Magnetic detection device

Abstract

Magnetic detection device, comprising: a magnetic moving body (1) in which N-poles and S-poles are arranged alternately on a circular outer circumference and which rotates with a shaft (4) as an axis; two magnetoresistive elements (2a, 2b) arranged such that they face the outer circumference of the magnetic moving body (1) and detect the changes in the magnetic field of the magnetic moving body (1); a signal processing unit (11) that processes signals from the magnetoresistive elements (2a, 2b); and a magnet (3) which applies a premagnetizing field to the magnetoresistive elements (2a, 2b), wherein a magnetization direction and a central axis (C) of the magnet (3) is parallel to the shaft (4) of the magnetic moving body (1); and the magnetoresistive elements (2a, 2b) are arranged in a plane perpendicular to the magnetization direction of the magnet (3), and the magnetoresistive elements (2a, 2b) are arranged next to each other in a radial direction and spaced apart from each other and are arranged in a radial direction of the magnetic moving body (1) and one of the magnetoresistive elements (2a, 2b) is positioned closer to the magnetic moving body (1) than the other of the magnetoresistive elements (2a, 2b), wherein a magnetic material of the magnetic moving body (1) and a magnetic material of the magnet (3) are identical to each other.

Description

BACKGROUND OF THE INVENTION [Technical Field]

[0001] The present invention relates to a magnetic detection device and, in particular, a magnetic detection device for detecting a magnetic field that changes over time, such as a magnetic field of a rotating body to which magnets are provided. [Description of the state of the art]

[0002] For example, JP 3 655 897 B2 discloses a conventional magnetic detection device for detecting a magnetic field that changes over time.

[0003] In such a conventional magnetic detection device, a disk-like magnetic body rotates circumferentially with a shaft as its axis. For example, if a shaft is attached to the crankshaft of an engine or a wheel axle, the magnetic body rotates integrally with the crankshaft or axle. The outer circumferential surface of the magnetic body is magnetized such that the N-poles and S-poles are arranged alternately. A detection element is positioned facing the magnetic body. The detection element detects changes in the magnetism of the magnetic body as it rotates. A magnetoresistive element is used as the detection element.When the magnetic moving body rotates, it passes in front of the detection element, and consequently, changes in the magnetic field can be detected by the detection element through the number of revolutions of the magnetic moving body.

[0004] Fig. Figure 10 is a perspective drawing depicting the configuration of a conventional magnetic detection device. The magnetic detection device is equipped with a magnetic moving body and magnetoresistive elements. Fig. 11A and Fig. Figure 11B shows enlarged drawings of a detection element section of the magnetic detection device of Fig. 10. Fig. 11A is a drawing of a side view and Fig. 11B is a drawing of a supervisor.

[0005] In Fig. 10, Fig. 11A and Fig. Reference numeral 101, reference numeral 11B, denotes a magnetic moving body. The outer circumferential surface of the magnetic moving body is magnetized such that N-poles and S-poles are arranged alternately. Reference numerals 102a and 102b denote magnetoresistive elements. Reference numeral 103 is a magnet that premagnetizes the magnetoresistive elements 102a and 102b. Reference numeral 102 is a processing circuit unit. The processing circuit unit 102 has a printed circuit board on whose surface conductive traces are applied. Reference numeral 104 is a shaft of the magnetic moving body 101. The shaft 104 and the magnetic moving body 101 rotate synchronously. The magnet 103 is magnetized in a direction parallel to the shaft 104 of the magnetic moving body 101, as indicated by the solid arrow in the figure. Fig. Figure 11A is shown. The magnet 103 is arranged at a given distance from the outer circumferential surface of the magnetic moving body 101. The magnetoresistive elements 102a, 102b are arranged above the magnet 103. The magnetoresistive elements 102a, 102b are arranged side by side along the circumferential direction of the magnetic moving body 101, as shown in Figure 11A. The magnet 103 is arranged at a given distance from the outer circumferential surface of the magnetic moving body 101. The magnetoresistive elements 102a, 102b are arranged side by side along the circumferential direction of the magnetic moving body 101, as shown in Figure 11A. Fig. Figure 11B shows the arrangement of magnetoresistive elements 102a and 102b. These elements are arranged with a given distance Le between them. The dashed arrows in Fig. 11A denotes a premagnetization field generated by magnet 103. A combined magnetic field of the premagnetization field generated by magnet 103 and the magnetic field generated by the magnetic moving body 101 is applied to the magnetoresistive elements 102a, 102b. The magnetoresistive elements 102a, 102b detect only a magnetic field in a plane perpendicular to the wave 104 within the combined magnetic field.

[0006] Fig. Figure 12 is a drawing that illustrates a characteristic of the magnetoresistive elements used in the conventional magnetic detection device. Fig. In Figure 12, the horizontal axis represents the magnetic field (A / m) applied to the magnetoresistive elements 102a and 102b. The vertical axis represents the rate of change in resistance (%) of the magnetoresistive element 102a and 102b. As shown in Figure 12, the horizontal axis represents the magnetic field (A / m) applied to the magnetoresistive elements 102a and 102b. Fig. As shown in Figure 12, the resistance value is at its maximum when the magnetic field applied to the magnetoresistive elements 102a, 102b is zero. Conversely, the resistance value decreases as the value of the applied magnetic field increases.

[0007] In the conventional magnetic detection device, as described above, a premagnetizing field is applied to the magnetoresistive elements 102a, 102b by the magnet 103. This premagnetizing field is in Fig. 12 is represented as a premagnetization field B0. When the magnetic moving body 101 rotates with the shaft 104 as an axis, the variation of the magnetic field applied to the magnetoresistive elements 102a, 102b by the magnetic field of the magnetic moving body 101, that is, the processing range of the magnetic field, is a range extending from B1 to B2 in Fig. 12 extends. In this case, the processing area of ​​the magnetic field of the magnetoresistive elements 102a and 102b is the same for both, since the magnetoresistive elements 102a, 102b are arranged at the fixed distance Le along the direction of rotation of the magnetic moving body 101.

