U.S. patent application number 11/008629 was filed with the patent office on 2005-06-23 for noise reducing device.
This patent application is currently assigned to TOKAI RUBBER INDUSTRIES, LTD.. Invention is credited to Iwata, Hideaki, Maruyama, Yuichiro, Shimizu, Daisuke, Yamada, Hiroshi.
Application Number | 20050132945 11/008629 |
Document ID | / |
Family ID | 34675198 |
Filed Date | 2005-06-23 |
United States Patent
Application |
20050132945 |
Kind Code |
A1 |
Yamada, Hiroshi ; et
al. |
June 23, 2005 |
Noise reducing device
Abstract
A noise-reducing device for water vehicles including: a rigid
housing having a fluid-tightly sealed chamber formed therein, and
fixable to a vibrating part of the water vehicle to be displaced
with the vibrating part; a mass member housed in the rigid housing
with a given gap therebetween so that the mass member is freely
movable in the vibrating direction relative to the rigid housing,
the mass member being adapted to come into collision with a contact
part of the housing during input of vibration; and an elastic
element formed on at least one surface of contact on the contact
part or mass member.
Inventors: |
Yamada, Hiroshi;
(Komaki-shi, JP) ; Maruyama, Yuichiro;
(Komaki-shi, JP) ; Iwata, Hideaki;
(Ichinomiya-shi, JP) ; Shimizu, Daisuke;
(Hamamatsu-shi, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
TOKAI RUBBER INDUSTRIES,
LTD.
Komaki-shi
JP
YAMAHA MARINE KABUSHIKI KAISHA
Hamamatsu-shi
JP
|
Family ID: |
34675198 |
Appl. No.: |
11/008629 |
Filed: |
December 10, 2004 |
Current U.S.
Class: |
114/55.5 |
Current CPC
Class: |
B63H 21/305 20130101;
B63H 21/30 20130101; B63H 11/08 20130101; B63B 34/10 20200201; F16F
7/10 20130101 |
Class at
Publication: |
114/055.5 |
International
Class: |
B63H 011/00; B63B
001/00; B63B 035/73 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 17, 2003 |
JP |
2003-419127 |
Claims
What is claimed is:
1. A noise-reducing device for water vehicles in which thrust is
provided when water taken in by a jet pump is pressurized and
accelerated, and is blasted to the rear by means of a jet nozzle,
the noise-reducing device comprising: a rigid housing having a
fluid-tightly sealed chamber formed therein, and fixable to a
vibrating part of the water vehicle to be displaced with the
vibrating part; a mass member housed in the rigid housing with a
given gap therebetween so that the mass member is freely movable in
the vibrating direction relative to the rigid housing, the mass
member being adapted to come into collision with a contact part of
the housing during input of vibration; and an elastic element
formed on at least one surface of contact on the contact part or
mass member.
2. A noise-reducing device according to claim 1, wherein the
noise-reducing device is formed so as to be attached to the jet
pump acting as the vibration source, thereby controlling the
vibration of the jet pump.
3. A noise-reducing device according to claim 2, wherein the
noise-reducing device is formed so as to be attached to an upper
portion of the jet pump.
4. A noise-reducing device according to claim 2, wherein the
noise-reducing device is formed so as to be attached to a part by
which the jet pump is fixed to a hull of the water vehicle, thereby
controlling the vibration of the jet pump.
5. A noise-reducing device according to claim 4, wherein the
noise-reducing device is attached to the jet pump using a fixing
hole where the jet pump is fixed to the hole with the fixing
part.
6. A noise-reducing device according to claim 1, wherein the
noise-reducing device is formed so as to be attached to a deck of a
hull of the water vehicle, where is subjected to vibration from the
jet pump, thereby controlling the vibration of the deck.
7. A noise-reducing device according to claim 1, wherein the rigid
housing has a cantilever bar protruding in a direction remote from
the fluid-tightly sealed chamber, the cantilever bar being fixable
at a protruding end portion thereof to the vibrating part of the
water vehicle so that the rigid housing is fixed to the vibrating
part in a cantilevered state.
