DE102004048495A1 - Method for improving the operation of a vehicle steering and vehicle steering - Google Patents

Abstract

In a method for improving the operation of a vehicle steering system, it is provided that an error or a deviation in an association between a measured or determined or estimated steering wheel angle and an actually detected or determined or estimated pivoting angle, which describes a position of pivotable vehicle wheels, is determined, and that a detected assignment error or a detected assignment deviation between the steering wheel angle and the pivoting angle is compensated.

Description

The The invention relates to a method for improving the operation a vehicle steering and on a vehicle steering system for motor vehicles, with an operable by the driver of the motor vehicle steering handle and one of the steered vehicle wheels associated actuator, which is operatively connected to the steering handle and by means of the optionally further elements, e.g. Tie rods and toe levers that steered vehicle wheels to set a desired Steering angle are pivotable, and which vehicle steering a Device for determining a steering wheel angle of the steering handle and a pivot angle, which is the position of the pivotable vehicle wheels describes.

Superposition steering systems, also denoted by the abbreviation "ESAS" are known. With the help of an electric motor and a superposition gear is it possible independently From the driver to superimpose an additional steering angle to the driver's steering angle.

The basic structure of a superposition steering is for example in the DE 197 51 125 A1 or DE 199 05 433 A1 shown.

It The object of the invention is the operation of a vehicle steering system to improve and a vehicle steering of the type mentioned indicate which ensures that the position of the steered vehicle wheels by a by the driver the steering wheel corresponds to the specified steering request.

The Invention solves this task by providing a vehicle steering with the characteristics of the independent Claims.

Especially advantageous embodiments of the invention are given in the dependent claims.

For the invention It is therefore essential that in the process an error or a deviation in an association between a measured or determined or estimated Steering wheel angle and one actually detected or determined or estimated pivot angle, the describes a position of pivotable vehicle wheels, it is determined and that a detected allocation error or a recognized allocation error balanced between the steering wheel angle and the pivot angle becomes.

To The invention provides that the steering wheel angle is measured becomes.

It is according to the invention also provided that the pivot angle is measured.

It is according to the invention provided that a mapping error or a mapping error is compensated by a measure the to no unwanted, a driver of the vehicle irritating steering movement leads.

It is according to the invention provided that a mapping error or a mapping error is compensated by a compensatory movement, the first Steering movement by the driver takes place after a journey.

To The invention uses the method for superposition steering.

According to the invention is a Assignment error or a mapping error offset by a compensation movement by means of a superposition function of the superposition steering.

The Task is also solved by vehicle steering for motor vehicles, with an operable by the driver of the motor vehicle steering handle and one of the steered vehicle wheels associated actuator, which is operatively connected to the steering handle and by means of the optionally further elements, e.g. Tie rods and toe levers that steered vehicle wheels to set a desired Steering angle are pivotable, and which vehicle steering a Device for determining a steering wheel angle of the steering handle and a pivoting angle, which is the position of the pivotable vehicle wheels describes, which is characterized in that the vehicle steering has a fault detection unit, by means of an error or a deviation in an association between the steering wheel angle and the Swiveling angle is determined, and that the vehicle steering a Compensation unit, by means of the assignment error or the allocation variance is cleared.

To The invention provides that the vehicle steering a Steering wheel angle sensor and a sensor for detecting the pivoting angle having.

It is according to the invention provided that the vehicle steering is a superposition steering and that is an allocation error or misalignment by an overlay actuator the superposition steering is compensated.

The term "superposition steering" means Tet here a steering system in which a driver input of the steering angle by a further angle (additional steering angle) in accordance with other variables, in particular driving dynamics variables, can be superimposed by means of a Überlagungsaktuators.

As overlay actuator is preferably an electric actuator, in particular an electric motor used on a superposition gearbox acts and set the additional steering angle largely independent of the driver can.

