Position detecting device

Abstract

To provide a position detection device capable of highly accurately detecting a position of a shaft moving forward and backward in an axial direction.SOLUTION: A stroke sensor 1 for detecting a position of a rack shaft 13 moving in an axial direction includes a substrate 3 on which an excitation coil 4 and detection coils 5, 6 are formed, and a detector 2 fixed to the rack shaft 13. In the detection coils 5 and 6, the first portion 51,61, the second portion 52,62, the third portion 53,63, and the fourth portion 54,64, in which an induced voltage is induced by interlinkage with the magnetic flux of the excitation coil 4, are arranged in the lateral direction of the substrate 3 perpendicular to the axial direction of the rack shaft 13. The detection unit 2 includes a first detection unit 21 facing the first portion 51,61, a second detection unit 22 facing the second portion 52,62, a third detection unit 23 facing the third portion 53,63, and a fourth detection unit 24 facing the fourth portion 54,64, and the first to fourth detection units 21 to 24 are separated from each other in the axial direction of the rack shaft 13.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a position detection device that detects the position of a shaft that moves back and forth in its axial direction. [Background technology]

[0002] Conventionally, position detection devices that detect the position of a shaft that moves back and forth in an axial direction have been used to detect the position of a rack shaft in a vehicle steering device, for example. The applicant has proposed such a position detection device as described in Patent Document 1.

[0003] The position detection device described in Patent Document 1 includes a target attached to a rack shaft, an excitation coil that generates an AC magnetic field, and two detection coils arranged along the axial direction of the rack shaft. The excitation coil and the two detection coils are formed as wiring patterns on a single substrate. When the two detection coils are viewed perpendicularly to the substrate, one detection coil has a shape made up of a pair of sinusoidal waveform conductor wires, and the other detection coil has a shape made up of a pair of cosine waveform conductor wires. When the rack shaft moves, the magnitude of the induced voltage induced in each of the two detection coils changes depending on the position of the target, and the position of the rack shaft can be detected based on the magnitude of this induced voltage. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2023-117379 Summary of the Invention [Problem to be solved by the invention]

[0005] In a position detection device configured as described above, if the rack shaft tilts relative to the board due to vibrations caused by vehicle movement, for example, the tilt changes the distance between the rack shaft and the target and the board, which could easily result in detection errors. Therefore, an object of the present invention is to provide a position detection device that can detect the position of a shaft that moves back and forth in the axial direction with higher accuracy. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems, the present invention provides a position detection device for detecting the position of a shaft that moves back and forth in an axial direction within a predetermined range, the device comprising: an excitation coil that generates an AC magnetic field; a detection body that is fixed to the shaft and is interlinked with the magnetic flux of the AC magnetic field; and a detection coil that is interlinked with the magnetic flux of the AC magnetic field, the detection coil having first to fourth parts in which an induced voltage is induced by the interlinkage of the magnetic flux of the AC magnetic field, and a connection part that connects the first to fourth parts, each of the first to fourth parts extending along a coil longitudinal direction that is parallel to the axial direction, and at least a part of each of the first to fourth parts being aligned in an alignment direction perpendicular to the coil longitudinal direction, and the detection body being located within the predetermined range. Provided is a position detection device having a first detection body part, at least a portion of which faces the first part within a first predetermined range, a second detection body part, at least a portion of which faces the second part within a second predetermined range within the predetermined range, a third detection body part, at least a portion of which faces the third part within a third predetermined range within the predetermined range, and a fourth detection body part, at least a portion of which faces the fourth part within a fourth predetermined range within the predetermined range, wherein the induced voltages induced in the first part to the fourth part change depending on the positions of the first detection body part to the fourth detection body part relative to the first part to the fourth part, respectively, and the first detection body part, the second detection body part, the third detection body part, and the fourth detection body part are arranged spaced apart in the axial direction of the shaft. [Effects of the Invention]

[0007] According to the position detection device of the present invention, it is possible to suppress detection errors caused by the tilt of the shaft and to detect the position of the shaft with high accuracy. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram of a vehicle equipped with a steer-by-wire steering device including a stroke sensor as a position detection device according to an embodiment of the present invention; [Figure 2] FIG. 2 is a cross-sectional view taken along line AA in FIG. [Figure 3] 1A is a perspective view showing the rack shaft, the housing body, the detector, and the substrate, and FIG. 1B is a configuration diagram showing the rack shaft and the detector as viewed from a direction perpendicular to the central axis of the rack shaft. [Figure 4] 1(a) and 1(b) are explanatory diagrams showing two detection coils, respectively. [Figure 5] FIG. 2 is an explanatory diagram showing an excitation coil and two detection coils. [Figure 6] 10(a) to 10(e) are explanatory diagrams showing changes in the relative positional relationship between the two detection coils and the first to fourth detection bodies when the rack shaft moves from the right side to the left side of the drawing relative to the substrate. [Figure 7] 10 is a graph showing an example of the relationship between the supply voltage supplied to the excitation coil from the power supply unit and the induced voltage induced in the two detection coils when the first detection body portion faces the first portions of the two detection coils. [Figure 8] 10 is a graph showing the relationship between the peak voltage, which is the peak value of the induced voltage induced in the first detection coil, and the position of the detection object. [Figure 9] 10 is a graph showing the relationship between the peak voltage, which is the peak value of the induced voltage induced in the second detection coil, and the position of the detection object. [Figure 10]1A is an explanatory diagram showing a relationship between the inclination of the rack shaft with respect to the substrate and the effect of the inclination of the rack shaft on the magnetic flux density interlinked with the first detection coil, and FIG. 1B is an explanatory diagram showing a relationship between the inclination of the rack shaft with respect to the substrate and the effect of the inclination of the rack shaft on the magnetic flux density interlinked with the second detection coil. [Figure 11] 6 is a graph showing an evaluation result of a detection error when the position of the rack shaft is detected by the stroke sensor according to the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] [Embodiment Mode] FIG. 1 is a schematic diagram of a vehicle equipped with a steer-by-wire steering device 10 equipped with a stroke sensor 1 as a position detection device according to an embodiment of the present invention.

