Patent Publication Number: US-11377983-B2

Title: Rotary valve internal combustion engine

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a National Stage Entry into the United States Patent and Trademark Office from International Patent Application No. PCT/EP2019/073559, filed on Sep. 4, 2019, which relies upon and claims priority to the following patent applications: (1) United Kingdom Patent Application No. GB 1814496.4 filed on Sep. 6, 2018; (2) United Kingdom Patent Application No. GB 1814502.9 filed on Sep. 6, 2018; (3) United Kingdom Patent Application No. GB 1814508.6 filed on Sep. 6, 2018; (4) United Kingdom Patent Application No. GB 1814512.8 filed on Sep. 6, 2018; (5) United Kingdom Patent Application No. GB 1814514.4 filed on Sep. 6, 2018; (6) United Kingdom Patent Application No. GB 1814530.0 filed on Sep. 6, 2018; and (7) United Kingdom Patent Application No. GB 1900656.8 filed on Jan. 17, 2019, the entire contents of all of which are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to a rotary valve internal combustion engine, particularly but not exclusively, for a manually held machine such as a horticultural grass trimmer or hedge trimmer, in which the control of the intake and exhaust gases of combustion is achieved by means of a rotary valve. 
     DESCRIPTION OF THE RELATED ART 
     A rotary valve internal combustion engine comprising: a piston connected to a crankshaft and that reciprocates in a cylinder, the cylinder having a combustion end, a combustion chamber being defined in part by the piston and the combustion end of the cylinder, a valve housing fixed at an outer portion of the combustion end of the cylinder and defining a bore and a rotary valve rotatable about a rotary valve axis in the bore in the valve housing, the rotary valve having a hollow valve body having an interior volume forming a part of the combustion chamber, wherein the interior volume of the hollow valve body is subjected to combustion gases throughout the combustion process, and further having in a wall part thereof a port giving, during rotation of the valve, fluid communication successively to and from the combustion chamber via inlet and exhaust ports in the valve housing. 
     SUMMARY OF THE INVENTION 
     The present invention seeks to provide such an engine suitable for use with a horticultural machine designed to be held and operated manually by an operator. The term horticultural machine is intended to include hand-held machines for use in horticulture, gardens and forestry for such purposes as grass trimmers, hedge trimmers, brush cutters, clearing saws, shredders, blowers vacuum collectors, mist blowers, and chainsaws. 
     According to the present invention there is provided a rotary valve internal combustion engine comprising: a piston connected to a crankshaft and that reciprocates in a cylinder, the cylinder having a combustion end, a combustion chamber being defined in part by the piston and the combustion end of the cylinder, a valve housing fixed at an outer portion of the combustion end of the cylinder and defining a bore and a rotary valve rotatable about a rotary valve axis in the bore in the valve housing, the rotary valve having a hollow valve body having an interior volume forming a part of the combustion chamber, wherein the interior volume of the hollow valve body is subjected to combustion gases throughout the combustion process, and further having in a wall part thereof a port giving, during rotation of the valve, fluid communication successively to and from the combustion chamber via inlet and exhaust ports in the valve housing, the engine having a carburetor for controlling the air/fuel mix into the engine and an exhaust muffler for the exhaust gases, wherein the port layout is arranged to position the exhaust muffler and carburetor on opposite sides of the engine, the port angles being arranged such that the main body of the carburetor and main body of the muffler are substantially parallel to the centerline of the engine, wherein when the engine is at top dead center, the valve port is angled a predetermined number of degrees from the crankshaft axis said angular offset reducing the radial offset of the inlet port that is required to achieve a mounting flange for the carburetor that is substantially parallel to the centerline of the engine, the centerline of the inlet port is offset towards the operator a predetermined number of degrees from a radial line from the cylinder axis, said angular offset allowing the mounting flange for the carburetor to be substantially parallel to the centerline of the engine, and the centerline of the exhaust port is offset a predetermined number of degrees from a radial line from the cylinder axis, said angular offset allowing the main body of the muffler to be substantially parallel to the centerline of the engine using an angled mounting flange. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which: 
         FIG. 1  shows a cross-sectional view of a single cylinder air cooled spark ignition rotary valve internal combustion engine. 
         FIG. 2  shows a part-sectional plan view of an embodiment of the engine for use with a manually held and operated horticultural machine such as a strimmer or hedge trimmer. 
         FIG. 3  shows a side view of part of the engine shown in  FIG. 2 . 
         FIG. 4  there is shown a sectional view of part of the engine of  FIG. 1  illustrating the air/fuel inlet tract. 
         FIG. 5  shows a cross-sectional view of part of a single cylinder air cooled spark ignition rotary valve internal combustion engine. 
         FIG. 6  is an enlarged schematic view of part of the rotary valve body and spark plug. 
         FIG. 7  shows a cross-sectional view of a single cylinder air cooled rotary valve internal combustion engine. 
         FIG. 8  is an enlarged schematic view of part of the rotary valve body and drive gear. 
         FIG. 9  shows a plan view of the rotary valve drive and driven gears. 
         FIG. 10  shows a cross-sectional view of a single cylinder air cooled rotary valve internal combustion engine. 
