Magnetostrictive torque sensor

Abstract

To provide a magnetostrictive torque sensor capable of securing sufficient rigidity while excellently securing a magnetic flux density improvement effect by a back yoke.SOLUTION: The magnetostrictive torque sensor includes: a coil unit 4 including a plurality of detection coils 6a to 6d and having a detection section 7 arranged around the rotation axis 2; and a back yoke 5 disposed around the detection part 7. The back yoke 5 has a magnetic ring 16 and a reinforcing ring 17 externally fitted to the magnetic ring 16, the magnetic ring 16 is constituted of a material having magnetic permeability higher than that of a material constituting the reinforcing ring 17, and the reinforcing ring 17 is constituted of a material having rigidity higher than that of the material constituting the magnetic ring 16.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a magnetostrictive torque sensor that measures torque applied to a rotating shaft. [Background technology]

[0002] As a sensor for measuring torque applied to a rotating shaft, a magnetostrictive torque sensor that measures torque applied to a rotating shaft by utilizing the inverse magnetostriction effect that occurs in the rotating shaft when torque is applied to the rotating shaft has been known for some time, as described in Japanese Patent Application Laid-Open Nos. 2016-200552 and 2017-049124.

[0003] The torque sensors described in JP 2016-200552 A and JP 2017-049124 A include a coil unit and a back yoke.

[0004] The coil unit has a cylindrical detection section that includes multiple detection coils and is arranged around the rotating shaft. The multiple detection coils generate a magnetic field around them when a voltage is applied, and change their inductance in response to changes in the magnetic permeability of the rotating shaft when torque is applied. The magnetostrictive torque sensor measures the torque applied to the rotating shaft based on the changes in inductance of the multiple detection coils.

[0005] The back yoke is a component that forms a magnetic path for the magnetic field generated by the multiple detection coils, and is cylindrically made of a magnetic material and arranged around the detection section of the coil unit. This back yoke can suppress leakage of magnetic flux to the outside, improving magnetic flux density and improving torque measurement accuracy. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-200552 [Patent Document 2] Japanese Patent Application Publication No. 2017-049124 Summary of the Invention [Problem to be solved by the invention]

[0007] In the conventional magnetostrictive torque sensors described in JP 2016-200552 A and JP 2017-049124 A, the back yoke for improving magnetic flux density is made of a ferromagnetic material, such as a powder core or a sintered core obtained by applying an insulating coating to soft magnetic metal powder and then compression molding it.

[0008] However, ferromagnetic materials such as powder magnetic cores and sintered magnetic cores generally have lower rigidity than hard metals such as bearing steel and carbon steel. Therefore, if the back yoke is made of a ferromagnetic material, it may be difficult to support the torque sensor on a fixed part such as a casing. And / or, the shape accuracy of the back yoke may decrease, making it impossible to stably form a magnetic circuit passing through the rotating shaft and the back yoke, which may result in a decrease in torque measurement accuracy.

[0009] An object of the present disclosure is to provide a magnetostrictive torque sensor that can ensure sufficient rigidity while favorably ensuring the effect of improving magnetic flux density by a back yoke. [Means for solving the problem]

[0010] The magnetostrictive torque sensor according to the first aspect of the present disclosure includes: a coil unit including a plurality of detection coils and having a detection unit disposed around a rotation axis; a back yoke disposed around the detection unit; Equipped with.

[0011] In particular, in the magnetostrictive torque sensor according to the first aspect of the present disclosure, the back yoke has a magnetic ring and a reinforcing ring fitted onto the magnetic ring, the magnetic ring is made of a material having a magnetic permeability higher than that of a material constituting the reinforcing ring, The reinforcing ring is made of a material having a higher rigidity than the material that makes up the magnetic ring.

[0012] In a magnetostrictive torque sensor according to a second aspect of the present disclosure, in the magnetostrictive torque sensor according to the first aspect of the present disclosure, the material constituting the reinforcing ring is metal.

[0013] A magnetostrictive torque sensor according to a third aspect of the present disclosure is the magnetostrictive torque sensor according to the first or second aspect of the present disclosure, further comprising a holder made of synthetic resin that holds the coil unit and the back yoke. [Effects of the Invention]

[0014] According to the magnetostrictive torque sensor of one aspect of the present disclosure, it is possible to ensure sufficient rigidity while favorably ensuring the effect of improving the magnetic flux density by the back yoke. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic cross-sectional view of a magnetostrictive torque sensor according to an embodiment of the present disclosure, taken along an imaginary plane including the central axis of a rotation shaft. [Figure 2] FIG. 2 is a diagram schematically illustrating a detection circuit including four detection coils. [Figure 3] FIG. 3 is a plan view of the flexible substrate. DETAILED DESCRIPTION OF THE INVENTION

[0016] An example of an embodiment of the present disclosure will be described with reference to FIGS. 1 to 3. FIG.