[0008] In the conventional magnetic detection device, the processing circuit unit 102 outputs a signal corresponding to the multipolar magnetization of the magnetic moving body 101, based on changes in the resistance values ​​of the magnetoresistive elements 102a, 102b. The processing circuit unit 102 determines a difference between the resistance values ​​of the magnetoresistive elements 102a, 102b and obtains an output signal Vc by performing a voltage conversion of the difference. The processing circuit unit 102 further transforms the output signal Vc into a waveform to obtain the final output signal Vo.

[0009] Fig. Figure 13 is an example of a flowchart showing the operation of the conventional magnetic detection device. Fig. 13 denotes (a) the resistance values ​​of the magnetoresistive elements 102a, 102b, (b) the output signal Vc, and (c) the output signal Vo. Furthermore, P is the distance between the magnetic poles of the N-poles and S-poles of the magnetic moving body 101.

[0010] The magnetic field applied to the magnetoresistive elements 102a, 102b varies according to the rotation of the magnetic moving body 101 with the shaft 104 as one axis. The resistance values ​​of the magnetoresistive elements 102a, 102b vary as a result, which in Fig. 13(a) is shown. In Fig. In Figure 13(a), the dashed line denotes the resistance value of magnetoresistive element 102a, and the solid line denotes the resistance value of magnetoresistive element 102b. Magnetoresistive elements 102a and 102b are arranged with a distance Le between them along the direction of rotation of the magnetic moving body 102. Accordingly, the resistance changes of the magnetoresistive elements 102a and 102b are phase-shifted from each other by a distance proportional to Le, as shown in Figure 13(a). Fig. 13(a) is shown. Therefore, the output signal Vc, which is shown in Fig. Figure 13(b) shows that the output signal Vo, corresponding to the magnetic poles of the magnetic moving body 101, can be obtained by determining the difference in resistance values ​​of the magnetoresistive elements 102a and 102b and performing a voltage conversion of the difference. The output signal Vo can be generated by converting it into a waveform by comparing the output signal Vc with a threshold voltage Vref, as shown in Figure 13(b). Fig. Figure 13(c) shows that the output signal Vc is essentially sinusoidal in a case where the distance between the magnetic poles P of the magnetic moving body 101 is essentially identical to the distance Le between the magnetoresistive elements 102a, 102b.

[0011] DE 198 50 460 A1, DE 103 25 317 A1, DE 101 38 908 A1, DE 100 10 042 A1, US 2005 / 0 179 429 A1 and REIF, Konrad (ed.): Speed ​​and velocity sensors. In: REIF, Konrad (ed.): Sensors in motor vehicles. 2nd, revised edition. Wiesbaden: Springer, 2012 (Bosch Automotive Technical Information), pp. 63-74, ISBN 978-3-8348-2208-6 represent further state of the art. DESCRIPTION OF THE INVENTION [Technical Problem]

[0012] The output signal Vc varies abruptly near the center of the magnetic pole of the magnetic moving body 101 in a case where the distance between the magnetic poles P of the magnetic moving body 101 and the distance Le between the magnetoresistive elements 102a, 102b are essentially identical, as described above. Accordingly, the rotational position of the magnetic moving body 101 can be detected with high precision even in the conventional magnetic detection device in a case where the distance P between the magnetic poles and the distance Le are essentially identical. However, the magnetization pattern of the magnetic moving body 101 can assume different patterns depending on the application of the magnetic moving body 101, while the distance P between the magnetic poles also varies depending on each application.

[0013] Fig. Figure 14 is another example of a flowchart illustrating the operation of the conventional magnetic detection device. The example shown in Fig. Figure 14 is an example in which the magnetic pole spacing P of the magnetic moving body 101 is greater than the spacing Le of the magnetoresistive elements 102a, 102b. Fig. 14 denotes (a) the resistance values ​​of the magnetoresistive elements 102a, 102b, (b) the output signal Vc, and (c) the output signal Vo. Fig. 14(a) the dashed line denotes the resistance value of the magnetoresistive element 102a and the solid line denotes the resistance value of the magnetoresistive element 102b.

[0014] As in Fig. As shown in Figure 14, the same magnetic field is applied to the magnetoresistive elements 102a and 102b in a case where the distance P between the magnetic poles of the magnetic moving body 101 is greater than the distance Le between the magnetoresistive elements 102a and 102b. As a result, a region (A) appears in which the output signal Vc is a fixed voltage, as shown in Figure 14. Fig. Figure 14(c) illustrates this. The output signal Vc and the threshold voltage Vref approach each other in such a region (A); as a result, the output signal Vc is easily disturbed by noise and the like, and false pulses are also likely to occur in the output signal Vo. Furthermore, the voltage change of the output signal Vc is shallow, and consequently, the positions of the falling and rising signals of the output signal Vo fluctuate easily, resulting in poor detection precision.

[0015] To avoid the above situation, it is effective to set the distance Le between the magnetoresistive elements 102a, 102b to correspond with the distance between the magnetic poles P of the magnetic moving body 101. However, a larger distance between the magnetic poles P of the magnetic moving body 101 leads to a larger distance Le between the magnetoresistive elements 102a, 102b. As a result, the circuit board forming the processing unit 102 becomes larger, and consequently, the magnetic detection device becomes larger and more expensive. The distance Le between the magnetoresistive elements 102a, 102b must also be adjusted for each magnetic moving body 101.

[0016] It is an objective of the present invention, which was achieved with the aim of solving the above problems, to obtain a magnetic detection device that is capable of detecting the rotation of a magnetic moving body with high precision, regardless of the distance between the magnetic poles of the N-poles and S-poles of the magnetic moving body. [Solution to the problem]

[0017] The invention is defined by claim 1. [Advantageous effects of the invention]

[0018] In the present invention, the magnetoresistive elements are arranged in the radial direction of the magnetic moving body and consequently an effect is produced to enable highly precise detection of the rotation of the magnetic moving body without dependence on the distance between the magnetic poles of the N-poles and S-poles of the magnetic moving body. BRIEF DESCRIPTION OF THE FIGURES [ Fig. 1] Fig. Figure 1 is a perspective drawing showing a configuration of a magnetic detection device according to embodiment 1 of the present invention; [ Fig. 2A] Fig. 2A is a drawing showing an enlarged side view of a detection unit in the magnetic detection device according to embodiment 1 of the present invention; [ Fig. 2B] Fig. 2B is a drawing of an enlarged top view of the detection unit in the magnetic detection device according to embodiment 1 of the present invention; [ Fig. 3] Fig. Figure 3 is a diagram showing a relationship between a distance L from a central axis of a magnet that applies a premagnetizing field to magnetoresistive elements and a magnetic field B in the magnet detection device according to embodiment 1 of the present invention; [ Fig. 4] Fig. Figure 4 is a diagram showing a characteristic of an MR loop of a magnetoresistive element in the magnetic detection device according to embodiment 1 of the present invention; [ Fig. 5] Fig. Figure 5 is a circuit diagram that represents an example of a signal processing switching unit of the magnetic detection device according to embodiment 1 of the present invention; [ Fig. 6] Fig. Figure 6 is a flowchart illustrating the operation of the magnetic detection device according to embodiment 1 of the present invention; [ Fig. 7A] Fig. Figure 7A is a drawing of an enlarged side view of a detection unit in the magnetic detection device according to embodiment 2 of the present invention; [ Fig. 7B] Fig. Figure 7B is a drawing of an enlarged top view of the detection unit in the magnetic detection device according to embodiment 2 of the present invention; [ Fig. 8] Fig. Figure 8 is a graph representing a characteristic of an MR loop of the magnetoresistive element in the magnetic detection device according to embodiment 2 of the present invention; [ Fig. 9] Fig. Figure 9 is a flowchart illustrating the operation of the magnetic detection device according to embodiment 2 of the present invention; [ Fig. 10] Fig. Figure 10 is a perspective drawing showing the schematic configuration of a conventional magnetic detection device; [ Fig. 11A] Fig. Figure 11A is a drawing of an enlarged side view of a detection unit in a conventional magnetic detection device; [ Fig. 11B] Fig. Figure 11B is a drawing of an enlarged top view of a detection unit in a conventional magnetic detection device; [ Fig. 12] Fig. Figure 12 is a drawing that shows a characteristic of an MR loop of a magnetoresistive element of a conventional magnetic detection device; [ Fig. 13] Fig. Figure 13 is a flowchart to explain the operation of a conventional magnetic detection device; and [ Fig. 14] Fig. Figure 14 is another flowchart to explain the operation of a conventional magnetic detection device. DETAILED DESCRIPTION OF THE PREFERRED EXECUTION FORMS Execution format 1

[0019] Fig. Figure 1 is a perspective drawing showing the configuration of a magnetic detection device according to embodiment 1 of the present invention. Fig. 2A and Fig. 2B are drawings of an enlarged view of a detection unit of a magnetic detection device. Fig. 2A is a drawing of a side view of a detection unit and Fig. 2B is a drawing of a top view of the detection unit.

[0020] As in Fig. As shown in Figure 1, the magnetic detection device according to embodiment 1 is formed from a magnetic moving body 1, magnetoresistive elements 2a, 2b, a circuit board 2, a magnet 3 and a shaft 4.

[0021] The magnetic moving body 1 has a disc or circular tube shape. The circular outer environment of the magnetic moving body 1 is magnetized into a ring shape such that the N-poles and S-poles are arranged alternately. A shaft 4 runs through the center of the magnetic moving body 1. The magnetic moving body 1 rotates in a circumferential direction with the shaft 4 as one axis.

[0022] The magnetoresistive elements 2a, 2b are mounted on the circuit board 2. A gap of a predetermined distance exists between the circuit board 2 and the outer circumference of the magnetic moving body 1. The circuit board 2 can be manufactured as a printed circuit board on which the magnetoresistive elements 2a, 2b are mounted, or it can be manufactured as an integrated circuit (IC) comprising the magnetoresistive elements 2a, 2b and a processing circuit. The magnetoresistive elements 2a, 2b can be located on the lower surface of the circuit board 2 instead of the upper surface.

[0023] As in Fig. As shown in Figure 1, the magnetoresistive elements 2a and 2b are arranged side by side in the radial direction of the magnetic moving body 1. The magnetoresistive elements 2a and 2b are spaced apart from each other at a fixed, predefined distance. The magnetoresistive element 2b is positioned closer to the magnetic moving body 1 than the magnetoresistive element 2a. Accordingly, the distance from the magnetoresistive element 2b to the magnetic moving body 1 is shorter than the distance between the magnetoresistive element 2a and the magnetic moving body 1.

[0024] In Fig. In 2A, magnet 3 is positioned below circuit board 2. This means that circuit board 2 and magnet 3 are arranged in this order in a direction parallel to shaft 4. Circuit board 2 is not directly above magnet 3; one end of circuit board 2 projects further towards the magnetic moving body 1 than one end of magnet 3. A gap of a predetermined distance exists between magnet 3 and circuit board 2 in a direction parallel to shaft 4. Magnet 3 applies a premagnetic field to the magnetoresistive elements 2a and 2b.

