Fluid-filled vibration damping device

A fluid-filled vibration damping device includes: an elastic body connecting a first mounting member and a second mounting member; and a partition member assembled with the second mounting member to form on its opposite sides a pressure receiving chamber partially defined by the elastic body and an equilibrium chamber partially defined by a flexible layer, both being filled with non-compressible fluid. The partition member defines an orifice passage connecting the two chambers, and including a first partitioning wall portion partitioning the orifice passage from the pressure-receiving chamber, and a second partitioning wall portion of rubber partitioning the orifice passage from the equilibrium chamber. A partial reinforcing member is provided to the partition member extending across the first and second partitioning wall portions to reinforce an opening of the orifice passage to the pressure-receiving chamber.

INCORPORATED BY REFERENCE

The disclosure of Japanese Patent Application No. 2003-207412 filed on Aug. 12, 2003 including the specification, drawings and abstract is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to fluid-filled vibration damping devices capable of exhibiting damping effect on the basis of flow action of non-compressible fluid sealed therein, and more particularly to a fluid-filled vibration damping device suitably applicable to engine mounts or other mounts for use in automotive vehicles, for example.

2. Description of the Related Art

Vibration-damping devices, typically including a first and a second mounting member elastically connected via a rubber elastic body, have been widely used in a variety of fields as vibration damping couplings or mounts which are interposed between two members of a vibration system. As one type of such vibration damping devices, there have been proposed a fluid-filled vibration damping device that is of construction further includes: a pressure-receiving chamber whose wall is partially defined by the rubber elastic body and undergoes fluid pressure fluctuation upon application of vibration between the first and second mounting members; an equilibrium chamber whose wall is partially defined by a flexible layer and permits a volumetric change thereof as a result of deformation of the flexible layer; a partition member assembled with the second mounting member so as to form on the opposite sides thereof the pressure-receiving chamber and the equilibrium chamber each having non-compressible fluid sealed therein; and an orifice passage for permitting a fluid communication between the pressure receiving chamber and the equilibrium chamber. Typical examples of such a fluid-filled vibration-damping device are disclosed in JP-A-7-243472 and JP-A-2001-165231, for example.

The fluid-filled vibration damping device of this construction is capable of exhibiting vibration damping effect on the basis of resonance or other flow action of the non-compressible fluid sealed therein, thereby readily affording low dynamic spring action and high attenuation action in the tuning frequency range at levels not achieved simply by damping action of a rubber elastic body. For this advantage, the fluid-filled vibration-damping device has been studied to apply to automotive vibration damping devices in which high levels of damping performance are required in certain specific frequency ranges.

Extensive researches conducted by the inventor has revealed that the fluid filled vibration damping device of conventional design may suffer from noises or vibrations induced therein when an impulsively large vibrational load is applied between the first and second mounting members.

SUMMARY OF THE INVENTION

It is therefore one object of this invention to provide a fluid-filled vibration damping device that is novel in construction and capable of preventing or minimizing generation of noises or vibrations when subjected to an impulsive and tremendous vibration or load, while effectively providing its damping performance on the basis of flow action of non-compressible fluid sealed therein.

As a result of further extensive study and analysis conducted by the inventor on phenomena of generation of noises or vibrations in the conventional fluid-filled vibration damping devices, it was revealed that when an impulsively large vibrational load is applied between the first and second mounting members, a large negative pressure induced in the pressure receiving chamber, causing dissolved air present in the non-compressible fluid to separate and form air bubbles, and leading to an explode-wide micro jet created within the pressure receiving chamber as the air bubbles disappear. The pressure or impact of the micro jet is exerted onto the first and second mounting members, thereby generating noises and vibrations as stated above. This is the mechanism of generation of noises and vibrations, found by the inventor.

As a result of further detail inspection conducted by the inventor, it was revealed that these bubbles are generated at around a specific position within the pressure-receiving chamber, more specifically at around an opening of the orifice passage to the pressure-receiving chamber. The present invention has been developed in view of this finding. While the reasons for creation of air bubbles in the pressure receiving chamber has not yet been sufficiently apparent, the inventor considered that these bubbles may be induced due to a basic reason of phase difference between one fluid pressure fluctuation applied to the pressure receiving chamber owing to resonance action of the fluid flowing through the pressure receiving chamber, and the other fluid pressure fluctuation induced in the pressure receiving chamber during input of vibration between the first and second mounting member, and may further be induced as a result of a so-called “liquid breakage phenomenon” that is caused by a relatively large decompression induced at around the opening of the orifice passage to the pressure receiving chamber under suitable conditions of the sealed fluid in terms of a degree of decompression, a temperature, a flowing state, a surface tension, a viscosity and the like.

