FTire/sim

FTire Stand-Alone Simulation

Documentation and User’s Guide

Contents

1 Quarter-Car (QC) 1
1.1 Modeling Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 QC Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

2 FTire/QC Stand-Alone Simulation with FTire/sim 3

2.1 Simulation Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.2 Input Variables (Sources) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.3 Road Profiles and Obstacles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

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General Remarks

This documentation describes the Flexible Ring Tire Model (FTire). In addition, it provides details of
the stand-alone simulation environment FTire/sim, as well as the invocation from MSC.ADAMS, and
the FTire specific road surface description in MSC.ADAMS. For more material about FTire, and other
tire simulation tools, please visit www.cosin.eu.

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1 Quarter-Car (QC)

A simple ‘Quarter-Car’ (QC) model is used in FTire/sim as a test ‘vehicle model’ to aid in evaluating
the performance of FTire.

1.1 Modeling Approach

QC comprises a model of the hub-carrier, with 3 degrees of freedom: longitudial, lateral, and verti- cal
displacement with respect to the car-body. The car-body itself, by default, has no degree of freedom.
Instead, its position and velocity is controlled through certain source variables, that is, through external
inputs to the simulation model (cf.. section 3.4 and cosin/io User’s Guide). Alter- natively, the vertical
displacement of the car-body can be given a degree of freedom by specifying a positive ‘sprung mass’.
The hub-carrier is coupled to the car-body by
• the condition ‘no rotation relative to car-body’,
• a nonlinear suspension spring that acts along a general direction vector, with a certain transmis-
sion ratio relative to wheel travel,
• a nonlinear shock-absorber that acts in the same direction as the suspension spring, but with a
different transmission ratio. The shock-absorber carries a nonlinear elastic bearing, inner fric- tion,
and a constant gas force,
• a linear longitudinal spring/damper combination, as well as a linear lateral spring/damper com-
bination. Both work along a general direction vector,
• up to 5 friction elements. Every element consists of a linear spring/damper element which is itself
in line with a dry friction element. The dry friction element is defined through two values, one
for static friction force, and one for sliding friction force. Every friction element works along an
individual direction vector. Transmission ratio for the friction element is defined to be 1.0.

1.2 QC Parameters

Name in input file Unit Meaning

sprung_mass kg portion of car-body mass that is
supported by the wheel. If
sprung_mass is not specified or set
to a value less or equal to zero, no
degree of freedom is assigned to the
car-body
unsprung_mass kg mass of hub-carrier, including
suspension parts, rim, brake, etc., but
excluding tire belt mass (cf. FTire
basic parameters)
-
transmission_ratio_suspension_spring spring deflection / wheel travel
transmission_ratio_shock_absorber- shock-absorber deflection / wheel
travel
shock_absorber_gas_force N constant gas force of shock-absorber,
tends to push hub-carrier down

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 Name in input file Unit Meaning
suspension_direction_vector - vector with three components in
hub-carrier-fixed frame, indicating
the direction of the suspension spring
and shock-absorber force Remarks:
1. direction vector needn’t be
normalized; this is done
automatically by QC

2. point of attack is not relevant,

because moments do not affect
hub-carrier (no ro- tation!)

long_stiffn_hubcarrier N/mm linear stiffness between car-body and

hub-carrier, essentially in longitudinal
direction
long_damping_hubcarrier Ns/mm linear damping between car-body and
hub-carrier, essentially in longitudinal
direction
long_stiffn_direction_vector - vector with three components in
hub-carrier-fixed frame, indicating
the exact direction of the longitudi-
nal stiffness and damping
lat_stiffn_hubcarrier N/mm linear stiffness between car-body and
hub-carrier, essentially in lateral
direction
lat_damping_hubcarrier Ns/mm linear damping between car-body and
hub-carrier, essentially in lateral
direction
lat_stiffn_direction_vector - vector with three components in
hub-carrier-fixed frame, indicating
the exact direction of the lateral
stiffness and damping
number_of_friction_elements - number of friction elements (between
0 and 5)
friction_element_i (i=1,...5) div data of friction elements.
friction_element_i consists of 7
components, that may all reside in
one or, equally well, in several
consecutive lines of the input-file (cf.
cosin/io User’s Guide):
1: stiffness [N/mm]
2: damping [Ns/m]
3: static friction force [N]
4: sliding friction force [N]
5-7: direction vector [-]
$suspension_spring mm, N spline data block for suspension
spring characteristic. Contains data
pairs in ([mm], [N]) for spring
deflection and spring force. Pre-load
is contained in the charac- teristic

