DE102016223328A1 - Method for determining a correction value in a steering control for a motor vehicle and steering control for a motor vehicle - Google Patents

Abstract

The invention relates to a method for setting a correction value (4) in a steering control (1) for a motor vehicle (50), wherein for controlling a steering angle of a steering (51) of the motor vehicle (50) a torque (30) by means of a mechanically with a Steering handle associated torque sensor (2) is detected and corrected by the steering controller (1) by the correction value (4), wherein the following steps are performed: Checking whether the steering handle is hand-torque-free, and if so: detecting the torque ( 30) by means of the torque sensor (2); Determining a return direction (7); Storing the determined return direction (7) and the detected torque (30) in a memory (5); Determining an average value (9-1, 9-2) for each of the return directions (7) from the respective stored torques; Setting the correction value (4) based on the determined average values (9-1, 9-2). Furthermore, the invention relates to an associated steering control (1).

Description

The invention relates to a method for determining a correction value in a steering control for a motor vehicle and a steering control for a motor vehicle.

Modern motor vehicles are equipped as standard with an electric steering assistance. In order to control such an electric steering, a steering request of the driver must be detected. This is done by a torque sensor for the driver's manual torque. Depending on the torque acting on the steering wheel of the motor vehicle and the current vehicle speed, a support torque is then provided on a toothed rack of the steering by means of an electric assisting motor and the desired steering angle is set on the wheels of the motor vehicle.

The torque sensor is calibrated prior to installation in the motor vehicle within the steering system. A steering control that takes into account a predetermined correction value, for example, from US 2003/0155879 A1 known.

Due to external influences, for example during installation of the steering system in the motor vehicle, however, the torque sensor may experience a manipulation. For example, mechanical stresses, magnetic influences, metal environments, etc., may cause the torque sensor to be affected, causing errors in the measurement of torque. Furthermore, environmental influences and aging effects can influence the torque sensor and cause a measurement error. The consequence of such a measurement error is a shift of the measured value output by the torque sensor by an offset, which has an especially strong effect on small manual torques and in particular in the case where the driver does not apply any manual torque to the steering wheel.

The invention is based on the technical problem of providing a method for determining a correction value in a steering control for a motor vehicle and a steering control for a motor vehicle, in which a correction value improved, in particular based on a current state of a steering of the motor vehicle, can be provided ,

The technical problem is solved by a method with the features of claim 1 and a steering control with the features of claim 10. Advantageous embodiments of the invention will become apparent from the dependent claims.

In particular, a method for setting a correction value in a steering control for a motor vehicle is provided, wherein for controlling a steering angle of a steering of the motor vehicle torque is detected by means of a mechanically connected to a steering handle torque sensor and is corrected by the steering control by the correction value, wherein the following steps are performed:

• - Erfassen des Drehmoments mittels des Drehmomentsensors;
• - Bestimmen einer Rückstellrichtung;
• - Speichern der bestimmten Rückstellrichtung und des erfassten Drehmoments in einem Speicher;
• - Bestimmen eines Mittelwertes für jede der Rückstellrichtungen aus den jeweils gespeicherten Drehmomenten;

Festlegen des Korrekturwertes auf Grundlage der bestimmten Mittelwerte.Check that the steering handle is free of hand torque, and if so:

• - detecting the torque by means of the torque sensor;
• - determining a return direction;
• - storing the determined return direction and the detected torque in a memory;
• Determining an average value for each of the return directions from the respectively stored torques;

Set the correction value based on the determined mean values.

Further, there is provided a steering control for a motor vehicle, comprising a torque sensor for detecting a torque on a steering handle mechanically connected to the torque sensor, a controller for controlling a steering angle of a steering of the motor vehicle based on the detected torque, wherein the controller detects the detected torque by a correction value corrected, and wherein the controller comprises a memory and is further configured to check whether the steering handle is handsomomentfrei. The torque sensor is further configured to detect the torque when the hand-held freedom of the steering handle is detected, and the controller is further configured to determine a reset direction when the hand-held freedom of the steering handle is determined and to store the determined return direction and the detected torque in the memory for each of the return directions from the respective stored torques and to determine the correction value based on the determined average values.

