KR20080022758A - Method for controlling yaw rate of electronic stability program - Google Patents

Abstract

A yaw rate control method for an ESP(Electronic Stability Program) system of a vehicle is provided to secure stability of the vehicle by stably limiting the yaw rate of the vehicle by controlling vehicle wheels through the momentum of the vehicle and road state and to judge the state of the vehicle exactly by using information about the slip angle of the vehicle on the low-friction road. A yaw rate control method for an ESP system of a vehicle comprises the steps of: measuring the real momentum of the vehicle by reading measurement values from plural sensors detecting motion information of the vehicle(S100,S110); setting a stable reference value that a driver wants, from steering angle and vehicle speed measured from the sensors of the vehicle(S120); comparing the measured momentum of the vehicle and the set stable reference value and judging road conditions according to the degree of measured lateral acceleration if the momentum of the vehicle is over the stable reference value(S130,S140); and deciding the yaw rate limit timing and limit degree according to the judged road condition(S150).

Description

Rotational speed control method of vehicle stability control system {Method for controlling Yaw rate of Electronic Stability Program}

1 is a conceptual diagram illustrating an oversteer situation when a vehicle is traveling in a circle;

2 is a conceptual diagram illustrating an understeer situation when the vehicle is traveling in a circle;

3 is a conceptual diagram illustrating a situation in which the oversteer and understeer behaviors appear in a complex manner when the vehicle is turning;

4 is a block diagram of a vehicle stability control system according to the present invention;

5 is an operation flowchart of a revolution speed control method of a vehicle stability control system according to the present invention;

Figure 6 is a graph showing the turning speed limit entry condition of the vehicle stability control system according to the present invention.

Explanation of symbols on the main parts of the drawings

10: steering angle sensor 20: vehicle speed sensor

30: revolution speed sensor 40: lateral acceleration sensor

60: ESP controller 61: reference momentum setting unit

62: vehicle momentum measurement unit 63: momentum error calculation unit

64: road decision unit 65: understeer / oversteer determination unit

66: understeer / oversteer control unit 70: brake control unit

80: engine control unit

The present invention relates to a swing speed control method of a vehicle stability control system for limiting a yaw rate, which is a criterion for determining vehicle stability in a vehicle stability control system.

In general, the electronic control system of a vehicle is to obtain a strong and stable braking force by effectively preventing the slip phenomenon of the vehicle, an anti-lock brake system (hereinafter referred to as ABS) to prevent the slip of the wheel during braking. ), A traction control system (hereinafter referred to as TCS) that prevents slippage of the drive wheel during sudden start or acceleration of the vehicle, and ABS and TCS are combined to control brake hydraulic pressure to improve driving stability of the vehicle. A vehicle stability control system (Electronic Stability Program) and the like are disclosed.

Among these, the vehicle stability control system is basically for controlling the yaw behavior of the vehicle. The vehicle stability control system controls the brake and the engine in a dangerous driving situation that reaches the tire contact limit when turning the vehicle so that the driver can turn to the desired trajectory. It is a device to guide.

In general, when the vehicle is turning, as shown in FIGS. 1 and 2, an over steer is a spin out in which the vehicle is rolled inward based on a stable turning trajectory, or vice versa. Understeer, which is a drift out, is pushed out, which impairs the stability of the vehicle.

In order to prevent this, the vehicle stability control system, as shown in FIG. 1, applies a braking force to the outer wheels of the front wheel during oversteer when the vehicle is rolled inwards and spins as compared to the trajectory desired by the driver while the rotation radius of the vehicle is rapidly reduced. By generating a compensating moment acting outward of the vehicle, the vehicle is prevented from inwardly shifting in the driving trajectory, and as shown in FIG. 2, as the turning radius of the vehicle increases, the undercut of the vehicle is pushed out of the trajectory desired by the driver. By applying braking force to the inner wheel of the rear wheel during steering, it creates a compensating moment acting inwardly of the vehicle to prevent the vehicle from being pushed outward from the desired trajectory, thereby maintaining the trajectory of the vehicle in a stable state.

As such, it is very important for the vehicle stability control system to determine whether the vehicle currently being driven is drawing a stable trajectory or oversteer or understeer in order to secure stability of the turning vehicle.

Therefore, in the related art, a reference vehicle model (Yaw Rate) is used as the input value of the driver's steering input and the driving speed of the vehicle, and the value obtained from the vehicle model is compared with the turning speed value measured by the turning speed sensor, thereby oversteering and understeering. Judging.

However, the conventional vehicle stability control method is relatively easy to determine the situation using a vehicle model in the case of high friction road surface, but in the case of low friction road surface road margin margin is very small compared to the high friction road surface in Figure 3 As shown, the oversteer behavior and the understeer behavior are compounded, and it is difficult to accurately determine the situation of the vehicle using only the existing speed model, so that proper control is impossible.

