JPH03159860A - Anti-skid braking method - Google Patents

Abstract

PURPOSE:To shorten the braking distance by setting the duration of the brake pressure reducing mode to different values in the case of the first occurrence of lock tendency and in the case of second time. CONSTITUTION:When anti-lock brake control is put in effect, the brake pressure in a wheel brake 6 for the wheel on which lock tendency is generated, is reduced by a brake pressure adjusting device 5 to be interposed in a brake circuit, and thereafter the brake pressure is boosted or retained. This brake pressure adjusting device 5 makes control on the basis of the outputs of a wheel speed sensor 9 and a brake switch 10 with the aid of an electronic controller 8. When the brake pressure reducing mode is put in effect, the duration of this mode is set to the initial reduction duration time T1 in the case of first lock tendency, while to the second reduction duration T2 (<T1) in the case of following occurrence of lock tendency, which facilitates recovery of the brake pressure thereafter.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an anti-skid braking method for preventing wheels from locking during braking of a motor vehicle.

(Prior art) This type of anti-skid braking method prevents wheel slippage during braking while a car is running on a low μ road such as a rain-wet road or snowy road, or when driving on a high μ road. Among other things, it is effective in preventing wheel slippage, that is, locking, caused by sudden braking.This prevents the vehicle from skidding during braking, ensures its steering stability, and improves braking. The distance can also be shortened.

In fact, when implementing the anti-skid braking method, when a wheel tends to lock, the locking tendency is first reduced by reducing the brake pressure of that wheel, and then the rotational trend of the wheel is corrected. Accordingly, the brake pressure is increased or maintained, or reduced as necessary, making it possible to stop the vehicle without causing the vehicle to skid.

(Problem to be solved by the invention) By the way, as mentioned above, the wheels tend to lock,
When the brake pressure on that wheel is reduced, this pressure reduction mode conventionally continues until the tendency to lock is resolved. Therefore, the brake pressure of the wheels suddenly decreases, and it takes time to increase the brake pressure to a predetermined level after the locking tendency is eliminated. In other words, since it takes time for the brake pressure to increase after the pressure reduction mode is implemented and for the wheels to brake effectively, the efficiency of shortening the braking distance is poor. Further, if the brake pressure of one wheel is significantly reduced, the maneuverability and running stability of the vehicle will also be adversely affected.

This invention was made based on the above-mentioned circumstances, and
The purpose of this is to effectively reduce the brake pressure on that wheel when a wheel tends to lock, thereby improving the rate of reduction in braking distance, as well as improving the maneuverability and running stability of the vehicle. The object of the present invention is to provide an anti-skid and braking method that can perform the following steps.

(Means for solving the problem) In the anti-skid braking method of the present invention, when the wheels first tend to lock and the pressure reduction mode is implemented, the brake pressure is initially reduced even during the pressure reduction mode. The decompression duration is kept within a predetermined time, and
Thereafter, when the wheels tend to lock up again and the pressure reduction mode is implemented, the next time the brake pressure continues to be reduced is set shorter than the initial pressure reduction duration even during the pressure reduction mode.

(Operation) According to the above-described anti-skid braking method, when the wheel initially has a tendency to lock and a decompression mode is implemented, this decompression mode is interrupted when the initial decompression duration time has elapsed. Furthermore, when the wheels tend to lock and the pressure reduction mode is implemented from the next time onwards, this pressure reduction mode will be interrupted when the next pressure reduction duration time, which is shorter than the initial pressure reduction duration time, has elapsed.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 schematically shows the structure of an anti-skid brake device installed in an automobile, and this anti-skid brake device is equipped with a tandem mask cylinder 1 equipped with a vacuum brake booster. This mask cylinder l is actuated by a brake pedal 2.

