Couldn’t you just put the truck in neutral and use the regular brakes?
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as my truckdriver step dad explained. It cools the engine and doesn’t wear on the brakes.
using neutral and braking would put a lot of wear on your brakes when your carrying 80,000lbs. At the very least using the gears would help slow you down and save your brakes too. Im not a truck driver so dont quote me on anything
My friend is a new trucker and burned out his brakes the first time he ran into a long decline not knowing about the jake brake.
Air brakes are reasonably reliable but can fade or fail altogether if they get too hot. Assisted engine braking gives a truck driver the ability to manage the rig’s energy without risking heating up the brakes, especially useful on runs with a lot of elevation changes.
Engine brakes are required for slowing heavy loads, especially on long downhills. If you don’t use it the brakes will quickly overheat on a long downhill and become useless. [This](https://en.wikipedia.org/wiki/2019_Lakewood_semi-truck_crash) is what happens when a trucker doesn’t use engine brakes and overheats the service brakes. This driver also bypassed more than one runaway ramp.
Even a passenger car benefits from engine braking on a long decline. Not quite the same as Jake Brakes, but similar principle & effect.
Engine compression doesn’t wear out your brakes. Putting your engine in neutral and using your brakes does. Also, using your brakes generates heat. Generate enough heat, on a very long hill or mountain for example, and you can actually boil your brake fluid causing catastrophic brake failure.
Can someone please ELI5 what exactly the Jake brake is and how it works?
When you use regular brakes, you are actually using the friction of the brake pads to slow the vehicle. This heats up the brake pads (and discs/drums) as well as wearing them out. The wear is small, but it adds up the more you use them. After you use the brakes enough, you will have to replace the pads. After a few times of replacing the pads, you will have actually worn enough of the steel brake discs/drums away that they will have to be replaced!
In addition to the wear, the heat can be significant. Heat into brakes can make them work less well, and can cause additional wear and even failure of brakes.
So anything you can do to use the brakes less is useful. It does not matter as much for small cars (even American SUVs), but it matters with large, heavily loaded trucks. One way to slow a car (or smaller vehicle) is to just coast. The friction and air resistance, even without the brakes, will slow the car down. Fully loaded trucks have so much weight (and momentum) that coasting will take a long time.
Instead of coasting or brakes, it is possible to use the engine to help slow down.
The engine makes power to accelerate or maintain speed, but it takes some of that energy just to run the engine itself. It turns out that you can increase the amount of energy it takes to run the engine, just by having the wheels turn the engine, instead of the other way around. If you do not give the engine any fuel, the wheels (and the momentum of the vehicle) are having to force the engine to spin.
Now, it is important to remember that an engine has to move air through it. It takes in fresh air, adds fuel, then burns that air to push on a piston (which creates the energy to turn the engine). After that, it has to get rid of the “burned” air through the exhaust. If you restrict the air coming into the engine, and you restrict the air going out of the engine, it makes it harder for the engine to turn. If you do not add any fuel, then the engine does not create any power, and so all of that air restriction means that it takes a lot of energy to turn the engine.
The end result is that the engine does not burn any fuel, and it helps slow the truck down without using the brakes. This does not do any harm to the engine, since the engine is just doing what it would normally do (minus burning fuel). Often, a heavy vehicle can go down a long declined road down a mountain, and only use the engine brake, or use the regular brake in short amounts. This is better for the brakes, and since the brakes will not heat up, it means that the brakes are in better shape for emergency use or intermittent use down the hill.
Even just slowing down from cruising speed is better done with the engine brake or engine brakes plus regular brakes, instead of just the regular brakes.
Note that engines do not create energy, heat and friction are more complex, and may other liberties were taken in the explanation above, due to ELI5 reasons.
Regular brakes work for a car pretty well, pinching the rotor can slow you down pretty quick.
But from the perspective of sheer mass, trying to rely on that for big trucks is simply so much more force. Divide up the forces, say 4 brakes for 4 wheels on a 4 thousand pound car(a bit heavy for an average sedan) is 1000 lbs per wheel. Now take an 18 wheeler, which typically only has 5 axles and so 10 brakes. That may be hauling 60,000 pounds on 10 brakes, it’s 6 times the force per brake. That’s A LOT more force you need to overcome and A LOT more heat being generated when you do so.
Combine the added stress on the brakes with the fact that so much more mass gains way more momentum when on a slope and you’ve got a recipe for overusing and overloading your brakes.
Enter the Jake break, where you can introduce a brake function into the engine itself to kill some of your momentum without touching the brake pedal. This is huge in areas with significant slopes but also just convenient because it allows an operator to save wear and tear on their truck brakes.
Trucks are very heavy, and pull very heavy things. You know how your car is kind of heavy? A truck with its load might weigh as much as 50 of your car. That means it’s a lot more work for the brakes to stop a truck. That work makes the brakes heat up, and if they get too hot then they stop working.
Engine braking or “jake braking” uses some of the power from the engine to slow down the truck, so that the brakes don’t have as much work to do. That way the brakes don’t heat up nearly as much, and they won’t wear out as quickly. Engine braking also keeps a truck from accelerating too fast when going downhill, which is important because keeping your foot on the brake pedal instead will make the brakes heat up too much and fail. That’s why you see truck “runaway ramps” in the mountains.
Yes, you can just use the foot brake to stop a truck, but if you always do that instead of engine braking then your brakes will need servicing and replacement much more often. That means you can’t drive your truck as much, and you only make money when you’re driving.
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