Device for generating a measurement signal

Abstract

The invention relates to a device (9) for generating a measurement signal (19) that depends on a torque (13) applied to a torsion shaft (10) around a rotational axis (8), comprising: - a magnet ring (16), fixed to a first axial position of the torsion shaft (10) and having a predefined number of magnetic poles (28, 29) for generating a magnetic field (17), characterized in that the device has - a magnet sensor (18), fixed to a second axial position of the torsion shaft (10) different from the first axial position and comprising - - a first sensor element (33), located in a radial plane (36) around the rotational axis (8) and outputting a first sensor signal that depends on the magnetic field (17) reaching the first sensor element (33), and - - a second sensor element (34, 38), located in the radial plane (36) of the first sensor element (33) but spaced from the first sensor element (33) by a distance (35) less than the circumferential extension of two adjacent magnetic poles, and outputting a second sensor signal that depends on the magnetic field reaching the second sensor element (34, 38), - an evaluation system (21), adapted to filter a stray field signal component (39) from the first sensor signal based on the second sensor signal and adapted to output the measurement signal (19) based on the filtered first sensor signal.

Description

Field of the Invention

[0001] The present invention relates to a device for measuring the angle of rotation about a rotational axis and to a vehicle comprising such a device. Background Art

[0002] A device for measuring the torque applied to a torsion shaft about a rotational axis is known from EP 1 870 684 A1. In this known device, a first sensor element is used for detecting the torque and a second sensor element is used for fault determination. This fault determination is carried out by a known process in which, for example, the outputs of the two sensor elements are compared in a time series and, when there is a significant difference between the outputs, the sensor element showing an unstable output change before and after this significant difference is determined to be in a fault condition. Summary of the Invention

[0003] An object of the present invention is to improve this device.

[0004] According to one aspect of the present invention, a device for generating a measurement signal that depends on the torque applied to a torsion shaft about a rotational axis, the device comprising a magnet ring fixed to a first axial position of the torsion shaft and having a predefined number of magnetic poles for generating a magnetic field. The device is characterized in that it has a magnet sensor fixed to a second axial position of the torsion shaft different from the first axial position and comprising a first sensor element located in a radial plane about the rotational axis and outputting a first sensor signal that depends on the magnetic field reaching the first sensor element; and a second sensor element located in the radial plane of the first sensor element but spaced from the first sensor element by a distance less than the circumferential extent of two adjacent magnetic poles and outputting a second sensor signal that depends on the magnetic field reaching the second sensor element. The device further comprises an evaluation system adapted to filter out a stray field signal component from the first sensor signal based on the second sensor signal and adapted to output a measurement signal based on the filtered first sensor signal.

[0005] The first sensor element is preferably adapted to measure the magnetic field reaching the first sensor element in Cartesian coordinates. Furthermore, the second sensor element is preferably adapted to measure the magnetic field reaching the second sensor element in Cartesian coordinates.

[0006] The device is based on the idea that in the device mentioned at the beginning, the second sensor element can only be used to monitor the correct functionality of the first sensor element by correcting the first sensor signal output by the first sensor element with respect to the second sensor signal. However, when the sensor elements are arranged in a common magnet sensor and are positioned close together, an interference field is generated that is superimposed on the magnetic field of the magnet ring, and the first sensor signal and the second sensor signal will have almost the same amount in the first sensor signal and the second sensor signal and can therefore be filtered out. The influence of the interference field can thus be reduced by 99%, which, for example in a steering control loop, significantly stabilizes the post-processing of the measurement signal.

[0007] In an embodiment of the provided device, the radius r of the outer circumference of the magnet ring 编码器 and the displacement angle of the sensor element as seen from the axis of rotation and hereinafter referred to as satisfy the equation where a is a value between 0.3 and 3. In the provided range of a, the surface of the magnet ring appears to be flat for the magnet sensor in one aspect, but ensures that different sensor elements obtain independent magnetic measurements, making it possible to filter out the interference field described above. The value of a can preferably be set to 2.

