User:Jobstbrandt
From Wikipedia, the free encyclopedia
Insert non-formatted text hereI sense that I stepped on some toes with my description of why desmodromic valve drive is no longer used for IC engine, except by Ducati where it seems to be a selling point.
The disadvantages I mention are all subjects that, had there been computers that could develop good cam contours, no one would have questioned. The items I mention are explained and need not be taken on faith. To believe that other engine manufacturers are fools for not recognizing desmodromic valve drive as valid and that it yields better performance and economical operation requires a leap of faith.
I don't begrudge Ducati their good sales and racing successes but am aware that with good management, even mediocre products can rise to the occasion. I have racing car and engine design experience in the Formula One business and recall how once exposed, all these concepts were obvious to the design team.
I hope the concept can be absorb with time and consideration. Meanwhile, I am searching the web for links for folks who don't believe this is possible.
Jobst
High speed photography showed that at specific resonant speeds, valve springs were lifting off at both ends leaving the valve floating before crashing into the cam on closure.
Who did this work? Where was it done? When was it published? If you make any specific claims, they must either be cited or be broad enough that they are general knowledge.
This work was done during the development of the Porsche 804 Formula One engine and subsequent TAG Formula One project when I was on that project in Stuttgart. I have no access to the proprietary information and data at Porsche but that should not make the description of the effects any less credible or believable, all the reasons are given in the text. These are things that any technically inclined person will recognize as valid just as we did in the lab when the results were reviewed.
If you think there are incorrect aspects to the description of valve control, I would like to see them and respond. Blandly saying you don't believe without citations is a cover for feeling that the sacred cow of desmodromic valve drive should not be questioned. I think I have given reasons and these are so clear and obvious to people who work with such designs that no further proof is required.
Desmo has more mass
Desmo has curved tappets that increase stress
Desmo cannot lift valves faster than conventional cams
Desmo cannot close valves faster than conventional cams
and above all
Desmo has been abandoned for automotive engines except at Ducati.
Instead of appearing to be preferential to desmodromic valve drive, you could ask why it is a vanishing technique. I have offered some of the reasons and ask that anyone knowing otherwise explain why any of what I have presented is erroneous.
Jobst 04:29, 23 January 2007 (UTC)
