US3498280A

US3498280A - Chain saw with carburetor heater

Info

Publication number: US3498280A
Application number: US744948A
Authority: US
Inventors: John Louis Zimmerer; James Franklin West
Original assignee: Mcculloch Corp
Current assignee: Mcculloch Corp
Priority date: 1968-07-15
Filing date: 1968-07-15
Publication date: 1970-03-03
Anticipated expiration: 1987-03-03
Also published as: SE339889B

Description

March 3, 1970y J, L ,zlMMEREVR ET'AL 3,498,280

' CHAIN sAw WITH icARBUREToR HEATER I 3 Sheeis-Sheet 1 Filed July 15, 1968 .3m/w, bow, watz'o; @www d ATTORNEYS March .3, 1970 J, L. ZIMMERERET AL 3,498,280

CHAIN SAW WITH CARBURETOR HEATER 3 Sheets-Sheet 2 Filed July 15. 1968 FIG. 4

mvmons JOHN L. ZIMMERER JAMES F. WEST ATTORNEYS March 3, 1970 J. L.. ZIMMERER ETAI- 3,4985280 CHAIN SAW WITH CARBURETOR HEATER Filed July 15, 1968l v s sheets-sheet s 5 FTWIMHTAO' '-II l- 32u INVENT ORS JOHN L. ZIMMERER JAMES F. WEST gums, bom genau, wu ATTORNEYS United States Patent O 3,498,280 CHAIN SAW WITH CARBURETOR HEATER John Louis Zimmerer, Torrance, and James Franklin West, Palos Verdes Peninsula, Calif., assignors to Mc- Culloch Corporation, Los Angeles, Calif., a corporation of Wisconsin Filed July 15, 1968, Ser. No. 744,948 Int. Cl. F02m 31/08; B27b 17/00; F02n 17/02 U.S. Cl. 123--122 10 Claims ABSTRACT OF THE DISCLOSURE A chain saw where a heater is mounted in an enclosed cavity defined by a fuel tank, air filter and engine mounting means. A carburetor is also enclosed in'this cavity. The heater is operable to transmit heat to the carburetor, air filter, and fuel tank.

GENERAL BACKGROUND, OBI ECTS AND SUM- MARY OF THE INVENTION The chain saw art has advanced to the state where the many lumbering operations are conducted with internal combustion engine operated, portable chain saws.

In extremely cold climates, some diiculty has been eX- perienced with ice tending to form in the carburetors and air filters associated with such chain saws. Further, the overall efficiency of the chain saw engines has been reduced because of the cold nature of the air fuel mixture supplied to the engine and the relatively cold fuel supplied to the carburetor.

Since compactness and structural simplicity are essential characteristics of modern-day chain saws, the problems involved in coping with icing tendencies, cold fuel, and cold fuel-air mixtures, without engender-ing structural complexity and excessive fabrication costs, are substantial.

It thus is a principal object of the present invention to provide a uniquely simple heater, adapted to be mounted in a chain saw so as to serve to minimize carburetor icing tendencies, and air filter icing tendencies.

It is a related object of the invention to provide such a chain saw heater which is operable to heat a carburetor, heat an air-fuel mixture flowing from the carburetor to an engine, and also, at least partially, heat a body of fuel in a fuel tank.

Another object of the invention is to provide such an improved chain saw structure including a system for passing exhaust fluid from an engine, circumferentiallyabout the engine, to a heater so as to minimize heat loss from the exhaust fluid enroute to the heater.

Another principal object of the invention is to provide a highly simplified heater structure which may be readily mounted in conventional chain saws without requiring extensive modification of the conventional chain saw structure.

It is also an object of the invention to provide a chain saw heater which is operable in a variety of operating positions, with an operator having control over the degree of heating provided -by the unit.

In accomplishing at least some of the foregoing objectives, there is presented through this invention a heater for a chain saw including first and second web means. The first web means includes a first passage operable to supply heated fluid. The first web means also includes a second passage operable to discharge heated fluid. The two passages are substantially coplanar, with respect to their central axes, and are mutually converging so as to intersect. The second web means is heat conductive and provides wall means operable to encircle an air-fuel passage 3,498,280 Patented Mar. 3, 1970 extending between a carburetor and an engine of a chain saw.

Another independently significant facet of the invention pertains to a conduit system extending circumferentially about the axis of an engine, which conduit system serves to transmit exhaust fluid between an engine and a heater.

Another independently significant facet of the invention entails the combination of engine mounting means, a fuel tank, and an air filter which serves to define an enclosed chamber. A carburetor is located in this chamber. A heater is mounted in the chamber and is operable to transmit heat to the air filter, fuel tank, and carburetor.

DRAWINGS In describing the invention, reference will be made to a preferred embodiment shown in the appended drawings.

In the drawings:

FIGURE 1 provides a fragmentary partially sectioned, elevational view of a chain saw illustrating structural relationships between an engine, air filter, fuel tank, carburetor and heater;

FIGURE 2 provides a top plan view of a portion of the FIGURE l assembly, with the air filter removed;

FIGURE 3 provides a perspective exploded format, view of the heater component of the FIGURE 1 assembly;

FIGURE 4 provides a transverse,` sectional view of a valve incorporated in the FIGURE l heater assembly, which valve serves to control the flow of exhaust fluid between a spark arrestor and the heater incorporated in the FIGURE 1 assembly;

FIGURE 5 provides a transverse sectional view of a spark arrestor associated with the FIGURE 1 assembly, illustrating the manner in which exhaust fluid is diverted from the spark arrestor to the heater; and

FIGURE 6 provides a transverse sectional view of another portion of the FIGURE 5 spark arrestor, illustrating the return flow of exhaust fluid from the heater to the spark arrestor for discharge to the atmosphere.

OVERALL STRUCTURE The overall structure of the chain saw carburetor heater assembly 1, of the present invention, is shown in FIG- URES l, 2, 5 and 6.

In order to delineate the context of the invention, conventional chain saw structure which may be associated with the heater assembly 1 is shown in a more or lesS fragmentary format in FIGURE l. l

As shown in FIGURE 1, the chain saw A includes a guide bar B supporting a cutter chain C. A handle D provides a trigger-type, throttle lever E. A two-cycle, internal combustion engine F, serves to impart power to the cutter chain C so as to cause the chain C to traverse the periphery of the guide bar B. A drive connection G interposed between the engine F and the cutter chain C may include a conventional, pull-type starter. Alternatively, an electrical self-starting system may be provided.

In any event, this structure is now well known in the chain saw art. It corresponds, in general, for example, to the basic structure described in a publicly available Mc- Culloch Shop Manual associated with the MAC l-lO and 2-10 chain saws manufactured by the McCulloch Corporation of Los Angeles, Calif.

This assembly comprises a fuel tank 2, an engine mounting bracket 3. Bracket 3 may comprise an integral portion of a casting or molded trnent which defines a portion of the fuel tank 2, as shown in FIGURE 1.

Engine mounting bracket 3 is provided with one or more boss-like surfaces 4. These bosses serve to attach the bracket 3 to the cylinder of the two-cycle internal combustion engine F which serves to drive the cutter chain C. This general mode of engine mounting in a chain saw is well known and incorporated, for example, in chain saws manufactured by the above-noted McCulloch Corporation.

-Engine mounting bracket 3 is concave and includes a peripheral, air filter supporting, lip means 4. An air filter 5, which may be premolded in a somewhat convex configuration, is supported on the lip 4. Filter 5 cooperates with the lip means 4 of engine mounting bracket 3 and the fuel tank 2 and defines a fully enclosed chamber or cavity 6.

A carburetor heater 7 is positioned in the cavity 6. Heater 7 includes a relatively thick, planar, web-like portion 8 and another relatively thin, planar, web-like, portion 9. lPortions 8 and 9 are generally parallel, with web portion 9 projecting laterally from one edge of the web 8.

A conventional carburetor 10 is mounted on web 9 by conventional threaded fasteners. In order to avoid obscuring the inventive facets of this disclosure, these conventional mounting means have not been illustrated.

Carburetor 10 includes an induction passage 11 including an air inlet 12. Flow through passage 11 is regulated by a butterfly valve 11a. Passage 11 communicates with an aperture 13 in the web 9 and an aperture 14 in the mounting bracket 3. The more-or-less coaxially aligned '

apertures

14 and 13 define a continuation of induction passage 11, operable to transmit a carbiurated air and fuel mixture to the intake port of an engine cylinder 15, as schematically shown in FIGURE 5.

