KR100907868B1 - Control method of vehicle stability control system - Google Patents

Abstract

The present invention relates to a control method of a stability control system of a vehicle, and in particular, the present invention not only can calculate the compensation moment necessary to compensate for the unwanted turning moment during oversteering or understeering, but also the actual driving conditions of the vehicle. It can be calculated accurately according to the vehicle trajectory can be estimated in a short time while maintaining the stability and adjustability of the vehicle to the desired trajectory of the driver.

To this end, the present invention provides an error in each understeer or oversteer when the magnitude of the error in the amount of revolution between the actual amount of revolution of the vehicle and the reference amount of revolution desired by the driver is outside the threshold range of the understeer or oversteer. After calculating the amount of compensation moment required to compensate for the turning moment that the driver does not want by using a preset equation using the magnitude of, the slope of the error, and the proportional constant value determined according to the error and the slope, By performing understeer or oversteer control based on the amount of compensation moment, the vehicle is returned to the normal state in a short time without losing the stability and controllability of the vehicle during the oversteer or understeer.

Description

Control method for electronic stability program in a vehicle

1 is a conceptual diagram illustrating a state of movement of a vehicle according to a road surface condition in a conventional vehicle stability system.

2 is a block diagram of a vehicle stability system according to the present invention.

3 is a control flowchart of a control method of a vehicle stability system according to an exemplary embodiment of the present invention.

4 is a table for determining the coefficient of limited reference revolution speed in accordance with the road friction coefficient and the pressure of the master cylinder.

5 is a graph for explaining weighting a reference turning speed and a limited reference turning speed.

6 is a diagram for explaining a map for calculating a reference turning speed limit entry condition.

7 is a view showing a change in the turning speed error during vehicle steering.

8 is a graph for explaining the weight of the compensation moment amount for each vehicle speed.

9 is a graph for explaining the relationship between the lateral acceleration and the road surface to correct the proportional constant value for each road surface.                 

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

101: measuring unit 102: estimating unit

103: vehicle momentum calculation unit 104: stable reference value setting unit

105: comparison unit 106: determination unit

107: engine control unit 108: braking pressure control unit

109: TCS control block 110; ABS control block

The present invention relates to a vehicle stability control system, and more particularly, to a control method of a vehicle stability control system for maintaining vehicle trajectory in a driving course desired by a driver when turning a vehicle to improve vehicle stability and maneuverability.

In general, an electronic stability program (ESP) of a vehicle is a system that moves a vehicle in a direction desired by a driver by controlling an appropriate wheel in a dangerous situation that reaches a tire contact limit during a driver's driving.

The stability control system of the vehicle is based on oversteer, which is a spin-out phenomenon that occurs when the adhesion limit between the tire and the road reaches the rear wheel first, and when the tire and the road surface reach the adhesion limit first. Understeering, which is a drift phenomenon that occurs, performs different control so that the vehicle moves in the direction desired by the driver. That is, during oversteering, the braking force is applied to the front wheels outside to create a compensating moment acting outward of the vehicle, and the understeering prevents the loss of control of the vehicle. Creating a compensating moment prevents the vehicle from being pushed outwards on the desired trajectory.

This compensation moment is the braking force of the appropriate wheel pressure control when the actual vehicle momentum is larger than the reference vehicle speed (stability criterion) calculated in the vehicle model of the actual vehicle motion controller obtained through the rotational speed sensor. Is generated by. In this case, the reference turning speed as a reference for the control is a stability criterion indicating the trajectory of the vehicle desired by the driver, which may be expressed as the turning speed. The driver's desired turning speed, or reference rdesired, is determined from the steering angle δteer and the vehicle speed Vx based on the basic physical law as follows.

The oversteer and understeer of the vehicle are determined from the turning speed error, which is the difference between the reference turning speed calculated from the above equation and the actual turning speed measured from the vehicle sensor, creating a compensation moment from the turning speed error. Independent control of the brakes on each wheel to ensure vehicle stability.

