Patent Publication Number: US-2019176605-A1

Title: Vibration-damping device

Description:
TECHNICAL FIELD 
     The present invention relates to a vibration-damping device which is applied to automobiles or industrial machinery, for example, and absorbs and attenuates vibration of a vibration-generating portion such as an engine. 
     Priority is claimed on Japanese Patent Application No. 2016-123966, filed on Jun. 22, 2016, the content of which is incorporated herein by reference. 
     BACKGROUND ART 
     In the related art, as a vibration-damping device of such a kind, a known configuration includes a tubular first attachment member that is coupled to one of a vibration-generating portion and a vibration-receiving portion, a second attachment member that is coupled to the other one of the vibration-generating portion and the vibration-receiving portion, an elastic body that couples both the attachment members to each other, and a partition member that divides a liquid chamber inside the first attachment member, in which liquid is sealed, into a main liquid chamber and a sub-liquid chamber. A restriction passage through which the main liquid chamber and the sub-liquid chamber communicate with each other is formed in the partition member. In this vibration-damping device, when vibration is input, both the attachment members are relatively displaced while causing the elastic body to be elastically deformed. Consequently, the liquid pressure in the main liquid chamber fluctuates, and the liquid flows in the restriction passage, so that vibration is absorbed and attenuated. 
     In this vibration-damping device, for example, when a significant load (vibration) is input due to unevenness or the like on a road surface, the liquid pressure in the main liquid chamber increases, and then a load is input in the opposite direction due to a rebound or the like of the elastic body, the main liquid chamber is under a negative pressure and the liquid flows into the main liquid chamber. In this case, cavitation in which many air bubbles are generated in the liquid occurs. Thereafter, sometimes an allophone is generated due to a collapse of cavitation in which the generated air bubbles collapse. When a collapse of cavitation occurs, shock waves accompanying the collapse are propagated to the first attachment member via the liquid. As a result, an allophone is generated. 
     Therefore, for example, as in the vibration-damping device disclosed in Patent Document 1, a configuration in which a valve body is provided inside a restriction passage is known. In this vibration-damping device, when vibration having a significant amplitude is input, the main liquid chamber is restrained from being under a negative pressure, so that the occurrence of cavitation can be restrained. 
     CITATION LIST 
     Patent Document 
     [Patent Document 1] Japanese Unexamined Patent Application, First Publication No. 2012-172832 
     SUMMARY OF INVENTION 
     Technical Problem 
     In order to restrain cavitation from occurring in a vibration-damping device, the inventor of this application has analyzed a process in which cavitation occurs. In the analysis, cavitation was reenacted in a vibration-damping device provided with no countermeasure for cavitation. At that time, relative displacement amounts of both attachment members and a liquid pressure in a main liquid chamber were measured. In addition, in order to detect a collapse of cavitation, the degree of a shock wave propagated to a first attachment member was measured as acceleration. 
     Moreover, in order to observe states of the occurrence and collapse of cavitation, the first attachment member was formed of an acryl resin such that the main liquid chamber was visually recognizable from outside. 
     The graph in  FIG. 4  illustrates the result thereof. The horizontal axis of the graph indicates a time showing that time elapses from the left side to the right side of the horizontal axis. A line L 1  of graph lines recorded in the graph indicates the relative displacement amounts of both the attachment members at each time. A line L 2  indicates the liquid pressure in the main liquid chamber at each time. A line L 3  indicates acceleration (degree) of a shock wave propagated to the first attachment member at each time. The vertical axis of the graph indicates the degrees of the displacement amount, the liquid pressure, and the acceleration. The fiducial point zero is indicated in the middle of the vertical axis. With respect to the fiducial point, the upper side indicates a positive side and the lower side indicates a negative side. A displacement amount having a positive value denotes that both the attachment members are relatively displaced in a direction in which the main liquid chamber is under a negative pressure. 
     As indicated with the line L 1  in  FIG. 4 , this graph illustrates a vibration-damping device during a period after both the attachment members have been relatively displaced in the direction in which the main liquid chamber is under a negative pressure until both the attachment members are displaced back and the liquid pressure in the main liquid chamber starts to be increased. It was confirmed that when both the attachment members start to be displaced back, acceleration (degree) of a shock wave fluctuates and a collapse of cavitation occurs, as indicated with the line L 3 . 
     The state of a collapse of cavitation can also be confirmed from  FIGS. 5 to 7 , which are photographs showing states of the main liquid chamber at each time.  FIGS. 5 to 7  are photographs showing the states of the main liquid chamber at each of times T 1 , T 2 , and T 3  illustrated in  FIG. 4 . In  FIG. 5  corresponding to the time T 1 , air bubbles due to cavitation are not generated. In  FIG. 6  corresponding to the time T 2 , air bubbles are generated about a position indicated with a reference sign C in the diagram. In  FIG. 7  corresponding to the time T 3 , it was confirmed that air bubbles collapse. It was confirmed that both the attachment members start to be displaced back at the time T 3  and a collapse of cavitation occurs at this timing. 
     In a vibration-damping device of this kind, when vibration is input, the liquid pressure in the main liquid chamber normally fluctuates in accordance with the relative displacement amounts of both the attachment members. Therefore, if this displacement amount increases, the liquid pressure in the main liquid chamber significantly fluctuates, so that the degree of a negative pressure in the main liquid chamber is likely to increase. 
     However, the inventor of this application has found that if both the attachment members are displaced in a relatively significant manner as that at the time of the foregoing analysis to an extent that the main liquid chamber is under a negative pressure until cavitation can occur, the liquid pressure in the main liquid chamber settles within a uniform range without following the relative displacement of both the attachment members, as indicated with the line L 2  in  FIG. 4 . In this case, cavitation occurs as illustrated in  FIG. 6 . 
     The present invention has been made in consideration of the foregoing circumstances, and an object thereof is to provide a vibration-damping device in which the occurrence of cavitation can be restrained. 
     Solution to Problem 
     According to a first aspect of the present invention, a liquid-sealed vibration-damping device is provided, including a tubular first attachment member that is coupled to any one of a vibration-generating portion and a vibration-receiving portion; a second attachment member that is coupled to the other one of the vibration-generating portion and the vibration-receiving portion; an elastic body that couples both the attachment members to each other; and a partition member that divides a liquid chamber inside the first attachment member into a main liquid chamber having the elastic body as a part of a wall surface, and a sub-liquid chamber. A restriction passage through which the main liquid chamber and the sub-liquid chamber communicate with each other is formed in the partition member. The partition member is provided with a flow-speed restraint portion which restrains a flow speed of liquid flowing in the restriction passage. The flow-speed restraint portion restrains a peak flow speed of the liquid flowing into the main liquid chamber from the restriction passage to 10 m/sec or lower, when a liquid pressure in the main liquid chamber is a negative pressure and a fluctuation rate of the liquid pressure within a predetermined time is 5% or lower. 
     Advantageous Effects of Invention 
     In the vibration-damping device according to the present invention, the occurrence of cavitation can be restrained. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a longitudinal sectional view of a vibration-damping device according to a first embodiment of the present invention. 
         FIG. 2  is a plan view of a partition member illustrated in  FIG. 1 . 
         FIG. 3  is a plan view of a partition member constituting a vibration-damping device according to a second embodiment of the present invention. 
         FIG. 4  is a graph illustrating an analysis result of a process in which cavitation occurs. 
         FIG. 5  is a photograph showing a state of a main liquid chamber at a time T 1  illustrated in  FIG. 4 . 
         FIG. 6  is a photograph showing a state of the main liquid chamber at a time T 2  illustrated in  FIG. 4 . 
         FIG. 7  is a photograph showing a state of the main liquid chamber at a time T 3  illustrated in  FIG. 4 . 
         FIG. 8  is a plan view illustrating a first modification example of a flow-speed restraint portion. 
         FIG. 9  is a plan view illustrating a second modification example of the flow-speed restraint portion. 
