Abstract:
A four-cycle engine wherein a fuel-air-oil mixture is compressed in a crank case chamber and directed therefrom along a pathway to a combustion chamber. The pathway contains actuating mechanism for actuating the fuel intake valve leading to the combustion chamber. The pathway is restricted in volume as permitted by the actuating mechanism, preferable to a range of two to four times the piston displacement.

Description:
Priority is claimed under 35 USC §119(a) based on Japanese Patent Application Serial No. 2001-239112 filed Aug. 7, 2001. 
     FIELD OF INVENTION 
     This invention relates to engines typically used for powered outdoor tools and particularly to such engines which are fueled with a gas lubricant mixture. 
     BACKGROUND OF THE INVENTION 
     It is considered desirable to use four-cycle engine technology over two-cycle engine technology, e.g., for powered outdoor hand tools as both noise and emissions are reduced. A typical four-cycle engine is fueled by a vaporized gasoline and air mixture and a gas flow path leads directly from the engine&#39;s carburetor to the engine&#39;s combustion chamber. Such engines provide oil reservoirs that provide the lubricants necessary for lubricating the moving components of the engine. Small engine use typically does not adapt to this form of lubrication. Small engines used for, e.g., portable powered outdoor tools like hedge trimmers and the like are used in a manner where the engine is turned sideways and even upside down during operation and the oil reservoir type of lubrication is not practical. 
     Accordingly, four-cycle engines have been developed that are fueled by a gas/oil mixture. (See U.S. Pat. No. 4,708,107). The path of the gas-oil flow is arranged so as to flow in and around the moving components and oil from the mixture is deposited on the components to provide the desired lubrication. 
     Whereas the use of the lubricant bearing fuel provides the desired result, i.e., lubrication of the parts while using four-cycle technology, and thus less noise and emissions pollution, there are problems as compared to prior two-cycle engines. 
     One problem is in starting the engines, e.g., with a recoil or starter rope (typical for small engine starting). The path of the fuel is substantially extended over a traditional four-cycle engine design and thus the volume of fuel that has to be pumped through the extended passage requires repeated pulls of the starter rope. Further, in the startup mode, because the flow of fuel initially moves slowly through the extended pathway and the lubricant readily collects on the components, following startup and more rapid flow of the fuel, much of the deposited oil re-enters the flow of fuel and the desired ratio of fuel to oil is altered resulting in incomplete combustion. A still further problem addressed by the present engine design is the desire to limit the engine&#39;s speed (revolutions per minute) when the engine is not under load. 
     BRIEF SUMMARY OF THE INVENTION 
     The present design reduces the volume of the extended fuel flow passage and thus the fuel that has to be pumped to achieve startup is reduced. The preferred embodiment of the invention provides valve actuating mechanism including a timing gear interconnected to a cam gear from which a cam lifter actuates a push rod and rocker arm, which in combination, controls the engine&#39;s intake and exhaust valves. The arrangement of these components also determines the flow path of the fuel. By strategic use of the periphery of the timing gear and cam gear, the rotation of these gears assists in boosting the fuel flow along the pathway. Also by maintaining a close tolerance around the working components the path is reduced in volume and requires less fuel to fill that volume. Such strategic use of the components and the tightening of the tolerances enables an engine design that provides a volume for the flow path of the fuel that can be matched to the displacement of the piston in a ratio of between two and four-to-one. This has been found to achieve the desired improvement in flow rate to improve both startup and initial idling of the engine without detrimental affect on the thereafter running of the engine. 
     Overrunning of the engine is also a consideration herein and is controlled at least in part by reducing the size of the fuel intake port entering the combustion chamber, e.g., to a size less than the air intake port entering the carburetor. 
     The above and further improvements will be more fully appreciated upon reference to the following detailed description and drawings referred to therein. 
    
    
     DESCRIPTION OF THE FIGURES 
     FIG. 1 is a sectional view of an embodiment of the invention illustrating the arrangement of components and fuel mix flow path from the crank case chamber to the combustion chamber; 
     FIG. 2 is a sectional view of the embodiment of FIG. 1 illustrating the air filter and source of fuel mixture which is converted to a vaporized form in a carburetor and including the flow path to a crank case chamber; 
     FIGS. 3 and 4 are diagrammatic illustrations of the flow path for the fuel as between the crank case chamber and the combustion chamber from a viewpoint generally indicated by directional arrows  4 — 4  of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Reference is first made to FIG. 2 which illustrates a fuel source  35  containing a mixture, e.g., of gasoline and oil, including a fuel supply pipe  34  and a fuel return pipe  36 . Fuel from the fuel source  35  is directed to a carburetor  1  via the supply pipe  34  and air is directed to the carburetor from air cleaner  30 , through filter  30   a  and into the carburetor air intake port  1   a . The fuel and air are converted to a vapor having oil droplets that is then directed through passage  29   a  through an insulating member  29  and, as permitted by valve cover  2   a , through check valve  6  and into a crank case chamber  5  (the fuel being passed through inner wall face  3   a ). 
