PAC2002_TDFT_rev5

MD Adams R4 - Beta - 1 - 25-Aug-09

ATR-005

PAC2002 Tire Data and Fitting Tool (TDFT)

Product(s): Adams/Car, Adams/Chassis, ADAMS/Tire

Feature(s): PAC2002 Tire Data and Fitting Tool

Directory: <adams_install_dir>/acar/shared_car_database.cdb/tires.tbl

Files: fm_data_example_tdft.txt pac2002_205_55R16_tdft.tir tdft_template.tir

Problem Statement

The PAC2002 Tire Data and Fitting Tool (TDFT) calculates PAC2002 tire model parameters out of tire measurement data or virtual test data for steady-state pure and combined slip

conditions including the option to visualize/modify tire characteristics. You’ll learn how to:

1. Create a measurement input data file for the tire parameter identification process. 2. Perform PAC2002 tire parameter identification. 3. Verify calculated tire parameters versus measurement data.

4. Plot tire characteristics.

Model Description

The use of Tire Data Fitting Tool (TDFT) on how to calculate and visualize PAC2002 tire model parameters out of tire measurement data or virtual data for steady-state pure and combined slip conditions has been demonstrated. An empty tire

property file does not have tire parameter identification or fitting data and loads default values from a template file (tdft_template.tir). An example measurement data file (fm_data_example_tdft.txt) containing measurement data for both pure and combined slip conditions has been used from shared_acar_database.cdb

database.

Steps in Running Example

1. Create a measurement input data file for the tire parameter identification

process:

This Section explains how to create a measurement/virtual data input file. The TDFT uses the following 3 keys to identify pure and combined slip measurement data in the

measurement data file:

1. [FX_PURE] - Pure longitudinal slip (kappa) versus longitudinal force (Fx) data. 2. [FYMZ_PURE] - Pure lateral slip (alpha) versus lateral force (Fy) and/or self-

aligning torque (Mz) data. 3. [FXYMZ_COMBINED] - Combined longitudinal and lateral slip versus longitudinal,

lateral and self-aligning torque data.


NOTE: It is important that measurement data is expressed in ISO coordinates. (See also Adams documentation: Adams/Tire -> Tire Models -> Using the PAC2002 Tire Model -> Axis

Systems and Slip Definitions).

An example measurement data file containing measurement data for both pure and combined slip conditions ‘fm_data_example_tdft.txt’ can be found in following directory

<adams_install>/acar/shared_car_database.cdb/tires.tbl.

Following Figures show some typical tire characteristics expressed in ISO coordinates and also show the sign convention used in the TDFT for longitudinal, lateral force and self-

aligning torque. The curves are created using the example measurement data file fm_data_example_tdft.txt.

Figure 1. Pure slip condition: longitudinal slip (kappa) versus longitudinal force

(Fx).

Figure 2. Pure slip condition: lateral slip (alpha) versus lateral force (Fy).


Figure 3. Pure slip condition: lateral slip (alpha) versus self-aligning torque (Mz).

Each measurement/virtual input data file must consist of 7 columns: 1. Lateral Slip (alpha) 2. Longitudinal Slip (kappa)

3. Inclination Angle (camber) 4. Vertical Load (fz) 5. Longitudinal Force (fx) 6. Lateral Force (fy)

7. Self-Aligning Torque (mz) which must be placed in Sections starting with [FX_PURE] for pure longitudinal slip data,

[FYMZ_PURE] for pure lateral slip data and [FXYMZ_COMBINED] for combined slip data. See also fm_data_example_tdft.txt for an example:

[FX_PURE] { alpha kappa camber fz fx fy mz } 0.0000000e+000 -1.0000000e+000 0.0000000e+000 2.0000000e+003 -1.8423142e+003 0.0000000e+000 0.0000000e+000

0.0000000e+000 -9.9900000e-001 0.0000000e+000 2.0000000e+003 -1.8423986e+003 0.0000000e+000 0.0000000e+000

0.0000000e+000 -9.9800000e-001 0.0000000e+000 2.0000000e+003 -1.8424832e+003 0.0000000e+000 0.0000000e+000

… The order of the measurement/virtual data signals must be specified. It is possible to do

this for each measurement/virtual data Section by adding Section [FX_PURE_SIGNALS], [FYMZ_PURE_SIGNALS] or [FXYMZ_COMBINED_SIGNALS] before each measurement/virtual data Section, e.g.

