FLUID-FILLED CYLINDRICAL ELASTIC MOUNT HAVING MOVABLE MEMBER IN FLUID CHAMBER

Abstract: A fluid-filled cylindrical elastic mount (16,40) having an inner and an outer sleeve (10,12) which are disposed in mutually spaced-apart relation with each other, and an elastic body (14) interposed between the inner and outer sleeves (10,12) so as to elastically connect the inner and outer sleeves (10,12). The elastic body (14) at least partially defines a fluid-filled chamber (30) located between the inner and outer sleeves (10, 12) in a load-receiving direction in which a vibrational load is applied to the elastic mount (16,40). The elastic body (14) includes a thin-walled portion (24, 24) which partially defines the fluid-filled chamber (30) and which elastically yields to permit the chamber (30) to be elastically deformed upon application of the vibrational load. A movable member (32) is accommodated in the fluid-filled chamber (30) such that the movable member (32) is freely movable over a predetermined distance in the load-receiving direction. The movable member (32) and inner surfaces of the fluid chamber (30) cooperate with each other to define resonance portions (34) having a predetermined radial depth as measured in the load-receiving direction.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates generally to a fluid-filled cylindrical elastic mount adapted to damp and/or isolate an input vibrational load, based on flows of a fluid in a fluid chamber, and more particularly to such a fluid-filled elastic mount which is simple in construction and which exhibits excellent vibration isolating characteristics with respect to high-frequency vibrations. Discussion of the Prior Art A cylindrical elastic mount such as a suspension bushing or engine mount used on an automotive vehicle is known for elastically connecting two members in a vibration system in a vibration damping or isolating manner, or for elastically mounting one of the two members on the other member such that the above one member is supported by the other member in a vibration damping or isolating manner. Such a cylindrical elastic mount has an inner and an outer sleeve which are disposed in coaxial or non-coaxial, mutually radially spaced-apart relationship with each other, and an elastic body which elastically connects the inner and outer sleeves. A suitable shaft member fixed to the above one member is fixedly inserted through the inner sleeve, while the other member as a support member is fitted on the outer sleeve. Thus, the elastic mount is interposed between the support member and the shaft member, so that input vibrations applied between these two members are damped and/or isolated based on elastic deformation of the elastic body of the elastic mount. The Document FR-A 2 551 161 shows another elastic mount with a resilient member interposed between an inner sleeve and an outer sleeve disposed radially outwardly of the inner sleeve. The resilient member has portions in which a plurality of fluid chambers are formed. This fluid chambers are filled with an incompressible fluid and held in fluid communication with each other through an orifice. A freely movable member is arranged in at least one of the plural fluid chambers to prevent an excessive displacement of the inner and outer sleeves relative to each other in the radial direction. If a large amount of elastic deformation occurs in the elastic body of the elastic mount, the movable member comes into abutment with the both the radially inner and radially outer portions of the fluid chamber. The application of the movable member to the inner and outer portion of the fluid chamber is effected in the case of low-frequency vibrations with high vibration amplitude. The movable member does not contribute to the damping of medium- to high-frequency vibrations which shall be damped by the elastic deformation of the resilient member. One particular disadvantage of the above mentioned prior art is that, since a rubber material is used as the elastic body in such cylindrical elastic mounts, the elastic mounts suffer from that the rubber elastic body exhibits an excessively high degree of stiffness due to its resonance upon application of vibrations having relatively high frequencies. The resonance of the elastic body usually occurs when the frequency of the input vibrations falls within a range of about 300-700Hz, where the cylindrical elastic mount is used as an engine mount for mounting an engine unit on a front-engine front-drive vehicle (FF vehicle), for example. Thus, the booming noises such as engine-transmitted noises, and other high-frequency vibrations cannot be sufficiently isolated by the elastic mount. In view of the recent increasing requirement for improved noise isolation and driving comfort of the motor vehicles, in particular, there has been a growing need for improving the vibration isolating characteristics of the elastic mount with respect to the high-frequency vibrations applied thereto. Still another elastic mount is known from the Document DE-A 3 721 444, said elastic mount has a damping member being connected with the elastic body and forming with the elastic body an annular