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Claims  |
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What is claimed is:
1. A fluid-filled elastic mount for flexibly connecting two members,
comprising:
an inner and an outer sleeve which are radially spaced apart from each
other and which are fixed to said two members;
an elastic body interposed between said inner and outer sleeves, for
elastically connecting the inner and outer sleeves;
said elastic body at least partially defining a first pressure-receiving
chamber which is filled with a non-compressible fluid and which is
disposed between said inner and outer sleeves such that a pressure in said
fluid in said first pressure-receiving chamber changes due to elastic
deformation of said elastic body upon application of a vibrational load
between said inner and outer sleeves;
partition means for partially defining a second pressure-receiving chamber
between said inner and outer sleeves and separating said first and second
pressure-receiving chambers from each other such that said second
pressure-receiving chamber is disposed outwardly of said first
pressure-receiving chamber in a radial direction of said inner and outer
sleeves, said second pressure-receiving chamber being filled with said
fluid;
said partition means including a flexible layer which is displaceable to
thereby permit a pressure change in said first pressure-receiving chamber
to be transmitted to said second pressure-receiving chamber;
a flexible diaphragm partially defining two separate sections of a
variable-volume equilibrium chamber between said inner and outer sleeves,
said equilibrium chamber being spaced apart from said first and second
pressure-receiving chambers in a circumferential direction of said inner
and outer sleeves and filled with said non-compressible fluid;
means for defining a first orifice passage for fluid communication between
said first pressure-receiving chamber and one of said two separate
sections of said equilibrium chamber; and
means for defining a second orifice passage for fluid communication between
said second pressure-receiving chamber and the other of said two separate
sections of said equilibrium chamber, a ratio of a transverse cross
sectional area to a length of said second orifice passage being larger
than that of said first orifice passage.
2. A fluid-filled elastic mount for flexibly connecting two members,
comprising:
an inner and an outer sleeve which are radially spaced apart from each
other and which are fixed to said two members;
an elastic body interposed between said inner and outer sleeves, for
elastically connecting the inner and outer sleeves;
said elastic body at least partially defining a first pressure-receiving
chamber which is filled with a non-compressible fluid and which is
disposed between said inner and outer sleeves such that a pressure in said
fluid in said first pressure-receiving chamber changes due to elastic
deformation of said elastic body upon application of a vibrational load
between said inner and outer sleeves;
partition means for partially defining a plurality of second
pressure-receiving chambers between said inner and outer sleeves and
separating said first and second pressure-receiving chambers from each
other, each of said plurality of second pressure-receiving chambers being
filled with said non-compressible fluid;
said partition means including a first flexible layer which is displaceable
to thereby permit a pressure change in said first pressure-receiving
chamber to be transmitted to said plurality of second pressure-receiving
chambers, said partition means further including at least one second
flexible layer for at least partially defining said plurality of second
pressure-receiving chambers such that said plurality of second
pressure-receiving chambers are spaced from each other in a radial
direction of said inner and outer sleeves, said at least one second
flexible layer being displaceable to permit said pressure change in said
first pressure-receiving chamber to be successively transmitted to said
plurality of second pressure-receiving chambers;
a flexible diaphragm partially defining a variable-volume equilibrium
chamber between said inner and outer sleeves, said equilibrium chamber
being spaced apart from said first and second pressure-receiving chambers
in a circumferential direction of said inner and outer sleeves and filled
with said non-compressible fluid;
means for defining a first orifice passage for fluid communication between
said first pressure-receiving chamber and said equilibrium chamber; and
means for defining a plurality of second orifice passages for fluid
communication of said equilibrium chamber with said plurality of second
pressure-receiving chambers, respectively, ratios of a transverse cross
sectional area to a length of said plurality of second orifice passages
being larger than that of said first orifice passage, said ratios of said
second orifice passages increasing with a radial distance of the
corresponding second pressure-receiving chambers from said first
pressure-receiving chamber.
3. A fluid-filled elastic mount according to claim 2, wherein said
plurality of second pressure-receiving chambers consist of a radially
inner second pressure-receiving chamber which is separated from said first
pressure-receiving chamber by a first partition member including said
first flexible layer and a radially outer second pressure-receiving
chamber which is separated from said radially inner second
pressure-receiving chamber by a second partition member including the
second flexible layer.
