Re: Stupid "free energy" idea

Most don't use any fuel as the computer shuts the injectors off on decel. You can see this on a scan tool by monitoring injector pulse width which will go to zero.

Just because the engine is running faster and

If you have your foot of the throttle there will be less air passing through the engine as the throlle plate will be closed.

It would be higher in that case as the injectors would be supplying fuel to the engine.

Ah, so if you go downhill with your foot off the throttle and the car in gear, fuel consumption will be zero because the computer will reduce the injector pulses to zero, but if you do the same with the car in neutral, there will still be fuel being injected at the idling rate? I hadn't realised that the computer could distinguish between these two cases.

So in a modern car, my grandpa's old fuel-saving technique (a left-over from driving during WWII!) of slipping the car into neutral as he was slowing down on the approach to a junction would actually be counter-productive!

It causes more fuel to be used because the engine compression retards your increase in speed, decreasing your roll out and requiring you to come onto the gas sooner.

If you let gravity accelerate you in neutral you WILL find that many hills will do work for you that require significant throttle just to overcome the engine compression at the RPMs that your engine spins at at this speed.

S*it...just coast on a flat. See how far you roll, losing little speed. Then, try the same thing by lifting your foot off the accelerator.

the fuel consumption is the same WHILE you are going downhill, HOWEVER, in SOME cases, overcoming engine compression requires ADDITIONAL fuel.

Trav

Totally wrong.

The engine at highway speed will be turning 2-3000 rpm. That compression ALONE will retard your speed and cost you FAR more in fuel economy because you will be forced to come back on the gas earlier to maintain speed.

I am not talking about slowing to a stop...I am talking about integrating coasting into your driving as a hybrid already does.

Listen, I've driven a Prius over many miles, city and highway. There were some times I went 3 miles on no fuel by being as aggressive as possible with the battery and having good downhills and not jackrabbiting at lights.

On certain downhill sections of highway, certain ramps, the Prius goes into neutral and shuts its engine off. I used to do the same neutral thing w/ my Passat and saw actual acceleration by gravity at highway speeds, whereas I had to use SIGNIFICANTLY more fuel to overcome engine pumping losses while in a drive gear. Almost every car has an instantaneous consumption meter...at least VWs do.

If you coast down a hill and roll out in neutral, you are using idle fuel. If the car is in gear, you will not gain as much speed on the downhill and your engine will brake you on the flats, requiring MUCH earlier throttle.

Jeezus, this stuff isn't revolutionary.

Trav

No, it isn't.

Have you ever even driven a hybrid? You are dead wrong

These hybrids with optimal RPM have been around for years:

snipped-for-privacy@i36g2000prf.googlegroups.com...

That doesn't really matter, since it's not how vehicle fuel consumption is calcuated. Since people have been using that lame idea with *everything* from *horses* to *elevators* to *trains* to

I'd expect it to be about as much as

Ah, I see what you're saying: you're prepared to accelerate down the hill to a speed above what you were doing on the flat, and let that carry you part of the way up the hill on the far side. Yes, I agree: coating in neutral will involve less braking so you'll go further up the other side before you have to go back on the power.

But I was assuming that considerations such as speed limits and safety (there may be a bend as the hill goes from downhill to uphill) require you to restrict your speed with some form of braking. Now that braking can be conventional disc brakes, engine braking or regenerative braking.

I was querying the statement that coasting downhill in gear uses more fuel than doing it in neutral, and you've agreed with me that it doesn't *while you are going downhill*.

I agree that regenerative braking is the best because the energy lost as heat in brakes or engine compression is put back into the battery for regenerative.

I'm surprised that the assertion about optimal engine speed resulting in better fuel economy isn't true. Maybe you do get better economy, but this is ffset by the losses in converting mechanical (kinetic) energy to electrical energy in a generator and then back to mechanical in the motors.

I really had my doubts about your theory until you started calling people names.

Now I'm convinced.

Yeah, that's the way we do things around here. We find it to be a superior way of arriving at the truth.

Yes, accelerate insofar as highway RPM engine pumping losses are a deceleration.

There are many cases where you will actually have to use gas on a downhill to overcome compression, whereas if you were coasting, you'd be at idle and a constant speed. The hybrid powertrains recognize this and shut the gas motor off.

I am not talking about just rolling to a higher speed. Find a minor downgrade. Drive down it at speed...then put your car into neutral and check your consumption meter in both cases.

Of course, zero throttle is zero throttle.

But many downgrades require nonzero throttle, as they are mild.

I didn't say that ASSERTION wasn't true, I said that the assertion that the hybrids do so well MPG-wise was because of "optimal engine speed." That's categorically incorrect.

Trav

If you want, you may test-drive a Prius.

I am surprised more people haven't. Their conservation program teaches you a lot about where cars waste fuel. ANY time the car would be better served by gravity, the Prius shuts off the engine. Even on the freeway. I have been doing 70mph in one and have had it shut gas power off. There was no need for it as gravity was more than sufficient. And, if my speed goes too high, I drag the brakes to put some of the excess into the batteries.

That is how hybrids work.

As far as my insulting people, I have 2 defenses: 1, that is just how we talk around here, 2, he actually was an idiot. Somebody crossposted a reply along the way.

Trav

It isn't at all. So that would be insofar as not at all.

Which, naturally, strengthened your argument, as it might not have enough strength against sensible people.

You're nobody till Trav has insulted you.

Sam

Your imagination is as vivid as it is inaccurate.

Trav

I honestly have no clue who the guy is nor why you are orbiting his nuts.

Trav

Aww, you got Dobbie all a *trembling* again!

-Mike K.

WOW!!!!!

Thanks for pointing that out. I'm quite sure nobody here got that at all until you stated it.

I got one side question tho, where'd the universe come from?

Trav

God cooked it in his kitchen. He got interrupted, though, which is why it's all half-baked.

--scott