When to use charge mode to increase fuel efficiency

[user 258]

Hi All,

This has developed from a couple of other postings so I thought I'd create a separate posting to discuss just this.

When making a journey that is longer that you can manage on battery alone the general advice is to use EV to the motorway, save mode on the motorway, and then battery once you leave the motorway. However, I feel that this is too simplistic and unless the total urban part of your journey was about 30 miles would not give the best economy.

Example 1)
100 mile journey - 20 miles to the motorway - 60 miles on the motorway - 20 miles from the motorway to destination
I would use EV mode to get to the motorway, engage charge mode once on the motorway ONLY until the battery reached 66% and then engage save mode for the remainder of the motorway, and again use purely battery mode once leaving the motorway for the final 20 miles of urban driving. Just using save mode on the motorway would leave you with 10 miles battery range to complete a 20 mile urban journey causing the car to run in series hybrid mode which is its least efficient mode.

Example 2)
60 mile journey - 10 miles to the motorway - 40 miles on the motorway - 10 miles from motorway to destination
Just using save mode on the motorway would result in completing the journey with 10 miles EV range remaining which is clearly sub-optimal. I would use EV mode on the motorway when the speed is reduced (heavy traffic/roadworks etc) or when descending inclines when minimal power can be used to maintain speed with the intention of ONLY having sufficient battery left when leaving the motorway to complete the urban part. The objective is to prevent the engine running when little power is required which is the engines least efficient mode (especially when coupled with series hybrid mode at speeds below about 42mph).

Example 3)
An urban journey that is in excess of the EV range
I'm still working this out the best technique but the principle I'm trying to apply is to ensure the car is in EV mode when minimal power is required (cruising at 30-40mph for example) and when more power is required such as accelerating away from lights upto 40mph select charge mode. Charge mode should NOT be used when minimal power is needed (i.e. do NOT just leave charge mode selected even when cruising at 30mph or stopped in traffic). Again, ending the journey with an empty battery.

The idea is to make the engine work a little harder when it HAS to be running anyway in order to have battery available to turn the engine off when little power is required. While charging from the engine is reasonably inefficient, running the engine during low power output is even LESS efficient.

Let me know your thoughts please.

Kind regards,
Mark

 

[jaapv]

I tried that. It doesn't work. Charge is always less efficient.
Two reasons: Series hybrid is more efficient than parallel hybrid, as the engine can run at optimum speed for the power demand and the car will use an extra 7% of battery power if needed even if the battery is officially empty.
Ending the journey with an empty battery is always good.
I find the car is at its most efficient if you normally let it do it's own thing, just switching to save when you enter the motorway. Charge is only useful if you want full electric reserves, for instance in the mountains, or if you have an emission- controlled zone ahead.

 

[user 258]

I tried that. It doesn't work. Charge is always less efficient.
Two reasons: Series hybrid is more efficient than parallel hybrid, as the engine can run at optimum speed for the power demand.

Hi jaapv

Thanks for responding. I believe that using charge mode intelligently can improve efficiency.

I think you are mistaken about series hybrid mode. In series hybrid mode the engine can rev high and therefore produce more power, but that isn't the same as being more efficient. It has to convert movement from the engine into electrical energy and then the electric motors have to convert that electrical energy back to movement and those conversions lose energy along the way. In parallel hybrid mode the engine drives the wheels directly so those conversion losses are avoided. This is why the preferred mode at speeds above about 40mph is parallel hybrid as it gives the best fuel economy.

That is a large part of my reasoning that using charge mode when the engine needs to run anyway is preferable to having to ruin in series hybrid mode die to a depleted battery.

Kind regards
Mark

 

[jaapv]

I'll be interested to see your results, if you are able to quantify them.
It is not correct to say that the engine uses excess energy to produce electricity.
The fuel economy of an engine is also determined by load, so running at a certain RPM and generating electricity will use more fuel than running at the RPM without generating electricity. As the RPM is determined by car speed the engine will not be running at the most economical RPM.
In series hybrid the computer will determine the most economical revs for the power demand.

 

[ufo]

Hi All,

This has developed from a couple of other postings so I thought I'd create a separate posting to discuss just this.

When making a journey that is longer that you can manage on battery alone the general advice is to use EV to the motorway, save mode on the motorway, and then battery once you leave the motorway. However, I feel that this is too simplistic and unless the total urban part of your journey was about 30 miles would not give the best economy.

