Patent Publication Number: US-2015059695-A1

Title: Long Power Stroke Engine

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Provisional Patent Application Ser. No. 61/690,836 filed Jul. 6, 2012 titled Long Power Stroke Engine. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     There was no federal sponsorship in the development of the present invention. 
     THE NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT 
     None. 
     BACKGROUND 
     The present invention is in the field of Otto cycle 4 stroke spark ignition internal combustion engines. 
     BRIEF SUMMARY OF THE INVENTION 
     Briefly, the present invention is a means and method of increasing the efficiency of a conventional 4 stroke spark ignition engine. This is done by increasing the length of the stroke of an engine by 50% to 100% and reducing the amount of air or fuel/air mixture that is taken into the cylinders by an amount such that at the end of the compression stroke the conditions in the combustion chamber are the same as those in the combustion chambers of prior art engines. Since the stroke length is greater than that of prior art engines the combustion gases remain in the cylinder for a longer time, thus extracting more energy from them. In addition, the longer stroke length results in greater torque being generated. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         FIG. 1  shows a comparison of the travel of a piston of a prior art engine with that of a piston of an engine of the present invention. 
         FIG. 2  shows an alternate means of achieving the improvement in efficiency of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The amount of energy in the combustion gases that is wasted by prior art engines is considerable. All prior art engines, when operated at high RPMs, waste enough heat energy out of the exhaust valves to cause the exhaust pipes to glow bright orange. This is a result of the shorter power stroke of prior art engines; at the end of the power stroke the combustion gases are still quite hot (i.e. there is considerable energy still in them) and this is wasted when the combustion gases are forced out of the cylinder by the piston on its exhaust stroke. By giving the engine of the present invention a much longer power stroke (and hence expansion stroke) this heat energy is converted to mechanical energy, as will be explained below. 
     In prior art engines the objective was to get the maximum amount of air or fuel/air mixture into the cylinder for all settings of the throttle plate. As will be shown below, in the engine of the present invention this is not the case because the compression ratio of the engine of the present invention is considerably above the compression ratio of current engines. 
     Otto cycle engines have a throttle plate in the intake system; opening and closing this throttle plate regulates the amount of air or fuel/air mixture that enters the cylinders, thereby regulating the speed of the engine. This is the only means of regulating the amount of air that enters the cylinders during the intake stroke of a prior art engine. By contrast, the engine of the present invention has a second means of restricting the amount of air that enters the cylinders in addition to the throttle plate. This second means is the reduced height or modified geometry of the inlet valve cam lobe or any of the means outlined below. 
     The advantages of the present invention will be evident from  FIG. 1 . In  FIG. 1  pistons P 10  and P 20  in engines E 10  and E 20 , respectively (not shown), have the same diameter, and the cylinder heads and combustion chambers CC 18  and CC 28 , respectively, are identical except for the intake valve cam lobes, as will be explained. In addition, the carburetors or fuel injector systems are identical. Assume that piston P 10  in engine E 10  has a stroke length of 5 inches, and piston P 20  in engine E 20  has a stroke length of 10 inches. Regardless of the compression ratio of engine E 10 , since pistons P 10  and P 20  are the same diameter but piston P 20 &#39;s stroke length is twice that of piston P 10 , the compression ratio of engine E 20  is twice that of engine E 10 . However, the intake valve cam lobe controlling the intake valve of piston P 20  (not shown) is modified to reduce the amount of air or fuel/air mixture taken in during piston P 20 &#39;s intake stroke to half that of piston P 10 . 
     As a result of this reduction in intake charge into the cylinder of engine E 20 , when the compression strokes of pistons P 10  and P 20  are completed the conditions in the combustion chambers of the cylinders of engines E 10  and E 20  are identical even though their compression ratios are different. That is, even though piston P 20  has traveled twice as far as piston P 10  in its compression stroke there was only half as much air or fuel/air mixture in the cylinder of engine E 20  as in the cylinder of engine E 10  at the start of the compression stroke. When this lesser amount of air or fuel/air mixture is compressed twice as much the resulting pressure in the cylinder of engine E 20  is the same as in the cylinder of engine E 10 . 
