JP2949741B2 - Anti-skid braking method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an anti-skid braking method for preventing wheel lock during braking of an automobile.

(Prior Art) This type of anti-skid braking method is based on a method in which a vehicle is traveling on a low μ road such as a wet road surface or a snowy road, and the vehicle slips on the braking and travels on a high μ road. Above all, it is effective in preventing slipping of wheels caused by sudden braking, that is, locking of the wheels, thereby preventing the skid of the vehicle at the time of braking, ensuring its steering stability, and braking. The distance can be shortened.

Actually, in implementing the anti-skid braking method, when a wheel has a tendency to lock, first, the brake tendency is reduced by reducing the brake pressure of the wheel, and then the rotation tendency of the wheel is reduced. Accordingly, the brake pressure is increased or maintained, or reduced as necessary. As a result, the vehicle can be stopped without causing the vehicle to skid.

(Problems to be Solved by the Invention) By the way, as described above, when the wheel tends to lock and the brake pressure of the wheel is reduced, this pressure reducing mode is conventionally continued until the locking tendency is eliminated. It had been. Therefore, the brake pressure of the wheel suddenly decreases, and it takes a long time after that, that is, after the locking tendency is eliminated, until the brake pressure is increased to a predetermined level. In other words, since the brake pressure is increased after the decompression mode is performed, and it takes time until the braking of the wheels works effectively, the efficiency of shortening the braking distance is poor. Further, if the brake pressure of one wheel is significantly reduced, the operability and running stability of the automobile will be adversely affected.

The present invention has been made based on the above-described circumstances, and an object of the present invention is to reduce the brake pressure of a wheel effectively when the wheel tends to lock, thereby reducing the shortening rate of the braking distance. It is an object of the present invention to provide an anti-skid braking method that can improve the driving performance and running stability of an automobile.

(Means for Solving the Problems) In the anti-skid braking method of the present invention, each time a wheel tends to lock during anti-skid brake control, the pressure-reducing mode is set according to a target duration determined according to the rotation trend of the wheel. During the first depressurization mode during the lock tendency occurrence, the actual duration of the depressurization mode reaches the initial allowable duration, and then the decompression mode is suspended. During the execution of the decompression mode when the locking tendency occurs, the execution of the decompression mode is interrupted after the actual duration of the decompression mode reaches the next allowable duration that is shorter than the first allowable duration.

(Operation) According to the above-described anti-skid braking method, the execution of the first pressure reduction mode is interrupted when the actual duration reaches the first allowable duration, so that the brake pressure of the wheel continues for the target duration. It does not decrease,
A large decrease in the brake pressure is prevented. In addition, the execution of the next decompression mode is also suspended after the actual duration reaches the next allowable duration, but since the next allowable duration is shorter than the initial allowable duration, the next decompression mode is the first decompression mode. It is interrupted earlier than in the mode, and in this case too, the brake pressure on the wheels does not drop too much.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 schematically shows a configuration of an anti-skid brake device incorporated in an automobile. The anti-skid brake device includes a tandem-type master cylinder 1 with a vacuum brake booster. The master cylinder 1 is operated by a brake pedal 2.

From the master cylinder 1, two master cylinder side brake lines 3, 4 extend through the brake pressure adjusting device 5, and 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 to the wheel brakes 6 of the right front wheel and the left rear wheel from the brake pressure adjusting device 5 via two brake lines 7, respectively. The pipeline 4 is connected from the brake pressure adjusting device 5 to the wheel brakes 6 of the left front wheel and the right rear wheel via the remaining two brake pipelines 7, respectively. That is, the brake pipeline extending from the master cylinder 1 to each wheel brake 6 is arranged in a so-called diagonal split system.

The brake pressure adjusting device 5 reduces the brake pressure in the wheel brake 6 at one of the wheels of the vehicle when the anti-skid brake control (ABS) is started due to the tendency of locking during braking. by doing,
The locking tendency of the wheel is released, and thereafter, the brake pressure is increased according to the rotation trend of the wheel, or the brake pressure is maintained as needed.

