Method And Apparatus For Heating Carburetor Air And Flushing An Air Filter In A Chain Saw

Abstract

A method and apparatus for preheating air passing to the carburetor of a chain saw engine and concurrently flushing a carburetor air filter. A method and apparatus for utilizing a stream of exhaust gas, generated by a chain saw engine, by directing said stream, as a free flow, through air toward a preselected location on a chain saw.

Description

GENERAL BACKGROUND, OBJECTS AND SUMMARY OF INVENTION

For several years it has been recognized that a chain saw could be operated more effectively under cold weather conditions by providing it with a mechanism for preheating the air which is passed to the carburetor air inlet of the saw.

A "closed" circuit, radiator-type system which has been found to be particularly effective for this purpose is disclosed in a U.S. Zimmerer et al. Pat. No. 3,498,280.

The Zimmerer et al. system is characterized by a circulation path which serves to direct exhaust gas from a spark arrestor or muffler to a carburetor air, heating radiator and from the radiator back to the spark arrestor or muffler.

In the sense that Zimmerer et al. proposes a confined flow of exhaust fluid between a spark arrestor or muffler and a radiator, the Zimmerer et al. concept may be characterized as entailing a "closed" system.

Other practitioners in the chain saw art concerned with cold weather operation have proposed "open" systems. For example, it has been proposed to utilize the fan of a chain saw engine to blow air around the chain saw engine cylinder, and across an air filter through which air must pass enroute to the air intake of the chain saw engine carburetor. This arrangement enables fan circulated air to be heated as it flows in heat absorbing contact with the cylinder and exhaust muffler or spark arrestor. In thus being heated, the circulated air enters the chain saw carburetor in a condition more amenable to supporting combustion.

While these prior concepts are individually unique and advantageous, there has remained a need for additional techniques which would be operable to facilitate the operation of chain saws under cold weather conditions.

It is believed that it would be particularly beneficial to utilize the advantages of the structural simplicity which characterizes "open," hot gas circulating systems while effectively utilizing the open flow to both heat carburetor intake air and flush a carburetor air filter.

It is also believed that it would be desirable to utilize a heated flow of gas to, at least to some extent, provide a flow of warmed air in the vicinity of a chain saw hand grip so as to improve operator comfort.

It is also believed that it would be desirable to utilize a confined flow of exhaust, generated by a chain saw engine, as a heating device of particular effectiveness, while causing the flow of exhaust gas to entrain with it at least some ambient air so as to concurrently transmit to a carburetor air inlet combustible air and a substantial amount of heat.

In accomplishing at least some of the foregoing objectives there is presented, through this invention, a method of operating a chain saw where a stream of at least a portion of exhaust gas generated by a chain saw engine is formed. This stream of exhaust gas is directed into throat means defined by a portion of the chain saw. A portion of the exhaust gas is passed from this stream through filter means, and then into a carburetor air inlet of the chain saw engine. Another portion of the exhaust gas from this stream functions as a flushing flow and is passed in generally surface flushing cooperation with a portion of the filter means.

In the context of this basic method approach, a second independently significant aspect of the invention involves a technique where the throat means functions as a venturi throat. In this manner, the exhaust gas passing through the throat means entrains fresh ambient air for transmittal to the carburetor air inlet.

Still in the context of the basic method above described, a third aspect of the invention involves the directing of a portion of the flushing flow, as it exits from the chain saw, generally toward a hand gripped portion of the chain saw so as to provide at least some warming effect in relation to an operator's hand.

Still in the context of the basic method above described, a fourth aspect of the invention involves the utilization of barriers so as to tend to isolate the above described throat means from a chain saw cutter chain. In this manner the heated gas passing through the throat means tends to be isolated from cuttings generated by the cutter chain during operation of the chain saw. In this fourth independent aspect of the invention, another barrier means is provided between the exiting flow of exhaust gas and the throat means so as to affirmatively tend to prevent a recycling of exhaust gas, which has completed its flushing action, back into the throat means.

