Starting with full charge, downhill for 2 miles, engine comes on

[The Gadgeteer]

Perhaps the Clarity runs the engine longer than the Insight and Accord once activated because the Insight and Accord don’t have a big battery that keeps the engine off for long periods of time therefore do not need the engine warmed up to help lubricate and burn off contaminates.

 

[insightman]

Perhaps the Clarity runs the engine longer than the Insight and Accord once activated because the Insight and Accord don’t have a big battery that keeps the engine off for long periods of time therefore do not need the engine warmed up to help lubricate and burn off contaminates.

True, the Accord Hybrid and Insight's engines are always warm due to their comparatively tiny batteries. That's a good explanation for why the Clarity runs its cold engine longer, but it doesn't explain why the Clarity PHEV starts the engine at all to deal with regen electricity when the battery is fully charged.

 

[JFon101231]

I really hope Honda's engineers someday publish a paper to explain this phenomenon...

My theory is that the heavier Clarity PHEV needs to dispense with more energy on a long decline than those other hybrids and the only way to do that is to have the starter motor/generator trying to slow down the running ICE. Certainly the ICE doesn't start up and drive the starter motor/generator to generate MORE electricity, so having the starter motor/generator fighting the ICE seems to be the only way to explain how the Clarity PHEV deals with the excess electricity.

Good point on why it may run longer. I doubt Honda will ever share their secret(s) sadly.

Eek, the thought of trying to slow down a running ICE is scary! I guess I'd be less annoyed in my situation if it truly was a long decline, but literally its 2 stop signs with negligble altitude change over a distance of < 1/3 mile. Over the next week or 2 I'll have to see if it happens in all 3 levels of regen (4th wouldn't activate), or only if I manually increase from 1 to 3 (sometimes I do even when full out of habit).

 

[ClarityBill]

I thought the conclusion here was the Clarity runs the starter motor against a dead engine to use up the excess energy. It then continues to run the 'live' engine to warmup, lubricate, and burn out the contaminants.

 

[JFon101231]

Ah, that would make a bit more sense. And to the suggestion noted by The Gadgeteer, that may be a longer cycle on the Clarity due to the fact the ICE may not otherwise run before parking.

Still don't understand why Honda has decided that this complicated approach is the best way for a PHEV versus the EV approach to just 'bypass' regen but alas "it is what it is". I just hope if I can remember not to increase from the 1 chevron of regen that I can avoid it.

 

[KentuckyKen]

I have an inductive pickup hour meter on mine so I can state that at least one spark plug is energized since it increments and two times I stopped and popped the hood to find the exhaust manifold hot. Also when it happens and I come to a stop, there is energy coming from the engine icon to the battery icon on the display, and the engine icon is illuminated.
(It’s very hard on my car and my old ears to hear the engine at idle). But it was idling the two times I popped the hood.

So I believe the engine is running and not just turning over.

 

[JFon101231]

I don't think anyone is disputing that the ICE ends up running, the question is whether its running when first trying to dissipate energy from regen or only afterwards to lubricate, burn off, etc.

 

[ClarityBill]

We are agreeing that the engine is running, but only after the excess regen is used up.

During the excess regen time, it 'may' be a dead engine - very difficult to confirm, but it makes more sense.

 

[Mark W]

I find it interesting that we have been debating this issue of why the engine turns on when the battery was full for months and months, and nobody can provide a good reason why it has to happen. Other automakers don't seem do handle it the way Honda did. My Leaf doesn't have a gas engine to run, and I have no problems with braking and regeneration with it. Why design a car to work in a way that seems so foreign to it's owners? Imagine how many owners don't come to a forum like this to get answers. I would think many of them bring the car back to the dealer claiming that the car is defective. From what we have heard here, it seems most service departments don't fully understand the way the car works either, so they probably get some vague, unsatisfying answer.

I wish Honda would provide some software update to lessen the "unexplained" times the engine has to run. Also, it seems for this particular issue that it would be very simple for them to provide an update that allows the user to stop charging at 90%, or whatever % needed so people who live at the top of hills would not have to deal with this. Even for those that don't live at the top of a hill, it would be useful to help lessen long term battery degredation.

