DE102011055935B4 - Method for operating a steering system of a vehicle - Google Patents

Abstract

Method for operating a steering system (1) of a motor vehicle, wherein a return for a steering means (10) of the steering system (1) is performed, characterized in that an actual slip angle velocity (β is.) Is determined, and that in a critical operating condition (20) of the vehicle a restoring moment (56; 76) for the steering means (10) in dependence on the actual float angle velocity (β is.) Is specified.

Description

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

Furthermore, the invention also relates to a computer program for a digital computing device for performing a corresponding method, as well as a control device, suitable for performing such a method and a computer program product in the form of a storage medium, on which a corresponding computer program is stored.

Methods for carrying out an active return for a steering wheel of a steering system are known. For this purpose, a desired steering wheel angular velocity is usually generated as a function of a current steering wheel angle. By comparing the target steering wheel angular velocity with the actual actual steering wheel angular velocity, a restoring torque is generated, which enables a return of the steering means or steering wheel to the middle position of the steering wheel.

Furthermore, a driving physical return is known in which the steering wheel is not in the steering wheel middle position, but the steering wheel is reset such that, for example, in the state of oversteer the steering wheel is returned in the direction of a stabilizing steering wheel angle for which a stable driving condition is expected.

It is also known that the stabilizing steering wheel angle, a slip angle of the vehicle can be assigned. Furthermore, it is known that the determination of the slip angle in the vehicle has problems. From a cost point of view, the slip angle can not be determined with sufficient accuracy or reliability on board the vehicle. The calculation effort for the slip angle is very high. Also, the construction of the chassis and / or the steering system can increase the overall effort to determine the slip angle further or even impossible.

From the DE 10 2006 019 790 A1 a method for controlling and / or controlling an electrically controllable steering is known. In this case, an assisting torque initiated by the servo unit is influenced by a corresponding control of the servo unit as a function of spatial movement processes of the vehicle. In particular, the servo unit is controlled as a function of an actual slip angle so that the steerable vehicle wheels are aligned in the actual direction of movement.

From the EP 2 208 659 B1 For example, a method for realizing an active return in a steering system is known. In the method, a current rack force is determined and a desired steering wheel angular velocity is determined in dependence on the current rack force.

The object of the invention is to provide a method for carrying out an active return, which reliably helps the driver of the vehicle to guide the vehicle from a border or transition area in a stable driving situation. The object of the invention is also to provide a computer program which implements a corresponding method, a control unit which is able to carry out such a method, and to provide a storage medium on which the computer program is stored.

The object is achieved by a method according to claim 1, by a computer program according to claim 13, by a control device according to claim 14 and by a storage medium according to claim 15. Advantageous developments are specified in the subclaims. Properties which are important for the invention can also be found in the following description and in the drawings, wherein the properties, both alone and in different combinations, can be important for the invention, without being explicitly referred to again.

Advantageously, an actual slip angle velocity is determined and used in a critical operating state of the vehicle to specify a restoring moment for a steering means. As a result, for example, waives an elaborate determination of the actual float angle and only the rate of change of the float angle, that is, the actual float angle used to determine the return torque for the steering means. Advantageously, a signal of the actual slip angular velocity is used only in or for the critical operating state, which makes good use of the fact that the signal of the actual slip angular velocity has a higher accuracy at high values than at low values.

In a particularly advantageous embodiment, the actual float angle velocity is determined from a subtraction of a yaw rate from the division of a lateral acceleration of the vehicle by the longitudinal velocity of the vehicle. As a result, a control unit present sensor signals are used to determine the actual Schwimmwinkelgeschwindigkeit in a simple manner. Furthermore, the restoring moment does not have to be determined from a rack power Therefore, the requirements are reduced in particular to the design of the steering system or the chassis. The reduced design requirements can reduce the overall steering system and chassis components costs.

In an advantageous embodiment, in the critical operating state, a desired steering-medium speed is determined as a function of the actual slip-angle velocity.

In an alternative advantageous embodiment, in the critical operating state, a desired slip angle velocity is predetermined, which is compared with the actual slip angle velocity.

In an advantageous development of the method, the target float angle velocity is set essentially at the time of entry into the critical operating state and the target float angle velocity remains substantially constant during the critical operating state. By setting at the time of entry into the critical operating state, a just stable operating state of the vehicle in terms of a still stable target slip angle velocity is set as a target state for a control in the critical operating state. The control assists the driver of the vehicle in restoring the vehicle's stable running condition as it existed when it entered critical condition.

