Reverse input cutoff clutch and torque limiter using same

Abstract

Provided is a new reverse input cutoff clutch with which a rolling element (10) is prevented from being excessively wedged between a cam surface (42) and the inner circumferential surface of an outer ring (4) when another side member (8) begins to rotate. Further provided is a torque limiter using said reverse input cutoff clutch. The cross-sectional shape of a circumferential end part (46) of the cam surface (42) is configured to extend linearly toward the radial outside while being inclined in the circumferential direction.

Description

Reverse input cutoff clutch and torque limiter using the same

[0001] The present invention relates to a reverse input cutoff clutch that utilizes the engagement of rolling elements, and a torque limiter that uses the same.

[0002] Reverse input cutoff clutches that utilize the engagement of rolling elements have been widely used in the past. One example is the reverse input cutoff clutch shown in Patent Document 1 below. This reverse input cutoff clutch includes a cylindrical outer ring and one-side and other-side members that are rotatable within the outer ring around a common rotation axis. The outer ring has an inner peripheral surface with a circular cross section, and a one-side engagement piece attached to the one-side member and a other-side engagement piece attached to the other-side member are combined and disposed inside the outer ring. The other-side engagement piece is formed with a concave cam surface that faces the inner peripheral surface of the outer ring, and rolling elements are disposed between the cam surface and the inner peripheral surface of the outer ring. The cross-sectional shapes of two ends located on both circumferential sides of the cam surface both extend radially outward in a convex arc shape. When the one-side member rotates relative to the outer ring, the one-side engagement piece, together with the other-side engagement piece, pushes the rolling elements to rotate the other-side member, but even if the other-side member tries to rotate relative to the outer ring, the rolling elements are unable to rotate because they become caught between the inner peripheral surface of the outer ring and the circumferential end of the cam surface. Therefore, if an operation to transmit rotation from the one-side member to the other-side member is an input and an operation to transmit rotation from the other-side member to the one-side member is a reverse input, the input is transmitted but the reverse input is blocked.

[0003] Furthermore, by accommodating the outer ring together with the one-side member and the other-side member in a fixed housing and disposing a braking torque applying means between the outer ring and the housing for applying a braking torque to the outer ring when the outer ring rotates relative to the housing, the reverse input cutoff clutch can be used as a torque limiter in which rotation from the one-side member to the other-side member is transmitted with no load or a light load, while rotation from the other-side member to the one-side member is transmitted against the braking torque. An example of this is shown in Patent Document 2 listed below.

[0004] Such a torque limiter is used, for example, as an angular position maintaining device in the opening / closing mechanism of a passenger vehicle hatchback. In this case, by connecting an electric motor, which is the driving member, to one member and the hatchback, which is the driven member, to the other member, the electric motor can swing the hatchback open or closed with no or light load, while when the hatchback is fully open or in an intermediate angle position, the angular position of the hatchback is maintained by the braking torque described above without using any other braking mechanism such as an electromagnetic brake. This allows the angular position maintaining device to be configured compactly.

[0005] JP 2013-174320 A International Publication No. 2015 / 137231 A

[0006] In the reverse input cutoff clutch disclosed in Patent Document 1, the cross-sectional shape of the circumferential end of the cam surface of the other-side engagement piece extends radially outward in a convex arc shape. Therefore, at this end, the ratio (slope) of change in the distance between the cam surface and the inner peripheral surface of the outer ring relative to the travel distance (displacement) on the cam surface is small. As a result, when the other-side member attempts to rotate, the rolling elements tend to become deeply engaged (i.e., further outward in the circumferential direction) between the cam surface and the inner peripheral surface of the outer ring. Therefore, if a large rotational torque is applied to the other-side member, the engagement becomes excessive, potentially locking the other-side member, or becoming completely immobile. In this case, even if the one-side engagement piece pushes the rolling elements, they cannot move, and therefore cannot push the other-side engagement piece. Therefore, the other-side member cannot rotate, and the reverse input cutoff clutch fails to function. In other words, the clutch malfunctions. Although Patent Document 2 does not clearly state the cross-sectional shape of the cam surface, as far as the drawings are concerned, the cross-sectional shape of the circumferential end of the cam surface extends in a convex arc shape in the circumferential direction toward the radially outward direction, and this presents the same risks as those described above that the reverse input cut-off clutch shown in Patent Document 1 has.

