Magnetostrictive torque measurement device

Abstract

Provided is a magnetostrictive torque measurement device with which accuracy and sensitivity of torque measurement are easily secured. A magnetostrictive torque measurement device 1 comprises: a support member 4 which is arranged around a rotary shaft 2 rotatably supported with respect to a structural element which does not rotate even in use, so as to be incapable of rotating relative to the structural element; a support bearing 5 which is arranged between the rotary shaft 2 and the support member 4 and supports the support member 4 so as to be able to rotate relative to the rotary shaft 2; and a magnetostrictive torque sensor 6 which is supported by the support member 4, and has an opposing surface 15 which is adjacent to and facing the outer peripheral surface of the rotary shaft 2, and a detection part 17 which is arranged on the outer diameter side of the opposing surface 15 and comprises a plurality of detection coils.

Description

Magnetostrictive torque measuring device

[0001] The present disclosure relates to a magnetostrictive torque measurement device that measures torque applied to a rotating shaft.

[0002] A magnetostrictive torque sensor has been known as a sensor for measuring torque applied to a rotating shaft, which measures the torque applied to the rotating shaft by utilizing the inverse magnetostrictive effect that occurs in the rotating shaft when torque is applied to the rotating shaft. The structure of such a magnetostrictive torque sensor is disclosed, for example, in Japanese Patent Laid-Open Publication No. 2023-127315.

[0003] The magnetostrictive torque sensor disclosed in Japanese Patent Application Laid-Open No. 2023-127315 includes a holder and a coil unit.

[0004] The holder is made of synthetic resin and has a cylindrical holder portion that is placed around the rotating shaft and is supported and fixed to a structural element such as a housing that does not rotate even when in use. The coil unit is placed around the cylindrical holder portion and has a detection portion consisting of multiple detection coils. The magnetostrictive torque sensor measures the torque applied to the rotating shaft based on changes in inductance of the multiple detection coils.

[0005] Japanese Patent Application Laid-Open No. 2023-127315

[0006] Conventional magnetostrictive torque sensors such as those disclosed in JP 2023-127315 A are used while being supported and fixed to a structural element that does not rotate even during use. For this reason, it is necessary to provide a radial gap of a predetermined size, for example, 0.1 mm to 1.0 mm, between the outer circumferential surface of the rotating shaft and the inner circumferential surface of the cylindrical holder, in order to prevent the outer circumferential surface of the rotating shaft from coming into contact with the inner circumferential surface of the cylindrical holder, even if the rotating shaft wobbles (tilts) relative to the structural element or elastic bending deformation occurs in the rotating shaft.

[0007] The coil unit having the detector is disposed around the cylindrical holder portion, so that the radial distance between the outer circumferential surface of the rotating shaft and the detector of the coil unit is greater than the radial distance between the outer circumferential surface of the rotating shaft and the inner circumferential surface of the cylindrical holder portion.

[0008] If the radial distance between the outer surface of the rotating shaft and the detection part of the coil unit is large, a large amount of the magnetic flux generated by the detection part of the coil unit will not pass through the outer surface of the rotating shaft, making it difficult to improve the accuracy and sensitivity of torque measurement.

[0009] An object of the present disclosure is to provide a magnetostrictive torque measurement device that can easily ensure torque measurement accuracy, torque measurement sensitivity, or both.

[0010] A magnetostrictive torque measuring device according to one embodiment of the present disclosure comprises: a support member arranged around a rotating shaft that is rotatably supported relative to a structural element such as a housing that does not rotate even when in use, such that relative rotation with respect to the structural element is not possible; a support bearing arranged between the rotating shaft and the support member, supporting the support member so that relative rotation with respect to the rotating shaft is possible; and a magnetostrictive torque sensor supported by the support member, having an opposing surface that faces closely to the outer peripheral surface of the rotating shaft, and a detection unit arranged on the outer diameter side of the opposing surface and consisting of a plurality of detection coils.

[0011] In the magnetostrictive torque measurement device according to one aspect of the present disclosure, the support member is capable of relative displacement in the radial direction with respect to the structural element.

[0012] In one aspect of the magnetostrictive torque measuring device of the present disclosure, when assembled to the rotating shaft, the size of the radial gap between the outer surface of the rotating shaft and the opposing surface is less than 0.1 mm (100 μm), and the size of the radial gap between the outer surface of the rotating shaft and the inner surface of the support bearing is less than the size of the radial gap between the outer surface of the rotating shaft and the opposing surface (including 0).

[0013] In one aspect of the magnetostrictive torque measuring device of the present disclosure, the size of the radial gap between the outer surface of the rotating shaft and the opposing surface is 80 μm or less, and the size of the maximum radial gap between the outer surface of the rotating shaft and the inner surface of the support bearing is 50 μm or less.

[0014] In a magnetostrictive torque measurement device according to one aspect of the present disclosure, the magnetostrictive torque sensor includes a holder that includes the opposing surface and has a bobbin portion that is arranged around the rotation axis.

[0015] In the magnetostrictive torque measurement device according to one aspect of the present disclosure, the holder has a protrusion that can be engaged with the support member in the circumferential direction.

[0016] In one aspect of the magnetostrictive torque measuring device of the present disclosure, the support bearing has an outer ring fitted inside the support member, an inner ring fitted outside the rotating shaft, and a plurality of rolling elements arranged to roll freely between the outer ring and the inner ring.

