Torque sensor and manufacturing method of torque sensor

Abstract

To provide a torque sensor capable of dispensing with backup molding when joining an input shaft part and a permanent magnet, and a manufacturing method of the torque sensor.SOLUTION: A torque sensor (10) is provided on a shaft. The shaft includes an input shaft part (12), an output shaft part, and a torsion bar coupling the input shaft part and the output shaft part to each other. The torque sensor includes a tubular permanent magnet (21) that is fixed to an outer circumferential surface of the input shaft part, and a tubular magnetic yoke that is fixed to an outer circumferential surface of the output shaft part and whose rotational position with respect to the permanent magnet changes in accordance with torsion of the torsion bar. An outer circumferential surface of the input shaft part and an inner circumferential surface of the permanent magnet are joined via a joining member (71) made of resin. The joining member is obtained by solidifying a molten resin injected into a gap between an outer circumferential surface of the input shaft part and an inner circumferential surface of the permanent magnet at a filling pressure less than an internal pressure strength of the permanent magnet.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a torque sensor and a method for manufacturing a torque sensor. [Background technology]

[0002] Conventionally, torque sensors that detect torque applied to a shaft have been known. For example, the torque sensor disclosed in Patent Document 1 is provided on a shaft. The shaft has an input shaft, an output shaft, and a torsion bar. The input shaft and the output shaft are connected via the torsion bar.

[0003] The torque sensor includes a permanent magnet and a magnetic yoke. The permanent magnet and the magnetic yoke are each cylindrical bodies with a circular cross section. The permanent magnet is attached to the outer circumferential surface of the input shaft via a resin fixing member. The magnetic yoke is attached to the outer circumferential surface of the output shaft. The permanent magnet is housed contactlessly inside the magnetic yoke.

[0004] The magnetic yoke includes a first yoke, a second yoke, and a holder. The holder is a resin molded product and is a cylindrical body with a circular cross section. The first yoke and the second yoke are annular bodies made of a magnetic material and are integrally formed with the holder by insert molding.

[0005] When torque is applied to the shaft, the torsion bar twists, causing a relative rotational displacement between the input shaft and the output shaft. This changes the magnetic flux generated in the first yoke and the second yoke. The torque applied to the shaft can be detected based on the change in the magnetic flux generated in the first yoke and the second yoke. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2020-128898 Summary of the Invention [Problem to be solved by the invention]

[0007] One possible method for joining the input shaft and the permanent magnet is injection molding. That is, when joining the input shaft and the permanent magnet, first, the input shaft and the permanent magnet are set in a mold. A gap that becomes the product cavity exists between the outer peripheral surface of the input shaft and the inner peripheral surface of the permanent magnet. Next, molten resin is injected into the gap between the outer peripheral surface of the input shaft and the inner peripheral surface of the permanent magnet. As the molten resin cools and solidifies, the aforementioned fixing member is formed, and the input shaft and the permanent magnet are joined via the fixing member.

[0008] In this case, the following concerns arise: The product cavity is located inside the permanent magnet. Therefore, depending on the internal pressure strength of the permanent magnet, there is a risk that cracks or breaks may occur in the permanent magnet when the molten resin is injected. Therefore, backup molding is required. In backup molding, a backup cavity is provided inside the mold. The backup cavity is located on the opposite side of the permanent magnet from the product cavity, i.e., outside the permanent magnet. The molten resin is injected into the product cavity and the backup cavity simultaneously.

[0009] This balances the radially outward force and radially inward force acting on the permanent magnet. This makes it possible to prevent cracks or breaks from occurring in the permanent magnet when molten resin is injected. However, when backup molding is performed, a backup cavity is provided inside the mold, making the mold structure complex. In addition, the resin molded product produced by backup molding is discarded, resulting in wasted material costs. [Means for solving the problem]

[0010] A torque sensor that can solve the above problem is a torque sensor provided on a shaft. The shaft includes an input shaft, an output shaft, and a torsion bar connecting the input shaft and the output shaft. The torque sensor includes a cylindrical permanent magnet fixed to the outer peripheral surface of the input shaft, and a cylindrical magnetic yoke fixed to the outer peripheral surface of the output shaft, the magnetic yoke being configured so that its rotational position relative to the permanent magnet changes in response to twisting of the torsion bar. The outer peripheral surface of the input shaft and the inner peripheral surface of the permanent magnet are joined via a resin joining member. The joining member is formed by solidifying molten resin injected into a gap between the outer peripheral surface of the input shaft and the inner peripheral surface of the permanent magnet at a filling pressure lower than the internal pressure strength of the permanent magnet.

