Abstract:
A four-stroke engine with an isolation chamber. The isolation chamber has a pressure-sensitive wall attached to or slidably mounted within the isolation chamber. The pressure-sensitive wall is substantially impervious to air, oil, and fuel. When the piston moves away from the crankcase, a vacuum is created in the crankcase. This draws the pressure-sensitive wall toward the crankcase, fluidwise, and movement of the pressure sensitive wall pulls air into the intake side of the isolation chamber through a one-way valve or time induction mechanism. When the piston moves toward the crankcase, increased pressure within the crankcase forces the pressure-sensitive wall away, fluidwise, from the crankcase and pushes air from the isolation chamber into the combustion chamber. The pressure-sensitive wall prevents oil from flowing from the crankcase. Power in a four-stroke engine is increased up to as much as 40%, without the necessity to employ superchargers or turbochargers.

Description:
RELATED PATENT APPLICATIONS  
       [0001]    This patent application claims priority from prior U.S. patent application Ser. No. 09/557,455 filed on Apr. 24, 2000, entitled Two-Stroke Internal Combustion Engine with Isolated Crankcase, the disclosure of which is incorporated herein in its entirety by this reference. 
     
    
     
       TECHNICAL FIELD  
         [0002]    This invention relates to a four stroke internal combustion engine, and more particularly to such an engine in which the crankcase is isolated from the combustion chamber.  
         BACKGROUND  
         [0003]    In a conventional two-stroke internal combustion engine, the vacuum caused by a piston moving away from the crankcase draws a mixture of fuel, air, and oil into the crankcase through a one-way valve or timed induction mechanism such as a piston or rotary valve. Increased pressure produced by the piston moving toward the crankcase forces the mixture of fuel, air, and oil into the piston cylinder on the side of the piston away from the crankcase and, therefore, into the combustion chamber, which is at the portion of the piston cylinder that is most distant from the crankcase, because such carbureted fuel cannot escape through the one-way valve or a now closed induction mechanism.  
           [0004]    In most two cycle engines, the crankcase is used as a compressor. This technical approach requires relatively close) tolerances between the crank and the crankcase. It is also required that the crankcase be sealed. These factors isolate the crankcase from any lubrication system that may be located in other parts of the engine. Therefore, a secondary lubrication system is necessary. However, any oil in the crankcase would readily be pushed into the combustion chamber. Therefore, to replace the oil that is pushed into the combustion chamber, oil is continuously added to the crankcase, but only in small quantities. In conventional two-stroke engines this is accomplished by either oil injection or by utilizing fuel which as been pre-mixed with a suitable quantity of oil. But no matter how the lubrication is achieved, in prior art two-stroke engines, oil will be introduced into the combustion chamber and combusted. During the combustion process, such oil creates considerable smoke and other pollution.  
           [0005]    Additionally, when a traditional two-stroke internal combustion engine of the crankcase compression type compresses the mixture of fuel, air, and oil (before the transport ports open), some of the fuel and oil can go past the piston skirt and into the exhaust port unburned. This adds to hydrocarbon pollution of the atmosphere and limits the attainable crankcase pressure.  
           [0006]    However, some types of two-stroke internal combustion engines avoid introducing oil into the carbureted air by not using the crankcase as a pump. Instead, such engines utilize superchargers, which are heavy and expensive. Overall, superchargers are usually somewhat inefficient because the blower is always turning and putting a load on the engine even when there is no demand from the engine for fuel or air, i.e., when the transfer ports are closed.  
           [0007]    Likewise, in four stroke engines, it has long been known that pressurizing the air on the intake side of the engine results in an increase in engine power output. Such power increases have long been accomplished with traditional superchargers (independently acting on the inlet air stream) and turbochargers (using exhaust gases to power the compression of the inlet air stream). And, even in four stroke engines, sealed crankcases have been utilized as inlet air compressors, such as is done with conventional two stroke engines.  
           [0008]    In general, using the crankcase as a compressor requires the crankcase to be fully sealed. It also requires relatively close clearances between the crank and the crankcase itself. Unfortunately, such characteristics isolate the crankcase from oil that may be in other parts of the engine. Consequently, a secondary lubrication system is necessary. However, oil in the crankcase is normally readily pushed into the combustion chamber.  
