Title:
MUFFLER FOR A PNEUMATIC PERCUSSION TOOL
United States Patent 3815705
Abstract:
A muffler for attenuating the sounds generated by the operation of a pneumatic percussion tool is disclosed, wherein the muffler is formed in two, symmetrically-shaped halves to facilitate mounting and demounting from the body of the tool. When mounted on the tool, the muffler surrounds a portion of the tool body including the exhaust ports and includes two expansion chambers and elongated passage means arranged in series flow relation. The first and second expansion chambers are arranged on opposite sides of the tool body and are defined in part by the outer surface of the body. A first orifice means having a predetermined area relationship with respect to the area of the exhaust ports, interconnects the first and second expansion chambers. A second orifice means having a predetermined area relationship with respect to the effective flow area of the first orifice means, interconnects the second expansion chamber with the elongated passage means. The exhaust air flow from the tool expands into the first expansion chamber, and undergoes successive expansions as it proceeds through the second expansion chamber and elongated passage means before discharging into the atmosphere. The sound level of the flow is thus attenuated as it expands and changes direction while passing through the muffler. The material of the muffler is an elastomer, which renders it durable and also contributes to its high frequency sound attenuating characteristics.
US Patent References:
Muffling device
Fuehrer - August 1938 - 2128742
Muffling device
Morrison - July 1939 - 2166218
Muffler attachment for air driven tools of the impact type
Fannen - April 1957 - 2789653
Percussive drill with noise silencer
Waldron - December 1965 - 3224527
DETACHABLE ELASTOMER MUFFLER FOR PNEUMATIC PERCUSSIVE TOOLS
Judd et al. - January 1971 - 3554316
Muffling device
Fuehrer - August 1938 - 2128742
Muffling device
Morrison - July 1939 - 2166218
Muffler attachment for air driven tools of the impact type
Fannen - April 1957 - 2789653
Percussive drill with noise silencer
Waldron - December 1965 - 3224527
DETACHABLE ELASTOMER MUFFLER FOR PNEUMATIC PERCUSSIVE TOOLS
Judd et al. - January 1971 - 3554316
Application Number:
05/311760
Publication Date:
06/11/1974
Filing Date:
12/04/1972
View Patent Images:
Export Citation:
Assignee:
Thor Power Tool Company (Aurora, IL)
Primary Class:
International Classes:
B25D17/12; B25D17/00; F01N1/08
Field of Search:
181/36A,33.4,47
Primary Examiner:
Wilkinson, Richard B.
Assistant Examiner:
Miska, Vit N.
Attorney, Agent or Firm:
Hibben, Noyes & Bicknell
Claims:
I claim
1. A muffler for reducing the operating noise level of a pneumatic percussion tool having an elongated body and exhaust port means in said body through which air under pressure discharges when said tool is in operation, said muffler comprising a jacket adapted to surround said tool body in the vicinity of said exhaust port means and having partition means therein adapted to coact with said body to define first and second expansion chambers therebetween, said first expansion chamber receiving air discharging from said exhaust port means, said second expansion chamber being connected to said first expansion chamber in continuous series flow relation by first orifice means external of said tool body, said jacket having at least one outlet port connecting said second expansion chamber with the atmosphere, and said first and second expansion chambers being arranged on laterally opposite sides of said tool body when said muffler is mounted thereon.
2. The muffler of claim 1, further characterized in that said expansion chambers are generally semi-cylindrical in form and are adapted to extend generally cicumferentially around said tool body.
3. The muffler of claim 1, further characterized in that said first orifice means is located substantially at one of the axial ends of said jacket.
4. The muffler of claim 1, further characterized in that said jacket has a generally cylindrical side wall portion spaced from the outer surface of said tool body when said jacket is mounted on said body, and said partition means comprises a pair of ribs on the inner surface of said side wall portion, said ribs having radially inner edges adapted to engage the body of said tool in sealing relation to define said expansion chambers.
5. The muffler of claim 4, further characterized in that said jacket has axially spaced end wall portions, said ribs extend axially from one of said end wall portions toward the other of said end wall portions, and at least one of said ribs terminates axially inwardly of the inner surface of said other end wall portion to define a gap therebetween, said gap comprising a portion of said first orifice means.
6. The muffler of claim 5, further characterized in that both said ribs terminate axially inwardly of said other end wall portion to define a pair of said gaps therebetween, said gaps comprising said first orifice means.
7. The muffler of claim 1, further characterized in that said first orifice means has an effective flow area of about 1.4 to about 1.5 times the flow area of said exhaust port means.
8. The muffler of claim 1, further characterized in that said jacket is formed in at least two, substantially symmetrical, separable parts, whereby said muffler may be easily mounted on or demounted from the body of said tool.