gap for damping high-frequency vibrations which substantially lies in a plane perpendicular to the load-receiving direction. Even though this elastic mount has improved damping characteristics regarding high-frequency vibrations, this elastic mount suffers from its costly complex construction. SUMMARY OF THE INVENTION The present invention was developed in view of the drawback encountered in the prior art. It is therefore an object of the present invention to provide a fluid-filled cylindrical elastic mount which is simple in construction and which exhibits improved vibration damping and isolating characteristics over a wide range of frequency of the input vibrations, while effectively avoiding stiffening of the elastic body upon application of the vibrations of relatively high frequencies. The above object may be achieved according to the principle of the present invention as stated in claim 1, which provides a fluid-filled cylindrical elastic mount having an inner and an outer sleeve which are disposed in mutually spaced-apart relation with each other, and an elastic body interposed between the inner and outer sleeves so as to elastically connect the inner and outer sleeves, wherein the improvement comprises: a single fluid-tightly closed fluid chamber at least partially defined by the elastic body and located between the inner and outer sleeves in a load-receiving direction in which a vibrational load is applied to the elastic mount, the fluid chamber being filled with a non-compressible fluid having a predetermined value of viscosity; a thin-walled portion of the elastic body which partially defines the fluid chamber and which elastically yields to permit the fluid chamber to be elastically deformed upon application of the vibrational load in the load-receiving direction; a movable member accommodated in the fluid chamber such that the movable member is freely movable over a predetermined distance within the fluid chamber in the load-receiving direction, wherein the movable member has opposite surfaces which, when the vibrational load is applied to the elastic mount, cooperate with opposite inner surfaces of the fluid chamber so as to define fluid flow passages. The fluid flow passages include a radially inner and a radially outer resonance portion which have respective radial depths in the load-receiving direction, such that, due to the vibrational load, the fluid oscillatingly flows in circumferential and axial directions of the elastic mount through the resonance portions and the movable member is held in a suspended state within said fluid, with the radial depths varying in a cyclic manner. The fluid-filled cylindrical elastic mount of the present invention constructed as described above exhibits a sufficiently low spring rate, based on the flows of the fluid through the resonance portions of the fluid chamber, while effectively preventing the stiffening of the elastic body, even when the elastic mount is subjected to high-frequency vibrations. Therefore, the instant elastic mount is capable of providing an excellent damping or isolating effect with respect to input vibrations over a wide frequency range, from medium- to high-frequency vibrations. The thin-walled portion of the elastic body may consist of axial end portions of the elastic body which define axial opposite ends of the fluid chamber. The elastic body may have an axial void which extends in an axial direction of the elastic mount. The fluid chamber and the axial void may be disposed at respective circumferential portions of the elastic mount which are diametrically opposite to each other in the load-receiving direction. The kinematic viscosity value of the non-compessible fluid which fills the fluid chamber is preferably not higher than 500mm²/s (centistokes), more preferably not higher than 100mm²/s (centistokes). The movable member may have a generally arcuate shape in cross section taken in a plane perpendicular to an axial direction of the elastic mount. In this case, the movable member has an outer and an inner arcuate surface which partially define the resonance portions. The inner surface of the movable member which defines one of the resonance portions may be held in contact with an inner surface of the elastic body partially defining the fluid chamber, when the elastic mount is installed for service with a static load applied thereto. Alternatively, the inner surface of the movable member may be held spaced apart from the inner surface of the elastic body which partially defines the fluid chamber when the elastic mount is installed for service with a static load applied thereto. The predetermined distance of movement of the movable member within the fluid chamber may preferably be within a range of 2-16mm, and the ratio of this movement distance to a radial dimension of the fluid chamber is preferably within a range of 0.05-0.50. BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and other objects, features and advantages of the present invention will be better understood by reading the following detailed description of a presently preferred embodiment of the invention, when considered in connection with the accompanying