JP2023174533A - position detection device - Google Patents

Abstract

To provide a position detection device that can enhance detection accuracy while suppressing increase in size.SOLUTION: A stroke sensor 1, which serves as a position detection device detecting a position of a shaft 13 back and forth movable in an axial direction, comprises: a target 2 that is fixed to the shaft 13; an exciting coil 31 that generates an AC magnetic field; a power source unit 4 which supplies an AC current to the exciting coil 31; and detection coils 32 and 33 that extend to be arranged along the axial direction of the shaft 13, and with which a magnetic flux of the AC magnetic field the exciting coil 31 generates interlinks. The exciting coil 31 is arranged so as to surround the detection coils 32 and 33. The detection coils 32 and 33, which have distortion-shape curve parts 301a, 302a, 303a, and 304a distorted with respect to a sine wave curve so that a peak value of a voltage to be induced when the shaft 13 moves at a fixed speed along the axial direction varies sinusoidally, are formed.SELECTED DRAWING: Figure 7

Description

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

2. Description of the Related Art Conventionally, a position detection device that detects the position of a shaft that moves forward and backward in an axial direction has been used, for example, to detect the position of a rack shaft in a steering device of a vehicle.

The detection unit described in Patent Document 1 detects the axial position of a rack shaft of an electric power steering device, and includes a DC power source, a permanent magnet, and a second sensor disposed between the permanent magnet and the rack shaft. The device includes an element group consisting of first to fourth magnetoresistive elements and a calculation unit that calculates the position of the rack shaft. In the element group, a series circuit in which first and second magnetoresistive elements are connected in series and a series circuit in which third and fourth magnetoresistive elements are connected in series are connected in parallel to form a bridge circuit. ing. The calculation unit includes a potential of a first terminal connected between the first magnetoresistive element and the second magnetoresistive element, and a potential of the first terminal connected between the third magnetoresistive element and the fourth magnetoresistive element. The potential of the second terminal is input. A plurality of grooves extending in a direction inclined with respect to the axial direction of the rack shaft are formed on the surface of the rack shaft facing the element group.

In the detection unit configured as described above, when the rack shaft moves in the axial direction due to rotation of the pinion gear shaft that meshes with the rack shaft, and the relative positions of the first to fourth magnetic resistance elements and the plurality of grooves change, The balance of electrical resistance of the first to fourth magnetoresistive elements changes, and the potentials of the first terminal and the second terminal change. The calculation section calculates the position of the rack shaft based on this change in potential.

International Publication No. 2021/210125

In the detection unit described in Patent Document 1, when the rack shaft moves in the longitudinal direction of the vehicle or rotates around the central axis due to vibrations caused by the running of the vehicle, for example, the first to fourth magnetic resistance elements and the plurality of magnetic resistance elements The relative position of the rack shaft relative to the groove changes, resulting in an error in the detected position of the rack shaft.

In order to develop a position detection device with high detection accuracy, the present inventors initially developed a detection coil in the shape of a combination of a pair of sinusoidal conductor wires, and a rectangular shape surrounding the detection coil. A printed circuit board having an excitation coil is placed facing the shaft, a detection body having higher magnetic permeability than the shaft is attached to the shaft, and an alternating magnetic field is generated by the excitation coil, and the magnitude of the voltage induced in the detection coil is determined. proposed a position detection device that detects the position of the shaft. However, in this position detection device, there is a detection error due to non-uniformity of magnetic flux density inside the excitation coil. , and the excitation coil needed to be sufficiently larger than the detection coil.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a position detection device that can improve detection accuracy while suppressing increase in size.

In order to solve the above problems, the present invention provides a position detection device that detects the position of a shaft that moves forward and backward in the axial direction, which includes a detection body fixed to the shaft and an excitation coil that generates an alternating magnetic field. a power supply unit that supplies an alternating current to the excitation coil; and a detection coil that is arranged to extend along the axial direction of the shaft and interlinked with the magnetic flux of the alternating magnetic field, the excitation coil , the detection coil is arranged so as to surround the detection coil, and the detection coil is arranged so that the peak value of the voltage induced in the detection coil changes in a sinusoidal manner when the shaft moves at a constant speed along the axial direction. Another aspect of the present invention provides a position detection device formed with a curved portion having a distorted shape with respect to a sinusoidal curve.

According to the position detection device according to the present invention, it is possible to increase the detection accuracy while suppressing the enlargement of the excitation coil.

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. 2 is a cross-sectional view of the rack shaft, housing, target, and substrate taken along line AA in FIG. 1. FIG. FIG. 3 is a perspective view showing the rack shaft, the main body of the housing, the target, and the substrate. (a) is an overall view of the wiring patterns formed on the first to fourth metal layers of the substrate, seen through from the front side. (b) is a partially enlarged view of (a). (a) to (d) are plan views showing the first to fourth metal layers, respectively, viewed from the front side. (a) is a graph showing the distribution of magnetic flux density inside the excitation coil in the substrate. (b) is a graph showing the distribution of magnetic flux density in the longitudinal direction along the central axis of the substrate. (c) is a graph showing the distribution of magnetic flux density in the transverse direction at the center in the longitudinal direction of the substrate. FIG. 2 is a schematic diagram schematically showing the shapes of a sine wave shape detection coil and a cosine wave shape detection coil according to the present embodiment with different scales in the longitudinal direction and the width direction of the substrate. FIG. 7 is a schematic diagram showing the shapes of a regular sine wave shape detection coil and a regular cosine wave shape detection coil shown as a comparative example. (a) is an enlarged view of part a in FIG. 7, and (b) is an enlarged view of part b in FIG. 8. It is a graph showing the relationship between the supply voltage supplied from the power supply unit to the excitation coil, the induced voltage induced in the sine wave shape detection coil, and the induced voltage induced in the cosine wave shape detection coil. FIG. 2 is an explanatory diagram schematically showing the relationship between a peak voltage, which is a peak value of an induced voltage induced in a sinusoidal waveform detection coil, and a target position. FIG. 2 is an explanatory diagram schematically showing the relationship between a peak voltage, which is a peak value of an induced voltage induced in a cosine wave shape detection coil, and a target position. It is a graph showing the result of evaluating the target position detection accuracy. 7 is a graph showing the results of evaluating the detection error of the target position. FIG. 7 is a schematic diagram showing the shapes of a sine wave shape detection coil and a cosine wave shape detection coil according to a modification. FIG. 7 is a schematic diagram showing the shapes of a sine wave shape detection coil and a cosine wave shape detection coil according to a modification. FIG. 7 is an exploded perspective view showing a configuration example of a target according to a modified example together with a shaft, a substrate, and a housing.

