Spring devices – Resilient shock or vibration absorber – Including energy absorbing means or feature
Reexamination Certificate
2002-04-16
2003-12-30
Butler, Douglas C. (Department: 3683)
Spring devices
Resilient shock or vibration absorber
Including energy absorbing means or feature
C267S035000, C267S122000, C267S219000
Reexamination Certificate
active
06669181
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a vibration isolating apparatus which prevents vibrations from being transmitted from a member which generates vibrations. This device can be applied to, for example, cases in which the transmission of vibrations from an engine mounted in a vehicle is to be prevented, or the like.
2. Description of the Related Art
As a vibration isolating apparatus, a structure is known which, for example, is disposed as an engine mount between an engine of a vehicle, which is a vibration generating portion, and the vehicle body, which is a vibration receiving portion, and which absorbs the vibrations generated by the engine so as to impede transmission of vibrations to the vehicle body.
An example of such a vibration isolating apparatus is the bush-type apparatus shown in FIG.
4
. This conventional vibration isolating apparatus will be described concretely hereinafter on the basis of FIG.
4
.
In the vibration isolating apparatus, an inner tube
114
is disposed, via an elastic body
116
, at the inner side of an outer tube
112
which is tubular and forms an outer frame. Further, a main fluid chamber
116
, and auxiliary fluid chambers
120
,
122
, which communicate with the main fluid chamber
118
by orifices
124
,
126
which are passages, are formed.
A diaphragm
128
, which is an elastic membrane made of rubber, forms a portion of a partitioning wall of the auxiliary fluid chamber
120
. The space between the diaphragm
128
and the outer tube
112
is an air chamber
130
. A through hole
132
is formed in a portion of the outer tube
112
which portion opposes the diaphragm
128
.
Accordingly, when the engines which is mounted to the vibration isolating device, vibrates and vibrations are generated, the vibrations are absorbed or the vibrations are damped by the fluid column resonance or the like of the fluid within the orifices
124
,
126
serving as low dynamic springs which communicate the main fluid chamber
118
and the auxiliary fluid chambers
120
,
122
, respectively. The transmission of vibrations to the vehicle body is thereby impeded.
However, in the above-described vibration isolating apparatus which impedes the transmission of vibrations by utilizing fluid column resonance and lowering the dynamic spring constant, the flow resistance of the orifice through which the fluid flows is set in accordance with the frequency of the vibrations to be absorbed. Thus, the flow resistance depends on the frequency of the vibrations.
Namely, in a conventional vibration isolating apparatus, there are two types of passages which are the orifice
124
, which is a passage for absorbing idle vibrations, and the orifice
126
, which is a passage for absorbing booming-noise vibrations. The orifices
124
,
126
prevent the transmission of vibrations of two frequencies.
SUMMARY OF THE INVENTION
However, vibrations of intermediate frequencies between the idle vibration region and the booming-noise vibration region, which is a higher frequency region than the idle vibration region, are not absorbed in either passage. Thus, there is the drawback that the frequency region between the idle vibration region and the booming-noise vibration region has a high dynamic spring constant, and the vibrations cannot be reduced.
Accordingly, it has been thought to increase the number of passages to decrease the dynamic spring constant in the above-mentioned frequency region. For example, a structure in which two passages are provided for one auxiliary fluid chamber is disclosed in Japanese Patent Application Laid-Open (JP-A) No. 7-233848.
However, in accordance with the structure disclosed in the aforementioned publication, as the peak-shaped frequency characteristic of the dynamic spring constant is shifted and becomes a broader characteristic, vibrations over a wide range of frequencies can be absorbed, but the spring constant of the frequency region between the idle vibration region and the booming-noise vibration region cannot be greatly decreased.
In view of the aforementioned, an object of the present invention is to provide a vibration isolating apparatus which can reduce vibrations even at frequencies between the idle vibration region and the booming-noise vibration region.
A vibration isolating apparatus relating to a first aspect of the present invention comprises: an outer tube which is tubular and which is connected to one of a vibration generating portion and a vibration receiving portion; an inner tube which is disposed at an inner peripheral side of the outer tube and which is connected to another of the vibration generating portion and the vibration receiving portion; an elastic body which is disposed between the outer tube and the inner tube and is elastically deformable; a main fluid chamber which contains a fluid with the elastic body serving as a portion of a partitioning wall of the main fluid chamber, and whose internal volume changes due to deformation of the elastic body; a first auxiliary fluid chamber which contains a fluid, at least a portion of a partitioning wall of the first auxiliary fluid chamber being elastically deformable; a diaphragm forming a portion of the elastically deformable partitioning wall of the first auxiliary fluid chamber, so as to expand and contract a space between the first auxiliary fluid chamber and the outer tube; a first passage which communicates the main fluid chamber and the first auxiliary fluid chamber; and a second passage which communicates the main fluid chamber and the first auxiliary fluid chamber, a passage sectional area of at least a portion of the second passage being smaller than a passage sectional area of the first passage, and a flow resistance of the second passage being smaller than a flow resistance of the first passage, wherein in a state in which internal pressure of the first auxiliary fluid chamber is low and there is little fluid within the first auxiliary fluid chamber, the diaphragm has a configuration which is sunk toward the first auxiliary fluid chamber, and in a state in which the internal pressure of the first auxiliary fluid chamber is high and there is much fluid in the first auxiliary fluid chamber, the diaphragm has a swollen configuration, and as the internal pressure of the first auxiliary fluid chamber rises and fluid flows into the first auxiliary fluid chamber, the diaphragm inverts and deforms into the swollen configuration.
In accordance with this structure, when vibrations are transmitted from the vibration generating portion which is connected to either the outer tube or the inner tube, the elastic body deforms, and the vibrations are damped by the elastic body. As the internal volume of the main fluid chamber changes due to the deformation of the elastic body, the fluid actively flows to the first auxiliary fluid chamber via the first passage. As a result, a change in pressure arises in the fluid within the first passage, and accompanying this change in pressure, the diaphragm, which is at least one portion of the partitioning wall of the first auxiliary fluid chamber, elastically deforms and the first auxiliary fluid chamber expands and contracts.
Namely, when vibrations are transmitted from the vibration generating portion, not only does the elastic body deform, but also, the dynamic spring constant decreases due to the first passage which connects the main fluid chamber and the first auxiliary fluid chamber. The vibrations are absorbed, and it is difficult for vibrations to be transmitted to the vibration receiving portion which is connected to one of the inner tube and the outer tube.
Moreover, not only the first passage, but the second passage as well also communicates with the main fluid chamber and the first auxiliary fluid chamber. The passage sectional area of at least a portion of the second passage is smaller than the passage sectional area of the first passage, and the flow resistance of the second passage is smaller than the flow resistance of the first passage.
Namely, the value of the passage sectional a
Okai Shigeki
Someya Katsumi
Bridgestone Corporation
Butler Douglas C.
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