[0011] With this configuration, the filling pressure of the molten resin when joining the input shaft portion and the permanent magnet by injection molding is less than the internal pressure strength of the permanent magnet. This prevents cracks or breaks from occurring in the permanent magnet when the molten resin is injected. Furthermore, unlike when the filling pressure of the molten resin is equal to or greater than the internal pressure strength of the permanent magnet, backup molding is not required when joining the input shaft portion and the permanent magnet.

[0012] In the torque sensor described above, the joining member may have a first flange and a second flange that sandwich the permanent magnet in the axial direction. This configuration suppresses axial movement of the permanent magnet relative to the input shaft, thereby enabling the permanent magnet to be properly held on the input shaft.

[0013] In the torque sensor, the shaft may be a steering shaft of a vehicle. The torque sensor is suitable for detecting torque of a steering shaft of a vehicle.

[0014] A method for manufacturing a torque sensor that can solve the above problem is a method for manufacturing a torque sensor mounted on a shaft. The shaft includes an input shaft, an output shaft, and a torsion bar connecting the input shaft and the output shaft. The torque sensor includes a permanent magnet fixed to the outer circumferential surface of the input shaft, and a cylindrical magnetic yoke fixed to the outer circumferential surface of the output shaft, the magnetic yoke being configured so that its rotational position relative to the permanent magnet changes in response to twisting of the torsion bar. The manufacturing method includes injecting molten resin into a gap between the outer circumferential surface of the input shaft and the inner circumferential surface of the permanent magnet at a filling pressure less than the internal pressure strength of the permanent magnet, and solidifying the injected molten resin to join the outer circumferential surface of the input shaft and the inner circumferential surface of the permanent magnet.

[0015] According to this manufacturing method, the filling pressure of the molten resin when joining the input shaft portion and the permanent magnet by injection molding is less than the internal pressure strength of the permanent magnet. This makes it possible to prevent cracks or breaks from occurring in the permanent magnet when the molten resin is injected. Furthermore, unlike when the filling pressure of the molten resin is equal to or greater than the internal pressure strength of the permanent magnet, backup molding is not required when joining the input shaft portion and the permanent magnet.

[0016] In the method for manufacturing a torque sensor, the molten resin may be a completely molten resin. Fully molten resin is resin that has completely melted. Completely molten resin has no voids, and can be molded thinner and more precisely while maintaining the resin's original functions. Completely molten resin also has high fluidity. This allows the filling pressure to be set lower. [Effects of the Invention]

[0017] According to the torque sensor and the method for manufacturing the torque sensor of the present invention, it is possible to eliminate the need for backup molding when joining the input shaft portion and the permanent magnet. [Brief explanation of the drawings]

[0018] [Figure 1]FIG. 1 is an exploded perspective view of an embodiment of a torque sensor. [Figure 2] 1 is a cross-sectional view of an input shaft portion according to an embodiment of the present invention, taken along an axial direction; [Figure 3] FIG. 1 is a half cross-sectional view of a mold according to an embodiment. [Figure 4] FIG. 10 is a half cross-sectional view of a mold according to a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0019] A torque sensor according to an embodiment will be described. <Overall configuration of torque sensor> As shown in FIG. 1 , the torque sensor 10 is provided on a shaft 11. The shaft 11 is, for example, a steering shaft of a vehicle. The shaft 11 has an input shaft portion 12, a torsion bar 13, and an output shaft portion 14. The input shaft portion 12 and the output shaft portion 14 are connected to each other via the torsion bar 13. The input shaft portion 12, the torsion bar 13, and the output shaft portion 14 are arranged on the same axis O.

[0020] The torque sensor 10 detects torque applied to a shaft 11. The torque sensor 10 includes a permanent magnet 21, a magnetic yoke 22, a substrate 23, a sensor housing 25, and a cover 26.

[0021] The permanent magnet 21 is a cylindrical body having a circular cross section. The outer peripheral surface of the permanent magnet 21 is magnetized with south poles and north poles alternately in the circumferential direction of the permanent magnet 21. The inner peripheral surface of the permanent magnet 21 is fixed to the outer peripheral surface of the input shaft portion 12.

