ELECTROMECHANICAL STEERING SYSTEM AND METHOD FOR COMPENSATING A MEASUREMENT SIGNAL FROM A TORQUE SENSOR DEVICE

Abstract

An electromechanical steering system includes a steering shaft by means of which a steering command can be specified by means of a steering handling device, a steering gear, which is designed to convert a steering command into a steering movement of steerable wheels of a motor vehicle, taking into account at least one input variable. A magnetic torque sensor device measures a torque applied to the steering shaft. The torque sensor device comprises a sensor for detecting an uncompensated measurement signal (T). The torque sensor device comprises a computing unit, which is designed to provide a first parameter and a second parameter for compensation of the uncompensated measurement signal (T) and to calculate a compensated measurement signal (T*) based on the uncompensated measurement signal (T) and the two parameters and to provide this compensated measurement signal (T) as the at least one input variable.

Claims

1.-15. (canceled)

16. An electromechanical steering system comprising: a steering shaft, by means of which a steering command can be specified by means of a steering handling device; a steering gear, that converts a steering command into a steering movement of steerable wheels of a motor vehicle, taking into account at least one input variable; and a magnetic torque sensor device for measuring a torque applied to the steering shaft, wherein the torque sensor device comprises a sensor for detecting an uncompensated measurement signal (T), wherein the torque sensor device is assigned a computing unit, that provides a first parameter (p_lin) and a second parameter (p_symm) for compensation of the uncompensated measurement signal (T) and calculates a compensated measurement signal (T*) based on the uncompensated measurement signal (T) and the first parameter (p_lin) and the second parameter (p_symm) and provides it as the at least one input variable.

17. The electromechanical steering system as claimed in claim 16, wherein the steering shaft comprises: an input shaft which is non-rotatably connected to a steering handling device and an output shaft connected to the input shaft by a torsion bar that is twistable, wherein the torque sensor device further comprises: a multi-pole magnetic ring non-rotatably connected to the input shaft for generating a magnetic field, a stator ring element non-rotatably connected to the output shaft and enclosing the magnetic ring, and a magnetic flux collector, wherein the sensor detects the uncompensated measurement signal (T) based on the magnetic field applied to the magnetic flux collector.

18. The electromechanical steering system as claimed in claim 17, wherein the computing unit provides the first parameter (p_lin) as a linearization parameter for compensation of nonlinear behavior.

19. The electromechanical steering system as claimed in claim 18, wherein the linearization parameter is a design-specific parameter.

20. The electromechanical steering system as claimed in claim 19, wherein the linearization parameter is a third-order polynomial parameter.

21. The electromechanical steering system as claimed in claim 20, wherein the computing unit provides the second parameter (p_lin) as a symmetrization parameter (p_symm) for compensation of asymmetrical behavior of the uncompensated measurement signal (T).

22. The electromechanical steering system as claimed in claim 21, wherein the symmetrization parameter (p_symm) is a component-specific parameter.

23. The electromechanical steering system as claimed in claim 22, wherein the symmetrization parameter (p_symm) is a second-order polynomial parameter.

24. The electromechanical steering system as claimed in claim 21, wherein the computing unit calculates the compensated measurement signal (T*) according to the following calculation formula:
T{circumflex over ( )}*=T+T{circumflex over ( )}2*p_symm+T{circumflex over ( )}3*p_lin; with T*=compensated measurement signal; T=uncompensated measurement signal; p_symm=second parameter; p_lin=first parameter.

25. A method for compensation of a measurement signal of a torque sensor device for an electromechanical steering system of a motor vehicle, wherein an input shaft, non-rotatably connected to a steering handling device is connected to an output shaft via a torsion bar that is twistable, and wherein the torque sensor device comprises a multi-pole magnetic ring, non-rotatably connected to the input shaft for generating a magnetic field, a stator ring element, non-rotatably connected to the output shaft and enclosing the magnetic ring, a magnetic flux collector, and a sensor for generating a measurement signal, including the following steps: generating an uncompensated measurement signal (T) by the sensor; providing a first parameter (p_lin) and a second parameter (p_symm) for compensation of the uncompensated measurement signal (T); and calculating a compensated measurement signal (T*) based on the uncompensated measurement signal (T) and the first parameter (p_lin) and the second parameter (p_symm).