As an example of the above-described brake pressure adjusting device 5, FIG. 2 shows a brake pressure control unit 50 for controlling the brake pressure of the wheel brake 6 in combination with one wheel brake 6, The brake pressure control unit 50 includes a hydraulic pressure control valve 51. The hydraulic pressure control valve 51 has a piston chamber 53 and a valve chamber 54 which are coaxially communicated with each other in a housing 52, and an expander piston 55 is slidably fitted in the piston chamber 53. Have been combined. Thereby, 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. This pressure chamber 56
It is connected to an accumulator 59 via a port 57 and a hydraulic line 58. A pressure fluid of a predetermined pressure is stored in the accumulator 59 when the vehicle is braked. An electromagnetic valve 60 is interposed in the hydraulic line 58. The solenoid valve 60 is composed of a two-port, two-position solenoid on-off valve. A check valve 61 that opens only toward the pressure chamber 56 is interposed at the open position. Further, the solenoid valve 60 and the pressure chamber 56
A return line 62 extends from a portion of the hydraulic line 58 between the first and second lines, and the return line 62 is connected to a reservoir 63. An electromagnetic valve 64 is also inserted in the return line 62. The solenoid valve 64 is a two-port, two-position solenoid on-off valve, and is opened only toward the reservoir 63 at the open position. Therefore, when the solenoid valve 60 is in the open position and the solenoid valve 64 is in the closed position, the pressure chamber 56
, A pressurized liquid is supplied from an accumulator 59 to raise the pressure inside the piston. In this case, the piston 55 is pushed down as shown in FIG.
It comes into contact with a step surface 65 that partitions the valve chamber 54 from the valve chamber 54. On the other hand, when the solenoid valve 60 is in the closed position and the solenoid valve 64 is in the open position, the pressure fluid in the pressure chamber 56 is returned to the reservoir 63 via the return line 62.

On the other hand, the valve chamber 54 is formed from a stepped hole having a small diameter on the piston chamber 53 side.
A stepped valve piston 66 is slidably fitted in the large-diameter hole of the valve chamber 54. Therefore,
2, the lower end of the valve piston 66, that is, the pressure chamber is located between the large-diameter piston and the lower end wall of the valve chamber 54.
A pressure chamber 67 is formed between the solenoid valve 60 and the accumulator via a port 68 and a hydraulic line 69.
59, and is connected to a portion of a hydraulic line 58. 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 determined by the pressure chamber 56.
Is smaller than the pressure receiving area of the expander piston 55 facing the front end.

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

A port 71 is provided on the inner peripheral surface of the large-diameter hole in the valve chamber 54.
Are open, so that this port 71
It is always in communication with 70. On the other hand, the port 71 is connected to the master cylinder 1 side via a corresponding upstream portion of the brake line 7. In the housing 52, a port 72 is formed, one end of which is open to the outer peripheral surface of the housing 52 and is connected to one wheel brake 6 via a downstream portion of the corresponding brake pipe 7. The other end of the port 72 is connected to the annular groove 73 formed on the step surface 65 between the piston chamber 53 and the valve chamber 54 described above. And
The annular groove 73 is connected to the passage 70 via a plurality of radiation grooves 74 also formed on the step surface 65. Therefore, the master cylinder 1 side and the wheel brake 6 side
The connection can be made via a passage 71, a passage 70, a radiation groove 74, an annular groove 73 and a port 72.

In the middle of the passage 70, that is, a step surface between the large-diameter hole portion and the small-diameter hole portion of the valve chamber 54 is formed as a valve seat 75, while the small-diameter portion and the intermediate-diameter portion in the valve piston 66 are formed. A sealing member cooperating with the valve seat 75 is provided on the step surface between
90 is installed.

Further, a valve chamber 76 is formed in the valve piston 66. The valve chamber 76 is formed from a stepped hole in the same direction as the valve chamber 54, and a valve member 77 is accommodated in the valve chamber 76. The valve member 77 is urged by a valve spring 79 toward a seal member 78 fixed to a step surface of the valve chamber 76. The valve member 77 passes through a small diameter portion of the valve chamber 76 through a rod portion. 80 is extended. The rod portion 80 extends from the valve chamber 76 to the outside of the valve piston 66, that is, the piston chamber 53.
In the valve piston 66, a radiation groove 81 similar to the radiation groove 74 described above is formed on the distal end surface on the piston chamber 53 side. Accordingly, the valve chamber 76 and the passage 70 are in communication with each other via the radiation groove 81. Further, the valve chamber 76 is always in communication with the passage 70 through the communication hole 82.