9. A muffler for attenuating the level of the sound generated by the operation of a pneumatic percussion tool or the like having an elongated body and exhaust port means in said body through which air under pressure discharges when said tool is in operation, said muffler comprising a generally cylindrical jacket adapted to be mounted on said tool body so as to enclose said exhaust port means, said jacket having a generally cylindrical side wall and axially spaced end walls adapted to coact with said body to define first and second expansion chambers therebetween, said first expansion chamber receiving air under pressure discharging from said exhaust port means and said second expansion chamber being connected to said first expansion chamber by first orifice means external of said tool body and arranged in series flow relation therewith, and said jacket having passage means in said second expansion chamber, one end of said passage means being connected to said second expansion chamber and the other end of said passage means being connected to an air outlet port in said jacket.
10. The muffler of claim 9, further characterized in that said passage means comprises at least one elongated passage communicating with said second expansion chamber.
11. The muffler of claim 10, further characterized in that said elongated passage extends axially in said jacket.
12. The muffler of claim 11, further characterized in that said elongated passage has a length approximately equal to 70 per cent of the length of said second expansion chamber.
13. The muffler of claim 10, further characterized in that said elongated passage is formed in a boss on the inner surface of said cylindrical side wall.
14. The muffler of claim 10, further characterized in that a pair of said elongated passages are provided in said jacket.
15. The muffler of claim 14, further characterized in that said pair of elongated passages have upstream ends communicating with said second expansion chamber and comprising second orifice means interconnecting said second and third expansion chambers.
16. The muffler of claim 15, further characterized in that the effective flow area of said second orifice means is about 3/4 to 7/8 times the effective flow area of said first orifice means.
1. A muffler for reducing the operating noise level of a pneumatic percussion tool having an elongated body and exhaust port means in said body through which air under pressure discharges when said tool is in operation, said muffler comprising a jacket adapted to surround said tool body in the vicinity of said exhaust port means and having partition means therein adapted to coact with said body to define first and second expansion chambers therebetween, said first expansion chamber receiving air discharging from said exhaust port means, said second expansion chamber being connected to said first expansion chamber in continuous series flow relation by first orifice means external of said tool body, said jacket having at least one outlet port connecting said second expansion chamber with the atmosphere, and said first and second expansion chambers being arranged on laterally opposite sides of said tool body when said muffler is mounted thereon.
2. The muffler of claim 1, further characterized in that said expansion chambers are generally semi-cylindrical in form and are adapted to extend generally cicumferentially around said tool body.
3. The muffler of claim 1, further characterized in that said first orifice means is located substantially at one of the axial ends of said jacket.
4. The muffler of claim 1, further characterized in that said jacket has a generally cylindrical side wall portion spaced from the outer surface of said tool body when said jacket is mounted on said body, and said partition means comprises a pair of ribs on the inner surface of said side wall portion, said ribs having radially inner edges adapted to engage the body of said tool in sealing relation to define said expansion chambers.
5. The muffler of claim 4, further characterized in that said jacket has axially spaced end wall portions, said ribs extend axially from one of said end wall portions toward the other of said end wall portions, and at least one of said ribs terminates axially inwardly of the inner surface of said other end wall portion to define a gap therebetween, said gap comprising a portion of said first orifice means.
6. The muffler of claim 5, further characterized in that both said ribs terminate axially inwardly of said other end wall portion to define a pair of said gaps therebetween, said gaps comprising said first orifice means.
7. The muffler of claim 1, further characterized in that said first orifice means has an effective flow area of about 1.4 to about 1.5 times the flow area of said exhaust port means.
8. The muffler of claim 1, further characterized in that said jacket is formed in at least two, substantially symmetrical, separable parts, whereby said muffler may be easily mounted on or demounted from the body of said tool.
9. A muffler for attenuating the level of the sound generated by the operation of a pneumatic percussion tool or the like having an elongated body and exhaust port means in said body through which air under pressure discharges when said tool is in operation, said muffler comprising a generally cylindrical jacket adapted to be mounted on said tool body so as to enclose said exhaust port means, said jacket having a generally cylindrical side wall and axially spaced end walls adapted to coact with said body to define first and second expansion chambers therebetween, said first expansion chamber receiving air under pressure discharging from said exhaust port means and said second expansion chamber being connected to said first expansion chamber by first orifice means external of said tool body and arranged in series flow relation therewith, and said jacket having passage means in said second expansion chamber, one end of said passage means being connected to said second expansion chamber and the other end of said passage means being connected to an air outlet port in said jacket.
10. The muffler of claim 9, further characterized in that said passage means comprises at least one elongated passage communicating with said second expansion chamber.
