Internal-combustion engines – Two-cycle – Rear compression
Reexamination Certificate
2000-03-02
2001-09-25
Argenbright, Tony M. (Department: 3747)
Internal-combustion engines
Two-cycle
Rear compression
Reexamination Certificate
active
06293234
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to two-stroke combustion engines and more particularly to port-controlled two-stroke combustion engines wherein the movement of a piston within a cylinder acts to open and close intake, exhaust and transfer ports of that engine.
Port-controlled two-stroke combustion engines generally comprise a cylinder, a piston working in the cylinder, a crankcase and one or more flywheels rotatably mounted in the crankcase. An intake port and an exhaust port are provided in the cylinder wall respectively for admitting and exhausting combustible mixture to the engine. Transfer ports are also provided in the cylinder wall. Transfer passages, which each extend between a respective crankcase transfer port and a respective combustion chamber transfer port, convey air/fuel mixture from the crankcase to the combustion chamber.
In two-stroke engines of this type, the combustible mixture flows through the intake port into the cylinder at the crankcase side of the piston when the piston is adjacent the cylinder head. As the engine fires and the piston moves towards the crankcase, this combustible mixture is then compressed in the crankcase. When the piston approaches its extremity of travel closest to the crankcase, it uncovers transfer ports in the cylinder wall. This allows the combustible mixture which has been compressed in the crankcase to flow along the transfer passages into the cylinder between the piston and the cylinder head.
The power of such two-stroke engines is dependent upon the efficiency of the circulation of the combustible mixture when the engine is in operation and, in particular, the efficient transfer of combustible mixture from inside the crankcase to the combustion chamber. For this reason, conventional two-stroke engines generally attempt to maximize the total cross-sectional of the transfer passages and associated porting by providing at least one transfer passage on each side of the cylinder wall and an auxiliary transfer passage on the same side of the cylinder wall as the intake port.
SUMMARY OF THE INVENTION
Nevertheless, it has been found during the development of the present invention that the delivery of the combustible mixture in the engine, notably through the transfer passages, is inadequate and results in unacceptable engine performance in many circumstances. It is an object of the invention to provide a port-controlled two-stroke engine which exhibits an improved delivery of combustible mixture within the engine during operation with respect to known port-controlled two-stroke engines.
It is a further object of the invention to provide a port-controlled two-stroke engine with improved delivery of combustible mixture during operation from the crankcase to the cylinder head.
It is another object of the invention to provide a port-controlled two-stroke engine which is simple, efficient and powerful.
It is still another object of the invention to provide a port-controlled two-stroke combustion engine which ameliorates or overcomes at least some of the disadvantages of known port-controlled two-stroke combustion engines.
With this in mind, the present invention provides a port-controlled two-stroke engine comprising a combustion chamber, a crankcase containing a combustible mixture, a cylinder having a front and a rear, a piston working in the cylinder, an intake duct terminating in an intake port in the front of the cylinder wall for delivering the combustible mixture to the engine, at least one flywheel rotatively mounted in the crankcase about an axis of rotation, the rotation of the flywheel acting to drive the boundary layer of the combustible mixture immediately adjacent the periphery of the flywheel around the periphery, and a transfer passage, extending from a first transfer port in the rear of the cylinder wall adjacent said crankcase to a second transfer port in the rear of the cylinder wall adjacent the combustion chamber, for conveying the combustible mixture from the crankcase to the combustion chamber, the flywheel having a plane of rotation which passes through one or more of the first transfer port, transfer passage and second transfer port, the intake port and the intake duct being oriented so as to deliver the combustible mixture directly into the crankcase, the intake duct being located in substantially the same plane as a plane of rotation of the flywheel.
According to such an arrangement, the first transfer port in the cylinder wall adjacent the crankcase is located to take advantage of the momentum imparted by the rotating flywheel or flywheels to the boundary layer of combustible mixture around its periphery. Placing this first transfer port, in addition to the transfer passage and second transfer port, in a plane of rotation of the flywheel enables the boundary layer of combustible mixture to be transferred directly into the transfer port and through the transfer passage, rather than the tortuous path provided in prior art two-stroke engines having laterally located transfer passages, and maximizes the efficiency of the transfer of the boundary layer of combustible liquid into the first transfer port and along and out of the transfer passage.
In known two-stroke internal combustion engines, the intake duct is arranged to deliver combustible mixture into the cylinder at a location remote from the crankcase. By direct delivery of the combustible mixture into the crankcase, the force applied to the boundary layer of combustible mixture by the flywheel or flywheels is taken advantage of to optimize the efficiency with which the combustible mixture drawn into the engine through the intake duct is transferred around the periphery of the flywheel or flywheels and into the transfer port in the cylinder wall adjacent the crankcase.
By locating, the intake duct and the transfer duct in substantially the same plane as a plane of rotation of the flywheel or flywheels, combustible mixture is drawn into the engine through the intake valve and it passes around the periphery of the flywheel, into the transfer port adjacent through crankcase and through the transfer passage into the combustion chamber in a relatively unrestricted manner, as this circulation takes place in the one plane without requiring rapid changes in direction of the combustible mixture.
In a preferred embodiment, a flywheel or flywheels have two opposed faces immediately adjacent interior surfaces of the crankcase. According to such an arrangement, the chambers located laterally of the opposing faces of the flywheel or flywheels, required in known two-stroke internal combustion engines in order for the combustible mixture to be provided from the crankcase and into the laterally located transfer passages, may be omitted. This enables the exterior faces of the flywheel or flywheels to be placed in close proximity to, or flush against, the interior wall of the crankcase. A reduction in the volume of combustible mixture is thus achieved, which increases the pressure of the combustible mixture in the crankcase to more efficiently drive this combustible mixture into the front-located transfer port or ports.
According to another aspect of the invention, the second transfer port in the cylinder wall adjacent the combustion chamber has a minimum radius of 1.0 mm between the cylinder wall and the transfer passage. This arrangement enables the efficiency of the two-stroke internal combustion engine to be improved by a reduction in the turbulent flow of the combustible mixture circulated in the engine.
In one embodiment, the first transfer port has a minimum radius of 2.0 mm, and preferably 2.5 mm, between the wall of the cylinder and the transfer passage. Preferably, the first transfer port has a progressively variable minimum radius between the wall of the cylinder and the transfer passage. The radius of the first transfer port may progress, for example, from a minimum of 2.0 mm at the wall of the cylinder to a minimum of 13 mm adjacent to the transfer passage so that the first transfer port has a bell-shaped mouth. This progressive radius change fu
Ali Hyder
Andrus Sceales Starke & Sawall LLP
Applied Automotive Concepts Pty LTD
Argenbright Tony M.
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