DE102011010491A1 - Method for activating electronics stability control device of e.g. all-wheel driven motor car, involves determining function such that function value increases with increasing lateral force of front and rear wheels - Google Patents

Abstract

The method involves determining a value of a variable from measured values of a yaw rate sensor (18) and a steering angle sensor (20), and defining another value of the variable. An electronics stability control (ESC) device (16) is activated if driving torque of front and rear wheels (12a, 12b) of a motor vehicle (10) is greater than a function value of function. The function is determined such that the function value decreases with increasing of understeering or oversteering degree during understeering or oversteering drivability and increases with increasing of lateral force of the wheels. An independent claim is also included for a control device for activating a driving dynamics control device of a motor vehicle.

Description

The invention relates to a method for activating a vehicle dynamics control of a motor vehicle with at least two wheels. The invention also relates to a control device for activating a vehicle dynamics control as well as a motor vehicle with such a control device.

In order to avoid or defuse critical driving situations, suitable driving dynamics control systems are provided in motor vehicles. For example, a vehicle dynamics control system known as Electronic Stability Control (ESC) or Electronic Stability Program (ESP) is known. With such a control device individual wheels of the motor vehicle can be braked targeted or specific drive torque can be transferred to them. As a result, oversteer or understeer of the motor vehicle when cornering can be counteracted. Such vehicle dynamics control usually uses appropriate yaw rate and / or steering angle sensors to detect the driving condition of the motor vehicle and initiate appropriate control.

A stability control system can combat understeer essentially through two measures. On the one hand, in engine situations under load, the engine torque can be dosed reduced or the engine power throttled. On the other hand, the entire wheel torque for individual wheels of the motor vehicle can be specifically influenced. For example, the inside rear wheel and / or the inside front wheel can be braked to create a Einrehendes moment about the vehicle's vertical axis, thus counteracting the understeer. Such retardation of individual wheels may additionally reduce vehicle speed.

From the DE 196 01 795 A1 is a method for increasing the yaw moment of a vehicle is known, which has an understeering behavior when driving through a curve. In this case, at least one brake actuation takes place on the inside rear wheel, wherein, depending on the slip of this wheel, a variable brake actuation is provided on the inside front wheel only in certain situations.

From the DE 10 2005 036 708 A1 a stabilization device for a vehicle is known. There are provided means for influencing a steering angle of the vehicle and stabilizing means. Based on a Seitenkraftbeiwerts the maximum achievable lateral force of a steered wheel is determined and taken into account when setting a steering angle.

In the vehicle dynamics control systems according to the prior art, however, there is the problem of activating the control at the right time. Activating the controller on a front-wheel drive vehicle is too late, pushing the vehicle over the front wheels in an understeer situation, resulting in increased space requirements. The steering does not react very directly. The driver has to choose a larger slip angle of the steerable wheels as it corresponds to the actually to be traveled curve radius. If, on the other hand, the regulation is activated too early, the driver may feel too much patronized by the automatically intervening driver assistance, because he can be too heavily patronized. B. in the case of a sporty driving behavior is not able to exhaust the dynamic range of his motor vehicle.

The problem of activating the regulation at the right time exists in particular for all-wheel drive vehicles. In 4WD vehicles, understeer situations are not necessarily detectable by slippage. Control systems based on the recognition of slippage can therefore only insufficiently intervene in the driving behavior.

The same problem arises when oversteer by vehicles with rear-wheel drive or four-wheel drive.

It is an object of the invention to provide a method, a control device and a motor vehicle, with which it can be determined under what circumstances a driving dynamics control is to be activated.

This object is achieved by a method having the features of claim 1, a control device having the features of claim 12, and a motor vehicle having the features of claim 13.

