Gen 4 ICE change when travelling down hills

[thecaretaker]

Has anybody else noticed this?

When travelling back to my home, there is several miles of down hill driving and the Battery indicator lights all the bars. At the very end of all this down hill driving is a set of lights where I have to stop. The engine cuts in as if to recharge the Battery and revs fairly hard. I then have to do a lot of stop start driving in town before I get to my house and even getting to 3/4 bars, the engine still demonstarates this strange behaviour. To stop it, at a set of lights I completely turn off and restart. Only then does the engine return to normal operation (EV light coming on while driving and engine off when stationary).

Is this a quirk with the software that controls the engine? At first, I wondered if it was using the engine to use up power (spark at plugs etc) and charger off to protect the Battery from over charge. But it doesn't come out of this 'mode' if it is a mode on it's own. Only turning off and back on again seems to fix it.

You need to live in an area where there is long stretches of down hill driving to notice this.

I'd like to hear if other Gen4 owners have noticed this and if it is something we ought to feed back to Toyota. I don't think my car will be unique or faulty.

[PeteB]

Does the EV button work in this state?

I've only experienced a maxed out HV Battery in my Gen 1 & 3 Prius - it'll be a while before I go anywhere near a big enough hill to do it in my Gen 4.  I don't recall this behaviour in either of those, so won't be able to comment further.

[QuantumFireball]

1 hour ago, thecaretaker said:

At first, I wondered if it was using the engine to use up power (spark at plugs etc) and charger off to protect the battery from over charge.

It's just engine braking - there is no consumption of fuel (no spark), you're just using the resistance of the ICE to slow the car down. It will do this if the Battery is fully charged and you're not applying any throttle, as it can't do any regen in this state. As to why it doesn't stop afterwards, I don't know. Maybe you're not waiting long enough for it to go back into its normal state? Or is it automatically shifting into B mode or something weird?

[thecaretaker]

4 hours ago, QuantumFireball said:

It's just engine braking - there is no consumption of fuel (no spark), you're just using the resistance of the ICE to slow the car down. It will do this if the battery is fully charged and you're not applying any throttle, as it can't do any regen in this state. As to why it doesn't stop afterwards, I don't know. Maybe you're not waiting long enough for it to go back into its normal state? Or is it automatically shifting into B mode or something weird?

It happens when I stop driving down hill and stop at the lights and it continues (engine running) for the remainder of the journey (30 mins) unless I physically turn off and back on again (like re-booting a computer).

 

5 hours ago, PeteB said:

Does the EV button work in this state?

I've only experienced a maxed out HV battery in my Gen 1 & 3 Prius - it'll be a while before I go anywhere near a big enough hill to do it in my Gen 4.  I don't recall this behaviour in either of those, so won't be able to comment further.

Good point, I've not tried switching to EV mode. I'll give it a go next time it happens.

[Joseph D]

5 hours ago, thecaretaker said:

It happens when I stop driving down hill and stop at the lights and it continues (engine running)

For how long are you stopped at the lights?  Is the A/C on?

The car will certainly rotate the engine (no fuel burn though) using the electric motor to burn off some electricity to make room in the Battery when it is totally full, as you get after a long decent. It does this while driving too.

The only other thing I can think of, and this is assuming the Gen 4 has the same basic design as its predecessors, is that it is at stage 3 transitioning to stage 4 at the lights, but if this is the case that would only take 10-15 secs, which seems a lot longer than that when you are waiting for it to shut off.

Like PeteB, I have no Gen 4 experience, so that is all I can offer.

[kithmo]

Could it be the electric motor turning the engine, even though the car's not moving, to use up the HV charge ?

Is it using any fuel Paul ? 

What's the instant mpg reading when it's doing it ?

[thecaretaker]

2 hours ago, kithmo said:

Could it be the electric motor turning the engine, even though the car's not moving, to use up the HV charge ?

Is it using any fuel Paul ? 

What's the instant mpg reading when it's doing it ?