Still other independently significant aspects of this invention involve unique combinations of apparatus means which synergistically interact to implement the foregoing method steps.

DRAWINGS

In describing the invention, reference will be made to a preferred embodiment shown in the appended drawing. In this connection, it will be understood that the drawings and following "Description of the Preferred Embodiment" reflect a preferred embodiment only and are not restrictive in relation to the scope of the invention.

IN THE DRAWINGS

FIG. 1 provides a fragmentary, partially sectioned, vertical elevational view of a representative chain saw which is provided with the carburetor air heating and carburetor air filter flushing features of the present invention;

FIG. 2 provides a fragmentary, perspective view of a portion of the FIG. 1 chain saw illustrating, in "exploded" format, various components of a spark arrestor and exhaust stream generating mechanism;

FIG. 3 provides a fragmentary, partially sectioned, transverse view of cylinder exhaust passage, spark arrestor, and exhaust stream generating means of the FIG. 2 assembly; and

FIG. 4 provides an external, side elevational view of the FIG. 1 chain saw.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The preferred embodiment of the invention as illustrated in FIGS. 1-4 comprises an operating structure through which certain objectives of the apparatus have been achieved.

In describing this preferred embodiment, reference will first be made to the overall chain saw structure, following which detailed aspects of the carburetor air heating and carburetor air filter flushing aspects of the invention will be described.

OVERALL CHAIN SAW STRUCTURE

As shown in FIG. 1, chain saw 1 comprises an engine 2. Engine 2 includes a cylinder head 2a and a cylindrical cylinder wall 2b. Cylinder wall 2b contains a piston (not shown) which reciprocates longitudinally of the chain saw, i.e., generally along the axis X.

The piston contained within the cylinder 2 is connected by conventional chain saw drive means 3 to a cutter chain 4. Cutter chain 4 is conventionally supported upon a guide bar 5, a portion only of which is shown in FIG. 1.

Chain saw 1 additionally includes a transverse handle 6 and a longitudinally extending handle 7.

An upper portion 7a of handle 7 supports a conventional throttle trigger 8.

In a manner, now well understood in the art, an operator may grasp handle 7a, for example with his right hand. With the index finger of the right hand, the operator may manipulate the throttle trigger 8. Concurrently, the operator may grip and support the chain saw handle 6 with his left hand.

Chain saw 1 may be provided with a variety of auxiliary mechanisms intended to facilitate and improve the overall operation of the saw 1. For example, an oiler actuating button 9 is schematically shown in FIG. 1 as being positioned in operating proximity to the operator's hand which manipulates the throttle 8.

The upper portion of chain saw 1 comprises housing means defining a fuel tank 10 and an enclosure 11. As shown in FIG. 1, enclosure 11 provides a carburetor housing cavity 12, the lower end portions of which are defined by enclosure wall means 11a and 11b. Side walls of enclosure 11 are defined by longitudinally extending wall means which interconnect rear and front wall means 11a and 11b in a conventional manner, similar, for example, to the arrangement described in the aforesaid Zimmerer et al. U.S. Pat. No. 3,498,280.

A conventional carburetor 13 is positioned in cavity 12 and is disposed in air flow transmitting communication with inlet passage means of cylinder means 2, in a now well known manner.

The upper portion 13a of carburetor 13 contains a conventional opening leading to an air transmitting or carburetor induction passage.

The upper portion of cavity 12 is closed by a preformed, foraminous air filter 14.

A cover 15 is detachably secured to housing means 16 of chain saw 1. This detachable securing of cover 15 is implemented by a threaded stud 17 which projects upwardly from, and supported upon, a bracket 18. Bracket 18, as shown in FIG. 1, may be supported by the body of carburetor 13. A threaded female fastener 19, journalled in an upper portion of cover 15, serves to threadably engage stud 17 in relation to the chain saw wall means 16.

