US3921290A

US3921290A - Chain saw with cyclically restricted and continuously vented acoustic filtering

Info

Publication number: US3921290A
Application number: US434654A
Authority: US
Inventors: Jay Richard Bailey
Original assignee: Mcculloch Corp
Current assignee: Mcculloch Corp
Priority date: 1972-01-25
Filing date: 1974-01-18
Publication date: 1975-11-25
Anticipated expiration: 1992-11-25

Abstract

A chain saw including a noise suppressing apparatus wherein a pulsing exhaust flow is passed through an acoustic filter and is cyclically restricted while permitting a continuous venting of at least a portion of the exhaust flow. Method and apparatus for effecting noise reduction of chain saws and engines wherein an expansion chamber, acoustic filter means, and cyclic flow restriction and continuous venting means coact to effect noise reduction. Method and apparatus for effecting noise reduction of chain saws and engines wherein a free ''''floating'''' or unbiased, cyclically operable flow restricting means is employed.

Description

United States Patent [191 Bailey CHAIN SAW WITH CYCLICALLY RESTRICTED AND CONTINUOUSLY VENTED ACOUSTIC FILTERING [75] Inventor: Jay Richard Bailey, Chatsworth,

Calif.

[73] Assignee: McCulloch Corporation, Los

Angeles, Calif.

[22] Filed: Jan. 18, 1974 [21] Appl. No.: 434,654

Related US. Application Data [63] Continuation-in-part of Ser. No. 220,632, Jan. 25,

1972, Pat. NO. 3,798,769.

[52] U.S. Cl. 30/381; 18l/64 R [51] Int. Cl. B27B 17/00; FOIN 1/16 [58] Field of Search 30/381, 383; 181/36, 40, 181/57, 58, 64 B, 64 R, 64 A; l73/DIG. 2

[56] References Cited UNITED STATES PATENTS 2,214,894 9/1940 Wilson 181/64 B 3,106,985 10/1953 Recupito 181/36 R 5H0 f h m0 702 L 509 ,6182" 5||b 502 L Nov. 25, 1975 Miller l8l/40 Nelson l8l/58 Primary ExaminerAl Lawrence Smith Assistant ExaminerJ. C. Peters Attorney, Agent, or FirmBurns, Doane, Swecker & Mathis [57] ABSTRACT A chain saw including a noise suppressing apparatus wherein a pulsing exhaust flow is passed through an acoustic filter and is cyclically restricted while permitting a continuous venting of at least a portion of the exhaust flow.

Method and apparatus for effecting noise reduction of chain saws and engines wherein an expansion chamber, acoustic filter means, and cyclic flow restriction and continuous venting means coact to effect noise reduction.

Method and apparatus for effecting noise reduction of chain saws and engines wherein a free floating or unbiased, cyclically operable flow restricting means is employed.

8 Claims, 12 Drawing Figures U. S. Patent Nov. 25, 1975 Sheet 1,0f3 3,921,290

U.S I"Patent Nov.25, 1975 Sheet3 0f3 3,921,290

INLET EXPANSION BAFFLE CYCLIC RESTRICTION AND VENTING DEFLECTION DISCHARGE FIG. l2

' CHAIN SAW WITH CYCLICALLY RESTRICTED AND CONTINUOUSLY VENTED ACOUSTIC FILTERING RELATED APPLICATION This application is a continuation in part of my prior and copending application Ser. No. 220,632 filed Jan. 25, l972, and entitled Apparatus for Reducing the Operating Noise of a Chain Saw, now U.S. Pat. No. 3,798,769.

The entire disclosure of this aforesaid copending application is incorporated by reference insofar as it relates to the claimed and/or disclosed subject matter of the present application.

GENERAL BACKGROUND, OBJECTS AND SUMMARY OF lNVENTlON With the-increasing societal emphasis upon ecological improvements, those dealing with cyclically operable internal combustion engines which are operated in public areas, or in the vicinity of workmen, have been subjected to increasing pressure to reduce the noise output of such engines and their associated components.

Particularly in the chain saw art has there been a continuingly intensified need to reduce the, at times, annoying noise characteristics of chain saw engines.

As is noted in the aforesaid copending application Ser. No. 220,632, a great deal of magic or art as opposed to predictable engineering is involved in ascertaining those combinations of noise suppressing techniques which will most effectively reduce the operating noise chain saws while maintaining an acceptable power output. v

As a part of the design dilemma facing those practicing in the chain saw art, it is desired to effect a reduction in the operating noise of chain saw engines during the medium and/or heavy cutting? operating range of chain saw engine speeds (i.e., on the-order of 6,000 to 7,000 rpm) where medium and/or heavy cutting are involved, while'minimizing the power loss of the generally small horsepower rated engines conventionally used in chain saws.

As will be recognized, at higher engine-speeds, such as those encountered during limbing operations, a significantly lower power requirement is imposed on the chain saw such that at these higher engine speeds a greater sacrifice of power can be tolerated in order to produce an acceptable reduction in noise level.

Taking these factors into consideration, it is an object of the present invention to advance the art by providing an improved noise suppressing technique having particular utility in the chain saw art which will effectively dissipate the noise producing energy of a chain saw engine exhaust over periods of time so as to reduce noise intensity and minimize the irritating crack type of noise often associated with chain saw operation.

It is a further object of the invention to effect such noise suppression in a unique manner soas to maintain an effective power level, particularly at the relatively low and/or median rpm levels of engine operation where heavy and/or medium load cutting are involved, while maintaining an acceptable or minimal reduction in power due to noise suppression.

A further object of the invention is to accomplish the hertofore stated objectives with respect to noise suppression and maintenance of effective engine power side in a technique characterized by the following method steps.

This method aspect involves a method for reducing the operating noise of a chain saw which includes chain saw cutting means including guide bar means, and cutter chain means supported on the guide bar means for traversal through a cutting path. The chain saw further includes chain saw power means including chain saw engine means having a working chamber means, and chain saw power transmitting means operable to transmit driving force to said cutter chain means and cause said cutter chain means to traverse said cutting path.

The inventive aspects of this method reside in cooperative steps including the provision of exhaust passage means communicating with the working chamber means of the chain saw engine means and transmitting a flow of cyclically pulsing exhaust gas from the working chamber means through the exhaust passage means. This flow of exhaust gasis cyclically restricted. A flow of at least a portion of this flow of exhaust gas through the exhaust passage means is continuously vented to the atmosphere. In this method aspect, the cyclic restricting of the flow of exhaust gas is caused to occur through the unimpeded, cycling action of a free floating, flow restricting element.

Another independently significant method aspect of the invention entails the following combination of method steps.

This method relates to the reducing of the operating noise of a chain saw, which chain saw includes chain saw cutting means having guide bar means, and cutter chain means supported on the guide bar means for traversal through a cutting path. The chain saw further includes chain saw power means including chain saw engine means having a working chamber means, and chain saw power transmitting means operable to transmit driving force to the cutter chain means and cause the cutter chain means to traverse the cutting path. Inventive aspects of this method reside in steps initiated by the provision of exhaust passage means communicating with the working chamber means of the chain saw engine means and transmitting a flow of cyclically pulsing exhaust gas from the working chamber means through this exhaust passage means. This flow of exhaust gas is passed into surge chamber means, with the flow being operable to expand therewithin. Acoustic filter means are provided including generally tubular means including lateral wall means defining interior passage means communicating with the atmosphere and extending within the surge chamber means. This acoustic filter means further includes transverse passage means intersecting the lateral wall means of the generally tubular means and providing restricted, acoustic filtering, fluid communication between the surge chamber means and the interior passage means of the generally tubular means. The flow of exhaust gas is acoustically filtered by passing the flow from the surge chamber means through the acoustic filter means. At least a portion of the flow of exhaust gas passing through said acoustic filter means is cyclically restricted and a portion of the flow of exhaust gas tothe atmosphere is continuously vented.

Particularly significant facets of the invention reside in uniquely interacting novel combinations of apparatus means operable to cooperatively implement either or both of the foregoing method concepts.

Broader aspects of the invention reside in the application of the foregoing method and apparatus concepts to noise suppression of cyclically operable internal combustion engines in a general sense.

More specific apparatus aspects of the invention entail the following combination, implemented in the context of the foregoing discussion.

In these more specificapparatus aspects, the flow restricting means is telescopingly associated with the tubular means and is supported by the noise reducing apparatus for substantially unimpeded reciprocating movement relative to the tubular means. The flow restricting means includes wall means telescopingly associated with the tubular means and is operable to cooperate with such lateral wall means and interior passage means of said tubular means to define generally annular passage means within the interior passage means. The continuously operable venting means comprises generally central venting passage means extending generally centrally and longitudinally of each of the flow restricting means and the annular passage means, with the venting passage means being defined by and carried by the flow restricting means. The generally annular passage means provides fluid communication between the generally central. venting passage means and the surge chamber means. The generally annular passage means is operable to provide fluid communication, independent of the generally central venting passage means, between the atmosphere and the surge chamber means. The flow restricting means includes generally annular, flow restricting wall means extending transversely of the generally annular passage means, which annular wall means is cyclically operable in response to the flow of exhaust gas to cyclically restrict a portion of the annular passage means communicating with the atmosphere. This generally annular wall means is opera- DRAWINGS Preferred embodiments of the present invention are illustrated in the appended drawings in which:

FIG. 1 provides a fragmentary, perspective view of a representative chain saw in which a preferred noise suppressing apparatus of the present invention is incorporated;

FIG. 2 provides an enlarged, exploded, perspective view of disassembled components of a preferred noise suppressing apparatus incorporated in the FIG. 1 chain saw; 7

FIG. 3 provides a still further enlarged sectional view of the FIG. 2 noise suppressing apparatus as viewed generally along section line 3-3 of FIG. 2;

FIG. 4 provides an enlarged sectional view of the FIG. 2 noise suppressing apparatus as viewed along section line 4-4 of FIG. 2;

FIG. 5 provides a still further enlarged, transverse, sectional view'of the FIG. 2 noise suppressing apparatus as viewed generally along section line 55;

FIG. 6 provides an elevational sectional view of the cyclically operable flow restricting mechanism illustrated in perspective view in FIG. 2;

FIG. 7 provides a transverse sectional viewof the FIGS. 2 and 6 exhaust flow restricting means as viewed along section line 7-7 of FIG. 6;

FIG. 8 provides a sectioned, elevational view of a first alternative form of a flow restricting mechanism which may be employed in lieu of the FIG. 6 device;

FIG. 9 provides a transverse sectional view of the alternative flow restricting embodiment shown in FIG. 8, as viewed along section line 9-9 of FIG. 8;

FIG. 10 illustrates in a sectional, elevational format, a still further alternative embodiment of a cyclically operable exhaust flow restricting mechanism which also may be employed in lieu of the mechanism shown in FIGS. 2 and 6; I

FIG. 11 provides a transverse sectional view of the FIG. 10 flow restricting device, as viewed along section line ll11 of FIG. 10; and I FIG. 12 provides, in a schematic format, an illustration of uniquely cooperating noise suppressing techniques which are believed to synergistically interact and produce improved noise suppressing techniques, particularly in the environment of a chain saw, as applicable to apparatus shown in FIGS. 1 through 11.

Having described the subject matter of the appended drawings, it is now appropriate to consider a representative chain saw context of the invention along with structural details of the improved noise suppressing apparatus and method of the present invention;

DETAILED DESCRIPTION OF INVENTION Representative Chain Saw Context of Invention FIG. 1 illustrates a representative 'chain saw 1, including a muffler ornoisesuppressing apparatus 2 fabricated in accordance with any of several embodiments of the present invention.

Chain saw 1 includes a guide bar 101. A cutter chain 102 is slidably supported on the periphery of the guide bar 101 for movement through a cutting plane defining a cutting path. This cutting plane may be considered to comprise a longitudinally extending, upright median plane coextensive with the generally ovate cutter chain configuration.

Chain saw '1 comprises an engine-assembly 103 including a piston and cylinder means 104. As shown in FIG. 1, a cylinder or working chamber component of the piston and cylinder assembly 104 may be oriented so that the axis of reciprocation of the piston longitudinally of the guide bar 101 and the aforesaid cutting plane.

A crankshaft means 106, including the external housing 107 shown in FIG. 1, is operated in a manner now well understood to translate reciprocating movement of the piston of the engine assembly 103 into rotary movement of a sprocket wheel which is disposed in driving engagement with a cutter chain 102.

This crankshaft is mounted for rotation about an axis of crankshaft rotation 108 which extends generally perpendicular to the aforesaid cutting plane, Le, a planar extension of the longitudinal upright median plane of the guide bar 101.

With this arrangement, the chain saw 1 will generate vibrations principally aligned with a plane extending generally parallel to or longitudinally of the aforesaid cutting plane. As a consequence, the axis of crankshaft rotation 108 may be deemed to pass generally perpendicular to this principal vibration plane.

In describing the various preferred embodiments of the muffler 2, reference will be made to a first embodiment illustrated in FIGS. 2 through 7, to a second embodiment illustrated in FIGS. 8 and 9, and a third embodiment illustrated in FIGS. 10 and 11.

Surge Chamber, Baffle, Acoustic Filter, and Deflector Aspects of the Noise Suppressing Apparatus The first embodiment of muffler 2 shown in FIGS. 2 through 7 comprises a conduit means 3 which is operable to transmit exhaust fluid from the cylinder means 105.

As is shown generally in FIGS. 1, 3 and 4, conduit means 3 may be disposed in direct metal-to-metal engagement with an exterior mounting boss 109 of the cylinder 105 and communicate directly with a cylinder exhaust port 110. This metal-to-metal juncture 111 may be supplemented by a gasket 111a as shown in FIGS. 3 and 4, but the metallic extremity of the conduit 3 is disposed largely in direct, contiguous, abutting engagement with the metallic cylinder boss 109. Conduit means 3 may have a generally rectangular cross section extending in a direction perpendicular of longitudinal axis 301 of conduit means 3, as depicted generally in FIG. 4.

This longitudinal axis 301 may extend generally parallel to the axis of crankshaft rotation 108, when the muffler 2 is installed as shown in FIG. 1.

As shown in FIG. 4, conduit means 3 may comprise a generally tubular metallic wall portion 302, having a generally rectangular (but round cornered, i.e., ended) cross section extending transversely of axis 301. Conduit 3 may be somewhat composite in nature, comprising a sheet metal portion 303 connected (as by brazing) with an apertured, plate-like terminus 304. The terminus 304, being plate-like and flat in configuration, will ensure contiguous, uniform and generally flush engagement between the end of the conduit 3 and the boss 109 at the juncture zone 111.

In certain instances, conduit means 3 may not be elongate as shown in FIGS. 2 through 6, but instead may merely comprise a port or passage means in the base of a surge or expansion chamber 4. Such an arrangement could result by fabricating the cylinder .mounting

bosses

109 and 112, shown in FIG. 4, so that they were generally coplanar and engageable with spaced portions of a flat boss of a muffler unit.

As noted, muffler 2 additionally includes a surge chamber 4. This surge chamber, as shown in FIG. 4, is operable to receive exhaust fluid from the conduit means 3 at a juncture or exhaust passage zone 401 between these components.

The surge chamber 4 may be fabricated from

metallic halves

402 and 403 which may be telecoped together and brazed or crimped at juncture zone 404.

Body or shell portion 403 of the surge chamber means may be provided with a mounting pad zone 405 which may be disposed in direct, metal-to-metal engagement with the aforesaid mounting boss 112 which is formed on the exterior of cylinder 105. In this manner, the surge chamber means 4 is supported directly on the exterior of the cylinder means 105.

As will be also understood from reference to FIG. 4, the conduit means 3 extends between the interior of the surge chamber means 4 to the juncture zone 111.

The surge chamber 4 may have an overall, generally rectangular configuration (albeit somewhat rounded) encircling the surge chamber interior 406 (within which exhaust gas expands) and includes a generally rectangular cross section extending generally parallel with the aforesaid principal vibration plane.

Muffler 2 further includes acoustic filter means 5 depicted generally in FIGS. 3, 4 and 5.

Acoustic filter means 5 comprises a first, generally perforate, sheet metal cylinder means 501 having a longitudinal axis extending generally parallel to the axis of crankshaft rotation 108. A longitudinal central axis 502 of the first cylinder means 501 is transversely displaced from the longitudinal central axis 301 of the conduit means 3. Thus, the perforate cylinder means 501 and the conduit means 3 may be considered as being mutually transversely offset along a plane extending parallel to the aforesaid principal vibration plane.

Acoustic filter means 5 may be considered to include a second cylinder means 503 which is contained within the first cylinder means 501. This second cylinder means 503 is somewhat smaller in diameter than the internal size of cylinder means 501 so as to be generally radially spaced inwardly thereof.

A cap-like, end wall or barrier 504 serves to close first end portion 505 of cylinder means 501. As shown in FIG. 5, this metallic barrier cap 504 may be partially telescoped within a first inner end 505 of cylinder 501 and be brazed into a fixed position relative to, and connected with, cylinder 501.

Thus, cap 504 comprises a barrier means which operates to close the first end portion 505 of the cylinder means 501. As will be further recognized, this first cylinder end portion 505 may be viewed as being generally mutually contiguous with the rim of cap 504 and housed within the interior of 406 of the surge chamber 7 means 4.

The second or outer end 508 of cylinder 501 may be deflected generally radially outwardly so as to provide a mounting ledge 508a. This ledge or rim may be abuttingly engageable with an annular mounting shoulder 407 of the surge chamber means. Similarly, an outwardly deflected and generally radially extending shoulder 509 of the cylinder means 503 may provide a shoulder or annular rim disposed axially outwardly of, but engageable with, the rounded inner corner of shoulder 508a of the first cylinder means 501.

This arrangement permits the cylinder means 501, including its closure or cap 504, to be telescoped through a surge chamber opening 408, provided by 7 shoulder 407, until shoulder 508a is disposed in abutting engagement with shoulder 407. Either before or after this assembly takes place, the inner cylinder 503 508a. In FIG. 5, sleeve 503 is shown displaced to the right from this engagement position.

' V. Cylinder 503 and its annular rim wall 509 provide an open-ended, generally tubular means which is telescopingly mounted within tubular means 501, for cyclic flow restricting purposes, as will be hereinafter described. This open-ended cylinder means provides a venting passage 511a disposed within interior passage 511 of tubular means 503 and communicating with interior 406 of surge chamber 4 via open end 511b.

With this arrangement, the rim defining, upper end 509 of the inner cylinder 503 comprises annular wall means extending generally transversely of and between the second or outer end portions of the first and second cylinder means 501 and 503. In addition, the upper end 509 of the cylinder 503, like the end 508 of cylinder 501, generally encircles the outlet means 510 which is operable to continuously transmit exhaust fluid to the exterior of the surge chamber means.

The flow of this exhaust fluid to the interior passage 511 of the composite cylinder means 501-503 is facilitated by perforate side wall 5010 of the cylinder means 501 and by the open end Sllb of cylinder 503.

Thus, as shown in FIGS. 3, 4 and 5, the outer cylinder 501 includes a plurality of generally radially extending, longitudinally elongate, and circumferentially spaced first perforations 512. As shown in FIGS. 5 andS, two such longitudinally displaced rows of perforations 512 may be provided. One row 512a discharges into annular passage 514 between

cylinders

501 and 503 while another row 512b discharges directly into interior 5116 at the innermost end of the acoustic filter.

It is contemplated that the width of each opening 512 may be on the order of 0.125 inches, with the length of each such opening 512 being on the order of 0.50 inches.

