JP2724862B2 - Vehicle anti-lock control method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an antilock control method for preventing a wheel from being locked during braking of a vehicle.

(Prior Art) In general, an anti-lock control device for a vehicle is based on an electric signal representing a wheel speed detected by a wheel speed sensor for the purpose of ensuring the steerability and running stability of the vehicle during braking and shortening the braking distance. The control mode of the brake fluid pressure is determined to open and close a hold valve and a decay valve each composed of an electromagnetic valve, thereby controlling the microcomputer to increase, hold, or reduce the brake fluid pressure.

FIG. 4 shows a wheel speed Vw, a wheel acceleration / deceleration dVw / dt, and a brake fluid pressure Pw in an example of such antilock control.
FIG. 6 is a control state diagram showing a change of a hold signal and a decay signal DS for opening and closing a hold valve and a decay valve.

When the brake is not operated while the vehicle is running, the brake fluid pressure Pw is not pressurized, and both the hold signal HS and the decay signal DS are OFF. Therefore, the hold valve is opened and the decay valve is closed. However, the brake fluid pressure Pw changes with time t0 due to the brake operation.
, And rapidly rises (normal mode), whereby the wheel speed Vw decreases. A pseudo wheel speed Vr that follows the wheel speed Vw with a speed difference lower by a constant speed ΔV is set, and the pseudo wheel speed Vr is determined by the deceleration (negative acceleration) dVw / dt of the wheel at time t1 When a predetermined threshold value, for example, -1.0 G is reached, the antilock control is started from this time point t1. Then, after the time point t1, it is set so as to decrease linearly with a deceleration gradient θ of -1.0G. The ON the hold signal HS at time t2 when the deceleration dVw / dt of the wheel reaches a predetermined threshold value (-G _max)
To hold the brake fluid pressure Pw.

The wheel speed Vw further decreases due to the holding of the brake fluid pressure Pw, and the wheel speed Vw and the pseudo wheel speed Vr at time t3.
The first cycle of the antilock control is started at this time t3, the decay signal DS is turned on, the decay valve is opened, and the brake fluid pressure Pw is reduced. Due to this pressure reduction, the wheel speed starts to accelerate at the low peak speed Vl at the time t4, but at this low peak time t4 or to 10% of the speed difference Y between the wheel speed Va and the low peak speed Vl at the pressure reduction start time t3. The speed Vb (= Vl + 0. 0) increased from the low peak speed Vl by a corresponding amount.
At time t5 when the signal has recovered to 1Y), the decay signal DS is changed to
Turn off, close the decay valve, end the reduction of the brake fluid pressure Pw, and hold the brake fluid pressure Pw (FIG. 4 shows a case where the decay signal is turned off at the low peak time t4). Next, the wheel speed Vw is restored to a speed Vc (= Vl + 0.9Y) increased by an amount corresponding to 90% of the speed difference Y between the wheel speed Va and the low peak speed Vl at the decompression start time t3, and the time t6 passes. The high peak is reached at t7, but the pressurization of the brake fluid pressure Pw is started again at time t7 when the high peak speed Vh is reached. The pressurization here is performed by turning on and off the hold signal HS relatively little by little, so that the pressurization and the holding of the brake fluid pressure Pw are alternately repeated.
Pw is slowly increased to decrease the wheel speed Vw, and the time t8
The pressure reduction mode of the second cycle is generated again from (corresponding to t3). The first pressurization period started from time t7
Tx is determined by determining the friction coefficient μ of the road surface based on the calculation of the average acceleration (Vc−Vb) / ΔT during the period ΔT between the time points t5 and t6. Alternatively, it is determined based on the wheel speed Vw detected immediately before pressurization. By the combination of pressurization, holding and pressure reduction of the brake fluid pressure Pw as described above,
The vehicle speed can be reduced by controlling the wheel speed Vw without locking the wheels.

By the way, as is clear from FIG. 4, the reduction of the brake fluid pressure started at the time point t3 ends at the low peak time point t4 and is kept in a state after that, but depending on the state of the road, the wheel speed Vw may vary. After the low peak time t4, there may be no recovery. In this case, for example, as shown in FIG. 5, there is a problem that the constant state of the brake fluid pressure is continued for a long time, whereby the wheel speed Vw remains reduced and the directional stability of the vehicle body is impaired.

(Objects of the Invention) Accordingly, an object of the present invention is to provide an antilock control method capable of promptly recovering the above-described drop in wheel speed.

(Constitution of the Invention) The present invention relates to the continuation of the state of holding the brake fluid pressure from the end point of the pressure reduction of the brake fluid pressure to the start point of the pressurization,
When a certain time T1 is set and the above-mentioned brake fluid pressure holding state continues for the certain time T1, a certain time T2 (however, T2 <T1)
It is characterized in that only the pressure is reduced.

