A two knob control for tractor and trailer parking brakes providing single knob application of both tractor and trailer parking brakes. It also provides for maintaining the tractor parking brakes in the applied condition while charging the trailer brake air system and for applying the trailer brakes independently of the tractor brakes. Automatic application of trailer parking brakes is provided upon trailer breakaway or a significant reduction in tractor reservoir air pressure.

An electronic braking system for wheeled vehicles comprising an electronic controller which produces, in response to driver braking demands, electronic signals for controlling the braking pressures applied to the vehicle wheels from a source of braking pressure. The system includes a second, back-up braking pressure source which can be selected when required, and means for switching over from the first-mentioned normal source of braking pressure to the back-up pressure source at selected occasions when the vehicle is being braked and has come to rest, provided that the prevailing driver's braking demand is above a predetermined minimum threshold. A test is then performed on the braking pressure signals generated by the system while it is energized by the back-up source and a warning signal is generated if the back-up source is found to be faulty.

An emergency and parking (E&P) brake system (6) is used with a brake system (2) of the type including an air brake coupled to a service brake actuator (8) by a slack adjustor (104) movable between brake released and brake applied positions. The E&P system includes an E&P actuator (80), located physically distant from the brake actuator, which has a variable volume spring brake chamber (82), a spring brake chamber diaphragm assembly (84) movable between first and second positions, a variable volume spring deflection compensation chamber (86), and a movable compensation chamber diaphragm assembly 88. A compression spring (90) is positioned between the two diaphragm assemblies. The spring brake chamber diaphragm assembly is connected to the slack adjustor by a flexible cable (110). The spring brake chamber is normally maintained in its first position by pressurizing the spring brake chamber. Depressurizing both chambers applies a lower, parking brake force through the cable and slack adjustor. By simultaneously pressurizing the compensation chamber and depressurizing the spring brake chamber, the compensation chamber diaphragm assembly recompresses the spring to apply a higher, emergency braking force.

An emergency compressed-air brake for automobiles has the advantage to combine integrally the emergency braking, the service braking and the parking braking, which can be widely used in various road vehicles. The combined braking air-chamber involved is simple in construction. The thrust of braking includes two parts, the air pressure thrust and the spring thrust, with the resultant force of the two thrusts as a service braking thrust, with the spring thrust as a parking and emergency braking thrust. Since the spring force throughout joins in the braking, the braking gets more smoothness and is able to anti-locking.

The present invention includes a pneumatic system for an agro-industrial vehicle including an air compressor, a dual circuit foot valve connected to the air compressor, and at least two air storage tanks connected to said dual circuit foot valve. The operation of the dual circuit valve establishes an air pressure link from the storage tanks to a rear air chamber as well as to a front air chamber. Each storage tank fills the rear or front air chambers and the movement of the rear air chamber and the front air chamber activate a brake device.