According to the above-described brake pressure control unit 50, when one solenoid valve 60 is in the open position and the other solenoid valve 64 is in the closed position, the state shown in FIG. 2 is obtained. At this time, the same pressure is supplied to both of the pressure chambers 56 and 67 from the accumulator 59. In this case, the difference between the pressure receiving areas of the expander piston 55 and the valve piston 66 increases the expander pressure. The piston 55 is moved downward to come into contact with the step surface 65 described above. At this time,
The valve piston 66 is pushed down so as to open the passage 70, and the valve member 77 is also pushed down via its rod 80 so as to be separated from the seal member 78. In such a state, the passage 70 in the hydraulic pressure control valve 51 is provided between the master cylinder 1 side and the wheel brake 6 side.
Etc., and therefore the master cylinder 1
The brake pressure that has been set up inside can be transmitted to the wheel brake 6 as it is.

2, when the solenoid valve 60 is switched to the closed position and the solenoid valve 64 is switched to the open position, in this case, the pressure chamber 56 is disconnected from the accumulator 59, and the reservoir 63 is disconnected. Therefore, the pressure in the pressure chamber 56 decreases, so that the expander piston 55 moves away from the valve piston 66 due to the brake pressure, that is,
In FIG. 2, the valve piston 66 is moved upward, and at the same time, the valve piston 66 is also moved upward. As a result, the passage member 70 is closed by the sealing member 90 of the valve piston 66 sitting on the valve seat 75. Further, since the rod 80 of the valve body member 77 projects from the valve piston 66, the valve member 77
Abuts against the seal member 78, whereby the path connecting the master cylinder 1 side and the wheel brake 6 side through the valve chamber 76 is also closed. Therefore, at this point, the connection between the master cylinder 1 and the wheel brake 6 is disconnected, and the brake pressure is not transmitted from the master cylinder 1 to the wheel brake 6. Also,
In this state, as described above, the expander piston 55
Moves upward, the volume defined between the expander piston 55 and the step surface 65 is increased, and as a result, the brake pressure of the wheel brake 6 is reduced.

When both of the solenoid valves 60 and 64 are switched to the closed position from the above-described state where the brake pressure is reduced, in this case, the pressure chamber 56 is in a hydraulically blocked state, so that the brake pressure of the wheel brake 6 is reduced. It will be kept at the pressure at that time.

Further, from the above-described brake pressure holding state, when only the solenoid valve 60 is switched to the open position, the pressure in the pressure chamber 56 is increased by connecting the pressure chamber 56 to the accumulator 59. , The expander piston 55 begins to move downward as seen in FIG. When the expander piston 55 moves downward in this manner, the above-described volume is reduced again, and as a result, the brake pressure in the wheel brake 6 is increased.

As is clear from the above description, the brake pressure control unit 50 reduces, holds, or increases the brake pressure of the wheel brake 6 during braking by switching the solenoid valves 60, 64. Can be.

The operation of the brake pressure adjusting device 5, that is, the operation of the brake pressure control unit 50 paired with each wheel brake 6,
The electronic controller 8 is controlled by an electronic controller 8. Therefore, the electronic controller 8 includes a wheel speed sensor 9 for detecting the wheel speed of each front wheel FW and each rear wheel RW, and a brake for detecting depression of the brake pedal 2. It is electrically connected to the switch 10 and the like. Therefore, the electronic controller 8 receives the sensor signals from the wheel speed sensor 9 and the brake switch 10 and, based on these sensor signals, based on these sensor signals, the brake pressure adjusting device 5, that is, the solenoid valve 60 of each brake pressure control unit 50. , 64 to output its operation control signal.

Next, the function of the electronic controller 8 will be described.
The function is performed according to the flowchart shown in the S main routine. That is, in step S1, the wheel speed VW and the wheel acceleration / deceleration GVW of the front wheel FW and the rear wheel RW are calculated based on the sensor signals from the wheel speed sensors 9, respectively. More specifically, in the case of this embodiment, the wheel speed sensor 9 includes a gear-shaped disk that rotates with the wheel,
The wheel speed sensor 9 is configured to output a pulse signal every time each tooth of the disk is detected. And the electronic controller 8
Receives the pulse signal from each wheel speed sensor 9, calculates the angular velocity of the wheel from the time interval of generation of the pulse signal, and multiplies it by the radius of the wheel, thereby obtaining the front wheel FW and the rear wheel RW of each wheel. Calculate the wheel speed VW. The wheel speed VW obtained in this way is temporarily stored in a memory (not shown) in the electronic controller 8. Then, the wheel speed VWn calculated this time and the wheel speed VWn-1 calculated last time are calculated.
, The wheel acceleration / deceleration GVW (VWn-VWn-1) at each of the front wheel FW and the rear wheel RW is calculated and obtained.

