Method for the traction control of a single-track motor vehicle taking the slip angle of the rear wheel into consideration

Abstract

A method for determining a slip angle λ.sub.r of a rear wheel of a single-track motor vehicle for the purpose of traction control of the rear wheel of the single-track motor vehicle by means of a closed loop control is provided. The slip angle λ.sub.r of the rear wheel is determined as a feedback value of the closed loop using at least one of three model-based steps. A slip angle λ.sub.r1, λ.sub.r2 or λ.sub.r3 is determined by one of the three steps representing the slip angle λ.sub.r or the slip angle λ.sub.r is determined from at least two of the slip angles λ.sub.r1, λ.sub.r2 and λ.sub.r3.

Claims

1. A method for determining a slip angle λ.sub.r of a rear wheel of a single-track motor vehicle for the traction control of the rear wheel of the single-track motor vehicle by a control loop, comprising the acts of: determining the slip angle λ.sub.r of the rear wheel as a feedback variable of the control loop by at least one of determining a first slip angle λ.sub.r1 using a first state estimator, wherein input variables of the first state estimator are at least one steering angle δ on a front wheel of the single-track motor vehicle and an orientation of the single-track motor vehicle in space, determining a second slip angle λ.sub.r2 using a second state estimator, wherein input variables of the second state estimator are at least one steering angle δ on the front wheel of the single-track motor vehicle and a movement vector of the single-track motor vehicle in a mass center of gravity of the single-track motor vehicle, and determining a third slip angle λ.sub.r3, wherein the third slip angle λ.sub.r3 is determined from a predetermined relationship for a single-track model between the steering angle δ, an Ackermann angle ΔA, a slip angle λ.sub.f of a front wheel, and the third slip angle λ.sub.r3 wherein the slip angle λ.sub.f is determined from a predetermined ratio of the slip angle λ.sub.f to a vehicle status, and the first slip angle λ.sub.r1, the second slip angle λ.sub.r2, or the third slip angle λ.sub.r3 represents the slip angle λ.sub.r, or the slip angle λ.sub.r is determined from at least two of the slip angles λ.sub.r1, λ.sub.r2, and λ.sub.r3.

2. The method according to claim 1, wherein the first state estimator is a Kalman filter or an expanded Kalman filter.

3. The method according to claim 2, wherein the second state estimator is a Kalman filter or an expanded Kalman filter.

4. The method according to claim 3, further comprising the act of: determining the orientation of the motor vehicle in space from a roll angle Φ, a yaw angle Ψ, and a pitch angle Θ of the motor vehicle.

5. The method according to claim 4, further comprising the act of: determining a curve radius R of a curve described by the single-track motor vehicle, and the curve radius R is an input variable of the first state estimator.

6. The method according to claim 5, wherein the curve radius R and the orientation of the motor vehicle are determined from a roll rate {dot over (ϕ)}, a yaw rate {dot over (ψ)}, and a pitch rate {dot over (Θ)} as well as an acceleration of the motor vehicle in space and a vehicle velocity v.

7. The method according to claim 6, further comprising the act of: determining a vehicle mass m of the single-track motor vehicle, wherein a coefficient of friction μ between a roadway and a tire of the rear wheel is determined, and the vehicle mass m and the coefficient of friction μ are input variables of the first state estimator.

8. The method according to claim 7, wherein the movement vector of the motor vehicle is determined as an input variable of the second state estimator from a change of a vehicle position ascertained using at least one of a GPS and from a change of an Earth's magnetic field measured using a magnetometer.

9. The method according to claim 1, further comprising the act of: determining the slip angle λ.sub.r from precisely two of the slip angles λ.sub.r1, λ.sub.r2, and λ.sub.r3 by data fusion.

10. The method according to claim 9, further comprising the acts of: determining as a measured value a measurement deviation between the slip angle λ.sub.r determined by the data fusion; and determining as a reference value and the slip angle λ.sub.r1, λ.sub.r2, or λ.sub.r3 not used in the determination of the slip angle λ.sub.r using the precisely two of the slip angles λ.sub.r1, λ.sub.r2, and λ.sub.r3.

