF set in step S242 or S244 becomes smaller than the reference wheel speed FSVW (at time t4 in FIG. 5A), the determination result in step S246 becomes affirmative, and the above-described step S234 is executed to perform the reference. Wheel speed FSVW based on vehicle speed VREF
Is set to a value equal to, the flag FGH is cleared, and the routine is ended. When the flag FGH is cleared,
The determination result of step S230 is negative, the determination result of step S232 is affirmative, and step S234 is executed.

Next, the braking is continued, and the prediction calculation of the road surface μ in step S208 is accurately performed. In step S212, the absolute value of the predicted road surface μ value MU1 is smaller than the predetermined value X _MU (0.45g). If it is determined to be small, that is, the road is a low μ road, the process proceeds to step S214, and it is determined whether or not the flag FGL is set. This flag FGL is a program control flag for instructing the calculation of the reference vehicle speed for low μ roads. If this flag is not set yet,
In step S216, the reference wheel acceleration GSVW is the predetermined value X _G1
(For example, −1.0 g) is determined. When it is large, that is, when the deceleration of the wheel speed is small, the reference vehicle body speed VREF is set to a value equal to the reference wheel speed FSVW, and the flag FGL is cleared (step S222), and the routine ends. .

The discriminant value X _G1 for the low μ road is set to a value smaller than the value for the high μ road, which accelerates the start time of the brake pressure reduction control,
Prevents wheel locking.

In step S216, the reference wheel acceleration GSVW is the predetermined value X
If it is smaller than _G1 (at time t10 in FIG. 5B), that is, if the deceleration of the wheel speed is large, the process proceeds to step S218, and the flag FG
Set L and proceed to step S220. In step S220, the reference vehicle speed VREF is calculated by the following equation (R6).

VREF = VREF-C1 × Δt (R6) Here, C1 is a constant (for example, 0.6 g) set to be smaller than the above-mentioned constant C2. As is clear from the above formula (R6), the reference vehicle body speed VREF is predicted to decelerate at the predetermined deceleration (C1 × Δt).

Then, in step S220, the set reference vehicle speed VR
The routine is ended by determining whether EF is smaller than the reference wheel speed FSVW.

Thus, on low μ roads where the road surface has a low coefficient of friction,
It is predicted that the reference vehicle speed VREF is decelerating at a deceleration (C1 × Δt) smaller than the deceleration on the high μ road (between time points t10 and t11 in FIG. 5B).

When the reference wheel speed FSVW is recovered by the brake pressure reduction control, which will be described later, and the reference vehicle body speed VREF becomes smaller than the reference wheel speed FSVW (at time t11 in FIG. 5B), the determination result of step S224 becomes affirmative, and the above-mentioned step Execute S222 and reference vehicle speed VR
EF is set to a value equal to the reference wheel speed FSVW, the flag FGL is cleared, and the routine ends. The flag FGL
When is cleared, the determination result of step S214 is negative, the determination result of step S216 is affirmative, and step S222 is executed.

When the reference vehicle speed VREF is calculated in this manner, the process returns to the main routine shown in FIG. 3 and step S3 is executed.

Calculation of slip amount ΔV In step S3, the slip amount ΔV of each wheel is calculated. FIG. 6 shows the details of the calculation procedure of the slip amount ΔV, and the electronic control unit 50 firstly performs steps S300 and S304.
At, it is determined whether or not ABS control is being performed and whether or not a rough road is being detected. These determinations are for performing accurate ABS control to perform smooth braking. As described above, the ABS control start condition is that the reference vehicle speed VREF is a predetermined value (10 km / h).
It is above, and the pressure reduction command value ΔP is the predetermined value (-
This is the case when the value is set to 3.1 kg / cm ² ) or less, and the ABS control is started only when this control start condition is satisfied. Then, once the ABS control is started, the ABS control is continued until a predetermined control end condition is satisfied. Also, bad road detection is
For example, the uneven state of the road surface is detected by the vibration cycle of the wheel acceleration GVW. At low vehicle speeds where ABS control does not start, or when a bad road is detected at low vehicle speeds,
There is a possibility that the detected wheel speed VW may include a large detection error, and the slip amount correction may be unfavorable. In steps S300 and S304, it is determined whether or not there is such a possibility.

If the determination result of step S300 is negative, and if the determination result of step S304 is positive, the process proceeds to step S301, and the calculated reference vehicle body speed VREF is a predetermined value X _REF (for example,
60 km / h) or less is determined. Since the influence of the detection error of the wheel speed VW is small at high speed, the process proceeds to step S306 described later. On the other hand, when the reference vehicle body speed VREF is less than the predetermined value X _REF proceeds to step S302, the slip amount compensation value DDV
Is set to the value 0.

On the other hand, if ABS control is in progress and no bad road is detected, step S306 is executed to determine whether or not the road is a low μ road. This determination is made by the same method as described above. If it is not a low μ road, the process proceeds to step S308, and a correction value DDV according to the reference vehicle speed VREF is set from the high μ table. FIG. 7A shows a correction table for high μ roads, where the correction value DDV is a negative value when the reference vehicle speed VREF is 60 km / h or less,
In the above cases, it is set to a positive value. On the other hand, if it is a low μ road, the process proceeds to step S310, and the correction value DDV corresponding to the reference vehicle speed VREF is read from the low μ road table. Figure 7B shows
The relationship between the reference vehicle speed VREF of the low μ road correction table and the correction value DDV is shown.

The electronic control unit 50 uses the correction value DD set as described above.
V, the slip amount ΔV is calculated from the wheel speed VW of each wheel obtained in steps S1 and S2 in FIG. 3 and the reference vehicle speed VREF by the following equation (S1) (step S312).

ΔV = VREF−VW−DDV (S1) The slip amount ΔV is calculated by using the formula (S1) for each wheel.
It is needless to say that it is calculated using.

FIGS. 8A to 8C show wheel speed VW, slip amount ΔV,
When the wheel speed VW deviates from the reference vehicle body speed VREF and the slip amount increases, the hydraulic pressure P of the wheel cylinder, which will be described later, is controlled to be reduced to avoid the locked state of the wheels. To be done. And the wheel speed VW
When is restored, the slip amount decreases, the hydraulic pressure P is controlled to increase again, and the vehicle speed decreases.

Calculation of basic pressure increase / decrease amount ΔP Next, the electronic control unit 50 calculates the slip amount ΔV and the wheel acceleration GVW calculated as described above from the basic pressure increase / decrease map stored in the storage device (not shown) in advance. Accordingly, the pressure increase / decrease value ΔP is read (step S4).

FIG. 9 is a graph conceptually showing the relationship between the slip amount ΔV and the wheel acceleration GVW of the basic pressure increase / decrease map stored in the storage device and the pressure increase / decrease amount ΔP read from these maps. Area is slip amount ΔV
And the wheel acceleration GVW. Areas A1 and A2 indicated by solid diagonal lines indicate pressure increasing areas, and in the area A1, for example, Δ
P is set to 0.5 kg / cm ² , and the area A2 is set to a higher value than the area A1, for example, 3.0 kg / cm ² . On the other hand, the areas D1 to D3 indicated by the dashed diagonal lines represent decompression areas. In the area D1, for example, ΔP is set to −0.5 kg / cm ² , and in the area D2, the area D
A value lower than 1, for example −3.5 kg / cm ² , in the area D3, the area
It is set to a value lower than D2, for example, −7.0 kg / cm ² .
And, the other area not shown by the diagonal lines is the holding area,
In this region, the brake pressure is held unchanged at the previous value.

The slip amount ΔV is corrected by the slip amount correction value DDV as described above. The correction value DDV is the low standard vehicle speed.
It is set to a negative value at VREF and a positive value at high reference vehicle speed VREF. Therefore, the slip amount ΔV is set to a larger value at the low reference vehicle body speed VREF and a smaller value at the high reference vehicle body speed VREF by the correction value DDV, as is apparent from FIG. And low standard vehicle speed
By performing this correction at the time of VREF, the pressure reduction control is facilitated. However, at low vehicle speeds, ABS
The correction value DDV is set to the value 0 when not controlled and when a rough road is detected. That is, the correction with the correction value DDV is prohibited. This allows unnecessary wheel vibration due to slight wheel vibration.
The inconvenience that the S control is performed is eliminated, and since the correction value DDV can be set to a large value, smooth braking is possible and the braking force is large. Also, to give a feeling of idling on a rough road (so-called “g omission” occurs)
There is no brake and smooth braking is possible.

Conversion of hydraulic pressure / increase / decrease time When the increase / decrease value ΔP is obtained, the electronic control unit 50 proceeds to step S5
Then, read the solenoid valve drive time ΔTP from the fluid pressure / pressure increase / decrease time conversion map.

