DE102010032061A1 - Device for measuring a rotation angle and / or a torque - Google Patents

Abstract

A device for torque and angle measurement with improved accuracy will be specified. The device in this case comprises magnetic sensors which are imposed on the back with a magnetic bias. Hall effect sensors or sensors based on the magnetoresistance effect can be used, the detection signal of which is modulated by changing the magnetic field direction and density due to the movement of a target with magnetic targets in front of the sensor. To correct the signal background and amplitude, two signals from a sensor are combined, each of which detects the rotation of the target. To determine the torque acting on an axis, a second sensor for detecting the angle of rotation of a second target is provided and the torque is determined directly from the angle difference of the first and second target from the corrected detection signals.

Description

The present invention relates to devices for measuring the angle of rotation of a rotatable body and / or the torque acting on it.

Such devices find particular application in automotive electric power steering systems, which are often used to assist the driver in steering.

In well-known electric power steering systems (eng. "Electric Power Steering, EPS" and eng., "Electric Power Assisted Steering, EPAS"), an electric-mechanical power steering system provides an electric power steering system that controls the steering movement from the driver to the steering wheel of the vehicle exerted force exerted by an electric motor.

The strength of the electric power steering depends on the steering movement, in particular on the angle of rotation and / or the torque.

This angle must be measured with good accuracy, not only to provide the necessary auxiliary steering force with precision, but also for safety reasons.

One commonly used mechanism for determining the torque acting on a steering wheel is to determine the twist angle of a "flexible" torsion bar of known torsional stiffness connecting an input shaft to an output shaft. The input shaft is connected to the steering wheel of the vehicle and the output shaft to the rack of the vehicle. The torsion bar converts the torque acting on the steering wheel into a twist angle of + -5 ° degrees.

By measuring the angle of rotation as the difference of the angles of the input shaft and the output shaft, the torque can be determined with the known torsional rigidity.

From the DE-A-100 60 287 a device for measuring an angle and / or a torque on a rotatable body is known, wherein the rotation angle is detected by means of magnetic or optical sensors. In one example, two detection wheels are proposed, each having two optically readable code tracks. In each detection wheel, the two code tracks are identically formed and arranged offset from one another, so that associated sensors output a digital signal which corresponds to the rotational movement of the code tracks. From the offset of the two digital signals, the angle of rotation of the detection wheel is calculated.

From the difference between the rotational angles of the two detection wheels, the so-called differential angle, thus also the torque transmitted by the rotatable body can be calculated.

However, such a device has the disadvantage that detection wheels with complex code tracks are needed to achieve a high angular resolution. Also, the integration of such a device in a steering shaft is difficult and must be done before assembling this. These disadvantages lead to increased complexity and cost of manufacture and assembly of such devices.

A device for determining the angle of rotation and the torque using two simpler detection wheels is from the EP-A-1 295 780 known. The rotation of each individual wheel is determined by a pair of magnetic sensors located at the edge of the wheel and spaced so as to provide a sufficient phase shift between the detection signals of the individual sensors. Each sensor of the sensor pair outputs a periodic detection signal corresponding to the rotation angle of the detection wheel. Since the angle determination around the maxima of the detection signal is associated with a larger error, it is determined which sensor is in the linear range of the detection signal and only the corresponding sensor for angle determination is used.

The aim of the present invention is to provide a torque and rotation angle sensor, which is particularly simple and inexpensive to produce, and also has an improved accuracy.

This is achieved in the present invention by use of magnetic sensors which are rearwardly imposed with a magnetic bias. In this case, Hall effect sensors or sensors based on the magnetoresistance effect can be used whose detection signal Change in the magnetic field direction and density due to the movement of a target with magnetic targets in front of the sensor is modulated.

Such sensors can be easily integrated, for example, in a steering system for a vehicle. Another advantage is the easy installation option of the target in such a system. In this case, the target can in particular be manufactured integrally with a shaft during the manufacturing process.

However, the accuracy of such sensors can be greatly influenced by the magnetic field strength, the distance to the target, the temperature, and other factors. Furthermore, the signal background is significant compared to the amplitude, so that signal correction is necessary to eliminate the influence of these effects.

The solution to this problem in the present invention is based on the combination of two signals of a rotationally biased rear magnetic sensor, each corresponding to the rotation of the target.

By means of signal processing, a background component is determined in each detection signal and a compensated detection signal is output.

