Modifier for vacuum booster reaction force

In a brake booster having a plunger located in a bore in a hub of a movable wall and responsive to an operator input force for controlling the flow of a first fluid to a first chamber to create a pressure differential with a second fluid in a second chamber, said pressure differential acting on the movable wall to develop an original output force that is transmitted through a reaction member to an output member for moving a pressurizing device to effect a desired brake application, said pressurizing device resisting movement by the original output force to develop a reaction force which is transmitted back through the reaction member to oppose and balance the operator input force and terminate the communication of the first fluid to said first chamber to terminate the development of said pressure differential, said original output force being a linear function of the operator input force, the improvement comprising:

• a lever having a first end and a second end, said lever engaging a fulcrum on said hub to define a ratio of the distances between the first and second ends and the fulcrum, said first end engaging said plunger;
• resilient means connected to said second end;
• and
• a solenoid carried by said moveable wall and responsive to an operational signal generated on initiation of a brake application for positioning said second end of said lever to provide said first end with a spring force from said resilient means, said spring force being combined with said operator input force during a brake application, said reaction force balancing said spring force and operator input force to produce a modified output force which is supplied to operate said pressurizing device, said modified operational output force being a function of said operational input force and having a greater gain than said original output force.