[bwilson4web]

Hi,

I first saw variable valve timing and delay at the Detroit Auto Show in January 2009 and subsequently read a Toyota paper about it. I understand this technology is in one of the Lexus models. Here is a 2001 article about a BMW version:
http://autospeed.com/cms/A_111539/article.html

. . . an engine which can steplessly alter both the timing of each camshaft and also the lift of the inlet valves.
. . .
The most radical aspect of the new system is that no throttle butterfly is used. Instead, the engine changes its volumetric efficiency by altering the amount of intake valve lift. Theodore Melcher, BMW Project Manager, Four Cylinder Engines, draws the parallel with the human respiratory system. "Whenever we are required to make a greater effort," he says, "human beings breathe with a deep and long process of ventilation. Whenever we need less air, we do not throttle the supply of air by, say, closing our nose or our mouth, but [instead] simply breathe in a shorter, flatter process of ventilation."
. . .

This is a nice introduction to an important technology. Our Atkinson cycle engines have traveled part way down this path with part of the charge being pushed back into the intake manifold. But the next great advance would be elimination of the throttle plate.

Bob Wilson

[2009Prius]

bwilson4web said:

. . . an engine which can steplessly alter both the timing of each camshaft and also the lift of the inlet valves.
. . .
The most radical aspect of the new system is that no throttle butterfly is used. Instead, the engine changes its volumetric efficiency by altering the amount of intake valve lift. Theodore Melcher, BMW Project Manager, Four Cylinder Engines, draws the parallel with the human respiratory system. "Whenever we are required to make a greater effort," he says, "human beings breathe with a deep and long process of ventilation. Whenever we need less air, we do not throttle the supply of air by, say, closing our nose or our mouth, but [instead] simply breathe in a shorter, flatter process of ventilation."
. . .

Not sure what that "parallel" means. It seems that by "altering the amount of intake valve lift" the air flow is restricted exactly the same way as using a throttle plate, i.e. partially blocking the air way. If they really want to mimic how humans regulate breathing then they need to come up with a design of a combustion chamber with variable volume to simulate our lungs - seems almost impossible.

[bwilson4web]

2009Prius said:

Not sure what that "parallel" means. It seems that by "altering the amount of intake valve lift" the air flow is restricted exactly the same way as using a throttle plate, i.e. partially blocking the air way. If they really want to mimic how humans regulate breathing then they need to come up with a design of a combustion chamber with variable volume to simulate our lungs - seems almost impossible.

Sometimes an allegory goes wrong and I agree this wasn't the best. The key has to do with the difference of pressure across the flow of the gas. When we meditate, when we 'Zen out', we do breath shallow but it is to minimize the rush of air. One can achieve the same effect by what has sometimes been called the complete breath - total empty of lungs and complete filling over an extended interval.

The key to this engine valve efficiency is to all but eliminate any pressure difference when filling the cylinder. To manage the engine power, a partial charge is needed which is achieved by letting some of the cylinder charge back into the intake manifold instead of using a restrictor plate to limit the charge. It is by managing how much flow is pushed back that engine power is changed without forcing the engine to lose energy via a throttle, restricter plate.

I'll have to go to my sources but it is a sophisticated, thermodynamic and fluid-flow problem ... ortifice or restricted plate flow.

Bob Wilson

[2009Prius]

Thanks for the explanation. That makes more sense now.