The basic idea of the invention is to continuously detect torques on the torque sensor for determining a correction value, namely when the steering handle is free of hand torque. The torques detected in the torque-free state are stored in a memory and collected there. In this case, in each case a return direction is determined and the detected torques in each case depending on their Reset direction ("coming from the left" / "coming from the right") is saved. For each of the return directions, an average value is determined from the stored torques. Based on the determined average values, the correction value is then redefined.

The advantage is that the correction value can always be adapted to a current state of the steering or of the torque sensor of the motor vehicle. A zero position of the steering can be determined more accurately. The current state of the steering can always be taken into account in the steering control in this way, so that, for example, even very small hand moments around the zero position can be detected correctly and reliably.

It may be provided here that the state "free of hand torque" of the steering wheel is derived, for example, from sensor signals or vehicle properties. For this purpose, for example, sensor signals of the motor vehicle are evaluated accordingly.

The described method is usually carried out in the electrical lag. Although the motor vehicle has already been switched off, at least some of the on-board electronics - which are usually not recognizable to the driver - are still in operation in the electric overrun. As a rule, this also includes the steering of the motor vehicle, which then performs the method as described.

In one embodiment, it is provided that the manual torque freedom of the steering handle is derived from a standstill of the motor vehicle. Such a standstill is derived, for example, with the aid of sensor signals or vehicle properties. If the vehicle is stationary, the controller concludes that the steering handle is free of hand torque. Here, however, the condition should be able to be established beyond doubt. Thus, a waiting of the motor vehicle at a traffic light, in which a driver of the motor vehicle may still have his hands on the steering wheel, must be distinguished from a parked state in which the driver has dropped out. One possibility, for example, is to determine a stoppage of the motor vehicle in the parked state with the aid of an ignition position. Only when the ignition position is "OFF" is it assumed that there is a stoppage in the parked state and the procedure for setting the correction value is carried out accordingly.

For automatic start / stop systems, a distinction should be made between a permanent and not just temporary ignition position "OFF".

In a further embodiment, it is provided that only detected torques whose magnitude is below a predetermined threshold value are stored and taken into account in averaging. In this way it can be prevented that outliers are included in the averaging. Such an outlier can occur, for example, if the vehicle was parked dirty and, for example, with a hammered front wheel abuts the curb of the road, so that the wheel is under tension. This voltage continues mechanically via the steering on the torque sensor, so that even if no manual torque is applied to the steering handle, it can measure extremely high values. Another similar case is when, for example, the steering lock is engaged. By means of a threshold value detection, extreme values can be sorted out and rejected when forming the mean value. Such a threshold value may be, for example, 0.5 Nm, whereby all torques which lie below in the hand-moment-free state are taken into account, torques which are equal to or greater than this value are not. In principle, the value can also be selected larger or smaller. It can be chosen differently, especially in different versions of steering.

In a further embodiment, it is provided that, for detecting the stoppage of the motor vehicle, at least one signal on a communication bus of the motor vehicle is evaluated by means of the control. For example, an ignition state can be queried. When the ignition state is "OFF", the control concludes that the vehicle is at a standstill. Furthermore, alternatively or additionally, further properties of the motor vehicle can be determined via the communication bus of the motor vehicle, either actively, by interrogating a state of the motor vehicle via the communication bus, or by passive listening and reading of communication messages, which are exchanged by devices of the motor vehicle via the communication bus. This may be, for example, a speed of the motor vehicle, an engine speed or a state of the gearshift, in which case, for example, an idling with the handbrake engaged or a parking position "P" can be used to indicate a standstill of the motor vehicle. Furthermore, a belt state ("belt driver's seat not closed") can be evaluated in order to conclude on a stoppage of the motor vehicle and a hand torque of the steering handle.

In a preferred embodiment it is provided that a standstill of the motor vehicle is detected by means of a door control signal. In this case, for example, communication messages which are transmitted via a communication bus of the motor vehicle from a driver's door of the motor vehicle transmitted by the controller. If after a drive of the motor vehicle a communication message "driver's door opened" and then a communication message "driver's door closed" recognized by the controller on the communication bus, then the control concludes that the motor vehicle is at a standstill and the steering handle is free of hand torque. In this case, the described method steps are carried out.

