air-cooled four-stroke aircraft engine

Abstract

The improved air-cooled aircraft engine includes an intake valve opening, an exhaust valve opening, and a compact combustion chamber having a generally elliptical shape having a major axis and a minor axis, the major axis intersecting both the intake valve opening and the exhaust valve opening. In some embodiments, the major axis is equal to or less than the diameter of a cylinder bore of the engine, and the minor axis is less than the major axis. Thus, combustion is constrained to an area smaller than the cylinder bore.

Description

[Background technology]

[0001] This invention relates generally to spark ignition, four-stroke, air-cooled aircraft engines, and more particularly to such engines having small combustion chambers.

[0002] Air-cooled four-stroke engines are commonly used to power airplanes, helicopters, and UAVs (unmanned aerial vehicles). A typical air-cooled engine may contain an aluminum cylinder head with heat fins exposed to the ambient air. Heat from combustion flows into the aluminum cylinder head and is rejected to the ambient air by conduction through the heat fins.

[0003] A typical air-cooled engine uses an open combustion chamber with widely spaced spark plugs, two per cylinder, to allow for redundant operation so that the engine can continue to operate if one spark plug fails. Summary of the Invention

[0004] Unfortunately, air-cooled engines suffer from certain drawbacks. Open combustion chambers often require the flame front initiated by the spark plug to travel long distances to traverse the entire combustion chamber volume. To accommodate the long travel times, spark plug timing is often significantly advanced, firing the spark plug more than 20 degrees before the top dead center (TDC) of the piston in each cylinder. This advanced spark plug firing results in negative work that is subtracted from the positive mechanical work performed by the engine. Furthermore, the relatively long distance required for the flame front to travel toward the exhaust valve within the combustion chamber causes unburned fuel-air mixture to remain in contact with hot exhaust components longer than necessary. This can lead to premature ignition of the hot fuel-air mixture near the exhaust components, resulting in knock. Knock can be at least partially ameliorated by using higher-octane fuels, but such fuels are more expensive than lower-octane fuels and are difficult to obtain in some parts of the world.

[0005] To at least partially address the above-mentioned deficiencies, an improved air-cooled aircraft engine includes a compact combustion chamber having a generally elliptical shape. The combustion chamber is formed by a cylinder head and a piston when the piston is positioned at or near its uppermost position within the cylinder bore. The cylinder head includes an intake valve opening and an exhaust valve opening. The elliptical shape has an area smaller than the area of ​​the cylinder bore and has a major axis that intersects both the intake valve opening and the exhaust valve opening.

[0006] A smaller combustion chamber offers several advantages. The flame front initiated by the spark plug's firing can traverse the entire volume of the combustion chamber in a shorter time, completing combustion more quickly and reducing the need to advance the spark plug timing (for example, from 20 degrees to 15 degrees before TDC). As a result, the engine performs less negative work than previous designs, improving efficiency. Furthermore, the smaller combustion chamber means that hot exhaust components have less time to heat the fuel-air mixture, reducing waste heat and preventing knocking. Eliminating knocking allows the use of cheaper, lower-octane fuels, significantly reducing operating costs and improving availability. Many other improvements and advantages are possible.

[0007] Certain embodiments are directed to an air-cooled aircraft engine. The engine includes a cylinder head having an intake valve opening, an exhaust valve opening, a plurality of spark plugs, and an inner surface. The engine further includes a cylinder bore having a cross-sectional area and including a piston configured for reciprocating movement within the cylinder bore. The engine further includes a combustion chamber having an upper region defined by the inner surface of the cylinder head and a lower region defined by the piston when the piston is in an uppermost position within the cylinder bore. The combustion chamber is elliptical in shape spanning a cross-sectional area smaller than the cross-sectional area of ​​the cylinder bore, the elliptical shape having a major axis intersecting the intake valve opening and the exhaust valve opening.

[0008] In some embodiments, the cylinder head has a flat shoulder region that abuts the flat outer region of the piston when the piston is in its uppermost position within the cylinder bore, and the flat shoulder region and the flat outer region constrain the combustion chamber to an elliptical shape.

[0009] In some embodiments, a plurality of spark plugs each include a respective electrode, and the electrodes of the plurality of spark plugs extend below an inner surface of the combustion chamber.

