Fluid-filled engine mount device

A fluid-filled engine mount device comprises an annular elastic block having inner and outer peripheral sections one of which is connected to a power unit side and the other connected to a vehicle body side; an annular elastic member connected to the elastic block; a partition plate member connected to and elastically supported by the annular elastic member, the partition plate member being formed with an orifice and defining between it and the elastic block a fluid chamber capable of being filled with a fluid; and a diaphragm member disposed in connection with the partition plate member and defining between it and the partition plate member an auxiliary chamber capable of being filled with the fluid, the auxiliary chamber being in communication with the fluid chamber through the orifice thereby effectively damping high frequency fine vibration applied from a power unit.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a fluid-filled engine mount device through which 
a power unit is mounted on a support body, and more particularly to an 
engine mount device damping high frequency vibration transmitted from the 
power unit. 
2. Description of the Prior Art 
Fluid-filled engine mount devices have been proposed for damping vibration 
generated in relation to an automotive engine and a vehicle body frame. In 
these engine mount devices, a rubber block is used to elastically support 
the engine, while defining a fluid chamber filled with a fluid such as a 
liquid. The fluid chamber is separate from an auxiliary chamber by a 
partition plate member, but these chambers communicate through an orifice 
in the partition plate member. Accordingly, elastic deformation of the 
rubber block, due to low frequency input vibration, causes a volume change 
in the fluid chamber, creating fluid movement between the fluid and 
auxiliary chambers, damping the low frequency vibration. However, high 
frequency input vibration from the engine is not effectively absorbed by 
the above-mentioned engine mount device and can be transmitted to the 
vehicle body frame, causing a booming noise within the vehicle passenger 
compartment and deteriorating riding comfort. 
SUMMARY OF THE INVENTION 
According to the present invention, an engine mount device comprises an 
annular elastic block having inner and outer peripheral sections one of 
which is connected to a power unit side and the other connected to a 
support body side. An annular elastic member is connected to the elastic 
block. A partition plate is connected to and elastically supported by the 
annular elastic block. The partition plate is formed with an orifice. The 
partition plate defines with the elastic block a fluid chamber at least a 
part of which is capable of being filled with a fluid. Additionally, a 
diaphragm is disposed in connection with the partition plate, defining 
between it and the partition plate an auxiliary chamber at least a part of 
which is capable of being filled with the fluid. The auxiliary chamber is 
in communication with the fluid chamber through the partition plate 
orifice. 
With the above engine mount device of the invention, even high frequency 
vibration from a power unit can be effectively absorbed, preventing high 
frequency fine vibration from being transmitted to the vehicle body side. 
This suppresses fine vibration of the vehicle body and booming noise 
within a vehicle passenger compartment, improving comfort.

DETAILED DESCRIPTION OF THE INVENTION 
To facilitate understanding of the present invention, a brief reference 
will be made to a conventional fluid-filled engine mount device, depicted 
in FIG. 1. The conventional engine mount device includes a ring-shaped 
rubber block 1 formed with inner and outer peripheral surfaces to which 
inner and outer frame members 2, 3 are respectively secured by 
vulcanization. Fixed to the inner frame member 2 is upper base plate 4 
connected to a power unit (not shown). A lower base plate 5 is fixed to 
the outer frame member 3 by caulking the peripheral section of the lower 
base plate member 5 over the lower end edge of the outer frame member 3. 
By this caulking, a partition plate member 6 and a diaphragm member 7 are 
peripherally secured to the outer frame member end edge and the lower 
plate member peripheral section as shown in the drawing. A fluid chamber 8 
is defined between the elastic block 1 and the partition plate member 6. 
Additionally, an auxiliary chamber 9 is defined between the partition 
plate member 6 and the diaphragm member 7. The fluid and auxiliary 
chambers 8, 9 are in communication with each other through an orifice 10 
formed in partition plate member 6. The fluid and auxiliary chambers 8, 9 
are filled with a fluid. Formed between the diaphragm member 7 and the 
lower base plate member 5 is an atmospheric chamber 11 which is in 
communication with atmospheric air through an opening. The reference 
numeral 12 denotes a bolt for connecting the upper base plate member 4 to 
the power unit side, and the reference numeral 13 a bolt for connecting 
the lower base plate member 5 to the vehicle body side such as a body 
frame. 
With the thus arranged conventional fluid-filled engine mount device, when 
the distance between the upper and lower base plate members 4, 5 varies 
under the action of input vibration, the rubber block 1 elastically 
deforms to vary the volume of fluid chamber 8. As a result, fluid flows 
between the fluid and auxiliary chambers 8, 9 through orifice 10, in which 
the fluid undergoes flow resistance during its passage through the 
orifice, thereby damping the input vibration. 