However, this control method only addresses the need for compensation moment control according to vehicle behavior and cannot calculate the amount of compensation moment necessary to compensate for the unwanted turning moment, so that appropriate oversteer or understeer control can be performed accordingly. Therefore, when oversteer or understeer, not only takes a long time for the vehicle to return to the normal state, but if each control is excessive, there is a problem that adversely affects the stability and adjustability of the vehicle.

The present invention is to solve the above-mentioned problems, an object of the present invention is to calculate the amount of compensation moment required to compensate for the unwanted turning moment during oversteer or understeer, and the braking force corresponding to the calculated amount of compensation moment The present invention provides a control method of a stability control system of a vehicle capable of generating a driving force.

Another object of the present invention is to provide a control method of a vehicle stability control system capable of accurately calculating a necessary compensation moment according to actual driving conditions of a vehicle such as a vehicle speed and a road surface.

The control method of the vehicle stability control system according to the present invention for achieving the above object is to detect the actual turning speed of the vehicle through the turning speed sensor, calculate the reference turning speed desired by the driver from the vehicle model, Calculate the magnitude of the error between the actual revolution speed and the reference revolution speed and the slope of the error, and if the magnitude of the calculated error is outside the threshold range of the understeer or oversteer, at each understeer or oversteer Using the magnitude of the error, the slope of the error, and the proportional constant value determined according to the error and the slope, the amount of compensation moment required to compensate for the turning moment that the driver does not want by the following equation Calculate,

(Where Q is the compensation moment amount, Δyaw is the error value between the actual revolution speed amount and the reference revolution speed amount, ΔyawSlope is the slope of the error value, and Kp and Kd are proportional constant values.)

By performing understeer or oversteer control based on the calculated amount of compensation moment, an effect of returning the vehicle to a normal state in a fast time without losing the stability and adjustability of the vehicle during oversteer or understeer is obtained. have.

Vehicle behavior, road surface by correcting the calculated compensation moment amount in consideration of the weight set in advance for each vehicle speed so as to discriminate the required amount of compensation moment for each vehicle speed, or by correcting the proportional constant value for each road surface so as to discriminate the compensation moment amount applied for each road surface. Conditions and the amount of compensation moment necessary for the actual driving conditions of the vehicle, such as the vehicle speed conditions can be accurately calculated, there is an effect that can improve the stability and controllability of the vehicle during oversteering or understeering.

In addition to the ABS vehicle speed sensor, the stability control system of the present invention requires a steering angle sensor to determine the driver's steering intention and is equipped with a turning speed and a lateral acceleration sensor to know the actual motion state of the vehicle. In addition, the brake pressure sensor is required to determine the driver's willingness to brake.

In the vehicle stability control system according to the present invention, a stability criterion value is determined using a road surface condition obtained based on the actual vehicle motion obtained through each sensor and the lateral acceleration detected from the lateral acceleration sensor. If the actual amount of vehicle movement is large, the stability of the vehicle is secured by controlling the appropriate wheels.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

2 is a block diagram of a vehicle stability system according to the present invention. As shown in FIG. 1, the vehicle stability control system according to the present invention includes a measuring unit 101, an estimating unit 102, a vehicle momentum calculating unit 103, a stability reference value setting unit 104, a comparing unit 105, And a determination unit 106, an engine control unit 107, a braking pressure control unit 108, and a TCS control block 109 for performing conventional traction control control and an ABS control block for performing anti-lock brake control ( And cooperative control.

The measuring unit 101 includes a vehicle speed sensor, a turning speed sensor, a steering angle sensor, a lateral acceleration sensor, a pressure sensor provided in a master cylinder, and the like, and processes signals measured from the sensors for controlling stability of the vehicle.

The estimator 102 estimates a friction coefficient between the tire and the road surface and a slip slip angle using the signal measured by the sensor of the measuring unit 101.

The vehicle momentum calculator 103 is connected to the output side of the measuring unit 101 and the estimating unit 102 and receives the measured value and the estimated value of the sensor to calculate the actual momentum of the vehicle.

The stability reference value setting unit 104 sets a stability criterion as a turning speed of the vehicle desired by the driver.

The comparison unit 105 compares the vehicle momentum calculated by the vehicle momentum calculation unit 103 with the stability reference value set by the stability reference value setting unit 104 and outputs a signal corresponding to the difference. The determiner 106 determines an understeer and an oversteer of the vehicle based on the signal from the comparator 105. The signal according to the determination is outputted to the engine controller / braking pressure controller 107, 108.

