JPH0674031B2 - Anti-skidding control method - Google Patents

Description

The present invention relates to an anti-skid control method for preventing skid of a wheel during braking of a vehicle, and more particularly to a friction coefficient between the wheel and a road surface. The present invention relates to an anti-skid control method capable of preventing premature locking even when μ is extremely low, that is, even on an extremely low μ road surface.

(Prior Art) In general, an anti-skid 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 steerability of the vehicle during control, traveling stability, and shortening a braking distance. Thus, the hold valve and the decay valve, which are electromagnetic valves, are opened and closed to control the brake fluid pressure to be increased, maintained, and reduced.

By the way, in this kind of anti-skid controller,
When the wheel speed that has been suddenly decelerated by the brake operation is restored by the subsequent brake fluid pressure reduction control, the brake fluid pressure holding control is performed again to shift to the pressurization control. When increasing the hydraulic pressure, if the friction coefficient μ between the wheel and the road surface is low,
It is desirable to increase the brake fluid pressure relatively slowly to prevent wheel locking. Therefore, conventionally, a pulse train generator such as a multivibrator is provided in the drive system of the hold valve, and the hold valve is opened and closed in small increments by the pulse train signal output from the multivibrator, thereby applying and holding the brake fluid pressure. It has been proposed to repeatedly increase the brake fluid pressure by repeating the above procedure.

However, in such a conventional control signal based on a pulse train signal, the duty ratio of the pulse train signal is constant or changes at a predetermined ratio, so that the friction coefficient μ corresponds to a road surface condition that changes momentarily. Proper anti-skid control was difficult.

Therefore, the applicant of the present invention has disclosed a method of pressurizing the brake fluid pressure, which is capable of performing an appropriate anti-skid control depending on the road surface condition, in Japanese Patent Application No. 60-170913 (August 2, 1985). -122858) was filed. In the method described in the specification of this prior application, as is apparent from FIG. 4 showing the relationship between the wheel speed Vw and the brake fluid pressure Pw, the brake fluid pressure reduction control period and the pressure reduction control period The skid of the wheel is prevented by a series of control cycles including a pressurization control period in which the brake fluid pressure is relatively slowly increased by alternately repeating pressurization and holding of the brake fluid pressure at relatively low intervals. In this case, the time length of pressurization and holding of the brake fluid pressure that is alternately repeated in the pressurization control period is determined based on the wheel deceleration immediately before each of these times, that is, the negative acceleration. . Further, the time length of the first pressurization in the pressurization control period is determined based on the change state of the wheel speed between the low peak and the high peak of the wheel speed. More specifically, the method of determining the first pressurization time will be described in detail. The speed difference A between the wheel speed Va at the start of depressurization and the wheel speed Vl at the low peak time is calculated, and the wheel speed Vl at the low peak time is calculated. To the speed increased by an amount corresponding to K1% and K2% of the speed difference A (K1 and K2 are preset percentages, for example, K1 is 15% and K2 is 80%). Time between two time points ΔT
Is calculated, and the average acceleration at that time ΔT is calculated,
This is a method of determining the first pressurization time Tx of the pressurization control period in which the brake fluid pressure is relatively slowly increased based on the calculation result.

With such a method, by determining the pressurizing and holding times in the pressurizing control period in which the brake fluid pressure is relatively slowly increased, it is possible to appropriately respond to changes in the friction coefficient μ between the wheel and the road surface. Brake fluid pressure can be controlled,
This is very effective in preventing wheel lock and shortening the braking distance.

(Problems to be Solved by the Invention) The present invention is premised on the method described in the above-mentioned prior application, and an object thereof is to provide an antilock control method further improved.

That is, for example, when the transmission gear or the differential gear vibrates by operating the transmission gear during vehicle braking, the time ΔT between the two time points between the low peak and the high peak of the wheel speed is significantly shortened. In some cases, if the time ΔT becomes shorter than 8 ms in that case, it becomes difficult to accurately determine the average acceleration. Therefore,
In this way, when the time ΔT is shorter than 8 ms, the maximum value of the preset values of the first pressurizing time may be used from the viewpoint of fail-safe. However, when the road surface is in an extremely low μ state as on ice, when the maximum set value is adopted as the first pressurization time, the wheel speed Vw sharply decreases and the brake fluid in the next control cycle is decreased. The pressure may not be reduced in time, and early locking may occur. Therefore, an object of the present invention is to provide an antilock control method capable of preventing early locking even on an extremely low road surface.

