INTERNAL COMBUSTION ENGINE

Abstract

An internal combustion engine (10) includes at least one cylinder (12) having a piston, and a cylinder head containing an inlet duct (3) incorporating an inlet valve 1 to allow flow in only one direction and an exhaust duct incorporating no mechanical flow restricting device and at least one chamber valve (2) through which both inlet and exhaust fluids pass from the ducts (3,4) into and out of the cylinder (12), and a combustion chamber (6) in the cylinder (12) that allows the chamber valve (2) to be significantly open when the piston (5) is at top dead centre enabling a transfer of fluid, fluid flow pressure and pressure waves between the cylinder, and the inlet (3) and exhaust ducts (4).

Claims

1. An internal combustion engine includes at least one cylinder having a piston, and a cylinder head containing an inlet duct incorporating an inlet valve to allow flow through said inlet duct in only one direction and an exhaust duct incorporating no flow restricting mechanisms or regions and at least one chamber valve through which both inlet and exhaust fluids pass from the ducts into and out of the cylinder, and a combustion chamber in the cylinder that allows the chamber valve to be significantly open when the piston is at top dead centre enabling a transfer of fluid, fluid flow pressure and pressure waves between the cylinder, and the inlet and exhaust ducts; and the at least one chamber valve is configured to receive injected fuel for atomising the fuel and/or for cooling the at least one chamber valve.

2. The internal combustion engine as claimed in claim 1, wherein the exhaust duct is tuned to accelerate the inlet fluid when the piston is near the top of its stroke, and to create negative pressure in the cylinder to aid cylinder filling with inlet fluid, through at least part of the induction stroke, by harnessing energy in the flow of exhaust fluid.

3. The internal combustion engine as claimed in claim 1, wherein the exhaust duct is tuned to harness energy and pressure waves in the exhaust flow to affect the dynamics and/or flow of inlet fluid to aid scavenging of the cylinder using reflected negative pressure waves from the exhaust flow.

4. The internal combustion engine as claimed in claim 1 wherein the exhaust duct is tuned to harness energy and pressure waves in the exhaust flow to affect the dynamics and/or flow of inlet fluid to assist cylinder filling using reflected positive pressure waves.

5. The internal combustion engine as claimed in claim 1 wherein the exhaust duct is tuned by adjusting the length and/or shape and/or diameter of the exhaust duct.

6. The internal combustion engine as claimed in claim 1, further comprising a wall separating the inlet and exhaust ducts, said wall guiding fluid into the cylinder in a first direction and guiding fluid out of the cylinder in a second direction, where said first and second directions are different directions.

7. The internal combustion engine as claimed in claim 1, wherein the combustion chamber is shaped to allow the chamber valve to be significantly open when the piston is at top dead centre placing substantially all of the remaining cylinder and combustion chamber space above a lower surface of a head of the chamber valve.

8. The internal combustion engine as claimed in claim 6, wherein the wall is a substantially vertical wall separating the inlet and exhaust ducts, located immediately above a chamber valve seat.

9-12. (canceled)

13. The internal combustion engine as claimed in claim 1, wherein one or both of the inlet and exhaust duct enter the cylinder at an angle to a longitudinal axis of a side wall of the cylinder.

14-15. (canceled)

16. The internal combustion engine as claimed in claim 1, wherein each cylinder has a single chamber valve.

17. The internal combustion engine as claimed in claim 1, wherein the inlet and exhaust ducts enter the cylinder upstream of the valve.

18. The internal combustion engine as claimed in claim 1, wherein the inlet and/or exhaust ducts enter a subsidiary chamber of the cylinder when the chamber valve is open.

19. The internal combustion engine as claimed in claim 18, wherein the chamber valve is located between the subsidiary chamber and the main chamber of the cylinder.

20. The internal combustion engine as claimed in claim 18, wherein the chamber valve has a valve seat which forms a boundary between the subsidiary chamber and the main chamber.

21-22. (canceled)

23. The internal combustion engine as claimed in claim 1, further comprising a compact circular part conical combustion chamber in the cylinder head with a ring shaped squish area.

24. (canceled)

25. The internal combustion engine as claimed in claim 1, wherein the combustion chamber is substantially a cylindrical depression in the piston with a ring shaped squish area that may have an inclination of between zero and thirty degrees.

26. The internal combustion engine as claimed in claim 25, wherein the depression further comprises at least one outwardly extending lobe, in which the lobe, in use, causes an eddy to form in fluid flowing around the depression.

