VIBRATION ISOLATING APPARATUS

Abstract: A vibration isolating apparatus for interposing between a vibration generating portion and a vibration receiving por­ tion includes a main body which has a portion constituted by a resilient menber (20) and encloses a liquid chamber (26A, 26B) which is capable of being expanded and contracted. The liquid chamber (26A, 26B) is divided by a partition (16) into small liquid chambers which communicate with each other through an orifice (40) which is able to absorb low-frequency vibrations. A resilient membrane (32) is provided between the small liquid chambers in such a manner as to suppress rise in pressure inside the small liquid chambers so that high-frequency vibrations are also absorbed.

Description: The present invention relates to a vibration isolating apparatus which is interposed between a vibration generating portion and a vibration receiving portion so as to absorb and damp vibrations from the vibration generating portion. One type of conventionally employed vibration isolating apparatus includes a hollow member of a resilient material which is filled with a liquid in such a manner as to enable it to be employed as a liquid chamber and which is partitioned into small liquid chambers through a limiting passage. This type of vibration isolating apparatus is arranged such that the liquid is caused to move between the two liquid chambers by the vibration acting on one of the chambers, whereby the vibration is absorbed by means of the fluid resistance of the liquid passing through the limiting passage. The conventional vibration isolating apparatus of this type, however, suffers from the following problem. Namely, high-frequency vibrations easily cause the limiting passage to be choked with the liquid, thus causing the dynamic scale factor to be undesirably increased, which fact involves a disadvantageously low capacity to absorb high-frequency vibrations. For this reason, employment of this type of vibration isolating apparatus as an engine mount may cause an occupant of the car in which it is employed to feel uncomfortable. In order to overcome the above-described problem, a vibration isolating apparatus has heretofore been proposed in which the partition wall which divides the liquid chamber is provided with a vibrating plate which is capable of vibrating with very small amplitudes. In this conventional apparatus, the volume of each of the liquid chambers is variable by virtue of the action of the vibrating plate. Therefore, even after the limiting passage has been choked at the time of generation of high-frequency vibrations, the dynamic to static ratio is favorably lowered due to the fact that the volume of the liquid chambers is conveniently varied by means of the vibrating plate. However, even the apparatus having such a vibrating plate involves the disadvantage that, when a vibration of relatively large amplitude occurs, the dynamic to static ratio is increased and this causes the vibration absorbing characteristic to be undesirably lowered. EP-A-22751 describes a vibration isolating apparatus adapted to be interposed between a vibration generating portion of a machine or other apparatus and a vibration receiving portion thereof, the vibration isolating apparatus comprising a first liquid chamber with a wall portion thereof provided by a resilient member through which the vibration generating and vibration receiving portions are connected in use, a second liquid chamber, a partition wall member separating the first and second liquid chambers and having a central opening, a resilient partition member secured to the partition wall member for closing the central opening, and a limiting member defining a long restricted passage having openings at its ends to open into the first and second liquid chambers and to define the long restricted passage therebetween, wherein further partition members are provided closely on either side of the resilient partition members which act to limit movement of the resilient partition member in both directions. In the above described apparatus the gap between the resilient partition member and the further partition members is narrow to the extent that they are brought into contact with each other when normal vibrations are input and, as stated above the further partition members are located both above and below the resilient partition member. Accordingly the vibration damping action of the resilient partition member is restricted even when normal large amplitude vibrations are input. To this end the present invention provides a hydraulically damped and vibration isolating mounting apparatus adapted to be interposed between a vibration generating portion of a machine or other apparatus and a vibration receiving portion thereof, the mounting apparatus comprising two axially opposed rigid end members connected to the vibration generating portion and respectively to the vibration receiving portion and liquid chambers arranged axially in series and containing damping fluid, the first and upper liquid chamber having a peripheral wall portion thereof provided by a resilient member through which the rigid end members are connected, a second and lower liquid chamber, a partition wall member separating the first and second liquid chambers, having a central opening and at least a portion thereof extending in a substantially radial plane around the central axis of the mounting, a resilient partition member secured to the partition wall member for closing the central opening, and a longitudinal path member defining a long restricted passage having openings at its ends to open into the first and second liquid chambers and to define the long restricted passage therebetween, wherein a further partition member is disposed in the second liquid chamber under the resilient partition member to divide in axial direction the second liquid chamber, and wherein at least one opening is provided in the further partition member and the combined opening area thereof is smaller than that of the central opening but larger than that of the restricted passage, characterised in that said further partition member is spaced from said resilient partition