Patent ID: 12237730

DETAILED DESCRIPTION

Example implementations will be described in more detail below with reference to the figures, elements with the same or a similar function being provided with the same references.

When compensation, in particular stray field compensation, is mentioned in this disclosure, this is intended to mean attenuation or reduction. A stray field compensation is therefore an attenuation or reduction of a measurement deviation due to the stray field. The term compensation may, however, also be understood herein as complete reduction or elimination of a measurement deviation.

As an introduction to the present subject matter,FIG.1Ashows by way of example an electric motor1having a rotating shaft2, on which transmission gearing may for example be arranged. The shaft2may have a rotation direction5. A magnetic angle sensor system is furthermore shown. The magnetic angle sensor system comprises a permanent magnet3arranged on the shaft2as well as a magnetic field sensor4arranged opposite the permanent magnet3.

The permanent magnet3is in this case arranged at the end of the shaft2. Such an arrangement is also referred to as an end-of-shaft (EOS) system.

The permanent magnet3is rotatable relative to the magnetic field sensor4. So that damage does not occur in this case, the permanent magnet3and the magnetic field sensor4are arranged at a distance from one another. There is thus a space between the magnetic field sensor4and the permanent magnet3, which is also referred to as an air gap. This air gap6is also referred to herein by the abbreviation AG.

The magnetic field sensor4may comprise a differentially measuring sensor technology. One example of this is shown inFIG.1B.FIG.1Bshows a plan view of a layout of a differentially measuring sensor technology with four lateral Hall plates Z1, . . . , Z4. This layout may be used for a magnetic angle sensor system100according to the innovative concept described herein. Instead of the Hall plates Z1, . . . , Z4mentioned here purely by way of example, other sensor elements may however also be used for the purpose of a differentially measuring sensor technology for the magnetic angle sensor system100. In principle, for example, xMR sensor elements, for example AMR, GMR, TMR, may also be used in order to implement such a differential sensor principle. For example, instead of the Hall plates Z1, . . . , Z4described here purely by way of example, laterally offset xMR elements may also be used.

In the example discussed here and shown inFIG.1B, the Hall plates Z1, . . . , Z4may be arranged concentrically, and therefore with an equal distance from one another. The Hall plates Z1, . . . , Z4are respectively arranged at a 90° angle to one another. Two opposite Hall plates respectively form a Hall plate pair, which respectively generates a differential signal.

The Hall plates Z1, . . . , Z4are sensitive to a Bz component of the magnetic field of the permanent magnet3. The signal of the Hall plate Z1may thus be referred to as Bztop and the signal of the opposite Hall plate Z3may be referred to as Bzbottom. In a similar way to this, the signal of the Hall plate Z4may be referred to as Bzleft and the signal of the opposite Hall plate Z2may be referred to as Bzright. The two opposite Hall plates Z1and Z3form a Hall plate pair which generates the differential sensor signal Bztop−Bzbottom. The Hall plates Z1and Z3form a first Hall plate pair which generates the differential sensor signal Bztop−Bzbottom. The opposite Hall plates Z2and Z4form a second Hall plate pair which generates the differential sensor signal Bzleft−Bzright.

The rotation angle of the shaft2is calculated from these two differential sensor signals that are generated by the Hall plate pairs (Bztop−Bzbottom) and (Bzleft−Bzright). Because of the differential signal path, homogeneous external magnetic fields are in this case substantially suppressed.

As already mentioned in the introduction, there is an air gap AG between the permanent magnet3and the magnetic field sensor4. With an increasing air gap AG, the signal amplitude of the differential sensor signals also becomes smaller. In order to obtain a sufficiently large signal amplitude, and therefore to produce a signal-to-noise ratio (SNR) which is as large as possible, the signal amplitude should naturally be as large as possible.

FIGS.2A and2Bshow the effect of the air gap AG on the signal amplitudes of the differential sensor signals without the presence of an external homogeneous magnetic stray field.FIG.2Ashows the differential sensor signal BzL−BzR of the two Hall plates Z4and Z2.FIG.2Bshows the differential sensor signal BzT−BzB of the two Hall plates Z1and Z3.

The curve31A depicted inFIG.2Ashows the signal amplitude with an air gap of 3.0 mm. The curve32A shows the signal amplitude with an air gap of 2.5 mm. The curve33A shows the signal amplitude with an air gap of 2.0 mm. The curve34A shows the signal amplitude with an air gap of 1.5 mm. The curve35A shows the signal amplitude with an air gap of 1.0 mm. The curve36A shows the signal amplitude with an air gap of 0.75 mm.

The curve31B depicted inFIG.2Bshows the signal amplitude with an air gap of 3.0 mm. The curve32B shows the signal amplitude with an air gap of 2.5 mm. The curve33B shows the signal amplitude with an air gap of 2.0 mm. The curve34B shows the signal amplitude with an air gap of 1.5 mm. The curve35B shows the signal amplitude with an air gap of 1.0 mm. The curve36B shows the signal amplitude with an air gap of 0.75 mm.

