SOLVED- Unexpected ICE Turns On

One would have to actually attach sensitive fuel flow monitors to each fuel injector to know for sure, or hack the ECU and see the engine run state. It is likely no issue for Honda to have all the spark plugs firing at all time the ICE is turning, to make absolutely sure that no unburned fuel leaves the engine. The only thing worse than inefficiency is failing an emissions test/certification.

However, using an electric motor to "oppose" a running gas engine (let's just say an irreversible torque source) is, well - a generator. And they are trying to dissipate electrical energy... The electric motor/starter must be driving some mechanical load that can absorb that rotational energy, as they cannot oppose each other without likely destroying each other. The ICE is simply taking the place of the fly-wheel in a mechanical energy storage system however in this case is a loss mechanism as a drag load. https://www.qpsolutions.net/2017/06/intro-to-the-flywheel-ups-powered-by-motion/

The point about why even bother with this versus just using the friction brakes was a good one. However I will go back to, without more detailed inverter diagrams and really detailed traction motor specifications, they likely have the real problem of where to put the generated angry pixies the traction motor is making while turning. Since in the previous article about the planetary drive configuration the traction motor cannot be mechanically decoupled from the front wheels in this configuration/design. So anytime the Clarity is moving, the PMA traction motor is kicking up the pixies, who want to go somewhere.

I think that this is a fun academic discussion, and why I love this forum. We are trying to figure out something that Honda has no interest in disclosing to the public. Kentucky will likely solve this whole discussion by attaching his ICE HOBBS meter to fuel flow sensors and gathering the requisite data!

Cheers,

Cash

 

I agree that the academic discussion of exactly how and why Honda chose to dissipate the energy in the running of the engine is interesting so I really don't want to take the wind out of any of that discussion. But it seems worth mentioning that we should try to avoid this behavior if possible. I live on the side of a mountain ridge (yes, even in Alabama). I rarely charge at home since I'm lucky enough to charge at work and have a relatively short commute, but when I do, I try hard to remember to stop charging at about 90%. That way, I have room in the battery as I go downhill and avoid the "waste" of the recharge energy. Strangely enough, this is one of the big reasons I love PHEV. In the past, wearing out brakes on ICE vehicles after the wasted cost to climb the hill always seemed like just the reality of living where I do. So PHEV has an added value to me to take away this cost of living on a big hill...

 

I keep the car in EV mode with the ECO button ON. Therefore I can mash the accelerator down right to the resistance point "ice activation point" and the ICE will NOT fire up. This for me has made all the difference in my overall satisfaction. Just finished up a 2400 mile EV only run. STILL LOVE THE CAR but why the hell do they not have a lane change camera on the drivers side?????? Grrrrrrrrr My only complaint really.

 

My guess is that Honda doesn't want you looking right to check out what's happening behind you on the left because there's a chance that a car ahead of the camera's view may have moved into the lane left of you.

 

Ahhhhh....so THIS is the technical thread everyone but me seemed to know existed...good reading! Very interesting info in here. Why I never read it before I'm not sure, but maybe cuz it's so dang long lol!!

Still can't say I fully comprehend the why and how of everything, and I still think there's something glitchy about the execution on the Clarity, but absolutely this helps clarify a lot of the concepts that were confusing my usually pea-sized brain in the other thread.

So I have nothing of any value to add here, other than to offer a formal thank-you to all those who have unearthed various facts about the patents, possibly this car, Honda's engineering ideas in general, and everything else. Interesting stuff.

 

I beg to differ. If you are running the starter/generator attached to the engine with reverse torque, Then it is trying to make the engine run backwards. If it succeeds, the engine will not be running, as the fuel injection and ignition timing will be totally wrong, as well as damage occurring to the oil pumps, etc.

If reverse torque is applied and the engine drives the shaft in the normal (forward) direction, then the motor/generator back EMF (backwards electro-motive force) will be such that the engine is creating energy in the form of electricity that would further charge the batteries (which you explicitly do NOT want at this time). Simply put, it will still operate the motor/generator as a generator, with a voltage higher than the voltage applied by the ECU.

Therefore, if you wish to dissipate energy for regenerative braking, you must either:
1) drive the running, idling engine faster than an idle, and use the engines torsional resistance to discard the energy.
or
2) drive the shut off engine forward (to avoid oil pump damage, etc) and use the total dead resistance of the engine to dissipate energy.

Of these, 2 is the best choice for a braking objective. I believe that the "reverse the engine ENG" interpretation of reverse torque is wrong, either in translation, or in how the patent was written. It will NOT work that way from a physics standpoint.

Nobody has given a cogent, definitive answer as to why you can not drive the engine for long periods of time without fuel or ignition. Is there one I am not aware of? Cold oil is pumped, and becomes warmed by viscous friction. No condensed fuel dilutes the oil because no fuel is injected. What's wrong with that.

Finally, frequent mention is made of "close the valves". While possible, this is an extremely mechanically complex function to add to the valve drive train. Also, closing the valves results in the trapped charge of the ICE being compressed and expanded repeatedly. This provides little, if any, braking force. Rather, you leave the valves to operate as normally and you use "pumping losses" to provide braking force. If you really want to get extreme, you provide a "Jake Brake" function like diesels have (Google it for details) to be really effective.

My best guess is that when you need to use the engine coupled motor/generator to dissipate energy it simply drives the engine in a forward rotation with the fuel cut off. This provides maximum braking for minimum cost.

 

Maybe I was too verbose in my earlier posts here for the conclusion, but I completely agree with Ken Wells' hypothesis above, and tried to state that Honda can absolutely drive the ICE as an non-operating mechanical load.

