KR20000010685A - Deciding method of nominal traveling conduct of vehicle - Google Patents

Abstract

PURPOSE: The deciding method is provided to prevent the output of nominal value corresponded to the conduct of over steering as considering the non-linear range of horizontal/slip angle characteristic curved line. CONSTITUTION: The nominal traveling conduct deciding method for deciding the nominal traveling conduct of a car in case of controlling the traveling conduct of a car having two car axles in a curved road, as continuously decreasing the slip rigidness value as increasing the slip angle when applying a linear one track tread model to a real car, increasing the slip angle and decreasing the slip rigidness continuously to be '0' of the inclination of the horizontal force/slip angle characteristic curve if horizontal force/slip angle characteristic curve of a car reaches to the maximum.

Description

How to determine the nominal driving behavior of the vehicle

The method of the above-mentioned type is disclosed in German Patent No. 40 30 653 A1 which describes a method for determining the slip angle and / or the lateral guiding force of the vehicle being decelerated. Based on the simplified vehicle model in which the speed, steering angle, yawing angular velocity and braking pressure of each wheel are used as measurable parameters, slip angle and / or lateral guidance force are determined as evaluation values. If we plot the lateral guidance force versus the instantaneous slip angle on the wheel, a linear relationship can be derived only when the slip angle is small. The slope of a straight line extending through zero is called the "slip rigidity" of each wheel. However, as the slip angle increases, the relationship between the lateral guiding force and the slip angle becomes nonlinear. As the slip angle increases, the lateral guiding force reaches its highest value and extends from this highest value back into the curved path. If the slip angle is in the nonlinear range of the lateral / slip angle characteristic curve, there is a significant difference between the actual yaw angular velocity and the simulated yaw angular velocity. When measuring yaw angular velocity according to a conventionally known method, the difference between the measured yaw angular velocity and the yaw angular velocity of the simulation shows the transition from the linear range to the nonlinear range of the lateral / slip angle characteristic curve. If it is detected that the linear range of the lateral force / slip angle characteristic curve is over, the relationship between the lateral guide force and the slip angle is defined as a straight line of approximately gentle slope. In order to apply the vehicle model accurately to the actual conditions, the prior art method has correspondingly modified the slip stiffness of the front and rear wheels so that the lateral force / slip angle characteristic curves of both axles fit in the actual curve path.

In general, efforts have been made to control the yaw moment when driving on a curve for neutral driving behavior, which means that the self-steering gradient should be "0" if possible. For this purpose it is easier to handle some understeer by locking the steering further rather than oversteering the vehicle. Neutral driving behavior occurs when the slip stiffness value of the rear axle multiplied by the distance from the vehicle center to the rear axle corresponds to the slip stiffness value of the front axle multiplied by the distance from the vehicle center to the front axle. Oversteer behavior occurs when the value for the rear axle is less than the value for the front axle. According to the basic design of modern vehicles, some understeer usually occurs. Assuming that the front and rear slip stiffness is the same, when the distance from the center of the vehicle to the rear axle exceeds the distance from the front axle, the slip stiffness is a constant value, so this vehicle model always exhibits understeer behavior in the linear range. However, if the slip stiffness value decreases as the slip angle increases, the slip angle of the rear axle may already be in a range where the slip stiffness value is decreased, but the slip angle of the front axle is still the linear range of the lateral / slip angle characteristic curve. May be at At this time, the vehicle model exhibits oversteer behavior. This poses a risk, especially when the vehicle model is used to calculate a preset nominal value of the nominal yaw angular velocity, for example. In this case, the vehicle controller receives a preset value corresponding to the oversteer behavior and thus requires a control operation in which the vehicle is oversteered. This poses a large risk because the driver is usually much harder to handle oversteer than it does for understeer. Even if the actual vehicle exhibits oversteer behavior without a control operation, this behavior corresponds to a preset nominal value so that vehicle control is not initially disturbed.

The invention relates to a method for determining the nominal driving behavior of a vehicle, of the type set forth in the preamble of claim 1.

1 is a plot of the lateral guiding force of the front axle versus the slip angle of the front axle of the one-track model, created with the coefficient of friction between the road surface and the tire as a variable.

The object of the invention is of the type as set forth in the preamble of claim 1, which is a nominal of the vehicle, which takes into account the nonlinear range of the lateral force / slip angle characteristic curve while preventing the generation of a preset nominal value corresponding to the oversteer behavior. It is to provide a method for determining driving behavior.

In the practice of the present invention, the foregoing problem is solved by the features of claim 1. The basic principle of the present invention is to keep the slip stiffness of the rear axle constant regardless of the magnitude of the slip angle of the rear axle. Since the slip stiffness of the rear axle of the vehicle model always corresponds to the highest value of the front axle, it may be less than the slip stiffness of the front axle when not driving. Thus, the preset nominal value optimally corresponds to neutral or slight oversteer behavior, i.e. driving conditions which are easy for the driver to handle.

