Heavy goods vehicles can often require increased braking, in situations where friction brakes could overheat and fail. This is achieved by using an exhaust brake.
An exhaust brake works by restricting the flow of exhaust gases through the engine. It achieves this by closing a butterfly valve located in the exhaust manifold. This maintains high pressure in the exhaust manifold and the engine cylinders, which in turn acts as a brake against the engine rotating. This then slows the road wheels through the transmission, or power train.
Other heavy goods vehicles use an engine brake that operates by altering valve timing, and stopping fuel being injected into the engine.