A first mode of the present invention provides a fluid-filled vibration damping device comprising: a first mounting member; a second mounting member; a rubber elastic body elastically connecting the first and second mounting members, and partially defining a pressure-receiving chamber filled with a non-compressible fluid whose pressure is fluctuated upon application of vibration between the first and second mounting members; a flexible layer partially defining an equilibrium chamber filled with the non-compressible fluid and whose volume is changed due to deformation of the flexible layer; a partition member assembled with the second mounting member so as to form on the opposite sides thereof the pressure-receiving chamber and the equilibrium chamber, said partition member defining an orifice passage that is partitioned from the pressure-receiving chamber and the equilibrium chamber and permits a fluid communication between the pressure-receiving chamber and the equilibrium chamber, and including a first partitioning wall portion adapted to partition the orifice passage from the pressure-receiving chamber, and a second partitioning wall portion formed of a rubber elastic body and adapted to partition the orifice passage from the equilibrium chamber; and a partial reinforcing member provided to the partition member such that the partial reinforcing member extends across the first and second partitioning wall portions so as to reinforce a first opening of the orifice passage opening to the pressure receiving chamber.

In the fluid-filled vibration damping device of construction according to this mode, the partition member defines the orifice passage to be partitioned from the pressure-receiving chamber and the equilibrium chamber, and the second partitioning wall portion partitioning orifice passage from the equilibrium chamber is formed of the rubber elastic body. This arrangement makes it possible to eliminate or minimize creation of air bubbles at around the first opening of the orifice passage opening to the pressure-receiving chamber.

That is, the creation of air bubbles at around the first opening of the orifice passage, which opens to the pressure-receiving chamber, is caused by a negative pressure generated in the pressure-receiving chamber during input of impulsively large vibrational load between the first and second mounting members. As one way to prevent generation of negative pressure in the equilibrium chamber, it is considered to make a wall spring stiffness of the pressure-receiving chamber small. However, if the wall spring stiffness of the pressure receiving chamber is made small, it is accordingly reduced the fluid pressure fluctuation generated in the pressure-receiving chamber during input of vibration between the first and second mounting members. This inevitably results in deterioration of vibration damping effect with the help of resonance of the fluid flowing through the orifice passage.

In view of the above described drawback, the fluid-filled vibration damping device of the first mode employs the second partitioning wall portion formed of the rubber elastic body, which partitions the orifice passage from the equilibrium chamber, and the partial reinforcing member provided in the partition member for reinforcing the first opening of the orifice passage opening to the pressure receiving chamber. With this arrangement, the present fluid-filled vibration-damping device is capable of generating a sufficient fluid pressure fluctuation in the pressure-receiving chamber during input of vibration in order to maintain an intended vibration damping effect on the basis of flow action of the fluid, while avoiding or minimizing generation of excessively large fluid pressure fluctuation enough to cause the “liquid breakage phenomenon” so that noises or vibrations caused by the excessively large fluid pressure fluctuation in the pressure receiving chamber can be minimized or eliminated.

More specifically, in the fluid-filled vibration damping device of this mode, the partition member is provided with the partial reinforcing member adapted to reinforce the first opening of the orifice passage opening to the pressure-receiving chamber. Therefore, effectively reinforced by means of the partial reinforcing member are the first opening of the orifice passage and the vicinity thereof, which are subjected to considerably large fluid pressure caused by phase difference between the fluid pressure fluctuation generated in the pressure receiving chamber and the flow of the fluid through the orifice passage. This arrangement makes it possible for the fluid-filled vibration damping device of this mode to provide sufficient wall spring stiffness of the pressure-receiving chamber, as well as sufficient fluid pressure fluctuation in the pressure-receiving chamber during input of vibration, thereby ensuring a sufficient amount of fluid flow through the orifice passage generated based on the fluid pressure fluctuation between the pressure-receiving chamber and the equilibrium chamber relative to each other. Thus, the fluid-filled vibration-damping device of construction according to the first mode is capable of exhibiting excellent vibration damping effect on the basis of flow action of the fluid sealed therein.

