Valve Train Spring Design

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I am using CREO 2.0 for a valve train analysis. I want to determine how much spring I need to return the valve, hopefully to keep the follower on the cam. So I place a trial return force on the valve and allow lift-off. Looking at a previous thread answered by Kas back in 2011, I place limits on the valve travel and allow cam lift-off, but my roller-follower never returns to the cam. I have tried using the exact limits as shown by the cam, or increasing those limits slightly --- still no luck. I have 3 cams in the train, but am allowing lift-off on only the main cam and roller-follower. The power of this tool is tremendous; if only I could figure out how to use it! Any help would be greatly appreciated. "rework"

 

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I have been banging my head against the wall on this one -- sure would like to make it work! I have abandoned the force on the valve to return it, and instead installed a strong spring. When I 'allow liftoff' on the main cam & roller, the roller still does not return to the cam. I was thinking my problem related to the translation axis numbers for the valve, but can't confirm that. I discovered that there is hardly any extra cam surface on the rocker arm, but it shouldn't have to run past the max stroke limit?

I could download my file-- is that possible? --- rework

 

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Rework here again. I would like to post my file, but the zip limit is 97.7kb. The smallest I can get it down to is 1.3 meg. This is a simple assembly. If you would be interesting in helping, I could email it to you,

Thanks --- rework

 

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I have attached a JPG of my valve Train.

 

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One thing seems wrong. When I open 'Edit Definition' on the valve, it shows translation measurements of the opposite sign to what my 'measures' show, which are correct with the CSO I have specified. I am suspecting this is the source of the problem. Is this a glitch in the program? I am running CREO 2.0, m060. Unfortunately my maintenance has expired. Again, unfortunately, when I asked for help from my current maintenance, they were usually unable to help with a 'Mechanism Dynamics' issue. Seems my $6,000 upgrade from Wildfire was a waste.

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Talking to myself again. I believe I have cracked the code. Having three cams in this train seems to be an issue. I had specified 'Liftoff' on the roller, and it sticks open. When I specified 'Liftoff' on the Valve Stem Cam Connection only, things worked as expected.

If someone needs help in the future with Valve Trains, I will be glad to help.

Thanks for looking --

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One more parting question. I am wondering if the program can handle 3 cams in line with 'Lift-off', as this example includes? I have experimented with various combinations, with no luck. It would be great if a CREO Mechanism Dynamics expert would comment on this.