[0010] In some embodiments, the electrodes of the plurality of spark plugs are positioned closer to the exhaust valve opening than to the intake valve opening.

[0011] In some embodiments, the piston includes a recess beneath an electrode of each of the plurality of spark plugs, and at least a portion of the piston is raised relative to the recess.

[0012] In some embodiments, the cylinder bore has a centerline and a radius, and the electrodes of the plurality of spark plugs are positioned at respective distances from the centerline that are less than 65% of the radius of the cylinder bore.

[0013] In some embodiments, the cylinder head further includes an intake valve seat that fits within the intake valve opening and an exhaust valve seat that fits within the exhaust valve opening.

[0014] In some embodiments, the intake valve seat and the exhaust valve seat are each constructed at least in part from copper infiltrated powder metal and / or solid alloy.

[0015] In some embodiments, the intake valve seat and the exhaust valve seat each have a respective inner region, each inner region having a plurality of discrete angled surfaces.

[0016] In some embodiments, the cylinder head further includes an intake valve positioned to selectively admit intake air into the combustion chamber through the intake valve opening. The intake valve has an intake valve stem and an intake valve head, the intake valve stem having a diameter of less than 9 mm. In such embodiments, the cylinder head further includes an exhaust valve positioned to selectively exhaust exhaust gases from the combustion chamber through the exhaust valve opening. The exhaust valve has an exhaust valve stem and an exhaust valve head, the exhaust valve stem having a diameter of less than 9 mm.

[0017] In some embodiments, the intake valve head and the exhaust valve head have a plurality of discrete angled surfaces adjacent their contact areas with the respective valve seats.

[0018] In some embodiments, the cylinder head includes an exhaust valve stem guide around the exhaust valve stem, the exhaust valve stem guide being constructed at least in part from copper and fabricated as a powdered metal and / or solid alloy.

[0019] In some embodiments, the intake valve stem and the exhaust valve stem each include a triple bead attachment to the respective valve retainer, each triple bead attachment constructed and arranged to facilitate rotation of the respective valve.

[0020] In certain embodiments, the engine further includes a high tumble intake port coaxial with the intake valve opening in the cylinder head, the high tumble intake port constructed and arranged to induce vertical flow within the combustion chamber.

[0021] Another embodiment is directed to an air-cooled aircraft engine including a plurality of cylinders, each cylinder including a cylinder head having an intake valve opening, an exhaust valve opening, a plurality of spark plugs, and an inner surface. The engine further includes a cylinder bore having a cross-sectional area and including a piston configured for reciprocating movement within the cylinder bore. The engine further includes a combustion chamber having an upper region defined by the inner surface of the cylinder head and a lower region defined by the piston when the piston is in a substantially uppermost position within the cylinder bore. The combustion chamber is elliptical in shape spanning a cross-sectional area smaller than the cross-sectional area of ​​the cylinder bore, the elliptical shape having a major axis intersecting the intake valve opening and the exhaust valve opening.

[0022] Yet another embodiment is directed to an aircraft including an air-cooled aircraft engine according to any of the above examples, in any combination.

[0023] Certain embodiments are directed to air-cooled aircraft engines, such as those having the features described in any of the examples above, in any combination. The engine may include any number of chambers (e.g., any number of cylinders) of the type described, arranged in any manner (e.g., linear, opposed, V-shaped, W-shaped, radial, etc.).

[0024] While the foregoing summary has been provided for illustrative purposes to enable the reader to readily grasp the exemplary features presented herein, this summary is not intended to specify essential elements or to limit the embodiments herein in any way. It should be understood that the features described above may be combined in any manner that makes sense in the art, and that all such combinations are intended to be disclosed herein, whether or not such combinations are expressly identified. [Brief explanation of the drawings]

[0025] The foregoing and other features and advantages will become apparent from the following description of specific embodiments, as illustrated in the accompanying drawings, in which like reference characters refer to the same or similar parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of various embodiments.

[0026] FIG. 1 is a bottom view of a cylinder head of an air-cooled aircraft engine according to one embodiment of the present disclosure.

[0027] 2a and 2b are cross-sectional side views of the embodiment of FIG. 1, with the cross section taken along the plane of the spark plug of FIG.

[0028] FIG. 3 is a cross-sectional side view of the embodiment of FIG. 1, the cross-section being taken along the plane of the valve of FIG.