Therefore, the present invention has been made to solve the above-mentioned conventional problems, the object of the present invention is to control the wheel by using the vehicle movement amount obtained through the sensor of the vehicle and the road surface state obtained through the estimation, etc. To provide a method of controlling the revolution speed of the vehicle stability control system to stably limit.

Another object of the present invention, in the case of low-friction road surface is to determine the vehicle situation more accurately using the vehicle body sliding angle information in addition to the vehicle model, the turning speed of the vehicle stability control system to apply the turning speed differentially according to the road conditions and driver will To provide a control method.

In order to achieve the above object, the present invention provides a method for controlling a turning speed in a vehicle stability control system, comprising: measuring actual vehicle movement by reading measurement values from a plurality of sensors for detecting motion information of a vehicle; Setting a stability reference value desired by the driver from the steering angle and the vehicle speed measured from the sensor of the vehicle; Comparing the measured vehicle movement amount with a set stability reference value and determining a road surface condition according to the magnitude of the measured lateral acceleration when the vehicle movement amount is greater than the stability reference value; And determining the turning speed limiting time and the limiting size according to the determined road surface condition.

In addition, the stability reference value is characterized in that the turning speed determined from the steering angle and the vehicle speed.

The determining of the turning speed limiting time and the limiting size may be performed by applying the turning time limiting time and the limiting size differently according to the stability reference value and the road surface condition.

In addition, the present invention is a method for limiting the turning speed in the vehicle stability control system, from the steering angle and the vehicle speed measured from the sensor of the vehicle to set a stable reference value of the turning speed desired by the driver, according to the magnitude of the measured transverse acceleration Determine the road condition, determine the time limit and size of the turning speed according to the set stability reference value and the road condition, and control the driving force or braking force according to the determined speed limit time and the limit size to secure vehicle stability. do.

Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

4 is a block diagram of a vehicle stability control system according to the present invention, which includes a steering angle sensor 10, a vehicle speed sensor 20, a turning speed sensor 30, a lateral acceleration sensor 40, a brake pressure sensor 50, ESP controller 60, brake control unit 70 and the engine control unit 80 is configured to include.

The steering angle sensor 10 detects the steering angle of the steering wheel during steering, and the vehicle speed sensor 20 is installed on a plurality of wheels (for example, four) to detect the vehicle speed.

The revolution speed sensor 30 detects the yaw rate of the vehicle, the lateral acceleration sensor 40 detects the lateral acceleration Ax of the vehicle, and the brake pressure sensor 50 detects the master pressure. .

The ESP controller 60 receives signals detected from the steering angle sensor 10, the vehicle speed sensor 20, the turning speed sensor 30, the lateral acceleration sensor 40, and the brake pressure sensor 50 to determine the situation of the vehicle. The reference momentum setting unit 61 and the vehicle momentum measuring unit determine whether the oversteer or the understeer, and control the brake control unit 70 and the engine control unit 80 for controlling the braking pressure and engine torque of each wheel. (62), an exercise amount error calculation unit 63, a road surface determination unit 64, an understeer / oversteer determination unit 65, and an understeer / oversteer control unit 66.

The reference momentum setting unit 61 sets a stable reference value representing the trajectory of the vehicle desired by the driver from the vehicle model by using the steering angle and the vehicle speed detected by the steering angle sensor 10 and the vehicle speed sensor 20. The stability reference, which indicates the trajectory of the desired vehicle, can be represented by the turning speed, which is determined from the steering angle and the vehicle speed based on the basic vehicle dynamics.

The vehicle momentum measuring unit 62 measures the actual vehicle momentum through values detected from the steering angle sensor 10, the vehicle speed sensor 20, the turning speed sensor 30, the lateral acceleration sensor 40, and the brake pressure sensor 50. And the momentum error calculation unit 63 compares the actual reference value measured by the vehicle momentum measurement unit 62 with the stable reference value set by the reference momentum setting unit 61, that is, the difference between the vehicle momentum and the stability reference value, that is, the amount of momentum. Calculate the error.

The road surface determination unit 64 uses the magnitude of the lateral acceleration detected by the lateral acceleration sensor 40 to determine the state of the road surface on which the vehicle travels, that is, the coefficient of friction between the tire and the road surface and the side slip angle. To judge.

The understeer / oversteer determination unit 65 determines whether the state of the vehicle is understeer using the difference in the amount of exercise calculated by the momentum error calculation unit 63 and the road friction coefficient determined by the road surface determination unit 64. Or oversteer.

