The myth of inefficent petrol motor charging on the PHEV.

[Grigou]

I do not dispute these points.
Imho, the alleged "reduced efficiency" of the save mode at, or above, 50 % SOC ...:/quote]
You don't dispute the alleged reduced efficiency? That's funny

1) running the ICE, due to low SOC, when stopped in traffic (you have no way to choose when the "zig" part of the hybrid mode starts) ;

But, I don't think the car will start to zig while stopped in in traffic. As a matter of fact, even if the car was zigging, it would stop zigging closely before coming to a full stop.

I'am afraid it's wrong.
Before that my plug was installed at home I had driven a lot with an empty battery, and I can tell that there are some zigs at 0 km/h, even without heating or AC.
And a zig (the ICE) can even start when the car is stopped for 30 seconds, not necessarily before stopping ...
Not absolutely sure, but it seems that this behaviour can also happen in Save mode with more than 30 % SOC, the difference with an empty battery is just that in this case you can switch in EV.

 

[Kristian]

+1

I find my PHEV much easier to drive with SAVE automatically selected for all drives. As soon as I hear the ICE start on a shorter drive, if I have forgotten to cancel SAVE mode,

How do you make the car automatically select SAVE mode?
Can you make it automatically select ECO mode too?

 

[anko]

Before that my plug was installed at home I had driven a lot with an empty battery, and I can tell that there are some zigs at 0 km/h, even without heating or AC.
And a zig (the ICE) can even start when the car is stopped for 30 seconds, not necessarily before stopping ...
Not absolutely sure, but it seems that this behaviour can also happen in Save mode with more than 30 % SOC, the difference with an empty battery is just that in this case you can switch in EV.

I would be very annoyed if that happened to me (if I was aware of that happening :? ). What I typically see is that if I approach a sharp bend or a roundabout with the engine running (in normal mode), the engine first starts idling with very low RPM and very low fuel consumption, and then dies out, just before reaching the bend or roundabout. I (don't say it doesn't but) cannot imagine why it would keep running while stopped. Unless one had been hammering his car very hard on a very low SOC, just before stopping, and had brought the SOC well below 26%. But that still doesn't explain why it would start running while stopped ....

 

[Grigou]

We had some discussions about that on a french forum : some have seen this behaviour, some others no.
Anyway, to be able to see it, it's better to drive frequently in town with an empty battery (or in Save mode I think).

 

[maby]

My old Prius would do very much the same - I think it is just the standard behaviour of a hybrid running with a SOC close to its floor level. The "staying running while stationary" is easiest to explain - starting the engine consumes some battery and is probably relatively wasteful on petrol compared with steady state running, so it makes sense to keep it running for a while - to make up for the charge used in starting it and to get the oil flowing. Repeated stopping and starting of the engine running only for a few seconds would be bad for it and would actually deplete the battery further rather than charge it.

As far as "starting while stationary" is concerned, this is probably just simplistic programming. The car wants to get a bit more charge into the battery and it doesn't bother to wait to see if you are going to start moving sometime in the next few minutes. It honestly does not worry me - and I guess that the designers didn't consider the possibility of owners who would be so sensitive to every teaspoon full of petrol going into it.

 

[Grigou]

My old Prius would do very much the same - ....

My recent Auris 2 HSD did the same much more rarely than the Outlander PHEV

I think that our PHEV could be better designed on this aspect, because it's battery has a much greater capacity. So it could wait a lot of time when the car is stopped, even under 30 % SOC ...
I could even suggest an algorithm to the engineers (using speed, time, SOC and clim parameters), it doesn't seem very complicated, does it ?

 

[FLYER34]

And a zig (the ICE) can even start when the car is stopped for 30 seconds, not necessarily before stopping ...

+1
I can confirm : a "Zig" (the ICE) can start at any time when the sofware decides that the battery needs charging.

It honestly does not worry me - and I guess that the designers didn't consider the possibility of owners who would be so sensitive to every teaspoon full of petrol going into it.

+1
All this thread is about "teaspoons of petrol".
I prefer to save teaspoons of petrol by preventing any "zig" when the car is stopped. (and any 4.500 rpm hill climb).
Others prefer to save teaspoons of petrol due to a better efficiency of the ICE when charging the battery at 27 % SOC rather than at 50 % SOC.
Others prefer to save teaspoons of petrol by using Charge instead of Save.

Best way to save teaspoons of petrol is an open question.

 

[anko]

And a zig (the ICE) can even start when the car is stopped for 30 seconds, not necessarily before stopping ...

