Patent Publication Number: US-2011056462-A1

Title: Four cycle engine carburetors

Description:
RELATED APPLICATIONS 
     The present application claims the benefit of priority of U.S. provisional patent application No. 61/275,925, entitled “INTEGRALLY CAST BLOCK AND UPPER CRANKCASE FOR FOUR CYCLE ENGINES”, which filed Sep. 5, 2009, and the entirety of which is incorporated by reference herein for all purposes. 
    
    
     BACKGROUND 
     Conventional four-stroke engines have certain disadvantages as they are complicated and difficult to manufacture and assemble because there are numerous parts as compared to two-stroke engines. The additional parts, for example include, valve trains consisting of intake and exhaust valves, followers in the case of push tube trains for transmitting motion from cam lobes to rockers, just rockers in the case of overhead cam and belt or chain drives for overhead cam types. Also included are cam gear or pulley as the case may be, valve springs and retainers, camshafts, and cam covers in some cases. Also, the method of assembling the main components varies depending on how the cylinder, crankcase, crankcase cover, piston rod and crankshaft assemblies are made. Also, in the conventional hand held four-stroke engines, the oil is either recirculated in a wet type lubrication or pre-mixed with fuel for mist lubrication. 
     It is known in the prior art that four-stroke engines have cylinder blocks (with or without a separate cylinder head) and crankcases as the case may be with or without crankcase covers. For example, cylinders manufactured by MTD Southwest has a cylinder head integral with the cylinder and has a separate crankcase which has main bearings to support the crankshaft and a separate volute attached to the crankcase. The volute also has bosses for the ignition module. Another example is a Honda engine which has a cylinder block including a cylinder, where the upper half of the crankcase is integral with the cylinder block and a lower half of the crankcase which, when assembled together, support the main bearings. In this case, there is no separate crankcase cover and the belt drive for the overhead valve system is a wet type, where the upper and lower half of the crankcases together form a reservoir for the lubricating oil and the belt is completely enclosed. The enclosure is integral with the upper half of the crankcase. A similar design is used for a push tube type of valve train. Reference may be made to U.S. Pat. Nos. 6,539,904, 6,672,273, 6,427,672, 6,508,224, 6,705,263 (belt drive), and 6,021,766 (push tube). 
     Some Honda full crank engines have the crankcases split at an angle to the crankshaft as disclosed in U.S. Pat. Nos. 6,250,273 and 6,644,290. The front half of the crankcase is integral with the cylinder block and has bearing boss to support the front half of the crankshaft and the rear half of the crankcase has another bearing boss to support the outboard side of the crankshaft. The cam gear or the pulley for transmitting the motion to the overhead valves is in the outboard side. 
     Another example of engines with push tubes are disclosed in U.S. Pat. Nos. 6,213,079, 7,243,632, and 6,119,648. Some engines use gears to transmit rotation from crankshaft to the overhead camshaft, which is running at half the crankshaft speed as disclosed in U.S. Pat. No. 6,152,098. In most cases where the engine has a two piece block, the top or front half and lower or outboard half of the crankcase, the valve train is on the outboard side. 
     In the case of upper and lower halves of crankcases (or left and right halves as in Kioritz U.S. Pat. No. 6,119,648, the disadvantages are that the upper and lower halves are first assembled together and then the bearing bores are machined. They are taken apart for the final assembly. They are not interchangeable. A sealing gasket is used to seal the two halves. As such, the cost of such a system is higher than the one proposed in the design disclosed herein. 
     Prior art disclosed in U.S. Pat. No. 2,287,508 refers to a wet lubrication, where the oil is pumped into various sections of the engine and oil is recirculated. The lubricating pump is not described clearly, but it is driven by the camshaft. In the handheld trimmer sold by Mitsubishi model TL  26 , the oil pump is driven by the crankshaft on the outboard side, but it is two-stroke engine and 100% of the air-fuel mixture enters the crankcase chamber. 
     Thus, engine designers are constantly trying to design engines that have less parts, are simpler, and less expensive to manufacture. 
     Disadvantage with conventional four stroke engines for hand held application is that the oil in the crankcase may seep into the combustion chamber and cylinder head when the equipment is turned upside down. 
     In some hand held engines, such as trimmers and blowers, the location and size of the fuel tank is constrained by the size of the engine and the shape and size of the crankcase cover. The constraint is more when the fuel is propane gas. Propane gas are typically made out of metal and preferably of cylindrical shape. Therefore the height of the whole engine is significantly higher when propane tank is mounted either on the top or bottom of the engine. The embodiments disclosed here provide many advantages over the prior arts. 
     In some electronic fuel injection system, the fuel is gasoline or diesel. However, in small hand-held engines, electronic fuel injection system is complex as it requires a separate fuel pump, either integral with the throttle body or a separate system. In either case, the cost of the system becomes expensive because of the additional parts. 
     The embodiment described here does not require a pump, as the fuel is already at a pressure in the LPG fuel tank or even in a compressed natural gas tank. The advantage described in this embodiment is that the throttle body can be integral with the pressure regulator and a metering chamber if necessary. It is also possible to have a pressure regulator only either integral with the throttle body or a separate pressure regulator commonly used with LPG tanks. 
     BRIEF SUMMARY 
     Accordingly, embodiments of the present inventions provide a new and improved method of cylinder manufacturing and assembling the four-stroke engines, particularly, four stroke engines (applicable to two stroke engine cylinders as well). A single piece cylinder crankcase block for half and full crank allow for the manufacture and assembly of a lower cost engine. A simpler crankcase for dry sump lubrication can also be used as the dry sump engine/mist lubrication allows engines for any attitude operation when used in hand-held applications. 
     The low cost simpler four-stroke engine is especially suited for hand-held, lawn and garden equipments such as trimmers, blowers, chainsaws, cultivators, lawn mowers, compressor engines, and generator engines. 
     Further, the conventional four-stroke engines have camshaft and reduction gear for running the cam lobes at half the crankshaft speed to operate the intake and exhaust valves only once every two rotations of the crankshaft speed. However, in the mono-shaft engine, the cam lobe is either integral with the counter-weight or a separate piece mounted on the crankshaft in a chamber between the bearing bosses. In the invention disclosed here, the method manufacturing the cylinder block is simplified. 
     The present inventions reduces the number of parts, particularly, the half-crank engine and simplifies the method of assembling the full crank engine. Further, the engine design disclosed here is applicable to a full crank engine, where in both the outer and inner main bearing bosses are cast in as a single piece, but has a new assembly procedure. 
     Some four stroke engines have a breather system for discharging excessive blow-by gases through the camshaft, particularly, in the case of push tube type valve train system. The camshaft, in this case, is substantially parallel to the crankshaft and is mounted between the cylinder head and the crankshaft. The breather passage is in the camshaft and it can be a stationary shaft, where the cam gear and lobe are rotating on the shaft. Further, there can be a breather passage in the crankshaft connecting the cam chamber to the ambient (instead of breather passage in the crankshaft). 
     Further, the embodiment of the present invention provide a new and improved lubricating system where in first fraction of the charge which consists of first fraction of air and first fraction of pre-mixed fuel goes to the crankcase chamber to lubricate the internal parts of the engine and second fraction of the charge consisting of second fraction of air and second fraction of pre-mixed fuel straight to the combustion chamber during intake stroke. The first fraction of the charge also enters the combustion chamber during the intake stroke. In another embodiment the first fraction of the air free of any fuel where in lubricating oil is injected into the first fraction of air to lubricate the internal parts. However, the first fraction of air and oil mixture returns to the intake port and into the combustion chamber during the intake process. 
     In another embodiment, the first fraction of the charge enters the crankcase chamber through a passage in the crankshaft. The first fraction of the charge in one embodiment returns to the intake port through a passage in the cylinder head through a check valve. In another embodiment first fraction of the charge returns to the intake port through a passage external to the valve chamber through a check valve. Yet, in another embodiment the first fraction of the charge returns to the combustion chamber through a separate intake port in a divided intake port. And in this case, the first fraction of the charge mixes with the second fraction of the charge only at the intake port and in the combustion chamber. In another embodiment the first fraction of air or charge entering through a passage in the crankshaft may be timed by a rotary valve in place of a one way valve. The second fraction of the charge may be a propane gas—air mixture or any liquid fuel—air mixture. The fuel may be injected into the second fraction of air. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional side view illustration of an exemplary embodiment of a half-crank mono-block four-stroke engine with a push tube valve train where the cam chamber is plugged at its bottom. 
         FIG. 1   b  is a cross-sectional side view illustration of a mono-block having integrally cast cylinder block, crankcase, cylinder head, and outer and inner bearing bosses in the engine illustrated in  FIG. 1 . 
