OT - Diesel Injection System/Jake Brake

Anonymous-0 · Mar 14, 2010

Trying to understand how diesel injection systems and Jake brakes work. I understand that the Jake brake works by opening the exhaust valve at the top of the compression stroke. I also understand they typically actuate the exhuast valve from the injector cam that fires the injector.

Due to my poor understanding of diesel fuel systems, what I don't understand is why there is a cam to fire the injector at all. I thought a conventional diesel injection system had a pump with a separate unit for each injector, and each injector just acts like a pressure relief valve when the injection pump pressurizes the line. So, I don't understand why the engine needs a lobe on the camshaft for each injector or what this cam lobe would do.

Can anyone explain or point me to a site that would explain?

Thanks,

Neil

JMOR · Mar 14, 2010

(quoted from post at 23:33:23 03/14/10) Trying to understand how diesel injection systems and Jake brakes work. I understand that the Jake brake works by opening the exhaust valve at the top of the compression stroke. I also understand they typically actuate the exhuast valve from the injector cam that fires the injector.

Due to my poor understanding of diesel fuel systems, what I don't understand is why there is a cam to fire the injector at all. I thought a conventional diesel injection system had a pump with a separate unit for each injector, and each injector just acts like a pressure relief valve when the injection pump pressurizes the line. So, I don't understand why the engine needs a lobe on the camshaft for each injector or what this cam lobe would do.

Can anyone explain or point me to a site that would explain?

Thanks,

Neil

hey are not universal. There are separate pump injector types, cam operated types, hydraulic, and hyd/electric, and etc. Pretty much gotta home in on a specific engine & model & year even in some cases.

Leyland-270 · Mar 14, 2010

Far too complex to cover in a forum. If you are just curious I would say forget about it, but if you are truly looking into becoming familiar with diesels I suggest you purchase a good text book from a tech school or even a diesel repair manual from an auto parts store.

Neil Powell · Mar 14, 2010

Thanks for the quick responses guys. I guess I"d fall somewhere between someone who is just curious and someone who should take a course on it - I need to write a paper about an innovation somebody made for a jake brake that actuates the exhaust valve from the cam lobe on the injector. The guy will walk me through it all, I"m sure, but I"d like to have some rudimentary understanding of the system before I talk to him, so I don"t sound like an idiot.

Anyway, based on the links below, I think I figured out the system is probably a unit injection system.

http://www.dieselpowermag.com/tech/0904dp_diesel_injection_pumps/index.html

http://en.wikipedia.org/wiki/Unit_Injector

Thanks again,

Neil

Neil Powell · Mar 14, 2010

My response above should have said "from the cam lobe for the injector," not "from the cam lobe on the injector."

skip33652 · Mar 14, 2010

a cummins or detroit used to use camshaft fired injectors so they could use the injector pushrod or lobe to operate jake brake.On an engine with out direct camshaft operated injectors such as older caterpillar you can find another valve that would be opening a different valve on a different cylinder at the right time to operate the jake. typically jake brakes use oil and hydraulics to operate the jake mechanism. when the electric solenoids are activated the engine oil is redirected to a hydraulic circuit that opens the exhaust valve at or near tdc on compression. hope this helped Paul

Neil Powell · Mar 14, 2010

Thanks, Skip. That does help fill in some holes. Think I have a pretty good handle on the basics now.

Neil

skip33652 · Mar 15, 2010

also to clarify prior to common rail fuel injection all diesels used a camshaft or cam lobe to operate a pump to make super high pressure fuel to inject into cylinder. some like john deere or caterpillar allis chalmers, ihc, etc have this camshaft inside an injection pump. some as in the case of cummins or detroit have this cam lobe on the regular camshaft. Many different designs but all made to inject high pressure fuel in really short time frames .Paul

Neil Powell · Mar 15, 2010

Paul,

Sorry I called you skip earlier, just missed your name at the end of your post. That further clarification helps, too. I knew about the cam lobes inside a conventional injection pump, but I also knew that those couldn"t serve to operate the Jake Brake, which was the source of my confusion. Now, I understand the concept of "unit injection," which uses a cam lobe on the main camshaft to actuate a pump integral to the injector itself. So, it all makes sense now.

One of the websites I looked at while trying to unravel all this implied that diesel engines are simpler than gasoline engines because they don"t require an ignition system. Not sure I"d subscribe to that theory - seems to me like the added complexity of the diesel fuel-injection system (and the varieties thereof) might counterbalance the simplicity of no ignition system.

Well, in any event, thanks to all for the help.

Neil

OT - Diesel Injection System/Jake Brake

Anonymous-0

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