[chbot] Filter

[Hartley, Robin (Nokia - NZ/Wellington)]

Hi Wallace,

Something to keep in mind when measuring cam profiles is the shape of the cam follower. Flat bottom followers result in a very different effective profile compared with roller followers. Some followers that appear flat actually have a profile to them.

When doing this the old fashion way with a DTI we would do it in situ using the followers, and we used to vibrate the bench at each measurement point to get the pointer to settle. When running the DTI directly on the cam drag on the end of the pointer causes stiction in the bearing that can give this semi cyclic error. A bit of vibration may help
 
For selecting between a set of cams I'd just use Excels curve fitting to smooth the curve. And then do the velocity calcs on the resultant curve.

Regards,
Robin

-----Original Message-----
From: Chchrobotics <chchrobotics-bounces at lists.ourshack.com> On Behalf Of Marshland Engineering
Sent: Saturday, October 20, 2018 10:30 AM
To: chchrobotics at lists.ourshack.com
Subject: Re: [chbot] Filter

After quite a few chats and emails, the problem has become clearer. In some way it may not really a filter issue. For a 4 stroke engine cam, there are basically 4 components, base circle, up ramp, over the nose and down ramp back to the base circle. 

So we have 0 velocity, acceleration to the up ramp, constant velocity, deceleration, stop (over the nose) acceleration, down ramp, deceleration and back to 0. 

The figures to look for are the acceleration. If it is too high then the valve/valve strings etc loose contact with the cam. 

The figure for acceleration (from memory) is 0.008" per degree or .2 mm/degree.  This is what I want to measure/compare. 

Here is some info on it.
http://www.profblairandassociates.com/GPB_4stHEAD_ValveLiftDesign_hmb.html

Basically I have several different cams and want to measure them all and choose the one with the most gentle profile. 

Cheers Wallace.


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