In this connection, it will be understood that conventional gasket means may be interposed between a boss surface 16 encircling the aperture 14 and a cylinder boss surface 17 encircling the cylinder air inlet 18. Such gasket means provides sealed communication between the passage 14 and the air-fuel inlet of the cylinder 15. Other such gasket means may be interposed between the web 9 and the carburetor 10, as well as between the web 9 and the surface 19 of the mounting bracket 3 which encircles the aperture 1-4 and faces the web 9.

As shown in FIGUR-E 1, a detachable cover H may be provided so as to shield the fuel filter 5. Cover H may be detachably secured in place by a threaded nut -I which threadably engages a mounting rod I. Rod J may be supported by a bracket K, carried by carburetor 10, and projects upwardly through apertured portions of the filter 5 and cover H to receive the cover and filter securing nut I.

As will be apparent by reference to FIGURE 1, cover H, when installed, defines a smooth, streamlined continuation of the fuel tank 2. Cover H provides an entry passage means L leading to the exterior of filter unit 5.

A spark arrestor 20 is mounted on one side of the cylinder 15, as shown in FIGURES l and 5. A conduit 21 extends from an exhaust port 22 of the cylinder 15, and serves to transmit exhaust fluid from the cylinder to the interior 23 of the spark arrestor 20.

An L-shaped supply conduit 24 extends from the spark arrestor to the heater web 8. This conduit 24, which extends generally circumferentially about the axis X of reciprocation of a piston contained within the cylinder 15, serves to supply a portion of the exhaust fluid which enters the interior zone 23 to the heater web 8 which f-unctions as a radiator. A return or discharge conduit 25, generally parallel lwith the L-shaped conduit 24, provides a return flow path for exhaust fluid, extending from the radiator 8 to a discharge passage 26 incorporated in the spark arrestor 20. Return conduit 25, like supply conduit 24 extends circumferentially about the reciprocation axis X.

As will be apparent by reference to FIGURES l, 2, and 5, themajor components are geometrically arranged so that the fiuel tank 2, carburetor 10, and heater 7, as well as the engine mounting means 3, are radially displaced from the axis X. However, these components are more-or-less aligned with a median plane 27 which extends longitudinally of the chain saw and coaxially with the reciprocation axis X. Spark arrestor 20 is displaced radially of the axis X, but is circumferentially displaced from the alignment plane 27, with respect to the reciprocation axis X.

STRUCTURAL DETAILS OF HEATER Structural details of the heater 7 are shown in FIG- URES 1 through 5.

Heater 7, as previously noted, includes the radiator portion 8 and the carburetor mounting web 9.

Supply conduit 24 is received within a conventional conduit coupling 28 in radiator 8. Discharge conduit 25 is coupled with a conventional conduit coupling 29 in the radiator 8. Each of the

couplings

28 and 29 may cornprise sockets formed in web body 8, with the ends of the cond-nits 24 and 2.9 telescopingly received within these sockets and brazed in place.

Coupling 28 communicates with an axially extending, supply passage or bore 30 formed in the radiator 8. Coupling 29 communicates with an axially extending discharge passage 31, also formed in the radiator 8.

Each of the

passages

30 and 31 comprises a straight bore, with the central axes of these bores being parallel to the upper and

lower surfaces

32a and 32b of the radiator 8. The central axes of the bores are thus coplanar and are mutually converging so as to cause the

passages

30 and 31 to intersect at the terminus 33.

With this arrangement, exhaust uid is transmitted from the supply conduit 24, through the supply passage 30, and terminus 33 to the exhaust passage 31. Exhaust fluid returns to the spark arrestor 20 by flowing from the exhaust passage 31, through the return conduit 25.

Heater 7 may be fabricated from a unitary piece of metal, such as soft aluminum, which functions as an effective heat radiator and an effective heat conductor. Thus, the web 9 provides a heat conductive media operable to transmit heat from the

passages

30 and 31 to a wall means 34. Wall means 34 is essentially cylindrical in nature and is generally coaxially oriented in relation to the passages 18 and 11. Wall means 34, which defines the connecting passage 13, provides a heat radiating surface operable to heat the air and fuel mixture passing from the carburetor passage 11 to the air-fuel inlet 18 of cylinder 15.

