Patent GB-629225-A (GB)
Title: Improvements in power braking systems
IPC: B60T15/02
Filed: 1943-02-22
Abstract: 629,225. Fluid-pressure-operated vehicle brakes. BENDIX AVIATION CORPORATION. Feb. 22, 1943, No. 2897. Convention date, July 20, 1942. [Class 103 (i)] In a fluid-pressure brake system for a tractor vehicle and a trailer coupled thereto, controlled by a main valve on the tractor, an initial pressure is applied to the trailer brakeoperating cylinder by an auxiliary valve operated by the main valve pedal, before an appreciable pressure is applied to the tractor brake cylinder by the main valve, further control of both brake cylinders being effected by the main valve alone.. As shown, the system is such in which vacuum is normally maintained on both sides of the pistons of brake cylinders 15, 16 of the tractor and trailer respectively. The forward chamber of cylinder 15 is connected to the engine intake 25 and that of cylinder 16 to a vacuum reservoir 28 connected by pipe 27 to the intake. The rear chamber of cylinder 15 is normally connected to the engine intake 25 by the main valve 17 and pipe 19 to which also pipe 20 is connected. The rear chamber of cylinder 16 is connected to the port 59 of a relay valve 23, thence to the chamber 52 of that valve. Valves 61, 62, operated by a diaphragm 53, connect chamber 52 either to atmosphere by port 57 or the vacuum reservoir 28 by port 55 and pipe 56. The control chamber 51 of valve 23 is connected by pipe 22 to the chamber 34 of an auxiliary valve 21 comprising diaphragms 30, 31 connected by a rod 35a and a cage 37 through which chamber 33 communicates with the interior of a tubular part 37b carried by diaphragm 31 and arranged to operate a valve 45 by which chamber 34 may be connected to chamber 33 or to atmosphere. Chamber 32 is connected at 40 to the reservoir 28, and chamber 33 at 42 to the main valve 17 by pipes 20, 19. The plunger 35 of a solenoid in circuit with a switch operated by the pedal of the main valve 17 bears on the diaphragm 30, Vacuum is thus normally maintained in the relay valve chamber 51 through the pipe 20 and valve 21 so that the valve chamber 52 and rear chamber of cylinder 16 are connected to the reservoir 28. Upon initial operation of the pedal the plunger 35 moves the diaphragms 30, 31 and valve 45 downwards, thus opening the chamber 34 to atmosphere, causing the vacuum valve 61 of relay valve 23 to close and the atmosphere valve 62 to open to admit air to the rear chamber of cylinder 16, thus applying the trailer brakes. When the pressure in chamber 34 is sufficient to overcome the force on the plungers 35, the valve 45 closes and the relay valve 23 returns to the lap position. Further pedal movement operates the main valve 17, admitting air to the rear chamber of cylinder 15 to apply the tractor brakes and also to chamber 33 of auxiliary valve 21. When the pressure,in chamber 33 substantially equals that in chamber 34 set up by the operation of the solenoid, the diaphragms 30, 31 with the member 37b are moved upwards to connect the pipes 20, 22 so that further control of the trailer cylinder 16 is effected with that of cylinder 15 by the main valve 17. When air is initially supplied to chamber 33 through pipe 20, the member 37b, before it is finally lifted to its uppermost position by the diaphragms, moves slightly to and from its seat on the valve 45, effecting slight pressure changes in chamber 34 and the relay valve. In a modification, the valves 17, 21 are operated by hydraulic pressure from a common pedal-operated master-cylinder, the arrangement being such as to ensure the operation of the valve 21 before the hydraulic pressure is sufficient to overcome the springs in the main valve 17. A spring interposed between the hydraulic piston of the valve 21 permits the re-closing of the valve 45. The valve 21 may instead be operated by a vacuum-responsive diaphragm or by a Bowden cable control.