MPC-based Control of Engine Deceleration with Open Torque Converter

We consider the speed control of a spark ignition engine with an open torque converter during vehicle deceleration. In these conditions, the torque transmitted from the engine to the wheels through the torque converter, and the corresponding torque load on the engine, is related to the torque converter speed ratio, the ratio between the turbine speed and the engine/impeller speed. The engine speed controller needs to effectively coordinate airflow and spark timing and to enforce constraints including engine stall avoidance, misfire avoidance, and desired actuator operating ranges. We formulate a model of the relevant powertrain dynamics, and propose a parametrization that removes a multiplicative nonlinearity, hence enabling the application of linear quadratic model predictive control (MPC). The MPC controller is synthesized as a piecewise affine state feedback and evaluated in simulations and in an experimental vehicle showing good performance in reference tracking and settling time, which translates in smooth and more consistent deceleration profiles and potential for fuel economy improvements.