Apparatus for supporting a vibrating object

An apparatus for supporting a vibrating object (, e.g., a power unit of a vehicle) which can reduce a plurality of vibrations transmitted therethrough by changing the resonant frequency of a dynamic fluid damper constituted by the apparatus according to a frequency change of the vibrations. The apparatus comprises: (a) a first fluid chamber located on the vibrating object and having at least one elastic wall thereof; (b) a second fluid chamber located on another object and having at least one elastic wall thereof; (c) a partitioning member disposed between the first and second fluid chambers; (d) a plurality of communication passages disposed through the partitioning member in parallel with each other for communicating the first and second chambers; and (e) communication passage open/close envelope which opens or close at least one of the communication passages according to a difference between vibration amplitudes of vibrations transmitted thereinto, whereby a plurality of vibrations transmitted through the apparatus are suppressed.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an apparatus for supporting a vibrating 
object applicable but not exclusively to an apparatus for supporting a 
power unit (, e.g., engine) of an automotive vehicle which effectively 
reduces various vibrations transmitted through the apparatus and mainly 
caused by the power unit. 
2. Description of the Prior Art 
Conventional apparata for supporting vibrating objects such as power units 
of automotive vehicles are exemplified by a Japanese Patent Application 
Unexamined Open No. Sho 60-113836 published on June 20, 1985. 
The above-identified Japanese Patent Application document discloses a fluid 
sealed mount having a structure such that an elastic object is intervened 
between an inner cylindrical member and an outer cylindrical member 
disposed outside the inner cylindrical member and a first fluid chamber 
and second fluid chamber, in both of which a noncompressible fluid is 
filled and between both of which the noncompressible fluid can mutually be 
moved, are formed on the elastic object. 
Furthermore, a plurality of communication passages are installed in the 
fluid sealed mount for communicating the above-described first fluid 
chamber and second chamber and valve means is also installed which is 
capable of switching between two states, one state being a state in which 
at least one of the plurality of communication passages is closed and the 
other state being a state in which the communication passage is not closed 
(open) and which is operated to switch from the above-described open state 
to the above-described close state by means of a communication action of 
the above-described noncompressible fluid. 
However, since in such a conventional vibrating object supporting apparatus 
as described above vibrations mainly caused by the vibrating object are 
absorbed essentially by means of the elastic object when the valve means 
is in the open state and are damped by means of a flow resistance 
generated when the fluid flows through the other communication passages 
which are not in the closed state with the valve means being switched to 
the closed state, a fluid dynamic damper effect to be described later has 
not completely been recognized. 
Therefore, although a transmission of a particular frequency vibration 
through the apparatus is accidentally suppressed, transmissions of a 
plurality of vibrations having particular frequencies through the 
supporting apparatus cannot effectively be reduced. 
In addition, since the valve means operated to switch between the open and 
closed states through the flow action of the fluid is used in the 
above-described supporting apparatus, an operation resistance of the valve 
means become increased and such a problem as sticking of the valve means 
in an intermediate position between the open and closed states occurs when 
a large external force is applied to the valve means which is derived from 
a load supporting or vibration inputs. Consequently, a smooth switching 
action of the valve means cannot be achieved. 
The performance demanded for most effectively utilizing the apparatus for 
supporting the vibrating object of such a fluid sealing type will be 
described below before explaining the present invention. 
The apparatus for supporting the vibrating object is required to have two 
functions simultaneously; a vibration prevention function for preventing a 
transmission of minute vibrations achievable by the reduction of a dynamic 
spring constant of a fluid dynamic damper and a vibration damping function 
for damping large vibrations achievable by an action of the fluid dynamic 
damper. The vibration prevention function required for the vibrating 
object supporting apparatus is achieved by a flow of an internal sealed 
fluid in the fluid chambers through communication passages along a 
vibration input direction so that the dynamic spring constant is reduced. 
The damping function also required for the apparatus is achieved by the 
fluid dynamic damper constituted by a fluid within the communication 
passages as a fluid mass and elasticity caused by the flow of the sealed 
fluid between the chambers and consequent expansion and constriction of 
the chambers as a fluid spring. Therefore, it is most effective for the 
apparatus to utilize both, so called, vibration prevention and vibration 
damping functions. 
In a case where the fluid chamber is partitioned into two chambers and an 
orifice is provided for communicating both chambers, the fluid dynamic 
damper is formed on the basis of a fluid within the orifice and a resonant 
frequency F of the fluid dynamic damper is expressed as follows: 
##EQU1## 
wherein K denotes the fluid dynamic spring constant and M denotes an 
equivalent mass of a fluid within the orifice. The above-described 
equivalent mass of the fluid M is determined by an actual mass of fluid 
within the communication passages and by a relationship of a cross 
sectional area of the fluid chamber and a cross sectional area of the 
orifice. 