Moreover, the second partitioning wall portion is at least partially formed of the rubber elastic body, except a portion that defines the first opening of the orifice passage to the pressure-receiving chamber. Therefore, if considerably large fluid pressure is generated at around the first opening of the orifice passage due to phase difference between the fluid pressure fluctuation generated in the pressure receiving chamber and the flow of the fluid through the orifice passage, such a large fluid pressure is quickly absorbed or moderated by the elastic deformation of the second partitioning wall portion situated in the vicinity of the first opening of the orifice passage. Accordingly, excessively large fluid pressure fluctuation generated locally i.e., in the vicinity of the first opening of the orifice passage opening to the pressure-receiving chamber, will be absorbed or moderated by means of the elastic deformation of the rubber elastic body, thus making it possible to eliminate or minimize noises or vibrations due to air bubbles crated in accordance with excessively large fluid pressure fluctuation.

A second mode of the present invention is a fluid-filled vibration damping device according to first mode, wherein the orifice passage circumferentially extends in an outer circumferential portion of the partition member with a circumferential length that is slightly smaller than that of a circumference of the partition member, and one of circumferentially opposite ends of the orifice passage is connected to the pressure-receiving chamber through a pressure-receiving-chamber-side communication hole, while an other one of circumferentially opposite ends of the orifice passage is connected to the equilibrium chamber through an equilibrium-chamber-side communication hole, wherein the partition member is formed with a partition wall formed of a rubber elastic body and adapted to partition the circumferentially opposite ends of the orifice passage from each other, and wherein the partial reinforcing member extends in the circumferential direction to a portion where the partition wall is formed so that deformation of the partition wall is restricted by means of the partial reinforcing member.

In the fluid-filled vibration damping device of construction according to this mode, restricted by the reinforcing member is the elastic deformation of the partition wall partitioning the circumferentially opposite ends of the orifice defining member, making it possible to effectively preventing elastic deformation of the partition wall due to considerably large fluid pressure exerted thereon, which is caused by fluid pressure difference between the pressure-receiving-side communication hole and the equilibrium-chamber-side communication hole. This arrangement prevents a short of the orifice passage due to elastic deformation of the partitioning wall, thereby ensuring vibration damping effect with the help of resonance of the fluid flowing through the orifice passage with enhanced stability. Additional advantage is that this mode makes it possible to restrict elastic deformation of the partition wall without requiring an additional part or member especially to do so, thereby enhancing vibration damping performance of the fluid-filled vibration damping device with simple construction.

A third mode of the present invention provides a fluid-filled vibration damping device according to the above-mentioned first or second mode, wherein a movable rubber plate is provided at a central portion of the partition member such that a fluid pressure of the pressure-receiving chamber is exerted on one of opposite major surfaces of the movable rubber plate, while a fluid pressure of the equilibrium chamber is exerted on an other one of opposite major surfaces of the movable rubber plate.

According to this mode of the invention, the movable rubber plate undergoes its elastic deformation on the basis of pressure difference between the pressure-receiving chamber and the equilibrium chamber. Therefore, when the fluid-filled vibration-damping device of this mode is subjected to input vibration of frequency higher than a tuning frequency of the orifice passage, the fluid pressure fluctuation induced in the pressure-receiving chamber is effectively absorbed or moderated. Thus, the fluid-filled vibration-damping device of this mode is capable of exhibiting enhanced vibration damping performance over a wide frequency range, with the help of damping effect by means of elastic deformation of the movable rubber plate as well as the orifice passage.

A fourth mode of the invention provides a fluid-filled vibration-damping device according to any one of the above-mentioned first to third modes, wherein the second mounting member has an approximately cylindrical configuration, and one of opposite open-end portions of the second mounting member is fluid-tightly closed by the rubber elastic body elastically connecting the second mounting member and the first mounting member disposed on a side of the one of opposite open-end portions with a distance therebetween, while the partition member is formed of the rubber elastic body and disposed within the second mounting member so as to extend in an axis-perpendicular direction of the second mounting member, and a support member is provided at least at an outer circumferential portion of the partition member so as to extend continuously over an entire circumference of the partition member, the support member being bonded at an outer rim portion thereof to the second mounting member and reinforcing the first partitioning wall portion, while being integrally formed with the partially reinforcing member.