drawings, in which: Fig. 1 is an elevational view in transverse cross section of a preferred embodiment of a fluid-filled cylindrical elastic mount of the present invetnion in the form of an engine mount for a motor vehicle; Fig. 2 is an elevational view in axial cross section of the engine mount of Fig. 1, taken along line II-II of Fig. 1; Fig. 3 is an elevational view in transverse cross section of the engine mount, when installed on a motor vehicle; Fig. 4 is an elevational transverse cross sectional view illustrating the engine mount during application of a vibrational load thereto; Fig. 5 is a graph showing experimental data indicating vibration damping/isolating characteristics or spring constant-frequency relationships of the engine mount of Figs. 1-4, as compared with those of comparative examples; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to Figs. 1 and 2, reference numeral 10 denotes a metallic inner sleeve of an engine mount suitably adapted for mounting an engine on a motor vehicle of a front-engine front drive (F-F) type. Radially outwardly of this inner sleeve 10, there is disposed a metallic outer sleeve 12, such that the inner and outer sleeves 10, 12 are radially spaced apart from each other by a predetermined suitable distance, when the engine mount is installed for service on the motor vehicle (as indicated in Fig. 3). Between the metallic inner and outer sleeves 10, 12, there is interposed an elastic body 14 having a generally annular configuration, whereby the inner and outer sleeves 10, 12 are elastically connected to each other. The present engine mount, generally indicated at 16 in Figs. 1-4, is installed on the motor vehicle for mounting an engine unit on the body of the vehicle in a vibration damping or isolating manner. The vehicle body is provided with mounting rods, while the engine unit has fixing brackets each having a mounting hole. Each mounting rod of the vehicle body is fixedly inserted through the inner sleeve 10, while the outer sleeve 12 is press-fitted in the mounting hole of the corresponding fixing bracket of the engine unit. With the engine mount 16 installed in position in this manner, the inner and outer sleeves 10, 12 are brought into coaxial relationship with each other, by weight of the engine unit, as indicated in Figs. 3 and 4. In this condition, the engine mount 16 receives a vibrational load applied thereto primarily in the radial direction in which the inner and outer sleeves 10, 12 are offset as indicated in Figs. 1 and 2 before installation of the engine mount 16 on the vehicle. This radial direction will be referred to as "load-receiving direction" of the engine mount, when appropriate. While the elastic body 14 is secured directly to the outer surface of the inner sleeve 10, it is indirectly secured to the inner surface of the outer sleeve 12, via a thin-walled sleeve 18 and a sealing rubber layer 28, such that the elastic body 14 is secured to the inner surface of the sleeve 18 while the rubber layer 28 is interposed between the sleeves 12, 18. The inner sleeve 10, elastic body 14 and thin-walled sleeve 18 are formed as an integral unit, as a result of vulcanization of an unvulcanized rubber material within a suitable mold in which the sleeves 10 and 18 are set in place relative to each other. The elastic body 14 has an axial void 20 formed axially through a portion thereof which is located on one of diametrically opposite sides of the inner sleeve 10 in the load-receiving direction, on which the distance between the inner and outer sleeves 10, 12 is shorter than that on the other side, as viewed in Figs. 1 and 2. That is, the axial void 20 is formed in a lower portion of the elastic body 14, such that the void 20 extends between substantially diametrically opposite positions on the outer circumference of the elastic body 14. This axial void 20 serves to minimize the amount of a tensile stress applied to the elastic body 14, due to the weight of the engine unit and an input vibrational load. In a portion of the elastic body 14 on the other side of the inner sleeve 10 on which the distance between the inner and outer sleeves 10, 12 is larger in the load-receiving direction, there is formed a pocket 22 such that the axial void 20 and the pocket 22 are diametrically opposite to each other in the load-receiving direction, with respect to the inner sleeve 10. The pocket 22 is open in the outer circumferential surface of the elastic body 14, and is aligned with an aperture or window 26 formed through the corresponding circumferential portion of the thin-walled sleeve 18, so that the pocket 26 is exposed to the inner surface of the sealing rubber layer 28. With the pocket 26 formed, the elastic body 14 has relatively thin-walled opposite axial end portions 24, 24, which permit the elastic body 14 to be easily displaceable in the axial direction. While the axial void 20 is provided to minimize the tensile stress or strain of the elastic body 14, the pocket 26 formed in the portion subject to a compressive stress serves to facilitate the radially inward deformation or compression of the elastic body 14, during application of a radial vibrational