Vibration isolator

A vibration isolator having a pair of pressure receiving fluid chambers between an outer cylinder and a mounting member, at two end sides along a main amplitude direction. A rubber elastic body changes the internal volumes of the pair of pressure receiving fluid chambers in directions opposite to each other, and fluid flows from the pressure receiving fluid chambers to an auxiliary fluid chamber through one of two orifices and flows from the auxiliary fluid chamber to the pressure receiving fluid chambers through the other orifice. Since a fluid pressure in the auxiliary fluid chamber is kept approximately constant, the fluid in the pair of pressure receiving fluid chambers smoothly flows, with a low resistance, into the auxiliary fluid chamber through the orifices. Therefore, any rise of the fluid pressure in the pressure receiving fluid chambers may be suppressed, such that rise of the dynamic spring constant may be suppressed.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No. PCT/JP2006/307573 filed on Apr. 10, 2006, claiming priority based on Japanese Patent Application No. 2005-114949, filed Apr. 12, 2005, the contents of all of which are incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a fluid filled vibration isolator that is applicable to an engine mount or the like of an automobile or a general industrial machine, for absorbing vibrations from a vibration generation portion such as an engine or the like, and for preventing vibration transmission to a vibration receiving unit, such as a vehicle body or the like.

RELATED ART

For example, a vibration isolator is disposed, as an engine mount, between an engine which is a vibration generating portion of a vehicle and the vehicle body which is a vibration receiving portion, and such vibration isolator absorbs vibrations generated by the engine and suppress vibration transmission to the vehicle body side. Vibration isolators, such as those described in a document 1 and a document 2, respectively, are known for this type of vibration isolator.

The vibration isolator in the document 1 is configured as a so-called differential pressure type vibration isolator, and is provided with a rubber elastic body inside an outer cylinder, a pressure receiving fluid chamber with a portion of an internal wall formed by the rubber elastic body, and an auxiliary fluid chamber with a portion of an internal wall formed by a diaphragm, the pressure receiving fluid chamber and the auxiliary fluid chamber being mutually communicated by a restrict passage. In such a differential pressure type vibration isolator, when vibration is input, the rubber elastic body elastically deforms, and also, along with the elastic deformation of the rubber elastic body, the internal volume of the pressure receiving fluid chamber expands and contracts, thereby absorbing the inputted vibration by the viscous resistance and the like of liquid flowing in the restrict passage communicating the pressure receiving fluid chamber and the auxiliary fluid chamber.

The vibration isolator of the document 2 is configured as a so-called differential motion of pressure type vibration isolator, provided with: an outer cylinder, connected to one or other of a vibration generating portion or a vibration receiving unit; an internal cylinder, connected to the other of the vibration generating portion or the vibration receiving unit; a rubber elastic body, disposed between the outer cylinder and the inner cylinder and elastically deforming when vibration is generated: a pair of fluid chambers, having a portion of a partitioning wall formed by the rubber elastic body, and the pair being disposed at both ends with the inner cylinder in between, and respectively expanding and contracting when vibration is generated; and a restrict passage connecting together the pair of fluid chambers. In this differential motion of pressure type vibration isolator, when vibration is inputted, the internal volume of one of the fluid chambers contracts, and the internal volume of the other of the fluid chambers expands, causing fluid to flow in the restrict passage due to a fluid pressure difference generated between this pair of fluid chambers. When this occurs, the change in the internal volume of one of the fluid chambers is in the mutually opposite direction to that of the other of the fluid chambers (one expands while the other contracts), therefore the fluid pressure difference between the pair of fluid chambers may be made greater, in comparison to the fluid pressure difference between the pressure receiving fluid chamber and the auxiliary fluid chamber in a differential pressure vibration isolator, and the to-and-fro flow of fluid between the fluid chambers via the restrict passage may be promoted, and the damping of vibrations, obtained by the viscous resistance of the fluid and the like, may be increased effectively.

In the vibration isolators of the above described document 1 and the document 2, the passage length and cross-sectional area of the restrict passage is set (tuned) so as to correspond to a vibration of a particular frequency region (a shake vibration, for example), and when vibration is inputted in this particular frequency region, resonance phenomena occurs (liquid column resonance) in fluid that is passing to-and-fro in the restrict passage between the pair of pressure receiving fluid chambers, and inputted vibration may be effectively absorbed by this liquid column resonance.Document 1: Japanese Patent Application Laid-Open (JP-A) No. 5-149374Document 2: Japanese Patent Application Laid-Open (JP-A) No. 8-233022

DISCLOSURE OF THE INVENTION

Problem to be Solved by the Invention

However, in the above described differential pressure type vibration isolator, since fluid pressure change, in order to cause fluid to flow through the restrict passage between the pressure receiving fluid chamber and the auxiliary fluid chamber, is only generated in the pressure receiving fluid chamber, it is difficult to increase the amount of damping of vibrations that is obtained by fluid flowing in the restrict passage, when compared to a differential motion of pressure vibration isolator.

On the other hand, in the above described differential motion of pressure vibration isolator, when vibrations are input that are outside of the frequency region corresponding to the restrict passage (such as, for example, high frequency vibrations of booming noise and the like), the restrict passage becomes in a blocked state and fluid pressure within the fluid chamber is readily raised, when compared to in a differential pressure vibration isolator, and the dynamic spring constant rises along with the rise in the fluid pressure within the fluid chamber, leading to a worsening of the ability to absorb high frequency vibrations.

An object of the present invention is, considering the above conditions, to provide a vibration isolator capable of efficiently increasing damping against inputted vibration, obtained by a fluid flowing in a restrict passage and also effectively suppressing the rise in dynamic spring constant when vibration is inputted therein.

Means of Solving the Problem

In order to achieve the above objective, the vibration isolator according to claim1includes: an outer cylinder member that is formed in a substantially cylindrical shape, and is connected to one of a vibration generating portion or a vibration receiving portion; a mounting member that is disposed at an inner peripheral side of the outer cylinder member, and is connected to the other of the vibration generating portion or the vibration receiving portion; a rubber elastic body that is disposed between the outer cylinder member and the mounting member, and elastically connects the outer cylinder member and the mounting member; a pair of first pressure receiving fluid chambers, each of which is provided between the outer cylinder member and the mounting member, at least a portion of an internal wall of each first pressure receiving fluid chamber being formed of the elastic body, and the first pressure receiving fluid chambers being filled with fluid; an auxiliary fluid chamber that is filled with fluid, an internal volume of the auxiliary fluid chamber being able to expand or contract according to changes in fluid pressure; and a pair of first restrict passages that communicate respectively the pair of first pressure receiving fluid chambers with the auxiliary fluid chamber, wherein one of the first pressure receiving fluid chambers is disposed between the outer cylinder member and the mounting member at one end side in a radial direction with the mounting member being at the center, and the other of the first pressure receiving fluid chambers is disposed between the outer cylinder member and the mounting member at the other end side in the radial direction, and when the rubber elastic body elastically deforms due to vibration being inputted in a main amplitude direction, along which direction the pair of pressure receiving fluid chambers and the mounting member are arranged, in the radial direction, the rubber elastic body changes internal volumes of the pair of first pressure receiving fluid chambers in directions that are mutually opposite to each other, accompanying with elastically deforming in the main amplitude direction.

Explanation will now be given of the operation of the vibration isolator according to claim1of the present invention.

