Opportunistic Charging in Parallel Mode

[Sunder]

Just another quick question on efficiency.

I have a drive where there's about 15km of 80km/h straight road, no traffic lights, followed by about 5km of 50km/h start and stop traffic. I usually run out of battery about halfway down the 80km/h zone, and it switches into parallel mode, with the occasional tiny top up in series mode. That means by the time I get to the 50km/h zone, the battery is still flat, and it goes into series mode.

I'm just wondering if it would be more efficient if for the last few km @ 80km/h I press the charge button - the motor is already running anyway, I'm just putting additional load on it. That way, I might arrive at the last 5km with 2 or 3 bars - just enough to run 100% electric home.

The reason I think this might be more efficient is that petrol motors are pretty inefficient at light load. To idle (produce no useful power) takes between 0.5-2L per hour. Adding a light load doesn't increase that all that much. If the motor is already running to move the car in parallel mode, what's a tiny bit more load to also charge the battery?

Thoughts, or better still, evidence?

 

[HHL]

The engine never actually idles, it runs at 1100rpm while decelerating or 1700rpm driving in serial mode (higher if more power is required). I doubt that it would be more efficient to charge with the engine. Why don't you just press the save button when the battery is down to a bar or two.

 

[Sunder]

The engine never actually idles, it runs at 1100rpm while decelerating or 1700rpm driving in serial mode (higher if more power is required). I doubt that it would be more efficient to charge with the engine. Why don't you just press the save button when the battery is down to a bar or two.

Thanks HHL, but I think you've misinterpreted my post. It could be badly worded, apologies if it is.

Let me explain it in a less verbose way:

Option 1:
Motor is already running in parallel mode to maintain speed - Burning A litres per hour. Turn on charge now, and make it A + B, where B is the fuel used to raise the load and charge the battery. Use the charge to do the final 5km.

Option 2:
Motor is already running in parallel mode to maintain speed - Burning A litres per hour. Run the battery down flat, when I get to the slow bit, go to series mode, and burn C, where C is the fuel used to run in series mode.

Option 3 (As you mentioned):
Motor is already running in parallel mode to maintain speed - Burning A litres per hour. When the battery gets to 2-3 bars, hit save preventing it from battery assisting, and make the motor run at A + D, where D is the additional load on the motor because the battery won't assist.

Which is smallest, B, C or D?

My suspicion is that it's either B or D. I can't see C being very efficient, because there is a minimum amount of fuel needed even to start the motor.

 

[anko]

The reason I think this might be more efficient is that petrol motors are pretty inefficient at light load. To idle (produce no useful power) takes between 0.5-2L per hour. Adding a light load doesn't increase that all that much. If the motor is already running to move the car in parallel mode, what's a tiny bit more load to also charge the battery?

This always has been and still is my line of thinking.

Has been, because the total amount of revolutions of the engine over the full trip is reduced, and with this the total amount of internal resistance that needs to be overcome. Totally in sync with your statement that a heavier loaded engine runs more efficiently the an idling or not so heavy loaded engine.

Still is, because I am having second thoughts. Although the engine might be running more efficiently, the energy generated during the "charge mode" phase must be stored into the battery and retrieved from the battery during the following "EV phase". This introduces additional losses that you do not have when using the electric power directly when it is being generated. So, the "charge mode" approach my result in a better engine efficiency, but the "no charge mode" approach reduces the amount of (dis)charge losses.

But my gut feeling still says the "charge mode" approach is still king. Especially, because if it wasn't, why would Mitsubishi bother introducing the hysteresis cycle?

 

[anko]

The engine never actually idles, it runs at 1100rpm while decelerating or 1700rpm driving in serial mode (higher if more power is required).

If it was running at 1100 rpm, wouldn't that be idling?

But, as a matter of fact, when coasting in parallel mode, you may find the engine running at an RPM dictated by your current speed, burning just enough fuel to overcome its own internal resistance (at 100 km/h, this is indeed somewhere in the one 2.5 liters / 100 km). I would call that idling too. When the car is in this 'state', the E-motors will actually draw electric power from the battery to eliminate their own (electric) internal resistance.

I doubt that it would be more efficient to charge with the engine. Why don't you just press the save button when the battery is down to a bar or two.

Technically and economically, there is no difference between these two approaches. All you do is play with the (amplitude and wavelength of the) hysteresis cycle. As long as you do not engage Save mode above 50% SOC (on the gauge), as this will limit the maximum charge rate, and thereby reduce the "more efficient running engine" effect Sunder refers to.

 

[HHL]

The engine never actually idles, it runs at 1100rpm while decelerating or 1700rpm driving in serial mode (higher if more power is required).

If it was running at 1100 rpm, wouldn't that be idling?

parallel mode engages at 65 km/h when the battery is around 30% SOC, the engine will turn over at 1700RPM at that speed, at 120km/h it runs at 3200RPM. Think of the fixed ratio behaving much like a car stuck in 4th gear. If it needs more torque at the lower end, i.e flooring it at 70km/h, the electric motors will assist, even if the SOC is lower than 30%. The engine delivers maximum power at 4500 RPM, which equates to 170 km/h.

1200 RPM is not idling, in fact, that is the engine speed in charge mode where it can fill the battery to about 80% in less than an hour.

I really think unless you're towing or about to climb a mountain, just letting the car smarts get on with it is probably the best way to drive it.

 

[anko]

parallel mode engages at 65 km/h when the battery is around 30% SOC, the engine will turn over at 1700RPM at that speed, at 120km/h it runs at 3200RPM. Think of the fixed ratio behaving much like a car stuck in 4th gear. If it needs more torque at the lower end, i.e flooring it at 70km/h, the electric motors will assist, even if the SOC is lower than 30%. The engine delivers maximum power at 4500 RPM, which equates to 170 km/h.

Thanks for clarifying this :lol:

But it was you who said "it runs at 1100rpm while decelerating or 1700rpm driving in serial mode". I guess what you meant was "it runs at 1100rpm while decelerating or 1700rpm or more when driving in parallel mode"

1200 RPM is not idling, in fact, that is the engine speed in charge mode where it can fill the battery to about 80% in less than an hour.

I don't think "idling" has anything to do with RPM. It has to do with "doing something useful or not". Looking at it that way, our engine can idle at (for example) roughly 3200 RPM when coasting at 120 km/h.

 

[TRT]

Just another quick question on efficiency.

I have a drive where there's about 15km of 80km/h straight road, no traffic lights, followed by about 5km of 50km/h start and stop traffic. I usually run out of battery about halfway down the 80km/h zone, and it switches into parallel mode, with the occasional tiny top up in series mode. That means by the time I get to the 50km/h zone, the battery is still flat, and it goes into series mode.

I'm just wondering if it would be more efficient if for the last few km @ 80km/h I press the charge button - the motor is already running anyway, I'm just putting additional load on it. That way, I might arrive at the last 5km with 2 or 3 bars - just enough to run 100% electric home.

The reason I think this might be more efficient is that petrol motors are pretty inefficient at light load. To idle (produce no useful power) takes between 0.5-2L per hour. Adding a light load doesn't increase that all that much. If the motor is already running to move the car in parallel mode, what's a tiny bit more load to also charge the battery?

Thoughts, or better still, evidence?

Mitsubishi make the claim that fiddling with the charge and save buttons will reduce fuel efficiency, and under normal driving conditions it is more economical to let the vehicle control systems choose the appropriate mode. My experience would suggest this is true, although it was not a totally controlled test for speed, traffic conditions, etc. But pretty much the same conditions each way.
Drive from Canberra to Sydney using save mode until I got to Sydney = 6.9 l/100km
Drive from Sydney to Canberra letting vehicle control everything = 6.2 l/100km

[Oh, and I don't use the vehicle displays for measuring anything - these figures are based on petrol put into fuel tank after each leg]

Only time I use charge is when I want to top-up low batteries so I can impress passengers with electric operations.

TRT

 

[anko]

Drive from Canberra to Sydney using save mode until I got to Sydney = 6.9 l/100km
Drive from Sydney to Canberra letting vehicle control everything = 6.2 l/100km

This is 280-ish km, mostly motorway, right? I can imagine trying to beat the system does more bad than good on such a long trip. But here we are talking about saving a little bit of charge for slow speed zones at the end of our trips. And here we can take advantage of our knowledge of what lays ahead of us .....

 

[HHL]

" But pretty much the same conditions each way.
Drive from Canberra to Sydney using save mode until I got to Sydney = 6.9 l/100km
Drive from Sydney to Canberra letting vehicle control everything = 6.2 l/100km

[Oh, and I don't use the vehicle displays for measuring anything - these figures are based on petrol put into fuel tank after each leg]

Only time I use charge is when I want to top-up low batteries so I can impress passengers with electric operations."

That's interesting that it used less going that way, I have done that trip many many times and fuel consumption going to Canberra in my "normal" car has always been 1 to 2 l/100 more as it is a steady climb (about 700m) from Sydney to Canberra, so coming home I always use noticeably less fuel. Would be interesting if you do the same test the other way round. I must say that anything below 7/100 for this type of vehicle is pretty good!

 

[Kim]

Sunder's trip computer should be able to shine a light on this if he drives the same route frequently.

I'd be very interested in the results and the differences between options 1, 2 and 3

 

[Sunder]

Fascinating discussion so far. What the lack of consensus tells me is that the difference is so little that it's hard to get consensus. If it made a huge difference in fuel economy, everyone would have an opinion one way or another.

One thing this car has been good for is to make more more conscious of all my energy usage - both in and out of the car. I accelerate more gently now, and start letting speed drop and braking earlier in the car, and have started putting things on timer and total power off (instead of sleep) outside the car.

I'm not quite turning into a total greenie nut, but it has made me realise every little bit counts

 

[Sunder]

Sunder's trip computer should be able to shine a light on this if he drives the same route frequently.

I do it every fortnight. Can you suggest the best way to track this, since the trip computer measures by L/100km, and doesn't show the actual fuel burned?

 

[westdevon]

My totally unscientific method is to use save if I'm doing 50 mph plus, and make sure the battery is empty by the time I get home unless the journey is short enough to be all EV

 

[anko]

My totally unscientific method is to use save if I'm doing 50 mph plus, and make sure the battery is empty by the time I get home unless the journey is short enough to be all EV

If this would happen very early in your trip, the battery would be near full and you would have transformed your expensive hybrid car into a heavy normal car.

 

[Grigou]

Thanks HHL, but I think you've misinterpreted my post. It could be badly worded, apologies if it is.

Let me explain it in a less verbose way:

Option 1:
Motor is already running in parallel mode to maintain speed - Burning A litres per hour. Turn on charge now, and make it A + B, where B is the fuel used to raise the load and charge the battery. Use the charge to do the final 5km.

Option 2:
Motor is already running in parallel mode to maintain speed - Burning A litres per hour. Run the battery down flat, when I get to the slow bit, go to series mode, and burn C, where C is the fuel used to run in series mode.

Option 3 (As you mentioned):
Motor is already running in parallel mode to maintain speed - Burning A litres per hour. When the battery gets to 2-3 bars, hit save preventing it from battery assisting, and make the motor run at A + D, where D is the additional load on the motor because the battery won't assist.

Which is smallest, B, C or D?

My suspicion is that it's either B or D. I can't see C being very efficient, because there is a minimum amount of fuel needed even to start the motor.

For your trip :
C > B (likely)
B = D (certain)

anko has given the explanations (and not only in this thread )

Save is OK for the trip you've described, but don't hesitate to use Charge in some other circumstances. I do that on long trips to re-build some battery's capacity for further circumstances - towns in EV mode, long uphill in Save mode ...

I keep 3 to 8 bars generally, depending of the trip. And of course, the aim is to have just 1 bar at the end of the trip if you can recharge

 

[Kim]

I do it every fortnight. Can you suggest the best way to track this, since the trip computer measures by L/100km, and doesn't show the actual fuel burned?

I don't know how long your car is parked before your trip, so you might want to hit reset on the ECO INFO display prior to take off.

Rest is easy; the lower your l/100km on your arrival, the better.

If you want to know exactly how much fuel you converted into CO2 and NOx during your trip, you divide the displayed l/100km by 100 and multiply by the km you've actually driven since the reset.

For example:

1.2(l/100km) / 100 x 70(km) = 0.84 liters

 

[gwatpe]

The PHEV seems to burn about 50ml of petrol when it is first started, prior to any generator load being applied. Those times in EV mode, when you accelerate just a tad fast and the ICE starts and then stops a short time later = at least 50ml with possibly no work done at all.

 

[Kim]

Those times in EV mode, when you accelerate just a tad fast and the ICE starts and then stops a short time later = at least 50ml with possibly no work done at all.

Gahww, yea, to my feeling that always stings like a bee.
It accidently happens about two times per month..

 

[Tipper]

Those times in EV mode, when you accelerate just a tad fast and the ICE starts and then stops a short time later = at least 50ml with possibly no work done at all.

Gahww, yea, to my feeling that always stings like a bee.
It accidently happens about two times per month..

And when it does I think ouch!...a stone cold engine start/stop...not good for the moving parts at all!
(I wonder if that's why the oil in my PHEV with only 8k miles on the clock is so grubby compared to that in my old MG with many more miles driven. I'm seriously considering an interim oil/filter change before the next service just to clean it up a bit.)