In the case of a Hall sensor, a 3D Hall sensor can be used and the angle of rotation of the target can be determined using the detection of the orthogonal components B _z and B _{x of} the magnetic flux density. In the case of detection due to the magnetoresistance effect of the rotation angle sensor is formed by a pair of sensors, which outputs the two necessary signals. For the application for determining the torque acting on an axis, in each case a second Hall sensor or a second sensor pair is used in detection on the basis of the magnetoresistance effect, which detect the angle of rotation of a second target. In this case, the first target is fixed to the above-mentioned axis, which is coupled via a torsion element with known torsional stiffness with the axis of the second target. From the difference angle between the first and second target then the torque can be determined directly from the corrected detection signals.

For a better understanding of the present invention, this will be explained in more detail with reference to the embodiments illustrated in the following figures. The same parts are provided with the same reference numerals and the same component names. Furthermore, individual features or combinations of features from the embodiments shown and described can in themselves represent independent inventive or inventive solutions.

1 shows a schematic representation of the structure of a first embodiment of the present invention, in which a device according to the invention for measuring the angle of rotation and a device according to the invention for measuring the torque are used;

2 shows a schematic representation of the curves of the detection signals of a device for measuring the angle of rotation according to 1 as a function of the relative angle of rotation.

3 shows a block diagram for the signal processing of the detection signals and the calculation of a differential angle according to the embodiment of the 1 ;

4 shows a schematic representation of the structure of a second embodiment of the present invention;

5 shows a schematic representation of the curves of the detection signals of a device for measuring the angle of rotation according to 4 as a function of the relative angle of rotation.

6 FIG. 12 is a block diagram for signal processing of the detection signals and differential angle calculation according to the second embodiment of the present invention. FIG.

1 shows a schematic representation of the structure of a device according to the invention for measuring the angle of rotation and a device according to the invention for measuring the torque, or torque sensor 1 ,

The device has a magnetic sensor 50 which is at a fixed position with respect to the outer edge of a rotatable body or rotating part, spaced.

The rotating part can be coaxial with an axis 2 , Are mounted on a shaft or to be rotated in a clockwise direction or in the mutual direction about the axis of rotation and to detect the corresponding angle of rotation.

In the illustrated embodiment, the rotating part is a target 10 that have a variety of magnetic targets 30 includes. The magnetic goals 30 are at substantially equal intervals over the circumference of the target 10 distributed and radially outward at the target 10 arranged.

In the event that the target 10 Made of ferromagnetic material, the goals become 30 formed by an outer tooth / groove profile, as in 1 is shown.

For attachment to the rotatable axle or shaft includes the target 10 Furthermore, fastening means in the form of an inner tooth profile 25 , But it can also be used other known attachment variants, such. B. grooves, etc.

The magnetic sensor 50 obtains a bias magnetic field (magnetic back-bias) by a bias magnetic field generating element 40 , z. B. a permanent magnet, the back of the magnetic sensor 50 is arranged, ie on the target 10 opposite side. The bias magnetic field generating element 40 and the magnetic sensor 50 are held in a fixed position relative to each other. In this case, the magnetic field generating element 40 together with the magnetic sensor 50 be integrated in a sensor component.

The bias magnetic field generating element 40 generates magnetic field lines through the magnetic sensor 50 flow and their change from the magnetic sensor 50 be recorded.

The magnetic sensor 50 is the target 10 positioned and spaced so that the rotational movement of the magnetic targets 30 with respect to the stationary magnetic sensor 50 a change in the magnetic flux through the magnetic sensor 50 generated.

Alternatively, an arrangement is conceivable in which the magnetic sensor moves with the rotary part, while magnetic targets are provided stationary around the rotary part.

When the magnetic goals 30 on the sensor 50 move past, the direction and / or density of the magnetic field lines of the bias magnetic field are changed at the location of the sensor. The magnetic sensor outputs a periodic detection signal representing the tooth profile of the target 10 maps. The signal amplitudes are largely independent of the speed of the target 10 , which represents a significant advantage over inductive systems.

Preferably, the bias magnetic field generating element generates 40 a substantially homogeneous bias magnetic field at the location of the sensor 50 leading to the plane of the magnetic sensor 50 is perpendicular or substantially perpendicular (eg in the Z-direction). So if a torque on the shaft and / or on the target 10 is applied, which is a rotational movement about the axis of rotation 2 causes the corresponding rotational angle in the direction of rotation by detecting the changes of the magnetic field lines by the magnetic sensor 50 be recorded.