In a further embodiment it is provided that the correction value is only determined if the amounts of the determined average values lie below a maximum correction value. This has the advantage that an excessive adaptation of the correction value can be prevented. It can be provided that no correction is made at all when the maximum correction value is reached or exceeded. However, it can also be provided that the correction value is adjusted only up to the maximum correction value, but a correction that goes beyond this is prevented. Such a maximum value may be, for example, 2 Nm or 0.5 Nm. Achieving the maximum correction value can also be used to trigger a warning message with a request for maintenance or replacement of the torque sensor.

In a further preferred embodiment it is provided that the setting of the correction value is performed stepwise as a sliding correction. This means that a current correction value is adjusted step by step to a new correction value. For example, it can be provided that a correction, that is to say a transfer of the current correction value into the new correction value, is carried out in five or ten sub-steps. Each time the motor vehicle is started, a further one of the substeps is implemented so that the correction takes place in a sliding manner. Here, the current average values are always taken into account.

In a further embodiment, it is provided that for determining the return direction, a sign of a gradient of the detected torque is stored and evaluated. For this purpose, a history of the detected torque is evaluated for a certain period of time. It can then be deduced from the gradient whether the steering handle returns to the zero position after a right-hand steering ("coming from the right") or after a left-hand steering ("coming from the left").

In a further embodiment, it is provided that the setting of the correction value takes place only when a predetermined minimum number of torques has been detected and stored in the memory. This ensures that the average value is formed from a sufficient number of detected torques and irregularities and statistical measurement errors are reduced. For example, such a predetermined minimum number may prescribe at least 10 torques recorded and stored in the torque-free state. The predetermined minimum number may also be higher, for example 50 or 100. In particular, it can be provided that the correction value is always formed from a predetermined minimum number of the last detected torques, for example always from the 10, 50 or 100 last detected torques.

It goes without saying for the person skilled in the art that features of individual embodiments can also be realized in combination.

Portions of the steering control may be individually or collectively configured as a combination of hardware and software, such as program code executed on a microcontroller or microprocessor.

• 1 eine schematische Darstellung einer Ausführungsform der Lenkungssteuerung für ein Kraftfahrzeug;
• 2a eine schematische Darstellung einer typischen Kennlinie eines Drehmomentsensors mit Hysterese;
• 2b eine schematische Darstellung einer typischen Kennlinie eines Drehmomentsensors mit Hysterese und zusätzlichem Versatz (Offset);
• 3 ein schematisches Ablaufdiagramm einer Ausführungsform des Verfahrens zum Festlegen eines Korrekturwertes in einer Lenkungssteuerung für ein Kraftfahrzeug.

The invention will be explained in more detail with reference to preferred embodiments with reference to the figures. Hereby show:

• 1 a schematic representation of an embodiment of the steering control for a motor vehicle;
• 2a a schematic representation of a typical characteristic of a torque sensor with hysteresis;
• 2 B a schematic representation of a typical characteristic of a torque sensor with hysteresis and additional offset;
• 3 a schematic flow diagram of an embodiment of the method for determining a correction value in a steering control for a motor vehicle.

In 1 is a schematic representation of an embodiment of the steering control 1 for a motor vehicle 50 shown. The steering control 1 includes a torque sensor 2 for detecting a torque at a mechanically connected to the torque sensor steering handle of the motor vehicle 50 and a controller 3 for controlling a steering angle of a steering 51 of the motor vehicle 50 based on the detected torque 30 , The detected torque 30 is from the controller 3 around a correction value 4 corrected. The correction value 4 is in a store 5 the controller 3 deposited.

As part of the procedure for setting the correction value 4 the steering control 1 checks the control 3 whether the steering handle of the motor vehicle 50 Handmomentfrei is. The test takes place, for example, by means of a bus interface 6 the steering control 1 a current state of the motor vehicle 50 via a communication bus 52 of the motor vehicle 50 is queried. It is envisaged that a hand-torque-free steering handle is closed when the motor vehicle 50 is at a standstill. Such a standstill here is a signal 40 on the communication bus 52 , in particular from a door control signal 53 , derived. The door control signal 53 For example, by default, a door sensor of the driver's door of the motor vehicle 50 over the communication bus 52 transmitted. Detects the controller 3 For example, the following sequence of communication messages "driver's door open", "driver's door closed", then closes the controller 4 that the driver has dropped out, the motor vehicle 50 is at a standstill and the steering handle is free of hand torque.