[0022] The magnetic yoke 22 is a cylindrical body with a circular cross-section. The magnetic yoke 22 accommodates the permanent magnet 21 in a non-contact manner. The magnetic yoke 22 includes a first yoke 31, a second yoke 32, and a holder 33. The first yoke 31 and the second yoke 32 are annular bodies made of a magnetic material. The holder is a resin molded product and is a cylindrical body with a circular cross-section. The first yoke 31 and the second yoke 32 are integrally formed in the holder 33 by insert molding. The first yoke 31 and the second yoke 32 are arranged along the axis O of the shaft 11. The outer periphery of the first yoke 31 and the outer periphery of the second yoke 32 are exposed to the outside from the outer periphery of the holder 33. The inner periphery of the magnetic yoke 22 is fixed to the outer periphery of the output shaft 14.

[0023] The first yoke 31 has a plurality of first teeth 31a. The first teeth 31a are arranged at equal intervals in the circumferential direction of the first yoke 31 inside the holder 33. The second yoke 32 has a plurality of second teeth 32a. The second teeth 32a are arranged at equal intervals in the circumferential direction of the second yoke 32 inside the holder 33. The first teeth 31a and the second teeth 32a extend on opposite sides of each other in the axial direction of the holder 33. The first teeth 31a and the second teeth 32a are arranged alternately in the circumferential direction of the holder 33. When no torsional deformation occurs in the torsion bar 13, the circumferential centers of the first teeth 31a and the second teeth 32a coincide with the boundary between the north pole and south pole of the permanent magnet 21. The first toothed portion 31a and the second toothed portion 32a are located closer to the first end of the two axial ends of the holder 33.

[0024] A permanent magnet 21 is disposed inside the magnetic yoke 22, that is, inside the first yoke 31 and the second yoke 32. The permanent magnet 21, the first yoke 31, and the second yoke 32 form a magnetic circuit.

[0025] The substrate 23 is a rectangular plate-like body. The substrate 23 has a first main surface and a second main surface located opposite each other in a direction along the axis O. The substrate 23 also has three support holes 41, a plurality of terminal connection holes 42, a first magnetic sensor 45, and a second magnetic sensor 46. The support hole 41 is provided near the center of the substrate 23. The support holes 41 are arranged in a row along the long side of the substrate 23. The terminal connection holes 42 are arranged, for example, in two rows along the first long side of the substrate 23. The first magnetic sensor 45 and the second magnetic sensor 46 are provided on the first main surface of the substrate 23. The first magnetic sensor 45 and the second magnetic sensor 46 are arranged along the second long side of the substrate 23. The first magnetic sensor 45 and the second magnetic sensor 46 are used to detect torque applied to the shaft 11 and are, for example, Hall sensors. The rotation angle of the shaft 11 is a physical quantity related to the rotational motion of the shaft 11.

[0026] The sensor housing 25 has an outer housing 25A and an inner housing 25B. The outer housing 25A and the inner housing 25B are each molded from resin. The inner housing 25B is a cylindrical body with a circular cross-sectional shape and is formed integrally with the outer housing 25A by insert molding. The outer housing 25A has an end wall that covers a portion of the first end of the inner housing 25B and a peripheral wall that covers the outer peripheral surface of the inner housing 25B. The second end of the inner housing 25B opens to the outside. The shaft 11 passes through the sensor housing 25 in the axial direction without contacting it.

[0027] The sensor housing 25 has an insertion hole 51 and a first accommodating chamber 52. The insertion hole 51 axially penetrates the end wall of the outer housing 25A. The insertion hole 51 is located on the axis O. The inner diameter of the insertion hole 51 is slightly larger than the outer diameter of the shaft 11 and slightly smaller than the outer diameter of the magnetic yoke 22. The first accommodating chamber 52 is an internal space of the inner housing 25B, and the inner circumferential surface of the inner housing 25B forms the inner circumferential surface of the first accommodating chamber 52. The first accommodating chamber 52 is located on the axis O. The inner diameter of the first accommodating chamber 52 is slightly larger than the outer diameter of the magnetic yoke 22. The first accommodating chamber 52 communicates with the insertion hole 51. The input shaft portion 12 is passed through the insertion hole 51 via the first accommodating chamber 52. The first accommodating chamber 52 accommodates the permanent magnet 21 and the magnetic yoke 22.