member by 0.5 mm or more and in that the first liquid chamber, axially above the resilient partition member, is not partitioned. Embodiments of vibration isolating apparatus according to the invention are described below with reference to the accompanying drawings. It should be understood that only Figures 6 and 9 show vibration isolating apparatus in accordance with the invention since only these Figures show apparatus incorporating a further partition member disposed under the resilient partition member in the second liquid chamber. The remaining Figures show comparative embodiments and are provided to show details of other preferred constructional features of such apparatus, so far as such features do not conflict with the requirements of claim 1. The first, second, and third comparative embodiments, however, are not in accordance with the present invention. In the drawings: FIG. 1 is a sectional view of a first comparative embodiment of vibration isolating apparatus; FIG. 2 is an exploded perspective view of an element for forming the orifice which is shown in Fig. 1; FIG. 3 is a sectional view of a second comparative embodiment of vibration isolating apparatus; FIG. 4 is a sectional view of a third comparative embodiment of vibration isolating apparatus; FIG. 5 is an exploded perspective view of an element for forming the orifice which is shown in Fig. 4; FIG. 6 is a sectional view of a first embodiment of a vibration isolating apparatus according to the invention; FIG. 7 is a graph representing the relationship between the dynamic to static ratio and the frequency, which shows the result of the experiment carried out on the first comparative embodiment; FIG. 8 is a graph representing the relationship between the dynamic to static ratio and the frequency, which shows the comparison between the third comparative embodiment and the first embodiment according to the invention and the prior art; and FIG. 9 is a sectional view of a second embodiment of a vibration isolating apparatus according to the invention. Fig. 1 shows a vibration isolating apparatus in accordance with a first comparative embodiment. In this embodiment, the apparatus is applied to a mount for an automotive engine. A base plate 10 which constitutes a part of a vibration isolating apparatus body has a bolt 12 secured to the center of its lower side so that the base plate 10 is secured to the body of an automobile (not shown) through the bolt 12. A tubular portion 10A projects upwardly from the periphery of the base plate 10. A flange 14 is integrally formed at the upper end of the tubular portion 10A. A partition wall member in the form of a plate 16 is secured to the flange 14. The periphery of a diaphragm 18 is fixedly clamped between the partition plate 16 and the flange 14. Thus, an air chamber is defined by the space between the diaphragm 18 and the base plate 10. The lower end of a cylindrical rubber member 20 which constitutes a vibration absorbing main body is bonded to the upper side of the partition plate 16 by means of vulcanization. A top plate 22 is bonded to the upper end of the rubber member 20 by means of vulcanization. A bolt 24 which projects upwardly from the upper surface of the top plate 22 is employed to secure the apparatus on an engine (not shown). The hollow portion which is defined between the top plate 22, the rubber member 20 and the diaphragm 18 is filled with a liquid, thus constituting a liquid chamber 26. As also shown in Fig. 2, the partition plate 16 has a circular bore 28 formed in its center. The upper end of a sleeve 30 is integrally connected to the periphery of the bore 28. The outer peripheral portion of a resilient partition member 32 is bonded to the inner peripheral portion of the sleeve 30 by means of vulcanization. The partition member 32 has a disk-like shape and is preferably formed of a resilient material which is deflectable by a predetermined degree, such as rubber. Thus, the partition plate 16 and the resilient partition member 32 in combination divides the liquid chamber 26 into upper and lower liquid chambers 26A and 26B. An abutment plate 34 is secured to the lower side of the partition plate 16. A tubular sleeve 36 projects from the inner peripheral portion of the abutment plate 34 and is secured to the outer periphery of the sleeve 30. A recess 38 with a rectangular cross-section is formed at the joint between the abutment plate 34 and the sleeve 36 in such a manner as to extend over about two thirds of the entire circumference of the sleeve 36. Thus, an orifice 40 which serves as a restricted passage is defined between the partition plate 16, the sleeve 30, the abutment plate 34 and the sleeve 36. One end of the orifice 40 is communicated with the upper liquid chamber 26A through a circular bore 42 which is formed in the partition plate 16, while the other end of the orifice 40 is communicated with the lower liquid chamber 26B through a circular bore 44 which is formed in the bottom of the recess 38. The following is a description of the operation of this embodiment. The base plate 10 is secured to the body of an automobile (not shown) through the bolt 12, while the engine is mounted on the top plate 22 and secured thereto by means of the bolt 24, thus completing the assembly. Engine vibrations are absorbed by virtue of the internal friction occurring between the rubber member 20 and the liquid sealed therein. When the frequency of vibrations is relatively low, the vibrations are absorbed by virtue of the fluid resistance of the liquid circulating between the upper and lower liquid chambers 26A and 26B through the orifice 40. On the other hand, when the frequency of vibrations is relatively high, the orifice 40 may be choked with the liquid. In such a case, however, the resilient partition member 32 favourably deflects by a given degree in such a manner as to move toward either of the upper and lower liquid chambers 26A, 26B and hence absorb a rise in the internal pressure thereof. Thus, it is possible for high-frequency vibrations to be absorbed. Since the resilient partition member 32 is employed in this embodiment, it is particularly possible to minimize the volume elasticity