         FIG. 11  shows the cross-sectional view of the engine illustrating the dividing line between the cylinder housing and the crankcase. 
         FIG. 12  shows a cross-sectional view of a single cylinder air cooled rotary valve internal combustion engine. 
         FIG. 13  is an enlarged schematic view of part of the rotary valve body and drive gear. 
         FIG. 14  shows a plan view of the rotary valve drive and driven gears. 
         FIG. 15  shows an enlarged sectional view of the rotary valve and drive gear. 
         FIGS. 16 a -16 b    show, respectively, plan and side views of a wave spring. 
         FIG. 17  shows a view of the valve and a driven gear. 
         FIG. 18  shows a view of the valve and a ball bearing. 
         FIG. 19  shows the path of escaping combustion gases. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENT(S) OF THE INVENTION 
     Referring now to  FIG. 1 , there is shown a single cylinder air cooled engine. The engine has a cylinder housing containing the cylinder  2 . A piston  1  is connected in the conventional manner to a crankshaft  3  mounted for rotation in a crankcase  14  for reciprocation in the cylinder  2 . The upper part of the cylinder  2  is closed by a combustion chamber  4  in a combustion chamber housing. The combustion chamber housing has an inlet port  27  for the flow of inlet air/fuel mix into the combustion chamber and an exhaust port  28  for venting the exhaust gas out of the combustion chamber  4 , the gas flows being controlled by a rotary valve  5 . In this embodiment, the valve  5  is rotatable in a valve housing  8  in the combustion chamber housing about an axis  5   a  which is co-axial with the axis of the cylinder  2 . In other embodiments, the axis of rotation of the valve body is offset from the axis  5   a  of the cylinder  2 . 
     At its end remote from the combustion chamber  4 , the rotary valve  5  has a concentric drive shaft  6  carrying a single race ball bearing  7  which rotatably supports the valve  5  in the valve housing  8 . The valve driveshaft  6  is secured to a coaxial driven gear  9  which meshes with a drive gear  10  of a drive arrangement  11  through which the driven gear  9  and hence the rotary valve  5  is connected to the crankshaft  3 . The drive arrangement  11  includes a drive shaft  12  which is located in a channel or tube  17  in the cylinder housing and mounted for rotation in an upper bearing  18  adjacent the drive gear  10  and a lower bearing  13  adjacent the crankshaft  3 . The driveshaft  11  carries a bevel gear  15  which meshes with a corresponding bevel gear  16  secured on the crankshaft for rotation with the crankshaft  3 . Thus, the rotation of the crankshaft  3  and hence the piston movement is coordinated with the rotation of the rotary valve  5  so that the engine operates on the conventional four stroke cycle. To achieve this, the diameter of the driven gear  9  is twice that of the drive gear  10  so that the rotary valve  5  rotates at half engine speed. The rotary valve  5  comprises a generally cylindrical rotary valve body  5  rotatable about a rotary valve axis  5   a  with a close sliding fit in the bore in the valve housing  8 , the rotary valve  5  having a hollow valve body  19  having an interior volume  20  forming a part of the combustion chamber. The valve has a generally cylindrical body part comprising the valve body  19  itself which is slightly larger in diameter than the shaft  6 , which forms a shoulder  14  against which the inner race of the ball bearing  7  is located. The valve body  19  extends into the combustion chamber and has in its interior volume  20  which forms part of the combustion chamber  4  and which is subject to combustion gases at all stages of the combustion process. 
     The shaft  6  part of the rotary valve  5  is only slightly smaller in diameter than the valve body  19  to provide the shoulder  14 . The shaft is solid to provide a good path for conducting heat from the valve body  19  to the exterior. 
     The rotary valve body  19  has a port  21  which, during rotation of the valve, enables fluid communication successively to and from the interior volume of the valve and hence the combustion chamber via the inlet and exhaust ports in the valve housing. In this embodiment the port  21  is in the form of a recess formed in the lower peripheral edge  22  of the wall  23  of the valve body adjacent to the combustion chamber  4  the recess extending upwardly from this lower edge of the wall of the valve to form the port  21  in the side of the valve 
     Ignition is provided by a spark plug secured into a plug bore  25  formed in the valve housing  8  and extending into the valve bore. 
     Referring now to  FIG. 2 , there is shown a plan view of an engine intended for a horticultural machine such as a grass trimmer or a hedge trimmer which is manually held and operated by an operator where the engine is positioned to one side and/or behind the operator. In such machines, it is a requirement that the exhaust and exhaust muffler is located away from the operator and a carburetor for controlling the air/fuel mix through the inlet is located towards the operator. This is due to the heat of the exhaust and fact that the operator may be required to adjust the carburetor. A carburetor with airbox assembly  29  is attached to the inlet port  27 , and an exhaust muffler  30  is connected to the exhaust port  28 . Ideally, both the carburetor airbox assembly  29  and the exhaust muffler  30  should be substantially parallel to the centerline of the crankshaft the inlet and exhaust ports should be straight rather than curved to enable diecasting of the cylinder  2 . Straight ports and exhaust muffler/carburetor airbox positions simplify manufacture, neaten the appearance of the engine and make the engine easier to package within a typical horticultural machine. However, in order to provide the correct valve timing of the engine, which is determined by the position of the inlet and exhaust openings in the valve housing, this will require both the inlet ports and exhaust ports to be angled away from their ideal angle which is aligned with a radius running from the cylinder axis. 
