SECTION 14 TIRES

Tires This section provides an overview of the calculation of tire forces and the available models.

Tires What’s in this section: Tire Overview Adams/Tire Modules Tire Models Road Types Example 2D Road (RAMP) Using the 3D Equivalent-Volume Model Example 3D Road 3D Spline Road Sample Road Data File Using the 3D Spline Road How You Use Adams/Tire

Tire Overview Adams/Tire calculates the forces and moments that tires exert on the vehicle as a result of the interaction between the tires and the road surface. dams dams

Tire Overview (Cont.) Adams/Tire is a set of shared object libraries that Adams/Solver calls through the GSE and GFOSUB subroutines. You can use Adams/Tire to model tires for either vehicle- handling or vehicle-durability analyses: Handling analyses are useful for studying vehicle dynamic responses to steering, braking, and throttle inputs. For example, you can analyze the lateral accelerations produced for a given steering input at a given vehicle speed. Durability analyses are useful for generating road load histories and stress and fatigue studies that require component force and acceleration calculation. These studies can help you calculate the effects of road profiles such as pothole, curb, or Belgian block.

Adams/Tire Modules Adams/Tire has a line of tire modules that you can use with Adams/View, Adams/Solver, Adams/Car, and Adams/Chassis. The modules let you model the rubber tires found on many kinds of vehicles such as cars, trucks, and planes. More specifically, the modules let you model the force and torque that tires produce to accelerate, brake, and steer vehicles. The modules available in Adams/Tire are: Adams/Tire Handling Module Adams/Tire 3D Contact Module Adams/Tire 3D Road Module Specific Tire Models Features in Adams/Tire Modules

Adams/Tire Modules (Cont.) Adams/Tire Handling Module Adams/Tire Handling incorporates the following tire models for use in vehicle dynamic studies: Pacejka 2002 tire model* Pacejka '89 and Pacejka '94 models* Fiala tire model UA tire model 5.2.1 tire model Adams/Tire Handling uses a point-follower method to calculate tire normal force and is limited to two-dimensional roads. * The formulae used in the Pacejka’tire models are derived from publications by Dr. H.B. Pacejka, and are commonly referred to as the Pacejka method in the automotive industry. Dr. Pacejka himself is not personally associated with the development of these tire models, nor does he endorse them in any way.

Adams/Tire Modules (Cont.) Adams/Tire 3D Contact Module Adams/Tire 3D Contact uses a three-dimensional equivalent-volume method to calculate tire normal force on three-dimensional roads for use in predicting vehicle loads for durability studies. With Adams/Tire 3D Contact with Adams/Tire Handling, you can use the Pacejka 2002, Pacejka '89, Pacejka '94, or Fiala models to calculate the tire handling forces and moments (lateral force, longitudinal force, aligning torque, and so on).

Adams/Tire Modules (Cont.) Adams/Tire 3D Smooth Road Module Adams/3D Road lets you define an arbitrary three-dimensional smooth road surface. In addition, you can place three-dimensional road obstacles, such as a curb, pothole, ramp, or road crown, on top of the underlying smooth road surface. You can use the 3D Road Module with any of the tire models in Adams/Tire. Use the smooth road part in combination with any of the handling tire models, or use the more advanced FTire model to deal with road obstacles for ride and comfort and durability analysis.

Adams/Tire Modules (Cont.) Specific Tire Models In addition to the tire models in the Adams/Tire Handling Module, Adams/Tire supplies specific tire models: Pacejka Motorcycle Tire Model A Pacejka tire model suitable for motorcycle handling analysis that can describe the tire-road interactions forces with tire-road inclination angles up to 60 degrees. Adams/Tire FTire Module FTire can describe the 3D tire dynamic response up to 120 Hz and beyond, due to its flexible ring approach for the tire belt. It can handle any road obstacle. All tire models support the Adams/Linear functionality.

Adams/Tire Modules (Cont.) Features in Adams/Tire Modules The table below lists the features available in Adams/Tire modules.

Adams/Tire Modules (Cont.) Which Tire Model Should You Use? Each tire model is valid in a specific area. Using a tire model outside this area can result in nonrealistic analysis results. The figure below shows the range of validity of each tire model while the next table indicates the tire model(s) that are the best to use for a number of applications. In general, the Adams/Tire Handling models are valid on rather smooth roads only: the wavelength of road obstacles should not be smaller than the tire circumference. If the wavelengths are shorter, you should use FTire model to cope with the nonlinear tire enveloping effects. The Handling Tire models can describe the first-order response of a tire, but do not take the Eigen frequencies of the tire itself into account. Therefore, the Handling Tire models are valid up to approximately 8 Hz. Beyond that, a tire model should be used, including modeling the tire belt, as FTire does.

Adams/Tire Modules (Cont.)