[0017] In the magnetostrictive torque measurement device according to one aspect of the present disclosure, the magnetostrictive torque sensor includes a back yoke arranged around the detection portion, and the back yoke is fitted inside the support member.

[0018] The magnetostrictive torque measurement device according to one aspect of the present disclosure includes an engagement member that is stretched between the structural element and the support member.

[0019] According to one aspect of the magnetostrictive torque measurement device of the present disclosure, the magnetostrictive torque sensor is not supported and fixed to a structural element such as a housing that does not rotate during use, but is supported via a support member and a support bearing to allow relative rotation with respect to the rotating shaft. This eliminates the need to consider preventing contact between the outer circumferential surface of the rotating shaft and the opposing surface of the magnetostrictive torque sensor, and allows the outer circumferential surface of the rotating shaft and the opposing surface of the magnetostrictive torque sensor to be closely opposed to each other. This makes it possible to provide a magnetostrictive torque measurement device that easily ensures torque measurement accuracy, torque measurement sensitivity, or both.

[0020] Fig. 1 is a schematic cross-sectional view of a magnetostrictive torque measurement device according to an embodiment of the present disclosure, taken along an imaginary plane including the central axis of a rotation shaft. Fig. 2 is an exploded perspective view of the magnetostrictive torque measurement device. Fig. 3 is a schematic diagram showing a detection circuit including four detection coils. Fig. 4 is a plan view showing an expanded state of a flexible substrate constituting the magnetostrictive torque measurement device.

[0021] An example of an embodiment of the present disclosure will be described with reference to FIGS. 1 to 4. FIG.

[0022] The magnetostrictive torque measuring device 1 is used to measure the torque transmitted by a rotating shaft 2 .

[0023] In the following description, unless otherwise specified, the axial, radial, and circumferential directions of the magnetostrictive torque measurement device 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 magnetostrictive torque sensor 6. 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.

[0024] The rotating shaft 2 is the object of torque measurement by the magnetostrictive torque measuring device 1. The rotating shaft 2 is rotatably supported by a bearing (not shown) relative to a structural element (not shown), such as a housing that does not rotate even during use or a member fixed to the housing. Note that, fundamentally, neither the rotating shaft 2 nor the structural element (such as the housing) constitutes the magnetostrictive torque measuring device 1.

[0025] The rotating shaft 2 is partially or entirely made of a material having magnetostrictive properties. Specifically, the rotating shaft 2 is partially or entirely made of an iron alloy such as, but not limited to, SC (carbon steel for machine construction), SUS (stainless steel), SCr (chrome steel), SCM (chrome molybdenum steel), or SNCM (nickel chrome molybdenum steel).

[0026] Of the rotating shaft 2, a part in the axial direction of the outer peripheral surface of the part made of the material having the magnetostrictive properties functions as the detected part 3. In this example, at least the axial part of the rotating shaft 2 including the detected part 3 is made of a cylindrical surface whose outer diameter does not change in the axial direction.

[0027] The magnetostrictive torque measuring device 1 includes a support member 4 , a support bearing 5 , and a magnetostrictive torque sensor 6 .

[0028] The support member 4 is disposed around the rotating shaft 2 so as to be unable to rotate relative to the structural elements. The support member 4, together with a support bearing 5, is an element that supports the magnetostrictive torque sensor 6 with respect to the rotating shaft 2.

[0029] The shape of the support member 4 is not particularly limited as long as it is configured to support the magnetostrictive torque sensor 6 .

[0030] In this example, the support member 4 is configured to have a generally cylindrical shape as a whole, and is disposed around the rotation shaft 2 coaxially with the rotation shaft 2 .

[0031] The support member 4 has a portion that supports the magnetostrictive torque sensor 6 and a portion that is supported relative to the rotating shaft 2 by the support bearing 5. The portion that supports the magnetostrictive torque sensor 6 and the portion that is supported relative to the rotating shaft 2 by the support bearing 5 are arranged in the axial direction.

[0032] The portion supported by the support bearings 5 ​​with respect to the rotating shaft 2 can be arranged on only one axial side of the portion supporting the magnetostrictive torque sensor 6. In this case, the support member 4 is supported by the support bearings 5 ​​in a cantilevered manner in the axial direction with respect to the rotating shaft 2. Alternatively, the portion supported by the support bearings 5 ​​with respect to the rotating shaft 2 can be arranged on both axial sides of the portion supporting the magnetostrictive torque sensor 6. In this case, the support member 4 is supported on both sides of the axial direction with respect to the rotating shaft 2 in a doubly supported manner in the axial direction by at least two support bearings 5 ​​arranged on both axial sides of the magnetostrictive torque sensor 6.

[0033] In the illustrated example, the support member 4 has a portion on one axial half that supports the magnetostrictive torque sensor 6, and a portion on the other axial half that is supported relative to the rotating shaft 2 by a support bearing 5.

[0034] The magnetostrictive torque sensor 6 is fitted into the portion of the support member 4 that supports the magnetostrictive torque sensor 6. This supports the magnetostrictive torque sensor 6 on the support member 4, and also positions the magnetostrictive torque sensor 6 in the radial direction relative to the support member 4. The manner in which the magnetostrictive torque sensor 6 is fitted into the portion of the support member 4 that supports the magnetostrictive torque sensor 6 is arbitrary, as long as the magnetostrictive torque sensor 6 is fitted into the portion that supports the magnetostrictive torque sensor 6 without any radial play, and may be any of an interference fit, an intermediate fit, or a clearance fit.

[0035] In the illustrated example, the inner circumferential surface of the portion supporting the magnetostrictive torque sensor 6 has a large-diameter cylindrical surface portion 38 located on one axial side, a sensor fitting surface portion 8 located on the other axial side and having a smaller diameter than the large-diameter cylindrical surface portion 38, and a connection surface portion 39 connecting the large-diameter cylindrical surface portion 38 and the sensor fitting surface portion 8 and facing one axial side, forming a stepped cylindrical surface. The sensor fitting surface portion 8 is formed by a cylindrical surface whose inner diameter does not change in the axial direction. The magnetostrictive torque sensor 6 is fitted into the sensor fitting surface portion 8.

[0036] The portion of the support member 4 that supports the magnetostrictive torque sensor 6 may include an engaging element that engages circumferentially with a portion of the magnetostrictive torque sensor 6. The engaging element allows the portion of the magnetostrictive torque sensor 6 to extend toward the outer diameter side of the support member 4. The engaging element also allows the magnetostrictive torque sensor 6 to be positioned circumferentially with respect to the support member 4.

[0037] In the illustrated example, one axial end of the support member 4, which is the portion having the large-diameter cylindrical surface portion 38 on its inner circumferential surface, has a notch 7 at one circumferential location. The notch 7 opens to the end on one axial side, the inner circumferential surface (large-diameter cylindrical surface portion 38), and the outer circumferential surface as an engaging element that circumferentially engages with part of the magnetostrictive torque sensor 6. The notch 7 circumferentially engages with the protrusion 23 of the holder 18 that constitutes the magnetostrictive torque sensor 6. A rear end surface 40 located at the other axial end of the inner surface of the notch 7 is located axially to one side of the connecting surface portion 39 in the illustrated example. However, the rear end surface 40 may alternatively be located at the same axial position as the connecting surface portion 39.

[0038] In the illustrated example, the magnetostrictive torque sensor 6 is positioned axially relative to the support member 4 by abutting the other axial side surface of the radially inner end of the protrusion 23 of the holder 18 against the rear end surface 40 of the notch 7, and by abutting the retaining ring 37 engaged in the engagement groove 41b provided at one axial end of the large-diameter cylindrical surface portion 38 against the side surface of one axial side of the first outward flange portion 21.

[0039] In the illustrated example, the support bearing 5 is fitted into the portion of the support member 4 that is supported on the rotating shaft 2 by the support bearing 5. The portion that is supported on the rotating shaft 2 by the support bearing 5 has, on its inner circumferential surface, a bearing fitting surface 9 that is used for fitting the support bearing 5 into the portion. In the illustrated example, the bearing fitting surface 9 is configured by a cylindrical surface whose inner diameter does not change in the axial direction, except for an engagement groove 41 a that is formed at the other axial end for engaging a snap ring 14, and has an inner diameter that is larger than the inner diameter of the sensor fitting surface 8.

[0040] There are no particular limitations on the structure for disabling relative rotation of the support member 4 with respect to the structural element when the magnetostrictive torque measurement device 1 is mounted on the rotating shaft 2. Examples of such a structure include a structure in which an engaging member is provided that spans between the structural element and the support member 4, a structure in which a portion of the support member 4 is engaged in the circumferential direction with the structural element, and a structure in which a portion of the magnetostrictive torque sensor 6 supported by the support member 4 is engaged in the circumferential direction with the structural element.

[0041] In the illustrated example, the magnetostrictive torque measurement device 1 includes an engagement member 36 that is stretched between the structural element and the support member 4 and prevents relative rotation of the support member 4 with respect to the structural element. There are no particular limitations on the shape of the engagement member 36, as long as it is configured to prevent relative rotation of the support member 4 with respect to the structural element.

[0042] In the illustrated example, the engaging member 36 is a pin. The support member 4 has an engaging hole 35 that opens to the outer circumferential surface in a circumferential portion of an axially intermediate portion. The radially inner end of the engaging member 36 is fitted into the engaging hole 35, and the radially outer end of the engaging member 36 is engaged with a portion of the structural element in a state in which relative displacement in the circumferential direction is prevented, thereby preventing relative rotation of the support member 4 with respect to the structural element.

[0043] The engaging member 36 can be made up of one or more engaging members 36. In the example shown, the engaging member 36 is made up of a plurality of engaging members 36. The plurality of engaging members 36 are arranged spaced apart in the circumferential direction. The support member 4 has engaging holes 35 at a plurality of circumferential positions in the axially intermediate portion.

[0044] When the magnetostrictive torque measurement device 1 is mounted on the rotating shaft 2, the support member 4 is positioned radially relative to the rotating shaft 2 by the support bearing 5. Therefore, it is not necessary to position the support member 4 radially relative to the structural element. In the illustrated example, the support member 4 is supported so as to be capable of relative radial displacement with respect to the structural element. Specifically, a radial gap is provided around the entire circumference between the inner circumferential surface of the structural element and the outer circumferential surface of the support member 4. Even if the rotating shaft 2 wobbles (tilts) relative to the structural element or elastic bending deformation occurs in the rotating shaft 2 during operation of an apparatus including the magnetostrictive torque measurement device 1 and the rotating shaft 2, the support member 4 arranged around the rotating shaft 2 is prevented from strongly hitting the structural element in the radial direction.

[0045] Alternatively, the support member 4 may be configured to be supported so as to be unable to move radially relative to the structural element. For example, a circumferential portion of the support member 4 may be radially engaged with the structural element, or a circumferential portion of the support member 4 may be fitted into the structural element. However, in this case as well, the support member 4 is supported with respect to the rotating shaft 2 by the support bearing 5, and is not supported by or fixed to the structural element.

[0046] It is preferable that the magnetostrictive torque measurement device 1 of this example be unable to move relative to the structural element in the axial direction when the magnetostrictive torque measurement device 1 is mounted on the rotating shaft 2. Therefore, the magnetostrictive torque measurement device 1 can optionally or additionally be provided with a structure for preventing relative axial displacement with respect to the structural element. For example, at least a portion of the support member 4 can be configured so that relative axial displacement with respect to the structural element is impossible. In the illustrated example, a configuration is adopted in which the radially outer end of the engaging member 36 is engaged with a portion of the structural element in a state in which relative axial displacement is prevented, thereby preventing relative axial displacement of the magnetostrictive torque measurement device 1 with respect to the structural element.

[0047] The configuration for preventing the support member 4 from being displaced in the axial direction relative to the structural element is not limited to this, and it is also possible to employ a configuration in which the radially outer end of the engaging member 36 is engaged with a part of the structural element to allow relative axial displacement, and another element or member prevents relative axial displacement of the magnetostrictive torque measurement device 1. For example, it is also possible to engage a part of the support member 4, or a part of the magnetostrictive torque sensor 6 supported by the support member 4, with a part of the structural element in a state in which relative axial displacement is prevented.

[0048] The support bearing 5 is disposed between the rotary shaft 2 and the support member 4 , and supports the support member 4 so as to be rotatable relative to the rotary shaft 2 .

[0049] Various rolling bearings and sliding bearings such as ball bearings, roller bearings (including needle bearings), tapered roller bearings, and spherical roller bearings can be used as the support bearings 5. When a rolling bearing is used as the support bearing 5, it does not matter whether it is a single-row or double-row bearing. Furthermore, the support bearing 5 can be made up of one or more support bearings 5.

[0050] The support bearing 5 can be composed of an outer ring 11 fitted inside the support member 4, an inner ring 12 fitted outside the rotating shaft 2, and a plurality of rolling elements 13 arranged to roll freely between the outer ring 11 and the inner ring 12. In the example shown, the support bearing 5 is composed of a single rolling bearing. More specifically, the support bearing 5 is composed of a single double-row ball bearing, and the multiple rolling elements 13 are made up of balls and are arranged in double rows in the axial direction.

[0051] The support bearing 5 is fitted into the support member 4. The fit between the support member 4 and the support bearing 5 may be any suitable fit, as long as the support bearing 5 is fitted into the support member 4 without any radial play, and may be an interference fit, a transition fit, or a clearance fit. In the illustrated example, the outer peripheral surface of the outer ring 11 constituting the support bearing 5 is fitted into the bearing fitting surface 9 of the support member 4. When the fit between the outer peripheral surface of the outer ring 11 and the bearing fitting surface 9 is a clearance fit, the size of the radial gap between the outer peripheral surface of the outer ring 11 and the bearing fitting surface 9, i.e., the difference between the outer diameter of the outer peripheral surface of the outer ring 11 and the inner diameter of the bearing fitting surface 9, is not limited to this, but is preferably several tens of μm or less, for example, 50 μm or less, and more preferably 30 μm or less, from the viewpoint of preventing contact between the outer peripheral surface of the rotating shaft 2 (the portion to be detected 3) and the opposing surface 15 of the magnetostrictive torque sensor 6.

[0052] The support bearing 5 is preferably positioned in the axial direction relative to the support member 4. In the illustrated example, the outer ring 11 is positioned in the axial direction by being sandwiched from both axial sides between a connection surface portion 10 of the support member 4 that faces the other axial direction and connects the sensor fitting surface portion 8 and the bearing fitting surface portion 9, and a retaining ring 14 that is engaged with an engaging groove 41 a provided at the end portion of the bearing fitting surface portion 9 on the other axial side.

[0053] The support bearing 5 is fitted onto the rotating shaft 2. The fitting manner between the rotating shaft 2 and the support bearing 5 is arbitrary as long as the support bearing 5 is fitted onto the rotating shaft 2 without any radial play, and may be an interference fit, a transition fit, or a clearance fit. In the illustrated example, the inner peripheral surface of the inner ring 12 constituting the support bearing 5 is fitted onto the outer peripheral surface of the rotating shaft 2. When the fitting manner between the inner peripheral surface of the inner ring 12 and the outer peripheral surface of the rotating shaft 2 is a clearance fit, the size of the radial gap between the inner peripheral surface of the inner ring 12 and the outer peripheral surface of the rotating shaft 2, i.e., the difference between the inner diameter of the inner peripheral surface of the inner ring 12 and the outer diameter of the outer peripheral surface of the rotating shaft 2, is not limited thereto, but is preferably several tens of μm or less, for example, 50 μm or less, and more preferably 30 μm or less, from the viewpoint of preventing contact between the outer peripheral surface of the rotating shaft 2 (the portion to be detected 3) and the opposing surface 15 of the magnetostrictive torque sensor 6.