11. The muffler of claim 10, further characterized in that said elongated passage extends axially in said jacket.
12. The muffler of claim 11, further characterized in that said elongated passage has a length approximately equal to 70 per cent of the length of said second expansion chamber.
13. The muffler of claim 10, further characterized in that said elongated passage is formed in a boss on the inner surface of said cylindrical side wall.
14. The muffler of claim 10, further characterized in that a pair of said elongated passages are provided in said jacket.
15. The muffler of claim 14, further characterized in that said pair of elongated passages have upstream ends communicating with said second expansion chamber and comprising second orifice means interconnecting said second and third expansion chambers.
16. The muffler of claim 15, further characterized in that the effective flow area of said second orifice means is about 3/4 to 7/8 times the effective flow area of said first orifice means.
Description:
This invention relates to sound attenuating devices, and more particularly relates to a muffler for reducing the operating noise level of a pneumatic percussion tool.
Pneumatic percussion tools, such as pavement breakers and the like, have long been objected to because of the noise level generated when such tools are in operation. Such noise level is disturbing not only because of its intensity but also because of the frequency range thereof. In other words, the sounds generated by the operation of unmuffled pneumatic percussion tools are not only of a low basic frequency but also include multiple harmonics extending through the whole sound frequency spectrum. Consequently, some, if not all, of these frequencies are objectionable to most people. In addition, since the motive fluid discharging from the exhaust ports of such tools is usually pulsating, the resulting sound is also pulsating and therefore objectionable for this additional reason.
Various types of muffling devices have been heretofore developed for attenuating the level of the sound generated by the operation of pneumatic percussion tools. Examples of some of these are disclosed in the Hayes U.S. Pat. No. 3,635,299, Fannen U.S. Pat. No. 2,789,653, Waldron U.S. Pat. No. 3,224,527, Wallace U.S. Pat. No. 3,255,844 and Barber et al. U.S. Pat. No. 3,365,022 patents. However, the muffling or silencing devices disclosed in these patents suffer from various shortcomings such as structural complexity, excessive bulk, lack of adaptability to use with different tools and insufficient attenuation of the sound levels generated by the tools with which they were associated.
Moreover, many of the devices heretofore advanced, while being capable of satisfactorily attenuating the sound levels generated by the associated tool, were only able to do so at a substantial loss in the operating efficiency of the tool. In addition, some of the muffling devices of the prior art were incapable of withstanding the normal rough handling incident to the operation of tools of this character.
Accordingly, it is the general object to provide a novel and improved muffler for a pneumatic percussion tool, which overcomes the aforementioned disadvantages of the prior art.
Another object is to provide a novel muffler for attenuating the sounds generated by a pneumatic percussion tool, which does not reduce the operating efficiency of the tool to any significant extent.
A further object is to provide a novel muffler for a pneumatic percussion tool, which is capable of attenuating substantially the entire frequency range of the sounds generated by the tool when the latter is in operation.
Still another object is to provide a novel muffler of the foregoing character having improved high frequency sound attenuation characteristics.
A particular object is to provide a novel muffler for a pneumatic percussion-type tool, which is compact in size, rugged in construction, durable in use, and economical to manufacture.
A still further object is to provide a novel muffler for a pneumatic tool, which may be easily and rapidly mounted on or demounted from an associated pneumatic tool.
These and other objects will become apparent from the following detailed description and accompanying sheets of drawings, in which:
FIG. 1 is a perspective view of a pneumatic percussion tool, in the present instance a paving breaker, the latter being equipped with a muffler embodying the features of the present invention;
FIG. 2 is a transverse cross sectional view taken substantially along the line 2--2 of FIG. 1;
FIG. 3 is a somewhat enlarged, transverse sectional view taken substantially along the line 3--3 of FIG. 1;
FIG. 4 is a somewhat enlarged, longitudinal sectional view taken along the line 4--4 of FIG. 2;
FIG. 5 is a longitudinal sectional view taken substantially along the line 5--5 of FIG. 4;
FIG. 6 is a staggered, transverse sectional view taken along the line 6--6 of FIG. 4; and
FIG. 7 is an exploded perspective view of the muffler illustrated in FIGS. 1-6, inclusive, and showing the parts of the muffler as they would appear in relation to an associated pneumatic tool.
Briefly described, the present invention contemplates a novel muffler for use with pneumatic percussion tools or the like, for attenuating the sounds generated by the operation of such tools. The muffler, to be hereinafter described in detail, is preferably constructed in two parts and utilizes what may be termed a "clamshell" construction. Thus, the muffler halves are preferably symmetrical in shape and adapted to surround a portion of the body of the associated percussion tool in the vicinity of the exhaust ports. When mounted on the tool body, the muffler forms a jacket which coacts with the exterior of the body to define at least one and preferably a plurality of expansion chambers therein. Internal ribs or baffles are provided on the inner surface of the muffler halves, such ribs coacting with the outer surface of the associated tool body to define two of the expansion chambers. A first orifice means having an effective flow area of a particular size interconnects these chambers. The muffler also includes a third expansion chamber provided by a pair of elongated passages which communicate at one end with the second expansion chamber and at their opposite ends with outlet ports in the jacket through which the expanded air from the exhaust ports of the tool finally discharges. The effective flow area of the third orifice means is likewise of a particular size. The muffler halves are of an elastomeric material which improves both the durability and high frequency sound attenuating characteristics of the muffler.