The radial gap between the

cylinders

501 and 503 provides the aforesaid, constricted annular flow path 514 extending longitudinally of and interposed generally radially between the first and second cylinder means'50l and 503. This flow path, along with the perforation512, is believed to perform a significant sound attenuating function.

The constricted annular flow path 514 extends generally along the axis 502. In this connection, it will be rethe aforsaid principal vibration plane and the engine 103 are operable to generate vibrations generally aligned with this principal vibration plane and acting on the first and second cylinder means 501-503. These vibrations are generated so as to be directed generally transversely of the constricted annular flow path 514 and in general alignment with the cutting plane.

Before discussing additional elements of the muffler 2, it is worth noting that the flow of exhaust fluid between surge chamber interior 406 and acoustic filter interior 511 may be somewhat multidirectional in character.

Some of this fluid may flow generally radially between interior space 406 and space 511, while some 8 fluid flow will be resisted by the solid wall portions of side wall means 503a of cylinder 503 so as to flow generally longitudinally of axis 502 along the path 514, both toward area 511(- and a flow restricting passage means 51 1d at the outer end of the acoustic filter which wiill be hereinafter described in greater detail.

Muffler 2 additionally may include a plurality of generally tubular components 6 which function as housings for fastening members. These components 6 may provide a form of internal baffle action in the surge chamber 4. These tubular components 6 also serve the function of reducing the unsupported or unbraced wall or panel area of the muffler chamber 4 and may act to reduce airborne noise eminating from vibrating wall or panel areas.

Thus, as shown in FIGS. 2 through 5, muffler 2 may include three generally tubular housing or

baffle members

601, 602 and 603.

Each such baffle member extends generally parallel to the axis of crankshaft rotation and thus parallel to the axes 502 and 301.

As shown in FIGS. 2 and 3, the tubular housing or baffle members 601-603 may be brazed to surge chamber shell portion 402 at a juncture 604 and extend through the surge chamber interior 406.

Two of the

baffles

601 and 602 may pass longitudinally through upper and lower ends of the conduit means 3, as generally shown in FIG. 3.

The inner ends of these baffle or housing members I 601-603, i.e., the ends disposed adjacent the cylinder 105, may be secured by a brazing arrangement involvcalled that axis 502 extends generally perpendicular to.

ing a telescoping assembly of components, as generally shown in FIGS. 3 and 4.

Thus, as shown in FIGS. 3 and 4, a representative tubular member 602 telescopingly receives a generally tubular and radially flanged fitting 605. Another end of fitting 605 passes through an apertured portion of end wall lip 305 of conduit means 3 so as to be telescopingly received within an aperture 306 of mounting plate 304. With these components telescopingly assembled in this manner, as shown generally in FIGS. 3 and 4, the brazing of a fitting 605 to an end of tubular member 602 and to the base plate 304 will serve to effectively interconnect the

components

602, 303 and 304.

The arrangement described in connection with member 602 is duplicated with respect to member 60].

This same general mode of assembly may be employed in connection with tubular member 603. This member may be secured by brazing to mounting pad portion 405 of shell 403. In this case, opposite ends of a tubular flanged fitment 606 may be partially telescopingly received within an end of tubular member 603 and an opening wall 405, respectively, and be brazed to these components so as to effect their interconnection.

With respect to the general orientation of components heretofore described, it is of significance to note that the conduit means 3, the first and second cylinder means 501 and 503, the constricted annular flow path 514, and the tubular baffle means 601603 are all arranged so that their longitudinal axes are generally mutually parallel. All of these components are subject to vibrations generated in general alignment with the principal vibration plane heretofore described.

The precise baffle phenomenon which may be attributable to the baffle means 601-603 is not fully understood. Nevertheless, it is believed that the nonsymmetric disposition of these baffle means, spaced generally radially outwardly of the cylinder means 501, contribexiting from outlet means 510 in a direction extending generally transversely of the axis of crankshaft rotation,

albeit displaced from this axis.

Thus, deflector means 7 may include arcuate wall 1 means 701 having a generally quarter-sphereconfiguration.

This quarter-sphere configuration is oriented such that its center of curvature 702 is generally coincident with the centrallongitudinal axis 502 common to the first and second cylinder means 501 and 503, respectively. I

The manner in-which the deflector means 7 is installed will be appreciated by reference to FIGS. 2 through 5.

Thus, as there shown, quarter-sphere wall 701 may be supported on a mounting rim 703 which has apertured clampor ear means 704 and 705.

With the

cylinder assemblies

501 and 503 positioned as shown in FIG. 5, the rim 703 may be positioned so as to dispose the

apertured ear portions

704 and 705 in general alignment with threaded fastener receiving openings 710 and 711 formed on surge chamber means 4. The insertion of threaded fasteners 712 and.713 through these ear portions and fastener receiving openings into threaded cooperation with threaded nut means 714 and .715 (brazed to the. interior of surge chamber 4) will complete the installation of the deflector assembly.

This completion of the deflector installation will concurrently serve to secure the cylinder means 501 in position and limit the telescoping movement of cylinder 503, as hereinafter described. This will result, as shown in FIG. 5, due to a generally abuttable engagement between the rim 703 and the cylinder flange 508a, and to deflector 701 providing a stop 701a to limit outer telescoping movement of cylinder503 relative'to cylinder 501 and, passage 511d. In this assembled position, opening 707 of rim 703 will be, coaxially aligned with, the generally coextensive with, outlet 510.

The position f the threaded

fasteners

712 and 713 and their associated threaded nut means 714 and 715 may besuch, as shown generally-in FIGS. 2 and '5, as to cause the deflector wall 701 to be disposed with its opening 716 directed directly downwardly, i.e., away from the upper part of the chain saw where an operators hands would be disposed.

In certain instances, the deflector may be inverted and the wall means 701 configured so as to provide a deflected flow of exhaust fluid onto an operators hands for operator hand warming purposes.

The deflector 701 may also be oriented so as to deflect warm exhaust fluid into portions of the chain saw for the purpose of warming components such as' the carburetor, air filter, etc. located generally in upper area 113 of the chain saw-,shown in FIG. 1.

While the general manner-in which the muffler 2 is mounting screws 609 which pass through the

fitments

605 and 606 into

cylinder bosses

109 and 112, respectively. Y

The muffler 2, as heretofore described, will function to effectively attenuate noise generated by the engine means 103 through the synergistically cooperating interaction of the exhaust passage means 3, surge chambermeans 4, acoustic filter means 5, and cyclically operable flow restricting means 503 and 509, possibly fa cilitated by baffle action provided by baffle means 6.

Exhaust fluid will flow from the cylinder discharge port 1 10 into the surge chamber interior 406 by way of exhaust passage 3 and expand therein. Baffling of this flow will result if the conduit means 3 and the cylinder means 501 and 503 are displaced. Further baffling of this flow may result from a nonsymmetric orientation and presence of the baffle means 601-603.

A thus baffled flow of fluid in the surge chamber 4 will pass through the perforation means 512 for acoustic filtering, i.e., noise attenuation, and thereafter be transmitted to the exhaust outlet 510.

Cyclically Operable Flow Restriction Subsequent to the initiation of acoustic filtering of the exhaust flow, a unique modification involving an advantageous blunting of pressure pulses, or dissipating or spreading of noise energy so as to reduce peak noise intensity, may be achieved by cyclically restricting the outflow of exhaust gas from the acoustic filter 5 while providing for continuous unimpeded venting of a portion of exhaust flow from the acoustic filter.

One manner in which cyclic restriction and continuous venting may be achieved is described in the aforesaid parent application Ser. No. 220,632 with reference to FIGS. 11 through 13. Accordingly, the disclosure of the aforesaid parent application Ser. No. 220,632 as it relates to this technique (i.e., the embodiment of FIGS. 11 through 13 of the parent application) is herein incorporated by reference. However, the present invention, while entailing certain generic aspects of the noise attenuating function of the continuously venting, cantilever reed arrangement featured in FIGS. 11 through 13 of the aforesaid parent application (which provides cyclic restriction and concurrent continuous venting of the exhaust flow issuing from an acoustic filter), materially and nonobviously departs from the species teaching of this parent application and provides a unique new species for achieving cyclic restriction and concurrent continuous venting;

Distinctive characteristics of this new concept reside in part in the utilization of a freely movable or unbiased, cyclically operable, flow restricting mechanism.

This new concept will now be described with reference to FIGS. 2, 5, and 6 through 11 of the present application.

Unimpeded, Cyclically Operable Flow Restriction and Concurrent Continuous venting 2. the perforate flow baffling, and acoustic filtering cylinder-like wall 501,

3. the annular passage 514 including the outlet, flowcontrolling, annular passage portion 511d,

4. the inner portion of the deflector 701 which cooperates with the rim 5080 to define stop means which determine the extremities of telescoping movement of the cylinder 503 relative to the annular passage 514 and the cylinder 501, and

5. continuous venting passage means 510-51 la-51 1c which communicate directly with openings 512b of the acoustic filter 5.

As will be apparent by reference to FIG. 5, where the assembled muffler 2 is shown, when the sleeve 503 is disposed in the innermost telescoped position, the sleeve flange 509 extends transversely across the annular passage means 511d so as to effectively restrict and substantially close off this portion of the exhaust gas flow path.

When the sleeve 503 telescopes to the left as shown in FIG. 5, the flange 509 moves away from the annular passage 511d so as to reduce flow restriction with respect to exhaust gas flowing to the left through annular passage 514 and to the atmosphere via cyclically restricted, annular passage 511d.

It is believed that impacting engagement between flange 509 and the interior 701a of deflector portion 701 will induce a rebounding or restitution effect, tending to cause the sleeve 503 to rebound back toward the right from the position shown in FIG. 5 so as to induce the increase in restriction of passage means 511d (by causing the flange 509 to progressively move into sub stantially closing cooperation with the passage portion 51 1d). 1

At this juncture, it is significant to note that the sleeve 503 is mounted for free telescoping movement and is not biased toward any particular extremity of its range of telescoping movement. Moreover, the sleeve 503 is free, to some extent and while at rest, to cant" within the outer sleeve 501.

