Title of Invention

EDDY CURRENT MEASURING DEVICE

Abstract

An eddy current measuring device for a speed indicator has a radailly magnetized permanent magnet (4) and a second axially magnetised permanent magnet (8). The radially magnetized permanent magnet (4) serves to generate eddy currents in an eddy current body (2), which controls the excursion of an indicator (7) attached to an indicator shaft (1) . The second, axially magnetised, permaneent magnet (8) is positioned vis-a-vis a fixed Hall element (10) at a minimum distance from it. To generate a particularly strong magnetic field, the permanent magnet (4) of the eddy current (2) is diametrically magnetized. The second permanent magnet (8) has several magnetic pole pairs and facilitates a high resolution of the angle of rotation of a drive shaft (3).

Full Text

2. The invention relates to an eddy current measuring device, in particular for a speed indicator having a radially magnetized permanent magnet attached to a drive shaft such that it cannot be rotated and a bel1-shaped eddy current body made of an electrically conductive material, extending over the permanent magnet and installed such that it cannot be rotated on an indicator shaft as we 11 as a Ha11 element for measurement of the revolutions per unit of time (rpm) of the drive shaft. Such eddy current measuring devices are used, for example, in speed indicators (speedometers) of vehicles to display road speed proportional to the rpm of the drive shaft and to determine the number of revolutions of the drive shaft and thus the distance travelled and are thus known. The permanent magnet thereby generates eddy currents in the eddy current body with increasing drive shaft rpm- The Hall element is located at a short distance from the side of the permanent magnet opposite the eddy current body; when a pair of magnetic poles of the permanent magnet move past it, it generates an electrical signal. The number of electrical signals is proportional to the number of drive shaft revolutions. A drawback of known eddy current measurement technology is that the permanent magnet is usually cylinder-shaped and produces only a weak magnetic field at its faces- To register weak 3. magnetic fields, high-cost Hall elements have to be used. A permanent magnet used to transmit the strongest possible magnetic field is also often diametrically magnetized which allows for only minimum resolution of the angle of rotation of the drive shaft by the Hall element. The invention is based on the problem of designing an eddy current measuring device of the type described at the outset so as to be economical and to determine the angle of rotation of the drive shaft as precisely as possible- The invention solves this problem by providing for at least one additional permanent magnet for the purpose of exciting the Hall element., This makes it passible for example, to magnetize the permanent magnet of the eddy current body diametrically to generate the strongest possible magnetic field, independent of the requirements of the Hall element. Since the Hall element is placed vis—a—vis its own or several permanent magnets, it generates electrical signals which clearly correspond to the magnetic, pole pairs moved past it. The number of revolutions of the drive shaft determined with an eddy current measuring devices as per the invention is therefore especially accurate. To determine the number of revolutions of the drive shaft, or its angular position, the simplest design would require only a single 4. Hal i element produced at a particularly low cost. The revolution of the angle of rotation is, in this case, dependent, on the number of magnetic pole pairs of the permanent magnet of the Hall sensor. For example, excitation of the Hall element could be realized by means of a single permanent magnet installed on a drive shaft extension. The eddy current measuring device is designed for particularly easy installation due to an advantageous further development of the invention by surrounding the drive shaft with a ring-shaped permanent magnet in the Hall element . Registraion of the intended angle of rotation could be realized, for example, by equipping the permanent magnet with a number of magnetic pole pairs on the side facing the Hal1 element. Mutual supenmposit ion of the magnetic fields of two permanent magnet© is reliably prevented by another advantageous further development of the invention by means of axial magnetization of the permanent magnet of the Ha11 element on the side not facing the permanent magnet of the eddy current body. This results in field lines of the permanent magnets roatated by 90tt, so that the permanent magnet of the eddy current body builds uo a much weaker magnetic field at the Hall element than the permanent magnet of the Hal 1 element . Faulty measurements by the Hall element due to the magnetic fields of the permanent magnet of the eddy current body are re 1iably prevented by this construction. 5. The eddy current measuring device is characterised by particularly small dimensions due to another advantageous, further development of the invention when the permanent magnet of the Hall element is contiguous with the permanent magnet of the eddy current body. Faulty measurements of the Hall sensor due to mutual superimposition of the magnetic fields are further reduced by another advantageous further development of the invention when the permanent magnet of the Hal1 element is attached with a minimum distance from the permanent magnet of the eddy current body. The magnetic field generated by the permanent magnets is weaker and more uniform with the possession of the more magnetic pole pairs. To register the angle of rotation of the drive shaft with a particularly high resolution, the permanent magnet of the Ha11 element could be equipped with a particularly large number of magnetic pole pairs- This would however, also require use of a particularly sensitive and thus costly Hall element. A particularly high resolution of the angle of rotation can be achieved by means of another advantageous further development of the invention using less sensitive and thus less costly Hal1 elements by using a number of Hall