DE102016005966A1 - Method for improving the yawing behavior of a motor vehicle - Google Patents

Abstract

The invention relates to a method for improving the yawing behavior of a motor vehicle (10), according to which a yawing moment to be expected in the motor vehicle is calculated model-dependently as a function of the speed and the steering angle of the motor vehicle (10), comprising the following steps: expected actual yawing moment (Mz actual) as a function of an actual speed (vx actual) and an actual steering angle (δv actual) of the motor vehicle (10), S2) calculation of a reference yawing moment (Mz Ref) for a predetermined reference Speed (Mx actual) and for the actual steering angle (δv actual) S3) Calculation of a corrective yaw moment (Mz korr) by subtraction (D = Mz st - Mz Ref) from actual yaw moment (Mz actual) and the reference yaw moment (Mz Ref).

Description

The invention relates to a method for improving the yaw behavior of a motor vehicle and to a control device for carrying out this method. The invention further relates to a motor vehicle with such a control unit.

As yaw axis is referred to in vehicle technology, the vertical axis of the vehicle-fixed coordinate system. A rotational movement about this axis is known as yawing or - in simplified terms - as yawing. Said yawing is completed by the so-called. Rolling motion of the vehicle about its longitudinal axis and by the so-called pitching movement about the transverse axis of the vehicle to the three basic rotational movements of each vehicle.

Yaw movements about the vertical axis can occur in motor vehicles in driving in a variety of driving situations, such as when driving on a curve or when changing lanes on a lane with multiple lanes. With regard to safety-critical Giereffekte particularly problematic is such a lane change especially when driving at high speeds, for example on highways or highways with multiple lanes per direction. By required for the lane change steering angle change of the steered axle of the motor vehicle can act on the vehicle acting yaw accelerations which act destabilizing on the motor vehicle or at least can give the driver of the motor vehicle such an impression. In general, unwanted gyro effects can occur even with small or short-term changes in the direction of travel of the motor vehicle, for example, caused by slight steering intervention by the driver. This effect increases with increasing vehicle speed in combination with high steering speed.

The prior art therefore includes various methods for increasing the driving stability of the motor vehicle in view of the avoidance of unwanted and, if appropriate, the operational safety of the vehicle to a not insignificant extent diminishing Giereffekte.

The DE 10 2006 048 835 A1 suggests a regulation of the yaw rate of the motor vehicle based on a regulation of the rear axle steering of the motor vehicle. Already the provision of such a rear axle steering is manufacturing technology associated with significant additional costs and just to see in the production of small and medium-sized cars as relatively uneconomical. In addition, the degree of improvement of the driving stability of the motor vehicle achievable by means of such a yaw rate control depends considerably on the quality of the yaw rate sensor system used for the control. In contrast, that used in the DE 10 2004 035 004 A1 described driving stabilization program a model-based method, which is characterized by a model-based feedforward control. However, such a method is technically relatively complex and thus error-prone.

It is therefore an object of the invention to provide a model-based method which allows the reduction of unwanted gyro effects of a motor vehicle, in particular at relatively high speeds. Further objects of the invention lie in the provision of a control device for carrying out such a method in a motor vehicle and a motor vehicle with such a control device.

These objects are achieved by the subject matter of the independent claims. Preferred embodiments are subject of the dependent claims.

The basic idea of the invention is accordingly to adapt the yawing behavior of the motor vehicle at high speeds to that at low speeds. This is achieved by the present invention by a - fully model-based - calculation of a so-called. Correction yaw moment which can be impressed on the motor vehicle during driving, for example, by a suitable one-sided control of the brake system, so that the resulting yaw behavior of the vehicle at the present high Driving speed is reduced to a yaw behavior, as would be present at a reduced compared to the real speed speed reference speed. Essential to the invention is that the entire calculation model-based - with the current steering angle of the steering axle and the current vehicle speed of the vehicle in the direction of travel as central input variables - takes place. In other words, special sensors installed in the vehicle for measuring the yaw rate are not required for calculating the correction yawing moment according to the invention.

The inventive method is essentially structured in three stages and comprises the following three method steps S1, S2 and S3:
In a first step S1, an actual yaw moment to be expected in the motor vehicle is calculated as a function of an actual speed and an actual steering angle of the motor vehicle. The calculation is done model-based, for example, using the familiar to the skilled person single track model, which describes the lateral dynamics of the motor vehicle. As free input variables of the actual steering angle of the motor vehicle, on which the correction yawing moment calculated by means of the method according to the invention is to be impressed, as well as its actual speed used. Both input variables can be readily determined based on sensors fitted as standard in modern motor vehicles for determining the steering angle or speed.

