Engine Braking

Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Engine braking is where the retarding forces within an engine are used to slow a vehicle down, as opposed to using an external braking mechanism such as friction brakes or magnetic brakes. The term is often confused with several other types of braking, most notably compression-release braking or "jake braking" which uses a different mechanism entirely. Correct use of the term only applies to petrol engines and other engines that throttle air intake. The term engine braking usually refers to the braking effect caused by the closed-throttle partial-vacuum in petrol engines when the accelerator pedal is released. While some of the braking force is due to friction in the drive train, this is negligible compared to the effect from the vacuum. When the throttle is closed, the air flow to the intake manifold is greatly restricted. The concept can be illustrated by the amount of effort required to blow/suck through a thin tube vs. a thicker one. It is the work the engine has to do against this restricted air flow that provides the braking effect.