of the upper liquid chamber 26A (the volume elasticity being represented by the reciprocal of the volume of the upper liquid chamber 26A which changes when the internal pressure of the chamber 26A is raised by a unit pressure) after the orifice 40 has been clogged with the liquid. Even for vibrations of relatively large amplitude, it is possible for the dynamic to static ratio to be lowered below 2, as shown in Fig. 7. Fig. 3 shows a second comparative embodiment of vibration isolating apparatus. In this embodiment, the partition plate 16, the sleeve 30, the abutment plate 34 and the sleeve 36 of the first comparative embodiment are integrally molded of a resilient material, together with the resilient partition member 32. It is possible according to this embodiment to obtain advantageous effects which are similar to those offered by the first embodiment. Referring next to Fig. 4, there is shown a third comparative embodiment of vibration isolating apparatus. In this embodiment, a tubing 50 is welded to the lower side of the partition plate 16 in such a manner that the inner periphery of the tubing 50 defines the orifice 40, as also shown in Fig. 5. For this purpose, the tubing 50 is bent in such a manner that its axis forms a ring shape. In addition, both end portions of the tubing 50 are closed by shut-off plates 52. A circular bore 54 is formed in the tubing 50 in the vicinity of one end thereof and is communicated with the circular bore 42 of the partition plate 16, and another circular bore 56 is formed in the tubing 50 in the vicinity of the other end thereof and is communicated with the lower liquid chamber 26B. The resilient partition member 32 is bonded to the peripheral edge portion of the circular bore 28 of the partition plate 16 by means of vulcanization. In consequence, the tubing 50 in this embodiment enables the inner diameter of the orifice 40 to be increased as compared with the conventional arrangement, so that it is possible for the dynamic to static ratio to be lowered at the time of generation of low-frequency vibrations. Fig. 6 shows a first embodiment of vibration isolating apparatus according to the invention. This embodiment is in accordance with the present invention. In this embodiment, the outer peripheral portion of a disk 58 is secured to the inner periphery of the tubing 50 which is employed in the above-described embodiment, and a circular bore 60 which is formed in the vicinity of the axial center of the disk 58 constitutes a second orifice. Accordingly, the cross-sectional area of the bore 60 is larger than that of the tubing 50 but smaller than the effective area of the resilient partition member 32 at the opening 28. Fig. 8 is a graph representing the relationship between the dynamic to static ratio and the frequency, which shows the comparison between the vibration isolating apparatuses in accordance with the third comparative embodiment and the first embodiment according to the invention and the conventional vibration isolating apparatus in which a vibrating plate is provided on its partition wall portion. In this case, the tubing 50 of the third comparative embodiment shown in Fig. 4 has an inner diameter of 10 mm and an effective length of 130 mm, while its resilient partition member 32 has a wall thickness of 5 mm and an effective opening area of 40 mm. In regard to the first embodiment according to the invention shown in Fig. 6, the tubing 50 has an inner diameter of 10 mm and an effective length of 110 mm; the resilient partition member 32 has a wall thickness of 5 mm and an effective opening area of 40 mm; the disk 58 has a wall thickness of 1.5 mm; the circular bore 60 has a diameter of 26 mm; and the distance between the disk 58 and the resilient partition member 32 is 3 mm. The loss factor tan δ at a frequency of 10 Hz was 0.46 for the prior art, 0.45 for the third comparative embodiment and 0.47 for the first embodiment according to the invention, while the dynamic to static ratio at a frequency of 100 Hz was 1.35 for the prior art, 1.55 for the third embodiment, and 1.45 for the first embodiment according to the invention. In the graph of Fig. 8, the lowering in the dynamic to static ratio at various frequency ranges is attained by virtue of the following factors: namely, the lowering in the dynamic to static ratio at frequencies below 20 Hz is mainly due to the fact that the inner diameter of the tubing 50 is relatively large; that at frequencies from 20 to 50 Hz is mainly due to the provision of the resilient partition member 32; and that at frequencies above 70 Hz is mainly due to the existence of the second orifice 60. Referring next to Fig. 9, there is shown a second embodiment of vibration isolating apparatus according to the invention. In this embodiment, a disk 62 is provided in the lower liquid chamber 26B, whereby the fifth embodiment offers advantageous effects similar to those of the first embodiment according to the invention which is shown in Fig. 6. It is necessary for the disk 62 employed in the second embodiment according to the invention to be spaced from the resilient partition member 32 by 0.5 mm or more. Although these embodiments exemplify an arrangement in which a single bore is formed in the axial center of the disk which is employed to form a second orifice, the present invention is not necessarily limited to the above-described arrangement, and it is also possible to obtain advantageous effects equivalent to those offered by the embodiments by forming a plurality of small bores in the disk. In such a case, the effective cross-sectional opening area of the second orifice thus formed is the sum total of the cross-sectional areas of the small bores. As has been described above, the vibration isolating apparatus according to the present invention is arranged such that a liquid chamber is divided by a partition member into a plurality of small liquid chambers which are communicated with each other through a limiting passage, and a resilient member is provided on the partition member. It is therefore advantageously possible to lower the dynamic to static ratio at the time of generation of vibrations of relatively large amplitude.

