Patent GB-1233048-A (GB)
IPC: F16D65/28
Filed: 1968-12-04
Abstract: 1,233,048. 048. Liquid level indication. BENDK CORP. Dec. 4, 1968 [Dec. 8, 1967], No. 57462/68. Heading G1H. [Also in Division F2] A hydraulic split braking system comprising a tandem type master cylinder connected to be supplied by a hydraulic reservoir and a failure indicating system is characterized in that the failure indicating system includes an electricallyactuated warning device controlled by relay means responsive to a first signal generated upon a modification of an electrical circuit as a result of an overtravel of one of the pistons of the master cylinder and to a second signal generated by a means detecting a predetermined low fluid level in the reservoir. As shown, a dual master cylinder 10 has a reservoir chamber 20, divided into two compartments 22, 24, and including an annular partition 26 forming a well 34. The well communicates with the compartments by passages 30, 32 respectively. Two pistons 40, 42 are operated in a bore 16 by a push rod 12, and are associated with secondary and primary fluid discharge ports 162, 160, respectively. The master cylinder housing is earthed at 98. Piston 40 is provided with an insulating ring 64 and is insulated as a whole from the housing 18. However, an electrical contact 56 is biased by a spring arm 58 into engagement with an intermediate part of piston 40, and is connected by a lead 84 and terminal 86 with one end of a pull-in coil 76, the other end of which is earthed and also connected to one end of a latching coil 74. The outer coil 76 is secured by adhesive 82 to the base of the well 34, and both coils surround the non-conductive housing 72 of a magneticallyoperable switch, one contact of which, 116, Fig. 2, is connected to the other end of latching coil 74, and the other contact 108 of which is connected by lead 78 and terminal 80 see also Fig. 1 through a lamp 100 and ignition switch 103 to the vehicles storage battery 102. The direct connection to earth of the intermediate part of piston 40 is completed by spring fingers 66 which touch the earthed housing of 68 and are normally in electrical contact with the piston. The parts 58, 56, 40, 66 and 68 of Fig. 1 are represented in Fig. 2 as the normally-closed switch 114 between lead 84 and earth connection 98. A cork float 88 having a curved magnet 90 on its underside floats in the hydraulic fluid in the well 34. In operation with ignition switch 103 closed, and assuming a normally-functioning master cylinder with an adequate fluid level, the circuit is in the condition (apart from switch 103) shown in Fig. 2, where both ends of coil 76 are earthed, and a resistor 110 between leads 78 and 84 has a value such that the current flow to earth through lamp 100 is too small to make the lamp glow visibly. Upon failure to develop sufficient discharge pressure at the secondary discharge port 162, piston 40 will over-travel until insulating ring 64 moves under contact 56. The earth connection at terminal 86 is thereby broken, Fig. 2, and current now flows through coil 76, whereby contacts 108, 116, are closed. Current now flows through latching coil 74, by-passing resistor 110 so that lamp 100 lights up. The current in this coil serves also to maintain contacts 108, 116, closed after the brake is released and switch sequence 114 thereby restored. Similarly, upon failure to develop sufficient discharge pressure at the primary discharge port 160, piston 42 will over-travel relative to piston 40, compressing spring 48 between them; caging means 52 moves to the left relative to spring retainer 50 until its end (not seen) serves to sever the connection between piston 40 and spring fingers 66 (by alternative constructions depicted in Figs. 3 and 4, not shown). Thereupon events follow as described in the preceding paragraph. Should the fluid level fall below passages 30, 32, magnet 90 effects closing of contacts 108, 116, whereupon lamp 100 lights and latching coil 74 is energized as before. In all cases, the lamp, coil and switch 108, 116 are restored by opening the ignition switch 103.