Jake Brake Operation

[Dean Upson]

Bob,



Thanks for that great explanation .



Dean

 

[Robin]

There is some confusion about Jake brakes and exhaust brakes. Over the years it has become common usage to call the Jacobs Engine Brake a Jake brake, even though Jacobs makes both the engine brake (Jake brake) and an exhaust brake. So it is incorrect to call an exhaust brake a Jake brake even though it might be made by Jacobs



A Cummins "B" series engine such as in Dodges or the "C" series used in motor homes cannot have a Jake brake installed because the fuel is injected by an injection pump. This applied to any Diesel engine with an injection pump as opposed to cam operated injectors.



On a Diesel engine with cam operated injectors a true Jake brake works like this. During normal operation while pulling: In each cylinder the cycle is in five steps like a gasoline engine' 1. a downward intake stroke where a cam opens the intake valve drawing in air but with with no fuel; 2. the upward compression stroke where the air taken in is compressed and reaches a high temperature; 3. At or near the top of the compression stroke, a cam punches the injector which squirts in fuel; The fuel burns because of the high temperature, oxygen rich compressed air; 4; The downward power stoke where the burning fuel forces the piston down; 5. The upward exhaust stroke where a cam opens the exhaust valves for the whole upward stroke.



When the Jake engine brake is turned on, there is a linkage that is shifted which causes the injector cam to no longer operate the injector, rather it operates the exhaust valve.



The Jake brake cycles are like this: During the downward intake stroke the intake valve is open same as normal operation and air is drawn in. 2. The upward compression stroke compresses the air same as normal operation; 3. Here's where the difference is, instead of the injector cam punching the injector, it punches the exhaust valve, opening it briefly. The compressed air is discharged explosively. There is no power stroke because the compressed air had been released and the cam does not inject any fuel. So the piston goes on the the next intake stroke.



This explosive discharge of air is what caused the braaaap sound.



A Diesel engine is notoriously poor as a retarding device as opposed to a gasoline engine. When no fuel is being fed by the injectors, the energy used to highly compress the air is nearly all returned by this compressed air pushing back down on the piston during the no-fuel power stroke. When the throttle is shut off on a gasoline engine, there is a retarding force commonly called compression braking. It is more accurately called vacuum braking because each piston is struggling to pull air in through the closed throttle plate during the intake stroke. This is the where the retarding force comes from, not compression. This is why a lot of blue smoke comes from a worn gasoline engine when descending a grade with the throttle closed. The vacuum pulls in oil past worn valve seals and worn piston rings.



Hope this clears up nomenclature and why a "B" engine cannot have a Jake brake. Sorry for getting long winded.



Bob

 

[Ladders]

had a quick thought today about brake lites and the e-brake. Run a wire from the hot side of the valve (the wire that activates the vac/pres valve) to the high mounted brake lite (lite on cab roof). Put a diode in it so the brake lite function cannot activate the e-brake valve (back feed the e-brake valve). You could add a two terminal flasher in this line before the diode. When the e-brake valve is energized the high mounted brake lite will come on. Dont know if the tail/brake lites would be fed too but another diode could prevent it if it does. Now when the e-brake energizes, the high brake lite would come on or flash warning the drivers behind you. I had a flasher on the y2k for this and a lot of persons thought that the flashing was "obnoxious" but it did get their attention which was the reason for it. Like the flasher box that Geno's sells (did not look to see if in current catalog). or use to sell.



Maybe I ought to copyright/patent this idea --- hmmmmm... ... ... .



SOTSU!

\\BF//

 

[Fireman]

What if?

Ben,

What if you are pulling a trailer? as most of us with exhaust brakes do. Just wire it to operate all the brake lights, then it would work with a trailer also. One night I noticed that the brake lights on the fire truck worked with the Jake Brake, so it can be done.

Fireman

 

[Ladders]

Hows bout using the backup lite connection on the 7way and then mounting a 3rd eye on the back of the trailer? This would give a warning (specially if its a flasher). OR you could do all the brake lites - but if the drivers is paying attention (as they should), your slow down shouldnt matter (yea, right!).



Anyhoos thats why we have the BIG ball hitch sticking out, just no protection for the trailers rear end.



SOTSU!

\\BF//

 

[dbothwell]

Jake Brake

This is a great forum! As the originator of this thread it turns out that the most useful response to me came from the posting that I made by mistake on the 2nd Gen forum. That response was simply that I use the switch that was provided to shut off the Jake Brake ... ooops ... excuuuse me (lesson from the 3rd gen forum) Jacobs Exhaust brake ... when warmed up and idling at a traffic light.



It's also interesting that the thread seems to have turned from the pros and cons of leaving the Jacobs Exhaust Brake turned on to how to illuminate the activation the the Exhause Brake.



Gotta love threads that twist and turn!!



Dave

 

[jlhartak]

The 3 stage engine brake on the big Cummins engines operates either 2, 4 or all 6 of the cylinders as selected by the operator.