         FIG. 10  is a perspective view illustrating a third modification example of the flow-speed restraint portion. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
     Hereinafter, a first embodiment of a vibration-damping device according to the present invention will be described based on the drawings. 
       FIG. 1  is a longitudinal sectional view of a vibration-damping device  10  of the present embodiment cut along an axial center O.  FIG. 2  is a plan view of a partition member. 
     The reference sign O illustrated in  FIG. 1  indicates a central axis line of the vibration-damping device  10  and will hereinafter be simply referred to as the “axial center O”. In addition, a direction along the axial center O is referred to as an “axial direction”, a direction orthogonal to the axial center O is referred to as a “radial direction”, and a direction around the axial center O is referred to as a “circumferential direction”. 
     As illustrated in  FIG. 1 , the vibration-damping device  10  includes a tubular first attachment member  11  that is coupled to any one of a vibration-generating portion and a vibration-receiving portion; a second attachment member  12  that is coupled to the other one of the vibration-generating portion and the vibration-receiving portion; an elastic body  13  that elastically couples the first attachment member  11  and the second attachment member  12  to each other; and a partition member  16  that divides the inside of the first attachment member  11  into a main liquid chamber  14  and a sub-liquid chamber  15  (which will be described below). Each of these members is formed to have a circular shape or a toric shape in a plan view state and is disposed coaxially with the axial center O. Hereinafter, the second attachment member  12  side along the axial direction is referred to as an upper side, and the partition member  16  side is referred to as a lower side. 
     For example, in a case where this vibration-damping device  10  is mounted in an automobile, the second attachment member  12  is coupled to an engine, which is the vibration-generating portion, and the first attachment member  11  is coupled to a vehicle body, which is the vibration-receiving portion. Accordingly, vibration of the engine is restrained from being transmitted to the vehicle body. 
     The second attachment member  12  is a column member extending in the axial direction. A lower end portion of the second attachment member  12  is formed to have a hemispherical surface shape. The second attachment member  12  has a brim portion  12   a  positioned above the lower end portion of the second attachment member  12 . The second attachment member  12  is provided with a screw hole  12   b  extending downward from an upper end surface of the second attachment member  12 . A bolt (not illustrated), which is an attachment tool on the engine side, is screwed into the screw hole  12   b . The second attachment member  12  is disposed in an upper end opening portion of the first attachment member  11 . 
     The elastic body  13  is subjected to vulcanized adhesion with respect to each of an inner circumferential surface of the upper end opening portion of the first attachment member  11  and an outer circumferential surface of the lower end portion of the second attachment member  12 . The elastic body  13  is a rubber body interposed between the inner circumferential surface and the outer circumferential surface. The elastic body  13  blocks the upper end opening portion of the first attachment member  11 . An upper end portion of the elastic body  13  is subjected to vulcanized adhesion with respect to the brim portion  12   a . Accordingly, the elastic body  13  adheres to the second attachment member  12  in a sufficiently tight manner and favorably follows displacement of the second attachment member  12 . A rubber film  17  liquid-tightly covering the inner circumferential surface of the first attachment member  11  is integrally formed in the lower end portion of the elastic body  13 . An elastic body formed of a synthetic resin can also be used as the elastic body  13 , in addition to that formed of rubber. 
     The first attachment member  11  is formed to have a cylindrical shape having a flange  18  in the lower end portion. The first attachment member  11  is coupled to the vehicle body or the like, which is the vibration-receiving portion, via the flange  18 . The upper end opening portion of the first attachment member  11  is blocked by the elastic body  13  as described above. A liquid chamber  19  is formed below the elastic body  13  in the first attachment member  11 . In the present embodiment, the partition member  16  is provided in a lower end opening portion of the first attachment member  11 . Moreover, a diaphragm  20  is provided below the partition member  16 . 
     The diaphragm  20  is formed to have a bottomed cylindrical shape formed of an elastic material such as rubber or a soft resin. The upper end portion of the diaphragm  20  liquid-tightly engages with a toric attachment groove  16   a  formed in the partition member  16 . The outer circumferential surface of the upper end portion of the diaphragm  20  is pressed to the partition member  16  side (the upper side) by a ring-shaped holding tool  21 . A flange portion  22  is formed on the outer circumferential surface of the partition member  16 . The holding tool  21  is brought into contact with the flange portion  22 . 
     The flange portion  22  and the holding tool  21  of the partition member  16  are brought into contact with a lower end opening edge of the first attachment member  11  in this order. The first attachment member  11 , the flange portion  22 , and the holding tool  21  are fixed by using a plurality of screws  23 . Accordingly, the diaphragm  20  is attached to the lower end portion of the first attachment member  11  via the partition member  16 , and the liquid chamber  19  is formed inside the first attachment member  11 . The liquid chamber  19  is installed inside the first attachment member  11 , that is, on an inner side of the first attachment member  11  in a plan view. The liquid chamber  19  is provided in a state of being liquid-tightly blocked between the elastic body  13  and the diaphragm  20 . Liquid L is sealed in (fills) the liquid chamber  19 . 
     Ethylene glycol, water, silicone oil, or the like is used as the liquid L. 
     The liquid chamber  19  is divided into the main liquid chamber  14  and the sub-liquid chamber  15  by the partition member  16 . The main liquid chamber  14  is formed to have a lower end surface  13   a  of the elastic body  13  as a part of a wall surface. The main liquid chamber  14  is a space surrounded by the elastic body  13 , the rubber film  17 , and the partition member  16 . The inner volume of main liquid chamber  14  changes due to deformation of the elastic body  13 . The sub-liquid chamber  15  is a space surrounded by the diaphragm  20  and the partition member  16 . The inner volume of the sub-liquid chamber  15  changes due to deformation of the diaphragm  20 . 
     The vibration-damping device  10  having such a configuration is a compression-type vibration-damping device which is used by being attached such that the main liquid chamber  14  is positioned on the upper side in a vertical direction and the sub-liquid chamber  15  is positioned on the lower side in the vertical direction. 
     A holding groove  16   b  liquid-tightly holding the lower end portion of the rubber film  17  is formed on an upper surface of the partition member  16 . Accordingly, a gap between the rubber film  17  and the partition member  16  is liquid-tightly blocked. A restriction passage  24  through which the main liquid chamber  14  and the sub-liquid chamber  15  communicate with each other is provided in the partition member  16 . 
     The restriction passage  24  generates resonance (liquid-column resonance) when preset vibration is input to the vibration-damping device  10  and the liquid L flows through the restriction passage  24 . The length of a flow channel and the cross-sectional area of the flow channel of the restriction passage  24  are set (tuned) such that the resonance frequency of the restriction passage  24  becomes the frequency of the preset vibration. Examples of the preset vibration include idle vibration (for example, a frequency ranging from 18 Hz to 30 Hz, and an amplitude of ±0.5 mm or smaller) and shake vibration (for example, a frequency of 14 Hz or lower, and the amplitude of ±0.5 mm or greater) having a frequency lower than that of the idle vibration. 
     As illustrated in  FIGS. 1 and 2 , the restriction passage  24  includes a circumferential groove  25  which is formed in the partition member  16 , a communication port  26  through which the circumferential groove  25  and the sub-liquid chamber  15  communicate with each other, a vortex chamber  27   a  through which the circumferential groove  25  and the main liquid chamber  14  communicate with each other, and a rectification path  27   b  which connects the circumferential groove  25  and the vortex chamber  27   a  to each other. The circumferential groove  25  is formed on the outer circumferential surface of the partition member  16  throughout approximately half the circumference along the circumferential direction. The communication port  26  is formed in one end portion of the circumferential groove  25 , and the vortex chamber  27   a  is formed in the other end portion of the circumferential groove  25 . The communication port  26  is an opening portion of the restriction passage  24  on the sub-liquid chamber  15  side. 
     The vortex chamber  27   a  is a recessed portion open in the main liquid chamber  14  and is formed to have a substantially circular shape in a plan view. 