Observations to dateindicate that the telescoping movement of sleeve-503 may-be related to the pressure pulses of the exhaust gas so as to be somewhat out of phase i.e., be delayed in opening movement relative to pressure pulse peaks.

In short, instead of the sleeve 503 moving away from the passage 511d as would be expected, surprisingly and unexpectedly the sleeve 503 and its flange 509 is believed to undergo movement to the right, from the position shown in FIG. 5, during positive pressure pulses.

Whatever the explanation may be, a heretofore unexpected reduction in the noise level of chain saws is produced which is particularly effective in the median and low speed range of chain saw operation in that a significant noise level reduction is accomplished while maintaining adequate engine power.

Moreover, these desirable objectives are achieved without generating annoying rattling noise as a result of the oscillating or telescoping action of the sleeve 503. It may well be that the significant absence of excessive rattling noise is a result of a form of air cushioning resulting from the cyclic movements of the sleeve 503 being in a somewhat out-of-phase relation with the pressure pulses of the exhaust gas, i.e., with the flange 509 tending to seat on the rim 508 during portions of positive pressure pulses.

12 Having now described in detail and in relation to one preferred embodiment what are believed to be significant structural and operating characteristics of the cyclic flowing restricting and venting mechanism 8, it is now appropriate to summarize the overall mode of operation of the muffler or noise reducing apparatus 2.

SUMMARY OF MODE OF OPERATION In summarizing the mode of operation of muffler 2, reference will be made to FIGS. 2 through 7 as well as to FIG. 12.

FIG. 12 schematically illustrates, in a functional sense, various noise reducing or attenuating functions which are performed by the totality of operations of the preferred embodiment. However, as will be apparent v by definitional aspects of the appended claims, at least some advantages of the invention may be attained by implementing only certain of the functions depictedby FIG. 12.

The overall improvement in the noise reducing apparatus 2 resides in an apparatus as follows.

An exhaust passage means 3 communicates with the working chamber means 105 of the chain saw engine means 103 and is operable to transmit a flow of cyclically pulsing exhaust gas therefrom. The surge chamber means 4 is operable to receive the flow of exhaust gas from the exhaust passage means 3 and transmit it to acoustic filter means 5.

The acoustic filter means 5 includes generally tubular means 501 including lateral wall means defining interior passage means 511 communicating with the atmosphere and extending within the surge chamber means 4. Acoustic filter means 5 further includes transverse passage means 512 intersecting the lateral wall means of the generally tubular means 501 and providing restricted, acoustic filtering, fluid communication between'the surge chamber means 4 and the interior passage means 511 of the generally tubular means 501.

A flow restricting means 8 is mounted in'the generally tubular means 501 and is operable to cyclically restrict at least a portion'of the flow of exhaust gas. A continuously operable venting means 511a-510 is operably associated with the generally tubular means 501 and is operable to maintain a continuously open flow path 511a-510 between the surge chamber'means 4 and the atmosphere, through which path at least a portion of the flow of exhaust gas from the chain saw engine means 103 may continuously pass.

The noise reducing apparatus 2 may include a plurality of asymmetrically arranged

tubular members

601, 602, 603 defining baffle means 6 contained within the surge chamber means 4 and operable to baffle the flow of exhaust gas within the surge chamber means 4 between the exhaust passage means 3 and the acoustic filter means 5.

The flow restricting means 8 is free floating and telescopingly associated with the tubular means 501 and is supported by the noise reducing apparatus 2 for substantially unimpeded reciprocating movement relative to the tubular means 501. This flow restricting means 8 includes wall means(i.e., 503a or 503a or 503a) telescopingly received with the tubular means 501 and operable to cooperate with the lateral wall means of the tubular me ans interior passage means 5 ll of the tubular means and define generally annular passage means 514 within the interior passage means 51 1. The annular passage means 514 is operable to deflect a flow of exhaust gas passing transversely of the lateral wall means through the transverse passage means 512 and cause this deflected flow of exhaust gas to flow generally longitudinally of the interior passage means 511 The continuously operable venting means 511a-510 comprises a generally central, venting passage means 511a extending generally centrally and longitudinally of each of the flow restricting means 8 and the annular passage means 514, with this venting passage means being defined by and carried by the flow restricting means 8.

The generally annular passage means 514 provides fluid communication between the generally central,

venting passage means 511a and the interior 406 of surge chamber means 4. The generally annular passage means 514 is also operable to provide fluid communication, independent of the generally central venting passage means 511a, between the atmosphere and said surge chamber means interior 406 via outlet 511d.

The flow restricting means 8 includes generally annular, flow restricting wall means 509 extending transversely of the generally annular passage means 514. The wall means 509 is cyclically operable in response to the flow of exhaust gas to cyclically restrict a portion 511d of the annular passage means 514 communicating with the atmosphere. The generally annular wall means 509 is operable to move away from the annular passage means 514 and tend to reduce restriction of the generally annular passage means area 511d and is operable to move toward the annular passage means portion 511d and increase restriction of the generally annular passage means 514.

The noise reducing apparatus 2 may further include flow deflecting means 7 providing exhaust gas deflecting, fluid communication between the flow of exhaust gas issuing from the interior passage means 51 1 and the atmosphere. This flow deflecting means 7 includes restitution means 701a operable 1) to be impacted by the flow restricting means 8, when the generally annular wall means 509 is moving away from the annular passage means 514 and tending to reduce the restriction of the generally annular passage means 514 and 2) to induce a rebounding of the flow restricting means 8 tending to move the generally annular wall means 509 toward the annular passage meand 514 and induce an increase in restricting of the generally annular passage means 514.

The transverse passage means 512 of the acoustic filter means may include a first plurality 512a of elongate openings extending longitudinally of the generally annular passage means 514, spaced circumferentially about the generally tubular means 501, and operable to discharge exhaust gas directly into the generally annular passage means 514. The transverse passage means 512 may further include a second plurality 51219 of elongate openings, comprising, in effect, a portion of the continuously operable venting means, and operable to discharge exhaust gas into the interior passage means 511C without passage through the generally annular passage means 514.

In summary, then, and by reference to FIG. 12, it will be appreciated that the following sound attenuating functions are performed by the totality of components included in muffler 2:

Exhaust gas is received by inlet passage means 3, as depicted in function block A of FIG. 12;

Exhaust gas is expanded within surge chamber 4, as depicted in block B of FIG. 12;

Exhaust gas is baffled by baffle means 6 and/or perforation means 512, as depicted by block C in FIG. 12;

Exhaust gas is acoustically filtered so as to attenuate noise levels by acoustic filter means 5, as depicted by block B of FIG. 12;

Exhaust gas is cyclically restricted and is continuously vented (as implemented by flow restricting and venting means 8), as generally depicted in block E of FIG. 12;

Exhaust gas is deflected by deflecting means 7 as it issues from the acoustic filter means 5 under the control of flow restricting and venting means, 8 as generally depicted by block F of FIG. 12; and

Noise modulated exhaust gas is discharged to the atmosphere as generally depicted by block G of FIG. 12.

ALTERNATIVE FORMS OF APPARATUS As will be recognized from the prior discussions, the invention may be practiced in a variety of structural and operational formats, consistent with disclosures of either or both of the present application and the aforesaid parent application Ser. No. 220,632. However, particularly significant results are attributed to the unbiased flow restricting action of the cyclic restricting and venting means 8 of the present invention.

For example, the dimensions and configurations and overall arrangement of interior passage means 3 and surge chamber 4 may be substantially varied, as may be the dimensions, arrangement, shapes and numbers of the baffle means 6 (i.e., 601, 602, 603) and/or passages 512.

Moreover, the deflector 7 may be significantly altered in form, size and shape as may be the acoustic filter 5.

Furthermore, the invention may be practiced without all of the components identified in FIG. 12 being necessarily present.

With respect to the phase restricting and venting means 8, a variety of structural modifications are foreseeable which would serve to vary the structural nature of the cylinder or floating thimble or valve" 503, the radial width of the gap 514, the size of the vent opening 510, and the weight and length of the mechanism 8.

For example, as shown in FIGS. 8 and 9, mechanism 8 may comprise a modified cylinder 503 having a perforate sidewall 503a and annular rim 509 which provides an orifice-like, central opening 510 and a somewhat narrower width for passage 514. Wall 5030 may be provided with a series of circumstantially spaced longitudinally elongate ports or openings 503b.

A still further modification of mechanism 8 is dis closed in FIGS. 10 and 11.

As they are shown, a cylinder-like component 503 is provided with side wall means 503a" defined by a plurality of circumferentially spaced, leg-like components 503C. The legs 503c are connected with a platelike rim defining component 509" which affords a central, orifice-like vent outlet 510".

With respect to the three embodiments of mechanism 8 heretofore described, it is believed that a variety of other configurations may be feasible along with these embodiments, but at the present time, the FIGS. 6 and 7 species is believed to be particularly effective, structurally simple, and operationally reliable.

In connection with all of the species heretofore described, it is contemplated that the length of the cylinder side wall (i.e., the side wall 503a of the FIGS. 6 and 7 species, for example) would be such as shown in FIG.

- 5 as to substantially overlap the outermost row of perforded by perforation means 512a will be cylically reduced as a result of the outer telescoping of the cylinder 503 (i.e., due to uncovering of perforation means 51211).

All this notwithstanding, it is believed that the invention might also be able to be effectively practiced with the length of the sleeve side wall (such as, for example, wall 503a) being extended so as to overlap in whole or in part the perforation means 51212 or extend generally deeper or further into'the cylinder 501.

' It is also contemplated that the wall structure of the acoustic filter 5 may vary, particularly in accordance with the prior teaching of our parent application Ser. No. 220,632.