[0010] As shown in FIG. 1, the steering device 10 includes a stroke sensor 1, tie rods 12 connected to steered wheels 11 (left and right front wheels), a metal rack shaft 13 connected to the tie rods 12, a cylindrical housing 14 that accommodates the rack shaft 13, a worm reduction mechanism 15 having a pinion gear 151 meshed with rack teeth 131 of the rack shaft 13, an electric motor 16 that imparts a moving force in the vehicle width direction to the rack shaft 13 via the worm reduction mechanism 15, a steering wheel 17 that is operated by the driver, a steering angle sensor 18 that detects the steering angle of the steering wheel 17, and a steering control device 19 that controls the electric motor 16 based on the steering angle detected by the steering angle sensor 18.

[0011] 1, the housing 14 is shown by an imaginary line. The rack shaft 13 is made of steel, such as carbon steel, and is supported by a pair of rack bushings 132 attached to both ends of the housing 14. The worm reduction mechanism 15 has a worm wheel 152 and a worm gear 153, and a pinion gear 151 is fixed to the worm wheel 152. The worm gear 153 is fixed to a motor shaft 161 of the electric motor 16.

[0012] The electric motor 16 generates torque by a motor current supplied from the steering control device 19, and rotates the worm wheel 152 and pinion gear 151 via the worm gear 153. When the pinion gear 151 rotates, the rack shaft 13 moves, and the left and right steered wheels 11 are steered. The rack shaft 13 can move to the right and left in the vehicle width direction from a neutral position where the steering angle is zero. In FIG. 1, a predetermined range R within which the rack shaft 13 can move in the vehicle width direction is indicated by a double-headed arrow.

[0013] (Stroke sensor 1 configuration) The stroke sensor 1 includes a detection body 2 fixed to a rack shaft 13, a circuit board 3 arranged parallel to the rack shaft 13 and facing the detection body 2, a power supply unit 7, and a calculation unit 8. The circuit board 3, the power supply unit 7, and the calculation unit 8 are connected by a connector 91 and a cable 92 attached to the circuit board 3. The circuit board 3 is fixed inside a housing 14 parallel to the rack shaft 13. The stroke sensor 1 detects the position of the rack shaft 13 relative to the housing 14 from the position of the detection body 2, and outputs information about the detected position to a steering control device 19. The steering control device 19 controls the electric motor 16 so that the position of the rack shaft 13 detected by the stroke sensor 1 corresponds to the steering angle of the steering wheel 17 detected by a steering angle sensor 18.

[0014] Fig. 2 is a cross-sectional view taken along line AA in Fig. 1. Fig. 3(a) is a perspective view showing the rack shaft 13, the main body 141 of the housing 14, the detection body 2, and the substrate 3. In Fig. 3(a), the central axis C of the rack shaft 13 is indicated by a dashed line. Fig. 3(b) is a configuration diagram of the rack shaft 13 and the detection body 2 as viewed from a direction perpendicular to the central axis C. The rack shaft 13 moves along the central axis C due to a moving force applied by the electric motor 16. Hereinafter, the direction parallel to the central axis C of the rack shaft 13 will be referred to as the axial direction.

[0015] The rack shaft 13 is a rod-shaped body made of steel and has a circular cross section, and moves back and forth in the axial direction within a predetermined range R shown in Fig. 1. The housing 14 has a metal main body 141 and a resin cover 142, and the cover 142 is fixed to the main body 141 by, for example, gluing or bolting. The main body 141 has a U-shaped cross section in which an accommodation space 140 for accommodating the rack shaft 13 is formed, and the accommodation space 140 is open vertically upward.

[0016] A gap of, for example, 1 mm or more is formed between the outer peripheral surface 13a of the rack shaft 13 and the inner surface 140a of the storage space 140. The lid 142 covers the storage space 140 from above in the vertical direction. The main body 141 is a non-magnetic material, for example, made of a die-cast aluminum alloy. The material of the lid 142 is not necessarily limited to resin, but it is preferable to use a non-magnetic and non-conductive material.

[0017] The detector 2 has a first detector portion 21, a second detector portion 22, a third detector portion 23, and a fourth detector portion 24. In the example shown in Fig. 2 and Figs. 3(a) and (b), the first detector portion 21, the second detector portion 22, the third detector portion 23, and the fourth detector portion 24 are separate bodies, and are individually attached to the rack shaft 13. The first detector portion 21, the second detector portion 22, the third detector portion 23, and the fourth detector portion 24 are provided at regular intervals in the axial direction of the rack shaft 13.

