Patent ID: 8841889

Claim:
A method of controlling a regulating device ( 8 ) of a motor vehicle alternator ( 1 ) locking a DC voltage (B+, B−) of an on-board electrical system ( 3 ) powered by said alternator ( 1 ) to a predetermined setpoint value (Vref) by controlling an excitation circuit ( 7 ), said method in a first nominal operating mode of said alternator ( 1 ), comprising the steps of: transmitting to said regulating device ( 8 ) by means of a communication line (COM) first width-modulated pulses having a predetermined period and a reference duty ratio (PWM 1 ) representative of said setpoint value (Vref) continuously comprised between a first reference duty ratio (DC 1 ) and a second reference duty ratio (DC 2 ); and detecting said first pulses by said regulating device ( 8 ) and generating said setpoint value (Vref); and in a second operating mode of said alternator ( 1 ) without power generation, comprising the steps of: transmitting to said regulating device ( 8 ) second width-modulated pulses having said predetermined period and a specific duty ratio (EXOF_R) less than the first reference duty ratio (DC 1 ) and lying between a low duty ratio (DCL) and a high duty ratio (DCH); detecting said second pulses by the regulating device ( 8 ) in a first step ( 22 , 23 , 24 ) and generating a signal (EXOF) for opening the alternator excitation circuit ( 7 ) in a second step ( 25 ); wherein in the second operating mode without power generation, said method also comprises the steps of: detecting ( 21 ) an activity on the communication line (COM) before said first step ( 22 , 23 , 24 ); if said communication line (COM) is active, computing ( 24 ) averages (DCavk) of current duty ratios (DCn) in a plurality of said first or second pulses disregarding ( 23 ) a first predetermined number of first said current duty ratios (DC 0 , DC 1 , DC 2 , DC 3 ) received, and comparing said averages (DCavk) to said low duty ratio (DCL) and high duty ratio (DCH) during said first step ( 22 , 23 , 24 ); and generating said opening signal (EXOF) during said second step ( 25 ) if a second predetermined number of said averages (DCavk, DCavk- 1 , DCavk- 2 ) are comprised between said low duty ratio (DCL) and said high duty ratio (DCH).