Also, when the slip angle is further increased, the lateral force / slip angle characteristic curve of the front axle can be adjusted to the actual curve in which the lateral guiding force of the predetermined slip angle is kept constant at the highest value.

When the strongest lateral guidance force is generated by the front wheels outside the curve when driving on a curve, the lateral force / slip angle characteristic curve of the front axle is fitted to the actual path by excellent control performance. Since the slip angles on the rear axle can each be clearly associated with the predetermined lateral guiding force, no instability occurs in the calculation of the vehicle condition even when the inclination is "0".

If the predetermined slip angle or the limit of the value associated with this slip angle is exceeded, the slip stiffness value of the front axle may be reduced. This applies when the slope of the lateral force / slip angle characteristic curve decreases to a low value or "0". Regardless of the decrease in slope or associated value, the slip angle can be determined in response to the coefficient of friction so that this is the limit for the onset and lift of the reduction in slip stiffness, so that the smaller the coefficient of friction between the road surface and the tire, the smaller the slip angle.

The additional dependent claims present a desirable relationship between the limit slip angle and the friction coefficient of the road surface.

The present invention will be described in more detail with reference to the accompanying drawings.

The paths of the actual lateral force / slip angle characteristic curves are described, for example, in "Zomotor, Fahrwerktechnik; Fahrverhalten", published in 1991, by the second edition of Vogel Verlag, Wurzburg. Related technology documents (Fig. 2.27).

The curve group shown shows the correlation between the slip angle and the transverse guide force with the friction coefficient increment ∧μ = 0.1. Slip stiffness is calculated from the inclination of a straight line connecting the zero point to the operating point on the characteristic curve represented by Equation 1 below.

C _i = F _si / α _i

In the linear range until the predetermined slip angle limit α _{1 / μ} is reached, the slope C _L of the straight line passing through the zero point below the curve corresponds to the slip stiffness. The slope of the curve area between the threshold values α _{1 / μ} , α _{2 / μ} is significantly reduced to the value C _NL . If the limit value α _{2 / μ} is exceeded, the slope of the curve is "0". As such, slip stiffness continues to decrease. Which slip angle is used as the limit value for reducing the slip stiffness to the slope C _NL of the lateral force / slip angle characteristic curve and the slope of “0” depends on the coefficient of friction. Instead of the slip angle, the associated lateral guiding force can be used as the limit value.

In the form of the embodiment as shown, the limit value α _{1 / μ} is as follows;

α _{1 / μ} = 7.7 ° ⋅ μ

The second limit value in which the slip stiffness is significantly reduced so that the slope of the lateral force / slip angle characteristic curve becomes "0" is expressed by the following equation (3);

α _{2 / μ} = 1.3 ° + 10.7 ° ⋅ μ

When the slip angle is α <α ₁ /0.5 according to the embodiment, the lateral guiding force of the front axle is calculated as in Equation 4 below;

F _s = C _L ⋅ α

If the slip angle of the front axle is in the range between the limits α _{1 / μ} , α _{2 / μ} , the lateral guidance force of the vehicle model is calculated based on the following equation (5);

F _S = C _L ⋅ α _{1 / μ} + C _NL ⋅ (α-α _{1 / μ} )

When the limit value (α _{2 / μ} ) is exceeded, the lateral guiding force is kept constant, and the slip stiffness becomes "0" by decreasing the slope of the lateral force / slip angle characteristic curve, so the maximum lateral guiding force is Follow;

F _smax = C _L ⋅ α _{1 / μ} + C _NL ⋅ (α _{2 / μ} -α _{1 / μ} )

How the value C _L is determined for a vehicle can be seen from the relevant technical literature. The value C _NL can be stored, for example, as a fixed part of the value C _L or as a fixed value. In either case, the values C _L and C _NL are determined by the characteristics of the vehicle.

With reference to the drawings, the reason why these characteristic curves for the front and rear axle wheels are not suitable for determining a preset nominal value of the vehicle will be described later using the vehicle model. If this diagram is also applicable to the rear axle of the vehicle, the slip angle of the front wheels is still within the linear range of the characteristic curve, while the slip of the rear wheels where the limit values α ₁ and α ₂ may differ from the front wheel limits. The angle may already be within a curved area with reduced slope. In this case, the opposite self steering gradient is calculated for the vehicle model, ie the preset nominal value corresponds to the oversteer behavior.