Thus. for example, the mechanism 8 of the present invention may be telescopingly mounted within a single cylinder 501 as shown in the aforesaid parent application or may be telescopingly mounted within a doublewalled acoustic filtering, cylinder arrangement depicted in FIG. 8 of the aforesaid parent application (i.e., telescopingly mounting within a perforated metal inner wall component 503 illustrated in FIG. 8 of the aforesaid parent application). This arrangement would produce a pair of coaxially arranged acoustic filtering,

annular passages, one existing between the

cylinder walls

501 and 503 of the aforesaid parent application and the other existing between the cylinder 503 of the aforesaid parent application and the side wall 503 of the mechanism 8 of the present invention (i.e., for example, 503a).

Moreover, it is contemplated that as a single cylinder 501 is employed, a uniform pattern of relatively small perforations could be employed, in lieu of the elongate slot featured in the present disclosure, along with other transverse opening arrangements. Such a uniform pattern arrangement is described, for example, in the aforesaid parent application in relation to inner sleeve or cylinder 503 of that application.

SUMMARY OF MAJOR ADVANTAGES AND SCOPE OF INVENTION A particular advantage of the invention resides in the manner in which effective noise reduction and attenuation is achieved without sacrificing excessive engine power, particularly at low and median speeds of engine operation. In the present invention, a noise level reduction on the order of five or so decibels has been attained.

The free floating (i.e., unimpeded or unbiased) aspects of mechanism 8 eliminate the necessity of employing biasing means and are believed to contribute to the attainment of the aforesaid phase control aspects of the invention.

A minimization or suppression of rattling of the control mechanism 8 is attained which is believed to be particularly desirable. This may be attributed, in part, to air cushioning which could result from the mechanism 8 cycling in a somewhat out-of-phase relation with positive pressure peaks of the exhaust gas.

Somewhat surprisingly, the oscillation of mechanism 8 occurs in the absence of a biasing or restoring mecha- 16 nism even with this mechanism being free to cant or incline within the acoustic filter. This feature alone attests to the unobviousness of the invention and constitutes an independently significant aspect of the invention.

Indications of the wide range of variations, of both a structural and functional sense, within which the invention may be practiced have heretofore been indicated. As will also be appreciated, the unique noise reducing aspects of the invention are believed applicable to operating contexts other than those associated with chain saws, even-though the chain saw environment is believed to constitute a particularly significant application of the invention. However, noise reducing aspects of the invention may be applied to other environments such as, for example, internal combustion engineoperated small generators where noise reduction of small engines is a highly desirable feature.

Bearing these criteria in mind, it will be recognized that those skilled in the art and familiar with the present disclosure and the disclosure of the aforesaid parent application may envision additions, deletions, substitutions, modifications or arrangements equivalent in whole or in part to the invention as heretofore described, but which would fall within the purview of the invention as set forth in the appended claims.

What is claimed is:

1. In a chain saw including an apparatus for reducing the noise generated by chain saw operation, and

, wherein said chain saw includes chain saw cutting means including guide bar means, and cutter chain means supported on said guide bar means for traversal through a cutting path; and chain saw power means including chain saw engine means having a working chamber means, and chain saw power transmitting means operable to transmit driving force to said cutter chain means and cause said cutter chain means to traverse said cutting path; the improvement in said noise reducing apparatus comprising: exhaust passage means communicating with said working chamber means of said chain saw engine means and operable to transmit a flow of cyclically pulsing exhaust gas therefrom; generally tubular, outlet passage means operable to receive said flow of exhaust gas and transmit said flow to the atmosphere; exhaust flow responsive, cyclically operable flow restricting means telescopingly mounted in said outlet passage means and operable in response to pressure pulsations in said flow of exhaust gas to cyclically restrict a portion of said flow of exhaust gas transmitted through said outlet passage means; continuously operable venting means operable to permit a continuous flow of a portion of said flow of exhaust gas through said outlet passage means to the atmosphere concurrent with said cyclic restriction of a portion of said exhaust flow through said outlet passage means; and 2. In a chain saw including an apparatus for reducing the noise generated by chain saw operation, and wherein said chain saw includes chain saw cutting means including guide bar means, and

chain saw power means including chain saw engine means having a working chamber 18 means being defined by and carried by said flow restricting means; said generally annular passage means providing fluid communication between said generally cenmeans, and tral, venting passage means and said surge chamchain saw power transmitting means operable to bet means;

transmit driving force to said cutter chain means Said generally annular passage means being operaand cause said cutter chain means to traverse ble to Provide fluid Communication, independent said cutting path; of said generally central venting passage means, improvement in said noise reducing apparatus combetween Said atmosphere and Said Surge chamber prising: means; exhaust passage means communicating with said said flow restricting means including generally working chamber means of said chain saw engine nular, flow restrifiting Wan means extendmg means and operable to transmit a flow of cyclitransversely of Sald generally annular Passage ll l i exhaust gas therefrom; means and cyclically operable in response to said surge chamber means operable to receive said flow flow 9 exhaust gas to cyclically restrict a P n of exhaust gas from said exhaust passage means; annular mefms Commumcatmg acoustic filt means including with said atmosphere, with said generally annular generally tubular means including lateral wall means bemg operable to move away from means defining interior passage means commu said annular passage means and tend to reduce .nicating with the atmosphere and extending restnct1on of said generally annular passage within Said Surge. chamber means, and I means and operable to move toward said annular transverse passage means intersecting said lateral passage means and Increase restncnon of Sald wall means of said generally tubular means and f f y?" passage i h l providing restricted, acoustic filtering, fluid h a m apparati; me u communication between said surge chamber e ecimg means P mg ex dust gas 8' means and the interior passage means of said flectmg cpminumcatlon i p Said flow generally tubular means; of exhaust gas issuing from said interior passage flow restricting means mounted in said generally $222: atmosphere Sald flow deflectmg tubular means and operable to cyclically restrict g restriction means operable to be impacted by at least a portion of said new of exhaust said flow restrictin means when said enercontinuously operable venting means operably asg ally annular wall means [8 moving away from soclated wlth $2.1m generally .tubular means and said annular passage means and tending to re- 1 operable to mamtam a continuously open flow duce the restriction of said generally annular path between said surge chamber means and said passage means and induce a rebounding of atmosphere through which lelast a Portion of said flow restricting means tending to move P flow of exhaust g from Sald cham Saw said generally annular wall means toward said gme means may continuously pass; annular passage means and induce an increase said noise reduc ng apparatus including a plurality 40 in restricting of Said generally annular passage of assymetrically arranged tubular members demeans; finmg baffle means comamed with! Surge said transverse passage means of said acoustic filter chamber means and operable to baffle said flow means including of exhaust gas within said surge chamber means a first plurality of elongate openings extending betweefl 531d exhaust Passage means and 531d longitudinally of said generally annular passage acoustic fine]- means; v means, spaced circumferentially about said said flow restricting means being telescopingly asgenerally tubular means and operable to Sociated with said tubular means and Supported charge exhaust gas directly into said generally by said noise reducing apparatus for substantially annmar passage means and unimpeded reciprocating movement relative to a Second plurality of elongate openings comp i Said la means; ing a portion of said continuously operable said flow restricting means including wall means venting means d bl to di h telescoping)? received with s tubular means haust gas into said interior passage means withand operable to cooperate lateral W3." out passage through generally annular pasmeans and interior passage means of said tubular sage means means and define generallyannular passage means within said interior passage means operable to deflect a flow of exhaust gas passing transversely of said lateral wall means through said transverse pas- 0 sage means and cause said deflected flow of exhaust gas to flow generally longitudinally of said interior passage means;

3. In a chain saw including an apparatus for reducing the noise generated by an operating chain saw, wherein said chain saw includes chain saw cutting means including guide bar means, cutter chain means supported on said guide bar means for movement through a cutting plane; chain saw engine means including said continuously operable venting means comprising generally central venting passage means extending generally centrally and longitudinally of each of said flow restricting means and said annular passage means, with said venting passage piston said cylinder means,

crankshaft means driven by said piston means of said piston and cylinder means, and operable to transmit driving force to said cutter chain means;

said noise reducing apparatus comprising:

19 conduit means operable to transmit cyclically pulsing exhaust fluid from said cylinder means of said piston and cylinder means; I surge chamber means,

said surge chamber means being operable to receive exhaust fluid from said conduit means; acoustic filter means including generally perforate, outlet passage defining means, said conduit means and said outlet passage defining means being mutually offset,

barrier means within said surge chamber means closing a first end portion of said outlet passage defining means.

outlet means provided by a second end of said outlet passage defining means,

said outlet means being operable to transmit exhaust fluid to the exterior of said surge chamber means,

said outlet passage defining means including a plurality of openings providing communication between said outlet means and the interior of said surge chamber means;

a plurality of tubular baffle means,

said tubular baffle means being located within the interior of said surge chamber means,

said tubular baffle means being mutually displaced and disposed nonsymmetrically in relation to said outlet passage defining means; and

flow restricting means operable to cyclically restrict a flow of said exhaust fluid passing through said acoustic filter means; a

continuously operable venting means operable to permit a continuous flow of at least a portion of a flow of said exhaust fluid through said acoustic filter means to the atmosphere; and support means mounting said flow restricting means for substantially unimpeded cyclic movement.

