The Clarity: i-MMD and Engine Engagement

Except for some BEV's with no backup, HEV's and PHEV's don't allow full charge/discharge cycles with most using a roughly 80/20% ratio. That's why they can easily make the 8-10 year mandated warranties.

 

Right but I referred to that in the very next sentence after the one that you quoted. Sorry if I wasn't clear.

And the point that I was making was in the next sentence after that:

 

Yeah, it's already done for you.

I look at this way: What's the point of not using capacity today to HOPEFULLY retain some capacity tomorrow? Either way, you're not using the battery to its full extent; especially when real world, there's a good chance by the time capacity has diminished one won't either own the car, accident, or some other major issue bricks the car?

Then there's the possibility that babying the battery today might extend its fail date to beyond the warranty period instead of failing within (early).

 

Are your referring to my last statement "I don't doubt that some battery longevity can be gained by steering even further away from the edges"?

If so then you are saying that the preset range limitation is set past the point where there would be any longevity gain by not charging to 100% or avoiding EV 0. I say we don't know. But I also say that even if there is any longevity gain we don't know how much, it might not be enough to be worth making any sacrifices in how we use our cars. Which is why I said a few sentences down from the others that you quoted:

Some may want to err on the side of caution, but personally I'm in agreement with you to not give up capability now if there isn't at least persuading evidence that it will have a noticeable impact later on.

Until now I assumed that by longevity everyone means how long until the battery fails, not trying to avoid reduced capacity when the battery ages. If it's about reduced capacity then sure I agree it doesn't seem worth it to reduce battery usage now to try and avoid reduced battery capacity later. But I'm not sure if anyone is thinking that.

 

Don’t BEV’s have a similar upper reserve? Would seem detrimental not to.

 

BEV's also have an upper reserve. Fotomoto mentioned some that don't, I am guessing those are older models.

Neither BEV's or PHEV's allow you to fully discharge the battery. That's what we refer to as the lower limit, lower buffer, etc., i.e. 0 miles and 0% is really 20% or something similar. The question is whether 20% or whatever it is can still be too low for someone whose goal is maximum longevity, as opposed to reasonable longevity. Obviously reasonable is a subjective term.

Something to keep in mind is that while 20% or whatever it is is the normal lower limit, you can go below that by sitting for a long period of time with the car on, especially when using HVAC. SOC will drop below the normal 8-10% as displayed on the app to about 1% before ICE starts up. Someone who is concerned about going too low on the battery should probably avoid this if possible and not sit still for long periods of time with 0 EV range.

For performance (i.e. efficiency) yes. However using manual modes for battery and ICE longevity, which is what your original question was about, the jury is out on that.

If you are referring to i-MMD hybrids only, I assume that the tradeoff decisions were similar to Clarity. As to your question whether they went with i-MMD just because it's what they already developed, but not necessarily the best choice for Clarity, that is an interesting question, with what I assume is yet another elusive answer.

 

When Chevy first released the Volt, they were very cagey about whether the ICE ever connected directly to the mechanical drivetrain. Eventually they admitted it was necessary to achieve the greatest efficiency for cruising at highway speeds. Honda clearly came to the same conclusion when they designed the i-MMD system. If it didn't provide greater efficiency than serial hybrid operation in certain situations, there would be no reason to add Engine drive's complexity, weight, space requirements, and cost to the Clarity PHEV. Getting 42 mpg from a 2-ton car is very impressive IMO--Engine drive contributes to that efficiency.

 

You can charge less than 100% by using scheduled charging, after you get experience with estimating charging times you could probably get within 5% of a target. Probably what you were referring to by "doesn't readily support".

Oddly the manual states on page 466:

"To help extend the lifespan of the battery, it is recommended that you fully charge the battery each time prior to driving."

But it doesn't say why. One guess is that fully charging reduces the chance of depleting EV range to 0 miles. But if so then that means they are saying that depleting EV to 0 range will shorten battery life in spite of the lower buffer. And yet they don't say that anywhere that I can find. And anyway that can be easily avoided by using HV as needed, but that requires strategy so maybe it's easier to just tell people to fully charge.

Or maybe it's just better in general to keep the battery operating in the upper half than the lower half when possible, which fully charging every time would help facilitate.

Now to parse words even more, it is supposedly not good to leave the battery sitting fully charged, it's better to reach full charge just before you drive off. Maybe they are alluding to that with the statement "it is recommended that you fully charge the battery each time prior to driving." Meaning it's not so much fully charging that extends battery life, but rather to avoid fully charging if you are not ready to drive off anytime soon. If so then it's too bad they don't have a departure time charging schedule like Prius Prime does. I guess as a workaround you could use schedule charging to charge up to say 90% during the night, then when you wake up use "Start Charging" on the app or key fob and by the time you are ready to leave for work it will be fully charged.

Or just forget about all that and just plug it in and charge