Patent Publication Number: US-7895978-B2

Title: Non-polluting two-stroke engine with air-cooled piston

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is in the field of internal combustion engines, and pertains more particularly to two-stroke internal combustion engines. 
     2. Description of Related Art 
     There are many sorts of two-stroke internal combustion engines known in the art at the time of the present patent application, and all of similar operating characteristics and similar problems. One commonality is that oil to lubricate cylinder and bore needs to be mixed with the gasoline used for fuel, because in such engines the crank case volume is not completely sealed from the intake and exhaust. Another is that the pistons in such engines heat very rapidly due to the two-stroke duty cycle, with each cylinder firing with every stroke. Two-stroke engines, however, typically provide substantially higher torque and substantially more power than comparable-sized four-stroke engines, but suffer from lower reliability and service life than comparable four-stroke engines. Further the two-stroke, due to the oil mixture with the fuel, are significantly polluting engines. 
     What is clearly needed is a two-stroke engine with an oil-bathed crankcase and an improved system for cooling the pistons. 
     BRIEF SUMMARY OF THE INVENTION 
     In an embodiment of the present invention a two-stroke internal combustion engine is provided, comprising at least one cylinder having a bore diameter, a central axis, a cylinder wall, and an upper and a lower extremity, a piston slip-fit in the cylinder, the piston having an overall height and a top surface, an upper portion and a lower portion each of approximately the bore diameter, each of the upper and lower portions having at least one seal ring between the piston and the cylinder wall, and a central portion of significantly less than the bore diameter and a height at least one-half of the overall piston height, providing an annular space between the central piston portion and the cylinder wall, a crank mechanism coupled to the piston in a manner providing a repeating stroke of a specific stroke length in the direction of the central axis of the cylinder, the repeating stroke providing a varying volume V between the top of the cylinder and the top surface of the piston, one or more exhaust ports through the cylinder wall, each exhaust port having a first height in the direction of the cylinder axis, centered at a first dimension from the top of the cylinder, one or more intake ports through the cylinder wall, each intake port having a second height in the direction of the cylinder axis, centered at a second dimension from the top of the cylinder, and a forced-air mechanism providing air to the one or more intake ports. For a significant portion of every stroke both the one or more exhaust ports and the one or more intake ports are open to the annular space between the central piston portion and the cylinder wall, allowing the air pump to force air from the one or more intake ports around the central piston portion to the one or more exhaust ports. 
     In one embodiment of the engine a fuel injection system is provided to allow timed injections of fuel into the air provided by the forced-air mechanism at the one or more intake ports, the first height of the exhaust ports overlaps with the second height of the intake ports, and the first dimension is greater than the second dimension, such that at one position in an upstroke the upper portion of the piston closes the one or more exhaust ports while the one or more intake ports are still partially open, allowing fuel injection into the varying volume V. 
     In another embodiment the piston overall height, the stoke length, and the position of the ports provides for the one or more seal rings in the lower portion of the piston to traverse always between the lower extremity of the cylinder and a position below either the one or more intake ports or the one or more exhaust ports, allowing for the crank mechanism to be oil-bathed, and the two-stroke engine to be operated with gasoline not mixed with oil. 
     In still another embodiment the engine may be operated as a diesel engine, and in some embodiments there is a spark firing mechanism in the cylinder top for firing compressed air-fuel mixture in the varying volume V. 
     Also in some embodiments there is a wick ring in the upper portion of the piston, wherein the stroke length is such that at a lower extremity of the stroke the wick ring wipes a portion of the cylinder wall exposed at the upper portion of the stroke to the oil-bathed crank mechanism, such the wick ring approaching the upper extremity of the stroke provides oil to an upper portion of the cylinder wall never exposed in operation to the oil-bathed crank mechanism. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1   a  is a sectioned illustration of an engine in an embodiment of the present invention with the piston substantially at top-dead-center. 
         FIG. 1   b  is a sectioned illustration of an engine in an embodiment of the present invention with the piston substantially at bottom-dead-center. 
         FIG. 2   a  is a sectioned illustration of an engine in an embodiment of the present invention with the piston on the up-stroke, having covered the exhaust port but not the intake port. 
         FIG. 2   b  is a sectioned illustration of an engine in an embodiment of the present invention with the piston on the up or the down-stroke, illustrating a way to air cool the piston. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to  FIG. 1   a , a piston  101  is shown in a cylinder  102  for an engine according to an embodiment of the present invention. Head  103  closes the cylinder, and spark-plug  104  provides spark to ignite compressed air/fuel mixture in volume  105 , with piston  101  near top-dead-center. Connecting rod pin  106  is to join piston  101  to a connecting rod not shown. 
     Piston  101  has an upper portion  107  and a lower portion  108  both of a diameter to fit the diameter of the cylinder bore. A central portion  109 , however, joins upper and lower portions  107  and  108  in the shape of a truncated cone diminishing in diameter toward the upper portion. The diameter of central portion  109  is everywhere substantially smaller than the bore diameter, creating substantial space between the central portion and any point on the cylinder inner wall. 
     An exhaust port  110  and an intake port  111  are strategically spaced and sized to provide, in conjunction with the piston design, for certain operating features more fully explained below. In the position shown piston lower portion  108  substantially blocks exhaust port  110  but not intake port  111 . A high-capacity blower or air-pump (not shown in  FIG. 1   a ) supplies cool air into the intake port on a continuing basis. 
