JP2782365B2 - 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. 5 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 simulated wheel speed Vr is set so that the wheel is fed at a speed difference that is lower than the wheel speed Vw by a constant speed ΔV. When a predetermined threshold value, for example, −1 G is reached at tl, the antilock control is started from this time tl. This pseudo wheel speed Vr is at time tl
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 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). 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 speed of the right front wheel is set as a control target wheel speed. For the left and right rear wheels, a wheel speed on a low speed side is selected from two wheel speeds (rear wheel select low), and this is set as a rear wheel control target wheel speed. A three-channel antilock control method for independently 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.

In view of the above, the present inventor has previously described in Japanese Patent Application No. 1-118722, for the right and left rear wheels, the lowest wheel speed (four wheel select low speed) of the four wheel speeds to be controlled. An anti-lock control method for a four-wheel drive vehicle in which the brake fluid pressure is controlled as a speed is proposed.

According to this method, the control hydraulic pressure of the rear wheel system is controlled to be lower than that of the front wheel system, and the braking force of the front wheels is smoothly transmitted to the rear wheels. Has the effect of eliminating.

However, as shown in FIG. 3, when the front wheel select low speed is mainly selected as the four-wheel select low speed, the brake fluid pressure is reduced based on the front wheel select low speed. Causes excessive pressure reduction, which causes a problem that the braking distance increases.

(Object of the Invention) Accordingly, the present invention reduces mutual interference relating 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. An object of the present invention is to provide an anti-lock control method capable of obtaining a smooth and sufficient braking force.

(Structure of the Invention) The present invention controls the brake fluid pressure for the left and right rear wheels with the lowest wheel speed of the four wheel speeds as the control target wheel speed. If the wheel speed on the low-speed side becomes higher than the lowest wheel speed of the above four wheel speeds, the brake fluid pressure reduction time for the left and right rear wheels in each antilock control cycle is limited to a predetermined time. It is characterized by doing.

(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 (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
Of the four wheel speeds of 3 and the right rear wheel speed Vw4, the lowest wheel speed (four wheel select low speed) is selected by the four wheel low select circuit 11, and is set as the third system speed Vs3, that is, the rear wheel system speed. It is sent to the third control logic circuit 12. Further, the lower wheel speed (rear wheel select low speed) of the left rear wheel speed Vw3 and the right rear wheel speed Vw4 is selected by the rear wheel low select circuit 17, and the output thereof is supplied to the third control logic circuit 12. Sent to Each control logic circuit 9, 1
In steps 0 and 12, the system speeds Vs1 to Vs3 are set as control target wheel speeds, and the ON / OFF control of the hold valve HV and the decay valve DV is performed based on the system speeds Vs1 to Vs3.

Further, signals representing the respective wheel speeds Vw1 to Vw4 are sent to a similar vehicle speed calculating circuit 13.The calculating circuit 13 selects the four wheel speeds Vw1 to Vw4 high, and further sets the following limit to the highest wheel speed ±. The speed limited to the range of 1 G is output to each of the control logic circuits 9, 10, and 12 as the approximate vehicle speed Vv.

Each of the control logic circuits 9, 10, and 12 has a decompression end determination circuit.
14, 15, and 16 are provided.
4, 15, and 16 are connected to the control logic circuits 9, 10, and 12 via switches SW1, SW2, and SW3. The switches SW1 to SW3 are turned on during the period from time t3 to time t4 shown in FIG. 5 for each system, and turned off during the other periods according to the outputs from the control logic circuits 9, 10, and 12. It is controlled to become.

Next, FIG. 2 is a diagram showing a method of determining the low peak point of the system speed, which is the end point of the brake fluid pressure reduction in each system of the antilock control. In the figure, the system speed Vs
Decreases and approaches the low peak point, the deceleration dVs / dt
, The time of the predetermined time TM1 is started from the point of time exceeding the −1 G line at the time of the rise, and it is determined that the system speed has reached the low peak when the predetermined time TM1 has elapsed.

FIG. 3 shows the relationship between the change in the front wheel select low speed, the rear wheel select low speed, and the four wheel select low speed, the decay signal for opening and closing the decay valve of the rear wheel system, and the hydraulic pressure of the rear wheel system. It is a figure shown in comparison with.
As is apparent from this figure, in this embodiment, when the rear wheel select low speed is higher than the four wheel select low speed,
Decrease time of brake fluid pressure, that is, decay signal is ON
The hydraulic pressure of the rear wheel system is maintained at a high level by shortening the time during which the decay valve is open to T1, which is shorter than the decompression time that ends at the low peak point of the system speed. Is shown.