In the next step S2, the reference vehicle speed VREF is calculated and calculated. In this case, regarding the calculation of the reference vehicle speed VREF,
During braking, in consideration of whether the ABS is operating or not, first, a reference wheel speed SVW is obtained from each wheel speed VW, and from this reference wheel speed SVW, a value of a road surface μ on which the vehicle travels,
Actually, the reference vehicle speed V is considered in consideration of the value of the wheel acceleration / deceleration GVW.
REF will be required. It is to be noted that, when the ABS main routine is started by depressing the brake pedal 2 at first, it is determined whether or not the ABS is operating.
Assuming that the vehicle is not operating and the vehicle is traveling on a so-called high μ road, the reference vehicle speed VREF is obtained, and when the reference vehicle speed VREF is a predetermined speed (for example, 10 km / h or more),
In addition, as shown in FIG. 4, the reference vehicle speed VREF and the wheel speed VW
Is greater than a predetermined value, AB
It is determined that S is operating. Further, once the operation of the ABS is started, the ABS operation is continued until a predetermined control condition is satisfied.

When the reference vehicle speed VREF is obtained in this way, the process proceeds to the next step S3, in which the slip amount ΔV of each wheel is calculated and obtained.

FIG. 5 shows a calculation routine of the slip amount ΔV in detail. In this calculation routine, steps S300, S
In 304, it is determined whether or not the ABS is operating and whether or not a bad road is being detected with respect to the traveling path of the vehicle. These determinations are for performing the operation of the ABS accurately and performing the smooth braking, and the conditions for starting the operation of the ABS are as described above. In addition, the detection of the rough road is to detect the unevenness of the road surface by the vibration cycle of the wheel acceleration / deceleration GVW, for example. More specifically, when the vehicle speed is low such that the operation of the ABS is not started, or when a rough road is detected at a low vehicle speed, a large detection error may be included in the detected wheel speed VW, which will be described later. In some cases, the correction of the slip amount ΔV is not preferable. Therefore, in steps S300 and S304, it is determined whether or not there is the above risk.

If the determination result in step S300 is negative (N), the process proceeds to step S301, where the reference vehicle speed VREF obtained in step S2 is equal to or less than a predetermined value XREF (for example, 60 km / h). Is determined. At high speeds, the effect of the detection error on the wheel speed VW is small, so the process proceeds to step S306.
If not greater than REF, the process proceeds to step S302, where the correction value DDV of the step amount ΔV is set to a value of 0.

On the other hand, when the ABS is operating and no rough road is detected, and the reference vehicle speed VREF is the predetermined value X as described above.
If it exceeds REF (for example, 60 km / h), step S306 is executed, and it is determined whether or not the traveling path of the vehicle is a low μ road. Here, as described above, when the ABS main routine is started, it is assumed that the traveling road is a high μ road, but the wheel acceleration / deceleration GV obtained in step S1 is determined.
When the value of the road surface μ estimated from W is larger than a predetermined value, it is determined that the road is a low μ road.

When it is determined in step S306 that the road is not a low μ road, the process proceeds to step S308, and in this step S308,
Correction value DD according to reference vehicle speed VREF from high μ road table
V is read. The high μ road table is shown in FIG. As is apparent from FIG. 6, the reference vehicle speed
When VREF is 60 km / h or less, the correction value DDV is set to a negative value, whereas when the reference vehicle speed VREF is higher than 60 km / h, the correction value DDV is set to a positive value. Is done.

On the other hand, when the determination in step S306 is positive (Y), the process proceeds to step S310, and in this step S310, the low μ
A correction value DDV corresponding to the reference vehicle speed VREF is read from the road table. The low μ road table is shown in FIG. As is apparent from FIG. 7, the reference vehicle speed VREF
Is less than 80 km / h, the correction value DDV is set to a positive value, and the reference vehicle speed VREF is set to 40 km / h.
In the following cases, the correction value DDV is set to a negative value.

