Fluid-filled type vibration damping device

A fluid-filled type vibration damping device including an elastic movable member attached to a partition member. The elastic movable member includes a clasped portion clasped by the partition member and a switching portion provided to an outer peripheral side of the clasped portion and positioned within a second orifice passage. An abutting portion is provided to the switching portion and projects to lengthwise opposite sides of the orifice passage. A switching mechanism is constituted for opening the orifice passage through a gap formed between the switching portion and the inside face of the orifice passage while closing the orifice passage by abutment of the abutting portion against the inside face of the orifice passage by means of a tilting motion of the switching portion relative to the clasped portion through elastic deformation of a thin portion provided between the clasped portion and the switching portion.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a fluid-filled type vibration damping device used for an automotive engine mount or the like. More particularly, the present invention pertains to a fluid-filled type vibration damping device capable of achieving vibration damping effect based on flow action of a fluid with respect to any of two or more vibration inputs having different frequencies.

2. Description of the Related Art

Conventionally, there is known a vibration damping device interposed between components that make up a vibration transmission system so as to elastically connect or elastically support those components. A fluid-filled type vibration damping device, which is one type of the vibration damping device, is adapted for use as an automotive engine mount or the like. The fluid-filled type vibration damping device includes a first mounting member, a second mounting member, a main rubber elastic body elastically connecting the first and second mounting members, a partition member supported by the second mounting member, and a pressure-receiving chamber and an equilibrium chamber disposed on either side of the partition member. The pressure-receiving chamber whose wall is partially defined by the main rubber elastic body is adapted to give rise to internal pressure fluctuations, while the equilibrium chamber whose wall is partially defined by a flexible film is adapted to permit changes in volume. A non-compressible fluid fills each of the chambers. In addition, the pressure-receiving chamber and the equilibrium chamber are interconnected through a first orifice passage and a second orifice passage, with the second orifice passage tuned to a higher frequency than the first orifice passage. At times of vibration input, a fluid flow will be produced between the pressure-receiving chamber and the equilibrium chamber so as to exhibit vibration damping effect based on resonance action or other flow action of the fluid. Japanese Unexamined Patent Publication No. JP-A-2007-155033 discloses one example of such a fluid-filled type vibration damping device, in which the second orifice passage is constituted by upper and lower through holes and a housing space of a movable rubber plate.

The fluid-filled type vibration damping device incorporating the first orifice passage and the second orifice passage having different tuning frequencies is sometimes furnished with a switching mechanism. This switching mechanism switches the second orifice passage, which is tuned to the higher frequency, between open state and closed state in order to effectively exhibit vibration damping effect of both orifice passages. Specifically, JP-A-2007-155033 discloses that the movable rubber plate is disposed on the path of the second orifice passage. At times of input of low-frequency, large-amplitude vibration, the movable rubber plate is pressed against the partition member while blocking off the upper and lower through holes, thereby closing the second orifice passage. This will ensure a sufficient amount of fluid flow through the first orifice passage.

However, with the fluid-filled type vibration damping device disclosed in JP-A-2007-155033, an impact during abutment of the movable rubber plate against the partition member may be transmitted as a noise to the vehicle body via the second mounting member. In particular, with the switching mechanism by means of the movable plate, the direction of exertion of pressure on the movable plate is generally coincident with the direction of abutment of the movable plate against the partition member. Accordingly, a differential in fluid pressure between the pressure-receiving chamber and the equilibrium chamber is likely to exert on the movable plate as an accelerating force, so that possible striking noise during abutment between the movable plate and the partition member tends to be a problem. Moreover, the movable plate is not supported by the partition member and freely displaces in the housing space without being appreciably decelerated. This makes it difficult to reduce the impact during the abutment.

SUMMARY OF THE INVENTION

It is therefore one object of this invention to provide a fluid-filled type vibration damping device of novel construction which is able to switch the second orifice passage between open and closed states so as to obtain excellent vibration damping effect, as well as to reduce striking noise generated during switching the second orifice passage between open and closed states.

A first mode of the present invention provides a fluid-filled type vibration damping device including: a first mounting member; a second mounting member having a cylinder portion; a main rubber elastic body elastically connecting the first and second mounting members; a partition member supported by the second mounting member; a pressure-receiving chamber whose wall is partially defined by the main rubber elastic body; an equilibrium chamber whose wall is partially defined by a flexible film, the pressure-receiving chamber and the equilibrium chamber being disposed on either side of the partition member and filled with a non-compressible fluid; a first orifice passage and a second orifice passage interconnecting the pressure-receiving chamber and the equilibrium chamber, with the second orifice passage being tuned to a higher frequency than the first orifice passage; and an elastic movable member attached to the partition member, wherein a clasped portion clasped by the partition member is provided to the elastic movable member, and a switching portion is provided to an outer peripheral side of the clasped portion and positioned on a fluid flow path of the second orifice passage, while fluid pressure of the pressure-receiving chamber is exerted on one side of the switching portion and fluid pressure of the equilibrium chamber is exerted on another side of the switching portion, wherein an abutting portion is provided to the switching portion so as to project to opposite sides as viewed in a lengthwise direction of the second orifice passage, wherein a thin portion is provided between the clasped portion and the switching portion so that a tilting motion of the switching portion is permitted relative to the clasped portion through elastic deformation of the thin portion, and wherein a switching mechanism is constituted for opening the second orifice passage through a gap formed between an outside peripheral face of the switching portion and an inside face of the second orifice passage while closing the second orifice passage by means of the tilting motion of the switching portion around the thin portion relative to the clasped portion based on relative pressure fluctuations of the pressure-receiving chamber and the equilibrium chamber so that an outside peripheral face of the abutting portion of the switching portion comes into abutment against the inside face of the second orifice passage.

