Patent GB-420069-A (GB)
Title: Improvements in hydraulic power transmission systems
IPC: B60T13/24
Filed: 1933-03-20
Abstract: 420,069. Hydraulic transmission of power. BENDIX AVIATION CORPORATION, 105, West Adams Street, Chicago, U.S.A. March 20, 1933, Nos. 8362 and 8363. Convention dates, May 6, 1932 and May 23, 1932. [A Specification was laid open to inspection under Sect. 91 of the Acts, Oct. 2, 1933.] [Classes 69 (ii) and 135] Hydraulic transmission systems for brakes and other purposes comprise a power device set in operation by initial movement of a pedal &c. to force liquid into a master cylinder behind a piston which applies an initial pressure to the system, subsequent actuation of the pedal displacing a second piston in the master cylinder to apply an increased pressure to the system. The power device may be a vacuum-or compressed air-operated auxiliary master cylinder. The brake system shown in Figs. 1 to 4 comprises a main master cylinder 40, a vacuum operated master cylinder 46 combined with a liquid reservoir and a device 54 for limiting the pressure applied by the device 46, which comprises a piston 76, Fig. 2, in a cylinder 74 connected through pipe 55 and valve 60 to the intake manifold 58 of a vehicle engine. The piston 76 is secured to a hollow plunger 72 which forms a reservoir for the pressure liquid and which slides in a cylinder 68 connected to the master cylinder 40 by pipe 48. With the plunger in the normal position shown, cylinder 68 communicates with the interior of the plunger by grooves in the fixed head 85 and ports 90. The reservoir liquid in plunger 72 may be maintained under slight pressure by the provision in the plate 70 of cylinder 74 of a pair of oppositely acting spring check-valves, one of which allows free inlet of air during downward movement of the piston 76 while the other permits escape of air on upward movement of the piston only when it is above a certain pressure. The pressure relief device 54, comprises a spring-urged piston 108, Fig. 3, in a cylinder connected to master cylinder 40 by pipes 51, 52 and to reservoir 72 by pipe 50 and ports 90. The master cylinder 40 comprises a plunger 122 operated by the pedal 42 and passing through a fixed head 120 and a sealing cup 134. A piston 124 is slidable on the plunger 122. In the normal position of plunger 122 and piston 124 shown, liquid can flow to or from the pipe lines 38 to the reservoir 72 through ports 142 in the plunger, passages through head 120, port 128 and pipes 51, 50. When the pedal 42 is depressed to apply the brakes, the valve 60 is first operated by the connection 62, to connect cylinder 74 to the engine manifold 58 so that plunger 72 forces liquid through pipe 48 to the master cylinder 40 behind piston 124 which forces liquid from the space 116, through passages in the head 120 past the cup 134 to the pipe lines 38 and the brake cylinders. When the pressure in the space 116 and in the part of pressure relief cylinder 54 connected thereto by pipe 52 reaches a value sufficient to overcome the spring 112, the piston 108 moves to the right and the pressure applied by the piston 124 is thus limited. The pressure may however be increased by the continued movement of plunger 122 by the pedal. If the power device 46 fails, piston 124 is actuated by the pedal through a ring 146 engaged by a projection on the plunger. In a modification, the separate pressure relief device 54 is dispensed with and the master cylinder, Fig. 6, is used. This is connected to the plunger reservoir 72, Fig. 2, by pipe 250 and to the cylinder 68, Fig. 2, by pipe 248. Pistons 358, 324 slidable on the pedal operated plunger 322 are connected by a spring 312. The valve 60, Fig. 1, is electrically controlled in this case by a switch operated by the pedal. The piston 358 acted upon by the liquid supplied by the power device 46, at first moves piston 324 through spring 312 and thus applies pressure to the liquid in pipe line 238. When this pressure reaches a certain value the spring is compressed, piston 324 ceases to move and the liquid between the pistons is returned to the reservoir through pipe 250. Figs. 9, 11 show a further arrangement wherein pressure can be applied to the liquid in the pipe line 1026 either by vacuum and pedal pressure when the pedal 1112 is actuated or by the combined action of vacuum and compressed air by operating a separate pedal 1116 as in emergency. The power device 1070 is similar to that shown in Fig. 2, except that the chamber above the piston 76 can be connected by a valve 1120 to a compressed air reservoir 1074 supplied by a compressor 1072 or by a hand pump through a connection 1085. The master cylinder 1028 has two pistons 1042, 1048, Fig. 11 and is connected to the cylinder and liquid reservoir of the power device by pipes 1078, 1080 and to the pipe line 1026 at 1034. Initial movement of the pedal 1112 closes the switch 1094 to actuate the valve 1088 thus connecting the power device 1070 to the engine manifold 1076. Liquid is thus forced into the master cylinder through pipe 1078 past the sealing-cup 1046 and acting against piston 1042 forces liquid into the pipe line 1026. The pressure applied in this way may be sufficient only to take up the slack in the brake system or to apply a light pressure to the brakes. Additional pressure is applied by the pedal acting on the piston 1042 through the piston 1048 and the liquid contained between the two pistons, the pressure being multiplied by reason of the difference in area of the pistons. If the power device fails, the piston 1042 is actuated mechanically by the pedal through the piston 1048 and the projection 1054 on the piston 1042. By depressing the pedal switch 1116 both valves 1088 and 1120 are operated to connect the power device simultaneously to the compressed air and vacuum sources 1074, 1076. The pressure of the compressed air in addition to acting on the piston 76, Fig. 2, is transmitted directly to the liquid in the pipe line 1026 through pipe 1080 and passages in the head 1039 Fig. 11. The Specification as open to inspection under Sect. 91 comprises also the following subjectmatter :-An arrangement in which the master cylinder has only a pedal operated piston and the power device such as 46, Fig. 1, 2, forces liquid into the cylinder forwardly of the piston thence directly to the pipe lines. The power device 1070, Fig. 9, may be used alone, that is, without the master cylinder 1028 and the means for applying pedal pressure to the liquid. The power device may comprise a vacuum piston attached to a bellows which contains the pressure liquid. The double-acting check valve 1064, Fig. 11 for retaining a slight pressure normally in the pipe lines may comprise an apertured metal cup 1232, Fig. 15 (Cancelled) or disc fitted in a rubber cup 1231 having a central aperture corresponding to the outlet from the cylinder 1032 and seated over a recess 1226 in the end of the cylinder. The cup 1232 receives the end of the spring 1066, Fig. 11. This subject-matter does not appear in the Specification as accepted.