AutoCTITire

Introduction

The tire models describe the interface between the wheel and the road. Tire models apply forces and moments on wheel body so as to simulate a real tire forces and moments that tires apply on the vehicle.

Altair MotionView and MotionSolve support multiple tire models through the CTI (www.cosin.eu) defined interface. These include: Altair’s HTire model (used for Handling analysis), Altair’s Fiala model (used for Handling analysis), and Cosin’s FTire model (used for Comfort and Durability). These models can be accessed in MotionView using the Auto Entity: AutoCTITire.

For this tire interface, the tire parameters and properties are set by a Tire Property File with the extension (.tir) while the road interface is described by a Road Property File with the extension (.rdf). Both of these property files are in the TeimOrbit file format. Example property files are provided in the MotionView installation at:

$(ALTAIR_HOME) \hw\mdl\autoentities\properties\Tires < tire property file with .tir extension>

$(ALTAIR_HOME) \hw\mdl\autoentities\properties\Tires < road property file with .rdf extension>

In addition to this, physical properties of the tire such as the unloaded radius, aspect ratio, width, mass, and moment of inertia’s need to be explicitly specified.

Connectivity

One Body, one Point, and two Marker connections need to be made to define the tire interface:

Connection	Significance
Body 1	The wheel body on which the tire forces act.
Point 1	The point corresponding to the wheel center.
Marker 1	The wheel reference marker which determines the direction in which the tire forces act.
Marker 2	The road reference marker, is the marker with respect to which the road is positioned and oriented for the simulation.

cti_tire_panel_mv

cti_tire_example_mv

cti_tire_example2_mv

Symmetry

The AutoTireCTI Auto Entity can be added to a full vehicle model as a Single entity or as a Pair. The Pair entity, like other Motion View Pair entities, establishes two symmetric (left and right) Tire models about the x axis.

cti_tire_panel_symmetry_mv

Tire Geometry and Physical Parameters

Information about the tire physical tire properties such as mass, inertia, and dimensions need to be provided correctly. These are specified in the panel in the section highlighted below:

cti_tire_panel_properties_mv

Parameter	Description	Units [Model Units]
Unloaded radius	Distance between the WC and the contact point of tire in unloaded conditions.	Length
Aspect ratio	Tire Sidewall profile aspect ratio. Describes the sidewall height as a percentage of the tire section width.	%
Width	Section width of the tire.	Length
Tire mass	Mass of the Tire.	Mass
Ixx,Iyy,Izz	Moment of Inertia of the tire (y-axis out of plane of tire).	Mass * Length2

Tire Models

The CTI interface implements three tire models:

•	HTIRE – Altair

•	FTIRE – Cosin

•	FIALA – Altair

The parameter PROPERTY_FILE_FORMAT in the MODEL section of the tire property file determines tire model used. The user is expected to choose a compatible road model with the tire model chosen via the property file.

Sample Property Files:

[UNITS]

LENGTH = 'mm'

FORCE = 'newton'

ANGLE = 'degree'

MASS = 'kg'

TIME = 'sec'

$--------------------------------------------------------------------------model

[MODEL]

property_file_format = 'FIALA'

use_mode = 2.0

$----------------------------------------------------------------------dimension

[DIMENSION]

unloaded_radius = 318.0

width = 195.0

aspect_ratio = 0.55

$----------------------------------------------------------------------parameter

[PARAMETER]

vertical_stiffness = 310.0 $[force/length]

vertical_damping = 10 $[force * time / length]

rolling_resistance = 20 $[length]

cslip = 20000.0 $[force]

calpha = 44000.0 $[force / angle]

cgamma = 0.0 $[force / angle]

umin = 0.85 $[-]

umax = 1.0 $[-]

$-------------------------------------------------------------------COSIN_HEADER

[COSIN_HEADER]

file_type = 'tir' $

file_version = 3.0 $

file_format = 'ASCII' $

(COMMENTS)

{comment_string}

'Tire Manufacturer - ?'

'Tire Type - ?'

'Tire Dimension - 205/55 R 16 90S 6.5J'

'Pressure - 2.50 & 3.00 bar'

'File Generation Date - 21/10/08 16:49'

$--------------------------------------------------------------------------UNITS

[UNITS]

force = 'newton' $

mass = 'kg' $

length = 'm' $

time = 'sec' $

angle = 'rad' $

$--------------------------------------------------------------------------MODEL

[MODEL]

property_file_format = 'PAC2002' $

use_mode = 25 $

vxlow = 2 $

longvl = 30 $

$ separate_animation = 14000001 $

additional_output_file = 1 $

log_file = 1 $

verbose = 0 $

output_time_step = 0.001 $

output_end = 999 $

animation_end = 999 $

road_grid_line_dist = 0.01 $

road_grid_size = 1 $

force_scaling = 1 $

(truncated)

$---------------------------------------------------------------------HEADER

[COSIN_HEADER]

FILE_TYPE = 'rdf'

FILE_VERSION = 5.00

FILE_FORMAT = 'ASCII'

(COMMENTS)

{comment_string}

'flat 2d contact road for testing purposes'

$--------------------------------------------------------------------------UNITS

[UNITS]

LENGTH = 'mm'

FORCE = 'newton'

ANGLE = 'radians'

MASS = 'kg'

TIME = 'sec'

$--------------------------------------------------------------------------MODEL

[MODEL]

METHOD = '2D'

FUNCTION_NAME = 'ARC901'

ROAD_TYPE = 'flat'

$-----------------------------------------------------------------------GRAPHICS

[GRAPHICS]

LENGTH = 160000.0

WIDTH = 80000.0

NUM_LENGTH_GRIDS = 16

NUM_WIDTH_GRIDS = 8

LENGTH_SHIFT = 10000.0

WIDTH_SHIFT = 0.0

$---------------------------------------------------------------------PARAMETERS

[PARAMETERS]

MU = 1.0

OFFSET = 0

Output Requests

The AutoTireCTI entity generates some standard output requests into the solver deck. These requests track the tire kinematics and the tire forces generated by the tire model.

Label	Description	Units
Wheel Omega	Y – Rotational speed of the tire.	rad/time
Radius OmegaActual OmegaFree	X – Deformed radius of the Tire. Y – Actual Rotational speed of the tire. Z – Rational Speed considering Unloaded radius.	length rad/time rad/time
LonSlip LatSlip IncAngle	X – Longitudinal Slip of the tire. Y – Lateral Slip of the tire. Z – Inclination angle of the tire. In the ISO axis system.	% rad rad
Tire CP Forces (W-Axis system)	Tire force and Moments with reference to the ISO- Axis system at the tire contact patch.	Force & Force*Length
Tire CP Forces	Tire force and Moments with reference to the SAE- Axis system at the tire contact patch.	Force & Force*Length
LonSlip LatSlip IncAngle	X – Longitudinal Slip of the tire. Y – Lateral Slip of the tire. Z – Inclination angle of the tire. In the SAE axis system.	[No Units] Deg Deg
Tire Hub Forces (C-Axis System)	Tire force and Moments with reference to the ISO axis system at the wheel center.	Force & Force*Length