Tire Models Tire data Tire data is essential in obtaining accurate tire forces during a simulation. If you use the Fiala model, you can generate the tire property file by hand. If you use a different tire model, you must use a fitting routine to obtain the coefficients for the tire property file. This is usually done by the testing facility that tests the physical tire. Unless the tire you want to use is tested already, a test must be performed to obtain the tire data necessary for a tire property file. Improve this workshop for the future: Run a simulation with a simple 2D flat road simulation and plot a result. Run the same simulation with a Pacejka tire model and plot the same result. Compare the ease of use and the accuracy. Run a 3D road to see how to change from Handling to Durability. How about using a flat sine road and a 3D sine road and compare tire forces? Here, the point is to see why and when to use 2D vs. 3D roads/tires.

Road Types The 2D road contact uses a point-follower method (for example, think of a disk of a plane). The following are the different road types that work with this method (primarily for FTIRE): DRUM - Tire test drum (requires a zero-speed-capable tire model). FLAT - Flat road. PLANK - Single plank perpendicular, or in oblique direction relative to x-axis, with or without bevel edges. POLY_LINE - Piece-wise linear description of the road profile. The profiles for the left and right track are independent. POT_HOLE - Single pothole of rectangular shape. RAMP - Single ramp, either rising or falling. ROOF - Single roof-shaped, triangular obstacle.

Road Types (Cont.) SINE - Sine waves with constant wave length. SINE_SWEEP - Sine waves with decreasing wave lengths. STOCHASTIC_UNEVEN - Synthetically generated irregular road profiles that match measured stochastic properties of typical roads. The profiles for left and right track are independent, or may have a certain correlation. Sample files for all the road types for Adams/Car are in the standard Adams/Car database: install_dir/acar/shared_car_database.cdb/roads.tbl/ Sample files for all the road types for Adams/Tire are in: install_dir/solver/atire/ Sample files for all the road types for Adams/Chassis are in: install_dir/achassis examples/rdf/

Example 2D Road (Ramp)

Using the 3D Equivalent-Volume Model The 3D equivalent-volume road model is a three-dimensional tire-to-road contact model that computes the volume of intersection between a road and tire. The road is modeled as a set of discrete triangular patches and the tire as a set of cylinders. This model lets you simulate a vehicle that is hitting a curb or pothole, or moving on rough, irregular road surfaces.

Using the 3D Equivalent-Volume Model (Cont.) About the 3D equivalent volume road model The 3D equivalent-volume road model is a general three-dimensional surface that is defined as a series of triangular patches. The figure depicts a road surface formed by six nodes numbered 1 through 6. The six nodes together form four triangular patch elements denoted as A, B, C, and D. The unit outward normal for each triangular patch is shown for the sake of clarity. Much like finite-element mesh convention, Adams/Tire requires that you define a road by first specifying the coordinates of each node in the roadreference- marker axis system. Subsequently, you specify the three nodes that form each triangular patch. For each triangular patch, you can specify a coefficient of friction.

Using the 3D Equivalent-Volume Model (Cont.) Defining the 3D road surface You use a road property file to define the three-dimensional road surface. The road property file consists of five data blocks: Header, Units, Model, Nodes, and Elements. These blocks of data can appear in any order in the file, and keywords can appear in any order within the block to which they belong.

Example 3D Road

3D Spline Road The 3D Spline road option lets you model many types of three-dimensional smooth roads, such as parking structures, race tracks, and so on. A smooth road is one in which the road curvature is less than the curvature of the tire. Adams/Tire stores the 3D road details in a standard TeimOrbit road data file (.rdf).

Sample Road Data File

Using the 3D Spline Road You can reference the 3D Spline road like you do any other .rdf by selecting your desired road from an appropriate database. In addition, Adams/Car has a 3D road event, called 3D Smooth Road. Graphics for the road are automatically generated for animation purposes. Example Using 3-D road for steering the vehicle:

How you use Adams/Tire You can create your own tire models or you can use the tire models that come with Adams/Tire. The following describes how you use Adams/Tire. For more about how you can create your own tire models, see the Adams/Tire online help. To use Adams/Tire: Define tires. How you define tires depends on the product you are using (Adams/Chassis, Adams/Car, or Adams/Solver). Regardless of the product you use, the product creates an Adams dataset (.adm), which contains the necessary statements that represent the tires in your Adams model, as well as other elements of the vehicle, such as the wheel, suspension, and landing gear strut. The primary statement for each tire is a GFORCE that applies the tire force to the wheel in your suspension.

How you use Adams/Tire (Cont.) Reference an existing tire property file from: Adams/Tire (Adams/Car shared database) Tire manufacturers or testing companies. Files that you create. For example, you can create your own tire property file for simple kinds of tire models, such as the Fiala model. A tire property file specifies what kind of tire model Adams/Tire should use. The tire property file contains the data that defines the tire’s force and moment characteristics. The amount and kind of data varies according to the type of tire model you use. A STRING statement in the Adams dataset holds the name of the tire property file. Reference an existing road property file. A road property file contains data that defines the road surface and coefficient of friction. The road can be flat or have a three-dimensional surface represented as triangular patches. A STRING statement in the Adams dataset provides the name of the road property file. Run a simulation of your model.

How you use Adams/Tire (Cont.) MD R2 Adams dataset .adm