CN116576761A

CN116576761A - Position detecting device

Info

Publication number: CN116576761A
Application number: CN202310089999.0A
Authority: CN
Inventors: 白川洋平; 杉山雄太; 池田幸雄
Original assignee: Bomeilicheng Co ltd
Current assignee: Bomeilicheng Co ltd
Priority date: 2022-02-10
Filing date: 2023-02-09
Publication date: 2023-08-11

Abstract

The invention provides a position detection device capable of detecting the position of a shaft moving forward and backward along an axial direction with high precision. A stroke sensor (1) for detecting the position of a rack shaft (13) that moves forward and backward in the axial direction is provided with: a target (2) mounted on the rack shaft (13); an excitation coil (31) for generating an alternating magnetic field; and detection coils (32, 33) arranged along the axial direction of the rack shaft (13), wherein the magnitude of the voltage induced by the detection coils (32, 33) changes according to the position of the target (2).

Description

Position detecting device

Technical Field

The present invention relates to a position detecting device for detecting a position of a shaft that moves forward and backward in an axial direction.

Background

Conventionally, a position detecting device that detects a position of a shaft that moves forward and backward in an axial direction is used for detecting a position of a rack shaft in a steering device of a vehicle, for example.

The detection means described in patent document 1 detects the position of the rack shaft in the electric power steering apparatus in the axial direction, and includes a dc power supply, a permanent magnet, an element group including first to fourth magnetoresistive elements arranged between the permanent magnet and the rack shaft, and a calculation unit that calculates the position of the rack shaft. In the element group, a series circuit in which the first magnetoresistive element and the second magnetoresistive element are connected in series and a series circuit in which the third magnetoresistive element and the fourth magnetoresistive element are connected in series are connected in parallel to form a bridge circuit. The potential of the first terminal connected between the first and second magneto-resistive elements and the potential of the second terminal connected between the third and fourth magneto-resistive elements are input to the operation unit. A plurality of grooves extending in a direction inclined with respect to the axial direction of the rack shaft are formed on the facing surface of the rack shaft with respect to the element group.

In the detection unit configured as described above, when the rack shaft moves in the axial direction by rotation of the pinion shaft engaged with the rack shaft and the relative positions of the first to fourth magnetoresistive elements and the plurality of grooves change, the balance of the resistances of the first to fourth magnetoresistive elements changes, and the potentials of the first terminal and the second terminal change. The operation unit calculates the position of the rack shaft based on the change in the potential.

Prior art literature

Patent literature

Patent document 1: international publication No. 2021/210125

Disclosure of Invention

In the detection unit described in patent document 1, for example, when the rack shaft moves in the vehicle longitudinal direction relative to the detection unit due to vibration accompanying running of the vehicle, the relative positions of the first to fourth magnetoresistive elements and the plurality of grooves change, and an error occurs in the detection position of the rack shaft. In addition, when the rotation direction of the pinion shaft is changed, even in the case where the rack shaft is slightly rotated around its central axis due to a change in tooth contact of the pinion shaft with the rack shaft, an error occurs in the detection position of the rack shaft. In particular, if the absolute position of the rack shaft in the axial direction is to be detected over the entire stroke range by the detection means described in patent document 1, the inclination angle of the plurality of grooves with respect to the axial direction must be made shallow, and a large error tends to occur in the detection result.

Accordingly, an object of the present invention is to provide a position detecting device capable of detecting the position of a shaft that moves forward and backward in the axial direction with high accuracy.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a position detection device for detecting a position of a shaft that moves forward and backward in an axial direction, the position detection device including: a detection body mounted on the shaft; an exciting coil that generates an alternating-current magnetic field; and a detection coil disposed along an axial direction of the shaft, wherein a magnitude of a voltage induced by the detection coil changes according to a position of the detection body.

According to the present invention, it is possible to provide a position detecting device capable of detecting the position of a shaft that moves forward and backward in the axial direction with high accuracy.

Drawings

Fig. 1 (a) is a schematic view of a vehicle mounted with a steer-by-wire steering device provided with a stroke sensor as a position detecting device according to an embodiment of the present invention, and (b) is a sectional view taken along line A-A of (a).

Fig. 2 is a perspective view showing a target and a base plate together with a part of a rack shaft.

Fig. 3 is a plan view of the substrate viewed from the front surface side.

Fig. 4 (a) to (d) are plan views each showing the first to fourth metal layers viewed from the front surface side.

Fig. 5 (a) to (d) are enlarged plan views of the first to fourth metal layers showing both ends in the longitudinal direction of the substrate as viewed from the front surface side.

Fig. 6 is a graph showing a relationship between a supply voltage supplied from the power supply unit to the exciting coil, and an induced voltage induced by the sine-wave-shaped detection coil and an induced voltage induced by the cosine-wave-shaped detection coil.

Fig. 7 is an explanatory diagram schematically showing a relationship between a peak voltage of an induced voltage induced in a sine wave-shaped detection coil and a position of a target.

Fig. 8 is an explanatory diagram schematically showing a relationship between a peak voltage of an induced voltage induced in a cosine wave-shaped detection coil and a position of a target.

Fig. 9 is a graph showing the result of evaluating the position detection accuracy of the stroke sensor using electromagnetic field simulation.

Fig. 10 is a plan view of a substrate according to a first modification.

Fig. 11 is a plan view showing a substrate and a target according to a second modification.

Fig. 12 is a plan view of a substrate according to a third modification.

Fig. 13 (a) to (d) are plan views showing first to fourth metal layers of a substrate according to a third modification.

Fig. 14 (a) is a perspective view showing a target of the fourth modification example together with a rack shaft, and (b) is a perspective view showing a state in which the target is attached to the rack shaft.

Fig. 15 (a) is a cross-sectional view showing a B-B line cross section of fig. 14 (B) together with a substrate. (b) The cross section of fig. 14 (b) is a cross section taken along with the substrate.

Fig. 16 (a) to (c) are perspective views showing targets of a fifth modification.

Fig. 17 (a) to (c) are cross-sectional views showing the cross-section of the target of the fifth modification example together with the substrate.

Detailed Description

Fig. 1 (a) is a schematic diagram of a vehicle mounted with a steering-by-wire steering device 10, and the steering device 10 includes a stroke sensor 1 as a position detection device according to an embodiment of the present invention. Fig. 1 (b) is a sectional view taken along line a to a of fig. 1 (a).