In the first embodiment, the measuring principle of the magnetic sensor is based 50 on the well-known Hall effect.

The used magnetic sensor 50 is designed to detect changes in magnetic flux density in two mutually orthogonal directions. The first direction is parallel to the surface of the magnetic sensor 50 (X-axis) and the second direction perpendicular thereto (Z-axis). This is the magnetic sensor 50 the goals 30 so arranged opposite, that the first direction tangential to the circumference of the target 10 (tangential direction) and the second direction radially to the target 10 (Radial direction), or perpendicular to the plane of the magnetically sensitive surface of the magnetic sensor 50 (ie perpendicular to the XY plane) are aligned. The tangential and radial directions are orthogonal to the direction of the rotation axis (Y-axis).

In the present embodiment, a so-called three-dimensional (3D) Hall sensor is preferably used, which in contrast to conventional Hall sensors, with which it is only possible to carry out measurements of the magnetic flux density in one direction (Z axis) with a Hall element, also allows detection in an additional orthogonal plane (XY plane).

2 represents the course of the components of the magnetic flux density B _z and B _x as a function of the relative rotation angle α of the target by the 3D Hall sensor 50 in the present embodiment. The upper part of the 2 schematically illustrates the relative positioning of the tooth / gap profile of the target 10 with respect to the 3D Hall sensor 50 and the rear side of the sensor arranged permanent magnet 40 representing the rotation of the target 10 results in a mechanical angle of rotation Ω in the illustrated direction of rotation. The explanation is the teeth 30 , one after the other on the sensor 50 pass by, numbered from 1 to 6. The (schematic) interpret between the tooth / gap profile and the sensor 50 the alignment of the magnetic flux lines around the sensor 50 and their change by the relative positioning of the tooth / gap profile with respect to the 3D Hall sensor. By the relative movement of the magnetic targets 30 and the sensor 50 Due to the bias magnetic field, both the periodic change of the component B _{Z of} the magnetic flux density in the radial direction (Z axis) and the component B _{X of} the magnetic flux density in the tangential direction (X axis) occur.

In the lower part of the 2 will be the one in the sensor 50 caused, rotation angle-dependent periodic change of the values of the components B _Z and B _{X of} the magnetic flux density as a function of the relative rotation angle α shown.

The vertical dashed lines represent values of components B _X and B _Z for those in the upper part of FIG 2 shown positioning of the teeth 1 to 6.

In this case, the maximum values of B _{Z are} numbered from 1 to 6, which are detected when the respective tooth is substantially opposite to the sensor 50 lies. These maximum values correspond to an orientation of the bias magnetic field substantially perpendicular to the plane of the sensor. The B _X component reaches a zero crossing.

On the other hand, the minimum value of the _BZ component is reached when there is a gap 35 opposite the sensor 50 lies, as in 2 for teeth 3 and 4 shown.

The two components of magnetic flux density, B _Z and B _X , are used in the 3D Hall sensor 50 which generates two different detection signals in the form of output voltage signals U _Z and U _X. These detection signals U _Z and U _X are proportional to the corresponding component of the magnetic flux density B _Z and B _X and have a phase difference of substantially 90 Degrees.

In a tooth / gap profile with N evenly spaced teeth 30 The values of these components, or the two detection signals, follow approximately a sine / cosine function with a period corresponding to a mechanical absolute rotation angle of 360 ° / N. It is noted that the mechanical rotation angle Ω of the target 10 as Ω = α / N from the relative rotation angle α, or as Ω = n × 360 ° / N + α ₀ / N, where n is the number of detected maxima since the zero position (eg the positioning of tooth 1 ), and α ₀ indicates the angle value since the last maximum. The angle value α ₀ can be calculated directly from the measured detection signals by the sine / cosine function.

For an absolute rotation angle smaller than 360 ° / N, no maxima since the zero position is detected (n = 0) and the absolute rotation angle simply results as Ω = α ₀ / N.

However, the angular accuracy of such sine / cosine sensor is limited by the magnetic offset effect.

