Secondary and complementary brake actuation retrofit

Abstract

A retrofit pneumatic circuit complements an existing factory braking system to preserve the original function of the driver's foot pedal while also adding the ability for a computer to actuate the brakes separately and independently. In the event where both the primary and secondary drivers are actuating the brakes at any time, the braking force applied is the maximum of the two. In the preferred approach, a shuttle valve is connected between a primary proportional valve and a copy of that proportional valve. Directional control valves are also included to isolate both the input and the output portions of the secondary circuit in order to enforce positive shutdown of computer control. One directional valve blocks a supply pressure to prevent bleeding of the system in any situation where pressure is requested when computer control is supposed to be disabled. A second directional valve vents any built-up pressure to the atmosphere, so that any residual pressure does not actuate the brakes after computer control is disabled.