[0018] The first detector 21, the second detector 22, the third detector 23, and the fourth detector 24 are fixed to the rack shaft 13 by welding, for example, so as to protrude from the outer peripheral surface 13a of the rack shaft 13 toward the base plate 3. However, this is not limiting, and for example, the first detector 21, the second detector 22, the third detector 23, and the fourth detector 24 may be integrally formed on a plate-shaped base member, which may be attached to the rack shaft 13 and used as the detectors.

[0019] The first to fourth detector portions 21 to 24 of the detector 2 are made of a material having a higher magnetic permeability than the rack shaft 13 or a material having a higher electrical conductivity than the rack shaft 13. When using a material having a higher magnetic permeability than the rack shaft 13 as the material for the first to fourth detector portions 21 to 24, it is desirable to use a magnetic material such as ferrite that has a high electrical resistance and is less likely to generate eddy currents. When using a material having a higher electrical conductivity than the rack shaft 13 for the first to fourth detector portions 21 to 24, the material can be, for example, a metal containing aluminum or copper as its main component.

[0020] In this embodiment, since the first to fourth detection body portions 21 to 24 protrude from the outer peripheral surface 13a of the rack shaft 13 toward the substrate 3, the actions and effects described below can be obtained even if a material having the same magnetic permeability as the rack shaft 13 or a material having the same electrical conductivity as the rack shaft 13 is used as the material for the detection body 2. However, in order to improve the position detection accuracy, it is desirable to use a high-permeability material having a higher magnetic permeability than the material of the rack shaft 13 or a high-electrical conductivity material having the same electrical conductivity as the material of the rack shaft 13 as the material for the first to fourth detection body portions 21 to 24.

[0021] The opposing surfaces 21a, 22a, 23a, and 24a of the first to fourth detectors 21 to 24 that face the substrate 3 are formed in a flat shape and face parallel to the back surface 3b of the substrate 3 via an air gap G. The front surface 3a of the substrate 3 is fixed to the lid 142 with an adhesive 143. When viewed from the substrate 3 side, the opposing surfaces 21a, 22a, 23a, and 24a of the first to fourth detectors 21 to 24 have a rectangular shape that is elongated in the axial direction.

[0022] The width W of the air gap G is, for example, 1 mm. The minimum thickness T of the first to fourth detectors 21 to 24 in the direction perpendicular to the opposing surfaces 21a, 22a, 23a, 24a of the first to fourth detectors 21 to 24 is, for example, 5 mm. Note that in this embodiment, the rack shaft 13 is formed to have a circular cross section, but the cross section of the rack shaft 13 is not limited to a circle and may be, for example, a D-shape with a portion formed linearly, or a polygonal shape.

[0023] The substrate 3 has a rectangular shape with its long sides aligned along the axial direction of the rack shaft 13. As shown in Fig. 2, when the first to fourth detectors 21 to 24 are viewed along the axial direction of the rack shaft 13, small gaps are formed in the short direction of the substrate 3 between the first detector 21 and the second detector 22, between the second detector 22 and the third detector 23, and between the third detector 23 and the fourth detector 24.

[0024] In this embodiment, the substrate 3 is a two-layer substrate having a first wiring layer 31, a second wiring layer 32, and a base material 33 between the first wiring layer 31 and the second wiring layer 32. Wiring patterns are formed on the first wiring layer 31 and the second wiring layer 32, and the wiring patterns of the first wiring layer 31 and the second wiring layer 32 are connected at multiple locations by vias 34. The first wiring layer 31 and the second wiring layer 32 are covered with resist films 35 and 36, respectively, which have electrical insulation properties. The base material 33 is a flat plate made of a dielectric material such as FR4 (glass fiber impregnated with epoxy resin and subjected to a heat curing process).

[0025] Next, the wiring configuration of the substrate 3 will be described with reference to Figures 4(a), (b), and 5. In Figures 4(a), (b), and 5, the left-right direction of the drawings corresponds to the longitudinal direction of the substrate 3. On the substrate 3, an excitation coil 4 that generates an AC magnetic field by an AC current supplied from a power supply unit 7, and two detection coils 5 and 6 with which the magnetic flux of the AC magnetic field generated by the excitation coil 4 interlinks are formed by wiring patterns on a first wiring layer 31 and a second wiring layer 32. However, the wiring patterns in Figures 4(a), (b), and 5 are shown as examples, and various types of wiring patterns can be adopted as long as the substrate 3 is formed so as to obtain the effects of the present invention.

[0026] Fig. 4(a) shows one of the two detection coils 5, 6, the detection coil 5. Fig. 4(b) shows the other of the two detection coils 5, 6, the detection coil 6. Fig. 5 shows the excitation coil 4 and the two detection coils 5, 6. Figs. 4(a), (b) and 5 show the shapes of the excitation coil 4 and the two detection coils 5, 6 when the substrate 3 is viewed from the front surface 3a side, with the portions formed by the wiring pattern of the first wiring layer 31 shown by solid lines and the portions formed by the wiring pattern of the second wiring layer 32 shown by dashed lines.

[0027] Hereinafter, one of the detector coils 5 shown in FIG. 4(a) will be referred to as the first detector coil 5, and the other detector coil 6 shown in FIG. 4(b) will be referred to as the second detector coil 6. The first detector coil 5 and the second detector coil 6 are stacked in the thickness direction of the substrate 3. The excitation coil 4 is formed in a rectangular shape so as to surround the first detector coil 5 and the second detector coil 6. The excitation coil 4 is formed across the first wiring layer 31 and the second wiring layer 32, and the portion formed on the first wiring layer 31 and the portion formed on the second wiring layer 32 are connected by vias 34 and overlap in the thickness direction of the substrate 3.

