Patent ID: 7077050

Claim:
A pneumatic brake booster, for a motor vehicle, comprising an axial piston ( 20 ) bearing on a thrust rod ( 32 ) by an intermediary of a reaction disk ( 30 ) made of substantially incompressible material and carried by the thrust rod, said reaction disk cooperating with a plunger ( 28 ) mounted at the end of a control rod ( 26 ) and guided in a sliding manner in an axial passage of the piston ( 20 ), characterized in that the thrust rod ( 32 ) carries an axial thermal expansion element ( 48 ) mounted between a stop ( 50 , 62 ) integral with the thrust rod ( 32 ) and a bearing element ( 58 , 42 ) on the reaction disk ( 30 ), with an axial play (a) between the thermal expansion element ( 48 ), the bearing element ( 58 , 42 ), the stop ( 50 , 62 ) of the thrust rod and the reaction disk ( 30 ), said axial play determining a point of change of assistance ratio, said thermal expansion element ( 48 ) having on this axial play, during variations in the operating temperature, an effect opposite to that of the reaction disk ( 30 ).