阅读说明：本技术 用于确定机动车辆转弯期间的浮动角的方法、用于执行该方法的驾驶员辅助系统及机动车辆 (Method for determining a float angle during a turn of a motor vehicle, driver assistance system for carrying out the method, and motor vehicle ) 是由 托比亚斯·蒙科 蒂莫·帕斯卡尔·贝伦斯 伯纳德·奥德迈耶 于 2020-05-14 设计创作，主要内容包括：本发明涉及用于确定在机动车辆的转弯期间的浮动角(beta)的方法,其中,检测以下输入变量并经由数学车辆模型(15)利用假设的线性单轨模型进行彼此关联：-预给定或测得的前车轴(2)与后车轴(3)之间的质心(S)的位置,-机动车辆(1)的当前的车速(v),-机动车辆的当前的转弯运动变量(psi点、a),-前车轴上的当前的转向角(delta)。为了简化在转弯期间确定浮动角,浮动角在以下假设的情况下确定,即,浮动角(beta)和阿克曼浮动角(beta0)之间的差与阿克曼角(deltaA)和转向角(delta)之间的差成比例,在此,从测得的转向角(delta)和阿克曼角(deltaA)之间的关系经由在同一弯道无打滑行驶时理论上存在的阿克曼浮动角(beta0)的比例关系推断出实际的浮动角(beta)。(The invention relates to a method for determining a float angle (beta) during a turn of a motor vehicle, wherein the following input variables are detected and correlated with each other via a mathematical vehicle model (15) using an assumed linear monorail model: -the position of the centre of mass (S) between the front axle (2) and the rear axle (3) being predetermined or measured, -the current vehicle speed (v) of the motor vehicle (1), -the current turning movement variable (psi point, a) of the motor vehicle, -the current steering angle (delta) on the front axle. In order to simplify the determination of the float angle during cornering, the float angle is determined under the assumption that the difference between the float angle (beta) and the ackermann float angle (beta0) is proportional to the difference between the ackermann angle (deltaA) and the steering angle (delta), where the actual float angle (beta) is deduced from the measured relationship between the steering angle (delta) and the ackermann angle (deltaA) via the proportional relationship of the ackermann float angle (beta0) which theoretically exists when driving on the same curve without slip.)

1. Method for determining the float angle (beta) during a turn of a motor vehicle, wherein the following input variables are detected and correlated with each other via a mathematical vehicle model (15) with the assumption of a linear monorail model:

-a position of a centre of mass (S) of the motor vehicle (1) between a front axle (2) and a rear axle (3) of the motor vehicle (1) is predetermined or measured,

-a current vehicle speed (v) of the motor vehicle (1),

-a current turning motion variable (psi point, a) of the motor vehicle,

-a current steering angle (delta) on the front axle,

characterized in that, in the case of a steady turn of the motor vehicle (1), the float angle (beta) is determined on the basis of the assumption that the difference between the float angle (beta) and the ackermann float angle beta0 is proportional to the difference between the ackermann angle (deltaA) and the steering angle (delta), wherein the actual float angle (beta) is deduced from the relationship between the measured steering angle (delta) and the ackermann angle (deltaA) via a proportional relationship from the ackermann float angle (beta0) which theoretically exists when driving on the same curve without skidding.

2. The method of claim 1, wherein the first and second light sources are selected from the group consisting of,

characterized in that the float angle (beta) is determined as the difference (18) of a first quotient (16) of the centroid (S) from twice the rear axle distance (Lh) to the rear axle with respect to a curve radius (a), which is taken into account as the ratio of the vehicle speed (v) to the turning motion variable (psi point, a), and a second quotient (17) of the product of the steering angle (delta) and the rear axle distance (Lh) to the axle distance (L) between the front axle (2) and the rear axle (3).

3. The method according to claim 1 or 2,

it is characterized by knowing or measuring the yaw rate (psi point) as a turning motion variable.

