JPH02299963A - Antilock control method for 4-wheel drive car - Google Patents

Abstract

PURPOSE:To reduce the occurrence of mutual interference between front and rear wheels related to braking by a method wherein, in a 3-channel antilock control method for a 4-wheel drive car, control of a brake liquid pressure is made on right and left rear wheels such that a wheel speed being the lowermost speed of four wheel speeds is a wheel speed to be controlled. CONSTITUTION:From outputs from wheel speed sensors 1 - 4 mounted to respective wheels, wheel speeds Vw1 - Vw4 are determined by computing circuits 5 - 8, respectively. Left and right front wheel speeds Vw1 and Vw2 produce first and second system speeds Vs1 and Vs2 as they are to send them to second control logic circuits 9 and 10. The lowermost wheel speed of the wheel speeds Vw1 - Vw4 is selected by a low select circuit 11, and is sent as a third system speed, i.e. a rear wheel system speed Vs3, to a third control logic circuit 12. By the control logic circuits 9, 10, and 12, ON and OFF control of a hold valve HV and a decay valve DV is effected such that the system speeds Vs1 - Vs3 are respective wheel speeds to be controlled.

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to an anti-lock control method for preventing wheels from locking during braking of a vehicle. (Prior art) Anti-lock system for vehicles in general? 1 device selects a brake fluid pressure control mode based on an electric signal that detects the wheel speed detected by a wheel speed sensor, with the aim of ensuring vehicle steering performance and running stability and shortening braking distance during braking. The decision is made to open and close the hold pulp consisting of a normally open solenoid valve and the decay valve consisting of a normally closed solenoid valve,
As a result, a control unit including a microcomputer controls the brake fluid pressure to be increased, maintained, or decreased. Figure 3 shows wheel speed Vw, wheel acceleration/deceleration dVw/dt, and brake fluid pressure P in such anti-lock control.
Changes in w and the hold signal H3 and decay signal DS for opening and closing the hold pulp and decay valve
FIG. When the brake is not operated while the vehicle is running, the brake fluid pressure Pw is not pressurized and both the hold signal H3 and the decay signal DS are OFF, so the hold pulp is open and the decay valve is closed. However, as the brakes are operated, the brake fluid pressure Pw
is pressurized rapidly from time point to (normal mode), and as a result, the wheel speed Vw decreases.The simulated wheel speed Vr follows this wheel speed Vw with a lower speed difference by a constant speed ΔV. is set, and this false wheel speed Vr is equal to the wheel deceleration (negative acceleration) dVw/d
When t reaches a predetermined threshold value, for example -IG, at time t1, anti-lock control is started from this time t1. This virtual wheel speed V' is set so that it decreases linearly with a deceleration gradient θ of -IG after time 1+.Then, when the wheel deceleration dVw/dt reaches a predetermined maximum deceleration, Kiiyu-G, , the point L when reached
At step 2, the hold signal H3 is turned ON, the hold pulp is closed, and the brake fluid pressure Pw is maintained. By maintaining this brake fluid pressure Pw, the wheel speed Vw further decreases, and at time t3, the wheel speed Vw becomes equal to the false wheel speed Vr, but at this time t3, the decay signal DS is turned ON and the decay valve is opened. , starts reducing the brake fluid pressure Pw. Due to this pressure reduction, the wheel speed shifts to acceleration after reaching a low peak at time t4, but 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 finished reducing. The wheel speed Vw reaches a high peak at the sixth time point t7 when the brake fluid pressure Pw is maintained, but the brake fluid pressure Pw starts to be increased again from this time point t7. The pressurization here is performed by alternately repeating pressurization and holding of the brake fluid pressure Pw by turning the hold signal H3 on and off in relatively small steps, thereby increasing the brake fluid pressure Pw.
is slowly increased to reduce the wheel speed Vw4-, and at time t
From 8 (corresponding to 13), the decompression mode is generated again. Note that the speed Vb increased from the low peak speed VZ by an amount corresponding to 10% of the speed difference Y between the wheel speed Va and the low peak speed VZ at the time t3 when pressure reduction starts
) and 80% of the above speed difference Y.
A time point t6 is detected when the speed has recovered to the speed Vc (=VJ+0.8Y) increased from the low peak speed vl by an amount corresponding to
x is the above time t5 and