Two mask cylinder side brake pipes 3 and 4 extend from the mask cylinder l, and these mask cylinder side brake pipes 3 and 4 extend through the brake pressure adjustment device 5, and are connected to the front wheel FW and the rear wheel. It is connected via a branch brake line 7 corresponding to the wheel brake 6 of the RW. In this embodiment, the brake line 3 is connected from the brake pressure regulator 5 to the wheel brakes 6 of the front right wheel and the rear left wheel via two brake lines 7, respectively. The pipe line 4 is connected from the brake pressure adjusting device 5 to the wheel brakes 6 of the front left wheel and the rear right wheel via the remaining two brake pipe lines 7, respectively. That is, the brake pipes extending from the mask cylinder 1 to each wheel brake 6 are arranged in a so-called diagonal split manner.

The brake pressure adjustment device 5 is configured to
When one wheel tends to lock and anti-skid brake control (ABS) is started, by reducing the brake pressure in the wheel brake 6 for that wheel,
The locking tendency of the wheels is released, and thereafter, the brake pressure is increased depending on the rotational trend of the wheels, or the brake pressure is maintained as necessary.

As an example of the brake pressure adjustment device 5 described above, FIG. 2 shows a brake pressure control unit 50 that is combined with one wheel brake 6 to control the brake pressure of this wheel brake 6. This brake pressure control unit 50 includes a hydraulic pressure control valve 5l.

The hydraulic pressure control valve 5l has a piston chamber 53 and a valve chamber 54 located coaxially within the housing 52 and communicating with each other, and an expander piston 55 is slidably fitted into the piston chamber 53. are combined.

As a result, a pressure chamber 56 is formed between the upper end of the expander piston 55 and the upper end wall of the piston chamber 53 as seen in FIG.
is in great shape. This pressure chamber 56 is connected to an accumulator 59 via a port 57 and a hydraulic line 58. Pressure fluid at a predetermined pressure is stored in the accumulator 59 during braking of the automobile. Further, a solenoid valve 60 is inserted into the hydraulic pressure line 58. The electromagnetic valve 60 is a two-port, two-position electromagnetic on-off valve, and a check valve 6l that opens only toward the pressure chamber 56 is inserted in its open position. Further, a return pipe 62 is connected from the hydraulic pressure pipe 58 between the solenoid valve 60 and the pressure chamber 56.
extends, and this return line 62 is connected to a reservoir 63. A solenoid valve 64 is also inserted into the return conduit 62.

This electromagnetic valve 64 is a two-port, two-position electromagnetic on-off valve, and in its open position, it is opened only towards the reservoir 63 side. Therefore, when the solenoid valve 60 is in the open position and the solenoid valve 64 is in the closed position, the pressure chamber 5
6 is supplied with pressure fluid from an accumulator 59 to build up pressure therein, and in this case, the piston 55 is pushed down as shown in FIG. 2 to fill the piston chamber. 56 and the valve chamber 54. On the other hand, the solenoid valve 60
is in the closed position and the solenoid valve 64 is in the open position, the pressurized liquid in the pressure chamber 56 can be returned to the reservoir 63 via the return line 62.

On the other hand, the valve chamber 54 is formed of a stepped hole with a smaller diameter on the piston chamber 53 side, and a stepped-shaped valve piston 66 is inserted into the large diameter hole of the valve chamber 54. It is slidably fitted to the holder.

Therefore, as seen in FIG. 2, the lower end of the valve piston 66,
That is, a pressure chamber 67 is formed between the large diameter piston portion and the lower end wall of the valve chamber 54, and this pressure chamber 67 is connected to the above-mentioned solenoid valve via a port 68 and a branch pressure line 69. 60 and the hydraulic line 58 between the accumulator 59 and the accumulator 59 . Here, the pressure receiving area of the valve piston 66 facing the pressure chamber 67, that is, the pressure receiving area of the large diameter piston portion described above, is smaller than the pressure receiving area of the expander piston 55 facing the pressure chamber 56.

Furthermore, the valve piston 66, except for its large-diameter piston portion, has a stepped shape that forms a predetermined gap, that is, a passage 70, between its outer circumferential surface and the inner circumferential surface of the valve chamber 54. Therefore, the tip of the smallest diameter portion of the valve piston 66 can protrude from the valve chamber 54 into the piston chamber 53.