[0025] Magnet 3 is magnetized in a direction parallel to shaft 4, as indicated by the solid arrow. Fig. 2a. The circuit board 2 is shown in a plane essentially perpendicular to the magnetization direction of magnet 3. As shown in Fig. 2a and Fig. In Figure 2b, the central axis C denotes the central axis of magnet 3 in the direction of magnetization. The central axis C is parallel to the shaft 4.

[0026] The magnetoresistive element 2a is arranged on the circuit board 2 at a position offset by a distance La from the central axis C to the magnetic moving body 1. The magnetoresistive element 2b is arranged on the circuit board 2 at a position offset by a distance Lb from the central axis C to the magnetic moving body 1. Assuming that the horizontal direction is perpendicular to the central axis C of the magnet 3, the distance La is the distance between the central line of the magnetoresistive element 2a in the horizontal direction and the central axis C of the magnet 3. Similarly, the distance Lb is the distance between the central line of the magnetoresistive element 2b in the horizontal direction and the central axis C of the magnet 3. The distances La and Lb must be different and can be set to any desired value.

[0027] The arrows with dashed lines in Fig. 2A denotes a premagnetization field generated by magnet 3. A combined magnetic field, composed of the premagnetization field generated by magnet 3 and the magnetic field generated by the magnetic moving body 1, is applied to the magnetoresistive elements 2a, 2b. The magnetoresistive elements 2a, 2b detect only a magnetic field in a plane perpendicular to wave 4 within the combined magnetic field.

[0028] Fig. Figure 3 represents a relationship between a magnetic field B through magnet 3 and a distance L from the central axis C of magnet 3. Fig. 3 is the horizontal axis, the distance L (mm) from the central axis C of magnet 3. The vertical axis is the magnetic field B (A / m), and the signs + / - indicate the orientation of the magnetic field B. The magnetic field B represents a component perpendicular to the magnetization direction of magnet 3 in the premagnetization field of magnet 3. The reference symbols La and Lb in Fig. 3 are the reference symbols La and Lb, which are in Fig. 2A are shown. The magnetic field Ba denotes a component perpendicular to a magnetization direction of magnet 3 in the premagnetization field from magnet 3 to the magnetoresistive element 2a. Similarly, the magnetic field Bb denotes a component perpendicular to the magnetization direction of magnet 3 in the premagnetization field from magnet 3 to the magnetoresistive element 2b. The reference symbols La', Lb', Ba' and Bb' in Fig. 3 are described below in embodiment 2.

[0029] Fig. Figure 4 is a diagram for representing a characteristic, specifically an MR curve, of a magnetoresistive element 2a, 2b. Fig. 4. The horizontal axis is the magnetic field (A / m) applied to the magnetoresistive elements 2a, 2b. The vertical axis is the rate of change of the resistance (%). The reference symbols Ba and Bb in Fig. 4 correspond to the reference symbols Ba and Bb in Fig. 3. The reference symbols ΔBa and ΔBb will be described later.

[0030] In the present embodiment, different premagnetization fields Ba, Bb are alternately applied to the magnetoresistive elements 2a, 2b by the magnet 3, as shown in Fig. 3 and Fig. Figure 4 shows the applied field. The premagnetization field Ba is stronger than the premagnetization field Bb and satisfies the relationship Ba>Bb.

[0031] When the magnetic moving body 1 rotates around the shaft 4, the magnetic field applied to the magnetoresistive element 2a by the magnetic field of the magnetic moving body 1 lies within a region of ΔBa. Accordingly, ΔBa forms the working region of the magnetic field of the magnetoresistive element 2a. Similarly, when the magnetic moving body 1 rotates around the shaft 4, the magnetic field applied to the magnetoresistive element 2b by the magnetic field of the magnetic moving body 1 lies within the region of ΔBb. Accordingly, ΔBb forms the working region of the magnetic field of the magnetoresistive element 2b. As in Fig. As shown in Figure 4, the working ranges of the magnetic field ΔBa of the magnetoresistive element 2a and the working range of the magnetic field ΔBb of the magnetoresistive element 2b are different, such that ΔBb is wider than ΔBa and the relationship ΔBb>ΔBa holds.

[0032] The strong bias field Ba is applied to the magnetoresistive element 2a and is positioned such that it leads to a saturated region in the MR curve. Accordingly, the resistance change in the magnetoresistive element 2a is small even when the magnetic field applied to it is altered by the rotation of the magnetic moving body 1. Conversely, the weak bias field Bb is applied to the magnetoresistive element 2b and is positioned in a region of abrupt resistance change in the MR loop. Accordingly, the resistance change in the magnetoresistive element 2b is large when the magnetic field applied to it changes in accordance with the rotation of the magnetic moving body 1.

[0033] As described above, magnetoresistive element 2b is located closer to the magnetic moving body 1 than magnetoresistive element 2a. Consequently, the variation in the applied magnetic field is large when the magnetic moving body 1 rotates, and the change in its value is also large. Magnetoresistive elements 2a and 2b must exhibit different variations in resistance value, and therefore the premagnetization field Ba applied to magnetoresistive element 2a must not lie in a saturation region of the MR curve.

[0034] The reason for using magnetoresistive element 2a, even though the resistance value change is small, is to improve the temperature characteristics. If a fixed resistor were used, at least hypothetically, instead of magnetoresistive element 2a, the output signal Vc would fluctuate significantly with temperature changes, based on the difference between the resistance values ​​of magnetoresistive element 2a and magnetoresistive element 2b, because the temperature coefficients differ between the resistance values ​​of magnetoresistive element 2b and the fixed resistor. This is described in detail below.

[0035] Changes in the resistance value in the magnetoresistive elements 2a, 2b are processed by a signal in the detection unit, which is located in Fig. 5 is shown, supplied. Fig. Figure 5 is a diagram illustrating a configuration of the detection unit of the magnetic detection device according to embodiment 1. The detection unit is formed from the magnetoresistive elements 2a, 2b and a signal processing unit 11 on the circuit board 2. A comparator 10 is provided in the signal processing unit 11.

