Method for testing a wheel speed sensor using a coil arrangement

Abstract

Method for testing a speed sensor (3) by means of a test device, wherein the speed sensor (3) has at least a first and a second sensitive structure (4), wherein the first and the second sensitive structure (4) are each formed as part of a magnetic field sensor element or are formed as a first and second half-bridge of a magnetic field sensor element, wherein the speed sensor (3) has at least one signal processing circuit, wherein the test device comprises at least a first and a second coil (1, 2) and a current and / or voltage source, wherein the test device is designed so and the test device and the speed sensor (3) are arranged relative to each other so, that the speed sensor is arranged between the first and the second coil (1, 2), wherein by means of the current and / or voltage source a first current (I) is generated through the first coil (1) and a second current (I) is generated through the second coil (2), characterized in that the first and second coils (1, 2) are designed as a gradient coil arrangement.

Description

[0001] The invention relates to a method for testing a wheel speed sensor using a test device.

[0002] Test methods for testing wheel speed sensors are known. Typically, a rotating magnetic encoder is part of the test device, which is configured in a wheel speed sensor array corresponding to the target to be sensed. These known methods usually require relatively precise positioning between the sensor to be tested and the test device.

[0003] DE 10 2008 050 018 A1 relates to an integrated magnetic sensor circuit comprising a plurality of magnetically sensitive elements and a test conductor, wherein the test conductor generates a differential magnetic field and applies it to the magnetically sensitive elements during a test mode.

[0004] DE 10 229 624 A1 deals with a method for the final inspection of a magnetic sensor, wherein a shape and / or size of output signals generated by the generated alternating magnetic field is recorded and compared with a reference size or shape.

[0005] The invention is based on the object of proposing a method for testing a speed sensor in which this positioning can be designed flexibly and / or relatively generously and / or which is relatively simple and / or cost-effective and / or precise, in particular independent of a magnetic application-specific encoder.

[0006] This object is achieved according to the invention by the method according to claim 1.

[0007] The invention is based in particular on the idea of positioning, in a test method, a speed sensor with at least two sensitive structures of one or two magnetic field sensor elements between the two coils of a gradient coil arrangement through which a current of essentially the same magnitude flows.

[0008] Due to the differential measurement and the use of the gradient coil arrangement, the measurement result or output signal is relatively independent of the center of the arrangement of the speed sensor between the two coils or the distance of the speed sensor to the two coils.

[0009] It is preferred that the first and second coils form a gradient coil arrangement, providing a magnetic field with a substantially constant spatial gradient between the two coils, or that the two coils of a gradient coil arrangement provide a spatial gradient with respect to the magnetic test field between the two coils. The speed sensor then differentially detects a constant difference value of the field strength when the distance or center of the speed sensor between the two coils is changed.

[0010] In particular, the result or the difference value of the differential measurement in the gradient coil arrangement is therefore essentially constant depending on the distance position of the speed sensor between the first and second coil.

[0011] In the gradient coil arrangement, the result of the differential measurement depends on the current strength through the two coils or through the first and second coil.

[0012] The first and second coils are designed as a gradient coil arrangement, or the first and second coils are designed as gradient coils.

[0013] The test device is designed such that the first and second coils are designed as a gradient coil arrangement.

[0014] The two coils are preferably spaced apart by a defined distance D and both have substantially the same radius R. In particular, the two coils are arranged substantially parallel to each other, with the speed sensor located between the two coils. Particularly preferably, the defined distance D is equal to the radius R.

[0015] It is preferred that the speed sensor is arranged substantially in the magnetic field region between the first and the second coil, which in the gradient coil arrangement has a homogeneous gradient, thereby substantially in relation to the distance D in the region between a quarter D, as the closest distance, to the first coil and a quarter D, as the closest distance, to the second coil and / or expediently the speed sensor is arranged substantially in a central region in relation to the radial cross-sectional area or the radial plane of the two coils.

[0016] The sensitive structures of the speed sensor are expediently designed as GMR, i.e. giant magnetoresistive, sensor structures or alternatively preferably as AMR, as anisotropic magnetoresistive, or TMR, i.e. tunnel magnetoresistive, or Hall structures.

[0017] It is preferred that the speed sensor is designed such that the output signals of the first and second sensitive structures are processed / evaluated differentially with respect to one another in the signal processing circuit.

[0018] It is expedient for the speed sensor to have four sensitive structures whose output signals are processed / evaluated in pairs differentially with respect to one another in the signal processing circuit. In particular, one sensitive structure of a pair is arranged on one side of the speed sensor, and the other sensitive structure of the pair is arranged on the other side of the speed sensor, particularly with respect to its chip area. By means of this configuration of the sensitive structures and, in particular, a pairwise differential evaluation in the signal processing circuit, the speed sensor is designed for rotation direction detection.

[0019] It is preferred that the current flow through the first and second coils, which is generated by means of the current and / or voltage source, is an alternating current flow and the current and / or voltage source is designed as an alternating current / alternating voltage source.

[0020] It is expedient that when designing the test device comprising a gradient coil arrangement having the first and the second coil, the first and second coils are arranged and electrically connected or controlled in such a way that first, a first current with a defined first, essentially constant current intensity or a constantly and / or continuously changing current intensity flows through the first coil and a second current with a defined second, essentially constant current intensity or a constantly and / or continuously changing current intensity flows or is set through the second coil, wherein the second current intensity is lower than the first current intensity, in particular by at least 1% to a maximum of 15% lower than the first current intensity or by 5% or 10% lower than the first current intensity, after which the current intensity of the second current through the second coil is increased and / or the current intensity of the first current through the first coil is reduced, so that essentially a changed first current through the first coil and / or a changed second current through the second coil is established such that the current intensity of the current through the first coil is lower than the current intensity through the second coil, in particular by at least 1% to a maximum of 15% lower than the current intensity through the second coil or by 5% or 10% lower than the current intensity through the second coil, wherein in particular the change or reversal of the first and second current occurs steadily and / or continuously.

[0021] It is preferred that, when designing the test device comprising a gradient coil arrangement having the first and the second coil, the first and second coils are arranged and electrically connected or controlled in such a way that a first current with a defined first, substantially constant current intensity or a constantly and / or continuously changing current intensity flows through the first coil and a second current with a defined second, substantially constant current intensity flows through the second coil or is set or adjusted, wherein the second current intensity is lower than the first current intensity, in particular by at least 1% to a maximum of 15% lower than the first current intensity or by 5% or 10% lower than the first current intensity.

[0022] Preferably, the first and second currents are set so low that the magnetic field detected by the sensitive structures does not lead to switching of the speed sensor or that no speed signal is generated or that the detected magnetic field remains below the switching thresholds of the signal processing circuit. The second current through the second coil is set lower than the first current, in particular 1 to 15% lower, whereby the direction detection is activated. The current in both coils is then increased, in particular with a nearly constant difference, at least to the extent that it exceeds the switching thresholds of the signal processing circuit or leads to switching of the speed sensor. The current difference between the first and second currents is then reversed orthe polarity is reversed, whereby the current in both coils is reduced, in particular with a nearly constant difference, to below the switching threshold of the signal processing circuit or a switching of the speed sensor. Particularly preferably, a similar cycle is subsequently run through, whereby at the beginning the first current through the first coil is set lower than the second current, whereby in particular the direction detection is activated in the other direction.

[0023] The speed sensor is advantageously designed as a differential measuring sensor and a speed sensor that detects the direction of rotation. The relative changes in the current strengths through the first and second coils and the reversing difference in the current strength through the two coils allow the speed sensor's detection of the direction of rotation to be tested.

[0024] The difference described above or the absolute value of this difference with regard to the current through the first and second coils should be adjustable, depending on the measurement accuracy.

[0025] In particular, during the process the current through both coils is increased or decreased simultaneously with a constant difference in order to activate the sensor function.

[0026] It is therefore preferred that both coils are operated with slightly different current strengths, sometimes the current through the first coil is greater than the current through the second coil by the said difference and then vice versa, with the current direction being inverse to each other.

[0027] The method is advantageously used in a test environment, particularly in a laboratory, or at the end of the sensor production line.

[0028] It is preferred that the speed sensor is designed as a wheel speed sensor, in particular as a wheel speed sensor with a direction of rotation detection.

[0029] The test device is preferably designed such that the phase of the two currents through the first and second coils is substantially equal.

