Rotation angle sensor

Abstract

Rotation angle sensor (1) comprising: a magnet (2) rotating about an axis of rotation (C), wherein the magnet (2) has an end face (2a) perpendicular to the axis of rotation (C) and has a magnetization in a direction perpendicular to the axis of rotation (C); and a magnetic sensor (5) which is located opposite the end face (2a) of the magnet (2) and detects a magnetic field generated by the magnet (2), wherein the rotation angle sensor (1) detects a rotation angle of the magnet (2) based on a determined output from the magnetic sensor (5), characterized by the fact that the magnet (2) includes the following: comprising a plate-shaped part (3) the end face (2a) of the magnet (2); and a ring-shaped part (4) which is located on a side of the plate-shaped part (3) further away from the end face (2a) and is coupled to the plate-shaped part (3); wherein the plate-shaped part (3) does not enclose a cavity through which the axis of rotation (C) runs, while the ring-shaped part (4) encloses a cavity (4a) through which the axis of rotation (C) runs, in each cross-section of the annular part (4) perpendicular to the axis of rotation (C) the outer edges of the annular part (4) have the same shape as the outer edges of the plate-shaped part (3) in each cross-section of the plate-shaped part (3) perpendicular to the axis of rotation (C), the plate-shaped part (3) and the ring-shaped part (4) have a magnetization in the same direction as the magnetization direction of the magnet (2), and the plate-shaped part (3) and the ring-shaped part (4) are a composite magnet based on NdFeB.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention

[0001] The present invention relates to a rotation angle sensor including a rotating magnet and a magnetic sensor for detecting a magnetic field generated by the magnet, wherein the rotation angle sensor detects the rotation angle of the magnet. 2. Description of the state of the art

[0002] In recent years, magnetic rotation angle sensors have been widely used to detect the rotational position of an object for various applications, such as detecting the rotational position of the steering of motor vehicles. For example, JP 2007-93280 A and JP 2010-66196 A disclose a magnetic rotation angle sensor that includes a rotating magnet and a magnetic sensor for detecting a magnetic field generated by the magnet. The magnetic rotation angle sensor detects the rotation angle of the magnet based on the detected output of the magnetic sensor.

[0003] In the rotation angle sensor including, for example, a rotating magnet and a magnetic sensor, the magnet has an end face perpendicular to the rotation axis and is magnetized in a direction perpendicular to the rotation axis, while the magnetic sensor is arranged opposite the end face of the magnet at a predetermined distance. The requirements for a rotation angle sensor with such a structure are that the magnetic field generated by the magnet and applied to the magnetic sensor should have a high intensity, and that a difference between the actual rotation angle of the magnet and the rotation angle of the magnet detected based on the detected output from the magnetic sensor should be small. The rotation angle of the magnet detected based on the detected output from the magnetic sensor is hereinafter referred to as the detection angle.The difference between the actual angle of rotation and the detected angle is referred to as the angle error.

[0004] The magnetic sensor may be exposed not only to the magnetic field generated by the magnet but also to other magnetic fields, such as a stray magnetic field from a motor or the earth's magnetic field. The requirement that the magnetic field generated by the magnet and applied to the magnetic sensor should have a high intensity is unavoidable in order to relatively reduce the effects of magnetic fields other than the magnetic field generated by the magnet to be applied to the magnetic sensor. Increasing the strength of the magnetic field generated by the magnet and applied to the magnetic sensor can be achieved, for example, by forming the magnet from a magnetic material with a high residual flux density or by enlarging the magnet.

[0005] On the other hand, one cause of the angular error is a misalignment between the magnet and the magnetic sensor. The relative positions of the magnet and the magnetic sensor may deviate slightly from their desired positions during the manufacturing of the angle sensor or during use of the angle sensor. It is assumed here that, on an imaginary plane parallel to the end face of the magnet, the direction of the magnetic field generated by the magnet, when viewed at the point where the axis of rotation intersects the imaginary plane, is parallel to the magnetization direction of the magnet. The aforementioned point is referred to as the center point hereinafter. It is assumed that the position of the magnetic sensor on the imaginary plane where the axis of rotation passes through the center of the magnetic sensor is a desired position of the magnetic sensor.At a location remote from the center point on the aforementioned imaginary plane, the direction of the magnetic field generated by the magnet may be different from that at the center point. Accordingly, if the position of the magnetic sensor deviates from the desired position on the aforementioned imaginary plane, the direction of the magnetic field detected by the magnetic sensor may be different from that detected when the magnetic sensor is in the desired position. An angular error may thus occur due to a misalignment between the magnet and the magnetic sensor. The rotation angle sensor is designed to exhibit a small angular error even in the presence of a misalignment between the magnet and the magnetic sensor.

[0006] JP 2007 - 93 280 A discloses a technology for reducing the angular error for a rotation angle sensor comprising a disc magnet and a magnetoelectric transducer, wherein the magnetoelectric transducer is arranged at such a position that the angular error resulting from a misalignment of the rotation axis of the disc magnet is reduced.

[0007] JP 2010-66196 A discloses a technology for reducing the angular error by designing the shape of the magnet and the arrangement of the magnetic detection part. In this technology, the magnet has a proximal part around the central rotation axis, a first outer peripheral part outside the proximal part, and a second outer peripheral part outside the first outer peripheral part. The thickness of the proximal part in a direction parallel to the central rotation axis is greater than the thickness of each of the first outer peripheral part and the second outer peripheral part in the direction parallel to the central rotation axis.

[0008] In a rotary angle sensor comprising a rotary magnet and a magnetic sensor as described above, it is required that the magnetic field generated by the magnet and applied to the magnetic sensor has a high strength and that the angular error resulting from misalignment between the magnet and the magnetic sensor is small.

[0009] One possible approach to meet these requirements is to increase the strength of the magnetic field generated by the magnet and to mount the magnetic sensor in such a position that the angular error resulting from misalignment between the magnet and the magnetic sensor is reduced.

[0010] The inventors of the present application have determined through simulation that near the end face of a cylindrical magnet, there is a region where the direction of the magnetic field is substantially the same as the direction of the magnetic field at the desired location. Such a region is referred to below as the parallel field region. The inventors have also determined that the area of ​​the parallel field region on an imaginary plane parallel to the end face of the magnet varies depending on the distance between the end face of the magnet and the imaginary plane. Therefore, it can be imagined that mounting the magnetic sensor on an imaginary plane that maximizes the area of ​​the parallel field region would reduce the angular error resulting from misalignment between the magnet and the magnetic sensor.

[0011] On the other hand, to increase the strength of the magnetic field generated by a cylindrical magnet, increasing the thickness of the magnet (dimension along the rotation axis) is effective. However, it has been found that increasing the thickness of the magnet would cause the following problem. That is, it has been found through simulation that increasing the thickness of the magnet reduces the distance between the end face of the magnet and the imaginary plane that maximizes the area of ​​the parallel field region. Accordingly, if the thickness of the magnet is increased and the magnetic sensor is mounted on the respective imaginary plane that maximizes the area of ​​the parallel field region, the distance between the end face of the magnet and the magnetic sensor may be excessively reduced, causing the magnetic sensor to touch the magnet and damage it.

[0012] Thus, when using a cylindrical magnet, it is difficult to increase the strength of the magnetic field generated by the magnet and applied to the magnetic sensor and to reduce the angular error resulting from misalignment between the magnet and the magnetic sensor without causing an excessive reduction in the distance between the magnet and the magnetic sensor. The techniques disclosed in JP-A-2007-93280 and JP-A-2010-66196 have not been able to solve this problem.

[0013] DE 10 2007 001 699 A1 shows a device for detecting the angle of rotation of a structural element, e.g. a shaft, to which a sensor magnet is attached, which controls at least one sensor element which is located axially in front of the magnet and with which the angle of rotation is detected.

[0014] JP 2010 - 85 394 A shows another magnetic angle sensor. OBJECT AND BRIEF DESCRIPTION OF THE INVENTION

[0015] It is an object of the present invention to provide a rotation angle sensor including a rotating magnet and a magnetic sensor for detecting a magnetic field generated by the magnet, wherein the rotation angle sensor detects the rotation angle of the magnet and is capable of increasing the strength of the magnetic field generated by the magnet and applied to the magnetic sensor and reducing the angular error resulting from a misalignment between the magnet and the magnetic sensor without causing an excessive reduction in the distance between the magnet and the magnetic sensor.

[0016] The object is achieved by a rotation angle sensor according to claim 1.

[0017] A rotation angle sensor of the present invention includes: a magnet that rotates about a rotation axis, the magnet having an end surface perpendicular to the rotation axis and magnetized in a direction perpendicular to the rotation axis; and a magnetic sensor that opposes the end surface of the magnet and detects a magnetic field generated by the magnet. The rotation angle sensor detects the rotation angle of the magnet based on a detected output from the magnetic sensor. The magnet includes a plate-shaped part having the end surface of the magnet and an annular part located on a side of the plate-shaped part farther from the end surface and coupled to the plate-shaped part. The plate-shaped part does not include a cavity through which the rotation axis passes, while the annular part includes a cavity through which the rotation axis passes.