Referring now to FIG. 1, a muffler embodying the features of the present invention is indicated generally at 10 and shown as it would appear when mounted on an associated pneumatic tool, such as paving breaker, indicated generally at B. The paving breaker B, in the present instance, comprises an elongated tool body 11 having handles 12 and a control lever 13 at the upper end thereof for controlling the operation of the tool. A work steel, such as a moil point 14 of the type disclosed in the copending Irvin R. Danielson U.S. Patent application, Ser. No. 260,373, filed June 7, 1972 and assigned to the assignee of this application, is shown mounted in the lower end, indicated at 16, of the tool body 11. The moil point 14 is releasably retained in the body 11 by a latch assembly 17.
Working fluid, in the present instance air under pressure, is supplied to the paving breaker B through an inlet fitting 18 at the upper end thereof, and an automatic valve (not shown) in the upper end of the body 11 serves to control the supply of air under pressure to a piston or a hammer 22 (FIG. 4) that is reciprocatively mounted in a bore 23 (FIG. 4) in the body 11. The piston 22 impacts against the upper end of a tappet 24 which is reciprocatively mounted in a stepped bore 25 in the tool body 11 and which imparts impact blows to the upper end of the steel 14. Air under pressure is exhausted from the tool body 11 at the completion of each working stroke of the piston 22 through exhaust port means in the form of a plurality of exhaust ports 26. The operation of the paving breaker B is continuous so long as the throttle lever 13 is held in a depressed position and air under pressure is continuously supplied to the inlet fitting 18.
Referring initially to FIG. 7, it will be seen that the muffler 10 is formed in two parts or halves 10a and 10b, which are preferably symmetrical and of an elastomeric material, such as polyurethane. The reasons for using this material, and the advantages obtained thereby, will be described hereinafter.
The muffler halves 10a and 10b respectively have generally semi-cylindrical side walls 32a and 32b, and upper and lower end walls 33a and 33b and 34a and 34b. The upper and lower end walls 33a and 33b and 34a and 34b are respectively provided with recesses 36a and 36b and 37a and 37b, which are shaped to closely conform to the external contours of the tool body 11 when the muffler 10 is mounted thereon. Thus, in the present instance, the recesses 36a and 36b in the upper end walls 33a and 33b are generally semicircular, while the recesses 37a and 37b in the lower end walls 34a and 34b are generally V-shaped in cross section.
In order to assure that the recesses 36a, 36b and 37a, 37b sealingly engage the exterior of the tool body 11 when the muffler 10 is assembled thereon, as shown in FIG. 1, a pair of clamps 42 and 43 are provided for surrounding and compressing axially outwardly extending flange portions 44a and 44b and 45a and 45b on the upper and lower end walls 33a and 33b and 34a and 34b, respectively. Thus, when the clamps 42 and 43 are drawn up, the recesses 36a and 36b and 37a and 37b will tightly engage the adjacent portions of the tool body 11.
In order to assure a pressure-tight seal between the abutting peripheral edges of the muffler halves 10a and 10b, such edges are provided with outwardly extending flanges 47a and 47b, respectively, having a plurality of openings 48a and 48b therethrough for receiving a plurality of fasteners such as screws 52. Since the flanges 47a and 47b, and the other portions of the muffler halves 10a and 10b are preferably of an elastomeric material, the flanges are reinforced with metal inserts. A pair of these inserts is indicated at 53b and 54b in FIG. 4 in the flange 47b of the muffler halve 10b. A similar pair of inserts are provided in the flange 47a of a muffler halve 10a. In the illustrated construction, the inserts 53b and 54b are threaded to receive the threaded shanks of the screws 52 and the inserts in the flange 47a are merely bored to permit the shanks of the screws 52 to extend through the flange 47a. Thus, when the screws 52 are drawn up, the flanges 47a and 47b sealingly engage each other.
