Wait for engine warm up question.

Letting a cold engine idle to "warm-up" wastes fuel and significantly increases pollution and engine wear. The entire powertrain (parts & fluids) heat up quicker when placed under light loads versus idling with no load.

 

Prius Chat crashed while I was replying last time. Anyways, Richard, you are right. The the engine will provide some energy to the wheels when you drive during warm up, you can see that from the energy screen. My point is that most (I can't stress that enough) of the energy comes from the battery if you wish to move the car during the warm up period. And that is bad for FE for the reasons I stated before.

As for other's point about idling will increase wear, I change engine oil every 10k miles, and the used oil analysis report shows other wise. Blackstone Labs suggest that I go with 12k mile oil change next time because of how low the wear is on the engine. The engine is also charging the battery during warm up, you can see from energy screen and other instrumentation. So it is under load.

On a normal car, what you all have said are correct. The Prius is not a normal car.

 

The generated electricity can be used to move the car instead of charging the battery, which will improve efficiency by avoiding all of the conversion losses you are trying to avoid by not moving. You can't have it both ways at the same time.

Tom

 

Ok, but this still doesn't make sense.

The rpm of MG2 is determined by the speed of the wheels.
The rpm of the ICE is determined by it's warm-up idle speed.
The speed of MG1 is determined by the PSD gearing ratio and the above 2 inputs.

So what I'm trying to understand is:

Does the Prius use MG1 as a generator during this warm up phase?
If so, then the amount of rotational resistance in MG1 required to generate power should translate to some amount of torque applied to the ring.
Additionally, that generated power can be sent to MG2 to drive the wheels rather than sending power into the battery while simultaneously drawing power out for MG2. This would make driving it more efficient than waiting, since you would avoid the conversion losses into and out of the battery.

Does the Prius use the battery to spin MG1 as a motor to prevent torque being applied to MG2?
If so, then the Prius is using the battery both to accelerate the vehicle and to counterspin MG1?
Is it really important to avoid any load on the ICE during warm up?
Does this mean that when standing still, power is still being drawn out of the battery to spin MG1?
This would seem to make driving the vehicle more efficient since the faster the vehicle is moving, the slower MG1 needs to spin.
All that fuel burned is simply to overcome internal friction in the ICE and create heat?

Does the Prius just let MG1 spin freely, while neither drawing power from it nor supplying power to it?
Ok, this at least seems more efficient than intentionally trying to spin MG1.
I don't understand enough how these motors work to understand how the ICE can spin MG1 while not generating power, but I suspect it has something to do with either creating a short or open circuit between the + and - terminals.
Again, Is it really important to avoid any load on the ICE during warm up?
It seems like if you are going to spin the ICE anyhow, and you aren't going to put power into the battery, it would be more efficient to use it to drive the wheels then to just throw it into the atmosphere.
All that fuel burned is simply to overcome internal friction in the ICE and create heat?

 

Hi Danny, Yes that’s correct: you have a good understanding of how it works, and the question is what is actually happening during about the first minute after a cold start.
And I probably should have written: In effect, the sun gear is counter spinning just enough to the planet gears to cancel out the rotation of the planet carrier.

Yes, but not immediately. Depending on how cold the ICE is, during the first couple seconds to about a half a minute, it lets the ICE idle with practically no load, even when gently accelerating. This is based on my observations last winter with temperatures down to around freezing.
Oops! In the meantime I have remembered: You lucky people with a U.S. spec. Prius have a thermos! If you live in a warm climate and drive every day, could it be that the thermos always preheats the ICE enough to skip this step?

I agree.

Looks like you know about as much as I do about that, but based on the fairly good gliding in “Nâ€, I speculate that somehow the MGs can spin pretty easily without power.

It’s definitely using the Battery for acceleration. Sometimes, when it’s cold, mine uses up two bars of SOC before it switches to recharging. As for using battery power to counterspin MG1, I don’t have the necessary instrumentation to determine that, so I don’t know. (Can anyone here measure MG1 power?)

Only for the first seconds to a minute or so, and only if it has to fulfil very strict emissions standards.

Yes, and that has to be balanced against the efficiency of MG2, the battery, and driving resistance. That is so complicated that I’m not going to try to speculate right now what the optimum warm up speed might be. But I will say: Accelerate gently the first couple minutes. (have to live up to my subtitle)

OK, first of all, during the first seconds after a cold start, the emissions controls are very ineffective, and the emissions are about a kajillion percent worse than when it’s warmed up. During this time, the best way to minimize emissions is to minimize the amount of fuel consumed. Now you might think that the best way is to warm up the engine as fast as possible by running it at high power. That would certainly warm the engine up faster, but the real question is how much fuel was consumed, and pollution produced, during that time and distance. The faster the combustion gasses move through the engine, the less time they have to transfer their heat to the engine. In the extreme case, under full power, a high power engine will push the combustion gasses through so fast that they are still glowing hot as they leave the exhaust pipe, thus releasing most of the heat to the atmosphere instead of to the engine. At the other extreme, the combustion gasses coming out of an engine that is just barely running are not very much hotter than the engine itself, because they move so slowly through the engine that they have had time to give up most of their heat. So to heat up an engine by a certain amount, it generally takes less fuel when the combustion gasses stay inside the engine longer. But, after a certain point, when the engine and emissions system are warm enough to operate more efficiently, then it is better to run at a higher power. That's when the Prius automatically switches from Battery assist to battery charging. All we have to do is not accelerate too hard the first couple minutes, and let the Prius do its thing. It decides all by itself how much to load the ICE.

 

Tom, there's a difference in magnitude here. If I let the car sit idle, I see charge ~5Amps if SOC is not too low (blue battery bars). If I move the car, the drain is anywhere from 30-60Amps or even higher depend on how fast you accelerate. You pick which loss you want to take.

I'm just telling you why I'm doing this. If you don't agree, that's totally fine with me. It's your car after all.... :car: