Abstract:
A vibration isolator in which an elastic body is stretched between inner and outer tubes connected to a vibration source and a vibration receiving member, respectively, and in which a pair of liquid chambers disposed on opposite sides of the inner tube communicate with each other through a restricted passage, and the vibration isolator has an intermediate tube provided between the inner and outer tubes and supported on the outer tube. The intermediate tube has a portion serving as a partition spaced apart from both the inner and outer tubes. One of the liquid chambers is formed between the partition and the elastic membranous member located outside the partition. Even if the inner and outer tubes are relatively displaced to a large extent, the relative dispalcement therebetween is limited by the contact between side inner and intermediate tubes.

Description:
This is a continuation of application Ser. No. 07/492,298 filed Feb. 28, 1990, now abandoned, which in turn is a continuation of application Ser. No. 07/260,676 filed Oct. 21, 1988, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to a bush type vibration isolator with an elastic body interconnected between inner and outer tubes. 
     In general, a vibration isolator which has an elastic body interconnected between inner and outer tubes is used for an engine mount, a cab mount or bushes of motor vehicles. The elastic body has a pair of liquid chambers which communicate with each other by a restricted passage in which liquid is contained. When vibrations occur, the liquid in one of the liquid chambers moves to the other chamber through the restricted passage and the vibrations are absorbed by the resistance to passage to the liquid. 
     It is possible to design this type of vibration isolator to enable the liquid pressure in the liquid chambers to be effectively changed in response to vibrations by disposing a pair liquid chambers on an opposite sides of the inner tube. In this bush type vibration isolator, however, the inner tube is generally placed eccentrically relative to the outer tube (e.g. Japanese Patent Laid-Open No. 224746/1987), the liquid chamber disposed in narrower space between the inner and outer tubes has a flat shape portion such that an elastic membranous member which forms a portion of a wall of this liquid chamber faces a side of the inner tube. Consequently, if an amplitude of vibration becomes large, this elastic membranous member contacts with the elastic body formed around disposed on a periphery of the inner tube, and durability of the elastic membranous member will inevitably reduced. 
     SUMMARY OF THE INVENTION 
     In view of the above facts, it is an object of the present invention to provide a bush type vibration isolator. 
     The present invention provides a vibration isolator in which an elastic body is disposed between inner and outer tubes, one connected to a vibration source and the other to a vibration receiving member and in which a pair of liquid chambers disposed on opposite sides of the inner tube communicate with each other via a restricted passage. The vibration isolator includes an intermediate tube provided between the inner and outer tubes and supported on the outer tube, and the intermediate tube has a portion which serves as a partition spaced apart from both the inner and outer tubes, and one of the liquid chambers is formed between the partition and the elastic membranous member located outside the partition. 
     In accordance with the present invention, even if the inner and outer tubes are relatively displaced to a large extent, the relative displacement therebetween is limited by contact between the inner tube and the partition portion of the intermediate tube. Therefore the elastic membranous member which constitutes a wall of the liquid chamber formed between the partition and the outer tube is not contacted with the elastic body fixed to the inner tube by the relative displacement between the inner and outer tubes. Accordingly, the durability of the vibration isolator is increased. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view of a vibration isolator of a first embodiment according the present invention, taken along the line I--I of FIG. 2; 
     FIG. 2 is a cross-sectional view taken along the line II--II of FIG. 1; 
     FIG. 3 is a cross-sectional view of a restricted passage taken along the line III--III of FIG. 1; 
     FIG. 4 is a perspective view of an intermediate tube of the first embodiment; 
     FIG. 5 is a cross-sectional view of a second embodiment of the present invention, corresponding to FIG. 1 and taken along the line V--V of FIG. 6; 
     FIG. 6 is a cross-sectional view taken along the line VI--VI of FIG. 5; 
     FIG. 7 is a cross-sectional view of a third embodiment of the present invention, corresponding to FIG. 1 and taken along the line VII--VII of FIG. 8; 
     FIG. 8 is a cross-sectional view taken along the line VIII--VIII of FIG. 7; 
     FIG. 9 is a cross-sectional view of a fourth embodiment of the present invention, corresponding to FIG. 2; 
     FIG. 10 is a cross-sectional view of a fifth embodiment of the present invention, corresponding to FIG. 1; 
     FIG. 11 is a cross-sectional view taken along the line XI--XI of FIG. 10; 
     FIG. 12 is a cross-sectional view of a sixth embodiment of the present invention, corresponding to FIG. 1 and taken along the line XII--XII of FIG. 13; 
     FIG. 12 is a cross-sectional view taken along the line XIII--XIII of FIG. 12; 
     FIG. 14 is a cross-sectional view of a seventh embodiment of the present invention, corresponding to FIG. 1 and taken along the line XIV--XIV of FIG. 15; and 
     FIG. 15 is a cross-sectional view taken along the line XV--XV of FIG. 14. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1 and 2 show a vibration isolator 10 which represents a first embodiment of the present invention in which an outer tube 12, and an inner tube 14 are disposed in such a manner that their axes are parallel to each other, one of the inner and outer tubes is connected to the body of a motor vehicle and the other is connected to the engine. 