In an advantageous development, the desired slip angle velocity is determined as a function of the actual slip angle velocity and a steering medium angle. The target slip angle velocity is set substantially at the time of entry into the critical operating state.

In an advantageous development of the method, the desired slip-angle velocity is determined as a function of the longitudinal speed of the vehicle, the lateral acceleration of the vehicle and in dependence on the steering-medium angle. Due to the fact that the target slip angle velocity is always updated, it is possible, for example, to take into account the condition of the roadway itself and changes in the condition of the roadway during the critical operating state, and the restoring torque can thereby be adapted accordingly.

In an advantageous embodiment of the method, a further return torque for the steering means is specified in a normal operating state of the vehicle and it is then detected starting from the normal operating state of the critical operating condition when the actual slip angle velocity reaches or exceeds a first limit. The actual float velocity is thus advantageously used to identify the critical operating condition.

In an advantageous development of the method, starting from the critical operating state, the normal operating state is recognized when the actual float angle velocity reaches or falls below a second limit value, the second limit value for the actual float angle velocity being smaller than the first limit value. Thus, in the sense of debouncing prevents unwanted switching between the critical operating state and the normal operating state and forth.

In an advantageous development of the method, the target slip angle velocity for the critical operating state is essentially determined to the first limit value. So that we set in a simple way, the target slip angle velocity and thus detects the just stable operating condition of the vehicle.

In an advantageous development of the method, a factor is determined as a function of the lateral acceleration and the longitudinal speed. The result of the comparison in the sense of the control difference is linked to the factor and the restoring moment is specified as a function of the link. By determining the factor, for example, the condition of the roadway or changes in the condition of the roadway during the critical state can advantageously be taken into account. In general, the changes in the vehicle dynamics which are essential for the restoring torque during the critical operating state are included in the specification of the restoring torque.

Other features, applications and advantages of the invention will become apparent from the following description of exemplary embodiments of the invention, which are illustrated in the figures of the drawing. All described or illustrated properties, alone or in any combination form the subject matter of the invention, regardless of their summary in the claims or their dependency and regardless of their formulation or representation in the description or in the drawing. It will be used for functionally equivalent sizes in all figures, even with different embodiments, the same reference numerals.

Hereinafter, exemplary embodiments of the invention will be explained with reference to the drawings. In the drawing show

1 a schematic representation of a steering system in a vehicle;

2 a one-track model of the vehicle;

3 a schematic state transition diagram;

4 a schematic block diagram of a preferred embodiment of the determination of an actual Schwimmwinkelgeschwindigkeit;

5 a schematic block diagram of an embodiment of a driving rewind;

6 a schematic block diagram of a preferred embodiment of the determination of a desired steering means speed;

7 a schematic block diagram of another embodiment of the driving rewind;

8a a schematic block diagram of an embodiment of the determination of a target Schwimmwinkelgeschwindigkeit; and

8b a schematic block diagram of another embodiment of the determination of the Soll Schwimmwinkelgeschwindigkeit.

1 shows a schematic representation of a steering system 1 in a vehicle. The steering system 1 includes a steering device 2 and a controller 3 , In the control unit 3 is a digital computing device 4 arranged, for example, via a data line with a storage medium 5 connected is. The methods described below can be used as a computer program for the digital computing device 4 be executed. The digital computing device 4 is suitable for carrying out the methods described below as a computer program. The digital computing device 4 includes in particular a microprocessor. The computer program is on the storage medium 5 stored.

Via a signal line 6 is the control unit 3 connected to a torque controller, for example, as an electric motor 7 is formed, so that a control of the electric motor 7 through the control unit 3 is possible. The electric motor 7 acts via a gearbox 8th on a torsion bar 9 , On the torsion bar 9 is a steering means 10 , For example, a steering wheel arranged. Instead of the steering wheel shown, the steering means 10 also different, for example, be designed as a joystick.

The steering device 2 also has a steering gear 11 on, which is designed as a rack and pinion steering gear. The steering gear 11 is about a pinion 12a and a rack 12b on each side of the vehicle with a steering linkage 13 , each preferably with a front wheel 14 cooperates, connected. On the torsion bar 9 is between the gearbox 8th and the steering means 10 a sensor 15 arranged, by means of the signal line 16 the current position of the steering means 10 to the control unit 3 transmitted. This in 1 illustrated steering system 1 represents one of many possible embodiments for the implementation of the methods explained below. In a so-called steer-by-wire system, for example, there is no direct mechanical connection between the steering means 10 and the steering linkage 13 ,

2 shows a Einspurmodell of the considered vehicle with a longitudinal axis x by the angle δ _f adjusted front wheel 14 , Along the longitudinal axis x is a center of gravity SP of the vehicle and the rear wheel 17 of the vehicle. Starting from the center of gravity SP, a speed v of the vehicle is plotted. The speed v of the vehicle can be divided into its components longitudinal speed v _x and transverse speed v _y . Between the speed v of the vehicle and the longitudinal axis x of the vehicle, a slip angle β is plotted. A yaw rate Ψ. is schematically drawn and describes the rotational angular velocity of the vehicle about its vertical axis, not shown, which passes through the center of gravity SP. A lateral acceleration a _y , not shown, is oriented or aligned in the one-track model like the lateral velocity v _y .

