U.S. patent application number 13/249918 was filed with the patent office on 2013-04-04 for pump piston assembly with acoustic dampening device.
This patent application is currently assigned to NEWPORT MEDICAL INSTRUMENTS, INC.. The applicant listed for this patent is Charlie Beuchat, Richard William Crawford, JR., Clayton Roy Platt, Fawn Zheng. Invention is credited to Charlie Beuchat, Richard William Crawford, JR., Clayton Roy Platt, Fawn Zheng.
Application Number | 20130081536 13/249918 |
Document ID | / |
Family ID | 47991407 |
Filed Date | 2013-04-04 |
United States Patent
Application |
20130081536 |
Kind Code |
A1 |
Crawford, JR.; Richard William ;
et al. |
April 4, 2013 |
PUMP PISTON ASSEMBLY WITH ACOUSTIC DAMPENING DEVICE
Abstract
A pump piston assembly has a pump cylinder, at least one hollow
piston slidably mounted for reciprocating motion in the pump
cylinder, the piston having an inner surface of a first diameter
and an outer surface of a second diameter, and a liner sleeve of a
different material from the piston mounted on the inner or outer
surface of the piston with a close or friction fit to the diameter
of the piston surface on which it is mounted. The liner sleeve is
of an acoustic dampening material which has a lower acoustic
frequency than the piston material and is configured to absorb
harmonic acoustic vibrations resulting from reciprocation of the
piston in the cylinder.
Inventors: |
Crawford, JR.; Richard William;
(Yucaipa, CA) ; Platt; Clayton Roy; (Lake Forest,
CA) ; Zheng; Fawn; (Irvine, CA) ; Beuchat;
Charlie; (Irvine, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Crawford, JR.; Richard William
Platt; Clayton Roy
Zheng; Fawn
Beuchat; Charlie |
Yucaipa
Lake Forest
Irvine
Irvine |
CA
CA
CA
CA |
US
US
US
US |
|
|
Assignee: |
NEWPORT MEDICAL INSTRUMENTS,
INC.
Costa Mesa
CA
|
Family ID: |
47991407 |
Appl. No.: |
13/249918 |
Filed: |
September 30, 2011 |
Current U.S.
Class: |
92/169.1 |
Current CPC
Class: |
F05C 2203/0808 20130101;
F05C 2225/00 20130101; F04B 53/166 20130101; F04B 53/001 20130101;
F05C 2225/02 20130101; F04B 53/14 20130101; F04B 53/143
20130101 |
Class at
Publication: |
92/169.1 |
International
Class: |
F04B 53/16 20060101
F04B053/16; F04B 19/22 20060101 F04B019/22; F04B 19/04 20060101
F04B019/04 |
Claims
1. A piston assembly, comprising: a cylinder of a first material;
at least one piston of a second material different from the first
material slidably mounted for reciprocating motion in the cylinder,
the piston being hollow and having an inner surface of a first
diameter and an outer cylindrical surface of a second diameter; at
least one liner sleeve mounted on one of said inner and outer
surfaces of the piston and having a close tolerance fit to the
diameter of the piston surface on which it is mounted, whereby the
opposing surfaces of the liner sleeve and piston are in face to
face engagement; and the liner sleeve being of an acoustic
dampening material which has a lower acoustic frequency than the
piston material.
2. The piston assembly of claim 1, wherein the liner sleeve is
mounted on the inner surface of the piston.
3. The piston assembly of claim 2, wherein the liner sleeve has a
central longitudinal axis and opposite axial ends, and the sleeve
has a slot extending between the axial ends configured to allow
compression of the sleeve during installation into the piston.
4. The piston assembly of claim 3, wherein the slot extends at an
angle to the central longitudinal axis of the sleeve.
5. The piston assembly of claim 1, wherein the liner sleeve is
mounted on the outer surface of the piston between the piston and
cylinder.
6. The piston assembly of claim 1, wherein the liner sleeve is a
straight cylindrical tube.
7. The piston assembly of claim 1, wherein the surface of the liner
sleeve facing the piston surface has a first mating formation and
the opposing surface of the piston has a second mating formation
configured for alignment and engagement with the first mating
formation when the sleeve is installed.
