Torque sensor

Abstract

One example of a challenge is further miniaturization of the torque sensor. [Solution] The torque sensor (100) comprises a holder (101) having an inner circumferential member (110) and an outer circumferential member (120), a bearing (102) disposed on the inner circumferential member (110), and a strain sensor (103). The outer circumferential member (120) has an elastic portion (122), and the strain sensor (103) is attached to the elastic portion (122). The elastic portion (122) and the strain sensor (103) each extend along a plane parallel to the axial direction.

Description

Technical Field

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

Background Art

[0002] As a torque sensor for detecting the force applied to a shaft, a magnetostrictive torque sensor is known. For example, Patent Document 1 discloses a strain detection device having a magnetic layer fixed on the outer peripheral surface of a shaft and a detection coil for detecting a change in the magnetic permeability of the magnetic layer.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When a magnetostrictive torque sensor is used, since it is necessary to arrange a detection coil or the like, the entire device around the shaft tends to be enlarged. The present invention takes miniaturization of the torque sensor as an example of the problem.

Means for Solving the Problems

[0005] The torque sensor of the present invention includes a holder having an inner peripheral member and an outer peripheral member, a bearing disposed on the inner peripheral member, and a strain sensor. The outer peripheral member has an elastic portion, the strain sensor is attached to the elastic portion, and the elastic portion and the strain sensor each extend along a plane parallel to the axial direction.

Brief Description of the Drawings

[0006] [Figure 1] It is a perspective view of a holder and a strain sensor of a torque sensor according to a first embodiment which is an example of the present invention. [Figure 2]This is a cross-sectional view of a torque sensor according to a first embodiment, which is an example of the present invention. [Figure 3] This is a cross-sectional view of a torque sensor according to a second embodiment, which is an example of the present invention. [Figure 4] This is a cross-sectional view of a torque sensor according to a third embodiment, which is an example of the present invention. [Figure 5] This is a cross-sectional view of a torque sensor according to a fourth embodiment, which is an example of the present invention. [Figure 6] This is a plan view of a torque sensor holder and a strain sensor according to a fifth embodiment, which is an example of the present invention. [Figure 7] This is a cross-sectional view of a torque sensor according to a fifth embodiment, which is an example of the present invention, and corresponds to the AA section in Figure 6. [Figure 8] This is a plan view of a torque sensor holder and a strain sensor according to a sixth embodiment, which is an example of the present invention. [Figure 9] This is a cross-sectional view of a torque sensor according to a sixth embodiment, which is an example of the present invention, and is a cross-sectional view corresponding to the BB cross-section in Figure 6. [Figure 10] This is a perspective view of a torque sensor holder and strain sensor according to a seventh embodiment, which is an example of the present invention. [Figure 11] This is a plan view of a torque sensor holder and strain sensor according to an eighth embodiment, which is an example of the present invention. [Modes for carrying out the invention]

[0007] In describing each embodiment of the present invention, for the sake of convenience, the direction of arrow a along the central axis (axis X) of the shaft S is referred to as the upper side or one side of the axial direction. The direction of arrow b along axis X is referred to as the lower side or the other side of the axial direction. Here, the direction of arrow ab is referred to as the up-down direction or the axial direction. However, the up-down direction does not necessarily coincide with the vertical direction. Furthermore, the direction of arrow cd is referred to as the radial direction, the direction of arrow c moving away from axis X is referred to as the outward side or one side of the radial direction, and the direction of arrow d moving towards axis X is referred to as the inward side or the other side of the radial direction. In addition, the direction along the tangent to the circle around axis X is referred to as the tangential direction.

[0008] [First Embodiment] Hereinafter, a first embodiment, which is an example of the present invention, will be described with reference to the drawings. Figure 1 is a perspective view of the holder 101 and strain sensor 103 used in the torque sensor 100 according to this embodiment. Figure 2 is a cross-sectional view showing the torque sensor 100 mounted on the shaft S and the external device 10.

[0009] The torque sensor 100 includes a holder 101, a bearing 102, and a strain sensor 103. In this embodiment, the bearing 102 is a ball bearing having an inner ring 102i, an outer ring 102o, and rolling elements. However, the bearing 102 is not limited to a ball bearing and may be any other type of bearing, such as a sleeve bearing.

[0010] As shown in Figure 1, the holder 101 has a cylindrical shape that is approximately square in plan view and has an inner circumferential member 110 and an outer circumferential member 120. The inner circumferential member 110 is a cylindrical member that extends in the axial direction and has a cylindrical inner circumferential surface 110a around the axis X. The outer circumferential member 120 is a member that is positioned radially outside the inner circumferential member 110 (on one radial side, in the direction of arrow c).

[0011] In the axial direction, the dimensions of the inner circumferential member 110 are the same as those of the outer circumferential member 120. In the axial direction, the upper end face (one side in the axial direction, in the direction of arrow a) and the lower end face (the other side in the axial direction, in the direction of arrow b) of the inner circumferential member 110 are coplanar with the upper end face and the lower end face of the outer circumferential member 120, respectively. Four roughly rectangular connecting portions 130 project radially outward from the inner circumferential member 110 at its radially outer and axially upper end. The four connecting portions 130 are positioned to be rotationally symmetric (hereinafter referred to as "four-fold symmetry"), overlapping when rotated 90° around axis X.

[0012] Each connection portion 130 is connected to a strain generating body 121 that is rectangular in plan view and approximately L-shaped in side view. The strain generating body 121 is a deformable part that deforms when subjected to stress, and undergoes elastic or plastic deformation when subjected to stress. The four strain generating bodies 121 constitute the outer peripheral member 120 in this embodiment. Therefore, the connection portion 130 connects the inner peripheral member 110 and the outer peripheral member 120. Since all four strain generating bodies 121 have the same configuration, only one strain generating body 121 will be described in detail from here on, and detailed descriptions of the other strain generating bodies 121 will be omitted.

