Patent Publication Number: US-7213546-B2

Title: Engine airflow management system

Description:
This application claims benefit of Provisional U.S. Appl. No. 60/277,762, filed Mar. 21, 2001. 

   FIELD OF THE INVENTION 
   The present invention relates to an intake/exhaust valve for an internal combustion engine and more specifically to a rotary intake/exhaust valve that may also incorporate a throttling mechanism. 
   BACKGROUND OF THE INVENTION 
   Virtually all internal combustion engines on the market today utilize poppet type valves.  FIGS. 1–4  illustrate schematically a single cylinder of a prior art internal combustion engine having typical poppet-type intake and exhaust valves installed therein. The poppet valve assembly  20  illustrated in  FIGS. 1–4  typically resides in the head  22  of the internal combustion engine  2 . Head  22  is bolted to the block  24  of the engine  2  immediately over cylinder  26 . Piston  28  is slidably received within cylinder  26  in close fitting conformity therewith. The crank arm  30  is coupled between the piston head  28  and crankshaft  32 , thereby translating the reciprocating, linear motion of the piston head  28  within the cylinder  26  into rotary motion about the axis of rotation of the crankshaft  32 . The internal combustion engine  2  illustrated in  FIGS. 1–4  is a four-stroke engine. 
   Poppet valves  34  have heads  36  that have cone shaped or beveled edges that mate with cooperating beveled edge of a valve seat  38  formed into the head  22 . Poppet valve rods  40  extend rearwardly from the poppet valve heads  36  through valve guide bores  42  formed through the head  22 . Poppet valves  34  are reciprocated longitudinally so as to selectively open and close an intake port  44  and an exhaust port  46  formed through the head  22 . The poppet valves  34  are actuated between open and closed positions by a camshaft  48  having a plurality of cams  50  extending therefrom. As camshaft  48  rotates, the cams  50  strike lifters  52  which pivot so as to force poppet valve  34  into cylinder  26  thereby permitting fluidic communication with the interior of cylinder  2  through the ports  44 ,  46 . It is to be understood that there exist many different variations on such an engine and that the prior art embodiment described in conjunction with  FIGS. 1–4  is illustrative only. 
   Even from the schematic representations of the prior art poppet-type valve assembly  20  illustrated in  FIGS. 1–4 , it can be appreciated that a poppet valve assembly  20  is a very complicated structure. The costs associated with manufacturing, assembling, and maintaining such an assembly are quite high. Furthermore, the airflow characteristics associated with poppet valve assembles  20  are relatively inefficient as air, fuel, and combustion gases must enter or exist the cylinder  26  through a relatively small annular opening created between the poppet valve head  36  and valve seat  38  when the poppet valves  34  are opened. Therefore, entry of air or an air/fuel mixture into the cylinder at the beginning of an induction stroke of a four-stroke internal combustion engine may not be complete, and similarly, the flushing of combustion gases that takes place during the exhaust stroke may not be complete either. This situation typically results in less than ideal combustion within the cylinder  26 . 
   Because of the tight tolerances necessary for a poppet-type valve assembly  20  to function properly, a great deal of care is required in both the manufacture and maintenance of the poppet valves  34 . Because of the rigorous stresses to which poppet valves  34  are subjected, these valves may quickly wear, thereby degrading the seal that is formed between the beveled or cone shaped edges of the poppet valve head  36  and the valve seat  38 . Furthermore, it is not uncommon for either the cone shaped edge of the poppet valve head  36  or the cooperating edge of the valve seat  38  to become pitted through use. In either case, the degree of compression that may be achieved within a cylinder  26  is lowered significantly. 
   Because a poppet-type valve assembly is such a complex mechanism, it is difficult to arrange an engine&#39;s components into a given engine compartment space. The arrangement of an engine&#39;s components is typically referred to as the “packaging” of the engine. The packaging of an engine may dictates the size and shape and also the location of the physical components thereof. The complexity and fragility of a poppet-type valve assembly  20  typically requires that the valve assembly  20  be readily accessible. Usually this means that the valve assembly  20  must be near the top of the engine  2 . The difficulty in positioning the valve assembly  20  is further complicated by the need to provide cooling to the assembly. The engine block  24  and head  22  are typically cooled by running a coolant through passage such as passages  23 . Such coolant passages  23  may not be able to sufficiently cool the valve assembly  20  when the engine  2  is under high stress. Subsequently, valve assemblies  20  may quickly become overheated and may become damaged. 
   Traditionally, internal combustion engines  2  using poppet-type valve assemblies  20  and particularly gasoline powered engines require the use of a carburetor or fuel injection system and mix and supply the requisite quantity of fuel and air so that the engine  2  may operate at a desired speed. These mechanisms are typically even more complex than the poppet valve  20  and correspondingly more expensive. 
   Accordingly, it is an object of the present invention to provide a rotary valve mechanism that is simple to manufacture and maintain, and that is also flexible enough to greatly simplify the packaging of the components of an engine. It is another object of the present invention to provide a rotary valve that increases the efficiency of air flow to and from a cylinder of an internal combustion engine and which allows for more complete combustion of the fuel supplied to the engine. Yet another object of the present invention is to provide a rotary valve that may incorporate a throttling mechanism that will obviate the need for a carburetor or fuel injection system as such. It is yet another object of this invention to provide a rotary valve assemble that may be easily constructed and arranged to simply replace a more complex poppet valve assembly. 
