OT: My brain is failing me again. Help with numerical / mechanical problem required. Message #1 Posted by Harald on 27 June 2013, 10:42 a.m.
I have the following problem and don't really find a way to solve it:
For a given cam I have the lift versus the rotation angle as numerical values. Which looks something like this:
If a cam runs on a flat surface tappet it is possible to reduce or increase the base circle and the lobe by the same amount, or in other words shift the curve in the picture down or up. If the distance between the surface of the tappet and the center of the cam is also change accordingly, the lift does not change. Edit: After thinking about this again, that is wrong. But at leas the difference is not that big. And when grinding a cam nobody really compensates for that. So far this is pretty straight forward. Now we get to the more difficult part. If a roller tappet is used instead of a flat tappet this is not the case anymore.
Firstly, to get the same lift, the lobe profile has to be different. This is because the contact point between the cam and the tappet isn't static anymore. It moves along the roller. Again, I have (or at least can measure) the cam profile. And secondly, because the contact point is moving, it is not possible anymore to simply shift the curve up and down without changing the lift. Now my question is, given the numerical cam profile data and the diameter of the roller, how do I calculate the new cam profile for a reduced base circle?
Sorry for the OT. But I think you guys appreciate a challenge and I appreciate your help :)
Cheers,
Harald
Edited: 27 June 2013, 4:14 p.m. after one or more responses were posted
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