As heretofore mentioned, the muffler 10 is provided with at least one and preferably a plurality of expansion chambers therein for receiving the high velocity, pulsating, flow of air from the discharge ports 26 of the tool, and for attenuating the level of the sound generated by such flow when the tool is in operation. To define these chambers in the muffler 10, the halves 10a and 10b are respectively provided with partition means defined by inner walls or partitions 56a and 56b (FIGS. 4-7, inclusive), which divide the interior of each muffler half into two compartments. Each of the partitions 56a and 56b is preferably formed integrally with the material of its respective muffler half and comprises a pair of longitudinally extending, transversely spaced ribs 57 and 58. The radial width of the ribs is such that the radially inner ends thereof contact and sealingly engage the outer surface of the tool body 11 when the muffler halves 10a and 10b are assembled thereon. Thus, when the muffler halves 10a and 10b are assembled on the tool body 11, as illustrated on FIG. 6, the partitions 56a and 56b define first and second expansion chambers 61 and 62, respectively, therein. These expansion chambers are generally semi-cylindrical in cross section and are arranged on the laterally opposite sides of the tool body.
As heretofore mentioned, the expansion chambers 61 and 62 are in series flow relation. To this end, first orifice means is provided for continuously interconnecting the chambers 61 and 62. Such orifice means is preferably provided by a pair of gaps 63 and 64 (FIG. 4 and 5) defined between the lower end edges 66 of the ribs 56a and 56b, and the adjacent end face, indicated at 67, of a flange 68 on the body 11 of the tool.
With the foregoing construction, the pulsating flow of air from the exhaust ports 26 of the tool B first discharges into the expansion chamber 61 at an angle determined by the exit angle of the ports 26. After entering the chamber 61, the flow expands and the sound level of the flow is attenuated. Some attenuation also occurs as a result of the interference between the pressure waves in the flow as the waves reflect back and forth from the various walls of the chamber 61.
After the exhaust air flow from the discharge ports 26 has fully expanded in the chamber 61, the flow proceeds through the first orifice means or gaps 63 and 64 at the lower ends of the partitions 56a and 56b, and then enters the second expansion chamber 62. The gaps 63 and 64 and other geometry of the muffler 10 are such that the area of the first orifice means is in the range of between about 1.4 to about 1.5 times the cumulative area of the exhaust ports 26 in the tool body 11.
After undergoing its first expansion in the chamber 61, the air flow from the exhaust ports 26 changes direction as it passes through the gaps 63 and 64 and then enters the lower end of the second expansion chamber 62. This change in direction of the exhaust air flow contributes to the attenuation of the sound level of the flow. Expansion of the exhaust air flow in the second expansion chamber results in further attenuation of the level of the sound in the exhaust flow.
On reaching the upper end of the second expansion chamber 62, the exhaust flow again changes direction and enters the upper end of passage means in the second expansion chamber 62. Such passage means is defined by a pair of elongated passages 72a and 72b (FIGS. 3-6) formed in a pair of longitudinally extending bosses 73a and 73b on the inner surface of the side walls 32a and 32b of the housing portions 10a and 10b. As will be apparent from FIGS. 4 and 6, the bosses 73a and 73b are formed integrally with the material of the muffler halves 10a and 10b and the cross sectional shape of the passages 72a and 72b is generally oval. The bosses 72a and 72b extend longitudinally through the second expansion chamber 62 from the lower end wall 34a and 34b of the muffler halves 10a and 10b toward the upper end walls 33a and 33b thereof but terminate short of the upper end walls, as is apparent from FIGS. 4, 5 and 7. The passages 72a and 72b are thus disposed in and isolated from the second expansion chamber 62, except for their upper ends 74a and 74b which comprise a second orifice means connecting the second expansion chamber 62 with the passages 72a and 72b.
The length of the passages 72a and 72b is preferably approximately 70 percent of that of the length of the expansion chamber 62, and the combined cross sectional area of the passages 72a and 72b is preferably in the range of about 3/4 to 7/8 times the area of the first orifice means.
After the exhaust air flow enters the upper ends 74a and 74b of passages 72a and 72b, the flow proceeds axially downwardly and expands through the passages and thence discharges into the atmosphere through outlet ports 76a and 76b in the lower end walls 34a and 34b of the muffler. The final expansion of the exhaust air flow takes place at the ports 76a and 76b.
The aforementioned area relationship between the first orifice means and the exhaust ports 26 of the tool body 11, and the area relationship between the second orifice means and the first orifice means, reduces the high frequency sounds generated by the exhaust air flow from the ports 26 and also inhibits frosting and/or freezing of water vapor present in the exhaust air. Moreover, the aforementioned area relationships do not appreciably increase the back pressure of the muffler and hence do not reduce the operating efficiency of the pneumatic motor of the tool.
As heretofore mentioned, the muffler 10 is preferably constructed from an elastomeric material such as polyurethane. The use of such a material not only contributes to the sound attenuating characteristics of the muffler but also serves to attenuate the sounds generated from the impacts of the piston 22 on the tappet 24 and from the tappet 24 hitting the upper end of the steel mounted in the tool body 11. Moreover, since the material of the muffler 10 is a resilient, durable, plastic, the possibility of damage to or destruction of the muffler due to rough handling, bumping or jarring, is substantially eliminated.