27. The internal combustion engine as claimed in claim 1 manufactured using a single component combining the cylinder block and cylinder head.

28. A method of aspirating an internal combustion engine, comprises directing fluid into a cylinder of the engine substantially at an angle to a longitudinal axis of a side wall of the cylinder.

29. (canceled)

30. A method of aspirating an internal combustion engine, comprising: arranging for the internal combustion engine to include at least one cylinder having a piston, and a cylinder head containing an inlet duct incorporating an inlet valve to allow flow through said inlet duct in only one direction and an exhaust duct incorporating no flow restricting mechanisms or regions and at least one chamber valve through which both inlet and exhaust fluids pass from the ducts into and out of the cylinder; arranging for a combustion chamber in the cylinder to allow the at least one chamber valve to efficiently open when the piston is at top dead centre for enabling a transfer of fluid, fluid flow pressure and pressure waves between the cylinder and the inlet and exhaust ducts; and injecting fuel for the internal combustion engine in operation on to the at least one chamber valve to atomise the fuel and/or cool the at least one chamber valve.

Description

[0039] Specific embodiments of the present invention will now be described by way of example with reference to the accompany drawings, in which:

[0040] FIG. 1 is a schematic partially cut away view from above of a single valve internal combustion engine;

[0041] FIG. 2 is a schematic partial cross section view of the engine in FIG. 1;

[0042] FIG. 3 is a schematic cross-sectional view of the engine showing the squish effect caused by the close proximity of the angled rim of the piston to the angled top of the cylinder at the end of the compression stroke;

[0043] FIG. 4 is a schematic partial cross-section of the engine showing an arrangement and possible gas flow at the point of ignition;

[0044] FIG. 5 is a schematic partial cross-section of the engine showing gas flow effect with the piston at Top Dead Centre prior to the induction stroke;

[0045] FIG. 6 is a schematic cross-sectional partial side view of the engine, showing possible gas flow within the engine during the induction stroke;

[0046] FIG. 7 is a schematic cross sectional partial top view of an alternative embodiment of the engine during a combustion step;

[0047] FIG. 8 is a schematic cross-sectional partial side view of an embodiment of the engine and exhaust showing pressure wave reflection in the exhaust prior to the end of the induction stroke;

[0048] FIG. 9 is a partial schematic cross-sectional side view of an alternative embodiment of the engine;

[0049] FIG. 10 is a schematic partially cut away top view of the engine of FIG. 9;

[0050] FIG. 11 is a schematic side view of an alternative embodiment with a flat topped piston and a circular combustion chamber above the piston;

[0051] FIG. 12 is a schematic cross-section view of the engine looking along the direction of arrow C in FIG. 11, showing a ring shaped squish area at the edge of the combustion chamber;

[0052] FIG. 13 is a schematic side view of an alternative embodiment with an oblong/oval combustion chamber above the piston;

[0053] FIG. 14 is a schematic cross-section view of the engine (looking along the direction of arrow D in FIG. 13 showing a D shaped squish area on 2 sides of the combustion chamber;

[0054] FIG. 15 is a schematic end view corresponding to FIG. 14.

[0055] FIG. 2 shows an internal combustion engine 10 having a single chamber valve 2 per cylinder 12, with an inlet duct 3 and an exhaust duct 4, both of which lead from an exterior face of the engine 10 to a chamber 7 above a main chamber of the cylinder 12. In the preferred embodiment of the invention inlet duct 3 and exhaust duct 4 may positioned on opposite sides of the cylinder and are separated by a substantially vertical wall 23 terminating close to the top of cylinder 12, thereby reducing chamber 7 to a minimal gap when the chamber valve 2 is closed. Whilst wall 23 is provided in the preferred embodiment of the invention, it is not essential and the engine may still operate without the wall separating the inlet and exhaust ducts. Other separation means between the inlet and exhaust ducts 3, 4 may alternatively be provided, and the type of separation provided will typically be dependent on the orientation of the inlet 3 and exhaust ducts 4 with respect to the combustion chamber 6. Valve 2 is located at a top end of the cylinder 12 and is arranged to open and close an opening in the top end of the cylinder 12. Preferably the chamber valve 2 is a poppet valve (and is a poppet valve in all of the illustrated embodiments) with a stem 18, and a valve head 16, but other types of valves may also be used. A piston 5 is located within the cylinder 12 and is arranged to move in the usual way. A combustion chamber 6 is located in an upper end of the piston 5 or in a space between the top of piston 5 and the lower surface of poppet valve head 16.