The understeer / oversteer control unit 66 controls cooperative control with the brake control unit 70, the engine torque control unit 80 alone or the ABS control block 71 and the TCS control block 81 according to the determined understeer or oversteer. By controlling the braking force or the engine driving force to secure the stability of the vehicle, and the rotational speed and the lateral acceleration estimated from the sensors 10 and 20 of the vehicle to limit the turning speed, which is the criteria for determining vehicle stability in the vehicle stability control system. Determine the turning speed limit time and limit size by judging the road surface according to the size of.

In addition, the understeer / oversteer control unit 66 may apply the braking device of the front wheel when an oversteer phenomenon occurs because the rear wheel first reaches the adhesion limit between the tire and the road surface according to the determination of the understeer / oversteer determining unit 65. Control to reduce the turning moment generated by the front wheels. On the contrary, when the front wheel first reaches the adhesion limit between the tire and the road surface and the understeer phenomenon occurs, the rear wheel is controlled to move the vehicle in the desired trajectory. When the road friction coefficient changes, a more severe oversteering phenomenon may occur. In this case, when the difference between the vehicle movement amount and the stabilization reference value increases by a change rate more than the prescribed value, the rear wheel outside wheel is also controlled to secure vehicle stability.

In addition, the understeer / oversteer control unit 66 minimizes rocking of the vehicle due to excessive braking force by reducing the driving force caused by the engine when the braking force is insufficient for optimum stability and riding comfort. The required driving force reduction is achieved through controller area network (CAN) communication with the engine ECU.

The brake control unit 70 controls the brake hydraulic pressure supplied to the wheel cylinder according to the braking signal output from the ESP controller 60 to cooperatively control the ABS control block 71 to generate the braking pressure so as to ensure the stability of the vehicle. In addition, the engine controller 80 controls the engine torque according to the engine control signal output from the ESP controller 60 to cooperatively control the driving force of the engine by cooperatively controlling the TCS control block 81 to secure the maximum stability of the vehicle.

Hereinafter, an operation process and an effect of the revolution speed control method of the vehicle stability control system of the present invention configured as described above will be described.

5 is an operation flowchart of a revolution speed control method of the vehicle stability control system according to the present invention.

In FIG. 5, the steering angle, vehicle speed, turning speed, lateral acceleration and master pressure of the driving vehicle are determined by the steering angle sensor 10, the vehicle speed sensor 20, the turning speed sensor 30, the lateral acceleration sensor 40, and the brake pressure sensor. Each read at 50 (S100).

The actual momentum of the vehicle is received from the vehicle momentum measuring unit 62 of the ESP controller 60 by inputting measurement values such as the steering angle, vehicle speed, turning speed, lateral acceleration, and master pressure read from each sensor 10 to 50. Measure the vehicle momentum (S110).

At this time, the reference momentum amount setting unit 61 of the ESP controller 60 sets a stability criterion indicating the trajectory of the desired vehicle by the basic vehicle dynamics, and the stability reference value is determined from the steering angle and the vehicle speed of the vehicle. It may be represented by the determined yaw rate (S120), and a method of setting a stable reference value will be described later.

In addition, the momentum error calculation unit 63 of the ESP controller 60 stabilizes the actual vehicle momentum measured by the vehicle momentum measurement unit 62 and the vehicle momentum desired by the driver set by the reference momentum setting unit 61, that is, the turning speed. Comparing the reference value to calculate the difference between the two momentum, that is, the momentum error.

Accordingly, the understeer / oversteer determination unit 65 of the ESP controller 60 determines whether the vehicle is understeer or oversteer based on the result of the comparison of the calculated momentum error, and determines whether the vehicle movement amount is greater than the stability reference value. (S130).

When the vehicle momentum is not greater than the stability reference value, the brake control unit 70 and the engine in the understeer / oversteer control unit 66 according to the understeer or oversteer determined by the understeer / oversteer determining unit 65 as in the prior art. The controller 80 alone or cooperatively controls the ABS control block 71 and the TCS control block 81 to control the braking force or the driving force of the engine to secure vehicle stability (S131).

On the other hand, when the vehicle movement amount is greater than the stability reference value, the road surface determination unit 64 of the ESP controller 60 determines the condition of the road surface according to the magnitude of the lateral acceleration read (S140), the understeer of the ESP controller 60 The oversteer control unit 66 limits the turning speed according to the vehicle speed or the road surface condition (S150).

That is, the understeer / oversteer control unit 66 controls the braking device of the front wheel when the oversteer phenomenon occurs because the rear wheel first reaches the adhesion limit between the tire and the road surface according to the determination of the understeer / oversteer determining unit 65. This reduces the turning moment caused by the front wheels. On the contrary, when the front wheel first reaches the adhesion limit between the tire and the road surface and the understeer phenomenon occurs, the rear wheel is controlled to move the vehicle in the desired trajectory. When the road friction coefficient changes, a more severe oversteering phenomenon may occur. In this case, when the difference between the vehicle movement amount and the stabilization reference value increases by a change rate more than the prescribed value, the rear wheel outside wheel is also controlled to secure vehicle stability.

