Importance of tread inertia and damping on the tyre/road contact stiffness

Predicting tyre/road interaction processes like roughness excitation, stick-slip, stick-snap, wear and traction requires detailed information about the road surface, the tyre dynamics and the local deformation of the tread at the interface. Aspects of inertia and damping when the tread is locally deformed are often neglected in many existing tyre/road interaction models. The objective of this paper is to study how the dynamic features of the tread affect contact forces and contact stiffness during local deformation. This is done by simulating the detailed contact between an elastic layer and a rough road surface using a previously developed numerical time domain contact model. Road roughness on length scales smaller than the discretisation scale is included by the addition of nonlinear contact springs between each pair of contact elements. The dynamic case, with an elastic layer impulse response extending in time, is compared with the case where the corresponding quasi-static response is used. Results highlight the difficulty of estimating a constant contact stiffness as it increases during the indentation process between the elastic layer and the rough road surface. The stiffness-indentation relation additionally depends on how rapidly the contact develops; a faster process gives a stiffer contact. Material properties like loss factor and density also alter the contact development. This work implies that dynamic properties of the local tread deformation may be of importance when simulating contact details during normal tyre/road interaction conditions. There are however indications that the significant effect of damping could approximately be included as an increased stiffness in a quasi-static tread model

The contribution of air-pumping to tyre/road noise

It is generally accepted that there are at least two tyre/road noise generation mechanisms commonly referred to as tyre vibrations and air-pumping. While the modelling of tyre vibrations is rather mature, the modelling of air-pumping is still on a basic stage and unsatisfactory in many aspects. Applying the fact that tyre vibrations and air-pumping have different vehicle speed dependency allows for identifying the contribution from each mechanism in field measurements of tyre/road noise. This paper presents an analysis of controlled pass-by measurements and simulations with the tyre/road simulation model at Chalmers. Results show that air-pumping is a major contributor to tyre/road noise. The question arises which physical mechanisms are behind the air-pumping noise observed in measurements and simulations. The analysis indicates that tyre vibrations in the contact may lead to air-pumping noise. This suggestion deviates from generation mechanisms usually assumed in the air-pumping context

Dynamic contact stiffness and air-flow related source mechanisms in the tyre/road contact

Two aspect of phenomena occurring in, and in the vicinity of the contact patch formed by a tyre rolling on a road are here investigated: 1. A detailed numerical time domain contact model is used to evaluate approximations of the tread response that are commonly embraced in tyre/road interaction models. 2. A statistical approach is applied in the search to quantify the contribution from air-flow related source mechanisms to the total tyre/road noise.Effects of inertia and material damping when the tread is locally deformed are often neglected in many tyre/road interaction models. How the dynamic features of the tread affect contact forces and contact stiffness is here assess by simulating the detailed contact between an elastic layer and a rough road surface. The dynamic case, with an elastic layer impulse response extending in time, is compared with the case where the corresponding quasi static response is used. The results indicate that the significant effect of material damping may approximately be included as an increased stiffness in a quasi static tread model if not very detailed processes are to be predicted.There are at least two main tyre/road noise generation mechanisms: tyre vibrations and air-flow related source mechanisms (commonly referred to as air-pumping). This study investigates the importance of air-flow related noise sources by employing the fact that their vehicle speed dependence differs from the noise produced directly by tyre vibrations. Results show that air-flow related sources are significant contributors to measured tyre/road noise. A comparison with results from calculated rolling noise indicates that tyre vibrations in/close to the contact may lead to noise with air-flow characteristics

Dynamic contact stiffness and air-flow related source mechanisms in the tyre/road contact

