JP2707318B2 - Anti-lock control method for four-wheel drive vehicle - 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 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. To determine the control mode of the brake fluid pressure, 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. 3 is a control 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 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 G is reached, 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, but at this low peak time t4, the decay signal DS is turned off, the decay valve is closed, the brake fluid pressure Pw is reduced, and the brake fluid pressure is ended. 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 alternately repeating pressurization and holding of the brake fluid pressure Pw by turning on / off the hold signal HS relatively little by little.
Pw is slowly increased to decrease the wheel speed Vw, and the time t8
The decompression mode is generated again (from t3). The time t5 at which the speed Vb (= Vl + 0.1Y) is increased from the low peak speed Vl 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, when the above-described anti-lock control method is applied to a vehicle, generally, for the left and right front wheels, the left front wheel,
The wheel speeds of the right front wheel are respectively set as control target wheel speeds, and for the left and right rear wheels, a low-speed wheel speed of the two wheel speeds is selected (low select), and this is set as the rear wheel control target wheel speed. A three-channel anti-lock control method for controlling the brake fluid pressure is widely used.

In this case, like a front wheel drive vehicle or a rear wheel drive vehicle,
In a vehicle having a structure in which the front and rear wheels are not connected to each other dynamically, even if the front and rear wheels are independently anti-lock controlled as described above, mutual interference related to the braking force between the front and rear wheels may occur. Will not occur.

However, when the above-described three-channel anti-lock control method is applied to a four-wheel drive vehicle as it is, mutual interference relating to the braking force between the front and rear wheels occurs, so that smooth braking characteristics cannot be obtained, and the existence of a so-called jerky feeling is denied. There was a problem that it was not possible.

Accordingly, an object of the present invention is to reduce mutual interference related to braking between front and rear wheels when a three-channel anti-lock control method using left and right front wheels independent and left and right rear wheel select rows is applied to a four-wheel drive vehicle. Accordingly, an object of the present invention is to provide an anti-lock control method capable of obtaining a smooth braking force.

(Constitution of the Invention) Accordingly, in the present invention, when the three-channel anti-lock control method is applied to a four-wheel drive vehicle, the lowest wheel speed among the four wheel speeds for the left and right rear wheels is controlled. It is characterized in that the brake fluid pressure is controlled as the speed.

(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 wheels Vw1 to Vw4 are obtained. Then, the front left wheel speed Vw1 and the front right wheel speed Vw2
First and second system speeds Vs1 and Vs2, respectively.
And sent to the second control logic circuits 9 and 10.

Also, front left wheel speed Vw1, front right wheel speed Vw2, rear left wheel speed Vw
The lowest wheel speed among the four wheel speeds of the rear wheel speed 3 and the right rear wheel speed Vw4 is selected by the low select circuit 11 and sent to the third control logic circuit 12 as the third system speed Vs3, that is, the rear wheel system speed. Can be Each control logic circuit 9,
In 10 and 12, the system speeds Vs1 to Vs3 are respectively set as control target wheel speeds (hereinafter simply referred to as “wheel speeds Vw”), and the ON / OFF control of the hold valve HV and the decay valve DV is performed based on the wheel speeds Vw. Do.

Further, signals representing the respective wheel speeds Vw1 to Vw4 are sent to a pseudo vehicle speed calculating circuit 13, which selects the four wheel speeds Vw1 to Vw4 in a high-selection manner and further sets a tracking limit for the fastest wheel speed to ± 1G. Is output to each of the control logic circuits 9, 10, and 12 as the pseudo vehicle speed Vv.

As described above, in the present embodiment, the system is configured based on the system speeds obtained by selecting the low-speed side of the left and right two wheels (low select) for the left and right wheels for the front wheels, and the system speed for the rear wheels, respectively. The three-channel anti-lock control method has been revised. As is apparent from the block diagram shown in FIG. 1, the method of obtaining the left and right front wheel system speeds Vs1 and Vs2 is the same as the conventional method, but the rear wheel system speed Vs3 is low. It is obtained by selecting the lowest wheel speed among the four wheel speeds Vw1 to Vw4 of the left and right front wheels and the left and right rear wheels by the selection circuit 11.

Therefore, as can be seen from the control state diagram according to the present invention shown in FIG. 2, the control of the rear wheels is performed by performing low-selection of four wheel speeds, so that the control hydraulic pressure of the rear wheel system is suppressed to be lower than that of the front wheel system. Since the braking force is smoothly transmitted from the front wheels to the rear wheels, mutual interference between the front and rear wheels is reduced.

(Effect of the Invention) As is clear from the above description, according to the present invention, 4
In a wheel drive vehicle, by controlling the brake fluid pressure for the left and right rear wheels using the lowest wheel speed of the four wheel speeds as the control target wheel speed, control of the rear wheel system compared to the front wheel system is performed. Since the hydraulic pressure is suppressed to a low level and the braking force of the front wheels is smoothly transmitted to the rear wheels, mutual interference between the front and rear wheels is reduced, and the jerky feeling can be 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 an explanatory diagram of the present invention, and FIG. 3 is a control state diagram in conventional antilock control. 1-4 wheel speed sensor 5-8 arithmetic circuit 9, 10, 12 control logic circuit 11 low select circuit 13 pseudo vehicle speed arithmetic circuit

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Megumi Eguchi 5-4-1, Higashi, Hanyu-shi, Saitama Prefecture Akebono Brake Industry Co., Ltd. (72) Katsuya Miyake 5-4-71, Higashi, Hanyu-shi, Saitama No. Akebono Brake Industry Co., Ltd. (72) Inventor Hideo Akima 1015 Uedanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Prefecture Inside Fujitsu Co., Ltd. Fujitsu Limited (56) References JP-A-62-251264 (JP, A) JP-A-62-105756 (JP, A)

Claims (1)

(57) [Claims] When a three-channel anti-lock control method for independently controlling brake fluid pressure for a left front wheel, a right front wheel, and left and right rear wheels is applied to a four-wheel drive vehicle, An anti-lock control method for a four-wheel drive vehicle, characterized in that the brake fluid pressure is controlled using the lowest wheel speed of the four wheel speeds as a control target wheel speed.