           [0009]    Some prior art two-stroke engines have incorporated devices to limit the amount of oil which flows into the combustion chamber, but most such devices are directed at capturing oil which has already been entrained, rather than preventing oil from being swept up in or injected into the entering combustion air supply stream.  
           [0010]    Another problem with may prior art crankcase compression designs is the phenomenon of piston blow-by, wherein the fuel-air mixture is contaminated by high pressure burned gases passing downward through the piston rings and into the air or mixture being compressed. In other words, on the power stroke when the piston is cycling toward the crankcase, the charge of air or fuel-air mixture is diluted with hot products of combustion. Thus, it can be seen that it would be desirable to provide a crankcase compression technique which would avoid the possibility of encountering piston blow-by.  
           [0011]    In summary, there remains a significant and as yet unmet need for a four-stroke engine which accomplishes high performance power output without appreciable emissions of pollutants due to combustion of lubrication oil as might normally be expected in two-stroke engines.  
         SUMMARY  
         [0012]    The present invention utilizes the pressure and vacuum cycles created within the crankcase of a crankcase compression four-stroke internal combustion engine to force air into the combustion chamber located within the piston cylinder of the engine. A flexible diaphragm, bellows, or floating piston is utilized to isolate the air that travels to the combustion chamber from the air within the crankcase. Therefore, no oil ever enters the combustion chamber from the crankcase.  
           [0013]    As the piston moves away from the crankcase, a vacuum is created within the crankcase. This draws the flexible diaphragm, bellows, or floating piston which is located within an isolation chamber toward the crankcase, creating a vacuum on the side of the diaphragm, bellows, or floating piston away from the crankcase. This allows a mixture of fuel and air (or plain air if either (a) a fuel injection system that injects fuel into the combustion chamber is utilized or (b) a charge former is located between the isolation chamber and the transfer port) to be drawn through a one-way valve (or timed induction mechanism) and into the isolation chamber on the side of the diaphragm, bellows, or floating piston that is away from the crankcase.  
           [0014]    When the piston moves toward the crankcase, the increased pressure pushes the diaphragm, bellows, or floating piston in the isolation chamber away from the crankcase. Because the mixture of fuel and air or pure air on the side of the diaphragm away from the crankcase cannot escape through the one-way valve or timed induction mechanism, such mixture of fuel and air or pure air is forced into the piston cylinder and, therefore, into the combustion chamber.  
           [0015]    Such mixture of fuel and air or pure air is, therefore, pumped into the combustion chamber without ever being exposed to oil that lubricates the crankcase. Moreover, this effect is accomplished without the use of a supercharger or a turbocharger.  
           [0016]    Preferably the piston is designed with a full-length skirt around the entire perimeter of the piston and with at least one ring around the piston. This ring is placed so that it is always between all ports and the crankcase in order to substantially preclude oil that is either maintained within and/or circulated through the crankcase from passing between the piston and the wall of the piston cylinder and thereby entering the exhaust port or the transfer port. (Oil in the exhaust port would be heated to such an extent that it would smoke or be pushed into the surrounding environment; oil in the transfer port would be pushed into the combustion chamber and create smoke during combustion which would then be exhausted to the surrounding environment.)  
           [0017]    In a four-stroke engine, an isolation chamber is used with a sealed crankcase. In one embodiment, the isolation chamber may be provided substantially the same as my earlier design adapted for a two-stroke engine. A pressure-holding chamber or plenum chamber, and a one-way valve between the isolation chamber and the plenum chamber which allows the air to travel only from the isolation chamber toward the plenum chamber must be utilized, however. This is because during the downward action of the power stroke, the intake valves are closed so that air cannot enter the combustion chamber. Yet, due to action of the piston, such air would, without the additional one-way valve, be drawn back into the isolation chamber during the upward action of the exhaust stroke, thereby impeding the pumping action of the isolation chamber.  