elements positioned at 6. intervals in relation to one another to measure the rpm or angle of rotation of the drive shaft. The distance between two Ha11 elements could, for instance, be equal to one-half the distance of a magnetic pole pair. The invention allows for a number of design variants. Two of the possible variants are shown in the drawings and described below for th® purpose of further clarification of the basic principle of the invention. The drawings accompanying show in Fig.l a section through an eddy current measuring device as per inventian. Fig.2 a section through the eddy current measuring device as per Figure 1 along the line II-II.. Figure 3 a further variant of the eddy current measuring device-Figure 1 shows an eddy current measuring device with a bell-shaped eddy current body attached to an indicator shaft 1. The eddy current body 2 extends over a radially magnetized permanent magnet 4 attached to a drive shaft 3. A return closure ring 5 is attached to the side of the eddy current body 2 opposite the permanent magnet 4. The indicator shaft 1 is pre—tensioned by a torsion spring 6 in its basic position and bears, on the end turned away from the eddy current body 2, an indicator 7. On the underside of the radially magnetized permanent magnet 4, a second 7. permanent magnet 8 is attached, which has several magnetic pole pairs 9 as shown in Figure 2 on the side opposite the radially magnetized permanent magnet 4. A hall element is attached at a minimum distance from the second permanent magnet 8, which element generates an electrical signal when one of the magnetic pole pairs 9 moves past it. Rotation of the drive shaft 3, and thus of the radially magnetized permanent magnet 4 generates eddy currents corresponding in strength to the angular frequency of the permanent magnet 4 in the eddy current body 2. These eddy currents move indicator shaft 1 against the force of torsion spring 6. The resulting excursion of the indicator 7 depends on rpm of drive shaft 3. The number of electrical signals generated by the Hal 1 element 10 is the product of the number of revolutions of the drive shaft 3 and the number of magnetic pole pairs 9 of the second permanent magnet 8. Figure 2 shows, in a sectional diagram of the eddy current measuring device as per Figure 1 along line II—II, that the second permanent magnet 8 bears a number of magnetic pole pairs 9, thus facilitating a particularly high resolution of the angle of rotation of drive shaft 3. The permanent magnet 4 of the eddy current body 2 is diametrically magnetized and thus has only one magnetic pole pair. This results in generation of particularly strong eddy currents in the eddy current body 2. 8. In a variant of the eddy current measuring device as per Figure 3, the second permanent magnet 8 is positioned at a minimum distance from the permanent magnet 4 of the eddy current body 2. This greatly reduces mutual superimposition of the magnetic fields of permanent magnets 4 and 8. Further, the eddy current measuring device also has two Hall elements 11 and 12, which are arranged in relation to one another with an offset of half the distance between the magnetic pole psirs of the second permanent magent 8. This doubles the resolution of the angle of rotation of drive shaft 3 for the same number of magnetic pole pairs. 9. WE CLAIM: 1. Eddy current measuring device, in particular for a speed indicator, with a radially magnetized first permanent magnet (4) attached to a drive shaft (3) such that it cannot be rotated and a bell-shaped eddy current body (2) made of an electrically conductive material, extending over the first permanent magnet (4) and installed such that it cannot be rotated an indicator shaft as well as a Ha11 element (10-12) for measurement of the revolutions per unit of time (rpm) of the drive shaft (3). characterized in that a ring shaped second permanent magnet (S) is disposed around said radially magnetized first permanent magnet (4) to excite the Hall element (10-12). 2. Eddy current measure device as claimed in claim 1 , wherein the drive shaft (3) is surrounded with the ring shaped permanent magnet (8) in the Hall element (10-12). 3. Eddy current measuring device as claimed in claim 1 or 2, wherein the second permanent magnet (8) of the Hall element (10-12) is disposed on a side not facing the first permanent magnet 4 of the eddy current body (2). 4. Eddy current measuring device as claimed in one of the above claims, where an the second permanent magnet (8) of the Ha11 element (11,12) is contiguous with the first permanent magnet (4) of the eddy current body (2). 10. 5. Eddy current measuring device as claimed in one of the above claims, wherein the permanent magnet (8) of the Hal 1 element (11,12) is positioned at a minimum distance from the first permanent magnet (4) of the eddy current body (2). 6. Eddy current measuring device as claimed in one of the above claims wherein a number of Ha11 elements (11,12) are disposed at intervals to register the rpm or angle of rotation of the drive shaft (3). An eddy current measuring device for a speed indicator has a radailly magnetized permanent magnet (4) and a second axially magnetised permanent magnet (8). The radially magnetized permanent magnet (4) serves to generate eddy currents in an eddy current body (2), which controls the excursion of an indicator (7) attached to an indicator shaft (1) . The second, axially magnetised, permaneent magnet (8) is positioned vis-a-vis a fixed Hall element (10) at a minimum distance from it. To generate a particularly strong magnetic field, the permanent magnet (4) of the eddy current (2) is diametrically magnetized. The second permanent magnet (8) has several magnetic pole pairs and facilitates a high resolution of the angle of rotation of a drive shaft (3).

Documents:

02305-cal-02305 abstract.pdf

02305-cal-02305 claims.pdf

02305-cal-02305 correspondence-1.1.pdf

02305-cal-02305 correspondence.pdf

02305-cal-02305 description(complete).pdf

02305-cal-02305 drawings.pdf

02305-cal-02305 form-1.pdf

02305-cal-02305 form-2.pdf

02305-cal-02305 form-3.pdf

02305-cal-02305 form-5.pdf

02305-cal-02305 pa.pdf

02305-cal-02305 priority document.pdf