A compression release engine brake, compression brake, or decompression brake, frequently called a Jacobs brake or Jake Brake, is an engine braking mechanism installed on some diesel engines. When activated, it opens exhaust valves to the cylinders, right before the compression stroke ends, releasing the compressed gas trapped in the cylinders, and slowing the vehicle. Clessie Cummins was granted a patent for the engine compression brake in 1965, and the first company to manufacture them was Jacobs Vehicle Systems. The terms Jacobs brake and Jake Brake properly refer to compression brakes manufactured by Jacobs, though the terms have now become generic trademarks, and are often used to refer to compression brakes in general, especially on large vehicles and heavy equipment. Function When the driver releases the accelerator on a moving vehicle powered by an internal combustion engine, the vehicle's forward momentum continues to turn the engine's crankshaft. Most diesel engines do not have a throttle body, so regardless of the throttle setting, air is always drawn into the cylinders (excluding the valve fitted to certain diesels, such as fire appliances and generators on oil and gas platforms, to prevent diesel engine runaway). The fuel-free air only mix that is compressed on the compression stroke now starts to act as an air spring. After the piston reaches maximum compression, the compressed air mixture returns its energy to the piston by pushing the piston back down. The result is that even if the fuel supply to the cylinder is stopped, some energy absorbed during the compression stroke is still returned to the crankshaft. Because of this returned energy, there is very little engine braking applied to the vehicle. The typical compression brake consists of a hydraulic system using engine oil which transfers the motion of the fuel injector rocker arm to the engine's exhaust valve(s). When activated, the exhaust valve opens very briefly near the engine's top dead center, and releases the compressed air in the cylinder so that the air compression energy is not returned to the crankshaft. A compression release engine brake can assist a vehicle to maintain or even reduce speed with minimal use of friction brakes. The power of this type can be around the same as the engine power. In contrast, a gasoline engine under deceleration runs with a closed throttle that prevents free flow of air into the cylinders, resulting in little pressure to release at