Abstract:
The present invention relates generally to an internal combustion engine and a method of operating the engine on a six stroke cycle, in which the fifth and sixth strokes cool the engine to improve efficiency and reduce emissions.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority under 35 U.S.C. §119 to U.S. Patent Application No. 61/859,075, entitled INTERNAL COMBUSTION ENGINE HAVING INDEPENDENTLY CONTROLLED VALVES AND A METHOD OF OPERATION, filed Jul. 26, 2014, the disclosure of which is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND OF INVENTION 
       [0002]    1. Field of Invention 
         [0003]    The invention relates generally to an internal combustion engine. More specifically, the invention relates to an internal combustion engine operating on a six stroke cycle. 
         [0004]    2. Description of Related Art 
         [0005]    Internal combustion engines have typically operated on a 4 stroke cycle, comprised of intake, compression, combustion, and exhaust strokes. When the cycle repeats, the intake stroke directly follows the exhaust stroke in which the hot combustion gases are evacuated from the cylinder. The heat from the combustion gases raises the temperature of the cylinder wall, which in turn heats the air-fuel charge during the intake stroke. Excessive air intake temperature can lead to knocking. To prevent knocking, the compression ratio of a typical engine is limited to the range of 8 to 11, which also limits the efficiency of the engine. 
         [0006]    Six stroke cycle engines have previously been disclosed that cool the cylinder and use the excess heat created by combustion to improve the operating efficiency of the engine. In U.S. Pat. No. 8,291,872 to Szybist, water is injected into the cylinder during the fourth stroke, when the combustion gases are typically exhausted. The water, which is heated by the combustion gases, is turned to steam and provides additional power during a fifth stroke. The sixth stroke exhausts the steam and combustion gases from the cylinder. Similarly, in U.S. Pat. No. 6,311,651 to Singh, water is injected during the fourth stroke of a six stroke cycle engine to improve engine efficiency, wherein the amount of water to be injected is calculated by determining the energy content of the cylinder. 
         [0007]    The previous examples of six stroke cycle engines have relied on complicated water injection systems to improve overall engine efficiency. The invention of the present disclosure overcomes this problem by cooling the cylinder during fifth and sixth strokes without the need for water injection. 
       BRIEF SUMMARY OF INVENTION 
       [0008]    The present invention relates generally to a six stroke cycle internal combustion engine. The first stroke is an intake stroke, in which fuel and air are drawn into the cylinder. During the second stroke, the contents of the cylinder are compressed. The third stroke is the combustion stroke where the air/fuel mixture is ignited. The fourth stroke exhausts the contents of the cylinder. The first four strokes are similar to those of a typical four stroke cycle engine. However, during a fifth stroke, air is drawn through an open intake valve. During this stroke, the fresh air absorbs heat from the piston and cylinder. In the sixth and final stroke, the heated air is expelled through an open exhaust valve. As the six stroke cycle repeats, the temperature of the cylinder is reduced compared to if the cycle repeated after the fourth stroke as in a typical four stroke cycle. 
         [0009]    The opening and closing of the valves can be accomplished through mechanical or electrical means. Typical internal combustion engines use cams, pushrods, or rocker arms to accomplish this task. In a four cycle engine, each valve is being opened only once during each cycle. Thus, the cam has only one lobe and rotates once per engine cycle. In the six stroke cycle engine of the present invention, the valves open twice per cycle. To accomplish this, the cam has two lobes. The same result can be accomplished by attaching a solenoid to the valve stem. In this configuration, a controller determines when to open and close each valve. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF DRAWINGS 
         [0010]      FIGS. 1-7  depict a cylinder of an internal combustion engine during each of six strokes according to an embodiment of the present invention, with a legend identifying the gases and fuel present in the engine. 
           [0011]      FIG. 8  depicts a cylinder of an internal combustion engine with independently controlled intake and exhaust valves. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0012]    In the preferred embodiment of the present invention, an internal combustion engine completes a six stroke cycle. The first four strokes are similar to that of a typical four stroke cycle engine. As shown in  FIG. 1 , the first stroke is an intake stroke. During this stroke, intake valve  10  is in an open position. Fresh air from the air intake  16  is drawn into the cylinder as piston  15  moves away from the valves  10  and  11 . Also, the fuel injector  12  injects fuel into the cylinder  14  during this stroke. In  FIG. 2 , the air/fuel mixture is compressed as the piston  15  moves in the opposite direction, towards valves  10  and  11 .  FIG. 3  shows the combustion stroke, where spark plug  13  ignites the compressed air/fuel mixture. The combustion of the air/fuel mixture forces the piston  15  away from the top of the cylinder  14 . During the second and third strokes, both the intake valve  10  and the exhaust valve  11  remain closed. In the fourth stroke, as shown in  FIG. 4 , the exhaust valve  11  opens and the combustion gases are expelled through the exhaust  17 . 
         [0013]      FIG. 5  depicts the fifth stroke in which the intake valve  10  is in the open position and fresh air is drawn into the cylinder  14  as the piston  15  moves toward the bottom of the cylinder  14 . In a typical four stroke cycle engine, the next stroke after the exhaust stroke would be a new intake stroke in which both fuel and air would be drawn into the cylinder. However, in the preferred embodiment of the present invention, only air is drawn into the cylinder  14  during this stroke. This fresh air, which is close to the ambient air temperature surrounding the engine, is heated by the walls of the cylinder  14  and piston  15 , causing a decrease in the temperature of those components. 