The inner peripheral surface of the large diameter hole in the valve chamber 54 has a bow}7
1 is open, so this port 71 is always in communication with the passage 70.

On the other hand, the port 7l is connected to the mask cylinder l side via the upstream portion of the corresponding brake pipe line 7. and,
A port 72 is formed in the hanging 52 and has one end open to the outer peripheral surface of the housing 9 zinc 52 and connected to one wheel brake 6 via the downstream portion of the corresponding brake pipe 7. The other end of this port 72 is connected to the piston chamber 53 and valve chamber 54 described above.
It is connected to an annular groove 73 formed in the stepped surface 65 between the two. This annular groove 73 also has a stepped surface 65.
It is connected to the passageway 70 via a plurality of radial grooves 74 shaped like . Therefore, the mask cylinder l side and the wheel brake 6 side include the port 71, passage 70, and radial groove 74.
, annular groove 73 and port 72.

The middle of the passage 70, that is, the stepped surface between the large diameter hole and the small diameter hole of the valve chamber 54 is shaped as a valve seat 75, while the small diameter part and the intermediate diameter of the valve piston 66 are shaped as a valve seat 75. A seal member 76 that cooperates with the valve seat 75 is attached to the stepped surface between the valve seat 75 and the valve seat 75.

Furthermore, a valve chamber 76 is formed within the valve piston 66 . This valve chamber 76 is formed with a step (i) hole facing in the same direction as the valve chamber 54l0, and a valve member 77 is accommodated in this valve chamber 76. A sealing member 78 fixed to the stepped surface of the chamber 76
is biased toward by the valve spring 79, and
A loft portion 80 extends from the valve member 77 through the small diameter portion of the valve chamber 76 .

This loft portion 80 extends from the valve chamber 76 to the valve piston 66.
In addition, in the valve piston 66, a radial groove 81 similar to the radial groove 74 described above is formed on the distal end surface of the piston chamber 53. There is. Therefore, the valve chamber 76 and the passage 70 are in communication with each other via the radial groove 8l. Further, the valve chamber 76 is constantly communicated with the passage 70 via the communication hole 82.

According to the brake pressure control unit 50 described above, one solenoid valve 60 is in the open position, and the other solenoid valve 64 is in the open position.
is in the closed position as shown in FIG. At this time, the same pressure is supplied from the accumulator 59 to both pressure chambers 56 and 67, but in this case, due to the difference in pressure receiving area between the expander piston 55 and the hub piston 1/n 6G, expander piston 55
is moved downward and comes into contact with the step surface 65 described above. At this time, the valve piston 66
The valve member 77 is also pushed open by its rod 8 away from the seal member 76.
It is pushed down through 0. In this state, the side of the mask cylinder 1 and the side of the wheel brake 6 are communicated through the passage 70 etc. in the hydraulic pressure control valve 5l, and therefore, there is a communication between the side of the mask cylinder 1 and the side of the wheel brake 6. The applied brake pressure can be directly transmitted to the wheel brake 6.

When the solenoid valve 60 is switched to the closed position and the solenoid valve 64 is switched to the open position from the state shown in FIG. Since it is connected to the pressure chamber 56
The pressure still decreases and therefore the expander piston 55
is moved away from the valve piston 66, that is, upwards in FIG. 2, by the brake pressure, and at the same time, the valve piston 66 is also moved upwards. As a result, the seal member 7G of the valve piston 66 seats on the valve seat 76, thereby closing the passage 70.

Further, the rod 80 of the valve body member 77 is connected to the valve piston 66.
By protruding from the valve body portion 77, the valve body portion 77 comes into contact with the sealing member 78, whereby the path connecting the mask cylinder l side and the wheel brake 6 side through the valve chamber 76 is also closed. Therefore, at this point, the connection between the mask cylinder l side and the wheel brake 6 side is cut off, and no brake pressure is transmitted from the mask cylinder 1 to the wheel brake 6.

