DE102010024171A1 - Method for adjusting restoring moment of electromechanical steering system of vehicle, involves determining deviation based on applicable function, and defining momentary position of zero return position based on determined deviation - Google Patents

Abstract

The method involves detecting same indicative signals with respect to momentary driving dynamic state during operation of a vehicle. An angular deviation (DELTApsiu) is determined using the signals based on an applicable function. A momentary position of a zero return position is defined based on the determined angular deviation. The zero return position is displaced according to a calculated displacement angle. Lateral acceleration (ay), yaw rate, vehicle velocity (Vfzg), wheel speed sensor signals and anti-lock braking system (ABS) sensor signals are detected as running condition signals. An independent claim is also included for an electromechanical steering system comprising an electronic control device.

Description

The invention relates to a method for setting a restoring torque in an electromechanical vehicle steering system, wherein the restoring torque is generated by driving an electromechanical steering auxiliary drive and serves to push back a deflected by the driver in the context of a steering operation from a return zero steering wheel in that return zero position. Furthermore, the invention relates to an electromechanical steering system, the servo motor is controlled such that via this an automatic return of a steering wheel in a return zero position can be brought about.

Through the use of electromechanical steering gears, which as such provide the function of an automatic steering wheel reset, it is possible to make the suspension so that the forces acting on the respective wheel on the wheel contact surfaces cause only relatively low reaction forces to the actuators of the corresponding steering gear. This circumstance proves to be particularly advantageous in vehicles with driven front axles, since the foreclosure or suppression of reaction forces from the area of the suspension significantly increases ride comfort. Thus, in such steering systems, the steering wheel similar to purely mechanical steering back into a leading back to straight center position, it is common in these electromechanical systems to build the restoring torque by appropriate control of the auxiliary steering motor "synthetic".

It is also possible to design the steering mechanism in electromechanical steering systems in such a way that it still provides a certain perceptibility for the steering forces acting in the region of the wheel suspension. This perceptibility can be increased by varying the steering assistance in dependence on the current operating state of the vehicle. Appropriate concepts are out DE 10 2006 025 254 A1 such as GB 2 372 020 A known.

The invention has for its object to provide solutions by which in vehicles that are equipped with electromechanical and a return function bidding vehicle steering systems, which is the respective driver performing steering characteristics further improved.

This object is achieved according to a first aspect of the present invention by a method for adjusting a restoring torque, which is urged in an electromechanical vehicle steering system, a vehicle steering wheel in a return zero position, wherein during the operation of the vehicle with respect to the current dynamic state of the same indicative signals are detected , An angular deviation is determined on the basis of an applicable function based on these signals, and the current position of the return zero position of the automatic reset is determined in accordance with the determined angular deviation.

This advantageously makes it possible to generate haptic feedback in the case of an electromechanical steering system which has characteristics that are typical of mechanical steering with a relatively large steering wheel radius and pronounced self-resetting. In particular, it is possible by the inventive concept to simulate a noticeable in mechanical steering systems with pronounced self-recovery with temporary oversteer or understeer of the vehicle and noticeable on the steering wheel drifting achievable by self-return return zero position. The temporary shift of the return zero position, and thus the setting of the return torque, preferably takes place with such high dynamics that it enables the driver to detect the position of the return zero position by a rapid swivel of the steering wheel and subsequently, as far as possible, the Vehicle to a course with reduced side slip to bring.

The inventive solution, it is also possible to change in an electromechanical steering system in the case of a steering operation that leads to oversteer or understeer, the restoring torque of the steering wheel in accordance with a calculation rule or function that maps a steering characteristic, as in a mechanical steering system with pronounced self-resetting. The phenomenon of a temporary shift of the return zero position of a reset function is not given in conventional electromechanical steering systems. By means of the concept according to the invention, it becomes possible to realize a clear feedback for dynamic driving limits. The inventive concept is particularly suitable for electromechanical steering systems of vehicles with high acceleration potential.

The inventive concept, the feedback for the driver is improved by reset errors due to oversteer or understeer in the steering system would naturally be present and in purely mechanical steering systems also present in the form of an angular deviation will be shown wanted.

According to a particularly preferred embodiment of the invention is characterized by a Applicable function generates a translation value that describes a false angle by which the return zero position is to be moved. The applicable function is preferably designed so that it takes into account current driving condition signals for the displacement of the return zero position and preferably also for a further modification of the characteristic of the return torque. In particular, these driving state signals can be taken into account by ultimately representing parameters of the applicable function or finding their way into these parameters.

According to a particularly preferred embodiment of the invention, the vehicle lateral acceleration is detected as a further driving state signal. Furthermore, the vehicle speed, the wheel torques, and / or the ABS sensor signals are preferably detected. The wheel torques can be calculated from the current engine and transmission operating state as well as the operating state of the brake system.

The function can also be designed so that it does not cause a reset at low vehicle speeds and low engine speeds, so that, for example, during a parking the steering wheel remains in the position set by the driver.

