Assembling method for magnetostrictive torque sensor, and magnetostrictive torque sensor

Abstract

Realized is an assembling method for a magnetostrictive torque sensor that can easily facilitate reduction in manufacturing costs. When the proportion of a body 12 of a flexible board 8 that faces the outer circumferential surface of a rotary shaft 2 is within a predetermined range in the case where the body 12 faces the whole circumference of the outer circumferential surface of the rotary shaft 2 is defined as 100%, a common flexible board 8 having the same length in the circumferential direction of the body 12 is used.

Description

Magnetostrictive torque sensor assembly method and magnetostrictive torque sensor

[0001] The present disclosure relates to a magnetostrictive torque sensor that measures torque applied to a rotating shaft and an assembly method thereof.

[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 magnetostrictive effect that occurs in the rotating shaft when torque is applied to the rotating shaft has been known for some time, as described in JP 2022-074405 A, for example.

[0003] A conventional magnetostrictive torque sensor described in JP 2022-074405 A includes a flexible substrate having a detection unit that includes multiple detection coils and is arranged around a rotating shaft. The magnetostrictive torque sensor detects torque applied to the rotating shaft based on changes in inductance of the detection coils.

[0004] Japanese Patent Application Laid-Open No. 2022-074405

[0005] The conventional magnetostrictive torque sensor described in JP 2022-074405 A is obtained by punching a base material to obtain a flexible substrate having a roughly rectangular plate-shaped main body portion equipped with a detection unit, and then wrapping the main body portion around a bobbin portion (inner cylindrical portion) of a holder (first resin member) to form it into a notched cylindrical shape.

[0006] There are many different outer diameters of rotating shafts, depending on the magnitude of the torque to be transmitted, the metal material of the rotating shaft, and other factors. Therefore, flexible substrates with different circumferential lengths of the main body provided with the detection unit are prepared for each outer diameter of the rotating shaft. This increases the number of types of flexible substrates, making it difficult to reduce the manufacturing costs of magnetostrictive torque sensors.

[0007] An object of the present disclosure is to provide a method for assembling a magnetostrictive torque sensor that can easily reduce manufacturing costs.

[0008] The inventors of the present disclosure have conducted extensive research into the effect on torque measurement accuracy of a magnetostrictive torque sensor of the proportion of the main body of the flexible substrate facing the outer circumferential surface of the rotating shaft, where 100% is the proportion of the main body facing the entire outer circumferential surface of the rotating shaft, and have found that sufficient torque measurement accuracy can be ensured as long as the proportion is within a predetermined range. A method of assembling a magnetostrictive torque sensor according to one aspect of the present disclosure and a magnetostrictive torque sensor according to one aspect of the present disclosure have been completed based on this finding.

[0009] A magnetostrictive torque sensor that is the subject of the magnetostrictive torque sensor assembly method of one embodiment of the present disclosure comprises: a holder having a bobbin portion that is arranged around a rotation axis to be measured; and a flexible substrate that is arranged around the bobbin portion and has a main body portion that is equipped with a detection unit consisting of a plurality of detection coils.

[0010] In one embodiment of the present disclosure, a method for assembling a magnetostrictive torque sensor uses a common flexible substrate having the same circumferential length for the main body portion when the percentage of the main body portion that faces the outer peripheral surface of the rotating shaft is within a predetermined range, where 100% is when the main body portion faces the entire outer peripheral surface of the rotating shaft.

[0011] In the method for assembling a magnetostrictive torque sensor according to one aspect of the present disclosure, the predetermined range is equal to or greater than 75% and less than 100%.

[0012] In the method for assembling a magnetostrictive torque sensor according to one aspect of the present disclosure, the predetermined range is equal to or greater than 80% and equal to or less than 90%.

[0013] A magnetostrictive torque sensor according to one aspect of the present disclosure includes: a holder having a bobbin portion arranged around a rotation axis; and a flexible substrate having a main body portion arranged around the bobbin portion and equipped with a detection unit consisting of a plurality of detection coils.

[0014] In particular, in one aspect of the magnetostrictive torque sensor of the present disclosure, the percentage of the main body portion facing the outer peripheral surface of the rotating shaft is 75% or more and less than 92%, where 100% is when the main body portion faces the entire outer peripheral surface of the rotating shaft.