With the fluid-filled type vibration damping device according to the above first mode, at times of input of low-frequency, large-amplitude vibration to which the first orifice passage is tuned, the second orifice passage is closed by the switching portion of the elastic movable member. Thus, sufficient amount of fluid flow can be obtained through the first orifice passage, thereby effectively attaining vibration damping action based on flow action of the fluid.

In addition, the switching portion undergoes a tilting motion relative to the clasped portion so that the abutting portion of the switching portion comes into abutment against the inside face of the second orifice passage. Accordingly, the direction of action of the fluid pressure on the switching portion and the direction of abutment of the abutting portion against the inside face of the second orifice passage are different from each other. Therefore, impact force of the abutment that acts during closing the second orifice passage will be reduced, thereby preventing occurrence of the striking noise.

Moreover, the switching portion is elastically supported with respect to the clasped portion via the thin portion. Thus, as the amount of the tilting motion of the switching portion becomes larger, the shape restoring action based on the elastic force of the thin portion will be more strongly exhibited, thereby limiting speed of the tilting motion. Accordingly, the impact energy during the abutment will be decreased, so that occurrence of the striking noise is avoided.

At times of input of relatively high-frequency, small-amplitude vibration to which the second orifice passage is tuned, the tilting motion of the switching portion will be limited. Accordingly, the gap formed between the outside peripheral face of the switching portion and the inside face of the second orifice passage places the second orifice passage in the open state. Therefore, vibration damping effect by the second orifice passage will be exhibited, realizing excellent vibration damping ability against the vibration of higher frequency than the tuning frequency of the first orifice passage.

Furthermore, at times of input of vibration of higher frequency than the tuning frequency of the second orifice passage, the switching portion undergoes displacement with minute amplitude. Consequently, the fluid pressure of the pressure-receiving chamber will be transmitted to the equilibrium chamber and absorbed by volume changes of the equilibrium chamber so as to avoid a marked development of high dynamic spring. This makes it possible to obtain excellent vibration damping ability with respect to the vibration of higher frequency than the tuning frequency of the second orifice passage as well.

A second mode of the present invention provides the fluid-filled type vibration damping device according to the first mode wherein the elastic movable member has an annular shape, and both of the clasped portion and the switching portion are provided continuously about an entire circumference of the elastic movable member.

According to the second mode, since the clasped portion is provided continuously about the entire circumference, the elastic movable member is stably supported by the partition member. Besides, since the switching portion is provided continuously about the entire circumference, it is possible to ensure a large passage cross sectional area of the second orifice passage without needing increase in size of the partition member in the diametrical direction. This will attain a greater degree of freedom in tuning of the second orifice passage. Moreover, when closing the second orifice passage, the outside peripheral face of the switching portion comes into abutment against the inside face of the second orifice passage about the entire circumference. This makes it possible to close the second orifice passage without leakage of the fluid, thereby efficiently preventing escape of the fluid pressure. Note that the switching portion, because of being provided to the outer peripheral side of the clasped portion, is permitted tilting motion even though provided continuously about the entire circumference.

A third mode of the present invention provides the fluid-filled type vibration damping device according to the first or second mode wherein the thin portion is constricted in width, and a regulating mechanism for regulating an amount of the tilting motion of the switching portion relative to the clasped portion is constituted by means of abutment between the switching portion and the clasped portion at the thin portion.

According to the third mode, the regulating mechanism is provided so as to regulate the amount of the tilting motion of the switching portion with respect to the clasped portion. With this arrangement, at times of input of low-frequency, large-amplitude vibration, the switching portion is stably retained by the regulating mechanism at the closing position of the second orifice passage. Thus, ample amount of fluid flow through the first orifice passage is more efficiently obtained, making it possible to advantageously exhibit desired vibration damping effect.

A fourth mode of the present invention provides the fluid-filled type vibration damping device according to any one of the first through third modes wherein the abutting portion is provided at an outer peripheral edge of the switching portion.

According to the fourth mode, even where the gap between the switching portion and the inside face of the second orifice passage is the same, the outside peripheral face of the abutting portion comes into abutment against the inside face of the second orifice passage and closes the second orifice passage at the stage where the amount of the tilting motion of the switching portion relative to the clasped portion is relatively small. Therefore, it is possible to ensure a large gap between the switching portion and the inside face of the second orifice passage so as to obtain a sufficient passage cross sectional area of the second orifice passage, while being capable of closing the second orifice passage during input of low-frequency, large-amplitude vibration.

A fifth mode of the present invention provides the fluid-filled type vibration damping device according to the fourth mode wherein the switching portion progressively becomes thicker towards an outer peripheral side, while the abutting portion progressively becomes narrower towards a projecting distal end thereof.