[0018] In the rotation angle sensor of the present invention, any cross section of the magnet including the rotation axis may have a shape symmetrical about the rotation axis. In this case, the plate-shaped part may be shaped like a circular plate, and the annular part may have an outer periphery and an inner periphery, both of which are circular in any cross section of the annular part perpendicular to the rotation axis.

[0019] The rotation angle sensor of the present invention may be constructed such that, in an imaginary plane which is parallel to the end face of the magnet and which is as far away from the end face as the distance between the end face and the magnetic sensor, the magnetic field generated by the magnet at a first location and a second location are in mutually parallel directions, wherein the first location is a location at which the rotation axis intersects the imaginary plane and wherein the second location is different from the first location.

[0020] In the rotation angle sensor of the present invention, the magnetic sensor may include a magnetoresistance.

[0021] In the rotation angle sensor of the present invention, the magnet includes a plate-shaped part having the end surface facing the magnetic sensor, and an annular part located on a side of the plate-shaped part farther from the end surface and coupled to the plate-shaped part. The plate-shaped part does not contain a cavity through which the rotation axis passes, while the annular part contains a cavity through which the rotation axis passes. The magnet of the present invention is capable of increasing the strength of the magnetic field generated by the magnet and applied to the magnetic sensor compared with a cylindrical magnet, provided, for example, that the optimal distance between the end surfaces of the magnet and the magnetic sensor is almost the same for the two magnets.Here, the optimal distance means a distance between the end face of the magnet and the magnetic sensor that allows the reduction of the angular error resulting from misalignment between the magnet and the magnetic sensor. Furthermore, the magnet of the present invention is capable of increasing the optimal distance compared with a cylindrical magnet, provided that, for example, the strength of the above-mentioned magnetic field at the optimal distance is almost the same for the two magnets. Consequently, the present invention enables the increase of the strength of the magnetic field generated by the magnet and applied to the magnetic sensor and the reduction of the angular error resulting from misalignment between the magnet and the magnetic sensor without causing an excessive reduction in the distance between the magnet and the magnetic sensor.

[0022] Other and further objects, features and advantages of the present invention will become more fully apparent from the following description. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view of the general structure of a rotation angle sensor according to an embodiment of the invention. Fig. 2 is an exploded perspective view of the Fig. 1 shown magnets. Fig. 3 is a side view of the general structure of the rotation angle sensor according to the embodiment of the invention. Fig. 4 is a plan view of the magnet and the magnetic sensor of the Fig. 3 shown angle sensor. Fig. 5 is a bottom view of the Fig. 3 magnets shown. Fig. 6 is a side view of the Fig. 3 magnets shown. Fig. 7 is an explanatory diagram of the definitions of directions and angles in the embodiment of the invention. Fig. 8 is a circuit diagram showing the circuit structure of the rotation angle sensor according to the embodiment of the invention. Fig. 9 is a perspective view of a portion of an MR element in the Fig. 8 shown magnetic sensor. Fig. Figure 10 is an explanatory diagram of the magnetic field distribution around the magnet determined by a first simulation. Fig. 11 is an explanatory diagram of the magnetic field distribution on a Fig. 10 shown imaginary plane PL1. Fig. 12 is an explanatory diagram of the magnetic field distribution on a Fig. 10 shown imaginary plane PL2. Fig. 13 is a characteristic diagram of the relationship between the distance of the magnet from the end face along a Fig. 10 shown imaginary straight line L and the angular error. Fig. Figure 14 is a characteristic diagram of the relationship between the thickness of the magnet and the optimal distance, determined by a second simulation. Fig. Figure 15 is a characteristic diagram of the relationship between the distance of the magnet from the magnetic sensor and the angular error determined by a third simulation. Fig. Figure 16 is a characteristic diagram of the relationship between the distance of the magnet from the magnetic sensor and the strength of the magnetic field applied to the magnetic sensor, determined by the third simulation. Fig. Figure 17 is a characteristic diagram of the relationship between the ratio of the thickness of the annular part of the magnet, the optimum distance, and the strength of the magnetic field at the optimum distance, determined by a fourth simulation. Fig. Figure 18 is a characteristic diagram of the relationship between the shape of the magnet, the optimal distance, and the strength of the magnetic field at the optimal distance, determined by a fifth simulation. Fig. Figure 19 is a characteristic diagram of the relationship between the distance between the magnet and the magnetic sensor, the strength of the magnetic field applied to the magnetic sensor, and the angular error determined by a sixth simulation. Fig. 20 is a plan view of a first modified example of the magnet of the embodiment of the invention. Fig. 21 is a plan view of a second modified example of the magnet of the embodiment of the invention. Fig. 22 is a cross-sectional view of a third modified example of the magnet of the embodiment of the invention. Fig. 23 is a cross-sectional view of a fourth modified example of the magnet of the embodiment of the invention. Fig. 24 is a cross-sectional view of a fifth modified example of the magnet of the embodiment of the invention. Fig. 25 is a cross-sectional view of a sixth modified example of the magnet of the embodiment of the invention. Fig. 26 is a cross-sectional view of a seventh modified example of the magnet of the embodiment of the invention. Fig. 27 is a cross-sectional view of an eighth modified example of the magnet of the embodiment of the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0023] A preferred embodiment of the present invention will now be described in detail with reference to the drawings. First, to describe the general structure of a rotation angle sensor according to an embodiment of the invention, reference will be made to Fig. 1 to Fig. 7 is referred to. Fig. 1 is a perspective view of the general structure of a rotation angle sensor according to the embodiment. Fig. 2 is an exploded perspective view of the Fig. 1 shown magnets. Fig. 3 is a side view of the general structure of the rotation angle sensor according to the embodiment. Fig. 4 is a plan view of the magnet and the magnetic sensor of the Fig. 3 shown angle sensor. Fig. 5 is a bottom view of the Fig. 3 magnets shown. Fig. 6 is a side view of the Fig. 3 magnets shown. Fig. 7 is an explanatory diagram about the definitions of directions and angles in the embodiment.

[0024] As in Fig. 1 and Fig. As shown in Figure 3, the rotation angle sensor 1 according to the embodiment includes a magnet 2, a substrate 8 (see Fig. 3) and a magnetic sensor 5 mounted on the substrate 8. The magnet 2 is secured to an axial end of a shaft 6 via a securing device 7. The shaft 6 rotates about a rotational axis C. The magnet 2 rotates in conjunction with the rotated shaft 6 about the rotational axis C.

[0025] The magnet 2 has an end face 2a perpendicular to the rotation axis C and is magnetized in a direction perpendicular to the rotation axis C. The magnet 2 includes a plate-shaped part 3 with the end face 2a and an annular part 4, which is located on a side of the plate-shaped part 3 further away from the end face 2a and is coupled to the plate-shaped part 3. The plate-shaped part 3 does not contain a cavity through which the rotation axis C passes, while the annular part 4 contains a cavity 4a through which the rotation axis C passes.

[0026] The plate-shaped part 3 has an N-pole and an S-pole, which are arranged symmetrically around an imaginary plane containing the rotation axis C. The magnetization direction of the magnet 2 runs from the S-pole to the N-pole of the plate-shaped part 3 and perpendicular to the boundary between the S-pole and the N-pole. Fig. 1, the arrow with the symbol M indicates the magnetization direction of the magnet 2. According to the invention, the plate-shaped part 3 and the ring-shaped part 4 have a magnetization in the same direction as the magnetization direction of the magnet 2. In Fig. 4, the arrow drawn on the plate-shaped part 3 indicates the direction of magnetization of the plate-shaped part 3. In Fig. 5, the direction of magnetization of the annular part 4 is indicated by the arrows drawn on the annular part 4.

[0027] Magnet 2 generates a magnetic field based on its own magnetization. Fig. 1, the arrow with the symbol H indicates the direction of the magnetic field generated by the magnet 2, viewed at a position on the axis of rotation C near the end face 2a.

[0028] The substrate 8 has a surface oriented toward the end face 2a of the magnet 2. The magnetic sensor 5 is attached to this surface of the substrate 8. The magnetic sensor 5 is located opposite the end face 2a of the magnet 2 and detects the magnetic field generated by the magnet 2. The rotation angle sensor 1 detects the rotation angle of the magnet 2 based on the output from the magnetic sensor 5.

[0029] Each cross section of the magnet 2 containing the rotation axis C has a shape symmetrical about the rotation axis C. Fig. 1 to Fig. 7 shows an example of the shape of the magnet 2. In this example, the plate-shaped part 3 is shaped like a circular plate and in each cross section of the annular part 4 perpendicular to the rotation axis C, both the outer and inner edges of the annular part 4 have the shape of circles around the rotation axis C.

[0030] As in Fig. 5 and Fig. 6, the diameter of the magnet 2 is represented by the symbol d1, and the inner diameter of the annular part 4, i.e., the diameter of the cavity 4a, is represented by the symbol d2. The diameter of the plate-shaped part 3 and the diameter of the annular part 4 are equal to the diameter d1 of the magnet 2. As shown in Fig. 6, the thicknesses (dimensions in a direction parallel to the rotation axis C) of the magnet 2, the plate-shaped part 3 and the annular part 4 are represented by symbols t2, t3 and t4, respectively.

