Secondary and complementary brake actuation retrofit

A vehicle brake actuation retrofit apparatus comprising:

• a retrofit pneumatic circuit, coupled to a vehicle brake system to preserve a braking function of the vehicle brake system as activated by a primary driver foot pedal,
• a secondary actuator, coupled to the retrofit pneumatic circuit and configured to activate the vehicle brake system separately and independently of the primary driver foot pedal, and also configured so that when both the primary driver foot pedal and the secondary actuator are actuating at a given time, a total brake force applied to the vehicle brake system is a maximum of a pneumatic force provided by the primary driver foot pedal and the secondary actuator;
• a retrofit proportional valve coupled via a shuttle valve to a vehicle proportional valve associated with the primary driver foot pedal;
• wherein the retrofit proportional valve is functionally equivalent to the vehicle proportional valve;
• a controller, configured to control the pneumatic force provided by the secondary actuator;
• and
• additionally comprising:
• one or more directional control valves disposed to isolate both an input and an output portion of the retrofit pneumatic circuit, and to enforce positive shutdown of the controller to prevent a malfunction, such that at least one directional control valve blocks supply pressure to prevent bleeding the apparatus where pressure is requested while the controller configures the apparatus in a disabled state, and such that at least one other directional control valve vents built-up pressure to atmosphere so that any residual pressure does not actuate the vehicle brake system.