           [0018]    In a four-stroke engine, the isolation chamber taught herein precludes oil from reaching the combustion chamber (thereby allowing oil to be used in a conventional manner to lubricate the crankcase). Also, the isolation chamber taught herein eliminates the power robbing of piston blow-by contamination. In one embodiment, to avoid having pressure generated within the crankcase by piston blow-by impeding the pumping action of the isolation chamber, a timed valve is utilized to open (i.e., vent) the crankcase to the surrounding atmosphere at the time when the piston is at about its closest point of approach to the crankcase, i.e, the bottom dead center position of the piston.  
           [0019]    In one embodiment, the plenum chamber can be provided with a pre-selected volume sufficient that, taking into account the engine displacement, the pressure variation within the plenum chamber will be minimized as the engine operates. Also, to prevent a vacuum from being created in a large area between the throttle and the intake valve, the throttle is preferably located near the intake valve. In one design, the carburetor or fuel injection nozzle is located in the vicinity of the throttle. In such designs, the intake chamber will pump only air into the plenum chamber. Thus, any airtight hollow member, including a hollow member that is a part of a structure on which the engine is mounted, can be utilized as part or all of the plenum chamber.  
           [0020]    Thus, it can be appreciated that the addition of an isolation chamber with flexible diaphragm, as well as a piston having an oil isolation ring located to keep oil out of the transfer ports and exhaust ports, enables a four-stroke engine to function efficiently and provides an exhaust which is relatively smokeless, comparable to conventional four-stroke engines. This is an important improvement in the design and operation of four-cycle engines. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]    In order to enable the reader to attain a more complete appreciation of the invention, and of the novel features and the advantages thereof, attention is directed to the following detailed description when considered in connection with the accompanying drawings, wherein:  
         [0022]    [0022]FIG. 1 illustrates a two-stroke engine with isolated crankcase utilizing a diaphragm as the pressure-sensitive wall.  
         [0023]    [0023]FIG. 2 portrays a two-stroke engine with isolated crankcase employing a bellows as the pressure-sensitive wall.  
         [0024]    [0024]FIG. 3 shows a two-stroke engine with isolated crankcase using a floating piston as the pressure-sensitive wall.  
         [0025]    [0025]FIG. 4 depicts the embodiment of FIG. 1 wherein oil is circulated through the crankcase by a pump.  
         [0026]    [0026]FIG. 5 illustrates a four-stroke engine with isolated crankcase during the compression stroke.  
         [0027]    [0027]FIG. 6 illustrates a four-stroke engine with isolated crankcase during the power stroke.  
         [0028]    [0028]FIG. 7 illustrates a four-stroke engine with isolated crankcase during the exhaust stroke.  
         [0029]    [0029]FIG. 8 illustrates a four-stroke engine with isolated crankcase during the intake stroke.  
         [0030]    [0030]FIG. 9 illustrates a four-stroke engine with isolated crankcase having a large plenum chamber during the compression stroke.  
     
    
       [0031]    The foregoing figures, being merely exemplary, contain various elements that may be present or omitted from actual implementations depending upon the circumstances. An attempt has been made to draw the figures in a way that illustrates at least those elements that are significant for an understanding of the various embodiments and aspects of the invention. However, various other elements of the two-stroke engine are also shown and briefly described to enable the reader to understand how various features may be utilized in order to provide an efficient, reliable engine.  
       DETAILED DESCRIPTION  
       [0032]    As taught in my earlier two-stroke engine patent application, illustrated in FIG. 1 is one embodiment of an engine with isolated crankcase. This configuration includes components of a traditional two-stroke internal combustion engine, while adding an isolation chamber  8  having a pressure-sensitive wall. Such a pressure-sensitive wall may be a flexible diaphragm  9  as illustrated in FIG. 1, a bellows  109  as portrayed in FIG. 2, or a floating piston  209  as shown in FIG. 3.  
         [0033]    The isolation chamber  8  is attached to a sealed crankcase  6  and communicates with the crankcase  6  through an aperture termed the crankcase-side aperture  17  in the isolation chamber  8 , and an isolation-side aperture  18  in the crankcase  6 . Preferably, a hollow member termed the activation passage  14  is used to connect the isolation chamber  8  to the crankcase  6 .  