     Moreover, as any restriction in flow in the inlet port due to a non-radial port angle will have a greater effect on engine power than the equivalent restriction in the exhaust port, the ports are angled such that the inlet port is closer to the ideal radial angle than the exhaust port. 
     In this embodiment, the top dead center timing point is angled towards the inlet side from the centerline of the crankshaft by 10°, in other words when the piston is at top dead center the centerline of the valve port is pointing 10 degrees towards the side of the engine nearest the operator. This enables the inlet port opening within the valve housing to be moved round 10 degrees towards the operator. This enables the inlet port  27  to be closer to the ideal radial angle than the exhaust port. The inlet port  27  is then angled a further 11° from the radial axis of the cylinder axis with the result that the mounting flange of the carburetor airbox assembly  29  is substantially parallel to the centerline of the engine 
     The centerline of the exhaust port  28  is offset 15° from the radial axis. The exhaust muffler has an angled flange  33  which mates with the exhaust port  28  so as to allow the main body of the exhaust muffler to be aligned substantially with the centerline  31  of the engine. 
     The exhaust muffler  13  is having a two-part shell construction of the muffler and a flange to mate with the angled exhaust port. This has the advantage of avoiding the use of a separate tube or pipe between the exhaust port and the muffler body. 
     As shown in up  FIG. 2 , the inlet side of the cylinder has a curved panel  34  which serves to guide cooling air around the rear of the cylinder to provide a cooling flow around the rear of the cylinder. 
     A closure plate  35  at the rear of the engine, shown in  FIG. 3 , forms a lower face of the cooling air flow passage, which forces the cooling air to exit from the rear of cowl, rather than short circuiting down into the cooling air intake. 
     Referring now to  FIG. 4  there is shown a sectional view of part of the engine of  FIG. 1  illustrating the air/fuel inlet tract. Part of the outer casing  29  of the engine comprises an air box  29   a , also known as a plenum chamber, which is divided by a wall  33  into an unfiltered air volume into which ambient air enters through inlet passages  31 , and a filtered air volume  32 . 
     The dividing wall  33  contains a filter  39  through which air from the unfiltered side passes into the filtered air side volume  32 . The inlet tract has a tuning pipe  35  secured to the carburetor. The tuning pipe  35  leads from the air inlet  36  of the carburetor  28  through a curved path passing through the unfiltered volume in the airbox, through the dividing wall and into the filtered air volume  32 . In one form, the tuning pipe  35  passes through the filter itself. The inlet  37  to the tuning pipe  35  is located in the filtered volume  32  and is flared outwardly to improve the flow of air into the tuning pipe  35  and hence into the engine. The curved path maximizes the length of the tuning pipe which increases the efficiency of the engine without causing a significant change to the overall size of the engine. 
     Although shown as a simple curve, it will be appreciated that the tuning pipe may have a more complex shape and may follow a serpentine path. 
     Referring now to  FIG. 5 , there is shown a single cylinder air cooled engine. The engine has a cylinder housing containing the cylinder  102 . A piston  101  is connected in the conventional manner to a crankshaft  103  mounted for rotation in a crankcase  114  for reciprocation in the cylinder  102 . The upper part of the cylinder  102  is closed by a combustion chamber  104  in a combustion chamber housing. The flow of inlet air/fuel mix and exhaust gas into and out of the combustion chamber  104  is controlled by a rotary valve  105 . In this embodiment, the valve  105  is rotatable in a valve housing  108  in the combustion chamber housing about an axis  105   a  which is co-axial with the axis of the cylinder  102 . In other embodiments, the axis of rotation of the valve body is offset from the axis  105   a  of the cylinder  102 . 
     At its end remote from the combustion chamber  104 , the rotary valve  105  has a concentric drive shaft  106  carrying a single race ball bearing  107  which rotatably supports the valve  105  in the valve housing  108 . The valve driveshaft  106  is secured to a coaxial driven gear  109  which meshes with a drive gear  110  of a drive arrangement  111  through which the driven gear  109  and hence the rotary valve  105  is connected to the crankshaft  103 . The drive arrangement  111  includes a drive shaft  112  which is located in a channel or tube  117  in the cylinder housing and mounted for rotation in an upper bearing  118  adjacent the drive gear  110  and a lower bearing  113  adjacent the crankshaft  103 . The driveshaft  112  carries a bevel gear  115  which meshes with a corresponding bevel gear  116  secured on the crankshaft for rotation with the crankshaft  103 . Thus, the rotation of the crankshaft  103  and hence the piston movement is coordinated with the rotation of the rotary valve  105  so that the engine operates on the conventional four stroke cycle. To achieve this, the diameter of the driven gear  109  is twice that of the drive gear  110  so that the rotary valve  105  rotates at half engine speed. 