   These and other objectives and advantages of the invention will appear more fully from the following description, made in conjunction with the accompanying drawings wherein like reference characters refer to the same or similar parts throughout the several views. 
   SUMMARY OF THE INVENTION 
   The objects of the present invention are realized in a rotary valve mechanism that comprises a valve body that has a bore formed therein with at least one port formed therethrough that intersects the bore. A valve cylinder is constructed and arranged for rotation within the bore of the valve body and has at least one cutout that corresponds to the port formed through the valve body. The cutout is formed such that as the valve cylinder rotates within the valve body, the cutout will selectively permit fluidic communication through the port of the valve body as the valve cylinder rotates within the bore. It is to be understood that there can be more than one port or cutout formed in the rotary valve mechanism and that preferably the rotary valve mechanism is constructed and arranged so as to implement the proper valve sequence of a four-stroke internal combustion engine. 
   The cutouts formed in the valve cylinder may have numerous shapes including regular geometric shapes cut into the face of the valve cylinder but may also be formed into more complex geometric shapes in order to control the flow of fluids and gases therethrough in a particular manner. Specifically, the cutouts formed in the valve cylinder may comprise channels that extend longitudinally and/or circumferentially around and along the valve cylinder. Such channels may increase, decrease, and otherwise modify the flow of combustion gases through the valve mechanism. Note that it is preferred that the cutouts be formed entirely on the exterior of the valve cylinder. 
   While the rotary valve mechanism of the present invention is ideally suited for use with a four-stroke internal combustion engine, it is also to be appreciated that this rotary valve mechanism may be utilized with virtually any type of internal combustion engine, including two-stroke engines, diesel engines, natural gas engines and the like. 
   In operation and in an embodiment adapted for use with a four-stroke internal combustion engine, the valve body of the rotary valve mechanism will comprise an intake cutout and an exhaust cutout that are periodically rotated into and out of fluidic communication with respective intake ports and exhaust ports formed through the valve body. The rotation of the valve cylinder within the valve body selectively permits fluidic communication through the rotary valve mechanism in order to facilitate the operation of the engine. In general, the valve cylinder will rotate at approximately one-half the rate at which the crank shaft of the engine rotates where adapted for use with a four-cylinder engine and at approximately the same speed as the crankshaft when used with a two-cycle engine. However, it is to be understood that in various embodiments, the rate of rotation of the rotary valve cylinder may be altered as applications require. 
   In an alternate embodiment of the present invention, an exhaust gas return valve (EGR valve) comprising a small channel formed either on the outer surface of the valve cylinder or through the body of the valve cylinder between the intake and exhaust ports may be included with the rotary valve mechanism. Typically, the channel that forms the EGR valve will have a predetermined diameter or cross-sectional area so as to meter the amount of combustion gases that may flow therethrough. The timing with which these exhaust gas return valves create fluidic communication between the intake ports and exhaust ports of the rotary valve mechanism will vary with the application and tuning of the engine. 
   One of the benefits of the rotary valve mechanism of the present invention is that the intake port cutout may be constructed and arranged to remain open during substantially an entire induction stroke of the four-stroke engine. What is more, the intake port cutout will typically fully open the intake port within 45 degrees of rotation of the crankshaft to which the valve cylinder is coupled. The solid cross-sectional area of the ports offers a much greater flow capability than the annular flow area presented by a typical prior art poppet valve. And, as the intake port typically remains open for between 180 and 182 degrees of rotation of the crankshaft to which the valve cylinder is coupled, larger quantities of fuel/air mixture burned in the cylinders may be brought into the cylinder for combustion. 
   Similarly, the exhaust port in a rotary valve mechanism according to the present invention will open earlier and close later than typically is possible for a poppet type valve. Specifically, the exhaust port will port will generally begin to open at between 535 and 540 degrees of rotation of the crankshaft to which the valve cylinder is coupled as measured from top dead center of the beginning of an engine cycle. The exhaust port will become fully open within 45 degrees of rotation of the crankshaft once it has started to open, and as indicated above, its flow area is typically much larger than that of the annular flow port created by a poppet type valve. Generally, the exhaust port will become fully closed at approximately 18 degrees after top dead center at the beginning of an engine cycle. 
   Another feature of the present invention is that by moving the valve cylinder longitudinally within the bore in the valve body one may control the aspect of the port cutout that is exposed to its corresponding port. What this means is that the flow of gases through the rotary valve mechanism may be controlled and the rotary valve mechanism of the present invention may therefore be used as a throttle. Where the rotary valve mechanism is utilized as a throttle, the valve cylinder will be longitudinally slidable within the bore formed through the valve body and will typically extend entirely through the bore and extend from either side of the valve body itself. The first end of the valve cylinder will be operatively coupled to a crankshaft of the internal combustion engine so as to transmit the rotation of the crankshaft to the valve cylinder in a predetermined ratio. In a four-cylinder engine, this ratio will typically be on the order of one-half the speed of the crankshaft, and in a two-cycle engine, the valve cylinder will rotate at approximately the same speed as the crankshaft. The second end of the valve cylinder extending from the valve body will typically have a biasing mechanism coupled thereto that longitudinally biases the valve cylinder into a first, idle position. It is important to make sure that the valve cylinder be biased into its idle position to avoid unwanted acceleration of the engine speed. In one embodiment, this biasing mechanism is simply a spring coupled to the valve cylinder. An actuation mechanism, which may be as simple as a lever that bears against the valve cylinder, is constructed and arranged to move the valve cylinder longitudinally within the valve body between its first, idle position and a second, wide open position. Note that this biasing mechanism may position the valve cylinder at any desired position between its first and second positions so as to selectively operate the engine at a predetermined rate. 