8. The piston assembly of claim 7, wherein one of said mating
formations comprises an annular rib and the other mating formation
comprises an annular groove.
9. The piston assembly of claim 1, wherein the acoustic dampening
material is plastic or rubber.
10. The piston assembly of claim 9, wherein the acoustic dampening
material of the sleeve is an acrylic plastic material.
11. The piston assembly of claim 1, wherein the cylinder is of
glass material and the piston is of graphite material.
12. A gas pump assembly for a medical ventilator, comprising: at
least a first gas piston assembly comprising a cylinder having a
longitudinal axis and a first hollow piston slidably mounted for
reciprocating movement in the cylinder and having a piston rod
extending out of one end of the cylinder; a drive unit drivably
linked to the piston rod and configured for driving the piston back
and forth in the cylinder; the piston being hollow and having an
inner surface of a first diameter and an outer cylindrical surface
of a second diameter; and at least one liner sleeve mounted on one
of said inner and outer surfaces of the piston and having a close
tolerance fit to the diameter of the piston surface on which it is
mounted, the liner sleeve being of an acoustic dampening material
which has a lower acoustic frequency than the piston material.
13. The assembly of claim 12, further comprising a second piston
assembly identical to the first piston assembly and having a second
cylinder with a longitudinal axis extending parallel to the
longitudinal axis of the cylinder of the first piston assembly, a
second hollow piston slidably mounted for reciprocating movement in
the second cylinder and having a second piston rod extending out of
the one end of the second cylinder, a second linkage connecting the
drive output of the drive motor to the second piston rod, and a
second liner sleeve identical to said one liner sleeve and mounted
on one of the inner and outer surfaces of the second piston.
14. The assembly of claim 12, further comprising a plurality of
additional piston assemblies identical to said first piston
assembly, each additional piston assembly having a piston rod
drivably linked to said drive motor and a respective hollow piston
slidably mounted in the cylinder of said additional piston
assembly, and each hollow piston having a liner sleeve of acoustic
dampening material mounted on one of the inner and outer surfaces
of the respective hollow piston.
Description
BACKGROUND
[0001] 1. Field of the Invention
[0002] The invention relates generally to piston assemblies for gas
pumps and the like having at least one piston reciprocating in a
cylinder, and is particularly concerned with an acoustic dampening
device for reducing any squeaking noise generated as the piston
slides in the cylinder.
[0003] 2. Related Art
[0004] Gas piston pumps are used in medical ventilators and other
applications. In some ventilator pumps, a piston of a first
material such as graphite reciprocates in a cylinder of a second
material such as glass. This has been found to generate squeaking
noise between the graphite and glass due to acoustic resonance
resulting from any slight misalignment between the piston and
cylinder. This noise can occur even for tiny misalignments between
the piston guide pin and the pump chamber or cylinder axis, and it
is difficult to correct such tiny misalignments due to the number
of components involved in such pump assemblies. Such squeaking
noises are a problem to users of home ventilators and the like,
particularly under high humidity conditions when the squeaking is
more prevalent.
[0005] Therefore, what is needed is a system and method that
overcomes these significant problems found in the conventional
systems as described above.
SUMMARY
[0006] It is an object of this invention to provide a pump piston
assembly with an acoustic dampening device which reduces or
eliminates the squeaking noise due to acoustic resonance when the
piston reciprocates in the chamber or cylinder.
[0007] In one aspect, a piston assembly is provided, which
comprises a cylinder of a first material, at least one piston of a
second material different from the first material slidably mounted
for reciprocating motion in the cylinder, the piston being hollow
and having an inner surface of a first diameter and an outer
cylindrical surface of a second diameter, and at least one liner
sleeve mounted on the inner or outer surface of the piston and
having a close tolerance fit or interference fit to the piston
surface on which it is mounted so that there is wall to wall
contact between the opposing surfaces of the liner sleeve and
piston. The liner sleeve is of an acoustic dampening material which
has a lower acoustic frequency than the piston material and is
configured to absorb harmonic acoustic vibrations resulting from
reciprocation of the piston in the cylinder.
