GB557981A - Improvements in or relating to brake holding devices - Google Patents

Abstract

557,981. Vehicle brakes. BENDIX AVIATION CORPORATION. June 9, 1942, No. 7877. Convention date, June 9, 1941. [Class 103(i)] Vehicle brake-holding devices, of the kind which operate automatically in certain circumstances to hold the brakes applied even when the brake pedal is released, include control means consisting of two control devices each having an operative and an inoperative position, and both of which must be in the operative position to render the brake-holding device operative, the first device being operative only when the brakes are applied and the second being responsive both to deceleration of the vehicle and to the position of one of the control members of the vehicle (such as the accelerator pedal) so that when the control member is in the position which it occupies when the vehicle is running the second device remains in the inoperative position, while when the control member is moved to the position it occupies when the vehicle is stationary, deceleration of the vehicle consequent upon the application of the brakes will maintain the second device in the inoperative position, until'the vehicle comes to rest, whereupon it moves to the operative position to render the brake-holding device operative. In the construction of hydraulic brakes shown both control devices are electric switches 28, 29 in series in a control circuit for a solenoid which, when excited, closes a valve 25 between a mastercylinder 23 and the brakes so as to retain the brakeapplying pressure. The switch 28, constituting the first control device, receives the brake line pressure on a flexible diaphragm 62, Fig. 7, serving to bring together, first, contacts 59, 61 for a stop-light and then, under increasing pressure, contacts 58, 65 of the solenoid circuit so that the first control device is in the operative position. The second control device is constituted by the gravity switch 29, shown in Fig. 9 with the accelerator 30 released so that the switch is positioned so as to be closed, when the vehicle is at rest, and the brakes are held applied owing to the solenoid circuit being completed ; prior to this, deceleration produced by the brakes will have caused the mercury to move forward and keep the switch open. The valve 25, which retains the brakeapplying pressure when closed by means of the solenoid 39 as shown in Fig. 3, comprises two oppositely-directed ball-valves 35, 36 held closed by plungers 37, 38 under the action of the solenoid 39 when the solenoid is inactive and the brakes are applied, fluid from the master-cylinder passes through a passage 42 and a passage 43, controlled by valve 36, into the brake-lines. The closing force exerted by the plunger 37 is, owing to its small size and position, the equivalent of that which would be exerted by a light spring ; but the closing force exerted by the plunger 38 is large enough to resist ordinary braking pressure but not so large as to resist excessive pressure such as may arise from heating of the brake drums.