KR100863552B1 - Control method for electronic stability program in a vehicle - Google Patents

Abstract

A vehicle stability control method is provided to secure operability and stability of a vehicle on the low-grip road as well as the high-grip road by limiting the reference turning speed by reflecting the road condition. A vehicle stability control method comprises the steps of: computing the reference turning speed from a vehicle model; calculating a maximum value of the limited turning speed by using lateral acceleration determined from the vehicle model; determining sensitivity by an error of turning speed indicating difference between the reference turning speed calculated from the vehicle model and the actual turning speed; judging whether the vehicle reaches the turning speed limit enter condition from the road limit status or not, on the basis of and an error(d1) of lateral acceleration between the lateral acceleration determined from the vehicle model and the actual lateral acceleration of the vehicle; computing a coefficient of nonlinear function indicating that the vehicle reaches the road limit status, if the vehicle is in the turning speed limit enter condition; determining the control reference turning speed as the reference turning speed if a coefficient of nonlinear function is 1; determining the control reference turning speed as a maximum value of the limited turning speed if a coefficient of nonlinear function is 0; and controlling braking power and driving power so that the actual turning speed of the vehicle follows up the control reference turning speed. Sensitivity of the turning speed limit enter condition is determined according to an error of turning speed between the reference turning speed calculated from the vehicle model and the actual turning speed of the vehicle.

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 a sealing example of the present invention.

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

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

5 is a diagram showing the entry condition sensitivity d1 of the turning speed limit according to the tendency of the turning speed error.

* 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 method, and more particularly, to a stability control method of a vehicle for maintaining the trajectory of the vehicle in the driving course desired by the driver when the vehicle turns.

In general, an electronic stability program system (ESP system) 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 when turning a vehicle.

This ESP system is based on oversteer, which is a spin-out phenomenon when the adhesion limit between the tire and the road reaches the rear wheel of the vehicle first, and the drift due to reaching the adhesion limit between the tire and the road surface on the front wheel first. In the case of understeering, which is a phenomenon, different control is performed so that the vehicle moves in the direction desired by the driver. That is, during oversteering, a braking force is applied to the front wheels outside to generate a compensation moment acting outward of the car, and in case of understeering, a steering force is prevented. Generating moments prevent the vehicle from being pushed outwards on the desired trajectory.

The determination of the oversteer and understeer is based on the difference between the actual turning speed of the vehicle and the reference turning speed calculated from the model of the vehicle, and if the actual turning speed of the vehicle is larger than the reference turning speed, it is judged as oversteer. If the actual turning speed of the vehicle is less than the standard turning speed, it is judged as understeer.

)과 차속(Vx)으로부터 결정된다.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 turning speed ( r desired ), is based on the fundamental physics, as shown in equation [1].

) And vehicle speed ( Vx ).

식 [1]

Formula [1]

FIG. 1 is a conceptual diagram illustrating a motion state of a vehicle according to a road surface condition in a conventional ESP system. As shown in FIG. 1, the high friction road surface shows that the vehicle satisfies the controllability and stability at the same time when the wheel is controlled based on the reference turning speed calculated using Equation [1]. On low friction roads, however, the vehicle's driving is controlled when there is no turning speed limit, but it does not satisfy the adjustability and stability.

Such control results indicate that the reference turning speed, which is the basis of control, is an essential criterion for judging the adjustability and stability of the vehicle. However, since the reference turning speed only shows stable vehicle motion on a high friction road, which is generally accepted, In the case of controlling on the basis of such a low friction road, there is a problem in that it is impossible to secure both the controllability and the stability of the vehicle.

The present invention is to solve the above-mentioned problems, an object of the present invention, when the vehicle is traveling on a low friction road surface, the vehicle that can ensure the controllability and stability of the vehicle on the low friction road surface by using the turning speed limit It is to provide a stability control method.