[0008] The liner sleeve acts as an acoustic dampening device so as
to absorb or reduce any squeaking noises as the piston reciprocates
in the cylinder, and may be mounted on the outer surface of the
piston or inside the hollow piston. The sleeve is configured such
that there is close wall to wall contact between the piston and
liner sleeve. The sleeve may be of any suitable acoustic dampening
material of relatively low acoustic frequency, and may be of hard
plastic material, rubber, or the like. The sleeve may be attached
to the inner or outer surface of the piston by an adhesive, or may
be press fit inside or outside the piston.
[0009] Other features and advantages of the present invention will
become more readily apparent to those of ordinary skill in the art
after reviewing the following detailed description and accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The details of the present invention, both as to its
structure and operation, may be gleaned in part by study of the
accompanying drawings, in which like reference numerals refer to
like parts, and in which:
[0011] FIG. 1 is a simplified longitudinal cross-sectional view of
one embodiment of a piston assembly for a gas pump incorporating an
acoustic dampening device;
[0012] FIG. 2 is a longitudinal cross-sectional view similar to
FIG. 1 but illustrating an alternative configuration of the
acoustic dampening device;
[0013] FIG. 3 is a perspective view of another embodiment of an
acoustic dampening device for use in a piston assembly of a gas
pump or the like;
[0014] FIG. 4 is a longitudinal cross-sectional view similar to
FIGS. 1 and 2 illustrating a second embodiment of a piston assembly
incorporating the acoustic dampening device of FIGS. 3; and
[0015] FIG. 5 is a simplified perspective view of a gas pump
assembly for a medical ventilator, with an acoustic dampening
device as in FIG. 1, 3 or 4 associated with each of the
pistons.
DETAILED DESCRIPTION
[0016] Certain embodiments as disclosed herein provide for a gas
pump assembly of a medical ventilator or the like incorporating an
acoustic dampening device to reduce or eliminate the squeaking
noise of one or more pistons of the pump assembly sliding in its
respective pump chamber or cylinder.
[0017] After reading this description it will become apparent to
one skilled in the art how to implement the invention in various
alternative embodiments and alternative applications. However,
although various embodiments of the present invention will be
described herein, it is understood that these embodiments are
presented by way of example only, and not limitation. As such, this
detailed description of various alternative embodiments should not
be construed to limit the scope or breadth of the present invention
as set forth in the appended claims.
[0018] FIG. 1 illustrates a first embodiment of a piston assembly
10 for a gas pump or the like incorporating an acoustic dampening
device or liner sleeve 12. Piston assembly 10 basically comprises a
hollow piston 14 slidably contained within a cylinder 15 inside
pump housing 16. A piston rod 18 extends from an end wall 19 of the
piston through a diaphragm seal 20 in one end of the cylinder and
is linked via a sliding drive linkage 34 to a drive assembly or
unit which drives piston 14 to reciprocate back and forth along
drive axis 22 in cylinder 15. The linkage 34 illustrated in FIG. 1
is configured to convert rotational movement of a drive shaft into
axial movement of piston 14 and piston rod 18, as described in more
detail in U.S. Pat. No. 7 654 802 of Crawford, Jr. et. al., the
contents of which are incorporated herein by reference. However,
the acoustic dampening device or liner sleeve 12 may be installed
on any piston where noise generated by sliding of the piston in its
associated cylinder is a problem, regardless of the piston drive
mechanism, and any suitable drive assembly and drive linkage may be
used to drive piston 14.
[0019] In a ventilator gas pump, piston 14 may be of graphite
material while cylinder 15 is of glass such as Pyrex.RTM. or the
like. In one embodiment, the liner sleeve or dampening device 12
may be of any suitable acoustic dampening material having a low
acoustic frequency so as to absorb harmonic vibrations resulting
from a graphite piston sliding in a glass cylinder, although the
piston and cylinder may be of different materials in alternative
embodiments. The acoustic frequency of the material of liner sleeve
12 is less than that of the piston material. Plastic material is
suitable for manufacture of the acoustic dampening sleeve due to
its low acoustic frequency, easy fabrication, and low cost.
However, other low acoustic frequency materials such as rubber may
be used in alternative embodiments. In one embodiment, a relatively
hard plastic material such as acrylic plastic or the like may be
used for the liner sleeve. In one embodiment, the liner sleeve 12
was of VisiJet.RTM. 200 plastic, manufactured by 3D Systems of Rock
Hill, S.C.
