Patent GB-554157-A (GB)
Title: Improvements in power brakes
IPC: B60T13/24
Filed: 1941-02-28
Abstract: 554,157. Fluid-pressure brakes. BENDIX AVIATION CORPORATION. Feb. 28, 1941, No. 2719. Convention date, Aug. 21, 1940. [Class 103 (i)] A relay valve for vacuum brakes comprises a pair of diaphragms operating a pair of poppet valves adapted respectively to connect the brake cylinder to atmosphere and to the vacuum source, under the control of the.pressure in chambers defined by the diaphragms and a fixed partition, two of the chambers being connected respectively to the cylinder and to a main valve. Systems are described in which brake cylinders on a tractor and a trailer vehicle are controlled by a common pedal operated valve acting as regards the trailer vehicle through the relay valve, the brake piston on one or both vehicles being normally subject on both sides to vacuum or to atmospheric pressure. The trailer brakes are also applied automatically by breakage of the pipe connections between the vehicles. As shown in Fig. 1, the relay valve comprises a pair of diaphragms 14, 15 connected by a rod 21 passing through a yieldable bushing 22 in a partition 16. The diaphragm 14 is connected by a rod 21<SP>1</SP> and a triangular floating lever 38 to the stems 34, 35 of poppet valves 32, 33, controlling ports 28, 29 connected respectively to atmospheric and to the vacuum source. The port 30 and thus the chamber 20 is connected to the brake cylinder. The connection of the other chambers 17, 18, 19 depend upon the system in which the valve is used. In the system shown in Fig. 3 the pistons of both the tractor and trailer brake cylinders 125, 126 are normally subject to atmospheric pressure on both sides. A pedal operated main valve 128 is connected by pipe 127 to the cylinder 125 and by pipe 119 to the engine manifold 109 which is the source of vacuum to which also a reservoir 134 in the trailer is connected by pipe 132, a non-return valve 133 being provided in the pipe. Chambers 17, 18 and port 29 of the relay valve 10 are connecter to this vacuum pipe by branches 137, 135 and 136 and chamber 19 to the main control valve and cylinder 125 by pipe 131. During release, the chamber 19 is connected to atmosphere through the main valve and the diaphragms 14, 15 are in the lower position in which the valves 33, 32 are respectively closed and open so that the cylinder 126 is connected to atmosphere. When by operation of the main valve the pipes 127, 131 are connected to the vacuum source the tractor brake is operated and the vacuum thus established in chamber 19 raises the diaphragms thus opening valve 33 to connect the trailer cylinder 126 to the vacuum pipe 132 through ports 30, 29. When the vacuum in the cylinder and chamber 20 corresponds to that in chamber 19 the diaphragms move downwards sufficiently to close the valve 33 but without opening the valve 32. Should the pipe 132 be fractured as by breaking of the vehicle coupling air enters the chamber 18 through pipe 135 but is prevented by the non-return valve 133 from entering the reservoir 134 and chamber 17 so that the diaphragms are operated to apply the trailer brake. In another system the tractor and trailer cylinders are respectively of the kind in which the piston is normally subject on both sides to atmospheric pressure and to vacuum. Chamber 18 is connected to the main valve and thus normally to atmosphere, and chambers 16, 19 are respectively connected to the vacuum pipe and atmosphere. The forward and rear chambers of the trailer cylinder are respectively connected to the vacuum pipe and to port 30 and as the valve 33 is open as shown during release, the rear chamber is also connected to the vacuum reservoir. Operation of the main valve simultaneously establishes vacuum in the tractor cylinder and in chamber 18 thus operating the valves 32, to connect the rear chamber of the trailer cylinder to atmosphere to apply the trailer brake. Upon fracture of the vacuum pipe, air is prevented from entering the vacuum reservoir and forward cylinder chamber by a non-return valve but enters chamber 17 thus operating the valves 32, 33 to apply the trailer brake. In a system in which the tractor and trailer brake pistons are normally subject on both sides to vacuum and to atmospheric pressure respectively, the rear chamber of the tractor cyclinder and valve chamber 18 are connected to the main valve and thus normally to the vacuum pipe. Chambers 17, 19 are connected respectively to the vacuum pipe and to atmosphere. During release the valves 32, 33 are normally open and closed respectively thus connecting the trailer cylinder to atmosphere. The forward chamber of the tractor cylinder is connected to the vacuum pipe. Operation of the main valve admits air to the tractor cylinder rear chamber and to chamber 18 raising the diaphragms to connect the trailer cylinder to the vacuum pipe and reservoir through ports 30, 29. Fracture of the'control pipe applies the trailer brake in the same way a non-return valve prevents entry of air to the vacuum reservoir and its connection the the port 29 upon breaking of the vacuum pipe. A further system is described in which both brake pistons are normally subject on both sides to vacuum, the forward chambers of the two cylinders being connected to the vacuum pipe and the rear chambers respectively to the main valve and to the port 30 of the relay valve the chamber 17 of which is connected to the main valve while the chambers 18, 19 are both connected to atmosphere. During release the relay valve is in the condition shown thus connecting the trailer cylinder rear chamber to the vacuum pipe. Operation of the main valve to apply the brake admits air to the tractor cylinder rear chamber and to chamber 17 this operating the relay valve to admit air also to the trailer cylinder rear chamber. Fracture of the control pipe effects application of the trailer brakes in the same way. A modification of the relay valve is shown in which the chambers 17, 19 are connected by passages through the casing wall respectively to the vacuum port 29 and the atmosphere chamber 28 thus enabling simpler pipe connection for the valve to be used in the systems in which vacuum normally exists in both cylinder chambers on one vehicle and atmosphere in the other. These passages may be closed when the valve is used in the other systems described.