JP2688917B2 - Anti-lock control method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a vehicle antilock control method, and more particularly to a brake fluid pressure reduction method that immediately responds to a road surface friction coefficient μ.

(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. The control mode of the brake fluid pressure is determined to open and close a hold valve and a decay valve each composed of an electromagnetic valve, thereby controlling the microcomputer to increase, hold, or reduce the brake fluid pressure.

FIG. 7 is a control state showing changes in wheel speed Vw, wheel acceleration w and brake fluid pressure Pw, and a hold signal HS and a decay signal DS for opening and closing the hold valve and the decay valve in an example of such anti-lock control. It is a figure.

When the brake is not operated while the vehicle is running, the brake fluid pressure Pw is not increased, and both the hold signal HS and the decay signal DS are OFF, so the hold valve is open and the deckle valve is closed. Although it is in the state, the brake fluid pressure Pw is changed to the time t0 with the brake operation.
, And rapidly rises (normal mode), whereby the wheel speed Vw decreases. Is set pseudo wheel speed V _T to follow with a low speed difference by a constant velocity ΔV with respect to the wheel speed Vw, the pseudo wheel speed V _T is the wheel deceleration (negative acceleration) w is the time t1 , When a predetermined threshold value, for example, -1.1 G is reached, the antilock control is started from this time point t1. Then, after the time point t1, the pseudo wheel speed V _T is set to linearly decrease with a deceleration gradient θ of −1.1 G. At time t2 when the wheel deceleration w reaches a predetermined threshold value (-G _max ), the hold signal HS is turned on to close the hold valve and hold the brake fluid pressure Pw.

By maintaining the brake fluid pressure Pw, the wheel speed Vw further decreases, and the wheel speed Vw becomes equal to the pseudo wheel speed V _T at the time point t3, but at this time point t3, the first cycle of the antilock control is started. , Decay signal DS is turned ON, the decay valve is opened, and brake fluid pressure Pw is reduced. Due to this pressure reduction, the low peak speed Vl at the wheel speed time t4
However, the speed Vb increased from the low peak speed Vl by an amount corresponding to 15% of the speed difference Y between the wheel speed Va and the low peak speed Vl at the depressurization start time point t3.
At the time point t5 when the voltage has recovered to (= Vl + 0.15Y), the decay signal DS is turned off, the decay valve is closed, the reduction of the brake fluid pressure Pw is completed, and the brake fluid pressure Pw is maintained.
Next, the wheel speed Vw recovers to a speed Vc (= Vl + 0.8Y) which is increased by an amount corresponding to 80% of the speed difference Y between the wheel speed Va and the low peak speed Vl at the pressure reduction start time t3, and then passes the time t6. The high peak is reached at t7, but the pressurization of the brake fluid pressure Pw is started again at time t7 when the high peak speed Vh is reached. The pressurization here is performed by turning ON / OFF the hold signal HS relatively little by little, thereby alternately repeating pressurization and holding of the brake fluid pressure Pw, thereby slowly increasing the brake fluid pressure Pw. The wheel speed Vw is decreased, and the pressure reduction mode of the second cycle is generated again from time t8 (corresponding to t3). The first pressurization period Tx starting from time t7
Is determined by determining the friction coefficient μ of the road surface based on the calculation of the average acceleration (Vc-Vb) / ΔT in the period ΔT between the time points t5 and t6. It is determined based on the wheel deceleration w detected immediately before pressurization. By the combination of pressurization, holding, and pressure reduction of the brake fluid pressure Pw as described above, the vehicle speed can be reduced by controlling the wheel speed Vw without locking the wheels.

However, as described above, if the brake fluid pressure is continuously reduced until the wheel speed is recovered from the low peak speed Vl to the speed Vb, the brake fluid pressure becomes too loose on the medium-high μ road, and the control distance is reduced. Will be extended,
Further, there is a problem that the vehicle body vibration occurs due to the increase in the pressure reduction amplitude.

