Coil spring compression by design table??? 2

Has anyone tried modeling a spring that can be compressed by equations and/or design tables in an assembly? ie. In the engine I'm building, I want to write an equation giving the gap that the valve spring should fill relative to crank rotation angle etc.
Also if I run this in-context part in multiple instances in the same assembly (which means the springs will be at different extensions), is SWX going to give me problems?

Thanks all

Oliver
Grad Mech

 

[krishnamurthy]

It is to create different configurations of Springs. In the Helix definition sketches, you can give different dimension values to represent gaps.
Well Multiple instances of the spring in a assembly will be of same dimensions. If you want one spring open, another instance closed and so on. I think you should use diferent configuraions in the spring part.

 

[FrenchCAD]

I have to agree here. I don't think there is a way to have what you want unless using many configs. FrenchCAD
Université Joseph FOURIER
Département Génie Mécanique
Grenoble
France
cyril.guichard@wanadoo.fr

 

[APPENG]

Oliver,

I think that because of the way you want to design your spring, or more to the point the way you want to use your srping, you should look into constructing a helix by using two sketches projected to form your sweep curve. That way you can use an in-context reference to define the spring height through the cycles of the valve train, and keep the same number of turns and all. no formulas, just geometric relations. Granted this may take a little more solve time than a standard helix (which are also rather taxing) this way would require you to model a new spring at each location as each would be unique to it own position (height) relative to the cam cycle.

the problem with doing it the other way, would require a lot of assembly and part configurations. and you would still be limited to the number of positions you could show the part in.

hope that helps a little Regards,
Jon
jgbena@yahoo.com

 

Jon, how do you mean two sketches to form the sweep curve? Do you mean the helix dia and also the sweep crossection? Could you tell me the syntax for defining the length of a helix in a design table ie 'D1@helix1' etc.

Thanks for your help

Oliver

engin_eer@hotmail.com

 

[meintsi]

I've done exactly what you want for a different application.

First be aware that the equation governing the spring length will be unique to this assembly and will basically keep you from using this part (or any other configuration of this part) in any other assembly. So I would recommend creating a spring part file (1 configuration only) which will be unique to your application and to the specific application only.

First, insert your spring and mate one end (coincident and the spring axis concentric) where it belongs. This fixes the spring end but still lets it rotate in place.I would recommend mating this end to the most complex geometry. Make sure that at this point, that your spring length is shorter than the area in which is to be inserted.

Second, on the part where the other end of the spring mates to the feature, open the part and insert a point on the surface of the mating area coincident to a reference plane.

Insert a second point back in a sketch on the spring end to be mated in a similar fashion. On the face ALREADY MATED and coincident to a reference plane. Now mated the two reference planes containing these points coincident. (This completes the spring mate.)

When you insert a dimension into your assembly between these points (the final length of spring) it will overdefine your assembly. Leave it that way.

Now open your spring file and make the driving dimension of your spring helix length a driven dimension.

The trick is to generate an equation in your assembly where the spring helix length is = (driven by)the dimension inserted in your assembly. Double-clicking the appropriate sketch in the feature manager tree allows access to both dimensions for equation writing.

When you force a rebuild of the assembly, the spring length is now driven by the relationship of the two parts it is mated to and fills the space between the two parts.

You can then go back and hide all your added sketches to keep them from appearing in your assembly.

I've done this for many valve models and the only drawback I've noticed is in some assemblies, and I can't explain why, sometimes two rebuilds are necessary in order for the spring to be generated as desired. Maybe it has something to do with the order the parts are brought into the assembly but I haven't had a chance to explore this option.