Rotary damper

Abstract

To provide a rotary damper which enables torque to be generated according to a rotation speed of a rotary part and can secure a large rotation speed range.SOLUTION: A rotary damper 1 includes: a housing 2 having a cylindrical wall part 6; a rotary part 3 which may rotate relative to the housing 2; and a viscous fluid 5 disposed between the wall part 6 and the rotary part 3 and generates torque by viscous resistance of the viscous fluid 5. The rotary part 3 includes: a rotating body 15 including an opposing part 20 which opposes an inner periphery part of the wall part 6 and partially exposed from the housing 2; a movable body 16 disposed between the opposing part 20 and the wall part 6 and formed separately from the rotating body 15; and biasing means 35 which biases the movable body 16 in a direction away from the wall part 6. The movable body 16 is disposed in a movable manner so as to change a gap 33 between the wall part 6 and the movable body 16 according to a magnitude relation between a centrifugal force generated by rotation of the rotary part 3 relative to the housing 2 and a biasing force generated by the biasing means 35.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a rotary damper that generates torque due to the viscous resistance of a viscous fluid.

Background Art

[0002] Conventionally, a rotary damper that attenuates the kinetic energy in a rotating mechanism by generating torque when a rotor rotates due to the viscous resistance of oil sealed inside a housing is known. Such a rotary damper is used, for example, to decelerate the falling speed when closing a lid or to attenuate the rising speed of a seat back of an automobile seat (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] The rotary damper according to claim 2 is the rotary damper according to claim 1, further comprising a convex portion formed on one of the opposing portion of the rotating body and the movable body, and a recess formed on the other of the opposing portion of the rotating body and the movable body, wherein the circumferential position of the movable body is restricted by contact between the convex portion and the recess in accordance with the rotational speed of the rotating body, and movement is assisted by a change in the contact position between the convex portion and the recess. [Effects of the Invention]

[0008] According to the rotary damper described in claim 1, in the range of low rotational speed of the rotating part, the gap between the wall and the movable body is relatively large, resulting in relatively small viscous resistance due to the viscous fluid and low torque. As the rotational speed increases, the gap between the wall and the movable body becomes relatively smaller due to the movement of the movable body, resulting in relatively large viscous resistance due to the viscous fluid and high torque. Therefore, the torque does not converge when the rotational speed of the rotating part is low, and a wide range of rotational speeds can be secured in which torque corresponding to the rotational speed of the rotating part can be generated.

[0009] According to the rotary damper of claim 2, in addition to the effects of the rotary damper of claim 1, the position of the movable body relative to the rotating body can be stabilized by the fitting of the recess and the protrusion, and the movable body can be easily moved radially by the centrifugal force acting on the movable body as a trigger without increasing the weight of the movable body, thus making it possible to achieve both a lighter rotary damper and a larger torque when the rotating part rotates at high speed. [Brief explanation of the drawing]

[0010] [Figure 1] This is a longitudinal cross-sectional view showing a rotary damper according to one embodiment of the present invention. [Figure 2] This is a cross-sectional view of the rotary damper shown above. [Figure 3] The above is a cross-sectional view of a part of the rotary damper, where (a) shows the case when the rotation speed of the rotating part is low, (b) shows the case when the rotation speed of the rotating part is medium, and (c) shows the case when the rotation speed of the rotating part is high. [Figure 4] This is an exploded perspective view of the rotary damper shown above. [Figure 5] This is a perspective view of the rotary damper shown above. [Figure 6] This graph shows an example of the relationship between rotational speed and torque for the rotary damper described above and the rotary damper in the comparative example. [Modes for carrying out the invention]

[0011] Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

[0012] In Figures 1, 4, and 5, 1 is a rotary damper. The rotary damper 1 generally comprises a housing 2 having a cylindrical wall portion 6 and a rotating portion 3 that is rotatable relative to the housing 2, with the rotating portion 3 being held in the housing 2 by a holder 4. A viscous fluid 5, such as silicone oil, is sealed inside the housing 2, that is, between the wall portion 6 of the housing 2 and the rotating portion 3. The rotary damper 1 of this embodiment is a viscous damper that generates torque by utilizing the viscous resistance of the viscous fluid 5 as the rotating portion 3 rotates relative to the housing 2, and uses this torque to dampen the kinetic energy in the rotating mechanism. For the sake of clarity in the following explanation, using Figure 1 as a reference, one direction along the rotation axis A of the rotary damper 1 (direction of arrow U) will be described as the upward direction, and the opposite direction (direction of arrow D) will be described as the downward direction. However, this does not mean that the vertical direction of the rotary damper 1 in use is limited to the vertical direction described in this embodiment.