3 shows a schematic state transition diagram 18 with a critical operating condition 20 of the vehicle and a normal operating condition 22 of the vehicle. The state transition diagram 18 is used to operate the steering system 1 of the vehicle, in particular of a motor vehicle. The state transition diagram 18 serves in particular to an active return for the steering means 10 of the steering system 1 perform. The active return generally comprises that of the steering system 1 independently performed return of the steering means 10 or the structure of a counter-torque to that of the driver on the steering means 10 applied torque toward a specific steering means position, the specific orientation of the front wheels 14 assigned.

The critical operating condition 20 is preferably an operating state in which an oversteer of the vehicle is present. An oversteer of the Vehicle means that the rear of the vehicle breaks out, with the rear of the vehicle moving outward in the curve. In the critical operating condition 20 becomes one of the 5 and 7 further explained restoring moment 46 . 76 for the steering means 10 depending on one based on the 4 closer explained actual float velocity β. _is given. The methods presented here serve, in particular, to assist the vehicle driver in keeping the vehicle in the critical operating state 20 to be able to control better. The vehicle driver is assisted in keeping the vehicle in a stable driving dynamic state or transferring it into this.

In the normal operating condition 22 , in which the vehicle is in a stable driving condition, is another return torque for the steering means 10 given in the context of the active return in the normal operating condition 22 the steering means 10 to perform a position that is essentially a straight ahead of the front wheels 14 equivalent.

Under the specification of the return torque 46 . 76 or the further restoring moment is the supply of the same via the line 6 towards the momentum of the 1 to understand. The restoring moment 46 . 76 or the additional restoring torque can also be specified as a partial moment of a total torque.

Starting from the normal operating condition 22 becomes the critical operating condition 20 according to the arrow 24 then recognized or is then in the critical operating condition 20 changed when the actual float angle velocity β. _is reached or exceeds a first limit. The first limit value can be selected permanently or can be determined as a function of specific operating or driving dynamics parameters with the aid of a characteristic map or a characteristic curve.

According to an arrow 26 gets from the critical operating condition 20 in the normal operating condition 22 changed or is based on the critical operating condition 20 the normal operating condition 22 then recognized when the actual float velocity β. _is reached or falls below a second threshold, wherein the second threshold for the actual Schwimmwinkelgeschwindigkeit β. _is less than the first limit. For the change between the critical operating state 20 and the normal operating condition 22 according to the arrows 24 and 26 Of course, other than the above-described conditions in the sense of the first and second limit can be used.

The 4 shows a schematic block diagram 28 a preferred embodiment of the determination of the actual Schwimmwinkelgeschwindigkeit β. _is the rate of change of the slip angle β off 2 represents. One block 30 are the lateral acceleration a _y , the longitudinal velocity v _x and the yaw rate Ψ. fed. The lateral acceleration a _y , longitudinal velocity v _x and the yaw rate Ψ. were already based 2 explained in detail and represent driving dynamics parameters that the control unit 3 available. Depending on the lateral acceleration a _y , the longitudinal velocity v _x and the yaw rate Ψ. the block generates 30 the actual float velocity β. _is . Preferably, the block generates 30 the actual float velocity β. _is by means of the following equation 1, wherein the actual float angle velocity β. _is essentially a subtraction of the yaw rate Ψ. is determined by dividing the lateral acceleration a _y by the longitudinal velocity v _x .

5 shows a schematic block diagram 32 an embodiment of a physical return, during the critical operating condition 20 is performed. One place 34 becomes a target steering-medium speed δ. _{LR, should} and an actual steering speed δ. _{LR, is} fed and at a control difference 36 linked, wherein preferably the actual steering-medium speed δ. _{LR, is} of the target steering speed δ. _{LR, should be} subtracted. The rule difference 36 becomes common with a factor 38 a job 40 fed and to another control difference 42 linked, where the control difference 36 with the factor 38 is multiplied. The further control difference 42 becomes a regulator 44 fed. Of course, only the control difference 36 instead of the further control difference 42 the controller 44 be supplied.