Apart from this, in view of its yaw transmission function form, a problem occurs in the vehicle model in the non-stop region because the damping ratio of the oversteered vehicle is smaller than "0" when correcting the slip stiffness of the rear axle. In this case, an action point may be included so that a preset nominal value may be applied. The preset nominal value is later inaccurate.

In a simple linear case where no bending point appears in the characteristic curve, this problem does not occur because the slip stiffness values cannot be different from each other irrespective of the operating point on the characteristic curve. However, when such a characteristic curve is used, the slip stiffness value of the rear axle should not be less than the slip stiffness value of the front axle. While modifying the front axle's slip stiffness value can certainly apply a single lubrication model to reality, it is impossible to have a preset nominal value corresponding to oversteer behavior.

According to many driving behavior manipulation methods, the friction coefficient between the road surface and the tire is determined only when control is made. In the real case of modifying the slip stiffness in response to the friction coefficient, a high friction coefficient of μ≥1 is always evaluated during stable driving, and this friction coefficient is difficult to adapt to actual road conditions only after control is started. have. This means that if the coefficient of friction suddenly changes, it will go through non-ideal transitional processes unless the vehicle model goes through the appropriate steps.

Therefore, the state variables of the model at the start of the friction coefficient evaluation are set to initial values according to the friction coefficient. Typically, yaw acceleration and lateral slip velocity are set to "0" when the stationary initial state is evaluated. However, these initial values can be used randomly to preset predetermined dynamic behavior.

Setting state variables to initial values may depend on one or more conditions. On the one hand, it may be necessary for the model to already proceed to the nonlinear part of the lateral force / slip angle characteristic curve, since in most cases the control deviation is expected only in this part and thus the friction coefficient evaluation begins. . On the other hand, setting of initial values may be necessary only if the friction coefficient is actually different from the predetermined high friction coefficient. Therefore, the actual friction coefficient should be less than the predetermined limit value. Otherwise, no adjustment of the initial values is necessary. Alternatively, the initial values may be taken unconditionally.

The yaw angular velocity of the vehicle model can be set, for example, by the highest value achievable in the optimal use of the friction coefficient, i.

g is the acceleration of gravity and V _REF is the vehicle's reference speed. Its advantage is closely related to physics.

In another variant for calculating the initial value of yaw angular velocity of the vehicle model, a stop limit value suitable for the current steering angle according to a linear single wheel model is substituted. The advantage of this variant is that the calculated yaw angular velocity values are better suited to a single rounder model. However, this applies only to a stable area of the single wheeler model, so the vehicle must be stable. In an unstable region, if the physical limit is exceeded, this computational approach provides a high end value corresponding to the stop behavior, which is inaccurate and unacceptable. The reason is that the calculation result of the steering angle of the vehicle is taken into account and the yaw angular velocity thus calculated is increased without limitation in accordance with the steering angle. Initial values at gradual locks beyond the stable curve region can impede the initiation of control, and for that reason this setting should only be used if the maximum value of the yawing angular velocity is limited.

However, the initial value determined according to one of the above-described settings, on the one hand, takes into account the overshooting of the actual vehicle during locking, and on the other hand it is possible to correct the friction coefficient, which is calculated too low at the start of control. May be raised to a predetermined degree. The point that has not yet reached the optimum utilization of the lateral force at the start of control can be corrected upon recognition of the friction coefficient, and this calculated friction value is raised.

In addition, the initial value for the lateral slip angle of the model may be set differently and calculated.

The lateral slip angle is most easily set to "0". In this case, at low friction coefficients, excessive yawing angular acceleration does not occur, and the transient state almost disappears to prevent overshooting. However, this only applies when the coefficient of friction is low and not high.

As another setting state, it is considered that it is preferable to set the conditions in different equations when the inclination of the yaw angular velocity, that is, the yaw angular acceleration starts at "0" at the start of control. The lateral slip angle is calculated such that the yaw acceleration assumes a value of "0", assuming that the lateral force of the front axle that is normally allowed at the start of control is close to maximum utilization. However, the lateral slip angle is not always within the range of acceptable values. It is also an advantage that the model can be strongly excited by an excessively large lateral slip angle, so that the initial horizontal yawing angular velocity can be started.

Thus, the third setting is extensive. The lateral force is estimated to be in the maximum utilization range so that the yawing angular velocity takes the maximum value of the following equation (8);

In the case of a preset value for estimating yaw angle acceleration and lateral slip acceleration as "0", an appropriate initial value for the lateral slip angle can be determined.

According to the fourth setting, the lateral slip angle remains at the last calculated value before the start of control. However, in the case of a low coefficient of friction this may initially lead to an undesirably increased yaw angular velocity, which leads to significant transitional processes in the model, since the previous lateral slip angle is high before the start of control. This is because it is assumed. When changing the dynamic steering state, the value of the lateral slip angle may not match the stopping point of action of the single wheeled model.

