This invention relates to an internal combustion engine.

Background of the Invention

Internal combustion engines tend to operate on either a two stroke or a four stroke cycle. A four stroke cycle means that a combustion event only occurs once in four back and forth movements of the piston. Two stroke engines by comparison perform a combustion event in only two back and forth movements of the piston, meaning that two stroke engines are often lighter for a given power output. This makes two stroke engines particularly useful in smaller applications where improved power cannot be easily achieved by simply increasing the size of the engine. Example uses of two stroke engines include hand held power tools, small bikes and remotely operated light aircraft.

In a four stroke engine, exhaust gas is expelled from the cylinder and a fresh draught of air and fuel is drawn into the cylinder in one back and forth movement of the piston, with combustion occurring in a separate back and forth movement of the piston. In a two stroke engine air and exhaust gas must be expelled and a fresh draught of air and fuel drawn into the cylinder in the same back and forth movement of the piston as combustion occurs. To achieve this, the crankcase is incorporated into the working volume of the engine. As the piston moves away from the crankcase a fresh draught of air and fuel is drawn in. Then, as the piston moves toward the crankcase, the air is displaced around the piston through a bypass valve and into the combustion chamber. Following combustion, exhaust gases are expelled through an opening in the combustion chamber wall when the piston moves toward the crankcase.

Four stroke engines tend to use the crank case as an oil reservoir for lubricating components of the engine. In a two stroke engine, the incorporation of the crankcase into the working volume of the engine prevents this as, over a short period, the constant stream of fuel-air mixture would carry away the lubricating oil into the combustion chamber while thinning the remainder with condensing fuel. Therefore, two stroke engines have typically required the fuel to be premixed with oil so that oil is introduced into the cylinder with the air and fuel. Unsurprisingly, this results in a greater quantity of oil being burned during combustion than in a four stroke engine, negatively affecting the engine’s emissions performance. Furthermore, once oil has been burned, it can no longer provide any lubrication.

More recent two stroke engines use a technology known as ‘auto-lube’, in which oil is stored in a separate tank and premixed with the fuel just prior to its introduction into the cylinder. This still results in oil being burned; however, given that the oil is not properly mixed with the fuel when burned in the combustion chamber, it translates into a slightly more efficient lubrication. Another problem associated with two stroke engines is that when the throttle is closed, fuel and oil is being delivered into the cylinder, resulting in oil starvation and increased engine wear.

It is an object of the invention to provide an internal combustion engine having improved lubrication performance.

It is a further object of the invention to provide a two stroke engine that offers improved emissions and lubrication performance. Statements of Invention

According to the invention there is provided a single acting internal combustion engine comprising at least one cylinder and a piston disposed within the cylinder, the piston being connected to a crankshaft by a connecting rod, wherein an oil outlet is provided to distribute oil between a cylindrical wall of the piston and the cylinder, said oil outlet communicating with an oil supply gallery extending through the connecting rod, the piston further comprising an oil inlet communicating with an oil return gallery extending through the connecting rod, the oil inlet being configured to absorb excess oil from the cylinder wall and transfer the excess oil along the oil return gallery; wherein the piston comprises upper and lower oil control rings that extend circumferentially around the piston between the cylindrical wall of the piston and the cylinder, the oil outlet and the oil inlet being disposed between the upper and lower oil control rings; and wherein the engine is configured to operate on a two stroke cycle.

The distance between the upper and lower oil control rings maybe between 50% and 100% of a height of the cylindrical wall of the piston. More preferably, said distance is between 50% and 95%, or 70% and 95% of the height of the cylindrical wall of the piston.

The upper and lower oil control rings may each comprise a chamfered edge in contact with the wall of the cylinder, the chamfered edge being configured to direct excess oil into a space between the upper and lower oil control rings.

The piston may be connected to the connecting rod by a gudgeon pin, the gudgeon pin comprising an oil supply bore that communicates with the oil supply gallery extending through the connecting rod, and wherein said oil outlet communicates with the oil supply bore in the gudgeon pin so that, during operation of the engine, oil passes through the oil supply gallery in the connecting rod, into the oil supply bore in the gudgeon pin and out of the oil outlet, for distribution between the cylindrical wall of the piston and the cylinder.

The oil supply bore may comprise an internal diameter that is 60-85% of the external diameter of the gudgeon pin.

The oil outlet maybe disposed in an end face of the gudgeon pin.

The diameter of the oil outlet may be 60-85% the external diameter of the gudgeon pin.