In other words, the resonant frequency F can be varied if either or both of 
the fluid spring constant K and fluid mass within the communication 
passages are changed. 
Therefore, it is an essential requirement for the performance imposed on 
the fluid-sealed type vibrating object supporting apparatus to enable an 
arbitrary setting state of the resonant frequency to suppress the 
plurality of vibrations and, in addition, to enable a smooth change of the 
resonant frequency under a strict environment of receiving strong 
vibration inputs. 
SUMMARY OF THE INVENTION 
With the above-described problems in mind, it is an object of the present 
invention to provide an apparatus for supporting a vibrating object which 
can achieve a smooth change of its resonant frequency to reduce the 
plurality of vibrations. 
It is another object of the present invention to provide an apparatus for 
supporting a vibrating object which can arbitrary set the resonant 
frequency with simple construction. 
The above-described objects can be achieved by providing an apparatus 
comprising: (a) a first fluid chamber located on a vibrating source and 
having at least one elastic wall thereof; (b) a second fluid chamber 
located on another object facing the vibrating source and having at least 
one elastic wall thereof; (c) a partitioning member disposed between the 
first and second fluid chambers; (d) a plurality of communication passages 
juxtaposed through the partitioning member for communicating the first and 
second chambers; and (e) means for opening and closing at least one of the 
communication passages according to a difference between vibration 
amplitudes of vibrations inputted thereto. 
The above-described objects can be achieved by providing an apparatus 
comprising: (a) first means for supporting a vibrating object on another 
object, the first means having a resonant frequency; and (b) second means 
included in the first means for receiving an amplitude of a vibration from 
either of the objects and for operating to change the resonant frequency 
of the first means according to a difference in amplitude between the 
received vibrations thereof.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENT 
Reference will hereinafter be made to the drawings in order to facilitate 
understanding of the present invention. 
The essential performance imposed on the apparatus for supporting the 
vibrating object has been described in the Description of the Prior Art. 
FIGS. 1 and 2 show a preferred embodiment according to the present 
invention. 
The apparatus for supporting the vibrating object shown in FIGS. 1 and 2 is 
applicable to an apparatus for supporting a power unit mounted on an 
automotive vehicle. 
The power unit supporting apparatus S is intervened between a vehicle body 
1 and power unit 2. As shown in FIG. 1, the power unit supporting 
apparatus S includes an internal cylinder 10, an outside cylinder 20, 
elastic object 30, first fluid chamber 40, second fluid chamber 50, first 
communication passage 60, second communication passage 70, sealed fluid W, 
and opening/closing means 80, 80'. The individual elements will be 
described below. 
The internal cylinder 10 is a cylindrical member fixed on the vehicle body 
1 and comprises: a first internal cylinder 11; and a second internal 
cylinder 12 inserted along an outer periphery of the first internal 
cylinder 11 under pressure. The first internal cylinder 11 is formed with 
a first spiral groove 13 and second spiral groove 14 at its peripheral 
part as shown in FIG. 3, so that a first communication passage 60 and 
second communication passage 70 are formed with the second internal 
cylinder 12 inserted so as to block the grooves under pressure. 
The second internal cylinder 12 is provided with first fluid holes 15, 15' 
at its peripheral part and second fluid holes 16, 16', the first and 
second fluid holes providing fluid flow ports for the first and second 
communication passages 60 and 70. 
The outer envelope 20 is a cylindrical member fixed on the power unit 2 and 
is constituted by first outer envelopes 21, 21 in the form of rings to 
which the above-described elastic object 30 is adhered, a second outer 
envelope 22 covering the whole elastic object 30. 
The elastic object 30 is vulcanized and adhered between the second internal 
cylinder 12 and first outer envelopes 21, 21. A first fluid chamber 40 and 
second fluid chamber 50 are formed within the elastic object 30, elastic 
object partitioning parts 30a, 30b and above-described circular cylinder 
10 constituting a partitioning member. 
The first communication passage 60 is formed with the above-described first 
fluid holes 15, 15' of the above-described internal envelope 10 
constituting the partitioning member and first spiral groove 13. The first 
communication passage 60 is a spiral communication path having a long 
length of the passage and a small cross sectional area of flow passage. 
