Rotation braking device

Abstract

To provide a rotation braking device which surely operates even if a slip occurs between a friction surface of a friction plate and an axial end surface of an outer ring.SOLUTION: An engaging protrusion 30 protruding in the axial direction toward the frictional plate 9 is provided on the 4a of the axial end surface of the outer ring 4, a plurality of groove portions 33 and a plurality of non-groove portions 34 extending in the circumferential direction are alternately formed in the circumferential direction on the 9a of the frictional surface, the engaging protrusion 30 falls into the groove portion 33 of the 9a of the frictional surface when the frictional plate 9 moves to the frictional engagement position, and the relative rotation between the frictional plate 9 and the outer ring 4 is restricted by the circumferential engagement between the engaging protrusion 30 and the non-groove portion 34.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a rotation braking device that can switch between a rotation preventing state in which rotation is prevented and a rotation allowing state in which rotation is allowed. [Background technology]

[0002] The inventor of the present application has already proposed a rotation braking device capable of switching between a rotation preventing state that prevents rotation and a rotation allowing state that allows rotation, as disclosed in Patent Document 1. The rotation braking device of Patent Document 1 has an engagement element clutch unit and an electromagnetic clutch unit for switching the state of the engagement element clutch unit.

[0003] The engaging element clutch unit has an outer ring, an inner ring disposed radially inside the outer ring, an engaging element incorporated between the outer ring and the inner ring, an engaging element retainer that holds the engaging element, and a centering spring. The engaging element retainer is supported so as to be movable in the circumferential direction between an engaging position where the engaging element is engaged between the outer ring and the inner ring, and a neutral position where the engaging element is disengaged, and is elastically held in the neutral position by the centering spring. The outer ring is a non-rotating member that is prevented from rotating relative to the case. The inner ring is supported by a bearing so as to be rotatable relative to the case.

[0004] The electromagnetic clutch unit includes a friction plate disposed axially opposite the outer ring of the engaging clutch unit, an armature disposed opposite the side of the friction plate facing the outer ring, an armature spring that axially biases the friction plate toward the outer ring via the armature, and an electromagnet disposed opposite the side of the armature facing the friction plate. The friction plate has a friction surface axially facing the axial end face of the outer ring. The friction plate is prevented from rotating by the engaging cage and is axially movable between a friction engagement position where the friction surface frictionally engages with the axial end face of the outer ring and a friction release position where the friction engagement is released.

[0005] When the electromagnet is de-energized, this rotation braking device is in a rotation-prevented state, preventing rotation of the inner ring. That is, when the electromagnet is de-energized, the friction plate is pressed against the axial end face of the outer ring, which is a non-rotating member, by the biasing force of the armature spring, and the friction surface of the friction plate frictionally engages with the axial end face of the outer ring. At this time, frictional resistance between the friction surface of the friction plate and the axial end face of the outer ring restricts rotation of the friction plate, and the rotation of the engagement element cage, which is prevented by the friction plate, is also restricted. When rotation is input to the inner ring in this state, the inner ring rotates relative to the engagement element cage, which is in a rotation-restricted state. This relative rotation moves the engagement element cage from the neutral position to the engagement position against the spring torque of the centering spring. As a result, the engagement element engages between the outer ring and the inner ring, preventing rotation of the inner ring.

[0006] On the other hand, when the electromagnet is energized, this rotation braking device enters a rotation-permitted state in which rotation of the inner ring is permitted. That is, when the electromagnet is energized, the electromagnet attracts the armature against the biasing force of the armature spring, so the biasing force of the armature spring no longer acts on the friction plate. As a result, the friction plate is released from frictional engagement with the axial end face of the outer ring and enters a freely rotatable state, and the engaging element cage, which is prevented from rotating by the friction plate, also enters a freely rotatable state. In this state, the engaging element cage is held in a neutral position by the spring torque of the centering spring, so even if the inner ring is rotated, the engaging element does not engage between the outer ring and the inner ring, and rotation of the inner ring is permitted. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2023-156039 Summary of the Invention [Problem to be solved by the invention]

[0008] The inventors of the present application repeatedly conducted tests to switch between a rotation-preventing state and a rotation-permitting state for a rotation braking device having the configuration of Patent Document 1. As a result, they encountered the problem that, although rotation of the inner ring should be prevented when the electromagnet is not energized, in rare cases, even when the power to the electromagnet is cut off, the state does not switch from the rotation-permitting state to the rotation-preventing state, or that even if the state does switch to the rotation-preventing state, it later unintentionally returns to the rotation-permitting state.

[0009] Upon investigating the cause of this problem, it was discovered that repeated switching between the rotation-preventing state and the rotation-permitting state caused the friction surfaces of the friction plates and the axial end faces of the outer ring to wear, making it impossible to generate sufficient frictional resistance between the friction surfaces of the friction plates and the axial end faces of the outer ring.

[0010] That is, in the rotation braking device having the configuration of Patent Document 1, in order to switch from a rotation-permitting state to a rotation-preventing state when the power to the electromagnet is cut off, and to maintain the rotation-preventing state thereafter, the magnitude of the friction resistance generated between the friction surface of the friction plate and the axial end face of the outer ring must exceed the magnitude of the spring torque of the centering spring (the circumferential force with which the centering spring attempts to return the engaging element holder to the neutral position).

