JP2900161B2 - Vehicle anti-lock control method - Google Patents

Description

Description: TECHNICAL FIELD 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 outputs an electric signal representing a wheel speed detected by a wheel speed sensor for the purpose of securing the steering characteristics and running stability of the vehicle during braking and shortening the braking distance. Determine the control mode of the brake fluid pressure based on it, open and close the hold valve consisting of a normally open solenoid valve and the decay valve consisting of a normally closed solenoid valve,
Thus, a control unit including a microcomputer is controlled to increase, maintain, or reduce the brake fluid pressure.

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

When the brake is not operated while the vehicle is running, the brake fluid pressure Pw is not pressurized, and the hold signal HS and the decay signal DS are both 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 G is reached, the antilock control is started from this time point t1. This pseudo wheel speed Vr is at time t1
Thereafter, it is set to decrease linearly with a deceleration gradient θ of −1G. And when the deceleration dVw / dt of the wheel reaches a threshold -G _max representing a predetermined maximum deceleration
At t2, the hold signal HS is turned on, the hold valve is closed, and the brake fluid pressure Pw is held.

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.
At this point in time t3, the decay signal DS
Is turned on to open the decay valve and start reducing the brake fluid pressure Pw. Due to this pressure reduction, the wheel speed starts to accelerate at the low peak at time t4.At this low peak time t4, the decay signal DS is turned off, the decay valve is closed, and the brake fluid pressure Pw is reduced to complete the brake fluid pressure Pw. The pressure Pw is maintained. Although the wheel speed Vw reaches the high peak at the time point t7, the application of the brake fluid pressure Pw is started again from the time point t7. The pressurization here is performed by turning the hold signal HS on and off relatively in small increments, so that the brake fluid pressure Pw
Pressurization and holding are alternately repeated, whereby the brake fluid pressure Pw is slowly increased to decrease the wheel speed Vw, and the time t8
The decompression mode is generated again (from t3). Note that at the time t5 when the vehicle speed has recovered from the low peak speed Vl to the speed Vb (= Vl + 0.1Y) increased by an amount corresponding 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.
And a time point t6 when the speed Vc (= Vl + 0.8Y) is recovered from the low peak speed Vl by an amount corresponding to 80% of the speed difference Y, and the first pressurization started from the time point t7 is detected. The period Tx is determined by the determination of the road friction coefficient μ based on the calculation of the average acceleration (Vc−Vb) / ΔT during the period ΔT between the time points t5 and t6. It is determined based on the wheel deceleration dVw / dt detected just before the holding or pressurization. Due to the combination of pressurization, holding, and depressurization of the brake fluid pressure Pw as described above, the wheel speed Vw can be set without locking the wheels.
To control the vehicle speed.

By the way, the braking force distribution between the front and rear wheels is always limited so that the front wheels are always locked first, so the fact that the front wheels started antilock control means that if the master cylinder fluid pressure rises as soon as This means that the rear wheels always start the antilock control.

Also, when the anti-lock control is started, the gradient of the hydraulic pressure rise of the master cylinder becomes considerably high if the driver depresses the brake pedal strongly, so that the wheel deceleration is also large and the anti-lock control is started. Even if the pressure is reduced, the slip ratio of the wheel increases. In particular, when the slip ratio of the rear wheels is large, there has been a problem that the yaw of the vehicle body becomes large, and in a rear wheel drive vehicle, the engine is easily stopped.

(Object of the Invention) Accordingly, an object of the present invention is to provide an antilock control device that improves the directional stability of a rear-wheel drive vehicle during braking and does not cause an engine stop during braking.

(Constitution of the Invention) In order to achieve the above object, according to the present invention, when the rear wheel anti-lock control is not started, the anti-lock control signal generated in the front wheel control system in the front wheel control first cycle is responded. To slowly increase the rear wheel brake pressure,
Thereafter, the brake pressure of the rear wheel is controlled by comparing the wheel speed of the rear wheel with a threshold value.