The engine control unit / braking pressure control unit 107, 108 performs cooperative control with the TCS control block 109 to adjust the driving force of the engine together when the braking force of the ABS control block 110 is insufficient. That is, when oversteer is determined by the decision unit 106, the rear wheel first reaches the adhesion limit between the tire and the road surface and spins out. Therefore, the front wheel is controlled by controlling the braking device of the front wheel. Reduces the turning moment generated. On the contrary, when understeer, the front wheel first reaches the adhesion limit between the tire and the road surface, so the phenomenon of plow occurs, and the rear wheel is controlled to allow the vehicle to move in the desired trajectory. In addition, when the road friction coefficient is changed, more severe oversteering phenomenon may occur.In this case, when the difference between the vehicle momentum and the stabilization reference value is increased by more than the prescribed value, the vehicle stability is also controlled by controlling the outside wheels in addition to the outside wheels. To secure. The vehicle stability system of the present invention minimizes the rocking phenomenon of the vehicle due to excessive braking force by reducing the driving force by the engine when the braking force is insufficient for optimal stability and riding comfort.                     

3 is a control flowchart of a control method of a vehicle stability system according to an exemplary embodiment of the present invention.

In step 100, the actual speed of the vehicle is detected through the speed sensor 100 (100). At this time, the vehicle speed, the steering angle and the steering angle, the actual turning speed, the lateral acceleration, and the pressure of the master cylinder are detected from the pressure sensors provided in the vehicle speed sensor, the steering angle sensor, the turning speed sensor, the lateral acceleration sensor, and the master cylinder, respectively.

In operation 110, a reference turning speed is calculated using the vehicle speed and the steering angle detected in operation 100, in operation 100. In more detail, the stability reference value representing the trajectory of the vehicle desired by the driver may be expressed as a yaw rate as described above, which is determined from the steering angle and the vehicle speed based on the basic physical law. In the vehicle stability control system of the present invention, the relationship between the steering angle, the vehicle speed, and the driver's desired turning speed is obtained by modeling the vehicle as a degree of freedom system.

That is, the turning speed rno with respect to the steering angle δsw can be determined as a function of the vehicle speed Vx, as shown in the following equation [1].

식 [1]

Formula [1]

Where Vch is the intrinsic velocity characteristic coefficient.                     

The reference revolution speed (rdesired) is determined from the revolution speed (rno) determined by the equation [1] from the filter determined by the vehicle speed (Vx) and the revolution speed (rno) of the equation [1] as shown in the following equation [2] ( 110).

식 [2]

Formula [2]

Where L is a low pass filter.

However, in the case of road surface with small road friction coefficient, if the vehicle is controlled by using the reference rdesired value calculated by Equation [2], the driving direction of the vehicle is moved in the direction desired by the driver, but the body slip angle is increased. The vehicle is controlled in an unstable state because of the loss of stability. Therefore, in such a case, by limiting the reference revolution speed (rdesired) it is possible to ensure the stability of the vehicle and the adjustment in the desired direction at the same time.

In order to calculate the limited reference turning speed (rlimited), the maximum value of the limited reference turning speed (rlimited, max) is first calculated using the maximum values of the vehicle speed and the lateral acceleration detected in step 100. The maximum value of this limited reference turning speed (rlimited, max) can be determined in the dynamic constraints of the basic vehicle motion. Here, the vehicle body lateral acceleration (ay) value is determined from the road friction coefficient (μ), the vehicle speed (V) and the like.                     

식 [3]

Formula [3]

The maximum value of the limited turning speed (rlimited, max) determined by the dynamic limiting condition of this equation (5) provides only basic ideas for practical vehicle control because the vehicle's motion conditions and road conditions vary. Therefore, the limited reference turning speed (rlimited) is a constant (K) determined by the pressure (Pmaster) of the master cylinder which is the driver's braking will and the road friction coefficient (μ) corresponding to the road surface condition as shown in FIG. The maximum value (rlimited, max) of the limited reference turning speed determined in Eq. At this time, the road friction coefficient is determined by the lateral acceleration detected from the lateral acceleration sensor.