As shown in fig. 1 (a), the steering device 10 includes: a stroke sensor 1; a tie rod 12 connected to the steered wheels 11 (left and right front wheels); a rack shaft 13 connected to the tie rod 12; a cylindrical case 14 accommodating the rack shaft 13; a worm reduction mechanism 15 having a pinion 151 engaged with the rack teeth 131 of the rack shaft 13; an electric motor 16 for applying an axial moving force to the rack shaft 13 via the worm reduction mechanism 15; a steering wheel 17 for steering operation by a driver; a steering angle sensor 18 that detects a 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.

In fig. 1 (a), the case 14 is shown by an imaginary line. The rack shaft 13 is made of steel material such as carbon steel, for example, and is supported by a pair of rack bushings 141 attached to both end portions of the housing 14. The worm reduction mechanism 15 includes a worm wheel 152 and a worm 153, and a pinion 151 is fixed to the worm wheel 152. Worm 153 is fixed to motor shaft 161 of electric motor 16.

The electric motor 16 generates torque by a motor current supplied from the steering control device 19, and rotates the worm wheel 152 and the pinion 151 via the worm 153. When the pinion 151 rotates, the rack shaft 13 advances and retreats in the axial direction, and the left and right steering wheels 11 are steered. The rack shaft 13 is movable to the right and left in the vehicle width direction within a predetermined range from a neutral position when the steering angle is zero. In fig. 1 (a), a range R in which the rack shaft 13 can move in the axial direction is indicated by a double arrow ₁ 。

(Structure of Stroke sensor 1)

The stroke sensor 1 includes a target 2 attached to a rack shaft 13, a substrate 3 disposed opposite to the target 2, a power supply unit 4, and a calculation unit 5. The base plate 3 is fixed in the housing 14. The stroke sensor 1 detects the position of the rack shaft 13 relative to the housing 14 from the position of the target 2, and outputs information of the detected position to the 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 the steering angle sensor 18.

Fig. 2 is a perspective view showing the target 2 and the base plate 3 together with a part of the rack shaft 13. The target 2 is formed in a rectangular parallelepiped shape long in the axial direction of the rack shaft 13. The facing surface 13a of the rack shaft 13 facing the substrate 3 is formed in a planar shape, and the target 2 is fixed to the facing surface 13a by fixing means such as adhesion or welding. The base plate 3 is rectangular in shape in which the axial direction of the rack shaft 13 is the longitudinal direction, and is arranged parallel to the facing surface 13a of the rack shaft 13 and perpendicular to the radial direction of the rack shaft 13.

The target 2 is one embodiment of the detection body of the present invention, and is a target for detecting the position of the rack shaft 13. The target 2 is made of a material having magnetic permeability equal to or higher than that of the rack shaft 13, or a material having electric conductivity higher than that of the rack shaft 13. When a material having a magnetic permeability equal to or higher than that of the rack shaft 13 is used for the target 2, a magnetic material such as ferrite can be used as the material. In the case where a material having conductivity equal to that of the rack shaft 13 or higher than that of the rack shaft 13 is used for the target 2, for example, iron, aluminum, or a metal containing copper as a main component is used as the material.

In the present embodiment, since the target 2 is provided so as to protrude from the facing surface 13a formed on the rack shaft 13 toward the substrate 3, the operation and effect described below can be obtained even when a material having the same magnetic permeability as the rack shaft 13 or a material having the same electric conductivity as the rack shaft 13 is used as the material of the target 2. However, in order to improve the accuracy of position detection, it is preferable to use a high magnetic permeability material having a higher magnetic permeability than the material of the rack shaft 13 or a high conductivity material having a higher conductivity than the material of the rack shaft 13 as the material of the target 2.

As shown in fig. 1 (b), the substrate 3 is a four-layer substrate in which a flat substrate 30 made of a dielectric material such as FR4 (glass fiber impregnated with an epoxy resin and heat-cured) is disposed between the first to fourth metal layers 301 to 304. The front (positive) surface 3a of the substrate 3 on the first metal layer 301 side faces the target 2 and the facing surface 13a of the rack shaft 13. The back surface 3b of the substrate 3 on the fourth metal layer 304 side is fixed to the inner surface 14a of the case 14 by the adhesive 6. The thickness of the base material 30 is, for example, 0.3mm. The thickness of each of the first to fourth metal layers 301 to 304 is, for example, 18 μm.

The case 14 is made of a non-magnetic metal such as an aluminum alloy formed by die casting. The case 14 of the portion where the substrate 3 is mounted may be made of a resin material. The target 2 has a rectangular parallelepiped shape, and the surface 20a facing the substrate 3 has a planar shape. The facing surface 20a of the target 2 is opposed to the surface 3a of the substrate 3 in parallel with an air gap G. The width of the air gap G in the direction perpendicular to the surface 3a of the substrate 3 is 10mm or less, for example, 1mm. The thickness of the target 2 is, for example, 5mm.

Fig. 3 is a plan view of the substrate 3 viewed from the front surface 3a side. In fig. 3, wiring patterns formed in the first to fourth metal layers 301 to 304 are seen through, the wiring pattern of the first metal layer 301 is indicated by a solid line, the wiring pattern of the second metal layer 302 is indicated by a broken line, the wiring pattern of the third metal layer 303 is indicated by a one-dot chain line, and the wiring pattern of the fourth metal layer 304 is indicated by a two-dot chain line. In fig. 3, the position of the target 2 in the case where the rack shaft 13 is positioned at one end and the other end among the range in which the stroke sensor 1 can detect the absolute position of the rack shaft 13 is shown to overlap the substrate 3. Length L of substrate 3 in the longitudinal direction ₀ For example, 470mm, and the width W of the substrate 3 in the short side direction is for example 20mm. Width W of target 2 in a direction parallel to the short side direction of substrate 3 ₀ Is equal to or wider than the width W of the substrate 3 in the short side direction of the substrate 3.

Fig. 4 (a) to (d) are plan views showing the first to fourth metal layers 301 to 304, respectively, as viewed from the front surface 3a side. Fig. 5 (a) to (d) are enlarged plan views showing the first to fourth metal layers 301 to 304 at both ends in the longitudinal direction of the substrate 3 as viewed from the front surface 3a side. Hereinafter, for convenience of explanation, one of the long side direction side and the other side of the substrate 3, which corresponds to the right side of fig. 4 (a) to (d) and fig. 5 (a) to (d), is referred to as the right side, and the other long side of the substrate 3, which corresponds to the left side of fig. 4 (a) to (d) and fig. 5 (a) to (d), is referred to as the left side. However, the right side and the left side do not necessarily refer to the left and right sides in the vehicle width direction in the mounted state of the vehicle.

