GB575417A - Compound master cylinder - Google Patents

Abstract

575,417. Hydraulic brakes. SCHNELL, S. July 19, 1943, No. 11723. [Class 103(i)] A hydraulic master cylinder for operating brakes &c. comprises a low pressure piston which is initially operative and carries a valve which when a predetermined pressure has been established in the cylinder is opened to render this piston ineffective and to render a high pressure piston effective. Communication between the reservoir and the cylinder is closed when an operation is initiated by axial movement of the cylinder as described in Specification 549,455. As shown, the master cylinder 9 is slidably mounted in a reservoir casing 1 by front and rear extensions 12, 14. Normally, the projection 12 uncovers a slot 17 to connect the reservoir to the outlet passage 3. A low pressure piston 22 is secured to a high pressure piston or plunger 24 of smaller diameter. A valve 36 urged by a spring 40 normally closes a passage 31 between the forward chamber of the cylinder and the rear chamber 30 and is connected to a normally unseated valve 38 which, with the sealing-cap 39, controls a passage 32 through the plunger 24. Upon forward movement of the piston the cylinder is moved forwardly to close the reservoir connection through the slot 17 either by the friction between the piston and cylinder or if this is inadequate, by the pressure which develops in the cylinder, acting on the cylinder wall 11. A spring-urged disc-valve 42 restricts flow from the cylinder to the reservoir and thus ensures rapid development of the cylinder pressure. This valve permits free flow in the reverse direction.. During the initial movement of the pistons in the cylinder, while the low pressure piston 22 is effective, liquid is drawn into the chamber 30 from the reservoir through the passages 15, 41, 32, 35. When the pressure forward of the piston 22 and in the pipe lines is sufficient to open the valve 36 against the action of the spring 40, the piston 22 is rendered ineffective and the plunger 24 becomes effective. The valve 38 is closed at this stage and with the seal 39 prevents flow from the cylinder to the reservoir through the passage 32.