JPH0424155A - Anti-lock control method for vehicle - Google Patents

Abstract

PURPOSE:To realize anti-lock control which fits the vehicle behavior by judging a bad degree of a running road by a map for judging a degree of a bad road based on a relation between wheel velocity and the amplitude of velocity change within a specific period, and changing a mode of pressurization and decompression of brake fluid pressure on the basis of the result of the judgment. CONSTITUTION:A system velocity Vs is calculated (12) from output of a rotational speed sensor 1 of each wheel, target velocity VT following with a fixed difference of velocity, a velocity Vv of a simulated car body as well as calculating (13) the velocity Vv of the simulated car body by selection of the maximum wheel velocity out of four wheel velocities Vw. Also, the time DELTAT of one cycle from a point of time when the system velocity Vs passes the target velocity VT in the accelerated condition up to a point of time when it passes the target velocity VT again in the accelerated condition is detected (15), and the amplitude of velocity change of the system velocity Vs within the time DELTAT of one cycle is calculated 16. Then, strength and weakness of bad degree of the running road is judged on the basis of output of a period detecting means 15 and an amplitude calculating means 16 by using a map 18 for judging the bad degree of road housed in the memory of a control part 17, and a mode of pressurization and decompression of brake fluid pressure on the basis of its result.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to an anti-lock control method for preventing wheels from locking during braking of a vehicle, and in particular to an anti-lock control method that improves braking characteristics on rough roads. Regarding the method.

(Prior art) In general, anti-lock control devices for vehicles convert wheel speeds detected by wheel speed sensors into electric signals for the purpose of ensuring vehicle steering performance and running stability and shortening braking distance during braking. Based on this, the brake fluid pressure control mode is determined, and a hold valve consisting of a normally open solenoid valve and a decay valve consisting of a normally closed solenoid valve are opened and closed to increase, maintain, or reduce the brake fluid pressure. It is controlled by a control unit containing a microcomputer.

FIG. 5 shows changes in wheel speed Vw, wheel acceleration/deceleration dVw/dt, and brake fluid pressure Pw in such anti-lock control, and the hold signal H8 and decay signal DS for opening and closing the hold valve and decay valve. It is a control state diagram shown. Note that the wheel speed Vw in FIG. 5 means the speed of the wheels to be controlled in each control system, and this will be referred to as system speed Vs in the following description.

When the brake is not operated while the vehicle is running, the brake fluid pressure Pw is not pressurized and both the hold signal H5 and the decay signal DS are OFF, so the hold valve is open and the decay valve is closed. condition, but the brake fluid pressure Pw decreases with brake operation.
is pressurized rapidly from time point to (normal mode), and as a result, the wheel speed Vw decreases. This wheel speed V
A reference speed Vr is set that follows w with a speed difference lower by a constant speed ΔV, and this reference speed Vr
is the wheel deceleration (negative acceleration) dVw/dt at time t
When a predetermined threshold, e.g. -IG, is reached in 1,
After this time point t1, it is set to decrease linearly with a deceleration gradient θ of -IG. Then, at a time t2 when the wheel deceleration dVw/dt reaches a threshold value -G, ... (for example -2G) for achieving a predetermined maximum deceleration, the hold signal H3 is turned ON, the hold valve is closed, and the brake fluid is Maintain pressure Pw.

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 reference speed Vr. At this time t3, the decay signal DS is turned ON to open the decay valve and the brake fluid is Start reducing pressure Pw. Due to this pressure reduction, the wheel speed Vw starts to accelerate 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 pressure reduction of the brake fluid pressure Pw is completed. Maintain pressure Pw. Although the wheel speed Vw reaches a high peak at time t5, pressurization of the brake fluid pressure Pw is started again from this time t5. 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 (slow build) to decrease the wheel speed Vw, and the depressurization mode is generated again from time t6 (corresponding to t3).

On the other hand, as a speed approximating the actual vehicle speed, the pseudo vehicle speed V
v is calculated. This pseudo vehicle body speed Vv is determined by selecting the highest wheel speed (select high) among the wheel speeds of the four wheels, and determining the acceleration side and deceleration side with respect to this selected fastest wheel speed (four-wheel select high speed) VwH. It is obtained by limiting the tracking limit of to a predetermined value (for example, ±IG).

By combining the pressurization, holding, and depressurization of the brake fluid pressure Pw as described above, it is possible to control the wheel speed Vw and reduce the vehicle speed without locking the wheels.