As shown in fig. 5 (a) to (d), first to fifth vias 341 to 345 for connecting wiring patterns of the first to fourth metal layers 301 to 304 to each other are provided on the substrate 3. Further, a connector connection portion 350 having first to sixth through holes 351 to 356 through which connector pins 71 to 76 of the connector 7 shown by two-dot chain lines in fig. 5 (a) are inserted, respectively, is provided at the left end portion of the substrate 3. The first through sixth through holes 351 through 356 are aligned in a straight line along the short side direction of the substrate 3. The connector 81 of the cable 8 for connecting to the power supply unit 4 and the operation unit 5 is connected to the connector 7 (see fig. 1 (a)).

The substrate 3 includes an exciting coil 31 for generating an ac magnetic field and two detection coils 32 and 33 formed so as to be surrounded by the exciting coil 31. That is, the exciting coil 31 and the detecting coils 32 and 33 are formed on one substrate 3. The exciting coil 31 and the detecting coils 32 and 33 are formed long in the longitudinal direction of the base plate 3, and are arranged along the axial direction of the rack shaft 13.

In the detection coils 32 and 33, an induced voltage is generated by the magnetic flux linkage of the magnetic field generated by the exciting coil 31. When the target 2 is made of a material having a magnetic permeability equal to the rack shaft 13 or a magnetic permeability higher than the rack shaft 13, the magnetic flux concentrates on the target 2, and the magnetic flux density of the portion of the substrate 3 facing the target 2 is higher than that of the other portion. In addition, when the target 2 is made of a material having an electric conductivity equal to that of the rack shaft 13 or higher than that of the rack shaft 13, the eddy current generated in the target 2 by the alternating magnetic field reduces the density of the magnetic flux interlinking with the detection coils 32 and 33, and the magnetic flux density in the portion facing the target 2 in the substrate 3 is lower than that in the other portion. Therefore, the magnitude of the voltage induced in the detection coils 32 and 33 varies according to the position of the target 2 relative to the substrate 3. In the case where a material having a magnetic permeability equal to or higher than that of the rack shaft 13 is used as the material of the target 2, a magnetic material having a high electric resistance and being less likely to generate eddy current is preferably used.

While the rack shaft 13 moves from one end of movement in the axial direction to the other end of movement, the phases of the voltages induced by the detection coils 32 and 33 are different from each other. In the present embodiment, the voltages induced in the detection coils 32 and 33 are 90 ° out of phase. Hereinafter, one detection coil 32 of the two detection coils 32 and 33 is a sine wave-shaped detection coil 32, and the other detection coil 33 is a cosine wave-shaped detection coil 33. The exciting coil 31, the sine-wave-shaped detecting coil 32, and the cosine-wave-shaped detecting coil 33 are formed in a distributed manner on the first to fourth metal layers 301 to 304.

Sine wave shape detection coil 32 and cosine wave shapeThe magnitude of the voltage induced by the shape detection coil 33 changes within a range of one cycle amount or less while the rack shaft 13 moves from one movement end to the other movement end in the axial direction. Thereby, the stroke sensor 1 can move in the axial direction over the entire range R of the rack shaft 13 ₁ The absolute position of the rack shaft 13 is detected.

The sine wave shape detection coil 32 and the cosine wave shape detection coil 33 are formed by combining a pair of sinusoidal wires in a shape as viewed from a direction perpendicular to the axial direction of the rack shaft 13. The pair of sinusoidal conductors are arranged with the symmetry axis A parallel to the axial direction of the rack shaft 13 ₁ ～A ₄ And symmetrical shape. That is, if one of a pair of sinusoidal leads is made to be opposite to the symmetry axis A ₁ ～A ₄ The other lead is shaped by vertically reversing the lead. In fig. 4 (a) to (d), the symmetry axis a is indicated by a dash-dot line ₁ ～A ₄ 。

The sine wave-shaped detection coil 32 is constituted by a waveform wire 321 of the first metal layer 301, a waveform wire 322 of the third metal layer 303, and a fourth passage 344. The waveform conductors 321, 322 are sinusoidal. The fourth path 344 connects right-side ends of the waveform conductors 321, 322 to each other. The left end of the wavy wire 321 of the first metal layer 301 is connected to the third via 353 through the connection wire 323 of the first metal layer 301. The left end of the wavy wire 322 of the third metal layer 303 is connected to the fourth via 354 through the connection wire 324 of the third metal layer 303.

The cosine wave shape detection coil 33 is composed of a waveform wire 331 of the second metal layer 302, a connection wire 332 of the first metal layer 301, a waveform wire 333 of the fourth metal layer 304, and third and fifth vias 343, 345. The waveform conductors 331, 333 are sinusoidal. The right end of the wavy conductor 331 of the second metal layer 302 is connected to the third via 343. The right end of the waveform wire 333 of the fourth metal layer 304 is connected to the fifth via 345. The connection wire 332 of the first metal layer 301 connects the third via 343 and the fifth via 345. The left end of the wavy conductor 331 of the second metal layer 302 is connected to the fifth via 355 through the connection conductor 334 of the second metal layer 302. The left end of the wave-shaped conductive wire 333 of the fourth metal layer 304 is connected to the second via 342, and the second via 342 and the sixth via 356 are connected by the connection conductive wire 335 of the third metal layer 303.

In this way, on the substrate 3, the waveform conductors 321 and 322 as part of the sine wave-shaped detection coil 32 are formed on the first metal layer 301 and the third metal layer 303, respectively, and the waveform conductors 331 and 333 as part of the cosine wave-shaped detection coil 33 are formed on the second metal layer 302 and the fourth metal layer 304, respectively. Thus, for example, compared with the case where one detection coil is formed by a combination of waveform wires formed on the first metal layer 301 and the second metal layer 302, and the other detection coil is formed by a combination of waveform wires formed on the third metal layer 303 and the fourth metal layer 304, the difference in average distance from the target 2 to the sine wave-shaped detection coil 32 and the cosine wave-shaped detection coil 33 is smaller.

As shown in fig. 3, the exciting coil 31 includes a pair of long side portions 31a and 31b extending in the longitudinal direction of the substrate 3 and sandwiching the sine-wave-shaped detection coil 32 and the cosine-wave-shaped detection coil 33 in the short side direction of the substrate 3, and a pair of short side portions 31c and 31d extending in the short side direction of the substrate 3 and sandwiching the sine-wave-shaped detection coil 32 and the cosine-wave-shaped detection coil 33 in the long side direction of the substrate 3, and is formed so as to surround the sine-wave-shaped detection coil 32 and the cosine-wave-shaped detection coil 33.

In the present embodiment, the exciting coil 31 has a first exciting coil portion 311 formed in the first metal layer 301 and a second exciting coil portion 312 formed in the fourth metal layer 304. The first exciting coil 311 has a leading end connected to the first through hole 351 and a terminating end connected to the first passage 341. The first end of the second exciting coil 312 is connected to the first passage 341, and the second end is connected to the second through hole 352.