According to the fifth mode, the abutting portion comes into abutment starting with its narrow distal end against the inside face of the second orifice passage. Thus, effective cushioning action will be exhibited during the abutment, thereby preventing occurrence of the striking noise. Besides, the abutting portion progressively becomes wider towards its proximal end, so that as the amount of the tilting motion of the switching portion increases, the force for limiting the tilting motion becomes larger on the basis of elasticity of the abutting portion. This will limit the tilting motion of the switching portion at the closing position of the second orifice passage, whereby desired vibration damping effect is achieved.

A sixth mode of the present invention provides the fluid-filled type vibration damping device according to any one of the first through fifth modes wherein a valve portion is integrally formed on an inner peripheral side of the clasped portion, wherein a short-circuit passage is formed in the partition member for interconnecting the pressure-receiving chamber and the equilibrium chamber, and the valve portion is disposed on the short-circuit passage, and wherein a relief mechanism is constituted for closing the short-circuit passage by means of abutment of an inside peripheral face of the valve portion against an inside face of the short-circuit passage while permitting fluid flow through the short-circuit passage between the pressure-receiving chamber and the equilibrium chamber by means of elastic deformation of the valve portion so as to be spaced away from the inside face of the short-circuit passage due to negative pressure of the pressure-receiving chamber acting on the valve portion.

According to the sixth mode, by providing the relief mechanism, at times of input of a large jarring load, an excessive negative pressure of the pressure-receiving chamber will be rapidly dispelled, thereby preventing occurrence of noises due to cavitation. Meanwhile, at times of input of normal vibration, the short-circuit passage is retained in the closed state, effectively attaining vibration damping effect based on the flow action of the fluid through the first and second orifice passages or the like.

Furthermore, since the valve portion that constitutes the relief mechanism is integrally provided to the elastic movable member, increase in the number of components is avoided.

According to the present invention, the switching portion for switching the second orifice passage between the open and closed states is provided to the elastic movable member supported by the partition member. Thus, vibration damping effects based on the flow action of the fluid through the respective first and second orifice passages are both effectively exhibited. Moreover, the switching portion is supported by the clasped portion via the thin portion, so that the switching portion undergoes tilting motion in a swinging manner. This will reduce the striking noise due to abutment against the inside face of the second orifice passage. In addition, by utilizing the tilting motion of the switching portion, even with the vibration of higher frequency than the tuning frequency of the second orifice passage, effective vibration damping action will be attained on the basis of liquid pressure-absorbing action.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring first toFIG. 1, there is depicted an automotive engine mount10according to a first embodiment of a fluid-filled type vibration damping device constructed in accordance with the present invention. The engine mount10has a construction in which a first mounting member12and a second mounting member14are connected by a main rubber elastic body16. In the description hereinbelow, as a general rule, the vertical direction refers to the vertical direction inFIG. 1, which coincides with the principal vibration input direction.

Described more specifically, the first mounting member12is a high rigidity component of small-diameter, generally circular post shape, and at its axially upper end, has a flange portion18that projects peripherally outward. The first mounting member12also has a bolt hole20that extends on the center axis and opens onto the upper face thereof. The bolt hole20is provided with a screw thread on its inside peripheral face.

The second mounting member14is a high rigidity component of thin-walled, large-diameter, generally cylindrical shape, and at its axially medial section, has a stepped portion22. With the axially upper side of the stepped portion22being a large-diameter cylinder portion24while the axially lower side being a small-diameter cylinder portion26, the second mounting member14has a stepped cylindrical shape overall. In the present embodiment, the entire second mounting member14serves as a cylinder portion.

Then, the first mounting member12is positioned in the upper opening of the second mounting member14so as to be coaxial with the second mounting member14, while the first mounting member12and the second mounting member14are elastically connected by the main rubber elastic body16. The main rubber elastic body16has a thick-walled, large-diameter, generally frustoconical shape. The first mounting member12is bonded by vulcanization to the small-diameter side end of the main rubber elastic body16, and the inner circumferential face of the second mounting member14is superposed and bonded by vulcanization to the outer circumferential face of the large-diameter side end of the main rubber elastic body16. In the present embodiment, the main rubber elastic body16takes the form of an integrally vulcanization molded component incorporating the first mounting member12and the second mounting member14.

A large-diameter recess28of inverted, generally bowl shape is formed opening onto the large-diameter end face (lower face) of the main rubber elastic body16. Besides, a seal rubber layer30is integrally formed with the outer peripheral side of the large-diameter recess28of the main rubber elastic body16and extends downward. The seal rubber layer30is a rubber elastic body of thin-walled, large-diameter, generally cylindrical shape whose outer circumferential face is superposed and bonded by vulcanization to the inner circumferential face of the small-diameter cylinder portion26of the second mounting member14. By so doing, the inner circumferential face of the second mounting member14is entirely covered by the rubber elastic body.

A flexible film32is attached to the lower opening of the second mounting member14. The flexible film32is a thin rubber film of generally circular disk shape or circular dome shape having ample slack in the vertical direction. In addition, the outer peripheral face of the flexible film32is bonded by vulcanization to a fixing member34of generally cylindrical shape or annular shape. Then, after the fixing member34being inserted into the lower opening of the second mounting member14, the second mounting member14is subjected to a diameter reduction process such as 360-degree radial compression. With this arrangement, the fixing member34is fixed to the second mounting member14so that the flexible film32is supported by the second mounting member14.