It is determined by determining the road surface friction coefficient μ based on the calculation of the average acceleration (Vc-Vb)/ΔT during the period ΔT between The vehicle body speed is controlled by controlling the wheel speed Vw without locking the wheels by a combination of pressurization, holding, and depressurization of the brake fluid pressure Pw, which is determined based on the detected wheel deceleration dVw/dL and is 0 or more. can be reduced. By the way, when applying the above-mentioned anti-lock control method to a vehicle, generally speaking, regarding the left and right front wheels, the left front wheel,
The wheel speed of the front right wheel is set as the wheel speed to be controlled, and for the left and right rear wheels, the lower wheel speed of the two wheel speeds is selected (low select) and this is set as the wheel speed to be controlled for the rear wheels, and each is independently controlled. A three-channel anti-lock control method for controlling brake fluid pressure is widely used. In this case, in vehicles with a structure in which the front and rear wheels are not dynamically connected to each other, such as front-wheel drive vehicles or rear-wheel drive vehicles, anti-lock control is applied to the front and rear wheels independently as described above. However, there is no mutual interference related to braking force between the front and rear wheels. However, when the above-mentioned three-channel anti-lock control method is applied as is to a four-wheel drive vehicle, mutual interference occurs between the front and rear wheels in terms of braking force, making it impossible to obtain smooth braking characteristics, resulting in the presence of a so-called jerky feeling. There was a problem that could not be denied. (Objective of the Invention) Therefore, the present invention aims to reduce mutual interference related to braking between the front and rear wheels when a three-channel anti-lock control method with independent left and right front wheels and select low left and right rear wheels is applied to a four-wheel drive vehicle. An object of the present invention is to provide an anti-lock control method that can obtain smooth braking force. (Structure of the Invention) Therefore, the present invention provides, when applying a 3-channel anti-lock control method to a four-wheel drive vehicle, the lowest of the four wheel speeds for the left and right rear wheels, i! ! The brake fluid pressure is controlled using the wheel speed as the controlled wheel speed. (Example) Examples of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram showing a three-system (three-channel) anti-lock control device to which the present invention is applied, in which the outputs of wheel speed sensors l to 4 are sent to calculation circuits 5 to 8 and calculated, and each wheel Vwl to A signal is obtained for each of Vw4. Then, the left front wheel speed Vwl and the right front wheel speed Vw2 are directly converted to the first system speed Vsl and the second system speed V32 to the first and second control logic circuits 9.1, respectively.
Sent to 0. In addition, the lowest wheel speed among the four wheel speeds of left front wheel speed Vwl, right front wheel speed Vw2, left rear wheel speed Vw3, and right rear wheel speed Vw4 is selected by the low select circuit 1 and the third system speed is selected. It is sent to the third control logic circuit 12 as Vs3, that is, the rear wheel system speed. Each control logic circuit 9.10. ．． 12, the system speed Vs
l-Vs3 are respectively controlled target wheel speeds (hereinafter simply referred to as wheel speeds VwJ), hold valve I (V and decay valve D
Performs ON/OFF control of V. Furthermore, a signal indicating each wheel speed Vwl to Vw4 is sent to the pseudo vehicle speed calculation circuit 13;
High selects the four wheel speeds Vwl to Vw4,
Furthermore, the speed with the follow-up limit for the fastest wheel speed limited to the range of ±1c is outputted to each control logic circuit 9, 10, and 12 as [12 vehicle body speed Vv. As described above, in this embodiment, the system speed is conventionally configured based on independent system speeds for the left and right wheels for the front wheels, and system speeds obtained by selecting the low speed side of the two left and right wheels (low selection) for the rear wheels. As is clear from the block diagram shown in Figure 1, the left and right front wheel system speeds Vsl and Vs2 are determined in the same way as before, but the rear wheel system speed Vs3 is now This is obtained by selecting the lowest wheel speed from the four wheel speeds Vwl to Vw4 of the left and right front wheels and the left and right rear wheels using the selection circuit 11. Therefore, as can be seen from the control diagram according to the present invention shown in FIG. 2, by low selecting the four wheel speeds for rear wheel control, the control fluid 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. (Effects of the Invention) As is clear from the above description, according to the present invention, in a four-wheel drive vehicle, for the left and right rear wheels, the lowest wheel speed among the four wheel speeds is set to the controlled wheel speed. By controlling the brake fluid pressure as a function of speed, the control fluid pressure in the rear wheel system is suppressed to a lower level than that in the front wheel system, and the braking force from the front wheels is smoothly transmitted to the rear wheels, reducing mutual interference between the front and rear wheels. This can reduce the jerkiness and eliminate the jerky feeling.

[Brief explanation of 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 n. 1-4-Wheel speed sensors 5-8-Arithmetic circuit 9.10, 12-Control ROSIC circuit IL--Low select circuit 13-Pseudo vehicle speed arithmetic circuit

Claims (1)

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