     An intermediate tube 18 is disposed inside the outer tube 12 with an elastic membranous member 16 in the form of a tube interposed therebetween. The intermediate tube 18 has a small thickness, as shown in FIG. 4. A rectangular aperture 20 is formed in the circumferential direction in the intermediate tube 18, and a recessed portion 22 to be used as a partition is formed in the outer peripheral surface of the intermediate tube 18 in a position opposite to this aperture. When the intermediate tube 18 is fitted in the outer tube 12 through the elastic membranous member 16 the intermediate tube 18 and the outer tube 12 pinch the elastic membranous member 16 except the aperture 20 and the recessed portion 22. Preferably, the pinched portion of the elastic membranous member 16 is sulphurizedly bonded to the outer tube 12 or the intermediate tube 18. 
     An elastic body 24 is disposed between the inner tube 14 and the intermediate tube 18. A through opening 26 is formed between the elastic body 24 and the recessed portion 22. The elastic body 24 has a recess 28 formed on one side of the inner tube 14 opposite to the through opening 26, and a liquid chamber 30 is defined in which water, oil, ethylene glycol or the like is contained. The liquid chamber 30 is closed at the outer periphery of the elastic body 24 by the elastic membranous member 16. 
     The portion of the elastic membranous member 16 between the recessed portion of the intermediate tube 18 and the inner periphery of the outer tube 12 serves as a diaphragm 16A which is spaced from the outer tube 12 and which is disposed in a free state. As shown in FIG. 2, the diaphragm 16A is pinched between the intermediate tube 18 and the outer tube 12 at its ends opposite to each other in the direction of the axes of the tubes, thereby forming a liquid chamber 32 between the elastic membranous member 16 and the recessed portion 22. 
     The liquid chambers 30 and 32 communicate with each other through a groove 34 which is formed in the outer peripheral surface of the intermediate tube 18. The groove 34 defines a restricted passage 36 between itself and the elastic membranous member 16 when it is in an assembled state shown in FIGS. 1 and 2. 
     The outer tube 12 has an aperture 12A formed in a position corresponding to that of the diaphragm 16A, thereby facilitating, the deformation of the diaphragm 16A. Alternatively, the diaphragm 16A may face the inner surface of an outer tube 12 which does not include an aperture 12A. 
     The operation of the present invention will be described below. 
     The inner tube 14 is connected to, for example, the body of a motor vehicle while the outer tube 12 is connected to the engine. 
     Vibrations of the engine are absorbed by the internal friction of the elastic body 24 and by the resistance to the liquid moving through the restricted passage 36 between the liquid chambers 30 and 32 when there is a difference in the liquid pressure in these chambers. 
     If the liquid pressure in the liquid chamber 32 increases, the diaphragm deforms elastically to allow the liquid chamber 32 to expand. 
     If the amplitude of vibration becomes large, a part of the elastic body 24 disposed around the inner tube 14 comes in contact with the recessed portion 22, and the relative movement between the outer tube 12 and the inner tube 14 is thereby limited. During this relative movement, however, there is no possibility of the elastic body 24 contacting the diaphragm 16A, thus preventing deterioration of the durability of the diaphragm 16A. 
     The portions of the elastic membranous member 16 other than the diaphragm 16A may be removed so long as there are suitable sealing properties of the connection between the intermediate tube 18 and the outer tube 12. 
     FIGS. 5 and 6 show a second embodiment of the present invention which is constituted by providing a curved or bent plate 42 in the liquid chamber 30 of the arrangement of the first embodiment. The bent plate 42 is in the form of a circular arc and tightly fitted to the inner peripheral surface of the elastic membranous member 16. The bent plate 42 has a groove which is formed in its outer periphery and which defines a restricted path 44 between the outer periphery of the bent plate 42 and the elastic membranous member 16. The restricted path 44 communicates at its one end with the restricted passage 36 and at its other end with the liquid chamber 30. 
