Patent GB-1444865-A (GB)
Title: Braking system for a light rail vehicle
IPC: B60T13/58
Filed: 1974-07-15
Abstract: 1444865 Aritiskid and load responsive braking systems GENERAL SIGNAL CORP 15 July 1974 [31 Aug 1973] 31215/74 Heading F2F A brake system for light rail vehicles comprises an electro-dynamic brake 29 generating variable electric current, at least a portion of which is fed to an impedance 136, a fluidoperated friction brake system, an electric control for energizing the brakes, a fluid pressure control including an electro-pneumatic transducer 140 responsive to electrical variations in the impedance 136 to vary the fluid pressure supplied to the friction brakes and a variable load valve 53 including a pneumatic spring 51 and a proportioning valve responsive to pressure variations therein to vary the fluid pressure, and skid control means including a wheel slip detector 56 and a release valve for venting fluid pressure supplied to the friction brake when a skid condition is determined. As shown dynamic brakes 28, 29 on at least two of the vehicles' trucks have controllers 30, 31 which respond to changes of current in a control line 11  and a pneumatically controlled friction brake system utilizing brakes 32 ... 37 has pneumatic to hydraulic converters 38 ... 40 responsive to pneumatic signals to operate hydraulic brake motors. Vvalves 44, 45, 46 blend the braking effort between dynamic and friction systems in response to signals from the control system. A main reservoir 48 fed by a compressor 47 supplies air for braking and to pneumatic spring 51 via check valve 50 and relay valve 52, a reserve reservoir 49 supplying pressure for the pneumatic control system. A hand brake or parking brake is provided by means of a second fluid motor in each of the converters 38 ... 40 which restrains a spring motor for actuating the hydraulic part of the converter, this second motor being controlled by a hand brake release valve 55 through a control line 15 or by hand venting a release valve 55a. The parking brake may also be manually released with a wrench at each of the converters 38 ... 40. Variable load system.-Spring 51 is in the form of flexible bags located between body and chassis, the air pressure within which is controlled by a valve 73 responsive to vertical movements of the body due to loading, and the variations of air pressure regulate a valve 53. Air from reservoir 49 passes via valves 55, 53, 52 to the blending valves 44, 45, 46. Blending control valves.-Each valve 44, 45, 46 has a pair of electrical torque motors 134, 135 responding respectively to current variations in control line 11 and in impedance 136, a pneumatic torque motor 138 applying to a shaft 137 a resisting torque decreasing linearly with increase in pressure applied to the friction brake system through a line 139, a pilot valve assembly or pressure transducer 140 driven by shaft 137 and controlling pilot pressure in passages 141, 142 and a supply and exhaust valve assembly 143 which regulates the input pressure to the friction brake system, the assembly 143 including supply and exhaust valves 145, 146 arranged to control flow to the main brake line 139 or to exhaust port 148. The valves 145, 146 are carried by spool portions 150, 150a reciprocating in axially aligned bores and arranged so that they can engage each other to move in a closing direction and are biased closed by a compression spring 149. The valves can be opened by motors formed by spring and diaphragm 151 or spring 152 and diaphragm 153. A separate solenoid valve 158 can be operated to vent the supply for transducer 140 so that a full service application of the brakes can be attained regardless of the braking effort of the dynamic brake. Friction brakes and slack adjuster.-Hydraulically applied disc brakes 162, 163 are pneumatically controlled by subsystems each including a pneumatic to hydraulic converter 38 ... 40, a handbrake control line 57, and an hydraulic slack adjuster 161, the converter having pneumatic motors with pistons 164, 165, an hydraulic motor with piston 166 and a spring motor 167 restrained by piston 165. The handbrake application releases pressure in a chamber 172 and the spring energizes the hydraulic motor to apply the brakes. The hydraulic motor and slack adjuster comprises three axially aligned stepped bores forming chambers 178, 179, 180 of which chamber 178 with piston 166 forms the hydraulic motor and the chambers 179, 180 house a differential piston 184 containing a valve unit 191. Upon actuation of the service brakes chamber 171 is pressurized and piston 164 causes displacement of the hydraulic piston 166 which seals a port 182 and displaces fluid from chamber 178 to chamber 179 to move piston 184 to displace fluid through a line 160 to the brake motors of brakes 162, 163. Shoe clearance prevailing at the end of brake release will be determined by the volumetric displacement of the piston 184 through chamber 180 so that if there is too little clearance it will be increased. If clearance is too great the quantity of hydraulic fluid displaced from chamber 178 will be greater than that returned when the brakes are released so that piston 184 will return to its initial position against an abutment 187 before the piston 166 has reached its retracted position so that oil will be transferred from reservoir 181 through port 183, working space 210, a passageway 205 and check valve 206 to chamber 178.