[0013] The housing 2, together with the holder 4, is a component that constitutes the casing of the rotary damper 1 while rotatably holding the rotating part 3. The housing 2 is formed from a metal material such as stainless steel.

[0014] The wall portion 6 is cylindrical and forms the outer circumference and shell of the housing 2, with the rotation axis A of the rotary damper 1 (rotating portion 3) as its central axis. In this embodiment, the wall portion 6 is formed in a flat, thin shape, with its axial dimension being smaller than its outer diameter.

[0015] Inside the wall portion 6, a cylindrical bearing portion 7 is formed coaxially or substantially coaxially with the wall portion 6 to rotatably support the rotating portion 3, and the lower end of the wall portion 6 and the lower end of the bearing portion 7 are connected by a planar closing portion 8 perpendicular to the axis. An upright portion 9 is formed at the lower end of the wall portion 6, extending in the axial direction. The upright portion 9 has a predetermined constant or substantially constant thickness. Furthermore, a holder mounting portion 10 is formed at the upper end of the wall portion 6, extending in the axial direction to which the holder 4 is attached. The holder mounting portion 10 is, for example, a female threaded portion formed on the inner circumference of the upper end of the wall portion 6. The upright portion 9 has a smaller diameter than the holder mounting portion 10, and a step is formed on the inner circumference of the wall portion 6 at the connection between the holder mounting portion 10 and the upright portion 9, that is, between the lower end of the holder mounting portion 10 and the upper end of the upright portion 9, and this step is formed as a support surface 11 that supports the holder 4.

[0016] The bearing portion 7 constitutes the inner circumference of the housing 2. The bearing portion 7 has an outer diameter smaller than the inner diameter of the wall portion 6 and is located inward from the wall portion 6. The rise of the bearing portion 7 from the closing portion 8 is set lower than that of the wall portion 6. For example, in the illustrated example, the rise of the bearing portion 7 from the closing portion 8 is less than half the height of the wall portion 6.

[0017] Furthermore, mounting portions 12 are formed on the outer periphery of the wall portion 6 for directly or indirectly attaching the housing 2 to the fixed first mounting member. The mounting portions 12 protrude outward from the wall portion 6 in a flange-like manner. In this embodiment, the mounting portions 12 are connected to the lower end of the wall portion 6. The mounting portions 12 are formed in a flat plate shape. The mounting portions 12 are located on opposite sides of each other with respect to the rotation axis A of the rotary damper 1 (rotating portion 3), for example. Each mounting portion 12 has a hole portion 13 formed in the vertical direction, which is the thickness direction, into which a mounting member such as a screw for attaching the housing 2 is inserted.

[0018] The rotating part 3 is also called a rotor, etc. The rotating part 3 has a rotating body 15, a movable body 16 separate from the rotating body 15, and a biasing means 35 that biases the movable body 16 in a direction away from the wall portion 6.

[0019] The rotating body 15 has a part exposed from the housing 2, and the exposed part is attached to a second attachment member on the rotating side that rotates with respect to the first attachment member on the fixed side. The rotating body 15 is formed in a substantially cylindrical shape. The rotating body 15 is formed of a metal member such as a brass material. In the present embodiment, the rotating body 15 is rotatable 360° with respect to the housing 2.

[0020] A flange portion 18 is formed on the outer peripheral portion of the rotating body 15 that faces the inner peripheral portion of the wall portion 6. The flange portion 18 extends continuously over the entire circumference of the rotating body 15. The flange portion 18 is located at the intermediate portion in the vertical direction of the rotating body 15. In the outer peripheral portion of the rotating body 15, the portion below the flange portion 18 is an opposing portion 20 that faces the inner peripheral portion of the wall portion 6, and the portion above the flange portion 18 is an outer peripheral seal portion 21 that faces the inner peripheral portion of the wall portion 6. The tip of the flange portion 18 is close to or in contact with the inner peripheral portion of the wall portion 6, and a fluid chamber 22 in which the viscous fluid 5 is accommodated is defined between the wall portion 6 and the closing portion 8 of the housing 2 and the flange portion 18 and the opposing portion 20 of the rotating body 15.