Configuration of the Invention (Means for Solving the Problem) A feature of the present invention is that a time ΔT between two time points between a low peak and a high peak of a wheel speed is set in advance.
When the time ΔT is longer than the set time as compared with Ts, the first pressurization time Tx in the pressurization control period for slowly increasing the brake fluid pressure is determined based on the average acceleration at the time ΔT, When the time ΔT is equal to or shorter than the set time Ts, the first pressurization time Tx is the pressurization time Tx ′ determined in the previous control cycle.
To be equal to. However, when the control cycle is the first time, the pressurizing time Tx is selected to be equal to the preset initial value To.

(Operation) Pressurization and holding after the brake fluid pressure reduction control is repeated in relatively small increments, whereby the first pressurization time in the pressure control period for slowly increasing the brake fluid pressure is It is determined according to the coefficient of friction between road surfaces.

(Example) An anti-skid control method according to the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a control characteristic diagram showing changes in wheel speed Vw, wheel acceleration / deceleration ± w, and brake fluid pressure Pw, and opening / closing operations of a hold valve and a decay valve. Further, FIG. 2 is a block diagram of a control circuit for operating the hold valve.

First, when the hold valve is open and the decay valve is closed, the wheel speed Vw is decreased and the wheel deceleration -w is gradually increased by pressurizing the brake fluid pressure Pw from the control start time t1. Further, the pseudo speed Vt follows the wheel speed Vw with a constant speed difference ΔV with respect to the wheel speed Vw.
The wheel speed Vw is detected by a wheel speed sensor 1 (Fig. 2) provided for the wheel. Next, when the wheel deceleration −w reaches the deceleration −G1 at the time point t2, the pseudo speed Vt decreases to the constant deceleration gradient θ.

When the wheel deceleration -w further increases and reaches -Gmax at time t3, the hold valve is closed and the brake fluid pressure Pw is held. Here, deceleration-Gmax is set for the purpose of preventing the brake fluid pressure from increasing above a certain value.

At a time point t4 when the wheel speed Vw sharply decreases and the wheel speed Vw and the pseudo speed Vt intersect, the decay valve opens and the brake fluid pressure starts to be reduced. The wheel speed Va at the time point t4 when the pressure reduction is started is stored in the storage device 2 which is reset by the open signal of the decay valve and reset by the close signal of the decay valve. The brake fluid pressure reduction continues until time t5 when the wheel speed reaches a low peak, at which time the decay valve closes and brake fluid pressure Pw
Is retained. Low peak detector 3 at time point t5
The wheel speed Vl at time t5 detected by
Memorized in. The memory 4 is reset by the close signal of the decay valve. The wheel velocities Va and Vl read out from the memories 2 and 4 are subtracted by the subtractor 5 to obtain the speed difference A.
(= Va-Vl) is obtained, and the multipliers 6 and 7 sometimes calculate the 15% value and the 80% value of the speed difference A. Further, the 15% value and the 80% value of these speed differences A are added by the adder 8
Wheel speed Vl at each low peak by and 9
Is calculated to calculate the wheel speeds Vb and Vc.

The wheel speed Vw starts to accelerate from the low peak time t5, and during this acceleration, the wheel speed Vw and the calculated speed Vb (= Vl + 0.
15A) and Vc (= Vl + 0.8A) are compared by comparators 10 and 11, respectively. Then, counting is started based on the output of the comparator 10 obtained when Vw ≧ Vb,
In addition, the timer 12 whose count is stopped based on the output of the comparator 11 obtained when Vw ≧ Vc causes the time ΔT between the time t6 when Vw = Vb and the time t7 when Vw = Vc.
Is measured. This time ΔT is compared with the set value Ts (= 8 ms) by the comparison circuit 13.

On the other hand, time points t6 and t7 at both ends of time ΔT are AND gates.
It is detected by 14 and given to the average acceleration calculator 15. Further, since the wheel speed Vw is constantly given to the calculator 15, the wheel speed Vb at the time point t6 in the calculator 15 is:
From the wheel speed Vc at time t7 and the time ΔT, the time Δ
The average acceleration (Vc-Vb) / ΔT at T is calculated, and the result is stored in the acceleration memory 16. This memory 16 is also a memory that is reset by the decay valve open signal.

