DE102004017845B4 - Method for determining the yaw moment - Google Patents

Abstract

Method for determining the yaw moment of a four-wheeled motor vehicle, with a vehicle reference model which determines the deviation (Δψ) of a measured yaw rate (ψ) from a reference yaw rate (ψ.ref) calculated as a function of a steering angle (δDRV) specified by the driver, comprising the steps of detecting a driving situation on a road surface with different friction coefficients (μ-split) determining the steering angle corrections (Δδkorr) required by the driving situation and correcting variables of the vehicle model in accordance with the steering angle corrections, characterized in that the correction of the sizes of the vehicle model is activated is when the driver specified steering angle (δDRV) exceeds a limit and the steering direction corresponds to a countersteering of the driver in the direction of low friction side.

Description

The invention relates to a method for determining the yawing moment according to the preamble of claim 1.

The fundamental ESP (Electronic Stability Program) strategy for stabilizing a vehicle is in the unbraked case in the targeted braking of individual wheels by active pressure build-up in the corresponding wheel brake cylinder. As a result, a stabilizing torque (yaw moment) is impressed into the vehicle structure by lateral force reduction and simultaneous longitudinal or braking force buildup. In contrast to the unbraked case must be assumed at the same time driver braking to initiate a stabilizing yaw moment of an existing Vordruck- and thus force distribution at the wheels, by the driver pre-pressure or possibly by the ABS (anti-lock braking system) controlled pressure level in the Wheel brake adjusts.

To better explain the ESP intervention in actively braked case with pressure reduction, the state is explained without pressure reduction. An overview of the essential calculation steps based on the controller output variable M _G (torque or yaw moment) up to the determination of the pressure requirement P _on is in 1 described in the following sections.

Calculation of the controller output M _G

The basic elements of the ESP control circuit are 2 refer to. The total controller output M _{G of} the PD controller (yaw rate ψ.) And P controller (float angle velocity β.) Is determined in the following manner:

sind abhängig vom Reibwert der Paarung Reifen/Fahrbahn (linearer Ansatz) und der Verstärkungsfaktor des P-Reglers

vom Grad der Stationarität der Fahrzeugbewegung.The index Fhz denotes the actual values of the yaw rate ψ., Yaw acceleration ψ .. and buoyancy angle velocity β. of the vehicle. The reference values dependent on the steering angle are denoted by the index ref, DRV. The control deviations of the yaw rate and yaw acceleration resulting from the difference of the actual and set values are Δψ. and Δψ ... The exit control thresholds can be recognized by the Index Out. The gain factors of the PD controller

are dependent on the coefficient of friction of the tire / track pairing (linear approach) and the gain of the P controller

the degree of stationarity of the vehicle movement.

Engagement unit and calculation of the pressure build-up request

The controller output variable M _G increases in proportion to the vehicle instability and thus also to the required yaw moment, which is necessary for the desired vehicle stabilization. This yaw moment is impressed into the vehicle structure by unilateral pressure build-up in the actuators (wheel brakes). In detail, the impressed braking torques on the wheels cause a braking force build-up in the vehicle longitudinal direction and a side force reduction in the transverse direction, which generate the desired yaw moment with a suitable selection of the meshing wheels. Thus, for a given tax tendency of the vehicle (understeer or oversteer) first to make this determination of the meshing wheels. Understeer the vehicle is selected for the pressure build-up the inside rear wheel and oversteer driving behavior, the outside front wheel.

The size of the necessary pressure increase Δp _{on is} determined for the front axle from the context Δp _{on, v} = | M _G |, 2) ie the controller output M _G (see equation (1)) is physically - apart from the sign - already a pressure. For the rear axle, the equation of determination is: Δp _{on, h} = K _Br | M _G |, 3)

The gradient of converting a brake cylinder pressure into a braking force is not the same for the front and rear axles. This factor is detected by the factor K _Br , which is calculated in the following way:

A_K

– Bremskolbenfläche

r_w

– wirksamer Bremsenhalbmesser

C*

– Bremsenkonstante

Here are:

A _K

- Brake piston surface

r _w

- effective brake radius

C *

- Brake constant

In Equation (4), it was assumed that both the coefficient of friction of the pair of brake pad / brake surface and the tire radii of the front and rear axles are the same. The pressure increase calculated in equation (2) or (3) in the unbraked case, ie for the admission pressure zero, is equal to the absolute pressure requirement p _{to be given} . For the braked case, however, a pre-pressure is already present in all wheel brakes, which must be taken into account for the pressure increase of the ESP. Therefore, the print request is determined in the following manner: p _on = p _ref + Δp _on (5)

The pressure p _ref is a reference pressure from which the pressure increase is made. This pressure is equal to the actual pressure of the wheel in the pressure build-up at control entry (value is stored), with a compensation of external factors during the control sequence is effective. Be detected here pressure increases on the opposite wheel of the same axis, the z. B. caused by increasing the driver pre-pressure or increasing the ABS control level (due to friction coefficient o. Ä.). The unbraked case is in Eq. (5) for p _ref = 0 included.