If standard, a permanent magnet 40 is used, shows the component of the magnetic flux density B _Z , as in 2 indicated, in principle, a significant background or offset value, B _{Z, offset} , of about 200-500 mT, the substantially constant and independent of the rotational movement of the target 30 is. In contrast, the amplitudes of the components B _X and B _Z changed by the mechanical rotation are generally in the range of 0.2 to 2 mT. Component B _X shows a relatively small offset value, B _{X, offset} compared to the amplitude.

Taking into account the offset effect caused by the magnetic bias, the two components B _Z and B _X , or the respective detection signals U _Z and U _{X, result} as follows: B _X = .DELTA.B _X × sin (α) + B _Xoffset B _Z = ΔB _Z × cos (α) + B _Zoffset where ΔB _X and ΔB _{Z are} the amplitudes of the respective components B _X and B _Z , and B _{Z, offset} , B _{X, offset} the respective _offset values.

The occurrence of such an offset in the two detection signals actually falsifies the rotational angle measurements that have to be made.

The present invention enables a simple determination of the amplitude and the offset value of the respective detection signals, so that on the basis of the determined values an adjusted rotation angle calculation is feasible.

The amplitude and offset of the respective detection signals can be determined from maximum and minimum values of the detection signal as follows.

To calculate the amplitudes ΔB _X and ΔB _Z , the maximum value and the minimum value of the respective detection signals of the respective components B _X and B _{Z are} determined and the amplitudes are then calculated as the difference between the determined maximum and minimum values for the respective components. The offset value B _Xoffset or B _{Zoffset is} calculated in each case as half of the sum of maximum value and minimum value.

The detection signals can then be compensated directly after a certain number of signal periods, and the sin (α) and cos (α) measured values by the corrected detection signals of the 3D Hall sensor 50 calculated as follows:

On the basis of such corrected measured values, the mechanical absolute rotation angle Ω = α / N can be calculated, for example, by the arctangent of the ratio of the thus obtained sine and cosine signals. For a rotation angle smaller than 360 ° / N is only a maximum of one target 30 in front of the sensor 50 passed by and the absolute rotation angle Ω can be determined directly from the measured detection signals. Otherwise, the number n of maxima of the B _z component is determined, and the corresponding angle component n × 360 ° / N is added to the measured value α ₀ , as described above. For example, would be for a target with 100 evenly spaced targets 30 the mechanical angle of rotation corresponding to the relative positioning of the in 2 illustrated tooth 2 of the above equation with n = 1, N = 100 and α ₀ = 45 ° are calculated.

By means of the method according to the invention, the magnetic offset of the magnetic sensor can be calculated and compensated in a simple manner during operation, which enables an increase in the angular accuracy. In particular, the illustrated method allows automatic offset adjustment in dynamic rotational movements.

To measure the torque is, as in 1 shown, in the direction of the axis of rotation, a second device for measuring the angle of rotation with a second target 20 and a second magnetic sensor 60 arranged. In this case, the structure and function of the device described above, ie, in particular the second magnetic sensor determines the rotation angle of the second target. In this case, the first target can be connected to an input shaft and the second target can be connected to an output shaft, which are coupled via a torsion element with known torsional rigidity.

Like the first magnetic sensor 50 also receives the second magnetic sensor 60 a bias magnetic field by the bias magnetic field generating element 40 ,

From the difference of the angle of rotation Ω1 of the first target 10 and the rotation angle Ω _{2 of} the second target 20 can then be determined by means of the known torsional rigidity, the torque. In this case, the torsion element is designed so that it operates at the expected angles in the elastic measuring range of the torsion element. The resulting torque is then directly proportional to the rotation angle difference.

In the present embodiment, the rotational angle difference becomes above the detection signals of the first and second 3D Hall sensors 50 . 60 detected.

If the first target 10 is rotated by a mechanical angle value Ω ₁ , provides the first 3D Hall sensor 50 two electrical detection signals U _Z1 and U _X1 , which are directly proportional to the orthogonal components of the magnetic field B _Z1 and B _X1 at the location of the first 3D Hall sensor 50 are. These components arise as: B _Z1 = ΔB _Z1 × sin (α) + B _Zoffset B _X1 = ΔB _X1 × cos (α) + B _Xoffset where ΔB _X1 , ΔB _{Z1 are} the amplitudes and B _Zoffset , B _{Xoffset are} the offset values of the respective components B _X1 and B _Z1 . α is the relative angle of rotation of the first target 10 ,

