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clutch damage law

clutch damage law

clutch damage law

Hi all,

I have recorded torque and rpm of the crank shaft during some conditions. I need to understand which conditions is more "damaging" for the main clutch, for example many engangement with low torque and low rpm or few engagements with high torque and high speed levels. For the gears I have computed the time at level and then I calculated the damage with the inverse power law, computed with the three different damage exponent according to the failure mode. Is there any similar method for the clutch? Any other suggestion is welcome
Thank you

Best regards

RE: clutch damage law

I've known a few drivers who have never had to change a clutch in any of their cars even at 100 kmiles.

Generally from a start or when shifting they engaged the clutch quickly, at low rpm, so there was little slippage.

RE: clutch damage law

i would think that the most "damaging" operation would be starting from a standstill (especially on a steep gradient). in that situation there is initially quite a bit of slippage that will cause wear. during shifting operations the load is much lower, although that may depend on the behavior of the operator.

RE: clutch damage law

Hi all,

thanks for your reply. Greg is right, I need a sort of equation that would permit to understand which is the most severe condition for the clutch. I do not need an absolute value. I contacted the clutch supplier but he wasn't of great help

RE: clutch damage law

Well, the clutch isn't a torque multiplying device. So, say you have the engine at X rpm and are slipping the clutch to produce Y rpm. You will also have Z torque being transferred to the transmission. By using speed and torque on both sides, you can then calculate input and output power and the difference goes into the clutch (XZ - YZ). I would have to believe the higher the number the more clutch wear but I can only guess about that relationship being non-linear with more damage quicker as the clutch reaches a certain temperature.

RE: clutch damage law

I may be captain obvious but Hi RPM/harsh engagement of the clutch will cause rapid heating/pressure at the point of contact ,I would think it would be possible under full demand such as a 'peel out' for the clutch to slip under its full pressure higher gears such as 3.73 in the mustang svo may help with the pressure/heat over time to full engagement

RE: clutch damage law

@TMoose, maybe I miss something but with the uniform theory I might be able to calculate the Torque in function of the axial force and not something related to the remaining life of the clutch.

@Greg, your link is really helpful. In my opinion the key is on the energy which goes into the clutch for each engagement as we know the energy of friction forces is proportional to wear and a clutch has no remaining life when it is completely worn out. Unfortunately I do not have any temperature of the clutch surface, but I suppose higher is energy and higher might be the temperature reached by the clutch disc, therefore I would use the Archard's law and I would weight the engaging energy with an exponent, something like:


k proportionality factor
T torque
ω slip velocity
A exponent
H is material hardness

Since k and H are related to the clutch I can say

W ∝ (T*ω)^A

and this number I can use it as clutch usage severity. Does it make sense for you? Moreover, look at figure 5 of the following paper, do clutch mununfactures usually provide this kind of plot in their datasheet?


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