A compression release engine brake, commonly known as the ‘Jake’ brake, is a pretty complex piece of equipment. The name Jake Brake comes from the Jacobs brand of engine brakes. But today, its used as a generic term for the compression brakes found on large trucks.
A gas motor makes use of intake manifold airflow to retain control over the mixture of air to fuel. The air is pushed to the cylinders of the motor and generating the stopping power. If you take your foot off the gas, the throttle closes and the airflow is confined. The braking force comes from the engine working against the limited airflow.
In a diesel motor, most often found in semi-trailer trucks, there is no device or method that confines airflow. A compression release engine brake can be added however, to discharge compressed air. This extra piece is added to the camshaft and has controls like an on/off switch and a multi-position switch dependent on the amount of cylinders in the truck.
The throttle and clutch are integrated with the compression release system. When the transmission is in gear, the clutch and throttle but be released to activate the brake. Upon activation, the compression brake is engaged and the vehicle will begin to slow down.
Today the compression braking system is credited with saving countless human lives, not to mention countless semi-tractor trailers. The most genius use of combustion byproduct since the turbocharger, compression braking exponentially improves stopping power, affording hundreds of feet of cushion space.