+1
I can confirm : a "Zig" (the ICE) can start at any time when the sofware decides that the battery needs charging.

Even with:
- aircon switched off
- electric heater switched off
- charge mode not enabled
- break pedal sufficiently depressed, so no power is leaked towards the motors
- etc?

So it just sits there, no power is being drained from the battery and all of a sudden the car decides to start the engine to recharge? Seriously, I cannot imagine I've ever experienced that. I think I would be in a state of shock if that happened to me (and I was aware of it)

 

[welljock]

And a zig (the ICE) can even start when the car is stopped for 30 seconds, not necessarily before stopping ...

+1
I can confirm : a "Zig" (the ICE) can start at any time when the sofware decides that the battery needs charging.

Even with:
- aircon switched off
- electric heater switched off
- charge mode not enabled
- break pedal sufficiently depressed, so no power is leaked towards the motors
- etc?

So it just sits there, no power is being drained from the battery and all of a sudden the car decides to start the engine to recharge? Seriously, I cannot imagine I've ever experienced that. I think I would be in a state of shock if that happened to me (and I was aware of it)

It definitely happens; I often sit waiting for my daughter coming out of her swimming, with the car in park and only the radio on and the ICE will start.

 

[maby]

And a zig (the ICE) can even start when the car is stopped for 30 seconds, not necessarily before stopping ...

+1
I can confirm : a "Zig" (the ICE) can start at any time when the sofware decides that the battery needs charging.

Even with:
- aircon switched off
- electric heater switched off
- charge mode not enabled
- break pedal sufficiently depressed, so no power is leaked towards the motors
- etc?

So it just sits there, no power is being drained from the battery and all of a sudden the car decides to start the engine to recharge? Seriously, I cannot imagine I've ever experienced that. I think I would be in a state of shock if that happened to me (and I was aware of it)

There will still be some current drain - the control systems, MMCS display, DRLs, radio etc. etc. - so there is a finite probability that the engine could kick in to top up the battery. I do think that the hysteresis loop in the power management algorithm is rather small - which results in more frequent and shorter runs of the petrol engine. The Prius would allow the battery to discharge quite significantly before starting the engine, then run it till it was significantly above the SOC floor level.

 

[anko]

There will still be some current drain - the control systems, MMCS display, DRLs, radio etc. etc. - so there is a finite probability that the engine could kick in to top up the battery. I do think that the hysteresis loop in the power management algorithm is rather small - which results in more frequent and shorter runs of the petrol engine. The Prius would allow the battery to discharge quite significantly before starting the engine, then run it till it was significantly above the SOC floor level.

It is not about the width of the loop, it is about the change that power consumption by 12v devices pulls the SOC below the set threshold. Because if isn't the 12v devices that pull it below the threshold, then what is? I would think the chance of this happening would be extremely small in normal daily use, especially taking into consideration that you normally will have done some regenerative breaking immediately prior to coming to a full stop.

 

[Grigou]

It is not about the width of the loop, it is about the change that power consumption by 12v devices pulls the SOC below the set threshold. Because if isn't the 12v devices that pull it below the threshold, then what is? I would think the chance of this happening would be extremely small in normal daily use, especially taking into consideration that you normally will have done some regenerative breaking immediately prior to coming to a full stop.

Theorically I agree with you.
Practically I don't, since I have seen the phenomenon many times (and without heating, cooling, etc ...). I'am happy not to be the only one.
No real explanation ... But you just have to wait : one day it will probably happen to you

Now, like Flyer34, I know what to do when I am in Save mode : switching in Normal mode when stopping. To be able to do that, I prefer to keep a comfortable % of SOC for the town and low speeds, in particular with AC in summer (no electric heating in my Intense french version).

 

[gwatpe]

+1

I find my PHEV much easier to drive with SAVE automatically selected for all drives. As soon as I hear the ICE start on a shorter drive, if I have forgotten to cancel SAVE mode,

How do you make the car automatically select SAVE mode?
Can you make it automatically select ECO mode too?

Hi Kristian,

I have mentioned my own designed modifications that allows the driver to choose which mode the PHEV powers ON with automatically, every time until the driver wants a change. This is very different to the default power ON "Discharge battery first"mode. There is a "sticky ECO button" thread in modifications, and a "sticky SAVE and CHARGE mode" threat in technical discussions.