8. A noise-reducing device assembly for water vehicles in which
thrust is provided when water taken in by a jet pump is pressurized
and accelerated, and is blasted to the rear by means of a jet
nozzle, the noise-reducing device comprising: a plurality of
noise-reducing device each including a rigid housing having a
fluid-tightly sealed chamber formed therein, and fixable to a
vibrating part of the water vehicle to be displaced with the
vibrating part; a mass member housed in the rigid housing with a
given gap therebetween so that the mass member is freely movable in
the vibrating direction relative to the rigid housing, the mass
member being adapted to brought into collision with a contact part
of the housing during input of vibration; and an elastic element
formed on at least one surface of contact on the contact part or
mass member; an attachment bracket having a body portion to which
the plurality of noise-reducing device are fixed, and a cantilever
bar protruding in a direction remote from the body portion, the
cantilever bar being fixable at a protruding end portion thereof to
the vibrating part of the water vehicle so that the attachment
bracket is fixed to the vibrating part in a cantilevered state.
Description
INCORPORATED BY REFERENCE
[0001] The disclosure of Japanese Patent Application No.
2003-419127 filed on Dec. 17, 2003 including the specification,
drawings and abstract is incorporated herein by reference in its
entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a noise-reducing device for
water vehicles or other small vessels in which thrust is provided
when water taken in by a jet pump is pressurized and accelerated,
and is blasted to the rear by means of a jet nozzle.
[0004] 2. Description of the Related Art
[0005] Recently, there has been more widespread recreational use
and the like of water vehicles in which thrust is provided when
water taken in by a jet pump is pressurized and accelerated, and is
blasted to the rear by means of a jet nozzle. The noise produced by
such water vehicles when in use has been pointed out as a
problem.
[0006] To cope with this problem, several attempts have been made
for reducing the noise by elastically supporting an engine on a
hull of the water vehicles, as disclosed in JP-2000-255491, for
example, in which the engine, i.e., a source of vibration in a
water vehicle, is elastically supported by engine mounts that
include rubber mounts. As noted above, thrust is provided in water
vehicles when water taken in by a jet pump is pressurized and
accelerated, and is blasted to the rear by means of a jet nozzle.
However, these conventional attempts are not still sufficient to
reduce noises produced by such water vehicles.
[0007] An extensive study on water vehicles conducted by the
present inventors has revealed that the jet pump can also act as a
source of vibration, and these vibrations can be transmitted to the
hull, particularly the deck, where the hull acts as a speaker,
producing noise.
[0008] As one means of solution of this problem, it would be
conceivable to affix a conventionally available mount rubber or
dynamic damper. However, these conventional vibration-damping
devices may suffer from inherent problem for use in water vehicles.
Namely, in the mount rubbers and the dynamic dampers, rubber
members as major components are exposed to the outside area, so
that these rubber members will be exposed to sea or flesh water,
resulting in a problem of deterioration of the rubber members, such
as rubber member separation by salt spray. In particular, the water
pump when in use is buried in fresh or sea water or at least
exposed to water or salt spray, it is impossible to affix the
rubber mounts or the dynamic damper to the water pump.
SUMMARY OF THE INVENTION
[0009] It is therefore one object of this invention to provide a
noise-reducing device for water vehicles which provide effective
noise reducing performance against noise originating primarily from
jet pump vibration (as well as against noise originating from other
vibrative member).
[0010] The above and/or optional objects of this invention may be
attained according to at least one of the following modes of the
invention. Each of these modes of the invention is numbered like
the appended claims and depending from the other mode or modes,
where appropriate, to indicate possible combinations of elements or
technical features of the invention. It is to be understood that
the principle of the invention is not limited to these modes of the
invention and combinations of the technical features, but may
otherwise be recognized based on the teachings of the present
invention disclosed in the entire specification and drawings or
that may be recognized by those skilled in the art in the light of
the present disclosure in its entirety.
[0011] A first mode of the present invention provides a
noise-reducing device for water vehicles in which thrust is
provided when water taken in by a jet pump is pressurized and
accelerated, and is blasted to the rear by means of a jet nozzle,
the noise-reducing device comprising: a rigid housing having a
fluid-tightly sealed chamber formed therein, and fixable to a
vibrating part of the water vehicle to be displaced with the
vibrating part; a mass member housed in the rigid housing with a
given gap therebetween so that the mass member is freely movable in
the vibrating direction relative to the rigid housing, the mass
member being adapted to brought into collision with a contact part
of the housing during input of vibration; and an elastic element
formed on at least one surface of contact on the contact part or
mass member.