4. The method of claim 3, wherein the first and second light sources are selected from the group consisting of,

characterized in that the first quotient (16) is determined from the product of twice the distance to the rear axle (Lh) and the yaw rate (psi point) with respect to the vehicle speed (v).

5. The method according to claim 1 or 2,

characterized in that the lateral acceleration (a) is known or measured as a turning motion variable.

6. The method according to any one of the preceding claims,

characterized in that the float angle (beta) is determined without a stable turn by integrating (14) the difference between the measured yaw rate (psi point) and the value of the yaw rate derived from the lateral acceleration (a).

7. Driver assistance system for a motor vehicle, configured to carry out a method according to any one of the preceding claims for determining a float angle (beta), wherein the driver assistance system is pre-given a hypothetical mathematical model with a linear single-track model for correlating the following input variables:

-a predetermined or measured position of a centre of mass (S) of the motor vehicle between a front axle and a rear axle of the motor vehicle,

-a current vehicle speed (v) of the motor vehicle (1),

-the current turning movement variable (psi point, a) of the motor vehicle (1),

-a current steering angle (delta) on the front axle,

characterized in that the mathematical vehicle model for determining the float angle (beta) during a steady turn of the motor vehicle comprises the assumption that the difference between the float angle (beta) and the ackermann float angle (beta0) is proportional to the difference between the ackermann angle (deltaA) and the steering angle (delta), wherein the driver assistance system is configured for deducing the actual float angle (beta) from the theoretically existing ackermann float angle (beta0) during a non-slip driving of the same curve via a proportional relationship from the measured relationship between the steering angle (delta) and the ackermann angle (deltaA).

8. Driver assistance system as claimed in claim 7,

characterized in that the driver assistance system is configured for determining an active steering and/or braking intervention taking into account the float angle (beta).

9. Driver assistance system according to claim 7 or 8,

characterized in that the driver assistance system is configured for determining a trajectory taking into account the float angle (beta).

10. Driver assistance system according to claim 7, 8 or 9,

characterized in that the driver assistance system is configured for detecting an oversteer or understeer tendency taking into account the float angle (beta).

11. Motor vehicle with a driver assistance system according to one of claims 7 to 10.

Technical Field

The invention relates to a method for determining a float angle during a turn of a motor vehicle according to the preamble of claim 1. The invention also relates to a driver assistance system for carrying out the method according to claim 7 and to a motor vehicle having such a driver assistance system according to claim 11.

Background

When the motor vehicle is turning, the center of mass of the motor vehicle does not move along the longitudinal axis of the vehicle. The angle between the direction of motion of the vehicle at the center of mass and the longitudinal axis of the vehicle when turning is called the float angle (Schwimmwinkel). The float angle consists of a geometric component related only to the location of the center of mass in the vehicle and the curve radius, as well as the bevel angle of the rear axle.

In many driving situations, the float angle can be used as a measure of the driving stability of the motor vehicle and can be made available to the driver assistance system, for example for driving dynamics control. In particular for heavy-duty vehicles, a large number of driver assistance functions are provided, the efficiency of which can be increased by knowing the current float angle. However, the float angle can only be measured very expensively and is usually determined by evaluation. Generally, input variables that are more easily measured or known here are detected and correlated via a mathematical vehicle model.

DE 102006009682 a1 discloses a method for determining the driving state of a two-track vehicle by estimating the float angle on the basis of values currently measured on the vehicle via a mathematical model and by means of observer estimation based on this model. In the known method, at least the tire or wheel forces in the transverse direction of the vehicle and at least one steering angle for both wheels of the front axle are used as values measured on the vehicle. Furthermore, information about the position of the center of mass of the vehicle between the front and rear axles is also taken into account, and furthermore, the use of the measured yaw rate or yaw acceleration and the longitudinal speed of the vehicle is taken into account for observer evaluation comparisons.

However, the known methods require knowledge of the tire lateral force, which cannot be measured during vehicle operation, or can only be measured very cost-effectively.