While only one embodiment of the invention has herein been illustrated and described, it will be understood that modifications and variations thereof may be effected without departing from the scope of the invention as set forth in the appended claims.
Pneumatic percussion tools, such as pavement breakers and the like, have long been objected to because of the noise level generated when such tools are in operation. Such noise level is disturbing not only because of its intensity but also because of the frequency range thereof. In other words, the sounds generated by the operation of unmuffled pneumatic percussion tools are not only of a low basic frequency but also include multiple harmonics extending through the whole sound frequency spectrum. Consequently, some, if not all, of these frequencies are objectionable to most people. In addition, since the motive fluid discharging from the exhaust ports of such tools is usually pulsating, the resulting sound is also pulsating and therefore objectionable for this additional reason.
Various types of muffling devices have been heretofore developed for attenuating the level of the sound generated by the operation of pneumatic percussion tools. Examples of some of these are disclosed in the Hayes U.S. Pat. No. 3,635,299, Fannen U.S. Pat. No. 2,789,653, Waldron U.S. Pat. No. 3,224,527, Wallace U.S. Pat. No. 3,255,844 and Barber et al. U.S. Pat. No. 3,365,022 patents. However, the muffling or silencing devices disclosed in these patents suffer from various shortcomings such as structural complexity, excessive bulk, lack of adaptability to use with different tools and insufficient attenuation of the sound levels generated by the tools with which they were associated.
Moreover, many of the devices heretofore advanced, while being capable of satisfactorily attenuating the sound levels generated by the associated tool, were only able to do so at a substantial loss in the operating efficiency of the tool. In addition, some of the muffling devices of the prior art were incapable of withstanding the normal rough handling incident to the operation of tools of this character.
Accordingly, it is the general object to provide a novel and improved muffler for a pneumatic percussion tool, which overcomes the aforementioned disadvantages of the prior art.
Another object is to provide a novel muffler for attenuating the sounds generated by a pneumatic percussion tool, which does not reduce the operating efficiency of the tool to any significant extent.
A further object is to provide a novel muffler for a pneumatic percussion tool, which is capable of attenuating substantially the entire frequency range of the sounds generated by the tool when the latter is in operation.
Still another object is to provide a novel muffler of the foregoing character having improved high frequency sound attenuation characteristics.
A particular object is to provide a novel muffler for a pneumatic percussion-type tool, which is compact in size, rugged in construction, durable in use, and economical to manufacture.
A still further object is to provide a novel muffler for a pneumatic tool, which may be easily and rapidly mounted on or demounted from an associated pneumatic tool.
These and other objects will become apparent from the following detailed description and accompanying sheets of drawings, in which:
FIG. 1 is a perspective view of a pneumatic percussion tool, in the present instance a paving breaker, the latter being equipped with a muffler embodying the features of the present invention;
FIG. 2 is a transverse cross sectional view taken substantially along the line 2--2 of FIG. 1;
FIG. 3 is a somewhat enlarged, transverse sectional view taken substantially along the line 3--3 of FIG. 1;
FIG. 4 is a somewhat enlarged, longitudinal sectional view taken along the line 4--4 of FIG. 2;
FIG. 5 is a longitudinal sectional view taken substantially along the line 5--5 of FIG. 4;
FIG. 6 is a staggered, transverse sectional view taken along the line 6--6 of FIG. 4; and
FIG. 7 is an exploded perspective view of the muffler illustrated in FIGS. 1-6, inclusive, and showing the parts of the muffler as they would appear in relation to an associated pneumatic tool.
Briefly described, the present invention contemplates a novel muffler for use with pneumatic percussion tools or the like, for attenuating the sounds generated by the operation of such tools. The muffler, to be hereinafter described in detail, is preferably constructed in two parts and utilizes what may be termed a "clamshell" construction. Thus, the muffler halves are preferably symmetrical in shape and adapted to surround a portion of the body of the associated percussion tool in the vicinity of the exhaust ports. When mounted on the tool body, the muffler forms a jacket which coacts with the exterior of the body to define at least one and preferably a plurality of expansion chambers therein. Internal ribs or baffles are provided on the inner surface of the muffler halves, such ribs coacting with the outer surface of the associated tool body to define two of the expansion chambers. A first orifice means having an effective flow area of a particular size interconnects these chambers. The muffler also includes a third expansion chamber provided by a pair of elongated passages which communicate at one end with the second expansion chamber and at their opposite ends with outlet ports in the jacket through which the expanded air from the exhaust ports of the tool finally discharges. The effective flow area of the third orifice means is likewise of a particular size. The muffler halves are of an elastomeric material which improves both the durability and high frequency sound attenuating characteristics of the muffler.