Furthermore, in this state, as the expander piston 55 moves upward as described above, the volume defined between the expander piston 55 and the step surface 65 increases, and as a result, the wheel The brake pressure of the brake 6 will be reduced.

From the reduced brake pressure state described above, the solenoid valves 60 and 64
When both are switched to the closed position, in this case, the pressure chamber 56 is hydraulically blocked, so that the brake pressure of the wheel brake 6 is maintained at the pressure at that time.

Furthermore, when only the solenoid valve 60 is switched to the open position from the above-described brake pressure holding state, the pressure chamber 56 is connected to the accumulator 59, and the pressure within the pressure chamber 56 increases. , expander piston 55
, it begins to move downward as seen in Figure 2. When the expander piston 55 moves downward in this manner, the aforementioned volume is reduced again, and as a result, the brake pressure within the wheel brake 6 is increased.

As is clear from the above description, the brake pressure control unit 50 can reduce, maintain, or increase the brake pressure of the wheel brake 6 during braking by switching and controlling the solenoid valves 60 and 64. Can be done.

The operation of the brake pressure adjustment device 5, that is, the operation of the brake pressure control unit 50 that is paired with each wheel brake 6, is as follows.
Therefore, the electronic controller 8 controls each front wheel FW and each rear wheel R.
It is electrically connected to a wheel speed sensor 9 that detects the wheel speed of each wheel W, a brake switch lO that detects depression of the brake pedal 2, and the like. Therefore, the electronic controller 8 receives the sensor signals from these wheel speed sensors 9 and the brake switch IO, and, based on these sensor signals, adjusts the brake pressure regulator 5, that is, the solenoid valve 60 of each brake pressure control unit 50. .64, outputs its operation control signal.

Next, the functions of the electronic controller 8 will be explained.
This electronic controller 8 is basically an ABS controller as shown in FIG.
Follow the flowchart as shown in the main routine.
perform its functions; That is, in step S1, the wheel speeds VW and wheel acceleration/decelerations GVW of the front wheels FW and rear wheels RW are calculated based on sensor signals from each wheel speed sensor 9, respectively.

15 To be more specific, in this embodiment, the wheel speed sensor 9 is composed of a gear-shaped disk that rotates together with the wheel, and a pickup coil that is fixed opposite to the tooth surface of this disk. Therefore, each wheel speed sensor 9 outputs a pulse signal every time it detects each tooth of the disk. Then, the electronic controller 8 receives pulse signals from each wheel speed sensor 9, and
Calculate the angular velocity of the wheel from the time interval of pulse signal generation,
By multiplying this by the wheel radius, the wheel speed VW of each wheel, that is, the front wheel FW and the rear wheel RW, is calculated. The wheel speed VW determined in this way is temporarily stored in a memory (not shown) within the electronic controller 8. Then, the wheel speed VWn calculated this time and the wheel speed V calculated last time are calculated.
Based on Wn-1, wheel acceleration/deceleration GVW (VWn −VWn-1
) is calculated.

In the next step S2, a reference vehicle speed VREF is calculated and determined. In this case, the reference vehicle speed VRl6 EF is determined by first determining the reference wheel speed SVW from each wheel speed VW, taking into account whether or not the ABS is in operation during braking, and then determining the reference vehicle speed SVW from the reference wheel speed SvW. The value of the road surface μ on which the vehicle is traveling is actually determined by taking into account the value of the wheel acceleration/deceleration GVW. Note that to determine whether or not ABS is in operation, first, when the ABS main routine is started by depressing the brake pedal 2, it is determined that ABS is not in operation and the vehicle is traveling on a so-called high-μ road. By assuming that the reference vehicle speed VREF is
okm/h) and when the deviation H between the reference vehicle speed VREF and the wheel speed VW becomes larger than a predetermined value as shown in Fig. 4, it is determined that ABS is in operation. do. Also, once the ABS starts operating, this ABS
BS operation will continue until predetermined control conditions are met.

Once the reference vehicle speed VREF has been determined in this manner, the process proceeds to the next step S3, and in this step S3, the slip amount ΔV of each wheel is calculated and determined.

