Control strategies for a powertrain with hydromechanical transmission

This paper deals with the management of an engine equipped with a continuous hydro-mechanical transmission. The traditional minimum fuel consumption control strategy requires the control system to keep the engine along the minimum fuel consumption line. However, this strategy may not be the best one, since the performance of the powertrain depends on both engine efficiency and transmission efficiency. Therefore, a methodology was developed in order to extend the minimum fuel consumption control strategy for the engine to the engine-transmission set, that is, to the whole powertrain. To achieve this goal, the case of an urban bus equipped with a dual-stage hydromechanical transmission was studied. The vehicle's powertrain model was first used to derive the family of minimum consumption curves for the powertrain; subsequently to simulate the behavior of the vehicle. The comparison between the minimum consumption criterion for the engine and the minimum consumption criterion for the powertrain shows a slight advantage of the latter.