Engine brakes did not always exist, in fact they appeared almost 65 years after the first successfully functioning diesel engine. And since their introduction, they have become a staple in larger diesel engine applications. Engine braking was born from a rocky beginning dating back to 1931, when Clessie L. Cummins and her crew had a near-fatal experience. This experience led him to start thinking about how to use the engine both as a means to push a vehicle uphill and to better control it on steep descents. In 1957 he came up with the idea of ​​using pre-existing, but modified components to open the exhaust valve. The idea was so unprecedented that it actually allowed for a broad but powerful patent to cover the idea. (Who we are: Jacobs Vehicle Systems) Early versions of engine braking were crude in their use of injector motion to achieve the goal of retarding the engine. And eventually it was realized that the hydraulic operations of the system would be much more efficient and practical. These internal engine retarders, more commonly known as compression release brakes, worked on the idea that to control power and slow the vehicle, the engine could vent compressed air before it ignited. And it helps slow the engine by eliminating a power hit. The disadvantage is that the exhaust becomes very loud and is therefore prohibited for use in most cities and towns. The actual engagement, or activation of the engine brake, is very simple. Once the diver turns the system on via a switch, the solenoids activate and lock the cylinder valve stem. Thus allowing the valve to be opened by the cam and the compressed air to be released from the exhaust. Several systems incorporate a switch that is not located in the center of the card, the crank turns and transfers the energy to the vanes of the housing. They are located on the drive housing, thus creating a fluid resistance that absorbs power and slows the vehicle. (Truck Troubles.com) Activation of this type of retarder is achieved by filling the chamber containing the rotor and housing vanes with oil. With the chamber full, the rotor and blade engage hydraulically and slow the engine. As the engine slows, a valve adjusts the amount of oil in the chamber to help maintain constant braking power, which is based on driver input or reaches a maximum when the clutch and accelerator are released. The oil used in this system is pressurized to control the amount of braking power applied, higher pressures result in stronger braking. While lower pressures result in lower breaking power. (Truck Troubles.com)