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

As shown in FIG. 1, the steering device 10 accommodates a stroke sensor 1, a tie rod 12 connected to steered wheels 11 (left and right front wheels), a rack shaft 13 connected to the tie rod 12, and a rack shaft 13. A cylindrical housing 14, a worm reduction mechanism 15 having a pinion gear 151 meshed with the rack teeth 131 of the rack shaft 13, and an electric motor 16 that applies an axial movement force 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 that controls the electric motor 16 based on the steering angle detected by the steering angle sensor 18. It is equipped with 19.

In FIG. 1, the housing 14 is shown in phantom lines. The rack shaft 13 is made of a steel material such as carbon steel, and is supported by a pair of rack bushes 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. Worm gear 153 is fixed to motor shaft 161 of electric motor 16.

The electric motor 16 generates torque using a motor current supplied from the steering control device 19 and rotates a worm wheel 152 and a pinion gear 151 via a worm gear 153 . When the pinion gear 151 rotates, the rack shaft 13 moves forward and backward in its axial direction, and the left and right steered 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 range _R1 within which the rack shaft 13 can move in the axial direction is indicated by double-headed arrows.

(Configuration 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 section 4, and a calculation section 5. The board 3 is fixed in the housing 14 parallel to the rack shaft 13. The stroke sensor 1 detects the position of the rack shaft 13 with respect to the housing 14 based on the position of the target 2, and outputs information on 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 becomes a position corresponding to the steering angle of the steering wheel 17 detected by the steering angle sensor 18.

FIG. 2 is a cross-sectional view of the rack shaft 13, housing 14, target 2, and substrate 3 taken along line AA in FIG. FIG. 3 is a perspective view showing the rack shaft 13, the main body 141 of the housing 14, the target 2, and the substrate 3.

The rack shaft 13 is a rod-shaped body made of steel and having a circular cross section. The housing 14 has a main body 141 made of metal and a lid 142 made of resin, and the lid 142 is fixed to the main body 141 by, for example, adhesive. 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 upward in the vertical direction. The diameter D of the rack shaft 13 is, for example, 25 mm.

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 housing space 140. The lid body 142 is formed in a flat plate shape and covers the upper part of the accommodation space 140 in the vertical direction. The main body 141 is a non-magnetic material, and is made of die-cast aluminum alloy, for example. Note that the material for the lid body 142 is not necessarily limited to resin, but it is desirable to use a non-magnetic and non-conductive material.

The target 2 is one aspect of the detection object of the present invention, and is an object for detecting the position of the rack shaft 13. The target 2 is made of a material with higher magnetic permeability than the rack shaft 13 or a material with higher electrical conductivity than the rack shaft 13. When a material with higher magnetic permeability than the rack shaft 13 is used for the target 2, a magnetic material such as ferrite can be used as the material. Further, when a material having higher conductivity than the rack shaft 13 is used for the target 2, a metal whose main component is aluminum or copper, for example, can be used as the material.

In this embodiment, since the target 2 is provided so as to protrude from the outer peripheral surface 13a of the rack shaft 13 toward the substrate 3, it is made of a material that has the same magnetic permeability as the rack shaft 13 or is conductive with the rack shaft 13. Even if materials with the same ratio are used as the material of the target 2, the functions and effects described below can be obtained. However, in order to improve the position detection accuracy, it is necessary to use a high magnetic permeability material that has higher magnetic permeability than the material of the rack shaft 13, or a high conductivity material that has the same electrical conductivity as the material of the rack shaft 13, or the material of the target 2. It is desirable to use it as

The target 2 is fixed to the upper part of the rack shaft 13 by a fixing means such as adhesive or welding. A facing surface 2a of the target 2 facing the substrate 3 is formed into a planar shape. The opposing surface 2a of the target 2 faces the front surface 3a of the substrate 3 in parallel with an air gap G interposed therebetween. The back surface 3b of the substrate 3 is fixed to the lid 142 with an adhesive 300. The shape of the opposing surface 2a viewed from the substrate 3 side is a rectangle with the axial direction of the rack shaft 13 being the long side direction.

The width _W1 of the air gap G is, for example, 1 mm. The minimum thickness T of the target 2 in the direction perpendicular to the opposing surface 2a is, for example, 5 mm. In this embodiment, the rack shaft 13 is formed to have a circular cross-section, but the cross-sectional shape of the rack shaft 13 is not limited to the circular shape, and may be, for example, a D-shape with a portion formed linearly, or a polygonal shape. It may be a shape.

