Jake brakes are trivial to understand: you’re compressing a spring and “magically” losing that energy instead of allowing it to be returned. But I don’t get how gasoline engine brakes work: from what I can tell the manifold holds a vacuum which resists the piston downstroke, but the vacuum returns the same energy in the piston’s upstroke (minus friction which is negligible). Furthermore, once all cylinders have undergone one full cycle, they all hold a vacuum so if one cylinder is being retarded, it’s opposite is being actuated meaning the force balance is pretty close to neutral. So where’s the energy loss here?
In: Engineering
Even with the throttle closed, airflow occurs and the engine pumps air, consuming energy.
Also, the engine has its own internal friction of the piston rings, valve springs on the cam, bearings, oil, crankcase windage, etc.
Latest Answers