Flatness-based control for an internal combustion engine cooling system

To further increase the efficiency of internal combustion engines, improved model-based control approaches for the thermal management become important. Due to time varying thermal loads in the dynamic operation of internal combustion engines active measures involving feedforward and feedback control must maintain a desired nominal engine temperature. Furthermore, both fuel consumption and harmful emissions could be reduced by a short heating-up phase till the optimal operating temperature of the engine. In this paper, hence, a control-oriented model of the thermal behaviour of the engine cooling system is presented. In this model, the volumes flows through the cooling unit as well as the bypass - which are decoupled from the engine angular velocity - are introduced as varying system parameters. Based on this system model, a nonlinear flatness-based control strategy with the engine temperature as flat output is developed. The control structure is extended by a disturbance observer providing estimates for the lost heat of the engine. The complete control structure is adapted to the varying volume flows using gain-scheduling. To allow for an experimental validation of the proposed control approach a small-scale test rig has been build up at the Chair of Mechatronics, University of Rostock. First experimental results show small tracking errors and an advantageous system behavior that allows for an optimization of heating-up strategies in future work.