Impact of SOC on performance / drivability

[anko]

...
I've no idea why this would be the case, as I understood from other postings that when the battery meter is "empty" there is still a significant amount of usable SOC left (20%?) to cope with power demand whilst the ICE kicks in to keep it charged at around that 20% "empty" level.
...

Neil

A plausible explanation would be that there are situations (moutain, towing) demanding battery's energy during a long time, so the system prevents from this full discharge a long time before reaching 25% SOC ?

It seems (just feeling, no measurements) that as much the SOC is low, as much the engine is trying to charge the battery, or simpy compensate the SOC.
Maybe it simply compensates at 30 % SOC, try to charge at < 30 %, and let discharge at > 30 ? If so, it let discharge the battery differently at 35 % than at 60 % IMHO ...

(all this in Save mode)

This info directly from Mitsubishi was posted on the forum earlier:

At 30% the battery indicator shows 1 segment. Below 30%, no segments are shown.

At speeds below 65 km/h, the car tries to maintain an SOC between 26 and 28 %.
At speeds above 65 km/h, the car tries to maintain an SOC between 31 and 32,5%.

When you keep demanding more power than the ICE can deliver at low SOC, the SOC may go lower.
At 22% the heater and A/C are killed.
At 20% the Limited Driving Capability warning will light up (Turtle mode).
At 13% the car comes to a halt when the petrol tank is empty.

 

[anko]

The battery protection kicks in by turtle mode.

Exactly. At least not yet at 23.5% as my graphics show. Or you must consider 64 kW a drop off. :mrgreen:
.

 

[anko]

I don't think this 25 to 30% floor on the battery charge is there to somehow leave us with something in reserve - I think it is more a case of protecting the battery.

I agree with you, and didn't spoke about "reserve".

The choice of ~25% and 30 % are for the preservation of the battery's life indoubtedly. But we can also consider that the ~15 % to 30 % range is a sort of "reserve", which the system is always trying to fill ...

I may be a matter of semantics, but I like to believe that only the 13 and 20% boundaries are there for the protection of the battery. I like to believe the other boundaries are there, not to protect the battery, but to keep the car drivable. You don't want to hit limited driving mode every time you only think about pushing at the throttle. Imagine driving around with SOC at or just 1% above the level at which the battery needs protection and output is reduced.... Would you dare overtaking? Thanks to these reserves, you can push the throttle a couple of times real deep, hard and long before you do.

 

[Trex]

Hi anko

As I empty the battery quite a bit but only on the highway when empting the drive battery after charging it do you want me to get involved?

Some of the stuff I am reading here I do NOT see on my Phev.

Regards Trex.

 

[Grigou]

And I'am afraid that I don't agree with anko writing "Once the engine is running* the car will try to fulfil the total power demand by the engine alone and potentially even recharge the battery a bit. Only when the engine cannot deliver what is needed for driving (because it is maxed out at 4100 RPM in serial mode or because it is maxed out at the RPM associated with current speed in parallel mode), the battery will assist."

In long uphill driving in Save (Savoy, 2 people on board, slope 5% to 8%) , the motors help the engine. And of course the SOC decreases constantly.

I don't see how what you are saying contradicts with what I am saying. I am pretty sure that on this slope the engine is maxed out given the limited RPM associated with your current speed. I mean, you can see see this already happen on an onramp of a bridge. You do not mention what speed this is, but don't forget, at 100 km/h you have no more than roughly 42 - 45 kW available. At lower speeds it is even less. Check your power meter. Is it 2/3 to 3/4 in the green? Then the E-motors will have to support as your engine is maxed out. Torque Pro will show you a relative load of 100%. Wanna bet?

Anko, my observations about the SOC influence in Savoy passes are typically in Save, at speeds between 30 kph (curves) and 70 kph, in serial mode. So the engine is theorically able to give 60 kW, which is enough to accelerate rather strongly after each airpin curve without help of the battery (theorically), and more than enough to maintain the speed plus charging the battery after the curve.
But the battery is always discharging. So I think that the battery helps more than necessary, just for the comfort of the passengers ... until there is no more SOC to use !

 

[jaapv]

I'm glad it's not only me! Several here such as jaapv are insistent that the SOC has no impact on driveability, but it always seems a bit underpowered to me when running with a flat battery. I suspect it is a question of how hard you drive it - I like the kick up the backside that goes with serial hybrid on a full battery!

And me too. To bad Jaap hasn't commented on my opening post (yet). I was pretty much in his camp (or he in mine) until this morning. We both believed the drivability as well as performance of the car was not impacted by SOC (until you hit 20% SOC).

