The myth of inefficent petrol motor charging on the PHEV.

[Trex]

Hi,

I see in many discussions in this forum about the inefficiency of charging using the petrol motor. First I will bring in these graphs from Page 1 of the sticky in technical discussions:



Now as I stated underneath this image:

"I think this is interesting because it shows our Phevs starting the petrol motor and charging the hv battery and then stopping petrol motor and going into ev mode, and then repeating, as we drive along in parallel mode speed. This is the sawtooth line showing on previous graph.

If my translation is right this test was done with a MUT-III at 1900kgs weight of the Phev."

Note: "it shows our Phevs starting the petrol motor and charging the hv battery and then stopping petrol motor and going into ev mode, and then repeating, as we drive along in parallel mode speed."

I think some people need to get their head around this statement because I see members stating that it inefficient to be using the petrol motor to charge the drive battery. Well as can be seen in the above graphs Mitsubishi are doing exactly that with the PHEV and Toyota also do it with their hybrids (I have owned a Prius and still own a Camry Hybrid which my oldest son drives as he works for me).

So the question is if it so inefficient in the conversion of petrol into electric to chemical to electric power why are companies doing it in their hybrids?

Well I think it is well known that petrol motors are inefficient as stated in Wikipedia: "Modern gasoline engines have a maximum thermal efficiency of about 25% to 30% when used to power a car. In other words, even when the engine is operating at its point of maximum thermal efficiency, of the total heat energy released by the gasoline consumed, about 70-75% is rejected as heat without being turned into useful work, i.e. turning the crankshaft."

Note: "even when the engine is operating at its point of maximum thermal efficiency". So when the petrol motor is not operating at its "sweetspot" it is even worse than 25% to 30% efficient! So hybrids when they have to run their petrol motors try to avoid the inefficient areas of running like idling when you are stopped by using a stored charge. That I think is well known here by most members.

We also know that the conversion of electric to chemical power is nowhere near as bad as 70 to 75% losses when the petrol motor is at its best. Here Wikipedia state for lithium ion batteries : "Charge/discharge efficiency 80–90%". That is for going both ways ie charge and then discharge. The Phev has also some generator, invertor losses of approx. 16% to produce electric power.

So the moral here is if you are going to run that bloody inefficient petrol motor(to drive the wheels) generate some electricity (especially at the petrol motor's sweetspot) and store it so you can turn off the petrol motor as much as possible. Mitsubishi and Toyota know it and we should too.

Regards Trex.

Image from anko

 

[maby]

I think you are misunderstanding the statements that various people have made on the subject. Of course hybrid vehicles charge the battery from the petrol engine, the perceived issue with the Outlander is the use of the "Charge" button to modify the power management strategy. The Outlander is a bit different to the Prius in this respect - it has no gearbox and must use electric transmission at speeds below something like 45mph. The Prius has the ability to drive the wheels mechanically all the way down to stationary.

Both the Prius and Outlander running in Normal mode will only run the petrol engine while the car is in motion (unless the battery has drifted below its charge floor, in which case the engine runs until the SOC is back within the design range). If the SOC is down at the lower limit, or if you have selected "Save" mode, the engine runs, driving the generator which in turn drives the wheels but rather than just generating enough power to meet the demand of the electric motors, it runs the engine at a relatively constant speed and dumps any spare output into the batteries - when it has accumulated enough charge above the floor limit, it switches to EV mode and consumes it before dropping back to petrol driven mode.

Put it in Charge, however, and the petrol engine is on pretty much all the time. Following suggestions from one of the contributors here, I tried staying in Charge mode for a couple of hours of normal driving - I observed the car stationary at the lights with the battery gauge showing 15 out of 16 bars and the engine running at moderately high revs - presumably trying to fill that last bar. There's no way that that makes sense. Charging the battery as part of the normal hybrid cycle is exactly what the car is designed to do, but pressing the Charge button to modify the power management algorithm and tell it to simply try to get the battery level as high as possible, as quickly as possible, does not make sense unless you actually need that power in the near future.

 

[Trex]

I think you are misunderstanding the statements that various people have made on the subject.

Hey Maby,

No sorry I am not misunderstanding statements I have seen on this subject and yes I know the difference between the mechanics of PHEV and Prius. In some ways the PHEV is more efficient than the Prius mainly to do with the fact that the PHEV has enough ev power to totally shut down the petrol motor at highway speeds. As for slow speeds where the Phev cannot go into parallel mode the Phev has a big enough drive battery where you should be in ev mode anyway even if you had to charge up the drive battery out on the highway while in parallel mode.