• – Bestimmen eines Wertes einer ersten Größe aus Messwerten zumindest eines Fahrdynamiksensors. Bei der ersten Größe kann es sich insbesondere um eine dimensionslose Größe bzw. Kenngröße handeln, die beispielsweise einen Wert zwischen 0 und 1 annehmen kann;
• – Festlegen eines Wertes einer zweiten Größe. Die zweite Größe kann insbesondere dimensionsbehaftet sein und insbesondere die Dimension eines Drehmoments oder einer Kraft haben, es kann sich insbesondere um das Kardanmoment handeln; und
• – für den Fall, dass ein Antriebsmoment an einem ersten der zumindest zwei Räder größer als ein über eine Funktion (bzw. vermittels einer Funktion bzw. Abbildungsvorschrift) aus dem Wert der ersten Größe und dem Wert der zweiten Größe ermittelter Funktionswert ist, Aktivieren der Fahrdynamikregelung. Ist das Antriebsmoment an dem ersten Rad kleiner oder gleich dem ermittelten Funktionswert, erfolgt kein Aktivieren der Fahrdynamikregelung. Hierbei wird die Funktion so festgelegt, dass die Funktionswerte der Funktion mit zunehmendem Grad des Untersteuerns bzw. Übersteuerns während eines untersteuernden bzw. übersteuernden Fahrverhaltens des Kraftwagens abnehmen und die Funktionswerte der Funktion mit zunehmender Seitenführungskraft oder maximaler Seitenführungskraft des ersten Rades des Kraftwagens zunehmen. Was vorliegend zum ersten Rad ausgesagt ist, kann eine vorbestimmte Teilmenge der Räder betreffen, insbesondere alle Antriebsräder, und insbesondere bei einem Allradantrieb auch sämtliche Räder überhaupt. Sofern hier von einer auf das erste Rad bezogenen Größe die Rede ist, kann im Falle der vorbestimmten Teilmenge bzw. allen Rädern dann ein geeigneter gemittelter Wert für die Größe berechnet und verwendet werden, z. B. ein mittleres Antriebsmoment. Dies gilt auch für die den Kammschen Kreis bestimmenden Größen.

The inventive method is used to activate a vehicle dynamics control of a motor vehicle with at least two wheels. In particular, the method makes it possible to determine circumstances or a point in time at which or at which a driving dynamics control should intervene at the earliest in the driving behavior of the motor vehicle. In this case, the driving dynamics control can in particular be carried out by any driver assistance system which can counteract under- and / or oversteering of the motor vehicle by suitable measures. The method according to the invention comprises the following steps:

• Determining a value of a first variable from measured values of at least one driving dynamics sensor. The first variable may in particular be a dimensionless variable or Act variable, for example, can take a value between 0 and 1;
• - Set a value of a second size. The second variable may in particular be dimensioned and in particular have the dimension of a torque or a force, it may in particular be the cardan moment; and
• In the event that a drive torque at a first of the at least two wheels is greater than a function value determined via a function (or by means of a function or mapping rule) from the value of the first variable and the value of the second variable, activating the vehicle dynamics control , If the drive torque at the first wheel is less than or equal to the determined function value, the vehicle dynamics control is not activated. Here, the function is set so that the function values of the function decrease as the degree of understeer or oversteer increases during understeer or oversteer drivability of the motor vehicle and the functional values of the function increase with increasing cornering force or maximum cornering force of the first wheel of the motor vehicle. What is said in the present case to the first wheel, may concern a predetermined subset of the wheels, in particular all drive wheels, and in particular in all-wheel drive all wheels at all. If a size referred to the first wheel is mentioned here, in the case of the predetermined subset or all wheels then a suitable averaged value for the size can be calculated and used, eg. B. a mean drive torque. This also applies to the Kamm's circle determining sizes.

The time at which the vehicle dynamics control is activated, thus depends on the degree of the currently prevailing understeer of the motor vehicle as well as the currently applied cornering forces. By the method can thus actively counteracted by activating the vehicle dynamics control understeer, but only if the current cornering forces or the instantaneous lateral acceleration of the motor vehicle can make this seem imperative with regard to the longitudinal guiding forces. It is reliably prevented that the vehicle dynamics control too early, d. H. In uncritical driving situations, automatically intervenes and patronized a driver regarding his driving instructions. On the other hand, a higher degree of driving safety is created in critical driving situations.