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 Name in input file Unit Meaning
$shock_absorber m/s, N spline data block for shock-absorber
characteristic. Contains data pairs in
([m/s], [N]) for shock-absorber
deflection velocity and
shock-absorber force. Coulomb
friction is contained in the
characteristic
$shock_absorber_bearing mm, N spline data block for shock-absorber
bearing charac- teristic. Contains
data pairs in ([mm], [N]) for bearing
deflection and bearing force. Pre-load
is contained in the characteristic

2 FTire/QC Stand-Alone Simulation with FTire/sim

Simulation environment FTire/sim allows for easy-to-run simulations with FTire alone or with the com-
bination FTire and QC. FTire/sim can be run under Windows 95/98/NT (for Windows-specific details
see the read.me-file on the installation diskette), and under Unix operating systems. In ei- ther case,
FTire/sim uses up to 7 input-files, and 2 output-files. Apart from the plot-data file, all files are in cosin/io
syntax. Of course, the input files can be merged to fewer files. In the end, one and only one input file
can contain all data:
• the cfd-file, that allocates the logical files ISIM, ISRC, ISTR, IPAR, IPPAR, IQPAR, OPPAR, OPLOT
(cf. cosin/io User’s Guide),
• the simulation data file (file identifier ISIM), which defines basic simulation data (cf. section 3.1),
• the source data file (file identifier ISRC), which defines time histories of all external input vari-
ables (‘sources’),
• the road data file (file identifier ISTR), which defines the road profile,
• the FTire basic parameter file (file identifier IPAR), which contains FTire basic parameters de-
scribed in section 1.4,
• the FTire preprocessed parameter file (file identifier IPPAR), which keeps preprocessed FTire pa-
rameters. By using this file, if FTire basic data haven’t changed from simulation run to simula-
tion run, some CPU-time can be saved,
• the QC parameter file (file identifier IQPAR), which contains QC parameters described in section
2.2,
• the FTire preprocessed parameter file (file identifier OPPAR), which is calculated during pre- pro-
cessing, for use in subsequent simulation runs,
• the plot data file (file identifier OPLOT), to be viewed in one of the plot-programs cosin/lean-plot
(Windows version) , cosin/ip (Unix version) , or in Matlab or Excel.
Normally, file with identifiers ISIM, ISRC, ISTR, are merged to one simulation file.

2.1 Simulation Data

In the simulation file (identifier ISIM), FTsim looks for the data block $simulation, and looks for the
following data in this block:

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 Name in input file Unit Meaning
preprocessing - 0 (default): try to read preprocessed
data in IPPAR- file. If not successful,
perform preprocessing
1: always perform pre-processing,
even if there are data available
simulation_mode - 0 (default): only FTsim. Source data
directly define hub-carrier position
and velocity
1: FTire + QC. Source data define
car-body position and velocity
animation_mode - 0 (default): no animation (FTsim
runs fastest)
1-9: animation with different viewing
angles;
101-109: same as 1-9, but preparing
the generation of an avi movie file
(attention, this feature temporarily
takes a lot of disk space!)
simulation s an array of three values:
1: simulation starting time [s],
normaly 0
2: time step [s], normally something
like 0.002 .. 0.004
3: simulation final time [s]
plot_output s an array of three values:
1: starting time of plot output [s]
2: time step of plot output [s]
3: final time of plot output [s]
If final time is less than start time,
plot output is com- pletely suppressed
plot_output_start_time s starting time in plot annotation. This
time may be defined independent on
simulation starting time and plot
output starting time. If not defined,
plots will start at plot_output(1)
or simulation(1), resp.
animation s an array of three values:
1: starting time of animation [s]
2: time step of animation [s]
3: final time of animation [s]
If final time is less than start time, or
anima- tion_mode = 0, animation
is completely suppressed
animation_zoom - zoom-factor for animation. You also
can zoom in and out during
animation, by dragging rectangles
with the mouse. Default value 1.0