26. The method as claimed in claim 25, wherein the first parameter (p_lin) includes the following step: providing a linearization parameter (p_lin) for compensation of nonlinear behavior of the uncompensated measurement signal (T), wherein the linearization parameter (p_lin) is a design-specific parameter.

27. The method as claimed in claim 26, wherein the linearization parameter (p_lin) is a third-order polynomial parameter.

28. The method as claimed in any claim 27, wherein the second parameter (p_symm) includes the following step: providing a symmetrization parameter (p_symm) for compensation of asymmetrical behavior of the uncompensated measurement signal (T), wherein the symmetrization parameter (p_symm) is a component-specific parameter.

29. The method as claimed in claim 28, wherein the symmetrization parameter (p_symm) is a second-order polynomial parameter.

30. The method as claimed in claim 29, wherein the compensated measurement signal (T*) is calculated according to the following calculation formula:
T{circumflex over ( )}*=T+T{circumflex over ( )}2*p_symm+T{circumflex over ( )}3*p_lin; with T*=compensated measurement signal; T=uncompensated measurement signal; p_symm=second parameter; p_lin=first parameter.

Description

[0033] Advantageous embodiments of the invention are explained in more detail below on the basis of the drawing. In the figures

[0034] FIG. 1 shows an exemplary embodiment of an electromechanical steering system designed according to the invention of a motor vehicle in a perspective, schematic representation,

[0035] FIG. 2 shows an exemplary embodiment of components of a torque sensor device for an electromechanical steering system in a perspective representation,

[0036] FIG. 3 shows a section of a further exemplary embodiment of an electromechanical steering system designed according to the invention of a motor vehicle in a schematic representation,

[0037] FIG. 4 shows a two-dimensional coordinate system in which by way of example values for the detected torque are shown against values for a reference torque,

[0038] FIG. 5 shows a two-dimensional coordinate system in which by way of example values for the magnetic flux density are shown against values for a difference angle,

[0039] FIG. 6 shows a two-dimensional coordinate system in which by way of example values for the measurement error in the detected torque are shown against values for a reference torque,

[0040] FIG. 7 shows a two-dimensional coordinate system in which by way of example values for the magnetic flux density are shown against values for a difference angle, taking into account the assembly tolerance that causes an asymmetry,

[0041] FIG. 8 shows a two-dimensional coordinate system in which by way of example values for the measurement error in the detected torque are shown against values for a reference torque, taking into account the assembly tolerance that causes an asymmetry.

[0042] In the different figures, identical parts are provided with the same reference signs and are therefore usually named or mentioned only once.

[0043] FIG. 1 shows an electromechanical steering system 1 in a perspective, simplified representation from diagonally in front in the direction of vehicle travel, wherein non-essential components are not shown for the sake of a better overview for the description of the invention.

[0044] The steering system 1 for a motor vehicle comprises a steering column with a steering shaft 2. The steering shaft 2 is mechanically coupled to the steerable wheels 4 of a motor vehicle via a steering gear 3. In this exemplary embodiment, the steering gear 3 comprises a pinion 5 and a toothed coupling rod 6, wherein the steering gear 3 serves to translate a rotational movement of the pinion 5 into a translational movement of the coupling rod 6 along its longitudinal axis. On the end of the steering shaft 2 nearer the driver, a steering handling device 7, in particular a steering wheel, for entering a driver's steering request or steering command is non-rotatably arranged, wherein a driver can turn the steering handling device 7 in the form of a steering wheel in a known manner for entering his steering command. In this exemplary embodiment, the coupling rod 6, which moves linearly along its longitudinal axis, is mechanically coupled to a tie rod 8 on both sides of the motor vehicle. The tie rods 8 are in turn each mechanically coupled to the vehicle wheels 4. The steering gear 3 is thus designed to convert a steering command into a steering movement of the steerable wheels 4 of the motor vehicle, taking into account at least one input variable. The steering system 1 further comprises a torque sensor device 40 shown only schematically in FIG. 1, which comprises a sensor 12 for detecting an uncompensated measurement signal T. The connecting line 30 in FIG. 1 symbolically represents the corresponding arrangement of the sensor 12 on the steering shaft 2, in which the sensor 12 can detect a torque applied to the steering shaft 2. Via a signal line 31, which may be wired or wireless, the detected uncompensated measurement signal T is transmitted to a computing unit 35 assigned to the torque sensor device 40. The computing unit 35 is part of the torque sensor device 40 in this exemplary embodiment. In particular, the computing unit 30 may be a microcontroller circuit, in particular an application-specific integrated circuit (ASIC). The computing unit is designed to provide a first parameter and a second parameter for compensation of the uncompensated measurement signal T and to calculate a compensated measurement signal T* on the basis of the uncompensated measurement signal T and the first parameter and the second parameter, in particular as the sum of the uncompensated measurement signal T and the product of the square of the uncompensated measurement signal T with the second parameter and the product of the uncompensated measurement signal T raised to the power of three and the first parameter. Furthermore, the computing unit 35 is designed to provide the calculated compensated measurement signal T* as an input variable via a signal line 32, which may be wired or wireless, in particular as a radio connection, in particular to the steering gear 3 or to a control unit assigned to the steering gear 3 (not shown in FIG. 1).

