JPH09118218A - Control method of anti-lock brake system of vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform an optimum ABS control suitable to a road surface from the start of control by determining the maximum surface frictional coefficient from the peak value of surface friction output of a stress sensor, and automatically selecting a preset control method or controlling set value of brake pressure in conformation to the maximum surface frictional coefficient. SOLUTION: A value of a surface frictional force F is measured by a surface frictional force F detecting means 1 formed of a stress sensor just after start of braking. The moment when the surface frictional force measured value F becomes a peak value is detected by a control timing detecting means 3. The road surface μ is judged on the basis of the magnitude of the detected peak value by a judging means 4. A preliminarily program-set control method or controlling set value of brake pressure is selected by a control switching means 5 in conformation to the judged road surface μ, and an ABS control means 6 formed of an actuator performs a control according to the selected control method or set value. Thus, the optimum ABS control suitable to the road surface μ can be performed from the start of control.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to control of an antilock brake system (ABS) for preventing wheel lock (sticking) during sudden braking of a vehicle, and more specifically, crosstalk components such as brake torque are mixed therein. The present invention relates to a road surface μ determination method for making a stable ABS control determination from the time when ABS control is started by using a stress sensor that provides an output proportional to the road surface friction force or an accurate road surface friction force and brake torque.

[0002]

2. Description of the Related Art In the conventional control of an anti-lock brake system (ABS), the road surface μ is determined by starting the control with an appropriately assumed control method and control set value and measuring the frequency of wheel slippage during the control. When the wheel slip frequently occurs, the control is shifted to a lower μ, and when the wheel slip does not occur, it is considered that the braking force is insufficient and the control is switched to a higher μ. However, if such control is performed, the braking force is large while the wheel slip is occurring on the low μ road surface, or the braking force loss is large while the braking force is conservatively set on the high μ road surface, and the braking distance is large. It becomes a problem that leads to the result.

[0003]

SUMMARY OF THE INVENTION In view of the above-mentioned problems of the prior art, the present invention provides a hole in the axle or in the vicinity of the axle, and a stress sensor consisting of a strain gauge is embedded in the hole, and the axle or the vicinity of the axle is applied by the wheel action force. By monitoring the behavior of the road surface friction force where the stress generated in the vehicle is directly detected by the stress sensor, the road surface μ can be determined at the same time as the ABS control is started or before the control is started, and the road surface μ can be handled from the beginning of the control. The purpose is to perform the optimum ABS control.

[0004]

According to a first aspect of the present invention, there is provided a stress sensor capable of obtaining an output proportional to a road friction force or an accurate road friction force and a brake torque in which a crosstalk component such as a brake torque is mixed. In an anti-lock brake system equipped with, the maximum road surface friction coefficient is obtained from the peak value of the road surface frictional force output of the stress sensor, and the brake pressure control method or control set value that is preset according to the obtained road surface friction coefficient is obtained. Is automatically selected to perform ABS control. According to a second aspect of the present invention, in the control method of the anti-lock brake system according to the first aspect, the sensor output is obtained from the road surface friction force value at the time when the first derivative of the road surface friction force output of the stress sensor reaches a peak. The maximum road friction coefficient is predicted before the peak reaches the peak, and the ABS control is performed by automatically selecting the preset brake pressure control method or control set value in accordance with the maximum road friction coefficient predicted value. I am supposed to do it. According to a third aspect of the present invention, in the control method of the anti-lock brake system according to the first aspect, the road surface friction force value at the time when the second derivative of the road surface friction force output of the stress sensor changes to a negative value. From this, the maximum road surface friction coefficient is predicted before the stress sensor output reaches its peak, and the preset braking pressure control method or control set value is automatically selected according to the maximum road surface friction coefficient predicted value. Then, ABS control is performed.