     In this embodiment, therefore, the restricted passage 36 is substantially elongated so as to obtain improved damping effects, thereby making it possible to rapidly absorb vibrations. 
     FIGS. 7 and 8 show a third embodiment of the present invention which is constituted by providing a restricted passage 48 in the arrangement of the first embodiment. The restricted passage 48 is formed in such a manner that a groove 47 is formed in the surface of the recessed intermediate portion 22 facing the liquid chamber 32 of the first embodiment, and an abutment plate 50 is attached to this portion from the side of the liquid chamber 32. The restricted passage 48 communicates with its one end with the restricted passage 36 and with its other end with the liquid chamber 32, and the restricted passage 36 is substantially elongated, thereby obtaining the same effects as the second embodiment. 
     FIG. 9 shows a fourth embodiment of the present invention which is constructed in such a manner that, in the arrangement of the first embodiment, portions of the elastic body 24 forming opposite sidewalls 24A of the liquid chamber 30 are depressed such that the capacity thereof becomes reduced, and that the sidewalls 24A are closer to each other at its intermediate portions. If the pressure in the liquid chamber 30 increases as the inner tube is moved downward as viewed in FIG. 9, the sidewalls 24A become closer to each other, thereby promoting increase in the liquid chamber 30. As a result, the movement of the liquid in the restricted passage is promoted, and the vibration absorption effects are improved. 
     FIGS. 10 and 11 show a fifth embodiment of the present invention which is constructed in such a manner that, a communication hole 54 is formed parallel to the restricted passage 36 in the arrangement of the first embodiment so as to provide communication between the liquid chambers 30 and 32, and a movable plate 56 is placed in the communication hole 54. Longitudinal ends of the movable plate 56 project into the liquid chambers 30 and 32. The longitudinal ends of the movable plate 56 is increased in size in diametral direction of the tubes, thereby forming extended portions 56A and 56B which function to limit the extent of movement of the movable plate 56 in the communication hole 54 in the longitudinal direction thereof . 
     In consequence, in this embodiment, the movable plate moves in the communication hole 56 in the longitudinal direction to limit the increase in the pressure in the liquid chamber 30 or 32 and keep the dynamic spring constant small when high-frequency vibrations occur such that the restricted passage 36 fail to allow the liquid chambers 30 and 32 to communicate with each other. 
     Preferably, an elastic material such as synthetic resin or rubber is selected to form the movable plate 56. 
     In this embodiment, the communication hole 54 and the restricted passage 36 are formed parallel to each other. However, it is possible to eliminate the need for the restricted passage 36 by providing a small hole which extends in the movable plate in the longitudinal direction thereof and which functions as the restricted passage. In this case, this means is not limited to the small hole formed through the movable plate 56. Instead, a groove is formed in the outer surface of the movable plate 56 through the overall longitudinal length thereof, or a groove may be formed in an inner surface portion of the communication hole 54, thereby enabling the liquid chambers to communicate with each other even when the movable plate is moved to one end of its stroke. 
     FIGS. 12 and 13 show a sixth embodiment of the present invention which is constructed in such a manner that, in the arrangement of the first embodiment, a support block 62 is fixed to the inner tube 14; and a wing 64 in the form of a disk or a rectangular plate is fixed to the support block 62. The wing 64 is located in the liquid chamber 30 such that liquid column resonance regions 66 are formed between the outer periphery of the wing 64 and the inner surface of the liquid chamber 30. The liquid column resonance regions are defined by gaps which have a sectional area greater than that of the restricted passage 36. In the case where restricted path 36 fails to establish suitable communication when high-frequency vibration occurs, the high frequency vibrations are observed by the resonance of the liquid in the liquid column resonance regions. 
     The wing 64 is also capable of functioning as a stopper to limit movement of the inner tube 14 when the inner tube 14 moves downward as shown in FIGS. 12 and 13 to a great extent relative to the outer tube 12. 
     FIGS. 14 and 15 show a seventh embodiment of the present invention in which, as shown in FIG. 15, the side walls 24A of the liquid chamber 30 are cure-bonded to side plates 70 fixed to the intermediate tube 18 and are thus supported on the outer tube 12. Consequently, the elastic body 24 is generally deformed by shearing forces and it becomes not liable to buckle, and durability is increased. 
     This embodiment also includes a reinforcement plate 72 which is embedded in the elastic body 24. 
     The above described embodiments may be modified to combine the above specific structures. 
     As described above, the present ensures an increase in the durability of the portion of the elastic membranous member that defines the liquid chamber placed on one side of the inner tube.