Patent GB-643864-A (GB)
Title: Improvements in control systems for automatic single-chamber compressed air brakes
IPC: B60T15/30
Filed: 1947-06-16
Abstract: 643,864. Automatic compressed air brake system. VERWALTUNGSGES. DER WERKZEUGMASCHINENFABRIK OERLIKON. June 16, 1947, No 15852. Convention date, June 20, 1946. [Class 103 (i)] The invention comprises an automatic compressed air brake system for railway trains that provides an improvement on existing systems in the following respects : (a) the interval between the operation of the driver's valve and the actual application of the brakes is reduced to the minimum possible with compressed air, this interval being the same both for service and emergency braking; (b) the rate of air flow into the brake cylinders to move the shoes into contact with the wheels is raised and made independent of the nature of the braking; (c) the pressure drop produced automatically by the accelerator in the brake control pipe for the first stage of the braking operation is made independent of the volume of the control pipe from which draw-off is effected; (d) the initial pressure produced in the brake cylinders to set the shoes in contact with the wheels is also made independent of the control pipe draw-off volume ; (e) the maximum pressure in the brake cylinder is kept constant whatever may be the piston stroke or the volume of the auxiliary reservoir; (f) for a given control pipe pressure, different intensities of braking are provided according to the load in goods trains or the speed in express passenger trains, the same brake cylinder charging and discharging times holding good for both brake pressure intensities; (g) the size of the charging passages is made so large that even the largest brake cylinder can be filled in a very short time; (h) the time for charging.the empty reservoirs is reduced to a half or one third that usually required. The system includes a maximum pressure limiting device I, which limits the maximum pressure possible in the brake cylinder, an accelerator II for the discharge of air from the control pipe L to atmosphere, a triple valve III including means for controlling the braking action in two different ratios with respect to the normal control pipe pressure, a discharge limiting device IV, which upon a definite pressure drop in the control pipe closes as a result of the pressure difference between the control pipe air and the control reservoir air; a cut-off unit V which during braking actions isolates the auxiliary reservoir, control reservoir and control pipe from one another; a header unit VI for effecting the initial brake application by an injection of air from the auxiliary reservoir into the brake cylinder. A minimum pressure limiting unit VII by which the injection is cut off when a predetermined pressure exists in the brake cylinder; a charging unit VIII having a valve operated by a diaphragm subject on opposing sides to the pressures in the control reservoir St and the auxiliary reservoir H; a setting valve IX by which the pressure ratio of the triple valve III and the charging and releasing times may be regulated to suit different operating requirements; a charging time control unit X, which ensures that for a certain setting of the valve IX, the time for charging the brake cylinder is kept constant on whichever pressure ratio the triple valve may be operating; and a discharge cut-off unit XI which co-operates with the discharge limiting device IV and in the event of there being insufficient pressure difference between the control pipe air and control reservoir air closes after a predetermined time interval as a result of the static pressure of the discharging control pipe air. Charging of the reservoirs takes place as follows. Air from the control pipe L, connected to the driver's valve, enters chamber 1 of unit I, passes through rod 6 to chamber 5, and thence through pipes 17 and 64 to chamber 61 of unit V. Valve 66 is lifted and air flows through pipe 65 and throttling passage 120 to the control reservoir St and also through the restricted passage 67 and pipe 68 to the auxiliary reservoir H. Due to the passage 67,. pressure in the auxiliary reservoir H is less than the pressure in the pipes 64 and 65. Therefore diaphragm 96 of unit VIII lifts valve 98 and connects chamber 95 with chamber 15, thus reducing pressure in chambers 12 and 15 to that of the auxiliary reservoir H so that valve 10 of unit I is opened and compressed air from pipe L can flow direct to the auxiliary reservoir H by way of throttling passage 14, chamber 15 and pipe 97. This reduces the time for charging the empty reservoirs to obtain characteristic (h) above. Spring 100 in unit VIII is of such a strength that valve 98 closes when the pressure in the auxiliary reservoir H rises to about 0.2 kg./cm.<SP>2</SP> below that in the control reservoir St. The initial braking operation takes place as follows. A drop in pressure is produced in the control-pipe L by the driver's valve. Owing to the restriction 67, pressure in chambers 1 and 5, pipe 17 and chamber 16 of unit II drops more rapidly than pressure in chamber 18 connected to auxiliary reservoir H. Diaphragm 23 thus lifts valve 24 and air from control pipes L can escape to atmosphere through valves 56 and 124 of units IV and XI. During the outflow of air a momentary high pressure is produced in chamber 57 of unit IV and chamber 75 of unit VI. Diaphragm 80 of unit VI thus lifts valve 78 so that air from the auxiliary reservoir H can this flow very rapidly through pipe 76, valve 78, chamber 81, valve 86 and nozzle 92 of unit VII, and pipe 93 to the brake cylinder Br. When the piston stroke is completed, the pressure in the cylinder and pipe 93 and chamber 84 rises suddenly and moves diaphragm 87 to close valve 86, thus completing the initial stage of the brake application. Pressure in chamber 83 has, during this operation, acted on diaphragm 71 of unit V to close valve 66, thus interrupting the connection between the supply pipe 64, auxiliary reservoir H, and control reservoir St. Characteristics (a) and (b) have therefore been obtained. When pressure in pipe L has fallen beyond that sufficient to carry out the initial stage of braking, just described, pressure in chamber 52 of unit IV is reduced to an amount below that in chamber 50, connected to the control reservoir St, so that diaphragm 54 closes the upper valve 56 and the outlet to atmosphere through valve 124 is thus shut off. Unit II is so constructed that once the valve 24 has been lifted by diaphragm 23, it will remain open no matter what are the pressures in chambers 16 and 18 until the upper valve 56 is closed. The characteristic (c) has thus been obtained. If the upper valve 56 has been closed by diaphragm 54 before the initial pressure in the brake cylinder Br has reached its required value; the control pipe pressure in chamber 16 is passed through lower valve 56, chamber 57 and pipe 60 to chamber 75 so that valve 78 is held open until charging of the brake cylinder is interrupted by the action of the unit VII. Thus characteristic (d) is obtained. Increased pressure on the brake shoes in correspondence with a gradual further reduction of pressure in the control pipe L is now produced by the action of the triple valve III. Upon a further pressure drop in chamber 29 of the triple valve III, which is in communication with pipe L by pipe 32, chamber 16, pipe 17 and unit I, diaphragm 31 moves spindle 36 to open valve 46 whereupon air passes from the auxiliary reservoir H by way of corresponding bores in the setting valve IX, pipe 49, chambers 44 and 42, pipe 43, chamber 103, and pipe 109 to the brake cylinder Br. Setting valve IX comprises inner and outer friction cones 110 and 111 respectively. The inner core 110 has two sets of axially-spaced charging and discharging passages 113, 114 and 115, 116 respectively which correspond to different charging times for different types of brake application. The outer cone 111 can be turned so as to span either passages 113 and 115 or 114 and 116. In the first case the chamber 41 of the triple valve III is simultaneously connected to atmosphere. In the second case it is connected to chamber 42. Thus by means of the inner cone, the device can be set according to charging or discharging times required for goods (G), passenger (P) or express (S) trains, while the outer cone, according as to whether it connects the chamber 41 to atmosphere or chamber 42, is used to set different ratios between the brake cylinder pressure and main pipe pressure drop, the latter cone being also connected to a speed-controlled unit U by which the ratio is automatically decreased with fall of speed. The time control unit X has an upper chamber 101 which is connected to chamber 41. When the higher ratio is being used, both chambers 41 and 101 are connected to atmosphere and air flows to the brake cylinder through the full bore of valve 107. If, however, the lower ratio is being used, brake pressure is also applied in chambers 41 and 101, the latter acting on diaphragm 104 to close valve 107 so that the air can only flow to the brake cylinder through the reduced area opening 108. Thus the same cylinder charging and discharging times apply for either pressure ratio and the characteristic (f) is obtained. If the pressure in pipe L should fall below that necessary to produce the required maximum pressure in the brake cylinder (i.e. by an amount greater than 1.5 kg./cm.<SP>2</SP>) then, due to the difference in pressure between chambers 1 and 4 of the unit I, the valve rod 6 is forced against the valve 10 and thus interrupts the connection between the pipe L and the rest of the system. In the event of a leaky brake cylinder, the valve 46 of unit III is lifted by valve-rod 36 because of the pressure drop in chambers 41 and/or 42 to allow a continuous flow from the auxiliary reservoir H to the brake cylinder Br. If, due to this flow, the pressure in the auxiliary reservoir H drops below that in pipe L, the valve 10 of the unit I opens and the auxiliary reservoir H is fed through the passage 14