[0054] If one of the fitting modes between the support member 4 and the support bearing 5 (in the illustrated example, the fitting mode between the bearing fitting surface portion 9 and the outer peripheral surface of the outer ring 11) and the fitting mode between the rotating shaft 2 and the support bearing 5 (in the illustrated example, the fitting mode between the outer peripheral surface of the rotating shaft 2 and the inner peripheral surface of the inner ring 12) is a clearance fit, it is preferable that the other fitting mode be an interference fit or an intermediate fit, from the viewpoint of ensuring concentricity of the support member 4 with the rotating shaft 2. In the illustrated example, the fitting mode between the outer peripheral surface of the outer ring 11 and the bearing fitting surface portion 9 is an interference fit, and the fitting mode between the inner peripheral surface of the inner ring 12 and the outer peripheral surface of the rotating shaft 2 is a clearance fit.

[0055] The magnetostrictive torque sensor 6 has a facing surface 15 that faces closely to the outer circumferential surface of the rotating shaft 2, and a detection unit 17 that is arranged on the outer diameter side of the facing surface 15 and is made up of a plurality of detection coils 16, and is supported by the support member 4. The facing surface 15 can be provided on the inner circumferential surface of the magnetostrictive torque sensor 6.

[0056] The magnetostrictive torque measuring device 1 uses multiple detection coils 16 to detect changes in the magnetic permeability of the rotating shaft 2 that occur when the rotating shaft 2 transmits torque based on the inverse magnetostrictive effect, and measures the torque transmitted by the rotating shaft 2.

[0057] The magnetostrictive torque sensor 6 has an opposing surface 15 and a detection section 17 consisting of a plurality of detection coils 16, and as long as it is configured to be supported by the support member 4, there are no particular limitations on its specific structure.

[0058] The magnetostrictive torque sensor 6 can include a holder 18 that includes an opposing surface 15 and has a bobbin portion 20 that is arranged around the rotating shaft 2. In a structure that includes the holder 18, the opposing surface 15 is formed by the inner peripheral surface of the bobbin portion 20 of the holder 18. The detection portion 17 is arranged around the outer diameter side of the bobbin portion 20 (on the outer diameter side of a portion of the opposing surface 15 of the bobbin portion 20 in the axial direction).

[0059] In this example, the holder 18 is made of synthetic resin. The synthetic resin that makes up the holder 18 is not limited to these, but thermoplastic resins such as epoxy resin, PPS (polyphenylene sulfide), PA (polyamide), and PPA (polyphthalamide) can be used. Furthermore, reinforcing fibers can be mixed into the synthetic resin that makes up the holder 18, if necessary.

[0060] The detection section 17 including the plurality of detection coils 16 is configured as a coil unit 19. The specific configuration of the coil unit 19 is not particularly limited. For example, but not limited to, the coil unit 19 can be configured from a flexible substrate 24, and the plurality of detection coils 16 can be configured from a wiring pattern formed on a wiring layer. Alternatively, the coil unit 19 can be configured from a bobbin section 20 of the holder 18 and a detection section 17 including the plurality of detection coils 16 formed by winding insulated wire around the bobbin section 20.

[0061] In a configuration including the holder 18, means for assembling the coil unit 19 to the holder 18 may include, but are not limited to, assembling the coil unit 19 to the holder 18, or embedding the coil unit 19 in the holder 18 at the same time as manufacturing the holder 18 by injection molding of synthetic resin. In the illustrated example, a configuration is employed in which the coil unit 19 is assembled to the holder 18 which is manufactured separately from the coil unit 19.

[0062] The bobbin portion 20 is configured in a cylindrical or partially cylindrical shape. In the illustrated example, the bobbin portion 20 is configured in a cylindrical shape, and the opposing surface 15 of the bobbin portion 20 is configured as a cylindrical surface whose inner diameter does not change in the axial direction.

[0063] The magnetostrictive torque sensor 6 of this example may include a back yoke 34 arranged around the detection section 17 of the coil unit 19 as an optional component.

[0064] The back yoke 34 has a function of suppressing external leakage of magnetic flux generated by the detection coil 16. The back yoke 34 is integrally formed from a magnetic material. The back yoke 34 can be formed from a ferromagnetic material such as, but not limited to, SUS (stainless steel).

[0065] The shape of the back yoke 34 is not limited as long as it can be arranged around the detection section 17 of the coil unit 19, and it can be configured, for example, as a cylindrical or parted cylindrical shape. In the example shown, the back yoke 34 is configured as a cylindrical shape. The back yoke 34 is held by the holder 18 in a state where it is arranged around the detection section 17 of the coil unit 19 and coaxially with the detection section 17. The other axial end of the back yoke 34 is externally fitted and fixed to the second outward flange portion 22, thereby holding the back yoke 34 relative to the holder 18.

[0066] The inner peripheral surface of the back yoke 34 and the outer peripheral surface of the main body 25 of the coil unit 19 can be arranged to be spaced apart in the radial direction, or they can be arranged in close contact with each other without being spaced apart in the radial direction. In the example shown, the outer peripheral surface of the main body 25 and the inner peripheral surface of the back yoke 34 are arranged to be spaced apart in the radial direction. Note that when the inner peripheral surface of the back yoke 34 and the outer peripheral surface of the main body 25 are arranged to be spaced apart in the radial direction, a non-magnetic material such as synthetic resin can be interposed between the inner peripheral surface of the back yoke 34 and the outer peripheral surface of the main body 25.

