Maintaining SOC while towing

[anko]

Several times, I have said that (IMHO) the biggest issue with towing a big trailer is how to maintain a decent SOC for when you need it. Cause: in parallel mode the engine can not / will not produce enough power (due to limited RPMs associated with towing speed) to propel the car + trailer and increase or even maintain SOC.

During my last towing trip, I noticed that from the moment I took off, the car decided not to engage parallel mode, not even at speeds above 50 MPH. As a consequence, the RPMs were higher and so was the amount of power the ICE could / would produce. At 50 - 60 MPH, RPMs were fluctuating around approx. 3200, a fair bit more than the 2100 - 2400 you would normally see in parallel mode at these speeds. Engine sound was still very acceptable. All I really noticed was the RPMs going up during take over manoeuvres or when dealing with small inclines and such. As you would expect from a CVT.

Initially, I was a bit concerned with this behaviour, as I realised all power produced bij the ICE had to be converted twice before being put on the road (once by the generator and once by the e-motor) and I feared extremely high consumption. But it was not too bad: approx. 22.5 MPG. Taking into account that SOC was actually going up instead of down, the corrected consumption was not bad at all.

At a certain moment I came to the conclusion that while towing, I prefer serial mode over parallel mode, especially as at these moments I am more concerned with maintaining SOC than I am with fuel economy. And serial mode allowed me to maintain SOC.

There was one problem, though: I had no idea what made the car decide for serial mode. For sure, it was not low fuel level or any of the other causes we know for getting stuck in serial mode. It was something I have never experienced before. For a moment, I thought ECU software must have been updated during the last service (which was after my last tow trip). But that would also mean the car had to be aware it was towing, as it never got stuck in serial mode when driving solo ....

Anyway, after about 40 - 50 miles it was time for a quick stop. After this stop, where I actually turned off the car, the car again engaged parallel mode, just as it did during earlier trips, and SOC started to drop gradually. I have not been able to persuade the car to drop out of parallel mode again (other than by 'flooring it').

Any thoughts on this phenomena?

 

[greendwarf]

Could it be different SoC at each start-up?

 

[jaapv]

Several times, I have said that (IMHO) the biggest issue with towing a big trailer is how to maintain a decent SOC for when you need it. Cause: in parallel mode the engine can not / will not produce enough power (due to limited RPMs associated with towing speed) to propel the car + trailer and increase or even maintain SOC.

During my last towing trip, I noticed that from the moment I took off, the car decided not to engage parallel mode, not even at speeds above 50 MPH. As a consequence, the RPMs were higher and so was the amount of power the ICE could / would produce. At 50 - 60 MPH, RPMs were fluctuating around approx. 3200, a fair bit more than the 2100 - 2400 you would normally see in parallel mode at these speeds. Engine sound was still very acceptable. All I really noticed was the RPMs going up during take over manoeuvres or when dealing with small inclines and such. As you would expect from a CVT.

Initially, I was a bit concerned with this behaviour, as I realised all power produced bij the ICE had to be converted twice before being put on the road (once by the generator and once by the e-motor) and I feared extremely high consumption. But it was not too bad: approx. 22.5 MPG. Taking into account that SOC was actually going up instead of down, the corrected consumption was not bad at all.

At a certain moment I came to the conclusion that while towing, I prefer serial mode over parallel mode, especially as at these moments I am more concerned with maintaining SOC than I am with fuel economy. And serial mode allowed me to maintain SOC.

There was one problem, though: I had no idea what made the car decide for serial mode. For sure, it was not low fuel level or any of the other causes we know for getting stuck in serial mode. It was something I have never experienced before. For a moment, I thought ECU software must have been updated during the last service (which was after my last tow trip). But that would also mean the car had to be aware it was towing, as it never got stuck in serial mode when driving solo ....

Anyway, after about 40 - 50 miles it was time for a quick stop. After this stop, where I actually turned off the car, the car again engaged parallel mode, just as it did during earlier trips, and SOC started to drop gradually. I have not been able to persuade the car to drop out of parallel mode again (other than by 'flooring it').