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 Name in input file Unit Meaning
plot_file_format - a character-string out of
standard dsp dspd matlab
matrix excel gnuplot
which defines the format of
plot-output (cf. cosin/ip User’s
Guide)
frame - defines the frame to be used for plot
output values of forces and torques:
0 (default): TYDEX C
1: TYDEX H
2: TYDEX W
3: ISO contact frame
9: all frames
10: TYDEX C, using kN and kNm
11: TYDEX W, using kN and kNm
road_file - file to be scanned for cosin/ev road
definition data. Default is the
simulation file
obstacle - string to be used instead of the
default road data- block name
road_type

2.2 Input Variables (Sources)

To define the external input variables, Sources&Sinks-routines of cosin/io are used, cf. cosin/io User’s
Guide, section 1.5). With these input variables, position and velocity of car-body or hub- carrier, resp.
are defined, thus controlling directly or indirectly the movement of the rim. In the sources file (identifier
ISRC), FTsim looks for the data block $sources, and interprets this block to define the following sources:

Name in input file Unit Meaning

rolling_speed m/s vehicle speed (rolling_speed = 0
allowed)
tire_deflection mm controls height of hub-carrier or
car-body, resp. Tire deflection
exactly is prescribed by this input
variable only if
(a) road is even with height zero
(b) simulation mode is FTire without
QC

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 Name in input file Unit Meaning
wheel_load kN approximately prescribes static wheel
load. Overrides tire_deflection.
On the basis of wheel_load , FTsim
estimates a related value for tire
deflection. At high rolling speeds,
wheel load will be underestimated to
a certain amount (if
wheel_load_regulated = 0). In
this case, the user should choose a
somewhat smaller value and check
the resulting actual wheel load in the
plot-file. Similarly, for large camber
an- gles, wheel load might be
overestimated and should be
corrected by choosing a greater value.
Alterna- tively, by choosing
wheel_load_regulated = 1, wheel
load can be regulated to nearly
exactly and automatically take the
prescribed value
wheel_slip % prescribes longitudinal slip. Only in
effect if free_spinning = 0 and
wheel_revs is not de- fined. Positive
for driving, negative for braking
wheel_revs rad/s wheel rotational speed. Overrides
wheel_slip. Only in effect if
free_spinning = 0
side_slip_angle deg slip angle. Positive if steady-state
side-force is positive, ie. lateral
sliding velocity is negative. Only
applicable if rolling_speed > 0.
Otherwise, use toe_in_angle to
apply side-force
drive_torque Nm prescribes driving torque. Only
applicable if free_spinning = 1.
May be positive or negative
brake_torque Nm prescribes braking torque. Only
applicable if free_spinning = 1.
Should be positive. Correct sign is
opposed to that of wheel rotational
speed and automatically observed in
FTire
toe_in_angle deg toe-in-angle to prescribe slip angle on
a test drum, when rolling_speed =
0. Positive toe-in results in positive
side-force. Rim toe-in angle exactly is
prescribed by this input variable only
if simulation mode is FTire without
QC

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 Name in input file Unit Meaning
camber_angle deg camber angle. Positive if positive
rotation along x-axis is applied to
hub-carrier (that is: camber_angle
normally is positive for left wheel and
negative for right wheel, in design
position). Rim camber angle exactly
is prescribed by this input variable
only if si- mulation mode is FTire
without QC
free_spinning - 0: prescribe wheel rotation velocity
1: prescribe driving and braking
moments and integrate wheel
rotation in FTire
wheel_load_regulated - 0: tire deflection estimated from
radial characteristic
1: tire deflection chosen by
wheel-load regulator
Remark: wheel load can alternatively
be regulated by using the cosin/ar
PID controller function, described in
the cosin/io documentation

2.3 Road Profiles and Obstacles

To specify road excitation, FTire/sim uses the package cosin/road. This package is described in a
separate manual.

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