Abstract:
An engine generally including a housing, an air/fuel mixing device coupled to the housing, and a cover coupled to the housing and cooperating with the housing to define a space. A muffler is disposed adjacent the space and is operable to heat air within the space. A flow guide is positioned adjacent the space. The flow guide includes a channel sized to deliver a predetermined quantity of air from the space to the air/fuel mixing device.

Description:
BACKGROUND  
       [0001]     The present invention relates generally to cold weather engines. More particularly, the present invention relates to cold weather engines that provide heated air for combustion.  
         [0002]     Snow throwers and other cold weather equipment often use small engines to provide the necessary power. These engines often include an air/fuel mixing device such as a carburetor that operates most efficiently (i.e., fuel efficiency as well as reduced emissions) when the air is provided to the carburetor within a specified temperature range. When operating in a cold environment it is often difficult to provide sufficient quantities of warm air to the carburetor to operate within this predefined range. This results in inefficient operation and higher emissions than would be achieved with optimal temperature air.  
       SUMMARY  
       [0003]     The present invention provides an engine generally including a housing, an air/fuel mixing device coupled to the housing, and a cover coupled to the housing and cooperating with the housing to define a space. A muffler is disposed adjacent the space and is operable to heat air within the space. A flow guide is positioned adjacent the space. The flow guide includes a channel sized to deliver a predetermined quantity of air from the space to the air/fuel mixing device.  
         [0004]     In another aspect, the invention generally provides an engine including a housing, a cylinder disposed within the housing, and a piston reciprocal within the cylinder and cooperating with the cylinder to define a characteristic volume. An air/fuel mixing device is coupled to the housing and is operable to mix a flow of fuel and a flow of heated air to produce an air/fuel mixture. A muffler is positioned adjacent the housing and a cover is coupled to the housing. The housing, the cover, and the muffler cooperate to substantially enclose a space. A flow guide is positioned adjacent the space and includes a channel having a flow area. The flow area is selected based upon the characteristic volume. The channel is positioned to deliver the flow of heated air from the space to the air/fuel mixing device.  
         [0005]     In still another aspect, the present invention generally provides an engine including a housing and a piston/cylinder arrangement disposed at least partially within the housing and having a characteristic volume. A carburetor is coupled to the housing. A heater box is at least partially defined by the housing. The heater box defines a space and includes a flow limiter having a flow area that is related to the characteristic size. A muffler is positioned adjacent the housing and is disposed adjacent the heater box. The muffler is operable to heat air disposed within the space.  
         [0006]     Additional features and advantages will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]     The detailed description particularly refers to the accompanying figures in which:  
         [0008]      FIG. 1  is a perspective view of an engine including a cover;  
         [0009]      FIG. 2  is a perspective view of the engine of  FIG. 1  with the cover removed;  
         [0010]      FIG. 3  is a side view of the engine of  FIG. 1  partially broken away to show a heater box;  
         [0011]      FIG. 4  is a perspective view of the exterior of the cover of  FIG. 1 ;  
         [0012]      FIG. 5  is bottom view of the cover of  FIG. 1 ;  
         [0013]      FIG. 6  is a perspective view of a flow guide;  
         [0014]      FIG. 7  is a section view of the flow guide of  FIG. 6  taken along line  7 - 7 ;  
         [0015]      FIG. 8  is a schematic illustration of a piston-cylinder arrangement;  
         [0016]      FIG. 9  is a perspective view of another flow guide; and  
         [0017]      FIG. 10  is a perspective view of another engine cover. 
     
    
     DETAILED DESCRIPTION  
       [0018]     With reference to  FIG. 1 , an engine  10  including a housing  15  and a cover  20  is illustrated. The engine  10  also includes a cylinder head  25 , a cylinder  30 , and a piston  35  that reciprocates within the cylinder  30  to drive a crankshaft. The crankshaft extends vertically from the bottom of the engine housing  15  and engages equipment for the engine  10  to drive. The cylinder head  25 , the piston  35 , and the cylinder  30  cooperate to at least partially define a combustion chamber  37  (shown in  FIG. 8 ) having a characteristic configuration or volume. The characteristic volume is a function of the size of the piston  35  and cylinder  30  as well as the geometry of the various components. For example, some constructions employ a cylinder head  25  that defines a portion of the combustion chamber  37 . The shape as well as the volume of this portion affects the volume of the combustion chamber  37 .  