Since such vibration damping force in general acts in one direction, 
particularly only in the upward and downward direction, it has been 
proposed to decrease the rigidity of the rubber block in its upward and 
downward direction in order to increase an absorbing effect to high 
frequency fine vibration. However, it is difficult to significantly 
decrease the rigidity of rubber block 1 in the horizontal direction; 
otherwise the power unit can swing. As a result the shape of the rubber 
block 1 of the conventional engine mount device is selected as shown in 
FIG. 1 in order to obtain a high shearing effect in the upward and 
downward direction and a high compression effect in the horizontal 
direction and the like. 
During input of high frequency fine vibration, the rate of volume change in 
the fluid chamber 8 is higher to increase the flow resistance of the fluid 
passing through the orifice 10, thereby confining the fluid within the 
fluid chamber 8. However, the elastic deformation of the rubber block 1 
causes the volume change in the fluid chamber 8, accompanying with the 
pressure variation within the fluid chamber 8. This fluid chamber pressure 
variation is propagated and transmitted to the partition plate member 6, 
and finally transmitted through the lower base plate member 5 to the 
vehicle body side. Therefore, the conventional engine mount device has 
encountered the disadvantage in which the high frequency fine vibration 
generated in the power unit side is considerably transmitted to the 
vehicle body side. 
In view of the above description of the conventional fluid-filled engine 
mount device, reference is made to FIG. 2, wherein a preferred embodiment 
of a fluid-filled engine mount device of the present invention is 
illustrated by the reference numeral 20. The engine mount device 20 
comprises an annular or ring-shaped block made of elastic (elastomeric) or 
resilient material such as rubber. The elastic block 22 is generally 
umbrella shaped and formed at a central section thereof with a 
frustoconical opening (no numeral) whose axis is aligned with that of the 
elastic block 22. The elastic block 22 is formed with an inner peripheral 
frustoconical surface 22a and an outer peripheral surface 22b of 
frustoconical shape; accordingly, the inner and outer peripheral surfaces 
22a, 22b are generally coaxial and parallel with each other. Additionally, 
the upper and lower surfaces 22c, 22d of the elastic block 22 are also 
generally of the frustoconical shape and generally parallel with each 
other. 
An inner frame member 24 is secured to the inner peripheral surface 22a of 
the elastic block 22 by vulcanization. The inner frame member 24 is 
generally cup-shaped and so located that its bottom section closes the 
opening of the elastic block 22. Connected to the inner frame member 24 is 
an upper base plate member 26 fixed to a power unit side or an automotive 
internal combustion engine side by means of a bolt 28. A generally annular 
outer frame member 30 is secured to the outer peripheral surface 22b 
vulcanization. The outer frame member 30 is formed with an annular flange 
30a with the axis of the elastic block 22 perpendicular to the flange 
section. The flange section 30a is fixed onto a vehicle body side such as 
a vehicle body frame 32. In this connection, the engine mount device 20 is 
installed by means of bolts and nuts 34 with the axis of the elastic block 
22 perpendicular to the flat surface of the vehicle body frame 32. 
As shown, the elastic block 22 is integrally formed at its lower peripheral 
part with a cylindrical elastic section or member 36 which extends 
downwardly in the axial direction of the engine mount device 20. The 
cylindrical elastic section 36 is made of the same material as in the 
elastic block 22, but is lower in ridigity than the elastic block 22. A 
partition plate member 38 is securely connected at its peripheral section 
with the free end portion of the cylindrical elastic section 36, 
maintaining fluid-tight seal therebetween. The partition plate member 38 
is formed at its central portion with an orifice 38a. A fluid chamber 40 
is defined between the partition plate member 38 and the lower surface 22d 
of the elastic block 22 in combination with the bottom section of the 
inner frame member 24. A diaphragm member 42 is securely connected at its 
peripheral section with the partition plate member 38, maintaining 
therebetween a fluid-tight seal. An auxiliary chamber 44 is defined 
between the diaphragm member 42 and the partition plate member 38. The 
auxiliary chamber 44 is in communication with the fluid chamber 40 through 
the partition plate member orifice 38a. The fluid and auxiliary chambers 
40, 44 are filled with a fluid, usually with a liquid. Securing the 
partition plate member 38 and the diaphragm member 42 in position is 
achieved by caulking the peripheral section of a bottom plate member 46 
over an annular plate member 48 which is secured to the cylindrical 
elastic section 36 of the elastic block 22 by vulcanization. The bottom 
plate member 46 defines between it and the diaphragm member 42 an 
atmospheric chamber 50 in communication with atmospheric air through an 
opening formed in the bottom plate member 46. 