Limitation of the pressure demand by the slip controller

If the pressure requirement P is _increased and the consequent pressure in the wheel brake cylinder increases, then the corresponding wheel first reaches the slip range of the largest coefficient of friction in the vehicle longitudinal direction. Up to this point, braking force is built up in the longitudinal direction and further reduced cornering force on the one hand. A further pressure increase subsequently causes no significant increase in the braking force more, but the cornering force is further reduced, ie, in this area, a further increase in pressure makes sense and is therefore carried out. However, this effect is limited in the case of large hatching (greater than 80%), in which only a slight decrease in lateral force is observed. For this reason and to prevent a comfort-reducing blocking of the wheel, the pressure requirement is limited to a certain level.

This level is determined by a slip control. Taking into account the actual _slip measured on the wheel, the latter continuously calculates in the background a setpoint pressure p _slip in the wheel cylinder which would lead to a setpoint slip of 50% ( 1 ). If this pressure p _{slip is} smaller than that of Eq. (5) certain print request _to p, then p is _slip the new print request _on p. Due to the control quality of the slip controller, a slip band of approx. 30-70% preferably arises in this operating range.

The slip control described in this section is used for the unbraked and braked case.

Intervention strategy in an actively braked case on roadways with different coefficients of friction (μ-split)

When braking on inhomogeneous road surfaces (ie lanes with different coefficients of friction on the left or right side of the vehicle) asymmetric braking forces occur due to the different coefficients of friction (right - left). From these asymmetric braking forces results in a yaw moment about the vehicle vertical axis, which puts the vehicle in a yawing motion in the direction of the road side with the higher coefficient of friction (see 3 ). This yawing moment can occur independently of a yawing moment occurring during cornering due to excessive lateral acceleration. In 3 a vehicle is shown on such an inhomogeneous roadway.

Vehicles without the electronic brake system ABS become unstable in such driving situations, as when locking the wheels, the cornering force of the tires is lost and thus offset by the asymmetric braking forces yaw moment for Hochreibwertseite the vehicle in rapid rotational movements about the vehicle's vertical axis (spin).

Vehicles with the ABS Electronic Brake System will prevent skidding during braking in these critical situations. Since ABS does not block the wheels, cornering forces on the wheels are maintained and the yawing moment around the vehicle's vertical axis resulting from the asymmetrical braking forces is supported by the lateral forces. However, this does not yet compensate for the yawing moment caused by the different coefficients of friction of the road surface, but the driver must accomplish this by countersteering. In order not to overstrain the driver when countersteering, the pressure difference on the front axle (left - right) and thus the yaw moment about the vehicle vertical axis is built up only slowly (yaw moment limitation). The rear axle is braked in most vehicles in such a way that the brake pressures are limited to the lower brake pressure and thus the low coefficient of friction potential (SelectLow).

If the vehicle is additionally equipped with an ESP system for driving stability control, then this countersteering of the driver is interpreted by the ESP system as a driving intention, since the ESP system determines the reference yaw rate of the vehicle directly from the steering wheel position specified by the driver using a model, eg. B. single-track or two-track model calculated. However, since the driver only compensates for the disturbance caused by the asymmetrical braking forces with his countersteering, the vehicle does not crave the reference yaw rate (in the extreme case of straight braking, it does not crave at all).

The ESP system calculates the yaw rate deviation of the vehicle on the basis of the reference yaw rate and the actual yaw rate, and if this yaw rate deviation exceeds a certain threshold, the ESP system intervenes with wheel-specific brake interventions. Since the driver has to steer counter to inhomogeneous coefficients of friction during braking, the ESP system erroneously interprets this countersteering as a desire for greed. However, as the vehicle yaws less, a large yaw rate deviation quickly results, which erroneously results in ESP interventions when the ESP intervention thresholds are exceeded. In order to prevent this, when such a μ-split situation is detected in the ESP system, the ESP intervention thresholds are widened in order to prevent undesired ESP interventions (see FIG 4 ).

An equipped according to the preamble of claim 1 vehicle is from the DE 195 15 059 A1 known. There, an additional yawing moment is determined from the logical combination of a measured yaw rate and a yaw rate determined in a vehicle model. Depending on the applied additional yaw moment, the brake pressures are applied to the separately controlled wheels. In addition, for example vehicles equipped with a superposition steering system or a steer-by-wire steering system are known ( DE 40 38 079 A1 ), which at least partially compensate for the yaw moment occurring in an μ-split driving situation during an ABS control by setting an autonomous compensation steering angle dependent on the difference between the separately adjusted braking pressures and superimposing the steering angle predetermined by the driver. The autonomous compensation steering angle (automatic countersteering) improves the controllability of the vehicle during braking on inhomogeneous roads. This requires an active steering system, ie a steering system with which an additional steering angle can be generated on the wheels actively and independently of the driver's specification.

From the DE 40 10 332 C2 A method for steering and braking control of a vehicle is known in which the steering and (with brakes applied) the braking force are regulated when the deviation between the actual value and the desired value of the lateral acceleration or the yaw rate exceeds a predetermined threshold.

From the DE 197 51 227 A1 a method is known in which the presence of a driving state (eg. μ-split braking) is detected and depending on the deviation between a detected yaw size and a certain desired yaw size a manipulated variable for a superposition gear of the steering system is determined.

