Restricted passage system in vibration damping device

A restricted passage system is used in a vibration damping device, and comprises at least three cylindrical members concentrically arranged from each other at an interval and alternately serving as positive and negative electrodes and having a hole per each member in a position opposite to each other in diameter direction and insulation members fixed to upper and lower end portions of these members.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a restricted passage system usable for use in a 
vibration damping device enclosing an electrorheological fluid therein, 
and more particularly to a restricted passage system capable of having a 
sufficiently long passage length for ensuring a large damping force. 
2. Description of the Related Art 
For example, Japanese Patent laid open No. 1-135938 and No. 2-176230 
disclose a vibration damping device enclosing an electrorheological fluid 
therein, in which a viscosity of the electrorheological fluid passing 
through electrodes in a restricted passage system can be increased in 
accordance with a voltage between the electrodes or an intensity of 
electric field to change a damping force. 
In the device described in Japanese Patent laid open No. 1-135938, the 
restricted passage is a zigzag passage extending outward and inward in the 
radial direction, so that the full length of the passage and hence the 
length of the electrode can not be prolonged to a satisfactory length and 
consequently the given damping force can not be obtained. Furthermore, the 
restricted passage is fastened at its one end to a side of a fastening 
member and at the other end to a portion of a movable member to change a 
sectional area of the passage in accordance with a relative displacement 
between the fastening member and the movable member, so that there is a 
problem that the occurrence of stable damping force can not always be 
obtained. 
In the device of the Japanese Patent laid open No. 2-176230, a full length 
of the restricted passage formed between a piston and a damper casing is 
short, so that there is caused a problem of causing no large damping 
force. 
SUMMARY OF THE INVENTION 
It is, therefore, an object of the invention to advantageously solve the 
aforementioned drawbacks of the conventional technique and to provide a 
restricted passage system for a vibration damping device capable of 
producing a large damping force in accordance with use purpose by 
sufficiently lengthening the length of the restricted passage to 
sufficiently make the length of the electrode long. 
According to the invention, there is the provision of a restricted passage 
system for a vibration damping device, comprising at least three 
cylindrical members each made from a conductive material and substantially 
concentrically arranged from each other at a given interval, which members 
alternately forming positive and negative electrodes; an insulation member 
fixed to each of upper end and lower end of these cylindrical members so 
as to liquid-tightly close a channel defined between the adjoining 
cylindrical members; and a hole formed in each of these members in 
opposite to each other in a diameter direction. 
In the restricted passage system according to the invention, at least two 
inner and outer channels are formed among these cylindrical members so as 
to communicate with each other through holes formed in these members. That 
is, each of these channels extends from the hole formed in the inside 
cylindrical member to the hole formed in the outside cylindrical member in 
opposite to the former hole in the diameter direction, so that the total 
length of the channels can sufficiently be lengthened. Furthermore, the 
cylindrical member itself serves as an electrode, so that the length of 
the electrode can sufficiently lengthened. Therefore, the damping force 
can be increased to an expected value in connection with voltage applied 
to the electrode. This becomes conspicuous as the number of the 
cylindrical members increases. 
Moreover, the channel formed between the adjoining cylindrical members is 
liquid-tightly closed by fixing the insulation member to each of the upper 
and lower ends of these cylindrical members, whereby the change of cross 
sectional area of the channel during the operation of the restricted 
passage system can surely be prevented. 
As a result, when such a restricted passage system is applied, for example, 
to a vibration damping device, vibration energy can be absorbed very 
effectively by the large damping force and hence hence the stable 
vibration damping force can always be developed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows an exploded perspective view of the restricted passage system 
according to the invention, in which numerals 1, 2 and 3 are cylindrical 
members each made from a conductive material, respectively. 
These innermost, intermediate and outermost cylindrical members 1, 2 and 3 
contributing to define a channel are concentrically arranged at a given 
interval in this order. Among these members, the intermediate cylindrical 
member 2 serves as a positive electrode, and the innermost and outermost 
cylindrical members 1 and 3 serve as a negative electrode, respectively. 
These cylindrical members 1, 2 and 3 are positioned to each other by 
liquid-tightly fitting and fixing a pair of closing members 4, 5 each made 
from an insulation material to each of upper end portions and lower end 
portions of these members 1, 2 and 3 and also the upper and lower ends of 
these members 1, 2 and 3 are liquid-tightly closed by these closing 
members 4 and 5. 
As seen from the lower closing member 5, each of these closing members 4 
and 5 comprises a wall surface 5a defining a through-hole and closely 
circumscribing with an outer peripheral surface of the innermost 
cylindrical member 1, an annular groove 5b permitting to fit the 
intermediate cylindrical member 2, and a vertical wall surface 5c closely 
inscribing with an inner peripheral surface of the outermost cylindrical 
member 3, and also inner and outer portions 5d and 5e adjacent to the 
annular groove 5b in each of the closing members 4, 5 serves as a plug 
fitting into a space between the adjoining cylindrical members, 
respectively. 