I'm pretty sure it is the engine running, but I could mistake it if the electric motor is turning the engine. I will check the mpg reading the next time it happens. But I would have thought once the Battery has lost some of its charge, it would revert to normal running.

I'm wondering if I can record video of this on my mobile so I can show exactly what's happening, but I don't know if it will be audible enough as the car is so quiet. the EV light doesn't show, maybe the picture of the car will show what's going on. I need to spend some time playing I think.

[johalareewi]

Do you have anything to monitor the OBD port?  Like scangauge or hybrid assistant?

Or the energy flow screen will show if the ICE is burning fuel or the electric motor is spinning the ICE (to burn off electricity).

 

[kithmo]

50 minutes ago, johalareewi said:

Do you have anything to monitor the OBD port?  Like scangauge or hybrid assistant?

Or the energy flow screen will show if the ICE is burning fuel or the electric motor is spinning the ICE (to burn off electricity).

 

Does the energy monitor show direction on the MG to ICE flow ? 

[QuantumFireball]

On 18/05/2017 at 1:22 AM, Joseph D said:

The car will certainly rotate the engine (no fuel burn though) using the electric motor to burn off some electricity to make room in the battery when it is totally full, as you get after a long decent. It does this while driving too.

Maybe I'm misunderstanding, but this is not a mode of operation that happens with the Prius. MG1 will only use electric power to start the ICE, or MG1 will be driven by the ICE to generate power - it will never "burn electricity". There is no such mode where it will waste energy from the Battery.

If you select B mode, or if you're going downhill when the traction Battery reaches a high state of charge, the transmission will apply engine braking using the ICE - essentially just like engine braking with any normal ICE car. Due to the way the transmission works, MG1 and MG2 are always going to be rotating in some fashion anyway.

[Joseph D]

25 minutes ago, QuantumFireball said:

There is no such mode where it will waste energy from the battery.

What is your source of this information?

[QuantumFireball]

There are various explanations of how engine braking works in the Prius online, including what it does in this situation of extended downhill driving. I can't find anything official, but this describes the main modes of operation:

https://en.wikipedia.org/wiki/Hybrid_Synergy_Drive

But it makes no sense for it to waste energy from the Battery anyway - it would be inefficient and unnecessary. Once the SOC gets to a certain high level it will just stop regeneration from MG2 and use the ICE instead to create resistance - it may be wasting kinetic energy to slow down the car, but no electric energy is being used from the traction Battery. The momentum of the car is turning the ICE.

Readouts from an OBD-II scanner during this mode will tell you what's really going on.

[YarisHybrid2016]

The weather is rubbish at the moment, so I'm not very inclined to go out, but there is a hill where I can just about max the Battery on the downhill, so I could try and see if I can persuade it here and see what happens? Sure my car isn't a Gen 4 Prius, but are they that different?

I have noticed times where the Battery is in a high SoC, but during deceleration/stopped, the ICE continues to run for no apparent reason. It does stop after about 30 seconds. It doesn't do it very often (maybe I'll spot it once a month).

As I understood a full Battery, it simply stopped regen, and started wasting energy via the engine and mechanical brakes. The rest of the operation is normal (if in D, anyway).

[Joseph D]

13 hours ago, QuantumFireball said:

...   But it makes no sense for it to waste energy from the battery anyway   ...

So, to summarise, you can't find any official information, but that doesn't matter because you think it makes no sense, therefore it doesn't do this. Would it rock your world if I said I have personally witnessed it?

Just to be clear, I am talking of the phenomena of the HSD configuring itself to use primarily electricity to propel the car, even when going 60+ mph, when it finds itself at 80% SoC (Full – 8 bars on the MFD graph).  The logic is for this, is that it does not know what lies ahead so will aim always to be at 60% SoC. When it has this abundance it diverts to electricity so that it can get to its happy place as soon as possible. To further be clear it only does this when it is completely full, so it will have ceased by the time the 8th bar disappears.

In my post above, I do not know whether it will do this when the car is stationery, but only offered it as a possible explanation as the OP said they come to a stop at the bottom of the decline so it seems logical that the HSD my run on for a bit to clear some headroom.

