Learning device and fuel injection system

A learning device that has a storing means for storing a model formula expressing a detected waveform with a mathematical expression, the detected waveform being detected with a sensor that detects a physical quantity change, the learning device configured to learn values of multiple parameters included in the model formula to improve an approximation degree of a model waveform expressed with the model formula with respect to the actual detected waveform, the learning device comprising:

• a parameter changing means for changing each of the multiple parameters to an increased side and to a decreased side with respect to a reference value set for each of the multiple parameters;
• an approximation degree calculating means for calculating the approximation degree for each combination of the changes of the multiple parameters;
• a determining means for determining whether an update end condition is satisfied, the update end condition being a condition that the approximation degree in the case where the multiple parameters are set at the reference values is higher than any of the approximation degrees in the case where the parameters are set at the changed values;
• a reference value updating means for updating the reference values by using the combination of the changes, which provides the highest approximation degree among the approximation degrees corresponding to the changed values, as the updated reference values while the update end condition is not satisfied;
• a learning value deciding means for deciding that the reference values are to be considered as learning values of the multiple parameters when the update end condition is satisfied;
• and
• an extracting means for extracting a waveform component resulting from an n-th injection by subtracting a waveform component resulting from an m-th injection preceding the n-th injection from a waveform portion of the detected waveform corresponding to the n-th injection when multiple injection for performing the fuel injection multiple times per combustion cycle is performed, wherein
• the change by the parameter changing means, the calculation by the approximation degree calculating means and the determination by the determining means are repeatedly performed every time the update is performed by the reference value updating means,
• the sensor is a fuel pressure sensor that is mounted to an internal combustion engine structured to distribute and supply fuel from a pressure accumulator accumulating the fuel to multiple injectors and that senses pressure of the fuel supplied to the injector as the physical quantity change,
• the sensor is arranged in a fuel passage, which extends from the pressure accumulator to an injection hole of the injector, at a position closer to the injection hole than the pressure accumulator, and
• the extracting means uses the model waveform defined by the parameters learned by the learning device as the waveform component resulting from the m-th injection.