FIG. 5 shows the calculation routine for the slip amount ΔV in detail. In this calculation routine, step S300
, In S304, it is determined whether the ABS is in operation and whether or not the road the vehicle is traveling on is being detected as a rough road.

These determinations are made to ensure accurate ABS operation and smooth braking, and the conditions for starting ABS operation are as described above. Further, detection of a rough road is, for example, by detecting an uneven state of the road surface based on the vibration period of the wheel acceleration/deceleration GVW. To explain further, if the vehicle speed is so low that ABS operation cannot be started, or if a rough road is detected at low vehicle speed, there is a risk that the detected wheel speed VW will include a large detection error, which will be discussed later. The correction of the slip amount ΔV may be rather undesirable. Therefore,
Step S300. In S304, it is determined whether or not there is the above-mentioned risk.

If the determination result in step S300 is negative (N), the process advances to step S'301, and this step S301
Then, it is determined whether the reference vehicle speed VREF obtained in step S2 is equal to or less than a predetermined value XREF (for example, 60 km/h). At high speeds, the influence of detection errors on the wheel speed VW is small, so the process proceeds to step 8306. On the other hand, if the reference vehicle speed VREF is less than or equal to the predetermined value X REF, the process proceeds to step S302, and this step S
In 302, the correction value DDV of the slip amount ΔV is set to the value 0.

On the other hand, if the ABS is in operation and no rough road has been detected, and the reference vehicle speed VREF is equal to or higher than the predetermined value XREF (for example, 60 km/h), step 8306 is executed, and here it is determined whether the road the vehicle is traveling on is a low μ road. In this determination, when the AS main routine is started as described above, it is assumed that the traveling road is a high μ road, but the road surface μ estimated from the wheel acceleration/deceleration GVW obtained in step S1 is When it is larger than the value, it is determined that the road is low μ.

If it is determined in step 8306 that the road is not a low μ road, the process advances to step 8308, and in step S308, the reference vehicle speed V is determined from the high μ road table.
A correction value DDV corresponding to REF is read out. A table for high μ roads is shown in FIG. As is clear from Fig. 6, when the reference vehicle speed VREF is 60 km/h or less, the correction value DD■ is set to a negative value; In the following cases, the correction value DDV is set to a positive value.

On the other hand, if the determination in step 8306 is positive (Y), the process advances to step S310, and this step S310
Then, the correction value DDV corresponding to the reference vehicle speed VREF is read from the low μ road table. The table for low μ road is
It is shown in FIG. As is clear from FIG. 7, when the reference vehicle speed VREF is a little less than 80 km/h or more, the correction value DDV is set to a positive value.
In addition, if the reference vehicle speed VREF is 40 km/h or less,
The correction value DDV is set to a negative value.

As described above, steps S301 and 330
820 and S310, when the correction value DDV is calculated,
From this correction value DDV, the wheel speed VW of each wheel already found in steps Sl and S2, and the reference vehicle body speed VREF,
The slip amount ΔV is calculated for each wheel using the following equation.

ΔV=VREF-VW'-DDV When the calculation routine of the slip amount ΔV is completed, next
The process advances to step S4 in the BS main routine. In this step S4, based on the basic brake pressure increase/decrease pressure map stored in advance in the memory of the electronic controller 8, the brake pressure control mode is determined from the slip amount Δ■ and the wheel acceleration/deceleration GVW. The pressure value ΔP is read out. The basic pressure increase/decrease map is shown in FIG. 8, and in FIG. 8, each control mode is divided by the slip amount Δ■ and the wheel acceleration/deceleration GVW.

Areas AI and A2 indicated by solid diagonal lines indicate pressure increase mode, and in area AI, for example, ΔP is 0.5 kg/c.
m", and in area A2, ΔP is set to, for example, 3.0 kg/cm2. On the other hand,
Broken 21 The diagonally shaded areas Di to D3 indicate the decompression mode, and in the areas DI, D2, and D3, ΔP is -0.
5kg/cm”, -3. 5kg/cm2, -7.
They are each set to 0 kg/Cm'.