FIG.2Cshows the rotation angle of the shaft, which can be calculated from the two differential sensor signals (FIGS.2A,2B), for example using the arctan function. Here again, angle errors occur as a function of the air gap. The angle error indicates the deviation of the calculated rotation angle in relation to the actual (mechanical) rotation angle or reference angle of the shaft2. With an ideal arrangement of the permanent magnet3(arranged on the shaft2) relative to the magnetic field sensor4, however, this angle error becomes very small.

As may be seen inFIG.2D, the angle errors can be deviations of less than 0.1 degree. Accordingly, although a larger air gap leads to smaller signal amplitudes, the angle error due to the air gap is nevertheless negligibly small with an otherwise ideal arrangement of the permanent magnet3relative to the magnetic field sensor4. This applies to the consideration given above without the presence of an external homogeneous magnetic stray field.

FIG.3, however, shows the effects of an external homogeneous magnetic stray field on the differential sensor signals. The graph depicted illustrates the effect of an external homogeneous magnetic stray field on the measurement of the useful magnetic field of the permanent magnet. The curve21shows the sinusoidal profile of the measured useful magnetic field in the Bz direction without the presence of an external homogeneous stray field. A maximum is denoted here by BZ1and a minimum is denoted by BZ2.

The curve22, on the other hand, shows the sinusoidal profile of the measured useful magnetic field in the Bz direction in the presence of an external homogeneous stray field. A maximum is denoted here byand a minimum is denoted by.

The straight line20indicates the amplitude of the homogeneous stray field. As may be seen, the homogeneous stray field leads to a displacement or an offset of the sensor signal. This offset is denoted here by BSf. The useful magnetic field may be calculated as follows with the differential sensor signals (BzT−BzB & BzL−BzR) while compensating for the homogeneous stray field (offset compensation):
Bsens=−=(Bz1+Bsf)−(Bz2+Bsf)=Bz1+Bsf−Bz2−Bsf=Bz1−Bz2=2·Bz1

Such homogeneous stray fields may thus be reduced relatively well or entirely compensated for using the method described above with the use of differential sensor signals.

It has now been found, however, that the material of the shaft2may likewise be a cause of angle errors. This has been observed particularly when the shaft2comprises a ferromagnetic material. The ferromagnetic material can lead to spatial distortions of the magnetic field lines of the per se homogeneous stray field. These spatial distortions lead to the per se homogeneous stray field having an inhomogeneous stray field component, which in turn leads to angle errors. Yet since these stray field components are inhomogeneous, as mentioned, these inhomogeneous stray field components cannot be compensated for by the method described above with the use of differential sensor signals.

Unfortunately, ferromagnetic shafts are widely used in such rotation angle determinations. The ferromagnetic shaft has a high magnetic permeability μmag. The magnetic permeability describes a resistance of a material to a magnetic field. In other words: it is a measure of the degree to which a magnetic field can permeate through a material.

Because of its low magnetic reluctance (e.g., high permeability), the ferromagnetic shaft acts as a flux concentrator for the magnetic field. Homogeneous magnetic (stray) fields in the environment of the sensor system are deflected and distorted by the shaft. The magnetic stray field is coupled into the signal path of the sensor. Since the stray field has a different size and direction at the individual Hall plates, it is no longer suppressed by the differential signal path and leads to an increased angle error.

The present innovative concept, however, provides means for compensating for these inhomogeneous stray field components and therefore ensuring a more accurate measurement result in the determination of the rotation angle of the shaft2.

FIG.4shows a simulation to illustrate the above-described spatial distortion of the per se homogeneous stray field.FIG.4shows a cross section (X-Z plane) of a ferromagnetic shaft2. The rotation axis of the shaft2is arranged in the Z direction. The X axis extends from left to right in the image. The Y axis extends into the image plane. The shaft2depicted here has, for example, a permeability of μmag=4000 and a diameter of 20 mm, a homogeneous 5 mT stray field having been applied in the X direction.

The shaft2depicted comprises a ferromagnetic material. A permanent magnet3is arranged at the axial shaft end.FIG.4shows only the external homogeneous magnetic stray field. Magnetic field lines of the permanent magnet3are not represented. That is to say, in this plot the permanent magnet3has been placed in a vacuum (μr=1). The permanent magnet3therefore does not influence the field distribution of the homogeneous stray field. The plot merely shows the magnetic stray field vectors but not the vectors of the magnetic field of the permanent magnet3. The influence of the ferromagnetic shaft2on the stray field may be seen clearly from this representation.

The homogeneous stray field shown here by way of example in this case extends in the positive X direction, e.g., from left to right in the image. The arrows depicted indicate the direction of the magnetic field lines at the respective locations. The color scale or grayscale depicted to the left inFIG.4indicates the magnitude of the magnetic field lines at the corresponding locations.

As may be seen fromFIG.4, at a sufficient distance from the shaft2the homogeneous stray field still has a homogeneous profile in the positive X direction (here: from left to right). The homogeneous stray field thus has a homogeneous stray field component in these regions. The homogeneous stray field is distinguished inter alia in that its magnetic field vectors substantially all extend in the same direction, e.g., in a main propagation direction (for example X direction).

