WO2005085042A1

WO2005085042A1 - Method for determining and adapting a steering handle angle wheel turning angle characteristic curve

Info

Publication number: WO2005085042A1
Application number: PCT/EP2005/002063
Authority: WO
Inventors: Bernd Danner; Thomas Dohmke; Eckart Fischer; Jesko Klandt; Jens KÖHNLEIN; Steen Kristensen; Jakob Seiler
Original assignee: Daimlercrysler Ag
Priority date: 2004-03-04
Filing date: 2005-02-26
Publication date: 2005-09-15
Also published as: DE102004010540A1

Abstract

The invention relates to methods for determining and adapting a (28) steering handle angle-wheel turning angle characteristic curve consisting in determining the actual wheel turning angle(β) or a quantity (RO) defining said turning angle, in detecting an actual steering handle angle and in correcting existing characteristic curve (28) by co-ordinating the actual wheel turning angle (β) of the quantity (RO) defining said turning angle with the actual steering handle angle or the characteristic curve (28). Steering handle angle wheel turning angle is produced on the basis of several coordinations thereof. The thus produced or adjusted characteristic curve takes into account the co-ordination modifications during a motor vehicle service life.

Description

Method for determining and adapting a steering handle angle-wheel steering angle characteristic curve

The invention relates to a method for determining and adapting a steering handle angle wheel steering angle characteristic curve.

With some safety and comfort functions in vehicles, it is crucial to know how the vehicle is moving relative to the environment or road. This own movement can be calculated using wheel encoder values and the position of the front wheels (odometry). However, there are generally no sensors in vehicles that can provide direct information about the position of the steering wheels. Therefore, this is determined via the position of the steering wheel. The relationship between the steering wheel angle and the angle of the front wheels (wheel steering angle) is described with a generally non-linear characteristic. This relationship is different for each vehicle. Furthermore, the relationship can change over the life of the vehicle. In particular, if the odometric detection of the vehicle movement is to be used for newer vehicle functions, such as parking assistance functions, it is necessary to detect the vehicle movement with a high degree of accuracy. For this it is necessary to determine the characteristic exactly and to adapt it over the life of the vehicle. From DE 43 20 171 AI a method for determining the wheel steering angle of a vehicle has become known, in which a mechanical steering ratio is effective between the steering wheel angle and the wheel steering angle. The steering wheel angle is measured and the wheel steering angle is corrected according to a given relationship.

From DE 196 01 826 AI a steering system for a motor vehicle has become known, which has a steering device for a motor vehicle with at least one steerable axle, an actuator, a superposition and a steering gear. The overlay and the steering gear each have a mechanical translation. The steerable axle, the actuator, the superposition gear and the steering gear are operatively connected to one another. By means of the superposition gear, the steering movements initiated by the driver are superimposed on the movements initiated by the actuator. The overall movement thus obtained is fed to the steering gear, which transmits this movement as a wheel steering angle to the wheels of the steerable axle. The mechanical ratio of the steering gear is variable. This allows the relationships between the steering wheel movements and the wheel steering angles of the steerable wheels to be set.

DE 100 21 903 AI describes a steering system for a vehicle. The steering system comprises a steering handle that can be actuated by a vehicle driver with at least one steerable vehicle wheel that is actuated as a function of actuations of the steering handle. The steering system further comprises a control system which enables the steering system to be operated in a steer-by-wire level and in a fallback level and which, at least in an emergency, moves from the steer-by-wire level to the Switches over the fallback level, an electrical and / or electronic coupling device that couples the steering handle to the steerable vehicle wheel in the steer-by-wire level and a hydraulic and / or mechanical coupling device that couples the steering handle with the steerable vehicle wheel in the fallback level , The steering system is designed such that the coupling between the steering handle and the steerable vehicle wheel takes place in the steer-by-wire level as a function of at least one first coupling coefficient and in the fallback level as a function of at least a second coupling coefficient. The coupling coefficients are each designed as a function of at least one operating parameter of the vehicle and / or the steering system. The coupling coefficient k can have a functional relationship with respect to an operating parameter p of the vehicle and / or the steering system. The operating parameter can be, for example, the steering angle set on the steering handle. An adaptation of the functional relationship over the life of the vehicle is not described in this document.

The object of the present invention is to provide a method and an apparatus for performing the method, which enables a more precise detection of the vehicle movement.