In addition, the understeer / oversteer control unit 66 minimizes rocking of the vehicle due to excessive braking force by reducing the driving force caused by the engine when the braking force is insufficient for optimal stability and riding comfort. The required driving force reduction is achieved through controller area network (CAN) communication with the engine ECU.

Next, a method of limiting the turning speed by setting a stable reference value will be described.

The stability threshold is set by modeling the vehicle from the Degree of Freedom system to determine the relationship between steering angle, vehicle speed and driver's desired turning speed.

Equation 1 below represents a vehicle motion equation for the vehicle's turning speed r and the vehicle sliding angle β .

[Equation 1]

By arranging this equation derived using the Newton's second law and the concept of derivation, the turning speed ( r _no ) for the steering angle ( δ _sw ) can be determined as a function of the vehicle speed ( V _x ) as shown in [Equation 2] below. have.

[Equation 2]

In this way, the target turning speed amount r _desired from the determined turning speed amount is determined from the filter determined by the vehicle speed V _x and the turning speed amount r _no of [Equation 2] as shown in [Equation 3] below.

[Equation 3]

When the road friction coefficient is small, if the control is performed using the target value of the _desired turning speed ( r _desired ) calculated above, the direction of the vehicle may be in the direction desired by the driver, but the slippage angle of the vehicle increases, resulting in loss of stability. The vehicle is controlled in an unstable state as a result of the absence of a limit of turning speed on a low friction road surface.

Therefore, in such a case, by limiting the target turning speed r _desired , vehicle stability and movement in a desired direction can be secured simultaneously.

The maximum value of the limited turning speed r _{limited, max} can be determined in the dynamic constraint of basic vehicle motion, as shown in FIG. 6. The vehicle lateral acceleration ( a _y ) is determined from the road friction coefficient ( μ ), the vehicle speed ( V ), and the like.

[Equation 4]

As such, the maximum value of the turning speed ( r _{limited, max} ) determined in the dynamic limiting conditions due to the variety of the movement conditions or the road surface conditions of the vehicle provides only the basic idea for the actual vehicle control.

The calculated lateral acceleration and the measured lateral acceleration magnitude in the vehicle model, which are the entry conditions for the turning speed limit, are determined using the body sliding angle measured in the vehicle. The unstable state of the vehicle is determined by the body slip angle, and the difference between the calculated lateral acceleration and the measured lateral acceleration is determined according to the magnitude of the generated body slip angle and the measured lateral acceleration corresponding to the road condition.

As described above, according to the turning speed control method of the vehicle stability control system according to the present invention, the turning speed of the vehicle by controlling the wheel using the vehicle movement amount obtained through the sensor of the vehicle and the road surface state obtained through the estimation, etc. There is an effect that can be securely limited to secure the vehicle stability.

In addition, the present invention, in the case of low friction road surface, by determining the vehicle situation more accurately using the vehicle sliding angle information in addition to the vehicle model, it is possible to increase the reliability of the vehicle stability control system by differentially limiting the turning speed according to the road condition and the driver's will. There is an effect.

What has been described above is only one embodiment for implementing the swing speed control method of the vehicle stability control system according to the present invention, the present invention is not limited to the above-described embodiment, it is within the technical scope of the present invention Various modifications are possible by those skilled in the art.

Claims (4)

In the method of controlling the turning speed in the vehicle stability control system, Measuring actual vehicle movement by reading measurement values from a plurality of sensors that detect movement information of the vehicle; Setting a stability reference value desired by the driver from the steering angle and the vehicle speed measured from the sensor of the vehicle; Comparing the measured vehicle movement amount with a set stability reference value and determining a road surface condition according to the magnitude of the measured lateral acceleration when the vehicle movement amount is greater than the stability reference value; And Determining a turning speed limit time and a limit size according to the determined road condition; Rotational speed control method of a vehicle stability control system comprising a. The method of claim 1, The stability reference value is a rotation speed control method of the vehicle stability control system, characterized in that the rotation speed determined from the steering angle and the vehicle speed. The method of claim 1, Determining the turning speed limit time and limit size, A turning speed control method for a vehicle stability control system, characterized in that the limiting time and the limiting size of the turning speed are applied differently according to the stability reference value and road surface conditions. A method for limiting turning speed in a vehicle stability control system, From the steering angle and the vehicle speed measured from the vehicle's sensors, the driver sets the reference value for the desired turning speed. The road condition is judged according to the measured lateral acceleration. Determine the time limit and size of turning speed according to the set stability reference value and road condition. A rotation speed control method of a vehicle stability control system, characterized in that to secure vehicle stability by controlling the driving force or braking force according to the determined turning speed limit time and limit size.

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