The substrate 3 has a flat base material 30 made of a dielectric material such as FR4 (glass fiber impregnated with epoxy resin and subjected to thermosetting treatment) between the first to fourth metal layers 301 to 304. This is a four-layer board. The thickness of each base material 30 is, for example, 0.3 mm. The thickness of each of the first to fourth metal layers 301 to 304 is, for example, 18 μm. The substrate 3 has a flat rectangular shape whose longitudinal direction is the axial direction of the rack shaft 13. The width W ₃ of the substrate 3 in the lateral direction is shorter than the diameter D of the rack shaft 13, and is, for example, 20 mm. The width W ₂ of the target 2 in the direction parallel to the lateral direction of the substrate 3 is equal to or wider than the width W ₃ of the substrate ₃ in the lateral direction.

FIG. 4(a) is an overall view of the wiring patterns formed on the first to fourth metal layers 301 to 304 of the substrate 3 seen through from the surface 3a side. FIG. 4(b) is a partially enlarged view of FIG. 4(a). FIGS. 5A to 5D are plan views showing the first to fourth metal layers 301 to 304, respectively, viewed from the surface 3a side. Note that the wiring patterns shown in FIGS. 4(a) and 4(b) and FIGS. 5(a) to 5(d) are merely examples, and various wiring patterns may be used as long as the substrate 3 is formed so as to obtain the effects of the present invention. It is possible to adopt various types of wiring patterns.

4(a) and (b) and FIGS. 5(a) to (d), the wiring pattern of the first metal layer 301 is shown as a solid line, the wiring pattern of the second metal layer 302 is shown as a broken line, and the wiring pattern of the third metal layer 301 is shown as a broken line. The wiring pattern of the metal layer 303 is shown by a chain line, and the wiring pattern of the fourth metal layer 304 is shown by a chain double-dot line. In addition, in FIG. 4(a), the central axis C that bisects the board 3 in the transverse direction and extends in the longitudinal direction is shown as a gray straight line, and the stroke sensor 1 can detect the absolute position of the rack shaft 13. The position of the target 2 when the rack shaft 13 is located at one end and the other end of the range is shown by a dotted line. Note that, as shown in FIG. 2, the substrate 3 and the target 2 overlap in the diametrical direction of the rack shaft 13, but in FIG. It shows.

A connector portion 340 having first through sixth through holes 341 to 346, through which the connector pins of the connector 7 shown by the two-dot chain lines in FIG. 4(b) are inserted, is provided at one end in the longitudinal direction of the board 3. ing. The first to sixth through holes 341 to 346 are arranged in a straight line along the width direction of the substrate 3. A connector 81 (see FIG. 1) of a cable 8 for connection with the power supply section 4 and the calculation section 5 is connected to the connector 7. Furthermore, first to third vias 351 to 353 are formed in the substrate 3 for interlayer connection of wiring patterns.

The first metal layer 301 includes a first curved section 301a, a first connector connection section 301b that connects one end of the first curved section 301a to a second through hole 342, and a second connector connection section 301b, which will be described later. An end connecting portion 301c is formed to connect the respective ends of the curved portion 302a and the fourth curved portion 304a. The second metal layer 302 is formed with a second curved portion 302a and a second connector connection portion 302b that connects one end of the second curved portion 302a to the fourth through hole 344. The third metal layer 303 is formed with a third curved portion 303a and a third connector connection portion 303b that connects one end of the third curved portion 303a to the third through hole 343. The fourth metal layer 304 is formed with a fourth curved portion 304a and a fourth connector connection portion 304b that connects one end of the fourth curved portion 304a to the fifth through hole 345.

The first curved portion 301a and the third curved portion 303a are connected at their other ends by a first via 351. The end connecting portion 301c has one end connected to the other end of the second curved portion 302a by the second via 352, and the other end connected to the other end of the fourth curved portion 304a and the third via 352. via 353.

The first to fourth curved portions 301a, 302a, 303a, and 304a are curved in a substantially sinusoidal shape. The first curved section 301a, the third curved section 303a, and the second curved section 302a, and the fourth curved section 304a have a symmetrical shape with respect to the central axis C of the substrate 3 as an axis of symmetry. It is.

The substrate 3 includes an excitation coil 31 that generates an alternating current magnetic field, and two detection coils 32 and 33 to which the magnetic flux of the magnetic field generated by the excitation coil 31 interlinks. The excitation coil 31 is supplied with a sinusoidal alternating current from the power supply section 4 . Among the two detection coils 32 and 33, one detection coil 32 is formed by a first curved part 301a and a third curved part 303a, and the other detection coil 33 is formed by a second curved part 302a and a fourth curved part 302a. It is formed by a curved portion 304a and an end connecting portion 301c.

The excitation coil 31 has a rectangular shape having a pair of long sides 311 and 312 extending in the axial direction of the rack shaft 13 and a pair of short sides 313 and 314 between the pair of long sides 311 and 312. , are arranged so as to surround the detection coils 32 and 33. In this embodiment, long side portions 311 and 312 and short side portions 313 and 314 are formed as a wiring pattern on first metal layer 301. Of the pair of short sides 313, 314, the short side 313 on the connector part 340 side is composed of two straight parts 313a, 313b sandwiching the first to fourth connector connecting parts 301b, 302b, 303b, 304b, Ends of the two straight portions 313a and 313b are connected to the first through hole 341 and the sixth through hole 346 by connector connecting portions 301d and 301e formed in the first metal layer 301, respectively.

