Tire Subroutine Arguments

The following tire subroutine arguments are available:
Argument   Type Description
NDEV Input Integer NDEV must specify the logical output device for error messages. USRMES and ERRMES can be used in place of writing to NDEV device.
ISWTCH Input Integer ISWTCH is a copy of USE_MODE which a variable in Tire property file. USE_MODE is a user controlled variable to select among the different operating modes of tire.

If a user has different kinds of tire model than in JOBFLG = 11 the User Tire Interface will send the ISWTCH as a input to the tire subroutine and at this JOBFLG specific algorithm is selected depending on the value of the ISWTCH.

Example:
USE_MODE
0: Evaluation of Fz only
1: Evaluation of all forces
10: Steady state behavior
20: Include relaxation behavior
100: Smooth road contact
200: Road contact for 3D roads
If USE_MODE = 121 than it means that the ISWTCH value at JOBFLG = 11 is 121 and this value specifies
  • Smooth road contact
  • Include relaxation behavior
  • Evaluation of all forces

In a similar manner, ISWTCH can be defined so that by addition of digits which represents the corresponding evaluation schemes can be represented by this parameter.
JOBFLG Input Integer The User Tire Interface calls the User Tire model several times during the simulation with different JOBFLG. The JOBFLG variable decides the execution model (initialization, reading tire property file, initial condition) of TYRE. The User Tire Interface expects some variables to be updated according to the JOBFLG value. The JOBFLG is called in following order:

JOBFLG = 1 initialization mode

This mode is for initialization of the tire, it will be called once for each tire. After this call the User Tire Interface expects the tire model to return the maximum array size for the arrays to store the tire properties, road properties, state variables and output variables.

Outputs:

NTYPAR NDEQVR, NVARS, NWORK, NIWORK, NROPAR

JOBFLG = 2 reading tire and road property files

In this mode tire model reads the tire and road property files and stores the parameters in TYPARR, ROPAR and WRKARR array.

Inputs:

NCHTDS, CHTDST, NCHRDS, CHRDST, ISWTCH, IDTYRE

Output:

TYPARR, ROPAR, WRKARR

JOBFLG = 11, actual array size

Depending on the ISWTCH or depending on the parameters in tire property file the number of differential equations can vary which in turn changes the number of states therefore User Tire Interface needs to be updated about the size of the state and work arrays.

Input:

ISWTCH

Output:

NTYPAR, NDEQVR, NVARS, NWORK, NIWORK

JOBFLG = 6, initial conditions

In this call depending on the kinematic inputs (position, velocity, orientation) of the wheel center, the initial conditions for state variables can be calculated.

Inputs:

ISWTCH, TIME, DIS, TRAMAT, ANGTWC, VEL, OMEGA, OMEGAR, DEQVAR, TYPARR, ROPAR

Output:

DEQINI

JOBFLG = 0, normal call

In this call tire model calculates the force and moments on tire.

Inputs:

ISWTCH, TIME, DIS, TRAMAT, ANGTWC, VEL, OMEGA, OMEGAR, DEQVAR, TYPARR, ROPAR Outputs: FORCE, TORQUE, DEQDER, VARINF, WRKARR, and IWRKAR

JOBFLG = 99, final call

This is the final call to tire model and is used to inform tire model to free allocated memory, etc.