(Object of the invention) Therefore, an object of the present invention is to provide an anti-lock control method capable of reducing the brake fluid pressure immediately corresponding to the friction coefficient μ of the traveling road surface (hereinafter referred to as “road surface μ”). .

(Structure of the invention) In order to achieve the above object, in the antilock control method according to claim 1 of the present invention, the wheel speed decelerated by pressurization of the brake fluid pressure is reduced by the subsequent reduction of the brake fluid pressure. Detects low peaks that turn into acceleration,
Based on the detection of the low peak, the pressure reduction of the brake fluid pressure is terminated, and the low peak speed is reduced to a speed corresponding to a predetermined ratio of the speed difference Y between the wheel speed Va at the time of starting the pressure reduction and the wheel speed Vl at the time of the low peak. Calculate the speed Vb over Vl, compare the wheel speed after the low peak time and the speed Vb, if the predetermined time has elapsed from the low peak time before the wheel speed is recovered to the speed Vb, Re-decompression is performed until the wheel speed reaches the speed Vb after a predetermined time has elapsed.

Further, in the antilock control method according to claim 2 of the present invention, the friction coefficient μ of the traveling road surface is determined for each control cycle consisting of pressurization and depressurization of the brake fluid pressure, and by applying the brake fluid pressure. The decelerated wheel speed detects the low peak where the deceleration from the deceleration to the acceleration due to the subsequent pressure reduction of the brake fluid pressure, and based on the detection of the low peak, the speed difference between the wheel speed Va at the depressurization start point and the wheel speed Vl at the low peak point. Speed Vb that exceeds the above low peak time Vl by a speed corresponding to a predetermined ratio of Y
And the road surface friction coefficient μ in the immediately preceding control cycle
When it is detected that the value of the friction coefficient μ is higher than a predetermined value, the decompression is terminated at the low peak time point, and the wheel speed after the low peak time point is compared with the speed Vb. When a predetermined time has elapsed from the low peak time before the wheel speed is recovered to the speed Vb, re-decompression is performed until the wheel speed reaches the speed Vb from the predetermined time elapsed time, in the control cycle immediately before. When it is detected by the determination of the road surface friction coefficient μ that the value of the friction coefficient μ is lower than the predetermined value, the wheel speed reaches the rising speed Vb without ending the pressure reduction at the low peak time. I am trying to continue until.

(Effect of the invention) In the antilock control method according to claim 1 of the present invention, as described above, when the pressure reduction of the brake fluid pressure is finished at the time of the low peak, and the recovery of the wheel speed thereafter is relatively slow. Since the vehicle is decompressed again, it is possible to prevent the wheels from being locked even on a low μ road. Further, after the decompression at the time of the low peak, when the wheel speed recovers to the ascending speed Vb within a predetermined time, the re-decompression is not performed, and therefore the brake fluid pressure becomes too loose on the medium-high μ road. As a result, it is possible to prevent the braking distance from being extended and to prevent the vibration of the vehicle body from occurring due to an increase in the amplitude of the brake fluid pressure.

Further, in the antilock control method according to claim 2, when the road surface μ determined in the immediately preceding control cycle is lower than a predetermined value, it is determined to be, for example, an extremely low μ road, and the wheel speed is the speed Vb. Since the depressurization is continued until the point reaches, the delay of wheel speed recovery due to the excessively high brake fluid pressure on the extremely low μ road can be prevented in addition to the effect according to the first aspect.

(Example) An example of an antilock control method according to the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an example of a three-system antilock control device to which the present invention is applied.
Output is sent to the wheel speed calculation circuits 5-8 for calculation,
Signals representing the respective wheel speeds Vw1 to Vw4 are obtained. The left front wheel speed Vw1 and the right front wheel speed Vw2 are sent as they are to the first and second control logic circuits 9, 10 as the first system speed Vs1 and the second system speed Vs2, respectively. The low-speed wheel speed of the wheel speeds Vw4 is selected by the low select circuit 11 and sent to the third control logic circuit 12 as the third system speed Vs3.

