Charge Mode vs Save mode on the highway

[zippyflu]

Hello!

Just purchased a 2018 PHEV GT USA (NEW).

Wondering if MPG differs when in Charge Mode vs Save mode on the highway?

 

[ganderpe]

As far as I was observing, the ICE charges with the same Kind in both Modes.
I've seen no Difference in charging while switching from Charge to Save when the paralell Hybrid Mode is on -> Speed greater then 70 km/h.

In seriell Hybrid Mode (Speed lowwer 65 km/h) the Charge Mode results in higher ICE rpm, because the ICE not only provides Power to Drive but also Charges the Batterie.

Peter

 

[user 4416]

That's interesting, I thought the opposite was true.

CHRG mode the ICE runs at its most efficient rpm to charge the battery, the car running on the battery.

SAVE mode the battery is saved, the car runs mostly on the ICE, so revs change with speed.

 

[Regulo]

In Save mode, when the battery charge falls from the level it was at when Save was engaged, the ICE starts to re-charge it. When the battery has reached the original level, the ICE turns off. This cycle continues until Save is turned off. Thus the ICE isn't running continuously in Save mode. In Charge mode, the ICE runs continuously, attempting to actually fully charge the battery. All the above in simple terms, no doubt someone will be along to give the full picture shortly!

 

[jaapv]

As long as you take care to use your electricity for the slower bits and the (sub)urban traffic you'll encounter once you leave the motorway, there is very little if any difference in mpg. However, playing with the charge and save buttons is very handy to make sure that you have the right amount of charge so that you arrive at your next charge point just as the battery is depleted. Also, if you know that the car will face heavy loads on the way, like long climbs, it is best to use Charge to ensure maximum supplementary battery reserve.

 

[ganderpe]

I "plan" my rides always this way:

1. if possible run always on battery
2. if charge is needed, do it with speeds above 70 km/h (paralell mmode)
this way the ICE runs on mostly on low rpm (sweet spot) because its mechanicly coupled with the front axl.
and if there is enough power it will charge the battery with it.
3. better use SAVE mode on low level speeds because it will have slightly lower rpm.

Peter

 

[ThudnBlundr]

Charge and Save modes both use exactly the same logic with how to run the engine, so there will be little difference in revs between Save and Charge on the same piece of road. As mentioned, Save turns off the ICE once the preset SOC is achieved, whereas Charge just runs the ICE till the SOC is nearly full.

As jaapv alluded to, the engine will run differently depending on load and road speed. In Series mode (below ~40mph), the ICE will run solely as a generator with any consequent losses. The ICE can run at any speed depending on the load. In Parallel mode (above ~40mph) the ICE will be connected directly to the front wheels, so will run like a normal car in "top" gear, with the ICE revs mirroring road speed. However, the car will try to make the ICE generate more power than is required, and it will feed this extra power into the generator to recharge the battery. It will try to run the ICE at its most efficient power for the given revs, so improving fuel economy.

So the car will use petrol more efficiently when in Parallel mode. Therefore on a long journey, you should try to use EV (and not run the ICE) when travelling below 40mph, and only use the ICE above 40mph. Also high power demands on the battery are bad for degradation, so try not use EV on the motorway. If you know you've got a long, slow drive at the end of a long drive, by all means use Charge to refill the battery, as it should be more efficient to do that and then use EV in town. Always try to arrive at your next charge point with an empty battery, as that will improve fuel economy.

So I switch Save on as soon as I get on the motorway (once the SOC has dropped a bit) and try not to use battery power at high speeds to preserve the battery. As soon as we slow down, I'll switch off Save.

Of course, you could just leave it in 'D' and let the car do the work. I'm not convinced that the economy would be much worse and it's a lot less hassle

 

[jaapv]

Well, TBH, after piano-playing the car when I just had it, I have settled down to pressing as few buttons as possible nowadays. I just hit "charge" for a long and fast motorway run, "save" for a short or slower one, and have found very little or no difference in mpg whatever I do.
I find that feathering the accelerator and driving with a light right foot in general has far more impact.

 

[ganderpe]

@ThudnBlundr: I agree with you 99%

I've got an Outlander MY16, with (I believe the latest Updates), and I am shure that at least with my car there's a difference in ICE rpm between CHARGE and SAVE mode when in series hybrid mode.
In both Modes the ICE rpm follows more or less the tork demand, while in SAVE mode the Charge Current is more or less zero, in the CHARGE mode there is mostly a Charging Current resulting in a higher rpm.

Peter

 

[jaapv]

That depends entirely on the SOC of the battery. In "save" mode the car will charge up to the preset SOC, in "charge" it will attempt to top up completely. That means that there will be a difference from time to time in ICE load.

 

[littlescrote]

Just because the engine speed is proportional to the vehicle speed in parallel mode, it doesn't mean that the fuel consumption will be. The generator load can be increased as well as the load on the engine from the transmission (e.g. uphill) so although engine rpm may be 'fixed. the throttle opening and injector duration are not, so it's not possible to state that parallel mode at 65 kph is the most efficient operating point.

 

[ThudnBlundr]

Indeed. At each engine speed, there will be a smallish range of load at which the ICE is most efficient. I assume that Mitsubishi try to run the ICE at that load and divert any extra power to charging. Under heavy load, such as on hills and at higher speeds, it will have to run outside that load range, but it will try to use the battery to keep ICE power demands down

 

[ganderpe]

The Sweetspot is always near the max Torque, the lower the rmp the better.
The Problem in the Parallel Mode is that the ICE Power may not be enough to drive the car and the Electric motors have to help driving. Under this circumstance the Batterie will not be charged but emptied and below Batterie SOC of 25% it will switch to seriell mode to charge the Batterie again.

https://www.myoutlanderphev.com/forum/viewtopic.php?f=10&t=3413&start=20

 

[ThudnBlundr]

I've no idea what you mean by sweetspot, but the highest efficiency is not better the lower the rpm. The highest efficiency will be at a fixed rpm and load, with the efficiency dropping off as either of those parameters are changed. Imagine the highest efficiency as the top of a hill, with a drop-off in every direction.

 

[jaapv]

If somebody cares to search the forum, there were a few ICE/load diagrams in the forum a few years ago.

 

[ganderpe]

Sweet Spot is the Range in rpm vs. torque where the efficiency ist best

 

[ganderpe]

..or even better in an Diagram of the GM Volt.
The Enemy of high Efficiency ist high rpm and partial load.

 

[ThudnBlundr]

FWIW I studied this during my degree.

The contour for highest efficiency seems to range from 1500-3500rpm in the Volt. The earlier graph looks more of an idealised map rather than an actual real-life graph. So you can get very high efficiency at a wide range of rpm, and it isn't a case of "the lower the rpm the better" as was stated earlier