Integrated control of a lean burn engine and a continuously variable transmission

A powertrain control method for controlling admission of air and fuel into a cylinder of a lean burn internal combustion engine and for controlling a continuously variable drive ratio of a continuously variable transmission coupled to the engine, comprising the steps of:

• sampling input signals indicating a current engine operating condition;
• estimating engine cylinder mean effective pressure;
• determining when the estimated engine cylinder mean effective pressure is less than a predetermined threshold pressure, indicating a low mean effective pressure condition;
• detecting when the current engine operating condition is a predetermined lean burn engine operating condition;
• sensing a commanded change in a powertrain output power level;
• and
• while the predetermined lean burn engine operating condition is detected, (a) selecting transmission drive ratio, engine fuel quantity per cylinder and engine air volume per engine cylinder as the control parameters that may be controlled to provide a powertrain output power level change corresponding to the commanded change in powertrain output power level with minimum emissions, and (b) increasing engine fuel quantity per cylinder and engine air volume per cylinder while decreasing transmission drive ratio to provide for the powertrain output power level change while the low mean effective pressure condition is indicated to provide for the commanded change in powertrain output power level with minimum emissions.