The first exciting coil portion 311 has a long-side direction wire 311a extending along one end 3c of the two ends in the short-side direction of the substrate 3, a short-side direction wire 311b extending along the right end 3d of the substrate 3, a long-side direction wire 311c extending along the other end 3e of the two ends in the short-side direction of the substrate 3, and short-side direction wires 311d, 311e extending along the left end 3f of the substrate 3, the short-side direction wire 311d being connected to the first through hole 351 by a connection line 311 f. The short-side direction wire 311e is connected to the first via 341.

The second exciting coil portion 312 has a long-side direction wire 312a extending along one end 3c of the two ends in the short-side direction of the substrate 3, a short-side direction wire 312b extending along the right end 3d of the substrate 3, a long-side direction wire 312c extending along the other end 3e of the two ends in the short-side direction of the substrate 3, and short-side direction wires 312d, 312e extending along the left end 3f of the substrate 3, the short-side direction wire 312e being connected to the second through hole 352 by a connection line 312 f. The short-side direction wire 312d is connected to the first via 341.

One long side portion 31a of the pair of long side portions 31a, 31b of the exciting coil 31 is constituted by a long side direction wire 311a of the first exciting coil portion 311 and a long side direction wire 312a of the second exciting coil portion 312. The other long side portion 31b is constituted by a long side direction wire 311c of the first exciting coil portion 311 and a long side direction wire 312c of the second exciting coil portion 312.

One short side portion 31c of the pair of short side portions 31c, 31d of the exciting coil 31 is constituted by a short side direction wire 311b of the first exciting coil portion 311 and a short side direction wire 312b of the second exciting coil portion 312. The other short side portion 31d is constituted by short side direction wires 311d, 311e of the first exciting coil portion 311 and 312d, 312e of the second exciting coil portion 312.

A buffer region E for suppressing a magnetic field generated by a current flowing through the pair of short side portions 31c and 31d and a voltage generated by the sine wave-shaped detection coil 32 and the cosine wave-shaped detection coil 33 is provided between each of the pair of short side portions 31c and 31d of the excitation coil 31 and the sine wave-shaped detection coil 32 and the cosine wave-shaped detection coil 33 ₁ 、E ₂ . This improves the accuracy of detecting the position of the stroke sensor 1. In the present embodiment, the buffer region E on the left side in the longitudinal direction of the substrate 3 ₁ Width W of (2) ₁ Buffer area E on the right side ₂ Width W of (2) ₂ Identical but width W ₁ And width W ₂ Or may be different.

As shown in fig. 5, the connection wire 323 of the first metal layer 301, the connection wire 334 of the second metal layer 302, and the connection wires 324, 335 of the third metal layer 303 are in the buffer region E ₁ Which extends linearly along the longitudinal direction of the substrate 3. The third through hole 353, which is the output end of the sine wave-shaped detection coil 32, is adjacent to the fourth through hole 354, and the fifth through hole 355, which is the output end of the cosine wave-shaped detection coil 33, is adjacent to the sixth through hole 356. This suppresses the fluctuation of the output voltage of the sinusoidal detection coil 32 due to the magnetic flux interlinked with the portion between the connection wire 323 of the first metal layer 301 and the connection wire 324 of the third metal layer 303. In addition, the output voltage of the cosine wave-shaped detection coil 33 can be suppressed from varying due to the magnetic flux interlinking with the portion between the connection wire 334 of the second metal layer 302 and the connection wire 335 of the third metal layer 303.

As shown in fig. 3, the lengths of the sine wave-shaped detection coil 32 and the cosine wave-shaped detection coil 33 in the longitudinal direction of the substrate 3 are L ₂ The length of the target 2 in this direction is L ₃ Length L of target 2 ₃ The longer the sine wave-shaped detection coil 32 and the cosine wave-shaped detection coil 33 corresponding to the position of the target 2, the larger the amount of change in output voltage, and the higher the position detection accuracy, but it is the length L of the target 2 that the stroke sensor 1 can accurately detect the positions of the target 2 and the rack shaft 13 ₃ Is included in the length L of the sine-wave-shaped detection coil 32 and the cosine-wave-shaped detection coil 33 ₂ Length L of target 2 ₃ The longer the stroke sensor 1, the narrower the detectable range. That is, the detectable range of the stroke sensor 1 is (L ₂ -L ₃ ) Length range of (c) is provided. Thus, the length L of the target 2 ₃ Preferably, the length L of the sine wave-shaped detection coil 32 and the cosine wave-shaped detection coil 33 ₂ 2 of (2) is less than 1, the length L of the target 2 ₃ Length L relative to sine wave shape detection coil 32 and cosine wave shape detection coil 33 ₂ More preferably, the range of (2) is 1% or more and 50% or less.

As shown in fig. 3, the length of the exciting coil 31 in the longitudinal direction of the substrate 3 is L ₁ The width of the exciting coil 31 in the short side direction of the substrate 3 is W _E The widths of the sine wave-shaped detection coil 32 and the cosine wave-shaped detection coil 33 in the short side direction of the substrate 3 are W _D Buffer area E in the longitudinal direction of substrate 3 ₁ 、E ₂ Width W of (2) ₁ 、W ₂ Preferably (W) _D /W _E )×L ₂ X 0.004 or more.

(action of the Stroke sensor 1)

Next, the operation and effects of the stroke sensor 1 for detecting the position of the target 2 relative to the substrate 3 will be described with reference to fig. 6 to 9. Here, the axial direction of the rack shaft 13 is defined as the X-axis, and the length L of the exciting coil 31 in the longitudinal direction of the substrate 3 is defined as ₁ The X coordinate of the position of the left end in the range of (a) is set to 0, and the X coordinate of the position of the right end is set to 1. The position of the target 2 is indicated by the X coordinate of the center portion in the longitudinal direction of the target 2.

Fig. 6 shows a supply voltage V supplied from the power supply unit 4 to the exciting coil 31 in the case where the X-coordinate of the target 2 is 0.18 ₀ And the induced voltage V induced by the sine-wave-shaped detection coil 32 ₁ Induced voltage V induced by cosine waveform detection coil 33 ₂ A graph of an example of the relationship of (a). The horizontal axis of the graph of FIG. 6 is the time axis, and the left and right vertical axes represent the supply voltage V ₀ Induced voltage V ₁ 、V ₂ . Induced voltage V ₁ The output voltage of the sine wave-shaped detection coil 32 is the induced voltage V ₂ Is the output voltage of the cosine wave-shaped detection coil 33.