Claims: A hydraulically damped and vibration isolating mounting apparatus adapted to be interposed between a vibration generating portion of a machine or other apparatus and a vibration receiving portion thereof, the mounting apparatus comprising two axially opposed rigid end members (10, 12; 22, 24) connected to the vibration generating portion and respectively to the vibration receiving portion and liquid chambers (26A,26B) arranged axially in series and containing damping fluid, the first and upper liquid chamber (26A) having a peripheral wall portion thereof provided by a resilient member (20) through which the rigid end members (10, 12; 22, 24) are connected, a second and lower liquid chamber (26B), a partition wall member (16) separating the first and second liquid chambers, having a central opening (28) and at least a portion thereof extending in a substantially radial plane around the central axis of the mounting, a resilient partition member (32) secured to the partition wall member (16) for closing the central opening (28), and a longitudinal path member (38;50) defining a long restricted passage (40) having openings (42,44;54,56) at its ends to open into the first and second liquid chambers and to define the long restricted passage (40) therebetween, wherein a further partition member (58;62) is disposed in the second liquid chamber under the resilient partition member (32) to divide in axial direction the second liquid chamber, and wherein at least one opening (60) is provided in the further partition member and the combined opening area thereof is smaller than that of the central opening (28) but larger than that of the restricted passage, characterised in that said further partition member (58;62) is spaced from said resilient partition member (32) by 0.5 mm or more and in that the first liquid chamber, axially above the resilient partition member (32), is not partitioned. The hydraulically damped and vibration isolating mounting apparatus as claimed in claim 1, wherein said resilient partition member (32) is constituted by a substantially flat rubber membrane. The hydraulically damped and vibration isolating mounting apparatus as claimed in claim 2, wherein said rubber membrane (32) is stretched on the partition wall member (16) which partitions the first and second liquid chambers (26A,26B). The hydraulically damped and vibration isolating mounting apparatus as claimed in claim 3, wherein said partition wall member is formed with a tubular portion (30), said rubber membrane (32) being secured to the inner periphery of said tubular portion. The hydraulically damped and vibration isolating mounting apparatus as claimed in claim 4, wherein the restricted passage is disposed in such a manner as to surround said tubular portion (46). The hydraulically damped and vibration isolating mounting apparatus as claimed in claim 5, wherein the restricted passage (40) is defined by the inner periphery of a looped tubing (50). The hydraulically damped and vibration isolating mounting apparatus as claimed in claim 5, wherein restricted passage (40) is defined between said partition wall member (16) and a plate member (34) disposed such as to abut against said partition wall member (16). The hydraulically damped and vibration isolating mounting apparatus as claimed in claim 7, wherein said partition wall member and said resilient partition member (32) are integrally formed of a resilient material. The hydraulically damped and vibration isolating mounting apparatus as claimed in any preceding claim, wherein said opening (60) is constituted by a through-hole (60) formed in a partition plate (58;62) employed for partitioning said second liquid chamber. The hydraulically damped and vibration isolating mounting apparatus according to claim 9, wherein said partition plate (58;62) is horizontally secured to an inner periphery of the longitudinal path member (38;50). The hydraulically damped and vibration isolating mounting apparatus according to claim 9 or claim 10, wherein said opening (60) is disposed coaxially with said resilient partition member (32). The hydraulically damped and vibration isolating mounting apparatus according to any preceding claim, wherein the second liquid chamber (26B) is partially defined by a diaphragm (18) able to be deformed by liquid pressure.

Inventors: NOGUCHI, TAKESHI, USHIJIMA, TAKAO
Applicants: BRIDGESTONE CORPORATION
Application year: 1985
Main classification: F16F13
IPC codes: B60K5, F16F13