Design and Analysis of an Innovative run-flat system for pneumatic tires

Pneumatic tires have been an essential part of the automobile since the early 20th century. Providing load carrying, braking, accelerating and turning capability as well as a certain degree isolation from the road, they fail to function without the presence of air pressure inside them. Run-flat tire systems allow the vehicle to continue running with reduced driving speeds for a certain specified range in case of loss of air pressure due to puncture or damage. In this work, the design of self-supporting and insert supported run-flat systems was approached using CAE. Two tire FE models of sizes 175/70 R14 and 175/60 R18 were used in this study. All structural and thermal simulations were done using ABAQUS and ENDURICA software was used for fatigue life simulation. Distance travelled before failure was used as the primary parameter for design evaluation along with secondary parameters of contact patch area and contact pressure, tire temperature profiles and rolling resistance. Ride comfort and handling characteristics are important performance parameters for a tire. Thus, a limited study to quantify the effect of run-flat system on the ride and handling properties was also conducted. The target design values for maximum load were fixed according to ETRTO standards while the maximum operating speed and the desired mileage in deflated condition was fixed at 45 mph and 50 miles, respectively. The initial part of the design process for the auxiliary supported design involved using a rigid cylindrical structure of varying height and thickness as a rim-mounted run-flat insert to get estimate of life of tire structure for different levels of deformation. The results were then used as input for designing a deformable rim mounted insert using reinforced rubber material. For the self-supported design, the sidewall of the tire was modified to increase its section thickness from an average value of 5 mm in the original design to 10 mm and 15 mm by addition of rubber material. For each thickness value, three designs based on the location in the tire structure where the material addition began relative to the belt edges of the tire were created. The designs were compared in terms of their fatigue life and contact patch area. For both types of run-flat designs, a candidate design, which satisfied the performance criteria, was found using the simulation results for the tire and run-flat system. It was concluded that a simulation-based approach can be used to design innovative run-flat systems for pneumatic tires.