Furthermore, each of opening holes 6, 7, 8 is formed in the respective 
cylindrical members 1, 2, 3 at a position in opposite to each other in a 
diameter direction. Preferably, each hole has an area approximately equal 
to a cross sectional area of a channel as mentioned later. 
In the restricted passage system of the above structure, inner and outer 
channels 9 are defined between the adjoining cylindrical members so as to 
communicate with each other through the opening hole 7 formed in the 
intermediate cylindrical member 7 and are communicated to exterior through 
the opening holes 6, 8 for the supply and discharge of fluid. 
For example, when an electrorheological fluid is passed from the hole 8 
through the channels 9 to the hole 6, as diagrammatically shown in FIG. 2, 
it flows from the hole 8 to the hole 7 located in opposite thereto in the 
diameter direction over about a half of peripheral length of the channel 9 
and further flows from the hole 7 to the hole 6 located in opposite 
thereto in the diameter direction along the channel 9, so that the flowing 
distance of the electrorheological fluid and hence the total length of the 
channels 9 become considerably long as compared with the conventional 
case. 
Thus, the length of the electrode becomes sufficiently long in the 
restricted passage system according to the invention, so that a very large 
damping force can be developed under an action of the electrorheological 
fluid flowing through the channels 9. Furthermore, the cylindrical members 
1, 2 and 3 in the restricted passage system are relatively restrained by 
the closing members 4 and 5, so that the cross sectional area of the 
channels is maintained at a constant level over the whole of the 
restricted passage system and consequently the damping property produced 
by this restricted passage system can always be made constant to ensure 
the occurrence of stable damping force. 
FIG. 3 is a first embodiment of the vibration damping device using the 
above restricted passage system. That is, the restricted passage system is 
applied to an upper end portion of a cylinder 11 comprising an inner 
sleeve 11a and an outer sleeve 11b separated from each other at a given 
interval. 
In this embodiment, the innermost and outermost cylindrical members 1, 3 
serve as a positive electrode, respectively and the intermediate 
cylindrical member 2 serves as a negative electrode, while the inner 
sleeve 11a arranged outside the outer periphery of the outermost 
cylindrical member 3 and an upper end closing sleeve 12 arranged inside 
the inner periphery of the innermost cylindrical member 1 serve as a 
negative electrode, respectively. Thus, the channel 9 has a substantially 
quartered structure having a very long total length. Further, the channel 
9 is communicated from an opening hole 11a formed in the inner sleeve 11a 
through a gap defined between the inner sleeve and the outer sleeve to a 
chamber located beneath a piston 13 slidably contacting with the inner 
surface of the inner sleeve in the cylinder 11 and further through an 
opening hole 12a formed in the upper end closing sleeve 12 to a chamber 
located above the piston 13. 
In this embodiment, the cylinder 11 is provided at its lower end portion 
with a closed gas chamber 15 defined by a free piston 14. Moreover, the 
closed gas chamber 15 may be communicated with atmosphere, if necessary. 
In the illustrated vibration damping device, when an electrorheological 
fluid 16 is filled in this device, if the relative displacement between 
the cylinder 11 and the piston 13 is a direction of compressing the 
chamber located beneath the piston 13, the electrorheological fluid 16 
existent in this chamber flows through the gap defined between the outer 
and inner sleeves constituting the cylinder 11 into the channel 9 while 
giving somewhat compressive deformation to the closed gas chamber and 
passes through the channels in the same manner as shown in FIG. 2 and then 
flows from the opening hole 12a of the upper end closing sleeve 12 through 
a gap defined between the sleeve 12 and a piston rod 13a into the chamber 
located above the piston 13. On the other hand, if the relative 
displacement between the cylinder 11 and the piston 13 is a direction of 
compressing the chamber located above the piston 13, the 
electrorheological fluid 16 flows existent in this chamber flows through 
the channels 9 into the chamber located beneath the piston 13 in a 
direction opposite to the former case. 
In such a flowing of the electrorheological fluid 16, when voltage is not 
applied between the positive electrode and the negative electrode, the 
damping force of the restricted passage system is a relatively low value 
determined by viscosity inherent to the electrorheological fluid 16, cross 
sectional area and length of channel for the electrorheological fluid 16 
and the like, so that when such a restricted passage system is applied to 
a vibration damping device, excellent vibration insulating performances 
against high frequency vibrations can be developed together with the 
expanded deformation of the closed gas chamber 15. 
On the other hand, when voltage is applied between the positive and 
negative electrodes, the electrorheological fluid 16 is subjected to 
electric field over a full length of the channels 9 having a quartered 
structure and hence the viscosity is enhanced in accordance with the 
intensity of the electric field, whereby a very high damping force, for 
example, vibration damping force can be developed based on the flowing of 
high viscosity electrorheological fluid 16 through the channels 9. 
