KR20040074175A - Anti-lock brake system for vehicle - Google Patents

Abstract

PURPOSE: An anti-lock brake system for a vehicle is provided to compute braking pressure applied on each vehicle wheel by a pressure sensor and to control a slip generated at the wheels to the calculated wheel pressure. CONSTITUTION: An anti-lock brake system for a vehicle is composed of a wheel speed sensor(10) for detecting the traveling speed of the vehicle; a pressure sensor(20) for measuring braking pressure acting on wheels; and a control unit(30) for controlling a slip generated at the wheels based on a braking pressure value detected by the pressure sensor. The anti-lock brake system comprises steps for outputting the wheel rotational speed and traveling speed of the vehicle and computing a slip ratio(31,33); estimating friction force by using the computed traveling speed and the barking pressure value applied on the wheels(32); computing a target slip ratio by the estimated friction force and slip ratio and the braking pressure value applied on the wheels(34); and controlling the braking pressure to follow a present slip ratio up to the computed target slip ratio(35).

Description

Anti-lock brake system for vehicle

The present invention relates to an anti-lock brake system, and in detail, an operation of an anti-lock brake system calculates a braking pressure applied to each wheel by using a pressure sensor during braking control, and generates the wheel pressure according to the calculated wheel pressure. This is to control the slip for more accurate ABS pressure control.

In general, automobiles are equipped with a brake system for stopping and speed control, and recently, an anti-lock brake system (hereinafter referred to as an anti-lock brake system) is used to improve the braking ability of the vehicle and to secure steering stability during braking. ABS is called).

ABS prevents the phenomenon by detecting the wheels during braking in advance to prevent the vehicle from slipping due to the failure to transfer the braking force to the road surface when braking during high-speed driving on roads with low braking friction coefficient. It is a system for doing so.

That is, this system estimates the vehicle speed by using wheel speed sensors installed on the front and rear wheels of the vehicle, calculates the current slip ratio and deceleration based on this, and uses these data as input variables. To predict the occurrence, reduce the brake pressure beforehand to bring the wheel speed closer to the vehicle speed, and again to increase the brake pressure to brake the wheel before the wheel speed exceeds a certain value. By controlling to maintain the desired state, the fixed state of the wheel is generated to prevent the loss of steering and loss of driving stability in advance, and improve the braking ability.

On the other hand, the friction coefficient between the wheel and the road surface changes according to the condition of the road surface, and compared to the road surface with a large friction coefficient, the wheel slippage is severe on the road surface with a small coefficient of friction, and thus the vehicle enters the fixed state even if a slight braking force is applied to the wheel. easy to do. Therefore, even in the ABS control, the braking pressure on the road surface having a small friction coefficient is generally smaller than that on the road surface having a low friction coefficient because the control method is different on a road surface having a large friction coefficient and a small road surface.

For this reason, if the friction coefficient changes rapidly according to the road surface condition, the control state must be changed quickly. That is, during braking, if there is a sudden change from the road surface with a low friction coefficient to the road surface, the threshold itself of the wheel wheel increases, so the braking pressure must be increased to improve the braking force.

Accordingly, the state of the road surface in the conventional ABS control is estimated by using a predetermined control logic by using the slip ratio of the wheel after the ABS control is started, which requires a predetermined judgment time to determine the state of the road surface. It was difficult to control according to the state, and since the state of the road surface calculated after a predetermined time was an estimated value rather than an accurate value, accurate ABS control was not performed according to the state of the road, which caused a decrease in control sensitivity and a loss of steering. There is this.

Accordingly, an object of the present invention is to calculate the braking pressure applied to each wheel by using a pressure sensor during braking control by the operation of the anti-lock brake system, and to control the slip generated in the wheel according to the calculated wheel pressure.

1 is a block diagram showing a control device of the present invention anti-lock brake system.

2 is a flow chart showing a control method of the present invention anti-lock brake system.

3 is a block diagram showing a control process of the present invention anti-lock brake system.

4 is a graph showing the relationship between the friction of the road surface and slip.

