DE102006036744A1 - Steering system controlling method for motor vehicle, involves representing short-term target wheel steering angle as function of vehicle speed and computing final target wheel steering angle from target actual deviation - Google Patents

Abstract

The method involves converting a steering wheel angle (deltaL) to a short-term target wheel steering angle based on a vehicle state variable e.g. vehicle condition. The short-term target wheel steering angle is converted into a target state variable representing transverse dynamics of a vehicle. The short-term target wheel steering angle and the target state variable are represented as a function of vehicle speed. The target state variable is compared with relative actual variable, and a final target wheel steering angle is computed from a target actual deviation in regulation.

Description

The The invention relates to a method for controlling a steering system in a vehicle according to the preamble of claim 1 and on a steering system for implementation the method according to claim 7.

In "ATZ Automotive Engineering Magazine 96 ", 1994, Pages 674 to 689, a procedure for driving dynamics control in Motor vehicles described which the Fahrzeuglängs- and Vehicle transverse dynamics considered. In this method, starting from the steering wheel angle specified by the driver determines a desired yaw rate, the transverse dynamics of the Vehicle represents. The target yaw rate is measured with a yaw rate compared and based on a regulation in which required for the vehicle transverse guidance Yaw moment is calculated over targeted brake interventions on the wheels of the vehicle is implemented.

Also known are regulated steering systems in motor vehicles, which have a superposition gear, which is superimposed on the steering wheel angle specified by the driver. Such a steering system is for example in the DE 196 01 826 A1 described. With the help of the superposition gearing, variable steering ratios can be generated both in terms of comfort and in terms of safety. Thus, for example, it is possible to change the gear ratio as a function of vehicle speed by selecting an indirect gear ratio at higher speeds and a more direct gear ratio at low vehicle speeds, thus facilitating, for example, parking.

at such steering systems with variable steering ratio is to pay attention that to fulfillment different target functions generated target wheel steering angle do not lead to conflicting results.

Of the Invention is based on the object in a steering system different To implement objectives without contradiction. It should in particular be a safe and at the same time comfort-driven driving possible.

These Task is according to the invention in a Method with the features of claim 1 and in a steering system to carry out the method with the features of claim 7 solved. The under claims give expedient further education at.

at the method according to the invention for controlling a steering system in a vehicle is starting from the predetermined by the driver steering wheel angle in several steps generates a set target wheel steering angle. For this, first in a first step of the driver's steering wheel angle under consideration at least one vehicle state quantity into a provisional desired wheel steering angle implemented, wherein the vehicle state quantity in particular the vehicle speed is. In a subsequent second step, this provisional desired wheel steering angle converted into a desired state variable, representing the lateral dynamics of the vehicle, in particular the Target yaw rate. After all In a third step, the desired state variable with a compared to actual size compared, wherein the deviation is fed to a control in which the final target wheel steering angle is calculated, which is to be set in the steering system.

In this stepped version of the method of regulating the steering system is the problem of different requirements for the wheel steering angle to be set viewed holistically and solved. Usually come both comfort-oriented and safety-oriented Aspects of the steering angle control to bear. By the stepped, hierarchical structure of the steering process, for example considers the comfort function in the first method step so that the provisional Target wheel steering angle already contains the information about the comfort function to be implemented. A Such comfort function is for example via a speed-dependent steering ratio displayed at the steering wheel operations at high speeds the driver only to relatively small Lead wheel steering angles, whereas at very low speeds, e.g. when parking size Steering translations are carried out the size Radlenkwinkeländerungen already at relatively small Steering wheel angles result.

In the subsequent process steps, ie in the calculation the desired state variable that the Represents lateral dynamics, and the target-actual comparison with subsequent regulation, the other aspects, in particular the safety aspects, automatically taken into account. Both in the determination of the desired state variable and in the subsequent Control step can Exemplary safety aspects are considered. Also included already the target-actual comparison for the transverse dynamics representing State variable in itself a safety function, since the regulation and the feedback in the Closed loop contributes to a desired stabilization.

In the steering system according to the invention, which is provided for carrying out the method, the adjustment of the Radlenkwinkels takes place the steered wheels by means of actuators as a function of the steering wheel angle specified by the driver, taking into account vehicle state variables. In a control unit of the steering system control signals are generated, act on the actuators in the vehicle.

Basically there it's two different ways in the steering system for adjusting the wheel steering angle. For one thing is it is possible a superposition steering gear to provide in the steering system, in the transmission path between the steering wheel and steered wheels is interposed. In the superposition steering gear is a superposition steering angle producible, which overlaps the steering wheel angle specified by the driver becomes. The overlay steering angle is generated here using the method described above and includes both appropriately comfort-relevant as safety-relevant functions.

According to one second embodiment is the steering system as a steer-by-wire system executed. In this version is at least in normal situations an immediate mechanical Penetration between the steering wheel and steered wheels not given, rather is the driver specified steering wheel angle in signal form actuators supplied in which considering Further Fahrzeugzustands- and operating variables the desired Radlenkwinkel to the steered wheels be set. This steer-by-wire system can be either with superposition steering gear or without superimposed steering gear accomplished be.

Further Advantages and expedient designs are the further claims, the figure description and the drawings. Show it:

1 a schematic representation of a steering system in a vehicle, with a superposition steering gear and a servo motor for steering assistance,

2 a block diagram for performing a steering control, via which the steering wheel angle specified by the driver as a function of driving state variables and taking into account comfort and safety aspects, a Radlenkwinkel is generated, which is set via actuators in the vehicle.