식 [4]

Formula [4]

Where Pmaster is the pressure of the master cylinder.

The constant (K = f (μ, pmaster) used to calculate the limited reference rspeed is in the range of 0.5 to 2.0, and when the constant is 1 or less, the turning speed is limited to less than the limit of the current road surface. By controlling the vehicle movement in terms of stability rather than adjustability, if it is greater than 1, the vehicle movement is controlled based on the adjustability rather than stability by limiting the turning speed to a range larger than the road surface limit range.                     

Such limited turning speeds should be applied differently depending on driving and road conditions. Therefore, the final reference turning speed (rdesired, control) of the vehicle stability control is calculated as a function as shown in equation (7) (130).

식 [5]

Formula [5]

The coefficient of the nonlinear function (k_mu) as a weight for selection used herein is calculated by subtracting the lateral acceleration detected from the lateral acceleration sensor (the degree of sliding to the side of the vehicle) as shown in FIG. Is determined. That is, since the smaller the value obtained by subtracting the lateral acceleration detected from the lateral acceleration sensor from the lateral acceleration calculated by the vehicle model of the vehicle, the relatively high friction road surface, k_mu = 1 according to the graph of FIG. 5 so that the reference turning speed is rdesired. It is determined by the final reference turning speed (rdesired, control), and the larger the value obtained by subtracting the lateral acceleration detected from the lateral acceleration sensor from the lateral acceleration calculated in the vehicle model of the vehicle, is relatively low friction road surface, so k_mu = When it becomes 0, the limited reference revolution speed (rlimited) is determined as the final reference revolution speed (rdesired, control).

Equation [5] determines only the magnitude of the final reference revolution speed (rdesired, control), and the sign is determined according to the reference revolution speed calculated from the vehicle model.

The value obtained by subtracting the measured lateral acceleration from the lateral acceleration calculated in the vehicle model is determined as shown in the three-dimensional graph of FIG. 6 by the steering angular velocity which is the steering intention of the driver and the measured lateral acceleration corresponding to the road surface condition. That is, on high friction roads with large lateral acceleration, the final reference turning speed is determined as the reference turning speed by largely determining d1 (orbital speed limit entry condition) according to the magnitude of the steering angle speed. On the other hand, in low friction roads with low lateral acceleration, d1 is determined when the steering angle speed is fast, and the final reference turning speed is determined as the limited reference turning speed. Determining the reference turning speed as the reference turning speed ensures adjustment by not limiting the driver's will.

On the other hand, the oversteer, which is a spin-out phenomenon that occurs when the rear wheel of the vehicle first reaches the adhesion limit between the tire and the road surface, and the drift that occurs when the front wheel first reaches the adhesion limit between the tire and the road surface. Since the understeer is determined from the revolution speed measured from the revolution speed sensor in step 100 and the revolution speed error (delta_yaw) which is the difference between the final reference revolution speed (rdesired, control) calculated by Equation [5], The revolution speed error delta_yaw is calculated (140).

The rotation speed error delta_yaw calculated in step 140 is compared with the threshold of the understeer or oversteer (150).

As a result of the comparison in step 150, if the turning speed error delta_yaw is less than the understeer threshold, it is determined as an understeer, and if it is larger than the oversteer threshold, it is determined as an oversteer. (190).                     

식 [6]

Formula [6]

In case of understeering, on the contrary, the driving force and braking force of the rear wheel are controlled to generate an outward moment with the compensation moment to perform the understeer control (180). In step 210, oversteer control is performed. This allows the actual turning speed to follow the final reference turning speed so that the vehicle can stably move the desired trajectory.

In this case, in steps 170 and 200, the respective compensation moments during understeer or oversteer are calculated, and the compensation moment Q in the emergency state of the vehicle is the revolution speed error ΔYaw calculated in Equation [6]. And its slope (ΔYawSlope) are calculated through equation (7) (170, 200).

식 [7]

Formula [7]

(Kp and Kd are preset proportional constants according to the error of the turning speed and its slope)

FIG. 7 is a diagram for explaining a vehicle turning amount error generated during steering, and a compensation moment at this time is calculated by dividing Kp and Kd in regions according to the magnitude and slope of the vehicle turning amount.

