Abstract: Methods and systems are described for monitoring air/fuel imbalance in cylinders of an engine. Engine speed signals are sampled and then run through a notch filter set to the sampling frequency. Based on a first frequency content of the resulting filtered engine speed, cylinder imbalance is detected and addressed.

Abstract: An engine, a first motor generator and a second motor generator are controlled by calculating an engine power target from a driving power target required for a vehicle, and finding a target engine operating point expressed by a set of an engine speed target and an engine torque target on a target operating line determined in response to the engine power target. When the found target engine operating point is different from the previously found one, a change in engine speed target is limited to a predetermined amount of change and the engine torque target of the set is reset versus an engine speed target involving the limited change based on the determined target operating line. Consequently, the engine power target and thus the driving power target are ensured so as to restrain or prevent sudden or frequent changes in engine speed with the efficiency kept high.