Note that the excitation coil 31 is not limited to the first metal layer 301, but may be formed in any of the second to fourth metal layers 302 to 304, or may be formed over multiple layers. Further, an excitation coil may be formed separately from the substrate 3.

An induced voltage is generated in the detection coils 32 and 33 due to interlinkage of the magnetic flux of the magnetic field generated by the excitation coil 31. When the target 2 is made of a material with higher magnetic permeability than the rack shaft 13, magnetic flux flows in a concentrated manner through the target 2, and the magnetic flux density of the portion of the substrate 3 facing the target 2 becomes higher than that of other portions. In addition, when the target 2 is made of a material with higher conductivity than the rack shaft 13, the density of the magnetic flux linking the detection coils 32 and 33 decreases due to the eddy current generated in the target 2 by the alternating magnetic field, and the The magnetic flux density of the portion facing 2 is lower than that of the other portion. Therefore, the magnitude of the voltage induced in the detection coils 32 and 33 changes depending on the position of the target 2 with respect to the substrate 3. Note that when using a material for the target 2 that has higher magnetic permeability than the rack shaft 13, it is desirable to use a magnetic material that has high electrical resistance and is less likely to generate eddy currents.

In this embodiment, the length of the target 2 in the axial direction of the rack shaft 13 is shorter than half the length of the detection coils 32 and 33 in the longitudinal direction of the substrate 3. A voltage having the same cycle as the alternating current supplied from the power supply unit 4 to the excitation coil 31 is induced in the detection coils 32 and 33, and the peak value of this induced voltage changes depending on the position of the target 2. Note that the peak value of the voltage herein refers to the maximum value of the absolute value of the voltage within a period of one cycle of the alternating current supplied to the excitation coil 31.

The phases of the voltages induced in each of the detection coils 32 and 33 are different from each other while the rack shaft 13 moves from one moving end to the other moving end in the axial direction. In this embodiment, the phases of the voltages induced in the detection coils 32 and 33 differ by 90°. Hereinafter, among the two detection coils 32 and 33, one detection coil 32 will be referred to as a sine wave shape detection coil 32, and the other detection coil 33 will be referred to as a cosine wave shape detection coil 33.

The peak value of the voltage induced in the sine wave shape detection coil 32 and the cosine wave shape detection coil 33 due to the interlinkage of the magnetic flux of the target 2 is the peak value of the voltage induced in the sine wave shape detection coil 32 and the cosine wave shape detection coil 33 from one end of the movement of the rack shaft 13 in the axial direction to the other end of the movement of the rack shaft 13 in the axial direction. While moving, it changes within a range of one cycle or less. Thereby, the stroke sensor 1 can detect the absolute position of the rack shaft 13 over the entire range _R1 in which the rack shaft 13 can move in the axial direction.

As shown in FIG. 4A, between each of the pair of short sides 313 and 314 of the excitation coil 31 and the sine wave shape detection coil 32 and the cosine wave shape detection coil 33, a pair of short side parts 313 and 314 are provided. , 314 are provided. First and second buffer regions E 1 and E 2 are provided to suppress the voltage induced in the sine wave shape detection coil 32 and the cosine wave shape detection coil 33 by the magnetic flux generated by the current flowing through the sine wave shape detection coil ₃₂ and the cosine wave shape detection coil ₃₃ . In the example shown in FIG. 4A, the length L ₁ of the first buffer region E ₁ and the length L 2 of the second buffer region E ₂ in the longitudinal direction of the substrate ₃ are the same, but L ₁ and _L2 may be different.

Incidentally, the magnetic flux density inside the excitation coil 31 generated by the alternating current supplied from the power supply section 4 is not uniform, and varies depending on the location. This non-uniformity of magnetic flux density causes a detection error in the position of the rack shaft 13. Below, the magnetic flux density inside the excitation coil 31 will be explained, and the respective shapes of the sine wave shape detection coil 32 and the cosine wave shape detection coil 33 for reducing detection errors due to non-uniformity of the magnetic flux density, and this. The effect of reducing detection errors due to shape will be explained.

FIG. 6A is a graph showing the distribution of magnetic flux density inside the excitation coil 31 in the substrate 3. FIG. FIG. 6(b) is a graph showing the distribution of magnetic flux density in the longitudinal direction along the central axis C of the substrate 3. FIG. FIG. 6(c) is a graph showing the distribution of magnetic flux density in the transverse direction at the central portion in the longitudinal direction of the substrate 3. FIG. In FIGS. 6(a) to 6(c), the vertical axis represents the magnetic flux density in decibels (dB). In addition, in FIGS. 6(a) to 6(c) and FIGS. 7 and 8, which will be described later, the point O shown in FIG. 4(a) is the origin, the longitudinal position of the substrate 3 is indicated by X (mm), and The position of No. 3 in the lateral direction is indicated by Y (mm). The maximum value of X (the length of the long sides 311, 312 of the excitation coil 31) is 250 mm, and the maximum value of Y (the length of the short sides 313, 314 of the excitation coil 31) is 18 mm. Point O is the intersection of the long side 312 and short side 313 of the excitation coil 31.

As shown in FIGS. 6(a) to 6(c), inside the excitation coil 31, the magnetic flux density is high near the long sides 311, 312 and the short sides 313, 314, and the closer the center of the excitation coil 31, the more the magnetic flux. The density is lower.

