Internal-combustion engines – Convertible cycle
Reexamination Certificate
1999-12-27
2001-09-11
Kamen, Noah P. (Department: 3747)
Internal-combustion engines
Convertible cycle
Reexamination Certificate
active
06286467
ABSTRACT:
FIELD OF THE INVENTION
This application relates to a method and apparatus for converting an internal combustion engine from four stroke operation to two stroke operation which is applicable to various sizes and configurations of engines having either spark or compression ignition.
BACKGROUND
Four stroke internal combustion engines having varying numbers of cylinders are commonly used in various types of vehicles as they are known to make relatively efficient use of fuel as opposed to a two stroke internal combustion engine. For certain applications however, it is desirable to make use of the improved torque characteristics associated with two stroke engines. Adapting a conventional four stroke engine however, into a conventional two stroke engine is generally a costly and time consuming procedure as adjustment of the relative orientation of the pistons as well as the location and timing of the valves comprises a substantial replacement of parts.
U.S. Pat. No. 5,154,141 to McWhorter describes an internal combustion engine which operates as a four stroke engine at low speeds and as a two stroke engine at higher speeds. The cycle frequency of the valve operation is doubled for two stroke operation by gearing the camshaft to rotate at crankshaft speed rather than at half crankshaft speed as in four stroke operation. In order to successfully convert from four stroke operation to two stroke operation the engine requires a complex arrangement of a gas ejector and an electronic timing circuit which controls the rate of fuel injection and spark ignition. The complex arrangement of numerous parts results in a costly and high maintenance engine design in order to make use of the benefits of two stroke operation.
SUMMARY
According to one aspect of the present invention there is provided a method of converting to two stroke operation a four stroke internal combustion engine having a plurality of pistons arranged for reciprocating movement within respective cylinders, an inlet valve and an exhaust valve associated with each cylinder, a crankshaft coupled to the pistons, the crankshaft being driven to rotate by reciprocation of the pistons, a original camshaft assembly coupled to the crankshaft, the camshaft assembly comprising at least one original camshaft carrying a plurality of original cams for actuating respective inlet and exhaust valves and an original drive assembly coupling the camshaft to the crankshaft such that the camshaft is rotated at half a speed of the crankshaft; said method comprising:
providing a replacement camshaft assembly for actuating the respective inlet and exhaust valves, the replacement camshaft being arranged to open the valves once per revolution of the crankshaft; and
replacing the original camshaft assembly with the replacement camshaft assembly.
A conventional four stroke, four cylinder engine is thus converted to a two stroke engine wherein two pistons are fired synchronously every half revolution of the crankshaft with a minimal replacement of parts. The resulting engine exhibits improved torque characteristics without expensive or time consuming engine refitting. The camshaft assembly can be replaced using conventional tooling without requiring extensive work to the engine.
The replacement camshaft assembly preferably comprises at least one replacement camshaft carrying a plurality of replacement cams, each replacement cam having a pair of lobes such that a corresponding one of the valves is opened twice per revolution of the camshaft. The pair of lobes of each replacement cam are preferably 180 degrees out of phase from each other. The replacement drive assembly thus comprises a driven sprocket on the replacement camshaft driven by a driving sprocket on the crankshaft, the driven sprocket having twice a number of teeth of the driving sprocket such that the replacement camshaft is rotated at half crankshaft speed.
Alternatively, the replacement camshaft assembly may comprise a replacement drive assembly having a driven sprocket on a replacement camshaft driven by a driving sprocket on the crankshaft, the driven sprocket having a number of teeth equal to a number of teeth on the driving sprocket such that the replacement camshaft is rotated at crankshaft speed. Each replacement cam thus preferably includes a single lobe such that a corresponding one of the valves is opened once per revolution of the camshaft.
The method may further include mounting a turbocharger, a supercharger or both on the engine in communication with the inlet valves.
When the engine includes electronic fuel injection, said method includes programming the electronic fuel injection to inject fuel in each cylinder once per revolution of the crankshaft.
Alternatively, when the engine includes a cam actuated fuel injector driven by the crankshaft, the method may include providing dual lobed fuel injector cams driven at half crankshaft speed for injecting fuel into the respective cylinders once per revolution of the crankshaft.
When the engine includes a cam actuated fuel injector driven by the crankshaft, said method may include providing a single lobed fuel injector cams driven at crankshaft speed for injecting fuel into the respective cylinders once per revolution of the crankshaft.
For an engine having a plurality of pairs of pistons, said method preferably includes firing each pair of pistons synchronously once per revolution of the crankshaft.
When using a supercharger or turbocharger, the method may include providing a pressure feed lubrication system within a sump of the engine.
According to a further aspect of the present invention there is provided a two stroke internal combustion engine comprising:
a plurality of pairs of pistons arranged for sliding movement within respective cylinders, a first and second piston of each pair of pistons being located in a same position relative to the respective cylinders as the first and second pistons are displaced within the respective pistons such that the first and second pistons are fired synchronously;
an inlet valve and an exhaust valve associated with each cylinder;
a crankshaft coupled to the pistons, the crankshaft being driven to rotate by reciprocation of the pistons;
a camshaft assembly coupled to the crankshaft, the camshaft assembly comprising:
a plurality of cams mounted on a camshaft for engaging respective inlet and exhaust valves; and
a drive assembly coupling the camshaft to the crankshaft such that the cams open the respective valves once per revolution of the crankshaft.
The operation of the pistons in a two stroke configuration makes use of the improved torque characteristics of two stroke engines. Firing the pistons synchronously in pairs further improves the torque characteristics of the engine for improved engine performance.
Each cam preferably includes a pair of lobes spaced 180 degrees apart about the camshaft and the drive assembly couples the camshaft to the crankshaft to rotate the camshaft at half crankshaft speed such that each of the valves is opened twice per revolution of the camshaft.
The engine preferably includes two pairs of pistons, the first and second pistons of each pair of pistons being arranged to fire synchronously once per revolution of the crankshaft. The pairs of pistons are preferably fired 180 degrees apart.
There may be provided air supply means mounted in communication with the inlet valves for supplying combustion air above atmospheric pressure to the cylinders.
There may be provided a cam actuated fuel injector for injecting fuel into the respective cylinders and dual lobed cams driven at half crankshaft speed for injecting fuel into the respective cylinders once per revolution of the crankshaft.
REFERENCES:
patent: 4018050 (1977-04-01), Murphy
patent: 4102130 (1978-07-01), Stricklin
patent: 4162662 (1979-07-01), Melchior
patent: 4353334 (1982-10-01), Neitz
patent: 4671226 (1987-06-01), Rinsum
patent: 5005539 (1991-04-01), Kawamura
patent: 5022353 (1991-06-01), Kamamura
patent: 5036801 (1991-08-01), Imajou
patent: 5113805 (1992-05-01), Kawamura
patent: 5154141 (1992-10-01), McWhorter
Battison Adrian D.
Huynh Hai
Kamen Noah P.
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