JP7609656B2 - Viscous Damper - Google Patents

Description

The present invention relates to a viscous damper.

Conventionally, a seismically isolated building has been known in which a laminated rubber layer made of multiple rubber plates and steel plates is provided on a foundation (substructure), along with energy absorbing means such as lead plugs, and the building (superstructure) is supported on top of these in a seismic isolation manner.
In such seismically isolated buildings, one possible method for controlling excessive displacement of the building (superstructure) in the event of an earthquake motion that exceeds the earthquake motion assumed in normal design (earthquake motion that exceeds the assumptions made in the design) is to further install a viscous damper extending horizontally between the lower structure and the superstructure.
However, if this method is used to respond to earthquake motions that exceed the design assumptions and are considered to have a very low occurrence frequency and probability, the viscous dampers will also exert damping force for earthquakes with a higher occurrence frequency and probability, reducing the seismic isolation performance and causing unnecessary seismic forces to be generated in the superstructure.

One possible solution is to install a viscous damper that has a mechanism for switching the damping force depending on the magnitude and velocity of the displacement occurring in the seismic isolation layer (see, for example, Patent Document 1).
The hydraulic shock absorber (viscous damper) of Patent Document 1 is provided with a passage through which oil passes and a variable throttle mechanism, and the damping force changes according to the displacement of the piston.

Japanese Patent Application Publication No. 1-269741

However, viscous dampers having a mechanism for switching damping force according to the magnitude and velocity of the displacement occurring in the seismic isolation layer, as described in Patent Document 1, have a complex configuration, so it is desirable to use a viscous damper with a simple configuration that can exert a damping force according to seismic motion that exceeds the assumptions in the design.
The present invention has been made in consideration of the above-mentioned circumstances, and aims to provide a viscous damper with a simple configuration that can exert a damping force in response to earthquake motion that exceeds the assumptions in the design, without reducing the seismic isolation performance against earthquake motion assumed in normal design.

In order to achieve the above-mentioned object, one embodiment of the present invention is a viscous damper comprising a cylinder filled with a viscous fluid, a piston rod arranged on the axis of the cylinder, and a piston connected to the piston rod, and is characterized in that the inner surface of the cylinder is provided with a plurality of inner diameter portions having different inner diameters.
Moreover, one embodiment of the present invention is characterized in that the multiple inner diameter portions have a large diameter inner diameter portion and a small diameter inner diameter portion having an inner diameter smaller than that of the large diameter inner diameter portion, the large diameter inner diameter portion is disposed in the center of the axial direction of the cylinder, and the small diameter inner diameter portions are provided on both sides of the large diameter inner diameter portion.
In addition, one embodiment of the present invention is characterized in that the small diameter inner diameter portions arranged on both sides of the large diameter inner diameter portion include a plurality of small diameter inner diameter portions having different inner diameters, and the plurality of small diameter inner diameter portions have smaller inner diameters each time they are arranged away from the large diameter inner diameter portion.
Moreover, one embodiment of the present invention is characterized in that the inner diameter portions adjacent to each other in the axial direction of the cylinder are connected by a connection surface where the inner diameter changes continuously between the inner diameter portions.
Moreover, one embodiment of the present invention is characterized in that the connection surface is an inclined surface that connects the inner circumferential surfaces of the inner diameter portions adjacent to each other in the axial direction of the cylinder.
Moreover, one embodiment of the present invention is characterized in that an inner peripheral surface of the cylinder is formed symmetrically with respect to a central portion in an axial direction of the cylinder.
In addition, one embodiment of the present invention is characterized in that the piston rod penetrates the cylinder from one end to the other end in the axial direction, and the piston is provided in the center of the piston rod in the longitudinal direction.
Moreover, one embodiment of the present invention is characterized in that the viscous damper is installed in a seismically isolated building having an upper structure supported for seismic isolation on a lower structure, the piston rod protruding from one end in the axial direction of the cylinder, and mounting members are attached to the end of the piston rod protruding from the cylinder and the other end in the axial direction of the cylinder, one of the mounting members is connected to the upper structure in a state in which it can swing around an axis extending in the vertical direction, and the other of the mounting members is connected to the lower structure in a state in which it can swing around an axis extending in the vertical direction.
Moreover, one embodiment of the present invention is characterized in that the viscous damper is installed in a seismically isolated building having an upper structure supported for seismic isolation on a lower structure, an attachment member is attached to an end of the piston rod protruding from one axial end of the cylinder, and a connecting member having a through hole is attached to the other axial end of the cylinder, the attachment member is connected to the upper structure in a state in which it can swing around an axis extending in the vertical direction, the end of the piston rod protruding from the other axial end of the cylinder through the through hole is inserted into a hole provided in the lower structure, and the connecting member is connected to a location of the lower structure around the hole.
Moreover, one embodiment of the present invention is characterized in that the viscous damper is installed in a seismically isolated building having an upper structure supported for seismic isolation on a lower structure, an attachment member is attached to an end of the piston rod protruding from one axial end of the cylinder, and a connecting member having a through hole is attached to the other axial end of the cylinder, the attachment member is connected to the lower structure in a state in which it can swing around an axis extending in the vertical direction, the end of the piston rod protruding from the other axial end of the cylinder through the through hole is inserted into a hole provided in the upper structure, and the connecting member is connected to a portion of the upper structure around the hole.

According to one embodiment of the present invention, the viscous damper has multiple inner diameter sections with different inner diameters on the inner circumferential surface of the cylinder, which makes it possible to switch the damping force exerted in response to seismic motion. This simple configuration is advantageous in exerting a damping force in response to seismic motion that exceeds the assumptions in the design without reducing the seismic isolation performance against seismic motion assumed in the normal design.

In addition, by configuring the multiple inner diameter sections on the inner circumferential surface of the cylinder with a large inner diameter section and a small inner diameter section with an inner diameter smaller than that of the large inner diameter section, with the large inner diameter section located in the center of the cylinder's axial direction and the small inner diameter sections provided on both sides of the large inner diameter section, it is possible, with a simple configuration, to move the piston in the large inner diameter section when earthquake motion assumed in the normal design occurs, without reducing the seismic isolation performance, and to move the piston in the small inner diameter section when earthquake motion that exceeds the design assumption occurs, thereby exerting a damping force corresponding to the earthquake motion that exceeds the design assumption.