   Though a preferred embodiment of the present invention utilizes a valve cylinder that selectively permits fluidic communication through a valve body by means of one or more cutouts formed in the exterior thereof, it is possible to replace the cutouts with a bore or bores formed through the valve body itself. This is particularly desirable when adapting the rotary valve mechanism of the present invention for use with a two-stroke internal combustion engine. The bore or bores formed through the valve body will be constructed and arranged to address their respective ports so as to permit the operation of the two-cylinder engine. In addition, the valve cylinder may also be constructed and arranged so that the rotary valve mechanism may be used as a throttle as described above. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross-sectional schematic representation of a single cylinder of a prior art four-stoke internal combustion engine that utilizes poppet type valves. The piston of the engine illustrated in  FIG. 1  is at the beginning of the induction stroke of the four-stoke cycle of the engine. 
       FIG. 2  is a cross-sectional schematic representation of the prior art engine of  FIG. 1  wherein the piston of the engine has completed the induction stroke and is beginning the compression stroke of the four-stroke cycle of the engine. 
       FIG. 3  is a cross-sectional schematic of the prior art engine of  FIG. 1  wherein the piston is beginning the power stroke of the four-stroke cycle of the engine. 
       FIG. 4  is a cross-sectional schematic representation of the prior art engine of  FIG. 1  wherein the piston of the engine has completed its power stroke and is beginning the exhaust stroke of the four-stroke cycle of the engine. 
       FIG. 5  is a cutaway, cross-sectional schematic illustration of a rotary valve of the present invention mounted over a cylinder of an internal combustion engine. 
       FIG. 6  is a schematic cross-section of a rotary valve taken along cutting lines  6 — 6  in  FIG. 5 , showing the valve cylinder of the rotary valve in a closed position. 
       FIG. 7  is a cross-sectional schematic representation of the rotary valve of  FIG. 6  wherein the valve cylinder of the rotary valve is in an open position and the piston head is moved away from the top of the cylinder. 
       FIG. 8  is a cross-sectional schematic representation of the rotary valve of the present invention further incorporating a throttling mechanism. The rotary valve is illustrated in its “wide-open” throttle position. 
       FIG. 9  is a schematic representation of the rotary valve of  FIG. 8  wherein the valve cylinder of  FIG. 9  is in its “idle” throttle position. 
       FIG. 10  is a close-up view through the valve body wherein the valve cylinder is in its “idle” throttle position. 
       FIG. 11  is a close-up view through a port formed in the valve body wherein the valve cylinder is in its “wide-open” throttle position. 
       FIG. 12  is a schematic representation of a two-cycle internal combustion engine featuring a rotary valve of the present invention. The valve cylinder is illustrated in its open position in  FIG. 12 . 
       FIG. 13  is a schematic cross-sectional illustration of a two-stroke engine wherein the valve cylinder of the rotary valve is in its closed position. 
       FIGS. 14   a  and  14   b  illustrate the position of the respective intake and exhaust port cutouts of the valve cylinder when the engine is at the beginning of its induction stroke. 
       FIGS. 15   a  and  15   b  illustrate the position of the port cutouts of the valve cylinder when the engine is has rotated approximately 45° past top dead center in its induction stroke. 
       FIGS. 16   a  and  16   b  illustrate the position of the port cutouts of the valve cylinder when the engine is at the transition between its induction stroke and its compression stroke. 
       FIGS. 17   a  and  17   b  illustrate the position of the port cutouts of the valve cylinder when the engine is within 10° to 15° of bottom dead center of its power stroke. 
       FIGS. 18   a  and  18   b  illustrate the position of the port cutouts of the valve cylinder when the engine is in its exhaust stroke. 
   

   DETAILED DESCRIPTION 
   Although the disclosure hereof is detailed and exact to enable those skilled in the art to practice the invention, the physical embodiments herein disclosed merely exemplify the invention, which may be embodied in other specific structure. While the preferred embodiment has been described, the details may be changed without departing from the invention, which is defined by the claims. 
   A valve assembly constructed according to the present invention may be readily adapted for use with four stroke and two stroke engines as well as with engines that operate on more complex principles. Furthermore, the present invention may be utilized with engines that burn gas, diesel, natural gas, kerosene or other combustibles. 
   Throughout this specification, top dead center refers to the uppermost position of the piston  28  within the cylinder  26 . The lowermost position of the piston  28  within cylinder  26  is known as bottom dead center. The piston  28  reciprocates within the cylinder  26  between top dead center and bottom dead center. The four stroke cycle of an engine results in the rotation of the crankshaft 30 through 720°. Top dead center at the beginning of the induction stroke is the point of reference for the cycle and is designated as 0°. All positions of the crankshaft  32  during the engine&#39;s cycle can be and are referenced to the 0° starting point. 
