Hydraulically damping device

Abstract: A hydraulically damping device has a pair of supporting members (5/51, 7/71) to be secured to a vibrating body and a frame, respectively, and a rubber block (1) disposed between the supporting members. A concave surface of the rubber block and a rubber sheet (2) which is joined to the rubber block define a liquid chamber filled with damping liquid. The liquid chamber is divided into a main liquid chamber (A) and an auxiliary liquid chamber (B) with a partition. The partition (3) has an opening (32) which is closed with an elastic rubber wall (4). The partition (3) is provided with a throttle passageway (31) which intercommunicates with both the main liquid chamber (A) and the auxiliary liquid chamber (B). The elastic rubber wall (4) has a flat surface (4a) facing the main liquid chamber (A), and a concavely curved surface (4b) facing the auxiliary liquid chamber (B) so as to have an arch-shaped cross-section. An inner periphery of the partition (3), which an outer periphery of the elastic rubber walls (4) contacts, has an inclined surface so that the diameter of the opening (32) of the partition decreases from the side of the main liquid chamber toward the auxiliary liquid chamber.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulically damping device, and more particularly to a hydraulically damping device having a partition of which a central opening is closed by an elastic rubber wall for both restraining low-frequency vibrations of large amplitudes, and absorbing high-frequency vibrations of small amplitudes. 2. Description of the Prior Art A hydraulically damping device is composed of a vessel-shaped thick rubber block which supports a vibrating body, and a deformable rubber sheet which closes an opening of the vessel-shaped thick rubber block. Within the thick rubber block, a main liquid chamber and an auxiliary liquid chamber are formed. The main liquid chamber is separated from the auxiliary liquid chamber with a partition having a throttle passageway. The auxiliary liquid chamber on its bottom side is defined by the deformable rubber sheet. The hydraulically damping device having the above-described construction achieves the vibration damping operation by forcing damping liquid enclosed within the main liquid chamber to flow into the auxiliary liquid chamber through the throttle passageway of the partition. Conventionally, in order to reduce high-frequency vibrations, various devices have been proposed(Japanese unexamined patent publication Sho 60-121339 (= FR-A-2554888), Japanese unexamined patent publication Sho 61-65934). These conventional devices are generally provided with an elastic rubber wall which closes an opening formed in a central portion of the partition. When high-frequency vibrations of small amplitudes are input, the elastic rubber wall deforms and absorbs the build-up of the inner pressure of the main liquid chamber. When low-frequency vibrations of large amplitudes are input to the hydraulically damping device, a higher pressure is built up in the main liquid chamber, as compared with the case of high-frequency vibrations of small amplitudes. This higher pressure is applied to the elastic rubber wall. With the above-described conventional devices in order to resist such a higher pressure, upper and lower surfaces of the elastic rubber wall have been formed into symmetric concave surfaces(Japanese unexamined patent publication Sho 60-121339) or into parallel surfaces(Japanese unexamined patent publication Sho 61-65934). The elastic rubber wall having concave or parallel surfaces, however, is likely to be fatigued with a large shear stress generated in its peripheral portion which is joined to the partition. SUMMARY OF THE INVENTION It is an object of the present invention to provide a hydraulically damping device of which an elastic rubber wall closing an opening of a partition is excellent in durability and has a greater useful life. The hydraulically damping device of the present invention has a pair of supporting members to be secured to a vibrating body and a frame, respectively, and a rubber block disposed between the supporting members. The rubber block has a liquid chamber defined by a concave surface of the rubber block and a rubber sheet which is joined to the rubber block so as to close the liquid chamber. A partition is provided for separating the liquid chamber into a main liquid chamber and an auxiliary liquid chamber. The partition has an opening and this opening is closed with an elastic rubber wall. The partition is provided with a throttle passageway for intercommunicating with both the main liquid chamber and the auxiliary liquid chamber. The elastic rubber wall has a flat surface facing the main liquid chamber, and a concavely curved surface facing the auxiliary liquid chamber so as to have an arch-shaped cross-section. Accordingly, the thickness of the elastic rubber wall gradually decreases from an outer peripheral portion to a central portion thereof. When low-frequency vibrations of large