VIBRATION ISOLATING DEVICES

Abstract: A sealed liquid-carrying vibration-proof structure, in which a partition wall (12) dividing a sealed chamber into two liquid chambers (13),(14) is provided therein with a gas chamber (19) which is independent of these two liquid chambers. The portion of the gas chamber which is adjacent to at least one liquid chamber is covered partially or wholly with a flexible film (18). When in this arrangement vibration of, especially, a high frequency and a small amplitude is imparted to the vibration-proof structure, the flexible film is deformed to absorb the vibration and thereby prevent the high-frequency vibration from causing an increase in the dynamic spring constant of the vibration-proof structure.

Description: This invention relates to a vibration isolating device suitable for use in automobiles and other vehicles, machinery instruments and the like, which serves to not only sufficiently damp low frequency, large amplitude vibrations but also effectively insulate high frequency, small amplitude vibrations. The conventional known vibration isolating device widely used, for instance, as an engine mount for automobile vehicles comprises a frame body connected to a vehicle chassis, a frame body connected to an engine, an elastic member disposed between these frame bodies and contributing to the formation of a closed chamber, water or other liquid filled in the closed chamber, a partition member secured at its peripheral edge to one of the above two frame bodies and dividing the closed chamber into two liquid chambers, and a passage arranged in the partition member to communicate the two liquid chambers with each other. When vibrations from the engine are transmitted to the vibration isolating device, they can be damped by a flow resistance subjected to the liquid when the liquid flows from the one liquid chamber to the other through the passage in addition to an internal friction of the elastic member. In this vibration isolating device, however, when the vibration transmitted to the device is, for example, high frequency, small amplitude vibrations of not less than 50 Hz, the communication passage between both the liquid chambers is rendered into a clogged state to raise the dynamic spring rate in the device, whereby the ride comfort of the vehicle is unfavourably deteriorated. In order to overcome the aforementioned problem, there has been proposed a vibration isolating device in Japanese Patent laid open No. 53-5,376 (Japanese Patent Application No. 52-78,477), wherein an oscillation plate is arranged at the boundary between both the liquid chambers. In this case, if high frequenty, low amplitude vibrations are transmitted to the vibration isolating device, the oscillation plate is oscillated in the liquid to absorb such vibrations. In this device, however, the oscillation plate absorbs the high frequency vibrations owing to its oscillation in liquid, so that the state wherein oscillation of the oscillation plate is not possible resulted from the friction force between the oscillation plate and the liquid, inertia force of liquid to be removed by the oscillation plate during the oscillation, i.e. rapid increase of dynamic spring rate is unfavourably caused at a relatively low frequency of 150-200 Hz in the high frequency zone. Attention is also drawn to prior art known by the disclosures of JP-U-58, 119643, EP-A-164081, and EP-A-115417, which is the basis for the first part of claim 1. The present invention aims to provide a vibration isolating device capable of effectively developing the conflicting properties between the damping of low frequency, large amplitude vibration and the insulation of high frequency, small amplitude vibration. The present invention provides a vibration isolating device comprising: two frame bodies adapted to be connected to the parts to be isolated, an elastomeric member arranged between said two frame bodies and forming part of a closed chamber, a liquid filling the closed chamber, a partition member secured at a peripheral edge thereof to one of the two frame bodies and dividing the closed chamber into two liquid chambers, and a passage extending circumferentially in the peripheral portion of the partition member to establish fluid communication between the liquid chambers, the partition member comprising first and second partition plates connected together to define said passage therebetween, and the partition member also defining a gas chamber at least partially enclosed by a flexible diaphragm which is subject to pressure vibrations in one of said liquid chambers, characterized in that one of said partition plates is made of elastomeric material and defines said flexible diaphragm. In a preferred embodiment of the vibration isolating device according to the invention, the first partition plate is made of elastomeric synthetic resin and the second partition plate is made of metal. In another preferred embodiment of the vibration isolating device according to the invention, the first partition plate is made of elastomeric synthetic resin and the second partition plate is made of reinforced synthetic resin. In the vibration isolating device according to the invention, when low frequency, large amplitude vibrations are transmitted to the device, the effective damping of such vibrations is attained mainly by the flow resistance subjected to the liquid flowing from one of the liquid chambers to the other