Explanations of ZWARP technology

Introduction

The wheel-related components of the chassis - i.e. tires, wheels, wheel hubs and wheel bearings - are highly stressed safety-relevant components, the wheel-related components of the chassis - i.e. tires, wheels, wheel hubs and wheel bearings - are highly stressed safety-relevant components, which are arranged directly and unsprung in the load path.

Today's tire cross-sections result in impressive lateral force potential, but especially in the case of tires with integrated run-flat properties - also in pronounced vertical stiffness, which provides an additional force effect. At the same time, the wheel design in particular is a key differentiating feature for the design effect of the vehicle and is therefore not necessarily designed to optimize weight or strength.

Against the background of these multi-layered requirements for functionality and safer service life, wheel-related components have been a focus of Fraunhofer LBF for many years. Starting with wheel testing activities with the first ZWARP laboratory testing facilities in the 1980s, Fraunhofer LBF engineers and scientists are now involved in a wide range of development and testing activities.

The direct measurement of wheel forces and torques is carried out with wheel load sensors (measuring wheels), which are used on test tracks as well as on public roads. The Fraunhofer LBF supports the complete metrological vehicle equipment with its own measuring wheels for passenger cars and heavy commercial vehicles, accompanies the driving operation measurements and carries out subsequent data analyses.

Fraunhofer ITWM provides the complete family of CDTire tire models for MBS complete vehicle analyses - also for driving on virtual test tracks. The development of the numerical tire models as well as their runtime optimization, which also includes the characterization of executed tires, is carried out directly by a group of experts. The experimental identification of tire parameters for large deformations of the tire slack is integrated into this process with measuring equipment available at the Fraunhofer LBF.

The tools for numerical simulation of the tire system are completed by LBF® WheelsStrength. With interfaces to the most frequently used FEM codes worldwide, this software for numerical fatigue analysis of wheels and wheel hubs can be integrated into existing CAE environments and offers powerful features, e.g. physical tire transfer functions or automatic calculation of the required fatigue strength for the node of the simulation model.

For the experimental testing of wheels and wheel hubs, Fraunhofer LBF offers the world's largest number of biaxial laboratory testing facilities for passenger cars and commercial vehicles. The methods of collective-based operational load simulation are implemented here in particularly effective, time-shortened load programs. This enables the stresses of an entire vehicle life to be represented in just a few days and ensures statistical validation with an economical sample size.

The W/ALT testing technology developed at the Fraunhofer LBF, with its parallel kinematics (hexapod) that can be positioned particularly flexibly and a powerful drive unit, has also been proving its worth for many years for testing wheel-integrated electromobility. This allows the performance and functions of wheel hub motors to be tested in a laboratory environment with simultaneously effective external forces from driving maneuvers or bad-path excitation.

In addition to the testing machines developed at the LBF with the inner drums, we also use a testing facility with an outer drum.