4. A fluid-filled elastic mount for flexibly connecting two members,
comprising:
an inner and an outer sleeve which are radially spaced apart from each
other and which are fixed to said two members;
an elastic body interposed between said inner and outer sleeves, for
elastically connecting the inner and outer sleeves;
said elastic body at least partially defining a first pressure-receiving
chamber which is filled with a non-compressible fluid and which is
disposed between said inner and outer sleeves such that a pressure in said
fluid in said first pressure-receiving chamber changes due to elastic
deformation of said elastic body upon application of a vibrational load
between said inner and outer sleeves;
partition means for partially defining at least one second
pressure-receiving chamber between said inner and outer sleeves and
separating said first and second pressure-receiving chambers from each
other, each of said at least one second pressure-receiving chamber being
disposed outwardly of said first pressure-receiving chamber in a radial
direction of said inner and outer sleeves, and filled with said fluid;
said partition means including a flexible layer which is displaceable to
thereby permit a pressure change in said first pressure-receiving chamber
to be transmitted to said at least one second pressure-receiving chamber;
a flexible diaphragm partially defining a variable-volume equilibrium
chamber between said inner and outer sleeves, said equilibrium chamber
being spaced apart from said first and second pressure-receiving chambers
in a circumferential direction of said inner and outer sleeves and filled
with said non-compressible fluid;
means for defining a first orifice passage for fluid communication between
said first pressure-receiving chamber and said equilibrium chamber; and
means for defining a second orifice passage for fluid communication between
said each second pressure-receiving chamber and said equilibrium chamber,
a ratio of a transverse cross sectional area to a length of said each
second orifice passage being larger than that of said first orifice
passage.
5. A fluid-filled elastic mount according to claim 4, further comprising a
resonance member which has a resonance portion disposed within said first
pressure-receiving chamber such that a restricted portion is defined
between a periphery of said resonance portion and an inner surface of said
elastic body which defines said first pressure-receiving chamber.
6. A fluid-filled elastic mount according to claim 4, wherein said means
for defining a first orifice passage and said means for defining a second
orifice passage comprise an orifice-defining sleeve having a first and a
second groove formed in an outer circumferential surface thereof, said
first and second grooves communicating with said equilibrium chamber, and
with said first pressure-receiving chamber and said at least one second
pressure-receiving chamber, respectively, said first and second grooves
being closed by an inner surface of said outer sleeve to thereby provide
said first and second orifice passages.
7. A fluid-filled elastic mount according to claim 6, further comprising an
intermediate sleeve disposed between said elastic body and said outer
sleeve, said intermediate sleeve having a circumferential groove which
accommodates said orifice-defining sleeve such that said first and second
grooves are closed by said outer sleeve.
8. A fluid-filled elastic mount according to claim 6, wherein said
orifice-defining sleeve consists of two generally semi-cylindrical
orifice-defining members.
9. A fluid-filled elastic mount according to claim 4, wherein said at least
one second pressure-receiving chamber consists of a single second
pressure-receiving chamber, said ratio of said first orifice passage being
determined so as to permit the elastic mount to exhibit a high damping
effect based on resonance of the fluid flowing through said first orifice
passage, with respect to vibrations having frequencies in the neighborhood
of 10 Hz, while said ratio of said second orifice passage being determined
so as to permit the elastic mount to exhibit a dynamic spring constant
which is sufficiently low for effectively isolate vibrations having
frequencies within a range of about 20-50 Hz, based on resonance of said
fluid flowing through said second orifice passage.
10. A fluid-filled elastic mount according to claim 4, wherein said
partition means includes a flat wall having a window which is closed by
said flexible layer. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to a fluid-filled cylindrical
elastic mount for damping or isolating vibrations based on resonance of a
fluid contained therein. More particularly, this invention is concerned
with such a fluid-filled cylindrical elastic mount capable of exhibiting
excellent vibration damping or isolating effect based on the resonance of
the fluid flows, over a wide range of frequency of the input vibration.