[0012] The noise-reducing device operates in the following manner.
When the vibrating part of the water vehicle begins to vibrate, the
contact part of the housing is displaced with it and begins to
vibrate in synchronization with the vibrating part. Meanwhile,
since the mass member is in a freely moving state in the vibrating
direction relative to the contact part, that is, since it
independently moves freely in the same direction relative to the
contact part, it collides with the contact part while the contact
part is vibrating, and counteracts the vibration of the contact
part, that is, the vibration of the vibrating part in the water
vehicle.
[0013] At that time, kinetic energy is imparted in the opposite
direction by the contact part to the mass member colliding with the
contact part (thus, some of the vibrating energy from the contact
part is absorbed as kinetic energy of the mass member), and the
mass member moves in the opposite direction. The mass member then
again collides with a contact surface in a location opposite the
first contact surface, again acting to counteract the vibration of
the contact part, that is, the vibrating part in the water
vehicle.
[0014] The mass member subsequently repeats the same movement in
opposite or different phases from that of the contact part.
Therefore, the mass member absorbs the vibrating energy of the
contact part at each collision, and converts the vibrating energy
to its own kinetic energy, thereby repeatedly colliding with the
contact part. Thus, the vibrating energy of the vibrating part in
the water vehicle is thus absorbed, and the excited vibrations are
damped, resulting in highly effective vibration control.
[0015] When both the contact part and mass member are made of a
rigid element, a loud, harsh noise (noise from impact) will be
produced. In the noise-reducing device of the present invention,
however, an elastic element such as resin or rubber is formed on at
least one contact surface of the contact part or mass member,
thereby avoiding the problem of loud, harsh noise during impact.
The sliding friction and the viscous behavior of the elastic
element during impact allow the vibration energy to be converted to
heat and absorbed. That is, the vibration damping by the elastic
element helps to attenuate the vibration of the vibrating part.
[0016] The noise-reducing device of the invention is more suitable
to damp vibration excited in water vehicles in comparison with the
case where a dynamic damper is mounted for the vibrating part in
the water vehicle to damp the vibration, in the following points,
for example. The dynamic damper adds damper mass to the vibrating
part by means of a spring. The natural frequency of the
supplemental vibration system comprising the damper mass and spring
can be tuned to the natural frequency of the primary vibration
system (natural frequency of the vibration part) so as to lower the
resonance magnification of the vibrating part and control its
vibration.
[0017] However, vibration damping by means of a dynamic damper is
effective only for the vibration of a single resonance frequency,
and cannot effectively prevent the resonance of other frequencies.
That is, it is ineffective against resonance of multiple
frequencies. Another problem with dynamic dampers is that separate
resonance is produced anew before and after the resonance point. In
addition, when a rubber elastic element is used as the spring, the
spring constant of the rubber elastic element is variable according
to temperature, making its damping properties (vibration damping
properties) highly temperature-dependent, with a decrease of
vibration controlling efficiency at elevated or lower
temperatures.
[0018] Additional problems are that considerable mass is required
for the damper mass in dynamic dampers (the mass must be about 10%
of the vibrating part), resulting in a heavier device as a whole
and the need for greater installation space, and that the direction
in which vibrations can be controlled is also fixed, making this an
ineffective option for multidirectional vibrations.
[0019] In the noise-reducing device of the present invention, the
mass member is independently moveable, allowing it to move and
collide with the contact part in opposite phases or different
phases from that of the vibrating part of the water vehicle where
vibration is to be controlled, thereby absorbing and damping the
vibration energy. Vibrations can therefore be controlled over a
wide range of frequencies, without any particular frequency
dependency. Multidirectional collisions are also a simple and easy
matter, allowing multidirectional vibrations to be controlled. In
addition, the minimal temperature dependency results in good
vibration control over a wide temperature range, from high to low
temperatures. The required mass of the mass member is also lighter
(only about 5% of the vibrating part), allowing the space needed
for the device as a whole to be reduced and made more compact, so
that it can be readily mounted on the vibrating part, among a
variety of other advantages.
