WO2010028897A1

WO2010028897A1 - Method for adjusting a steering system in a vehicle

Info

Publication number: WO2010028897A1
Application number: PCT/EP2009/059296
Authority: WO
Inventors: Ernst Schermann; Ralph Koestlmeier; Thomas Haeussler
Original assignee: Robert Bosch Gmbh
Priority date: 2008-09-10
Filing date: 2009-07-20
Publication date: 2010-03-18
Also published as: DE102008041962A1

Abstract

In a method for adjusting a steering system in a vehicle, a supporting torque (Ms) is supplied to the steering system (1) via a servo-unit as a function of a vehicle state variable. A cross-dynamic state variable (ay) is taken into consideration as the state variable, wherein the amount of the supporting torque is selected such that the steering wheel torque (ML) to be applied by the driver linearly increases together with the cross-dynamic state variable.

Description

description

title

Method for adjusting a steering system in a vehicle

The invention relates to a method for adjusting a steering system in a vehicle according to the preamble of claim 1.

State of the art

US Pat. No. 6,499,559 B2 describes a steering system in a motor vehicle which is equipped with an electric servomotor for steering torque assistance, by way of which a support torque can be fed into the steering system. Due to the targeted control of the servo motor can be a from the

Driver independent torque can be generated, which is perceived by the driver by a correspondingly reduced or increased manual steering torque. For example, with increasing speed, the assist torque is reduced or directed counter to the steering angle excursion, causing the driver to perceive a hardening of the steering motion and to apply a higher manual steering torque.

Disclosure of the invention

Based on this prior art, the invention is based on the object to design a steering system in a vehicle so that the driver receives information about the current state of the vehicle via the steering wheel torque. This object is achieved with the features of claim 1. The dependent claims indicate expedient developments.

The method according to the invention is applicable to steering systems in vehicles which are equipped with an adjustable servo unit for steering torque assistance, it being possible for an assist torque to be fed into the steering system via the servo unit as a function of a vehicle state variable. According to the invention, a lateral-dynamic state variable is taken into account as the state variable, wherein the magnitude of the assisting moment, which is fed into the steering system by the servo unit, is selected such that the steering wheel torque to be applied by the driver increases linearly or progressively with the lateral dynamic state variable. The term "progressive" is understood to mean an increase with increasing steepness or increasing gradient.

In contrast to steering adjustments, in which the steering torque increases linearly, in particular as a function of the lateral acceleration only during relatively small lateral acceleration values, whereas with increasing lateral acceleration, the increase of the steering wheel torque usually degressive and finally falls again, a continuous linear increase is selected according to the invention. This linear increase gives the driver a better, more harmonious steering feel, since the increase in the steering wheel torque is also subjectively correlated with the increase in lateral dynamic state variable and perceived by humans accordingly. According to a preferred embodiment, the lateral-dynamic state quantity is the lateral acceleration, whereby in principle other transverse dynamic state variables such as, for example, the yaw rate also come into consideration. The lateral acceleration is registered by the driver directly via human sensory perceptions, as well as the invention linear increase of the steering wheel torque, which the driver has to raise. This correlation gives a better driving experience. But even in situations in which the lateral acceleration or the other lateral dynamic state variable is perceived by the driver only in a reduced subjective manner, for example by partial compensation via a roll compensation in the vehicle, the driver receives additional information through the linearly increasing steering wheel torque. A higher steering torque is accompanied by an increase in the lateral dynamic state variable, after which the driver with appropriate countermeasures, such as reducing the

Vehicle speed while driving through curves, can respond. The adjustment of the steering system according to the invention thus also contributes to driving safety.

The linear increase of the steering wheel torque is expediently only in stable driving situations. Advantageously, the linear steering wheel torque increase is performed only in the event that the vehicle is not oversteering. In addition, according to a further advantageous embodiment, the linear increase is performed only until the beginning of a strong understeer of the vehicle. Both the oversteering and the understeering can be determined during vehicle driving using the on-board sensor system, for example by evaluating the yaw rate, the slip angle and / or the slip angle. For example, a comparison between the desired and the actual yaw rate can be used and both model-based and measured slip angles or slip angles can be taken into account.

The linear increase of the steering wheel torque is preferably carried out until a state variable limit value of the lateral dynamic state variable is reached. In the case of taking into account the transverse acceleration, this is an acceleration limit value that is advantageously determined during operation and, in particular, is set to the beginning of a severe understeer of the vehicle. Understeer, as stated above, is at the model level or at the level - A -

measured state variables such as the slip angle and can be adapted to the current driving situation.

However, it is also possible to set the limit value for the lateral-dynamic state variable to a fixed value or to a value that depends on the current road surface or other environmental situations. For dry roads, for example, a yaw acceleration limit of about 9m / s ² comes into consideration, this value may be worse

Weather conditions, for example, be reduced in wet or at temperatures below 0 °.