2. Discussion of the Prior Art
There has been a growing requirement for improving the operating
characteristic and function of a vibration damping or isolating device for
flexibly connecting two members. In view of the difficulty in satisfying
the requirement on a conventional elastic vibration damper or isolator
which relies solely on the elastic nature of an elastic body to provide a
vibration damping or isolating effect, an elastic mount or bushing filled
with a fluid has been recently proposed.
An example of such a fluid-filled elastic mount is disclosed in laid-open
Publication No. 56-164242 of unexamined Japanese patent application,
wherein an elastic body made of a rubbery material is formed between an
inner and an outer sleeve which are radially spaced apart from each other.
The elastic body flexibly connects the inner and outer sleeves, so that
two members of a vibration system that are fixed to the inner and outer
sleeves are connected to each other by the elastic mount in a vibration
damping or isolating manner. Between the inner and outer sleeves, there
are formed a plurality of fluid chambers filled with a suitable
non-compressible fluid. The fluid chambers are held in communication with
each other through an orifice passage. Upon application of a vibrational
load in a diametrical direction of the elastic mount, the fluid is forced
to flow between the fluid chambers through the orifice passage. This type
of fluid-filled cylindrical elastic mount relies on the resonance of the
fluid flowing through the orifice passage, and exhibits an excellent
vibration damping or isolating effect that cannot be obtained with the
conventional elastic mount or damper which uses only an elastic body.
The fluid-filled cylindrical elastic mount of the type described above is
capable of effectively damping or isolating input vibrations received in
various diametrical directions, and can be readily adapted to prevent an
excessive amount of relative displacement of the two members flexibly
connected by the elastic mount. Further, this elastic mount can be made
compact and small in size. For these advantages, the fluid-filled
cylindrical elastic mount is suitably used as an engine mount, a
differential mount, a member mount and a suspension bushing for motor
vehicles. These elastic mounts used for the vehicles are usually subject
to various vibrations having different frequencies, which occur depending
upon the varying running conditions of the vehicles. Accordingly, the
elastic mounts are required to exhibit different operating characteristics
for effectively damping or isolating such different bands of the input
vibrations, i.e., to deal with a relatively wide range of the input
vibrations.
For instance, an engine mount for a motor vehicle is required to exhibit a
low dynamic spring constant with respect to medium-frequency vibrations
such as engine idling vibration having a frequency range of about 20-50
Hz, while the vehicle is stopped with the engine running in an idling
condition. While the vehicle is cruising, the engine mount is also
required to exhibit a high damping effect with respect to low-frequency
vibrations such as engine shake and bounce having frequencies in the
neighborhood of 10 Hz, and also exhibit a low dynamic spring constant with
respect to high-frequency vibrations such as booming noises having
frequencies in the neighborhood of 100 Hz.
However, the conventional fluid-filled cylindrical engine mount exhibits a
sufficient damping or isolating effect based on the resonance of the
fluid, with respect to only the vibrations whose frequencies fall within a
relatively narrow range including the specific resonance frequency
obtained by tuning the orifice passage. Hence, the known fluid-filled
cylindrical engine mount is not satisfactory in terms of the
above-indicated different requirements. If the resonance frequency of the
orifice passage is tuned to provide a high damping effect with respect to
the engine shake and bounce or other low-frequency vibrations having
frequencies in the neighborhood of 10 Hz, the orifice passage operates as
if it was substantially closed when the engine mount receives medium- to
high-frequency vibrations whose frequencies are considerably higher than
10 Hz. In this case, therefore, the engine idling vibrations and booming
noises cannot be effectively damped or isolated. If the resonance
frequency of the orifice passage is tuned to exhibit a sufficiently low
dynamic spring constant with respect to the idling vibrations or other
medium-frequency vibrations of 20-50 Hz, then the engine mount is not
sufficiently capable of damping the low-frequency vibrations such as the
engine shake and bounce, and the dynamic spring constant exhibited by the
engine mount is not sufficiently low with respect to the high-frequency
vibrations such as the booming noises.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a
fluid-filled elastic mount which is capable of satisfying the
conventionally incompatible requirements, that is, which exhibits
excellent damping or isolating characteristics based on the resonance of
the fluid, for a wide range of frequency of the input vibrations.