The manner of operation of the engine mount device 20 will be discussed 
hereinafter. 
The elastic block 22 is designed to support the power unit in the upward 
and downward direction or the axial direction of the elastic block 22 
mainly by its shearing stress and in the horizontal direction or the 
direction perpendicular to the axis of the elastic block 22 mainly by its 
compressive stress. Under this action, the rubber block 22 elastically 
deforms in the upward and downward direction when input vibration is 
applied thereto. In case where this input vibration is of low frequency as 
during bound and rebound of the vehicle body, the volume change of the 
fluid chamber 40 occurs, so that fluid movement takes place between the 
fluid chamber 40 and the auxiliary chamber 44 through the partition plate 
member orifice 38a, thereby generating flow resistance of the fluid 
passing through the orifice 38a. This flow resistance damps the input 
vibration applied to the engine mount device 20. 
In case where the input vibration is from the power unit and of high 
frequency, the amount of deformation of the elastic block 22 is smaller 
due to the fact that the amplitude of the input vibration is smaller. This 
causes a smaller pressure variation in the fluid chamber 40. However, the 
rate of pressure variation within the fluid chamber 40 is higher due to 
the high frequency vibration, which causes the flow resistance of the 
fluid through the orifice 38a to become higher, thus combining the fluid 
within the fluid chamber 40. Under this condition, the volume of the fluid 
chamber 40 changes due to the elastic deformation of the elastic block 22, 
which seems to make the pressure variation within the fluid chamber 40. 
However, in response to this pressure variation within the fluid chamber 
40, the cylindrical elastic section 36 of the elastic block 22 expands and 
contracts in the upward and downward direction, thereby, in fact, 
suppressing the pressure variation within the fluid chamber 40. Thus, the 
high frequency fine vibration applied to the engine mount device 20 is 
certainly absorbed by the elastic deformation of the cylindrical elastic 
section 36. Furthermore, since the pressure variation is not made in the 
fluid chamber 40, there is no transmission of the high frequency fine 
vibration due to the pressure variation within the fluid chamber 40. As a 
result, the high frequency fine vibration from the power unit is 
effectively prevented form being transmitted to the vehicle body side. 
FIG. 3 illustrates another embodiment of the engine mount device according 
to the present invention. In this embodiment, a lower base plate member 52 
is securely connected at its peripheral section with a peripheral flange 
section 30b of the outer frame member 30 by caulking or crimping the lower 
base plate member peripheral section over the outer frame member 
peripheral flange section. By this caulking, an annular plate member 54 is 
secured between the outer frame member flange section 30b and the lower 
base plate member 52, and the diaphragm member 42 is securely connected to 
the annular plate member 54. In this case, the partition plate member 38' 
is connected to the annular plate member 54 through an annular elastic 
member 36' so that the partition plate member 54 is movably supported 
while defining the fluid chamber 40 between the elastic block 22 (with the 
inner frame member 24) and the partition plate member 38' in combination 
with the annular elastic member 36' and the annular member 54. In this 
connection, the auxiliary chamber 44 is defined between the diaphragm 
member 42 and the partition plate member 38' in combination with the 
members 36', 54. It will be understood that the atmospheric chamber 50 is 
formed between the diaphragm member 42 and the inner surface of the lower 
base plate member 52. The lower base plate member 52 is connected to the 
vehicle body side by means of a bolt 56 secured thereto. With this 
arrangement, the movement of the partition plate member 38' due to the 
pressure variation within the pressure chamber 40 is made under the 
elastic deformation of the annular elastic member 36' in the shearing 
direction thereof. It will be understood that the configuration and 
operation of the other parts of the engine mount device of this embodiment 
are similar to those of the device shown in FIG. 2. 
As is appreciated from the above, according to the present invention, the 
partition plate member of the engine mount device is elastically supported 
by an annular elastic member. Therefore, even if fine pressure variation 
is generated within the fluid chamber of the engine mount device during 
the input of high frequency fine vibration, the pressure variation can be 
absorbed by virtue of the elastic deformation of the annular elastic 
member, thereby preventing the transmission of the vibration to the 
vehicle body side. This effectively suppresses the fine vibration of the 
vehicle body and booming noise within a passenger compartment, thus 
improving the vehicle comfortableness to ride in. Furthermore, according 
to the present invention, since the pressure variation within the pressure 
chamber can be absorbed, the elastic block is not expected to absorb the 
pressure variation, which reduces the requirements to the elastic block in 
its designing. This increases the freedom in selecting the ratio between 
the rigidies in the vertical direction and in the direction perpendicular 
to the vertical direction.