Torque sensor

Abstract

Provided is a durable torque sensor.　A torque sensor (100, 200, 300, 400, 500, 600) comprises: a member (S) that is displaced in the axial direction; a strain-generating body (101, 201, 301, 401, 501, 601); and a housing (104) that accommodates the member (S) and the strain-generating body (101, 201, 301, 401, 501, 601). The strain-generating body (101, 201, 301, 401, 501, 601) is provided with a protrusion (111, 211, 311, 411) that protrudes in the axial direction. The protrusion (111, 211, 311, 411) faces an inner circumferential surface (104 ci) of the housing (104, 501, 601) in the radial direction.

Description

Torque Sensor

[0001] The present invention relates to a torque sensor.

[0002] A torque sensor using a strain sensor is known as a torque sensor for detecting torque in a shaft. For example, Patent Document 1 discloses a torque sensor in which a strain sensor is disposed on the surface of a member having a specific shape.

[0003] Japanese Patent Application Laid-Open No. 2000-193540

[0004] A torque sensor using a strain sensor includes a member that is subjected to repeated stress, and therefore, improvement in durability is sometimes desired. An object of the present invention is to provide a torque sensor having durability.

[0005] The torque sensor of the present invention comprises a member that displaces in the axial direction, a strain generating body, and a housing that accommodates the member and the strain generating body, the strain generating body having a protrusion that protrudes in the axial direction, and the protrusion faces the inner peripheral surface of the housing in the radial direction.

[0006] FIG. 6 is a perspective view of a strain generating element of a torque sensor according to a first embodiment which is an example of the present invention. FIG. 7 is a cross-sectional view of a torque sensor according to a first embodiment which is an example of the present invention. FIG. 8 is a partial cross-sectional view of a torque sensor according to a second embodiment which is an example of the present invention. FIG. 9 is a partial cross-sectional view of a torque sensor according to a third embodiment which is an example of the present invention. FIG. 10 is a partial cross-sectional view of a torque sensor according to a fourth embodiment which is an example of the present invention. FIG. 11 is an enlarged view of a part of FIG. 6. FIG. 12 is a partial cross-sectional view of a torque sensor according to another modified example of the present invention.

[0007] In describing the embodiments of the present invention, for convenience of explanation, the direction of arrow a along axis X (the central axis of the shaft S) is defined as one side in the axial direction. The direction of arrow b along axis X is defined as the other side in the axial direction. Here, the direction of arrows ab is referred to as the axial direction. Furthermore, the direction of arrows cd perpendicular to axis X is referred to as the radial direction, the direction of arrow c away from axis X is referred to as the outer side or one side in the radial direction, and the direction of arrow d approaching axis X is referred to as the inner side or other side in the radial direction. Furthermore, the direction of rotation around axis X is referred to as the circumferential direction.

[0008] [First embodiment] A first embodiment, which is an example of the present invention, will now be described with reference to the drawings. Fig. 1 is a perspective view of a strain element 101 of a torque sensor 100 according to this embodiment. Fig. 2 is a cross-sectional view of the torque sensor 100 according to this embodiment.

[0009] The torque sensor 100 includes a shaft S, which is a member that displaces in the axial direction, a strain body 101, a bearing 102, a plurality of (four in this embodiment) strain sensors 103, and a housing 104 that accommodates a portion of the shaft S and the strain body 101. In this embodiment, the bearing 102 is a ball bearing that has an inner ring 102i, an outer ring 102o, and rolling elements. Note that the bearing 102 is not limited to a ball bearing, and may be various other bearings, such as a sleeve bearing.

[0010] As shown in FIG. 1 , the strain body 101 has an inner portion (holding portion 110), an outer portion (plurality of mounting portions 120) that surrounds the holding portion 110 in the radial direction, a connecting portion 130, and a tubular (cylindrical) protruding portion 111 that is connected to the other axial side (direction of arrow b) of the holding portion 110 and to the inner side in the radial direction (direction of arrow d) and that protrudes to the other axial side (direction of arrow b).

[0011] The holding portion 110 is a cylindrical portion extending in the axial direction and having a cylindrical inner peripheral surface 110a around the axis X. The holding portion 110 is a portion that supports the shaft S via a bearing 102. In FIG. 1 , the outer shape (outer shape in the radial direction) of the holding portion 110 is approximately square when viewed in the axial direction, but the outer shape of the holding portion 110 is not limited to this and may be any shape, such as a circle, an approximately circle, an ellipse, a polygon, or a shape including complex irregularities.

[0012] 2 , the dimensions of the retaining portion 110 in the axial direction are the same or approximately the same as the dimensions of the mounting portion 120. In the radial direction, the end face of the retaining portion 110 on one side in the axial direction (the direction of arrow a) is in a different position (on the bearing 102 side) from the end face of the mounting portion 120 on one side in the axial direction (the direction of arrow a).

