A piston damper in FIG. 6(a) is a damper which is used in the damper unit of an embodiment of the present invention and is the same type as a structure disclosed in Patent Document 1. This piston damper 5 comprises a cylinder 50; a piston 52 dividing the inside of the cylinder in an axis direction; a piston rod 53 connected to the piston 52; urging means 7 provided between a retainer 57 placed in an inner end of the piston rod and an inner bottom face of the cylinder; and an accumulator 56 held through a retainer 55. The piston rod 53 is projected to the outside from the central hole of a cap 51 through a seal member 59. Also, the piston 52 comprises an inner member 54a integrated with the inner end of the piston rod 53, and an outer member 54b loosely fitted in the inner member 54a and forming a tubular orifice with a bottom which slides and contacts the inner periphery face of the cylinder 50. Also, the piston 52 includes a coil spring 58 disposed between both members 54a, 54b and separating them in the axis direction.
In the above-mentioned piston damper 5, usually, as shown in the above-mentioned figure, the piston rod 53 is largely projected to the outside by an urging force of the urging means 7. Also, the outer member 54b is in a state of being bumped into the retainer 57 which is placed in the piston rod 27 by an urging force of the coil spring 58. From this state, if the piston rod 53 is hit into, for example, a moving body, such as a door and the like, and pushed, the piston rod 53 is pushed into the cylinder 50 against the urging force of the urging means 7. Thereby, viscous fluid on a bottom side of the cylinder moves to a top side through the orifice of the outer member 54b and a space between both members 54b, 54a, and a fluid resistance at the time diminishes the energy applied to the piston rod 53. Also, if the compression coil spring 58 is set so as to compress by a fluid resistance applied to the outer member 54b when the piston 52 moves by a certain speed or above, the inner member 54a is entered into the outer member 54b accompanied by the contraction of the coil spring 58, so that the space between both members 54a, 54b is narrowed, and a braking force due to the fluid resistance increases.
A piston damper in FIG. 6(b) is a damper which is used in a modified example of the embodiment of the present invention and is the same type as a structure disclosed in Patent Document 2. In the above-mentioned figure, the same symbols are assigned to the same functional members shown in FIG. 6(a). This piston damper 5A comprises the cylinder 50 with the cap 51; the piston 52 dividing the inside of the cylinder in the axis direction; and the piston rod 53 connected to the piston 52. The piston rod 53 is projected to the outside from the central hole of the cap 51 through a seal member which is not shown in the figure. Also, the piston 52 comprises a stopper 8 firmly fixed to the inner end of the piston rod 53, and a sliding body 9 loosely fitted in the outer periphery portion of the stopper so as to be freely movable. The sliding body 9 includes a communicating hole (orifice) with a small cross-section area which is located near the outer periphery and penetrates right and left faces, and a communicating hole with a large cross-section area which is located near the inner periphery and penetrates the right and left faces. When the piston 52 moves, a fluid passes through, so that a damping force is produced. Specifically, in this structure, for example, if the piston rod 53 is moved in a direction projecting from the inside of the cylinder 50, or inversely, if the piston rod 53 is moved in a direction wherein a projecting amount is reduced, the sliding body 9 is pushed by a left end portion or a right end portion of the stopper 8 by a frictional force produced between the sliding body 9 and the cylinder 50, and closes the above-mentioned large communicating hole. Accordingly, the sliding body 9 is moved from the orifice on the top side of the cylinder to the bottom side, or inversely, the fluid on the bottom side of the cylinder is moved from the orifice to the top side, so that a braking force due to the frictional force and the fluid can be obtained.
Patent Document 1: Japanese Unexamined Patent Publication No. 2006-29564.
Patent Document 2: Japanese Patent No. 3465978.