Gm Global Technolgoy Operations, Inc.

Aparicio J Gomez

Paul E Reinke

Douglas E Trombley

Steven D Stiles

Kenneth J Buslepp

Dennis W Montville

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.

Method and means for determining exhaust backpressure in a crankcase

A method and apparatus are described for determining the mass of air available for combustion within a cylinder of a crankcase scavenged two-cycle engine, without the use of a mass-air flow sensor. This is achieved by estimating the mass of air under compression within a crankcase chamber, prior to its transfer to a cylinder combustion chamber. The estimate for air mass is based upon the integration of crankcase pressure over the interval of decreasing crankcase volume, while air within the crankcase is under compression. The volume of the air within the crankcase chamber is derived as a function of engine cycle position, with crankcase air temperature being derived as a function of intake air temperature. Air pressure during compression is monitored with a crankcase pressure sensor. The estimate for air mass is corrected to account for air leakage and incomplete transfer of the air between the crankcase and combustion chambers.

Method and means for determining air mass in a crankcase scavenged

A method and means are described for determining the mass of air available for combustion within a cylinder of a crankcase scavenged two-cycle engine, without the use of a mass-air flow sensor. This is achieved by estimating the mass of air under compression within a crankcase chamber, prior to its transfer to a cylinder combustion chamber during the engine operating cycle. The estimate for air mass is based upon the polytropic behavior of a portion of the crankcase compression process, and the pressure, volume and temperature of the air at two predetermined engine rotational positions during the polytropic phase of compression. The volume of the air within the crankcase chamber is determined as a function of engine rotational angle, with crankcase air temperature being derived as a function of intake air temperature. Air pressure during the polytropic phase of compression is sensed with a pressure sensor disposed within the crankcase chamber. The estimate for air mass is corrected to account for air leakage and imperfect transference of the air between the crankcase and combustion chambers.

A method and means are described for determining the mass of air available for combustion within a cylinder of a crankcase scavenged two-cycle engine, without the use of a mass-air flow sensor. This is achieved by estimating the mass of air under compression within a crancase chamber, prior to its transfer to the cylinder combustion chamber. The estimate for air mass is based upon the integration of crankcase pressure over the interval of decreasing crankcase volume, while air within the crankcase is under compression. The volume of the air within the crankcase chamber is derived as a function of engine cycle position, with crankcase air temperature being derived as a function of intake air temperature. Air pressure during compression is monitored with a crankcase pressure sensor. The estimate for air mass is corrected to account for air leakage and incomplete transfer of the air between the crankcase and combustion chambers.

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Birmingham, MI, United States of America

Aparicio J Gomez