DE 102010050278 a1 discloses a method for estimating the float angle, in which information about input variables is linked via a hypothetical linear single-rail model, the state variables of which are ultimately the float angle. The steering angle and the speed of the vehicle are measured as input variables. At least one further variable, namely the yaw acceleration and/or the lateral acceleration, is calculated from the mathematical model on the basis of these measured values. In this case, when using the monorail model, the variables determined by the position of the center of mass of the motor vehicle between the front axle and the rear axle are also taken into account. In order to estimate the float angle based on the single-track model, the known method requires a new value of the unmeasured parameter, i.e. the cornering stiffness at the at least one wheel. Known methods achieve determination of the cornering stiffness via observer estimation in the case of using a kalman filter. Finally, the float angle is determined by means of a linear monorail model, to be precise by means of the respective current values for the cornering stiffness.

Disclosure of Invention

The object of the invention is therefore to simplify the determination of the float angle during cornering of a motor vehicle, in particular a load-carrying vehicle.

According to the invention, this object is achieved by a method for determining a float angle during a turn of a motor vehicle having the features of claim 1. The object is also achieved by a driver assistance system for carrying out the method having the features of claim 7 and a motor vehicle having such a driver assistance system according to claim 11.

According to the invention, the float angle in the case of a stationary turning of the motor vehicle is determined under the assumption that the difference between the float angle and the float angle under ackerman conditions, the so-called ackerman float angle, is proportional to the difference between the ackerman angle and the steering angle. A curve in which the known driving dynamics variable lies within a predetermined stability criterion, beyond which an intervention in the driving stability can be indicated, is understood as a stable curve. A stable turn may be, for example, a steady circular or constant circular driving, wherein a change in the value of the steering angle and/or the longitudinal speed and/or the lateral acceleration in consideration of a predetermined stability criterion in consideration of the radius of the curve satisfies a dynamically stable driving condition, and may be regarded as a quasi-steady state. The assumption according to the invention corresponds to the following equation:

(beta-beta0)～(deltaA-delta) (1)

wherein, beta floating angle

beta0 Ackerman floating angle

delta steering angle

Angle of deltaA Ackerman

The ackerman angle is the angle enclosed by the polar lines from the instantaneous extreme of the turn to the front axle and the rear axle. The ackerman floating angle is understood to be the floating angle which theoretically occurs when driving without skidding on the same curve. The actual float angle is deduced from the proportional relationship of the measured steering angle to the ackerman angle and from the ackerman float angle. The following relationships, in view of the linear proportionality, are obtained, namely the relationship of the difference between the float angle and the ackermann float angle to the ackermann float angle and the difference between the ackerman angle and the steering angle to the ackerman angle, from which the sought information about the float angle is derived:

(beta-beta0)/beta0＝(deltaA-delta)/deltaA

＝>beta＝beta0+(deltaA-delta)*beta0/deltaA (2)

according to the invention, the mathematical model on which the driver assistance system determines the float angle comprises the above-mentioned assumption according to equation 2.

The present inventors have recognized that both the ackerman angle and the ackerman float angle are theoretically slip-free driving conditions and can be determined using knowledge of the wheelbase and the position of the center of mass solely by the measured steering angle and the current turning motion variables of the motor vehicle.

The invention therefore provides a way of determining the float angle during a stable turn of the motor vehicle, which float angle is determined sufficiently accurately based only on the currently measured input variables, that is to say the vehicle speed, the steering angle of the motor vehicle and the turning movement variables of the motor vehicle.

The actual steering angle is known, for example, by a steering angle sensor on the steering column. It is preferably considered to use, as the turning motion variable, a variable which is already provided to the driver assistance system for other functions. Here, the lateral acceleration can be determined as a suitable turning motion variable, for example, by means of an ESC sensor. Information about the speed of the motor vehicle is provided via the measurement values of rotational speed sensors (e.g. pole wheel sensors) on the wheels.