As is generally described, for example, in the aforesaid Zimmerer et al. U.S. Pat. No. 3,498,280, upwardly facing ledge means 16a, provided by wall means 16, encircles cavity 12 and provide peripheral support for lower edge means 15a of cover 15. Ledge means 16a may generally encircle wall means 11 to insure that cover 15 fully houses cavity 12 and filter 14 when seated on ledge means 16a.

In a manner generally described in United States Zimmerer et al. U.S. Pat. No. 3,498,280, cover means 15 may be provided with rim means which engage the sides and forward peripheries of the filter means 14 so as to press these portions of the filter means firmly against filter seat means, i.e., upper edge or rim means 11c of wall means 11.

Such a filter securing and cover mounting arrangement is utilized, for example, on a model CP 125 chain saw manufactured by and available from McCulloch Corporation, 6101 West Century Boulevard, Los Angeles, Calif. 90045.

As is also shown in FIG. 1, a resilient, gasket-like washer 20 may be interposed between the lower portion of fastener 19 and the upper surface of filter 14, with gasket 20 encircling stud 17. With this arrangement, when fastener 19 is threadably engaged with stud 17, it will press gasket 20 against filter 14 so as to secure the filter 14 against the mounting bracket 18 and thus provide intermediate stabilization for the filter 14.

Peripheral stabilization for the filter 14 will be provided by the aforesaid ledge means 11c and the filter side and forward edge engaging portions of cover 15, which engage lower and upper portions, respectively, of filter 14.

FIG. 1 illustrates the manner in which portion 16b of wall means 16 and portion 11a of wall means 11 cooperate to define a generally upwardly converging and downwardly opening mouth 21a of venturi throat means 21. Venturi throat means 21 extends upwardly through the assembly shown in FIG. 1, and passes through a restricted throat zone 21b disposed intermediate the filter 14 and a portion 15a of the cover 15. Venturi throat means 21 generally enlarges in zone 21c, i.e., in a zone disposed generally between portion 14b of filter 14 and portion 15b of cover 15.

As is apparent from reference to FIG. 1, filter portion 14a generally overlies the air inlet providing, upper portion 13a of carburetor 13.

The rearward portion of cover 15 is provided with rearwardly directed opening means 22. Such opening means 22 may comprise, as shown in FIG. 4, a series of laterally displaced openings 23, separated by generally vertically extending web means 24.

A spark arrestor and/or muffler 25 is mounted on the right side of the cylinder wall 2 by viewing the chain saw 1 so as to look forward from the handle 7 toward the cutter chain 4. An exhaust stream defining conduit 26 is connected with spark arrestor 25 and communicates through transverse passage means 27 with the interior of spark arrestor 25.

Spark arrestor 25 is also mounted in communicating relation with an exhaust passage 2c of cylinder 2. Thus, exhaust gas will be transmitted through passage 2c from the interior of cylinder 2 into the spark arrestor 25. At least a portion of this exhaust gas will then pass through passage means 27 into stream defining conduit 26.

Conduit 26, as shown in FIGS. 2 and 3, is curved upwardly and rearwardly away from opening 27 and is also inclined inwardly toward venturi throat means 21.

As will be apparent from reference to FIGS. 2 and 3, an outlet end 28 of conduit means 26 will direct a generally jet stream-like configuration of exhaust gas from conduit means 26 into venturi throat means 21.

As is shown in FIGS. 2 and 3, venturi throat means 21 may be elongate in a direction extending laterally of the longitudinal median plane of the chain saw 1. Throat means 21 may be divided along its length into a series of vertically extending openings 29, separated by generally vertical wall means or web means 30.

With this arrangement, the stream of exhaust gas issuing from the conduit means opening 28 will probably enter a plurality of segmental openings 29 of venturi throat means 21.