FIG. 7 is a schematic diagram schematically showing the shapes of the sine wave shape detection coil 32 and the cosine wave shape detection coil 33 according to the present embodiment with different scales in the longitudinal direction and the lateral direction of the substrate 3. The first curved portion 301a and the third curved portion 303a that constitute the sinusoidal shape detection coil 32 are induced in the sinusoidal shape detection coil 32 when the rack shaft 13 moves at a constant speed along the axial direction. It has a distorted shape with respect to a sinusoidal curve so that the peak value of the voltage varies sinusoidally. Further, the second curved portion 302a and the fourth curved portion 304a that constitute the cosine wave shape detection coil 33 are connected to the cosine wave shape detection coil 33 when the rack shaft 13 moves at a constant speed along the axial direction. The distortion shape is distorted with respect to the sine wave curve so that the peak value of the induced voltage changes into a sine wave shape (cosine wave shape) whose phase is 90° different from the voltage induced in the sine wave shape detection coil 32. have.

FIG. 8 is a schematic diagram showing the shapes of a regular sine wave shape detection coil 36 and a regular cosine wave shape detection coil 37 shown as a comparative example. The regular sine wave shape detection coil 36 is composed of a pair of curved portions 361 and 362 having a sine wave shape without distortion. The regular cosine wave shape detection coil 37 is composed of a pair of curved portions 371 and 372 that have an undistorted sine wave shape and have a phase difference of 90 degrees from the pair of curved portions 361 and 362 of the regular sine wave shape detection coil 36. . In FIGS. 7 and 8, L ₁ and L ₂ are 10 mm.

In FIG. 7, the shapes of the curved portions 361 and 362 of the regular sine wave shape detection coil 36 and the shapes of the curved portions 371 and 372 of the regular cosine wave shape detection coil 37 are compared to the shapes of the sine wave shape detection coil 32 and the cosine wave shape detection coil. 33 is shown as a gray curve. The dimensional difference ΔY ₁ between the shape of the sine wave shape detection coil 32 and the shape of the regular sine wave shape detection coil 36 in the lateral direction of the substrate 3 is the amount of distortion of the sine wave shape detection coil 32 with respect to the sine wave curve. The dimensional difference ΔY ₂ between the shape of the cosine wave shape detection coil 33 and the shape of the regular cosine wave shape detection coil 37 in the transverse direction of the substrate 3 is the amount of distortion of the cosine wave shape detection coil 33 with respect to the sine wave curve. The amount of distortion of the sine wave shape detection coil 32 and the cosine wave shape detection coil 33 increases as the position is closer to the excitation coil 31 in both the longitudinal direction and the lateral direction of the substrate 3.

As shown in FIG. 7, the sinusoidal waveform detection coil 32 has a minimum coil width near both ends and near the center of the excitation coil 31 in the long side direction. The cosine wave shape detection coil 33 has a maximum coil width near both ends and near the center of the excitation coil 31 in the long side direction. Here, the coil width of the sine wave shape detection coil 32 is the distance between the first curved part 301a and the third curved part 303a in the short side direction of the excitation coil 31, and The coil width is the distance between the second curved portion 302a and the fourth curved portion 304a in the short side direction of the excitation coil 31.

Further, as shown in FIG. 7, the maximum values W ₃₃₁ and W _{332 of the coil width of the cosine wave shape detection coil 33 near both ends of the excitation coil 31 in the long side direction are different from the maximum values W 331 and W 332} of the coil width at the center of the excitation coil 31 in the long side direction. It is smaller than the local maximum value W ₃₃₃ of the coil width of the cosine wave shape detection coil 33 in the vicinity. This is because the cosine wave shape detection coil 33 is close to the short sides 313 and 314 of the excitation coil 31 near both ends of the excitation coil 31 in the long side direction. The maximum value W ₃₃₃ of the coil width in the cosine wave shape detection coil 33 is, for example, 10 mm.

Next, a method for setting the shapes of the sine wave shape detection coil 32 and the cosine wave shape detection coil 33 will be explained with reference to FIGS. 9(a) and 9(b). 9(a) is an enlarged view showing the periphery of the fourth curved portion 304a in section a of FIG. 7, and FIG. 9(b) is an enlarged view showing the periphery of the curved portion 372 in section b of FIG. It is an enlarged view shown in enlarged form. Further, in FIG. 9A, the magnetic flux density generated by the current flowing through the excitation coil 31 is represented by light and shade of color, and the darker the color, the higher the magnetic flux density. FIG. 9(b) shows a case where the magnetic flux density is uniform. It is assumed that the magnetic flux density at the center of the excitation coil 31 is the same in FIGS. 9(a) and 9(b). That is, in FIG. 9(a), the magnetic flux density increases as it approaches the long side 311 of the exciting coil 31 from the center of the exciting coil 31, and in FIG. 9(b), the magnetic flux density increases from the center of the exciting coil 31 to A case is shown in which the magnetic flux density up to the long side portion 311 is constant.

In this example, a minute section ΔX in the transverse direction of the excitation coil 31 is assumed, and the integral value of the magnetic flux density from the central axis C to the fourth curved portion 304a in this minute section ΔX is the magnetic flux inside the excitation coil 31. The position of the fourth curved portion 304a in the minute section ΔX is determined so that it is the same as the integral value from the central axis C to the curved portion 372 when the density is uniform. This arithmetic processing is performed for each minute period in the long side direction of the exciting coil 31 to determine the shape of the fourth curved portion 304a. Further, similar arithmetic processing is performed on the first to third curved portions 301a, 302a, and 303a to set the shapes of the sine wave shape detection coil 32 and the cosine wave shape detection coil 33.