$----------------------------------------------------------------units

[FX_PURE_SIGNALS]

ALPHA = 1 KAPPA = 2

CAMBER = 3

FZ = 4

FX = 5

FY = 6

MZ = 7

$----------------------------------------------------------------fx_pure

[FX_PURE]


{ alpha kappa camber fz fx fy mz }

0.0000000e+000 -1.0000000e+000 0.0000000e+000 2.0000000e+003 -1.8423142e+003 0.0000000e+000 0.0000000e+000

0.0000000e+000 -9.9900000e-001 0.0000000e+000 2.0000000e+003 -1.8423986e+003 0.0000000e+000 0.0000000e+000

0.0000000e+000 -9.9800000e-001 0.0000000e+000 2.0000000e+003 -1.8424832e+003 0.0000000e+000 0.0000000e+000

It is also possible to define a Section [SIGNALS] that specifies the order of the measurement data/virtual data signals for all measurement/virtual data Sections, e.g. $----------------------------------------------------------------units

[SIGNALS] ALPHA = 1

KAPPA = 2

CAMBER = 3

FZ = 4

FX = 5

FY = 6

MZ = 7

If the Section [SIGNALS] is present, the Sections [FX_PURE_SIGNALS], [FYMZ_PURE_SIGNALS] and [FXYMZ_COMBINED_SIGNALS] will be ignored.

Note:

a) It is not necessary to store all data in a single file. Multiple measurement data files can be used as input to the TDFT.

2. Perform PAC2002 tire parameter identification:

This Section explains how to add measurement data to a tire and how to perform the PAC2002 tire parameter identification by means of an example.

1. To start the PAC2002 Tire Data and Fitting Tool in Adams/Car: From the Simulate menu, point to Component Analysis, and then select PAC2002 Tire Data and Fitting Tool…


Figure 4: PAC2002 Tire Data and Fitting Tool (TDFT)

2. Create an empty tire by selecting File -> Create New Tire Property (default

values) from the menu bar (see red arrow in Figure 4). Default values are specified in <adams_install>/acar/shared_car_database.cdb/tires.tbl/tdft_template.tir

It is also possible to use an existing PAC2002 tire property file as a base for the tire

identification process to add new and/or overwrite existing tire parameters. To import a tire property file, select File -> Open Tire Property and Add to Tire Database… from the menu bar.


Figure 5: PAC2002 TDFT; Create an empty tire

3. It is important to verify that following parameters are specified because these

parameters are used in the PAC2002 tire model to make the tire parameters

dimensionless: Under entry Vertical in the left column (see red arrow of Figure 5): FNOMIN

($Nominal wheel load) Under entry Dimension in the left column (see red arrow of Figure 5): UNLOADED RADIUS ($Free tire radius)


4. Select the tire by clicking on the top of the tire data column (1). Click on the Tire Fit button (see red arrow in Figure 6) in the PAC2002 Tire Data and Fitting Tool or select

Run -> Tire Fit from the menu bar to start the Tire Fit Tool.

Figure 6: PAC2002 TDFT; Starting PAC2002 Tire Fit


Figure 7: PAC2002 TDFT; PAC2002 Tire Fit

5. Figure 7 below shows the Tire Fitting Tool. Clicking on the available entries to the

left, start values and lower/upper boundaries for each parameter of the identification

process are shown and may be modified, see Figure 8. Default values are specified in <adams_install>/acar/shared_car_database.cdb/tires.tbl/tdft_template.tir.

Figure 8: PAC2002 TDFT; start values and lower/upper bounderies

6. Select Add Measurements (see red arrow in Figure 9) and add the measurement data files to the Measurement File(s) Table. See <adams_install>/acar/shared_car_database.cdb/tires.tbl/fm_data_example_tdft.txt

for an example measurement data file containing steady-state force and moment measurement data for pure and combined slip conditions.


Figure 9: PAC2002 TDFT; start values and lower/upper bounderies

7. If measurement data for both pure and combined slip conditions is available, select

Characteristic = All under Fitting Parameters and click on Start. Now, all tire characteristics will be fitted in following order:

1. Fx_pure

2. Fy_pure 3. Mz_pure 4. Fx_combined

5. Fy_combined 6. Mz_combined

It is also possible to fit each tire characteristic separately if not all measurement data

is available. Select the desired Characteristic under Fitting Parameters. Force/Moment expressions for the combined slip conditions are based on the expressions for the pure slip conditions. Therefore, the force and/or moment for pure

slip conditions need to be fitted first before fitting the combined slip conditions. Note:

a) Fy (and Fx in case of combined slip conditions) needs to be fitted before Mz because the Mz formulation depends on the lateral force Fy.

b) The .log files in the working directory show the result of the tire identification process. The fit error (=100*sqrt(((measurement data)^2 – (model

data)^2)/(measurement_data)^2) ) and variations of each tire parameter are shown.