[0007] The present invention has been made in view of the above circumstances, and its first technical object is to provide a new and improved reverse input cutoff clutch that prevents the rolling elements from excessively meshing between the cam surface and the inner peripheral surface of the outer ring when the other-side member attempts to rotate. The second technical object of the present invention is to provide a torque limiter that uses the above reverse input cutoff clutch.

[0008] After careful consideration, the inventors discovered that the first technical problem can be solved by configuring the cross-sectional shape of the circumferential end of the cam surface to extend linearly and inclined circumferentially outward in the radial direction.

[0009] That is, according to the present invention, there is provided a reverse input cutoff clutch that solves the first technical problem described above, comprising a cylindrical outer ring, and one-side and other-side members that are rotatable within the outer ring around a common rotation axis, wherein the outer ring has an inner peripheral surface that is circular in cross section, and a one-side engagement piece attached to the one-side member and an other-side engagement piece attached to the other-side member are arranged in combination on the inside of the outer ring, a cam surface that faces the inner peripheral surface of the outer ring is formed on the other-side engagement piece, and rolling elements are arranged between the cam surface and the inner peripheral surface of the outer ring, and when the one-side member rotates relative to the outer ring, the one-side engagement piece pushes the rolling elements together with the other-side engagement piece to rotate the other-side member, but even if the other-side member tries to rotate relative to the outer ring, the rolling elements are unable to rotate because they are caught between the inner peripheral surface of the outer ring and the end of the cam surface in the circumferential direction. In this reverse input cutoff clutch, The reverse input disconnecting clutch is characterized in that the cross-sectional shape of the end of the cam surface extends linearly and inclined circumferentially radially outward.

[0010] Preferably, the cam surface is concave, and the cross-sectional shapes of the two ends located on both sides of the cam surface in the circumferential direction both extend linearly and inclined radially outward in the circumferential direction. In this case, the interior angle between the two lines along the two ends located on both sides of the circumferential direction is preferably 165 to 175 degrees.

[0011] Furthermore, according to the present invention, there is provided a torque limiter that solves the second technical problem, in which the outer ring is housed in a fixed housing together with the one-side member and the other-side member, and braking torque applying means is disposed between the outer ring and the housing for applying a braking torque to the outer ring when the outer ring rotates relative to the housing, and rotation from the one-side member to the other-side member is transmitted with no load or a light load, while rotation from the other-side member to the one-side member is transmitted against the braking torque.

[0012] Preferably, the braking torque applying means is a coil spring attached to the outer peripheral surface of the outer ring, the coil spring comprising a spirally wound wire portion and two hook portions formed by bending the wire outward in the radial direction at both axial ends of the winding portion. When the coil spring is in a free state, the inner diameter of the winding portion is smaller than the outer diameter of the cylindrical outer ring. Each of the two hook portions is positioned at a different circumferential position and is inserted into a hook groove formed in the inner peripheral surface of the housing, preventing the coil spring from rotating relative to the housing. When the outer ring attempts to rotate relative to the housing, one of the two hook portions is relatively pressed by the hook groove in a direction that expands the diameter of the winding portion. Preferably, an auxiliary braking torque applying means for applying a braking torque to the rolling element is disposed within the housing. In this case, the braking torque applying means is preferably a wave washer that axially biases the rolling element.

[0013] In the reverse input cutoff clutch of the present invention, the cross-sectional shape of the circumferential end of the cam surface extends linearly and inclined radially outward, so that the ratio of the change in the distance between the cam surface and the inner circumferential surface of the outer ring to the circumferential movement distance (displacement) on the cam surface at the end is sufficiently large. This prevents the rolling elements from becoming too deeply engaged between the cam surface and the inner circumferential surface of the outer ring when the other member attempts to rotate, thereby preventing the other member from being locked.

[0014] It should be noted in advance that the above-mentioned Patent Documents 1 and 2 disclose that the cross-sectional shape of the circumferential end of the cam surface is a convex arc or a convex arc shape, i.e., a curve, but do not consider making it a straight line. The reverse input cutoff clutch of the present invention achieves the above-mentioned special effects because the cross-sectional shape of the circumferential end of the cam surface is a straight line as described above.

[0015] 1 is a diagram showing the structure of a torque limiter using a reverse input cut-off clutch configured according to the present invention. A diagram showing the torque limiter shown in FIG. 1 disassembled and arranged for each component. A diagram showing the internal structure of the torque limiter shown in FIG. 1 with the shield removed. A diagram showing one side member of the torque limiter shown in FIG. 1 alone. A diagram showing the other side member of the torque limiter shown in FIG. 1 alone. A diagram showing the housing of the torque limiter shown in FIG. 1 alone. A diagram showing a state in which rotational torque is applied to one side member in the torque limiter shown in FIG. 1. A diagram showing a state in which rotational torque is applied to the other side member in the torque limiter shown in FIG. 1.