Referring now to FIG. 1, a muffler embodying the features of the present invention is indicated generally at 10 and shown as it would appear when mounted on an associated pneumatic tool, such as paving breaker, indicated generally at B. The paving breaker B, in the present instance, comprises an elongated tool body 11 having handles 12 and a control lever 13 at the upper end thereof for controlling the operation of the tool. A work steel, such as a moil point 14 of the type disclosed in the copending Irvin R. Danielson U.S. Patent application, Ser. No. 260,373, filed June 7, 1972 and assigned to the assignee of this application, is shown mounted in the lower end, indicated at 16, of the tool body 11. The moil point 14 is releasably retained in the body 11 by a latch assembly 17.
Working fluid, in the present instance air under pressure, is supplied to the paving breaker B through an inlet fitting 18 at the upper end thereof, and an automatic valve (not shown) in the upper end of the body 11 serves to control the supply of air under pressure to a piston or a hammer 22 (FIG. 4) that is reciprocatively mounted in a bore 23 (FIG. 4) in the body 11. The piston 22 impacts against the upper end of a tappet 24 which is reciprocatively mounted in a stepped bore 25 in the tool body 11 and which imparts impact blows to the upper end of the steel 14. Air under pressure is exhausted from the tool body 11 at the completion of each working stroke of the piston 22 through exhaust port means in the form of a plurality of exhaust ports 26. The operation of the paving breaker B is continuous so long as the throttle lever 13 is held in a depressed position and air under pressure is continuously supplied to the inlet fitting 18.
Referring initially to FIG. 7, it will be seen that the muffler 10 is formed in two parts or halves 10a and 10b, which are preferably symmetrical and of an elastomeric material, such as polyurethane. The reasons for using this material, and the advantages obtained thereby, will be described hereinafter.
The muffler halves 10a and 10b respectively have generally semi-cylindrical side walls 32a and 32b, and upper and lower end walls 33a and 33b and 34a and 34b. The upper and lower end walls 33a and 33b and 34a and 34b are respectively provided with recesses 36a and 36b and 37a and 37b, which are shaped to closely conform to the external contours of the tool body 11 when the muffler 10 is mounted thereon. Thus, in the present instance, the recesses 36a and 36b in the upper end walls 33a and 33b are generally semicircular, while the recesses 37a and 37b in the lower end walls 34a and 34b are generally V-shaped in cross section.
In order to assure that the recesses 36a, 36b and 37a, 37b sealingly engage the exterior of the tool body 11 when the muffler 10 is assembled thereon, as shown in FIG. 1, a pair of clamps 42 and 43 are provided for surrounding and compressing axially outwardly extending flange portions 44a and 44b and 45a and 45b on the upper and lower end walls 33a and 33b and 34a and 34b, respectively. Thus, when the clamps 42 and 43 are drawn up, the recesses 36a and 36b and 37a and 37b will tightly engage the adjacent portions of the tool body 11.
In order to assure a pressure-tight seal between the abutting peripheral edges of the muffler halves 10a and 10b, such edges are provided with outwardly extending flanges 47a and 47b, respectively, having a plurality of openings 48a and 48b therethrough for receiving a plurality of fasteners such as screws 52. Since the flanges 47a and 47b, and the other portions of the muffler halves 10a and 10b are preferably of an elastomeric material, the flanges are reinforced with metal inserts. A pair of these inserts is indicated at 53b and 54b in FIG. 4 in the flange 47b of the muffler halve 10b. A similar pair of inserts are provided in the flange 47a of a muffler halve 10a. In the illustrated construction, the inserts 53b and 54b are threaded to receive the threaded shanks of the screws 52 and the inserts in the flange 47a are merely bored to permit the shanks of the screws 52 to extend through the flange 47a. Thus, when the screws 52 are drawn up, the flanges 47a and 47b sealingly engage each other.
As heretofore mentioned, the muffler 10 is provided with at least one and preferably a plurality of expansion chambers therein for receiving the high velocity, pulsating, flow of air from the discharge ports 26 of the tool, and for attenuating the level of the sound generated by such flow when the tool is in operation. To define these chambers in the muffler 10, the halves 10a and 10b are respectively provided with partition means defined by inner walls or partitions 56a and 56b (FIGS. 4-7, inclusive), which divide the interior of each muffler half into two compartments. Each of the partitions 56a and 56b is preferably formed integrally with the material of its respective muffler half and comprises a pair of longitudinally extending, transversely spaced ribs 57 and 58. The radial width of the ribs is such that the radially inner ends thereof contact and sealingly engage the outer surface of the tool body 11 when the muffler halves 10a and 10b are assembled thereon. Thus, when the muffler halves 10a and 10b are assembled on the tool body 11, as illustrated on FIG. 6, the partitions 56a and 56b define first and second expansion chambers 61 and 62, respectively, therein. These expansion chambers are generally semi-cylindrical in cross section and are arranged on the laterally opposite sides of the tool body.
