Patent Abstract:
A cylinder head  12  showing a guideway in which is located a rotatable valve  10, 12  comprising a fluid port operable to effect fluid communication between a cylinder and a fulid manifold in the guideway, whereby rotation of the valve effects alignment of the fluid port with the combustion chamber of a cylinder  4  to enable fluid flow between the valve  10, 12  and a cylinder  4 , and wherein the cylinder head  2  further comprises a seal  22  which, in use, is movable from a first, non-sealing position in which the seal  22  is biased away from the valve  10, 12 , and a second, sealing position in which the seal  22  is biased onto the valve by gaseous pressure from within a cylinder  4.

Full Description:
FIELD OF THE INVENTION 
   The present invention relates to cylinder heads for combustion engines, and in particular, but not exclusively to cylinder heads for four-stroke internal combustion engines. 
   BACKGROUND TO THE INVENTION 
   In a conventional four-stroke internal combustion engine, a power piston is disposed for reciprocating movement within a cylinder. The top of the cylinder is closed by a cylinder head that carries one or more induction poppet valves and one or more exhaust poppet valves. The induction poppet valve is timed so as to open as the power piston moves down the cylinder and, with the resultant partial vacuum, draws a combustible gas past the open poppet valve and into the cylinder. In respect of pressurised induction systems, the partial vacuum becomes positive pressure being forced into the negative pressure part of the cylinder as the piston moves down the cylinder. The induction poppet valve is then timed so as to close at the point when the piston is near the lowest point of its travel, thereby trapping a cylinder full of combustible gas. As the power piston is pushed back up the cylinder, by virtue of being connected to a crank that continues to rotate, it compresses the gas. At a point near the top of this cycle, called the compression stroke, a spark plug, which has been designed into the cylinder head, is sparked, causing the gas to ignite and rapidly expand as it explodes, pushing the piston down. As the piston comes back up again, the exhaust poppet valve (or valves) is (or are) timed to open, allowing the gases to escape. 
   Poppet valves have been used in internal combustion engines for many years, but display some disadvantages. Poppet valves are relatively expensive to manufacture and incorporate into cylinder heads of combustion chambers, due to the fine machining required to effect tolerances required for use of the valves in the hostile environment within the cylinder head. 
   Poppet valves, although fairly robust in construction, and although they initially create fluid-tight seals, restrict the flow of fuel and gases into and out of the engine, as the fuel and gas must flow around the valve and its associated stem. Poppet valves are also a source of vibration and noise through the effects of metal to metal contact with the cylinder head of the engine. Furthermore, as revolutions of the engine increase, the ability of poppet valves to open and close in time decreases in efficiency to the point where power output cannot increase further. Poppet valves are also a large source of friction, as is the camshaft and spring loaded follower generally used to open and close the valve. 
   There are known engines which do not comprise poppet valves, such as rotary engines and two-stroke piston engines, but such engines are generally inefficient in fuel consumption and costly to maintain. 
   It is therefore an aim of preferred embodiments of the present invention to overcome or mitigate a problem of the prior art, whether expressly mentioned hereinabove or not. 
   SUMMARY OF THE INVENTION 
   According to the present invention there is provided a cylinder head for mounting on a cylinder of a combustion engine, the cylinder head comprising a guideway in which is located a rotatable valve comprising a fluid port operable to effect fluid communication between a cylinder and a fluid manifold in the guideway, whereby rotation of the valve effects alignment of the fluid port with the combustion chamber of a cylinder to enable fluid flow between the valve and a cylinder, and wherein the cylinder head further comprises a seal which, in use, is movable from a first, non-sealing position in which the seal is biased away from the valve, and a second, sealing position in which the seal is biased onto the valve by gaseous pressure from within a cylinder. 
   Preferably there is a single rotatable valve which comprises two fluid ports comprising a fluid inlet and a fluid outlet, cooperable with corresponding inlet and outlet manifolds in the guideway. 
   The fluid inlet may be diametrically opposite to the fluid outlet on the rotatable valve. Preferably however the fluid inlet is axially spaced apart from the fluid outlet along the rotatable valve. 
   Alternatively the cylinder head may comprise a first rotatable valve located in a first guideway, and a second rotatable valve, located in a second guideway, the first valve comprising a fluid inlet and the second valve comprising a fluid outlet. 