       FIG. 1   b  is a cross section of the same engine as  FIG. 1   a , but with piston  101  near bottom-dead-center. In  FIG. 1   b  the parts bear the same element numbers as in  FIG. 1   a . With the piston near bottom-dead-center as shown in  FIG. 1   b  both the intake and the exhaust port are uncovered. Also, although not shown in detail in  FIG. 1   a  and  1   b  the exhaust and the intake both have multiple openings from a manifold and passing through the cylinder wall around the diameter of the cylinder, providing for free and unimpeded flow of air, fuel and exhaust. 
     As the piston approaches the bottom-dead-center position on a power stroke as shown in  FIG. 1   b , at one point the upper piston portion  107  reaches the uppermost extent of the intake port. By this time the pressure in the cylinder, due to expanding volume, is reduced enough to limit backflow of exhaust into the intake manifold against the pressure provided by the air blower. As the piston continues its downward travel, the exhaust port is uncovered. Then as the piston continues down, and for a small portion of the next up-stoke the air blower or pump efficiently sweeps all combustion products from the cylinder volume into the exhaust manifold. 
       FIG. 2   a  illustrates the same engine as in  FIGS. 1   a  and  1   b , with piston  101  in a position on upstroke just at the point that the exhaust port becomes blocked, but the intake port is still partially open. At this position one or more fuel injectors positioned just outside the cylinder inject fuel (no oil mixture in the fuel) into the stream of air entering the volume  105 . In some cases the fuel may begin to be injected just before the exhaust is entirely closed. A timing mechanism is used to time the fuel injection to be appropriate under different conditions, such as higher engine RPM or maximum power required. As the piston continues upstroke the intake valve closes to the volume  105  and compression begins, and continues until the spark plug fires near top-dead-center. 
       FIG. 2   b  illustrates the same piston further in the compression stroke, or at the same position on the power stroke. For a long portion of both the compression stroke and the power stroke the volume around central portion  101  of the piston is swept by cooling air driven by the air blower or pump through the intake port and out the exhaust port. This provides for significant cooling of the piston not available in other two-stroke engines. 
     Referring again to  FIGS. 1   a  and  1   b , a piston compression ring  113  is shown around the lower piston portion  108 , and the design and the stroke is such that the crankcase is always isolated from the intake and exhaust ports and from volume  105 . The crankcase can thus be oil-carrying, and may have conventional four-stroke style oil splash and delivery features. Oil is thus provided to the lower portion of the cylinder bore up to about just below the intake and exhaust ports. A wick ring  113  is provided at upper portion  107  of the piston, and in the lower extremities of travel of the piston, this wick ring wipes oil from the lower part of the cylinder bore, so as the piston travels upward, oil is provided the cylinder bore above the intake and exhaust ports. 
     Following the descriptions provided above, using the various drawings provided, a two-stroke internal combustion engine according to an embodiment of this invention may have at least one cylinder having a bore diameter, a central axis, a cylinder wall, and an upper and a lower extremity, and a piston slip-fit in the cylinder, the piston having an overall height and a top surface, an upper portion and a lower portion each of approximately the bore diameter, each of the upper and lower portions having at least one seal ring between the piston and the cylinder wall, and a central portion of significantly less than the bore diameter and a height at least one-half of the overall piston height, providing an annular space between the central piston portion and the cylinder wall. There may also be a crank mechanism coupled to the piston in a manner providing a repeating stroke of a specific stroke length in the direction of the central axis of the cylinder, the repeating stroke providing a varying volume V between the top of the cylinder and the top surface of the piston, one or more exhaust ports through the cylinder wall, each exhaust port having a first height in the direction of the cylinder axis, centered at a first dimension from the top of the cylinder, and one or more intake ports through the cylinder wall, each intake port having a second height in the direction of the cylinder axis, centered at a second dimension from the top of the cylinder. There may further be a forced-air mechanism providing air to the one or more intake ports, and for a significant portion of every stroke both the one or more exhaust ports and the one or more intake ports may be open to the annular space between the central piston portion and the cylinder wall, allowing the air pump to force air from the one or more intake ports around the central piston portion to the one or more exhaust ports. 
     The engine in an embodiment of the invention may also have a fuel injection system to provide timed injections of fuel into the air provided by the forced-air mechanism at the one or more intake ports, and the first height of the exhaust ports may overlap with the second height of the intake ports, and the first dimension is greater than the second dimension, such that at one position in an upstroke the upper portion of the piston closes the one or more exhaust ports while the one or more intake ports are still partially open, allowing fuel injection into the varying volume V. 
     In some engines according to the invention the piston overall height, the stoke length, and the position of the ports provides for the one or more seal rings in the lower portion of the piston to traverse always between the lower extremity of the cylinder and a position below either the one or more intake ports or the one or more exhaust ports, allowing for the crank mechanism to be oil-bathed, and the two-stroke engine to be operated with gasoline not mixed with oil. Such an engine may be operated either as a diesel engine or as a spark-filed engine. 
     In some such engines there may be a wick ring in the upper portion of the piston, wherein the stroke length is such that at a lower extremity of the stroke the wick ring wipes a portion of the cylinder wall exposed at the upper portion of the stroke to the oil-bathed crank mechanism, such the wick ring approaching the upper extremity of the stroke provides oil to an upper portion of the cylinder wall never exposed in operation to the oil-bathed crank mechanism. 
     Some examples have been provided of the elements and practice of the present invention, but there are many changes that might be made that will fall within the spirit and scope of the invention. For example, there may be more than one compression ring and more than one wick ring per piston. Many materials may be suitable for different parts of the engine, and dimensions may vary widely. Engines may be built incorporating these inventive features having multiple cylinders arranged in many different ways, such as in-line or V. Diesel versions may be provided as well by adjusting the stroke and compression and eliminating the spark plug. There are many other such changes that may be made within the spirit and scope of the invention. The invention is limited only by the scope of the claims that follow.