ICE runs after going down a hill at the beginning of my drive.

You nailed it. General consensus is when the battery is full regen needs to dump power somewhere so (still s puzzle to me) the engine is used to dump power.

I have a similar driving situation but it is about 1/2 mile to the beginning of the 1/2 mile 14% grade. In my case the engine does not come on.

 

Some other subtleties (see the “ICE breaker” thread for much more detail): -Activities such as running heater/heated seats are reported to generally use up enough battery power to prevent this, so it may be a seasonal thing for you depending.

-No one is sure how much fuel if any is burned by the engine running “backwards” in this circumstance, but general feeling is that it burns some—at a minimum because the ICE stays on longer than the hill, perhaps because there is a minimum run time to bring it up to temperature.

 

I would suggest that when the engine turns on for whatever reason that you let it run. This ensures that any condensation is burned off. Engines don’t like to be started and not run to operating temps. The computer will turn it off if it’s not needed after it warms up. Mine stays in for just 6 min or less according to the hour meter I installed. Also I suspect that turning off the engine before the System Check is finished may cause the algorithm to try to finish the SC later and cause more engine operation.

 

Well said. This seems to be the least understood, or accepted operating feature of the Clarity. Note the supporting comment on page 13 of the Owner's Manual: "Once the engine starts, it will continue to run until the system reaches operating temperature." I don't pretend to be an expert on this subject, but this seems totally sensible to me, and consistent with engine longevity, for the reasons you stated.

 

Highland58, I've been waiting for someone who lives and recharges atop a hill to determine if the engine starts up every time the Clarity tries to add regenerated electricity to a fully charged battery. You seem to have answered that question: "Sometimes the engine starts..." As you gain more experience, it would be great if you could figure out a way to make it happen every time. However, the usual case with the Clarity PHEV is that experiments rarely produce repeatable results.

When its battery is fully charged, the Accord Hybrid burns off excess electricity generated by the traction motor by using that electricity in the starter motor/generator as it spins the unfueled engine. How the Clarity PHEV can use up excess electricity by running the engine is the biggest mystery in my list of Clarity mysteries.

 

The inconsistent behavior is what is most frustrating. Drove my similar route today. ICE did NOT come one. Yesterday it did several times.

 

Maybe bring it up to Honda, they will probably blow you off unless you push them hard on it which may or may not be worth the effort.

Many users have seen that the car will start the engine on a full charge while going down hill/braking. The Volt left a buffer of battery capacity to charge before it has to get creative burning off the extra energy, something like 0.5 or 1 kWh.

Some suggestions are to not quite charge the car totally (schedule it to end slightly after you leave) or do something to burn off some power before you leave (climate for a few minutes).

My thought this is an issue that Honda should adjust software for, maybe allow it to slightly overcharge or at least display a message. Maybe have it burn the extra energy using the climate system, or do something other than start the engine. I realize it is a hybrid with 0-47 mile range (can start engine any time), but most would like to drive it without the engine running as much as possible.

 

Anecdotal here (but so I suppose is much of this) but I find after intended use of the Hybrid mode during out of town trips, the car seems to utilize the ICE for about 3-5 minutes the following 2-3 days early on in my morning commute. But with extended periods of EV use only, I've not noticed the ICE activating unintentionally.

 

I have found a reliable way to mitigate this issue. If you coast down most of the hill in neutral, the ICE will remain dormant. I have found a hill greater that 1/4 mile will trigger the ICE, though this is likely dependent on the grade. The regeneration system doesn't seem to have the ability to disengage, thus as @jdonalds and others have noted, the system must exercise the battery via the ICE.

To avoid the ICE on a full charge while parked up a large hill:
1. Start the car and drive as usual
2. Once safely up to your desired speed and proceeding downhill, shift into "N" (if legal in your territory)
3. Apply the brakes as needed (you will notice the regeneration indicator does not move)
4. Once near the end of the downhill, shift into "D"

Note: Many US states "have no-coasting on a downgrade" law. In Canada, at least one province has a similar law described as "Coast down grade illegally".