[0021] The opposing portion 20 is formed in a substantially cylindrical surface shape and is located away from the rotation axis A side, that is, the radially inner side, of the housing 2's wall portion 6 with respect to the rotary damper 1 (rotating portion 3). A movable body 16 is interposed between the opposing portion 20 and the wall portion 6.

[0022] The outer peripheral seal portion 21 is formed in a substantially cylindrical surface shape and is located away from the rotation axis A side, that is, the radially inner side, of the housing 2's wall portion 6 with respect to the rotary damper 1 (rotating portion 3). A seal member 24 is interposed between the outer peripheral seal portion 21, the wall portion 6, and the holding body 4 to prevent the outflow of the viscous fluid 5 from the fluid chamber 22 to the upper part of the housing 2. The seal member 24 is formed in an annular shape, the outer peripheral portion is press-fitted to the inner peripheral portion of the wall portion 6, and the inner peripheral portion is press-fitted to the outer peripheral seal portion 21. As the seal member 24, for example, an X-ring having an X-shaped cross section is preferably used.

[0023] Furthermore, the rotating body 15 has a recessed fitting portion 26 at its lower end into which the bearing portion 7 of the housing 2 is slidably fitted. The fitting portion 26 is a recess with a circular cross-section, into which the bearing portion 7 is inserted and fitted from below, so that the rotating body 15 is rotatably supported by the bearing portion 7. The upper end of the fitting portion 26 is exposed downward through the inside of the bearing portion 7.

[0024] An inner circumferential seal portion 28 is formed below and outward from the fitting portion 26, located on the back side of the opposing portion 20. That is, a step is formed at the connection between the lower end of the fitting portion 26 and the upper end of the inner circumferential seal portion 28. The inner circumferential seal portion 28 is formed in a generally cylindrical shape. A seal member 29 is interposed between the inner circumferential seal portion 28 and the bearing portion 7 of the housing 2 to prevent the viscous fluid 5 from flowing out of the fluid chamber 22 to the lower part of the housing 2. The seal member 29 is formed in an annular shape, with its outer circumference pressed against the inner circumferential seal portion 28 and its inner circumference pressed against the outer circumference of the bearing portion 7. As the seal member 29, for example, an X-ring with an X-shaped cross-section is preferably used.

[0025] Furthermore, the rotating body 15 has an insertion portion 30 formed at its upper end, which is inserted and fitted into the holder 4. The insertion portion 30 is formed in a cylindrical shape with a reduced diameter relative to the outer peripheral seal portion 21, and is connected to the upper part of the outer peripheral seal portion 21 in a stepped manner. The insertion portion 30 is coaxial or substantially coaxial with the outer peripheral seal portion 21.

[0026] Furthermore, the insertion portion 30 has a connection hole 31 which connects to the second mounting member on the rotating side. The connection hole 31 is formed in the insertion portion 30 along the rotation axis A of the rotary damper 1 (rotating portion 3). The connection hole 31 penetrates from the upper end to the lower end of the insertion portion 30 and is connected to the fitting portion 26. The connection hole 31 is formed with a non-circular cross-section to prevent the second mounting member on the rotating side and the rotating body 15 from rotating freely with each other, and in this embodiment it is a square-shaped (square-shaped) corner hole.

[0027] Furthermore, the rotating body 15 has multiple holding portions 32 that protrude radially outward from its outer circumference. For example, the number of holding portions 32 is set according to the number of movable bodies 16. In the illustrated example, each holding portion 32 is positioned between the movable bodies 16, 16. The multiple holding portions 32 also define the circumferential range of movement of the movable bodies 16 relative to the rotating body 15. The multiple holding portions 32 are in close proximity to or in contact with the inner circumference of the wall portion 6.

