FTire parameterization software on basis of experimental data
FTire/fit is the parameter identification and validation toolbox for FTire.
FTire/fit is a comprehensive tool for FTire parameterization, much more than just a mathematical parameter fitting procedure. It uses the following kinds of experimental data:
- static tire properties like radial, longitudinal, lateral, and torsional stiffness on different surface geometries,
- footprint shape bitmaps,
- tire properties in steady-state rolling conditions, and
- time- and/or frequency-domain measurements of cleat tests that excite large-amplitude tire vibrations,
to determine some or all FTire model data for a given tire brand, tire size, and inflation pressure. This is done such that the measurements are approximated by tire simulations in the sense of minimized mean squares.
The data to be fitted can be defined in a very flexible way. Thus, the actual availability and properties of measurements can easily be taken into account in an optimal way. At the same time, the model data to be fitted can be chosen with a similar flexibility, starting from one or only few parameters up to a nearly complete set.
During the evolution process of FTire, an important experience was made about the role of modal data. They seem to contain less relevant information than static measurements (in contrast to what had been assumed in the early days of FTire), and typically it is rather laborious to obtain them. There is one obvious cause for the lack of relevant information: during modal measurements on an unloaded tire, only small amplitudes will be reached. However, these measurements are then used to parameterize FTire for load cases with large to extreme deflection values, that is, in completely different operating points.
Another experience is about the large amount of valuable information that is contained in footprint bitmaps. The same holds for several kinds of static deflection curves without and with camber angle, on flat surface or on certain well-defined obstacles. Moreover, handling properties like cornering stiffness and pneumatic trail show a high correlation with certain out-of-plane stiffness data. In many cases, after a thorough analysis of static and steady-state behavior, there remain only few dynamically relevant parameters to be adjusted in order to get also a good correlation in cleat tests.