         [0014]      FIG. 6  shows the sixth and final stroke. In this stroke, the intake valve  10  is in a closed position and the exhaust valve  11  is in an open position. As the piston  15  moves towards the valves  10  and  11 , the fresh and heated air is forced out of the cylinder  14  through the exhaust  17 . Consequently, the temperature of the cylinder  14 , piston  15 , and other components defining the combustion chamber is lower than it was after the fourth stroke. When the cycle repeats, the air/fuel mixture drawn into the cylinder  14  will be heated to a lesser extent than without the fifth and sixth strokes. With a cooler air charge, the compression ratio of the engine can be increased to increase the overall efficiency of the engine. Other engine operation parameters can be adjusted as well to take advantage of the decreased air and fuel mixture temperature. 
         [0015]    By exhausting fresh air into the exhaust  17 , unburnt fuel will have the opportunity to complete combustion. In addition, most modern car engines require an exhaust gas recirculation (EGR) system. The EGR system is designed to reduce the nitrous oxide emissions that are created at high temperatures in the exhaust  17 . In an EGR system, a portion of the exhaust gas is recirculated into the intake of the engine to displace combustible air. This has the effect of reducing combustion chamber temperatures. However, while reducing emissions, the EGR system further has the effect of reducing peak power output of the engine. The fifth and sixth strokes of the present invention cause a reduction in the temperature of the exhaust without the need for an EGR system. 
         [0016]    A person having skill in the art will appreciate that various configurations of the engine components can be used in a six stroke cycle. For example, two valves or four valves can be used in the same manner as described in this disclosure. Moreover, the figures depict a cylinder  14  having direct injection, where the fuel injector  12  puts fuel directly into the cylinder  14 . The fuel injection  12  can alternatively be placed in the intake  16  to each cylinder. Also, the internal combustion engine of the present invention can run on gasoline, diesel, natural gas, or other fuels that have been used in traditional four stroke internal combustion engines. 
         [0017]    To allow the intake  10  and exhaust  11  valves to open twice per cycle, a cam is provided with two lobes. In a typical four stroke cycle engine, the cam has only one lobe. Because the cam completes one rotation per cycle, the cam in the six stroke cycle engine of the present invention rotates 60 degrees per stroke. Referring to the figures, the intake valve  10  is open during the intake stroke, as shown in  FIG. 1 . This open condition corresponds with a lobe of the cam contacting the valve stem or rocker arm, depending on the configuration of the engine. As the cam rotates 60 degrees during the next stroke, the lobe disengages and the intake valve  10  moves to the closed position. As the engine moves through the third and fourth strokes, the intake valve  10  remains closed and the cam has rotated an additional 120 degrees. In the fifth stroke, the cam rotates another 60 degrees and the second lobe of the cam engages the valve stem and the intake valve  10  moves to the open position, as shown in  FIG. 5 . The intake valve  10  moves to the closed position as the cam rotates during the sixth stroke. Since the valve is open during the first and fifth strokes, the two lobes on the cam are correspondingly located at the zero degree and 240 degree positions. The cam for the exhaust valve works in the same manner, but the lobes are located at the 180 degree and 300 degree positions since the exhaust valve  11  is in the open position at during the fourth and sixth strokes. 
         [0018]    In the alternative embodiment of the present invention, electronically controlled solenoids  20  are used as the actuation mechanism for the intake  10  and exhaust valves  11  of the engine. Each intake  10  and exhaust valve  11  has separate solenoids  20  so that the valve timing in each cylinder  14  can be controlled independent of other cylinders or engine rotation. The valve will be held in a normally closed position by a valve spring  18 , as shown in  FIG. 8 . When an electrical signal is sent to the solenoid  20  by a controller  21 , the solenoid  20  depresses the valve, causing it the move to the open position. 
         [0019]    In one embodiment of the present invention, the controller  21  is further electronically connected to sensors providing information such as throttle position, intake air temperature, and engine speed, among others. In other embodiments of the present invention, the controller  21  is part of the engine control unit. The controller  21  has the ability to vary the sequence of opening and closing of the valves  10  and  11  based on the needs of the engine. 
         [0020]    The controller  21  further has the ability to control the duration of the time a valve is opened. For example, if a cylinder is running rich, the duration that the intake valve  10  is open can be decreased to limit the amount of fuel entering the cylinder for a port injected engine, similar to a choke operation on a carbureted engine. The timing of the valves can eliminate rich conditions that result in backfires and high carbon emissions. When undesired air/fuel mixtures are eliminated, fuel efficiency will be improved and the engine will have improved response to load changes. 
         [0021]    With independent control of the valves and fuel delivery, the operation of the engine can be varied depending on engine load, engine conditions, sensor input, or external conditions. For example, in cold conditions, the engine can operate as a standard four stroke cycle engine until the cylinder  14  reach a temperature that requires further cooling. As another example, during highway cruising in which a relatively light load is placed on the engine, individual cylinders can have fuel cut-off and the valves  10  and  11  opened to reduce pumping losses, reducing the effective displacement of the engine. In this method of operation, in which certain cylinders are not receiving fuel, fuel economy can be increased.