If the hand-held freedom of the steering handle is detected, the torque sensor detects 2 then the torque. The control 3 determines a return direction 7 (eg "coming from the left" / "coming from the right"), for example, in a designated Rückstellrichtungsbestimmungsmodul 8th , The control 3 Defines the specific return direction 7 and the detected torque subsequently in the memory 5 ,

Out of those in the store 5 stored torque determines the control 3 an average 9-1 , 9-2 for each of the return directions 7 from the respectively stored torques, for example in averaging modules provided for this purpose 10-1 . 10-2 , In this case, for example, the arithmetic mean can be used as a basis. Based on the determined mean values 9-1 , 9-2 sets the control 3 a (new) correction value 4 fixed and overwrites the one in the memory 5 stored (old) correction value 4 , The correction value 4 for example, based on the arithmetic mean of the means 9-1 , 9-2. A steering control by the controller 3 is then always taking into account the newly set correction value 4 ,

In further embodiments, it may additionally be provided that the controller 3 only detected torques 30 whose amounts are below a predetermined threshold 11 lie. Such a check may, for example, be in an additional threshold check module 12 respectively.

Furthermore, it can be provided in further embodiments that the controller 3 the correction value 4 only restates if the amounts of the specific averages 9-1 , 9-2 below a maximum correction value 13 lie. Such a check may, for example, be in an additional maximum correction check module 14 respectively.

In addition, it can be provided in further embodiments that the setting of the correction value 4 only occurs if a predetermined minimum number 15 captured by torques and in memory 5 Such a check may, for example, be in an additional minimum check module 16 respectively.

In 2a is a schematic representation of a typical characteristic 18 a torque sensor shown. In this case, the torque actually acting on the torque sensor (here in particular the manual torque) is shown on the x-axis 20. The y-axis 21 represents the torque detected or measured by the torque sensor. It can be clearly seen that the torque sensor in a trace 22 measures other values than a return 23 such that the torque sensor is hysteretic.

In 2 B is a schematic representation of another typical characteristic 19 a torque sensor with additional offset 24 (Offset) shown. In this case, the torque actually acting on the torque sensor (here in particular the manual torque) is again shown on the x-axis 20. The y-axis 21 represents the torque detected or measured by the torque sensor. It can be clearly seen that the torque sensor in a trace 22 measures other values than a return 23 such that the torque sensor is hysteretic. In addition to the hysteresis, however, the torque sensor has an offset 24 (Offset) on. This means that the characteristic curve is opposite to a zero position 25 around the offset 24 (Offset) is shifted. In the example shown, the offset results 24 (Offset) to that the entire characteristic curve 19 on the y-axis 21 is shifted down to negative values. The method described and the steering control described 1 (please refer 1 ) now ensure that the offset 24 (Offset) is corrected by means of the always newly determined correction value, so that the characteristic 19 again in the direction of the zero position 25 is moved and the figure of the in the 2a shown characteristic 18 accepts.

In 3 FIG. 12 is a schematic flowchart of one embodiment of the method for determining a correction value in a steering control for a motor vehicle. After the start 100 of the method, a check is made in a first method step 101 as to whether the steering handle is hand-torque-free. Here it can be provided, in particular, that the freedom of movement from a hand Standstill of the motor vehicle is derived. In particular, it may be provided to derive the standstill from a door control signal on a communication bus of the motor vehicle. If the steering handle is not free of hand torque, the method step 101 is repeated.

If, however, the steering handle is hand-torque-free, then, in method step 102, the torque acting on a steering handle is detected by means of a torque sensor and forwarded to a controller. In a method step 103, it can additionally be provided that it is checked whether the detected torque lies below a threshold value. If the detected torque is equal to the threshold value or greater than the threshold value, then the method step 101 is jumped back. On the other hand, if the detected torque lies below the threshold value, the method continues.

In method step 104, a return direction of the steering handle is determined by means of the controller. It can be provided that the return direction is derived here via the sign of a gradient of the detected torque.

In method step 105, the detected torque and the determined reset direction are stored in a memory. The detected torques are in each case stored as a function of the specific return direction.