     The opening portion of the vortex chamber  27   a  is an opening portion of the restriction passage  24  on the main liquid chamber  14  side. A central axis of the vortex chamber  27   a  is eccentric with respect to the axial center O. The vortex chamber  27   a  forms a swirling flow of the liquid L in accordance with the flow speed of the liquid L flowing in from the rectification path  27   b.    
     The rectification path  27   b  extends linearly. The rectification path  27   b  extends from the inner circumferential surface of the vortex chamber  27   a  along a tangential direction of this inner circumferential surface. Liquid flowing into the vortex chamber  27   a  from the rectification path  27   b  flows through the rectification path  27   b  and is rectified in this tangential direction. Thereafter, the liquid flows along the inner circumferential surface of the vortex chamber  27   a  and swirls. 
     A porous body  28  is fitted into the opening portion of the vortex chamber  27   a . The porous body  28  is screwed to the partition member  16 . The porous body  28  is formed of a metal or a resin having a disk shape. The porous body  28  has a flange portion  29  which comes into contact with an opening edge portion of the vortex chamber  27   a  and is screwed thereto, and a lid portion  30  which is fitted into the opening portion of the vortex chamber  27   a  and covers the vortex chamber  27   a . A plurality of hole portions  31  are formed in the lid portion  30  in a parallel manner. 
     The hole portions  31  are formed to have a circular shape in a plan view. Through the hole portions  31 , the porous body  28  communicates with a space positioned on the main liquid chamber  14  side and the porous body  28  communicates with a space positioned on the sub-liquid chamber  15  side, individually. These hole portions  31  are disposed throughout the entire area of the lid portion  30  in a zigzag manner. The central axis of each of the hole portions  31  lies along the axial direction. The inner diameter of each of the hole portions  31  is equally formed throughout the entire length. The multiple hole portions  31  are formed to have shapes and sizes equal to each other. For example, the size, the shape, the number, and the like of the hole portions  31  can be suitably changed by increasing the sum total of the opening areas of the multiple hole portions  31  to be greater than the minimum value of the cross-sectional area of the flow channel of the restriction passage  24 . 
     In the present embodiment, the partition member  16  is provided with a flow-speed restraint portion  32  which restrains the flow speed of the liquid L flowing in the restriction passage  24 . The flow-speed restraint portion  32  reduces the flow speed of the liquid L by narrowing the cross-sectional area of the flow channel of the restriction passage  24  to generate resistance to the liquid L. 
     The flow-speed restraint portion  32  includes a first restraint portion  33  and a second restraint portion  34 . The first restraint portion  33  is formed by the porous body  28 . The second restraint portion  34  is formed by the rectification path  27   b  and the vortex chamber  27   a.    
     The flow-speed restraint portion  32  is installed in the restriction passage  24 . The flow-speed restraint portion  32  is disposed on the main liquid chamber  14  side of a middle part of the restriction passage  24  along a flow channel direction of the restriction passage  24 . In the illustrated example, both the first restraint portion  33  and the second restraint portion  34  are disposed on the main liquid chamber  14  side of this middle part. The flow-speed restraint portion  32  is disposed in an end portion of the restriction passage  24  on the main liquid chamber  14  side. 
     In the vibration-damping device  10 , when vibration is input, both the attachment members  11  and  12  are relatively displaced while causing the elastic body  13  to be elastically deformed. Consequently, the liquid pressure in the main liquid chamber  14  fluctuates, and the liquid L inside the main liquid chamber  14  flows into the sub-liquid chamber  15  through the restriction passage  24 . In addition, the liquid L inside the sub-liquid chamber  15  flows into the main liquid chamber  14  through the restriction passage  24 . That is, a part of the liquid L inside the sub-liquid chamber  15  returns to the main liquid chamber  14 . 
     In a case where input vibration is the foregoing preset vibration, resonance (liquid-column resonance) is generated inside the restriction passage  24 , so that the vibration is absorbed and attenuated. In this case, the second restraint portion  34  (the rectification path  27   b  and the vortex chamber  27   a ) functions as a part of the restriction passage  24 . The cross-sectional area of the flow channel or the length of the flow channel of each of the hole portions  31  of the first restraint portion  33  is set such that resonance of the liquid L inside the restriction passage  24  is not hindered. 
     On the other hand, if input vibration is different from the foregoing preset vibration, that is, if vibration having an amplitude greater than that of this vibration is input, for example, both the attachment members  11  and  12  are displaced in a relatively significant manner. If both the attachment members  11  and  12  are displaced in a relatively significant manner to an extent that the main liquid chamber  14  is under a negative pressure until cavitation can occur, the liquid pressure in the main liquid chamber  14  settles within a uniform range at a negative pressure, so that the fluctuation rate of the liquid pressure within a predetermined time becomes 5% or lower. 
     The inventor of this application has found that the occurrence of cavitation depends on a peak flow speed of the liquid L flowing into the main liquid chamber  14  from the restriction passage  24  when the liquid pressure in the main liquid chamber  14  settles within a uniform range at a negative pressure. Thus, the inventor has conceived that the occurrence of cavitation is restrained by restraining this peak flow speed. 
     In the present embodiment, the flow-speed restraint portion  32  restrains the peak flow speed of the liquid L flowing into the main liquid chamber  14  from the restriction passage  24 , when the liquid pressure in the main liquid chamber  14  is a negative pressure and the fluctuation rate of the liquid pressure within the predetermined time is 5% or lower (which will hereinafter be referred to as “when being in a stable state of a negative pressure”) to 10 m/sec (m/second) or lower. 
     For example, the predetermined time can be set to ⅓ of one cycle of input vibration. The peak flow speed is the maximum flow speed of the liquid L during a period in which the liquid pressure in the main liquid chamber  14  is in a stable state of a negative pressure. For example, measurement of the flow speed of the liquid L can be performed by providing the first attachment member  11  formed of a permeable material (for example, an acryl resin), and then performing image analysis of an image of the main liquid chamber  14  captured from outside using a camera. 
     In the present embodiment, after the second restraint portion  34  restrains the flow speed of the liquid L inside the sub-liquid chamber  15  flowing into the main liquid chamber  14  through the restriction passage  24 , the first restraint portion  33  further restrains the flow speed of the liquid L. That is, the peak flow speed is restrained due to operations of both the first restraint portion  33  and the second restraint portion  34 . 
     In the second restraint portion  34 , first, the liquid L flows into the vortex chamber  27   a  from the rectification path  27   b . In this case, if the flow speed of the liquid L is increased to a certain speed or higher, a swirling flow of the liquid L is formed inside the vortex chamber  27   a . As a result, for example, the flow speed of the liquid L is reduced due to an energy loss caused by viscous resistance of the liquid L or by forming a swirling flow, or an energy loss caused by friction between the liquid L and the wall surface of the vortex chamber  27   a . When the flow speed of the liquid L flowing into the vortex chamber  27   a  is low, the liquid L is restrained from swirling inside the vortex chamber  27   a . Therefore, the flow speed is restrained from being excessively reduced by the second restraint portion  34 . 
     In the first restraint portion  33 , the porous body  28  becomes resistance to the liquid L, so that the flow speed of the liquid L is restrained. The flow speed of the liquid L is accurately restrained based on the size, the shape, the number, and the like of the hole portions  31 . 
     As described above, in the vibration-damping device  10  according to the present embodiment, the peak flow speed is restrained to 10 m/sec or lower by the flow-speed restraint portion  32  when vibration having a significant amplitude is input to an extent that the main liquid chamber  14  is under a negative pressure until cavitation can occur, and when the liquid pressure in the main liquid chamber  14  is in a stable state of a negative pressure. Accordingly, the occurrence of cavitation can be restrained. For example, generation of an allophone can be restrained. That is, in a case where the peak flow speed is higher than 10 m/sec, there is a possibility that cavitation will occur. 
     When an analysis, of which the result is shown in  FIG. 4 , was performed, it was confirmed that the peak flow speed was 12 m/sec and cavitation occurred consequently. 
     Table 1 shows a result of the image analysis described above regarding the presence or absence of the generation of bubbles in a case where the peak flow speed was changed from a small value to a large value. At this time, the vibration frequency was 13 Hz and ethylene glycol was used as the liquid L. 
     