As shown in the understeer or oversteer control reserved area of FIG. 7 (for example, (3) and (6)), when the error of the turning speed is larger than the under_Threshold and less than the over_Threshold, the turning speed is obtained. The compensation moment amount is calculated by setting Kp and Kd in Equation [7] according to the slope of the error of the amount (220), and the oversteer is predicted and controlled according to the calculated compensation moment amount (230).

On the other hand, as in the understeer or oversteer control region of FIG. 7 (for example, (1), (2), (4), and (5)), as a result of the comparison in step 150, the error of the turning speed amount is smaller than the under_Threshold If it is small, calculate the amount of compensation moment needed to compensate for the unwanted turning moment during understeer and then perform the understeer control by controlling the appropriate braking and driving force according to the calculated compensation moment amount, and the error of the turning speed is over_Threshold In the larger case, the amount of compensation moment necessary to compensate for the unwanted turning moment during oversteering is calculated, and then the over braking and driving force are controlled according to the calculated amount of moment.

That is, the areas (1) and (2) are areas in which the understeer phenomenon occurs in the vehicle, and the compensation moment amount is calculated by setting Kp and Kd of the formula (9) in each of the areas (1) and (2). And understeer control.

Areas (4) and (5) are areas in which the vehicle is oversteered, and in each of areas 4 and 5, Kp and Kd of equation (9) are set to calculate the amount of compensation moment, Oversteer control.                     

On the other hand, in the emergency state of the vehicle, the degree of occurrence and the magnitude of the necessary compensation moment are different according to the traveling speed of the vehicle. Therefore, the compensation moment amount is determined by changing the weight to the compensation moment determined in Equation [7] according to the traveling speed.

8 is a weighted map according to the driving speed. In addition to the medium speed (70 to 90 kph), which is a general driving speed, the speed is in a range such as low speed (v1 to v2), medium high speed (v3 to v4), high speed (160 kph) or more. The areas are divided and weights P1, P2, P3, and P4 are set according to the areas.

In addition, the compensation moment of Equation [7], which is determined according to the same turning speed error and the slope of error, should be applied differently according to the road surface. To reflect this, the compensation moment amount is calculated by setting Kp and Kd in Equation [7] according to the road surface.

9 is a road determination region set according to the magnitude of the lateral acceleration. According to the area of lateral acceleration, three road surfaces are determined and Kp and Kd are set independently according to this area, but the middle area uses the median value of each area.

As described in detail above, the present invention can calculate the amount of compensation moment required to compensate for the unwanted turning moment, so that the vehicle can be quickly recovered without losing the stability and control of the vehicle during oversteer or understeer. It has the effect of returning to the normal state.

In addition, the present invention can accurately calculate the amount of compensation moment required according to the actual driving conditions of the vehicle, such as vehicle behavior, road conditions, and vehicle speed conditions to improve the stability and controllability of the vehicle during oversteer or understeer. It can be effective.

Claims (3)

The actual speed of the vehicle is detected by the speed sensor, Calculate the reference turning speed desired by the driver from the vehicle model, Calculating the magnitude of the error between the actual revolution speed amount and the reference revolution speed amount and the slope of the error, When the magnitude of the calculated error is out of the threshold range of the understeer or oversteer, the magnitude of the error at each understeer or oversteer, the slope of the error, and the error and the slope are determined. Using the proportionality constant, the amount of moment needed to compensate for the turning moment that the driver does not want is calculated by the following equation,

(Where Q is the compensation moment amount, Δyaw is the error value between the actual revolution speed amount and the reference revolution speed amount, ΔyawSlope is the slope of the error value, and Kp and Kd are proportional constant values.) And controlling understeer or oversteer based on the calculated amount of compensation moment. The control method of claim 1, wherein the calculated compensation moment is corrected in consideration of a weight previously set for each vehicle speed so as to discriminate the required amount of compensation moment for each vehicle speed. The control method of claim 1, wherein the proportional constant value is corrected for each driving surface such that the amount of compensation moment applied to each driving surface is differentiated.

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