 

[The Gadgeteer]

A pure EV would have a much larger battery that is able to accept more charge/over overcharge regen without damage plus an EV may use electricity (motors working against travel direction) to slow down in an extreme case. Although this is speculation on my part. Anyway, the Clarity has at its disposal an engine so its own version of engine braking is strange but a good and possibly required safety feature. I would hate to be heading down a long steep mountain with 4000 lbs car, a full battery, overheated friction brakes and no other way to slow down.

Only we can decide how we want to feel about it. We can think of it as an excuse for a blast of indulgent climate control to use up some electrons and/or do some spirited driving in sport mode if the engine is going to be running for several minutes anyway. Hopefully the logic is such that once the engine runs there is that much less need for the engine to run later for maintenance reasons.

 

[Robert_Alabama]

For a while, I was one of the more vocal posters about how much I disliked this. Time has mellowed me a good bit. I can usually manage this with preemptive use of the climate control since my occurrence is very predictable. When I forget or miss the amount of climate load to impede the ICE, I've gotten to where it doesn't bother me as much. Just a part of the operation of the car. Still don't like it, but it's small potatoes compared to all that I do like about the car. In the grand scheme of things, it's just not enough of an issue to continue to stress over for me. I suspect that in 10 months that I have burned maybe a gallon or two of gas due to this...

 

[2002]

Let the car do what it is programmed to do.

As smart as the car is you would think it would recognize that the engine was run only briefly on the previous drive and automatically run it for a few minutes on the next drive. Because there can be legitimate situations that you can get into, for example ICE just happens to come on just as you reach your destination. So another way to look at it is that the software was wrong for not starting ICE when they restarted the car at the bottom of the hill. Or maybe it had determined that ICE had already run just about long enough during the previous drive and that's why it didn't start.

Regen is like a really really fast charge for a short period of time.

That's a good point, we tend to focus on overcharging the battery (or charging beyond whatever upper limit is internally set to prolong battery life). But I would think that regen charging can be pretty hot and that is probably another reason why they want to avoid regen when the battery is nearly full, especially in extreme temperatures, and would explain ICE coming on when the battery is nearly full but not quite at 100%.

My theory is that the heavier Clarity PHEV needs to dispense with more energy on a long decline than those other hybrids and the only way to do that is to have the starter motor/generator trying to slow down the running ICE.

That is an interesting theory. It would indicate they are really struggling to get rid of the excess energy in situations where regen is not available, which I suppose is quite possible considering the weight of the car. It would be an added complexity and a small waste of gas, but then again not needed very often, and thus maybe a better overall solution than installing heavier brakes. I guess we could call your theory the "retro-fire" theory, or maybe the "reverse-thrust" theory

The regen on this car sucks compared to my Fit EV. But now that I'm thinking of it, the 'best' 4 bar regen on this car is probably about equal to the 'worst' regen on the Fit when battery was full or when it was too cold.

I have heard this comment before about "better" regen on one car compared to another, but I don't know what exactly is meant by "better" regen. Assuming it is about the quantity of regen available, that's determined by the crossover threshold between regen and friction braking, something that is not easily determined. So I'm not sure how you can compare regen capability between cars unless you have access to that data.

What I think is throwing some people (not you) is they are looking at default coasting regen, which can be stronger on some cars than others, and they make the wrong assumption that more default coasting regen is better than less, when actually the opposite is true because the closer you can get to "neutral" while coasting the better, whereas regen, although certainly better than friction braking, still has quite a bit of losses. In your case you are looking at paddle regen, which is not as strong as on your Fit. Others complain if they can't do one pedal driving like you can on some cars. I'm not disagreeing with those complaints, but that's just a matter of convenience, not efficiency, since you can get all the regen you want by using the brake pedal, again limited only by whatever the threshold is for the friction brakes to engage.

