Search Results

Currently used tire models have shown a certain lack of accuracy in some advanced handling applications. This lack of accuracy is believed to be partly due to thermal effects. In reality, the tire rubber temperature is not constant during the normal operating conditions and it's really well known that the tire friction coefficient strongly depends on the temperature level. The temperature generation, propagation and evolution are the result of a dynamic energy equilibrium between phenomena of different natures. Various mechanisms create a non-uniform temperature distribution in various parts of the tire structure: heat is generated in zones with large cyclic deformations due to the energy dissipated from the rubber strains and in the sliding part of the contact patch due to friction. The rubber cools down because the heat energy transferred to the air (internally and externally) and to the asphalt in the stick zone of the contact patch.

The full vehicle simulation on durability proving grounds is a well established technique in the development process of passenger car manufacturers. The respective road surfaces are designed to generate representative spindle loads and typically include events that will result in large tire deformations. Depending on manufacturer and the combination of vehicle size and wheel properties, these deformations can be so large that the tire belt and/or sidewall have contact with the rim crown (protected by the tire sidewall). The current tendency to low-aspect ratio tires reduces the available deformation capability of the tire while simultaneously introducing larger nonlinearities in the sidewall behavior. After a short overview of the standard modeling technique used by the CDTire model family to handle such events, a refinement of this technique is introduced, modeling both the non-linearity behavior of the sidewall and a possible subsequent rim contact.

Today's tire models used in MBD full vehicle application scenarios like Ride&Comfort or Durability are parameterized with a variety of ‘spindle load’ measurements: quasi-static (e.g. vertical, lateral and circumferential stiffness), quasi-steady-state (e.g. pure lateral and longitudinal slip) and transient (e.g. cleat run) tests in well defined tire stand-alone test rigs measure the accumulated tire force acting on the wheel center. While some tests are designed to induce local deformations (e.g. vertical stiffness on cleats), no measurement of local reactions (e.g. sidewall displacement or rim strain) are performed in a standardized way - apart from footprint and contour tests. The level of detail in structural FEA tire models renders them unfeasible for most full vehicle applications due to the implied computational effort; however, dedicated tire stand-alone scenarios are well within reach of today's R&D IT infrastructures.

The tire plays a fundamental role in the generation of acoustically perceptible driving noise and vibrations inside the vehicle. An essential part of these vibrations is induced by the road excitation and transferred via the tire into the vehicle. There are two basic ways to study NVH behavior: Simulations in time and frequency domains. The system can be simulated using a transient simulation method with the disadvantage of high simulation and process turnaround times. Alternatively, a linearization around a stationary state is performed and solved in frequency domain with fast numerical schemes. Modelling the tire transfer behavior in frequency domain requires special attention to the rotation of the tire. This paper shows the approach taken by the authors to include the transfer behavior in the frequency range up to 250 Hz from geometric road excitations to resulting spindle forces in frequency domain. Special care has been used in the modelling of local road excitations.