     Referring now to  FIG. 6  also, there is shown more detail of the rotary valve  105  which comprises a generally cylindrical rotary valve body  105  rotatable about a rotary valve axis  105   a  with a close sliding fit in the bore in the valve housing  108 , the rotary valve  105  having a hollow valve body  119  having an interior volume  120  forming a part of the combustion chamber. The valve has a generally cylindrical body part comprising the valve body  119  itself which is slightly larger in diameter than the shaft  106 , which forms a shoulder  114  against which the inner race of the ball bearing  107  is located. The valve body  119  extends into the combustion chamber and has in its interior a volume  120  which forms part of the combustion chamber  104  and which is subject to combustion gases at all stages of the combustion process. The valve body  119  is rotatable in a bore in a valve housing  108  with a close sliding fit. The valve  105  and the valve housing  108  are formed of aluminum. 
     The shaft  106  part of the rotary valve  105  is only slightly smaller in diameter than the valve body  119  to provide the shoulder  114 . The shaft is solid to provide a good path for conducting heat from the valve body  119  to the exterior. 
     The rotary valve body  119  has a port  121  which, during rotation of the valve, enables fluid communication successively to and from the interior volume of the valve and hence the combustion chamber via inlet and exhaust ports in the valve housing. In this embodiment the port  121  is in the form of a recess formed in the lower peripheral edge  122  of the wall  123  of the valve body adjacent to the combustion chamber  104  the recess extending upwardly from this lower edge of the wall of the valve to form the port  121  in the side of the valve. 
     Ignition is provided by a spark plug  124  secured into a plug bore  125  formed in the valve housing  108  and extending into the valve bore. The axis of the plug bore  125  where it meets the valve body is axially below the centerline of the valve ports. In this way, the point of ignition is closer to the main mass of the incoming fuel mixture. 
     The plug bore is formed with a screw thread just long enough to secure the plug  124  in the plug bore  125 , the remaining part of the plug bore  125  between the end of the screw thread supporting the plug and the opening of the plug bore  125  into the combustion chamber comprises a spark plug bore volume  126  the bore of which is smooth to improve the flow of the incoming fuel charge and to speed the passage of the flame front from the spark plug into the main volume of the combustion chamber  104 . 
     The plug bore volume  126  is inevitably present since it is necessary to ensure that there is a gap between the body of the spark plug itself and the rotating valve. However, this does have the disadvantage in that it forms a pocket for exhaust gases after ignition which tends to delay the incoming charge/air mixture for the next cycle and also prevents the maximum possible amount of charge/air mix reaching the spark plug. To obviate this disadvantage a vent  127  is provided leading from the spark plug bore volume  126  to the main volume of the combustion chamber so that the spark plug bore volume  126  is in fluid communication with the main volume of the combustion chamber  104 . This vents the volume  126  prior to the next input of fresh fuel charge for the next cycle. As shown in  FIG. 6 , the vent  127  comprises a bore in the valve housing leading from the volume  126  into the combustion chamber  104 . In alternative constructions, the vent may be formed by a channel or groove formed in the valve housing  108 . 
     The embodiment of  FIGS. 5 and 6  shows a rotary valve internal combustion engine comprising: a piston connected to a crankshaft and that reciprocates reciprocatable in a cylinder, the cylinder having a combustion end, a combustion chamber being defined in part by the piston and the combustion end of the cylinder, a valve housing fixed at an outer portion of the combustion end of the cylinder and defining a bore and a rotary valve rotatable about a rotary valve axis in the bore in the valve housing, the rotary valve having a hollow valve body having an interior volume forming a part of the combustion chamber, wherein the interior volume of the hollow valve body is subjected to combustion gases throughout the combustion process, and further having in a wall part thereof a port giving, during rotation of the valve, fluid communication successively to and from the combustion chamber via inlet and exhaust ports in the valve housing, wherein the engine is a spark ignition engine, the spark plug being screwed into a plug bore in the valve housing adjacent the valve body, a spark plug bore volume being formed in the plug bore between the plug and the valve body, and a vent is located in the valve housing between the spark plug volume and the main cylinder volume, to vent combustion gases in the spark plug volume into the main cylinder volume. 
     In a preferred form, the vent comprises a bleed bore in the valve housing or a channel or groove in the valve housing. 
     Referring now to  FIG. 7 , there is shown a single cylinder air cooled engine. The engine has a cylinder housing containing the cylinder  202 . A piston  201  is connected in the conventional manner to a crankshaft  203  mounted for rotation in a crankcase  214  for reciprocation in the cylinder  202 . The upper part of the cylinder  202  is closed by a combustion chamber  204  in a combustion chamber housing. The flow of inlet air/fuel mix and exhaust gas into and out of the combustion chamber  204  is controlled by a rotary valve  205 . In this embodiment, the valve  205  is rotatable in a valve housing  208  in the combustion chamber housing about an axis  205   a  which is co-axial with the axis of the cylinder  202 . In other embodiments, the axis of rotation of the valve body is offset from the axis  205   a  of the cylinder  202 . 