load between the inner and outer sleeves 10, 12. The outer sleeve 12 having the sealing rubber layer 28 secured to its inner surface is pressed fitted on the integral unit or intermediate product 10, 14, 18 prepared by vulcanization of the elastic body 14. Then, the outer sleeve 12 is radially inwardly pre-compressed at its axial end portions, by a roll-calking technique. As a result, the pocket 22 is fluid-tightly closed by the sealing rubber layer 28, whereby a fluid chamber 30 having a suitable volume is defined. The fluid chamber 30 is filled with a non-compressible fluid having a relatively low viscosity. This filling is effected while the outer sleeve 12 is fitted on the integral intermediate product 10, 14, 18, within a mass of the selected non-compressible fluid contained in a suitable vessel. For a sufficient degree of fluidity of the fluid, the kinematic viscosity of the fluid is preferably not higher than 500mm²/s (centistokes), and more preferably not higher than 100mm²/s (centisokes). For instance, the non-compressible fluid is suitably selected from the group which includes water, ethylene glycol, propylene glycol, other alkylene glycols, low-viscosity polyalkylene glycol, low-viscosity silicone oil, and mixtures thereof. When a radial vibrational load to be damped by the instant engine mount 16 is applied between the inner and outer sleeves 10, 12, the axial end portions 24, 24 are axially outwardly elastically displaced, while the portion defining the axial void 20 is elastically expanded so as to reduce the volume of the void 20, and the fluid chamber 30 is deformed such that the radial distance in the load-receiving direction is reduced. Within the pressure-receiving chamber 30, there is accommodated a movable block 32 having a generally arcuate cross sectional shape as indicated at 31, 33 in Fig. 1. The movable block 32 is freely movable within the chamber 30, and the inner arcuate surface 33 has a profile substantially following the shape of the inner surface of the chamber 30 which is assumed when the engine mount 16 is installed in place with the weight of the engine unit acting on the outer sleeve 12, as indicated in Fig. 3. In the present embodiment, the movable block 32 is formed of an aluminum alloy, and is held in contact with the lower surface of the chamber 30, as indicated in Fig. 3, while the engine mount 16 is in a static-load condition wherein no dynamic load acts on the engine mount 16. Upon application of a dynamic vibrational load to the engine mount 16 in the load-receiving direction, the inner and outer sleeves 10, 12 are displaced relative to each other in the load-receiving direction, whereby the radial distance or dimension (indicated at "A" in Fig. 3) of the fluid chamber 30 in the load receiving direction is cyclically increased and decreased, and the chamber 30 is elastically deformed. The shape of the non-compressible fluid mass is accordingly changed, with the axial end portions 24 and the axial void 20 being elastically displaced or deformed. As a result, there arise flows of the fluid in the fluid chamber 30. The flows of the fluid cause the movable block 32 to be kept away from the lower surface of the chamber 30 and be held in a suspended state within the fluid mass, as indicated in Fig. 4. Around the movable block 32 in the suspended state during application of the vibrational load between the inner and outer sleeves 10, 12, there are formed fluid flow passages which include arcuate resonance portions 34 that are defined between the outer and inner arcuate surfaces 31, 33 of the movable block 32, and the radially opposite outer and inner surfaces of the chamber 30 (more precisely, the corresponding surfaces of the elastic body 14 and sealing layer 28). These arcuate resonance portions 34 have a radial depth "t" and extend along the outer and inner arcuate surfaces 31, 33 of the movable block 32. With the vibrational load applied between the inner and outer sleeves 10, 12, the fluid oscillatingly flows in the circumferential and axial directions of the engine mount 16, particularly through the resonance portions 34, with the radial depth "t" varying in a cyclic manner. As a result, the dynamic spring constant of the engine mount 16 is effectively lowered, based on the flows or resonance of the fluid within the fluid chamber 30, whereby the vibrational load is accordingly isolated. The range of frequency of the vibrations to which instant engine mount 16 exhibits a reduced dynamic spring constant is selected or determined as desired, by adjusting the radial depth "t" and other dimensions of the arcuate resonance portions 34, and thereby tuning the resonance frequency of the fluid flowing through the resonance portions 34, depending upon the modulus of elasticity (dynamic spring constant) of the elastic body 14, weight or specific gravity of the movable block 32 and the viscosity of the non-compressible fluid. The instant engine mount 16 may be tuned so that the resonance frequency of the fluid in the fluid chamber 30 is relatively high. More specifically, the dimensions of the arcuate resonance portions 34 including the depth "t" are normally determined such