Patent Publication Number: US-9903239-B2

Title: Engine with rotary valve apparatus

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to internal combustion engines, and more particularly to engines using rotary valves. 
     Internal combustion engines are well known and are used in various applications. For example, internal combustion engines are used in automobiles, farm equipment, lawn mowers, and watercraft. Internal combustion engines also come in various sizes and configurations, such as two stroke or four stroke and ignition or compression. 
     Typically, internal combustion engines ( FIG. 1 ) include a multitude of moving parts, for example, they include intake and exhaust valves, rocker arms, springs, camshafts, connecting rods, pistons, and a crankshaft. One of the problems with having a multitude of moving parts is that the risk of failure increases (particularly in the valve train) and efficiency decreases due to frictional losses. Special lubricants and coatings may be used to reduce friction and certain alloys may be used to prevent failure; however, even with these enhancements, the risk of failure and the frictional losses remain high. 
     Accordingly, there remains a need for a valvetrain for an internal combustion engine with low friction, good reliability, and a small number of parts. 
     BRIEF SUMMARY OF THE INVENTION 
     This need is addressed by the present invention, which provides a valvetrain incorporating a pair of rotating valve shafts with apertures therein that function to open and close intake and exhaust ports of an internal combustion engine. 
     According to one aspect of the invention, an engine includes: a block defining a cylinder bore; a crankshaft mounted for rotation in the block; a piston disposed in the cylinder bore; a connecting rod interconnecting the piston to the crankshaft; and a cylinder head coupled to the block and including: a combustion chamber aligned with the cylinder bore and having an intake opening and an exhaust opening communicating therewith; an intake port; an exhaust port; a rotatable inlet valve barrel disposed between the intake opening and the intake port and having a first diameter; and a rotatable exhaust valve barrel disposed between the exhaust opening and the exhaust port and having a second diameter different from the first diameter. 
     According to another aspect of the invention, the first diameter is greater than the second diameter; 
     According to another aspect of the invention, a ratio of the first diameter to the second diameter is about 4:1 to about 1:1. 
     According to another aspect of the invention, the inlet and exhaust valve barrels are interconnected with the crankshaft, so as to rotate at one-quarter of a rotational speed of the crankshaft 
     According to another aspect of the invention, the engine further includes: a crank pulley connected to the crankshaft; an idler pulley connected to the crankshaft by a first drive belt at a 2:1 drive ratio; a drive assembly including a pulley connected to each valve barrel; and a second drive belt connecting the drive assemblies to the idler pulley at a 2:1 drive ratio. 
     According to another aspect of the invention, the engine includes at least one axial bank of cylinders, each bank including an inlet valve shaft comprising multiple inlet valve barrels and an outlet valve shaft comprising multiple outlet valve barrels, each shaft coupled to a drive assembly including a pulley. 
     According to another aspect of the invention, the drive assembly includes a pulley and a coupler. 
     According to another aspect of the invention, a relative angular position of the pulley and the coupler is variable. 
     According to another aspect of the invention, a relative angular position of the pulley and the coupler is variable. 
     According to another aspect of the invention, the pulley is attached to the coupler with bolts passing through slots in the pulley and engaging the coupler. 
     According to another aspect of the invention, the pulley includes a scale showing the relative angular position of the pulley and the coupler. 