Further, the signals representing the respective system speeds Vs1 to Vs3 are sent to the acceleration computing circuits 13 to 15 for calculation, and the signals representing the respective system accelerations s1 to s3 are respectively represented in the control logic circuits 9, 10, 12 respectively. Sent to.

Further, a signal representing each wheel speed Vw1 to Vw4 is sent to the pseudo vehicle body speed calculation circuit 16, where the fastest wheel speed of the four wheel speeds Vw1 to Vw4 is selected, and the fastest wheel speed A speed in which the acceleration is limited within a range of ± 1 G is calculated as the pseudo vehicle body speed Vv, and signals representing the speed Vv are also sent to the control logic circuits 9, 10 and 12, respectively.

Further, in this anti-lock control device, low peak determination circuits 17 to 19 and re-decompression determination circuit 20 are provided for each system.
22 to 22 and road surface μ determination circuits 23 to 25 are provided.

In the low peak determination circuits 17 to 19, each system speed Vs1 to Vs3 decelerated by pressurization of the brake fluid pressure detects a low peak point at which deceleration changes from acceleration to deceleration by the subsequent reduction of the brake fluid pressure, and the detection signal is controlled by each control. It is sent to the logic circuits 9, 10 and 12. Further, the above circuits 17 to 19 include control logic circuits 9, 10 and 12 and switches SW1 to SW3, respectively.
These switches SW1 to SW3 are connected through
Is configured to be turned on only for each system from the time when the brake fluid pressure starts to be reduced to the time when the low peak occurs.

Further, in each of the re-decompression determination circuits 20-22, it is determined whether to start the re-decompression after finishing the decompression at the time of the low peak and the time when the started re-decompression is finished, and a signal representing them is given. It is sent to the control logic circuits 9, 10 and 12. Further, these respective circuits 20 to 22 are connected to the respective control logic circuits 9, 10 and 12 via switches SW4 to SW6, respectively, and these switches SW4 to SW6 are each system from the low peak time point. Each system speed Vs1 to Vs3
Is turned on only until the speed reaches the above-mentioned speed Vb (= Y × 0.5 + Vl).

Furthermore, in the road surface μ determination circuits 23 to 25, while determining the road surface μ in each control cycle, based on the determination result, set the control value in the next control cycle,
The control logic circuits 9, 10, 12 are provided with signals representing these.
Sent to. Further, each of these circuits 23 to 25 includes the above control logic circuits 9, 10, 12 and switches SW7 to S, respectively.
These switches SW7-SW9 are connected through W9
For each system, the system speed Vs1 to Vs3 is the above-mentioned speed Vb.
From the time when (= Y × 0.15 + Vl) is reached, the speed Vc (=
It is configured to turn on only until the time when (Y × 0.8 + Vl) is reached.

Based on each signal sent as above,
The above control logic circuits 9, 10, 12 are connected to each system speed Vs1.
By controlling the hold valve and decay valve ON / OFF for each system with Vs3 as the system controlled speed, each system performs independent 3-channel antilock control. The switch shown in FIG.
SW1 to SW9 are shown for ease of understanding, and show the operating states of the flags.

Next, FIG. 2 is a control state diagram showing changes in the brake fluid pressure of one brake system among the brake fluid pressures controlled by the antilock control device of FIG. The same parts as those in FIG. 6 described above are designated by the same reference numerals, and overlapping description will be omitted. In order to simplify the description, the system speeds Vs1 to Vs3 will be hereinafter referred to as wheel speeds Vw.