         FIG. 1   c  is a cross-sectional top view illustration of a mono-block having integrally cast cylinder block, crankcase, cylinder head, and outer and inner bearing bosses in the engine illustrated in  FIG. 1 . 
         FIG. 2  is a cross-sectional front view illustration of the engine illustrated in  FIG. 1 . 
         FIG. 3  is an enlarged cross-sectional front view illustration of a cam chamber with a breather passage in a camshaft of the engine illustrated in  FIG. 1 . 
         FIG. 4  is a cross-sectional side view illustration of a second exemplary embodiment of a half-crank mono-block four-stroke engine with a push tube valve train where the cam chamber is open at its bottom and the cam chamber and crankcase chamber are in communication through a cut-out passage. 
         FIG. 5  is a cross-sectional side view illustration of a third exemplary embodiment of a half-crank mono-block four-stroke engine with a carburetor for supplying pre-mixed lubrication and air-fuel mixture. 
         FIG. 5   b  is a cross-sectional side view illustration of a mono-block having integrally cast cylinder block, crankcase, cylinder head, outer and inner bearing bosses and carburetor port in the engine illustrated in  FIG. 5 . 
         FIG. 5   c  is a cross-sectional side view illustration of another exemplary embodiment of a half-crank mono-block four-stroke engine with a camshaft driven oil pump for injecting oil to lubricate parts. 
         FIG. 6  is a cross-sectional view illustration of another embodiment of the mono-block four stroke engine with a cam lobe on the crankshaft between inner and the outer bearing bosses. 
         FIG. 7  is a cross-sectional view illustration of another embodiment of the mono-block four stroke engine with a full crank and a single block to support the full crankshaft. 
         FIG. 8  is a cross-sectional view illustrating an outboard shaft being pressed into a counter-weight in the engine illustrated in  FIG. 7 . 
         FIG. 9  is a cross-sectional view illustrating main shaft being pressed into the counter-weight in the engine illustrated in  FIG. 7 . 
         FIG. 9   b  is a cross-sectional view illustration of the engine illustrated in  FIG. 9  with an oil chamber attached to a bottom of a crankcase. 
         FIG. 9   bb  is a cross-sectional side view illustration of a mono-block having integrally cast cylinder block, crankcase, cylinder head, and bearing boss in the engine illustrated in  FIG. 7 . 
         FIG. 9C  is a cross-sectional side view illustration of another embodiment of the mono-block four stroke engine with a half-crank and one half of the outboard bearing boss being integral with the cylinder block. 
         FIG. 10  is a cross-sectional side view illustration of another embodiment of the mono-block four stroke engine with a separate oil chamber with an oil slinger attached to the crankshaft. 
         FIG. 11  is a cross-sectional side view illustration of a front part of a cam chamber closed with separate cam cover. 
         FIG. 11   b  is a cross-sectional view illustration of a mono-block having separate cam cover shown in  FIG. 11 , but prior to machining left over material between cam and crank gear chambers. 
         FIG. 11   c  is an enlarged cross-sectional view illustration of a mono-block having separate cam cover shown in  FIG. 11 . 
         FIG. 12  is a cross-sectional side view illustration of another embodiment of the mono-block four stroke engine with a belt driven overhead cam and an oil chamber and a slinger. 
         FIG. 12   b  is a cross-sectional side view illustration of another embodiment of mono-block having oil pump between inner and the outer bearing. 
         FIG. 12   c  is a cross sectional side view illustration of a belt driven over head cam mono-block engine with belt drivel oil pump. 
         FIG. 13  is a cross-sectional side view illustration of a half-crank embodiment of the mono-block four stroke engine illustrated in  FIG. 9   b  with another embodiment of a wall separating the crankcase chamber and oil sump 
         FIG. 13   b  is a cross-sectional side view illustration of the engine illustrated in  FIG. 13  with cylinder head in down attitude. 
         FIG. 13   c  is a cross-sectional side view illustration of the engine illustrated in  FIG. 13  with cylinder head in sideways attitude. 
         FIG. 14  is a cross-sectional side view illustration of an exemplary embodiment of a half-crank mono-block four-stroke engine with a L-head and a valve train. 
         FIG. 14   b  is a cross-sectional side view illustration of a mono-block having integrally cast cylinder block, crankcase, cylinder head, outer and inner bearing bosses in the engine illustrated in  FIG. 14 . 
         FIG. 14   c  is a cross-sectional front view illustration of another embodiment of a mono-block having integrally cast cylinder block, crankcase, cylinder head, outer and inner bearing bosses, valve assembly on the side of the cylinder block in the engine illustrated in  FIG. 14 , and an intake system with one way valve in the intake passage. 
         FIG. 14   d  is a cross-sectional top view illustration of another embodiment of an engine with a divided intake system with one way valve in one intake passage and oil injection into said passage. 
         FIG. 14   e  is an enlarged cross-sectional view illustration of engine illustrated in  FIG. 14   d  showing partition on intake system at the intake. 
         FIG. 14   f  is a cross-sectional side view illustration of an exemplary embodiment of a four-stroke engine with a L-head and a valve train with LPG fuel tank at the bottom. 
         FIG. 14   g  is a cross-sectional side view illustration of an exemplary embodiment of a half-crank mono-block four-stroke engine with a L-head and a valve train with LPG fuel tank on the top. 
         FIG. 15  is a front cross sectional view of an embodiment with divided intake port in a dual intake system. 
         FIG. 16  is a front cross sectional view of an embodiment with divided intake port in a dual intake system showing flow of first fraction of charge and passage external to valve chamber. 
         FIG. 17  is a front cross sectional view of an embodiment with divided intake port in a dual intake system showing flow of second fraction of charge. 
         FIG. 18  is a cross sectional view of another embodiment with intake system showing first fraction passage through crankshaft and return passage through single intake port and showing the locations of a propane fuel tank and an oil tank. 
         FIG. 18   b  shows enlarged sectional view of  FIG. 18 . 
         FIG. 18   c  shows enlarged sectional view of  FIG. 18  with cast fuel line integral with the mono-block. 
         FIG. 19  is a cross sectional view of another embodiment with intake system showing first fraction passage through cam shaft and return passage through single intake port and showing the locations of a propane fuel tank and an oil tank. 
         FIG. 19   b  is a front view of the cam gear on a camshaft with the first fraction passage in the center of the shaft with a timing slot. 
         FIG. 19   c  is a cross sectional view of another embodiment with intake system showing first fraction passage through crankshaft and return passage through an oil separation chamber integral with the air filter system and oil return to oil tank and has a propane fuel tank tucked on to the crankcase cover. 
         FIG. 19   cc  shows enlarged view of the location of the LPG fuel tank and the shape of the crankcase cover shown in  FIG. 19   c.    
         FIG. 19   d  shows enlarged view of the embodiment shown in  FIG. 19   c.    
         FIG. 19   e  is a cross sectional view of another embodiment with intake system showing first fraction passage through crankshaft and return passage through an oil separation chamber between the valve chamber and the intake passage and oil return to oil tank. 
         FIG. 19   f  shows enlarged view of the embodiment shown in  FIG. 19   e.    
         FIG. 20   a  is a cross sectional front view of an embodiment of a fuel mixer with two sliding valves on a common sliding drum. 
         FIG. 20   b  is a cross sectional side view of  FIG. 20   a.    
         FIG. 20   c  is a view of  FIG. 20   b  with sliding drum partially lifted up. 
         FIG. 21  is a cross sectional front view of an embodiment of an electronic LPG fuel injected throttle body with butterfly valve, fuel metering chamber, and fuel pressure regulator. 
         FIG. 22  is side view of the  FIG. 21   
         FIG. 23  is a cross sectional front view of an embodiment of electronic LPG fuel injected throttle body with slide valve with fuel pressure regulator. 
         FIG. 24  is a cross sectional front view of another embodiment of throttle body with electronic LPG fuel injection system, butterfly valve, and fuel pressure regulator only. 
         FIG. 25  is a cross sectional front view of an embodiment of an electronic LPG fuel injected throttle body with dual intake butterfly valves, fuel metering chamber, and fuel pressure regulator. 
         FIG. 26  is side view of  FIG. 25 . 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1 ,  1   b , and  1   c  illustrate an exemplary embodiment of a half-crank mono-block four-stroke engine  1  with a push tube valve train  2  and a cam chamber  3  plugged at its bottom  4 . The engine  1  includes a one half-crank mono-block  10  having a cylinder block  20  surrounding a cylinder bore  12 , a crankcase  30 , and cylinder head  40  all integral as a mono-block as further illustrated in  FIG. 1   b . The crankcase  30  includes integrally cast outer and inner bearing bosses  21   a  and  21   b  configured to support a half crankshaft  22 . The inner bearing boss  21   b  supports an inner bearing  41  closest to a counter-weight  32  on the crankshaft  22 . An outer bearing  28  is supported by the outer bearing boss  21   a  on a flywheel side  29  of an outer frame  25  of the crankcase  30 . The outer frame  25  is spaced apart from the cylinder block  20 . A piston assembly  756  disposed within the cylinder bore  12  includes a generally cylindrical piston  758  and a connecting rod  734  connected to the piston  758  by a piston pin  760 . 