   As indicated above, in operation the crankshaft  32  of a four-stroke internal combustion engine  2  rotates 720 degrees in order to complete a full cycle. The respective strokes of the four stroke cycle are generally referred to as the induction, compression, combustion, and exhaust strokes.  FIGS. 1–4  illustrate this four stroke cycle as implemented in a prior art engine  2  comprising a poppet-type valve assembly  20 . In  FIG. 1  engine  2  is illustrated with its crankshaft  32  and piston head  28  positioned near tope dead center at the beginning of the first, induction stroke. During the induction stroke, the valve assembly  20  must open for so as to admit air or an air/fuel mixture into the cylinder. During the second, compression stroke of the four stroke cycle (illustrated in  FIG. 2 ), the valve assembly  20  is closed so that as the piston  28  moves from bottom dead center toward top dead center, the air or fuel/air mixture in the cylinder  26  is compressed. In a four stroke diesel engine, fuel is typically injected into the cylinder during this stroke. By the time the piston  28  reaches top dead center of the compression stroke, combustion of the fuel/air mixture within the cylinder has occurred and the piston  28  is driven back towards bottom dead center in its combustion stroke (see  FIG. 3 ). The valve assembly  20  remains closed through the greater part of the combustion stroke so that the pressure within the cylinder  26  may be transferred to the crankshaft  32 . As the combustion stroke is completed, the piston  28  moves from bottom dead center toward top dead center once again. See  FIG. 4 . The valve assembly  20  remains open during the exhaust stroke to vent the combustion gasses from the cylinder  26 . 
   The position of the poppet valves  34  with respect to the piston  28  of engine  2  during the four stroke cycle illustrated in  FIGS. 1–4  is as follows. Typically an intake poppet valve  34  will begin to open between 35° and 40° before top dead center of the induction stroke, i.e. 35°–40° before the 0° reference for the four stroke cycle of the engine  2 . Note that when referring to the opening and closing of a poppet type valve, it is common to refer to a 50/1000 th  rule. That is, a poppet valve will be said to be open once it has traveled 50/1000 th  of an inch and similarly will be considered closed when it is within 50/1000 th  inches of being fully seated. This rule simply recognizes that only negligible airflow through the valve occurs when the poppet valve is within 50/1000 th   inches of its seat. This rule also applies to the present invention. 
   It is preferred to have both the intake port and exhaust port of a poppet type valve assembly  20  open simultaneously near the beginning of the induction stroke of the engine  2  in order to create an air flow that will draw in the fuel/air mixture and force our exhaust gases. However, the exhaust port poppet valve will typically not close until the crankshaft  32  of the engine  2  has rotated approximately 25° past top dead center into the induction stroke. What is more, the poppet type valve of the intake port will not achieve its fully open position until the crankshaft  32  has rotated through approximately 105°–115°. 
   The exhaust port of a poppet type valve assembly  20  will remain closed through the compression stroke of engine  2 . However, the poppet valve  34  of the intake port will not usually be closed until the crankshaft  32  has rotated through approximately 235°–240° (55°–60° past bottom dead center). 
   During the power stroke of the engine  2 , the poppet valve  34  of the exhaust port will begin to open at approximately 55°–60° before bottom dead center or at approximately 480°–485° of crankshaft  32  rotation. The exhaust poppet valve  34  will thereafter be fully opened at between 605°–615° of crankshaft rotation. 
   From this description of a typical poppet type valve assembly  20  it can be appreciated that poppet type valves tend to open very early and also close late. In addition, these types of valves take longer to achieve their fully opened positions. This situation results in generally lower compression or in lower quality compression and also contributes to inefficient combustion of fuel in the engine  2 . 
   Referring now to  FIGS. 5–7  there is illustrated a rotary valve assembly  60  of the present invention. The rotary valve assembly  60  essentially comprises a valve body  62  having a cylindrical bore  64  formed therein. Where the valve assembly  60  is adapted for use with a four-cycle internal combustion engine, the valve body  62  will have formed there through an intake port  66   a  and an exhaust port  66   b . While the specific geometry of the respective ports  66   a  and  66   b  may differ from one another, these ports are functionally equivalent. Therefore, when referring to an intake or exhaust port in general, the reference numeral  66  will be used. 
   Ports  66  are constructed and arranged to intersect the bore  64  formed into the valve body  62 . A valve cylinder  68  is sized to be received within the bore  64  formed in the valve body  62  in a tight sliding fit. Port cutouts  70   a  and  70   b  are formed in the side of valve cylinder  68  adjacent the ports  66   a  and  66   b , respectively. Where referring to a specific port cutout the reference numerals  70   a  or  70   b  will be utilized. However, where reference is made to a port cutout in general, the reference numeral  70  will be used. 
   As can be appreciated from  FIGS. 6 and 7 , valve cylinder  68  may be rotated within the bore  64  in the valve body  62  so as to occlude a port  66 . When the valve cylinder  68  is in such a position, there is no fluidic communication through the port  66 .  FIG. 6  illustrates the valve cylinder  68  in a closed position in which there is no fluidic communication through the port  66 . In  FIG. 6  the cutout  70  is rotated away from the port  66  and the tight fit between the cylinder  68  and the bore  64  prevents the leakage of gases therebetween. 