     At its end remote from the combustion chamber  204 , the rotary valve  205  has a concentric drive shaft  206  carrying a single race ball bearing  207  which rotatably supports the valve  205  in the valve housing  208 . The valve driveshaft  206  is secured to a coaxial driven gear  209  which meshes with a drive gear  210  of a drive arrangement  211  through which the driven gear  209  and hence the rotary valve  205  is connected to the crankshaft  203 . The drive arrangement  211  includes a drive shaft  212  which is located in a channel or tube  217  in the cylinder housing and mounted for rotation in an upper bearing  218  adjacent the drive gear  210  and a lower bearing  213  adjacent the crankshaft  203 . The channel or tube  217  is cast into the cylinder housing. The channel or tube  217  is formed integrally with the cylinder housing, which may be formed by a casting process. The driveshaft  211  carries a bevel gear  215  which meshes with a corresponding bevel gear  216  secured on the crankshaft for rotation with the crankshaft  203 . Thus, the rotation of the crankshaft  203  and hence the piston movement is coordinated with the rotation of the rotary valve  205  so that the engine operates on the conventional four stroke cycle. To achieve this, the diameter of the driven gear  209  is twice that of the drive gear  210  so that the rotary valve  205  rotates at half engine speed. 
     Referring now to  FIG. 8  also, there is shown more detail of the rotary valve  205  which comprises a generally cylindrical rotary valve body  205  rotatable about a rotary valve axis  205   a  with a close sliding fit in the bore in the valve housing  208 , the rotary valve  205  having a hollow valve body having an interior volume  219  forming a part of the combustion chamber. The valve has a generally cylindrical body part comprising the valve body  219  itself which is slightly larger in diameter than the shaft  206 , which forms a shoulder  214  against which the inner race  228  of the ball bearing  207  is located. The valve body  219  extends into the combustion chamber and has in its interior a volume  220  which forms part of the combustion chamber  204  and which is subject to combustion gases at all stages of the combustion process. The valve body  219  is rotatable in a bore in a valve housing  208  with a close sliding fit. The valve  205  and the valve housing  208  are formed of aluminum. 
     The shaft  206  part of the rotary valve  205  is only slightly smaller in diameter than the valve body  219  to provide the shoulder  214 . The shaft is solid to provide a good path for conducting heat from the valve body  219  to the exterior. 
     The rotary valve body port  221 , during rotation of the valve, enables fluid communication successively to and from the interior volume of the valve and hence the combustion chamber via inlet and exhaust ports in the valve housing. In this embodiment the port  221  is in the form of a recess formed in the lower peripheral edge  222  of the wall  223  of the valve body adjacent to the combustion chamber  204  the recess extending upwardly from this lower edge of the wall of the valve to form the port  221  in the side of the valve. 
     Referring further to  FIG. 8  and  FIG. 9 , there is shown the connection between the driven gear  209  and the rotary valve  205 . The driven gear  209  is secured coaxially to the rotary valve  205  by means of a counter sunk screw  230 . The driven gear  209  has a concentric recess which accommodates the outer end of the shaft  206  and the recess has an annular ring  231  which is aligned with the inner race  228  of the ball bearing  207 . A small axial clearance  232  is provided between the annular ring  231  and the inner race  228  to allow a small degree of axial float which means that the valve  205  is not clamped to the inner race  228  and can therefore move slightly radially to accommodate any small concentric offset between the bearing  207  and the valve bore in which the rotary valve rotates. 
     The correct location of the rotary valve  205  relative to the valve gear, which determines the timing of the engine, is achieved by a timing pin  233 . The drive gear  210  has a timing mark  234  which indicates when the engine is at top dead center. The driven gear  209  connected to the rotary valve has a timing hole  235  adapted to receive the timing pin  233  and the driven gear has a corresponding timing hole through which the timing pin is inserted to secure the driven gear  209  to the rotary valve  205  to hold the rotary valve in its top dead center position. The counter sunk screw  230  is then inserted to secure the driven gear  209  to the rotary valve  205  in the correct timing position and the counter sunk head of the screw  230  engages the end of the timing pin  230  to secure this in position. Other means such as a washer on the screw  230  may be used to secure the timing pin  233  in position. 
     Because the rotary valve has a port  221  cut in its peripheral wall, it is recognized that the mass of the valve is not uniformly disposed about its periphery and this generates out of balance forces as the rotary valve rotates in practice. In a further embodiment of the engine, a counterbalance or counterbalancing mass is created on the valve train, particularly by adding material to the driven gear  209  or by removing material at an appropriate position in the driven gear  209 . 
     The embodiment of  FIGS. 7, 8 and 9  shows a rotary valve internal combustion engine comprising: a piston connected to a crankshaft and that reciprocates in a cylinder, the cylinder having a combustion end, a combustion chamber being defined in part by the piston and the combustion end of the cylinder, a valve housing fixed at an outer portion of the combustion end of the cylinder and defining a bore and a rotary valve rotatable about a rotary valve axis in the bore in the valve housing, the rotary valve having a hollow valve body having an interior volume forming a part of the combustion chamber, wherein the interior volume of the hollow valve body is subjected to combustion gases throughout the combustion process, and further having in a wall part thereof a port giving, during rotation of the valve, fluid communication successively to and from the combustion chamber via inlet and exhaust ports in the valve housing, a sealing function being carried out between the surface of the main body of the rotary valve and a contiguous surface of the bore in the valve housing, wherein the rotary valve is mounted in the valve housing for rotation by the crankshaft through a gear drive train, the drive train comprising a drive gear connected to the crankshaft through a bevel drive arrangement, the drive gear being meshed with a driven gear rotatable about the rotary valve axis, the driven gear being rotationally fast with the rotary valve and is located in the correct timing position relative to the rotary valve by a locating pin and is secured to the rotary valve by a securing device which also locks the locating pin in position. 