By the way, when a vehicle equipped with the above-mentioned anti-lock control device drives on a rough road with many bumps, the wheels often become suspended in the air, and if the brakes are activated at that time, the wheels may become suspended in the air. A wheel suddenly decelerates, and when the suddenly decelerated wheel touches the ground, it starts rotating again. For this reason, the change in wheel speed exhibits a different aspect from that on a normal road. That is, when driving on a rough road, the control cycle becomes faster than in normal situations. Therefore, when anti-lock control is started by applying the brakes while driving on a rough road as described above, the change in wheel speed caused by the rough road is mistakenly recognized as the wheel speed controlled by anti-lock control, resulting in frequent depressurization. The problem was that the brake fluid pressure did not increase and the braking distance increased.

Therefore, in anti-lock control, for example, the time from one pressure reduction start point to the next pressure reduction start point is measured, and if this time is shorter than a predetermined time, this is determined to be a rough road and the brake fluid pressure is increased or An anti-lock control method that changes the rate of decompression has been proposed, but even though the roads are generally rough, there are also corrugated and gravel roads.
There is a problem in that it is not possible to perform anti-lock control accurately in accordance with the road surface conditions by simply changing the manner of pressurization and depressurization.

(Object of the Invention) The present invention provides an anti-lock control method for a vehicle that can secure braking force suitable for various rough roads by accurately determining the degree of rough road depending on the road surface on which the vehicle is traveling. purpose.

(Structure of the Invention) In order to achieve the above object, the present invention provides a target speed VT that follows the pseudo vehicle speed Vv with a predetermined speed difference.
Control target wheel speed V that sets and repeats acceleration and deceleration
The time ΔT of one cycle from when s passes the target speed VT in an accelerated (or decelerated) state until it passes the target speed VT again in an accelerated (or decelerated) state is measured.

Then, the rough road condition on the driving road is expressed as the measurement time ΔT,
The control target wheel speed Vs within this measurement time Δτ
A map for determining the rough road condition is prepared, which is expressed in relation to the amplitude of the speed change, and the mode of pressurization and depressurization of the brake fluid pressure is changed based on the rough road condition determined by reading this map.

(Example) Examples of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram of a control system applied to the implementation of the present invention. In FIG. 1, 1 is a wheel rotation speed sensor attached to each of the four wheels, 2 is a control unit consisting of a computer, 3 is a mask cylinder operated by a brake pedal 4, and 5 is a normally open electromagnetic valve. A modulator includes a hold valve (HV) 6, which is a hold valve, and a decay valve (DV) 7, which is a normally closed electromagnetic valve. 8 is a reservoir, and the brake fluid is pumped up from the reservoir 8 by a pump 9 and stored in an accumulator 1o. has been done. 4a is a brake switch that is turned on when the brake pedal 4 is depressed, and 11 is a wheel cylinder of a wheel brake device.

The control unit 2 includes a speed calculation means 12 that calculates a system speed (controlled target wheel speed in each control system) Vs from the output of each wheel rotation speed sensor 1, and selects the highest wheel speed among the four wheel speeds Vw. (Select High)
and a pseudo vehicle speed calculating means 13 for obtaining a pseudo vehicle speed Vv through a filter of acceleration/deceleration ±IG, and a target speed for calculating a target speed VT that follows the pseudo vehicle speed Vv with a constant speed difference ΔV1. Arithmetic means 14
and a cycle detection means for detecting one cycle of time ΔT from the time when the system speed Vs passes the target speed VT in an accelerated state until it passes the target speed VT again in an accelerated state. Furthermore, the control unit 2 includes an amplitude calculation means 16 that calculates the amplitude (difference between high peak and low peak) a of the speed change of the system speed Vs within the time ΔT of one cycle. Reference numeral 17 denotes a control section, and a memory of this control section 17 stores a map 18 for determining the degree of rough road. As shown in FIG. 2, this map 18 for determining the rough road level is obtained from the cycle detection means 15, and is calculated from the time when the system speed Vs passes the target speed VT in an accelerated state until it passes again in an accelerated state. The degree of roughness of the running road is expressed by taking the cycle time ΔT as the vertical axis and the amplitude a of the speed change of the system speed Vs within the above-mentioned time ΔT obtained from the amplitude calculating means 16 as the horizontal axis. It is. The control unit 18 controls ON/OFF of the hold valve 6 and the decay valve 7 based on the output from each means 12.13 to pressurize, maintain, and reduce the brake fluid pressure in the wheel cylinder 11. When the vehicle is traveling on a rough road, the manner in which the brake fluid pressure is increased or decreased is changed based on the strength of the rough road read from the rough road determination map 18.