   While exhaustive investigation of the present invention and all of its operating characteristics have not been undertaken, it has been shown through the creation of a working model that a rotary valve assembly  60  of the present invention may be successfully employed without observable leakage of high pressure gasses. While sealing mechanisms of various stripe, including standard ring-type seals, may be employed with the rotary valve assembly  60  of the present invention, it is to be understood that such sealing mechanisms are optional, and in a preferred embodiment, such sealing mechanisms are omitted. In the aforementioned working model of the rotary valve  60  adapted for use with a five horsepower, four-cycle engine, the rotating valve cylinder  68  included no sealing mechanism. The valve cylinder  68  of this embodiment was fashioned of a bronze alloy and was received in a steel sleeve that formed the bore  64  of the valve body  62 . The valve cylinder  68  of this embodiment fitted the bore  64  within a tolerance of between 3–5 ten thousandths of an inch. After approximately 100 hours of operation, the working model of the present invention exhibited no appreciable wear and no leakage of gases was remarked. 
     FIG. 7  illustrates the valve cylinder  68  in a fully open position in which the port cutout  70  is completely aligned with the port  66  and there is fluidic communication through port  66 . As the valve cylinder  68  rotates, the degree of exposure of the cutout  70  to port  66  will vary from fully closed (as seen in  FIG. 6 ) to fully open ( FIG. 7 ) and back to fully closed ( FIG. 6 ). The exact rotational position of the valve cylinder  68  within the valve body  62  in relation to the position of the piston head  28  at various stages in the operation of engine  2  will be described in more detail herein below. 
     FIGS. 14–18  illustrate schematically the relative positions of the port cutouts  70  formed in the rotating valve cylinder  68 . As the rotating valve cylinder  68  rotates, port cutout  70  become aligned with ports  66  formed through the valve body  62  so as to allow fluidic communication through the valve body  62  and into the cylinder  26 . Each of the  FIGS. 14–18  is comprised of two parts, respectively labeled a and b. Part “a” of these Figures illustrates a cross-sectional view of the rotary valve assembly  60  taken through the intake ports  66   a . Part “b” of  FIGS. 14–18  illustrate cross-sectional views of the rotary valve assembly  60  taken through the exhaust ports  66   b .  FIGS. 14–18  therefore illustrate the position of the port cutouts  70   a  and  70   b  with respect to ports  66   a  and  66   b , respectively, during each stroke of the four-stroke internal combustion engine&#39;s cycle. 
     FIGS. 14   a  and  14   b  illustrate the position of the port cutouts  70   a  and  70   b  of valve cylinder  68  when the internal combustion engine  2  is positioned at top dead center (0° degrees) at the beginning of the induction stroke of the engine. Note that at the beginning of the induction stroke, when the piston  28  is at top dead center, the valve cylinder  68  is rotatably positioned such that the intake port cutout  70   a  and the exhaust port cutout  70   b  are both slightly open. Therefore, for a brief period of time there exists a path of fluidic communication from the intake port into the cylinder  26  and through the exhaust port  66   b  of the valve assembly  60 . During this brief window, combustion gases remaining within the cylinder  26  are swept out (or scavenged), ensuring that the cylinder  26  are emptied of combustion gases as the induction stroke begins. The exhaust port cutout  70   b  may be fully closed within 2 to 5 degrees past top dead center. However, the closure of the exhaust port  66   b  may be delayed as long as approximately 18° past top dead center to facilitate the inflow of the fuel/air mixture. 
   As illustrated in  FIGS. 15   a  and  15   b  the intake port cutout  70   a  will have fully opened intake port  66   a  by the time the crankshaft  32  has rotated approximately 45 degrees past top dead center. Note that ports  66 , when opened, form extremely large flow passages having few sharp edges. The size and arrangement of ports  66  therefore allow for relatively higher flow rates and an even distribution of air and fuel/air mixtures within the cylinders  26 . Specifically, the flow rates realized through ports  66  are much greater than flow rates that are typically found through ports  44 ,  46  governed by poppet-type valves  34 . It should also be pointed out that the ports  66  defined by the valve cylinder  68  are due the cutouts  70  that are formed on the exterior of the valve cylinder  68 , rather than through the valve cylinder. This facilitates the manufacture of the valve cylinder  68  and the formation of the large flow passage described above. 
   As the pistons  28  move towards bottom dead center at the end of the induction stroke and therefore to the beginning of the compression stroke, the rotation of the valve cylinder  68  will begin to rotate the intake cutout  70   a  out of alignment with the intake port  66 A. This begins to occur at approximately 45 degrees before bottom dead center (crankshaft rotation of approximately 135 degrees). By the time the piston  28  has reached bottom dead center (crankshaft rotation of 180 degrees), the intake port  66   a  will be entirely occluded as illustrated in  FIG. 16A . As illustrated in  FIG. 16   b  the exhaust port  66   b  remains occluded. The intake port  66   a  will be fully closed at or slightly after the piston  28  reaches bottom dead center. Intake port  66   a  will be entirely occluded no later than 2 degrees past bottom dead center (182 degrees of crankshaft rotation). Note that the intake port  66   a  remains open much longer than would a similar intake valve of a poppet type valve assembly. 