When increasing / decreasing the brake pressure, increase / decrease the brake pressure supplied to each wheel cylinder by turning on / off the solenoid valves 30, 32, 34, 40, 42, 44 shown in FIG. 1 as described above. However, the drive time ΔTP of the solenoid valve with respect to the pressure increase / decrease value ΔP varies depending on the hydraulic pressure supplied to the wheel cylinder as shown in FIG. FIG. 10 shows the relationship between the pressure increase / decrease value ΔP and the current hydraulic pressure of the wheel cylinder, and the drive time ΔTP of the solenoid valve. For example, when the hydraulic pressure of the wheel cylinder is Px, this hydraulic pressure is In order to further increase the pressure increase value ΔPx by, the driving time ΔTPx value should be read from the intersection of the straight lines passing through these values. That is, as is clear from FIG. 10, the same boost value ΔPx
On the other hand, the higher the current hydraulic pressure P is, the longer the driving time ΔTP becomes.

By the way, in order to detect the hydraulic pressure of each wheel cylinder 3a to 6a, it is necessary to attach a hydraulic pressure sensor to each wheel cylinder, and the number of parts increases accordingly, but in this embodiment, the wheel cylinders are The predicted road surface μ value is used instead of detecting the hydraulic pressure. The reason for using the predicted road surface μ will be described below.

Now, considering the brake torque T _B, brake torque T _B
Can be calculated by the following equation (B1).

T _B = k × P (B1) where k is a proportional constant and P is the current hydraulic pressure in the wheel cylinder.

On the other hand, from the vehicle body deceleration a, the brake torque T _B can be calculated by the following equation (B
It can also be obtained by 2).

T _B = r × a × W (B2) where r is the wheel radius and W is the vehicle load. Formula (B
From 1) and (B2), the hydraulic pressure P can be expressed as P = (r × W / k) × a, so that the hydraulic pressure P is proportional to the vehicle body deceleration a. On the other hand, since the road surface μ substantially corresponds to the vehicle body deceleration, the hydraulic pressure P is eventually proportional to the road surface μ.

FIG. 11 shows a hydraulic pressure / pressure increase / decrease time conversion map used in this embodiment, and shows the relationship between the electromagnetic valve drive time ΔTP read according to the road surface μ and the pressure increase / decrease value ΔP.

In this way, the solenoid valve drive time ΔTP corresponding to the pressure increase / decrease value ΔP can be obtained for the wheel cylinder of each wheel, for example, the wheel cylinder 3a of the left front wheel 1L.
When increasing the pressure, the solenoid valve 40 should be turned off for the ΔTP time from the holding state shown in FIG. 2, and for decreasing the pressure, the solenoid valve 30 should be turned on for the ΔTP time. do it.

As described above, the electronic control unit 50 controls the solenoid valve drive time ΔTP.
When the calculation of is finished, the execution of the ABS main routine is finished.

Driving of Solenoid Valve FIG. 12 shows a 1 msec interrupt solenoid valve drive routine executed by the electronic control unit 50, and each solenoid valve shown in FIG. 1 is driven by execution of this routine. Note that the routine shown in FIG. 12 does not specify individual solenoid valves, but actually there are routines similar to this routine in the number of solenoid valves, and each routine controls the drive of the corresponding solenoid valve. Be seen.

The electronic control unit 50 first increments the 8 msec program timer T8 by a value of 1 (step S500), and then determines whether this timer value T8 is equal to a value of 8 (step S502). If the timer value T8 is not equal to the value 8, the process proceeds to step S510, which will be described later.
After resetting T8 to 0 (step S504), step S5
Go to 06. That is, the execution of step S506 is performed once every 8 msec.

In step S506, the solenoid valve drive time ΔTP is the drive timer TP
It is determined whether it is greater than the value of. And drive time Δ
When TP is smaller than the timer value TP, the process proceeds to step S510,
If it is larger, the timer value TP is rewritten to the drive time value ΔTP, and then the process proceeds to step S510. In this way, in steps S506 and S508, when the drive time ΔTP is set to a value larger than 8 msec, the execution cycle of the main routine is 8 msec.
Although the drive time that could not be processed even after is passed until the next loop, the remaining drive time is processed in the next loop. At this time, if the newly set drive time ΔTP is longer than the remaining drive time,
The remaining drive time is not executed and is truncated.

In step S510, it is determined whether the timer value TP is 0. If the determination result is negative, the process proceeds to step S512, the ON signal for driving the solenoid valve is output, the timer value TP is decremented by the value 1, and the routine ends. On the other hand, when the timer value TP is 0, the process proceeds to step S514, the solenoid valve is turned off, and the routine ends.