     In a full crank engine, an outer oil seal may replace the outer bearing. The outer frame  25  may be designed either for a reverse or forward air flow. Reverse air flow is where the frame has openings around the outer circumference for flow of air from behind the engine and forward air flow has openings in the front housing for flow of air. The combination of forward and reverse air flow has openings in the frame  25  as well as in the front housing for flow of air. A longitudinally extending open valve train chamber  88 , formed in the mono-block  10  between an outboard wall  89  and the cylinder block  20 , a lower opening  88   a  at a lower end  87  of the valve train chamber  88  that may be closed with a cover  89   a , if necessary, or may be open to a crankcase chamber  48 . A top end  86  of the valve train chamber  88  located near the cylinder head  40  is open to allow a valve train  60  to transmit motion from crankshaft  22  to an intake valve  98  and to an exhaust valve (not illustrated) which is behind the intake valve  98 . 
     The intake valve  98  and the exhaust valve are in a valve chamber  106 . The valve train  60  includes cam gear  182 , cam lobe  108 , followers  288 , and push tubes  300  (also referred to as push rods). The valve train chamber  88  houses crank gear  122  and cam gear  182  with the followers  288 . The valve train chamber  88  is formed, such as by casting, so that there is at least one slot  34  between the outer bearing boss  21   a  and the inner bearing boss  21   b  at the lower end of the valve train chamber  88 . The slot  34  illustrated in  FIGS. 1 and 1   b  is the lower end  87  of the valve train chamber  88 . 
     The valve train chamber  88  is cored out using a slide in casting tool. The push tubes  300  may be disposed in push tube passages  88   e . It may also be possible to core out part of push tube passages  88   e  and/or a belt drive passage  1288   e  illustrated in  FIG. 12 , together with the entire valve train chamber  88 . Thus, the mono-block  10  allows coring out of the valve train chamber  88  or belt drive passage  1288   e  from the crankcase chamber  48  to form a single piece block without any additional cover piece or machining process. 
     The top end  86  of the valve train chamber  88  may be open to the overhead valve chamber  106  through the cast in push tube passage (or passages)  88   e  or may be just open for a dry type belt drive as illustrated in  FIG. 12  or a passage for the wet type belt drive to drive the overhead camshaft through a cam gear or a pulley as the case may be. 
     An embodiment of the engine  1  illustrated in  FIGS. 4 and 5  includes a single continuous valve train chamber  88  extending between the crankcase chamber  48  and the overhead valve chamber  106  (or cam chamber if belt driven) in  FIGS. 4 and 5 . The valve train chamber  88  is a single continuous passage from the crankcase chamber  48  to the valve chamber  106  without any other additional piece attached as a cover to provide an enclosed passage and no separate push tube passages  88   e .  FIG. 5  illustrates how the air-fuel mixture may be supplied into the crankcase chamber  548  through a carburetor  500 . The functioning of the piston ported intake system is similar to a commonly used two stroke engine. However, the lube oil mixed charge enters a crankcase chamber  548  and flows into a combustion chamber  51  through an intake valve  598 . The intake system may be similar to any standard intake system, such as reed valve or rotary valve system. The mixture enters the valve train chamber  88  through the opening  88   a  from the crankcase chamber  548  and into valve chamber  106  and into the combustion chamber  51  when the intake valve  98  is opened. Also, when a separate oil pump  1505  as shown in  FIG. 5C  is used, the fuel may not be pre-mixed with oil.  FIG. 5C  also illustrates where the pump  1505  is driven directly by the camshaft  82  either at same speed as camshaft or at a different speed through gears  1511 . Prior art disclosed in 2,287,508 refers to a wet lubrication, where the oil is pumped into various sections of the engine and oil is re-circulated. However, in the embodiment disclosed here, the oil is injected into the intake system and mixed with the charge or air as the case may be. The oil pump  1505  has an inlet  1507  and an outlet  1509  for oil. The outlet feeds into the intake passage. The pump system may have an oil sensor  1513  to turn on an indicator when there is no oil in the reservoir or pump fails to pump oil. 
     Illustrated in  FIG. 6  is an alternative embodiment of the engine  600  that is similar in construction to the engine  1  in FIG.  1 , except the engine  600  has the cam lobes  608  with channels  609  similar to U.S. Pat. No. 7,000,581. The construction and functionality of the engine  600  is similar to the prior art. However,  FIG. 6  shows where the cam lobe  608  is between the inner and the outer bearing bosses  21   b ,  21   a  respectively. As shown in  FIG. 6 , the engine  600  has push tube type valve train. A valve train chamber  688  is similar to valve train chamber  88  in engine  1  where the lower end of the chamber  88  may be open to the crankcase chamber  48  as shown in  FIG. 5  or may be closed as shown in  FIG. 1 . 
       FIG. 3  illustrates a cam assembly  182   a  including a camshaft and a cam gear  182 . A breather system includes a breather passage  910  through the camshaft  82  that connects a breather tube  911  to the ambient to a hole  913  to the inside of the engine to relive the crankcase chamber pressure built-up due to blow-by gases. The breather passage  910  and its function are similar to the expired U.S. Pat. No. 6,502,565. 
     Lubrication of the push tube valve train  2  is achieved by providing an oil passage  808  through the center of the crankshaft that runs axially from the crankcase chamber  48  and then radially to the valve train chamber  88 . Unlike breather passages disclosed in U.S. Pat. Nos. 6,039,020 and 6,047,678, the purpose is to supply a small amount of oil from the crankcase chamber into the valve train chamber  88 , which in turn lubricates the valve train  2 . (claim this feature where oil is supplied through central passage in the crankshaft) The lower opening  88   a  is closed and there may be an oil seal in the inner bearing boss  21   b  (or the bearing  41  could be a sealed bearing that prevents direct flow of oil from crankcase chamber into the valve train chamber  88 . 
     The small amount of oil that gets on the cam gears  182  and the crank gear  122  is splashed to help lubricate the intake valves  98  and rockers  102   b . Oil condensed in the valve train chamber  88  is returned to the crankcase chamber  48  through a check valve  999  on the cover  89   a , which opens when the crankcase chamber pressure drops as the piston assembly  756  moves upward. Other types of valves may be used. The opening  88   a  may be used for many usages such as described above to have a check valve for return of oil from the valve train chamber  88  to crankcase chamber  48 , or can be used to have a oil pump, as shown in  FIG. 12   b  or for a rotary valve between the valve train chamber  88  and crankcase chamber  48  or a rotary check valve for supply and or return of lubricating oil when a separate reservoir for oil is used either for dry type or mist lubrication shown in  FIG. 12 . Oil that escapes through the breather passage is collected in a separation chamber (not shown) and then returned to the crankcase chamber through a check valve. (This is a prior art) The oil passage through the crankshaft prevents oil from flowing into the valve train chamber  88  and subsequently into the breather or valve chamber  106  when the engine is stored in almost any attitude because the inlet  808   a  is always above the oil level. The oil pump  1505  shown in  FIG. 12   b  is driven by the gear  1502  on the crankshaft  1222 . However, it is possible for the gear to be an integral part of the crank gear  1286  ( 122  in other FIGS). The gear could just be a swash plate to drive the gear on the pump  1505 . Pump may be driven off of the belt or cam gear  12821284 . 
     A full crank engine  700 , illustrated in  FIGS. 7-9 , is similar in construction to engine  1 , illustrated in  FIGS. 1-3 . The full crank engine  700  includes an outboard bearing boss  731  to support a full crankshaft  722  which includes inboard and outboard crankshaft halves  722   a  and  722   b . In most conventional full crank engines, the crankcase is split into two crankcase halves either vertically in line with the central line of the cylinder bore  12  or at an angle as in U.S. Pat. Nos. 6,439,215 and 6,250,273 or horizontally along the axis of the crankshaft as in U.S. Pat. Nos. 6,332,440, 6,021,766, and 5,947,075. The disadvantage is that the two crankcase halves are first assembled together first in order to machine the bearing bore and then detached for final assembly. Typically, the two crankcase halves stay as pairs. The embodiment of the engine  700  shown in  FIGS. 7-9  has a single cylinder block  20  to support the full crankshaft  722 . First, second, and third bearing bores  723   a ,  723   b , and  723   c  may be machined at the same time concentric to each other as well as perpendicular to the cylinder bore  12  and with a better quality control. The alignment of the front and rear bearings are also better. Alternatively, an upper half  733   b  of the outboard bearing boss  733   a  may be integral with the cylinder block  20  while a lower half  733   c  of the outboard bearing boss  733   a  may be part of the crankcase cover  744  as illustrated in  FIG. 9   c.    
     Assembly of the inboard and outboard crankshaft halves  722   a ,  722   b  will be different than the conventional methods. A method of assembling the camshaft  82 , cam gear  182 , and the followers  288 , as illustrated in  FIGS. 1 and 3 , includes pressing the camshaft  82  into the cylinder block  20  through a hole  83 . The camshaft  82  may be free to rotate in the hole  83  in the block  20  when the camshaft is pressed into the cam gear  182  and the lobe  108 . Alternatively, the camshaft  82  may have an interference fit within the hole  83  in the block  20  while the cam gear  182  and the lobe  108  are rotating on the camshaft  82 . 
     A method of assembling the full crank engine  700  with integral bearing bosses includes assembling first and second counter-weights  732   a ,  732   b , installing crank pin  736  through the first and second counter-weights  732   a ,  732   b , connecting rod  734 , as illustrated in  FIG. 9 . The second counter-weight  732   b  may be just a yoke for an outboard starter in case of a simulated full crank. The counter-weight assembly procedure may also include installing the piston pin  760  through the piston assembly  756  and the connecting rod  734  of the piston assembly  756 . However, it is also possible to assemble the piston assembly  756  separately to the connecting rod  734  after the crankshaft has been installed. It is done by inserting the piston pin  760  through a hole placed in the cylinder block  20  as done in the case of some Briggs and Stratton engines. Alternatively, as illustrated in  FIG. 11 , the hole  760   a  in the cylinder block  20  for inserting the piston pin  760  may be located in the valve train chamber  88 . 
