A Universal Approach to Tire Forces Estimation by Accelerometer-Based Intelligent Tire: Analytical Model and Experimental Validation

ABSTRACT Efforts to improve the performance and safety of vehicles include placing active sensing components (e.g., embedded microsensors) within tires result in intelligent tires. One application of intelligent tire is tire force estimation based on accelerometers. However, its development is limited due to the difficulty of relating the tire force to kinematical information by model-based theory. In this manuscript, a universal approach to tire forces estimation by the accelerometer-based intelligent tire is formulated and experimentally validated. First, a microelectromechanical system accelerometer-based intelligent tire prototype is established with the function of on-board monitoring of tire forces. Then, a theoretical rolling kinematics model is proposed for illustrating the mechanisms of acceleration fields, resulting from the coupling effect of rigid body motion and elastic deformation. An analytical model is formulated to estimate the vertical force in real time. Furthermore, the beam model is adopted to describe lateral deformations of the tire belt, directly linking lateral acceleration and lateral force. Finally, the lateral force can be estimated by lateral acceleration and vertical force already estimated. Based on a universal analytical model, the lateral force estimation method realizes high accuracy under different circumstances, even with unified coefficients, by clarifying and eliminating the influence of ply steer. A field test and two bench experiments have been conducted to fully validate the developed model. It can be concluded that the theoretical-analysis-based estimation model realizes an encouraging tire force estimation application with an intelligent tire hardware system.

Investigation of the Influence of Snow Track Density on Tire Tread Block Traction by Experiments and Discrete Element Method Simulation

ABSTRACT While in nature, snow properties change from day to day or even minute by minute, one of the great advantages of lab tests is the stability and reproducibility of testing conditions. In our labs at the Institute of Dynamics and Vibration Research, Leibniz Universität Hannover, we currently run three test rigs that are able to conduct tests with tire tread blocks on snow and ice tracks [1,2]: High-Speed Linear Tester (HiLiTe) [3], Portable Friction Tester (PFT), and Reproducible Tread Block Mechanics in Lab (RepTiL). In the past years, we have run a project on the influence of snow track properties on friction and traction test results with those test rigs. In this article, we will present a first excerpt of the results concentrating on the RepTiL test rig. Because this rig reproduces the movement of rolling tire tread blocks [2], we executed a test campaign with special samples for the analysis of snow friction mechanics. We evaluated penetration into the snow, maximum longitudinal force level, and longitudinal force gradient. On the other hand, we varied the snow density while preparing our tracks to assess the influence of the snow track density on the friction mechanics. In parallel, we have accompanied our experiments with discrete element method simulations to better visualize and understand the physics behind the interaction between snow and samples. The simulation shows the distribution of induced stress within the snow tracks and resulting movement of snow particles. Hypotheses for the explanation of the friction behavior in the experiments were confirmed. Both tests and simulations showed, with good agreement, a strong influence of snow density and sample geometry.

Theoretical Tire Model for Wear Progress of Tires with Tread Pattern Considering Two-Dimensional Contact Patch

ABSTRACT A new theoretical tire model for the wear progress of tires with tread block pattern is developed considering a two-dimensional contact patch. In the model, the wear energy is calculated from the shear force and pressure distribution in a two-dimensional contact patch that are changed with not only shear forces in a contact patch but also with the wear and irregular wear of tires. The fore–aft shear force in a contact patch consists of six mechanisms related to slip ratio, camber, contact between a tire and a road, barrel deformation of a loaded block, rolling resistance, and a rolling tire with rounded crown shape, whereas the lateral shear force consists of three mechanisms related to slip angle/camber, contact of a tire with rounded crown shape, and barrel deformation of a loaded block. The heel and toe irregular wear and the progress of irregular wear under pure slip condition qualitatively agree with the conventional knowledge of tire engineers. The expected wear energy is introduced to predict the wear progress under combined slip condition in the wear course. Using the vehicle dynamics to predict the tire force history, a histogram of external forces is obtained by transforming from it. Calculating wear energies by changing slip angle and slip ratio, the relation between external forces and the wear energy is expressed as the response surface. Multiplying the wear energy by the histogram, the expected wear energy distribution in a block is calculated. Assuming that the worn depth is proportional to the expected wear energy, the wear progress is predicted.

Self-Excited Full-Vehicle Oscillations Caused by Tire–Road Interaction: Virtual and Real-World Experimental Investigation

ABSTRACT In this article, self-excited full-vehicle oscillations (power-hops) are introduced. Initially, results of full-vehicle measurements are shown followed by the presentation of a specially build test rig (longitudinal dynamics test rig). Subsequently, these oscillations are investigated by using simulation-based tools within multibody simulation–related full-vehicle modeling. Tire–road interaction is evaluated in this process either by characteristic curves or by a proprietary quasistatic tire model that returns overall tangential forces by evaluating the state of every discretized element within the footprint area.