In the following method step 106, an average value is determined for each of the return directions from the torques stored in the memory, for example as an arithmetic mean. In method step 107, it can then additionally be provided that the controller checks whether the amounts of the mean values lie below a maximum correction value. If this is not the case, the method jumps back to method step 101. If this is the case, however, then in method step 108, a correction value provided for correcting an offset in a characteristic curve of the torque sensor is newly determined on the basis of the mean values. Here, in particular in some embodiments, it may be provided that the setting is carried out by a sliding correction, that is, in the context of a plurality of sub-steps. The process is then completed 109. However, the process is usually repeated cyclically.

In parallel to the described method, the controller controls a steering of the motor vehicle, taking into account the respective set correction value.

LIST OF REFERENCE NUMBERS

1

steering control

2

torque sensor

3

control

4

correction value

5

Storage

6

bus interface

7

Return direction

8th

Return direction determination module

9-1

Average

9-1

Average

10-1

Averaging module

10-2

Averaging module

11

threshold

12

Schwellwertprüfungsmodul

13

Maximum correction value

14

Maximum correction check module

15

minimum number

16

Minimum check module

18

curve

19

curve

20

X axis

21

y-axis

22

trace

23

returns

24

offset

25

zero position

30

detected torque

40

signal

50

motor vehicle

51

steering

52

communication

53

Door control signal

100-109

steps

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 2003/0155879 A1 [0003]

Claims (10)

Method for determining a correction value (4) in a steering control (1) for a motor vehicle (50), wherein for controlling a steering angle of a steering (51) of the motor vehicle (50), a torque (30) by means of a torque sensor mechanically connected to a steering handle ( 2) and corrected by the steering control (1) by the correction value (4), characterized in that the following steps are carried out: checking whether the steering handle is free of hand torque, and if so: - detecting the torque ( 30) by means of the torque sensor (2); - determining a return direction (7); - storing the determined return direction (7) and the detected torque (30) in a memory (5); - determining an average value (9-1, 9-2) for each of the return directions (7) from the respectively stored torques; Setting the correction value (4) based on the determined average values (9-1, 9-2). Method according to Claim 1 , characterized in that the hand torque of the steering handle is derived from a standstill of the motor vehicle (50). Method according to Claim 1 or 2 , characterized in that only detected torques (30) whose amount is below a predetermined threshold value (11), stored and taken into account in the averaging. Method according to one of Claims 2 or 3 , characterized in that for detecting the stoppage of the motor vehicle (50) at least one signal (40) on a communication bus (52) of the motor vehicle (50) by means of the controller (3) is evaluated. Method according to Claim 3 , characterized in that a stoppage of the motor vehicle (50) by means of a door control signal (53) is detected. Method according to one of the preceding claims, characterized in that the correction value (4) is determined only if the amounts of the determined mean values (9-1, 9-2) are below a maximum correction value (13). Method according to one of the preceding claims, characterized in that the setting of the correction value (4) is performed stepwise as a sliding correction. Method according to one of the preceding claims, characterized in that for determining the return direction (7) a sign of a gradient of the detected torque (30) is evaluated. Method according to one of the preceding claims, characterized in that the setting of the correction value (4) only takes place when a predetermined minimum number (15) of torques (30) has been detected and stored in the memory. A steering control (1) for a motor vehicle (50), comprising: a torque sensor (2) for detecting a torque (30) on a steering handle mechanically connected to the torque sensor (2), a controller (3) for controlling a steering angle of a steering (51 ) of the motor vehicle (50) on the basis of the detected torque (30), wherein the controller (3) corrects the detected torque (30) by a correction value (4), characterized in that the controller (3) comprises a memory (5) and further configured to check whether the steering handle is free of hand torque, and wherein the torque sensor (2) is designed to detect the torque (30) when the hand-held freedom of the steering handle is detected, and wherein the controller (3) is further configured in this way to determine a return direction (7) when the hand-held freedom of the steering handle is detected, and to store the determined return direction (7) and the detected torque (30) in the memory (5) to determine an average (9-1, 9-2) for each of the return directions (7) from the respective stored torques and to set the correction value (4) based on the determined average values (9-1, 9-2).

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