Best mode for long upgrades

Discussion in 'Clarity' started by neal adkins, Oct 17, 2019.

  1. Batteries can accept a charge from 2 different sources. This is very common in marine and RV applications. Shore power and solar for instance. Both sources are regulated and will prevent overcharging.

    I believe I have witnessed both the ICE generator and the front wheels sending a charge to the batteries simultaneously.
  2. ClarityBill

    ClarityBill Active Member

    I have been frustrated that 'dual charging' is very limited. It seems like the ICE generator minimum capacity is about the maximum charging capacity of the battery. The ICE stops charging very quickly when the power meter dips into the regen area.

    The ICE will charge the battery when the power meter is less than the output of the ICE (ICE is producing more power than is needed to drive the wheels), but if there is no power required to drive the wheels, the full output of the ICE cannot be accepted by the battery.
    David Towle likes this.
  3. HagerHedgie

    HagerHedgie Member

    It’s a relatively small battery so I think Honda limits charging to preserve battery life. I have had one or two times with a very low SOC where the car seemed to rev up pretty high just to charge the battery. It was cold and I was finishing a 3-4 mile 1000’ climb on the interstate at 80mph. As I started going downhill the revs stayed high and the car gained a few miles of EV range in a minute or so, then revs dropped down to closer to an idle.

    Sent from my iPhone using Inside EVs
  4. Teslawannabe

    Teslawannabe Active Member

    Will keep this in mind when the long grade comes along. Thank you.
    neal adkins likes this.
  5. Sthomasa

    Sthomasa Member

    I loved the Tesla but have to do Vegas a few times a year. Even stopping for 15 min in Barstow is awful.
    Thus the best of all worlds Clarity.
    Trip to Vegas 280 miles, made it to stateline, bought 2 gallons of nealy 5.00 gas.
    Filled up 4 gallons again in Vegas. Chargers are not everywhere in Vegas. TREASURE ISLAND, NONE.
    Palazzo had a few free chargers so i filled batteries. Made it the downhill home on those fillups. 586 miles. 48 miles per gallon. That was much better 17 Accord hybrid. (40mpg)
    Love the slow speed follow. 20191022_153740.jpg
    neal adkins likes this.
  6. I’m not certain that “dual charging” was a goal for the Honda engineers. In HV the car is attempting to operate as efficiently as possible with the available power sources. It would be logical that the ICE would shut down if no power was required to drive the wheels. Why burn gas? The ICE may stay on longer when adding some charge is necessary to restore the batteries to a set SOC.

    Do you know the charging output of the generator? Or the amount of charge provided by regeneration, either coasting with chevrons or on the brakes?
    Lithium batteries can accept very high charge rates. I believe in HV+, the batteries are accepting the full output from the generator?
  7. ClarityBill

    ClarityBill Active Member

    I agree that in HV+ the batteries will accept the full output of the generator, but not much more.

    My problem is the ICE will be at high RPM going up a hill, because SOC has dropped slightly. Going down the next hill, the ICE will shut off because there is a small amount of regen. SOC will not recover, and the ICE will be high RPM on the next upgrade: It seems like a little more 'dual charging' would have recovered the SOC and eliminated some high RPM operation.

    Keeping the ICE in the most efficient RPM range was also not a goal for the Honda engineers.
  8. HagerHedgie

    HagerHedgie Member

    Without access to thermodynamic efficiency curves for the ice I’m guessing, but I think the engine is most efficient between 2-4K rpms. Low loads are bad for efficiency. So it’s almost like the engineered a pulse and glide affect into the ice to get a few more MPG‘s.
    The other factor is the car simply can’t see the next hill coming up so it cant plan ahead. it would be great if they integrated GPS or even a long range camera system into to the HV algorithm.
    It frustrating when the engine cycles off for two seconds when you’re on rolling-hills especially when I don’t even move the gas pedal during the whole process.

    Sent from my iPhone using Inside EVs
  9. neal adkins

    neal adkins Active Member

    I can see that happening if your soc is high when you enter the climb. However even with an almost full soc my car in hv is a little spuratic in how it performs. It wont use available battery power in hv mode in tandom with ice in an effective way(probably trying to maintain current soc)Thus the inconsistent performance. So now if i have a full battery i use normal ev sport mode until i get to about 50% soc then hit hv charge. Then my car reacts in a more predictable manner and maintains speed without using all my charge when i reach the top. I think its smart use of a little fuel in the climb.
  10. David Towle

    David Towle Active Member

    I agree and this is what makes me think that Honda didn't do much of anything to modify the HV program from what they had with non PHEV hybrids. Especially if as we seem to believe here the batteries can absorb charging from 2 sources at once, why not just leave the engine charging on downhills till you are a few miles ahead of where you started the SOC, then turn it off for a few miles. This would also allow the engine to run at a steadier (more efficient?) speed.

    All that turning the engine on and off can't be as good for efficiency (even if the clutches might be built to last forever). With a "normal" small battery hybrid you have no choice, but for a PHEV there is a choice and Honda just didn't take it.
    HagerHedgie likes this.
  11. insightman

    insightman Well-Known Member

    Do you believe that Honda just plopped a bigger battery into an Accord Hybrid drivetrain and didn't do anything to measure and fine-tune the PHEV's efficiency?

