Electronic fail safe circuit for electro-pneumatic brake control

Abstract

An electronic fail safe circuit ensures that if there is a microprocessor failure during a brake application, this failure does not result in a release of the brakes. This is accomplished by the fail safe circuit forcing the appropriate solenoids to the self-regulating valve's hold state for a certain amount of time. This, in combination with the self regulating valve, accomplishes the desired outcome of a minimum disruption in the brake application and, specifically, prevention of an erroneous brake release. To further enhance the reliability of the system, a dual battery power supply is used. Each battery is tested prior to doing a brake application. Each battery has to pass the test, i.e., each battery individually must have enough charge to complete the brake application, before the brake application is undertaken. This redundancy concept is carried into the wiring of the release solenoid so that a single failure in the wiring will not result in de-energizing the release solenoid during a service brake application. Finally, a hardware interlock is enabled whenever a service brake application is started and is disabled otherwise. When enabled, the hardware interlock prevents the microprocessor from directly de-energizing the supply solenoid when the exhaust solenoid is also de-energized which, if allowed, could cause the brake pipe pressure rate of reduction to exceed the allowed limits.