[0015] In the magnetostrictive torque sensor according to one aspect of the present disclosure, the predetermined range is equal to or greater than 80% and equal to or less than 90%.

[0016] According to the magnetostrictive torque sensor and the assembly method thereof of one aspect of the present disclosure, it is possible to easily reduce manufacturing costs.

[0017] FIG. 1 is a schematic diagram of a cross section of a magnetostrictive torque sensor according to an embodiment of the present disclosure, cut along an imaginary plane including the central axis of a rotation shaft. FIG. 2 is a cross section taken along the line X-X in FIG. 1. FIG. 3 is a partially enlarged cross section showing a detection section of a flexible substrate. FIGS. 4(a) to 4(d) are development views of the first to fourth wiring layers as viewed from the radially outer side. FIG. 5 is a schematic diagram showing a detection circuit including four detection coils. FIG. 6 is a plan view showing the flexible substrate in an unfolded state.

[0018] The inventors of the present disclosure have conducted extensive research into the effect that the proportion of the main body of the flexible printed circuit board facing the outer circumferential surface of the rotating shaft, assuming that the proportion is 100%, on the accuracy of torque detection of the rotating shaft by a magnetostrictive torque sensor, and have found that sufficient torque detection accuracy can be ensured if the proportion is in the range of 75% or more and less than 100%, preferably in the range of 80% or more and 90% or less. The present disclosure has been completed based on this finding.

[0019] An example of an embodiment of the present disclosure will be described with reference to FIGS. 1 to 6. FIG.

[0020] The magnetostrictive torque sensor 1 is used to measure the torque transmitted by the rotating shaft 2 .

[0021] 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 holder 5 and also coincide with the axial, radial, and circumferential directions of the magnetic ring 26. 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.

[0022] 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 the 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.

[0023] 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 a steel material such as, but not limited to, SC (carbon steel for mechanical structures), SUS (stainless steel), SCr (chrome steel), SCM (chrome molybdenum steel), or SNCM (nickel chrome molybdenum steel).

[0024] The magnetostrictive torque sensor 1 comprises a holder 5 having a bobbin portion 4 arranged around a rotating shaft 2, and a flexible substrate 8 having a main body portion 12 arranged around the bobbin portion 4 and equipped with a detection portion 7 consisting of a plurality of detection coils 6. 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 detection portion 7 consisting of the plurality of detection coils 6, and measures the torque transmitted by the rotating shaft 2.

[0025] The holder 5 is made of synthetic resin, which is a non-magnetic and non-conductive (insulating) material. Specifically, the holder 5 is made of a thermoplastic resin such as epoxy resin, polyphenylene sulfide (PPS), PA (polyamide), or PPA (polyphthalamide). In this example, the holder 5 is integrally formed by injection molding of the synthetic resin. Alternatively, the holder 5 can be formed by combining multiple parts.

[0026] The holder 5 is supported and fixed to a fixed part that does not rotate during use, such as a housing, with the bobbin part 4 arranged coaxially around the detection target part 3 of the rotary shaft 2 .

[0027] In this example, the bobbin portion 4 is cylindrically configured, i.e., the bobbin portion 4 has a cylindrical inner peripheral surface whose inner diameter does not change in the axial direction, and a cylindrical outer peripheral surface whose outer diameter does not change in the axial direction.

[0028] Alternatively, the bobbin portion 4 may be configured as a partially cut cylindrical portion.

[0029] The inner peripheral surface of the bobbin portion 4 faces the detection target portion 3 of the rotary shaft 2 with a radial gap 11 therebetween.

[0030] In this example, the holder 5 has, as optional elements, a first outward flange portion 9 extending radially outward from the end on one axial side of the bobbin portion 4 around the entire circumference, and a second outward flange portion 10 extending radially outward from the end on the other axial side of the bobbin portion 4 around the entire circumference.

[0031] The first outward flange portion 9 has an attachment portion for supporting and fixing the holder 5 to the fixed portion, a wiring accommodating portion for accommodating cables or signal lines that electrically connect the detection coils 6a to 6d to an external device, and the like.

[0032] In this example, the outer diameter of the first outward flange portion 9 is larger than the outer diameter of the second outward flange portion 10. However, the outer diameter of the first outward flange portion 9 can be the same as the outer diameter of the second outward flange portion 10, or can be smaller than the outer diameter of the second outward flange portion 10.

[0033] The flexible substrate 8 is configured to be elastically deformable by disposing a wiring layer 13 made of a conductor on the surface or inside of a base film 14 made of an insulator. In the unfolded state of the flexible substrate 8 as shown in Fig. 6, the main body 12 provided with the detection unit 7 is configured in the shape of a strip or a substantially rectangular plate. In the assembled state of the magnetostrictive torque sensor 1, the main body 12 is wound around the bobbin part 4 of the holder 5 and formed into a notched cylindrical or cylindrical shape.

[0034] The flexible substrate 8 has a laminated structure having a plurality of wiring layers 13 that constitute the detection coil 6. Each wiring layer 13 is composed of a wiring pattern formed by etching copper foil, which is a conductor.

[0035] Each wiring layer 13 is formed on the surface of a base film 14 and is covered with a coverlay film 16. The coverlay film 16, the wiring layer 13, and the base film 14 are bonded together by an adhesive layer 15.

[0036] The coverlay film 16 and the base film 14 are made of thin films of insulating material such as polyimide or polyester. The coverlay film 16 is a protective film for protecting the wiring layer 13. The adhesive layer 15 is made of an epoxy resin, acrylic resin, or polyimide resin adhesive.

[0037] The number, configuration, and arrangement of the multiple detection coils 6 are not particularly limited as long as they can detect changes in the magnetic permeability of the rotating shaft 2. For example, the multiple detection coils 6 can be arranged overlapping each other in the radial direction, arranged side by side in the axial direction, or arranged overlapping each other in the radial direction and arranged side by side in the axial direction. The number of the multiple detection coils 6 can be any number equal to or greater than two.

[0038] The flexible substrate 8 has wiring layers 13 the number of which corresponds to the number and arrangement of the detection coils 6. In this example, the flexible substrate has four detection coils 6 (first detection coil 6a to fourth detection coil 6d), and therefore has four wiring layers 13 (first wiring layer 13a to fourth wiring layer 13d).

[0039] Specifically, as shown in Figure 3, the flexible substrate 8 is constructed by stacking, from the radially outer side, a first coverlay film 16a, a first adhesive layer 15a, a first wiring layer 13a, a first base film 14a, a second wiring layer 13b, a second adhesive layer 15b, a second coverlay film 16b, a third adhesive layer 17, a third coverlay film 16c, a fourth adhesive layer 15c, the third wiring layer 13c, the second base film 14b, a fourth wiring layer 13d, a fifth adhesive layer 15d, and a fourth coverlay film 16d.

[0040] The first wiring layer 13a is formed on the radially outer surface of the first base film 14a, the second wiring layer 13b is formed on the radially inner surface of the first base film 14a, the third wiring layer 13c is formed on the radially outer surface of the second base film 14b, and the fourth wiring layer 13d is formed on the radially inner surface of the second base film 14b.

[0041] The first adhesive layer 15a, the second adhesive layer 15b, the fourth adhesive layer 15c, and the fifth adhesive layer 15d bond the coverlay films 16a to 16d to the wiring layers 13a to 13d, or the wiring layers 13a to 13d to the base films 14a and 14b, respectively. The third adhesive layer 17 bonds the two coverlay films 16c and 16d to each other.

[0042] In this example, the first detection coil 6a is formed by the first wiring layer 13a, the second detection coil 6b is formed by the second wiring layer 13b, the third detection coil 6c is formed by the third wiring layer 13c, and the fourth detection coil 6d is formed by the fourth wiring layer 13d.

[0043] The detection unit 7 is arranged around the bobbin unit 4 and is composed of a plurality of detection coils 6 .

[0044] In this example, the detection unit 7 includes four detection coils 6 (first detection coil 6a to fourth detection coil 6d), and the main body 12 including the detection unit 7 is wound around the outer circumferential surface of the bobbin unit 4, thereby being disposed around the bobbin unit 4. The main body 12 is wound around the outer circumferential surface of the bobbin unit 4 so as not to float above the outer circumferential surface of the bobbin unit 4. For this reason, the main body 12 can be adhesively fixed to the outer circumferential surface of the bobbin unit 4, or pressed from the radially outer side by a pressing member (not shown).

[0045] The ends of the main body 12 on both sides in the circumferential direction do not overlap each other in the radial direction.

[0046] In this example, the flexible substrate 8 is used as a common component among a plurality of types of magnetostrictive torque sensors 1 used to measure torque for a plurality of types of rotating shafts 2 with different outer diameters. Specifically, the holder 5 and magnetic ring 26 are designed specifically for each outer diameter of the rotating shaft 2, whereas the flexible substrate 8 is designed to fit the circumferential length of the main body 12 (the long side dimension L in the unfolded state shown in FIG. 6 ) when the outer diameter of the rotating shaft 2 is within a predetermined range. １２ Therefore, assuming that the area where the main body 12 faces the entire circumference of the detection target 3 of the rotating shaft 2 is 100%, the percentage of the area where the main body 12 faces the detection target 3 of the rotating shaft 2 varies depending on the outer diameter of the rotating shaft 2.

[0047] Specifically, in a magnetostrictive torque sensor 1 for measuring torque on a rotating shaft 2 with the smallest outer diameter among multiple types of rotating shafts 2 for which flexible substrates 8 with the same circumferential length of the main body 12 are used, the percentage is 92% or more and less than 100%, and preferably 96% or more and 98% or less. In contrast, in a magnetostrictive torque sensor 1 for measuring torque on a rotating shaft 2 with the largest outer diameter among multiple types of rotating shafts 2 for which flexible substrates 8 with the same circumferential length of the main body 12 are used, the percentage is 75% or more and 91% or less of the entire circumference, and preferably 80% or more and 90% or less.

[0048] In the assembled state of the magnetostrictive torque sensor 1, it is preferable that the main body 12 has a notched cylindrical shape regardless of the outer diameter of the rotating shaft 2 to be measured. That is, it is preferable that the main body 12 also has a notched cylindrical shape in a magnetostrictive torque sensor 1 for measuring the torque of a rotating shaft 2 with the smallest outer diameter among multiple types of rotating shafts 2 for which flexible substrates 8 having the same circumferential length of the main body 12 are used. In other words, it is preferable that a circumferential gap 18 exists between both circumferential ends of the main body 12 in a magnetostrictive torque sensor 1 for measuring the torque of a rotating shaft 2 with the smallest outer diameter.

[0049] In this example, the four detection coils 6a to 6d are arranged to overlap in the radial direction. Specifically, the four detection coils 6a to 6d are arranged to overlap in the order of the first detection coil 6a, the second detection coil 6b, the third detection coil 6c, and the fourth detection coil 6d from the outside in the radial direction.

[0050] As shown in Figures 4(a) to 4(d), each of the detection coils 6a to 6d is formed by arranging a plurality of coil pieces 19a to 19d, 20a to 20d in the circumferential direction, that is, in the direction of the long side of the main body 12 in the state before it is bent into a partially cylindrical shape (the expanded state shown in Figure 6).

[0051] Specifically, the first detection coil 6a is constructed by connecting in series a plurality of coil pieces 19a, 20a arranged in the circumferential direction, the second detection coil 6b is constructed by connecting in series a plurality of coil pieces 19b, 20b arranged in the circumferential direction, the third detection coil 6c is constructed by connecting in series a plurality of coil pieces 19c, 20c arranged in the circumferential direction, and the fourth detection coil 6d is constructed by connecting in series a plurality of coil pieces 19d, 20d arranged in the circumferential direction.

[0052] Of the coil pieces 19a to 19d and 20a to 20d, the coil pieces 19a to 19d 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 20a to 20d are configured by arranging the wiring pattern so as to be wound in an approximately parallelogram shape when viewed from the radial direction.

[0053] The coil pieces 19a and 20a constituting the first detector coil 6a and the coil pieces 19c and 20c constituting the third detector 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 main body 12 when the flexible substrate 8 is in the unfolded state). The coil pieces 19b and 20b constituting the second detector coil 6b and the coil pieces 19d and 20d constituting the fourth detector 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.

[0054] The four detection coils 6 a to 6 d are electrically connected to an external device 21 .

[0055] The external device 21 includes an oscillator 22 that applies a voltage between two points, and a voltmeter 23 that detects the voltage between the two points.

[0056] There are no particular limitations on the manner in which the plurality of detection coils 6 are electrically connected to the external device 21, and any known means can be applied. In this example, the four detection coils 6a to 6d are electrically connected to the external device 21 by signal lines 24a to 24d formed on the wiring layers 13a to 13d of the flexible substrate 8, and by cables connected to the external device 21.

[0057] That is, the flexible substrate 8 of this example includes a band-shaped signal line portion 25 (see FIG. 6) that is pulled out in the radial direction, the axial direction, or both the radial and axial directions from the main body portion 12. The signal line portion 25 has four stacked signal lines 24a to 24d.

[0058] Of the four signal lines 24a to 24d, the first signal line 24a 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 22 via the cable.

[0059] The second signal line 24b 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 22 via the cable.

[0060] The third signal line 24c 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 23 via the cable.

[0061] The fourth signal line 24d 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 23 via the cable.

[0062] Oscillator 22 applies an AC voltage between contact A between one end of first detection coil 6a and one end of second detection coil 6b, and contact B between one end of third detection coil 6c and one end of fourth detection coil 6d. Voltmeter 23 detects the voltage between contact C between the other end of first detection coil 6a and the other end of third detection coil 6c, and contact D between the other end of second detection coil 6b and the other end of fourth detection coil 6d. In other words, the four detection coils 6a to 6d that make up detection unit 7, together with oscillator 22 and voltmeter 23, form a bridge circuit.

[0063] 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 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 the voltmeter 23, and the direction and magnitude of the torque transmitted by the rotating shaft 2 are determined based on this detected value.

[0064] The magnetostrictive torque sensor 1 of this example includes a magnetic ring 26 as an optional component.

[0065] The magnetic ring 26, also called a back yoke, has the function of preventing the magnetic flux generated by the detection coils 6a to 6d from leaking to the outside. The magnetic ring 26 is made of a magnetic material and is integrally formed as a whole. Examples of the magnetic material that can be used for the magnetic ring 26 include iron-based alloys such as mechanical structural alloy steel and stainless steel.

[0066] The magnetic ring 26 has a cylindrical shape. The magnetic ring 26 is disposed around the main body 12 (detection unit 7) of the flexible substrate 8 and coaxially with the main body 12, and is fixedly coupled to the holder 5. In this example, the other axial end of the magnetic ring 26 is fitted and fixed to the second outward flange 10, thereby fixing the magnetic ring 26 to the holder 5.

[0067] The method for assembling the magnetostrictive torque sensor 1 of this example can be widely applied to magnetostrictive torque sensors 1 that include a holder 5 having a bobbin portion 4 that is arranged around the rotation axis to be measured, and a flexible substrate 8 that is arranged around the bobbin portion 4 and has a main body portion 12 that is equipped with a detection unit 7 made up of a plurality of detection coils 6. Below, the method for assembling the magnetostrictive torque sensor 1 of this example will be described with reference to the magnetostrictive torque sensor 1 of this example that has the above-mentioned configuration, although the method is not limited to this.

[0068] In the assembly method of the magnetostrictive torque sensor 1, a common flexible substrate 8 having the same circumferential length of the main body 12 is used when the proportion of the main body 12 facing the outer peripheral surface of the rotating shaft 2 (detectable portion 3) is within a predetermined range, with 100% being the proportion when the main body 12 of the flexible substrate 8 faces the entire outer peripheral surface of the rotating shaft 2 (detectable portion 3).

[0069] In this example, when the ratio is in the range of 75% or more but less than 100%, preferably in the range of 80% or more but less than 90%, a common flexible substrate 8 having the same circumferential length of the main body portion 12 is used.

[0070] The assembly method of the magnetostrictive torque sensor 1 of this example includes a bending step in which the belt-shaped or approximately rectangular plate-shaped main body portion 12 equipped with the detection unit 7 of the flexible substrate 8, as shown in the unfolded state in Figure 6, is wound around the bobbin portion 4 to form it into a notched cylindrical or cylindrical shape.

[0071] In preparation for carrying out the bending process, first, a plurality of types of holders 5 are prepared, each having a different inner diameter and outer diameter of the bobbin portion 4. The number of types of holders 5 is equal to or less than the number of types of outer diameter of the rotating shaft 2.

[0072] In this example, the number of types of holders 5 is the same as the number of types of outer diameters of the rotating shaft 2. In other words, holders 5 designed specifically for each outer diameter of the rotating shaft 2 are used, specifically holders 5 having bobbin portions 4 with different inner and outer diameters for each outer diameter of the rotating shaft 2.

[0073] However, the number of types of holders 5 may be less than the number of types of outer diameters of the rotating shafts 2. Even in this case, the number of types of holders 5 is greater than the number of types of flexible substrates 8.

[0074] The circumferential length of the main body 12 (the long side dimension L in the unfolded state shown in FIG. 6) １２ The number of types of flexible substrates 8 is less than the number of types of outer diameters of the rotating shafts 2 and less than the number of types of holders 5.

[0075] In this example, two or more types of flexible substrates 8 are prepared so that the ratio falls within the range of 75% or more and less than 100%, preferably 80% or more and 90% or less, within the range of the outer diameter of the rotating shaft 2 that can be measured.

[0076] Furthermore, in this example, multiple types of magnetic rings 26, which are optional components, are prepared with different inner diameters. The number of types of magnetic rings 26 is equal to or less than the number of types of outer diameters of the rotating shaft 2.

[0077] In this example, the number of types of magnetic rings 26 is the same as the number of types of outer diameters of the rotating shafts 2. In other words, the number of types of magnetic rings 26 is the same as the number of types of holders 5.

[0078] However, the number of types of magnetic rings 26 may be less than the number of types of outer diameters of the rotating shaft 2. In this case, the number of types of magnetic rings 26 may be the same as the number of types of holders 5, or may be less than or greater than the number of types of holders 5.

[0079] Next, a holder 5 having a bobbin portion 4 with an optimum outer diameter and inner diameter is selected from among multiple types of holders 5 in accordance with the outer diameter of the rotating shaft 2 to be measured. In this example, a holder 5 specifically designed to match the outer diameter of the rotating shaft 2 to be measured is selected from among multiple types of holders 5.

[0080] Furthermore, a flexible substrate 8 having the ratio within a predetermined range is selected from among multiple types of flexible substrates 8 in accordance with the outer diameter of the rotating shaft 2 to be measured. In this example, a flexible substrate 8 having the ratio of 75% or more and less than 100%, preferably 80% or more and 90% or less, is selected from among multiple types of flexible substrates 8. More specifically, a flexible substrate 8 having the smallest distance between the circumferential ends of the main body portion 12 in a state where the main body portion 12 is wound around the bobbin portion 4 of the selected holder 5 and formed into a notched cylindrical or cylindrical shape is selected from among the multiple types of flexible substrates 8 prepared.

[0081] Furthermore, in this example, a magnetic ring 26 having an optimum inner diameter that matches the outer diameter of the rotating shaft 2 to be measured is selected from among multiple types of magnetic rings 26. In this example, a magnetic ring 26 that is specially designed to match the outer diameter of the rotating shaft 2 to be measured is selected from among multiple types of magnetic rings 26.

[0082] Next, the selected holder 5, flexible substrate 8 and magnetic ring 26 are combined together.

[0083] For this purpose, first, a bending process is carried out in which the main body portion 12 of the flexible substrate 8, which is provided with the detection portion 7, is wound around the bobbin portion 4 of the holder 5 and formed into a notched cylindrical or cylindrical shape.

[0084] In order to prevent the main body portion 12 from floating up from the bobbin portion 4, if necessary, it may be adhesively fixed to the outer peripheral surface of the bobbin portion 4 or pressed down from the radially outer side by a pressing member not shown.

[0085] Furthermore, the signal line portion 25 of the flexible substrate 8 is pulled out in the axial or radial direction from the holder 5 through a wiring accommodating portion provided in the holder 5 .

[0086] Next, the magnetic ring 26 is coupled and fixed to the holder 5 while being disposed coaxially around the main body 12. Specifically, the other axial end of the magnetic ring 26 is fitted and fixed to the second outward flange 10, and the magnetic ring 26 is coupled and fixed to the holder 5.

[0087] In this example, the magnetostrictive torque sensor 1 is assembled in the manner described above.

[0088] The magnetostrictive torque sensor 1 and the assembly method thereof according to this embodiment can easily reduce the manufacturing costs of the magnetostrictive torque sensor 1. The reason for this will be explained below.

