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An engine management system for an internal combustion engine, which has at least one cylinder pressure sensor and at least one engine actuator, includes a data processor arranged to receive and process cylinder pressure data from the cylinder pressure sensor and the actuator controller arranged to

An engine management system for an internal combustion engine, which has at least one cylinder pressure sensor and at least one engine actuator, includes a data processor arranged to receive and process cylinder pressure data from the cylinder pressure sensor and the actuator controller arranged to control the actuator to optimize engine performance based on the processed data, in which the cylinder pressure data is obtained during a performance optimized engine cycle or cycles. The processor processes the data to construct a cylinder pressure variation function for the engine cycle or cycles and derive control data therefrom for the actuator controller.

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The invention claimed is: 1. An engine management system for an internal combustion engine having at least one cylinder pressure sensor and at least one engine actuator, the system comprising a data processor arranged to receive and process cylinder pressure data from the cylinder pressure sensor a

The invention claimed is: 1. An engine management system for an internal combustion engine having at least one cylinder pressure sensor and at least one engine actuator, the system comprising a data processor arranged to receive and process cylinder pressure data from the cylinder pressure sensor and an actuator controller arranged to control the actuator to optimize engine performance based on the processed data, in which the cylinder pressure data is obtained during a performance optimized engine cycle or cycles and the processor processes the data to construct a cylinder pressure variation function for the engine cycle or cycles and derive control data therefrom for the actuator controller, in which the processor derives an offset pressure value from the cylinder pressure data. 2. A system as claimed in claim 1 in which the processor processes cylinder pressure data for each cylinder in the engine. 3. A system as claimed in claim 1 in which the processor processes cylinder pressure data for each engine cycle. 4. A system as claimed in claim 3 in which the actuator controller controls actuation for an engine cycle based on the processed cylinder pressure data from the engine cycle immediately preceding. 5. A system as claimed in claim 1 in which the processor further processes crank angle data. 6. A system as claimed in claim 5 for a multi-cylinder engine in which data is obtained for each cylinder at a respective crank angle position in the cycle or cycles of each cylinder. 7. A system as claimed in claim 1 further including an in cylinder pressure sensor for providing cylinder pressure data to the data processor. 8. A system as claimed in claim 1 further comprising an engine actuator comprising at least one of: a spark plug; a fuel injector. 9. A system as claimed in claim 1 in which the cylinder pressure data is filtered. 10. A system as claimed in claim 1 in which the offset pressure value is derived from the polytropic gas law PVn=K using cylinder pressure data and corresponding volume data to obtain n and K. 11. A system as claimed in claim 1 in which the processor derives a pressure ratio function from the constructed pressure variation function comprising a ratio between combustion and motoring pressure. 12. A system as claimed in claim 11 in which the processor derives the motoring pressure for each engine cycle or cycles from the pressure sensor data in a pre-combustion phase of the engine cycle(s). 13. A system as claimed in claim 12 in which the motoring pressure derivation is based on filtered pressure sensor data. 14. A system as claimed in claim 11 in which the engine actuator comprises a spark plug and the actuator controller controls the timing of firing the spark plug based on closed loop control of a pressure ratio control variable. 15. A system as claimed in claim 14 in which the pressure ratio control variable is a fixed proportion of the fuel Mass Fraction Burnt (MFB). 16. The system as claimed in claim 15 wherein the fixed proportion of the fuel Mass Fraction Burnt is 50% MFB. 17. A system as claimed in claim 11 for a multi-cylinder engine in which the pressure ratio is derived for each engine cylinder and the actuator controller controls an actuator for each engine cylinder. 18. A system as claimed in claim 11 in which the processor processes the pressure sensor data to obtain the indicated mean effective pressure (IMEP). 19. A system as claimed in claim 18 for a multi-cylinder engine in which the processor obtains the IMEP for each cylinder, identifies as the weakest cylinder the cylinder having the lowest IMEP and the actuator control controls each cylinder to balance the IMEP to that of the weakest cylinder. 20. A system as claimed in claim 19 in which the cylinders are controlled by adjusting the spark timing for each cylinder. 21. A system as claimed in claim 20 in which the cylinder balancing is based on closed loop control. 