       
         
           
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Peak flow speed 
                   
               
               
                 [m/sec] 
                 State of bubbles 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                 1.514976 
                 Absent 
               
               
                 2.800551 
                 Small bubbles are slightly observed 
               
               
                 3.058716 
                 Small bubbles are slightly observed 
               
               
                 3.59149 
                 Generated 
               
               
                 3.586132 
                 Generated 
               
               
                 3.730659 
                 Generated 
               
               
                   
               
            
           
         
       
     
     From Table 1, the generation of bubbles was recognized in a case where the peak flow speed was 3.59149 m/sec or higher. Therefore, bubbles were not generated in a case where the value of the peak flow speed was smaller than 3.3 m/sec. Accordingly, in a case where the value of the peak flow speed was smaller than 3.3 m/sec, it can be ascertained that there is no possibility of the occurrence of cavitation. 
     Therefore, since the peak flow speed can be restrained to a value smaller than 3.3 m/sec by the flow-speed restraint portion  32 , the occurrence of cavitation can be restrained. For example, generation of an allophone can be restrained. 
     Second Embodiment 
     Next, a vibration-damping device in a second embodiment according to the present invention will be described with reference to  FIG. 3 . 
       FIG. 3  is a plan view of a partition member. 
     In the second embodiment, the same reference signs are applied to the same constituent elements as in the first embodiment. Description thereof will be omitted, and only the different points will be described. 
     In a vibration-damping device  40  according to the present embodiment, in place of the configuration in which the flow-speed restraint portion  32  includes both the first restraint portion  33  and the second restraint portion  34 , the flow-speed restraint portion  32  includes only the first restraint portion  33 . The first restraint portion  33  restrains the peak flow speed alone to 10 m/sec or lower. 
     In place of the rectification path  27   b  and the vortex chamber  27   a , the restriction passage  24  includes a connection port  41  through which the circumferential groove  25  and the main liquid chamber  14  communicate with each other. The connection port  41  is an opening portion of the restriction passage  24  on the main liquid chamber  14  side. 
     The porous body  28  is integrally formed with the partition member  16 . The porous body  28  has a shape and a size equal to those of the connection port  41  in a plan view of the partition member  16 . An outer circumferential edge of the porous body  28  is coupled to an inner circumferential edge of the connection port  41  throughout the entire circumference. 
     A plurality of the hole portions  31  are disposed at intervals in the radial direction. The hole portions  31  disposed at intervals in the radial direction form hole rows  42 . In the present embodiment, the hole portions  31  form a plurality (two) of hole rows  42 . The plurality of the hole portions  31  (the hole rows  42 ) are disposed at intervals in the circumferential direction. 
     As described above, in the vibration-damping device  40  according to the present embodiment, it is possible to exhibit operational effects similar to those of the embodiment described above. 
     That is, similar to the first embodiment, even in the vibration-damping device  40  according to the second embodiment, since the flow-speed restraint portion  32  restrains the peak flow speed to 10 m/sec or lower, the occurrence of cavitation can be restrained. For example, generation of an allophone can be restrained. 
     Moreover, since the flow-speed restraint portion  32  restrains the peak flow speed to a value smaller than 3.3 m/sec, the occurrence of cavitation can be restrained. For example, generation of an allophone can be restrained. 
     The technical scope of the present invention is not limited to the embodiment described above, and various changes can be applied within a range not departing from the scope of the present invention. 
     The flow-speed restraint portion  32  may include both the first restraint portion  33  and the second restraint portion  34 , may include only the first restraint portion  33 , or may include only the second restraint portion  34 . 
     The first restraint portion  33  and the second restraint portion  34  are not limited to the configuration illustrated in the embodiment described above. 
     The flow-speed restraint portion  32  can employ a form different from those of the first restraint portion  33  and the second restraint portion  34 . For example, it is possible to employ a different form in which the cross-sectional area of the flow channel of the restriction passage  24  is narrowed to generate resistance to the liquid L. 
     The flow-speed restraint portion  32  does not have to be disposed in the end portion of the restriction passage  24  on the main liquid chamber  14  side. 
     The flow-speed restraint portion  32  does not have to be disposed at an intermediate position along the flow channel direction of the restriction passage  24 . 
     In the embodiment described above, the partition member  16  is disposed in the lower end portion of the first attachment member  11 , and the flange portion  22  of the partition member  16  is brought into contact with the lower end surface of the first attachment member  11 . However, the present invention is not limited thereto. For example, the sub-liquid chamber  15  may be formed from the lower end portion of the first attachment member  11  to a bottom surface of the diaphragm  20  by disposing the partition member  16  above the lower end surface of the first attachment member  11  and installing the diaphragm  20  on the lower side of this partition member  16 , that is, the lower end portion of the first attachment member  11 . 
     In the embodiments described above, the compression-type vibration-damping devices  10  and  40  have been described. However, the present invention is not limited thereto. For example, the present invention can also be applied to a suspension-type vibration-damping device in which the main liquid chamber  14  is positioned on the lower side in the vertical direction, and the sub-liquid chamber  15  is attached to be positioned on the upper side of the vertical direction. 
     The vibration-damping devices  10  and  40  according to the present invention are not limited to an engine mount of a vehicle and can also be applied to a mount other than the engine mount. For example, the vibration-damping devices  10  and  40  can be applied to a mount of a generator installed in construction equipment or can be applied to a mount of a machine installed in a factory or the like as well. 
     Modification examples of the flow-speed restraint portion  32  will be described below. 
     In the following description, the same reference signs are applied to the same parts of the constituent elements in the first embodiment. Description thereof will be omitted, and only the different points will be described. 
     Flow-speed restraint portions  260 ,  261 ,  2600 , and  2900  illustrated in  FIGS. 8 to 10  are the modification examples of the flow-speed restraint portion  32 . 
       FIG. 8  illustrates a first modification example of the flow-speed restraint portion  260  constituted of a first communication portion  260 .  FIG. 9  illustrates a second modification example of the flow-speed restraint portion  261  constituted of a first communication portion  261 . 