4, In a chain saw including an apparatus for reducing the noise generated by an operating chain saw, wherein said chain saw includes chain sawcutting means includin guide bar means,

cutter chain means supported on said guide bar means for movement through a cutting plane with said cutting plane being aligned in generally parallel relation with a principal vibration plane of a chain saw;

chain saw engine means including piston and cylinder means,

and said crankshaft means being mounted for rotation about an axis of crankshaft rotation extending generally perpendicular to said principal vibration plane; said noise reducing apparatus comprising:

conduit means operable to transmit cyclically pulsing exhaust fluid from said cylinder means of said piston and cylinder means,

said conduit means having a longitudinal axis extending generally parallel to said axis of crankshaft rotation;

surge chamber means,

said surge chamber means being operable to receive exhaust fluid from said conduit means,

said surge chamber means having a generally rectangular cross section extending generally parallel with said principal vibration-planej acoustic filter means including a generally perforate cylinder means having a longitudinal axis extending generally parallel to said axis of crankshaft rotation,

a longitudinal, generally central axis of said cylinder means being transversely displaced from a longitudinal, generally central axis of said conduit means, with said conduit means and said cylinder means being mutually, transversely offset,

barrier means within said surge chamber means closing a first end portion of said cylinder means,

outlet means provided by a second end of said cylinder means, I Y

said outletmeans being operable to transmit exhaust fluid to the exterior of said surge chamber means,

said cylinder means including a plurality of generally radially opening and circumferentially spaced perforation means,-

said cutter chain means and chain saw engine means being operable to generate vibrations generally aligned with said principal vibration plane and acting on said cylinder means to generate vibrations therein directed generally transversely thereof and in general alignment with said principal vibration plane;

' flow restricting means operable to cyclically restrict a flow of said exhaust fluid passing through said acoustic filter means;

continuously operable venting means operable to permit a continuous flow of at least a portion of a flow of said exhaust fluid through said acoustic filter means to the atmosphere; and

support means mounting said flow restricting means for substantially unimpeded cyclic movement.

5. In a chain saw including an apparatus for reducing the noise generated by an operatingchain saw, wherein said chain saw includes I chain saw cutting means including guide bar means, i cutter chain means supported on said guide bar means for movement through a cutting plane, with said cutting plane being aligned in generally parallel relation with a principal vibration plane of a chain saw; 1 i chain saw engine means including piston and cylinder means, crankshaft means driven by said piston means 'of said piston and cylinder means, andgoperable to transmit driving force to said cutter chain means, said'crankshaft means being mounted for rotation about an axis of crankshaft'rotation extending generally perpendicular to said principal vibration plane; said noise reducing apparatus comprising:

conduit means operable to transmit cyclically pulsing exhaust fluid from said cylinder means of said piston and cylinder means, said conduit means having a generally rectangularlyelongate cross section, and

said conduit means having a longitudinal axis extending generally parallel to said axis of crankshaft rotation; surge chamber means,-

said surge chamber means being supported on the exterior of said cylinder means,

said conduit means extending from said surge chamber means and being directly connected with the exterior of said cylinder means and disposed in direct, metal-to-metal engagement therewith,

said surge chamber means having a generally rectangular configuration including a generally rectangular cross section extending generally parallel with said principal vibration plane;

acoustic filter means including generally perforate cylinder means having a longitudinal axis extending generally parallel to said axis of crankshaft rotation,

barrier means within said surge chamber means.

closing a first end portion of said cylinder means, outlet means provided by a second end of said second cylinder means, said outlet means being operable to transmit exhaust fluid to the exterior of said surge chamber means, said cylinder means including a plurality of generally radially opening and circumferentially spaced perforation means, and said cutter chain means and chain saw engine means being operable to generate vibrations generally aligned with said principal vibration plane and acting on said cylinder means to generate vibrations therein directed generally transversely thereof and in general alignment with said principal vibration plane; a plurality of tubular baffle means,

said tubular baffle means being located within the interior of said surge chamber means, each said tubular baffle means extending generally parallel to said axis of crankshaft rotation, and said tubular baffle means being mutually displaced and spaced generally radially outwardly of said cylinder means; said conduit means, said cylinder means, and said tubular baffle means being generally mutually parallel and subject to said vibrations generated in general alignment with said principal vibration plane; flow restricting means operable to cyclically restrict a flow of said exhaust fluid passing through said acoustic filter means; continuously operable venting means operable to permit a continuous flow of at least a portion of a flow of said exhaust fluid through said acoustic filter means to the atmosphere; and support means mounting said flow restricting means for substantially unimpeded cyclic movement. 6. A noise reducing apparatus for a cyclic, internal combustion engine, said apparatuscomprising:

exhaust passage means operable to communicate with a working chamber means of cyclic, internal combustion engine means and operable to transmit a flow of cyclically pulsing exhaust gas therefrom;

22 generally tubular, outlet passage means operable to receive said flow of exhaust gas and transmit said flow to the atmosphere; exhaust flow responsive, cyclically operable, flow restricting means telescopingly mounted in said outlet passage means and operable in response to pressure pulsations in said flow of exhaust gas to cyclically restrict a portion of said flow of exhaust gas transmitted through said outlet passage means;

continuously operable venting means operable to permit a continuous flow of a portion of said flow of exhaust gas through said outlet passage means to the atmosphere concurrent with said cyclic restriction of a portion of said exhaust gas flow through said outlet passage means; and

support means including said outlet passage means,

telescopingly mounting said flow restricting means for substantially unimpeded cyclic movement.

7. In a chain saw including an apparatus for reducing the noise generated by chain saw operation. and wherein said chain saw includes chain saw cutting means including guide bar means, and cutter chain means supported on said guide bar means for traversal through a cutting path; and chain saw power means including chain saw engine means having a working chamber means, and chain saw power transmitting means operable to transmit driving force to said cutter chain means and cause said cutter chain means to traverse said cutting path; the improvement in said noise reducing apparatus comprising:

exhaust passage means communicating with said working chamber means of said chain saw engine means and operable to transmit a flow of cyclically pulsing exhaust gas therefrom;

surge chamber means operable to receive said flow of exhaust gas from said exhaust passage means;

acoustic filter means including generally tubular means including lateral wall means defining interior passage means communicating with the atmosphere and extending within said surge chamber means, and

transverse passage means intersecting said lateral wall means of said generally tubular means and providing restricted, acoustic filtering, fluid communication between said surge chamber means and the interior passage means of said generally tubular means;

flow restricting means mounted in said generally tubular means and operable to cyclically restrict at least a portion of said flow of exhaust gas; and

' continuously operable venting means operably associated with said generally tubular means and operable to maintain a continuously open flow path between said surge chamber means and said atmosphere through which at least a portion of said flow of exhaust gas from said chain saw engine means may continuously pass;

said flow restricting means being telescopingly associated with said tubular means and supported by said noise reducing apparatus for substantially unimpeded reciprocating movement relative to said tubular means;

said flow restricting means including wall means telescopingly received with said tubular means and op- 23 erable to cooperate with said lateral wall means and interior passage means of said tubular means and define generally annular passage means within said interior passage means;

said continuously operable venting means comprising generally central venting passage means extending generally centrally and longitudinally of each of said flow restricting means and said annular means, with said venting passage means being defined by and carried by said flow restricting means;

said generally annular passage means providing fluid communication between said generally central, venting passage means and said surge chamber means;

said generally annular passage means being operable to provide fluid communication, independent of said generally central venting passage means, be-

tween said atmosphere and said surge chamber means; and

said flow restricting means including generally annular, flow restricting wall means extending transversely of said generally annular passage means and cyclically operable, in response to said flow of exhaust gas, to cyclically restrict a portion of said annular passage means communicating with said atmosphere. with said generally annular wall means being operable to move away from said annular 1 passage means and tend to reduce restriction of said generally annular passage means and operable to move toward said annular passage means and increase restriction of said generally annular passage means.

8. In a chain saw including an apparatus for reducing the noise generated by chain saw operation. and wherein said chain saw includes chain saw cutting means including guide bar means, and

cutter chain means supported on said guide bar means for traversal through a cutting path; and

chain saw power means including chain saw engine means having a working chamber means, and

chain saw power transmitting means operable to transmit driving force to said cutter chain means and cause said cutter chain means to traverse said cutting path;

the improvement in said noise reducing apparatus comprising: exhaust passage means communicating with said working chamber means of said chain saw engine means and operable to transmit a flow of cyclically pulsing exhaust gas therefrom; surge chamber means operable to receive said flow of exhaust gas from said exhaust passage means. acoustic filter means including generally tubular means including lateral wall means defining interior passage means communicating with the atmosphere and extending within said surge chamber means, and transverse passage means intersecting said lateral wall means of said generally tubular means and providing restricted, acoustic filtering, fluid communication between said surge chamber means and the interior passage means of said generally tubular means;

24 flow restricting means mounted in said generally tubular means and operable to cyclically restrict at least a portion of said flow of exhaust gas; and continuously operable venting means operably as sociated with said generally tubular means and operable to maintain a continuously open flow path between said surge chamber means and said atmosphere through which at least a portion of said flow of exhaust gas from said chain saw engine means may continuously pass; said noise reducing apparatus including baffle means contained within said surge chamber means and operable to baffle said flow of exhaust gas within said surge chamber means between said exhaust passage means and said acoustic filter means; said flow restricting means being telescopingly associated with said tubular means and supported by said noise reducing apparatus for substantially unimpeded reciprocating movement relative to said tubular means; said flow restricting means including wall means telescopingly received with said tubular means and operable to cooperate with said lateral wall means and interior passage means of said tubular means and define generally annular passage means within said interior passage means operable to deflect a flow of exhaust gas passing transversely of said lateral wall means through said transverse passage means and cause said deflected flow of exhaust gas to flow generally longitudinally of said interior passage means; said continuously operable venting means comprising generally central venting passage means extending generally centrally and longitudinally of each of said flow restricting means and said annular passage means, with said venting passage means being defined by and carried by said flow restricting means; said generally annular passage means providing fluid communication between said generally central, venting passage means and said surge chamber means; said generally annular passage means being operable to provide fluid communication, independent of said generally central venting passage means, between said atmosphere and said surge chamber means; said flow restricting means including generally annular, flow restricting wall means extending transversely of said generally annular passage means and cyclically operable in response to said flow of exhaust gas to cyclically restrict a portion of said annular passage means communicating with said atmosphere, with said generally annular wall means being operable to move away from said annular passage means and tend to reduce restriction of said generally annular passage means and operable to move toward said annular passage means and increase restriction of said generally annular passage means; and said noise reducing apparatus further including flow deflecting means providing exhaust gas deflecting, fluid communication between said flow of exhaust gas issuing from said interior passage means and said atmosphere, said flow deflecting means including 25 26 restitution means operable to be'impacted by said flow restricting means tending to move said flow restricting means, when said genersaid generally annular wall means toward said ally annular wall means is moving away from I annular passage means and induce an increase said annular passage means and tending to re v in restricting of said generally annular passage duce the restriction of said generally annular means. passage means, and induce a rebounding of Patent No 3, 921, 290 Dated November 25, 1975 Inventor s) Jay Richard Bailey It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 67,