The oil outlet maybe disposed in the cylindrical wall of the piston. The oil outlet may comprise a plurality of outlets spaced about the cylindrical wall of the piston.

The connecting rod may comprise an upper bearing to locate the gudgeon pin, and wherein a bearing surface of the upper bearing is in moving contact with an outer surface of the gudgeon pin, the oil supply bore in the gudgeon pin and the oil supply gallery extending through the connecting rod each opening into a groove that extends around the outer surface of the pin and/ or the bearing surface of the upper bearing to communicate oil between the oil supply gallery extending through the connecting rod and the oil supply bore in the gudgeon pin, irrespective of rotation of the gudgeon pin relative to the connecting rod during operation of the engine. An oil supply gallery may extend through the crankshaft to communicate with the oil supply gallery extending through the connecting rod to supply the oil supply gallery extending through the connecting rod with oil during operation of the engine. Opposite ends of the crankshaft may be supported by main bearings, a bearing surface of each of the main bearings supporting respective main bearing journals of the crankshaft, and wherein the oil supply gallery extending through the crankshaft is open at a surface of a first main bearing journal to pick up oil fed between the first main bearing journal and a respective first main bearing during operation of the engine.

The connecting rod may comprise a lower bearing to connect the connecting rod to a connecting rod journal of the crankshaft, and wherein a bearing surface of the lower bearing is in moving contact with said connecting rod journal, the oil supply gallery extending through the crankshaft and the oil supply gallery extending through the connecting rod each opening into a groove that extends around said connecting rod journal and/or the bearing surface of the lower bearing, to communicate oil between the oil supply gallery extending through the crankshaft and the oil supply gallery extending through the connecting rod, irrespective of rotation of the journal relative to the connecting rod during operation of the engine.

The oil inlet may communicate with an oil return bore in the gudgeon pin, which in turn communicates with oil return galleries that extend through the connecting rod and crankshaft, respectively. Brief Description of the Figures

Fig. 1 is a schematic view of a two stroke internal combustion engine;

Fig. 2 is a detail schematic view of a piston and gudgeon pin assembly of the engine of Fig. 1;

Fig. 3 is a detail schematic view of an alternative piston and gudgeon pin assembly of the engine of Fig. 1;

Fig. 4 is a cross section showing features of the engine of Fig 1;

Fig. 5 is a cross section showing features of the engine of Fig 1;

Fig. 6 shows features of the engine of Fig. 1; and

Fig. 7 shows a gudgeon pin according to embodiments of the invention. Detailed Description

A schematic diagram of an internal combustion engine l is shown in fig. l. The engine l comprises: a cylinder 2; a piston 3 disposed within the cylinder 2; a crankshaft 4 and a connecting rod 5 that connects the piston 3 to the crankshaft 4. Reciprocal movement of the piston 3 within the cylinder 2 turns the crankshaft 4 in the usual way.

Embodiments of the engine described herein are single acting. By ‘single acting’ it is meant that the working fluid (expanding combustion gases) act on one side of the piston only, as will be readily appreciated by anyone skilled in the art.

Embodiments of the engine 1 described herein operate on a conventional two stroke cycle, a detailed description of which is omitted.

The engine 1 comprises an external oil reservoir 6 which forms part of a closed loop oil distribution system 7 to ensure lubrication of the various moving parts of the engine 1.

The distribution system 7 comprises a network of oil supply galleries that take oil from the reservoir 6 and distribute oil between moving surfaces of the engine 1. When the oil distribution system 7 is used in combination with an engine operating on a two stroke cycle, the requirement that fuel supplied to the engine be premixed with oil is eliminated, substantially alleviating some of the disadvantages mentioned above.

A pump 8 may be provided to circulate oil around the distribution system 7. In particular, lubrication may be achieved by pumping oil through oil supply galleries in the crankshaft 4, connecting rod 5 and associated pins and bearings, as will be explained hereinafter.

Referring to Fig. 2, the piston comprises a cylindrical wall 9, or piston skirt. The piston 3 is connected to the connecting rod 5 by a piston pin 10, or gudgeon pin. The gudgeon pin 10 is rotatably located at either end by bearings 11 in the cylindrical wall 9 of the piston.

