Fuel Pressure Monitoring
Fuel Pressure MonitoringGeneral Description
Low fuel pressure system
The low pressure system is the fuel delivery system to the high pressure system. In order to keep the delivery pressure in a certain range the fuel pressure is controlled via fuel pressure sensor. The low pressure system has no direct impact on Air/Fuel mixture and emissions.
High fuel pressure system
The electrical controlled, mechanical-driven high pressure fuel pump provides the injection pressure. The fuel pressure sensor and the control valve in the high pressure system control the high pressure between approximately 3 and 11 MPa. The target pressure depends mainly on engine speed and torque request.
OBD monitors are electrical faults, out of range checks, rationality checks on the low and high pressure systems.
Monitoring function description
A. Strategy description
The pinpointing-strategy is based on the fact that incorrect pressure information will cause Lambda deviations due to the pressure based calculation of the injection time.
Incorrect pressure information can only be caused by positive or negative offset-faults of the high pressure sensor.
However faults of the pump control valve also influence the pressure control activity but they will be completely corrected (Lambda controller deviation ~0) through the calculation of the corresponding injection time.
Through combination and evaluation of the following characteristics therefore a differentiation of faults and drifts between sensor and actuator is possible:
- pressure controller deviation
- lambda controller deviation
Pinpointing schematic for High pressure system
B. Explanations
Pressure controller deviation
Depending on deviation between target and actual pressure, the pressure control system becomes active.
Total pressure control output consisting of proportional value, integral value and adaptation value. The total pressure control output influences the high pressure control valve in order to adjust the nominal pressure value.
Lambda controller deviation
Lambda controller deviation determines the factor of the Lambda-controller including the additive and multiplicative correction values of the fuel trim.