With the overall structure of the chain saw having been described, it now becomes appropriate to consider, in some detail, those aspects of the invention which are directed to the utilization of the stream of exhaust gas issuing from conduit means 26 for the purposes of heating carburetor inlet air, flushing the upper surface of filter means 14, and at least to some extent providing a flow of heated air issuing through opening means 22 in the vicinity of an operator's hand grip portion 7a.

Structure and Mode of Operation of Carburetor Air Inlet Heater and Filter Flusher

With the arrangement shown in FIGS. 1, 3 and 4, operation of the chain saw engine causes exhaust gas to pass from the exhaust port means 2c of cylinder 2 and enter an interior cavity 31 of spark arrestor 25 through a spark arrestor inlet passage defining means 32. Exhaust gas passes from an inner portion 31a of cavity 31, through a foraminous spark arresting screen 33, and into an outer cavity portion 31b. Some of the exhaust gas leaves cavity portion 31b through louvers 34, some of which are shown in FIGS. 2 and 3.

Another, extracted portion of the exhaust gas enters conduit 26 through conduit inlet passage means 27.

As shown in FIG. 3, the end extremity of conduit 26 adjacent passage means 27 is plugged by plug means 35. The other end 28 of the conduit means 26 is open and provides an exit for a stream of exhaust gas.

Thus, the portion of exhaust gas extracted from cavity 31, via conduit means 26, issues from conduit means outlet 28 as a jet stream, schematically depicted in FIG. 1 by flow line 36.

This stream of gas 36 is directed generally rearwardly of the cutting chain 4, and inwardly of saw 1 toward throat means 21, so as to pass upwardly into the venturi throat means 21.

A generally intermediate portion of chain saw 1, including wall means 11a, operably provides first barrier means interposed generally longitudinally between the venturi throat means and the cutter chain 4. This barrier means, generally depicted by reference numeral 37, includes engine mounting wall means and operates to tend to prevent or impede cuttings, generated by operation of the chain 4, from being carried directly into the throat means 21.

Because of the venturi nature of throat means 21, the jet-like stream 36 will entrain ambient fresh air with the exhaust gas of the stream 36 and carry such fresh air into the venturi throat means 21.

A portion of stream 36, generally depicted by reference numeral 38, in the restricted or relatively high pressure portion of throat 21b, will flow through the filter means or filter web 14 and into the carburetor air inlet end 13a. Thus, this diversion of carburetor feeding air 38 occurs in the relatively narrow portion 21b of the venturi throat means, i.e., the portion downstream of the relatively wide mouth portion 21a of the venturi throat means.

Another portion of the flow of exhaust gas and entrained air, generally depicted by flow direction 39, passes generally longitudinally over the exterior surface of filter means 14. This exterior surface is disposed in communication with ambient air.

The flushing flow 39 of exhaust gas and entrained air serves to maintain the exterior surface of the filter means 14 in a relatively clean condition, free of excessive accumulations of cutting operation generated, wood cuttings.

The flow of fluid in the throat portion 21c will be reversed, due to closed throat end 21d, as generally depicted by flow direction 40. This reversal in flow will cause some exhaust gas and entrained air to flow rearwardly out of the chain saw, through passage means 22. This rearward flow of gas will be directed generally toward the hand of the operator which is gripping the hand grip portion 7a. In this manner, a flow of at least partially warmed air will be directed toward the operator'hand so as to tend, at least to some extent, to improved operator comfort.

The exiting air flow 40 will carry with it at least some of any cuttings which may have accumulated in the throat 21. It will here be recognized that the flushing action of stream portion 39 will have made such accumulated cuttings amenable to removal from the cavity throat 21 by operation of the exiting flow 40, i.e., the exiting flow of the prior flushing flow 39.

In order to tend to ensure that the exiting flow 40 is not recycled back into the venturi throat means 21, a cover provided wall means 15c functions as second barrier means interposed between the exiting zone 22 and the entry zone or throat 21.

Having described the basic mode of operation of the heating and flushing aspects of the chain saw system, it now becomes appropriate to consider certain detailed aspects of the spark arrestor and the conduit mechanism which provides the diverting flow of exhaust gas for heating and flushing purposes.