In other words, the shapes of the curved portions 361 and 362 of the regular sine wave shape detection coil 36 are functions of x, y ₁ (x) and y ₂ (x), and the first and third curve portions of the sine wave shape detection coil 32 are The shapes of the curved portions 301a and 303a are functions of x, z ₁ (x) and z ₂ (x), and the magnetic flux density is Bs when the magnetic flux density is uniform, and when the magnetic flux density is non-uniform, When the actual magnetic flux density inside the excitation coil 31 is B (B changes depending on the position (y) in the short direction of the excitation coil 31), the value of Ds obtained by the following formula [1] is sufficiently small. The shape of the sine wave shape detection coil 32 is determined by searching for z ₁ (x) and z ₂ (x).

Further, the shapes of the curved portions 371 and 372 of the regular cosine wave shape detection coil 37 are functions of x, y ₃ (x) and y ₄ (x), and the second and fourth curve portions of the cosine wave shape detection coil 33 are When the respective shapes of the curved portions 302a and 304a are defined as z _{3 (} x) and z ₄ (x), which are functions of x) and z ₄ (x) to determine the shape of the cosine wave shape detection coil 33.

Note that z ₁ (x), z ₂ (x), z ₃ (x), and z ₄ (x) may be derived from equations [1] and [2] by arithmetic operations with Ds and Dc = 0. . Furthermore, since the first curved section 301a and the third curved section 303a have symmetrical shapes, if the shape is set for either the first curved section 301a or the third curved section 303a, the shape can be reversed. to set the shape of the other. Similarly, if the shape of either the second curved portion 302a or the fourth curved portion 304a is set, that shape can be reversed and the shape of the other can be set.

(Operation of stroke sensor 1)
Next, the operation and effect of the stroke sensor 1 for detecting the position of the target 2 with respect to the substrate 3 will be explained with reference to FIGS. 10 to 14. In the following description, the position of the target 2 refers to the position of the center of the target 2 in the longitudinal direction of the substrate 3.

FIG. 10 shows that when the target 2 is located near the position of X=50 mm in the longitudinal direction of the substrate 3, the supply voltage V ₀ supplied from the power supply section 4 to the excitation coil 31 and the voltage induced in the sine wave shape detection coil 32 are shown. 2 is a graph showing the relationship between the induced voltage V ₁ induced in the cosine wave shape detection coil 33 and the induced voltage V ₂ induced in the cosine wave shape detection coil 33 . The horizontal axis of the graph in FIG. 10 is the time axis, and the left and right vertical axes indicate the supply voltage V ₀ and the induced voltages V ₁ and V ₂ .

In the example shown in FIG. 10, the supply voltage V ₀ supplied to the excitation coil 31 and the induced voltages V ₁ and V ₂ induced in the sine wave shape detection coil 32 and the cosine wave shape detection coil 33 are in phase. , when the position of the target 2 in the longitudinal direction of the substrate ₃ is on the right side of X=125 mm in FIG _. The phase is reversed. Further, the induced voltage V ₂ induced in the cosine wave shape detection coil 33 changes between in-phase and anti-phase every time the target 2 passes a position where the second curved part 302a and the fourth curved part 304a cross. Switch. The excitation coil 31 is supplied with a high-frequency alternating current voltage of, for example, about 1 MHz to 1 GHz as a supply voltage V ₀ .

FIG. 11 is an explanatory diagram schematically showing the relationship between the peak voltage Vs, which is the peak value of the induced voltage V ₁ induced in the sine wave shape detection coil 32, and the position of the target 2. FIG. 12 is an explanatory diagram schematically showing the relationship between the peak voltage Vc, which is the peak value of the induced voltage V ₂ induced in the cosine wave shape detection coil 33, and the position of the target 2. In the graphs of peak voltages Vs and Vc shown in FIGS. 11 and 12, the position of the target 2 is shown on the horizontal axis.

The stroke sensor 1 has an axial range R 2 that is calculated by subtracting the length L ₄ of the target 2 in the same direction from the length L ₃ of the sine wave shape detection coil 32 and the cosine wave shape detection coil 33 in the longitudinal direction of the substrate ₃ , The absolute position of the target 2 can be detected. In the graphs shown in FIGS. 11 and 12, the horizontal axis coordinate when the target 2 is at one end of the axial range _R2 (the end on the connector part 340 side) is _P1 , and the target 2 is at the axial range R2. Peak voltages Vs and Vc at each position are shown with the horizontal axis coordinate at the other end of _R2 being _P2 .

Furthermore, in the graphs shown in FIGS. 11 and 12, the peak voltage Vs of the sine wave shape detection coil 32 is the same as the induced voltage V ₁ induced in the sine wave shape detection coil 32 and the voltage V ₀ supplied to the excitation coil 31. When they are in phase, it is a positive value, and when they are out of phase, it is a negative value. Similarly, the peak voltage Vc of the cosine wave shape detection coil 33 is a positive value when the induced voltage _V2 induced in the cosine wave shape detection coil 33 is in phase with the voltage _V0 supplied to the excitation coil 31, When the phase is reversed, the value is negative.

式［４］及び［５］より、図１１及び図１２に示すグラフにおけるターゲット２の座標値Ｘｐは、式［６］によって求められる。つまり、演算部５は、ピーク電圧Ｖｓ，Ｖｃに基づいて、ターゲット２の位置を演算によって求めることができる。

Here, if ωx is defined as in equation [3], the peak voltages Vs and Vc are calculated by equations [4] and [5], where Xp is the coordinate value of the horizontal axis of target 2 in the graph shown in FIG. Each is required. Note that A in equations [4] and [5] is a predetermined constant.