After reaching the state quantity limit, the linear increase of the steering wheel torque is advantageously terminated. In

Consideration is in particular a drop in the steering wheel torque with increasing lateral dynamic state variable, preferably the support torque of the servo unit is lowered within a short time, ie with a high gradient to a smaller value. This smaller value of the assist torque preferably results from a basic function implemented in the steering system for the course of the assist torque as a function of the lateral dynamic state variable, the course of this basic function increasing linearly only in the case of small values of the transverse dynamic state variable, with the exceeding of a lower limit value up to Reaching a maximum degressive increases and then decreases again after exceeding the maximum. The linear function according to the invention is added to the basic function as a compensation function, so that in particular in the course of the degressive increase of the basic function via the compensation function a progressively increasing proportion is added. When the limit value is reached, however, the total value of the steering wheel torque with the strong gradient falls back to the basic function, thus overriding the compensation function. In order to achieve the linear increase of the steering wheel torque, both a feedforward control without control comes into consideration, which is based in particular on the lateral dynamic state variable, preferably on the lateral acceleration, as well as a regulated setting in which in particular the desired and actual values of the steering wheel torque subjected to a regulation become.

The inventive method is implemented in a control or control device in the steering system or in the vehicle. The steering system preferably comprises as a servo unit an electric servomotor (Electrical Power Steering - EPS), via which the positive or negative assist torque is fed into the steering system. In principle, however, other versions of servo units come into consideration, in particular electro-hydraulic servo units or possibly also hydraulic servo units.

Further advantages and expedient embodiments can be taken from the further claims, the description of the figures and the drawings. Show it:

1 is a schematic representation of a steering system in a vehicle,

2 shows a vehicle during cornering in plan view,

3 is a graph showing the course of the steering wheel torque as a function of the lateral acceleration,

4 is a flowchart for setting a

Steering wheel torque, which depends linearly on the lateral acceleration.

The steering system 1 shown in FIG. 1 in a motor vehicle comprises a steering handle 2 designed as a steering handle, a

Steering shaft 3, a steering gear 4 and a steering linkage 5 and an electric servomotor 7. About the steering system 1 is a Preset by the driver steering wheel angle δ _L in a wheel steering angle δ _{v implemented} on the steerable front wheels 6 of the vehicle. Via the electric servomotor 7, a positive or negative assisting torque M _s can be fed into the steering system. The steering wheel torque M _{L to be} applied by the driver is influenced by the assisting torque M _s , wherein a positive assisting torque M _s leads to a reduction of the steering wheel torque M _L and a negative assisting torque leads to an increase of the steering wheel torque.

Due to the design of the servo unit as an electric servo motor 7 is an electrical power steering (EPS). In principle, however, alternative designs for servo units come into consideration, in particular an electro-hydraulic servo unit.

In Fig. 2, the vehicle 8 is shown, which follows a predetermined lane 9, in the exemplary embodiment, a curve. In the center of gravity 10 of the vehicle when cornering, the lateral acceleration a _y .

In Fig. 3 is a graph showing the course of the steering wheel torque M _L as a function of the lateral acceleration a _y . With a solid stitch of the steering torque curve 11 is shown without so-called compensation function, in which up to a lower limit, which is about 4 m / s ² in the embodiment, a linear increase of the steering wheel torque M _{L is present} as a function of the lateral acceleration a _y . Between the lower limit and an upper limit a _y , _{Limr in} the _exemplary embodiment at about 9 m / s ² , the increase of the steering wheel torque M _L according to the steering torque curve 11 is degressive and increases with increasing lateral acceleration always weaker. At the upper limit a _y , _L i _m , the maximum of the steering wheel torque M _{L is achieved} according to curve 11. In the course of the steering wheel torque M _L decreases again. The steering torque curve 11, which is set without compensation function, is achieved by a corresponding application of the electric servomotor with a support torque M _s . It is thus at the steering wheel torque M _L to the resulting torque, which must be applied by the driver via the steering wheel.

Dashed line 12 shows the steering torque curve with compensation function. The steering torque curve 12 is designed as the straight line of origin, the section between the lower and upper transverse acceleration limits has the same slope as the lower section between the origin and the lower limit. In comparison to the steering torque curve 11 without compensation function, a clear increase in steering wheel torque M _{L is} achieved until reaching the upper limit value a _y , _L i _m , so that the driver also has to apply an increasing steering wheel torque M _L with increasing lateral acceleration a _y . Here, the hatched area between the curve 11 and the curve 12 represents the compensation function 13, which characterizes an additional steering torque, which is generated via a corresponding setting of the corresponding servomotor and superimposed on the basic function according to the steering torque curve 11.

