Patent GB-629466-A (GB)
Title: Improvements in or relating to vehicle brake control systems
IPC: B60T8/32
Filed: 1945-11-23
Abstract: 629,466. Fluid-pressure-operated brakes. TECALEMIT. Nov. 23, 1945, No. 31716. Convention date, Jan. 8. [Class 103 (i)] In a fluid-pressure brake-control system for vehicles wherein the brakes are applied by means of triple valves responsive to a control pressure which varies according to the vehicle speed and the adhesion of the wheels in relation to the track, the release of the brakes, as well as the application thereof is caused to vary with the control pressure by the provision of exhaust valves adapted to give a graduated release and which normally replaces the usual exhaust means of the triple valves. The several exhaust valves on a train of vehicles may be electrically actuated under the control of a single pneumatic switch. A series of electrically actuated brake-pipe venting valves controlled by a common pneumatic switch may also be provided. The system shown comprises on each vehicle of a train a triple valve 107 controlled by the pressure in a brake pipe 83 to connect a brake cylinder 108 to an auxiliary reservoir 55 or to atmosphere, an electricallycontrolled valve 114 being provided for effecting release of the cylinder pressure independently of the triple valve so that graduated release in accordance with brake pipe pressure increase may be effected. Brake pipe pressure reduction to effect brake application is initiated by a drivers control valve 52, Figs. 1C, 3, and is then regulated in accordance with the adhesion of the wheels and the speed by the device described in Specification 611,918. This device comprises shafts 7, 7<SP>1</SP>, driven respectively from track wheels 10, 101 through helical gearing 5, 5<SP>1</SP>. The effective load 11 on the wheels is a little nearer the wheel 10<SP>1</SP> than to wheel 10 so that when a dog-clutch 9 is engaged, the wheel 10 is driven by the wheel 10<SP>1</SP> and at a greater speed by reason of the relative speed ratio of the gearing 5, 5<SP>1</SP>. The driving reaction on the gear 5 is transmitted by a thrust-bearing 12 to a piston 14 which is subject on one side to the constant pressure in the main reservoir 69 through pipe 39 and which operates a slide valve 16 controlling the pressure in the other chamber 15 of the piston. The speed control device comprises pairs of opposed pistons 35, 36 and 37, 38 and a slide valve 48 connected to a lever 41 fulcrummed on a sector 42, the axis 53 of which is slidable in a slot 43 by a centrifugal device 45 driven by an axle of the vehicle. The curvature of the lower edge of the sector and of the slot 43 is so designed as to take account of the variation of the coefficient of sliding friction with speed, in the adjustment of the fulcrum. Piston chambers 32, 33 are connected to reservoir 69 by pipe 39, chamber 31 to chamber 15 by pipe 25 and chamber 34 to the brake pipe 83 by pipe 77. The drivers control valve 52, Figs. 1C, 3, comprises pistons 64, 65 and a slide valve 76 connected to a lever 63 fulcrummed on a manually-adjustable member 62. Chambers 66, 67 are connected respectively to the reservoir 69 and to the pipe 74 leading to chamber 15. Normally the fulcrum 62 is equidistant between the connections of the pistons so that the pressure in chamber 62 and pipe 74 equals that in chamber 66 and reservoir 69, the pipes 74, 71 being connected as shown by the valves. The brakes are thus released. To initiate a brake application the fulcrum 62 is moved to the right, causing downward movement of piston 65 and valve 76 to connect pipe 74 and chamber 67 to atmosphere. When the pressure fall in chamber 67 corresponds to the changed leverage of the pistons, these return with the valve to close the pipe 74. Initial reduction of pressure in pipe 74 and thus in piston chamber 15, 31 effects movement of pistons 35, 36 and valve 48 to cut off pipe 77 from the reservoir pipe 39 and connect it to atmosphere port 49. When the fall in pressure in pipe 77 corresponds to that in pipe 74 taking account of the position of the fulcrum of the lever 41 and thus the speed, the valve 48 shuts off the pipe 77. Further reduction of pressure in pipes 74, 25 acting on piston 29 effects engagement of the dog-clutch 9 and acting on piston 23 causes slide valve 22 to cut off the pipe 74 and drivers valve 52 and connect reservoir 69 to chamber 27 of piston 14. The pressure in the chambers 15 and 31 and thus also in pipe 77 then becomes dependent upon the thrust on the bearing 12 and thus on the adhesion between the wheels and the tracks. The pipe 77 is connected by a restricted passage 82, Fig. 1B, to the brake pipe 83 and also to a pneumatic switch 78, the contacts 87 of which are connected to train wires 84, 86 to which are connected a number of vent valves 88. Thus pressure reduction in pipe 77 causes piston 79 to energize the valves 88 and thus to vent the brake pipe to apply the brake until the pressures on the two sides of the pistons equalises. If the current fails the brake pipe is still vented through the passage 82. Graduated release of the brake cylinder pressure with rise of pressure in the pipes 77, 83 is effected by a magnet valve device 114 comprising an exhaust valve 125, Fig. 5, controlling a branch 106 from the passage which connects the brake cylinder 108 with the triple valve 107 and controlled by a pneumatic switch 103, Fig. 1B, one piston chamber of which is connected by pipe 100 to the chamber 102 of a piston 101 and a slide valve 99 connected to a lever 96. The chambers 93, 94 of pistons 91, 92 also connected to lever 96 are open respectively to the brake pipe 83 and main reservoir pipe 95. The valve device 114 is normally energized by a source 128, train wires 130, 131 and conductors 116, 17 so that the plunger 122A holds a slide valve 111A in the position shown to close the triple valve exhaust passage 110. The switch chamber 103 is normally open to atmosphere through valve 99 so that the contacts 132A are open. When the brake pipe pressure is reduced to apply the brakes, the valve 99 is moved by pistons 91, 92 to connect the chamber 103 to the supply pipe 95 until the pressure acting on piston 101 returns the valve to lap, but as the brake cylinder pressure set up by the triple valve and acting in switch chamber 103<SP>1</SP> is substantially equal, the contacts 132A remain open. Increase of brake pipe pressure acting on the valve 99 through the pistons 91, 92 reduces the pressure in chamber 103 to a corresponding extent so closing the contacts 132A to connect a current source 129 of voltage higher than that of source 128 across the conductors 130, 131. The increased energization of the valve device 114 effects opening of a valve 119 to vent a chamber 122 by port 127, causing a piston 123 to open a valve 125 to vent the brake cylinder until when the pressure fall equals that in chambers 102, 103, the contacts 132A are re-opened. Upon closing of the valve 119 and the consequent equalizing of the pressure on the two sides of the perforated piston 123 the valve 125 also closes. If the current fails, the plunger 112A is moved by a spring 121 to position the valve 111A to open the passage 110 so that exhaust of the brake cylinder can be effected by the triple valve in the usual manner.