By so doing, the upper opening of the second mounting member14is closed off by the main rubber elastic body16, while the lower opening of the second mounting member14is closed off by the flexible film32, thereby forming a fluid-filled zone36between the main rubber elastic body16and the flexible film32. The fluid-filled zone36is sealed off from the outside and filled with a non-compressible fluid. While no particular limitation is imposed on the sealed non-compressible fluid filling the fluid-filled zone36, it would be favorable to use water, an alkylene glycol, a polyalkylene glycol, a silicone oil, a some mixture of these for example. In order to effectively achieve vibration damping effect based on flow action of the fluid (discussed later) a low-viscosity fluid having viscosity of 0.1 Pa·s or lower is preferred.

A partition member38is disposed within the fluid-filled zone36. As depicted inFIGS. 2 through 4, the partition member38is of thick-walled, large-diameter, generally circular disk shape including a partition member main body40and a base plate member42.

The partition member main body40is a high rigidity component of thick-walled, large-diameter, generally circular disk shape overall, and includes an annular outer peripheral portion44and a center portion46which is inserted into the center hole of the outer peripheral portion44and spaced apart therefrom by a prescribed distance in the radial direction. Outer peripheral connecting portions58to be described later interconnect the upper ends of the outer peripheral portion44and the center portion46.

Described more specifically, the outer peripheral portion44has a large-diameter, annular shape which extends continuously about the entire circumference in the circumferential direction. A slot48opens onto the outer circumferential face of the outer peripheral portion44and extends just short of once around the circumference. Besides, the center portion46disposed in the center hole of the outer peripheral portion44has a central abutting section50of circular post shape. A flange-shaped inner peripheral connecting portion52is integrally formed with the upper end of the central abutting section50, and a clasping projection54is provided to the outer peripheral edge of the inner peripheral connecting portion52about the entire circumference and projects downward. In addition, the inner peripheral connecting portion52includes at several locations along the circumference (three in the present embodiment) upper through-holes56which have a prescribed length in the circumferential direction and pierce the inner peripheral connecting portion52in the thickness direction.

Also, the center portion46is inserted and positioned within the center hole of the outer peripheral portion44, so that the inner circumferential face of the outer peripheral portion44and the outer circumferential face of the center portion46are opposed to each other with a prescribed distance therebetween. Moreover, the outer peripheral portion44and the center portion46have an integral structure whose upper end portions are interconnected by the outer peripheral connecting portions58provided at several locations along the circumference (three in the present embodiment). With this arrangement, the partition member main body40including the outer peripheral portion44and the center portion46is constituted. Note that upper communication holes60are formed circumferentially between the outer peripheral connecting portions58so as to pass through in the axial direction with a prescribed length in the circumferential direction.

Meanwhile, the base plate member42is a high rigidity plate of generally annular disk shape overall. The base plate member42includes an outer peripheral support portion62of annular disk shape, a tubular stepped portion64projecting upward from the inner peripheral edge of the outer peripheral support portion62, and an internal flange-shaped clasping piece66integrally formed with the upper end of the stepped portion64and projecting peripherally inward. In addition, a plurality of lower communication holes68having a prescribed length in the circumferential direction pierce the inner peripheral portion of the outer peripheral support portion62in the thickness direction. Note that the base plate member42has an outside diameter dimension substantially equal to that of the partition member main body40, and an inside diameter dimension substantially equal to that of the clasping projection54of the partition member main body40while being larger than the diameter of the central abutting section50.

Then, the partition member main body40and the base plate member42are superposed in the axial direction and fixed to each other by means of engaging, bonding or the like. In this assembled state, radially between the outer peripheral portion44and the central abutting section50of the partition member main body40, the partition member main body40and the base plate member42are spaced away from each other in the axial direction. This provides an annular housing space69formed between axially opposed faces of the partition member main body40and the base plate member42. Besides, the central abutting section50of the partition member main body40is inserted into the center hole of the base plate member42, thereby providing an annular lower through-hole70between the central abutting section50and the clasping piece66of the base plate member42.

The partition member38constructed as above is housed within the fluid-filled zone36and supported by the second mounting member14. Described more specifically, the partition member38is inserted into the small-diameter cylinder portion26of the second mounting member14. The outer peripheral portion of the partition member38is superposed against the lower end face of the main rubber elastic body16so that the partition member38is positioned in the axial direction. Then, by means of diameter-constricting process of the second mounting member14, the partition member38is fixed to the second mounting member14together with the fixing member34. With this arrangement, the partition member38whose outer peripheral portion is supported by the second mounting member14is disposed so as to extend in the axis-perpendicular direction within the fluid-filled zone36.

Moreover, by disposing the partition member38, the fluid-filled zone36is bifurcated into upper and lower parts disposed on either side of the partition member38. This provides to the upper side of the partition member38a pressure-receiving chamber72whose wall is partially defined by the main rubber elastic body16and that is subjected to internal pressure fluctuations during input of vibration, and to the lower side of the partition member38an equilibrium chamber74whose wall is partially defined by the flexible film32and that readily permits changes in volume. Note that the pressure-receiving chamber72and the equilibrium chamber74are filled with the non-compressible fluid filling the fluid-filled zone36.

