Explanations of ZWARP technology

Wheel, tire and roadway

Introduction

The contact area between the vehicle and the road surface is the size of that which footballs make with any surface – and transfers the circumferential forces and driving forces of powerful, highly dynamic cars driven.

The wheel-related components of the chassis, in other words, the tyres, wheels, wheel hubs and wheel bearings are heavy-duty, safety-related components that are unsprung and arranged directly in the load path. The current tyre cross-sections result in an impressive lateral force potential – and also in a pronounced vertical rigidity specifically for tyres with integrated emergency running properties, this ensuring an additional force action. At the same time, the wheel design is just a key distinguishing feature for the design effect of the vehicle and therefore the design has not necessarily been optimised with regard to a weight or strength.

Against the background of these complex requirements for functionality and a more secure service life, Fraunhofer LBF has been focussing on these wheel-related components for many years. Fraunhofer LBF engineers and scientists have been involved in diverse development and testing activities since the 1980s; the first job that we successfully completed was to inspect wheels using the first ZWARP laboratory test equipment.

Measuring wheels

Direct measurements of wheel forces and wheel torques are made using wheel load sensors (measuring wheels), which are used on test tracks, as well as on public roads. Fraunhofer LBF supports the complete metrological vehicle equipment including our own measuring wheels for passenger cars and heavy commercial vehicles, accompanies driving test measurements and performs subsequent data analyses.

CDTire tyre models

Fraunhofer LBF provides the complete family of CDTire tyre models for complete MKS vehicle analyses and driving virtual test tracks. Moreover, a group of experts from Fraunhofer LBF directly develops the numerical tyre models and their run-time optimisation, and also the characterisation of tyres being exported. Experimental identification of tyre parameters is included in this process, which comprises large deformations of the tyre shuffle using the measuring systems provided by Fraunhofer LBF.

Numerical analysis of the operating stability of wheels and wheel hubs

The tools for numerical simulating the wheel/tyre system will be completed by LBF® WheelsStrength. With interfaces to the world's most widely used FEM codes, this software can be integrated for numerical analyses of operating stability for wheels and wheel hubs in existing CAE environments. It also provides powerful and effective features such as physical tyre transfer functions or automatic calculations in respect to the necessary vibration resistance for the nodes of the simulation model.

Operating load simulation in the laboratory of wheels and wheel hubs

Fraunhofer LBF provides the world's largest number of biaxial laboratory test equipment in the experimental testing of wheels and wheel hubs for passenger cars and commercial vehicles. Here, our methods for collective-based operating load simulations are implemented in load programs which are particularly effective and take considerably less time to be performed. Thus, in a few days, the stresses, strains and loads that the vehicle has been subjected to over its entire service life so far are displayed and will be included in the statistical certainty using an economic sample size.

This is the latest development in testing technology from Fraunhofer LBF within a particularly flexibly positionable parallel kinematics system (hexapod), which allows the testing of wheel integrated electromobility in connection with a powerful and high-performance drive unit. Thus, outputs and functions of wheel hub motors can be tested in a laboratory environment, at the same time as effective external forces from driving manoeuvres, or bad or improper displacements.