Exhaust Brake

An exhaust brake is a means of slowing a diesel engine by closing off the exhaust path from the engine, causing the exhaust gases to be compressed in the exhaust manifold, and in the cylinder. Since the exhaust is being compressed, and there is no fuel being applied, the engine works backwards, slowing down the vehicle. The amount of negative torque generated is usually directly proportional to the back pressure of the engine.

Since diesel engines lack a throttle valve on the intake manifold, there is no intake vacuum when the engine is not using fuel. The intake vacuum creates the drag effect felt in gasoline engines when going down a hill with the throttle closed.

Exhaust brakes are manufactured by many companies, including competitors Pacbrake and Jacobs. The brakes vary in design, but essentially operate as described above. More advanced exhaust brakes have exhaust pressure modulation (EPM) that controls the back pressure which in turn improves the braking performance across a range of engine speeds.