I think the ICE is being driven by the starter/generator in this case, either completely "fuel-less" or OFF, or at a low level of fuel/ignition. The one thing the Atkinson cycle ICE can do well is vary it's compression and over rev without causing the fuel mixtures to go lean and detonate. So, basically I think that both "over driven idle" or "dead engine braking" is an option, but cannot test these theories, without being able to cause the event in question and live monitor the ICE operating parameters (EGT/CHT/O2/Fuel Flow). Unfortunately just causing it and immediately stopping to "feel the exhaust" will not work as once the engine is turning, and the electrical "passive load" is no longer needed, it makes sense for Honda to program a test cycle on the engine. This would follow other ICE start cycle logic where it continues to idle and "warm up" when caused by brief hard "acceleration." For example, full battery, in HV mode, start to drive and the ICE comes on, but will remain on until it has warmed up. However once warmed up, in HV, it will start and stop with the vehicle as expected. So again, it is the testing of this theory I cannot find a way to do.

But I attempted, and obviously failed, to allude to exactly that conclusion in earlier posts. Love the fact that we even care to talk about this... Wonder if we will ponder the Mr. Fusion as deeply in the near future (available in the 2019 Honda Clarity!... um, Canadian models only...) ;-)

Cheers,

Cash

 

While I have no definitive proof on how running the ICE helps protect a fully charged battery from over charging by somehow dissipating the regen energy, I can state with certainty that the spark plugs are firing in the process since I have an inductive pickup hour meter attached to the number 1 plug. I have seen it increment. And several times when this has happened I have popped the hood and found the engine either running or warm. These two observations lead me to believe that the ICE is actually running and consuming fuel during this event.
As to exactly how all this works, I have no idea.

 

I'm way out of my area of expertise, as I struggled in electric circuits class, but I visualize the ICE as creating a reverse current through the generator that operates in opposition to the current provided through the regen braking in the motor. The concept is sort of hinted at in this video...

 

I wish Honda engineers would publish a paper explaining how running the engine uses up regen power that cannot go to a fully charged battery. However, it's clear that, unlike the i-MMD Accord Hybrid and Insight, which shut off their engines to use up regen power, the Clarity starts its engine to deal with this situation.

When the battery is fully charged, the only electrical component that can use up the electricity generated by the traction motor operating as a generator is the starter motor/generator operating as a motor.

There must be an interaction between the starter motor/generator and the engine that is using up the electricity that would otherwise go to the battery. That interaction could be the starter motor/generator trying to either speed up the engine or slow down the engine. I guessed that the Clarity Plug-In Hybrid's computer would know exactly how much reverse torque it can use to almost, but not completely balance out the forward torque of the engine. I'm willing to listen to/read any one else's explanation how that power can be dissipated by running the engine that was dormant until regen braking was initiated.

 

Your theory may be correct. When I cruise down my steep street with a full battery (and the temps are above about 65 degrees) my ICE comes on and I have seen the EV range go down even though I'm going downhill without any throttle applied (i.e. in what would normally be a regen condition).

 

Cool, this is really good data. Neat to have an hours meter on the plug.
You can certainly shut off the gas and still have the ignition functioning when the engine is being run in "dissipate energy mode". The engine would get warm, but not hot from friction. If you found the exhaust manifold was hot when you stopped after running in this mode that would prove that gasoline was being used. I don't live on top of a hill, nor do I have any large hills nearby to try this on, so I will have to get my data from you guys. Keep up the good work!

 

Comes down to this. A lousy design by Honda.

 

The Accord Hybrid and the new Insight turn off the ignition and close the valves if regen braking occurs when the battery is fully charged. I would be surprised if the Clarity would spin the engine without also turning off the ignition. People on this forum have reported gas usage when the Clarity is expending power that cannot go to the fully charged battery.

I'll admit it does seem strange that the Clarity would run its engine rather than turning it off like the Accord Hybrid and Insight. The only reason I can imagine is because the Clarity is heavier and the traction motor is generating more power that needs to be dissipated to provide the same level of regen braking.

 

I don't think the Chevy Volt does this. Similar car to Clarity.

 

I agree with the fact that they shut off the ignition, but it would be mechanically expensive and complex to "close the valves". Additionally, closing the valves would reduce the overall rotational resistance of the engine. Do you have any documentation or further description of how these cars close their valves? Or by close their valves do you just mean to shut off the gasoline supply?

 

How about installing a cutoff switch for the ICE? The driver can turn it on when HV is required!

 

Bob,
My 2008 Prius did something like this when the battery went to full bars from carefully efficient commuting and a long coast down.
I dreaded it, even though the battery was spinning a dead engine because it was wasting drive power (I was averaging entire tanks at 60-80 MPG in the summer)
It would spin the engine for a while after a complete stop to reduce the state of charge.
I hated it, but assumed it was necessary to manage the battery.
I ended up modifying that one spot in my commute to consume some EV power before the coast down.
This issue doesn't happen on my Clarity, but I understand and share your frustration.

 

I'm wimping out here. For the past hour I've been googling for the source of my claim but cannot find any specific information about how the Accord Hybrid deadens its engine to provide resistance to the starter motor/generator in order to use up regenerated power that cannot go to the fully charged battery. What I did find is this text from Green Car Reports that illustrates how flexible the Accord Hybrid's valvetrain is (making it feasible that manipulating the valve timing and lift could increase the unpowered engine's resistance):

The system combines E-VTC (Electronic Variable Timing Control), which continuously adjusts the intake camshaft phase, with Variable Valve Timing and Lift Electronic Control (VTEC), which changes the lift profile, timing and duration of the intake valves’ operation.

 

Isn't interesting that full EV cars like the Leaf do not and cannot have this issue since they have no ICE? So, how do they handle the "full battery" issue?