Patent ID: 7827857

Claim:
An estimation method of the crank angle at which 50% of the fuel mass has been burnt in a cylinder ( 2 ) of an internal combustion engine ( 1 ) with spontaneous ignition of the mixture provided with a drive shaft ( 4 ) coupled to a phonic wheel ( 5 ) presenting a number N of teeth ( 6 ); the method comprises the steps of: reading the passage of each tooth ( 6 ) of the phonic wheel ( 5 ) in front of a sensor ( 7 ); determining the angular speed (ω i ) of the drive shaft ( 4 ) at each tooth event of the phonic wheel ( 5 ); determining, by means of a frequency analysis the angular speeds (ω i ) of the drive shaft ( 4 ), at least one harmonic (Ω n ) of the speed signal characterized by its own module (|Ω n |) and is own phase (Arg(Ω n )); determining an inverse mechanical model (H(j{acute over (ω)})=T/Ω) of the transmission which represents, in the ({acute over (ω)}) frequency domain, the relation between the Fourier transforms of the angular speed (Ω) and of the torque (T) of the internal combustion engine ( 1 ); determining at least one torque harmonic (T n ) characterized by its own module (|T n |) and by its own phase (Arg(T n )) by applying the inverse mechanical model (H(j{acute over (ω)})=T/Ω) of the transmission to the speed signal harmonic (Ω n ); determining a first algebraic function (Ψ) which puts a combustion index (MFB50) into relation with the phase (Arg(T n )) of the n th torque harmonic (T n ); and determining the combustion index (MFB50) by applying the first algebraic function (Ψ) to the n th torque harmonic (T n ).