JPH0379459A - Antiskid braking method - Google Patents

Abstract

PURPOSE:To improve braking performance in a one wherein brake pressure of wheel is controlled according to the deviation between wheel speed and vehicle body speed by classifying and detecting fluctuation of wheel speed according to the magnitude of amplitude of wheel acceleration, and correcting the increased and decreased quantity of brake pressure according to the detection result. CONSTITUTION:In an antiskid braking device for antiskid brake, an oil pressure control circuit 16 controlled by an ECU 18 is interposed in an oil passage 14 between the wheel cylinder 10 of each wheel W and a master cylinder 12, and the oil pressure control circuit 16 is provided with an oil pressure control valve for increasing and decreasing the liquid pressure of the wheel cylinder 10. The ECU 18 predicts a standard vehicle body speed from wheel speed and wheel acceleration, and conducts increasing and decreasing control of the brake pressure of the wheel on the basis of a slip quantity determined from the predicted standard vehicle body speed and the wheel speed. In this case, the fluctuation of the wheel speed is classified and detected depending on the magnitude of amplitude of wheel acceleration, and according to this detection result, the increased and decreased quantity of the brake pressure is corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an anti-skid braking method suitably applied to a braking device for an automobile, and particularly to a braking method on rough roads.

(Prior technology) Anti-skid braking that prevents wheel slippage, ensures steering stability, and stops the vehicle in a short braking distance when braking on low μ roads such as rain-soaked driving roads. method is known. In this braking method, the rotational speed of each wheel is detected to determine the respective wheel speed, and the slip rate of each wheel is determined based on the deviation (slip amount) between the wheel speed and the vehicle body speed. The brake pressure of each wheel is controlled to increase or decrease so that the friction coefficient of each wheel is maintained near the optimum slip ratio where the coefficient of friction of the wheel is maximized.

In such an anti-skid braking method,
Accurately detecting the amount of slip is extremely important, but on rough roads such as gravel roads with severe unevenness, the detected wheel speed also fluctuates because the wheels judder (vibrate) up and down. Figures 5 (a) and (b) show changes in wheel speed VW and wheel cylinder hydraulic pressure P when braking is performed on such a rough road, and the detected wheel speed VW varies. Therefore, in the conventional anti-skid braking method, the brake fluid pressure is controlled in a relaxed manner, resulting in a problem that the brake fluid pressure decreases and sufficient braking force cannot be obtained.

Therefore, conventionally, wheel judder is detected, and when judder is detected, the amount of increase or decrease in the hydraulic pressure of the wheel cylinder is corrected. More specifically, the control device is equipped with an internal down counter, detects the wheel acceleration GVW, and after the wheel decelerates suddenly such that the acceleration GVW falls below a predetermined negative threshold value a, the acceleration GVW drops to a predetermined positive value. If sudden acceleration exceeding the threshold value S is performed, it is determined that there is a judder, and when this judder is detected, a predetermined value n is added to the count value of the above-mentioned down counter (Fig. 6 (a)).
and (b)). The down counter decrements its count value at a predetermined period (gradient m) when no judder is detected. That is, if the judder detection period is short, the count value of the down counter becomes large.

Then, the state of judder is determined based on the size of this count value, and the larger the count value, the more the control to reduce or maintain the fluid pressure in the wheel cylinder is suppressed to prevent a drop in fluid pressure when judder occurs. That's what I do.

(Problems to be Solved by the Invention) By the way, the judder as described above is a resonance phenomenon of a spring of a vehicle suspension, and its frequency substantially matches the unsprung resonance frequency. Since the unsprung resonance frequency of a general wheel is about 10-odd Hz, the wheel is characterized by a large vibration (vibration) near that frequency.

In the conventional judder state detection described above, only one set of threshold values a and bL is used to determine the wheel acceleration, so when judder occurs with the same period but different amplitude, the comparative Road surface conditions with small amplitudes and road surface conditions with relatively large amplitudes shown by the broken line are detected in the same way.
The count value of the down counter becomes the same value as shown in FIG. 6(b). Therefore, the conventional method has a problem in that the same correction is performed even though the road surface conditions are different.

The present invention was made to solve such problems,
It is an object of the present invention to provide an anti-skid braking method that correctly detects road surface conditions and more accurately corrects the amount of increase or decrease in brake pressure according to the road surface conditions.

(Means for Solving the Problems) In order to achieve the above object, according to the present invention, wheel speeds and vehicle body speeds are detected, and the wheel slip rate is determined according to the deviation between the detected wheel speeds and the vehicle body speed. In an anti-skid braking method in which wheel brake pressure is increased or decreased so that the wheel brake pressure is maintained near a predetermined value, fluctuations in wheel speed are detected in classes based on the magnitude of the amplitude of wheel acceleration, and each detected An anti-skid braking method is provided, which is characterized in that the amount of increase or decrease in brake pressure is corrected in accordance with fluctuations in wheel speed of a class.

