Bidirectional torque limiter

Abstract

Provided is a novel bidirectional torque limiter which has a small number of parts and is easy to assemble, and in particular, a bidirectional torque limiter which is capable of changing the magnitude of rotational torque for starting rotation when rotational torque is applied from one of two connected members and the magnitude of rotational torque for starting rotation when rotational torque is applied from the other member. An inner coil spring (76) and an outer coil spring (82) are respectively mounted on the inner peripheral surface and the outer peripheral surface of a shared ring member (10).

Description

Bidirectional Torque Limiter

[0001] The present invention relates to a bidirectional torque limiter, and in particular to a bidirectional torque limiter that can change the magnitude of the rotational torque at which rotation begins when rotational torque is applied from one of two connected members, and the magnitude of the rotational torque at which rotation begins when rotational torque is applied from the other member.

[0002] One example of the bidirectional torque limiter described above is the bidirectional torque limiter disclosed in Patent Document 1 (hereinafter, this bidirectional torque limiter may be referred to as a "precedent bidirectional torque limiter"). The precedent bidirectional torque limiter includes a fixed housing, a one-side member, an other-side member, an outer ring, and an inner ring, all of which share a common central axis within the housing. The one-side member is formed with a one-side locking piece extending in the axial direction, and the other-side member is formed with a other-side locking piece extending in the axial direction, respectively. The one-side locking piece and the other-side locking piece are combined and arranged so that two gaps are present in the circumferential direction. An outer coil spring is attached to the outer peripheral surface of the outer ring. In a free state, the inner diameter of the outer coil spring is smaller than the outer diameter of the outer ring, and the outer coil spring is held in close contact with the outer ring with a relatively small force. If the torque generated by the outer coil spring being in close contact with the outer ring is referred to as the outer holding torque, this outer holding torque is relatively small. The outer coil spring has two outer hook portions at different angular positions in the circumferential direction, and each of the two outer hook portions is inserted into one of the two gaps. An inner coil spring is attached to the outer peripheral surface of the inner ring. In a free state, the inner diameter of the inner coil spring is smaller than the outer diameter of the inner ring, and the inner coil spring is held in close contact with the inner ring with a relatively large force. If the torque generated by the inner coil spring being in close contact with the inner ring is referred to as the inner holding torque, this inner holding torque is relatively large. The inner coil spring has two inner hook portions at different angular positions in the circumferential direction, and each of the two inner hook portions is inserted into a hook groove formed in the inner peripheral surface of the outer ring.

[0003] When a rotational torque is applied to the one-side member, the one-side locking piece pushes one of the two outer hook portions in the direction that expands the diameter of the outer coil spring. Because the outer coil spring is attached to the outer peripheral surface of the outer ring, the outer ring attempts to rotate together with the outer coil spring, pushing one of the two inner hook portions of the inner coil spring in the direction that expands the diameter of the inner coil spring. At this time, because the outer holding torque is smaller than the inner holding torque, if the rotational torque applied to the one-side member is greater than the outer holding torque, the outer coil spring slips relative to the outer ring before the inner coil spring slips relative to the inner ring. In other words, the outer coil spring starts to rotate relative to the outer ring before the inner coil spring starts to rotate relative to the inner ring, i.e., while the outer ring is held by the inner coil spring. Then, after the outer hook portion pushed by the one-side locking piece abuts against the other-side locking piece, the one-side locking piece pushes the other-side locking piece via the outer hook portion, and the one-side member, the outer coil spring, and the other-side member rotate together. In other words, the rotation applied to one member is transmitted to the other member. Note that if the rotational torque applied to one member is smaller than the outer holding torque, the one member will not rotate and will be held by the outer holding torque.

[0004] On the other hand, when a rotational torque is applied to the other-side member, the other-side locking piece pushes one of the two outer hook portions in a direction that causes the outer coil spring to contract. This strengthens the tight contact between the outer coil spring and the outer ring, causing the outer ring to rotate integrally with the outer coil spring. Because the outer coil spring is attached to the outer peripheral surface of the outer ring, the outer ring attempts to rotate together with the outer coil spring, pushing one of the two inner hook portions of the inner coil spring in a direction that causes the inner coil spring to expand in diameter. Therefore, if the rotational torque applied to the other-side member is greater than the inner holding torque, the inner coil spring will slip relative to the inner ring. In other words, the inner coil spring will begin to rotate relative to the inner ring, and the other-side member, the outer coil spring, the outer ring, and the inner coil spring will rotate integrally relative to the inner ring. Then, after the outer hook portion pressed by the other-side locking piece abuts against the one-side locking piece, the other-side locking piece pushes the one-side locking piece via the outer hook portion, and the other-side member, outer coil spring, and one-side member (and further the outer ring and inner coil spring) rotate together. In other words, the rotation applied to the other-side member is transmitted to the one-side member. Note that if the rotational torque applied to the other-side member is smaller than the inner holding torque, the other-side member does not rotate and is held by the inner holding torque.

[0005] In other words, in a leading bidirectional torque limiter, the magnitude of the rotational torque at which slippage, i.e., rotation, begins is different when the rotational torque is transmitted from one side member to the other side member and when the rotational torque is transmitted from the other side member to the one side member, and is set smaller in the former case than in the latter case.

