U.S. patent number 3,554,316 [Application Number 04/879,679] was granted by the patent office on 1971-01-12 for detachable elastomer muffler for pneumatic percussive tools.
This patent grant is currently assigned to Chicago Pneumatic Tool Company. Invention is credited to Paul J. Bilodeau, Sebastian F. Judd.
United States Patent |
3,554,316 |
Judd , et al. |
January 12, 1971 |
DETACHABLE ELASTOMER MUFFLER FOR PNEUMATIC PERCUSSIVE TOOLS
Abstract
A one-piece muffler formed of elastomer material, having a
C-configuration adapted to collar over the exhaust ports of a
pneumatic percussive demolition tool, and adapted to be detachably
clamped in fluid tight relation to the tool. The muffler defining
with the surface of the tool a pair of internal connected chambers,
each tuned to filter out certain objectionable noise
characteristics of the air exhausting from the tool before the
exhaust air is discharged to atmosphere. The elastomer construction
serves to minimize ice formation within the muffler, and to resist
damage from rough handling and impact blows.
Inventors: |
Judd; Sebastian F. (Whitesboro,
NY), Bilodeau; Paul J. (Utica, NY) |
Assignee: |
Chicago Pneumatic Tool Company
(New York, NY)
|
Family
ID: |
25374664 |
Appl.
No.: |
04/879,679 |
Filed: |
November 25, 1969 |
Current U.S.
Class: |
181/230;
173/DIG.2 |
Current CPC
Class: |
B25D
17/12 (20130101); F01B 11/04 (20130101); Y10S
173/02 (20130101) |
Current International
Class: |
B25D
17/00 (20060101); B25D 17/12 (20060101); F01B
11/04 (20060101); F01B 11/00 (20060101); F01n
001/08 () |
Field of
Search: |
;181/36,36.1,47,57,47.1 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Ward, Jr.; Robert S.
Claims
We claim:
1. In a pneumatic tool having a cylinder section provided with
exhaust ports through which spurts of air spent in reciprocating a
piston rapidly and forcefully issue, a one-piece noise muffler
formed of resilient flexible material detachably mounted to the
cylinder section of the tool defining with the outer surface of the
latter a pair of sound filtering chambers, the area of contact of
the muffler with the cylinder section being fluid tight, the
exhaust ports being of equal area dimension and opening into one of
the chambers, ports corresponding in number and area dimension to
that of the exhaust ports connecting the one chamber to the second
chamber, a discharge port from the second chamber corresponding in
area dimension to that of an exhaust port, so that exhaust air flow
from the exhaust ports through the pair of chambers to the
discharge port is without consequent back pressure, and the
chambers being unequal in volume and length, so that each chamber
differs in its design sound wave frequency from that of the
other.
2. A pneumatic percussive tool having a cylinder section provided
with exhaust port means through which spurts of air spent in
reciprocating a piston rapidly and forcefully issue, a one-piece
noise muffler having a C-configuration formed of elastomeric
material detachably mounted to the cylinder section defining with
the outer surface of the latter a sound filtering chamber system
into which the exhaust port means opens, the chamber system having
an exhaust air discharge port means connecting the chamber system
with atmosphere, wherein means is provided for detachably clamping
the muffler to the tool in such manner that its perimetric edges
are in fluid tight contact with the surface of the cylinder section
of the tool.
3. A pneumatic percussive tool as in claim 2, wherein the cylinder
section includes a radial rib along its back and an adjacent curved
forward portion through which the exhaust port means opens, the
muffler has a curved wall portion collaring the curved portion of
the cylinder section and has a pair of free end walls clamped to
opposite faces of the rib.
4. A pneumatic percussive tool as in claim 3, wherein the muffler
has top and bottom walls offset radially from corresponding ends of
its curved wall portion, the top and bottom walls each having an
inner radiused axially extending narrow wall in conforming contact
relation with the curved forward portion of the cylinder
section.
5. A pneumatic percussive tool as in claim 4, wherein the cylinder
section has upper and lower radial flat shoulders lying
respectively in backing relation to the top wall and the bottom
wall of the muffler so as to support said top and bottom walls from
being blown resiliently outwardly relative to the muffler under
force of exhaust air entering the muffler.
6. A pneumatic percussive tool as in claim 4, wherein the inner
radiused axially extending narrow wall of the top wall of the
muffler has a depending lip tapered toward the curved forward
portion of the cylinder section and resiliently pressed upon the
latter, and wherein the radiused axially extending narrow wall of
the bottom wall has an upwardly extending lip tapered toward the
curved forward portion of the cylinder section and resiliently
pressed upon the latter.