[0016] A reverse input cutoff clutch constructed according to the present invention and a torque limiter using the same will be described in further detail below with reference to the accompanying drawings. In the following description, the terms "one axial side" and "other axial side" refer to the right side and the left side in the state shown in the cross section A-A in Figure 1, unless otherwise specified.

[0017] 1 to 3 show preferred embodiments of a reverse input cutoff clutch constructed according to the present invention and a torque limiter using the same. The reverse input cutoff clutch is indicated by the number 1, and the torque limiter is indicated by the number 2. The reverse input cutoff clutch 1 comprises a cylindrical outer ring 4, one side member 6, the other side member 8, and rolling elements 10. The torque limiter 2 further comprises a housing 12 and braking torque applying means 14.

[0018] The reverse input cutoff clutch 1 will be described first. Referring to Figures 1 to 3 and also to Figure 4, the metal one-side member 6 includes a one-side main portion 16 extending in the axial direction and a one-side engagement piece 18 attached to the one-side main portion 16. The one-side main portion 16 has a circular cross-sectional shape, and is divided axially from one side to the other into a small-diameter portion 20, a medium-diameter portion 22, and a large-diameter portion 24. The small-diameter portion 20, the medium-diameter portion 22, and the large-diameter portion 24 share a common central axis, and a through-hole 26 having a circular cross-section is formed axially through the one-side main portion 16 along the central axis. The small-diameter portion 20 has a longer axial length than the medium-diameter portion 22 and the large-diameter portion 24. A one-side connecting portion 28 is formed on the outer peripheral surface of the small-diameter portion 20, and the one-side member 6 is connected to either a driving-side or driven-side external device (not shown) via the one-side connecting portion 28. In the illustrated embodiment, the one-side connecting portion 28 is a male serration consisting of multiple axially linearly extending protrusions spaced apart in the circumferential direction. A circular recess 29 is formed in the center of the other axial end face of the large-diameter portion 24, leaving an annular protrusion 30 remaining on the outer peripheral edge. Five one-side engaging pieces 18 are arranged at equal angular intervals in the circumferential direction. The cross-sectional shape of each one-side engaging piece 18 is a generally T-shape with a fan-shaped cross section formed by cutting out the radially inner ends of both circumferential ends into a generally rectangular shape. Each circumferential end face of the one-side engaging piece 18 is divided into an outer pressing portion 32 located radially outward and protruding outward, and an inner pressing portion 34 located radially inward and recessed inward. One end of each one-side engaging piece 18 is connected to the other axial end face of the annular protrusion 30 and the other axial end of the outer peripheral surface of the large-diameter portion 24, and extends axially beyond the other axial end face of the one-side main portion 16. Therefore, when viewed in the axial direction, the inner peripheral edge of the one-side engaging piece 18 is located at the radially middle portion of the annular ridge 30 , and the outer peripheral edge is located radially outward of the outer peripheral edge of the large diameter portion 24 .

[0019] 1 to 3 and also with reference to FIG. 5, the metal other-side member 8 includes a cylindrical other-side main portion 36 penetrating in the axial direction and an other-side engagement piece 38 attached to the outer peripheral surface of the other-side main portion 36. An other-side connection portion 40 is formed on the inner peripheral surface of the other-side main portion 36, and the other-side member 8 is connected to either a driving side or a driven side external device (not shown) via the other-side connection portion 40. In the illustrated embodiment, the other-side connection portion 40 is a female serration consisting of multiple circumferentially spaced protrusions extending linearly in the axial direction. The other-side engagement pieces 38 correspond to the number of one-side engagement pieces 18 formed on the one-side member 6, i.e., five in the illustrated embodiment. The five other-side engagement pieces 38 are arranged at equal angular intervals in the circumferential direction. The other-side engagement pieces 38 extend axially from one axial end of the other-side main portion 36 to an axial intermediate portion. The cross-sectional shape of the other-side engagement piece 38 (as viewed in the axial direction) includes a cam surface 42 facing radially outward and a circumferentially pressed surface 44 that extends linearly radially inward from both circumferential ends of the cam surface 42 and connects to the outer circumferential surface of the other-side main portion 36. Here, in the reverse input disconnect clutch of the present invention, it is important that the cross-sectional shape of the end 46 of the cam surface 42 extends linearly and inclined circumferentially toward the radially outward direction. In the illustrated embodiment, the cross-sectional shape of the cam surface 42 extends linearly on both circumferential sides from a valley line 48 that extends linearly parallel to the central axis, and is line-symmetrical with respect to a line L0 that passes through the valley line 48 and the central axis. In other words, the cam surface 42 is concave, and the cross-sectional shapes of the two end portions 46 located on both circumferential sides of the cam surface 42 both extend linearly and inclined radially outward. When the inner diameter of the outer ring 4 is 16.2 mm and the outer diameter of the rolling element 10 is 2.0 mm, it is preferable that the interior angle θ of the two straight lines L1 and L2 along the ends 46 on both sides of the circumferential direction of the cam surface is 165 to 175 degrees, and in the illustrated embodiment, the interior angle θ is 172 degrees.