Finally, the fifth setting is based on an empirically determined initial value for the lateral slip angle. To this end, it is necessary to find the correlation between the friction coefficient and the lateral slip angle. Also, the initial value of the lateral slip angle is the stop limit value at the original stability limit. In general, when demonstrating that a straight line is used, as a simplification, a polynomial is used for the first approximation.

It can be seen that not all settings are suitable for determining the initial values for each friction coefficient of the road surface. Depending on the coefficient of friction, each suitable setting for determining the initial value can be used. However, if possible, a circular setting common to the entire coefficient of friction range should be used.

When obtaining an initial value, it is important to apply it to the model only if the initial value of the yawing angular velocity with the same sign is less than the actual yaw angular velocity calculated by the model under the assumption that the friction coefficient is high. Otherwise, the model continues to be calculated from the current value of the yawing angular velocity.

However, when the initial value is obtained, there are two variants of the calculation of the subsequent model. If the control is out of spite of obtaining the initial value adjusted by the amount exceeding the threshold for starting the yawing moment control, the control is promoted and the friction calculation is continued. Starting from the initial values obtained, the model continues to be calculated based on the latest friction coefficient. However, if the limit for starting control falls back down through the initial value and the actual calculated friction coefficient, control is not promoted and the friction coefficient is set back to the "high friction coefficient".

Once the initial value is obtained, the control limit value falls so that no control begins, or instead, the friction factor calculation can continue until the end of the run through the curve or the new exit limit for the evaluation of the friction factor Falls down. However, in the above-described mode of operation, it is believed that the friction coefficient can be reliably evaluated only in the range of utilization of the total lateral force. However, the friction coefficients evaluated too low in the above-described modifications result in inducing undesirable start of oversteer control.

If the control limit continues to fall while getting the initial value to prevent the start of control, another variant can be followed to continue the process. For example, the model can be immediately reset with state variables that are tailored to high coefficients of friction and indicate that control limits have been exceeded. In this case, the state variables do not need to be gradually readjusted due to the high preset friction coefficient. The so-called "up-rising" of model variables is reasonably fast, and no reset of state variables is necessary. The gradual application of state variables has the additional advantage that the model is not excited during the transitional process. However, such excitation may be prevented by the last calculated state variables being obtained and updated in the current calculation loop before obtaining the initial value during the reset of the state variables. In either case, in view of an excessively low initial value, for example an excessively low coefficient of friction, the vehicle is prevented from exhibiting strong understeer behavior by unregulated control operations to be initialized.

Claims (7)

When applying a single linear model to a real vehicle, the slip stiffness value continues to decrease with increasing slip angle so that the slope of the lateral force / slip angle characteristic curve becomes a small value (C _NL ) rather than "0". In the nominal driving behavior determination method for determining the nominal driving behavior of the vehicle when controlling the driving behavior of a vehicle equipped with two axles in A method for determining nominal driving behavior, characterized in that only the front axle wheels have reduced slip stiffness (C _L ). The slip stiffness of the vehicle according to claim 1, wherein, when the lateral force / slip angle characteristic curve of the actual vehicle reaches a maximum value, the slip stiffness continues to decrease while the slip angle increases so that the slope of the lateral force / slip angle characteristic curve becomes “0”. How to determine the nominal driving behavior. The slope of the lateral force / slip angle characteristic curve according to claim 1 or 2, if the calculated or measured slip angle exceeds the predetermined limit (α _{1 / μ} , α _{2 / μ} ) or a parameter explicitly related to the slip angle. A method of determining a nominal travel behavior, characterized in that it is reduced and becomes "0". 4. The nominal running according to claim 3, wherein the predetermined limit values α _{1 / μ} and α _{2 / μ} depend on the calculated road friction coefficient μ, so that the predetermined limit value also increases as the road friction coefficient increases. How to determine the behavior. 5. The predetermined slip angle α _{1 / μ} when the slip stiffness C _L is reduced to a smaller slope value C _NL is characterized in that it is directly proportional to the road surface friction coefficient μ. How to determine the nominal driving behavior. 6. The method of claim 5, wherein when the slip stiffness decreases to a smaller slope value C _NL , the predetermined slip angles α _{1 / μ} , α _{2 / μ} are equations α _{1 / μ} = k ₁ ⋅ μ k ₁ is a constant determined according to a specific path of the vehicle. 5. The method of claim 4, wherein when the slip stiffness decreases toward the slope of " 0 &quot;, the predetermined slip angle α _{2 / μ} is equal to the friction coefficient. α _{2 / μ} = α _2/0 + k ₂ ⋅ μ (k ₂ and α _2/0 are constant coefficients determined according to a specific route of the vehicle).