DE102007001965B4 - Method for operating a power steering system - Google Patents

Abstract

Method for operating a power steering system (10) in a motor vehicle, in which a steering angle adjustment is performed, wherein
a steering angle offset is determined over a predetermined period of time,
characterized in that the particular steering angle offset influences a motor angle δ _M applied by a motor (18).

Description

The invention relates to a method for operating a power steering system according to the preamble of claim 1, a computer program and a computer program product for carrying out the method, and a power steering system according to the preamble of claim 8.

In motor vehicles, for example, due to bent tie rods, asymmetric tie rods or other mechanical defects, there is an offset of the steering angle, the so-called steering angle offset. This has the consequence that the driver must set a certain steering angle in order to execute a straight ahead. As a rule, this steering angle offset or steering angle skew should not be compensated so that the driver acquires knowledge of the mechanical defect.

In power steering systems, it is customary to add to the steering angle introduced by the driver a motor angle applied by a motor, usually an electric motor, of a servo drive. The applied motor angle is usually also dependent on the speed of the vehicle. This means, however, that in the presence of a steering angle offset, the driver, for example, has to compensate for the changing engine angle when braking, ie. H. the driver must move the steering wheel to ensure straight ahead driving.

For this reason, it is necessary to determine the steering angle offset in a power steering system of the type described in order to possibly take into account when setting the motor angle, in particular when specifying the time course.

The publication DE 102 44 070 A1 describes a generic method for steering assistance for motor vehicles with electromechanical steering. In this case, a correction value is determined, from which a support torque is derived. It is thus applied even when driving straight ahead, if necessary, a moment.

The object is achieved by a method having the features of claim 1, by a computer program with program code means having the features of claim 6, by a computer program with program code means having the features of claim 7 and by a power steering system having the features of claim 8. Advantageous Further developments emerge from the subclaims.

The claimed method for operating a power steering system in a motor vehicle provides that a steering angle adjustment is performed, wherein a steering angle offset over a predetermined period, typically based on a filtered steering angle of the steering angle offset is preferably determined as a function of speed. According to the invention, the particular steering angle offset affects a motor angle applied by a motor.

The predeterminable time period can be specified as a fixed time value or as a function of a traveled distance. Here, for example, a value of 40 km has been found to be expedient. Thus, with the method according to the invention of long-term balancing, a steering wheel slant, which is caused, for example, by asymmetric tie rods, can be determined during active operation. If desired, the steering angle may be corrected for the value of the steering wheel angle. This is not necessarily intended to compensate for the steering wheel tilt or steering angle offset mechanically. Rather, it is intended to prevent the variable steering ratio from changing the engine angle due to the steering angle offset during straight-ahead driving and during heavy braking.

The described concept of long-term matching is based on the assumption that "on average" is driven straight ahead. Furthermore, it can be assumed that the probability of driving straight ahead increases with increasing speed. Therefore, it is provided in an embodiment that the speed of the motor vehicle is taken into account, so that the steering angle offset is only determined when the speed of the vehicle exceeds a limit of, for example, 15 km / h.

If these conditions are not fulfilled, error adjustments can not be excluded. In particular, it can be problematic when driving rounds. In the case of round trips with two long and two short curves, a "simple" long-term filter will cause error adjustments. To prevent this, an additional start condition, such as a lap detection, can be realized.

Thus it can be provided that a yaw angle is taken into account. This yaw angle is determined, for example, via the yaw rate signal or wheel speeds of the motor vehicle. In this way, a round trip can be detected. In an embodiment, it is provided to calculate the steering angle offset only as long as the yaw angle does not exceed an applicable limit value, for example 180 °, and the vehicle thus drives straight ahead.

With the presented method it is possible, based on the determined steering angle offset, to influence an engine angle applied by a motor and thus to relieve the driver during heavy braking.

• – Prüfung der Einschaltbedingungen
• – Berechnung des Lenkwinkeloffset

Furthermore, it is provided in an embodiment to check predefinable switch-on conditions before the determination of the steering angle offset. In this case, the procedure is divided into two areas:

• - Checking the switch-on conditions
• - Calculation of the steering angle offset

• – der Lenkwinkel befindet sich für eine applizierbare Zeitdauer innerhalb applizierbarer Grenzen;
• – der Betrag der Lenkwinkeländerung ist kleiner als ein applizierbarer Grenzwert;
• – Die Geschwindigkeit ist größer als ein applizierbarer Grenzwert;
• – die Rundenerkennung auf Basis der Raddrehzahlen ist erfüllt.

So that the steering angle offset can be accurately calculated, it should be determined as accurately as possible whether the vehicle is driving straight ahead. This can be achieved by meeting the following conditions:

• - The steering angle is for an applicable period of time within applicable limits;
• - The amount of steering angle change is smaller than an applicable limit value;
• - The speed is greater than an applicable limit value;
• - The lap detection based on the wheel speeds is fulfilled.

