INTERNAL COMBUSTION ENGINE

Abstract: An internal combustion engine (10) has a crankshaft (12), with aligned crankpins (13), which are connected to pistons (20, 21) in respective cylinders (18, 19). An intake valve (32) connects an intake port (31) to the "pumping" cylinder (18) and an exhaust valve (34) connects the "power" cylinder (19) to an exhaust port (33). A transfer port (35), controlled by transfer valves (36, 37) interconnects the two cylinders (18, 19). On each revolution of the crankshaft (12), the air/fuel mixture is compressed in the "pumping" cylinder (18) and is transferred to the "power" cylinder (19), via the transfer port (35), for ignition by the spark plug (38) on the power stroke of the power cylinder (19) on the succeeding revolution of the crankshaft (12).

Description: Title; "INTERNAL COMBUSTION ENGINE" BACKGROUND OF THE INVENTION (1 ) Field of the Invention This invention relates to improvements in internal combustion engines. (2) Prior Art Many proposals have been advanced' in the past to improve the efficiency of normally aspirated (i.e. non-turbocharged/non-supercharged) four stroke internal combustion engines. For example, Australian Patent Application -No. 91386/82 (Thompson) and Australian Patent No. 512069 (Kee) both disclose parallel-twin engines where the ai /fuel mixture is compressed in the crankcase similar to a two-stroke engine. Australian Patent No. 213330 (Hammick) . discloses a two-cylinder engine where the second piston is connected to a crankshaft geared at a ratio of 2: 1 to the crankshaft of the first piston to give a complex stroke pattern for the two cylinders. Australian Patent No. 19315/34 (Groves) discloses a two-cylinder engine with common combustion chambers with the pistons connected to offset crankpins to extend the overall time of the power stroke. All these engines are fairly complex and none appear to have ever reached commercial manufacture. SUMMARY OF THE PRESENT INVENTION It is an object of the present invention to provide an engine having .at least one pair of cylinders where a firing stroke occurs for every revolution of the crankshaft. It is a preferred object to provide an engine where the incoming air/fuel mixture is compressed in one cylinder and is ignited (or fired) in the second cylinder, It is a further preferred object to provide an engine where the first cylinder can have a greater capacity than the second cylinder to pressurize (or "supercharge") the second cylinder. Other preferred objects of the present invention will become apparent from the following description. In one aspect the present invention resides in a two-cylinder internal combustion engine including: a crankcase having a crankshaft rotatably mounted therein and fitted with a cylinder head assembly; a first (or "pumping") cylinder and a second (or "power") cylinder in the crankcase; a piston in each cylinder connected to aligned crankpins on the crankshaft; an intake port in the cylinder head assembly connected to the first cylinder and closable by an intake valve; an exhaust port in the cylinder head connected to the second cylinder and closable by an exhaust valve; and a transfer port in the cylinder head assembly interconnecting the first and second cylinder and closable by a transfer valve; and spark ignition means in the second cylinder; so arranged that: on each revolution of the crankshaft, the —incoming air/fuel mixture enters and is compressed in the first cylinder and is transferred to the second cylinder for ignition and exhaust on the next revolution of the crankshaft. The first cylinder may have a greater capacity than the second cylinder to "supercharge" the air/fuel mixture entering the second cylinder. The transfer port may be closed at each end by respective transfer valves, where the transfer valve adjacent the first cylinder may close before the valve adjacent the second cylinder. In a second aspect, the present invention resides in a multi-cylinder engine having two or more pairs of cylinders as hereinbefore described. BRIEF DESCRIPTION OF THE DRAWINGS To enable the invention to be fully under¬ stood preferred embodiments will now be described with reference to the accompanying drawings in which: FIG. 1 is a sectional side view of a first embodiment, being a two-cylinder engine; FIGS. 2 to 6 are schematic views showing the relative positions of the ' pistons and valves as the crankshaft completes one revolution; and FIG. 7 is a schematic side view of an eight cylinder engine, having four pairs of cylinders. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, the engine 10 is of the overhead cam shaft type having an engine block with a crankcase 11 supporting a crankshaft 12, with aligned crankpins 13, in suitable bearings 14. A flywheel 15 is mounted on one end of the crankshaft 12, while a cam- belt pulley 16 and crankpulley 17 are mounted at the other end of the crankshaft. A pair of cylidners 18, 19 are provided in the engine block and each is provided with a piston 20, 21 connected to respective crankpins 13 by connecting rods 22. As can be clearly seen, the pistons move up and down in the cylinders in unison as the crankshaft 12 is rotated. A cylinder head assembly 23 is mounted on top of the engine block to close the cylinders 18, 19. A camshaft 24 is mounted in bearings 25 in the head assembly and is driven by a cam belt 26 via a pulley 27, the cam belt being tensioned by an idler pulley 28. . The cam shaft operates to open and close a pair of valves in each cylinder 18, 19, via cam followers 29 and valve springs 30. An intake port 31 in the head assembly 23 is connected at one end to an intake manifold (not shown) provided with a carburettor or fuel injection unit (not shown) which provides an air/fuel mixture to be burnt in the engine. An intake valve 32, controlled by the camshaft 24, selectively allows the mixture to enter the first cylinder 18. An exhaust port 33 is connected at one end to an exhaust manifold (not shown). An exhaust valve 34, also controlled by the camshaft 24, selectively allows the exhaust gases to be expelled from the second cylinder 19. A transfer port 35 interconnects the two cylinders, the port being selectively closed by first and second transfer valves 36, 37 controlled by the camshaft 24. The operation of the engine will now be described. The first cylinder 18 At, or just before top dead centre (TDC) of the piston 20 (FIG. 2), intake valve 32 opens the intake port 31 to enable the air/fuel mixture to be drawn into the cylinder as the piston moves towards bottom dead centre (BDC). Transfer valve 36 remains closed. At (FIG. 3), or just before BDC (FIG 4), the intake valve • closes. As the piston now moves up towards TDC (FIG. 5), the air/fuel mixture is compressed until, just before TDC (FIG. 6), the transfer valves 36, 37 open to allow the non compressed mixture to be transferred to the second cylinder 19 via transfer port 35. At, or just after TDC the transfer valves 36, 37 close, with valve 36 closing just " before valve 37. (Overlap between the opening of the intake valve 32 and transfer valve 36 ensures complete - J5E_ O PI filling of the first cylinder 18 with the incoming air/ fuel mixture and assists the transfer of the compressed mixture through the transfer port 35). The second cylinder 19 As the piston 21 moves down from TDC (FIG. 2) the compressed air/fuel mixture enters the cylinder and is ignited by a sparkplug 38(FIG. 3). The burning air/fuel pushes the piston down on a power stroke to BDC (FIG. 4). At or just after BDC (FIG. 5), the exhaust valve 34 opens and- the now burnt gas is expelled out through the exhaust port 33 as the piston approaches TDC (FIG. 6), where the exhaust valve 34 closes and the transfer valves 36, 37 open to enable a fresh change to be transferred from the first cylinder 18. (Overlap between the opening of transfer valve 37 and closing of exhaust valve 34 to ensure the incoming air/fuel mixture assists the scavenging of the exhaust gases from cylinder 19). For each rotation of the crankshaft, the first cylinder 18 undergoes an intake stroke and a compression stroke and the second cylinder undergoes a power stroke and exhaust stroke of the mixture compressed in the first cylinder in the previous rotation of the cranshaft, By making first cylinder 18 larger than the second cylinder 19, the ai /fuel mixture will be "supercharged" to further improve the efficiency of the engine. While a pair of transfer valves 36, 37 are shown, only one is required, this being preferably provided at the second-cylinder end of the transfer port to reduce the combustion chamber capacity (and thereby increase the compression ratio of the second cylinder) than if provided at the first cylinder end of the transfer port. OMPI Referring now to FIG. 7, an eight cylinder engine has four pairs of cylinders 18, 19 indicated by pairs 1-4. Each pair of cylinders has pistons 18, 19 connected by connecting rods 12 to a crankshaft 12a, supported in bearings 14, in the manner hereinbefore described. •The crankshaft has four pairs of aligned crankpins 13 where the crankpins 13 for one pair of cylinders are offset 90° from the crankpins 13 of the preceding and succeeding pairs of cylinders. Therefore, each pair of cylinders will compress and fire the air/ fuel mixture (in the manner hereinbefore described) for every revolution of the crankshaft and the overlapp¬ ing firing strokes of the second cylinders 19 will ensure-a smooth delivery of power. In the engine 50, the cylinder pairs operate in the order 1, 3, 4, 2 but this may be changed to e.g. 1, 2, 3, 4 if preferred. It will be readily apparent to the skilled addressee that the invention can be applied to any engines having 2n cylinders (where n ■= integral number) and to overhead valve (OHV) as well as overhead cam (0HC) engines. The invention can also be applied to "Diesel" engines, where a fuel injection nozzle replaces the sparkplug 38 in the second cylinder 19. Various changes and modifications may be made to the embodiments described without departing from the scope of the present invention.