In the above control, first, the brake fluid pressure is started to be reduced at the pressure reduction start time point t3, and then the pressure reduction is ended and held at the low peak time point t4 when the wheel speed Vw reaches the low peak. Further, at the low peak time point t4, only the speed corresponding to a predetermined ratio, for example, 15% of the speed difference Y1 between the wheel speed Va1 at the pressure reduction start time point t3 and the wheel speed Vl1 at the low peak time point t4, for example, 15%, is the low peak speed Vl.
Calculate a speed Vb1 (= Y1 × 0.15 + Vl1) that exceeds 1 and a speed Vc1 (= Y1 × 0.8 + Vl1) that exceeds the low peak speed Vl1 by a speed corresponding to a predetermined ratio of the speed difference Y1 such as 80%. . Then, the elapsed time T from the low peak time t4 is measured, and from this time t4 a predetermined time T1 (for example, 20
ms) has elapsed, at the time point ts, the wheel speed Vw is
When it has recovered to Vb1, it continues to hold the brake fluid pressure until time t7 as shown by the one-dot chain line in the figure, and when it has not recovered to the above speed Vb1, it shows the above point as shown by the solid line in the figure. Re-decompression is started from ts, and this re-decompression is terminated at time t5 when the wheel speed Vw recovers to the above speed Vb1.

Further, in this control, for each control cycle starting from each pressurization start point, for example, the wheel speed Vw is
The average acceleration AV: G1 of the wheel speed Vw in the period ΔT from the time t5 when the speed is recovered to 1 to the time t6 when the speed is further recovered to the above speed Vc1 is calculated, and the average acceleration AV: G1 is calculated as the predetermined acceleration G1, G2, G3. The road surface μ is determined by comparison with (for example, 3G, 7G, 9G). If the average acceleration AV: G1 in this control cycle exceeds the predetermined house degree G1 (for example, 3G), the next pressurization start point A
The next pressurization start point B (time point t7) from (time point t7)
In the next control cycle up to, the low peak time point t4 and the speeds Vb2 and V corresponding to the above speeds Vb1 and Vc1 as described above.
c2 is calculated, decompression is terminated, and the time T from the low peak time point t4 is measured. At a time point t5 when a predetermined time T1 (for example, 20 ms) has elapsed from this time point t4, the wheel speed Vw becomes the Vb1. When recovering to the corresponding Vb2, continue to hold the brake fluid pressure until time t7,
When the speed has not recovered to the speed Vb2, the re-decompression is started from the time point ts, and the re-decompression is finished at the time t5 when the wheel speed Vw has recovered to the speed Vb2.

Also, the average acceleration A in the previous control cycle
If V: G1 is less than the above specified acceleration G1 (for example, 3G),
In the next control cycle, as shown by the broken line in the figure, the pressure reduction is not completed at the low peak time t4, and the wheel speed Vw
Is the speed V calculated by the formula (Va2-Vl2) x 0.15 + Vl2
The decompression is continued until time t5 when b2 is reached.

FIG. 3 is a flow chart showing the operation of the low peak judging circuits 17 to 19 shown in FIG. 1, which will be described below with reference to FIG.

First, in step S1, it is determined whether or not the deceleration w of the wheel speed Vw after the pressure reduction start time t3 in FIG. 2 is a predetermined value -GK, for example, -1G or more. If the determination is "NO", the timer is reset to 0 in step S2, and if the determination is "YES", the process proceeds to step S3 to start counting up the timer. Next, in step S4, the count T _M of the timer is the predetermined time.
Whether T _M 1 or more is determined, and when T _M ≧ T _M 1, it is determined in step S5 that it is a low peak point.

Next, at step S6, the average acceleration AV: G between the times t5 and t6 of the immediately preceding control cycle in FIG.
For example, it is determined whether it is 3G or less. Then, if this determination is "NO", the flow proceeds to step S7, the reduction of the brake fluid pressure is ended, and the flow proceeds to step S8. In addition, this judgment is "YE
If “S”, the process directly proceeds to step S8 without ending the pressure reduction. In step S8, the speed Vb described above with reference to FIG. 2 is calculated by the expression Vb = (Va−Vl) × 0.15 + Vl. Further, in step S9, the above-mentioned speed Vc is calculated by the formula Vc = (Va−Vl) × 0.8 + V
Calculate by l. As described above, the determination as to whether or not it is the low peak point, the determination as to whether or not the reduction of the brake fluid pressure is completed, and the calculation of the speeds Vb, Vc are performed.

Next, FIG. 4 is a flow chart showing the operation of the re-decompression determination circuits 20 to 22 shown in FIG. 1, which will be described below with reference to FIG.