In the example shown in fig. 6, the supply voltage V supplied to the exciting coil 31 ₀ Induced voltage V induced by sine wave-shaped detection coil 32 and cosine wave-shaped detection coil 33 ₁ 、V ₂ In phase, but if the X coordinate of the target 2 exceeds 0.5, the induced voltage V induced by the sine wave-shaped detection coil 32 ₁ And the supply voltage V to the exciting coil 31 ₀ Is in opposite phase. In addition, an induced voltage V induced in the cosine waveform-shaped detection coil 33 ₂ The in-phase and the anti-phase are switched every time the target 2 passes through the position where the waveform wire 331 of the second metal layer 302 crosses the waveform wire 333 of the fourth metal layer 304. An alternating voltage of a high frequency, for example, about 1MHz to 1GHz is supplied as a supply voltage V to the exciting coil 31 ₀ 。

Fig. 7 schematically shows the induced voltage V induced by the sine wave-shaped detection coil 32 ₁ Peak value, i.e. peak voltage V _s An explanatory diagram of the relationship with the position of the target 2. FIG. 8 schematically shows the induced voltage V induced by the cosine wave shape detection coil 33 ₂ Peak value, i.e. peak voltage V _c An explanatory diagram of the relationship with the position of the target 2.

The stroke sensor 1 can be used for measuring the length L from the sine wave-shaped detection coil 32 and the cosine wave-shaped detection coil 33 ₂ Subtracting the length L of target 2 ₃ The axial range R ₂ The position of the target 2 is detected internally. In the graphs shown in fig. 7 and 8, the target 2 is located in the axial range R ₂ The X coordinate at the left end of (2) is P ₁ Locating target 2 in axial range R ₂ The X coordinate at the right end of (2) is P ₂ Showing the peak voltage V at each location _s 、V _c . Peak voltage V of sine wave-shaped detection coil 32 _s Induced voltage V induced in sine wave-shaped detection coil 32 ₁ And the voltage V supplied to the exciting coil 31 ₀ Positive in phase and negative in phase. Similarly, peak voltage V of cosine wave shape detection coil 33 _c Induced voltage V induced in cosine waveform detection coil 33 ₂ And the voltage V supplied to the exciting coil 31 ₀ Positive in phase and negative in phase.

Here, if the formula [ 1]]If ωx is defined as such, the X coordinate of target 2 is set to X _p Through [ 2]]And [ 3]]Respectively find peak voltage V _s 、V _c . [ 2]]And [ 3]]Is a predetermined constant.

[ 1]

[ 2]

V _s ＝Asin{ω _x (X _p -W ₁ )}…[2]

[ 3]

V _c ＝Acos{ω _x (X _p -W ₁ )}…[3]

According to [ 2]]Formula [ 3]]Through [ 4]]Determination of the X coordinate X of target 2 _p . That is, the arithmetic unit 5 can be based on the peak voltage V _s 、V _c The X coordinate of the target 2 with respect to the substrate 3 is obtained by calculation.

[ 4]

Fig. 9 is a graph showing the result of evaluating the position detection accuracy of the stroke sensor 1 using electromagnetic field simulation. In the graph, the horizontal axis represents the X coordinate of the target 2, and the vertical axis represents the X coordinate X of the target 2 based on the calculation result _p Is a calculation value of (a). As shown in fig. 9, the stroke sensor 1 can detect the position of the target 2 with high accuracy. However, small errors occur due to the difference in the distance between the first to fourth metal layers 301 to 304 and the target 2 in the substrate 3 and the non-uniformity in the magnetic flux density corresponding to the distance from the long side portions 31a and 31b of the inner portion of the exciting coil 31. However, since this error is not generated accidentally due to vibration or the like, but is generated stably as a detection characteristic, it can be corrected by calculation. That is, the computing unit 5 calculates the X coordinate X of the target 2 obtained by the above-described calculation _p By performing a correction operation according to the detection characteristic, the position of the target 2, that is, the position of the rack shaft 13 can be detected with higher accuracy.

Further, since the substrate 3 is more likely to thermally expand than the rack shaft 13, the X coordinate X of the target 2 obtained by calculation can be also calculated _p Temperature correction is performed on the value of (2). In this case, for example, the arithmetic unit 5 performs a temperature correction operation based on a detection value of a temperature sensor mounted on the substrate 3. This enables more accurate position detection.

(action and Effect of the embodiment)

As described above, in the stroke sensor 1 of the present embodiment, the position of the rack shaft 13 can be detected with high accuracy. In addition, even if the rack shaft 13 is displaced in the vehicle longitudinal direction with respect to the housing 14 due to vibration accompanying running of the vehicle, or the rack shaft 13 is slightly rotated about its central axis, for example, the displacement and rotation have little influence on the detection accuracy of the position. In addition, since the exciting coil 31, the sine-wave-shaped detecting coil 32, and the cosine-wave-shaped detecting coil 33 are formed as wiring patterns on one substrate 3, these coils can be formed at low cost, and the housing 14 can be prevented from being excessively bulky.

(first modification)

Fig. 10 is a plan view of a substrate 3A according to a first modification. In the above-described embodiment, the case where the waveform wire 321 of the first metal layer 301, the waveform wire 331 of the second metal layer 302, the waveform wire 322 of the third metal layer 303, and the waveform wire 333 of the fourth metal layer 304 are sinusoidal has been described, but in the first modification, these waveform wires 321, 331, 322, 333 are triangular. On the substrate 3A, the first detection coil 32A is formed by combining the waveform conductor 321 of the first metal layer 301 and the waveform conductor 322 of the third metal layer 303, and the second detection coil 33A is formed by combining the waveform conductor 331 of the second metal layer 302 and the waveform conductor 333 of the fourth metal layer 304. During the movement of the rack shaft 13 from one end of movement in the axial direction to the other end of movement, the voltages induced in the first and second detection coils 32A, 33A are out of phase by 90 °.

In the case of using the substrate 3A, the position of the target 2 can be detected with high accuracy by the output voltages of the first detection coil 32A and the second detection coil 33A, as in the above-described embodiment.

(second modification)

Fig. 11 is a plan view showing the substrate 3B and the target 2B according to the second modification. In the above-described embodiment, the case where the sine-wave-shaped detection coil 32 and the cosine-wave-shaped detection coil 33 are overlapped in the thickness direction of the substrate 3 has been described, but in the second modification, the sine-wave-shaped detection coil 32B and the cosine-wave-shaped detection coil 33B are formed so as to be aligned in the short side direction of the substrate 3B and not overlapped in the thickness direction of the substrate 3B. The width of the substrate 3B in the short side direction is wider than the substrate 3 of the above embodiment, and the width of the target 2B along the short side direction of the substrate 3B is equal to the width of the substrate 3B or wider than the width of the substrate 3B.