* Description of the symbols for the main parts of the drawings *

10: wheel speed sensor 20: wheel pressure sensor

30 control unit 40 hydraulic modulator

The present invention for achieving the above object is a vehicle equipped with a wheel speed sensor for detecting the running speed of the vehicle, and a pressure sensor for measuring the braking pressure applied to the wheel, the braking detected by the pressure sensor The controller is configured to control the slip occurring on the wheel based on the pressure value.

The controller inputs a speed signal output from the wheel speed sensor to calculate a driving speed of the vehicle and a rotation speed of the wheel, and based on the driving speed output from the speed calculator and the pressure value detected by the pressure sensor. A friction force estimator for estimating the frictional force of the currently running road surface, a slip calculator for calculating a slip ratio by inputting a traveling speed and a wheel rotation speed output from the speed calculator, and each of the friction force estimator and the slip calculator Braking pressure control so that a target slip calculation unit for calculating a target slip ratio to be controlled by inputting a friction force and a slip ratio and a slip value output from the target slip calculation unit follow the slip value currently generated to the input slip value. It is composed of a pressure control unit for outputting a signal.

According to the present invention having the above configuration, estimating the frictional force of the currently running road surface, calculating a target slip ratio using the estimated frictional force and a slip ratio that is currently generated, and presently generated the target slip ratio. Controlling the braking pressure so that the slip ratio is followed.

Hereinafter, the configuration and operation of the present invention will be described in detail with reference to the accompanying drawings.

1 is a block diagram showing a control device of the present invention anti-lock brake system, Figure 2 is a flow chart showing a control method of the present invention anti-lock brake system, Figure 3 is a block showing the control of the present invention anti-lock brake system. Is leading.

First, the configuration will be described with reference to FIG. 1.

The wheel speed sensor 10 for detecting the wheel speed of the vehicle, the wheel pressure sensor 20 for detecting the braking pressure applied to the wheel, and the wheel based on the braking pressure value detected by the wheel pressure sensor 20. The controller 30 is configured to control the slip occurring in the air, and the hydraulic modulator 40 is configured to input or decrease the braking pressure applied to the wheel by inputting a control signal of the controller 30.

The controller 30 inputs a speed signal output from the wheel speed sensor 10 to calculate a driving speed of the vehicle and a rotation speed of the wheel, and a driving output from the speed calculating unit 31. The friction force estimator 32 estimates the frictional force of the currently running road surface based on the speed and the pressure value detected by the wheel pressure sensor 20, and the driving speed and the wheel rotation speed output from the speed calculator 31 are input. A slip calculation unit 33 which calculates a slip rate by calculating a target slip rate to be controlled by inputting respective frictional forces and slip ratios output from the friction force estimating unit 32 and the slip calculation unit 33 And a pressure control unit 35 for inputting a slip value output from the target slip calculation unit 34 and outputting a braking pressure control signal so that the slip value currently generated follows the input slip value.

The control method is shown in Figure 2,

Calculating a wheel rotation speed and a running speed of the vehicle in operation and calculating a slip ratio generated, estimating a friction force using the calculated driving speed and a braking pressure value applied to the wheel, the estimated friction force and the current Calculating a target slip ratio using the generated slip ratio, and controlling a braking pressure applied to the wheel so that the currently generated slip ratio follows the calculated target slip ratio.

Hereinafter, the detailed operation will be described.

The speed calculator 31 of the controller 30 inputs the speed signal detected by the wheel speed sensor 10 to calculate the wheel rotation speed and the traveling speed of the vehicle. The friction force estimating unit 32 inputs the driving speed of the vehicle calculated by the speed calculating unit 10 and the braking pressure applied to the wheel measured by the wheel pressure sensor 20 to estimate the frictional force of the currently running road surface.

In addition, the slip calculator 33 inputs the driving speed and the wheel rotation speed calculated by the speed calculator 10 to calculate the slip ratio that is currently generated.

The target slip calculator 34 inputs and controls the friction force and the slip ratio estimated by the friction force estimator 32 and the speed calculator 10 and the braking pressure value of the wheel pressure sensor 20. It is calculated as shown in the following equation.