7. A pneumatic percussive tool as in claim 3, wherein a bead
portion is formed vertically of each of the free end walls and is
resiliently pressed against the corresponding face of the rib.
8. A pneumatic percussive tool as in claim 4, wherein a partition
wall is offset radially from the curved wall portion of the muffler
in axially spaced relation between the top and bottom walls and has
a inner radiused axially narrow wall engaging the curved wall
portion of the cylinder section of the tool so as to define an
upper chamber and a lower chamber for the muffler.
9. A pneumatic percussive tool as in claim 8, wherein the exhaust
ports of the tool open radially into the upper chamber, the upper
chamber communicates with the lower chamber by means of a pair of
openings through the partition wall at opposite ends of the upper
chamber, each opening being defined in part by a vertical wall
portion of the muffler and in part by a wall portion of the
cylindrical section of the tool.
10. A pneumatic percussive tool as in claim 9, wherein the length
of one chamber relative to that of the other is in the ratio of
2:1.
11. An elastomer muffler unit for the exhaust of a pneumatically
percussive tool, comprising a one-piece curved body of
C-configuration having an outer curved side wall, a top wall offset
radially from the upper end of the sidewall, a bottom wall offset
radially from the lower end of the sidewall in parallel relation to
the top wall, and having an intermediate wall offset radially from
the sidewall between the top and bottom walls, the several walls
terminating at opposite ends in a pair of spaced opposed common
vertical end walls each having a broad inner face in opposed
relation to the other and each having an inner vertical sidewall, a
notch formed in one end of the partition wall having as one edge
thereof the inner vertical side of one end wall, and a similarly
formed notch in the opposite end of the partition, each of the
radial walls having an inner radiused wall adapted to engage about
a complementary surface of a pneumatic tool, and the vertical end
walls being adapted to be detachably mounted to opposite faces of a
back rib of the said tool.
12. An elastomer muffler as in claim 11, wherein a bar insert is
embedded in each of the inner faces of the end walls, the insert
having a plurality of openings spaced one above the other for
reception of mounting bolts.
13. An elastomer muffler as in claim 11, wherein a lip coextensive
with the inner radiused wall of the top wall is inclined downwardly
and radially inwardly of the said radiused wall, and wherein a
similar lip in opposed relation to the lip of the top wall is
coextensive with the inner radiused wall of the bottom wall.
Description
BACKGROUND OF THE INVENTION
This invention is directed to an elastomer muffler for the exhaust
of pneumatic percussive tools.
The invention is especially suited for application to percussive
tools of the demolition type such as are used in breaking up
concrete and in tearing up the pavement of city streets. In this
kind of tool, a heavy piston is pneumatically reciprocated to
repeatedly pound in anvil against a work steel. The piston is
reciprocated at a rapid rate. With each piston stroke spent
operating air normally exhausts directly to atmosphere and expands
to produce objectionable pulsating noise varying in intensity and
pitch.
The general objective of this invention is to transform this
objectionable noise into an auditorily acceptable substantially
nonpulsating steady sound of comparatively low pitch and reduced
intensity; and to provide a detachable muffler for this purpose of
an improved nature.
The muffler of the present invention is in the nature of a hood
which collars the housing of the tool over its exhaust ports.
A problem associated with mufflers of this general nature is icing
of its internal wall surfaces due to excessive cooling of the tool
by the rapidly exhausting air and consequent freezing of the water
vapor normally present in the operating air.
Mufflers of this general hood nature for percussive tools are known
from U.S. Pat. No. 3,224,527 and from the British Pat.
Specification No. 932,373. The muffler known from the U.S. patent
is of metal construction made integral with the housing of the
tool. This known structure, while having acceptable silencing
characteristics, adds excessively to the weight of the tool.
Internal icing of this metal muffler results in external surface
condensation.
The muffler of the present invention is formed of tough, resilient
plastics or elastomeric material which, because of its light
weight, improves over the metal type. Because of its resilience, as
well as its inherent smoothness and slipperiness, problems of
internal icing and external condensation are reduced to a minimum.
Because of its resilience, air exhausting from the tool tends to
vibrate the muffler's walls to cause ice coatings developing
thereon to shatter and fall away before they can build up to an
undesirable degree. Because of its toughness, the muffler is
capable of resisting abrasion and is able to absorb the impact of
heavy blows without cracking or tearing. The muffler material is
not subject to deterioration from the oil and water moisture
usually present in the operating air.