[0089] In this example, when the proportion of the body portion 12 of the flexible substrate 8 facing the outer circumferential surface of the rotating shaft 2 (detection target portion 3) is defined as 100%, a common flexible substrate 8 having the same circumferential length of the body portion 12 is used if the proportion of the body portion 12 facing the outer circumferential surface of the rotating shaft 2 falls within a predetermined range. To achieve this, a flexible substrate 8 having this proportion within the predetermined range is selected from multiple types of flexible substrates 8 in accordance with the outer diameter of the rotating shaft 2 to be measured. More specifically, a flexible substrate 8 having this proportion between 75% and 100%, preferably between 80% and 90%, is selected from multiple types of flexible substrates 8. Therefore, the number of types of flexible substrates 8 is smaller than the number of types of outer diameters of the rotating shaft 2 that can be measured. Therefore, the magnetostrictive torque sensor 1 and its assembly method of this example can reduce the number of types of flexible substrates 8 to be prepared, compared to the conventional case in which multiple types of flexible substrates with different circumferential lengths of the body portion are prepared for each outer diameter of the rotating shaft, thereby making it easier to reduce manufacturing costs.

[0090] Conventionally, flexible substrates having a substantially rectangular plate-shaped main body portion equipped with a detection unit have been used that are specifically designed for each outer diameter of a rotating shaft. When a flexible substrate specifically designed for each outer diameter of a rotating shaft is used, the percentage of the main body portion facing the outer peripheral surface of the rotating shaft, where 100% is defined as the percentage of the main body portion facing the entire outer peripheral surface of the rotating shaft, is 92% to 98%.

[0091] In contrast to this, in this example, when the case where the main body 12 faces the entire outer peripheral surface of the rotating shaft 2 (detection target 3), the proportion of the main body 12 facing the outer peripheral surface of the rotating shaft 2 is 75% or more and less than 100%, and preferably 80% or more and 90% or less, assuming that 100% is the proportion. Therefore, when the flexible substrate 8 is applied to a magnetostrictive torque sensor 1 having the torque of a rotating shaft 2 having an outer diameter other than the optimum outer diameter for application of the flexible substrate 8, the proportion is 75% or more and less than 92%, and preferably 80% or more and 90% or less, or greater than 98% and less than 100%.

[0092] REFERENCE SIGNS LIST 1 Magnetostrictive torque sensor 2 Rotating shaft 3 Detected portion 4 Bobbin portion 5 Holder 6 Detector coil 6a First detector coil 6b Second detector coil 6c Third detector coil 6d Fourth detector coil 7 Detector portion 8 Flexible substrate 9 First outward flange portion 10 Second outward flange portion 11 Radial gap 12 Main body portion 13 Wiring layer 13a First wiring layer 13b Second wiring layer 13c Third wiring layer 13d Fourth wiring layer 14 Base film 14a First base film 14b Second base film 15 Adhesive layer 15a First adhesive layer 15b Second adhesive layer 15c Fourth adhesive layer 15d Fifth adhesive layer 16 Coverlay film 16a First coverlay film 16b Second coverlay film 16c Third coverlay film 16d Fourth coverlay film 17 Third adhesive layer 18 Circumferential gap 19a to 19d Coil pieces 20a to 20d Coil pieces 21 External device 22 Oscillator 23 Voltmeter 24a to 24d Signal line 25 Signal line portion 26 Magnetic ring 27 Radial gap

Claims

1. A method for assembling a magnetostrictive torque sensor comprising: a holder having a bobbin portion arranged around the rotating shaft to be measured; and a flexible substrate having a main body portion arranged around the bobbin portion and equipped with a detection portion consisting of multiple detection coils, wherein a common flexible substrate having the same circumferential length for the main body portion is used when the proportion of the main body portion facing the outer peripheral surface of the rotating shaft falls within a predetermined range, where 100% is when the main body portion faces the entire outer peripheral surface of the rotating shaft.

2. The method for assembling a magnetostrictive torque sensor according to claim 1, wherein the predetermined range is equal to or greater than 75% and less than 100%.

3. A magnetostrictive torque sensor comprising: a holder having a bobbin portion arranged around a rotating shaft; and a flexible substrate having a main body arranged around the bobbin portion and equipped with a detection portion consisting of multiple detection coils, wherein the proportion of the detection portion facing the outer peripheral surface of the rotating shaft is 75% or more but less than 92%, assuming that the proportion of the detection portion facing the entire outer peripheral surface of the rotating shaft is 100%.

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