[Equation 1]

_{f S (P, μ, e} S) = K p (P, μ, e S) and _S + K _d e (P, μ, _S e) _S e and △

Where P is the braking pressure applied to the wheel, μ is the road frictional force, e _S is the error between the reference slip and the current slip,

f _S is a slip control type, K _P is a proportional gain value, and K _d is a derivative gain value.

Each of the proportional gain value Kp and the derivative gain value K _d is determined by three variables, ie, wheel pressure P, friction force μ, and slip error e _S as shown in Equation 1 above. As a value for, the sequential design is possible by decomposing into two independent structures as shown in the following equation.

[Equation 2]

K _P (P, μ, e _S ) = K _P1 (μ) K _P2 (P, e _S )

K _d (P, μ, e _S ) = K _d1 (μ) _Kd2 (P, e _S )

As described above, if the gain structure for three variables, wheel pressure (P), road friction force (μ), slip error (e _S ) is decomposed into two independent design structures, sequential design is possible. By setting the proportional gain and derivative gain of road surface friction force (μ) coefficient on the high road surface as 1 (K _p1 = 1, K _d1 = 1), each of K _p2 and K _d2 is designed and then various road conditions What is necessary is to determine the K _p1 and K _d1 through actual vehicle experiments corresponding to.

Each of the K _p2 and K _{d2 may} also be easily determined according to the slip error (e _S ), which will be described later with reference to FIG. 4.

(One). e _S > 0 (Case I)

K _p2 (P, e _S ) = K _pⅠ (P)

K _d2 (P, e _S ) = K _dI (P)

(2). 0 ≥ e _S > S _thr (Case II)

K _p2 (P, e _S ) = K _pII (P)

K _d2 (P, e _S ) = K _dII (P)

(3). e _S ≤ _{S thr} (Case III)

K _p2 (P, e _S ) = K _pIII (P)

K _d2 (P, e _S ) = K _dIII (P)

S _thr is a slip threshold value for the frictional force.

That is, in the stable region (Case I), the K _pI (P) and the K _dI (P) are set in a direction to quickly converge the current slip to the reference slip (S _ref ), and the allowable region (Case II) In this case, the K p _II (P) and K _{d II} (P) are set to maintain the slip occurring as close as possible to the reference slip (S _ref ). In the unacceptable area (Case III), wheel locking is prevented from occurring. in a direction to reduce the slip to quickly generated that are to be set to K _pⅢ (P) and K _dⅢ (P).

Hereinafter, setting K _pn (P) and K _dn (P) for each case will be described with reference to the following equation.

[Equation 3]

{Case Ⅰ}

K _PI (P) = K _PH (P _H -P), if P _H > P

C _PH , if P _H ≤ P

K _dI (P) = K _dH (P _H -P), if P _H > P

C _dH , if P _H ≤ P

Where P _H is the highest value of the wheel pressure of the previous cycle,

K _PH , C _PH , K _DH and C _DH are constant parameters.

The smaller the current wheel pressure (P) is below the pressure peak (P _H ) of the previous cycle, the higher the K _PI (P) and the K _dI (P), allowing the slip to converge more quickly to the reference value (S _ref ), When the wheel pressure P approaches the maximum pressure P _H , the K _DI (P) and K _dI (P) are reduced to reduce the pressure change. In addition, if the slip that occurs even when the wheel pressure P exceeds the maximum value P _H is present in the stable region, it is regarded as a change in the road surface, that is, a change in the friction coefficient (μ), and K _PI (P) and K _dI ( Switch P) to the constant parameters C _PH , C _DH to slowly converge the slip to the reference slip (S _ref ).

Each of the constant parameters K _PH , C _PH , K _DH , and C _DH is determined through actual vehicle experiments in consideration of specifications such as braking distance, noise, and adaptation demand speed when changing road surfaces.

[Equation 4]

{Case II}

K _PII (P) = K _PL ㆍ (P-P _L ), if P> P _L

C _PL , if P ≤ P _L

K _{d II} (P) = K _dL (P-P _L ), if P> P _L

C _dL , if P ≤P _L

Where P _L is the lowest value of the wheel pressure of the previous cycle,

K _Pl , C _Pl , K _Dl , C _Dl are constant parameters.

