Hot-rodding the Toyota MGR

[pearl62]

I purchased a MGR from a 2006 Highlander from eBay, and it should arrive next week.

I am going to tear it down to start looking at how hard it will be to rewire the stator for delta... Is there any instructions out there? I'm not a motor guy

[freebeard]

I know e*clipse has opened one up. I'd be reluctant to do that myself, because I'm not sure how to prevent a layer of magnetic grit adhering to the permanent magnets. I think they're super rare-earth magnets.

It's been awhile since I've thought about it but there may be something about how it's wired that makes re-wiring moot.

Have you skimmed the thread? I think I tried to edit down the content, but gave up about page six. I see it's over 30 now.

[e*clipse]

Originally Posted by pearl62

I purchased a MGR from a 2006 Highlander from eBay, and it should arrive next week.

I am going to tear it down to start looking at how hard it will be to rewire the stator for delta... Is there any instructions out there? I'm not a motor guy

That's one I'm not willing to take on (rewinding) - why would you like to do rewind it for delta??

I do know it's a pretty involved distributed winding. Something tells me you'd have to find a pretty experienced motor shop to do this motor. I did call the shops around here to find out about motor rewinding, mostly to reduce the voltage required. Their questions to me led me to slowly back away...

E*clipse

[pearl62]

I'm still not sure myself either... Maybe I will first just try it with Prius inverter, which is supposedly limited to just 20kW output from the voltage doubler. If it really is a bottleneck, I could maybe try a Lexus LS600H inverter, which is supposed to be good for 39.6kW?

[e*clipse]

Originally Posted by pearl62

I'm still not sure myself either... Maybe I will first just try it with Prius inverter, which is supposedly limited to just 20kW output from the voltage doubler. If it really is a bottleneck, I could maybe try a Lexus LS600H inverter, which is supposed to be good for 39.6kW?

Huh. That's interesting. I wonder why they rated the motor for such a high voltage, then made it's critical supply far short on the power output??

Maybe it has to do with when the boost is working - I mean, up to about 6000 rpm, the BEMF is less than 250Vrms. (2010 Prius motor data) Perhaps they're using the booster only if necessary for high speeds?

- E*clipse

[pearl62]

Originally Posted by e*clipse

Huh. That's interesting. I wonder why they rated the motor for such a high voltage, then made it's critical supply far short on the power output??

Maybe it has to do with when the boost is working - I mean, up to about 6000 rpm, the BEMF is less than 250Vrms. (2010 Prius motor data) Perhaps they're using the booster only if necessary for high speeds?

- E*clipse

That's a good point, maybe it really won't matter... I think I will just try with it as Toyota designed it first. If the results aren't as good as I'd like I can always try new things then...

[e*clipse]

Originally Posted by pearl62

That's a good point, maybe it really won't matter... I think I will just try with it as Toyota designed it first. If the results aren't as good as I'd like I can always try new things then...

I have to say, the more I learn about this motor & controller ( this includes all Yota Hybrid stuff ) the more I'm impressed with their engineering.

In some ways it's dissappointing - I mean - I thought I'd be able to find ways the get a lot more power out of this thing. OTOH, learning about this motor has been (and still is) an excellent learning experience, in a good way.

- E*clipse

[freebeard]

Technology good enough to be indistinguishable from magic. Best not to mess with it.

The way they reduce back-EMF at high RPMs and such.

[e*clipse]

A while ago, I introduced this topic as a means of exploring ways to get more power out of the MGR. I'd like to return to that.

As is well known by folks in the motor design world, and is well illustrated in the tests by ORNL, cooling is a very important issue. That's great - because that's something that doesn't require a doctorate in EE to understand. In fact a BS in ME will do just fine!

So, I started exploring the cooling in a bit more detail. When I first heard the MGR used oil spray cooling directly on the end windings, I thought they were just looking for the cheapest way to cool the motor. Not true. Actually it's one of the most effective ways to cool stuff. In fact the military is actualy working on direct spray cooling. Here are a couple of interesting links about it:
https://www.highpowermedia.com/blog/...oling-concepts
An Overview of Liquid Coolants for Electronics Cooling « Electronics Cooling Magazine – Focused on Thermal Management, TIMs, Fans, Heat Sinks, CFD Software, LEDs/Lighting
Spray Cooling Electrical and Electronic Equipment - COTS Journal

In the first link, it mentions that a typical passively cooled motor can handle 5-8A/mm^2. A cooling jacket will allow about 10-15A/mm^2. The highest ratings were for direct spray cooling: 30A/mm^2.

In the second link, a bunch of sooper-dooper coolants are mentioned.

In the third link, the military's interest in the topic is illustrated:

Testing by Southern California Edison on a GE 85HP traction motor was significant and consistent with NAVSEA’s FIAL efficiency data. The GE 85HP traction motor was fully loaded and tested with air-cooling and spray cooling (Figure 2).

In the mid- to 3/4-loads, a 25% to 30% improvement in efficiency was reported with spray cooling. Also, a 10% improvement was reported at 85 HP load and a 15% improvement in sustained overload at 100 HP (total power, in direct contact with the liquid, exceeded 73,000 watts). The test rig and shaft were not designed to operate at higher loads; however, the designer indicated that sustained overloads of at least 200% of rated load were possible. The overload results show that the use of less costly, lighter and more efficient generators and motors in ship, air and spaceborne applications is possible with spray cooling.

Wow! a 25% to 30% increase in efficiency! Also a 200% increase in the rated load! I'm interested!

- E*clipse

[e*clipse]

While Toyota did a fine job designing the MGR, and also used some neat cooling techniques like spray cooling, I think they fell a bit short on the MGR:

The spray cooling is delivered to one side of the windings through gaps in the spline shaft between the motor and gearbox. This is close to "spray" cooling, but it is only on one side of the windings. A high performance spray cooling system actually makes a mist that evaporates when it contacts the high temperature windings. Hosing the windings is actually less effective!

This will require a high pressure (not dribble flow) coolant pump system. It will also require a means of spraying coolant on both end windings as well as cooling the stator iron. I'm working on that in the new gearbox design. It will also require a means for cooling the oil.

This brings up another important topic: Cooling the oil. How much oil flow is necessary, and how big of an oil cooler is necessary?

As a stab in the dark, let's say we must get rid of whatever waste heat the motor generates at maximum power. At 90% efficiency (ORNL show a worst case of 92% in the high power ranges) the 50kW motor would need to dump 5kW of waste heat. For those of us stuck in the "imperial" unit system, that's about 17,000Btu/hr. Please note that this is for 1 motor - my dual motor setup will require twice that!

Setrab makes high quality oil coolers and has some good data on their website:
Setrab Oil Coolers | susa
The test conditions for their coolers are this:
dT = 130F (temperature differential - on a 110F day, the oil will be at least 240F! Most electronic stuff is rated for 150C/300F.
oil flow rate: 0.75gpm to 1.5gpm
air flow rate: 60mph to 80mph
an oil cooler that is 12.00" X 7.6" will dump between 16,000Btu and 27,000Btu.

Also note that if the oil flow rate is increased to 5gpm, the cooling ability of that same cooler increases to 33,100Btu!

So, a real oil pump and a real oil cooler is necessary to get rid of the heat generated by this motor.

While researching dry sump oil systems, in "Prepare to Win" Carroll Smith said, "Oil coolers are not radiators; they are oil to air heat exchangers. In order to function they must be supplied with large amounts of the coolest air possible."

Notice he did not say "Meh, just shove the thing in the back, where the hot air from the engine might get to it and don't bother with a cooler; the case is a fine radiator..."

- E*clipse