In the fluid-filled vibration damping device of construction according to this mode, the support member reinforces the outer circumferential portion of the partition member, while having the partition member firmly fixed to and supported by the second mounting member. This arrangement further effectively induces flow of the fluid through the orifice passage due to fluid pressure fluctuation in the pressure-receiving chamber during input of vibration, and assures further improved vibration damping performance on the basis of fluid flow action. Additionally, the partition member is formed as a part of the support member, leading to advantages of the small number of components as well as easy manufacture.

A fifth mode of the invention provides a fluid-filled vibration-damping device according to the above-mentioned fourth mode, wherein the support member is of generally annular configuration having a center bore and is provided with a reinforcing rib at an inner circumferential edge portion thereof, and the center bore of the support member is fluid-tightly closed by a rubber plate having a given thickness so as to provide the movable rubber plate that is exerted at the one of opposite surfaces thereof to the fluid pressure in the pressure receiving chamber, and at the other of opposite surfaces thereof to the fluid pressure in the equilibrium chamber.

In the fluid-filled vibration damping device according to this mode, the reinforcing rib of the support member provides an effective bonding area with respect to the movable rubber plate, thereby improving durability of the movable rubber plate and other components.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring first toFIG. 1, there is shown a fluid-filled vibration-damping device in the form of an engine mount10for use in automotive vehicles, which is constructed according to a first embodiment of the invention. The engine mount10is of structure having a first mounting member12of metal, a second mounting member14of metal and a rubber elastic body16by which the first and second mounting members are elastically connected with each other. The first mounting member12is mounted on a power unit side, while the second mounting member14is mounted on a body side of an automotive vehicle, so that the power unit is mounted on the body of the vehicle in a vibration damping fashion, via the engine mount10. In the following description, the vertical direction will be basically used to refer to the vertical direction as seen inFIGS. 1 and 2, or approximately the vertical direction of the engine mount10installed on the vehicle as described above in which a vibrational load is primarily applied to the engine mount10.

Described more specifically, the first mounting member12has an approximately solid cylindrical block shape provided with a flange portion18integrally formed at its upper end portion in the axial direction, while extending diametrically outwardly. The first mounting member12is also provided with a tapped hole20open in an upper end face thereof and extending downward along a center axis thereof with a given axial direction. By means of a fastening bolt threaded into the tapped hole20, the first mounting member12is fixed to the power unit (not shown) of the vehicle.

The second mounting member14has a large-diameter generally cylindrical configuration, and is formed with a caulking portion22extending diametrically outward at a lower open-end portion in the axial direction thereof. The first mounting member12is disposed above and away from the second mounting member14in the axial direction in an approximately coaxial fashion. The first and second mounting members12,14are elastically connected with each other via the rubber elastic body16.

The rubber elastic body16has an approximately truncated conical configuration in its entirety, and is formed with a large-diameter recess24open in its large-diameter end face. During vulcanization of a rubber material for forming the rubber elastic body16, the rubber elastic body16is bonded at its small-diameter end face to the first mounting member12, while being bonded at an outer circumferential surface of its large-diameter end portion to the second mounting member14. Namely, the rubber elastic body16provides an integrally vulcanized product including the first mounting member12and the second mounting member14. With this arrangement, the first mounting member extends into the rubber elastic body16from the small-diameter end face, whereby the substantially entire area, except an upper axial end face, of the first mounting member12is coated by the rubber elastic body16. On the other hand, the second mounting member14is disposed about and bonded onto the large-diameter end portion of the rubber elastic body16, over its substantially entire inner surface area, except the caulking portion22.

