Method and means for determining exhaust backpressure in a crankcase

Abstract

A method and means are described for determining the average backpressure at a cylinder exhaust port in a crankcase scavenged two-cycle engine. The exhaust backpressure is determined by averaging the pressure of air within a crankcase chamber associated with the cylinder, during a portion of the engine operating cycle when the cylinder inlet and exhaust ports are simultaneously open. The overlap interval in port openings creates a channel for airflow between the crankcase chamber and the cylinder exhaust port, and except for an initial portion of the interval assocated with the pressure equalization between the cylinder and its crankcase chamber, the crankcase pressure substantially equals the backpressure appearing at the cylinder exhaust port. In the preferred embodiment of the invention, a pressure sensor is disposed within the crankcase chamber to sample air pressure at specified engine rotational positions during the overlap interval. These samples are then numerically averaged to obtain the average exhaust backpressure, which is used for compensating the amount of air inducted per cylinder per engine cycle to determined the amount of air per cylinder trapped and available for combustion within the engine. The control of the engine is thereby automatically corrected to account for changes in the engine exhaust system, the altitude of engine operation, and local barometric pressure.