Unwanted gas engine charging

With the battery fully charged any breaking or downhill will cause regen. There's no room in the battery for more charge so the Clarity uses the engine to dump power. The engine starts. Common wisdom here says once the engine starts it must run until it is warmed up which might be 5 - 10 minutes.

The suggested way to defeat this issue is not to fully charge the car if your charge station supports that feature. Leave a bit of the battery uncharged and see what happens.

 

Or if the time where the engine starts is predictable (where you are decelerating hard enough), I have had decent luck turning on the defroster or climate control on high to help give a drain for the regen energy to go instead of the engine starting. You will need to start the intentional climate control loading about a minute or so prior to hitting the brakes or using the paddles for regen for this strategy to help. Being as soft as possible on deceleration also helps early in the drive after a full charge. Now that you know the culprit that causes the engine to start, hopefully you can find a strategy that makes you more happy with making it stay off.

 

Would be cool if they implemented P1901 so the car and EVSE could actually communicate. Sure, it's only a PHEV, but we'd still like to maintain our batteries as well as possible.

 

Do the test that jdonalds recommends and if that works, then your choice going forward is to avoid fully charging the car as he said, or avoiding regen during the first few miles as Robert_Alabama mentioned. One way to avoid full charging is the obvious one, don't charge if you already have enough EV miles remaining for your next days driving. The other way to is to stop charging when the battery is between 80-90% full. Unfortunately there isn't a way to tell it to only charge to a certain percent, so what you do is schedule an amount of charging time that will only charge it to 80-90%. You will probably need to gain more experience charging to find out how much time that is, to make it easier concentrate on the percent of charge instead of miles remaining since that can fluctuate a bit.

Avoiding regen during the first few miles is the other method, which may or not be possible depending on your drive and if you have some big downhill segments early on where regen is unavoidable. If you haven't noticed yet on the display screen the power meter shows when power is driving the wheels and when regen is occurring. If you keep the needle in between the two the car is coasting. If no one is behind you try coasting to your first few stops with as little regen as possible and this might keep the engine from coming on. The last few seconds before stopping you will notice that regen does not occur anyway, that is because the friction brakes take over at the very end of the stop.

There are other reasons and times that the engine might come on, but after you get some experience and also adjust your charging schedule you should be able to drive EV only for the majority of your trips that are within EV range.

 

Excellent advice from all the above!
I’ll just mention that I got mine to hardly ever engage the ICE in “the limited regen to protect the battery from overcharging” scenario by using the brake pedal gingerly and not the paddle for the first few miles. That works for me but may not work if you have a significant downhill or a heavy braking foot.

Also, please be aware that once the ICE starts if will stay on until it reaches operational temperature. It does this to protect the engine and exhaust system from condensation and moisture. IMHO, its best to let it stay on until it warms up. And you can’t keep it 100% off since it will occasionally perform a System Check. Just accept the brief and mostly seldom ICE operation and don’t worry about it. It’s keeping your engine happy, healthy, and ready to run when actually called on. I’ve gone 9 months and 7,000 miles between HV trips and haven’t major a bar on the gas gauge to the infrequent, brief ICE starts.

And technically, when this happens it’s not charging your battery, it’s protecting it by somehow not allowing the regen to overcharge it. The BMS may act in seemingly mysterious ways (especially since Honda doesn’t give us any info on it) but it is doing a great job keeping our batteries healthy.

 

socalclarity

Or you could just let the car run until it reaches temp (140-170 degrees f) then it will cycle off. Link to another post on this topic contains some additional info if you are interested.

https://insideevsforum.com/community/index.php?threads/ice-engaging-at-strange-times.5286/

As a matter of course, I do not charge to full which limits ICE activation when leaving the house since I happen to live on a mtn. When I do charge to full...the ICE tends to come on and I let it run until it cycles off. Depending on ambient temps...that can be less than 5 minutes or upwards of 10 minutes. I take no action to limit nor discourage ICE activation...I let the Clarity do what it is designed to do.

No right or wrong...just preference.

Hope this helps

 

There is one flaw in our theory regarding Regen Overcharge Protection, and it's this:

What do BEVs do when the battery is full and regen is used since they don't have an ICE to dump excess power?

I've also noticed that if my low gas indicator is on (less than 35 miles on the HV guess-o-meter), the engine doesn't seem to start up in the way we've been describing. This has to be substantiated and I'm wondering if anyone else here has noticed this change of behaviour?

As mentioned many times previously, this is one of the biggest mysteries of the Clarity PHEV, and if Honda could answer only one of our questions I think this would be it.

I can confirm that when it happens for me, the engine does turn off after 5 minutes (when it reaches temperature). I cannot force it to go off by turning HV on and off, and the HV guess-o-meter drops about 2-3 miles, so gas is being used.

One of the benefits of having a PHEV is to be future proof against legislation that may ban ICE use in urban environments. This "feature" would be in direct violation of such a law.