A flexible layer in the form of a flexible diaphragm26is disposed at the lower open-end portion of the second mounting member14in the axial direction, so as to fluid-tightly close the lower open-end portion. The flexible diaphragm26is a thin rubber layer of canopy like shape, having a slack enough to facilitate its elastic deformation. To the periphery of the flexible diaphragm26, is bonded a fixing metal28of approximately cylindrical configuration. Namely, the periphery of the flexible diaphragm26is bonded to an axially lower edge portion of the fixing metal28through vulcanization of a rubber material for forming the flexible diaphragm26. To an axially upper edge portion of the fixing metal28, on the other hand, a fixing flange portion30extending diametrically outward is integrally formed. The fixing flange portion30is superimposed against the caulking portion22provided at the lower open-end portion of the second mounting member14, and is fixed by caulking to the second mounting member14in a fluid-tight fashion. In the present embodiment, inner and outer circumferential surfaces of the fixing metal28are substantially entirely coated by a thin coating rubber layer32integrally formed with the flexible diaphragm28.

As illustrated above, the second mounting member14is fluid-tightly closed at its upper open-end portion by means of the rubber elastic body16, and at its lower open-end portion by means of the flexible diaphragm18, thereby defining between the rubber elastic body16and the flexible diaphragm26a fluid sealing area34sealed off from the external area. This fluid sealing area34is filled with a non-compressible fluid. For effective damping of input vibration based on resonance of the fluid flowing through an orifice passage42, which will be described later, it is preferable to employ a low-viscosity fluid whose viscosity is not higher than 0.1 Pa.s, such as water, alkylene glycol, polyalkylene glycol and silicone oil.

The fluid sealing area34houses a partition member36disposed therein. The partition member36partitions the fluid sealing area34into a pressure receiving chamber38and an equilibrium chamber40. The pressure-receiving chamber38is partially defined by the rubber elastic body16so as to undergo fluctuation in internal pressure on the basis of elastic deformation of the rubber elastic body16during vibration input. The equilibrium chamber40, on the other hand, is partially defined by the flexible diaphragm26so as to readily permit change in volume based on elastic deformation of the diaphragm40, thereby canceling fluid pressure fluctuation quickly. The orifice passage42is formed at an outer circumferential portion of the partition member36. Through the orifice passage42, the pressure-receiving chamber38and the equilibrium chamber40are held in fluid communication with each other.

The partition member36is of thick disk-like configuration in its entirety, and is formed of a rubber elastic body. The thickness dimension of the partition member36is especially made large at its outer circumferential portion so as to provide an orifice defining portion44of annular block configuration continuously extending with an approximately constant cross sectional shape all the way around its circumference. At a lower end peripheral edge portion of the partition member36, there is formed a circumferential groove46circumferentially extending with a constant inverted L shape in cross section, over a circumferential length slightly smaller than a circumference of the partition member36. In other words, the circumferential groove46is blocked by means of a partition wall48formed at a circumferential position thereof so that a pair of circumferentially opposite ends of the circumferential groove46are opposed to each other with the partition wall48interposed therebetween in the circumferential direction.

The central portion of the partition member36serves as a movable rubber plate50. The movable rubber plate50is of a disk-shape configuration having a given thickness. The peripheral portion of the movable rubber plate50extends downwards to form an inclined fringe, whereby the movable rubber plate50has an inverted dish-like configuration, where a central portion thereof projects upward slightly. This movable rubber plate50is disposed in a center bore of the orifice defining portion44, while extending in an axis perpendicular direction and being integrally bonded at its inclined fringe to an axially medial portion of an inner circumferential surface of the orifice defining portion44of the partition metal38, through vulcanization of a rubber material for forming the movable rubber plate50, whereby providing the partition member36formed as an integral vulcanization product including the movable rubber plate50and the orifice defining portion44. With this arrangement, a center bore of the orifice defining portion44is fluid-tightly closed.

A support member52is fixed to the partition member36. Referring toFIGS. 3 to 5showing solely the support member52, the support member52is of thin annular plate shape overall, and has a reinforcing portion54situated at a given circumferential position and extending radially inwardly. The reinforcing portion54has a circumferential length of about one third of the circumference of the support member52, and consists of a widthwise plate portion56extending in a direction perpendicular to the axis direction of the reinforcing portion54, and a lengthwise plate portion58extending vertically downward in the axis direction, which is formed by bending inner peripheral portion of the widthwise plate portion56vertically downwardly. The widthwise plate portion56is perforated through its thickness by a communication hole60at a location close to one circumferential end portion thereof. The lengthwise plate portion58, on the other hand, has a lower edge portion slightly inwardly curled so as to be reinforced, and is formed with a communication window62of cutout shape at a location close to one circumferential end portion thereof.