In the description and the appended claims, the actual yaw moment is understood to mean a torque about the yaw axis which, in addition to the torque required for the ideal drive curve, bears against the vehicle and thus causes the spongy driving behavior at high speeds.

In the second step S2, the calculation of the yawing moment is repeated analogously to step S1, but in contrast to step S1 for a predetermined reference speed. On the other hand, the actual steering angle used as an input in step S1 is also adopted in step S2. The resulting yaw moment is referred to below as the reference yaw moment.

In the description and the appended claims, the reference yawing moment is understood to mean a torque about the yaw axis which, in addition to the torque required for the ideal driving curve, is applied to the vehicle at the reference speed.

In a third step S3, the desired correction yaw moment is determined by subtraction of the actual yaw moment calculated in step S1 with the reference yaw moment calculated in step S2. Typically, this correction yawing moment will only take effect if the actual speed of the vehicle used in step S1 is greater than the predetermined reference speed. The corrective yawing moment then corresponds in terms of magnitude to that yaw moment which occurs in the motor vehicle due to the actual speed, which is higher than the reference speed. By imposing the correction yawing moment on the motor vehicle, the yaw moment additionally occurring due to the speed can be compensated, so that the resulting yawing moment occurring at the actual speed as a consequence of such compensation corresponds to that at the reference speed. Since the method according to the invention allows the calculation of the correction yaw moment at any actual speeds, such a compensation is possible in principle for any actual speeds. Preferably, the correction yaw moment is only implemented if the actual speed is greater than the reference speed.

According to the invention, an adaptive model is used to calculate the actual yaw moment and the reference yaw moment, which can take into account, in particular, a change in the mass, the center of gravity, the tires, the tire air pressure and the roadway. Thus, the interventions can be made more targeted, so that the load on the brake system can be reduced.

By iterative application of the method according to the invention and an associated "artificial" generation of the thus determined correction yawing moment in the motor vehicle, the yawing behavior of the motor vehicle can be reduced to that at the predetermined reference speed substantially independently of its actual actual speed.

• – Querbeschleunigung des Kraftfahrzeugs,
• – Giergeschwindigkeit (dψ/dt) des Kraftfahrzeugs,
• – Gierbeschleunigung (d²ψ/dt²) des Kraftfahrzeugs,
• – Lenkgeschwindigkeit (dδ_v/dt) des Kraftfahrzeugs.

In a preferred embodiment, which allows the consideration of further, additional input parameters for the calculation of the correction yawing moment, the model-based calculation of the yawing moment may additionally be effected as a function of at least one of the following variables, the integration of these quantities or the derivation of these quantities:

• Lateral acceleration of the motor vehicle,
• Yaw rate (dψ / dt) of the motor vehicle,
• Yaw acceleration (d ² ψ / dt ² ) of the motor vehicle,
• - Steering speed (dδ _v / dt) of the motor vehicle.

A favorable solution provides that the yaw acceleration (d ² ψ / dt ² ) and / or the steering speed (dδ _v / dt) each have a dynamic and a temporally stationary portion that the calculation of a dynamic correction yawing moment as a function of dynamic Proportion of the yaw acceleration (d ² ψ / dt ² ) and / or the steering speed (dδ _v / dt) is performed on the basis of a first model, and that the calculation of a steady-state correction yaw moment as a function of the stationary component of the yaw acceleration (d ² ψ / dt ² ) and / or the steering speed (dδ _v / dt) is performed on the basis of a second model. Thereby, the accuracyδ of the adaptation can be improved if the model available only sufficiently accurately calculates either only the dynamic or the stationary component.

For the model-based calculation of yawing moments in the course of the method according to the invention, it is particularly expedient to use the so-called linear single-track model by means of which the yaw transmission behavior of the motor vehicle can be modeled. This allows a detailed description of both the stationary and unsteady lateral dynamics of the motor vehicle. It is also conceivable use of other models, for example models with more than two degrees of freedom or similar. In the case of the single-track model, the well-known differential equation can be used as the basic equation ψ ... + 2D _ψ ω _ψ ψ .. + ω 2 / ψψ = V _δ (δ _v + T _δ δ _v ) + V _M (M _z + T. _M M. _z ) (1) be used for the model-based calculation of the yawing moments. Dψ / dt is the yaw rate, d ² ψ / dt ² the yaw acceleration, d ³ ψ / dt ³ the yaw pressure, D _ψ the yaw damping, ω _ψ the natural frequency, δ _v the wheel-related steering angle, dδ _v / dt the wheel-related steering speed, V _{δ is} the steering gain, T _{δ is} the steering lead time, M _{z is} the correction yaw moment, dM _z / dt is the time derivative of the corrective yaw moment, V _{M is} the yaw moment gain, and T _{M is} the yaw momentum hold time.