[0029] FIG. 4 is a cross-sectional side view of the embodiment of FIG. 1 showing a triple bead arrangement for the valve stem.

[0030] FIG. 5 is an enlarged view of a portion of FIG. 3, showing an example of the contact area between the valve head and the valve seat. DETAILED DESCRIPTION OF THE INVENTION

[0031] Next, embodiments of the improved technology will be described, with the understanding that such embodiments are provided by way of example to illustrate certain features and principles, and are not intended to be limiting.

[0032] The improved technology provides an air-cooled aircraft engine including a compact combustion chamber having a generally elliptical shape. The combustion chamber is defined by a cylinder head and a piston when the piston is positioned at or near its uppermost position within the cylinder bore. The cylinder head includes an intake valve opening and an exhaust valve opening. The elliptical shape has an area smaller than the area of ​​the cylinder bore and has a major axis that intersects both the intake valve opening and the exhaust valve opening.

[0033] In some embodiments, the engine includes a spark plug with an electrode positioned closer to the exhaust valve than the intake valve, which means that hot exhaust components have less time to heat the fuel-air mixture, reducing waste heat and preventing knocking.

[0034] In some embodiments, the spark plug is positioned parallel to the minor axis of the elliptical area and is positioned closer to the exhaust valve than the intake valve.

[0035] In some embodiments, the piston has an upper surface with one or more recesses formed therein, hi some embodiments, the recesses have a shape that substantially mirrors the shape of the interior of the cylinder head.

[0036] In some embodiments, the cylinder head includes a valve seat constructed at least in part of copper-infiltrated powder metal. Such copper-infiltrated powder metal has a higher thermal conductivity than stainless steel (e.g., 130% higher) while providing similar wear resistance. The valve seat is heat-fitted into the cylinder head, providing a large contact area with the cylinder head and forming a low thermal resistance attachment. Thus, the valve seat provides a higher thermal conduction path between the valve head and the surrounding cylinder head.

[0037] In some instances, the valve seat has a narrow profile, which reduces the surface area exposed to combustion and reduces direct heating.

[0038] One of the functions of the valve seat is to act as a heat sink to cool the valve head. In some embodiments, the backside of the valve head includes a flat area that matches a corresponding flat area on the valve seat. This contact area allows heat to flow from the valve head to the valve seat, then to the engine block, where it is radiated to the surrounding air via heat fins. Additional angles adjacent to the contact area (multi-angle design) provide a venturi shape for more efficient airflow.

[0039] In some embodiments, the valves include narrow valve stems. A narrower valve stem reduces the valve's mass, allowing the camshaft to actuate the valve more aggressively, opening and closing the valve more rapidly. This feature helps prevent the valve from opening or closing longer than necessary. For example, the valve remains seated longer during each combustion cycle, allowing more time for heat to be transferred to the valve seat and cylinder head. A longer valve seating also increases the effective compression and expansion ratios, improving efficiency. Additionally, a narrow stem expands less with increasing temperature, helping to maintain centricity and cylindricity, reducing valve distortion, leakage, and wear. It also promotes more effective breathing by reducing obstruction of intake and exhaust port space.

[0040] In some examples, one or both valves have a valve stem and a highly thermally conductive valve stem guide, such as one made from copper-infiltrated powder metal and / or a highly thermally conductive solid copper alloy, such as a brass billet. In some examples, the valve stem may have an elongated hollow interior region containing sodium. When the valve stem is heated, the sodium melts and sloshes within the hollow region, drawing heat from the valve head. The heat then travels up the valve stem and laterally to the highly thermally conductive valve guide and into the cylinder head.

[0041] In some embodiments, the valve stems are actuated by a camshaft, which opens and closes each valve via a respective cam and lever. A spring biases the valve to close, and the rotating camshaft biases the valve to open via a lever.

[0042] In some embodiments, the valve stem is free to rotate, and the repeated compression and expansion of the valve spring gradually rotates the valve, for example, at a rate of between 0.25 and 5 revolutions per minute. Such valve rotation tends to more evenly distribute heat within the valve head and clean any deposits that may have formed in the seal area between the valve head and valve seat.

[0043] In some embodiments, the valve stems are coupled to their respective springs via a triple-bead design, where the end of each valve stem has three grooves for engaging with keys that attach the valve stem to the upper spring seat, reducing stress on the valve stem and increasing valve rotation compared to a single-bead design.