 

[JFon101231]

What I think is throwing some people (not you) is they are looking at default coasting regen, which can be stronger on some cars than others, and they make the wrong assumption that more default coasting regen is better than less, when actually the opposite is true because the closer you can get to "neutral" while coasting the better, whereas regen, although certainly better than friction braking, still has quite a bit of losses. In your case you are looking at paddle regen, which is not as strong as on your Fit. Others complain if they can't do one pedal driving like you can on some cars. I'm not disagreeing with those complaints, but that's just a matter of convenience, not efficiency, since you can get all the regen you want by using the brake pedal, again limited only by whatever the threshold is for the friction brakes to engage.

Yes, I'm referring to coasting regen, which is generally the same as enabling 1 pedal driving.
With my Fit, I rarely used the brake pedal. It decelerated in a manner that was similar to conservative driving and a reasonable stopping distance similar to an ICE car with a manual transmission. In other words, I was slowing down in the same "zone" prior to a stop sign etc as most ICE car would be.

With my Clarity, I either have to start coasting much further away from stopping point, which is potentially unsafe, or have to use the brake pedal. I compare the Clarity coast decel to be similar to an automatic car, i.e. hardly noticeable. Since its not possible, at least for me, to determine when the friction brakes are engaging as I push the brake pedal, I perceive it that I am using friction brakes more than I would not have previously. Perhaps I'm actually not and its all regen just with a pedal and brake lights - guess as a data nerd I'd be interested to know.

 

[thecompdude]

Yes, I'm referring to coasting regen, which is generally the same as enabling 1 pedal driving.
With my Fit, I rarely used the brake pedal. It decelerated in a manner that was similar to conservative driving and a reasonable stopping distance similar to an ICE car with a manual transmission. In other words, I was slowing down in the same "zone" prior to a stop sign etc as most ICE car would be.

With my Clarity, I either have to start coasting much further away from stopping point, which is potentially unsafe, or have to use the brake pedal. I compare the Clarity coast decel to be similar to an automatic car, i.e. hardly noticeable. Since its not possible, at least for me, to determine when the friction brakes are engaging as I push the brake pedal, I perceive it that I am using friction brakes more than I would not have previously. Perhaps I'm actually not and its all regen just with a pedal and brake lights - guess as a data nerd I'd be interested to know.

Pressing the brakes when going downhill generates more Regen than 4 chevrons as can be observed by the pointer in the green Regen region.

Also, the numbers in the EV range ticks up much faster.

On a side note, anyone surprised by how you get EV range down to a decimal point on the dash, but there energy monitor has no decimal point precision, even though there is so much more real estate in the center display console!

 

[KentuckyKen]

With my Clarity, I either have to start coasting much further away from stopping point, which is potentially unsafe, or have to use the brake pedal.

Why don’t you just do what I do and use the paddle instead?
I look ahead and take my foot off the go pedal as soon as I see the light change. Then if I need to slow down quicker, I don’t even have to move my foot at all by using the left paddle. I only move my foot to the brake for the last 5 mph or so and only if the light hasn’t changed to green by the time I get there. It’s practically effortless and I like it a lot better than an EV with one pedal driving and the constant feathering of the go pedal. IMHO, it’s the laziest way to drive and the most economical. (Although I bet light to moderate brake pedal force is practically the same as using the paddle). I just like not having to move my foot much and instead just moving a finger instead.

 

[MNSteve]

On a side note, anyone surprised by how you get EV range down to a decimal point on the dash, but there energy monitor has no decimal point precision, even though there is so much more real estate in the center display console!

Agreed. And the other somewhat odd thing is that there's no rounding; if the dash shows 12.9 the console shows 12.

 

[thecompdude]

Why don’t you just do what I do and use the paddle instead?
I look ahead and take my foot off the go pedal as soon as I see the light change. Then if I need to slow down quicker, I don’t even have to move my foot at all by using the left paddle. I only move my foot to the brake for the last 5 mph or so and only if the light hasn’t changed to green by the time I get there. It’s practically effortless and I like it a lot better than an EV with one pedal driving and the constant feathering of the go pedal. IMHO, it’s the laziest way to drive and the most economical. (Although I bet light to moderate brake pedal force is practically the same as using the paddle). I just like not having to move my foot much and instead just moving a finger instead.