As described above, when the correction value DDV is obtained in steps S301, S308, and S310, the correction value DDV, and the wheel speed VW of each wheel already obtained in steps S1 and S2,
From the reference vehicle speed VREF, a slip amount ΔV is calculated and obtained for each wheel by the following equation.

ΔV = VREF−VW−DDV When the calculation routine of the slip amount ΔV ends, next,
Proceed to step S4 in the ABS main routine. In step S4, based on the basic brake pressure increase / decrease map of the brake pressure stored in the memory of the electronic controller 8, the control mode of the brake pressure, that is, the amplified pressure value of the brake pressure is calculated from the slip amount ΔV and the wheel acceleration / deceleration GVW. ΔP is read. The basic increase / decrease map is shown in FIG. 8, in which each control mode is divided by the slip amount ΔV and the wheel acceleration / deceleration GVW. Regions A1 and A2 indicated by solid oblique lines indicate the pressure increasing mode, and in the region A1,
For example, ΔP is set to 0.5 kg / cm ² and the area A2
In this example, ΔP is set to, for example, 3.0 kg / cm ² . On the other hand, regions D1 to D3 indicated by dashed hatched lines indicate a decompression mode, and in regions D1, D2, and D3, ΔP is −0.5 kg / cm ² , −3.
5kg / cm ^2, are respectively set to -7.0kg / cm ^2.

In FIG. 8, an area without hatching indicates a holding mode, in which the brake pressure is held at the time. That is, in this case, Δ
P will be set to 0.

When the pressure increase / decrease value ΔP is obtained as described above,
Proceeding to step S5, the brake pressure of the wheel brake 6 of the wheel that tends to lock is actually controlled in step S5. Therefore, in controlling the brake pressure, in step S5, first, in the brake pressure control unit 50 paired with the wheel brake 6, the solenoid valve driving time ΔTP of the solenoid valves 60 and 64 is set. Here, the solenoid valve driving time ΔTP indicates a time during which the open / close positions of both the solenoid valves 60 and 64 are in the above-described brake pressure decreasing, holding, or pressure increasing state.

Here, the solenoid valve driving time ΔTP with respect to the pressure increase / decrease value ΔP
Is different from the brake pressure in the wheel brake 6 at that time, that is, the hydraulic pressure value at that time, as shown in FIG. Here, FIG. 9 shows the relationship between the pressure increase / decrease value ΔP and the current brake pressure, that is, the fluid pressure in the wheel brake 6, and the solenoid valve drive time ΔTP. For example, the fluid pressure in the wheel brake 6 In the case of Px, in order to further increase the hydraulic pressure by the pressure increase value ΔPx, the value of the solenoid valve drive time ΔTPx may be read from the position of the intersection of a straight line passing these values. That is, as is clear from FIG. 9, even with the same positive pressure increasing / decreasing value ΔPx, the higher the current hydraulic pressure P, the longer the solenoid valve drive time ΔTP.

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, respectively, but in this case, the number of parts increases. Therefore, in this embodiment, the road surface μ value described above is used instead of actually detecting the hydraulic pressure in the wheel brake 6. Hereinafter, the reason for using the road μ value will be described.

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

TB = K × P where K is a proportional constant and P is the current wheel brake 6
2 shows the hydraulic pressure inside.

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

 TB = r × a × W where r is the radius of the wheel and W is the vehicle weight.

From the above two equations, the hydraulic pressure P can be expressed as P = (r × a × W) × a, so the hydraulic pressure P is proportional to the vehicle body deceleration a. On the other hand, the road surface μ is the vehicle acceleration / deceleration GVW, that is,
Since the hydraulic pressure P can be obtained according to the vehicle body deceleration a, the hydraulic pressure P is eventually proportional to the road surface μ value.

FIG. 10 shows a hydraulic pressure / pressure increasing / decreasing map used in this embodiment. From this hydraulic pressure / pressure increasing / decreasing map, the solenoid valve drive time ΔTP is determined according to the road surface μ value and the pressure increasing / decreasing value ΔP. It can be obtained by reading.