[0067] The back yoke 34 is fitted into the support member 4. The fitting manner between the support member 4 and the back yoke 34 is arbitrary as long as the back yoke 34 is fitted into the support member 4 without any radial play, and may be any of an interference fit, an intermediate fit, or a clearance fit. In the illustrated example, with the magnetostrictive torque sensor 6 supported by the support member 4, the back yoke 34 is fitted into the sensor fitting surface portion 8 with a clearance fit. As a result, the magnetostrictive torque sensor 6 is positioned radially relative to the support member 4.

[0068] The structure for fitting the magnetostrictive torque sensor 6 into the support member 4 and the associated radial positioning of the magnetostrictive torque sensor 6 relative to the support member 4 can also be achieved by using a portion of the magnetostrictive torque sensor 6 other than the back yoke 34. For example, the radial positioning of the magnetostrictive torque sensor 6 relative to the support member 4 can be achieved by fitting or engaging a portion of the holder 18 with or with the support member 4.

[0069] When the magnetostrictive torque measuring device 1 of this example is assembled to the rotating shaft 2, the opposing surface 15 is disposed coaxially around the detection target 3 of the rotating shaft 2, closely facing the detection target 3, but not in contact with the detection target 3. The size of the radial gap between the outer circumferential surface of the rotating shaft 2 (detection target 3) and the opposing surface 15, i.e., the difference between the outer diameter of the outer circumferential surface of the rotating shaft 2 (detection target 3) and the inner diameter of the opposing surface 15, is not limited to this, but is preferably less than the lower limit of the setting range for conventional structures at room temperature (e.g., 25°C), i.e., less than 0.1 mm (100 μm), and more preferably 80 μm or less.

[0070] When the magnetostrictive torque measurement device 1 of this example is assembled to the rotating shaft 2, the size of the radial gap between the outer circumferential surface of the rotating shaft 2 and the inner circumferential surface of the support bearing 5 is less than (including zero) the size of the radial gap between the outer circumferential surface of the rotating shaft 2 and the opposing surface 15. When the support bearing 5 is fitted to the rotating shaft 2 with an interference fit or an intermediate fit, the size of the radial gap between the outer circumferential surface of the rotating shaft 2 and the inner circumferential surface of the support bearing 5 is substantially zero (no radial gap exists). Even when the support bearing 5 is fitted to the rotating shaft 2 with a clearance fit, the size of the radial gap between the outer circumferential surface of the rotating shaft 2 and the inner circumferential surface of the support bearing 5 (the inner circumferential surface of the inner ring 12) is kept to several tens of μm or less, i.e., 50 μm or less, preferably 30 μm or less, which is sufficiently smaller than the size of the radial gap between the outer circumferential surface of the rotating shaft 2 (the portion to be detected 3) and the opposing surface 15.

[0071] It is preferable that the size of the radial gap between the outer surface of the rotating shaft 2 and the opposing surface 15 is 250 μm or less, and the size of the maximum radial gap between the outer surface of the rotating shaft 2 and the inner surface of the support bearing 5 is less than 100 μm.

[0072] Furthermore, it is more preferable that the sum of the radial gap between the inner surface of the support member 4 (bearing mating surface portion 9) and the outer surface of the support bearing 5 (outer surface of the outer ring 11), the radial gap between the outer surface of the rotating shaft 2 and the inner surface of the support bearing 5 (inner surface of the inner ring 12), and the radial internal gap of the support bearing 5 is smaller than the radial gap between the outer surface of the rotating shaft 2 (detectable portion 3) and the opposing surface 15.

[0073] In the magnetostrictive torque measuring device 1 of this example, the support member 4 supporting the magnetostrictive torque sensor 6 is not fixedly supported on the structural element, but is supported by a support bearing 5 so as to be rotatable relative to the rotating shaft 2 which is rotatably supported on the structural element.

[0074] In the illustrated example, the magnetostrictive torque sensor 6 is not positioned radially relative to the structural element, but is positioned radially relative to the rotating shaft 2 via the support bearing 5 and support member 4. Therefore, even if the rotating shaft 2 wobbles (tilts) relative to the structural element or elastic bending deformation occurs in the rotating shaft 2 during operation of the apparatus including the magnetostrictive torque measurement device 1 and the rotating shaft 2, the radial distance between the detection target 3 provided on the outer peripheral surface of the rotating shaft 2 and the opposing surface 15 of the magnetostrictive torque sensor 6 remains almost unchanged over the entire circumference.

[0075] Furthermore, even if the rotating shaft 2 is inclined relative to the support bearing 5 and the support member 4, for example, the size of the radial gap between the outer surface of the rotating shaft 2 and the inner surface of the support bearing 5 will be less than (including 0) the size of the radial gap between the outer surface of the rotating shaft 2 and the opposing surface 15, so the detected part 3 of the rotating shaft 2 and the opposing surface 15 of the magnetostrictive torque sensor 6 will not come into contact.

[0076] Even when a configuration is adopted in which the support member 4 is supported so that radial relative displacement with respect to the structural element is not possible, even if the rotating shaft 2 oscillates (tilts) with respect to the structural element or elastic bending deformation occurs in the rotating shaft 2, the amount of oscillation or bending deformation of the rotating shaft 2 can be kept extremely small due to the presence of the support bearing 5 sandwiched between the rotating shaft 2 and the support member 4.

