Patent GB-480688-A (GB)
Title: Improvements in or relating to compound master cylinders for fluid pressure controlling systems
IPC: B60T11/224
Filed: 1936-08-24
Abstract: 480,688. Hydraulic brake systems. AUTOMOTIVE PRODUCTS CO., Ltd., and BROCK, D. T. Aug. 24, 1936, No. 23255. [Class 103 (i)] [Also in Group XXIX] A master cylinder unit comprising a cylinder barrel having a front portion fitted with a main piston so as to enclose a working space from which the pressure liquid is delivered, and a rear portion containing a high-pressure piston of smaller cross-sectional area than the main piston, means such as a pedal for actuating the high-pressure piston, a coiled compression spring between said pistons serving to transfer force mechanically from the high-pressure piston to the main piston, and a reservoir for feeding working liquid to the intermediate space between the two pistons, whereby actuation of the high-pressure piston creates in said intermediate space liquid pressure which acts on the back of the main piston, is characterized by the fact that a restraining device is provided which prevents the spring expanding to its full extent, thus causing the unit to act as a compound master cylinder, the spring serving as a substantially non-resilient thrust transmitting member during the initial low-pressure stage of the operation. One form, Fig. 1, comprises a high-pressure piston 15 actuated by pedal 18 and working in cylinder 13 ; a spring 35 is interposed between the piston 15 and main piston 14 working in cylinder 12 and delivering liquid from the space 25 through connection 30 and pipe line system 31 to the wheel cylinders 32 of vehicle brakes 33. The spring 35 bears at one end against the flange 36 of a thimble 37 engaging the head 39 of a screw 38, so that the spring is under initial compression. Main piston 14 is acted on by a return spring 21 ; in the inoperative position, the front cylinder space 25 communicates through port 27 with reservoir 10, and the intermediate space 26 between the pistons 14, 15 communicates through port 28 with reservoir 10 ; an annular recess 23 on main piston 14 is in constant communication through port 24 with the reservoir 10, the piston 14 being provided with packings 20, 22 acting as oneway valves permitting liquid from recess 23 to pass either to the front cylinder space 25 or to the intermediate space 26. The head 39 of the screw 38 working in the thimble 37 acts as a dashpot to prevent premature movement of the high pressure piston 15 relative to the main piston 14. In a modification, Fig. 3, the main piston is acted on by two return springs 21a, 21b, one of which actuates a pressurecontrolling delivery valve 34 to maintain the pressure in the brake system at a value greater than atmospheric. The ports 27, 24 communicate with the reservoir through an inclined passage 40. Two springs 35a, 35b are provided between the main and high-pressure pistons, the latter being extended to form a feed piston 42 working in cylinder 41. Said feed piston is acted on by a return spring 43, and during its return movement, liquid passes from the reservoir through passages 45, 46, 47 and non- return valve 48 into the space 44 which communicates through grooves or flats 49 with the intermediate space 26, and also through a restricted passage 50 with the reservoir. On gentle operation of the pedal, liquid from the space 44 escapes to reservoir through passage 50 but a slight pressure is maintained in space 44 and thus in the intermediate space 26 ; on violent actuation of the pedal, liquid in the space 44 is unable to escape through passage 50 and the high-pressure thus built-up in space 44 and also in space 26 prevents premature movement of the high-pressure piston relative to the main piston.