A decade ago, Vianney RABHi,TheRevva wrote:. . .
I _must_ be missing something truly fundamental here.
I don't see the additional hardware costs as being prohibitively more than current engine technology (and as mentioned above, there are SOME savings that help to offset them!)
It all seems so easy that I cannot believe _someone_ hasn't already done it and it's about to reach mass production?
the inventor of the Variable Compression Ratio - VCRi - mechanism of the well known French company mce-5 (quote from mce-5 website: "Funds invested in MCE-5 R&D to 31 December 2011: 75 M€"),
was patenting / developing a cam-less hydraulic VVA (variable valve actuation) system.
From his communication with pattakon it seems that, among others, there were problems with the micro-alignment among the various cylinders epsecially at light load operation.
The cam-less hydraulic VVA project of Vianney Rabhi was rejected for some reason; then he focused on the rack-gear VCR of the mce-5. You can try to contact and ask him where the true problem was.
You can also make a search in the patent offices ( starting with the USPTO at http://patft.uspto.gov/ , for instance) to find-out what is the current state of the art in the cam-less hydraulic VVA systems and where the last applications / patents of this class are focused.
Thanks
Manousos Pattakos