THE TWENTY-NINTH ANNUAL MEETING AND CONFERENCE ON TIRE SCIENCE AND TECHNOLOGY
Session
Student 1
Chair
Marion Pottinger
M'gineering LLC
This session presents papers by graduate students concerned with tire performance with respect to mobility, handling, and noise.
Presentations
Experimental and Numerical Study of Friction and Handling Characteristics of Rolling Tires
René van der Steen1, Ines Lopez1, Henk Nijmeijer1, Bart de Bruijn2 and Antoine Schmeitz3, (1)Department of Mechanical Engineering, Eindhoven University of Technology, Eindhoven, Netherlands, (2)Apollo Vredestein B.V., Enschede, Netherlands, (3)TNO Science and Industry / Business Unit Automotive, Helmond, Netherlands
The aim of this study is to develop a friction model, which captures observed effects of dry friction on the handling characteristics of rolling tires. A phenomenological friction model is chosen, where the parameters are identified using a two step experimental / numerical approach. Firstly friction experiments are performed on a Laboratory Abrasion and skid Tester to develop a pressure part of the friction model [1]. Secondly braking experiments at different velocities with a specially designed non-production tire are conducted to obtain a velocity dependent parameter set. This is described in the present contribution.
The derived friction model is coupled to a FE model of the tire, which is constructed in the commercial FE package ABAQUS. The steady-state transport approach is used to efficiently compute steady-state solutions. The basic handling characteristics, such as pure braking, pure cornering, and combined slip under different loads, inflation pressures and velocities are evaluated and compared with experiments performed with the TNO Tyre Test Trailer.
Acknowledgements: This research is funded by the CCAR project ‘FEM Tyre Modelling’, in cooperation with Apollo Vredestein B.V. and TNO Science and Industry.
[1] R. van der Steen, I. Lopez, H. Nijmeijer, “Experimental and numerical study of friction and stiffness characteristics of small rolling tires”, Tire Science and Technology, Accepted for publication.
A Finite Element Tire Modelling Approach for Car Indoor Noise Simulation
Raffaela Chiarello and Udo Nackenhorst, Institute for Structural and Numerical Mechanics, Leibniz Universität Hannover, Hannover, Germany
A finite element approach for the simulation of the dynamic behaviour of tires rolling on rough roads for the car indoor noise prediction is presented. Based on a detailed finite element model valid for the nonlinear stationary rolling analysis a modal tire model to be coupled with a total vehicle dynamics simulation approach has been developed, where special care is taken on the physical consistency. Modal coupling can be performed directly or by transfer functions approaches.
The finite element (universal) tire model consists of about 200.000 unknowns taking into account 16 different material groups within the cross section. In a first step a stationary non-linear rolling analysis is performed, cp. [1,2]. In this pre-stressed state an eigenvalue analysis is computed for the rolling wheel, incorporating gyroscopic effects, see [3]. The modal tire model is reconstructed considering a limited number of eigenmodes corresponding to a user defined limit frequency.
The dynamic characteristics for the individual tire model are fitted to results obtained from standardized laboratory experiments. By a physically motivated hierarchical optimization strategy the model parameters are identified such that the measured dynamic axis reaction response spectra are represented best by the modal tire model. Besides the adjustment of eigenfrequencies and modal damping parameters special effort has been paid on the excitation function which defines the response amplitudes.
The importance of a physically consistent modelling approach will be underlined by the meaning of gyroscopic effects. By this approach a physical reliable and numerical efficient model is presented, whose parameters are obtained from laboratory experiments for individual tires.