From the post-published WO 2004/005 093 A1 For example, a method of stabilizing a vehicle on inhomogeneous friction roads is known. In the case of active steering interventions, which are superimposed on the steering angle predefined by the driver, a disturbance variable component is taken into account, which is determined from the course of the track or the driving state of the vehicle.

The invention has for its object to provide a method for determining a yaw moment, which is more accurate and allows safe detection and assessment of driving dynamics situations.

The object is achieved by a method for determining a yaw moment with the features of claim 1. Advantageous developments emerge from the additional claims.

The method comprises the steps:
Recognition of a driving situation on a road with different coefficients of friction (μ-split)
Determining the required by the driving situation steering angle corrections and
Correcting magnitudes of the vehicle model in accordance with the steering angle corrections, wherein the correction of the sizes of the vehicle model is activated when the driver predetermined steering angle exceeds a limit and the steering direction corresponds to a steering in the direction of low friction side.

F ^_x,i

= Bremskraft an einem Rad i

r

= dynamischer Reifenradius

B

= Bremsenkennwert

p_i

= Radbremsdruck

J_Whl

= Trägheitsmoment des Rades

ω ._i

= Drehbeschleunigung eines Rades i

oder F ^_x,i = f{r, B, p_i} ermittelt. Das Störgiermoment wird in Abhängigkeit von den Bremskräften nach der Beziehung M ^_z = f{F ^_FL, s_FL, F ^_FR, s_FR, l_F, F ^_RL, s_RL, F ^_RR, s_RR, δ} mit

F ^_FL

= Bremskraft vorne links

s_FL

= halbe Spurweite des Vorderrades links

F ^_FR

= Bremskraft vorne rechts

s_FR

= halbe Spurweite des Vorderrades rechts

l_F

= Abstand der Vorderachse vom Schwerpunkt

F ^_RL

= Bremskraft hinten links

s_RL

= halbe Spurweite des Hinterrades links

F ^_RR

= Bremskraft hinten rechts

s_RR

= halbe Spurweite des Hinterrades rechts

δ

= Radeinschlagswinkel der gelenkten Räder

ermittelt. Aus den getrennt eingeregelten Bremsdrücken bzw. Bremskräften wird vorteilhaft ein Kompensations-Lenkwinkel ermittelt.The method uses the brake pressures in the front wheels to determine the steering angle corrections, which provide a measure of the utilized braking force to a first approximation. The difference .DELTA.p of the pressures is therefore a measure of the disturbance or Bremsgiermoment. Here, the Störgiermoment M _{z is} determined by a logical combination of Radeinschlagwinkel the steered wheels, the brake pressures and the rotational behavior of the wheels. From the applied brake pressures are the braking forces
after the relationship F ^ _{x, i} = f {r, B, p _i , J _Whl , ω. _i } With

F ^ _{x, i}

= Braking force on a wheel i

r

= dynamic tire radius

B

= Brake characteristic value

p _i

= Wheel brake pressure

J _Whl

= Moment of inertia of the wheel

ω. _i

= Spin of a wheel i

or F ^ _{x, i} = f {r, B, p _i } determined. The parasitic yaw moment becomes dependent on the braking forces according to the relationship M ^ _z = f {F ^ _FL , s _FL , F ^ _FR , s _FR , I _F , F ^ _RL , s _RL , F ^ _RR , s _RR , δ} With

F ^ _FL

= Braking force front left

s _FL

= half track of the front wheel on the left

_FR ^ _FR

= Braking force front right

s _FR

= half track of the front wheel on the right

l _F

= Distance of the front axle from the center of gravity

F ^ _RL

= Braking force rear left

s _RL

= half track of the rear wheel left

F ^ _RR

= Braking force in the back right

s _RR

= half track of the rear wheel on the right

δ

= Wheel angle of the steered wheels

determined. From the separately adjusted brake pressures or braking forces advantageously a compensation steering angle is determined.

The compensation steering angle can be superimposed on at least one further disturbance compensation component, this second disturbance compensation component being determined from the (driving state) trajectory of the vehicle.

The variables taken into account in the driving stability control-steering angle and reference yaw rate-can be determined more accurately by modifying the driver-specified steering angle as the size of the vehicle reference model, in particular single-track or two-track model, as a function of the compensation steering angle.

In the vehicle reference model, the model-based reference yaw rate is determined at least from the vehicle reference speed and the steering angle as well as constant vehicle sizes and / or the lateral acceleration and / or their derivatives or substitute signals.

To activate the correction of the variables of the vehicle model, it is provided that the correction of the variables depends on conditions which take into account at least one limit value of the steering angle predetermined by the driver and the steering direction.

In order to prevent implausible corrections, it is advantageously provided that the correction of the reference yaw rate is limited in accordance with changes in the reference yaw rate by the countersteering of the driver from the detection of a driving situation on a roadway with different coefficients of friction (μ-split).

δ_DRV

= der vom Fahrer vorgegebene Lenkwinkel

Δδ_korr

= f(M_z, p_i, F_x,i, v, ...)

als Größe zur Bestimmung der Referenzgierrate für eine ESP Regelung zugeführt wird.It is advantageous that the vehicle model has a reference steering _angle δ _ref according to the relationship δ _ref = δ _DRV - Δδ _corr , With

δ _DRV

= the steering angle given by the driver

Δδ _corr

= F (M _z, p _i, F _{x, i,} v, ...)

is supplied as a quantity for determining the reference yaw rate for an ESP control.

