Overlap model based unknown offset-free MPC scheme for torque balancing control in multi-cylinder SI engines

Torque generated from combustion is an important index for advanced engine control and improved torque performance is beneficial to the life of crankshaft, speed smoothness and noise suppression control at idle. For multi-cylinder SI engines, factors such as injector variability and aging lead to imbalance in torque generation between cylinders. The cylinder-to-cylinder imbalance problem is addressed in this paper. Firstly, an index indicating torque imbalance in ignition-event scale is introduced and the individual Spark Advance (SA) is chosen as the actuator. Then the overlap effect between SAs and the proposed index is described by a discrete-time model. In this model, the imbalance in torque generation is represented as unknown offset in inputs. Based on this model, an unknown offset-free MPC controller is designed. Finally, the proposed model and MPC controllers are validated by experiments.