[0011] However, when the friction surface of the friction plate or the axial end face of the outer ring wears, the friction resistance generated between them when the friction surface of the friction plate frictionally engages with the axial end face of the outer ring decreases.If the magnitude of the friction resistance generated between the friction surface of the friction plate and the axial end face of the outer ring cannot exceed the spring torque of the centering spring due to abnormal wear or the like, even if the friction surface of the friction plate is pressed against the axial end face of the outer ring to frictionally engage, slippage will occur between the friction surface of the friction plate and the axial end face of the outer ring.As a result, it has been found that even if power to the electromagnet is cut off, the rotation braking device will not switch from the rotation-permitted state to the rotation-prevented state, or even if it has switched to the rotation-prevented state, it may unintentionally return to the rotation-permitted state thereafter.

[0012] The problem to be solved by this invention is to provide a rotation braking device that operates reliably even if slippage occurs between the friction surface of the friction plate and the axial end face of the outer ring. [Means for solving the problem]

[0013] In order to solve the above problems, the present invention provides a rotation braking device having the following configuration. [Configuration 1] The outer ring and an inner ring disposed radially inside the outer ring; an engaging element incorporated between the outer ring and the inner ring; an engaging element holder supported so as to be movable in a circumferential direction between an engaging position where the engaging element is engaged between the outer ring and the inner ring and a neutral position where the engaging element is released; a centering spring that elastically holds the engaging element retainer in the neutral position; a friction plate having a friction surface axially opposing an axial end face of the outer ring, the friction plate being provided so as to be movable in the axial direction between a friction engagement position where the friction surface frictionally engages with the axial end face of the outer ring and a friction release position where the friction surface releases frictional engagement with the axial end face of the outer ring while being prevented from rotating by the engaging element cage; an armature disposed opposite to a side of the friction plate facing the outer ring; an armature spring that urges the friction plate toward the outer ring in the axial direction via the armature; an electromagnet disposed opposite to the side of the armature facing the friction plate, the electromagnet attracting the armature against the biasing force of the armature spring when energized, an engaging protrusion that protrudes in the axial direction toward the friction plate is provided on an axial end surface of the outer ring, a plurality of circumferentially extending groove portions and a plurality of non-groove portions are formed alternately in the circumferential direction on the friction surface, and when the friction plate moves to the friction engagement position, the engaging convex portions drop into the groove portions of the friction surface, and the circumferential engagement between the engaging convex portions and the non-groove portions restricts relative rotation between the friction plate and the outer ring.

[0014] With this configuration, when the friction surface of the friction plate frictionally engages with the axial end face of the outer ring, the engaging protrusions provided on the axial end face of the outer ring fall into the grooves of the grooves and non-groove portions formed alternately in the circumferential direction on the friction surface of the friction plate, and the engagement between the engaging protrusions and non-groove portions makes it possible to restrict relative rotation between the friction plate and the outer ring.As a result, even when the friction resistance generated between the friction surface of the friction plate and the axial end face of the outer ring becomes small, it is possible to prevent the state from switching from a rotation-permitted state (a state in which relative rotation between the outer ring and the inner ring is permitted) to a rotation-prevented state (a state in which relative rotation between the outer ring and the inner ring is prevented), or from unintentionally returning to the rotation-permitted state after switching to the rotation-prevented state.

[0015] [Configuration 2] the engaging protrusion is a member separate from the outer ring and inserted axially movably into an outer ring hole formed in an axial end surface of the outer ring, 2. The rotation braking device according to claim 1, wherein the engaging protrusion is biased in a direction protruding from the outer ring hole by an elastic member incorporated in the outer ring hole.

[0016]

[0003] By adopting this configuration, it is possible to prevent deformation, etc., of the engaging convex portion or non-groove portion due to excessive load when an unexpectedly large torque acts between the outer ring and the friction plate while the engaging convex portion is in a state where it has fallen into the groove. In other words, if an unexpectedly large torque acts between the friction plate and the outer ring after the friction surface of the friction plate frictionally engages with the axial end surface of the outer ring and the engaging convex portion has fallen into the groove, but before the engaging element engages between the outer ring and the inner ring to prevent relative rotation between the outer ring and the inner ring, the engaging convex portion or non-groove portion may be subjected to excessive load and may be deformed, etc.

[0004] To address this problem, by adopting a configuration in which the engaging convex portion is a separate member from the outer ring that is inserted into the outer ring hole so as to be axially movable, and the engaging convex portion is biased by an elastic member in a direction that protrudes from the outer ring hole, when an unexpectedly large torque acts between the friction plate and the outer ring while the engaging convex portion is in a state where it has fallen into the groove, the engaging convex portion moves axially due to the reaction force it receives from the non-groove portion and disengages from the non-groove portion. In this way, when the engaging protrusion falls into the groove portion and a torque greater than expected acts between the outer ring and the friction plate, it is possible to prevent excessive load from being applied to the engaging protrusion and non-groove portion.

[0017] [Configuration 3] 3. The rotation braking device according to configuration 2, wherein the engaging protrusion is a sphere.

[0018] With this configuration, because the engaging protrusions are spherical, when the engaging protrusions engage the non-groove portions in the circumferential direction, the reaction force they receive from the non-groove portions includes an axial component. Therefore, when an unexpectedly large torque acts between the friction plate and the outer ring while the engaging protrusions are in the grooved portion, the reaction force they receive from the non-groove portions can reliably move the engaging protrusions in the axial direction.

[0019] [Configuration 4] Engagement surfaces with which the engaging protrusions engage are formed at both ends of the non-groove portions in the circumferential direction, 4. The rotary braking device according to claim 2 or 3, wherein the engagement surface is an inclined surface inclined in the circumferential direction with respect to the axial direction.

[0020] With this configuration, the engagement surfaces on both circumferential sides of the non-groove portion are inclined circumferentially with respect to the axial direction, so that when the engagement convex portion engages with the non-groove portion in the circumferential direction, the reaction force received from the non-groove portion includes an axial component force. Therefore, when an unexpectedly large torque acts between the friction plate and the outer ring with the engagement convex portion depressed into the groove portion, the reaction force received from the non-groove portion can reliably move the engagement convex portion in the axial direction.