[0028] The magnetic flux of the AC magnetic field generated by the excitation coil 4 interlinks with the first to fourth detection body portions 21 to 24 of the detection body 2, in addition to the first detection coil 5 and second detection coil 6. The magnetic flux interlinking with the first to fourth detection body portions 21 to 24 affects the intensity distribution of the magnetic flux interlinking with the first detection coil 5 and second detection coil 6, and the magnitude of the induced voltage induced in the first detection coil 5 and second detection coil 6 by the AC magnetic field generated by the excitation coil 4 changes depending on the positions of the first to fourth detection body portions 21 to 24 with respect to the substrate 3.

[0029] More specifically, if the first to fourth detectors 21-24 are made of a material with a higher magnetic permeability than the rack shaft 13, magnetic flux will flow concentratedly in the first to fourth detectors 21-24, and the magnetic flux density will be higher in the portions of the substrate 3 facing the first to fourth detectors 21-24 than in other portions. Also, if the first to fourth detectors 21-24 are made of a material with a higher conductivity than the rack shaft 13, eddy currents generated in the first to fourth detectors 21-24 by the AC magnetic field will cause the magnetic flux density to be lower in the portions of the substrate 3 facing the first to fourth detectors 21-24 than in other portions. As a result, the magnitude of the induced voltage induced in the first detector coil 5 and the second detector coil 6 will change depending on the positions of the first to fourth detectors 21-24 with respect to the substrate 3.

[0030] The phases of the induced voltages induced in the first detection coil 5 and the second detection coil 6 while the rack shaft 13 moves from one axial movement end to the other axial movement end within the predetermined range R shown in FIG. 1 are different from each other (see FIGS. 8 and 9 described below). In this embodiment, the phases of the induced voltages induced in the first detection coil 5 and the second detection coil 6 are different by 90°. Furthermore, while the rack shaft 13 moves from one end to the other end of the predetermined range R, the magnitudes of the induced voltages induced in the first detection coil 5 and the second detection coil 6 change within a range of one cycle or less.

[0031] The first detection coil 5 has a first portion 51, a second portion 52, a third portion 53, and a fourth portion 54 in which an induced voltage is induced by the magnetic flux of the AC magnetic field of the excitation coil 4 interlinking with each other, connection portions 551 to 553 connecting the first to fourth portions 51 to 54, and an output line portion 56 that outputs the induced voltage induced in the first detection coil 5. The first to fourth portions 51 to 54 each extend along a coil longitudinal direction that is parallel to the axial direction of the rack shaft 13, and at least a portion of each is aligned in an alignment direction perpendicular to the coil longitudinal direction. In this embodiment, the first to fourth portions 51 to 54 have the same length in the coil longitudinal direction, and the entire coil longitudinal direction of each of the first to fourth portions 51 to 54 is aligned in a row along the alignment direction perpendicular to the coil longitudinal direction.

[0032] When viewed from a direction perpendicular to the substrate 3, the first portion 51, second portion 52, third portion 53, and fourth portion 54 of the first detection coil 5 each have a shape formed by combining a pair of curved conductor lines that are symmetrical about an axis of symmetry along the longitudinal direction of the coil, and that form a sine wave of a quarter wavelength (one wavelength is equal to the length of the predetermined range R). In Fig. 4(a), these axes of symmetry 5L1, 5L2, 5L3, and 5L4 are indicated by dashed dotted lines.

[0033] 4(a), the first portion 51 and the third portion 53 have gradually increasing widths perpendicular to the longitudinal direction of the coil, while the second portion 52 and the fourth portion 54 have gradually decreasing widths perpendicular to the longitudinal direction of the coil. When the first portion 51, the second portion 52, the third portion 53, and the fourth portion 54 are aligned in a line along the longitudinal direction of the coil, the overall shape forms a sinusoidal wave.

[0034] Furthermore, since the conductor wires of the first detection coil 5 cross at the connection portion 552 connecting the second portion 52 and the third portion 53, when the strength of the magnetic field changes in a direction perpendicular to the substrate 3, the direction of the induced voltage induced in the first portion 51 and the second portion 52 is opposite to the direction of the induced voltage induced in the third portion 53 and the fourth portion 54. As a result, when a uniform alternating magnetic field is applied to the entire first portion 51, the second portion 52, the third portion 53, and the fourth portion 54, the induced voltage induced in the first portion 51 and the second portion 52 and the induced voltage induced in the third portion 53 and the fourth portion 54 cancel each other out.

[0035] Similarly, the second detection coil 6 has a first portion 61, a second portion 62, a third portion 63, and a fourth portion 64 in which an induced voltage is induced by the magnetic flux of the AC magnetic field of the excitation coil 4 interlinking with each other, connection portions 651 to 653 connecting the first to fourth portions 61 to 64, and an output line portion 66 that outputs the induced voltage induced in the second detection coil 6. The first to fourth portions 61 to 64 each extend along a coil longitudinal direction parallel to the axial direction of the rack shaft 13, and at least a portion of each is aligned in a direction perpendicular to the coil longitudinal direction. In this embodiment, the first to fourth portions 61 to 64 have the same length in the coil longitudinal direction, and the entire coil longitudinal direction of each of the first to fourth portions 61 to 64 is aligned in a row along the direction perpendicular to the coil longitudinal direction.

