Patent Number: 
Section: claims

1. A fault detector for detecting valve movement of a valve in a fuel injector of an engine system, the valve comprising an electromagnetic actuator arranged to move the valve between first and second valve positions during a valve cycle, the engine system comprising a sensor for sensing a current through the actuator, the detector comprising:a controller arranged to control the sensor;an input for receiving from the sensor data related to the current through the actuator;a processor arranged to analyze the received data for current discontinuities; andoutputs for outputting a valve movement signal in dependence upon the current discontinuities determined by the processor;wherein the controller is arranged to enable the sensor during a finite sampling window; to move the sampling window from a first window position for a first injection event to a progressively later window position for one or more subsequent injection events; to determine a new sampling window position on the basis of a valve movement signal output for at least two of the preceding window positions; and to feedback, within the controller, the new sampling window position for a subsequent injection event. 2. A detector as claimed in claim 1, wherein subsequent injection events are successive injection events. 3. A detector as claimed in claim 1, wherein subsequent injection events are one of pilot, main or post injection events within successive injection cycles. 4. A detector as claimed in claim 1, wherein the new sampling window position is determined as a median position of at least two of the preceding window positions, for which a valve movement signal is output. 5. A detector as claimed in claim 1, wherein the sensor is arranged to sample the current at a plurality of sample points during the sampling window. 6. A detector as claimed in claim 1, wherein the current parameter is the current through the sensing resistor. 7. A detector as claimed in claim 1, wherein the sensor is arranged to sense the current through the actuator. 8. A detector as claimed in claim 1, wherein the sensor comprises a sensing resistor and the data received at the inputs is related to the current through the sensing resistor or the voltage across the sensing resistor. 9. A detector as claimed in claim 1, wherein the valve cycle comprises a pull-in region, during which a first voltage potential is applied across the actuator so that the valve is caused to move from a first state to a second state and a hold region, during which a second voltage potential or series of pulses at a second voltage potential is applied across the actuator. 10. A detector as claimed in claim 9, wherein the controller is arranged to enable the sensor between the pull-in and hold regions of the valve cycle. 11. A detector as claimed in claim 9, wherein the controller is arranged to enable the sensor after the hold region of the valve cycle. 12. A detector as claimed in claim 11, wherein the controller is arranged to output a control signal to one or more control switches in order to isolate the actuator from a power supply and to open a current path comprising the actuator and the sensor. 13. A detector as claimed in claim 9, wherein the controller is arranged to progressively move the sampling window away from the end of the hold region in successive injection cycles. 14. A detector as claimed in claim 1, wherein the processor is arranged to analyze the received data by determining the second derivative of the current through the actuator with respect to time. 15. A detector as claimed in claim 14, wherein the processor is arranged to determine the presence of a current discontinuity if a maxima or minima is detected in the second derivative of the current through the actuator. 16. A detector as claimed in either claim 14, wherein the processor is arranged to determine the presence of a current discontinuity if the second derivative of the current through the actuator exceeds a threshold value. 17. A detector as claimed in claim 16, wherein the processor is arranged to determine the presence of a current discontinuity if the second derivative of the current through the actuator exceeds a threshold value for a set period of time. 18. A detector as claimed in claim 14, wherein the processor is arranged to determine the location of the current discontinuity by determining the third derivative of the current, I, with respect to time, the location of the discontinuity being equal to the time when d3I/dt3=0. 19. A detector as claimed in claim 1, wherein the valve movement signal output by the detector is the location with respect to time of the current discontinuities. 20. A method of detecting valve movement of a valve in a fuel injector of an engine system, the valve comprising an electromagnetic actuator that is arranged to move the valve between first and second positions during a valve cycle, the method comprising:sampling the current through the actuator during a finite sampling window with a controller,analyzing the sampled current for current discontinuities with the controller, anddetermining valve movements in dependence upon the current discontinuities with the controller,wherein the sampling window is moved from a first window position for a first injection event to a progressively later window position for one or more subsequent injection events, and in that the method further comprises calculating a new sampling window position on the basis of a fault detect signal output for at least two of the preceding window positions; and feeding back, within the controller, the new sampling window position for a subsequent injection event. 21. A computer program on a computer readable memory or storage device for execution by a computer, the computer program comprising a computer program software portion that, when executed, is operable to implement a method of claim 20. 22. An engine control unit for a vehicle comprising a detector for detecting valve movement of a valve in a fuel injector of an engine system, the valve comprising an electromagnetic actuator arranged to move the valve between first and second valve positions during a valve cycle, the engine system comprising a sensor for sensing a current through the actuator, the detector comprising:a controller arranged to control the sensor;an input for receiving from the sensor data related to the current through the actuator;a processor arranged to analyze the received data for current discontinuities; andoutputs for outputting a valve movement signal in dependence upon the current discontinuities determined by the processor;wherein the controller is arranged to enable the sensor during a finite sampling window; to move the sampling window from a first window position for a first injection event to a progressively later window position for one or more subsequent injection events; to determine a new sampling window position on the basis of a valve movement signal output for at least two of the preceding window positions; and to feedback, within the controller, the new sampling window position for a subsequent injection event.