4.3.5 Creating Tire and Road

1. Creating Tire Property File

The five tire models were provided in the ADAMS/View, Table 4.11 shows the models.

The TIRE statement has five required arguments, the tire id, the J marker id, the tire mass, the tire inertia properties, and the associated tire property file.

Table 4.11 Overview of Tire Models

Tire type	Data required	Applicability
Fiala (Default)	Basic tire properties	Handling analysis Pure slip
University of Arizona (UA)	Basic tire properties	Handling analysis Comprehensive slip
Smithers	Coefficients from fitted tire test data	Handling analysis Pure slip
Delft	Coefficients from fitted tire test data	Handling analysis Comprehensive slip
User Defined	User	User

Default Dynamic Analysis Tire Model

An enhanced version of the so-called Fiala model is available as a default in ADAMS/Solver. The default tire model calculates tire forces in the longitudinal, lateral, and vertical directions as well as aligning moment and rolling resistance in response to slip angle, slip ratio and normal deflection. Camber thrust is not modeled. While rather simple, this model is capable of providing reliable results for situations not involving comprehensive slip, i.e., situations where longitudinal slip and lateral slip are not present simultaneously. This model is automatically invoked by ADAMS/Solver during a dynamic simulation involving tires translating at moderate to fast rates.

UA-Tire Dynamic Analysis Model

The UA-Tire model developed by Nikravesh and Gim at the University of Arizona, is part of the optional ADAMS/Tire module. The UA-Tire model computes normal, longitudinal, and lateral forces as well as aligning torque and rolling resistance under comprehensive slip

conditions. These forces and moments are determined by explicit formulations which are analytically derived depending on the coupled properties of slip ratio, slip angle, inclination angle, normal deflection, and other dynamic tire properties.

The UA-Tire model is much more comprehensive and accurate than the simpler Fiala model. It always provides much better results for aligning moments than the Fiala model. Additionally, in situations of comprehensive slip, the UA-Tire model provides much more realistic values for the other forces and torques.

Smithers Dynamic Analysis Tire Model

The Smithers tire model is part of the optional ADAMS/Tire module. This model is also referred to as the BNPS or Bakker-Nyborg-Pacejka-Smithers model. The Smithers model computes the lateral force and the aligning moment from the slip angle, inclination angle, vertical force, and data provided by Smithers Scientific Services. The Fiala tire model computes the other tire forces and torques. The Smithers model comes complete with three sample tire property files, which you can use until you obtain the specific tire property files for your perspective tires.

DELFT Dynamic Tire Model

The DELFT tire model is part of the optional ADAMS/Tire module. This model was developed by TNO Road-Vehicle Research Institute in the Netherlands. It is a Pacejka “magic formula” tire model. The model computes lateral, longitudinal, and vertical forces and the aligning moment from fitted coefficients TNO provides.

User-Defined Tire Models

You have the option of defining your own tire model. A user-written subroutine, TIRSUB, is provided to facilitate this. Instantaneous tire kinematic contact properties and tire material properties are provided as input to TIRSUB. In addition, users can use the UPARAMETER and USTRINGS arguments to pass real values and character strings to TIRSUB. TIRSUB should return to ADAMS/Solver the three forces and the three torques acting at the contact patch in the instantaneous SAE coordinate system. ADAMS/Solver transfers the forces and torques to the tire hub center and apply them.

The UA tire model was selected in the example. The tires are P215/80R16 meridian tire. The tire property shown in Table 4.12.

Table 4.12 P215/80R16 Meridian Tire Property

Model	R1 R1 /mm	R2 R2 /mm	CNORMAL Cz /(N/mm)	CSLIP Cs /(N/mm)	CALPHA Cα /(N/rad)
Analytical	375	107.5	261.3	30000	46000

CGAMMA Cγ /(N/rad)	CRR f	RDR	U0	U1
4000	0.015	0.75	0.94	0.74

CALPHA: The tire’s cornering stiffness: the partial derivative of lateral force (Fy) with regard to slip angle (α) at zero slip angle. CALPHA = Cα = r1*r2. CALPHA should have units of force per radian or degree.

CGAMMA: The tire’s camber stiffness: the partial derivative of lateral force (Fy) with regard to inclination (camber) angle at zero camber angle. Note that CGAMMA = Cγ = r1*r2.

CNORMAL: The tire’s vertical stiffness: the partial derivative of vertical force (Fz) with regard to ire vertical penetration (such as deflection) at zero vertical penetration. Note that CNORMAL = Cz = r1*r2.

CRR: Specifies the conversion factor and the rolling resistance moment coefficient. Note that CRR = Cr = r1*r2. CRR should have units of length.

CSLIP: The tire’s longitudinal slip stiffness: the partial derivative of longitudinal force (Fx) with regard to longitudinal slip (s) at zero longitudinal slip. Note that CSLIP=Cs = r1*r2. CSLIP should have units of force.

R1: Specifies the conversion factor and the unloaded tire radius, that is, radial distance from the tire center to the crown of the tread.

R2: Specifies the conversion factor and the carcass radius of a toroidal (or doughnut shaped) tire. This is equal to one half the greatest distance from one sidewall to the other, when measured along an axis parallel to the tire spin axis.