 

Member 2002 provided some excellent advice.

Once I got the feel for how much % of charge I could get from each hour of charge on my 16 amp ZenCar EVSE, I adjust the amount of time my car charges in the HondaLink app. I usually start each day with around 80% charge, and keep my ICE usage to a minimum.

To mix things up, some weeks I let the car go several days without charging and let the charge level fall to less than 15%, then adjust the time in the HondaLink app on a overnight session to charge for several hours to try and hit my 80% charge target.

 

I've been completely fascinated by the Clarity's penchant for using the ICE to dispense with regen power when the battery is fully charged. Still waiting for Honda to write a scholarly paper to describe the "feature" (and for @Ray B to find it). The lesser Honda hybrids don't run the ICE--they just shut off the ignition and fuel injection and send the regen power to the starter motor/generator so it can use up the excess power by turning the deadened ICE.

BEVs, of course, cannot do either of these tricks with the ICE, so when their batteries are fully charged they cannot allow regen to occur and I assume the friction brakes have to shoulder the full burden of slowing the car. This lack of regen must result in some hot brakes when coming down a mountain after the regen has topped off the battery's charge.

 

Which is why Chevy Bolt has a "hilltop" charge mode so it doesn't fully charge the battery with this setting. Tesla recommends not fully charging.

Honda needs to add more charging options.

 

Sport mode

 

One observation, FWIW.
When my Clarity was new I got several of the engine starts when first leaving home on a full charge. This is with a stop sign ~600 ft and another one at ~700 ft with only a very, very slight downhill. Sometimes it was so quiet, I didn’t notice it until a couple of miles away. Now at 1+ year and 10,000+ miles, I haven’t had it do that in seemingly forever.
I wonder if the battery has slightly lost just barely enough capacity that it doesn’t trigger the threshold of not accepting any more regen charge since I’m not really on a hill.
Anybody else see a reduction in engine starting after full charge as their Clarity has gotten older?

 

Myth busted: I was able to get the engine to start using aggressive regen this morning despite the low fuel warning.

 

Hi KentuckyKen....nope mine is just the opposite - I have an increase in engine starting in my second year - and an increase in range - up to 104 km now... going neutral down our downhill driveway - so using friction - seems to help; and avoiding regen as much as possible for the first 10 km or so - but it is still a complete crapshoot.
Gassed up in early May and used less than a 1/4 tank to now with 2 legitimate 'gas' drives range 580 km down to 440 km.

 

Gas engine doesn't come on to "dump charge" or "protect the battery". It comes on to stop the vehicle vehicle without using mechanical brakes. As at high level of charge it's impossible for battery to do that without using electricity (plugging) which is horribly inefficient. To regulate the rate of braking, using electromagnetic braking, the vehicle must be able to regulate the current flowing through the generators while braking.

For electromagnetic braking to work the battery must function as a load and be able to pull enough current to generate a magnetic field to stop the vehicle. Since the batteries have an exponential increase in resistance as they reach full state of charge (85+ percent) there is a point where the batteries physically can't sink enough current to stop the vehicle. It's not about protecting the battery, it just the battery resistance it to high at that point. If battery is full, it just not physically possible for it to pull enough current to stop vehicle. Different manufacturer's dealt with the physics of this in different ways.

In the case of the clarity the choices for the drive train is to use mechanical brakes, use plugging (consume electricity) or use the ICE. It's choices are more limited due to fact that it doesn't have variable gearing. It's braking behavior is a design choice and assume they looked at efficiency and wear on components etc.

In the Tesla they have vehicle only charge to 80% by default. This allows enough room to allow for electromagnetic braking through regen. When battery reaches full the vehicles only choice is to use the mechanical brakes. So Tesla tries really hard to NOT let battery hit 100%.

On Chevy Bolt the 100% charge isn't really 100% charge. It's closer to around a ~92% charge on the pack even though dash says 100%. If you happen to charge a Bolt to 100%(as indicated on dash), when you brake you get a white indicator on the dash instead of a green one. Which indicates the electromagnetic/regen braking is limited and the vehicle will depend more on the physical brake pads when the indicator is white. You also will find that when at 100% the vehicle will only use regen at lower speeds as the battery can't function as a large enough load at higher speeds (current would need to be much higher).

On the Chevy Volt at a 100% state of charge, (depending on which gen you have) there is a point where the regen paddle does nothing when coming down a hill. You can tap it, and you don't slow down. You just get a warning. You have to use the brake pedal to slow down, which uses a little bit of regen but mostly uses mechanical braking.

BEV can pull the trick of not really charge to 100% to allow electromagnetic braking because the batteries are big enough that the missing range is built into the design and doesn't negatively effect the owner. In the PHEV they are trying to get every last mile out of the pack, as it's much smaller, so they tend to result to tricks like plugging or using the ICE to sink enough current to allow vehicle to stop. As the "feel" of the mechanical braking vs electromagnetic braking is usually significantly different and they don't want to have a negative effect on the driving experience.