[0021] [Configuration 5] a plurality of the engaging protrusions are provided at equal intervals in the circumferential direction on the axial end surface of the outer ring, The plurality of non-groove portions are provided at equal intervals in the circumferential direction on the friction surface, The circumferential lengths of the plurality of grooves are equal to one another, 5. The rotation braking device according to any one of configurations 1 to 4, wherein the number of the engaging protrusions and the number of the grooves are different from each other.

[0022] With this configuration, when the multiple engaging protrusions fall into the multiple grooves, respectively, the circumferential distance from each engaging protrusion to the adjacent non-groove portion varies depending on the engaging protrusion. As a result, when slippage occurs between the friction surface of the friction plate and the axial end face of the outer ring, it is possible to keep small the rotation angle of the friction plate from the time the slippage occurs until the relative rotation between the friction plate and the outer ring is restricted by engagement between the engaging protrusions and the non-groove portion.

[0023] [Configuration 6] 6. The rotation braking device according to configuration 5, wherein the difference between the number of the engaging protrusions and the number of the grooves is one.

[0024] By adopting this configuration, when slippage occurs between the friction surface of the friction plate and the axial end face of the outer ring, it is possible to particularly effectively keep small the rotation angle of the friction plate from the time the slippage occurs until the relative rotation between the friction plate and the outer ring is restricted by the engagement of the engaging convex portion and the non-groove portion. [Effects of the Invention]

[0025] In the rotation braking device of this invention, when the friction surface of the friction plate frictionally engages with the axial end face of the outer ring, the engaging convex portions provided on the axial end face of the outer ring fall into the groove portions of the groove portions and non-groove portions that are formed alternately in the circumferential direction on the friction surface of the friction plate, and the engagement between the engaging convex portions and the non-groove portions can restrict the relative rotation of the friction plate and the outer ring. Therefore, even when the friction resistance generated between the friction surface of the friction plate and the axial end face of the outer ring becomes small, it is possible to prevent the state from switching from the rotation-permitted state to the rotation-blocked state, or to prevent an unintended return to the rotation-permitted state after switching to the rotation-blocked state. [Brief explanation of the drawings]

[0026] [Figure 1] 1 is a cross-sectional view of a rotation braking device according to a first embodiment of the present invention; [Figure 2] Enlarged view of the friction plate and its surroundings in Figure 1 [Figure 3] Cross-sectional view along line III-III in Figure 1 [Figure 4] Cross-sectional view along line IV-IV in Figure 1 [Figure 5] FIG. 3 is an enlarged view of the vicinity of the engaging protrusion of FIG. 2; [Figure 6] Cross-sectional view along line VI-VI in Figure 5 [Figure 7] FIG. 7 is a diagram showing a state in which slippage occurs between the friction plate and the outer ring shown in FIG. 6, causing the engaging convex portion to engage with the non-groove portion. [Figure 8] The figure shows the state in which the engagement projection enters the outer ring hole and disengages from the non-groove portion when a torque greater than expected acts between the friction plate and outer ring shown in Figure 7. [Figure 9] FIG. 1 is a diagram showing a second embodiment of the present invention, corresponding to FIG. [Figure 10] Enlarged view of the area around the friction plate in Figure 9 [Figure 11] Cross-sectional view taken along line XI-XI in Figure 9 [Figure 12] Cross-sectional view along line XII-XII in Figure 9 DETAILED DESCRIPTION OF THE INVENTION

[0027] 1 shows a rotation braking device according to a first embodiment of the present invention. This rotation braking device has a roller clutch unit 1, an electromagnetic clutch unit 2 for switching between a rotation-preventing state and a rotation-permitting state of the roller clutch unit 1, and a cylindrical case 3 for accommodating the roller clutch unit 1 and the electromagnetic clutch unit 2.

[0028] As shown in Figure 2, the roller clutch unit 1 has an outer ring 4, an inner ring 5 arranged coaxially radially inside the outer ring 4, a plurality of rollers 6 assembled at intervals in the circumferential direction between the outer ring 4 and the inner ring 5, a roller retainer 7 that holds the plurality of rollers 6, and a centering spring 8.

[0029] The axial direction is the direction parallel to the central axis of the outer ring 4, the radial direction is the direction perpendicular to the central axis of the outer ring 4, and the circumferential direction is the direction along the circumference that goes around the central axis of the outer ring 4.

[0030] The electromagnetic clutch unit 2 has a friction plate 9 arranged axially opposite the outer ring 4, an armature 10 arranged opposite the side of the friction plate 9 facing the outer ring 4 (right side in the figure), an armature spring 11 that urges the friction plate 9 axially toward the outer ring 4 via the armature 10, and an annular electromagnet 12 arranged opposite the side of the armature 10 facing the friction plate 9 (right side in the figure).

[0031] As shown in FIG. 1 , the outer ring 4 is rotatably supported relative to the case 3 by a bearing 13 provided on the inner periphery of the case 3. The outer ring 4 is provided with a rotating shaft connecting portion 14 to which an external rotating shaft S is connected. On the other hand, the inner ring 5 is a non-rotating member that is prevented from rotating relative to the case 3. Specifically, the inner ring 5 is prevented from rotating relative to the electromagnet 12 by spline-fitting the outer periphery of an inner ring shaft portion 5a, which is provided integrally with the inner ring 5, onto the inner periphery of the electromagnet 12, and the electromagnet 12 is prevented from rotating relative to the case 3 by a non-rotating member (such as a key member) not shown. In this way, the inner ring 5 is prevented from rotating relative to the case 3 via the electromagnet 12. In addition, a bearing 15 that supports the outer ring 4 rotatably relative to the inner ring 5 is incorporated between the outer ring 4 and the inner ring 5.