     When the spark plugs (not shown) are fired and the fuel/air mixtures are ignited, both pistons are driven down to position A (a distance of 5 inches) with a total force of F. For piston P 1  this is bottom dead center, and piston P 1  starts to rise up and force the combustion gases out of the exhaust valve (not shown). However, piston P 20  has traveled only half of its stroke length; it continues on to position B and then starts to rise up. 
     Since piston P 20  has traveled a greater distance in its power stroke than piston P 10 , it has extracted more energy from the combustion gases; however, they exert a lesser force on piston P 20  during the second half of its travel. Assume that the total force on piston P 20  for the second half of its travel is half that of the total force on it for the first half of its travel. Therefore the total force on piston P 20  for its entire stroke length is 1.5F. 
     The torque on the crankshaft of an internal combustion engine is directly proportional to the stroke length of the pistons attached to it; since piston P 20  has a stroke length that is twice that of piston P 10 , the torque on the crankshaft (not shown) exerted by piston P 20  will be twice that exerted by piston P 10 . Since the horsepower generated by an internal combustion engine is directly proportional to the product of the force on the pistons multiplied by the stroke length of the pistons, and since the total force exerted on piston P 20  is assumed to be 1.5 times that exerted on piston P 10  and the stroke length of piston P 20  is twice that of piston P 10 , it is obvious that in this example engine E 20  generates 3 times the horsepower of engine E 10  (1.5 times the total force exerted at twice the stroke length). Since conditions in the combustion chambers of engines E 10  and E 20  at the end of the compression strokes are made identical (by limiting the amount of air or fuel/air mixture inducted into the cylinders of engine E 20 ), the amounts of fuel in cylinders  10  and  20  are identical. Thus engine E 20  develops 3 times the horsepower of engine E 10  while burning the same amount of fuel. 
     Obviously the force on piston P 20  during the second half of its travel is governed by the amount of energy remaining in the combustion gases at the start of the second half of its travel, the point at which prior art engines begin pumping combustion gases out the exhaust valve. However, that energy is considerable. All engines, when run at high RPMs, waste enough heat energy out of the exhaust valves to cause the exhaust pipes to glow orange. The configuration of the engine of the present invention converts a substantial amount of this heat energy that would otherwise be wasted into mechanical energy in the form of additional force on the piston during its longer stroke. 
     The primary criterion in the design of a long power stroke engine of the present invention is to see that the pressure in the combustion chamber just prior to ignition is approximately the same as the pressure in a prior art engine for the same application. This pressure can be measured by putting a piezoelectric pressure transducer such as those sold by Piezocryst Advanced Sensors GMBH or PCE Piezotronics in the engine. Substituting this for a spark plug and then cranking the engine with the starter motor (or, if it is a multicylinder engine, running it with such a transducer in one of the cylinders) will allow the peak pressure in the combustion chamber of the prior art engine to be measured, which will establish the corresponding pressure to be obtained in the long power stroke version of that engine. The pressure in the combustion chamber of the long power stroke engine at the conclusion of the compression stroke is determined by varying the amount of air that is inducted during the intake stroke. This in turn can be varied by changing the length of time the intake valve(s) is open, changing the amount that the intake valve(s) is open, changing the diameter of the intake valve(s), by adding a second lobe to the exhaust valve(s) cam lobe so that some air is vented during the compression stroke, or by any other means desired. All of these methods are dependent on the contours of the cam lobes, which will probably require some testing and experimentation to determine. 
       FIG. 2  shows an exhaust valve cam lobe  30  having conventional exhaust lobe  32  and an additional lobe  34  opposite it for use when fuel is directly injected into the cylinder. This additional lobe  34  is for the purpose of obtaining the proper pressure in the combustion chamber by venting excess air that has been inducted into the cylinder during the intake stroke instead of changing the geometry of the intake valve(s) cam lobe(s). 
     It will be obvious to those skilled in the art of engine design that the compression ratios, expansion ratios, and stroke lengths shown above are for illustration purposes only; the actual values will vary depending on the application. It will also be obvious to those skilled in the art of engine design that other types of valves can be used to control the flow of air or fuel/air mixture into the cylinder and the flow of exhaust gases out of the cylinder, and that these valves can be operated by other than lobes on a camshaft.