[0045] FIG. 2 shows components of a torque sensor device, in particular for a torque sensor device 40 according to FIG. 1, for an electromechanical steering system of a motor vehicle in a perspective representation.

[0046] The components comprise a multi-pole magnetic ring 9 for generating a magnetic field to be non-rotatably connected to an input shaft not shown in FIG. 2. The magnetic ring 9 comprises a plurality of individual magnetic poles, wherein individual poles arranged directly next to each other or adjacent each have different poles. The input shaft can be arranged in the central opening of the magnetic ring 9, so that the input shaft and the magnetic ring 9 are arranged coaxially to each other. Furthermore, the components comprise a stator ring element 10 non-rotatably connected to an output shaft that is also not shown in FIG. 2 and radially enclosing the magnetic ring 9, a magnetic flux collector 11, and a sensor 12 for generating a measurement signal.

[0047] The stator ring element 10 is formed in two parts and comprises a first stator sub-ring element 13 and a second stator sub-ring element 14. The magnetic flux collector 11 is also formed in two parts and comprises a first magnetic flux sub-collector 15 and a second magnetic flux sub-collector 16. The sensor 12 is a Hall sensor, preferably in a dual-die package.

[0048] In FIG. 3, a section of an electromechanical steering system 1 is shown schematically, wherein it may be in particular a steering system as explained with reference to FIG. 1. The steering system 1 comprises a steering shaft 2, which comprises an input shaft 201 non-rotatably connected to a steering handling device 7 and an output shaft 202 connected to the input shaft 201 via a torsion bar 203 that can be twisted. Furthermore, the steering system comprises a magnetic torque sensor device 40 for measuring a torque applied to the steering shaft 2. In this exemplary embodiment, the torque sensor device 40 comprises a multi-pole magnetic ring 9 non-rotatably connected to the input shaft 201, in particular as shown in FIG. 2, for generating a magnetic field. Furthermore, the torque sensor device 40 comprises a stator ring element 10 non-rotatably connected to the output shaft 202, enclosing the magnetic ring 9 and having a first stator sub-ring element 13 and a second stator sub-ring element 14, a magnetic flux selector 11 and a sensor 12 for generating a measurement signal T, wherein the corresponding components, in particular the magnetic ring 9, the stator ring element 10, the magnetic flux collector 11 and/or the sensor 12, are advantageously of the form as shown in FIG. 2. In this exemplary embodiment, the sensor 12 is designed to detect the uncompensated measurement signal T based on the magnetic field applied to the magnetic flux collector 11, in particular as a function of a change in the magnitude and/or the direction of the magnetic field strength. The uncompensated measurement signal T is transmitted via a signal line 31 to a computing unit 35 assigned to the torque sensor device 40, in particular a central ECU (ECU: electronic control unit) of the motor vehicle. However, the computing unit 35 may in particular also be a computing unit included in the torque sensor device 40, for example an ASIC. The computing unit 35 is designed to provide a first parameter and a second parameter for compensation of the uncompensated measurement signal T, in particular from a memory unit of the computing unit which is not explicitly shown in FIG. 3, and to determine a compensated measurement signal T* based on the uncompensated measurement signal T and the first parameter and the second parameter. The compensated measurement signal T* is advantageously provided to the steering actuator of the steering system 1, in particular to the steering gear 3, as an input variable. As a result, improved control of the steering controller can advantageously be achieved. In particular, the steering actuator has a control unit which is not explicitly shown in FIG. 3, in particular a proportional controller.

