Hydraulic brake force-multiplying device

A braking force multiplying device for use in a hydraulic braking system of the type including a master cylinder, a source of hydraulic fluid, and a fluid drain, said device comprising:

• a body coupled to said master cylinder, said body having a projecting portion extending toward said master cylinder;
• a cup-shaped power piston having a first open end and a second closed end, said projecting portion having an outer periphery sealingly and slidably received through said open end of said power piston, said closed end of said power piston cooperating with a piston of said master cylinder;
• a working chamber defined between said power piston and said projecting portion;
• a bore extending through said body coaxially with respect to said power piston;
• a valve seat member slidably fitted in said bore, a first end of said valve seat member extending into said working chamber and sealingly extending through a first diameter portion of said bore, a second end of said valve seat member being in a second diameter portion of said bore, said second diameter portion having a greater diameter than said first diameter portion, said valve seat member and said body defining therebetween a pressure chamber, said pressure chamber being permanently connected to said source of hydraulic fluid;
• said valve seat member having a guide bore extending therethrough;
• a valve stem member being slidably and sealingly fitted in said guide bore;
• a first normally closed valve means formed by a valve body on said valve stem member and a seat on said valve seat member;
• an input shaft slidably and sealingly fitted in said body, said input shaft being normally spaced from said valve seat member;
• an intermediate chamber defined between a first inner end of said input shaft and said valve seat member;
• first passage means in said valve stem member for permanently communicating said intermediate chamber with said working chamber;
• second passage means in said input shaft for providing communication between said intermediate chamber and said fluid drain;
• a second valve means formed between said input shaft and said valve stem member, when said input shaft is moved inwardly of said body, for blocking communication between said intermediate chamber and said fluid drain;
• and
• said input shaft comprising means, when said input shaft is moved inwardly of said body, for opening said first valve means and for communicating said intermediate chamber with said pressure chamber.