[0020] FIG. 1 schematically compares an embodiment of the
noise-reducing device of the invention to a dynamic damper, where 1
is the noise-reducing device, and 2 is the dynamic damper. The
numeral 3 is the mass member, 4 is the elastic element formed on
the surface of the mass member 3, that is, the contact surface, and
5 is the housing forming the contact part. 6 is the damper mass in
the dynamic damper 2, and 7 is the spring (rubber). 8 is the
vibrating part.
[0021] When the dynamic damper 2 in FIG. 1B is mounted, it can
control resonance in a specific frequency range, yet separate
resonance is produced anew before and after the resonance point.
The noise-reducing device of FIG. 1C, on the other hand, can
control vibrations over a wide frequency range, from high to low
frequencies, and does not new resonance before or after the
resonance point.
[0022] As is evident in view of the above, attaching the
noise-reducing device according to the invention to the vibrating
part of a water vehicle allows the vibration in the vibrating part
to be well controlled, and can thus effectively control noise
originating from the vibrations of the vibrating part.
[0023] Moreover, the noise-reducing device of the present invention
has the rigid housing with the fluid-tightly sealed chamber, and
the mass member is housed within the sealed chamber. Thus, the
noise-reducing device is able to provide desired vibration damping
effect based on collisions of the mass member against the contact
part with high stability and without being adversely influenced by
water flows or sprays. Especially, the elastic element is held
inside the sealed chamber, thereby eliminating conventional problem
as discussed above, namely deterioration of rubber members due to
salt spray or ambient water.
[0024] The rigid housing including the contact part in the
invention may be made of a metal such as iron or an aluminum alloy,
a hard resin, or another hard material. Preferably, employed is a
rigid material having high resistance to salt, such as stainless
steel and titanium. The mass member may itself be made of an
elastic element such as rubber or a resin. It is preferably made of
a rubber, resin, or the like having a high specific gravity,
comprising an admixture of metal powder or the like in the
interior. When the mass member is made of an elastic element such
as rubber or resin, the mass member itself can constitute the
elastic element of rubber, resin, or the like formed on at least
one contact surface of the rigid contact part or mass member. The
mass member can also be made of a foamed elastic element of rubber,
resin, or the like.
[0025] The mass member is preferably made of a metal such as iron,
aluminum alloy, or lead to ensure more effective vibration
control.
[0026] In such cases, an elastic element of rubber, resin, or the
like is formed on at least one contact surface of the rigid contact
part or mass member.
[0027] The gap in the present invention means the gap that is
necessary to allow the mass member to most effectively collide with
the contact part. In that sense, the gap distance D should be 0.05
to 2.0 mm, and more preferably 0.2 to 1.0 mm (see FIG. 5A).
[0028] The elastic member in the invention may be made of rubber or
a resin. Examples of rubbers which can be used include NR, SBR, and
BR, and other diene rubbers, EPDM rubbers, urethane rubbers,
silicone rubbers, and the like. Examples of resins which can be
used include thermoplastic resins such as polypropylene and
polyamide, thermoplastic elastomers such as polyolefins, urethane,
and polyesters, and the like.
[0029] The elastic element may be adhesively fixed through
vulcanization of a rubber material for forming thereof to a contact
surface of the mass member or contact part, or alternatively it may
be formed on a contact surface in an unbonded state.
[0030] Further, the rigid housing is formed separately from the
vibrating part in the water vehicle, and can be fixed to the
vibrating part along with the mass member. This will allow the
noise-reducing device to be easily attached and fixed to the
vibrating part in the water vehicle.
[0031] A second mode of the present invention provides a
noise-reducing device according to the above described first mode,
wherein the noise-reducing device is formed so as to be attached to
the jet pump acting as the vibration source, thereby controlling
the vibration of the jet pump. This will allow the vibrations of
the water vehicle originating from the jet pump to be effectively
controlled so as to reduce noise.
[0032] A third mode of the present invention provides a
noise-reducing device according to the above described second mode,
wherein the noise-reducing device is formed so as to be attached to
an upper portion of the jet pump. With this arrangement, the
noise-reducing device is less likely influenced by water flow
energy or other energy created by water existing around the device,
making it enable for the noise-reducing device to exhibit desired
damping effect with high stability.