The electric motor driven superposition gear is preferably between a torsion bar of a steering valve (Torsionsstab) and a steering gear or a pinion of a rack and pinion steering arranged.

Advantageous is still in this electromechanical powertrain mechanical locking and / or a self-locking design of the superposition gearing intended. This ensures that one, for applying an additional steering angle required, rotary motion of the electric motor only by the setting a corresponding engine torque, and not an attacking one Engine load torque (e.g., driver or jerk) is made can be.

The structure and function of the method according to the invention and of the vehicle steering system will now be described with reference to FIGS. 1 to 4 ) explained in more detail by way of example.

It demonstrate:

1 a schematic representation of a superposition steering with a control according to the invention,

2 a block diagram of a control concept for an intervention of a vehicle dynamics controller,

3 a block diagram of a control concept for compensating a steering angle error position, and

4 a plot of a rise limit function.

The basic structure of an ESC (Electric Steer Assisted Steering) with a control according to the invention is in 1 shown schematically.

The superposition gearbox ( 1 ) is here in a superposition steering ( 2 ) in the split steering column ( 3 ) a conventional power steering ( 4 ) built-in. By means of a motor ( 5 ) can by the superposition gear ( 1 ) an additional or reduced steering angle ( 6 ) on the front wheels ( 7 ) are generated (variable steering ratio).

The steering angle resulting from the variable steering ratio is controlled by a 8th ), which the electric motor ( 5 ) controls. The controller ( 8th ) signals from rotational angle sensors ( 9 . 10 ), by means of which the angle of rotation δ _H ( 11 ) of the steering column ( 3 ) in front of the torsion bar ( 13 ) (Torsionsstab) of the steering valve ( 14 ) and the angle of rotation after the superposition gear ( 1 ), which determines the pivoting angle of the wheels 6 . 7 indicates to be detected. The pivoting angle is defined as the angle of rotation δ _R ( 15 ) of the pinion ( 32 ) ("Pinion angle") of the steering gear ( 31 ) detected.

The driver uses a steering wheel ( 29 ) set steering wheel angle δ _H ( 11 ) preferably with a steering wheel angle sensor used as standard in vehicles with a vehicle dynamics control system (ESP systems) ( 9 ) detected.

Between steering wheel angle δ _H ( 11 ) and an input angle δ _T ( 12 ) of the superposition gearing ( 1 ) exists depending on the stiffness of the torsion bar ( 13 ) (Torsionsstabs) of the steering valve ( 14 ) and applied by the driver steering torque a differential angle.

In addition to the rotation angle of the pinion ( 32 ) of the steering gear ( 31 ), the "pinion angle" δ _R ( 15 ), with a third sensor ( 33 ) also the motor angle δ _Mot ( 34 ) of the motor ( 5 ) detected. The requirements for accuracy and resolution for the sensors ( 10 . 33 ) when detecting the angle of rotation δ _{R of} the pinion ( 33 ) and the motor angle δ _Mot ( 34 ) are higher than the steering wheel angle sensor ( 9 ).

The hydraulic pressure for the conventional power steering ( 4 ) is controlled by a pump ( 16 ), which here via a drive ( 17 ) with the drive motor ( 18 ) is connected to a vehicle. Advantageously, it is alternatively provided that the pump ( 16 ) is driven by an electronically controlled motor (electric motor) as needed.

Driver assistance is provided by a hydraulic cylinder ( 19 ), which has two chambers ( 20 . 21 ), which by a hydraulic piston ( 22 ), which is connected to a rack ( 23 ) of the steering. For a supply and a discharge from the hydraulic chambers ( 20 . 21 ) for pressure control are hydraulic lines ( 24 . 25 . 26 . 27 ) and a pressure medium reservoir ( 28 ) intended.