[0028] The movable body 16 is also called a vane or the like. The entire movable body 16 is housed between the housing 2 and the retaining body 4 and is not exposed to the outside. One or more movable bodies 16 are set up. In this embodiment, multiple movable bodies 16, for example three, are set up and are equally distributed in the circumferential direction of the rotating body 15. The movable body 16 is formed in an arc shape and is interposed between the opposing part 20 of the rotating body 15 and the wall part 6 of the housing 2, and is located within the fluid chamber 22. At least the outer circumference of the movable body 16, and in this embodiment the entire body, is located within the viscous fluid 5. The movable body 16 is formed from a metal member such as brass. In the fluid chamber 22, a gap (clearance) 33 is formed between the outer circumference of the movable body 16 and the inner circumference of the wall part 6 through which the viscous fluid 5 passes. The movable body 16 is arranged to move radially toward and away from the opposing part 20 of the rotating body 15, and this movement increases or decreases the size of the gap 33.

[0029] The movable body 16 is biased by the biasing means 35 in a direction away from the wall portion 6, that is, towards the rotation axis A of the rotary damper 1 (rotating portion 3), i.e., radially inward. In other words, the movable body 16's radially outward movement relative to the opposing portion 20 of the rotating body 15 is elastically restricted by the biasing means 35. In this embodiment, the biasing means 35 is preferably an elastic member such as a coil spring. For example, the biasing means 35 is arranged to wrap around the entire outer circumference of a plurality of movable bodies 16, and biases the movable bodies 16 from the outer circumference side of the movable bodies 16.

[0030] In the illustrated example, the biasing means 35 is formed by circumferencing a linear elastic material in a spiral shape coaxial with or substantially coaxial with the rotation axis A of the rotary damper 1 (rotating part 3), and the linear elastic material is positioned close to or in contact with the outer circumference of the movable body 16. In this embodiment, the biasing means 35 holds the movable body 16 in contact with the opposing part 20 of the rotating body 15. That is, the biasing means 35 functions as a holding means that holds the movable body 16 relative to the rotating body 15. In other words, the movable body 16 is not connected to the rotating body 15, is movable radially and circumferentially relative to the rotating body 15, and is held by the biasing means 35 or the holding part 32 of the rotating body 15 so as to rotate in the same direction as the rotating body 15. The biasing force of the biasing means 35 is set according to the diameter of its circumferential portion, and the larger the diameter of the circumferential portion is compared to the natural state, the greater the biasing force. The biasing force of the biasing means 35 is set based on the relationship between the rotational speed and torque required for the rotary damper 1, by setting the wire diameter and number of turns of the elastic material, so as not to exceed the centrifugal force generated on the movable body 16 in accordance with the rotational speed of the rotating part 3 (rotating body 15) and the total weight of the movable body 16 (weight per unit × number of units). In this embodiment, the biasing means 35 may or may not apply a biasing force to the movable body 16 when the movable body 16 is in close contact with the opposing part 20 of the rotating body 15.

[0031] Preferably, the biasing means 35 is held in a retaining groove 37 formed in the movable body 16, as shown in Figures 2 and 4. The retaining groove 37 is formed on the outer circumference of the movable body 16, extending circumferentially across both ends of the movable body 16. The retaining groove 37 positions the biasing means 35 so as not to protrude radially outward, i.e., toward the wall portion 6, relative to the outer circumference of the movable body 16, and is positioned away from the wall portion 6. Similarly, the biasing means 35 is held in a retaining groove 38 formed in the retaining portion 32 of the rotating body 15. The retaining groove 38 is formed on the outer circumference of each retaining portion 32, extending circumferentially across both ends of each retaining portion 32.

[0032] Preferably, as shown in Figure 2, a movement assisting means 40 is provided to assist the radial movement of the movable body 16 relative to the rotating body 15. The movement assisting means 40 consists of a convex portion 41 and a concave portion 42. The convex portion 41 is formed on one of the opposing portion 20 of the rotating body 15 and the movable body 16, and the concave portion 42 is formed on the other of the opposing portion 20 of the rotating body 15 and the movable body 16. In this embodiment, the convex portion 41 is formed on the opposing portion 20 and the concave portion 42 is formed on the movable body 16. In the illustrated example, two convex portions 41 and two concave portions 42 are set for each movable body 16, spaced apart in the circumferential direction.

[0033] The convex portion 41 has an outer circumference formed in an arc shape and protrudes radially, while the concave portion 42 is recessed in an arc shape corresponding to the shape of the outer circumference of the convex portion 41. The amount of protrusion of the convex portion 41 from the opposing portion 20 is set to be less than or equal to the maximum size of the gap 33.