The above object may be achieved according to the principle of the present
invention, which provides a fluid-filled elastic mount for flexibly
connecting two members, comprising: (a) an inner and an outer sleeve which
are radially spaced apart from each other and which are fixed to the two
members; (b) an elastic body interposed between the inner and outer
sleeves, for elastically connecting the inner and outer sleeves, the
elastic body at least partially defining a first pressure-receiving
chamber which is filled with a non-compressible fluid and which is
disposed between the inner and outer sleeves such that a pressure in the
fluid in said first pressure-receiving chamber changes due to elastic
deformation of the elastic body upon application of a vibrational load
between the inner and outer sleeves; (c) partition means for partially
defining at least one second pressure-receiving chamber between the inner
and outer sleeves and separating the first and second pressure-receiving
chambers from each other, each of the at least one second
pressure-receiving chamber being filled with the fluid, the partition
means including a flexible layer which is displaceable to thereby permit a
pressure change in the first pressure-receiving chamber to be transmitted
to the at least one second pressure-receiving chamber; (d) a flexible
diaphragm partially defining a variable-volume equilibrium chamber between
the inner and outer sleeves, the equilibrium chamber being spaced apart
from the first and second pressure-receiving chambers in a circumferential
direction of the inner and outer sleeves and filled with the
non-compressible fluid; (e) means for defining a first orifice passage for
fluid communication between the first pressure-receiving chamber and the
equilibrium chamber; and (f) means for defining a second orifice passage
for fluid communication between the each second pressure-receiving chamber
and the equilibrium chamber The first and second orifice passages are
tuned such that a ratio of a transverse cross sectional area to a length
of each second orifice passage is determined to be larger than that of the
first orifice passage.
In the fluid-filled elastic mount of the present invention constructed as
described above, the first orifice passage is tuned differently from each
second orifice passage, so that the differently tuned first and second
orifice passages are selectively brought into their operative state, to
permit the elastic mount to exhibit different vibration damping or
isolating characteristics, depending upon the frequency of the input
vibration. That is, the present elastic mount is capable of exhibiting
excellent operating characteristics based on the resonance of the fluid
flowing through the specifically tuned first and second orifice passages,
so as to deal with the input vibrations over a wide frequency range.
The partition means may further and preferably include at least one second
flexible layer, in addition to the flexible layer disposed as a first
flexible layer adjacent to the first pressure-receiving chamber. The at
least one second flexible layer at least partially defines a plurality of
second pressure-receiving chambers which are spaced from each other in a
radial direction of the inner and outer sleeves. The at least one second
flexible layer is displaceable to permit the pressure change in the first
pressure-receiving chamber to be successively transmitted to the plurality
of second pressure-receiving chambers, which communicate with the
equilibrium chamber through a plurality of second orifice passages,
respectively. The ratios of the transverse cross sectional area to the
length of the second orifice passage chambers are determined to increase
with a radial distance of the second pressure-receiving chambers from the
first pressure-receiving chamber.
In the above preferred form of the invention, the plurality of second
orifice passages for fluid communication of the respective two or more
second pressure-receiving chambers with the equilibrium chamber are
differently tuned as described above, whereby the elastic mount is capable
of exhibiting three or more different operating characteristics based on
the resonance of the fluid flowing through the three or more orifice
passages, so as to effectively damp or isolate three or more different
bands of the input vibrations.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other objects, features and advantages of the present
invention will be better understood by reading the following detailed
description of some presently preferred embodiments of the invention, when
considered in connection with the accompanying drawings, in which:
FIG. 1 is an elevational view in transverse cross section of one embodiment
of a fluid-filled elastic member of the present invention in the form of a
vehicle engine mount;
FIG. 2 is a cross sectional view taken along line 2--2 of FIG. 1;
FIG. 3 is a cross sectional view taken along line 3--3 of FIG. 1;
FIG. 4 is an elevational view in transverse cross section of an inner unit
of the engine mount of FIG. 1, which is prepared by vulcanization of an
elastic body between an inner and an intermediate sleeve;
FIG. 5 is a cross sectional view taken along line 5--5 of FIG. 4;
FIG. 6 is an elevational view in transverse cross section of an
orifice-defining sleeve incorporated in the engine mount of FIG. 1;
FIG. 7 is a cross sectional view taken along line 7--7 of FIG. 6;
FIG. 8 is a transverse cross sectional view of another embodiment of the
engine mount of the present invention;
FIG. 9 is a cross sectional view taken along line 9--9 of FIG. 8;
FIG. 10 is a transverse cross sectional view of a further embodiment of the
invention;
FIG. 11 is a cross sectional view taken along line 11--11 of FIG. 10; and
FIG. 12 is a cross sectional view taken along line 12--12 of FIG. 10.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring first to FIGS. 1 through 3, there is shown one embodiment of the
present invention in the form of an engine mount of an F-F (front-engine,
front-drive) motor vehicle. In these figures, reference numerals 10 and 12
denote an inner and an outer sleeve 10, 12, respectively. These inner and
outer sleeves 10, 12 are disposed such that the two sleeves are eccentric
with each other with a suitable radial offset distance. The inner and
outer sleeves 10, 12 are elastically connected to each other by an elastic
body 14 formed therebetween. The elastic body 14 has a generally annular
cross sectional shape and a relatively large wall thickness.
