Patent ID: 6948416

Claim:
A process for the determination of the instantaneous value of the amplification provided by a pneumatic-assistance servomotor in a braking device for a motor vehicle, wherein the servomotor ( 14 ) comprises a negative-pressure chamber ( 24 ) and a working chamber ( 26 ), which are separated by a moving partition wall bearing a piston for the actuation of a hydraulic master cylinder ( 16 ) of the braking device, said instantaneous amplification being proportional to the pressure difference, (ΔP) between the chambers of the servomotor, and wherein said process comprises measurements of the pneumatic pressure in the servomotor and of the hydraulic pressure at the exit from the master cylinder ( 16 ), characterised in that it consists in: making use of the characteristic saturation curve (C) of the servomotor ( 14 ), such curve consisting of all the operating points for which the pressure inside the working chamber ( 26 ) is equal to the atmospheric pressure, and being represented by a line segment in an orthonormal plot of axes (Pfc, Pmc), where Pfc is the relative vacuum level in the negative-pressure chamber ( 24 ) of the servomotor, whereas Pmc stands for the hydraulic pressure at the exit from the master cylinder ( 16 ); measuring the instantaneous values (Pmci) of the hydraulic pressure at the exit from the master cylinder ( 16 ), and (Pfci) of the relative vacuum level (Pfc) in the negative-pressure chamber of the servomotor; determining, on said characteristic saturation curve (C), in the course of a braking operation, the point (Ps) the coordinate of which, on the axis (Pfc), is the measured instantaneous value (Pfci) of said vacuum level; determining the coordinate (Pmcs) of the point (Ps) on the axis (Pmc); and, if the measured instantaneous value (Pmci) is lower than the coordinate (Pmcs), in taking, as the pressure difference (ΔP), the coordinate, on the axis (Pfc), of the point on said saturation curve (C), the other coordinate of which is equal to (Pmci), or in determining the pressure difference (ΔP) from the measured instantaneous value (Pmci) of the pressure at the exit from the master cylinder, multiplied by a constant; and, if the measured instantaneous value (Pmci) is higher than or equal to the coordinate (Pmcs) of the point (Ps), in taking, as the pressure difference (ΔP), the measured value (Pfci) of the relative vacuum level in the negative-pressure chamber ( 24 ) of the servomotor ( 14 ).