through the restricted passage. On the other hand, when high frequency, small amplitude vibrations are transmitted to the device, sufficient insulation of such vibrations is attained by the deformation of the flexible diaphragm based on the difference in pressure between the liquid chambers. Moreover, such a deformation of the flexible diaphragm brings about the expansion and shrinkage deformation of the gas chamber, and hence the friction force between the gas chamber and the liquid in the deformation of the flexible diaphragm and the inertia force of the liquid to be removed in the deformation become very small, so that the insulation of high frequency vibrations based on the deformation of the flexible diaphragm is made possible against vibrations of fairly high frequency, for example, 200-250 Hz as compared with the prior art. The invention will be further described, by way of example only, with reference to the accompanying drawings, in which: Figs. 1a and 1b are a longitudinal section view of an embodiment of a vibration isolating device according to the invention and a perspective view of constructional components of the partition member thereof, respectively; Fig. 2 is a longitudinal section view of another embodiment of a vibration isolating device according to the invention; and Figs. 3a and 3b are a sectional view of a further embodiment of a vibration isolating device according to the invention and a perspective view of constructional components thereof, respectively. In the drawings, reference numeral 1 is a frame body, for example connecting to a vehicle chassis, numeral 2 another frame body, for example connecting to an engine, and numeral 3 an elastic member arranged between the frame bodies 1 and 2 and closely adhered thereto and contributing to the formation of a closed chamber as mentioned later. The frame body 1 is composed by fixing a lower end flange 6a of a cylindrical member 6 to a flange 5a of a dish-like member 5 provided at its lower surface with a fitting bolt 4 protruding downward from the central portion thereof. On the other hand, the frame body 2 is composed by securing a cup-like member 9 to a lower surface of a flat plate 8 provided at its upper surface with a fitting bolt 7 protruding upward from the central portion thereof. Furthermore, the elastic member 3 may be made of rubber or rubbery elastomeric material, and has a hollow and substantially frustoconical shape. The elastic member 3 is closely adhered to the frame bodies 1, 2 by bonding the lower surface to an upper end enlarged portion of the cylindrical member 6 and the upper surface to the peripheral face of the cup-like member 9 through vulcanization or other process, respectively. The elastic member 3 contributes to the formation of a closed chamber 11 together with the cylindrical member 6 of the frame body 1, the cup-like member 9 of the frame body 2 and a diaphragm 10 clamped at its peripheral portion between the dish-like member 5 and the cylindrical member 6 in the frame body 1. In this illustrated embodiment, water or other liquid is filled in the whole of the closed chamber 11 defined by these members. The closed chamber 11 filled with the liquid is divided into two liquid chambers 13, 14 by a partition member 12 liquid-tightly clamped at its peripheral portion between the dish-like member 5 and the cylindrical member 6. These liquid chambers 13, 14 communicate with each other through a restricted passage 15 formed in the partition member 12 and opening to the chambers. The restricted passage 15 having an arc shape in transverse section communicates with each of the liquid chambers 13, 14 at positions opposite to each other in radial direction. Of course, these opening positions may optionally be selected in accordance with the required extending length of the restricted passage 15. In the case of using the vibration isolating device of the above construction as an engine mount, the frame body 1 and the frame body 2 are connected to the vehicle chassis and the engine through the fitting bolts 4 and 7, respectively. In this case, vibrations transmitted from an engine (not shown) to the frame body 2 are somewhat damped by the internal friction of the elastic member 3. In particular, when the vibration is low frequency, large amplitude vibration, the liquid filled in the liquid chambers 13, 14 flows from one of the liquid chambers to the other liquid chamber through the restricted passage 15 based on alternate increase and decrease of internal pressures in the liquid chambers. Therefore, the motion energy of the liquid is absorbed by the restricted passage 15, whereby the effective damping of low frequency, large amplitude vibration is attained. In the embodiment according to the invention shown in Fig. 1, a partition member 12 fixed together with the diaphragm 10 between the dish-like member 5 and the cylindrical member 6 in the frame body 1 is constructed with a lower partition 16 made of a reinforced plastic (synthetic resin) plate and an upper partition 17 secured to the outside of the lower partition 16 and made of an elastomeric plastic (synthetic resin) plate. The upper partition 17 having a substantially hat-like shape has a cylindrical part 17b at its central portion, and a top plate 17c is arranged on the top of the cylindrical part 17b. The lower partition 16 is secured to the top plate 17c. As shown in Fig. 1b, the lower partition 16 is provided at its