1. WORKSHOP 8
TIRE MODELING

3. WORKSHOP 8 – TIRE MODELING
Problem Statement
Determine how various vehicle design changes affect the understeer characteristics of a vehicle.

4. WORKSHOP 8 – TIRE MODELING (CONT.)
Model Description
You will use the achassis_gs database full-vehicle model and analyze the effect of changing the engine location and tire properties on the understeer behavior of this model.
The front suspension of the achassis_gs vehicle uses an SLA front suspension with rack-and-pinion steering.
The rear suspension of the achassis_gs vehicle uses a solid axle with four control links and a Panhard bar.

5. WORKSHOP 8 – TIRE MODELING (CONT.)
Changing tire parameters in Adams/Chassis
Here you will see the effects on vehicle handling that result from making changes to tire parameters in Adams/Chassis
To set up the vehicles:
Start a new session.
In Build mode, load the achassis_gs_full_sys.xml full-vehicle model.
Modifying vehicle setup 1
Here you set the engine towards the front of the vehicle (for example, a family sedan with standard sedan tires).
To modify the vehicle:
In the treeview, select achassis_gs_body.
Click the Parts tab.
Modify the location of the CG of the body (chassis part) so it is located at 2600, -12, 877(mm).

6. WORKSHOP 8 – TIRE MODELING (CONT.)
To modify the vehicle(Cont.):
Click Save As, enter achassis_gs_body_sedan.xml and then click Yes to update references.
In the treeview, select achassis_gs_full_sys, click Save As, and then enter achassis_gs_full_sys_sedan.xml
In Test mode, expand Full Vehicle, expand Handling Analyses, and double-click Constant Radius.
Use the parameters shown below:

7. WORKSHOP 8 – TIRE MODELING (CONT.)
To modify the vehicle(Cont.):
Click Build and Run Selected Events.
In Review mode, click Execute Selected Plots.
Look at the plot, “Steering Wheel Angle vs. Acc Y (Lateral Acceleration)”
Notice that the steering wheel angle increases in magnitude with a steep slope as the lateral acceleration goes from 0 to -0.7 Gs. The slope, in deg/G, is a measure of the understeer gradient of the vehicle. The increasing steering wheel angle necessary for higher lateral acceleration is a characteristic of an understeer vehicle.

8. WORKSHOP 8 – TIRE MODELING (CONT.)
Modifying the vehicle setup 2
Here you set the engine towards the rear of the vehicle (for example, a Porsche with sedan tires).
To modify vehicle setup 2:
Return to Build mode.
In the treeview, select Body subsystem.
Click the Parts tab.
Modify the location of the CG of the body so it is located at 3200, -12, 877 (mm).
Click Save As, enter achassis_gs_body_sports_car_1.xml and click select Yes to update references.
Select the modified system in the treeview, select Save As, and then enter achassis_gs_full_sys_sports_car_1.xml
In Test mode, right-click Constant Radius in the bookshelf to select Add Event to Current Fingerprint Using Model, and then select achassis_gs_full_sys_sports_car_1.xml.

9. WORKSHOP 8 – TIRE MODELING (CONT.)
To modify vehicle setup 2 (Cont.):
Use the same parameters from Step7 in setup.
Click Build and Run Selected Events.
In Review mode, select both events and then click Execute Selected Plots.
Look at the plot, “Steering Wheel Angle vs. Acc Y (Lateral Acceleration)” for both the sedan and sports_car_1 models.
Notice that the steering wheel angle curve for the sports car does not increase in magnitude with as much of a slope as the sedan did. This means that the sports car with sedan tires has a little less understeer than the sedan with sedan tires. It is not oversteer but it is heading in that direction and, therefore, not as stable as the sedan.

10. WORKSHOP 8 – TIRE MODELING (CONT.)
Modifying vehicle setup 3
Now you define a sports car with wider rear tires.
To modify vehicle setup 3:
In the Build mode treeview, select achassis_gs_rear_wheels, and then click the Wheels tab.
Click the Edit tool for the current tire property file, achassis_gs_tir.
The tire property file uses a Pacejka '94 model. This model uses a parameter called DLAT which scales the lateral performance curves.
In the .tir file, change DLAT to 3.0 (or, E+01).
The DLAT value is representative of wider tires and/or tires with more traction. This extreme value was chosen to clearly show the effects of the different tires on the full-vehicle simulation.
Save it as a new .tir property file named new_rear_tire.tir
Note: You may need to change the name of the file to new_rear_tire.tir using Windows Explorer since Wordpad may add .txt to the file name.

11. WORKSHOP 8 – TIRE MODELING (CONT.)
To modify vehicle setup 3 (Cont.):
In the property editor, use the Find tool to select new_rear_tire.tir as the tire property file.
Click Save As, and enter achassis_gs_rear_wheels_sports_car_2.xml
Click Yes to update references.
Highlight the modified system in the treeview, click Save As, and then enter achassis_gs_full_sys_sports_car_2.xml
In the Test mode bookshelf, right-click Constant Radius, select Add Event to Current Fingerprint Using Model, and then select achassis_gs_full_sys_sports_car_2.
Use the same parameters from Step 7 in the original vehicle setup and then click Build and Run Selected Events.
In Review mode, select all three events, and then click Execute Selected Plots.

12. WORKSHOP 8 – TIRE MODELING (CONT.)
To modify vehicle setup 3 (Cont.):
Look at the plot, Steering Wheel Angle vs. Acc Y (Lateral Acceleration) for all three events: sedan, sports_car_1, and sports_car_2.
It should appear as shown below:

13. WORKSHOP 8 – TIRE MODELING (CONT.)
To modify vehicle setup 3 (Cont.):
Notice how the addition of new rear tires to the sports car begins to bring the curve back towards the sedan's curve, making it more stable. In other words, the wider tires have helped increase the understeer characteristics of this car in a steady-state turn. To make it more stable, you may want to make even more changes to the model in other areas besides tires, such as the camber and toe setting. This should give you a feel for how Adams/ Chassis uses tires.
Compare the understeer budget for these vehicles by overlaying the reports.
Where is the understeer coming from in the different configurations?

14. WORKSHOP 8 – TIRE MODELING (CONT.)
Section Review
What are the four major types of tire models currently available in Adams/Chassis?_________________________
Answer 1: Handling, 3D Contact, SWIFT, and FTire