(Function) Since fluctuations in wheel speed are detected by classifying them into classes, road surface conditions can be accurately detected, from mildly rough roads with small irregularities to extremely rough roads with severe irregularities. Since the correction amount is determined according to the detected wheel speed fluctuations of each class, the amount of increase or decrease in brake pressure can be accurately corrected.

(Example) An example of the present invention will be described in detail below based on the drawings.

First, the schematic structure of an anti-skid brake device in which the method of the present invention is implemented will be explained with reference to FIG.

The anti-skid brake device includes a hydraulic control circuit 16 installed in the oil passage 14 between the wheel cylinder IO of each wheel W and the mask cylinder 12, an electronic control unit (ECU) 18 that controls the hydraulic control circuit 16, etc. configured with
The hydraulic control circuit 16 has an expander piston, and the movement of the expander piston causes the wheel cylinder I to
A hydraulic control valve that increases or decreases the hydraulic pressure of O, a hydraulic source that supplies hydraulic pressure to the hydraulic control valve to move the expander piston, and a solenoid valve disposed between the hydraulic control valve and the hydraulic source (all not shown). Consists of etc.

Each wheel W is provided with a wheel speed sensor 2° that detects the wheel speed, and the brake pedal 12a is provided with a brake switch 22 that detects depression of the brake hydraulic pressure lever, and these are connected to the input side of the electronic control unit 8. It is electrically connected and supplies a detection signal to the electronic control unit 18 .

The wheel speed sensor 20 includes, for example, a gear-shaped rotating disk that has a large number of protrusions equally spaced on the outer periphery and rotates together with the wheel, and a pickup coil that faces the protrusions of the disk and is attached to the stationary side. Each time the pickup coil detects a protrusion, it supplies a pulse signal to the electronic control unit 18. The electronic control unit 18 calculates the angular velocity of the wheel from the generation time interval of this pulse signal, and calculates the wheel speed vW by multiplying this by the wheel radius. Then, the wheel speed VW calculated this time and the wheel speed V calculated last time are
W, -1 to wheel acceleration GVW (=VW.

−VW, , ) are calculated.

The electronic control device 18 predicts a reference vehicle speed VREF from the wheel speed VW and wheel acceleration GVW described above, and calculates the slip amount Δ from the predicted reference vehicle speed VREF and wheel speed vw.
Find V.

ΔV=VREF−VW −・−・−(1) The above-mentioned method for predicting the reference vehicle speed is a method in which a G sensor is provided separately and prediction is made from the vehicle acceleration detected by the G sensor and the wheel speed W. Various methods have been proposed, including the above, but the gist of the present invention is not particularly in the method of calculating the vehicle body speed VREF, so a detailed explanation will be omitted.

Then, the electronic control device 18 performs rough road correction, which will be described later, on the slip amount ΔV obtained as described above, and sets the increase/decrease amount ΔP of the hydraulic pressure of the wheel cylinder 10 in accordance with the corrected slip amount ΔV. By opening and closing the electromagnetic valve of the hydraulic control circuit 16 described above in accordance with the set pressure increase/decrease amount ΔP, the hydraulic pressure of the wheel cylinder IO is controlled to increase or decrease.

This pressure increase/decrease control method is also not particularly related to the gist of the present invention, so a detailed explanation thereof will be omitted.

Next, a rough road correction method using the electronic control device 18 will be explained.

The electronic control device 18 classifies the fluctuations in the wheel speed vW of the wheel acceleration GVW described above according to the magnitude of the amplitude of the fluctuation period. More specifically, as shown in FIG. 2, for example, the electronic control device 18 is equipped with three sets of determination threshold values for determining the magnitude of the amplitude of the wheel acceleration GVW, and also has three internal down counters A to C. We are prepared. After the wheels suddenly decelerate and the wheel acceleration GVW exceeds a negative predetermined threshold value XG)l, these counters suddenly accelerate to a positive predetermined threshold value X. When the value exceeds P, it is determined that a judder state has been detected, and the count value of the counter is set to a predetermined value n.
is added, and if there is no addition, the count value for a predetermined value is decreased every time a predetermined time elapses.

For example, the counter A is a counter that detects a slightly rough road, and the wheel acceleration GVW is a negative predetermined threshold value X. When a judder state in which the count exceeds □ and falls below □ and exceeds a positive predetermined threshold value XGP+ is detected, a predetermined value n is added to the count value NA. However, the counter A will detect even if the vehicle is in a judder state on a moderately rough road or in a judder state on a very bad road. Counter B is a counter that detects a moderately rough road, and the wheel acceleration GvW is a negative predetermined threshold value X. , exceeds 1ffi and falls below a positive predetermined threshold X. When a judder state exceeding P□ is detected, a predetermined value n is added to the count value N. This counter B also detects the judder condition on extremely bad roads, but cannot detect the judder condition on mildly bad roads.

