Abstract:
An air filter assembly for an engine such as a chain saw engine. The filter assembly includes a cage, a foam filter having a sidewall surrounding a sidewall of the cage, a retaining member pressing an endwall of the filter against an endwall of the cage and a nut. The nut receives a threaded end of an anchor bolt passing through axially aligned holes in the endwalls of the cage and the filter and a hole in the retaining member. The filter assembly provides high flow rates therethrough and substantially avoids penetration of dirt around the nut connection.

Description:
This application is a continuation of application Ser. No. 07/588,019, filed Sep. 25, 1990 now U.S. Pat. No. 5,100,443. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to an air filter assembly for cleaning air for an engine such as an engine of a chain saw. 
     BACKGROUND OF THE INVENTION 
     Small gasoline engines power a wide variety of lawn and garden equipment such as lawn mowers, lawn tractors, chain saws, and so forth. In such engines, an air cleaner filters out grit from air entering a carburetor to prevent dirt from getting into the engine, where it would cause excessive wear of moving parts. The air cleaner may have one or more filter elements which must be cleaned or replaced periodically. For instance, most manufacturers suggest cleaning or replacing the filter after every 25 to 50 hours of engine operation, but if the engine is operated in an unusually dusty or sandy area, service of the air cleaner should be performed at even shorter intervals. 
     Air cleaners typically include paper, foam, or metal air filters. Such filters eventually become clogged, making the engine difficult to start and may cause the engine to stall, run hesitantly, or overheat. Chain saw filters can clog after being used for less than 10 hours. 
     Most air filters for chain saw engines are located toward the top or rear of the engine, and are either attached directly to the carburetor or connected to it by a short adapter. One conventional air filter, for example, includes a bowl with a layer of oil therein, a filtering element within the bowl with a lower perforated surface thereof facing the layer of oil, and a cover fitted over the filtering element and the bowl such that air enters through an opening between the cover and the bowl, passes between the filtering element and the bowl, then passes upwardly through the lower surface of the filtering element and downward through a pipe at the center of the bowl. 
     Another conventional air filter includes a metal housing having a lower wall with openings therethrough, a foam filter supported within the housing, and a pipe passing through the foam filter with a lower end of the pipe in fluid communication with an opening through the bottom wall of the housing. The foam filter overlaps the upper edge of the housing and a cover clamps the foam filter against the housing. Air enters the openings in the lower surface of the housing, passes upwardly through the air filter and then downward through the pipe and into the carburetor. 
     A third type of conventional air filter includes a paper element and a foam sleeve fitted around the paper element. This type of filter includes a lower plate having an opening therethrough in fluid communication with the carburetor and a cylindrical cover which clamps the foam sleeve and paper element against the lower plate such that air passes through an opening between the cover and the lower plate, passes through the foam sleeve, then through the paper element and then through the opening in the lower plate. 
     Each of the three types of air filters described above includes a bolt passing through the cover for purposes of attaching the cover to the air filter assembly. With such arrangements, dirt can find its way through the opening in the cover and lead to engine problems. Accordingly, there exists a need in the art for a air filter assembly which eliminates the problem of dirt entering through the cover of the air filter assembly. 
     SUMMARY OF THE INVENTION 
     Generally speaking, the present invention provides a filter assembly useful for cleaning air for an engine such as an engine of a chain saw. In the preferred embodiment, the filter assembly includes a cage, or case, a filter, connector and a retaining member. In practice, the cage includes opposed first and second spaced-apart endwalls and a sidewall extending therebetween. The sidewall includes air inlet means for passage of air therethrough, the first endwall includes a hole therethrough and the second endwall includes air outlet means for passage of air therethrough. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention can be further understood with reference to the following description in conjunction with the appended drawings, wherein like elements are provided with the same reference numerals. In the drawings: 
     FIG. 1 shows a cross-section of the air filter assembly of the invention and a piece of equipment to which the air filter assembly can be attached; 
     FIGS. 2-5 show details of a cage according to the invention, FIG. 2 being a side view thereof, FIG. 3 being a bottom view thereof, FIG. 4 being a side view of part of the cage and FIG. 5 being a cross-section of the part shown in FIG. 4 taken along the line V--V; 
     FIGS. 6-7 show details of a retaining plate according to the invention, FIG. 6 being a top view thereof and FIG. 7 being a side view thereof; 
     FIGS. 8-9 show details of a nut which can be used in the air filter assembly according to the invention, FIG. 8 being a bottom view thereof and FIG. 9 being a cross-section taken along the line IX--IX in FIG. 8; 
     FIG. 10 shows details of a filter element according to the invention, FIG. 10 being a side view of the filter element. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The filter assembly 1 can be attached to a piece of equipment such as a part of an engine 2 as shown in FIG. 1. The filter assembly includes a cage 3, a retaining member 4, connector means comprising a nut 5 and a filter 6 such as a porous plastic foam filter. This filter assembly 1 can be used for filtering air which is delivered to a carburetor of an engine such as a chain saw engine. 
