Abstract:
A stroke internal combustion engine includes a piston slideably disposed within a cylinder. The cylinder and said piston together define a combustion chamber. The piston is configured to have a two-stroke cycle comprising a downstroke when said piston slides from an upper position to a lower position within said cylinder and an upstroke when said piston slides from said lower position to said upper position within said cylinder. Further, the engine includes a supply of lubricating fluid that is isolated from any fuel.

Description:
BACKGROUND  
         [0001]    The present invention relates to an improved two-stroke internal combustion engine.  
           [0002]    Two-stroke engines are commonly-used in a variety of devices, such as powered lawn and garden equipment, chain saws, personal watercraft, small outboard motors, etc. Two-stroke engines are more desirable in some applications relative to conventional four-stroke engines (commonly-used in automobiles) because two-stroke engines are usually less complex (fewer parts), lighter, and less expensive to manufacture. Nonetheless, two-stroke engines have several disadvantages relative to four-stroke engines. For example, two-stroke engines typically have a significantly shorter useful life than a four-stroke engine. The shorter life is at least partially attributable to the fact that known configurations of two-stroke engines tend to cause the fuel to contaminate the lubricating oil in the engine&#39;s crankcase, thereby reducing the lubrication effectiveness of the oil. Thus, moving parts in a two-stroke engine tend to wear out faster than in a four-stroke engine. Further, known configurations of two-stroke engines tend to cause oil from the engine&#39;s crankcase to contaminate the air/fuel mixture in the combustion chamber of the. engine&#39;s cylinder(s), thereby resulting in higher emissions of undesirable pollutants from the combustion process. This cross-mixing of fuel and oil in a two-stroke engine results in high oil consumption and thereby requires the fuel to be mixed with relatively expensive two-stroke oil, which increases the cost to operate a two-stroke engine. Additionally, the conventional configuration of a two-stroke engine results in a certain amount of unburned fuel to be exhausted through the exhaust port. Not only does this significantly reduce the fuel efficiency of a two-stroke engine, but, because the exhaust of unburned fuel would quickly render known catalytic converters inoperative, known two-stroke engines cannot generally be used in concert with a pollution-reducing catalytic converter. The inability to combine a two-stroke engine with a catalytic converter is one reason why two-stroke engines have not heretofore be used in automobiles. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0003]    [0003]FIG. 1A is a cross-sectional view of an exemplary improved two-stroke engine.  
         [0004]    [0004]FIG. 1B is a cross-sectional view of the exemplary two-stroke engine in FIG. 1A, shown here at the end of the combustion/exhaust cycle.  
         [0005]    [0005]FIG. 1C is a cross-sectional view of the exemplary two-stroke engine in FIG. 1A, shown here at the beginning of the induction/compression cycle.  
         [0006]    [0006]FIG. 1D is a cross-sectional view of the exemplary two-stroke engine in FIG. 1A, shown here as the compression portion of the induction/compression cycle begins.  
         [0007]    [0007]FIG. 1E is a cross-sectional view of the exemplary two-stroke engine in FIG. 1A, shown here at the beginning of the combustion/exhaust cycle.  
         [0008]    [0008]FIG. 1F is a cross-sectional view of the exemplary two-stroke engine in FIG. 1A, shown here at the end of the power portion of the combustion/exhaust cycle. 
     
    
     DETAILED DESCRIPTION  
       [0009]    The present invention is hereinafter described in the context of one particular embodiment. It should be noted that one of skill in the art will recognize that modifications to the disclosed embodiment could be made and still remain within the scope and spirit of the invention.  
         [0010]    [0010]FIGS. 1A-1F illustrate an exemplary embodiment of a single cylinder (at different stages of its cycle) of an improved two-stroke engine. One skilled in the art will recognize that a two-stroke engine may include one or more such cylinder(s). When a two-stroke engine contains more than one cylinder, all of the cylinders could be operated in the same manner as described herein with respect to the single cylinder illustrated in FIGS. 1A-1F.  
         [0011]    With reference to FIG. 1A, relevant components of the improved two-stroke engine  10  will now be described. The engine  10  includes a cylinder  12  and a piston  16  slidably disposed in the interior of cylinder  12 . While it is common that cylinder  12  actually has a cylindrical shape, it is not necessary to be so. Piston  16  is connected to crank shaft  20  through connecting rod  18 . Piston  16  is configured to slide within cylinder  12 , thereby causing connecting rod  18  to turn crank shaft  20  to generate rotational movement, which can be used by the device powered by the two-stroke engine. The piston  16  may include sealing gaskets  32 .  