amplitudes are input to the hydraulically damping device of the present invention, a high pressure is built up in the main liquid chamber. This causes a large deforming force to be applied to the elastic rubber wall. However, the elastic rubber wall of the present invention is prevented from being excessively deformed because the elastic rubber wall has an arch-shaped cross section. Therefore, the elastic rubber wall exhibits good durability, and stress is prevented from being concentrated in a peripheral portion of the elastic rubber wall. Furthermore, by forming the inner periphery of the partition, which defines the opening, into an inclined surface so that the diameter of the opening gradually decreases from the main liquid chamber side to the auxiliary liquid chamber side, shear stress which would be generated in the peripheral portion of the elastic rubber wall surrounded by the inner periphery of the partition, can be reduced. In addition, by providing a flat surface in at least one part of the inclined inner periphery of the partition in parallel with the upper surface of the partition, the shear stress which would be generated in the flat surface is reduced to nearly zero. As a result, shear stress which would be generated in the overall inner periphery of the partition can be further reduced. If the elastic rubber wall is not required to have increased durability, it is unnecessary to incline the inner periphery of the partition nor to provide a flat surface in the inner periphery of the partition. The above-described flat surface may be provided at plural parts of the inclined inner periphery of the partition. BRIEF DESCRIPTION OF THE DRAWING Other objects, features and characteristics of the present invention will become apparent upon consideration of the following description and the appended claims with reference to the accompanying drawings, all of which form a part of the specification. Fig. 1 is a cross-sectional view of one embodiment of a hydraulically damping device in accordance with the present invention. DETAILED DESCRIPTION OF THE PREFERRED EXEMPLARY EMBODIMENT Regarding Fig. 1, to an upper surface of a vessel-shaped thick rubber block 1, an upper plate 5 is joined. A bolt 51 is secured to the upper plate 5 and supports an engine(not shown). Within a lower portion of the rubber block 1, an upper portion of a cylindrical side plate 6 is embedded. A lower portion of the cylindrical side plate 6 is secured to an upper portion of a bottom plate 7 by caulking. The bottom plate 7 is secured to a vehicle frame by a bolt 71. A ring-shaped partition 3 is provided in a space defined by the rubber block 1 and the bottom plate 7. A rubber sheet 2 is provided under the partition 3. The peripheral portions of the respective partition 3 and rubber sheet 2 are secured to an inner periphery of the bottom plate 7 by caulking so as to be integral with a lower end of the cylindrical side plate 6. An opening 32 is formed in the central portion of the partition 3. The opening 32 is closed by an elastic rubber wall 4. The periphery of the elastic ruber wall 4 is bonded to an inner periphery of the partition 3, which defines the opening 32, by vulcanization. The rubber block 1 and the rubber sheet 2 define an enclosed chamber. The enclosed chamber is divided into a main liquid chamber A and an auxiliary liquid chamber B with the partition 3 and the elastic rubber wall 4. These chambers A, B are filled with damping liquid. A recess 31 is continuously formed along an outer periphery of the partition 3 so as to communicate with both the main liquid chamber A and the auxiliary liquid chamber B. This recess 31 acts as a throttle passageway. The inner periphery of the partition 3 is formed into an inclined surface. Accordingly, the diameter of the opening 32 gradually decreases from the main liquid chamber A side toward the auxiliary liquid chamber B. Furthermore, at a middle of the inclined surface, a nearly horizontal flat surface 32a is formed. The horizontal flat surface 32a is nearly parallel with an upper surface of the partition 3. The elastic rubber wall 4 has an upper flat surface 4A which is flush with the upper surface of the partition 3. A lower surface 4b of the elastic rubber wall 4, which faces the auxiliary liquid chamber B, is a concavely curved surface. Accordingly, the thickness of the elastic rubber wall 4 gradually decreases from its peripheral portion to its central portion so that the elastic rubber wall 4 has an arch-shaped cross-section. With the hydraulically damping device having the above-described construction, when a high pressure is built up in the main liquid chamber A due to the input of low-frequency vibrations of large amplitudes, the elastic rubber wall 4 is prevented from being excessively deformed because the elastic rubber wall 4 has an arch-shaped cross section. Accordingly, a sufficiently high pressure is built up in the main liquid chamber A, and highly pressurized damping liquid flows into the auxiliary liquid chamber B through the throttle passageway 