that (a) a distance "B" (indicated in Fig. 3) over which movable block 32 is movable in the load-receiving direction is within a range of 2-16mm, preferably 3-10mm, that (b) a ratio of the distance "B" to the radial dimension "A" in the non-load state is within a range of 0.05-0.50, preferably 0.10-0.40, and that (c) a total area of the outer and inner arcuate surfaces 31, 33 of the movable block 32 is at least 100mm², preferably at least 2000mm². The instant engine mount 16 constructed as described above exhibits a low dynamic spring constant for effectively isolating the input vibrations in a relatively high frequency range, based on the flows or resonance of the fluid in the arcuate resonance portions, 34 on the opposite outer and inner sides of the movable block 32, with the depth "t" of each resonance portion 34 varying at the resonance frequency of the fluid. Thus, the engine mount 16 is effectively prevented from exhibiting excessively high stiffness due to resonance of the elastic body 14, even when the frequency of the input vibrations is comparatively high. In other words, the instant engine mount 16 may be suitably adapted to exhibit comparatively soft spring characteristics with respect to the input vibrations of medium and high frequency ranges, whereby these medium- and high-frequency vibrations may be effectively damped and/or isolated, permitting considerably reduced noises heard within the vehicle compartment, and significantly improved driving comfort of the vehicle. The graph in Fig. 5 shows experimental data indicating the relationship between the absolute value of complex spring constant of the instant engine mount 16 and the frequency of the input vibrations, as compared with those of comparative examples 1 and 2. The comparative example 1 uses an elastic block which does not have a fluid-filled chamber and a movable block. The comparative example 2 uses an elastic block which has a fluid-filled chamber but does not have a movable block in the fluid-filled chamber. In the experiment, the fluid chamber was filled with water, in the instant embodiment and comparative example 1, and the movable block 32 of the instant embodiment was formed of an aluminum alloy. Further, the experiment was conducted with an initial static load of 1050 N (Kgf) applied between the inner and outer sleeves (10, 12), and with a dynamic vibrational load of ±10G applied therebetween. It will be apparent from the graph of Fig. 5 that the dynamic spring constant of the instant embodiment was kept at a sufficiently low level for the medium- and high-frequency vibrations, while the dynamic spring constants of the comparative examples 1 and 2 were comparatively high for such medium- and high-frequency vibrations. This means excellent damping/isolating capability of the instant engine mount 16, for the input vibrations over a relatively wide range of frequency. The improved damping/isolating capability of the instant engine mount 16 for the relatively high-frequency vibrations may be accomplished by simply inserting the movable block 32 in the fluid chamber 30 during assembly of the mount, namely, without using a complicated arrangement. The movable block 32 may also be formed of a material other than aluminum alloys, such as a resin or stainless steel, depending upon the specific gravity and other properties of the non-compressible fluid. Further, the movable block 32 may take a suitable form other than an arcuate shape, such as a rectangular or cylindrical or columnar shape, depending upon the shape of the fluid chamber 30. The movable block 32 may be a hollow member, or may have a specific gravity lower than that of the non-compressible fluid so that the movable block 32 may float on the fluid mass, with a static load applied to the engine mount. Although the illustrated embodiments are adapted to be used as engine mounts for a motor vehicle, the concept of the invention may be embodied as vehicle suspension bushings, and other fluid-filled elastic mounts whose applications are not limited to the motor vehicle. A fluid-filled cylindrical elastic mount having an inner and an outer sleeve which are disposed in mutually spaced-apart relation with each other, and an elastic body interposed between the inner and outer sleeves so as to elastically connect the inner and outer sleeves. The elastic body (14) at least partially defines a single fluid-tightly closed fluid-filled chamber (30) located between the inner and outer sleeves (10, 12) in a load-receiving direction in which a vibrational load is applied to the elastic mount. The elastic body includes a thin-walled portion (24, 24) which partially defines the fluid-filled chamber and which elastically yields to permit the chamber to be elastically deformed upon application of the vibrational load. A movable member (32) is accommodated in the fluid-filled chamber such that the movable member is freely movable over a predetermined distance in the load-receiving direction. The movable member and inner surfaces of the fluid chamber cooperate with each other to define resonance portions (34) having a predetermined radial depth as measured in the load-receiving direction.