With the achievement of the upper transverse acceleration limit a _y , _L i _m and the steering torque curve 12 is compensated with compensation function within a short time until reaching the steering torque curve 11 without compensation, which is marked on the section 12a. Background of this strong high-gradient waste is the fact that in the area of the upper

Transverse acceleration limit a _y , _L i _m the vehicle in increased understeer device, which should be brought to the driver by a drop in the steering wheel torque M _L to the knowledge. By returning the steering torque curve to the curve 11 without compensation, the compensation function 13 is disabled. FIG. 4 shows an exemplary embodiment with method steps for setting the linear steering wheel torque increase as a function of the lateral acceleration. The linear torque function is based on a non-linear torque function, which is identified in FIG. 3 with the torque curve 11. The non-linear torque function f _nl as a function of the lateral acceleration a _y is predetermined according to method step V 1 via a corresponding application of the servomotor. Starting from this nonlinear moment function, the superimposition takes place

Setting the linear torque function, as shown in Fig. 3 with the curve 12 is drawn.

However, the linear torque function assumes that the vehicle is not in a state of oversteer. In order to determine this, according to method step V2, a query is started as to whether, for example, the current slip angle β falls below an assigned slip angle oversteer limit ß limit, o. If this is not the case, then the no-branching ("n") is returned to the first method step V1, since the vehicle is in the state of oversteer and accordingly no linear dependence of the steering wheel torque M _L on the lateral acceleration is to be set; it is the previously set nonlinear function retained with degressive increase of the steering wheel torque according to step Vl.

Otherwise, the vehicle is not in the state of oversteer and it is the yes-branching ("y") proceeding to the next step V3, in which a

Check is made whether the vehicle is in the state of understeer. To this end, it is queried whether the current float angle ß an associated Schwimmwinkel- understeer limit ß _G Conference, _u falls below. If this is not the case, there is understeer and this will be the

Branching again returned to the first step Vl. Otherwise, there is no understeer or only Understeer within a permissible level before and it is the yes-branch following proceeding to the next step V4.

The float angle limits ß _G Conference, o and p _G Conference, _and for oversteer and understeer probably differ in terms of their signs and their absolute amount.

In step V4 is superimposed with a compensation function, a linear steering torque increase as

Origin straight line as a function of the lateral acceleration a _y according to the function M _L = f _λ (a _y ) set. The determined linear torque increase is realized by a corresponding application of the electric servo motor.

In the next step V5 a query is started, whether the current transverse acceleration value a _y an upper limit value a _y, i _L _m below. This upper lateral acceleration limit a _y , _L i _m marks the beginning of the strong understeer. If this limit is reached or exceeded, the no-branch is returned following the first method step Vl, the linear torque increase is aborted and it is returned to the non-linear function curve for the steering wheel torque. Otherwise, the lateral acceleration limit a _y , _L i _m is not yet reached and it is the yes branch following proceeding to step V4 and determined another value for the linear torque increase in the steering wheel torque.

Claims

claims

1. A method for adjusting a steering system in a vehicle, wherein depending on a vehicle state variable via a servo unit a support torque (M _s ) in the steering system (1) is fed, characterized in that as a state variable a lateral dynamic state variable (a _y ) is taken into account, wherein the magnitude of the assist torque (M _s ) is selected so that the steering wheel torque (M _L ) to be applied by the driver increases linearly or progressively with the lateral dynamic state quantity (a _y ).

2. The method according to claim 1, characterized in that the lateral dynamic state variable (a _y ) is the vehicle lateral acceleration (a _y ).

3. The method according to claim 1 or 2, characterized in that the linear increase of the steering wheel torque (M _L ) is performed only until reaching a state quantity limit value (a _y , _L im).

4. The method according to claim 3, characterized in that with the achievement of the state quantity limit value (a _y , _L im) the assist torque (M _s ) is selected so that the steering wheel torque (M _L ) decreases with further increasing lateral dynamic state variable (a _y ) ,

5. The method according to claim 4, characterized in that with the achievement of the state quantity limit value (a _y , _L im) the support torque (M _s ) is lowered with a high gradient to a smaller value.

6. The method according to any one of claims 3 to 5, characterized in that the state quantity limit value (a _y , _L im) is set to the onset of severe understeer of the vehicle (8).

7. The method according to any one of claims 1 to 6, characterized in that the linear increase of the steering wheel torque (M _L ) is based on an unregulated control.

8. The method according to any one of claims 1 to 7, characterized in that the linear increase of

Steering wheel torque (M _L ) a control of the steering wheel torque (M _L ) is based.

9. The method according to any one of claims 1 to 8, characterized in that the linear increase of

Steering wheel torque (M _L ) is performed only in the event that the vehicle (8) is not overdriven.

10. The method according to any one of claims 1 to 9, characterized in that the understeer / oversteer of the vehicle (8) based on the yaw rate, the slip angle and / or the slip angle (ß) is determined.

11. regulating or control device for carrying out the method according to one of claims 1 to 10.

12. Steering system in a vehicle with a control or control device according to claim 11.

13. Steering system according to claim 12, characterized in that the servo unit is designed as an electric servomotor.