In addition, the outer circumferential face of the partition member38is superposed against the inner circumferential face of the second mounting member14via the seal rubber layer30. With this arrangement, the outer circumferential opening of the slot48is sealed off fluid-tightly by the second mounting member14, thereby forming a tunnel-like passage extending in the circumferential direction. One end of the tunnel-like passage communicates with the pressure-receiving chamber72via a first passage hole76, while the other end thereof communicates with the equilibrium chamber74via a second passage hole78. This provides a first orifice passage80that interconnects the pressure-receiving chamber72and the equilibrium chamber74. Note that the first orifice passage80is tuned to a low frequency of around 10 Hz that corresponds to engine shake by adjusting the ratio (A/L) of the passage cross sectional area (A) to the passage length (L) in consideration of wall spring rigidity of the pressure-receiving chamber72and the equilibrium chamber74.

Besides, a second orifice passage82is formed radially between the center portion46and the outer peripheral portion44. Specifically, in the housing space69, a ring-shaped area is defined radially between the center portion46and the outer peripheral portion44. The ring-shaped area communicates with the pressure-receiving chamber72via the upper communication holes60formed circumferentially between the outer peripheral connecting portions58, while communicating with the equilibrium chamber74via the lower communication holes68formed in the base plate member42. This provides the second orifice passage82that interconnects the pressure-receiving chamber72and the equilibrium chamber74. Note that the tuning frequency of the second orifice passage82is set to a higher frequency than that of the first orifice passage80. That is, the second orifice passage82is tuned to a midrange to high frequency of ten or more Hz and above that corresponds to idling vibration or driving rumble.

Additionally, in the housing space69, an area defined radially between the central abutting section50and the clasping projection54communicates with the pressure-receiving chamber72via the upper through-hole56that pierces the inner peripheral connecting portion52, while communicating with the equilibrium chamber74via the lower through-hole70formed radially between the central abutting section50and the base plate member42. With this arrangement, a short-circuit passage84described later is formed in the partition member38for interconnecting the pressure-receiving chamber72and the equilibrium chamber74so as to pass through radially between the central abutting section50and the clasping projection54(seeFIG. 7C). Note that with the short-circuit passage84, it is desirable that the ratio of the passage cross sectional area to the passage length be set still larger than that of the second orifice passage82so that the flow resistance is smaller than that of the first and second orifice passages80,82.

Furthermore, an elastic movable member86is disposed within the housing space69of the partition member38. As depicted inFIG. 5, the elastic movable member86is a component of generally annular shape or annular disk shape formed of a rubber elastic body, and is integrally equipped with an annular clasped portion88, a valve portion90provided to the inner peripheral side of the clasped portion88, and a switching portion92provided to the outer peripheral side of the clasped portion88.

The clasped portion88has an annular shape that extends continuously with substantially unchanging cross section about the entire circumference. When viewed in vertical cross section, the clasped portion88has a configuration in which an inner peripheral portion of generally circular shape and an outer peripheral portion of generally rectangular shape are combined. Besides, a compressed protrusion94that projects in the axially opposite directions is integrally formed with the inner peripheral portion of the clasped portion88. The outside peripheral face of the clasped portion88has a cylindrical shape extending in the substantially axial direction.

A valve portion90is integrally formed on the inner peripheral side of the clasped portion88. The valve portion90extends with substantially unchanging cross section about the entire circumference, and includes an outer peripheral basal end96projecting peripherally inward from the clasped portion88while expanding in the substantially axis-perpendicular direction, and an inner peripheral distal end98projecting peripherally inward from the outer peripheral basal end96. In addition, the upper face of the outer peripheral basal end96and the inner peripheral distal end98are defined by a smooth concave curve surface100. Meanwhile, the lower face of the outer peripheral basal end96is defined by an axis-perpendicular plane102that expands in the substantially axis-perpendicular direction, and the lower face of the inner peripheral distal end98is defined by a tapered surface104that progressively slopes upward towards the inner peripheral side. With this arrangement, the outer peripheral basal end96becomes slightly thicker towards the inner peripheral side and expands in the substantially axis-perpendicular direction, while the inner peripheral distal end98becomes gradually thinner towards the inner peripheral side so as to have tapered contours that progressively slopes upward towards the inner peripheral side. Since the inner peripheral distal end98becomes thinner towards its projecting distal end, the valve portion90is made thicker in the outer peripheral portion rather than in the inner peripheral portion. Also, the outermost circumference part of the valve portion90has a thickness dimension smaller than the maximum thickness dimension of the clasped portion88(namely, the diameter of the circular inner peripheral portion when viewed in vertical cross section). Besides, since the upper face of the valve portion90is defined by the concave curve surface100that progressively slopes upward towards the inner peripheral side, there is formed a valley line at the boundary between the clasped portion88and the valve portion90on the upper face.

A switching portion92is provided to the outer peripheral side of the clasped portion88. The switching portion92has an annular shape that extends continuously with substantially unchanging cross section about the entire circumference, and its inside and outside peripheral faces have concentric cylindrical shapes. Note that the switching portion92progressively becomes thicker towards the outer peripheral side.

Also, the switching portion92has the axially opposite faces each defined by a concave curving surface whose slope angle becomes larger towards the outer peripheral side with respect to the axis-perpendicular direction. An abutting portion106is provided at the outer peripheral edge of the switching portion92and projects mostly to axially outer sides. The abutting portion106progressively becomes narrower in the radial direction towards the axially outer side (towards the projecting distal end thereof), and its projecting distal end face is constituted by an arcuate curving surface. Note that when viewed in vertical cross section, the switching portion92including the abutting portion106is axisymmetric in shape with respect to the centerline in its thickness direction (which is indicated by the dot-and-dash line inFIG. 5).