The rotation of the torsion element is the on the first target 10 acting torque proportional. Therefore, a difference Δα results in the relative rotation angle of the first one 10 and second target 20 , The second sensor 60 also provides two electrical detection signals U _Z2 and U _X2 , which are directly proportional to the orthogonal components of the magnetic field B _Z2 and B _X2 at the location of the second 3D Hall sensor 60 are. These components arise as: B _Z2 = ΔB _Z2 × sin (α + Δα) + B _Zoffset B _X2 = ΔB _X2 × cos (α + Δα) + B _Xoffset where ΔB _X2 , ΔB _{Z2 are} the amplitudes and B _Zoffset , B _{Xoffset are} the offset values of the respective components B _X2 and B _Z2 . α + Δα is the relative angle of rotation of the second target 20 ,

Preferably, in this embodiment, the two 3D Hall sensors 50 . 60 similar properties and distance with respect to the respective target 10 . 20 , Then, the detection signals for the respective components B _Z and B _{x of} the two 3D Hall sensors 50 . 60 equal amplitudes and offset values, which simplifies the calculation accordingly.

The amplitudes and offsets of the respective detection signals are determined by the methods described above.

As described above, the sin (α) and cos (α) values can be detected by the corrected detection signals B _{Z1, Korr} and B _{X1, Korr of} the first 3D Hall sensor 50 calculated as follows:

The values sin (α + Δα) and cos (α + Δα) are determined by means of the corrected detection signals B _{Z2, Korr} and B _{X2, Korr of} the second 3D Hall sensor 60 calculated:

The difference angle Δα can then be calculated by the known sine-cosine formula: sin (α - (α + Δα)) = sin (α) × cos (α + Δα) - cos (α) × sin (α + Δα) sin (-Δα) = sin (α) × cos (α + Δα) - cos (α) × sin (α + Δα)

For differential angle values Δα less than 4 °, sin (-Δα) ≈ -Δα applies. The relative error in the angular interval (-4.4 ° to + 4.4 °) is only 0.1% maximum.

oder kann direkt aus den korrigierten Detektionssignalen B_X1,korr, B_Z1,korr, B_X2,korr und B_Z2,korr durch die folgende Formel berechnet werden: –Δα = B_X1,korr × B_Z2,korr – B_Z1,korr × B_X2,korr The difference angle Δα is then determined as follows:

or can be calculated directly from the corrected detection signals B _{X1, corr} , B _{Z1, corr} , B _{X2, corr} and B _{Z2, corr} by the following formula: -Δα = B _X1, corrx B _{Z2, corr} -B _{Z1, corrx} B _{X2, corr}

This evaluation method is very sensitive to the smallest angle differences.

The differential angle can be determined by analogous electronic operations (multiplication, subtraction, comparison), as in 3 is shown. By the procedure described above, the torque can be determined directly from the angular difference.

To perform the above-described operations, the torque measuring device further includes a process unit 3 which processes the detection signals. The process unit 3 is schematic in 3 shown. It includes a peak detector 310 . 311 . 312 . 313 for each detection signal which determines the maximum and minimum values of each detection signal. The offset value is calculated for each detection signal by means of the determined maximum and minimum values and then to a respective subtraction unit 320 . 321 . 322 . 323 which subtracts the offset value from the measured signal.

Minimum and maximum values are also passed to a respective amplitude calculation unit, which calculates the amplitudes of the respective signal as described above.

The offset corrected signal is from the subtraction unit 320 . 321 . 322 . 323 to a respective division unit 330 . 331 . 332 . 333 which outputs the obtained signal by the calculated amplitude to output a corrected detection signal B _{X1, corr} , B _{Z1, corr} , B _{X2, corr} and B _{Z2, corr} .

The calculation of the corrected detection signals is carried out correspondingly for all four detection signals B _Z1 , B _X1 , B _Z2 and B _X2 .

The resulting corrected detection _signals B _Z1korr and B _X2korr , and B _Z2korr and B _X1korr then become in a corresponding multiplication unit 340 . 341 multiplied by each other.

In another subtraction unit 360 then the rotation angle difference is calculated as the difference of the above products.

The signal processing can also be performed on a digital level in a digital signal processor (DSP).

4 shows a schematic representation of the structure of a second embodiment of the device for measuring the angle of rotation and the device for measuring the torque, or torque sensor 4 , according to the invention.

