Help pls in DMU Kinematics with valve-gear modelling 1

[bajszi]

Hy everybody!

I have to make a four-stroke engine model, and I have to analising in the DMU Kinematics. It's my final project at my university. But I've stucked with the valve-gear.
I've been trying to find a solution for 2 days, but I haven't found anything yet. I've read the documentations, but I couldn't use the Point-, Roll Curve Joint...

Here is a good animation, what I want to manage:

http://upload.wikimedia.org/wikipedia/commons/4/41/Nockenwelle_ani.gif

Thx for helping me!

Cheers, Bajszi

 

[itsmyjob]

according to the gif picture what you need is sliding curve joint.

I made a ref part (fixed) as a support fir the rotation (Revolute) and the translation (cylindrical)

have fun

Eric N.
indocti discant et ament meminisse periti ​

 

[bajszi]

Thanks for the help, but I think it's not enough.

I fixed one part, which is a rectangle with a hole. The valve goes into this hole with a cylindrical joint.

I have to put the camshaft into a holder with a revolute joint.
I've done these.

But I need another joint between the camshaft and the valve to make the control. But I can't make this special joint.

 

[ryengnut]

Make sure you have a point on the valve that represents the contact point between the two parts.
Then have a curve that represents the path that the point follows as the camshaft rotates.
Should you then be able to create a point on curve joint between the two an get the mechanism to work.

ryengnut

 

[bajszi]

I've tried this before, but I got an error message every time, when I try it.

It says select a point on the curve! But how? The joint should take these two things together, shouldn't it?

I've made a 'Print screen', it may helps a bit:

http://balintmadar.extra.hu/kepek/catia/problem.jpg

 

[bajszi]

I've found a similar point on curve joint on the documentation.
The tip of the pencil is on the point here, but how? what kind of constrains do I need? Because here is nothing.
And what is this Geometrical set on the history tree?
Does somebody know this?

Here is the picture:

http://balintmadar.extra.hu/kepek/catia/problem2.jpg

 

[itsmyjob]

I've used a slide curve between the camshaft and the valve.

on the camshaft : create a section curve that goes all around

on the valve : create a curve in the same plane as the one on the camshaft.

TIP : in order to create the joint you need the 2 curves to be 'in contact'. You might need to create some points in order to have this contact.

Eric N.
indocti discant et ament meminisse periti ​

 

[bajszi]

What I don't know is this 'in contact'. How can I make this 2 curves to be in contact? In the Part design? or in the assembly or in Kinematics?
And these example files in the documentation have this 'Geometrical set'. I think I need this but how?
Sorry for not being able to understand what you wrote, but it's not easy now for me. But very important for me to manage it.
The engine block, the oil-tank, the rod, the piston, the crankshaft... so everything is done, fully modelled. But I can't manage this valve controll.
Is it possible to send me this example file what you made?

 

[bajszi]

Thx for everybody! Finally I could manage it.

It wasn't easy, I had to put the curves together, with points. And it was only possible in the DMU Navigator.

 

[itsmyjob]

nice ! So slide curve works...

Eric N.
indocti discant et ament meminisse periti ​

 

[bajszi]

yes, it works!

And I have another questions, but it could be another topic. I've been learning IT, so I'm not a proper engineer. But when you build a mechanism, for example now this 4 stroke engine, do you apply offset between the parts?

For example when a bearing attached to something, do they have offset (~0.1mm) between each other? Or we have to biuld it with touching each other?

 

[bajszi]

I've nearly finished my project, only some analysing has left. Here is one videoclip, I you are interested in

http://balintmadar.extra.hu/video/moto.avi

Cheers, and thanks for you help guys!

Bajszi

 

[jakemanr]

I'm in a similar situation. I have managed to create the joints but the simulation doesn't work as it should.

I have a valve running in a guide with a cylindrical joint. Revolute joint between the cam and head. Then I’ve used the slide curve joint linking a curve around the surface of the cam lobe to a curve on the top of the valve stem.

When I run the simulation the curve on the valve follows the base circle diameter of the lobe until the valve should begin to open, then it jumps through the cam lobe to join with the base centre circle again (see linked photos). I have tried limiting the valves movement in the cylindrical joint but this doesn't seem to help.

http://img103.imageshack.us/my.php?image=valvetrain1ho4.jpg

http://profile.imageshack.us/user/jakemanr/images/detail/#77/valvetrain2ar9.jpg

Any ideas?

 

[bajszi]

Hiya!

I've had the same problem, especially when I used high speeds and rotations...
My stuff: I had a curve with point, and a line with another point. And I used the slide curve joint with the two points. So the line and the curve are touching each others by the points. This was I could not use a staight line in the curve. But this way it works.

 

[jakemanr]

That was a quick reply, thanks.

I've sorted it now, I was trying to use a straight line on the top of the valve stem, putting a curved line here (in the plane of the lobe) solved it.

Thanks,

 

[bajszi]

That's great!

Your welcome!

Cheers,
Bajszi