   Both the intake and exhaust ports  66   a  and  66   b  remain completed occluded during the compression stroke and well into the power stroke of the four-stroke internal combustion engine  2 . As the piston  28  moves towards top dead center, at approximately 25 to 35 degrees before top dead center of the compression stroke (between 325 and 335 degrees of crankshaft rotation), the compressed fuel/air mixture present within the cylinder  26  is ignited by the introduction of a spark into the cylinder by a spark plug (not shown). As can be understood by those skilled in the art, sparkplugs are typically used in internal combustion engines that burn gasoline whereas internal combustion engines that burn diesel rely on the compression of the fuel/air mixture or upon glow plugs to induce combustion in the cylinder. 
   The intake and exhaust ports  66   a  and  66   b  remain occluded by the valve cylinder  68  through the majority of the power stroke. The valve cylinder  68 , by the time the piston  28  is within 10 to 15 degrees of bottom dead center of the power stroke (between 535° and 540° of crankshaft rotation), begins to open the exhaust port  66   b  as illustrated in  FIG. 17   b . The valve cylinder  68  will rotate approximately 45 degrees to fully open the exhaust port  66   b  as illustrated in  FIG. 18B . Accordingly, the exhaust port  66   b  will have been fully opened by the time piston  28  is 30 to 35 degrees into the exhaust stroke of the internal combustion engine  2  (approximately 570 to 575 degrees of crankshaft rotation). Completion of the exhaust stroke ends the four-stroke cycle of the internal combustion engine  2  and brings the valve assembly  60  back to the position illustrated in  FIGS. 14   a  and  14   b.    
   Throughout the four-stroke cycle, the rotary valve assembly  60  provides a greater degree of fluidic communication between the cylinder  26  and the exterior thereof than would a standard poppet type valve assembly  20 . In addition, where needed, the rotating valve assembly  60  of the present invention seals the cylinder  26  for longer periods during the four-stroke cycle than a poppet type valve assembly  20  is able to. Consequently, an engine  2  fitted with a rotary-type valve assembly  60  allows for more efficient intake of air or fuel/air mixtures into the cylinder  26 , provides for longer and more complete compression during the compression stroke of the four-stroke cycle, and allows for longer and more complete combustion of the fuel/air mixture within the cylinder. 
   Cylinder  68  is preferably driven at approximately ½ the speed at which the crankshaft  32  rotates. This may be simply accomplished as illustrated in  FIG. 5  by using of a timing belt or chain  74  coupled between the crankshaft  32  and the valve cylinder  68 . In order to step down the speed of the crankshaft  32 , a pulley or sheave (not shown) attached to the crankshaft  32  will be one half the size of the pulley or sheave  72  that is secured to an end of the valve cylinder  68  that extends from the valve body  62 . As indicated above, belt  74  that drives the valve cylinder  68  maybe a tooth belt or a chain as needed. 
   In a preferred embodiment of the rotating valve assembly  60 , the valve body  62  or more specifically, the material that forms the bore  64  of the valve assembly  60 , will be fashioned of a material that is slightly harder and more wear resistant than that of the valve cylinder  68 . In this way, wear on the valve assembly  60  will occur primarily in the valve cylinder  68 . When compression within the cylinder  26  of the engine  2  falls below an acceptable level, the worn valve cylinder  68  may be removed and replaced with a replacement valve cylinder sized to fit the bore  64  formed within the body  62  within a predetermined tolerance. The cylinder  68  may be formed of a bronze alloy, a graphite impregnated ceramic composite material or any other suitable material. In this manner, the rotating valve assembly  60  may be easily and cheaply maintained so as to preserve a desirable tolerance between the valve cylinder  68  and the valve body  60 . This will in turn maintain a desired compression level within an operating cylinder  26  of engine  2 . In addition, because of the simplicity of the rotating valve assembly  60 , there are fewer parts that require maintenance or adjustment than with a standard poppet-type valve assembly  20 . 
   In its simplest form, the valve cylinder  68  is simply a cylinder having a flat(s) machined into its side to form the cutouts  70 . These cutouts  70  may be of any suitable geometry but will preferably direct flow through the ports  66  in a smooth and efficient manner. As illustrated in  FIGS. 10 and 11 , the cutouts  70  may have a longitudinally oriented channel  91  formed therein to modify the flow characteristics through the cutouts  70  when the valve assembly  60  is simultaneously used as a throttling device as described hereinbelow in more detail. In addition, the cutouts  70  may be formed with circumferentially extending channels or slots (not shown) of varying size, shape, and disposition that act to control air flow through the ports in a desired manner. Geometrically regular cutouts  70  may have none or one or both types of channels or slots formed therein to control the flow of gases therethrough. It is also to be understood that channels of these shapes may be obviated by forming cutouts with complex geometric shapes that facilitate the flow of gases in a prescribed manner. This flexibility also extends to the exact timing of the opening and closing of the ports  66 . As can be appreciated by those skilled in the art, the timing of the opening and closing of the ports  66  will in large part be dictated by the application for which the engine is intended. The shape, disposition and orientation of the cutouts  70  are therefore not to be limited to just those arrangements shown or described herein. 