Moreover, the switching portion92connects with the clasped portion88via a thin portion108, and is integrally formed with the clasped portion88. The thin portion108is provided radially between and at the axially center section of the outside peripheral face of the clasped portion88and the inside peripheral face of the switching portion92, while being made thinner than both of the outer peripheral edge and the inner peripheral edge of the switching portion92. With this arrangement, a tilting motion of the switching portion92is permitted with respect to the clasped portion88through elastic deformation of the thin portion108.

Furthermore, in the present embodiment, the thin portion108is constricted in width in the radial direction, so that the outside peripheral face of the clasped portion88and the inside peripheral face of the switching portion92are opposed to each other with a short distance therebetween in the radial direction. As a result, when the switching portion92undergoes an appreciable tilting motion with respect to the clasped portion88, the inside peripheral face of the switching portion92comes into abutment against the outside peripheral face of the clasped portion88on axially outer side of the thin portion108. By so doing, a regulating mechanism for regulating the amount of the tilting motion of the switching portion92relative to the clasped portion88is constituted by means of abutment between the clasped portion88and the switching portion92at the thin portion108.

The elastic movable member86of the above construction is disposed between the partition member main body40and the base plate member42(seeFIG. 6). Specifically, the clasped portion88of the elastic movable member86is positioned between axially opposed faces of the clasping projection54of the partition member main body40and the clasping piece66of the base plate member42, and is clasped between and supported by the clasping projection54and the clasping piece66in the axial direction. Here, the compressed protrusion94integrally formed with the clasped portion88is greatly compressed between the clasping projection54and the clasping piece66, thereby sufficiently achieving positioning action of the elastic movable member86with respect to the partition member38.

In addition, the valve portion90of the elastic movable member86is disposed radially between the clasping projection54and the central abutting section50. The valve portion90projects peripherally inward beyond the base plate member42and is pressed against the outside peripheral face of the central abutting section50. With this arrangement, in the stationary state in the absence of input vibration, the valve portion90is disposed on the fluid flow path of the short-circuit passage84so that the short-circuit passage84is closed by the valve portion90. Furthermore, the fluid pressure of the pressure-receiving chamber72is exerted on the upper face of the valve portion90via the short-circuit passage84(upper through-hole56), while the fluid pressure of the equilibrium chamber74is exerted on the lower face of the valve portion90via the short-circuit passage84(lower through-hole70). Note that while it would also be acceptable for the valve portion90to be in abutment against the central abutting section50without being compressed, in the present embodiment, the valve portion90is pressed and pre-compressed against the central abutting section50in the radial direction.

On the other hand, the switching portion92of the elastic movable member86is disposed radially between the outer peripheral portion44and the center portion46so as to be positioned on the fluid flow path of the second orifice passage82. Besides, the outside peripheral face of the switching portion92is positioned radially inward of the inner circumferential face of the outer peripheral portion44so as to be in opposition thereto with a prescribed distance, so that an annular gap110is formed radially between the outside peripheral face of the switching portion92and the inner circumferential face of the outer peripheral portion44and extends continuously in the axial direction. By so doing, in the stationary state in the absence of input vibration, the second orifice passage82is open through the gap110. Additionally, the fluid pressure of the pressure-receiving chamber72is exerted on the upper face of the switching portion92via the second orifice passage82(upper communication holes60), while the fluid pressure of the equilibrium chamber74is exerted on the lower face of the switching portion92via the second orifice passage82(lower communication holes68). It should be appreciated that in the stationary state, since the abutting portion106projects to opposite sides as viewed in the lengthwise direction of the second orifice passage82(the vertical direction inFIG. 1), the second orifice passage82is open without being blocked by the abutting portion106.

The engine mount10of the above construction is arranged such that the first mounting member12is mounted onto a power unit (not shown) while the second mounting member14is mounted onto a vehicle body (not shown), thereby providing vibration damping support of the power unit on the vehicle body via the engine mount10.

With the engine mount10mounted onto the vehicle, at times of input of low-frequency, large-amplitude vibration corresponding to engine shake, fluid flow will be produced through the first orifice passage80between the pressure-receiving chamber72and the equilibrium chamber74based on internal pressure fluctuations within the pressure-receiving chamber72relative to the equilibrium chamber74. By so doing, desired vibration damping effect (high attenuating or damping action) will be exhibited based on resonance action or other flow action of the fluid.

Moreover, at times of input of low-frequency, large-amplitude vibration, as depicted inFIG. 7A, the switching portion92closes the second orifice passage82. Specifically, when low-frequency, large-amplitude vibration corresponding to engine shake is input, based on a differential in fluid pressure between the pressure-receiving chamber72and the equilibrium chamber74, the switching portion92, which is connected to the clasped portion88via the thin portion108, undergoes a tilting motion with respect to the clasped portion88through elastic deformation of the thin portion108. Accordingly, the outside peripheral face of the abutting portion106that projects from the switching portion92in the lengthwise direction of the second orifice passage82is pressed against the inner circumferential face of the outer peripheral portion44of the partition member main body40that constitutes the inside face of the second orifice passage82. As a result, the second orifice passage82is closed by the switching portion92, and the fluid pressure of pressure-receiving chamber72is prevented from being transmitted to the equilibrium chamber74through the second orifice passage82. Thus, sufficient amount of fluid flow can be efficiently obtained through the first orifice passage80. Note that whileFIG. 7Ashows the state where a positive pressure is applied to the pressure-receiving chamber72, also in the state where a negative pressure is applied, the abutting portion106is pressed at its lower side against the inner circumferential face of the outer peripheral portion44so that the second orifice passage82is closed by the switching portion92.

