Method for calculating the air charge for an internal combustion engine with variable valve timing

In an internal combustion engine equipped with an intake pipe and a control apparatus to control the engine, the engine having a cylinder defining a work volume and which, during engine operation, contains a total gas charge including a mixture charge and residual combusted gas with the mixture charge including a fresh-air portion conducted under pressure in the intake pipe with said fresh-air portion being indicative of the load on said engine, the cylinder including an inlet valve and an outlet valve for facilitating an exchange of said total gas charge and the engine including valve control means for controlling the opening and closing of said valves in dependence upon an operating parameter of said engine, a method for dynamically correctly computing said fresh-air portion wherein the exchange of said total gas charge is influenced in dependence upon said operating parameter the opening phases of said valves being shifted relative to each other thereby defining an overlap variable indicative of the duration that said valves are simultaneously open to said total gas charge, the method comprising the steps of:

• determining said pressure of said fresh-air portion in said intake pipe to obtain a value thereof;
• measuring said duration to obtain a value thereof;
• and,
• computing said fresh-air portion from the values of said pressure and said duration thereby providing an indication of the load on said engine.