     The cage 3 includes a sidewall 8 extending between a first endwall 9a and a second endwall 9b as shown in FIG. 2. The cage includes an air inlet means and an air outlet means. In the preferred embodiment, the air inlet means comprises at least one opening 7 in the sidewall 8 and the air outlet means comprises a flow passage 10 in the second endwall 9a. Alternatively, the cage 3 could be substituted with a suitably shaped structure which does not include openings through the sidewall 8 and/or endwall 9a. For instance, the cage could comprise a paper or foam filter element. 
     In the preferred embodiment, the cage is elliptical in shape and includes eight spaced-apart openings 7a-h in the sidewall 8 as shown in FIG. 3. The openings 7a-h are separated by portions 8a-h of the sidewall 8. Each of the openings 7a-h can have a diameter greater than one-half a distance between the first and second endwalls 9a, 9b. For instance, the diameter of the holes 7a-h can be three-fourths the distance between the endwalls 9a, 9b. The openings 7 can be separated from each other by a distance less than one-half the diameter of the openings 7. 
     The cage can comprise a single piece or multi-piece construction. For instance, the cage 3 can include an outer part 3a and an inner part 3b. The outer part 3a includes the first endwall 9a and the sidewall 8 as shown in FIG. 2. The inner part 3b includes the second endwall 9b and can be L-shaped in cross-section as shown in FIG. 5. In one embodiment, the inner part 3b includes an outer wall 13 having a height of about one-half the height of the sidewall 8 and an inner wall 14 connected to the outer wall 13 by the second endwall 9b. As shown in FIG. 4, the outer wall 13 includes extensions 15 which define semicircular openings 16 therebetween. The openings 16 are the same size as the openings 7 and when the inner part 3b is fitted within the outer part 3a, the openings 7 and 16 are coincident with each other. 
     In another embodiment, the inner part 3b includes an additional wall 17 (shown in dotted lines in FIG. 5) which together with the wall 13 extends the full height of the sidewall 8 as shown in FIG. 2. The wall 17 includes the openings 16 therein. The inner part 3b can be glued to outer part 3a or, alternatively, the inner part 3b and the outer part 3a can be welded together. For instance, the inner and outer parts can be made of plastic and spot welded together by melting adjoining portions of the inner and outer parts. 
     The cage 3 also includes a hole 11 extending through the first endwall 9a. The hole 11 can be located in an optional recessed portion 12 of the first endwall 9a as shown in FIG. 1. In the preferred embodiment, the hole 11 is located in the center of the first endwall 9a. 
     In the preferred embodiment, the retaining member 4 comprises a flat rigid plate having a first surface 18 on one side thereof and a second surface 19 on the opposite side thereof as shown in FIGS. 6 and 7. The plate is elliptical in shape and an outer periphery of the plate is spaced inwardly of an outer periphery of the filter 6 as shown in FIG. 1. The retaining member also includes a hole 21 which is aligned in an axial direction A with the hole 11 in the cage 3. The retaining member 3 tightens up the foam filter 6 as well as reduces the likelihood that dirt and rain will enter the carburetor. 
     In the preferred embodiment, the connector means 5 comprises a nut having a head 22 and a shank 23, the shank 23 being small enough to fit through the opening 21 in the retainer plate 4. The shank 23 includes at least one resilient finger 24 extending outwardly therefrom. In particular, the shank 23 includes two resilient fingers 24, 25 which are inclined to the axial direction A. The finger 24 is deformable to a first position to allow the shank to pass through the hole 21 in the retaining member 4. The finger 24 is normally in a second position when not deformed such that the retaining plate is slidable on the shank 23 between the head 22 and the finger 24. 
     The head 22 and shank 23 can be of plastic and a metal insert 26 having an internally threaded bore 26a therein can be fitted within a bore extending into a free end 23a of the shank 23. The metal insert 26 can include an outwardly tapered portion 29 between the threaded bore 26a and the free end 23a of the shank 23. The tapered portion 29 makes it easy to thread the nut on an anchor bolt. 
     The head 22 includes a rectilinearly extending slot 27 on a surface thereof opposite to the free end 23a of the shank 23. A screwdriver can be inserted in the slot 27 for tightening or loosening the nut. The head 22 also includes a bearing surface 28 having a diameter greater than a diameter of the hole 21 in the retaining member 4. The bearing surface 28 contacts the first surface 18 of the retaining member and presses the retaining member against the filter 6 for tightening the filter when in use o a piece of equipment. 
     The free end 23a of the shank presses against the first endwall 9a of the cage 3. In particular, the free end 23a of the shank has a diameter greater than a diameter of the hole 11 in the first endwall 9a of the cage and an outer periphery of the free end 23a of the shank 23 completely surrounds the hole 11 so as to provide a seal when the connector 6 attaches the filter assembly 1 to a piece of equipment. 
     In the preferred embodiment, the filter 6 comprises a single piece of porous plastic foam. The filter 6 includes a first endwall 31, a second endwall 32 and a sidewall 30 extending therebetween. A hole 34 in the first endwall 31 is axially aligned with the hole 11 in the cage 3 and the hole 21 in the retaining member 4. An air flow passage 33 in the second endwall 32 is in fluid communication with the flow passage 10 in the cage 3. 
     The filter 6 is supported by the cage 3 with the sidewall 30 of the filter 6 surrounding the sidewall 8 of the cage 3 as shown in FIG. 1. The combined thickness in the axial direction of the retaining member 4 and the first endwall 31 of the filter 6 can be less than the distance between the free end 23a of the shank 23 and the bearing surface 28. In this case, the first endwall 31 of the filter 6 is compressed between the retaining member 4 and the first endwall 9a of the cage 3 when the connector means attaches the filter assembly to a piece of equipment to thereby provide an effective seal around the nut connection. 
     As shown in FIG. 1, the engine part 2 can include a support surface 35, an anchor bolt 36 supported on the support surface 35 with a threaded free end 37 of the anchor bolt facing away from the support surface and an air inlet 40 to a carburetor of an engine extending into the support surface. The bolt 36 can include a flange 38 which engages the underside of the first endwall 9a of the cage 3. A rubber gasket 39 is supported on the support surface and extends around the anchor bolt 36 and the air inlet 40 in the support surface 35. The free end 37 of the anchor bolt 36 extends through the hole 11 in the cage, the hole 34 in the filter 6 and the hole 21 in the retaining member 4. The connector 5 is threaded into the threaded end 36 of the anchor bolt 36 to sealingly engage the second endwall 9b of the cage 3 with the gasket 39. The support surface 35 can be of plastic and include a metal insert 40 which defines the air inlet 40 as well as provides support for the bolt 36. 
     As shown in FIG. 1, a portion 32a of the second endwall 32 of the filter can be folded inwardly so as to be compressed between an outer periphery of the sidewall 8 of the cage 3 and an inner periphery of the sidewall 30 of the filter. Alternatively, the portion 32a of the second endwall 32 of the filter 6 can remain as shown in FIG. 10 so as to underlie the endwall 9b of the cage 3. 
     The above-described filter design breathes better, cleans easier and costs less than the Stihl O.E.M. factory heavy duty filter for the Stihl 044, 064 and 084 professional chain saws. The filter system is simple and can be provided in different combinations of cages, filters and covers. The following example illustrates the effectiveness of the air filter system. 
     EXAMPLE 
     In a test on a Superflow 110 flow bench using 9&#34; of water as a reference, the following results were obtained: 
     
         ______________________________________Filter System         Flow Rate______________________________________1.     Stock Stihl H.D. Filter                      77 CFM  Used Oiled and Cleaned Per  Factory Instructions2.     Stock Stihl H.D. Filter                      89 CFM  New, No Oil3.     Stock Stihl H.D. Filter,                     122 CFM  New and Inventive Outer  Filter, Oiled4.     Inventive 3 Piece Filter                     135 CFM  System Including Cage, Oiled  Filter and Nut Plate______________________________________ 
    
     When the inventive filter is combined with the factory filter, flow is 60% better than a used and cleaned H.D. filter and 35% better than a new un-oiled filter. 
     For maximum airflow, the inventive filter utilizing the special replacement cage provides flow increases of 75%. 
     The foregoing has described the principles, preferred embodiments and modes of operation of the present invention. However, the invention should not be construed as limited to the particular embodiments discussed. Instead, the above-described embodiments should be regarded as illustrative rather than restrictive, and it should be appreciated that variations may be made in those embodiments by workers skilled in the art without departing from the scope of present invention as defined by the following claims.