         [0012]    A combustion chamber  14  is defined by the walls and head of the cylinder  12  and the head of the piston  16 . The combustion chamber  14  is configured to receive a mixture of air and fuel, which is compressed by the upward movement of piston  16 . The compressed air/fuel mixture is ignited by a spark generated by spark plug  22 . Though a gasoline engine is illustrated in the exemplary embodiment, the invention could be implemented in a diesel engine, wherein the air/fuel mixture is ignited by compression. The energy created by the expanding gases from the ignition of the air/fuel mixture in the combustion chamber  14  causes the piston  16  to slide within the cylinder  12 . Air is forced into the combustion chamber  14  under pressure through intake port  26 . Air can be forced into the combustion chamber  14  in a variety of ways. For instance, an air pump, turbo charger or super charger (none shown in the Figures) could be used to force air into the combustion chamber  14 . Fuel can be delivered to the combustion chamber in a variety of ways as well. For instance, fuel can be directly injected into the combustion chamber through a direct fuel injector (not shown) or it could be atomized into the air stream in the intake port  26 . Other known methods for causing fuel to be received in the combustion chamber  14  could be used as well. Exhaust gases produced from the combustion of the air/fuel mixture are expelled through exhaust port  24 .  
         [0013]    In contrast to known configurations of two-stroke engines, intake port  26  is positioned at a higher position within cylinder  12  relative to exhaust port  24 . Further, an intake valve  30  is disposed in intake port  26 . Intake valve  30  is controlled to selectively open and close the flow path between the intake port  26  and the combustion chamber  14 . The intake port  26  is positioned near the upper portion of the cylinder  12  such that air (or an air/fuel mixture, depending on the method of fuel delivery) is delivered to the combustion chamber at the upper portion of the cylinder. Further, exhaust valve  28  is disposed in exhaust port  24 . Exhaust valve  28  is controlled to selectively open and close the flow path between the exhaust port  24  and the combustion chamber  14  (which exists when the piston  16  is sufficiently low in the cylinder such that the walls of the piston do not cover the exhaust port  24 ). Exhaust port  24  is positioned in a lower portion of a sidewall of cylinder  12  such that a flow path between the exhaust port  24  and the combustion chamber  14  can be established only when the piston  14  approaches approximately the lowest part of its oscillation within cylinder  12 . The intake valve  30  and the exhaust valve  28  can be controlled (electronically, pneumatically, mechanically or otherwise) by a controller (not shown in the Figures).  
         [0014]    A crankcase  34  surrounds crank shaft  20 . The crankcase  34  houses a lubricating fluid, such as oil, which maintains adequate lubrication of the various moving components in the system. In contrast to known two-stroke engines, the crankcase  34  is fluidly-isolated from the intake port  26 , the exhaust port  24 , and the combustion chamber  14 . That is, oil from the crankcase  34  cannot pass into the intake port  26 , the exhaust port  24 , or the combustion chamber  14 .  
         [0015]    Now, operation of the exemplary configuration of the improved two-stroke engine will be described with reference to FIGS. 1B-1F. A two-stroke engine has two strokes of the piston  16  for each cycle: (i) an induction/compression stroke when the piston  16  is moving upward in the cylinder  12  (also referred to as an “upstroke”); and (ii) a combustion/exhaust stroke when the piston  14  is moving downward in the cylinder  12  (also referred to as a “downstroke”). During the induction/compression stroke, air and fuel are delivered to the combustion chamber  14  and then the air/fuel mixture is compressed as the piston  16  continues to move upward in the cylinder  12  (away from the crank case  34 ), thereby decreasing the size of the combustion chamber  14 . During the combustion/exhaust stroke, the air/fuel mixture is combusted, thereby causing the piston  16  to be forced downward in the cylinder  12  (toward the crank case  34 ), and the exhaust gases are expelled from the combustion chamber  14 . FIG. 1B illustrates the exemplary embodiment when the piston  16  is at the end of its combustion stroke, at which time the piston  16  is near the bottom of the cylinder  12 . At this point in the cycle, the air/fuel mixture in the combustion chamber  14  has been combusted and the expanding gas from the combustion has forced the piston  16  downward in the cylinder  12 , thereby enlarging the combustion chamber  14  such that it extends at least down to the exhaust port  24 . Because the piston  16  is below the exhaust port  24 , a flow path can exist between the combustion chamber  14  and the exhaust port  24 . The exhaust valve  28  is open to allow exhaust gas from the combustion of the air/fuel mixture to be expelled from the combustion chamber  14 . Further, the intake valve  30  is open to allow pressurized air to be injected into the combustion chamber  14  through intake port  26 . The pressurized air actually forces the exhaust gases from the combustion of the air/fuel mixture out of the combustion chamber  14  through exhaust port  24  to ready the combustion chamber for the induction/compression stroke of the cycle. The exhaust valve  28  can be maintained in its open position for a determined amount of time to allow all (or substantially all) of the exhaust gases to be expelled from the combustion chamber  14 . The exhaust valve  28  may be controlled such that it is moved to its “closed” position at or before the time when the head of the piston  16  begins to pass by the exhaust port  24 . In this way, lubricating oil from the crank case  34  and the exterior walls of the piston  16  are prevented from being expelled into the exhaust through the exhaust port  24 . As a result, undesirable emissions are reduced relative to known two-stroke engines.  