If the current wheel pressure (P) is greater than the pressure minimum value (P _L ) of the previous cycle, increase K _PII (P) and K _dII (P) to converge the slip more quickly into the stable zone (Case I), and the wheel pressure (P) by the close-up when the pressure (P _L) of the lowest level reduces the K _DⅡ (P) and K _dⅡ (P) reduces the pressure change. In addition, if the slip that occurs even if the wheel pressure P is lower than the minimum value P _L is present in the stable region, it is regarded as a change in the road surface, that is, a change in the friction coefficient (μ), and K P _II (P) and K _{d II} ( P) is converted into constant parameters C _PL , C _DL and the slip gradually converges to the stable region (Case I).

Each of the constant parameters K _PL , C _PL , K _DL , and C _DL is determined through actual vehicle experiments in consideration of specifications such as braking distance, noise, and adaptation demand speed when the road surface changes.

[Equation 5]

{Case III}

K _PIII (P) = C _P

K _dIII (P) = C _d

Where C _P and C _d are constant parameters.

In case III, the present slip is present in the unacceptable area, so it is important to quickly reduce the slip occurring irrespective of the wheel pressure P.

The constant parameters C _P and C _d are determined in consideration of specifications such as a required dump speed when a slip occurs in the wheel.

As described above, when the proportional gain value K _P and the differential gain value K _d are designed for each case, a target slip value to be controlled is calculated through Equation 1, and when the target slip value is calculated, The target wheel pressure value to be controlled is calculated using the equation.

[Equation 6]

P _T (n) = f _S (P, μ, e _S ) + P (n-1)

The P _T (n) is a target pressure value, P (n-1) is the actual wheel pressure value of the previous period, fs is a slip control type.

When the target wheel pressure value is calculated as shown in Equation 6, the pressure controller 35 of the controller 30 outputs a control signal to the hydraulic modulator 40 to control the braking pressure to reach the target wheel pressure value. will be.

As described above with reference to FIGS. 2 and 3, a series of processes are performed at predetermined intervals so that an optimum braking operation can be performed when the vehicle is driven.

As described above, in the present invention, since a pressure sensor is mounted on each wheel of the vehicle and the slip generated based on the pressure value detected by the pressure sensor is controlled, accurate road surface estimation is performed when estimating the frictional force of the road surface for calculating the target slip. This makes it possible to use the sensed value of the pressure sensor when controlling the wheel pressure so that the current slip on the target slip is followed, thereby reducing the pressure error, thereby performing a reliable braking operation, thereby providing a good braking system to the user. Will be provided.

Claims (12)