Δδ_korr

= MINIMUM[Δδ_DRV,Br; f(M_z, p_i, F_x,i, v, ...)]

Δδ_DRV,Br

= Veränderung des vom Fahrer aufgebrachten Lenkwinkels seit Beginn der Bremsung und/oder Erkennung der μ-Split Situation (Gegenlenkanteil des Fahrers),

begrenzt wird.It is expedient that the reference yaw rate determined in the vehicle model depends on the relationship δ _ref = δ _DRV - Δδ _corr , With

Δδ _corr

= MINIMUM [Δδ _{DRV, Br} ; f (M _z , p _i , F _{x, i} , v, ...)]

Δδ _{DRV, Br}

= Change of the steering angle applied by the driver since the beginning of the braking and / or detection of the μ-split situation (counter-steering part of the driver),

is limited.

Furthermore, it can advantageously be provided as a further exemplary embodiment that a model-based compensation reference yaw rate is determined as a function of the determined compensation steering angle.

ψ ._ref,DRV

= f(δ_ref,DRV) und

Δψ ._korr

= f(Δδ_korr)

ermittelt.It is expedient that the reference yaw rate determined as a function of the steering angle predetermined by the driver is corrected by means of the compensation reference yaw rate. The reference yaw rate ψ. _{ref, korr} for the ESP vehicle dynamics control is preferred after the relationship ψ. _{ref, corr} = ψ. _{ref, DRV} - Δψ. _corr With

ψ. _{ref, DRV}

= f (δ _{ref, DRV} ) and

Δψ. _corr

= f (Δδ _corr )

determined.

ψ ._ref,DRV

= f(δ_ref,DRV) und

Δψ ._korr

= MINIMUM[f(Δδ_DRV,Br); (Δδ_korr)] wobei

Δδ_DRV,Br

= Veränderung des vom Fahrer aufgebrachten Lenkwinkels seit Beginn der Bremsung und/oder Erkennug der μ-Split Situation (Gegenlenkanteil des Fahrers)

A limitation of the reference yaw rate im determined in the vehicle model. _{ref, korr} advantageously takes place as a function of the relationship ψ. _{ref, corr} = ψ. _{ref, DRV} - Δψ. _corr With

ψ. _{ref, DRV}

= f (δ _{ref, DRV} ) and

Δψ. _corr

MINIMUM = [f (Δδ _{DRV, Br);} (Δδ _corr )] where

Δδ _{DRV, Br}

= Change of the steering angle applied by the driver since the beginning of the braking and / or recognition of the μ-split situation (driver's countersteering portion)

Advantageous developments are specified in the subclaims.

Advantageously, a computing unit calculates a "desired correction steering angle" at the front axle for a fault torque compensation; but the driver has to countersteer himself.

With the aid of this "desired correction steering angle" determined by the arithmetic unit, either the steering wheel angle of the driver as input for the ESP reference model or directly the reference yaw rate of the ESP reference model can be corrected by the corrected driver's request (steering angle) or the corrected reference yaw rate of the vehicle ESP entry thresholds are not widened during braking on inhomogeneous coefficients of friction. The ESP threshold widening becomes superfluous when braking on inhomogeneous friction coefficients. Thus, there are no undesired ESP interventions even when the driver steers. Furthermore, an optimization of the braking distance is possible, since the corrected reference yaw rate makes it possible to optimize the yaw moment influencing factor (GMB) for the countersteering driver.

Reference to the drawing, an embodiment of the invention will be explained.

Show it:

1 a schematic of the basic elements of the print request from the controller size MG

2 the ESP control concept

3 a schematic representation of a vehicle on a roadway with pages of different coefficient of friction

4 a representation of an ESP threshold widening when detecting a μ-split situation

5 a schematic representation of the ESP reference yaw rate when detecting a μ-split situation

6 a block diagram with the representation of the computing system with disturbance determination and superimposed driving state determination,

7 a block diagram with the representation of the Störgrößenermittlung with estimation of Störgiermoments,

8th a block diagram showing the superimposed driving condition determination

In the present first exemplary embodiment, the correction of the driver's steering angle δ _{DRV is} discussed.

The brake pressures in the front wheels provide in a first approximation a measure of the utilized braking force, the difference of the pressures thus a measure of the Bremsgiermoment.

The determination of the corrective steering angle necessary for the correction of the steering angle applied by the driver is performed by the computing unit 30 ( 6 ), which composes the correction steering angle from at least one (disturbance variable component) or from two components (disturbance component component and superimposed driving state component).