     Referring to  FIG. 7 , step  1  of a method for assembling the full crankshaft  722  includes, with an inner bearing  741  already pressed into the bearing boss  721   b , inserting the piston assembly  756  and the connecting rod  734  into the cylinder bore  12 . Then aligning the first and second counter-weights  732   a  and  732   b  correctly with respect to the bearing bores  723   a ,  723   b , and  723   c . Referring to  FIG. 8 , step  2  of the method includes pressing the outboard crankshaft halves  722   b  into the counter-weight  732   b  while the counter-weight  732   b  is supported by the tools  2010   a  and  2010   b . The tool  2010   a  passes loosely through the inner bearing  741 . Referring to  FIG. 9 , step  3  of the method includes supporting the outboard crankshaft halves  722   b  with a special tool  2020   a  that passes around the outboard crankshaft halves  722   b  and through the bearing bore  723   c  in the outboard bearing boss  733   a , supporting the first counter-weight  732   a  with a special tools  2020   b , and pressing the inboard crankshaft halves  722   a  into the counter weight  32   a . Referring to  FIG. 9   b , step  4  of the method includes pressing first and third oil seals  928   a ,  928   b  into the first and third bearing bores  723   a  and  723   c.    
     It should be noted that the oil seal or oil seals may be used in conjunction with the bearings at any bearing bosses  21   a ,  21   b  and  731  as necessary depending on lubrication systems and breather systems. Step  5 . Insert the outboard bearing  731  (or bearings for outboard starter) and oil seals  728   a . The outboard bearing may either slide fit on the outboard crankshaft halves  722   b  and may be secured in place with the cir-clip. 
     Referring to  FIGS. 9 and 9   b , installation of the outboard crankshaft halves  722   b  in case of a half-crank with outboard starter will be a lot more easy since the yoke is not rigidly pressed onto the crank pin  736 . In this case, the outboard bearing boss may be just top half integral with the cylinder block, while the lower half is part of the crankcase cover  44   b  as shown in  FIG. 9C . However, the outer edge of the boss  735 , shown in  FIG. 9C  is still integral with the cylinder block. This helps to improve sealing of crankcase cover  744  with the block  10 . 
       FIG. 9   b  shows the assembled engine with a separate oil chamber  948   b  attached to the bottom of the crankcase cover  944   a  with a slot  964  for the slinger  934   b  on the connecting rod  934  to splash the oil. It may be noticed, that when the engine is turned upside down the oil does not poor down into the crankcase chamber  948   a  because of a separation wall  966 . However, the bleed passage  952  allows a small amount of oil to drip onto the first and second counter-weights  932   a ,  932   b  so the piston assembly  756  gets lubricated and also some oil goes into the valve train chamber  88  for lubricating the valve train. It is possible to time the opening of the bleed passage  952  with the counter-weight  932   a  so that the bleed passage  952  is open when the piston assembly  756  moves upward causing negative pressure in crankcase chamber  948   a  and close it when the piston is in downward motion causing positive pressure in the crankcase chamber  948   a . The oil condensed in the valve train chamber  88  and valve chamber  106  is returned to the crankcase chamber  948   a  or possibly directly back into the separate oil chamber  948   b  through a check valve  999  shown in  FIG. 9   b . It is also possible to drain the oil from the valve chamber  106  into the oil chamber through an additional return passage and check valve, particularly, when the engine is run upside down. 
     In another embodiment of the engine illustrated in  FIG. 10 , the oil chamber  1048   b  may be a separate chamber similar to the dry sump lubrication system described in Honda&#39;s U.S. Pat. Nos. 5,947,075 and 6,021,766, etc. The disadvantage with Honda&#39;s design is that the crankcase consists of two separate halves that have to be machined first and the two pair have to stay together during production and is not a cost effective design. Secondly, as seen in those patents, the engine is a full crank engine. As illustrated in  FIG. 10 , the oil chamber  1048   a  can be molded such that the entire chamber is an integral part of the cylinder block  1000  as shown in  FIG. 10 . The casting, machining and assembly are much simpler. The bottom of the oil chamber is easily plugged with a cover  1089   a.    
       FIGS. 11 ,  11   b , and  11   c  illustrate the second bearing bore  723   b  as being bored all the way till to the inside of the outer bearing (or oil seal). When the wall thickness of the outer bearing boss is less than the OD of the inner bearing bore a pocket will be formed above a valve train chamber  1088 . In this case, the lower end of the valve train chamber  1088  is closed and there is no need for any kind of plug. However, the front face  1189  of the valve train chamber  1088  has to be cored out from the front for inserting the cam gear and followers. This calls for a separate cam cover  1190  as illustrated in  FIG. 11C . 
       FIGS. 12 and 12   b  illustrate another embodiment of the engine  1200  having a wet belt drive, similar to the Honda described in the prior art. An overhead cam pulley  1282  running at half the engine speed is driven by a timing belt  1284  and a crank pulley  1286  on the crankshaft  1222 . The crank pulley  1286  may be either in a separate chamber  1288  adjacent to the oil chamber  1248   b  with an oil seal between the two chambers or the valve train and oil chambers  1288  and  1248   b  may be commonly cored out from the bottom. The slingers  1234   b  is attached to the crankshaft  1222 . There may be more than one pair of slingers. A belt drive passage  1288   e  is cored out from bottom as well as top of the cylinder block  1210 . The follower  102   b  and rocker  102   a  shown in  FIG. 12  are only for representation of the valve train. It is well known how to operate the intake valve  98  and exhaust valve with the overhead cam  1208 .  FIG. 12   b  illustrates a lubricating oil pump  1505  attached to the cylinder block  30  and is driven by the crankshaft  1222  through a worm gear  1502  and a gear  1503 . The pump may also be driven off the crank gear  122  through reduction gear in the oil pump. The pump  1505  has an inlet  1507  to receive oil from an oil reservoir and an outlet  1509  to deliver oil to the intake passage  126   a  as shown in  FIG. 14   d  or into the crankcase chamber  48 . 
       FIG. 12   c  illustrates an oil pump  1505  driven by the belt  1284  driving the overhead cam gear  1282 . IN the embodiment disclosed here, the oil pump  1505  mounted on the mono-block  1210  is driven by the toothed belt  1284  at a desired gear ratio. As described earlier the oil pump has an inlet  1507  from a oil tank and an outlet  1509  to mix with the first fraction of air in the passage with oil or directly injected into a passage/hole at the center of the camshaft  82  which communicates with the cam chamber  48  through chamber  88 . 
     FIGS.  13 , 13   b , and  13   c  illustrate an alternative embodiment of the half-crank engine illustrated in  FIG. 9   b , which prevents oil from getting into the cylinder head  40  when engine  1300  is upside down or sideways. A slinger  1318  is inside a tube  1320  protruding into the oil sump  1348  which is disposed between a crankcase cover  1312  and a wall  1314  ( 1344 ?) separating the crankcase chamber  48  and the oil sump  1348 . As the connecting rod slinger  1318  moves, the oil in the oil sump is splashed into the inside of the crankcase chamber  48  so that the oil hits the cylinder wall  12   a , and moving parts such that they are all lubricated. The oil droplets (or mist) is also carried to lubricate the valve train, consisting of cam  1208 , cam gear  1282 , followers  102   a  (rockers, etc.), The oil mist or droplets may be carried into the cam chamber  1288  and the valve chamber  106  through a passage  808   a  in the crankshaft or through bearing passages. An oil level  1334  is illustrated in  FIG. 13  when the engine  1300  is in an upright position. When the engine is turned sideways or upside down, as illustrated in  FIG. 13   b , the oil in the oil sump does not spill into the cylinder bore or crankcase chamber, instead oil may drip into the crankcase chamber  48  through oil passage(s)  1328  in a standoff tube  1324 . There may be more than one such standoff tube, such that the engine is lubricated in all attitudes. Elements  1352  are serrations on the slinger or scoops like (or any similar) to help splash oil into the crankcase chamber  48 . The oil supply passages to the cylinder head and returns may be located in the crankcase chamber such that excessive oil does not get to the head. 
       FIGS. 14 ,  14   b ,  14   c ,  14   d , and  14   e  illustrate another embodiment of the engine  1400  having an integral L head mono-block including an integral (one piece) cylinder block  20  and crankcase  30 .  FIG. 14   f  illustrate engine similar to  FIG. 14  with a LPG tank  2007  at the bottom and  FIG. 14   g  is similar to engine  14 , but the engine is upside down with LPG Tank  2007  at the top. A cylinder bore  12  is disposed within the cylinder block  20  and a valve train chamber  88  is disposed between the cylinder block  20  and an outboard wall  89  integrally cast with the cylinder block  20  as part of the mono-block  10 . The integral casting of the mono-block  10  is illustrated in  FIG. 14   b . A valve chamber  106  ( 107 ), the valve train chamber  88 , and the crankcase chamber  48  are all interconnected through passages and disposed between the cylinder block  20  and at the bottom of the chamber  88  and the passage at the top of the combustion chamber  51 . The chamber  88  and valve chamber  106  ( 107 ) are substantially in line with each other. And valve chamber  106  ( 107 ) is substantially inline with the axis of the cylinder. 
     The valve chamber  106  ( 107 ) has a valve assembly  120  (for intake) (and  120   b  for exhaust valve) that includes a valve seat  4002  and a valve guide  4024  (for intake and  4026  for exhaust), valve spring  1408 , and valve retainer  1409  and is tightly attached to the mono-block  10  in the passage  107 ? between the cam chamber  88  and the combustion chamber  51 , to form a leak proof combustion chamber  51 . The valve assembly may be a modular piece where valve seat  4002 , valve guide  4024 , valve spring  1408 , and valve retainer  1409  are all assembled separately prior to attaching to the mono-block  10 . The valve assembly  120  has an opening  124  to the ambient through an inlet port  126  connecting a carburetor  500  fuel-air mixer). The valve assembly  120  can have an opening  122  connecting the carburetor  500  to the crankcase chamber  48  where the air-fuel mixture is mixed with lubricant oil. A passage  502  connecting the carburetor  500  and the crankcase chamber  48  may have a one-way valve  128  (shown in  FIG. 14   c ) to prevent the charge from flowing back into the ambient when the piston is moving downward. 
       FIGS. 14   f  and  14   g  show where the crankcase cover  44  is formed to match the curvature R of the fuel tank  2007  at fractional section  44   b  of the crankcase cover  44 . The radius of curvature R is such that it provides enough clearance for the connecting rod  734  and crank pin  738  to freely rotate without interference. Secondly the center line  2007   a  of the fuel tank  2007  is below the axis  2927  of the crankshaft  22  and the center line  2007   a  is off set from the axis  12   a  of the cylinder  12  when the fuel tank  2007  is located at the bottom of the engine as shown in  FIG. 14   f . When the attitude of the cylinder block  20  is such that crankcase chamber  48  is above the center line  2927  of the crankshaft  22  the fuel tank  2007  is located at the top of the crankcase cover  44 . The LPG tank may also be located vertically in line with the axis  12   a  of the cylinder  12 . The advantage is a smaller package. Also, the oil tank  3008  containing oil  3010  to lubricate the engine may be attached to the fuel tank and above the center line  2007   a  of the fuel tank. The fuel tank  2007  is inside a frame  2907  which may be attached to the crankcase cover  44  or cylinder block  20  OR element  30 . When the fuel tank  2007  is at the bottom, the frame  2907  has a leg  2907   a  for the engine block  20  to rest on the floor. However, when the fuel tank  2007  is above the center line, the oil chamber  3010  is used to supply oil to the oil pump for injecting oil into the intake system. 
     By definition charge means mixture of fuel and air and pre-mixed fuel or charge means fuel pre-mixed with oil. First fraction of charge means first fraction of the air and first fraction of fuel (could be pre-mixed fuel) and second fraction of charge means second fraction of air mixed with second fraction of fuel (could be pre-mixed). The fuel may be any liquid or gaseous fuel, including propane. 
     In an another embodiment shown in  FIGS. 14   c ,  14   d , and  14   e  the intake valve assembly  120  may have dual inlet passages;  126   b  that connects carburetor  500  directly to the cylinder  12  (combustion chamber  51 ) during the intake process, and the passage  126   a  that connects carburetor to the crankcase chamber  48 . A partition wall  4008  runs all the way across the intake passage separating the flow all the way from the carburetor  500  to the valve  98  and across to minimize short circuit of the two mixtures until just before they enter the cylinder  12 . A fraction of the charge 25% to 75% goes into the crankcase chamber  48  through the passage  126   a  (or may have separate passage, not shown) when the piston is moving upward during compression and exhaust strokes when the piston is moving toward the combustion chamber  51 . The passage  126   b  is connected from the carburetor  500  to the cylinder  12  when the intake valve  98  is open during intake stroke. The fraction of the pre-mixed charge going into the crankcase chamber  48  is to lubricate the engine parts (internal parts), particularly the valve train and parts in the crankcase chamber  48 . It is also possible to inject lubricating oil separately into the passage  126   a  at  101  when the fuel is not pre-mixed with oil. In which case rich charge free of oil goes into the combustion chamber  51  and oil mixed charge (or oil mixed with just air) goes into the crankcase chamber  48 . Amount of charge is controlled by the carburetor valve  584  and may have separate valves  584   a  and  584   b  to regulate the mass flow into passages  126   a  and  126   b  respectively. When oil is injected into the passage  126   a , only air may be inducted through the passage  126   a . Essentially the divided intake passage  126  may have either only air going into crankcase chamber  48  through passage  126   a  when oil is injected into the air stream to lubricate the parts; or may have air-fuel mixture when oil is pre-mixed with the fuel, OR may have lean air-fuel mixture free of oil when oil is injected into the lean mixture in passage  126   a , while rich mixture flows through the passage  126   b  OR the mixture may be of uniform air-fuel ratio going through both the passages  126   a  and  126   b . Also, when only air passes through passage  126   a , fuel supplied through  126   b  may be a propane fuel or any gaseous fuel, such as compressed natural gas, bio gas, etc. The advantage of injecting oil into air inducted into crankcase chamber is that the fuel either liquid form as in the case of gasoline or gaseous as in the case of propane can flow directly into the combustion chamber during the intake process, while oil injected into air lubricates the valve train (cam gear, crank gear, followers, valves, cam lobe, etc) and bearings in the crankcase chamber  48 . Another advantage is that the engine can be operated in many attitudes as there is no oil in the crankcase chamber that would flow into the cylinder when engine is operated upside down. The dual intake system where passage  126  is divided into two separate passages  126   a  and  126   b  may also be applied to overhead valve chamber  106  shown in  FIG. 1 , but with a passage  126   a  connecting the valve chamber  106  and only air entering the valve chamber  106  and crank chamber  48 , with oil injected for lubricating the valve train and parts in the crankcase chamber  48 . 
     During the compression stroke when the piston assembly  756  travels upward, the intake valve  98  is closed and the crankcase chamber  48  experiences negative pressure and the charge (oil mixed charge) is inducted into the crankcase chamber  48  from the carburetor  500  through the passage  126   a , the port  122 , the chamber  88 . The one-way valve  128  opens due to differential pressure cross the one-way valve (typically a reed valve is used). 
     When the piston moves downward during power stroke and expansion stroke, the crankcase pressure is built up. 
     During the intake stroke, the intake valve  98  opens and the charge from the crankcase chamber  48  enters the combustion chamber  51 . At the same time, the rich charge enters the combustion chamber  51  directly from the carburetor  500  through the passage  126   b.    
     The concept of dual passage (lean charge going into crankcase chamber  48  and rich charge going directly into combustion chamber is applicable to all Four-stroke engines. 
     The oil pump may be driven by the crankshaft  22  as shown in  FIG. 12   b  or by the camshaft  82  as shown in  FIG. 5   b . The pump may also be driven by the crankshaft  722   b , shown in  FIG. 9   b  (and  FIG. 9 ) where the pump is mounted outboard. 
     Fuel used in the oil injected engine may be propane gas commonly known as LPG (liquefied petroleum gas or compressed gaseous fuel. 
     The U.S. Pat. No. 6,199,532 discloses engine where intake passage is not divided into separate passages and the fuel is pre-mixed with oil and the valve chamber is substantially spaced above the combustion chamber. 
     In another embodiment shown in  FIGS. 15 ,  16 ,  17 , and  18  the engines  3000 ,  4000 , and  2000  have the valves above the combustion chamber  50 , commonly known as over head valves (OHV). In  FIGS. 15 ,  16 , and  17  the intake passages from the carburetor  500  is divided into two separate passages  126   a  and  126   b . The passage  126   a  may carry first fraction of charge  810  consisting of first fraction of air and pre-mixed fuel into the crankcase chamber  48  through a port  808  in the block. The first fraction of air may be free of any pre-mixed fuel, in which case oil is injected into the first fraction of air by an injector  101 , which may be just an orifice connected to either a separate pump as shown in  FIGS. 5   c  and  12   b  or an oil reservoir. The first fraction of air carrying the oil enters the crankcase chamber to lubricate the internal parts and return to the combustion chamber during intake process as explained above for  FIG. 14 . The second fraction of the charge  812  which consists of second fraction of air and either fuel only or pre-mixed fuel as the case may be enters the combustion chamber  51  through intake passage  126   b . A partition wall  4008  runs all the way across the intake passage separating the flow all the way from the carburetor  500  to the valve  98  and across to minimize short circuit of the two mixtures until just before they enter the cylinder  12 . The first fraction of the charge (or air free of fuel) 25% to 75% goes into the crankcase chamber  48  through the passage  126   a  as shown in  FIGS. 15 ,  16 , and  17  when the piston is moving upward during compression and exhaust strokes when the piston is moving toward the combustion chamber  51 . The passage  126   b  is connected from the carburetor  500  to the cylinder  12  when the intake valve  98  is open during intake stroke. The fraction of the charge going into the crankcase chamber  48  is to lubricate the engine parts, particularly the valve train and parts in the crankcase chamber  48 . It is also possible to inject lubricating oil separately into the passage  126   a  at  101  when the fuel is not pre-mixed with oil. In which case second fraction of charge free of oil goes into the combustion chamber  51  and oil mixed first fraction of the charge (or oil mixed with just air) goes into the crankcase chamber  48 . Amount of charge is controlled by the carburetor valve  584  and may have separate valves  584   a  and  584   b  to regulate the mass flow into passages  126   a  and  126   b  respectively. When oil is injected into the passage  126   a , only first fraction of air free of fuel