[0032] As shown in Figures 2 and 3, a plurality of cam surfaces 16 are provided at equal intervals in the circumferential direction on the outer periphery of the inner ring 5. A cylindrical surface 17 is provided on the inner periphery of the outer ring 4, radially opposing the cam surfaces 16. As shown in Figure 3, the cam surface 16 is a surface that forms a wedge space between itself and the cylindrical surface 17 that gradually narrows from the circumferential center toward both circumferential ends, and is, for example, a flat surface that radially opposes the cylindrical surface 17. One roller 6 is incorporated between each cam surface 16 and the cylindrical surface 17.

[0033] 2, roller cage 7 is a cylindrical member having a plurality of radially penetrating pockets 18 formed at intervals in the circumferential direction, with rollers 6 housed in each of pockets 18. Roller cage 7 is supported circumferentially movable relative to inner ring 5 between an engagement position where rollers 6 are engaged between cam surface 16 and cylindrical surface 17 by moving rollers 6 circumferentially from the circumferential center of cam surface 16, and a neutral position where rollers 6 are disengaged from cam surface 16 and cylindrical surface 17 by moving rollers 6 circumferentially to the circumferential center of cam surface 16.

[0034] As shown in Fig. 3, the centering spring 8 is composed of a C-shaped annular portion 20 formed by winding a steel wire in a C shape, and a pair of extension portions 21 extending radially outward from both ends of the C-shaped annular portion 20. The C-shaped annular portion 20 is fitted into a circular spring accommodating recess 22 formed in the axial end face of the inner ring 5. The pair of extension portions 21 are inserted into radial grooves 23 formed in the axial end face of the inner ring 5 so as to penetrate radially outward from the spring accommodating recess 22.

[0035] The extension portion 21 of the centering spring 8 protrudes from the radial outer end of the radial groove 23, and the portion of the extension portion 21 protruding from the radial groove 23 is inserted into a cage groove 24 formed in the roller cage 7. The radial groove 23 and the cage groove 24 are formed to have the same circumferential width. The extension portion 21 of the centering spring 8 contacts the inner surface of the radial groove 23 and the inner surface of the cage groove 24, respectively, and elastically holds the roller cage 7 in the neutral position by the circumferential force acting on these contact portions. In other words, when the roller cage 7 moves circumferentially relative to the inner ring 5 from the neutral position shown in FIG. 3, a spring torque (a circumferential force that attempts to return the roller cage 7 to the neutral position) acts on the roller cage 7 from the centering spring 8.

[0036] As shown in Fig. 2, the armature 10 is supported by a cylindrical surface formed on the outer periphery of the inner ring shaft portion 5a so as to be rotatable and axially movable relative to the inner ring shaft portion 5a. The armature 10 is a disk-shaped member made of a magnetic material (iron, silicon steel, etc.). The armature spring 11 is incorporated between the armature 10 and the electromagnet 12 while being compressed in the axial direction, and biases the armature 10 in a direction that moves it away from the electromagnet 12 in the axial direction. The armature spring 11 may be, for example, a wave washer, a disc spring, or a compression coil spring.

[0037] The friction plate 9 is an annular plate-shaped member incorporated between the outer ring 4 and the armature 10. The friction plate 9 is made of a non-magnetic material (for example, an aluminum alloy, a copper alloy, etc.). The friction plate 9 has a friction surface 9a that faces the axial end face 4a of the outer ring 4 in the axial direction. The friction plate 9 is provided so as to be movable in the axial direction between a friction engagement position where the friction surface 9a frictionally engages with the axial end face 4a of the outer ring 4, and a friction release position where the friction surface 9a releases the frictional engagement with the axial end face 4a of the outer ring 4. The friction plate 9 is pressed against the axial end face 4a of the outer ring 4 by the biasing force of the armature spring 11.

[0038] An intermediate plate 25 is provided between the roller holder 7 and the friction plate 9 to prevent the friction plate 9 from rotating relative to the roller holder 7 so that the friction plate 9 rotates integrally with the roller holder 7 while allowing the friction plate 9 to move axially.

[0039] As shown in FIG. 3 , anti-rotation protrusions 27 that engage with anti-rotation recesses 26 formed in the roller cage 7 are formed on the outer periphery of the intermediate plate 25. The intermediate plate 25 is prevented from rotating on the roller cage 7 by the engagement of the anti-rotation protrusions 27 and the anti-rotation recesses 26. Furthermore, as shown in FIG. 2 , the intermediate plate 25 is formed with axial protrusions 28 that extend in the axial direction toward the friction plates 9. As shown in FIGS. 2 and 4 , the friction plates 9 are formed with axial holes 29 into which the axial protrusions 28 of the intermediate plate 25 are inserted so as to be slidable in the axial direction. The engagement of the axial protrusions 28 with the axial holes 29 prevents the friction plates 9 from rotating on the intermediate plate 25 while allowing them to move in the axial direction. Here, the friction plates 9 shown in FIG. 2 are prevented from rotating on the roller cage 7 via the intermediate plate 25, and are axially movable between a position where the friction surface 9 a frictionally engages with the axial end face 4 a of the outer ring 4 and a position where the frictional engagement is released while remaining in the prevented-rotation state.