The first component is determined by means of a disturbance variable determination from the disturbance yaw moment M ^ _z caused during braking by the asymmetric braking forces. This Störgiermoment is in an in 7 schematically shown determination unit 40 essentially estimated first from the brake pressure information of the individual wheels according to the following equations 6 and 7:

Estimation of brake forces from brake pressures:

Balance equation of a wheel neglecting drive torque and assuming that the wheel contact force acts on the wheel contact point J _Whl ω. _i = M _{br, i} + F _{x, i} r _Whl . Eq. 6

As a result of the braking torque M _{Br, I} = B * p _i for the estimation of the peripheral force F ^ _{x, i} of the wheel acceleration and brake pressure

For lower accuracy requirements, the dynamic component 1 / rJ _Whl ω. _i neglected and stationary results for the braking force of the context

Estimation of the disturbance yaw moment from the braking forces

F

= Vorderachse

R

= Hinterachse

L

= links

R

= rechts

der Fahrzeuggeometrie zu

The Störgiermoment results for vehicles with front wheel steering with the wheel angle δ and the sizes s (half gauge) and l (distance of the axis from the center of gravity) with the indices

F

= Front axle

R

= Rear axle

L

= left

R

= right

the vehicle geometry too

The determination unit 40 For this purpose, the wheel brake pressures p _i , the wheel speeds ω _i and the returned wheel steering angle δ _{WHL are} supplied as input variables. To determine the wheel brake pressures, an electronic brake system is required, which either estimates the braking pressures at the individual wheels based on models or observes the brake pressures at the individual wheels with the aid of pressure sensors measures or a brake-by-wire system (EHB / EMB) based on these quantities. The determination of the Störgiermoments based on equation 7 on the braking forces F ^ _{x, i} at the wheels. The braking forces may be calculated essentially from the brake pressure information, as indicated in Equation 1, or systems may be used which directly measure the braking forces (eg, sidewall torsion sensor, wheel hubs, or the like). From the estimated Störgiermoment, depending on driving state variables (eg, vehicle speed, brake pressure difference between high and low friction, average brake pressure level, etc.) adaptively required for correcting the Störgiermoments Radeinschlagwinkel δ _Z calculated ( 7 ). Disturbance determination does not determine the interference yaw moment in all cases exactly enough, because it overlaps with other disturbances and inaccuracies that are not detected by the disturbance variable determination. Inaccuracies can occur, for example, due to changes in the brake disc friction coefficient.

Therefore, the disturbance determination, as in 6 shown, a driving condition determination 50 superimposed. This in 8th described in detail and described in more detail later determines, depending on driving state variables, such as the yaw rate and optionally also from the lateral acceleration or the slip angle of the vehicle, an additional Radeinschlagwinkel δ _R. The determination device 50 operates adaptively, ie depending on, for example, the vehicle speed v and / or the lateral acceleration, the controller gains of the individual returned driving states are adjusted.

These two steering angles δ _R and δ _Z (from disturbance determination and superimposed driving state determination) are preferably in an adder 31 added and placed in the form of a correction steering angle Δδ _corr available.

• • Bremslichtschaltersignal (BLS)
• • Drucksensorsignal des Tandemhauptzylinders (THZ)
• • Drucksensorsignale der Radbremskreis
• • Raddrehzahlsensoren
• • Gierratensensor(en)
• • Querbeschleunigungssensor(en)
• • interner ESP-Status (ESP-Signale bezüglich ESP-Eingriffe)

The steering angle correction system works as follows:
The activation of the method for compensating steering angle correction is released as a function of a detected μ-split situation. The detection of a μ-split driving situation is based on an advantageous exemplary embodiment on the following sensor signals:

• • Brake light switch signal (BLS)
• • Pressure sensor signal of the tandem master cylinder (THZ)
• • Pressure sensor signals the wheel brake circuit
• • Wheel speed sensors
• Yaw rate sensor (s)
• • lateral acceleration sensor (s)
• • internal ESP status (ESP signals regarding ESP interventions)

By yaw rate and lateral acceleration, a distinction is made between straight-ahead driving and cornering (right-hand or left-hand bend). Depending on the straight-ahead or cornering, the following signals must be present in order to activate the compensation steering angle correction:
The driving situation μ-split is recognized as follows when driving straight ahead:
Minimum THZ pressure, driver braking is detected by THZ pressure and forward drive has been detected and at least one front wheel is in ABS control
or if, after exceeding a first time-dependent limit value, one front wheel is in ABS control and the other front wheel is not in ABS control
or when both front wheels are in the first ABS cycle and the pressure differential at the front axle is greater than a first pressure dependent limit
or when, after exceeding a second time-dependent limit both front wheels are in the ABS control and at least one front wheel has an ABS blocking pressure of greater than a second pressure-dependent limit and the ABS blocking pressure at a front wheel at least x times the blocking pressure of the other front wheel is

An already recognized driving situation μ-split when driving straight ahead is reset as follows:
There is no front wheel in the ABS control or there is no more minimum THZ pressure or driver braking is not detected -
or there is still the minimum THZ pressure and the driver's braking is detected and, after exceeding a time-dependent limit, the ABS lock pressure at both front wheels is less than a pressure-dependent limit or the ABS lock-up pressure at a front wheel is no longer at least x times the blocking pressure of the other front wheel.

