GB736937A - Improvements in and relating to a fluid pressure brake system comprising a series of brakes brought into action successively - Google Patents

Abstract

736,937. Fluid-pressure brakes. DAIMLER-BENZ AKT.-GES. Oct. 5, 1953 [Oct. 3, 1952], No. 27283/63. Class 103 (1). In a fluid-pressure brake system in which a control member (i.e. a brake pedal) when moved through a short distance from a resting position moves a first valve controlling the actuation of the first brake and when moved through a larger distance from a resting position shifts both first and second valves which control sequential actuation of the first and second brakes, a third valve is provided such that when shifted, the second brake is operated irrespective of the condition of the second valve, the third valve being shiftable by delayed-action means operable coincidentally to the operation of the first brake. As illustrated, the invention is concerned with pneumaticallyoperated brakes for tractor-trailer vehicles in which the trailer brakes are operated before those of the tractor vehicle. The diagram shows both the tractor or second brake 15 and the trailer or first brake 14 in their released positions; the tractor brake being held inoperative by a spring 39 and the trailer brake being held inoperative by air pressure in the brake cylinder 23. Hence the tractor brake 15 is applied by compressed air and released by spring and the trailer brake 14 is applied by spring and released by compressed air. The compressed air produced by compressor 18 is stored in a reservoir 19. In operation, when it is desired to apply the brakes gently, the pedal 10, pivotally mounted at 11 on a sliding member 13 loaded by a spring 12, is partially depressed. The trailer piston valve or first valve 16 is thus displaced to the left and the tractor differential piston valve 17 (the second valve) to the right, the arrangement being such that the first valve 16 at once closes the pipe 20 and connects the pipe 22 through 26 to atmosphere thus releasing the air in the trailer brake cylinder chamber 23 and allowing spring 25 to apply the first brake 14. The second valve 17, however, is not moved far enough by partial depression of the pedal to make any alteration of the control conditions apertaining to it. If the pedal is left in this position the tractor vehicle brake would remain inoperative in the absence of further provision. However, a third valve 34 is influenced by change of pressure at the first brake 14 by way of pipe 43, throttle 45 and pipe 44; the pipe 43 being deprived of pressure at the same time as pipe 22, the compressed air can escape slowly from the space 42 through a throttle 45 thus permitting after a certain time-lag, the large diameter piston portion 41 of the third valve 34 to close the pipe 32 and hence pipe 31 leading to atmosphere so that the small diameter piston portion of the third valve 34 opens pipe 48 so that compressed air passes via pipe 36 to actuate the piston 38 of the brake cylinder of the tractor vehicle and apply the second brake 15. If the pedal 10 is fully and quickly depressed, however, for full or hard braking, it has to overcome the increasing resistance of the spring 30. As before, the first valve 16 instantly, and during the initial part of the depression, releases pressure from the trailer brake cylinder 23 so that the spring 25 can apply the first brake 14. The full depression of the pedal 10 then causes the left-hand piston of the second valve 17 to close the vent 31 to atmosphere, the right-hand piston portion 29 at the same time uncovering the port of the pipe 27 whereby pressure can pass from the reservoir 19 to the tractor brake cylinder space 37 via 27, 28, 32, 33 and 36. The second brake 15 will then be applied by the piston 38 a short interval after the first brake 14 has been applied. On release of the brake pedal 10, the first valve 16, the second valve 17 and the third valve 34 are all returned to the positions illustrated; the tractor and trailer brakes being released. The third valve 34 is assisted to return to the position illustrated quickly by means of air in pipe 43 opening by-pass valve 47 and allowing air to pass into pipe 44 to assist the return action of the spring 35 and for the exhaustion of the brake cylinder space 37 and the release of the second brake 15. The third valve 34 may, if desired, be constructed similarly to the second valve 17 and mechanically connected to the pedal 10, so that the driver can feel the intensity of braking.