     In  FIG. 8 , a restriction passage  240  includes a circumferential groove  250  which is disposed inside a partition member  160 , the first communication portion  260  through which the circumferential groove  250  and the main liquid chamber  14  communicate with each other, and a second communication portion  270  through which the circumferential groove  250  and the sub-liquid chamber  15  communicate with each other. 
     The circumferential groove  250  extends along the circumferential direction inside the partition member  160 , and a flow channel direction R of the circumferential groove  250  and the circumferential direction are directions equal to each other. The circumferential groove  250  is formed to have an arc shape disposed coaxially with the axial center O and extends along the circumferential direction throughout approximately the entire circumference. Both the end portions of the circumferential groove  250  along the circumferential direction are isolated from each other by a division wall  280   a  extending in the radial direction and the axial direction. 
     The circumferential groove  250  is defined by a first barrier wall  280  facing the main liquid chamber  14 , a second barrier wall  290  facing the sub-liquid chamber  15 , an upper flange portion (not illustrated), the rubber film  17 , and the division wall  280   a . The first barrier wall  280  and the second barrier wall  290  do not have to define the circumferential groove  250 . 
     The first barrier wall  280  is formed to have a tubular shape extending downward from the inner circumferential edge of the upper flange portion. As illustrated in  FIG. 8 , on the outer circumferential surface of the first barrier wall  280 , a part in which the first communication portion  260  is installed gradually faces the outer side in the radial direction while being distanced from the second communication portion  270  in the flow channel direction R. Accordingly, in the circumferential groove  250 , a flow channel area of a connection part  250   a  with respect to the first communication portion  260  is gradually reduced while being distanced from the second communication portion  27  in the flow channel direction R. 
     The second barrier wall  290  is formed to have a plate shape of which front and rear surfaces are directed in the axial direction. The upper surface of the second barrier wall  290  and a lower end of the first barrier wall  280  are connected to each other. The first barrier wall  280  is sandwiched by the circumferential groove  250  and the main liquid chamber  14  in the radial direction and is positioned between the circumferential groove  250  and the main liquid chamber  14 . The second barrier wall  290  is sandwiched by the circumferential groove  250  and the sub-liquid chamber  15  in the axial direction and is positioned between the circumferential groove  250  and the sub-liquid chamber  15 . 
     The first communication portion  260  includes a plurality of fine holes  260   a  which penetrate the first barrier wall  280  in the radial direction and are disposed along the flow channel direction R. The plurality of fine holes  260   a  are disposed in a part forming the end portion on one side of the circumferential groove  250  along the circumferential direction in the first barrier wall  280 . 
     The second communication portion  270  is an opening penetrating the second barrier wall  290  in the axial direction. The second communication portion  270  is disposed in a part forming the end portion on the other side of the circumferential groove  250  in the circumferential direction in the second barrier wall  290 . 
     Each of the plurality of fine holes  260   a  is formed to have a rectangular parallelepiped shape. Each of the opening portions of the plurality of fine holes  260   a  facing the main liquid chamber  14  is formed to have a rectangular shape being longer in the axial direction than in the circumferential direction in a front view seen from the inner side in the radial direction. The cross-sectional area of the flow channel of each of the plurality of fine holes  260   a  is equally formed throughout the entire length of the flow channel of each of the fine holes  260   a . The widths of the plurality of fine holes  260   a  in the circumferential direction are equal to each other. The plurality of fine holes  260   a  are disposed at intervals equal to each other in the circumferential direction. 
     In addition, the length of each of the plurality of fine holes  260   a  in the axial direction is reduced as the fine hole  260   a  is positioned away from the second communication portion  270  in the flow channel direction R. Accordingly, the projected area or the opening area of the smallest cross section of each of the plurality of fine holes  260   a  is reduced as the fine hole  260   a  is positioned away from the second communication portion  270  in the flow channel direction R. As a result, in the first barrier wall  280 , the ratio of the projected area or the opening area of the smallest cross section of each of the fine holes  260   a  per predetermined area on the inner circumferential surface facing the main liquid chamber  14  is gradually reduced as the fine hole  260   a  is distanced from the second communication portion  270  in the flow channel direction R. 
     In addition, the length of the flow channel of each of the plurality of fine holes  260   a  is increased as the fine hole  260   a  is positioned away from the second communication portion  270  in the flow channel direction R. According to those described above, resistance of each of the plurality of fine holes  260   a  when the liquid L flows in the fine hole  260   a  is increased as the fine hole  260   a  is positioned away from the second communication portion  270  in the flow channel direction R. 
     The “projected area” indicates a projected area directed in a direction in which the center line of the fine hole passing through the middle of the smallest cross section of the fine hole  260   a  extends toward a surface positioned inside the main liquid chamber  14  or inside the sub-liquid chamber  15  in the first barrier wall  280  or the second barrier wall  290 . 
     In a vibration-damping device  100  having such a configuration, when vibration is input, both the attachment members  11  and  12  are relatively displaced while causing the elastic body  13  to be elastically deformed. Consequently, the liquid pressure in the main liquid chamber  14  fluctuates, and the liquid L inside the main liquid chamber  14  flows into the sub-liquid chamber  15  through the restriction passage  240 . In addition, the liquid L inside the sub-liquid chamber  15  flows into the main liquid chamber  14  through the restriction passage  240 . That is, a part of the liquid L inside the sub-liquid chamber  15  returns to the main liquid chamber  14 . In this case, for example, a part of the liquid L evaporates and air bubbles are generated due to the main liquid chamber  14  under a negative pressure, thereby causing a collapse of cavitation. Alternatively, a flow of the liquid L, which flows in the circumferential groove  250  and is directed toward the first communication portion  260 , passes through the plurality of fine holes  260   a  due to inertia. Thereafter, the liquid L collides with the division wall  280   a  and flows into the main liquid chamber  14  in a biased manner from the fine hole of the plurality of fine holes  260   a  positioned close to the division wall  280   a . Therefore, the flow speed of the liquid L which has passed through the plurality of fine holes  260   a  is locally increased, so that there are cases where air bubbles are generated and a collapse of cavitation occurs. 
