Vibration isolator of bushing type with liquid chambers in elastic body

Abstract: The invention provides an improved vibration isolator (10) for use, for example, in an automotive engine mounting. The vibration isolator has a hollow outer cylinder (14) and an inner cylinder (12) disposed in and parallel to the outer cylinder. One of the two cylinders is to be connected with a member that vibrates and the other with another member to be isolated from vibration. An elastic body (20) tightly interposed between the outer and inner cylinders is formed with a hollow (22) so that tensile force may not act on this body. Opposite to the hollow with respect to the inner cylinder the elastic body is formed with radially inner and outer liquid chambers (26A, 26B) which are connected to each other by a flow restrictive passage (32). An elastic membrane (16) is attached to the inner surface of the outer cylinder, and a part of the membrane serves as a flexible diaphragm defining the radially outer periphery of the outer liquid chamber. In a region where the elastic membrane is used as the diaphragm, the cylindrical wall of the outer cylinder is formed with an opening to expose the diaphragm to the atmosphere. This vibration isolator can easily and accurately be assembled in the liquid to be filled into the liquid chambers without need of any extra operation for extracting the liquid from any other space or chamber in the assembled device.

Description: BACKGROUND OF THE INVENTION This invention relates to a vibration isolating device of a bushing type using an elastic body interposed between a hollow outer cylinder and an inner cylinder and an incompressible liquid filled into two chambers formed in the elastic body. Vibration isolators of the above mentioned type are used in automobiles and ohter vehicles for engine mounting, cab mounting, body mounting, and so on. More particularly, the outer and inner cylinders are in a parallel arrangement, and one of the two cylinders are connected with a member that vibrates and the other with another member to be isolated from vibration. The two liquid chambers are connected to each other by a flow restrictive passage, and at least one of the liquid chambers is partly defined by a flexible diaphragm. For example, JP-A 62-118133 shows a vibration isolator of this type. In the vibration isolator, vibration is damped by elastic deformation of the elastic body and movement of the liquid through the flow restrictive passage caused by deformation of the liquid chambers. In Japanese patent application No. 62-152609 filed June 19, 1987 (not published yet) and corresponding U.S. patent application Serial No. 206,718 filed June 15, 1988, we and co-workers have proposed to form a hollow in the elastic body of a vibration isolator of the above described bushing type to prevent cracking or deterioration of the elastic body by the action of tensile force thereon. The hollow is located opposite to the liquid chambers with resect to the inner cylinder and extends over the entire length of the elastic body. In a vibration isolator disclosed in the aforementioned patent applications, two liquid chambers are formed by scooping out the elastic body to provide a hollow opening in the cylindrical outer surface of the body and inserting a partition plate to divide the hollow into a radially inner chamber and a radially outer chamber. A hollow intermediate cylinder is fitted around the elastic body and is formed with an opening in a region facing the outer liquid chamber. A tubular elastic membrane is tightly inserted between the outer cylinder and the intermediate cylinder, and the tubular membrane is dented radially inward in a region where the intermediate cylinder is formed with the opening such that the dented part of the tubular membrane defines the radially outer periphery of the outer liquid chamber. The outer cylinder has a small hole in a section covering the opening in the intermediate cylinder so that the space between the outer cylinder and the dented part of the tubular elastic membrane becomes an air chamber communicating with the atmosphere. This vibration isolator is assembled in a liquid to be filled into the liquid chambers. In advance the elastic body formed with the hollows is bonded to the inner cylinder and the intermediate cylinder by vulcanization or curing. In the liquid the tubular elastic membrane is fitted around the intermediate cylinder, and then the outer cylinder is fitted around and fixed by crimping to the intermediate cylinder. In the operations in the liquid it is not easy to accurately position the locally dented tubular membrane with respect to the opening in the wall of the intermediate cylinder, and, after that, it is difficult to completely extract the liquid from the aforementioned space to be made the air chamber by using the small hole in the outer cylinder. A vibration isolating device according to the preamble of claim 1 is known from JP-A-62 167 949 (see also US-A-4,728,086). SUMMARY OF THE INVENTION It is an object of the present invention to provide an improved vibration isolating