The closer the stray field comes in the direction of the shaft2, however, the more significantly both the magnitude and the direction of the magnetic field lines of the homogeneous stray field vary. This means that the per se homogeneous stray field experiences a spatial distortion here, which causes an inhomogeneous stray field component. The inhomogeneous stray field component is distinguished inter alia in that the direction of the magnetic field vectors deviates from the main propagation direction (for example with components in the X and Y directions).

In the left-hand part of the ferromagnetic shaft2, the magnetic field lines enter the shaft2and are so to speak attracted by the ferromagnetic shaft2. The direction of the magnetic field lines or magnetic field vectors changes from the pure X direction (left to right) into a direction toward the ferromagnetic shaft2. This means that the direction of the magnetic field lines acquires a positive component in the Z direction (upward) in addition to the X direction.

In the right-hand part of the ferromagnetic shaft2, conversely, the magnetic field lines emerge from the shaft2and are so to speak repelled by the ferromagnetic shaft2. The direction of the magnetic field lines changes from the pure X direction (left to right) into a direction away from the ferromagnetic shaft2. This means that the direction of the magnetic field lines acquires a negative component in the Z direction (downward) in addition to the X direction.

This now leads in total to stray field values with opposite signs at the Hall plate pairs Z1, . . . , Z4described above, and to corresponding measurement errors in the differential sensor signals (Bzleft and Bzright or Bztop and Bzbottom). These stray field values can therefore no longer be suppressed by the differential sensor principle.

The homogeneous magnetic stray field thus experiences a spatial distortion because of the ferromagnetic material of the shaft2, which is reflected in a deflection of the magnetic field lines. This spatial distortion now leads to the per se homogeneous stray field having an inhomogeneous stray field component in the vicinity of the ferromagnetic shaft2.

As already mentioned in the introduction, this inhomogeneous stray field component cannot be compensated for using a differentially measuring sensor technology. This inhomogeneous stray field component leads to the magnetic field varying in the detection region of the magnetic field sensor (in comparison with a situation in which there is no stray field). This in turn leads to measurement errors in the determination of the rotation angle of the shaft2.

The innovative concept described herein therefore proposes magnetic circuit concepts in order to reduce the influence of ferromagnetic shafts, which leads to an increased stray field immunity of the differential magnetic angle sensor system.

The most effective solution would be to avoid ferromagnetic materials for the shaft. This is not always possible, however, for example because of mechanical restrictions. Essentially three different concepts are therefore proposed herein in order to reduce or compensate for the inhomogeneous stray field components that occur when using a ferromagnetic shaft.

FIG.5shows by way of example a magnetic angle sensor system100according to the innovative concept described herein. The magnetic angle sensor system100comprises inter alia a rotatable shaft102. The shaft102comprises a ferromagnetic material.

The magnetic angle sensor system100also comprises a permanent magnet103coupled, in particular coupled in movement, to the rotatable shaft102. With reference to the following figures, a pair of examples of the way in which the coupling of the permanent magnet103to the rotatable shaft102may be implemented will be mentioned.

The magnetic angle sensor system100furthermore comprises a magnetic field sensor104. The magnetic field sensor104may for example be arranged on a substrate105, for example a PCB (printed circuit board). The magnetic field sensor104is arranged opposite the permanent magnet103. The magnetic field sensor104may be arranged coaxially with the rotatable shaft102.

The magnetic field sensor104comprises a detection region106. InFIG.5, this detection region106is indicated purely by way of example with dashed lines. The detection region106may of course in reality have a geometry and/or size other than those depicted purely by way of example here. In some implementations, however, the detection region106is configured in such a way that it detects a magnetic field generated by the permanent magnet103. The magnetic field generated by the permanent magnet103is the magnetic field of interest in this application, since the magnetic angle sensor system100can determine the current rotation angle of the shaft102based on this magnetic field. The magnetic field generated by the permanent magnet103is therefore also referred to herein as a useful magnetic field. InFIG.5, however, this useful magnetic field is not indicated for the sake of clarity.

As may be seen inFIG.5, there is in this case an external homogeneous magnetic stray field107, which is indicated by the magnetic field vectors depicted. Components of this stray field107likewise fall within the detection region106of the magnetic field sensor104. As described above with reference toFIG.4, the stray field107may have inhomogeneous stray field components because of the ferromagnetic material of the shaft102. Due to the design of such magnetic angle sensor systems100, these inhomogeneous stray field components in particular lie in the detection region106of the magnetic field sensor104.

Accordingly, the magnetic field prevailing in the detection region106of the magnetic field sensor104is thus composed of the useful magnetic field of the permanent magnet103and an inhomogeneous stray field component of the otherwise homogeneous stray field107.

In order to determine the current rotation angle of the shaft102, the magnetic angle sensor system100may for example comprise a differentially measuring sensor technology as described above with reference toFIGS.1A to3. Accordingly, the magnetic field sensor104may be configured to generate, in response to the magnetic field detected in the detection region106, at least two differential sensor signals110,120. Based on these differential sensor signals110,120, a rotation angle130of the shaft can be determined, for example by using the arctan function. Furthermore, homogeneous stray field components may be compensated for based on these at least two differential sensor signals110,120.