When the solenoid valve driving time ΔTP is obtained in this way, next, a 1 msec interrupt solenoid valve driving routine shown in FIG. 11 is executed. This drive routine is for executing the pressure reduction mode of the brake pressure in one wheel brake 6, but in practice, a similar drive routine is prepared for each wheel brake 6. Also, for the brake pressure holding mode and the pressure increasing mode, it goes without saying that a solenoid valve driving routine suitable for the control mode is prepared.

In the driving routine shown in FIG. 11, in step S500, the value of the 8 msec program timer T8 is incremented by one, and in the next step S502, the value of the timer T8 becomes eight.
Is determined. No determination here (N)
In the case of, the process proceeds to step S524. In this step S524, it is determined whether or not the drive timer TP of the solenoid valve is 0. At this time, since the desired value of the drive timer TP is set to 0, the determination in step S524 is positive (Y), and the process proceeds to step S528. In this step S528, 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 turned off (the solenoid valve 60: open, the solenoid valve 64: closed). 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 the process proceeds to step S06. That is, the execution from step S506 is performed every 8 msec.

In step S506, it is determined whether or not the solenoid valve driving time ΔTP indicating the target continuation time of the pressure reduction mode is longer than the driving timer TP. Again, the value of the drive timer TP is still
Since the expected value is 0, the determination in this step S506 is positive (Y), and in the next step S508,
The value of the solenoid valve drive time ΔTP is written into the drive timer TP, and the process proceeds to step S510. In step S510, it is determined whether or not to execute the depressurization mode. If the determination is negative (N), the value of the counter CNT indicating the actual duration of the depressurization mode is set to 0, and step S528 is executed. I do.
The desired value of the counter CNT is set to 0.

On the other hand, if the determination in step S510 is positive (Y),
In step S514, the value of the counter CNT is incremented by 1, and the process proceeds to step S516. In this step S516, it is determined whether or not the ABS is started, and the first wheel tends to lock, and skid control is performed. If the determination is positive (Y), the next step S5
Proceeding to 18, in this step S518, it is determined whether or not the value of the counter CNT is 4 (or 5). At this time, since the value of the counter CNT is 1, as described above, the determination in step S518 is negative (N), and the process proceeds to step S524. In 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. You. In step S526, the solenoid valve is turned on, and the drive timer TP
Is decremented by 1 and the process returns to step S500.
Here, turning on the solenoid valve means that in the brake pressure control unit 50, the solenoid valve 60 is set to the closed position and the solenoid valve 64 is set to the open position. After returning from step S526 to step S502, step S5 is repeated until one of the determinations in steps S502 and S524 becomes positive (Y).
26 will be performed.

In this case, if the value of the solenoid valve drive time ΔTP is longer than 8 msec, the drive timer TP set in step S508
Is also greater than 8 msec, but since the program timer T8 is set to 8 msec as described above, before the determination in step S524 becomes positive (Y), steps S500, S502, The loop of S524 and S526 ends. Therefore, in this case, the solenoid valve drive time ΔTP read from FIG. 10 cannot be processed, but the remaining drive time will be processed in the next loop. Also, the remaining drive time is 8msec
If it is larger than the above, steps S502 to S504
To step S506, and this step S5
At 06, the value of the solenoid valve drive time ΔTP read next and the value of the drive timer TP are again compared, and the solenoid valve drive time ΔTP is compared.
If TP is greater than the current value of the drive timer TP,
The new solenoid valve drive time ΔTP is set to the value of the drive timer TP. Therefore, even in this case, the drive time that could not be processed is discarded.

As is apparent from the above description, when the operation of the ABS is started and the state of the pressure reduction mode for reducing the brake pressure of the wheel is continued, the first skid control (step S516) is performed at this time. In this case, the routine passing through step S518 is repeatedly executed. In this case, when the value of the counter CNT becomes 4, the process proceeds from step S518 to step S520. In this step S520, for example, the value 6 is forcibly subtracted from the value of the drive timer TP (the solenoid valve drive time ΔTP), so that the solenoid valve ON state executed via step S526 is shortened.

On the other hand, if the determination in step S516 is negative (N), that is, if the locking tendency of the wheel has not started for the second time since the ABS operation was started, instead of step S518, Then, step S522 is executed. In this step S522, it is determined whether or not the value of the counter CNT has reached 3. If this determination is positive (Y), the above-described step S520 is executed.
The solenoid valve ON state executed via step S526 will be shortened.

As described above, when ABS operation is started,
First, in the initial skid control, until the value of the counter CNT becomes 4, the solenoid valve is turned on in accordance with the solenoid valve drive time ΔTP, that is, only the initial allowable continuation time indicated by T1 in FIG. , The decompression mode will be continued,
However, when the value of the counter CNT becomes 4, step S520 is executed, so that even during the decompression mode,
The time is shortened, that is, the pressure reduction mode is interrupted, and the holding mode and the pressure reduction mode are repeated.
On the other hand, after executing the first skid control, that is,
In the case of the second or subsequent skid control, when the value of the counter CNT becomes 3, that is, when the next allowable continuation time T2 is shorter than the first allowable continuation time T1, the time of the depressurization mode is shortened. Similarly, the holding mode and the pressure reducing mode are repeated.

Although the description regarding the holding of the brake pressure and the execution of the pressure increasing mode is omitted, the solenoid valve driving routine in these holding and pressure increasing modes is the same as the operation of the solenoid valves 60 and 64 of the brake pressure control unit described above. , And the solenoid valve driving routine of FIG. 11 can be easily obtained.

(Effect of the Invention) As described above, according to the anti-skid braking method of the present invention, each time a wheel tends to lock, the pressure reduction mode is set according to the target duration determined according to the rotation trend of the wheel. When implemented, in the case of the first lock tendency, the execution of the decompression mode is suspended after reaching the first allowable duration, and in the case of the next lock tendency, the execution of the decompression mode is initially permitted. Since the suspension is performed after reaching the next allowable duration shorter than the duration, there is a tendency for the wheels to lock, and even if the decompression mode is executed, the brake pressure on the wheels does not drop significantly. After that, the brake pressure can be recovered, that is, the pressure can be rapidly increased. As a result, the effect of shortening the braking distance can be enhanced, and the operability and running stability of the vehicle can be ensured.

In addition, the brake pressure at the time when the wheel tends to lock next time is a value lower than the brake pressure at the time of the first pressure reduction mode, but in the case of the present invention, the next allowable duration is set to the initial allowable duration. In this case, the brake pressure of the wheel is not significantly reduced, which is excellent in shortening the braking distance.

[Brief description of the drawings]

BRIEF DESCRIPTION OF THE DRAWINGS The drawings show an embodiment of the present invention, FIG. 1 is a schematic structural view of a brake device for implementing the method of the present invention, FIG. 2 is a sectional view of a brake pressure control unit, and FIG. FIG. 4 is a flowchart showing the wheel speed, brake pressure and operating state of the solenoid valve during ABS operation, FIG. 5 is a flowchart of a slip amount calculation routine, and FIGS. 6 and 7 are slip amount correction values and reference values. FIG. 8 is a diagram showing a basic increase / decrease map, FIG. 9 is a diagram showing a relationship between a wheel brake fluid pressure and an increase / decrease amount, and FIG. 10 is a road surface μ and electromagnetic relationship. FIG. 11 is a diagram showing the relationship with the valve drive time. FIG. 11 is a flowchart of a solenoid valve drive routine. 1 ... master cylinder, 5 ... brake pressure adjusting device, 6
... wheel brake, 8 ... electronic controller, 9 ...
... wheel speed sensor, 10 ... brake switch, 50 ... brake pressure control unit, FW ... front wheel, RW ... rear wheel.

Continuation of front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B60T 8/58

Claims (1)

(57) [Claims] 1. An anti-skid which eliminates the locking tendency by executing a pressure reducing mode for reducing the brake pressure of each wheel of the vehicle during the anti-skid braking control every time the tendency of the locking of the wheel occurs. In the braking method, when the locking tendency occurs for the first time, the decompression mode is started in accordance with the target duration determined according to the rotation trend of the wheel, and the actual duration of the decompression mode is allowed for the first time. After reaching the time, the execution of the decompression mode is interrupted, and thereafter, when the next lock tendency occurs, the execution of the decompression mode is started according to the target duration determined according to the rotation trend of the wheel, After the actual continuation time of the decompression mode reaches the next allowable continuation time set shorter than the first allowable maximum continuation time, the decompression mode Anti-skid braking method characterized by interrupting the implementation.