[0028] The sensor housing 25 has a second accommodating chamber 53. The second accommodating chamber 53 is provided in a protruding portion of the sensor housing 25. The protruding portion is a box-shaped portion of the sensor housing 25 that protrudes radially outward from the inner housing 25B. The second accommodating chamber 53 is an internal space of the protruding portion and accommodates the substrate 23. The second accommodating chamber 53 has a rectangular opening 53a. The opening 53a opens radially outward from the inner housing 25B. The opening 53a is closed by the cover 26.

[0029] Three support protrusions 54 are provided on the inner surface of the end wall of the protrusion. The support protrusions 54 are, for example, stepped columnar bodies. The support protrusions 54 are arranged in a row along the long side of the opening 53a. Each support protrusion 54 corresponds to a respective support hole 41 in the substrate 23. In addition, first ends of a plurality of terminals 55 are provided to protrude from the inner surface of the end wall of the protrusion. The terminals 55 are arranged, for example, in two rows along the long side of the opening 53a. The terminals 55 are positioned radially outward from the support protrusions 54. Each terminal 55 corresponds to a respective terminal connection hole 42 in the substrate 23.

[0030] The substrate 23 is attached to the inner surface of the end wall of the protrusion. A first main surface of the substrate 23 faces away from the inner surface of the end wall of the protrusion. The first main surface is the surface on which the first magnetic sensor 45 and the second magnetic sensor 46 of the substrate 23 are provided. Each support protrusion 54 penetrates a corresponding support hole 41 of the substrate 23 in the thickness direction of the substrate 23. This restricts movement of the substrate 23 relative to the inner surface of the end wall of the protrusion. Furthermore, a first end of each terminal 55 penetrates a corresponding terminal connection hole 42 of the substrate 23 in the thickness direction of the substrate 23. The first end of the terminal 55 is joined to the substrate 23 by soldering. This electrically connects the terminal 55 to the pattern wiring of the substrate 23.

[0031] A connector fitting portion 56 is provided on the outer surface of the end wall of the protrusion. The connector fitting portion 56 is a cylindrical body with a rectangular cross-sectional shape. A second end of the terminal 55 penetrates the end wall of the protrusion and is exposed inside the connector fitting portion 56. A wiring connector that electrically connects the terminal 55 of the board 23 to an external device is fitted into the connector fitting portion 56. The external device is, for example, a vehicle control device or a steering control device.

[0032] The sensor housing 25 has a first magnetic flux collecting ring 61 and a second magnetic flux collecting ring 62. The first magnetic flux collecting ring 61 and the second magnetic flux collecting ring 62 are provided integrally with the inner housing 25B by insert molding. The first magnetic flux collecting ring 61 and the second magnetic flux collecting ring 62 are plate-shaped bodies that curve along the outer periphery of the magnetic yoke 22. The first magnetic flux collecting ring 61 and the second magnetic flux collecting ring 62 are exposed on the inner circumferential surface of the first accommodating chamber 52, i.e., the inner circumferential surface of the sensor housing 25. The first magnetic flux collecting ring 61 and the second magnetic flux collecting ring 62 are arranged along the axis O of the shaft 11.

[0033] The axial position of the first magnetic flux collecting ring 61 corresponds to the axial position of the first yoke 31. The first magnetic flux collecting ring 61 faces the outer periphery of the first yoke 31 in the radial direction. That is, the first magnetic flux collecting ring 61 surrounds the periphery of the first yoke 31. The first magnetic flux collecting ring 61 guides the magnetic flux from the first yoke 31. The axial position of the second magnetic flux collecting ring 62 corresponds to the axial position of the second yoke 32. The second magnetic flux collecting ring 62 faces the outer periphery of the second yoke 32 in the radial direction. That is, the second magnetic flux collecting ring 62 surrounds the periphery of the second yoke 32. The second magnetic flux collecting ring 62 guides the magnetic flux from the second yoke 32.

