Holistic Evaluation of CO
Saving Potentials for New Degrees of Freedom in SI Engine Process Control Based on Physical Simulations
Specific shifting of load points is an important approach in order to reduce the fuel consumption of gasoline engines. A potential measure is cylinder deactivation, which is used as a study example. Currently CO2 savings of new concepts are evaluated by dynamic cycles simulations. The fuel consumption during driving cycles is calculated based on consumption-optimized steady-state engine maps. Discrete load point shifts occur as shifts within maps. For reasons of comfort shifts require neutral torque. The work of deactivated cylinders must be compensated by active cylinders within one working cycle. Due to the larger time constant of the air path the air charge must be increased or decreased in order to deactivate or activate cylinders without affecting the torque. A working-cycle-resolved, continuously variable parameter is prerequisite for process control. Manipulation of ignition timing enables a reduction of efficiency and gained work. So far dynamic cycle simulation does not take into account additional fuel consumption due to shifts of operating points. A new method is developed to investigate the influence of these highly dynamic operating events on total CO2 savings. Relevant operating point shifts are determined by dynamic cycle simulations. Additional fuel consumption is calculated by use of a one-dimensional model of air path and a predictive zero-dimensional model of the combustion chamber. A wheel-neutral discrete shift of operating points is controlled by automatically generated setpoint trajectories of process parameters. Applying cost functions enables the evaluation of different degrees of freedom in process control independently from the controller’s quality. After calculating setpoint trajectories for an engine configuration the results are applicable to further driving cycles and vehicle configurations without additional effort. This method is examined on various driving cycles. Taking into account the consumption by shift operations the advantages of cylinder deactivation in cycle simulation decrease with increasing operating dynamics.
Tim Wandschneider, Katharina Wiege, Wolfram Gottschalk
International Powertrains, Fuels & Lubricants Meeting