Example 1)
100 mile journey - 20 miles to the motorway - 60 miles on the motorway - 20 miles from the motorway to destination
I would use EV mode to get to the motorway, engage charge mode once on the motorway ONLY until the battery reached 66% and then engage save mode for the remainder of the motorway, and again use purely battery mode once leaving the motorway for the final 20 miles of urban driving. Just using save mode on the motorway would leave you with 10 miles battery range to complete a 20 mile urban journey causing the car to run in series hybrid mode which is its least efficient mode.

Example 2)
60 mile journey - 10 miles to the motorway - 40 miles on the motorway - 10 miles from motorway to destination
Just using save mode on the motorway would result in completing the journey with 10 miles EV range remaining which is clearly sub-optimal. I would use EV mode on the motorway when the speed is reduced (heavy traffic/roadworks etc) or when descending inclines when minimal power can be used to maintain speed with the intention of ONLY having sufficient battery left when leaving the motorway to complete the urban part. The objective is to prevent the engine running when little power is required which is the engines least efficient mode (especially when coupled with series hybrid mode at speeds below about 42mph).

Example 3)
An urban journey that is in excess of the EV range
I'm still working this out the best technique but the principle I'm trying to apply is to ensure the car is in EV mode when minimal power is required (cruising at 30-40mph for example) and when more power is required such as accelerating away from lights upto 40mph select charge mode. Charge mode should NOT be used when minimal power is needed (i.e. do NOT just leave charge mode selected even when cruising at 30mph or stopped in traffic). Again, ending the journey with an empty battery.

The idea is to make the engine work a little harder when it HAS to be running anyway in order to have battery available to turn the engine off when little power is required. While charging from the engine is reasonably inefficient, running the engine during low power output is even LESS efficient.

Let me know your thoughts please.

Kind regards,
Mark

Hi Mark,

I saw your comment about fuel efficiency under the thread "Rockford Fosgate System" in Technical Discussions section, thanks for that.

I am writing my experience that I included in that thread also here;

Yesterday I did app. 160 kms about 100 km on freeway at 100-110 kms/hr. and 60 km city driving. Started with full battery with 50 km EV range, by the time I got to freeway I had 32 EV range left, then hit the save button until freeway driving finished (50 km). During that 50 km PHEV was sometimes running on pure EV, sometimes ICE running, charging the drive battery and driving front wheels, sometimes just charging, sometimes just driving front wheels no charging and this was running on ACC (Adaptive Cruise Control) all the way. At the end when I reach destination city and got out of save mode and switched to pure EV, I had still 32 km pure EV range left. Driving in pure EV mode in destination City, I depleted all of the EV range and when I got back to freeway, I hit the charge button.
PHEV ran all the way back 50 km this way again on ACC. ICE was running all the time (whereas with save mode it would cut in & out many times), sometimes running alone just driving front wheels, sometimes charging drive battery at the same time, sometimes while ICE is driving front wheels drive battery running rear wheels. This way when I finished freeway driving my pure EV range increased from 0 to 16 kms and this was enough to get me back home on pure EV. I had only 1 km pure EV range when I got back home and PHEV was reporting my petrol consumption was 3.3 lt/100 km which is pretty good.

Your General comment in your above post using only save mode on motorway being too simplistic is right. One should always combine save & charge mode depending on percentage of urban and motorway/freeway driving to be done on each trip. That’s what I was trying to achieve in my above experience.

Example 1) You are 100% right.

Example 2) I think you made mistake here. Completing 10 miles to motorway will leave you 22 mile EV range not 10 (assuming you left with full charge) So if you use save mode, you will still have 22 mile EV range when you finish motorway and start urban travel. So no problems covering last 10 mile urban travel on pure EV. Since you would still have 12 mile EV range when you reach your destination it is not the most efficient way if you aim to have zero charge when you reach your destination.