outer periphery with a cylindrical part 16c which is secured to the inner periphery of the cylindrical part 17b. In the joint portion between a top plate 16d and the cylindrical part 16c in the lower partition 16 is formed a groove 16e having a substantially L-shaped section perpendicular to the circumferential direction, which forms a restricted passage 15 together with the upper partition 17. The restricted passage 15 is C-shape in transverse section, one end in longitudinal direction of which communicates with the liquid chamber 13 through a circular hole 17d formed in the top plate 17c of the upper partition 17 and the other end communicating with the liquid chamber 14 through a circular hole 16f formed in a part of the groove 16e. The top plate 17c of the upper partition 17 has a substantially spheroidal recess 17e at its lower surface so as to gradually reduce the thickness toward axial center, which forms an air chamber 19 together with the top plate 16d of the lower partition 16. In this illustrated embodiment, since the upper partition 17 is made of the elastomeric plastic (synthetic resin) plate and the lower partition 16 is made of the reinforced plastic (synthetic resin) plate, as the internal pressure of the air chamber 19 increases, the top plate 17c can be deformed in a direction of reducing the air chamber 19. Therefore, when vibrations transmitted from the engine to the vibration insulating device are, for example, relatively low frequency of less than 50 Hz, the liquid chamber 13 receiving the vibration from the engine reduces in size to allow the liquid to flow into the liquid chamber 14 through the restricted passage 15. As a result, the low frequency vibrations are absorbed by resistance force produced in the restricted passage 15. On the other hand, when the vibrations from the engine are high frequency, the restricted passage 15 is rendered into a clogged state. Therefore, as the pressure inside the liquid chamber 13 rises, dynamic spring rate increases, and the vibrations are directly transmitted from the engine to the vehicle chassis. In this embodiment, however, since the air chamber 19 is existent, the top plate 17c can deform so as to expand or reduce the air chamber 19, so that the volume of the liquid chamber 13 can be changed to control the rising of the pressure, whereby the high frequency vibration is absorbed. In particular, when the upper partition 17 and lower partition 16 are integrally united with each other as in this embodiment, the space inside the liquid chamber can be utilized effectively, so that effective vibration absorption can be attained by making a ratio of maximum diameter of the air chamber 19 to inner diameter of the liquid chamber (opening ratio) large. Fig. 2 shows a further embodiment of a vibration insulating device according to the invention. In this embodiment, a recess 16g is formed in the top plate 16d of the lower partition 16 in addition to the aforementioned recess 17e of the top plate 17c. The air chamber 19 is defined between the recesses 16g and 17e. In the embodiment shown in Fig. 3, an air chamber 19 is defined by a protruding central portion of a top plate 17c with a constant thickness upward to form a recess 17f at the inner face. Furthermore, in this embodiment, a helical groove 16h is formed on the periphery of a lower partition 16 as shown in Fig. 3b, whereby a helically long restricted passage 15 can be formed together with the inner periphery of a cylindrical part 17b. As mentioned above, the vibration insulating device according to the invention can attain not only sufficient damping of low frequency, large amplitude vibrations but also effective insulation of high frequency, small amplitude vibrations over a fairly high frequency zone when applied to automobiles and other vehicles, machinery instruments and the like.

Claims: A vibration isolating device comprising: two frame bodies (1,2) adapted to be connected to the parts to be isolated, an elastomeric member (3) arranged between said two frame bodies and forming part of a closed chamber, a liquid filling the closed chamber, a partition member (12) secured at a peripheral edge thereof to one of the two frame bodies and dividing the closed chamber into two liquid chambers (13, 14), and a passage (15) extending circumferentially in the peripheral portion of the partition member to establish fluid communication between the liquid chambers, the partition member comprising first and second partition plates (16, 17) connected together to define said passage (15) therebetween, and the partition member also defining a gas chamber (19) at least partially enclosed by a flexible diaphragm which is subject to pressure variations in one of said liquid chambers, characterized in that one of said partition plates is made of elastomeric material and defines said flexible diaphragm. A vibration isolating device as claimed in claim 1, characterized in that the first partition plate is made of elastomeric synthetic resin and the second partition plate is made of metal. A vibration isolating device as claimed in claim 1, characterized in that the first partition plate is made of elastomeric synthetic resin and the second partition plate is made of reinforced synthetic resin.

Inventors: DAN, TAKUYA, KOJIMA, HIROSHI, ORIKAWA, MICHIHIRO, BS KAMIYABE
Applicants: BRIDGESTONE CORPORATION
Application year: 1985
Main classification: F16F13
IPC codes: B60K5, F16F13