         [0019]     The engine housing  15  at least partially defines the cylinder  30  and provides support for various other components such as a muffler  40 , a fuel tank  45 , and a carburetor  50 . The carburetor  50 , shown in  FIGS. 2 and 3 , receives a flow of fuel from the fuel tank  45  and mixes it with a flow of air to produce an air/fuel mixture. The air/fuel mixture than flows to the combustion chamber  37  for combustion. After combustion, the piston  35  forces exhaust gas out of the combustion chamber. The exhaust gas passes through the muffler  40  and out of the engine  10 . The flow of exhaust gas within the muffler  40  is quite hot and functions to heat the muffler  40 .  
         [0020]     The cover  20 , shown in  FIGS. 1 and 4 - 5 , engages the engine housing  15  and cooperates with the engine housing  15  and other engine components to define a substantially enclosed chamber  55 . The cover  20  is a generally thin-walled member formed to closely fit with the various engine components to substantially seal the chamber  55 . The cover  20  can be formed from plastic, metal, composite, or any other material suitable for use with engines  10 . The cover  20 , or housing  15 , may also include seal members (e.g., stick-on rubber strips) that attach to the cover  20 , or other component in contact with the cover  20 , and engage the other components to provide an improved seal. Of course, air leakage into or out of the chamber  55  may occur, as an air tight seal is not critical to the function of the invention.  
         [0021]     The cover  20  includes an interior wall  60 , illustrated in  FIG. 5 , that separates the chamber  55  from other engine components such as a fan  65 . The interior wall  60  can be formed as part of the cover  20 , may be separate from the cover  20 , or may be attached to the cover  20 . The shape and position of the wall  60  is largely determined by the available space under the cover  20 . As such, many different arrangements of the interior wall  60  are possible.  
         [0022]      FIGS. 2 and 6 - 7  illustrate a flow guide  70  that is positioned adjacent the chamber. The flow guide  70  includes a wall portion  75  that cooperates with the interior wall  60  of the cover  20  to separate the chamber  55  from the other engine components. The wall portion  75  is contoured to allow it to fit within the confined space defined by the housing  15  and the cover  20 . As such, the wall portion  75  may include turns or elevation changes that allow for a more compact engine  10 . The contours of the wall portion  75  function to conserve space. As such, different engines  10  may require different wall contours.  
         [0023]     The wall portion  75  also includes an aperture  80  that provides fluid communication between the chamber  55  and the carburetor  50 . A tube portion  85  extends between the aperture  80  and the carburetor  50  to complete a flow path between the chamber  55  and the carburetor  50 . The tube  85  includes an attachment portion  90  that attaches directly to the carburetor air intake. The tube portion  85  also includes a channel  95  having a throat region  100  that defines a minimum flow area. The minimum flow area is sized based at least partially on the characteristic volume of the combustion chamber  37 . More specifically, the carburetor  50  is designed to deliver a precise air/fuel mixture to the combustion chamber  37  and the air cleaner is designed to allow the proper volume of air to pass through the carburetor  50  for a given vacuum. The throat region  100  is sized to allow substantially the same volume of air to pass as the air cleaner. In this way, the throat region  100  does not create an additional flow constraint. Channel  95  and throat regions  100 , together with the carburetor venturi, are sized to create the correct partial vacuum during the intake stroke to draw in the correct proportion of fuel and air into the combustion chamber.  
         [0024]     In most constructions, the tube portion  85  and the wall portion  75  are formed as a single component. However, other constructions may employ two or more separate components that attach to one another to define the flow guide  70 . Constructions that employ separate components have additional sources of potential leakage at the interface between the components. As such, gaskets or other seal-aiding devices (e.g., grease, o-rings, and the like) may be required.  
         [0025]     As shown in  FIG. 3 , with the cover  20  installed in its operating position, the chamber  55  completes a fluid connection between the exterior of the muffler  40  and the carburetor inlet. The muffler  40  is positioned adjacent an open portion  105  of the cover  20 . Thus, air entering the chamber  55  through the open portion  105  passes near, and is heated by the hot muffler  40 . The heated air fills the chamber  55  and is drawn from the chamber  55  by the carburetor  50  via the tube  85 , as required by the engine  10 .  
         [0026]      FIG. 9  illustrates another construction of a flow guide  200  that includes a breather tube  205 . A first end  210  of the breather tube extends into an interior region  215  of the flow guide via a cut out portion  220 . A second end  225  of the tube  205  connects with the engine breather assembly where combustible gasses sometimes collect. These gasses are often very moist, thus making them susceptible to freezing in cold operating climates. When the engine is operating, a partial vacuum is produced adjacent the first end  210  of the tube  205 . The partial vacuum draws gasses from the breather and directs them into the carburetor and the engine for combustion.  
         [0027]      FIG. 10  illustrates another construction of an engine cover  250 . The cover  250  is substantially similar to the cover  20  of  FIG. 1 . The cover  250  includes an interior wall  255  that is substantially similar to, and functions much the same as, the interior wall  60 . The cover  250  also includes a second interior wall  260 , a transverse wall  265 , and a cover portion  270 . The second interior wall  260 , the transverse wall  265 , and the first interior wall  255  cooperate to separate the inlet of the flow guide  200  from areas where cold air might collect. Thus, as the engine produces a vacuum to draw in combustion air, a larger percentage of the air is drawn from a chamber  275  adjacent the hot engine components, including the muffler  40  (shown in  FIG. 2 ).  
         [0028]     The cover portion  270  includes a resilient material, such as but not limited to foam (shown in  FIG. 10 ). The cover portion  270  attaches to the inner surface of the cover  250  immediately above the flow guide  200 . When the cover  250  is positioned in place, the foam contacts the flow guide  200  and substantially seals the open top of the flow guide  200 . In another construction, a rigid cover (e.g., plastic, composite, metal, ceramic, and the like) may be integrally-formed with the flow guide  200  to inhibit the entry of air into the flow guide  200  from above. Again, the cover forces a larger percentage of the air used for combustion to be drawn from the chamber  275  immediately surrounding the muffler  40  and other hot engine components.  
         [0029]     During engine operation, the carburetor  50  produces a partial vacuum at its air inlet. The partial vacuum draws the desired quantity of air from the chamber  55  into the carburetor  50 . Because the air inlet is directly connected to the tube portion  85  of the flow guide  70 , the low-pressure produced by the carburetor  50  draws air from the chamber  55  into the tube  85 . The throat  100  helps to determine the quantity of air that can be drawn by the carburetor  50 . The air drawn in by the carburetor  50  mixes with a flow of fuel and enters the combustion chamber  37 . Once in the combustion chamber  37 , the air/fuel mixture is combusted to produce usable power and exhaust gas. The exhaust gas is expelled from the combustion chamber  37  and directed to the muffler  40 . The muffler  40  quiets the exhaust flow before finally discharging it to the atmosphere. The exhaust flow remains quite hot even as it exits the muffler  40 . As such, the muffler  40  also gets quite hot. The muffler&#39;s location adjacent the chamber  55  allows the hot muffler  40  to heat air within the chamber  55  and to heat any air that may enter the chamber  55  adjacent the muffler  40 . The heated air remains in the chamber  55  until it is drawn from the chamber  55  by the carburetor  50 . Thus, the carburetor  50  provides all of the motive force required to draw heated air for the engine  10 , while the chamber  55  serves as a hot air reservoir. It should be noted that the minimum flow area defined by the throat  100  is the minimum flow area in the tube portion  85  only. The carburetor  50  or other engine components may define a flow area that is smaller than the minimum flow area of the tube portion  85 .  
         [0030]     The system just described is capable of providing air to the carburetor  50  that is at least 20 degrees F. hotter than the ambient air in which the engine  10  operates. In some constructions, even greater air temperature increases are achievable.  
         [0031]     Although the invention has been described in detail with reference to certain preferred embodiments, variations and modifications exist within the scope and spirit of the invention as described and defined in the following claims.