4.8.2.13. TIRE_FORCE

This subroutine defines a user - defined tire force.

Table 4.37 Function Name

Language type	Subroutine
FORTRAN	tire_usub (TIME, ITIME, CONPROP, TIREPROP, MASSPROP, UPAR, NPAR, JFLAG, IFLAG, TFSAE, RFSAE, FCOEF)
C/C++	tire_usub (double time, double itime, double conprop[], double tireprop[], double massprop[], double upar[], int npar, int jflag, int iflag, double tfsae[3], double rfsae[3], double fcoef[2])

Table 4.38 Parameter information

Variable Name	Size	Description
time	double	Current simulation time of RecurDyn/Solver.
itime	double	Past time for saved values.
conprop	double[10]	Contact property for computing Tire force. conprop(1) = Longitudinal slip ratio. conprop(2) = Lateral slip angle in radian conprop(3) = Camber angle in radian. conprop(4) = Normal penetration of tire into road surface conprop(5) = Normal velocity of penetration of tire into road surface. conprop(6) = Longitudinal sliding velocity of contact patch. conprop(7) = Loaded radius of tire. conprop(8) = Angular velocity about spin axis of tire. conprop(9) = Longitudinal velocity of tire tread base. conprop(10) = Lateral velocity of tire tread base.
tireprop	double[11]	Geometry and Material property of TIRE. tireprop(1) = Undeformed radius of tire. tireprop(2) = Carcass radius of a toroidal tire. tireprop(3) = Normal stiffness. tireprop(4) = Longitudinal stiffness. tireprop(5) = Lateral stiffness due to slip angle. tireprop(6) = Lateral stiffness due to camber angle. tireprop(7) = Rolling moment resistance coefficient. tireprop(8) = Normal damping ratio. tireprop(9) = Friction coefficient at zero slip. tireprop(10) = Friction coefficient at full slip. tireprop(11) = Friction coefficient at the current slip value.
massprop	double[2]	Mass property of TIRE.
upar	double[100]	Parameters defined by the user. The maximum size of array is 100.
npar	int	Number of user parameters.
jflag	int	When RecurDyn/Solver evaluates the Jacobian, the flag is true. Otherwise, the flag is false.
iflag	int	When RecurDyn/Solver makes its initial call to this routine, the flag is true. Otherwise, the flag is false.
tfsae	double[3]	Returned force vector acting at the contact point in the SAE coordinate system and this is three dimensional arrays. tfsae(1) = Longitudinal force at the contact point(SAE Coordinate system). tfsae(2) = Lateral force at the contact point(SAE Coordinate system). tfsae(3) = Normal force at the contact point(SAE Coordinate system).
rfsae	double[3]	Returned torque vector acting at the contact point in the SAE coordinate system this is three dimensional arrays. rfsae (1) = Overturning moment at the contact point(SAE Coordinate system). rfsae (2) = Rolling resistance moment(SAE Coordinate system). rfsae (3) = Aligning moment at the contact point(SAE Coordinate system).
fcoef	double[2]	Returned friction coefficients this is two dimensional arrays. fcoef(1) = Longitudinal friction coefficient between tire and road. fcoef(2) = Lateral friction coefficient between tire and road.

Example

Figure 4.117 Tire model

Note

If the user wants to run this model using a user subroutine, the user can refer it in the directory (<install dir>\Help\usub\**).

Listing 4.25 Fortran code for Tire Force

C---- SUB. TIRE_FORCE
      SUBROUTINE TIRE_FORCE
   &          (TIME,ITIME,CONPROP,TIREPROP,MASSPROP,UPAR,NPAR,
   &           JFLAG,IFLAG,TFSAE,RFSAE,FCOEF)
C---- TO EXPORT * SUBROUTINE
      !DEC$ ATTRIBUTES DLLEXPORT,C::TIRE_FORCE

C---- INCLUDE SYSTEM CALL
      INCLUDE 'SYSCAL.F'

