Engine management system - EDC (Boost control): Description and operation

Boost control

Boost control is achieved by a pneumatic actuator operating a mechanical flap situated in the turbocharger which, when operated, allows exhaust gases to bypass the turbine side of the turbocharger, so decreasing the rotational speed of the turbine thereby reducing the pressure of the intake air.

The pneumatic actuator consists of a diaphragm connected to a mechanical linkage which is opposed by an internal spring. Pressure from the compressor side of the turbocharger is applied to the pneumatic actuator via a sensing pipe. The pressure acting on the pneumatic actuator diaphragm builds up until it exceeds the opposing force of the internal spring (approx. 17 psi or 1.2 Bar) causing the mechanical linkage to move, thereby opening the flap on the turbocharger and so reducing the boost pressure. As boost pressure is reduced the mechanical linkage will move the other way closing the flap on the turbocharger allowing the pressure to increase again. With the engine under load the pneumatic actuator will be constantly opening and closing the flap on the turbocharger.