In my 1 year of ownership (happy birthday Phev) I have never seen my Phev try to charge past 14 bars (out of 16) on the display. The petrol motor always shuts down at 14 bars automatically with the charge button pressed. Until I take about 5kms out of a fully charged battery ie 16 bars (60kph zones) the charge button does nothing(or the save button) unless I hold down the charge button for 10secs to bring up maintenance mode.

Regards Trex.

 

[maby]

I think you are misunderstanding the statements that various people have made on the subject.

Hey Maby,

No sorry I am not misunderstanding statements I have seen on this subject and yes I know the difference between the mechanics of PHEV and Prius. In some ways the PHEV is more efficient than the Prius mainly to do with the fact that the PHEV has enough ev power to totally shut down the petrol motor at highway speeds. As for slow speeds where the Phev cannot go into parallel mode the Phev has a big enough drive battery where you should be in ev mode anyway even if you had to charge up the drive battery out on the highway while in parallel mode.

In my 1 year of ownership (happy birthday Phev) I have never seen my Phev try to charge past 14 bars (out of 16) on the display. The petrol motor always shuts down at 14 bars automatically with the charge button pressed. Until I take about 5kms out of a fully charged battery ie 16 bars (60kph zones) the charge button does nothing(or the save button) unless I hold down the charge button for 10secs to bring up maintenance mode.

Regards Trex.

Perhaps there are differences in the programming between the models in different markets - mine will happily try to charge beyond 15 bars - and other European owners have suggested the same. The drive battery is certainly bigger than the Prius, but not big enough for a full day of EV driving in many cases - and certainly not in cold weather - which is probably not a problem for you!

 

[gwatpe]

The petrol motor always shuts down at 14 bars automatically with the charge button pressed. Until I take about 5kms out of a fully charged battery ie 16 bars (60kph zones) the charge button does nothing(or the save button) unless I hold down the charge button for 10secs to bring up maintenance mode.

I am also in AUS I have seen the same ICE operation in CHARGE and SAVE mode.

Interesting about the maintenance mode. Will try this on my long, away from corded recharging, trip.

 

[Trex]

Perhaps there are differences in the programming between the models in different markets - mine will happily try to charge beyond 15 bars - and other European owners have suggested the same. The drive battery is certainly bigger than the Prius, but not big enough for a full day of EV driving in many cases - and certainly not in cold weather - which is probably not a problem for you!

Yes there maybe are differences in programming but can I ask have you ever just pressed the charge button with a low SOC when stationary and just watched and waited to see what happens? Does the petrol motor even stop? What bars are showing if it does?

Yes if I go to the big smoke (what we call Sydney) I can run out of ev charge before getting out of there and like I have said before in another discussion I hate driving around with a "empty" drive battery. I always "save" about 1/4 to a 1/3 so it does not feel sluggish to me.

Next time I go there I am going to do extended charge and then ev mode like I do on the highway now to see what fuel consumption I get as I find that at 60kph the petrol motor never shuts off ,unless pulling up at traffic lights, ie where ever the petrol motor runs now in serial mode with save button pressed I will have charge button pressed and charge up the drive battery so I can ev mode later in 60kph zones . But not while standing still.

I have been to Europe and Great Britain back in the 80s (I went there surfing and travelling with a mate) and loved it mainly except for the language and currency problems (Before euros, having to change my money from one country to another in a land no bigger than Australia) and yes it was a lot colder than here (I went in summer over there) except down towards Lisbon where we had our surfboards stolen but that is another story. I had some very good friends in Netherlands I had met in Bali (again surfing)that I stayed with for a while and loved those girls in the windows in Amsterdam. :lol:

Regards Trex.

 

[maby]

Perhaps there are differences in the programming between the models in different markets - mine will happily try to charge beyond 15 bars - and other European owners have suggested the same. The drive battery is certainly bigger than the Prius, but not big enough for a full day of EV driving in many cases - and certainly not in cold weather - which is probably not a problem for you!

Yes there maybe are differences in programming but can I ask have you ever just pressed the charge button with a low SOC when stationary and just watched and waited to see what happens? Does the petrol motor even stop? What bars are showing if it does?

...
Regards Trex.

No, I must admit that I've never sat stationary in Charge mode for the 3/4 of an hour or thereabouts necessary to recharge the battery. I assume you are not suggesting that would make economical sense, are you? I occasionally use charge mode while driving - generally if I've forgotten to hit "save" and let the battery run down - but I would only charge up to 50% or thereabouts. The episode I referred to earlier was an experiment to test out the suggestion that driving in Charge full time made for better fuel efficiency - I was driving in normal suburban conditions for an hour or two and turned charge on soon after starting - the battery dropped to 14 bars, then the engine ran continuously - including with the car stationary - bringing the battery up to 15 bars and apparently trying for 16.

 

[Trex]

No, I must admit that I've never sat stationary in Charge mode for the 3/4 of an hour or thereabouts necessary to recharge the battery. I assume you are not suggesting that would make economical sense, are you?

Au contraire maby where have I said to sit there for 3/4 of an hour or it makes economical sense. It actually take an hour and 3.2lts of fuel in my Phev to charge from "empty" and yes I did it once so I can find out what exactly happens which I posted here and even the fuel did not go to a total waste as I drove around later in ev mode.

But in your case you could drop it down to around 12 or 13 bars and press the charge button and let the petrol motor start and see what happens. You too will not even waste your money.

Regards Trex.

 

[anko]

I don't think mine will try to charge beyond (approx.) 80%, let alone increase revs in order to do so. But, getting back to the beginning of this topic, I think the statement that it is inefficient to charge on the ICE relates to "charging while parked", not "charging while driving". "Charging while driving" clearly is part of the efforts to make the PHEV more efficient.

The combined load associated with propelling the car + charging the battery results in an increased efficiency of the ICE. Applying only the load for charging or only the load for propelling does not result in good efficiency. The increased efficiency outweighs (I may hope) the additional transformation losses between generator and e-motor.

 

[Grigou]

In my car, in Charge mode the system stops charging when it reaches 15 bars, then it decreases very quickly to 14 bars and so on ...

Until now, as a lot of owners, for long distance travel I used the Save mode. But I am thinking to try this strategy for my next travel : Charge mode when driving in parallel mode (hignways and so on), and EV mode for slow traffic (<70 kph).
+ another rule : if the battery reaches ~ 12 bars (after a long time in Charge mode), replacing Charge by Save.

 

[maby]

I don't think mine will try to charge beyond (approx.) 80%, let alone increase revs in order to do so. But, getting back to the beginning of this topic, I think the statement that it is inefficient to charge on the ICE relates to "charging while parked", not "charging while driving". "Charging while driving" clearly is part of the efforts to make the PHEV more efficient.

The combined load associated with propelling the car + charging the battery results in an increased efficiency of the ICE. Applying only the load for charging or only the load for propelling does not result in good efficiency. The increased efficiency outweighs (I may hope) the additional transformation losses between generator and e-motor.

Even for "Charging while driving", I think it is valid to ask about the economics of "Charge mode". If the battery is not fully charged and the engine is running for any reason, the power control system will usually charge the battery to some degree, but Charge mode significantly shifts the policy from relative trickle charging with periodic periods of EV to active charging at a rate which is comparable with a ChaDeMo unit and little or no EV operation. If this is the most fuel efficient option, why is it not the default?

 

[Trex]

I don't think mine will try to charge beyond (approx.) 80%, let alone increase revs in order to do so. But, getting back to the beginning of this topic, I think the statement that it is inefficient to charge on the ICE relates to "charging while parked", not "charging while driving". "Charging while driving" clearly is part of the efforts to make the PHEV more efficient.

The combined load associated with propelling the car + charging the battery results in an increased efficiency of the ICE. Applying only the load for charging or only the load for propelling does not result in good efficiency. The increased efficiency outweighs (I may hope) the additional transformation losses between generator and e-motor.

Hey anko,

You were going good there for awhile in your statement above until you wrote:" (I may hope)".

Surely you have no doubt? :lol: Mitsubishi and Toyota don't.

Regards Trex.

 

[Tweeds]

I use charge mode based on the assumption that parallel hybrid is more efficient for charging, and Save mode can't predict the future road conditions whereas I can.

I've become quite obsessive about not wanting the engine running whilst driving around town, as my assumption is that this is the least efficient, so I choose when to charge to ensure this doesn't happen.

Plus it makes the trip more interesting/fun!

 

[Trex]

Even for "Charging while driving", I think it is valid to ask about the economics of "Charge mode". If the battery is not fully charged and the engine is running for any reason, the power control system will usually charge the battery to some degree, but Charge mode significantly shifts the policy from relative trickle charging with periodic periods of EV to active charging at a rate which is comparable with a ChaDeMo unit and little or no EV operation. If this is the most fuel efficient option, why is it not the default?