C---- DEFINE VARIABLES
C     Parameter Information
C     TIME     : Simulation time of RD/Solver. (Input)
C     ITIME    : Past time for saved values. (Input)
C     CONPROP  : Contact property for computung Tire force. (Input)
C     TIREPROP : Geometry and Material property of TIRE. (Input)
C     MASSPROP : Mass property of TIRE. (Input)
C     UPAR     : Parameters defined by user. (Input)
C     NPAR     : Number of user parameters. (Input)
C     JFLAG    : When RD/Solver evaluates a Jacobian, the flag is true. (Input)
C     IFLAG    : When RD/Solver initializes arrays, the flag is true. (Input)
C     TFSAE    : Returned force vector acting at the contact point in the SAE coordinate system. (Output, Size : 3)
C     RFSAE    : Returned torque vector acting at the contact point in the SAE coordinate system. (Output, Size : 3)
C     FCOEF    : Returned friction coefficients. (Output, Size : 2)

      DOUBLE PRECISION TIME, ITIME, UPAR(*)
      DOUBLE PRECISION CONPROP(*), TIREPROP(*), MASSPROP(*)
      INTEGER NPAR
      LOGICAL JFLAG, IFLAG
      DOUBLE PRECISION TFSAE[REFERENCE](3), RFSAE[REFERENCE](3)
      DOUBLE PRECISION FCOEF[REFERENCE](2)

C---- USER STATEMENT
      DOUBLE PRECISION VALUE1
      DOUBLE PRECISION zkForce, zcForce, new_zcForce
      DOUBLE PRECISION ver_stiff, pen, mass, damping, dot_pen, max_pen
      LOGICAL errflg

c     step function
      pen = CONPROP(4)
      max_pen = 0.01* TIREPROP(2)
      CALL rd_step(pen, 0, 0, max_pen, 1, 1, VALUE1, errflg)

c     CACLULATION FOR NORMAL FORCE
      ver_stiff = TIREPROP(3);
      zkForce = -ver_stiff*pen;

      mass = MASSPROP(1)
      damping = TIREPROP(8)
      dot_pen = CONPROP(5)

      new_zcForce = -2.0*sqrt(mass*abs(ver_stiff))*damping*dot_pen
      zcForce = VALUE1*new_zcForce

c     Z AXIS NORMAL FORCE
      TFSAE(3) = min(0.0, zkForce+zcForce)

      RETURN
      END

Listing 4.26 C/C++ code for Tire Force

#include "stdafx.h"
#include "DllFunc.h"
#include "math.h"

TireForce_API void __cdecl tire_force
   (double time, double itime, double conprop[], double tireprop[], double massprop[],
   double upar[], int npar, int jflag, int iflag, double tfsae[3], double rfsae[3], double fcoef[2])
{
   using namespace rd_syscall;
   // Parameter Information
   //   time     : Simulation time of RD/Solver. (Input)
   //   itime    : Past time for saved values. (Input)
   //   conprop  : Contact property for computung Tire force. (Input)
   //   tireprop : Geometry and Material property of TIRE. (Input)
   //   massprop : Mass property of TIRE. (Input)
   //   upar     : Parameters defined by user. (Input)
   //   npar     : Number of user parameters. (Input)
   //   jflag    : When RD/Solver evaluates a Jacobian, the flag is true. (Input)
   //   iflag    : When RD/Solver initializes arrays, the flag is true. (Input)
   //   tfsae    : Returned force vector acting at the contact point in the SAE coordinate system. (Output, Size : 3)
   //   rfsae    : Returned torque vector acting at the contact point in the SAE coordinate system. (Output, Size : 3)
   //   fcoef    : Returned friction coefficients. (Output, Size : 2)

   // User Statement
   double value;
   double zkForce, zcForce, new_zcForce;
   double ver_stiff, pen, mass, damping, dot_pen, max_pen;
   int errflg;

   //step function
   pen = conprop[3];
   max_pen = 0.01* tireprop[1];
   rd_step(pen, 0, 0, max_pen, 1, 1, &value, &errflg);

   //calculation for normal force
   ver_stiff = tireprop[2];
   zkForce = -ver_stiff*pen;

   mass = massprop[0];
   damping = tireprop[7];
   dot_pen = conprop[4];

   new_zcForce = -2.0*sqrt(mass*abs(ver_stiff))*damping*dot_pen;
   zcForce = value*new_zcForce;

   //z axis normal force
   tfsae[2] = min(0.0, zkForce+zcForce);
}