One of the problems with not using much of the brake pedal is not having the brake light turn on to warn the car behind that you are slowing down. Could cause an accident if the person behind is not paying attention.

I wish the brake light would turn on, if you go beyond a certain Regen level.

 

[insightman]

The regen-braking ICE start-up is my favorite Clarity PHEV topic of discussion.

There is a limit to the charge the battery in any PHEV or BEV can hold. When the battery is fully charged (leaving a safety buffer to prevent battery degradation), regen braking is not an option. There is nowhere for the regenerated electricity to go. With a fully-charged battery, a BEV has no option but to use its friction brakes to slow down. A hybrid vehicle, however, has the option of using its ICE in some manner to reduce the dependence on its friction brakes, which is a good thing when coming down from the top of a mountain.

When their batteries are fully charged, it's clear that the Accord Hybrid and Insight continue using the traction motor as a generator, but instead of charging their batteries, they direct the energy from the traction motor to the starter motor/generator operating as a motor to turn the unpowered ICE. This technique has been successful since the i-MMD hybrid system was introduced in 2014.

So why not use the exact same technique in the Clarity? Why, instead, would Honda set up their top hybrid, their most energy-efficient car, to burn gasoline to allow the traction motor to perform regen braking? I believe that Honda didn't use the simpler, more fuel-efficient technique from their non-plug-in hybrid cars because something was different about the Clarity PHEV. The most obvious difference is the greater weight of the Clarity PHEV. The engineers didn't do all the extra work to create a more complicated, less fuel-efficient regen braking technique just to show off. They did all the extra work to provide an alternative to using friction brakes to limit the Clarity PHEV's speed while descending a mountain.

If the Clarity had more than one speed in its clutch-connected gearbox, then the car could use engine compression like a regular car to limit its speed while going down a mountain. However, the tall single gear that comes into play when the Clarity PHEV's Engine drive clutch is activated cannot effectively slow the car.

When the battery is fully charged and the ICE starts up in response to regen braking, it is unthinkable to me that the ICE would be turning the starter motor/generator to generate even MORE electricity. So I believe the regen braking energy is going to the starter motor/generator to perform its function as a motor. If the starter motor/generator is operating as a motor, and the ICE is running, then the motor is either trying to speed up the ICE or slow down the ICE. The latter makes more sense to me, but it could be the former.

The idea that the Clarity PHEV turns the unpowered ICE for a while and then starts the ICE later doesn't reflect my experience or the experiences of many members of this forum. When the battery is fully charged, the ICE can start the instant you initiate even mild regen braking.

 

[JFon101231]

Exactly @thecompdude - if needed based on a determination that over some level its not safe, just turn on the light. Think Tesla may do this, but not positive. But I doubt regen is much different than a stick car in a lower gear, in most cases if downshifting actively I'd say it slows down less quickly but has been a few years since I've driven a passenger vehicle with 'standard' trans.

@KentuckyKen - I could have been more clear. When I say coast, that meant removing foot from accelerator and engaging paddles. Even at 4 chevrons, in many cases (at least for my roads/driving style) that is not enough to slow the car down between light change and stop line without applying brakes. I'll have to try to safely watch the needle to see where in the brake travel it stops 'dipping' at which point it would be inferred I assume it added friction brakes

I'd rather not have to move my foot either - 100% personal preference but I'd rather module 1 pedal than need to move foot or have to engage paddles (PS EVERY FREAKING STOPPING EVENT for the latter). OK I feel like I'm tantruming like a spoiled child, so I'm going to take a break

 

[JFon101231]

Hmm. Perhaps I'd argue (starting to feel like a lawyer) that makes sense for prolonged and/or significant declines in order to avoid overheating brakes on a pass out of Colorado, but not in my instance for sake of argument here of 2 consecutive stops in short distance from call it 30mph. In those situations, it forces the first call it 4 miles give or take of my daily commute to be with ICE. If by chance I made the return trip and had the same issue, in theory, my round trip commute for the day would be 100% ICE haha.