In addition, if the small inner diameter sections arranged on both sides of the large inner diameter section are configured to include multiple small inner diameter sections with different inner diameters, and the inner diameter of each of the multiple small inner diameter sections is reduced as they are positioned away from the large inner diameter section, when earthquake motion that exceeds the design assumption occurs, the piston can be moved sequentially to the multiple small inner diameter sections, thereby gradually increasing the damping force according to the magnitude of the earthquake motion that exceeds the design assumption.

In addition, if adjacent inner diameter sections in the axial direction of the cylinder are connected by a connection surface where the inner diameter changes continuously, when seismic motion occurs that exceeds the assumptions in the design, the piston passes through the connection surface in such a way that the damping force changes continuously as it moves from the large inner diameter section to the small inner diameter section, so that the damping force changes gradually when the damping force switches, which is advantageous in preventing or mitigating impact forces due to the damping force switching.

In addition, if the inner circumferential surfaces of adjacent inner diameter sections in the axial direction of the cylinder are connected by an inclined surface, when an earthquake motion occurs that exceeds the assumptions made in the design, the piston passes through the inclined surface so that the damping force changes smoothly as it moves from the large inner diameter section to the small inner diameter section, so that the damping force gradually increases as the damping force switches, which is advantageous in preventing or mitigating the impact force caused by the switch in damping force.

In addition, forming the inner circumferential surface of the cylinder symmetrically with respect to the center of the cylinder's axis is advantageous in that it produces the same level of damping force regardless of the direction in which the upper structure moves along the axis of the cylinder.

Furthermore, if the piston rod penetrates the cylinder from one end to the other in the axial direction and the piston is located in the center of the piston rod in the longitudinal direction, the piston rod is supported at both ends of the cylinder, which alleviates concerns about buckling. In addition, the diameter of the piston rod can be made smaller than when the piston rod protrudes only from one end of the cylinder, which is advantageous in reducing the weight of the viscous damper.
Furthermore, by installing the piston rod penetrating from one end to the other end in the axial direction of the cylinder, the internal mechanism of the cylinder when the piston is located in the center of the axial direction of the cylinder can be made symmetrical with respect to the center, and the same damping mechanism is obtained regardless of whether the piston moves in any direction in the axial direction of the cylinder, which is advantageous in providing a stable damping force against piston displacement.

In addition, if mounting members are attached to the end of the piston rod protruding from the cylinder and the other end in the axial direction of the cylinder, and one mounting member is connected to the upper structure in a state in which it can swing about an axis extending vertically, and the other mounting member is connected to the lower structure in a state in which it can swing about an axis extending vertically, the viscous damper can be swung horizontally even if the upper structure moves horizontally relative to the lower structure due to seismic motion, which is advantageous in avoiding damage to the viscous damper.

In addition, if an attachment member is attached to the end of the piston rod protruding from one axial end of the cylinder, a connection member with a through hole is attached to the other axial end of the cylinder, the attachment member is connected to the upper structure in a state in which it can swing around an axis extending in the vertical direction, the end of the piston rod protruding from the other axial end of the cylinder through the through hole is inserted into a hole provided in the lower structure, and the connection member is connected to a location on the lower structure around the hole, the other axial end of the cylinder is inserted into the hole in the lower structure, which is advantageous in reducing the installation space of the viscous damper.

In addition, if an attachment member is attached to the end of the piston rod protruding from one axial end of the cylinder, and a connection member with a through hole is attached to the other axial end of the cylinder, the attachment member is connected to the lower structure in a state in which it can swing around an axis extending in the vertical direction, the end of the piston rod protruding from the other axial end of the cylinder through the through hole is inserted into a hole provided in the upper structure, and the connection member is connected to a location on the upper structure around the hole, then the other axial end of the cylinder is inserted into the hole in the upper structure, which is advantageous in reducing the installation space of the viscous damper.

1 is a schematic diagram showing a seismically isolated building provided with a viscous damper according to a first embodiment. 1 is a configuration diagram of a viscous damper according to a first embodiment; 4 is an explanatory diagram showing a state in which the viscous damper according to the first embodiment is most compressed; FIG. 4 is an explanatory diagram showing a state in which the viscous damper according to the first embodiment is fully extended; FIG. FIG. 4 is an explanatory diagram showing a viscous damper according to the first embodiment provided with a cover; FIG. 4 is a configuration diagram of a viscous damper according to a modified example of the first embodiment. FIG. 11 is a configuration diagram of a viscous damper according to a second embodiment. FIG. 11 is an explanatory diagram showing a state in which the viscous damper according to the second embodiment is most compressed. FIG. 11 is an explanatory diagram showing a state in which the viscous damper according to the second embodiment is fully extended. FIG. 11 is a configuration diagram of a viscous damper according to a modified example of the second embodiment. FIG. 13 is a configuration diagram of a viscous damper according to a third embodiment.

(First embodiment)
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
As shown in Figure 1, a seismically isolated building has an upper structure 4 (building) supported in a seismically isolated manner on a lower structure 2 (foundation), and a laminated rubber 6 and a viscous damper 10A are installed between the lower structure 2 and the upper structure 4.

The laminated rubber 6 is an isolator that supports the upper structure 4 and moves the upper structure 4 horizontally when an earthquake occurs, thereby making it difficult for ground vibrations caused by an earthquake to be transmitted to the upper structure 4.
In the example of FIG. 1, a laminated rubber is used as the isolator, in which multiple rubber plates and steel plates are alternately stacked. However, in addition to this, the isolator may also use a rolling bearing, a sliding bearing, or the like.

The viscous damper 10A exerts a horizontal damping force against the shaking of the upper structure 4, which is displaced horizontally by the laminated rubber 6 when an earthquake occurs.
In this embodiment, an example is shown in which the viscous damper 10A is installed vertically between the foundation as the lower structure 2 and the building as the upper structure 4, but it may also be installed between each floor of a building, such as between the lower and upper floors of the building, or it may be installed horizontally between the building and a foundation provided on the periphery of the building.

As shown in Figures 2 to 4, the viscous damper 10A comprises a cylinder 12, a piston rod 14, a piston 16, and mounting members 18 and 20, all of which are made of metal.

The cylinder 12 is a container composed of a cylindrical peripheral wall 1202 and a disk-shaped first end wall 1204 and a second end wall 1206 respectively provided at both axial ends of the peripheral wall 1202, and a viscous fluid, hydraulic oil V, is sealed inside.
The hydraulic oil V is, for example, a highly viscous oil (silicon oil) that has excellent heat resistance, cold resistance, and chemical stability, is non-corrosive, does not adversely affect other materials, and is harmless.
The interior of the cylinder 12 is divided into two areas by the piston 16, with the area on the first end wall 1204 side of the piston 16 being the first cylinder chamber 12A, and the area on the second end wall 1206 side being the second cylinder chamber 12B.
The inner diameter of the inner circumferential surface 1202A of the peripheral wall 1202 of the cylinder 12 will be described later.

The piston rod 14 is a rod-shaped member connected to the piston 16 and arranged on the axis of the cylinder 12, and protrudes from a first end wall 1204 at one end 12C of the cylinder 12 in the axial direction.
The piston rod 14 is liquid-tightly inserted through an opening 1204A formed in the center of the first end wall 1204 via a seal member (not shown).
One mounting member 18 is attached to one end 14A of the piston rod 14 protruding from the cylinder 12.

The piston 16 is a disk-shaped member, and is disposed so that the center of the disk is aligned with the axis of the cylinder 12 via the piston rod 14 .
A gap S through which hydraulic oil V can pass is provided between the outer peripheral surface 16A of the piston 16 and the inner peripheral surface 1202A of the peripheral wall 1202 of the cylinder 12.

The mounting members 18, 20 are provided at both ends of the viscous damper 10A, respectively.
In this embodiment, one mounting member 18 is attached to one end 14A of the piston rod 14 protruding from the cylinder 12 as described above, and the other mounting member 20 is attached to the second end wall 1206 at the other axial end 12D of the cylinder 12.
As shown in FIG. 1, one mounting member 18 is connected to the upper structure 4 in a state in which it can swing about an axis 4B extending vertically, and the other mounting member 20 is connected to the lower structure 2 in a state in which it can swing about an axis 2B extending vertically.

Specifically, for example, an axis 4B inserted through an attachment hole 1802 provided in one of the attachment members 18 is connected to a retaining member 4A attached to the lower part of the upper structure 4, thereby connecting one of the attachment members 18 to the upper structure 4 in a state in which the one of the attachment members 18 can swing around an axis passing through the center of the attachment hole 1802.
Similarly, the axis 2B inserted into the mounting hole 2002 provided in the other mounting member 20 is connected to the retaining member 2A attached to the upper part of the lower structure 2, so that the other mounting member 20 is connected to the lower structure 2 in a state in which it can swing around an axis passing through the center of the mounting hole 2002.

In this embodiment, one mounting member 18 is connected to the upper structure 4, and the other mounting member 20 is connected to the lower structure 2, but they may be arranged in the opposite manner. In other words, one mounting member 18 may be connected to the lower structure 2, and the other mounting member 20 may be connected to the upper structure 4.

Next, the inner circumferential surface 1202A of the peripheral wall 1202 of the cylinder 12 will be described.
The viscous damper 10A has a plurality of inner diameter portions (large inner diameter portion 30, small inner diameter portion 32) having different inner diameters on the inner circumferential surface 1202A of the cylinder 12.
In this embodiment, the multiple inner diameter portions include a large diameter inner diameter portion 30 and two small diameter inner diameter portions 32 having an inner diameter smaller than that of the large diameter inner diameter portion 30, and a small diameter inner diameter portion 32 is provided on each side of the large diameter inner diameter portion 30.
That is, a large inner diameter portion 30 is disposed in the axial center of the cylinder 12 , and small inner diameter portions 32 are provided on both sides of the large inner diameter portion 30 , extending to both ends of the cylinder 12 .

Adjacent inner diameter portions in the axial direction of the cylinder 12, i.e., the large inner diameter portion 30 and the small inner diameter portion 32, are connected by a connection surface 34A where the inner diameter changes continuously between the large inner diameter portion 30 and the small inner diameter portion 32.
In this embodiment, the connection surface 34A is configured as an inclined surface 34 that connects the inner peripheral surfaces of the large inner diameter portion 30 and the small inner diameter portion 32.
The inclined surface 34 is inclined so that the cross-sectional area of the cylinder 12 decreases from the center of the cylinder 12 in the axial direction toward both ends, and the boundaries with the large inner diameter portion 30 and the boundaries with the small inner diameter portion 32 are connected so as not to create any steps.
In this embodiment, the connecting surface 34A is configured as an inclined surface 34 having a straight cross section, but any connection may be used as long as the surface has a continuously changing inner diameter. That is, the connecting surface 34A may be configured as a connecting surface 34A having a cross section formed by combining a plurality of semicircles, or a connecting surface 34A having a wave-shaped cross section.

The inner peripheral surface 1202A of the cylinder 12 is formed symmetrically with respect to the central portion of the cylinder 12 in the axial direction.
That is, the large inner diameter portion 30 is disposed with the same length from the center toward both ends in the axial direction of the cylinder 12 .
The inclined surfaces 34 are disposed from both ends of the large inner diameter portion 30 toward both ends of the cylinder 12 at symmetric angles with respect to the axial direction of the cylinder 12 and with the same length.
The small-diameter inner diameter portions 32 are disposed with the same length from both ends of the inclined surface 34 to both ends of the cylinder 12 .

In addition, when the piston 16 moves inside the large diameter inner portion 30, a gap S1 is formed between the outer peripheral surface 16A of the piston 16 and the inner peripheral surface of the large diameter inner portion 30 of the cylinder 12, as shown in FIG.
When the piston 16 moves inside the small diameter inner portion 32, a gap S2 narrower than the gap S1 is formed between the outer peripheral surface 16A of the piston 16 and the inner peripheral surface of the small diameter inner portion 32 of the cylinder 12, as shown in Figures 3 and 4.
Therefore, since gap S2 is narrower than gap S1, the damping force F2 generated by the hydraulic oil V passing through gap S2 when the piston 16 moves inside the small diameter inner diameter portion 32 is greater than the damping force F1 generated by the hydraulic oil V passing through gap S1 when the piston 16 moves inside the large diameter inner diameter portion 30.

When seismic motion occurs, the laminated rubber 6 causes a horizontal reciprocating movement, causing a displacement between the upper structure 4 and the lower structure 2. Accordingly, the piston rod 14 of the viscous damper 10A moves in the axial direction of the cylinder 12, and the piston 16 moves reciprocatingly inside the cylinder 12 in the axial direction.
Taking this into consideration, the axial length L1 of the large diameter inner diameter portion 30 and the inclined surface 34 combined is the length that allows the piston 16 to move axially of the cylinder 12 in the event of earthquake motion assumed in normal design.
The combined length L1 of the large inner diameter portion 30 and the inclined surface 34 shown in FIG. 2 is, for example, about 450 mm.
Additionally, the axial length L2 of the small-diameter inner portion 32 is a length that allows the piston 16 to move axially of the cylinder 12 in the event of an earthquake motion that exceeds the design assumption.
The length L2 of the small inner diameter portion 32 shown in FIG. 2 is, for example, about 250 mm.

Next, the operation of the viscous damper 10A will be described.
First, in the event of earthquake motion assumed in a normal design, which is considered to have a relatively high occurrence frequency and probability, when the upper structure 4 moves in the X1 direction (see Figure 1), the viscous damper 10A is pressed in the X1 direction where the piston rod 14 is inserted into the cylinder 12, and the piston 16 moves in the X1 direction within the large diameter inner portion 30 as shown in Figure 2.
Then, the hydraulic oil V in the cylinder 12 flows from the second cylinder chamber 12B through the gap S1 to the first cylinder chamber 12A, thereby exerting a damping force F1.

On the other hand, when the upper structure 4 moves in the X2 direction (see FIG. 1), the viscous damper 10A is pulled in the X2 direction in which the piston rod 14 is pulled out of the cylinder 12, and the piston 16 moves in the X2 direction within the large diameter inner portion 30 as shown in FIG. 2.
As a result, the hydraulic oil V in the cylinder 12 flows from the first cylinder chamber 12A through the gap S1 to the second cylinder chamber 12B, thereby exerting a damping force F1.
In this way, when earthquake motion assumed in normal design occurs, a damping force F1 can be exerted without reducing the seismic isolation performance of the laminated rubber 6.

In the event of earthquake motion that exceeds the design assumptions, which is considered to have a relatively low occurrence frequency and probability, when the upper structure 4 moves in the X1 direction (see Figure 1), the viscous damper 10A is pressed in the X1 direction where the piston rod 14 is inserted into the cylinder 12, and as shown in Figure 3, the piston 16 moves in the X1 direction within the large diameter inner diameter portion 30 and then further moves in the X1 direction within the small diameter inner diameter portion 32.
As a result, the hydraulic oil V in the cylinder 12 flows from the second cylinder chamber 12B through the gap S1 to the first cylinder chamber 12A, thereby exerting a damping force F1, and the hydraulic oil V further flows from the second cylinder chamber 12B through the gap S2 to the first cylinder chamber 12A, thereby switching the damping force F1 and exerting a damping force F2 greater than the damping force F1.

On the other hand, when the upper structure 4 moves in the X2 direction, the viscous damper 10A is pulled in the X2 direction as the piston rod 14 is pulled out of the cylinder 12, and as shown in FIG. 4, the piston 16 moves in the X2 direction within the large diameter inner portion 30 and then further moves in the X2 direction within the small diameter inner portion 32.
As a result, the hydraulic oil V in the cylinder 12 flows from the first cylinder chamber 12A through the gap S1 to the second cylinder chamber 12B, thereby exerting a damping force F1, and the hydraulic oil V further flows from the first cylinder chamber 12A through the gap S2 to the second cylinder chamber 12B, thereby switching the damping force F1 and exerting a damping force F2 greater than the damping force F1.
In this way, when earthquake motion occurs that exceeds the design assumption, a damping force F2 corresponding to the earthquake motion can be exerted.

When the piston 16 moves from inside the large inner diameter section 30 to inside the small inner diameter section 32, it passes through the inclined surface 34 so that the damping force changes smoothly, so that the damping force gradually increases when switching from damping force F1 to damping force F2, and no impact force is generated due to the switch in damping force, or the impact force can be mitigated.

Thus, according to this embodiment, in a viscous damper 10A comprising a cylinder 12 filled with hydraulic oil V, a piston rod 14 arranged on the axis of the cylinder 12, and a piston 16 connected to the piston rod 14, a plurality of inner diameter portions (large diameter inner diameter portion 30, small diameter inner diameter portion 32) having different inner diameters are provided on the inner surface 1202A of the cylinder 12.
Therefore, the damping force exerted in response to seismic motion can be switched depending on the position to which the piston 16 moves within the cylinder 12, and the simple configuration is advantageous in exerting a damping force in response to seismic motion that exceeds the design assumptions, without reducing the seismic isolation performance against seismic motion assumed in normal designs.

