Abstract:
A lubricating system for a two-stroke engine is provided in which oil is more reliably pumped into the two-stroke engine. The oil travels through passages that are integrally cast into the cylinder and/or crankcase. The oil may be injected directly into the crankcase chamber or intake passage. The oil pump may be a rotary pump mounted on the crankcase concentric to the crankshaft. It is also possible to not use an oil pump, and have the oil drawn into the engine by vacuum created in the crankcase.

Description:
[0001]    This patent application claims the benefit of and priority of U.S. Provisional Patent Application Ser. No. 61/326,662, entitled “Lubricating. System for a Two Stroke Engine” by Nagesh Mavinahally, David Kostka, and Bernardo Herzer, filed on Apr. 22, 2010. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    This invention relates to an internal combustion engine. In particular it pertains to a lubricating system for two stroke or two cycle engines. 
         [0004]    2. Description of the Related Art 
         [0005]    Conventional low cost two stroke engines, particularly the ones used in lawn and garden applications typically mix lubricating oil with the fuel to lubricate the internal parts of the engine. The disadvantage with pre-mixing is that the ratio of fuel to oil is very much dependent on the manufacturer, duty cycle of the engine, and model of the equipment. Having to use different ratios for different engines/models can confuse the user as to how much oil has to be mixed with the fuel. Secondly, if the ratio of fuel to oil is not correct the engine will either be overly lubricated or under lubricated, both of which are detrimental. A separate lubrication pump which eliminates the need for pre-mixing the oil with the fuel is known to be used in more expensive two-stroke engines, such as motorcycles and in some lawn and garden equipment, such as Mitsubishi&#39;s 23 cc trimmer engine. The disadvantage with current systems are that external fittings and hoses are used to inject oil into the intake manifold, which can leak oil at the hose or fitting junctions and add cost to the equipment because of additional parts. Also, in existing designs, the oil pump is driven by gears and the pump has a reciprocating plunger, which adds additional components and cost. 
       SUMMARY OF THE INVENTION 
       [0006]    A new and improved method of lubricating engines is described in this invention. In an embodiment, the improved lubricating engine is applied to a hand-held gaseous fueled two-stroke engines, and lawn and garden engines in general. 
         [0007]    The design described here eliminates the disadvantages of the current systems by not having external hoses, fewer parts, and therefore lowers the cost and increases the robustness of the lubrication system. In one of the embodiments, the oil passages from the oil tank to the oil pump and from pump to the engine (into intake passage or crankcase) are integrally cast into the cylinder and crankcase, thus eliminating the external oil pipes/hoses. In another embodiment, the oil pump is a rotary pump mounted on the crankcase concentric to the crankshaft. In yet another embodiment, there is no oil pump, the oil is drawn into the engine by vacuum created in the crankcase during the engine operating cycle. 
         [0008]    The improved two stroke engine is especially well suited for hand held, lawn and garden equipment such as trimmers, blowers, chainsaws, generator engines, and mopeds. 
         [0009]    The present invention reduces the number of parts and reduces the potential for oil leaks between the joints, particularly in the oil supply line, where the pressure is higher than atmospheric. The additional improvement to the oil pump design simplifies the construction and operation of the pump by driving the oil pump directly without the need for intermediate gears between the drive shaft (crankshaft) and the driven shaft (in the oil pump), or in the last embodiment, the elimination of the pump entirely. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    A more complete appreciation of the invention and many of the advantages thereof will be readily obtained as the same becomes better understood by reference to the detailed description when considered in connection with the accompanying drawings, wherein: 
           [0011]      FIG. 1  shows the front view of an embodiment of the engine with a front mounted oil pump. 
           [0012]      FIG. 2  shows the top sectional view of an embodiment of the engine&#39;s crankcase, crankshaft, and the oil pump. 
           [0013]      FIG. 3  shows the sectional side view of an embodiment of the engine having direct crankcase oil injection. 
           [0014]      FIG. 4  shows the sectional side view of an embodiment of the engine having oil injection into intake passage. 
           [0015]      FIG. 5  shows the sectional side of an embodiment of the engine having an oil pump concentrically driven off of the crankshaft. 
           [0016]      FIG. 6  shows a Gerotor pump as an example of a rotary pump that may be used on an engine. 
           [0017]      FIG. 7  shows the sectional side view of an embodiment of an engine having no oil pump but rather, a means for crankcase vacuum to draw the oil into the engine. 