device of the above-described bushing type, which is good in performance and durability and can easily and accurately be assembled. This object is solved according to the invention by the subject matter of claim 1. A preferred embodiment of the invention is the subject matter of claim 2. In this vibration isolator, the hollow in the elastic body is effective for prevention of tensile force acting on the elastic body and thereby preventing cracking or deterioration of the elastic body. Furthermore, this device can easily and accurately be assembled in the liquid to be filled into the liquid chambers, without need of any extra operation to remove the liquid from any space or chamber in the assembed device, by virtue of the attachment of the elastic membrane to the outer cylinder and the provision of the opening in the wall of the outer cylinder in the region where the elastic membrane is used as the diaphragm defining the second liquid chamber. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a longitudinal sectional view of a vibration isolating device as an embodiment of the invention, taken along the line 1-1 in Fig. 2; Fig. 2 is a cross-sectional view of the device of Fig. 1, taken along the line 2-2 in Fig. 1; Fig. 3 is an exploded perspective view of the device of Figs. 1 and 2; Fig. 4 is a longitudinal sectional view of the outer cylinder of the device of Figs. 1 to 3, taken along the line 4-4 in Fig. 5; Fig. 5 is a cross-sectional view taken along the line 5-5 in Fig. 4; and Fig. 6 is is a longitudinal sectional view of another vibration isolating device which is a minor modification of the device of Figs. 1 to 3. DESCRIPTION OF THE PREFERRED EMBODIMENTS As an embodiment of the present invention, Figs. 1 to 3 show a vibration isolator 10 for use as a part of engine mounting in an automobile. The vibration isolator 10 has an inner cylinder 12 to be connected to the automotive engine and an outer cylinder 14 to be fitted into brackets (not shown) fixed to a member of the car body. The inner diameter of the outer cylinder 14 is fairly larger than the outer diameter of the inner cylinder 12. The longitudinal axis of the outer cylinder 14 is parallel to the longitudinal axis of the inner cylinder 12, though the two cylinders 12, 14 are not necessarily coaxial. These two cylinders 12, 14 are metal cylinders. The inner surface of the outer cylinder 14 is covered with a tubular elastic membrane 16. Preferably the elastic membrane 16 is bonded to the surface of the cylinder 14 by vulcanization or curing. An intermediate cylinder 18, which is a metal cylinder, is fitted into the outer cylinder 14 lined with the elastic membrane 16. The inner diameter of this cylinder 18 is fairly larger than the outer diameter of the inner cylinder 12. A major part of the space between the inner cylinder 12 and the intermediate cylinder 18 is filled up with an elastic body 20 formed of a rubber or the like. The elastic body 20 tightly covers and adheres to the outer surface of the inner cylinder 12 and, at its radially outer periphery, adheres to the inner surface of the intermediate cylinder 18. The elastic body 20 is scooped out over its entire length so as to provide a hollow 22. In any cross-section of the vibration isolator 10 the hollow 22 intersects a plane P₁ containing both the axis of the inner cylinder 12 and the axis of the outer cylinder 14 and is substantially symmetrical with respect to this plane P₁, but does not intersect a plane P₂ which contains the axis of the inner cylinder 12 and is perpendicular to the plane P₁. The hollow 22 modulates elasticity of and permits elastic deformation of the elastic body 20 so that tensile force may not act on the elastic body 20 when a load of the engine is transmitted thereto via the inner cylinder 12. To narrow a middle section of the hollow 22, a fraction 24 of the elastic body 20 protrudes radially inwarod from the inner surface of the intermediate cylinder 18. Alternatively, this protuberance 24 may be a separate member of an elastic material such as rubber. The protuberance 24 serves as a stopper to limit the amount of relative movement of the inner and outer cylinders 12 and 14. On the opposite side of the aforementioned plane P₂ there is a liquid chamber 26 which is provided by hollowing out the elastic body 20 from its radially outer surface so as not expose the inner cylinder 12. Actually, the elastic body 20 is molded with a hollow to be used as the liquid chamber 26 by inserting a core corresponding in shape and size to the hollow into the mold. Lengthwise of the vibration isolator 10 the liquid chamber 26 is shorter than the outer cylinder 14 and than the elastic body 20, so that in the both end sections of the outer cylinder 14 the elastic body 20 remains extending from the inner cylinder 12 to the intermediate cylinder 18. As will be described hereinafter, an incompressible liquid 36 such as water or oil is filled into the liquid chamber 26. In a region corresponding to the liquid chamber 26 the intermediate cylinder 18 is cut out to provide an opening 18A. In the same region the