IDTYRE Input Integer Specifies the tire ID.
TIME Input Real Current simulation time.
DIS Input Real array (3) Specifies the x, y, z coordinates of the wheel carrier at the wheel center with respect to the earth-fixed axis system expressed in the earth-fixed axis system. Earth fixed axis system and Road reference marker coordinate system are same.
TRAMAT Input Real array (3,3) Specifies the transformation matrix to transform data from the wheel Carrier coordinate system to the earth-fixed axis system.
ANGTWC Input Real Specifies the rotation angle of the rim w.r.t. the wheel carrier (used for positioning /triggering of non-uniformities of the tire).
VEL Input Real array (3) Specifies the translational velocities of the wheel career at the wheel center with respect to the earth-fixed axis system expressed in the C-frame (defined in the TYDEX - Format).
OMEGA Input Real array (3) Specifies the angular velocities of the wheel carrier with respect to the earth-fixed axis system expressed in the wheel carrier (C-frame) axis system.
OMEGAR Input Real Specifies the rotation speed of the rim with respect to the wheel carrier.
NDEQVR Input Integer Specifies the dimension of the DEQVAR array. It is the number of states required by tire model.
DEQVAR Input Real array (NDEQVR) DEAQVAR contains the integrated values of the DEQDER. The initial values are given by DEQINI.
NTYPAR Input Integer Specifies the dimension of the TYPARR array. If NTYPAR is equal to zero than TYPARR contains no available values.
TYPARR Input Real array (NTYPAR) It contains the parameters of the current tire model. If TYPARR is not available than NTYPAR must be 0 and in this case tire parameters can be read from a data file specified in CHTDST.
NCHTDS Input Integer Specifies the dimension of CHTDST array. If NCHTDS is 0 than CHTDST contains no file name and in this case the simulation will be terminated as tire property file is used to inform User Tire Interface about the Tire subroutine name and the library name.
CHTDST Input Character array

(NCHTDS)

 It contains the tire property file name which has tire parameters stored in it.
ROAD Input Function Pointer It contains the road subroutine which is called by the tire subroutine to calculate normal of the road and the tire contact point with the road.
IDROAD Input Integer Specifies which road model is used. Currently this parameter is not supported in User Tire Interface.
NROPAR Input Integer Specifies the array size of ROPAR. If NROPAR is 0 than the road properties are read from a file specified in CHRDST.
ROPAR Input Real array

(NROPAR)

 It contains the road parameters. If ROPAR is not available than NROPAR should be set to 0.
NCHRDS Input Integer Specifies the dimension of CHRDST array. If NCHRDS is 0 than CHRDST contains no file name. If the road function from MotionSolve is used CHRDST should contain the name of the road property file otherwise the simulation will be terminated as road property file contains the name of the road function which is being used.
CHRDST Input Character array

(NCHRDS)

 It contains the name of the file which contains the road parameters. It should contain the name of the road function and “mbdtire” as the library name while using the road function from MotionSolve.
FORCE Output Real array (3) It contains the force applied by the tire onto rim at the center of the wheel. It is expressed in wheel career axis system (C-frame).
TORQUE Output Real array (3) It contains the torque applied by the tire onto the rim. It is expressed in the wheel career axis system (C-frame).
DEQINI Output Real array

(NDEQVR)

 Initial conditions of the DEQVAR. At JOBFLG = 6 the tire model should return the initial conditions for the DEQVAR. The value of DEQINI is ignored at other JOBFLGS.
DEQDER Output Real array

(NDEQVR)

 It contains the derivative of the DEQVAR that needs to be integrated by the MotionSolve. At JOBFLG =0 and JOBFLG = 6, the tire subroutine should return the derivative of the DEQVAR in DEQDER array.
TYRMOD Output Character array (256) It contains the information about name, type, release of the tire model.
NVARS Output Integer Specifies the dimension of the VARINF array.
VARINF Output Real array

(NVARS)