There are some other limits you might see when near a 100% charge on the clarity. At 100% charge, at high speed, even with ICE on, the number of deceleration indicators on the dash you see from the deceleration paddles may often be less than when battery isn't at a full state of charge. You can find you have one less than if the battery wasn't at a 100% state of charge.

 

An interesting theory and take on the Clarity’s engine start at full charge scenario that makes a lot of sense.
Could it be that both reasons are in play, as in the resistance of the just charged battery is too high to accept a high amount of regen and the BMS is trying to prevent overcharging past whatever %SOC it considers safe?

Based on several posts’ data, it appears that about 24% of the 17 kWh battery is reserved for a buffer and we’ve assumed it’s split (ratio unknown) between too and bottom since that is common in Li-ion battery applications.
I also notice that for the first few miles after a full charge that we all see the amount of regen on the power meter reduced to only about 1/3 to 1/4 of the full range. That Is completely compatible with your resistance theory. I guess the real question is that if the BMS is keeping a small buffer at the top end of the SOC, then what is the battery resistance at that point of maximum allowable charge?

Now you got me thinking...
So is the limited regen with a full battery akin to the limited or taper charge at the end of the charge cycle?
And then both events are due to increased battery resistance at full allowable charge? So then there is a physical limit to the amount of charge due to resistance and the BMS is protecting the battery from overheating? And at the same time the BMS is monitoring battery voltage to protect against overcharging past its maximum allowable charge? Only one going on, both?? Please help me out here; I’m a bio guy not a physics guy.

Reverse engineering this inscrutable Oriental electronic marvel is quite a challenge!

In any event, hats off to the Honda engineers that gave us such smooth braking that its almost impossible to tell how much braking is regen and how much is physical by just pedal feel. And ditto for the BMS and liquid cooled battery’s 8/10 yr warranty that makes me feel like it’s a great design too.

 

I disagree. I'll admit I don't understand the concept of "plugging", so perhaps everything I believe is wrong.

You wrote that the gas engine "comes on to stop the vehicle without using mechanical brakes." How is that possible? The engine is sometimes connected to the wheels through the Engine drive clutch only when the car is traveling at speeds greater than 45 mph (or 42 mph with my Clarity), so the engine has no way to slow the car at lower speeds when it starts running in response to regen braking with a fully charged battery.

The Clarity never allows the battery to charge to its nominal 17 kWh because fully charging a Li-Ion battery--especially for a long time--is reportedly not good for its health. So the Clarity protects its battery by not allowing either EVSE charging or regen-brake charging to charge the battery beyond its preset buffer. Members of this forum have reported the battery can accept up to a maximum of about 14.1 kWh while charging. There is also a bottom-end buffer below which the Clarity will not allow the battery to discharge, so the maximum charge is 14.1 kWh plus the size of that bottom-end buffer, but always less than 17 kWh.

So why does the engine start up in response to regen braking when the battery is fully charged? One clue is that when the battery is fully charged with Honda's lesser i-MMD hybrids, they use the excess energy coming from regen braking to power the starter motor/generator to spin the engine after shutting off the engine's fuel injection and ignition systems. Why doesn't the Clarity do that, too? Perhaps because the Clarity is a heavier car and more energy needs to be dissipated. My theory is that the starter motor generator in the Clarity is actually fighting the rotation of the powered-up engine to dissipate more energy than the "dead-engine" technique used by the lesser i-MMD hybrids. I could be wrong. I'm hoping expert sleuth @Ray B will discover a paper written by Honda engineers that explains this process.

 

The answer may be here:

Engine braking with a dead engine and no CVT would only be at one level. However if the engine is running the effort needed for engine braking to turn the engine could be controlled through engine RPM. At low engine RPM there would be more resistance to turning the engine than at higher RPM. So not fighting against the running engine like in your theory, more like engine braking is fighting to turn the engine, but the engine itself can help to varying degrees, thus controlling the load.

 

Yep. It's part of same reason why the ICE can only recharge battery up to a certain point in generator mode. As there also is a point when engine is running in generator mode it horribly inefficient to charge the battery as you are generating much more power than battery can consume as it hits the end of its charge cycle.

At around 80-90% charge the internal resistance of the battery is such that the max charge current is roughly half of 10% charged battery. Depending on battery pack design at above 80-90% generally a max constant voltage has been reached by the BMS and the max current draw for battery has been reached for its charge state. At a certain point (since voltage is fixed, and resistance of battery is increasing) the battery can not sink enough of a current to allow a large enough magnetic field in the generator to stop the vehicle. This point on the curve hits WAY before you hit a problem of overcharging the battery so its not a battery protection issue. The BMS doesn't kick in to protect battery way later than point where battery isn't sufficient enough of a load to allow electromagnetic braking. (due to exponential increase in battery resistance)