From equations [4] and [5], the coordinate value Xp of target 2 in the graphs shown in FIGS. 11 and 12 is determined by equation [6]. That is, the calculation unit 5 can calculate the position of the target 2 based on the peak voltages Vs and Vc.

13 and 14 show cases in which a sine wave shape detection coil 32 and a cosine wave shape detection coil 33 having the shapes shown in FIG. 7 is a graph showing the results of evaluating the position detection accuracy of the target 2 using electromagnetic field simulation in the case where the detection coil 37 is used. In the graphs of FIGS. 13 and 14, the horizontal axis indicates the actual position of the target 2. The vertical axis of the graph in FIG. 13 indicates the position of target 2 based on the above calculation result. Further, the vertical axis of the graph in FIG. 14 indicates the ratio of the detection error of the position of the target 2 to the total length of the axial range _R2 in which the position of the target 2 can be detected.

As shown in FIGS. 13 and 14, when using the sine wave shape detection coil 32 and the cosine wave shape detection coil 33 of the present embodiment shown in FIG. 7, the normal shape of the shape shown in FIG. 8 according to the comparative example is The position of the target 2 can be detected with higher accuracy than when the sine wave shape detection coil 36 and the regular cosine wave shape detection coil 37 are used. In the graph shown in FIG. 14 when using the sine wave shape detection coil 32 and the cosine wave shape detection coil 33 of this embodiment, the maximum value of the detection error ratio in the positive direction is 0.05%, and The maximum value of the detection error rate is -0.10%. That is, in this embodiment, the magnitude of the detection error is suppressed to 0.10% or less.

(Actions and effects of embodiments)
As described above, the stroke sensor 1 according to the present embodiment can detect the position of the rack shaft 13 with high accuracy. In addition, in the stroke sensor 1 according to the present embodiment, the first to fourth curves have a distorted shape that is distorted with respect to the sine wave curve so as to suppress the influence of non-uniformity of magnetic flux density inside the excitation coil 31. By using the sine wave shape detection coil 32 and the cosine wave shape detection coil 33 having the sections 301a, 302a, 303a, and 304a, it is possible to increase the detection accuracy while suppressing the enlargement of the excitation coil 31.

(Modified example of sine wave shape detection coil 32 and cosine wave shape detection coil 33)
15 and 16 show the sine wave shape detection coil 32 and the cosine wave shape detection coil ₃₃ when the length L ₁ of the first buffer region E ₁ and the length L ₂ of the second buffer region E 2 are changed. An example of the shape is shown. FIG. 15 shows the optimum shapes of the sine wave shape detection coil 32 and the cosine wave shape detection coil 33 when L ₁ and L ₂ are 3 mm. FIG. 16 shows the optimal shapes of the sine wave shape detection coil 32 and the cosine wave shape detection coil 33 when L ₁ and L ₂ are 1 mm. These modifications also provide the same effects as above.

(Modified example of target 2)
FIG. 17 is an exploded perspective view showing a configuration example of a target 2A according to a modified example together with a shaft 13, a substrate 3, and a housing 14. In the above embodiment, the target 2 is arranged so as to protrude from the outer peripheral surface 13a of the shaft 13 toward the substrate 3 side, and the portion facing the target 2 is caused by the eddy current generated in the target 2 by the alternating magnetic field of the excitation coil 31. A case has been described in which the stroke sensor 1 is configured such that the density of magnetic flux interlinking with the detection coils 32 and 33 is low. In the modification shown in FIG. 17, the length of the target 2A in the axial direction of the shaft 13 is longer than the sine wave shape detection coil 32 and the cosine wave shape detection coil 33, and a recess 20 is formed in the target 2A. The recess 20 is formed by being depressed in a direction perpendicular to the substrate 3 from the surface 2a of the target 2A facing the substrate 3.

The recess 20 is formed along the lateral direction of the substrate 3 so as to cross between both side surfaces 2b and 2c of the target 2A. The bottom surface 20a of the recess 20 is a plane parallel to the opposing surface 2a, and both end surfaces 20b and 20c of the recess 20 face each other along the axial direction of the rack shaft 13 with the bottom surface 20a in between. The depth of the recess 20 in the direction perpendicular to the opposing surface 2a is, for example, 5 mm. The target 2A is made of a material having a higher magnetic permeability than the rack shaft 13 or a material having a higher conductivity than the rack shaft 13, like the target 2 in the above embodiment.

While the rack shaft 13 moves from one moving end to the other moving end in the axial direction, the bottom surface 20a of the recess 20 always faces the surface 3a of the substrate 3, and the area other than the part where the recess 20 is formed faces the target 2A. Surface 2a faces surface 3a of substrate 3. When the ratio of the length of the recess 20 in the axial direction of the rack shaft 13 to the length _L3 of the sine wave shape detection coil 32 and the cosine wave shape detection coil 33 is u, the calculation unit 5 calculates (1-u)L. The position of the rack shaft 13 can be determined within a length range of ₃ . The length of the detection target 2 in the axial direction of the rack shaft 13 is 2(1-u) _L3 or more.

Even when the target 2A according to this modification is used, the magnitude of the voltage induced in the sine wave shape detection coil 32 and the cosine wave shape detection coil 33 changes depending on the position of the target 2 with respect to the substrate 3, and the above-mentioned As in the embodiment, the position of the target 2 can be determined by calculation.

(Summary of embodiments)
Next, technical ideas understood from the embodiments described above will be described using reference numerals and the like in the embodiments. However, each reference numeral in the following description does not limit the constituent elements in the scope of the claims to those specifically shown in the embodiments.