The vehicle stability control method of the present invention for achieving the above object is to calculate a reference turning speed from the vehicle model, calculate the maximum value of the limited turning speed using the lateral acceleration determined from the vehicle model, and calculates from the vehicle model Sensitivity is determined by the turning speed error, which is the difference between the reference turning speed and the actual turning speed of the vehicle, and the vehicle is in a road limit state based on the difference in the lateral acceleration determined from the vehicle model and the actual lateral acceleration of the vehicle. Judging whether or not the turning speed limit entry condition is determined from reaching or not, if the turning speed limit entry condition is determined, a nonlinear function coefficient which is a weight indicating a degree of reaching the road limit state is calculated, and when the nonlinear function coefficient is "1", the control criterion If the revolution speed is determined as the reference revolution speed, and the nonlinear function coefficient is "0", the control criterion Determining the turning speed as the maximum value of the limited turning speed, and controlling the braking force and the driving force so that the actual turning speed of the vehicle estimates the control reference turning speed.

In addition, the turning speed limit entry condition may include determining the sensitivity according to a turning speed error that is a difference between the reference turning speed calculated from the vehicle model and the actual turning speed of the vehicle.

In addition, when the turning speed error is a stable region, the sensitivity of the turning speed limiting entry condition is set to be large so that the judgment according to the difference in the lateral acceleration between the lateral acceleration and the actual lateral acceleration calculated from the vehicle model is reduced. If the speed error is close to or stays on the road surface limit region, the sensitivity of the turning speed entry condition is set to be less so that the judgment according to the difference in the lateral acceleration between the lateral acceleration calculated from the vehicle model and the actual lateral acceleration is included. do.

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

The ESP system of the present invention allows the vehicle to move in the direction desired by the driver by controlling the appropriate wheels in dangerous situations that reach the contact limit of the tire while the driver is driving. This system prevents the vehicle from being pushed outward from the track and prevents steering loss of the vehicle by applying braking force to the outer wheels of the front wheels when the vehicle is oversteered. The determination of understeer and oversteer of a vehicle uses the basic physical principle (vehicle dynamics), Newton's second law, which is the relationship between force and acceleration acting on a vehicle.

The cooperative control with the existing wheel control device ABS and TCS is inevitable and should not adversely affect ABS and TCS by the ESP system of the present invention, and on the contrary, the performance of the system should not be reduced by ABS and TCS. do. Rather, by using the sensors used in the ESP system of the present invention described below it can improve the performance of the ABS and TCS and can ensure the optimal stability by cooperative control.

In addition to the ABS vehicle speed sensor, the ESP system of the present invention requires a steering angle sensor to determine the driver's steering intention and is equipped with a turning speed sensor and a lateral acceleration sensor of the vehicle 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 ESP system of the present invention, the actual vehicle motion amount is more than a predetermined stability criterion 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. In this case, the stability of the vehicle is ensured by controlling the appropriate wheels.

2 is a block diagram of a vehicle stability system according to an embodiment of the present invention. As shown in FIG. 1, the ESP system of the present invention includes a measuring unit 101 and an ESP control unit 102 to 109. The ESP control unit 102 to 109 includes an estimating unit 102, a vehicle momentum computing unit 103, a stable reference value setting unit 104, a comparing unit 105, a determining unit 106, an engine control unit 107, and a braking pressure control unit. And a cooperative control with the TCS control block 109 for performing conventional traction control control and the ABS control block 110 for performing antilock brake control.

The measuring unit 101 includes a vehicle speed sensor, a turning speed sensor, a steering angle sensor, a lateral acceleration sensor, a brake pressure sensor, etc. for controlling the stability of the vehicle, and processes signals measured from the respective sensors.

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 indicating the amount of turning speed desired by the driver determined by the basic vehicle dynamics.

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 vehicle stability control method according to an embodiment of the present invention. Referring to Figure 3, the vehicle stability control method of the present invention comprises the step of calculating the reference speed from the vehicle model (S100), the step of calculating a limited reference speed (S110), calculating the speed error (S120), Determining the sensitivity of the turning speed limit entry condition using the turning speed error (S130), determining the turning speed entry condition (S140), determining the control reference turning speed (S150), the actual turning speed is controlled And controlling to follow the reference turning speed (S160).

Looking at each of the above processes in more detail, first, the vehicle speed, steering angle and steering angle speed, actual turning speed, lateral acceleration, brake pressure from the pressure sensor provided in the vehicle speed sensor, steering angle sensor, turning speed sensor, lateral acceleration sensor, master cylinder, respectively Detect.