In particular, in the method according to the invention, no knowledge of the cornering stiffness is required. The assumption in practice is based on the notional driving situation considered not being completely slip-free, but rather should only be very close to ackermann conditions. Therefore, it is assumed for determining the float angle according to the present invention that the equation of the linear monorail model is valid, thereby enabling the ratio of the cornering stiffnesses of the front and rear axles to have an influence on the steering angle and the float angle even in this theoretical driving state. However, since the cornering stiffness of these front and rear axles is very close to the steering and floating angles in the case of completely non-skid driving, the method according to the invention deliberately ignores this deviation.

In particular, the influence of cornering stiffness need not be taken into particular account in the case of determining the float angle during a stable turn according to the invention. By knowing the respective wheelbase and the position of the center of mass in the longitudinal direction of the vehicle, it is thus possible to calculate the steering angle and the float angle from kinematic relationships under ackermann conditions, which are theoretically required for negotiating curves while driving infinitely slowly (and therefore without slip). The present inventors have recognized that the ratio of cornering powers is constant over the range considered, and therefore the numerator and denominator in the comparative example relationship have the same effect, so that it is not necessary to know the exact cornering power ratio. In other words, the steering angle and the float angle under ackermann conditions are to some extent the origin of the observed turn, the motor vehicle getting farther away from this origin as the speed increases. By assuming the linearity of the tire characteristics in the active region of the linear monorail model, the actual float angle can be inferred from the actual steering angle, always starting from this origin in this range. In an electronic embodiment of the invention, the position of the center of mass between the axles is determined via electronic evaluation, for example, of the measurement values from the on-board sensors. The information about the wheelbase of the motor vehicle is fixed in the design structure and can be used for the centroid determination.

The sought-after floating angle can be determined by means of an easily manageable relationship of the difference between a first quotient of the product of the steering angle and the distance to the rear axle relative to the axle distance between the front axle and the rear axle and a first quotient of the center of mass from twice the distance to the rear axle relative to the radius of the curve.

Since the curve radius is determined in a linear monorail model as the ratio of the vehicle speed to the turning motion variable, the following equation can be given in an advantageous embodiment of the invention, in which the yaw rate is known or measured as the turning motion variable:

beta 2 Lh psi point/v-delta Lh/L.

Wherein, the distance from Lh to the rear axle

L wheel base

psi point deflection speed

v vehicle speed

If, as an alternative to yaw rate, the lateral acceleration a is known or measured as a turning motion variable, the following equation is derived to determine the sought float angle:

beta＝2*Lh*a/(v**2)-delta*Lh/L

wherein, a lateral acceleration

In an advantageous embodiment of the invention, the driver assistance system is configured to determine an active steering intervention taking into account the float angle. In this case, the method according to the invention for determining the float angle during a steady-state turn makes it possible to provide information about the driving stability and to calculate corresponding interventions very quickly and precisely.

In a further preferred embodiment, the driver assistance system is configured for determining the trajectory taking into account the float angle.

The constantly updatable float angle information allows accurate conclusions to be drawn about the tendency of the vehicle to oversteer or understeer. In this context, the driver assistance system according to the invention is configured for detecting an oversteer or understeer tendency taking into account the float angle.

When no stable turn is given, the float angle is determined according to methods known per se with an observer system or integration. The float angle is then preferably determined by integrating the difference between the measured yaw rate and a yaw rate value derived from the lateral acceleration.

Drawings

Embodiments of the present invention are explained in more detail below with reference to the drawings. Wherein:

fig. 1 schematically shows a motor vehicle with an embodiment of the driver assistance system according to the invention;

FIG. 2 shows a flow chart of an embodiment of a method for determining a float angle during a turn of a motor vehicle;

FIG. 3 shows a geometric relationship diagram on a motor vehicle according to the monorail model;

FIG. 4 shows a geometric relationship under Ackerman conditions according to a single-rail model;

FIG. 5 shows a graphical representation of steering angle versus float angle during steady state cornering.