[0040] As shown in Fig. 2, the axial end face 4a of the outer ring 4 is provided with an engaging protrusion 30 that protrudes in the axial direction toward the friction plate 9. As shown in Fig. 3, a plurality of engaging protrusions 30 (four in the figure) are provided at equal intervals in the circumferential direction. As shown in Fig. 5, the engaging protrusion 30 is a sphere that is inserted axially movably into an outer ring hole 31 formed in the axial end face 4a of the outer ring 4. The engaging protrusion 30 is biased in the direction of protrusion from the outer ring hole 31 by an elastic member 32 incorporated in the outer ring hole 31. In the figure, the outer ring hole 31 is a blind hole extending in the axial direction.

[0041] As shown in FIGS. 2 and 4, groove portions 33 extending in the circumferential direction and non-groove portions 34 separating the groove portions 33 are alternately formed in the circumferential direction on the friction surface 9a of the friction plate 9. As shown in FIG. 4, the groove portions 33 are partial circumferential grooves (i.e., discontinuous circumferential grooves) extending over a range corresponding to a circular arc obtained by dividing the circumference into multiple portions, and have a constant depth along the circumferential direction. A plurality of non-groove portions 34 (five in the figure) are provided at equal intervals in the circumferential direction. The same number of groove portions 33 (five in the figure) as the number of non-groove portions 34 are also provided, and the circumferential lengths of the groove portions 33 are equal to each other. Here, the number of engaging protrusions 30 shown in FIG. 3 (four in the figure) and the number of groove portions 33 shown in FIG. 4 (five in the figure) are different from each other, and the difference between the numbers is set to 1.

[0042] As shown in Figures 5 and 6, when the friction surface 9a of the friction plate 9 frictionally engages with the axial end face 4a of the outer ring 4, the engaging protrusions 30 drop into the grooves 33 of the friction surface 9a. When the friction plate 9 and the outer ring 4 rotate relative to each other in this state, the engaging protrusions 30 circumferentially engage with the non-groove portions 34, as shown in Figure 7, and this engagement restricts the relative rotation between the friction plate 9 and the outer ring 4. Here, the depth of the grooves 33 is set smaller than the radius of the engaging protrusions 30 (spheres). Furthermore, engagement surfaces 35 with which the engaging protrusions 30 engage are formed at both circumferential ends of the non-groove portions 34 (both upper and lower ends in the figure). The engagement surfaces 35 are inclined circumferentially with respect to the axial direction.

[0043] An example of the operation of the above-mentioned rotation braking device will now be described.

[0044] When the electromagnet 12 shown in FIG. 1 is de-energized, the outer ring 4 is placed in a rotation-prevented state, where rotation is prevented. That is, when the electromagnet 12 is de-energized, the friction plate 9 shown in FIG. 2 is pressed against the axial end face 4a of the outer ring 4 by the biasing force of the armature spring 11, and the friction surface 9a of the friction plate 9 frictionally engages with the axial end face 4a of the outer ring 4. When rotation is input to the outer ring 4 in this state, the friction plate 9 rotates together with the outer ring 4 due to the friction resistance between the friction surface 9a of the friction plate 9 and the axial end face 4a of the outer ring 4, and the roller cage 7, which is prevented from rotating by the friction plate 9, also rotates together with the outer ring 4. Then, due to the co-rotation of the roller cage 7 and the outer ring 4, the roller cage 7 shown in FIG. 3 moves from the neutral position to the engaged position against the spring torque of the centering spring 8. As a result, the rollers 6 are engaged between the cam surface 16 on the outer periphery of the inner ring 5 and the cylindrical surface 17 on the inner periphery of the outer ring 4, preventing the outer ring 4 from rotating.

[0045] On the other hand, when the electromagnet 12 is energized, the outer ring 4 enters a rotation-permitted state in which rotation is permitted. That is, when the electromagnet 12 shown in FIG. 2 is energized, the electromagnet 12 attracts the armature 10 against the biasing force of the armature spring 11, and the biasing force of the armature spring 11 no longer acts on the friction plate 9. As a result, the friction plate 9 is released from frictional engagement with the axial end surface 4a of the outer ring 4 and becomes freely rotatable relative to the outer ring 4, and the roller cage 7, which is prevented from rotating by the friction plate 9, also becomes freely rotatable relative to the outer ring 4. In this state, the roller cage 7 is held in a neutral position by the spring torque of the centering spring 8 (see FIG. 3). Therefore, even if the outer ring 4 is rotated, the rollers 6 do not engage between the cam surface 16 on the outer circumference of the inner ring 5 and the cylindrical surface 17 on the inner circumference of the outer ring 4, and rotation of the outer ring 4 is permitted.

[0046] Here, when the power supply to the electromagnet 12 is cut off, in order to switch from a rotation-permitted state (a state in which rotation of the outer ring 4 is permitted) to a rotation-prevented state (a state in which rotation of the outer ring 4 is prevented) based on the mechanism described above, and to maintain the rotation-prevented state thereafter, the magnitude of the friction resistance generated between the friction surface 9a of the friction plate 9 shown in FIG. 2 and the axial end face 4a of the outer ring 4 must exceed the magnitude of the spring torque of the centering spring 8 shown in FIG. 3 (the circumferential force with which the centering spring 8 attempts to return the roller retainer 7 to the neutral position).

[0047] However, when the friction surface 9a of the friction plate 9 or the axial end face 4a of the outer ring 4 shown in Fig. 2 wears, the friction resistance generated between them when the friction surface 9a of the friction plate 9 frictionally engages with the axial end face 4a of the outer ring 4 decreases. If the magnitude of the friction resistance generated between the friction surface 9a of the friction plate 9 and the axial end face 4a of the outer ring 4 cannot exceed the spring torque of the centering spring 8 shown in Fig. 3 due to abnormal wear or the like, even if the friction surface 9a of the friction plate 9 shown in Fig. 2 is pressed against the axial end face 4a of the outer ring 4 to cause frictional engagement, slippage will occur between the friction surface 9a of the friction plate 9 and the axial end face 4a of the outer ring 4, causing relative rotation between the friction plate 9 and the outer ring 4. As a result, there is a problem that the state will not switch from the rotation-permitted state to the rotation-blocked state even when power to the electromagnet 12 is cut off, or that even if the state does switch to the rotation-blocked state, it may unintentionally return to the rotation-permitted state thereafter.