Two aspect of phenomena occurring in, and in the vicinity of the contact patch formed by a tyre rolling on a road are here investigated: 1. A detailed numerical time domain contact model is used to evaluate approximations of the tread response that are commonly embraced in tyre/road interaction models. 2. A statistical approach is applied in the search to quantify the contribution from air-flow related source mechanisms to the total tyre/road noise.Effects of inertia and material damping when the tread is locally deformed are often neglected in many tyre/road interaction models. How the dynamic features of the tread affect contact forces and contact stiffness is here assess by simulating the detailed contact between an elastic layer and a rough road surface. The dynamic case, with an elastic layer impulse response extending in time, is compared with the case where the corresponding quasi static response is used. The results indicate that the significant effect of material damping may approximately be included as an increased stiffness in a quasi static tread model if not very detailed processes are to be predicted.There are at least two main tyre/road noise generation mechanisms: tyre vibrations and air-flow related source mechanisms (commonly referred to as air-pumping). This study investigates the importance of air-flow related noise sources by employing the fact that their vehicle speed dependence differs from the noise produced directly by tyre vibrations. Results show that air-flow related sources are significant contributors to measured tyre/road noise. A comparison with results from calculated rolling noise indicates that tyre vibrations in/close to the contact may lead to noise with air-flow characteristics

Contact stiffness in tyre/road noise modelling and speed dependencies of tyre/road noise generation mechanisms

Tools for simulating tyre/road noise are highly valuable in the efforts to limit the negative consequences of road traffic noise.A numerical tyre/road noise simulation tool was in this study used to investigate how the contact stiffness parameter affects the predicted tyre/road noise. It includes a contact model with contact springs that accounts for the effect of local small-scale tread deformation. Results showed that simulated noise was sensitive to the value of the spring stiffness, primarily as it affected the total contact force. A non-linear contact spring formulation resulted in a reduction of the high-frequency content in the contact forces and simulated noise.Aspects of small-scale tread dynamics were evaluated by simulating the detailed contact between an elastic layer and a rough road surface using a numerical time domain contact model including non-linear contact springs to account for small-scale roughness. Contact stiffness increased as the number of contact points grew as well as the deformation of their non-linear contact springs. The results imply that dynamic properties of the local tread deformation may be of importance when simulating contact details during normal tyre/road interaction conditions, but that effects of damping could, as a first approximation, be included as an increased stiffness in a quasi-static tread model.The speed dependency of measured and simulated tyre/road noise was analysed. A large part of the noise had a high speed exponent, traditionally connected with air-pumping. However, the results showed that tyre vibrations can generate noise with a speed exponent that verges on what is expected from air-pumping. Due to the overlap in the speed exponents of the main generation mechanisms, they cannot be distinguished through a speed exponent analysis.The most important contribution of this work is an increased understanding of how the contact spring formulation affects the simulated noise. The work has also provided insights into the speed dependency of tyre/road noise generation mechanisms

Evaluation of approximations used for the tread layer response and road surface roughness in numerical models of the tyre/road contact

The detailed behaviour at the interface between automotive tyres and roads is important in numerical contact models aiming at prediction of rolling resistance, traction, wear, excitation of vibrations, and noise generation. The detailed behaviour depends on the local dynamic response of the tread and the small-scale roughness of the road surface. For complete tyre-road interaction simulations predicting global vibrations, the tread layer has commonly been modelled using approximations such as a set of uncoupled linear springs or an elastic half-space. These computational efficient approximations have been introduced in an ad hoc manner and they have seldom been evaluated in detail. This paper evaluates these two simplified approaches by comparison to results from a detailed numerical model for a tread layer on a rigid backing that is pressed into a road surface. The detailed contact model is formulated in the time-domain and includes the effect of small-scale roughness by non-linear force-indentation functions between each pair of contact elements. The results show that the effect of the inertia in the tread layer is insignificant for typical contact conditions. The stiffness of the linear springs and the elastic half-space must be tuned to account for the actual coupling within the tread layer and the small-scale roughness of the road. The set of uncoupled linear springs can be tuned to closely follow the force-indentation relation of the detailed model. The elastic half-space can only be tuned for a specific indentation, force or contact stiffness, since its relation has a slightly different character. It is concluded that purely elastic models of the tread are relevant and that the set of uncoupled linear springs performs better than the elastic half-space. However, the tuning of the stiffness is not trivial without results from more elaborate models including the influence of local tread properties and small-scale surface roughness

Evaluation of approximations used for the tread layer response and road surface roughness in numerical models of the tyre/road contact

The detailed behaviour at the interface between automotive tyres and roads is important in numerical contact models aiming at prediction of rolling resistance, traction, wear, excitation of vibrations, and noise generation. The detailed behaviour depends on the local dynamic response of the tread and the small-scale roughness of the road surface. For complete tyre-road interaction simulations predicting global vibrations, the tread layer has commonly been modelled using approximations such as a set of uncoupled linear springs or an elastic half-space. These computational efficient approximations have been introduced in an ad hoc manner and they have seldom been evaluated in detail. This paper evaluates these two simplified approaches by comparison to results from a detailed numerical model for a tread layer on a rigid backing that is pressed into a road surface. The detailed contact model is formulated in the time-domain and includes the effect of small-scale roughness by non-linear force-indentation functions between each pair of contact elements. The results show that the effect of the inertia in the tread layer is insignificant for typical contact conditions. The stiffness of the linear springs and the elastic half-space must be tuned to account for the actual coupling within the tread layer and the small-scale roughness of the road. The set of uncoupled linear springs can be tuned to closely follow the force-indentation relation of the detailed model. The elastic half-space can only be tuned for a specific indentation, force or contact stiffness, since its relation has a slightly different character. It is concluded that purely elastic models of the tread are relevant and that the set of uncoupled linear springs performs better than the elastic half-space. However, the tuning of the stiffness is not trivial without results from more elaborate models including the influence of local tread properties and small-scale surface roughness

Influence of tread inertia during deformation using a detailed numerical tyre/road contact model

Predicting tyre/road interaction processes like stick-slip and stick-snap and their resulting tyre/road noise requires detailed information about the road surface and the dynamics of the tread at the interface. Inertial effects in the tread layer are neglected in many of the existing tyre/road interaction models without explicit justification. The objective of this paper is to investigate the potential importance of these effects for the case of a tread material indenting a rough road surface in the normal direction. A comprehensive numerical contact model operating in the time-domain which includes the effects of interfacial details is used for this purpose. Contact forces at the surface of the tread and at the interface between the tread and the belt are studied in the normal direction during the simulated loading. The inertial case, with a tread impulse response extending in time, is compared with the non-inertial case where the corresponding quasi-static response is used. Results show that the difference in contact force and contact stiffness between a quasi static and a dynamic simulation is small for loading rates that could be found in typical tyre/road contact conditions. Only for extremely high loading rates is there a significant difference. This work implies that inertial effects of the tread are negligible for the local tread response when simulating normal tyre/road contact situations

Influence of tread inertia during deformation using a detailed numerical tyre/road contact model

Predicting tyre/road interaction processes like stick-slip and stick-snap and their resulting tyre/road noise requires detailed information about the road surface and the dynamics of the tread at the interface. Inertial effects in the tread layer are neglected in many of the existing tyre/road interaction models without explicit justification. The objective of this paper is to investigate the potential importance of these effects for the case of a tread material indenting a rough road surface in the normal direction. A comprehensive numerical contact model operating in the time-domain which includes the effects of interfacial details is used for this purpose. Contact forces at the surface of the tread and at the interface between the tread and the belt are studied in the normal direction during the simulated loading. The inertial case, with a tread impulse response extending in time, is compared with the non-inertial case where the corresponding quasi-static response is used. Results show that the difference in contact force and contact stiffness between a quasi static and a dynamic simulation is small for loading rates that could be found in typical tyre/road contact conditions. Only for extremely high loading rates is there a significant difference. This work implies that inertial effects of the tread are negligible for the local tread response when simulating normal tyre/road contact situations