[0033] A fourth mode of the present invention provides a
noise-reducing device according to the above described first mode,
wherein the noise-reducing device is formed so as to be attached to
a part by which the jet pump is fixed to a hull of the water
vehicle, thereby controlling the vibration of the jet pump.
According to a fifth mode of the present invention, the
noise-reducing device is attached to the jet pump using a fixing
hole where the jet pump is fixed to the hole with the fixing part.
With this arrangement, the noise-reducing device is preferably
attached to a part by which the jet pump is fixed to the hull. In
this case, it is also desirable to attach the noise-reducing device
to the jet pump using a fixing hole by which the fixing part is
fixed to the hull.
[0034] A sixth mode of the present invention provides a
noise-reducing device according to the above described first mode,
wherein the noise-reducing device is formed so as to be attached to
a deck of a hull of the water vehicle, where is subjected to
vibration from the jet pump, thereby controlling the vibration of
the deck. Since the deck undergoes vibrations transmitted from the
jet pump, this arrangement will control the vibration of the deck,
serving as the source of resonance, to allow noise in the water
vehicle to be more effectively reduced.
[0035] A seventh mode of the present invention provides a noise
reducing device according to any one of the above described first
through sixth modes, wherein the rigid housing has a cantilever bar
protruding in a direction remote from the fluid-tightly sealed
chamber, the cantilever bar being fixable at a protruding end
portion thereof to the vibrating part of the water vehicle so that
the rigid housing is fixed to the vibrating part in a cantilevered
state. With this arrangement, since the fluid-tightly sealed
chamber is supported on the vibrating part of the water vehicle by
the cantilever bar in a cantilevered state or one end supported
manner, the sealed chamber is more likely displaced or oscillated
with the help of spring of the cantilever bar. This arrangement is
effective to excite displacement of the mass member within the
chamber and resultant collision or impact of the mass member
against the contact part of the housing. Therefore, the present
noise-reducing device is capable of efficiently providing desired
damping effect owing to collision of the mass member against the
contact part of the housing, even if the displacement of the
housing is somewhat reduced by resistance of water. A plurality of
cantilever bars may be employed.
[0036] A eighth mode of the present invention provides a
noise-reducing device assembly for water vehicles in which thrust
is provided when water taken in by a jet pump is pressurized and
accelerated, and is blasted to the rear by means of a jet nozzle,
the noise-reducing device comprising: a plurality of noise-reducing
device each including a rigid housing having a fluid-tightly sealed
chamber formed therein, and fixable to a vibrating part of the
water vehicle to be displaced with the vibrating part; a mass
member housed in the rigid housing with a given gap therebetween so
that the mass member is freely movable in the vibrating direction
relative to the rigid housing, the mass member being adapted to
come into collision with a contact part of the housing during input
of vibration; and an elastic element formed on at least one surface
of contact on the contact part or mass member; an attachment
bracket having a body portion to which the plurality of
noise-reducing device are fixed, and a cantilever bar protruding in
a direction remote from the body portion, the cantilever bar being
fixable at a protruding end portion thereof to the vibrating part
of the water vehicle so that the attachment bracket is fixed to the
vibrating part in a cantilevered state.
[0037] This noise-reducing device assembly facilitate installation
of the plurality of noise-reducing devices on the water vehicle.
Like in the seventh mode of the invention, the plurality of
noise-reducing devices and their fluid-tightly sealing chambers are
supported on the vibrating part of the water vehicle via the
cantilever bar of the attachment bracket in a cantilevered state or
one end supported manner, whereby the sealed chambers are more
likely displaced or oscillated with the help of spring of the
cantilever bar of the attachment bracket, resulting in further
excited collisions of the mass member against the housing. Thus,
the present noise-reducing device assembly is capable of
efficiently providing desired damping effect owing to excited
collision of the mass members against the contact parts of the
housings. A plurality of cantilever bars may be employed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0038] The foregoing and/or other objects features and advantages
of the invention will become more apparent from the following
description of a preferred embodiment with reference to the
accompanying drawings in which like reference numerals designate
like elements and wherein:
[0039] FIG. 1 is a view schematically illustrating a noise-reducing
device of the present invention, together with conventional dynamic
dampers;
[0040] FIG. 2 is a fragmentary sectional view showing a
noise-reducing device assembly of construction according to one
embodiment of the present invention, which is installed on a water
vehicle;
[0041] FIG. 3 is a fragmentary enlarged view of the noise-reducing
device assembly of FIG. 2 and ambient components;
[0042] FIG. 4 is a fragmentary enlarged front view of the
noise-reducing device assembly of FIG. 2 and ambient
components;
[0043] FIGS. 5A-5C are views showing a noise-reducing device of the
noise-reducing device assembly of the invention;
[0044] FIG. 6 is a fragmentary enlarged front view of the
noise-reducing device assembly of construction according to another
embodiment of the present invention and ambient components.