• – Bestimmen eines Wertes einer Fahrdynamikgröße aus den Messwerten des zumindest einen Fahrdynamiksensors, wobei die Fahrdynamikgröße so festgelegt wird, dass die Werte der Fahrdynamikgröße mit zunehmendem Grad des Untersteuerns während eines untersteuernden Fahrverhaltens des Kraftwagens zunehmen. Bei der Fahrdynamikgröße kann es sich insbesondere um einen so genannten Untersteuerindikator handeln, wobei die Werte des Untersteuerindikators umso größer werden, je stärker das Untersteuern des Kraftwagens ausgeprägt ist. Bei der Fahrdynamikgröße kann es sich insbesondere um eine dimensionslose Größe bzw. Kenngröße handeln, deren Werte insbesondere zwischen 0 und 1 liegen können; und
• – Bestimmen des Wertes der ersten Größe aus dem Wert der Fahrdynamikgröße über eine Zuordnungsvorschrift, wobei die Zuordnungsvorschrift so festgelegt wird, dass die Werte der ersten Größe mit zunehmenden Werten der Fahrdynamikgröße abnehmen. Die erste Größe kann dann eine aus der Fahrdynamikgröße abgeleitete Hilfsgröße sein. Eine solche Hilfsgröße kann dann insbesondere eine dimensionslose Größe bzw. Kenngröße sein, deren Werte insbesondere in einem Wertebereich von 1 bis 0 liegen können.

The method step of determining the value of the first variable is preferably subdivided into the following substeps:

• Determining a value of a driving dynamics variable from the measured values of the at least one driving dynamics sensor, wherein the driving dynamics variable is determined such that the values of the driving dynamics variable increase with increasing degree of understeering during an understeering driving behavior of the motor vehicle. The driving dynamics parameter may, in particular, be a so-called understeer indicator, the values of the understeer indicator becoming greater the more pronounced the understeer of the motor vehicle is. The driving dynamics parameter may be, in particular, a dimensionless variable or parameter whose values may in particular be between 0 and 1; and
• Determining the value of the first variable from the value of the driving dynamics variable via an assignment rule, wherein the assignment rule is set so that the values of the first variable decrease with increasing values of the driving dynamics parameter. The first variable may then be an auxiliary variable derived from the vehicle dynamics quantity. Such an auxiliary variable can then be, in particular, a dimensionless variable or parameter whose values can be in particular in a value range from 1 to 0.

Preferably, then the assignment rule is set on the Kamm circle of the first wheel. By Kamm's circle the adhesion limit of a wheel is described in a known manner, which marks the transition from static to sliding friction and should not be exceeded by the vehicle. Vector addition allows the maximum allowable lateral and longitudinal forces to be determined. The first variable or auxiliary variable can scale, in particular with a given cornering force or lateral acceleration or predetermined degree of understeer, with the maximum permissible longitudinal guide force defined above the adhesive limit of the circle. The first size is then optimally adapted to the driving dynamics characteristics of the first wheel of the motor vehicle. It can be determined very precisely when the vehicle dynamics control is to be activated.

In this case, the assignment rule is preferably determined in such a way that the values of the first variable decrease monotonically, in particular strictly monotone, with increasing values of the driving dynamics parameter. The higher the degree of understeer during the understeering driving behavior, the lower the drive torque at the first wheel is then the activation of the vehicle dynamics control. This embodiment is very useful, since in this way exceeding the adhesive limit of the first wheel is reliably prevented.

The second variable is preferably set such that the values of the second variable increase monotonically, in particular strictly monotonically, with increasing lateral acceleration of the motor vehicle and / or increasing coefficient of friction between the first wheel and a roadway. In particular, the second variable can scale with the radius of the circle of the first wheel. In particular, the second variable may be set such that its values increase with the maximum permissible lateral acceleration of the first wheel at which the first wheel just does not yet exceed the adhesion limit. As the coefficient of friction increases, the criticality threshold is also reached only at relatively high drive torques, so that the activation of the vehicle dynamics control must also begin only with larger drive torques. This embodiment thus allows a tracking of the control threshold with increasing coefficients of friction and thus a very needs-based determination of the circumstances under which an activation of the vehicle dynamics control is to take place.

It is preferably provided that the value of the second variable is determined via measured values of the at least one driving dynamics sensor and / or the value of the first variable. For example, the lateral acceleration can be derived from the measured values of the vehicle dynamics sensor. The first size is a measure of the understeer behavior of the motor vehicle. Both sizes allow to draw conclusions about the maximum cornering force or the maximum permissible lateral acceleration or the coefficient of friction. If appropriate, a lower limit or an estimated value for the values of these variables can be specified. The measurement effort is reduced overall.