[0044] In some embodiments, the valve stems are isolated from the oil filling the upper valve train via molded elastomeric rings or other seals. For example, each valve stem guide has its own seal. The seals prevent low-octane oil from leaking past the valves into the combustion chamber.

[0045] In some embodiments, the intake port to the combustion chamber generates a high tumble vertical swirl flow within the combustion chamber, which tends to move the fuel in the fuel-air mixture closer to the spark plug (by centrifugal action) and promote effective ignition.

[0046] In some embodiments, the spark plug has an electrode that extends into the combustion chamber to promote direct propagation of the flame front, for example, the end of the plug is flush with the combustion chamber and the electrode extends into the main combustion chamber volume.

[0047] In some embodiments, the pistons include dual compression rings (e.g., made of steel). These compression rings prevent gases from entering the bore space with the piston and also prevent blow-by of combustion gases around the piston. In some embodiments, each piston includes a separate oil control ring (e.g., made of stainless steel). The oil control ring is located below the compression ring of each piston and serves to prevent oil in the crankcase from seeping over and around the piston and into the combustion chamber.

[0048] In some arrangements, the valves are positioned at an angle to each other. In other arrangements, the valves are positioned parallel to each other and parallel to the direction of piston movement.

[0049] These and additional features will now be described with reference to the accompanying figures.

[0050] FIG. 1 illustrates an exemplary cylinder head 100 for an engine according to certain embodiments. The depicted cylinder head 100 is shown from the bottom. Therefore, the portion facing the reader is generally the portion facing the cylinder bore 200 (FIGS. 2a and 2b). An intake valve 110 is shown on the left, and an exhaust valve 120 is shown on the right. The intake valve 110 rests within an intake valve seat 114 located within an intake valve opening 112. Similarly, the exhaust valve 120 rests within an exhaust valve seat 124 located within an exhaust valve opening 122. In one example, the valve seats 114 and 124 are thermally interference-fit into their respective valve openings 112 and 124, although other mounting styles may be used.

[0051] Spark plugs 130 are positioned between the two valves 110 and 120. Each spark plug 130 includes an electrode 132, e.g., a pair of electrodes for each spark plug. As shown, the spark plugs 130 may be positioned such that the electrode 132 is closer to the exhaust valve 120 than to the intake valve 110. Although two spark plugs 130 are shown, alternative embodiments may include more than two spark plugs.

[0052] The cylinder head 100 serves to define a combustion chamber having an elliptical shape 140. The elliptical shape 140 has a major axis 142 and a minor axis (not shown). As shown, the major axis 142 intersects the valves 110 and 120. In some embodiments, the major axis 142 has a length that substantially corresponds to the diameter of the cylinder bore 200. In other embodiments, the major axis 142 is less than the diameter of the cylinder bore 200. It should be understood that the elliptical shape 140 does not need to be a perfect ellipse. Rather, all that is required is that the shape 140 be approximately elliptical in shape, i.e., curved and longer in one direction (the major axis) than in the vertical direction (the minor axis).

[0053] 1, a centerline 150 (shown as a dot) of cylinder bore 200 is located along major axis 142 near intake valve 110. Electrodes 132 of upper and lower spark plugs 130 are positioned at respective radial distances 152 and 154 from centerline 150. Also shown is a radius 156 of cylinder bore 200 relative to the same centerline 150.

[0054] In some embodiments, the cylinder head 100 distinguishes itself from prior designs in the placement of the electrode 132. For example, the radii 152 and 154 may be less than 65% of the radius 156 of the cylinder bore 200. In some embodiments, the radii 152 and 154 may be less than 50% of the radius 156 of the cylinder bore 200. In this manner, the electrode 132 is more centrally located within the cylinder head 100 than is typical, and this more central location promotes more uniform and efficient combustion.

[0055] Cylinder head 100 has an inner surface 102 that is within the boundaries of an elliptical shape 140 and a flat shoulder region 104 that is outside the boundaries of elliptical shape 140. Typically, combustion occurs within the area defined by inner surface 102 (within the ellipse) but not within region 104 (outside the ellipse). Thus, combustion is typically constrained to the area of ​​ellipse 140, which is smaller than the area of ​​cylinder bore 200 (defined by radius 156). Limiting the area in which combustion occurs further promotes efficiency, for example, by shortening the path length of the combustion front.