11. The method according to claim 9, further comprising the acts of: determining a deviation between the slip angles λ.sub.r1, λ.sub.r2, and λ.sub.r3; and determining the slip angle λ.sub.r by the data fusion of the two slip angles of the slip angles λ.sub.r1, λ.sub.r2, and λ.sub.r3 having the smallest deviation from one another.

12. The method according to claim 1, further comprising the act of: determining a vehicle status for determining the third slip angle λ.sub.r3 using a vehicle velocity v of the motor vehicle, a curve radius R of a curve described by the motor vehicle, and a roll angle Φ.

13. The method according to claim 12, further comprising the act of: determining a tire lateral force F.sub.s,f on a tire of the front wheel from the curve radius R and the vehicle velocity v using a third state estimator, wherein the slip angle λ.sub.f is predetermined for the roll angle Φ and the tire lateral force F.sub.s,f.

14. A method for traction control of a rear wheel of a single-track motor vehicle by a control loop, wherein a slip angle λr of the rear wheel is determined as a feedback variable of the control loop, comprising the acts of: determining the slip angle λr of the rear wheel as a feedback variable of the control loop; and controlling traction of the rear wheel using the determined slip angle λr in the control loop, wherein the act of determining the slip angle λr of the rear wheel as a feedback variable of the control loop is performed by at least one of determining a first slip angle λr1 using a first state estimator, wherein input variables of the first state estimator are at least one steering angle δ on a front wheel of the single-track motor vehicle and an orientation of the single-track motor vehicle in space, determining a second slip angle λr2 using a second state estimator, wherein input variables of the second state estimator are at least one steering angle δ on the front wheel of the single-track motor vehicle and a movement vector of the single-track motor vehicle in a mass center of gravity of the single-track motor vehicle, and determining a third slip angle λr3, wherein the third slip angle λr3 is determined from a predetermined relationship for a single-track model between the steering angle δ, an Ackermann angle λA, a slip angle λf of a front wheel, and the third slip angle λr3 wherein the slip angle Δf is determined from a predetermined ratio of the slip angle λf to a vehicle status, and wherein the first slip angle λr1, the second slip angle λr2, or the third slip angle λr3 represents the slip angle λr, or the slip angle λr is determined from at least two of the slip angles λr1, λr2, and λr3.

15. A system for traction control of a rear wheel of a single-track motor vehicle, comprising: a control unit, the control unit being configured to determine a slip angle λ.sub.r as a feedback variable of the control loop by at least one of determining a first slip angle λ.sub.r1 using a first state estimator, wherein input variables of the first state estimator are at least one steering angle δ on a front wheel of the single-track motor vehicle and an orientation of the single-track motor vehicle in space, determining a second slip angle λ.sub.r2 using a second state estimator, wherein input variables of the second state estimator are at least one steering angle δ on the front wheel of the single-track motor vehicle and a movement vector of the single-track motor vehicle in a mass center of gravity of the single-track motor vehicle, and determining a third slip angle λ.sub.r3, wherein the third slip angle λ.sub.r3 is determined from a predetermined relationship for a single-track model between the steering angle δ, an Ackermann angle ΔA, a slip angle λ.sub.f of a front wheel, and the third slip angle λ.sub.r3 wherein the slip angle λ.sub.f is determined from a predetermined ratio of the slip angle λ.sub.f to a vehicle status, and the first slip angle λ.sub.r1, the second slip angle λ.sub.r2, or the third slip angle λ.sub.r3 represents the slip angle λ.sub.r, or the slip angle λ.sub.r is determined from at least two of the slip angles λ.sub.r1, λ.sub.r2, and λ.sub.r3.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a method for determining the slip angle λ.sub.r in accordance with an embodiment of the present invention.

(2) FIG. 2 shows a method for determining the slip angle λ.sub.r3 in accordance with an embodiment of the present invention.

