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Jake Brake

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albert460

11-06-2006 19:04:28

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Always been curious how the jake brake in a semi truck engine works. What does it do to produce the extra engine braking?

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Oldmax

11-08-2006 05:18:40

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Re: Jake Brake in reply to albert460, 11-06-2006 19:04:28

Some early attemps to brake engines with a valve on exhaust pipe did little to slow trucks down . But the new type jak brakes work good .

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GeorgeH

11-06-2006 23:13:24

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Re: Jake Brake in reply to albert460, 11-06-2006 19:04:28

Here is a link to Jake material.

http://www.jakebrake.com/support/faqs.php

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NC Wayne

11-06-2006 20:10:29

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Re: Jake Brake in reply to albert460, 11-06-2006 19:04:28

To put the operation into it's simplest terms a Jake Brake effectively turns the engine into an air compressor which robs power from the drivetrain instead of supplying power to it. To show you how effective they can be, my service truck has a 275 HP detroit and the Jake, on high, provides about 200HP of braking capacity, and if I set the computer to cause the fan to kick in at the same time, the fan alone provides another 10HP of braking to the mix. I won't attempt to describe the exact process in every make engine but they are all pretty similar. Here's how it's done in the modern 50 and 60 series Detroit 4 stroke engines. Basically the Jake allows a normal 4 stroke cycle of the engine/piston with the exception that on the power stroke it shuts off fuel to the injector and a third cam lobe, one for every two cylinders, strokes a hydraulic piston which in turn strokes another piston through an actuator body/valve. The second cylinder opens the exhaust valve at the last second to dump compression. This is done to capture/rob the power it took to compress the air instead of adding fuel and igniting the mix to gain power. The hydraulic actuator takes oil from the engines oil system and allows it to free flow through it through a normal open solenoid valve. When the Jake is activated the solenoid valve on the actuator closes causing the oil to then be in a closed system so when the third cam lobe rides against the one piston the motion is transmitted hydraulically to the other piston to open the valve. On the Detroits there is an actuator for every two cylinders (ie 2actuators for 4 cylinder, and 3 for a 6 cylinder). That's how they can vary the braking ability of the system. On my 4 cylinder I've got two braking power choices, High gives all 4 cylinders and Low gives just two. The larger series 60 6 cylinder engines usually have High, medium , and low, or 2, 4, or all 6 cylinders. This is what happens in the most basic way i know to describe it. I hope it helps you understand what's going on and what's making all that noise when you hear one going past.

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Dave 2N

11-07-2006 03:01:32

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Re: Jake Brake in reply to NC Wayne, 11-06-2006 20:10:29

Good explanation.

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Don-Wi

11-06-2006 22:27:17

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Re: Jake Brake in reply to NC Wayne, 11-06-2006 20:10:29

So, is there a toggle switch in the cab to turn it on or off when inside city limits where they don't allow engine braking? When it has power to the system, does it just activate everytime you hit the brakes?

Makes me curious...

Donovan from Wisconsin

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john in la

11-07-2006 00:17:56

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Re: Jake Brake in reply to Don-Wi, 11-06-2006 22:27:17

Yes there is a switch in the cab. Actually 2 switches.
1 switch is for on and off and the other is to set it on high; med; or low power.

You can go into the computer and set up how the jake works.
Set up 1
The cruise switch has no control on the jake system in this set up.
If your foot is on the throttle or the clutch it will not come on.
If the throttle and clutch are in the rest position the jake will automatically come on. The brake pedal has nothing to do with the jake coming on or not.
Set up 2
This works like above if the cruise is off but if the cruise is turned on (does not need to be set at a speed just switch turned to on) the jake will not come on till you touch the brake pedal.

I like set up 2 a lot better. With the cruise set to on you can shift with out the clutch with no fear that the jake will come on each time you let off the throttle to shift. You can coast in traffic for a slow down. But if you need to stop the jake is on helping you bring the rig to a safe stop the second you touch the brake.

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Pooh Bear

11-06-2006 19:36:35

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Re: Jake Brake in reply to albert460, 11-06-2006 19:04:28

I have been given two explanations.
The first one, compressed air is injected into the
cylinders retarding the motion of the pistons.

The second explanation I saw on a TV show.
Used to be a show called Shade Tree Mechanic.
On one episode they installed a Jake Brake on a
one ton truck. The way it worked was to close off
the muffler creating back pressure in the cylinders.
It was a valve placed inline with the muffler at the manifold.

Either explanation is just as likely for big trucks.

Pooh Bear

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J Schwiebert

11-07-2006 03:25:19

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Re: Jake Brake in reply to Pooh Bear, 11-06-2006 19:36:35

If memory serves me corectly the Jake brake was actually developed or they had a hand in it by the Cummins engine company. One other thing and I am not a truck guy on that end but since it involves the valve train they are just like 50 years ago when a good tune up involved "running the overhead' adjustment on the Jake brake should also be checked.

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KEB

11-06-2006 20:07:29

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Re: Jake Brake in reply to Pooh Bear, 11-06-2006 19:36:35

Let me add a little more info. An "exhaust brake" is what the Shadetree mechanic installed, NOT a Jake Brake. As Tooly noted, a Jake Brake (a brand name, by the way) works by opening the exhaust valve at the top of the compression stroke so that the energy used to compress the air in the cylinder is released into the exhaust rather than pushing the piston back down. Essentially turns the engine into a giant air compressor...

A exhaust brake works by increasing exhaust back pressure. Some smaller diesels, such as those used in pickups, don't have enough clearance between the exhaust valve & piston to allow the valve to be opened at the top of the compression stroke. I'd love to have a true engine brake on my Ford 7.3 diesel coming down some of the grades here in Colorado with our 5th wheel travel trailer on behind the truck.

Keith

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Jon Hagen

11-06-2006 20:52:20

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Re: Jake Brake in reply to KEB, 11-06-2006 20:07:29

OK,lets really confuse things "Jake" the brand name makes both the compression brakes for large(semi) truck engines,and exhaust brakes for the little 1 ton and smaller diesel pickups,so a "jake brake" can be either a compression or exhaust brake. (:0)

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Sid

11-06-2006 19:34:59

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Re: Jake Brake in reply to albert460, 11-06-2006 19:04:28

Like tooley said.

Here be more info

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Sid

11-06-2006 19:34:31

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Re: Jake Brake in reply to albert460, 11-06-2006 19:04:28

Like tooley said.

Here be more info

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tooly

11-06-2006 19:14:13

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Re: Jake Brake in reply to albert460, 11-06-2006 19:04:28

As I remember , the extra braking power is achieved by a mechanism which opens the exhaust valve when the piston is at the top of its compression stroke, therefore there is no tendancy for the piston to be forced down by the compressed air above it . Thats about it in as few words as possible. Hope this does more than confuse you....(smile)

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