Yes maby you may have a valid reason about the charge rate as I stated in a previous discussion:" About the only downside I see in using the charge mode on my car would be it could be considered a rapid charge and if done too often may cause the Hv battery to age quicker than normal but in our case we do not travel longer distances frequently."

But the Phev is already using the same charge rate but not as long as pressing the charge button ie a deeper cycle or depth of charge/discharge for the charge button. I guess time will tell if it affects the aging of the drive battery.

As why not the default mode? The Phev does not know our individual trip patterns.

Regards Trex.

 

[jaapv]

Perhaps there are differences in the programming between the models in different markets - mine will happily try to charge beyond 15 bars - and other European owners have suggested the same. The drive battery is certainly bigger than the Prius, but not big enough for a full day of EV driving in many cases - and certainly not in cold weather - which is probably not a problem for you!

Yes there maybe are differences in programming but can I ask have you ever just pressed the charge button with a low SOC when stationary and just watched and waited to see what happens? Does the petrol motor even stop? What bars are showing if it does?

Yes if I go to the big smoke (what we call Sydney) I can run out of ev charge before getting out of there and like I have said before in another discussion I hate driving around with a "empty" drive battery. I always "save" about 1/4 to a 1/3 so it does not feel sluggish to me.

Next time I go there I am going to do extended charge and then ev mode like I do on the highway now to see what fuel consumption I get as I find that at 60kph the petrol motor never shuts off ,unless pulling up at traffic lights, ie where ever the petrol motor runs now in serial mode with save button pressed I will have charge button pressed and charge up the drive battery so I can ev mode later in 60kph zones . But not while standing still.

I have been to Europe and Great Britain back in the 80s (I went there surfing and travelling with a mate) and loved it mainly except for the language and currency problems (Before euros, having to change my money from one country to another in a land no bigger than Australia) and yes it was a lot colder than here (I went in summer over there) except down towards Lisbon where we had our surfboards stolen but that is another story. I had some very good friends in Netherlands I had met in Bali (again surfing)that I stayed with for a while and loved those girls in the windows in Amsterdam. :lol:

Regards Trex.

Most are not really girls nowadays...

 

[maby]

...

Most are not really girls nowadays...

I think we'll all take your word on that!

 

[Trex]

Most are not really girls nowadays...

Bloody hell jaapv I am just about to go to sleep and now I will have nightmares. :lol: :lol: :lol:

Regards Trex.

 

[maby]

...
As why not the default mode? The Phev does not know our individual trip patterns.

Regards Trex.

Quite true. I guess that what I would prefer to see in place of the "Charge", "Save" and "Eco" buttons would be a set of usage style settings - things like "Suburban", "Motorway", "Long range", "Towing" - which select active power management strategies designed to suit those conditions selecting a power management policy that takes into account a combination of fuel economy, performance and battery life expectancy. I'm sure that it is possible to achieve the best results through a suitable combination of Charge and Save across your journey, but it really should not be necessary to be so actively involved in these decisions.

 

[anko]

Even for "Charging while driving", I think it is valid to ask about the economics of "Charge mode". If the battery is not fully charged and the engine is running for any reason, the power control system will usually charge the battery to some degree, but Charge mode significantly shifts the policy from relative trickle charging with periodic periods of EV to active charging at a rate which is comparable with a ChaDeMo unit and little or no EV operation. If this is the most fuel efficient option, why is it not the default?

This is not true. There is no difference in charge rate between Save, Charge of Normal mode. When the engine is running in normal mode (depleted battery) pressing Save or Charge has no effect on instanteneous fuel consumption. You may therefor assume that there is also no difference in how much power is output by the engine.

 

[maby]

Even for "Charging while driving", I think it is valid to ask about the economics of "Charge mode". If the battery is not fully charged and the engine is running for any reason, the power control system will usually charge the battery to some degree, but Charge mode significantly shifts the policy from relative trickle charging with periodic periods of EV to active charging at a rate which is comparable with a ChaDeMo unit and little or no EV operation. If this is the most fuel efficient option, why is it not the default?

This is not true. There is no difference in charge rate between Save, Charge of Normal mode. When the engine is running in normal mode (depleted battery) pressing Save or Charge has no effect on instanteneous fuel consumption. You may therefor assume that there is also no difference in how much power is output by the engine.

The instantaneous charge current may be the same, but there is a massive difference in the effective charge current and power output otherwise Save or Normal mode would be taking the battery back up to full in an hour or so. You don't put upwards of 10kWh into the battery in an hour without increasing average power output.