     Preferably, the driven gear has an out-of-balance mass to counter-balance an out of balance mass in the rotary valve body. 
     Referring now to  FIG. 10 , there is shown a single cylinder air cooled engine. The engine has a cylinder housing containing the cylinder  302 . A piston  301  is connected in the conventional manner to a crankshaft  303  mounted for rotation in a crankcase  314  for reciprocation in the cylinder  302 . The upper part of the cylinder  302  is closed by a combustion chamber  304  in a combustion chamber housing. The flow of inlet air/fuel mix and exhaust gas into and out of the combustion chamber  304  is controlled by a rotary valve  305 . In this embodiment, the valve  305  is rotatable in a valve housing  308  in the combustion chamber housing about an axis  305   a  which is co-axial with the axis of the cylinder  302 . In other embodiments, the axis of rotation of the valve body is offset from the axis  305   a  of the cylinder  302 . 
     At its end remote from the combustion chamber  304 , the rotary valve  305  has a concentric drive shaft  306  carrying a single race ball bearing  307  which rotatably supports the valve  305  in the valve housing  308 . The valve driveshaft  306  is secured to a coaxial driven gear  309  which meshes with a drive gear  310  of a drive arrangement  311  through which the driven gear  309  and hence the rotary valve  305  is connected to the crankshaft  303 . The drive arrangement  311  includes a drive shaft  312  which is located in a channel or tube  317  formed integrally in the cylinder housing and mounted for rotation in an upper bearing  318  adjacent the drive gear  310  and a lower bearing  313  mounted in the cylinder housing adjacent the crankshaft  303 . The channel or tube  317  is formed in the cylinder housing, which may be formed by a casting process. The driveshaft  312  carries a bevel gear  315  which meshes with a corresponding bevel gear  316  secured on the crankshaft for rotation with the crankshaft  303 . Thus, the rotation of the crankshaft  303  and hence the piston movement is coordinated with the rotation of the rotary valve  305  so that the engine operates on the conventional four stroke cycle. To achieve this, the diameter of the driven gear  309  is twice that of the drive gear  310  so that the rotary valve  305  rotates at half engine speed. 
     Referring now to  FIG. 11  also, where like references denote like parts, the crankcase  314  has a bore  336  which has a diameter slightly larger than the outer diameter of the bevel gear  315  so that when the cylinder housing carrying the drive arrangement is offered up to the crankcase, the bevel gear  315  can enter the crankcase to mesh with the associated bevel gear  316  which is secured to the crankshaft  314 . The upper surface of the crankcase  314  is arranged to mate with the lower surface of the cylinder housing assembly when this is lowered onto the crankcase. The lower bearing  313  is secured in a counter bore  337  formed in the cylinder housing so as to be concentric with the crankcase bore  336  a slight axial clearance is provided between the outer race of the lower bearing  313  and the end of the counter bore  337  within which the bearing sits to ensure that the cylinder housing assembly, including the drive arrangement  311  can mate correctly with the top face  314   a  of the crankcase  314 . 
     In this way, the assembly of the cylinder housing including the rotary valve  305  and the main part of the drive gear arrangement  311  is formed as a sub assembly for mating with the crankcase  314 . For final assembly, the piston which is carried by the crankcase  314  is fed into the piston bore in the cylinder housing  302  and at the same time the bevel gear  315  is fed through the crankcase bore  336  to complete the engine assembly. 
     The embodiment of  FIGS. 10 and 11  shows a rotary valve internal combustion engine comprising: a crankcase containing a crankshaft, a piston being connected to the crankshaft and reciprocatable in a cylinder in a cylinder housing connected to the crankcase, the cylinder having a combustion end, a combustion chamber being defined in part by the piston and the combustion end of the cylinder, a valve housing at an outer portion of the combustion end of the cylinder and defining a bore and a rotary valve rotatable about a rotary valve axis in the bore in the valve housing, the rotary valve having a hollow valve body having an interior volume forming a part of the combustion chamber, wherein the interior volume of the hollow valve body is subjected to combustion gases throughout the combustion process, and further having in a wall part thereof a port giving, during rotation of the valve, fluid communication successively to and from the combustion chamber via inlet and exhaust ports in the valve housing, wherein the rotary valve is mounted on a bearing secured in the valve housing for rotation by the crankshaft through a gear drive train, the drive train comprising a drive gear connected to the crankshaft through a bevel drive arrangement, the drive gear being meshed with a driven gear rotatable about the rotary valve axis, the driven gear being secured for rotation with the rotary valve, the bevel drive arrangement comprising a bevel gear rotationally fast on the crankshaft meshed with a bevel gear secured at one end of a drive shaft mounted for rotation in the cylinder housing, the drive shaft carrying the drive gear on its end opposite the bevel gear, wherein a mating surface of the cylinder housing is adapted to mate with a corresponding surface on the crankcase, the crankcase incorporating an opening through which, on assembly, the bevel gear on the driveshaft enters the crankcase to engage with the bevel gear on the crankshaft. 