Further, in FIG. 8, the area without diagonal lines indicates a holding mode, and in this holding mode, the brake pressure is held at the current brake pressure.

That is, in this case, ΔP is set to 0.

Once the pressure increase/decrease value ΔP is determined as described above, the process proceeds to step S5, and in this step S5, the brake pressure of the wheel brake 6 of the wheel that has a tendency to lock is actually controlled.

Therefore, in controlling the brake pressure, first, in step S5, the solenoid valve driving time ΔTP of the solenoid valve 60, 64 is set in the brake pressure control unit 50 that is paired with the wheel brake 6. Here, the solenoid valve drive time ΔTP means that the opening and closing positions of both the solenoid valves 60 and 64 are
This represents the time during which the brake pressure is reduced, maintained, or increased as described above.

22 Here, as shown in FIG. 9, the solenoid valve drive time ΔTP with respect to the pressure increase/decrease value ΔP is different from the brake pressure in the wheel brake 6 at that point, that is, the hydraulic pressure value at that point. . Here, FIG. 9 shows the pressure increase/decrease value ΔP and the current brake pressure in the wheel brake 6, that is, the hydraulic pressure,
It shows the relationship with the solenoid valve driving time ΔTP, for example,
When the hydraulic pressure in the wheel brake 6 is Px, in order to further increase this hydraulic pressure by the pressure increase value ΔPx, the solenoid valve drive time ΔTPx value can be read from the position of the intersection of the straight lines passing through these values. It turns out. That is, as is clear from FIG. 9, even if the pressure increase/decrease value ΔPx takes the same positive value, the higher the current hydraulic pressure P, the longer the solenoid valve drive time ΔTP becomes.

By the way, in order to detect the brake pressure in each wheel brake 6, that is, the hydraulic pressure, it is necessary to attach a pressure sensor to each wheel brake 6, but in this case, the number of parts increases.

Therefore, in this embodiment, instead of actually detecting the hydraulic pressure in the wheel brake 6, the road surface 23 μ value described above is used. The reason for using the road surface μ value will be explained below.

Now, considering the brake torque TB, the brake torque T can be determined by the following equation.

TB=KXP where K is the proportionality constant and P is the current wheel brake 6
It shows the hydraulic pressure inside.

On the other hand, the brake torque TB can also be determined from the vehicle body acceleration/deceleration GVW, that is, the vehicle body deceleration a from the following equation.

TB:rxaxW Here, r represents the radius of the wheel, and W represents the vehicle weight.

From the above two equations, the hydraulic pressure P can be expressed as P=(rXaXW)Xa, so the hydraulic pressure P is proportional to the vehicle deceleration a. On the other hand, since the road surface μ can be determined in accordance with the vehicle body acceleration/deceleration GVW, that is, the vehicle body deceleration a, the hydraulic pressure P is ultimately proportional to the road surface μ value.

24 Figure 1O shows the hydraulic pressure/pressure increase/decrease map used in this example, and from this hydraulic pressure/pressure increase/decrease map, the solenoid valve drive time ΔTP can be determined according to the road surface μ value and the pressure increase/decrease value ΔP. can be found by reading out.

Once the solenoid valve drive time ΔTP is determined in this manner, the l msec interrupt solenoid valve drive routine shown in FIG. 11 is executed. This drive routine is for implementing a brake pressure reduction mode in one wheel brake 6, but in reality, a similar drive routine is prepared for each wheel brake 6. Furthermore, it goes without saying that electromagnetic valve driving routines suitable for the brake pressure holding mode and pressure increasing mode are also prepared.