The inhomogeneous stray field components prevailing in the detection region106of the magnetic field sensor104(see the magnetic field vectors, which also extend in the positive or negative Z direction besides the X direction) cannot, however, be compensated for using the differentially measuring sensor technology. This leads to angle errors in the determination of the rotation angle130of the shaft102. According to the innovative concept described herein, however, the magnetic angle sensor system100comprises means for reducing and/or compensating for the inhomogeneous stray field component. The form which these means may take will be explained in more detail below with reference to the following figures.

FIG.6shows a first example implementation of such means140for reducing and/or compensating for the inhomogeneous stray field component. Here, the means for reducing and/or compensating for the inhomogeneous stray field component comprise a spacer140which is configured to arrange the permanent magnet103at a distance from and on the shaft102.

As described with reference toFIG.4, the stray field107has in particular homogeneous stray field components at a sufficient distance from the ferromagnetic shaft102. The spacer140therefore provides a way of arranging the permanent magnet103at a certain distance D1from the axial end154of the shaft102, so that the permanent magnet103is placed closer to the region of the homogeneous stray field components. This has the advantage that the magnetic field sensor104can also be arranged at a certain distance D2from the axial end154of the shaft102, so that the magnetic field sensor104is also placed closer to the region of the homogeneous stray field components.

The advantage in this case is, in particular, that the air gap AG between the permanent magnet103and the magnetic field sensor104can still be kept very small. That is to say, if the permanent magnet103were left at the axial end154of the shaft102and only the magnetic field sensor104were arranged further away, in order to place it in the region of the homogeneous stray field components, the air gap AG would then also be increased. This, however, would lead to smaller signal aptitudes and larger angle errors (seeFIGS.2A to2D).

The spacer140, however, provides a solution for this problem by increasing the distance D1of the permanent magnet103from the axial end154of the shaft102, while simultaneously maintaining a small air gap AG between the permanent magnet103and the magnetic field sensor104. In this way, the distance D2of the magnetic field sensor104from the axial end154of the shaft102can be increased overall, so that the magnetic field sensor104is placed further away from the ferromagnetic shaft102and therefore in a region with primarily homogeneous stray field components. This means that the detection region106of the magnetic field sensor104primarily detects homogeneous stray field components, which can be compensated for using the differentially measuring sensor technology.

The spacer140may comprise, on a first side141, a receiving section143in which the permanent magnet103can be arranged. On a second side142opposite the first side141, the spacer140may comprise a fitting section144using which the spacer140is fitted on the shaft102.

The receiving section143for the permanent magnet103may, for example, be configured in the form of a recess on the first side141of the spacer140. The recess143may, for example, be as deep as the thickness (in the axial direction) of the permanent magnet103. The permanent magnet103can therefore be inserted accurately into the recess143, as is shown by way of example inFIG.6.

The fitting section144, with which the spacer140is fitted on the shaft102, may be configured in the form of a recess144on the second side142of the spacer140. This recess144may have a diameter which substantially has the same size as the diameter of the ferromagnetic shaft102. The spacer140can therefore be fixed accurately on the shaft102, for example with a press-fit.

If the spacer140comprises the aforementioned recesses143,144on the first and second sides141,142, in terms of shape the spacer140resembles the letter H. This allows simple and therefore economical production of the spacer140in mass production.

The spacer140may preferably be connected rotationally fixed to the shaft102, so that the spacer140co-rotates with the shaft102. Furthermore, the permanent magnet103may preferably be arranged rotationally fixed in the spacer140. The permanent magnet103is therefore coupled, in particular coupled in movement, to the shaft102.

The shaft102has a rotation axis145(mid-axis of the shaft102). Along this rotation axis145, the spacer140is arranged using its fitting section144on an axial end section of the shaft102. The permanent magnet103is arranged in the spacer140in such a way that the permanent magnet103is aligned coaxially with the shaft102. This ensures smooth running without imbalance during the rotation of the shaft102.

According to one example implementation, the spacer140may comprise a nonmagnetic material. This is advantageous insofar as a nonmagnetic material does not interfere with the magnetic field lines of the homogeneous stray field, that is to say spatial distortions do not occur as in the case of a ferromagnetic material (seeFIG.4).

It is furthermore conceivable for the spacer140to create a distance D1of between 4 mm and 30 mm between the permanent magnet103and the shaft102. In particular, the spacer140may create a distance of between 10 mm and 20 mm between the permanent magnet103and the shaft102. The advantages in this regard will be described below with reference toFIGS.7A to7C.

FIGS.7A to7Cshow graphical plots of simulations carried out with different air gaps and different thicknesses of the spacers140. The thickness of a spacer140is measured in the axial direction, that is to say in the direction of the rotation axis145. The simulations were carried out with the assumption of a ferromagnetic shaft102having a diameter of 20 mm and a permeability μr=4000. A diametrically magnetized disk with a diameter of 6 mm and a height of 3 mm is used as the permanent magnet103. The remanence Br is 515 mT and the coercivity is −355 kA/m.

