Patent GB-548279-A (GB)
Title: Improvements in or relating to hydraulic braking systems
IPC: B60T17/22
Filed: 1941-02-17
Abstract: 548,279. Road-traffic signals for vehicles. BENDIX AVIATION CORPORATION. Feb. 17, 1941, No. 2177. Convention date, Feb. 21, 1940. [Class 118 (ii)] [Also in Group XXXIV] Hydraulic master cylinders particularly for brakes, comprise two co-axial working spaces with independent outlets, connected for instance respectively to the front and rear brakes of a vehicle, the piston device comprising a forward piston operated by mechanical engagement with a rear piston of larger diameter and the adjacent parts of the pistons forming a valve which is closed as the pistons advance but open in the retracted position to connect at least one of the working spaces with a reservoir. In Fig. 2, the piston 66 slidable through a partition 52 having limited axial floating movement is normally separated from a piston 58 as shown so that a working space 56 connected by pipe 30 to the rear brakes of a vehicle communicates with a reservoir 48 through an opening 70 a recess 62 in the piston and a tube 64. This position of the piston 66 is determined by the contact of a rod 74 therein with the tube 64. The space 54 is connected by pipe 28 to the front brakes and is normally open to reservoir 50 through a valve 80 controlled by a rod 78 having a lost motion connection with the piston 66. Upon operation of piston 58 it seats upon the piston 66 and moves it forward, the spaces 54, 56 being then cut off from the reservoirs. The partition 52 by its floating movement equalizes the pressure in the two spaces and as this movement is limited ensures that one of the pistons remains effective, in the event of failure of the pressure applied by the other. Annular sealing cups may be arranged on either side of the partition 52. The closing spring of the valve 80 may be disposed between the valve and the end of the piston 66. In a modification, the piston 66 is tubular and its conical end is separate and normally spaced therefrom as well as from the piston 58 to connect a single reservoir with both working spaces 56, 54. Indicators applications of. For indicating deficiency of liquid in either system and also brake applications, pressure operated switches 32, 34 are connected to the pipes 28, 30, and to lamps 36, 38, 96, each switch comprising a resilient contact member connected to battery wire 92 and adapted to engage upper and lower contacts connected respectively to wires 94, 98 and 94, 100. The normal hydrostatic pressure in release acting on the diaphragm for instance of switch 32 is sufficient to hold the resilient member out of contact with the contact wire 98 but insufficient to engage the contact of wire 94. Thus, if the release pressure falls, the circuit of lamps 36 is completed. Also, if the system is in order when the master cylinder is operated to apply the brakes, the rise of pressure causes the contact of wire 94 to complete the circuit of lamp 96. The Specification as open to inspection under Sect. 91 comprises also the following subjectmatter :-According to Figs. 13, 14, (both Cancelled and not shown) the pistons are integral with each other and the forward piston extends through a partition similar to the piston 52 and a reservoir is connected to the space 56 through a port in the cylinder wall that is covered by movement of the rear-piston. In Fig. 14, the space 54 is connected to a second reservoir by a valve similar to the valve 80, Fig. 2, but in Fig. 13 there is a single reservoir and the space 54 is normally connected to it through the space 56 and a port in a tubular extension of the forward piston, this port being covered by the partition 52, when the piston moves. In Fig. 11 (Cancelled) the piston 458 has a tubular extension 466 slidable over a floating partition 452 mounted on a fixed conduit 484 which connects the space 454 with the front brakes, the space 442 being connected by pipe 430 to the rear brakes. The reservoir 444 is normally connected to space 454 by a valve 474 held open by engagement with the tube 464 and the space 454 is normally connected to space 442 by port 478. In Figs. 8, 9 (Cancelled) a pair of parallel pressure chambers 227, 227a are connected by pipes 228, 230 to the front and rear brakes respectively and to the chamber 242 of the master-piston 258 floating pistons 229 are normally held by springs 231 in a position in which they cover vertical passages 233, 233a which are connected by diagonal passages 235, 235a respectively to vertical passages 237, 237a. If, when the piston 258 is operated the systems are working normally the pistons 229 move forward to uncover the passages 233, 233a, and are thus by-passed, but if one of the systems fails, the low pressure therein will cause the corresponding piston 229 to be .moved forward until it is held by engagement with spring fingers 241 so that no more liquid is supplied to the faulty system. Valves 281 by which a light pressure is normally retained in the systems and indicator switches 232, 234 similar to the switches 32, 34, Fig. 2 are provided. Fig. 10 (Cancelled and not shown) shows a similar system in which there is a separate master cylinder and piston for each chamber 227, 227a. Fig. 15 (Cancelled and not shown) shows a pair of chambers with floating pistons similar to the chambers 227, 227a, Figs. 8, 9 (Cancelled), but connected respectively to the chambers 54, 56 of a master cylinder such as shown in Fig. 2. Fig. 4 (Cancelled) shows a brake comprising' shoes 114, 116 operated by a hydraulic cylinder 24 and comprising adjustable members 126 extending through the shoes and normally abutting on stops 124. As the shoe lining wears, the members 126 are moved inwards and are held by pawls 130 adjustment for wear of the linings being thus obtained. Figs. 5, 6 (Cancelled and not shown) shows a construction of the switches 32, 34, Fig. 2 comprising a resilient contact member arranged for operation through a ball by a diaphragm subject to the hydraulic pressure. This subject-matter does not appear in the Specification as accepted.