VVT vs VCT

[ItsuMitsubishi]

Originally Posted By: chrome
Originally Posted By: NateDN10
I've often thought it would be cool to do away with camshafts entirely and use oil pressure or solenoids to directly actuate the valves. From what I've read, this is difficult because of amount of force needed in a short amount of time. Still, a cool idea.


BMW have that in some of their production engines for many years now... Valvetronic?


Valvetronic doesn't work like that. There are still cams and springs, in fact there are also extra "return" springs.

 

[d00df00d]

Originally Posted By: chrome
Originally Posted By: NateDN10
I've often thought it would be cool to do away with camshafts entirely and use oil pressure or solenoids to directly actuate the valves. From what I've read, this is difficult because of amount of force needed in a short amount of time. Still, a cool idea.


BMW have that in some of their production engines for many years now... Valvetronic?

VALVETRONIC allows infinite adjustment of valve lift. It is used in combination with VANOS, which allows infinite adjustment of cam timing (and has been around for the better part of 20 years).

In other words, VALVETRONIC and VANOS are basically doodads that change how the cams act on the valves. They still need cams and valve springs to work. What NateDN10 was talking about was replacing the springs and camshafts entirely with something else.

 

[SteveSRT8]

gotta quit using that word "infinite".

It's just not true.

 

[d00df00d]

Well, not infinite in terms of range. Effectively infinite in terms of resolution, I guess.

The point is, it's not an on-off switch or a 2- or 3-stage system.

 

[ARCOgraphite]

IIRC, The INZFE in my rolling grape on 4 wheels has VVTi with 40 deg variability on the intake. I think the "infinite" relate to the cam phasing margins withing the Otto cycle; still not a good word choice.

 

[SteveSRT8]

agreed. And that's just what many of the oil operated systems do, simply from one point to another, no real variability.

VTEC is one that is simply on/off. A couple of newer Detroit engines do the same. I don't even like the word 'variable' because to me that implies that it varies in relation to some operating parameter like load/rpm, etc. Not just in/out, on/off.

 

[SteveSRT8]

oops, double post