[0008] In a further embodiment of the provided device, the distance of each sensor element from the axis of rotation is between 3% and 15% of r 编码器 and preferably 7%. In this distance range, the magnetic field of the magnet ring is sufficiently undisturbed to enable accurate detection of the torsion of the torsion element.

[0009] In a preferred embodiment of the provided device, the second sensor element is circumferentially spaced from the first sensor element. Basically, the second sensor element can be randomly arranged in the radial plane around the first sensor element. However, when the second sensor element is positioned circumferentially spaced from the first sensor element, the magnet ring can be designed very simply in structure.

[0010] In a further embodiment of the provided device, the magnet sensor further comprises a third sensor element and a fourth sensor element. The third sensor element is circumferentially positioned and axially spaced from the first sensor element and outputs a third sensor signal depending on the magnetic field reaching the third sensor element. The fourth sensor element is circumferentially positioned at the second sensor element, axially positioned at the third sensor element and outputs a fourth sensor signal depending on the magnetic field reaching the third sensor element, and wherein the circumferential distance is less than half of the circumferential extension of one magnetic pole. By this means, interfering fields can be eliminated from the sensor signals. This can be most easily achieved when filtering out stray field signal components from the first sensor signal by generating the quotient between the difference of the first sensor signal and the fourth sensor signal and the difference of the second sensor signal and the third sensor signal.

[0011] In yet another embodiment of the provided device, the circumferential distance is one third of the circumferential extension of one magnetic pole.

[0012] According to another aspect of the invention, a vehicle comprises a chassis movable in a driving direction, two rear wheels movably carrying the chassis at the rear side seen in the driving direction, two front wheels movably carrying the chassis at the front side seen in the driving direction, a steering wheel for rotating a steering column about a rotation axis to steer the front wheels, and one of the devices provided above for measuring the rotation angle of the steering column about the rotation axis. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The above-described features, characteristics and advantages of the present invention and the manner in which they are achieved will be further understood based on the following description of embodiments, which will be explained in more detail with reference to the accompanying drawings. The drawings show:

[0014] Figure 1 is a schematic perspective view of the principle of an automobile,

[0015] Figure 2 is for measuring rotation about Figure 1 a schematic cross-sectional view of the principle of a device for measuring the rotation angle of the rotation axis in an automobile,

[0016] Figure 3 is according to a first embodiment of the present invention Figure 2 a cross-sectional view of the magnet ring and the integrated circuit with sensors in the device,

[0017] Figure 4 is Figure 3 a top view of the magnet ring and the integrated circuit in the device,

[0018] Figure 5 is Figure 5 and6 Top view of the part in a measurement environment in a first arrangement

[0019] Figure 6 is Figure 5 and 6 Top view of the part in a measurement environment in a second arrangement

[0020] Figure 7 is Figure 5 and 6 Top view of the part in a measurement environment in a third arrangement

[0021] Figure 8 is Figure 5 and 6 Top view of the part in a measurement environment in a fourth arrangement

[0022] Figure 9 is a diagram of the measurement result

[0023] Embodiment

[0024] In the drawings, identical technical features are provided with the same reference signs and are described only once. The drawings are purely schematic and do not specifically reflect actual geometric proportions

[0025] Reference Figure 1 , Figure 1 is a schematic perspective view of a vehicle 1 including a steering system 2

[0026] In the present embodiment, the vehicle 1 includes a chassis 5 supported by two front wheels 3 and two rear wheels 4. The front wheels 3 can be rotated by the steering system 4 by a wheel deflection angle 28, such that the vehicle 1 can be steered in a curve

[0027] The steering system 2 includes a steering wheel 6 mounted on a first steering shaft 7, and the first steering shaft 7 is in turn mounted so as to be rotatable about a rotation axis 8. The first steering shaft 7 is guided into a device 9 for generating a measurement signal 19 which depends on the torque applied to a torsion element 10, and the first steering shaft 7 is connected to the torsion element 10 in a manner not shown in more detail. A second steering shaft 11 is connected to the torsion element 10 on the side opposite to the first steering shaft 7 on the rotation axis 8 and is connected to a wheel steering gear 12. If the steering wheel 6 is rotated by a steering torque 13, then the steering torque is accordingly transmitted to the wheel steering gear 12, which in response steers the front wheels 3 to drive in a curve using the wheel deflection angle 28