Equation (1) can be transformed into the frequency domain by means of Laplace transformation as follows: (s ² + 2D _ψ ω _ψ s + ω 2 / ψ) Ψ (s) = (V _δ + V _δ T _δ s) Δ (s) + (V _M + V _M T _M s) M _z (s) (2) and solve in frequency space, where Ψ, Δ, and M _z denote the Laplace transforms of yaw rate, steering angle, and yaw moment, and s denotes the complex frequency jω.

As an alternative to the use of the abovementioned linear single-track model, more complex, so-called non-linear models are also available compared to the linear single-track model. In this case, it is conceivable to store the nonlinear relationship between yawing moment and steering angle as well as speed in a characteristic diagram and to use this for calculating the yawing moment. Alternatively or additionally, it is also conceivable to define or at least approximate the desired nonlinear relationship by means of a suitable analytical function. Both variants can be used both in the calculation of the actual yaw moment M _z ^actual and the reference yaw moment M _z ^Ref in the course of the method presented here. This results in particular in the advantage that the calculated corrective yawing moments in a motor vehicle can be generated by activation phases of the brake system that last only for a short time, without them excessively overheating or wearing out.

The invention further relates to a control device for a motor vehicle, which is designed to carry out the method presented above. In such a control unit may be a conventional control unit, which is installed as standard in modern vehicles and as part of a bus system such. B. the controller area network (CAN) allows the control of various vehicle components including the braking system. Such a control unit may comprise a control unit (ECU) and a memory unit cooperating therewith, in which the method according to the invention - encoded in software code - may be stored for execution by the control unit. The execution of the method is preferably carried out iteratively.

In the event that the calculation of the yawing moments, as explained above, should be done using non-linear models, the required for setting the non-linear relationships maps or analytical functions can be stored in a memory unit of the controller.

Advantageously, the control unit calculates the expected actual yaw moment of the motor vehicle as a function of an actual speed and an actual steering angle of the motor vehicle, a reference yaw moment for the actual steering angle and a predetermined reference speed, and then determines from the calculated Actual yaw moment and the calculated reference yaw moment by subtraction a correction yaw moment.

The invention also relates to a motor vehicle with the above-described control unit and with at least one vehicle component, by means of which the correction yawing moment calculated by the control unit can be generated in the motor vehicle. It makes sense to use as such vehicle component already installed in the motor vehicle as standard brake system, when the four wheels of the motor vehicle associated brake units from the control unit, eg. B. can be controlled individually via the CAN bus system of the motor vehicle. The correction yawing moment calculated by means of the method according to the invention can be generated by a one-sided actuation of one or the two of the left or right brake units with respect to the longitudinal direction of the motor vehicle.

Typically, the yaw acceleration and / or the steering speed each have a dynamic and a temporally stationary portion. It is therefore particularly expedient to carry out the calculation of the corrective yaw moment exclusively as a function of the dynamic portion of the yaw acceleration and / or the steering speed, but not of the stationary portion of the yaw acceleration and / or the steering speed. If the correction yaw moment calculated in a motor vehicle by means of the method presented here is determined by unilateral activation of the left or right brake units generated so only relatively simple braking maneuvers of short duration are required in the proposed consideration exclusively dynamic shares, whereby the wear of the brake system can be reduced to a considerable extent; In particular, an undesirable overheating of the brake units of the brake system of the motor vehicle is avoided in this way.

Other important features and advantages of the invention will become apparent from the dependent claims, from the drawings and from the associated figure description with reference to the drawings.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination given, but also in other combinations or in isolation, without departing from the scope of the present invention.

Preferred embodiments of the invention are illustrated in the drawings and will be described in more detail in the following description, wherein like reference numerals refer to the same or similar or functionally identical components.

In each case show schematically:

1 a schematic flow diagram of the method according to the invention,

2 a roughly schematically illustrated motor vehicle, in which the method of 1 when the lane change comes to execution,

3 a one-dimensional representation of the yawing moments calculated by means of the method according to the invention,

4 a diagram illustrating the dynamic yaw gain in the motor vehicle.