The driving situation μ-split is detected during cornering as follows:
A minimum THZ pressure is present and driver braking is detected by THZ pressure and forward drive has been detected and at least one front wheel is in ABS control and
the outside front wheel comes in front of the inside front wheel in ABS control
or
when both front wheels are in the ABS control for more than a predetermined period of time and at least one front wheel has an ABS lock pressure of more than a limit pressure and the ABS lock pressure at the inside front wheel is at least x times the lock pressure of the outside front wheel

An already recognized driving situation μ-split during cornering is reset as follows:
There is no front wheel in the ABS control or there is no longer a minimum THZ pressure or driver braking is not detected
or a minimum THZ pressure is present and the driver's braking is detected and for longer than a predetermined period of time the ABS lock pressure at both front wheels is less than a limit brake pressure or the ABS lock pressure at the inside front wheel is no longer at least the x times the blocking pressure of the outside front wheel.

Correction steering angle determination

To activate the determination of the steering angle correction, the driving situation μ-split must first be detected and the determination device must have been activated, as described above. The correction steering angle Δδ _corr is based on two components: The first component δ _{Z is} determined by a disturbance compensation which is intended to compensate the acting disturbance yaw moment. This proportion is superimposed on the yaw behavior of the vehicle based share δ _R. The two parts described below are added together and give the total correction steering angle Δδ _corr Δδ _corr = Δδ _Z + Δδ _R.

• • Drucksensorsignalen in jedem Radbremskreis
• • Gierratensignalen
• • Sollenkwinkelsignalen „Fahrerlenkwinkelwunsch”
• • Summenlenkwinkelsignalen am Rad
• • Raddrehzahlsensorsignalen
• • Querbeschleunigungssignalen
• • BLS-Signalen
• • Drucksensorsignalen des THZ
• • ESP-Status (ESP-Eingriffe)
• • ESP-Status (Eispurmodell-Reset)

The steering angle determination is based on the following sensor signals:

• • Pressure sensor signals in each wheel brake circuit
• • yaw rate signals
• • desired steering angle signals "driver steering angle request"
• • Total steering angle signals at the wheel
• • Wheel speed sensor signals
• • lateral acceleration signals
• • BLS signals
• • Pressure sensor signals of the THZ
• • ESP status (ESP interventions)
• • ESP status (ice track model reset)

Störgrößenermittlung

weitgehend kompensiert. Das geschätzte Störgiermoment ist dabei die direkte Eingangsgröße für den Lenkwinkel δ_Z des ersten Anteils (FFW = Feed Forward Control). Es gilt die Beziehung

The first portion of the correction steering angle corresponds to a disturbance compensation. In this case, the disturbance yaw moment M _z acting as a disturbance variable, which originates from the asymmetrical braking forces, is achieved by direct feedback via the compensation gain

largely compensated. The estimated Störgiermoment is the direct input variable for the steering angle δ _{Z of} the first portion (FFW = Feed Forward Control). It applies the relationship

The Störgiermoment is estimated using the kinematic rigid body relationships of the braking forces of the individual wheels and the Radeinschlagwinkel the front wheels. The static braking forces of the individual wheels are determined from the ABS locking pressures of the individual wheels and the dimensions of the wheel brake. To calculate the dynamic braking forces, the wheel accelerations must also be taken into account.

wird über dem mittleren Bremsdruck an der Vorderachse adaptiert. Wenn beide Vorderräder in der ABS-Regelung sind, entspricht der mittlere Bremsdruck der Vorderachse dem insgesamt (linke und rechte Fahrzeugseite gemittelt) zur Verfügung stehenden Reibwertpotential. Dieses Reibwertpotential hat wiederum auf den zu ermittelnden Korrekturlenkwinkel Einfluss.The compensation gain factor

is adapted above the mean brake pressure at the front axle. If both front wheels are in ABS control, the mean brake pressure of the front axle corresponds to the total friction coefficient potential (averaged on the left and right sides of the vehicle). This coefficient of friction in turn has an influence on the correction steering angle to be determined.

The additional steering angle detecting δ _Z is at low driving speeds (10 to 2 km / h) linearly to δ = 0 _Z lowered (faded out).

Summary:

The steering ratio based on the disturbance determination is substantially dependent on the wheel turning angle of the front wheels and the ABS locking pressures which, as described later, are substantially based on the pressure sensor signals and the ABS phase information (determined from the wheel speed sensor signals).

Second share

The based on the yaw behavior of the vehicle second portion δ _R of the correction steering angle determination is composed of a P component δ _{R, P} (controller variable yaw rate deviation), and a D component δ _{R, D} (controlled variable yaw acceleration deviation). The P and D fractions described below add up to the total second fraction δ _R as follows δ _R = δ _{R, P} + δ _{R, D.}

P component (yaw rate deviation)

The size of the P component is the yaw rate deviation Δψ. The relationship applies to the correction steering angle component resulting from the P component δ _{R, P} = K _{FB, P} (v) · Δψ ..

The yaw rate deviation Δψ. is the difference between the measured yaw rate of the vehicle ψ. _is and the reference yaw rate of the vehicle aus determined from the direction of the driver's direction (given by the driver steering angle including variable steering ratio). _ref (single-track model) defines and thus results in Δψ. = ψ. _is - ψ. _ref .

The actual yaw rate of the vehicle ψ. _is measured directly with a yaw rate sensor. The yaw rate sensor is arranged together with a lateral acceleration sensor in a sensor cluster in which both the yaw rate and the lateral acceleration can be measured.

