Does coasting to a stop in neutral save more gas than just simply taking your foot off the gas and getting some regen?

My instant FE meter shows that I am actually using more gas when I put the Civic in neutral and coast. ie. the L/100klm goes off the chart (maximum).

Whereas taking my foot off the gas drops the FE meter to 0 L/100klm with some regen.

What's going on?

 

When coasting in D the valves shut completely and you are essentially coasting while using no fuel. In N the valves remain open. There was a discussion a while back that determined using FAS techniques was not applicable to the HCH2 for this reason. If I can find the link, I'll send it to you. They did a much better job of explaining it than I can at the moment. In the meantime, what I do is coast, but when the IFCD reaches 100mpg I press lightly on the gas to cancel out the regen. Depending on the situation you may go into EV mode at which point you will let up on the accelerator pedal enough to cancel that out. I prefer not to coast using EV as it uses up some of your SOC. I find it best to stay just in between regen and EV with the valves shut and coast for as long as possible.

 

Try this link from another forum should answer many of your questions.

http://www.cleanmpg.com/forums/showthread.php?t=1306

 

On any vehicle with fuel-cut, coasting in neutral will use more fuel on the gauge but the difference is that keeping the engine spinning in most vehicles generates a lot of resistance by sucking air through the valves, which at most speeds -- especially faster ones -- requires much more fuel to overcome than simply running the engine at idle. (0.1 gallons/hour is about the consumption rate on the HCH-I)

In the case of the Civic Hybrid II, removing your foot from the gas seals all 4 cylinders (HCH-I seals just 3), dropping this internal resistance by about 2/3rds, however, the charging kicks in, simulating the feeling of a normal vehicle by generating resistance as well (though it gives you something back). If is not necessary to stop or slow down, you are usually better off keeping up your momentum-- if by charging and slowing yourself down, you need to use more fuel to (for example) get up the next hill, you're worse off than neutral-coasting.

However, as far as I know, the HCH-II has a trick where you can barely tap the gas pedal and no fuel will be injected, but the valves will still be closed. This will still have slightly more resistance than neutral, but you're not burning fuel at idle either, so it's probably your most economical bet.

On the HCH-I, sometimes I have gone into neutral, but the problem is that the battery pack aggressively charges in many cases where I want to coast, and there is no way to stop it without burning more fuel -- tapping the gas pedal always injects fuel on the HCH-I. On rare occasions where my pack is completely full, the car coasts in gear with very minimal resistance due to sealing 3 out of 4 cylinders. I'm glad they fixed this in the Gen-II model, though.

 

This is a good question. The gen2 folks are pretty proud of all that fancy new tech hardware but nothing beats a good ole manual FAS. The regen process is only about 30% efficient and slows the car down a good little bit. You should only regen if you are stopping anyway.

The valve closing is a good idea but you are still generating resistance even if you are not burning gas.

Coasting in N with the ICE on does burn a tiny bit of gas but you can save this amount by doing a FAS. Someone else will need to go over the details required to safely FAS a CVT. If you can do it safely the FAS is the best option (FE wise) because you are not causing any extra drag and you are not burning ANY gas.

 

Where did you hear that coasting with all valves sealed drops resistance by 2/3? I do it often and it seems to me that resistance is a lot lower. The vehicle will coast just about as far in "valves shut" mode as is does in neutral.

Also, the term "tap" the gas pedal may be misleading. The way to cancel regen is to hold the foot on the pedal constantly and lightly. The more pressure, the fewer regen bars you see, until you get to no bars showing. At that point you're coasting with no fuel consumption and very little loss of momentum. Given this smooth coasting ability, I wouldn't ever consider doing a FAS in the HCH II.

 

If I recall correctly, the valves are not sealed when you remove your foot from the gas. There is a 10 minute movie from the Honda website that demonstrates the engine from the HCHII in great detail. In particular, valves are opened during coasting to lower resistance. Does anybody else remember this? I don't want to watch the movie again. I do not have the link at the moment, but I can post it later--or somebody else can post it.

 

This sounds exactly backwards of the way I remember it. The valves are closed to reduce "pumping" losses. If I remember correctly......

Please post that link if you can find it....

 

Maybe so. I'll post later on after I get home tonight.

 

That is exactly right. I knew I should have waited to watch the movie before I opened my mouth.

Here's the link:
movie