GB1290611A - - Google Patents

Abstract

1290611 Hydrokinetic brakes; air control of; fluid-operated friction brakes BRITISH RAILWAYS BOARD 5 Jan 1971 [13 Jan 1970] 1720/70 Headings F2E and F2F A control system of a hydrokinetic brake, 1 or 2, comprises a pressurized working-fluid reservoir 3 connected to the brake 1 or 2 by fluid feed and return lines, a regulating device 16 to 19 arranged to set the pressure in the reservoir at a value related to a required braking torque, and provision for controlling the inlet pressure of the hydrokinetic brake so that it is maintained at a fixed value lower than the reservoir pressure during normal braking operation. As shown, the inlet of each brake is vented to atmosphere to maintain it at the fixed value by connecting the centres of the brake toroids to atmosphere through non-return valves 7, 8, and an open reservoir 6. Liquid from pressurized reservoir 3 may flow through either valve 9 or valve 10 (as shown) to hydrodynamic brake 1 or 2, respectively, mounted on the axle of a rail vehicle, the selection of brake being according to direction of vehicle travel (see below). The brakes by their pumping action return the liquid to reservoir 3 past non-return valves 4, 5. The valves 9 and 10 are opened, when appropriate, by air from an air reservoir 12 and closed by springs. Air is admitted (or not) to valves 9, 10, through a cut-off valve 13 whose lateral position is controlled by air pressure from a pressure-regulating valve 16 (see below), this pressure being equivalent to that applied to reservoir 3, so that cut-off is effected when the pressure of reservoir 3 is below that corresponding to the minimum required braking torque. A cut-off valve 14 similar (but solenoidenergized) to valve 13, and in series with it, is operated to cut off air to valves 9, 10 when its solenoid 43 is energized by a signal at 45 generated when the vehicle speed is below the minimum at which the hydrodynamic brakes 1, 2 can make a significant contribution to the braking effort. A further valve 15, located between valve 14 and valves 9, 10, is a solenoidoperated changeover valve set by the directon of travel of the vehicle to select the appropriate valve 9 or 10, and is energized through lines 46 which include changeover switch 47. The liquid in reservoir 3 is pressurized, by direct contact of compressed air with the liquid surface, from the air reservoir 12 through the pressure-regulating valve 16. The setting of this valve is variably controlled, (a) mainly by a proportional solenoid 17 energized by whatever "driver's brake rate demand" signal is being transmitted along lines 19, and (b) partly by an axle-load-responsive jack 20. Thus, valve 16 constitutes the regulating means arranged to set the pressure in the reservoir at a value related to a required braking torque. For zero current input to solenoid 17, valve 16 provides a pressure in reservoir 3 to produce a predetermined braking rate, so on failure of solenoid 17 the brakes will be applied. When the current has a value such that the reservoir pressure falls below a predetermined value, cut-off valve 13 closes. Reversal of the polarity of the current increases the reservoir pressure to a value sufficient to give emergency-stop braking. Pressure in air reservoir 12 is maintained by a compressor 22. The liquid in reservoir 3 is cooled by pumping it at 24 around a circuit 25. A temperature sensor in reservoir 3 operates a by-pass valve 29 when the liquid temperature is sufficiently low. The circuit incorporates an ejector pump 26 which, when the brakes are on, as shown, returns to reservoir 3 any liquid from reservoir 6 which may have escaped through the vent lines from the brakes. When the brakes are off, this pump reduces air pressure within the brakes, thus reducing parasitic drag. The changeover between these two functions is performed by a valve 28 operated by the pressure line between valves 14 and 15. Mechanical brakes 39, 40, are also provided, and are actuated by fluid-mechanical jacks 35, 36, simultaneously fed from a further liquid reservoir 37 by a pump 38 through a pressureregulating valve 34. The setting of the valve 34 is governed by the differential between the outlet pressure (representing the braking torque being produced), of whichever hydrodynamic brake is operating, along line 30, and the reservoir pressure (representing the braking torque requirement), along line 31. The mechanical brakes are operated when the hydrodynamic braking torque falls below the demand. Valve 41 cuts off the mechanical brakes when there is no braking demand, or when the speed is above that for safe operation of them, or when a sensor on the shoes indicates that their temperature exceeds a safe maximum. A wheel-slide signal cuts off the hydrodynamic and mechanical brakes.