[0017] The magnetostrictive torque sensor 1 is used to measure the torque transmitted by the rotating shaft 2 .

[0018] In the following description, unless otherwise specified, the axial, radial, and circumferential directions of the magnetostrictive torque sensor 1 refer to the axial, radial, and circumferential directions of the rotating shaft 2. The axial, radial, and circumferential directions of the rotating shaft 2 coincide with the axial, radial, and circumferential directions of the coil unit 4 and also coincide with the axial, radial, and circumferential directions of the back yoke 5. Furthermore, one axial side refers to the left side in FIG. 1, and the other axial side refers to the right side in FIG. 1.

[0019] The rotating shaft 2 has a detection target 3, which is a cylindrical surface whose outer diameter does not change in the axial direction, on part of its outer peripheral surface in the axial direction. The rotating shaft 2 is rotatably supported via a bearing (not shown) on a fixed part that does not rotate even during use.

[0020] The rotating shaft 2 is made of a material having magnetostrictive properties in part or in whole, including at least the detected portion 3. Specifically, the rotating shaft 2 can be made of an iron alloy such as, but not limited to, SC (carbon steel for mechanical construction), SUS (stainless steel), SCr (chromium steel), SCM (chromium molybdenum steel), or SNCM (nickel chromium molybdenum steel).

[0021] The magnetostrictive torque sensor 1 includes a coil unit 4 having a detection section 7 that includes multiple detection coils 6a to 6d and is arranged around the rotating shaft 2, and a back yoke 5 that is arranged around the detection section 7. The magnetostrictive torque sensor 1 detects changes in the magnetic permeability of the rotating shaft 2 that occur when the rotating shaft 2 transmits torque based on the inverse magnetostriction effect using the multiple detection coils 6a to 6d, and measures the torque transmitted by the rotating shaft 2.

[0022] The configuration of the coil unit 4 is not particularly limited as long as it has a detection section 7 consisting of a plurality of detection coils 6a to 6d arranged around the rotation shaft 2. For example, the coil unit 4 can be configured from a flexible substrate 8, and the plurality of detection coils 6a to 6d can be configured from a wiring pattern formed on a wiring layer. Alternatively, the coil unit 4 can be configured from a coil holder (bobbin) made of synthetic resin and a plurality of detection coils formed by winding insulated wire around the coil holder.

[0023] In this example, the coil unit 4 is configured by a flexible substrate 8, and the plurality of detection coils 6a to 6d are configured by wiring patterns formed on a wiring layer.

[0024] Of the flexible substrate 8, the detection section 7 in which the plurality of detection coils 6a to 6d are arranged is configured in a cylindrical or partially cylindrical shape.

[0025] In the unfolded state of the flexible substrate 8 as shown in Fig. 3, the detection section 7 is configured in the shape of a strip or a rectangular plate. That is, the detection section 7 constituting the magnetostrictive torque sensor 1 is configured in the shape of a cylinder by rolling the detection section 7 in the shape of a strip or a rectangular plate as shown in Fig. 3, or in the shape of a notched cylinder having a discontinuous portion at one location in the circumferential direction.

[0026] In this example, the detection unit 7 has four detection coils 6a to 6d. As shown in Fig. 2, each of the detection coils 6a to 6d is configured by arranging a plurality of coil pieces 9a to 9d, 10a to 10d in the circumferential direction (the direction of the long sides of the detection unit 7 when the flexible substrate 8 is in the unfolded state).

[0027] Specifically, the first detection coil 6a is formed by connecting in series a plurality of coil pieces 9a, 10a arranged in the circumferential direction, the second detection coil 6b is formed by connecting in series a plurality of coil pieces 9b, 10b arranged in the circumferential direction, the third detection coil 6c is formed by connecting in series a plurality of coil pieces 9c, 10c arranged in the circumferential direction, and the fourth detection coil 6d is formed by connecting in series a plurality of coil pieces 9d, 10d arranged in the circumferential direction.

[0028] Of the coil pieces 9a to 9d, 10a to 10d, the coil pieces 9a to 9d located at both ends in the circumferential direction are configured by arranging the wiring pattern so as to be wound in an approximately triangular shape when viewed from the radial direction, and the remaining coil pieces 10a to 10d are configured by arranging the wiring pattern so as to be wound in an approximately parallelogram shape when viewed from the radial direction.