In the vibration isolator according to claim1, one of the first pressure receiving fluid chambers is disposed at the one side along the main amplitude direction between the outer cylinder member and the mounting member, and also the other of the first pressure receiving fluid chamber is disposed at the other side along the radial direction between the outer cylinder member and the mounting member. Thereby, when vibration in the radial direction is inputted to the outer cylinder member or the mounting member, the internal volumes of the pair of first pressure receiving fluid chambers are respectively changed (expanded or contracted), and since the fluid pressures within the pair of first pressure receiving fluid chambers also change (increases or decreases), fluid flows to-and-fro through one of the restrict passages between one of the first pressure receiving fluid chambers and the auxiliary fluid chamber, and fluid flows to-and-fro through the other of the restrict passages between the other of the first pressure receiving fluid chambers and the auxiliary fluid chamber.

When this occurs, if the length and the cross-sectional area of the first restrict passages, that is to say, if the resistance to fluid flow, is set (tuned) to correspond to the vibration frequency inputted in along the main amplitude direction, then resonance occurs (liquid column resonance) in the fluid flowing to-and-fro through one of the first restrict passages between one of the first pressure receiving fluid chambers and the auxiliary fluid chamber, and resonance (liquid column resonance) also occurs in the fluid flowing to-and-fro through the other of the first restrict passages between the other of the first pressure receiving fluid chambers and the auxiliary fluid chamber, therefore inputted vibration along the main amplitude direction can be effectively absorbed by the liquid column resonance occurring in the pair of the restrict passages.

Furthermore, in the vibration isolator according to claim1, when the rubber elastic body elastically deforms, due to the inputted vibration along the main amplitude direction of alignment of the pair of the pressure receiving fluid chambers and the mounting member, along with this elastic deformation in the main amplitude direction, the rubber elastic body changes the internal volume of each of the pair of first pressure receiving fluid chambers in directions that are mutually opposite to each other (expands one and contracts the other), and changes the fluid pressure within each of the pair of the pressure receiving fluid chambers in directions that are mutually opposite to each other (lowers one and raises the other). Thereby, while vibration is being inputted along the main amplitude direction, independent of the frequency of the inputted vibration, when fluid flows into the auxiliary fluid chamber from one of the pressure receiving fluid chambers through one of the restrict passages, fluid flows out from the auxiliary fluid chamber to the other of the pressure receiving fluid chambers through the other of the restrict passages. Therefore, even though the frequency of the inputted vibration is outside of the frequency regions corresponding to the restrict passages, the fluid pressure within the auxiliary fluid chamber is always maintained substantially constant, and an increase in the fluid pressure within the auxiliary fluid chamber can be made sufficiently small.

Therefore, in the vibration isolator according to claim1, when vibration is being inputted along the main amplitude direction, even though the frequency of the inputted vibration is outside of the frequency region corresponding to the restrict passages, an increase in the flow resistance of fluid flowing through one of the restrict passages between one of the pressure receiving fluid chambers and the auxiliary fluid chamber and an increase in the flow resistance of fluid flowing through the other of the restrict passages between the other of the pressure receiving fluid chambers and the auxiliary fluid chamber, due to an increase in the fluid pressure within the auxiliary fluid chamber, can each be suppressed. Therefore, when one of the first pressure receiving fluid chambers contracts, there is a smooth flow, with low resistance, of liquid out from the first pressure receiving fluid chamber, through the restrict passage, to the inside of the auxiliary fluid chamber. As a result of this, a rise in the fluid pressure within the pressure receiving fluid chamber can be suppressed, and therefore a rise in the dynamic spring constant with respect to the inputted vibration can be suppressed.

Also, in a case in which the frequency of the inputted vibration is within the frequency region corresponding to the restrict passages, the change in the fluid pressure (fluid pressure rise) within the auxiliary fluid chamber becomes sufficiently small, and there is no impediment to fluid flow within the restrict passages by a rise in the fluid pressure within the auxiliary fluid chamber, and therefore fluid can flow smoothly, with low resistance, through the pair of restrict passages, between each of the pair of pressure receiving fluid chambers and the auxiliary fluid chamber, respectively. As a result of this, the damping effect, obtained due to fluid undertaking liquid column resonance within each of the pair of restrict passages, can be effectively increased.

Furthermore, the vibration isolator according to claim2of the present invention is the vibration isolator of claim1, wherein the mounting member is disposed so as to pass through the internal peripheral side of the outer cylinder member.

The vibration isolator according claim3is the vibration isolator of claim1or claim2, including: a second pressure receiving fluid chamber that is at the inner peripheral side of the outer cylinder member, and is provided between the rubber elastic body and a dividing member that is disposed at an axial direction outside of the rubber elastic body, the second pressure receiving fluid chamber being filled with fluid; and a second restrict passage that mutually communicates the second pressure receiving fluid chamber and the auxiliary fluid chamber.

The vibration isolator according to claim4is the vibration isolator of any one of claim1to claim3, wherein, at the rubber elastic body, a pair of elastic partitioning wall portions that partition respectively the pair of first pressure receiving fluid chambers from external space are formed, and the cross-sectional shape in the radial direction of each elastic partitioning wall portion is shaped so as to protrude in a convex manner toward chamber inside of the first pressure receiving fluid chamber.

Effect of the Invention

As explained above, according to the vibration isolator of the present invention, damping against inputted vibration, provided by a fluid flowing in a restrict passage, can be effectively increased, and also any rise in dynamic spring constant when vibration is inputted can be effectively suppressed.

BEST MODE OF IMPLEMENTING THE INVENTION

Explanation will now be given of vibration isolators according to exemplary embodiments of the present invention, with reference to the drawings.

First Exemplary Embodiment

FIG. 1shows a vibration isolator according to a first exemplary embodiment of the present invention. This vibration isolator10is one that is used in an engine mount of a vehicle, supporting an engine, which is a vibration generating portion, on a vehicle body, which is a vibration receiving unit, in a manner that isolates vibrations. It should be noted that in the figures, the indicator S shows the axial center of the device, and explanation will be given below with “device axial direction” referring to the direction along this axial center S, and with “device radial direction” referring to a direction that is perpendicular to this axial center S.

As shown inFIG. 1, in the vibration isolator10, there is provided a metal outer cylinder12, which is formed into a thin-walled, substantially circular cylindrical shape that is open at both ends in the axial direction thereof, at the outer peripheral side, and at the internal peripheral side of this outer cylinder12is disposed a metal mounting member20that is formed into a substantially circular pillar shape. In the outer cylinder12there is a flange portion14and a flange portion16, at one end portion and the other end portion in the axial direction thereof, respectively, formed bending around and extending toward the outer peripheral side.

In the vibration isolator10, there is an orifice forming member18fitted over the outer peripheral side of the outer cylinder12and inserted between the flange portion14and the flange portion16, the orifice forming member18being formed from a resin into a thick walled circular cylindrical shape. In the outer cylinder12, after the orifice forming member18has been inserted and fitted over the outer peripheral side thereof, the flange portion14is formed at one end by bending around the outer cylinder12toward the outer peripheral side. By so doing, movement of the orifice forming member18in the axial direction is restrained by the pair of flange portions14and16, and the orifice forming member18is fixed to the outer peripheral side of the outer cylinder12. In the vibration isolator10, there is also a bracket member (not shown in the drawings) provided fixed and connected to the outer peripheral side of the outer cylinder12, via the orifice forming member18, and it is attached to a vehicle body through this bracket member.

One end in the axial direction (the right side inFIG. 1) of the mounting member20protrudes out to the outside in the axial direction of the outer cylinder12. There is a threaded hole21provided to open at one end face along the axial center S of the mounting member20. A bolt (omitted in the drawings) is screwed into the threaded hole21, and the mounting member20is attached to the engine side through this bolt.