In addition, the multiple inner diameter portions of the inner surface 1202A of the cylinder 12 have a large diameter inner diameter portion 30 and a small diameter inner diameter portion 32 having an inner diameter smaller than that of the large diameter inner diameter portion 30, and the large diameter inner diameter portion 30 is disposed in the center of the axial direction of the cylinder 12, and the small diameter inner diameter portions 32 are provided on both sides of the large diameter inner diameter portion 30.
Therefore, with this simple configuration, when seismic motion anticipated in the normal design occurs, the piston 16 can be moved within the large diameter inner diameter portion 30 without reducing the seismic isolation performance, and when seismic motion exceeding the design assumption occurs, the piston 16 can be moved within the small diameter inner diameter portion 32 to exert a damping force corresponding to the seismic motion exceeding the design assumption.

The large inner diameter portion 30 and the small inner diameter portion 32 that are adjacent in the axial direction of the cylinder 12 are connected by a connection surface 34A whose inner diameter changes continuously.
Therefore, in the event of seismic motion that exceeds the design assumption, as the piston 16 moves from the large inner diameter portion 30 to the small inner diameter portion 32, it passes through the connection surface 34A in a manner that continuously changes the damping force, and as the damping force switches, the damping force changes gradually, which is advantageous in preventing or mitigating the impact force due to the switch in damping force.

Additionally, the large inner diameter portion 30 and the small inner diameter portion 32 that are adjacent in the axial direction of the cylinder 12 are connected by an inclined surface 34 that connects the inner peripheral surfaces of these inner diameter portions.
Therefore, in the event of seismic motion that exceeds the design assumption, as the piston 16 moves from within the large inner diameter portion 30 to the small inner diameter portion 32, it passes through the inclined surface 34 in such a way that the damping force changes smoothly, and as the damping force switches from damping force F1 to damping force F2, the damping force gradually increases, which is advantageous in preventing or mitigating the impact force due to the switch in damping force.

Further, the inner peripheral surface 1202A of the cylinder 12 is formed symmetrically with respect to the central portion of the cylinder 12 in the axial direction.
Therefore, it is advantageous in terms of exerting the same degree of damping force whether the upper structure 4 moves in the X1 direction or the X2 direction.

In addition, the piston rod 14 protrudes from one end 12C in the axial direction of the cylinder 12, and mounting members 18, 20 are attached to the end 12A of the piston rod 14 protruding from the cylinder 12 and the other end 12D in the axial direction of the cylinder 12, respectively, and one mounting member 18 is connected to the upper structure 4 in a state where it can swing around an axis 4B extending in the vertical direction, and the other mounting member 20 is connected to the lower structure 2 in a state where it can swing around an axis 2B extending in the vertical direction.
Therefore, even if seismic motion causes the upper structure 4 to move horizontally relative to the lower structure 2 in a direction intersecting the axial direction of the cylinder 12, the viscous damper 10A can oscillate, thereby allowing the viscous damper 10A to function while avoiding damage to the viscous damper 10A.

Also, as in a viscous damper 10B shown in FIG. 5, a cover 22 may be provided to cover the piston rod 14 protruding from the first end wall 1204 of the cylinder 12.
That is, the cover 22 is a cylindrical member extending from the end of one of the mounting members 18, and is formed with a length that is capable of covering the piston rod 14 protruding from the first end wall 1204 of the cylinder 12, even when the piston rod 14 is pulled out to the fullest extent from the cylinder 12 (when the viscous damper 10A shown in Figure 4 is fully extended).
By providing such a cover 22, it is possible to prevent dust and the like from adhering to the piston rod 14, and also to guide the piston rod 14 so that the piston rod 14 can move back and forth along the axis of the cylinder 12.

(Modification of the first embodiment)
In the first embodiment, the large inner diameter portion is disposed in the center of the cylinder in the axial direction, and one small inner diameter portion is provided on each side of the large inner diameter portion. In contrast, in this modified example, the large inner diameter portion is disposed in the center, and the small inner diameter portions disposed on both sides of the large inner diameter portion include two small inner diameter portions with different inner diameters.
In the following description of the embodiments and modifications, the same parts and components as those in the first embodiment will be given the same reference numerals and their description will be omitted, and the description will focus on the differences from the first embodiment.

With reference to FIG. 6, an inner circumferential surface 1202A of a peripheral wall 1202 of a cylinder 12 of a viscous damper 10C according to this modified example will be described.
In this modified example, there is provided a large inner diameter portion 40, a first small inner diameter portion 42 having an inner diameter smaller than that of the large inner diameter portion 40, and a second small inner diameter portion 44 having an inner diameter even smaller than the first small inner diameter portion 42, and the first small inner diameter portion 42 and the second small inner diameter portion 44 are provided in order on both sides of the large inner diameter portion 40, respectively.

That is, in the axial direction of the cylinder 12, a large diameter inner diameter portion 40 is provided in the center, and on both sides of it are first small diameter inner diameter portions 42 extending toward both ends of the cylinder 12, and on both sides of those are second small diameter inner diameter portions 44 extending to both ends of the cylinder 12.
Therefore, the first small inner diameter portion 42 and the second small inner diameter portion 44 have smaller inner diameters each being disposed farther away from the large inner diameter portion 40 .

Adjacent inner diameter portions in the axial direction of the cylinder 12, i.e., the large inner diameter portion 40 and the first small inner diameter portion 42, and the first small inner diameter portion 42 and the second small inner diameter portion 44, are connected by inclined surfaces 46, 48, which are connecting surfaces 46A, 48A that connect the inner circumferential surfaces of those inner diameter portions, respectively.
The inclined surfaces 46, 48 are inclined so that the cross-sectional area becomes smaller from the center toward both ends in the axial direction of the cylinder 12, and are connected so that there are no steps at the boundaries with the large inner diameter portion 40, the first small inner diameter portion 42, and the second small inner diameter portion 44.
The inner circumferential surface 1202A of the cylinder 12 is formed symmetrically with respect to the central portion in the axial direction of the cylinder 12, similarly to the first embodiment.