[0028] The steering process can be supported by an auxiliary motor 15 that is capable of assisting the rotation of the second steering shaft 11. For this purpose, the device 9 detects the steering torque 13. Then, among other things, the auxiliary motor 15 steers the second steering shaft 11 based on the detected steering torque 13 using the wheel deflection angle 28.

[0029] To detect the steering torque 13, the device 9 includes a magnetic generator element in the form of a magnet ring 16 that is connected to the first steering shaft 7 and induces a magnetic field 17. The device 9 also includes a magnet sensor 18 that is connected to the second steering shaft 11 and measures the magnetic field 17 induced by the magnet ring 16, and the magnetic field 17 depends on the relative angular position of the first steering shaft 7 and thus the magnet ring 16 with respect to the second steering shaft 11 and thus with respect to the magnet sensor 18.

[0030] The magnet sensor 18 transmits an array of sensor signals 20 to an evaluation system 21. The array of sensor signals 20 will be described in more detail below. The evaluation system 21 receives the array of sensor signals 20 and calculates a measurement signal 19 thereon, and the measurement signal 19 depends on the relative rotational position between the two steering shafts 7, 11 and thus on the torque applied to the torsion shaft 10. This measurement signal 19 is then used to drive the auxiliary motor 15 to set the wheel deflection angle 28 based on the steering torque 13.

[0031] The device will now be described in more detail based on Figure 2 More detailed description:

[0032] The first steering shaft 7 is pressed into a first receiving socket 22 that is rotatable about a rotational axis 8. The first receiving socket 22 also includes a flange 23 that bears the magnet ring 16 opposite the first steering shaft 7, such that when the first steering shaft 7 is rotated, the magnet ring 16 will be rotated about the rotational axis. Similarly, the second steering shaft 11 is pressed into a second receiving socket 24 that is also rotatable about the rotational axis 8. In it, the second receiving socket 24 includes a flange 25 opposite the second steering shaft 11. A holder 26 that bears the evaluation system 21 is attached to this flange 25, and the holder 26 is embodied as Figure 2 a printed circuit board in

[0033] Together with the evaluation system 21, the holder 26 carries the magnetic sensor on the axial level 27 of the magnet ring 16. Since the torsion shaft 10 is twistable about the rotation axis 8, when the magnet ring 16 is turned about the rotation axis 8 due to the steering torque 13, the torsion shaft 10 will be twisted about the rotation axis 8 due to the inertia of the second steering shaft 11, so that the magnet ring 16 will be relatively displaced in the circumferential direction about the rotation axis 8 against the magnetic sensor 18. This circumferential displacement is the relative angular position of the first steering shaft 7 relative to the second steering shaft 11 described above. The magnetic field 17 from the magnet ring 16 that reaches the magnetic sensor 18 will depend on this circumferential displacement between the magnet ring 16 and the magnetic sensor 18. That is, the circumferential displacement indicates the twisting of the torsion shaft 10 and thus the steering torque 13, and can therefore be used to generate the measurement signal 19 described above.

[0034] The measuring principle described above requires that the magnetic field 17 from the magnet ring 16 reaches the magnetic sensor 18 undisturbed. In a real environment, there is always an external magnetic field which interferes with the magnetic field 17 of the magnet ring 16 .

[0035] The following description shows two embodiments that make it possible to eliminate external and interfering magnetic fields.

[0036] In the first embodiment, the magnet ring 16 and the magnet sensor 18 are embodied in a special form and are Figure 3 and 4 Indicated schematically in .

