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Discussion Starter #1
are there any? I know there isn't an alternator ... what mechanism pumps the coolant to the engine and electric motors during normal driving ?
 

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water pumps
 

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Just one pump. Why they didn't make it electric, I don't know. Guess they figured since the engine cooling system doesn't really need to circulate unless the engine is actually running, and a direct mechanical connection is more efficient than taking power from 12V, they did the conventional method of a belt system. They have other pumps that are electric though, for cabin heating and to move coolant to/from the thermos.
But eliminating the belt would have reduced one more painful maintenance item. Belts on transverse engines are a pain to get to.
 

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sansabelt

DanMan32 said:
...Just one pump. Why they didn't make it electric, I don't know...

I like this idea also, DanMan. Would it not eliminate the need for the thermostatic valve on the ICE coolant loop? How about a variable-speed electric motor, based upon coolant temps when above 85C?

DAS
 

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Discussion Starter #5
thanks so much for the info.

I read somewhere that the electric motors are water-cooled, but maybe that was wrong. Seems like convection cooling would be suffieient for them.

Too bad about the one lousy belt, but as you say probably more energy-efficient. I guess we can put up with a small inconvience for the sake of the overall philosophy!
 

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No, the water jacket does not extend down to the electric motors.. They are cooled by conduction through the transaxle housing..

The inverter/converter is liquid cooled, with an electric water pump (is it the inverter/converter that has the dual circulation- conventional belt-driven water pump while ICE is active and electric pump when ICE is off??)
 

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The inverter has its own cooling circuit independent of the ICE cooling. Therefore, it has its own electric motor. You can hear that thing run when the car is parked in READY.

You still would need the thermostat, as you would want to circulate coolant around the engine and not send it to the radiator until it reached operating temperature. This is how you maintain uniform engine temperature. Without coolant circulating within the engine, you would develop hot spots, and also would not be able to properly monitor engine temperature.

Hmm,, this gives thought that I should leave my home HVAC to always run the central fan. In fan only mode, it runs slow so it should be energy efficient.
 

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heat exchange

c4 said:
No, the water jacket does not extend down to the electric motors.. They are cooled by conduction through the transaxle housing...
C4, you have quite piqued my interest, because using Graham Davies' miniscanner on the 2001 Prius I see (under high-load conditions) that MG1 will rarely reach 103o C. MG2 does not get so hot.

Indeed I had assumed that the inverter coolant loop extended to both MG's, but you say that this is not the case. May we talk more about this?

DAS
 

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The last time I checked there were two cooling loops, ICE and MG/inverter package. I also understand that on the ICE, there is a 3 way valve and both electric and mechanical water pumps. The 3 way valve is used when the ICE replaces cold coolant with the warm coolant from the thermos at startup, while the engine is running to maintain the temperature of the coolant in the thermos by doing a coolant exchange while running, and at power down to put warm coolant into the thermos, unless the coolant in the thermos is already hot, or has recently been exchanged during a running exchange. The coolant system on the Prius is pretty dynamic.

Also, I understand there are 2 electric water pumps on the ICE, one used for thermos coolant exchange (the one you hear at startup and shutdown), and one that is used to cycle coolant through the engine when it is not running, but the vehicle is running and the engine has recently been deactivated by the ECU (while in stealth mode). This makes sense because it would be foolish to just store hot coolant in the ICE during off and on cycles. The temperature differentials created by that activity could be very damaging to the block as it might contribute to block warp. While underway and the ICE is running a belt driven water pump is in operation.

The MGs and inverter/converter use their own cooling loop, have their own isolated coolant supply (although same fluid as is used in the ICE) and pump. They also operate at a significantly lower temperature than the ICE. This makes sense because the ICE is burning fuel, however the MGs and inverter/converter are warm due to electrical resistance through the various electrical conversion processes. That generates a whole lot less heat than burning fuel.
 

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Close. The thermos exchange is done before ICE starts when you first turn on the car. You can hear the servo move, followed by the electric pump, THEN ICE starts. Sometimes, if SOC is really low, ICE might start nearly right away.

I believe the other electric pump is for the cabin heater core.
 

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Dan, where is the water valve physically located? It sounds like the kind of item that can become stuck, clogged, etc. It would be nice to know how hard it is to get to. Reminds me of heat risers and exhaust manifold flaps--unlibricated, high-temp valves are a relability liability.
 

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Doug-

I went and checked the NCF again, and I'm both right and wrong..

I was right that the ICE water jacket does not extend down to the transaxle, and indeed with a conventional transaxle, unless you have a "transmission fluid cooler" (ie, a separate radiator for tranny fluid), cooling of the transaxle is by conduction through the casing and free-air convection.

I was also wrong because I thought the hybrid cooling system only served the inverter/converter, but there's actually another loop through the MG casing after the fluid exits the inverter/converter and the electric pump, so the MG are actually liquid cooled.. That also makes me wonder though- the fluid capacity of the hybrid cooling system is comparatively small, and the portion of the radiator allocated to hybrid cooling is also rather small: so how much of the temperature readings of the inverter are due to the components getting heated by insufficiently cooled coolant vs. actual dissipative heating from circuit operation?? Certainly they saved some space vs. the original Japanese Prius by integrating ICE and Hybrid into a single radator, but would cooling have been more effective on the original Japanese with its 3 separate AC/ICE/Hybrid radiators??
 

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KTPhil said:
Dan, where is the water valve physically located? It sounds like the kind of item that can become stuck, clogged, etc. It would be nice to know how hard it is to get to. Reminds me of heat risers and exhaust manifold flaps--unlibricated, high-temp valves are a relability liability.
Good question. I can't find it anywhere in the repair manual. Looked under cooling repair section and found the storage container and its pump, but no valve. Then had the bright idea to look at the HVAC repair section, no go there either. Found the heater water pump though.

Wiring diagram shows its connector to the left (passenger side) of the storage tank on the driver's side of the car. Near MG2

Edit: Ah, there it is, listed in the SFI (Engine) diagnostic section, page 5-8.
 

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second coolant loop

c4 said:
...there's actually another loop through the MG casing after the fluid exits the inverter/converter and the electric pump, so the MG are actually liquid cooled.. That also makes me wonder though- the fluid capacity of the hybrid cooling system is comparatively small, and the portion of the radiator allocated to hybrid cooling is also rather small: so how much of the temperature readings of the inverter are due to the components getting heated by insufficiently cooled coolant vs. actual dissipative heating from circuit operation??...
Still interested in the effectiveness of the inverter/MG coolant (second) loop, even though I am hijacking this metal belt thread. Talking about the NHW11 (2001-2003) Prius in particular; that is what I drive, and monitor temperatures from w/the miniscanner.

Attached see an image composed from the service manuals. These seem to be the best views of the second coolant loop, and cross sections of the MGs. If anyone can tell where the coolant passages are in the MGs, that would be great.

Typical miniscanner temperature data for the inverters would be in the 70's C, MG2 low 80's, MG1 high 80's. Under heavy load it is the MG1 that spikes up. This is why I suspect that it may not quite as well "plumbed" for heat transfer. There is also a chance that MG1 is being heated via conduction from the engine, but the temperature spike go up and down too quickly for that?

During these MG1 temperature excursions, the inverter temps do not rise very much, so I suppose that the extra heat is not getting out to the second coolant loop very well. Later I will log temperature data during one of these high-load drives.

DAS
 

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