In class this week, the instructor attempted to describe for us the Jake Brake.Here's what I understood. He said that the Jake Brake on my engine (ISX 15) is called the Interbrake. It is built into the engine by Cummins and works by introducing fuel during the exhaust cycle of the cylinder movement and withholding fuel from the compression phase. In other words, instead of helping to propel the drive shaft forward during the compression phase, the engine applies pressure to the cylinder when it's in the exhaust phase effectively applying the same amount of force it would to propel the engine to effectively slow the engine. It's almost the same as reversing the current on an electric motor while it's in motion.He said that in the past, Jacobs made Jake Brakes that were bolted on to the engine and did the same thing, but these systems weren't muffled and in some cases, you could see flames shooting out of the exhaust. I'm assuming this was either a separate exhaust or fuel was introduced in the exhaust system somewhere down further.Other engine brakes restrict the exhaust to slow the engine but these systems are not as powerful as shooting fuel into the exhaust phase of the cylinder. Jacobs claims that their systems can produce as much braking power as the engine has horsepower. One of the confusing parts of this explanation is that every brake designed by Jacobs is considered to be a Jake Brake even though it may work differently.Is my understanding correct? Can anyone add to or help me correct this?

A true jake brake is electrical components, a toggle switch on the dash,a switch at the foot throttle. When the switch is on and the foot pedal is disengaged the electric solenoids in the rocker box hold the exhaust valves open, so the compression & heat isn't there to fire the fuel. Thus this is the noise you hear out the exhaust pipe. I never hear of flames coming out of the exhaust. Only back in the day when old timers would mix a ratio of gas to diesel in the winter, to prevent gel up.

yrusoslo wrote:A true jake brake is electrical components, a toggle switch on the dash,a switch at the foot throttle. When the switch is on and the foot pedal is disengaged the electric solenoids in the rocker box hold the exhaust valves open, so the compression & heat isn't there to fire the fuel. Thus this is the noise you hear out the exhaust pipe. I never hear of flames coming out of the exhaust. Only back in the day when old timers would mix a ratio of gas to diesel in the winter, to prevent gel up.I'm not sure I understand that at all. If the compression and heat isn't there to fire the fuel, isn't that simply called coasting? Your description sound like it would result in zero slowing power. Perhaps the exhaust valve is closed on the downstroke to create a vacuum? Where is the backwards braking power introduced at the engine?

The compression brake, originally called jake brake which a trademark, as mentioned, in the early days was added onto the heads of a cummins engine. As I understand it it reverses the action of the valves to turn the engine into a compressor ( not really that simple ) there may be a small amount of fuel introduced to keep the cylinders from running dry.I drove a 1962 Kenworth and we had one of the first 'jake' brakes installed. I could go down the g****vine grade with a 25 ton load and just touch the service brakes. Like I said in another post, this was the greatest invention ever for the heavy truck industry.

Thanks for bringing this up. I would also like to understand it, though I have never had a Diesel engine. Good old Wikipedia has an explanation that is helpful. https://en.m.wikipedia.org/wiki/Compression_release_engine_brake

I started to do some links but there are too many entries to do.Google "wiki diesel braking' and wiki retarder braking and wiki jake brake.There are some good simple descriptions.

What is a Jake Brake? | Good Sam Community

bigdog2
Explorer
Aug 20, 2015
passin thru, in California the weight limit was 76,800 with a 3% tolerance= 79,100. At Osterkamp Trucking, where I worked from '62 till '74 we pulled 27' flatbed doubles which weighed in at barely over 26,000 empty. We were legal with a little more than 26 tons.
Passin_Thru
Explorer
Aug 20, 2015
BWAHAHA This stoopid site blanks out G**** Vine. I guess you have to put berry, typically green (classified as white), purple, red, or black, growing in clusters on a vine, eaten as fruit, and used in making wine non consensual sex.
Passin_Thru
Explorer
Aug 20, 2015
Let me add my 2 cents. I doubt you went down the G****vine in 1962 with 50K on a truck. I drove truck starting in 1966 and CGRW was 73,280lb. They had scales on both ends of the G****vine then too. It was still 2 lane until late 1966 but maybe you did. A lot of log trucks used water cooled brakes too.
wolfe10
Explorer
Aug 20, 2015
I don't have a good source at Cummins, but do at Caterpillar. And the answer is as long as the engine is above idle speed (we are talking about automatic transmissions here, since that is what RV's have) no fuel is injected.

If someone has a reliable source at Cummins (not just a kid who answers the phone, would certainly like to hear from them. Again, the question is when you release the throttle at speed, is any fuel injected?

BTW, for any of those with Silverleaf or ScanGauge D, within seconds of closed throttle, instant MPG goes to infinity (or on my ScanGauge D to 999.99 MPG).

Yes, this is more a curiosity question than one relevant to how we drive, but interesting none the less.
holstein13
Explorer
Aug 20, 2015
bigdog2 wrote:
"There is ZERO fuel involved (boy, that was a really strange one)."

Brett, it took me a while, but after talking to a couple of techs and a few drivers here's what I got from them. If you release the throttle ( to engage the compression brake, or in case of a standard transmission, take it out of gear ) what happens? It goes back to IDLE. It takes fuel to idle. Even though it is running against compression the ONLY time there is NO fuel would be if you turn the key off ( or otherwise shut off the pump ).

I would like to know where you got the information there is no fuel introduced?
Makes sense. Thanks for inquiring about this. I think this was a great thread.
bigdog2
Explorer
Aug 20, 2015
"There is ZERO fuel involved (boy, that was a really strange one)."

Brett, it took me a while, but after talking to a couple of techs and a few drivers here's what I got from them. If you release the throttle ( to engage the compression brake, or in case of a standard transmission, take it out of gear ) what happens? It goes back to IDLE. It takes fuel to idle. Even though it is running against compression the ONLY time there is NO fuel would be if you turn the key off ( or otherwise shut off the pump ).

I would like to know where you got the information there is no fuel introduced?
wolfe10
Explorer
Aug 09, 2015
holstein13 wrote:
Do the valves close after the compressed air is released, thereby creating a partial vacuum in the cylinder on the downstroke?

Whether the exhaust valve closes or not (I do not know the answer), it would make no difference. There is no "throttle plate" on a modern diesel engine, so the "most vacuum" it could pull would be atmospheric pressure. Said another way, zero vacuum.
holstein13
Explorer
Aug 09, 2015
Also, are the valves closed on both the compression cycle and the exhaust cycle? Since there is no fuel introduced, I guess the engine doesn't need to exhaust anything and could act as a compressor on the exhaust cycle as well.

On Edit: I see that Ivylog already addressed this question and stated that there is no way to close the valves on the exhaust cycle.
holstein13
Explorer
Aug 09, 2015
FIRE UP. Thanks for the great explanation. But I still have one unanswered question. Do the valves close after the compressed air is released, thereby creating a partial vacuum in the cylinder on the downstroke? I can't seem to find the answer anywhere.

I'm guessing it stays open to provide the air to be compressed on the next stroke. But it could be reopened at the bottom just like the compressed air is released at the top.
wolfe10
Explorer
Aug 09, 2015
bigdog2 wrote:

Brett, There is probably a small amount of fuel injected during the braking cycle.

Sonney,

With the modern electronic engines, there is ZERO fuel injected on closed throttle until engine RPM approaches idle speed.

In fact, one of the questions I get is "why does my coolant temperature drop below 'normal' when I descend very long downgrades"?

The answer is zero fuel injected means zero heat.

Don't see why zero fuel would have any negative impact on cylinder wall wear-- oil is still being circulated.

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