The connecting rod 5 comprises an upper bearing 12 to connect the connecting rod 5 to the gudgeon pin 10. The upper bearing 12 is a through hole in an upper end of the connecting rod 5 which receives the gudgeon pin. An inner surface of the upper bearing 12 is in moving contact with the gudgeon pin 10. The connecting rod 5 further comprises a lower bearing 13 to connect the connecting rod 5 to a journal 14 of the crankshaft, herein referred to as the connecting rod journal 14. This is illustrated most clearly in the cutaway sections of Figs. 4 and 5. The lower bearing 13 comprises a through hole in a lower end of the connecting rod 5 which receives the connecting rod journal 14. During operation of the engine, an inner surface of the lower bearing 13 is in moving contact with the connecting rod journal 14.

The crankshaft 4 is rotatably located at either end by first and second main bearings 15, 16 (shown in the schematic of Fig. 1). The main bearings 15, 16 support respective first and second main bearing journals 17, 18 of the crankshaft 4. The first and second main bearing journals 17, 18 are shown most clearly in Fig. 6. During operation of the engine, surfaces of the main bearings 15, 16 are in moving contact with corresponding surfaces of the main bearing journals 17, 18. Oil is fed through an oil feed 19 which opens into the first main bearing 15. Therefore, during operation of the engine 1, oil is distributed between the surfaces of the first main bearing 15 and the corresponding first main bearing journal 17.

As shown in Fig. 4, an oil supply gallery 20 extends through the crankshaft 4 between the first main bearing journal 17 and the connecting rod journal 14. During operation of the engine, oil is picked up from between the surfaces of the main bearing journal 17 and the main bearing 15 and supplied into the lower bearing 13 along said oil supply gallery 20 in the crankshaft 4. Oil fed along the oil supply gallery 20 in the crankshaft 4 is distributed between the surfaces of the lower bearing 13 and the connecting rod journal 14, before being picked up by an oil supply gallery 21 in the connecting rod 5. Said oil supply gallery 21 extends between the lower and upper bearing 13, 12 surfaces to supply oil into the upper bearing 12.

Oil supplied into the upper bearing 12 is picked up by openings 22 in a cylindrical wall 23 of the gudgeon pin 10 and fed into an oil supply bore 24. The oil supply bore 24 extends axially from a first face 25 of the gudgeon pin 10. The oil supply bore 24 extends only partially through the gudgeon pin 10 for reasons that will become apparent below. Referring to Fig. 2, oil in the oil supply bore 24 passes out through the end of the bore 24 at the first face 25 of the gudgeon pin 10, so that oil is distributed between the cylindrical wall 9 of the piston and the cylinder 2. Therefore, said end of the bore 24 forms an oil outlet 50.

In one embodiment, the oil supply bore 24 comprises a relatively large internal diameter. By relatively large internal diameter, it is meant that the diameter of the oil supply bore 29 may be 60-85% of the external diameter of the gudgeon pin 10. Advantageously, by providing a relatively large internal diameter, the flow of oil through the oil supply bore 24 is increased and therefore more oil can be distributed between the cylindrical wall 9 of the piston and the cylinder 2. This largely increases the lubrication and cooling capabilities of the engine.

The piston 3 comprises upper and lower oil control rings 26, 27 that extend circumferentially around the piston 3 between the cylindrical wall 9 of the piston 3 and the cylinder 2. The upper and lower oil control rings 26, 27 are disposed either side of the gudgeon pin 10. Therefore oil distributed between the piston 3 and the cylinder 2 is mostly retained by the upper and lower oil control rings 26, 27. Only a thin film of oil remains in the cylinder 2 outside the oil control rings 26, 27. Said thin film of oil is maintained by reciprocal movement of the piston 3 during operation of the engine 1.

In one embodiment, the upper and lower oil control rings 26, 27 are spaced relatively far apart. By relatively far apart, it is meant that the distance between the upper and lower oil control rings 26, 27 is between 50% and 100% of the height of the cylindrical wall 9 of the piston 3. More preferably, the spacing of the upper and lower oil control rings 26, 27 is between 50% and 95%, or 70% and 95%, of the height of the cylindrical wall 9 of the piston 3. In embodiments where the spacing of the oil control rings 26, 27 is 100% of the height of the cylindrical wall 9 of the piston 3, the upper and lower oil control rings 26, 27 are disposed as close to upper and lower ends of the cylindrical wall 9 of the piston 3 as is practicably possible. By spacing the upper and lower oil control rings 26, 27 relatively far apart, a larger volume of oil is trapped between the cylindrical wall 9 of the piston 3 and the cylinder 2, increasing the cooling effect of the oil.

