Patent GB-1506005-A (GB)
Title: Brake system for a light rail vehicle
IPC: B60T8/18
Filed: 1975-05-05
Abstract: 1506005 Rail vehicle brakes; valves GENERAL SIGNAL CORP 5 May 1975 [17 June 1974] 18711/75 Headings F2F and F2V A braking system for an electrically driven rapid transit rail vehicle having driven and non- driven axles combines dynamic braking (where the drive motors act as generators so braking the axle) on the driven axles with friction braking on both driven and non-driven axles, the latter being controlled by load-responsive proportional braking where the braking effort is dependent on the weight of the vehicle, the system also including a parking brake, an emergency braking system, the latter having separate control and actuation from that of the main system, and an anti-skid system. Friction brake actuation (Fig. 7).-A first hydraulic motor 321 comprising piston 322 in housing 320 operates to apply pads 324 and 325 to disc 314 actuating the brake. A second hydraulic motor 327 comprising piston 326 normally operates to resist spring motor 325 but if there is a sufficient reduction in pressure in the space between piston 326 and rear wall 351, normally maintained by means of check valve 530 at the maximum pressure in hydraulic motor 321, caused by operation of the emergency or parking brake control by opening of magnet valve 301 to vent the pressure in the second fluid motor 327 so that spring motor 325 actuates the brake. Lead screw 359 comprises a mechanical slack adjusting means while hydraulic slack adjusting means 41 is also provided (Fig. 4, not shown). Wheel slip control (Fig. 1).-Wheel slip control 27 receives input signals from slip detection means and sends signals to dump valves 59, 60, 61 which temporarily de-activate the corresponding friction brake until slip ceases. The detection means detect differences in speed between axles and monitor angular acceleration when synchronous slip occurs. Dump valves (Fig. 5).-Dump valve 59 is opened by application of an electrical control signal to winding 270 surrounding armature 271 which is displaced to the right in Fig. 5, displacing spool 262 to the right to open communication between dump chamber 215b and air line 79 and when the electromagnet 270 is deenergized the spool is returned by spring 267. Control valves (Fig. 2).-Control valves 45 comprise four main components:-(i) Electrical torque motor 134 responding to signal variations in control line 19 and exerting a proportional torque on comparator shaft 137. (ii) A pneumatic torque motor 138 applies a torque to shaft 137 resisting that of motor 134, this torque decreasing linearly with the pressure applied to the friction brake system through output line 139a. (iii) Pressure transducer 140 driven by shaft 137 which controls the pressure in pilot passages 141 and 142 according to its angular position. (iv) Supply and exhaust valve assembly 143 regulating the input pressure from line 16a, in accordance with the pilot pressure in passages 141 and 142, to the output 17. The braking system as a whole (Fig. 1) is actuated by logical electronic signals from brake command control which are then converted to pneumatic signals by control valves 45 and 46 and are finally converted to hydraulic pressure signals at converters 38, 39, 40. The particular embodiment described discloses a three-car train of which only the end cars are powered and therefore the centre car has only friction brakes.