tubular elastic membrane 16 is dented into the liquid chamber 26 such that a dented part 16A of the membrane 16 serves as a flexible diaphragm which defines the radially outer end of the liquid chamber 26. In the same region the outer cylinder 14 is cut out to provided an opening 14A. Therefore, the outer surface of the diaphragm 16A is exposed. A partition plate 28 shaped correspondingly to the diaphragm 16A is fixedly inserted into the liquid chamber 26 to divide the chamber 26 into a first liquid chamber 26A, which is a radially inner chamber, and a second liquid chamber 26B which is a radially outer chamber defined between the partition plate 28 and the diaphragm 16A. As shown in Fig. 3, the partition plate 28 is a part of a metal member 29 having nearly semicylindrical support portions. The nearly semicylindrical edges of the metal member 29 are tightly inserted between the elastic body 20 and the elastic membrane 16. As shown in Fig. 1, along the longitudinal ends of the opening 18A the intermediate cylinder 18 is folded so as to form sectionally L-shaped shoulder portions 18B for limiting the amount of movement of the inserted member 29 toward the inner cylinder 12. The intermediate cylinder 18 is formed with a cross-sectionally C-shaped dent 30 which is opposite to the aforementioned opening 18A with respect to the inner cylinder 12. Therefore, a cross-sectionally C-shaped flow restrictive passage 32 is formed between the inner surface of the elastic membrane 16 and the outer surface of the dented region 30 of the intermediate cylinder 18. One end 32A of this passage 32 opens in the second liquid chamber 26B and the other end 32B in the first liquid chamber 26A. As shown in Fig. 4, in end sections of the tubular elastic membrane 16 on the both sides of the dent 16A, annular protuberances 16B are formed on the inner surface of the tubular membrane 16. These annular protuberances 16B serve the purpose of augmenting the airtight sealing between the elastic membrane 16 and the outer surface of the intermediate cylinder 18. In assembling the vibration isolator 10, the inner cylinder 12, the intermediate cylinder 18 and the elastic body 20 are united into a main body by vulcanizing or curing the elastic body 20 so as to tightly adhere to the two cylinders 12 and 18. As described above the elastic body 20 is formed with the hollow 22 and another hollow for use as the liquid chamber 26. The metal member 29 having the partition plate 28 is fitted into the hollowed elastic body 20. Separately, the tubular elastic membrane 16 is inserted into the outer cylinder 14 and vulcanized or cured to tightly adhere to the inner surface of the cylinder 14. The outer cylinder 14 is formed with the opening 14A, and the tubular membrane 16 is formed with the dent 16A in the corresponding region. Therefore, the dented region 16A of the membrane is free of the outer cylinder 14. Next, in a liquid to be filled into the liquid chambers 26, the main body (assembly of inner cylinder 12, intermediate cylinder 18, elastic body 20 and metal member 29) is fitted into the outer cylinder 14 lined with the elastic membrane 16. Naturally, the liquid chambers 26A, 26B and the flow restricting passage 32 are filled with the liquid. For easing this operation the inner diameter of the tubular elastic membrane 16 is made larger than the outer diameter of the intermediate cylinder 18 by about 2 mm. Since the tubular membrane 16 is firmly adhering to the outer cylinder 14 it is easy to bring the dent 16A into the proper position with respect to the hollow 26 in the main body by turning and axially moving the outer cylinder 14. Then, still in the liquid, the outer cylinder 14 is radially constricted to accomplish tight contact of the elastic membrane 16 with the intermediate cylinder 18. By this working the assemblage of the vibration isolator 10 is completed. When the vibration isolator 10 is taken out of the liquid, the liquid in the dent 16A of the cylindrical outer periphery soon drains away through the opening 14A of the outer cylinder 14. That is, without need of any extra operation the liquid does not remain between the outer cylinder 14 and the dented region 16A of the tubular membrane 16. In the thus constructed vibration isolator 10 the opening 14A in the wall of the outer cylinder 14 is accurately in position with respect to the dent 16A of the tubular elastic membrane 16, and the dent 16A is accurately positioned with respect to the liquid chamber 26B. Therefore there is not possibility of local choking of the flow restrictive passage 32 or leakage of the liquid 36 from the liquid chambers 26A, 26B. Fig. 6 shows another vibration isolator 10A embodying the invention in a longitudinal sectional view corresponding to Fig. 1. This vibration isolator 10A is almost identical with the vibration isolator 10 of Figs. 1-3 and differs only in that the outer cylinder 14 is slightly extended lengthwise and that each end section 14C of the outer cylinder 14 is crimped radially inward, whereby the outer cylinder 14 is very securely fixed to the intermediate cylinder 18.