   Preferably the rotatable valve comprises a rotatable shaft or bar, and more preferably comprises a rotatable shaft or bar having a substantially circular cross-section. 
   Suitably the fluid port of the rotatable valve comprises a cut-out portion of the valve. 
   Preferably the fluid port of the rotatable valve comprises an aperture or slot extending diametrically through the valve such that rotation of the valve effects movement between an open position in which the aperture or slot is substantially aligned with a cylinder and the fluid manifold in the guideway, and a closed position in which the slot or aperture is substantially aligned with the surface of the guideway. 
   Preferably the seal is in fluid communication with a cylinder. 
   Suitably the seal comprises a resilient biasing means, the resilient biasing means being arranged to bias the seal to the first non-sealing position, until such a time in the combustion cycle of the combustion engine when the build-up of exhaust gases effects sufficient pressure to effect movement of the seal against the resilient biasing means to the second, sealing position. 
   Suitably the resilient biasing means is a spring, preferably a helical spring. 
   Preferably the seal is located in a port or duct in the cylinder head which at one end opens into a cylinder and at the other end opens into the guideway of the cylinder head. Preferably the seal, in the first position, is located substantially within the port or duct, and in the second position extends from the port or duct into the guideway to effect abutment with the rotary valve. 
   Suitably, in the second position the seal is arranged to extend partway into the rotary valve fluid port when said fluid port is in substantial alignment with the seal. 
   The cylinder head may be dimensioned to be mounted on a plurality of cylinders and the rotary valve may comprise a fluid port for each cylinder, wherein rotation of the valve effects temporally separate alignment of each fluid port with the combustion chamber of a prescribed cylinder. Suitably the guideway comprises a fluid manifold for each fluid port of the rotary valve. The rotary valve may comprise two fluid ports for each cylinder, comprising a fluid inlet and fluid outlet, cooperable with corresponding fluid manifolds in the guideway. Preferably the cylinder head further comprises at least one cylinder isolation seal, which extends substantially around the rotary valve between the valve and the interior of the guideway, each isolation seal arranged to prevent fluid from flowing through the guideway between adjacent cylinders. 
   Suitably the rotary valve is arranged to be operably connected to a crankshaft of a combustion engine when the cylinder head is mounted on a cylinder, such that the rotary valve is rotated relative to the crankshaft at one quarter of the speed of the crankshaft. 
   According to a second aspect of the present invention there is provided a cylinder head for mounting on a cylinder of a combustion engine, the cylinder head comprising a single guideway in which is located a rotary valve comprising a fluid inlet and a fluid outlet, operable to effect fluid communication between a cylinder and a corresponding inlet manifold and outlet manifold in the guideway, wherein rotation of the valve effects alignment of the fluid inlet and fluid outlet with a combustion chamber of a cylinder to enable, in use, fluid flow between the valve and a cylinder, and wherein the fluid inlet and fluid outlet are axially spaced along the rotary valve. 
   Preferably the rotatable valve comprises a rotatable shaft or bar, and more preferably comprises a rotatable shaft or bar having a substantially circular cross-section. 
   Suitably the fluid inlet and fluid outlet comprise cut-out portions of the valve. 
   Preferably the fluid inlet and fluid outlet comprise an aperture or slot extending diametrically through the valve such that rotation of the valve effects movement between an open position in which the aperture or slot of the inlet or outlet is substantially aligned with a cylinder and the corresponding inlet manifold or outlet manifold in the guideway, and a closed position in which the aperture or slot is substantially aligned with the surface of the guideway. 
   Suitably movement of the fluid inlet between the open and closed position is effected at a different time to movement of the fluid outlet between the open and closed position, and this may be effected by providing a fluid inlet and outlet which each comprise an aperture or slot extending diametrically through the valve at an angle to one another. 
   Suitably the rotary valve is arranged to be operably connected to a crankshaft of a combustion engine when the cylinder head is mounted on a cylinder, such that the rotary valve is rotated relative to the crankshaft at one quarter of the speed of the crankshaft. 
   The cylinder head may further comprise one or more seals as described hereinabove for the first aspect of the invention. The cylinder head may be dimensioned to be mounted on a plurality of cylinders and the rotary valve may comprise a fluid inlet and fluid outlet for each cylinder, wherein rotation of the valve effects temporally separate alignment of each fluid inlet and fluid outlet with the combustion cylinder of a prescribed cylinder. 