In addition, in the present embodiment, there is provided the regulating mechanism for regulating the amount of the tilting motion of the switching portion92relative to the clasped portion88by means of abutment between the inside peripheral face of the switching portion92and the outside peripheral face of the clasped portion88. Therefore, at times of input of low-frequency, large-amplitude vibration, the switching portion92is stably retained at the closing position of the second orifice passage82, thereby preventing the fluid pressure of the pressure-receiving chamber72from escaping to the equilibrium chamber74through the second orifice passage82.

Meanwhile, at times of input of midrange-frequency, small-amplitude vibration corresponding to idling vibration or the like, as depicted inFIG. 7B, the second orifice passage82is opened for interconnecting the pressure-receiving chamber72and the equilibrium chamber74by means of the abutting portion106of the switching portion92being retained so as to be spaced away from the inside face of the second orifice passage82. This will actively produce fluid flow through the second orifice passage82, thereby attaining desired vibration damping effect (low dynamic spring effect) on the basis of flow action of the fluid. In this way, the engine mount10is furnished with a switching mechanism constituted for switching the second orifice passage82between open and closed states utilizing the tilting motion of the switching portion92according to the amplitude of the input vibration. Note that the first orifice passage80, which is tuned to a lower frequency than the input vibration, is substantially closed due to antiresonance or the like. Thus, sufficient amount of fluid flow through the second orifice passage82is efficiently obtained.

Furthermore, at times of input of high-frequency, small-amplitude vibration corresponding to driving rumble or the like, in the open state of the second orifice passage82depicted inFIG. 7B, the second orifice passage82is substantially closed due to antiresonance, while the switching portion92vibrates with minute amplitude in the vertical direction. Accordingly, the fluid pressure of the pressure-receiving chamber72is transmitted to the equilibrium chamber74, so that the pressure-receiving chamber72is prevented from being substantially sealed off. Thus, desired vibration damping effect (low dynamic spring effect) will be effectively exhibited on the basis of liquid pressure-absorbing action.

In this way, by switching the second orifice passage82between the open and closed states, the engine mount10is able to selectively exhibit vibration damping effect through the first orifice passage80and vibration damping effect through the second orifice passage82according to the frequency of the input vibration. Besides, even for the vibration of higher frequency than the tuning frequency of the second orifice passage82, the switching portion92functions as a movable membrane and is able to obtain effective vibration damping action. Therefore, with the engine mount10, it is possible to achieve excellent vibration damping effect against vibration over a wide frequency range.

Also, the switching portion92undergoes a tilting motion relative to the clasped portion88due to the fluid pressure acting in the axial direction, and the abutting portion106comes into abutment against the inside face of the second orifice passage82. Thus, the direction of action of the fluid pressure and the direction of abutment of the abutting portion106against the inside face of the second orifice passage82are different from each other. Therefore, impact force will be reduced during abutment between the abutting portion106and the inside face of the second orifice passage82, thereby preventing occurrence of contact noise.

Moreover, as the amount of the tilting motion of the switching portion92relative to the clasped portion88becomes larger, the tilting motion will be more strongly limited on the basis of elasticity of the thin portion108, thereby decreasing speed of the tilting motion of the switching portion92. At the time of abutment of the abutting portion106against the inside face of the second orifice passage82, the amount of the tilting motion of the switching portion92is sufficiently large. Thus, the speed of the tilting motion of the switching portion92is limited, thereby reducing the impact force at the time of the abutment. This makes it possible to prevent occurrence of striking noise due to abutment of the abutting portion106against the inside face of the second orifice passage82.

In addition, the abutting portion106, which projects from the switching portion92and is made thin (narrow) in the radial direction, is adapted to come into abutment against the inside face of the second orifice passage82. Accordingly, the impact during abutment will be absorbed by the shear deformation of the abutting portion106, thereby more effectively reducing the striking noise.

Besides, the abutting portion106is provided at the outer peripheral edge of the switching portion92. Thus, an ample width of the gap110in the radial direction will be ensured without increasing the amount of the tilting motion of the switching portion92required for closing the second orifice passage82. Therefore, it is possible to sufficiently obtain the substantial passage cross sectional area of the second orifice passage82with excellent space efficiency, thereby achieving a great degree of freedom in tuning the second orifice passage82.