     According to another aspect of the invention, the drive assembly comprises an active adjustment mechanism operable to change the angular relationship of the valve shaft to the pulley. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention may be best understood by reference to the following description taken in conjunction with the accompanying drawing figures in which: 
         FIG. 1  is a schematic cross-sectional view of a prior art internal combustion engine; 
         FIG. 2  is a schematic perspective of an internal combustion engine constructed in accordance with an aspect of the present invention; 
         FIG. 3  is a cross-sectional view of the internal combustion engine of  FIG. 1 ; 
         FIG. 4  is an exploded perspective view of a cylinder head assembly of the engine shown in  FIG. 2 ; 
         FIG. 5  is a bottom plan view of a lower section of the cylinder head assembly of  FIG. 4 ; 
         FIG. 6  is a bottom plan view of a upper section of the cylinder head assembly of  FIG. 4 ; 
         FIG. 7  is an exploded perspective view of a valve shaft assembly; 
         FIG. 8  is a front elevational view of a valve barrel; 
         FIG. 9  is a rear elevational view of a valve barrel; 
         FIG. 10  is a cross-sectional view of a portion of the cylinder head assembly of  FIG. 4 , showing a valve shaft assembly installed therein; 
         FIG. 11  is a top plan view of a cylinder head assembly shown in  FIG. 4 , with valve shafts installed therein; 
         FIG. 12  is an exploded perspective view of a portion of the cylinder head assembly shown in  FIG. 4 , showing a first embodiment thereof; 
         FIG. 13  is a view taken along lines  13 - 13  of  FIG. 12 ; 
         FIG. 14  is a top plan view of a seal constructed in accordance with an aspect of the present invention; 
         FIG. 15  is a side elevation view of the seal of  FIG. 14 ; 
         FIG. 16  is a front elevation view of the seal of  FIG. 14 ; 
         FIG. 17  is a side elevation view of a seal spring constructed in accordance with an aspect of the present invention; 
         FIG. 18  is a front elevation view of the seal shown in  FIG. 17 ; 
         FIG. 19  is an exploded perspective view of a portion of the cylinder head assembly shown in  FIG. 4  showing a second embodiment thereof; 
         FIG. 20  is a view taken along lines  20 - 20  of  FIG. 19 ; 
         FIG. 21  is a top plan view of a seal shoe constructed in accordance with an aspect of the present invention; 
         FIG. 22  is a view taken along lines  22 - 22  of  FIG. 21 ; 
         FIG. 23  is a front elevational view of a drive assembly; 
         FIG. 24  is a rear elevational view of a drive assembly; 
         FIG. 25  is a schematic view of a portion of the engine in operation, during an intake stroke; 
         FIG. 26  is a schematic view of a portion of the engine in operation, during a compression stroke; 
         FIG. 27  is a schematic view of a portion of the engine in operation, during a power stroke; and 
         FIG. 28  is a schematic view of a portion of the engine in operation, during an exhaust stroke. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to the drawings wherein identical reference numerals denote the same elements throughout the various views,  FIGS. 2 and 3  illustrate an exemplary internal combustion engine  10  constructed according to an aspect of the present invention. 
     The illustrated example is an eight-cylinder engine  10  of vee configuration, commonly referred to as a “V-8”, with two banks of four cylinders set 90 degrees to each other. However, it will be understood that the principles of the present invention are applicable to any internal combustion engine, for example engines running various cycles such as Otto or Diesel cycles, or similar machine requiring valves to open and close fluid flow ports. 
     The engine includes a block  12  which serves as a structural support and mounting point for the other components of the engine  10 . Generally cylindrical cylinder bores  14  are formed within the block  12 . As noted above the cylinder bores  14  are arranged in two longitudinal cylinder banks  16  of four cylinder bores  14  each. A crankshaft  18  having offset crankpins  20  is mounted in the block  12  for rotation in suitable bearings. A piston  22  is disposed in each cylinder bore  14 , and each piston  22  is connected to one of the crankpins  20  by a piston rod  24 . The crankshaft  18 , piston rods  24 , and pistons  22  collectively define a rotating assembly  26 . In operation, gas pressure in the cylinder bores  14  causes linear movement of the pistons  22 , and the rotating assembly  26  is operable in a known manner to convert linear movement of the pistons to rotation of the crankshaft. 
     The engine includes one cylinder head assembly  28  attached to each cylinder bank  16 . The cylinder head assembly  28  has a generally concave combustion chamber  30  formed therein corresponding to and aligned with each cylinder bore  14 . Collectively, each cylinder bore  14  and the corresponding combustion chamber  30  defines a cylinder  32 . 