is inducted through the passage  126   a . Essentially the divided intake passage  126  may have either only air going into crankcase chamber  48  through passage  126   a  when oil is injected into the air stream to lubricate the parts; or may have air-fuel mixture when oil is pre-mixed with the fuel, OR may have lean air-fuel mixture free of oil when oil is injected into the lean mixture in passage  126   a , while rich mixture flows through the passage  126   b  OR the mixture may be of uniform air-fuel ratio going through both the passages  126   a  and  126   b . Also, when only air passes through passage  126   a , fuel supplied through  126   b  may be a propane fuel or any gaseous fuel, such as compressed natural gas, bio gas, etc. The advantage of injecting oil into air inducted into crankcase chamber is that the fuel either liquid form as in the case of gasoline or gaseous as in the case of propane can flow directly into the combustion chamber during the intake process, while oil injected into air lubricates the valve train (cam gear, crank gear, followers, valves, cam lobe, etc) and bearings in the crankcase chamber  48 . Another advantage is that the engine can be operated in many attitudes as there is no oil in the crankcase chamber that would flow into the cylinder when engine is operated upside down. The dual intake system where passage  126  is divided into two separate passages  126   a  and  126   b  may also be applied to overhead valve chamber  106  shown in  FIG. 1 , but with a passage  126   a  connecting the valve chamber  106  and only air entering the valve chamber  106  and crank chamber  48 , with oil injected for lubricating the valve train and parts in the crankcase chamber  48 . 
     During the compression stroke when the piston assembly  756  travels upward, the intake valve  98  is closed and the crankcase chamber  48  experiences negative pressure and the charge (oil mixed charge) is inducted into the crankcase chamber  48  from the carburetor  500  through the passage  126   a , the port  122 , the chamber  88 . The one-way valve  128  opens due to differential pressure cross the one-way valve (typically a reed valve is used). When the piston moves downward during power stroke and expansion stroke, the crankcase pressure is built up. 
     During the intake stroke, the intake valve  98  opens and the charge from the crankcase chamber  48  enters the combustion chamber  51 . At the same time, the rich charge enters the combustion chamber  51  directly from the carburetor  500  through the passage  126   b.    
     The concept of dual passage (first fraction  810  going into crankcase chamber  48  and second fraction of charge  812  going directly into combustion chamber is applicable to all mono-block engines and any conventional cylinder crankcase blocks. 
     The oil pump  1505  may be driven by the crankshaft  22  as shown in  FIG. 12   b  or by the camshaft  82  as shown in  FIG. 5   b . The pump may also be driven by the crankshaft  722   b , shown in  FIG. 9   b  (and  FIG. 9 ) where the pump is mounted outboard. The pump may be a diaphragm pump operated by the variation in the pressure in the crankcase chamber  48 . 
     Fuel used in the oil injected engine may be propane gas commonly known as LPG (liquefied petroleum gas or compressed gaseous fuel. 
     In the  FIG. 18 , the passage  126   a  is connected to the crankcase chamber  48  through a passage  808   a  as shown in  FIG. 18 . The cross drilled passage  2809  on the crankshaft  22  is in gaseous communication with the passage  126   a  through packet of space formed between the outer sealed bearing  28  and an oil seal  2028 . The pocket of space may also be between the inner bearing  41  and an oil seal (not shown). Therefore in this case there is a gaseous passage between the crankcase chamber  48  and the intake passage  2194  in the heat dam  2300 . The first fraction of the air now mixed with oil returns to the combustion chamber through a passage  82   e  connecting the crankcase chamber  48  and the over head valve chamber  106 , passage  2126  and into the intake passage  2310  through a one way valve  2089  in the heat dam  2300 . 
     The oil may also be injected at the carburetor  500  and the shaft  2079  may be used to regulate the amount of coil injected into the first fraction of the air. 
       FIG. 18  shows the location of the propane fuel tank  2007  located below the center line  2927  of the crankshaft attached to the crankcase cover  44 . The pressure regulator  2917  is attached to the crankcase cover  44  with the fuel line  2927   a  feeding the pressure regulator  2917  from the fuel tank  2007 . Fuel line  2927   b  from the pressure regulator  2917  feeds the carburetor  500 . The pressure regulator  2917  may be an integral of the carburetor  500 . Also, the fuel lines  2927   b  can be cast into the cylinder block  10  and the heat dam  2300  can have an internal passage connecting the cast in fuel line  2927   b  to the carburetor  500  as shown in  FIG. 18   c . This helps heat the fuel line  2927   b  to vaporize the propane fuel. Also, the propane tank  2007  may be cast into the crankcase cover  44  to be an integral part of the engine block. 
     The oil reservoir  1511  is above the centerline  2927  and may be a cast feature of the cylinder block  20 . The oil outlet line  1513  feeds the oil pump  1505  driven either off of the camshaft  82  shown in detail in  FIG. 5   c  or driven off of the crankshaft  22  in a half crank as shown in  FIG. 12   b . The oil pump may also be driven by the outboard shaft  722   b  similar to an oil pump in a commercially available Mitsubishi&#39;s HL26 cc two-stroke trimmer. 
     The pressure regulator  2917  may be an integral part of the crankcase cover  44  or the mono-block  10 . 
       FIG. 19  illustrates where the first fraction of charge or just air and oil is supplied into the crankcase chamber  48  through a central passage  1988  in the camshaft  82 . In one embodiment the central passage  1988  is off-centered in the camshaft  82  and a similarly off-centered hole  1982  in the cylinder block  20  aligns periodically with each other. The hole  1992  communicates with the crankcase chamber  48 . The camshaft  82  is rotating at half the crankshaft speed. Therefore it is possible for the passage  1988  and hole  1992  to align only when the piston is moving upward during either exhaust stroke or compression stroke. The passage is cut off from the crankcase chamber when the piston is moving downward. Thus the one-way valve  128  may be eliminated. In another embodiment the opening and closing of the passage  1988  may be controlled by the rotating cam gear  182  in which case the camshaft  82  will be stationery. Again the opening and closing of the cross drilled passage  1994  may be accomplished by the cut out  1996 , which has an leading edge  1996   a  to open the passage  1994  and a trailing edge  1996   b  to close the passage  1994 . Again the communication of passage  126   a  with the crankcase chamber  48  is open and closed appropriately. It is open when the piston is moving upward and closed during downward stroke of the piston. Again, the one-way valve  128  may be eliminated. It is also possible to use camshaft as a way to eliminate the one-way valve  2089  as well. 
     The return of charge from the crankcase chamber into the combustion chamber may be from any convenient location. As described above one fraction of the charge may enter the crankcase chamber to lubricate the parts through a passage in the crankshaft or camshaft and the charge may return from the crankcase chamber into the intake passage or from the valve chamber  106  as the case may be. The camshaft may be located above the combustion chamber in the valve chamber  106   
     The U.S. Pat. No. 6,199,532 discloses engine where intake passage is not divided into separate passages and the fuel is pre-mixed with oil and the valve chamber is substantially spaced above the combustion chamber. The U.S. Pat. No. 7,096,850 describes 100% of the pre-mixed fuel and air going into the crankcase chamber to lubricate the internal parts. In U.S. Pat. No. 7,398,759 the carburetor does not have dual passage system and the intake port is not divided as described in this embodiment. Secondly the first fraction of the charge enters the crankcase chamber through a passage in the crankshaft and may be timed according to the stroke of the piston and not have the check valve  128 . 
     In another embodiment, engine  2020  having over head valve  98  shown in  FIG. 19   c , the first fraction of the charge carrying oil vapors and or droplets of oil is returning into the intake air filter  2095 . However, the first fraction is first passed through a one-way valve  2089  and into an oil separation chamber  107  which is integral with the air filter box  2095 . The condensed oil is then returned to through line  1513   b  into the oil tank  1511 . The first fraction now inducted into the combustion chamber through the intake passage  2310 .  FIG. 19   c  also shows the location of the LPG fuel tank  2007  and the crankcase cover  44  has a radius of curvature R 1  plus a few millimeters to closely match the curvature R 1  of the LPG fuel tank  2007 . As explained with  FIG. 14   f , the centerline of  2007   a  of the fuel tank  2007  is below the axis  2927  of the crankshaft  22  and is also offset from the axis  12   a  of the cylinder  12 . In order to minimize heating of fuel tank  2007  and provide a softer cushion between the crankcase cover  44  and fuel tank  2007 , a vibration absorbent and low heat conductive material  44   c  is used between the fuel tank  2007  and crankcase cover  44  at  44   b  as shown in  FIG. 19   cc .  FIG. 19   d  shows enlarged view of the carburetor  500  and the oil separation chamber  107  integral with the air filter box  2095 . 