Now I still believe performance is not impacted (until you hit same 20% SOC) but I think that (perceived) drivability at low speeds is impacted by having the engine run, regardless of whether this is a result of Charge or Save mode or because of low SOC.

Typical scenario to explain:

While towing the caravan, I firmly pull away from the first roundabout in EV mode. This is quiet and seems totally effortless. Big smiles on all faces in the car. At the next roundabout, I pull out in Charge mode. This results in high revving of the engine. And a nasty smell as a bonus. Even with significant SOC. No more smiles on the faces in the car. Except for mine. So, from a comfort perspective, it would be best to disengage Charge mode. But from a "I am towing and therefor I want to have as much SOC as possible" perspective, it is much better to keep Charge mode engaged. As most likely, the battery is being recharged, even while pulling out of the roundabout. This is why there was still a smile on my face. As I was the driver

And yes, because of the high revving in Charge mode and the hard work the engine is delivering, the car may seem underpowered. But don't forget, the same battery power that was available when pulling away from the first roundabout is still there as a reserve just in case the engine couldn't cope.

Oh- I still agree fully. Maybe we should have a couple of cars doing a standing quarter mile side by side at different SOC levels to prove the point.

It is very clear that subjective perception -the balance between ICE and EV will vary with SOC, giving a different feel- will never replace objective measurement.

Anyway, I was not able to participate before as I spent last month in rural Central Africa with virtually no internet access (no electricity, telephone or running water either)

 

[Neverfuel]

I'm glad it's not only me! Several here such as jaapv are insistent that the SOC has no impact on driveability, but it always seems a bit underpowered to me when running with a flat battery. I suspect it is a question of how hard you drive it - I like the kick up the backside that goes with serial hybrid on a full battery!

And me too. To bad Jaap hasn't commented on my opening post (yet). I was pretty much in his camp (or he in mine) until this morning. We both believed the drivability as well as performance of the car was not impacted by SOC (until you hit 20% SOC).

Now I still believe performance is not impacted (until you hit same 20% SOC) but I think that (perceived) drivability at low speeds is impacted by having the engine run, regardless of whether this is a result of Charge or Save mode or because of low SOC.

Typical scenario to explain:

While towing the caravan, I firmly pull away from the first roundabout in EV mode. This is quiet and seems totally effortless. Big smiles on all faces in the car. At the next roundabout, I pull out in Charge mode. This results in high revving of the engine. And a nasty smell as a bonus. Even with significant SOC. No more smiles on the faces in the car. Except for mine. So, from a comfort perspective, it would be best to disengage Charge mode. But from a "I am towing and therefor I want to have as much SOC as possible" perspective, it is much better to keep Charge mode engaged. As most likely, the battery is being recharged, even while pulling out of the roundabout. This is why there was still a smile on my face. As I was the driver

And yes, because of the high revving in Charge mode and the hard work the engine is delivering, the car may seem underpowered. But don't forget, the same battery power that was available when pulling away from the first roundabout is still there as a reserve just in case the engine couldn't cope.

Oh- I still agree fully. Maybe we should have a couple of cars doing a standing quarter mile side by side at different SOC levels to prove the point.

It is very clear that subjective perception -the balance between ICE and EV will vary with SOC, giving a different feel- will never replace objective measurement.

Anyway, I was not able to participate before as I spent last month in rural Central Africa with virtually no internet access (no electricity, telephone or running water either)

Damn good to have you back Jaapv - hope you got some great pictures. I think the forum has missed your calming influence over the last month!

 

[anko]

...do you want me to get involved?

Hi Trex,

Must be a language thing but I do not know how to read this? How do you want me to involve you?

Cheers,

Anko

 

[Trex]

...do you want me to get involved?

Hi Trex,

Must be a language thing but I do not know how to read this? How do you want me to involve you?

Cheers,

Anko

Ok I will take that a yes. :lol:

"Obviously, once you get up to parallel mode speeds things change - engine speed is dictated by road speed. With a low SOC, it does not have the option of dropping down into Serial mode for additional acceleration, so you can find yourself without that electric turbo kick if you floor it at 50 or 60mph."

Never seen that. My Phev can still go into serial mode if the power needs require it.

As I said I hardly ever empty my battery as charge button is pushed once it get there.

I probably should stay out of this discussion.

Regards Trex.

 

[anko]

Oh- I still agree fully....

Hi Jaap, I just said I changed my mind. so, how con you still fully agree? :lol:

But from your writing, I take it you now also agree that SOC can have an impact on EV / Engine balance (and perhaps even high revving?), something easily associated with drivability?