The reference yaw rate of the vehicle ψ. _ref is determined by means of a single-track model of the vehicle. The most important input variables for the single-track model are the driver's direction request and the vehicle speed. The current coefficient of friction of the roadway is determined by means of the measured lateral acceleration and the resulting coefficient of friction potential is taken into account in the calculation of the reference yaw rate.

The gain factor K _{FB, P} (v) for the controller feedback of the yaw rate deviation Δψ. is adapted over the current vehicle speed v. Since the vehicle speed significantly influences the driving behavior of the vehicle, this is taken into account in the gain.

D component (yaw acceleration deviation)

The quantity for the D component is the yaw acceleration deviation Δψ. The relationship applies to the steering angle component resulting from the D component δ _{R, D} = K _{FB, D} (v) · Δψ ...

The yaw acceleration deviation Δψ .. is determined by differentiation of the yaw rate deviation Δψ. determined

The yaw acceleration deviation is thus based on the same signal sources as the yaw rate deviation: Measured actual yaw rate of the vehicle ψ. and ψ _is the reference yaw rate of the vehicle. _ref , which in turn depends directly on the driver's direction request and the vehicle speed. (Consideration of the current coefficient of friction of the roadway by means of measured lateral acceleration).

The gain factor K _{FB, D} (v) for the controller feedback of the yaw acceleration deviation Δψ .. is adapted above the current vehicle speed. Since the vehicle speed substantially influences the driving behavior of the vehicle, this is taken into account in the controller gain and thus also in the closed loop of the vehicle via the controller.

Summary second share

The proportion δ _R is essentially based on the signal of the yaw rate sensor,, the driver's steering angle (driver predetermined steering angle) δ _DRV including steering angle correction Δδ _corr ("corrected driver's request") and the vehicle speed v, which in turn is based on the signals of the wheel speed sensors.

Activation of the correction

The correction is activated only when the driver applies a minimum steering angle and steers in the right direction (countersteering in the direction of the low friction side). The correction of the reference yaw rate can be limited in such a way that it is at most as large as the change in the Referenzgierrate by the countersteering of the driver since the beginning of the braking and / or detected μ-split situation.

Correction of the driver's steering wheel angle:

Δδ_korr

= f(M_z, p_i, F_x,i, v, ...)

If the vehicle has no active steering system for automatic countersteering, the steering angle δ _DRV applied by the driver to compensate for the disturbance yaw moment is corrected by the "desired correction steering angle" Δδ _corr calculated by the computing unit. The steering angle δ _ref resulting from this correction is interpreted as a "corrected driver request" and used to calculate the reference yaw rate for the ESP system. δ _ref = δ _DRV - Δδ _corr Equation 1 With

Δδ _corr

= F (M _z, p _i, F _{x, i,} v, ...)

Δδ_korr

= MINIMUM[Δδ_DRV,Br; f(M_z, p_i, F_x,i, v,.)].

During braking to inhomogeneous coefficients of friction, the driver must counter-steer in order to compensate for the disturbance (disturbing yaw moment). At the same time, however, the driver can also superimpose the desire of a change of direction on the disturbance torque compensation steering angle if, for example, he wishes to leave the current lane or change lane. In this situation, the question of how to interpret the driver's steering angle arises when calculating the ESP reference yaw rate. Depending on the interpretation of the driver's steering angle, it is possible to limit the previously described correction of the driver's steering angle in such a way that the reference yaw rate of the vehicle is corrected by the correction at most by the change in the reference yaw rate that has occurred since the beginning of the braking. Equation 1 then changes to δ _ref = δ _DRV - Δδ _corr Equation 1a With

Δδ _corr

= MINIMUM [Δδ _{DRV, Br} ; f (M _z , p _i , F _{x, i} , v ,.)].

Here, Δδ _{DRV, Br is} the change in the driver's steering angle since the beginning of the braking and / or detection of the μ-split situation.

Correction of the reference yaw rate:

ψ ._ref,DRV

= f(δ_ref,DRV) und

Δψ ._korr

= f(Δδ_korr).

If the vehicle does not have an active steering system for automatic countersteering, the steering angle δ _DRV specified by the driver, as is usual today, is used to determine the reference yaw rate of the vehicle ψ. _{ref, DRV} used. From the determined by the computing unit "desired correction steering angle" Δδ _corr is a correction reference yaw rate Δψ. _corr , analogous to the calculation of the reference yaw rate from the steering wheel position. The reference yaw rate for the ESP system ψ. _ref, korr then results from the driver reference yaw rate ψ. _{ref, DRV} corrected by the correction reference yaw rate Δψ. _corr . ψ. _{ref, corr} = ψ. _{ref, DRV} - Δψ. _corr Equation 2 With

ψ. _{ref, DRV}

= f (δ _{ref, DRV} ) and

Δψ. _corr

= f (Δδ _corr ).

ψ ._ref,DRV

= f(δ_ref,DRV) und

Δψ ._korr

= MINIMUM[f(Δδ_DRV,Br); f(Δδ_korr)].