     In another embodiment  19   e  shows the engine  2000  having overhead valve  98  similar to engine  2000 , first fraction of the charge flows from the inside of the engine, in this case from the valve chamber  106  through a passage  2126   a  into an oil separation chamber  107  where the oil vapors and droplets are separated fairly well and the first fraction of charge now relatively free of oil returns to the combustion chamber  51  during the intake process through a passage  2126   b  through a one-way valve  2089  into the intake passage  126 . As explained earlier the first fraction after flowing through the oil separation chamber may enter the intake port  124  through a separate passage as explained for engine  3000 . The condensed oil in the oil separator  107  is returned into the oil tank or engine. The oil in the oil separation chamber is pumped back into the engine or oil tank  1511  periodically by the partial vacuum formed in the oil tank  1511 , particularly when oil tank  1511  is connected to the crankcase chamber  48  or may even be pumped back into the injector  101  using the oil pump  1505 , as shown by dotted line  1513   c  in  FIG. 19   c . The oil pump  1505  may be driven either by a camshaft, crankshaft, or a cam gear or belt drive or flywheel. The flywheel, typically used as a cooling fan and a magneto may have teeth cut on the circumference to drive an oil pump. The oil pump may also be a diaphragm pump operated by the pressure pulsation in crankcase chamber  48  caused by the upward and downward movement of the piston  756 . 
     The oil may also be inducted automatically into the intake passage  126   a  by the vacuum or low pressure in the intake passage  126   a  when the piston is traveling upward away from the crankcase chamber  48 . 
     The fuel take off point inside the LPG Tank may be at a location where the liquid fuel cannot enter the pickup point. One proffered location is the center of the tank  2007  with a metal or a rigid pipe. With this arrangement the liquid fuel does not enter the fuel line at any attitude of the engine or the tank. 
     Also, the fuel supply line  3017  may always be immersed into the liquid form of LPG in the fuel tank  3007  if liquid form of fuel is required. Such a liquid fuel may be desired when liquid form of LOG is injected into the engine or intake passage. Secondly, when the liquid form of LPG is delivered into the intake system, particularly when the fuel is to go through the crankcase chamber, the oil may be pre-mixed with oil. Thus when fuel and air passes through the crankcase chamber  48 , the oil lubricates the internal parts of the engine. 
     Also, it is possible to use the pressure in the LPG fuel tank  2007  to pump oil into the engine to lubricate the parts. A diaphragm may be used to separate the oil and LPG fuel from getting in contact with each other. 
     In another embodiment the propane tank may be located in the front side of the block  89  above the crankshaft  22 . In which case, the flywheel and starter may be located on the back side. 
     The dual valve carburetor  500  may be rotary valve type or a butterfly valve type described in U.S. Pat. No. 6,901,892. The valves  584   a  and  584   b  may be mounted on a common shaft  2079  or have separate shaft for each. The dual valve carburetor  500  may also be of sliding valve type, commonly used in LPG Carburetors or motor cycle carburetors. The Carburetor may a liquid fuel carburetor or a gaseous fuel, such as propane type carburetor. A sliding valve is commonly employed for propane gas carburetion or mixing, the sliding valve may be combined with any other type of valve for the regulation of first fraction of the charge or air OR the sliding valve may have dual passages with a slot cut on the sliding valve to regulate either first or second fraction of air. 
     The application of such embodiments described in here may be trimmers, blowers, chainsaws, generators, or any lawn and garden equipment. 
       FIGS. 20   a ,  20   b  and  20   c  illustrates embodiment of a sliding valve type fuel mixer  700 . It consists of a body  2034   b  and a sliding drum  2079   a . The drum  2079   a  has a through  404  hole cut out in the drum  2079   a  for regulating the first fraction of the air (or charge) and the second fraction of the air (or charge) is regulated by the flow area under the lower edge  2080  of the sliding drum  2079   a . The drum  2079   a  has a fuel regulating needle  407  attached to the drum. The needle  407  is a taper needle which increases the flow area for the fuel as the drum is lifted up. The cut out  404  increases the flow area for the first fraction as the drum is lifted up. The drum has a spring  2037  to keep the drum pushed down in its free state. The upper cap  2034   c  keeps the spring and the drum inside the body  2034   b . The cross sectional area of the passage  2194  to regulate the first fraction of charge may be 2% to 75% of the cross sectional area of the second passage  2581 . When fuel is mixed with first fraction of the charge the fuel metering jet  410  may extend into the passage  2194  as described in U.S. Pat. No. 6,901,892. As as the sliding drum  2079   a  is lifted up with a cable  2035 , the flow area  2581   a  under the lower edge  2080  increases and at the same time, it also increases the flow area  2194   a  for the first fraction. The fuel supplied to the fuel mixer  700  may be LPG fuel or gasoline. However, the sliding valve is preferred for regulating the gaseous fuel, such as LPG. The LPG when it reaches the mixer  700 , it is in gaseous form. The fuel mixer  700  has a pressure regulator  414  to maintain a uniform flow of fuel. The cut out  404  in the fuel mixer  700  may be rectangular, oval or circular in shape. 
       FIG. 21 through 26  illustrate embodiments of electronically controlled LPG or compressed natural gas injected throttle body as applied to small engines. The pressure in an LPG tank typically is about 100 inches of water and the pressure is reduced in regulator to about 10 inches of water. The Throttle body  100  consists of a body  102  that has one primary passage  180  that connects the engine&#39;s intake passage  126  ( 126   b ) in a four-stroke engine for example shown in  FIGS. 14 ,  14   d  and or in  FIG. 1 . The intake passage  180  has a throttle valve  162  which is a butterfly valve (or a slide valve  462  shown in  FIG. 23  to regulate the amount air going into the engine. The throttle valve is controlled by the throttle shaft  160  (or  468 ). The throttle body  100  has an electronic control unit  136 , commonly called as ECU or ECM mounted on the body  102  such that the throttle shaft  160  passes through the ECU  136  which has a throttle position sensor  142  to sense the position of the throttle, which can range from full closed for low speed and load at idle, to fully open position at full speed or load. The ECU  136  has inputs or sensors connected to it to measure engine speed  148 , engine temperature or exhaust temperature  150 , intake air temperature of air filter body temperature  146 . The ECU  136  has already programmed fuel and timing maps to control the amount of fuel injected through an injector  138  and also it can control the spark timing, which is a common practice. 
     The Throttle body  102  has an integral pressure regulator  103  consisting of an LPG inlet  110 , pressure chamber  105 , diaphragm  107 , needle valve  111 , arm  108 , pressure spring  109 , vent hole  129  in the pressure regulator cover  127 . 
     The pressure P 1  is normally at about 50 to 100 inches of water in the LPG tank enters the pressure chamber  105  where the flow is regulated by the needle valve  111 . The needle valve  111  is connected to the diaphragm  107  through a pin  118  and an arm  108 . As the pressure increases in the chamber  105  the needle valve closes the flow of LPG fuel because the pressure pushes the diaphragm outward against a pressure spring  109 . The pressure P 2  in the pressure chamber is controlled by the spring  109 , which may be pre-set to any level equal to or below the inlet pressure P 1 , The fuel pressure chamber is connected to a fuel metering chamber  104  through a passage  176  between the pressure chamber  105  and the fuel metering chamber  116 . The metering chamber  116  is connected to the LPG fuel injector  138  through a fuel passage  126 , which can also be an external hose outside the throttle body  102 . As the fuel flows into the fuel metering chamber  116 , the pressure in the pressure regulator chamber  105  drops, thus opening the needle valve  111  for the fuel to flow into the pressure chamber, thus maintaining almost a constant pressure. 
     The fuel metering chamber  116  also a diaphragm  124 , needle valve  122 , arm  124 , pin  118 , metering chamber cover  126  and a vent hole  128 . Operation of the metering chamber is similar to the pressure regulator chamber, where the pressure now at about 10 inches of water is maintained constant while the fuel is fed to the fuel injector  138 . Fuel in the metering chamber  116  is connected to the injector  138  through a fuel passage  126 , as the fuel is depleted in the metering chamber due to fuel injection into the passage  180 , the pressure P 2  drops in the metering chamber. The needle  122  opens and maintains a nearly constant pressure P 2 . The needle valve  122  is activated by the diaphragm through the pin  118  and the arm  124 . The needle valve is tries to stay closed because of the spring  120  in the metering chamber  116 . Typically this spring  120  is a very small spring compared to the spring  109 . P 2  in metering chamber is slightly lower than P 2  due to pressure loss across the needle valve  122 . 
     The amount of fuel injected depends on throttle position, intake temperature TI, engine block or exhaust gas temperature TB, engine speed RPM, and sometimes, intake manifold pressure MAP. 
       FIG. 23  illustrates a throttle body  300  similar to  100 . However, the throttle body  300  has a sliding valve  462  inplace of butterfly valve and does not have fuel metering chamber. It only has pressure chamber which also acts as a metering chamber. The principle of operation is similar as explained above. However, the ECU  136  has a linear position sensor  442  in place of a rotary position sensor  142 . 
       FIG. 24  illustrates a throttle body similar to throttle body  21 , but has only pressure regulator (also acts as a fuel metering chamber). It is possible to have a throttle body where the pressure regulator is external to the throttle body. And the commonly used pressure regulator as in cooking gas stove may be used. 
       FIGS. 25 and 26  illustrate a dual intake throttle body consisting of primary intake passage  180  having a throttle valve  162  to control the flow of charge (mixture of air and fuel) and a secondary passage  480  for air only having a throttle valve  432  to regulate only the air. The dual intake system may be used in place of the carburetor  500  explained earlier on an engine shown in  FIGS. 14 ,  14   d , and  15  or in a two-stroke stratified engines. Throttle valves  162  and  432  are on the same throttle shaft  160  or it can be a rotary valve or a sliding valve disclosed in many prior arts. 
     Advantages: 
     1. It is a mono-block and hence there is no separate head, or gaskets for cylinder head or valve chamber or cam chamber.
 