The invention further relates to a computer program with program code means for carrying out a method for operating a power steering system of the type described above, when the computer program is executed on a microprocessor of a computer, in particular in a control unit of the power steering system.

The computer program can be stored on a computer-readable data carrier, such as floppy disk, CD, DVD, hard disk, USB memory stick or the like, or an Internet server as a computer program product and be transferred from there into the memory element of the control unit.

The claimed power steering system of a motor vehicle has a steering handle, a servo drive with a motor and an electronic control unit for controlling the motor. It is inventively provided that the electronic control unit is designed to carry out a method described above.

Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

The invention is illustrated schematically with reference to an embodiment in the drawing and will be described below in detail with reference to the drawings.

1 shows a schematic representation of an embodiment of the power steering system according to the invention.

2 illustrates in a block diagram the calculation of the steering angle offset.

In 1 is an embodiment of the power steering system according to the invention, in total with the reference numeral 10 designated, shown. The illustrated power steering system 10 has a steering handle designed as a steering wheel 12 , an electrical control unit 14 as well as a servo drive 16 with a motor 18 on. With this wheels are 20 a motor vehicle steered.

In addition to one with the steering handle 12 predetermined steering angle δ _L becomes one of the engine 18 in the servo drive 16 Applied motor angle δ _M on the wheels 20 transmitted in support of the driver. For this purpose, the servo drive 16 from the controller 14 driven. According to the invention, it is now provided that the control unit 14 additionally determined via a low-pass filtering of the steering angle δ _L a steering angle offset and this considered in the specification of the motor angle δ _M. This ensures that the driver does not have to compensate for a changing engine angle δ _M even during heavy braking.

In 2 is a block diagram of the calculation of the steering angle offset in a SAC Calculation (short SAC: stearing angle correction) designated subsystem 30 shown. In this one will be from a first entrance 32 v_X and a second input 34 delta_S the steering angle offset (offset_delta_S) is determined and at an output 36 output. SAC is active s. Fig. 5 STATUS_SAC = 1 SAC is inactive offset_delta_S = offset_delta_S (t - 1) STATUS_SAC = 0 SAC is initialized offset_delta_S = offset_from_eeprom STATUS_SAC = 2 Table 1

GF

= Gewichtungsfaktor der Geschwindigkeit

v_k

aktuell gefilterter Offset

u_k

alter Offset

v_k-1

gefilterter Offset aus dem letzten Abtastschritt

It should be determined over a travel distance of 40 km a possible steering angle offset. For this purpose, a speed-variable PT1 filter is used (equation 1). v _k = b ₀ u _k + a _{1 vk-1} (Equation 1) With b ₀ = GF / 100000 a ₁ = 1 - b ₀

GF

= Weighting factor of the speed

v _k

currently filtered offset

u _k

old offset

v _k-1

filtered offset from the last sampling step

Table 2 shows the relationship between the driving distance, a time constant T and the weighting factor GF. v_X [kmh] Time t [s] T d a_1 b_0 GF 80 1800.00 360.00 36000.00 0.999972223 2.77774E-05 2.78 140 1028.57 205.71 20571.43 0.99995139 4.86099E-05 4.86 200 720.00 144.00 14400.00 0.999930558 6.9442E-05 6.94 300 480.00 96.00 9600.00 0.999895839 0.000104161 10:42 Table 2

Claims (8)

Method for operating a power steering system ( 10 ) in a motor vehicle in which a steering angle adjustment is performed, wherein a steering angle offset is determined over a predetermined period of time, characterized in that the determined steering angle offset one of a motor ( 18 ) applied motor angle δ _M influenced. The method of claim 1, wherein additionally a calculated yaw angle is taken into account. The method of claim 2, wherein the yaw angle is determined by wheel speeds of the motor vehicle. Method according to one of claims 1 to 3, wherein the speed of the motor vehicle is taken into account. Method according to one of Claims 1 to 4, in which predefinable switch-on conditions are checked prior to the determination of the steering angle offset. Computer program with program code means for providing a method for operating a power steering system ( 10 ) in a motor vehicle according to one of claims 1 to 5, when the computer program is stored on a microprocessor of a computer, in a control unit ( 14 ) of the power steering system ( 10 ), is performed. A computer program product comprising program code means stored on a computer-readable medium for providing a method for operating a power-assisted steering system (US Pat. 10 ) in a motor vehicle according to one of claims 1 to 5, when the computer program is stored on a microprocessor of a computer, in a control unit ( 14 ) of the power steering system ( 10 ), is performed. Power steering system of a motor vehicle, comprising: a steering handle ( 12 ), a servo drive ( 16 ) with a motor ( 18 ), an electronic control unit ( 14 ) for controlling the motor ( 18 ), characterized in that the electronic control unit ( 14 ) is designed for carrying out a method according to one of claims 1 to 5.

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