Unit for estimating the rotational speed of a turbocharger

Disclosed is a method and unit 40 for estimating the rotational speed of a turbo­charger 16. The unit 40 comprises a microprocessor comprising input ports for receiving measurement signals from an exhaust gas recirculation flow control system of the internal combustion engine 11 and an output port for outputting a signal in­dicative of a rotational speed of the turbocharger 16. The input ports receive a first set of measurement signals and a second set of measurement signals. The signals may relate to the pressure and temperature at different points along the intake and exhaust flow paths. The micro­processor is adapted to calculate an estimated rotational speed of the turbocharger 16 using a turbocharger model, based on the first set of measurement signals and the second set of measurement signals. The second set of signals comprises signals being indicative of a pressure difference across a turbine 20 of the turbocharger 16, the pressure drop being used to determine the rotational ...