[0045] FIGS. 7A and 7B are views showing a noise-reducing device of
the noise-reducing device assembly of the invention of FIG. 6;
[0046] FIG. 8 is a graph showing results of measurements of
vibration at oscillating point P of FIG. 10, for the case where the
present noise-reducing device assembly is installed and the case
where no device is installed;
[0047] FIG. 9A is a graph showing results of measurements of
vibration at upper surface of a jet pump of FIG. 10, for the case
where the present noise-reducing device assembly is installed and
the case where no device is installed, and FIG. 9B is a graph
showing results of measurements of vibration at upper surface of a
deck of FIG. 10, for the case where the present noise-reducing
device assembly is installed and the case where no device is
installed;
[0048] FIG. 10 is a view showing designated measuring points for
vibration measuring tests; and
[0049] FIG. 11 is a fragmentary sectional view showing a
noise-reducing device of construction according to yet another
embodiment of the present invention, which is installed on a water
vehicle.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0050] Referring first to FIGS. 2 and 10, there is shown a water
vehicle 10 which glides on water. The water vehicle includes a hull
12 and a steering handle 14 with a pair of handle grips 16.
[0051] This water vehicle 10 is equipped with an engine 18 and jet
pump 20. The jet pump 20 is equipped with an impeller 24 in the
interior of a pump housing 22. The impeller 24 is operationally
connected to the engine 18 by a drive shaft 26.
[0052] In the water vehicle 10, the impeller 24 in the jet pump 20
is rotated and driven by the drive shaft 26 through the output from
the engine 18. Thus, water that has been taken up through the
intake 28 in the bottom of the hull is pressurized and accelerated
in the pump housing 22 of the jet pump 20, and is blasted from the
end jet nozzle 30 to the rear in the form of a rushing jet flow.
The water vehicle 10 glides on the water on the basis of the thrust
thus provided.
[0053] As illustrated in FIGS. 3 and 4, the jet pump 20 has a
fixing flange 32 at the outer periphery of the pump housing 22, and
is fixed to the hull 12 side by means of fixing bolts 36 threaded
into fixing holes 34 (sea FIG. 3) in the fixing flange 32. A
noise-reducing device assembly 38 of construction according to a
first embodiment of the invention is attached and fixed to the
fixing flange 32 by which the jet pump 20 is fixed to the hull
12.
[0054] As illustrated in FIG. 4, the noise-reducing device assembly
38 in this embodiment has an attachment bracket 40, and a plurality
(in this case, three) noise-reducing devices 42 fixed to a body
portion 40a of the attachment bracket 40. The attachment bracket
40, which is rigid as a whole, is made of a member in the form of a
plate, and is attached and fixed with its cantilever bars 40b, 40b
to the fixing flange 32 by means of the fixing bolts 36 threaded
into the fixing holes 34 in the fixing flange 32.
[0055] The plurality of noise-reducing devices 42 all have the same
structure in this embodiment. The specific structure is shown in
detail in FIG. 5. As shown in that figures, each noise-reducing
device 42 has a pair of rigid columnar housings 44, 44 located side
by side, with free movement chambers 46, 46 formed inside. A pair
of mass members 48, 48 of solid cylinder shapes are housed in a
freely moving state, by means of a certain gap, and are covered on
the surface with elastic elements 50.
[0056] In this embodiment, a gap is formed between the elastic
element 50 closely covering the mass member 48 and the inner
surface of the housing 44 to allow the mass member 48 to move
freely in either the perpendicular or axial directions. In other
words, the mass members 48 can move freely in either the
perpendicular or axial directions in the free movement chambers 46.