[0036] As in Fig. As shown in Figure 5, the magnetoresistive elements 2a and 2b, which are connected in series, form a bridge circuit. Fig. 5. Vc is an output signal of the bridge circuit. Furthermore, Vref is the threshold voltage applied to comparator 10, and Vo is the output signal of comparator 10. The magnetoresistive elements 2a, 2b are connected in series between a constant voltage Vcc and ground. Accordingly, a change in the resistance values ​​of the magnetoresistive elements 2a, 2b is converted into a voltage to obtain the output signal Vc. The output signal Vc is input to the comparator. The input output signal Vc is converted into a waveform in comparator 10 by comparing it with the threshold voltage Vref to obtain and output the output signal Vo.

[0037] In the detection unit, which is in Fig. As shown in Figure 5, the output signal is therefore determined based on the difference between the resistance values ​​of the magnetoresistive elements 2a and 2b. In cases of large temperature changes, the output signal Vc contains an error if the temperature coefficients of the magnetoresistive elements 2a and 2b differ. Therefore, it is preferable to use identical elements that have the same temperature coefficient, i.e., the magnetoresistive elements 2a and 2b. Magnetoresistive element 2a is used for this reason, even though changes in its resistance value are small.

[0038] Fig. Figure 6 is a flowchart illustrating the operation of the magnetic detection device according to the present embodiment 1. Fig. 6 denotes (a) the change in the resistance values ​​of the magnetoresistive elements 2a, 2b when the magnetic moving body 1 rotates with the shaft 4 as one axis, (b) the output signal Vc of the bridge circuit, and (c) the output signal Vo of the comparator 10. Fig. 6(a) the dashed line denotes the resistance value of the magnetoresistive element 2a and the solid line denotes the resistance value of the magnetoresistive element 2b.

[0039] The magnetic field applied to the magnetoresistive elements 2a, 2b varies according to the rotation of the magnetic moving body 1 with the shaft 4 as one axis. The resistance values ​​of the magnetoresistive elements 2a, 2b vary as a result, as shown in Fig. Figure 6(a) illustrates this. At this point, the magnetoresistive elements 2a, 2b are spaced apart from each other at a fixed distance, which is predefined, in the radial direction of the magnetic moving body 1. Accordingly, there is no phase difference in the resistance change of the magnetoresistive elements 2a, 2b. On the other hand, as in Fig. Figure 4 shows that, since the operating ranges of the magnetic fields ΔBa and ΔBb are different, the resistance values ​​of the magnetoresistive elements 2a and 2b are different. An output signal Vc of the bridge circuit, which is shown in Fig. The result shown in Figure 6(b) is obtained accordingly. As a result, it becomes possible to obtain a signal corresponding to the magnetic poles of the magnetic moving body 1 as the output signal Vo of the comparator 10, as shown in Figure 6(b). Fig. Figure 6(c) shows that in this case, the output signal Vc of the bridge circuit changes abruptly at a boundary between the N-poles and the S-poles of the magnetic moving body 1. As a result, the fluctuation in the falling and rising positions of the output signal Vo of the comparator 10 is small, and the rotation of the magnetic moving body 1 can be detected with high precision. In the present embodiment, a signal corresponding to the magnetic poles of the magnetic moving body 1 can therefore be obtained as the output signal Vo of the comparator 10, and accordingly, the revolutions or rotation angles of the magnetic moving body 1 can be obtained with high precision by measuring the number of pulses of the output signal Vo.

[0040] In the present embodiment 1, the range in which the output signal Vc of the bridge circuit and the threshold voltage Vref are close to each other is small and false pulses derived from noise do not easily occur.

[0041] The direction in which the magnetoresistive elements 2a, 2b are arranged is the radial direction of the magnetic moving body 1, and the direction of movement of the magnetic moving body 1 is the circumferential direction. Consequently, the direction in which the magnetoresistive elements 2a, 2b are arranged differs from the direction of movement of the magnetic moving body 1. Accordingly, highly precise detection is enabled regardless of the distance between the magnetic poles of the magnetic moving body 1.

[0042] A detection method according to the present embodiment 1 is suitable for detecting a magnetic moving body 1, in particular if it has a small number of magnetic poles per rotation of a rotor and in which individual distances of the magnetic poles are relatively large, for example in a magnetized rotor that is attached to a camshaft of a motor.

[0043] The magnetic detection device according to embodiment 1 of the present invention is therefore provided with: the magnetic moving body 1, in which N-poles and S-poles are arranged alternately on a circular outer circumference and which rotates with the shaft 4 as an axis; the two magnetoresistive elements 2a, 2b, which are arranged facing the outer circumference of the magnetic moving body 1 and which detect changes in the magnetic field of the magnetic moving body 1; the signal processing unit 11, which processes the signals of the magnetoresistive elements 2a, 2b; and the magnet 3, which applies a premagnetization field to the magnetoresistive elements 2a, 2b. The magnetization direction of the magnet 3 is parallel to the shaft 4 of the magnetic moving body 1. The magnetoresistive elements 2a, 2b are arranged in a plane perpendicular to the magnetization direction of the magnet 3.The magnetoresistive elements 2a, 2b are arranged side by side and spaced apart from each other in the radial direction of the magnetic moving body 1. In the present embodiment 1, the magnetic detection device is configured in this way; consequently, the magnetoresistive elements 2a, 2b are arranged side by side in the radial direction of the magnetic moving body 1, not in the circumferential direction. Therefore, the magnetic detection device is not affected by the distance between the magnetic poles of the N-poles and S-poles of the magnetic moving body 1, and it is accordingly possible to detect the rotation of the magnetic moving body 1 with high precision, independent of the magnet spacing.