[0020] In the embodiment of FIG. 1, liner sleeve 12 is a straight
cylindrical tube having an outer diameter which is approximately
the same as the inner diameter of piston 14, so that it is a close
fit inside the piston. The liner sleeve may be mechanically
attached inside the piston in any suitable manner, for example
using adhesive, or may be simply press fitted into the piston with
no additional attachment means. The sleeve 12 is designed to have a
close tolerance or friction fit to the piston so that there is wall
to wall or face to face contact between sleeve 12 and piston 14
along the entire length of the sleeve.
[0021] Although liner sleeve 12 fits inside the piston in the
embodiment of FIG. 1, it may alternatively be designed to fit
around the outside of the piston 14, as illustrated in FIG. 2, with
the inner surface 12 in face to face contact with the outer surface
of piston 14.
[0022] The liner sleeve 12 has a lower acoustic frequency than the
graphite material of piston 14 and tends to absorb harmonic
vibration in the graphite piston/glass sleeve assembly. The lower
acoustic frequency of the sleeve coupled to the piston wall shifts
the natural harmonic frequency of the piston to a lower frequency,
so that the piston is unable or less likely to sustain a harmonic
vibration. This reduces or eliminates the squeaking noise which
would otherwise occur when the graphite piston alone slides in the
cylinder. The dampening action can be compared to what happens when
a tin can is struck with a hard object so that it "rings", but if a
thin rubber sheet is glued to the inside of the can, it no longer
rings when struck, but instead makes more of a dull, "thunk"-like
noise.
[0023] In one embodiment, liner sleeve 12 is a straight tubular
member with smooth cylindrical inner and outer walls, as
illustrated in FIGS. 1 and 2. FIGS. 3 and 4 illustrate an
alternative embodiment in which a liner sleeve or acoustic
dampening device 25 is designed with an annular rib 26 extending
around its outer surface for mating engagement in a corresponding
annular groove 28 in the inner surface of the piston wall (see FIG.
4). In an alternative arrangement, the outer surface of sleeve 25
may have an annular groove for engagement with a corresponding
annular rib on the inner surface of the piston wall. Alternatively,
a sleeve for fitting over the outer surface of the piston as in
FIG. 2 may have an annular rib or groove on its inner surface for
engagement with a corresponding groove or rib, respectively, on the
outer surface of the piston. In alternative embodiments, other
mateable formations may be provided on the opposing surfaces of the
liner sleeve and piston to aid in attachment, such as holes, slots,
ribs, bumps, grooves, flanges, and the like.
[0024] An angled slot 28 is cut through the wall of sleeve 25 so as
to extend at an angle to the central axis of the sleeve. This
allows the sleeve to be compressed during installation into the
piston. The slot 28 may be parallel with the sleeve axis in
alternative embodiments, but the angled slot allows for additional
compression as the opposing angled faces 29 of the slot slide
against one another. In one embodiment, slot 28 may extend at an
angle of around 45 degrees to the central longitudinal axis of the
sleeve. The angled slot can be of minimal width and helps to ensure
that the sleeve is not displaced during operation. Since the slot
allows for compression of the sleeve during installation, the
sleeve may have an oversized outer diameter slightly greater than
the inner diameter of the piston in this embodiment, to ensure full
wall contact between the liner sleeve and piston faces. The slot
removes excessive stress or the need for expensive tolerances
during manufacture of the part, due to the compressibility of the
sleeve.
[0025] Although the sleeve is generally tubular or cylindrical in
the above embodiments, it may be of a variety of different
configurations or shapes as long as it has a face substantially
matching the opposing piston face and in close contact with that
face along the entire length of the sleeve or dampening device.
Although a single, one-piece sleeve is used as the dampening device
in the foregoing embodiments, two or more sleeves may be inserted
into the piston in alternative embodiments, providing a multi-layer
acoustic dampening device. The sleeves may be of the same materials
or different materials. In one embodiment, a first sleeve may be of
hard plastic while a second sleeve is of rubber. Multiple dampening
sleeves of different materials may help to tune the piston at a
desired acoustic frequency or may aid in attachment to the piston
due to the tendency of rubber to adhere to the harder plastic
material.