Since the driving time ΔTP is set in this embodiment in units of 1 msec, the interrupt routine is also executed every 1 msec, but when the minimum setting unit of the driving time ΔTP is 1 msec or less, or more In this case, the drive routine may be interrupted in the cycle of the minimum unit.

(Effects of the Invention) As described above in detail, according to the anti-skid braking method of the present invention, the deceleration of the wheel speed is obtained, and when the deceleration of the wheel speed becomes larger than the first predetermined value, the reference value is obtained. The deviation between the wheel speed and the reference vehicle speed after a lapse of a predetermined time from the time when the vehicle speed decelerates at the second predetermined deceleration and the wheel speed deceleration becomes larger than the first predetermined value. Is greater than a predetermined value, the reference vehicle speed is predicted to be decelerated at a third predetermined deceleration smaller than the second predetermined deceleration, so that the road surface μ can still be accurately detected. However, even immediately after the start of the brake pressure increase / decrease control, it is possible to quickly and accurately predict the reference vehicle speed, so that the brake pressure increase / decrease control can be accurately performed.

[Brief description of drawings]

The drawings show an embodiment of the present invention. FIG. 1 is a hydraulic circuit diagram of an anti-skid brake device for carrying out the method of the present invention, and FIGS. 2A to 2D are hydraulic control valves 16 shown in FIG.
3 is an operation explanatory view of the electronic control unit 50 shown in FIG.
FIG. 4A to FIG. 4C are flowcharts of the main routine showing the control procedure of the brake pressure increase / decrease control executed by
FIG. 5 is a flow chart of a reference vehicle body speed calculation routine, FIGS. 5A and 5B are graphs showing a time change relation between the reference wheel speed FSVW and the reference vehicle body speed VREF, and FIG. 6 is a flow chart of a slip amount ΔV calculation routine. Figures 7A and 7B show
Graphs showing the relationship between the reference vehicle speed VREF and the slip amount correction value CCV set accordingly, FIGS. 8 (a) to 8 (c) are wheel speed VW, slip amount ΔV, and wheel cylinder. FIG. 9 is a graph showing the change over time of the hydraulic pressure P,
From basic pressure increase / decrease map, slip amount ΔV and wheel acceleration GV
FIG. 10 is a graph showing the relationship between the brake pressure increase / decrease amount ΔP read according to W, the current hydraulic pressure P and the pressure increase / decrease amount ΔP of the wheel cylinder, and the solenoid valve drive time ΔTP read according to these. FIG. 11 is a graph showing the relationship between the road surface μ and the pressure increase / decrease amount ΔP, and the driving time ΔTP of the solenoid valve read in accordance with them.
FIG. 12 is a flowchart of a 1 msec interrupt routine executed by the electronic control unit 50 to drive and control the solenoid valve. 1L, 1R, 2L, 2R ... Wheels, 3,4,5,6 ... Wheel cylinders, 10 ...
Master cylinder, 16,18,20,22 ... Hydraulic control valve, 30,32,34,
40, 42, 44 ... Solenoid valve, 46 ... Accumulator, 50 ... Electronic control unit, 52, 53, 54, 55 ... Wheel speed sensor.

Claims (3)

[Claims] 1. A wheel speed is detected, a reference vehicle speed is predicted from the detected wheel speed, and a slip ratio of the wheel is maintained near a predetermined value based on a deviation between the wheel speed and the predicted reference vehicle speed. In an anti-skid braking method for controlling wheel brake pressure, a deceleration of a wheel speed is obtained, and when the deceleration of the wheel speed becomes larger than a first predetermined value, the reference vehicle speed is a second predetermined deceleration. When the deviation between the wheel speed and the reference vehicle body speed after a predetermined time has elapsed from the time when the deceleration of the wheel speed becomes greater than the first predetermined value is predicted to be decelerated, the reference vehicle body speed is Is predicted to be decelerated at a third predetermined deceleration smaller than the second predetermined deceleration, the anti-skid braking method. 2. When the deviation between the wheel speed and the reference vehicle speed after the lapse of the predetermined time is less than or equal to the predetermined value, it is predicted that the reference vehicle speed will decelerate again at the second predetermined deceleration. The anti-skid braking method according to claim 1, wherein: 3. Whether the wheel speed is equal to the predicted reference vehicle speed,
The anti-skid braking method according to claim 1 or 2, wherein when the value becomes larger than this value, the reference vehicle body speed is predicted to change at a value equal to the wheel speed.