Example 3) In this scenario, previously I thought it would be best to leave PHEV to manage the situation, i.e. run on pure EV until battery is depleted and let PHEV do whatever it wants to do. I tried this approach. What happened was, it ran on Pure EV until battery was depleted and started charging battery in series mode but stopped charging very quickly (EV range display has not changed from -- to anything) and only after a few hundred meters start charging again and then stopped again and started charging again and kept going on like that. I suppose this is not good at all for ICE to start and stop so frequently like this in the long run. Also what I noticed doing above is that when more power is needed such as going steep uphill, it seems like it puts too much strain on ICE (you can here ICE labouring, audible ICE noise, actually this is the only time ICE was audible so far in my experience with PHEV) because there is no charge left in battery and ICE has to supply all the power needed and this situation puts a lot of strain on ICE because PHEV cannot get any power from drive battery and has to rely on ICE only. So I think best approach in this scenario would be to use pure EV range until battery range comes down to app. 15-20% than switch to save mode. This way PHEV decides when to turn on ICE but also always has 15-20% battery power to supplement ICE in case of increased power is needed. Also because there is still some reserve power is available with drive battery, I would assume it would not turn ICE on & off so frantically. One can also discuss if it would be better to turn charge mode on instead of save mode in this scenario. It might be better to use charge if ICE keeps switching on & off frantically in save mode even though there is still 15-20 % battery capacity is left. But then you have to closely watch the charge amount because any extra capacity that is generated above 15-20 % battery level would be more expensive than from what you would obtain from a plug-in source. Of course jury is out there, would like to hear what other owners’ experience and recommendations are. Also what percentage of EV power rather than 15-20% to leave as reserve is open to discussion?

Cheers

 

[jaapv]

The assumption that the ICE has to supply all the power when the battery is "empty" is incorrect.
When the battery indicates --.-- there is 20% of charge left in the battery. The car will still use the battery power to supplement the ICE power and will charge the battery up to 20% again inbetween when this is efficient.
The lower limit for this mode is 13% battery charge. Under 13% (a rare occurrence) the car will go into emergency power mode, supplying limited driving power, displaying a turtle symbol on the dash and charging up to 20% as soon as possible, after which it will go into the standard running mode again.
The sound of the engine revving is not the engine labouring. In this case there is no connection between the ICE and the wheels - no gearbox, remember. It is the ICE running up to the most efficient charging state.
As for the impact of the engine starting up and stopping, this has been engineered in and the system is conceived for 300.000 Km.
The efficiency of the engine whilst charging is exactlythe same as running the car in "empty" mode as it is doing exactly the same switching as you are doing yourself, except at higher speeds, where the coupling of engine and wheels will be less efficient than running the car in series hybrid mode. (the speed is low enough in that case to let the choose the optimal engine speed for charging as it is running independently of the wheels) So it is more efficient letting the car regulate the charging at lower speeds in series than to force it to charge at higher speeds in parallel.

After more than 20.000 Kms of experimenting my conclusion is that button pushing will result in more fuel consumption overall. Just tell the car you are on the Motorway by pushing "save", take care to arrive empty of electricity and only use "charge" in exceptional circumstances. The computers and goblins in the car are smarter than you are

 

[user 258]

I'll be interested to see your results, if you are able to quantify them.
It is not correct to say that the engine uses excess energy to produce electricity.
The fuel economy of an engine is also determined by load, so running at a certain RPM and generating electricity will use more fuel than running at the RPM without generating electricity. As the RPM is determined by car speed the engine will not be running at the most economical RPM.
In series hybrid the computer will determine the most economical revs for the power demand.

Hi jaapv

I agree with every word you have said above. But you have failed to understand that 1) parallel hybrid mode is more efficient than series hybrid mode and this is FACT and 2) that while charging is inefficient running in series hybrid mode with a flat battery is even more inefficient.

Kind regards
Mark

 

[user 258]

Sorry for poor quoting but I'm using my phone on holiday.

Example 2) I think you made mistake here. Completing 10 miles to motorway will leave you 22 mile EV range not 10 (assuming you left with full charge) So if you use save mode, you will still have 22 mile EV range when you finish motorway and start urban travel. So no problems covering last 10 mile urban travel on pure EV. Since you would still have 12 mile EV range when you reach your destination it is not the most efficient way if you aim to have zero charge when you reach your destination.