Depending on the interpretation of the driver's steering behavior (only compensation of the interference or superimposition of interference compensation and Richtungswunschungsänderung) a limitation of the correction intervention is possible and indeed in such a way that the correction is at most as large as the result of the driver's action since the beginning of braking change in the reference yaw rate. Equation 2 then changes to ψ. _{ref, corr} = ψ. _{ref, DRV} - Δψ. _corr Equation 2a With

ψ. _{ref, DRV}

= f (δ _{ref, DRV} ) and

Δψ. _corr

= MINIMUM [f (Δδ _{DRV, Br} ); f (Δδ _corr)].

Here, Δδ _{DRV, Br is} the change in the driver's steering angle since the beginning of the braking and / or detection of the μ-split situation.

Claims (15)

A method of determining the yaw moment of a four-wheeled motor vehicle, with a vehicle reference model, which is the deviation (Δψ.) Of a measured yaw rate (ψ _is.) Calculated from a function of a predefined by the driver steering angle (δ _DRV) reference yaw rate (ψ. _Ref) determined comprising the steps of detecting a driving situation on a road surface with different friction coefficients (μ-split) determining the steering angle corrections (Δδ _corr ) required by the driving situation and correcting variables of the vehicle model in accordance with the steering angle corrections, characterized in that the correction of the magnitudes of the Vehicle model is activated when the driver specified steering angle (δ _DRV ) exceeds a limit and the steering direction corresponds to a countersteering of the driver in the direction of low friction side. A method according to claim 1, characterized in that the steering angle corrections (Δδ _corr) as a function of the space formed from the separately the adjusted brake pressures or brake forces the first disturbance compensation proportion (δ _Z) are determined. A method according to claim 2, characterized in that the correction steering angle (Δδ _corr ) is additionally formed from at least one second disturbance compensation component (δ _R ), said second disturbance compensation component determined from the driving condition and / or trajectory of the vehicle and including the braking force differences on the braked wheels formed first disturbance compensation component (δ _Z ) is superimposed. Method according to one of claims 1 to 3, characterized in that the vehicle reference model is a single-track or two-track model. Method according to one of claims 1 to 4, characterized in that the predefined by the driver steering angle (δ _DRV) is modified as the input size of the vehicle model as a function of the correction steering angle (Δδ _korr). Method according to one of claims 1 to 5, characterized in that the reference yaw rate calculated in the vehicle model (ψ _ref.) Is modified as a function of the correction steering angle (Δδ _korr). Method according to one of claims 1 to 6, characterized in that the model-based reference yaw rate (ψ _ref ) at least from the vehicle reference speed (v) and the steering angle including correction component (δ _ref ) and constant vehicle sizes and / or the lateral acceleration (a _y ) and / or whose derivatives or substitute signals are determined. Method according to one of claims 1 to 7, characterized in that the correction of the reference yaw rate (ψ _ref ) in accordance with change of the reference yaw rate by the countersteering of the driver from the detection of a driving situation on a roadway with different friction coefficients (μ-split) is limited. Method according to one of claims 1 to 8, characterized in that the vehicle model, a reference steering _angle δ _ref according to the relationship δ _ref = δ _DRV - Δδ _corr , with δ _DRV = the driver predetermined steering angle Δδ _corr = f (M _Z , p _i , F _{x, i} , v, ...) is supplied as a variable for determining the reference yaw rate (ψ _ref ). A method according to claim 9, characterized in that the reference yaw rate (ψ _ref ) for a vehicle brake control, in particular an ABS or ESP control, is provided. Method according to claim 9 or 10, characterized in that the reference yaw rate (ψ _ref ) determined in the vehicle model depends on the relationship δ _ref = δ _DRV - Δδ _corr , with Δδ _corr = MINIMUM [Δδ _{DRV, Br} ; f (M _z , p _i , F _{x, i} , v,...)] Δδ _{DRV, Br} = variation of the driver's predetermined steering angle since the beginning of the braking and / or detection of the μ-split situation (counter-steering component of the driver) limited becomes. A method according to any one of claims 1 to 11, characterized in that in response to the determined correction steering angle (Δδ _korr) a model-based compensation reference yaw rate (Δψ. _Corr) is determined. A method according to claim 12, characterized in that the reference yaw rate determined in response to the input by the driver steering angle (ψ _{ref., DRV)} by means of the compensation reference yaw rate (Δψ. _Korr) is corrected. A method according to claim 12 or 13, characterized in that the reference yaw rate (ψ _{ref, corr} ) for the ESP vehicle dynamics control according to the relationship ψ. _{ref, corr} = ψ. _{ref, DRV} - Δψ. _corr with ψ. _{ref, DRV} = f (δ _{ref, DRV} ) and Δψ. _corr = f (Δδ _corr ) is determined. Method according to one of claims 12 to 14, characterized in that the determined in the vehicle model reference yaw rate ψ. _{ref, korr} depending on the relationship ψ. _{ref, corr} = ψ. _{ref, DRV} - Δψ. _corr with ψ. _{ref, DRV} = f (Δδ _{ref, DRV} ) and ψ. _corr = MINIMUM [f (Δδ _{DRV, Br} ); (Δδ _corr)] where Δδ _{DRV, Br} = change in the steering angle predetermined by the driver since the start of braking and / or detection of the μ-split situation (the driver's counter-steering portion) is restricted.

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