Digital application and release brake control signals generated by an electronic operating unit in accordance with the difference between a desired retardation signal and the available dynamic brake effort are provided to control a pair of thyristors in an a.c. control circuit for energizing one or the other of separate field windings of a torque motor, the output shaft of which drives a pneumatic relay valve device between application, lap and release positions, accordingly. The output of the relay valve provides friction brake effort sufficient to compensate for the inability of the dynamic brake to satisfy the desired level of ratardation called for. A pneumatic means of controlling the relay valve device independent of the torque motor is available to assure friction braking in the event the torque motor drive fails.
Combination fluid pressure and electric operable trip cock emergency brake apparatus for use with railway vehicles including a trip cock device having a fluid pressure portion and an electrical portion, both operable concurrently, when a trip lever thereon is actuated by a trip arm located on the roadway, for providing concurrent fluid pressure and electrical pilot signals to cause operation of a common control switch which in turn, when so operated, actuates propulsion and brake control devices to cause propulsion power to be cut off and an emergency brake application to be effected concurrently. The fluid pressure and electric portions of the trip cock device complement each other to insure that one or the other, if not both, will effect the desired results in an emergency situation.
A system or method for compensating for low vacuum levels in a brake-by-wire system includes continually monitoring the level of vacuum in a vacuum booster. The state or condition of the vacuum source is also monitored to determine whether it is on or off. When the vacuum source is off, the level of vacuum is measured to determine whether it is at or below a critical level. If the level of vacuum is critically low, the vacuum source is turned on. If the vacuum level is not critically low, the hydraulic boost gain is modified in order to provide more braking pressure in response to brake force exerted at the brake pedal.
