Fuel metering control system and cylinder air flow estimation method in internal combustion engine

A method for estimating cylinder air flow in an internal combustion engine having an air intake passage provided with a throttle valve, a plurality of engine operation detecting sensors, a microcomputer and a plurality of injectors, said method comprising the steps of:

• determining air flow passing through said throttle valve in response to throttle opening based upon a coefficient, throttle projection area, air density at throttle's upstream side, gravitational acceleration, air specific weight on throttle's upstream side, pressure on throttlers upstream side, pressure on throttle's downstream side;
• determining a quantity of air filling a chamber in said passage extending from said throttle valve to an intake port of said cylinder using ideal-gas law;
• determining a change of said quantity of air in said chamber from change in pressure in said chamber;
• estimating a cylinder air flow based upon said change of said air in said chamber and said throttle passing air flow;
• and
• injecting fuel into individual cylinders of the engine through at least one injector based upon said estimated cylinder air flow.

A system for controlling fuel metering in a multi-cylinder internal combustion engine comprising.:

• a plurality of engine operating detecting sensors;
• a microprocessor means, said microprocessor means being programmed to operate to
• determine a desired cylinder fuel flow at a combustion cycle at or earlier than a last combustion cycle in response to operating states of said engine;
• determine an actual cylinder air flow at a combustion cycle at or earlier than a last combustion cycle;
• determine an actual cylinder fuel flow for individual cylinders at a combustion cycle at or earlier than a last combustion cycle by dividing said actual cylinder air flow by an air/fuel ratio in said cylinder at the same combustion cycle;
• establish an adaptive controller model for controlling an engine model which simulates behavior of fuel adhering to an air intake passage of said engine;
• establish a wall adherence correction compensator model having a transfer characteristic inverse to that of said engine model in series to said engine model;
• adjust a parameter of said transfer characteristic of said wall adherence correction compensator model in accordance with a characteristic predetermined in response to the operating states of said engine;
• wherein said wall adherence correction compensator model is presumed to be a simulated model and when a transfer characteristic of said simulated model becomes other than appropriately 1, said adaptive controller model operates such that a transfer characteristic of said engine model and adaptive controller model becomes appropriately 1;
• and
• at least one injector for injecting fuel into individual cylinders according to said transfer characteristic of said engine model output by said microcomputer.