[0005]

According to the present invention as set forth in claim 1, an anti-stress sensor is provided which is capable of obtaining a road frictional force mixed with a crosstalk component such as a brake torque or an accurate road frictional force and an output proportional to the brake torque. In the lock brake system, the road surface friction coefficient is obtained from the peak value of the road surface frictional force output of the stress sensor, and the preset braking pressure control method or control setting value is automatically selected according to the road surface friction coefficient. It is possible to realize optimum ABS control adapted to the road surface from the time when the control is started. According to the second aspect of the present invention, in the control method for the antilock brake system according to the first aspect, from the road surface friction force value at the time when the first derivative of the road surface friction force output of the stress sensor reaches a peak, Predict the maximum road surface friction coefficient before the stress sensor output reaches its peak, and automatically select the preset brake pressure control method or control setting value according to the predicted maximum road surface friction coefficient value. As a result, it is possible to implement ABS control in which no wheel slippage occurs at the start of control due to control delay. According to the third aspect of the present invention, in the control method for the anti-lock brake system according to the first aspect, the road surface friction at the time when the second derivative of the road surface frictional force output of the stress sensor changes to a negative value. The maximum road friction coefficient is predicted from the force value before the stress sensor output reaches its peak, and the preset brake pressure control method or control setting value is automatically set according to the maximum road friction coefficient prediction value. By selecting “1”, it is possible to implement ABS control without causing wheel slippage at the start of control due to control delay.

[0006]

The present invention is an example of the preferred embodiment, and the scope of the claims is not limited to the embodiment shown here. An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a road surface frictional force measurement value F (a, b, c) immediately after the start of pressurization of a brake obtained from a stress sensor used in the present invention, and its first derivative F ′ and second derivative F ″. The example of the time change of is shown. In addition,
The measured values F, a, b, and c, respectively, correspond to the maximum road surface friction coefficient of the traveling road surface, and have a characteristic that the peak signal increases as the road surface has a higher maximum road surface friction coefficient. FIG. 2 shows a functional system diagram. Immediately after the start of braking at t0 in FIG. 1, the road surface frictional force measurement value F measured by the road surface frictional force F detecting means 1 including a stress sensor is as shown in FIG.
It increases like a for low μ, b for medium μ, and c for high μ. However, when the frictional force obtained from the road surface reaches its limit, the measured value F shows a peak at t2 and then decreases. Therefore, the control timing detection means 3 of FIG. 2 detects t2, which is the moment when the road surface frictional force measurement value F reaches the peak value. In the determination means 4, the F peak value at time t2 is near Pa on a low μ road surface (road surface with a low maximum road surface friction coefficient), near Pb on a medium μ road surface (road surface with a medium maximum road surface friction coefficient), and on a high μ road surface ( On the road surface having a large maximum road surface friction coefficient), the road surface μ changes as in the vicinity of Pc. Therefore, the road surface μ is determined based on the magnitude of the obtained peak value. The control switching means 5 determines μ
A braking pressure control method or a preset value for control which is programmed in advance is selected in accordance with the above, and the ABS control means 6 comprising an actuator performs control according to the selected control method or preset value. The above corresponds to claim 1. The stress sensor of the road surface frictional force F detecting means 1 is described in Japanese Patent Application No. 3-130840 previously proposed by the present applicant.
Japanese Unexamined Patent Publication (Kokai) No. 4-331336 discloses four piezoresistive strain gauges, two on each of the upper and lower surfaces of the substrate facing each other.
The one-segment method, in which the stress sensors are crossed and attached, is installed in the holes provided in the structure, each strain gauge is assembled in a bridge circuit, and the output is processed. The stress applied to the structure is transmitted to each strain gauge of the piezoresistive through the substrate of the stress sensor, and the strain gauge changes its resistance. There is regularity in the resistance change of the strain gauge depending on the direction of stress,
By utilizing this regularity, logical calculation is performed to obtain the shear stress (road surface frictional force F) in the target direction. The computing means 2, the control timing detecting means 3, the judging means 4, and the control switching means 5 are integrally configured as a computer.