[0056] Figures 2a and 2b are respective cross-sectional views of the cylinder head 100 of Figure 1, the cross section in each view being through the spark plug 130. Figure 2b is an enlarged view of a portion of Figure 2a, with contour lines and other details removed.

[0057] As shown, a combustion chamber 220 is formed between the cylinder head 100 and the piston 210. The combustion chamber 220 has an upper region 220a defined by the inner surface 102 described above, and a lower region 220b defined by the piston 210.

[0058] A piston 210 is configured to reciprocate within a cylinder bore 200 defined by a cylinder barrel 202. As shown, the piston 210 is in an uppermost position corresponding to top dead center (TDC).

[0059] When the piston 210 is in its top position, the aforementioned flat shoulder region 104 of the cylinder head 100 directly opposes the flat outer region 240 of the piston 210, effectively reducing the space between the cylinder head 100 and the piston 210 and constraining combustion to a more radially central location. Note that the elliptical shape 140 (FIG. 1) is not visible from the perspective of FIGS. 2a and 2b. However, the width of the combustion chamber 220 shown in FIGS. 2a and 2b corresponds approximately to the minor axis of the ellipse.

[0060] 2a and 2b, the electrode 132 of the spark plug 130 extends into the combustion chamber 220. For example, the body of the spark plug 130 may be flush with the interior surface 102, with the electrode 132 extending into the main volume of the combustion chamber 220. The depicted arrangement promotes rapid propagation of the flame front, unlike many prior designs in which the electrode is recessed (highly positioned), slowing combustion.

[0061] To further promote efficient combustion, piston 210 may include one or more recesses 230 located beneath electrodes 132 of spark plug 130. In some embodiments, recess 230 may be a single recess extending, for example, annularly, completely surrounding the top surface of piston 210. In other embodiments, two separate recesses 230 may be formed, one beneath each electrode 132. In some embodiments, a central raised region 232 may be formed in piston 210 between the electrodes. Raised region 232 limits the volume of combustion chamber 220 while recess 230 allows a flame front to develop.

[0062] Figure 3 is a cross-sectional view of the engine, showing a cross section through valves 110 and 120. Visible in Figure 3 is an intake port 310 for supplying intake air to combustion chamber 220 via intake valve 110 and an exhaust port 320 for delivering exhaust gases from combustion chamber 220 via exhaust valve 120. In some embodiments, intake port 310 is a high tumble port constructed and arranged to induce a vertical flow of fuel and air into combustion chamber 220.

[0063] FIG. 3 further illustrates valves 110 and 120 in greater detail. Here, intake valve 110 is shown closed against intake valve seat 114. Intake valve 110 includes an intake valve head 110a and an intake valve stem 110b. Intake valve stem 110b is surrounded by an intake valve stem guide 110c along at least a portion of its length. Similarly, exhaust valve 120 is shown to include an exhaust valve head 120a and an exhaust valve stem 120b. Exhaust valve stem 120b is surrounded by an exhaust valve stem guide 120c along at least a portion of its length. In one embodiment, exhaust valve stem 120b includes a hollow region 120d containing sodium. When exhaust valve stem 120b is heated, the sodium melts and sloshes within hollow region 120d, drawing heat from exhaust valve head 120a. This heat rises up the valve stem 120 b , is transferred laterally to the valve guide 120 c , and is transferred to the cylinder head 100 .

[0064] In one embodiment, valve stems 110b and 120b each have a diameter of less than 9 mm, and in some cases less than 8 mm. In one embodiment, intake valve 110 has a mass of less than 145 grams (e.g., 130 grams) and exhaust valve 120 has a mass of less than 130 grams (e.g., 104 grams).

[0065] In some embodiments, the intake valve stem guide 110c is comprised of at least 55% copper. Similarly, the exhaust valve stem guide 120c is comprised of at least 20% copper. The materials may be provided as, for example, a homogeneous solid alloy or powdered metal.

[0066] In some embodiments, valve seats 114 and 124 each comprise a minimum of 15% copper and may be manufactured as powdered metal or a homogeneous solid alloy.