Next, FIG. 3 is a flowchart showing a rough road countermeasure routine in this embodiment.

First, in step S1, it is determined whether or not it is the time for determining the degree of bad road, that is, the time when the system speed Vs in the accelerated state passes the target speed VT for the second time or later after the start of the anti-lock control (as shown in FIG. It is determined whether the timing is from time tll to time t15 in the control timing chart shown in FIG. If it is time to judge the rough road degree, the strength of the millet road degree is read out from the rough road degree determination map (FIG. 2) in step S2, and the process proceeds to the next step S3. In this step S3, it is determined whether the rough road degree read from the map 18 is "strong" or not, and when the rough road degree is "strong", the pressurization cycle is made shorter than normal. Step S4 should be changed to
), and while the system speed Vs exceeds the target speed VT, depressurization will not start even if the normal depressurization start point is reached.
The depressurization start point is delayed until the system speed Vs decreases and becomes equal to the target speed VT (step S5). Through the processing in steps S4 and S5, high brake fluid pressure is ensured when the road condition is "strong".

Further, when the determination result in step S3 is rNOJ, it is determined in step S6 whether or not the degree of rough road is "medium". When the rough road condition is "medium", the pressurization cycle is shortened and the rising gradient of brake fluid pressure is made steeper (step S7), as in step S4 above, but the start of pressure reduction is as usual. It is assumed that the process is performed from the depressurization starting point (step S8).

On the other hand, when the determination result in step S6 is rNOJ, that is, when the degree of rough road is "weak," pressurization and depressurization in normal conditions are performed (step S9). In this embodiment, one pressurization cycle is defined as one unit of a combination of a pressurization period and a holding period when the brake fluid pressure is increased in a stepwise manner by repeating pressurization and holding of the brake fluid pressure. However, each pressurization period is constant, and the pressurization cycle is changed by changing the holding period.

FIG. 4 is a diagram for explaining the control state when the rough road countermeasure routine described above is executed.

In the figure, a predetermined speed difference Δ with respect to the pseudo vehicle speed Vv
A target speed VT to be followed by V1 is set, and the increase in brake fluid pressure is started from the time when the system speed Vs in the accelerated state passes the target speed VT. Then, the time elapsed from the time tlo when the system speed Vs in the accelerated state passes the target speed VT until the time tll when the system speed Vs, which is in the accelerated state again after passing through high peak and low peak, passes the target speed VT, i.e. The time ΔT of one cycle of the speed change of the system speed Vs is measured. Similarly, subsequent time points tll to t12, time points t12 to t13, etc.
. . . Sequentially measure the time ΔT of each period. Furthermore, the amplitude a of the speed change in the system speed Vs within the measurement time ΔT of each cycle is measured, and these time ΔT and amplitude a are written in a rough road evaluation map. and,
At each rough road degree judgment time point (t11 to t15), the rough road degree determined in the relationship between the time ΔT and the amplitude a of one cycle immediately before is read from the map 18. Based on this readout, it is determined whether the roughness of the driving road corresponds to "strong", "medium", or "weak" at each determination point, and the brake fluid pressure is increased or decreased depending on the determination result. We are changing the aspect of That is, at judgment time tll in FIG. 4, the immediately preceding period ΔT is long and the amplitude a is large, so the rough road degree is determined to be "medium" from the map 18, and therefore, the rough road degree is determined to be "medium" between time tll and t12. Shorten the pressurization cycle.

Furthermore, at the determination time point t14, T is short and the amplitude a is small for one period immediately before that, so in this case as well, the map 18
Since the rough road condition is determined to be "medium", the pressurization cycle between time points t14 and t15 is shortened. On the other hand, at the determination time point t12, the immediately preceding period ΔT is short and the amplitude a is large, so the rough road condition is determined to be "strong" from the map.