[0013] Four plate-shaped connecting portions 130 protrude radially outward (in the direction of arrow c) from the end of the holding portion 110 on one side in the axial direction (in the direction of arrow a). The four connecting portions 130 are arranged in positions that are rotationally symmetric (hereinafter also referred to as "four-fold symmetry"), overlapping when rotated 90° around the axis X. That is, the four connecting portions 130 are arranged at equal intervals (every 90°) in the circumferential direction. However, the arrangement and number of connecting portions 130 may vary depending on the arrangement and number of mounting portions 120. In the radial direction, the outer side (in the direction of arrow c) of each connecting portion 130 is connected to the end of one side in the axial direction (in the direction of arrow a) of the mounting portion 120. Therefore, the connecting portions 130 connect the holding portion 110 and the mounting portion 120 (particularly, the deformable surface 122 described below). The connecting portions 130 are elastic and can be deformed in response to external forces.

[0014] The mounting portion 120 is a portion that can be used to mount the flexure element 101 to the housing 104, and has a substantially L-shaped cross section. In this embodiment, the flexure element 101 is provided with four mounting portions 120. However, the number of mounting portions 120 on the flexure element 101 is not limited to four, and may be one, two, three, five or more. In this embodiment, the four mounting portions 120 are arranged at positions that are quadrilaterally symmetric about the axis X. That is, the four mounting portions 120 are arranged at equal intervals (every 90°) in the circumferential direction. However, the multiple mounting portions 120 do not have to be arranged at equal intervals in the circumferential direction. For example, a second mounting portion 120 may be arranged at an interval of n° from a first mounting portion 120, a third mounting portion 120 may be arranged at an interval of (180-n)° from there, and a fourth mounting portion 120 may be arranged at an interval of n° from there. The mounting portions 120 are capable of elastically or plastically deforming in response to an external force. Since all four mounting portions 120 have the same configuration, only one mounting portion 120 will be described in detail below, and detailed descriptions of the other mounting portions 120 will be omitted.

[0015] The mounting portion 120 has a deformable surface 122 extending in the axial direction. The strain element 101 has a gap 140 (described later) between a portion 121 (portion extending in the axial direction) of the mounting portion 120 having the deformable surface 122 and a portion of the retaining portion 110 that is on the bearing 102 side of the deformable surface 122. Due to the shape of the gap 140, the portion 121 of the mounting portion 120 having the deformable surface 122 has a thinner wall thickness (radial thickness) than the other portions of the mounting portion 120, making it more susceptible to deformation accompanied by strain.

[0016] As shown in Fig. 2, the mounting portion 120 faces the holding portion 110 in the radial direction, with a gap 140 interposed therebetween. In the axial direction, the gap 140 is formed on the other side of the connecting portion 130 (in the direction of arrow b). Due to the presence of the gap 140, the mounting portion 120 and the holding portion 110 are spaced apart by a predetermined distance on the other side of the connecting portion 130 in the axial direction (in the direction of arrow b). The gap 140 penetrates the strain element 101 in the circumferential direction (the depth direction in Fig. 2).

[0017] The gap 140 includes two through holes (holes) of different shapes. The gap 140 shown in FIG. 2 includes a first through hole (hole) 141 having a circular or approximately circular cross section and a second through hole (slit) 142 connected to the first through hole 141. In the axial direction, the second through hole (slit) 142 is connected to the other side of the first through hole 141 (the direction of arrow b). The second through hole (slit) 142 has a width (radial dimension) narrower than the size (diameter) of the first through hole 141. However, the shape of the gap 140 is not limited thereto and may be any shape, such as a shape having only the second through hole (slit), a shape having a combination of multiple through holes having circular or approximately circular cross sections, or a shape having the second through hole (slit) extending in the radial direction.

[0018] Due to the formation of the first through hole 141, a recess is formed on the radially inner surface (direction of arrow d) of the mounting portion 120, which is recessed radially outward (direction of arrow c), and a recess is formed on the axially other side (direction of arrow b) of the connecting portion 130, which is recessed axially to one side (direction of arrow a), and a recess is formed on the radially outer surface (direction of arrow c) of the holding portion 110, which is recessed radially inward (direction of arrow d).

[0019] Since each mounting portion 120 has a deformable surface 122, the strain element 101 of the torque sensor 100 has a plurality of deformable surfaces as a whole (eight in this embodiment, including the surfaces 131 of the connecting portions 130, which will be described later). The plurality of deformable surfaces are arranged in a line at positions that are four-fold symmetric (rotationally symmetric) in the circumferential direction (FIG. 1).

[0020] A strain sensor 103 is attached to the radially outer side (direction of arrow c) of the deformable surface 122. By attaching a strain sensor 103 to each of the multiple deformable surfaces 122, the torque sensor 100 is equipped with multiple (four in this embodiment) strain sensors 103. However, it is not necessary for a strain sensor 103 to be attached to all of the multiple deformable surfaces 122. Furthermore, the strain directions detected by the individual strain sensors 103 may be different from each other. The deformable surfaces 122 and the strain sensors 103 may be attached to surfaces extending in the axial direction, circumferential direction, or radial direction, respectively. The strain sensors 103 are attached so as to be able to detect strain on the deformable surfaces 122. The strain sensors 103 are attached to the deformable surface 122 so that the grid orientation of the strain sensors 103 (typically the longitudinal direction of the strain sensors 103) is in a predetermined direction (which may be any of the axial, circumferential, or radial directions; in the illustrated example, it is the axial direction). The orientation of the grids of the multiple strain sensors 103 is not limited to the axial direction, but may also be the circumferential direction, the radial direction, or a direction oblique to the axial direction. Of the multiple strain sensors, the grid orientation of two opposing strain sensors 103 may be the axial direction, and the grid orientation of the other two opposing strain sensors 103 may be the circumferential direction. Alternatively, the grids of two opposing strain sensors 103 may be oriented in a direction where the radial and circumferential directions meet (a diagonal direction (first direction)), and the grids of two other opposing strain sensors 103 may be oriented in a direction where the radial and circumferential directions meet (a diagonal direction (second direction)), with the first and second directions intersecting each other. If the strain sensors 103 are strain gauges, the strain of the deformable surface 122 is detected as a change in resistance value. Note that the strain sensors 103 may also be various other sensors, such as resistive elements or piezoelectric elements.

[0021] As described above, in this embodiment, the strain sensor 103 is attached to the radially outer side (in the direction of arrow c) of the deformable surface 122. However, the strain sensor 103 may also be attached to the surface 131 of the connecting portion 130 (for example, the surface on one side in the axial direction (in the direction of arrow a)) as indicated by reference symbol 103a in FIG. 1 . In this case, the surface 131 of the connecting portion 130 is a deformable surface extending in the radial or circumferential direction. Furthermore, the strain sensor 103 may also be attached to both the deformable surface 122 and the surface of the connecting portion 130. Furthermore, some of the strain sensors 103 may be attached to the deformable surface 122, and other strain sensors 103 may be attached to the surface of the connecting portion 130.

[0022] A fixed portion 123 connected to the housing 104 is disposed radially outward (in the direction of arrow c) of the mounting portion 120 relative to the deformable surface 122. The fixed portion 123 is a rectangular plate-like portion extending radially outward (in the direction of arrow c) from the end of the deformable surface 122 on the other axial side (in the direction of arrow b). A hole 123h having a circular or nearly circular cross section and extending in the axial direction is formed, for example, in the center of the fixed portion 123. A mounting hole 104h extending in the axial direction is formed in the housing 104 at a position corresponding to the hole 123h of the flexure element 101. The mounting portion 120 is fixed to the housing 104 by fastening members such as bolts (not shown) that are axially inserted through the hole 123h of the fixed portion 123 and the mounting hole 104h of the housing 104. This fixes the entire flexure element 101 to the housing 104.

[0023] In the radial direction, the bearing 102 is disposed inside (in the direction of arrow d) the holding portion 110 of the flexure body 101. The bearing 102 is held by the holding portion 110 of the flexure body 101. The inner ring 102i of the bearing 102 is bonded or press-fitted with a joining material such as resin to the outer peripheral surface (the outer surface in the radial direction) of a portion S1 of the cylindrical or approximately cylindrical shaft S that is supported by the bearing 102. In this way, the inner ring 102i of the bearing 102 is fixed to the shaft S. The outer ring 102o of the bearing 102 is press-fitted into the inner peripheral surface 110a of the holding portion 110 of the flexure body 101. The bearing 102 supports the shaft S rotatably with respect to the flexure body 101.

[0024] The shaft S is a cylindrical or approximately cylindrical member extending in the axial direction. The shaft S is supported by the strain body 101 via a bearing 102. In the axial direction, an annular convex portion S2 extending radially is formed on one side (in the direction of arrow a) of a portion S1 of the shaft S supported by the bearing 102. In the axial direction, the surface on the other side (in the direction of arrow b) of the convex portion S2 contacts the surface on one side (in the direction of arrow a) of an inner ring 102i of the bearing 102. This positions the shaft S in the axial direction. In the axial direction, the end portion on the other side (in the direction of arrow b) of the shaft S protrudes outside the housing 104 through a hole 104a of the housing 104, which will be described later. Outside the housing 104, a first crank arm A1 (shown by a phantom line in FIG. 2) is connected to the other axial end (in the direction of arrow b) of the shaft S, and a second crank arm (not shown) is connected to one axial end (in the direction of arrow a) of the shaft S. In this embodiment, the shaft S is deformed when subjected to a radial or axial external force (or a radial or axial component of the external force), and the deformation of the shaft S causes the strain body 101 to deform via the bearing 102.

[0025] A cylindrical (cylindrical) protrusion 111 extending toward the other side (arrow b direction) is connected to the end of the other side (arrow b direction) of the holding portion 110 of the strain body 101 in the axial direction. The protrusion 111 has a cylindrical outer peripheral surface 111o extending in the axial direction on the radially outer side (arrow c direction). In the radial direction, the inner peripheral surface 111i of the protrusion 111 has a size (inner diameter) smaller than the size (inner diameter) of the inner peripheral surface 110a of the holding portion 110, and the outer peripheral surface 111o of the protrusion 111 has a size (outer diameter) slightly larger than the size of the inner peripheral surface of the holding portion 110. However, the size of the outer peripheral surface 111o of the protrusion 111 may be larger, may be equal to the size of the inner peripheral surface 110a of the holding portion 110, or may be smaller than the size of the inner peripheral surface 110a of the holding portion 110.

[0026] In this embodiment, an end face of the protrusion 111 on one axial side (in the direction of arrow a) is in contact with an end face of the outer ring 102o of the bearing 102 on the other axial side (in the direction of arrow b). As a result, the protrusion 111 supports the bearing 102 in a state where movement of the bearing 102 to the other axial side (in the direction of arrow b) is restricted.

[0027] The wall 104w of the housing 104 forms an annular hole 104a that penetrates in the axial direction. The hole 104a of the housing 104 is defined by a tube 104c formed coaxially with the shaft S and a ring-shaped portion 104b that protrudes radially inward (in the direction of arrow d) from the end of the tube 104c on the other side in the axial direction (in the direction of arrow b). In this embodiment, a ring-shaped recess is formed in the wall 104w of the housing 104 that forms the hole 104a. The tube 104c is a portion of the wall 104w of the housing 104 that surrounds the ring-shaped recess. The tube 104c has a cylindrical inner circumferential surface 104ci that extends axially on the radially inward side (in the direction of arrow d). This cylindrical inner circumferential surface 104ci, the hole 104a, and the surface 104bi connecting the inner circumferential surface 104ci and the hole 104a form an annular recess in the wall of the housing 104. In this embodiment, the inner circumferential surface 104ci is the inner circumferential surface of the housing 104 (the inner circumferential surface around the axis X) and also the inner circumferential surface of the cylinder 104c.

[0028] The cylinder 104c of the housing 104 accommodates a portion of the protrusion 111 of the flexure element 101. In the radial direction, the protrusion 111 of the flexure element 101 faces the inner circumferential surface 104ci of the housing 104. In this embodiment, the protrusion 111 of the flexure element 101 is press-fitted into the inner circumferential surface 104ci of the housing 104. The outer circumferential surface 111o of the protrusion 111 of the flexure element 101 contacts the inner circumferential surface 104ci of the housing 104 over the entire or substantially entire overlapping portion in the axial direction (portion facing each other in the radial direction).

[0029] When the torque sensor 100 is used in a bicycle, the shaft S is a crankshaft to which the crank arms (the above-mentioned first crank arm A1 and second crank arm) and pedals are connected. When one pedal is pressed, a force acts on the pedal side (side a or side b) of the shaft S to tilt downward in FIG. 2 , causing the bearing 102 to move radially, pressing a portion of the flexure element 101 radially outward (in the direction of arrow c) and pulling another portion of the flexure element 101 radially inward (in the direction of arrow d). This causes stress to concentrate in a portion of the flexure element 101 near the gap 140 (e.g., the deformable surface 122 of the mounting portion 120 or the connecting portion 130), resulting in deformation and strain in the portion near the gap 140.

[0030] The presence of multiple strain sensors 103 makes it possible to detect strain in the strain element 101 in response to tilt in all directions of the shaft S. In particular, in the torque sensor 100, the four mounting portions 120 are located at positions that are four-fold symmetric about the axis X, making it possible to more accurately detect strain in all directions.

[0031] The torque sensor 100 has a simple configuration including a strain element 101, a bearing 102, and a strain sensor 103, and can be made smaller because a detection coil, etc., which is required when using a magnetostrictive sensor, is not arranged around the shaft S. Furthermore, since no processing such as attaching a magnetic layer to the shaft S is required, manufacturing is easy.

[0032] In the torque sensor 100, the mounting portion 120 faces the holding portion 110 in the radial direction with a gap 140 therebetween. This allows the strain element 101 in the torque sensor 100 to deform easily, enabling stress to be detected with high sensitivity.

[0033] In the torque sensor 100, the protruding portion 111 of the flexure element 101 is press-fit into the inner circumferential surface 104ci of the housing 104 in the radial direction and faces the inner circumferential surface 104ci of the housing 104. The outer circumferential surface 111o of the protruding portion 111 of the flexure element 101 is in contact with the inner circumferential surface 104ci of the housing 104 over the entire or substantially entire overlapping portion in the axial direction (the portion facing in the radial direction). Therefore, the external force acting on the torque sensor 100 is mainly received by the protruding portion 111 of the flexure element 101, thereby preventing fatigue failure of the mounting portion 120 due to repeated stress. In other words, the torque sensor 100 is less susceptible to fatigue failure, thereby improving durability.

[0034] Second Embodiment A second embodiment of the present invention will now be described with reference to the drawings. Fig. 3 is a partial cross-sectional view of a torque sensor 200 according to this embodiment. The torque sensor 200 has the same configuration as the torque sensor 100 of the first embodiment, except that it includes a flexure element 201 instead of the flexure element 101. The flexure element 201 has the same configuration as the flexure element 101 of the first embodiment, except for the shape of the protrusion. Hereinafter, members and parts having the same functions and configurations as those of the torque sensor 100 according to the first embodiment will be denoted by the same reference numerals, and detailed description thereof will be omitted.

[0035] As shown in FIG. 3 , the strain body 201 has an inner portion (holding portion 110), an outer portion (plurality of mounting portions 120) that surrounds the holding portion 110 in the radial direction, a connecting portion 130, and a tubular (cylindrical) protruding portion 211 that is connected to the other axial side (direction of arrow b) of the holding portion 110 and to the inner side in the radial direction (direction of arrow d) and that protrudes and extends to the other axial side (direction of arrow b).

[0036] In the radial direction, the inner circumferential surface 211i of the protrusion 211 has a size (inner diameter) smaller than the size (inner diameter) of the inner circumferential surface 110a of the holding part 110, and the outer circumferential surface 211o of the protrusion 211 has a size (outer diameter) slightly larger than the size of the inner circumferential surface 110a of the holding part 110. However, the size of the outer circumferential surface 211o of the protrusion 211 may be even larger, may be equal to the size of the inner circumferential surface 110a of the holding part 110, or may be smaller than the size of the inner circumferential surface 110a of the holding part 110.

[0037] In this embodiment, an end face of the protrusion 211 on one axial side (in the direction of arrow a) is in contact with an end face on the other axial side (in the direction of arrow b) of the outer ring 102o of the bearing 102. As a result, the protrusion 211 supports the bearing 102 in a state where movement of the bearing 102 to the other axial side (in the direction of arrow b) is restricted.

[0038] The cylinder 104c of the housing 104 accommodates the protrusion 211 of the flexure element 201. In the radial direction, the protrusion 211 of the flexure element 201 faces the inner circumferential surface 104ci of the housing 104. In the radial direction, a predetermined annular gap G2 is present between the protrusion 211 of the flexure element 201 and the inner circumferential surface 104ci of the housing 104. In this embodiment, the radial dimension of the gap G2 is smaller than the minimum radial dimension of the gap 140 (the dimension of the second through hole (slit) 142). In addition, in this embodiment, the radial dimension of the gap G2 is smaller than the radial dimension of the protrusion 211. The overlapping portion of the outer peripheral surface 211o of the protrusion 211 of the strain element 201 in the axial direction with the inner peripheral surface 104ci of the housing 104 (the portion facing in the radial direction) is separated from the inner peripheral surface 104ci of the housing 104 by a predetermined distance.

[0039] Like the torque sensor 100 according to the first embodiment, the torque sensor 200 according to this embodiment is easy to manufacture and can detect stress with high sensitivity.

[0040] Furthermore, in the torque sensor 200, a predetermined annular gap G2 is formed in the radial direction between the protrusion 211 of the strain element 201 and the inner circumferential surface 104ci of the housing 104, and the gap G2 is formed circumferentially. Therefore, when the external force acting on the torque sensor 200 is within a certain range, the strain element 201 has a high degree of freedom of deformation, and the surface on which the strain sensor 103 is attached is easily deformed, thereby enabling high-sensitivity stress detection. On the other hand, when an external force greater than a certain level is applied, the strain element 201 deforms and the protrusion 211 comes into contact with the inner circumferential surface 104ci of the housing 104. As a result, the protrusion 211 mainly receives the external force, thereby preventing fatigue failure of the mounting portion 120 due to repeated stress. In other words, the torque sensor 200 is highly sensitive yet resistant to fatigue failure, thereby improving durability.

[0041] Third Embodiment A third embodiment of the present invention will now be described with reference to the drawings. Fig. 4 is a partial cross-sectional view of a torque sensor 300 according to this embodiment. The torque sensor 300 has a similar configuration to the torque sensor 100 of the first embodiment, except that it includes a flexure element 301 instead of the flexure element 101. The flexure element 301 has a similar configuration to the flexure element 101 of the first embodiment, except for the shape of the protrusion. Hereinafter, members and parts having the same functions and configurations as those of the torque sensor 100 according to the first embodiment will be denoted by the same reference numerals, and detailed description thereof will be omitted.

[0042] As shown in FIG. 4 , the strain body 301 has an inner portion (holding portion 110), an outer portion (plurality of mounting portions 120) that surrounds the holding portion 110 in the radial direction, a connecting portion 130, and a tubular (substantially cylindrical) protruding portion 311 that is connected to the other axial side (direction of arrow b) of the holding portion 110 and the inner side in the radial direction (direction of arrow d), and that protrudes and extends to the other axial side (direction of arrow b).

[0043] The other axial end (arrow b direction) of the protrusion 311 is provided with an annular convex portion 311a extending radially outward (arrow c direction) toward the inner circumferential surface 104ci of the housing 104. Note that instead of the annular convex portion 311a, multiple convex portions 311a may be arranged in a circumferential direction. The protrusion 311 has a cylindrical outer circumferential surface 311o extending axially on one axial side (arrow a direction) of the convex portion 311a, radially outward (arrow c direction). In the radial direction, the size (inner diameter) of the inner circumferential surface 311i of the protrusion 311 is smaller than the size (inner diameter) of the inner circumferential surface 110a of the holder 110. The size (diameter) of the outer circumferential surface 311o of the protrusion 311 is substantially the same as the size (inner diameter) of the inner circumferential surface 110a of the holder 110. However, the size (diameter) of the outer peripheral surface 311o may be larger or smaller than the size (inner diameter) of the inner peripheral surface 110a of the holding portion 110. The convex portion 311a of the protrusion 311 has a cylindrical outer peripheral surface 311ao extending in the axial direction on the radially outer side (direction of arrow c). The size (diameter) of the outer peripheral surface 311ao of the convex portion 311a is larger than the size (diameter) of the outer peripheral surface 311o of the protrusion 311.

[0044] In this embodiment, an end face of the protrusion 311 on one axial side (in the direction of arrow a) is in contact with an end face of the outer ring 102o of the bearing 102 on the other axial side (in the direction of arrow b). As a result, the protrusion 311 supports the bearing 102 in a state where movement of the bearing 102 to the other axial side (in the direction of arrow b) is restricted.

[0045] The cylinder 104c of the housing 104 accommodates the protruding portion 311 of the flexure element 301. In the radial direction, the protruding portion 311 of the flexure element 301 faces the inner circumferential surface 104ci of the housing 104. In the radial direction, there is a predetermined annular gap G3 between the outer circumferential surface 311o of the protruding portion 311 of the flexure element 301 and the inner circumferential surface 104ci of the housing 104. In this embodiment, the radial dimension of the gap G3 is smaller than the radial dimension of the gap 140 (the dimension of the second through hole (slit) 142). In addition, in this embodiment, the radial dimension of the gap G3 is smaller than the radial dimension of the protruding portion 311.

[0046] In this embodiment, the convex portion 311a of the protrusion 311 is in contact with the inner circumferential surface 104ci of the housing 104. Specifically, the outer circumferential surface 311ao of the protrusion 311a is in contact with the inner circumferential surface 104ci of the housing 104. Therefore, in this embodiment, the protrusion 311 is lightly press-fitted (loosely fitted) into the inner circumferential surface 104ci of the housing 104. Note that in this embodiment, "lightly press-fitted" means that the protrusion 311 is press-fitted with a force smaller than that of the first embodiment.

[0047] Like the torque sensor 100 according to the first embodiment, the torque sensor 300 according to this embodiment is easy to manufacture and can detect stress with high sensitivity.

[0048] Furthermore, in the torque sensor 300, a predetermined annular gap G3 is formed in the radial direction between the protrusion 311 of the flexure element 301 and the inner circumferential surface 104ci of the housing 104, and the protrusion 311 of the flexure element 301 contacts the inner circumferential surface 104ci of the housing 104 only at the convex portion 311a. Therefore, when the external force acting on the torque sensor 300 is within a certain range, the flexure element 301 has a high degree of freedom of deformation, and the surface on which the strain sensor 103 is attached is easily deformed, enabling stress to be detected with high sensitivity. On the other hand, when an external force greater than a certain level is applied, the flexure element 301 deforms, changing, for example, the manner of contact between the flexure element 301 and the inner circumferential surface 104ci of the housing 104, and increasing the proportion of the external force received by the protrusion 311 of the flexure element 301. This prevents fatigue failure of the mounting portion 120 due to repeated stress. That is, the torque sensor 300 is highly sensitive yet resistant to fatigue failure, thereby improving durability.

[0049] Fourth Embodiment A fourth embodiment of the present invention will now be described with reference to the drawings. Fig. 5 is a partial cross-sectional view of a torque sensor 400 according to this embodiment. The torque sensor 400 has a similar configuration to the torque sensor 100 of the first embodiment, except that it includes a flexure element 401 instead of the flexure element 101. The flexure element 401 has a similar configuration to the flexure element 101 of the first embodiment, except for the shape of the protrusion. Hereinafter, members and parts having the same functions and configurations as those of the torque sensor 100 according to the first embodiment will be denoted by the same reference numerals, and detailed description thereof will be omitted.

[0050] As shown in FIG. 5 , the strain body 401 has an inner portion (holding portion 110), an outer portion (plurality of mounting portions 120) that surrounds the holding portion 110 in the radial direction, a connecting portion 130, and a tubular (substantially cylindrical) protruding portion 411 that is connected to the other axial side (direction of arrow b) of the holding portion 110 and to the inner side in the radial direction (direction of arrow d) and that protrudes and extends to the other axial side (direction of arrow b).

[0051] The protrusion 411 has an inclined side surface as an outer peripheral surface 411o on the radially outer side (in the direction of arrow c). In the illustrated example, the outer peripheral surface 411o of the protrusion 411 forms a truncated cone. The size (diameter) of the outer peripheral surface 411o of the protrusion 411 increases toward the other axial side (in the direction of arrow b). Therefore, the outer peripheral surface 411o of the protrusion 411 is inclined relative to the inner peripheral surface 104ci of the housing 104. The size of the inner peripheral surface 411i of the protrusion 411 is smaller than the size (inner diameter) of the inner peripheral surface 110a of the holding portion 110. The size (diameter) of the outer peripheral surface 411o of the protrusion 411 at one end in the axial direction (direction of arrow a) is approximately the same as the size (inner diameter) of the inner peripheral surface 110a of the holding part 110, and at the end on the other end in the axial direction (direction of arrow b) is slightly larger than the size (inner diameter) of the inner peripheral surface 110a of the holding part 110. However, the relationship between the size (diameter) of the outer peripheral surface 411o of the protrusion 411 and the size (inner diameter) of the inner peripheral surface 110a of the holding part 110 is not limited to the above.

[0052] In this embodiment, an end face of the protrusion 411 on one axial side (in the direction of arrow a) is in contact with an end face of the outer ring 102o of the bearing 102 on the other axial side (in the direction of arrow b). As a result, the protrusion 411 supports the bearing 102 in a state where movement of the bearing 102 to the other axial side (in the direction of arrow b) is restricted.

[0053] The cylinder 104c of the housing 104 accommodates the protrusion 411 of the flexure element 401. The protrusion 411 of the flexure element 401 faces the inner circumferential surface 104ci of the housing 104 in the radial direction. A predetermined annular gap G4 is formed between the outer circumferential surface 411o of the protrusion 411 of the flexure element 401 and the inner circumferential surface 104ci of the housing 104 in the radial direction. The radial dimension of the gap G4 is larger toward one axial side (the direction of arrow a) and smaller toward the other axial side (the direction of arrow b). Therefore, as shown in FIG. 5 , a small gap G4b is formed between a portion of the protrusion 411 and the inner circumferential surface 104ci of the housing 104 in the radial direction, and a large gap G4a is formed between another portion of the protrusion 411 (in this embodiment, the portion closer to one axial side) and the inner circumferential surface 104ci of the housing 104. It should be noted that the terms "large" and "small" merely refer to the relative size relationship between gaps G4a and G4b, and do not imply any absolute size. In this embodiment, the maximum radial dimension of gap G4 is smaller than the radial dimension of gap 140 (the dimension of second through-hole (slit) 142). Also, in this embodiment, the maximum radial dimension of gap G4 is smaller than the radial dimension of protrusion 411.

[0054] In the present embodiment, the end of the protrusion 411 on the other axial side (the direction of the arrow b) is in contact with the inner circumferential surface 104ci of the housing 104. Therefore, in the present embodiment, the protrusion 411 is lightly press-fitted (loosely fitted) into the inner circumferential surface 104ci of the housing 104.

[0055] Like the torque sensor 100 according to the first embodiment, the torque sensor 400 according to this embodiment is easy to manufacture and can detect stress with high sensitivity.

[0056] Furthermore, in the torque sensor 400, a predetermined annular gap G4 is formed between the protrusion 411 of the flexure element 401 and the inner circumferential surface 104ci of the housing 104 in the radial direction, and the protrusion 411 of the flexure element 401 contacts the inner circumferential surface 104ci of the housing 104 only at its end. Therefore, when the external force acting on the torque sensor 400 is within a certain range, the flexure element 401 has a high degree of freedom of deformation, and the surface on which the strain sensor 103 is attached is easily deformed, allowing stress to be detected with high sensitivity. On the other hand, when an external force greater than a certain level is applied, the flexure element 401 deforms, changing, for example, the manner of contact between the flexure element 401 and the inner circumferential surface 104ci of the housing 104, and increasing the proportion of the external force received by the protrusion 411 of the flexure element 401. This prevents fatigue failure of the mounting portion 120 due to repeated stress. That is, the torque sensor 400 is highly sensitive yet resistant to fatigue failure, and durability can be improved.

[0057] Although the torque sensor of the present invention has been described above with reference to preferred embodiments, the torque sensor of the present invention is not limited to the configurations of any of the above embodiments. For example, although the torque sensors according to the above embodiments are used in power-assisted bicycles, the torque sensor of the present invention is not limited to those used in power-assisted bicycles.

[0058] The torque sensors according to the above-described embodiments have a common structure except for the protrusion of the strain element, but the structure of the strain element in the torque sensor of the present invention is not limited to these. For example, in a case where there is a possibility that a portion of the strain element is prone to fatigue failure due to repeated application of stress, any torque sensor having a strain element structured so that it can receive an external force by a protrusion that faces the inner peripheral surface of the housing in the radial direction is included in the torque sensor of the present invention.

[0059] In the torque sensor of the present invention, the gap between the protruding portion of the strain generator and the inner peripheral surface of the housing may vary along the axial direction. For example, the outer peripheral surface of the protruding portion of the strain generator may be inclined with respect to the axial direction, or a convex portion spaced apart from the inner peripheral surface of the housing may be provided on the outer peripheral surface of the protruding portion of the strain generator.

[0060] In the torque sensor of the present invention, the annular convex portion in the third embodiment may be provided at another portion of the protrusion in the axial direction, and a plurality of convex portions may be provided side by side in the circumferential or axial direction. Furthermore, when a plurality of convex portions are provided, the shapes and sizes of the respective convex portions may be the same or different.

[0061] In the torque sensor of the present invention, the size of the outer peripheral surface of the protrusion may be larger toward one side in the axial direction (the direction of arrow a). Furthermore, in the axial direction, the outer peripheral surface of the protrusion has one end (one side (the direction of arrow a)), the other end of the outer peripheral surface of the protrusion (the other side (the direction of arrow b)), and an intermediate portion between both ends, and the size (outer shape) of the intermediate portion H of the outer peripheral surface of the protrusion, the size of one end I (one side (the direction of arrow a)), and the size of the other end J (the other side (the direction of arrow b)) may satisfy a relationship such as H > I = J, H > I > J, or H > J > I.

[0062] The torque sensor of the present invention may be a torque sensor 500 shown in FIGS. 6 and 7 . The torque sensor 500 has a configuration similar to that of the torque sensor 100 of the first embodiment, except for the points described below. The torque sensor 500 includes a flexure element 501. The flexure element 501 has a configuration generally similar to that of the flexure element 101 of the first embodiment, except that a strain sensor 503 is attached to a surface 531 (a surface on one axial side (in the direction of arrow a)) of a connecting portion 530. A fixing portion 523 protruding to the other axial side (in the direction of arrow b) is inserted into a recess 504c formed in a housing 504. A fastening member B1, such as a bolt, is inserted into a hole 523h formed in the fixing portion 523 and threaded into a mounting hole 504h formed in the housing 504. As shown in FIG. 7 , the recess 504c formed in the housing 504 has a wall 504o, which is a surface extending in the axial direction, at an end on the inner side in the radial direction (in the direction of arrow d). The fixing portion 523 of the strain body 501 has a surface 523i extending in the axial direction at the end on the inner side in the radial direction (in the direction of the arrow d). The distance in the radial direction between the wall 504o of the housing and the surface 523i of the strain body 501 is defined as D. １ Furthermore, the radial distance between the outer peripheral surface Bo of the fastening member B1 and the hole 523h of the strain body 501 is defined as D ２ Here, when the fastening member B1 has a thread at a portion facing the hole 523h of the strain body 501, the "outer peripheral surface Bo of the fastening member B1" refers to a cylindrical surface including the ridge line of the thread. １ D ２ is smaller than (D １ <D ２ The fixing portion 523 may be press-fitted into the recess 504c of the housing 504, in which case the wall 504o of the housing and the surface 523i of the strain element 501 are in contact with each other (D １ = 0). In this way, the positional deviation of the strain element 501 is suppressed, and the detection sensitivity of the torque sensor 500 is improved.

[0063] The torque sensor of the present invention may be a torque sensor 600 shown in FIG. 8. It should be noted that while FIG. 8 is a cross-sectional view taken along a plane including the axis X, it is a cross-sectional view taken along a plane different from that shown in FIGS. 2 to 7. The torque sensor 600 has a configuration similar to that of the torque sensor 100 of the first embodiment, except for the following points. The torque sensor 600 includes a flexure element 601. The flexure element 601 has a configuration generally similar to that of the flexure element 101 of the first embodiment, except that a cylindrical portion 610b having a hole 610h extending in the axial direction is connected to the outer circumferential surface of a holding portion 610. The torque sensor 600 includes a substrate 605 on which a circuit or the like is formed that processes signals input from, for example, a strain sensor (not shown). The substrate 605 and the flexure element 601 are fixed to a housing 604 by fastening members B2 such as bolts. Specifically, a single fastening member B2 is inserted through the substrate 605, any spacer 606, and the cylindrical portion 610b (hole 610h) in that order from one axial side (direction of arrow a) to the other axial side (direction of arrow b), and is then screwed into a mounting hole 604h formed in the housing 604. Here, the hole 610h may be a cylindrical hole or a female-threaded hole. This improves the durability of the entire torque sensor 600 when the substrate 605 is included.

[0064] Furthermore, those skilled in the art can appropriately modify the torque sensor of the present invention and change the shapes, dimensions, and combinations of various components according to conventional knowledge. As long as such modifications still provide the configuration of the present invention, they are, of course, included in the scope of the present invention. For example, the inner ring of the bearing may face the outer circumferential surface of the shaft with a predetermined radial gap (e.g., the gap P formed between the shaft S and the bearing 102 in FIG. 9 ), and the bearing 102 may rotatably support the shaft S (either a clearance fit, an intermediate fit, or an interference fit). This modification can be applied to any of the above-described embodiments, and it is considered that the application of this modification to each embodiment is described.

[0065] 100, 200, 300, 400, 500, 600... torque sensor, 101, 201, 301, 401, 501, 601... strain element, 102... bearing, 104, 504, 604... housing, 104c... cylinder, 104ci... inner peripheral surface, 110, 610... inner portion (holding portion), 120... outer portion (mounting portion), 130, 530... connecting portion, 111, 211, 311, 411... protrusion, 311a... convex portion, S... member (shaft), G2, G3, G4... gap, G4a... large gap, G4b... small gap.

Claims

1. A torque sensor comprising: a member that displaces in an axial direction; a flexure body; and a housing that accommodates the member and the flexure body, the flexure body having a protrusion that protrudes in the axial direction, the protrusion facing an inner circumferential surface of the housing in the radial direction.

2. The torque sensor according to claim 1, wherein the housing comprises a cylinder that houses the protrusion, and the inner circumferential surface of the housing is the inner circumferential surface of the cylinder.

3. The torque sensor according to claim 1 or 2, wherein the protrusion is press-fitted or lightly press-fitted into the inner circumferential surface.

4. The torque sensor according to claim 1, wherein a predetermined gap is provided between the protrusion and the inner peripheral surface in the radial direction.

5. The torque sensor according to claim 4, wherein there is a small gap between a part of the protrusion and the inner circumferential surface in the radial direction, and there is a large gap between another part of the protrusion and the inner circumferential surface in the radial direction.

6. A torque sensor according to claim 1, wherein the protrusion has a convex portion extending radially toward the inner circumferential surface.

7. A torque sensor according to claim 1, wherein said protrusion has a surface that is inclined with respect to said inner circumferential surface in the radial direction.

8. A torque sensor according to any one of claims 1 to 7, wherein the strain body comprises an inner part that supports the member, an outer part that surrounds the inner part, and a connecting part that connects the inner part and the outer part, and the connecting part has elasticity.

9. A torque sensor according to any one of claims 1 to 8, wherein the member is supported by the strain element via a bearing.

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