[0036] When viewed from a direction perpendicular to the substrate 3, the first portion 61, second portion 62, third portion 63, and fourth portion 64 of the second detection coil 6 each have a shape formed by combining a pair of curved conductor lines in which quarter-wavelength cosine waves (sine waves with a 90° phase shift) are line-symmetrical with respect to an axis of symmetry along the longitudinal direction of the coil. In Fig. 4(b), these axes of symmetry 6L1, 6L2, 6L3, and 6L4 are indicated by dashed dotted lines.

[0037] 4(b), the first portion 61 and the third portion 63 have gradually narrower widths perpendicular to the longitudinal direction of the coil, while the second portion 52 and the fourth portion 54 have gradually wider widths perpendicular to the longitudinal direction of the coil. When the first portion 61, the second portion 62, the third portion 63, and the fourth portion 64 are aligned in a line along the longitudinal direction of the coil, the overall shape of the coil forms a cosine wave.

[0038] Furthermore, in the second detection coil 6, the conductor wires cross at the connection portion 651 connecting the first portion 61 and the second portion 62 and at the connection portion 653 connecting the third portion 63 and the fourth portion 64. Therefore, when the strength of the magnetic field in the direction perpendicular to the substrate 3 changes, the direction of the induced voltage induced in the first portion 61 and the fourth portion 64 is opposite to the direction of the induced voltage induced in the second portion 62 and the third portion 63. As a result, when a uniform alternating magnetic field is applied to the entire first portion 61, the second portion 62, the third portion 63, and the fourth portion 64, the induced voltage induced in the first portion 61 and the fourth portion 64 and the induced voltage induced in the second portion 62 and the third portion 63 cancel each other out.

[0039] The induced voltage induced in the first detection coil 5 and the induced voltage induced in the second detection coil 6 are output to the calculation unit 8 via the respective output line units 56, 66, connector 91, and cable 92. The calculation unit 8 calculates the position of the rack shaft 13 from the induced voltages induced in the first detection coil 5 and the second detection coil 6, and transmits information about the position of the rack shaft 13 to the steering control device 19. Note that the function of the calculation unit 8 may be realized by a CPU (arithmetic processing unit) mounted on the substrate 3. In this case, information about the position of the rack shaft 13 is transmitted from the CPU to the steering control device 19.

[0040] 3(b) shows center points C1, C2, C3, and C4 on the opposing surfaces 21a, 22a, 23a, and 24a of the first to fourth detector bodies 21 to 24. A distance D1 between the center point C1 of the first detector body 21 and the center point C2 of the second detector body 22 in the axial direction of the rack shaft 13, a distance D2 between the center point C2 of the second detector body 22 and the center point C3 of the third detector body 23, and a distance D4 between the center point C3 of the third detector body 23 and the center point C4 of the fourth detector body 24 are the same as the length L (see FIG. 5) of the portion of the substrate 3 excluding the output line portions 56 and 66 of the first detector coil 5 and the second detector coil 6 in the longitudinal direction. Hereinafter, the area on the substrate 3 where the portions of the first detector coil 5 and the second detector coil 6 excluding the output line portions 56 and 66 are formed is referred to as a coil formation area.

[0041] 6(a) to 6(e) are explanatory diagrams showing changes in the relative positional relationship between the first and second detection coils 5 and 6 and the first to fourth detection bodies 21 to 24 when the rack shaft 13 moves from the right side to the left side of the drawing relative to the substrate 3. In FIGS. 6(a) to 6(e), the coil formation range is indicated by the reference numeral 30.

[0042] Fig. 6(a) shows a state in which the rack shaft 13 is at one end of the predetermined range R in the axial direction, and Fig. 6(e) shows a state in which the rack shaft 13 is at the other end of the predetermined range R in the axial direction. Fig. 6(c) shows a state in which the rack shaft 13 is in the center (neutral position) of the predetermined range R. Fig. 6(b) shows a state in which the rack shaft 13 is in a position between the position shown in Fig. 6(a) and the position shown in Fig. 6(c), and Fig. 6(d) shows a state in which the rack shaft 13 is in a position between the position shown in Fig. 6(c) and the position shown in Fig. 6(e).

[0043] In the state shown in FIG. 6(a), the entire first detector 21 overlaps the coil formation area 30. In the state shown in FIG. 6(b), half of each of the first detector 21 and the second detector 22 overlaps the coil formation area 30. In the state shown in FIG. 6(c), half of each of the second detector 22 and the third detector 23 overlaps the coil formation area 30. In the state shown in FIG. 6(d), half of each of the third detector 23 and the fourth detector 24 overlaps the coil formation area 30. In the state shown in FIG. 6(e), the entire fourth detector 24 overlaps the coil formation area 30.

[0044] In this embodiment, as described above, the distances D1, D2, D3, and D4 are the same as the length L of the coil forming range 30, so that in the axial direction of the rack shaft 13, the total length of the opposing length between the first parts 51, 61 of the first detection coil 5 and the second detection coil 6 and the first detection body part 21, the opposing length between the second parts 52, 62 of the first detection coil 5 and the second detection coil 6 and the second detection body part 22, the opposing length between the third parts 53, 63 of the first detection coil 5 and the second detection coil 6 and the third detection body part 23, and the opposing length between the fourth parts 54, 64 of the first detection coil 5 and the second detection coil 6 and the fourth detection body part 24 is constant (length L) throughout the entire specified range R.

