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Why will a Simscape model solve with a Gear and a slipping clutch - but the identical model with the Gear replaced with a CVT (at the same fixed ratio) will not solve?

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Tom Jenkins
Tom Jenkins on 21 Oct 2016
Answered: Steve Miller on 6 Aug 2020
As a novice user I am experimenting with simple mechanical components and assemblies mostly with good success.
A model with an Engine, Gear and Clutch driving an inertia solves without problems and in accordance with expectations including transition to clutch slip as clutch pressure is reduced. An identical model with the Gear replaced by a (Driveline) Variable Ratio Transmission will not solve into the slip region giving a "failure to converge error". I have tried different solvers, reduced time steps, modified clutch parameters and added dampers but with no success.
Has anyone got any ideas?
  1 Comment
Swarooph on 21 Oct 2016
I don't have a direct answer. But something to bring to your attention. I was looking at the Variable Ratio Transmission block documentation. Take a look at this particular section where it talks about an ideal motion and torque transfer and how it depends on the compliance parameters.
In short this relative compliance factor is the difference between the variable transmission block and a gear box/simple gear blocks it seems. You might need to see how to get these values for your model.

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Answers (1)

Steve Miller
Steve Miller on 6 Aug 2020
The compliance in the Variable Ratio transmission is the difference between these models. If you make the compliance very stiff, the results in the scopes line up pretty well. I made those adjustments and uploaded the models.
Note that you should use a variable step solver for these simulations, and for fixed step simulation instead of ode14x enable the Simscape Local Solver.

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