Nitrogen as an inflation gas for passenger car and light truck tires use is widely available commercially.  Consumers are confronted with a bewildering selection of offerings, and suppliers tout the purity of their nitrogen generation systems and effectiveness of using the gas in place of air.  This paper develops models for the initial tire nitrogen purity, the inflation pressure loss rate, and the evolution of the nitrogen gas purity in the tire as a function of the gas used to top off the tire over its life.  A series of simulations using the basic model is developed for air and various purities of nitrogen initial inflation with monthly top-off using air or various purities of nitrogen.  The initial inflation pressure loss rate is shown as a function of the tire’s initial nitrogen purity.  This paper proposes the use of the total oxygen passing through the tire over its lifetime as a metric for evaluation of various inflation schemes.  This metric is developed for several of the popular available nitrogen inflation purities using both air and nitrogen as a top-off gas. 

Development of the laboratory-based accelerated service life testing - “tire aging test”- encountered difficulties due to complexity of multi-disciplinary processes in the tire materials while trying to induce thermo-oxidative degradation, similar to that taking place in the ‘worst case’ in-service. Preliminary experience with the oven aging at elevated temperatures showed that in some light truck tires damaging conditions occur in the form of sidewall blisters/detachments and casing separations due to inflation gas built up in interior tire layers during aging, even prior the roadwheel endurance testing [1].

Analysis and comprehensive modeling techniques are developed for gas diffusion and oxidation in the tire structure, with focus on the Intra-Carcass Pressure (ICP) build-up predictions.  In Finite Element models temperature dependent diffusion properties are used with account for their high heterogeneity in different tire components. Results of transient simulations predict higher oxidation/ degradation rate in the sidewall and detrimental effect of ICP build-up for Load Range E tires. Influence of the butyl liner barrier permeability and gauge is evaluated, as well as impact of other construction variations. Predicted trends agree with the available observations and measurements. ICP levels in simulations of the long-term gas diffusion under regular service conditions are significantly lower than in the aging test modeling.

Modified aging test conditions are proposed that will greatly reduce deleterious side-effect of the ICP buildup, as assessed in simulations.

1.  DOT HS 810799 “Research Report to Congress on Aging” (2007)

Tire overturning moment measurements have traditionally been used primarily for rollover threshold analysis, and have often been ignored for linear range maneuvers. This paper explains how overturning moment is related to aligning torque for a tire under tractive force. This relationship can be used to develop a better understanding of tire properties necessary to achieve better steering refinement. A free rolling overturning moment measurement is shown to provide useful information for aligning torque performance. Example force and moment test results are shown to illustrate the concepts.

New advances in automotive technology have made significant inroads to making vehicles safer and reducing injuries and fatalities.  Protocols developed by the US Department of Transportation and the automotive industry, such as NCAP rollover tests, FMVSS 126 electronic stability control, and the TREAD Act, promise to be second only to seat belts in reducing fatalities and accidents.  These new performance specifications, though, are also quite expensive to develop, often leading to more prototype vehicles for proving ground testing.  

Automotive companies can greatly reduce the design cycle through simulation, with one major limitation - accurate tire data, particularly in the varying environments that a vehicle sees.  Tire companies are seeking ways to validate performance more accurately under extreme conditions to meet the criteria laid out by their automotive customers.  Current capabilities are limited to laboratory conditions to provide repeatability, but at the expense of accuracy.  

Camber Ridge has been working with automotive companies, tire companies, controls companies and testing equipment companies to develop a new generation of tire testing capabilities to address many of the limitations of current equipment.  This presentation will address the shortcomings identified by the industry, the desire for new dynamic testing capabilities, and the approach to developing a custom built capability to address these needs.