22. A system as claimed in claim 18 in which the processor obtains the gross IMEP and detects misfire if the gross IMEP falls below a threshold value. 23. A system as claimed in claim 22 in which, on misfire detection, the actuator controller resets to an actuator controller state prior to misfire detection. 24. A system as claimed in claim 18 in which the processor further derives a function of the variance of IMEP between engine cycles and compares the function against a threshold value to determine whether a steady state condition exists. 25. A system as claimed in claim 24 in which the processor switches from IMEP balancing if non-steady state is determined. 26. A system as claimed in claim 24 in which the IMEP variance or variability is derived iteratively as a function of a preceding variance or variability value and a current IMEP value coupled with a forgetting factor. 27. A system as claimed in claim 26 in which the IMEP variance or variability iteration includes an initialization sequence in which the forgetting factor is successively increased for each iteration to a target value. 28. A system as claimed in claim 18 in which, in a start-up mode, the processor derives a function of the variability of IMEP between engine cycles and compares the function against a threshold value, and the actuator controller controls the actuator based on this comparison. 29. A system as claimed in claim 28 in which the actuator is a spark plug and the actuator controller retards the spark plug timing based on the comparison. 30. A system as claimed in claim 28 in which a further actuator comprises a fuel injector and the actuator controller controls fuel injection based on the function of the IMEP variability. 31. A system as claimed in claim 28 in which the actuator control is performed under closed loop control to a target IMEP variability. 32. A system as claimed in claim 28 in which the start-up mode is entered based on engine coolant temperature sensor data. 33. A system as claimed in claim 22 in which the threshold value is based on an average of the IMEPs obtained for all cylinders, other than the current cylinder for which misfire is being detected, during the same cycle. 34. A system as claimed in claim 1 in which the processor further processes pressure sensor data to detect cylinder knock. 35. A system as claimed in claim 34 in which the actuator comprises a spark plug, and the processor and actuator controller, upon knock detection, retard the spark plug timing and incrementally increase the timing for subsequent engine cycles until a spark timing threshold is reached. 36. A system as claimed in claim 35 in which the actuator controller resets an actuator controller state prior to knock detection once the spark timing threshold is reached. 37. An internal combustion engine including at least one cylinder pressure sensor, at least one engine actuator and an engine management system as claimed in claim 1. 38. A diagnostic system for an internal combustion engine as claimed in claim 1, having at least one cylinder pressure sensor and a processor arranged to process sensed cylinder pressures over a cylinder cycle and construct a cylinder pressure variation function, the system further comprising a processor arranged to detect engine misoperation from the constructed function. 39. A system as claimed in claim 38 in which engine misoperation includes at least one of engine faults, inlet manifold leaks, inlet or exhaust valve leaks, piston ring failure or leakage and head gasket leakage. 40. A system as claimed in claim 38 in which the misoperation processor identifies engine misoperation by comparison of the constructed function with a modelled function. 41. A system as claimed in claim 38 in which the processor identifies engine misoperation using pattern recognition. 42. A system as claimed in claim 38 in which the engine has a plurality of cylinders and respective cylinder pressure sensors, and the processor cross-correlates constructed functions for each cylinder to identify faults common to multiple cylinders. 43. An engine management system for an internal combustion engine having a plurality of cylinders each having at least one cylinder pressure sensor and at least one engine actuator, the system comprising a data processor arranged to process cylinder pressure data from each pressure sensor in which the processor constructs a cylinder pressure variation function for each cylinder from the cylinder pressure data, derives a measure of the performance of each cylinder from the respected pressure variation function and balances the cylinder performances, by means of identifying the weakest cylinder and retarding the timing on the other cylinders to match the work done by the weakest cylinder. 44. A system as claimed in claim 43 further comprising an actuator controller arranged to control each cylinder actuator to balance cylinder performance. 45. A system as claimed in claim 44 in which the actuator controller controls the cylinder spark timing. 