In the overlay function of the steering is the driver's steering angle δ _H ( 11 ), over the torsion bar ( 13 ) and the transmission ( 1 ) with a translation factor ν1 directly onto the steering gear ( 31 ) acts, according to the desired basic steering function (essentially steering ratio) of the steering controller ( 8th ) an additional steering angle (motor angle φ _Mot ) ( 35 ), which has a transmission ( 36 ) with a second ratio factor ν2 ( 37 ) on the steering gear ( 31 ) acts, superimposed. The overlay results in a certain angle of rotation of the pinion ( 32 ) of the steering gear ( 31 ), ie the "pinion angle" δ _R ( 15 ).

The controller ( 8th ) is an error determination ( 40 ), by means of which an error or a deviation in an association between the steering wheel angle, the driver steering angle δ _H ( 11 ), and the pivot angle, here the "pinion angle" δ _R ( 15 ), is determined. By means of a compensation control, an assignment error or an assignment deviation according to the invention by a corresponding control of the engine ( 5 ) balanced.

In the 2 a block diagram of the control concept for an intervention of a vehicle dynamics controller is shown.

Driving dynamics steering intervention of the driving dynamics controller ( 38 ) are used as additional steering angle Δδ _ESP ( 39 ), which intervenes to correct the system. In this case, according to the driver's steering angle ( 11 ) and a desired anc translation i _ESAS a gain factor ν _{δ, ESAS} ( 41 ), from which the driver's request δ _{CMD, DRV} ( 42 ). This is with the from the driving dynamics controller ( 38 ) additional steering angle Δδ _ESP ( 39 ) superimposed. The resulting setpoint for the steering angle δ _{R, CMD} ( 43 ) is added to the control loop ( 44 ) for the superposition steering. Thus, the resulting steering angle δ _R = δ _sum ( 15 ), the resulting steering angle ( 15 ) as an input to the control loop ( 44 ) is returned ( 45 ).

By the overlay can according to a recognized driving situation, the driving behavior and the vehicle dynamics are positively influenced, with the driving stability on the one hand as well as the agility of the Vehicle be increased can. In particular, dynamic driving interventions are realized in order to the driver in his steering activity to support.

During the initialization phase of the superposition steering system after a POWERON reset, which means a start of the vehicle with a new ignition run, it may happen that the association between the driver steering angle δ _H determined by means of the steering angle sensors (FIG. 11 ), hereinafter also referred to as "steering wheel angle", and the pivoting angle, the "pinion angle" δ _R ( 15 ), due to the basic steering function required at system startup δ R = (ν δ, ESAS · δ H ) does not match.

Possible causes therefor On the one hand are steering movements that are disabled with superposition steering carried out be, e.g. in the event of an error or when the system is switched off, or Remaining correction angle, which is not completely closed by the vehicle dynamics controller Zero be reduced. It is also conceivable that the system with a from the present required deviating steering ratio was turned off.

Without the method according to the invention, a compensation of the described assignment error during the initialization phase would be achieved by presetting a corresponding steering angle setpoint (δ _{CMD, DRV} = νδ _{, ESAS} * δ _H ) for the control of the superposition steering, depending on the size of the angle to be compensated Move the steered wheels or the steering wheel. This movement was not wanted by the driver or was not initiated by him. Therefore, the driver will find this movement irritating or at least very annoying.

According to the invention, the allocation error is detected and compensated. This is in the 3 shown in more detail. The steering wheel misalignment resulting from the described allocation error is thereby compensated in such a way that they do not lead to unwanted and irritating steering movements for the driver. Ideally, the driver does not notice the compensation of this allocation error.

Reached will do this by, after the ESAS system initialization phase, e.g. by turning on the "ignition" of the vehicle, the Balancing movement of the first steering movement of the driver superimposed will and at the latest is completed when driving straight ahead of the vehicle.