The engine mount is installed on the vehicle such that the outer sleeve 12
is fixed to an engine unit of the vehicle, while the inner sleeve 10 is
fixed to the body of the vehicle. Thus, the power unit is flexibly
connected to and supported by the vehicle body, in a vibrational damping
or isolating manner. With the engine mount installed on the vehicle, the
weight of the power unit acts on the outer sleeve 12 in the direction in
which the two sleeves 10, 12 are radially offset from each other, so that
the two sleeves 10, 12 are concentric or coaxial with each other. In this
condition, the engine mount primarily functions to damp or isolate
vibrations received in the direction of offset of the two sleeves 10, 12,
i.e., in the vertical direction (as seen in FIG. 1). This direction will
be referred to as "load-receiving direction" where appropriate.
Described more specifically, the inner sleeve 10 has a relatively large
radial wall thickness. Radially outwardly of this inner sleeve 10, there
is disposed a metallic intermediate sleeve 16 having a relatively small
wall thickness such that the sleeve 16 is eccentric with respect to the
inner sleeve 10, with a suitable radial offset distance. The elastic body
14 is formed by vulcanization such that the elastic body is bonded to the
outer surface of the inner sleeve and the inner surface of the
intermediate sleeve 16. Thus, an inner unit of the engine mount as shown
in FIGS. 4 and 5 is prepared.
The elastic body 14 has an axial void 18 formed in the axial direction
through a circumferential portion thereof at which the radial offset
distance between the inner and intermediate sleeves 10, 16 is relatively
small. The axial void 18 has a cross sectional shape as shown in FIG. 4,
so as to cover substantially a half of the circumference of the
intermediate sleeve 16. The axial void 18 functions to reduce a tensile
strain of the elastic body 14 due to elastic deformation caused by the
weight of the power unit acting on the outer sleeve 12 of the engine mount
when installed in position on the vehicle.
The elastic body 14 has a first pocket 20 formed in a circumferential part
of an axially intermediate portion thereof, at which the radial offset
distance between the inner and intermediate sleeves 10, 16 is relatively
large. That is, the first pocket 20 is located on one of diametrically
opposite sides of the inner sleeve 10, which is remote from the axial void
18. The first pocket 20 is open in the outer surface of the intermediate
sleeve 16, through a window 22 formed through the sleeve 16 in alignment
with the pocket 20.
A resonance member 24 having a resonance portion is fixed to an axially
intermediate portion of the inner sleeve 10, so that the resonance portion
is located within the first pocket 20 of the elastic body 14, so as to
substantially divide the depth of the first pocket 20 into upper and lower
halves. The resonance portion takes the form of a rectangular plate
extending in a plane which is parallel to the axial direction of the inner
sleeve 10 and substantially perpendicular to the direction of depth of the
pocket 20.
