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Old 10-24-2006, 01:11 PM   #1
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Lightbulb A crackpot idea

During research into Atkinson engines, I thought of something I haven't seen anywhere else: A gasoline engine with no throttle. Here's the idea:

Atkinson cycle engines use late valve closure to trap less air and fuel in each cylinder, generally in conjunction with high compression heads (to be technically correct, high expansion heads). My idea is to carry this concept to an to extreme, and use variable valve timing to vary the amount of air and fuel trapped in each cylinder and thereby vary the power output.

At idle, the intake valve would close at ~5-15 degrees BTDC, but the throttle would be wide open. (For that matter, why even install a throttle?) Then, when more power is desired, advance the intake valve closure to take bigger gulps of air. Full power output would be with intake valve closure at about BDC. (For really high expansion ratios (<13:1) full throttle would have to be ~30 degrees ABDC (~150 degrees BTDC) to avoid ping.)

Drawing air in at essentially atmospheric pressure instead of the vacuum that the throttle creates would substantially reduce pumping loss. Since VVT has already been developed, little new tooling would be needed, only a change in cam actuator programming.

The only problem I see so far is that there would be no manifold vacuum to run power brakes, but that's not a big deal to fix, since diesels use vacuum pumps anyway.

Maybe I should patent this idea. Or send it to Toyota. Has anybody seen anything like this?
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Old 10-24-2006, 01:22 PM   #2
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Honda has been using this for a few years in its i-VTEC engines.

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Old 10-24-2006, 01:32 PM   #3
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Hmmm, extreme Atkinson eh? I don't see why this could be done, except for the percieved needs regarding acceleration? For instance the 1NZ-FXE suffers from less low end torque due to pushing some of the air back in the intake manifold, and wasn't deemed suitable for a stand alone drivetrain. This would be even more efficient by pushing out all but the air it needs, eliminating pumping losses, but it would have even less low end torque, so it wouldn't be suitable for most new cars, i.e. luxo-barges. If someone were to say, drop it in a smaller ~1600-1800lb echo, then that would make for one heck of a economy car. It'd probably have 3L lupo performance, with 3L lupo mpg. In terms of comparable tech, it sounds a lot like Toyota's Duel VVT-i, but with more of an economy angle. And it sounds kinda like BMW's throttleless valvetronic deal, which is naturally in a luxo barge, so probably isn't aimed at economy specifically. I think the difference is that BMW managed to have continuously variable valve lift, with variable valve timing.

edit- SVOboy, so i-VTEC expells air back out the manifold after BDC? The only engine I heard doing this was the one in the Prius, everyone else just uses the same variation on VVT-whatever to have the intake valves open early for more low end torque.
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Old 10-24-2006, 01:33 PM   #4
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Quote:
Originally Posted by SVOboy
Honda has been using this for a few years in its i-VTEC engines.

<sigh> Leave it to Honda to do something so smart. What compression ratio does this engine have?
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Old 10-24-2006, 01:49 PM   #5
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What the honda engine does is use the intake valve timing to eliminate the need for a variable throttle and just runs WOT but narrows down the VT accordingly.
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Old 10-24-2006, 02:33 PM   #6
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What

Quote:
Originally Posted by SVOboy
What the honda engine does is use the intake valve timing to eliminate the need for a variable throttle and just runs WOT but narrows down the VT accordingly.
You mean I've been driving around all over town at WOT in the TSX! JK

It is a great feature -- the Variable Cam Timing does a great job at idle to reduce emissions. The rest of the time it seems to do something to get good mileage...

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Old 10-24-2006, 03:33 PM   #7
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Yeah, if i-VTEC is running WOT all the time then it's probably a refined version of what every manufacturer's (VVT-whatevertheheckwellcallit) doing along with drive by wire. Since the engine can't operate at WOT when cruising at low load(the little thing needs at most, maybe 6-10hp@55mph?), the mileage could be much better if they were able to push some of the air out during low load to reduce pumping losses, which is what Sludgy's talking about. But... since they didn't, the civic, even though is has less reference area, less drag, less weight, and probably less rolling resistance, still gets ~7mpg (btu adjusted) less than a TDI.
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Old 10-24-2006, 03:36 PM   #8
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Sludgy: you're as smart as BMW!

http://en.wikipedia.org/wiki/Valvetronic
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Old 10-24-2006, 04:11 PM   #9
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The i-VTEC only runs WOT under low load, I'm assuming this has something to do with running the engine efficienty, but it's not all i-vtec, just that with the fancy drive by wire business. So yeah, fun stuff.
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Old 10-24-2006, 05:53 PM   #10
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So how...?

Quote:
Originally Posted by SVOboy
The i-VTEC only runs WOT under low load, I'm assuming this has something to do with running the engine efficienty, but it's not all i-vtec, just that with the fancy drive by wire business. So yeah, fun stuff.
So how would you drive this car most efficiently? Put it in D and take it easy, or use the AutoStick to get it to the highest gear with little throttle input at cruise? (VCT and TBW)

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