Namely, with each mass member 48 situated concentrically with the
corresponding columnar housing 44, the mass member 48 is completely
separate from the inner surface of the housing 44 with a gap
therebetween in all-radial directions thereof, thereby permitting
freely movement or displacement of the mass member 48 within the
columnar housing 44. The vibrations of the jet pump 20 are
primarily vibrations in the perpendicular and axial rotating
directions.
[0057] Each noise-reducing device 42 has a pair of cantilever bars
in the form of arms 52, and are fixed to the attachment bracket 40
by means of the fixing bolts 56 threaded into the fixing holes 54
at the tips of the arms 52 (see FIGS. 4).
[0058] As illustrated in FIG. 5A, the main body 58 of the
noise-reducing device 42 is formed by placing a first member 58-1
and a second member 58-2 on top of each other, and then inserting a
sealing member 60 at the surface where they are placed on top of
each other, so as to entirely encompass the pair of housings 44,
44. That is, the first member 58-1 and the second member 58-2 are
fixed by welding or the like on top of each other, with the sealing
member 60 sandwiched between them. The sealing member 60 keeps the
interior of the housings 44, that is, the free movement chambers
46, water-tight, thus preventing water from penetrating into the
free movement chambers 46.
[0059] In the noise-reducing device assembly 38 in this embodiment,
the housings 44 of the noise-reducing devices 42 are displaced with
the jet pump 20 as it begins to vibrate, and they begin to vibrate
in synchronization with the jet pump 20, or more exactly, the pump
housing 22, but since the mass members 48 housed in the housings 44
independently move freely in a free moving state in the direction
of vibration relative to the housings 44, the mass members 48 come
into collision or impact in the direction of vibration against the
housings 44 when the housings 44 are vibrating, and counteract the
vibrations of the housings 44, that is, the vibrations of the jet
pump 20. With this regards, since the attachment bracket 40 is
affixed to the flange 32 of the jet pump 20 in a cantilevered
manner, the vibrations of the housings 44 are also excited owing to
the spring of the cantilever bars 40b.
[0060] At that time, kinetic energy in the opposite direction is
imparted by the housings 44 to the mass members, and the mass
members 48 move in the opposite direction. The mass members 48 then
again collides with a contact surface in a location opposite the
first contact surface, acting to counteract the vibration of the
housings 44, that is, the jet pump 20.
[0061] The mass members 48 subsequently repeat the same movement in
opposite or different phases than the housings 44 to absorb the
vibrating energy of the housings 44, that is, the jet pump 20, at
each collision, and converts it to its own kinetic energy. In this
way, and also as a result of the sliding friction at each
collision, the vibrating energy of the jet pump 20 is absorbed, and
the vibrations are damped, resulting in highly effective vibration
control.
[0062] FIGS. 6 and 7 illustrate a second embodiment of the
noise-reducing device assembly 38. As illustrated in FIG. 6, a
plurality of (three in this case) noise-reducing devices 68 in this
noise-reducing device assembly 38 as well are attached and fixed to
the fixing flange 32 of the jet pump 20 by the attachment bracket
40 shared in common.
[0063] FIGS. 7A and 7B illustrate the specific structure of the
noise-reducing device 68 in this noise-reducing device assembly 38.
As illustrated, each noise-reducing device 68 in this embodiment
has a dome-shaped rigid housing 70, inside of which a mass member
74 consisting of a ball coated on the surface with an elastic
element 76 is housed freely moveable in three directions, by means
of a certain gap therebetween.
[0064] As illustrated in FIGS. 6 and 7, each noise-reducing device
68 in this embodiment is equipped with a pair of arms 80 at the
main body 78, and is fixed to the attachment bracket 40 shared in
common by means of fixing bolts 56 at the arms 80. In the
noise-reducing device assembly 38 in FIGS. 6 and 7, the mass
members 74 move freely in the free movement chambers 72 formed in
the rigid housings 70, and collide with the rigid housings 70 to
absorb energy and damp vibrations in the same manner as described
above with respect to the first embodiment.