[0045] At least a portion of the first detector 21 faces the first portions 51, 61 of the first detector coil 5 and the second detector coil 6 in a first predetermined range of the predetermined range R. At least a portion of the second detector 22 faces the second portions 52, 62 of the first detector coil 5 and the second detector coil 6 in a second predetermined range of the predetermined range R. At least a portion of the third detector 23 faces the third portions 53, 63 of the first detector coil 5 and the second detector coil 6 in a third predetermined range of the predetermined range R. Furthermore, at least a portion of the fourth detector 24 faces the fourth portions 54, 64 of the first detector coil 5 and the second detector coil 6 in a fourth predetermined range of the predetermined range R. In the axial direction of the rack shaft 13, the first predetermined range and the second predetermined range, the second predetermined range and the third predetermined range, and the third predetermined range and the fourth predetermined range overlap at their respective ends.

[0046] The induced voltages induced in the first portions 51, 61 of the first and second detector coils 5, 6 vary depending on the position of the first detector 21 relative to the first portions 51, 61. The induced voltages induced in the second portions 52, 62 of the first and second detector coils 5, 6 vary depending on the position of the second detector 22 relative to the second portions 52, 62. The induced voltages induced in the third portions 53, 63 of the first and second detector coils 5, 6 vary depending on the position of the third detector 23 relative to the third portions 53, 63. The induced voltages induced in the fourth portions 54, 64 of the first and second detector coils 5, 6 vary depending on the position of the fourth detector 24 relative to the fourth portions 54, 64. This allows the calculation unit 8 to calculate the position of the rack shaft 13 over the entire predetermined range R.

[0047] An induced voltage having the same period as the period of the AC current supplied to the excitation coil 4 is induced in the first detection coil 5 and the second detection coil 6, and the peak value of this induced voltage changes depending on the positions of the first to fourth detection bodies 21 to 24 relative to the substrate 3. Note that the peak value of the induced voltage here refers to the maximum absolute value of the induced voltage within one period of the AC current supplied to the excitation coil 4.

[0048] 7 is a graph showing an example of the relationship between the supply voltage V0 supplied to the excitation coil 4 from the power supply unit 7 and the induced voltage V1 induced in the first detection coil 5 and the induced voltage V2 induced in the second detection coil 6 when the first detection body unit 21 faces the first portions 51, 61 of the first detection coil 5 and the second detection coil 6. The horizontal axis of the graph in FIG. 7 represents time, and the left and right vertical axes represent the supply voltage V0 and the induced voltages V1, V2. In the example shown in FIG. 7, the supply voltage V0 and the induced voltages V1, V2 are in phase, but depending on the position of the detection body 2 with respect to the substrate 3, one or both of the induced voltages V1, V2 may be out of phase with the supply voltage V0.

[0049] FIG. 8 is a graph showing the relationship between the peak voltage Vs, which is the peak value of the induced voltage V1 induced in the first detector coil 5, and the position of the detection object 2. FIG. 9 is a graph showing the relationship between the peak voltage Vc, which is the peak value of the induced voltage V2 induced in the second detector coil 6, and the position of the detection object 2. The horizontal axis of the graphs shown in FIGS. 8 and 9 indicates the position of the detection object 2. In the graph shown in FIG. 8, the peak voltage Vs of the first detector coil 5 is positive when the induced voltage V1 induced in the first detector coil 5 is in phase with the voltage V0 supplied to the excitation coil 4, and negative when the phases are opposite. In the graph shown in FIG. 9, the peak voltage Vc of the second detector coil 6 is positive when the induced voltage V2 induced in the second detector coil 6 is in phase with the voltage V0 supplied to the excitation coil 4, and negative when the phases are opposite.

[0050] On the horizontal axis of the graphs in Figures 8 and 9, P0 represents the position of the detection object 2 when the rack shaft 13 is in the neutral position, P1 represents the position of the detection object 2 in the state shown in Figure 6(a), and P2 represents the position of the detection object 2 in the state shown in Figure 6(e). As shown in Figures 8 and 9, the peak voltage Vs and the peak voltage Vc do not have the same value in the range from P1 to P2. This allows the calculation unit 8 to uniquely determine the absolute position of the rack shaft 13 based on the peak voltage Vs and the peak voltage Vc.

[0051] However, if the rack shaft 13 tilts relative to the substrate 3 due to vibrations while the vehicle is running, changing the distance between the substrate 3 and the rack shaft 13, the degree to which the rack shaft 13 and the detection body 2 affect the magnetic flux intensity distribution inside the excitation coil 4 will vary depending on their positions in the longitudinal direction of the substrate 3. In this embodiment, the effect of the tilt of the rack shaft 13 on the detection accuracy of the position of the detection body 2 is suppressed by arranging the first portions 51, 61, second portions 52, 62, third portions 53, 63, and fourth portions 54, 64 of the first detection coil 5 and the second detection coil 6 in the short direction of the substrate 3. Next, the operation and effect of this configuration will be described with reference to FIG. 10.