In this case, as mentioned above, not only the pressurization cycle from time t12 to t13 (same as from time t13 to t14) is shortened, but also normal depressurization is performed while the system speed Vs exceeds the target speed VT. Do not start decompression even after reaching the starting point,
Depressurization is started after waiting for the system speed Vs to decrease until it becomes equal to the target speed VT. This ensures brake fluid pressure suitable for rough roads. In addition, due to the sudden deceleration of the system speed Vs, the first judgment point t11 at which it becomes possible to judge the degree of rough road after the anti-lock control is started.
Until then, the brake fluid pressure is increased or decreased in accordance with a normal road (flat road) with a "weak" rough road condition.

Step 83 in the flowchart of FIG. 3 described above
~The processing in S5 is performed when the road surface is extremely uneven, such as a wavy road, and therefore, when a vehicle performing anti-lock control is running, the cycle of speed changes in the system speed Vs is short and the amplitude is large. The processing in steps 86 to S8 is applicable to roads such as gravel roads, for example, where the speed change period of the system speed Vs during driving is short but the amplitude is relatively small. It corresponds to roads.

As described above, in this embodiment, the period from the time when the system speed Vs in the accelerated state passes the target speed VT to the time when the system speed Vs in the accelerated state passes the target speed VT again is treated as one cycle. However, the present invention is not limited to this, and the period until the system speed Vs in the deceleration state passes the target speed VT is one cycle, and this time ΔT
may be measured, and the rough road degree may be determined based on the amplitude of the speed change in the system speed Vs within this measurement time ΔT.

(Effects of the Invention) As is clear from the above description, according to the anti-lock control method of the present invention, a target speed VT that follows the pseudo vehicle speed Vv with a predetermined speed difference is set, and acceleration and deceleration are controlled. Measuring the time ΔT of one cycle from the time when the repeatedly controlled wheel speed Vs passes the target speed VT in an accelerated (or decelerated) state until it passes the target speed VT in an accelerated (or decelerated) state again, A map for determining the degree of bad road is prepared which expresses the degree of rough road on the traveling road in terms of the relationship between the value of the measurement time ΔT and the amplitude of the speed change of the controlled wheel speed Vs within this measurement time Δτ. The mode of pressurization and depressurization of the brake fluid pressure is changed based on the rough road judgment based on the readout. Therefore, when driving on a rough road with many unevenness, it is possible to avoid a situation where brake fluid pressure is insufficient due to frequent start of depressurization due to sudden changes in the controlled wheel speed Vs, and it is possible to secure braking force. .

Furthermore, as described above, by determining the roughness of the road based on both the time ΔT and the magnitude of the amplitude in one cycle of the speed change of the controlled wheel speed Vs, it is also possible to distinguish between a wavy road and a gravel road. Therefore, it is possible to realize highly reliable anti-lock control that matches the behavior of the wheels.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the control system applied to the implementation of the present invention, Fig. 2 is a map for determining the degree of rough road, Fig. 3 is a flowchart showing the rough road countermeasure routine, and Fig. 4 is the control system. The timing chart in FIG. 5 is an explanatory diagram of a conventional anti-lock control method. 1...Wheel rotation speed sensor 2...Control unit 3...Mask cylinder 4...Brake pedal 5
...Modulator 6...Hold valve 7.
... Decay valve 8 ... Reservoir 9 ... Pump 10 ... Accumulator 17 ... Control section 18 ... Map for determining rough road

Claims (1)

[Claims] Based on the detection of changes in the controlled wheel speed Vs in each brake control system, the brake fluid pressure is alternately increased or decreased, thereby preventing wheels from locking during braking. In the anti-lock control method for a vehicle, a target speed VT is set to follow a pseudo vehicle speed Vv, which is calculated based on the highest wheel speed among the four wheel speeds during braking, with a predetermined speed difference, The time Δ of one cycle from the time when the controlled target wheel speed Vs, which repeats acceleration and deceleration, passes the target speed VT in an accelerated state until it passes the target speed VT in an accelerated state again.
T or the time ΔT of one cycle from the time when the controlled target wheel speed Vs passes the target speed VT in a decelerated state to the time when it passes the target speed VT again in a decelerated state, and road stiffness, the measurement time ΔT, and the controlled target wheel speed V within the measurement time ΔT.
A map for determining the degree of rough road expressed in relation to the amplitude of the speed change of s is prepared, and the mode of pressurization and depressurization of the brake fluid pressure is changed based on the degree of rough road determined by reading this map. An anti-lock control method for a vehicle, characterized in that: