Thread: What's more helpful to FE in city driving; Assist or Eco mode?
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Old 10-04-2005, 04:02 AM
gonavy gonavy is offline
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Real Name: Bryan
Location: Severna Park, MD
Hybrids: HAH...waiting for the Fusion
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Default Re: What's more helpful to FE in city driving; Assist or Eco mode?
It's nice to be able to recover energy, BUT...

I don't buy the claim that IMA accounts for anywhere near 60% city savings. I think that autostop and eco mode have a lot more to do with it for all but the biggest leadfoots.

- 3 beats 6 every time, no matter how you cut it. Rely on VCM, not IMA for your savings. Our IMA is really just a strange supercharger, when you think about it.

- You would need to maintain 5 or 6 bars constantly to enable any IMA assist in all but the fastest starts. That's doable with a lot of braking. The question is whether even that level will enable IMA to kick on early enough, and whether IMA is strong enough to make up for the extra ICE losses incurred with the fast start. I believe that IMA is not big enough to make it up (6% assist @ max ICE power, probalby 10-12% for normal conditions). Even if it were, energy still got thrown out the window during a hard acceleration.

An ICE is never never never efficient when its gunned/floored/opened up/whatever. Peak efficiency is between 1/3 and 2/3 loaded- right where a reasonably slow acceleration takes you. (I have a scangage that shows me loading now... ) Doubling the engine load from 50 to 100% more than doubles fuel consumption. So getting to the same speed at full throttle always uses more fuel than doing do at 1/2 throttle, even if it takes 1/2 the time to get there. And the energy put back in by regen only cares about what the speed at the start of decelleration was, not how fast you got there. So you threw away energy just to get up to speed in less time.

Having said that, please try it out and let us know your results! The HAH is a lone duck in the pond, and has nowhere near the amount of combined experience as the HCH.

My suspicion is that 30-32 in town is about the best that mortal drivers like us will do without FAS. No matter what, there are 6 thirsty cylinders drinking gas every time the ICE is started up, and every time you coast in N. I believe its best to make those front 3 work as little as possible, then put them to bed every chance you get.
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