[0052] FIG. 10(a) is an explanatory diagram schematically illustrating the relationship between the inclination of the rack shaft 13 with respect to the substrate 3 and the effect of the inclination of the rack shaft 13 on the magnetic flux density interlinking with the first detection coil 5. FIG. 10(b) is an explanatory diagram schematically illustrating the relationship between the inclination of the rack shaft 13 with respect to the substrate 3 and the effect of the inclination of the rack shaft 13 on the magnetic flux density interlinking with the second detection coil 6. In FIGS. 10(a) and 10(b), the bisector BL of the longitudinal direction of the first detection coil 5 and the second detection coil 6 is indicated by a two-dot chain line, and the rack shaft 13 is shown tilted in the vertical direction of the drawing around a point indicated by a target mark TM on this bisector BL. The rack shaft 13 and the detection object 2 are tilted so that the portions to the left of the target mark TM shown in dark gray in the drawing are closer to the substrate 3, and the portions to the right of the target mark TM shown in light gray in the drawing are farther away from the substrate 3. It should be noted that the inclination of the rack shaft 13 is exaggerated in FIGS. 10(a) and 10(b).

[0053] In this embodiment, the first portions 51, 61, second portions 52, 62, third portions 53, 63, and fourth portions 54, 64 of the first detection coil 5 and the second detection coil 6 are arranged in the short-side direction of the substrate 3, so that the length L of the coil formation area 30 in the axial direction of the rack shaft 13 is shorter than that of the detection coil shown in, for example, the above-mentioned Patent Document 1. As a result, even if the rack shaft 13 is tilted, changes in the width W of the air gap G (see FIG. 2) and the distance between the rack shaft 13 and the substrate 3 are kept small, and the peak voltage Vs and the peak voltage Vc are less likely to change. This makes it possible to detect the position of the rack shaft 13 with high accuracy.

[0054] 11 is a graph showing evaluation results of detection errors when the position of the rack shaft 13 is detected by the stroke sensor 1 according to this embodiment. The horizontal axis of the graph represents the amount of movement of the rack shaft 13, with the neutral position of the rack shaft 13 being 0 (mm). The vertical axis of the graph represents the detection error in %FS (FS stands for full scale) of the position of the rack shaft 13 when the rack shaft 13 is tilted by 0.5°.

[0055] As shown in FIG. 11, with the stroke sensor 1, the detection error (%FS) when the rack shaft 13 is in the positions shown in FIGS. 6(b), (c), and (d) is approximately 0.04% at most, but overall it is kept to 0.05% or less, ensuring sufficient detection accuracy.

[0056] (Summary of the embodiment) Next, the technical ideas grasped from the above-described embodiments will be described by using the reference numerals and the like in the embodiments. However, the reference numerals in the following description do not limit the components in the claims to the members and the like specifically shown in the embodiments.

[0057] [1] A position detection device (stroke sensor 1) for detecting the position of a shaft (rack shaft 13) that moves back and forth in an axial direction within a predetermined range (R), comprising: an excitation coil (4) that generates an AC magnetic field; a detection body (2) that is fixed to the shaft (13) and is interlinked with the magnetic flux of the AC magnetic field; and detection coils (5, 6) that are interlinked with the magnetic flux of the AC magnetic field, wherein the detection coils (5, 6) have first to third portions in which an induced voltage is induced by the interlinking magnetic flux of the AC magnetic field. The coil has a fourth portion (51-54, 61-64) and a connecting portion (551-553, 651-653) that connects the first portion to the fourth portion (51-54, 61-64), and the first portion to the fourth portion (51-54, 61-64) each extend along a coil longitudinal direction that is parallel to the axial direction, and at least a portion of each is aligned in an alignment direction that is perpendicular to the coil longitudinal direction, and the detection body (2) is at least partially aligned in a first predetermined range of the predetermined range (R). a first detection body (21) at least a portion of which faces the first portion (51, 61); a second detection body (22) at least a portion of which faces the second portion (52, 62) in a second predetermined range of the predetermined range (R); a third detection body (23) at least a portion of which faces the third portion (53, 63) in a third predetermined range of the predetermined range (R); and a fourth detection body (24) at least a portion of which faces the fourth portion (54, 64) in a fourth predetermined range of the predetermined range. a position detecting device (1) having: a first detecting body portion (21), a second detecting body portion (22), a third detecting body portion (23), and a fourth detecting body portion (24) arranged at intervals in the axial direction of the shaft (13);

[0058] [2] A position detection device as described in [1] above, wherein the first predetermined range and the second predetermined range, the second predetermined range and the third predetermined range, and the third predetermined range and the fourth predetermined range overlap at their respective ends in the axial direction of the shaft (13).

[0059] [3] The position detection device (1) described in [2] above, wherein the total length of the opposing length of the first portion (51, 61) and the first detection body portion (21), the opposing length of the second portion (52, 62) and the second detection body portion (22), the opposing length of the third portion (53, 63) and the third detection body portion (23), and the opposing length of the fourth portion (54, 64) and the fourth detection body portion (24) in the axial direction of the shaft (13) is constant throughout the specified range (R).

[0060] [4] A position detection device (1) according to any one of [1] to [3] above, wherein the lengths of the first to fourth parts (51 to 54, 61 to 64) in the longitudinal direction of the coil are equal, and the first to fourth parts (51 to 54, 61 to 64) are aligned in a row along an alignment direction perpendicular to the longitudinal direction of the coil.

[0061] [5] A position detection device described in any of [1] to [3] above, wherein the first to fourth parts (51 to 54, 61 to 64) are shaped by combining a pair of sinusoidal conductor wires that are symmetrical about a symmetry axis (5L1, 5L2, 5L3, 5L4, 6L1, 6L2, 6L3, 6L4) extending in the longitudinal direction of the coil.