[0067] FIG. 4 is another cross-sectional view of the cylinder head 100. Like FIG. 3, this cross-section is taken through the valves 110 and 120. As shown in the upper right corner of FIG. 4, the top of the exhaust valve stem 120b includes a triple bead shape 410, which resembles three concentric circular grooves. A triple bead key 420 engages the triple bead shape 410. The triple bead key 420 is secured (e.g., wedged) to an upper spring seat 430. A coil spring (not shown) is held in compression between the upper spring seat 430 and a lower spring seat 440. The spring may be concentric with the valve stem 120b and acts to push up on the valve retainer 430, ensuring that the valve head 120a is biased upward against the valve seat 124. A rocker 450 is configured to repeatedly push down on the valve stem 120b as the rocker rocks up and down in response to rotation of the camshaft (not shown). When the rocker 450 is depressed, the valve retainer 430 compresses the spring, forcing open the valve 120. When the rocker 450 stops depressing, the spring pushes the valve retainer 430 back, forcing the valve 120 to close.

[0068] The triple bead key 420 maintains the triple bead shape 410 of the valve stem 120b without concentrating stresses, as occurs with single bead or rotator valve designs. Therefore, the triple bead design is well suited to thin, lightweight valve stems 120b that may wear or break prematurely during normal operation.

[0069] Preferably, the triple bead key 420 does not fit tightly into the triple bead lock 410, but rather maintains a slight radial and axial clearance. For example, a 0.05 mm clearance can be maintained between the triple bead profile 410 and the triple bead key 420. This clearance allows the valve stem 120b, and thus the entire valve 120, to rotate within the valve retainer 430. The rotation can be achieved incrementally with successive compressions of the spring. For example, a coil spring imparts a slight rotation each time it is compressed. A portion of the rotation is applied to the valve stem 120b, causing it to rotate at a rate of, for example, between 0.25 and 5 revolutions per minute. This rotation of the valve 120 distributes heat more evenly within the valve head 120a and tends to clean deposits that may form in the sealing area between the valve head 120a and the valve seat 124.

[0070] Although the triple bead arrangement has been described in connection with the exhaust valve 120, a similar or identical arrangement may be used for the intake valve 110. In fact, Figure 4 shows the same features for both valves. Thus, both the intake valve 110 and the exhaust valve 120 can benefit from the durability and valve rotation afforded by the triple bead construction.

[0071] Although a triple bead structure is specifically shown, in some embodiments, more than two beads may be employed. For example, a quadruple bead structure may be used. However, it should be understood that any multi-bead arrangement having more than two beads necessarily includes a triple bead structure.

[0072] Figure 5 is a cross-sectional view of intake valve 110 closed against intake valve seat 114. As shown in Figure 1, intake valve seat 114 is a ring that extends completely around and surrounds intake valve opening 112.

[0073] As shown on the left side of Figure 5, the valve head 110a has a plurality of discretely angled surfaces 510, each extending completely around the outer periphery of the intake valve head 110a. In a complementary manner, the valve seat 114 has a plurality of discretely angled surfaces 520, each extending completely around the inner periphery of the valve seat 114. One of the surfaces 510 maintains contact with a corresponding surface 520 to effectively seal the valve head 110a against the valve seat 114 when the valve 110 is closed. As temperature increases, the radial contact area between the two surfaces may change, but the tangential contact of the surfaces is maintained.

[0074] Polygonal surfaces 510 and 520 promote smooth and efficient airflow between intake port 310 and combustion chamber 220 when valve 110 is open. For example, air is efficiently channeled through the gap formed between surfaces 510 and 520. Thus, surfaces 510 and 520 facilitate the introduction of air into combustion chamber 220 and promote efficient combustion.

[0075] 5 is directed to intake valve 110 and intake valve seat 114, exhaust valve head 120a and exhaust valve seat 124 may be arranged in a similar or identical manner. Thus, exhaust valve head 120a and exhaust valve seat 124 may each include multiple discretely angled surfaces, as described above. Exhaust gases may thus follow a similarly smooth path from combustion chamber 220 to exhaust port 320 (FIG. 3).

[0076] While specific embodiments have been described, many alternative embodiments or variations are possible. For example, while the embodiments have been described in relation to air-cooled engines, the same principles can be applied to liquid-cooled engines. Thus, the features described herein are not limited to air-cooled engines.

[0077] Furthermore, although features have been illustrated and described with reference to particular embodiments herein, such features may be included in any of the disclosed embodiments and variations thereof and are also included herein. Thus, a feature disclosed in connection with any embodiment may be included in any other embodiment.