[0020] The one-side member 6 and the other-side member 8 are arranged within the outer ring 4 to be rotatable about a common rotation axis o. The one-side engagement piece 18 attached to the one-side member 6 and the other-side engagement piece 38 attached to the other-side member 8 are arranged in combination. In the illustrated embodiment, the outer ring 4 has a cylindrical shape penetrating in the axial direction and has inner and outer circumferential surfaces with circular cross sections. As shown in FIG. 3 , when viewed in the axial direction, the one-side engagement pieces 18 and the other-side engagement pieces 38 are arranged alternately in the circumferential direction inside the outer ring 4, and the rolling elements 10 are arranged between the cam surface 42 and the inner circumferential surface of the outer ring 4. In the illustrated embodiment, the rolling elements 10 are metallic, cylindrical rollers. The outer pressing portion 32 defined on the circumferential end surface of the one-side engagement piece 18 faces the rolling elements 10, and the inner pressing portion 34 faces the circumferential pressed surface 44 of the other-side engagement piece 38, respectively, in the circumferential direction. At this time, as shown in the cross-sectional view of line A-A in Figure 1, one axial side of the other-side member 8 is housed inside the one-side engaging piece 18 of the one-side member 6, and one axial side end face of the other-side member 8 faces the axial end face of the annular ridge 30 of the one-side member 6 and is supported in the axial direction thereby.

[0021] The operation of the reverse input cutoff clutch 1 will now be described. When the one-side member 6 rotates clockwise relative to the outer ring 4 (as viewed from the right of the A-A cross section in FIG. 1; the same applies below), as can be understood by comparing FIG. 3 with FIG. 7, the one-side engagement piece 18 moves clockwise relative to the other-side engagement piece 38 and the rolling element 10, and the inner pressing portion 34 (more specifically, the inner pressing portion 34 on the downstream side in the clockwise direction) of the one-side engagement piece 18 presses the circumferential pressed surface 44 (more specifically, the circumferential pressed surface 44 on the upstream side in the clockwise direction) of the other-side engagement piece 38 (more specifically, the other-side engagement piece 38 located downstream in the clockwise direction), and the outer pressing portion 32 (more specifically, the outer pressing portion 32 on the downstream side in the clockwise direction) presses the rolling element 10 (more specifically, the rolling element 10 located downstream in the clockwise direction), causing the other-side member 8 to rotate clockwise. At this time, the rolling element 10 is pressed together with the other-side engaging piece 38 by the one-side engaging piece 18, preventing the rolling element 10 from moving relative to the cam surface 42, and the rolling element 10 does not become caught between the cam surface 42 and the inner peripheral surface of the outer ring 4. The same applies when the one-side member 6 rotates counterclockwise relative to the outer ring 4.

[0022] 3 and 8, when the other-side member 8 attempts to rotate clockwise relative to the outer ring 4, the other-side engagement piece 38 moves clockwise relative to the one-side engagement piece 18 and the rolling element 10, causing the rolling element 10 to move relatively from the circumferential central region of the cam surface 42 to the end 46 upstream in the clockwise direction, and the rolling element 10 becomes engaged at the end 46 between the cam surface 42 and the inner peripheral surface of the outer ring 4. This prevents the other-side member 8 from rotating counterclockwise relative to the outer ring 4. The same applies when the other-side member 8 attempts to rotate counterclockwise relative to the outer ring 4.