The upper and lower oil control rings 26, 27 may comprise a chamfered edge 28 in contact with the cylinder 2, the chamfered edge 28 being configured to direct excess oil into a space between the upper and lower oil control rings 26, 27. Referring again to Figs. 2 and 5, an oil return bore 29 extends axially from an opening 51 in a second face 30 of the gudgeon pin 10. The oil return bore 29 extends only partially through the gudgeon pin 10. Because the oil return bore 29 and the oil supply bore 24 extend only partially from opposing faces 25, 30 of the gudgeon pin 10, a partition wall 31 is provided which separates the oil return bore 29 from the oil supply bore 24.

Similar to the oil supply bore 24, the oil return bore 29 may also have a relatively large diameter. The diameter of the oil return bore 29 may be 60-85% of the external diameter of the gudgeon pin. Preferably the diameter of the oil supply bore 24 and the oil return bore 29 are identical. Providing the oil return bore 29 with a large diameter increases the flow of oil around the gudgeon pin and allows the oil to flow quickly through the oil distribution system. Therefore, the lubrication and cooling capabilities of the engine are improved.

Oil distributed between the piston 3 and the cylinder 2 is picked up by the oil return bore 29 and returned to the oil reservoir 6 through oil return galleries 32, 33 extending through the connecting rod 5 and crankshaft 4, respectively. In this way, the opening 51 in the second face 30 of the gudgeon pin acts as an oil inlet configured to absorb excess oil from the cylinder 2 for return to the reservoir 6.

Oil picked up by the oil return bore 29 passes through an oil return opening 34 in the cylindrical wall 23 of the gudgeon pin 10 and is fed into the upper bearing 12. Oil is picked up in the upper bearing 12 and fed to the lower bearing 13 by the oil return gallery 32 extending through the connecting rod 5 from the upper bearing 12 to the lower bearing 13. Oil is picked up in the lower bearing 13 and fed to the second main bearing 16 by the oil return gallery 33 extending through the crankshaft 4 from the connecting rod journal 14 to the second main bearing journal 18. Drain ports 35 are provided in the second main bearing 16 to allow oil to return to the reservoir 6 via an oil return feed 36.

Spherical valves 37 are optionally provided in the oil supply and return bores 24, 29 of the gudgeon pin 10 to limit the flow of oil out of and into of the oil supply galleries 20, 21 and oil return galleries 32, 33, respectively. Each valve 37 comprises a solid metal sphere having a diameter marginally less that the diameter of the bore 24, 29 in which it is received. Therefore a small gap is provided between the inner surface of the bore 24, 29 and the valves 37 to control the rate of flow of oil by simple restriction.

Each of the upper and lower bearings 12, 13 comprise separate oil supply and oil return tracts to prevent oil from returning to the reservoir 6 prematurely by passing directly from an oil supply gallery 20, 21 to an oil return gallery 33, 32. Specifically, in the lower bearing 13, said separate tracts prevent oil from passing directly between the oil supply and oil return galleries 20, 33 of the crankshaft 4; while in the upper bearing 12 said separate tracts prevent oil from passing directly between the oil supply and oil return galleries 21, 32 in the connecting rod 5.

The oil supply and oil return tracts comprise grooves 38, 40, 39, 41 that extend around the upper and lower bearings 12, 13 as explained in more detail below. Additionally or alternatively corresponding grooves 43, 44, 42, 45 may also be provided on the gudgeon pin 10 and connecting rod journal 14 - as illustrated.

An upper end of the oil supply gallery 21 in the connecting rod 5 opens into an oil supply groove 38 in the upper bearing (as shown in Fig. 4); while a lower end of the oil supply gallery 21 opens into an oil supply groove 39 in the lower bearing 13. Likewise, an upper end of the oil return gallery 32 in the connecting rod 5 opens into an oil return groove 40 in the upper bearing 12; while a lower end of the oil return gallery 32 in the connecting rod 5 opens into an oil return groove 41 in the lower bearing 13.

In the illustrated embodiment, the gudgeon pin 10 and connecting rod journal 14 comprise corresponding oil supply 43, 42 and oil return grooves 44, 45 that align with the oil supply 38, 39 and oil return grooves 40, 41 of the upper bearing and lower bearing, respectively, to form oil supply and oil return channels. The oil supply channels define a path for oil fed from the reservoir 6 around the upper and lower bearings 12, 13. Oil is supplied along said path to the oil supply bore 24 in the gudgeon pin 10 and is distributed between the piston 3 and the cylinder 2. In a similar way, the oil return channels define a path around the upper and lower bearings 12, 13 to ensure that oil is returned efficiently to the reservoir 6.