A rubber elastic body22is disposed in the vibration isolator10between the outer cylinder12and the mounting member20, the rubber elastic body22being formed overall into a substantially thick-walled circular cylindrical shape. The outer peripheral face of the rubber elastic body22is bonded to the inner peripheral face of the outer cylinder12, and the inner peripheral face of the rubber elastic body22is bonded by vulcanization to the outer peripheral face of the mounting member20. The outer cylinder12is thereby elastically attached to the mounting member20by the rubber elastic body22.

In the vibration isolator10, a thin-walled metal circular cylindrical shaped support fastening24is fitted into the internal peripheral side of the outer cylinder12at the other end thereof. This support fastening24has a flange portion26formed thereto by bending, the flange portion26protruding toward the outer peripheral side from an end portion at the outside in the axial direction of the support fastening24, and the flange portion26abuts the flange portion16of the outer cylinder12. The outer cylinder12has the rubber elastic body22bonded to the inner peripheral face thereof, and, after the support fastening24is fitted into the inner peripheral side, the outer cylinder12is crimped toward the inner peripheral side so as to shrink the diameter thereof. The rubber elastic body22is thereby compressed (pre-compressed) in the radial direction and also the support fastening24is fixed to the inside of the outer cylinder12.

There is a thin membrane, circular plate-shaped diaphragm28disposed to the inner peripheral side of the support fastening24, and the whole of the circumference of the outer peripheral portion of the diaphragm28is bonded by vulcanization to the inner peripheral face of the support fastening24. A fluid chamber space is formed thereby between the diaphragm28and the rubber elastic body22at the inside of the outer cylinder12, the fluid chamber being partitioned off from external portions, and a fluid, such as ethylene glycol, silicone oil or the like, is filled into the fluid chamber to form an auxiliary fluid chamber30. Here, the diaphragm28curves in a wave-like form, in cross-section along a radial direction, so as to be in a slack state, thereby, the diaphragm28deforms with relatively small resistance in accordance with changes in the fluid pressure inside the auxiliary fluid chamber30, and the internal volume of the auxiliary fluid chamber30is able to expand and contract.

As shown inFIG. 1, there is a circular cylindrical portion32formed at an intermediate portion in the axial direction of the rubber elastic body22, and there is also a pair of hollow portions34and36at the outer peripheral side of the circular cylindrical portion32, formed as concave shapes from the outer peripheral face toward the internal peripheral side. As is shown here inFIG. 2, the hollow portion34and the hollow portion36sandwich the mounting member20therebetween in a radial direction, and are provided respectively at one end and the other end of the rubber elastic body22. The hollow portions34and36each form a substantially trapezoidal shape in cross-section along the axial direction, such that the width in the axial direction gets narrower on progression from the respective outer peripheral side to the respective internal peripheral side. Further, the inner peripheral face of the circular cylindrical portion32is bonded by vulcanization to an intermediate portion in the axial direction of the mounting member20.

As shown inFIG. 1, there is a partitioning wall portion38formed in a substantially circular plate shape to one end in the axial direction of the rubber elastic body22. The partitioning wall portion38is of substantially constant thickness in the axial direction at given positions on the radial direction thereof, and the inner peripheral face of the partitioning wall portion38is bonded by vulcanization to the outer peripheral surface at one end side of the mounting member20and the outer peripheral face of the partitioning wall portion38is bonded to the inner peripheral surface at one end side of the outer cylinder12. The partitioning wall portion38is formed here into a curved shape in cross-section in the axial direction, protruding in a convex manner toward the inside of the hollow portions34and36.

There is a partitioning wall portion40formed in a substantially circular thick-walled plate shape to the opposite end in the axial direction of the rubber elastic body22to the end of the partitioning wall portion38, via the circular cylindrical portion32. The partitioning wall portion40also has a substantially constant wall thickness, and the wall thickness thereof is thicker than the thickness of the partitioning wall portion38. The inner peripheral face of the partitioning wall portion40is bonded by vulcanization to the outer peripheral face at the other end side of the mounting member20, and also the outer peripheral face of the partitioning wall portion40is bonded to the inner peripheral face of the outer cylinder12, at a position thereon that is near the support fastening24.

As shown inFIG. 2, in the rubber elastic body22there is a pair of dividing walls42and44formed integrally to, and extending out to the outer peripheral side along radial directions from, the circular cylindrical portion32. These dividing walls42and44are each formed in a plate shape with a wall thickness in the circumferential direction that gradually gets thicker on progression from the internal peripheral side to the outer peripheral side, and the dividing walls42and44extend out in opposite directions to each other, with the circular cylindrical portion32at the center thereof. Outer peripheral edge portions of this pair of dividing walls42and44are each bonded to the inner peripheral face of the outer cylinder12. The space that is formed between the partitioning wall portion38and the partitioning wall portion40in the rubber elastic body22is thereby divided up, by the dividing wall42and the dividing wall44, into the hollow portion34and the hollow portion36.

In the vibration isolator10, the outer peripheral side of the hollow portions34and36is closed off by the inner peripheral face of the outer cylinder12, and the internal portions of the hollow portions34and36each form a fluid space that is partitioned off from the outside. Each of this pair of fluid spaces is filed with the same liquid as that of the auxiliary fluid chamber30, and forms a pair of pressure receiving fluid chambers46and48.

As shown inFIG. 3, there are two lengths of internal peripheral grooves50and52formed in the inner peripheral face of the orifice forming member18, each of these being inclined to the circumferential direction, that is to say they are formed so as to extend in a spiral form. The internal peripheral grooves50and52each extend around approximately half of the circumference of the inner peripheral face of the orifice forming member18. In the internal peripheral grooves50and52, one end portions in the length direction thereof are positioned respectively at portions that are facing the pair of hollow portions34and36(pressure receiving fluid chambers46and48) in the rubber elastic body22, and other end portions that are positioned facing the auxiliary fluid chamber30. It should be noted that the lengths (passage length) of the internal peripheral grooves50are adjustable by increasing or decreasing the number of turns thereof, respectively, around the inner peripheral face of the orifice forming member18.

As shown inFIG. 1, there are cut out portions54and56formed to the outer cylinder12facing the respective one end and other end in the length direction of the one internal peripheral groove50, and there are cut out portions58and60formed to the outer cylinder12facing the respective one end and other end in the length direction of the other internal peripheral groove52. Thereby, the one end of the one internal peripheral groove50communicates through the cut out portion54to the pressure receiving fluid chamber46, and the other end thereof communicates through the cut out portion56to the auxiliary fluid chamber30. The one end of the other internal peripheral groove52communicates through the cut out portion58to the pressure receiving fluid chamber46, and the other end thereof communicates through the cut out portion60to the auxiliary fluid chamber30.

As shown inFIG. 1, the internal peripheral grooves50and52are each closed off on the inner peripheral side thereof by the outer peripheral face of the outer cylinder12, therefore long narrow spaces that each extend in a spiral form are formed inside each of the internal peripheral grooves50and52. The space formed within the internal peripheral groove50configures an orifice62that mutually communicates the one pressure receiving fluid chamber46and the auxiliary fluid chamber30. Also, the space formed within the internal peripheral groove52configures an orifice64that mutually communicates the other pressure receiving fluid chamber48and the auxiliary fluid chamber30. The passage length and the cross-sectional area of the pair of orifices62and64that communicate respectively the pair of pressure receiving fluid chambers46and48with the auxiliary fluid chamber30, are tuned to correspond to a shake vibration that is a low frequency vibration (such as 8 to 12 Hz, for example).