[0062] [6] The position detection device (1) described in [5] above, wherein the magnitude of the induced voltage induced in the detection coils (5, 6) changes within a range of one cycle or less while the shaft (13) moves from one end of the predetermined range (R) to the other end of the predetermined range (R).

[0063] [7] The position detection device (1) according to [6] above, comprising two detection coils (5, 6), wherein the phases of the induced voltages induced in the two detection coils (5, 6) are different from each other while the shaft (13) moves from one end of the predetermined range (R) to the other end of the predetermined range (R).

[0064] [8] The position detection device (1) described in [7] above, wherein the excitation coil (4) and the two detection coils (5, 6) are formed on a single substrate (3), and the two detection coils (5, 6) are stacked in the thickness direction of the substrate (3).

[0065] Although the embodiments of the present invention have been described above, the invention according to the claims is not limited to the above embodiments. It should be noted that not all of the combinations of features described in the embodiments are necessarily essential to the means for solving the problems of the invention. Furthermore, the present invention can be appropriately modified and implemented without departing from the spirit of the invention, and can be modified as follows, for example.

[0066] In the above embodiment, the first detector 21, the second detector 22, the third detector 23, and the fourth detector 24 are provided so as to protrude from the rack shaft 13 toward the substrate 3, but this is not limiting. For example, the detector 2 may be formed in the shape of a long flat plate in the axial direction of the rack shaft 13, and the first to fourth detectors 21 to 24 may be formed as recesses or notches. Even in this case, the magnetic flux density differs between the portion facing the first to fourth detectors 21 to 24 and the portion not facing them, so the position of the rack shaft 13 can be detected in the same way as in the above embodiment.

[0067] In the above embodiment, the conductor wires of the first portions 51, 61, second portions 52, 62, third portions 53, 63, and fourth portions 54, 64 of the first detection coil 5 and the second detection coil 6 are sinusoidal, but the conductor wires may be triangular, for example. Furthermore, the excitation coil 4 and the first detection coil 5 and the second detection coil 6 do not necessarily have to be formed on a substrate. [Explanation of symbols]

[0068] 1... Stroke sensor (position detection device) 13... Shaft (rack shaft) 2...Detection body 21...First detection body part 22... Second detection body 23... Third detection body 24...Fourth detection body 3...Substrate 4...Excitation coil 5...First detection coil 51...First part 52...Second part 53…3rd part 54…4th part 551~553...Connections 5L1, 5L2, 5L3, 5L4...Symmetrical axis 6... Second detection coil 61... First part 62…Second part 63…Third part 64...Fourth part 651~653...Connection part 6L1, 6L2, 6L3, 6L4...symmetrical axis R...predetermined range

Claims

1. A position detection device that detects the position of a shaft that moves back and forth in an axial direction within a predetermined range, an excitation coil that generates an AC magnetic field; a detection body fixed to the shaft and interlinked with the magnetic flux of the AC magnetic field; a detection coil with which the magnetic flux of the AC magnetic field interlinks, the detection coil has first to fourth portions in which an induced voltage is induced by the magnetic flux of the AC magnetic field interlinking with each other, and a connection portion connecting the first to fourth portions; the first to fourth portions each extend along a coil longitudinal direction parallel to the axial direction, and at least a portion of each is aligned in an alignment direction perpendicular to the coil longitudinal direction, The detection body has a first detection body portion, at least a portion of which faces the first portion in a first predetermined range of the predetermined range, a second detection body portion, at least a portion of which faces the second portion in a second predetermined range of the predetermined range, a third detection body portion, at least a portion of which faces the third portion in a third predetermined range of the predetermined range, and a fourth detection body portion, at least a portion of which faces the fourth portion in a fourth predetermined range of the predetermined range, the induced voltages induced in the first to fourth portions vary depending on the positions of the first to fourth detection body portions relative to the first to fourth portions, respectively; The first detection body portion, the second detection body portion, the third detection body portion, and the fourth detection body portion are provided spaced apart in the axial direction of the shaft. Position detection device.

2. In the axial direction of the shaft, the first predetermined range and the second predetermined range, the second predetermined range and the third predetermined range, and the third predetermined range and the fourth predetermined range overlap at their respective ends. The position detection device according to claim 1 .

3. In the axial direction of the shaft, the total length of the opposing length between the first portion and the first detection body portion, the opposing length between the second portion and the second detection body portion, the opposing length between the third portion and the third detection body portion, and the opposing length between the fourth portion and the fourth detection body portion is constant throughout the predetermined range. The position detection device according to claim 2 .

4. The first to fourth portions have the same length in the coil longitudinal direction, The first to fourth portions are aligned in a line along an alignment direction perpendicular to the longitudinal direction of the coil. The position detection device according to any one of claims 1 to 3.

5. Each of the first to fourth portions has a shape formed by combining a pair of sinusoidal conductor wires that are symmetrical with respect to a symmetry axis extending in the longitudinal direction of the coil. The position detection device according to any one of claims 1 to 3.

6. the magnitude of the induced voltage induced in the detection coil changes within a range of one cycle or less while the shaft moves from one end of the predetermined range to the other end of the predetermined range; The position detection device according to claim 5 .

7. two detection coils are provided, and the phases of the induced voltages induced in the two detection coils while the shaft moves from one end of the predetermined range to the other end of the predetermined range are different from each other; The position detection device according to claim 6.

8. the excitation coil and the two detection coils are formed on a single substrate, The two detection coils are stacked in the thickness direction of the substrate. The position detection device according to claim 7.

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