SOLVED- Unexpected ICE Turns On

I think I saw a symptom of the engine braking system with an OBDII recorder system. The mass airflow meter went to a very low reading when the motor RPM's were still around 1500. There had been a period of regeneration. I was in HV mode, and the battery was reaching the top of the 'target' charge, SOC was around 50%. Engine braking lasted about 30 seconds once, then 20 seconds a second time. I don't have a record of fuel flow, or spark, during this time. The first time, I was driving 73 mph and slowed to take an exit: The ICE was powering the car in HV mode, and battery SOC started to go up with regen for the exit. The second time, I was driving 60 mph +-, and came into a small town, and regen was driving up the SOC. Both times, the engine did not shut off, but just 'lost' air flow in a step drop. At other times the air flow is relatively proportional to engine speed.

I drive most of my miles in HV mode (I drive lots of 100+ mile trips.), so I haven't noticed the EV mode engine braking.

I just started recording mass airflow, to see if this would show engine braking... Seems like it does.

 

ClarityBill,

I'm totally fascinated by the original theme of this thread, which refers to the Clarity in EV Drive mode starting the ICE in response to regen braking (paddle or pedal) when the battery is fully charged. Are you finding other times when the ICE starts up in response to regen braking when the battery is not fully charged?

In HV Mode, the Clarity selects from EV (EV Drive mode), ICE (Hybrid Drive mode), ICE+EV+clutch (Engine Drive mode) and regen braking as it sees fit. I don't believe it ever starts the ICE to dissipate power unless the battery is fully charged.

1. You saw what you believe is a symptom of "engine braking." Are you referring to the ICE driving the starter motor/generator in such a way as to use up the power coming from the traction motor operating as a generator to slow the car?
2. When you say "motor RPM's were still around 1500" are you speaking of the traction motor, the starter motor/generator, or the ICE?
3. "There had been a period of regeneration." Does that mean regen braking had been taking place? Was it due to a downhill section? I assume HV CHARGE Mode didn't spontaneously take over. Did regen braking then stop because the battery became fully charged or because the bottom of the hill was reached?
4. "I was in HV mode, and the battery was reaching the top of the 'target' charge, SOC was around 50%" Is the top of the target charge the 57.7% charge maximum for HV CHARGE Mode or was 50% the SOC level that was displayed when you pressed the HV button?
5. "Engine braking lasted about 30 seconds once, then 20 seconds a second time." Are you interpreting low mass-airflow as evidence of "engine braking?"

If the ICE starts up unexpectedly in response to regen braking after leaving their garage with a fully charged battery, it doesn't seem that there would be low mass-airflow because the engine is making sparks, sucking in air, and generating power. However, I wouldn't be surprised by anything happening in HV Mode unless that thing happening uses up more fuel (as ICE counter-intuitively does when it starts up in response to regen braking with a fully charged battery).

I really wish Honda would explain the difference between the operation of their non-plug-in hybrids and the operation of the Clarity when regen braking occurs while driving in EV Drive mode with a fully charged battery!

 

Insightman:

Early in the thread there was some discussion that the ICE starting to dissipate surplus energy may not be using fuel, but just acting as a load on the system. Kentucky indicated the sparkplugs were firing, because he saw his hourmeter logging. The low air flow that I saw would indicate the engine is 'running' with the throttle plate closed. I was seeing a time that the ICE did not shut down, when I thought it should.

1. I was thinking the regeneration energy was running the starter motor to turn the ICE and use up the energy that can not go to the battery.

2. The ICE was around 1500 rpm, with air flow much less than when it is running at 1500 rpm in 'normal operation'.

3. There was regenerative braking due to slowing from 73 mph, to exit ramp speed. It appeared regenerative braking was not allowed to charge the battery any higher, and the surplus energy went to spin the ICE, without air (or fuel).

4. My definition of 'target charge' is the SOC when I press the HV button. (Very disappointing that the surplus energy was not allowed to charge the battery past target charge, when actual SOC was still less than 50%).

5. Yes, low air flow is my evidence of 'engine braking'.

I am suggesting that the experiences of ICE 'running' when first starting in EV mode with full battery and regenerative braking may actually be this 'engine braking' that I saw: Very low air flow, so no fuel consumed, but spark is activated to assure no unburned fuel leaves the engine. I am suggesting that mass airflow readings may be a way for us to check what is happening during the unwanted ICE operations.

 

Mine is behaving a little differently in that it is burning some fuel. The engine keeps running beyond the regen needed state to warm and burns fuel for a few minutes before it shuts down. If you overly use regen again, it will start and burn fuel again, maybe for not so long a time as the first, but for a definite duration of actually running and burning fuel (even if car is stationary).

 

Robert:

How do you know it is burning fuel?

My suggestion was the starter motor was turning the ICE, but not actually burning fuel.

 

It keeps running even if the car is completely stopped. I don't think the battery is making the engine turnover. On top of that, the mpg on the trip computer (under info) declines while the car is stopped and the engine is running. But what is to "know" a thing?

 

Interesting theory @ClarityBill
My Torque App doesn't have such a parameter to log, though it has some fuel ratio, EGR, and O2 sensor options. I doubt they will be useful for this exercise.