The second communication passage 70 is, in turn, formed with the 
above-described second fluid holes 16, 16' constituting the partitioning 
member and second spiral groove 14. The second communication passage 70 is 
a spiral communication path having a long length of the passage and a 
large cross sectional area of the flow passage. It is noted that the first 
communication passage 60 and second communication passage 70 are installed 
so as to communicate between the first fluid chamber 40 and second fluid 
chamber 50. 
Such a noncompressible fluid as a nonfreezing solution is used as the 
sealed fluid W which has been sealed into both of the above-described 
fluid chambers 40, 50 and both communication passages 60, 70. 
The open/close means 80, 80' provides means for opening the above-described 
second communication passage 70 when an idling vibration input occurs and 
means for closing the second communication passage 70 when an engine 
shaking vibration input occurs. In this embodiment, the open/close means 
80, 80' includes introduction envelopes 81, 81', stop rubber members 82, 
82', and rubber film 83. The introduction envelopes 81, 81' are installed 
at positions of the above-described second fluid holes 16, 16' so as to 
project toward the inner surface of the second outer envelope 22. The 
projecting ends of the introduction envelopes 81, 81' are baked with the 
stop rubber members 82, 82', respectively. 
The rubber film 83 is baked to the inner surface of the second outer 
envelope 22. Clearances t, t' between the rubber film 83 and stop rubber 
members 82, 82' under a static weight supporting condition have slightly 
smaller lengths than those of the vibration amplitudes of the engine 
shaking vibration such that both stop rubber member 82 (or 82') and rubber 
film 83 are not brought in contact with each other when the idling 
vibration input occurs and such that they are brought in contact with each 
other when the engine shaking vibration input occurs. The amplitude 
remaining after both rubber members 82 (or 82') and 83 are contacted with 
each other is absorbed through an elastic deformation thereof. 
The resonant frequency is set in the following way by a utilization of flow 
of the sealed fluid W within the first communication passage 60 and second 
communication passage 70. 
In general, the resonant frequency F of the fluid dynamic damper can be 
expressed as follows: 
##EQU2## 
wherein K denotes the fluid spring constant and M denotes an equivalent 
mass of fluid within a communication passage. 
The fluid equivalent mass M within the communication passage can be 
expressed as follows with reference to FIG. 4: 
##EQU3## 
wherein m denotes an actual mass of the sealed fluid, A.sub.1 denotes a 
cross sectional area of the fluid chamber, and A.sub.2 denotes a cross 
sectional area of the communication passage. 
In addition, the sealed fluid mass m can be expressed as follows: 
EQU m=.rho..times.A.sub.2 .times.l (3) 
wherein .rho. denotes a specific gravity of the sealed fluid and l denotes 
a length of the communication passage. 
When the equations (2) and (3) are substituted into the equation (1), the 
following equation is established. 
##EQU4## 
If the length of the communication passage l, cross sectional area A.sub.1 
of the fluid chamber, and fluid spring constant K are constant, the 
following equation is established. 
EQU F=.alpha..times.A.sub.2 (5) 
wherein .alpha. denotes a constant. 
In other words, if the cross sectional area A.sub.2 of the communication 
passage is enlarged, the resonant frequency F is increased. 
Hence, in the idling operating state the open/close means 80, 80' 
constituting the apparatus in the embodiment is left open and the cross 
sectional area of the flow passage is achieved by the sum of the two 
communication passages 60, 70. Consequently, the resonant frequency 
f.sub.1 is increased so that the frequency f.sub.2 at which the dynamic 
spring constant is lowest and which appears on a slightly lower frequency 
band than the resonant frequency f.sub.1 coincides with approximately 25 
Hertz which is a frequency of a second harmonic component of the engine 
revolution speed at the time of engine idling state, as shown in FIG. 5. 
In addition, when the engine shaking vibration input occurs, the open/close 
means 80, 80' is closed in response to a vibration amplitude of the engine 
shaking vibration. The cross sectional area of the flow passage is derived 
from only the first communication passage 60. Consequently, the resonant 
frequency f.sub.1 ' is settable approximately to 11 Hertz which is a 
frequency of the engine shaking vibration generated during vehicle 
running, as shown in FIG. 6(B). 
If the ratio of cross sectional area of flow passage at the time of engine 
idling state and at the time of engine shaking is set approximately to 
1:6, the apparatus can set the resonant frequency at the above-described 
two points. 
Next, the operation of the preferred embodiment will be described below. 
(A) Idling 
When the engine is in the idling state after the engine starts, the 
vibration amplitude of the idling vibration is smaller than each of the 
clearances t, t' and the open/close means 80, 80' are left open. 