[0006] Patent No. 6967687

[0007] Therefore, the bidirectional torque limiter disclosed in Patent Document 1 has a large number of parts, and there is room for improvement in terms of the assembly process, weight, and cost. Also, the inner hook portion of the inner coil spring attached to the outer peripheral surface of the inner ring must be aligned when inserted into the hook groove formed in the inner peripheral surface of the outer ring, making the assembly process complicated.

[0008] The present invention has been made in view of the above facts, and its main technical object is to review the structure of the preceding bidirectional torque limiter and provide a new bidirectional torque limiter that has fewer parts and is easier to assemble than the preceding bidirectional torque limiter.

[0009] According to the present invention, a bidirectional torque limiter that solves the above-mentioned main technical problem comprises a fixed housing, a one-side member, an other-side member, and a cylindrical ring member that have a common central axis within the housing, wherein the one-side member is formed with a one-side locking piece extending in the axial direction, and the other-side member is formed with a other-side locking piece extending in the axial direction, and the one-side locking piece and the other-side locking piece are combined and arranged so that two gaps are present in the circumferential direction, an inner coil spring is attached to the inner peripheral surface of the ring member, the outer diameter of the inner coil spring in a free state is larger than the inner diameter of the ring member, and the inner coil spring is brought into close contact with the ring member with a relatively small force, and the inner coil spring has two inner hook portions at different angular positions in the circumferential direction, and each of the two inner hook portions is inserted into one of the two gaps, an outer coil spring is attached to the outer peripheral surface of the ring member, the inner diameter of the outer coil spring in a free state is smaller than the outer diameter of the ring member, the outer coil spring is brought into close contact with the ring member with a relatively large force, the outer coil spring has two outer hook portions at different angular positions in the circumferential direction, and each of the two outer hook portions is inserted into a recess formed in the inner peripheral surface of the housing, when a rotational torque is applied to the one-side member, one of the two inner hook portions is pushed by the one-side locking piece in a direction in which the inner coil spring expands in diameter, and one of the two outer hook portions is pushed by the housing in the recess in a direction in which the outer coil spring expands in diameter, the one-side member rotates integrally with the inner coil spring and the ring member against the relatively large braking torque of the outer coil spring and transmits the rotation to the other-side member,When a rotational torque is applied to the other-side member, one of the two inner hook portions is pushed by the other-side locking piece in the direction in which the inner coil spring contracts in diameter, and one of the two outer hook portions is pushed by the housing in the recess in the direction in which the outer coil spring expands in diameter, and with the ring member held by the outer coil spring, the other-side member rotates together with the inner coil spring relative to the ring member against the relatively small braking torque applied by the inner coil spring, transmitting the rotation to the one-side member, thereby providing a bidirectional torque limiter.

[0010] Preferably, the cross sections of the one-side locking piece and the other-side locking piece are both arc-shaped extending around the central axis. In this case, a notch is formed at each of the circumferential ends of both axial end portions of the one-side locking piece, and the circumferential end face of the one-side locking piece is divided into a notched end face where the notch is formed and a non-notched end face where the notch is not formed, and when the one-side member rotates, the notched end face presses one of the two inner hook portions and the non-notched end face presses the circumferential end face of the other-side locking piece, so that one of the two inner hook portions pressed by the notched end face moves away from the circumferential end face of the other-side locking piece, while when the other-side member rotates, the circumferential end face of the other-side locking piece presses the non-notched end face of the one-side member together with one of the two inner hook portions, so that one of the two inner hook portions pressed by the other-side locking piece moves away from the notched end face of the one-side locking piece. The housing preferably has an annular groove into which both axial ends of the ring member are loosely fitted. Preferably, the one-side member, the other-side member, the ring member, the inner coil spring, and the outer coil spring are made of metal, while the housing is made of synthetic resin.

[0011] The above-mentioned main technical problem is to provide a rotary knives comprising a fixed member, a one-side member and an other-side member having a common central axis, and a cylindrical ring member, wherein the one-side member is formed with a one-side locking piece extending in the axial direction, and the other-side member is formed with a other-side locking piece extending in the axial direction, and the one-side locking piece and the other-side locking piece are combined and arranged so that two gaps are present in the circumferential direction, an outer coil spring is attached to the outer peripheral surface of the ring member, the inner diameter of the outer coil spring in a free state is smaller than the outer diameter of the ring member, and the outer coil spring is brought into close contact with the ring member with a relatively small force, the outer coil spring has two outer hook portions at different angular positions in the circumferential direction, and each of the two outer hook portions is inserted into one of the two gaps, an inner coil spring is attached to the inner peripheral surface of the ring member, the outer diameter of the inner coil spring in a free state is larger than the inner diameter of the ring member, the inner coil spring is brought into close contact with the ring member with a relatively large force, the inner coil spring has two inner hook portions at different angular positions in the circumferential direction, and each of the two inner hook portions can be engaged with an engaging means provided on the fixing member, when a rotational torque is applied to the one-side member, one of the two outer hook portions is pushed by the one-side engaging piece in a direction in which the outer coil spring contracts in diameter, and one of the two inner hook portions is pushed by the engaging means in a direction in which the inner coil spring contracts in diameter, the one-side member rotates integrally with the outer coil spring and the ring member against the relatively large braking torque applied by the inner coil spring and transmits the rotation to the other-side member, This problem can also be solved by a bidirectional torque limiter in which, when a rotational torque is applied to the other-side member, one of the two outer hook portions is pushed by the other-side locking piece in the direction in which the outer coil spring expands in diameter, and one of the two inner hook portions is pushed by the locking means in the direction in which the inner coil spring contracts in diameter, and with the ring member held by the inner coil spring, the other-side member rotates together with the outer coil spring relative to the ring member against a relatively small braking torque applied by the outer coil spring, transmitting the rotation to the one-side member.

[0012] In the bidirectional torque limiter of the present invention, the inner coil spring and the outer coil spring are respectively attached to the inner and outer peripheral surfaces of a common ring member. In contrast, in the leading bidirectional torque limiter, the inner coil spring is attached to the outer peripheral surface of the inner ring and the outer coil spring is attached to the outer peripheral surface of the outer ring, i.e., the inner coil spring and the outer coil spring are respectively attached to the outer peripheral surfaces of two different ring members. The ring member in the bidirectional torque limiter of the present invention combines the inner ring and outer ring of the leading bidirectional torque limiter, thereby enabling the bidirectional torque limiter of the present invention to reduce the number of parts by one compared to the leading bidirectional torque limiter. Furthermore, in the bidirectional torque limiter of the present invention, alignment between the outer coil spring and the inner coil spring and the ring member is not required, thereby simplifying the assembly process. In the leading bidirectional torque limiter, the inner coil spring and the outer ring must be aligned separately.

[0013] As a preliminary note, there is a bidirectional torque limiter in which an inner coil spring and an outer coil spring are respectively attached to the inner and outer peripheral surfaces of a common ring member, such as the bidirectional torque limiter disclosed in Japanese Patent Laid-Open Publication No. 2002-155973, which was filed by the applicant of the present application prior to the present application and has already been published (hereinafter referred to as the "reference bidirectional torque limiter"). However, this reference bidirectional torque limiter changes the magnitude of the rotational torque at which rotation begins in forward and reverse rotation, and is completely different in nature from the bidirectional torque limiter of the present invention and the preceding bidirectional torque limiter disclosed in Patent Document 1.

[0014] 1 is a diagram showing the structure of a bidirectional torque limiter configured according to the present invention. A diagram showing the bidirectional torque limiter shown in FIG. 1 disassembled and arranged into its component parts. A diagram showing the internal structure of the bidirectional torque limiter shown in FIG. 1 with the shield removed. A diagram showing the housing of the bidirectional torque limiter shown in FIG. 1 alone. A diagram showing one side member of the bidirectional torque limiter shown in FIG. 1 alone. A diagram showing the other side member of the bidirectional torque limiter shown in FIG. 1 alone. A diagram showing a state in which rotational torque is applied to one side member in the bidirectional torque limiter shown in FIG. 1. A diagram showing a state in which rotational torque is applied to the other side member in the bidirectional torque limiter shown in FIG. 1. A diagram showing a modified example of a bidirectional torque limiter configured according to the present invention.

[0015] Hereinafter, a more detailed description will be given with reference to the accompanying drawings showing a preferred embodiment of a bidirectional torque limiter constructed according to the present invention.

[0016] Explaining with reference to FIGS. 1 to 3, the bidirectional torque limiter generally designated by the numeral 2 comprises a fixed housing 4, and a one-side member 6, an other-side member 8, and a ring member 10, which have a common central axis o within the housing 4.

[0017] Referring to FIG. 4 along with FIGS. 1 to 3, the housing 4 includes a housing main body 12 shown in FIG. 4(a) and a shield 14 shown in FIG. 4(b). In the illustrated embodiment, the housing main body 12 and the shield 14 are integrally formed from an appropriate synthetic resin. The housing main body 12 includes a circular end plate 16 disposed perpendicular to the axial direction and a cylindrical outer wall 18 extending axially from the outer periphery of the end plate 16. A bulge 20 with a circular cross section is formed in the center of the end plate 16 and bulges axially to the other side. A circular recess 22 is formed in the center of one axial side of the bulge 20, and a circular hole 24 is formed in the center of the circular bottom surface of the recess 22 and penetrates axially. A circular residual rib 26 is present on one axial side of the end plate 16, surrounding the outer periphery of the recess 22. A circular depression 28 is formed on the inside of the residual rib 26, and a circular groove 30 is formed on the outside of the residual rib 26. Six arc-shaped protrusions 32 projecting axially are arranged at equal angular intervals around the outer peripheral edge of the other axial side of the end plate 16. The housing 4 is fixed to a wall or the like (not shown) via the protrusions 32. The inner peripheral surface of the outer peripheral wall 18 is formed with a plurality of arc-shaped recesses 34 (six in the illustrated embodiment) spaced apart around the periphery by locally increasing the inner diameter. The recesses 34 extend in the axial direction. The circumferential lengths of the recesses 34 are not necessarily the same and may be varied as appropriate. A circumferentially extending step 36 is formed at the axially extending end of the inner peripheral surface of the outer peripheral wall 18 in a circumferential angular region where no recesses 34 are formed. The axially extending end surface of the outer peripheral wall 18 is formed with a plurality of arc-shaped extension pieces 38 (six in the illustrated embodiment) spaced apart around the periphery, continuing axially toward one axial side and further extending axially. In the illustrated embodiment, the extension piece 38 substantially corresponds to the circumferential angular region in which the recessed portion 34 is formed. A locking rib 40 extending in the circumferential direction is formed at the axially extending end portion of the inner peripheral surface of the extension piece 38.

[0018] The shield 14 includes a disk-shaped support wall 42 disposed perpendicular to the axial direction and a cylindrical mounting wall 44 extending axially from the outer periphery of the support wall 42. A circular hole 46 is formed in the center of the support wall 42, penetrating the axial direction. An outer rib 48 and an inner rib 50 are formed on the outer periphery of the other axial side of the support wall 42, surrounding the outer periphery of the hole 46. A ring-shaped groove 51 is formed between the outer rib 48 and the inner rib 50. The outer diameter of the mounting wall 44 is larger than that of the support wall 42. The outer periphery of the mounting wall 44 is formed with arc-shaped protrusions 52, which are formed by locally increasing the outer diameter. A plurality of protrusions 52 are formed, corresponding to the number of extension pieces 38 formed on the housing body 12 (i.e., six in the illustrated embodiment), and the protrusions 52 are arranged at equal angular intervals in the circumferential direction. The circumferential distance between two circumferentially adjacent protrusions 52 corresponds to the circumferential length of the extension piece 38. A circumferentially extending locking protrusion 54 is formed on the outer peripheral surface of the mounting wall 44 between two circumferentially adjacent protrusions 52. When attaching the shield 14 to the housing body 12, the extension piece 38 of the housing body 12 is aligned between the two circumferentially adjacent protrusions 52, and then the shield 14 is forced axially toward the end plate 16 of the housing body 12, causing the locking protrusion 54 to resiliently overcome the locking protrusion 40 of the extension piece 38. When the shield 14 is attached to the housing body 12, the outer peripheral edge of the support wall 42 of the shield 14 abuts against the step 36 of the housing body 12, and the protrusion 52 of the shield 14 abuts against the axial end face of the outer peripheral wall 18 of the housing body 12 (excluding the extension piece 38).

[0019] The description will be continued with reference to FIG. 5 along with FIGS. 1 to 3. In the illustrated embodiment, the one-side member 6 is made of metal and integrally formed by powder metallurgy. The one-side member 6 includes a cylindrical one-side connecting portion 56 that connects to either a driving-side or driven-side external device (such external device is not shown), and a one-side locking piece 58 attached to the outer circumferential surface of the one-side connecting portion 56. The one-side connecting portion 56 penetrates in the axial direction, and serration-like internal connecting teeth 60 are formed on the inner circumferential surface. As shown in the A-A cross-sectional view of FIG. 1, one axial end of the one-side connecting portion 56 is fitted into a recess 22 formed in the end plate 16 of the housing main body 12 and rotatably supported. The one-side locking piece 58 extends from an axially intermediate portion of the outer circumferential surface of the one-side connecting portion 56 beyond the other axial end of the one-side connecting portion 56 to the other axial side. The cross section of the one-side locking piece 58 is arc-shaped extending around the central axis o. Notches 62 and 64 are formed at the circumferential ends of both axial ends of the one-side locking piece 58, respectively, and the circumferential end face of the one-side locking piece 58 is divided into a notched end face 65a where the notch 62 or 64 is formed and a non-notched end face 65b where the notch 62 or 64 is not formed. In the illustrated embodiment, the notch 62 is formed only at the downstream end in the clockwise direction in the left drawing of Fig. 5, and the notch 64 is formed only at the downstream end in the clockwise direction in the right drawing of Fig. 5. Therefore, when viewed from one axial direction, the notches 62 and 64 are located on opposite sides in the circumferential direction.

[0020] The description will be continued with reference to FIG. 6 in addition to FIGS. 1 to 3. In the illustrated embodiment, the other-side member 8 is also made of metal and integrally formed by powder metallurgy. The other-side member 8 includes a cylindrical other-side connection portion 66 connected to either the driving side or the driven side of an external device (such external device is not shown), a disk-shaped intermediate portion 68 connected to one axial end of the other-side connection portion 66, and an other-side locking piece 70 attached to the outer circumferential surface of the intermediate portion 68. The other-side connection portion 66 and the intermediate portion 68 extend axially in common. Serration-like external connection teeth 72 are formed on the outer circumferential surface of the other-side connection portion 66. As shown in the A-A cross-sectional view of FIG. 1, the intermediate portion 68 is positioned in a hole 46 formed in the support wall 42 of the shield 14 to axially support the one-side connection portion 56 of the one-side member 6. The other-side locking piece 70 extends from an axially intermediate portion of the outer circumferential surface of the intermediate portion 68 beyond one axial end of the intermediate portion 68 to one axial direction. The cross section of the other-side locking piece 70 is in the shape of a circular arc extending around the central axis o. Although not necessarily clearly shown, the other axial end face of the other-side locking piece 70 faces the support wall 42 of the shield 14, thereby preventing the one-side member 6 and the other-side member 8 from moving axially and falling off the housing 4. Here, as can be understood by referring to Figure 3, the one-side locking piece 58 and the other-side locking piece 70 are arranged in combination so that two gaps 74a and 74b are present in the circumferential direction.

[0021] The description will continue with reference to Figures 1 to 3. In the illustrated embodiment, the ring member 10 is made of metal and is a cylindrical rigid body with a required axial width and radial thickness (plate thickness). As shown in the A-A cross-sectional view of Figure 1, one axial end of the ring member 10 is fitted (loosely fitted) into an annular groove 30 formed in the end plate 16 of the housing main body 12, and the other axial end is fitted (loosely fitted) into an annular groove 51 formed in the support wall 42 of the shield 14, so that the ring member 10 is supported from both axial sides by the housing 4.

[0022] An inner coil spring 76 is attached to the inner peripheral surface of the ring member 10. In FIG. 3, the inner coil spring 76 is lightly shaded for ease of understanding (the same applies to FIGS. 7 and 8, which will be described later). In the illustrated embodiment, the inner coil spring 76 is made of a metal wire rod having a rectangular cross section. The inner coil spring 76 includes an inner winding portion 78 formed by spirally winding the wire rod, and two inner hook portions 80a and 80b formed by bending the wire rod radially inward at both axial ends of the inner winding portion 78. In a free state, the outer diameter of the inner coil spring 76, i.e., the outer diameter of the inner winding portion 78, is larger than the inner diameter of the ring member 10, and the inner coil spring 76 is held in close contact with the ring member 10 with a relatively small force. When the inner coil spring 76 is attached to the ring member 10 and no force is acting on either of the two inner hook portions 80a and 80b, the torque generated by the inner coil spring 76 tightly contacting the ring member 10 is referred to as the inner holding torque, and this inner holding torque is relatively small. The two inner hook portions 80a and 80b are disposed at different angular positions in the circumferential direction, and as shown in FIG. 3, each of the two inner hook portions 80a and 80b is inserted into each of the two gaps 74a and 74b described above. A lubricant is applied to the inner coil spring 76.

[0023] An outer coil spring 82 is also attached to the outer peripheral surface of the ring member 10. In FIG. 3, the outer coil spring 82 is also lightly shaded for ease of understanding (the same applies to FIGS. 7 and 8, which will be described later). In the illustrated embodiment, the outer coil spring 82 is positioned in axial alignment with the inner coil spring 76. The outer coil spring 82 is also formed from a metal wire rod having a rectangular cross section. The outer coil spring 82 includes an outer winding portion 84 formed by spirally winding the wire rod, and two outer hook portions 86a and 86b formed by bending the wire rod radially outward at both axial ends of the outer winding portion 84. The winding direction of the wire rod as viewed from one axial direction is the same for the inner coil spring 76 and the outer coil spring 82. In a free state, the inner diameter of the outer coil spring 82, i.e., the inner diameter of the outer wound portion 84, is smaller than the outer diameter of the ring member 10, and the outer coil spring 82 is held in close contact with the ring member 10 by a relatively large force. When the outer coil spring 82 is attached to the ring member 10 and no force is acting on either of the two outer hook portions 86a and 86b, the torque generated by the outer coil spring 82 in close contact with the ring member 10 is referred to as the outer holding torque, and this outer holding torque is relatively large. The two outer hook portions 86a and 86b are disposed at different angular positions in the circumferential direction, and as shown in FIG. 3, each of the two outer hook portions 86a and 86b is inserted into two of the multiple recesses 34 formed in the inner circumferential surface of the outer wall 18 of the housing main body 12. A lubricant is also applied to the outer coil spring 82.

[0024] Next, the operation of the bidirectional torque limiter 2 will be described. First, a case where rotational torque is applied to the one-side member 6 in the clockwise direction (as viewed from the right of the A-A cross-sectional view in FIG. 1; the same applies below) from one of the external devices (not shown) will be described with reference to FIG. 1, FIG. 3, and FIG. 7. In this case, the one-side locking piece 58 rotates clockwise, and its circumferential end face (more specifically, the circumferential end face on the downstream side in the clockwise direction) pushes the inner hook portion 80a of the inner coil spring 76 in the clockwise direction. In the illustrated embodiment, the notched end face 65a pushes the inner hook portion 80a. Because the outer coil spring 82 is also mounted on the outer peripheral surface of the ring member 10 to which the inner coil spring 76 is mounted, when the inner hook portion 80a is pushed clockwise and the ring member 10 attempts to rotate clockwise together with the inner coil spring 76, the outer hook portion 86a is pushed counterclockwise by the housing 4 at the recess 34. Here, when the inner hook portion 80a is pressed clockwise, the inner coil spring 76, i.e., the inner wound portion 78, is expanded in diameter, and the tight contact between the outer peripheral surface of the inner wound portion 78 and the inner peripheral surface of the ring member 10 is strengthened. Therefore, the ring member 10 tends to rotate clockwise together with the inner coil spring 76. On the other hand, when the outer hook portion 86a is pressed counterclockwise, the outer coil spring 82, i.e., the outer wound portion 84, is expanded in diameter, and the tight contact between the inner peripheral surface of the outer wound portion 84 and the outer peripheral surface of the ring member 10 is weakened. For this reason, when the rotational torque applied to the one-side member 6 is greater than the relatively large outer holding torque, the ring member 10 slips relative to the outer coil spring 82. In other words, with the outer coil spring 82 held in the housing 4, the ring member 10 begins to rotate relative to the outer coil spring 82, and the one-side member 6, the inner coil spring 76, and the ring member 10 begin to rotate clockwise together. Then, after the non-notched end surface 65b of the one-side locking piece 58 comes into contact with the circumferential end surface of the other-side locking piece 70 (more specifically, the circumferential end surface on the upstream side in the clockwise direction), the one-side member 6, the inner coil spring 76, and the ring member 10 rotate clockwise together with the other-side member 8, as shown in Figure 7. In other words, the clockwise rotation applied to the one-side member 6 is transmitted to the other-side member 8. At this time, the inner hook portion 80a moves away from the circumferential end surface of the other-side locking piece 70.When the rotational torque applied to the one-side member 6 is smaller than the relatively large outer holding torque, the one-side member 6 does not rotate and is held by the outer holding torque.

[0025] When the one-side member 6 rotates counterclockwise, the operation is the same as when the one-side member 6 rotates clockwise, except that the one-side locking piece 58 presses the inner hook portion 80b of the inner coil spring 76 and the housing 4 presses the outer hook portion 86b of the outer coil spring 82, and therefore a detailed description thereof will be omitted. Note that in this case as well, both the inner hook portion 80b and the outer hook portion 86b are pressed in directions that expand the diameter of each coil spring. The magnitude of the rotational torque that causes the ring member 10 to begin rotating relative to the outer coil spring 82 is the same as when the one-side member 6 rotates clockwise.

[0026] Next, a case where a rotational torque is applied to the other-side member 8 in the counterclockwise direction from the other external device (not shown) will be described with reference to FIGS. 1, 3, and 8. In this case, the other-side locking piece 70 rotates counterclockwise, and its circumferential end face (more specifically, the circumferential end face downstream in the counterclockwise direction) pushes the inner hook portion 80a of the inner coil spring 76 counterclockwise. Because the outer coil spring 82 is also mounted on the outer peripheral surface of the ring member 10 to which the inner coil spring 76 is mounted, when the inner hook portion 80a is pushed counterclockwise and the ring member 10 attempts to rotate counterclockwise together with the inner coil spring 76, the outer hook portion 86b is pushed clockwise by the housing 4 at the recess 34. When the inner hook portion 80a is pushed counterclockwise, the inner coil spring 76, i.e., the inner wound portion 78, is reduced in diameter, and the tight contact between the outer peripheral surface of the inner wound portion 78 and the inner peripheral surface of the ring member 10 is weakened. Furthermore, when the outer hook portion 86b is pressed clockwise, the outer coil spring 82, i.e., the outer wound portion 84, is expanded in diameter, and the tight contact between the inner peripheral surface of the outer wound portion 84 and the outer peripheral surface of the ring member 10 is weakened. For this reason, when the rotational torque applied to the one-side member 6 is greater than the relatively small inner holding torque, the inner coil spring 76 slips relative to the ring member 10. In other words, with the ring member 10 held by the outer coil spring 82, the inner coil spring 76 begins to rotate relative to the ring member, and the other-side member 8 and the inner coil spring 76 begin to rotate counterclockwise as a unit. 8 , the circumferential end face of the other-side locking piece 70 (more specifically, the circumferential end face on the downstream side in the counterclockwise direction) together with the inner hook portion 80a abuts against the non-notched end face 65b of the one-side member 6 (the non-notched end face 65b is located on the upstream side in the counterclockwise direction) and pushes them counterclockwise, causing the other-side member 8 and the inner coil spring 76 to rotate counterclockwise together with the one-side member 6. In other words, the counterclockwise rotation applied to the other-side member 8 is transmitted to the one-side member 6. At this time, the inner hook portion 80a moves away from the notched end face 65a of the one-side locking piece 58. Note that if the rotational torque applied to the other-side member 8 is smaller than the relatively small inner holding torque, the other-side member 8 will not rotate and will be held by the inner holding torque.

[0027] When the other-side member 8 rotates clockwise, the other-side locking piece 70 presses the inner hook portion 80b of the inner coil spring 76 and the housing 4 presses the outer hook portion 86a of the outer coil spring 82, and the other-side rotation is the same as when the other-side member 8 rotates counterclockwise, so detailed description will be omitted. In this case as well, the inner hook portion 80b is pressed in the direction that causes the inner coil spring 76 to contract, and the outer hook portion 86a is pressed in the direction that causes the outer coil spring 82 to expand. The magnitude of the rotational torque that causes the inner coil spring 76 to start rotating relative to the ring member 10 is the same as when the other-side member 8 rotates counterclockwise.

[0028] In other words, in the bidirectional torque limiter 2, the magnitude of the rotational torque at which slippage begins, i.e., rotation begins, differs when the rotational torque is transmitted from one member 6 to the other member 8 and when the rotational torque is transmitted from the other member 8 to one member 6, and is set to be greater for the former than the latter. For this reason, if, for example, a hatchback, which is a driven external device, is connected to the one-side connecting portion 56 of the one-side member 6, and an electric motor, which is a driving external device, is connected to the other-side connecting portion 66 of the other member 8, the electric motor can open and close the hatchback with a relatively light load, while when the hatchback is fully open or in an intermediate angle position, the angular position of the hatchback is maintained with a relatively light load due to external disturbances such as wind, without flapping. Therefore, the bidirectional torque limiter according to the present invention can also be used as an angular position maintaining device.

[0029] Among bidirectional torque limiters having such properties, in the bidirectional torque limiter of the present invention, the inner coil spring 76 and the outer coil spring 82 are respectively attached to the inner and outer peripheral surfaces of the common ring member 10, which reduces the number of parts by one compared to, for example, a leading bidirectional torque limiter in which the inner coil spring and the outer coil spring are respectively attached to the outer peripheral surfaces of two different ring members (inner ring and outer ring). Furthermore, in the bidirectional torque limiter of the present invention, alignment between the outer coil spring and the ring member is not required, which simplifies the assembly process. In the case of a leading bidirectional torque limiter, the inner coil spring and the outer ring must be aligned separately.

[0030] Furthermore, in the illustrated embodiment, the one-side member 6, the other-side member 8, the ring member 10, the inner coil spring 76, and the outer coil spring 82 are made of metal, but the housing 4 is made of synthetic resin. Therefore, when the one-side locking piece 58 and the other-side locking piece 70 abut against the inner hook portion 80 a or 80 b of the inner coil spring 76, a sound is generated due to a collision between metals. However, when the outer hook portion 86 a or 86 b of the outer coil spring 82 abuts against the housing 4, almost no sound is generated due to a collision between metal and synthetic resin. If the housing 4 were made of metal, the sound generated when the outer hook portion 86 a or 86 b collided with the housing 4 would be added, making the sound generated during operation excessively loud. While it is possible to make the one-side member and the other-side member out of synthetic resin, these members are required to have relatively high strength because they are connected to external members, and therefore are preferably formed of metal, particularly powder metallurgy.

[0031] Furthermore, in the illustrated embodiment, when the one-side member 6 rotates, the notched end face 65a presses one of the two inner hook portions 80a and 80b, and the non-notched end face 65b presses the circumferential end face of the other-side locking piece 8, so that either of the two inner hook portions 80a and 80b pressed by the notched end face 65a moves away from the circumferential end face of the other-side locking piece 70, while when the other-side member 8 rotates, the circumferential end face of the other-side locking piece 70 presses either of the two inner hook portions 80a and 80b against the non-notched end face 65b of the one-side member 6, so that either of the two inner hook portions 80a and 80b pressed by the other-side locking piece 70 moves away from the notched end face 65a of the one-side locking piece 58. In other words, even when rotational torque is applied from either the one-side member 6 or the other-side member 8, the inner hook portions 80a and 80b are not pinched between the circumferential end faces of the one-side locking piece 58 and the other-side locking piece 70, and the inner hook portions 80a and 80b are not positioned on the path of transmission of the rotational torque from the one-side member 6 to the other-side member 8 or vice versa. Therefore, when the rotational torque is applied, force is prevented from concentrating on the inner hook portions 80a and 80b, and damage to the inner hook portions 80a and 80b is prevented.

[0032] The bidirectional torque limiter constructed according to the present invention has been described above in detail with reference to the accompanying drawings. However, the present invention is not limited to the above-described embodiment, and appropriate modifications and variations are possible without departing from the spirit and scope of the present invention. For example, in the above-described embodiment, the two inner hook portions 80a and 80b of the inner coil spring 76 are inserted into the two gaps 74a and 74b formed when the one-side locking piece 58 and the other-side locking piece 70 are combined. However, instead, the two outer hook portions of the outer coil spring may be inserted into the two inner hook portions. Such a variation will be described with reference to FIG. 9 . FIG. 9 corresponds to FIG. 3 . In FIG. 9 , the same components as those in FIG. 3 are indicated by the same reference numerals with an '' symbol, and detailed description thereof will be omitted. In this variation, the outer coil spring 82' is brought into close contact with the ring member 10' with a smaller force than the inner coil spring 76'. A locking means 88' having an arc-shaped cross section and extending linearly in the axial direction is formed in the center of the housing 4' serving as the fixed member (therefore, the locking means 88' is fixed), and the inner coil spring 76' is disposed along the outer circumferential surface of the locking means 88'. When a rotational torque is applied to either the one-side member 6' or the other-side member 8' and the inner coil spring 76' attempts to rotate together with the ring member 10', one of the two inner hook portions 80a' and 80b' is pressed by the locking means 88', more specifically, its circumferential end face, in a direction that reduces the diameter of the inner coil spring 76'. Therefore, when a rotational torque is applied to the one-side member 6', one of the two outer hook portions 86a' and 86b' is pushed by the one-side locking piece 58' in the direction in which the outer coil spring 82' contracts in diameter, and one of the two inner hook portions 80a' and 80b' is pushed by the locking means 88' in the direction in which the inner coil spring 76' contracts in diameter, and the one-side member 6' rotates integrally with the outer coil spring 82' and the ring member 10' against the relatively large braking torque of the inner coil spring 76' and transmits the rotation to the other-side member 8'.On the other hand, when a rotational torque is applied to the other-side member 8', one of the two outer hook portions 86a' and 86b' is pushed by the other-side locking piece 70' in the direction expanding the diameter of the outer coil spring 82', and one of the two inner hook portions 80a' and 80b' is pushed by the locking means 88' in the direction contracting the diameter of the inner coil spring 76'. With the ring member 10' held by the inner coil spring 76', the other-side member 8' rotates together with the outer coil spring 82' relative to the ring member 10' against the relatively small braking torque of the outer coil spring 82' and transmits the rotation to the one-side member 6'. In this modified example, the locking means 88' does not necessarily have to be disposed on the housing 4' as long as it is fixed, and therefore the housing 4' may be omitted. If the housing 4' is omitted, the locking means 88' may itself become a fixed member or be provided as part of a separate fixed member (not shown).

[0033] In addition, in the illustrated embodiment, the cross sections of the one-side locking piece and the other-side locking piece are both arc-shaped extending around the central axis and are each composed of a single member, but the one-side locking piece and the other-side locking piece may each be composed of two separate columnar members spaced apart in the circumferential direction. Depending on the intended use, all of the constituent members may be made of synthetic resin or metal. Furthermore, the cross sections of the wire material that constitutes the inner coil spring and the outer coil spring may also be circular rather than rectangular.