In the vibration isolator10according to the present exemplary embodiment, the mounting direction is set such that, in the state in which it is mounted to a vehicle as an engine mount, of the radial directions with the axial center S as the center, the direction along which the pressure receiving fluid chamber46, the mounting member20and the pressure receiving fluid chamber48are arranged, the main amplitude direction (the direction H inFIG. 2), substantially matches the vehicle up-down direction, and the device axial direction substantially matches the vehicle front-rear direction or substantially matches the vehicle left-right direction. Thereby, in the vibration isolator10, when vibration (main vibration) is inputted along the main amplitude direction, which substantially matches the main amplitude direction through the outer cylinder12or through the mounting member20, the rubber elastic body22elastically deforms in the main amplitude direction and also the rubber elastic body22changes (expands or contracts) the internal volume of the pair of the pressure receiving fluid chambers46and48. When this occurs, the rubber elastic body22changes the internal volume of each of the pressure receiving fluid chambers46and48in directions that are mutually opposite to each other, that is to say when the internal volume of one of the pair of pressure receiving fluid chambers46and48is expanded, the internal volume of the other is contracted.

Explanation will now be given of the operation of the vibration isolator10according to the present exemplary embodiment that has been configured as described above.

In the vibration isolator10, when an engine connected to the mounting member20is operated, vibrations from the engine are transmitted to the rubber elastic body22through the mounting member20. When this occurs, the rubber elastic body22acts as a vibration absorbing main body, and the inputted vibrations are absorbed by damping action due to internal friction and the like of the rubber elastic body22. When this occurs, the major vibrations input to the vibration isolator10from the engine may be seen as the vibration (main vibration) generated from the reciprocating movement of the pistons within the cylinders in the engine, and the vibration (secondary vibration) occurring with changes in the rotation speed of the crankshaft within the engine. When the engine is an in-line engine, the said main vibration has an amplitude direction (main amplitude direction) that substantially matches the vehicle up-down direction, and furthermore, the said secondary vibration has an amplitude direction (secondary amplitude direction) that is orthogonal to the amplitude direction of the main vibration that substantially matches either the vehicle front-rear direction (when the engine is transverse mounted) or the left-right direction (when the engine is longitudinal mounted). The rubber elastic body22is capable of absorbing the vibration by damping action due to internal friction and the like, both if the inputted vibration is the main vibration along the main amplitude direction, and if the inputted vibration is the secondary vibration along with the secondary amplitude direction.

In the vibration isolator10, the one pressure receiving fluid chamber46is disposed at one side in the main amplitude direction between the outer cylinder12and the mounting member20, and also the other pressure receiving fluid chamber48is disposed at the other side in the main amplitude direction between the outer cylinder12and the mounting member20, and when vibration in the main amplitude direction is inputted to the outer cylinder12or to the mounting member20, the internal volumes of the pair of pressure receiving fluid chambers46and48are respectively changed (expanded or contracted). Since, therefore, the fluid pressures inside the pair of pressure receiving fluid chambers46and48also change (increases or decreases), fluid flows to-and-fro through the one orifice62between the pressure receiving fluid chamber46and the auxiliary fluid chamber30, and fluid flows to-and-fro through the other orifice64between the pressure receiving fluid chamber48and the auxiliary fluid chamber30.

When this occurs, the lengths and the cross-sectional areas of the orifices62and64, that is to say the resistance to fluid flow, are tuned to correspond to a shake vibration that is of a low frequency vibration (8 to 12 Hz, for example), and therefore the when the inputted vibration is the shake vibration, resonance phenomena occurs (liquid column resonance) in the fluid flowing to-and-fro through the one orifice62between the pressure receiving fluid chamber46and the auxiliary fluid chamber30, and liquid column resonance also occurs in the fluid flowing to-and-fro through the other orifice64between the pressure receiving fluid chamber48and the auxiliary fluid chamber30. Therefore inputted vibration (shake vibration) in the main amplitude direction may be effectively absorbed by the liquid column resonance occurring in the pair of orifices62and64.

Furthermore, when the rubber elastic body22elastically deforms, due to the inputted vibration in the main amplitude direction of the direction of alignment of the pressure receiving fluid chamber46, the mounting member20and the pressure receiving fluid chamber48, along with elastic deformation in the main amplitude direction, the rubber elastic body22changes the internal volumes of each of the pair of pressure receiving fluid chambers46and48in directions that are mutually opposite to each other (expands one and contracts the other) and changes the fluid pressures within each of the pair of pressure receiving fluid chambers46and48in directions that are mutually opposite to each other (lowers one and raises the other). Thereby, when vibration in the main amplitude direction is input, independent of the frequency of the inputted vibration, when fluid flows into the auxiliary fluid chamber30from the pressure receiving fluid chamber46through the orifice62, fluid also flows out from the auxiliary fluid chamber30to the pressure receiving fluid chamber48through the other orifice64. Therefore, even though the frequency of the inputted vibration is outside of the frequency region corresponding to the orifices62and64, the fluid pressure within the auxiliary fluid chamber30is always maintained substantially constant, and an increase in the fluid pressure within the auxiliary fluid chamber30is suppressed.

That is, in the auxiliary fluid chamber30, since a portion of partitioning wall is formed from the low rigidity diaphragm28, naturally (ideally), even if fluid flows into the auxiliary fluid chamber30, rising of fluid pressure is not generated within the auxiliary fluid chamber30. However, in reality, when the durability of the diaphragm28and the like are considered, it is difficult to make the rigidity of the diaphragm28sufficiently small, and therefore when the fluid inflow amount to the auxiliary fluid chamber30becomes greater than the fluid outflow amount, a rise in the fluid pressure may occur, corresponding to the difference between the inflow amount and the outflow amount within the auxiliary fluid chamber30. However, in the vibration isolator10according to the present exemplary embodiment, when vibration is inputted in the main amplitude direction, since the fluid inflow amount and outflow amount of the auxiliary fluid chamber30become substantially equal, any rise in the fluid pressure within the auxiliary fluid chamber30can be made sufficiently small.

Therefore, according to the vibration isolator10of the present exemplary embodiment, when vibration is inputted in the main amplitude direction, even if the frequency of the inputted vibration is outside of the frequency region corresponding to the orifices62and64, an increase in the flow resistance of fluid flowing through the one orifice of the orifice62between the pressure receiving fluid chamber46and the auxiliary fluid chamber30and an increase in the flow resistance of fluid flowing through the other orifice of the orifice64between the pressure receiving fluid chamber48and the auxiliary fluid chamber30, due to an increase in the fluid pressure within the auxiliary fluid chamber30, can be suppressed. Therefore, when one of the pressure receiving fluid chambers46and48contracts, there is a smooth flow, with low resistance, of liquid out from the one of the pressure receiving fluid chambers46and48, through the respective orifice62and64, to the inside of the auxiliary fluid chamber30. As a result of this, a rise in the fluid pressure within the pair of pressure receiving fluid chambers46and48can be suppressed, and therefore a rise in the dynamic spring constant of the device can be suppressed.

Further, if the frequency of the inputted vibration is within the frequency region corresponding to the orifices62and64, the change in the fluid pressure within the auxiliary fluid chamber30(fluid pressure rise) becomes small, and there is no impediment to fluid flow within the restrict passage by a rise in the fluid pressure within the auxiliary fluid chamber30. Therefore, fluid flows smoothly, with low resistance, through the pair of orifices62and64, between each respective chamber of the pair of pressure receiving fluid chambers46and48and the auxiliary fluid chamber30. As a result of this, the damping effect, due to fluid being in a state of liquid column resonance within the respective of the orifices62and64, can be effectively increased.

