A Model Based Calibration Process for Robust Optimal Cam Position Selection Under all Engine Operating Conditions

A traditional problem with calibration of optimal cam positions is that the calibration usually needs to compromise torque at normal operating conditions on good fuel (ie highest RON/MON) in order to avoid drivability issues via high COV of IMEP under more extreme (eg lowest RON, high ambient temperature) conditions.

A traditional approach to optimal calibration of VVT (Variable Valve Timing) positions uses one target fuel at one inlet air temperature. Often torque (BSFC) under normal conditions (eg emissions cycle) takes priority over the degradation in drivability under more extreme conditions, yielding non-robust cam calibration. Depending on the calibration approach, ignition angle may not be part of the design of experiment. With this traditional approach the effect of different fuels (RON/MON) and ambient conditions such as inlet air temperature are difficult to build into a robust cam calibration.

In this paper a calibration process is presented which takes into account the change in ignition angle efficiency (via decreasing RON and increasing inlet air temperature) and the corresponding optimal cam positions to allow best torque (BSFC) whilst satisfying COV limits to prevent drivability issues. The process outlined in this paper is a model based calibration process utilizing 1 and 2-stage statistical response models generated using MATLAB and the Model Based Calibration Toolbox.