In this substrate 3B, the magnetic field generated due to the current flowing in the sine-wave-shaped detection coil 32B is suppressed from inducing a voltage in the cosine-wave-shaped detection coil 33B, and the magnetic field generated due to the current flowing in the cosine-wave-shaped detection coil 33B is suppressed from inducing a voltage in the sine-wave-shaped detection coil 32B. This enables the position of the target 2B to be detected with higher accuracy.

Further, if the substrate 3B is a two-layer substrate, for example, the waveform wire 331 and the connecting wire 332 of the cosine-waveform detecting coil 33B are formed on the same layer as the waveform wire 321 of the sine-waveform detecting coil 32B, and the waveform wire 333 of the cosine-waveform detecting coil 33B is formed on the same layer as the waveform wire 322 of the sine-waveform detecting coil 32B, the distance between the target 2B and the sine-waveform detecting coil 32B and the cosine-waveform detecting coil 33B can be shortened, and the distance between the target 2B and the sine-waveform detecting coil 32B and the distance between the target 2B and the cosine-waveform detecting coil 33B can be made the same. This enables the position of the target 2B to be detected with further high accuracy.

(third modification)

Fig. 12 is a plan view of a substrate 3C according to a third modification. Fig. 13 (a) to (d) are plan views showing the first to fourth metal layers 301 to 304 of the substrate 3C. In the above-described embodiment, the case where the phase difference of the voltages induced by the sine-wave-shaped detection coil 32 and the cosine-wave-shaped detection coil 33 is 90 ° was described, but in the third modification, the sine-wave-shaped detection coil 32C and the cosine-wave-shaped detection coil 33C whose phase difference is not 90 ° are formed on the substrate 3C. In fig. 12 and (a) to (d) of fig. 13, the case where the phase difference of the voltages induced by the sine wave-shaped detection coil 32C and the cosine wave-shaped detection coil 33C is smaller than 90 ° and 45 ° is shown as an example, but the sine wave-shaped detection coil 32C and the cosine wave-shaped detection coil 33C may be formed so that the phase difference is larger than 90 °.

Even when the substrate 3C is used, the absolute position of the target 2C can be uniquely detected by calculating the position of the target 2C using a predetermined arithmetic expression in the calculating unit 5 based on the output voltages of the sine-wave-shaped detection coil 32C and the cosine-wave-shaped detection coil 33C, as in the above-described embodiment.

(fourth modification)

Fig. 14 (a) is a perspective view showing the target 2D of the fourth modification example together with the rack shaft 13D to which the target 2D is attached. Fig. 14 (b) is a perspective view showing a state in which the target 2D is attached to the rack shaft 13D. Fig. 15 (a) is a cross-sectional view showing a section taken along line B-B of fig. 14 (B) together with the substrate 3 facing the target 2D. Fig. 15 (b) is a cross-sectional view showing a c—c line section of fig. 14 (b) together with the substrate 3 facing the target 2D.

In the above-described embodiment, the case where the target 2 is fixed to the facing surface 13a of the rack shaft 13 and the substrate 3 formed in a planar shape has been described, but in the fourth embodiment, the concave portion 130 is formed in the rack shaft 13D, and a part of the target 2D is buried in the concave portion 130. The recess 130 is defined by a bottom surface 130a and a pair of side surfaces 130b, 130c opposed to each other in the axial direction of the rack shaft 13D with the bottom surface 130a interposed therebetween. The bottom surface 130a is a plane parallel to the substrate 3.

The target 2D is formed in a rectangular parallelepiped shape as in the target 2 of the above embodiment, and is made of a material having a magnetic permeability equal to or higher than that of the rack shaft 13D or a material having a magnetic conductivity equal to or higher than that of the rack shaft 13D, but in this modification, the target 2D is fixed to the rack shaft 13D in a state where a part of the target 2D is embedded in the recess 130. The rack shaft 13D is circular in cross section perpendicular to the axial direction at the front and rear portions in the axial direction of the portion where the recess 130 is formed, as shown in fig. 15 (b).

As shown in fig. 15 (a), the depth D of the recess 130 in the direction perpendicular to the substrate 3 is equal to the thickness T of the target 2D in the direction. However, the thickness T of the target 2D may be thicker than the depth D of the recess 130. In addition, the whole target 2D may be embedded in the concave portion 130. That is, at least a part of the target 2D may be buried in the concave portion 130.

According to this fourth modification, the protruding amount of the target 2D from the concave portion 130 toward the substrate 3 side can be suppressed to 0 (zero) or less while ensuring the thickness of the target 2D. That is, the closest point between the rack shaft 13D and the base plate 3 in the axial direction of the portion where the recess 130 is formed is defined as a point P as shown in fig. 15 (b) ₁ In the case of 2D targeting the target to the point P ₁ The protruding amount on the substrate 3 side is suppressed to 0 (zero) or less. Thereby, space saving of the stroke sensor can be achieved.

In addition, even when a material having a magnetic permeability equal to that of the rack shaft 13D or a material having a conductivity equal to that of the rack shaft 13D is used as the material of the target 2D, the rack shaft 13D has a circular cross-sectional shape before and after the portion where the recess 130 is formed, and the opposing surface 20D of the target 2D opposing the substrate 3 has a planar shape parallel to the substrate 3, so that a difference in magnetic flux density occurs between the portion of the substrate 3 opposing the target 2D and the non-opposing portion. This allows the position of the rack shaft 13D to be detected in the same manner as in the above embodiment. However, in order to improve the detection accuracy of the position, it is preferable to use a high magnetic permeability material having a higher magnetic permeability than the rack shaft 13D or a high electric conductivity material having a higher electric conductivity than the rack shaft 13D as the material of the target 2, as in the above-described embodiment.

(fifth modification)

Fig. 16 (a) to (c) are perspective views showing targets 2E, 2F, and 2G of the fifth modification. Fig. 17 (a) to (c) are cross-sectional views showing the cross-sections of the targets 2E, 2F, 2G together with the substrate 3. In FIGS. 17 (a) - (c), arrow A is used _L Display substrate3 in the longitudinal direction of arrow A _S The short side direction of the substrate 3 is shown. Fig. 17 (a) to (c) show cross sections perpendicular to the longitudinal direction of the substrate 3.

