WO2025191737A1 - Torque sensor and method for manufacturing torque sensor - Google Patents

Abstract

A torque sensor (10) is provided to a shaft (11). The shaft comprises an input shaft part (12), an output shaft part (14), and a torsion bar (13) that connects the input shaft part and the output shaft part to each other. The output shaft part has protruding sections (71, 73) that protrude radially outward from the outer circumferential surface of the output shaft part. The torque sensor includes a permanent magnet (21) fixed to the outer circumferential surface of the input shaft part, and a cylindrical magnetic yoke (22) fixed to the outer circumferential surface of the output shaft part. The rotation position of the magnetic yoke with respect to the permanent magnet changes in accordance with the torsion of the torsion bar. The outer circumferential surface of the output shaft part and the inner circumferential surface of the magnetic yoke are joined via a resin joining member (81). The joining member is obtained by solidifying a molten resin injected into a cavity (82) formed by the outer circumferential surface of the output shaft part, the inner circumferential surface of the magnetic yoke, and the protruding sections.

Description

Torque sensor and method for manufacturing the same

This disclosure relates to a torque sensor and a method for manufacturing a torque sensor.

Torque sensors that detect torque applied to a shaft are known. For example, the torque sensor disclosed in Patent Document 1 is mounted on a shaft. The shaft has an input shaft portion, an output shaft portion, and a torsion bar. The input shaft portion and the output shaft portion are connected via the torsion bar.

The torque sensor has a permanent magnet and a magnetic yoke. The permanent magnet and magnetic yoke are each cylindrical bodies with a circular cross-sectional shape. The permanent magnet is attached to the outer peripheral surface of the input shaft. The magnetic yoke is attached to the outer peripheral surface of the output shaft. The permanent magnet is housed inside the magnetic yoke without contact.

The magnetic yoke has a first yoke, a second yoke, and a holder. The holder is a resin molded product, a cylindrical body with a circular cross-sectional shape. The first yoke and second yoke are annular bodies made of magnetic material, and are integrally attached to the holder by insert molding.

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 and second yokes. The torque applied to the shaft can be detected based on the change in magnetic flux generated in the first and second yokes.

There are also torque sensors in which the magnetic yoke is attached to the output shaft via a collar, as disclosed in Patent Document 2, for example. The collar is a metallic cylindrical body with a circular cross section that is integrally attached to the holder by insert molding. The inner circumferential surface of the collar is exposed inside the holder. The output shaft is press-fitted into the collar.

JP 2023-107479 A Japanese Patent Application Laid-Open No. 2020-076661

When a collar is provided on the magnetic yoke, as in Patent Document 2, the following concerns arise. Because the output shaft is press-fit into the collar, the machining precision of the collar's inner surface must be strictly controlled. For this reason, collars are expensive.

A torque sensor according to one aspect of the present disclosure is 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 output shaft has a protruding portion that protrudes radially outward from the outer circumferential surface of 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 outer circumferential surface of the output shaft and the inner circumferential surface of the magnetic yoke are joined via a resin joining member. The joining member is formed by solidifying molten resin injected into a cavity formed by the outer circumferential surface of the output shaft, the inner circumferential surface of the magnetic yoke, and the protruding portion.

A torque sensor manufacturing method according to one aspect of the present disclosure is a method for manufacturing a torque sensor mounted 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 output shaft portion has a protruding portion that protrudes radially outward from the outer circumferential surface of the output shaft portion. The torque sensor includes a permanent magnet fixed to the outer circumferential surface of the input shaft portion, and a cylindrical magnetic yoke fixed to the outer circumferential 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 cavity formed by the outer circumferential surface of the output shaft portion, the inner circumferential surface of the magnetic yoke, and the protruding portion, and solidifying the injected molten resin to join the outer circumferential surface of the output shaft portion and the inner circumferential surface of the magnetic yoke.