[0037] The magnet ring 16 is divided into twenty-four magnets in the circumferential direction, each of which has a north pole 28 and a south pole 29 radially attached to the north pole 28. Therefore, the magnet ring 16 in the first embodiment includes a total of forty-eight poles, wherein the magnet ring 16 includes a full axial height 30 of 8 mm and a radius of 20.5 mm.

[0038] The magnetic sensor 18 is placed with an air gap 32 displaced radially by 1.09 mm. The magnetic sensor 18 comprises a first sensor element 33 and a second sensor element 34 which are placed equally radially and circumferentially. The two sensor elements 33, 34 are displaced axially by an axial displacement 35 of 1.84 mm. Therein, the radial distance 36 of the sensor elements 33, 34 from the magnet ring 16 is 1.39 mm. The first sensor element 33 and the second sensor element 34 have the same axial distance from the axial magnetic pole boundary, wherein the first sensor element 33 is axially located at the axial upper magnetic pole and the second sensor element 34 is axially located at the axial lower magnetic pole.

[0039] The third sensor element 38 and a fourth sensor element (not shown) are placed to be circumferentially displaced from the first and second sensor elements 33, 34 by a circumferential distance 37 of 1.84 mm. Similarly to the first and second sensor elements 33, 34, the third sensor element 38 and the fourth sensor element are placed equally in the radial direction and in the circumferential direction. That is, the third sensor element 38 and the fourth sensor element are axially displaced by an axial displacement 35 of 1.84 mm, and the radial distance 36 of the third sensor element 38 and the fourth sensor element from the magnet ring 16 is 1.39 mm. The third sensor element 38 and the fourth sensor element have the same axial distance from the axial magnetic pole boundary, where the third sensor element 38 is axially located at the axial magnetic pole and the fourth sensor element is axially located at the axial lower magnetic pole, such that the fourth sensor element is Figure 3 and 4 not visible in the perspective view of.

[0040] The magnetic field 17 of the magnet ring 16 reaching the first sensor element 33 and the third sensor element 38 can be divided into a radial component B r 、a circumferential component B t and an axial component B a . At the axial position where the magnet sensor 18 is placed, the axial magnetic field component B a can be regarded as being constant with respect to the circumferential displacement between the magnet ring 16 and the magnet sensor 18 and thus can be ignored. That is, the magnetic field 17 reaching the magnet sensor 18 can be regarded as a vector rotating in the axial plane. The angle of the vector of the magnetic field 17 measured by one of the sensor elements 33, 34, and 38 directly depends on the circumferential displacement between the magnet ring 16 to be measured and the magnet sensor 18.

[0041] However, the angle of the vector of the magnetic field 17 measured by one of the sensor elements 33, 34, and 38 may not be directly measured because each of the sensor elements 33, 34, and 38 measures the magnetic field not in cylindrical coordinates but in Cartesian coordinates. For example, each of the sensor elements 33, 34, and 38 can be embodied by three Hall generators, where each Hall generator measures the magnetic field 17 in one Cartesian space direction.

[0042] Many magnet sensors, such as the Melexis MLX90372 sold by Melexis NV at the filing date of this patent application, use at least two of the sensor elements 33, 34, and 38, which are circumferentially displaced to compare their measurement results and to filter out stray fields, especially interfering magnetic fields. However, since one of the sensor elements, such as sensor element 33, always circumferentially guides another of the sensor elements, such as sensor element 38, the application of many strategies for filtering out stray fields is not feasible in the application of the magnet ring 16.

[0043] However, an exemplary measurement test using the magnet sensor Melexis MLX90372 described above as the magnet sensor 18 has shown that a strategy for filtering out stray fields can be trusted when the radius 31 of the magnet ring 16, hereinafter referred to as r 编码器 and the displacement angle 37 between the first sensor element 33 and the third sensor element 38, seen from the axis of rotation 8 and hereinafter referred to as satisfy the following equation:

[0044]

[0045] where a is a value between 0.3 and 3.

