Engine & Compression Brake

Engine braking is an alternative way of slowing down a train, without wearing and overheating the brake shoes. It is a dynamic braking feature of diesel-mechanical vehicles.

To engage the engine brake, the driver needs to disengage the throttle and have the reverser set in the direction the vehicle is moving. The losses in the engine cause it to slow down over time, and even more so at higher RPM. With a mechanical transmission, this slowing down directly affects the vehicle speed too. Therefore, selecting a gear where RPM is the highest, within safe limits, will get the most out of the engine brake, and if a train is light enough it will slow down from mere disengagement of the throttle.

Some diesel-mechanical vehicles are also equipped with a compression brake. Typically operated by a lever, this brake functions by modifying the engine exhaust process in a way that creates extra load on the engine, causing it to slow down quicker than it would normally. This supplements the effect of the engine brake.

Engine brake and compression brake both exert braking force on the transmission, which may contribute to the heating up of the transmission hydraulic fluid.

It is crucial to monitor both the transmission fluid temperature, as well as the engine RPM when using any form of engine braking, to ensure safe operation.

Engine and compression braking, featured only on some motorized vehicles, does not provide a very powerful braking force for large trains, but it can slow them down over time if used tactfully. The lower the RPM, the weaker the braking force, and at low enough speeds it can practically have no effect. To bring a vehicle to a complete halt, the driver must use braking methods that rely on brake shoes.

The driver needs to disengage the compression brake to operate the throttle, reverser and gearbox controls again.