In addition, when the piston 16 moves inside the large diameter inner portion 40, a gap S1 is formed between the outer peripheral surface 16A of the piston 16 and the inner peripheral surface of the large diameter inner portion 40 of the cylinder 12, as shown in FIG.
When the piston 16 moves inside the first small diameter inner portion 42, a gap S2 narrower than the gap S1 is formed between the outer peripheral surface 16A of the piston 16 and the inner peripheral surface of the first small diameter inner portion 42 of the cylinder 12.
When the piston 16 moves inside the second small diameter inner portion 44, a gap S3 narrower than the gap S2 is formed between the outer peripheral surface 16A of the piston 16 and the inner peripheral surface of the second small diameter inner portion 44 of the cylinder 12.

Therefore, since gap S2 is narrower than gap S1, the damping force F2 generated by the hydraulic oil V passing through gap S2 when the piston 16 moves inside the first small diameter inner diameter portion 42 is greater than the damping force F1 generated by the hydraulic oil V passing through gap S1 when the piston 16 moves inside the large diameter inner diameter portion 40.
Furthermore, since gap S3 is narrower than gap S2, the damping force F3 generated by the hydraulic oil V passing through gap S3 when the piston 16 moves inside the second small diameter inner diameter portion 44 is greater than the damping force F2 generated by the hydraulic oil V passing through gap S2 when the piston 16 moves inside the first small diameter inner diameter portion 42.
In other words, the further the piston 16 moves toward the end within the cylinder 12, the greater the damping force becomes.

The combined axial length L1 of the large diameter inner diameter portion 40 and the inclined surface 46 is the length that allows the piston 16 to move axially of the cylinder 12 in the event of earthquake motion assumed in normal design, as in the first embodiment.
In addition, the combined axial length of the first small inner diameter portion 42, the second small inner diameter portion 44 and the inclined surface 48, and the length of the second small inner diameter portion 44 can be designed arbitrarily taking into account the magnitude of the seismic motion.

Next, the operation of the viscous damper 10C will be described.
In the case where an earthquake motion assumed in a normal design occurs, the process is the same as in the first embodiment.
In the event of earthquake motion that exceeds the assumptions of the design, which is considered to have a relatively low occurrence frequency and probability, when the upper structure 4 moves in the X1 direction (see FIG. 1 ), the viscous damper 10C is pressed in the X1 direction where the piston rod 14 is inserted into the cylinder 12, and the piston 16 moves in the X1 direction within the large diameter inner diameter portion 40, and then further moves in the X1 direction within the first small diameter inner diameter portion 42 and the second small diameter inner diameter portion 44 in that order.
As a result, the hydraulic oil V in the cylinder 12 flows from the second cylinder chamber 12B through the gap S1 to the first cylinder chamber 12A, thereby exerting a damping force F1, and the hydraulic oil V further flows from the second cylinder chamber 12B through the gap S2 to the first cylinder chamber 12A, thereby switching the damping force F1 and exerting a damping force F2 greater than the damping force F1.
Then, the hydraulic oil V further flows from the second cylinder chamber 12B through the gap S3 to the first cylinder chamber 12A, thereby switching the damping force F2 to produce a damping force F3 greater than the damping force F2.

On the other hand, when the upper structure 4 moves in the X2 direction (see FIG. 1), the viscous damper 10C is pressed in the X2 direction where the piston rod 14 is inserted into the cylinder 12, and the piston 16 moves in the X2 direction within the large inner diameter portion 40, and then moves in the X2 direction within the first small inner diameter portion 42 and the second small inner diameter portion 44 in that order.
As a result, the hydraulic oil V in the cylinder 12 flows from the first cylinder chamber 12A through the gap S1 to the second cylinder chamber 12B, thereby exerting a damping force F1, and the hydraulic oil V further flows from the first cylinder chamber 12A through the gap S2 to the second cylinder chamber 12B, thereby switching the damping force F1 and exerting a damping force F2 greater than the damping force F1.
Then, the hydraulic oil V further flows from the first cylinder chamber 12A through the gap S3 to the second cylinder chamber 12B, thereby switching the damping force F2 and exerting a damping force F3 larger than the damping force F2.
In this way, when earthquake motion occurs that exceeds the design assumption, damping forces F2, F3 corresponding to the earthquake motion can be exerted.

When the piston 16 moves from the large inner diameter section 40 into the first small inner diameter section 42, and when it moves from the first small inner diameter section 42 into the second small inner diameter section 44, it passes through the inclined surfaces 46, 48, respectively, so that the damping force changes smoothly. Therefore, when the damping force F1 switches to the damping force F2, F3, the damping force gradually increases, and no impact force is generated due to the switch in the damping force, or the impact force can be mitigated.

In this way, according to this modified example, in addition to the same effects as the first embodiment, when an earthquake motion that exceeds the design assumption occurs, the piston 16 can be moved sequentially into the first small inner diameter portion 42 and then into the second small inner diameter portion 44, thereby exerting a damping force that gradually increases in accordance with the magnitude of the earthquake motion that exceeds the design assumption.

In this modified example, a large inner diameter section 40 is provided in the center of the inner circumferential surface 1202A of the peripheral wall 1202 of the cylinder 12, and two first small inner diameter sections 42 and two second small inner diameter sections 44 are provided on either side of the large inner diameter section 40, but three or more small inner diameter sections may be provided. In that case, the three or more small inner diameter sections have smaller inner diameters each time they are positioned away from the large inner diameter section, and are formed symmetrically with respect to the center in the axial direction of the cylinder 12. This allows the damping force to be exerted in a stepwise manner in response to the magnitude of earthquake motion that exceeds the design assumption.

Second Embodiment
The difference between the first embodiment and the present embodiment is that the piston rod protrudes from the first end wall of the cylinder, whereas the piston rod protrudes from both the first end wall and the second end wall of the cylinder.

As shown in Figures 7 to 9, the viscous damper 10D of this embodiment includes a cylinder 12, a piston rod 24, a piston 16, and mounting members 18 and 26, all of which are made of metal.

The piston rod 24 is a rod-shaped member that is arranged on the axis of the cylinder 12 and penetrates from one end 12C to the other end 12D in the axial direction of the cylinder 12, and protrudes from a first end wall 1204 and a second end wall 1206 at both ends of the cylinder 12 in the axial direction.
The piston rod 24 is liquid-tightly inserted through openings 1204A, 1206A formed in the centers of the first end wall 1204 and the second end wall 1206, respectively, via a seal member (not shown).
One mounting member 18 is attached to one end 24A of the piston rod 24 protruding from the first end wall 1204 of the cylinder 12.