[0049] FIG. 4 shows a two-dimensional coordinate system in which values for the detected torque in Nm (Nm: Newton meters) are displayed on the vertical axis against values for a reference torque in Nm plotted on the horizontal axis.

[0050] The idealized curve 17, represented as a solid line, corresponds to the desired curve, namely such that the detected torque corresponds exactly to the reference torque. In contrast, the actual curve 18 shown as a dashed line corresponds to the true, S-shaped curve, namely such that the detected torque deviates from the reference torque. The deviation in the negative reference torque region (in FIG. 4 on the left) and the deviation in the positive reference torque region (in FIG. 4 on the right) are of opposite sign. In other words, in the negative reference torque region, the detected torque deviates “upwards” from the reference torque, and in the positive reference torque region, the detected torque deviates “downwards” from the reference torque.

[0051] FIGS. 5 and 6 show the compensation of the measurement signal generated by the sensor of the torque sensor device, namely by linearization.

[0052] FIG. 5 shows a two-dimensional coordinate system in which values for the magnetic flux density in mT (mT: millitesla) are represented on the vertical axis against values plotted on the horizontal axis for a difference angle in ° (°: degrees).

[0053] The curve 19 is sinusoidal, i.e. considerably nonlinear. In an angular range of about −5° to about +5°, shown as curve section 20, the curve 19 is less significantly nonlinear. The curve section 20 is approximately linear, wherein the curve section 20 has an S-shaped profile. The center of the coordinate system is in the center of the curve section 20. Accordingly, the curve section 20 is symmetrical with respect to the coordinate center.

[0054] FIG. 6 shows a two-dimensional coordinate system in which values for the measurement error in the detected torque in Nm are shown on the vertical axis against values plotted on the horizontal axis for a reference torque in Nm.

[0055] The uncompensated curve 21 shown as a dashed line corresponds to the profile of the measurement signal T before the compensation of the nonlinearity according to the invention. In contrast, the compensated curve 22 shown as a solid line corresponds to the profile of the measurement signal T* after the compensation of the nonlinearity according to the invention.

[0056] The arrow indicates the linearization of the uncompensated curve 21 towards the compensated curve 22.

[0057] FIGS. 7 and 8 show the compensation of the measurement signal generated by the sensor of the torque sensor device, namely by linearization and symmetrization. Signal artifacts of the nonlinearity and the asymmetry overlap here.

[0058] FIG. 7 shows a two-dimensional coordinate system in which values for the magnetic flux density in mT are shown on the vertical axis against values plotted on the horizontal axis for a difference angle in ° (degrees).

[0059] The curve 23 is sinusoidal, i.e. considerably nonlinear. However, in an angular range of about −5° to about +5°, shown as curve section 24, the curve 23 is less significantly nonlinear. The curve section 24 is approximately linear, wherein curve section 24 has an S-shaped profile. In contrast to the curve 19 from FIG. 5, the center of the coordinate system is not in the middle of the curve section 24, but off-center. The curve section 24 is therefore asymmetrical with respect to the coordinate center. The arrow indicates the asymmetry of the curve section 24.

[0060] FIG. 8 shows a two-dimensional coordinate system in which values for the measurement error in the detected torque in Nm are shown on the vertical axis against values plotted on the horizontal axis for a reference torque in Nm.

[0061] The uncompensated curve 25 shown as a dashed line corresponds to the profile of the measurement signal T before the compensation of the nonlinearity and the asymmetry according to the invention. In contrast, the compensated curve 26 shown as a solid line corresponds to the profile of the measurement signal T* after the compensation of the nonlinearity and the asymmetry according to the invention. The arrow indicates the linearization of the uncompensated curve 25 towards the compensated curve 26. Compared to the curve 21 from FIG. 6, the center of the coordinate system along the horizontal axis is not in the middle of the plateau of the curve 25, but off-center. The curve 25 is therefore asymmetrical relative to the coordinate center.