Counter C is a counter that detects extremely bad roads, and when wheel acceleration GVW exceeds a negative predetermined threshold value Xa, ls,
When a judder state exceeding a positive predetermined threshold value Xaps is detected, a predetermined value n is added to the count value Nc. This counter C detects only the judder condition on extremely bad roads, and cannot detect the judder condition on moderately rough roads and light rough roads.

Then, the electronic control unit 18 corrects the above-mentioned slip amount ΔV according to the flowchart shown in FIG. That is, first, in step SlO, it is determined whether or not the count value NA of the counter A for detecting a light rough road condition is larger than a predetermined value XA. A predetermined value DA is subtracted and corrected from the slip amount ΔV (step 812). If the count value NA is smaller than the predetermined value XA, the process proceeds to step S14 without performing slight rough road correction.

In step S14, a counter B for detecting a moderately rough road condition is
It is determined whether the count value N, is larger than the predetermined value X, and if it is larger, the predetermined value DB is calculated from the slip amount ΔV.
is further subtractively corrected (step 516). If the count value N is smaller than the predetermined value XB, the process proceeds to step S18 without performing the medium-to-rough road correction.

In step S18, a counter C for detecting extremely bad road conditions is
It is determined whether the count value Nc is larger than a predetermined value X, and if it is larger, the predetermined value DC
is further subtractively corrected (step 520). The count value Nc is a predetermined value X. If it is smaller, it is determined that no extremely rough road judder condition has been detected, and the routine ends.

Figure 4 shows the relationship between the fluctuation of wheel speed VW and the magnitude of the correction amount, and is divided into classes to detect judder conditions,
Furthermore, it can be seen that the larger the fluctuation in wheel speed VW, the larger the correction amount is set.

In this way, by correcting the slip amount ΔV on rough roads, the slip amount ΔV on rough roads is corrected to a smaller value according to the road surface condition, so the pressure reduction control or holding control of the hydraulic pressure of the wheel cylinder IO is performed. This makes it difficult for wheel cylinders to increase or decrease the pressure in the vicinity of the appropriate hydraulic pressure.

In addition, in the above embodiment, the slip amount Δ is adjusted depending on the road surface condition.
Although V is corrected, the amount of pressure reduction may be directly corrected according to the amount of correction shown in FIG. The pressure reduction control or holding control may be made difficult to perform by, for example, changing the timing of starting these controls and delaying the start timing of these controls.Furthermore, the correction may be made to greatly correct the pressure increase amount.

Further, it goes without saying that the number of counters, the value of the predetermined value n added to the count value of each counter, the correction amount DA, etc. can be variously changed depending on the vehicle type and the like.

4゜(Effects of the Invention) As detailed above, according to the anti-skid braking method of the present invention, fluctuations in wheel speed are detected divided into classes depending on the magnitude of the amplitude of wheel acceleration, and each detected class is Since the amount of brake pressure increase/decrease is corrected according to fluctuations in wheel speed, brake pressure increase/decrease control can be performed appropriately depending on the degree of rough road, even when judder occurs. A large braking force can be obtained.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a schematic configuration of an anti-skid braking device that implements the method of the present invention, and FIG. 2 is a graph showing the relationship between wheel acceleration GVW and a discriminant value for determining the magnitude of its amplitude. FIG. 3 is a flowchart of a rough road correction routine executed by the electronic control unit 18 shown in FIG. 1, and FIG. 4 is a graph showing the relationship between the magnitude of fluctuation in wheel speed VW and the magnitude of the correction amount. Figure 5 is a graph showing the change in hydraulic pressure over time when the hydraulic pressure in the wheel cylinder is controlled to increase or decrease using a conventional braking method when wheel judder occurs. It is a graph which shows the relationship between the change of wheel acceleration GVW and the change of the count value of a counter in a method. IO...Wheel cylinder, 12...Mask cylinder, 16...Hydraulic pressure control circuit, 18...Electronic control device, 20...Wheel speed sensor.

Claims (1)

[Claims] An anti-skid braking method that detects wheel speed and vehicle body speed, and controls the increase or decrease of wheel brake pressure so that the wheel slip rate is maintained near a predetermined value according to the deviation between the detected wheel speed and vehicle body speed. In the anti-static system, the variation in wheel speed is detected by classifying it into classes depending on the magnitude of the amplitude of wheel acceleration, and the amount of increase or decrease in brake pressure is corrected according to the detected variation in wheel speed of each class. skid braking method.