ICE comes on when Stopped -- yet monitor shows it's OFF

Just to add to the above, as temperatures drop in the UK, I’m observing more and more of this interesting fuel emissions saving mode.

You’re usually stopped at traffic lights or a junction. It’s cold. You might have the heating or Airconditioning online (mine is set to 16c) to clear foggy windows in our oft damp UK climatic conditions.

The engine appears to be running, but NOT A DROP of fuel is being expended. Rather, the HV battery is spinning the engine via the “power split device”, purely in an attempt to warm the I.C.E. up to optimal operational conditions for maximum fuel saving efficiency.

Typically, the temperature was 7c outside early in the morning as I was starting my commute - and I observed this fuel emissions saving mode in operation.

I later pulled up to traffic lights in silence, then 30 seconds later, the I.C.E. kicked in again, with clearly no fuel being used; and ran for about 45 seconds before shutting down again. Yes, I had the windscreen demist (defogging?) function online and set to a minimal 16c - just to save fuel.

Once the engine has fully warmed up, this phenomenon usually ceases to occur, unless you were stuck in traffic for a long time with heating online AND a full HV Traction battery - the latter plays a very important role in whether this actually happens - or whether your Prius decides to use fuel to spin your engine to generate heat - or bring it up to optimal operational thermal parameters.

I am truly fascinated whenever I observe this happening. Amazing technology!


iPhone 6s +

 

How do you know it's not using fuel?

 

I suspect he "knows" because of the in-dash mpg display. But yeah, I'm not buying that either.

 

iPhone 6s +

 

That deescalated quickly.

 

The whole concept of the ICE cranking while off is alien to me, not saying it doesn't happen, it probably does.
But naming a few of the reasons why it does happen in the Prius, always helps those that don't believe it to at least understand that it does happen.

I'm more interested in how much charge the defroster uses as ambient temps decrease.

 

That’s an entirely valid question.
About approximately 4 years ago, on a very cold frosty morning, I fired up “The Spaceship” and proceeded to scrape some light frost off the windows.

It was one of those overtly damp mornings typical of London UK, when the exhaust gases coming out of your vehicle’s pipe take on the resemblance of a whitish steam related smokescreen - especially when your I.C.E. is stone cold.

Working on dislodging frozen ice from the rear window (aided by the rear defogging lines), I was watching the steamy exhaust coming out from under the rear of The Spaceship, when it suddenly decreased dramatically then stopped altogether. The tone of the I.C.E. changed slightly shortly before. I looked at the MFD and could see the fuel feed indicator had ceased to show a flow of fuel to the engine.

In fact nothing was flowing. And the engine was still turning! I did have a full battery at the time. This continued till I got behind the wheel and pressed the throttle pedal to drive off - at which point fuel flow resumed.

That was probably the first time I categorically noticed this happening. Was I puzzled? Yes. But browsing through articles on the HSD, I quickly realised this was exactly what it was supposed to be doing - reduce polluting emissions by every means possible.
This is one of them


iPhone 6s +

 

The full defrost button in the Prime will usually start the engine. If you want to defrost in EV mode without the engine running, you can set the climate control output to what I call "defrost plus feet". The heat pump down to about 13F, but I've seen it keep working a degree or two colder without the engine coming on.

In very cold temperatures it uses quite a lot of power and it's pretty weak at actually defrosting the windshield. That combined with the fact that the battery has lower capacity at cold temperatures means I've seen as bad as half the normal EV range, about 15 miles of range. I can hear the compressor and HVAC fan changing speeds as the defroster runs, so it might be doing something besides just heating, for example maybe periodically running in reverse (cooling mode) to dehumidify the cabin and defrost the outside heat exchanger. I don't know, that's just speculation.

I think someone tested the heat pump with the power display on Hybrid Assistant and saw over 5kW. That's huge, since the AC might use only around 2kW. I can test it more as the weather gets colder.

I also camped in my car once, and in the morning I ran the heat to warm up. It was around freezing outside (and inside). I ran it for about an hour, and it used around 25% of the battery. Of course towards the end of the hour the temperature was getting close to comfortable, so it wasn't running at full power.

It seems to be very efficient in mild weather, but if it's above freezing whatever jacket and gloves I wear for walking outside also keeps me warm enough in the car with just the seat heater on. So I usually only use the heat when it's colder outside.

I hope that helps give you an idea of how much energy it uses.

 

@m8547 Thanks for your findings.
I typically don't use A/C, Heater during EV driving, except preconditioning and experimenting with settings occasionally before an EV trip just in case I absolutely need to switch it on. The better half is even using it less, now that I manually precondition with extra heat in the colder months during both charging and pretrip. But she still turns it on when I'm not available to get the car ready like I'd do for myself. And once in a while will fiddle with the climate settings when I've set them too high of low or haven't been paying close enough attention to temp changes..

In HV mode I use both A/C and heat to make the cabin comfortable, especially if there're passenger(s).

Two drivers makes it harder to tell what are actual vehicle limits and which are vehicle adapted adjustments the computers reset per driver.
Thanks again for taking the time to explain.

 

I really think it was a shortcoming of the displays, don't see how the engine can run without using fuel.

 

The electric motor could turn the engine. But I can't think of any reason why it would, unless maybe there is a coolant pump or something that's driven off the engine that needs to keep running. Otherwise doing so is going to waste electricity and isn't going to generate any significant amount of heat compared to burning a tiny amount of fuel. It sounds like @Data Daedalus is speculating that generating heat is the reason for this behavior.

The display is not very helpful. It's more of a cartoon representation of what's going on than an actual way to monitor what the car is doing.