[0056] In more detail, the inlet duct 3 extends downwards at an angle of approximately 60 degrees from an upper end of the engine 10 to the chamber 7 however this angle may vary between 30-90 degrees. The inlet duct 3 joins the chamber 7. A short distance up stream of the chamber 7, the inlet duct 3 widens and a reed valve 1 is positioned to prevent the passage of exhaust fluid back up the inlet duct 3. Typically, the reed valve 1 is a pressure sensitive one way flow device.

[0057] The exhaust duct 4 extends from the chamber 7 and follows a path which is approximately a mirror image of the inlet duct 3(see FIG. 2), although the exhaust duct may follow an alternative (non-mirrored) pathway. The exhaust duct 4 is of relatively large diameter and has smooth sides to promote the rapid departure of exhaust gas to an exhaust tube 8 (as shown in FIG. 8). Preferably the exhaust duct 4 is a valve less system and does not include any other physical flow restrictions. Of course, the exhaust duct 4 may connect to a standard exhaust system 8 for use with a 2 or 4 stroke engine which may be provided with physical restrictions or valves to restrict flow in the subsequent exhaust system.

[0058] The poppet valve 2 effectively forms a lid on the combustion chamber 6. The poppet valve has a head portion 16 in the form of a disc which is arranged for movement to optionally seal the chamber 7 from the cylinder 12, by movement of a stem portion 18. The poppet valve head 16 may have a diameter or width which is approximately 50% of the diameter of the piston. As shown (in FIG. 5) the head 16 of poppet valve 2 is shaped to fit snugly in the base of the combustion chamber 6 in the iteration of the engine that uses a bowl in piston combustion chamber.

[0059] To enable the desired flow of gas/fluid out of and into the engine with minimal restriction, the combustion chamber 6 is configured to allow the poppet valve 2 to be substantially open when the piston 5 is at the top of its stroke (top dead centre-tdc) and combustion chamber 6 may be formed as a bowl in the piston crown or as a recess in the cylinder head below the poppet valve 2 and above the piston crown. The combustion chambers 6 shown in FIGS. 2 to 15 enable free entry and exit of fluid into the cylinder, combined with a compact chamber shape thus allowing good compression due to use of shapes and volumes that allow a high compression ratio. This enables good combustion of the inlet air/fuel mixture. Combustion will be further aided by the significant squish areas 22 illustrated in later figures.

[0060] When the combustion chamber is in the top of the piston 5 it is generally circular in cross-section, but it may also incorporate a recess 20 which may be in the shape of a lobe and is shaped to allow a spark plug to intrude into chamber 6 (see FIG. 7). As shown, this combustion chamber 6 is substantially cylindrical, with a substantially flat base, although the base may be provided with small protrusions. The head 16 of poppet valve 2 also has a flat base, and when the valve is on the bottom of the combustion chamber 6 as shown in FIG. 5, the valve head 16 sits snugly on the top of the base of combustion chamber 6 (see FIG. 5). In this embodiment of the invention, the valve head 16 and base of the combustion chamber 6 are both flat, but other shapes may be considered. For example, the combustion chamber 6 may be hemi-spherical shaped, with concave sides rather than vertical sides. It may have a dished floor, in which cases the valve head 16 could be similarly shaped. Although a preferred embodiment of the invention has a cylindrical combustion chamber 6, with flat valve head 16, the precise shape of the combustion chamber 6 and valve head 16 is less important than the fact that the two are shaped so that the valve head 16 will fit snugly against the interior of the combustion chamber 6 and in particular prevent pockets of fluid being trapped between the bottom surface of the valve head and the combustion chamber floor.

[0061] When incorporated, the recess 20 also serves the purpose of allowing the tip of a spark plug 9 to have the necessary clearance from the piston 5 where it projects into the combustion chamber 6. Two or more spark plugs 9 may be used around the circumference of the combustion chamber, each having their own recess 20. Of course, if engine 10 is to be used with diesel fuel then spark plugs (and associated recesses) may not be necessary. Preferably, a diesel compression ignition version is very likely to use an even more compact combustion chamber bowl in the piston crown.

[0062] The various stages of operation of one embodiment of the engine 10 are shown in FIGS. 3-6.