[0029] The coil pieces 9a and 10a constituting the first detection coil 6a and the coil pieces 9c and 10c constituting the third detection coil 6c have straight line portions inclined at a predetermined angle (for example, +45 degrees) in a predetermined direction with respect to the axial direction of the rotation shaft 2 (the direction of the short side of the detection unit 7 when the flexible substrate 8 is in the unfolded state). The coil pieces 9b and 10b constituting the second detection coil 6b and the coil pieces 9d and 10d constituting the fourth detection coil 6d have straight line portions inclined at a predetermined angle (for example, -45 degrees) in a direction opposite to the predetermined direction with respect to the axial direction of the rotation shaft 2.

[0030] The four detection coils 6a to 6d are electrically connected to an external device 11.

[0031] The external device 11 includes an oscillator 12 that applies a voltage between two points, and a voltmeter 13 that detects the voltage between the two points.

[0032] There are no particular limitations on the manner in which the detection coils 6a to 6d are electrically connected to the external device 11. In this example, the detection coils 6a to 6d and the external device 11 are electrically connected to each other by signal lines 14a to 14d (see FIG. 2) formed on the wiring layer of the flexible substrate 8 and a cable connected to the external device 11.

[0033] That is, flexible substrate 8 of this example includes band-shaped signal line portion 15 extending radially and / or axially from detection portion 7. Signal line portion 15 has four stacked signal lines 14a to 14d.

[0034] Of the four signal lines 14a to 14d, the first signal line 14a connects one end of the first detection coil 6a and one end of the second detection coil 6b in series, and is electrically connected to one terminal of the oscillator 12 via the cable.

[0035] The second signal line 14b connects one end of the third detection coil 6c and one end of the fourth detection coil 6d in series, and is electrically connected to the other terminal of the oscillator 12 via the cable.

[0036] The third signal line 14c connects the other end of the first detection coil 6a and the other end of the third detection coil 6c in series, and is electrically connected to one terminal of the voltmeter 13 via the cable.

[0037] The fourth signal line 14d connects the other end of the second detection coil 6b and the other end of the fourth detection coil 6d in series, and is electrically connected to the other terminal of the voltmeter 13 via the cable.

[0038] Oscillator 12 applies an AC voltage between a contact point A between one end of first detection coil 6a and one end of second detection coil 6b, and a contact point B between one end of third detection coil 6c and one end of fourth detection coil 6d. Voltmeter 13 detects a voltage between a contact point C between the other end of first detection coil 6a and the other end of third detection coil 6c, and a contact point D between the other end of second detection coil 6b and the other end of fourth detection coil 6d. That is, the four detection coils 6a to 6d that make up detection unit 7, together with oscillator 12 and voltmeter 13, form a bridge circuit.

[0039] When torque T is applied to the rotating shaft 2, stresses σ with opposite signs act on the outer surface of the rotating shaft 2 in a direction inclined at +45° to the axial direction and a direction inclined at -45° to the axial direction. Due to the inverse magnetostriction effect, the magnetic permeability increases in the direction in which tensile stress (+σ) acts, and decreases in the direction in which compressive stress (-σ) acts. In the magnetostrictive torque sensor 1 of this example, the voltage of the bridge circuit, which changes in accordance with the change in magnetic permeability of the rotating shaft 2, is detected by a voltmeter 13, and the direction and magnitude of the torque transmitted by the rotating shaft 2 are determined based on this detected value.

[0040] The back yoke 5 has a magnetic ring 16 and a reinforcing ring 17 fitted onto the magnetic ring 16. The magnetic ring 16 is made of a material having a higher magnetic permeability than the material making up the reinforcing ring 17. In contrast, the reinforcing ring 17 is made of a material having a higher rigidity (modulus of longitudinal elasticity) than the material making up the magnetic ring 16.

[0041] The magnetic ring 16 mainly functions as a magnetic path for the magnetic flux generated by the detection coils 6a to 6d. The magnetic ring 16 can be made of, but is not limited to, a ferromagnetic material such as a powder magnetic core obtained by applying an insulating coating to soft magnetic metal powder and then compression molding it, or stainless steel (SUS).

[0042] The shape of the magnetic ring 16 is not limited as long as it can be arranged around the detection section 7 of the coil unit 4, and it can be configured, for example, in a cylindrical or partially cylindrical shape. In this example, the magnetic ring 16 is configured in a cylindrical shape.

[0043] The radial thickness t1 of the magnetic ring 16 is not limited to this, but can be, for example, 0.1 mm to 3.0 mm. Note that a radial thickness t1 of approximately 0.1 mm to 0.2 mm is sufficient for the magnetic ring 16 to function as a magnetic path for the magnetic flux generated by the detection coils 6a to 6d, but considering manufacturing convenience, it is preferable to set the radial thickness t1 to 0.6 mm to 3.0 mm.