[0030] In a preferred embodiment of the test device as a gradient coil arrangement, current flows through the first and second coils with identical or identical current intensity or, for testing a speed sensor with a direction of rotation detection, with a defined difference in current intensity, but / and a direction inverse to each other, wherein the second coil is arranged geometrically rotated by 180° to the first coil.

[0031] When using a Helmholtz coil arrangement in the test facility, the two coils are conveniently connected in series and the same current flows through both.

[0032] Preferably, the method indicates a detected error or defect of the speed sensor if the output signal of the speed sensor is not zero and / or not independent of the amount of current flowing through the coils.

[0033] The test device is preferably designed such that the current through the first and second coils is substantially 3A, in particular as an effective current value.

[0034] Alternatively, the test device preferably comprises a third and fourth coil, wherein the first and third coils are connectable in series, as are the second and fourth coils.

[0035] The magnetic field detected by the sensitive structures is now adjusted by the first current through the first and / or third coil and by the second current through the second and / or fourth coil.

[0036] The first and third coils as well as the second and fourth coils each form a partial coil arrangement in which it is possible to adjust how many turns the first or second current flows through, in particular by connecting or disconnecting the third or fourth coil or by an adjustable or displaceable tap of the two partial coil arrangements.

[0037] It is expedient that in the course of the method the first and the second current are set in such a way that they are in particular equal and constant, and / or the third or fourth coil are switched in such a way or the first and the second partial coil arrangement are controlled or switched with regard to their current-carrying turns in such a way that initially the first partial coil arrangement generates a stronger magnetic field than the second and subsequently the second partial coil arrangement generates a stronger magnetic field than the first, with regard to the detection of the magnetic fields by the first and second sensitive structure.

[0038] Advantageously, the third and fourth coils have fewer turns than the first and second coils, in particular the third and fourth coils have less than 10% or 10% of the turns of the first and second coils, respectively.

[0039] Alternatively, the first and second partial coil arrangements each preferably comprise two or more series-connected coils, which can be variably connected or disconnected to provide the magnetic field and / or can be switched or tapped with respect to the number of current-carrying turns. In particular, the coils of a partial coil arrangement are arranged substantially concentrically to one another and designed accordingly.

[0040] Advantageously, the first and second coils, as part of the first and second partial coil arrangements, have a different coil diameter than the third and fourth coils or than other coils of these partial coil arrangements.

[0041] They show in schematic, exemplary representation

[0042] Fig. 1a) shows an example of a test device not belonging to the invention, comprising first and second coils 1, 2, which are designed, arranged, and connected as a Helmholtz coil arrangement, for example. The two coils 1, 2 are electrically connected in series, and the identical current I is driven through both coils by means of a current and / or voltage source (not shown). The two coils 1, 2 are aligned substantially parallel to one another and spaced apart from one another in the x-direction by the distance D. The first and second coils 1, 2 have the radius R. The speed sensor 3, with its sensor head 4, is arranged substantially centrally between the two coils 1, 2 with respect to the radial plane and also with respect to the x-direction, which is the distance direction between the coils. The sensor head 4 comprises the sensitive structures (not shown).The speed sensor 3 is designed, for example, as a wheel speed sensor and has a sealed plastic housing and a fastening device 5 as well as a plug 6, wherein a cable can also be designed instead of a plug 6.

[0043] Based on the Fig. 1 b) shows the field strength curve B as a function of the x-direction. The two dashed lines illustrate the center position of the two coils in the x-direction. It can be seen that the field strength curve is essentially constant between the two coils, especially in a central region 7. With differential detection of the superimposed magnetic field of the two coils 1, 2, this leads to a relatively high degree of independence from the position of the speed sensor 3 in the x-direction between the two coils 1, 2, which enables a significantly simplified test procedure with regard to the positioning or placement of the speed sensor under test.