     The cylinder head assembly  28  has a plurality of intake ports  34  formed therein; each intake port  34  extends from one of the combustion chambers  30  to an intake plane  36  at an exterior surface of the cylinder head assembly  28 . As will be described in detail below, an intake valve barrel  38  is disposed across each intake port  34  and includes an intake aperture  40  passing therethrough. The intake port  34 , intake valve barrel  38 , and intake aperture  40  are arranged such that in a first angular orientation of the intake valve barrel  38 , fluid flow is permitted between the intake plane  36  and the combustion chamber  30 , and at a second angular orientation of the intake valve barrel  38 , fluid flow is blocked between the intake plane  36  and the combustion chamber  30 . 
     The cylinder head assembly  28  also includes a plurality of exhaust ports  42  formed therein; each exhaust port  42  extends from one of the combustion chambers  30  to an exhaust plane  44  at an exterior surface of the cylinder head assembly  28 . As will be described in detail below, an exhaust valve barrel  46  is disposed across each exhaust port  42  and includes an exhaust aperture  48  passing therethrough. The exhaust port, exhaust valve barrel  46 , and exhaust aperture  48  are arranged such that in a first angular orientation of the exhaust valve barrel  46 , fluid flow is permitted between the exhaust plane  44  and the combustion chamber  30 , and at a second angular orientation of the exhaust valve barrel  46 , fluid flow is blocked between the exhaust plane  44  and the combustion chamber  30 . 
     The engine  10  includes a fuel delivery system  50  which is operable to receive an incoming airflow, meter a hydrocarbon fuel such as gasoline into the airflow to generate a combustible intake mixture, and deliver the intake mixture to the cylinders  32 . 
     The fuel delivery system  50  may be continuous flow or intermittent flow, and the fuel injection point may be at the individual cylinders  32  or at an upstream location. Optionally the fuel injection point may be within the cylinders  32 , a configuration commonly referred to as “direct injection”, in which case the intake ports  34  deliver only air to the cylinders  32 . Known types of fuel delivery systems include carburetors, mechanical fuel injection systems, and electronic fuel injection systems. The specific example illustrated is an electronic fuel injection system with one intake runner  52  connected to each intake port  34 . 
     The engine  10  includes an ignition system comprising one or more spark plugs  54  mounted in each combustion chamber  30 , to ignite the intake mixture. An appropriate ignition power source is provided, such as a conventional Kettering ignition system with a coil and distributor, or a direct ignition system with a trigger module and multiple coils. The ignition power source is connected to the spark plugs  54 , for example with leads  56 . 
       FIG. 4  is an exploded view of one of the cylinder head assemblies  28 . The cylinder head assembly  28  includes one or more stationary components that are configured to be mounted to the cylinder bank  16  and to enclose the operating parts. The cylinder head assembly  28  includes a cylinder head  57 . In the illustrated example, the cylinder head  57  is made up of a lower section  58  attached to an upper section  60  with bolts. Alternatively, the cylinder head  57  could be made from a single block. 
     The lower section  58  is a block-like element which may be formed by casting or machining from billet. It includes an exterior surface  62  which incorporates the combustion chambers  30  (see  FIG. 5 ), and an opposed interior surface  64 . Adjacent the interior surface  64 , the lower section  58  has a plurality of semi-cylindrical intake barrel recesses  66  formed therein, arranged in a longitudinal line. Each intake barrel recess  66  communicates with an intake opening  68 . A plurality of semi-cylindrical bearing recesses  70  alternate with the intake barrel recesses. The lower section  58  also has a plurality of semi-cylindrical exhaust barrel recesses  72  formed therein, arranged in a longitudinal line. Each exhaust barrel recess  72  communicates with an exhaust opening  74  (see FIG.  3 ). A plurality of semi-cylindrical bearing recesses  70  alternate with the exhaust barrel recesses  72 . 