[1] U. Nackenhorst, Comp. Meth. Appl. Mech. Engg., 193 (39-41), 2004
[2] M. Ziefle and U. Nackenhorst, Comput. Mech. 42, 2008
[3] M. Brinkmeier and U. Nackenhorst, Tire Sci. and Technol. 37 (47-59), 2009
An Investigation Into Wheel Sinkage on Soft Sand
Noel Hathorn, MEng, James Brighton, EngD and Kim Blackburn, PhD, Centre for Automotive Technology, Cranfield University, Bedford, United Kingdom
Sinkage is an empirically significant factor in vehicle performance as it can result in an immobile vehicle or environmental damage. Bernstein first proposed a pressure sinkage relationship in 1913, subsequent work by Janosi and Hanamoto and Hedegus concluded that longitudinal wheel slip also plays a role in sinkage. Shinone, Nakashima, Takatsu, Kasetani and Matsukawa identified a linear relationship between slip and sinkage on a lightly loaded tire. In this study the effects of vertical wheel load, wheel slip and tire inflation pressure on wheel sinkage on soft sand were investigated, in order to relate sinkage to a vehicular operating condition.
The tests in this study were conducted using the Cranfield University Single Wheel Tester (SWT) on soft, desert-like sand in the Cranfield Off-Road Dynamics facility soil bin. The SWT uses a closed loop servo-controlled hydraulic ram to actively control vertical wheel load and similar active wheel speed control via a hydraulic motor. The SWT apparatus is mounted on an independent prime mover tractor unit which controls forward speed. True forward speed is continuously measured against a fixed reference point and used to calculate the required wheel speed in real time to give the desired slip profile.
A series of controlled load tests were conducted using a Goodyear G90 tire (7.50 R16C) on a dry desert sand material. Four discrete inflation pressures (10, 20, 30 and 40 psi) and four vertical loads (1, 2, 3, 4 and 5 kN) were chosen to represent the operating range of the tire. Each test run consisted of a slow (30s) ramp of slip ratio from 85% (driven) to -15% (braked).
Although a near linear response was identified for slips greater than 10% as Shinone et al. also found, the overall relationship between slip and sinkage was found to be non-linear.
Derivation of LuGre Tire Parameters Using Laboratory Tests
Madhura Rajapakshe, Civil and Environmental Engineering, University of South Florida, Tampa, FL
In most of its past applications LuGre tire friction model has been empirically calibrated by tuning its parameters to fit measured tire-pavement friction data or an already calibrated friction model. However, physical significance of the model parameters is one important advantage of this widely used analytical tire friction model. It enables this model to provide physically intuitive guidelines for harmonizing different tire-pavement friction measuring devices by introducing modifications to their measurement mechanisms. In modeling dynamic tire forces using the LuGre model, the mechanical properties of the tire are represented by stiffness and damping parameters of the brushes/bristles that resemble the contact surface of the tire. In this study, specially designed laboratory tire tests were carried out to measure stiffness and damping properties of the ASTM E524 standard smooth tire used for testing pavement friction. The properties were measured in vertical, lateral and longitudinal directions and used to derive lumped LuGre tire parameters. Derived tire parameters were found to be closely comparable to those obtained using data fitting methods, hence validating both derivation and optimization approaches for LuGre model parameterization.
An off-Road Tire Model for Vehicle Handling Studies
Brad Hopkins, Mechanical Engineering, Virginia Tech, Blacksburg, VA and Saied Taheri, Mechanical Engineering, Virginia Polytechnic Institute and State University, Danville, VA
An off-road tire model has been developed for use in vehicle handling studies. A baseline force and moment model was first developed for the studied tire by performing force and moment testing on a rolling road. Forces and moments were recorded in response to slip angle, camber angle, and vertical load inputs and a Pacejka Magic Formula model was determined. This baseline force and moment tire model is applicable for a dry asphalt driving surface.
Next, off-road tire testing was performed on a passenger tire by using a portable tire test rig. The tire was subjected to slip angle sweeps at various vertical loads while being driven on dry asphalt, dirt, and gravel. Lateral force scaling factors for use in the Magic Formula were obtained for the dirt and gravel driving surfaces. The scaling factors were then applied to the studied tire to extend its lateral force behavior on dry asphalt to dirt and gravel. The off-road tire model was then used in commercially available vehicle simulation software to simulate vehicle handling behavior on dirt and gravel driving surfaces.