In the driving routine shown in FIG. 11, step S500
In step S502, the 8 msec program timer T8 is incremented by the value l, and in the next step S502,
It is determined whether the value of timer T8 is equal to eight. If the determination here is negative (N), the process advances to 9e1 step S524. In this step S524,
It is determined whether the drive timer TP of the solenoid valve is 0 or not. At this time, since the initial value of the drive timer TP is set to 0, the determination in step S524 is positive (Y), and the process proceeds to step 8528. In this step 8528, the solenoid valve is turned off. Here, the solenoid valve off means that in the brake pressure control unit 50, both the solenoid valves 60 and 64 are placed in the closed position, and in this case, the brake pressure control unit 50 is in a normal state. .

On the other hand, if the determination in step S502 is positive (Y), the timer T8 is reset to 0 in the next step S504, and then the process proceeds to step SO6.

That is, execution from step 8506 is performed every 8 msec.

In step 8506, it is determined whether the solenoid valve drive time ΔTP is longer than the drive timer TP. even here,
Since the value of the drive timer TP is still at its initial value 0, the determination in step 8506 is positive (Y), and in the next step 26 S508, the drive timer TP is set to the solenoid valve drive time Δ.
The value of TP is written and the process advances to step S510.

In this step S510, it is determined whether or not to carry out an intimidation mode. If this determination is negative (N), the value of the counter CNT is set to 0, and step 7'S528 is executed. Note that the initial value of the counter CNT is set to 0.

On the other hand, if the determination in step S510 is positive (Y), the value of the counter CNT is incremented by 1 in step S514, and the process proceeds to step S516. In step S516, ABS operation is started, and it is determined whether or not the wheel has a tendency to lock for the first time, and skid control is performed. If this determination is positive (Y), the process advances to the next step S518, and this step 351
At step 8, it is determined whether the value of the counter CNT is 4 or 5. At this time, as described above, since the value of the counter CNT is l, the determination at step 8518 is negative (N), and the process advances to step S524. In this step S524, since the drive timer TP already has a value corresponding to the solenoid valve drive time ΔTP, the determination here is negative (N), and therefore the next step S526 is executed. In this step s526, the solenoid valve is turned on, the value of the drive timer TP is decremented by one, and the process returns to step S500.

Here, the solenoid valve on means that in the brake pressure control unit 50, the solenoid valve 60 is placed in the closed position and the solenoid valve 64 is placed in the open position. Also, step 8526
After returning to step S502, the determination in either step S502 or S524 is positive (Y).
Step 8526 will be executed until .

In this case, if the value of the solenoid valve drive time ΔTP is larger than 8 msec, the value of the drive timer TP set in step S508 also takes a value larger than 8 msec, but as described above, the program timer T8 is set to 8 msec, step S5
Before the determination in 24 becomes positive (Y), step S500
, S502, S524, and S52628 will end. Therefore, in this case, the solenoid valve drive time ΔTP read from FIG. 10 cannot be completely processed, but the remaining drive time is
It will be processed in the next loop. If the remaining drive time is greater than 8 msec, the process advances from step S502 to step S504 to step 3506, and in step S506, the next read electromagnetic valve drive time ΔTP and drive timer are The value is compared with TP, and the solenoid valve drive time ΔTP
is larger than the value of the drive timer TP at that time,
A new electromagnetic valve driving time ΔTP is set to the value of the driving timer TP, and therefore, even in this case, the unprocessed driving time is discarded.

As is clear from the above explanation, when ABS operation is started and the state of pressure reduction mode 1, which reduces the brake pressure of that wheel, continues, at this time, the first skid control (
If step 8516) is being executed, the routine 29 that goes through step 3518 will be executed repeatedly, but in this case, if the value of counter CNT becomes 4, step 351
8 to step S520. In this step S520, a drive timer TP (electromagnetic valve drive time ΔT
Since the value 6, for example, is forcibly subtracted from the value of P), the solenoid valve ON state executed via step S526 is shortened.

On the other hand, if the determination in step 8516 is negative (N), that is, if the wheel has a tendency to lock not for the first time but for the second time or more after the ABS operation started,
Instead of step 8518, step S522 is executed. In this step S522, it is determined whether or not the value of the counter CNT has reached 3, and this determination is positive (Y).
In this case, the above-described step S520 is executed, so that even in this case, the solenoid valve ON state executed via step 852G is shortened.