 

[anko]

Ok I will take that a yes. :lol:

Haha. Now I see it :mrgreen: .
to get me ...
me to get ...

Easily missed

Sure, I want you to!

 

[jaapv]

Oh- I still agree fully....

Hi Jaap, I just said I changed my mind. so, how con you still fully agree? :lol:

But from your writing, I take it you now also agree that SOC can have an impact on EV / Engine balance (and perhaps even high revving?), something easily associated with drivability?

I never said the car could not have a different feel in different circumstances. However I think that it was designed not to vary in performance within its normal operating range.

As for high revving, experiences vary so much between users that it is quite impossible to draw any conclusions at all. I found that the venerable practice of "feathering the throttle" (which means pushing the accelerator to obtain a certain speed/acceleration and then easing up marginally without losing the power - I've been doing that since the stone age on cars varying from an A Ford to a Morgan, so it is an automatism for me) works well and reduces racing the ICE significantly.

It is all a question of how sensitively the car is driven. but as I said, without objective performance testing at different SOCs it all remains a matter of opinion from both sides.

 

[anko]

I never said the car could not have a different feel in different circumstances.

Then I must have misinterpreted things you wrote. Sorry

 

[jaapv]

I can be quite woolly in my posts

 

[Ozukus]

Just a thought with regard to this.

Consider a basic everyday Torch.

The Torch operates at its best when brand new batteries are inserted, and then tends to maintain that brightness for a period of time.

At some point the quality of the light drops, and this seems to be exponential as the available power in the battery disipates.

I think this is the best simple example I can make a comparison with as to why higher SOC is better for driveability and performance.

 

[Neverfuel]

I don't notice a difference in performance with a low SOC, however, if I don't know much about the route ahead I get a bit twitchy if I have exhausted the charge. The other day I had forgotten to hit charge before I hit some significant hills in Derbyshire (Slack Hill etc.) and was surprised by the cars performance up hill.

 

[anko]

This morning, I decided to collect some data on my way to work. Started with clearing most of my SOC, partly secondary road, partly motorway:

Then I tried to do a test for Grigou (will come back to that in another topic):

Then, IIRC (as top speed was 162 km GPS) I made a detour to Germany, lost the last bit of SOC and started trashing it on the Autobahn:

Apart from the first section pf this graph where SOC was roughly 32.5%, it was well below 30% most of the time. First of all, notice how battery is over and over discharged with 60 or more kW (sample peeks 70.73 kW at 28.5% SOC, 66.01 kW at 27.5% SOC and 57.95 at 24.5% SOC). Second, notice how the engine manages to maintain SOC at a safe level, even though I was driving as aggressive as traffic allowed :mrgreen:

Finally, when I arrived at my destination town, I kept trashing it at the last couple of kilometers to my work location:

We are definitely in serial mode country here. SOC between 25 and 28% all the time. Again, SOC does not seem to drop any further. Several peaks of 60-and-a-little-bit kW at 26 and 26.5% SOC. I think more wouldn't make sense as the engine produces 60 kW already most of the time and the E-motors cannot handle more than 120 kW.

At 1938, you see battery power kicking in when I floor it at a traffic light (SOC 26.5%) with the engine turned off. Peeks at 55 kW, when the car decides battery alone will not be enough or SOC gets to low and gets the engine involved. When that happens battery support is strongly reduced, I believe because at that speed, the motors cannot handle the combined power of generator and battery.

At 1987 something similar happens. Battery peeks at 60.5 kW @ 25.5% SOC before the engine kicks in.

Like I said, I don't think performance is impacted by low SOC. Drivability? Not during this test, as with this driving style the engine would have started up most of the time anyway.

 

[anko]

Anko, my observations about the SOC influence in Savoy passes are typically in Save, at speeds between 30 kph (curves) and 70 kph, in serial mode. So the engine is theorically able to give 60 kW, which is enough to accelerate rather strongly after each airpin curve without help of the battery (theorically), and more than enough to maintain the speed plus charging the battery after the curve.
But the battery is always discharging. So I think that the battery helps more than necessary, just for the comfort of the passengers ... until there is no more SOC to use !

At 28 km/h the E-motors can absorb all the E-power the engine can produce. At 56 km/h they can absorb all the power the engine and battery can produce together. Also, when I enter the motorway, I must be rather gentle with the throttle to prevent the engine from stepping in. I mean, battery power is easily exhausted, especially when climbing. Are you sure the engine is not maxed out with what you are doing?

 

[Grigou]

Yes I'am pretty sure.
But my new dongle + Torque will help me to be 100 % sure
Not before the end of the year I'am afraid.