Patent ID: 7008024

Claim:
A pneumatic brake-booster comprising a front chamber ( 1 ) that is connected to a source of vacuum ( 2 ), a rear chamber ( 3 ) that is connected to a high-pressure inlet ( 5 ), a sealed moving partition ( 6 ) between the front and rear chambers, a moving gear ( 8 ) that is carried along with the moving partition and connected to a hydraulic braking circuit ( 10 ), a valve device ( 4 ) for letting a high-pressure fluid into the rear chamber at the time of braking, and a hydraulic actuator ( 20 ) for providing hydraulic fluid to said braking circuit ( 10 ) to assist said pneumatic brake booster in effecting a brake application, characterized in that said hydraulic actuator ( 20 ) is responsive to an electronic circuit ( 19 ) during as brake application said electronic circuit ( 19 ) being defined by a memory ( 48 ) that stores a first pressure (Pmem) measured in said front chamber( 1 ), a second pressure (pfc) measured in said rear chamber ( 3 ) during a brake application and controls ( 34 , A) the actuator ( 19 ) as a function (α) of a difference (Pestim) between the first pressure and the second pressure, said electronic circuit ( 19 ) comprises a microprocessor ( 25 ) and a programmable memory ( 27 ) containing a recorded program ( 34 , 35 ) for producing a signal (A) to be applied to the hydraulic actuator ( 19 ), the value of said signal being a function of the difference between a third pressure measurement (Pc) of the hydraulic pressure at a point in the hydraulic circuit ( 10 ) and an estimated value of a hydraulic pressure in the hydraulic circuit ( 10 ) wherein the estimated value (Pestim) of the hydraulic pressure is compared ( 51 ) with a current value (Pc) of the third pressure measurement, and the estimated pressure is corrected ( 50 ) when the estimated pressure (Pestim) is lower than the current third pressure measurement (Pc).