1 hour ago, YarisHybrid2016 said:

...   there is a hill where I can just about max the battery on the downhill   ...

You will need to totally max out the Battery such that you hear it change to engine braking (when it switches off the regen) whilst still on the descent.  You will be hard pressed to find such a decline in the UK.

[YarisHybrid2016]

I fill all the bars, so it must be pretty close??

[PeteB]

It takes a while after the 8th bar lights up before the Battery shows signs of being maxed out.

[Joseph D]

2 hours ago, YarisHybrid2016 said:

I fill all the bars, so it must be pretty close??

 

1 hour ago, PeteB said:

It takes a while after the 8th bar lights up before the battery shows signs of being maxed out.

As PeteB says, but not as long as it takes to fill the 7th bar though.

To make my point again, you have to be maxed out (such that regen is swapped out for engine braking – when that happens you will know), so "pretty close" will not cut it.  You will not see the effect when "pretty close".  I'd also wager, you'd be surprised to find out how long it takes to get maxed out, and that you're not as close to maxed out as you think.

[YarisHybrid2016]

Well, I could get *close* without trying (meaning ensuring the Battery has a high SoC before attempting the hill). Challenge accepted!

I know how it sounds when the engine starts taking over! hehe!! B mode, braking hard from 40 MPH down a very steep hill (35% gradient) makes the engine come alive rather alarmingly.

[Joseph D]

3 minutes ago, YarisHybrid2016 said:

I know how it sounds when the engine starts taking over! hehe!! B mode

Maybe it's terminology, but it is much more alarming than B mode.

I'm not trying to be discouraging, just want it to be understood what we are going for.

[YarisHybrid2016]

1 minute ago, Joseph D said:

Maybe it's terminology, but it is much more alarming than B mode.

I'm not trying to be discouraging, just want it to be understood what we are going for.

I've heard it in B mode - not slightly, but where the RPM really comes up.

[kithmo]

I can barely hear it in the Gen 4.

[YarisHybrid2016]

In the Yaris, it's a bit quieter than max throttle, but sounds different.

[johalareewi]

On 5/19/2017 at 2:37 PM, QuantumFireball said:

But it makes no sense for it to waste energy from the battery anyway - it would be inefficient and unnecessary. 

Readouts from an OBD-II scanner during this mode will tell you what's really going on.

The 'wasting electricity' happens when the HV Battery SOC gets too high.  MG1 will spin the ICE to use up electricity in the HV Battery.

 

[johalareewi]

On 5/19/2017 at 11:42 AM, kithmo said:

Does the energy monitor show direction on the MG to ICE flow ? 

Now you mention it, it might not. But it does show ICE to MG flow so I assume it will show it going the other way when it happens.

I haven't had it happen and now I have a plugin, I not likely to.

[QuantumFireball]

On 20/05/2017 at 4:11 AM, Joseph D said:

Just to be clear, I am talking of the phenomena of the HSD configuring itself to use primarily electricity to propel the car, even when going 60+ mph, when it finds itself at 80% SoC (Full – 8 bars on the MFD graph).  The logic is for this, is that it does not know what lies ahead so will aim always to be at 60% SoC. When it has this abundance it diverts to electricity so that it can get to its happy place as soon as possible. To further be clear it only does this when it is completely full, so it will have ceased by the time the 8th bar disappears.

That does happen, but I'm talking about a situation when you're going downhill with zero throttle. Once the SOC is at the high state it should just stop generation and use engine braking - I find it hard to believe there is anywhere for electric energy to be used in this state where there's enough momentum (assuming you're trying to slow down). Maybe after the descent it will try using more Battery, but not during. It's hard for me to replicate with the Plug-in, and maybe the 2nd gen is different anyway.

29 minutes ago, johalareewi said:

The 'wasting electricity' happens when the HV battery SOC gets too high.  MG1 will spin the ICE to use up electricity in the HV battery.

 

MG1 is nearly always spinning when the ICE is running, sometimes backwards :) But the wheels are primarily rotating the ICE in this situation.