 It contains the information about the internal variables of the tire model. These are values like slip angle, longitudinal slip, etc.
See the complete list below:
  1. FX_CP_W
    Force on contact patch in TYDEX -W axis system, X component.
    Unit: N
NO Variable Details Unit
1 FX_CP_W Force on contact patch in TYDEX -W axis system, X component N
2 FY_CP_W Force on contact patch in TYDEX -W axis system, Y component N
3 FZ_CP_W Force on contact patch in TYDEX -W axis system, Z component N
4 MX_CP_W Torque on contact patch in TYDEX -W axis system, X component Nm
5 MY_CP_W Torque on contact patch in TYDEX -W axis system, Y component Nm
6 MZ_CP_W Torque on contact patch in TYDEX -W axis system, Z component Nm
7 LAT_SLIP Lateral slip rad
8 LONG_SLIP Longitudinal slip -
9 CAMBER Camber rad
10      
11      
12      
13      
14      
15      
16      
17      
18      
19      
20      
21      
22      
23      
24      
25      
26 FX_W_SAE Tire Forces on wheel centre SAE axis system, X component N
27 FY_W_SAE Tire Forces on wheel centre SAE axis system, Y component N
28 FZ_W_SAE Tire Forces on wheel centre SAE axis system, Z component N
29 MX_W_SAE Tire moments on wheel centre SAE axis system, X component Nm
30 MY_W_SAE Tire moments on wheel centre SAE axis system, Y component Nm
31 MZ_W_SAE Tire moments on wheel centre SAE axis system, Z component Nm
32 FX_HUB_C Tire Forces on HUB in TYDEX -C axis system, X component N
33 FY_HUB_C Tire Forces on HUB in TYDEX -C axis system, Y component N
34 FZ_HUB_C Tire Forces on HUB in TYDEX -C axis system, Z component N
35 MX_HUB_C Tire Moments on HUB in TYDEX -C axis system, , X component Nm
36 MY_HUB_C Tire Moments on HUB in TYDEX -C axis system, , Y component Nm
37 MZ_HUB_C Tire Moments on HUB in TYDEX -C axis system, Z component Nm
38 FX_CP_ISO Force on contact patch in ISO axis system, X component N
39 FY_CP_ISO Force on contact patch in ISO axis system, Y component N
40 FZ_CP_ISO Force on contact patch in ISO axis system, Z component N
41 MX_CP_ISO Torque on contact patch in ISO axis system, X component Nm
42 MY_CP_ISO Torque on contact patch in ISO axis system, Y component Nm
43 MZ_CP_ISO Torque on contact patch in ISO axis system, Z component Nm
44 EFF_PEN Tyre deflection m
45 VEL_CP_VRT TYRE penetration/closing velocity m/s
46 VEL_CP_LON Longitudinal slip velocity at contact patch m/s
47 VEL_CP_LAT Lateral slip velocity at contact patch m/s
48 WC_LON Longitudinal velocity at Wheel Centre m/s
49 ROL_RAD Effective rolling radius m
50 OMEGAR Tire rotational velocity  
51      
52      
53      
54      
55 MUX_TYR Longitudinal friction coefficient  
56 MUY_TYR Lateral friction coefficient  
57 IPT Pneumatic trail m
58 MZR Residual torque Nm
59 FX_ARM Moment arm of FX m
60 ISGKPO Longitudinal relaxation length m
61 ISGKLO Lateral relaxation length m
62 MZYR Gyroscopic moment Nm
63      
64      
65      
66 CP_X Contact patch location - x coordinate m
67 CP_Y Contact patch location - y coordinate m
68 CP_Z Contact patch location - z coordinate m
69      
70      
71      
72      
73      
74      
75 DIS_TRA Distance traveled m
76 EFF_PLA_HEI_PTR Effective Plane Height m
77 EFF_PLA_ANG_PTR Effective Plane Angle rad
78 EFF_PLA_CUR_PTR Effective Plane Curvature 1/m
79 EFF_PLA_BAN_PTR Effective Plane Banking Angle rad
NWORK Output Integer Specifies the dimension of the real work array (WRKARR).
WRKARR Output Real array

(NWORK)

 It is for the internal use by the tire model, generally contains the last content of the work array.
NIWORK Output Integer Specifies the dimension of the real work array (IWRKAR).
IWRKAR Output Integer array

(NIWORK)

 Same as WRKARR but for integers.
IERR Output Integer It contains an integer value that specifies the type of error.
0
No error
1
Warning
2
Error- don’t use the actual results
3
Fatal error- Calling program should stop.