[0023] In other words, in the reverse input cutoff clutch 1, when the one-side member 6 rotates relative to the outer ring 4, the one-side engagement piece 18, together with the other-side engagement piece 38, pushes the rolling element 10, causing the other-side member 8 to rotate, but even if the other-side member 8 tries to rotate relative to the outer ring 4, the rolling element 10 gets caught between the inner peripheral surface of the outer ring 4 and the cam surface 42, and more specifically, between the end 46 of the cam surface 42, and is therefore unable to rotate. Therefore, if an operation to transmit rotation from the one-side member 6 to the other-side member 8 is taken as an input, and an operation to transmit rotation from the other-side member 8 to the one-side member 6 is taken as a reverse input, the input is transmitted but the reverse input is cut off.

[0024] In the reverse input cutoff clutch of the present invention, the cross-sectional shape of the circumferential end 46 of the cam surface 42 extends linearly while inclining circumferentially radially outward, so that the ratio of change in the distance L (see the enlarged view of portion X in FIG. 3 ) between the cam surface 42 and the inner circumferential surface of the outer ring 4 to the circumferential movement distance (displacement) on the cam surface 42 at the end 46 is sufficiently large. This prevents the rolling elements 10 from being excessively deeply engaged between the cam surface 42 and the inner circumferential surface of the outer ring 4 when the other-side member 8 attempts to rotate, thereby preventing the other-side member 8 from being locked. Therefore, when the one-side member 6 rotates relative to the outer ring 4, the one-side engagement pieces 18 push the other-side engagement pieces 38 together with the rolling elements 10, allowing the other-side member 8 to rotate sufficiently reliably.

[0025] Next, we will explain the torque limiter 2 that uses the reverse input cutoff clutch 1. As described above, the torque limiter 2 further includes a housing 12 and a braking torque applying means 14. The housing 12 houses the outer ring 4 together with the one-side member 6 and the other-side member 8, and is fixed to a wall or the like by appropriate fixing means (not shown).

[0026] Referring to Figures 1 to 3 and Figure 6, the housing 12 is comprised of a synthetic resin housing body 50 shown in Figure 6(a) and a synthetic resin shield 52 shown in Figure 6(b). The housing body 50 includes a circular end plate 54 disposed perpendicular to the axial direction and a cylindrical outer wall 56 extending axially from the outer periphery of the end plate 54. A support hole 58 with a circular cross section is formed in the center of the end plate 54 and penetrates the axial direction. An annular shoulder 60 with a reduced inner diameter is formed at the other axial end of the support hole 58. The other axial end of the other-side member 8 is inserted into the support hole 58, and this other axial end is rotatably supported by the support hole 58 and axially supported by the shoulder 60. Six arc-shaped recesses 62 are formed at equal angular intervals in the circumferential direction in the radial middle of one axial side of the end plate 54. The recesses 62 are formed for the purpose of reducing material. Six arc-shaped pedestals 64 are formed at equal angular intervals around the circumferential direction on the outer peripheral edge of one axial side of the end plate 54, connecting to the inner peripheral surface of the outer peripheral wall 56 and protruding to one axial direction. All six pedestals 64 have the same shape. The circumferential centers of the pedestals 64 and the recesses 62 are aligned, and the circumferential length of the pedestals 64 is slightly shorter than the circumferential length of the recesses 62. Auxiliary ridges, each with an arc-shaped cross section, are formed on the upper surface of each of the six pedestals 64, connecting to the inner peripheral surface of the outer peripheral wall 56 and extending to one axial direction. The six auxiliary ridges are designated 66a to 66f, arranged clockwise in the right diagram of Figure 6(a). The inner diameters of the auxiliary ridges 66a to 66f are larger than the inner diameter of the base portion 64, and as shown in Fig. 3, the inner peripheral surfaces of the auxiliary ridges 66a to 66f face the outer peripheral surface of a wound portion 90 (described later) of the braking torque applying means (coil spring 14). When viewed in the axial direction, that is, in the right-hand view of Fig. 6(a), both circumferential ends of the auxiliary ridges 66b and 66e are aligned with both circumferential ends of the respective base portions 64. However, for the auxiliary ridges 66a and 66d, while the clockwise downstream ends are aligned with the clockwise downstream ends of the respective base portions 64, the clockwise upstream ends are displaced downstream of the clockwise upstream ends of the respective base portions 64.Furthermore, the clockwise upstream ends of the auxiliary ribs 66c and 66f are aligned with the clockwise upstream ends of the respective seat portions 64, but the clockwise downstream ends of the auxiliary ribs 66c and 66f are displaced upstream relative to the clockwise downstream ends of the respective seat portions 64. As a result, the circumferential gaps between the circumferentially adjacent auxiliary ribs 66a and 66f and between the auxiliary ribs 66c and 66d are wider than the circumferential gaps between any two other circumferentially adjacent auxiliary ribs, and hook grooves 68 are defined between the auxiliary ribs 66a and 66f and between the auxiliary ribs 66c and 66d. In other words, the hook grooves 68 are formed on the inner peripheral surface of the housing 12. Six arc-shaped extension pieces 70 are attached to one axial end face of the outer peripheral wall 56 at equal angular intervals in the circumferential direction, extending further toward one axial side. When viewed in the axial direction, each of the six extension pieces 70 is disposed between two circumferentially adjacent base portions 64. A locking ridge 72 extending in the circumferential direction is formed on the inner surface of the extending end of each extension piece 70.

