Jake Brake
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Forum Discussion
Ivylog wrote:Big Katuna wrote:
It doesn't rely on compression, it prevents it.
You might want to rethink this statement as it is totally wrong.
OK, how an engine compression brake (AKA Jake brake) works:
It take a LOT of energy as the piston comes up on the compression stroke to do the 15:1 or more compression.
If the engine brake is not on, once past TDC most of that work is returned, pushing the piston back down. Yes, there is a little friction loss.
What the engine compression brake does, is as the piston reaches TDC, it OPENS the exhaust valve. That allows all that work stored in the compressed air in the cylinder to escape out the exhaust. So that amount of work is lost. Most are two stage-- with 3 or 6 cylinders doing this.
And, the wiring is connected to the Allison ECM so the transmission also downshifts toward the pre-select gear. This part the same for engine compression brakes and exhaust brakes.