[0044] The above explanation described an example in which the magnetoresistive elements 2a, 2b are arranged on the circuit board 2 at positions displaced by distances La, Lb from the central axis C in a direction towards the magnetic moving body 1. However, the embodiment is not limited to this, and the magnetoresistive elements 2a, 2b can be arranged on the circuit board 2 at positions displaced by distances La, Lb from the central axis C in a direction away from the magnetic moving body 1. In this case, however, the magnetoresistive element 2b is further away from the magnetic moving body 1 than the magnetoresistive element 2a, and consequently, the operation in the embodiment is reversed with respect to this feature. Naturally, the effect achieved is identical to that of embodiment 1. Design 2

[0045] Fig. 7A and Fig. Figure 7B shows enlarged drawings of a detection unit of a magnetic detection device according to embodiment 2 of the present invention. Fig. Figure 7A shows a drawing of a side view of a detection unit and Fig. Figure 7B shows a top view drawing of a detection unit. The general configuration of the magnetic detection device according to the present embodiment is identical to the configuration of embodiment 1, which is shown in Fig. 1 is shown, and is not explained here.

[0046] In Fig. In embodiment 7A, the magnet 3 is magnetized in a direction parallel to the shaft 4, which is represented by the solid arrow, similar to embodiment 1. The circuit board 2 is arranged in a plane substantially perpendicular to the magnetization direction of the magnet 3. The magnetoresistive elements 2a and 2b are arranged on both sides of the central axis C of the magnet 3 in the magnetization direction across the central axis C. The magnetoresistive element 2b is arranged closer to the magnetic moving body 1 than the magnetoresistive element 2a. The magnetoresistive element 2a is positioned by a distance La' from the central axis C of the magnet 3 on the side opposite that of the magnetic moving body 1. The magnetoresistive element 2b is positioned by a distance Lb' from the central axis C of the magnet 3 on the side of the magnetic moving body 1.The distance La' is here the distance between the central line of the magnetoresistive element 2a in the horizontal direction and the central direction of the magnet 3, assuming that the horizontal direction is considered to be a direction perpendicular to the central axis C of the magnet 3. Similarly, the distance Lb' is the distance between the central line of the magnetoresistive element 2b in the horizontal direction and the central axis C of the magnet 3. Fig. 7. The distance La' and the distance Lb' differ from each other, and the relationship Lb' > La' holds. However, the embodiment is not limited to this, and Lb' can be <La' gelten.

[0047] The arrows made of dashed lines in Fig. 7A denotes the magnetic field generated by magnet 3. A combined magnetic field, consisting of the magnetic field generated by magnet 3 and the magnetic field generated by the magnetic moving body 1, is applied to the magnetoresistive elements 2a and 2b. The magnetoresistive elements 2a and 2b detect only a magnetic field in a plane perpendicular to wave 4 within the combined magnetic field. Here, the magnetic field Ba' is applied to magnetoresistive element 2a and the magnetic field Bb' to magnetoresistive element 2b, as shown in Fig. 3 shown.

[0048] Fig. Figure 8 represents a graph that depicts a characteristic, in particular an MR curve, of the magnetoresistive elements 2a, 2b. Fig. In Figure 8, the horizontal axis represents the magnetic field (A / m) applied to the magnetoresistive elements 2a and 2b. The vertical axis represents the rate of change of the resistance (%) of the magnetoresistive elements 2a and 2b. Fig. 8 denotes the magnetic field Ba' as a component perpendicular to the magnetization direction of magnet 3 in the premagnetization field from magnet 3 to the magnetoresistive element 2a. Similarly, the magnetic field Bb' denotes a component perpendicular to the magnetization direction of magnet 3 in the premagnetization field from magnet 3 to the magnetoresistive element 2b.

[0049] As described above, in the present embodiment the magnetoresistive elements 2a, 2b are arranged on both sides of the central axis C of the magnet 3 in the magnetization direction across the central axis C. Accordingly, the premagnetization fields Ba', Bb', which have different orientations, are each applied to the magnetoresistive elements 2a, 2b by the magnet 3, as shown in Fig. 8 shown.

[0050] As described above, the distances of the magnetoresistive elements 2a, 2b from the central axis C of the magnet 3 are different, and consequently, the strengths of the premagnetization fields Ba', Bb' are different. The premagnetization field Ba' is stronger than the premagnetization field Bb', and the relationship |Ba'|>|Bb'| holds. Therefore, the change in resistance is small even when the magnetic field applied to the magnetoresistive element 2a changes as the magnetic moving body 1 rotates. In contrast, the weak premagnetization field Bb' is applied to the magnetoresistive element 2b, and consequently, the change in resistance caused by changes in the magnetic field applied as the magnetic moving body 1 rotates is large. As in Fig. As shown in Figure 8, the working range of the magnetic field ΔBa',ΔBb', when the magnetic moving body 1 rotates with the wave 4 as one axis, satisfies the relationship ΔBa'<ΔBb'. Here, ΔBa' is the working range of the magnetic field of the magnetoresistive element 2a and ΔBb' is the working range of the magnetic field of the magnetoresistive element 2b.

[0051] Changes in the resistance values ​​in the magnetoresistive elements 2a, 2b undergo signal processing in the detection unit, which is located in Fig. Figure 5 is shown, which is explained for embodiment 1.

[0052] Fig. Figure 9 is a flowchart describing the operation of the magnetic detection device according to the present embodiment 2. Fig. 9 denotes (a) the change in resistance of the magnetoresistive elements 2a, 2b when the magnetic moving body 1 rotates around the shaft 4, (b) the output signal Vc of the bridge circuit, and (c) the output signal Vo of the comparator 10. Fig. 9(a) the dashed line denotes the resistance value of the magnetoresistive element 2a and the solid line denotes the resistance value of the magnetoresistive element 2b.