In the second embodiment, the measuring principle of the magnetic sensors based on the known magnetoresistance effect.

In this embodiment, so-called AMR, GMR or TMR sensors may preferably be used. For the sake of simplicity, these sensors are referred to below as XMR sensors.

The magnetic sensors are designed so that they can detect changes in the magnetic flux density parallel to the magnetically sensitive surface of the sensor (X-axis) and output a corresponding detection signal.

To the rotation angle of the target 10 In the second embodiment, two XMR sensors which output two different detection signals are applied.

As in 4 illustrated, the device for measuring the rotation angle of the upper target 10 a first XMR sensor R1 and a second XMR sensor L1 stationary with a fixed distance in the radial direction of the target 10 are arranged. The two XMR sensors R1, L1 are next to each other at a fixed distance from each other in the tangential direction with respect to the rotational movement of the target 10 arranged.

Each XMR sensor R1, L1 is given a magnetic bias. For this purpose, as in the first embodiment, a magnetic field generating element is arranged on the back of the sensor. This element may, for example, be a permanent magnet 40 be.

Due to the magnetic bias, the rotational movement of the tooth / gap profile in front of the XMR sensors R1, L1 results in a periodic change in the magnetic flux density B _X in the tangential direction of the rotational movement (X axis) as a function of the angle of rotation XMR sensors R1, L1 can be detected.

5 shows a schematic representation of the curves of the detection signals of the device for measuring the angle of rotation according to 4 as a function of the relative angle of rotation of the target.

The upper part of the 5 schematically illustrates the relative positioning of the tooth / gap profile of the target 10 with respect to the juxtaposed XMR sensors R1, L1 and the rear side of the XMR sensors arranged permanent magnet 40 The lines shown between the Gap / Gap profile and each XMR sensor indicate alignment of the magnetic flux lines around the respective XMR sensor and their change by the relative positioning of the Gap / Gap profile with respect to the XMR sensor.

To illustrate the formation of the sensor signal, the teeth are as in 2 numbered from 1 to 6. The maxima of the resulting signal B _XL are numbered consecutively from 1 to 6, with the maximum n (n = 1 to 6) corresponding to the respective position of the tooth n in the center of the sensor.

As in the first embodiment, a waveform corresponding to a circular angle function is obtained for each XMR sensor R1, L1. According to the invention, the distance between the XMR sensors is selected such that a specific phase difference results between the detection signal as a function of the relative rotational angle α of the first XMR sensor R1 and the second XMR sensor L1. To simplify the determination of the rotation angle α, the two XMR sensors are here spaced such that the phase difference between the detection signals is at 90 °.

There are therefore two detection signals which are proportional to the following measured components B _{X of} the magnetic flux density: B _XL = ΔB _XL × cos (α) + B _Xoffset B _XR = ΔB _XR × sin (α) + B _Xoffset where ΔB _XL and B _{Xoffset are} the amplitude and offset of the component B _X at the location of the XMR sensor L1, and ΔB _{XR is} the amplitude of the component B _X at the location of the XMR sensor R1.

The first XMR sensor R1 and the second XMR sensor L1 can be further selected to have identical sensitivity.

In the above-described choice of XMR sensors and their positioning, both background B _Xoffset and the amplitude ΔB _XL and ΔB _{XR are} to be regarded as identical for both detection signals.

The rotational angle difference Δα between the first target 10 and the second target 20 is detected by the detection signals from four XMR sensors.

The mechanical angle of rotation Ω = α / N the first target 10 is determined by the electrical detection _signals output from the first XMR sensor R1 and second XMR sensor L1, which are directly proportional to the parallel components of the magnetic fields B _XR1 and B _XL1 at the location of the respective XMR sensor R1 and L1, respectively: B _XR1 = ΔB _X1 × sin (α) + B _X1offset B _XL1 = ΔB _X1 × cos (α) + B _X1offset where ΔB _X1 and B _{X1, offset are} the amplitude and the offset value of the components B _XR1 and B _XL1 .

The first and second target 10 . 20 are coupled together as in the first embodiment by a torsion element. Therefore, in the second embodiment as well, a difference Δα in the rotational angles of the first and second targets results 10 . 20 due to the torque applied to the target.