The elastic body 14 further has a second pocket 26 formed in a
circumferential part of the axially intermediate portion thereof, at which
the radial offset distance between the inner and intermediate sleeves 10,
16 is relatively small, and which is radially outward of the axial void
18. That is, the second pocket 26 is formed on the side of the inner
sleeve 10 which is diametrically opposite to the first pocket 20. In other
words, the first and second pockets 20, 26 are formed in the diametrically
opposite circumferential portions of the elastic body 14, as viewed in the
load-receiving direction. The second pocket 26 is open in the outer
surface of the intermediate sleeve 16, through a window 28 formed through
the sleeve 16 in alignment with the pocket 26. The axial void 18 and the
second pocket 26 cooperate with each other to define a relatively thin
wall which serves as a flexible diaphragm 32 which is easily elastically
deformable. The flexible diaphragm 32 defines the thickness of the axial
void 18 (as viewed in FIGS. 1 and 4), and the bottom of the second pocket
26.
The intermediate sleeve 16 has a circumferential groove 30 formed in an
axially intermediate portion thereof. As most clearly shown in FIG. 3, the
circumferential groove 30 is open radially outwardly of the sleeve 16 and
has a bottom whose diameter is smaller than the other portion of the
sleeve 16 by a suitable amount. This circumferential groove 30 connects
the windows 22, 28 through which the first and second pockets 20, 26 of
the elastic body 14 are open in the outer circumferential surface of the
sleeve 16.
The inner unit of FIGS. 4 and 5 constructed as described above is subjected
to a drawing operation on the intermediate sleeve 16 so as to radially
inwardly pre-compress the elastic body 14, before the outer sleeve 12 is
mounted on the inner unit. Further, a generally cylindrical
orifice-defining sleeve 38 as shown in FIGS. 6 and 7 is received in the
circumferential groove 30 of the intermediate sleeve 16. The
orifice-defining sleeve 38 consists of a generally semi-cylindrical first
orifice-defining member 34 and a semi-cylindrical second orifice-defining
member 36. The first orifice-defining member 34 is positioned on the side
of the window 22 and first pocket 20, while the second orifice-defining
member 36 is positioned on the side of the window 28 and the second pocket
26.
The orifice-defining sleeve 38 has a flat wall 46 on the first
orifice-defining member 34, as also shown in FIGS. 6 and 7. The flat wall
46 is positioned within the first pocket 20, as most clearly shown in FIG.
2, when the orifice-defining sleeve 38 is fitted in the circumferential
groove 30. As a result, the first pocket 20 is divided by the flat wall 46
into a radially inner and a radially outer portion. The flat wall 46 has
an aperture 44 in a central portion thereof.
A channel member 48 having a U-shaped opening 40 (as seen in FIG. 2) and a
bottom wall 42 rests on the radially outer surface of the flat wall 46 of
the orifice-defining sleeve 38, such that the bottom wall 42 are laid on
the flat wall 46. The bottom wall 42 has a window 50 aligned with the
aperture 44 of the flat wall 46. The window 50 and the aperture 44 are
filled with and thereby closed by a flexible layer 52 formed by
vulcanization. The flexible alayer 52 is reinforced by a suitable material
such as a canvas.
The orifice-defining sleeve 38 has a first arcuate U-groove 54 and a second
arcuate U-groove 56 formed in the outer circumferential surface thereof.
As shown in FIG. 6, the first U-groove 54 communicates at its opposite
ends with the inside of the orifice-defining sleeve 38, while the second
U-groove 56 communicates at one of its opposite ends with the inside of
the sleeve 38, and at the other end with the outside of the sleeve 38.
With the sleeve 38 received in the circumferential groove 30, the first
U-groove 54 communicates with the radially inner portion of the first
pocket 20 and the second pocket 26, while the second U-groove 56
communicates with the radially outer portion of the first pocket 20 and
the second pocket 26. As described below in detail, the first U-groove 54
has a relatively small width and a relatively large length, while the
second U-groove 56 has a relatively large width and a relatively small
length.
After the orifice-defining sleeve 38 constructed as described above is
fitted on the inner unit of FIGS. 4 and 5, the outer sleeve 12 is mounted
on the inner unit, in contact with the intermediate and orifice-defining
sleeve 16, 38. The outer sleeve 12 is subjected to a drawing operation to
radially inwardly compress the intermediate sleeve 16, whereby the outer
sleeve 12 is fixedly mounted on the inner unit with the orifice-defining
sleeve 38. The sealing rubber layer 58 formed on the inner circumferential
surface of the outer sleeve 12 provides fluid tightness between the outer
and intermediate sleeves 12, 16.
With the outer sleeve 12 fluid-tightly fitted on the inner unit, the first
pocket 20 and the second pocket 26 are both closed by the outer sleeve 12.
The closed pockets 20, 26 are filled with a suitable non-compressible
fluid, preferably a fluid having a high degree of fluidity or a relatively
low viscosity value, such as water, alkylene glycol, polyalkylene glycol,
silicone oil, or a mixture thereof. For example, the filling of the
pockets 20, 26 may be accomplished by mounting the outer sleeve 12 on the
inner unit, within a mass of the selected non-compressible fluid contained
in a suitable vessel.
With the flat wall 46 of the orifice-defining sleeve 38 extending through
the closed first pocket 20, a first pressure-receiving chamber 60 is
formed radially inwardly of the flat wall 46. Upon application of a
vibrational load between the inner and outer sleeves 10, 12, the pressure
of the fluid within the first pressure-receiving chamber 60 changes due to
elastic deformation of the elastic body 14 caused by the vibrational load.
The first pressure-receiving chamber 60 is substantially divided by the
resonance portion of the resonance member 24. Namely, a small clearance is
provided between the outer periphery of the resonance portion of the
resonance member 24 and the inner surface of the pressure-receiving
chamber 60. This small clearance around the periphery of the resonance
portion serves as a restricted portion 63 of the pressure-receiving
chamber 60. This restricted portion 63 permits restricted flows of the
fluid therethrough upon application of the vibrational load.
Further, a second pressure-receiving chamber 62 is formed radially
outwardly of the flat wall 46 of the orifice-defining sleeve 38. This
second pressure-receiving chamber 62 is partially defined by the opening
40 of the U-shaped channel member 48. When, the pressure in the first
pressure-receiving chamber 60 changes upon application of a vibrational
load to the engine mount, the pressure of the fluid within the second
pressure-receiving chamber 60 changes due to elastic deformation or
displacement of the flexible layer 52 which partially defines the two
pressure-receiving chambers 60, 62.
With the second pocket 26 closed by the outer sleeve 12, there is formed a
variable-volume equilibrium chamber 64. The flexible diaphragm 32 absorbs
or accommodates a change in the pressure of the fluid in the equilibrium
chamber 64. Namely, elastic deformation or displacement of the flexible
diaphragm 32 upon application of the vibrational load permits changes in
the volume of the equilibrium chamber 64, thereby absorbing the pressure
change in the equilibrium chamber 64.
The outer sleeve 12 also closes the first and second arcuate U-grooves 54,
56, thereby providing a first orifice passage 66 corresponding to the
U-groove 54, and a second orifice passage 68 corresponding to the U-groove
56. More particularly, the first orifice passage 66 effects fluid
communication between the first pressure-receiving chamber 60 and the
equilibrium chamber 64, and permits the fluid to flow between these two
chambers 60, 64 therethrough. On the other hand, the second orifice
passage 68 effects fluid communication between the second
pressure-receiving chamber 62 and the equilibrium chamber 64, and permits
the fluid to flow between these two chambers 62, 64 therethrough.
The first orifice passage 66 is dimensioned or tuned such that the ratio of
the transverse cross sectional area to the length is smaller than that of
the second orifice passage 68. More specifically, the first orifice
passage 66 is tuned so that the engine mount exhibits a high damping
effect based on the resonance of the fluid flowing through the passage 66,
with respect to low-frequency vibrations such as engine shake and bounce,
whose frequencies are in the neighborhood of 10 Hz. On the other hand, the
second orifice passage 68 is tuned so that the engine mount exhibits a
sufficiently low dynamic spring constant based on the resonance of the
fluid flowing through the passage 68, with respect to medium-frequency
vibrations such as engine idling vibration, whose frequencies fall within
a range of 20-50 Hz.
When a vibrational load is applied between the inner and outer sleeves 10,
12 of the thus constructed engine mount, a periodic change in the fluid
pressure occurs in the first pressure-receiving chamber 60, causing a
pressure difference between the first pressure-receiving and equilibrium
chambers 60, 64, whereby the fluid is forced to flow between these
chambers 60, 64 through the first orifice passage 66. Further, the
pressure change in the first pressure-receiving chamber 60 is more or less
transmitted to the second pressure-receiving chamber 62 by means of the
periodic elastic oscillatory displacement of the flexible layer 52,
whereby a similar pressure difference occurs between the second
pressure-receiving chamber 62 and the equilibrium chamber 64, causing the
fluid to flow through the second orifice passage 68.
Where the frequency of the input vibration is lower than the tuned
resonance frequency of the first orifice passage 66, the pressure change
in the first pressure-receiving chamber 60 is not completely accommodated
by the elastic displacement of the flexible layer 52, but the pressure
change causes the fluid to flow through the first orifice passage 66,
since the fluid flow resistance of the first orifice passage 66 is
relatively low. Consequently, the relatively low-frequency vibrations such
as engine shake can be effectively damped based on the resonance of the
fluid flowing through the first orifice passage 66.
Where the frequency of the input vibration is higher than the tuned
resonance frequency of the first orifice passage 66, the fluid flow
resistance of the passage 66 is considerably increased, and the passage 66
operates as if it was substantially closed. Consequently, the pressure
change caused in the first pressure-receiving chamber 60 is transmitted to
the second pressure-receiving chamber 62 through the oscillating flexible
layer 52, causing the fluid to flow through the second orifice passage 68.
Therefore, the present arrangement is effective to minimize an increase in
the dynamic spring constant of the engine mount which would otherwise
occur due to substantial closure of the first orifice passage 66 upon
application of a medium- or high-frequency vibration. Namely, the present
engine mount is capable of exhibiting an effectively lowered dynamic
spring constant based on the resonance of the fluid flowing through the
second orifice passage 68, with respect to medium-frequency vibrations
such as engine idling vibration.
It will be understood from the above description that the present engine
mount exhibits not only a high damping effect with respect to
low-frequency vibrations such as engine shake and bounce, but also a
sufficiently low dynamic spring constant with respect to medium-frequency
vibrations such as engine idling vibration. These two different operating
characteristics are both derived from the resonance of the fluid. Thus,
the present engine mount provides improved vibration damping or isolating
characteristics over a wide range of frequency of the input vibrations,
thereby assuring significantly improved driving comfort.
It is also noted that the first and second orifice passages 66, 68 are
automatically selectively brought into their operative state, depending
upon the frequency of the received vibration, without having to use any
actuator for controlling the passages 66, 68. Accordingly, the present
engine mount having the excellent damping or isolating characteristics
derived from the passages 66, 68 can be available at a relatively low cost
with a relatively simple construction. In this respect, the instant
fluid-filled engine mount has an industrial significance.
Further, the instant engine mount is capable of exhibiting a low dynamic
spring constant with respect to even high-frequency vibrations such as
beats or engine-transmitted noises whose vibrations are higher than the
tuned resonance frequency of the second orifice passage 68. That is, this
excellent characteristic with respect to the high-frequency vibrations can
be obtained by suitably tuning the dimensions and configuration of the
restricted portion 63 formed around the resonance portion of the resonance
member 24 within the first pressure-receiving chamber 60, so that the
high-frequency vibrations are effectively isolated based on the resonance
of the fluid flowing through the resonance portion 63.
Modified embodiments of the vehicle engine mount of the present invention
will be described, by reference to FIGS. 8-12, in which the same reference
numerals as used in FIGS. 1-7 will be used to identify the functionally
corresponding components. No redundant description of these components
will be provided.
Referring to FIGS. 8 and 9 illustrating the second embodiment of the
invention, the equilibrium chamber 64 provided in the first embodiment is
replaced by two mutually independent equilibrium chambers 70, 72. The
first equilibrium chamber 70 communicates with the first
pressure-receiving chamber 60 through the first orifice passage 66, while
the second equilibrium chamber 72 communicates with the second
pressure-receiving chamber 62 through the second orifice passage 68.
While the first orifice passage 66 in this second embodiment has a smaller
length than that in the first embodiment, the transverse cross sectional
area is accordingly reduced so that the ratio of the transverse cross
sectional area to the length is substantially equal to that in the first
embodiment. Hence, the first orifice passage 66 of the instant embodiment
provides a similar damping effect with re | | |