[0048] To address this problem, in the rotation braking device of the above embodiment, as shown in Fig. 2, when the friction surface 9a of the friction plate 9 frictionally engages with the axial end face 4a of the outer ring 4, the engaging protrusions 30 provided on the axial end face 4a of the outer ring 4 fall into the groove portions 33 of the groove portions 33 and non-groove portions 34 formed alternately in the circumferential direction on the friction surface 9a of the friction plate 9, as shown in Fig. 6 and Fig. 7, and the engagement of the engaging protrusions 30 with the non-groove portions 34 makes it possible to restrict the relative rotation between the friction plate 9 and the outer ring 4. Therefore, even when the frictional resistance generated between the friction surface 9a of the friction plate 9 and the axial end face 4a of the outer ring 4 shown in Fig. 2 becomes small, it is possible to prevent the state from switching from the rotation-permitted state (a state in which rotation of the outer ring 4 is permitted) to the rotation-blocked state (a state in which rotation of the outer ring 4 is blocked) or from unintentionally returning to the rotation-permitted state after switching to the rotation-blocked state.

[0049] Furthermore, as shown in Figures 5 and 6, this rotation braking device can prevent deformation, etc., of the engaging protrusions 30 or non-groove portions 34 due to excessive load when a torque greater than expected acts between the outer ring 4 and the friction plate 9 with the engaging protrusions 30 dropped into the grooves 33. That is, as shown in Figures 5 and 6, after the friction surface 9a of the friction plate 9 frictionally engages with the axial end face 4a of the outer ring 4 and the engaging protrusions 30 drop into the grooves 33, if a torque greater than expected acts between the friction plate 9 and the outer ring 4 before the roller 6 shown in Figure 2 engages between the cam surface 16 on the outer circumference of the inner ring 5 and the cylindrical surface 17 on the inner circumference of the outer ring 4 to prevent relative rotation between the outer ring 4 and the inner ring 5, there is a problem in that the engaging protrusions 30 or non-groove portions 34 may be subjected to excessive load and may become deformed, etc.

[0050] To address this problem, as shown in Figures 5 and 6, this rotation braking device employs a configuration in which the engaging protrusions 30 on the axial end face 4a of the outer ring 4 are separate members from the outer ring 4 that are inserted into the outer ring hole 31 so as to be able to move axially, and the engaging protrusions 30 are biased by an elastic member 32 in the direction of protruding from the outer ring hole 31. Therefore, when an unexpectedly large torque acts between the friction plate 9 and the outer ring 4 with the engaging protrusions 30 dropped into the grooves 33 as shown in Figure 7, the engaging protrusions 30 move axially due to the reaction force received from the non-groove portions 34 and enter the outer ring hole 31, thereby releasing their engagement with the non-groove portions 34, as shown in Figure 8. In this way, when an unexpectedly large torque acts between the outer ring 4 and the friction plate 9 with the engaging protrusions 30 dropped into the grooves 33, it is possible to prevent excessive loads from being applied to the engaging protrusions 30 and the non-groove portions 34.

[0051] 7, this rotation braking device uses spheres as the engaging protrusions 30, so when the engaging protrusions 30 engage with the non-groove portions 34 in the circumferential direction, the reaction force received from the non-groove portions 34 includes an axial component force. Therefore, when a torque greater than expected acts between the friction plate 9 and the outer ring 4 with the engaging protrusions 30 dropped into the groove portions 33, the reaction force received from the non-groove portions 34 can reliably move the engaging protrusions 30 in the axial direction.

[0052] 7, in this rotation braking device, the engagement surfaces 35 on both circumferential sides of the non-groove portion 34 are inclined circumferentially with respect to the axial direction, so that when the engagement protrusions 30 engage with the non-groove portion 34 in the circumferential direction, the reaction force received from the non-groove portion 34 includes an axial component force. Therefore, when a torque greater than expected acts between the friction plate 9 and the outer ring 4 with the engagement protrusions 30 dropped into the groove portion 33, the reaction force received from the non-groove portion 34 can reliably move the engagement protrusions 30 in the axial direction.

[0053] 3 and 4, in this rotation braking device, the number of engaging protrusions 30 (four in the figures) and the number of grooves 33 (five in the figures) are different from one another, so that when multiple engaging protrusions 30 fall into multiple grooves 33, the circumferential distance from each engaging protrusion 30 to the non-groove portion 34 adjacent to that engaging protrusion 30 varies depending on the engaging protrusion 30. Therefore, as shown in FIG. 6, when slippage occurs between the friction surface 9a of the friction plate 9 and the axial end face 4a of the outer ring 4, it is possible to keep small the rotation angle of the friction plate 9 from the time the slippage occurs until the relative rotation between the friction plate 9 and the outer ring 4 is restricted by engagement between the engaging protrusions 30 and the non-groove portion 34. In particular, in this embodiment, the difference between the number of engaging protrusions 30 and the number of grooves 33 is 1, so it is possible to particularly effectively keep small the rotation angle of the friction plate 9 from the time when slippage occurs between the friction surface 9a of the friction plate 9 and the axial end face 4a of the outer ring 4 until the relative rotation between the friction plate 9 and the outer ring 4 is restricted by the engagement of the engaging protrusions 30 and the non-groove portions 34.