46. A method of managing an internal combustion engine based on cylinder pressure data from a cylinder pressure sensor comprising the steps of obtaining the cylinder pressure data across one or more performance optimized engine cycles, processing the cylinder pressure data to construct a pressure variation function for the engine cycle or cycles and controlling an engine actuator to optimize engine performance based on the constructed pressure variation function, and further comprising deriving an offset pressure value from cylinder pressure data. 47. The method as claimed in claim 46 in which the cylinder pressure data is filtered. 48. An engine management system for an internal combustion engine having at least one cylinder pressure sensor, the system comprising a sensor controller arranged to retrieve a plurality of cylinder pressure readings per cylinder cycle and a processor arranged to process the readings to construct a cylinder pressure variation function in which sufficient readings are retrieved per cycle to allow noise filtering in the pressure variation function and further comprising a processor for processing the constructed cylinder pressure variation function to identify at least one of engine faults, inlet manifold leaks, inlet or exhaust valve leaks, piston ring failure or leakage, and head gasket leakage. 49. An engine management system for an internal combustion engine having at least one cylinder pressure sensor and at least one engine actuator, the system comprising a data processor arranged to receive and process cylinder pressure data from the cylinder pressure sensor and an actuator controller arranged to control the actuator to optimize engine performance based on the processed data, in which the cylinder pressure data is obtained during a performance optimized engine cycle or cycles and the processor processes the data to construct a cylinder pressure variation function for the engine cycle or cycles and derive control data therefrom for the actuator controller, in which the processor processes the pressure sensor data to obtain an indicated mean effective pressure (IMEP). 50. An engine management system for an internal combustion engine having at least one cylinder pressure sensor and at least one engine actuator, the system comprising a data processor arranged to receive and process cylinder pressure data from the cylinder pressure sensor and an actuator controller arranged to control the actuator to optimize engine performance based on the processed data, in which the cylinder pressure data is obtained during a performance optimized engine cycle or cycles and the processor processes the data to construct a cylinder pressure variation function for the engine cycle or cycles and derive control data therefrom for the actuator controller, in which the processor obtains a gross indicated mean effective pressure (IMEP) and detects misfire if the gross IMEP falls below a threshold value. 51. An engine management system for an internal combustion engine having at least one cylinder pressure sensor and at least one engine actuator, the system comprising a data processor arranged to receive and process cylinder pressure data from the cylinder pressure sensor and an actuator controller arranged to control the actuator to optimize engine performance based on the processed data, in which the cylinder pressure data is obtained during a performance optimized engine cycle or cycles and the processor processes the data to construct a cylinder pressure variation function for the engine cycle of cycles and derive control data therefrom for the actuator controller, in which the processor further derives a function of the variance of an indicated mean effective pressure (IMEP) between engine cycles and compares the function against a threshold value to determine whether a steady state condition exists. 52. An engine management system for an internal combustion engine having at least one cylinder pressure sensor and at least one engine actuator, the system comprising a data processor arranged to receive and process cylinder pressure data from the cylinder pressure sensor and an actuator controller arranged to control the actuator to optimize engine performance based on the processed data, in which the cylinder pressure data is obtained during a performance optimized engine cycle or cycles and the processor processes the data to construct a cylinder pressure variation function for the engine cycle of cycles and derive control data therefrom for the actuator controller, in which in a start-up mode, the processor derives a function of the variability of an indicated mean effective pressure (IMEP) between engine cycles and compares the function against a threshold value, and the actuator controller controls the actuator based on the comparison. 53. An engine management system for an internal combustion engine having at least one cylinder pressure sensor and at least one engine actuator, the system comprising a data processor arranged to receive and process cylinder pressure data from the cylinder pressure sensor and an actuator controller arranged to control the actuator to optimize engine performance based on the processed data, in which the cylinder pressure data is obtained during a performance optimized engine cycle or cycles and the processor processes the data to construct a cylinder pressure variation function for the engine cycle of cycles and derive control data therefrom for the actuator controller, in which the processor further processes pressure sensor data to detect cylinder knock.