[0031] Now, with reference to Fig. 7 describes the definitions of directions and angles in the embodiment. First, a direction parallel to the direction shown in Fig. 1 and extends from the end face 2a of the magnet 2 to the magnetic sensor 5 is defined as the Z-direction. Next, two mutually perpendicular directions on an imaginary plane perpendicular to the Z-direction are defined as the X-direction and the Y-direction. Fig. 7, the X direction is shown as the right direction, and the Y direction is shown as the up direction. The direction opposite to the X direction is defined as the -X direction. The direction opposite to the Y direction is defined as the -Y direction.

[0032] To describe the angle of rotation of the magnet 2, a reference direction DR in space and a magnetic reference direction DM, which rotates with the magnet 2, are defined. The reference direction DR is, for example, the Y-direction. The magnetic reference direction DM is defined, for example, as the direction opposite to the magnetization direction of the magnet 2. Furthermore, the angle that the magnetic reference direction DM forms with the reference direction DR is defined as the angle of rotation θ of the magnet 2. It is assumed that the magnet 2 and the magnetic reference direction DM are in Fig. 7 in a counterclockwise direction. The angle θ is expressed as a positive value when viewed in a counterclockwise direction from the reference direction DR and as a negative value when viewed in a clockwise direction from the reference direction DR.

[0033] Consider here an imaginary plane that runs parallel to the end face 2a of the magnet 2 and is spaced from the end face 2a by a distance equal to the distance between the end face 2a and the magnetic sensor 5. This imaginary plane is referred to below as the sensor mounting surface. The magnetic sensor 5 detects a magnetic field generated by the magnet 2 essentially on the sensor mounting surface. The symbol H0 represents the magnetic field generated by the magnet 2, detected at a position on the sensor mounting surface where the rotation axis C intersects the sensor mounting surface. The direction of the magnetic field H0 is parallel to the magnetization direction of the magnet 2 and coincides with the magnetic reference direction DM. Consequently, the angle formed by the direction of the magnetic field H0 with the reference direction DR coincides with the rotation angle θ.

[0034] The symbol H srepresents the magnetic field generated by the magnet 2 and applied to the magnetic sensor 5 on the sensor mounting surface. The magnetic field H s detected. The rotation angle sensor 1 detects the rotation angle θ of the magnet 2 based on the detected output of the magnetic sensor 5. In practice, the rotation angle sensor 1 detects an angle θs based on the detected output of the magnetic sensor 5 as an angle corresponding to the rotation angle θ, which the direction of the magnetic field H s to the reference direction DR. The angle θs is hereinafter referred to as the detection angle. The definition of positive and negative detected angles θs is the same as that for the angle θ. Ideally, the detection angle θs corresponds to the rotation angle θ.

[0035] A position of the magnetic sensor 5 in which the rotation axis C passes through the center of the magnetic sensor 5 is defined as the target position of the magnetic sensor 5. When the magnetic sensor 5 is in the target position, the magnetic field H s equal to the magnetic field H0 and accordingly, the detection angle θs is equal to the rotation angle θ. However, if the magnetic sensor 5 is located at a position on the sensor mounting surface that is offset from the target position, the direction of the magnetic field H s differ from the direction of the magnetic field H0. Fig. Figure 7 shows an example of such a case. In this case, the detection angle θs does not match the rotation angle θ. The difference between the detection angle θs and the rotation angle θ is called the angle error and is represented by the symbol dθ. In the Fig. In the example shown in Figure 7, the angular error dθ is equal to the angle that the direction of the magnetic field H s to the direction of the magnetic field H0. The definition of positive and negative angular errors dθ is the same as that for the angle θ.

[0036] To describe the circuit structure of the angle of rotation sensor 1, Fig. 8 is referred to. Fig. Figure 8 is a circuit diagram of the circuit structure of the rotation angle sensor 1. The magnetic sensor 5 includes a first detection circuit 11 and a second detection circuit 12. The substrate 8 has differential detectors 13 and 14 and an arithmetic circuit 15. The arithmetic circuit 15 can be implemented, for example, by a microcomputer.

[0037] The first detection circuit 11 detects the strength of a component of the magnetic field H sin one direction and outputs a signal indicating the strength. The second detection circuit 12 detects the strength of a component of the magnetic field H s in a different direction and output a signal indicating the strength. Each of the first and second detection circuits 11 and 12 contains at least one magnetic detection element.

[0038] Each of the first and second detection circuits 11 and 12 may include, as the at least one magnetic detection element, a pair of series-connected magnetic detection elements. In this case, each of the first and second detection elements 11 and 12 may comprise a Wheatstone bridge circuit including a first pair of series-connected magnetic detection elements and a second pair of series-connected magnetic detection elements. The following description will deal with the case where each of the first and second detection circuits 11 and 12 comprises such a Wheatstone bridge circuit.

[0039] The first detection circuit 11 includes a Wheatstone bridge circuit 16. The Wheatstone bridge circuit 16 includes a power supply terminal V1, a ground terminal G1, two output terminals E11 and E12, a first pair of series-connected magnetic detection elements R11 and R12, and a second pair of series-connected magnetic detection elements R13 and R14. One end of each of the magnetic detection elements R11 and R13 is connected to the power supply terminal V1. The other end of the magnetic detection element R11 is connected to one end of the magnetic detection element R12 and the output terminal E11. The other end of the magnetic detection element R13 is connected to one end of the magnetic detection element R14 and the output terminal E12. The other end of each of the magnetic detection elements R12 and R14 is connected to the ground terminal G1.A power supply voltage of a predetermined magnitude is applied to the power supply terminal V1. The ground terminal G1 is grounded.

[0040] The second detection circuit 12 includes a Wheatstone bridge circuit 17. The Wheatstone bridge circuit 17 includes a power supply terminal V2, a ground terminal G2, two output terminals E21 and E22, a first pair of series-connected magnetic detection elements R21 and R22, and a second pair of series-connected magnetic detection elements R23 and R24. One end of each of the magnetic detection elements R21 and R23 is connected to the power supply terminal V2. The other end of the magnetic detection element R21 is connected to one end of the magnetic detection element R22 and the output terminal E21. The other end of the magnetic detection element R23 is connected to one end of the magnetic detection element R24 and the output terminal E22. The other end of each of the magnetic detection elements R22 and R24 is connected to the ground terminal G2.A power supply voltage of a predetermined magnitude is applied to the power supply terminal V2. The ground terminal G2 is grounded.

[0041] In the embodiment, all magnetic detection elements included in the Wheatstone bridge circuits 16 and 17 (hereinafter referred to as bridge circuits) are magnetoresistive resistance elements (MR) or, more specifically, tunneling magnetoresistive resistance elements (TMR). Giant magnetoresistive elements (GMR) can be used instead of TMR elements. The TMR elements or GMR elements each comprise a pinned magnetization layer whose magnetization direction is pinned, a free layer whose magnetization direction changes according to the direction of an applied magnetic field, and a non-magnetic layer arranged between the pinned magnetization layer and the free layer. In TMR elements, the non-magnetic layer is a tunneling barrier layer.In GMR elements, the non-magnetic layer is a non-magnetic conductive layer. TMR elements or GMR elements change their resistance depending on the angle between the magnetization direction of the free layer and the magnetization direction of the pinned layer. The resistance reaches its minimum value when the above angle is 0°. The resistance reaches its maximum value when the above angle is 180°. In the following description, the magnetic detection elements included in bridge circuits 16 and 17 are referred to as MR elements. In . Fig. In Figure 8, the filled arrows indicate the magnetization directions of the layers with pinned magnetization in the MR elements. The open arrows indicate the magnetization directions of the free layers in the MR elements.

[0042] In the first detection circuit 11, the pinned magnetization layers of the MR elements R11 and R14 are magnetized in the -X direction, and the pinned magnetization layers of the MR elements R12 and R13 are magnetized in the X direction. In this case, the voltage difference between the output terminals E11 and E12 varies with the strength of the magnetic field component H. s in the -X direction. The first detection circuit 11 therefore detects the strength of the component of the magnetic field H s in the -X direction and outputs a signal indicating the strength. In particular, the voltage difference between the output terminals E11 and E12 is the output signal of the first detection circuit 11. When the Fig. 7 shown angle θs is 0° and 180°, the strength of the component of the magnetic field H sin the -X direction is zero. If the angle θs is greater than 0° and less than 180°, the strength of the component of the magnetic field H s in the -X direction is positive in value. If the angle θs is greater than 180° and less than 360°, the strength of the component of the magnetic field H s negative in value in the -X direction.

[0043] In the second detection circuit 12, the pinned magnetization layers of the MR elements R21 and R24 are magnetized in the Y direction, and the pinned magnetization layers of the MR elements R22 and R23 are magnetized in the -Y direction. In this case, the voltage difference between the output terminals E21 and E22 varies with the strength of the magnetic field component H. s in the Y direction. The second detection circuit 12 therefore detects the strength of the component of the magnetic field H sin the Y direction and outputs a signal indicating the strength. In particular, the voltage difference between the output terminals E21 and E22 is the output signal of the second detection circuit 12. When the Fig. 7 is 90° and 270°, the strength of the component of the magnetic field H s in the Y-direction is zero. If the angle θs is greater than 0° and less than 90° and if the angle θs is greater than 270° and less than 360°, the strength of the component of the magnetic field H s in the Y-direction is positive in value. If the angle θs is greater than 90° and less than 270°, the strength of the component of the magnetic field H s negative in value in the Y direction.