First, during the system initialization phase, that means Init: S = 1 ( 50 ) once the value for the steering angle error position as the difference between the steering angle command value δ _{CMD, DRV} and actually present pinion angle δ _R determined ( 51 ) Δδ 0 = δ CMD, DRV - δ R = (ν δ, ESAS · δ H ) - δ R

This value for the steering angle error is then used as the start value ( 52 ) of the target specification δ _{CMD, DRV} superimposed for the steering angle control ( 54 ) (Δδ _{0, B} = Δδ ₀ for S = 1).

After completion of the system initialization phase, S = 0 is set and then with the aid of a slope limiting function ( 55 ) with the target value Δδ _{0, W} = 0 (zero) ( 56 ) is now the value of the steering angle error position Δδ _{0, B} degraded slowly to zero.

The value for the maximum angle change ( 57 ) of the increase limiting function ( 55 ) is of the steering speed ( 58 ) of the driver: From the differentiation ( 59 ) of the driver's request δ _{CMD, DRV} ( 42 ) determined steering speed δ. _{CMD, DRV} ( 58 ), a maximum increase limit | dΔδ _{0, max} | ( 57 ) ( 60 ).

So long the driver performs no steering movement, the steering angle error position not dismantled either. The maximum angle change is zero. The same applies to the period during which the system is in the initialization phase (S = 1) is located.

Once the driver has a δ based on the steering speed. _{CMD, DRV} ( 58 ) performs measurable steering movement, the slope limiting function ( 55 ) also a change of Δδ _{0, B} too.

Due to the increase limiting function ( 55 ) determines with which maximum angle change per controller loop (1 loop corresponds to the execution of a program in the controller) an increase-limited steering angle error position Δδ _{0, B} ( 61 ) approaches its target value Δδ _{0, W} = 0.

As long as this compensation movement takes place (Δδ _{0, BSP} different from zero), no ESP steering angle interventions are possible: Δδ ESP = 0, as long as Δδ 0, BSP <> 0

The reduction of the determined during the Systeminitialisierungsphase steering angle error Δδ ₀ to zero takes place in the following manner:
The currently calculated value of the steering angle error position Δδ _{0, B} , which is superimposed on the steering angle setpoint specification Δδ _{CMD, DRV} ( 54 ), is returned ( 68 ) to a time-discrete deadtime element ( 62 ) which delays the signal Δδ _{0, B} by one controller clock cycle (loop). At the subtraction point ( 66 ) is then the value of the steering angle error position Δδ _{0, B of} the previous controller clock of target value Δδ _{0, W} = 0 ( 56 subtracted.

The calculated difference is a limiter function ( 63 ), which, taking into account the maximum increase limit | dΔδ _{0, max} | ( 57 ) determines the possible change of the value Δδ _{0, B} in the current controller clock cycle (loop) or to the maximum value | dΔδ _{0, max} | ( 57 ) limited.

The thus determined output signal dΔδ ₀ is used as an input variable to a time-discrete integrating module ( 64 ), in which the new output of the module ( 64 ) is calculated from the addition of the old output and the signal dΔδ ₀ . Since after completion of the system initialization phase the value S = 0, the selection module ( 65 ) the value 1 and the selection module ( 53 ) the value 0, which means that the output variable of the time-discrete integrating module ( 64 ) represents the newly determined, limited value dΔδ _{0, B} for the steering wheel tilt.

The newly determined by these steps, limited value Δδ _{0, B} for the steering angle error position is fed to the superposition for the steering angle control ( 54 ).

In the determination ( 60 ) of the maximum value | dΔδ _{0, max} | ( 57 ) for the increase limitation, it is provided on the one hand to achieve the fastest possible but also comfortable reduction of the angular misalignment. On the other hand, it is provided that the modified specification of the steering angle setpoints accordingly 3 : δ CMD, DRV = (ν δ, ESAS · δ H ) - Δδ 0, B does not cause the sign of the steering wheel angular velocity to differ from that of the steering angle setpoint.

In order to achieve this, the determination of the maximum value for the increase limitation in accordance with the 4 made procedure described.