The targets 2E, 2F, 2G are fixed to the rack shaft 13 and disposed to face the substrate 3. The targets 2E, 2F, 2G are made of a material having an electric conductivity equal to that of the rack shaft 13 or higher than that of the rack shaft 13. The opposing surface 20E of the target 2E opposing the substrate 3, the opposing surface 20F of the target 2F opposing the substrate 3, and the opposing surface 20G of the target 2G opposing the substrate 3 are formed in a concave shape so that the distance from the substrate 3 is longest among positions where the central portions of the sine-wave-shaped detection coil 32 and the cosine-wave-shaped detection coil 33 are aligned in the thickness direction of the substrate 3.

As shown in fig. 17 (a), the facing surface 20E of the target 2E facing the substrate 3 has a concave curved surface shape. As shown in fig. 17 (b), the facing surface 20F of the target 2F facing the substrate 3 is a valley shape formed by inclined surfaces 201F, 202F inclined with respect to a direction parallel to the short side direction of the substrate 3. As shown in fig. 17 (c), the facing surface 20G of the target 2G facing the substrate 3 includes a bottom surface 200G parallel to the short side direction of the substrate 3 and inclined surfaces 201G and 202G inclined with respect to the direction parallel to the short side direction of the substrate 3, and an angle θ between the bottom surface 200G and the inclined surfaces 201G and 202G ₁ Is an obtuse angle.

By using the targets 2E, 2F, 2G, the strength of the magnetic field inside the exciting coil 31 of the substrate 3 in the portion facing the targets 2E, 2F, 2G is uniformed, and the induced voltage V induced by the sine-wave-shaped detecting coil 32 ₁ Induced voltage V induced by cosine waveform detection coil 33 ₂ The detection accuracy of the position of (2) is improved. That is, since the facing surfaces 20E, 20F, 20G facing the substrate 3 are concave in the targets 2E, 2F, 2G, the effect of reducing the magnetic flux density, in which the density of the magnetic flux interlinking with the sine wave-shaped detection coil 32 and the cosine wave-shaped detection coil 33 is reduced by the eddy current generated in the targets 2E, 2F, 2G, is reduced in the central portion in the short side direction of the substrate 3, the intensity of the magnetic field inside the excitation coil 31 of the substrate 3 is uniformed, and the detection accuracy of the position is improved.

In fig. 17 (a) to (c), of the opposing surfaces 20E, 20F, 20G of the targets 2E, 2F, 2G, the sine-wave-shaped detection coil 32 and the cosine-wave-shaped detection coil 33 are aligned with the central portion of the substrate 3 in the short-side direction thereof, and the positions P are used in the thickness direction of the substrate 3 ₂₁ The position P is shown where the pair of long side portions 31a and 31b of the exciting coil 31 are aligned in the thickness direction of the substrate 3 ₂₂ 、P ₂₃ And (3) representing. P in the thickness direction of the substrate 3 ₂₁ And P ₂₂ 、P ₂₃ Distance D between ₁ For example 1mm.

(summary of embodiments and modifications)

Next, the technical ideas grasped from the embodiments and the modifications will be described by referring to the reference numerals and the like in the embodiments and the modifications. However, the reference numerals in the following description do not limit the constituent elements in the claims to the components and the like specifically shown in the embodiments and the modifications.

[1] A position detection device (stroke sensor 1) that detects a position of a shaft (rack shafts 13, 13D) that moves forward and backward in an axial direction, wherein the position detection device (stroke sensor 1) includes: a detection body (targets 2, 2A to 2G) mounted on the shafts 13, 13D; an exciting coil 31 that generates an alternating-current magnetic field; and detection coils 32, 33/32A, 33A/32B, 33B/32C, 33C arranged along the axial direction of the shafts 13, 13D, wherein the magnitude of the voltage induced by the detection coils 32, 33/32A, 33A/32B, 33B/32C, 33C is changed according to the positions of the detection bodies 2, 2A-2G.

[2] The position detecting device 1 according to the above [1], wherein the magnitude of the voltage induced by the detecting coils 32, 33/32A, 33A/32B, 33B/32C, 33C is changed within a range of one cycle amount or less during the period in which the shafts 13, 13D are moved from one moving end to the other moving end in the axial direction.

[3]According to [1] above]In the position detecting device 1, the shape of the detecting coils 32, 33/32A, 33A/32B, 33B/32C, 33C as viewed from the direction perpendicular to the axial direction of the shafts 13, 13D is to be sandwiched by the shafts 13,13D with an axially parallel symmetry axis a ₁ ～A ₄ And a symmetrical pair of sinusoidal conductors.

[4] The position detection apparatus 1 according to any one of [1] to [3] above, wherein the position detection apparatus comprises a plurality of detection coils 32, 33/32A, 33A/32B, 33B/32C, and 33C, and the phases of voltages induced by the plurality of detection coils 32, 33/32A, 33A/32B, 33B/32C, and 33C are different from each other during movement of the shafts 13 and 13D from one movement end to the other movement end in the axial direction.

[5] The position detecting device 1 according to the above [4], wherein the exciting coil 31 and the plurality of detecting coils 32, 33/32A, 33A/32B, 33B/32C, 33C are formed on one substrate 3, 3A, 3B, 3C.

[6] The position detecting device 1 according to [5] above, wherein the substrate 3, 3A, 3C is a four-layer substrate in which first to fourth metal layers 301 to 304 are formed in order from the detection body 2, 2A to 2G side, two of the detection coils 32, 33/32A, 33A/32C, 33C are formed on the substrate 3, 3A, 3C, one of the detection coils 32/32A/32C is formed on the first metal layer 301 and the third metal layer 303, and the other of the detection coils 33/33A/33C is formed on the second metal layer 302 and the fourth metal layer 304.

[7] The position detecting device 1 according to the above [5], wherein the exciting coil 31 is formed on the substrate 3, 3A, 3B, 3C so as to surround the plurality of detecting coils 32, 33/32A, 33A/32B, 33B/32C, 33C.

[8]According to [7] above]In the position detecting device 1, the substrate 3 has a rectangular shape with the axial direction of the shaft 13 being a longitudinal direction, and the exciting coil 31 includes: a pair of long side portions 31a, 31b extending in the long side direction of the substrate 3 and sandwiching the plurality of detection coils 32, 33 in the short side direction of the substrate; and a pair of short side portions 31c, 31d extending in the short side direction of the substrate 3 and sandwiching the plurality of detection coils 32, 33 in the long side direction of the substrate 3, each of the pair of short side portions 31c, 31dBuffer areas E are arranged between the detection coils 32 and 33 ₁ 、E ₂ The buffer region suppresses voltages generated in the plurality of detection coils 32 and 33 due to a magnetic field generated by a current flowing through the pair of short side portions 31c and 31 d.