The relative rotation angle α + Δα of the second target 20 is determined by a second pair of sensors. The second pair of sensors comprises a third XMR sensor R2 and a fourth XMR sensor L2, which also output two electrical detection signals proportional to the following components: B _XR2 = ΔB _X2 × sin (α + Δα) + B _X2offset B _XL2 = ΔB _X2 × cos (α + Δα) + B _X2offset where ΔB _X2 and B _{X2offset are} the amplitude and the offset of the components B _XR2 and B _XL2 , and α + Δα are the angles of rotation of the second target 20 is.

In the exemplary embodiment, all XMR sensors have similar properties, in particular with respect to their sensitivity and spacing from the respective targets. Therefore, the amplitudes and offset values of the detection signals for the respective XMR sensors can be considered equal.

The amplitudes and offsets of the respective detection signals are determined by the methods described above, and the sine and cosine values of the rotation angles α and α + Δα are calculated by the corrected detection signals.

The corrected detection _signals B _{XL1, korr} and B _{XR1, corr of} the XMR sensor L1 and the XMR sensor R1 are then calculated as follows:

The corrected detection signals B _{XL2, korr} and B _{XR2, corr of} the XMR sensor L2 and the XMR sensor R2 are calculated as follows:

oder kann direkt hinsichtlich der korrigierten Detektionssignale durch die folgende Formel berechnet wird: –Δα = B_XL1,korr × B_XR2,korr – B_XR1,korr × B_XL2,korr According to the sine-cosine formula sin [α - (α + Δα)] for small angles, the difference angle can be calculated as follows:

or can be calculated directly with respect to the corrected detection signals by the following formula: -Δα = B _{XL1, corr} × B _{XR2, corr} - B _{XR1, corr} × B _{XL2, corr}

Analogously to the first embodiment, the torque measuring device in this embodiment comprises a process unit for performing the above-described operations.

The calculation of the corrected detection signals and the rotation angle difference then proceeds accordingly by analogous electronic operations (multiplication, subtraction, comparison) as discussed above for the first embodiment. The signal processing can also be performed on a digital level in a digital signal processor (DSP).

However, because of the above-mentioned equality of the amplitude and offset values of the individual detection signals for each pair of XMR sensors, these need only be calculated once. Therefore, the process unit can be simplified accordingly. As in 6 is shown, includes the process unit 6 in the second embodiment, only two peak detectors 610 . 620 which determine the maximum and minimum values of the detection signals for each pair of XMR sensors. The offset value and the amplitude are calculated for these detection signals by means of the determined maximum and minimum values as discussed in the first embodiment.

The peak detector 610 determines the maximum and minimum values of the detection signal from an XMR sensor of the first sensor pair R1, L1, z. B. the XMR sensor R1, and calculates the offset value B _{X1, offset} and the amplitude .DELTA.B _X1 for the two XMR sensors R1 and L1.

The offset value B _{X2, offset} and the amplitude ΔB _X2 for the XMR sensors of the second sensor pair R2, L2 are determined by the second peak detector 620 calculated, the maximum and minimum value of the detection signal of only one XMR sensor of the second sensor pair R2, L2 determined, z. B. the XMR sensor R2.

The calculated offset values and amplitudes are then passed to the subtraction units and division units. In this case, the corrected detection signals by separate subtraction units 320 . 321 . 322 . 323 and division units 330 . 331 . 332 . 333 for each XMR sensor R1, L1, R2, L2 calculated as described in the first embodiment.

The rotational angle difference Δα is then calculated from the corrected detection _signals B _{XL1, corr} , B _{XR1, corr} , B _{XL2, corr} , B _{XR2, corr} through the two multiplication _units 340 . 341 and the division unit 350 calculated. These operations are essentially the same as those in 3 represented process unit 3 and therefore will not be described again.

In an advantageous variant, the process unit could 3 of the first embodiment are used to determine maximum and minimum values from the detection signal of each XMR sensor and to determine the corresponding offset value and amplitude for the respective XMR sensor.

The calculation of the corrected detection signals and the rotation angle difference then proceeds as for the above-described process unit 3 ,

Nevertheless, the invention is not limited to the illustrated embodiments.