[0027] The shield 52 includes a disk-shaped support wall 74 arranged perpendicular to the axial direction and a cylindrical mounting wall 76 extending axially from the outer periphery of the support wall 74. A circular hole 78 is formed in the center of the support wall 74, penetrating it in the axial direction. Two annular ridges, an outer ridge 80 and an inner ridge 82, are formed on the other axial side of the support wall 74, and an annular groove 84 is provided between the outer ridge 80 and the inner ridge 82. The inner ridge 82 surrounds the outer periphery of the hole 78 and is slightly lower than the outer ridge 80 from the support wall 74. As shown in the A-A cross section of FIG. 1 , one axial end of the outer ring 4 is inserted into the groove 84, which rotatably supports the outer ring 4. The outer periphery of the mounting wall 76 is formed with an arc-shaped protrusion 86, which is formed by locally increasing the outer diameter. A plurality of protrusions 86 are formed corresponding to the number of extension pieces 70 formed on the housing body 50; thus, six in the illustrated embodiment, the plurality of protrusions 86 are arranged at equal angular intervals in the circumferential direction. The circumferential distance between two adjacent protrusions 86 corresponds to the circumferential length of the extension pieces 70. A circumferentially extending locking rib 88 is formed in the axially intermediate portion of the outer circumferential surface of the mounting wall 76 between the two adjacent protrusions 86. When attaching the shield 52 to the housing body 50, the extension pieces 70 of the housing body 50 are aligned between the two adjacent protrusions 86, and then the shield 52 is forced axially toward the end plate 54 of the housing body 50, causing the locking rib 72 of the extension pieces 70 to resiliently ride over the locking rib 88. When the shield 52 is attached to the housing main body 50, the medium diameter portion 22 of the one-side member 6 is positioned inside the hole 78 formed in the support wall 74, and the inner peripheral edge of the other axial side surface of the support wall 74 faces the axial one-side end surface of the large diameter portion 24 of the one-side member 6 and supports it in the axial direction.

[0028] 1 to 3 , in the illustrated embodiment, the braking torque applying means 14 is a coil spring that is attached to the outer peripheral surface of the outer ring 4. Hereinafter, the coil spring will be referred to as 14. The coil spring 14 includes a wound portion 90 in which a wire is wound helically, and two hook portions 92 formed by bending the wire radially outward at both axial ends of the wound portion 90. When the coil spring 14 is in a free state, i.e., when no force is acting on either of the two hook portions 92, the inner diameter of the wound portion 90 is smaller than the outer diameter of the cylindrical outer ring 4, and therefore the inner peripheral surface of the wound portion 90 is in close contact with the outer peripheral surface of the outer ring 4. The two hook portions 92 are positioned at different circumferential positions and are inserted into hook grooves 68 formed in the inner peripheral surface of the outer peripheral wall 56 of the housing main body 50. In the illustrated embodiment, two hook grooves 68 are formed on the inner peripheral surface of the outer peripheral wall 56, and the two hook portions 92 are commonly inserted into one of the two hook grooves 68. By commonly inserting the two hook portions 92 into the hook grooves 68, the coil spring 14 is unable to rotate with respect to the housing 12, and when the outer ring 4 attempts to rotate with respect to the housing 12, one of the two hook portions 92 is relatively pressed by the housing 12 at the hook groove 68 in a direction that expands the diameter of the wound portion 90.

