Fuel metering system for an internal combustion engine

A fuel metering system for an internal combustion engine for determining a desired fuel flow rate based upon the mass of air flow into the engine and a desired air-to-fuel ratio, the engine having a passage through which a mixture of air and fuel is inducted into the combustion chamber or chambers of the engine, the fuel metering system comprising:

• (a) a fuel system having electrically settable means for controlling the rate at which fuel is metered into the engine's intake passage, the fuel metering system determining the settings of the electrically settable fuel system without modification of the desired fuel flow rate except during selected conditions of engine operation, and providing an electrical signal that determines the setting of the fuel system;
• (b) means for modifying the rate at which fuel is metered into the engine's intake passage to take into account the rate at which fuel is transferred from the surfaces of the intake passage to the inducted air/fuel mixture or from the inducted air/fuel mixture to the surfaces of the intake passage;
• said means for modifying the rate at which fuel is metered being a digital computer programmed to calculate repetitively a value representing a current transfer rate of the intake surface fuel and the calculated value being used to modify the rate at which fuel otherwise would be metered into the engine's intake passage by generating a control signal that modifies the desired fuel flow rate to take into account the rate at which fuel enters or leaves the inducted mixture as it passes through the intake passage;
• said means for modifying the rate at which fuel is metered including:
• means for calculating current equilibrium intake surface fuel quantity (EISF.sub.n) as a function of engine operating parameters;
• means for calculating the current intake system time constant (ISTC.sub.n) as a function of engine operating parameters;
• means for calculating current actual intake surface fuel (AISF.sub.n) as a first order differential function of time, previous actual intake surface fuel (AISF.sub.n-1), and previous transfer rate of intake surface fuel (TRISF.sub.n-1);
• and
• means for calculating current transfer rate of intake surface fuel (TRISF.sub.n) as a function of current equilibrium intake surface fuel quantity (EISF.sub.n), current intake system time constant (ISTC.sub.n), and current actual intake surface fuel (AISF.sub.n), so that the transfer rate of the intake surface fuel is repetitively calculated and combined with the desired fuel flow rate to obtain the electrical signal that determines the fuel flow demand from the engine's fuel metering system, the engine operating parameters being used to determine the quantity of liquid fuel that would be present on the surfaces of the engine's intake passage under equilibrium conditions of engine operation and wherein the actual intake surface fuel in the liquid state on such surfaces determines the modification of the desired fuel flow rate, and the actual intake surface fuel is approximated from a previous transfer rate of the intake surface fuel.