FIG. 4 is a flowchart showing the operation of the pressure reduction end determination circuit 16 of the rear wheel control system according to the present embodiment. First, at step S1, the time point at which the brake fluid pressure starts to be reduced (the time point shown in FIG. 5)
Start measuring the time T elapsed from t3), and then proceed to the next step S2
Proceed to. In step S2, the deceleration dVs3 / d of the rear wheel system speed
It is determined whether the gradient of t is gentler than a predetermined deceleration gradient (−1G), and if dVs3 / dt ≧ −1G (the deceleration gradient of Vs3 is gentler than the deceleration gradient of −1G), the step is performed. DVs3 / d at S3
Timing of the elapsed time TM from the time when t ≧ −1G is started, and the process proceeds to step S4. If it is determined in step S2 that dVs3 / dt <−1G (the deceleration gradient of Vs3 is steeper than the deceleration gradient of −1G), the process proceeds to step S4 without counting the elapsed time TM in step S5. In step S4, it is determined whether or not the elapsed time TM has reached the predetermined time TM1, and if TM ≧ TM1, it is determined in step S5 ′ that the system speed Vs3 has reached the low peak, It is determined that the pressure reduction stop condition is satisfied, and the hold valve is turned ON (closed) and the decay valve is turned OFF (closed) in step S6 to end the reduction of the brake fluid pressure for the left and right rear wheels.

On the other hand, in step S4, the elapsed time TM is equal to the predetermined time TM.
While the value is less than 1, the determination result is “NO”, and the process proceeds to step S7. In step S7, the rear wheel select low speed is compared with the four-wheel select low speed. If the rear wheel select low speed is higher than the four-wheel select low speed, the process proceeds to step S8, and further proceeds to step S8. Proceeding to S6, decompression is terminated before the rear wheel system speed Vs3 reaches a low peak at which decompression should be terminated. That is, in step S8, the elapsed time T from the start of pressure reduction is equal to the predetermined time.
It is determined whether or not T1 has been reached, and if T ≧ T1, step S6
Turn on the hold valve and turn off the decay valve
To reduce the brake fluid pressure for the left and right rear wheels within a predetermined time T1. Step S7
If the rear wheel select low speed is equal to the four wheel select low speed in step S9, the process proceeds to step S9, where the hold valve is kept ON (closed) and the decay valve is kept ON (open) until the low peak is determined. Continue to reduce the brake fluid pressure for the left and right rear wheels. If T <T1 in the determination in step S8, the process proceeds to step S9 to continue the decompression, and ends the decompression when T ≧ T1, but if it is determined that the peak is low before T ≧ T1, The decompression is terminated at the low peak point.

As described above, in the present embodiment, regarding the rear wheel system speed Vs3, the wheel speed based on the four-wheel select low is selected in the circuit 11, and after the start of depressurization of the rear wheel system, the rear wheel select low speed becomes lower than the four-wheel select low speed. Is also determined to be a high speed, that is, when the start of depressurization of the rear wheel system is not based on the rear wheel select low speed but on the basis of either the left or right front wheel select low speed that is the four-wheel select low speed. As shown in the control state of FIG. 3, the pressure reduction of the rear wheel system is limited so as not to continue for a predetermined time T1 or more, thereby preventing an excessive pressure reduction. However, when the rear-wheel select low speed is equal to the four-wheel select low speed, the decompression end point of the rear wheel system is determined based on the low peak point of the four-wheel select low speed, and the time limit T1 for the depressurization is not applied. ing.

As described above, it is needless to say that the decompression is terminated when it is determined that the system speed has reached the low peak even when the elapsed time from the decompression start time is less than the predetermined time T1.

(Effects of the Invention) As is apparent from the above description, according to the present invention, for the left and right rear wheels, the brake fluid pressure is controlled using the four-wheel select low speed as the rear wheel system speed, and the rear wheels are controlled. When the select low speed becomes higher than the four-wheel select low speed, the time for reducing the hydraulic pressure for the left and right rear wheels in each antilock control cycle is limited to a predetermined time. In the case where the method is applied to a four-wheel drive vehicle, it is possible to prevent the brake fluid pressure from being excessively reduced for the left and right rear wheels, and to shorten the braking distance.

[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 a method for determining a low peak point of system speed, and FIG. FIG. 4 is a diagram showing the operation of the pressure reduction end determination circuit according to the present invention, and FIG. 5 is a control state diagram of the antilock control in the conventional method. 1-4 wheel speed sensors 5-8 arithmetic circuits 9, 10, 12 control logic circuit 11 four-wheel low select circuit 13 pseudo vehicle speed arithmetic circuits 14, 15, 16 ... decompression end Decision circuit 17: Rear wheel low select circuit

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-29963 (JP, A) JP-A-3-42363 (JP, A) JP-A-62-105756 (JP, A) JP-A-62-105756 251264 (JP, A) JP-A-62-251267 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B60T 8/58

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, On the other hand, the brake fluid pressure is controlled using the lowest wheel speed of the four wheel speeds as the control target wheel speed, and the lower wheel speed of the left and right rear wheel speeds is adjusted to the above four wheel speeds. The anti-lock system of a four-wheel drive vehicle, wherein when the wheel speed becomes higher than the lowest wheel speed, the pressure reduction time of the brake fluid pressure for the left and right rear wheels in each anti-lock control cycle is limited to a predetermined time. Control method.