As illustrated, web 8, as well as the body of web 9, provide heat radiating means operable to radiate heat throughout the interior of the cavity 6. This radiated heat is effective to heat fuel in the longitudinally adjacent fuel tank 2, and also heat the superposed air filter 5.

By interposing the radiator 7 so that it is radially interposed between the mounting bracket 3 and the filter 5, and aligned so as to extend more-or-less longitudinally of the filter 5, optimum heat transfer between the radiator portion 8 and the filter 5 is effected.

It will also be appreciated that the body of the carburetor 10 is heated both by radiation and by conduction. The web 9 serves as a heat conductive device, operable to transmit heat directly to the body of carburetor 10, while the radiator web 8 imparts heat to the atmosphere surrounding the carburetor body.

A fuel transfer conduit 35 extends from the fuel reservoir 2 to the carburetor 10. This fuel transfer conduit, in passing through the heated cavity 6, will serve to impart additional heat to fuel entering the passage 11.

STRUCTURAL DETAILS OF SPARK ARRESTOR Structural details of spark arrestor 20 are shown in FIGURES 1, 5 and 6.

Spark arrestor 20 includes a concave base 36 and a convex cover 37. Convex cover 37 is telescoped partially over the base 36 so as to define the interior zone 23.

Exhaust conduit 21, extending from a cylinder exhaust port 22, provides fluid communication with the cavity 23 by way of a port or opening 38 in the rear Wall of casing 36. A spark arresting, foraminous barrier 39 extends entirely across the cavity space 23 between the =port 38 and the inlet 40 of supply conduit 24. As illustrated, inlet 40.

may be connected by a brazed, telescoped connection 41 to cover 37.

A plurality of louvered openings 42 are provided in the cover 37. These openings provide a substantial flow path, providing direct communication between the discharge passage 26 and the supply port 38, interrupted only by the spark arresting screen or barrier 39.

A thermal barrier or shield 43 is associated with the spark .arrestor 20 and serves to protect an operator from the high temperature of the spark arrestor. Thermal shield 43 includes a generally L-shaped outer Wall 44 and a pair of generally parallel,

planar side walls

45 and 46.

Side walls

45 and 46 telescopically embrace with

outer side Walls

47 and 48 of cover 37. With this telescoping relation, the thermal shield 43 and the cover 37 provide a generally L-shaped configuration for the discharge passage 26. Discharge passage 26 includes a lowermost opening 49 communicating with the atmosphere and facing away from the

conduits

24 and 25. Another opening 50, at the upper end of the passage 26, faces directly toward engine F.

As shown in FIGURE 6, the lower ends 51a and 51b of the supply conduit 24 and the return conduit 25 are connected to the cover 37 and thermal shield 43 by brazed, telescoped connections 52a and 52b. As illustrated, with this connecting arrangement, the return conduit 25 communicates directly with the discharge passage 26 and the supply conduit communicates with zone 23. Screen 39 is interposed between conduit 24 and port 38.

At this point, it will be appreciated that a portion of the exhaust uid entering the cavity 23 flows directly to the atmosphere through the louvered outlets 42. Another portion of this exhaust uid flows through the conduit 24 to the radiator 8. The resistance to outflow of exhaust fluid from the zone 23, as provided by the louvered outlets 42, ensures the desired degree of diverted exhaust flow into the supply conduit 24.

A plug valve 53 may be incorporated in the supply passage 30 to regulate the amount of exhaust ow through the communicating

passages

30 and 31.

As shown in FIGURES 2, 3 and 4, plug valve 53 includes a generally cylindrical spindle 54. Spindle 54 is journaled in an aperture 55 formed in the body of radiator 8. Aperture 55 transversely intersects the passage 30 as shown in FIGURE 4.

Spindle 54 is provided with a passage 56 operable to coaxially align With the passage 30, depending upon the rotary position of the spindle 54. A snap ring tment 57 may be provided to secure the spindle in place. An enlarged spindle head 58 provides a manually operable knob to facilitate the manipulation of the spindle 54. If desired, a screwdriver engageable slot 59 may be formed on the fiat outer periphery 60 of the operating knob 58. A Belleville spring 61 may be interposed between knob 58 and web surface 31 to brace fitment 57 against surface 32a so as to minimize vibration.

As shown in FIGURE 6, the lower end 51 of the return conduit 25 is connected to the thermal shield 43 by a brazed, telescoped connection 52. As illustrated, with this connecting arrangement, the return conduit 25 communicates directly with the discharge passage 26.

At this point, it will be appreciated that a portion of the exhaust uid entering the cavity 23 flows directly to the atmosphere through the louvered outlets 42. Another portion of this exhaust fluid flows through the conduit 24 to the radiator 8. The resistance to outflow of exhaust fluid from the zone 23, as provided by the louvered outlets 42, insures the desired degree of diverted exhaust flow into the supply conduit 24.

A plug valve 53 may be incorporated in the supply passage 30 to regulate the amount of exhaust flow through the communicating

passages

30 and 31.

As shown in FIGURES 2, 3 and 4, plug valve 53 includes a generally cylindrical spindle 54. Spindle 54 is journaled in an aperture 55 formed in the body of radia- 6 tor 8. Aperture 55 transversely intersects the passage 30 as shown in FIGURE 4.

Spindle 54 is provided with a passage 56 operable to coaxially align with the passage 30, depending upon the rotary position of the spindle 54. A snap ring tment 57 may be provided to secure the spindle in place. An enlarged spindle head 58 provides a manually operable knob to facilitate the manipulation of the spindle 54. If desired, a screwdriver engageable slot 59 may be formed on the flat outer periphery 60 of the operating knob 58. A Belleville spring 61 may be interposed between knob 58 and web surface 31 to brace fitment 57 against surface 32 so as to minimize vibration.

By rotating the knob 58 so as to align the opening 56 with the passage 30, a maximum flow of exhaust fluid through the

passages

30 and 31 will result. By rotating the knob 58 so as to cause the spindle passage 56 to extend transversely of the radiator passage 30, the passage of exhaust fluid through the radiator 8 is prevented. Obviously, by adjusting the rotary position of the knob 58, the desired degree of exhaust flow through the

passages

30 and 31 may be obtained.

OVERALL MODE OF OPERATION At the outset of operation, an operator will adjust the knob 58 to obtain the desired flow capacity for the communicating

radiator passages

30 and 31.

With these radiator passages open, exhaust fluid will enter the spark arrestor cavity 23, pass through the foraminous spark arrestor barrier 39, and enter the supply conduit 24. Fluid flowing through conduit 24 will tend to retain its heat in view of the circumferentially maintained proximity of the conduit 24 to the hot engine cylinder 15. This fiuid will then flow through the communicating

radiator passages

30 and 31 and return, by way of the conduit 25, to the spark arrestor discharge passage 26.

Concurrent with this flow of exhaust fluid to the radia? tor 8, a portion of the engine exhaust will flow directly to thzdischarge passage 26 by way of the louvered openings The exhaust fluid supplied to the radiator 8 will heat the body of this radiator. This heat will be radiated throughout the cavity 6 so as to heat the air filter 5, the carburetor 10, and at least the adjacent portion of the fuel tank 2. This radiated heat will tend to prevent ice from forming in the fuel filter, tend to prevent carburetor icing, and tend to provide a warmer supply of fuel passing to the carburetor 10 by heating fuel in tank 2, in conduit 35 and in the carburetor body.

The web means 9 will conduct heat to the passage 13 and thus serve to radiate further heat to the air-fuel mlxture passing from the carburetor 10 to the inlet port 18 of the cylinder 15.

As a result of the diverted exhaust flow, the body of heater 7 may have a temperature on the order of over l2() degrees Fahrenheit, even when the ambient temperature is as low as minus 20 to minus 30 degrees Fahrenheit. The present invention has been found to maintain temperatures in the carburetor bore 11 as high as 36 to 84 degrees Fahrenheit under these conditions, i.e., Well above the freezing point. Even under engine idling conditions, freezing is minimized or avoided.

SUMMARY OF ADVANTAGES AND SCOPE OF INVENTION f heat is imparted to the air filter, the carburetor, the fuel tank, the fuel transfer conduit and the air-fuel passage leading to the engine. The heater unit is uniquely compact so as to avoid adding to the bulk of an overall chain saw structure.

The heater is located in a protected location where inadvertent damage is unlikely to occur. The structural nature of the heater is such as to yield nominal fabrication and installation costs.

Even the structure of the spark arrestor associated with the heater is such as to provide a low cost, efiicient installation, maintaining optimum safety conditions.

We claim:

1. A chain saw comprising:

engine means including a piston mounted for reciprocation along an axis;

fuel tank means displaced laterally of said axis of piston reciprocation; carburetor means displaced laterally of said axis of piston reciprocation and displaced generally longitudinally along said axis from said fuel tank means;

exhaust-treating means displaced laterally of saidaxis of piston reciprocation and displaced circumferentially from said carburetor means with reference to said axis;

heater means interposed generally radially between said carburetor means and said engine means, with reference to said axis;

first conduit means for deflecting a portion of exhaust fluid from said exhaust treating means and conveying exhaust fluid generally circumferentially about said axis, to said heater means;

second conduit means for returning exhaust fluid from said heater means to said exhaust treating means through a path extending generally circumferentially about said axis.

2. A chain saw comprising:

engine means including a piston mounted for reciprocation along an axis;

exhaust-treating means displaced laterally of said axis of piston reciprocation and displaced circumferentially from said carburetor means with reference to said axis;

first conduit means for deecting a portion of exhaust fluid from said exhaust treating means and conveying exhaust fluid ygenerally circumferentially about said axis, to said heater means;

second conduit means for returning exhaust uid from said heater means to said exhaust treating means through a path extending generally circumferentially about said axis;

said heater means including generally planar, rst web means including a first, generally axially extending, heated fluid supplying passage, and a second, generally axially extending, heated fluid discharging passage, the central axes of said rst and second passages being snbstantially coplanar, with said first passage intersecting said second passage and being inclined relative thereto, heat conductive, second web means, said second web means being generally parallel with said first web means and extending laterally thereof, and wall means carried by said second web means and defining a heat radiator encircling an aperture, said radiator being operable to extend circumferentially about an air and fuel passage, between a carburetor and an engine of a chain saw. 3. A chain saw comprising:

engine means including a piston mounted for reciprocation along an axis; fuel tank means displaced laterally of said axis of piston reciprocation; carburetor means displaced laterally of said axis of piston reciprocation and displaced generally longitudinally along said axis from Vsaid fuel tank means; exhaust-treating means displaced laterally of said axis of piston reciprocation and displaced circumferentially from said carburetor means with reference to said axis; heater means interposed generally radially between said carburetor means and said engine means, with reference to said axis; first conduit means for defiecting a portion of exhaust uid from said exhaust treating means and conveying exhaust fluid generally circumferentially about said axis, to said heater means; second conduit means for returning exhaust uid from said heater means to said exhaust treating means through a path extending generally circumferentially about said axis;

said exhaust treating means including casing means connected with said engine means, first conecting means placing said first conduit means and said casing means in fluid cornmunicating relation, ermal shield means spaced from said casing means and cooperating with said casing means to define an exhaust discharge passage, second connecting means providing fluid communication between said second conduit means and said discharge passage, by-pass passage means providing fluid communication between said discharge passage and the interior of said casing means to enable exhaust fluid to iiow directly from the interior of said casing means to said discharge passage, side wall means carried by said thermal shield means and telescopingly receiving said casing means said casing means when telescopingly received by said side wall means providing said discharge passage, with said discharge passage having a first opening communicating with the atmosphere and facing generally away from said first and second connecting means and a second opening facing generally toward said engine means. 4. Chain saw comprising: engine mounting means; fuel tank means; air filter means; said engine mounting means, fuel tank means and air filter means cooperating to define enclosed chamber means; carburetor means mounted in said enclosed chamber means; heater means mounted in said enclosed chamber means and operable to transmit heat to said air filter means, said fuel tank means and said carburetor means. 5. A chain saw as described in claim 4 and further including air and fuel passage means extending between said carburetor means and an engine means; and

heat conductive web means extending from said heater means and encircling said air and fuel passage means, said web means being operable to radiate heat into said air and fuel passage means.

6. A chain saw as described in claim 4:

wherein said chain saw includes air and fuel passage means extending between said carburetor means and said engine means; and wherein said heater means includes generally planar, first web means including a first, generally axially extending, heated fluid supplying passage, and a second, generally axially extending, heated fluid discharging passage, e central axes of said first and second passages being substantially coplanar, with said first passage intersecting said second passage and being inclined relative thereto, heat conductive, second web means, said second web means being generally parallel with said rst web means and extending laterally thereof, and wall means carried by said second web means and defining a heat radiator encircling said air and fluid passage means; said first and second web means extending generally longitudinally of said air filter means. 7. In a chain saw including an internal combustion engine, a carburetor heater comprising:

generally planar, rst web means including a first, generally axially extending, heated fluid supplying passage, and a second, generally axially extending, heated fluid discharging passage, the central axes of said first and second passages being substantially coplanar, with said first passage intersecting said second passage and being inclined relative thereto; heat conductive, second web means, said second web means being generally parallel with said first Web means and extending laterally thereof; wall means carried by said second web means and defining a heat radiator encircling an aperture, said radiator being operable to extend circumferentially about an air and fuel passage, between a carburetor and an engine of a chain saw. 8. A chain saw comprising: engine means; fuel tank means; carburetor means; exhaust-treating means; heater means interposed generally between said carburetor means and said engine means; first conduit means for deflecting a portion of exhaust fluid from said exhaust treating means and conveying exhaust fluid generally circumferentially about said engine means to said heater means; second conduit means for returning exhaust fluid from said heater means to said exhaust treating means; engine mounting means; air filter means; said engine mounting means, fuel tank means and air filter means cooperating to define enclosed chamber means; said carburetor means being mounted in said enclosed chamber means; and said heater means being mounted in said enclosed chamber means and operable to transmit heat to said air filter means, said fuel tank means and said carburetor means. 9. An apparatus as described in claim 8: wherein said exhaust treating means includes casing means connected with said engine means; first connecting means placing said first conduit means and said casing means in fluid communieating relation; thermal shield means spaced from said casing means and cooperating with said casing means to define an exhaust discharge passage;

second connecting means providing fluid communication between said second conduit means and said discharge passage; and by-pass passage means providing fluid communication between said discharge passage and the interior of said casing means to enable exhaust fluid to flow directly from the interior of said casing means into said discharge passage. 10. A chain saw comprising: engine means; fuel tank means; carburetor means; exhaust-treating means; heater means interposed generally between said carburetor means and said engine means; first conduit means for deflecting a portion of exhaust fluid from said exhaust treating means and conveying exhaust fluid generally circumferentially about said engine means to said heater means; second conduit means for returning exhaust fluid from said heater means to said exhaust treating means; housing means; air filter means; said housing means, fuel tank means and air filter means cooperating to define enclosed chamber means; said carburetor means being mounted in said enclosed chamber means; said heater means being mounted in said enclosed chamber means and operable to transmit heat to said air filter means, said fuel tank means and said carburetor means; said heater means including generally planar, first web means including a first, generally axially extending, heated fluid supplying passage, and a second, generally axially extending, heated fluid discharging passage, the central axes of said first and second passages being substantially coplanar, with said first passage intersecting said second passage and being inclined relative thereto, heat conductive, second web means, said second web means being generally parallel with said firsdt web means and extending laterally thereof, an Wall means carried by said second web means and defining a heat radiator encircling an aperture, said radiator being operable to extend circumferentially about an air and fuel passage, between said carburetor means and said engine means; and valve means mounted in said heater means and operable to control a flow of engine exhaust fluid between said heater means and said exhaust-treating means.

References Cited UNITED STATES PATENTS 1,269,252 6/1918 Brown 123-122 1,706,242 3/ 1929 Markovetz 123-122 2,256,831 9/1941 Karey 143-32 3,088,447 5/ 1963 Henderson 123-122 FOREIGN PATENTS 70,329 4/ 1941 Czechoslovakia. 158,688 9/ 1954 Australia. 587,014 11/1959 Canada. 625,149 8/ 1961 Canada.

MARK M. NEWMAN, Primary Examiner DOUGLAS HART, Assistant Examiner U.S. Cl. X.R. 123-142.5; 143-32 ggsgo UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTIGN Patent No. 3, 498, 280 Dated March 3, 1970 Inventor(s) John L. Zimmerer and James F. West It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In Column 2, line 65, after "2, add and In Column 3, line 27, delete "carburated" and insert in its place Delete the following: Column 5, line 56, through Column 6, line 13.

In Column 8, line 44, after "means" (first occurrence) add a comma SIEM-Ill AM3 S FMH) SEMS-1970 (SEAL) Attest:

Edward M. member. Jr

Awning Of" Ummm E. som, JR.

@omissioner af Patents l