         [0034]    Whether utilized in a two-stroke or a four-stroke engine application, the pressure-sensitive wall is substantially impervious to air, oil, and the fuels used in an internal combustion engine. The pressure sensitive wall ( 9 ,  109 , or  209 , as applicable), together with the inner surface  19  of the isolation chamber  8 , forms a displaceable barrier that is substantially impervious to air, oil, and the fuels used in an internal combustion engine. When a diaphragm  9  or a bellows  109  is utilized, the diaphragm  9  or bellows  109  is attached to the inner surface  19  of the isolation chamber  8  in such a manner that oil and air cannot pass from the side termed the crankcase side  10  of the isolation chamber  8  (normally the side that is toward the crankcase  6 ) to the side termed the intake side  11  of the isolation chamber  8  (normally the side that is away from the crankcase  6 ). Preferably, the diaphragm  9  is attached near the center of the isolation chamber whereas the bellows  109  is attached near the crankcase-side aperture  17 . The floating piston  209  is slidably in contact with the inner surface  19  of the isolation chamber  8  so that neither oil nor air can pass between the floating piston  209  and the inner surface  19  of the isolation chamber  8 . This can be accomplished with a floating piston seal  103  which can be a flared or flared and flexible rim  103  that is an integral part of the floating piston  209 ; a ring, termed a piston ring,  103 ; or any other form of seal that is well known in the art.  
         [0035]    The ring  103  is preferably a pressure ring. The floating piston  209  is preferably nonmetallic, e.g. carbon fiber or nylon, which is beneficially lighter than a metallic piston  209 . This is possible because the pressure, heat, and quantity of oil to which the floating piston  209  is exposed are considerably lower than the pressure, heat, and quantity of oil to which the piston  1  is subject.  
         [0036]    Attachment of the diaphragm  9  or the bellows  109  to the isolation chamber  8  could, e.g., be done with an adhesive or, alternatively friction if the isolation chamber  8  is split in half and clamped together, preferably with a portion of the diaphragm  9  or the bellows  109  inserted between the halves of the isolation chamber  8 .  
         [0037]    A second aperture termed the intake aperture  22  in the isolation chamber  8  is on the intake side  11  of the isolation chamber  8 . Connected to the isolation chamber  8  and communicating with the isolation chamber  8  through the intake aperture  22  is a flow regulator. The flow regulator can be either a one-way valve  13  that permits air to pass into, but not escape from, the intake side  21  of the isolation chamber  8  or a timed induction mechanism, such as a rotary valve, that is open when the piston  1  of the engine is moving away from the crankcase  6  but closed when the piston  1  of the engine is moving toward the crankcase  6  so that air will flow into, but not escape from, the intake side  21  of the isolation chamber  8 .  
         [0038]    A third aperture  23  is located in the intake side  11  of the isolation chamber  8 . Also, an aperture designated as transfer port  24  exists in the wall  25  of a piston cylinder  26 . The piston cylinder  26  is attached to the crankcase  6 . The isolation chamber  8  is attached to the wall  25  of the piston cylinder  26  in such a manner that the isolation chamber  8  communicates with the piston cylinder  26  and, therefore, with the combustion chamber  16 . The combustion chamber  16  is at the portion of the piston cylinder  26  that is the most distant from the crankcase  6 , and communicates with the third aperture  23  and the transfer port  24 . Preferably the isolation chamber  8  is connected to the wall  25  of the piston cylinder  26  with a hollow member named the transfer passage  2 .  
         [0039]    A piston  1  is slidably mounted within the piston cylinder  26 . The piston  1  is connected, as is well known in the art, to the crankshaft  27 .  
         [0040]    Also in the wall  25  of the piston cylinder  26  is an additional aperture named an exhaust port  28 . The top  32  of the exhaust port  28  is higher than the top  33  of the transfer port  24  so that, on the movement of the piston  1  toward the crankcase  6 , the top  31  of the piston  1  will reach the top  32  of the exhaust port  28  before reaching the top  33  of the transfer port  24  to facilitate the movement of combustion gases from the combustion chamber  16  through the exhaust port  28 .  
         [0041]    Although for purposes of clarity of illustration only a single third aperture  23  of the isolation chamber  8 , a single transfer port  24  in the wall  25  of the piston cylinder  26 , and a single transfer passage  2  are shown. It is preferable to have multiple transfer ports  24  and multiple transfer passages  2  so as to enhance the efficiency in the scavenging of exhaust gases.  
         [0042]    Carbureted air can be fed into the flow regulator, carburetion can occur between the isolation chamber  8  and the transfer port  24 , or fuel can be injected into the combustion chamber  16 .  
         [0043]    The piston  1  has an oil ring  3  for precluding oil pushed by pressurized air from leaving the crankcase  6  and reaching the transfer port  24  and the exhaust port  28  by passing between piston  1  and the wall  25  of the piston cylinder  26 . The bottom  34  of the piston  1  must have a full-length skirt  35  around the entire perimeter of the piston  1 . A piston seal  3 , which is preferably an oil ring  3  but which can be a flared or flared and flexible rim must be around the piston  1  sufficiently close to the bottom  34  of the piston that the piston seal  3  is always between the crankcase  6  and the bottoms  29 ,  30  of the exhaust port  28  and the transfer port  24 .  
         [0044]    At least one traditional pressure or compression ring  7  is also located around the piston  1  near the top  31  of the piston  1 . Preferably; a pressure or compression ring  4  is placed around the piston  1  above and near the piston seal  3 .  
         [0045]    As can be understood from the preceding discussion, the pressure-sensitive wall, i.e., the diaphragm  9 , the bellows  109 , or the floating piston  209  isolates the oil within the crankcase  6  from the combustion chamber  16 .  
         [0046]    As the piston  1  moves away from the crankcase  6 , the pressure is decreased within the crankcase  6 , thereby, when a diaphragm  9  is utilized, drawing the diaphragm  9  toward the crankcase so that, when the piston  1  has reached its upper limit of travel, the diaphragm  9  is approximately in position B, as shown in the ghost illustration of FIG. 1. (Similarly, if a bellows  109  were used, the closed end of the bellows  109  would be drawn toward the crankcase  6 ; and if a floating piston  209  were employed, the piston would be pulled toward the crankcase  6 .) This naturally draws air through the flow regulator, preferably the one-way valve  13 , and the intake aperture  22  into the intake side  11  of the isolation chamber  8 . Then, the movement of the piston  1  toward the crankcase  6 , increases the pressure within the crankcase  6 , thereby pushing the diaphragm  9  (or the closed end of the bellows  109  or the floating piston  209 ) away from the crankcase  6  so that, when the piston  1  has reached its lower limit of travel, the diaphragm  9  is approximately in position A, as depicted in the ghost illustration of FIG. 1.  
         [0047]    Because the air on the intake side  11  of the diaphragm  9  (or the bellows  109  or the floating piston  209 ) cannot escape through the flow regulator, preferably the one-way valve  13 ,-such air is forced into the combustion chamber  16 .  
         [0048]    But since temperature changes within the crankcase  6  can interfere with the synchronization of movement between the piston  1  and the diaphragm  9  (or the bellows  109  or the floating piston  209 ), it is preferable to have a vent aperture  36  within the isolation chamber  8 , the crankcase  6 , or the activation passage  14  on the crankcase side  10  of the pressure-sensitive wall, which vent aperture  36  communicates between the surrounding environment and the isolation chamber  8 , the crankcase  6 , and the activation passage  14 . This is accomplished by having the vent tube  15  attached to a vent aperture  36 , which vent aperture can be in the crankcase side  10  of the isolation chamber  8 , the crankcase  6 , or the activation passage  14 . Furthermore, to minimize the possibility of any contamination entering the vent aperture  36 , it is preferable to have a hollow vent tube  15  attached to the isolation chamber  8 , the crankcase  6 , or the activation passage  14  around the vent aperture  36 . The vent tube  15  communicates with, and leads away from, the vent aperture  36 . Optionally, a filter can be placed on the end of the vent tube  15  that is away from the vent aperture  36 .  
         [0049]    Because of the sealed nature of the crankcase  6 , if the temperature within the crankcase  6  increases rapidly as the piston  1  begins to travel upward, the diaphragm  9  (or the bellows  109  or the floating piston  209 ) will not begin moving toward the crankcase  6  immediately when the piston  1  begins to move away from the crankcase  6 . Similarly, if the temperature within the crankcase  6  decreases rapidly as the piston  1  begins its movement toward the crankcase  6 , the diaphragm  9  (or the bellows  109  or the floating piston  209 ) will not begin moving away from the crankcase  6  immediately when the piston  1  begins to move toward the crankcase  6 .  
         [0050]    A vent aperture  36  is selected to have a diameter of such a size that the vent aperture  36  will eliminate the delay in movement of the diaphragm  9  (or the bellows  109  or the floating piston  209 ) produced by temperature changes within the crankcase  6  while not permitting such a quantity of air to enter or leave the crankcase side  10  of isolation chamber  8 , the crankcase  6 , or the activation passage  14  that the action of the diaphragm  9  (or the bellows  109  or the floating piston  209 ) would be impeded to such an extent that performance of the engine would be negatively measurably affected.  
         [0051]    Optionally, through any means that is well known in the art, the vent aperture  36  can be coordinated with the engine speed, e.g. the vent tube  36  can be closed when the throttle is closed and also when the engine is operating at very high speeds.  
         [0052]    Air introduced into the combustion chamber  16  through the pumping action of the diaphragm  9  (or the bellows  109  or the floating piston  209 ) not only provides the air for combustion, but also scavenges the exhaust products of combustion through the exhaust port  28 .  
         [0053]    Although only a single piston cylinder  26  has been illustrated, an isolation chamber  8  can similarly successfully be employed with multiple cylinder two-stroke engines because the portions of the crankcase  6  associated with a given piston cylinder  26  would be sealed from and, therefore, would not communicate with one another. In such a case, each piston cylinder  26  would have its own isolation chamber  8 .  
         [0054]    Also, rather than using just one isolation chamber  8 , it would be possible to use multiple isolation chambers  8  for a given piston cylinder  26 .  
         [0055]    As another option, if all pistons  1  of a multiple-cylinder two-stroke engine fire at substantially the same time, a single isolation chamber  8  can communicate with all the piston cylinders  26 ; and it would not be necessary to have the portions of the crankcase  6  associated with different piston cylinders  26  sealed from one another.  
         [0056]    Oil can either be held within the crankcase  6  or, as illustrated in FIG. 4, circulated through the crankcase  6  by any means that is well known in the art for conventional four-stroke engines, such as by a pump  50 .  
         [0057]    Attention is now directed more directly to the use of an isolation chamber in a four-stroke engine with isolated crankcase. On one embodiment, the isolation chamber  8  for the four-stroke engine is constructed like the isolation chamber  8  for the two-stroke engine. However, because as illustrated in FIG. 6, the intake valve or valves  101  are closed during the power stroke, when the descending piston  1  is forcing air from the isolation chamber  8  through the third aperture  23 , a pressure holding chamber or plenum chamber  103  is needed to store the air that has been drawn into the isolation chamber  8  during the compression stoke, which is illustrated in FIG. 5, and forced from the isolation chamber  8  during the power stroke. To prevent such stored air from escaping back into the isolation chamber  8 , an additional one-way valve  102  is necessary between the third aperture  23  and the plenum chamber  103 .  
         [0058]    A first open end  104  of the plenum chamber  103  communicates with the isolation chamber  8  through the additional one-way valve  102 . A second open end  105  of the plenum chamber  103  communicates, through intake valve  101 , with the intake port  106  of the piston cylinder  26 .  
         [0059]    Since the downward movement of piston  1  toward the crankcase during the power stroke, as depicted in FIG. 6, and the downward movement of piston  1  toward the crankcase during the intake stroke, as depicted in FIG. 7, respectively, result in compression of the air in the crankcase, the air introduced into the combustion chamber  16  will be of greater density than atmospheric air that would otherwise be charged into the combustion chamber.  
         [0060]    The additional one-way valve  102  precludes air from being drawn from the plenum chamber  103  into the isolation chamber  8 .  
         [0061]    In a four-stroke engine using crankcase compression as taught herein, the crankcase  6  must be sealed. However, other components in such a modified four-stroke engine using crankcase compression as taught therein with an isolation chamber, such as the exhaust port  107  and exhaust valve  108 , are the same as in a conventional four-stroke engine. Also, because of the use of the isolation chamber  8 , any traditional lubrication system  109  can be used to provide lubricating oil to the moving parts within the crankcase  6 .  
         [0062]    The vent aperture  36  communicates with vent tube  15 , which tube  15  leads away from aperture  36 . Aperture  36  is also attached to and communicates with an air supply tube  110  that may be connected to and in communication with the intake aperture  22  of the isolation chamber  8 .  
         [0063]    In order to avoid formation of a vacuum in the large area between the intake valve  101  and the throttle  111 , the throttle  111  is preferably placed near the intake valve  101 . The carburetor or fuel injection system utilized to form the mixture charged for combustion may also be located near the intake valve  101 .  
         [0064]    As discussed above, a large volume is desirable for plenum chamber  103 . Optionally, as portrayed in FIG. 9, the plenum chamber  103  can be effectively increased in volume by utilizing any sealed, hollow member of the vehicle or other apparatus to which the engine is mounted, such as the frame of a motorcycle. Since neither oil nor fuel is necessarily within plenum chamber  103 , in such a design, through flow is not necessary in such hollow structure used as part of the plenum chamber  103 . Optionally, a relief valve  113  can be provided for plenum chamber  103 , for the purpose of limiting the maximum pressure which can be established within the plenum chamber  103 . Such a valve can also be used to minimize pressure variations seen on the discharge pressure to the piston.  
         [0065]    Since piston blow-by is confined within the crankcase  6  by the isolation chamber  8 , a timed valve  120  can be utilized to open the crankcase to the surrounding environment when the piston  1  is at or near the bottom dead center position. The opening of the timed valve  120  can be accomplished by suitable apparatus, such as a rotary valve, a poppet valve, or an electronically controlled magnetic valve.  
         [0066]    Also, in a four-stroke engine design, it is not necessary to provide an oil ring near the bottom  34  of piston  1 , as is the case in the two-stroke engine design.  
         [0067]    The use of the isolation chamber as taught herein provides increased engine power output and efficiency without addition of mechanical parts such as superchargers or turbochargers. Positive intake pressure increase is provided without a supercharger or turbocharger. Power output can be increased up to 40% or 45% over standard four-cycle technology, when applied to applications such as motorcycles or personal watercraft. Also, the design provides an oil efficient, smokeless design, when compared to prior art devices. And, increased engine life may be expected, since full engine lubrication can be expected. The design is easy to manufacture, and is of light weight and compact design that can be integrally incorporated into a device using such a four-stroke engine, such as a motorcycle or personal watercraft. Moreover, the design is stackable, in the use of pairs of cylinders, i.e., twin cylinders for many small four-stroke applications, can be utilized. Alternately, 4, or 6, or even 8 cylinder engines may utilize the teachings hereof to achieve increased power output.  
         [0068]    With the use of the isolation chamber taught herein in conjunction with a four-cycle engine, such an engine can be thought of as being a five-cycle engine which provides increased intake pressure without supercharging or turbocharging.  
         [0069]    It is to be appreciated that various aspects and embodiments of the engine designs described herein are an important improvement in the state of the art of four-cycle engines. Although only a few exemplary embodiments have been described in detail, various details are sufficiently set forth in the drawings and in the specification provided herein to enable one of ordinary skill in the art to make and use the invention(s), which need not be further described by additional writing in this detailed description. Importantly, the aspects and embodiments described and claimed herein may be modified from those shown without materially departing from the novel teachings and advantages provided by this invention, and may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Therefore, the embodiments presented herein are to be considered in all respects as illustrative and not restrictive. As such, this disclosure is intended to cover the structures described herein and not only structural equivalents thereof, but also equivalent structures. Numerous modifications and variations are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention(s) may be practiced otherwise than as specifically described herein. Thus, the scope of the invention(s), as set forth in the appended claims, and as indicated by the drawing and by the foregoing description, is intended to include variations from the embodiments provided which are nevertheless described by the broad interpretation and range properly afforded to the plain meaning of the claims set forth below.