FIG.7Ashows a diagram in which the angle error with different air gaps AG is represented for differently thick spacers. The dimensions of the air gap between 0.5 mm and 3.0 mm are plotted on the X axis. The angle errors in degrees are plotted on the Y axis. The different curves in the diagram represent spacers with different thicknesses of between 0 mm (no spacer) and 20 mm. The plot depicted inFIG.7Ashows a scenario in which there is no stray field. Accordingly, the angle errors occurring in this case are small or negligible.

For the purpose of the simulation, a parameter study was carried out with different stray field amplitudes of between 0.1 mT and 5 mT, and the resulting angle errors were determined for a different spacer thickness d and different sensor air gaps AG. Purely by way of example,FIG.7Bshows a plot with an applied homogeneous stray field (in the X direction) with a simulated stray field amplitude of 1 mT, andFIG.7Cpurely by way of example shows a plot with an applied homogeneous stray field (in the X direction) with a simulated stray field amplitude of 5 mT.

The curves171A,171B with a spacer thickness of 0 mm (no spacer) have as expected the greatest angle error. As may be seen with the aid of the curves172A,172B, a spacer thickness of only 4 mm is already sufficient to reduce the magnitude (amplitude) of the angle error significantly. With a spacer thickness of 7 mm, the curves173A,173B flatten out even more.

With a spacer thickness in a range of between 10 mm and 20 mm, the positive effects of the spacer140can be seen most clearly. Here, it may be seen that the angle error becomes vanishingly small even with an increasingly large air gap. By increasing the spacer thickness, the effect of the stray fields, and in this case particularly the effect of the inhomogeneous stray field components caused by the ferromagnetic shaft102, is thus reduced and the measurement accuracy can be increased significantly.

The spacer140additionally has the effect that less permanent magnetic field is “absorbed” by the ferromagnetic shaft102. This means that the magnetic flux density available at the magnetic field sensor104is increased in the case in which a spacer140is used. A higher SNR reduces the angle error. Thus, a stronger permanent magnet could in principle also be used instead of a spacer140. The spacer is, however, the more effective and more economical solution.

This is revealed by comparing the differential signal amplitudes for the setups with a spacer thickness of 10 mm and 20 mm (FIGS.7B and7C). Both setups lead to signal amplitude values of the same size, that is to say the permanent magnet103is already sufficiently far away from the ferromagnetic shaft102. With these distances D1(spacer thicknesses d), the shaft102no longer influences the available field at the sensor positions, that is to say the magnetic field in the detection region106of the magnetic field sensor104. Nevertheless, the resulting angle error for a 20 mm spacer140is much less than for a 10 mm spacer (compareFIGS.7B and7C). This confirms that the improved angle accuracy is due not only to an increased magnetic field but also to a reduced stray field effect (=noise). In both cases (spacer140or stronger magnet), the SNR is improved.

FIGS.8A and8Bshow a further example implementation of a magnetic angle sensor system100having corresponding means for reducing and/or compensating for the inhomogeneous stray field component according to the innovative concept described herein.

Here, the means for reducing and/or compensating for the inhomogeneous stray field component comprise a holding device150. The holding device150is stationary relative to the rotatable shaft102, that is to say the holding device150does not rotate with the shaft102.

The magnetic field sensor104is arranged on or in the holding device150. For example, the holding device150may comprise a recess152inside which the magnetic field sensor104can be arranged. The recess152in the holding device150may, for example, be as deep as the thickness (in the axial direction) of the magnetic field sensor104. The magnetic field sensor104can therefore be inserted accurately into the recess152, as is shown by way of example inFIGS.8A and8B.

The holding device150may be arranged opposite an axial end154of the shaft102, in particular where the permanent magnet103is arranged. The holding device150may be arranged relative to the shaft102in such a way that the recess152together with the magnetic field sensor104arranged therein lies opposite the permanent magnet103.

Furthermore, the holding device150is arranged coaxially with the shaft102, that is to say the rotation axis145of the shaft102also extends through the holding device150. For example, the rotation axis145may extend through the recess152, and therefore also through the magnetic field sensor104arranged therein, so that the magnetic field sensor104arranged in the holding device150lies opposite the permanent magnet103.

In order to avoid damage during the rotation of the shaft102, the holding device150is arranged at a certain distance D2from the shaft102. This furthermore has the advantage that the magnetic field sensor104arranged in the holding device150is distanced further from the axial end154of the shaft102, so that the magnetic field sensor104can be arranged in a region with a primarily homogeneous stray field component (cf.FIG.4).

In addition, the holding device150may comprise a soft magnetic or ferromagnetic material. Likewise, as described above with reference toFIG.4for a ferromagnetic shaft102, the magnetic field lines of the external homogeneous magnetic stray field107may also penetrate into the holding device150. The penetrating field lines in this case extend inside the holding device150, or through the holding device150. As may be seen inFIG.8A, this has the advantage that the penetrating magnetic field lines are guided past the recess152and therefore past the magnetic field sensor104arranged therein (see the schematically indicated magnetic field line151).