In an anti-lock brake system of a vehicle having a wheel speed sensor for detecting a driving speed of the vehicle and a pressure sensor for measuring a braking pressure applied to the wheel, And a control unit for controlling a slip occurring in the wheel based on the braking pressure value detected by the pressure sensor. The method of claim 1, The controller inputs a speed signal output from the wheel speed sensor to calculate a driving speed of the vehicle and a rotation speed of the wheel, and based on the driving speed output from the speed calculator and the pressure value detected by the pressure sensor. A friction force estimator for estimating the frictional force of the currently running road surface, a slip calculator for calculating a slip ratio by inputting a traveling speed and a wheel rotation speed output from the speed calculator, and each of the friction force estimator and the slip calculator Braking pressure control so that a target slip calculation unit for calculating a target slip ratio to be controlled by inputting a friction force and a slip ratio and a slip value output from the target slip calculation unit follow the slip value currently generated to the input slip value. An anti-lock brake system for a vehicle, characterized in that the pressure control unit for outputting a signal. In the anti-lock brake system of the vehicle for performing a braking control by detecting a slip generated in the wheel is provided with a plurality of sensors for detecting the movement information of the vehicle, A first step of calculating a wheel rotation speed and a traveling speed of the vehicle, and calculating a slip ratio using the calculated wheel rotation speed and the traveling speed, and using the calculated driving speed and a braking pressure value applied to the wheel. A second step of estimating a second step of calculating a target slip rate using the estimated frictional force, a slip rate and a braking pressure value applied to the wheel, and to follow the slip rate currently generated in the calculated target slip rate. The anti-lock brake system for a vehicle, characterized in that performed in a fourth step of controlling the braking pressure applied to the wheel. The method of claim 3, wherein And the slip ratio of the third step is an error slip ratio between a preset reference slip ratio and a currently generated slip ratio. The method of claim 3, wherein Computing the target slip value of the third step is achieved by the following equation. [Equation] _{f S (P, μ, e} S) = K p (P, μ, e S) and _S + K _d e (P, μ, _S e) _S e and △ Where P is the braking pressure applied to the wheel, μ is the road friction force, es is the error between the reference slip and the current slip, fs is slip-controlled, K _P is proportional gain, and K _d is differential gain to be.) The method of claim 5, Each of the proportional gain value K _P and the derivative gain value K _d is calculated by dividing the slip into a plurality of sections based on the frictional force, and calculating the slip using the following equation in the corresponding section according to the slip generated. Vehicle anti-lock brake system, characterized in that. [Equation] K _P (P, μ, e _S ) = K _P1 (μ) K _P2 (P, e _S ) K _d (P, μ, e _S ) = K _d1 (μ) _Kd2 (P, e _S ) Where P is the wheel pressure value, μ is the frictional force on the road, e _S is the slip between the reference slip and the current slip, K _P 1 is the proportional gain for friction, K _d 1 is the differential gain for friction K _P 2 is the proportional gain for wheel pressure and slip error, K _d 2 is the differential gain for wheel pressure and slip error) The method of claim 6, The plurality of sections are divided into a driving stable region and an unstable region of a vehicle during braking control due to slip occurrence, and the unstable region is divided into an allowable region and an unacceptable region in which antilock braking operation is determined. Vehicle anti-lock brake system. The method of claim 7, wherein Each of the stable region and the unstable region is divided by the following equation. [Equation] (One). Stable area. e _S > 0 (2). Unstable Area e _S ≤ 0 (E _S is the error slip rate between the reference slip and the slip currently generated) The method of claim 7, wherein And the allowable region and the unacceptable region are divided by the following equation. [Equation] (One). Acceptable area. 0 ≥ e _S > S _thr (2). Unacceptable Zone. e _S ≤ _{S thr} (E _S is the error slip ratio between the reference slip and the currently occurring slip, and S _thr is the threshold hold value of the slip against friction.) The method of claim 6, And the proportional gain value (K _P 1) and the differential gain value (K _d 1) for each friction force are calculated through actual vehicle experiments according to the friction force of the road surface. The method of claim 6, Each of the proportional gain value K _P 2 and the derivative gain value K _d 2 is calculated by the following equation. [Equation] (One). e _S > 0 K _P2 = K _PH (P _H -P), if P _H > P C _PH , if P _H ≤P K _d2 = K _dh (P _h -P), if P _H > P C _dh , if P _H ≤ P (2). 0 ≥ e _S S _thr K _P2 = K _PL (P-P _L ), if P> P _L C _PL , if P ≤ P _L K _d2 = K _dL (P-P _L ), if P> P _L C _dL , if P ≤P _L (3). es ≤S _thr K _P2 = C _P K _d2 = C _d Where e _S is the error between the reference slip and the currently occurring slip, S _thr is the threshold hold value of the slip against friction, P _H is the highest value of the wheel pressure of the previous cycle, and P _L is the wheel pressure of the previous cycle. K _PH , C _PH , K _DH , C _DH, K _Pl , C _Pl , K _Dl , C _Dl, C _P , C _d are constant parameters.) The method of claim 3, wherein The controlling of the braking pressure in the fourth step is to calculate a target wheel pressure value by the following equation and control to reach the target wheel pressure value. [Equation] P _T (n) = f _S (P, μ, e _S ) + P (n-1) (The P _T (n) is the target pressure value, P (n-1) is the actual wheel pressure value of the previous period, fs is a slip control formula for calculating the target slip.)