Detailed Description

Fig. 1 shows a schematic view of a motor vehicle 1 having a front axle 2 and a rear axle 3, on each of which a wheel 4 is arranged. The wheels 4 of the front axle 2 can be steered via a steering wheel 5. Each wheel 4 is equipped with a wheel brake 6, which can be actuated individually by a driver assistance system 7. The measured values relating to the dynamic vehicle parameters are continuously supplied to the driver assistance system 7. The vehicle speed v is taken into account by the driver assistance system 7 and is determined from the measured values of the rotational speed sensors 8 of the wheels 4. In the exemplary embodiment shown, a rotational speed sensor 8 is arranged on each wheel 4, which rotational speed sensor interacts, for example, with a pole wheel and generates an electrical signal with information about the rotational speed.

The driver assistance system 7 determines a float angle beta of the motor vehicle 1 during a turn, which float angle is taken into account as a measure for determining driving stability. The basis of the driver assistance system for determining suitable interventions for the driving stability of the motor vehicle 1 in accordance with its active and/or passive work tasks is the current float angle beta. For this purpose, the driver assistance system is configured to determine an active steering and/or braking intervention taking into account the float angle beta. Advantageously, the driver assistance system 7 is configured for detecting an oversteer or understeer tendency taking into account the float angle beta. In a further possible work task, the driver assistance system 7 is configured for determining a trajectory taking into account the float angle beta, for example trajectory control.

In order to determine 9 the current float angle beta, a current steering angle delta, which is determined via the deflected position of the steering wheel 5 of the front axle 2, is specified as an input variable to the driver assistance system 7. In the exemplary embodiment shown, the steering angle delta is detected via a steering wheel sensor 10 and is used by the driver assistance system 7. The driver assistance system 7 detects as a further input variable a turning motion variable of the motor vehicle 1 with respect to its center of mass S. The turning motion variable may be the yaw rate psi point or the lateral acceleration a of the motor vehicle 1. The driver assistance system 7 is assigned a lateral acceleration sensor 11, the measurement signals of which provide information about the turning motion variables of the motor vehicle 1, in particular the yaw rate psi point and/or the current lateral acceleration a.

The driver assistance system 7 also takes into account the position of the center of mass S between the axles 2, 3 as an input variable for determining the float angle beta. The position of the center of mass S, in particular in relation to the load of the motor vehicle, is measured by the detection means 12 as required. For this purpose, for example, the measurement results using an on-axis sensor can be taken into account, and the centroid position can be determined electronically using suitable algorithms.

The determination 9 of the float angle beta is schematically shown in fig. 2. The float angle beta is determined during a stationary turning of the motor vehicle in the manner explained below under the simplifying assumptions according to the invention. In a first step, it is checked and clarified in a stability query 13 whether a stable turn is present. To this end, the input variables are monitored over time. If either the steering angle delta, the vehicle speed v or the detected turning motion variable (yaw rate psi point or lateral acceleration a) changes and leaves the range of the predefined stability criterion, it is assumed that no stable turn is given. In this case, the float angle beta is determined by integrating 14 the difference between the measured yaw rate psi point and the theoretical value of the yaw rate, which is derived from the lateral acceleration a.

During a steady turn, the detected input variables are related to each other via a mathematical vehicle model 15 with a linear single-track model assumption. The angular relationships for the monorail model are shown in figures 3 and 4. Fig. 3 shows a turn around the instantaneous pole P with a curve radius R, wherein the front wheels are deflected with a steering angle delta. The curve radius is based here on the position of the center of mass S of the motor vehicle, which is at a distance Lh from the axis of the rear wheel to the rear axle. The wheel base L, i.e. the distance between the front axle and the rear axle, is fixed in design. The curve radius R is determined in the single-track model as the quotient of the vehicle speed v and yaw rate psi points, respectively, acting at the center of mass S. The float angle beta is defined by the direction of movement of the motor vehicle in the center of mass S during a turn and the direction of the vehicle longitudinal axis.