c) The X[0], X[1], X[2], etc are the tire parameters that are identified and could be

seen in the log file generated in your working directory. For instance, if you perform a tire fit for the FX_PURE coefficients then following parameters are being identified (see also pac2002_205_55R16_tdft.tir, Section Longitudinal_Coefficients):

PCX1 = 1.3178 $Shape factor Cfx for longitudinal force PDX1 = 1.0455 $Longitudinal friction Mux at Fznom


PDX2 = 0.063954 $Variation of friction Mux with load PDX3 = 0 $Variation of friction Mux with camber

PEX1 = 0.15798 $Longitudinal curvature Efx at Fznom PEX2 = 0.41141 $Variation of curvature Efx with load PEX3 = 0.1487 $Variation of curvature Efx with load squared PEX4 = 3.0004 $Factor in curvature Efx while driving

PKX1 = 23.181 $Longitudinal slip stiffness Kfx/Fz at Fznom PKX2 = -0.037391 $Variation of slip stiffness Kfx/Fz with load PKX3 = 0.80348 $Exponent in slip stiffness Kfx/Fz with load PHX1 = -0.00058264 $Horizontal shift Shx at Fznom

PHX2 = -0.0037992 $Variation of shift Shx with load PVX1 = 0.045118 $Vertical shift Svx/Fz at Fznom PVX2 = 0.058244 $Variation of shift Svx/Fz with load

PTX1 = 0.85683 $Relaxation length SigKap0/Fz at Fznom PTX2 = 0.00011176 $Variation of SigKap0/Fz with load PTX3 = -1.3131 $Variation of SigKap0/Fz with exponent of load PTX4 = 0.1

You can find these parameters under the entry Longitudinal in the left column of the PAC2002 Tire Fit Tool as well. Please note that both pure and combined

slip parameters are shown. The order of the parameters logged in the log file is the same as in the Longitudinal entry of the PAC2002 Tire Fit Tool. This is also applicable for other tire characteristics.

8. The next step will be to verify the calculated tire parameters versus measurement data and to generate a tire property file which will be discussed in next Section.

3. Verification of calculated tire parameters versus measurement data:

In this Section you’ll learn how to verify the resulting tire model parameters by graphically

comparing measurement/virtual test data to the PAC2002 model. Force/Moment characteristics are by default created using the embedded plotter and can be exported to Adams/Postprocessor by selecting Plot -> Adams/PPT under Plot Parameters.

Select Settings -> Plot Units… to change the default plot units (SI).

1. Select Measurement Data = Yes under Plot Parameters, see Figure 10. This means that measurement data (as added to the tire for the tire parameter identification process) is plotted against PAC2002 model data. Longitudinal (kappa), lateral (alpha) slip data, inclination angle (camber) and vertical tire load (Fz)

extracted from the measurement data files will be used as input to the PAC2002 tire model and the resulting forces/moment will be plotted against measured forces/moment.

2. Select Slip Condition = Pure under Plot Parameters, see Figure 9.

Set Slip Condition to Pure to plot pure slip tire characteristics (i.e. only

braking/traction or only cornering) or set Slip Condition to Combined to plot combined slip tire characteristics (i.e. cornering while braking/driving).


3. Select X-axis = Longitudinal Slip and select Y-axis = Fx for plotting the longitudinal slip-force characteristic versus measurement data for pure slip

conditions.

4. Click on Tire Plot in the Main GUI (see red arrow in Figure 9) or select Run - > Tire Plot from the menu bar to plot the PAC2002 tire model results versus measurement

data. Plots are by default created using the embedded plotter. Click on Clear Tire Plot(s) or select Run -> Clear Tire Plot(s) to remove the plots from the embedded plot window.

Figure 11 shows the resulting longitudinal slip-force characteristic versus measurement data for pure slip conditions using Adams/Postprocessor.

Figure 10: PAC2002 TDFT; Plotting Results


Figure 11: Longitudinal slip-force characteristic versus measurement data for pure

slip conditions using Adams/Postprocessor

Note: a) Only the X-axis, Y-axis and Slip Condition need to be selected if Measurement Data

is set to Yes. The other options do not have any effect as input data is taken from

the measurement data files.

5. Following Table (see Table 1 below) provides more information about selections for

Slip Condition, X-axis and Y-axis for plotting of the tire model results versus measurement data for pure and combined slip conditions.

Fx_

pure

Fy_

pure

Mz_

pure

Fx_

combined

Fy_

combined

Mz_

combined

Slip

Condition

Pure Pure Pure Combined Combined Combined

X-axis Long.

Slip

Lat.

Slip Angle

Lat.

Slip Angle

Long.

