I just got my car last Thursday, and have driven only 400km (250 miles) so far, but even as an electrical engineer with experience in the design of control systems, there is something I don't understand.

I have seen on 2 occasions now that when I am at a steady speed and hold my speed (once at 50mph and once at 70mph), and my battery is charged (more than half, to one bar below full), that one bar of Regen showed up, while the FE meter for the ICE stayed at its position where it was when I had no Assist and no Regen.
I could understand the Regen if I was idling the motor, but then the FE meter should drop and my speed should drop too.
This 1 bar Regen may go on for half a mile or so, and then it disappears. All the time the FE meter is steady and my speed and rpm's are steady. On one occasion I was on cruise control, and the other time I was not.

Am I looking at the tolerances of the sensors here (I guess that the Assist and Regen in the end are the display of current flow going out, and going into the battery respectively), or is there something else going on that I am not aware of? Or could it still be that I'm easing off the gas? I don't think it could come from going downhill, since our country is perfectly flat.

I'm quite happy with the car. So far, I have managed 5,6l/100km = 42 mpg. With our speed limit on the highways (75 mph), it is much better than the 29mpg of my previous Honda Accord. I also checked my tire pressure. At 34 psi it is a little over the 31 psi that is recommended. I'm not a hypermiler, so I will not change that.

I am curious if other people have also noticed this one bar Regen phenomenon.

 

Hi Arjen;

Glad to read you're enjoying your car.

If I understand you correctly:

I believe the regen phenomenon you are referring to is a form of "forced regen" that simply uses surplus load from the gas engine. Sometimes this type of regen may be so small in value that no regen bars actually appear. In this latter case, we often call it "hidden regen". Many folks are surprised when they see their SoC slowly rise and yet they seen no regen bars at all.
This phenomenon can be cancelled by using a "fake shift" but at a later time the algorithm may trigger it back on if the conditions are right. Interesting eh?

With regards to your FE: Yes, 5.6 l/100km is good for those speed ranges however, I believe you could lower your average to 4.9 of better if you raise you tire pressures to 42 in the front and 40 in the rear tires. I am running 48 and 46.

At the moment, this nets me 3.8l/100km in city driving at 60km/h and lower. On the highway at 100km/h and steady state driving I get 4.1l/100km. My FE would be poorer if I travelled at 110Km/h or higher but I believe I could still muster 4.6l/100km or lower.


Cheers;

MSantos

 

Hello MSantos,

Thank you for your reply, but did you ever have this yourself?
You would think that the algorithm would favour dropping the engine load when the battery is sufficiently charged rather then using it to charge it more. Anyhow, I will not question the Honda engineers' ability; judging by the FE they have done a good job. BTW: How do you perform a 'fake shift'?

I also noticed it is not hard to keep the battery sufficiently charged when you mostly Regen brake and avoid using the pads. I guess that's what's happening when you 'brake' until the Regen bars just hit max. and try to keep them there. You are not using the brake pads then I think, but are only braking on the electric motor/generator.

I understand that the recommended tire pressure is an average based on comfort, handling and FE, and I may try to increase the pressure to the high 30's or even raise it to 40 psi, but usually I will lower it again, because of the more bumpy ride and tire noise. However, it would be nice to see the effect on the FE, but I'm not sure I could accept the loss of comfort for the gain in FE.

 

Arjen;

You'll probably want to check Tarabell's article. It has become the "bible" for many HCH-2 owners for almost a year now. In the article, you'll see references to the regens we discussed and GaryG's fake shift technique. The fake shift basically consists of a slight (1-2sec) foot-off-the-gas-pedal when accellerating or at powered steady state. This has the effect of lowering the RPM by tricking the CVT into a less aggressive ratio. In addition to achieving better fuel economy it has also been know to reset the battery (and assist) management algorithm.

Yes, the best is NOT to stop or slow down at all. But when we most stop or slow down, then engaging in long decellerating coasts is most helpful as it nets us the most regen by avoiding brake pad use.

You are right, raising the tire pressure amounts a bit of a comfort compromise. In my case it is barely noticeable, but for many folks it may not be acceptable. But hey, you'll never know for sure until you try ity.


Cheers;

MSantos

 

Hi Arjen-

Just thought I'd chime in here since I've dealt with the same questions in these forums. Yes, I have certainly seen it and sometimes gotten a bit annoyed about the charge management algorithms on my HCHII. It will run one-bar of forced regen at fairly unpredictable times, even when the SoC is at 7 bars, so what you are seeing isn't that unusual. Although when you say there is no effect on the iFE meter, that is a bit odd, as usually any increased drag from regen should hit your MPG at equivalent load. You are probably right then about blaming the sensor thresholds. Not terribly discrete. Below the threshold there is no regen or 'hidden regen', and then at some point it breaks the barrier to show 1 bar, although the difference in the drag on the engine is very small.

Generally I see it happen after a hill or accel when I use even a small amount of Assist.

It's usually no big deal at all, except when the car has been charging itself to almost 90% full, and then you hit an off ramp at 60mph and the battery can't accept all of the E. Just a tad wasteful then. But hey, the car can't read your mind, or the road ahead. Just plugs away doing what it thinks is best for the longevity of the battery.

Cheers,
Keith

 

Arjen,

I just completed the first half of my trip today (1300 miles) in my Accord Hybrid. It does the same thing as yours. I could almost predict the moment it would happen and for how long.

The accord would show one bar of regen for almost 1 minute while cruising at 70mph. Then it would shut off and then 10 seconds later it would appear again and this time it would only last for about 15 seconds and would always turn off when the battery indicator jumped up two bars.

Then, maybe 20-30 mins later, it would do this same procedure again.

While it didnt do this continuously, it did this for maybe 3 hours and never again that I could see. Maybe I missed it?

I could feel the regen start and stop only because I was waiting for it.

I also think that even while I rarely see the assist come on, I can feel that as well. I dont think the assist indicator lites as easily as it should. I feel the assist is causing the battery level to drop two bars approx every 30 mins while I was in some hilly parts of the country. It never happened on the flat areas.

I have driven the accord hybrid now for over 20k miles and like you, in the beginning, I questioned everything it does. I simply trust its abilities now and enjoy seeing it do something different whenever it wants to.

Best of luck with you new car.
Tony

 

Hello all,

Thanks again for your replies.

Thank you for the link to the article, msantos. It is very extensive and has many well documented observations and techniques to learn from.

The reason the FE meter may not have changed could have been due to the resolution of it. There are maybe 20 (?) discrete steps to indicate 0 to 100 mpg (0 to 12 l/100km in my case), and although it is probably not linear, it requires a certain change in FE to trigger the next bar. But I agree, any Regen while the engine is under load decreases the FE.

Anyway, my mind is put at ease, knowing that other people are also seeing this behaviour, and I'll tell myself that this is a 'battery longevity strategy' of some sort, like suggested.

I will try to keep my eyes more on the road, rather then focussing on the dials and gauges all the time.

Thanks again, and many happy miles for everyone,
Arjen

 

I've seen the same thing in both the HCH1 & HCH2 when the IMA battery runs low (usually after a lot of city driving). I'll see 1-3 "charge" bars on the meter until the IMA is back up to snuff.

Guess it's no different from a regulary battery that's low on juice. When I was a kid, my father insisted on turning on the headlights when traveling in the daytime on 2-lane highways. More often than not, he'd leave them on during a stop, causing the battery to drain. Once we were on the road again (with the lights off!), the ammeter would stay pegged at the far right "charge" mark for several miles.

 

I live on the top of a mountain, and have a 4 mile 8% grade to climb to get home. To make the climb,at 50 mph, my rpms are always above 4500, and the SOC depletes quickly to 4 bars. Usually halfway up the hill, my car goes into regen of 3 or 4 bars even if my SOC is still 4 bars. That hill really kills my mileage, as my iFCD shows only 2 or 3 bars (10 to 15 mpg) coming up the hill. Mileage is great as long as I don't come home

 

Kephra, sounds like you need msantos' regen inhibit modification. Basically it prevents that forced regen from taking place, so while you won't be getting any boost on the way up, you won't be fighting the battery either. Then on the way down, you can use the 'S' gear to force regen as soon as you start and get the charge back.