[0034] Preferably, the circumferential lengths of the convex portion 41 and the concave portion 42 are set to be greater than the circumferential distance between the end of the movable body 16 and the holding portion 32 of the rotating body 15. In other words, the lengths of the convex portion 41 and the concave portion 42 are set so that they overlap circumferentially even when the end of the movable body 16 has moved circumferentially relative to the rotating body 15 until it contacts the holding portion 32 of the rotating body 15.

[0035] The retainer 4 shown in Figures 1 and 4 is also called a plug or the like. The retainer 4 is attached to the upper part of the housing 2 and holds the rotating part 3 in the housing 2. The retainer 4 is formed in a disc shape, and a mounting portion 45 is formed on its outer circumference to be attached to the retainer mounting portion 10 of the housing 2. In this embodiment, the mounting portion 45 is, for example, a male threaded portion that is screwed into the retainer mounting portion 10. In addition, a circular opening 46 is formed in the center of the retainer 4 into which the insertion portion 30 of the rotating part 15 is inserted. The retainer 4 is made of a metal material such as stainless steel.

[0036] The rotary damper 1 is constructed by attaching a sealing member 29, a movable body 16, a biasing means 35, and a rotating body 15 to the housing 2, injecting a viscous fluid 5, and then attaching a sealing member 24 and a holder 4. In this state, the sealing member 29 is pressed against the inner circumferential sealing portion 28 and the bearing portion 7, and the sealing member 24 is pressed against the outer circumferential sealing portion 21, the wall portion 6, and the holder 4, so that the viscous fluid 5 is held liquid-tight in the fluid chamber 22.

[0037] The rotary damper 1 is used with the housing 2 attached to the first mounting member on the fixed side, and the rotating body 15 of the rotating part 3 attached to the second mounting member on the rotating side.

[0038] When the second mounting member rotates relative to the first mounting member, the rotating body 15 of the rotating part 3 rotates in accordance with it around the rotation axis A relative to the housing 2. In the rotating part 3, the movable body 16, which is held by the rotating body 15 by the biasing means 35, rotates integrally with the rotating body 15 in the same direction.

[0039] At this time, a centrifugal force acts on the movable body 16 radially outward due to the rotation of the rotating part 3, and this centrifugal force increases as the rotational speed of the rotating part 3 increases. On the other hand, a biasing force acts on the movable body 16 radially inward from the biasing means 35. Therefore, the radial position of the movable body 16 changes according to the relative magnitudes of these centrifugal forces and biasing forces.

[0040] When the rotational speed of the rotating part 3 (rotating body 15) is low, the centrifugal force acting on the movable body 16 is relatively small, and as shown in Figure 3(a), the movable body 16 is held in close proximity to or in close contact with the opposing part 20 of the rotating body 15, and the gap 33 is set to be relatively wide. As a result, the viscous resistance of the viscous fluid 5 passing through the gap 33 is relatively suppressed, and the resulting torque is small.

[0041] Furthermore, the greater the rotational speed of the rotating part 3 (rotating body 15), the greater the centrifugal force acting on the movable body 16 relative to the biasing force. As a result, the movable body 16 moves radially outward, deforming the biasing means 35 outward against the biasing force of the biasing means 35. At this time, the movement of the movable body 16 due to centrifugal force triggers the recess 42 to ride up onto the convex portion 41, and the contact position between the convex portion 41 and the recess 42 changes circumferentially. This assists in increasing the radially outward movement of the movable body 16 in proportion to the rotational speed of the rotating part 3 (rotating body 15), as shown in Figures 3(b) and 3(c). Therefore, as the rotational speed of the rotating part 3 (rotating body 15) increases, the gap 33 narrows, and the viscous resistance of the viscous fluid 5 passing through the gap 33 increases, resulting in a larger torque.

[0042] Figures 3(a) to 3(c) illustrate the state in which the rotating part 3 (rotating body 15) is rotated in a clockwise direction, but the same applies when the rotation direction is counterclockwise. Also, for the sake of clarity, only the positional relationship between one protrusion 41 of the rotating body 15 and one recess 42 of one movable body 16 is illustrated, but the same applies to the remaining recess 42 of this movable body 16, as well as the other protrusions 41 and the recesses 42 of the other movable bodies 16.