Slip

Long.

Slip

Long.

Slip

Y-axis Fx Fy Mz Fx Fy Mz

Table 1: Input selection for plotting of tire model results versus measurement

data.

6. To generate a tire property file, select Save Tire property file (see red arrow in

Figure 11) or select File -> Save Tire Property File from the menu bar.


Figure 12: PAC2002 TDFT: Save Tire Property File

7. To save the database, i.e. calculated tire parameters for a tire, loaded tires and references to measurement data files, select Save Tire Database (see red arrow in Figure 13) or select File -> Save Tire Database from the menu bar. Tire Database files can be loaded by clicking on Open Tire Database which is located next to the

Save Tire Database button.


Figure 13: PAC2002 TDFT; Save/Open Tire Database

4. Plotting tire characteristics:

This Section explains how to plot tire characteristics by means of an example (longitudinal slip-force characteristic) by evaluating the PAC2002 tire model for a given set of input data.

1. Open Tire Property File

<adams_install>/acar/shared_car_database.cdb/tires.tbl/pac2002_205_55R16_tdft

in the PAC2002 Tire Data and Fitting Tool and select the tire by clicking on the first column (1).


Figure 14: PAC2002 TDFT; Plot Parameters

1. Set Measurement Data = No under the Plot Parameters, see Figure 15. This

means that measurement data (added in Tire Fit) is not used for plotting but only input data entered in the Plot Parameters is used to evaluate the PAC2002 tire model.

2. Set Slip Condition = pure to plot pure slip tire characteristics (i.e. braking/traction without cornering and vice versa). To plot tire characteristics for combined slip conditions, set Slip Condition =

combined (i.e. cornering while braking/driving).

3. Set X-axis = Longitudinal Slip and set Y-axis = Fx for plotting the longitudinal slip along the X-axis and longitudinal force along the Y-axis.


4. Set Sweep = Longitudinal Slip. The Sweep variable is varied along each curve.

Input data for Longitudinal Slip can be entered in the Longitudinal Slip input field. Enter -1:0.01:1 to specify a range of values from -1 to 1 using a 0.01 step size. Other possible input data formats:

0.0 - single values 1,2,3 - values separated by a comma

5. Set Independent = Vertical Load. The independent variable is constant for each curve. Input data as shown in Figure 15 will produce 3 curves, one for each vertical load (2000, 4000 and 6000 N.). Input data for the Vertical Load can be entered in

the Vertical Load input field, see Figure 13. Enter: 2000, 4000, 6000.

6. Data for remaining fields must also be entered as this is input to the PAC2002 tire model.

Set Lateral Slip Angle = 0.0. Set Inclination Angle = 0.0.

For a pure longitudinal slip-force characteristic, the lateral slip will not be used and vice versa. However, it is recommend to use a single value (for instance 0) for the fields that are not used in order not to evaluate unnecessary data points and not to increase calculation time.

7. Click on Tire Plot or select Run -> Tire Plot from the menu bar. You can either use

the embedded plotter or Adams/Postprocessor. Figure 16 shows the longitudinal slip-force tire characteristic for pure slip conditions using Adams/Postprocessor.

Figure 16: Pure slip condition: longitudinal slip (kappa) versus longitudinal force

(Fx).

More examples of typical tire characteristics are shown below:


Measurement Data: No

Slip Condition: Pure X-axis: Lateral Slip Angle Y-axis: Fy Sweep: Lateral Slip Angle

Independent: Vertical Load Vertical Load: 2000, 4000, 6000 Longitudinal Slip: 0.0

Lateral Slip Angle: -0.2:0.002:0.2 Inclination Angle: 0.0

Figure 17: Pure slip condition: lateral slip (alpha) versus lateral force (Fy). Measurement Data: No Slip Condition: Pure

X-axis: Lateral Slip Angle Y-axis: Mz Sweep: Lateral Slip Angle Independent: Vertical Load

Vertical Load: 2000, 4000, 6000 Longitudinal Slip: 0.0

Lateral Slip Angle: -0.2:0.002:0.2 Inclination Angle: 0.0


Figure 18: Pure slip condition: lateral slip (alpha) versus self-aligning torque (Mz).

Measurement Data: No

Slip Condition: Combined X-axis: Fx Y-axis: Fy

Sweep: Longitudinal Slip Independent: Lateral Slip Angle Vertical Load: 2000, 4000, 6000

Longitudinal Slip: -1.0:0.01:1.0 Lateral Slip Angle: -0.2:0.002:0.2 Inclination Angle: 0.0

Figure 19: Combined slip condition: Longitudinal force versus lateral force.

PAC2002_TDFT_rev5

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