[0077] In this way, the magnetostrictive torque measurement device 1 of this example can prevent contact between the detection target 3 provided on the outer peripheral surface of the rotating shaft 2 and the opposing surface 15 of the magnetostrictive torque sensor 6, while allowing the radial distance between the detection target 3 and the opposing surface 15 to be set much smaller than in conventional structures. Therefore, with the magnetostrictive torque measurement device 1 of this example, the radial distance between the detection target 3 and the detection unit 17 can be made smaller than in conventional structures, and as a result, leakage magnetic flux that does not pass through the detection target 3 can be kept small, making it easier to ensure torque measurement accuracy, torque measurement sensitivity, or both.

[0078] In a configuration in which the magnetostrictive torque sensor 6 includes the holder 18, the radial thickness T 20is not limited to this, but is preferably 1.8 mm or less (0 < T 20 <1.8 mm).

[0079] In the illustrated example, the holder 18 includes a first outward flange portion 21 that extends radially outward from one axial end of the bobbin portion 20 around the entire circumference, and a second outward flange portion 22 that extends radially outward from the other axial end of the bobbin portion 20 around the entire circumference. The holder 18 may further include a protrusion 23 that can be engaged with the support member 4 in the circumferential direction. The protrusion 23 protrudes radially outward from one circumferential location of the first outward flange portion 21.

[0080] The first outward flange portion 21 and the protrusion portion 23 have a wiring accommodating portion that accommodates a cable 32 that electrically connects the detection coil 16 provided in the coil unit 19 to an external device 28, or a signal line, or both.

[0081] In the illustrated example, the outer diameter of the first outward flange portion 21 is larger than the outer diameter of the second outward flange portion 22. However, the outer diameter of the first outward flange portion 21 can be the same as the outer diameter of the second outward flange portion 22, or can be smaller than the outer diameter of the second outward flange portion 22. Also, in the illustrated example, the outer diameter of the first outward flange portion 21 is smaller than the inner diameter of the large-diameter cylindrical surface portion 38 of the support member 4.

[0082] In the illustrated example, the coil unit 19 is configured by a flexible substrate 24, and the plurality of detection coils 16 are configured by wiring patterns formed on a wiring layer.

[0083] The flexible substrate 24 has a detection section 17 made up of a plurality of detection coils 16, and a main body 25 configured in a cylindrical or partially cylindrical shape.

[0084] In the unfolded state of the flexible substrate 24 as shown in Fig. 4, the main body 25 is configured in a belt-like or rectangular plate-like shape. That is, the main body 25 is configured in a cylindrical shape or a notched cylindrical shape having a discontinuous portion at one location in the circumferential direction by wrapping the main body 25 in a belt-like or rectangular plate-like shape as shown in Fig. 4 around the bobbin portion 20 of the holder 18.

[0085] In the illustrated example, the coil unit 19 is held in the holder 18 by fixing the inner peripheral surface of the main body 25 to the outer peripheral surface of the bobbin portion 20 with an adhesive. However, the coil unit 19 can also be held in the holder 18 by joining the ends on both circumferential sides of the main body 25 of the flexible substrate 24 wrapped around the bobbin portion 20 with an adhesive or adhesive tape, or by wrapping a holding band around the main body 25 of the flexible substrate 24 wrapped around the bobbin portion 20.

[0086] In the illustrated example, the main body 25 has four detection coils 16a to 16d. As shown in Fig. 3, each of the detection coils 16a to 16d is configured by arranging a plurality of coil pieces 26a to 26d and 27a to 27d in the circumferential direction (the direction of the long sides of the main body 25 when the flexible substrate 24 is in the unfolded state).

[0087] Specifically, the first detection coil 16a is constructed by connecting in series a plurality of coil pieces 26a, 27a arranged in the circumferential direction, the second detection coil 16b is constructed by connecting in series a plurality of coil pieces 26b, 27b arranged in the circumferential direction, the third detection coil 16c is constructed by connecting in series a plurality of coil pieces 26c, 27c arranged in the circumferential direction, and the fourth detection coil 16d is constructed by connecting in series a plurality of coil pieces 26d, 27d arranged in the circumferential direction.

[0088] Of the coil pieces 26a to 26d and 27a to 27d, the coil pieces 26a to 26d 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 27a to 27d are configured by arranging the wiring pattern so as to be wound in an approximately parallelogram shape when viewed from the radial direction.

[0089] The coil pieces 26a and 27a constituting the first detector coil 16a and the coil pieces 26c and 27c constituting the third detector coil 16c 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 main body 25 when the flexible substrate 24 is in the unfolded state). The coil pieces 26b and 27b constituting the second detector coil 16b and the coil pieces 26d and 27d constituting the fourth detector coil 16d 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.

[0090] The four detection coils 16a to 16d are electrically connected to an external device .

[0091] The external device 28 includes an oscillator 29 that applies a voltage between two points, and a voltmeter 30 that detects the voltage between the two points.

[0092] There are no particular limitations on the manner in which the detection coils 16a to 16d are electrically connected to the external device 28. In this example, the detection coils 16a to 16d are electrically connected to the external device 28 by signal lines 31a to 31d (see FIG. 3, not shown in other figures) formed on the wiring layer of the flexible substrate 24 and a cable 32 connected to the external device 28.