The translation according to the invention of the return zero position of the characteristic curve of the return torque can be provided for a speed range which is above a limit value above which a dynamic driving feedback is of importance. This limit value can be set relatively low, so that the inventive displacement of the return zero position on snowy and icy surfaces becomes apparent at an early stage.

According to a particularly preferred embodiment of the invention, the steering system is designed such that it is determined on the basis of the driving state signals, whether an oversteer exists, and that an angular deviation is calculated, which describes a reset error, as it is to be imaged in their behavior (eg. purely mechanical) steering is to be expected in case of oversteer, and that in accordance with this calculated angle deviation, the return zero position function is shifted so far that with it a return characteristic is achieved, as would be expected in the steering to be imaged.

Furthermore, it is also possible to design the steering system in such a way that it is determined on the basis of the driving status signals whether an understeer is present, and that an angular deviation is calculated which describes a resetting error, as it is to be modeled in its behavior (eg purely mechanical ) Steering is to be expected at understeer, and that in accordance with this calculated angular deviation, the return zero position of the characteristic curve of the restoring torque is shifted.

It is possible to realize the steering system so that an operating mode in which the steering system provides the shift of the return zero position of the function is selectively switchable.

The object mentioned above is also achieved in device-technical terms by an electromechanical steering system with a steering gear for applying the required to achieve a required wheel alignment actuating forces, said steering gear includes a steering shaft and a mechanically coupled with this auxiliary steering motor, and the steering assist motor via an electronic control device is controlled such that on the steering shaft, a restoring torque is effective, which urges the steering wheel in that return zero position upon deflection of a tailed to the steering shaft from a zero position, the control device is designed such that it is the position of the zero position against a Rückstellradgeradellung at entry of Over or under tax changed.

Further details and features of the invention will become apparent from the following description taken in conjunction with the drawings. It shows:

1 a block diagram illustrating the inventive concept for adjusting the position of the return zero position of the return torque in an electromechanical steering gear;

2 a graph illustrating the inventive concept of shifting the return zero position of a torque representing the return torque curve.

1 shows a block diagram, which as such further illustrates the inventive concept. This concept makes it possible to artificially represent restoring errors due to oversteer or understeer in a steering system that has to be tracked in its behavior, in the form of an angular deviation. _According to the invention, an applicable function is provided which calculates an angular deviation Δφ _u on the basis of the steering wheel angle φ, the lateral acceleration a _y , the vehicle _speed v _Fzg , the yaw rate dψ / dt and other steering-inherent variables. This error angle corresponds to the return angle of an ideal steering without electromechanical or automatic reset.

Alternatively, an override or underride signal of a brake control unit from which the angular deviation Δφ _{u is} generated can also be used at this point.

The angular deviation Δφ _u is used as the basis for determining the return zero position of the automatic return. In addition, this function can be based on the setting of an additional rack force F _u , which can be impressed on the steering system.

According to the inventive concept, a change in the position return zero position of the automatic return takes place when detecting oversteer and understeer. The forces F _U and F _ARS are added to the force calculated for the steering assist. The angle Δφ _u and the force F _U can be limited for safety purposes. The described functionality according to the invention can optionally be switched on for the operation of a "sports mode".

In 2 is a graphic illustrating the setting of the return torque MR in an inventive electromechanical steering system. On the abscissa of the steering wheel angle φ is exemplified in increments of 30 °. Steering wheel turns to the right are shown to the right of the steering wheel zero position O. Steering wheel turns to the left are correspondingly shown on the left of the steering wheel zero position O. The return torque MR is shown as an amount. The orientation or the sense of rotation of this return torque MR is such that a rotation is caused in a return zero position RN. According to the invention, the position of this return zero position RN with respect to the steering wheel zero position O (ie the "straight-ahead travel position") is varied in a particular way.

The restoring moment MR is set in accordance with a function f. This function f is set to give some progressivity. As a result of this progressivity, the restoring moment MR increases with increasing deflection from the zero position RN. The degree of progressivity may be varied taking into account vehicle speed, engine speed and other driving dynamics parameters. The graphs f2 and f3 shown in sections correspond to the function f at different, low speeds.

In normal driving dynamic conditions, d. H. driving dynamic states without oversteer or understeer, the reset zero position RN corresponds to the function f of the steering wheel zero position O. The function f is set so that this amount has a functional minimum. This minimum function is at the reset zero position RN, which in turn is normal, d. H. essentially side slip-free driving at the steering wheel zero position O is. The position of the minimum of the return torque MR determining function f or the reset zero position RN is changed according to the invention, in particular shifted to the left or right, in accordance with signals that correlate closely with the extent of oversteer or understeer. The amount of shift of the return zero position RN relative to the steering wheel zero position O is preferably determined based on a function applied to the steering wheel angle, lateral acceleration, vehicle speed, yaw rate, and other steering-inherent quantities, and thus calculates that shift.