The field lines151are thus, similarly as in the case of the shaft102, “attracted” into the holding device150because of the ferromagnetic (=soft magnetic) material and thereby guided past the magnetic field sensor104. This applies both for the homogeneous and for the inhomogeneous stray field component of the per se homogeneous stray field107. This means that the inhomogeneous stray field component, which cannot be compensated for using the differentially measuring sensor technology and would therefore lead to measurement errors, is guided through the holding device150and therefore guided past the magnetic field sensor104, so that this inhomogeneous stray field component does not interfere with the measurement results of the magnetic field sensor104. The inhomogeneous stray field component can therefore be reduced or compensated for using the holding device150.

The holding device150thus causes a deviation of the stray field, and in particular a deviation of the homogeneous and inhomogeneous stray field components. The holding device150hence acts as a kind of magnetic pole and may therefore also be referred to as a pole piece or flux conducting platelet. The magnetic field sensor104may be placed in the interior of the recess152of the pole piece150. The pole piece150engages with the stray field107and deviates it out from the sensor plane.

FIG.8Bshows a measurement structure such as was used for a simulation in order to assess the effectiveness of the pole piece or the holding device150. The parameters correspond to those ofFIGS.7A and7B, that is to say a ferromagnetic shaft102having a diameter of 20 mm and a permeability μr=4000 is assumed. A diametrically magnetized disk with a diameter of 6 mm and a height of 3 mm is used as the permanent magnet103. The remanence Br is 515 mT and the coercivity is −355 kA/m. The permanent magnet103is arranged directly on the axial end154of the shaft102, that is to say no spacer140(seeFIG.6) is arranged between the permanent magnet103and the shaft102. According to one example implementation, however, it is naturally conceivable for the pole piece or holding device150to be combined with the spacer140.

In the setup shown inFIGS.8A and8B, an air gap AG of 1.5 mm is simulated. According toFIG.7C, without a spacer140with an air gap of 1.5 mm an angle error of 1.3° is expected. Because of the holding device150, which deviates the stray field and guides it past the magnetic field sensor104, the angle error may however be reduced significantly.

The results of the simulation carried out with the measurement structure according toFIG.8Bare shown inFIGS.9A to9C.FIG.9Ashows the corresponding differential signals such as may be determined by the differentially measuring sensor technology. The curve181in this case depicts the signal (BzL−BzR) determined using a first Hall plate pair. The curve182depicts the signal (BzT−BzB) determined using the second Hall plate pair. As already mentioned in the introduction with reference toFIG.1B, the Hall plate pairs are mentioned here merely as a nonlimiting example of the implementation of a differentially measuring sensor technology. As an alternative to the Hall plates, other magnetoresistive sensor elements, for example xMR (AMR, GMR, TMR), may also be used for the innovative magnetic angle sensor system100described herein.

FIG.9Bshows the rotation angle183of the shaft102, which can be calculated from the two differential signals181,182, for example using the arctan function.

FIG.9Cshows the angle error184determined. As may be seen, an angle error of about 0.24 degrees is found. It is much less than the angle error of 1.3 degrees to be expected fromFIG.7Cwith an air gap of 1.5 mm. This shows that the holding device150can effectively reduce or compensate for the inhomogeneous stray field component.

The example implementations discussed so far with reference toFIGS.6to9Cmay be implemented both with a diametrically magnetized permanent magnet and with an axially magnetized permanent magnet, and in particular with a bipolarly axially magnetized permanent magnet. The magnetization direction describes the course of the magnetic axis inside the permanent magnet, at the end of which the poles are located. The terms diametrically and axially as mentioned herein refer in this case to the rotation axis145of the shaft102. The magnetization direction or magnetic axis is represented using an arrow in the respective figures.

Thus, for example, a diametrically magnetized permanent magnet103is depicted inFIGS.6and8A, which is symbolized by the arrow extending from left to right. The two poles of the permanent magnet103are arranged opposite one another in the arrow direction. The arrow symbolizes the magnetic axis, which accordingly extends diametrically, e.g., perpendicularly to the rotation axis145of the shaft.

An axially magnetized permanent magnet which may likewise be used in the implementations discussed so far, and in particular a bipolarly axially magnetized permanent magnet, will be described in more detail below with reference toFIGS.10A to10C.

FIGS.10A to10Cshow a further example implementation of a magnetic angle sensor system100having corresponding means for reducing and/or compensating for the inhomogeneous stray field component according to the innovative concept described herein.

Here, the means for reducing and/or compensating for the inhomogeneous stray field component comprise a bore160inside the shaft102. This bore160extends along the shaft longitudinal axis or rotation axis145starting from an axial end section154of the shaft102. That is to say, the bore160extends into the shaft102from the axial end section154of the shaft102.

The permanent magnet103may be arranged inside this bore160. The permanent magnet103may in this case be arranged rotationally fixed to the shaft102so that the permanent magnet103co-rotates with the shaft102. Optionally, the magnetic field sensor104may additionally be arranged in the bore160. The magnetic field sensor104may in this case be stationary relative to the shaft102so that the magnetic field sensor104does not co-rotate with the shaft102. The magnetic field sensor104may therefore also be stationary relative to the permanent magnet103, so that the permanent magnet103co-rotates together with the shaft102while the permanent magnet103and the shaft102rotate together relative to the stationary magnetic field sensor104.

