Valve Train

[Bob_W]

I have tried to animate models in the past that are similar to a cam and valve train but have had no luck. I had another one the other day to do and I tried again with no luck. I don't use Mechanism very much so my skills are limited in that area.


The problem is with a valve that has a clearance between the tappet and the valve stem. When the cam is set up with lift-off disabled it works fine except for the representing the clearance properly and the valve will not stop when seated. With Lift-off enabled, the valve is pushed open but then remains open when the tappet returns. How do I get the valve to follow the tappet back until the valve seats? I do have the valve limits set at the seating point but until I can get the valve to return that doesn't matter.


There must be something simple I am overlooking. Any help would be appreciated.


Bob

 

[Kaz Z06]

In order to make lashed valve trains work, you must conduct a "dynamic" analysis. Kinematic analyses will allow cam pairs to contact and move a valve open, but when the rocker moves to the closing side, the valve will stay where it is since there are no loads acting on it (unless you forgot the valve spring in a dynamic analysis). I've conducted hundreds of analyses on valve trains, and you can easily get this type of interface to work well - I'm working on one now with an e-foot! Run a dynamic analysis, make sure you have a valve spring, a closed limit on the travel of your valve and select "enable lift-off" for your cam pair.

Cheers,

Kaz

 

[Bob_W]

Kaz


Thanks for the reply. I hadn't thought of doing a dynamic analysis so I will have to give that a try. This will be the first one, so it will be a learning experience for me. I have the limits and cam already set so hopefully it will go well.


Thanks


Bob
Edited by: Bob_W

 

[Bob_W]

Kaz:


I finally got to work on the valve train today and was able to get it to work. It took several attempts but I got it.


Thanks for the help


Bob

 

[Kaz Z06]

Glad it solved the problem for you - enjoy!