Comprehensive Grounding Performance Evaluation of Tires Based on the Analytic Hierarchy Process

ABSTRACT The contact patch between tire and road surface has a direct impact on tire grounding performance. Acquiring tire grounding performance either by testing or simulation is not only time intensive but comes at a high cost. This paper proposes an effective means of evaluating tire grounding performance based on the tire-ground contact pressure distribution. This paper adopts fifteen characteristics to describe the tire-ground contact patch in which twelve structural schemes were designed for a certain type of tire. By using the simulation test method, the grounding performance characteristics such as grip performance, rolling resistance, wear performance, and the tire footprint characteristics were obtained. Correlation analysis was used to explore the relationship between tire grounding performance and footprint characteristics. Based on the correlation analysis and expert judgement, the analytic hierarchy process (AHP) model for comprehensive grounding performance evaluation of a tire was constructed. Then judgment matrix of the AHP model was established, and the consistency or otherwise of the judgment matrix was verified. The model was then used to evaluate and predict the four design schemes of tires. The evaluation results were in good agreement with the simulation test results, which shows that the construction method of the tire comprehensive grounding performance evaluation system proposed in this paper is practical. It is also evident that grounding performance evaluation of a tire based on the tire footprint is feasible.

Wheel Speed Effect on Transient Lateral Force and Its Characterization by Ramp-Step Steer Test Method

ABSTRACT The concept “relaxation length” serves as one of several ways to characterize the transient lateral response for a rolling tire. Most test methods developed to identify relaxation length tightly link to Pacejka's single-contact-point linear transient model. Its underlying assumption is that the traveled distance during the transition interval is always a constant regardless of the wheels' linear rolling speed. The current research provides physical data against this strong assumption. The data is acquired through a newly-developed test method named the “ramp-step steer method”. The ramp-step steer method features a nonstop, high rolling speed, and fast-changing slip angle procedure that cannot be fulfilled by the conventional “start-stop-resume” step steer method. Thanks to the high dynamic capability of the equipment in GCAPS Corp., the proposed test method becomes feasible. A novel data postprocessing scheme accompanies the test method as well. The ramp-step steer method is independent of any specific models and replicates the scenario of a rolling tire subjected to a sudden slip angle change from on-vehicle to an indoor environment. The wheel speed effect on the tires' transient lateral response is reflected through a proposed quantity, Ly, which is a more general descriptor and can downscale to relaxation length under specific circumstances. Ly itself does not associate with any model, so the remaining study explains the speed effect through an updated model. The present research aims to provide a better way of characterizing tires' lateral transient behavior and is not an alternative to identify the key parameter “relaxation length” in Pacejka's model. Another contribution of the research is categorizing and separating the hierarchy of various transient tire models.

Virtual Generation of Flexible Ring Tire Models Using Finite Element Analysis: Application to Dynamic Cleat Simulations

ABSTRACT The main goal of this work is to investigate if finite element (FE) model techniques with special applications of material properties accurately estimate the parameters of flexible ring tire models. It is known that commercially available ring tire models are used as standard tools for simulating and predicting vehicle ride and durability, e.g., rigid ring MF-Swift [1] and flexible ring Flexible Structure Tire Model (FTire) [2–5]. Despite wide acceptance of these models, difficulty in model parameterization limits their application in the vehicle development process. For estimation of tire dynamic stiffnesses and inertial properties, rolling tire cleat test data are required for most ring models. Although this test method produces reliable models, the parameterization is not time and cost effective as it requires measurement and processing of cleat data at multiple speeds and loads and is prone to test rig dynamic compliance variations. This approach also limits the ability to evaluate tire performances during the virtual stages of tire design. The objective of this work is to develop virtual data using time and cost effective FE-based methods towards the estimation of flexible ring model parameters rather than relying on measured cleat data on physical tires. Commercial product ABAQUS is used for the FE simulations and FTire for tire flexible ring model simulations. Two FE modeling techniques are utilized in this work. Firstly, it is shown that the dynamic stiffness of a rolling tire can be estimated from a steady state eigensolution modal analysis of a static tire using material properties characterized for a rolling tire. Secondly, a method of separation of the sidewall from the tread band is developed for the estimation of mass and bending properties of the tread band. The estimated stiffnesses, inertias, and dimensions from the FE model results are converted into FTire model parameters. Finally, to validate the virtually generated FTire model, simulated dynamic cleat data response trends at multiple inflation pressures and velocities are compared with measurements. The virtual FE based techniques presented in this work can be applied to other ring based models as well.

Research on the Contradiction Mechanism of Tire Rolling Resistance and Grip Performance

ABSTRACT In order to clarify the contradictory mechanism between tire rolling resistance and grip performance, 10 205/55 R16 radial tires with different tread patterns were selected as the research objects. Based on digital image correlation method, the pressure and deformation distribution in the contact area of test tires were obtained and the relevant grounding parameters were extracted. The partial least square regression (PLSR) method was used to establish the relationship between the identified grounding parameters and tire performance indicators. Using the bootstrap resampling method, the significance test of the PLSR coefficients were carried out, and the grounding characteristic parameters with significant explanatory effect on the performances were selected, identifying the main function area for the two performances. The results show that in order to improve the grip performance of the tire, it is necessary to reduce the transverse tensile strain of the tread in the contact area and increase the longitudinal tensile strain of the tread; but, with the increase of the longitudinal tensile strain, the rolling resistance of the tire will also increase, which leads to the contradiction between tire rolling resistance and grip performance.