First, in step S11, the elapsed time T from the low peak time t4 in FIG.
It is determined whether or not it has exceeded ms. And the time T
This judgment is "YE
Therefore, the process proceeds to step S12, the wheel speed Vw at that time point ts is compared with the speed Vb corresponding to the above-mentioned speeds Vb1 and Vb2, and when Vw <Vb, the process proceeds to step S13 to start the re-decompression. , Go to step S14. Wheel speed in step S14
It is determined whether Vw is equal to or higher than the speed Vb, and if this determination is "YES", the speed difference between the wheel speeds (Va1, Va2) and the low peak speeds (Vl1, Vl2) at the pressure reduction start point in step S15. It is determined that the wheel speed Vw has recovered from the low peak speed by a speed corresponding to 15% of the, and the process proceeds to step S16 to end the pressure reduction. As described above, the start point and the end point of the re-decompression of the brake fluid pressure are determined.

FIG. 5 is a flowchart showing the operation of the road surface μ determination circuits 23 to 25 in FIG. 1 for determining the road surface μ for each control cycle and setting the control value for the next control cycle based on the determination. Will be described with reference to.

First, in step S21, the speed Vb corresponding to the speeds Vb1 and Vb2 described above, the VC corresponding to the speeds Vc1 and Vc2 described above, and the wheel speed Vw recovered to the speed Vb described above at time t5 in FIG.
When (+ 15% point) is recovered to the above speed Vc
From the period ΔT up to t6 (+ 80% point) and the formula (Vc-Vb) /
From ΔT, the average acceleration AV: G of the wheel speed Vw in the period ΔT is calculated, and then the process proceeds to step S22 and this AV:
The road surface μ is determined by comparing G with predetermined accelerations G1, G2, G3 (for example, 3G, 7G, 9G). Then, according to the road surface μ determined here, from the pressurization start time t7 (high peak point A) in FIG. 2 which is the next control cycle to the next pressurization start time t7.
Control values in the (high peak point B), for example pseudo after the wheel speed V _T tracking speed difference ΔV with respect to the wheel speed Vw, the value of the deceleration gradient θ pseudo wheel speed V _T is gradually linearly reduced, and the next pressure The value of the first pressurization period Tx1 from the start time t5 is set. That is, if AV: G ≤ G1, step
Proceed to S23 to set the control value according to the extremely low μ road. Also G
If 1 <AV: G ≦ G2, the process proceeds to step S24 to set the control value according to the low μ road. Further, when G2 <AV: G ≦ G3,
In step S25, set the control value according to the medium μ road, AV: G> G
In the case of 3, a control value corresponding to the high μ road is set in step S26. As described above, the road surface μ is determined for each control cycle, and the control value for the next control cycle is set.

FIGS. 6 (a) to 6 (c) are diagrams showing a change state of the brake fluid pressure in one control cycle from the pressurization start point to the next pressurization start point. FIG. 6 (a) shows the control of the brake fluid pressure suitable for the medium and high μ roads, the pressure reduction of the brake fluid pressure is finished at the low peak time point t4, and the time T from the low peak time point t4 to the + 15% time point t5 is predetermined. Time T1 eg
Since it is within 20ms, the brake fluid pressure is maintained until the next pressurization start time without directly reducing pressure again.

FIG. 6 (b) shows the control of the brake fluid pressure suitable for the low μ road, and once the pressure reduction of the brake fluid pressure is finished at the time of the low peak, the low peak time t4 is + 15% of the time.
Since the time T up to t5 is longer than the predetermined time T1, the re-decompression is started at the time ts when the predetermined time T1 elapses from the low peak time, and the re-decompression is finished at + 15% time t5.

FIG. 6 (c) shows the control of the brake fluid pressure suitable for an extremely low μ road, in which the average acceleration AV: G of the wheel speed Vw in the period ΔT from the + 15% time point to the + 80% time point of the previous control cycle is predetermined. Since the acceleration was less than G1 (for example, 3G), the pressure reduction was not completed at the low peak time t4 of the current control cycle,
Decompression is continued until 15% time point t5.