[0044] In Fig. 2 a) an embodiment is shown, whereby, in contrast to the example not belonging to the invention from Fig. 1 a) the test device comprises a gradient coil arrangement with coils 1, 2. Current I flows through the first and second coils 1, 2 with an identical current intensity but in the inverse direction. For an alternative test method of a speed sensor with rotation direction detection, the currents through the first and second coils are impressed or generated with a defined difference, wherein during the course of this test method the current through the first and / or second coils 1, 2 is changed such that the difference is reversed. For example, first the current through the first coil is greater and then the current through the second coil. The two coils 1, 2 are also arranged parallel to one another, spaced apart by D in the x-direction and each have the radius R. Speed sensor 3 is, as already described with reference to the Fig. 1 a) and is arranged with its sensor head 4 centrally in the x-direction and also centrally with respect to the radial plane between the coils 1, 2.

[0045] Based on the Fig. Figure 2 b) illustrates the field strength curve B as a function of the x-position between the coils 1, 2, whose center position in the x-direction is shown by a dashed line. The field strength B is 0 in the center between the two coils 1, 2 and essentially linear in the central region 7 up to halfway from the center. The speed sensor 3 detects the magnetic field and measures it differentially, resulting in an output signal of essentially 0 V from the speed sensor, at least with regard to the position of the sensor head 4 in the entire central region 7.

Claims

[1] Method for testing a speed sensor (3) by means of a test device, wherein the speed sensor (3) has at least a first and a second sensitive structure (4), wherein the first and the second sensitive structure (4) are each formed as part of a magnetic field sensor element or are formed as a first and second half-bridge of a magnetic field sensor element, wherein the speed sensor (3) has at least one signal processing circuit, wherein the test device comprises at least a first and a second coil (1, 2) and a current and / or voltage source, wherein the test device is designed so and the test device and the speed sensor (3) are arranged relative to each other so, that the speed sensor is arranged between the first and the second coil (1, 2), wherein by means of the current and / or voltage source a first current (I) is generated through the first coil (1) and a second current (I) is generated through the second coil (2), characterized by that the first and second coils (1, 2) are designed as a gradient coil arrangement. [2] Method according to claim 1, characterized by that by means of the first and second coils (1, 2) as a gradient coil arrangement, a magnetic field with a substantially constant spatial gradient is provided between the two coils. [3] Method according to at least one of claims 1 to 2, characterized by that the sensitive structures are designed as GMR sensor structures. [4] Method according to at least one of claims 1 to 3, characterized bythat the speed sensor is designed such that the output signals of the first and second sensitive structure (4) are processed / evaluated differentially with respect to one another in the signal processing circuit. [5] Method according to at least one of claims 1 to 4, characterized by that the speed sensor has four sensitive structures, the output signals of which are processed / evaluated in pairs differentially with respect to one another in the signal processing circuit, and wherein in particular one sensitive structure of a pair is arranged on one side and the other sensitive structure of the pair is arranged on the other side of the speed sensor, in particular with regard to its chip area. [6] Method according to at least one of claims 1 to 5, characterized bythat both coils (1, 2) are operated with slightly different current strengths, sometimes the current through the first coil is greater than the current through the second coil by the said difference and then vice versa, whereby the current direction is inverse to each other. [7] Method according to at least one of claims 1 to 6, characterized by that when forming the test device, comprising a gradient coil arrangement, having the first and the second coil (1, 2), the first and second coil are arranged and electrically connected or controlled in such a way that first, a first current with a defined first, substantially constant current intensity or a constantly and / or continuously changing current intensity flows through the first coil (1) and a second current with a defined second, substantially constant current intensity or a constantly and / or continuously changing current intensity flows or is set through the second coil, wherein the second current intensity is lower than the first current intensity, in particular by at least 1% to a maximum of 15% lower than the first current intensity or by 5% or 10% lower than the first current intensity, after which the current intensity of the second current through the second coil (2) is increased and / or the current intensity of the first current through the first coil (1) is reduced, so that essentially a changed first current through the first coil and / or a changed second current through the second coil is set such that the current intensity of the current through the first coil is lower than the current intensity through the second coil, in particular by at least 1% to a maximum of 15% lower than the current intensity through the second coil or by 5% or 10% lower than the current intensity through the second coil, wherein in particular the change in the first and second current occurs steadily and / or continuously. [8] Method according to at least one of claims 1 to 7, characterized by that the method is used in a test environment, in particular in a laboratory, or at the end of the production line of a sensor. [9] Method according to at least one of claims 1 to 8, characterized bythat the speed sensor is designed as a wheel speed sensor, in particular as a wheel speed sensor with a direction of rotation detection.

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