I have been googling this for 10 minutes and it seems the same to me. Are both methods not just using the air from the intake to add more resistance to the pistons and crankshaft?
In: Engineering
Regular engine braking air is still getting drawn into the cylinder, and you don’t have as much compression fighting your kinetic energy. From my understanding, a jake is a rocker arm that seals the cylinder off, increasing the resistance across more of the stroke, and you get more compression fighting. It’s just more of the engines’ cycle is resisting basically because it’s like an airlock
Edit: You don’t nessasarily get more compression, probably just a tiny amount. It’s that it holds the compression for much longer
A “Jake Brake”, so called because it was invented by Jacobs Vehicle Systems, is an engine brake that also redirects exhaust gasses into the engine in addition to air from the intake.
[This thread](https://www.reddit.com/r/explainlikeimfive/comments/16s4vf8/eli5_what_are_engine_brakes_and_jake_brakes/?utm_source=share&utm_medium=mweb3x&utm_name=mweb3xcss&utm_term=1&utm_content=share_button) might help
Engine braking has two possible mechanisms that may cause the engine to slow:
Resistance against pulling on a vacuum during downstroke.
Resistance against pushing gasses together during upstroke.
The problem is that if no valves open or close then a significant portion of the energy used to pull or push is given back to the engine during the next stroke (you pulled against a vacuum during intake, but now the vacuum is helping you during compression OR you compressed gas during compression but now it’s helping you push back down during power stroke).
A jake brake releases the energy that would otherwise go back in to the system. At the end of the compression stroke, the pressure is released from the combustion chamber via a valve so that:
The compressed gas doesn’t help the piston back down.
The valve may close again so that the piston pulls on a vacuum during power stroke.
Yes, but how they operate varies.
A regular gas vehicle engine mostly works on the principle that there’s a near-vacuum on the intake (which is controlled by the gas pedal) whereas the output via the exhaust is at full pressure. So there’s naturally pressure there against the engine spinning and no matching pressure to help speed it up.
A diesel vehicle has a very different fuel system, and so Jake Brakes work differently. Instead, when the cylinder is at the point where ignition of the fuel is expected to happen with the air in the cylinder fully compressed, the exhaust path opens prematurely as a secret escape hatch allowing the air in the cylinder to escape. Engine momentum was spent compressing the air, but with the air escaped it does NOT help press against the cylinder again for what would be the combustion/power stroke. It basically makes the engine work as an air compressor and letting all the compressed air out, which is why it makes that distinct noise and why you see signs on the road like “Avoid use of [unmuffled] engine brakes]” for the noise.
Think of it as an engine cylinder that still must do all the work of the compression stroke but doesn’t receive a power stroke in return. The cylinders providing engine braking prevent a load to the engine with no corresponding power output. Jake brakes are generally only on some cylinders (stages are driver selectable) for varying amounts of engine braking.
BTW Jake or Jacobs Engine Brake is a brand name for an engine brake.
General engine braking, via letting off the throttle, just uses the drag of the engine to slow down. The valves still open and close at their normal timing. A Jake brake, or engine brake is only on diesel engines, and when you let off the throttle, instead of the valves opening in their normal sequence, an exhaust valve will be forced open right at the top of the compression stroke for a given cylinder, but before fuel is injected, and this will dump all of the compressed air out of that cylinder before it can produce any power. The engine uses some power to compress that air, but it doesn’t get any power from a combustion event, so it slows down even more.
Imagine blowing up a balloon, and letting the balloon push air back into your mouth, that’s similar to normal engine braking. Yeah, it took a little effort on your part to blow up the balloon, but when the balloon pushes back, you have air in your lungs. Now imagine every time you blew up the balloon, someone popped it with a needle. You’d have to take a whole new breath, and blow up a new balloon, and it would take a lot more effort from you. That’s kind of what a Jake brake does.
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