The support member52further includes a reinforcing rib64integrally formed at an inner circumferential portion thereof extending over a circumferential length of about two thirds of the circumference thereof, except an area where the reinforcing portion54is formed. The reinforcing rib64projects upwardly while curving radially outwardly to have a curl-like configuration. In order to facilitate the formation of the reinforcing rib64, a pair of separation voids66,66of arcuate cutout shape are formed at portions adjacent to circumferentially opposite ends of the reinforcing portion54.

As shown inFIGS. 1 and 2, the support member52of construction as stated above is bonded to the partition member36through the vulcanization, with a portion thereof being embedded within the orifice-defining portion44of the partition member36. That is, the partition member36is formed as an integral vulcanization molded product having the support member52.

This support member52is affixed to a first partitioning wall portion68situated on the side of the pressure-receiving chamber, which is constituted by an upper wall portion of the circumferential groove46of the orifice defining portion44. With this state, an outer rim portion of the support member52projects radially outward from the partition member36all the way around the circumference thereof. This projected outer rim portion of the support member52serves as a fixing portion70. On the other hand, an inner rim portion of the support member52is superimposed onto and bonded to the lower face of the first partition wall portion68. In other words, the upper face of the support member52is substantially entirely coated by a rubber elastic body of the partition member36having a given thickness. The support member52may be disposed extending across an entire width dimension of the circumferential groove46, or alternatively may be disposed bonded to the first partition wall portion68with a radial dimension not enough to cover the entire width dimension of the circumferential groove46.

The reinforcing portion54of the support member52is bonded to the first partitioning wall portion68with the widthwise plate portion56covering the circumferential groove46across the entire widthwise dimension of the circumferential groove46. In the present embodiment, the first partitioning wall portion68is not formed at a location where the communication hole60is formed, so that the widthwise plate portion56is exposed to the pressure receiving chamber38. With this arrangement, the first partitioning wall portion68is interrupted in the circumferential direction at a location where the communication hole60is formed. On the other hand, the lengthwise plate portion58is bonded in an embedded manner to a second partitioning wall portion72situated on the side of the pressure-receiving chamber40, which is an inner circumferential wall portion of the circumferential groove46of the orifice defining portion44. The lower end of the lengthwise plate portion58is extends downwardly with a length that is slightly insufficient to reach the bottom of the second partitioning wall portion72, whereby the lower end of the lengthwise plate portion58is coated by a rubber elastic body that constitutes the second partitioning wall portion72.

The support member52is positioned relative to the partition member36in the circumferential direction by situating the reinforcing portion54onto a portion where the partition wall48is formed (seeFIG. 6). With this arrangement, the upper portion as well as the inner circumferential portion of the partition wall48is reinforced by means of the support member52continuously over the entire area.

The communication hole60of the reinforcing portion54is situated to a first circumferential end of the circumferential groove46of the partition member36, so that the first circumferential end of the circumferential groove46is open to the upper side of the partition member36through the communication hole60. The communication window62, on the other hand, is situated to the other circumferential end of the circumferential groove46of the partition member36, so that the other circumferential end of the circumferential groove46is open to the radially inner side of the partition member36through the communication window62.

The partition member36of construction as stated above is housed within the fluid sealing area34, and situated at the lower open end portion of the second mounting member14, while extending in an axis-perpendicular direction of the second mounting member14. The outer rim portion of the support member52bonded through vulcanization to the partition member36, i.e., the fixing portion70is superimposed onto the caulking portion22of the second mounting member14, and then is fixed caulkwise to the lower open end portion of the second mounting member14in a fluid-tight fashion, together with the fixing flange portion30of the fixing metal28, by pressingly bending the caulking portion22of the second mounting member14against the outer rim portion of the support member52and the fixing flange portion30in the process of caulking fixation. With the partition member36fixed caulkwise to the lower open end portion of the second mounting member14, the lower end of the orifice defining portion44, i.e., the lower end of the second partition wall portion72is superimposed onto a shoulder portion73formed at an axially medial portion of the fixing metal28. With this regards, a part of the coating rubber layer32, which part is adhered to the inner circumferential surface of the fixing metal28is made thick at a portion around the shoulder portion73, thereby providing an annular superimposing face71. Against this annular superimposing face71, the lower end of the second partition wall portion72is superimposed, whereby the inner circumferential side and the outer circumferential side of the second partitioning wall portion72are separated from each other in a fluid-tight fashion. Also, with the fixing portion70fixed caulkwise to the lower open end portion of the second mounting member14, the upper side and the lower side of the first partitioning wall portion68are separated from each other in a fluid tight fashion.

