Method for identifying anomalous behaviour of a dynamic system

A method for detecting anomalous behaviour of a common rail fuel supply system of an internal combustion engine including a pressurised common rail fuel volume arranged to receive fuel from a pumping arrangement and to supply pressurised fuel to a plurality of fuel injectors and a controller arranged to monitor the pressure of fuel within the common rail fuel volume and control the output of the pumping arrangement so as to cause the pressure of fuel within the common rail fuel volume to substantially correspond to a demand rail pressure value, the method including:

• determining a model of the common rail fuel supply system including a plurality of characteristic parameters to define the common rail fuel supply system;
• the plurality of characteristic parameters including one or more of i) a steady state gain value, ii) a system time constant value, and iii) a system time lag value;
• calculating one or more metrics indicative of the current system performance of the common rail fuel supply system based on the plurality of characteristic parameters;
• wherein the one or more calculated metrics include values of i) the steady state gain value, ii) a rate of change of the steady state gain value, iii) the system time constant, and iv) a rate of change of the system time constant,
• comparing the one or more calculated metrics with one or more predetermined metrics that include one or more of i) the steady state gain value, ii) the rate of change value of the steady state gain value, iii) the system time constant value, and iv) the rate of change of the system time constant, said predetermined metrics being indicative of anomalous system behaviour of the common rail fuel supply system;
• and
• identifying a predetermined system fault condition if one or more of the calculated metrics corresponds to one or more of the predetermined metrics.