The other mounting member 26 is attached to the second end wall 1206 at the other axial end 12D of the cylinder 12, and is composed of a cylindrical portion 2602 protruding axially from the second end wall 1206 and a mounting portion 2604 provided at the end of the cylindrical portion 2602.
The cylindrical portion 2602 is formed to have a length capable of accommodating the piston rod 24 protruding from the second end wall 1206 of the cylinder 12 when the piston 16 moves to the second end wall 1206 (see FIG. 8).
The other mounting member 26 is connected to the lower structure 2 by an attachment portion 2604 in a state in which it can swing around an axis 2B extending vertically, similar to the other mounting member 20 of the first embodiment.

In this embodiment, one mounting member 18 is connected to the upper structure 4, and the other mounting member 26 is connected to the lower structure 2, but they may be arranged in the opposite manner. In other words, one mounting member 18 may be connected to the lower structure 2, and the other mounting member 26 may be connected to the upper structure 4.

The inner surface 1202A of the peripheral wall 1202 of the cylinder 12 in the viscous damper 10D of this embodiment is the same as that of the first embodiment.

Moreover, the operation of the viscous damper 10D is similar to that of the first embodiment, and therefore will be briefly described with reference to FIGS.
First, when an earthquake motion assumed in a normal design occurs and the upper structure 4 moves in the X1 or X2 direction (see FIG. 1), in the viscous damper 10D, the piston rod 24 moves in the X1 or X2 direction, and the piston 16 moves in the X1 or X2 direction within the large inner diameter portion 30 as shown in FIG. 7. Then, the hydraulic oil V in the cylinder 12 passes through the gap S1, thereby exerting a damping force F1.
In this way, when earthquake motion assumed in normal design occurs, a damping force F1 can be exerted without reducing the seismic isolation performance of the laminated rubber 6.

Furthermore, in the event of earthquake motion exceeding the design assumption, when the upper structure 4 moves in the X1 or X2 direction (see FIG. 1), the piston rod 24 of the viscous damper 10D moves in the X1 or X2 direction, and the piston 16 moves in the X1 or X2 direction within the large-diameter inner portion 30, and then moves in the X1 or X2 direction within the small-diameter inner portion 32, as shown in FIGs. 8 and 9. Then, the hydraulic oil V in the cylinder 12 passes through the gap S1 to exert a damping force F1, and the hydraulic oil V passes through the gap S2 to switch the damping force F1 and exert a damping force F2 greater than the damping force F1.
In this way, when earthquake motion occurs that exceeds the design assumption, a damping force F2 corresponding to the earthquake motion can be exerted.

As described above, according to the present embodiment, in addition to the same effects as those of the first embodiment, the following effects are achieved.
In this embodiment, the piston rod 24 is arranged to penetrate from one end 12C to the other end 12D in the axial direction of the cylinder 12 and is supported by the first end wall 1204 and the second end wall 1206 of the cylinder 12, thereby reducing concerns about buckling.
In addition, since the piston rod 24 is supported by the first end wall 1204 and the second end wall 1206, the diameter of the piston rod 14 can be made smaller than in the case where the piston rod 24 protrudes only from the first end wall 1204 of the cylinder 12, which is advantageous in reducing the weight of the viscous damper 10D.

In addition, by providing the piston rod 24 penetrating from one end 12C to the other end 12D in the axial direction of the cylinder 12, the internal mechanism of the cylinder 12 when the piston 16 is located in the central portion of the axial direction of the cylinder 12 can be made symmetrical with respect to the central portion.
Therefore, the same damping mechanism is used when the piston 16 moves in the X1 direction and when it moves in the X2 direction, which is advantageous in exhibiting a stable damping force against the displacement of the piston 16.

The viscous damper 10D of the second embodiment may also be configured with a cover 22, as in the viscous damper 10B of the first embodiment (see Figure 5).

(Modification of the second embodiment)
In the second embodiment, the large inner diameter portion is disposed in the center of the cylinder in the axial direction, and one small inner diameter portion is provided on each side of the large inner diameter portion. In contrast, in this modified example, the large inner diameter portion is disposed in the center, and the small inner diameter portions disposed on both sides of the large inner diameter portion include two small inner diameter portions with different inner diameters.
As shown in FIG. 10, a viscous damper 10E of this modification is obtained by applying the inner peripheral surface of the cylinder 10C of the modification of the first embodiment to the viscous damper 10D of the second embodiment.
In this way, according to this modification, the same effects as those of the modification of the first embodiment and the second embodiment are achieved.

Third Embodiment
In the second embodiment, the cylinder was connected to the lower structure by the other mounting member attached to the other end in the axial direction of the cylinder, whereas in the present embodiment, the cylinder is connected to the lower structure via a connecting member attached to the other end in the axial direction of the cylinder, which is different.

As shown in FIG. 11, the viscous damper 10F of this embodiment includes a cylinder 12, a piston rod 24, a piston 16, an attachment member 18, and a connecting member 28.

In this embodiment, a concrete seismic isolation pit is provided in a recess formed by excavating the ground, and a seismic isolation device is placed in the seismic isolation pit.
The seismic isolation pit is, for example, rectangular and is surrounded by a horizontal pit floor and a pit wall 2P extending vertically from the pit floor at the outer periphery of the building, and the laminated rubber 6 is arranged between the upper structure 4 and the pit floor.
In this embodiment, a hole 2H for accommodating a piston rod 24 is provided in a pit wall surface 2P that constitutes the lower structure 2.
The other end 24B of the piston rod 24 protruding from the second end wall 1206 of the cylinder 12 is inserted into the hole portion 2H.