   According to a third aspect of the invention there is provided a combustion engine comprising a cylinder head of the first or second aspects of the invention, mounted to a cylinder. Preferably the combustion engine is an internal combustion engine and is more preferably a four-stroke engine. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the various aspects of the invention, and to show how embodiments of the same may be put into effect, preferred embodiments of the invention will now be described with reference to the accompanying drawings, in which: 
       FIGS. 1A–1D  illustrate front sectional views of a preferred embodiment of a cylinder head of the invention, mounted to a cylinder of a four-stroke internal combustion engine, moving through the exhaust, induction, compression and power strokes. 
       FIG. 2A  illustrates a front sectional view of part of the preferred embodiment of a cylinder head mounted on a cylinder of  FIGS. 1A–1D , during the induction stroke of the combustion cycle according to the invention; 
       FIG. 2B  illustrates the front sectional view of  FIG. 1A , during the exhaust stroke of the combustion cycle. 
       FIGS. 3A–3D  illustrate front sectional views of a second preferred embodiment of a cylinder head of the invention, mounted to a cylinder of any four-stroke internal combustion engine, moving through the exhaust, induction, compression and power strokes of the combustion cycle. 
       FIG. 4  illustrates a front sectional view of part of the cylinder head of  FIGS. 3A–3D , during the exhaust stroke of the combustion cycle; and 
       FIG. 5  illustrates a side sectional view of a rotary valve useful in a cylinder head (not shown) of the present invention, which is mounted on four cylinders in a four cylinder combustion engine. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring firstly to  FIGS. 1A–1D , and  FIGS. 2A and 2B , a first preferred embodiment of a cylinder head  2  of the invention, is mounted on a cylinder  4  of a four-stroke internal combustion engine. The cylinder  4  comprises a combustion chamber  5  within which is mounted a piston  6 , rotatably connected to the crankshaft  8  of the engine. 
   The cylinder head comprises two rotary valves  10  and  12 . The rotary valve  10  comprises a port in the form of an inlet  14  which is a cut-out portion of the rotary valve extending diametrically therethrough. 
   The rotary valve  12  comprises a port in the form of an outlet  16  which is a cut-out portion of the rotary valve  12  extending diametrically therethrough. 
   The rotary valves  10  and  12  are linked to the crankshaft  8  by means well known to persons skilled in the art, such that they are arranged to rotate at one quarter the speed of the crankshaft  8 . 
   The cylinder head  2  also includes a spark plug  18  which is in communication with the combustion chamber  5  of the cylinder  4 . 
   We turn to  FIGS. 2A and 2B , which show a close-up sectional view of the cylinder head  2  showing the rotary valve  10  and inlet  14 . The rotary valve  10  is mounted in a guideway  11 , which guideway is in fluid communication with a manifold inlet port  13  in the cylinder head  2 . The cylinder head  2  also includes two seals  20  which are radially mounted in ducts  24  in fluid communication with the rotary valve  10  and the combustion chamber  5 . The seals  20  comprise a sealing member in the form of a resilient plug  22  which is connected within the ducts  24  by two resilient biasing means in the form of helical springs  26 . The plugs  22  are in communication with the guideway  11  and the ducts  24 . 
   The rotary valve  12  is mounted in a similar guideway (not shown) which includes a manifold outlet, and the cylinder head  2  comprises two further seals  20  which are mounted in ducts in fluid communication between the rotary valve  12  and the combustion chamber  5 . 
   In use the engine is started as is known to persons skilled in the art. The engine runs through a four-stroke cycle as shown in  FIGS. 1A–1D , comprising an exhaust stroke ( FIG. 1A ), induction stroke ( FIG. 1B ), compression stroke ( FIG. 1C ) and power stroke ( FIG. 1D ), which cycle is well known. During the power stroke, the spark plug  18  is activated to create a spark which ignites fuel injected or carburated into the combustion chamber  5  of the cylinder  2  during the induction stroke. 
   As the cycle reaches the induction stroke as shown in  FIG. 1A , the rotary valve  10  comprising the inlet  14  is rotated by way of rotation of the crankshaft  8  such that the inlet  14  becomes aligned in fluid communication between the inlet manifold  13  and the combustion chamber  5 , as illustrated in  FIG. 2A . In this position fuel, or fuel and air, is injected through the inlet manifold  13 , through the inlet  14  and into the combustion chamber  5 . 