[0078] As used throughout this specification, the words "comprise," "include," "contain," and "have" are intended to define particular items, steps, elements, or aspects of something in an open-ended manner. Also, as used herein, unless specifically stated to the contrary, the word "set" means one or more of something. This is true whether the phrase "set of" is followed by a singular or plural object or whether a singular or plural verb is conjugated. Also, a "set" of elements may refer to less than all elements present. Thus, there may be additional elements of the same type that are not included in the set. Furthermore, ordinal terms such as "first," "second," and "third" may be used as adjectives herein for identification purposes. Unless specifically indicated, these ordinal terms do not imply any order or sequence. Thus, for example, a "second" event may occur before or after a "first" event, or may occur even if the first event does not occur. Furthermore, identifying a particular element, feature, or act herein as the "first" such element, feature, or act should not be construed as requiring that a "second" or other such element, feature, or act must also be present. Rather, the "first" item may be unique. Also, unless specifically stated to the contrary, "based on" is intended to be non-exclusive. Thus, "based on" should be interpreted to mean "based at least in part on," rather than "based exclusively on," unless otherwise specified. While certain embodiments are disclosed herein, it should be understood that these are provided by way of example only and should not be construed as limiting.

[0079] Thus, it will be appreciated by those skilled in the art that various changes in form and detail can be made in the embodiments disclosed herein without departing from the scope of the following claims. [Explanation of symbols]

[0080] 100 cylinder head 102 Cylinder head inner surface 104 Cylinder head flat shoulder area 110 Intake valve 110a intake valve head 110b intake valve stem 110c intake valve stem guide 112 Intake valve opening 114 Intake valve seat 120 Exhaust valve 120a exhaust valve head 120b exhaust valve stem 120c exhaust valve stem guide 120d hollow region containing sodium 122 Exhaust valve opening 124 Exhaust valve seat 130 Spark plug 132 Spark plug electrode 140 Elliptical shape of combustion chamber 142 Major axis of ellipse 150 Cylinder bore centerline 152 Radial distance to the electrode of the upper spark plug 154 Radial distance to electrode of lower spark plug 156 Cylinder bore radius 200 Cylinder bore diameter as shown 202 Cylinder barrel 210 Piston 220 Combustion chamber 220a Upper combustion chamber region 220b Lower combustion chamber region 230 depression 232 Raised area 240 Flat outer area of ​​piston 310 high tumble intake port 320 exhaust port 410 triple beadlock on valve stem 420 triple bead key 430 Valve retainer (upper spring seat) 440 Lower spring seat (allows the spring (not shown) to push up on the valve retainer) 450 Rocker (connected to camshaft) 510 Multiple discretely angled surfaces on valve head 520 Multiple discretely angled surfaces on valve seats

Claims

1. a cylinder head having an intake valve opening, an exhaust valve opening, a plurality of spark plugs, and an interior surface; a cylinder bore having a cross-sectional area and including a piston configured for reciprocating movement within the cylinder bore; and a combustion chamber having an upper region defined by the inner surface of the cylinder head and a lower region defined by the piston when the piston is in an uppermost position within the cylinder bore; an intake valve arranged to selectively admit intake air into the combustion chamber through the intake valve opening, the intake valve having an intake valve stem and an intake valve head; and an exhaust valve arranged to selectively exhaust exhaust gases from the combustion chamber through the exhaust valve opening, the exhaust valve having an exhaust valve stem and an exhaust valve head; wherein the combustion chamber has an elliptical shape that extends to a cross-sectional area smaller than a cross-sectional area of ​​the cylinder bore, and the elliptical shape has a major axis that intersects the intake valve opening and the exhaust valve opening; each of the intake valve stem and the exhaust valve stem includes a triple bead attachment to a respective valve retainer, each triple bead attachment constructed and arranged to facilitate rotation of the respective valve within the respective valve retainer; Where, air-cooled aircraft engines are: a first spring disposed between an intake valve retainer and a first spring seat of the cylinder head, the first spring constructed and arranged to incrementally rotate the intake valve within the intake valve retainer upon successive compression of the first spring; a second spring disposed between an exhaust valve retainer and a second spring seat of the cylinder head, the second spring constructed and arranged to incrementally rotate the exhaust valve within the exhaust valve retainer upon successive compression of the second spring; further comprising Air-cooled aircraft engine.