)에 대한 차량운동방정식을 나타낸다.The reference turning speed r desired is calculated from the vehicle model using the vehicle speed and the steering angle. 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. The following equation is used for body turning speed (r) and body sliding angle (

Vehicle movement equation for.

식 [2]

Formula [2]

Where N _δ is the control moment derivative (-l _f c _f )

Y _δ is the control force derivative (c _f )

N _r is the yaw damping derivative {(l _f ² c _f + l _r ² c _r ) / V}]

Y _β is the side slip damping derivative (c _f + c _r )

N _β is the static directional stability derivative {(l _f c _f -l _r c _r )}]

Y _r is the lateral force / yaw coupling derivative {(l _f c _f -l _r c _r ) / V}]

I _z is the vehicle inertia of moment about z-axis

m is the vehicle mass

l is the distance of the axle and the center of gravity

Subscript f, r denotes front and rear wheels, respectively

c is the tire cornering stiffness

V is the vehicle speed.)

)에 대한 선회속도(r no)는 차속 (Vx)의 함수로 결정할 수 있다.This equation (2) derived using the Newton's second law and the derivative concept is summarized as shown in equation (3).

The rotational speed ( r no ) can be determined as a function of the vehicle speed ( Vx ).

식 [3]

Formula [3]

Where Vch is the intrinsic velocity characteristic coefficient.

The reference revolution speed r desired is determined from the revolution speed r no determined by equation (3) from the low pass filter determined by the vehicle speed Vx and the revolution speed of equation (3), as shown in equation (4).

식 [4]

Formula [4]

Where L is a low pass filter.

However, if the same control is applied to the low friction road surface having a low road friction coefficient by using the reference turning speed ( r desired ) calculated by Equation (4), the driving direction of the vehicle is moved in the direction desired by the driver, but the body slip angle is The vehicle is controlled in an unstable state because it becomes large and loses stability. Therefore, in such a case, it is possible to secure vehicle stability and adjustability in a desired direction by limiting the reference turning speed r desired .

), 차속(V) 등으로부터 결정된다.In order to calculate the limited reference revolution speed ( r limited ), the maximum value of the limited reference revolution speed ( r limited, max ) is calculated using the maximum values of the vehicle speed and the lateral acceleration. The maximum value of this limited reference turning speed ( r limited, max ) can be determined from the dynamic constraints of the basic vehicle motion. Where the body lateral acceleration ( ay ) is the road friction coefficient (

), Vehicle speed V and the like.

식 [5]

Formula [5]

The maximum value of the limited turning speed ( r limited, 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 control reference turning speed ( r desired, control ) of the vehicle stability control is determined according to the condition of the vehicle, that is, convergence to the road surface limit, as shown in Equations [6] and [7] (140).

식 [6]

Formula [6]

식 [7]

Formula [7]

Here, the coefficient k_mu of the nonlinear function in Equation [6] is a weight representing whether the vehicle has reached the road limit state. If k_mu = 1 then the current vehicle is within road limits and the reference turning speed ( r desired, control ) used for vehicle control is the target turning speed ( r desired ) calculated in the vehicle model. In addition, k_mu = 0 means that the vehicle has reached the road limit sufficiently so that the reference turning speed ( r desired, control ) should be at the maximum turning speed ( r limited, max ). To indicate that

If the target turning speed determined by the vehicle model is less than the maximum reference turning speed ( r desired, control, saturation ) , the target turning speed ( r desired ) calculated in the vehicle model is calculated regardless of the k_mu value as shown in [7].

The degree to which the vehicle behavior reaches the road surface limit, that is, k_mu may be determined by the lateral acceleration calculated in the vehicle model as shown in FIG. 4 and the measured lateral acceleration magnitude d1. This equation determines only the magnitude of the reference turning speed ( r desired, control ), and its sign is determined according to the reference turning speed calculated in the vehicle model as shown in [7].