Any thoughts on this phenomena?

Could it be that the VTech box is not quite stable?

 

[anko]

Could it be that the VTech box is not quite stable?

Quite possible that is not (although I don't think it is not). But I do not see how it would be related to this experience. All the box does is remap the throttle position and the throttle acceleration. It should in no way result in the car deciding on sticking to serial mode when driving at a constant speed. As a matter of fact, it did so while driving on CC.

 

[anko]

Could it be different SoC at each start-up?

Something that did cross my mind. But I think the moment I engaged Charge mode was not very different from when I did at other trips. Also, after my brief stop the SOC (about 85% at that time) can't have been much different from when I hit Charge the first time. Simply because Charge mode will not engage (in my car) when SOC is much higher than that. I will try at my next towing trip to engage Charge as soon as possible and try to replicate.

BTW: Conditions were quite good during my trip. Resulting in 1/3rd SOC remaining (on the dash) after 300 km of towing. Mostly thanks to a moderate tail wind and the fact that the last bit of the trip was mainly secondary roads, with many inclines and declines as well as many roundabouts and such. These type of roads result in lots of serial mode driving and allow for some SOC build up.

 

[Grigou]

Sometimes, rarely, my car (always driving in solo) stays in serial mode during a long time and I don't understand why ... I think that heating demand could be involved, but I am not sure at all. Quite mysterious indeed.

 

[Steepndeep]

Hi Anko

A similar thing happened to me this winter when it was really cold outside (-15 C). I used preheat for app 20 minutes and then drove away. First I thought there was something wrong with the car as it never went into parallell mode above 70 km/h. I also had a rather high revving ICE in serial mode (no tach so I cannot judge how high revs, they just felt high). After app 45 minutes drive it suddenly went into parallell mode.

My assumption is that the battery at lower temp cannot deliver necessary current for "normal" highway driving so Mitsu has implemented a "parallell block" at lower temp, until the drivepackage has reached sufficient temperature. There must be more parameters than just temp though because I can drive at -10 on pure EV at lower speeds when I make short trips to the grocery store. Note that the car had been sitting for 3 days in sub -10C so battery pack was indeed cold from start. I also went directly to highway and drove at 100 km/h so battery was getting a rather good cooling from the wind.

 

[maby]

I've never towed with the PHEV, but I have seen examples of it sticking in serial mode longer than is necessary in response to demands for high power.

 

[anko]

Sometimes, rarely, my car (always driving in solo) stays in serial mode during a long time and I don't understand why ... I think that heating demand could be involved, but I am not sure at all. Quite mysterious indeed.

When the ICE is started for heating purposes, rather than power demand, it will not engage in parallel mode, not even when speed goes above 40 MPH. Unless you select Charge mode at the same time. Something similar happens when the petrol reserve goes below approx. 5 liters. When the ICE is started due to low SOW or heating requirements, it will not engage parallel mode. Selecting Charge mode offers no solution in this case, as Charge mode is not available when fuel reserve is that low.

In my case, the heater was off, petrol reserve was about 50% and Charge mode was selected.

I've never towed with the PHEV, but I have seen examples of it sticking in serial mode longer than is necessary in response to demands for high power.

And it lasted for 40 - 50 miles or so. Not just a few seconds .... That being said, I don't think the serial mode was triggered by high power demand.

 

[anko]

Hi Anko

A similar thing happened to me this winter when it was really cold outside (-15 C). I used preheat for app 20 minutes and then drove away. First I thought there was something wrong with the car as it never went into parallell mode above 70 km/h. I also had a rather high revving ICE in serial mode (no tach so I cannot judge how high revs, they just felt high). After app 45 minutes drive it suddenly went into parallell mode.

My assumption is that the battery at lower temp cannot deliver necessary current for "normal" highway driving so Mitsu has implemented a "parallell block" at lower temp, until the drivepackage has reached sufficient temperature. There must be more parameters than just temp though because I can drive at -10 on pure EV at lower speeds when I make short trips to the grocery store. Note that the car had been sitting for 3 days in sub -10C so battery pack was indeed cold from start. I also went directly to highway and drove at 100 km/h so battery was getting a rather good cooling from the wind.