[0063] In use, fluid is drawn into the inlet duct 3 by a suction caused by the downward movement of the piston 5 within the cylinder 12 and negative pressure caused by the fast flowing exhaust fluids moving through the exhaust duct 4 and exhaust tube 8. The fluid is caused to move into the cylinder 12 because the downward orientation of the inlet duct 3 flows the inlet gas/fluid with a downward direction and momentum, drawn by the negative pressure created by both the movement of the piston 5 downwards and the fast moving column of exhaust gas acting in an opposite upwards direction. This combination of negative pressure forces creates a strong sucking effect in the space being vacated by the movement of the piston within the cylinder 12 allowing the engine 10 to efficiently fill with inlet fluid. This flow of fluid is guided by separating wall 23 that helps guide inlet fluid into the cylinder 12 and prevents it being drawn into the exhaust duct 4 when efficient cylinder filling is required. At this stage of operation the poppet valve 2 is in the open position (as shown in FIGS. 2 and 6) which allows the fluid to be drawn into the cylinder 12. As fluid is being drawn into the cylinder 12, fuel can be injected into the moving air stream or inducted through a carburetor. It is preferred to inject fuel directly into the combustion chamber 6; however, this is not a requirement of the system described herein.

[0064] Before the compression stroke begins, the poppet valve 2 closes and the commencement of upward movement of piston 5 compresses the gas and fuel mixture in the cylinder 12.

[0065] In the embodiments of the invention as shown in FIGS. 2 to 15, as the piston 5 reaches top dead centre (shown in FIGS. 3 and 4) a pronounced effect known as squish is created between the outer rim 22 of the head of the piston 5 and the corresponding rim of the top of the cylinder head wall. Squish is a well-known and desirable phenomenon which helps to promote efficient combustion, although use of the squish phenomenon is not critical for this invention. It has the effect in this engine of squeezing the outer, fuel mixture into the combustion chamber 6 in a state of extreme agitation. The layouts shown allows for a much greater squish area than in conventional engines because of the lack of conflict between piston and valve movement. In the axial induction embodiment above conservation of angular momentum means that the speed of the mixture will be dramatically increased at top dead centre when it is compressed into the combustion chamber 6. The squish area is largest with the combustion chamber 6 as a bowl in the piston because of the angled piston top. In this embodiment of the invention, the outer rim of piston 5 is angled between 0-35 from horizontal downwardly from the top of the piston.

[0066] Referring now to FIG. 7, ignition of the compressed fuel and air mixture can take place in a recess 20 at the outer edge of the combustion chamber 6. When the recess 20 takes the shape of a lobe it is profiled to collect an eddy of rich mixture, which, when ignited, provides a good initiation to the flame front. Propagation of the flame will be fast and efficient owing to the extreme agitation and movement of the mixture allied to the compact nature of the combustion chamber 6, and the ability of the engine to work with a high compression ratio with reduced risk of detonation. This latter factor is aided by the lower working temperature of the single poppet valve 2 when compared to conventional separate inlet and exhaust valves.

[0067] The main advantage of the engine working with a stratified charge as described above is its ability to run with lean mixtures (lean burn). This allows for efficient part load running with the engine able to work with excess air, but with the correct fuel/air mixture at the point of ignition. It is expected that the engine could be developed to run with a throttle or in a throttle less state, with power controlled solely by the quantity of fuel injected, particularly when direct injection is used, along with variable valve timing.

[0068] The arrangements of the engine 10 described herein allow a large valve area and high lift of the poppet valve 2 without interference from the piston 5. This lack of interference allows for a very efficient inlet and exhaust cycle. After combustion (see FIG. 4) the piston 5 moves downwards in its power stroke. Prior to the piston 5 reaching bottom dead centre, the poppet valve 2 begins to open, this can be later than in a conventional engine, which will have more resistance to escape of exhaust fluid. This also allows the combustion chamber 6 of the engine 10 to be 100% scavenged. The longer power stroke should further aid efficiency. As the valve 2 opens there will be a pressure transfer to the inlet duct 3 and exhaust duct 4. This pressure will close valve 1 on the inlet duct 3. As the fluids pass the poppet valve 2 into the chamber 7 the fluid will follow its natural path (into the exhaust duct 4, where it will move into an exhaust system 8 (FIG. 8) creating a column of fast moving fluid. At some stage in the exhaust cycle some air may also be drawn into the exhaust duct 4 by the momentum of the exhaust fluid. As piston 5 approaches top dead centre (TDC) the column of fluid should have fully scavenged the cylinder, and the poppet valve 2 will be fully inside combustion chamber 6. This enables complete scavenging of the engine, as there is no space for any residual exhaust fluid. The engine will also then have maximum valve lift at the end of the exhaust stroke and beginning of the induction stroke. This promotes good exhaust flow, and the connection between the inlet duct 3 and exhaust duct 4 promotes early acceleration of the inlet charge, because of the momentum of the exhaust fluid in the exhaust duct 4.

[0069] The momentum of the fluid passing through the exhaust duct 4 will begin to create a negative pressure in the chamber 7, thereby causing the inlet reed valve 1 to open and draw through air for the next inlet stroke. By the time the piston 5 has reversed direction to commence the inlet stroke, there will already be a momentum of inlet fluid following the natural path into the chamber 7, and the exhaust fluid flow may cause a column of inlet fluid to be drawn behind it up exhaust duct 4 when the piston is around Top Dead Centre prior to the piston 5 beginning its downward suction stroke. This flow of fluid is additional to that caused by the downward movement of the piston 5 described at the start of the cycle described above.

[0070] FIG. 8 illustrates the effect of pressure waves within the exhaust duct 4 when the exhaust length, and/or shape and/or diameter is tuned to the operating speed of the engine. As the valve 2 begins to close at the end of the induction stroke, a positive pressure wave can be reflected from the open end of exhaust tube 8 or by pressure reflection chambers, resonance chambers and devices of the sort more typically used in 2 stroke motorcycles as understood in the art. (not shown) This reflection of negative and/or positive pressure waves can result in inlet gas or fluid that may have been drawn up the exhaust duct 4 being reflected back down the exhaust duct and forced back into cylinder 12 (see arrow 50), thereby providing improved cylinder filling for a particular inlet charge. Use of the pressure waves in the exhaust duct 4 means that the exhaust duct 4 may not need to be provided with any physical valves or other restricting devices, and the exhaust duct 4 can be tuned to harness the exhaust pressure waves to assist inlet filling and exhaust scavenging.

[0071] Preferably, the dynamic energy in the flow of exhaust fluid in the exhaust duct 4 is harnessed by the engine 1, to accelerate the inlet air or fluid when the piston 5 is near the top of its stroke, and this acceleration of the exhaust fluid helps create a negative pressure in the cylinder 12, which aids filling of the cylinder 12 with inlet air or fluid through all or part of the induction stroke of the engine 1.

[0072] The exhaust duct 4 may also be tuned to harness dynamic (kinetic) energy in the exhaust fluid dynamics and to use pressure waves in the exhaust fluid. This can affect the dynamics and flow of the inlet gas or fluid. Harnessing dynamic energy in the exhaust fluid, and the use of pressure waves in the exhaust fluid can assist scavenging of the cylinder 12 with reflected negative pressure waves from the exhaust. Harnessing this energy can also assist in the subsequent filling of the cylinder 12, (after the previous scavenging) using reflected positive pressure waves from the exhaust fluid. The negative pressure enhanced cylinder scavenging and positive pressure enhanced cylinder filing may be independent events, or may be linked.

[0073] The cycle of inlet stroke, compression stroke, power stroke and exhaust stroke can be repeated in the same manner described above.

[0074] In the alternative embodiment of the engine as shown in FIGS. 9 & 10 as the piston 5 moves up the cylinder 12 the speed of the vortex induced by the axial induction of the fluid will tend to increase within the cylinder 12. Centrifugal forces on the mixture will tend to urge denser fuel particles towards the edge of the cylinder 12. This has the effect of stratifying the charge with the more dense, or richer, mixture of liquid fuel and air being forced toward the outside of the cylinder 12, where the spark plugs 9 are located.

[0075] FIGS. 9 and 10 show an alternative arrangement of inlet and exhaust ducts. In this embodiment the ducts 3 and 4 enter the chamber 7 tangentially creating a swirl around the axis of the centre line of the cylinder. Otherwise, the engine functions in the same manner as described above.

[0076] FIGS. 11 and 12 show different views of an engine 10, with a circular combustion chamber 6. In this alternative embodiment of the invention, a combustion chamber 6 is formed between a recess in the cylinder head 12 and a flat or slightly recessed top surface of piston 5. Looking upwards (in direction of arrow C) from the top of piston 5 (FIG. 12) the shape of combustion chamber 6 may be circular, and of a greater diameter than the poppet valve 2 and of an equal or lesser diameter than the cylinder 12. Looking from a side view (FIG. 11) the walls of the combustion chamber 6 may slope or curve from the greater diameter 31, at the base of the combustion chamber 6 to the lesser diameter 32 of the valve seat. When combustion chamber 6 is formed with a lesser diameter 32 than the cylinder 12 a ring shaped squish area 22 may be formed between the piston top and this smaller diameter of the combustion chamber recess.

[0077] FIGS. 13, 14 and 15 show different views of a further embodiment of engine 10, with a substantially oval combustion chamber 6. In this embodiment of the invention, combustion chamber 6 is formed between a recess in the cylinder head and a flat or slightly recessed top surface of piston 5. Looking upwards (in the direction of arrow D) from the piston top (FIG. 14), the recess in the cylinder head may be approximately oval or oblong in shape. The length of the oval or oblong profile may be the same or slightly less than the diameter of the cylinder bore. The width of the oval or oblong may be the same or slightly greater than the diameter of the head 16 of the poppet valve 2. The longer walls of the chamber 6 may be vertical and the narrower walls 34 may incline upwards at an angle to meet the poppet valve seat 16. This shape of the combustion chamber allows for a squish area 22 between the top of the piston 5 and the cylinder head adjacent to the narrow sides of the combustion chamber 6.

[0078] The embodiments described herein have significant advantages over the prior art in, at least, the following respects.

[0079] The engine 10 is compatible with 4 stroke petrol or diesel engines, where it can overcome some of the breathing problems caused by valve/piston clearance restrictions resulting from a high compression ratio. It is particularly suited to burn gaseous fuels such as propane, methane and hydrogen since it can combine good volumetric efficiency with a high compression ratio. In addition, aspects of this invention could be adapted for other engines that do not operate on a four-stroke cycle, such as a two-stroke, or a six-stroke engine.

[0080] This engine layout allows for long periods of high valve lift combined with a large valve area which allows good volumetric efficiency (i.e. breathing)

[0081] The effect of full valve opening at top dead centre enables the early flow of inlet fluid drawn into the engine by negative pressure generated by exhaust flow. This creates inlet fluid momentum before the piston begins its pumping stroke aiding cylinder filling improving volumetric efficiency and reducing pumping losses.

[0082] The compact combustion chamber 6 aided by pronounced squish and tumble or spiral movement of fluids allows a fast, clean and complete burn.

[0083] The column of air drawn into the exhaust duct 4 allows for resonant wave tuning to the resonant frequency of the exhaust duct (as used in 2 stoke motorcycle engines) to improve flow characteristics and volumetric efficiency. Also on multi-cylinder versions of the engine, an effective degree of self-super charging can be achieved by connecting exhaust ducts and using the exhaust pressure of one cycle to force residual air in a neighbouring exhaust port back into the cylinder as the valve closes, as is known in the art.

[0084] The cool inlet fluids flowing over the poppet valve 2 will reduce the valve temperature, thereby increasing the engine's detonation threshold. This feature allows the engine to work safely at higher compression ratios, or with poorer fuel quality.

[0085] The above design permits a free breathing, long stroke engine combining good power and torque. Traditional long stroke engines are limited by their inability to breathe efficiently at high revs because of limited valve area.

[0086] The arrangement described above is simple to build and has fewer moving parts than a conventional engine, and should be adaptable to any existing crank case/cylinder block. It also leaves scope for further more complicated designs with different types of manifold inlet and exhaust duct valving. In the preferred architecture of the engine as shown in all of the accompanying illustrations the position of the poppet valve on the same vertical centreline as the cylinder bore allows the engine to be manufactured easily using a single component combining the cylinder block and cylinder head, this is commonly referred to in the art as a monobloc construction, and the engine may be machine finished in production using a single drilling and boring process for the poppet valve aperture and cylinder.

[0087] Friction in the valve train will be reduced owing to lesser acceleration and deceleration forces inherent to this design and because the engine has fewer moving components, thus improving mechanical efficiency and enhancing durability.

[0088] The engine described above is concerned primarily with the design of an engine for economy and emission benefits. However, the efficiency, and therefore high specific power output may give the engine benefits for sports and racing engines.

[0089] 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.

[0090] 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.

[0091] The invention is not restricted to the details of the foregoing embodiment(s). The invention extends 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.