[0053] The magnetic field applied to the magnetoresistive elements 2a, 2b varies according to the rotation of the magnetic moving body 1 about the axis of the shaft 4, and the resistance values ​​of the magnetoresistive elements 2a, 2b vary as shown in Fig. Figure 9(a) shows that the orientation of the premagnetization fields Ba', Bb', which are applied to the magnetoresistive elements 2a, 2b by the magnet 3, are different at this time, as shown in Fig. Figure 8 illustrates this, and consequently, the resistance changes of the magnetoresistive elements 2a and 2b are different. In a case where, for example, the S-pole of the magnetic moving body 1 faces the detection unit, the orientation of the magnetic field from magnet 3, which is applied to the magnetoresistive element 2a, and the orientation of the magnetic field from the magnetic moving body 1 are in opposite directions. Accordingly, the magnetic field applied to the magnetoresistive element 2a is weak, and the resistance value is higher. On the other hand, for the magnetoresistive element 2b, the orientation of the magnetic field from magnet 3 and the orientation of the magnetic field from the magnetic moving body 1 are the same, and accordingly, the applied field is stronger, and the resistance value is lower. An output signal Vc of a bridge circuit, which is in Fig. The output signal Vo of comparator 10, which corresponds to the magnetic poles of magnetic moving body 1 as shown in 9(b), is obtained as a result. Fig. 9 (c).

[0054] As in embodiment 1, in the present embodiment the output signal Vc of the bridge circuit varies abruptly at the boundaries between the N-poles and the S-poles and accordingly the fluctuation in the falling position and the rising position of the output signal Vo of the comparator 10 is small and the rotation of the magnetic moving body 1 can be detected with high precision.

[0055] In the present embodiment, as described above, the magnetoresistive elements 2a, 2b are arranged side by side in the radial direction of the magnetic moving body 1 and are therefore not affected by the distance between the magnetic poles of the magnetic moving body 1. Accordingly, the present embodiment allows for highly precise detection without dependence on the distance between the magnetic poles of the magnetic moving body 1, similar to embodiment 1. embodiment 3

[0056] In embodiment 3 of the present invention, the distances La' and Lb', at which the magnetoresistive elements 2a, 2b are arranged in embodiment 2 as described above, are set such that they satisfy the following relationship La'=Lb'. In embodiment 1, the magnetoresistive elements 2a, 2b are arranged on the same side with respect to the central axis C of the magnet 3, and consequently, the relationship La=Lb cannot be applied here. In the present embodiment, however, the magnetoresistive elements 2a, 2b are arranged on both sides of the central axis C of the magnet 3 across the central axis C, and it is possible to set La'=Lb'. Embodiment 3 is identical to embodiments 1 and 2 with respect to the other features, and consequently, these features are not explained here.

[0057] In the present embodiment, the distances La' and Lb' at which the magnetoresistive elements 2a, 2b are arranged are set to be equal, that is, La' = Lb'. Accordingly, the magnetic fields Ba', Bb' applied to the magnetoresistive elements 2a, 2b satisfy Ba' = -Bb'. As a result, the magnetic fields Ba', Bb' applied to the magnetoresistive elements 2a, 2b are magnetic fields of identical strength but different orientations. As in Fig. As shown in Figure 8, the change in resistance of the magnetoresistive elements 2a, 2b depends not on the orientation but on the strength of the magnetic field. The resistance values ​​of the magnetoresistive elements 2a, 2b, which are subjected to magnetic fields of identical strength but different orientations, are therefore identical. Consequently, the resistance values ​​of the magnetoresistive elements 2a, 2b change in the same way even if the resistance values ​​of the magnetoresistive elements 2a, 2b change depending on an external factor such as temperature. The threshold voltage Vref of the comparator 10, which is in Fig. The value shown in 5 can be set as follows. Vref=Vcc / 2

[0058] As a result, the rotation of the magnetic moving body can be detected with high precision, even if a disturbing factor such as temperature or the like exists.

[0059] It has been described that, similar to embodiments 1 and 2, the present embodiment enables high-precision detection without dependence on the distance between the magnetic poles of the magnetic moving body 1. In the present embodiment, the magnetoresistive elements 2a, 2b are arranged at identical distances from the central axis C of the magnet 3 in the direction of magnetization. Therefore, the rotation of the magnetic moving body can be detected with high precision, even if an interfering factor such as temperature or the like is present. Design 4

[0060] In embodiment 4 of the present invention, the magnetic field (hereinafter referred to as magnetic field Bmag) of the magnet 3, which applies the premagnetization field to the magnetoresistive elements 2a, 2b, is set in such a way that in the configurations of embodiments 1 to 3, a combined magnetic field strength of the magnetic field (hereinafter referred to as magnetic field Btarget) of the magnetic moving body 1, as detected by the magnetoresistive elements 2a, 2b, and the magnetic field Bmag of the magnet 3 is at all times as follows: Btarget+Bmag>0.

[0061] As a result, the change in the magnetic field applied to the magnetoresistive elements 2a, 2b does not occur via a zero magnetic field and consequently good signals can be obtained.

[0062] It has been described, similarly to embodiments 1 to 3, that the present embodiment enables highly precise detection independent of the distance between the magnetic poles of the magnetic moving body 1. In the present embodiment, the strength of the magnetic field of the magnet 3 is set such that the strength of the combined magnetic field Btarget+Bmag of the magnetic field of the magnetic moving body 1, as detected by the magnetoresistive elements 2a, 2b, and the magnetic field of the magnet 3 is never zero. Therefore, the magnetic field applied to the magnetoresistive elements 2a, 2b never changes beyond a zero magnetic field, and consequently, good signals can be obtained. Design 5

[0063] In embodiment 5 of the present invention, giant magnetoresistive elements (hereinafter referred to as GMR elements) of a strength detection type are used as the magnetoresistive elements 2a, 2b in embodiments 1 to 3.