In 1 a flowchart of the method according to the invention is shown. The 2 shows a motor vehicle 10 with a control unit 11 , in which the inventive method can be executed, roughly schematic in a plan view, namely when initiating a lane change - in the direction of travel right - on a road 20 with two adjacent lanes 20a . 20b , The required for such a lane change steering angle change to the steerable front axle 14 of the motor vehicle 10 , triggered by a corresponding steering movement of the driver on the steering wheel of the motor vehicle 10 , generates a yaw moment in the motor vehicle 10 ,

In order to be able to reduce this yawing moment to that yawing moment occurring at the reference speed v _x ^Ref , the method according to the invention is used. On the one hand, the instantaneous steering angle δ _{v of} the motor vehicle and, on the other hand, the instantaneous driving speed v _x ^{actual of} the motor vehicle serve as external input variables 10 in the direction of travel X. Current values of both variables when driving the motor vehicle 10 can the controller 11 be made available by means of a suitable sensor: so can the current steering angle δ _{v of} the motor vehicle 10 by means of one in the vehicle 10 built in and in the 2 only roughly schematically indicated steering angle sensor 12 determine. To determine the instantaneous driving speed v _x ^Ist , one or more speed sensors installed in the motor vehicle can be used 13 be used. Both sensors 12 . 13 use for transmitting the steering angle δ _v or the vehicle speed v _x ^is to the control unit 11 for example, in the vehicle 10 implemented CAN bus.

In a first step S1 is now the control unit 11 by using the so-called linear one-track model in the motor vehicle 10 expected actual yaw moment M _z ^is dependent on the instantaneous actual speed v _x ^{actual of} the motor vehicle 10 and its current actual steering angle δ _v ^Ist calculated. The moment on the motor vehicle 10 Actual actual yawing moment M _z ^Ist can depend on a large number of factors or parameters. In particular, such a yaw moment in the motor vehicle 10 caused by - already minor - caused by the driver steering movements. Generally speaking, that is undesirable because of high steering speeds, because the driving stability of the motor vehicle 10 impairing yaw effects occur with increasing vehicle speed v _{x of} the motor vehicle 10 increase.

In a step S2 following the first step S1, a reference yaw moment M _z ^{Ref is} calculated for the same instantaneous actual steering angle δ _v ^actual , but a reference yaw moment M _z ^{Ref is} calculated for a different reference speed v _x ^Ref from the actual speed v _x ^Ist . The value of the reference yaw moment M _z ^Ref can be used as the target value for the motor vehicle 10 at the current actual speed v _x ^{is to be} understood. To achieve this, the motor vehicle must 10 "Artificially" an additional correction yaw moment M _z ^{Korr be} imprinted. Since the correction yaw moment M _z ^{Korr is} typically only implemented when the actual speed v _x ^{actual is} greater than the reference speed v _x ^Ref , it counteracts the actual yaw moment M _z ^actual . In other words, the actual yaw moment M _z ^actual determined in step S1 must be reduced by the difference D between the reference yaw moment M _z ^Ref and the actual yaw moment M _z ^Ist . This is in the diagram of 3 schematically shown, in which the vector quantities M _z ^actual , M _z ^Ref and M _z ^korr are shown one-dimensional.

In a third step S3, the difference D is calculated from actual yaw moment M _z ^actual and reference yaw moment M _v ^Ref , ie D = M _z ^actual - M _z ^Ref . This difference D is identical to that of the motor vehicle 10 correction yawing moment M _z ^{Korr to be imposed} , that is, D ≡ M _z ^corr .

To reduce the in the motor vehicle 10 Actual yawing moment M _z acting on the lane change ^is possible from the control unit 11 in a suitable vehicle component of the motor vehicle 10 be set. It makes sense, as such vehicle component in the motor vehicle 10 already used as standard built brake system. The four wheels 15l . 15r of the motor vehicle 10 associated brake units 16l . 16r let go of its control unit 11 - for example, via the CAN bus system - individually control. By one-sided driving one or the two left brake units 16l manages to the motor vehicle 10 the desired correction torque M _z ^Korr (see also 3 ).

For model-based calculation of the yawing moments, an adaptive model is preferably used. The adaptive model can change the vehicle 10 consider. In particular, the loading condition, the center of gravity, the tire condition and the road condition can be taken into account. To take account of these parameters, for example, an axle load measuring device can be provided. It is also conceivable that the model calculation between summer tires and winter tires is switchable.

The above-described implementation of the method according to the invention mentions the one-track model used for model-based yaw moment calculation and known to the person skilled in the art only in a brief form. The use described in the present example scenario only two input variables, namely actual speed v _x ^actual and instantaneous steering angle δ _v ^actual , can be determined by the skilled person by suitable measures, such as the consideration of additional input variables for improved modeling of the driving dynamics of the motor vehicle 10 significantly improve. Conceivable, other input variables are, for example, the lateral acceleration of the motor vehicle 10 , the yaw rate (dψ / dt), the steering speed (dδ _v / dt) or the yaw acceleration (d ² ψ / dt ² ).

