Internal-combustion engines – Particular piston and enclosing cylinder construction
Reexamination Certificate
1999-03-05
2001-06-05
McMahon, Marguerite (Department: 3747)
Internal-combustion engines
Particular piston and enclosing cylinder construction
C123S054400
Reexamination Certificate
active
06240892
ABSTRACT:
BACKGROUND OF THE INVENTION
Designs for turbocharged two stroke cycle internal combustion engines have been known for a long time. The turbocharger is used to draw in outside air and pressurize it to a desired pressure. The pressurized air is then supplied to the intake ports of the cylinders in the engine. When the piston in a cylinder is near the bottom of its stroke, the intake ports are open which allow the pressurized air to enter the cylinder and push exhaust gas out of the cylinder. Fresh air is left behind in the cylinder for the next combustion cycle. After the piston begins its upward movement, a fuel injector injects fuel into the top of the cylinder.
A drawback of prior two stroke cycle engine designs becomes apparent when one tries to start them. Since the turbocharger uses the exhaust gas from the engine for its source of power and since there is no appreciable exhaust gas during startup, the turbocharger lacks the exhaust gas needed to operate efficiently and so there is no pressurized air available at the intake ports of the cylinders during startup.
Common solutions to this startup problem have included “Roots blowers” and other mechanical superchargers and scavenge pumps which are mechanically coupled to the crankshaft of the engine. The rotational movement of the crankshaft by the starter motor drives the Roots blower, supercharger or pump which then provides the startup air pressure to get the two stroke cycle engine started. Once started, the turbocharger receives the exhaust gas needed to become operational and the turbocharger thereafter supplies most of the compressed air for normal operation of the engine.
As noted, however, such a design requires a fairly complicated blower, supercharger or pump which has a substantial cost. Further, when the engine is for use in boats or airplanes, the additional weight of the blower, supercharger or pump is particularly undesirable.
Another drawback of conventional designs for two stroke cycle engines is that they include separate cylinder heads, separate cylinder walls, and/or a separate crankcase. Each of the separate components must be joined together with suitable fasteners, such as bolts, which add significant weight to the engine design. At each joint between components, a gasket is often used to prevent leaks. The gasket is sandwiched between opposing faces which are drawn tightly together. To insure a good seal, the opposing faces are typically thicker than adjoining materials. The increased thickness of the opposing faces adds further weight to the design.
Accordingly, there is a need for a lightweight, high output two stroke cycle turbocharged engine which starts reliably without use of heavy mechanical blowers.
SUMMARY OF THE INVENTION
Among the objects of the present invention are to provide an improved method and apparatus for a two stroke cycle internal combustion engine; to provide such improved method and apparatus which is relatively light in weight and has relatively high output power; to provide such improved method and apparatus which starts reliably without; need for an external mechanical blower, supercharger or pump; to provide such improved method and apparatus which operates efficiently and can be manufactured at low cost; and to provide such improved method and apparatus which has the cylinder head, cylinder wall and upper portion of the crankcase integrally formed from the same material.
In one embodiment, the invention comprises a two stroke cycle engine having an intake port for passing air into a cylinder of the engine. The engine includes a piston within the cylinder for reciprocal movement between a top dead center position and a bottom dead center position. The engine also includes a crankcase, an intake valve in a wall of the crankcase, a plenum chamber for supplying air to the intake port and an output valve between the crankcase and the plenum chamber. The engine also has an air compressor and an air compressor valve between the air compressor and the plenum chamber. The engine has a first mode of operation during startup wherein the piston draws air into the crankcase through the intake valve a the piston moves towards its top dead center position and wherein the piston forces air from the crankcase, through the output valve, into the plenum chamber and to the intake port as the piston moves towards its bottom dead center postion. The engine has a second mode of operation during which the engine is running wherein the air compressor forces air through the air compressor valve, into the plenum chamber and to the intake port.
In another embodiment, the invention comprises a kit for retrofitting a two stroke cycle engine to allow the engine to startup without use of a startup air compressor. The engine includes an intake port for passing air into a cylinder of the engine and a piston within the cylinder for reciprocal movement between a top dead center position and a bottom dead center position. The engine further includes a run-time air compressor and a plenum chamber for supplying air from the air compressor to the intake port. The engine also has a crankcase. The kit includes an intake valve adapted for use in a wall of the crankcase to allow air to pass into the crankcase during startup of the engine as the piston moves towards its top dead center position. The kit also includes an output valve adapted for use between the crankcase and the plenum chamber to allow air to pass from the crankcase into the plenum chamber during startup of the engine as the piston moves towards its bottom dead center position. The kit also includes an air compressor valve adapted for use between the run-time air compressor and the plenum chamber to allow air to pass from the run-time air compressor into the plenum chamber while the engine is running.
In yet another embodiment, the invention comprises a two stroke cycle engine having a plurality of cylinder assemblies. Each cylinder assembly has a cylinder and a cylinder head. The engine includes a removable fastener and a crankcase having an upper portion and a lower portion. The lower portion of the crankcase is secured to the upper portion with the removable fastener. The cylinder assemblies are directly connected to the upper portion of the crankcase. The upper portion of the crankcase fits against the lower portion of the crankcase in approximately a same plane and the cylinders, cylinder heads and upper portion of the crankcase are all integrally formed from a same material.
In yet another embodiment, the invention comprises a two stroke cycle engine having an intake port for passing air into a cylinder of the engine and a piston within the cylinder for reciprocal movement between a top dead center position and a bottom dead center position. The engine includes a crankcase, a one way intake valve in a wall of the crankcase, a plenum chamber for supplying air to the intake port and a one way output valve between the crankcase and the plenum chamber. The engine also includes an air compressor and a one way air compressor valve between the air compressor and the plenum chamber.
In yet still another embodiment, the invention comprises a method of retrofitting a two stroke cycle engine to allow the engine to startup without use of a startup air compressor. The engine has an intake port for passing air into a cylinder of the engine and has a piston within the cylinder for reciprocal movement between a top dead center position and a bottom dead center position. The engine further has a run-time air compressor and a plenum chamber for supplying air from the air compressor to the intake port. The engine also has a crankcase. The method includes the step of providing an intake valve in a wall of the crankcase to allow air to pass into the crankcase during startup of the engine as the piston moves towards its top dead center position. The method also includes the step of providing an output valve between the crankcase and the plenum chamber to allow air to pass from the crankcase into the plenum chamber during startup of the engine as the piston moves tow
Benton Jason
Fox III Angus C.
McMahon Marguerite
LandOfFree
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