[0093] That is, the flexible substrate 24 of this example includes a band-shaped signal line portion 33 that is drawn out radially, axially, or in both the radial and axial directions from the main body portion 25. The signal line portion 33 has four stacked signal lines 31a to 31d.

[0094] Of the four signal lines 31a to 31d, the first signal line 31a connects one end of the first detection coil 16a and one end of the second detection coil 16b in series, and is electrically connected to one terminal of the oscillator 29 via a cable 32.

[0095] The second signal line 31b connects one end of the third detection coil 16c and one end of the fourth detection coil 16d in series, and is electrically connected to the other terminal of the oscillator 29 via a cable 32.

[0096] The third signal line 31c connects the other end of the first detection coil 16a and the other end of the third detection coil 16c in series, and is electrically connected to one terminal of the voltmeter 30 via a cable 32.

[0097] The fourth signal line 31d connects the other end of the second detection coil 16b and the other end of the fourth detection coil 16d in series, and is electrically connected to the other terminal of the voltmeter 30 via a cable 32.

[0098] Oscillator 29 applies an AC voltage between a contact A connecting one end of first detector coil 16a and one end of second detector coil 16b, and a contact B connecting one end of third detector coil 16c and one end of fourth detector coil 16d. Voltmeter 30 detects a voltage between a contact C connecting the other end of first detector coil 16a and the other end of third detector coil 16c, and a contact D connecting the other end of second detector coil 16b and the other end of fourth detector coil 16d. In other words, the four detector coils 16a to 16d that make up main body 25, together with oscillator 29 and voltmeter 30, form a bridge circuit.

[0099] When torque T is applied to the rotating shaft 2, stresses σ with opposite signs act on the outer circumferential surface of the rotating shaft 2 in a direction inclined at +45° with respect to the axial direction and in a direction inclined at -45° with respect to the axial direction. Due to the inverse magnetostrictive 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 6 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 the voltmeter 30, and the direction and magnitude of the torque transmitted by the rotating shaft 2 are determined based on this detected value.

[0100] REFERENCE SIGNS LIST 1 Magnetostrictive torque measuring device 2 Rotating shaft 3 Part to be detected 4 Support member 5 Support bearing 6 Magnetostrictive torque sensor 7 Notch 8 Sensor mating surface 9 Bearing mating surface 10 Connection surface 11 Outer ring 12 Inner ring 13 Rolling element 14 Retaining ring 15 Opposing surface 16 Detection coil 16a First detection coil 16b Second detection coil 16c Third detection coil 16d Fourth detection coil 17 Detection unit 18 Holder 19 Coil unit 20 Bobbin portion 21 First outward flange portion 22 Second outward flange portion 23 Protrusion 24 Flexible substrate 25 Main body portion 26a to 26d Coil pieces 27a to 27d Coil pieces 28 External device 29 Oscillator 30 Voltmeter 31a First signal line 31b Second signal line 31c Third signal line 31d Fourth signal line 32 Cable 33 Signal line portion 34 Back yoke 35 Engagement hole 36 Engagement member 37 Retaining ring 38 Large diameter cylindrical surface portion 39 Connection surface portion 40 Back end surface 41a, 41b Engagement groove

Claims

1. A magnetostrictive torque measuring device comprising: a support member arranged around a rotating shaft that is rotatably supported relative to a structural element that does not rotate even when in use, such that relative rotation with respect to the structural element is not possible; a support bearing arranged between the rotating shaft and the support member, and supporting the support member so that relative rotation with respect to the rotating shaft is possible; and a magnetostrictive torque sensor supported by the support member, having an opposing surface that faces closely to the outer circumferential surface of the rotating shaft, and a detection unit arranged on the outer diameter side of the opposing surface and consisting of multiple detection coils.

2. The magnetostrictive torque measuring device according to claim 1, wherein the support member is capable of relative displacement in the radial direction with respect to the structural element.

3. A magnetostrictive torque measuring device as described in claim 1 or 2, wherein, when assembled to the rotating shaft, the size of the radial gap between the outer surface of the rotating shaft and the opposing surface is less than 0.1 mm, and the size of the radial gap between the outer surface of the rotating shaft and the inner surface of the support bearing is less than the size of the radial gap between the outer surface of the rotating shaft and the opposing surface (including 0).

4. A magnetostrictive torque measuring device as described in claim 3, wherein the size of the radial gap between the outer surface of the rotating shaft and the opposing surface is 80 μm or less, and the size of the maximum radial gap between the outer surface of the rotating shaft and the inner surface of the support bearing is 50 μm or less.

5. A magnetostrictive torque measuring device according to any one of claims 1 to 4, wherein the magnetostrictive torque sensor comprises a holder including the opposing surface and having a bobbin portion disposed around the rotation axis.

6. The magnetostrictive torque measuring device according to claim 5, wherein the holder has a protrusion that can be engaged with the support member in the circumferential direction.

7. A magnetostrictive torque measuring device as described in any one of claims 1 to 6, wherein the support bearing has an outer ring fitted inside the support member, an inner ring fitted outside the rotating shaft, and a plurality of rolling elements arranged to roll freely between the outer ring and the inner ring.

8. A magnetostrictive torque measuring device according to any one of claims 1 to 7, wherein the magnetostrictive torque sensor comprises a back yoke arranged around the detection portion, and the back yoke is fitted inside the support member.

9. A magnetostrictive torque measuring device according to any one of claims 1 to 8, further comprising an engaging member stretched between the structural element and the support member.

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