Brake booster

A brake booster comprising a valve body slidably disposed within a shell, a valve mechanism comprising a valve plunger disposed within the valve body, an input shaft for driving a valve plunger back and forth to switch a flow path in the valve mechanism, an output shaft slidably mounted in the valve body, a reaction disc interposed between an end of the output shaft and the valve plunger, and reaction transmitting means interposed between the reaction disc and the valve plunger for transmitting a brake reaction from the reaction disc to the valve plunger, characterized in that:

• the reaction transmitting means comprises a parallel combination of a first and a second reaction transmission path, each path transmitting a brake reaction from the reaction disc to the valve plunger, the first reaction transmission path comprising a spring biased to a preset load and transmitting a brake reaction from the reaction disc to the valve plunger and the second reaction transmission path comprising a viscoelastic member, wherein the brake reaction is transmitted from the reaction disc through the first reaction transmission path and the viscoelastic member of the second reaction transmission path to the valve plunger as a result of compression of the spring when the brake reaction exceeds the preset load of the spring.