           [0018]      FIG. 8  shows an embodiment of an engine with an oil reservoir integral with the plastic housing. 
           [0019]      FIG. 9  shows an embodiment of an engine with an oil reservoir integral with the flywheel housing. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]      FIG. 1  is an embodiment of the present invention.  FIG. 1  shows an oil injected two-stroke engine  200  having an oil tank  220 , and an oil pump  210  mounted on to the side of the crankcase  242  by screws. The pump  210  has a gear  212  and is driven by the crankshaft  208  having a gear  214 . The gears  212  and  214  can be of pinion and worm type or any other type. The two-stroke engine  200  can be a liquid or gaseous fueled engine. The engine  200  has a cylinder  204 , crankshaft  208 , and intake manifold  218 . The rest of the parts necessary for operation of the two-stroke engine, such as piston, connecting rod, muffler, fuel metering device, etc are very much similar to any two-stroke engine and can be constructed by anyone skilled in the art. The oil supply line  226  from the oil reservoir  220  feeds into the oil pump  210 . The oil pump  210  may have an oil return line, not shown here, to return excess oil back into the oil reservoir  220 . 
         [0021]      FIG. 2  shows the partial top sectional view of the oil injected engine from  FIG. 1 , having an oil pump  210  injecting oil directly into the crankcase chamber  234 . Also shown is the oil pump drive gear  214  which is located concentrically on the crankshaft  208 . The oil supply passage  226  from the oil tank to the oil pump, which is cast integrally into the crankcase  242 , is shown. 
         [0022]      FIG. 3  shows an embodiment of the sectional side views of the engine from  FIG. 1 , showing the oil passage  224  in the oil pump  210  and the oil passage  227  in the crankcase  242 . The oil passage  224   227  from the pump to the crankcase chamber  234  has a check valve  231 . The check valve  231  has a spring  232  and a valve  230 . The check valve is a one way valve allowing the oil to flow into the crankcase chamber  234 , while preventing the crankcase gases from entering the oil pump  210 . It also prevents the flow of oil into the crankcase when the engine is not operating. The spring loaded valve shown here is an example of a one way valve. It is understood there are many different types of check valves. Another example is a duck bill valve as used in many carburetors or fuel caps. It is shown in  FIGS. 2 and 3  that the length of the oil passage from the oil pump  210  to the crankcase chamber  234  is very short and the passage  227  in the crankcase is directly in line with the outlet passage  224  in the pump  210 . Also, it is shown that the oil supply line  226  from the oil reservoir  220  to the oil pump  210  is through a cast passage  226  in the crankcase  242 . However, depending on the location of the oil reservoir, a portion of the cast passage  226  can be in the cylinder  204 . 
         [0023]      FIG. 4  shows another embodiment of the invention where the oil is injected into the intake passage  230 . The construction of the engine  300  is similar to the engine of  FIG. 3 , however, the oil passage  222  from the pump to the intake passage  230  terminates at orifice  228  in the intake passage  230 . A portion of the cast passage  222  could be in the crankcase  242  and another portion be in the cylinder  204 . 
         [0024]      FIG. 5  shows an engine  400  which is another embodiment where the oil pump  330  has a wobble plate or screw  314  concentrically mounted on the crankshaft  208 . The oil pump  330  may have more than one wobble plate or teeth on the screw. Deeply cut grooves in place of wobble plates or screw teeth on the crankshaft  208  may also be used as a pump. The oil pump  330  has an oil inlet  326 , which can be a cast passage. A check valve  331  may be integrated into the passage  326  or into the inlet to the pump  329 . The outlet passage  324  from the oil pump  330  may feed the oil directly into the crankcase chamber  234  through passageway  229  and another check valve  332  at the outlet. 
         [0025]      FIG. 6  shows an end view of a gerotor type pump which is yet another pump type that may be used in the embodiment depicted in  FIG. 5 . 
         [0026]    All of the embodiments depicted in  FIGS. 1 through 6  use pumps of the positive displacement type, and any type of pump may be used and deemed to be in the spirit and scope of the invention. 
         [0027]      FIG. 7  shows another embodiment of an engine.  FIG. 7  shows a partial cutaway of a two stroke engine  500  which lubricates the engine without the use of a pump. The system operates by making use of the alternating pressure and vacuum pulses present in the crankcase chamber  234  caused by the reciprocating action of the piston when the engine is operating. Oil is fed from a reservoir mounted on or integral to the engine through passageway  326  until it contacts the crankshaft at orifice  502 . The orifice in the crankcase casting  502  is sized according to the oil requirements of the engine. Another passage in the crankshaft  501  connects to the orifice  502  and passageway  326  at preselected degrees of crankshaft rotation so that the flow of oil from the reservoir is connected to the crankcase chamber  234  when a vacuum is present in the crankcase chamber  234 . At the exit of passageway  501  is a check valve assembly  531  consisting of a check ball  530 , a spring  532  and a hollow retaining plug  533 . The purpose of the check valve is to close the passageway when the engine is not operating. When the engine is operating and the crankshaft  208  is spinning, centrifugal force will cause the ball to retract from the seat in the passageway and flow of oil into the engine will be unobstructed. It is to be noted that the orientation of the exit of the passageway  501  allows centrifugal force to aid in the flow of oil during operation of the engine. With this invention it is also possible to vary the oil delivery rate to the engine according to it&#39;s needs by the size of the orifice  502 , the timing and duration that the orifice  502  is making a connective path between passageways  326  and  501 , and by the distance of the exit of passageway  501  from the rotational centerline of the crankshaft  208  thus affecting the amount of centrifugal force acting to aid the flow. 
         [0028]    In another embodiment, as shown in  FIG. 8 , it may be preferable to have the oil reservoir  220  be an integral part of the plastic housing  410  of the small engine. The oil reservoir may also be integral part of the aluminum casting, such as crankcase or flywheel housing  412 , as shown in  FIG. 9 . The oil reservoir may also be in the front on the front crankcase. 
         [0029]    In  FIGS. 8 and 9 , it is preferable to have the shape of the reservoir  220  as a hemispherical doughnut such that the oil filter  252  is immersed in the oil at all attitudes. Secondly, the oil supply line  250  inside the oil reservoir  220  is flexible such that it is free to rotate and bend to keep the oil filter  252  in downward position at all attitudes of the engine, including but not limited to inverted attitude. That is, the flywheel housing  412  is in upward attitude. The shape of the oil reservoir  220  could also be spherical. 
         [0030]    Operation 
         [0031]    In a pre-mixed fuel, as in a conventional low cost two-stroke engine, the fuel-oil mixture and air is inducted into the crankcase chamber  234  and the oil present in the mixture lubricates the internal parts of the engine, mainly the bearings, the piston and the cylinder. The oil present in the mixture, is eventually burned with the fuel in the combustion chamber. The ratio of fuel to oil is dependent on the engine manufacturer and ranges anywhere from 20:1 to 50:1, which is quite a range and as such if the user mixes 50:1 oil in an engine that requires 20:1 ratio, the engine could easily starve for oil and lead to severe damage. On the other hand excessive oil in the fuel could build up carbon in the engine, particularly in combustion chamber and exhaust ports and lead to poor performance of the engines, and also require frequent removal of carbon build up in the engine. Also in engines equipped with an exhaust catalyst for the purpose of reducing harmful exhaust emissions, the catalyst can become damaged. 
         [0032]    In an embodiment of the present invention, the lubricating oil is stored in an oil reservoir and with the injection of oil directly into the crankcase chamber, the time taken for purging the system, particularly when the oil is refilled into a completely empty reservoir, is very short and helps lubricate the engine quickly and prevent any damage that could potentially occur to the engine when a longer oil passage is used. 
         [0033]    Therefore there are several significant advantages in using the new oil injected lubricating system in a two-stroke engine. The main advantages in oil injected two-stroke engines are: 1) The consumer does not have to worry about ratio of oil to fuel. 2) Any type of fuel can be used, including but not limited to LPG fuel. 3) The shape of the oil reservoir lets the user operate the engine in any attitude. 4) Internal cast passages eliminate potential leaks and extra parts. 5) Direct injection of oil into the crankcase purges the passage faster. 6) Integral oil tank eliminates extra parts (oil reservoir and fasteners). 7) Internal passages help warm the oil temperature and maintain the optimum viscosity of oil as it enters the crankcase chamber, at very cold ambient temperatures. 
         [0034]    The present invention has been described in an illustrative manner. It is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation. While there have been described herein, what are considered to be preferred and exemplary embodiments of the present invention, other modifications of the invention shall be apparent to those skilled in the art from the teachings herein and, it is, therefore, desired to be secured in the appended claims all such modifications as fall within the true spirit and scope of the invention.