I have a different theory (not based on evidence). I think the ICE firing up during regen on a full/near full EV battery doesn't physically do anything to use up the kinetic energy of the car. I think that the car triggers HV mode when certain extremes are reached (like the overcharging SoC limit or regen power limit), and thus the ICE comes to life to step into action. HV is like a safe-mode in this case. Remember that this car is an evolved version of the i-MMD SPORT Accord with a bigger EV battery, and not an EV with an ICE back-up. When I read through this paper: https://www.hondarandd.jp/point.php?pid=965&lang=en , I get the impression that the EV limit triggers HV mode and nothing more. The friction brakes will step in to manage the deceleration, and the running ICE is just a consequence of the car suddenly deciding that HV is a safer mode.

In reality, it doesn't really accomplish anything by switching into HV. So this doesn't make any logical sense (to me). But the reference never talks about engine braking for regen opt-out deceleration, nor do any other references that I can find on Honda hybrids. So my guess is that the Clarity EV also probably just applies friction brakes as well when the regen power limit or SoC limit is triggered - since there is no HV mode in that car it just carries on as before.

 

Thank you for answering all my questions about your theory. You've come up with a plausible explanation of why the spark plugs might still be firing even after the fuel is cut off. The spark-plug activation was key to my belief that the ICE was actually burning fuel to dispense with energy that can't go into the fully charged battery. Now I'm less sure the ICE is running and I'm wondering if the Clarity, Accord Hybrid and Insight all handle the excess power the same way.

 

Ok, guys. I'm pretty sure that mine is burning fuel. As I said the engine continues to run when the car is completely stopped after the regen has forced it to start. The trip recorded mpg drops when this is happening (I can watch it fall since it is so early in the trip and I've watched this several times since it always happens at the same location). Further the engine sounds like gas is being burned (reasonable audible sound that you would expect from a running engine, not near silent like I would expect without burning fuel.) I guess I could get out and put my hand near the exhaust to see if the exhaust is hot, or get a sample to see if it is high CO2, but I don't think that level of proof is necessary to convince me.

 

Hi Robert,

My experience definitely was the engine running for a different reason, and then seemed like the fuel-air mixture was shut off with the ICE still turning.

Your experience with the engine running after the car is stopped is a different situation. I was just suggesting my experience might help us understand yours... or not.

I also have a significant hill when I leave my house with a fully charged battery, but I have never heard my engine run. When I get back to town, I will record the OBDII information, and see if there are RPM's without air on my hill. Again, just more data that may not mean anything...

I normally use a level 2 charger till it shuts off. Should that give me enough charge to cause engine start, if my hill is big enough?

 

Yes, I'd think the level 2 charger will essentially push the battery to what the Hondalink describes as 100% and should make you vulnerable to having to run the ICE for regen absorption. As to the hill being big enough, I think if you have to use the regen paddle at 4 and especially if you also have to hit the brakes for a reasonable stretch, it should kick on the ICE. Be curious as to what you find. I live on top of a small mountain ridge, but I rarely charge the car at home (lucky enough to usually just charge at work). Still, the grade is pretty gradual and I first have a short slight uphill grade, so I've never had the ICE start on this stretch. Figuring out this beast is anything but straightforward.

 

Would tracking the ICE temperature provide a way to determine if it's running or not?

 

Robert, is the heat on during these fuel burning events?

 

No, but it might help to keep the regen into the battery at a lower level. I hadn't thought about trying to preemptively try that. Might give it a try the next time I forget and charge to 100%.

 

Trying to reverse engineer all this is quite an undertaking.
Here are my observations:
On all the occasions where the ICE seemed to come on after a full charge, my inductive pickup hour meter incremented which indicates the spark plugs were energized (technically that the #1 plug was). One one single occasion, I pulled over immediately and heard and felt the engine running at idle and found the exhaust manifold too hot to touch. On several occasions, I checked under the hood when I got to my destination (which was after the engine had stopped) and found the exhaust manifold warm. And on all occasions, the engine icon on the power display illuminated the same as it does in HV when the engine is on and the HV range estimate decreased by a couple of miles. And finally, the ICE only comes on for me outside of HV immediately after a full charge (I drive in ECON and don’t go past the click and virtually all my trips are less than the EV range).
Until the info about the MAF going down, I would have said 100% definitely that the engine was running normally at idle speed. Now I’m not sure how to merge these observations with the MAF data. More data is needed.

I’d like to add an OBDII and app to track all this. What OBDII and app is recommended?

 

I use this one https://www.amazon.com/gp/product/B005NLQAHS/ along with the Torque pro app (~$5). I like this one because it reports the EV battery state of charge. Not sure if all of them do, but I read in the reviewer comments that it did, and sure enough I found it as one of the options to include in the logging. It is cheap and it works well enough.

 

Hi Ray,

Does it track any other hybrid specific data? EV battery or generator voltage, amps?
Do you have to start a new log every time the car is started?

I use the Blue Driver system, it does track SOC. A little more expensive ($100), and probably not worth the extra money.

I would like to get a system the has more Hybrid specific data, and logs automatically.

 

I have attached a graph of the OBDII data that I believe shows my 'engine braking'. It occurs at minutes 2.6 and 3.7 on the graph. Both times, the air flow (lower blue line) has a step decrease, and the ICE RPM's (upper blue line) were dropping more slowly.

 

I'll try the idea generated by @The Gadgeteer (was the heat on) and @MNSteve (why not use resistor question) and turn the heat on just prior to the location that causes this for me. It's pretty predictable as it is the same stop from about 40 mph for a left turn each day. So today, I'll charge to 100% and then see if the heat load will stop it. If it works, should take less than a minute of heat to avoid the ICE.