This in 1 illustrated steering system 1 includes a steering wheel 2 , about which the driver has a steering wheel angle δ _L pretends that via a steering shaft 3 on a rack 7 is transferred, whereupon the steered wheels 8th a wheel steering angle δ _V established. For steering assistance - possibly also to reduce the steering torque given by the driver - is a servomotor 9 provided that an additional steering torque via a steering gear 6 feeds the rack 7 applied. The servomotor 9 is designed in particular as an electric motor, wherein a hydraulic steering assistance is also considered.

Furthermore, a superposition steering gear 4 provided, via which an additional overlay steering angle δ _M is adjustable. This additional overlay steering angle δ _M becomes the steering wheel angle δ _L , which is given by the driver, to the steering wheel angle δ _L ' superimposed. The superposition steering gear is a servomotor 5 assigned, which is expediently also designed as an electric motor.

The setting of both the optional overlay steering gear 4 as well as the steering gear 6 or the respectively associated motors 5 respectively. 9 takes place by means of actuating signals of a control and regulating device 10 depending on the state and operating variables of the vehicle and possibly also the environment.

The steering system 1 may be formed according to an advantageous embodiment as a steer-by-wire system, in which the directly mechanical penetration between the steering wheel 2 and the steered wheels 8th is interrupted. In this case is via a sensor 11 the information of the steering wheel angle set by the driver δ _L detected and the control and regulating device 10 supplied as an input signal, in which control or output signals for adjusting the steering gear 6 or the servo motor 9 be generated. This steer-by-wire system basically works without superimposed steering gear 4 However, the superimposed steering gear can also be provided as part of the steer-by-wire system.

The block diagram according to 2 illustrates the method for controlling the steering system. In a first step in the block 12 is symbolized, is first given by the driver steering wheel angle δ _L in a provisional target wheel steering angle δ ν / R, shall implemented, taking into account comfort features such as a variable steering ratio and depending on various state and operating variables of the vehicle such as the vehicle longitudinal speed v _x , the steering wheel angular velocity δ. _L and other sizes. The provisional target wheel steering angle δ ν / R, shall is used as an input to the next block 13 in which the target yaw rate ψ. _should is determined. The target yaw rate ψ. _should represents the lateral dynamics of the vehicle. In principle, however, any other state variable can also be used to determine a desired value, which contains the information about the vehicle transverse dynamics. Vehicle transverse dynamics are decisive for vehicle stability.

The target yaw rate ψ. _should is subsequently associated with an actual yaw rate ψ. _is compared, wherein the deviation between the setpoint and the actual value of a control according to block 14 is supplied. This regulation represents the third process step, in the regulation becomes the final target wheel steering angle δ _{R, shall} calculated, which should be set in the steering system. The target wheel steering angle δ _{R, shall} is supplied to the actuators in the steering system, so the servo or servo motors of the steering gear and / or the superposition steering gear. With optimal implementation of the desired wheel steering angle δ _{R, shall} , is the actually adjusting wheel steering angle δ _V identical to this setpoint.

1

steering system

2

steering wheel

3

steering shaft

4

Superimposed steering mechanism

5

servomotor

6

steering gear

7

rack

8th

front

9

servomotor

10

Rule- and control unit

11

sensor

12

block

13

block

14

block

δ _L

steering wheel angle

δ. _L

Steering wheel angle speed

δ ν / R, shall

provisional target wheel steering angle

δ _{R, shall}

final target wheel steering angle

δ _V

Actual wheel steering angle

δ _M

Superimposed steering angle

ψ. _should

Target yaw rate

ψ. _is

Actual yaw rate

V _x

vehicle speed

Claims (9)

Method for controlling a steering system in a vehicle, wherein a steering wheel angle specified by the driver ( δ _L ) as a function of vehicle state variables in a wheel steering angle ( δ _V ) on the steered wheels ( 8th ), characterized in that - in a first step, the steering wheel angle ( δ _L ) taking into account at least one vehicle state variable (v _x ) into a provisional desired wheel steering angle ( δ ν / R, shall ) is implemented, - that in a second step, the provisional target wheel steering angle ( δ ν / R, shall ) in a the transverse dynamics of the vehicle representing desired state variable ( ψ. _should ), that in a third step the desired state variable ( ψ. _should ) with a corresponding actual size ( ψ. _should ) and from the desired-actual deviation in a control a final target wheel steering angle ( δ _{R, shall} ) calculated in the steering system ( 1 ) is set. A method according to claim 1, characterized in that the transverse dynamics of the vehicle representing desired state variable, the target yaw rate ( ψ. _should ). Method according to claim 1 or 2, characterized in that the provisional nominal wheel steering angle ( δ ν / R, shall ) and the desired state variable ( ψ. _should ) can be displayed as a function of the vehicle speed (v _x ). Method according to one of claims 1 to 3, characterized in that the provisional desired wheel steering angle ( δ ν / R, shall ) and the desired state variable ( ψ. _should ) as a function of steering wheel angular velocity ( δ. _L ) are representable. Method according to one of claims 1 to 4, characterized in that the to be carried out in the first step implementation of the steering wheel angle ( δ _L ) into the provisional desired wheel steering angle ( δ ν / R, shall ) taking into account comfort aspects. Method according to claim 5, characterized in that that a variable steering ratio is selected as the comfort function, which can be represented in particular as a function of the vehicle speed (v). Steering system for carrying out the method according to one of Claims 1 to 6, with actuators for setting a wheel steering angle ( δ _V ) on the steered wheels ( 8th ) depending on the driver's steering angle ( δ _L ) taking into account vehicle state variables (v _x ), and with a control and regulating device ( 10 ) for generating actuating signals acting on the actuators. Steering system according to claim 7, characterized in that in the transmission path between the steering wheel ( 2 ) and steered wheels ( 8th ) a superposition steering gear ( 4 ) is interposed via which an overlay steering angle ( δ _M ) is producible. Steering system according to claim 7 or 8, characterized through an execution as a steer-by-wire system.