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

FIG. 1 is a block diagram showing a three-system 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 and calculated, and the respective wheel speeds Vw1 to Vw1 are calculated.
A signal representing each of w4 is obtained. Then, the front left wheel speed Vw1 and the front right wheel speed Vw2 remain unchanged from the first system speed Vs1.
And the second system speed Vs2 as the first and second system speeds, respectively.
Is sent to the control logic circuits 9 and 10 of the left rear wheel speed Vw.
3 and the right rear wheel speed Vw4 are sent to the low select circuit 11,
The wheel speed on the low-speed side of them is selected and sent to the third control logic circuit 12 as the third system speed Vs3.

The control logic circuits 9 and 10 control the first and second system speeds.
Using Vs1 and Vs2 as control target wheel speeds, respectively, the hold signals HS1 and HS2 based on the change in the system speeds Vs1 and Vs2.
And decay signals DS1, DS2 are generated and applied to modulators 14, 15, respectively.

The control logic circuit 12 generates a hold signal HS3 and a decay signal DS3 based on a change in the third system speed Vs3, and these signals HS3 and DS3 determine the control mode.
It is provided to modulator 17 via switching circuit 16.

Further, the hold signals HS1 and HS2 output from the control logic circuits 9 and 10, respectively, are applied to an OR circuit 13, and the output of the OR circuit 13 is supplied to the control mode determination / switching circuit 16 described above.
Sent to

FIG. 2 is a flowchart showing a control mode determination / switching routine executed by the circuit 16. First, in step S1, the presence or absence of the hold signal HS3 and the decay signal DS3 output from the control logic circuit 12 of the third system is detected to determine whether or not the anti-lock control for the rear wheels has been started. If this determination is "NO", the flow proceeds to step S2, and it is determined whether or not the anti-lock control for the front wheels has been started based on the output of the OR circuit 13. If the determination in step S2 is also "NO", the process returns to step S1.

Next, in a state where the determination of step S1 is “NO”, if the determination of step S2 is “YES”, the process proceeds to step S3,
A pulse signal is output to the hold valve of the rear wheel modulator 17, and the hold valve is opened and closed at a fixed timing, and the brake fluid pressure for the rear wheel rises in a stepwise manner as indicated by the symbol A in FIG. And return to step S1.

The control mode determination / switching circuit 16 includes the control logic circuit 12
When the hold signal HS3 is output from the controller, it is determined that the anti-lock control for the rear wheel has been started, and the process proceeds from step S1 to step S4, where the output of the pulse signal to the hold valve of the rear wheel modulator 17 is stopped. Stop the fixed timing operation of the hold valve. Thereafter, the output of the control logic circuit 12 is directly supplied to the rear wheel modulator 17 so as to perform switching so that the antilock control in the normal mode is performed.

By such an operation of the control mode determination / switching circuit 16, the rear wheel control hydraulic pressure in the first cycle gradually increases in a stepwise manner, so that the drop in the rear wheel speed is reduced as is apparent from FIG.

(Effects of the Invention) As is apparent from the above description, in the present invention, in the first control cycle, the rear wheel brake pressure is slowly increased in response to the antilock control signal generated in the front wheel control system, thereby increasing the rear wheel pressure. Since the antilock control of the wheel control system is started, it is possible to prevent the rear wheel speed from dropping as in the related art. Therefore, the directional stability at the start of the antilock control in the rear wheel drive vehicle is improved, and the inability to control due to the engine stop is also eliminated.

[Brief description of the drawings]

FIG. 1 is a block diagram of a three-system antilock control device to which the present invention is applied, FIG. 2 is a flowchart of control executed by the control mode determination switching circuit, FIG. 3 is a timing chart for explaining the present invention, and FIG. FIG. 4 is a timing chart showing a conventional antilock control method, and FIG. 5 is a timing chart for explaining problems in the conventional antilock control method. 1-4 Wheel speed sensor 5-8 Arithmetic circuit 9, 10, 12 Control logic circuit 11 Low select circuit 13 OR circuit 14, 15, 17 Modulator 16 Control mode determination Switching circuit

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

Claims (1)

(57) [Claims] A comparison between wheel speeds of front and rear wheels and a threshold value,
An antilock control method for a vehicle that controls brake pressures of front and rear wheels independently of each other, wherein an antilock control signal generated in a front wheel control system in a front wheel control first cycle when rear wheel antilock control is not started. A brake pressure of the rear wheel is controlled by gently increasing the brake pressure of the rear wheel in response to the vehicle speed, and thereafter comparing the wheel speed of the rear wheel with a threshold value.