Research into Wear & Tear of a hybrid (Start-Stop) engine

[zzcoopej]

A friend of mine commented that he thought it might be a problem having the PHEV engine start/stop much more frequently than a conventional car. I googled and found this research paper on the topic http://papers.sae.org/2014-01-1476/ (You can see the first 5 pages here. I have NOT read the full report)
Hope that's of interest as I havn't seen it on any of the PHEV threads (sorry if its already been posted).

Notes -
1. The research is on a Prius and Camry so based on Toyota engines, not Mitsubishi.
2. They used a taxi Prius that had done 400,000 miles (about 200,000 miles of ICE engine use). If my PHEV lasts that long I won't be complaining about engine wear!
3. Findings were that there was not much more wear, significantly more sludge and significantly more varnish when compared to an ICE of 200,000 miles.

My conclusion - we don't have anything to worry about!

PS I've only had my PHEV for 2 weeks, however I've noticed that my ICE can engage in parallel mode (MMCS "orange" engine, dash arrow from ICE to wheel) at speeds anywhere above about 60km/h when in Save mode. Everywhere I read it talks about parallel only above 120km/h, is that something that has changed, or different car setting for Australia, or am I misinterpreting the MMCS/dash symbols?

 

[gwatpe]

PS I've only had my PHEV for 2 weeks, however I've noticed that my ICE can engage in parallel mode (MMCS "orange" engine, dash arrow from ICE to wheel) at speeds anywhere above about 60km/h when in Save mode. Everywhere I read it talks about parallel only above 120km/h, is that something that has changed, or different car setting for Australia, or am I misinterpreting the MMCS/dash symbols?

I believe that in normal mode, ICE comes on above 120kph as the EV mode has insufficient power to do it alone. parallel hybrid mode may be engaged.

I have my PHEV power ON in SAVE mode automatically all the time now. I control the battery use, restrict it mainly to stop-start city driving and to use up battery reserves at the end of a trip. Very happy PHEV driver now.

 

[PolishPilot]

...
PS I've only had my PHEV for 2 weeks, however I've noticed that my ICE can engage in parallel mode (MMCS "orange" engine, dash arrow from ICE to wheel) at speeds anywhere above about 60km/h when in Save mode. Everywhere I read it talks about parallel only above 120km/h, is that something that has changed, or different car setting for Australia, or am I misinterpreting the MMCS/dash symbols?

I have the same observations in Save mode or empty battery, and I believe it is normal.

I also believe, this is the most effective way of charging the battery when driving,
when the engine while running the wheels in parallel mode is using excess power to
charge the battery. Software takes care of optimal load p on the ICE for lowest fuel consumption.

You can observe, that once you press the pedal harder, charging stops and just
the wheels are powered, when you slightly release the pedal charging starts again.

I also believe that in normal mode, ICE comes on only above 120kph because EV mode
has insufficient power to do it alone at such speed.

 

[jaapv]

No, you are misinterpreting the system. The ICE MAY come in in parallel mode over 60 KPH depending on power demand and WILL come in over 120 KPH. 120 is an approximation depending again on power demand. Coasting downhill at higher speeds the ICE will disengage, for instance.

The engine does not really produce excess power, of course. Coupled to the wheels by a clutch that is quite impossible. If you demand extra power for charging it will apply its power reserve at that moment by the engine management and fuel consumption will go up. It will be more efficient at certain revs, though.

 

[zzcoopej]

Ok thanks guys, that clears it up for me.

I have my PHEV power ON in SAVE mode automatically all the time now.

It would be nice to have Eco Mode on by default, have you considered that? I'm not sure default to Save mode would suit my normal usage however when on holidays with 2 hourly breaks over a 13 hour journey I did the following 7 changes each time I got back in the car -
1. Start,
2. ECO,
3. Save,
4. Drive or Reverse (still getting used to opposite direction to what you want),
5. B5,
6. ACC on,
7. ACC range 3bars down to 1bar,

Ok, can start driving, lol!
Wow the ACC is wonderful on single lane roads when stuck behind a clueless driver, but got caught out a few times on multilane roads when the guy in front just slowed down gradually so I didn't notice for a while that I was only doing 90 instead of 110 etc when I would normally just overtake. I've never used ACC in a petrol car (only simple cruise), however I'm amazed how in the PHEV can bring the car smoothly to a stop from 80+km/h and restart all without accelerator or brake (mind you I cover the brake just in case).

 

[PolishPilot]

...
The engine does not really produce excess power, of course. Coupled to the wheels by a clutch that is quite impossible.

Of course, it is possible!
The ICE is permanently coupled to the generator and if software decides s additional
power can be won by the torque applied by the generator to to the ICE on top of torque
transferred to the wheels directly. Power = torque x rpm, hence additional power
is available through the generator.