     In this embodiment the drive shaft maybe located in a passage formed in the cylinder housing, and the drive shaft maybe located rotationally in bearings mounted in the cylinder housing. 
     Referring now to  FIG. 12 , there is shown a single cylinder air cooled engine. The engine has a cylinder housing containing the cylinder  402 . A piston  401  is connected in the conventional manner to a crankshaft  403  mounted for rotation in a crankcase  414  for reciprocation in the cylinder  402 . The upper part of the cylinder  402  is closed by a combustion chamber  404  in a combustion chamber housing. The flow of inlet air/fuel mix and exhaust gas into and out of the combustion chamber  404  is controlled by a rotary valve  405 . In this embodiment, the valve  405  is rotatable in a valve housing  408  in the combustion chamber housing about an axis  405   a  which is co-axial with the axis of the cylinder  402 . In other embodiments, the axis of rotation of the valve body is offset from the axis  405   a  of the cylinder  402 . 
     At its end remote from the combustion chamber  404 , the rotary valve  405  has a concentric drive shaft  406  carrying a single race ball bearing  407  which rotatably supports the valve  405  in the valve housing  408 . The valve driveshaft  406  is secured to a coaxial driven gear  409  which meshes with a drive gear  410  of a drive arrangement  411  through which the driven gear  409  and hence the rotary valve  405  is connected to the crankshaft  403 . The drive arrangement  411  includes a drive shaft  412  which is located in a channel or tube  417  in the cylinder housing and mounted for rotation in an upper bearing  418  adjacent the drive gear  410  and a lower bearing  413  adjacent the crankshaft  403 . The channel or tube  417  is cast into the cylinder housing. The channel or tube  417  is formed integrally with the cylinder housing, which may be formed by a casting process. The driveshaft  411  carries a bevel gear  415  which meshes with a corresponding bevel gear  416  secured on the crankshaft for rotation with the crankshaft  403 . Thus, the rotation of the crankshaft  403  and hence the piston movement is coordinated with the rotation of the rotary valve  405  so that the engine operates on the conventional four stroke cycle. To achieve this, the diameter of the driven gear  409  is twice that of the drive gear  410  so that the rotary valve  405  rotates at half engine speed. 
     Referring additionally to  FIGS. 14 and 15 , there is shown more detail of the rotary valve  405  which comprises a generally cylindrical rotary valve body  405  rotatable about a rotary valve axis  405   a  with a close sliding fit in the bore in the valve housing  408 , the rotary valve  405  having a hollow valve body  419  having an interior volume  420  forming a part of the combustion chamber. The valve has a generally cylindrical body part comprising the valve body  419  itself which is slightly larger in diameter than the shaft  406 , which forms a shoulder  414  against which the inner race  428  of the ball bearing  407  is located. The valve body  419  extends into the combustion chamber and has in its interior a volume  420  which forms part of the combustion chamber  404  and which is subject to combustion gases at all stages of the combustion process. The valve body  419  is rotatable in a bore in a valve housing  408  with a close sliding fit. The valve  405  and the valve housing  8  are formed of aluminum. 
     The shaft  406  part of the rotary valve  405  is only slightly smaller in diameter than the valve body  419  to provide the shoulder  414 . The shaft is solid to provide a good path for conducting heat from the valve body  416  to the exterior 
     The rotary valve body port  421 , during rotation of the valve, enables fluid communication successively to and from the interior volume of the valve and hence the combustion chamber via inlet and exhaust ports in the valve housing. In this embodiment the port  421  is in the form of a recess formed in the lower peripheral edge  422  of the wall  423  of the valve body adjacent to the combustion chamber  404  the recess extending upwardly from this lower edge of the wall of the valve to form the port  421  in the side of the valve. 
     Referring further to  FIG. 13  and  FIG. 14 , there is shown the connection between the driven gear  409  and the rotary valve  405 . The driven gear  409  is secured coaxially to the rotary valve  405  by means of a countersunk screw  430 . The driven gear  409  has a concentric recess which accommodates the outer end of the shaft  406  and the recess has an annular rib  431  which is aligned with the inner race  428  of the ball bearing  407 . An axial clearance  432  is provided between the annular ring  431  and the inner race  428  to allow a small degree of axial float which means that the valve  405  is not clamped to the inner race  428  and can therefore move slightly radially to accommodate any small concentric offset between the bearing  407  and the valve bore in which the rotary valve rotates. 
     In operation, the forces generated by the combustion gases tend to move the valve body axially relative to the valve housing. To prevent hammering of the shoulder  414  against the inner race  428  of the bearing  407  caused by axial movement of the valve body  416  relative to the inner race  428  of the bearing, which would otherwise occur during every combustion cycle, a resilient element in the form of a wave spring  424  biases driven gear  409  to urge the shoulder  414  of the valve body  416  upwards into contact with the lower face of the inner race  428 , as shown in  FIG. 15 , with a sufficient force to prevent hammering or chattering between the two components during operation but not too powerful to prevent the slight radial movement of the valve body necessary to accommodate slight misalignment between the valve and the valve housing which will occur in practice as a result of slight differences caused by manufacturing tolerances of the components. 
     As shown in  FIGS. 16 a -16 b   , the wave spring consists of a generally annular plate-like body. Throughout its annular length, the wave spring  424  has a plurality of wave forms curving the spring out of a radial plane as shown particularly in  FIGS. 5 b  and 5 c   . In this embodiment the wave spring is formed out of a spring steel. The spring element could be formed of other materials, designs or profiles, providing they meet the objective of being able to provide the resilient damping effect required and being able to cope with the harsh environmental conditions in the engine. 
       FIG. 17  illustrates a schematic perspective view of the rotary valve  405  and the driven gear  409  with the wave spring  424  in position between the inner race  428  of the bearing and the driven gear  409 .  FIG. 18  illustrates a similar schematic perspective view of the rotary valve  405  and the driven gear  409  with the single race ball bearing  407  in position. As shown also in  FIG. 19 , the space between the inner and outer races  428  and  429  of the bearing  407  is closed at its lower edge by a metal seal  426 . 
     It has been found that in practice some combustion gases escape between the interface between the rotary valve body  405  and the valve housing  408 . These waste combustion gases can pass through the bearing  407  past the balls  425  and into the chamber containing the driven gear and the wave spring causing a buildup of carbon which adversely affects the performance and durability of the valve and the high temperature and corrosive action of the hot gases can cause premature failure of the wave spring. To prevent, or at least minimize, the combustion gases leaking across the bearing  407 , the seal  426  closes the gap between the inner and outer races  428  and  429  of the bearing. The seal is formed of a metal to cope with the harsh environmental conditions. Furthermore, the seal limits the escaping combustion gases from damaging or destroying the resilient spring. 
     Referring now to  FIG. 19  there is shown an enlarged view of the valve and bearing arrangement illustrating an improvement in which a vent passage  437  is provided from the narrow annular space  428  between the annular metal seal  426  and the valve housing leading into the inlet port as illustrated by the black arrows  440 . This has the advantage that the escaping combustion gases are fed back into the inlet port  439  where they are recycled through the engine to improve the engine emissions performance. 
     Because the rotary valve has a port  421  cut in its peripheral wall, it is recognized that the mass of the valve is not uniformly disposed about its periphery and this generates out of balance forces as the rotary valve rotates in practice. In a further embodiment of the engine, a counterbalance or counterbalancing mass is created on the valve train, particularly by adding material to the driven gear  409  or by removing material at an appropriate position in the driven gear  409 . The embodiment described is a single cylinder air cooled engine but it will be understood that the invention is equally applicable to multicylinder and/or watercooled engines. 
     The embodiment of  FIGS. 12 to 19  show a rotary valve internal combustion engine comprising: a piston connected to a crankshaft and that reciprocates in a cylinder, the cylinder having a combustion end, a combustion chamber being defined in part by the piston and the combustion end of the cylinder, a valve housing fixed at an outer portion of the combustion end of the cylinder and defining a bore and a rotary valve rotatable about a rotary valve axis in the bore in the valve housing, the rotary valve having a hollow valve body having an interior volume forming a part of the combustion chamber, wherein the interior volume of the hollow valve body is subjected to combustion gases throughout the combustion process, and further having in a wall part thereof a port giving, during rotation of the valve, fluid communication successively to and from the combustion chamber via inlet and exhaust ports in the valve housing, a sealing function being carried out between the surface of the main body of the rotary valve and a contiguous surface of the bore in the valve housing, wherein the rotary valve is mounted in the valve housing for rotation by the crankshaft through a gear drive train, the drive train including a driven gear rotatable about the rotary valve axis, the driven gear being rotationally fast with the rotary valve, a bearing being provided between the driven gear and the valve body, the bearing comprising a single bearing, wherein the space between the inner and outer races of the bearing is closed by a seal to substantially limit combustion gases passing through the bearing. 
     Preferably, the seal is on the valve side of the single race ball bearing thereby shielding the ball bearing from the combustion gases, and the seal maybe formed of metal. 
     In a further development, a vent passage maybe provided to vent combustion gases from between the space between the valve body and the valve housing back into the inlet port, the vent consisting of either a drilled bore or a groove in the valve bore face. 
     In a further development as an embodiment, a predetermined axial gap Is provided between the driven gear and the bearing in which the rotary valve is mounted, and the driven gear has an annular rib aligned with the inner race of the bearing, the axial gap being formed between the annular rib and the inner race of the bearing. 
     In this embodiment, the seal preferably comprises a resilient annular element, being co-axial with the rotary valve and may be a wave spring. 
     It is to be understood that the features of the various embodiments described herein may be combined with each other, unless specifically noted. 
     Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present invention. This application is intended to cover any adaptions or variations of the specific embodiments discussed herein. Therefore, it is intended that this invention be limited only by the claims and the equivalents thereof.