The green car shaped EV mode "light" is another flawed indicator of whether the engine might be running.

 

Or how spinning the engine without fuel can heat it up or just keep it warm. When the M/G spins up the engine to for engine braking, or to get rid of excess charge, the engine is now pumping colder air through it and the catalytic converters, cooling them.

 

That is the point of spinning the engine. Quickly using up excess electricity is important for battery longevity.

 

Simple; the Atkinson cycle engine (I.C.E.) is an integral part of the Hybrid Synergy Drive - which is an internal combustion engine mated to two electric motors and a planetary gear set for a transmission. All connected via a power split device.

Those huge electric motors MG1 and MG2 are powerful; one serves as a traction motor, which can reverse polarity during deceleration and dump energy into the HV Traction Battery; the other is powerful enough to spool up the engine at startup, so much so, that you don’t even hear it spin - it’s literally part of the propulsion system.

Unlike conventional cars and their puny starter motors making familiar whizzing (wheezing?) starter noises when turning an engine, the Prius electric motor responsible for turning the engine does it with minimal revolutions and no wheezing.

That same motor can easily spin the engine, powered by the traction battery for a short while, preventing the Prius from spewing harmful gases into the environment - while striving to either generate heat for the heating system or more likely, simply get the engine up to optimal temps for best fuel sipping operation.

The same motor will kick in and spin the engine if you drive down a very long incline while effectively utilising regenerative braking, and you literally top up your HV battery to the max.

I experienced this for the first time in 6 years earlier this week when I got to the bottom of an incline with absolutely FULL green bars. Came to a halt and there was a sudden rumble I’d never heard before - it was the engine being spun at higher revs than I’d ever heard - all being spun by the electric motor trying to dump excess energy from the HV battery pack.

For these brief moments, fuel is definitely not used. It’s being done with electric power.

BTW, there’s an excellent YouTube video that adequately explains how the HSD works; brilliant graphics explains the power split device and how those electric motors and the engine interact in different operational modes.

It’s exhilarating technology (or witchcraft worthy of a pond dunking for whoever designed it....).

I’m deeply amused and astonished in equal measure, when absolute dullards deride the Prius, not realising what revolutionary (almost alien) tech is lurking under the bonnet.

If only they knew the true secrets of the HSD!


iPhone 6s +

 

Spinning the engine gets the pistons pumping; the friction quickly warms the engine block - and the coolant (and oil) coursing within the engine block


iPhone 6s +

 

The the priority in the Prius is low emissions. Engine warm isn't just about getting it to operating temperature, which is important for emissions, but also for heating up the catalytic converters so they can do their job. That is done with hot exhaust. Also, if the internal friction is high enough to warm up the engine block, it would hamper the engine's efficiency.

What you are likely seeing is the same behavior all modern cars have on start up. The engine runs at a relatively higher load to quickly heat up the engine and emission control systems. Once the proper temperatures are reached, the engine slows down to a normal idle speed and load. The actual fuel consumption at those conditions is probably too low for the display's programming.

The other possibility is that the battery became overcharged during the warm up cycle, and the engine is being spun afterwords to get rid of the energy. This has nothing to do with engine warming, and will actually cool it with the cold air being pumped through its heart.

 

You are of course correct and highly accurate on several points.

Just to underline; this virtually always happens (to me) with a fully charged battery, depending on the external temperatures, shortly after starting the engine from cold, and always when at a standstill. Even in summer on a super hot day.

It never happens with a half filled battery or less, regardless of climatic conditions.

If sensors detect that the cat is warm enough, having been warmed quickly by fuel derived exhaust gases (in auto-choke like mode), they may well send a command to cut off fuel, and let the electric motors continue to spin the engine to heat the block - and as you correctly pointed out, expend that excess energy

Considering the complexity of engines, I firmly believe in this. A lot of friction goes on in an engine. Pistons do their metal on metal thing - cold air at, say around 10c certainly isn’t going to chill an engine spinning at about 800 revs minimum per minute.

I, quite sadly, can clearly see the physics (and chemistry) in my head .


iPhone 6s +

 

In a regular Prius (not plug-in), electricity is valuable. It ultimately all comes from the engine in some way or another. There is conversion loss to go from engine power into the battery and back through the motors, so using the engine directly is better if it can run efficiently. If creating heat is the goal, there are very few situations where it would make sense to do so by running the electric motors. If the engine is up to 40% efficient, and the conversion from engine power to battery energy back to motor power is 90% efficient, only 36% of the energy from gas originally burned to make electricity can be made back into heat. Whereas idling the engine with no load is almost 100% efficient at creating heat.

I agree that the engine spins with no fuel used when going down a long hill. That's hardly any different from any other modern car (they will cut off fuel if it's not needed), and in this case the electric motors are just replicating the behavior of a transmission.

I'm still skeptical that there's any time while the car isn't moving that the electric motor is spinning the engine with no fuel being used. It doesn't make much sense.

"Using up" excess electricity doesn't make sense, because excess electricity wouldn't be stored in the first place. Either the battery has room for it or it doesn't. And if it does, might as well save that for driving.

 

The battery has a buffer capacity that isn't used in the form of not discharging it below a certain point and not charging it above another point. The programing allows the car to exceeds those limits at time, but it get to the allowed zone as soon as possible, because spending too much time outside it will shorten the battery's life. Which is why the car will spin the engine instead of saving extra electricity outside that zone for later, and it will spin the engine to use that up even while stopped, but that situation rarely comes up for most people.

 

I had to lookup HSD since I have acronym overload, and now that I know what it is I'll add an new one too
PSD.

HSD
PSD
and its getting so much better all the time Sargent Peppers
good call Deadalus

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