Preferably, the function is determined by the product of the first and second sizes. In the event that a drive torque at the first wheel is greater than the product of the value of the first size and the value of the second size, then activating the vehicle dynamics control takes place. If the drive torque at the first wheel meets a predetermined threshold criterion with respect to this product, it is e.g. B. less than or equal to this product, there is no activation of the vehicle dynamics control. This embodiment is particularly advantageous if the first variable is an auxiliary variable derived from a driving dynamics variable whose values decrease with increasing values of the driving dynamics parameter.

Preferably, the method comprises a checking step, in which it is additionally checked whether a threshold criterion is fulfilled for the value of the first variable or another variable which indicates a measure of understeer or oversteer, and in which the threshold value is met depending on the fulfillment of the threshold criterion Vehicle dynamics control is activated. It is particularly preferred if the threshold value criterion is met as soon as the value of the first variable exceeds a predefinable threshold value. According to this condition, the understeer has to be sufficiently pronounced for an activation of the vehicle dynamics control to be possible at all. In particular, a robustness measure is provided by the threshold value criterion, which indicates that the vehicle is approaching a dynamic driving limit area. The threshold criterion allows a process graded in terms of criticality to activate the vehicle dynamics control, in which more complex method steps are only initiated after certain threshold conditions are met. The additional test step can also be carried out subsequently, ie after the function value has met the threshold criterion stated in patent claim 1.

Preferably, in the context of the vehicle dynamics control system, a regulation relating to a drive motor of the motor vehicle can be activated, in which case the drive torque at the first wheel is greater, in particular. as the function value determined by the function of the value of the first quantity and the value of the second quantity, a torque provided by the drive motor is reduced. In particular, the torque can only be reduced at a certain wheel, differently reduced at several wheels, or reduced in a similar manner on all wheels of the motor vehicle. This can be done, for example, by providing less engine power.

Preferably, a target yaw rate is determined from a measured value of a steering angle sensor and an actual yaw rate for the motor vehicle is determined from a measured value of a yaw rate sensor, and the value of the first variable is determined from a deviation of the actual yaw rate from the target yaw rate. The target yaw rate is in particular a yaw rate, the z. Without under- or Übersteuerndes behavior of the motor vehicle. B. would be measured by the yaw rate sensor. In contrast, the yaw rate sensor detects the actual yaw rate, i. H. the actual yaw rate. The first variable may in particular be formed by subtracting the actual yaw rate from the target yaw rate and subsequent normalization, or otherwise using actual yaw rate and target yaw rate, taking into account further variables. Such a first quantity is also called a sub-control indicator.

Preferably, in the event that the drive torque at the first wheel is greater than the function value determined via the function of the value of the first variable and the value of the second variable, the vehicle dynamics control is activated and a regulating intervention of the vehicle dynamics control in dependence on a specific, carried out on the motor vehicle related size. For example, can a different understeer dynamics (change in the yaw rate deviation desired-actual) of the motor vehicle also influence driving dynamics differently (by further algorithms).

A control device according to the invention is used to activate a vehicle dynamics control of a motor vehicle with at least two wheels. The control device is designed to receive measured values of at least one driving dynamics sensor and to determine a value of a first variable from these measured values. It is further adapted to set a value of a second size. In addition, it is configured to determine a function value from the value of the first variable and the value of the second variable via a function, wherein the function is set so that the function values of the function with increasing degree of understeer or oversteer during an understeering or oversteer driving behavior of the motor vehicle and increase with increasing maximum cornering force of the first wheel of the motor vehicle. Finally, in the event that a drive torque at a first of the at least two wheels is greater than the determined functional value, the control device is designed to activate the vehicle dynamics control, but otherwise does not activate the vehicle dynamics control.

A motor vehicle according to the invention comprises a control device according to the invention. In particular, the motor vehicle may be a four-wheel drive motor vehicle, or it may be a front-engined motor vehicle. The overdriven functionality may also be a rear-wheel drive vehicle.

The preferred embodiments and their advantages described with reference to the method according to the invention apply correspondingly to the control device according to the invention and the motor vehicle according to the invention.

Reference to exemplary embodiments, the invention is explained in more detail below. Show it:

1 a schematic representation of an understeering behaving motor vehicle;

2 a comb circle for explaining the method according to the invention;

3 a curve for a quantity dependent on a lateral acceleration; and

4 a curve for an auxiliary variable in. Dependence of a sub-tax indicator.

In the figures, identical or functionally identical elements are provided with the same reference numerals.

1 shows a car 10 with a vehicle dynamics control device in the form of an ESC (Electronic Stability Control) 16 , The motor vehicle moves in the embodiment in the direction of travel r and this describes a left turn, since the slip angle of the front wheels 12a is different from zero with respect to the direction of travel r. The car 10 also includes rear wheels 12b that are not steered. The slip angle at the front wheels 12a is via a steering wheel 22 set by a vehicle driver. Taking into account the slip angle of the front wheels 12a should the car 10 drive on the desired lane F1 in the left turn. The car 10 understeer, so pushes over the front wheels 12a in the left turn to the outside right, so that he actually moves on an actual lane F2.

This understeering driving behavior can be controlled by the ESC 16 be at least partially compensated. The ESC 16 is this with a yaw rate sensor 18 and a steering angle sensor 20 coupled. With the yaw rate sensor 18 the actual actual yaw rate is determined while from the measured values of the steering angle sensor 20 a target yaw rate is calculated which would prevail if F1 and F2 coincided. By subtracting the actual yaw rate from the desired yaw rate and then normalizing, the ESC 16 calculate a sub-control indicator kUNT whose dimensionless values are in the interval between 0 and 1

The ESC 16 can z. B. on a motor 14 of the motor vehicle 10 act in such a way that the understeering driving behavior of the motor vehicle 10 is at least partially compensated and a turning moment is achieved to the left, so that the actual lane F2 approaches the target lane F1.

With an exemplary embodiment of the method according to the invention, it is now possible to determine the correct time at which the ESC 16 regulating the driving behavior of the motor vehicle 10 engages, that is activated. This is based on the tire model of the Kamm circle.

2 shows a Kamm circle 24 who is on the front wheels 12a or rear wheels 12b characterized by attacking forces. A longitudinal direction x is for the rear wheels 12b parallel to the direction of travel r. A transverse direction y is a direction perpendicular thereto, in which when cornering lateral acceleration on the cars 10 Act. These lateral accelerations can be achieved by an optional lateral acceleration sensor 28 measure which of the associated measurement signals is the ESC 16 provides. Depending on the parameters characterizing the respective wheel, instead of the Kamm's circle 24 be given an elliptical shape. The circle edge of the Kammschen circle 24 represents the adhesive limit of the associated wheel. Within the Kamm circle 24 the static friction of the wheel is large enough to build up sufficient cornering potential and the car 10 to keep on its circular path. In the environment of the Kamm circle 24 there is a continuous transition from static friction to sliding friction. To a stable driving behavior of the motor vehicle 10 To enable it, it is necessary to all at the wheels 12a and 12b occurring forces within the Kamm circle 24 to keep. For this purpose, the peak of vector resulting from vector addition of lateral guiding forces pointing in the transverse direction y and longitudinal vectors pointing in the longitudinal direction x must not be outside the adhesive boundary of the circle 24 to come to rest. Already on approach of the resulting force vector to the Kamm circle 24 should therefore the ESC 16 regulate intervene to avoid a critical driving situation.

A scale 26 for the understeer indicator kUNT is in the Kamm circle with some explicitly stated values 24 of the 2 located. A value of kUNT = 0 means that no understeer driving behavior of the motor vehicle 10 is present. A value of kUNT = 1 indicates a maximum degree of understeer.

• 1) kUNT > kUNT_Schwelle
• 2) MAnt > P = MAntMaxay·kkUNT

This is to be regulated (ie the ESC 16 activated), two conditions must be fulfilled:

• 1) kUNT> kUNT_Schwelle
• 2) MAnt> P = MAntMaxay · kkUNT

Condition 1 is a robustness measure indicating that the car 10 approaching the border area. kUNT_Schwelle is suitably chosen depending on the vehicle. Ie. that at values of kUNT between 0 and kUNT_Schwelle no regulation by the ESC 16 and no condition 2 test takes place. You are far from a critical driving situation.