Claims: A fluid-filled cylindrical elastic mount (16) having an inner and an outer sleeve (10, 12) which are disposed in mutually spaced-apart relation with each other, and an elastic body (14) interposed between said inner and outer sleeves (10, 12) so as to elastically connect Said inner and outer sleeves, said elastic body (14) at least partially defining a single fluid-tightly closed fluid chamber (30) located between said inner and outer sleeves (10, 12) in a load-receiving direction in which a vibrational load is applied to the elastic mount (16), said fluid chamber (30) being filled with a non-compressible fluid having a predetermined value of viscosity, said elastic body (14) including a thin-walled portion (24) which partially defines said fluid chamber (30) and which elastically yields to permit said fluid chamber to be elastically deformed upon application of the vibrational load in said load-receiving direction, a movable member (32) being accommodated in said fluid chamber (30) such that said movable member is freely movable over a predetermined distance (B) within said fluid chamber in said load-receiving direction, said movable member (32) having opposite surfaces (31, 33) which are opposite to each other in said load-receiving direction, wherein, when the vibrational load is applied to said elastic mount (16), said opposite surfaces (31, 33) of said movable member (32) cooperate with opposite inner surfaces of said fluid chamber (30) so as to define fluid flow passages, said passages including a radially inner and a radially outer resonance portion (34) which have respective radial depths (t) in said load-receiving direction, such that, due to the vibrational load, the fluid oscillatingly flows in circumferential and axial directions of the elastic mount (16) through the resonance portions (34) and the movable member (32) is held in a suspended state within said fluid, with the radial depths (t) varying in a cyclic manner. A fluid-filled cylindrical elastic mount according to claim 1, characterized in that said thin-walled portion of said elastic body (14) consists of axial end portions (24) of said elastic body which define axial opposite ends of said fluid chamber (30). A fluid-filled cylindrical elastic mount according to claim 1 or 2, characterized in that said elastic body (14) has an axial void (20) which extends in an axial direction of the elastic mount, said fluid chamber (30) and said axial void (20) being disposed at respective circumferential portions of the elastic mount which are diametrically opposite to each other in said load-receiving direction. A fluid-filled cylindrical elastic mount according to any one of claims 1 - 3, characterized in that said non-compressible fluid has a kinematic viscosity value not higher than 500 mm²/s. A fluid-filled cylindrical elastic mount according to any one of claims 1 - 4, characterized in that said non-compressible fluid has a kinematic viscosity value not higher than 100 mm²/s. A fluid-filled cylindrical elastic mount according to any one of claims 1 - 5, characterized in that said movable member (32) has a generally arcuate shape in cross section taken in a plane perpendicular to an axial direction of the elastic mount, said movable member having an outer and an inner arcuate surface (31, 33) which partially define said resonance portions (34). A fluid-filled cylindrical elastic mount according to any one of claims 1 - 6, characterized in that said movable member (32) has an inner surface (33) which is held in contact with an inner surface of said elastic body (14) partially defining said fluid chamber (30), when said elastic mount is installed for service with a static load applied thereto. A fluid-filled cylindrical elastic mount according to any one of claims 1 - 6, characterized in that said movable member (32) has an inner surface (33) which is held spaced away from an inner surface of said elastic body (14) partially defining said fluid chamber (30), when said elastic mount is installed for service with a static load applied thereto. A fluid-filled cylindrical elastic mount according to any one of claims 1 - 8, characterized in that said predetermined distance (B) of movement of said movable member (32) is within a range of 2 - 16 mm. A fluid-filled cylindrical elastic mount according to any one of claims 1 - 9, characterized in that a ratio of said predetermined distance (B) of movement of said movable member (32) to a radial dimension (A) of said fluid chamber (30) is within a range of 0.05 - 0.50.

Inventors: GOTO, KATSUHIRO
Applicants: TOKAI RUBBER INDUSTRIES, LTD., TOYOTA JIDOSHA KABUSHIKI KAISHA
Application year: 1989
Main classification: F16F13
IPC codes: F16F13