[0034] 2: Bidirectional torque limiter 4: Housing 6: One-side member 8: Other-side member 10: Ring member 34: Recess (of housing) 58: One-side locking piece 70: Other-side locking piece 74a and 74b: Gaps 76: Inner coil spring 80a and 80b: Inner hook portions 82: Outer coil spring 86a and 86b: Outer hook portions

Claims

1. A rotor comprising a fixed housing, a one-side member, an other-side member, and a cylindrical ring member, each of which has a common central axis within the housing; a one-side locking piece extending in the axial direction is formed on the one-side member, and a other-side locking piece extending in the axial direction is formed on the other-side member, the one-side locking piece and the other-side locking piece being combined and arranged so that there are two gaps in the circumferential direction; an inner coil spring is attached to the inner peripheral surface of the ring member, the outer diameter of the inner coil spring in a free state is larger than the inner diameter of the ring member, the inner coil spring is brought into close contact with the ring member with a relatively small force, and the inner coil spring has two inner hook portions at different angular positions in the circumferential direction, and each of the two inner hook portions is inserted into each of the two gaps; an outer coil spring is attached to the outer peripheral surface of the ring member, an inner diameter of the outer coil spring in a free state is smaller than an outer diameter of the ring member, the outer coil spring is brought into close contact with the ring member with a relatively large force, the outer coil spring has two outer hook portions at different angular positions in the circumferential direction, and each of the two outer hook portions is inserted into a recess formed in the inner peripheral surface of the housing, when a rotational torque is applied to the one-side member, one of the two inner hook portions is pushed by the one-side locking piece in a direction in which the inner coil spring expands in diameter, and one of the two outer hook portions is pushed by the housing in the recess in a direction in which the outer coil spring expands in diameter, the one-side member rotates integrally with the inner coil spring and the ring member against the relatively large braking torque applied by the outer coil spring to transmit the rotation to the other-side member, When a rotational torque is applied to the other-side member, one of the two inner hook portions is pushed by the other-side locking piece in the direction in which the inner coil spring contracts, and one of the two outer hook portions is pushed by the housing at the recess in the direction in which the outer coil spring expands, and with the ring member held by the outer coil spring, the other-side member rotates together with the inner coil spring relative to the ring member against the relatively small braking torque applied by the inner coil spring, transmitting the rotation to the one-side member.

2. The bidirectional torque limiter according to claim 1, wherein the cross sections of said one-side engaging piece and said other-side engaging piece are both arc-shaped extending around said central axis.

3. A bidirectional torque limiter as set forth in claim 2, wherein a notch is formed at each of the circumferential ends of both axial end portions of said one-side locking piece, and the circumferential end face of said one-side locking piece is partitioned into a notched end face in which said notch is formed and a non-notched end face in which said notch is not formed, and when said one-side member rotates, said notched end face presses one of said two inner hook portions and said non-notched end face presses the circumferential end face of said other-side locking piece, so that one of said two inner hook portions pressed by said notched end face moves away from the circumferential end face of said other-side locking piece, while when said other-side member rotates, the circumferential end face of said other-side locking piece presses one of said two inner hook portions against the non-notched end face of said one-side member, and so that one of said two inner hook portions pressed by said other-side locking piece moves away from the notched end face of said one-side locking piece.

4. A bidirectional torque limiter as set forth in claim 1, wherein said housing is provided with an annular groove into which both axial ends of said ring member are loosely fitted.

5. The bidirectional torque limiter according to claim 1, wherein said one-side member, said other-side member, said ring member, said inner coil spring and said outer coil spring are made of metal, but said housing is made of synthetic resin.

6. A device comprising a fixed member, a one-side member and an other-side member having a common central axis, and a cylindrical ring member, wherein the one-side member is formed with a one-side locking piece extending in the axial direction, and the other-side member is formed with an other-side locking piece extending in the axial direction, the one-side locking piece and the other-side locking piece are combined and arranged so that there are two gaps in the circumferential direction, an outer coil spring is attached to the outer circumferential surface of the ring member, the inner diameter of the outer coil spring in a free state is smaller than the outer diameter of the ring member, the outer coil spring is brought into close contact with the ring member with a relatively small force, the outer coil spring has two outer hook portions at different angular positions in the circumferential direction, and each of the two outer hook portions is inserted into each of the two gaps, an inner coil spring is attached to the inner peripheral surface of the ring member, an outer diameter of the inner coil spring in a free state is larger than an inner diameter of the ring member, the inner coil spring is brought into close contact with the ring member with a relatively large force, the inner coil spring has two inner hook portions at different angular positions in the circumferential direction, and each of the two inner hook portions can be engaged with an engaging means provided on the fixed member, when a rotational torque is applied to the one-side member, one of the two outer hook portions is pushed by the one-side engaging piece in a direction in which the outer coil spring contracts in diameter, and one of the two inner hook portions is pushed by the engaging means in a direction in which the inner coil spring contracts in diameter, the one-side member rotates integrally with the outer coil spring and the ring member against the relatively large braking torque applied by the inner coil spring to transmit the rotation to the other-side member, When a rotational torque is applied to the other-side member, one of the two outer hook portions is pushed by the other-side locking piece in the direction in which the outer coil spring expands in diameter, and one of the two inner hook portions is pushed by the locking means in the direction in which the inner coil spring contracts in diameter, and with the ring member held by the inner coil spring, the other-side member rotates together with the outer coil spring relative to the ring member against the relatively small braking torque applied by the outer coil spring, transmitting the rotation to the one-side member.

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