[0013] As shown in Figure 2, in the radial direction, the strain generating body 121 (outer peripheral member 120) and the inner peripheral member 110 face each other via a gap 140 extending in the tangential direction. The gap 140 includes a through hole 141 that is circular or substantially circular in side view, and a slit 142 connected to the axially lower side of the through hole 141, with a width (radial width) narrower than the diameter of the through hole 141. Due to the presence of the through hole 141, the strain generating body 121 (outer peripheral member 120) has a recess 141a that is recessed radially outward on its radially inner surface (the other radial side, in the direction of arrow d), the connecting portion 130 has a recess 141b that is recessed axially upward on its axially lower surface, and the inner peripheral member 110 has a recess 141c that is recessed radially inward on its radially outer surface. Furthermore, recesses 141a, 141b, and 141c do not have defined boundaries, but are connected as a smoothly continuous curved surface.

[0014] The distortion generating body 121 (outer peripheral member 120) has an elastic portion 122. That is, a part of the distortion generating body 121 (outer peripheral member 120) functions as the elastic portion 122. Among the portions of the distortion generating body 121 that extend along a plane perpendicular to the radial direction, a region slightly above the axial center (the region where the concave portion 141a is formed) is the elastic portion 122. Note that the portion that extends along a plane perpendicular to the radial direction may be a portion that extends in the axial direction. In the radial direction, the elastic portion 122 and the inner peripheral member 110 face each other with a gap 140 therebetween. The elastic portion 122 has a concave portion 141a that is recessed outward in the radial direction on the surface facing the inner peripheral member 110. Due to the formation of the concave portion 141a, the elastic portion 122 has a thinner thickness (radial thickness) compared to other portions of the distortion generating body 121 (outer peripheral member 120), and elastic strain deformation is likely to occur.

[0015] Since each distortion generating body 121 of the torque sensor 100 has an elastic portion 122, the torque sensor 100 as a whole includes a plurality (four in this embodiment) of elastic portions 122. In the circumferential direction, the plurality of elastic portions 122 are arranged side by side at positions that are rotationally symmetric four times outside the holder 101 (radially outside the inner peripheral member 110) (FIG. 1).

[0016] In the radial direction, a strain sensor 103 is attached to the outer surface of the elastic portion 122. The elastic portion 122 and the strain sensor 103 each extend along a plane parallel to the axial direction (extend along a plane perpendicular to the radial direction). The strain sensor 103 is attached so as to be able to detect the strain in a direction along a plane perpendicular to the tangential direction of the elastic portion 122. Therefore, when the strain sensor 103 is a strain gauge, it is attached to the elastic portion 122 such that the direction of the grid (gauge) (typically, the longitudinal direction of the strain gauge) is along the axial direction. When the strain sensor 103 is a strain gauge, the strain of the elastic portion 122 is detected as a change in the resistance value. Note that the strain sensor 103 is not limited to a strain gauge and may be various other sensors such as a piezoelectric element.

[0017] In the radial direction, outside the elastic portion 122 of the strain generating body 121, a fixing portion 123 connected to the external device 10 is arranged. The fixing portion 123 is a rectangular plate-like portion extending radially outward from the lower end portion in the axial direction of the elastic portion 122. A circular through-hole 123h is formed near the central portion of the fixing portion 123. The strain generating body 121 is fixed to the external device 10 via the spacer 105 by a bolt 104 inserted through the through-hole 123h. Thereby, the holder 101 is fixed to the external device 10.

[0018] In the radial direction, the bearing 102 is arranged inside the inner peripheral member 110 of the holder 101. The bearing 102 is held by the inner peripheral member 110 of the holder 101. The inner ring 102i of the bearing 102 is adhered or press-fitted to the outer peripheral surface (the radially outer surface) of the cylindrical shaft S. Thereby, 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 to the inner peripheral surface 110a of the inner peripheral member 110 of the holder 101. The bearing 102 supports the shaft S so as to be rotatable with respect to the holder 101. The lower end portion in the axial direction of the shaft S protrudes outside the external device 10 from the through-hole 11 of the external device 10.

[0019] The holder 101 has an annular contact portion 111 protruding radially inward at the lower end portion in the axial direction. In the present embodiment, the contact portion 111 protrudes radially inward from the inner peripheral member 110 of the holder 101. In the axial direction, the contact portion 111 is in contact with the lower end surface of the outer ring 102o of the bearing 102. Thereby, the contact portion 111 supports the bearing 102 in a state of restricting downward movement in the axial direction.

[0020] When the torque sensor 100 is used in an electric assist bicycle, the shaft S is a crankshaft equipped with pedals. When one pedal is pressed, a force acts on the pedal side of the shaft S that causes it to tilt vertically downward, so the bearing 102 tries to move radially, and a part of the holder 101 is pressed radially outward. In the holder 101, stress tends to concentrate in the elastic portion 122 of the strain generating body 121, so elastic strain deformation occurs in the elastic portion 122. This strain deformation is detected by the strain sensor 103.

[0021] If multiple elastic sections 122 to which strain sensors 103 are attached are arranged, stress corresponding to the tilt of the shaft S in any direction can be detected. In particular, in the torque sensor 100 according to this embodiment, since the four strain bodies 121 are arranged in positions that are symmetrical four times around the axis X, stress in all directions on the shaft S can be detected more accurately. The output of the motor of the electric assist bicycle can be adjusted according to the detected stress.

[0022] The torque sensor 100 according to this embodiment does not use a magnetostrictive sensor, but has a simple configuration comprising a holder 101, a bearing 102, and a strain sensor 103. Since it does not require the placement of detection coils and the like around the shaft S that are necessary when using a magnetostrictive sensor, the device can be made smaller. In addition, since no processing such as attaching a magnetic layer to the shaft S is required, the manufacturing of the torque sensor 100 becomes easier.

[0023] In the torque sensor 100 according to this embodiment, the strain generating body 121 (outer peripheral member 120) and the inner peripheral member 110 face each other in the radial direction with a gap 140 between them. The elastic portion 122 has a recess 141a that is recessed in the radial direction on the surface facing the inner peripheral member 110, and the connecting portion 130 has a recess 141b that is recessed in the axial direction upward on the axially lower surface. As a result, in the torque sensor 100 according to this embodiment, the elastic portion 122 of the strain generating body 121 is easily deformed by strain, and stress can be detected with high sensitivity.