As is clear from the above description, in this embodiment,
Since the period and the mode of pressure reduction of the brake fluid pressure are determined according to the condition of the road surface μ, it is possible to prevent the brake fluid pressure from being excessively loosened on the medium-high μ road, and increase the amplitude of the brake fluid pressure to increase the vehicle body. It is possible to avoid vibration. Further, according to the present embodiment, it is possible to prevent the wheels from being locked on the low μ road, and even on the extremely low μ road, avoid the delay in the recovery of the wheel speed due to the excessively high brake fluid pressure. can do.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an example of the configuration of an antilock control device to which the present invention is applied, FIG. 2 is a control state diagram of brake fluid pressure in an embodiment of the present invention, and FIG. 3 is a low peak point determination routine. 4 is a flowchart of the re-decompression determination routine, FIG. 5 is a flowchart of the road surface μ determination routine, and FIGS. 6 (a) to 6 (c) are
FIG. 7 is a diagram showing a brake fluid pressure control state suitable for a medium-high μ road, a low μ road, and an extremely low μ road, respectively, and FIG. 7 is a brake fluid pressure control state diagram by a conventional antilock control method. 1 to 4 ... wheel speed sensor 5 to 8 ... wheel speed calculation circuit 9, 10, 12 ... control logic circuit 11 ... low select circuit 13 to 15 ... acceleration calculation circuit 16 ... pseudo vehicle body speed calculation circuit 17 〜19 …… Low peak point judgment circuit 20〜22 …… Re-decompression judgment circuit 23〜25 …… Road surface μ judgment circuit

Claims (2)

(57) [Claims] 1. An anti-lock control method in which each wheel speed is detected, and pressurization and depressurization of brake fluid pressure are alternately performed based on the detected wheel speed, wherein the wheel speed decelerated by pressurization of brake fluid pressure is Detects a low peak that changes from deceleration to acceleration by reducing the brake fluid pressure, and based on the detection of this low peak, the brake fluid pressure reduction is terminated, and the wheel speed Va at the start of pressure reduction and the wheel speed at the low peak time are detected. The speed Vb that exceeds the low peak speed Vl by a speed corresponding to a predetermined ratio of the speed difference Y from Vl is calculated, and the wheel speed after the low peak time and the speed Vb are compared, and the wheel speed is the speed Vb. If a predetermined time has passed from the low peak time before the recovery to the above, the wheel speed reaches the speed Vb from the time when the predetermined time has passed. Anti-lock control method is characterized in that to perform the re-reduced to. 2. A wheel lock during braking is prevented by detecting each wheel speed and repeating pressurization and depressurization of the brake fluid pressure based on this as one control cycle to repeat the control cycle. In the anti-lock control method described above, the friction coefficient μ of the traveling road surface is determined for each control cycle, and the wheel speed decelerated by pressurization of the brake fluid pressure causes a low peak that changes from deceleration to acceleration due to the subsequent reduction of the brake fluid pressure. Based on the detection of the low peak, the wheel speed Va at the start of decompression and the wheel speed at the low peak
The speed Vb that exceeds the low peak speed Vl by a speed corresponding to a predetermined ratio of the speed difference Y from Vl is calculated, and the value of the friction coefficient μ is determined from the predetermined value by the determination of the road surface friction coefficient μ in the immediately previous control cycle. If it is detected to be high, the pressure reduction is terminated at the time of the low peak, and the wheel speed and the speed Vb after the time of the low peak are terminated.
Compared with, when a predetermined time has elapsed from the low peak time before the wheel speed is recovered to the speed Vb, re-decompression is performed until the wheel speed reaches the speed Vb from the predetermined time elapsed time, When it is detected by the determination of the road surface friction coefficient μ in the immediately preceding control cycle that the value of the friction coefficient μ is lower than the predetermined value, the pressure reduction is not ended at the low peak time, and the wheel speed is An anti-lock control method, characterized in that it is continued until the speed reaches Vb.