If condition 1 is fulfilled, condition 2 is checked. This is the case in the exemplary embodiment if kUNT> kUNT_Schwelle. Condition 2 calculates a maximum drive torque that can be deducted in an understeer situation, even without starting up a motor controller or activating the ESC 16 can be coped with. Is the drive torque to a driving wheel of the motor vehicle 10 greater than a product P becomes the ESC 16 activated.

The product P is calculated by multiplying a quantity MAntMaxay by an auxiliary quantity kkUNT. It represents a drive torque threshold that just barely activates the ESC 16 can be coped with. If the drive torque MAnt exceeds this product P, the ESC 16 activated. The size MAntMaxay is in 3 as a function of a lateral acceleration ay, while the auxiliary quantity kkUNT in 4 is shown as a function of the sub-control indicator kUNT.

This characteristic curve or curve K1 represents the relationship of higher drive torques to be compensated for increasing transverse accelerations ay. Instead of the transverse acceleration ay, a coefficient of friction between the wheels could also be used 12a . 12b and the roadway on which the car 10 moved, used. The quantity MAntMaxay increases in a strictly monotonic manner with the lateral acceleration ay according to curve K1. The size MAntMaxay scales with the radius of the Kamm circle 24 , The greater the coefficients of friction, the greater the maximum permissible lateral accelerations ay at which static friction is still present, the greater the radius of the Kamm circle 24 ,

The second factor in the product P is the auxiliary quantity kkUNT. According to 4 this decreases strictly monotonically with increasing value of the understeer indicator kUNT. Is the radius of the Kamm circle 24 constant, kkUNT scales with the product P in 2 is drawn as a double arrow, if this double arrow the distance in the longitudinal direction x between the Kamm circle 24 and the scale 26 quantitatively reproduces. The larger kUNT, the more the double arrow of the product P in shortens 2 , the more the auxiliary quantity kkUNT decreases in 4 , The curve K2 represents the relationship between lower drive torque to be compensated with increasing understeer.

For a smooth, comfortable use of the ESC 16 sets the control provided by them on the current, predetermined by the driver drive torque or engine torque. With this controller concept, the occurring dynamics can be regulated very well, especially at low coefficients of friction. To the dynamics of the motor vehicle 10 even at medium coefficients of friction (wetness) to increase, the method described above is carried out first. When applying the control by the ESC 16 However, taking into account the understeer dynamics of the motor vehicle 10 , After it is decided whether to regulate, it is determined how is regulated. The greater the understeer dynamics of the motor vehicle 10 is, the earlier you start the scheme or the lower you choose the requested drive torque. The regulatory intervention can either be sudden or for reasons of comfort also ramped.

Overall it prevents when cornering the motor vehicle 10 too much drive torque MAnt is provided. In particular, in all-wheel drive vehicles so a very safe driving behavior can be generated. Is that ESC 16 Once activated, the control can be carried out by different reference variables.

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 19601795 A1 [0004]
• DE 102005036708 A1 [0005]

Claims (13)