[0024] [Second Embodiment] Next, a second embodiment, which is an example of the present invention, will be described with reference to the drawings. Figure 3 is a cross-sectional view showing the torque sensor 200 according to this embodiment mounted on the shaft S and the external device 10. The torque sensor 200 has the same configuration as the torque sensor 100 according to the first embodiment, except that it is equipped with a holder 201 instead of a holder 101. The holder 201 has the same configuration as the holder 101 according to the first embodiment, except that it is equipped with an inner circumferential member 210 instead of an inner circumferential member 110 and has a gap 240 that is slightly different in shape from the gap 140. Hereinafter, members and components having the same function and configuration as those in the first embodiment will be denoted by the same reference numerals as in the first embodiment, and their detailed description will be omitted.

[0025] The holder 201 is cylindrical in shape, approximately square in plan view, and has an inner circumferential member 210 and an outer circumferential member 120. The inner circumferential member 210 is a cylindrical member extending in the axial direction, having a cylindrical inner circumferential surface 210a around the axis X. In the axial direction, the dimensions of the inner circumferential member 210 are the same as those of the outer circumferential member 120. In the axial direction, the upper and lower end faces of the inner circumferential member 210 are coplanar with the upper and lower end faces of the outer circumferential member 120, respectively. Four approximately rectangular connecting portions 130 project radially outward from the inner circumferential member 210 at its radially outer and axially upper end. The four connecting portions 130 are positioned in a four-fold symmetrical arrangement around the axis X.

[0026] As shown in Figure 3, in the radial direction, the strain-generating body 121 (outer peripheral member 120) faces the inner peripheral member 210 via a gap 240 extending in the tangential direction. The gap 240 includes a through hole 241 that is circular or substantially circular in side view, and a slit 242 that is connected to the axially lower side of the through hole 241, slightly radially inward, and has a width (radial dimension) narrower than the diameter of the through hole 241. In the radial direction, the dimension of the slit 242 is larger than the dimension of the slit 142 according to the first embodiment.

[0027] Due to the presence of the through hole 241, the strain-generating body 121 (outer peripheral member 120) has a recess 241a that is recessed radially outward on the radially inward surface (the other radial side, in the direction of arrow d), the connecting portion 130 has a recess 241b that is recessed axially upward on the axially lower surface, and the inner peripheral member 210 has a recess 241c that is recessed radially inward on the radially outer surface. The recesses 241a, 241b, and 241c do not have defined boundaries but are connected as a smoothly continuous curved surface. In the radial direction, the elastic portion 122 and the inner peripheral member 210 face each other with a gap 240 in between.

[0028] In the radial direction, the bearing 102 is positioned inside the inner circumferential member 210 of the holder 201. The bearing 102 is held by the inner circumferential member 210 of the holder 201. The outer ring 102o of the bearing 102 is press-fitted into the inner circumferential surface 210a of the inner circumferential member 210 of the holder 201. The bearing 102 rotatably supports the shaft S relative to the holder 201.

[0029] The holder 201 has an annular contact portion 211 that protrudes radially inward at its axially lower end. In this embodiment, the contact portion 211 protrudes radially inward from the inner circumferential member 210 of the holder 201. In the axial direction, the contact portion 211 is in contact with the lower end face of the outer ring 102o of the bearing 102. As a result, the contact portion 211 supports the bearing 102 in a state that restricts its downward movement in the axial direction.

[0030] In this embodiment, a semicircular or substantially semicircular recess 212 is formed near the axially lower end of the inner circumferential surface 210a of the inner circumferential member 210 when viewed from the side. The recess 212 is formed in an annular shape around the axis X above the contact portion 211. The axially lower end of the concave surface of the recess 212 smoothly connects to the axially upper end face of the contact portion 211.

[0031] The torque sensor 200 according to this embodiment has the same characteristics as the torque sensor 100 according to the first embodiment. Furthermore, in the torque sensor 200 according to this embodiment, a recess 212 is formed in addition to the gap 240, and the radial width of the slit 242 is wider than that of the slit 142 (Figure 2) according to the first embodiment. As a result, the thickness of the inner circumferential member 210 near the axially lower end is reduced, making the contact portion 211 more susceptible to elastic deformation toward the axially lower direction. This allows the contact portion 211 to absorb the effects of the preload even when a preload is applied to the bearing 102 toward the axially lower direction.

[0032] Therefore, in the torque sensor 200 according to this embodiment, the preload on the bearing 102 is suppressed from appearing as strain in the elastic portion 122, and the strain sensor 103 can detect stress with high sensitivity.

[0033] [Third Embodiment] Next, a third embodiment, which is an example of the present invention, will be described with reference to the drawings. Figure 4 is a cross-sectional view showing the torque sensor 300 according to this embodiment mounted on the shaft S and the external device 10. The torque sensor 300 has the same configuration as the torque sensor 100 according to the first embodiment, except that it is equipped with a holder 301 instead of a holder 101. Hereinafter, members and components having the same function and configuration as those in the first embodiment will be denoted by the same reference numerals as in the first embodiment, and their detailed descriptions will be omitted.

[0034] The holder 301 has a cylindrical shape that is approximately square in plan view and has an inner circumferential member 310 and an outer circumferential member 320. The inner circumferential member 310 is a cylindrical member that extends in the axial direction and has a cylindrical inner circumferential surface 310a around the axis X. The outer circumferential member 320 is a member that is positioned radially outward from the inner circumferential member 310.

[0035] In the axial direction, the dimensions of the inner circumferential member 310 are smaller than those of the outer circumferential member 320. In the axial direction, the upper end face of the inner circumferential member 310 and the upper end face of the outer circumferential member 320 lie on the same plane. Four substantially rectangular connecting portions 330 project radially outward from the inner circumferential member 310 at its radially outer and axially upper end. Similar to the torque sensor 100 according to the first embodiment, the four connecting portions 330 are arranged in positions that are four times symmetrical around axis X.

[0036] Each connection portion 330 is connected to a strain generating body 321 that is rectangular in plan view and approximately inverted T-shaped in side view. The strain generating body 321 is a deformable part that deforms when subjected to stress, and undergoes elastic or plastic deformation when subjected to stress. The four strain generating bodies 321 constitute the outer peripheral member 320 in this embodiment. Therefore, the connection portion 330 connects the inner peripheral member 310 and the outer peripheral member 320. Since all four strain generating bodies 321 have the same configuration, only one strain generating body 321 will be described in detail from here on, and detailed descriptions of the other strain generating bodies 321 will be omitted.

[0037] As shown in Figure 4, in the radial direction, the strain-generating body 321 (outer peripheral member 320) faces the inner peripheral member 310 via a gap 340 extending tangentially. The gap 340 includes a first through-hole 341 which is circular or substantially circular in side view, a second through-hole 342 connected to the axially lower side of the first through-hole 341 and having a diameter equal to or slightly smaller than that of the first through-hole 341, and a slit 343 extending radially inward from the axially lower end of the second through-hole 342 to the bearing 102.

[0038] Due to the presence of the first through hole 341, the strain-generating body 321 (outer peripheral member 320) has a recess 341a on its radially inner surface that is recessed radially outward, the connecting portion 330 has a recess 341b on its axially lower surface that is recessed axially upward, and the inner peripheral member 310 has a recess 341c on its radially outer surface that is recessed radially inward. The recesses 341a, 341b, and 341c do not have defined boundaries but are connected as a smoothly continuous curved surface.

[0039] The strain generating body 321 (outer peripheral member 320) has an elastic portion 322. Of the portion of the strain generating body 321 that extends along a plane perpendicular to the radial direction, the region slightly above the axial center (the region where the recess 341a is formed) is the elastic portion 322. In the radial direction, the elastic portion 322 and the inner peripheral member 310 face each other with a gap 340 in between. The elastic portion 322 has a recess 341a on the surface facing the inner peripheral member 310 that is recessed radially outward. Due to the formation of the recess 341a, the elastic portion 322 has a thinner wall thickness (radial thickness) compared to other parts of the strain generating body 321 (outer peripheral member 320), making it more susceptible to elastic strain deformation.

[0040] Similar to the torque sensor 100 according to the first embodiment, the torque sensor 300 has multiple (four in this embodiment) elastic portions 322, since each strain-generating body 321 has an elastic portion 322. In the circumferential direction, the multiple elastic portions 322 are arranged in a symmetrical manner four times on the outside of the holder 301 (radially outward from the inner circumferential member 310).

[0041] In the radial direction, a strain sensor 103 is attached to the outer surface of the elastic portion 322. The elastic portion 322 and the strain sensor 103 each extend along a plane parallel to the axial direction (or along a plane perpendicular to the radial direction). The strain sensor 103 is attached so as to detect strain in the elastic portion 322 in a direction along the plane perpendicular to the tangential direction. Therefore, if the strain sensor 103 is a strain gauge, it is attached to the elastic portion 322 such that the orientation of the grid (gauge) (typically the longitudinal direction of the strain gauge) is along the axial direction. If the strain sensor 103 is a strain gauge, the strain in the elastic portion 322 is detected as a change in resistance value. Note that the strain sensor 103 is not limited to a strain gauge, but may be any other type of sensor, such as a piezoelectric element.

[0042] In the radial direction, the bearing 102 is positioned inside the inner circumferential member 310 of the holder 301. The bearing 102 is held by the inner circumferential member 310 of the holder 301. The outer ring 102o of the bearing 102 is press-fitted into the inner circumferential surface 310a of the inner circumferential member 310 of the holder 301. The bearing 102 rotatably supports the shaft S relative to the holder 301.

[0043] The holder 301 has a plate-shaped contact portion 324 that protrudes radially inward at its axially lower end. In this embodiment, the contact portion 324 protrudes radially inward from the axially lower end of the strain-generating body 321 (outer peripheral member 320) of the holder 301. In the axial direction, the contact portion 324 faces the inner peripheral member 310 through the slit 343. The tangential dimensions of the contact portion 324 are the same as the tangential dimensions of the elastic portion 322 and the fixed portion 123. However, the contact portion 324 may be formed in an annular shape around the axis X. In the axial direction, the contact portion 324 is in contact with the lower end face of the outer ring 102o of the bearing 102. As a result, the contact portion 324 supports the bearing 102 in a state that restricts downward movement in the axial direction.

[0044] The torque sensor 300 according to this embodiment has the same characteristics as the torque sensor 100 according to the first embodiment. In addition, in the torque sensor 300 according to this embodiment, a plate-shaped contact portion 324 that protrudes radially inward from the outer peripheral member 320 of the holder 301 supports the bearing 102 in the axial direction. As a result, even when a preload is applied to the bearing 102 in the downward axial direction, the contact portion 324 elastically deforms, thereby absorbing the effect of the preload. Furthermore, since the contact portion 324 is not provided on the inner peripheral member, the effect of the preload is not transmitted to the elastic portion 322 via the connecting portion 330.

[0045] Therefore, in the torque sensor 300 according to this embodiment, the preload on the bearing 102 is further suppressed from appearing as strain in the elastic portion 322, and the strain sensor 103 can detect stress with higher sensitivity.

[0046] [Fourth Embodiment] Next, a fourth embodiment, which is an example of the present invention, will be described with reference to the drawings. Figure 5 is a cross-sectional view showing the torque sensor 400 according to this embodiment mounted on the shaft S and the external device 40. The torque sensor 400 has the same configuration as the torque sensor 100 according to the first embodiment, except that it has a holder 401 instead of a holder 101, and the external device 10 is replaced by an external device 40. The holder 401 has the same configuration as the holder 101 according to the first embodiment, except that it has an inner circumferential member 410 instead of an inner circumferential member 110, and the gap 140 is a gap 440 of a different shape. Hereinafter, members and components having the same function and configuration as those in the first embodiment will be denoted by the same reference numerals as in the first embodiment, and their detailed description will be omitted.

[0047] The holder 401 is cylindrical in shape, approximately square in plan view, and has an inner circumferential member 410 and an outer circumferential member 120. The inner circumferential member 410 is a cylindrical member extending in the axial direction, having a cylindrical inner circumferential surface 410a around the axis X. In the axial direction, the dimensions of the inner circumferential member 410 are smaller than the dimensions of the outer circumferential member 120. In the axial direction, the upper end face of the inner circumferential member 410 and the upper end face of the outer circumferential member 120 are on the same plane. Four approximately rectangular connecting portions 130 project radially outward from the inner circumferential member 410 at its radially outer and axially upper end. The four connecting portions 130 are positioned in a four-fold symmetrical arrangement around the axis X.

[0048] As shown in Figure 5, in the radial direction, the strain-generating body 121 (outer peripheral member 120) faces the inner peripheral member 410 via a gap 440 extending in the tangential direction. The gap 440 includes a through hole 441 that is circular or substantially circular in side view, and a slit 442 connected to the axially lower side of the through hole 441, with a width (radial dimension) narrower than the diameter of the through hole 441. The slit 442 widens radially inward in an arc shape in side view as it extends axially downward.

[0049] Due to the presence of the through hole 441, the strain-generating body 121 (outer peripheral member 120) has a recess 441a that is recessed radially outward on the radially inward surface (the other radial side, in the direction of arrow d), the connecting portion 130 has a recess 441b that is recessed axially upward on the axially lower surface, and the inner peripheral member 410 has a recess 441c that is recessed radially inward on the radially outer surface. The recesses 441a, 441b, and 441c do not have defined boundaries but are connected as a smoothly continuous curved surface. In the radial direction, the elastic portion 122 and the inner peripheral member 410 face each other with a gap 440 in between.

[0050] In the radial direction, the bearing 102 is positioned inside the inner circumferential member 410 of the holder 401. The bearing 102 is held by the inner circumferential member 410 of the holder 401. The outer ring 102o of the bearing 102 is press-fitted into the inner circumferential surface 410a of the inner circumferential member 410 of the holder 401. The bearing 102 rotatably supports the shaft S relative to the holder 401.

[0051] The external device 40 has a projection 42 that is formed in an annular shape around the axis X and projects axially upward toward the bearing 102. However, the projection 42 may be a plurality of convex portions arranged on the circumference around the axis X. In the axial direction, the projection 42 is in contact with the lower end face of the bearing 102. In this way, the projection 42 supports the bearing 102 in a manner that restricts downward movement in the axial direction. More specifically, in the axial direction, the projection 42 supports the bearing 102 by contacting the lower end face of the outer ring 102o.

[0052] The torque sensor 400 according to this embodiment has the same characteristics as the torque sensor 100 according to the first embodiment. In addition, in the torque sensor 400 according to this embodiment, since the protrusion 42 supports the bearing 102 in the axial direction, the axial preload on the bearing 102 does not appear as strain in the elastic portion 122, and the strain sensor 103 can detect stress with higher sensitivity.

[0053] [Fifth Embodiment] Next, a fifth embodiment, which is an example of the present invention, will be described with reference to the drawings. Figure 6 is a plan view of the holder 501 and strain sensor 503 of the torque sensor 500 according to this embodiment. Figure 7 is a cross-sectional view showing the cross-section corresponding to cross-section AA in Figure 6, with the torque sensor 500 mounted on the shaft S and the external device 50.

[0054] The torque sensor 500 includes a holder 501, a bearing 502, and a strain sensor 503. In this embodiment, the bearing 502 is a ball bearing having an inner ring 502i, an outer ring 502o, and rolling elements. Note that the bearing 502 is not limited to a ball bearing, and may be any other type of bearing, such as a sleeve bearing.

[0055] The holder 501 has a cylindrical shape that is approximately square in plan view and has an inner circumferential member 510 and an outer circumferential member 520. The inner circumferential member 510 is a cylindrical member that extends in the axial direction and has a cylindrical inner circumferential surface 510a around the axis X. The outer circumferential member 520 is a member that is positioned radially outward from the inner circumferential member 510.

[0056] In the axial direction, the dimensions of the inner circumferential member 510 are the same as those of the outer circumferential member 520. In the axial direction, the upper and lower end faces of the inner circumferential member 510 are coplanar with the upper and lower end faces of the outer circumferential member 520, respectively.

[0057] In the radial direction, two strain bodies 521 are connected to the outside of the inner circumferential member 510 so as to be mirror-symmetric with respect to a plane containing axis X. The strain bodies 521 are deformable parts that deform when subjected to stress, and undergo elastic or plastic deformation when subjected to stress. The strain bodies 521 are approximately rectangular parallelepipeds with the tangential direction as the longitudinal direction, and in the center of the longitudinal direction, they have an arc-shaped cutout that follows the outer shape of the inner circumferential member 510 to about half of the radial dimension. The two strain bodies 521 constitute the outer circumferential member 520 in this embodiment. Since the two strain bodies 521 have the same configuration, only one strain body 521 will be described in detail from here on, and a detailed description of the other strain body 521 will be omitted.

[0058] As shown in Figure 6, two through-holes 541, which are circular or substantially circular in plan view and penetrate axially, are formed near the midpoint between the longitudinal center and both ends of the strain-generating body 521. In addition, two slits 542 are formed in the strain-generating body 521, extending tangentially from near the connection point with the inner circumferential member 510 on the surface facing the inner circumferential member 510 to the through-holes 541. The width of the slits 542 is narrower than the diameter of the through-holes 541. The through-holes 541 and the slits 542 constitute a gap 540.

[0059] The strain generating body 521 (outer peripheral member 520) has an elastic portion 522. The elastic portion 522 is the region of the strain generating body 521 that extends along a plane perpendicular to the radial direction, near the through hole 541. In the radial direction, the elastic portion 522 and the inner peripheral member 510 face each other with a gap 540 in between. The elastic portion 522 has a radially recessed area (part of the through hole 541) on the surface facing the inner peripheral member 510. Due to the presence of the through hole 541, the elastic portion 522 is thinner than other parts of the strain generating body 521 (outer peripheral member 520), making it more susceptible to elastic strain deformation.

[0060] The torque sensor 500 has multiple (four in this embodiment) elastic portions 522, since each strain-generating body 521 has an elastic portion 522. In the circumferential direction, the multiple elastic portions 522 are arranged side by side on the outside of the holder 501 (radially outward from the inner circumferential member 510).

[0061] Two strain sensors 503 are mounted on the side of each strain body 521 opposite to the side connected to the inner circumferential member 510. The strain sensors 503 are mounted on the elastic portion 522 of the strain body 521. The elastic portion 522 and the strain sensors 503 extend along a plane that extends axially and longitudinally along the strain body 521. The strain sensors 503 are mounted so as to detect strain in the elastic portion 522 along a plane perpendicular to the axial direction. Therefore, if the strain sensor 503 is a strain gauge, it is mounted on the elastic portion 522 such that the orientation of the grid (gauge) (typically the longitudinal direction of the strain gauge) is aligned with the longitudinal direction of the strain body 521. If the strain sensor 503 is a strain gauge, the strain in the elastic portion 522 is detected as a change in resistance. Note that the strain sensor 503 is not limited to a strain gauge, but may be any other type of sensor, such as a piezoelectric element.

[0062] The longitudinal ends of the strain generating body 521, beyond the elastic portion 522, form fixed portions 523 that connect to the external device 50. Near the center of the fixed portion 523, a through hole 523h is formed, which penetrates axially and is circular in plan view. As shown in Figure 7, the strain generating body 521 is fixed to the external device 50 via a spacer 505 by a bolt 504 inserted through the through hole 523h from the axial upper side. In this way, the holder 501 is fixed to the external device 50.

[0063] In the radial direction, the bearing 502 is positioned inside the inner circumferential member 510 of the holder 501. The bearing 502 is held by the inner circumferential member 510 of the holder 501. The inner ring 502i of the bearing 502 is bonded or press-fitted to the outer circumferential surface (radially outer surface) of the cylindrical shaft S. In this way, the inner ring 502i of the bearing 502 is fixed to the shaft S. The outer ring 502o of the bearing 502 is press-fitted to the inner circumferential surface 510a of the inner circumferential member 510 of the holder 501. The bearing 502 rotatably supports the shaft S relative to the holder 501. The axially lower end of the shaft S protrudes to the outside of the external device 50 through the through hole 51 of the external device 50.

[0064] The holder 501 has an annular contact portion 511 that protrudes radially inward at its axial lower end. In this embodiment, the contact portion 511 protrudes radially inward from the inner circumferential member 510 of the holder 501. In the axial direction, the contact portion 511 is in contact with the lower end face of the outer ring 502o of the bearing 502. As a result, the contact portion 511 supports the bearing 502 in a state that restricts downward movement in the axial direction.

[0065] When the torque sensor 500 is used in an electric assist bicycle, the shaft S is a crankshaft equipped with pedals. When one pedal is pressed, a force acts on the pedal side of the shaft S that causes it to tilt vertically downward, so the bearing 502 tries to move radially, and a part of the holder 501 is pressed radially outward. In the holder 501, stress tends to concentrate in the elastic portion 522 of the strain generating body 521, so elastic strain deformation occurs in the elastic portion 522. This strain deformation is detected by the strain sensor 503.

[0066] In the torque sensor 500 according to this embodiment, since the four elastic parts 522 to which the strain sensor 503 is attached are arranged in a line on the outside of the holder 501 in the circumferential direction, stress in all directions can be detected more accurately. In particular, in the torque sensor 500, since the two strain bodies 521 are arranged so as to be mirror-symmetric with respect to a plane containing axis X, stress in the two directions in which the strain bodies 521 are arranged can be detected with higher sensitivity. The output of the motor of the electric assist bicycle can be adjusted according to the detected stress.

[0067] The torque sensor 500 according to this embodiment does not use a magnetostrictive sensor, but has a simple configuration comprising a holder 501, a bearing 502, and a strain sensor 503. Since it does not require the detection coil and other components that are necessary when using a magnetostrictive sensor to be arranged around the shaft S, the device can be made smaller. In particular, the torque sensor 500 has only two strain-generating elements, allowing for a compact configuration, which enables further miniaturization of the device. In addition, since processing such as attaching a magnetic layer to the shaft S is unnecessary, the manufacturing of the torque sensor 500 becomes easier.

[0068] In the torque sensor 500 according to this embodiment, the elastic portion 522 and the inner circumferential member 510 face each other in the radial direction with a gap 140 between them, and the elastic portion 522 has a radially recessed recess on the surface facing the inner circumferential member 510. As a result, in the torque sensor 500 according to this embodiment, the elastic portion 522 of the strain generating body 521 is easily deformed by strain, and stress can be detected with high sensitivity.

[0069] [Sixth Embodiment] Next, a sixth embodiment, which is an example of the present invention, will be described with reference to the drawings. Figure 8 is a plan view of the holder 601 and strain sensor 503 of the torque sensor 600 according to this embodiment. Figure 9 is a cross-sectional view showing the cross-section corresponding to the BB cross-section in Figure 8, with the torque sensor 600 mounted on the shaft S and the external device 60. The torque sensor 600 has the same configuration as the torque sensor 500 according to the fifth embodiment, except that it is equipped with a holder 601 instead of a holder 501. Hereinafter, members and components having the same function and configuration as those in the fifth embodiment will be denoted by the same reference numerals as in the fifth embodiment, and their detailed description will be omitted.

[0070] The torque sensor 600 comprises a holder 601, a bearing 502, and a strain sensor 503. The holder 601 is cylindrical in shape, approximately square in plan view, and has an inner circumferential member 610 and an outer circumferential member 620. The inner circumferential member 610 is a cylindrical member extending in the axial direction, having a cylindrical inner circumferential surface 610a around an axis X. The outer circumferential member 620 is a member positioned radially outside the inner circumferential member 610. The general configuration of the holder 601 is similar to that of the holder 501 of the torque sensor 500 according to the fifth embodiment, but differs in that the axial dimension of the inner circumferential member 610 is longer, and the inner circumferential member 610 and the outer circumferential member 620 are connected so as to be offset from each other in the axial direction.

[0071] As shown in Figure 9, in the axial direction, the dimensions of the inner circumferential member 610 are larger than those of the outer circumferential member 620. In the axial direction, the upper and lower end faces of the inner circumferential member 610 are positioned above the upper and lower end faces of the outer circumferential member 620, respectively. The axial upper end of the outer circumferential member 620 is connected near the axial lower end of the inner circumferential member 610.

[0072] The holder 601 has an annular contact portion 611 that protrudes radially inward slightly above its axial center. In the axial direction, the contact portion 611 is located above the axial upper end of the outer peripheral member 620. In this embodiment, the contact portion 611 protrudes radially inward from the inner peripheral member 610 of the holder 601. In the axial direction, the contact portion 611 is in contact with the lower end face of the outer ring 502o of the bearing 502. As a result, the contact portion 611 supports the bearing 502 in a state that restricts downward movement in the axial direction.

[0073] In the axial direction, the portion of the inner circumferential member 610 below the contact portion 611 penetrates the external device 60 and extends below the external device 60. In the axial direction, the outer circumferential member 620 is positioned below the external device 60 (outside the external device 60). A bolt 504 is inserted from the axial lower side through a through hole 523h formed in the fixing portion 523 of the strain generating body 521 of the outer circumferential member 620. The strain generating body 521 is screw-fixed to the external device 60 via a spacer 505.

[0074] The torque sensor 600 according to this embodiment has the same characteristics as the torque sensor 500 according to the fifth embodiment. In addition, in the torque sensor 600 according to this embodiment, the outer peripheral member 620 is located outside the external device 60, so the internal structure of the external device 60 is further simplified, and the device can be made even smaller.

[0075] [Seventh Embodiment] Next, a seventh embodiment, which is an example of the present invention, will be described with reference to the drawings. Figure 10 is a perspective view of the torque sensor holder 701 and strain sensor 703 according to this embodiment.

[0076] The torque sensor according to this embodiment includes a holder 701, a bearing (not shown), and a strain sensor 703. The holder 701 is flat and has an inner circumferential member 710 and an outer circumferential member 720. The inner circumferential member 710 is a plate-like member that is substantially square in plan view and has a cylindrical inner circumferential surface 710a around the axis X. The outer circumferential member 720 is a member that is positioned radially outward from the inner circumferential member 710.

[0077] Of the outer circumferential surfaces (radially outer surfaces) of the inner circumferential member 710, one strain-generating body 721 is connected to each of the two opposing surfaces with the axis X in between, at their respective centers. The strain-generating body 721 is a member that extends radially as its longitudinal direction, with its radially outer end being approximately semicircular in plan view. In the tangential direction, the dimensions of the strain-generating body 721 are smaller than the dimensions of the inner circumferential member 710. The two strain-generating bodies 721 constitute the outer circumferential member 720 in this embodiment. Since the two strain-generating bodies 721 have the same configuration, only one strain-generating body 721 will be described in detail from here on, and a detailed description of the other strain-generating body 721 will be omitted.

[0078] The strain-generating body 721 (outer peripheral member 720) has a through-hole (gap) 740 that penetrates axially near the connection point with the inner peripheral member 710. The through-hole 740 has a shape in which two circular or substantially circular holes in plan view, aligned tangentially, are connected by a rectangular hole in plan view.

[0079] The strain generating body 721 (outer peripheral member 720) has elastic portions 722. In the strain generating body 721, two portions facing each other tangentially via a through hole 740 constitute the elastic portions 722. Due to the formation of the through hole 740, the elastic portions 722 are thinner than other portions of the strain generating body 721 (outer peripheral member 720), making them more susceptible to elastic strain deformation.

[0080] The holder 701 has multiple (four in this embodiment) elastic portions 722, since each strain-generating body 721 has two elastic portions 722. In the circumferential direction, the multiple elastic portions 722 are arranged side by side on the outside of the holder 701 (radially outward from the inner circumferential member 710).

[0081] Two strain sensors 703 are attached to the outer circumferential surface of each strain-generating body 721. The strain sensors 703 are attached to the elastic portion 722. The elastic portion 722 and the strain sensors 703 extend in the axial direction and in the protruding direction (longitudinal direction) of the strain-generating body 721. The strain sensors 703 are attached so as to detect strain in the elastic portion 722 in a direction along a plane perpendicular to the axial direction. Therefore, if the strain sensor 703 is a strain gauge, it is attached to the elastic portion 722 such that the orientation of the grid (gauge) (typically the longitudinal direction of the strain gauge) is aligned with the protruding direction (longitudinal direction) of the strain-generating body 721. If the strain sensor 703 is a strain gauge, the strain in the elastic portion 722 is detected as a change in resistance. Note that the strain sensor 703 is not limited to a strain gauge, but may be any other type of sensor, such as a piezoelectric element.

[0082] In the radial direction, the portion of the strain-generating body 721 outside the elastic portion 722 is a fixed portion 723 connected to an external device (not shown). A circular through-hole 723h is formed near the center of the fixed portion 723. The holder 701 can be fixed to the external device by bolts or the like through the through-hole 723h.

[0083] In the radial direction, a bearing (not shown) is positioned inside the inner circumferential member 710 of the holder 701. The holder 701 has an annular contact portion 711 that protrudes radially inward at its axially lower end. In this embodiment, the contact portion 711 protrudes radially inward from the inner circumferential member 710 of the holder 701. In the axial direction, the contact portion 711 contacts the lower end face of the bearing. As a result, the contact portion 711 can support the bearing in the axial direction.

[0084] When a torque sensor equipped with a holder 701 is used in an electric assist bicycle, the shaft S is a crankshaft equipped with pedals. When one pedal is pressed, a force acts on the pedal side of the shaft S that causes it to tilt vertically downward, so the bearing tries to move radially, and a part of the holder 701 is pressed radially outward. In the holder 701, stress tends to concentrate in the elastic portion 722 of the strain generating body 721, so elastic strain deformation occurs in the elastic portion 722. This strain deformation is detected by the strain sensor 703.

[0085] The torque sensor according to this embodiment does not use a magnetostrictive sensor, but has a simple configuration comprising a holder 701, a bearing, and a strain sensor 703. Since it does not require the placement of detection coils and other components around the shaft that are necessary when using a magnetostrictive sensor, the device can be miniaturized. In addition, since processing such as attaching a magnetic layer to the shaft is unnecessary, the manufacturing of the torque sensor becomes easier. In particular, the torque sensor according to this embodiment has a flat holder 701 and is fixed to an external device with only two fixing parts 723, resulting in a simple structure and further miniaturization of the device.