 

I have this problem too. It's really a shame - i'd be perfectly fine to trade a lower maximum usable capacity for full regen ability and no ICE activation like my previous chevy volt.

 

I wish we had a better understanding if why, when the battery is full, Honda doesn’t just use the brakes as friction brakes (bypassing regen). The workarounds to spill energy other ways (running the ICE as in this case, or as for other cars keeping a secret extra amount of charge unused) may have a spind engineering reason, but without knowing this it is just driving us crazy...and foiling non-engineering bit satisfying goals such as 0% ICE.

 

You wouldn't want to use only brakes to come down a mountain (the extreme case for which Honda must prepare), but the Clarity PHEV cannot use traditional engine braking, so it needs another way to slow the car without using the brakes.

The Accord Hybrid performs pseudo engine braking by taking the electricity coming from the traction motor and sending it to the starter motor/generator, which spins the engine. The Accord Hybrid's engine doesn't start up in this situation because the system doesn't give it any fuel. The engine pumps air through its cylinders to provide the resistance that ultimately expends the energy generated by the traction motor as it slows the car.

It is likely (but not confirmed--can someone confirm this, please?) that the Clarity PHEV can also spin its unfueled engine to provide pseudo engine braking. The big difference between the Accord Hybrid and the Clarity PHEV is that the Accord's engine has certainly been running and its oil is warm, whereas the Clarity PHEV's engine may have never run since the car was purchased (again, the extreme case), so its oil is not guaranteed to be warm. So the Clarity needs to start its engine to warm the oil before it proceeds to run in unfueled pseudo engine-braking mode.

My apologies to all who have read me expound on this conundrum ad nauseum.

 

Makes sense, insightman, though I am still baffled by the idea that the engine is being used to provide braking by internal friction*, but that because this generates wear and tear on a cold engine, one needs to detonate fuel in the cold engine to warm it up....to reduce friction. Which reduces the engine braking.

Just seemed to me that unfortunately the wear and tear/internal friction is the desired effect, in that the heat generated IS the engine braking, and that if it is high it will warm the engine by itself anyway.

I will, however, gladly concede that what doesn’t make sense to me is still 100x more likely to be a considered design choice than a mistake. Maybe a warm engine (warmed by combustion, not just friction) provides the right amount of internal friction to supplement the brakes, while a cold engine provides too much (great to have for braking, but more wear and tear than needed).

Still wish, as we all do, they’d explain it. Someday we will all have an “ohhh, that is why” moment, even if we don’t agree with the reasons.


*assuming no air compression release, aka noisy “jake brake”.

 

So, when ICE comes on it is NOT burning fuel, or is it? I can see the HV miles go down when it comes on. Doesn't mean it IS burning fuel?

 

Would be interesting to learn if ICE is rotating without power. On my previous PHEV, the engine would rotate at exactly 960RPM when the vehicle was coasting, zero gas being used. The way to get there was to find the 'sweet spot' between regen and power (essentially zero on that scale), which generally involved some level of pressure to the go pedal. I used it frequently on downhill. Engine speed would drop to 960RPM and MPG would peg at 999.9… This can be done on the Clarity, but I can't be sure that ICE rotates. We need more data. This - if it worked on Clarity - could circumvent putting the car into neutral on a downhill run. This method worked for those with the original Prius PHEV - but it took a few months of trial and error for drivers to make it work consistently.

 

That would be great information to have.

 

Hope this helps.
Every time my ICE has come on after a full charge and slight downhill, the hour meter I installed has registered engine time showing that the spark plugs are being fired. Also when I then pull over, the ICE is running

 

That echos my experience today. Full charge. Going UPHILL to a stop sign, ICE came on. Even after stopped. HV range went from 196 to 195 indicating fuel was being burned. And ICE stayed on for a few minutes. Everyone this is happening to should start a ticket with Honda. The rep I talked to said I was the only one who has reported this behavior. Oh, and Honda does not read forums.