[0044] From the difference detector 13, a signal corresponding to the voltage difference between the output terminals E11 and E12 is output to the arithmetic circuit 15 as the first signal S1. From the difference detector 14, a signal corresponding to the voltage difference between the output terminals E21 and E22 is output to the arithmetic circuit 15 as the second signal S2. The first signal S1 and the second signal S2 change periodically with the same signal period T. In the embodiment, the second signal S2 preferably differs in phase from the first signal S1 by an odd number of 1 / 4 times the signal period T. However, considering the manufacturing accuracy of the magnetic detection elements and other factors, the phase difference between the first signal S1 and the second signal S2 might slightly differ by an odd number of 1 / 4 times the signal period T.In the following description, it is assumed that the phase of the first signal S1 and the phase of the second signal S2 satisfy the preferred relationship described above.

[0045] In the Fig. In the example shown in Fig. 8, the magnetization directions of the pinned magnetization layers of the MR elements in the second detection circuit 12 are orthogonal to the magnetization directions of the pinned magnetization layers of the MR elements in the first detection circuit 11. Ideally, the first signal S1 has a sine waveform, while the second signal S2 has a cosine waveform. In this case, the second signal S2 differs in phase from the first signal S1 by 1 / 4 of the signal period T, that is, by π / 2 (90°). The arithmetic circuit 15 calculates the detection angle θs based on the first signal S1 and the second signal S2. Specifically, the arithmetic circuit 15 calculates, for example, θs by Equation (1) below. Note that "atan" represents an arctangent. θs=atan(S1 / S2)

[0046] The term "atan (S1 / S2)" of equation (1) represents the arctangent calculation for determining θs. Within the range of 360°, θs in equation (1) has two solutions that differ by 180° in value. Which of the two solutions of θs in equation (1) is the true solution for θs can be determined from the combination of positive and negative signs of S1 and S2. In particular, when S1 has a positive value, θs is greater than 0° and less than 180°. When S1 is negative in value, θs is greater than 180° and less than 360°. When S2 is positive in value, θs is greater than or equal to 0° and less than 90° or is greater than 270° and less than or equal to 360°. If S2 is negative in value, θs is greater than 90° and less than 270°. The arithmetic circuit 15 determines θs in the range of 360° using equation (1) and based on the previous determination of the combination of positive and negative signs at S1 and S2.

[0047] Note that it is possible to determine θs not only when the second signal S2 differs in phase from the first signal S1 by 1 / 4 of the signal period T, but also when the second signal S2 differs in phase from the first signal S1 by an odd number of 1 / 4 times the signal period T.

[0048] An example of the structure of the MR elements will now be described with reference to Fig. 9 described. Fig. 9 is a perspective view of a portion of an MR element in the Fig. 8. In this example, the MR element includes a plurality of lower electrodes, a plurality of MR films, and a plurality of upper electrodes. The plurality of lower electrodes 42 are arranged on a substrate (not shown). Each of the lower electrodes 42 has a long, slender shape. Two lower electrodes 42 adjacent in the longitudinal direction of the lower electrodes 42 have a gap between them. As shown in Fig. As shown in Figure 9, MR films 50 are provided on the upper surfaces of the lower electrodes 42 near opposite ends in the longitudinal direction. Each of the MR films 50 includes a free layer 51, a non-magnetic layer 52, a magnetization-locked layer 53, and an antiferromagnetic layer 54 stacked in this order, with the free layer 51 closest to the lower electrode 42. The free layer 51 is electrically connected to the lower electrode 42. The antiferromagnetic layer 54 is made of an antiferromagnetic material. The antiferromagnetic layer 54 is in exchange coupling with the magnetization-locked layer 53 to determine the magnetization direction of the magnetization-locked layer 53. The plurality of upper electrodes 43 are arranged over the plurality of MR films 50.Each of the upper electrodes 43 has a long, slender shape and establishes an electrical connection between the respective antiferromagnetic layers 54 of two adjacent MR films 50 disposed on two lower electrodes 42 adjacent to each other in the longitudinal direction of the lower electrodes 42. In such a structure, the plurality of MR films 50 are arranged in the manner shown in FIG. Fig. 9 is connected in series by the plurality of lower electrodes 42 and the plurality of upper electrodes 43. It is understood that the layers 51 to 54 of the MR films 50 are arranged in the reverse order to that shown in Fig. 9 shown can be stacked.

[0049] The operation and effects of the rotation angle sensor 1 will now be described. Based on the detected output from the magnetic sensor 5, the detection angle θs is detected by the rotation angle sensor 1 as the angle corresponding to the rotation angle θ of the magnet 2. When the magnetic sensor 5 is located at the desired position, as already described, the magnetic field H applied to the magnetic sensor 5 is s equal to the magnetic field H0 and accordingly, the detection angle θs is equal to the rotation angle θ. However, if the magnetic sensor 5 is located at a position offset from the desired position on the sensor mounting surface due to a misalignment between the magnet 2 and the magnetic sensor 5, the direction of the magnetic field H smay differ from the direction of the magnetic field H0. In such a case, the detection angle θs does not match the rotation angle θ, resulting in the angular error dθ.

[0050] The angular error dθ of the rotation angle sensor 1 should be small even if there is a misalignment between the magnet 2 and the magnetic sensor 5. The rotation angle sensor 1 also requires that the magnetic field generated by the magnet 2 and applied to the magnetic sensor 5 be strong. This is to relatively reduce the effect of magnetic fields that may be applied to the magnetic sensor 5 other than the magnetic field generated by the magnet 2. Furthermore, the rotation angle sensor 1 requires that the distance between the magnet 2 and the magnetic sensor 5 not be excessively small, so that the magnetic sensor 5 does not touch and damage the magnet 2.According to the embodiment, the use of the magnet 2 with the plate-shaped part 3 and the annular part 4 makes it possible to increase the strength of the magnetic field generated by the magnet 2 and applied to the magnetic sensor 5 and to reduce the angular error dθ resulting from a misalignment between the magnet 2 and the magnetic sensor 5, without causing an excessive reduction in the distance between the magnet 2 and the magnetic sensor 5. This advantage will now be described in detail with reference to the results of several simulations.

[0051] First, a description of the results of a first simulation performed to investigate the magnetic field distribution around the magnet is given. In the first simulation, the finite element method (FEM) was used to determine the magnetic field distribution around magnet 2. Fig. 10 is an explanatory diagram of the magnetic field distribution around the magnet 2 determined by the first simulation. Fig. 11 is an explanatory diagram of the magnetic field distribution on a Fig. 10 shown imaginary plane PL1. Fig. 12 is an explanatory diagram of the magnetic field distribution on a Fig. 10 shown imaginary plane PL2. Fig. 10 shows a cross section along the line 10-10 in Fig. 11 and Fig. 12.

[0052] In Fig. 11 and Fig. 12, the arrows in the solid frame indicate the directions of the magnetic field. Fig. 10 to Fig. 12, the area designated by the symbol "R+" represents the area in which the angular error dθ has a positive value, while the area designated by the symbol "R-" represents the area in which the angular error dθ has a negative value. The area designated by the symbol "RO" represents the area in which the angular error dθ is essentially zero, that is, the area in which the direction of the magnetic field H s forms an angle of essentially zero with the direction of the magnetic field H0. The region R0 is referred to below as the parallel field region. The expressions used here "the angular error dθ is essentially zero" and "the direction of the magnetic field H s forms an angle of substantially zero to the direction of the magnetic field H0" include not only the position in which the angular error dθ (the angle that the direction of the magnetic field H sto the direction of the magnetic field H0) is zero, but also a position in which the angular error dθ falls within a tolerance range for the rotation angle sensor 1. Note that in Fig. 10 to Fig. 12 For convenience, the boundary between adjacent areas is represented by a line. In practice, however, the angular error dθ does not change discontinuously from this line, but rather changes continuously with changing position, albeit abruptly near the line.

[0053] Fig. 10 to Fig. 12 show that the parallel field region R0 exists near the end face 2a of the magnet 2, and the area of ​​the parallel field region R0 on an imaginary plane parallel to the end face 2a varies depending on the distance between the end face 2a and the imaginary plane. The imaginary planes PL1 and PL2 are each an imaginary plane parallel to the end face 2a and are located at different distances from the end face 2a. The imaginary plane PL1 is one of a plurality of imaginary planes that can be obtained by varying the distance from the end face 2a, and it is the plane on which the parallel field region R0 has a maximum or almost maximum area. The parallel field region R0 has a smaller area on the imaginary plane PL2 than on the imaginary plane PL1.

[0054] In the embodiment, the distance between the imaginary plane PL1 and the end face 2a is referred to as the optimum distance. Now, with reference to Fig. 13 describes how to determine the optimal distance, that is, how to determine the position of the imaginary plane PL1. First, take as in Fig. 10, an imaginary straight line L is shown, which runs parallel to the rotational axis C. The distance between the rotational axis C and the straight line L should, for example, be approximately the maximum value of the amount of expected misalignment between the magnet 2 and the magnetic sensor 5 and should be between 0% and 10% of the diameter d1 of the magnet 2. In the Fig. In the example shown in Figure 10, the diameter d1 of the magnet 2 is 15 mm and the distance between the rotation axis C and the straight line L is 0.3 mm, which amounts to 2% of the diameter d1. In Fig. 10 and Fig. 11, point P1 indicates the point where the rotation axis C intersects the imaginary plane PL1, while point P2 indicates the point where the straight line L intersects the imaginary plane PL1. In Fig. 10 and Fig. 12, point P11 indicates the point where the axis of rotation C intersects the imaginary plane PL2, while point P12 indicates the point where the straight line L intersects the imaginary plane PL2.