FIG. 4 shows a second embodiment of the vibration damping device in which 
the restricted passage system is applied to a piston slidably moving in a 
cylinder. In this case, the piston 13 comprises an innermost cylindrical 
member 1 and an outermost cylindrical member 3 serving as a positive 
electrode, an intermediate cylindrical member 2 serving as a negative 
electrode, an outer shell 18 enclosing the outermost cylindrical member 3 
at a somewhat interval in the radial direction and slidably contacting 
with an inner wall surface of a cylinder 11, and an inner shell 19 located 
inward from the innermost cylindrical member 1 at a somewhat interval in 
the radial direction and integrally united with the outer shell 18. 
Moreover, the outer shell 18 and the inner shell 19 serve as a negative 
electrode, respectively. Thus, a long channel 9 having substantially a 
quartered structure is formed in the piston likewise the embodiment of 
FIG. 3 and is communicated to a rod-side chamber located above the piston 
13 through an opening hole 18a formed in the outer shell 18 and to a 
head-side chamber located beneath the piston 13 through an opening hole 
19a formed in the inner shell 19. 
Even in the second embodiment of the vibration damping device, the 
electrorheological fluid 16 enclosed in the cylinder flows one chamber to 
the other chamber defined by the piston 13 through the long channel 9 in 
the relative displacement between the cylinder 11 and the piston 13, so 
that a very high damping force can be developed by applying a high voltage 
between the electrodes and enhancing the viscosity of the 
electrorheological fluid in accordance with the intensity of the electric 
field. 
FIG. 5 shows a third embodiment of the vibration damping device in which 
the restricted passage system is applied to an outer peripheral side of 
the cylinder. In this case, an accumulator 21 is connected to a head-side 
chamber of the cylinder 11 circumscribing with the piston 13, while the 
head-side chamber is communicated with a rod-side chamber through an outer 
path 22. The restricted passage system is arranged in a portion of the 
outer path 22 opening to the rod-side chamber. 
Such a restricted passage system comprises the cylinder 11 serving as an 
innermost cylindrical member, an intermediate cylindrical member 2 and a 
rod cover 23 serving as an outermost cylindrical member, which are 
positioned to each other and fixed by electric insulation members 24, 25. 
In this case, the cylindrical member 2 serves as a positive electrode, 
while the cylindrical and rod cover 23 serve as a negative electrode, 
respectively. Further, the opening holes 11c, 7 and 23a formed in these 
members are located in opposite to each other in the diameter direction, 
and also the opening hole 23a of the rod cover 23 is connected to the 
outer path 22, whereby the channel 9 can sufficiently be lengthened to 
have substantially a double structure and also the length of the electrode 
can sufficiently be lengthened. As a result, the desired damping force can 
be developed under an action of the electrorheological fluid 16 flowing 
through the channel 9 as shown in FIG. 2. 
FIG. 6 shows a fourth embodiment of the vibration damping device in which 
the restricted passage system having substantially the same structure as 
in the piston of FIG. 4 is fixed to the inside of the head-side chamber in 
the cylinder 11 and the innermost and outermost cylindrical members 1, 3 
serve as a positive electrode and the other members serve as a negative 
electrode. 
According to this embodiment, when the piston 13 is slidably moved with 
respect to the cylinder 11, a part of the electrorheological fluid 16 
flows between the head-side chamber and the rod-side chamber through a 
through-hole 13a formed in the piston 13, and the remaining portion of the 
electrorheological fluid 16 flows between the piston side and the free 
piston side through the long channel 9 having a substantially quartered 
structure. As a result, a sufficiently large damping force can be 
developed based on the action of such a restricted passage system. 
FIG. 7a shows a fifth embodiment of the vibration damping device in which a 
restricted passage system as shown in FIG. 7b is arranged in the course of 
the outer path 22 communicating both chambers defined by the piston 13 in 
the cylinder 11 with each other. In this case, two piston rods are 
extended upward and downward from both surfaces of the piston 13. The 
restricted passage system comprises a housing 31 serving as an outermost 
cylindrical member, an intermediate cylindrical member 2 and a center 
cylinder 32 serving as an innermost cylindrical member, which are 
concentrically arranged at a given interval with each other. The 
intermediate cylindrical member serves as a positive electrode, and the 
other members serve as a negative electrode, respectively. As shown in 
FIG. 7c, opening holes 31a, 7 and 32a are formed in the housing 31, the 
intermediate cylindrical member 2 and the center cylinder 32 at positions 
opposite to each other in the diameter direction, respectively. 
Even in this embodiment, a large damping force can be developed through the 
long channel 9 having a substantially double structure. 
As mentioned above, in the restricted passage system according to the 
invention, the length of the channel and hence the length of the electrode 
defining the channel can sufficiently be lengthened and consequently the 
desired damping force can be developed. 
Furthermore, when the restricted passage system is applied to the vibration 
damping device, the cross sectional area of the channel is unchanged over 
the full length of the channel irrespectively of relative displaced state 
between the cylinder and the piston, so that the damping property is 
always stable.