     In the vibration-damping device  100  according to the present embodiment, when the liquid L flows out to the main liquid chamber  14  from the circumferential groove  250  through the plurality of fine holes  260   a , the liquid L flows in each of the fine holes  260   a  while causing a pressure loss due to the first barrier wall  280  in which these fine holes  260   a  are formed. Accordingly, the flow speed of the liquid L flowing in each of the fine holes  260   a  can be restrained from being increased. Moreover, since the liquid L flows in the plurality of fine holes  260   a  instead of a single fine hole  260   a , the liquid L can flow in a plurality of branched holes. Therefore, the flow speed of the liquid L which has passed through each of the fine holes  260   a  can be reduced. Accordingly, the difference in the flow speed caused between the liquid L which has passed through the fine holes  260   a  and has flowed into the main liquid chamber  14  and the liquid L inside the main liquid chamber  14  can be minimized, so that generation of a vortex due to the difference between the flow speeds and generation of air bubbles due to this vortex can be restrained. 
     Moreover, in the first barrier wall  280 , the ratio of the projected area or the opening area of the smallest cross section of each of the fine holes  260   a  per predetermined area on the inner circumferential surface facing the main liquid chamber  14  is gradually reduced as the fine hole  260   a  is distanced from the second communication portion  270  in the flow channel direction R. Therefore, when the liquid L flowing inside the restriction passage  240  arrives at the first communication portion  260  from the second communication portion  270 , the liquid L can be restrained from passing through the fine hole  260   a , of the plurality of fine holes  260   a , positioned on the second communication portion  270  side in the flow channel direction R due to an inertial force on the fine hole  260   a  side positioned away from the second communication portion  270  in the flow channel direction R. Accordingly, the liquid L is likely to flow out from the fine hole  260   a  positioned on this second communication portion  270  side, so that the flow speed of the liquid L flowing out from each of the fine holes  260   a  becomes uniform to be restrained from being locally high. Therefore, it is possible to more effectively inhibit generation of air bubbles and generation of an allophone due to a collapse of cavitation. 
     In addition, the projected area or the opening area of the smallest cross section of each of the plurality of fine holes  260   a  is reduced as the fine hole  260   a  is positioned away from the second communication portion  270  in the flow channel direction R. 
     Therefore, a structure in which in the first barrier wall  280  the ratio of the projected area or the opening area of the smallest cross section of each of the fine holes  260   a  per predetermined area on the inner circumferential surface facing the main liquid chamber  14  is gradually reduced as the fine hole  260   a  is distanced from the second communication portion  270  in the flow channel direction R can be reliably realized in a simple configuration. 
     In addition, the length of the flow channel of each of the plurality of fine holes  260   a  is increased as the fine hole  260   a  is positioned away from the second communication portion  270  in the flow channel direction R. Therefore, it is possible to increase a pressure loss of the liquid L flowing in the fine hole  260   a , of the plurality of fine holes  260   a , positioned away from the second communication portion  270  in the flow channel direction R. Therefore, a large amount of liquid can be restrained from flowing out at a high speed from the fine hole  260   a , of the plurality of fine holes  260   a , positioned away from the second communication portion  270  in the flow channel direction R. 
     In addition, in the circumferential groove  250 , the flow channel area of the connection part  250   a  with respect to the first communication portion  260  is gradually reduced while being distanced from the second communication portion  270  in the flow channel direction R. Therefore, flow resistance gradually increases during a process while the liquid L flows in the connection part  250   a , so that the flow speed of the liquid L is restrained. Accordingly, the liquid L is inhibited from passing through the fine hole  260   a  positioned on the second communication portion  270  side in the flow channel direction R due to inertia, so that the liquid is likely to flow out from the fine hole  260   a  on the second communication portion  270  side. Therefore, a large amount of the liquid L can be reliably restrained from flowing out at a high speed from the fine hole  260   a  positioned away from the second communication portion  270  in the flow channel direction R. 
     In the second modification example of the flow-speed restraint portion  261  illustrated in  FIG. 9 , a plurality of fine holes  261   a  are disposed at different intervals in the circumferential direction. 
     In the second modification example of the flow-speed restraint portion  261  illustrated in  FIG. 9 , the intervals at which the plurality of fine holes  261   a  are disposed in the circumferential direction are not uniform. Specifically, the interval between the fine holes  261   a  adjacent to each other in the flow channel direction R becomes gradually wide while being distanced from the second communication portion  270  in the flow channel direction R. 
     In such a configuration, the interval between the fine holes  261   a  adjacent to each other in the flow channel direction R becomes gradually wide while being distanced from the second communication portion  270  in the flow channel direction R. Therefore, a structure in which in the first barrier wall  280  the ratio of the projected area or the opening area of the smallest cross section of each of the fine holes  261   a  per predetermined area on the inner circumferential surface facing the main liquid chamber  14  is gradually reduced as the fine hole  261   a  is distanced from the second communication portion  270  in the flow channel direction R can be reliably realized in a simple configuration. 
       FIG. 10  is a perspective view illustrating a third modification example of flow-speed restraint portions  2600  and  2900  constituted of a first communication portion  2600  and a vortex chamber  2900 . As illustrated in  FIG. 10 , a circumferential groove  2500  includes a rectification path  2800  and the vortex chamber  2900 . The rectification path  2800  is formed to have a circumferential groove shape on the outer circumferential surface of a partition member  1600 . The rectification path  2800  extends throughout at least half the circumference or longer on the outer circumferential surface of the partition member  1600 . The rectification path  2800  is formed in an outer circumferential portion  3200   a  which is formed between a side surface of a recessed portion  3100  formed on the upper surface of the partition member  1600 , and the outer circumferential surface of the partition member  16 . In the rectification path  2800 , the flow channel direction R of a restriction passage  2400  is the circumferential direction. 
     The vortex chamber  2900  is provided in a first end portion (not illustrated) of two end portions of the rectification path  2800  in the circumferential direction. The first end portion is a connection part with respect to the vortex chamber  2900  in the rectification path  2800 . 
     As illustrated in  FIG. 10 , the cross-sectional area of the flow channel of the first end portion (not illustrated) is reduced while being distanced from the second communication portion  2700  along the flow channel direction R. The first end portion is reduced in the axial direction while being distanced from a second communication portion  2700  along the flow channel direction R. 