[9]According to [1 ] above]In the position detecting device 1, the length L of the detecting body 2, 2A to 2G in the axial direction of the shafts 13, 13D ₃ The length L2 of the detection coils 32, 33/32A, 33A/32B, 33B/32C, 33C in the axial direction of the shafts 13, 13D is less than 1 per 2.

[10] The position detecting device 1 according to the above [1], wherein the detecting bodies 2, 2A to 2D are made of a material having a magnetic permeability equal to that of the shafts 13, 13D or a magnetic permeability higher than that of the shafts 13, 13D.

[11] The position detecting device 1 according to the above [1], wherein the detecting bodies 2, 2A to 2G are made of a material having an electric conductivity equal to that of the shafts 13, 13D or a higher electric conductivity than that of the shafts 13, 13D.

[12] The position detecting device 1 according to [10] or [11], wherein at least a part of the detection body 2D is embedded in a recess 130 formed in the shaft 13D.

[13] The position detecting device 1 according to the above [7], wherein the substrate 3 has a rectangular shape in which an axial direction of the shaft 13 is a longitudinal direction, and the exciting coil 31 has: a pair of long side portions 31a, 31b extending in the long side direction of the substrate 3 and sandwiching the plurality of detection coils 32, 33 in the short side direction of the substrate 3; and a pair of short side portions 31c, 31d extending in the short side direction of the substrate 3 and sandwiching the plurality of detection coils 32, 33 in the long side direction of the substrate 3, wherein the detection bodies 2E, 2F, 2G are made of a material having an electric conductivity equal to or higher than that of the shaft 13, and the opposed surfaces 20E, 20F, 20G of the detection bodies 2E, 2F, 2G to the substrate are formed in a concave shape so as to have a longest distance from the substrate 3 at positions aligned in the thickness direction of the substrate 3 with respect to the central portions of the detection coils 32, 33 in the short side direction.

[14] The position detecting device 1 according to the above [1], wherein the shafts 13, 13D are rack shafts of a steering device of a vehicle.

The embodiments and modifications of the present invention have been described above, but the embodiments and modifications are not limited to the inventions according to the claims. Note that all combinations of the features described in the embodiments and modifications are not necessarily essential to means for solving the problems of the invention.

The present invention can be implemented by appropriately modifying the present invention within a range not departing from the gist thereof. For example, in the above embodiment, the case where the detection target of the position of the stroke sensor 1 is the rack shaft 13 of the steering device 10 has been described, but the present invention can also be applied to detection of the position of a shaft that moves forward and backward in the axial direction other than the rack shaft 13. In addition, a part of the targets 2E, 2F, 2G of the fifth modification may be embedded in the rack shaft as in the fourth modification.

Symbol description

1-a stroke sensor (position detection device); 13. 13D-rack shaft (shaft); 2. 2A to 2G-targets (detectors); 20a, 20d, 20e, 20f, 20 g-opposing faces; 3. 3A, 3B, 3C, 3D-substrate; 31-an exciting coil; 31a, 31 b-long side portions; 31c, 31 d-short side portions; 32. 32B, 32C-sine wave shaped detection coils; 32A-a first detection coil; 33. 33B, 33C-cosine wave shape detection coils; 33A-a second detection coil; a is that ₁ ～A ₄ -an axis of symmetry; e (E) ₁ 、E ₂ -a buffer area.

Claims

1. A position detecting device detects the position of a shaft which moves forward and backward in the axial direction,

the position detection device is characterized by comprising:

a detection body mounted on the shaft;

an exciting coil that generates an alternating-current magnetic field; and

a detection coil disposed along an axial direction of the shaft,

the magnitude of the voltage induced by the detection coil varies according to the position of the detection body.

2. The position detecting apparatus according to claim 1, wherein,

the magnitude of the voltage induced by the detection coil changes within a range of one cycle amount or less while the shaft moves from one moving end to the other moving end in the axial direction.

3. The position detecting apparatus according to claim 1, wherein,

the shape of the detection coil, as viewed from a direction perpendicular to the axial direction of the shaft, is a shape formed by combining a pair of sinusoidal wires that are symmetrical with each other with a symmetry axis parallel to the axial direction of the shaft interposed therebetween.

4. A position detecting apparatus according to any one of claims 1 to 3, wherein,

the motor is provided with a plurality of detection coils, and the phases of voltages induced by the detection coils are different from each other during the period when the shaft moves from one moving end to the other moving end in the axial direction.

5. The position detecting apparatus according to claim 4, wherein,

the exciting coil and the plurality of detecting coils are formed on one substrate.

6. The position detecting apparatus according to claim 5, wherein,

the substrate is provided with a first metal layer, a second metal layer, a third metal layer and a fourth metal layer in order from the side of the detection body, two detection coils are formed on the substrate,

a part of one of the detection coils is formed in each of the first metal layer and the third metal layer, and a part of the other of the detection coils is formed in each of the second metal layer and the fourth metal layer.

7. The position detecting apparatus according to claim 5, wherein,

the exciting coil is formed on the substrate so as to surround the plurality of detection coils.

8. The position detecting apparatus according to claim 7, wherein,

the substrate has a rectangular shape in which the axial direction of the shaft is a longitudinal direction,

the exciting coil has: a pair of long side portions extending in a long side direction of the substrate and sandwiching the plurality of detection coils in a short side direction of the substrate; and a pair of short side portions extending in a short side direction of the substrate and sandwiching the plurality of detection coils in a long side direction of the substrate,

A buffer region is provided between each of the pair of short side portions and the plurality of detection coils, the buffer region suppressing a voltage generated at the plurality of detection coils by a magnetic field generated by a current flowing through the pair of short side portions.

9. The position detecting apparatus according to claim 1, wherein,

the length of the detection body in the axial direction of the shaft is 1 or less of 2 times the length of the detection coil in the axial direction of the shaft.

10. The position detecting apparatus according to claim 1, wherein,

the detection body is made of a material having a magnetic permeability equal to or higher than that of the shaft.

11. The position detecting apparatus according to claim 1, wherein,

the detection body is made of a material having an electrical conductivity equal to or higher than that of the shaft.

12. The position detecting apparatus according to claim 10 or 11, wherein,

at least a part of the detection body is embedded in a recess formed in the shaft.

13. The position detecting apparatus according to claim 7, wherein,

the detection body is made of a material having an electrical conductivity equal to or higher than that of the shaft,

the opposite surface of the detection body to the substrate is formed in a concave shape so that a distance from the substrate is longest at a position aligned in a thickness direction of the substrate with a central portion of the detection coil in the short side direction.

14. The position detecting apparatus according to claim 1, wherein,

the shaft is a rack shaft of a steering device of a vehicle.