[0029] Explaining with reference to FIGS. 1 and 2, in the illustrated embodiment, an auxiliary braking torque applying means is further disposed within the housing 12, which applies a braking torque to the rolling element 10. The braking torque applied to the rolling element 10 by the auxiliary braking torque applying means is smaller than the braking torque applied to the outer ring 4 by the braking torque applying means (coil spring 14). In the illustrated embodiment, the auxiliary braking torque applying means is a wave washer 94. The wave washer 94 is a metal thin, annular member processed into a wave shape, and it biases the rolling element 10 in the axial direction. The frictional force caused by this bias applies the braking torque to the rolling element 10. As can be seen by referring to the cross-sectional view of line A-A in FIG. 1, both axial ends of the rolling element 10 are supported by metal thin, annular washers 96a and 96b. The inner diameters of the washer 96a located on the shield 52 side and the washer 96b located on the end plate 54 side of the housing body 50 are approximately equal. On the other hand, the outer diameter of washer 96a is smaller than the outer diameter of washer 96b, and washer 96a is housed inside the outer ring 4, while washer 96b supports the other axial end face of the outer ring 4 together with the other axial end face of the rolling element 10 on the outside of the outer ring 4. As described above, one axial end of the rolling element 10 is rotatably supported by the groove 84 formed in the shield 52. The wave washer 94 is disposed axially adjacent to washer 96a on the inside of the outer ring 4. A washer 96c having the same shape as washer 96a is also disposed between the wave washer 94 and the shield 52.

[0030] The operation of the torque limiter 2 will now be described. The case where the one-side member 6 rotates clockwise will be described with reference to FIGS. 3 and 7 . When the one-side member 6 rotates clockwise, as described above, the inner pressing portion 34 (more specifically, the inner pressing portion 34 on the downstream side in the clockwise direction) of the one-side engagement piece 18 presses the circumferential pressed surface 44 (more specifically, the circumferential pressed surface 44 on the upstream side in the clockwise direction) of the other-side engagement piece 38, and the outer pressing portion 32 (more specifically, the outer pressing portion 32 on the downstream side in the clockwise direction) presses the rolling element 10 (more specifically, the rolling element 10 located downstream in the clockwise direction), causing the other-side member 8 to rotate clockwise. At this time, the outer ring 4 is held by the coil spring 14, and the one-side member 6 and the other-side member 8 rotate together with the rolling element 10 relative to the outer ring 4 and the housing 12. In the illustrated embodiment, an auxiliary braking torque is applied to the rolling element 10 by the wave washer 94, so the one-side member 6 and the other-side member 8 rotate against the auxiliary braking torque, which is a relatively light load. The same applies when the one-side member 6 rotates counterclockwise.

[0031] Next, the case where the other-side member 8 rotates in the clockwise direction will be described with reference to FIGS. 3 and 8 . When the other-side member 8 rotates in the clockwise direction, as described above, the rolling element 10 is engaged between the cam surface 42 and the inner circumferential surface of the outer ring 4 at the end 46 on the upstream side in the clockwise direction. This engagement causes the other-side member 8, the rolling element 10, and the outer ring 4 to become one unit. Therefore, when the other-side member 8 rotates in the clockwise direction, the coil spring 14 attached to the outer circumferential surface of the outer ring 4 also rotates in the clockwise direction, and the hook portion 92 located on the downstream side in the clockwise direction is engaged by the housing 12 in the hook groove 68. At this time, the hook portion 92 is relatively pressed by the housing 12 in the direction in which the wound portion 90 expands in diameter, so that the other-side member 8, together with the rolling element 10 and the outer ring 4, can rotate in the clockwise direction against the braking torque of the coil spring 14 (braking torque applying means). Then, after the other-side member 8 rotates clockwise and the circumferential pressed surface 44 of the other-side engagement piece 38 (more specifically, the circumferential pressed surface 44 on the downstream clockwise side) abuts against the inner pressing portion 34 of the one-side engagement piece 18 (more specifically, the inner pressing portion 34 on the upstream clockwise side of the one-side engagement piece 18 located downstream in the clockwise direction), the circumferential pressed surface 44 presses the inner pressing portion 34, causing the one-side member 6 to rotate clockwise. On the other hand, if the rotational torque applied to the other-side member 8 is smaller than the braking torque, the other-side member 8 is held in place by the braking torque without rotating. The same is true when the other-side member 8 rotates counterclockwise.