     The upper section  60  is also a block-like element which may be formed by casting or machining from billet. It includes an exterior surface  76 , and an opposed interior surface  78  which mates with the interior surface  64  of the lower section  58 . The intake ports  34  described above are formed as part of the upper section  60 . Adjacent the interior surface  78 , the upper section  60  has a plurality of semi-cylindrical intake barrel recesses  69  formed therein, arranged in a longitudinal line (see  FIG. 6 ). Each intake barrel recess  69  communicates with one of the intake ports  34 . A plurality of semi-cylindrical bearing recesses  70  alternate with the intake barrel recesses  69 . The lower section  58  also has a plurality of semi-cylindrical exhaust barrel recesses  71  formed therein, arranged in a longitudinal line. Each exhaust barrel recess  71  communicates with one of the exhaust ports  42 . A plurality of semi-cylindrical bearing recesses  70  alternate with the exhaust barrel recesses  71 . 
     Provisions made be incorporated for liquid cooling all or part of the cylinder head  57 . In the illustrated example, the upper section  60  includes a hollow interior chamber (not shown) disposed between the interior surface  78  and the exterior surface  76 . A series of coolant inlet holes  77  ( FIG. 6 ) are formed in the interior surface  78  and communicate with the interior chamber. A coolant outlet  79  (see  FIG. 4 ) is formed in the exterior surface  76 . In operation, a suitable liquid coolant, such as water or water mixed with an antifreeze agent, is supplied to the coolant inlet holes  77  through matching coolant transfer holes  81  in the interior surface  64  of the lower section  58 . The coolant circulates through the interior chamber, absorbing heat, and is then passed out through the coolant outlet  79 . It may then be cooled, for example using a conventional radiator (not shown), and recirculated for reuse. 
     The lower section  58  and upper section  60  receive an intake valve shaft  80 A and an exhaust valve shaft  80 B. The valve shafts  80 A and  80 B are generally similar in construction to each other, with the intake valve shaft  80  being slightly larger in scale. The construction of the intake valve shaft  80 A will be described in detail, with the understanding that the details are applicable to both of the valve shafts  80 A,  80 B. 
     It is also noted that, while the illustrated example includes inlet and exhaust valve shafts  80 A and  80 B, it should be appreciated that the modular valve shaft construction described herein could also be applied to a single valve shaft having both intake and exhaust valve barrels, or to valve barrels having both intake and exhaust apertures therein. 
     Referring to  FIG. 7 , The intake valve shaft  80 A includes a plurality of intake valve barrels  38  laid out along an axis  82 . Each intake valve barrel  38  is a generally cylindrical element with an annular peripheral surface  84  extending between forward and aft end faces  86 ,  88 . An intake aperture  90  extends transversely through the intake valve barrel  38 , communicating with the peripheral surface  84  on opposite sides. The cross-sectional flow area of the aperture  90  is constant over its length. In the illustrated example the intake aperture  90  has a “racetrack” cross-sectional shape, with two parallel sides connected by two semicircular ends. Other cross-sectional shapes may be used. 
     The lateral dimension of the intake aperture  90  (perpendicular to the axis  82 ), the diameter of the intake valve barrel  38 , and the rotational speed of the intake valve shaft  80 A relative to the crankshaft speed all effect the valve open time or “duration”, and these effects are inter-related. This is also true for the exhaust valve barrels  46 . These variables may be manipulated in order to adapt the intake valve shaft  80 A and/or exhaust valve shaft  80 B to suit a particular application. For example, the intake valve barrels  38  could be a different diameter than the exhaust valve barrels  46 . In one non-limiting example, the ratio of the diameter of the intake valve barrels  38  to the diameter of the exhaust valve barrels  46  could be about 1:1 to about 4:1. 
     The intake valve barrel  38  may be made from a rigid, wear-resistant material such as a metal alloy or ceramic. A wear coating such as ceramic or carbide may be applied to all or part of the intake valve barrel  38 , particularly the peripheral surface  84 , to improve its wear properties. 
