Oil pump driven *how*?!

[ChapmanF]

I was flipping through the NHW11 shop manuals for some light bedtime reading,
but suddenly I'm not sleepy.

The ICE oil pump lives in the timing chain cover and is driven by the
crankshaft, so only when the ICE is running. Standard stuff, didn't really
expect anything different, ok fine.

The transaxle oil pump lives on the outside end of MG2. I think I must have
been assuming that MG2 drove it. Or maybe MG1 somehow. But the drawings on
pages HT-12 and HT-13 pretty clearly show an Oil Pump Drive Shaft that goes
clear through MG2 and engages in - it looks like - the input shaft / planet
carrier, which is the part that's splined to the ICE.

So the transaxle oil pump also turns only when the ICE turns.

In a hybrid?!

Ok, so that sure explains why they warn against towing with the front wheels
down.

But what about stealth? What were they thinking? Do they just figure that
because the stealth range is short, the ICE's going to start every mile or
two and pump some oil around, and that's good enough? Has anybody seen the
inside of one of these transaxles closely enough to see what parts rely on
oil from the pump, as opposed to plain splash or something? Have I misread
something, or is there some fact I've overlooked that would make this make
sense?

Rather curiously,
-Chap

[Patrick Wong]

Originally Posted by ChapmanF

...So the transaxle oil pump also turns only when the ICE turns.

In a hybrid?! ...

But what about stealth? What were they thinking? Do they just figure that
because the stealth range is short, the ICE's going to start every mile or
two and pump some oil around, and that's good enough?

Hi Chap,

Yes, this is one reason why engineering a PHEV Prius with extended battery-only range is not a trivial exercise. That oil pump problem is one of many to be solved.

[qbee42]

Splash oiling can work pretty well. Our marine diesel only uses splash oiling - no oil pump. The valves are manually oiled through a drip oiler. That engine will still be running after our Prius is a pile of rust and plastic.

The Prius doesn't run very long or fast without the ICE, and at speed the ICE spins even when it isn't running.

Tom

[hobbit]

The transaxle parts don't depend on a continuous *feed* of oil
the same way as an engine does. Think of it like the oil you'd
put into a regular manual transmission -- enough to bathe the
gears and get thrown around when it's turning, but in most
cases those don't need an actual pump to push it around. All
the pump does is push oil down the center shaft where it then
bleeds out side holes into the various bearings, most of which
are ball or roller in the NHW20 and can run quite a while on
their own without additional feed and without "going dry".
.
So far the PHEV folks have racked up many EV-only miles and not
reported any problems, but if PHEV Priuses get more widespread
and start going through many ICE-free drive cycles across the
usual thermal/humidity/stress changes, then we'll see.
.
_H*