Spark Arrestor and Conduit Mechanism

Components of the spark arrestor and flow diverting mechanism have previously been described in connection with FIG. 3, and will now be described in greater detail in connection with FIGS. 2 and 3.

Spark arrestor 25 is fabricated from two shell-like or cup-like halves 41 and 42. Shell half 41 may be secured to the base wall of cylinder means 2 by conventional threaded fasteners (not shown) which pass through a flange portion 43 of inlet passage defining means 32 into the body of the cylinder side wall 2b.

In the arrangement shown in FIG. 3, the base wall 44 of shell half 41 is supported, at least in part, on cylinder cooling ribs 45. Base wall 44 may also be secured by threaded fastening means 46 to boss portion (not shown) of cylinder wall means 2b.

Passage defining means 32 may be secured to the shell half 41 of spark arrestor 25 by web means 47. As shown in FIG. 3, web means 47 comprises an integral but extended portion of the left-most wall 32a of passage defining means 32. Web means 47 may be secured at its upper and lower ends to the interior of shell 41 by spot-welded, tab means 48.

The foraminous or perforate disc 33, of outwardly directed, concave configuration, is provided with openings 49 and is supported on a lip portion 50 of shell half 41 as generally shown in FIG. 3. As is also shown in FIG. 3, outer shell half 42 is provided with a rim 51 which engages the outermost rim portion 52 of perforate disc 33 as to provide a sandwiched assembly of components 41, 33 and 42.

A conventional, circumferentially constrictable, clamp means 53 serves to grippingly engage the sandwiched rim means 51, 52 and 50 so as to secure the components 42, 33 and 41 in the assembled relation depicted in FIG. 3.

With the components disposed in this assembled relation, exhaust gas passing into the cavity 31 will be obliged to pass through the openings 49 of perforate disc means 33 before reaching the louvers 34 or the conduit means inlet 27. Exhaust gas, in passing through the perforations 49 of disc 33, will tend to cause sparks to be extinguished or to be prevented from flowing out of the spark arrestor 25.

As an additional safety device, a heat shield and outflow baffle plate 54 may be secured, by brazing or welding, to the outer cup-like member 42. As shown in FIG. 3, heat shield and baffle means 54 is disposed in outwardly spaced relation relative to the louvers 34, recognizing, of course, that louvers disposed immediately behind the baffle means 53 are not illustrated in FIG. 2.

Conduit means 26 is secured by brazing or welding to component 42 of the spark arrestor so as to cause an inwardly facing transverse aperture 27a of conduit means 26 to be aligned with an outwardly facing aperture 27b of component 42. With the apertures 27a and 27b thus aligned, and conduit means 26 oriented as above-described, the conduit means 26 may be permanently connected, as by brazing or welding, to the exterior of the component 42.

SUMMARY OF MAJOR ADVANTAGES AND SCOPE OF INVENTION

In large part, the significant advantages of the invention reside in an effective concept for supplying a flow of heated fluid to the vicinity of a carburetor air filter to perform both air heating and filter flushing functions.

Significantly, this dual function action is accomplished without requiring significant modification of the basic chain saw structure. Primarily, all that is involved is the addition of a simple diversion conduit which is uniquely placed and oriented so as to generate a stream of exhaust gas operable to concurrently perform intake air heating and air filter cleaning functions.

It is also noteworthy that residual heat in the gas, passed across the filter, is directed back towards an operator's hand so as to enable such residual heat to perform a hand warming function.

The effective placement of barrier means relative to the gas intake throat, the gas exit, and the cutting chain, minimize tendencies for cuttings to be circulated or recirculated into the vicinity of the air filter.

As will be apparent, other configurations and arrangements may be employed for conveying a flow of exhaust fluid to the vicinity of the air filter means 14.

