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• # Calculation of clutch lever ratio

Discussion in 'The main mechanical design forum' started by k.udhay, Jul 26, 2012.

1. ### k.udhayMember

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Mar 2012
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Hi,

I recently got an opportunity to work on a clutch assembly. The clutch is an old model one which has six helical springs that keep pressing the pressure plate, clutch plate and engine flywheel against each other. The cross section is:

To give a brief working principle, when the release bearing presses the release lever (shown in fig.) towards right, the other end of it pulls the pressure plate on the opposite direction. The pivot is also shown in the fig. Like you can see, the lever ratio is mentioned as 1:4.6 clearly. But when I measured the dimensions 'a' and 'b' and found th ratio between them, I got a value 2.5. Can somebody explain me if there is anything wrong in what I have done pl.?

Thanks a lot.

2.
3. ### cwarner7_11Well-Known Member

Joined:
Oct 2009
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It appears you are using the wrong pivot point. It appears that the actual pivot point will be the center of the support shaft. It also appears that you are using the wrong terminal point for the lift arm- it will most likely be acting at the end point of the pivot arm, not at the first contact point.
Draw a line From the contact point at the which the release lever contacts the bearing plate, to the end of the lever arm at the bottom of the engagement socket. Where this line intersects the centerline of the shaft should be fairly close to the center of the shaft. Measure the ratios between the two parts of the line, and you should come closer to the specified ration.

4. ### k.udhayMember

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Mar 2012
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Hi Warner,
Thanks for that. Infact I tried with that also. But I didn't get a ratio of 4 even in that case also. You can even visualize that the distance between pivot point and release bearing contact point will not be of 4 times the distance between pivot point and bottom point of lever arm.

5. ### paulvNew Member

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Jul 2011
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Two problems: Firstly the lever does not push on the pressure plate where you have assumed - it would have a life of about 5 minutes if it did. I think the section is a tad misleading here. The lever actually pushes on the pin or plate with rounded end via the nice concave part of the lever. It appears that this pin then reacts against the pressure plate. Secondly, you need the lever arm dimension perpendicular to the direction of travel of the pressure plate. If you do it this way the ratio comes out nicely at 4.6

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