The wheel speed Vw rises from the low peak at the time point t5, reaches the high peak speed Vh through the speed Vb at the time point t6 and the Vc at the time point t7, and the hold valve opens at the high peak time point t8, and thereafter, the hold valve opens and closes relatively smallly. Thus, the pressurization control period for increasing the brake fluid pressure relatively slowly is started. When the wheel speed Vw reaches the high peak speed at time t8, the average acceleration (Vc-Vb) / ΔT at the time ΔT stored in the acceleration memory 16 is read and supplied to the pressurization time selection circuit 17. In the pressurization time selection circuit 17, the set value of the first pressurization time Tx started from time t8 in the pressurization control period in which the brake fluid pressure is slowly increased is the average acceleration (Vc− In relation to Vb) / ΔT, it is stored as shown in Table 1 below.

By the way, as described above, the time t6 when the wheel speed Vw increases
The time ΔT between T and t7 is compared by the comparator 13 and ΔT
When T> 8ms, the output of the comparator 13 is the pressurization time selection circuit 1
7, the pressurization time selection circuit 17 reads out the pressurization time Tx according to the above Table 1 and outputs it to the pressurization device 18 only when the output from the comparator 13 is received. , The first pressurization time from time t8 to time t9 is determined, and the brake fluid pressure starts to increase.

On the other hand, as is clear from FIG. 2, a storage device 19 for storing the pressurization time Tx ′ determined in the previous control cycle,
A storage device 20 for storing a preset initial value To of the pressurizing time is provided, and the output side thereof is connected to the pressurizing time selecting circuit 17 via the switch circuit 21. When the output from the comparator 13 is not given to the pressurization time selection circuit 17, that is, when ΔT ≦ 8 ms, the storage device 1
The output from either one of 9 and 20 is supplied to the pressurization time selection circuit 17. In this case, only when the current control cycle is the first time, the pressurizing time To read from the storage device 20 is given to the pressurizing device 18 via the pressurizing time selecting circuit 17, and the present control cycle is 2 times. If it is after the first time,
The value of the previous pressurization time Tx ′ read from the storage device 19 is supplied to the pressurization device 18 via the pressurization time selection circuit 17.

Based on the pressurization time Tx thus determined, when the first pressurization period started from the time point t8 ends,
At time t9, the hold valve is closed and the brake fluid pressure is maintained. The first holding period starting from this time point t9 is determined by the wheel deceleration -w detected immediately before the end of the first pressurizing period. Then, the hold valve is opened again, and the second pressurization is started. The second pressurization time is determined by the wheel deceleration -w detected until immediately before the end of the first hold period. To be done.
Similarly, the hold valve is opened and closed in small steps, and the brake fluid pressure slowly rises.

Table II below shows an example of the set values of the pressurization time and the holding time after the time t9 in relation to the wheel deceleration -w detected immediately before the start of those times.

Repeated opening and closing of the hold valve like this
When the −Gmax is detected at the time point tn, the control cycle similar to the control cycle started from the time point t3 is started from the time point tn.

Further, when -Gmax is not detected within a predetermined time, the antiskid control returns to the initial state.

Next, FIG. 3 is a flow chart for explaining the operation for determining the first pressurization time Tx in the control circuit of FIG. First, in step 51, it is determined whether or not the decay valve is "ON". If NO, this determination is repeated, and if YES, the process proceeds to step 52. Step 52
Then, when the decay valve is "ON", that is, the brake fluid pressure Pw
The wheel speed Va at the time point t4 when the pressure reduction is started is stored. Next, in step 53, it is determined whether or not the low peak of the wheel speed Vw is detected.