[0086] [Eighth Embodiment] Next, an eighth embodiment, which is an example of the present invention, will be described with reference to the drawings. Figure 11 is a plan view of the torque sensor holder 801 and strain sensor 803 according to this embodiment.

[0087] The torque sensor according to this embodiment includes a holder 801, a bearing (not shown), and a strain sensor 803. The holder 801 is flat and has a roughly rhombic shape in plan view, and has an inner circumferential member 810 and an outer circumferential member 820. The inner circumferential member 810 is an annular member having a cylindrical inner circumferential surface 810a around an axis X. The outer circumferential member 820 is a member positioned radially outward from the inner circumferential member 810.

[0088] In the radial direction, two small annular fixing portions 823 are positioned slightly away from the inner circumferential member 810, at positions that are twice symmetrical about axis X, on the outside of the inner circumferential member 810. Near the four tangent lines that circumscribe the inner circumferential member 810 and the two fixing portions 823, four beam-shaped elastic portions 822 connect the inner circumferential member 810 and the two fixing portions 823. The two fixing portions 823 and the elastic portions 822 constitute the outer circumferential member 820 in this embodiment. In the circumferential direction, the four elastic portions 822 are arranged side by side on the outside of the holder 801 (radially outward from the inner circumferential member 810). A gap 840 is formed between the inner circumferential member 810 and the fixing portions 823. In the radial direction, the elastic portions 822 and the inner circumferential member 810 face each other with the gap 840 in between.

[0089] A strain sensor 803 is attached to the surface of each elastic portion 822 opposite to the surface facing the inner circumferential member 810. The elastic portion 822 and the strain sensor 803 each extend along a plane parallel to the axial direction. The strain sensor 803 is attached so as to detect strain in the elastic portion 822 in a direction along a plane perpendicular to the axial direction. Therefore, if the strain sensor 803 is a strain gauge, it is attached to the elastic portion 822 such that the orientation of the grid (gauge) (typically the longitudinal direction of the strain gauge) is aligned with the longitudinal direction of the elastic portion 822. If the strain sensor 803 is a strain gauge, the strain in the elastic portion 822 is detected as a change in resistance value. Note that the strain sensor 803 is not limited to a strain gauge, but may be any other type of sensor, such as a piezoelectric element.

[0090] The fixing portion 823 is the part that connects to an external device (not shown). In the radial direction, the fixing portion 823 is located outside the elastic portion 822. A circular through hole 823h is formed near the center of the fixing portion 823. The holder 801 can be fixed to the external device by bolts or the like through the through hole 823h.

[0091] In the radial direction, a bearing (not shown) is positioned inside the inner circumferential member 810 of the holder 801. The holder 801 has an annular contact portion 811 that protrudes radially inward at its axially lower end. In this embodiment, the contact portion 811 protrudes radially inward from the inner circumferential member 810 of the holder 801. In the axial direction, the contact portion 811 contacts the lower end face of the bearing. As a result, the contact portion 811 can support the bearing in the axial direction.

[0092] The torque sensor according to this embodiment has the same characteristics as the torque sensor according to the seventh embodiment. In addition, because the holder 801 of the torque sensor according to this embodiment is lightweight, the weight of the device can be reduced.

[0093] Although preferred embodiments of the torque sensor of the present invention have been described above, the torque sensor of the present invention is not limited to the configuration of the above embodiments. For example, although each torque sensor according to the above embodiments is used in electric assist bicycles, the torque sensor of the present invention is not limited to use in electric assist bicycles.

[0094] Furthermore, those skilled in the art can modify the torque sensor of the present invention as appropriate and change various combinations of its components in accordance with conventionally known knowledge. As long as such modifications still possess the configuration of the present invention, they are of course included within the scope of the present invention. [Explanation of Symbols]

[0095] 10, 40, 50, 60…External device, 42…Protrusion, 100, 200, 300, 400, 500, 600…Torque sensor, 101, 201, 301, 401, 501, 601, 701, 801…Holder, 102, 202, 302, 402, 502, 602, 702, 802…Bearing, 103, 203, 303, 403, 503, 603, 703, 803…Strain sensor, 110, 210, 310, 410, 510, 610, 710, 810... Inner circumferential members, 111, 211, 324, 511, 611, 711, 811... Contact parts, 120, 220, 320, 420, 520, 620, 720, 820... Outer circumferential members, 122, 222, 322, 422, 522, 622, 722, 822... Elastic parts, 123, 223, 323, 423, 523, 623, 723, 823... Fixing parts, 140, 240, 340, 440, 540, 640, 740, 840... Gaps.

Claims

1. A holder having an inner circumferential member, an outer circumferential member, and a connecting portion that protrudes radially from the end of the inner circumferential member in the axial direction, A ball bearing is positioned inside the inner circumference member, Equipped with a strain sensor, The connecting portion connects the inner circumferential member and the outer circumferential member, The outer peripheral member has an elastic portion, The strain sensor is attached to the elastic portion, A torque sensor in which the elastic portion and the strain sensor each extend along a plane parallel to the axial direction.

2. The system comprises a plurality of elastic parts, including the aforementioned elastic part, The torque sensor according to claim 1, wherein the plurality of elastic portions are arranged side by side on the outside of the holder in the circumferential direction.

3. The torque sensor according to claim 1, wherein in the radial direction, the elastic portion and the inner circumferential member of the holder face each other with a gap in between.

4. The torque sensor according to claim 3, wherein the elastic portion has a radially recessed recess on the surface facing the inner circumferential member.

5. The torque sensor according to claim 3, wherein the connection portion has a recess that is recessed in the axial direction.

6. The torque sensor according to claim 1, wherein the holder has a contact portion that contacts the bearing in the axial direction.

7. The torque sensor according to claim 6, wherein the contact portion protrudes from the inner circumferential member of the holder in the radial direction.

8. The torque sensor according to claim 6, wherein the contact portion protrudes radially from the outer peripheral member of the holder.

9. It has a fixed part that connects to an external device, The torque sensor according to claim 1, wherein the fixed portion is positioned outside the elastic portion in the radial direction.

10. The torque sensor according to claim 9, wherein the external device has a protruding portion that protrudes toward the bearing.

Images