2. Not all of the charge goes to the crankcase chamber which may take extra time for charge to each combustion chamber.
 
3. Rich charge goes directly into the combustion chamber and hence faster response to throttle and faster acceleration.
 
4. Only a fraction of the charge going into the crankcase chamber may be lubricated, thus, reducing oil consumption. In a dual intake system, only air can be inducted into crankcase chamber with oil injection into the air intake passage. Or oil may be injected directly into crankcase chamber.
 
5. Assembly has few parts—less number of screws.
 
6. Valve lash may be adjusted in an L head using the screw  299 .
 
7. Valve assembly can be a modular part where the valve seal can be inspected prior to assembling into the block. Cost of the rejected parts is less and the parts can be salvaged easily.
 
8. The camshaft  82  may be inserted through the crankcase chamber and, thus, minimizes leak into the ambient.
 
9. Piston pin may be assembled through the opening in the crankcase and hence assembly is simpler.
 
10. Divided passage as shown in  FIG. 14   e  has an advantage where engine responds faster to throttle because fuel does not have to travel through crankcase chamber.
 
10. The LPG tank when mounted close to the crankcase cover, it gets warmed up sooner.
 
11. When the LPG fuel tank is mounted on top of the engine, the radiation and convection heat from the warm engine heats the LPG fuel tank.
 
12. The pressure regulator may be integral with the fuel tank.
 
13. The pressure regulator may be integral with the engine block.
 
14. The oil tank may be mounted on the fuel tank or may be integral with the fuel tank.
 
15. The oil tank may be pressurized using the fuel pressure.
 
16. The oil injection may occur due to pressure difference between the crankcase and the oil tank.
 
17. The LPG Fuel with dual intake system may easily be used on two-stroke stratified engines, particularly with oil injection into the first fraction of air that goes into the transfer passages and the oil is injected into the second fraction so the oil goes straight into the crankcase chamber.
 
18. The design with dual intake system with one fraction of air only going into the crankcase chamber and oil being injected into the first fraction of air may be used in conjunction with fuel injection into the second fraction of the air.
 
19. The dual intake slide valve fuel mixer shown in  FIG. 20  may be used on two-stroke stratified engines. 20 . Electronically controlled LPG fuel injection system has many advantages; better fuel control, compensation for temperature, faster response, fuel efficiency is better, emission is lower, speed governing is easier.
 
     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. 
     Part Numbers: 
     
         
           100  LPG EFI Throttle Body 
           101  LPG/Natural gas fuel 
           102  Throttle body 
           103  Pressure regulator 
           104  Metering chamber 
           105  Pressure chamber 
           107  Diaphragm—pressure chamber 
           108  Arm—pressure chamber 
           109  Spring—pressure regulator 
           110  LPG inlet 
           111  Needle valve—pressure chamber 
           116  Metering chamber 
           118  Pin—Diaphragm 
           120  Spring—needle valve 
           122  Needle valve—metering chamber 
           124  Arm—metering chamber 
           124  Diaphragm—metering chamber 
           126  Fuel passage 
           126  Cover—metering chamber 
           127  Cover—Pressure regulator 
           128  Vent hole—metering chamber 
           129  Vent hole—pressure chamber 
           136  ECU 
           138  LPG Injector 
           140  Injector wires 
           142  TPS—throttle position sensor—rotary 
           146  Inlet air temperature 
           148  Cylinder or exhaust temperature—input signal 
           150  RPM—Engine speed 
           160  Throttle shaft 
           162  Primary butterfly throttle valve 
           162  Throttle lever 
           172  Feed passage 
           180  Primary inlet passage 
       
    
     New 
     
         
           190  Kill switch 
           192  Fuel shut off valve 
           194  Kill wire 
           200  EFI Throttle body 
           300  EFI Throttle body—sliding valve 
           303  Pressure regulator 
           309  Adjustable screw—pressure 
           327  Cover—pressure regulator 
           442  Throttle position sensor—linear 
           462  Slide valve 
           464  Spring—slide valve 
           468  Throttle cable 
           480  Inlet passage 
           400  Dual intake throttle body 
           432  Secondary butterfly throttle valve 
           480  Secondary inlet passage 
       
    
     Accordingly, what is desired to be secured by Letters Patent of the United States is the invention as defined and differentiated in the following claims: