Advise on how to get best MPG?

[jaapv]

I admit to not having steep uphill runs here , but I cannot say mine behaves like that. Obviously there are quite a few variables involved in the car going into high-power series hybrid mode, but I have never observed this behaviour in nearly 30.000 Km and over a year of use.

 

[DrSlackBladder]

I have experienced what maby reports....moderate to steep inclines on a depleted battery are certainly an uncomfortable struggle for the screaming 2 litre petrol engine (of course not surprising given the size/weight of the PHEV). I found this over the Christmas break when visiting some friends who live in the highest village of North Wales! I did that return journey twice over the holiday; the second time I saved battery until I got to the hills, so much better!

 

[anko]

I think we could say: with 30% SOC the car does not handle different than it does with 80% SOC, but starting off with 80% SOC it takes longer before you reach such a low SOC that the car will start to behave different.

To prevent reaching such low SOC in challenging circumstances, you would be better off running in Charge mode than Save mode. In Save mode, your SOC may drop below the set point when driving uphill, but the lost SOC will not be recovered going down on the other side of the hill.

Edit: "with 30% SOC the car " should be "with any SOC above 30% SOC the car ".

 

[anko]

I have experienced what maby reports....moderate to steep inclines on a depleted battery are certainly an uncomfortable struggle for the screaming 2 litre petrol engine (of course not surprising given the size/weight of the PHEV). I found this over the Christmas break when visiting some friends who live in the highest village of North Wales! I did that return journey twice over the holiday; the second time I saved battery until I got to the hills, so much better!

How fast were you driving up hill, if I may ask?

 

[DrSlackBladder]

I have experienced what maby reports....moderate to steep inclines on a depleted battery are certainly an uncomfortable struggle for the screaming 2 litre petrol engine (of course not surprising given the size/weight of the PHEV). I found this over the Christmas break when visiting some friends who live in the highest village of North Wales! I did that return journey twice over the holiday; the second time I saved battery until I got to the hills, so much better!

How fast were you driving up hill, if I may ask?

The journey I spoke about is mostly B roads with national speed limit, some twisty steep parts at 20 mph, some straight moderate inclines at 40-50 mph. It's clearly best to have both motors and engine pulling 1900 kg up hill at any speed!

 

[maby]

I have experienced what maby reports....moderate to steep inclines on a depleted battery are certainly an uncomfortable struggle for the screaming 2 litre petrol engine (of course not surprising given the size/weight of the PHEV). I found this over the Christmas break when visiting some friends who live in the highest village of North Wales! I did that return journey twice over the holiday; the second time I saved battery until I got to the hills, so much better!

How fast were you driving up hill, if I may ask?

In my experience, the issue is with getting up to sufficient speed for the car to switch to parallel hybrid mode. Attempting either significant acceleration (as in trying to beat another vehicle off the lights because you have chosen the wrong lane and need to cross over) or proceeding from a standing start up a moderately steep hill with a target speed of 30 or 40mph are both uncomfortable exercises with a normal flat battery. The car is underpowered and the engine races to drive the generator sufficiently to provide the required power in serial hybrid mode. Once you make it up to something over 40mph, the car can transition to parallel hybrid and it runs smoothly. This is very much the same as a Prius with a flat battery - I user to dread trying to climb the hill out of our town in our Prius if the battery was showing minimum.

 

[jaapv]

Yes-but it will do that regrdless of battery state. The generator kicks in because the battery cannot provide enough power for fully running electromotors, regardless of state of charge Remember, "empty"is not empty....

 

[maby]

Yes-but it will do that regrdless of battery state. The generator kicks in because the battery cannot provide enough power for fully running electromotors, regardless of state of charge Remember, "empty"is not empty....

Quite true, but the demand placed on the generator seems to be significantly greater when the battery is at minimum than it does with a significant level of charge in the battery. With the instrumentation available, it is difficult to be objective about this, so it is an opinion based on perception of engine note and available acceleration. I'm not sure it is something to get too exercised about - my strategy result in a minor reduction in fuel economy under some circumstances, but the difference will be small and only really apply to trips that start with twenty miles or more on slow roads and end with some tens of miles of high speed motorway driving. Under those circumstances, I will use up the last of my battery at motorway speeds that are perhaps not the best way to use it.

P.S. to this - with a practical example... I had to go out this lunchtime to deliver some documents to a neighbouring town. I had arrived home last night late and tired and didn't bother plugging up, so my entire journey today was on an empty battery. It handled fine to start with, but the road back home includes an up-hill of perhaps half a mile or so which is quite steep, starting from traffic lights at the bottom. It's a 30mph speed limit, so no possibility of getting into parallel hybrid mode. Everything was fine at the beginning - car in serial hybrid and the energy flow display showing drive from both the generator and battery with the engine running at a reasonably low RPM. I was able to accelerate to close to 30mph and the car was relaxed, but as I approached the top - still at the same speed - the engine revs kicked up significantly. The revs stayed at this higher level after I got to the top of the hill onto the flat and then joined a dual carriageway with a 70mph speed limit - accelerating away was again met with significant increases in engine revs. It was only after a mile or two running that things got back to normal.

 

[jaapv]

Agreed, it is rather marginal.
I have never seen an output curve of the batteries, but I would imagine it to be fairly linear. However, as the electromotors can deliver 120 KW and the battery only half that, the engine will always have to run (nearly) flat out if you demand full power, whatever the state of charge.
The situation you describe probably signified the battery getting close to its lowest state of charge and the engine cutting in to recharge it to its normal "empty"state.

 

[anko]

... and didn't bother plugging up, ...

Shame on you :lol:

... running at a reasonably low RPM.

How do you tell, with the instrumentation available? By hearing?

Everything was fine at the beginning - car in serial hybrid and the energy flow display showing drive from both the generator and battery with the engine running at a reasonably low RPM.

That is weird. I would expect that, if the battery could cope by itself, the engine would be shut off. And if the battery couldn't cope, the engine would do the larger part of the work and the battery would only assist. Resulting in high revs. And it would make sense for the car to do so, as it would be silly for the car to run on batteries, only assisted by the engine. I mean, when the engine is running anyway, why not make it work?

If the speed was higher, it would sound like going uphill in parallel mode assisted by the battery and then disengaging the parallel mode as the battery was depleted. But with that speed, indeed that wouldn't name sense.

 

[anko]

However, as the electromotors can deliver 120 KW and the battery only half that, the engine will always have to run (nearly) flat out if you demand full power, whatever the state of charge.
The situation you describe probably signified the battery getting close to its lowest state of charge and the engine cutting in to recharge it to its normal "empty"state.

This seems like a contradiction. First, you say (and I agree) that you would expect the engine would run flat out if you demand full power. Then you say then battery got depleted to a below 'zero' SOC while the engine was apparently not going full throttle. But why would it deplete the battery without first maxing out the engine?

 

[jaapv]

Yep- you've got a point there. One would expect to have the engine runnnig at max power before. Muddled thinking... Maybe the incline gets steeper towards the end.

 

[anko]

Maybe the incline gets steeper towards the end.

Confusing. Even then, if the incline got steeper, you would expect the engine to run flat out, before power was drained from the battery. Apparently, power was already being drained from the battery, while the engine wasn't maxed out?

 

[maby]

... and didn't bother plugging up, ...

Shame on you :lol:

... running at a reasonably low RPM.

How do you tell, with the instrumentation available? By hearing?

Everything was fine at the beginning - car in serial hybrid and the energy flow display showing drive from both the generator and battery with the engine running at a reasonably low RPM.

That is weird. I would expect that, if the battery could cope by itself, the engine would be shut off. And if the battery couldn't cope, the engine would do the larger part of the work and the battery would only assist. Resulting in high revs. And it would make sense for the car to do so, as it would be silly for the car to run on batteries, only assisted by the engine. I mean, when the engine is running anyway, why not make it work?

If the speed was higher, it would sound like going uphill in parallel mode assisted by the battery and then disengaging the parallel mode as the battery was depleted. But with that speed, indeed that wouldn't name sense.

I think this is only true while there is a moderate amount of charge in the battery and the systems are not set to "Save" mode.

As has rightly been pointed out, the notional "flat" for the battery is actually something like 20% charge. When you get down to that level, the control systems will take steps to keep it around there - some patterns of usage can defeat this and you can get down to the "Turtle" mode at which point more stringent protection measures kick in to avoid damage to the batteries and make sure you are not left with a car that has such a flat battery that it simply cannot restart the engine. The default behaviour once the battery gets down to 20% is to allow it to oscillate up ad down a bit so that you still get the hybrid efficiency and the boost effect of the battery and do not have to race the engine for short power surges.

Once the battery has gone flat, the control systems will not recharge it significantly unless you hit the "Charge" button. I don't think "Charge" does anything particularly special - it just sets the flat battery target charge level up to around 80% from the default 20% - hence the engine keeps on running longer but the behaviour is pretty much the same as you would get if you turtled it without charge selected - all it does is to reset the minimum charge level.

I believe the same is true for the "Save" button - when you press it, it has the effect of shifting the minimum charge level up from 20% to whatever level it is at the time you press the button. However, I do believe that if you hit Save with a half charged battery, the control systems give themselves more leeway than they do if the battery is allowed to run down in normal mode. I spend a lot of my time driving in Save with a half charged battery and the level seems to be allowed to drop quite a lot with it being subsequently brought back up to the target charge level in a fairly relaxed manner.

So, in summary, I think the explanation of the behaviour that I reported is that when I started climbing the hill, the battery was sitting at the notional "flat" level, but the control systems allowed it to be depleted a bit more, providing a lot of the motive power to climb the hill and the engine running at relatively low revs to support the batteries. By the time I got half way up the hill, this load on the battery was pulling it down more than the control algorithm would permit and the systems kicked up the engine revs, taking more power from the generator and reducing the drain on the battery. If the hill had been longer and steeper, it may possibly have pulled the battery down to turtle levels and the engine would have been racing.

I compare the behaviour of the Outlander with that of the Prius - OK, the Prius has a much smaller battery, but its strategy is similar to that of an Outlander either in save mode or with a flat battery. Both cars are true petrol electric hybrids under these conditions - they play the petrol engine off against the batteries and motors to improve performance and fuel economy. At least with the Outlander in serial hybrid mode, the drive to the wheels is always electric - both the Outlander and the Prius are drawing power from the battery for preference, but using the petrol engine and generator to keep the battery charge close to some target level. Short term demand for extra power is satisfied from the battery provided there is sufficient charge in it - once the level drops too low, that demand has to be satisfied mostly from the generator and the engine races. This is much more noticeable on the Prius with its small battery pack - stop-start driving or a long hill climb will rapidly pull the charge level down to the absolute minimum permissible at which point the engine screams and performance drops off dramatically. I believe that the same happens to an Outlander, but the higher battery capacity makes it less dramatic. However, using save to bring the lower charge limit up does seem to give the car a lot more headroom and it takes a lot more abuse to drive it into screaming engine mode.

Looking at jaapv's point - maximum engine power is not the same as maximum engine revs. The efficiency of a hybrid comes from managing the engine power by using the batteries almost as an electric turbo-charger to level out the demands on the engine.

 

[maby]

Maybe the incline gets steeper towards the end.

Confusing. Even then, if the incline got steeper, you would expect the engine to run flat out, before power was drained from the battery. Apparently, power was already being drained from the battery, while the engine wasn't maxed out?

Of course it was - that is the way that serial hybrid works - the generator charges the batteries and the motors draw from the batteries - the power flow is adjusted to keep the charge level close to whatever floor has been set, but fluctuations in power demand are met from the batteries as first choice - the engine RPM is increased if necessary to meet longer term demand. This is what is responsible for the improved fuel economy of a hybrid - decoupling your right foot from the petrol supply.

 

[anko]

[that is the way that serial hybrid works - the generator charges the batteries and the motors draw from the batteries

To be honest, I tend to disagree. In series mode, the engine is supposed power to drive the car AND charge the battery. So that after a while you can drive in EV mode for a while. Just like it does in parallel mode. Let's not forget, once the engine is started most of the inefficiency of the engine is already occurring. Better to make the engine work harder for a shorter time than less hard for a longer time. That is where the efficiency gain comes from, IMHO.

Also, despite the graphics on the dashboard, I don't think the engine is providing power to the battery and the battery to the wheels at the same time. Engine power is going to the wheels and any power surplus goes to the battery / shortage comes from the battery.

 

[jaapv]

Looking at jaapv's point - maximum engine power is not the same as maximum engine revs. The efficiency of a hybrid comes from managing the engine power by using the batteries almost as an electric turbo-charger to level out the demands on the engine.

That is true - the engine when it seems to be at max revs is, I read somewhere, running at 4500 RPM. I don't think it will run up to its maximum rev in series mode - there would be no sense in doing so. Anyway, when I floor the "accelerator" the ICE will always run up to max, whatever the state of the battery. I'll have to try it out, but I think it will even switch from parallel to series if possible.
Confession - after three months I switched away from the drive information panels as I found that knowing which drive mode the car is in does not add anything relevant.

 

[anko]

Looking at jaapv's point - maximum engine power is not the same as maximum engine revs. The efficiency of a hybrid comes from managing the engine power by using the batteries almost as an electric turbo-charger to level out the demands on the engine.

That is true - the engine when it seems to be at max revs is, I read somewhere, running at 4500 RPM. I don't think it will run up to its maximum rev in series mode - there would be no sense in doing so. Anyway, when I floor the "accelerator" the ICE will always run up to max, whatever the state of the battery. I'll have to try it out, but I think it will even switch from parallel to series if possible.
Confession - after three months I switched away from the drive information panels as I found that knowing which drive mode the car is in does not add anything relevant.

In case of the PHEV max engine power is as good as synonym to max engine revs: 89 kW @ 4500. In series mode, the engine will max out at 82 kW @ 4100 rpm. 82 to the generator => 70 to the convertor => 60 kW to the motors.

Yes, if power demand is more than what the engine can deliver (with revs being limited due to parallel mode) + what the battery can deliver, it will switch to series mode in order to allow the engine to rev up.

For sure, the engine will (almost) max out when you floor it, at least at speeds above 58 km/h (this is the minimal speed at which the E-motors can handle the full 120 kW). But the question is / would be: what if power demand is more than 60 kW but less than 120 kW? Where will the power come from? How much from the engine and how much from the battery? I believe there larger part will come from the engine and the rest from the battery. Not the other way around.

Again, hybrid efficiency is not achieved by spreading out the load over longer time. It is achieved by concentrating the load in a shorter amount of time alowing the engine to shut off during the rest of the time. Otherwise, why would the car turn the engine on and off all the time when coasting on the motorway?

 

[user 258]

Again, hybrid efficiency is not achieved by spreading out the load over longer time. It is achieved by concentrating the load in a shorter amount of time alowing the engine to shut off during the rest of the time. Otherwise, why would the car turn the engine on and off all the time when coasting on the motorway?

Hi,
I believe the ICE turning on and off while in save mode (or depleted battery) while cruising on motorways is simply because the ICE will use surplus torque (i.e. it will put load onto the generator when it has surplus energy) so the drive battery is often being charged even in save mode. When the charge level exceeds the charge level that save mode was selected at, it switches to EV mode until the charge level drops back down again.

Mitsubishi themselves actually state that using charge mode, then EV mode, rather than just running in save mode will use about 20% more fuel. Presumably, this is due to the inefficiency of charging and discharging the battery. As opposed to the "surplus" but lesser amounts of energy used to recharge the battery in save mode.

While talking about battery charge levels. The most authoritive comment on these forums that is consistent with my observations was from anko who said:

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.

Kind regards,
Mark

 

[jaapv]

It is a misconception to think that the “surplus” power when the ICE is running at less than maximum is free, or wasted when not used. The motormanagement keeps the engine running as optimal as possible related to the power demand. If power demand gets higher because of the generator the added power demand will result in the engine being adapted to deliver more, resulting in a higher consumption.