The regulator 44 generates the restoring moment 46 for the steering means 10 in the critical operating condition 20 of the vehicle. The restoring moment 46 becomes an actuator 48 supplied, wherein the actuator 48 for example, the moment adjuster the 1 equivalent. Alternatively, the restoring torque 46 also be a partial moment of the momentum generator supplied total torque. The actuator 48 generates a manipulated variable 50 that the controlled system 52 is supplied. The manipulated variable 50 corresponds for example in the 1 by the torque adjuster actually on the torsion bar 9 applied moment. Under the controlled system 52 is the entire system of vehicle and driver too subsume. The controlled system 52 then generates an actual steering means speed δ. _{LR, is, act} , which is a measuring element 54 is supplied. The measuring element 54 corresponds to 1 the sensor 15 or the sensor 15 together with the control unit 3 , With the sensor 15 the steering center angle is measured and the control unit 3 can from the time course of the measured steering means angle, the actual steering means speed δ. _{LR, is} how they are in 5 from the measuring element 54 is generated.

The factor 38 is from a block 56 generated. The block 56 determines the factor 38 for example by means of a map as a function of the lateral acceleration a _y and the longitudinal velocity v _{x of} the vehicle. The result of the comparison in the sense of the rule difference 36 becomes with the factor 38 linked and the restoring moment 46 is dependent on the link, that is, depending on the further control difference 42 , given.

6 shows a schematic block diagram 58 a preferred embodiment of the determination of the desired steering means speed δ. _{LR, shall} . One block 60 the actual float velocity β. _is and the steering center angle δ _LR supplied. Depending on the supplied quantities, the block determines 60 the target steering-medium speed δ. _{LR, shall} . This determines the block 60 the target steering-medium speed δ. _{LR, is} to be dependent on the actual float velocity .beta. _is . In conjunction with the block diagram 32 out 5 becomes the target steering-medium speed δ. _{LR, should} with the actual steering speed δ. _{LR, is} compared and depending on the result of the comparison becomes the restoring moment 46 for the steering means 10 specified.

In 7 is a schematic block diagram 62 another embodiment of the driving physical return for the critical state 20 shown the vehicle. One place 64 become a target slip angle velocity β. _should and an actual float velocity β. _is supplied. The spot 64 generates a control difference 66 that share a factor 68 a job 70 is supplied. The spot 70 generated as a function of the control difference 66 and the factor 68 another rule difference 72 that a regulator 74 is supplied. The regulator 74 generates the restoring moment 76 that is an actuator 78 is supplied. The actuator 78 generates a manipulated variable 80 that of a controlled system 82 is supplied. The controlled system 82 generates an actual present float angle velocity β. _{is, act} , with the help of a measuring element 84 detected and as actual swimming angle velocity β. _is in the control unit 3 is present. One block 86 are used to determine the factor 68 the longitudinal velocity v _x and the lateral acceleration a _y supplied. The explanations regarding the elements of the 5 with the reference numerals 34 to 56 apply equally to the elements of the 7 with the reference number 64 to 86 , According to the 7 becomes in the critical operating condition 20 the target float velocity β. _{should be} specified, the target float velocity β. _shall be with the actual float velocity β. _is compared and depending on the result of the comparison becomes the restoring moment 76 for the steering means 10 specified.

In a preferred embodiment, the target slip angle velocity β. _should essentially at the time of entry into the critical operating condition 20 set and the target slip angle velocity β. _should remain during the critical operating state 20 until returning to normal operating condition 22 essentially constant. In a development, the target float velocity β. _intended for the critical operating condition 20 essentially on the closer to the 3 described first limit determined. In another development, the first limit value is variable in time and is determined, for example, by means of time-variable variables from a characteristic field or a characteristic curve. At the time of entering the critical operating condition, the target slip angular velocity is set at the value of the first threshold present at that time.

8a shows a schematic block diagram 88 an embodiment of the determination of the target slip angle velocity β. _should . One block 90 the actual float velocity β. _is and the steering center angle δ _LR supplied. Furthermore, the block 90 supplied in a manner not shown a time signal, wherein the time signal to the block 90 the time to enter the critical operating state 20 signaled. The block 90 generated for the critical operating state 20 from the actual float angle velocity β. _is and the steering medium angle δ _LR the target slip angle velocity β. _should and sets this essentially at the time of entry into the critical operating state, wherein the target slip angle velocity β. _should during the critical operating state 20 remains essentially constant. The block 90 thus ensures that the target float velocity β. _{should be} up to the exit from the critical operating condition 20 is maintained at a substantially constant value.