(3) The figures are schematic and by way of example. Identical reference signs in the figures indicate identical functional and/or structural features.

DETAILED DESCRIPTION

(4) FIG. 1 schematically shows the sequence in the determination of the slip angle λ.sub.r using all three slip angles λ.sub.r1, λ.sub.r2, λ.sub.r3.

(5) The roll rate {dot over (ϕ)}, yaw rate {dot over (ψ)}, and pitch rate {dot over (Θ)}, as well as the accelerations a.sub.x, a.sub.y, and a.sub.z in the three spatial directions x, y, and z are determined by the inertial measurement unit 10 (IMU) and provided to the conversion 20. In the conversion 20, the roll angle Φ, which is also referred to as the slip angle, the yaw angle Ψ, and the pitch angle Θ, as well as the curve radius R of the curve described by the motor vehicle are determined from roll rate {dot over (ϕ)}, yaw rate {dot over (ψ)}, and pitch rate {dot over (Θ)}, and from the vehicle velocity v.

(6) The three slip angles λ.sub.r1, λ.sub.r2, and λ.sub.r3 are subsequently determined in three different ways, so that a possible error or a deviation of the respective slip angle λ.sub.r1, λ.sub.r2, and λ.sub.r3 from the actual slip angle at the rear wheel may be compensated for.

(7) The first state estimator 30 is a Kalman filter, in which a linear vehicle model is stored. The first slip angle λ.sub.r1 is determined from a vehicle mass m, a coefficient of friction μ, the variables ascertained by the IMU 10, and the steering angle δ.

(8) Both the vehicle mass m and also the coefficient of friction μ can be “estimated” based on sensor data. For example, the vehicle mass can be composed of individual values added to one another. For this purpose, an empty weight of the vehicle can be known, a fuel weight can be determined by a tank fill level, and, for example, a weight of the persons on the vehicle can be ascertained from a spring behavior acquired by sensors.

(9) The following applies for the determination of the first slip angle λ.sub.r1:

(10) $\begin{array}{c}{\lambda }_{r1}=\frac{F_{s,r}}{a_r}\\ F_{s,r}=f_1\left\{\mu ,\Phi ,F_{N,r}\right\}\\ a_r=f_2\left\{\mu ,\Phi ,F_{N,r}\right\}\\ F_{s,f}*\cos \Delta +F_{s,r}+m*Y_G*{\Psi }^2=0\end{array}$

(11) The functions f1 and f2 are each stored here in the first state estimator 30.

(12) The second slip angle λ.sub.r2 is determined subsequently or in parallel to the first slip angle λ.sub.r1. For this purpose, a second state estimator 40 implemented as an expanded Kalman filter is used, which uses the yaw angle Ψ, the course angle ν, and the steering angle δ as input variables, wherein the observation or the use of a nonlinear model of the vehicle is possible due to the expanded Kalman filter.

(13) The course angle ν can be determined from a change of the vehicle position, which can be ascertained by a GPS. Alternatively thereto, it is possible to determine the course angle ν by way of a change of the Earth's magnetic field measured using a magnetometer. To obtain an exact course angle ν, the embodiment shown provides that a course angle ν is used which originates from a data fusion. For this purpose, a first course angle ν1 is ascertained with the aid of the GPS and a second course angle ν2 is ascertained with the aid of the magnetometer and these two course angles ν1, ν2 are offset to form a course angle ν. One very simple option is, for example, to determine the mean value of the course angles ν1, ν2 and use it as the course angle ν. Alternatively thereto, however, a data fusion can also be carried out by means of a further Kalman filter.

(14) Subsequently or in parallel, a third slip angle λ.sub.r3 is ascertained by the determination 50. For this purpose, the steering angle δ and the roll angle Φ determined by the IMU 10 and the radius R are used as essential input variables. The determination 50 of the third slip angle λ.sub.r3 is explained in greater detail by way of example with respect to FIG. 2.

(15) For the determination of all three slip angles λ.sub.r1, λ.sub.r2, and λ.sub.r3, a database acquired at the same time is used in each case, so that, for example, the steering angle δ is identical in each case.

