Fault diagnosis and protection for fuel injection ofhigh-pressure common rail diesel engine

Abstract: The high pressure common rail injection pressure has a great impact on the performance of the diesel engine; The fuel injection mass and engine emission depend greatly on the injection pressure control accuracy. In order to strengthen the reliability and accuracy of the rail pressure control, fuel injection pressure fault detection schemes were completed based on the research of the rail pressure sensor sampling process and a fuel injection pressure control algorithm, including the faults of rail pressure closed-loop control and the pressure limiting valve fault. The diagnostic function software and appropriate protection strategies were designed basing on the existing common rail electronic control unit with the Matlab/Simulink and RTW Embedded Coder toolsets. Based on the difference of target rail pressure and actual rail pressure, and output value of rail pressure close loop control, the positive and negative control failures were identified by a diagnostic function. The purpose of the pressure relief valve (PRV) monitoring is to detect the opening of the PRV, and to force it to open in cases where it did not open during too high rail pressure, or in cases where the fuel pressure sensor is broken. The diagnostic function software recognizes an opened PRV by tracing the pressure breakdown in the rail. If the pressure limiting valve opens under the normal operating state, the gradient of rail pressure is calculated by a diagnostic function, and appropriate failure was identified if the gradient exceeded the corresponding limit. If the pressure limiting valve does not open under high rail pressure, then diagnostic function would force the pressure limiting valve to open by increasing pump fuel, and the appropriate failures were identified if the pressure limiting valve was still closed. Finally, the diagnostic function software was tested in a diesel engine test rig; Test results showed that the diagnostic function software can effectively identify various fuel injection pressure failures, neither underreporting nor misstatements, and corresponding protection strategies can put the engine into a safe state, and improve the reliability of the injection pressure control.