The muffler known from the British patent specification is formed
of resilient material. But this muffler has various structural and
mounting deficiencies creating various problems. It is made of two
separable halves clamped together, a condition which tends, for one
thing, to reduce its overall resiliency. It has mounting faults,
particularly at its neck end which, together with sound deadening
material disposed in a chamber of the device, are likely to cause
undesirable back pressure and leakage. Back pressure would effect
the operating efficiency of the tool; exhaust leakage around the
neck of the muffler would interfere with comfortable handling of
the tool by the operator. Icing that might accumulate in the
deadening material is very likely to impede exhaust flow.
The muffler of the present invention also materially improves over
that of the known British structure. It is a one-piece structure
detachably mountable to the tool. It is of an open collar or C-form
having mounting means at its terminal end which does not
undesirably affect its resiliency. It is associated with the
housing of the tool in a clamping manner so that undesirable
exhaust leakage is avoided; and the ends of the muffler are not
likely to be blown out by the force of exhausting air. It does not
require deadening material in its interior since it functions to
silence the exhaust noise by means of sound filtering chambers. It
further includes internal exhaust flow passages so arranged that it
is difficult for them to become blocked by pieces of ice that might
fall from the wall of the muffler. These passages allow free flow
of the exhaust air through the muffler to atmosphere without
undesirable development of back pressure .
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawing:
FIG. 1 is a view in vertical section of a pneumatic percussive
demolition tool embodying the invention;
FIG. 2 is a section taken on line 2-2 of FIG. 1;
FIG. 3 is a section taken on line 3-3 of FIG. 1;
FIG. 4 is a view in front elevation of the muffler apart from the
tool;
FIG. 5 is a section taken on line 5-5 of FIG. 4;
FIG. 6 is a top plan view of FIG. 4, part being shown in a section
made on line 6-6 of FIG. 5; and
FIG. 7 is a fragmentary section taken on line 7-7 of FIG. 5.
DESCRIPTION OF PREFERRED EMBODIMENT
Reference is now directed to the drawing wherein there is disclosed
a conventional pneumatic percussive tool 10 of the demolition type
to which an elastomeric muffler unit 11 is detachably mounted. The
tool includes a general housing 12 having a piston cylinder section
13 connected at one end to a backhead handle section 14 and
connected at its other end to a front end section 15. A
manipulative throttle valve 16 in the handle section controls
feeding of operating air from a supply inlet 17 to a valve chamber
18. The inlet is connected by hose line 19 to an external source of
live air having a constant pressure. A conventional air driven
slide valve 21 is reciprocable in the valve chamber in known manner
to cause the inlet air to be applied alternately to opposite ends
of a piston chamber 22 to reciprocate a heavy piston 23.
The piston reciprocates at the rate of about 20 cycles per second
to pound an anvil 24 against a work steel 20. Following each piston
stroke, which occurs about 2,400 times per minute, the spent air
exhausts forcefully from the tool through a pair of side ports 25.
Except for the muffler unit 11, the exhausting air upon issuing
from the side ports to atmosphere would expand and produce an
objectionable loud pulsating noise varying in intensity and
pitch.
The piston cylinder section 13 of the housing is substantially
cylindrical or curved for the major portion of its length except
for a radial rib 26 extending lengthwise of its back. The rib
serves to accommodate a pair of vertical inlet air feed passages 27
connecting with the lower end of the piston chamber. The exhaust
ports 25 open radially at the same level through the curved portion
of the piston cylinder at about midway of the length of the
latter.
The muffler 11 is a separable unit of a general C-configuration. It
serves to materially attenuate the noise of the exhaust air. It is
in the nature of a hood which collars the piston cylinder portion
of the housing over its exhaust ports 25. The muffler is a
one-piece structure formed as by molding from tough elastomeric
material. It includes a top wall 28, a bottom wall 29 and an
intermediate partition wall 31, all being parallel and concentric
to one another. Each wall is offset radially inward from a common
curved outer sidewall 32. The several walls, including the
sidewall, extend for approximately three-fourths of a circle and
terminate at their free ends in a pair of common opposed laterally
spaced vertical end walls 33. The top, bottom and intermediate
walls have narrow inner radiused walls 34 which conform to the
curvature of the piston cylinder and snugly engage the latter. Each
end wall 33 is thickened so as to define a vertical pad having a
broad inner face which overlies a corresponding side face of the
rib of the tool and is detachably bolted thereto, as in FIG. 2.
A metal bar insert 35 molded into the inner face of each end wall
at the time of forming the muffler provides a means for rigidly
mounting the muffler to the tool. A series of bolts 36 extending
through the inserts and threadedly drawn tightly into holes 37 in
the sides of the housing rib securely retain the muffler to the
tool.