Column 3, line 50, Column 7, line 54,

Column 8, line 53, Column 9, line 38,

Column 12, Column 13, Column 14,

Column 16,

Column 1 7,

Column 1 8,

Column 18, Column 23,

[SEAL] beiorel'stated" change "hertofore" to .heretofore after 'means"insert and after "the" change "aforsaid" to aforesaid after "opening" insert in after "to delete "a".

line 64, before "interior" insert and line 45, after "passage change "meand" to means line 12, after "means" delete the comma and after "8" insert a comma line 63, after "and" add the following:

support means, including said outlet passage means, telescopingly mounting said flow restricting means for substantially unimpeded cyclic movement. line 10, before "improvement" insert the line 31, before "means" change "restriction" to restitution line 64 after "piston" change "said" to and line 9, after "annular" insert passage Signed and Scaled thus twenty-fifth Day Of May Attest:

C. MARSHALL DANN Commissioner of Parents and Trqdemarks f RUTH c. MASON Arresting Officer UTED STATES PATENT OFFICE QE'HMCATE 0F CORRECTION Patent No. 3, 921, 290 Dated November 25, 1975 Inventor(s) Jay Richard Bailey It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 67, before "stated" change "hertofore" to heretofore Column 3, line 50, after "means" insert and Column 7, line 54, after "the" change "aforsaid' to aforesaid Column 8, line 53, after "opening" insert in Column 9, line 38, after "to" delete "a".

Column 12, line 64, before "interior" insert and Column 13, line 45, after "passage" change "meand" to means Column 14, line 12, after "means' delete the comma and after "8" insert a comma Column 16, line 63, after "and" add the following:

support means, including said outlet passage means, telescopingly mounting said flow restricting means for substantially unimpeded cyclic movement.

Column 17, line 10, before "improvement" insert the Column 18, line 31, before "means" change "restriction" to restitution Column 18, line 64 after "piston" change "said" to and Column 23, line 9, after "annular" insert passage Saigncd and Scaled this twenty-fifth Day of May 1976 [SEAL] Arrest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner of Parents and Trademarks

Claims

1. In a chain saw including an apparatus for reducing the noise generated by chain saw operation, and wherein said chain saw includes chain saw cutting means including guide bar means, and cutter chain means supported on said guide bar means for traversal through a cutting path; and chain saw power means including chain saw engine means having a working chamber means, and chain saw power transmitting means operable to transmit driving force to said cutter chain means and cause said cutter chain means to traverse said cutting path; the improvement in said noise reducing apparatus comprising: exhaust passage means communicating with said working chamber means of said chain saw engine means and operable to transmit a flow of cyclically pulsing exhaust gas therefrom; generally tubular, outlet passage means operable to receive said flow of exhaust gas and transmit said flow to the atmosphere; exhaust flow responsive, cyclically operable flow restricting means telescopingly mounted in said outlet passage means and operable in response to pressure pulsations in said flow of exhaust gas to cyclically restrict a portion of said flow of exhaust gas transmitted through said outlet passage means; continuously operable venting means operable to permit a continuous flow of a portion of said flow of exhaust gas through said outlet passage means to the atmosphere concurrent with said cyclic restriction of a portion of said exhaust flow through said outlet passage means; and

2. In a chain saw including an apparatus for reducing the noise generated by chain saw operation, and wherein said chain saw includes chain saw cutting means including guide bar means, and cutter chain means supported on said guide bar means for traversal through a cutting path; and chain saw power means including chain saw engine means having a working chamber means, and chain saw power transmitting means operable to transmit driving force to said cutter chain means and cause said cutter chain means to traverse said cutting path; improvement in said noise reducing apparatus comprising: exhaust passage means communicating with said working chamber means of said chain saw engine means and operable to transmit a flow of cyclically pulsing exhaust gas therefrom; surge chamber means operable to Receive said flow of exhaust gas from said exhaust passage means; acoustic filter means including generally tubular means including lateral wall means defining interior passage means communicating with the atmosphere and extending within said surge chamber means, and transverse passage means intersecting said lateral wall means of said generally tubular means and providing restricted, acoustic filtering, fluid communication between said surge chamber means and the interior passage means of said generally tubular means; flow restricting means mounted in said generally tubular means and operable to cyclically restrict at least a portion of said flow of exhaust gas; continuously operable venting means operably associated with said generally tubular means and operable to maintain a continuously open flow path between said surge chamber means and said atmosphere through which at least a portion of said flow of exhaust gas from said chain saw engine means may continuously pass; said noise reducing apparatus including a plurality of assymetrically arranged tubular members defining baffle means contained within said surge chamber means and operable to baffle said flow of exhaust gas within said surge chamber means between said exhaust passage means and said acoustic filter means; said flow restricting means being telescopingly associated with said tubular means and supported by said noise reducing apparatus for substantially unimpeded reciprocating movement relative to said tubular means; said flow restricting means including wall means telescopingly received with said tubular means and operable to cooperate with said lateral wall means and interior passage means of said tubular means and define generally annular passage means within said interior passage means operable to deflect a flow of exhaust gas passing transversely of said lateral wall means through said transverse passage means and cause said deflected flow of exhaust gas to flow generally longitudinally of said interior passage means; said continuously operable venting means comprising generally central venting passage means extending generally centrally and longitudinally of each of said flow restricting means and said annular passage means, with said venting passage means being defined by and carried by said flow restricting means; said generally annular passage means providing fluid communication between said generally central, venting passage means and said surge chamber means; said generally annular passage means being operable to provide fluid communication, independent of said generally central venting passage means, between said atmosphere and said surge chamber means; said flow restricting means including generally annular, flow restricting wall means extending transversely of said generally annular passage means and cyclically operable in response to said flow of exhaust gas to cyclically restrict a portion of said annular passage means communicating with said atmosphere, with said generally annular wall means being operable to move away from said annular passage means and tend to reduce restriction of said generally annular passage means and operable to move toward said annular passage means and increase restriction of said generally annular passage means; said noise reducing apparatus further including flow deflecting means providing exhaust gas deflecting, fluid communication between said flow of exhaust gas issuing from said interior passage means and said atmosphere, said flow deflecting means including restriction means operable to be impacted by said flow restricting means, when said generally annular wall means is moving away from said annular passage means and tending to reduce the restriction of said generally annular passage means, and induce a rebounding of said flow restricting means tending to move said generally annular wall means toward said annular passage means and induce an increase in restricting of said generallY annular passage means; said transverse passage means of said acoustic filter means including a first plurality of elongate openings extending longitudinally of said generally annular passage means, spaced circumferentially about said generally tubular means, and operable to discharge exhaust gas directly into said generally annular passage means, and a second plurality of elongate openings comprising a portion of said continuously operable venting means and operable to discharge exhaust gas into said interior passage means without passage through said generally annular passage means.

3. In a chain saw including an apparatus for reducing the noise generated by an operating chain saw, wherein said chain saw includes chain saw cutting means including guide bar means, cutter chain means supported on said guide bar means for movement through a cutting plane; chain saw engine means including piston said cylinder means, crankshaft means driven by said piston means of said piston and cylinder means, and operable to transmit driving force to said cutter chain means; said noise reducing apparatus comprising: conduit means operable to transmit cyclically pulsing exhaust fluid from said cylinder means of said piston and cylinder means; surge chamber means, said surge chamber means being operable to receive exhaust fluid from said conduit means; acoustic filter means including generally perforate, outlet passage defining means, said conduit means and said outlet passage defining means being mutually offset, barrier means within said surge chamber means closing a first end portion of said outlet passage defining means, outlet means provided by a second end of said outlet passage defining means, said outlet means being operable to transmit exhaust fluid to the exterior of said surge chamber means, said outlet passage defining means including a plurality of openings providing communication between said outlet means and the interior of said surge chamber means; a plurality of tubular baffle means, said tubular baffle means being located within the interior of said surge chamber means, said tubular baffle means being mutually displaced and disposed nonsymmetrically in relation to said outlet passage defining means; and flow restricting means operable to cyclically restrict a flow of said exhaust fluid passing through said acoustic filter means; continuously operable venting means operable to permit a continuous flow of at least a portion of a flow of said exhaust fluid through said acoustic filter means to the atmosphere; and support means mounting said flow restricting means for substantially unimpeded cyclic movement.

4. In a chain saw including an apparatus for reducing the noise generated by an operating chain saw, wherein said chain saw includes chain saw cutting means including guide bar means, cutter chain means supported on said guide bar means for movement through a cutting plane with said cutting plane being aligned in generally parallel relation with a principal vibration plane of a chain saw; chain saw engine means including piston and cylinder means, crankshaft means driven by said piston means of said piston and cylinder means, and operable to transmit driving force to said cutter chain means; and said crankshaft means being mounted for rotation about an axis of crankshaft rotation extending generally perpendicular to said principal vibration plane; said noise reducing apparatus comprising: conduit means operable to transmit cyclically pulsing exhaust fluid from said cylinder means of said piston and cylinder means, said conduit means having a longitudinal axis extending generally parallel to said axis of crankshaft rotation; surge chamber means, said surge chamber means being operable to receive exhaust fluid from said conduit means, said surge chamber means having a geNerally rectangular cross section extending generally parallel with said principal vibration plane; acoustic filter means including generally perforate cylinder means having a longitudinal axis extending generally parallel to said axis of crankshaft rotation, a longitudinal, generally central axis of said cylinder means being transversely displaced from a longitudinal, generally central axis of said conduit means, with said conduit means and said cylinder means being mutually, transversely offset, barrier means within said surge chamber means closing a first end portion of said cylinder means, outlet means provided by a second end of said cylinder means, said outlet means being operable to transmit exhaust fluid to the exterior of said surge chamber means, said cylinder means including a plurality of generally radially opening and circumferentially spaced perforation means, said cutter chain means and chain saw engine means being operable to generate vibrations generally aligned with said principal vibration plane and acting on said cylinder means to generate vibrations therein directed generally transversely thereof and in general alignment with said principal vibration plane; flow restricting means operable to cyclically restrict a flow of said exhaust fluid passing through said acoustic filter means; continuously operable venting means operable to permit a continuous flow of at least a portion of a flow of said exhaust fluid through said acoustic filter means to the atmosphere; and support means mounting said flow restricting means for substantially unimpeded cyclic movement.

