Quote:
Originally Posted by Frank Lee
I have a suspicion that eliminating the throttle plate won't cut pumping losses, if it's done by manipulating valve timing, cuz then the restriction that the piston sees on the downward stroke would be caused by the intake valve. However if Toyota is doing something else then good.
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I'll try to illustrate the difference with a couple of idealized graphs.
valvetime.png shows piston position on the x-axis and cylinder pressure on the y-axis. the green line shown cylinder pressure in an engine that uses no throttle, and instead only has the intake valve open until the needed charge had been drawn in. The red line shows cylinder pressure in a conventional throttled engine. The mild green area illustrates the energy saved on each intake stroke.
pushout.png illustrates the effect of having a less restrictive throttle and keeping the intake valve open "too long" after BDC. The red line is again a conventional engine and the mild green area represents the energy saved on each intake stroke.
Minor oops: the area marked after BDC shouldn't be green, it should be brown or something instead, since it doesn't represent energy saved. (but rather the opposite)