Method for evaluating a fuel injection deviation in an internal combustion engine of a hybrid power system

Disclosed is a method for evaluating a fuel injection devia­tion in an internal combustion engine 110 of a hybrid powertrain 100. The hy­brid powertrain 100 comprises the internal combustion engine 110 and an electric motor unit 500. The method comprises a learning phase includ­ing the steps of acquiring a first value FQ1 of a fuel quantity that is requested to be in­jected in the internal combustion engine 110 while the internal combustion engine 110 is operated at a constant engine speed value ES_C and the motor-generator electric unit 500 is operated at a first preset torque value TQ1, acquiring a second value FQ2 of the fuel quantity that is requested to be injected in the internal combustion engine 110 while the internal combustion engine 110 is operated at the same con­stant engine speed value ES_C and the motor-generator electric unit 500 is operated at a second preset torque value TQ2. A value AFQ of a variation between the first and the second acquired value FQ1, FQ2 of the requested fuel quantity is calculated. A value A_Inj% of a parameter indicative of the fuel injection deviation is also calculated on the basis of a difference A_Inj between the calculated value AFQ of the requested fuel quantity variation and an expected value AFQ_EX thereof. The deviation between the expected and measured values is then used in a closed loop correction sequence to correct the fuel injection duration and timing in the internal combustion engine.