[0034] The first magnetic flux collecting ring 61 has a first magnetic flux collecting protrusion 61a and a second magnetic flux collecting protrusion 61b. The first magnetic flux collecting protrusion 61a and the second magnetic flux collecting protrusion 61b are exposed to the inside of the second housing chamber 53. The first magnetic flux collecting protrusion 61a and the second magnetic flux collecting protrusion 61b are arranged at intervals in the circumferential direction of the first magnetic flux collecting ring 61. The second magnetic flux collecting ring 62 has a third magnetic flux collecting protrusion 62a and a fourth magnetic flux collecting protrusion 62b. The third magnetic flux collecting protrusion 62a and the fourth magnetic flux collecting protrusion 62b are exposed to the inside of the second housing chamber 53. The third magnetic flux collecting protrusion 62a and the fourth magnetic flux collecting protrusion 62b are arranged at intervals in the circumferential direction of the second magnetic flux collecting ring 62. The first magnetic flux collecting protrusion 61a and the third magnetic flux collecting protrusion 62a face each other in a direction along the axis O. The second magnetic flux collecting protrusion 61b and the fourth magnetic flux collecting protrusion 62b face each other in a direction along the axis O.

[0035] When the substrate 23 is attached inside the second housing chamber 53, the first magnetic sensor 45 is interposed between the first magnetic flux collecting protrusion 61a and the third magnetic flux collecting protrusion 62a. When the substrate 23 is attached inside the second housing chamber 53, the second magnetic sensor 46 is interposed between the second magnetic flux collecting protrusion 61b and the fourth magnetic flux collecting protrusion 62b.

[0036] When torque is applied to the input shaft 12, the torsion bar 13 undergoes torsional deformation. A relative rotational displacement occurs between the input shaft 12 and the output shaft 14 in response to the torque applied to the input shaft 12. This causes a change in the rotational position of the magnetic yoke 22 relative to the permanent magnet 21. Because the relative position between the permanent magnet 21 and the first yoke 31 in the rotational direction changes, the magnetic flux induced from the permanent magnet 21 to the first magnetic flux collecting ring 61 via the first yoke 31 changes. Furthermore, because the relative position between the permanent magnet 21 and the second yoke 32 in the rotational direction changes, the magnetic flux induced from the permanent magnet 21 to the second magnetic flux collecting ring 62 via the second yoke 32 changes.

[0037] The first magnetic sensor 45 generates an electric signal in response to the magnetic flux leaking between the first magnetic protrusion 61a and the third magnetic protrusion 62a. The second magnetic sensor 46 generates an electric signal in response to the magnetic flux leaking between the second magnetic protrusion 61b and the fourth magnetic protrusion 62b. The electric signals generated by the first magnetic sensor 45 and the second magnetic sensor 46 change in response to the torsional deformation of the torsion bar 13, i.e., the torsion angle of the torsion bar 13. The external device can calculate the torque applied to the shaft 11 based on the electric signals generated by the first magnetic sensor 45 and the second magnetic sensor 46. Torque is a physical quantity related to the rotational motion of the shaft 11.

[0038] <Joint structure between input shaft portion 12 and permanent magnet 21> Next, the joining structure between the input shaft portion 12 and the permanent magnet 21 will be described. As shown in FIG. 2, the permanent magnet 21 is attached to the outer peripheral surface of the input shaft portion 12 via a resin joining member 71. The input shaft portion 12 has a first opposing surface 12A. The first opposing surface 12A is a region of the outer peripheral surface of the input shaft portion 12 that faces radially to the inner peripheral surface of the permanent magnet 21 via the joining member 71. The inner peripheral surface of the permanent magnet 21 is a second opposing surface 21A. The second opposing surface 21A faces radially to the first opposing surface 12A of the input shaft portion 12 via the joining member 71.

[0039] The joining member 71 has a main body portion 71A, a first flange portion 71B, and a second flange portion 71C. The main body portion 71A is a cylindrical body having a circular cross-sectional shape. The main body portion 71A is interposed between the first opposing surface 12A and the second opposing surface 21A. The first flange portion 71B is provided around the entire outer periphery of the first end portion of the main body portion 71A. The second flange portion 71C is provided around the entire outer periphery of the second end portion of the main body portion 71A. The first flange portion 71B and the second flange portion 71C sandwich the permanent magnet 21 in the axial direction.

[0040] The joining member 71 is formed by solidifying molten resin injected into the gap between the first opposing surface 12A and the second opposing surface 21A. The first opposing surface 12A and the second opposing surface 21A are joined via the joining member 71.