Personally, I don't think such a block exists. During normal driving in parallel mode, the ICE provides surplus power, allowing the battery to be recharged bit by bit. So, most of the time, it does not depend on the battery. Or at least, not significantly. As I said, I think a different strategy applies when the ICE runs for heating purposes. The reasoning behind this different strategy is for now a mystery to me.

 

[Yoran]

BTW: Conditions were quite good during my trip. Resulting in 1/3rd SOC remaining (on the dash) after 300 km of towing. Mostly thanks to a moderate tail wind and the fact that the last bit of the trip was mainly secondary roads, with many inclines and declines as well as many roundabouts and such. These type of roads result in lots of serial mode driving and allow for some SOC build up.

Wait what? How can you tow 300km and have anything remaining? My battery is depleted after 30.. So you mean you pressed charge?

 

[anko]

BTW: Conditions were quite good during my trip. Resulting in 1/3rd SOC remaining (on the dash) after 300 km of towing. Mostly thanks to a moderate tail wind and the fact that the last bit of the trip was mainly secondary roads, with many inclines and declines as well as many roundabouts and such. These type of roads result in lots of serial mode driving and allow for some SOC build up.

Wait what? How can you tow 300km and have anything remaining? My battery is depleted after 30.. So you mean you pressed charge?

Of course I did. Even with a depleted battery the car will still tow pretty well but it will regularly resort to high revving (4100 rpm) to prevent the battery from draining beyond damage. And during climbing you may end up in a situation where power is limited. To prevent this, it is well advised to hit Charge mode as soon as you take off.

 

[Yoran]

Ah! My bad

 

[anko]

Ah! My bad

Haha. No sweat.

Today, on my return trip, I hit Charge as soon as I started the car. The blue Charge indicator lit up, but the ICE did not start. The ICE started a bit later when I encountered a first incline. As hoped, the car selected and stayed in serial mode. SOC was kept above 85% all the time. When I had to stop for gas (some 25 miles down the road), I kept the car in Ready mode, and after taking off, it was still stuck in serial mode.

Fuel consumption was a bit high (like 14 liter / 100 km or 20 MPG), but I think this was primarily related to the fact that I was crossing the Belgium Ardennes south to north, and was climbing a lot. Anyway, at some point (again after about 50 miles) I noticed the SOC had dropped to approx. 75%. As I did not understand why, I looked at other readings and realised the car had selected parallel mode again.

Whether SOC started dropping because the car went to parallel mode or the car selected parallel mode because SOC dropped below a certain point, I do not know. I think maybe the reason for selecting parallel mode was (risk of) overheating of the e-motors. We must not forget, in serial mode, they are doing all the hard work.

 

[HHL]

Ah! My bad

Haha. No sweat.

Today, on my return trip, I hit Charge as soon as I started the car. The blue Charge indicator lit up, but the ICE did not start. The ICE started a bit later when I encountered a first incline. As hoped, the car selected and stayed in serial mode. SOC was kept above 85% all the time. When I had to stop for gas (some 25 miles down the road), I kept the car in Ready mode, and after taking off, it was still stuck in serial mode.

Fuel consumption was a bit high (like 14 liter / 100 km or 20 MPG), but I think this was primarily related to the fact that I was crossing the Belgium Ardennes south to north, and was climbing a lot. Anyway, at some point (again after about 50 miles) I noticed the SOC had dropped to approx. 75%. As I did not understand why, I looked at other readings and realised the car had selected parallel mode again.

Whether SOC started dropping because the car went to parallel mode or the car selected parallel mode because SOC dropped below a certain point, I do not know. I think maybe the reason for selecting parallel mode was (risk of) overheating of the e-motors. We must not forget, in serial mode, they are doing all the hard work.