(16) After the three slip angles λ.sub.r1, λ.sub.r2, and λ.sub.r3 have been determined they are offset with one another by the data fusion 60. The data fusion 60 determines in the embodiment shown the slip angle λ.sub.r, which corresponds to the actual slip angle at the rear wheel with a higher probability than each of the three slip angles λ.sub.r1, λ.sub.r2, and λ.sub.r3 as such, by means of a further Kalman filter. The slip angle λ.sub.r thus determined is subsequently provided to the traction control 70.

(17) Alternatively to the method shown in FIG. 1, for example, only a part of the slip angles λ.sub.r1, λ.sub.r2, and λ.sub.r3 can also be used to determine the slip angle λ.sub.r.

(18) The models or the state estimators and the calculations and the constants required for this purpose can be stored, for example, in a control unit or in the control unit of the traction control, so that the determination of the slip angle λ.sub.r can be carried out using the control unit, wherein the further required sensor values or variables are provided to the control unit, for example, by the IMU 10 and a steering angle sensor.

(19) FIG. 2 shows by way of example the sequence for determining the third slip angle λ.sub.r3. In addition to the steering angle δ, the slip or roll angle Φ, and the curve radius R, the velocity v of the vehicle are also used as input values for the determination 50. In addition, the constant castor angle ε and the wheelbase p are additionally used to determine the third slip angle λ.sub.r3.

(20) In the determination 51 of the kinematic steering angle Δ, i.e., the theoretical steering angle resulting in the actual cornering, the actual steering angle δ and also the roll angle Φ and the castor angle ε are taken into consideration, which jointly result in the kinematic steering angle Δ.

(21) Moreover, the Ackermann angle Δ.sub.A is determined by the calculation 52, which results according to the single-track model under the assumption of small angles for Δ.sub.A=p/R.

(22) Furthermore, the following applies for the single-track model at small angles:

(23) $\Delta =\frac{p}{R}+{\lambda }_f-{\lambda }_r{\lambda }_r={\Delta }_A+{\lambda }_f-\Delta$

(24) To determine the front slip angle λ.sub.f, with the aid of a third state estimator 53, the tire lateral force F.sub.s,f on the front tire is determined from a traveled curve radius R and the vehicle velocity v. The ratio of the front tire lateral force F.sub.s,f at an inclination described by the roll angle Φ in relation to the front slip angle λ.sub.f is known and is stored, for example, by a characteristic map or a function, so that the front slip angle λ.sub.f is determinable therefrom and the rear slip angle λ.sub.r is determinable as the third slip angle λ.sub.r3 therefrom.

(25) The invention is not restricted in its embodiment to the above-described preferred exemplary embodiments. Rather, a number of variants is conceivable, which also makes use of the described solution in fundamentally differently designed embodiments.

LIST OF VARIABLES AND REFERENCE NUMERALS

(26) δ steering angle Δ kinematic steering angle ε castor angle p wheelbase Y.sub.G distance of the vehicle center of gravity to the axis of rotation v vehicle velocity R curve radius Δ.sub.A Ackermann angle m mass of the vehicle ν course angle μ coefficient of friction between roadway and tire αr slip stiffness characteristic value of the tire installed on the rear wheel FN,r tire normal force front Fs,f tire lateral force front Fs,r tire lateral force rear λr slip angle rear λf slip angle front Φ roll angle (inclination angle) Ψ yaw angle Θ pitch angle {dot over (ϕ)} roll rate (roll velocity) {dot over (ψ)} yaw rate (yaw velocity) {dot over (Θ)} pitch rate (pitch velocity) ax acceleration in x direction ay acceleration in y direction az acceleration in z direction 10 inertial measurement unit (IMU) 20 conversion 30 first state estimator 40 second state estimator 50 determination of the third slip angle λr3 51 determination of the kinematic steering angle Δ 52 determination of the Ackermann angle ΔA 53 third state estimator 54 determination of the front slip angle λf 60 data fusion 70 traction control