A study was conducted on step-change faults in oil pressure differential signals for a certain type of engine,following the occurrence of such faults in multiple engines during batch production and delivery.The Fault Tree Analysis(FTA)method was employed to investigate step-change faults in the oil pressure differential signals of the engine's digital control system,confirming that the faults were caused by abnormal operation of the oil pressure differential acquisition system.Through analysis of the oil pressure differential acquisition circuit principles in the engine's Digital Electronic Controller(DEC),along with dedicated power-off tests and simulation-based investigations of the DEC,the root cause of the step-change faults was identified.The results indicated that mismatched electrical parameters between the phase margin compensation capacitor in the DEC's oil pressure differential excitation circuit and the external cables/sensors,combined with insufficient phase margin,led to excitation oscillations in the oil pressure differential system.These oscillations subsequently caused abnormal step-changes in sensor outputs.To address this issue,the phase margin compensation capacitor value in the DEC's oil pressure differential excitation circuit was modified from 300 pF to 30 pF.The effectiveness of this corrective measure was verified through stability simulations,laboratory tests,and on-engine validation.
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