   During the induction stroke the outlet  16  is not in fluid communication with the combustion chamber  5 . After the fuel, or fuel and air, has been injected, the crankshaft  8  continues to rotate, which in turn rotates the valves  10  and  12 . As the crankshaft  8  rotates, the cylinder moves to the compression stroke as shown in  FIG. 1B , in which the piston  6  of the cylinder is moved up towards the cylinder head  2 , compressing the fuel (and air). During the compression stroke, neither of the rotary valves  10  or  12  are in fluid communication with either the combustion chamber  5  or their associated guideway manifolds. 
   At the end of the compression stroke the spark plug  18  is activated to create a spark in the combustion chamber and ignite the fuel or fuel/air mixture. The resultant combustion within the combustion chamber  5  drives the piston downwardly, rotating the crankshaft  6  and thus the valves  10  and  12 . During this power stroke, as illustrated in  FIG. 1C , the rotation of the valves  10  and  12  does not result in them moving into fluid communication with the combustion chamber  5  or their associated guideway manifolds. 
   When the piston has reached its most downward point, further rotation of the crankshaft  8  pushes the piston towards the cylinder head  2  in the exhaust stroke, as illustrated in  FIG. 1D . As the cylinder enters the exhaust stroke, the valve  10  comprising the inlet  14  is rotated via the crankshaft  5  such that it remains in non-fluid communication between the combustion chamber  5  and its associated manifold inlet  13  of the guideway  11 . The rotary valve  12  is rotated during the exhaust stroke such that the outlet  16  moves into fluid communication between the combustion chamber  5  and the associated manifold outlet (not shown) of its guideway (not shown). Thus as the piston  6  is pushed upwardly, the exhaust gas generated by combustion in the induction stroke is forced through the outlet  16  in valve  12 , through the manifold outlet of the guideway and out of the cylinder head  2 , to the engine&#39;s exhaust (not shown). 
   We turn now to  FIGS. 2A and 2B . During the four-stroke cycle of the engine, a large quantity of gas is generated, especially in the form of exhaust gases. In order to prevent flow of exhaust gases, or any other fluid present, between the valves  10  and  12  and their associated guideways, seals  20  are utilised. 
   In use, when sufficient gas has built up within the combustion chamber  5 , usually during the exhaust stroke, the seals  20  are activated to prevent fluid flow between the valves  10  and  12  and the guideways. 
   As gas builds up within the combustion chamber  5 , gaseous pressure builds up in the ducts  24  until the pressure is sufficient to overcome the bias of springs  26  and push the sealing members  22  on to the valves  10  and  12 , thereby forming a seal across their associated guideways in which the valves  10  and  12  are located. 
   As shown in  FIG. 2B , during the exhaust stroke, the valve  10  is oriented such that one end of the inlet  14  is adjacent to, and facing one of the sealing members  22 . Thus as the sealing member  22  is pushed onto the valve  10 , it is pushed into the open end of the inlet  14 , thereby creating a fluid tight seal. The use of rubber or similar material in the sealing member  22  helps to create a fluid-tight seal due to compression of the member  22  as it enters the inlet  14 . 
   As the four-strike cycle continues and the gaseous pressure drops within the combustion chamber  5 , the drop in pressure in the ducts  24  allows the springs  26  to bias against the lowered pressure and pull the sealing member  22  away from the valves  10  and  12  and allow unrestricted rotation of the valves, as illustrated in  FIG. 2A . 
   Turning now to  FIGS. 3A–3D  and  4 , a second preferred embodiment of a cylinder head of the present invention is similar to that of  FIGS. 1A–1D ,  2 A and  2 B. Like reference numerals describe like features. 
   In this embodiment the cylinder head  2  comprises only one rotary valve  28  which comprises two ports in the form of an inlet  30  and outlet  32 . The inlet  30  and outlet  32  are axially spaced apart, one behind the other, along the rotary valve  28  and each comprises a cut-out portion of the valve  28  extending diametrically therethrough. 
   The valve  28  is located in a guideway  34  in the cylinder head  2 , as shown in  FIG. 4 . The guideway includes an outlet manifold  13  and an inlet manifold (not shown) which are spaced apart along the guideway  34 . Thus the manifolds are arranged in guideway  34  at locations parallel with the outlet  32  and inlet  30  of the valve  28  located within the guideway  34 . 
