Patent ID: 7867119

Claim:
A transmission system comprising: a first ( 4 ) and a second ( 5 ) flexible link, that couple a crankshaft of a combustion engine to a shaft ( 1 ) of an alternator-starter; a two-state coupling device, wherein a first state of the two-state coupling device corresponds to a phase for starting the engine, in which the shaft ( 1 ) of the alternator-starter (ATD) drives the crankshaft (V) of the engine (M) with a first transmission ratio, and a second state of the two-state coupling device corresponds to a phase in which the crankshaft (V) of the engine (M) drives the shaft ( 1 ) of the alternator-starter (ATD) with a second transmission ratio, and in that the first transmission ratio is higher than the second transmission ratio; and a first ( 2 ) and a second ( 3 ) pulley coaxial with said shaft ( 1 ) of the alternator-starter (ATD), wherein, when the two-state coupling device is in the first state, the first pulley ( 2 ) is coupled to the shaft ( 1 ) of the alternator-starter (ATD) to provide the first transmission ratio and, wherein, when the coupling device is in the second state, the second pulley ( 3 ) is coupled to the shaft ( 1 ) of the alternator-starter (ATD) to provide the second transmission ratio; wherein the two-state coupling device is arranged between the first ( 2 ) and the second ( 3 ) pulleys and includes at least one coupling element ( 10 ) that moves longitudinally parallel to the axis of the shaft ( 1 ) of the alternator-starter (ATD) between two positions corresponding to the first and second coupling device states respectively, as a function of the relative rotation speed between one of said first ( 2 ) or second ( 3 ) pulleys and the shaft ( 1 ) of the alternator-starter (ATD); and wherein said longitudinally movable coupling element comprises a selector ( 10 ) having a helical connection ( 12 ) to the shaft ( 1 ) of the alternator-starter (ATD), having at least a lateral face ( 10 ′, 10 ″) bearing a power transmission element ( 15 , 16 ), and facing a flank ( 2 ′, 3 ′) of one of the first ( 2 ) and second ( 3 ) pulleys, and a control element ( 11 , 14 , 18 , 22 , 22 ′) able to move with respect to the selector ( 10 ) and generating a minimum torque that is required for the correct displacement of the selector ( 10 ) along the helical connection ( 12 ).