Furthermore, in the vibration isolator10according to the present exemplary embodiment, since the cross-section of the partitioning wall portion38in the rubber elastic body22is curved so as to protrude in a convex shape toward the inside of the pressure receiving fluid chambers46and48, when vibration has been input in the main amplitude direction, effective expansion and contraction of the internal volume of the pressure receiving fluid chambers46and48can be achieved in comparison to a case in which the partitioning wall portion38is a flat plate shape, or in comparison to a curved shape so as to protrude in a convex shape toward the outside of the pressure receiving fluid chambers46and48.

That is, in the vibration isolator10, along with the input of vibration in the main amplitude direction, the mounting member20relatively displaces to one end side in the main amplitude direction, and one of the pressure receiving fluid chambers46and48disposed at one end side in the main amplitude direction compresses, and the other of the pressure receiving fluid chambers46and48disposed at the other end side expands. When this occurs, in the vibration isolator10, one end side of the partitioning wall portion38elastically deforms (flexure deformation) so that there is an increase in the amount that it intrudes (amount of curvature) in toward one of the pressure receiving fluid chambers46and48, and at the same time the other end side of the partitioning wall portion38elastically deforms so that there is a decrease in the amount that it intrudes (amount of curvature) in toward the other of the pressure receiving fluid chambers46and48. Thereby, in the vibration isolator10, when vibration is inputted in the main amplitude direction, the reduction in internal volume of the one of the pressure receiving fluid chambers46and48that is deforming by compressing is effectively promoted, and also the increase in the internal volume of the other of the pressure receiving fluid chambers46and48that is expanding is effectively promoted, when compared with a case in which the partitioning wall portion38is a flat plate shape, or compared with a curved shape so as to protrude in a convex shape toward the outside of the pressure receiving fluid chambers46and48.

As a result, by the vibration isolator10according to the present exemplary embodiment, when vibration is inputted in the main amplitude direction, the amount of fluid flowing via the orifices62and64between the pressure receiving fluid chambers46and48and the auxiliary fluid chamber30can be effectively promoted, and therefore, inputted vibrations in the secondary amplitude direction can be effectively absorbed by the viscous resistance of fluid flowing within the orifices62and64, and by pressure changes.

It should be noted that, in the vibration isolator10according to the present exemplary embodiment, the outer cylinder12is attached to the vehicle body side via a bracket member, and also the connection fastener36is attached to the engine side via a bolt, however, this may be reversed, and the outer cylinder12may be attached to the engine side and the mounting member20may be attached through the bolt to the vehicle body side.

Furthermore, in the vibration isolator10, tuning is carried out such that the passage lengths and the cross-sectional areas of the orifices62and64correspond to the shake vibration that is low frequency vibration (such as, for example, 8 to 12 Hz), however, the frequency range corresponding to the pair of orifices62and64can be adjusted by changing the passage lengths and the cross-sectional areas of the orifices62and64.

Second Exemplary Embodiment

A vibration isolator according to a second exemplary embodiment of the present invention is shown inFIG. 4. This vibration isolator70is one that is used in an engine mount of a vehicle, supporting an engine, which is a vibration generating portion, on a vehicle body, which is a vibration receiving unit, in a manner that isolates vibrations. It should be noted that in the figures, the indicator S shows the axial center of the device, and explanation will be given below with “device axial direction” referring to the direction along this axial center S, and with “device radial direction” referring to a direction that is perpendicular to this axial center S.

As shown inFIG. 4, in the vibration isolator70, there is provided a metal outer cylinder72, which is formed into a thin-walled, substantially circular cylindrical shape that is open at both ends in the axial direction thereof, at the outer peripheral side, and at the internal peripheral side of this outer cylinder72is disposed a metal internal cylinder74that is formed into a thick-walled circular cylindrical shape. The internal cylinder74passes through the outer cylinder72at the inner peripheral side thereof, and both ends of the internal cylinder74protrude out respectively from the inside of the outer cylinder72. There is a connecting hole76passing through the internal cylinder74along the axial center S. There is a bent portion78formed at one end portion in the axial direction (at the left end side inFIG. 4) of the outer cylinder72, formed so as to be bent and extend toward the inner peripheral side.

In the vibration isolator70, there is also a bracket member (not shown in the drawings) provided fixed to the outer peripheral side of the outer cylinder72, the outer cylinder72is attached to the vehicle body side via this bracket member, and the internal cylinder74is connected to the engine side by a connecting member such as a bolt or the like (not shown in the drawings), which has passed through the inside of the connecting hole76of the internal cylinder74.

There is a thin membrane-shaped covering rubber80made of rubber bonded by vulcanization to the whole of the inner peripheral face of the outer cylinder72, and an outer peripheral support fastening82, a first partitioning member84and an intermediate cylinder86are inserted and fitted in, in this sequence, toward one end side in the axial direction of the outer cylinder72, from the other end side thereof. In the vibration isolator70there is a rubber elastic body88disposed between the intermediate cylinder86and the internal cylinder74. This rubber elastic body88is formed overall into a thick, circular cylindrical shape, the inner peripheral face thereof being bonded by vulcanization to the outer peripheral face of the internal cylinder74, and the outer peripheral face thereof being bonded by vulcanization to the inner peripheral face of the intermediate cylinder86. In this manner the internal cylinder74and the intermediate cylinder86are connected together elastically via the rubber elastic body88.

The outer peripheral support fastening82is formed into a thin-walled circular cylindrical shape that is short in the axial direction, and the outer peripheral face of the outer peripheral support fastening82is pressure bonded to the inner peripheral face of the outer cylinder72via the covering rubber80, and the other end portion in the axial direction of the outer peripheral support fastening82abuts the bent portion78of the outer cylinder72. There is further an inner peripheral support fastening90, which is formed into a thin-walled circular cylindrical shape, disposed in the vibration isolator70at the inner peripheral side of the outer peripheral support fastening82, the inner peripheral support fastening90being press fitted to the outer peripheral side of the internal cylinder74, with a portion at the other end thereof abutted against a bottom plate portion94of the first partitioning member84. A thin membrane circular plate-shaped diaphragm92is disposed between the outer peripheral support fastening82and the inner peripheral support fastening90, and the whole of the circumference of the outer peripheral portion of the diaphragm92is bonded by vulcanization to the inner peripheral face of the outer peripheral support fastening82, and also the whole of the circumference of the inner peripheral portion of the diaphragm92is bonded by vulcanization to the outer peripheral face of the inner peripheral support fastening90. Here, the diaphragm92curves in a wave-like form, in cross-section along a radial direction, and adopts a slack shape. Thereby, the diaphragm92deforms with relatively small resistance in accordance with changes in the fluid pressure inside an auxiliary fluid chamber98, described later, and the internal volume of the auxiliary fluid chamber98is able to expand and contract.

As shown inFIG. 4, the resin first partitioning member84is inserted and fitted inside the outer cylinder72so as to be adjacent to the outer peripheral support fastening82. The other end of the first partitioning member84, at the side of the outer peripheral support fastening82, is formed with a bottomed circular cylindrical shaped bottom plate portion94. As shown inFIG. 6, there is an opening96formed in a circular shape at the central portion of the bottom plate portion94. There are spaces (fluid chambers) formed in the vibration isolator70, inside the outer cylinder72between the diaphragm92and the bottom plate portion94, and between the bottom plate portion94and the rubber elastic body88, these spaces being respectively partitioned off from the outside, but mutually communicated with each other through the opening96of the bottom plate portion94. This fluid chamber is filled with a fluid, such as ethylene glycol, silicone oil or the like, and forms the auxiliary fluid chamber98.

