What the diaphragm does...

lowenbrau

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I got a PM asking what the diaphragm does and decided to post it up for all to see. Feel free to add corrections if need be.

I should post this somewhere because it's what makes 3Bs cool.

The system is based on an injections system called the Ricardo Comet Mk IV, invented in England. Typical diesels have a big pipe going into the intake manifold and no restriction on air. The speed of the engine is controlled by injecting more or less fuel. The air/fuel ratio sorts itself out once the engine meets the speed of the operator is asking of it. With the Ricardo system, there is a butterfly or throttle at the entrance to the intake and there is a pipe in the air stream above and below it. These pipes run to each side of the diaphragm which directly connected to the fuel rail of the injector pump. When the butterfly is closed, the engine is trying to draw air in and there is a difference in the vacuum on each side of the butterfly, that difference is transferred to the diaphragm and the fuel real is shut down. The engine runs very slowly. AS the operator opens the throttle, the difference in vacuum is reduced and the fuel rail begins to open. The engine begins to accelerate. All the while the air fuel radio is optimized. Once the throttle is opened completely there is no difference in the vacuum above or below the butterfly and the diaphragm moves to its natural position, maximum fuel. The engine accelerates until the throttle is let off or the centrifugal over speed limiter pulls back on the fuel at 4250 RPM. It’s a brilliant system considering its all mechanical. Computers need not apply!
 

brownbear

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That's a very good description. I basically understood it that way.

How do you think a turbo adding pressure to the intake changes this relationship of differential? Do turbo'd 3B's de-accelerate slower or anything like that?

That's why those lines and diaphragm are soo important. ;)
 
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Some of the first generation Nissan GQ Patrol TD4.2s had the same set-up with an inline IP before going over to the rotary VE IP. There was recently a thread on the Aussie Patrol forum where a guy in Ireland was modding his truck for comps - part of that being a turbo. The general feeling was that it was best to go with the standard GQ manifold and a rotary pump (modded with a bigger plunger) to get the best torgue & hp. Others had tried turboing the first gen system with the inline IP and butterfly w diaphrtam set-up but were not able to get very good hp and torque results. But that is all hear say until you see the dyno results of two trucks with the two different systems.
 

brownbear

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So the Brits CAN make something reliable :p

Pretty interesting stuff

Oh the Brits have great engineering.... but the Japanese just build it better.

Must be something in the production part of the manufacturing. British designs are quite good in many ways. But the Japanese just have a way of using better quality control and closer tolerances etc when they build something.

Same with American designs. The American engineers do design and invent some really good things, but the like the brits they fail in the build process.

Why is the big question..................
 
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Bruce!

While your discription of the process is great, do you think you are confusing the pre-cup invention of Sir Harry Ricardo and his role in the developement of the engine for the British Mark V tank with the process you are discribing? (among his many achievements)

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

gb
 

lowenbrau

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Bruce!

While your discription of the process is great, do you think you are confusing the pre-cup invention of Sir Harry Ricardo and his role in the developement of the engine for the British Mark V tank with the process you are discribing? (among his many achievements)

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

gb

He invented the in direct injection, for sure. I have come to believe the butterfly control was a part of it but can't seem to find it referenced anywhere.
 
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He invented the in direct injection, for sure. I have come to believe the butterfly control was a part of it but can't seem to find it referenced anywhere.

I've look and looked too. It would be an interesting piece of trivia to confirm or deny a link between the precombustion chamber invention and the butterfly control. RM might have an idea...

gb
 

denis

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Bruce,

I think you're mixing up the Ricardo combustion chambers and Bosch diesel injection systems :doh:
BTW pneumatic governor pumps usually don't have a centrifugal governor (a.k.a. speed limiter)
 

lowenbrau

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Bruce,

I think you're mixing up the Ricardo combustion chambers and Bosch diesel injection systems :doh:
BTW pneumatic governor pumps usually don't have a centrifugal governor (a.k.a. speed limiter)

AS I said before, I can't seem to find any documentation that the Sir Ricardo came up with the diaphragm control. It's entirely possible that I have indeed mixed that up. In the case of the 3B Denso pump. It does actually have both pneumatic control and centrifugal speed limiter.
 
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The timing of this post couldn't be better.

I just tweaked my HAC on the injection pump to lean out my 3B. According to fuel economy (and my neighbors), I was running slightly rich. The engine was just rebuilt and by the looks of the wires on the adjustment nuts, the HAC was never reset. 1/2 turn to the lean side did the trick but it had me a tad confused. I always understood (wrongly) that the operator controlled the amount of fuel entering the cylinder directly. But based on the description of the diaphram, the operator directly controls air flow via the butterfly. The pressure differential across the butterfly controls the amount of fuel by loading the diaphram. Lastly, the HAC meters the maximumm allowable fuel flow.

Is that correct?


Jeff
 
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british engineering , i guess none of you are familar with lucas :) .

having owned an MG midget , i can atest to the brillance of british engineering :rolleyes:
 
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Correct, with the 3B you are not directly linked to the fuel rack of the injection pump. The diaphragm controls the rack position.

Adjusting the HAC or "fuel screw" (BJ60s don't usually have a HAC in Canada) changes amount of fuel delivered right across the full range of the fuel map. The HAC is the high altitude compensator and is supposed to adjust fuel delivery dependending on elevation.



I just tweaked my HAC on the injection pump to lean out my 3B. According to fuel economy (and my neighbors), I was running slightly rich. The engine was just rebuilt and by the looks of the wires on the adjustment nuts, the HAC was never reset. 1/2 turn to the lean side did the trick but it had me a tad confused. I always understood (wrongly) that the operator controlled the amount of fuel entering the cylinder directly. But based on the description of the diaphram, the operator directly controls air flow via the butterfly. The pressure differential across the butterfly controls the amount of fuel by loading the diaphram. Lastly, the HAC meters the maximumm allowable fuel flow.

Is that correct?


Jeff
 

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