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Ron George
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Join Date: May 2009
Location: IN
Posts: 99
Good Answers: 1

CVT Spring Forces

04/21/2010 11:48 PM

Hi. I happen to have a blue colored compression spring with me from a CVT. The spring sits in the secondary clutch of the CVT and acts both in compression but mainly in twist, in order to provide side force to the belt. One can adjust the range of pre-loads by placing the spring's vertical end in 9 different holes spaced along a half-circle, so you're basically twisting the spring by different amounts after you install the spring with bolts. The spring together with a helix ramp & roller bearing provides the side force to the belt.

I wish to calculate the pre-load on the spring. If I'm thinking about this correctly, it will be a sum of the initial compression and the initial twist when the CVT is not running. Spring constant in compression was estimated to be 70 lbs/in through this online calculator http://www.engineersedge.com/spring_comp_calc_k.htm I don't have any handy spring tester to check twist or compression. Any ideas?

Free length of spring = 3.2"

Outer Diameter of coil = 2.43"

Wire Diameter = 0.160"

Material = Steel

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Join Date: Mar 2007
Location: City of Light
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#1

Re: CVT Spring Forces

04/30/2010 11:05 AM

I see that you did not get any answer till now. I dare say that I am quite surprised that participants did not have the possibility to do it!

I think that the spring is loading the ramp mainly by twist which is a consequence of the wire BENDING as the action in compression depends on TORSION.

It is possible to compute the stiffness in bending if you also indicate the number of windings since this action is as the torsion function of it.

For the computation you consider a circular beam with the radius = mean diameter of winding/2 for an angle of 180 or 360° as you wish and with a radial & tangential force at free end. The problem is that the force remains tangential and the "displacement" is not straight but circular. If you do not come to a result by your own ask for more information. How is your project going on?
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PlanetSpring
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Join Date: Jul 2010
Location: california
Posts: 5
Good Answers: 1
#2

Re: CVT Spring Forces

07/27/2010 12:54 PM

I can't see the photo of the spring on the website, but if you have the number of active coils, this calculator may be helpful:

http://planetspring.com/pages/compression-spring-calculator-coil-calculator.php
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