Master cylinder

Abstract

A dual master cylinder has a secondary piston which when actuated pressurizes fluid in two secondary chamber sections with one chamber section increasing pressure at a faster rate than the other as the piston is stroked. The piston has passage means therein interconnecting the two chamber sections, a proportioning valve mechanism in the passage means acting to proportion fluid pressure from the one chamber section to the other chamber section after a predetermined pressure differential exists in the two chamber sections. A shuttle piston also mounted in the secondary piston is responsive to pressure generated in the one secondary chamber section and in the primary pressurizing chamber between the primary and secondary master cylinder pistons. If a pressure loss is suffered in the primary pressurizing chamber during master cylinder actuation, the shuttle piston moves to render the proportioning valve mechanism inoperative and permit substantially unrestricted pressure flow from the one secondary chamber section to the other secondary chamber section and thence to the fluid brake circuit connected thereto. The shuttle piston also has suitable cams which actuate a cam follower arrangement mounted on the secondary piston which in turn actuates a warning switch mechanism when the shuttle piston is moved in either direction because of a pressure loss in one of the two chambers to which it is pressure connected. The primary pressurizing chamber has an outlet in which a metering valve mechanism is provided, the pressurized fluid then passing to another fluid brake circuit. A modified embodiment of the invention uses a proportioner piston between a single secondary pressurizing chamber and an outlet chamber, with one end of the shuttle piston also functioning to define the small diameter portion of the proportioner mechanism.