Cylinder balancing control calibration in diesel engines

Automotive control systems have become a driving factor in automotive innovation over the last thirty years. In order to meet the enhanced requirements for lower fuel consumption, lower exhaust emissions, improved safety as well as comfort and convenience functions, automotive control had to be applied. Nowadays the interest toward fuel consumption reduction in reciprocating internal combustion engines has achieved a key role, these concerns grew simultaneously with the interest towards drivability improvement. Drivability strongly depends on engine behavior, torque production is the direct consequence of gases expansion inside the combustion chamber as a result of fuel combustion and is not evenly distributed over a crankshaft revolution. In 4 cylinders engine for example, peaks of torque will occur each 180° of revolution. To meet NVH requirements, in multi cylinders engines, it is important to have the same torque produced by each cylinder, otherwise, the engine would produce vibrations which degrade drivability indexes. Direct responsible for fuel injections is the injector, with the advances in electronics and digital technologies, it became feasible to electronically control the fuel injections to increase the fuel combustion efficiency while reducing emissions. The problem with electronic fuel-injection systems is the need of periodic calibration of the injections. Without calibration, the amounts of fuel injected into the cylinders deviate significantly. This deviations, called drifts, are mainly produced by the aging of the injectors or manufacturing errors and lead to the degradation of NVH performances. Knowing the cause of injection errors and their consequences, it is clear how a control system that manages the injections to equalize cylinder-wise torque contributions is needed. This control system is called Cylinder Balancing, his purpose is to correct the amount of fuel injected by evaluating the engine unbalance from flywheel signals. Depending on the engine, CB needs to be calibrated accordingly. This activity requires to be performed by means of tests on vehicle because of the strong dependance of CB behavior from the driveline, following that all tests needed are highly cost demanding, moreover, in the calibration procedure under consideration it is required a huge amount of hours on vehicle to get to a final calibration. The aim of the thesis is to analyze the current calibration procedure in order to detect areas of improvement in the calibration effort and standardization. The goal of the reviewed calibration procedure is to limit the tests at the roller test bench together with the workload to be exploited at the desk by the calibrator while preserving performances of the control system. At first the current procedure was studied and the area of improvements were highlighted. For some calibration procedures it was possible to virtualize the calibration by retrieving results based on available information instead of new tests, for others it was built a simulation environment on Simulink, able to reproduce the engine response relative to signals of interests, avoiding the need to perform tests at the Dyno. Some of the calibration procedures could not get virtualized in their whole, meaning that tests at the Dyno are the only way to get the information needed to calibrate. In these situations, calibration tools were developed in Python, whose purpose is to assist the calibrator reducing the manual effort and consequently the total time for calibration.