[0041] <Method of joining input shaft portion 12 and permanent magnet 21> Next, a method for joining the input shaft portion 12 and the permanent magnet 21 will be described. As shown in FIG. 3, the input shaft portion 12 and the permanent magnet 21 are joined using, for example, a small injection molding machine. When joining the input shaft portion 12 and the permanent magnet 21, the input shaft portion 12 and the permanent magnet 21 are set in a mold 80. The mold 80 includes an inner mold 81 and an outer mold 82. The inner mold 81 and the outer mold 82 are each a metallic cylindrical body having a circular cross-sectional shape and are attached to the outer peripheral surface of the input shaft portion 12. A first end of the outer mold 82 opens to the outside. A second end of the outer mold 82 is closed by an end wall. The inner mold 81 is fitted into the first end of the outer mold 82. The inner mold 81 has a gate 81A, which is a passage for molten resin. The molten resin is completely molten resin. The gate 81A penetrates the inner mold 81 in the axial direction.

[0042] The input shaft portion 12 is supported by penetrating the inner mold 81 and the outer mold 82 in the axial direction. The permanent magnet 21 is sandwiched in the axial direction between a part of the inner mold 81 and a part of the outer mold 82. A cavity 83 is formed by the input shaft portion 12, the inner mold 81, the outer mold 82, and the permanent magnet 21. The cavity 83 is a closed space corresponding to the shape of the joining member 71.

[0043] With the input shaft portion 12 and permanent magnet 21 set in the mold 80 in this manner, molten resin is filled into the cavity 83 through the gate 81A. However, as shown in the following formula (1), the filling pressure P1 is a pressure less than the internal pressure strength P2 of the permanent magnet 21. The filling pressure P1 is the pressure for filling the interior of the cavity 83 with molten resin, and is transmitted to the interior of the cavity 83. The internal pressure is a radial pressure from the inside to the outside of the permanent magnet 21. The internal pressure strength P2 is the pressure resistance of the permanent magnet 21 against the internal pressure.

[0044] P1 <P2 …(1) The molten resin is cooled and solidified to form joining member 71, and input shaft portion 12 and permanent magnet 21 are joined together via joining member 71. By opening mold 80, the joined input shaft portion 12 and permanent magnet 21 can be removed.

[0045] <Effects of the embodiment> According to this embodiment, the following effects are achieved. (1) The outer peripheral surface of the input shaft portion 12 and the inner peripheral surface of the permanent magnet 21 are joined via a resin joining member 71. The joining member 71 is formed by solidifying molten resin injected into the gap between the outer peripheral surface of the input shaft portion 12 and the inner peripheral surface of the permanent magnet 21 at a filling pressure P1 less than the internal pressure strength P2 of the permanent magnet 21. With this configuration, the filling pressure P1 of the molten resin when joining the input shaft portion 12 and the permanent magnet 21 by injection molding is a pressure less than the internal pressure strength P2 of the permanent magnet 21. This makes it possible to prevent cracks or breaks from occurring in the permanent magnet 21 when the molten resin is injected. Furthermore, unlike when the filling pressure P1 of the molten resin is a pressure equal to or greater than the internal pressure strength P2 of the permanent magnet 21, backup molding is not required when joining the input shaft portion 12 and the permanent magnet 21.

[0046] (2) Since backup molding is not required, the structure of the mold 80 can be simplified. In addition, the mold 80 can be made smaller. As shown in FIG. 4, when backup molding is performed, a backup cavity 84 is provided between the permanent magnet 21 and the outer mold 82. The backup cavity 84 is located on the opposite side of the permanent magnet 21 from the cavity 83, i.e., outside the permanent magnet 21. In addition, when backup molding is performed, a backup gate 82A is provided in the outer mold 82. The molten resin is injected into the cavity 83 and the backup cavity 84 simultaneously. According to this embodiment, there is no need to provide the backup cavity 84 between the permanent magnet 21 and the outer mold 82. In addition, there is no need to provide the backup gate 82A in the outer mold 82.

[0047] (3) Resin molded products formed by backup molding are discarded. According to the torque sensor 10 of the present embodiment, no wasteful resin molded products are formed and discarded. This allows for saving on material costs.

[0048] (4) Compared to when the filling pressure P1 of the molten resin is equal to or greater than the internal pressure strength P2 of the permanent magnet 21, the radial thickness of the permanent magnet 21 can be made thinner. (5) The joining member 71 has a first flange 71B and a second flange 71C that axially sandwich the permanent magnet 21. This configuration suppresses axial movement of the permanent magnet 21 relative to the input shaft 12. This allows the permanent magnet 21 to be properly held on the input shaft 12.

[0049] (6) The shaft 11 may be a steering shaft of a vehicle. The torque sensor 10 of this embodiment is suitable for detecting the torque of a steering shaft of a vehicle. (7) The manufacturing method of the torque sensor 10 includes a first stage and a second stage. The first stage is a stage in which molten resin is injected into the gap between the outer circumferential surface of the input shaft portion 12 and the inner circumferential surface of the permanent magnet 21 at a filling pressure P1 that is less than the internal pressure strength P2 of the permanent magnet 21. The second stage is a stage in which the injected molten resin is solidified to bond the outer circumferential surface of the input shaft portion 12 and the inner circumferential surface of the permanent magnet 21 together. This manufacturing method can achieve the same effect as the effect described in section (1) above. Furthermore, for example, the outer circumferential surface of the input shaft portion 12 and the inner circumferential surface of the permanent magnet 21 can be appropriately bonded together regardless of the machining accuracy of the outer circumferential surface of the input shaft portion 12 and the machining accuracy of the inner circumferential surface of the permanent magnet 21.

[0050] (8) The molten resin used to join the input shaft portion 12 and the permanent magnet 21 is fully molten resin. Fully molten resin is resin that has completely melted. Fully molten resin has no voids, and can be molded thinner and more precisely while maintaining the original functionality of the resin. Furthermore, fully molten resin has high fluidity. Therefore, the filling pressure P1 can be set to a lower pressure.

[0051] <Other embodiments> This embodiment may be modified as follows. The shaft 11 is not limited to a steering shaft. The torque sensor 10 can be used to detect torque applied to the shaft 11 of various mechanical devices. [Explanation of symbols]

[0052] 10...Torque sensor 11...Shaft 12...Input shaft 13...Torsion bar 14...Output shaft 21...Permanent magnet 22...Magnetic yoke 71... Joint material 71B...First flange 71C...Second flange

Claims

1. A torque sensor provided on a shaft, the shaft includes an input shaft portion, an output shaft portion, and a torsion bar connecting the input shaft portion and the output shaft portion to each other; The torque sensor is a cylindrical permanent magnet fixed to an outer peripheral surface of the input shaft portion; a cylindrical magnetic yoke fixed to an outer peripheral surface of the output shaft portion, the magnetic yoke being configured so that its rotational position relative to the permanent magnet changes in response to twisting of the torsion bar; an outer peripheral surface of the input shaft portion and an inner peripheral surface of the permanent magnet are joined via a resin joining member, The joining member is a torque sensor formed by solidifying molten resin injected into the gap between the outer peripheral surface of the input shaft portion and the inner peripheral surface of the permanent magnet at a filling pressure lower than the internal pressure strength of the permanent magnet.

2. 2. The torque sensor according to claim 1, wherein the joining member has a first flange and a second flange that axially sandwich the permanent magnet.

3. 3. The torque sensor according to claim 1, wherein the shaft is a steering shaft of a vehicle.

4. A method for manufacturing a torque sensor provided on a shaft, comprising: the shaft includes an input shaft portion, an output shaft portion, and a torsion bar connecting the input shaft portion and the output shaft portion to each other; The torque sensor is a permanent magnet fixed to an outer peripheral surface of the input shaft portion; a cylindrical magnetic yoke fixed to an outer peripheral surface of the output shaft portion, the magnetic yoke being configured so that its rotational position relative to the permanent magnet changes in response to twisting of the torsion bar; The manufacturing method includes: injecting molten resin into a gap between an outer peripheral surface of the input shaft portion and an inner peripheral surface of the permanent magnet at a filling pressure lower than the internal pressure strength of the permanent magnet; and solidifying the injected molten resin to join the outer peripheral surface of the input shaft portion and the inner peripheral surface of the permanent magnet.

5. The method for manufacturing a torque sensor according to claim 4, wherein the molten resin is a completely molten resin.

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