As heretofore mentioned, the expansion chambers 61 and 62 are in series flow relation. To this end, first orifice means is provided for continuously interconnecting the chambers 61 and 62. Such orifice means is preferably provided by a pair of gaps 63 and 64 (FIG. 4 and 5) defined between the lower end edges 66 of the ribs 56a and 56b, and the adjacent end face, indicated at 67, of a flange 68 on the body 11 of the tool.
With the foregoing construction, the pulsating flow of air from the exhaust ports 26 of the tool B first discharges into the expansion chamber 61 at an angle determined by the exit angle of the ports 26. After entering the chamber 61, the flow expands and the sound level of the flow is attenuated. Some attenuation also occurs as a result of the interference between the pressure waves in the flow as the waves reflect back and forth from the various walls of the chamber 61.
After the exhaust air flow from the discharge ports 26 has fully expanded in the chamber 61, the flow proceeds through the first orifice means or gaps 63 and 64 at the lower ends of the partitions 56a and 56b, and then enters the second expansion chamber 62. The gaps 63 and 64 and other geometry of the muffler 10 are such that the area of the first orifice means is in the range of between about 1.4 to about 1.5 times the cumulative area of the exhaust ports 26 in the tool body 11.
After undergoing its first expansion in the chamber 61, the air flow from the exhaust ports 26 changes direction as it passes through the gaps 63 and 64 and then enters the lower end of the second expansion chamber 62. This change in direction of the exhaust air flow contributes to the attenuation of the sound level of the flow. Expansion of the exhaust air flow in the second expansion chamber results in further attenuation of the level of the sound in the exhaust flow.
On reaching the upper end of the second expansion chamber 62, the exhaust flow again changes direction and enters the upper end of passage means in the second expansion chamber 62. Such passage means is defined by a pair of elongated passages 72a and 72b (FIGS. 3-6) formed in a pair of longitudinally extending bosses 73a and 73b on the inner surface of the side walls 32a and 32b of the housing portions 10a and 10b. As will be apparent from FIGS. 4 and 6, the bosses 73a and 73b are formed integrally with the material of the muffler halves 10a and 10b and the cross sectional shape of the passages 72a and 72b is generally oval. The bosses 72a and 72b extend longitudinally through the second expansion chamber 62 from the lower end wall 34a and 34b of the muffler halves 10a and 10b toward the upper end walls 33a and 33b thereof but terminate short of the upper end walls, as is apparent from FIGS. 4, 5 and 7. The passages 72a and 72b are thus disposed in and isolated from the second expansion chamber 62, except for their upper ends 74a and 74b which comprise a second orifice means connecting the second expansion chamber 62 with the passages 72a and 72b.
The length of the passages 72a and 72b is preferably approximately 70 percent of that of the length of the expansion chamber 62, and the combined cross sectional area of the passages 72a and 72b is preferably in the range of about 3/4 to 7/8 times the area of the first orifice means.
After the exhaust air flow enters the upper ends 74a and 74b of passages 72a and 72b, the flow proceeds axially downwardly and expands through the passages and thence discharges into the atmosphere through outlet ports 76a and 76b in the lower end walls 34a and 34b of the muffler. The final expansion of the exhaust air flow takes place at the ports 76a and 76b.
The aforementioned area relationship between the first orifice means and the exhaust ports 26 of the tool body 11, and the area relationship between the second orifice means and the first orifice means, reduces the high frequency sounds generated by the exhaust air flow from the ports 26 and also inhibits frosting and/or freezing of water vapor present in the exhaust air. Moreover, the aforementioned area relationships do not appreciably increase the back pressure of the muffler and hence do not reduce the operating efficiency of the pneumatic motor of the tool.
As heretofore mentioned, the muffler 10 is preferably constructed from an elastomeric material such as polyurethane. The use of such a material not only contributes to the sound attenuating characteristics of the muffler but also serves to attenuate the sounds generated from the impacts of the piston 22 on the tappet 24 and from the tappet 24 hitting the upper end of the steel mounted in the tool body 11. Moreover, since the material of the muffler 10 is a resilient, durable, plastic, the possibility of damage to or destruction of the muffler due to rough handling, bumping or jarring, is substantially eliminated.
While only one embodiment of the invention has herein been illustrated and described, it will be understood that modifications and variations thereof may be effected without departing from the scope of the invention as set forth in the appended claims.