The function f can also be further modified in addition to the shift of the position of the function minimum or the return zero position RN indicated here (i.e., that angular position in which the steering does not cause the steering wheel to reverse). Thus, as indicated by the functions f2 and f3, z. B. lower driving speeds lower restoring moments and also flatter increases the restoring moments may be provided. At higher travel speeds, the return torque to the return zero position RN and the progressivity (i.e., the increase in the return torque in the event of a deviation from the return zero position) are increased. Furthermore, the reset zero position RN is shifted. The function f can also temporarily be given a certain asymmetry with respect to the vertical axis passing through the reset zero position.

The graph f 'illustrates the characteristic of the steering wheel return torque MR in a vehicle operating condition in which oversteer occurs at a medium speed error angle of about 30 °. As can be seen, the function f 'is so "shifted to the left" that the offset of the reset zero position RN' relative to the steering wheel zero position O essentially maps the excessive and oversteer leading Fehlwinkel. This approach results in a haptic feedback for the driver of a corresponding vehicle, which has the character of a mechanical steering with pronounced self-recovery.

The method described here is preferably carried out by an electronic control, by which ultimately the torque of a support motor of the steering gear is adjusted such that the vehicle steering wheel in 2 illustrated characteristic of the return torque with variable reset zero position RN is achieved. The functions underlying the determination of the course of the restoring torque or the angular displacement of the return zero position can be determined by the electronic control in FIG the steering system can be implemented by these functions are actually processed by the controller. It is also possible to deposit in the controller a map, which can be used and in the present case understood as a function in the broader sense. The inventive displacement of the reset zero position can also be realized by an analog signal processing or influencing the current steering angle supplied to the controller. The functionality according to the invention can also be achieved without concrete execution of this function by transmission systems which are sufficiently similar in their effect.

The invention is characterized by the approach that the reset zero position RN, in which the steering wheel is urged by applying a correspondingly oriented restoring torque, is moved taking into account a occurring in over- or understeer Fehlwinkelereignisses in such a way that a return characteristic results, as they is typical for mechanical steering systems, especially those with a relatively large steering wheel radius in such dynamic driving conditions.

The invention has been explained in more detail herein with reference to an embodiment and possible modifications. However, it is not limited thereto, but includes all embodiments defined by the claims, even if they have not been expressly described above.

LIST OF REFERENCE NUMBERS

F _ARS

force

F _u

Rack force

MR

Restoring torque

O

Steering wheel zero position

RN

Reset zero position

a _y

lateral acceleration

v _vehicle

vehicle speed

φ

Steering wheel angle

dψ / dt

yaw rate

Δφ _u

angular deviation

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102006025254 A1 [0003]
• GB 2372020 A [0003]

Claims (10)

A method for adjusting a restoring torque by which, in an electromechanical vehicle steering system, a vehicle steering wheel is urged to a return zero position, in which: During the operation of the vehicle, indicative signals are detected with regard to the momentary dynamic state of the vehicle, - An angular deviation is determined on the basis of an applicable function based on these signals, and - According to the determined angular deviation, the current position of the return zero position is determined. A method according to claim 1, characterized in that the return zero position is shifted in accordance with a calculated error angle. A method according to claim 1 or 2, characterized in that the driving state signals find in parameters of the function input. Method according to at least one of Claims 1 to 3, characterized in that the vehicle lateral acceleration and / or the yaw rate are detected as the driving state signal. Method according to at least one of claims 1 to 4, characterized in that the vehicle speed is detected as the driving condition signal. Method according to at least one of claims 1 to 5, characterized in that the wheel speed sensor signals and / or ABS sensor signals are detected as driving status signals. Method according to at least one of claims 1 to 6, characterized in that it is determined on the basis of the driving state signals, whether an oversteer exists, and that an angular deviation is calculated, which describes a reset error, as it is to be imaged in their behavior (eg. purely mechanical) steering is to be expected in the case of oversteer, and that the position of the return zero position is shifted in accordance with this calculated angular deviation. Method according to at least one of claims 1 to 7, characterized in that it is determined on the basis of the driving state signals, whether an understeer exists, and that an angular deviation is calculated which describes a reset error, as in a behavior to be imaged in their behavior (eg mechanical) steering is to be expected at understeer, and that in accordance with this calculated angle deviation, the position of the reset zero position is shifted. Method according to at least one of claims 1 to 8, characterized in that an operating mode in which the steering system provides the displacement of the position of the reset zero position, is selectively switched on. Electromechanical steering system with a steering gear for applying the necessary to achieve a required wheel alignment actuating forces, this steering gear includes a steering shaft and a steering assist motor, and the steering assist motor is controlled via an electronic control device such that on the steering shaft a restoring torque is effective, the deflection at a Steering wheel connected to the steering shaft from a zero position, the steering wheel urges to the zero position, wherein the electronic control device is designed such that it changes the position of the return zero position relative to a Lenkradgeradestellung upon entry of oversteer or understeer.

Images