In the outer circumferential portion of the fluid-sealing area34, there is formed an annular region74between the orifice defining portion44and the fixing metal28. This annular region74is blocked at one circumferential position thereof in a fluid-sealing fashion, so that the annular region74extends in the circumferential direction with a circumferential length slightly smaller than the entire circumference thereof, while maintaining a substantially constant cross sectional shape over the entire circumferential length. A first circumferential end of the annular region74is held in fluid communication with the pressure-receiving chamber38through the communication hole60, while the other end of the annular region74is held in fluid communication with the equilibrium chamber40through the communication window62, whereby is formed an orifice passage42for permitting a fluid communication between the pressure-receiving chamber38and the equilibrium chamber40.

The movable rubber plate50is disposed within the fluid sealing area34so as to extend in the axis perpendicular direction of the second mounting member14, and is therefore subjected at its upper face to the fluid pressure in the pressure-receiving chamber38, and at its lower face to the fluid pressure in the equilibrium chamber40.

Further, a metallic plate76is superimposed onto the lower face of the partition member36in the present embodiment. Referring toFIGS. 7 and 8solely shown is the metallic plate76of thin-disk configuration overall. The metallic plate76includes the suitable number of engaging jaws78integrally formed at respective circumferential positions on its outer rim portion so as to project upwardly. Each of the engaging jaws78includes an engaging projection80. The metallic plate76is perforated through its thickness at its central portion by a plurality of through holes82. The metallic plate76of construction stated above is forcedly sandwiched between the lower end face of the partition member36and the shoulder portion73of the fixing metal28, with the engaging projections80formed at the engaging jaws78mated with engaging recesses84formed onto and open in an outer circumferential surface of the second partitioning wall portion72of the partition member36. With this state, the metallic plate78is assembled with the second mounting member14.

With the metallic plate76assembled with the second mounting member14as stated above, the metallic plate76extends in the axis-perpendicular direction of the second mounting member14, while being disposed between the movable rubber plate50and the diaphragm26with a spacing therebetween. With this arrangement, the metallic plate76partitions the equilibrium chamber70into sections located on the upper and lower sides thereof, which are mutually held in fluid communication through the through holes82. The orifice passage42may be open to either side of the metallic plate. In the present embodiment, the orifice passage42is open to the side of the movable rubber plate50.

As will be understood from the forgoing description, the reinforcing portion54, in the present embodiment, constitutes a partial reinforcing member, and the communication hole60constitutes a pressure-receiving chamber side communication hole, while the communication window62constitutes an equilibrium chamber side communication hole.

The engine mount10of construction as stated above is installed between the power unit and the body of the vehicle, with the first mounting member fixed to the power unit side by means of a fixing bolt threaded into the tapped hole20, and with the second mounting member fixed to the body side via a bracket or another fixing member. With the engine mount10installed in position as described above, when a vibrational load is applied between the first and second mounting members12,14, flows of the fluid through the orifice passage42is caused due to a relative pressure fluctuation between the pressure receiving chamber38and the equilibrium chamber40, whereby the engine mount10can exhibit excellent vibration damping effect on the basis of resonance of the fluid flowing through the orifice passage42. A ratio of a cross sectional area to a length of the orifice passage42is suitably adjusted so that the engine mount10exhibits desired damping effect on the basis of the resonance of the fluid with respect to a desired frequency band. For instance, the orifice passage42may be adjusted so that the engine mount10can exhibit effective damping performance with respect to engine shakes or other low frequency vibrations that may be occurred during driving of the vehicle.