5. In a chain saw including an apparatus for reducing the noise generated by an operating chain saw, wherein said chain saw includes chain saw cutting means including guide bar means, cutter chain means supported on said guide bar means for movement through a cutting plane, with said cutting plane being aligned in generally parallel relation with a principal vibration plane of a chain saw; chain saw engine means including piston and cylinder means, crankshaft means driven by said piston means of said piston and cylinder means, and operable to transmit driving force to said cutter chain means, said crankshaft means being mounted for rotation about an axis of crankshaft rotation extending generally perpendicular to said principal vibration plane; said noise reducing apparatus comprising: conduit means operable to transmit cyclically pulsing exhaust fluid from said cylinder means of said piston and cylinder means, said conduit means having a generally rectangularly elongate cross section, and said conduit means having a longitudinal axis extending generally parallel to said axis of crankshaft rotation; surge chamber means, said surge chamber means being operable to receive exhaust fluid from said conduit means, said surge chamber means being supported on the exterior of said cylinder means, said conduit means extending from said surge chamber means and being directly connected with the exterior of said cylinder means and disposed in direct, metal-to-metal engagement therewith, said surge chamber means having a generally rectangular configuration including a generally rectangular cross section extending generally parallel with said principal vibration plane; acoustic filter means including generally perforate cylinder means having a longitudinal axis extending generally parallel to said axis of crankshaft rotation, a longitudinal, generally central axis of said cylinder means being transversely displaced from a longitudinal, generally central axis of said conduit means, with said conduit means and said cylinder means being mutually, transversely offset, barrier means within said surge chamber means closing a first end portion of said cylinder means, outlet means provided by a second end of said second cylinder means, said outlet meaNs being operable to transmit exhaust fluid to the exterior of said surge chamber means, said cylinder means including a plurality of generally radially opening and circumferentially spaced perforation means, and said cutter chain means and chain saw engine means being operable to generate vibrations generally aligned with said principal vibration plane and acting on said cylinder means to generate vibrations therein directed generally transversely thereof and in general alignment with said principal vibration plane; a plurality of tubular baffle means, said tubular baffle means being located within the interior of said surge chamber means, each said tubular baffle means extending generally parallel to said axis of crankshaft rotation, and said tubular baffle means being mutually displaced and spaced generally radially outwardly of said cylinder means; said conduit means, said cylinder means, and said tubular baffle means being generally mutually parallel and subject to said vibrations generated in general alignment with said principal vibration plane; flow restricting means operable to cyclically restrict a flow of said exhaust fluid passing through said acoustic filter means; continuously operable venting means operable to permit a continuous flow of at least a portion of a flow of said exhaust fluid through said acoustic filter means to the atmosphere; and support means mounting said flow restricting means for substantially unimpeded cyclic movement.

6. A noise reducing apparatus for a cyclic, internal combustion engine, said apparatus comprising: exhaust passage means operable to communicate with a working chamber means of cyclic, internal combustion engine means and operable to transmit a flow of cyclically pulsing exhaust gas therefrom; generally tubular, outlet passage means operable to receive said flow of exhaust gas and transmit said flow to the atmosphere; exhaust flow responsive, cyclically operable, flow restricting means telescopingly mounted in said outlet passage means and operable in response to pressure pulsations in said flow of exhaust gas to cyclically restrict a portion of said flow of exhaust gas transmitted through said outlet passage means; continuously operable venting means operable to permit a continuous flow of a portion of said flow of exhaust gas through said outlet passage means to the atmosphere concurrent with said cyclic restriction of a portion of said exhaust gas flow through said outlet passage means; and support means including said outlet passage means, telescopingly mounting said flow restricting means for substantially unimpeded cyclic movement.

7. In a chain saw including an apparatus for reducing the noise generated by chain saw operation, and wherein said chain saw includes chain saw cutting means including guide bar means, and cutter chain means supported on said guide bar means for traversal through a cutting path; and chain saw power means including chain saw engine means having a working chamber means, and chain saw power transmitting means operable to transmit driving force to said cutter chain means and cause said cutter chain means to traverse said cutting path; the improvement in said noise reducing apparatus comprising: exhaust passage means communicating with said working chamber means of said chain saw engine means and operable to transmit a flow of cyclically pulsing exhaust gas therefrom; surge chamber means operable to receive said flow of exhaust gas from said exhaust passage means; acoustic filter means including generally tubular means including lateral wall means defining interior passage means communicating with the atmosphere and extending within said surge chamber means, and transverse passage means intersecting said lateral wall means of said generally tubular means and providing restricted, acoustic filtering, fluid communication between said surge chamber means and the interior passage means of said generally tubular means; flow restricting means mounted in said generally tubular means and operable to cyclically restrict at least a portion of said flow of exhaust gas; and continuously operable venting means operably associated with said generally tubular means and operable to maintain a continuously open flow path between said surge chamber means and said atmosphere through which at least a portion of said flow of exhaust gas from said chain saw engine means may continuously pass; said flow restricting means being telescopingly associated with said tubular means and supported by said noise reducing apparatus for substantially unimpeded reciprocating movement relative to said tubular means; said flow restricting means including wall means telescopingly received with said tubular means and operable to cooperate with said lateral wall means and interior passage means of said tubular means and define generally annular passage means within said interior passage means; said continuously operable venting means comprising generally central venting passage means extending generally centrally and longitudinally of each of said flow restricting means and said annular means, with said venting passage means being defined by and carried by said flow restricting means; said generally annular passage means providing fluid communication between said generally central, venting passage means and said surge chamber means; said generally annular passage means being operable to provide fluid communication, independent of said generally central venting passage means, between said atmosphere and said surge chamber means; and said flow restricting means including generally annular, flow restricting wall means extending transversely of said generally annular passage means and cyclically operable, in response to said flow of exhaust gas, to cyclically restrict a portion of said annular passage means communicating with said atmosphere, with said generally annular wall means being operable to move away from said annular passage means and tend to reduce restriction of said generally annular passage means and operable to move toward said annular passage means and increase restriction of said generally annular passage means.

8. In a chain saw including an apparatus for reducing the noise generated by chain saw operation, and wherein said chain saw includes chain saw cutting means including guide bar means, and cutter chain means supported on said guide bar means for traversal through a cutting path; and chain saw power means including chain saw engine means having a working chamber means, and chain saw power transmitting means operable to transmit driving force to said cutter chain means and cause said cutter chain means to traverse said cutting path; the improvement in said noise reducing apparatus comprising: exhaust passage means communicating with said working chamber means of said chain saw engine means and operable to transmit a flow of cyclically pulsing exhaust gas therefrom; surge chamber means operable to receive said flow of exhaust gas from said exhaust passage means; acoustic filter means including generally tubular means including lateral wall means defining interior passage means communicating with the atmosphere and extending within said surge chamber means, and transverse passage means intersecting said lateral wall means of said generally tubular means and providing restricted, acoustic filtering, fluid communication between said surge chamber means and the interior passage means of said generally tubular means; flow restricting means mounted in said generally tubular means and operable to cyclically restrict at least a portion of said flow of exhaust gas; and continuously operable venting means operably associated with said generally tubular means and operable to maintain a continuously open flow path between said surge cHamber means and said atmosphere through which at least a portion of said flow of exhaust gas from said chain saw engine means may continuously pass; said noise reducing apparatus including baffle means contained within said surge chamber means and operable to baffle said flow of exhaust gas within said surge chamber means between said exhaust passage means and said acoustic filter means; said flow restricting means being telescopingly associated with said tubular means and supported by said noise reducing apparatus for substantially unimpeded reciprocating movement relative to said tubular means; said flow restricting means including wall means telescopingly received with said tubular means and operable to cooperate with said lateral wall means and interior passage means of said tubular means and define generally annular passage means within said interior passage means operable to deflect a flow of exhaust gas passing transversely of said lateral wall means through said transverse passage means and cause said deflected flow of exhaust gas to flow generally longitudinally of said interior passage means; said continuously operable venting means comprising generally central venting passage means extending generally centrally and longitudinally of each of said flow restricting means and said annular passage means, with said venting passage means being defined by and carried by said flow restricting means; said generally annular passage means providing fluid communication between said generally central, venting passage means and said surge chamber means; said generally annular passage means being operable to provide fluid communication, independent of said generally central venting passage means, between said atmosphere and said surge chamber means; said flow restricting means including generally annular, flow restricting wall means extending transversely of said generally annular passage means and cyclically operable in response to said flow of exhaust gas to cyclically restrict a portion of said annular passage means communicating with said atmosphere, with said generally annular wall means being operable to move away from said annular passage means and tend to reduce restriction of said generally annular passage means and operable to move toward said annular passage means and increase restriction of said generally annular passage means; and said noise reducing apparatus further including flow deflecting means providing exhaust gas deflecting, fluid communication between said flow of exhaust gas issuing from said interior passage means and said atmosphere, said flow deflecting means including restitution means operable to be impacted by said flow restricting means, when said generally annular wall means is moving away from said annular passage means and tending to reduce the restriction of said generally annular passage means, and induce a rebounding of said flow restricting means tending to move said generally annular wall means toward said annular passage means and induce an increase in restricting of said generally annular passage means.