Introducing Adams Tire

Adams Tire software is a module that you can use with Adams Car, Adams Solver, or Adams View for adding tires to your mechanical model in order to simulate maneuvers such as braking, steering, acceleration, free-rolling, or skidding. Adams Tire lets you model the forces and torques that act on a tire as it moves over roadways or irregular terrain.

Adams Tire is a set of shared object libraries that Adams Solver calls through the Adams GFOSUB and GSESUB subroutines. These subroutines calculate the forces and moments that tires exert on a vehicle as a result of the interaction between the tires and the road surface.

You can use Adams Tire to model tires for either vehicle-handling, ride and comfort, and vehicle-durability analyses:

See the section Adams File Types for more information on Adams Tire extenision.

Adams Tire has a line of tire modules that you can use with Adams View, Adams Solver, and Adams Car. 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 four modules available in Adams Tire are:

Adams Tire Handling incorporates the following tire models for use in vehicle dynamic studies:

The Adams Tire Handling models can deal with all road and tire-road contact methods.

*The formulae used in the Pacejka tire models are derived from publications, 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.

In addition to the tire models in the Adams Tire Handling Module, Adams Tire supplies specific tire models:

All tire models support the Adams Linear functionality.

Next to an interface for user-written roads, the Adams Tire Road Module offers 4 types of roads that are supported by all Adams Tire models:

The Adams Tire 2D Road supports the description of roads with a range of two-dimensional obstacles.

Adams 3D Spline Road lets you define an arbitrary three-dimensional smooth road surface. In addition, you can superimpose three-dimensional road obstacles, such as a curb, pothole, ramp, or road crown, on top of the underlying smooth road surface.

Adams Tire 3D Shell Road describes a road surface by triangular meshed elements. The road can work with the default 3D Equivalent Volume Contact method or with the 3D Enveloping Contact.

The OpenCRG Road is based on the open source road from the OpenCRG® organization (http://www.opencrg.org). OpenCRG provides a series of open file formats and tools for the detailed description of (measured) road surfaces.

RGR road has been developed by cosin scientific software (www.cosin.eu) and is dedicated to measured 3D road surfaces similar to OpenCRG road. Next to the road library also tools are provided for generating, modifying and visualizing this road format.

Different methods are available to model the contact in between the tire and the road. For rather smooth roads (length of the road obstacles is larger than the tire circumference), the default One Point Follower Contact method can be used. For shorter obstacles the vertical tire response can show non-linear effects due to tire enveloping behavior. In such cases the 3D Enveloping Contact method should be used.

In addition a special method (Tire Cross-Section Profile Contact Method) is available for motorcycle tires, in which the effect of large camber is taken into account.

The fourth method, the 3D Equivalent Volume Contact method can be considered as a one point contact method as well, but it has advantages for road friction variations and meshed road surfaces.

Additional tools are provided to support the use of the Adams Tire modules:

Each tire model is valid in a specific area. Using a tire model outside this area can result in non-realistic analysis results. The Typical Applications for Each Tire Model table indicates the tire model(s) that are the best to use for a number of applications.

The Handling Tire models can describe the first-order response of a tire, but do not take the eigenfrequencies of the tire itself into account. Therefore, the Handling Tire models are valid up to approximately 8 Hz. The PAC2002 can also use a more advanced transient method that extends the validity range up to 15 Hz. Beyond that frequency range, a tire model should be used that includes the dynamic effects of the tire belt. PAC2002 can offer also a basic approach of belt dynamics (rigid ring part) to increase validity up to 70 - 80 Hz; FTire is using a more complex approach with a more detailed contact patch and a flexible ring approach, which allows simulations to higher frequencies and a wider range of applications.

In the table below an overview of all features of the Adams tire models are shown. Next to the tire and road model, the contact method plays an important role.

All the tire models can deal with all Adams road types, however not all contact methods can be used with all road and tire model combinations.

In general the One Point Follower, the 3D Equivalent Volume Contact and the Tire Cross Section Profile Contact are valid for rather smooth roads only: the length of the obstacles on the road should be larger than the tire circumference. The 3D Enveloping Contact can deal with any shape and size of road obstacles at all road types (2D Road, 3D Spline, 3D meshed, OpenCRG Road and RGR Road).

For the tire models (PAC89, PAC94, PAC2002, PAC-MC, Fiala, UA-Tire, 521-Tire, Air Basic, Air Enhanced, Air TRR64, Soft Soil tire model), Adams Tire has four different contact methods that model the contact in between the tire model and the road:

Within Adams Tire all tire models can calculate the tire force response in steady state mode (instantaneous tire response to input changes) or in transient mode. In transient mode a linear relaxation length approach is used. As an exception, the PAC2002 model also supports a non-linear transient approach valid up to higher frequencies (around 15 Hz).

In general the transient mode should be used, valid up to 7 Hz, unless the dynamic response of the tire is not importance or should be avoided (that is, plotting tire characteristics in the tire test rig).

For increasing validity up to 70 - 80 Hz the PAC2002 tire model can use the belt dynamics feature: an additional part in the Adams model is used to add the dynamics of the tire belt so that the model dataset can be used for applications in the ride control area.

For modeling passenger car and truck tires a linear tire stiffness is adequate. In special cases (that is, low tire pressure or exposure to high vertical loads, for example with aircraft tires) a non-linear relation between vertical load and tire deflection can be specified in the tire property file for each tire model:

See also the example tire property files in this manual and the Adams delivery.

The PAC2002 and the aircraft tire models can account for the contact in between the rim and the road using a basic approach. Based on cylindrical rim geometry, the location and orientation of the wheel a rim deflection is calculated, if applicable. Then the contact force results from the deflection - force input data given in the tire property file.

The Rim-Road contact approach is valid for roads having obstacles larger than the tire circumference.

See also the sections Wheel Bottoming in the PAC2002 and Aircraft tire manuals.

In case the vehicle height (axle) height is important (that is, race applications), the PAC2002 offers a more advanced loaded and effective radius modeling. This method takes into account the effects of the longitudinal and lateral tire forces and tire rotational speed on the vertical tire stiffness and rolling radius, see Contact Methods and Normal Load Calculation.

The PAC2002 tire model is able to model the so-called 'parking torque' for a steering standing tire due to the friction in between the tire and road. In this advanced (non-linear) transient mode not only the parking torque comes into the model, but also the turn-slip effects due to turning at short turning radii and low speed. For further details see the section Non linear transient model in the PAC2002 manual.

The stiffness and damping rates for a standing tire can differ considerably from a rolling tire due to the different boundary conditions in the contact patch. While in many cases a rolling tire has low damping and a (almost) linear vertical stiffness, a standing tire has damping and stiffness rates that depend on frequency. The PAC2002 model enhances a Maxwell element that can introduce frequency dependent stiffness, see Non-rolling vertical tire stiffness and damping properties.

The PAC2002, PAC-MC, PAC-TIME and FTire model support the definition of DOE parameters within Adams Car and Adams View, see Adams Tire support for DOE.

In general the tire properties stay constant during a simulation. With the on-line scaling feature within PAC2002 it is possible to change the scaling factors that are available during the simulation according to any desired function. Because this requires a different setup of your model (needs a state variable for each scaling parameter), a detailed description can be found in the technical article KB8016467: http://simcompanion.mscsoftware.com/infocenter/index?page=content&id=KB8016467.

For vehicle modeling in Adams Car the SmartDriver-Tire interface insures that the exact same tire model is used for the Adams SmartDriver road preprocessing. User-written tire models can also support this interface, see KB8019634: http://simcompanion.mscsoftware.com/infocenter/index?page=content&id=KB8019634.