[0064] The GMR elements are constructed from a so-called artificial lattice film, that is, a stack in which magnetic and non-magnetic layers have thicknesses ranging from several angstroms to several tens of angstroms, stacked alternately. Compared to magnetoresistive elements (MR elements), GMR elements exhibit a remarkably pronounced MR effect (rate of change of MR) and show characteristic changes in resistance depending on the strength of the magnetic field in the stack plane. By using GMR elements in the magnetoresistive elements 2a, 2b, the SN ratio and noise immunity can therefore be increased.

[0065] It has been described, similarly to embodiments 1 to 3, that the present disclosure enables high-precision detection independent of the distance between the magnetic poles of the magnetic moving body 1. In the present embodiment, the magnetoresistive elements 2a, 2b are made of giant magnetoresistive elements which use an artificial grid film, and consequently it becomes possible to increase the SN ratio and noise immunity. Design 6

[0066] In embodiment 6, which is not part of the claimed invention, a ferrite is used as the magnetic material of the magnetic moving body 1 in embodiments 1 to 3. In particular, the outer circumference of the magnetic moving body 1 is magnetized using a ferrite in such a way that N-poles and S-poles alternate.

[0067] Ferrite is inexpensive, but its magnetic force is weak, and consequently, changes in the magnetic field during the rotation of the magnetic moving body 1 are small. However, by using the magnetoresistive elements 2a, 2b as detection elements, a sufficient change in resistance can be detected, and a high-precision detection device can be obtained economically, even if the changes in the magnetic field are small.

[0068] It has been described, similarly to embodiments 1 to 3, that the present embodiment enables high-precision detection independent of the distance between the magnetic poles of the magnetic moving body 1. In the present embodiment, costs can be reduced while ensuring high-precision magnetic detection, since ferrite is used as the magnetic material of the magnetoresistive elements 2a, 2b. Model 7

[0069] In embodiment 7 of the present invention, a magnet is used as the magnetic material of the magnetic moving body 1 in embodiments 1 to 3. In particular, the outer circumference of the magnetic moving body 1 is magnetized using a magnet in such a way that N-poles and S-poles are arranged alternately. In the present embodiment, a material that is essentially identical to that of the magnet 3, which applies a premagnetizing field to the magnetoresistive elements 2a, 2b, is used as the magnet that serves as the magnetic material of the magnetic moving body 1.

[0070] The temperature characteristics of the magnet's magnetic forces vary depending on the magnetic material used. For example, the temperature coefficient of a remanent flux density shows a five times greater difference between SmCo-based magnets and ferrite-based magnets. By using a material that is essentially identical to the magnetic material of the moving body 1 and the magnetic material of the magnet 3, it becomes possible to obtain good signals without the magnetic field applied to the magnetoresistive elements 2a, 2b reaching zero, even under temperature changes.

[0071] It has been described, similarly to embodiments 1 to 3, that the present invention enables highly precise detection independent of the distance between the magnetic poles of the magnetic moving body 1. In the present embodiment, the magnetic material of the magnetic moving body 1 and the magnet 3 is also made of the same material. Therefore, advantageous signals are obtained, whereby the magnetic field applied to the magnetoresistive elements 2a, 2b never becomes a zero magnetic field, even with changes in temperature.

Claims

[1] Magnetic detection device comprising: a magnetic moving body (1) in which N-poles and S-poles are arranged alternately on a circular outer circumference and which rotates with a shaft (4) as an axis; two magnetoresistive elements (2a, 2b) arranged such that they face the outer circumference of the magnetic moving body (1) and detect the changes in the magnetic field of the magnetic moving body (1); a signal processing unit (11) that processes signals from the magnetoresistive elements (2a, 2b); and a magnet (3) which applies a premagnetizing field to the magnetoresistive elements (2a, 2b), wherein a magnetization direction and a central axis (C) of the magnet (3) is parallel to the shaft (4) of the magnetic moving body (1); and the magnetoresistive elements (2a, 2b) are arranged in a plane perpendicular to the magnetization direction of the magnet (3), and the magnetoresistive elements (2a, 2b) are arranged next to each other in a radial direction and spaced apart from each other and are arranged in a radial direction of the magnetic moving body (1) and one of the magnetoresistive elements (2a, 2b) is positioned closer to the magnetic moving body (1) than the other of the magnetoresistive elements (2a, 2b), wherein a magnetic material of the magnetic moving body (1) and a magnetic material of the magnet (3) are identical to each other. [2] Magnetic detection device according to claim 1, wherein the two magnetoresistive elements (2a, 2b) are displaced by distances La, Lb from the central axis (C) in a direction towards the magnetic moving body (1). [3] Magnetic detection device according to claim 1, wherein the two magnetoresistive elements (2a, 2b) are arranged on both sides of the central axis (C) of the magnet (3). [4] Magnetic detection device according to claim 3, wherein the two magnetoresistive elements (2a, 2b) are arranged at an equal distance from the central axis (C) of the magnet (3). [5] Magnetic detection device according to one of claims 1 to 4, wherein the magnitude of the magnetic field of the magnet (3) is set such that the strength of a combined magnetic field, as detected by the magnetoresistive elements (2a, 2b), from the magnetic field of the magnetic moving body (1) and the magnetic field of the magnet (3) is not zero. [6] Magnetic detection device according to any one of claims 1 to 5, wherein the magnetoresistive elements (2a, 2b) detect a magnetic field strength in a plane perpendicular to the wave (4) of the magnetic moving body (1). [7] Magnetic detection device according to any one of claims 1 to 6, wherein the magnetoresistive elements (2a, 2b) are giant magnetoresistive elements using an artificial grating film.

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