Since slip always occurs on the wheels during actual driving, the wheels move at oblique angles alphav, alphah, respectively. The bevel angle is correlated with the final floating angle beta to be determined. According to the monorail model, the bevel angle alphah of the rear wheel is the difference between the floating angle beta and the quotient of the distance to the rear axle and the curve radius, according to the following equation:

lphah ═ Lh/(v/psi point) -beta.

However, no slip occurs under the so-called ackerman conditions. In this situation, as shown in fig. 4, the front wheels are set to an angle at which the imaginary extended front axle and the imaginary extended rear axle intersect at the instant pole P. This steering angle is referred to as the ackerman angle deltaA and corresponds to the quotient of the wheelbase L and the curve radius R. In the case of ackermann conditions, the float angle designated ackermann float angle beta0 likewise has no slip share.

According to the present invention, when the mathematical vehicle model assumes that the difference between the float angle beta and the ackermann float angle beta0 is proportional to the difference between the ackermann angle deltaA and the steering angle delta, the float angle beta during steady-state turning can be determined even in the case where no slip-related variable is detected. This relationship is graphically illustrated in fig. 5 and corresponds to the following scale:

(beta-beta0)～(deltaA-delta)

from the measured relationship between the steering angle delta and the ackerman angle deltaA, the actual float angle beta sought according to the method of fig. 2 is deduced via the proportional relationship of the ackerman float angle beta0 which theoretically exists when driving on the same curve without slip. Here, the present invention utilizes the correlation according to the principle of the section-line theorem shown in fig. 5 and assumes that the difference between the float angle beta and the ackermann float angle beta0 divided by the ackermann float angle is equal to the difference between the ackermann angle deltaA and the steering angle delta divided by the ackermann angle deltaA. This gives the following equation:

(beta-beta0)/beta0＝(deltaA-delta)/deltaA。

this assumption relates to the difference in ackermann conditions proportional to the respective value assumption, wherein it is known that no slip occurs. The relationship between steering angle and float angle under ackermann conditions, that is to say the relationship between ackerman angle and ackerman float angle, defined in the monorail model is used to determine the float angle sought.

The following equation for the float angle is obtained for the embodiment according to fig. 2 using the detected yaw rate psi point:

beta 2 Lh psi point/v-delta Lh/L.

Thus, in the embodiment according to fig. 2, the first quotient 16 is determined as the product of twice the rear axle distance Lh and the yaw rate psi point divided by the vehicle speed v. The second quotient 17 is formed by dividing the product of the steering angle delta and the distance to the rear axle Lh by the axle distance L. The difference 18 between the first quotient 16 and the second quotient 17 is the sought float angle beta during a steady-state turn.

In a second embodiment, the lateral acceleration a is learned or measured as a turning motion variable instead of the yaw rate psi point. Here, the first quotient is determined by dividing the product of twice the rear axle distance Lh and the lateral acceleration a by the square of the vehicle speed v. The float angle beta is then given by the following equation:

beta＝2*Lh*a/(v**2)-delta*Lh/L。

list of reference numerals

1 Motor vehicle

2 front axle

3 rear axle

4 wheel

5 steering wheel

6 wheel brake

7 driver assistance system

8 rotating speed sensor

9 determination

10 steering wheel sensor

11 lateral acceleration sensor

12 detection device

13 stability queries

14 integral

15 mathematical vehicle model

16 first quotient

17 second quotient

18 difference

a lateral acceleration

alpha bevel angle

Bevel angle of alphah rear wheel

Bevel angle of alphav front wheel

Angle of beta floating

beta0 Ackerman floating angle

delta steering angle

Angle of deltaA Ackerman

L wheel base

Lh to rear axle distance

psi point deflection speed

Radius of R curve

S center of mass

v vehicle speed