Brake anti-lock modulator with bypass valve

Claim 1

A pressure modulator having a piston movable in response to variations in a sensed condition and comprising: a housing having first and second valve chambers therein; fluid inlet means communicating fluid pressure from an intermittently operable pressure source to said first valve chamber; first and second passages formed in said housing and in parallel flow relationship connecting said first and second valve chambers; modulator valve means located in said first valve chamber and being unseated by differential pressure to permit fluid flow through said first passage in one direction only from said second valve chamber to said first valve chamber; bypass valve means located in said first valve chamber and permitting fluid flow through said second passage when unseated; fluid outlet means in said housing communicating fluid pressure from said second valve chamber to a fluid pressure operated apparatus; first check valve means located in said second valve chamber and being unseated by differential pressure to permit fluid flow through said second passage in one direction only from said first valve chamber to said second valve chamber; said piston unsealingly extending through said first passage and permitting fluid flow therethrough when in one position to unseat said modulator valve means and seat said bypass valve means when said bypass valve means is unseated thereby permitting free fluid communication between said first valve chamber and said second valve chamber through said first passage and preventing fluid flow through said second passage; means permitting movement of said piston by pressure in said second valve chamber in a direction permitting said modulator valve means to seat and to increase the volume of said first passage to decrease second valve chamber pressure in response to variations in the sensed condition, pressure in said first valve chamber preventing said bypass valve means from unseating upon movement of said piston from said one position; and spring means unseating said bypass valve means upon interrupted operation of said fluid pressure source and consequent reduction of fluid pressure in said first valve chamber when said modulator valve means is seated to allow free fluid communication from said first valve chamber to said second valve chamber upon subsequent operation of said pressure source; said piston movement permitting means forcibly moving said piston to decrease the volume of said second passage to increase said second valve chamber pressure and thereby seat said first check valve means when unseated, and upon further variation in said sensed condition said piston returning to said one position unseating said modulator valve and seating said bypass valve means when unseated.