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

FIG. 1 is a block diagram showing a three-system (three-channel) antilock control device to which the present invention is applied. The outputs of the wheel speed sensors 1 to 4 are sent to arithmetic circuits 5 to 8 to be calculated.
Signals representing the respective wheel speeds Vw1 to Vw4 are obtained. The left front wheel speed Vw1 and the right front wheel speed Vw2 are sent as they are to the first and second control logic circuits 9, 10 as the first system speed Vs1 and the second system speed Vs2, respectively. The low-speed wheel speed of the wheel speeds Vw4 is selected by the low select circuit 11 and sent to the third control logic circuit 12 as the third system speed Vs3.
In each of the control logic circuits 9, 10, 12, the system speed Vs1
~ Vs3 as the wheel speeds to be controlled for each channel, and hold valve based on this system speed Vs1 ~ Vs3
Performs ON / OFF control of HV and decay valve DV.

Further, signals representing the wheel speeds Vw1 to Vw4 are sent to a pseudo vehicle speed calculating circuit 13, which calculates
The two wheel speeds Vw1 to Vw4 are set to high select, and the speeds in which the limits of the acceleration and deceleration are limited to the range of ± 1 G are output to the control logic circuits 9, 10, and 12 as the pseudo vehicle speed Vv. Each of the control logic circuits 9, 10, 12 is provided with a multi-stage decompression circuit 14, 15, 16, which is provided between the end of decompression (low peak) and the start of pressurization (high peak), ie, FIG. Switches SW1 to SW3 between time points t4 and t7
Is turned on, and the multistage pressure reducing circuits 14 to 16 operate.

In the multi-stage pressure reducing circuits 14 to 16, a fixed time T1 is set with respect to the continuation of the state of holding the brake fluid pressure, and a brake fluid pressure reducing time T2 (where T2≪T1) is set. Then, as shown in FIG. 2, for example, as shown in FIG. 2, when the system speed Vs1 does not recover after the low peak time t3 and the state of holding the brake fluid pressure continues for a certain time T1, the pressure is reduced for a certain time T2. After that, if the system speed Vs1 does not recover and the state of holding the brake fluid pressure continues for the predetermined time T1 again, the pressure is reduced again for the predetermined time T2. It should be noted that in this case, estimated vehicle speed lower than Vv, and to this Vv, threshold speed Vr to follow with at a predetermined speed difference [Delta] V ₁ or a certain ratio,
Is maintained, and until the system speed Vs1 recovers to the threshold speed Vr, the holding of the time T1 and the pressure reduction of the time T2 are repeated to quickly recover the system speed Vs1. The operations of the other multi-stage pressure reducing circuits 15 and 16 are the same as described above.

Next, FIG. 3 is a flowchart showing a control routine performed by each of the multi-stage pressure reducing circuits 14 to 16 by taking the circuit 14 as an example.

First, to set the threshold speed Vr as Vr = Vv-ΔV ₁ in step S1. Next, in step S2, it is determined whether or not the system speed Vs1 is lower than the threshold speed Vr. If the determination in step S2 is "YES", step S3
It is determined whether or not the brake fluid pressure is in the holding state. If the determination in step S3 is "YES", a holding timer with a time-up time of T1 is set in step S4, and the holding timer is incremented each time this flow is repeated. If it is determined in step S5 that the hold timer has expired, the hold timer is cleared to zero in step S6. In the next step S7, the pressure reduction signal is turned ON, pressure reduction is started, and the process returns to step S1.

Next, when pressure reduction is started, the determination in step S3 is “NO”.
Then, the process proceeds to step S8, in which a decompression timer having a time-up time of T2 is set, and the decompression timer is incremented each time this flow is repeated. If it is determined in step S9 that the time of the pressure reducing timer has expired, the pressure reducing timer is cleared to zero in step S10. In the next step S11, the holding signal is turned ON, the brake fluid pressure at that time is held, and the process returns to step S1. Note that the holding timer and the pressure reducing timer are cleared to zero at the time of the low peak of the system speed Vs1.

(Effects of the Invention) As is clear from the above description, according to the present invention, if the state of holding the brake fluid pressure from the end of depressurization to the start of pressurization becomes longer, the pressure is reduced stepwise. As a result, the wheel speed recovers quickly, and the directional stability of the vehicle body can be secured.

[Brief description of the drawings]

1 is a block diagram of a three-system antilock control device to which the present invention is applied, FIG. 2 is an explanatory diagram of the present invention, FIG. 3 is a flowchart thereof, FIG. 4 is a control state diagram in conventional antilock control, FIG. 5 is an explanatory diagram thereof. 1-4 Wheel speed sensor 9, 10, 12 Control logic circuit 11 Low select circuit 14, 15, 16 Multistage pressure reducing circuit

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Katsuya Miyake 5-4-7 Higashi, Hanyu-shi, Saitama Prefecture Akebono Brake Industry Co., Ltd. Development Headquarters (56) References JP-A-58-26660 (JP, A)

Claims (1)

(57) [Claims] 1. An anti-lock control method for a vehicle in which a brake fluid pressure is reduced, held and increased in response to a change in wheel speed during braking. A predetermined time T1 is set for the continuation of the state of holding the brake fluid pressure until the start time, and when the holding state of the brake fluid pressure continues for the certain time T1, the pressure is reduced for a certain time T2 (where T2 <T1) An anti-lock control method for a vehicle, comprising: