SECTION 8 TIRE MODELING

TIRE MODELING What does this section contain? Tire/Wheel Setup Constant Radius Analysis

TIRE/WHEEL SETUP Tire/Wheel setup utility Found in the suspension subsystem editor. Different from the alignment options as it orients the tire during design configuration, not after a static simulation. An axis that a tire/wheel rotates about is defined by two points: wheel center (pt 9) and the spindle alignment point (pt 11). If you change the camber and toe of the tire in Adams/ Chassis, it simply changes the relative location of the spindle alignment point to the wheel center, which changes the orientation of the spin axis. Note that this does not change other parameters such as lower or upper ball joint locations.

TIRE/WHEEL SETUP (CONT.) In the set up utility: Spindle align vector length (distance between pt 9 and pt 11 along spin axis) Toe Camber Loaded tire radius Spindle alignment point (pt 11) and tire patch (pt 10) are calculated based on these parameters, along with the wheel center hardpoint location. Select Apply to paste the current values to the hardpoint table.

TIRE/WHEEL SETUP (CONT.)

TIRE MODELING Several tire models are available since tires have a large effect on vehicle handling. Example files are stored in <examples>/tir. You can find information on the types of tire models in the Adams/Tire documentation. Adams/Tire calculates the equivalent forces and moments on the spindle due to tire/road interaction.

TIRE MODELING (CONT.) Three types of tire modules: Adams/Tire Handling module - Incorporates the following tire models for use in vehicle dynamic studies: Fiala tire model (least advanced, no camber effects) Pacejka’89 and Pacejka’94 models Pacejka 2002 (also known as PAC2002), replaces version 2003 and older MF-Tyre (Delft-Tyre) from TNO UA-Tire model includes relaxation effects, both in longitudinal and lateral direction 5.2.1 Tire model, the original Adams/Tire model, offers two methods calculating slip forces and moments and two contact models Adams/Tire Handling uses a point-follower method to calculate tire normal force and is limited to 2-D roads.

TIRE MODELING (CONT.) Three types of tire modules (Cont.): Adams/Tire 3D Contact module Uses a 3D equivalent-volume method to calculate tire normal force on three-dimensional roads for use in predicting vehicle loads for durability studies. When you purchase Adams/Tire and Adams/Tire 3D Contact module separately, you can only use the Fiala model to calculate tire handling forces and moments.

TIRE MODELING (CONT.) Three types of tire modules (Cont.): Adams/Tire FTire module - The FTire module is the latest addition to Adams/Tire. It is a new tire model for durability and ride and handling applications that: Offers an effective compromise between model fidelity and detail, and computational speed. Provides valid results up to 120 Hz in the frequency domain. Lets you easily derive model parameters from tire measurement data. Provides valid results for short obstacles with wavelengths down to half the size of the tire-road contact patch. For more information, see http://www.ftire.com.

CONSTANT RADIUS ANALYSIS Constant radius analysis analyzes: The model in a steady-state cornering condition The behavior of the vehicle in constant radius turn at different lateral acceleration levels Report metrics such as: Understeer gradient Roll gradient Understeer budget

CONSTANT RADIUS ANALYSIS (CONT.) Understeer budget You will use understeer budget in this workshop. Understeer budget lists contributions to understeer gradient from different sources. The Adams/Chassis online help contains detailed calculations used to determine understeer budget.