Double-piston master cylinder with central booster-driven piston driving surrounding low pressure piston

A dual-piston hydraulic pressure transmitter for use with a brake actuator, comprising:

• (a) a first actuation member movable under the influence of fluid pressure to achieve a brake-applying operation upon movement in a first direction and a brake-releasing operation upon movement in a second direction, said first actuation member having a rod portion extending therefrom;
• (b) a first hydraulic piston connected to said rod portion and movable within a first hydraulic chamber such that, braking fluid is communicated through a first delivery passage to the brake actuator in response to such movement of said first actuation member;
• (c) a second hydraulic piston elastically connected to said first actuation member and movable within a second hydraulic chamber such that, braking fluid is communicated through a second delivery passage to the brake actuator in response to such movement of said first actuation member, said second delivery passage being larger in cross-sectional area than said first delivery passage;
• (d) elastic transmission means disposed between said first actuation member and said second hydraulic piston for transmitting forces between said first actuation member and said second hydraulic piston in an elastic manner such that, said first hydraulic piston can move independent of said second hydraulic piston;
• (e) a first check valve disposed in said second delivery passage and oriented such that, such braking fluid flows through said second delivery passage only in a direction from said second hydraulic chamber to the brake actuator;
• (f) fluid communication means disposed between said first hydraulic chamber and said second hydraulic chamber and being effective, during at least a portion of such brake-applying operation, for communicating a portion of such braking fluid from said second hydraulic chamber to said first hydraulic chamber and, during at least a portion of such brake-releasing operation, for returning a second portion of such braking fluid from said first hydraulic chamber to said second hydraulic chamber;
• and
• (g) fluid-reducing means cooperatively engaging said second hydraulic piston for reducing the level of such braking fluid in said second hydraulic chamber to a preselected amount upon movement of said second hydraulic piston to a predetermined position during such brake-releasing operation.