The lateral acceleration calculated from the vehicle model, which is the entry condition of the turning speed limit, and the measured lateral acceleration magnitude (d1) are the difference between the vehicle model turning speed corresponding to the driver's will calculated by the model of the vehicle and the turning speed measured in the actual vehicle. The sensitivity may be determined according to the turning speed error (delta_yaw_model).

delta_yaw_model = r measurement-r model

delta_yaw_model> 0, over steer tendency

delta_yaw_model <0, under steer tendency expression [8]

FIG. 5 is a diagram of the entry condition sensitivity d1 of the turning speed limit according to the tendency of the turning speed error defined as in Equation [8]. That is, when the turning speed error is stable, the entry condition sensitivity (d1) of the turning speed limit is set large to make the judgment according to the lateral acceleration calculated by the vehicle model and the measured lateral acceleration magnitude less, and the turning speed error is the road limit area. Approaching, or staying at, sets the sensitivity of the entry conditions less, resulting in faster turning speed limits. This determination further adjusts the sensitivity in accordance with the magnitude of the vehicle measured lateral acceleration. On high friction roads with large measured lateral acceleration, d1 is determined according to the turning speed error to actively determine the turning speed limit condition. On low friction roads with low lateral acceleration, the d1 is determined according to the turning speed error. Reserve it to prevent misjudgment.

When the rear wheel of the vehicle first reaches the adhesion limit between the tire and the road surface, the over-steer, the spin out phenomenon, and the front wheel first reach the limit of the tire and road surface, and the drift understeer is 8 is determined from the rotation speed amount error ( delta_yaw ), which is a difference between the measured rotation speed amount r measurement and the control reference turning speed amount r _{limited and control} (150). That is, if the revolution speed error ( delta_yaw ) is positive, it is determined as oversteer (160), and if it is negative, it is determined as understeer.

delta_yaw = r measurement-r limited, control

delta_yaw> 0, over steer

delta_yaw_model <0 under steer expression [9]

When the rear wheel first reaches the adhesion limit between the tire and the road surface, the spin out phenomenon occurs, thereby reducing the turning moment generated by the front wheel by controlling the brake system of the front wheel. On the contrary, when the front wheel first reaches the adhesion limit between the tire and the road surface, and the drift occurs, the rear wheel is controlled to allow the vehicle to move in the desired trajectory. That is, in oversteer, the inward moment is generated by controlling the driving force and braking force of the front wheel, and during understeer, the inverse moment is generated by controlling the driving and braking force of the rear wheel, so that the measured turning speed follows the reference turning speed. Allows the vehicle to stably move the desired trajectory.

As described in detail above, according to the present invention, by limiting the reference turning speed by reflecting the driving road surface, it is possible to secure both the controllability and the stability of the vehicle even on the low friction road surface.

Claims (3)

Calculate the reference speed from the vehicle model, Using the lateral acceleration determined from the vehicle model to calculate the maximum value of the limited turning speed, The sensitivity is determined by a turning speed error, which is a difference between the reference turning speed calculated from the vehicle model and the actual turning speed of the vehicle, and is based on the difference in the lateral acceleration (d1) between the lateral acceleration determined from the vehicle model and the actual lateral acceleration of the vehicle. Judging from the vehicle reaching the road limit condition, the turning speed limit entry condition is determined. If the turning speed limit entry condition, the non-linear function coefficient (k-mu), which is a weight indicating the degree of the vehicle reaching the road limit state, is calculated, and if the non-linear function coefficient is "1", the control reference turning speed is referred to as the reference turning speed. If the nonlinear function coefficient is "0", the control reference turning speed is determined as the maximum value of the limited turning speed, Controlling braking force and driving force such that the actual turning speed of the vehicle estimates the control reference turning speed, The turning speed limit entry condition includes determining a sensitivity according to a turning speed error that is a difference between a reference turning speed calculated from the vehicle model and an actual turning speed of the vehicle. delete The method of claim 1, wherein when the turning speed error is a stable region, the sensitivity of the turning speed limiting entry condition is set to be large so that the judgment according to the difference between the lateral acceleration calculated from the vehicle model and the actual lateral acceleration is insensitive. And if the turning speed error approaches or stays on the road surface limit area, setting the sensitivity of the turning speed entry condition to be less so as to speed up the determination according to the difference between the lateral acceleration calculated from the vehicle model and the actual lateral acceleration. Vehicle stability control method.

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