The rated output of the electric motors is only 25kW, so on a long climb at moderate speeds in serial mode, they would certainly warm up a bit if they are asked to provide close to maximum (60kW). Also, when towing and driving in parallel mode, only the rear motor supplements engine power when required, again, the petrol motor would not be even close to maximum power at towing speeds, and the rear motor would work quite hard. I would think under those conditions, the car may revert to serial mode to even the load on the electric motors.

 

[anko]

The rated output of the electric motors is only 25kW, so on a long climb at moderate speeds in serial mode, they would certainly warm up a bit if they are asked to provide close to maximum (60kW).

I have always assumed that this 25 kW limitation was per motor. Still do. So, close to 50 kW sustained should be no problem. Believe it or not, most of the time, I stay well below that, even when towing.
Hence my "maybe" .... ;-)

Also, when towing and driving in parallel mode, only the rear motor supplements engine power when required, ...

Are you sure about this? I know the rear motor always supplies power (to maintain a AWD experience), but I've never read something that suggested it only provides power. I have the tools to monitor this, but I never checked power distribution over the two E-motors under this particular condition.

..., the petrol motor would not be even close to maximum power at towing speeds, and the rear motor would work quite hard.

Max electric power to distribute is 60 kW (as the generator will be useless under these conditions). As a matter of fact, some of the 60 kW from the battery will be used to eliminate E-drag in the generator :shock: . Anyway, other than your statement, I have no reason yet to believe all battery power will go to the rear motor in parallel mode. Must check some day.

I would think under those conditions, the car may revert to serial mode to even the load on the electric motors.

I don't think I have ever seen the car switch to serial mode for other reasons than power demand being more than what is available from the ICE in parallel mode + what is available from the battery (including low SOC conditions).

Plus, after starting from the assumption that the car might select parallel mode to relieve the E-motors, we are now at the assumption that the car might select serial mode to relieve the E-motors. I cannot imagine both assumptions are true :mrgreen:

 

[HHL]

Yes, of course the 25kW rating is per motor.
Somewhere in the tech manual it does say that in parallel mode only the rear motor will contribute, the front one has only enough power going into it to eliminate drag.
As for you last point, I can imagine under certain conditions (say less than 100km/h and towing), there would be more power available in serial mode, as the engine can fully drive the generator to 70kW, making about 60 available for the motors, plus whatever the battery can contribute when required.

Anyway, who knows... I have driven at highway speeds (around 100), not towing, fairly level, and the car stayed in serial mode for quite some time.... really can't see a reason for it, but I am sure the engineers who designed it would know why!

 

[anko]

Somewhere in the tech manual it does say that in parallel mode only the rear motor will contribute, the front one has only enough power going into it to eliminate drag.

I checked today, when returning my caravan to storage location. In parallel mode, the front motor reports 0 Nm at various RPMs. So, 0 kW mechanical power produced. Indeed consumed electrical power is > 0 as this is needed to eliminate drag. The rear motor typically reports < 1 kW. As soon as the ICE load hits 100%, produced mechanical kW for both E-motors go up. Front even a bit more than rear.

 

[Claymore]

Oh, Anko, Anko, Anko......' a CVT'?

How could you?

:?

JimB

Several times, I have said that (IMHO) the biggest issue with towing a big trailer is how to maintain a decent SOC for when you need it. Cause: in parallel mode the engine can not / will not produce enough power (due to limited RPMs associated with towing speed) to propel the car + trailer and increase or even maintain SOC.

During my last towing trip, I noticed that from the moment I took off, the car decided not to engage parallel mode, not even at speeds above 50 MPH. As a consequence, the RPMs were higher and so was the amount of power the ICE could / would produce. At 50 - 60 MPH, RPMs were fluctuating around approx. 3200, a fair bit more than the 2100 - 2400 you would normally see in parallel mode at these speeds. Engine sound was still very acceptable. All I really noticed was the RPMs going up during take over manoeuvres or when dealing with small inclines and such. As you would expect from a CVT...............................

 

[anko]

Oh, Anko, Anko, Anko......' a CVT'?

How could you?

:?

JimB

As you would expect from a CVT......

How could I what? Or are you just trying to lure me and others back into that old discussion again?