openinverter forum

In the Toyota hybrid trans, MG1 and MG2 are permanently connected via a planetary gearset mounted in between them.

If you have an app where you want to use MG1 and MG2 for different tasks (eg MG2 for driving wheels and MG1 for a PTO output on a tractor) you have to decouple them.

In an ideal world, simply removing the planetary gears would de-couple them, but doing this also decouples MG1 from the ICE input/output shaft because MG1 is connected to the planetary gear assembly via a splined tube.

So once you remove the gears, you have to join the ICE shaft with MG1's driveshaft.

Here are some photos from my nearly successful 1st attempt at gearshaft modifying.
Here you see the end of the planetary gear set. In the very centre is the ICE shaft with a splined hole that drives an internal oil pump. There a 4 welds around the outside that hold the gearcradle in place and you an see the small shafts for the planetary gears are held in place by squishing out a tubular bit (not sure what the technical term for this is).
Now the welds have been taken out with a cutting wheel on a angle grinder and the shafts are partially drilled out.
Once that is done the carrier and gears are discarded.
Placing MG1's driveshaft tube back on the ICE shaft, you can see that the two do not have a common bearing surface so the tube has a lot of slop in it. This is not good. Note that the centre gear of the planetary gearset (seen at the back) is no longer used and just sits there minding it's own business.

So these two items need to be permanently joined but maintaining concentricity.
Firstly I decided to practice me little-used lathe skills to get rid of the extra bits of flange.
This leaves us with a fairly neat unit ready to join the inner and outshafts together. Now the tricky bit - ensuring the shafts are concentric.

(continued in next post)

If the mg1 driveshaft and ICE shaft are place back where they're supposed to be, they appear to be concentric, so my plan was to tack weld in-situ. While doing this I held the welders earth cable up against the flange - to limit the current flow to the immediate location, so I didn't weld any bearing surfaces together.
Once tacked in 2 locations 180 deg apart, the tube appeared to be concentric to the ICE shaft.
So then it was back to the lathe to complete the welds.
I think I was up to far on current and feed rate so I welded over the MG2 drive spline a bit so will need to dremel there to get it back in.
Here is it fitted up but not quite going in all the way due to welds in the spline. Unfortunately the MG1 drive tube is NOT concentric with the ICE shaft. In hindsight I thing I should have had more than 2 tacks on the flange end and also tacked the other end in a few places before going for the full weld.

I'll grind all the weld off and hopefully be able to make a 2nd attempt. If not, I'll have to go and get another P410 for attempt #2.

Some sort of thin tubular sleeve in between the 2 shafts would make it easier to maintain concentricity during welding.

Or place welds on the driveshaft first and then turn them down to the correct diameter so the tube fits snug?

Or maybe drill holes and use drive pins to take the welding heat out of the equation?

Suggestions gratefully received.

Thanks for all the photos, it explains a lot.

I’m not a good welder myself, so that’s one task I’d have to call for help … and can see it’ll be difficult to undo. Hopefully you can grind enough away to get it loose … or even enough to press it straight perhaps.

If you can get it apart, a thin sleeve like you suggested sounds like a good approach.

What inverter drive system are you planning to use?

Well, I managed to get the MG2 splined tube off by cutting through the welds on the lathe. Quite a mission.

I decided that since I'm welding the thing up anyway, the best way to make sure the tube is centred correctly would be to lay two welds down on the ICE shaft. Rough as guts welding here, but it doesn't matter.
Then turn them down to the correct diameter in the lathe.
This also means you don't have to do any tack welds while the shafts are actually in please, so no messy stuff done around the open transmission case.

Then the modified shaft just gets shoved back in, ready for the two halfs of the transmission to be reattached.
But before I do that, I need to weld up the diff and block off the unused driveshaft hole in the transmission case. I'm sure someone's done this already and knows the best way to do it?

Roger, I'm yet to decide on the inverter, I'm assu,ing at this stage the Prius Gen 3 (because I have it here already) with openinverter controller.

As for the rest of the system, I'm leaning towards grabbing the battery pack and full loom out of a PHEV Gen 3 Prius and then just substituting Leaf modules for the Prius ones to boost kWh rating. Has anyone done that before? I guess I need to match battery chemistry for the Prius BMS/Charger stuff to stay happy?

One I get this running and my MG2/MG2 split mod doesn't explode into tiny pieces, I'll put the mod up on the wiki.