Quote:
Originally Posted by ChazInMT
OK, so I've read through some articles (find below) and educated myself on CVVL. I see it is mentioned that there is potential to eliminate the throttle, but, I don't see where anyone has done so completely yet.
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The main take away I'm getting from all this is that by closing the inlet valve before the piston reaches BDC (er... Bottom Dead Center) you can control the "charge" that way and thus eliminate pumping loss. It appears a small amount of "loss" is good in that it creates a healthy swirl to promote better combustion which off sets the loss and then some.
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Valvetronic, Valvematic, and VVEL are capable of 100% throttle independent output control. The throttle is backup only. They can cut duration to under 20% maximum duration, which is enough to idle. Engines that do so need pumps and motors to drive traditionally vacuum boosted things.
The pumping loss that early intake valve closure induces is not so bad because the pressure drop happens at the valve, and the air at low pressure is contained completely within the cylinder and so a greater percentage of the initial power consumption drawing air past the restriction is recovered on the compression stroke. The bigger downside is probably that on the intake stroke as the charge is expanding, it absorbs more heat from the cylinder walls and thus incurs some more pumping loss, but I am not sure how big of a deal this is.
Joeggernaut, throttle by wire is not actually very different from cable throttle. Most engines are not equipped with any kind of variable lift system, and the only variable valve timing is cam phasing. The advantage that electronic throttle control allows is for the cam phasing system to work together with the throttle, rather than responding to a throttle input (and lagging behind, throwing away some of the efficiency benefits). However the amount of control that intake cam phasing has over volumetric efficiency is not nearly as good as Valvetronic. The range of positions for cam movement has been increasing, but retarding the opening of the intake much past TDC starts to incur significant pumping loss. As long as there is significant vacuum to deal with a warm air intake has the potential to improve fuel economy because throttling losses tend to be quite serious.