Furthermore, the oil supply and oil return grooves 39, 42, 38, 43, 40, 44, 41, 45 ensure that a path for oil is provided around the upper and lower bearings 12, 13, irrespective of movement of the gudgeon pin 10 and connecting rod journal 14 relative to the respective upper and lower bearings 12, 13. For example, during operation of the engine 1, the connecting rod journal 14 rotates about its axis. Therefore, the position of the openings to the oil supply 20 and oil return galleries 32 in the connecting rod journal 14 will change relative to the corresponding openings for the oil supply 21 and oil return galleries 32 in the lower bearing 13. The grooves 39, 41, 42, 45 ensure sufficient capacity for oil to pass through the lower bearing 13, even when said openings are not aligned. Likewise, the position of the openings to the oil supply and oil return bores 24, 29 in the gudgeon pin 10 will change relative to the openings for the oil supply and oil return galleries 21, 32 in the upper bearing 12. Again, the grooves 38, 40, 43, 44 ensure sufficient capacity for the oil to pass through the upper bearing 12, even when said openings are not aligned.

In another embodiment illustrated by Fig. 3, in which like features retain the same reference numbers, the oil supply bore 24 and oil return bore 29 are not open at end faces 25, 30 of the gudgeon pin 10, but are instead closed off. Oil is distributed through an internal supply channel 55 that extends around the cylindrical wall 9 of the piston 3. Outlets 54 extend radially between the cylindrical wall 9 of the piston 3 and the supply channel 55. The supply channel 55 opens into a groove in bearings 11 to fluidly communicate with passages 53 in the gudgeon pin 10. The passages extend between the oil supply bore 24 and the outer cylindrical surface 23 of the gudgeon pin 10. Therefore, oil is distributed under pressure from the oil supply bore 24, out through passages 53, into the supply channel 55 and then from outlets 54.

In such embodiments, oil may be returned to the oil return bore 29 through oil inlets 56 in the cylindrical wall 9 of the piston 3. The oil inlets 56 communicate with an oil return channel 58 which extends internally about the cylindrical wall 9 of the piston 3. Passages 57 connect the oil return channel 58 with the oil return bore 29. Therefore oil maybe returned to bore 29 through oil inlets 29, into the oil return channel 58 and then through passages 57.

The oil outlets 54 and the oil inlets 56 are spaced around the circumference of the cylindrical wall 9 of the piston 3, with the oil inlets 56 located below the oil outlets 54.

Although the oil control rings 26, 27 are not shown in Fig. 3, it shall be appreciated that this is for brevity only. It is intended that such embodiments comprise upper and lower oil control rings 26, 27 disposed above and below outlets 54 and inlets 56, respectively. Fig. 7 shows a gudgeon pin 10 according to an embodiment which may be used interchangeably with the gudgeon pin 10 of any of the above described embodiments.

In the embodiment of Fig. 7, the diameter of the opening 50 of the oil supply bore 24 and the opening 51 of the oil return bore 29 each comprise a relatively large diameter. By relatively large internal diameter, it is meant that the diameter of each of the respective openings 50, 51 maybe 60-85% of the external diameter of the gudgeon pin 10. Each opening 50, 51 may be countersunk. In other words, each opening 50, 51 may be enlarged by machining a frustoconical surface into respective ends 50, 51 of the oil supply bore 29 and the oil return bore 29. Providing each opening 50, 51 with a relatively large diameter enables oil contact on a larger surface area of the cylinder wall, retained between the upper and lower oil control rings 26, 27 and increases the flow of oil around the gudgeon pin 10, allowing the oil to flow quickly through the oil distribution system. Therefore, the lubrication and cooling capabilities of the engine are improved

It shall be appreciated that oil distribution over the moving components of an internal combustion engine is essential for both lubrication and cooling. By distributing oil along internal galleries 20, 21, 32, 33 in the connecting rod 5 and the crankshaft 4, the cooling effect of the oil is enhanced. The cooling effect is yet further enhanced by directing oil around a large area of the piston wall 9, between upper and lower oil control rings 26, 27. In the present invention, oil can carry heat from both the inside and outside of the crankshaft, connecting rod and piston. In known systems, heat is only carried away by oil splashed onto external surfaces of engine components, which is less effective. In particular, cooling the piston is one of the biggest challenges in a conventional two stroke combustion engine. This problem is made worse in long stroke engines in which oil often fails to reach the upper parts of the cylinder. Keeping the piston cool is important for keeping combustion temperature down and, therefore, controlling emissions. More effective cooling also allows higher compression ratios to be used without causing engine knock, further enhancing thermodynamic efficiency.