As explained above, when the ABS operation is started, first in the first skid control, the solenoid valve drive time ΔTP is maintained until the value of the counter CNT reaches 4.
Accordingly, in the ON state of the solenoid valve, that is, in FIG.
The decompression mode will continue for the initial decompression duration indicated by . However, if the value of the counter CNT is 4.
When this happens, step S520 is executed, thereby shortening the time even in the depressurization mode, that is, the depressurization mode is interrupted, and the holding mode and the depressurization mode are repeated. On the other hand, after the first skid control is executed, that is, in the case of the second or later skid control, when the value of the counter CNT becomes 3, that is, the next decompression duration T2 is shorter than the initial decompression duration TI. In this case, the time in the pressure reduction mode is shortened, and thereafter, the holding mode and the pressure reduction mode are repeated in the same manner.

Note that explanations regarding the implementation of brake pressure holding and pressure increase modes are omitted, but the solenoid valve drive routine in these brake pressure hold and pressure increase modes requires 3L to operate the solenoid valves 60 and 64 of the brake pressure control unit mentioned above. This can be easily obtained by referring to the related explanation and the electromagnetic valve driving routine shown in FIG.

(Effects of the Invention) As explained above, according to the anti-skid braking method of the present invention, when a wheel tends to lock and a brake pressure reduction mode is implemented, the duration of this pressure reduction mode is In the case of the first tendency to lock, the initial decompression duration is set, and in the case of the next tendency to lock, the next decompression duration is set to be shorter than the initial decompression duration, so that the wheels tend to lock. Even if the pressure reduction mode is implemented, the brake pressure of the wheels will not be significantly reduced, and the subsequent brake pressure can be quickly restored, that is, increased, and the efficiency of reducing the braking distance can be increased. Moreover, the maneuverability and running stability of the automobile can also be ensured.

Furthermore, if the wheels tend to lock next time, the brake pressure at that point will be lower than the brake pressure at the time when the pressure reduction mode was started for the first time, but in the case of this invention, the next time the pressure reduction duration is Since it is set to be shorter than the initial continuous time, the brake pressure at the wheels will not be significantly reduced even in this case. It becomes something.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention; FIG. 1 is a schematic configuration diagram of a brake device implementing the method of the present invention, FIG. 2 is a sectional view of a brake pressure control unit, and FIG. 3 is a diagram of an ABS main routine. Flowchart, FIG. 4 is a diagram showing the wheel speed, brake pressure, and operating state of the solenoid valve during ABS operation, FIG. 5 is a flowchart of the slip amount calculation routine, and FIG.
Figure 7 and Figure 7 are diagrams showing the relationship between the slip amount correction value and the standard vehicle speed, Figure 8 is a diagram showing the basic pressure increase/decrease map, and Figure 9 is the relationship between the hydraulic pressure of the wheel brake and the amount of pressure increase/decrease. FIG. 10 is a diagram showing the relationship between the road surface μ and the electromagnetic valve driving time, and FIG. 11 is a flowchart of the electromagnetic valve driving routine. DESCRIPTION OF SYMBOLS 1... Mask cylinder, 5... Brake pressure adjustment device, 6... Wheel brake, 8... Electronic controller, 33 9... Wheel speed sensor, 10... Brake switch, 50... Brake pressure control unit, FW...Front wheel, RW...Rear wheel.

Claims (1)

[Claims] During anti-skid brake control, by implementing depressurization mode when the car's wheels tend to lock,
In an anti-skid braking method in which the brake pressure of the wheel is reduced to eliminate the locking tendency, when the wheel first has a locking tendency and the pressure reduction mode is implemented, the wheel is in the pressure reduction mode. However, if the brake pressure continues to be reduced for the first time within a predetermined time, and the wheels tend to lock again and the above pressure reduction mode is implemented, the next time for the brake pressure to be reduced even during the pressure reduction mode. An anti-skid braking method characterized in that the initial decompression duration is set shorter than the above-mentioned initial decompression duration time.