[0046] This should be shown based on experimental results, where the value a has been chosen to be 2. External and interfering magnetic fields have been experimentally eliminated using the test setup shown in Figures 5 to 8 using the Melexis MLX90372 as the magnet sensor 18. In it, the magnet ring 16 and the magnet sensor 18, together with the evaluation system 21 of the device 9, have been placed stationary relative to each other between two Helmholtz coils 39 that simulate external and interfering magnetic fields.

[0047] Seen towards the axis of rotation 9, the Helmholtz coils 39 are arranged point-symmetrically with respect to the axis of rotation 9. For the experiment, the magnet ring 16 and the magnet sensor 18, which are stationary relative to the magnet ring 16, can be rotated together about the axis of rotation 9 by any rotation angle 40. If Figure 5 shows the test setup in the first position 41 with a rotation angle 40 of 0°, then Figure 6 shows the test setup in the second position 42 with a rotation angle 40 of 90°, Figure 7 shows the test setup in the third position 43 with a rotation angle 40 of 180° and Figure 8 shows the test setup in the fourth position 44 with a rotation angle 40 of 270°.

[0048] Regardless of whether the measurement signal 19 is generated using the stray field filtering technique of Melexis MLX90372 or whether only one of the sensor elements 33, 34, and 38 is used to generate the measurement signal 19, the measurement signal 19 should always output the same measurement signal 19 when no external and interfering magnetic fields are applied. The measurement signal 19 will only change with the rotation angle 40 if the Helmholtz coil 39 is activated and an external and interfering magnetic field is applied to the test setup.

[0049] In the first run of the test setup, the measurement signal 19 has been generated with four different external and interfering magnetic fields, where no stray field filtering strategy has been applied. As already mentioned, this can be achieved by considering the output of only one of the sensor elements 33, 34, or 38 of, for example, only the magnet sensor 18.

[0050] The resulting curves are shown in Figure 9 The first curve 45 shows the run of the measurement signal 19 generated by the magnet sensor with the rotation angle 40 when the external and interfering magnetic field is 0 A / m. The second curve 46 shows the run of the measurement signal 19 generated by a prior art magnet sensor with the rotation angle 40 when the external and interfering magnetic field is 1000 A / m. The third curve 47 shows the run of the measurement signal 19 generated by a prior art magnet sensor with the rotation angle 40 when the external and interfering magnetic field is 2500 A / m, and the fourth curve 48 shows the run of the measurement signal 19 generated by a prior art magnet sensor with the rotation angle 40 when the external and interfering magnetic field is 4000 A / m.

[0051] As can be seen from Figure 9 In the absence of an external and interfering magnetic field being applied, the measurement signal 19 continuously remains at the operating point 49 of the device including a conventional magnet sensor. If an external and interfering magnetic field is applied, then the measurement signal 19 oscillates around the operating point 49 without an additional reference amplitude depending on the strength of the external and interfering magnetic field.

[0052] In another run of the test setup, the measurement signal 19 has additionally been generated by using the stray field filtering function of Melexis MLX90372. In it, the measurement signal 19 has been generated with the same four different external and interfering magnetic fields as above. The resulting curves are shown in Figure 9 in window 50, which magnifies Figure 9 a part of the diagram of dist= 0 A / m. The sixth curve 52 shows the run of the measurement signal 19 generated by the magnet sensor 18 as a function of the rotation angle 40, where B dist = 1000 A / m. The seventh curve 53 shows the run of the measurement signal 19 generated by the magnet sensor 18 as a function of the rotation angle 40, where B dist = 2500 A / m, and the eighth curve 54 shows the run of the measurement signal 19 generated by the magnet sensor 18 as a function of the rotation angle 40, where B dist = 4000 A / m.

[0053] As can be seen from Figure 9 it, in the case where no external and interfering magnetic field is applied, the measurement signal 19 generated by the magnet sensor 18 continuously remains at the operating point 55 of the device 9 including the magnet sensor 18. If an external and interfering magnetic field is applied, then the measurement signal 19 oscillates around the operating point 55 without an additional reference amplitude depending on the strength of the external and interfering magnetic field. These amplitudes are less than the amplitudes of the curves 45 to 48 by up to 99%.

