Control system and method for turbocharged throttled engine

A method of controlling a turbo-charged throttled engine having an intake air compressor, an exhaust turbine which receives engine exhaust, an air throttle between the compressor and the engine, and a wastegate communicated with engine exhaust upstream and downstream from the turbine, the method comprising:

• generating a desired air mass value per engine stroke value as a function of a desired fuel flow amount and stored compressor surge characteristics;
• generating a desired pressure boost value as a function of the desired manifold pressure value and the stored compressor surge characteristics;
• generating a desired manifold air pressure value as a function of the desired air mass value and sensed engine parameters;
• determining an offset value representing a desired pressure drop across the air throttle;
• adding the offset value to the desired manifold air pressure value to produce a desired boost pressure value;
• computing a maximum allowable pressure boost to avoid compressor surge or overspeed;
• comparing the desired pressure boost value to the maximum allowable pressure boost value;
• if the desired pressure boost value is greater than the maximum allowable pressure boost value, then setting the desired pressure boost value equal to the maximum allowable pressure boost value;
• controlling the wastegate so that an actual boost pressure matches the desired boost pressure;
• and
• controlling the air throttle so that an actual manifold air pressure matches the desired manifold air pressure.