Patent ID: 6672197
Filing Date: 2004-01-06
Classification: B60T

Abstract:
An automatic brake booster including a valve body slidably disposed in a shell, a power piston mounted on the valve body for partitioning the interior of the shell into a constant pressure chamber and a variable pressure chamber, a valve mechanism mounted on the valve body for switchably controlling a flow path through which a fluid is supplied to or discharged from the variable pressure chamber, an input shaft for switchably operating the valve mechanism, a solenoid mounted on the valve body for switchably operating the valve mechanism, an output shaft for externally transmitting an output from the power piston, and a reaction disc for transmitting a reaction from the output shaft to the valve mechanism; the valve mechanism comprising a vacuum valve seat formed on the valve body, a solenoid plunger slidably mounted in the valve body, an atmosphere valve seat formed on the solenoid plunger, a valve element which can be seated on the vacuum valve seat and the atmosphere valve seat, and a valve plunger slidably mounted on the valve body and coupled to the input shaft for displacing the solenoid plunger forwardly as the input shaft is driven forward to operate the valve mechanism, the solenoid having a magnetic path which is defined in part by the solenoid plunger and a holder mounted on the valve body and located forwardly of the solenoid plunger, the solenoid plunger being displaced forwardly as the solenoid is energized to operate the valve mechanism;characterized in that the solenoid plunger comprises a rear member on which the atmosphere valve seat is formed and disposed in opposing relationship with the holder with a clearance therebetween and adapted to be displaced forwardly by the solenoid, a front member disposed to be displaceable with respect to the rear member and capable of abutting against the reaction disc, and a first resilient member disposed between the front member and the rear member for maintaining both members spaced apart, the arrangement being such that when a current fed to the solenoid is less than a given value, the first resilient member remains as charged to maintain a given clearance between the rear member and the holder so as to reduce the output change of the booster with respect to the supply current to the solenoid and when the current fed to the solenoid increases above the given value, the first resilient member becomes flexed to permit the clearance between the rear member and the holder to be reduced by a given amount corresponding to the flexure as compared with the given clearance so as to increase the output change of the booster with respect to the supply current to the solenoid.