    I have total faith that Honda's engineers worked very hard to maximize the Clarity Plug-In Hybrid's efficiency. A 4,000-lb car that gets 42 mpg in hybrid mode is pretty amazing in my opinion. I have no way to assess how efficient the other modes are, but I'm certain the engineers worked very hard to maximize their efficiency, too. I just wish Honda would be more forthcoming on why this car works the way it does.
    Last edited: Oct 25, 2019
  12. With the exception of gear mode, the engine is simply acting as a generator to provide electricity to the electric motor. It’s a constant balance based on inputs from the right foot.

    There are a number of functions on this car that we don’t completely understand. There are some that we can’t control. It may be in our best interest that we can’t control them.
    insightman likes this.
  13. David Towle

    David Towle Active Member

    Yes I do believe that. And I've thought of a good reason why they would do that. In cold weather, if the methodology I described was used, both the engine and the passengers could be subjected to excessive temperature cycling. When the engine is off no heat is being produced, so both the engine and passengers would see lower temperatures, then these temperatures would come back up when the engine is on. Not good for people or engines. With a standard HV system this problem only exists on very long downhills, so much less frequent in nature.

    Yes the car is amazing. But you know sometimes even great engineers don't get to do all that they want to do. Engineering projects always have to balance results versus cost and time. That's what engineering is. Sometimes a company determines that a better result is not worth the cost or delays to promised product release dates. Sometimes they think we'll make it better later, but that opportunity to improve may or may not come about. Even at Honda (although I do think they put more emphasis into the engineering back in company founder Soichiro's day).
  14. insightman

    insightman Well-Known Member

    I hope some Honda engineer gets upset when reading your post and opens up with all the info people on this forum have been craving.
    David Towle likes this.
  15. David Towle

    David Towle Active Member

    And 2 more things to add:
    1. If they did redo the algorithm just for this car it would probably violate one of the most important principles of engineering: "If it ain't broke don't fix it" Since they didn't maybe it means the Clarity shares some code with your original Insight?
    2. The efficiency penalty of weight is much less in a hybrid than a gas car. It takes more work to get a heavier car moving, but with a hybrid you get much of that work back with regen.
  16. insightman

    insightman Well-Known Member

    I doubt there's anything shared between my 2006 or 2010 NiMH IMA Insights and Honda's Li-Ion i-MMD hybrids. I can get 60 mpg from my 2006 1,900-lb Insight, but it's tough to get 42 mpg from the 2010 Fit-based Insight, which is more than 1,000 lbs lighter than the Clarity.

    I guess because I'm a Honda fanboy (er, fangeezer), I believe that Honda wanted to maximize the Clarity PHEV's efficiency rather than just add a bigger battery to the original i-MMD Accord Hybrid's guts. I agree that it's not a completely different system, but I'm sure it was improved.

    Look how the current i-MMD Accord Hybrid has a different 181-hp electric motor than the 181-hp electric motor in the Clarity PHEV. It would have been easier to use the same electric motor in both cars. They didn't take the "If it ain't broke don't fix it" approach in this instance.
  17. skylines

    skylines New Member

    I can think of a possible reason Honda wouldn't do this, and also why the original suggestion that started this thread is probably best used in very limited circumstances. The few times I have tried HV charge for an extended period on the highway it seems to build up EV miles as fast, or maybe even faster, than level 2 charging while also driving at highway speeds. HV charge is also restricted to about 60%. All this suggests that HV charge is effectively something like an internal DC fast charging mode for the PHEV. If HV mode always defaulted to this (which is along the lines of what you are suggesting too) the battery is likely to degrade very fast. Maybe even much faster than EVs that always use DC fast charging because at least they aren't driving on the highway when doing this so and the battery management system can deal with it better.

    The internal combustion engine has enough capacity to rev up and provide extra charge when needed. It will be okay even if it makes a bit more noise. A lot of people seem to get annoyed by the sound of the engine. But it still is very efficient. Trying to eke out slightly more efficiency or limit short bursts of higher engine revs might come at a huge long term cost to the battery. If this is the reason, I much rather prefer this compromise.
    neal adkins and Lowell_Greenberg like this.
  18. ClarityBill

    ClarityBill Active Member

    I am another vote for poor engineering in the lack of optimization with the larger battery: HV mode uses less than 20% of the battery before it goes to high-rpm.

    I see temperature cycling of the ICE as a reason for the short-cycling: Better engineering would factor ICE temperature into the algorithm (it does not appear to be in the existing programming).

    I don't see temperature cycling of the passengers as an issue, Clarity freely uses the resistance heater to maintain passenger compartment temperature, even with a warm engine.
    Last edited: Oct 26, 2019
  19. David Towle

    David Towle Active Member

    The connection to the Insight was meant as humor, I also think its very unlikely.
    Its quite possible you are right about optimization, I just like to point out engineering is always full of cost compromises.
    insightman likes this.
  20. TomL

    TomL Member

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