     Optionally, longitudinal holes  92  or other openings may be formed in the intake valve barrel  38  extending between the forward and aft end faces  86 ,  88 . These holes  92  may be used to reduce the mass of the intake valve barrel  38 , for balancing purposes, and/or to provide a cooling air flow. 
     A cylindrical forward stub shaft  94  extends from the forward end face  86 , and a cylindrical aft stub shaft  96  extends from the aft end face  88 . 
     The stub shafts  94 ,  96  may include mating mechanical alignment features to transfer torque between two adjacent intake valve barrels  38  and to maintain a specific angular relationship therebetween. For example, the forward stub shaft  94  may include a ring of axial pins  98  ( FIG. 8 ), and the aft stub shaft may include a ring of corresponding drive holes  100  ( FIG. 9 ). The intake valve shaft  80 A can be “built up” in a modular fashion by inserting the axial pins  98  of each intake valve barrel  38  into the drive holes  100  of the adjacent intake valve barrel  38 . It will be understood that the intake aperture  90  of each intake valve barrel  38  must have a specific angular orientation which is dependent on the cylinder firing sequence of the engine  10 . The mechanical alignment feature described above may be configured so that any intake valve barrel  38  may be used in any location within the intake valve shaft  80 A, that is, the mechanical alignment feature may accommodate multiple angular alignments, or alternatively the mechanical alignment feature may be configured to produce only a single angular alignment, in which case each intake valve barrel  38  would need to be placed in a specific location within the intake valve shaft  80 A. 
     Optionally, the valve stub shafts  94 ,  96  could be connected to each other using fasteners, a mechanical interlock, or a bonding method such as welding or structural adhesives. Also, alternatively, the valve shaft  80  could be manufactured as a single integral component instead of being built up from individual intake valve barrels  38 . 
     As seen in  FIGS. 7 and 10 , the intake valve shaft  80 A is provided with a plurality of bearings  102 . In the illustrated example, the bearings are simple cylinders. They may be configured as plain bearings or bushings, and made of a self-lubricating material, or they may be configured as hydrodynamic bearings and provided with a pressurized oil supply. Alternatively, rolling element bearings could be used. The bearings  102  may be installed over the stub shafts  94 ,  96  when the intake valve shaft  38  is built up, and then installed into the bearing recesses  70  of the lower section  58  and the upper section  60 . Alternatively, the bearings  102  could be provided as split shells instead of fully annular components. 
     When assembled, the intake valve shaft  80 A and exhaust valve shaft  80 B are received in the bearing recesses  70  and barrel recesses  66 ,  72 , and are clamped between the lower section  58  and the upper section  60 , which may be coupled together using conventional fasteners (not shown). The intake and exhaust valve shafts  80 A,  80 B are then free to rotate within the cylinder head assembly  28 .  FIG. 11  shows the valve shafts  80 A,  80 B installed in the lower section  58 . 
     As noted above, each intake barrel recess  66  communicates with an intake opening  68 , and each exhaust barrel recess  72  communicates with an exhaust opening  74 . Each of these openings incorporates a sealing assembly. A single sealing assembly at one of the intake openings  68  will be described in general with reference to  FIGS. 12-18 , with the understanding that this description is applicable to all of the sealing assemblies, both intake and exhaust. 
     A seal slot  104  is formed around the periphery of the intake opening  68 . A seal  106  is received in the seal slot  104  and operates to reduce or prevent leakage between the cylinder  32  and the intake valve barrel  38 . 
     The seal  106  is shown in more detail in  FIGS. 14-16 . The seal  106  is generally in the shape of an elongated ring and includes a sealing face  108 , an opposed back face  110 , an inner peripheral face  112 , and an outer peripheral face  114 . in plan view the seal has a racetrack shape, with two long sides connected by semicircular ends. A width “W” of the seal, measured between the inner and outer peripheral faces  112  and  114 , is selected to be slightly less than a corresponding width of the seal slot  104  so as to allow the seal to slide relative to the seal slot  104 . As seen in  FIG. 16 , the sealing face  108  has a concave curvature which matches the curvature of the peripheral surface  84  of the intake valve barrel  38 . The thickness “T” of the seal  106 , measured between the sealing face  108  and the back face  110 , is constant along the sides of the racetrack shape, tapering to a smaller thickness at the semicircular ends. 
     The seal  106  may be made from a rigid, wear-resistant material such as a metal alloy or ceramic. A wear coating such as ceramic or carbide may be applied to all or part of the seal  106  to improve its wear properties. 
     A pair of seal springs  116  are disposed in the seal slot  104  underneath the seal  106 . As shown in  FIGS. 17 and 18 , the seal springs  116  are elongated and may be made from a pair of strips  118  of spring steel, each having one or more waves or undulations  120  formed therein. The strips  118  may be attached to each other by brazing or other suitable bonding method. As seen in  FIG. 13 , the seal springs  116  urge the seal  106  outwards relative to the seal slot  104  and into contact with the peripheral surface  84  of the intake valve barrel  38 . The seal springs  116  are intended to provide a preload and maintain the seal  106  in the correct assembled position, but do not provide the primary energizing force of the seal  106 . 
     As further seen in  FIG. 13 , the intake opening  68  has one or more small gas ports  121  formed therein that communicate with the seal slot  104 . In operation, rising gas pressure in the cylinder  32  passes into the gas ports  121  and impinges the back face  110  of the seal  106 , providing an energizing force which presses the sealing face  108  of the seal  106  into contact with the peripheral surface  84  of the intake valve barrel  38 . This in turn resists fluid leakage between the sealing face  108  and the peripheral surface  84 . As pressure in the cylinder  32  drops off, the force acting on the seal  106  drops off as well. This provides a “timed” sealing effect in which large forces on the seal  106  are applied only when needed, and also significantly reduces frictional sliding forces and wear between the seal  106  and the intake valve barrel  38 . 
     The seal slot  104  described above may be machined directly into the lower section  58 . However, optionally, as seen in  FIGS. 19-22 , the lower section  58  may have a pocket  122  formed therein around the intake opening  68 . A shoe  124  is received in the pocket  122  and secured thereto, for example using fasteners, an interference fit, or a bonding process such as brazing or welding. The shoe  124  has an exterior surface  126  which defines a portion of the intake barrel recess  66  and is provided with a seal slot  104 , seal  106 , and seal springs  116  as described above. The function of the seal  106  is the same as described above. 
     In the assembled engine, a drive assembly  128  ( FIG. 7 ) is provided for each valve shaft  80  which includes a pulley  130  and a coupler  132 . The coupler  132  includes a mechanical alignment feature  134 , such as the slots seen in  FIG. 23 , which is shaped and sized to mate with the mechanical alignment feature of the valve shaft  80 , such as the axial pins  98  described above. 
     The pulley  130  is configured to engage a drive belt, chain, or similar transmission element. In the illustrated example the pulley  130  has teeth  136  around its periphery and is configured to engage a conventional toothed drive belt. 
     The drive assembly  128  may be adjustable. More specifically, the relative angular position of the pulley and the mechanical alignment feature  134  may be variable. In the example shown in  FIGS. 7 and 24 , the pulley  130  is attached to the coupler  132  with bolts  138  passing through slots  140 . The bolts  138  can be loosened, the pulley rotated to a selected orientation, and the bolts retightened. A scale  142  may be provided to aid in adjustment. This adjustment allows the physical timing of the valve shaft  80  to be altered to tune the operating characteristics of the engine  10 . 
     As shown in  FIG. 2 , one drive assembly  128  may be provided for each valve shaft  80 . A first drive belt  144  connects the two drive assemblies  128  of one cylinder bank  16  with an idler pulley  146 , and a second drive belt  148  connects the idler pulley  146  to a crank pulley  150  of the engine  10 . The crank pulley  150 , idler pulleys  146 , and drive assemblies  128  are sized such that each valve shaft  80  rotates at one-quarter of the rotational speed of the crankshaft  18 , or in other words the drive arrangement provides a 4:1 speed reduction. Optionally, one or more of the drive assemblies  128  may incorporate an active adjustment mechanism (not shown) of a known type which is effective to change the angular relationship of the valve shaft  80  to the pulley  130 , for example under control by an electronic control unit (not shown). This type of device is commonly referred to as a “cam phaser”. This device may be used to actively control the angular orientation or phase of one or both of the valve shafts  80 A,  80 B relative to the crankshaft  18 . This capability is useful for actively controlling operating characteristics of the engine  10  during operation. In a Diesel cycle engine, this capability could be used to serve the function of a compression brake, by selectively advancing the intake valve shaft  80 A when braking is desired. 
     The operation of the engine  10  will be described with reference to  FIGS. 25 through 28 , which schematically depict a single cylinder  32  of the engine  10 . As noted above, the intake valve shaft  80 A and exhaust valve shaft  80 B are driven by belts or other suitable drive apparatus and rotate at one-quarter of the rotational speed of the crankshaft  18 . During the four strokes of the engine  10  using a conventional Otto cycle, the intake valve shaft  80 A and exhaust shaft  80 B continuously rotate to position their respective apertures  40 ,  48  in the proper position relative to the ports  34 ,  42 . As shown, during the intake stroke ( FIG. 25 ), the intake aperture  40  of the intake valve shaft  80 A is substantially aligned with the intake port  34  to allow air into the combustion chamber  30 . The exhaust aperture  48  of the exhaust valve shaft  80 B is positioned such that exhaust valve shaft  80 B closes the exhaust port  42  and air or gas is prevented from escaping the combustion chamber  30  through the exhaust port  42 . During the compression stroke,  FIG. 26 , the apertures  40  and  48  of the intake and exhaust valve shafts  80 A and  80 B are both rotated to close off the intake port  34  and exhaust port  42 . During the power stroke,  FIG. 27 , the apertures  40  and  48  of the intake and exhaust shafts  80 A and  80 B continue to keep the intake and exhaust ports  34 ,  42  closed. Finally, during the exhaust stroke,  FIG. 28 , the intake valve shaft  80 A continues to close the intake port  34  and the exhaust valve shaft  80 B is positioned such that the exhaust port  42  is now opened by substantially aligning the exhaust aperture  48  with the exhaust port  42 . The cycle then continues. During this process, there may be overlap of the openings of the valve shafts  80 A and  80 B similar to valve overlap in a conventional poppet-valve engines. For example, the intake port  34  may start opening as the exhaust port  42  begins to close, such that the intake port  34  and exhaust port  42  are both open for some period of time. This overlap can be beneficial in accelerating filling of the cylinder  32  with the intake mixture. As noted above, the angular separation of the apertures  40  and  48  may be adjusted to change the timing of valve events and the degree of overlap. 
     The apparatus described above has several advantages over the prior art. The rotary valve structure has significantly lower parts count and frictional losses as compared to a conventional poppet valvetrain. The rotary valve structure also has the potential to be much more reliable than a conventional valvetrain because it does not require reciprocating movement and does not rely on highly-stressed valve springs for operation at high engine speeds. 
     Furthermore, the sealing assembly described herein will provide effective sealing of the rotary valve apparatus while permitting low mechanical loads and long component life. 
     It will be understood that the present invention may be implemented as a complete engine, or that the cylinder head assemblies described herein may be retrofitted to an existing internal combustion engine, or that the rotary valve apparatus and/or the sealing assembly may be incorporated into a cylinder head design. 
     The foregoing has described a rotary valve apparatus, a seal apparatus for a rotary valve apparatus, and an engine with a rotary valve apparatus. 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 embodiment(s). The invention extends 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.