As far as I know there is no factory option. I did offer to make this modification available, but no one had contacted me. Some prominent forum members see no need for a sticky ECO button and I can agree with this. No real benefit on general operations of the PHEV. I have found that having my PHEV start in SAVE mode, allows me to fiddle with any other button when the time comes. Draining the battery down to a low state of charge impacts my longer drives too much so I came up with a solution that helps me every time the PHEV is powered ON. I now no longer need a pre-drive checklist and I can essentially start driving on a longer drive, without having to remember to press a particular button first, like any other traditional car.

I checked a drive to the city [250km round trip] yesterday and mix of about 190km highway and city drives the PHEV returned 6.7L/100km, with about 220km running in SAVE mode. Did toggle SAVE mode in city driving to keep ICE OFF when stopped. Returned with over 50%battery indicated. Car indicated 50%EV driving, so a big portion was driven EV, on energy that had been recharged back into the battery when running in SAVE mode. The electrics have to be efficient for the car to return the low average petrol consumption. I did have the energy flow screen visible and at certain times had EV only at highway speeds. [It is really hard to drive, and check instruments for a 250km round trip, so a lot of possibly interesting data segments were missed]

 

[Kristian]

Thanks. I dont personally feel a need for a sticky Charge or Save button, living in the city with mostly short drives, I would want to start almost always without using these options. However as a matter of principle and user friendliness I think most options should have the possibility of choosing the default. The LDW will be default off as far as I understand if you hold the button in for a few sec (called LDW2). The ECO should be the same (have anybody tried btw?), and Charge/Save could have been similar. I would have liked to have ECO as default ON. Alternatively these options could remain in the state they had when the car was shut down, but this is probably a post that should have been on the wish list for a better PHEV.

 

[greendwarf]

And a zig (the ICE) can even start when the car is stopped for 30 seconds, not necessarily before stopping ...

+1
I can confirm : a "Zig" (the ICE) can start at any time when the sofware decides that the battery needs charging.

Even with:
- aircon switched off
- electric heater switched off
- charge mode not enabled
- break pedal sufficiently depressed, so no power is leaked towards the motors
- etc?

So it just sits there, no power is being drained from the battery and all of a sudden the car decides to start the engine to recharge? Seriously, I cannot imagine I've ever experienced that. I think I would be in a state of shock if that happened to me (and I was aware of it)

Although I don't recall having this happen to me, what I have noticed that when coasting in B0 when using the ICE it does take a while to shut down.

 

[Grigou]

It's easy to notice that there are some accessories wich permanently drain the 12 V battery, but also some technical parts (wich perhaps drains directly the 300 V battery).

Accessories : day lights, radio, MMCS, often the cooling fan ...
And if you open the bonnet, you will hear some electrical noise, and the water flowing in the cooling circuit (for cooling the inverters and all the power electronics). I think that these parts under the bonnet are the most concerned in the consumption of electricity.

 

[FLYER34]

The Nissan Leaf has 3 separate steam gauges to monitor electric consumption :
- one for the motor ;
- one for heating/AC ;
- one for ancillaries.

With NO ventilation ; diriving lights ; wipers ; radio etc... the # 3 gauge indicates an average of 300 W.

The various PHEV systems probably drain the low voltage battery by a comparable amount.

By the way, on the PHEV, the low voltage battery seems to be permanently charged (voltage above 14 V at all times with power ON).

 

[Grigou]

These 300 W are interesting ... lets say 500 W with some accessories (lights, radio ...)

Question : at how many kWh is a zig (or a zag) equivalent ? The answer could allow to calculate the average time before the ICE starts when we stop at a light
Or the probability that the ICE starts when you stop 1 mn, il you prefer

 

[anko]

Let's say a zig gives you a kilometer of EV range. That means there is about 200 wH between the low and high watermarks. Statistically, you will halfway between them. So, you can loose 100 wH before hitting the low water mark. At a burning rate of 300 watts, this would take an average of about 20 minutes, much longer than your average stop in normal traffic.

But this still ignores the fact that your SOC is raised a bit, simply by stopping. That may not be much, but I think significant compared to 300 watt usage.

Also, the PHEV has a different low water mark for speeds > 50 km/h (approx 30%) and one for speeds below 50 km/h (approx 26%). So far, based on my own observations I have assumed the PHEV has yet another low water mark for 0 km/h. But I'll keep an eye open from now.

 

[Trex]

Although I don't recall having this happen to me, what I have noticed that when coasting in B0 when using the ICE it does take a while to shut down.

Same here but I find if I give it a momentary "hit" of B2 I can shut it down quicker.

Regards Trex.