The permanent magnet103may be arranged entirely inside the bore160. The magnetic field sensor104may also be arranged entirely inside the bore160. Accordingly, the magnetic field sensor104may, as seen in the axial direction, be arranged between the permanent magnet103and the axial end section154of the shaft102.

The bore160may be configured as a blind hole, as is shown by way of example inFIG.10A. The permanent magnet103may be arranged at the end of the blind hole160. This has the advantage that the ferromagnetic material of the shaft102on the rear side of the permanent magnet103increases the useful magnetic field of the permanent magnet103, so that a significantly greater useful magnetic field is available for the magnetic field sensor104in order to determine the rotation angle.

The bore160may have a diameter which corresponds approximately to the diameter of the permanent magnet103. The permanent magnet103may therefore be inserted accurately into the bore160.

As may be seen particularly inFIG.10B, the bore160acts as a kind of shield of the magnetic field sensor104against the stray field107, and in particular against the inhomogeneous stray field components. As explained with reference toFIG.4, the ferromagnetic shaft102attracts the magnetic field lines of the stray field107. The magnetic field lines are in this case distributed inside the shaft102. They do not enter the bore160, however, so that the permanent magnet103arranged inside the bore160and the magnetic field sensor104are protected or shielded against the stray field.

FIG.10Bessentially shows the stray field distribution in an XZ cross section of a magnetic angle sensor system100according to the innovative concept described herein with a bore160in the shaft102. For representational purposes, the permanent magnet103is here again placed in a vacuum so that only the external stray field107, which is applied in the X direction (5 mT), can be seen. The ferromagnetic shaft102deflects the field lines of the homogeneous stray field107and shields the magnetic field sensor104against the stray field107.

As mentioned in the introduction, both the permanent magnet103and the magnetic field sensor104may be arranged entirely inside the bore160, which leads to particularly good shielding. Since the permanent magnet103rotates relative to the magnetic field sensor104, a sufficiently large air gap AG should here again be provided between the permanent magnet103and the magnetic field sensor104. Owing to the fact that the ferromagnetic material of the shaft102increases the useful magnetic field of the permanent magnet103, the air gap AG may be configured with a somewhat greater tolerance than in the two implementations discussed above.

InFIG.10C, the useful magnetic field of the permanent magnet103arranged inside the bore160(curve230) is compared with a permanent magnet on its own outside a shaft with a bore (curve240) and with a permanent magnet having a ferromagnetic plate on the rear side (curve250).

In the simulation according to the curve250, the ferromagnetic plate increases the useful magnetic field of the permanent magnet103, which is available for the sensor side. This is therefore comparable to an arrangement in which the permanent magnet103is arranged at the end of the bore160configured as a blind hole and is in contact with the shaft102there. Here, the inwardly offset shaft end, on which the permanent magnet103bears, serves as an amplifier of the useful magnetic field. This means that the ferromagnetic shaft102has a similar effect to the simulated ferromagnetic plate on the rear side of the permanent magnet (see curve250).

As may be seen inFIG.10C, the configuration with field amplification (curve250) shows the highest field amplitudes. The ferromagnetic material on the rear side of the permanent magnet103amplifies the useful magnetic field which is available for the sensor104. The ferromagnetic side walls of the bore160absorb a certain proportion of this magnetic field, however. In the case of small air gaps of up to about 0.75 mm, the magnetic field sensor104therefore benefits from the amplified useful magnetic field due to the ferromagnetic material on the rear side of the permanent magnet103(curve250). With air gaps becoming larger, however, the ferromagnetic side walls become dominant (curve230). These reduce the useful magnetic field a little, compared with the permanent magnet on its own (curve240).

EXAMPLES

In all examples discussed here for the simulations carried out, the same magnet dimensions and materials were used. Very large differential signals are therefore obtained for the purpose of clear visualization. In principle, a weaker magnetic material (for example isotropic ferrite with a remanence Br=230 mT) would also deliver sufficiently large fields for the sensor.

The permanent magnet103arranged inside the bore160may be an axially magnetized cylinder with a north pole and a south pole on the lower side. This may in particular be a bipolarly axially magnetized permanent magnet.

As may be seen inFIGS.10A and10C, the permanent magnet103may comprise a first pole pair211,212in a left half. The first pole pair211,212may comprise two opposite magnetic poles211,212arranged above one another in the axial direction. The magnetic flux direction or the magnetic axis extends axially, that is to say parallel to the rotation axis145of the shaft, which is indicated by the arrow (extending from top to bottom) shown in the left half of the permanent magnet103.

In a right half, the permanent magnet103may comprise a second pole pair213,214. The second pole pair213,214may likewise comprise two opposite magnetic poles213,214arranged above one another in the axial direction. The magnetic flux direction or the magnetic axis extends axially, that is to say parallel to the rotation axis145of the shaft, which is indicated by the arrow (extending from bottom to top) shown in the right half of the permanent magnet103.

The two magnetic poles211,212of the first pole pair are arranged mirror-symmetrically with respect to the two magnetic poles213,214of the second pole pair. For example, in the first pole pair a north pole may be arranged at the top (as seen in the axial direction) and a south pole may be arranged at the bottom, in which case a south pole would be arranged at the top and a north pole at the bottom in the second pole pair. The effect of this is that although the magnetic axes of the two pole pairs both extend axially, they do so in the opposite direction. This is therefore a bipolarly axially magnetized permanent magnet.