This object is achieved by a method of the type mentioned at the outset, in which the current wheel steering angle or a current size describing the wheel steering angle is determined, a current steering handle angle is recorded and an existing characteristic curve is corrected on the basis of the assignment of the current wheel steering angle or the descriptive quantity to the current steering handle angle is a steering handle angle-radius angle characteristic curve or is derived from several such assignments is fathered. The steering handle angle-wheel steering angle characteristic curve can be determined adaptively from the wheel steering angle, which is always being determined again and again, or the size describing it and the associated detected steering handle angle. This means that this characteristic curve, which is different for each vehicle and develops differently for each vehicle due to wear, accidents, tires, etc., does not have to be measured, but can be learned and adjusted automatically. The use of additional sensors and encoders is not necessary. This saves production costs and ensures that the odometry functions properly over the life of the vehicle. The wheel steering angle itself does not necessarily have to be determined. It may be sufficient to determine a variable that is related to the wheel steering angle, such as, for example, the radius of a circle that a rear wheel describes when cornering and whose center lies on a line through the rear axle. This means that a steering handle angle - wheel steering angle characteristic curve is also to be understood as a characteristic curve which represents an assignment of steering handle angles to the variables describing the wheel steering angle.

In a particularly preferred variant of the method, it can be provided that the distances traveled by at least two wheels are recorded and the parameters describing the wheel steering angles or the wheel steering angles are determined from them, in particular from partial routes. When a vehicle travels a non-straight route, the wheels move on different trajectories on the road, ie they cover different distances. The distance covered by a wheel within a given period of time can be recorded, for example, using wheel encoders. It can be provided that a certain number of pulse signals of one revolution of a wheel detected by the wheel encoders that corresponds. If the different distances from at least two wheels are known, the driven partial trajectory and thus the wheel steering angle can be deduced using mathematical-geometric methods. Even if this method is used to determine the wheel steering angle, it is advantageous for the odometry to determine the wheel steering angle via the steering handle angle and the characteristic curve. This means that the steering handle angle is actually recorded and a wheel steering angle is assigned via the characteristic curve. This is particularly advantageous in the case of stationary or slow-moving vehicles, since a partial trajectory cannot be precisely determined in the case of stationary or slow-moving vehicles.

In a preferred development of the method it can be provided that the distances traveled are recorded at least on two wheels arranged on different sides with respect to a central longitudinal axis of the vehicle. This means that a route is recorded on the left side of the vehicle and a route on the right side of the vehicle. Knowing the distance between the two wheels, the wheel steering angle can be determined from the partial trajectories with the aid of a simple vehicle model. Determining trajectories or partial trajectories has the advantage that no separate sensors or encoders for determining the wheel steering angle have to be provided on the steerable wheels. However, it is fundamentally conceivable to provide such sensors in order to directly detect the wheel steering angle. A simple steering model, for example, consists of a straight rod with wheels suspended at the end. If the ^" paths of a front and a rear wheel are determined, the steering model advantageously consists of three rods, two rods respectively describing the front and rear axles of the vehicle and one rod describing the front and rear axles withstands. It is also think-fc> ar to create steering models that take into account a slip in the steering line and the mechanics in the steering line. It goes without saying that the more precisely the model reproduces reality, the more precisely the wheel steering angle or the quantity describing it can be detected. It should be noted here that a single-track model is preferably used to determine the wheel steering angle. This means that the wheel steering angle describes a wheel position as it would have to be in a wheel arranged in the middle between the two steered wheels. This takes into account that the steered wheels actually have different wheel steering angles when cornering.

If there is a deviation of the wheel steering angle or the size and / or the steering handle angle that describes the wheel steering angle from an existing characteristic curve by more than a predetermined value, this assignment of the wheel steering angle or the size describing it to the steering handle angle is for a Correction of the characteristic discarded. This means that in such a case these values are not taken into account for a correction of the characteristic. Normally - after determining a current wheel steering angle, this wheel steering angle is correlated with the currently recorded steering handle angle or assigned to it and the existing characteristic curve is corrected if necessary if a deviation from the characteristic curve is detected. However, this procedure can deliver incorrect results when the coefficient of friction is low, for example when the vehicle slides on black ice. For this reason, outliers that deviate significantly from the previous characteristic are not taken into account. This measure increases the accuracy of the characteristic curve. In an advantageous method variant, it is provided that a distinction is made for determining and correcting the characteristic after driving forwards and backwards. For example, it can be provided that the characteristic curve is only determined or corrected when driving forwards or backwards. However, it is also conceivable for a characteristic curve for the forward and reverse travel to be determined or corrected in each case in accordance with a development of the method. With this measure, an exact and correct assignment is made separately for the forward and reverse travel. This takes into account the fact that a characteristic curve, by means of which a wheel steering angle or a variable describing it is assigned to a steering handle angle, depends on the direction of travel.