For example, in certain situations it is contemplated that exhaust gas may be transmitted directly upwardly out of a muffler and/or spark arrestor so as to flow transversely across the air filter 14 rather than longitudinally of the air filter as described in connection with the preferred embodiment.

It is also contemplated that the diverted flow of exhaust fluid may be transmitted toward the air filter in the form of a flattened or broad stream instead of in the form of a rod-like stream issuing from a flow diverting conduit. Desirably, such a flattened stream of exhaust fluid would be directed so as to cause the flattened stream to flow generally contiguously with the exterior surface of the air filter so as to achieve optimum flushing action.

Those familiar with the chain saw art and this disclosure may well recognize additions, deletions, substitutions or other modifications which could be effected in order to accomplish some or all of the objectives of this invention.

However, it will be recognized that the overall scope of invention is set forth in the appended claims.

Claims

I claim:

1. A method of operating a chain saw comprising:

operating a chain saw with an internal combustion engine;

forming a stream of at least a portion of exhaust gas generated by said engine;

directing said stream of exhaust gas

into a throat means defined by a portion of said chain saw:

passing a portion of said exhaust gas from said stream through filter means and into a carburetor air inlet means of said internal combustion engine; and

passing another portion of said exhaust gas from said stream, as a flushing flow, into generally surface flushing cooperation with a portion of said filter means.

2. A method of operating a chain saw as described in claim 1:

wherein said throat means functions substantially as venturi throat means; and

wherein said stream of exhaust gas, directed into said throat means, entrains ambient air therewith.

3. A method of operating a chain saw as described in claim 1:

wherein said flushing flow of exhaust gas, subsequent to passing in generally flushing cooperation with said filter means, is directed generally toward a hand grasped portion of said chain saw.

4. A method of operating a chain saw as described in claim 1:

wherein said stream of exhaust gas, while being directed into said throat means, is substantially isolated from a cutter chain of said chain saw by the imposition of barrier means between said throat means and said cutter chain; and

wherein said flushing flow of exhaust gas, while being directed to exit from said chain saw, is substantially isolated from said throat means by the imposition of barrier means between said throat means and said exiting flow of exhaust gas.

5. A method of operating a chain saw comprising:

operating a chain saw with an internal combustion engine;

passing at least a portion of the exhaust gas generated by said internal combustion engine through spark arrestor means;

extracting a portion of exhaust gas from said spark arrestor means and forming a jet stream of exhaust gas issuing from said spark arrestor means;

directing said stream of exhaust gas

generally rearwardly of a cutting chain of said chain saw, and

into venturi throat means defined by a housing portion of said chain saw;

providing barrier means interposed generally longitudinally between said venturi throat means and said cutter chain;

entraining ambient air with said jet stream of exhaust gas as said exhaust gases pass into said venturi throat means;

passing a portion of said exhaust gas and entrained ambient air from said venturi throat means

through filter means, and

into a carburetor air inlet of said internal combustion engine;

passing another portion of said exhaust gas and entrained air, as a flushing flow, from said venturi throat means into generally surface flushing cooperation with an exterior portion of said filter means disposed in communication with ambient air;

directing an exiting flow of said flushing flow of exhaust gas and entrained air rearwardly away from said chain saw, generally toward a hand-grasped portion of said chain saw; and providing barrier means between said exiting flow of said flushing flow and the said venturi throat means.

6. A method of utilizing a stream of exhaust gas, generated by a chain saw engine including a carburetor induction passage, to treat a portion of said chain saw, said method comprising:

generating exhaust gas in a working chamber of a chain saw internal combustion engine;

passing at least a portion of said exhaust gas into stream defining conduit means;

directing exhaust gas through said conduit means and causing said exhaust gas to exit from said conduit means as a generally unconfined stream directed generally toward a preselected location on said chain saw;

said preselected location comprising passage means communicating with, and operable to transmit air to, said carburetor induction passage of said chain saw engine; and

said exhaust gas stream exiting from said conduit means as a generally unconfined, warmed gas flow and, in passing through said passage means, entraining and warming a flow of fresh air flowing to said carburetor induction passage.