[0026] In the embodiments of FIGS. 1 to 4, the wall thickness of
liner sleeve 25 is about the same as the wall thickness of piston
12, but a thicker or thinner liner sleeve may be provided in
alternative embodiments, depending on the noise dampening qualities
required for a particular application. As noted above, the liner
sleeve 12 or 25 may be used for reducing squeaking noise during
operation of a gas pump piston assembly, such as the piston
assembly of a medical ventilator. Such squeaking noises can be
annoying or disruptive during use of medical ventilators in a
homecare environment, hospital, or during transportation of
patients. For example, the HT70 ventilator of Newport Medical
Instruments, Newport Beach, Calif. has a pump piston assembly which
includes two or four piston assemblies driven by a common pump
drive unit, as described in more detail in U.S. Pat. No. 7,654,802
referenced above. Squeaking noises as described above have been
encountered during use of this pump, and can be reduced or avoided
by installation of a noise dampening device or liner sleeve as
described above in connection with FIGS. 1 to 4 on each of the
pistons of the pump.
[0027] FIG. 5 illustrates part of a dual piston ventilator pump 40
which has two pistons 14 driven by a reciprocating drive assembly
30 identical to that described in U.S. Pat. No. 7,654,802
referenced above, which has a rotational drive or motor 32 and a
sliding drive linkage 34 at each end of the rotational drive which
converts rotation of the opposing drive or crank shafts 35 into
linear reciprocating movement of the pistons. The glass cylinder
and pump housing in which each piston slides is omitted in FIG. 5
for clarity. Pistons 14 of FIG. 5 are identical to the piston 14
described above in connection with FIGS. 1 to 4. A liner sleeve 25
is press fitted inside the inner diameter of each piston 14 for
acoustic dampening purposes. Alternatively, a straight tubular
liner sleeve 12 as illustrated in FIG. 1 may be fitted inside
pistons 14, or the sleeve may be mounted around the outer surface
of the piston, as in FIG. 2. In a four piston pump assembly, a
similar acoustic dampening sleeve or liner sleeve is associated
with all four pistons to reduce or eliminate squeaking noises.
[0028] In one embodiment of a liner sleeve designed for
installation in the inner diameter of a pump of the HT70 ventilator
described above, the sleeve has an inner diameter of about 0.98
inches, an outer diameter of approximately 1.14 inches, and a
height of around 0.5 inches. However, sleeves may be made of any
suitable dimensions depending on the dimensions of the piston in
which they are to be fitted. The outer diameter should be as close
as possible to the inner diameter of the piston, or slightly
greater than the inner diameter of the piston in the case of a
sleeve 25 with an angled slot 26 as in FIG. 4. The goal is to have
an interference or friction fit between the opposing surfaces of
the piston and liner sleeve, so as to shift or change the natural
frequency of the graphite material of the piston to the combined
frequency of the graphite material and the plastic material of the
liner sleeve. This helps to avoid or limit acoustic resonance or
squeaking noises. With a graphite material piston alone, acoustic
resonance is found to occur in the frequency range correlated to
200 to 350 rpm. The acoustic resonance frequency of the combined
plastic and graphite material in the assemblies of FIGS. 1, 2, 4
and 5 is shifted away from this range so that little or no sound
due to resonance is emitted in the normal operating range of the
pump. A number of HT70 ventilator pumps known to have a squeaking
problem were modified to include a liner sleeve as described above,
and the pumps were found to have no squeaking noise in a five day
burn-in test. In other embodiments, a liner sleeve 12 or 25 may
alternatively be installed on the pistons of other types of pumps
or other devices in which piston noise or squeaking is a
problem.
[0029] The above description of the disclosed embodiments is
provided to enable any person skilled in the art to make or use the
invention. Various modifications to these embodiments will be
readily apparent to those skilled in the art, and the generic
principles described herein can be applied to other embodiments
without departing from the spirit or scope of the invention. Thus,
it is to be understood that the description and drawings presented
herein represent a presently preferred embodiment of the invention
and are therefore representative of the subject matter which is
broadly contemplated by the present invention. It is further
understood that the scope of the present invention fully
encompasses other embodiments that may become obvious to those
skilled in the art and that the scope of the present invention is
accordingly limited by nothing other than the appended claims.
[0030] We claim:
* * * * *