The connecting member 28 is attached to the second end wall 1206 at the other axial end 12D of the cylinder 12, and is composed of a metallic disc member 2802, a metallic disc member 2804 having a larger diameter than the disc member 2802, and a disc-shaped rubber plate 2806 having a smaller diameter than the disc member 2802 and sandwiched between the disc member 2802 and the disc member 2804.
The disk member 2802 is attached to the second end wall 1206 of the cylinder 12, and the disk member 2804 is attached to the pit wall surface 2P of the lower structure 2.

A through hole 28A is formed in the center of the connecting member 28 along the axial direction of the cylinder 12, and the other end 24B of the piston rod 24 protruding from the second end wall 1206 of the cylinder 12 passes through it.
The connecting member 28 is attached to a portion of the pit wall surface 2P around the hole portion 2H so that the axis of the hole portion 2H provided in the pit wall surface 2P of the lower structure 2 coincides with the axis of the through hole 28A.
Because the connecting member 28 has a rubber plate 2806, the cylinder 12 is connected to the lower structure 2 in a state in which it can swing slightly relative to the pit wall surface 2P, so that the viscous damper 10F can be swung horizontally, which is advantageous in avoiding damage to the viscous damper 10F.

The operation of the inner circumferential surface 1202A of the peripheral wall 1202 of the cylinder 12 and the viscous damper 10F is the same as in the second embodiment.

As described above, according to the present embodiment, in addition to the same effects as those of the second embodiment, the following effects are achieved.
In the present embodiment, the piston rod 24 has the other end 24B inserted into the hole 2H of the pit wall surface 2P that constitutes the lower structure 2, which is advantageous in reducing the installation space of the viscous damper 10F.

In this embodiment, the hole 2H having a diameter into which the piston rod 24 can be inserted is provided in the pit wall surface 2P constituting the lower structure 2, and the viscous damper 10F is attached to the pit wall surface 2P, but the viscous damper 10F may be attached to another member constituting the lower structure 2. For example, a hole having a diameter into which the piston rod 24 can be inserted may be provided in a footing (concrete foundation) constituting the lower structure 2, and the viscous damper 10F may be attached to the footing.
In addition, in this embodiment, one of the mounting members 18 is connected to the upper structure 4, and the connecting member 28 is connected to the lower structure 2, but they may be arranged in the opposite manner. That is, one of the mounting members 18 may be arranged to be connected to the lower structure 2, and the connecting member 28 may be arranged to be connected to the upper structure 4.
Also, the viscous damper 10F of the third embodiment may be configured to be provided with a cover 22, as in the viscous damper 10B of the first embodiment (see FIG. 5).

2 Lower structure 2A Holding member 2H Hole 2P Pit wall surface 4 Upper structure 4A Holding member 6 Laminated rubber 10A, 10B, 10C, 10D, 10E, 10F Viscous damper 12 Cylinder 1202 Circumferential wall 1202A Inner peripheral surface 1204 First end wall 1206 Second end wall 14, 24 Piston rod 16 Piston 16A Outer peripheral surface 18 Mounting member (one of the mounting members)
20, 26 Mounting member (the other mounting member)
22 Cover 2602 Cylindrical portion 2604 Mounting portion 28 Connection member 2802, 2804 Disc member 2806 Rubber plate 30, 40 Large inner diameter portion 32 Small inner diameter portion 34, 46, 48 Inclined surface 34A, 46A, 48A Connection surface 42 First small inner diameter portion 44 Second small inner diameter portion

Claims (2)

A viscous damper comprising a cylinder in which a viscous fluid is sealed, a piston rod disposed on an axial center of the cylinder, and a piston connected to the piston rod,
The cylinder has an inner circumferential surface provided with a large inner diameter portion and a small inner diameter portion having an inner diameter smaller than that of the large inner diameter portion,
The large inner diameter portion is disposed in a central portion of the cylinder in an axial direction, and the small inner diameter portions are disposed on both sides of the large inner diameter portion,
The inner diameter portions adjacent to each other in the axial direction of the cylinder are connected by an inclined surface that connects the inner circumferential surfaces of the inner diameter portions so as not to generate a step ,
The piston rod is provided to penetrate the cylinder from one end to the other end in the axial direction,
The piston is provided at the center of the piston rod in the longitudinal direction,
The viscous damper is installed in a seismically isolated building having an upper structure supported on a lower structure,
An attachment member is attached to an end of the piston rod protruding from one end of the cylinder in an axial direction,
A connecting member having a through hole is attached to the other end of the cylinder in the axial direction,
The mounting member is connected to the upper structure in a state in which the mounting member can swing about an axis extending in a vertical direction,
an end of the piston rod protruding from the other end of the cylinder in the axial direction through the through hole is inserted into a hole provided in the lower structure,
The connecting member is connected to a portion of the lower structure around the hole.
A viscous damper comprising: A viscous damper comprising a cylinder in which a viscous fluid is sealed, a piston rod disposed on an axial center of the cylinder, and a piston connected to the piston rod,
The cylinder has an inner circumferential surface provided with a large inner diameter portion and a small inner diameter portion having an inner diameter smaller than that of the large inner diameter portion,
The large inner diameter portion is disposed in a central portion of the cylinder in an axial direction, and the small inner diameter portions are disposed on both sides of the large inner diameter portion,
The inner diameter portions adjacent to each other in the axial direction of the cylinder are connected by an inclined surface that connects the inner circumferential surfaces of the inner diameter portions so as not to generate a step,
The piston rod is provided to penetrate the cylinder from one end to the other end in the axial direction,
The piston is provided at the center of the piston rod in the longitudinal direction,
The viscous damper is installed in a seismically isolated building having an upper structure supported on a lower structure,
An attachment member is attached to an end of the piston rod protruding from one end of the cylinder in an axial direction,
A connecting member having a through hole is attached to the other end of the cylinder in the axial direction,
The mounting member is connected to the lower structure in a state in which the mounting member can swing about an axis extending in a vertical direction,
an end of the piston rod protruding from the other end of the cylinder in the axial direction through the through hole is inserted into a hole provided in the upper structure,
The connecting member is connected to a portion of the upper structure around the hole.
A viscous damper comprising:

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