The 4 is a plot of the gradient Δδ. ₀ , with which the steering angle error can be compensated as

Function of the steering speed δ. _{CMD, DRV of} the driver's request.

The steering angle speed interval limited by the values + ∈ and -∈ represents a dead band for the compensation of the steering angle error position. If the steering speed is δ. _{CMD, DRV of} the driver's request within this interval, then Δδ. ₀ = 0, a compensation of the steering angle error position does not take place due to the driver's insufficient steering movement.

The straight lines with the gradient K ₁ and K ₂ here mean the maximum speed value for the compensation of the steering angle tilt depending on the driver's steering request δ. _{CMD, DRV} . If, for example, the value determined for the system initialization phase is Δδ ₀ > 0, the straight line with the gradient K ₂ is valid for the determination of the maximum increase limit. For a value of that Driver's wish δ. _{CMD, DRV} = δ. _{CMD, DRV, AP} can then be correspondingly 4 the value for Δδ. ₀ = Δδ. _{0, AP} can be determined.

The value Δδ. _{0, MAX} represents the maximum value for the rate of change with which the steering angle inclination is compensated. Analogously, the value -Δ .δ _{0, MAX is} the corresponding minimum value.

The values of the insensitivity threshold ± ∈, the slopes K ₁ and K ₂ and the limits for the maximum compensation speed ± Δδ. _{0, MAX} can be selected according to comfort aspects as well as due to the available actuator dynamics.

Thus, the maximum increase limit | dΔδ is _{0, max} | ( 57 ) a function of the steering angle error position Δδ ₀ and the differentiated steering angle error position Δ .δ ₀ , normalized to the controller loop time. | dΔδ 0, max | (57) = | Δδ. 0 (Δδ , 0 , Δδ 0 ) | / Reglerloopzeit.

With "controller loop time" here is the time for a program run of the steering control program. The loop time is typical 2 msec (milliseconds) to 5 msec.

Claims (10)

Method for improving the operation of a vehicle steering system, characterized in that an error or a deviation in an association between a measured or determined or estimated steering wheel angle and an actually detected or determined or estimated pivoting angle, which describes a position of pivotable vehicle wheels, is determined, and a detected allocation error or a detected allocation deviation between the steering wheel angle and the pivoting angle is compensated. Method according to claim 1, characterized in that that the steering wheel angle is measured. Method according to claim 1 or 2, characterized that the pivoting angle is measured. Method according to one of claims 1 to 3, characterized that a mapping error or mismatch offset is determined by a measure the not to unintentional, irritating a driver of the vehicle Steering movement leads. Method according to one of claims 1 to 4, characterized that a mapping error or mismatch offset is due to a compensatory movement that occurs during a first steering movement done by the driver after a journey. Method according to one of claims 1 to 5, characterized that the procedure for a superposition steering is used. Method according to Claim 6, characterized that a mapping error or mismatch offset is due to a compensation movement by means of an overlay function the superposition steering. Vehicle steering for Motor vehicles, operable by a driver of the motor vehicle Steering handle and an associated with the steered vehicle wheels actuator, the connected is with the steering handle and by means of the possibly further elements, such as. Tie rods and toggle, the steered vehicle wheels to Setting a desired Steering angle are pivotable, and which vehicle steering device for determining a steering wheel angle of the steering handle and a pivoting angle having, which describes the position of the pivotable vehicle wheels, characterized in that the vehicle steering comprises a fault detection unit, by means of an error or a deviation in an association between the steering wheel angle and the pivot angle is determined, and that the vehicle steering having a compensation unit, by means of the assignment error or the assignment deviation is balanced becomes. Vehicle steering system according to claim 8, characterized in that the vehicle steering system includes a steering wheel angle sensor and a sensor For detecting the pivoting angle. Vehicle steering system according to claim 8 or 9, characterized characterized in that the vehicle steering is a superposition steering and that is an allocation error or misalignment by an overlay actuator the superposition steering is compensated.