[0044] The reinforcing ring 17 mainly functions to reinforce the magnetic ring 16 and ensure its rigidity. The material constituting the reinforcing ring 17 is not particularly limited as long as it has a rigidity higher than that of the material constituting the magnetic ring 16. For example, hard metals such as SUJ2 (high carbon chromium bearing steel) and SC (carbon steel for mechanical structures), high-strength plastics, etc. can be used. When the reinforcing ring 17 is made of a hard metal, it can be subjected to heat treatment such as induction hardening. Furthermore, when the reinforcing ring 17 is made of a hard metal, the hard metal may be a magnetic metal or a non-magnetic metal. In this example, the reinforcing ring 17 is made of a hard metal.

[0045] The shape of the reinforcing ring 17 is not limited as long as it has an inner peripheral surface that can be fitted onto the magnetic ring 16. In this example, the magnetic ring 16 has a cylindrical shape. Therefore, the back yoke 5 is configured to have a cylindrical shape as a whole.

[0046] The radial thickness t2 of the reinforcing ring 17 is not limited to this, but can be, for example, 1 mm or more and 3 mm or less. In this example, the radial thickness t2 of the reinforcing ring 17 is greater than the radial thickness t1 of the magnetic ring 16 (t2>t1), but when implementing the present disclosure, the radial thickness t2 of the reinforcing ring 17 can also be set to be equal to or less than the radial thickness t1 of the magnetic ring 16 (t2≦t1).

[0047] In this example, the back yoke 5 is configured by fitting the reinforcing ring 17 onto the magnetic ring 16 without any radial rattle. For example, the back yoke 5 can be configured by fixing the outer circumferential surface of the magnetic ring 16 to the inner circumferential surface of the reinforcing ring 17 with an adhesive, or by press-fitting the outer circumferential surface of the magnetic ring 16 into the inner circumferential surface of the reinforcing ring 17. However, the magnetic ring 16 and the reinforcing ring 17 that configure the back yoke 5 do not necessarily have to be joined and fixed to each other as long as radial rattle and relative axial displacement are prevented when the holder 18 of the magnetostrictive torque sensor 1 is supported on the fixed portion.

[0048] Furthermore, when implementing the present disclosure, it is sufficient that the back yoke 5 is configured so that the reinforcing ring 17 is fitted onto the magnetic ring 16, in other words, so that the magnetic ring 16 is held on the inner peripheral surface of the reinforcing ring 17. Therefore, when implementing the present disclosure, for example, the magnetic ring 16 can be made by attaching a magnetic tape made by applying an adhesive to one side of a strip-shaped material made of a ferromagnetic material to the inner peripheral surface of the reinforcing ring 17, or by forming a ferromagnetic coating on the inner peripheral surface of the reinforcing ring 17.

[0049] The back yoke 5 is disposed around the detection unit 7 of the coil unit 4 and coaxially with the detection unit 7. The outer peripheral surface of the detection unit 7 and the inner peripheral surface of the back yoke 5 (the inner peripheral surface of the magnetic ring 16) can be disposed radially spaced apart, or can be disposed in close contact with each other without being radially spaced apart. When the outer peripheral surface of the detection unit 7 and the inner peripheral surface of the back yoke 5 are disposed radially spaced apart, a non-magnetic material such as synthetic resin can be interposed between the outer peripheral surface of the detection unit 7 and the inner peripheral surface of the back yoke 5. In this example, the outer peripheral surface of the detection unit 7 and the inner peripheral surface of the back yoke 5 are radially spaced apart.

[0050] The magnetostrictive torque sensor 1 of this example further includes, as an optional component, a holder 18 made of synthetic resin that holds the coil unit 4 and the back yoke 5. The shape of the holder 18 is not limited as long as it is configured to hold the coil unit 4 and the back yoke 5.

[0051] When implementing the present disclosure, a magnetostrictive torque sensor can also be configured by combining the coil unit 4 and the back yoke 5 without using a holder as a component.

[0052] When implementing the present disclosure and using holder 18 as a component, it is possible to employ a configuration in which coil unit 4 and back yoke 5 are assembled to holder 18 that is manufactured separately from coil unit 4 and back yoke 5, or a configuration in which coil unit 4 and back yoke 5 are embedded in holder 18 at the same time as holder 18 is manufactured by injection molding of synthetic resin. In this example, a configuration is employed in which coil unit 4 and back yoke 5 are assembled to holder 18 that is manufactured separately from coil unit 4 and back yoke 5.

[0053] The synthetic resin that can be used to form the holder 18 is epoxy resin or a thermoplastic resin such as PPS (polyphenylene sulfide), PA (polyamide), or PPA (polyphthalamide).

[0054] In this example, holder 18 has a cylindrical bobbin portion 19 that is arranged around rotating shaft 2. Holder 18 arranges bobbin portion 19 coaxially around and around detection target portion 3 of rotating shaft 2, and is supported and fixed to a fixed portion that does not rotate during use, such as a housing, with the inner circumferential surface of bobbin portion 19 closely facing detection target portion 3 in the radial direction.

[0055] In this example, the coil unit 4 is held in the holder 18 by wrapping the detection portion 7 of the flexible substrate 8 around the bobbin portion 19 and fixing the inner peripheral surface of the detection portion 7 to the outer peripheral surface of the bobbin portion 19 with an adhesive. However, when implementing the present disclosure, the coil unit 4 can also be held in the holder 18 by joining the ends on both sides in the circumferential direction of the detection portion 7 of the flexible substrate 8 wrapped around the bobbin portion 19 with an adhesive or adhesive tape, or by wrapping a restraining band around the detection portion 7 of the flexible substrate 8 wrapped around the bobbin portion 19.

[0056] In this example, the holder 18 has a first outward flange portion 20 extending radially outward from the end on one axial side of the bobbin portion 19 around the entire circumference, and a second outward flange portion 21 extending radially outward from the end on the other axial side of the bobbin portion 19 around the entire circumference.

[0057] The first outward flange portion 20 has an attachment portion for supporting and fixing the holder 18 to the fixed portion, and / or a wiring accommodating portion for accommodating cables and / or signal lines that electrically connect the detection coils 6a to 6d and the external device 11.

[0058] In this example, the outer diameter of the first outward flange portion 20 is larger than the outer diameter of the second outward flange portion 21. However, the outer diameter of the first outward flange portion 20 can be the same as the outer diameter of the second outward flange portion 21, or can be smaller than the outer diameter of the second outward flange portion 21.

[0059] In this example, the back yoke 5 is arranged coaxially around the detection portion 7 of the coil unit 4, and the other axial end of the back yoke 5 is externally fitted and fixed to the second outward flange portion 21, thereby being connected and fixed to the holder 18.

[0060] In the magnetostrictive torque sensor 1 of this example, the back yoke 5 has a magnetic ring 16 and a reinforcing ring 17 fitted around the magnetic ring 16, the magnetic ring 16 being made of a material having a higher magnetic permeability than the material making up the reinforcing ring 17, and the reinforcing ring 17 being made of a material having a higher rigidity (modulus of longitudinal elasticity) than the material making up the magnetic ring 16. Therefore, it is possible to ensure sufficient rigidity while favorably ensuring the effect of improving the magnetic flux density provided by the back yoke 5.

[0061] That is, the magnetic density improving effect of the back yoke 5 can be sufficiently ensured by using a material with high magnetic permeability as the material for the magnetic ring 16 arranged radially inside. On the other hand, the rigidity of the back yoke 5 can be sufficiently ensured by using a material with high rigidity as the material for the reinforcing ring 17 arranged radially outside. [Explanation of symbols]

[0062] 1. Magnetostrictive torque sensor 2 rotation axes 3. Detected part 4 Coil Unit 5 Back Yoke 6a First detection coil 6b Second detection coil 6c Third detection coil 6d Fourth detection coil 7. Detection unit 8 Flexible PCB 9a~9d Coil pieces 10a~10d Coil pieces 11 External device 12 Oscillators 13 Voltmeter 14a First signal line 14b Second signal line 14c Third signal line 14d Fourth signal line 15 Signal line section 16 Magnetic ring 17 Reinforcement ring 18 Holder 19 Bobbin section 20 First outward flange 21 Second outward flange

Claims

1. a coil unit including a plurality of detection coils and having a detection unit disposed around a rotation axis; a back yoke disposed around the detection unit; Equipped with the back yoke has a magnetic ring and a reinforcing ring fitted onto the magnetic ring, the magnetic ring is made of a material having a magnetic permeability higher than that of a material constituting the reinforcing ring, The reinforcing ring is made of a material having a higher rigidity than the material constituting the magnetic ring. Magnetostrictive torque sensor.

2. 2. The magnetostrictive torque sensor according to claim 1, wherein the reinforcing ring is made of a metal.

3. 3. The magnetostrictive torque sensor according to claim 1, further comprising a holder made of synthetic resin that holds the coil unit and the back yoke.

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