Why does the interpolation not work correctly when setting capacity factor parametrization of torque converter block to "Ratio of impeller torque to square of speed"?

I am testing the torque converter block and have built a test bench to verify its behavior. I have noticed that when specifying Ratio of speed to square root of impeller torque for the capacity factor parametrization parameter, the interpolation does not seem to work properly. My model looks like this: 

The interpolation method is set to linear; hence, I expect that for a speed ratio of 0.8, as specified in the model, the capacity factor should be 0.002. Therefore, the input torque will be 2000 Nm. However, this does not appear to be the case, as shown in the model above.

Answer 1

[MathWorks Support Team]

This is the expected behavior. The block interpolates as intended.

The block uses the tablelookup function. When Ratio of impeller torque to square of speed is selected for capacity factor parametrization, the block does not use the capacity factor vector directly as specified in the mask in the tablelookup function. Instead, the input vector is transformed to represent the Ratio of speed to square root of impeller torque.

This ensures that the block's behavior is consistent for both parametrization methods. For example, the following two settings are consistent:

•  Capacity factor parametrization set to Ratio of speed to square root of impeller torque and the capacity factor vector specified as 1./sqrt([0.001 0.003 0.005])  rad/s/(N*m)^(1/2)
•  Capacity factor parametrization set to Ratio of impeller torque to square of speed and the capacity factor vector specified as [0.001 0.003 0.005] N*m/(rad/s)^2