[0043] In this way, the movable body 16 interposed between the opposing portion 20 of the rotating body 15 and the wall portion 6 of the housing 2 is biased by the biasing means 35 in a direction away from the wall portion 6, and the movable body 16 is made movable so that the gap 33 between the wall portion 6 and the movable body 16 changes according to the relationship between the magnitude of the centrifugal force generated by the rotation of the rotating part 3 relative to the housing 2 and the biasing force by the biasing means 35. In the range where the rotation speed of the rotating part 3 (rotating body 15) is small, the gap 33 between the wall portion 6 and the movable body 16 is relatively large, so the viscous resistance due to the viscous fluid 5 is relatively small and the torque is small. As the rotation speed increases, the gap 33 between the wall portion 6 and the movable body 16 is automatically adjusted by the movement of the movable body 16 and becomes relatively small, so the viscous resistance due to the viscous fluid 5 is relatively large and the torque is large. Therefore, compared to a comparative example where the gap 33 is constant, the torque does not converge when the rotational speed of the rotating part 3 (rotating body 15) is low, and a larger range of rotational speeds can be secured in which torque corresponding to the rotational speed of the rotating part 3 (rotating body 15) can be generated. For example, in the rotary damper 1 of this embodiment, as shown by the solid line in Figure 6, the relationship between rotational speed (angular velocity) and torque can be set linearly over a wider range of rotational speeds compared to the conventional example shown by the dashed line, and the torque increases proportionally and gradually in the entire usable range of rotational speeds as the rotational speed of the rotating part 3 (rotating body 15) increases. Therefore, the rotary damper 1 of this embodiment can be used for new applications that were not applicable to the rotary damper of the conventional example.

[0044] Furthermore, by forming a convex portion 41 on one of the opposing portion 20 of the rotating body 15 and the movable body 16, and a concave portion 42 on the other, the circumferential position of the movable body 16 relative to the rotating body 15 is restricted by the contact between the convex portion 41 and the concave portion 42 according to the rotational speed of the rotating part 3 (rotating body 15), and the radial movement of the movable body 16 is assisted by the change in the contact position between the convex portion 41 and the concave portion 42. Thus, the position of the movable body 16 relative to the rotating body 15 can be stabilized by the fitting of the convex portion 41 and the concave portion 42, and it becomes possible to easily move the movable body 16 radially using the centrifugal force acting on the movable body 16 as a trigger without increasing the weight of the movable body 16. In this way, it is possible to achieve both a reduction in the weight of the rotary damper 1 by reducing the weight of the movable body 16 and an increase in the torque when the rotating part 3 (rotating body 15) rotates at high speed. [Industrial applicability]

[0045] The present invention is suitably used, for example, as a damping device for reducing kinetic energy in a rotating mechanism. [Explanation of Symbols]

[0046] 1 Rotary damper 2 Housing 3. Rotating part 5 Viscous fluid 6 Wall 15. Solids of revolution 16 Movable body 20 Opposing part 33 gaps 35. Biasing means 41 Convex part 42 recess

Claims

1. A rotary damper comprising a housing having a cylindrical wall, a rotating part rotatable relative to the housing, and a viscous fluid interposed between the wall and the rotating part, wherein torque is generated by the viscous resistance of the viscous fluid, The rotating part is A rotating body having an opposing portion that faces the inner circumference of the wall portion, and a portion of which is exposed from the housing, A movable body, separate from the rotating body, is interposed between the opposing portion and the wall portion. The movable body has a biasing means that biases it away from the wall portion, The movable body is positioned to move in such a way that it changes the gap between the wall and the movable body according to the relationship between the centrifugal force generated by the rotation of the rotating part relative to the housing and the biasing force provided by the biasing means. A rotary damper characterized by the following features.

2. A protrusion formed on one of the opposing parts of the rotating body and the movable body, The rotating body comprises a recess formed on the other side of the opposing part and the movable body, The circumferential position of the movable body relative to the rotating body is restricted by the contact between the protrusion and the recess in accordance with the rotational speed of the rotating part, and its movement is assisted by the change in the contact position between the protrusion and the recess. The rotary damper according to feature 1.

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