   The inlet  30  and outlet  32  of the valve  28  extend diametrically through the valve  28  at a different angle to each other such that when the valve  28  is rotated, the inlet  30  and outlet  32  are in fluid communication between the combustion chamber  5  and their respective manifold inlet and outlet at different times in the combustion cycle. 
   The cylinder head further comprises four seals  20 . Two seals are provided in the cylinder head adjacent to the guideway  34  axially parallel with the location of the inlet  30  of the valve  28  located in the guideway as shown in  FIG. 4 . A further two seals are provided in the cylinder head  2  parallel with the location of the outlet  32  (not shown). The seals  20  are substantially as described for the embodiment of  FIGS. 1A–1D  and  2 A– 2 B. 
   In use the combustion cycle is repeated as for the embodiment of  FIGS. 1A–1D ,  2 A and  2 B but in this embodiment the single valve rotates at a quarter of the speed of the crankshaft and the diametric angles of the inlet  30  and outlet  32  is such that during the exhaust stroke, the outlet  30  is aligned to provide fluid communication between the combustion chamber  5  and the outlet manifold  40  for passage of exhaust gases from the combustion chamber  5 . At the same time, during the exhaust stroke, the inlet  30  is not in fluid communication between the combustion chamber  5  and the inlet manifold (not shown) due to the different diametric angle of the inlet  30  through the valve  28 , as shown in  FIG. 4 . 
   When the engine enters the induction stroke the valve  28  is rotated such that the outlet  32  moves out of fluid communication between the combustion chamber  5  and the outlet manifold  40  of the guideway  34 . At the same time the inlet  30  is rotated to effect fluid communication between the combustion chamber  5  and the inlet manifold of the guideway  34 , such that fuel or fuel and air, is injected into the combustion chamber. 
   During the compression and power strokes of the combustion cycle, the valve  18  is rotated such that neither the inlet  30  and outlet  32  are in fluid communication with the combustion chamber  5 , as shown in  FIGS. 3C and 3D . 
   The seals  20  work in substantially the same way as do the seals of the embodiment of  FIGS. 1A–1D  and  2 A– 2 B. 
   We turn now to  FIG. 5 , which shows a side-sectional view of a rotary valve of a cylinder head of the invention mounted on four cylinders in a four cylinder combustion engine. The cylinder head is not shown in this embodiment. 
   The rotary valve  10  which is located in a guideway (not shown) in the cylinder head, is connected to the cylinder head by bearings  36  located at either end of the valve  10 . The valve  10  is a cylindrical member having four pairs of inlet and outlets (not shown), each pair being spaced apart axially along the valve  10  and each inlet and outlet of a pair being spaced apart axially of each other. 
   The cylinder head is mounted on top of a four cylinder engine block such that each of the pairs of inlets and outlets of the valve  10  is located aligned over a cylinder  4 A– 4 D. 
   The valve  10  is connected to the crankshaft of the engine and arranged to rotate at one quarter of the speed of the eligine. The inlets and outlets of the valve  10  are as described for the embodiment of  FIGS. 3A–3D  and  4  and operate in the same manner. Thus rotation of the valve  10  will move the inlets and outlets through the induction, compression, power and exhaust strokes as described hereinbefore. 
   Each pair of inlets and outlets are oriented off-set to each of the other pairs, such that each of the four cylinders will separately be in one of the four-strokes of the combustion cycle at any one time. 
   The rotary valve  10  also comprises split seal gaskets  38  extending substantially around the valve  10  within the guideway, located at either end of the guideway and between each of the cylinders  4 A to  4 D. The split seal gaskets  38  are dimensioned to contact both the valve  10  and guideway and create a seal therebetween. Thus any gas or fluid which may escape into the guideway of the cylinder head will be retained in a prescribed section of the guideway between two of the gaskets  38  and thus prevented from escaping into another cylinder of inlet or outlet of the valve  10 . 
   The split seal gaskets  38  may be used on the valve  28  of the embodiment of the cylinder head  2  described for  FIGS. 3A–3D  and  4 , or for each of the valves  10  and  12  of the cylinder head  2  of  FIGS. 1A–1D  and  2 A– 2 B. 
   The reader&#39;s attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference. 
   All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. 
   Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features. 
   The invention is not restricted to the details of the foregoing embodiments(s). The invention extend to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Technology Classification (CPC): 5