In the mounted condition of the muffler (FIG. 1) its top wall 28
lies in abutment with an overhead radial shoulder 38 extending
about the piston cylinder; and its bottom wall 29 is seated upon a
second radial shoulder 39 extending about the lower end of the
piston cylinder. Further, in the mounted condition of the muffler,
a first curved chamber 41 is defined above the partition wall 31.
This chamber connects by means of a pair of openings or passages 42
through the partition wall with a second curved chamber 43 defined
below the partition. The exhaust ports 25 open into the upper
chamber. Air exhausting in conventional manner from the tool into
the upper chamber passes through the openings 42 to the lower
chamber and exits to atmosphere through a discharge port 44. The
latter is located at the front of the muffler opposite to the rib
26; and directionally away from the position normally taken by the
operator so that the venting air does not inconvenience the
operator.
The construction of the muffler and its mounting arrangement with
the tool is such that its areas of contact with the housing are
sealed against leakage of the exhaust air forcefully flowing
through the muffler. In this respect, a bead 45 of the elastomeric
material forming the muffler extends lengthwise of each of the free
end walls 33 of the muffler. Upon tightening of the mounting bolts
36, each bead is resiliently compressed against the corresponding
face of the rib of the housing as appears in FIG. 3, to seal
against leakage from the muffler in the area of the rib.
The surface contact with the tool of the inner radiused wall 34 of
the top wall 28 of the muffler is axially extended by means of a
lip portion 46 tapering downwardly toward the tool's surface. A
similar oppositely extending lip 47 is provided on the inner
radiused wall 34 of the bottom wall 29 of the muffler. In the
unmounted condition of the muffler, as appears in FIG. 5, the lip
portions 46 and 47 incline slightly inwardly of normal. In the
mounted condition of the muffler, as in FIG. 1, these lip portions
are resiliently pressed tightly about the tool housing in fluid
tight sealing relation to the latter. By means of this mounting
arrangement of the muffler, undesirable leakage of exhaust air
about the top and bottom walls of the muffler is avoided. Leakage
in these areas would cause discomfort to the operator; and would
create an undesirable working condition.
The housing shoulders 38 and 39 provide a rigid backing for the top
and bottom walls of the muffler. The support provided prevents
these resilient walls from being blown outwardly relative to the
tool by the force of the air exhausting into the muffler.
It is to be noted from FIGS. 3 and 6 that the muffler extends for
about three-quarters of a circle and that the spacing 48 between
the free ends 33 thereof is shorter than the outer diameter of the
curved portion of the piston cylinder. This is of advantage in that
it permits the muffler to be resiliently mounted in a naturally
clamped condition about the tool.
The muffler may be readily mounted to the tool without difficulty.
In this operation, its resiliently expansible free ends 33 are
passed over the cylindrical portion of the piston cylinder between
the housing shoulders 38 and 39 until the cylindrical portion of
the cylinder is fully received into the complementary central open
area 49 of the muffler. The free ends 33 are then drawn rearwardly
a little to align the holes 51 of the inserts with those 37 of the
housing rib 26 and to cause simultaneous compression of the lip
portions 46, 47 into sealing contact with the tool. The bolts are
then entered and securely tightened sufficiently to compress the
beads 45 fluid tight against opposite faces of the rib.
To remove the muffler for replacement or repairs, the bolts 36 are
removed and the muffler is resiliently withdrawn from about the
tool.
A problem associated with mufflers of the general hood type is a
tendency of moisture usually present in the operating air to freeze
and coat the interior wall area of the muffler with ice. This
problem is favorably minimized in the muffler of the present
invention by the resilient and flexible nature of the muffler as
well as by a smooth and slippery condition of its internal wall
surface. The particular arrangement of the exhaust ports 25 of the
tool relative to the muffler also aids in preventing ice buildup on
the muffler. In this respect, the exhaust ports open out of the
tool about 60.degree. apart, as appears in FIG. 3, and in such
manner that exhaust air forcefully issuing from each port strikes
an area of the opposed muffler sidewall that is centered between
the front or crest of the muffler and an end 33 of the muffler.
This is an area of the muffler which will most readily be flexed by
the striking air stream.
It can be seen by this advantageous construction of the muffler and
its arrangement relative to the exhaust ports, that it will be
difficult for ice to adhere to its smooth and slippery surface; and
that any coating of ice that should form will readily crack up and
fall away as the muffler walls are flexed and vibrated by the
spurting exhaust air stream.
