I was just struck by this idea this morning.
It's been said a few times, how much better it would be to have a fuel pump lubricated by engine oil...
I don't have the engineering degree to back this up, but still thought it was an idea.
so here it is:

Why cant the high pressure fuel pump run with engine oil, and where the pistons now push fuel out, instead they force oil against a bladder of some type, which pushes diesel?

The diesel would flow through check valves, as it would now, but never enter the pump itself.
You could literally pump water all day long, and the pump would be fine.
And since the pump only operates at engine speed, I can't imagine there would be any performance issues.

The main problem i see is that the entire pump is all one sealed unit, which pretty much disables any tampering.

 

I see your point, and although yes it would keep the pump lubricated with engine oil, it's the bladder that concerns me. With hot engine oil on one side, and diesel fuel on the other, under those kinds of pressures, I can't imagine the bladder lasting very long... at the very minimum it would be a new maintenance item.

Personally I like the idea of cam-driven injectors

Carl

 

The bladder doesn't really hold pressure, just flexes back and forth with the piston.

Cam driven injectors could have been done.

They have some that are electronically piezo controlled, i would think it would have worked out way better ?!

 

Actually there would be pressure on a bladder or it wouldn't work there has to be some positive pressure for it to work, much the bladder in a tank if your house has a well, but thats another story. I think what you are talking about is a positive displacement hydraucially acuated diaphragm pump. Nothing new. First what you will find is that these pumps have a piston or plunger just like the pumps you are trying to get rid of. The diaphragm is only there as a barrier so to speak between the product and the drive componets of the pump because these are typically used for metering harsh chemicals like Sulfuric Acid. Diaphragms range from Buna rubber to very thin plates of steel. These are used everyday in the petroleum industry. Google Milton Roy Pumps as one example. here's the problem the smaller the diaphragm is the less "Stroke length" you have plus all diaphragms have a stroke life. When they rupture the product or in this case fuel will enter the cavity or the drive end of the pump or engine that holds hydraulic fluid, which leads to the next problem. Standard conventional oils don't lend themselves to be good in most hydraulic situations and even more so at higher pressures. So you will need a pump that houses hydraulic fluid to move the diaphragms in and out. These pumps would be hard to fit under the hood of a truck because of their complexity.

 

I should have said there would be much "differential" pressure on the bladder.

I understand what you are saying about the pistons, but I don't think theres anything really wrong with the current design, except for using diesel as the lubricant. If they can run with ulsd diesel as a lubricant, IMHO pretty near any oil would fair better.

The stroke lifespan would be a concern, but I'd think the solution could be found.

 

If you want to improve the design of the existing pump its simple, like I said in previous post replace the bushings "line bearings" on each side of the lobe that acuates the piston with either ball or roller bearings just like a turbo with bearings instead of bushings. Yes you will need to redesign the pump a little so that the bearings are isolated and lubricated by the engine oil just like the turbo. This solves 2 major concerns, side loading or "metal to metal" contact of internal parts at higher pressures because now the lobe is in a fixed position so to speak. Also lubrication is not a concern because it always has fresh oil passing through the bearings. This IMHO is where someone needs to look at improving the design, this can be done with little if any additonal spacing required.

 

Those rollers on the pump plungers have bushings? BUSHINGS? I thought for sure they would have roller bearings. W.....T......F.......?

I second the thought about running engine oil through the cam and roller housing. It just seems like common sense to me. The plungers would carry some engine oil between them and the barrels too I think, and the whole thing would last MUCH longer.