[0055] When determining the optimal distance, the relationship between the distance d L from the end face 2a on the straight line L and the angular error dθ. Note that the angular error dθ is assumed to be the angle formed by the direction of the magnetic field at a point on the straight line L determined by simulation to the direction of the magnetic field H0. Fig. 13 shows the relationship between the distance d L and the angular error dθ. In Fig. 13 the horizontal axis represents the angular error dθ and the vertical axis represents the distance d L In Fig. 13, the area to the left of the vertical axis represents the area in which the angular error dθ has a positive value, while the area to the right of the vertical axis represents the area in which the angular error dθ has a negative value. Fig. In the example shown in Figure 13, the angular error dθ changes with increasing distance d L from a positive value to a negative value. Next, the Fig. 13 shown ratio a distance d L which makes the angular error dθ zero, and the optimal distance d L0 Note that, depending on the position of the imaginary line L, in contrast to Fig. 13 the angular error dθ with increasing distance d Lfrom a negative value to a positive value. In this case, too, a distance d L which makes the angular error dθ zero and is considered the optimal distance d L0 be defined.

[0056] To reduce the angular error dθ resulting from a misalignment between the magnet 2 and the magnetic sensor 5, it is preferable that the magnetic sensor 5 is located on the imaginary plane PL1. This is described below. Fig. In Figure 11, the frame indicated by a broken line and designated by symbol 5a shows the magnetic sensor 5 positioned so that the position P1 and the center of the magnetic sensor 5 are aligned with each other on the imaginary plane PL1. It can be said that the frame indicated by the broken line with symbol 5a is the desired position of the magnetic sensor 5 on the imaginary plane PL1. Fig. 11, the frame shown by a broken line and designated by the symbol 5b shows the magnetic sensor 5 as positioned such that the position P2 and the center of the magnetic sensor 5 are aligned with each other on the imaginary plane PL1, i.e., the magnetic sensor 5 is located at a position offset from the target position. In Fig. In Figure 12, the frame indicated by a broken line and symbol 5c indicates that the magnetic sensor 5 is positioned such that the position P11 and the center of the magnetic sensor 5 are aligned with each other on the imaginary plane PL2. It can be said that the frame indicated by the broken line and symbol 5c is the target position of the magnetic sensor 5 on the imaginary plane PL2. Fig. 12, the frame indicated by a broken line and symbol 5d shows the magnetic sensor 5 positioned so that the position P12 and the center of the magnetic sensor 5 are aligned with each other on the imaginary plane PL2, that is, the magnetic sensor 5 is located at a position offset from the target position.

[0057] As in Fig. As shown in Figure 11, the parallel field region R0 on the imaginary plane PL1 is wide, so that the frame denoted by symbol 5a (the magnetic sensor 5) and the frame denoted by symbol 5b (the magnetic sensor 5) are both located within the parallel field region R0. Accordingly, when the magnetic sensor 5 is located on the imaginary plane PL1, the angular error dθ is zero, regardless of whether the magnetic sensor 5 is located at the target position denoted by symbol 5a or at the offset position denoted by symbol 5b.

[0058] In contrast, the parallel field region R0 is as in Fig. 12, the angle error dθ is narrow on the imaginary plane PL2, so that while the frame denoted by symbol 5c (the magnetic sensor 5) is mainly located within the parallel field region R0, a large part of the frame denoted by symbol 5d (the magnetic sensor 5) is located outside the parallel field region R0. Accordingly, when the magnetic sensor 5 is located on the imaginary plane PL2, the angular error dθ is zero when the magnetic sensor 5 is located at the target position denoted by symbol 5c. However, when the magnetic sensor 5 is located at the offset position denoted by symbol 5d, the angular error dθ has a large absolute value.

[0059] As can be seen from the above descriptions, positioning the magnetic sensor 5 on the imaginary plane PL1 allows reducing the angular error dθ resulting from misalignment between the magnet 2 and the magnetic sensor 5. It is therefore preferable to position the magnetic sensor 5 on the imaginary plane PL1. On the imaginary plane PL1, the magnetic field generated by the magnet 2 extends in directions parallel to each other at positions P1 and P2. Position P1 is the position where the rotation axis C intersects the imaginary plane PL1, and position P2 is different from position P1. Accordingly, the imaginary plane PL1 corresponds to the "imaginary plane parallel to the end face of the magnet and spaced from the end face by a distance equal to the distance between the end face and the magnetic sensor" according to the invention.The position P1 corresponds to the first position according to the invention, while the position P2 corresponds to the second position according to the invention.

[0060] Note that the regions R0, R+, and R- exist not only near the end face of the magnet 2 of the embodiment, but also near the end face of a cylindrical magnet or a ring-shaped magnet, which will be described later as magnets of comparative examples. However, the distribution of the regions R0, R+, and R- varies depending on the shape of the magnet. The terms magnetic field H0 and magnetic field H described above s , angular error dθ and optimal distance d L0 are also used for the magnets in the comparison examples.

[0061] A description will now be given of the results of a second simulation in which a magnet of a first comparative example is used to investigate the relationship between the thickness of the magnet and the optimum distance d L0 was used. The magnet of the first comparative example is a cylindrical NdFeB-based bonded magnet with the same shape as the plate-shaped part 3 of the magnet 2. In the second simulation, the diameter and thickness of the magnet of the first comparative example were used to determine the optimal distance d L0 changed. The other conditions for the second simulation were the same as those for the first simulation.

[0062] Fig. 14 is a characteristic diagram of the relationship between the thickness of the magnet of the first comparative example and the optimum distance d determined by the second simulation L0 . In Fig. 14, the diameter of the magnet of the first comparative example is represented by the symbol d5, while the thickness of the magnet of the first comparative example is represented by the symbol t5. In Fig. 14 the horizontal axis represents the thickness t5 and the vertical axis represents the optimal distance d L0 represents. Fig. 14 shows that the optimal distance d L0 is reduced with increasing thickness t5. It is also shown that the optimal distance d L0 is reduced with decreasing diameter d5.

[0063] Next, a description is given of the results of a third simulation in which the relationship between the distance between the magnet and the magnetic sensor 5 and the strength of the magnetic field H applied to the magnetic sensor 5 son a magnet 2 of a practical example and magnets of a second to a fourth comparative example. The magnet 2 of the practical example is one of the examples of the magnet 2 of the embodiment. Each magnet used in the third simulation was an NdFeB-based bonded magnet. The magnet 2 of the practical example is shaped as follows. The diameter d1 of the magnet 2 is 15 mm, and the diameter d2 of the cavity 4a (the inner diameter of the annular part 4) is 4 mm. The thickness t2 of the magnet 2, the thickness t3 of the plate-shaped part 3, and the thickness t4 of the annular part 4 are 6 mm, 3 mm, and 3 mm, respectively.

[0064] The magnets of the second and third comparative examples are cylindrical NdFeB-based bonded magnets, each with the same shape as the plate-shaped part 3 of the magnet 2. The magnet of the fourth comparative example is an NdFeB-based bonded magnet with the same shape as the ring-shaped part 4 of the magnet 2. The magnets of the second and fourth comparative examples all have a diameter of 15 mm. The diameter of the cavity of the magnet (the inner diameter of the magnet) of the fourth comparative example is 4 mm. The magnet of the second comparative example has a thickness of 3 mm. The magnets of the third and fourth comparative examples all have a thickness of 6 mm.

[0065] In the third simulation, the distance d G between the end face of the magnet and the magnetic sensor 5 for determining the strength of the magnetic field H applied to the magnetic sensor 5s and the angular error dθ. Note that it was assumed that the strength of the magnetic field H s is the strength of the magnetic field H0 at a position on the rotation axis C which is spaced by the distance d G from the front face of the magnet. It was assumed that the angular error dθ is the angle formed by the direction of the magnetic field on the imaginary straight line L to the direction of the magnetic field H0 on an imaginary plane that is parallel to the front face of the magnet and spaced from the front face by the distance d G The other conditions for the third simulation were the same as those for the first simulation.

[0066] Fig. 15 is a characteristic diagram of the relationship between the distance d G and the angular error dθ determined by the third simulation. Fig. 16 is a characteristic diagram of the relationship between the distance d Gand the strength of the magnetic field H applied to the magnetic sensor 5 s , determined by the third simulation. In Fig. 15 the horizontal axis represents the distance d G and the vertical axis represents the angular error dθ. In Fig. 16 the horizontal axis represents the distance d G and the vertical axis represents the strength of the magnetic field H s The unit of strength of the magnetic field H s is Oe (1 Oe = 79.6 A / m).

[0067] Referring to Fig. 15 is the distance d G , in which the angular error dθ is zero, the optimal distance d L0 . The distance d L0 is approximately 2.5 mm for the magnet 2 of the practical example, approximately 2.3 mm for the magnet of the second comparative example, approximately 1.5 mm for the magnet of the third comparative example, and approximately 5.1 mm for the magnet of the fourth comparative example.