As shown inFIG. 4, at the first partitioning member84, the one end portion of the outer peripheral support fastening82abuts against the outer peripheral side of the bottom plate portion94. The first partitioning member84is thereby clamped and supported, restrained from moving in the axial direction, between the bent portion78of the outer cylinder72and the first partitioning member84. The outer peripheral face of the first partitioning member84is also pressed against the inner peripheral face of the outer cylinder72, with the covering rubber80therebetween.

In the first partitioning member84, as shown inFIG. 6, there is a thin, long, outer peripheral groove100formed extending in a spiral shape at the outer peripheral face thereof, and there is also a thin, long, outer peripheral groove102, formed extending in a spiral shape that is of the opposite rotation direction to that of the outer peripheral groove100, at the outer peripheral face thereof. These outer peripheral grooves100,102extend, respectively, around nearly a complete circumference of the outer peripheral face of the first partitioning member84. Furthermore, in the first partitioning member84, as shown inFIG. 4, there are a communication opening104and a communication opening106formed, respectively, at one end and the other end of the outer peripheral groove100, to respectively penetrate outer side in the axial direction, and there are a communication opening108and a communication opening110formed, respectively, at one end and the other end of the outer peripheral groove102, to respectively penetrate outer side in the axial direction.

As shown inFIG. 4, there is a large diameter circular cylindrical shaped large diameter portion112formed at one end side in the axial direction of the intermediate cylinder86, and there is a circular cylindrical shaped small diameter portion116, having a smaller diameter than that of the large diameter portion112and integrally formed thereto via a step portion114that extends toward the inner peripheral side from the other end side of the large diameter portion112. The small diameter portion116here has an outer diameter that corresponds to the internal diameter of the first partitioning member84. In the intermediate cylinder86, the outer peripheral face of the large diameter portion112is pressed against the inner peripheral face of the outer cylinder72, with the covering rubber80therebetween, and the small diameter portion116is inserted and fitted into the inner peripheral side of the first partitioning member84. When this is being carried out, in the intermediate cylinder86, the step portion114contacts with one end face of the first partitioning member84. The first partitioning member84is thereby held clamped by the outer peripheral support fastening82and the step portion114, and movement in the axial direction is restrained. Furthermore, after inserting and fitting the intermediate cylinder86to the inner peripheral side of the outer cylinder72, a crimped portion118is formed at one end of the outer cylinder72, by bending toward the inner peripheral side thereof. The intermediate cylinder86is thereby held clamped by the first partitioning member84and the crimped portion118, and movement thereof in the axial direction is restrained.

As shown inFIG. 4, there is a pair of hollow portions120and122formed to the rubber elastic body88, as concave shapes from the outer peripheral side of the large diameter portion112toward the internal peripheral side thereof at the internal peripheral side of the large diameter portion112. These hollow portions120and122are provided at one end side and the other end side, respectively, of the rubber elastic body88, with the internal cylinder74in the radial direction between the hollow portion120and the hollow portion122, and the hollow portions120and122are formed into substantially V-shapes, with the width along axial direction cross-section getting gradually narrower on progression from the outer peripheral side to the internal peripheral side thereof.

As shown inFIG. 5, there is a partitioning wall portion124formed in a substantially circular plate shape to one end in the axial direction of the rubber elastic body88. The partitioning wall portion124is of substantially constant thickness in the axial direction at given positions on the radial direction thereof, and the inner peripheral face of the partitioning wall portion124is bonded by vulcanization to the outer peripheral surface at one end side of the internal cylinder74, and the outer peripheral face thereof is bonded by vulcanization to the internal peripheral face of the large diameter portion112of the intermediate cylinder86. The partitioning wall portion124is formed here into a curved shape in cross-section in the axial direction, protruding in a convex manner toward the inside of the hollow portions120and122.

There is a partitioning wall portion126formed in a substantially circular thick-walled plate shape to the opposite end in the axial direction of the rubber elastic body88to that of the partitioning wall portion124, with the hollow portions120and122therebetween. The partitioning wall portion126also has a substantially constant wall axial direction thickness at given positions along the radial direction, and the inner peripheral face of the partitioning wall portion126is bonded by vulcanization to the outer peripheral face of the internal cylinder74, and the outer peripheral face of the partitioning wall portion126is bonded to the inner peripheral face of the small diameter portion116of the intermediate cylinder86.

As shown inFIG. 5, there is a pair of dividing walls128and130formed integrally to the rubber elastic body88, the dividing walls128and130each extending out from the center portion to the outer peripheral side along radial directions. These dividing walls128and130are each formed in a plate shape with a wall thickness in the circumferential direction that gradually gets thicker on progression from the internal peripheral side to the outer peripheral side, and the dividing walls128and130extend out in opposite directions from each other with the internal cylinder74at the center thereof. Outer peripheral edge portions of this pair of dividing walls128and130are each bonded by vulcanization to the inner peripheral face of the large diameter portion112of the intermediate cylinder86. The space that is formed between the partitioning wall portion124and the partitioning wall portion126in the rubber elastic body88is thereby divided up, by the dividing wall128and the dividing wall130, into the hollow portion120and the hollow portion120. Furthermore, there is an opening portion132and an opening portion134, formed, respectively, of a rectangular shape to the large diameter portion112of the intermediate cylinder86and facing each of the hollow portion120and the hollow portion120.

In the vibration isolator70, as shown inFIG. 5, the outer peripheral side of the hollow portions120and122is closed off, via the covering rubber80, by the inner peripheral face of the outer cylinder72, and the internal portions of the hollow portions120and122each form a fluid chamber that is separated from the outside. Each chamber of this pair of fluid chambers is filed with the same liquid as the auxiliary fluid chamber98, and form a pair of first pressure receiving fluid chambers136and138.

The outer peripheral sides of the pair of outer peripheral grooves100,102in the first partitioning member84are closed off by the inner peripheral face of the outer cylinder72, via the covering rubber80. The one outer peripheral groove100that has been closed off at the outer peripheral side is configured with a first orifice140, mutually communicating the first pressure receiving fluid chamber136and the auxiliary fluid chamber98, and the other outer peripheral groove102is configured with a first orifice142that mutually communicates the first pressure receiving fluid chamber136and the auxiliary fluid chamber98. The passage length and the cross-sectional area of the pair of first orifices140,142are tuned to correspond to a shake vibration that is a low frequency vibration (such as 8 to 12 Hz, for example).

In the vibration isolator70according to the present exemplary embodiment, the mounting direction is set such that, in the state in which it is mounted to a vehicle as an engine mount, of the radial directions with the axial center S as the center, the direction along which the first pressure receiving fluid chamber136, the internal cylinder74and the first pressure receiving fluid chamber138are arranged, that is the main amplitude direction (the direction H inFIG. 5) substantially matches the vehicle up-down direction, and the device axial direction substantially matches the vehicle front-rear direction or matches the left-right direction. Thereby, in the vibration isolator70, when vibration (main vibration) is inputted in the main amplitude direction, which substantially matches the main amplitude direction via the outer cylinder72or through the internal cylinder74, the rubber elastic body88elastically deforms in the main amplitude direction and also the rubber elastic body88changes (expands or contracts) the internal volume of the pair of the first pressure receiving fluid chambers136and138. When this occurs, the rubber elastic body88changes the internal volume of each of the first pressure receiving fluid chambers136and138in directions that are mutually opposite to each other, that is to say when the internal volume of one of the pair of first pressure receiving fluid chambers136and138is expanded, the internal volume of the other is contracted.

Explanation will now be given of the operation of the vibration isolator70according to the present exemplary embodiment that has been configured as described above.