In the first and second embodiments, the bias magnetic field of each magnetic sensor becomes the same as the bias magnetic field generating element 40 provided or generated. Alternatively, the bias magnetic field for each magnetic sensor may be provided by a separate bias magnetic field generating element. This element can be integrated in every sensor component. Advantageously, the bias magnetic field generating element can be replaced in the second embodiment by two permanent magnets, one for each pair of sensors. Since, by the present invention, the background effect of the bias magnetic field in the detection signal from each magnetic sensor can be advantageously compensated, differences between the individual bias magnetic field generating elements are simply canceled.

In the illustrated embodiments, the target is a gear made of ferromagnetic material having a radial tooth / gap geometry.

In an advantageous variant, the target can also be produced integrally with the rotatable shaft. In another alternative embodiment, the magnetic targets may be recessed directly in the rotatable shaft.

In another advantageous embodiment, instead of the illustrated target, a tubular rotatable member having an annularly arranged plurality of apertures as targets may be used. In this case, the tubular part itself may consist of a magnetic material. LIST OF REFERENCE NUMBERS numeral description 1 first rotation angle sensor 2 axis of rotation 10 first target (upper) 20 Second target (lower) 25 inner tooth profile 30 aim 35 gap 40 permanent magnet 50 . 60 3D Hall sensors 55 the side of the sensor facing the target 3 process unit 310 . 311 . 312 . 313 Peak detector 320 . 331 . 332 . 333 first subtraction unit 330 . 331 . 332 . 333 Division unit 340 . 341 multiplication unit 350 second subtraction unit 4 second rotation angle sensor with XMR sensors R1, L1, R2, L2 XMR sensors 6 second process unit 610 . 620 Peak detector

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• DE 10060287 A [0008]
• EP 1295780A [0011]

Claims (14)

Device for measuring the angle of rotation of a rotatable body, comprising: means for detecting ( 50 , R1, L1), which are designed to output a detection signal, which is one of the rotation of a mounted on the rotatable body targets ( 30 indicates induced change of a magnetic field, means for applying a bias magnetic field ( 40 ) to the detection means ( 50 , R1, L1); and signal processing means ( 3 ) configured to detect a background component caused by the bias magnetic field in the detection signal and to output a compensated detection signal. Device according to claim 1, wherein the signal processing means ( 3 ) are adapted to determine a minimum and a maximum value in the amplitude of the detection signal, to calculate an offset value and a distance value of the detection signal using the determined minimum and maximum values, and to compensate the detection signal. Apparatus according to claim 2, wherein the offset value is an average of the determined minimum and maximum values and the distance value is the difference of the determined minimum and maximum values. Device according to one of the preceding claims, wherein the detection signal is compensated after a predetermined number of detection periods. Device according to one of the preceding claims, wherein the means for detecting ( 50 , R1, L1) are adapted to output a detection signal containing a first detection signal and a second detection signal with a phase difference of 90 degrees. Device according to one of the preceding claims, wherein the first detection signal of a component of the magnetic field parallel to that of the targets ( 30 ) facing side ( 55 ) the means of detection ( 50 , R1, L1), and the second detection signal of a component of the magnetic field perpendicular to that of the targets ( 30 ) facing side ( 55 ) the means of detection ( 50 , R1, L1). Device according to one of the preceding claims, wherein the means for detecting a 3D Hall sensor ( 50 ) contain. The apparatus of claim 5, wherein the means for detecting includes a first magnetoresistive sensor (R1) for outputting the first detection signal and a second magnetoresistive sensor (L1) for outputting the second detection signal, the first and second detection signals being parallel to a component of the magnetic field to the goals ( 30 ) facing side ( 55 ) of the respective magnetoresistive sensor (R1, L1). The device of claim 8, wherein the first (R1) and second (L1) magnetoresistive sensors are spaced so that the first and second detection signals have a phase difference of 90 degrees. Device according to one of the preceding claims, wherein the rotatable body is a target ( 10 ) with a tooth / gap profile with magnetic targets ( 30 ). Device according to one of the preceding claims, comprising the rotatable body ( 10 ). Device for measuring a torque applied to a shaft, comprising: a first device according to one of claims 1 to 10 for measuring the angle of rotation of the shaft, a second device according to one of claims 1 to 10 for measuring the angle of rotation of a second shaft, wherein the shaft is coaxially connected to the second shaft by a torsion element, and wherein the torque is determined in proportion to the differential rotation angle of the rotation angle of the shaft and the rotation angle of the second shaft. The device of claim 12, wherein the shaft is a steering shaft of a steering system. A steering system comprising a device according to any one of the preceding claims.

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