Quote:
Originally Posted by Formula413
Great post.
That BMW concept of essentially letting the intake valve serve as the throttle plate is fascinating, I had never heard of that before. I've learned all kinds of neat stuff on here.
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It's been a few years since I've been in touch with BMW's experimental works. Some of their stuff has made it into current vehicles, some hasn't. I know they sold a car that had constantly variable lift on the intake valves as well as timing, that could accomplish most of this. Timing is pretty common on cars, but they varied lift by mounting the rocker arms on an eccentric that varied the rocker arm ratio. This engine also used a throttle plate, but I think the throttle plate (throttle by wire) didn't do much - and was more of a backup in case the lift deal broke down. The end goal was fully electronic actuation of the valves (get rid of the camshaft) and do anything and everything with a computer.
The idea is that if you can hold the intake valve open during part of the compression stroke, you can spit out some air and operate at "part throttle" even without a throttle plate. Simply throttling at the valve through low lift or low duration doesn't rid you of pumping work losses since the piston (the pump) still sees vacuum during the intake stroke.
Thanks for the compliment. If you want to learn more, check my recent posts where ohm's law is explored. Aparently it can mean different things when you try to change it to prove poor theory.