Furthermore, the switching portion92becomes progressively thicker towards the outer peripheral side, and in association therewith, the abutting portion106becomes progressively narrower towards its projecting distal end. At the time of abutment of the abutting portion106against the inside face of the second orifice passage82, the abutting portion106gradually comes into abutment starting with its narrow distal end. Thus, the impact force during initial abutment for which occurrence of striking noise is likely to be a problem will be ameliorated, thereby preventing occurrence of the striking noise. Subsequently, the amount of abutment of the abutting portion106against the inside face of the second orifice passage82increases and the abutment area gradually broadens towards its proximal end of wider width. Accordingly, the tilting motion of the switching portion92is limited due to elasticity of the abutting portion106, so that the switching portion92will be stably retained at the closing position of the second orifice passage82. Note that the engine mount10is provided with the regulating mechanism utilizing abutment between the inside peripheral face of the switching portion92and the outside peripheral face of the clasped portion88, which regulates the amount of the tilting motion of the switching portion92in cooperation with the elasticity of the abutting portion106.

Additionally, since the elastic movable member86has an annular shape and the clasped portion88is provided continuously about the entire circumference, the elastic movable member86is stably clasped between the partition member main body40and the base plate member42. Also, since the switching portion92is provided continuously about the entire circumference, when closing the second orifice passage82, the fluidtightness can be readily obtained. Concomitantly, it is possible to ensure a large passage cross sectional area of the second orifice passage82without needing increase in size of the partition member38.

On the other hand, when the vehicle drives over a bump or the like during driving, a large jarring load is input across the first mounting member12and the second mounting member14. Consequently, the pressure-receiving chamber72is subjected to an excessive negative pressure, and as depicted inFIG. 7C, the valve portion90undergoes elastic deformation. Specifically, by means of the valve portion90being suctioned towards the pressure-receiving chamber72on the basis of relative pressure differential between the pressure-receiving chamber72and the equilibrium chamber74, the valve portion90is spaced away from the central abutting section50, forming a gap between the valve portion90and the central abutting section50. By so doing, the short-circuit passage84that interconnects the pressure-receiving chamber72and the equilibrium chamber74is opened, permitting fluid flow through the short-circuit passage84from the equilibrium chamber74into the pressure-receiving chamber72. The negative pressure within the pressure-receiving chamber72will be rapidly reduced or dispelled thereby. As a result, occurrence of bubbles caused by cavitation will be minimized, thereby reducing shockwaves arising during dissipation of the bubbles. Thus, cavitation noise will be reduced or avoided. Note that with the short-circuit passage84, the ratio (A/L) of the passage cross sectional area (A) to the passage length (L) is set even greater than that of the second orifice passage82, so that flow resistance of the fluid is set smaller than that of the first and second orifice passages80,82. Also, in the engine mount10, a relief mechanism is constituted including the short-circuit passage84for permitting communication between the pressure-receiving chamber72and the equilibrium chamber74as well as the valve portion90for switching the short-circuit passage84between open and closed states.

Moreover, the valve portion90that constitutes the relief mechanism is integrally provided to the elastic movable member86. This will avoid increase in the number of components due to providing the relief mechanism, thereby preventing increase in the number of assembly operation steps of the components or the like as well.

It should be appreciated that when a positive pressure is applied to the pressure-receiving chamber72, the valve portion90is more strongly pressed against the central abutting section50, whereby the short-circuit passage84is retained in the closed state. Accordingly, during acting of the positive pressure for which occurrence of cavitation noise does not pose any problems, internal pressure in the pressure-receiving chamber72is ensured without escaping to the equilibrium chamber74through the short-circuit passage84. Thus, vibration damping effect by the fluid flow through the first orifice passage80will be exhibited.

An embodiment of the present invention has been described in detail above, but the present invention is not limited to those specific descriptions. For example, the valve portion90is not essential to the elastic movable member. The elastic movable member may alternatively be constituted by the clasped portion88supported by the partition member38and the switching portion92integrally provided to the clasped portion88via the thin portion108. In this case, it is to be understood that the short-circuit passage84provided to the partition member38in the preceding embodiment is not necessary.

Also, the shape of the abutting portion106provided to the switching portion92is not limited to the one that progressively becomes narrower towards its distal end, as illustrated in the preceding embodiment. The abutting portion106may, for example, has a generally unchanging width dimension from its basal end to its distal end. Besides, the abutting portion106is not necessarily be provided to the outer peripheral edge of the switching portion92, but may be provided to the radially middle section or the inner peripheral edge of the switching portion92.

In addition, the elastic movable member is not necessarily be limited to an annular or annular disk shape. Similarly, neither the clasped portion nor the switching portion that constitutes the elastic movable member is limited to an annular shape. For example, it would also be acceptable that the switching portion is disposed only on the fluid flow path of the second orifice passage82which is provided partially along the circumference, and therefore has a length less than once around the circumference.

Furthermore, while it is desirable that the thin portion108be constricted in width in the radial direction so as to constitute the regulating mechanism for regulating the amount of the tilting motion of the switching portion92, it would also be possible for example that the radial dimension (width dimension) of the thin portion108is made larger so that the switching portion92readily undergoes the tilting motion. That is, the width dimension of the thin portion108is to be appropriately set depending on the required ability, and is not necessarily set such that the outside peripheral face of the clasped portion88and the inside peripheral face of the switching portion92come into abutment.

Moreover, the present invention is not always limited to engine mounts only, and is adaptable to implementation in body mounts, sub-frame mounts, differential mounts or the like. Additionally, the fluid-filled type vibration damping device according to the present invention is not limited to implementation in automobiles, and may preferably be implemented in motorized two wheeled vehicles, rail vehicles, industrial vehicles or the like.