Development of a Control-Oriented Cylinder Air-Charge Model for Gasoline Engines with Dual Independent Cam Phasing 2022-01-0414
Cylinder air-charge is one of the most important parts of the torque control in a gasoline engine, due to the necessity to keep a stoichiometric air-fuel ratio, for the three-way catalyst to work efficiently. Throttle and phasing of the camshafts are actuators that have a big effect on the cylinder air-charge, this results in a cross-coupling between the actuators. One approach to handle the cross-coupling that occurs with multiple actuators is to use model predictive control (MPC), that handles the cross-coupling through the use of models and optimization. Models that support computation of gradients and hessians are desirable for use in MPC.
To support the model design experimental data of cylinder pressure, from an inline four-cylinder engine with dual independent cam phasing, supported by gas exchange simulation, the effects from variable valve timing on the cylinder air-charge are investigated during the valve overlap period. The analysis highlights the effect of a phase described using the path of the least resistance as having an inhibiting effect on the backflow of residual gases during the overlap period. Making the flow reversal over the exhaust valves an important event to keep track of the residual gases.
From the analysis of the effects on air-charge, a model is developed and proposed for the volumetric efficiency, the engine’s ability to fill the cylinders with fresh air. The model structure is derived using partial volumes, and it fits into the Mean Value Engine Model (MVEM) framework, making it is especially useful for control design. The model is validated against stationary measurements and the results show that the proposed model captures the important behaviors and changes in the air-charge related to the variable valve timing. Making it suitable for usage in an MPC framework.