However, if control is started after the road surface frictional force F reaches a peak, there is a mechanical control delay,
By the time the control actually begins to take effect, the road surface frictional force decreases and the wheel slippage increases. Therefore, the calculating means 2 obtains the primary differential F ′ of the road surface frictional force F value, and the control timing detecting means 3 detects the time point t1 at which the primary differential F ′ shows a peak. The values of the road surface frictional force F at t1 seen by the judging means 4 are Ya and Y in the cases of a, b and c, respectively.
Since b and Yc are obtained, μ of the traveling road surface is predicted from the correspondence between these values and the road surface μ. The control switching means 5 selects a control method or a set value for control corresponding to the predicted μ, and the ABS control means 6 composed of an actuator controls according to the selected control method or set value. As described above, the prediction of the road surface μ is completed before the road surface frictional force reaches its peak and the corresponding control is started, so that the optimum ABS control can be performed without increasing the slippage of the wheels. The above corresponds to claim 2.

It is impossible to predict what the peak value of the first derivative F'will be. Therefore, in order to recognize that F'has reached the peak, it is necessary to hold the past value of F'and constantly repeat the comparison with the newly obtained F '. Therefore, the peak position t of F ′ can be more easily
In order to obtain 1, the calculating means 2 obtains F ″ which is a second derivative of the road surface friction coefficient F, and the control timing detecting means detects the moment when the second derivative F ″ changes from a positive value to a negative value. By detecting in 3, it is possible to determine t1 and perform μ determination. (Corresponding to claim 3) In this method, it is not necessary to hold the past value of the first derivative F ′, and only the moment when the second derivative F ″ becomes zero or less is detected, so that the determination is easier. Become.

[0009]

According to the present invention, since it is possible to predict μ of the road surface before starting the ABS control, it is possible to select a control method or a set value for control that matches the road surface μ in advance. From the beginning of the ABS control, it is possible to obtain the optimum control effect without causing wheel slippage or the like.

[Brief description of the drawings]

[Fig. 1] Road frictional force measurement values F, F immediately after the start of sudden braking
FIG. 7 is a behavior diagram of the first derivative value F ′ of F, and the second derivative value F ″ of F.

FIG. 2 is a functional system diagram of the present invention.

[Explanation of symbols]

 F Road friction measurement value F ′ F First derivative value F ″ F Second derivative value of F a Behavior of F on low μ road surface b Behavior of F on medium μ road surface c Behavior of F on high μ road surface Pa F peak value on low μ road surface Pb F peak value on medium μ road surface Pc F peak value on high μ road surface Ya F value at F'peak on low μ road surface Yb F'peak on medium μ road surface F value Yc F value at peak F'on high μ road surface t0 At sudden braking start t1 F'Peak time t2 F Peak time 1 Road surface friction force F detection means 2 Calculation means 3 Control timing detection means 4 Judgment means 5 Control switching Means 6 ABS control means

Claims (3)

[Claims] 1. An anti-lock brake system equipped with a stress sensor capable of obtaining an output proportional to a road friction force mixed with a crosstalk component such as a brake torque or an accurate road friction force and a brake torque. A vehicle characterized by obtaining a maximum road surface friction coefficient from a peak value of force output and automatically selecting a preset brake pressure control method or a preset value for control in accordance with the obtained maximum road surface friction coefficient. Anti-lock brake system control method. 2. The anti-lock brake system control method according to claim 1, wherein the stress sensor output reaches a peak from the road surface friction force value at the time when the first derivative of the road surface friction force output of the stress sensor reaches a peak. Anticipating the maximum road friction coefficient previously, and automatically selecting a preset brake pressure control method or control set value in accordance with the maximum road friction coefficient predicted value. Control method of lock brake system. 3. The anti-lock brake system according to claim 1, wherein the stress sensor output peaks from the road friction force value at the time when the second derivative of the road friction force output of the stress sensor changes to a negative value. The maximum anti-friction coefficient of the road surface is predicted before reaching the maximum value, and the preset method for controlling the brake pressure or the preset value for control is automatically selected corresponding to the predicted value of the maximum road friction coefficient. Control method of lock brake system.