<p>This thesis work has been performed at the department of diagnosis and dependability at Volvo Car Company, Torslanda. The background of this project is based on interest in ascertaining how different factors possibly can affect a diagnosis method, which has been developed to find leaks in the fuel tank and evaporation system. According to the OBD II requirements leaks with an orifice diameter larger or equal to 0,5 mm, must be detected. The idea of the diagnosis method is to create an over pressure in the system with an air-pump. The current through the pump is measured and correlates to the power consumed by the pump. As the power is a function of the pressure difference over the pump, the pump current correlates to the pressure in the tank. Thus, the pump current can be used as a measure of the impenetrability. Changes in the system pressure, not caused by the pump, are accordingly disturbances to the method. </p><p>The object of this work was to develop mathematical models, describing the lapse where the system is pressurized by the pump under the influence of different physical factors. The model is for instance considering variations in temperature and height, flow resistance in lines and valves, component characteristics, fuel evaporation, leaks etc. Furthermore the pump current is treated by the diagnosis evaluation algorithm with purpose to judge whether there is a leak in the system. </p><p>The model has been implemented in Matlab/Simulink and it can consequently be used in dynamic simulations according to the over pressure leakage detection concept. Numerical experiments can be done in purpose to examine how changes in environmental conditions or component characteristics will affect the diagnosis method. Good agreement has been found between measurements and simulated results. The diagnosis function produces correct decisions under different conditions with disparity in leak sizes, additionally confirming the reliability of the model.</p>

This thesis work has been performed at the department of diagnosis and dependability at Volvo Car Company, Torslanda. The background of this project is based on interest in ascertaining how different factors possibly can affect a diagnosis method, which has been developed to find leaks in the fuel tank and evaporation system. According to the OBD II requirements leaks with an orifice diameter larger or equal to 0,5 mm, must be detected. The idea of the diagnosis method is to create an over pressure in the system with an air-pump. The current through the pump is measured and correlates to the power consumed by the pump. As the power is a function of the pressure difference over the pump, the pump current correlates to the pressure in the tank. Thus, the pump current can be used as a measure of the impenetrability. Changes in the system pressure, not caused by the pump, are accordingly disturbances to the method. The object of this work was to develop mathematical models, describing the lapse where the system is pressurized by the pump under the influence of different physical factors. The model is for instance considering variations in temperature and height, flow resistance in lines and valves, component characteristics, fuel evaporation, leaks etc. Furthermore the pump current is treated by the diagnosis evaluation algorithm with purpose to judge whether there is a leak in the system. The model has been implemented in Matlab/Simulink and it can consequently be used in dynamic simulations according to the over pressure leakage detection concept. Numerical experiments can be done in purpose to examine how changes in environmental conditions or component characteristics will affect the diagnosis method. Good agreement has been found between measurements and simulated results. The diagnosis function produces correct decisions under different conditions with disparity in leak sizes, additionally confirming the reliability of the model.

Diagnosis of faults associated with hydraulic actuators is essential to avoid accidents or loss of system functionality. This thesis focuses on internal leakage fault diagnosis in valve controlled hydraulic actuation systems (VCA) as well as electrohydrostatic actuation systems (EHA). For the VCA, the hydraulic actuator is driven in a closed loop mode to track a pseudorandom input signal whereas for the EHA, an actuator is driven in an open loop mode to track a sinusoidal input. Motivated by developing a method that does not rely on the model of the system or type of fault, signal processing techniques based on the ratio of metric lengths of pressure signals, autocorrelation of pressure signal, cross correlation between chamber pressure signals, and cross correlation between control signal and piston displacement is employed for internal leakage diagnosis. For the VCA, autocorrelation of pressure signals performed well at lower lags (less than 4) and at a window size of 200 data points; both cross correlation between pressure signals and cross correlation between control signal and piston displacement performed well at higher lags (higher than 8) and at a window size of 100 data points; ratio of metric lengths of pressure signals was found to be more effective at higher lag ratios (more than 16:3). All methods were sensitive to the lowest simulated leakage of 0.047 L/min, though with different level of success; ratio of metric lengths produced 84% sensitivity, autocorrelation 19% sensitivity, cross correlation between pressure signals 25% sensitivity and cross correlation between piston displacement and control signal 20% sensitivity. For the EHA, all methods were capable of identifying small leakage of 0.98 L/min. The ratio of metric lengths produced 6.7% sensitivity, autocorrelation 2.59% sensitivity, cross correlation between pressure signals 9.4% sensitivity and cross correlation between piston displacement and control signal 31.9% sensitivity. The low leakage detection achieved without requiring a model of the actuator or leakage type make these methods very attractive for industrial implementation