As an alternative to using the above-mentioned linear single-track model, the integration of suitable nonlinear models is also conceivable. For example, it is conceivable to store the nonlinear relationship between yawing moment and steering angle or speed in a characteristic diagram and to use this to calculate the yawing moment. Alternatively or additionally, it is also conceivable to define or at least approximate the desired nonlinear relationship by means of a suitable analytical function. Both options can be used both in the calculation of the actual yaw moment M _z ^actual and the reference yaw moment M _z ^Ref .

The yaw behavior has a dynamic and a temporally stationary share. The calculation of the correction yaw moment can also be separated into a dynamic and a stationary part. In this case, the calculation of the dynamic correction yawing moment is carried out in dependence on a first model and the calculation of the steady-state correction yawing moment is carried out on the basis of a second model. As a result, both the stationary and the dynamic yaw behavior can be adjusted.

Particular advantages are provided by a frequency-dependent consideration or modeling in the single-track model, ie the steering movement of the motor vehicle 10 is considered as a function of time in frequency space, for example by Laplace transform. 4 exemplifies such a frequency-dependent consideration of the yaw rate per steering angle as a function of the frequency of the steering angle of the motor vehicle, in the form of an amplitude-frequency diagram (AF diagram) of the so-called dynamic yaw gain. The one with 17a designated graph shows that in a motor vehicle 10 actual occurring frequency-dependent yaw amplification at a vehicle speed of 180 km / h, with 17b also called the graph actually occurring frequency-dependent yaw gain at a vehicle speed of 120 km / h. The one with 17c designated graph finally shows the model-based determined in the motor vehicle 10 expected yaw gain corrected by the method according to the invention at 180 km / h. A comparison of the graphs 17b and 17c shows that the application of the method according to the invention an adaptation of the dynamic yawing behavior of the motor vehicle 10 at 180 km / h to that at a reduced speed of 120 km / h.

It is understood that the application of the method presented here is not limited to the driving maneuver explained in the example scenario in the form of a lane change; Rather, the inventive method for improving the yaw behavior in driving maneuvers of various kinds can be used. Furthermore, the o. G. Reference speed v (x, Ref) can be seen as an example and is chosen individually depending on the vehicle variant.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102006048835 A1 [0005]
• DE 102004035004 A1 [0005]

Claims (4)

Method for improving the yaw behavior of a motor vehicle ( 10 ), according to which model-based as a function of the speed and the steering angle of the motor vehicle ( 10 ) in the motor vehicle ( 10 is calculated expected yaw moment, comprising the following steps: S1) calculation of an expected actual yaw moment (M _z ^actual ) in dependence on an actual speed (v _x ^actual ) and an actual steering angle (δ _v ^actual ) of the motor vehicle ( 10 ), S2) Calculation of a reference yaw moment (M _z ^Ref ) for a predetermined reference speed (v _x ^Ref ) and for the actual steering angle (δ _v ^Ist ) S3) Calculation of a correction yaw moment (M _z ^Korr ) by subtraction (D = M _z ^actual - M _z ^Ref ) from the actual yaw moment (M _z ^actual ) and the reference yaw moment (M _z ^Ref ) A method according to claim 1, characterized in that the model-based calculation of the yawing moment using an adaptive linear single-track model or an adaptive non-linear model, taking into account the mass, the center of gravity, the tires and / or the tire air pressure. Method according to one of the preceding claims, characterized in that the model-based calculation of the yaw moment additionally takes place as a function of at least one of the following variables, the integration of these quantities or the derivation of these variables: - lateral acceleration of the motor vehicle ( 10 ), Yaw rate (dψ / dt) of the motor vehicle ( 10 ), Yaw acceleration (d ² ψ / dt ² ) of the motor vehicle ( 10 ), - steering speed (dδ _v / dt) of the motor vehicle ( 10 ). A method according to claim 3, characterized in that - the yaw acceleration (d ² ψ / dt ² ) and / or the steering speed (dδ _v / dt) each have a dynamic and a temporally stationary portion, - the calculation of a dynamic correction yaw moment in Dependence of the dynamic portion of the yaw acceleration (d ² ψ / dt ² ) and / or the steering speed (dδ _v / dt) is carried out on the basis of a first model, - the calculation of a steady-state correction yaw moment as a function of the stationary component of the yaw acceleration (d ² ψ / dt ² ) and / or the steering speed (dδ _v / dt) is performed on the basis of a second model.

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