Moreover, the pressure receiving chamber38and the equilibrium chamber40are both partially defined by the movable rubber plate50. With this arrangement, if the input vibrational load has a frequency higher than the frequency to which the orifice passage42is tuned, the movable rubber plate50undergoes slight elastic displacement, thus making it possible to absorb or minimize fluid pressure variation occurred in the pressure-receiving chamber38by means of the slight elastic displacement of the movable rubber plate50. Accordingly, the engine mount10of the present embodiment can also prevent significant increase in the dynamic spring constant thereof, and exhibit a high damping effect, when subjected to a booming noise or other vibrations extending over an intermediate and a high frequency band, which may occurred during idling or driving of the vehicle. It should be appreciated in the present embodiment that the presence of the through holes82formed through the metallic plate76disposed within and partitioning the equilibrium chamber82makes it possible to more precisely tune the damping effect on the basis of the elastic deformation of the movable rubber plate50to a desired frequency range.

According to the present embodiment, the communication hole60and the vicinity thereof are provided with a great rigidity by means of the reinforcing portion54, thereby effectively ensuring a desired rigidity of a wall of the pressure-receiving chamber38, so that the pressure-receiving chamber38undergoes sufficient fluid pressure fluctuation during input of vibration between the first and second mounting members. This arrangement ensures a sufficient amount of fluid flowing through the orifice passage42due to the fluid pressure fluctuation between the pressure-receiving chamber38and the equilibrium chamber40, resulting in sufficient vibration damping effect on the basis of flow action of the fluid.

Further, the second partitioning wall portion72is reinforced by means of the lengthwise plate portion58at a first portion where is located in the vicinity of the communication hole60, and is formed of a rubber elastic body at the other portion except the first portion. With this arrangement, if a relatively large fluid pressure induced in the vicinity of the communication hole60due to the phase difference between the fluid pressure fluctuation in the pressure receiving chamber38and the fluid flow through the orifice passage42, the induced relatively large fluid pressure will be quickly absorbed or moderated based on the elastic deformation of the second partitioning wall portion72situated in the vicinity of the communication hole60.

Therefore, the engine mount10of construction according to the present embodiment effectively permits the fluid pressure fluctuation in the pressure receiving chamber38during input of vibration so as to provide a desired vibration damping effect on the basis of fluid flow action, while preventing or moderating excess fluid pressure fluctuation in the pressure receiving chamber38, which is large enough to cause a so-called “fluid breakage phenomenon” wherein dissolved air present in the non-compressible fluid to separate and form air bubbles, thereby preventing or minimizing generation of noises or vibrations caused by appearance and disappearance of the bubbles.

Additionally, the partition wall48is continuously reinforced at its upper portion and the inner circumferential portion by means of the reinforcing portion54, thereby effectively preventing deformation of the partition wall48, and accordingly preventing a short of the orifice passage42due to elastic deformation of the partition wall48. Thus, the engine mount10of this embodiment is able to exhibit vibration-damping effect on the basis of the resonance of the fluid flowing through the orifice passage42with further improved stability.

Furthermore, the reinforcing rib64provided to the support member52makes it possible for the support member52to obtain a sufficient contact area with the first partitioning wall portion68, thereby assuring durability of the first partitioning wall portion68.

While the present invention has been described in the presently preferred embodiment in detail, it is to be understood that the invention is not limited to the details of the illustrated embodiment, and that the invention may be otherwise embodied.

For instance, while the first partitioning wall portion68is formed of a rubber elastic body in the illustrated embodiment, it may be formed of metal or other rigid materials.

While the orifice passage42extends circumferentially with the circumferential length slightly smaller than its entire circumference, the orifice passage42may be formed with a desired length such as a half of the circumference, a length longer than the circumference, or other possible length, depending on the required characteristics of the engine mount10.

Further, the movable rubber plate50employed in the illustrated embodiment is not essential to practice the present invention.

Likewise, the metallic plate76employed in the illustrated embodiment is not essential to practice the present invention.

While the circumferential groove46of cutout shape is formed at the outside edge portion of the lower end of the orifice defining member44, so as to extend with the circumferential length slightly smaller than that of the circumference of the orifice defining member44, in the illustrated embodiment, the circumferential groove46may have a variety of configuration including a circumferential groove of lateral “U” shape cross sectional shape, which is open in the outer circumferential surface of the orifice defining member44.

It is also to be understood that the present invention may be embodied with various other changes, modifications and improvements, which may occur to those skilled in the art, without departing from the spirit and scope of the invention defined in the following claims.