FIG. 1 is an exploded perspective view of an embodiment of a torque sensor. FIG. 2 is a cross-sectional view of a main part of the torque sensor of FIG. 1 cut in the axial direction. FIG. 3 is a perspective view showing a main part of the output shaft portion of FIG. 2. FIG. FIG. 4 is a perspective view of the biting projection of FIG. FIG. 5 is a perspective view showing a first example of the configuration of the magnetic yoke of FIG. FIG. 6 is a perspective view showing a second configuration example of the magnetic yoke of FIG. FIG. 7 is a perspective view of the joining member of FIG. 2. FIG. FIG. 8 is a cross-sectional view of an injection molding machine. FIG. 9 is a cross-sectional view of a main part of a torque sensor according to another embodiment, cut in the axial direction.

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.

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

The permanent magnet 21 is a cylindrical body with a circular cross-section. The outer peripheral surface of the permanent magnet 21 is magnetized with alternating south and north poles 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.

The magnetic yoke 22 is a cylindrical body with a circular cross-section. The magnetic yoke 22 accommodates the permanent magnet 21 without contact. The magnetic yoke 22 has 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 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 with 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.

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

A permanent magnet 21 is arranged inside the magnetic yoke 22, i.e., inside the first yoke 31 and second yoke 32. The permanent magnet 21, first yoke 31, and second yoke 32 form a magnetic circuit.

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 the 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 located 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 located 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.

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-section 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 surface of the inner housing 25B. The second end of the inner housing 25B is open to the outside. The shaft 11 passes through the sensor housing 25 in the axial direction without contacting it.

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 the internal space of the inner housing 25B, and the inner surface of the inner housing 25B forms the inner 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 is connected to 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.

The sensor housing 25 has a second storage chamber 53. The second storage 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 storage chamber 53 is the internal space of the protruding portion and contains the circuit board 23. The second storage 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.

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 pillars. Each support protrusion 54 is arranged in a row along the long side of the opening 53a. Each support protrusion 54 corresponds to one of the support holes 41 in the board 23. In addition, first ends of multiple terminals 55 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 one of the terminal connection holes 42 in the board 23.

A 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 each 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 each 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.

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. The second end of the terminal 55 passes through 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.

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 formed 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.

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 radially to the outer periphery of the first yoke 31. In other words, the first magnetic flux collecting ring 61 surrounds the periphery of the first yoke 31. The first magnetic flux collecting ring 61 guides 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 radially to the outer periphery of the second yoke 32. In other words, the second magnetic flux collecting ring 62 surrounds the periphery of the second yoke 32. The second magnetic flux collecting ring 62 guides magnetic flux from the second yoke 32.

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 inside the second accommodating 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 inside the second accommodating 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.

When the substrate 23 is mounted inside the second storage chamber 53, the first magnetic sensor 45 is located between the first magnetic flux collecting protrusion 61a and the third magnetic flux collecting protrusion 62a. When the substrate 23 is mounted inside the second storage chamber 53, the second magnetic sensor 46 is located between the second magnetic flux collecting protrusion 61b and the fourth magnetic flux collecting protrusion 62b.

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 changes the relative position of the permanent magnet 21 and the first yoke 31 in the rotational direction. As a result, the magnetic flux induced from the permanent magnet 21 to the first magnetic flux collector ring 61 via the first yoke 31 changes. In addition, the relative position of the permanent magnet 21 and the second yoke 32 in the rotational direction changes. As a result, the magnetic flux induced from the permanent magnet 21 to the second magnetic flux collector ring 62 via the second yoke 32 changes.

The first magnetic sensor 45 generates an electrical signal in response to the magnetic flux leaking between the first magnetic collector protrusion 61a and the third magnetic collector protrusion 62a. The second magnetic sensor 46 generates an electrical signal in response to the magnetic flux leaking between the second magnetic collector protrusion 61b and the fourth magnetic collector protrusion 62b. The electrical 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 electrical 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.

<Support structure of output shaft portion 14>
Next, the support structure of the output shaft portion 14 will be described.
As shown in Fig. 2, the output shaft portion 14 is a stepped columnar body having a circular cross-sectional shape. The output shaft portion 14 has a first bearing 71 and a second bearing 72. The first bearing 71 and the second bearing 72 are attached to the outer peripheral surface of the output shaft portion 14. The first bearing 71 and the second bearing 72 are arranged at an interval in the axial direction of the output shaft portion 14. The first bearing 71 is closer to the first end of the output shaft portion 14 than the second bearing 72. The first bearing 71 and the second bearing 72 rotatably support the output shaft portion 14 with respect to the sensor housing 25.

The first bearing 71 is a rolling bearing. The first bearing 71 has a first inner ring 71A, a first outer ring 71B, and a plurality of first rolling elements 71C. The first rolling elements 71C are, for example, balls, and are held rollably between the first inner ring 71A and the first outer ring 71B. The first bearing 71 corresponds to a protruding portion that protrudes radially outward from the outer peripheral surface of the output shaft portion 14. The second bearing 72 has a similar configuration to the first bearing 71. That is, the second bearing 72 has a second inner ring 72A, a second outer ring 72B, and a plurality of second rolling elements 71C.

The first bearing 71 is attached to the output shaft 14 from the first end side of the output shaft 14. The first end is the end of the output shaft 14 where the magnetic yoke 22 is attached. The first bearing 71 is positioned in the axial direction by the first stepped surface 14A of the output shaft 14. The first stepped surface 14A is a flat surface that extends radially outward from the output shaft 14 and is provided around the entire circumference of the output shaft 14. The first inner ring 71A abuts against the first stepped surface 14A in the axial direction. This restricts movement of the first bearing 71 in the direction from the first end to the second end of the output shaft 14.

The second bearing 72 is attached to the output shaft 14 from the second end side of the output shaft 14. The second end is the end opposite the first end of the output shaft 14. The second bearing 72 is positioned in the axial direction by the second stepped surface 14B of the output shaft 14. The second stepped surface 14B is a flat surface that extends radially outward from the output shaft 14 and is provided around the entire circumference of the output shaft 14. The second inner ring 72A abuts against the second stepped surface 14B in the axial direction. This restricts movement of the second bearing 72 in the direction from the second end of the output shaft 14 toward the first end.

<Joint structure between magnetic yoke 22 and output shaft portion 14>
Next, the joining structure between the magnetic yoke 22 and the output shaft portion 14 will be described.
2, a first end of the output shaft portion 14 is inserted into a second end of the magnetic yoke 22. The second end is the end opposite to the first end of the magnetic yoke 22. The second end of the magnetic yoke 22 abuts against the first inner ring 71A in the axial direction.

The output shaft portion 14 has a first opposing surface 14C. The first opposing surface 14C is a region of the outer peripheral surface of the output shaft portion 14 that faces radially toward the inner peripheral surface of the magnetic yoke 22. The magnetic yoke 22 has a second opposing surface 22A. The second opposing surface 22A is a region of the inner peripheral surface of the magnetic yoke 22 that faces radially toward the outer peripheral surface of the output shaft portion 14.

A joining member 81 is interposed between the first opposing surface 14C and the second opposing surface 22A. The joining member 81 is a cylindrical body with a circular cross-sectional shape. The joining member 81 fills the cavity 82. The cavity 82 is a space formed by the first opposing surface 14C, the second opposing surface 22A, and the first inner ring 71A. The joining member 81 is formed by solidifying molten resin injected into the cavity 82. The first opposing surface 14C and the second opposing surface 22A are joined via the joining member 81. The end face of the joining member 81 opposite the first bearing 71 is exposed inside the magnetic yoke 22.

As shown in Figure 3, the first opposing surface 14C is an uneven surface with fine irregularities across its entire surface, and has numerous fine protrusions 14D. The protrusions 14D are formed by, for example, applying a knurling process to the first opposing surface 14C to create a twill weave. As shown in Figure 4, the protrusions 14D are, for example, quadrangular pyramidal.

As shown in Figure 5, the second opposing surface 22A has multiple interlocking protrusions 22B. The interlocking protrusions 22B are rectangular plate-shaped bodies that curve along the inner circumferential surface of the second opposing surface 22A. The interlocking protrusions 22B are arranged at equal intervals around the circumference of the second opposing surface 22A.

As shown in FIG. 6, the meshing protrusion 22B may have a first protrusion 22B1 and a second protrusion 22B2. The first protrusion 22B1 and the second protrusion 22B are arranged offset from each other in the circumferential direction of the magnetic yoke 22B.

As shown in FIG. 7, the inner peripheral surface of the joining member 81 is an uneven surface with fine irregularities all over, and has numerous biting recesses 81A. The biting recesses 81A are formed when molten resin is injected into the cavity 82 to form the joining member 81. The biting recesses 81A are blind holes that correspond to the shape of the biting protrusions 14D. When the biting protrusions 14D are pyramidal, the biting recesses 81A are pyramidal holes. The biting protrusions 14D are maintained in a biting recessed state within the biting recesses 81A. The outer surfaces of the biting protrusions 14D and the inner surfaces of the biting recesses 81A mesh with each other in the axial and circumferential directions of the output shaft portion 14. The biting protrusions 14D and the biting recesses 81A form a first anti-slip structure that prevents slippage between the output shaft portion 14 and the magnetic yoke 22.

The outer peripheral surface of the joining member 81 has a plurality of interlocking recesses 81B. The interlocking recesses 81B are formed when molten resin is injected into the cavity 82 to form the joining member 81. The interlocking recesses 81B are blind holes that correspond to the shape of the interlocking protrusions 22B and are arranged at equal intervals in the circumferential direction. In Figure 6, the shape of the interlocking recesses 81B corresponds to the shape of the interlocking protrusions 22B shown in Figure 5 above. The interlocking protrusions 22B are maintained in a state of being bitten into or fitted into the interlocking recesses 81B. The outer surfaces of the interlocking protrusions 22B and the inner surfaces of the interlocking recesses 81B interlock with each other in the axial and circumferential directions of the output shaft portion 14. The outer surfaces include the side surfaces of the interlocking protrusions 22B extending circumferentially of the magnetic yoke 22 and the side surfaces of the interlocking protrusions 22B extending axially of the magnetic yoke 22. The inner surface includes a side surface of the meshing recess 81B extending circumferentially of the joining member 81 and a side surface of the meshing recess 81B extending axially of the joining seat 81. The meshing protrusion 22B and meshing recess 81B form a second anti-slip structure that prevents slippage between the output shaft 14 and the magnetic yoke 22.

<Method of joining the output shaft portion 14 and the magnetic yoke 22>
Next, a method for joining the output shaft portion 14 and the magnetic yoke 22 will be described.
8, the output shaft 14 and the magnetic yoke 22 are each prepared in advance as a subassembly. A first bearing 71 and a second bearing 72 are attached to the output shaft 14.

The output shaft portion 14 and the magnetic yoke 22 are joined together using, for example, a small injection molding machine 90. The injection molding machine 90 has a filling machine 91 and a filling mold 92.
The filling machine 91 heats raw resin supplied from the outside to produce molten resin. The molten resin is resin in a molten state. The filling machine 91 has a nozzle 91A. The nozzle 91A is provided at the bottom of the filling machine 91. The filling machine 91 injects the molten resin from the nozzle 91A. The molten resin injected from the nozzle 91A is supplied into the interior of a filling mold 92. The filling machine 91 can be raised and lowered by a drive device.

The filling mold 92 is a solid cylindrical metal body with a circular cross-section. The filling mold 92 has a passage for molten resin. The passage is provided inside the filling mold 92. The passage includes a sprue 82A, a runner 82B, and a gate 82C. The sprue 82A is a passage extending in the axial direction of the filling mold 81. A first end of the sprue opens into a first end face of the filling mold 92. A second end of the sprue is connected to the runner 82. The runner 82B is a passage extending in the radial direction of the filling mold 92. A first end of the gate 82C is connected to the runner 82B. A second end of the gate 82C opens into a second end face of the filling mold 92. The second end face is the end face opposite the first end face of the filling mold 92. The filling mold 92 can be inserted inside the magnetic yoke 22.

When joining the output shaft portion 14 and the magnetic yoke 22, the output shaft portion 14 and the magnetic yoke 22 are set in an injection molding machine 90. The output shaft portion 14 and the magnetic yoke 22 are held in a predetermined position on the table of the injection molding machine 90 by a jig. The jig holds the output shaft portion 14 so that the first end of the output shaft portion 14 faces upward in the direction of gravity. The magnetic yoke 22 is placed on the first bearing 71. The jig holds the magnetic yoke 22 in a predetermined position on the first bearing 71. The output shaft portion 14 and the magnetic yoke 22 are positioned coaxially. The first end of the output shaft portion 14 is inserted into the second end of the magnetic yoke 22. The first opposing surface 14C and the second opposing surface 22A face each other radially. The first opposing surface 14C, the second opposing surface 22A, and the first inner ring 71A form a cavity 82. The cavity 82 opens to the interior of the magnetic yoke 22.

In this state, the filling mold 92 is set inside the magnetic yoke 22. The second end of the gate 82C is positioned directly above the cavity 82. The filling mold 92 is then moved so that the tip of the nozzle 91A is connected to the sprue 91A of the filling mold 92. When the filling machine 91 injects molten resin from the nozzle 91A, the molten resin fills the interior of the cavity 82 via the sprue 91A, runner 91B, and gate 91C. The molten resin cools and solidifies to form the joining member 81, and the output shaft portion 14 and the magnetic yoke 22 are joined together via the connecting member 81. The filling mold 92 is then removed from inside the magnetic yoke 22, yielding the output shaft portion 14 and magnetic yoke 22 joined together.

<Effects of the embodiment>
This embodiment has the following advantages.
(1) The outer peripheral surface of the output shaft portion 14 and the inner peripheral surface of the magnetic yoke 22 are joined via a resin joining member 81. The joining member 81 is formed by solidifying molten resin injected into a cavity 82 formed by the outer peripheral surface of the output shaft portion 14, the inner peripheral surface of the magnetic yoke 22, and the first bearing 71. Therefore, there is no need to provide the magnetic yoke 22 with a metal collar into which the output shaft portion 14 is press-fitted. Product costs can be reduced by eliminating the need for an expensive collar. Furthermore, because a collar is no longer necessary, the weight of the magnetic yoke 22 can also be reduced.

(2) The first opposing surface 14C of the output shaft portion 14 has a plurality of fine first protrusions that bite into the inner circumferential surface of the joining member 81. The first protrusions are biting protrusions 14D. When the output shaft portion 14 and the magnetic yoke 22 are joined, the entire first opposing surface 14C, including the biting protrusions 14D, is covered with molten resin. As a result, a large number of biting recesses 81A corresponding to the biting protrusions 14D are formed on the inner circumferential surface of the joining member 81. The biting protrusions 14D and the biting recesses 81A mesh with each other in the axial and circumferential directions of the output shaft portion 14. Therefore, slippage between the output shaft portion 14 and the joining member 81, and ultimately between the output shaft portion 14 and the magnetic yoke 22, can be suppressed. Slippage includes slippage in the rotational direction of the output shaft portion 14 and slippage in the axial direction of the output shaft portion 14.

(3) The second opposing surface 22A of the magnetic yoke 22 has multiple second protrusions that bite into the outer peripheral surface of the joining member 81. The second protrusions are interlocking protrusions 22B. When joining the output shaft portion 14 and the magnetic yoke 22, the entire second opposing surface 22A, including the interlocking protrusions 22B, is covered with molten resin. As a result, multiple interlocking recesses 81B are formed on the outer peripheral surface of the connecting member 81. The interlocking protrusions 22B and the interlocking recesses 81B interlock in the axial and circumferential directions of the output shaft portion 14. As a result, slippage between the joining member 81 and the magnetic yoke 22, and ultimately between the output shaft portion 14 and the magnetic yoke 22, can be suppressed. Slippage includes slippage in the rotational direction of the output shaft portion 14 and slippage in the axial direction of the output shaft portion 14.

(4) The joining member 81 is formed by filling the cavity 82 with molten resin. The cavity 82 is formed by the first opposing surface 14C of the output shaft portion 14, the second opposing surface 22A of the magnetic yoke 22, and the axial end surface of the first inner ring 71A. This simplifies the mold used to form the joining member 81.

(5) The manufacturing method of the torque sensor 10 includes a first step and a second step. The first step is a step of injecting molten resin into a cavity 82 formed by the outer peripheral surface of the output shaft portion 14, the inner peripheral surface of the magnetic yoke 22, and the first bearing 71, which is the protruding portion. The second step is a step of joining the outer peripheral surface of the output shaft portion 14 and the inner peripheral surface of the magnetic yoke 22 by solidifying the molten resin injected into the cavity 82. In this way, the outer peripheral surface of the output shaft portion 14 and the inner peripheral surface of the magnetic yoke 22 can be appropriately joined, for example, regardless of the machining accuracy of the outer peripheral surface of the output shaft portion 14 and the machining accuracy of the inner peripheral surface of the magnetic yoke 22.

<Other embodiments>
This embodiment may be modified as follows.
As shown in FIG. 9 , depending on product specifications, the output shaft 14 may be configured without the first bearing 71. In this case, the output shaft 14 may have the following configuration. Specifically, the output shaft 14 has a flange member 73. The flange member 73 is a metal plate with a circular cross-section and is attached to the outer circumferential surface of the output shaft 14. The second end of the magnetic yoke 22 abuts against the flange member 73 in the axial direction. The cavity 82 is formed by the first opposing surface 14C, the second opposing surface 22A, and the flange member 73. The flange member 73 may be formed integrally with the output shaft 14. The flange member 73 corresponds to a protruding portion that protrudes radially outward from the outer circumferential surface of the output shaft 14. In the example shown in FIG. 9 , the second inner ring 72A of the second bearing 72 is formed integrally with the output shaft 14.

- The shape of the sensor housing 25 may be changed as appropriate depending on product specifications, etc.

Claims (5)

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 output shaft portion having a protruding portion protruding radially outward from an outer circumferential surface of the output shaft portion;
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;
an outer peripheral surface of the output shaft portion and an inner peripheral surface of the magnetic yoke are joined via a resin joining member,
The joining member is a torque sensor formed by solidifying molten resin injected into a cavity formed by the outer peripheral surface of the output shaft portion, the inner peripheral surface of the magnetic yoke, and the protrusion portion. The torque sensor according to claim 1, wherein the protrusion is a bearing mounted on the outer peripheral surface of the output shaft, or a flange member provided on the outer peripheral surface of the output shaft. a region of the outer circumferential surface of the output shaft portion that faces the inner circumferential surface of the magnetic yoke in the radial direction is a first opposing surface,
3. The torque sensor according to claim 1, wherein the first opposing surface has a plurality of minute first protrusions configured to bite into the inner circumferential surface of the joining member. a region of the inner circumferential surface of the magnetic yoke that faces the outer circumferential surface of the output shaft portion in the radial direction is a second opposing surface,
3. The torque sensor according to claim 1, wherein the second opposing surface has a plurality of second protrusions configured to bite into the outer peripheral surface of the joining member. 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 output shaft portion having a protruding portion protruding radially outward from an outer circumferential surface of the output shaft portion;
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 cavity formed by an outer circumferential surface of the output shaft portion, an inner circumferential surface of the magnetic yoke, and the protruding portion;
and solidifying the injected molten resin to join the outer peripheral surface of the output shaft portion and the inner peripheral surface of the magnetic yoke.