[0054] The measurement results using it show that the embodiments described above reduce the influence of external and interfering magnetic fields, even if the sensor element of the magnet sensor 18 detects the magnetic field in Cartesian coordinates.

Claims

1. An apparatus (9) for generating a measurement signal (19) that depends on a torque (13) applied to a torsion shaft (10) about a rotational axis (8), the apparatus (9) comprising: a magnet ring (16) fixed to a first axial position of the torsion shaft (10) and having a predefined number of magnetic poles (28, 29) for generating a magnetic field (17), characterized in that the apparatus (9) further comprises: a magnet sensor (18) fixed to a second axial position of the torsion shaft (10) different from the first axial position, and the magnet sensor (18) comprises: a first sensor element (33) located in a radial plane about the rotational axis (8) and outputting a first sensor signal that depends on the magnetic field (17) reaching the first sensor element (33), and a second sensor element (38) located in the radial plane of the first sensor element (33) but spaced from the first sensor element (33) by a distance less than the circumferential extent of two adjacent magnetic poles and outputting a second sensor signal that depends on the magnetic field reaching the second sensor element (38), the apparatus (9) further comprising: an evaluation system (21) adapted to filter a stray field signal component (39) from the first sensor signal based on the second sensor signal and adapted to output the measurement signal (19) based on the filtered first sensor signal, wherein the radius r of the outer periphery (31) of the magnet ring (16) 编码器 and the displacement angle of the sensor element, seen from the rotational axis (8) and hereinafter referred to as satisfy the equation where a is a value between 0.3 and 3.

2. The apparatus (9) according to claim 1, wherein the first sensor element is adapted to measure the magnetic field reaching the first sensor element in Cartesian coordinates, and wherein the second sensor element is adapted to measure the magnetic field reaching the second sensor element in Cartesian coordinates.

3. The device (9) according to claim 1 or 2, wherein the distance of each sensor element (33, 34, 38) from the magnet ring (16) is a distance (36) between 3% and 15% of said r 编码器 ​ 4. The apparatus (9) according to the preceding claim 1, wherein the second sensor element (38) is circumferentially spaced from the first sensor element (33) by a circumferential distance (37).

5. The apparatus (9) according to claim 4, wherein the magnet sensor (18) further comprises a third sensor element (34) and a fourth sensor element, the third sensor element (34) being circumferentially positioned on the first sensor element (33) and axially spaced from the first sensor element (33) and outputting a third sensor signal that depends on the magnetic field (17) reaching the third sensor element (34), the fourth sensor element being circumferentially positioned on the second sensor element (38) and axially positioned on the third sensor element (34) and outputting a fourth sensor signal that depends on the magnetic field (17) reaching the third sensor element (34), the third sensor element (34) and the fourth sensor element being circumferentially spaced by the circumferential distance (37), and wherein the circumferential distance (37) is less than half of the circumferential extent of a magnetic pole (28, 29).

6. The device (9) according to claim 5, wherein the evaluation system (21) is adapted to filter the stray field signal component from the first sensor signal by generating a quotient between the difference of the first sensor signal and the fourth sensor signal and the difference of the second sensor signal and the third sensor signal.

7. The device (9) according to the preceding claim 1, wherein the interval is one third of the circumferential extension of one magnetic pole.

8. The device (9) according to the preceding claim 1, wherein the value of a is 2.

9. The device (9) according to claim 3 above, wherein the distance of each sensor element (33, 34, 38) from the magnet ring (16) is the distance (36) which is 7% of said r 编码器 .

10. A vehicle (1), comprising a chassis (5), which is movable in the driving direction, two rear wheels (4), which movably carry the chassis (5) at the rear side seen in the driving direction, two front wheels (3), which movably carry the chassis (5) at the front side seen in the driving direction, a steering wheel (6) for rotating a steering column (7) about a rotation axis (8) to steer the front wheels (3), and the device (9) according to the preceding claim 1, for measuring the torque applied to the steering column (7) to steer the front wheels (3) using an actuator.

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