FIG. 13 is an explanatory diagram of a conventional rotary damper. The rotary damper in FIG. 13 includes a cylinder 1391 providing mutually confronting support parts 13911, a rotary shaft 1392 supported by the support parts 13911, 13911′ and being free to rotate by a specified angle, and providing communication paths 13921, 13921′ at both leading ends, and control valves 1393, 1393′ having a nearly U-shape form and provided at internal confronting positions of the cylinder 1391, and freely fitted with a leading end of the rotary shaft 1392. The control valves 1393, 1393′ are provided with control openings 13931, 13931′ at one side of nearly U-shape form, and control walls 13932, 13932′ at positions confronting the control openings 13931, 13931′. The cylinder 1391, having the confronting support parts 13911, 13911′, the leading end of the rotary shaft 1392, and the control walls 13932, 13932′, composes a decompression chamber 13941, a pressurizing chamber 13942, a decompression chamber 13943, and a pressurizing chamber 13944 (in clockwise direction) (the rotating direction of the rotary shaft 1392 is the counterclockwise direction in the drawing).
Suppose the rotary shaft 1392 rotates counterclockwise as indicated by the arrow, the leading end of the rotary shaft 1392 contacts with the control walls 13932, 13932′ of the cylinder 1391, and the pressure is raised in the adjacent pressurizing chambers 13942, 13944. On the other hand, the rotary shaft 1392 rotates in the opposite direction of the arrow (clockwise) In this case, the leading end of the rotary shaft 1392 is departed from the control walls 13932, 13932′. As a result, the decompression chambers 13941, 13943 are decompressed as the oil flows out through the communication paths 13921, 13921′ and the control openings 13931, 13931′ provided at the leading end of the rotary shaft 1392. The detail of the rotary damper is described, for example, in Japanese Patent Publication No. 2882109.
There was a problem that the conventional rotary damper was thin in the wall thickness of the rotary shaft 1392, the communication paths 13921, 13921′, the control valves 1393, 1393′, the control openings 13931, 13931′, and the control walls 13932, 13932′, and was poor in durability, and could not withstand a large load. To solve the problem, there was a problem that the rotary damper must be increased in thickness or size of the entire structure. For example, the toilet seat or toilet lid must be installed in a predetermined narrow place, and a reduced diameter was expected but it was not realized. Besides, the rotary damper used in the toilet seat or toilet lid is used by unspecified people, such as guests or children, not knowing how to increase or decrease the applying force, and if an excessive force is applied accidentally when closing, there was no rotary damper to withstand sufficient intensity.
To solve these problems, it is hence an object of the invention to present a breakdown preventive mechanism (device) of a rotary damper, reduced in the size of the rotary damper, and capable of preventing from breaking down if a force more than specified is applied.