Two-stage reaction device for vacuum brake booster valves

Claim 1

A two-stage reaction device for a vacuum brake booster comprising: a vacuum chamber in which a constant pressure prevails and a working chamber in which varying pressures prevail, the chambers being separated by a movable wall and having a central axis, a control housing including a control valve actuatable by a brake pedal and governing differentials of pressure acting on the movable wall, a push rod coupled to act on a master cylinder and being generally aligned with the central axis of the chambers, said push rod having a pressure member connected thereto, levers in engagement with the movable wall at a first location and with the pressure member at a second location, the said first location being arranged radially farther outwardly from said central axis than the second location, the levers being acted upon by a crowned spring at a third location, the said crowned spring being positioned on the side of the levers nearest to the vacuum chamber, the third location having a smaller radial distance from said central axis than the first location, a spring plate interposed between the crowned spring and the levers, a valve piston being displaceable by a piston rod upon actuation of the brake, said piston rod being supported in the control housing, said valve piston including at an end close to the push rod two oppositely disposed abutment surfaces against which the radially inwardly disposed edges and the lateral surface of the levers abut, the distance between the two abutment surfaces, which surfaces partially embrace the facing ends of the levers enabling a tilting movement of the levers in the event of the relative movement between the push rod and the valve piston, with said pressure member connected to said push rod bearing against the lever, the valve piston in conjunction with the two abutment surfaces being a rotationally symmetric element, said valve piston including a flange-like head having one of said abutment surfaces thereon and said flange-like head being connected to the valve piston adjacent to the piston rod by a neck portion.