Method for activating a vehicle dynamics control ( 16 ) of a motor vehicle ( 10 ) with at least two wheels ( 12a . 12b ), which comprises the following steps: determining a value of a first variable (kUNT, kkUNT) from measured values of at least one driving dynamics sensor ( 18 . 20 ); - setting a value of a second size (MAntMaxay); In the event that a drive torque (MAnt) at a predetermined subset or all of the at least two wheels ( 12a . 12b ) is greater than a function value determined via a function (P) from the value of the first variable (kUNT, kkUNT) and the value of the second variable (MAntMaxay), activation of the vehicle dynamics control ( 16 ), otherwise activating the vehicle dynamics control ( 16 ), wherein the function (P) is set so that the function values of the function (P) with increasing degree of understeer or oversteer during an understeer or oversteer driving behavior of the motor vehicle ( 10 ) and with increasing cornering force of the wheels of the predetermined subset or all wheels ( 12a . 12b ) of the motor vehicle ( 10 ) increase. Method according to Claim 1, characterized by the steps of: determining a value of a driving dynamics variable (kUNT) from the measured values of the at least one driving dynamics sensor ( 18 . 20 ), wherein the driving dynamics quantity (kUNT) is set such that the values of the driving dynamics variable (kUNT) with increasing degree of understeering or oversteering during an understeering driving behavior of the motor vehicle ( 10 ) increase; and - determining the value of the first quantity (kkUNT) from the value of the driving dynamics quantity (kUNT) via an assignment rule, wherein the assignment rule is set so that the values of the first quantity (kkUNT) decrease with increasing values of the driving dynamics quantity (kUNT). A method according to claim 2, characterized in that the assignment rule is set so that the values of the first variable (kkUNT) with increasing values of the driving dynamics quantity (kUNT) monotonically, in particular strictly monotone decrease (K2). Method according to one of the preceding claims, characterized in that the second variable (MAntMaxay) is determined with the aid of an assignment rule such that the values of the second variable (MAntMaxay) with increasing lateral acceleration (ay) of the motor vehicle ( 10 ) and / or increasing coefficient of friction between at least one wheel ( 12a . 12b ) of the particular subset or all wheels, and a roadway monotonically, in particular strictly monotone, increase (K1). Method according to one of claims 2 to 4, characterized in that the assignment rule for the first and / or the second size over a Kamm circle ( 24 ) is determined for the predetermined subset of wheels or for all wheels ( 12a . 12b ) is defined. Method according to one of the preceding claims, characterized in that the value of the second variable (MAntMaxay) via measured values of the at least one driving dynamics sensor ( 18 . 20 . 28 ) and / or the value of the first size (kUNT, kkUNT). Method according to one of the preceding claims, characterized in that the function (P) is determined by the product of the first (kkUNT) and second size (MAntMaxay). Method according to one of the preceding claims, characterized by a checking step in which it is checked whether a threshold criterion is fulfilled for the value of the first variable (kUNT, kkUNT), and depending on the fulfillment of the threshold criterion the driving dynamics control ( 16 ) becomes activatable. A method according to claim 8, characterized in that the threshold criterion is met when the value of the first size (kUNT) exceeds a predetermined threshold (kUNT threshold). Method according to one of the preceding claims, characterized in that within the framework of the vehicle dynamics control system ( 16 ) a regulation concerning a drive motor ( 14 ) of the motor vehicle ( 10 ) is activatable, wherein in particular in the event that the drive torque (MAnt) at the predetermined subset or all wheels ( 12a . 12b ) is greater than the function value determined via the function (P) from the value of the first variable (kUNT, kkUNT) and the value of the second variable (MAntMaxay), one from the drive motor ( 14 ) Torque is limited. Method according to one of the preceding claims, characterized in that from a measured value of a steering angle sensor ( 20 ) a desired yaw rate and from a measured value of a yaw rate sensor ( 18 ) an actual yaw rate for the motor vehicle ( 10 ) and the value of the first quantity (kUNT) is determined from a deviation of the actual yaw rate from the target yaw rate. Control device for activating a vehicle dynamics control ( 16 ) of a motor vehicle ( 10 ) with at least two wheels ( 12a . 12b ), which is formed, - measured values of at least one driving dynamics sensor ( 18 . 20 ) and to determine a value of a first quantity (kUNT, kkUNT) from these measurements; - set a value of a second size (MAntMaxay); Determine a function value from the value of the first variable (kUNT, kkUNT) and the value of the second variable (MAntMaxay) via a function (P), the function (P) being determined such that the function values of the function (P) with increasing degree of understeer or oversteer during understeer or oversteer of the motor vehicle ( 10 ) and with increasing cornering force of at least one wheel ( 12a . 12b ) of the motor vehicle ( 10 ) increase; and - which is formed in the event that a drive torque (MAnt) at a predetermined subset or all of the at least two wheels ( 12a . 12b ) is greater than the determined function value, the vehicle dynamics control ( 16 ), but otherwise the driving dynamics control ( 16 ) not to activate. Car ( 10 ) with a control device according to claim 12.

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