A further accuracy of the characteristic curve can be achieved if speed ranges are defined and characteristic curves are created or corrected for the speed ranges. A field of characteristics is created by differentiating between different speed ranges.

The object is also achieved by a steering system for a vehicle, with a steering handle which can be actuated by a driver, in particular a steering wheel on which a steering handle angle can be set, with at least one steerable vehicle wheel on which a wheel steering angle is set as a function of actuations of the steering handle and with a steering handle angle detection means, wherein a computer unit is provided, which is connected to a wheel steering angle detection device and the steering handle angle detection means and generates a characteristic curve or corrects an existing characteristic curve from an assignment of the current steering handle angle and current wheel steering angle. With such a steering system, which is particularly suitable for carrying out the method. net, a characteristic curve can be learned and adjusted "on-line". This means that characteristic curves no longer have to be generated with great effort and effort. In addition, a characteristic curve can be generated and corrected individually for each vehicle Assignment of a steering handle angle to a wheel angle It can also be provided that in the computer unit a variable describing the wheel steering angle is assigned to the currently set and recorded steering handle angle.

The characteristic curve can be generated or corrected with particularly simple means if the wheel steering angle detection device comprises at least two wheel path detection means, in particular wheel encoders. In particular, wheel encoders present on the vehicle wheels can be used anyway. Such wheel encoders are also referred to as pulse ring counters.

Further features and advantages of the invention result from the following description of an embodiment of the invention, with reference to the figures of the drawing, which show details essential to the invention, and from the claims. The individual features can each be implemented individually or in groups in any combination in a variant of the invention.

An embodiment is shown in the schematic drawing and is explained in the following description. Show:

Figure 1 is a schematic representation to illustrate the inventive method.

2 shows a schematic illustration of a steering system; 3 shows the determination of a variable describing the wheel steering angle on the basis of the front wheels;

4 shows a representation of the determination of the wheel steering angle; and

5 shows the determination of a variable describing the wheel steering angle on the basis of the rear wheels.

1 shows a vehicle model 1 in a first position. According to the vehicle model, the rear wheels 2, 3 are attached to a rear axle 4. The distance between the rear axle 4 and the front axle 6 is determined by a rod 5. The steerable front wheels 7, 8 are arranged on the front axle 6. In the illustration, the front wheels 7, 8 are turned to the left. If a vehicle now drives with this turning of the front wheels 7, 8, the front wheel 7 moves on the trajectory 9 and the front wheel 8 on the trajectory 10. In FIG. 1 it can be seen that the wheels 7, 8 have different paths return. This applies not only to the length, but also to the radius of the respective trajectories 9, 10. At the end of the trajectories 9, 10, the wheels 7, 8 assume the positions 11, 12. The track width of the vehicle is determined by the front axle 6 or rod. The distances traveled on the trajectories 9, 10 are recorded. Due to the cornering, the trajectories have different paths. Knowing the track width, the wheel angle β can be determined from this difference. This wheel angle β is correlated with a steering handle angle via a characteristic curve.

A steering system 20 is shown schematically in FIG. 2. The steering system 20 comprises a steering handle 21 designed as a steering wheel, by the actuation of which the wheels 22, 23 are formed. can be steered or a wheel steering angle can be set. The steering handle angle set by actuating the steering handle 21 is detected by a steering handle angle detection device 24 and fed to a computer unit 25. Furthermore, the paths covered by the wheels 22, 23 are detected by wheel path detection means 26, 27, which can be designed as pulse ring counters, and delivered to the computer unit 25. The wheel path detection means 26, 27 can form a wheel steering angle detection device with part of the computer unit 25. In the computer unit 25, a wheel steering angle or a variable describing it is first determined from the paths detected by the wheel path detection means 26, 27 and the distance between the wheels 22, 23. This current wheel steering angle is assigned to the steering handle angle detected by the steering handle angle detection means 24. An existing characteristic curve 28 can be corrected with a single assignment of this type, on the other hand a characteristic curve 28 can be generated from several such assignments.