   The valve cylinder  68  is also suitable for the application of exhaust gas return (EGR) mechanisms. In their simplest form, EGR mechanisms might comprise a channel or bore formed through the valve body that would allow for fluidic communication between the ports  66   a  and  66   b  during predetermined intervals. These channels or ports may be of a predetermined size and arrangement to control the flow of gases therethrough.  FIG. 5  illustrates schematically an embodiment of an EGR mechanism  63  that is a channel that connects cut-outs  70   a  and  70   b.    
   While  FIGS. 1–18  are schematic in nature, they are illustrative of the simplicity of the rotating valve assembly  60  of the present invention. Ideally, the simple rotary valve assembly  60  may be constructed and arranged so as to replace a preexisting poppet type valve assembly of the type illustrated in  FIGS. 1–4 . In this manner, engines  2  currently utilizing poppet-type valve assemblies  20  may be retrofit with the rotating valve assembly  60  of the present invention. What is more, the simplicity of the rotating valve assembly  60  offers engine designers greater flexibility in the design of the architecture of an engine  2 . For instance, coolant channels (not shown) may be run directly through the solid body  62  of the rotating valve assembly  60  or even through the valve body  68  itself so as to cool the rotating valve assembly. Presently, cooling of a poppet-type valve assembly is limited to relatively compact structures such as sodium filled poppet valve stems  40 . 
   As indicated above, a rotating valve assembly  60  of the type illustrated in  FIG. 5  will have connected to its intake port  66   a  a carburetor or fuel injection system that will provide the fuel/air mixture that will be introduced into the cylinder of the engine  2 . The exhaust port  66   b  of the rotating valve assembly  60  is connected to a manifold (not shown) of the exhaust system of the engine  2 . Where so desired, a rotating valve assembly  60  of the type illustrated in  FIG. 5  may be adapted as illustrated in  FIG. 8  so that a carburetor or fuel injection system may be omitted. In its place, a simple chamber (not shown) for mixing fuel and air may be used. 
   The rotating valve assembly  80  illustrated in  FIG. 8  comprises a body  82  having a bore  84  formed entirely therethrough. Because the engine  2  illustrated in  FIG. 8  is a four-cycle engine, body  82  is provided with an intake port  88   a  and an exhaust port  88   b . Port cutouts  90   a  and  90   b  formed in the valve cylinder  86  are constructed and arranged to open and seal the ports  88  in the manner illustrated in  FIGS. 14–18 . The main difference between rotating valve assembly  60  and rotating valve assembly  80  is that the valve cylinder  86  of rotating valve assembly  80  is longitudinally movable within the bore  84  of body  82 . In this manner, the aspect of the port cutouts  90   a  and  90   b  that addresses their respective ports  88   a  and  88   b  as the engine  2  runs through a four-stroke cycle may be strictly controlled. In order to accomplish this longitudinal motion, a throttle assembly comprising a lever arm  92  that is rotatably mounted upon beam  94  is provided. Beam  94  is solidly secured to body  82  of the rotating valve assembly  80 . Lever  92  rotates about pin  93  such that an end  96  of lever  92  may bear against an end of valve cylinder  86 . Preferably, valve cylinder  86  will be longitudinally biased within bore  84  into a first, “idle” position as illustrated in  FIG. 9 . This is achieved by securing a collar  98  to the end of valve cylinder  86  that is addressed by the lever  92 . A spring  100  is retained around the valve cylinder  86  between the body  82  and collar  98 , thereby acting to bias the valve cylinder  86  to the right into its “idle” position. Note that in  FIG. 8  lever  92  has been actuated to slide the valve cylinder  86  to a second, “wide open throttle” position in which the entire port cutouts  90   a  and  90   b  are addressed to their respective intake and exhaust ports  88   a  and  88   b.    
   By moving the valve cylinder  86  longitudinally within the bore  82 , the flow rate of air or fuel/air mixtures and exhaust into and out of the cylinder  26  may be controlled. Control of the flow rate of the air or air/fuel mixture and combustion gases to and from the cylinder  26  allows operator of engine  2  to control the speed at which the engine will operate. While a mechanism such as a port injector for mixing air and fuel will still be needed in a gasoline powered engine, the more complex throttle mechanisms associated with carburetors and fuel injection systems may be omitted where the valve assembly  80  is utilized. 
   The valve cylinder  86  of valve assembly  80  is preferably driven at one-half the rotational speed of the crankshaft  36 . A belt or chain  102  drives an elongate spur gear  104 . Elongate spur gear  104  in turn drives a spur gear  106  that is secured to an end of the valve cylinder  86 . Spur gear  104  is spatially fixed, i.e. is not moveable longitudinally. However, because of its greater width, gear  106  of valve cylinder  86  may move across the face of gear  104  while maintaining driving contact therewith. In this manner, valve cylinder  86  may be continuously driven while simultaneously being moved longitudinally within bore  84  of valve body  82 . Note that the ratio of the gears and pulleys which connect the crankshaft  32  to the valve cylinder  86  must be such that the angular speed of the valve cylinder  86  is approximately one half that of the crankshaft  32 . 
   It must be understood that many different mechanisms may be utilized to provide motive power to the valve cylinder  86  and to longitudinally slide the valve cylinder  86  within its bore  84 . For example, a worm gear may be utilized in place of the lever  92 . The range of mechanisms capable of sliding the valve cylinder  86  longitudinally within its bore  84  or of providing motive power to the valve cylinder  86  is not to be limited to the embodiments described or illustrated in the Figures. 
     FIGS. 10 and 11  are close-up views of a port cutout  70  of valve cylinder  86  through a port  88 . In  FIG. 10  a valve cylinder  86  is illustrated in its first, idle position. 
   Note that only a small aspect  91  of port cutout  90  is exposed to the port  88 . In this position, only a limited amount of fuel or fuel/air mixture may flow through the port  88 . The exit of combustion gases from the cylinder is similarly restricted, however the exhaust port cutout  90   b  may be sized to exposed a relatively larger aspect to the exhaust port  88   b  at any given time. In  FIG. 11 , the valve cylinder  86  has been slid to its second, wide-open throttle position. In this position, the maximum aspect of the port cutout  90  is addressed to the port  88 . This permits the maximum flow of air or fuel/air mixture into the cylinder and the maximum flow of combustion gases from the cylinder of engine  2 . When valve cylinder  86  is in its idle position as illustrated in  FIG. 10 , the speed of engine  2  is at its minimum. When the valve cylinder  86  is in the position illustrated in  FIG. 11 , the operational speed of engine  2  is at its maximum. By exposing a predetermined aspect of the port cutout  90  to the port  88 , the engine  2  may be driven at a desired speed. As can be appreciated, the use of the relatively simple rotating valve assembly  80  may obviate the use of more complex carburetor or fuel injection systems. 
   In a two stroke internal combustion engine, a cylinder  120  of the engine typically has an exhaust port (not shown) formed through the cylinder wall such that as the piston of the engine moves downward in its power stroke, the piston head will expose the exhaust port and combustion gases will escape through the exhaust port. Note that such an exhaust port does not incorporate a valve as such, though one may be included. This structure requires the use of fixed rings on the piston of the engine so as to avoid damage to the rings and piston were the rings to become snagged on the exhaust port. Such an engine is of simple construction but fails to achieve a satisfactory level of efficiency. 
   In another embodiment of the present invention, a rotating valve assembly  110  may be adapted for use with a two-stroke engine  110 . A schematic cross section view of a port of this embodiment is illustrated in  FIGS. 12 and 13 . Rotating valve assembly  110  comprises a body  112  having a port  114  formed entirely therethrough. A valve cylinder  116  is rotatably disposed within a bore  117  formed through the body  110 . A port bore  118  is formed through the valve cylinder  116  such that as the valve cylinder  116  is rotated, the port bore  118  will selectively open a path of fluidic communication through the port  114  into a cylinder  120  of engine block  122 .  FIG. 12  illustrates the valve cylinder  116  orientated such that port bore  118  allows fluidic communication with the interior of cylinder  120  through port  114 . In  FIG. 13 , valve cylinder  116  of rotating valve assembly  110  is rotated such that the port  114  formed through body  112  is entirely occluded. 
   It is envisioned that the valve body  112  of valve assembly  110  may have an intake port and an exhaust port formed therethrough in the same manner as the valve assemblies illustrated in  FIGS. 5 and 8 . Similarly, valve cylinder  116  of valve assembly  110  may have two port bores  118  formed therethrough, the port bores  118  corresponding to respective ports  114 . Where valve assembly  110  is so constructed, the exhaust port typically formed through the cylinder wall may be excluded in favor of the exhaust port  114  in the valve assembly  110 . This allows for more efficient combustion, better compression in the cylinder  120 , and less maintenance of the engine. In addition, the valve assembly  110  may also be adapted to act as a throttle in the same manner as illustrated in  FIGS. 8 and 9 . The rotating valve assembly  110  may also be adopted as an intake pathway alone, with a fuel/air mixture entering the cylinder  120  through port  114  and passage  118  and exhaust gases exiting cylinder  120  through a typical two-stroke engine exhaust port (not shown). 
   In operation, the exhaust port of valve assembly  110  will be opened by the valve cylinder  116  as the piston moves past a predetermined point in its power stroke. The opening of the intake port of the valve assembly  110  will lag behind the opening of the exhaust port as in a typical two stroke engine. For a time prior to bottom dead center of the first or power stroke and past bottom dead center of the second or compression stroke of the two stroke engine, the port bores  118  of both the intake and exhaust ports  114  will be open simultaneously. Thereafter, both the exhaust and intake port bores will be rotated out of alignment with ports  114 , thereby sealing the cylinder  120  as is typical during the second, compression stroke of the two stroke engine. 
   Typically a valve cylinder of a rotating valve assembly  110  that is constructed and arranged for use with a two-stroke internal combustion engine will operate at approximately the same rotational speed as the crankshaft of the two-stroke engine  110 . 
   The invention described above may be embodied in other forms without departing from the spirit or essential characteristics thereof. The embodiments disclosed in this application are to be considered in all respects as illustrative and not restrictive. The scope of the invention is indicated by the appended claims rather than by the foregoing description and all changes, which come within the meaning and range of equivalency of the claims, are intended to be embraced therein.