Claims: A vibration isolating device comprising: a hollow outer cylinder (14) formed with an opening in its cylindrical wall; an inner cylinder (12) which has an outer diameter smaller than the inner diameter of the outer cylinder (14) and is disposed in and parallel to the outer cylinder (14), one of the outer and inner cylinders being to be connected with a member which vibrates and the other to be connected with another member which is to be isolated from vibration; an elastic body (20) which is tightly interposed between the outer and inner cylinders (14,12) and is formed with a radially inner first liquid chamber (26A) and a radially outer second liquid chamber (26B), said liquid chambers being hydraulically connected on the same side of a plane (P₂) comprising the longitudinal axis of the inner cylinder (12); a partition plate (28) dividing a recess provided on one side of said plane (P₂) in order to form said first and second liquid chambers (26A,26B), means (32) for defining a flow restrictive passage which connects said first and second liquid chambers (26A, 26B) to each other; an elastic membrane (16) which is tightly attached to the inner surface of said outer cylinder (14) and partly serves as a flexible diaphragm (16A) defining the radially outer periphery of said second liquid chamber (26B), the cylindrical wall of said outer cylinder (14) being formed with an opening (14A) in a region where said elastic membrane is used as said diaphragm; and an incompressible liquid (36) filled into said first and second liquid chambers and said flow restrictive passage, characterized in that the elastic body (20) is formed with a hollow (22), that the two liquid chambers (26A,26B) are only provided on one side of said plane (P₂) while the hollow (22) is located on the other side, that the elastic membrane (16) is tubular and has a radially inwardly dented part (16A) which serves as said flexible diaphragm, that the opening (14A) in the outer cylinder (14) occupies an area opposite to substantially the entire area of said indented part (16A) of said tubular membrane (16), and that the tubular elastic membrane (16) is tightly bonded by vulcanization to the inner surface of said outer cylinder (14). A device according to claim 1, wherein said means (32) for defining the flow restrictive passage comprises a hollow intermediate cylinder (18) which is disposed between the tubular elastic membrane (16) and said elastic body (20) and is locally dented radially inward such that a cross-sectionally C-shaped passage (32) opening at its one end in said first liquid chamber (26A) and at the other end in said second liquid chamber (26B) is provided between said elastic membrane (16) and the outer surface of said intermediate cylinder (18), said intermediate cylinder (18) being formed with an opening in a region corresponding to said opening (14A) of said outer cylinder (14).

Inventors: ISHIYAMA TATSURO, TABATA TOSHIYUKI, ISHIYAMA, TATSURO, TABATA, TOSHIYUKI
Applicants: BRIDGESTONE CORP, NISSAN MOTOR, BRIDGESTONE CORPORATION, NISSAN MOTOR CO., LTD.
Application year: 1989
Main classification: F16F13
IPC codes: F16F13, B60K5, B62D27