31, thereby achieving speedy vibration damping operation against low-frequency vibrations of large amplitudes. In accordance with the present embodiment, the stress, which would be generated in the peripheral portion of the elastic rubber wall 4 can be restrained because the elastic rubber wall 4 has an arch-shaped cross section. Even if the stress is generated, it is mainly compressive or tensile stress. Shear stress is generated at only a small rate because the inner periphery of the partition 3, which defines the opening 32, has the above-described configuration. These operational effects are combined together to prevent fatigue of the elastic rubber wall 4 certainly. With the hydraulically damping device of the present embodiment, when high-frequency vibrations of small amplitudes are input, the thin central portion of the elastic rubber wall 4 deforms so as to absorb the variation of the pressure in the main liquid chamber A, thereby absorbing and reducing high-frequency vibrations of small amplitudes. In order to obtain sufficient adhesive strength of the elastic rubber wall to the partition, conventionally, adhesive has been applied to respective end edges of both upper and lower surfaces of the partition, and then an outer peripheral portion of the elastic rubber wall has been bonded to the end edges of the both upper and lower surfaces of the partition. This conventional bonding method is troublesome. In contrast, with the present embodiment, adhesive is applied to the inner periphery of the partition 3 from only the upside of the partition 3, and then, the outer peripheral portion of the elastic rubber wall 4 is bonded to the inner periphery of the partition 3. By this method, a sufficiently high adhesive strength of the elastic rubber wall 4 to the partition 3 can be obtained with shortened joining process. As described above, the hydraulically damping device of the present invention can effectively prevent fatigue of the elastic rubber wall, whereby good vibration damping characteristics can be maintained over a long period of time.

Claims: A hydraulically damping device comprising: a pair of supporting members to be secured to a vibrating body and a frame, respectively; a rubber block disposed between said supporting members and having a liquid chamber defined by a concave surface of said rubber block and a rubber sheet which is joined to said rubber block so as to close said liquid chamber; a partition for separating said liquid chamber into a main liquid chamber and an auxiliary liquid chamber; said partition having an opening; an elastic rubber wall for closing said opening of said partition; and a throttle passageway provided in said partition for intercommunicating with both said main liquid chamber and said auxiliary liquid chamber; said elastic rubber wall having a flat surface facing said main liquid chamber, and a concavely curved surface facing said auxiliary liquid chamber, the thickness of said elastic rubber wall gradually decreasing from an outer peripheral portion to a central portion thereof. The hydraulically damping device according to claim 1, wherein an inner periphery of said partition, which an outer periphery of said elastic rubber wall contacts has an inclined surface so that the diameter of said opening of said partition decreases from the side of said main liquid chamber toward said auxiliary liquid chamber. The hydraulically damping device according to claim 2, wherein said inclined surface has a flat surface at at least one part thereof, which is nearly parallel with a flat surface of said partition. The hydraulically damping device according to claim 1, wherein said rubber block has a vessel-shaped configuration and is provided with an opening at its lower side, said rubber block supports the vibrating body on its upper surface through an upper plate, a lower end of said rubber block along said opening is joined to an upper end of a cylindrical side plate, an outer periphery of said partition closely contacts an inner periphery of said cylindrical side plate, said rubber sheet is provided under said partition, a vessel-shaped bottom plate is provided under said rubber sheet, outer peripheries of said rubber sheet and said partition are respectively secured to an upper end of said bottom plate by caulking so as to be integral with said cylindrical side plate, said liquid chamber defined by said concave surface of said rubber block and said rubber sheet is filled with damping liquid, a main liquid chamber is located over said partition and an auxiliary liquid chamber is located under said partition, and a recess is continuously formed along an outer periphery of said partition and intercommunicates with said main liquid chamber and said auxiliary liquid chamber, thereby acting as said throttle passageway.

Inventors: MAENO TAKASHI C O TOYODA GOSEI, MAENO, TAKASHI, Maeno, Takashi, c/o Toyoda Gosei Technical Center
Applicants: TOYODA GOSEI KK, TOYODA GOSEI CO., LTD.
Application year: 1991
Main classification: F16F13
IPC codes: F16F13, F16M7