[0068] A comparison between magnet 2 of the practical example and the magnet of the second comparison example shows the following. As in Fig. 15, the optimal distance d L0 for magnet 2 of the practical example and that of the magnet of the second comparison example are almost the same. As in Fig. 16, however, the strength of the magnetic field H s at the optimal distance d L0 higher for magnet 2 of the practical example than for the magnet of the second comparison example. The optimal distance d L0 is a distance between the end face of the magnet and the magnetic sensor 5, which allows to reduce the angular error dθ resulting from a misalignment between the magnet and the magnetic sensor 5. It can therefore be seen that the magnet 2 of the embodiment is used to increase the strength of the magnetic field H scompared to a cylindrical magnet (the magnet of the second comparative example), under the condition that the optimal distance d L0 , ie a distance between the end face of the magnet and the magnetic sensor 5, which allows to reduce the angular error dθ resulting from a misalignment between the magnet and the magnetic sensor 5, is almost the same for the two magnets.

[0069] A comparison between the magnet of the second comparative example and the magnet of the third comparative example shows that in the case of using a cylindrical magnet, increasing the thickness of the magnet increases the strength of the magnetic field H s at the optimal distance d L0 increased, but the optimal distance d L0Accordingly, in the case of using a cylindrical magnet, a change in the thickness of the magnet is attempted to maintain the strength of the magnetic field at the optimal distance d L0 and to reduce the angular error dθ resulting from a misalignment between the magnet and the magnetic sensor 5, an excessive reduction in the distance between the magnet and the magnetic sensor 5 may result.

[0070] Furthermore, a comparison between the magnet of the third comparative example and the magnet of the fourth comparative example shows that a ring-shaped magnet (the magnet of the fourth comparative example) has the optimal distance d L0 However, in the case of using a ring-shaped magnet (the magnet of the fourth comparative example), the strength of the magnetic field H s at the optimal distance d L0 very low.

[0071] The above discussion shows that the magnet 2 of the embodiment enables increasing the strength of the magnetic field generated by the magnet 2 and applied to the magnetic sensor 5 and reducing the angular error dθ resulting from misalignment between the magnet 2 and the magnetic sensor 5 without causing an excessive reduction in the distance between the magnet 2 and the magnetic sensor 5. This advantage cannot be achieved with a cylindrical or annular magnet.

[0072] A description of the results of a fourth simulation is now given, in which the relationship between the optimal distance d L0 and the strength of the magnetic field H s at the optimal distance d L0was investigated on magnet 2 of the practical example. Magnet 2 of the practical example for the fourth simulation is shaped as follows. The diameter d1 of magnet 2 is 15 mm, and the diameter d2 of the cavity 4a (the inner diameter of the annular part 4) is 4 mm. The thickness t2 of magnet 2 is 3 mm. In the fourth simulation, t4 / t2, or the ratio of the thickness t4 of the annular part 4 to the thickness t2 of magnet 2 (hereinafter referred to as the thickness ratio of the annular part), was used to determine the optimal distance d L0 and the strength of the magnetic field H s at the optimal distance d L0in the range of 0% to 100%. The other conditions for the fourth simulation were the same as those for the third simulation. Note that a magnet with an annular portion thickness ratio of 0% is a cylindrical magnet, while a magnet with an annular portion thickness ratio of 100% is an annular magnet. Although a magnet 2 with an annular portion thickness ratio of 0% and a magnet 2 with an annular portion thickness ratio of 100% are excluded from the magnet 2 of the embodiment, they are included in the magnet 2 of the practical example for convenience.

[0073] Fig. 17 is a characteristic diagram of the relationship between the thickness ratio of the annular part t4 / t2 of the magnet 2, the optimum distance d L0 and the strength of the magnetic field H s at the optimal distance d L0 , determined by the fourth simulation. In Fig. 17, the horizontal axis represents the thickness ratio of the annular part t4 / t2, while the vertical axis to the left represents the strength of the magnetic field H s at the optimal distance d L0 and the vertical axis to the right the optimal distance d L0 represents. Fig. 17 shows that the optimal distance d L0 as a linear function of the thickness ratio of the annular part t4 / t2 increases with increasing thickness ratio of the annular part t4 / t2. Fig. 17 also shows that the strength of the magnetic field H s at the optimal distance d L0 decreases with increasing thickness ratio of the annular part t4 / t2 as a linear function of the thickness ratio of the annular part t4 / t2. As can be seen from these facts, according to the embodiment, it is possible to obtain the optimal distance d L0 and the strength of the magnetic field H s by adjusting the thickness ratio of the annular part.

[0074] If, with reference to Fig. 15 and Fig. 16 a comparison is made between the magnet of the second comparative example and the magnet of the third comparative example used in the third simulation, it can be seen that in the case of using a cylindrical magnet, reducing the thickness of the magnet in an attempt to achieve the optimal distance d L0 to increase, causes the strength of the magnetic field H s at the optimal distance d L0 is excessively reduced compared to the case of using the magnet 2 of the embodiment.

[0075] As already mentioned, a magnet with a thickness ratio of the annular part of 0% and a magnet with a thickness ratio of the annular part of 100% are excluded from the magnet 2 of the embodiment. In the embodiment as shown in Fig. As shown in Figure 17, the magnet 2 with a thickness ratio of the annular part higher than 0% and lower than 100% has a different property from that of the magnet with thickness ratios of the annular part of 0% and 100%, namely with regard to the optimal distance d L0 and the strength of the magnetic field H s at the optimal distance d L0 Accordingly, the thickness ratio of the annular part of the magnet 2 of the embodiment only needs to be higher than 0% and lower than 100%. However, in order to clearly distinguish the magnet 2 of the embodiment from a magnet with a thickness ratio of the annular part of 0% or 100%, that is, from a cylindrical or annular magnet, the thickness ratio of the annular part of the magnet 2 of the embodiment preferably falls within the range of 5% to 95%.

[0076] Now, a description of the results of a fifth simulation is given, in which the relationship between the shape of the magnet, the optimal distance d L0 and the strength of the magnetic field H s at the optimal distance d L0 on the magnet 2 of the practical example and on magnets of a fifth to seventh comparative example. The magnet 2 of the practical example for the fifth simulation is shaped as follows. The diameter d1 of the magnet 2 is 15 mm. The thickness t2 of the magnet 2, the thickness t3 of the plate-shaped part 3, and the thickness t4 of the ring-shaped part 4 are 3 mm, 1.5 mm, and 1.5 mm, respectively. The magnets of the fifth to seventh comparative examples are cylindrical magnets, each having the same shape as the plate-shaped part 3 of the magnet 2, and their diameters are 10 mm, 15 mm, and 20 mm, respectively.

[0077] In the fifth simulation, the ratio of the diameter d2 of the cavity 4a (the inner diameter of the annular part 4) to the diameter d1 of the magnet 2 (hereinafter referred to as the ratio of the inner diameter of the hollow part) was used to determine the optimal distance d L0 and the strength of the magnetic field H s at the optimal distance d L0 in the range from 0% to 100%. In the fifth simulation, the optimal distance d L0 and the strength of the magnetic field H s at the optimal distance d L0 The thicknesses of the magnets in the fifth to seventh comparative examples were also changed for each of the magnets in the fifth to seventh comparative examples. The other conditions for the fifth simulation were the same as those for the third simulation.

[0078] Fig. 18 is a characteristic diagram of the relationship between the shape of the magnet, the optimal distance d L0and the strength of the magnetic field H s at the optimal distance d L0 , determined by the fifth simulation. In Fig. 18 the horizontal axis represents the optimal distance d L0 and the vertical axis represents the strength of the magnetic field H s at the optimal distance d L0 The near respective points in Fig. The numerical values ​​given in Figure 18 indicate the thickness of the magnet (in mm). Symbol 61 represents a point where the hollow part inner diameter ratio is 0%, symbol 62 represents a point where the hollow part inner diameter ratio is 50%, and symbol 63 represents a point where the hollow part inner diameter ratio is 100%. The four points between the hollow part inner diameter ratios of 0% and 50% are the hollow part inner diameter ratios of 10%, 20%, 30%, and 40%, respectively, listed in order of proximity to the 0% point. On the other hand, the four points between the hollow part inner diameter ratios of 50% and 100% are the hollow part inner diameter ratios of 60%, 70%, 80%, and 90%, respectively, listed in order of proximity to the 50% point. In Fig. Figure 18 shows a plurality of dashed curved lines representing the properties of cylindrical magnets determined with varying diameters and constant thicknesses. Specifically, the dashed curved line designated by symbol 64 represents the property of a 3 mm thick cylindrical magnet determined with varying diameters. The dashed curved line designated by symbol 65 represents the property of a 1.5 mm thick cylindrical magnet determined with varying diameters.

[0079] A magnet 2 with a hollow part inner diameter ratio of 0% is a cylindrical magnet with a thickness of 3 mm and is the same as the magnet of the sixth comparative example with a thickness of 3 mm. A magnet 2 with a hollow part inner diameter ratio of 100% is a cylindrical magnet with a thickness of 1.5 mm and is the same as the magnet of the sixth comparative example with a thickness of 1.5 mm. The magnets 2 with hollow part inner diameter ratios of 0% and 100% are excluded from the magnet 2 of the embodiment, but are included in the magnet 2 of the practical example for convenience.