That was exactly my point. Just using save mode on the motorway would mean you arrive at the destination with unused battery which means you used more petrol than you needed to. This is resolved by using EV on the motorway in order to arrive with an almost depleted battery.

jaapv resolved perfectly to your other points. Now if I could only convince him that series hybrid mode is LESS efficient than parallel hybrid mode

Kind regards
Mark

 

[jaapv]

Mark, how do you arrive at this fact. In series parallel mode the ICE runs only to drive the generator and can be optimized for that use by the motormanagement and EV computer systems.
In parallel hybrid mode the ICE is used primarily to drive the front wheels and is coupled directly, no gearbox.. The driving of the generator is an extra task which will often be done at suboptimum revs etc. for the power demand. above 120 Km/h it will not charge the battery at all.

As for series hybrid. The car cannot be driven in pure EV mode. The power the electric motors can bring to the wheels is 120 kW.
The maximum power drain the battery can deliver is 60 kW
Thus as soon as you demand power over 60 kW from the electrical drive train, the ICE will come in in series hybrid mode to supply the failing 60 kW. That is the revving sound one hears.

And yes, the aim is to arrive at the destination with the battery flat, provided you are able to charge.
Interesting point, though: after the battery indicates --.--, you will be able to run 3-5 kms in nearly pure EV mode with the ICE coming in only sporadically.

Using "save" is for extended Motorway journeys, when you will have secondary roads/urban driving at the end to use up the electricity, as it is more efficient to use EV driving in urban traffic than driving at motorway speeds. Driving 10 miles on the Motorway on electric power will use up not 10 miles of range, but more like 20.

Using "charge" will make the car drink petrol like a Liverpool fan drinks beer...

 

[user 258]

Mark, how do you arrive at this fact.

Hi jaapv
I agree with virtually everything you wrote. Your knowledge is very good, apart from this one thing.
It is a scientific fact that converting movement to electricity and then converting that electricity back to movement is not 100% efficient as energy is lost at each stage. Having the engine drive the wheels directly avoids these losses. That is the science. That is why the default mode over about 42mph IS parallel hybrid mode. Mitsubishi could very easily have made series hybrid mode the default at all speeds below 74mph. If it was more efficient they would have. I also have a recollection that when the Volt/Ampera came out it did only have series hybrid mode and fuel economy suffered so they modified the design by adding a direct engine to wheel drive aka parallel hybrid mode.
Kind regards
Mark

 

[ufo]

Sorry for poor quoting but I'm using my phone on holiday.

Example 2) I think you made mistake here. Completing 10 miles to motorway will leave you 22 mile EV range not 10 (assuming you left with full charge) So if you use save mode, you will still have 22 mile EV range when you finish motorway and start urban travel. So no problems covering last 10 mile urban travel on pure EV. Since you would still have 12 mile EV range when you reach your destination it is not the most efficient way if you aim to have zero charge when you reach your destination.

That was exactly my point. Just using save mode on the motorway would mean you arrive at the destination with unused battery which means you used more petrol than you needed to. This is resolved by using EV on the motorway in order to arrive with an almost depleted battery.

Oh, OK, so we are saying the same thing.

In general we (you, Jaapv and me) are saying similar things. But you can't achieve best just by running PHEV on save mode on highway. In my example if I were to run PHEV on save mode on highway section of the return trip, I would have arrived with no battery power to the last urban section of the trip and PHEV would have to run in series all the time, ICE kicking in & out frantically. Jappv, yes the vehicle might have been designed with this in mind but why would I put extra strain on it where I can avoid it? In terms of durabilty/longevity, it is always much better to run an ICE continously than frantic start and stops.
When it comes to the point which mode being more efficient (series or paralel) , I think it all depends on the conditions at the time such as, speed, urban or highway travel, battery power remaining and how the remaining portion of the travel will be completed. Without considering these factors one can claim one mode being more efficient than the other just in terms of pure enginering but that's not the whole picture, all the above factors must be included to decide which mode is more effective for the given journey. PHEV supposed to do this automatically and probably it does but the question is, can we better it by selecting modes depending on the travel itinary. Even though PHEV has a lot of computer power to select the most efficient propulsion method for a given time, it has no idea about what the future portion of the travel will be like.

 

[Fergee]

I have now done 800 miles in mine including a 440 mile round trip today to London and this is what I have discovered. Let me just clarify the findings below first:-

All mpg figures are base on-

No Aircon on just the fan
Running in Eco mode
Radio on
70 mph when on the motorway with cruise control on.

Firstly I'm averaging about 39mpg on save mode whilst on the motorway ( I have now done 500 ish motorway miles in save mode)

I ran the car on the M6 Toll today on charge for 10 miles and got 25.3 mpg at steady state 70mph with an uplift in my EV range of 7 miles(0-7)

In pure EV mode my electricity cost is 40% of the diesel cost (46mpg AudiA4)

Therefore if we look at the actual costs of my charge mode motorway run today the 10 miles has cost me £2.36 (petrol cost of £1.31) but I gained 7 miles of EV a benefit. Therefore what I can conclude is that if I had of needed the 7 miles at the end of a journey the actual cost to me would have been £2.36. Now if I had of just left it and done the last 7 miles on the ICE then the motorway cost would have been £1.52 at 39mpg and £1.39 for the remaining 7 miles (best guess of 30 mpg in town) a total cost of £2.91.

What we can therefore conclude from the very small and unscientific test is that I would have saved £0.55. So to my surprise I have concluded that it is cheaper to charge to ensure the urban miles are done in EV mode.

 

[davewigan]

What do you average on the motorway in hybrid mode.

Does motorway driving in ev mode significantly reduce the range?

On such long round trips is it not worth stopping at one of the free motorway charging points.... Assuming you needed a comfort break.. A cup of coffee or just stretch your legs

 

[Fergee]

I generally run in save mode on the motorway unless I need to burn off extra Electricty to arrive home with the EV range at Zero.

As I said I average 39 mpg on the motorway in save mode.

I have stopped off and charged at several free Ecotricity charging points, Charnock being one of them Dave. It has taken on average 22 minutes to charge from showing 0 miles on the range ( actually shows that the battery is at 30%) when you plug it in to 23 miles when it is complete. I'm pretty keen on using these at the minute but I'm sure the notion will wear off, and I really only intend to use them when stopping for a coffee.

Just to give you a bit of additional info, I'm no eco warrior and only got this vehicle to save just over £2000 per annum in BIK tax, as well as marketing for my company. I have also noticed that some of the Ecotricity stations don't require you to validate the charge with your card (this certainly applies to Charnock)

 

[user 258]

Hi all

Great stuff. While unscientific your sample of one seems to support the theory of using charge mode when in parallel hybrid mode to enable running in EV mode on the urban part of trips which would otherwise be done in the inefficient serial hybrid mode.

I would also support "about" 40mpg on the motorway at 65-70 mph with A/C off (fan on).

As an aside, it is possible to set it so the A/C stays off when you turn climate control on by pressing and holding the cooler button in for about 10 seconds.

Kind regards
Mark

 

[jaapv]

One point: Mitsubishi warns that frequent forced charging will shorten the lifespan of the batteries.

 

[user 258]

One point: Mitsubishi warns that frequent forced charging will shorten the lifespan of the batteries.

Hi jaapv

By forced charging you mean the charge to 80% in 30 minutes rapid charging? Yes, I've read that too. They advise against using this on a regular basis. I'm still looking to try it out for novelty value though

Kind regards
Mark

 

[jaapv]

Exactly. Just sayin'
I found over about 9.000Km of motorway driving that I get the best economy by using save instead of charge, but then the normal driving speed I use is considerably higher than in the UK. Our max speed is 130 Kph, as on large stretches of Autobahn. As the car will not charge anyway at that speed there is a different situation. And it is not particularly economical either.

 

[ufo]

Exactly. Just sayin'
I found over about 9.000Km of motorway driving that I get the best economy by using save instead of charge, but then the normal driving speed I use is considerably higher than in the UK. Our max speed is 130 Kph, as on large stretches of Autobahn. As the car will not charge anyway at that speed there is a different situation. And it is not particularly economical either.

Again what you are saying basically supports the fact that what mode to use depends on a lot of factors as I said before. One of them is also the speed, max speed is 110 Kms/hr on freeways in Australia and it is even less on other highways, so one can charge the battery while running at these speeds whereas in your case, you are right, PHEV can not charge doing 130 kms/hour. But again what type of driving to be done in later stages of the trip is also important, i.e. you want to save some battery for pure EV use or not.

 

[thegurio]

I would also support "about" 40mpg on the motorway at 65-70 mph with A/C off (fan on).

How do you guys drive to get this? Are you the type who overtakes at every chance? Or the type who will sit behind until a double lane overtaking section? Or is it 50mph (80kmh) and take the easy way there?