Since, when the open/close means 80, 80' is in the open state, the 
frequency f.sub.2 at which the dynamic spring constant is lowest coincides 
approximately with the frequency band (approximately 25 Hz) of the second 
harmonic component of the engine revolution speed at the time of the 
engine idling state, the idling vibration can be reduced by having a 
vibration prevention function caused by the reduction of the dynamic 
spring constant. 
It should be noted that a high vibration prevention function with a large 
reduction of the dynamic spring constant can be achieved by the large flow 
passage cross sectional area of both communication passages 60, 70 and by 
the increased fluidity when the sealed fluid W passes through both 
communication passages 60, 70. 
In addition, such a vibration input as the vibration frequency equal to or 
more than 25 Hz and falling within the frequency band including a 
frequency higher or lower than the resonant frequency f.sub.1 can be 
damped through the vibration damping function caused by the action of the 
fluid dynamic damper when the engine is in the idling state. 
(B) Engine Shaking 
When the engine shaking vibration having a frequency slightly higher or 
lower than the vibration frequency of 11 Hz occurs, the vibration 
amplitude of the engine shaking vibration is larger than the length of 
each clearance t, t'. The open/close means 80, 80' located on the first 
fluid chamber 40 and second fluid chamber 50 are alternatingly closed 
according to the vibration amplitude. Although in such an alternate close 
and open state the second communication passage 70 is temporarily open 
while one of the open/close means 80, 80' is closed (or open) and 
simultaneously the other open/close means 80, 80' is open (or closed), the 
sealed fluid W does not reciprocate within the second communication 
passage 70 due to the closing action of the open/close means so that the 
action of the dynamic damper is not achieved by means of the second 
communication passage 70. 
Since the resonant frequency f.sub.1 ' set through the sealed fluid W 
moving within the first communication passage 60 coincides approximately 
with the engine shaking vibration frequency (about 11 Hz) when the 
open/close means 80, 80' is closed, the engine shaking vibration can be 
damped with the damping function caused by the fluid dynamic damper 
action. 
In addition, when the vehicle runs, the vibration input having a frequency 
slightly higher or lower than the frequency f.sub.2 ' below 11 Hertz can 
be damped with the damping function provided due to the reduction of the 
dynamic spring constant as shown in FIG. 6(A). 
In this way, since the open/close means 80, 80' in the power unit 
supporting apparatus S of the preferred embodiment provides means for 
spontaneously operating according to an amplitude difference of the input 
vibration and, in other words, provides means for directly utilizing the 
vibration-responsive operation caused by the input vibration, such movable 
members operating by external forces as valves are not required, and 
accurate, smooth opening and closing operation can be achieved with simple 
construction and economy. 
Furthermore, a fine tuning of the resonant frequency can easily be carried 
out by setting of the cross sectional areas of both communication passages 
60, 70. 
Although the power unit supporting apparatus in the cylindrical bushing 
construction has been described in the preferred embodiment, the present 
invention is applicable to supporting apparatus having a construction 
other than the preferred embodiment such as a power unit supporting 
apparatus in which the elastic object is adhered between plates. 
In addition, although in the preferred embodiment the two communication 
passages are provided and the cross sectional areas thereof are stepwise 
changed to change the resonant frequency, the apparatus according to the 
present invention may have three or more communication passages and may 
change the lengths of the communication passages in place of a change of 
the cross sectional area. 
Although the power unit supporting apparatus in the preferred embodiment 
reduces the idling and engine shaking vibrations, the present invention is 
also applicable to a power unit supporting apparatus which reduces the 
vibrations other than those in the preferred embodiment. 
Since as described hereinabove the vibrating object supporting apparatus 
according to the present invention has a plurality of communication 
passages communicating between first and second fluid chambers in parallel 
to each other and open/close means for opening and closing at least one 
communication passage among the plurality of communication passages, 
different resonant frequencies can be set according to the open state and 
closed state of the corresponding communication passage. Consequently, the 
plurality of vibrations can effectively be reduced by the utilization of 
the vibration prevention function provided by the reduction of the dynamic 
spring constant and the damping function provided by the action of fluid 
dynamic damper. 
In addition, since the above-described open/close means provides means for 
spontaneously operating according to an amplitude difference of the input 
vibrations, in order words, means for directly utilizing the 
vibration-responsive operation caused by the input vibrations, accurate 
and smooth opening and closing operations can be achieved without 
requiring such movable members as valves. 
It will clearly be understood by those skilled in the art that the 
foregoing description is made in terms of the preferred embodiment, and 
various changes and modifications may be made without departing from the 
scope of the present invention which is to be defined by the appended 
claims.