Often while driving, I have noticed a road sign labeled “No Engine Brake.” These signs can usually be found in residential neighborhoods, and most likely right before a steep decline in the road. Today I learned what engine brakes are used for.
Since most transportation trucks weigh a lot, slowing them down from high speeds takes a lot of force. Relying on brake pads alone to do this job deteriorates the brakes along with the wheels while also raising a possibility of a potential failure. Therefore, truck manufacturers install engine brakes in truck engines which essentially convert a power-producing engine into a power absorbing air compressor.
A diesel engine in a truck does not have a spark plug. Instead, it compresses air and uses the heat of the compressed air to ignite the directly injected fuel. An engine brake simply opens a valve at the top of the piston movement which releases the compressed air and does not push the piston back down preventing the crankshaft from turning. This slows the engine down considerably and saves the strain on the brake pads.
The release of air into the exhaust system produces a lot of noise, especially if the system is not muffled properly. This noise can be a huge nuisance to people in residential neighborhoods, hence, the signs prohibiting the use of engine brakes. Engine brakes are also called jake brakes, named after the biggest manufacturer Jacobs Vehicle Systems.