The software is applying optimal combined (wheels + gen) torque to the ICE at any
given rpm to obtain optimal fuel economy. The engine will run then at its "sweet spot".

If you demand extra power for charging it will apply its power reserve at that moment by the engine management and fuel consumption will go up. It will be more efficient at certain revs, though.

The fuel consumption per time unit and km may go up, but the combined energy won in this case
including energy used to charge the battery will be more effective, due to the stored energy
used later for pure EV driving with no fuel used.

This is at least what I have been told by some knowledgeable hybrid system specialist.
The optimized algorithm is the key.

 

[jaapv]

The optimized algorithm is the key.

Well, yes, that is rather obvious.
Still, you have to take conversion losses from fuel to electricity and from electricity to movement into consideration.

 

[maby]

The optimized algorithm is the key.

Well, yes, that is rather obvious.
Still, you have to take conversion losses from fuel to electricity and from electricity to movement into consideration.

I don't think it would ever make financial sense to run the engine purely to charge the battery - the trick in the power control algorithms is to keep the engine running at or near its most efficient point on the power curve.

 

[gwatpe]

My observations with Lithium batteries as a rechargeable power source for the last 5 years on my house.

At high currents the I^2R losses in the battery affect kW efficiency. at 60kW the efficiency may be as low as 90%, however at 30kW the efficiency will be about 96%, and at 10kW, the battery efficiency will be around 99%.

My house power system includes DC-DC converters with synchronous rectifiers and an inverter-charger for high system efficiency. The PHEV may only have normal rectifiers, but will have DC-DC converters for regen and generator to match loading to the supply. The PHEV electric systems seem to be high efficiency with minimal radiator cooling systems compared to the ICE radiator.

With the PHEV we only have rudimentary motor power readings available for comparisons. We only have an arrow and no kW for the generator. My observations with the rate of charging at highway speeds puts typical surplus power from the ICE operation at under 10kW.

I expect that the losses in using some surplus ICE power for battery recharging are overstated.

 

[gwatpe]

It would be nice to have Eco Mode on by default, have you considered that?

ECO mode is just a single purpose application of the same idea I use for CHARGE and SAVE mode. I had considered this in my original design, but figured that getting interconnecting wiring between possibly separate sub systems might introduce ground loop problems. Charge and Save are mutually exclusive operations and have to be memorized in the same way that the PHEV works. The buttons are close together and share the same ground, so I went that path.

Really would want to have another button in addition to ECO to make better use of components. I have held off on ECO for the moment as I don't think there is much benefit to be gained if a driver forgets to press it, compared to say SAVE. I do believe the driver would have feel good browny points if this PHEV, an ECO car actually powered ON in ECO mode. I have not found a way yet to get the ECO button out of the dash. Might be able to get a hand in behind if the glove compartment was not in the way.

Getting a little off topic, so I would be inclined to start a sticky ECO thread elsewhere.

 

[anko]

The optimized algorithm is the key.

Well, yes, that is rather obvious.
Still, you have to take conversion losses from fuel to electricity and from electricity to movement into consideration.

I don't think it would ever make financial sense to run the engine purely to charge the battery - the trick in the power control algorithms is to keep the engine running at or near its most efficient point on the power curve.

Indeed. Otherwise, why would the car alternate between parallel and EV mode when the battery is ”empty" or Save mode is engaged? But in order to reach it's maximum efficiency, it needs a near fairly depleted battery.

BTW: I beieve we don't get anywhere near the sweetspot. If the engine was operating near the sweetspot (which would require a longer gear ratio), the slightest bit of acceleration or climbing would require e-assistance, resulting in draining the battery without having an opportunity to recover the lost charge.

 

[Trex]

BTW: I beieve we don't get anywhere near the sweetspot. If the engine was operating near the sweetspot (which would require a longer gear ratio),

Hi anko,

So you think we need an overdrive gear ratio?

But you also say: Otherwise, why would the car alternate between parallel and EV mode when the battery is ”empty" or Save mode is engaged?

That could be considered something just as good as overdrive ie shut the petrol motor off after charging the hv battery for a period of time could it not? An electric overdrive? Yep, I like that name.

Regards Trex.

 

[anko]

So you think we need an overdrive gear ratio?

I don't think we need one. I only think we would needed one if we were aiming for optimal efficiency of the engine. But the increased efficiency could be nulled out by the increased weight, complexity, cost, etc.

BTW: I did not necessarily mean an overdrive, but a longer gear.

But you also say: Otherwise, why would the car alternate between parallel and EV mode when the battery is ”empty" or Save mode is engaged?

That could be considered something just as good as overdrive ie shut the petrol motor off after charging the hv battery for a period of time could it not? An electric overdrive? Yep, I like that name.

Sure. It was a rethorical question But still, due to limitation of the charge current, this electric overdrive does not allow us to achieve the sweet spot. The amount of torqued reden for driving + charging is simply to low. More so if the battery is not empty.