3 shows a possibility of determining a variable related to the wheel steering angle on the basis of the front wheels 31, 32 of a simple vehicle model. The solid lines represent the position of the vehicle at time t _0. The dotted line describes the position of the right front wheel 32 at the following time ti. In the meantime between times t ₀ and t _x , the vehicle travels the angle on a circle α. The following relationships apply: s ₀ ² = ι ² + r ² (i) s ² = l ² + (r ₀ + h) ² (2) where r _{0 is} the distance of the right rear wheel 33 from a pivot point 34 on a line through the rear axle, s ₀ and Si are the distances of the front wheels 31, 32 from the pivot point 34, 1 the wheelbase, ie the distance between the axles and h the Track width, ie the distance between the wheels of an axle.

The movement of the front wheels 31, 32 in the time interval can be expressed as: s _o a = b ₀ (3) sa = b (4)

where b ₀ and bi are the distances or trajectories traveled by the front wheels 31, 32 in the time interval.

From equations (1) - (4) we get:

and this results in:

The size r ₀ represents a size describing the wheel steering angle.

4 shows how the wheel steering angle β is determined using a single-track model. It is assumed that the vehicle has only one steerable front wheel 30, which is arranged in the middle between the wheels 31, 32, i.e. a

Put r ₀ + h / 2 from the pivot point 34. The wheel steering angle ß is so with an average of the wheel steering angles of the wheels 31, 32. The wheel steering angle can therefore be determined from equation (6) using the single-track model as follows:

(r ₀ + h 12) tan (-?) = / « ^• ß = - arctan () (7) r ₀ + h 12

5 shows a possibility of determining the quantity r ₀ describing the wheel steering angle on the basis of the rear wheels. The position of the vehicle at time t ₀ is shown with solid lines, that at time ti with dashed lines. The trajectories of the wheels 31, 32, 33, 35 are shown in dotted lines. The following relationships apply: a _Q = r ₀ - a (8)

which results in:

(10) r ₀ + h

From equation (10) one obtains r ₀ = - —h (11) α, -α ₀

The assigned wheel steering angle β is again obtained from equation (7).

Claims

claims

Method for determining and adapting a steering handle angle - wheel steering angle characteristic curve (28), characterized in that a current wheel steering angle (β) or a variable (r ₀ ) describing the current wheel steering angle (β) is determined; a current steering handle angle is detected; an existing characteristic curve (28) is corrected on the basis of an assignment of the current wheel steering angle (β) or the size (r ₀ ) describing it to the current steering handle angle or a steering handle angle - wheel steering angle characteristic curve (28) is generated from several such assignments.

A method according to claim 1, characterized in that the distances covered (9, 10, b _{0 /} bi, a ₀ , aj.) Detects at least two wheels (7, 8, 22, 23, 31, 32, 33, 35) are and from them, in particular from sections, the wheel steering angle (ß) or the wheel steering angle (ß) describing variables (r ₀ ) are determined.

3. The method according to claim 2, characterized in that the distances traveled (9, 10, b ₀ , bi, a ₀ , ai) of at least two wheels (2, 3, 7, arranged on different sides with respect to a central longitudinal axis of the vehicle) 8, 22, 23, 31, 32, 33, 35) are recorded.

4. The method according to any one of the preceding claims, characterized in that in the event of a deviation of the wheel steering angle (β) or the size (r ₀ ) describing the wheel steering angle (β) and / or the steering handle angle from an existing characteristic curve (28) by more than one predetermined value, this assignment of the wheel steering angle (β) or the variable (r ₀ ) describing the wheel steering angle (β) to the steering handle angle for a correction of the characteristic curve (28) is rejected.

5. The method according to any one of the preceding claims, characterized in that a distinction is made for the determination and correction of the characteristic curve (28) after driving forward and backward.

6. The method according to claim 5, characterized in that in each case a characteristic curve (28) for the forward and reverse travel is determined or corrected.

7. The method according to any one of the preceding claims, characterized in that speed ranges are defined and characteristic curves (28) are created or corrected for the speed ranges.

8. Steering system (20) for a vehicle, with a steering handle (21) which can be actuated by a driver, in particular a steering wheel on which a steering handle angle can be set, with at least one steerable vehicle wheel (7, 8, 22, 23, 31, 32) , on which a wheel steering angle (β) is set as a function of actuations of the steering handle (21), and with a steering handle angle detection means (24), characterized in that a computer unit (25) is provided which is equipped with a wheel steering angle detection device and the steering handle angle detection means ( 24) is connected and a characteristic curve (28) is generated or an existing characteristic curve (28) is corrected from an assignment of the current steering handle angle and the current wheel steering angle (β).

9. Steering system according to claim 8, characterized in that the wheel steering angle detection device comprises at least two wheel path detection means (26, 27), in particular wheel encoders.