Understanding the Cavity Mode of Tires

Ford Motor Company

Background:
The purpose of this research is to be able to predict the natural frequencies associated with the cavity modes of tires mounted oil wheels. Ford has experienced difficulties in the past when these natural frequencies have aligned themselves with the natural frequencies of other vehicle components and hence caused an objectionable noise in the vehicle. The goal of this project is to provide the tools to Ford to allow them to make decisions in advance of mounting tire/wheel combinations on vehicles by estimating what these tire cavity natural frequencies will be. It is anticipated that to fully understand the frequencies of the tire cavity modes will require a combination of modeling and experimental testing.

Approach:
To meet these objectives start with a finite element model of the cavity of a tire mounted on a wheel. The initial model includes effectively a rigid tire and wheel. This model is not a coupled vibro-acoustic model but instead just an estimate the natural frequencies of the tire cavity itself with zero velocity boundary conditions. This model will be modified to simulate the change in the tire cavity shape when the wheel is loaded in a static configuration. The results of the loaded and unloaded models are compared to help to understand the effects of changing the tire cavity’s shape. If the results of this model show promise, simpler modeling methods will be explored.

The next step in the modeling process includes a flexible tire and wheel and be a fully coupled vibro-acoustic model. In this model, the wheel will have actual material properties assigned while the tire will be modeled as an isotropic material with estimated material properties that will be iterated to achieve natural frequencies of the coupled system similar to those measured in the laboratory of a stationary tire. This model will then be modified to a statically loaded condition and the model re-run to observe the effects of loading the tire on the natural frequencies.

Models will be validated experimentally by testing a tire/wheel assembly in the laboratory at MTU. Testing will be done in the both the unloaded and the statically loaded case by exciting both the wheel and the tire patch in separate tests. Natural frequencies will be estimated from all tests and used to validate the models. Models and testing will be performed on several different tire/wheel combinations to assess the ability to estimate the natural frequencies of different configurations. Based on the results of the modeling and testing the final deliverable from this project will be the simplest approach that can be determined for estimating the natural frequencies of a tire cavity based on a minimum set of information or data.

Investigators: Jason Blough