8b shows a schematic block diagram 92 a further embodiment of the determination of the target slip angle velocity β. _should . One block 94 the longitudinal velocity v _x , the lateral acceleration a _y and the steering-medium angle δ _{LR are} fed, the block 94 as a function of the quantities supplied, the desired slip angle velocity β. _{should be} determined. To determine the target slip angle velocity β. _should depend on the supplied quantities, the block 94 use individual characteristics or maps. In this further embodiment, the determination of the target slip angle velocity β. _shall be the target float velocity β. _should always be continuously updated depending on the quantities supplied during the critical operating condition. A change in the supplied quantities thus leads to a change in the desired float angle velocity β. _should during the critical operating condition 20 ,

Claims (15)

Method for operating a steering system ( 1 ) of a motor vehicle, wherein a return for a steering means ( 10 ) of the steering system ( 1 ) Is carried out, characterized in that an actual slip angular velocity (β. _Is) is determined, and that (in a critical operating state 20 ) of the vehicle a restoring moment ( 56 ; 76 ) for the steering means ( 10 ) (In function of the actual slip angle β speed. _Is) is set. A method according to claim 1, characterized in that the actual float angle velocity (β _is ) by means of the equation

is determined, where Ψ. a yaw rate, a _{y is} a lateral acceleration of the vehicle, and ν _{x is} a longitudinal speed of the vehicle. Method according to claim 1 or 2, characterized in that in the critical operating state ( 20 ), A target steering means speed (δ. _{LR, setp)} (in function of the actual-slip angle velocity β. _Is), it is determined that the target steering means speed (δ. _{LR, soll)} with an actual steering means speed (δ. _{LR is} ) and that, depending on the result of the comparison, the restoring moment ( 56 ) is given. Method according to claim 1 or 2, characterized in that in the critical operating state ( 20 ) A target slip angular velocity (β. _Should be given), that the target slip angular velocity (β _should.) (With the actual slip angular velocity (β. _Is) is compared, and that in dependence on the result of the comparison, the restoring moment 76 ) is given. A method according to claim 4, characterized in that the target slip angular velocity (β _should.) Substantially at the time of entry (in the critical operating state 20 ), and that the target slip angle velocity (β, _soll ) during the critical operating state ( 20 ) remains substantially constant. A method according to claim 5, characterized in that the target slip angular velocity (β _should.) As a function of the actual slip angular velocity (β _is.) And a steering center angle (δ _LR) is determined. A method according to claim 4, characterized in that the target slip angular velocity (β. _Soll) as a function of the transverse acceleration (a _y), the longitudinal velocity (ν _x), and a steering center angle (δ _LR) is determined. Method according to one of the preceding claims, characterized in that in a normal operating state ( 22 ) of the vehicle a further restoring moment for the steering means ( 10 ) and that starting from the normal operating state ( 22 ) the critical operating condition ( 20 ) Is then detected when the actual slip angular velocity (β. _Is) reaches a first limit value or above. Method according to claim 8, characterized in that starting from the critical operating state ( 20 ) the normal operating state ( 22 ) Is then detected when the actual slip angular velocity (β. _Is) reaches a second threshold value or falls, and that the second limit value for the actual slip angular velocity (β. _Is) is smaller than the first threshold. Method according to one of claims 4 or 5 and one of claims 8 or 9, characterized in that the target slip angle velocity (β, _soll ) for the critical operating state ( 20 ) is determined substantially at the first limit. Method according to one of claims 3 to 10, characterized in that a factor ( 38 ; 68 ) is determined as a function of a lateral acceleration (a _v ) and a vehicle speed (ν _x ) that the result of the comparison of Target steering means speed (δ. _{LR, soll)} with the actual steering means speed or the target attitude angle speed (δ. _{LR is)} (β. _Soll) with the actual slip angular velocity (β _is.) (By the factor 38 ; 68 ) and that, depending on the link, the restoring moment ( 56 ; 76 ) is given. Method according to one of the preceding claims, characterized in that the critical operating state ( 20 ) comprises an operating state of the oversteer. Computer program for a digital computing device ( 4 ), which is adapted to carry out the method according to any one of the preceding claims. Control unit ( 3 ) for a steering system ( 1 ) of a motor vehicle that is equipped with a digital computing device ( 4 ) is provided in particular a microprocessor on which a computer program according to claim 13 is executable. Storage medium ( 5 ) for a control unit ( 3 ) of a steering system ( 1 ) of a motor vehicle according to claim 14 on which a computer program according to claim 13 is stored.

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