[0065] FIGS. 8 and 9 show a result of measurements when the
noise-reducing device assembly 38 in FIGS. 4 and 5 was set up, and
vibrations were produced at oscillating point P in FIG. 10 to
measure the vibrations at that oscillating point P as well as
vibration receiving points Q.sub.1 and Q.sub.2. In this case,
oscillating point P was a location at the lower surface of the jet
pump 20, vibration receiving point Q.sub.1 was a location at the
upper surface of the jet pump 20, and vibration receiving point
Q.sub.2 was a location at the upper surface of the deck 82 aft of
the hull 12.
[0066] FIG. 8 gives the results for the vibration measured at
oscillating point P, FIG. 9A gives the results for the vibration
measured at the upper surface of the jet pump 20, which was
vibration receiving point Q.sub.1, and FIG. 9B gives the results
for the vibration measured at the upper surface of the aft deck 82,
which was vibration receiving point Q.sub.2. In each of the
figures, the dashed lines show the results for vibration measured
when the noise-reducing device assembly 38 of the embodiment was
not used, and the solid lines show the results for vibration
measured when the noise-reducing device assembly 38 of the
embodiment was used. The horizontal axis indicates frequency, and
the vertical axis indicates vibration level.
[0067] As is evident in the figures, the noise-reducing device
assembly 38 of the embodiment controlled vibrations over a wide
frequency range.
[0068] Since an elastic element 50 is formed on the surface of the
mass members 48 in the noise-reducing device assembly 38 of the
invention, no loud, harsh noise is produced by the collision of the
mass members 48 against the housings 44, and sliding friction and
the viscous behavior of the elastic element during impact allow the
vibration energy to be converted to heat and absorbed. That is, the
vibration damping by the elastic element 50 helps to attenuate the
vibration of the jet pump 20.
[0069] In the noise-reducing device assembly 38 of the present
invention, the mass members 48 are independently moveable, allowing
them to move and collide with the contact part in opposite phases
or different phases than the jet pump 20 of the water vehicle 10,
thereby absorbing and damping the vibration energy. Vibrations can
therefore be controlled over a wide range of frequencies, without
any particular frequency dependency. Multidirectional collisions
are also a simple and easy matter, allowing multidirectional
vibrations to be controlled. In addition, the minimal temperature
dependency results in good vibration control over a wide
temperature range, from high to low temperatures. The required mass
of the mass members 48 is also lighter, allowing the space needed
for the device as a whole to be reduced and made more compact, so
that the noise-reducing device assembly 38 can be readily mounted
on the jet pump 20.
[0070] The noise-reducing device assembly 38 in this example is
attached to the jet pump 20 of the water vehicle 10, allowing the
vibrations in the jet pump 20 to be controlled better and thus
allowing better control of noise originating from the vibrations of
the jet pump 20.
[0071] In this embodiment, the noise-reducing device assembly 38 is
equipped with the rigid housings 44 to form the contact parts. The
mass members 48 are housed in a freely moving state in the free
movement chambers 46 of the housings 44. The housings 44 are formed
separately from the jet pump 20 in the water vehicle 10, allowing
the noise-reducing device assembly 38 to be easily attached and
fixed to the jet pump 20 of the water vehicle.
[0072] Embodiments of the invention were described in detail for
the illustrative purpose only, the present invention may otherwise
be embodied. For instance, as illustrated in FIG. 11, embodiments
of the noise-reducing device of the invention other than the
noise-reducing device assembly 38 illustrated above may be mounted
on certain parts of the hull 12 other than the aft deck 82 where
vibrations are transmitted from the jet pump 20 in order to control
the vibrations of the hull 12 itself, allowing noise produced by
the water vehicle 10 to be controlled.
[0073] While the noise-reducing device assembly of the present
invention has been described in detail, the principle of the
present invention may be embodied in a single noise reducing
device. For instance, the noise-reducing device may be directly
attached to the vibrating part of the water vehicle, preferably in
a cantilevered manner with its cantilever bar, thereby providing
the same vibration damping effect as described above with respect
to the noise-reducing device assembly 38. In this case, the
noise-reducing device may be attached to the vibrating part via a
suitable bracket. Alternatively, a plurality of noise-reducing
devices may be directly affixed to the vibrating part of the water
vehicle.
[0074] It is also to be understood that the present invention may
be embodied with various other changes, modifications and
improvements, which may occur to those skilled in the art, without
departing from the spirit and scope of the invention defined in the
following claims.
* * * * *