[0054] 9 shows a second embodiment of the present invention. The second embodiment differs from the first embodiment only in that the relationship between the outer ring 4 and the inner ring 5 is reversed; specifically, in the first embodiment, the outer ring 4 is a member rotatably supported with respect to the case 3 (i.e., the stationary system), and the inner ring 5 is a non-rotating member prevented from rotating by the case 3, whereas in the second embodiment, the outer ring 4 is a non-rotating member prevented from rotating by the case 3, and the inner ring 5 is a member rotatably supported with respect to the case 3; otherwise, the configuration is the same. Therefore, parts corresponding to those in the first embodiment are designated by the same reference numerals, and their description will be omitted.

[0055] As shown in Figure 9, the outer ring 4 is prevented from rotating relative to the case 3 by a rotation-preventing member 36 (a key member in the figure). Meanwhile, the inner ring 5 is rotatably supported relative to the case 3 by a bearing 37. The inner ring 5 is provided with a rotating shaft connecting portion 14 for connecting an external rotating shaft S. In addition, a bearing 38 is incorporated between the outer ring 4 and the inner ring 5 to support the inner ring 5 rotatably relative to the outer ring 4.

[0056] 10 and 12, anti-rotation protrusions 40 that engage with anti-rotation recesses 39 formed in the roller cage 7 are formed on the inner periphery of the friction plate 9. The friction plate 9 shown in Fig. 10 is prevented from rotating on the roller cage 7 by the engagement of these anti-rotation protrusions 40 with the anti-rotation recesses 39, and is capable of moving in the axial direction while remaining in this prevented state between a position where the friction surface 9a frictionally engages with the axial end face 4a of the outer ring 4 and a position where the frictional engagement is released.

[0057] As shown in FIG. 11, a plurality of engaging protrusions 30 (four in the figure) are provided at equal intervals in the circumferential direction. As shown in FIG. 12, groove portions 33 extending in the circumferential direction and non-groove portions 34 separating the groove portions 33 are alternately formed in the circumferential direction on the friction surface 9a of the friction plate 9. A plurality of non-groove portions 34 (five in the figure) are provided at equal intervals in the circumferential direction. The same number of groove portions 33 (five in the figure) as the number of non-groove portions 34 are also provided, and the circumferential lengths of the groove portions 33 are equal to each other. The number of engaging protrusions 30 shown in FIG. 11 (four in the figure) and the number of groove portions 33 shown in FIG. 12 (five in the figure) are different from each other, and the difference between the numbers is set to 1.

[0058] An example of the operation of this rotation braking device will now be described.

[0059] When the electromagnet 12 shown in FIG. 9 is de-energized, the inner ring 5 is placed in a rotation-blocked state, where rotation is blocked. That is, when the electromagnet 12 is de-energized, the friction plate 9 shown in FIG. 10 is pressed against the axial end face 4a of the outer ring 4, which is a non-rotating member, by the biasing force of the armature spring 11, and the friction surface 9a of the friction plate 9 frictionally engages with the axial end face 4a of the outer ring 4. At this time, the rotation of the friction plate 9 is restricted by frictional resistance between the friction surface 9a of the friction plate 9 and the axial end face 4a of the outer ring 4, and the rotation of the roller cage 7, which is prevented from rotating by the friction plate 9, is also restricted. In this state, when rotation is input to the inner ring 5 from the rotating shaft S shown in FIG. 9, the inner ring 5 shown in FIG. 11 rotates relative to the roller cage 7, whose rotation is restricted, and this relative rotation moves the roller cage 7 from the neutral position to the engaged position against the spring torque of the centering spring 8. As a result, the rollers 6 engage between the cam surface 16 on the outer periphery of the inner ring 5 and the cylindrical surface 17 on the inner periphery of the outer ring 4, preventing the inner ring 5 from rotating.

[0060] On the other hand, when the electromagnet 12 is energized, the inner ring 5 enters a rotation-permitted state in which rotation is permitted. That is, when the electromagnet 12 shown in FIG. 10 is energized, the electromagnet 12 attracts the armature 10 against the biasing force of the armature spring 11, and the biasing force of the armature spring 11 no longer acts on the friction plate 9. As a result, the friction plate 9 is released from frictional engagement with the axial end surface 4a of the outer ring 4 and enters a freely rotatable state, and the roller cage 7, which is prevented from rotating by the friction plate 9, also enters a freely rotatable state. In this state, the roller cage 7 is held in a neutral position by the spring torque of the centering spring 8 (see FIG. 11). Therefore, even if the inner ring 5 is rotated, the rollers 6 do not engage between the cam surface 16 on the outer circumference of the inner ring 5 and the cylindrical surface 17 on the inner circumference of the outer ring 4, and rotation of the inner ring 5 is permitted.

[0061] Here, when the power supply to the electromagnet 12 is cut off, in order to switch from a rotation-permitted state (a state in which rotation of the inner ring 5 is permitted) to a rotation-prevented state (a state in which rotation of the inner ring 5 is prevented) based on the mechanism described above, and to maintain the rotation-prevented state thereafter, the magnitude of the frictional resistance generated between the friction surface 9a of the friction plate 9 shown in FIG. 10 and the axial end face 4a of the outer ring 4 must exceed the magnitude of the spring torque of the centering spring 8 shown in FIG. 11 (the circumferential force with which the centering spring 8 attempts to return the roller retainer 7 to the neutral position).

