A Jake brake is an engine braking mechanism that receives its name from the Jacobs Vehicle Systems brand of engine brakes. The name Jake brake has become a trademarked term used to refer to compression release engine brakes. Jake brakes are common on large vehicles and diesel engines.
The Jake brake increases the effectiveness of the braking system and reduces brake failure on heavy equipment and large vehicles, such as buses or semi-trailers. When the brakes are activated, the mechanism opens the exhaust valves located inside the cylinders. Once the compression cycle is complete, the compressed air inside the cylinders is released, which slows down the vehicle.