Suspension KnC parameters Error: Not changing Monotonously

The error ‘xxx is not de/increasing monotonously’ has to do with CarMaker not been able to interpret correctly the data that is getting from the SKC file. In this case it is a problem with the wheel compression, the spring length, damper length, buffer length, and stabilizer length, which correspond to the columns tz, lSpring, lDamp, lBuf, and lStabi in the SKC file (see image).


The format of the error is:
xxx is not de/increasing monotonously [Data (Arg0, Arg1) … Data (Arg0, Arg1)],

For example:
Compression tz in not increasing monotonously [0 (1,7) … -0.0370904 (2,7)],

The 0 is the value found at row (1,7), column tz, while -0.0370904 is the value found at row (2,7), column tz in the SKC file. This error is thrown because the value is not increasing and it is either decreasing or is constant. For a double wishbone suspension SKC file generated with IPGKinematics, the Arg0 corresponds to q0(wheel compression), while Arg1 corresponds to q2(steering wheel position). The vales at (0,7) and (1,7) are likely the ones that correspond to maximum wheel extension with zero steering wheel angle.

The troubleshoot the problem one should start by taking a look at the data in the SKC file. The SKC file is a mapping of the suspension kinematics. If possible one should plot the data (tx, ty, … lStabi) with respect to wheel compression (Arg0) and make sure that the graphs are smooth and continuous. In general one should avoid data that has sections that are completely vertical (derivative approaches infinity) or completely flat (derivative approaches zero).

I will suspect that the root cause has to do with the geometry data inputted in IPGKInematics. Two common causes are the suspension bottoming out or maxed out (invalid compression range) or the use of ‘Forces on’ option with invalid parameters (such as misaligned bushings).

Could you please share your .skc or .kin file? Or could you plot the data found on the SKC?