[0062] However, when the friction surface 9a of the friction plate 9 or the axial end face 4a of the outer ring 4 shown in Fig. 10 wears, the friction resistance generated between the friction surface 9a of the friction plate 9 and the axial end face 4a of the outer ring 4 when they frictionally engage with each other decreases. If, due to abnormal wear or the like, the magnitude of the friction resistance generated between the friction surface 9a of the friction plate 9 and the axial end face 4a of the outer ring 4 is no longer able to exceed the spring torque of the centering spring 8 shown in Fig. 11, even if the friction surface 9a of the friction plate 9 shown in Fig. 10 is pressed against the axial end face 4a of the outer ring 4 to cause frictional engagement, slippage will occur between the friction surface 9a of the friction plate 9 and the axial end face 4a of the outer ring 4, causing relative rotation between the friction plate 9 and the outer ring 4. As a result, even if the power to the electromagnet 12 is cut off, there is a problem that the state will not switch from the rotation-permitted state to the rotation-blocked state, or that even if the state does switch to the rotation-blocked state, it may unintentionally return to the rotation-permitted state thereafter.

[0063] To address this problem, as shown in Figure 10, in the rotation braking device of this embodiment, when the friction surface 9a of the friction plate 9 frictionally engages with the axial end face 4a of the outer ring 4, the engagement protrusions 30 provided on the axial end face 4a of the outer ring 4 fall into the grooves 33 of the grooves 33 and non-groove portions 34 formed alternately in the circumferential direction on the friction surface 9a of the friction plate 9, and the engagement between the engagement protrusions 30 and the non-groove portions 34 can restrict the relative rotation between the friction plate 9 and the outer ring 4. Therefore, even when the friction resistance generated between the friction surface 9a of the friction plate 9 and the axial end face 4a of the outer ring 4 becomes small, it is possible to prevent the state from switching from the rotation-permitted state (a state in which rotation of the inner ring 5 is permitted) to the rotation-blocked state (a state in which rotation of the inner ring 5 is blocked), or from unintentionally returning to the rotation-permitted state after switching to the rotation-blocked state. Other functions and effects are also similar to those of the first embodiment.

[0064] In each of the above embodiments, rollers 6 are used as engaging elements that engage between the outer ring 4 and the inner ring 5, but it is also possible to use engaging elements such as balls or sprags instead of rollers 6.

[0065] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0066] 4 outer ring 4a Axial end face 5. Inner Circle 6 Roller (engagement element) 7 Roller retainer (engager retainer) 8 Centering spring 9 Friction plate 9a Friction surface 10 Armature 11 Armature spring 12 Electromagnet 30 Engagement protrusion 31 Outer ring hole 32 Elastic member 33 Groove 34 Non-groove section 35 Engagement surface

Claims

1. outer ring (4), an inner ring (5) disposed radially inside the outer ring (4); an engaging element (6) incorporated between the outer ring (4) and the inner ring (5); an engaging element holder (7) supported movably in a circumferential direction between an engaging position where the engaging element (6) is engaged between the outer ring (4) and the inner ring (5) and a neutral position where the engaging element (6) is released; a centering spring (8) that elastically holds the engaging element retainer (7) in the neutral position; a friction plate (9) having a friction surface (9a) axially opposed to the axial end surface (4a) of the outer ring (4), and provided so as to be movable in the axial direction between a friction engagement position where the friction surface (9a) frictionally engages with the axial end surface (4a) of the outer ring (4) and a friction release position where the friction surface (9a) releases the frictional engagement with the axial end surface (4a) of the outer ring (4) in a state where the friction plate is prevented from rotating by the engaging element cage (7); an armature (10) disposed opposite to the side of the friction plate (9) facing the outer ring (4); an armature spring (11) that axially biases the friction plate (9) toward the outer ring (4) via the armature (10); an electromagnet (12) disposed opposite to the side of the armature (10) facing the friction plate (9), and attracting the armature (10) against the biasing force of the armature spring (11) when energized, An engaging protrusion (30) protruding in the axial direction toward the friction plate (9) is provided on an axial end surface (4a) of the outer ring (4), A rotational braking device characterized in that a plurality of circumferentially extending groove portions (33) and a plurality of non-groove portions (34) are formed alternately in the circumferential direction on the friction surface (9 a), and when the friction plate (9) moves to the friction engagement position, the engaging convex portions (30) fall into the groove portions (33) of the friction surface (9 a), and the relative rotation of the friction plate (9) and the outer ring (4) is restricted by the circumferential engagement of the engaging convex portions (30) and the non-groove portions (34).

2. the engaging protrusion (30) is a member separate from the outer ring (4) and inserted axially movably into an outer ring hole (31) formed in an axial end face (4a) of the outer ring (4), 2. The rotational braking device according to claim 1, wherein the engaging protrusion (30) is biased in a direction of protruding from the outer ring hole (31) by an elastic member (32) incorporated in the outer ring hole (31).

3. 3. The rotational braking device according to claim 2, wherein the engaging protrusion (30) is a sphere.

4. Engagement surfaces (35) with which the engagement protrusions (30) engage are formed at both circumferential ends of the non-groove portions (34), 4. The rotary braking device according to claim 2, wherein the engagement surface (35) is an inclined surface inclined in the circumferential direction with respect to the axial direction.

5. The engaging protrusions (30) are provided in plurality at equal intervals in the circumferential direction on the axial end face (4a) of the outer ring (4), The plurality of non-groove portions (34) are provided at equal intervals in the circumferential direction on the friction surface (9a), The circumferential lengths of the plurality of grooves (33) are equal to each other, 4. The rotational braking device according to claim 1, wherein the number of said engaging protrusions (30) and the number of said grooves (33) are different from each other.

6. 6. The rotational braking device according to claim 5, wherein the difference between the number of said engaging projections (30) and the number of said grooves (33) is one.

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