7. A method as described in claim 6 wherein:

said directed stream of exhaust gas

flushes at least a portion of said preselected location.

8. Apparatus for operating a chain saw, said apparatus comprising:

an internal combustion engine;

means operable to form a stream of at least a portion of exhaust gas generated by said engine;

throat means defined by a portion of said chain saw;

carburetor means including air inlet means;

air filter means operable to filter air passing to said air inlet means;

means operable to direct said stream of exhaust gas into

said throat means defined by a portion of said chain saw;

means operable to pass a portion of said exhaust gas from said stream through said filter means and into said carburetor air inlet means; and

means operable to pass another portion of said exhaust gas from said stream, as a flushing flow, into generally surface flushing cooperation with a portion of said filter means.

9. An apparatus for operating a chain saw as described in claim 8:

wherein said throat means is operable to function substantially as venturi throat means; and

wherein said throat means is operable to cause said stream of exhaust gas to entrain ambient air therewith.

10. An apparatus for operating a chain saw as described in claim 8 including:

means for directing said flushing flow of exhaust gas, subsequent to its passing in generally flushing cooperation with said filter means, generally toward a hand grasped portion of said chain saw.

11. An apparatus for operating a chain saw as described in claim 8 including:

first barrier means interposed generally between said throat means and a cutter chain of said chain saw;

exiting means operable to direct said flushing flow out of said chain saw and away from a cutter chain thereof; and

second barrier means interposed between said throat means and said exiting means.

12. Apparatus for operating a chain saw, said apparatus comprising:

an internal combustion engine;

a cutter chain drivenly engaged with said engine;

spark arrestor means;

means operable to pass at least a portion of exhaust gas generated by said internal combustion engine through said spark arrestor means;

means for extracting a portion of exhaust gas from said spark arrestor means and forming a jet stream of exhaust gas issuing from said spark arrestor means;

venturi throat means defined by a portion of said chain saw;

carburetor means including air inlet means;

air filter means operable to filter air passing to said air inlet means;

means for directing said stream of exhaust gas

generally rearwardly of said cutting chain, and

into said venturi throat means defined;

barrier means interposed generally longitudinally between said venturi throat means and said cutter chain;

said venturi throat means being operable to cause the entraining of ambient air by said jet stream of exhaust gas as said exhaust gases pass into said venturi throat means;

means for passing a portion of said exhaust gas and entrained ambient air from said venturi throat means

through said filter means, and

into said carburetor air inlet;

means for passing another portion of said exhaust gas and entrained air, as a flushing flow, from said venturi throat means into generally surface flushing cooperation with an exterior portion of said filter means disposed in communication with ambient air;

a hand graspable portion of said chain saw;

means for directing an exiting flow of said flushing flow of exhaust gas and entrained air rearwardly away from said chain saw, generally toward said hand-graspable portion of said chain saw; and

barrier means interposed generally between said exiting flow of said flushing flow and the said venturi throat means.

13. Apparatus for utilizing a stream of exhaust gas, generated by a chain saw engine including a carburetor induction passage, to treat a portion of said chain saw, said apparatus comprising:

stream defining conduit means;

means for passing at least a portion of chain saw engine generated exhaust gas into said stream defining conduit means; and

means for causing exhaust gas to exit from said conduit means as a generally unconfined stream directed generally toward a preselected location on said chain saw;

said preselected location comprising

passage means communicating with, and operable to transmit air to, said carburetor induction passage of said chain saw engine; and

said passage means being operable to receive said exhaust gas stream, which exits from said conduit means as a generally unconfined, warmed gas flow, with said warmed gas flow passing through said passage means and entraining therewith and warming a flow of fresh air flowing to said carburetor induction passage.

14. Apparatus as described in claim 13 including:

means operable to cause said directed stream of exhaust gas to

flush at least a portion of said preselected location.