If the determination result in step 53 is NO, this determination is repeated, and if YES, the process proceeds to step 54. At step 54, the wheel speed Vl at the low peak time t5 is stored. Then, in step 55, the speed difference A (= Va-Vl) between the two wheel speeds Va and Vl is calculated. Next, at step 56, the wheel speed Vb at the low peak time t5 is added to the 15% value of the speed difference A to obtain the wheel speed Vb. Further steps
At 57, the wheel speed Vc at the low peak time t5 is added to the 80% value of the speed difference A to obtain the wheel speed Vc. Next, at step 58, the time ΔT until the wheel speed changes from Vb to Vc is measured. This measured time ΔT
At 59, it is compared with 8 ms to determine if the time ΔT is less than or equal to 8 ms. If the determination result in step 59 is NO, in step 60, the time Δ
The first pressurization time Tx is determined based on the average acceleration (Vc-Vb / ΔT) at T (see Table I). If the decision result in the step 59 is YES, in a step 61,
It is determined whether or not this control cycle is the first control cycle. If YES, the preset initial value To is selected as the first pressurizing time, and if NO, it is determined in the previous control cycle. The applied pressurization time Tx 'is selected as the first pressurization time. The above control flow is executed every predetermined time (for example, 4 ms).

EFFECTS OF THE INVENTION According to the method of the present invention, the first pressurization time in the pressurization control period in which the brake hydraulic pressure is slowly increased by relatively small increments of pressurization and holding after the brake fluid pressure is reduced. Can be easily determined in accordance with the friction coefficient μ between the wheel and the road surface, so that the steering performance of the vehicle at the time of braking, ensuring traveling stability, shortening the braking distance, etc.
It can be reliably achieved regardless of the condition of the road surface, and is particularly effective for anti-skid control on a road surface having a very low coefficient of friction.

[Brief description of drawings]

FIG. 1 is a control characteristic diagram for explaining an anti-skid control method according to the present invention, FIG. 2 is a block diagram of a control circuit for operating a hold valve, and FIG. 3 is a diagram for explaining the operation of the control circuit of FIG. FIG. 4 is a control characteristic diagram showing an anti-skid control method which is a premise of the present invention. In the drawings, 1 is a wheel speed sensor, 2 and 4 are storage devices,
3 is a low peak detector, 5 is a subtractor, 6 and 7 are multipliers,
8 and 9 are adders, 10 and 11 are comparators, 12 is a timer, 14 is an AND gate, 15 is an average acceleration calculator, 16 is an acceleration memory, 17 is a pressurizing time selection circuit, 18 is a pressurizing device, Reference numeral 19 indicates a previous pressurizing time storage device, and 20 indicates an initial value storage device.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hideo Akuma, Hideo Akima, 1015 Kamiodanaka, Nakahara-ku, Kawasaki, Kanagawa, Fujitsu Limited (72) Inventor Sho Hoashi, 1015, Uedaka, Nakahara, Kawasaki, Kanagawa, Fujitsu Limited ( 56) References JP-A-60-47751 (JP, A)

Claims (1)

[Claims] 1. A pressure reducing control period in which a brake fluid pressure is reduced based on an electric signal representing a vehicle wheel speed, and a brake fluid pressure is increased after the pressure reducing control period in accordance with the electric signal. Anti-skid designed to prevent wheel skid by a series of control cycles each including holding and alternating relatively small steps, and a pressurizing control period for increasing brake fluid pressure relatively slowly. In the control method, the wheel speed Va is determined by detecting the sudden deceleration of the wheel speed caused by the braking operation, and the wheel speed Va at the start point of the pressure reduction control period and the brake fluid pressure reduction started from this point. Is calculated from the speed difference A with the wheel speed Vl at the low peak time when the vehicle shifts from deceleration to acceleration. From the speed Vl at the time when the speed Vb is increased to the speed Vb increased by an amount corresponding to the first ratio set in advance for the speed difference A, and the wheel speed is changed from the speed Vl at the low peak time to the speed difference. A time ΔT between the time point when the speed Vc is increased by an amount corresponding to a second preset ratio for A and the time point when the speed Vc is recovered is compared with a preset time Ts, and the time ΔT is set to the preset time Ts. Longer than
The time Tx of the first pressurization in the pressurization control period in which the brake fluid pressure is relatively slowly increased is determined based on the average acceleration at the time ΔT, and whether the time ΔT is equal to the set time Ts. Or if it is shorter than this and the control cycle is the first time,
When the pressurization time Tx is selected to be equal to a preset initial value To, the time ΔT is equal to or shorter than the set time Ts, and the control cycle is the second time or later, the pressurization time is increased. An anti-skid control method characterized in that the time Tx is selected to be equal to the pressurization time Tx ′ determined in the previous control cycle.