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Old 05-19-2017, 10:08 AM   #6
Live, eat, and sleep by TSL
Join Date: Mar 2005
Posts: 1,819
Oil Pump musings

In my quest for knowledge, I learned a lot about oil pumps. The pump that is used in the 9-5 is a gerotor pump. It is very common in automotive. My Honda used an almost identical design! A gerotor pump always has one less lobe on the drive gear than on the driven gear. The drive gear is the center smaller gear, and in our case is driven directly off of the crankshaft. The larger gear (outer) is eccentric, meaning it does not rotate around the same axis as the driven gear. There are lots of good animations online that deal with this so I will just say that as the gears separate the oil is drawn in to the pump, and as the gears come together the oil is forced out creating flow. The pump is a constant flow pump, meaning that it draws in a specific volume of oil per lobe and pushes that same volume out. I thought a lot about what that volume is. There are better ways of measuring this, but I wanted to approximate the flow of the pump. I just took into consideration ONE gearset. In reality there is more area opened up between the two cavity's.

I measured the diameter at the bottom of the lobe.

I measured the diameter at the top of the lobe.

I measured the peak to peak of the lobes.
I measured the thickness of the gear (forgot that picture)
I created a triangle to approximate the volume in the lobe.
The volume was 343 cubic millimeters. With 15 lobes on the inner gear, for every full rotation the pump will push out 343 cubic millimeters 15 times. Or 5145 cubic millimeters. So at 1000 RPM (idle) that is 5,145,000 cubic millimeters per minute OR 1.35 Gallons per minute. And that is an approximation, there is definitely more area in that lobe than a triangle. I would "guess" this pump is probably 1.5 gal per minute at 1000 RPM. I could just not imagine where 1.5 gal per minute was going on a fresh motor! I looked at the scoring on the pump cover and thought there is no way 1.5 Gal per minute is going through those small grooves!!

****Remember this was just an approximation of just one of the gears. In reality space is created between the inner and the outer gear so the volume would be even higher!
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