     As illustrated in  FIG. 10 , the vortex chamber  2900  is provided throughout a plate-shaped middle part  3200   b  blocking the insides of the outer circumferential portion  3200   a  and the outer circumferential portion  3200   a . The vortex chamber  2900  is formed to have a circular shape in a top view. The inner circumferential surface of the vortex chamber  2900  forms the outer circumferential edge of the vortex chamber  2900  in a top view. The diameter of the vortex chamber  2900  is smaller than the diameter of the partition member  1600 , and the central axis line of the vortex chamber  2900  is eccentric with respect to the axial center O. In a top view, the outer circumferential edge of the vortex chamber  2900  is internally in contact with the outer circumferential surface of the partition member  1600 . 
     The vortex chamber  2900  forms a swirling flow of the liquid L in accordance with the flow speed of the liquid L from the rectification path  2800 . When the flow speed of the liquid L flowing into the vortex chamber  2900  is low, the liquid L is restrained from swirling inside the vortex chamber  2900 , but when the flow speed of the liquid L is high, a swirling flow of the liquid L is formed inside the vortex chamber  2900 . A swirling flow swirls along a direction around the central axis line of the vortex chamber  2900 . That is, a swirling direction T of a swirling flow of the liquid L formed in the vortex chamber  2900  becomes a direction around the central axis line of the vortex chamber  2900  in a plan view of a vibration-damping device  1000  seen in the axial direction. 
     A front side along the swirling direction T becomes the counterclockwise side in a top view, and a rear side along the swirling direction T becomes the clockwise side in a top view. Hereinafter, in a plan view of the vibration-damping device  1000  seen in the axial direction, a direction orthogonal to the central axis line of the vortex chamber  2900  will be referred to as a swirling radial direction. 
     As illustrated in  FIG. 10 , a groove portion  3300  is formed on the bottom surface of the recessed portion  3100 . The groove portion  3300  extends along the swirling direction T. The groove portion  3300  is formed to have an arc shape in a top view. In a top view, the groove portion  3300  is disposed along the outer circumferential edge of the vortex chamber  2900 . In a top view, both end portions of the groove portion  3300  reach the side surfaces of the recessed portion  3100 , and the groove portion  3300  divides the bottom surface of the recessed portion  3100  into two regions. 
     As illustrated in  FIG. 10 , in the side surfaces of the groove portion  3300 , a first side surface  3300   a  facing the outer side in the swirling radial direction extends in a manner parallel to the axial direction. In the side surfaces of the groove portion  3300 , a second side surface  3300   b  facing the inner side in the swirling radial direction includes an inclination surface  3300   c , a horizontal surface  3300   d , and a vertical surface  3300   e . The inclination surface  3300   c , the horizontal surface  3300   d , and the vertical surface  3300   e  are provided downward from above in this order. The inclination surface  3300   c  gradually extends toward the inner side in the swirling radial direction while extending downward from above. The horizontal surface  3300   d  extends toward the inner side in the swirling radial direction from the lower end portion of the inclination surface  3300   c . The vertical surface  3300   e  extends downward from the end portion of the horizontal surface  3300   d  on the inner side in the swirling radial direction. The bottom surface of the groove portion  3300  is disposed to be flush with the lower surface of the vortex chamber  2900 . 
     As illustrated in  FIG. 10 , the partition member  1600  includes a first barrier wall  3400  facing the main liquid chamber  14 , and a second barrier wall  3500  facing the sub-liquid chamber  15 . The first barrier wall  3400  is formed by a part positioned between the inner circumferential surface of the vortex chamber  2900  and the first side surface  3300   a , in the partition member  1600 . The first barrier wall  3400  extends along the swirling direction T. The second barrier wall  3500  is formed by a part positioned between the inner surface of the rectification path  2800  and the lower surface of the partition member  1600 , in the partition member  1600 . The second barrier wall  3500  extends along the flow channel direction R. 
     The first communication portion  2600  is formed in the first barrier wall  3400  and is open in the main liquid chamber  14 . The second communication portion  2700  is formed in the second barrier wall  3500  and is open in the sub-liquid chamber  15 . 
     At least one of the first communication portion  2600  and the second communication portion  2700  includes a plurality of fine holes  2600   a  penetrating the first barrier wall  3400  or the second barrier wall  3500 . In the example illustrated in  FIG. 10 , the first communication portion  2600  includes the plurality of fine holes  2600   a  penetrating the first barrier wall  3400 . 
     The plurality of fine holes  2600   a  are disposed in the first barrier wall  3400  along the swirling direction T. The plurality of fine holes  2600   a  are disposed at intervals in the swirling direction T. The fine holes  2600   a  penetrate the first barrier wall  3400  in the swirling radial direction. Each of the opening portions of the plurality of fine holes  2600   a  facing the main liquid chamber  14  is formed to have a rectangular shape extending in the axial direction in a front view seen from the outer side in the swirling radial direction. The lower end portions of the fine holes  2600   a  are positioned on the lower surface of the vortex chamber  2900  (the bottom surface of the groove portion  3300 ). The cross-sectional area of the flow channel of each of the plurality of fine holes  2600   a  gradually increases toward the outer side from the inner side in the length direction of the flow channel (in the illustrated example, the swirling radial direction) of each of the fine holes  2600   a.    
     The ratio of the opening area or the projected area of the smallest cross section in each of the fine holes  2600   a  per predetermined area in the first barrier wall  3400  gradually increases toward the front side from the rear side in the swirling direction T. The “projected area” indicates a projected area directed in a direction in which the center line of the fine hole passing through the middle of the smallest cross section of the fine hole  2600   a  extends toward a surface positioned inside the main liquid chamber  14  in the first barrier wall  3400 . In the example illustrated in  FIG. 10 , the “projected area” indicates a projected area of the fine holes  2600   a  in the swirling radial direction (the length direction of the flow channel) to the first side surface  3300   a  of the smallest cross section. 
     In the present embodiment, the widths of the plurality of fine holes  2600   a  in the circumferential direction are equal to each other. The plurality of fine holes  2600   a  are disposed at intervals equal to each other in the circumferential direction. The length of each of the plurality of fine holes  2600   a  in the axial direction gradually increases toward the front side from the rear side in the swirling direction T. Accordingly, the foregoing ratio gradually increases toward the front side from the rear side in the swirling direction T. 
     In the illustrated example, a part avoiding the fine holes  2600   a  in the first side surface  3300   a  is provided with a bridge portion  3600  connecting the first side surface  3300   a  and the second side surface  3300   b  to each other. The lower surface of the bridge portion  3600  is fixed to the bottom surface of the groove portion  3300 , and the upper surface of the bridge portion  3600  is formed to be flush with the horizontal surface  3300   d.    
