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