Fuel delivery system for hand-held two-stroke cycle engines

A method of injecting gasoline and oil premix fuel in a two-stroke engine of the cylinder-wall-ported, crankcase-transfer passage aspirated type adapted for powering a hand-held portable tool, the engine being equipped with a fuel injection PT nozzle having a spring-biased outlet valve, a high pressure fuel pump, a crankcase feeding carburetor and a piston and cylinder conjointly defining a combustion chamber and a crankcase wherein gas pressure is developed in response to movement of the piston, the method comprising the steps of:

• (a) operably connecting the piston to mechanically drive the pump to provide a pulsating high pressure output of the pumped fuel in synchronism with cyclical piston reciprocation,
• (b) conducting the pump fuel output via a bypass pressure regulator to the injection nozzle,
• (c) conducting gas pressure from the crankcase to act on the bypass regulator for bypassing the pumped fuel in dependence thereon and for controlling fuel pressure for injecting into the cylinder via the nozzle and burning the same in the engine,
• (d) causing the bypass regulator to cooperate with pumped fuel pressure and the nozzle outlet valve for triggering the injection process and initiating the injection of fuel into the combustion chamber in response to an increase in the crankcase gas pressure caused by engine operational power output above start-up idle and off idle (light load),
• (e) regulating the gas pressure conducted from the crankcase which acts on the bypass regulator in dependence upon at least one of the following parameters;
• the rotational speed of the engine and the load on the engine, and
• (f) continuously aspirating an ambient air/gasoline/oil mixture into the combustion chamber via the carburetor and crankcase under all engine operating conditions and at a rate sufficient only for developing enough engine power for engine start-up idle and off idle (light load).