You could almost say the Ford system as used in the Escape is
sort of like this, where the electronics module is basically a
big wart on top of the transaxle and part of the same overall
housing. It really doesn't matter where the electronics go,
as long as the whole mess can be adequately cooled. Toyota simply
chose to decouple the two [less vibration to the electronics,
I'll point out] and string a few more wires between the parts.
.
_H*

For the Toyota hybrids, the electric motors and ICE are cooled by the same coolant. Inverter is cooled by a seperate coolant because of the operating temperature differences. I believe it is the reason Toyota seperated the units.

Ideally, if the inveter can operate at the same temp as the ICE, we can get away with just one coolant and everything can be housed in the same module.

ice and mg's on the same cooling line?
are you sure because i never see the mg's temp ga anywhere near the ice temp and the inverter and mg's temp are more close then the ice temp.
also is the electric pump not going from the inverter down to the mg's and then to the underpart of the radiator and back to the pump.

Not quite. The motor and the inverter make up one coolant loop, the engine and cabin heater form the other.

Engines like running relatively hot. It keeps their lubricant flowing freely. The engine control software goes into closed loop control - where the amount of fuel injected is varied with the detected air/fuel ratio, using the air/fuel sensor (O2 sensor) just before the catalytic converter - at 73°C, and the thermostat opens at 80 to 84°C. The fan operates at above 93°C.

In contrast the inverter should be stone cold, as cold as it is possible to achieve. That's why the inverter coolant pump runs continuously. Silicon junctions don't work well at high temperatures. Intel's Pentium 4-family processors have thermal throttling that started to kick in at 55-65°C. Clearly running the engine coolant through the inverter would be more likely to damage it than to keep it at decent operating temperatures.

Honda have decided to air-cool their power electronics, rather than using liquid cooling, but then their motors are only 10kW rather than the Prius 50kW (Gen 2) or 60kW (Gen 3).

I've read that Gen 3 has a variable-speed inverter coolant pump, rather than the single-speed pump used on Gen 2. Presumably this saves a small amount of power.

Thanks guys. I stand corrected.

My point is still somewhat valid. In theory, the ICE, inverter and MGs can be in the same housing but you'll have to worry about heat transfer and they still have to be cooled by different coolant pipe.

From a maintainability standpoint, it is sometimes desirable to have separate, field replaceable units. For example, the motors are integral to the transaxle and having to replace the whole transaxle is not a trivial task. However, an inverter is relatively light weight with a handful of connectors and cooling loops. Also having the hybrid vehicle control computer as a separate unit again allows field replacement instead of whole assembly.

This is not a trivial problem but there is a case to be made for keeping some units seperate if nothing else to keep field maintenance costs reasonable.

Bob Wilson

Keep in mind that you are thinking of a specific design/blueprint. There are other designs out there, and her thesis might be based on a different design.

(consider a rotary engine versus a V6 versus and inline6. there is more than one way to do a lot of things)

The 2010 is *said* to have a variable-speed inverter coolant
pump, but so far when I've had a chance to feel one with a car
powered up it seems to be going full-blast just like in the
second-gens. It would be nice if some third-gen owners could
keep track of this and check their own pumps under different
operating and ambient-temp conditions and tell us whether the
thing actually ever slows down or not.
.
Tapping the pump motor's speed-feedback leads would provide
even finer-grained data, of course... should be doable under the
dash at the power-management ECU.
.
_H*

Could be like my laptop fan, where it's noisy at normal temperature/duty cycle but really, really noisy when hot!