In the vibration isolator70, when an engine connected to the internal cylinder74is operated, the vibrations from the engine are transmitted to the rubber elastic body88via the internal cylinder74. When this occurs, the rubber elastic body88acts as a vibration absorbing main body, and inputted vibrations are absorbed by damping action due to internal friction and the like of the rubber elastic body88.

In the vibration isolator70, the one first pressure receiving fluid chamber136is disposed at one side in the main amplitude direction between the outer cylinder72and the internal cylinder74, and the other first pressure receiving fluid chamber138is disposed at the other side in the main amplitude direction between the outer cylinder72and the internal cylinder74, and when vibration in the main amplitude direction is inputted to the outer cylinder72or the internal cylinder74, the internal volumes of the pair of first pressure receiving fluid chambers136and138are respectively changed (expanded or contracted). Therefore, since the fluid pressures inside the pair of first pressure receiving fluid chambers136and138also change (increases or decreases), fluid flows to-and-fro through the one first orifice140between the first pressure receiving fluid chamber136and the auxiliary fluid chamber98, and fluid flows to-and-fro through the other first orifice142between the first pressure receiving fluid chamber138and the auxiliary fluid chamber98.

When this occurs, the length and the cross-sectional area of the first orifices140and142, that is to say the resistance to fluid flow, are tuned to correspond to a shake vibration that is of a low frequency vibration (8 to 12 Hz, for example), and therefore when the inputted vibration is the shake vibration, resonance occurs (liquid column resonance) in the fluid flowing to-and-fro through the one first orifice140between the first pressure receiving fluid chamber136and the auxiliary fluid chamber98, and liquid column resonance also occurs in the fluid flowing to-and-fro through the other first orifice142between the first pressure receiving fluid chamber138and the auxiliary fluid chamber98. Therefore, inputted vibration (shake vibration) in the main amplitude direction can be effectively absorbed by the liquid column resonance occurring in the pair of first orifices140and142.

Furthermore, in the vibration isolator70when the rubber elastic body88elastically deforms, due to the inputted vibration in the main amplitude direction of alignment of the first pressure receiving fluid chamber136, the internal cylinder74and the first pressure receiving fluid chamber138, along with the elastic deformation in the main amplitude direction, the rubber elastic body88changes the internal volumes of each of the pair of first pressure receiving fluid chambers136and138in directions that are mutually opposite to each other (expands one and contracts the other) and changes the fluid pressures within each of the pair of first pressure receiving fluid chambers136and138in directions that are mutually opposite to each other (lowers one and raises the other). Thereby, while vibration in the main amplitude direction is inputted, independent of the frequency of the inputted vibration, when fluid flows into the auxiliary fluid chamber98from the first pressure receiving fluid chamber136through the first orifice140, fluid also flows out from the auxiliary fluid chamber98to the first pressure receiving fluid chamber136through the other first orifice142. Therefore, even if the frequency of the inputted vibration is outside of the frequency region corresponding to the first orifices140and142, the fluid pressure within the auxiliary fluid chamber98is always maintained substantially constant.

That is, in the auxiliary fluid chamber98, since a portion of partitioning wall is formed from the low rigidity diaphragm92, naturally (ideally), even if fluid flows into the auxiliary fluid chamber98, rising of fluid pressure is not generated within the auxiliary fluid chamber98. However, in reality, when the durability of the diaphragm92and the like are considered, it is difficult to make the rigidity of the diaphragm92sufficiently small, and therefore when the fluid inflow amount to the auxiliary fluid chamber98becomes greater than the fluid outflow amount, a rise in the fluid pressure may occur, corresponding to the difference between the inflow amount and the outflow amount within the auxiliary fluid chamber98. However, in the vibration isolator70according to the present exemplary embodiment, when vibration is inputted in the main amplitude direction, since the fluid inflow amount and outflow amount of the auxiliary fluid chamber98become substantially equal, any rise in the fluid pressure within the auxiliary fluid chamber98can be made sufficiently small.

Therefore, according to the vibration isolator70of the present exemplary embodiment, when vibration is inputted along the main amplitude direction, even if the frequency of the inputted vibration is outside of the frequency region corresponding to the first orifices140and142, an increase in the flow resistance of fluid flowing through one orifice of the first orifice140between the first pressure receiving fluid chamber136and the auxiliary fluid chamber98, and an increase in the flow resistance of fluid flowing through the other orifice of the first orifice142between the first pressure receiving fluid chamber138and the auxiliary fluid chamber98, due to an increase in the fluid pressure within the auxiliary fluid chamber98, can both be suppressed. Therefore, when one of the first pressure receiving fluid chambers136and138contracts, there is a smooth flow, with low resistance, of liquid out from the one of the first pressure receiving fluid chambers136and138, through the first orifices140and142, to the inside of the auxiliary fluid chamber98. As a result of this, a rise in the fluid pressure within the pair of first pressure receiving fluid chambers136and138can be suppressed, and therefore a rise in the dynamic spring constant of the device may be suppressed.

Also, if the frequency of the inputted vibration is within the frequency region corresponding to the first orifices140and142, there is no change generated in the fluid pressure within the auxiliary fluid chamber98(fluid pressure rise), and there is no impediment to fluid flow within the restrict passage by the fluid pressure within the auxiliary fluid chamber98, and therefore fluid flows smoothly, with low resistance, through the pair of first orifices140and142between each of the respective pair of first pressure receiving fluid chambers136and138and the auxiliary fluid chamber98. As a result of this, the damping, due to fluid being in liquid column resonance within the respective of the first orifices140and142can be effectively increased.

Furthermore, in the vibration isolator70according to the present exemplary embodiment, since the cross-section of the partitioning wall portion124in the rubber elastic body88is curved so as to protrude in a convex shape toward the inside of the first pressure receiving fluid chambers136and138, in the same manner as with the vibration isolator10according to the first exemplary embodiment, when vibration has been input in the main amplitude direction, effective expansion and contraction of the internal volume of the first pressure receiving fluid chambers136and138can be achieved, in comparison to a case in which the partitioning wall portion is a flat plate shape, or a curved shape so as to protrude in a convex shape toward the outside of the first pressure receiving fluid chambers136and138.

As a result, in the vibration isolator70according to the present exemplary embodiment, when vibration is inputted in the main amplitude direction, the amount of fluid flowing in the first orifices140and142between the first pressure receiving fluid chambers136and138and the auxiliary fluid chamber98can be effectively promoted. Therefore, inputted vibrations in the secondary amplitude direction can be effectively absorbed by the viscous resistance of fluid flowing within the first orifices140and142, and by pressure changes.

It should be noted that, in the vibration isolator70according to the present exemplary embodiment, the outer cylinder72is attached to the vehicle body side via a bracket member, and also the internal cylinder74is attached to the engine side through a connecting member, however, this may be reversed, and the outer cylinder72may be attached to the engine side and the internal cylinder74may be attached via a connecting member to the vehicle body side.

Furthermore, in the vibration isolator70, tuning is carried out such that the passage lengths and the cross-sectional areas of the first orifices140and142correspond to shake vibrations that are low frequency vibrations (such as, for example, 8 to 12 Hz), however, the frequency range corresponding to the pair of first orifices140and142may be adjusted by changing the passage lengths and the cross-sectional areas of the first orifices140and142.