         [0016]    [0016]FIG. 1C illustrates the exemplary embodiment as the piston  16  begins the induction/compression stroke of the cycle. The momentum of the crank shaft  20  causes the piston  16  to start to slide upward in the cylinder  12 . The exhaust valve  28  is closed before the lower edge of the piston  16  begins to pass the exhaust port  24 . Once the exhaust port  24  is closed, fuel may be dispensed into the incoming charge or directly into the combustion chamber  34 . The intake valve  30  remains open to allow pressurized air to be forced into combustion chamber  14 . Because there is no longer any flow path from the combustion chamber  14  through the exhaust port  24 , the incoming air is trapped in the combustion chamber  14 .  
         [0017]    [0017]FIG. 1D illustrates the exemplary embodiment as the piston  16  slides further up into the cylinder during the induction/compression stroke of the cycle. As illustrated, after a given period of time, the intake valve  30  has been closed to close off the flow path between the intake port  26  and the combustion chamber  14 , thereby fully enclosing the combustion chamber  14 . Once the exhaust port  24  is closed, fuel can be delivered to the combustion chamber  14  according to various methods at different times during the induction/compression stroke of the cycle. For instance, fuel could be mixed with the pressurized air forced into the combustion chamber in the intake port  26 , or fuel can be directly injected into the combustion chamber  14  by a direct fuel injector (not shown). In any event, the piston  16  continues to slide upward in the cylinder  12 , thereby compressing the trapped air/fuel mixture.  
         [0018]    [0018]FIG. 1E illustrates the exemplary embodiment  10  as the piston  16  reaches the end of the induction/compression stroke at the top of the cylinder  12 . At this point in the cycle, there is maximum compression of the air/fuel mixture in the combustion chamber  14 . The spark plug  22  is caused to emit a spark to ignite the compressed air/fuel mixture. In the case where the engine is a diesel engine (not shown), the air/fuel mixture is ignited by the compression alone. The ignition of the air/fuel mixture generates expanding gases, which force the piston  16  downward in the cylinder, which begins the combustion/exhaust stroke of the cycle. As the piston  16  is driven downward in the cylinder  12 , the connecting rod  18  turns the crank shaft  20 , which generates rotational movement.  
         [0019]    [0019]FIG. 1F illustrates the exemplary embodiment  10  as the piston  16  continues to slide downward in the cylinder  12 , just as the head of the piston  16  starts to pass the exhaust port  24 . FIG. 1 illustrates the end of the power-generating portion of the combustion/exhaust stroke. Once the head of piston  16  passes the exhaust port  24 , both the exhaust valve  24  and the intake valve  30  open to allow pressurized air to be forced into the combustion chamber  14  and expel the exhaust gases through the exhaust port  24 . Accordingly, the cycle begins again as illustrated in FIG. 1B.  
         [0020]    The particular configuration and operation of the improved two-stroke engine described herein provides several operational benefits over known two-stroke engines. In particular, cross contamination of fuel and lubricating oil (common in known two-stroke engines) is eliminated in the described embodiment. As a result, the need for oil additives in the fuel is eliminated and oil consumption and undesirable emissions are reduced compared to known two-stroke engines. Further, the described embodiment experiences better fuel efficiency because there is reduced opportunity for unburned fuel to be expelled from the combustion chamber through the exhaust port. Finally, with the exhaust port  24  positioned near the bottom of the cylinder  12 , the length of time during the combustion/exhaust stroke before a flow path through the exhaust port is opened is longer, which increases the power-generating portion of the combustion/exhaust stroke.  
         [0021]    While the present invention has been particularly shown and described with reference to the foregoing preferred and alternative embodiments, those skilled in the art will understand that many variations may be made therein without departing from the spirit and scope of the invention as defined in the following claims. By way of example only, while the described embodiment discloses isolating the exhaust port  24  from the lubricating oil in the crank case  34  by using an exhaust valve  28 , one skilled in the art would recognize, in light of this disclosure, that such isolation could be achieved without an exhaust valve  28  if the exhaust port  24  were positioned such and the piston  16  was sufficiently large that the wall of the piston  16  completely covered the exhaust port  24  when the piston reached the top of the induction/compression stroke. Accordingly, this description of the invention should be understood to include all novel and non-obvious combinations of elements described herein, and claims may be presented in this or a later application to any novel and non-obvious combination of these elements. The foregoing embodiments are illustrative, and no single feature or element is essential to all possible combinations that may be claimed in this or a later application. Where the claims recite “a” or “a first” element of the equivalent thereof, such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Further, the use of the words “first”, “second”, and the like do not alone imply any temporal order to the elements identified. The invention is limited only by the following claims.