     The pathway for directing the fuel from the crank case chamber  5  to the combustion chamber  21  will be later described in connection with FIGS. 1,  3  and  4 . From FIG. 2 it will be appreciated that the fuel from the carburetor is drawn into the crank case chamber  5  as the piston  4  is moved upwardly in the cylinder  3 , which increases the volume of the crank case chamber  5 . As the volume is increased, a suction (negative pressure) occurs which pulls check valve  2  open and draws the fuel-air mixture (in vapor form) into the crank case chamber. In the downward stroke of piston  4 , the volume in chamber  5  is decreased to produce a positive pressure that closes check valve  2  and prevents return flow of the fuel. The fuel within chamber  5  is thereby compressed. 
     Reference is now made to FIG. 1 which is a view generally from the direction of view lines  1 — 1  of FIG.  2 . Within chamber  5  is the crank case shaft  7  which defines a center of rotation for crank pin  28  which carries connecting rod  27  which connects the piston  4  to the crank pin  28 . As the piston reciprocates up and down the crank shaft  7  is rotated. 
     As previously explained, the downward movement of the piston produces compression of the fuel in chamber  5  and this compression opens check valve  6  allowing fuel to flow from the chamber and into a flow path that extends to the combustion chamber  21  as will now be described. 
     Appreciation for the flow path of the fuel from the check valve  6  will be further appreciated with reference also to FIGS. 3 and 4. The passage through check valve  6  first leads to the periphery of a timing gear  8  mounted and rotatable with the crank shaft  7 . The flow of fuel is directed around the timing gear  8  as indicated by arrows. Timing gear  8  is inter-engaged with and produces rotation of cam gear  10  which rotates around cam gear shaft  9 . 
     A cam  17  rotatable with cam gear  10  produces actuation of rocker arms  13  and  13 ′ via actuation of cam lifters  11  connected to lift arms  12  which are connected to rocker arms  13 ,  13 ′. (See FIG.  4 ). As the cam gear  10  rotates (see the dash line arrow of FIG.  3 ), the flow of fuel is directed along the upward direction of rotation of cam gear  10  and into the cavity housing one or both push rods  12  as can be seen in either of FIGS. 3 and 4. Whereas the flow of the fuel can travel along either or both push rods  12 , the circumferential flow dictated by cam  10  directs the fuel flow largely into the path surrounding the rod for rocker arm  13  as indicated by the arrows. It is considered feasible to design the positioning of the rods  12  whereby fuel flow is effectively limited to flow along that push rod. In either event the guide way along the push rod or rods  12  is restricted to a size that will closely confine the rods and thereby minimize the pathway  14 . 
     Fuel flows upwardly into the area of the rocker arms  13 ,  13 ′ and into passage  15  that leads to valve  16 . The chamber  14 ″ whereat the rocker arms  13 ,  13 ′ reside are formed by cover  37  into a tight enclosure that is differentiated from prior enclosures indicated by dash lines  37   a.    
     From the above it will be noted that the flow path can be separated into three components. A first component  14  extends from the check valve  6  up to and through the timing gear  8  and cam gear  10 . A second component  14 ′ extends along push rod  12  and into the overhead chamber housing the rocker arms  13 ,  13 ′. Movement through the chamber housing the rocker arms is the third component  14 ″ which leads to the intake port  15  and intake valve  16  which is operated via the rocker arms  13 , spring  24  and valve stem  23 . 
     Other features to be noted include the spark plug  25  for igniting the fuel and the recoil starter  26  earlier discussed. Also shown in FIG. 1, is an exhaust valve  31 , its valve stem  32  and actuating spring  33  which urges a counter movement to that of rocker arm  13 ′. 
     The objective of limiting the revolutions per minute (RPMs) of the engine is enabled by restriction of fuel intake port  15  to a size less than the air intake port  1   a  of the carburetor. This size differentiation is preferably established by first determining the fuel-air flow necessary for optimum engine speed of the engine under load and sizing the intake port  15  to enable that RPM while avoiding excessive running or increased RPMs when the engine is not under load, e.g. to an rpm of [12000 min −1] or less. 
     Whereas the above description is directed to a specific embodiment considered a preferred embodiment herein, those skilled in the art will understand and appreciate that numerous variations can be made to the structures above described without departing from the scope of the invention. The invention is accordingly determined by the claims appended hereto which are intended to have their usual meaning within the trade.