[0080] As in Fig. As shown in Fig. 18, according to the embodiment, it is possible to determine the optimum distance d L0 and the strength of the magnetic field H sby adjusting the inner diameter ratio of the hollow part. Now, a description will be given of the advantageous effects of the embodiment obtained from the results of the Fig. 18 shown fifth simulation.

[0081] First, the magnet 2 of the practical example and the magnet of the sixth comparative example, which have the same diameter, are compared under the condition that the optimal distance d L0 for the two magnets is the same. From the Fig. 18 it can be seen that the strength of the magnetic field H s at the optimal distance d L0 for the magnet 2 of the practical example is higher than for the magnet of the sixth comparative example, except when the inner diameter ratio of the hollow part of the magnet 2 is 0% and 100%. Thus, the magnet 2 of the embodiment is suitable for increasing the strength of the magnetic field H scapable in comparison with a cylindrical magnet (the magnet of the sixth comparative example) under the condition that the optimal distance d L0 , ie the distance between the end face of the magnet and the magnetic sensor 5, which allows to reduce the angular error dθ resulting from a misalignment between the magnet and the magnetic sensor 5, is almost the same for the two magnets.

[0082] Next, the magnet 2 of the practical example and the magnet of the sixth comparative example are compared under the condition that the strength of the magnetic field H s at the optimal distance d L0 for the two magnets is the same. From the Fig. 18 it can be seen that the optimal distance d L0for the magnet 2 of the practical example is larger than for the magnet of the sixth comparative example, except when the inner diameter ratio of the hollow part of the magnet 2 is 0% and 100%. Thus, the magnet 2 of the embodiment is compared with a cylindrical magnet (the magnet of the sixth comparative example) under the condition that the strength of the magnetic field H s is almost the same for the two magnets, to increase the optimal distance d L0 capable, ie the distance between the end face of the magnet and the magnetic sensor 5, which allows a reduction of the angular error dθ resulting from a misalignment between the magnet and the magnetic sensor 5.

[0083] From the above, it can be seen that according to the embodiment, it is possible to adjust the strength of the magnetic field H sand to reduce the angular error dθ resulting from a misalignment between the magnet 2 and the magnetic sensor 5 without causing an excessive reduction in the distance between the magnet 2 and the magnetic sensor 5.

[0084] As already mentioned, a magnet with an inner diameter ratio of the hollow part of 0% and a magnet with an inner diameter ratio of the hollow part of 100% are excluded from the magnet 2 of the embodiment. Fig. 18, the magnet 2 is in terms of the optimal distance d L0 and the strength of the magnetic field H s at the optimal distance d L0Compared to a cylindrical magnet, it is advantageous if the magnet 2 has an inner diameter ratio of the hollow part higher than 0% and lower than 100%. Accordingly, the inner diameter ratio of the hollow part of the magnet 2 of the embodiment only needs to be higher than 0% and lower than 100%. However, in order to clearly distinguish the magnet 2 of the embodiment from a magnet with an inner diameter ratio of the hollow part of 0% or 100%, that is, from a cylindrical magnet, the inner diameter ratio of the hollow part of the magnet 2 of the embodiment preferably falls within the range of 5% to 95%.

[0085] The properties of the magnet 2 of the Fig. The curved line indicating the practical example shown in Figure 18 shows that when the inner diameter ratio of the hollow part of the magnet 2 falls within the range of more than 0% to not more than 50%, the following effects occur in particular. That is, when the inner diameter ratio of the hollow part is within this range, compared with the case of increasing the optimal distance d L0 by reducing the thickness of the magnet of the sixth comparative example from 3 mm to 1.5 mm, both the effect that a larger optimal distance, d L0 is achieved, as well as the effect that a higher thickness of the magnetic field H s at the optimal distance d L0 is achieved is more noticeable. Accordingly, if these noticeable effects are desired, the inner diameter ratio of the hollow part preferably falls within the range of more than 0% to not more than 50%, more preferably within the range of 5% to 50%.

[0086] Referring to the properties of the magnet 2 of the Fig. 18, when the inner diameter ratio of the hollow part of the magnet 2 falls within the range of more than 50% to not more than 100%, it is still possible to obtain the optimum distance d L0 by reducing the inner diameter ratio of the hollow part without a large change in the strength of the magnetic field H s at the optimal distance d L0 If it is desired to determine the optimal distance d L0 without a major change in the strength of the magnetic field H s at the optimal distance d L0 to cause, the inner diameter ratio of the hollow part preferably falls in the range of more than 50% to not more than 100%, more preferably in the range of more than 50% to not more than 95%.

[0087] The above-mentioned tendency derived from the results of the fifth simulation does not depend on the thickness ratio of the annular part.

[0088] As described with reference to the results of the first to fifth simulations, according to the embodiment, it is possible to determine the strength of the magnetic field H s and to reduce the angular error dθ resulting from a misalignment between the magnet 2 and the magnetic sensor 5 without causing an excessive reduction in the distance between the magnet 2 and the magnetic sensor 5.

[0089] In Fig. 18 shows the multitude of dashed curved lines that for a cylindrical magnet, increasing the diameter of the magnet increases the optimal distance d L0 allowed without any noticeable reduction in the strength of the magnetic field H s at the optimal distance d L0. However, in the case of the cylindrical magnet, increasing the diameter of the magnet increases the volume of the magnet and consequently increases the cost of the magnet compared with the case of the magnet 2 of the embodiment.

[0090] This will now be described with reference to a specific example. Fig. 18, a comparison is made between the magnet of the seventh comparative example with a diameter of 20 mm and a thickness of 2.8 mm and the magnet 2 of the practical example with an inner diameter ratio of the hollow part of 15%. These two magnets represent almost the same optimal distance d L0 and almost the same strength of the magnetic field H s at the optimal distance d L0 However, the magnet of the seventh comparison example with the dimensions mentioned above has a volume of 880 mm 3, while magnet 2 with an inner diameter ratio of the hollow part of 15% has a volume of 524 mm 3 Thus, according to the embodiment, the magnet 2 is smaller in volume and therefore more cost-effective compared to a cylindrical magnet under the condition that the optimal distance d L0 almost the same and the strength of the magnetic field H s at the optimal distance d L0 is almost the same for the two magnets.

[0091] A description will now be given of the results of a sixth simulation in which the relationship between the distance between the magnet 2 and the magnetic sensor 5 and the strength of the magnetic field H applied to the magnetic sensor 5 is determined. s on the magnet 2 of the embodiment. In the sixth simulation, a first magnet 2 and a second magnet 2 were used, which were capable of maintaining the same optimal distance d L0These two magnets are 15 mm in diameter d1 and 3 mm in thickness t2. In the first magnet 2, the diameter d2 of the cavity 4a (the inner diameter of the annular part 4) is 4 mm and the thickness t4 of the annular part 4 is 1.5 mm. In the second magnet 2, the diameter d2 of the cavity 4a (the inner diameter of the annular part 4) is 7 mm and the thickness t4 of the annular part 4 is 1 mm. The first magnet 2 has a volume of 511 mm 3 while the second magnet 2 has a volume of 492 mm 3 In the sixth simulation, the distance d was determined for each of the first and second magnets 2 G between the end face 2a of the magnet 2 and the magnetic sensor 5 for determining the strength of the magnetic field H s and the angular error dθ. Note that the definitions of the strength of the magnetic field H used in the sixth simulation sand the angular error dθ are the same as those used in the third simulation, which have already been described. The other conditions for the sixth simulation were the same as those for the third simulation.

[0092] Fig. 19 is a characteristic diagram of the relationship between the distance d G between the magnet 2 and the magnetic sensor 5, the strength of the magnetic field H applied to the magnetic sensor 5 s and the angular error dθ determined by the sixth simulation. In Fig. 19 the horizontal axis represents the distance d G while the vertical axis on the left represents the strength of the magnetic field H s and the vertical axis on the right represents the angular error dθ. The dashed line in Fig. 19 shows the distance d G at which the angular error dθ of the first and second magnet 2 is zero, i.e. the optimal distance d L0 . As in Fig. 19, the strength of the magnetic field H s at the optimal distance d L0 higher for the first magnet 2 than for the second magnet 2. The probable reason for this is that the second magnet 2 is larger in volume than the first magnet 2. As can be seen from these results, to obtain the same optimal distance d L0 by changing the inner diameter d2 and the thickness t4 of the annular part 4 while keeping the diameter d1 and the thickness t2 of the magnet 2 constant, an annular part 4 having a smaller inner diameter d2 and a larger thickness t4 is more advantageous for increasing the strength of the magnetic field at the optimal distance d L0 as an annular part 4 with a larger inner diameter d2 and a smaller thickness t4.

