Big Tea wrote: ↑
Sat Jun 29, 2019 10:56 pm
Dr. Acula wrote: ↑
Sat Jun 29, 2019 10:50 pm
NL_Fer wrote: ↑
Sat Jun 29, 2019 5:39 pm
They don’t need pneumatic valvesprings for current engine rpm’s.
No they don't rpm vise. But as far as i know pneumatic valve springs can be set up relatively soft compared to a mechanical spring for the same rpm/valve setup. So they end up with a few extra horses by still using them.
Do they 'release' the pressure as the cam lobe rises? if there is no (or little, plus the pressure in the cylinder) resistance, it must save a huge amount of lost power in both force and friction. I had never considered this before. It only needs to stop the valve dropping off its seat until it 'follows' the close profile. Would the air be quick enough venting to do this?
Not based on what has been published to date - they only have a PRV that opens when pressure increases from oil accumulation in the pneumatic volume. This doesn't happen every cycle.
I see what you are saying though - the pressure requirement peaks when valve acceleration is at its maximum on the opening ramp however the peak pressure inside the "air spring" peaks at maximum lift which means that there is a portion of the cycle where the air spring pressure exceeds the pressure requirement. This is just wasted power.
I am not aware of any current means of mitigating this but here could be a few practical solutions.