The advantage of such a bipolarly axially magnetized permanent magnet is that it is significantly more economical in comparison with ring magnets.

The innovative concept described herein will be briefly summarized again below in other terms:

The present concept relates to magnetic end-of-shaft angle sensor systems. For such applications, diametrically magnetized disk magnets are conventionally fitted on a shaft end. A magnetic field sensor is fastened coaxially at a particular distance from the magnet. Magnetic field sensors are, however, susceptible to external magnetic stray fields.

Normally, a homogeneous stray field can be compensated for using a differential measurement. In that case, with a homogeneous stray field, the same component (magnitude and direction) of the undesired stray field acts on both sides (top/bottom and left/right).

In the case of ferromagnetic shafts, however, spatial distortions of the (intrinsically) homogeneous stray field occur, that is to say by distortion of the stray field in the shaft the intrinsically homogeneous stray field then becomes partially inhomogeneous. For example, the field vectors point upward when entering the shaft and downward when emerging from the shaft. This means that the vectors have different signs on the left and right. The (partially inhomogeneous) stray field therefore cannot be compensated for accurately enough with the differential measurement alone, since for the purpose of the compensation using differential measurement there would have to be an entirely homogeneous magnetic field that has the same magnetic field components (magnitude and direction) on both sides (left/right and top/bottom).

Despite the differential measurement principle, stray fields cannot be compensated for entirely since uncompensatable inhomogeneous components remain, which are superimposed on the useful magnetic field of the permanent magnet and thus lead to measurement errors in the sensor.

The present concept now attempts to compensate for these inhomogeneous components so that these inhomogeneous components are no longer superimposed on the useful magnetic field of the permanent magnet and the sensor can therefore measure just the actual magnetic field of the permanent magnet. The homogeneous components of the stray field may in this case still be compensated for by the differential measurement.

With this concept, in particular three magnetic circuit concepts are proposed in order to increase the immunity of differential magnetic sensors against stray fields.

In a first example implementation, it is proposed to provide a nonmagnetic spacer140between the permanent magnet103and the shaft102. The addition of a nonmagnetic spacer140between the magnet103and the ferromagnetic shaft102improves the stray field robustness dramatically. By addition of this spacer140, the sensor104and the magnet103are moved further away from the ferromagnetic shaft102and the effect of the stray field107is therefore reduced. That is to say, the distance D2between the shaft102and the sensor104is increased. Stray fields107, which are deflected and distorted by the ferromagnetic shaft102, therefore influence the sensor signals much less. This spacer140may fulfill the function of a holder for the permanent magnet103in order to arrange the latter at a distance from and on the shaft102. The cross section of the spacer140may be shaped like the letter “H”, in which case one end may be applied over the shaft102while the other end is used as a holder for the magnet103. This allows robust fixing of the magnet103on the shaft102. The spacer140may, however, have different shapes. For example, the spacer140may be configured in the form of a solid disk. In each case, the spacer140allows robust and accurate fitting of the magnet103on the shaft102.

In a second example implementation, a ferromagnetic holding device150or a ferromagnetic pole piece may be provided. The pole piece150may be shaped like a soup dish, in which case the magnetic field sensor104may be arranged in the middle. The sensor chip104may, for example, be placed inside a recess152in the pole piece150. The ferromagnetic pole piece150can act as a deviation for the stray fields. The pole piece250deviates the stray field107and therefore diverts the stray field107away from the sensor chip104, or out from the sensor plane, so as to reduce the angle error.

In a third example implementation, a bore160can be provided inside the shaft102, in which case the permanent magnet103and optionally also the magnetic field sensor104may be arranged inside this bore160. In this case, an axially magnetized cylindrical or ring magnet having two poles each on one side of the permanent magnet103may be used. The magnet103may be integrated into the shaft102. In this case, the ferromagnetic shaft102acts as a mirror for the magnet103and increases the useful magnetic field at the sensor position, that is to say in the detection region106of the magnetic field sensor104. This is thus an integrated end-of-shaft solution, in which case the sensor104and the magnet103may be integrated in the interior of a bore160at the end154of the shaft102. The magnet103may be an axially magnetized cylinder having two poles on one side. The ferromagnetic shaft102on the rear side of the magnet103assists an increase in the magnetic field at the sensor position. The shaft102itself acts as shielding against external fields.

The examples described above merely represent an illustration of the principles of the innovative concept described herein. It is to be understood that modifications and variations of the arrangements and details described herein will be clear to other persons skilled in the art. It is therefore intended that the concept described herein be restricted only by the protective scope of the appended patent claims and not by the specific details that have been presented herein with the aid of the description and the explanation of the examples.

Although many aspects have been described in connection with a device, it is to be understood that these aspects also represent a description of the corresponding method, so that a block or a component part of a device is also to be understood as a corresponding method step or as a feature of a method step. Similarly, aspects which have been described in connection with or as a method step also represent a description of a corresponding block or detail or feature of a corresponding device.