[0093] The other effects of the embodiment will now be described. In the embodiment, the shape of any cross section of the magnet 2 including the rotation axis C is symmetrical about the rotation axis C. According to the embodiment, the use of the magnet 2 having such a shape serves to prevent the occurrence of an angular error attributable to the shape of the magnet 2. An exemplary magnet 2 that satisfies the above-mentioned shape requirement is the magnet 2 described so far, that is, the magnet 2 in which the plate-shaped part 3 is shaped like a circular plate and the annular part 4 has an outer periphery and an inner periphery, both of which are circular in any cross section of the annular part 4 perpendicular to the rotation axis C. However, examples of the magnet 2 of the embodiment include magnets of various other shapes, such as those described below as a variety of modification examples.The magnets of the modification examples have a plate-shaped part and an annular part, wherein the plate-shaped part does not include a cavity through which the rotation axis C passes, while the annular part includes a cavity through which the rotation axis C passes. The shape of any cross section of the magnets of the modification examples containing the rotation axis C is symmetrical about the rotation axis C. The various advantageous effects described so far are achievable with such magnets compared with the case of using a cylindrical magnet. [Examples of modifications]

[0094] It will now be described to describe first to eighth modification examples of the magnet 2 of the embodiment on Fig. 20 to Fig. 27 referred to. Fig. 20 is a plan view of the first modification example of the magnet 2. Fig. 21 is a plan view of the second modification example of the magnet 2. As shown in Fig. 1 to Fig. 3, the magnet 101 of each of the first and second modification examples has an end face 101a perpendicular to the rotation axis C (not shown) and is magnetized in a direction perpendicular to the rotation axis C. The magnet 101 includes a plate-shaped part 102 having the end face 101a and an annular part (not shown) located on a side of the plate-shaped part 102 farther from the end face 101a and coupled to the plate-shaped part. The plate-shaped part 102 is shaped like an elliptical plate, which in Fig. 20 or Fig. 21 is extended in the vertical direction. The plate-shaped part 102 does not contain a cavity through which the rotation axis C runs.

[0095] The annular part comprises an outer circumference and a cavity through which the rotation axis C passes. In any cross-section of the annular part perpendicular to the rotation axis C, the outer circumference of the annular part has an elliptical shape similar to the shape of the outer circumference of the plate-shaped part 102 in any cross-section of the plate-shaped part 102 perpendicular to the rotation axis C. The inner circumference of the annular part can be either elliptical or circular in any cross-section of the annular part perpendicular to the rotation axis C.

[0096] The plate-shaped part 102 of the first modification example has an N-pole and an S-pole, which are arranged in Fig. 20 are arranged in the horizontal direction. The plate-shaped part 102 of the second modification example has an N-pole and an S-pole, which are arranged in Fig. 21 are arranged in the vertical direction. The magnetization of the magnet 101 of each of the first and second modification examples is in a direction from the S pole to the N pole of the plate-shaped part 102 and perpendicular to the boundary between the S pole and the N pole.

[0097] Fig. 22 to Fig. 26 are cross-sectional views of the third to seventh modification examples of the magnet 2. As shown in Fig. 1 to Fig. 3, the magnet 2 of each of the third to seventh modification examples has an end face 2a perpendicular to the rotation axis C (not shown) and magnetized in a direction perpendicular to the rotation axis C. The magnet 2 of each of the third to seventh modification examples comprises a plate-shaped part 3 having the end face 2a and an annular part 4 located on a side of the plate-shaped part 3 further away from the end face 2a and coupled to the plate-shaped part 3. The plate-shaped part 3 of the third to seventh modification examples has the same shape as that of the Fig. 1 to Fig. 4 shown plate-shaped part 3. As in Fig. 1 to Fig. 3 and Fig. 5, the annular part 4 of the third to seventh modification examples includes a cavity 4a through which the rotation axis C passes. In the third to seventh modification examples, the annular part 4 has an outer surface and an inner surface, both of which are circular in any cross section of the annular part 4 perpendicular to the rotation axis C.

[0098] In the Fig. 22 to Fig. In the third to fifth modification examples shown in Fig. 24, the inner diameter of the annular part 4, that is, the diameter of the cavity 4a, increases with increasing distance from the end face 2a of the magnet 2. As shown in Fig. 22, the cavity 4a of the third modification example has a truncated cone shape. In the fourth modification example, as shown in Fig. 23, the inner diameter of the annular part 4, that is, the diameter of the cavity 4a, is zero at the boundary between the plate-shaped part 3 and the annular part 4. The cavity 4a of the fourth modification example has a conical shape. As shown in Fig. 24, the cavity 4a of the fifth modification example has a hemispherical shape.

[0099] In the Fig. 25, the inner diameter of the annular part 4, that is, the diameter of the cavity 4a, decreases with increasing distance from the end face 2a of the magnet 2. In the embodiment shown in Fig. In the seventh modification example shown in Figure 26, the cavity 4a comprises a first part closer to the end surface 2a and a second part farther from the end surface 2a. The first part is larger in diameter than the second part. The diameter of the first part is constant regardless of the distance from the end surface 2a. The diameter of the second part is also constant regardless of the distance from the end surface 2a.

[0100] Fig. 27 is a cross-sectional view of the eighth modification example of the magnet 2. As shown in Fig. 1 to Fig. 3, the magnet 103 of the eighth modification example has an end surface 103a perpendicular to the rotation axis C (not shown) and is magnetized in a direction perpendicular to the rotation axis C. The magnet 103 includes a first plate-shaped part 104, an annular part 105, and a second plate-shaped part 106. The first plate-shaped part 104 includes the end surface 103a. The annular part 105 is located on a side of the first plate-shaped part 104 farther from the end surface 103a and is coupled to the first plate-shaped part 104. The second plate-shaped part 106 is located on a side of the annular part 105 farther from the end surface 103a and is coupled to the annular part 105. The first plate-shaped part 104 corresponds to the plate-shaped part according to the invention.None of the first and second plate-shaped parts 104 and 106 includes a cavity through which the rotation axis C passes, while the annular part 105 includes a cavity 105a through which the rotation axis C passes. The first and second plate-shaped parts 104 and 106 are both shaped like a circular plate. The annular part 105 has an outer surface and an inner surface, both of which are circular in any cross-section of the annular part 105 perpendicular to the rotation axis C. In the eighth modification example, the cavity 105a is defined by the first and second plate-shaped parts 104 and 106 and the annular part 105.

[0101] The magnet 2 of the embodiment may be designed such that its planar shape (viewed in a direction perpendicular to the end face) looks as shown in Fig. 20 or Fig. 21 and the shape of any cross section containing the axis of rotation C as in any of Fig. 22 to Fig. 27. The magnet 2 of the embodiment may have a square, rectangular, hexagonal, or octagonal planar shape, as long as the shape of any cross section including the rotation axis C is symmetrical about the rotation axis C.

[0102] The present invention is not limited to the above embodiment, and various modifications may be made thereto. For example, the magnetic sensor 5 may use anisotropic magnetoresistive (AMR) elements for all of the magnetic detection elements in the bridge circuits 16 and 17.

[0103] It is clear that the present invention may be embodied in various forms and modifications in light of the above descriptions. Accordingly, within the scope of the following claims and their equivalents, the present invention may be practiced other than the most preferred embodiment mentioned above.

Claims

[1] Angle of rotation sensor (1) comprising: a magnet (2) rotating about an axis of rotation (C), the magnet (2) having an end face (2a) perpendicular to the axis of rotation (C) and having a magnetization in a direction perpendicular to the axis of rotation (C); and a magnetic sensor (5) which is opposite the end face (2a) of the magnet (2) and detects a magnetic field generated by the magnet (2), wherein the rotation angle sensor (1) detects a rotation angle of the magnet (2) based on a detected output from the magnetic sensor (5), characterized by , that the magnet (2) comprises: a plate-shaped part (3) comprising the end face (2a) of the magnet (2); and an annular part (4) which is located on a side of the plate-shaped part (3) further away from the end face (2a) and is coupled to the plate-shaped part (3); wherein the plate-shaped part (3) does not enclose a cavity through which the axis of rotation (C) runs, while the annular part (4) encloses a cavity (4a) through which the axis of rotation (C) runs, in each cross-section of the annular part (4) perpendicular to the axis of rotation (C), the outer edges of the annular part (4) have the same shape as the outer edges of the plate-shaped part (3) in each cross-section of the plate-shaped part (3) perpendicular to the axis of rotation (C), the plate-shaped part (3) and the ring-shaped part (4) have a magnetization in the same direction as the magnetization direction of the magnet (2), and the plate-shaped part (3) and the ring-shaped part (4) are a bonded magnet based on NdFeB. [2] Rotation angle sensor (1) according to claim 1, wherein any cross section of the magnet (2) including the rotation axis (C) has a shape symmetrical about the rotation axis (C). [3] Rotation angle sensor (1) according to claim 2, wherein the plate-shaped part (3) is shaped like a circular plate and the annular part (4) has an outer circumference and an inner circumference, both of which are circular in any cross section of the annular part (4) perpendicular to the rotation axis (C). [4] Rotation angle sensor (1) according to any one of claims 1 to 3, which is arranged such that in an imaginary plane which is parallel to the end face (2a) of the magnet (2) and is as far away from the end face (2a) as the distance between the end face (2a) and the magnetic sensor (5), the magnetic field generated by the magnet (2) at a first location and a second location lies in mutually parallel directions, the first location being a location at which the axis of rotation (C) intersects the imaginary plane and the second location being different from the first location. [5] Rotation angle sensor (1) according to any one of claims 1 to 4, wherein the magnetic sensor (5) comprises a magnetoresistance.

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