[1] A position detection device (1) that detects the position of a shaft (13) that moves forward and backward in the axial direction, which detects a detection body (targets 2, 2A) fixed to the shaft (13) and an alternating magnetic field. An excitation coil (31) that generates an alternating current, a power supply section (4) that supplies an alternating current to the excitation coil (31), and a power supply unit (4) that is arranged to extend along the axial direction of the shaft (13), and that generates an alternating current magnetic field. Detection coils (32, 33) interlinked with magnetic flux, the excitation coil (31) being arranged to surround the detection coil (32, 33), and the detection coil (32, 33) comprising: relative to a sinusoidal curve so that the peak value of the voltage induced in the detection coil (32, 33) changes sinusoidally when the shaft (13) moves at a constant speed along the axial direction. A position detection device (1) formed with a curved portion having a distorted shape.

[2] The position detection device (1) according to [1], wherein the detection coil (32, 33) has a larger amount of distortion with respect to the sine wave curve as the position nearer to the excitation coil (31) increases.

[3] The peak value of the voltage induced in the detection coil (32, 33) is within a range of one cycle or less while the shaft (13) moves from one end of movement in the axial direction to the other end of movement. The position detection device (1) according to the above [1], wherein the position detection device (1) changes at

[4] The detection coil (32, 33) has a pair of curved portions (301a, 302a, 303a, 304a) that are symmetrical with respect to an axis of symmetry that is parallel to the axial direction of the shaft (13). The position detection device (1) according to [1] above.

[5] The plurality of detection coils (32, 33) are provided, and the plurality of detection coils (32, 33) are provided while the shaft (13) moves from one moving end in the axial direction to the other moving end. The position detection device (1) according to [1] above, wherein the phases of the voltages induced in each of the voltages are different from each other.

[6] The excitation coil (31) includes a pair of long sides (311, 312) extending in the axial direction of the shaft (13), and a pair of long sides (311, 312) between the pair of long sides (311, 312). It has a rectangular shape having short sides (313, 314), and one of the two detection coils (32, 33), the detection coil (33), is located at both ends of the excitation coil (31) in the long side direction. The width of the excitation coil (31) in the short side direction reaches a maximum value near the part and the center part, and the width of the one of the detection coils (33) reaches a maximum value near the both ends of the excitation coil (31). (W ₃₃₁ , W ₃₃₂ ) is smaller than the local maximum value (W ₃₃₃ ) of the width of the one of the detection coils (33) near the center of the excitation coil (31), according to [5] above. Position detection device (1).

[7] The other detection coil (32) of the two detection coils (32, 33) is located near both ends and the center of the excitation coil (31). The position detection device (1) according to [6] above, wherein the width in the short side direction is a minimum value.

[8] The position detection according to any one of [5] to [7] above, wherein the excitation coil (31) and the two detection coils (32, 33) are formed on one substrate (3). Device (1).

[9] The position detection device (1) according to [1] above, wherein the shaft (13) is a rack shaft (13) of a steering device (10) of a vehicle.

Although the embodiments of the present invention have been described above, the embodiments described above do not limit the invention according to the claims. Furthermore, it should be noted that not all combinations of features described in the embodiments are essential for solving the problems of the invention.

1... Stroke sensor (position detection device) 2, 2A... Target 3... Substrate 301a... First curved part 302a... Second curved part 303a... Third curved part 304a... Fourth curved part 4... Power supply part 13 ...Rack shaft (shaft) 31...Excitation coils 311, 312...Long side portion 313, 314...Short side portion 32...Sine wave shape detection coil 33...Cosine wave shape detection coil

Claims (9)

A position detection device that detects the position of a shaft that moves forward and backward in an axial direction,
a detection body fixed to the shaft;
an excitation coil that generates an alternating magnetic field;
a power supply unit that supplies alternating current to the excitation coil;
a detection coil extending along the axial direction of the shaft and interlinked with the magnetic flux of the alternating magnetic field;
The excitation coil is arranged to surround the detection coil,
The sensing coil is distorted with respect to a sinusoidal curve so that the peak value of the voltage induced in the sensing coil changes sinusoidally when the shaft moves at a constant speed along the axial direction. It is formed with a curved part in the shape,
Position detection device. The detection coil has a larger amount of distortion with respect to the sine wave curve at a position closer to the excitation coil.
The position detection device according to claim 1. The peak value of the voltage induced in the detection coil changes within a range of one period or less while the shaft moves from one moving end to the other moving end in the axial direction.
The position detection device according to claim 1. The detection coil has a pair of curved portions that are symmetrical with respect to an axis of symmetry that is parallel to the axial direction of the shaft.
The position detection device according to claim 1. Two of the detection coils are provided, and the voltages induced in each of the plurality of detection coils are different in phase while the shaft moves from one moving end to the other moving end in the axial direction.
The position detection device according to claim 1. The excitation coil has a rectangular shape having a pair of long sides extending in the axial direction of the shaft and a pair of short sides between the pair of long sides,
In one of the two detection coils, the width of the excitation coil in the short side direction reaches a maximum value near both ends and the center of the excitation coil in the long side direction,
A maximum value of the width of the one of the detection coils near the both ends of the excitation coil is smaller than a maximum value of the width of the one detection coil near the center of the excitation coil.
The position detection device according to claim 5. The other of the two detection coils has a width in the short side direction of the excitation coil that has a minimum value near both ends and near the center of the excitation coil.
The position detection device according to claim 6. the excitation coil and the two detection coils are formed on one substrate;
The position detection device according to any one of claims 5 to 7. the shaft is a rack shaft of a steering device of a vehicle;
The position detection device according to claim 1.

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