Claims: CLAIMS 1. A two-cylinder internal combustion engine including: a crankcase having a crankshaft rotatably mounted therein and fitted with a cylinder head assembly; a first (or "pumping") cylinder and a second (or "power") cylinder in the crankcase; a piston in each cylinder connected to aligned crankpins on the crankshaft; an intake port in the cylinder head assembly connected to the first cylinder and closable by an intake valve; an exhaust port in the cylinder head connected to the second cylinder and closable by an exhaust valve; and a transfer port in the cylinder head assembly interconnecting the first and second cylinder and closable by a transfer valve; and spark ignition means in the second cylinder; so arranged that: on each revolution of the crankshaft, the incoming air/fuel mixture enters and is compressed in the first cylinder and is transferred to the second cylinder for ignition and exhaust on the next revolution of the crankshaft. 2. An engine as claimed in claim 1 wherein: the first cylinder has a greater capacity than the second cylinder to "supercharge" the air/fuel mixture entering the second cylinder. 3. An engine as claimed in Claim 1 or Claim 2 wherein: the transfer port is closed at each end by respective transfer valves, where the transfer valve adjacent the first cylinder closes before the transfer valve adjacent the second cylinder. 4. An engine as claimed in Claim 3 wherein: the opening of the intake valve and the transfer valve adjacent the first cylinder overlap to ensure complete filling of the first cylinder by the in¬ coming air/fuel mixture and to assist the transfer of the already compressed air/fuel mixture from the first cylinder through the transfer port to the second cylinder. 5. An engine as claimed in Claim 3 wherein: the opening of the exhaust valve " and the transfer valve adjacent the second cylinder overlap to enable the compressed air/fuel mixture entering the second cylinder to assist the scavenging of the exhaust gases from the second cylinder. 6. A multiple cylinder engine having two or more pairs of cylinders as ' claimed in any one of Claims 1 to 5 wherein the aligned pairs of crankpins are equally angularly spaced to provide an equal period between the firing of the second cylinders in each pair of cylinders for each revolution of the crankshaft. O PI

Inventors: LENAHAM JAMES, LENAHAM, JAMES
Applicants: LENAHAM JAMES, LENAHAM, JAMES
Application year: 1984
Main classification: F02B33
IPC codes: F02B1, F02B33