In the vibration isolator70according to the present exemplary embodiment, since the internal cylinder74, which is a mounting member, passes through the inside of the outer cylinder72, the load of the engine can be made to act more uniformly over the entire length of the internal cylinder74, in comparison with the vibration isolator10according to the first exemplary embodiment. Thereby, since the internal cylinder74does not relatively incline with respect to the outer cylinder72when load is input, deformation (compression or extension deformation) can be made uniform in the radial direction at given locations along the axial direction in the rubber elastic body88. As a result of this, by the vibration isolator70according to the present exemplary embodiment, the durability of the rubber elastic body88can be increased and there is effective expansion and contraction of the internal volume of the first pressure receiving fluid chambers136and138when vibration is input, in comparison to the vibration isolator10according to the first exemplary embodiment.

Third Exemplary Embodiment

A vibration isolator according to a third exemplary embodiment of the present invention is shown inFIG. 7. This vibration isolator148, as with the vibration isolator70according to the second exemplary embodiment, is one that is used in an engine mount of a vehicle. In the vibration isolator148according to the present exemplary embodiment, the components that are similar to those of vibration isolator70according to the second exemplary embodiment are allocated the same reference numerals, and explanation thereof will be omitted.

The vibration isolator148according to the present exemplary embodiment is different from the vibration isolator70according to the first exemplary embodiment in the point that in the outer cylinder72, there is a second partitioning member150disposed additionally between the outer peripheral support fastening82and the first partitioning member84. The second partitioning member150is formed in a circular plate shape that has an internal peripheral side that is thicker than the outer peripheral side, and an extending portion154is integrally formed thereto, extending out in a flange shape to the outer peripheral side at the other end portion of the outer peripheral face of the second partitioning member150. There is an orifice forming portion156formed in a circular protrusion shape that protrudes out toward the rubber elastic body88side at the internal peripheral side of the extending portion154.

The second partitioning member150inserts and fits the orifice forming portion156through the opening96of the first partitioning member84into a recess portion152that has been formed in a central portion at end face of the rubber elastic body88, and also the second partitioning member150contacts the extending portion154with the other end face of the first partitioning member84. Furthermore, the outer peripheral side of the extending portion154of the second partitioning member150is clamped between the outer peripheral support fastening82and the first partitioning member84, and movement in the axial direction thereof is restrained. By so doing, in the vibration isolator148, a fluid chamber space that is formed inside the outer cylinder72between the diaphragm92and the rubber elastic body88, is divided into two individual small spaces. The small space on the diaphragm92side of these small spaces is filled with a fluid such as ethylene glycol, silicone oil or the like, and is an auxiliary fluid chamber158. The small space on the rubber elastic body88side is filled with the same fluid as that in the auxiliary fluid chamber158and is a second pressure receiving fluid chamber178.

There is an outer peripheral groove160formed as a recess shape in the outer peripheral face of the orifice forming portion156of the second partitioning member150, formed extending along the circumferential direction thereof around nearly a complete circumference. There is also an inner peripheral cutout portion162formed to the second partitioning member150, facing one end portion of the outer peripheral groove160and passing through to the second pressure receiving fluid chamber178side. There is also an inner peripheral cutout portion164formed to the second partitioning member150, facing the other end portion of the outer peripheral groove160and passing through to in the axial direction auxiliary fluid chamber158side. The outer peripheral side of the outer peripheral groove160is closed by the internal peripheral face of the first partitioning member84and the internal peripheral face of the recess portion152of the rubber elastic body88. The outer peripheral groove160, with the outer peripheral side thereof closed off, is a second orifice166that mutually communicates the second pressure receiving fluid chamber178and the auxiliary fluid chamber158.

Vibration in the up-down direction (main vibration) generated by the engine of a vehicle as the vibration source is known to be a shake vibration with a relatively low frequency (8 to 15 Hz, for example), however, if this shake vibration is categorized in more detail then, generally, it may be categorized into an engine bounce vibration (referred to below simply as “bounce vibration”) with a frequency of less than 10 Hz, and a pitching vibration having a frequency of 10 to 15 Hz. In the vibration isolator148according to the present exemplary embodiment, the passage length and cross-section of the second orifice166that communicates the second pressure receiving fluid chamber178and the auxiliary fluid chamber158are set (tuned) so as to correspond to the frequency of the bounce vibration (up to 10 Hz).

Furthermore, in the second partitioning member150there are outer peripheral cutout portions168and170formed to the extending portion154where it faces, respectively, the communication opening106and the communication opening1110of the first partitioning member84, and the other ends of the first orifices140and142are communicated with the auxiliary fluid chamber158through the outer peripheral cutout portions168and170, respectively.

In the second partitioning member150, there is an opening portion172formed in a circular shape to a central portion of the orifice forming portion156, and a support fastening174is disposed to the inner peripheral side of the opening portion172coaxially, and also a ring shaped rubber membrane176is disposed between the inner peripheral face of the opening portion172and the outer peripheral face of the support fastening174. The outer peripheral face of this rubber membrane176is bonded to the inner peripheral face of the opening portion172, and the inner peripheral face thereof is bonded by vulcanization to the outer peripheral face of the support fastening174. Furthermore, the support fastening174is press inserted and fixed between the inner peripheral support fastening90at the outer peripheral side of the internal cylinder74and the rubber elastic body88. The rubber membrane176thereby forms a portion of a partitioning wall partitioning the second pressure receiving fluid chamber178and the auxiliary fluid chamber158, and elastically deforms such that the internal volume of the second pressure receiving fluid chamber178is able to expand and contract according to the fluid pressure change within the second pressure receiving fluid chamber178.

Explanation will now be given of the operation of the vibration isolator148according to the present exemplary embodiment configured as described above.

In the vibration isolator148according to the present exemplary embodiment, basically the same operational effects may be obtained as with the vibration isolator70according to the second exemplary embodiment. In addition, in the vibration isolator148according to the present exemplary embodiment, there is the second pressure receiving fluid chamber178provided, at the internal peripheral side of the outer cylinder72, between the rubber elastic body88and the partitioning members84and150. Due to the second orifice166mutually communicating the second pressure receiving fluid chamber178and the auxiliary fluid chamber158, when vibration (secondary amplitude) is inputted in the axial direction (secondary amplitude direction) through the internal cylinder74or through the outer cylinder72, since the rubber elastic body88elastically deforms in the secondary amplitude direction, and the internal volume of the second pressure receiving fluid chamber178is made, therefore fluid reciprocally flows through the second orifice166between the second pressure receiving fluid chamber178and the auxiliary fluid chamber158.

When this occurs, since the passage length and the cross-section of the second orifice166are set so as to correspond to the frequency of the bounce vibration, therefore when the input main inputted vibration is the bounce vibration, resonance occurs (liquid column resonance) in fluid flowing mutually between the second pressure receiving fluid chamber178and the auxiliary fluid chamber158through the second orifice166, in synchronization with the inputted vibration, and bounce vibration inputted in the secondary amplitude direction can be particularly effectively absorbed by this liquid column resonance.

Also, in the vibration isolator148, in a case in which the frequency of the inputted main vibration is higher than the frequency of bounce vibration and the amplitude thereof is small, for example, in a case in which the inputted vibration is an idling vibration (20 to 30 Hz, for example) with an amplitude of about 0.1 mm to 0.2 mm, in the second orifice166which is tuned to correspond to the bounce vibration, a clogged state occurs, and fluid flow in the second orifice166becomes difficult. However, by elastic deformation of the rubber membrane176according to changes in the fluid pressure within the second pressure receiving fluid chamber178, a rise in the fluid pressure within the second pressure receiving fluid chamber178is suppressed. Therefore, even when a high frequency vibration is inputted in the secondary amplitude direction, a rise in the dynamic spring constant accompanying a rise in fluid pressure within the second pressure receiving fluid chamber178can be suppressed, and high frequency vibrations can be effectively absorbed, by elastic deformation of the rubber elastic body88and the like.