The problem of blocking the muffler's internal passages 42 with
falling chunks of ice is also favorably minimized in this respect,
as best indicated in FIG. 3, each of the two openings or passages
42 communicating the upper chamber of the muffler with the lower
chamber is located at an end of the chamber. By means of this
location, the walls of the passage are defined in part by a
vertical wall portion 52 of the muffler and in part by a vertical
wall portion of the piston cylinder 13. It can be seen that, should
chunks of ice fall upon the partition wall 31, the vertical wall
portions 52 and 13 will tend to prevent the ice from landing in a
blocking condition over the passages 42.
The discharge port 44 for the muffler is inclined downwardly
through the crest or front area of the lower chamber 43 of the
muffler. This location and form of the discharge port reduces the
possibility of ice chunks landing to clog it. Port 44 also serves
to conduct exhaust air forwardly and away from the operator. A
small drain hole 53 for water developing in the muffler is located
in its bottom wall 29.
A further advantage of the muffler is provided by its resilience
and its inherent toughness. Because of these characteristics, the
muffler is capable of absorbing forceful impacts occasioned by
rough handling and dropping; and, as a consequence, it is not
subject to cracking.
The elastomer from which the muffler is molded is characterized by
its inherent resistance to water, oil and abrasion by its smooth
and slippery properties and by its resilience. Here, an elastomer
material preferred for this purpose is a polyurethane resin
containing about 10 percent Teflon.
If the exhausting air stream from the tool were permitted to issue
directly to atmosphere, it would produce an objectionable complex
pulsating noise, characterized by sounds of a varying low basic
frequency with multiple harmonics extending through the sound
frequency spectrum and further characterized as having a high
decibel noise level. The muffler of the present invention is
designed to materially attenuate and smooth out the objectionable
nature of this noise. To this end, the muffler is designed to
define a sound filtering system through which the exhausting air
stream must pass before issuing to atmosphere.
The exhaust air is caused, as its sound wave pattern is being acted
upon by the muffler, to pass through the muffler in such manner
that no undesirable back pressure develops to interfere with the
operating efficiency of the tool. The exhaust sound that finally
issues from the tool to atmosphere is relatively steady without
objectionable pulsation; is substantially reduced in intensity and
pitch; and is relatively quiet.
The air stream exhausts in spurts from the exhaust ports 25 in two
streams into the upper chamber 41 slightly above the partition or
floor 31 of the upper chamber. Each air stream spurts forcefully
against the opposed resilient sidewall 32 of the muffler causing
the latter wall to develop an oscillating frequency in phase with
the issuance of the stream. This tends to initially reduce the
intensity of the moving air. The air stream then circulates about
the upper chamber and enters in equal volume in two streams through
the openings 42 to the lower chamber 43 at opposite ends of the
latter. After entering the lower chamber, the two air streams are
guided by the parallel curved walls of the piston cylinder and the
sidewall of the muffler an equal distance to the discharge port 44
located at the front or crest of the muffler. Some of this air also
issues in small volume through the drain hole 53.
It is to be noted that the openings 42 in the dividing partition
wall 31 of the muffler correspond in dimension to the exhaust ports
25 of the tool and that the volume of the upper chamber 41 is
relatively large to the volume of exhaust air that can spurt from
the exhaust ports with each stroke of the piston. Accordingly, no
undesirable back pressure will develop in the upper chamber that
might affect the operating efficiency of the tool. And, since the
spurting of exhaust air into the muffler is intermittent, the
continuously open discharge port 44 is adequate to allow continuous
discharge of spent air from the lower chamber 43 without
undesirable back pressure developing. The discharge port
corresponds in its cross dimension to that of one of the exhaust
ports. In effect, the rate and volume of fluid entering from the
exhaust ports into the upper chamber does not exceed that flowing
through the openings 42 into the lower chamber; and the rate and
volume of fluid entering the lower chamber does not exceed that
being discharged from the discharge port 44.
The upper and lower chambers 41 and 43 are in the nature of sound
filtering chambers tuned to different design frequencies, as
determined by their size and vertical dimension, whereby
undesirable sound frequencies are materially attenuated. The upper
chamber functions to attenuate objectionable high sound frequencies
and some of the lower sound frequencies. The lower chamber serves
to further attenuate objectionable high sound frequencies escaping
from the upper chamber as well as undesirable lower sound
frequencies.
It is to be noted that the length of the upper chamber is
approximately twice that of the lower chamber, or in the ratio of
2:1. The volume of the upper chamber to the lower chamber is also
approximately in the same ratio. It has been found that this
construction is productive of good sound attenuating results. The
final sound that issues to atmosphere is relatively quiet, free of
objectionable pulsing, and materially reduced in intensity and
pitch.
* * * * *