     The second communication portion  2700  penetrates the second barrier wall  3500  in the axial direction. The second communication portion  2700  is formed to have a rectangular shape elongated in the flow channel direction R. The second communication portion  2700  is open in a second end portion  2800   b  of the rectification path  2800 . 
     In the restriction passage  2400 , the first communication portion  2600  and the second communication portion  2700  communicate with each other through the circumferential groove  2500 . In the circumferential groove  2500 , the vortex chamber  2900  is formed in the connection part with respect to the first communication portion  2600  which is at least one of the first communication portion  2600  and the second communication portion  2700 . The vortex chamber  2900  forms a swirling flow of the liquid L in accordance with the flow speed of the liquid L from the second communication portion  2700  side which is the other side of the first communication portion  2600  and the second communication portion  2700 , and this liquid L flows out through the fine holes  2600   a.    
     In the vibration-damping device  1000  having such a configuration, when vibration is input, both the attachment members  11  and  12  are relatively displaced while causing the elastic body  13  to be elastically deformed. Consequently, the liquid pressure in the main liquid chamber  14  fluctuates, and the liquid L inside the main liquid chamber  14  flows into the sub-liquid chamber  15  through the restriction passage  2400 . In addition, the liquid L inside the sub-liquid chamber  15  flows into the main liquid chamber  14  through the restriction passage  2400 . That is, a part of the liquid L inside the sub-liquid chamber  15  returns to the main liquid chamber  14 . 
     In the vibration-damping device  1000  according to the example illustrated in  FIG. 10 , in a case where a significant load (vibration) is input to the vibration-damping device  1000 , and when the liquid L flows into the vortex chamber  2900  from the second communication portion  2700  side, if the flow speed of the liquid L is sufficiently high and a swirling flow of the liquid L is formed inside the vortex chamber  2900 , for example, a pressure loss of the liquid L can be increased due to an energy loss caused by forming this swirling flow, or an energy loss caused by friction between the liquid L and the wall surface of the vortex chamber  2900 . Moreover, when the liquid L flows out through the plurality of fine holes  2600   a , while the liquid L causing a pressure loss due to the first barrier wall  3400  in which these fine holes  2600   a  are formed, the liquid L flows in the fine holes  2600   a , so that the flow speed of the liquid L flowing in the plurality of fine holes  2600   a  can be restrained from being increased. Moreover, since the liquid L flows in the plurality of fine holes  2600   a  instead of a single fine hole  2600   a , the liquid L can flow in a plurality of branched holes. Therefore, the flow speed of the liquid L which has passed through each of the fine holes  2600   a  can be reduced. Accordingly, the difference in the flow speed caused between the liquid L which has passed through the fine holes  2600   a  and has flowed into the main liquid chamber  14  and the liquid L inside the main liquid chamber  14  can be minimized, so that generation of a vortex due to the difference between the flow speeds and generation of air bubbles due to this vortex can be restrained. Moreover, even if air bubbles are generated, since the plurality of fine holes  2600   a  are disposed, generated air bubbles can be separated from each other and can be easily maintained in a state where the air bubbles are restrained from being joined and growing such that the air bubbles are finely dispersed. In addition, even if air bubbles are generated inside the restriction passage  2400  instead of the main liquid chamber  14 , the air bubbles are divided into small air bubbles and then can be dispersed, when the air bubbles pass through the fine holes  2600   a.    
     As described above, generation of air bubbles itself can be restrained, and for example, even if air bubbles are generated, the air bubbles can be easily maintained in a state of being finely dispersed. Therefore, even if a collapse of cavitation in which air bubbles collapse occurs, generation of an allophone can be minimized. 
     In addition, if a swirling flow of the liquid L is formed inside the vortex chamber  2900 , a pressure loss of the liquid L is caused. Therefore, the flow speed of the liquid L is gradually reduced toward the front side from the rear side in the swirling direction T. That is, if the liquid L forming a swirling flow is positioned closer to the rear side in the swirling direction T, the inertial force toward the outer side in the swirling radial direction increases. 
     The foregoing ratio gradually increases toward the front side from the rear side in the swirling direction T, and the foregoing ratio can be restrained on the rear side in the swirling direction T in which the flow speed of the liquid L is high. Therefore, due to an inertial force acting on the liquid L, the liquid L forming a swirling flow is restrained from flowing out from the vortex chamber  2900  through the fine hole  2600   a , of the plurality of fine holes  2600   a , positioned on the rear side in the swirling direction T, and the liquid L can also flow out from the fine hole  2600   a  positioned on the front side in the swirling direction T. Accordingly, a large amount of the liquid L can be restrained from locally flowing out at a high speed from the fine hole  2600   a  positioned on the rear side in the swirling direction T. Therefore, the liquid L can flow out from all of the plurality of fine holes  2600   a  while the flow speed is restrained from fluctuating, and generation of air bubbles can be effectively restrained. 
     In addition, since the projected area or the opening area of the smallest cross section of each of the plurality of fine holes  2600   a  increases as the fine hole  2600   a  is closer to the front side in the swirling direction T, it is possible to reliably realize a structure in which the foregoing ratio is gradually increased toward the front side from the rear side in the swirling direction T in a simple configuration. 
     In addition, since the cross-sectional area of the flow channel of the first end portion (not illustrated) is gradually reduced while being distanced from the second communication portion  2700  in the flow channel direction R, flow resistance gradually increases during a process while the liquid L flows in the first end portion, so that the flow speed of the liquid L is restrained. Accordingly, the flow speed of the liquid L flowing into the vortex chamber  2900  can be reduced, and the liquid L can be reliably restrained from flowing out from the fine hole  2600   a  positioned on the rear side in the swirling direction T due to inertia. 
     Furthermore, within a range not departing from the scope of the present invention, the constituent elements in the embodiments described above can be suitably replaced with known constituent elements. In addition, the foregoing modification examples may be suitably combined. 
     INDUSTRIAL APPLICABILITY 
     In a vibration-damping device according to the present invention, the occurrence of cavitation can be restrained. 
     REFERENCE SIGNS LIST 
     
         
           10 ,  40  vibration-damping device 
           11  first attachment member 
           12  second attachment member 
           13  elastic body 
           14  main liquid chamber 
           15  sub-liquid chamber 
           16  partition member 
           19  liquid chamber 
           24  restriction passage 
           27   a  vortex chamber 
           27   b  rectification path 
           28  porous body 
           32  flow-speed restraint portion 
           33  first restraint portion 
           34  second restraint portion 
         L liquid