2. 2. The air-cooled aircraft engine of claim 1, wherein the cylinder head has a flat shoulder region that abuts a flat outer region of the piston when the piston is in the uppermost position within the cylinder bore, the flat shoulder region and the flat outer region constraining the combustion chamber to the elliptical shape.

3. 3. The air-cooled aircraft engine of claim 2, wherein said plurality of spark plugs each include a respective electrode, said electrodes of said plurality of spark plugs extending below said interior surface of said combustion chamber.

4. 4. The air-cooled aircraft engine according to claim 3, wherein the electrodes of the plurality of spark plugs are positioned closer to the exhaust valve opening than to the intake valve opening.

5. 4. The air-cooled aircraft engine of claim 3, wherein the piston includes a recess beneath the electrode of each of the plurality of spark plugs, and at least a portion of the piston is raised relative to the recess.

6. 4. The air-cooled aircraft engine of claim 3, wherein the cylinder bore has a centerline and a radius, and the electrodes of the plurality of spark plugs are positioned at respective distances from the centerline that are less than 65% of the radius of the cylinder bore.

7. 7. The air-cooled aircraft engine according to claim 1, wherein the cylinder head further includes an intake valve seat that fits within the intake valve opening, and an exhaust valve seat that fits within the exhaust valve opening.

8. 8. An air-cooled aircraft engine according to claim 7, wherein said intake valve seat and said exhaust valve seat are each constructed at least in part from copper-infiltrated powder metal and / or solid alloy.

9. 8. The air-cooled aircraft engine of claim 7, wherein the intake valve seat and the exhaust valve seat each have a respective inner region, each inner region having a plurality of discrete angled surfaces.

10. the intake valve stem has a diameter of less than 9 mm, and the exhaust valve stem has a diameter of less than 9 mm; 8. An air-cooled aircraft engine according to claim 7.

11. 8. The air-cooled aircraft engine of claim 7, wherein the intake valve head and the exhaust valve head have a plurality of discrete angled surfaces adjacent their contact areas with the respective valve seats.

12. 11. The air-cooled aircraft engine of claim 10, wherein the cylinder head includes an exhaust valve stem guide around the exhaust valve stem, the exhaust valve stem guide being constructed at least in part from copper and manufactured as a powdered metal and / or solid alloy.

13. 7. The air-cooled aircraft engine of claim 1, further comprising a high tumble intake port coaxial with the intake valve opening of the cylinder head, the high tumble intake port constructed and arranged to induce vertical flow into the combustion chamber.

14. 1. An air-cooled aircraft engine including a plurality of cylinders, each cylinder comprising: a cylinder head having an intake valve opening, an exhaust valve opening, a plurality of spark plugs, and an interior surface; a cylinder bore having a cross-sectional area and including a piston configured for reciprocating movement within the cylinder bore; a combustion chamber having an upper region defined by the inner surface of the cylinder head and a lower region defined by the piston when the piston is in an uppermost position within the cylinder bore; an intake valve positioned to selectively admit intake air into the combustion chamber through the intake valve opening, the intake valve having an intake valve stem and an intake valve head; and an exhaust valve positioned to selectively discharge exhaust gases from the combustion chamber through the exhaust valve opening, the exhaust valve having an exhaust valve stem and an exhaust valve head; wherein the combustion chamber has an elliptical shape that extends to a cross-sectional area smaller than a cross-sectional area of ​​the cylinder bore, and the elliptical shape has a major axis that intersects the intake valve opening and the exhaust valve opening; each of the intake valve stem and the exhaust valve stem includes a triple bead attachment to a respective valve retainer, each triple bead attachment constructed and arranged to facilitate rotation of the respective valve within the respective valve retainer; Where, air-cooled aircraft engines are: a first spring disposed between an intake valve retainer and a first spring seat of the cylinder head, the first spring constructed and arranged to incrementally rotate the intake valve within the intake valve retainer upon successive compression of the first spring; a second spring disposed between an exhaust valve retainer and a second spring seat of the cylinder head, the second spring constructed and arranged to incrementally rotate the exhaust valve within the exhaust valve retainer upon successive compression of the second spring; further comprising Air-cooled aircraft engine.

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