[0032] In other words, in the torque limiter 2, rotation from the one-side member 6 to the other-side member 8 is transmitted with a light load, while rotation from the other-side member 8 to the one-side member 6 is transmitted against a relatively large braking torque applied by the coil spring 14 (braking torque applying means). Furthermore, in the illustrated embodiment, rotation from the one-side member 6 to the other-side member 8 and rotation from the other-side member 8 to the one-side member 6 are both possible in forward and reverse directions, so the torque limiter 2 is a bidirectional torque limiter. If the auxiliary braking torque applying means 94 were omitted, rotation from the one-side member 6 to the other-side member 8 would be transmitted with substantially no load. However, in order to stabilize the posture of the rolling elements 10 and ensure that they mesh reliably between the end 46 of the cam surface 42 and the inner circumferential surface of the outer ring 4 when rotational torque that attempts to rotate the one-side member 6 is applied from the other-side member 8, it is preferable to provide the auxiliary braking torque applying means 94.

[0033] The reverse input cutoff clutch and torque limiter using the same constructed according to the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above-described embodiment, and appropriate modifications and changes can be made without departing from the scope of the present invention. For example, in the illustrated embodiment, the rolling elements are cylindrical rollers, but they may also be spherical balls. Furthermore, in the torque limiter, the braking torque applying means may be of any type as long as it can apply a braking torque to the outer ring, and leaf springs, ring springs, tolerance rings, etc. can be used in addition to coil springs.

[0034] 1: Reverse input cutoff clutch 2: Torque limiter 4: Outer ring 6: One side member 8: Other side member 10: Rolling element 12: Housing 14: Braking torque applying means (coil spring) 18: One side engaging piece 38: Other side engaging piece 42: Cam surface 46: End portion (of cam surface)

Claims

1. A reverse input cut-off clutch comprising a cylindrical outer ring, and one-side and other-side members rotatable within the outer ring about a common rotation axis, the outer ring having an inner peripheral surface with a circular cross section, a one-side engagement piece attached to the one-side member and a other-side engagement piece attached to the other-side member being combined and disposed inside the outer ring, the other-side engagement piece being formed with a cam surface that faces the inner peripheral surface of the outer ring, and rolling elements being disposed between the cam surface and the inner peripheral surface of the outer ring, and when the one-side member rotates relative to the outer ring, the one-side engagement piece pushes the rolling elements together with the other-side engagement piece to rotate the other-side member, while even if the other-side member attempts to rotate relative to the outer ring, the rolling elements are unable to rotate as they become caught between the inner peripheral surface of the outer ring and the circumferential end of the cam surface, wherein the cross-sectional shape of the end of the cam surface extends linearly, inclined circumferentially toward the radially outward.

2. A reverse input cut-off clutch as set forth in claim 1, wherein said cam surface is concave, and the cross-sectional shapes of the two ends located on both circumferential sides of said cam surface both extend linearly and inclined radially outwardly in the circumferential direction.

3. A reverse input cutoff clutch as claimed in claim 2, wherein the interior angle between the two straight lines along the two ends located on both circumferential sides is 165 to 175 degrees.

4. A torque limiter using a reverse input cut-off clutch as claimed in any one of claims 1 to 3, wherein the outer ring together with the one-side member and the other-side member is contained in a fixed housing, and braking torque applying means is disposed between the outer ring and the housing for applying a braking torque to the outer ring when the outer ring rotates relative to the housing, and rotation from the one-side member to the other-side member is transmitted with no or a light load, while rotation from the other-side member to the one-side member is transmitted against the braking torque.

5. The torque limiter according to claim 4, wherein the braking torque applying means is a coil spring attached to the outer peripheral surface of the outer ring, the coil spring comprising a winding portion in which wire is wound in a spiral shape and two hook portions formed by bending the wire radially outward at both axial ends of the winding portion, the inner diameter of the winding portion when the coil spring is in a free state is smaller than the outer diameter of the cylindrical outer ring, each of the two hook portions is arranged at a different circumferential position and the two hook portions are inserted into hook grooves formed in the inner peripheral surface of the housing so that the coil spring cannot rotate relative to the housing, and when the outer ring attempts to rotate relative to the housing, one of the two hook portions is pushed relatively in the hook groove in the direction in which the winding portion expands in diameter.

6. A torque limiter according to claim 4, further comprising an auxiliary braking torque applying means disposed within said housing for applying a braking torque to said rolling elements.

7. A torque limiter according to claim 6, wherein said braking torque applying means is a wave washer which biases said rolling elements in the axial direction.

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