THE EFFECTS OF AGE ON THE STIFFNESS PROPERTIES OF A SUV TYRE

The pneumatic tyre is a difficult component to model accurately in all natural vehicle environments. Proposed tyre models should be validated with real test data collected on the specific tyre being modelled under the specified application conditions. The rubber in a tyre oxidises with the oxygen in the air used to inflate it as well as the oxygen in the air surrounding it. The effects of a tyre‘s age on the performance characteristics of a tyre such as vertical, longitudinal and lateral stiffness, are not well researched. In this study, the effects of a tyre’s age on stiffness parameters were determined. A tyre was artifically aged and tested periodically during the aging process. Simplified methods of quantifying the age of the tyre were investigated and used to update a validated FTire model. The results indicate that the vertical and longitudinal stiffnesses of the tyre have convincing dependencies on the age of the tyre. The use of the Shore A hardness of the tyre tread to update the FTire model was found to have good potential in accounting for the age of the tyre

MODELLING AND VALIDATION OF A TESTING TRAILER FOR ABS AND TYRE INTERACTION ON ROUGH TERRAIN

The main purpose of a vehicle anti-lock braking system (ABS) is to prevent the tyres from locking-up in order to brake efficiently whilst maintaining steering control and stability. Sport utility vehicles (SUV) are designed to drive on various roads under different driving conditions, making it challenging to identify optimal operating conditions for ABS algorithms to be implemented. This paper describes the development and modelling of a testing trailer that is designed to benefit the research of a SUV tyre operating in ABS braking modes on non-deformable rough terrain. The test trailer can be to investigate the variation of tyre contact forces and vibration characteristics influenced by ABS braking and rough terrain excitation. Undesirable fluctuations of wheel speed, normal force and braking moments make measurements more complicated and limits the performance of active safety systems. A trailer made from a Land Rover Defender chassis is used with standard ABS components and is implemented with a Bosch ABS algorithm for experimental tests. In addition to the ABS system the necessary measuring equipment such as Wheel Force Transducers (WFT), accelerometers, brake pressure transducers, GPS and vehicle speed measurement instrumentation is used. An Adams model of the trailer in co-simulation with ABS and test control in MATLAB/Simulink is created to validate the model. The centre of gravity position and inertia characteristics of the trailer are determined through experimental testing. A validated FTire tyre model, suitable for off-road conditions, is incorporated to accurately resemble the specific tyre used during tests. The validated Adams model and test trailer will enable further development of ABS algorithms including the identification of key parameters through which ABS braking can be optimised for various roads as well as optimizing interaction with semi-active suspension systems

Parameterization and modelling of large off-road tyres for ride analyses: Part 2 – Parameterization and validation of tyre models

Every mathematical model used in a simulation is an idealization and simplification of reality. Vehicle dynamic simulations that go beyond the fundamental investigations require complex multi-body simulation models. The tyre–road interaction presents one of the biggest challenges in creating an accurate vehicle model. Many tyre models have been proposed and developed but proper validation studies are less accessible. These models were mostly developed and validated for passenger car tyres for application on relatively smooth roads. The improvement of ride comfort, safety and structural integrity of large off-road vehicles, over rough terrain, has become more significant in the development process of heavy vehicles. This paper investigates whether existing tyre models can be used to accurately describe the vertical behaviour of large off road tyres while driving over uneven terrain. [1] Presented an extensive set of experimentally determined parameterization and validation data for a large off-road tyre. Both laboratory and field test are performed for various loads, inflation pressures and terrain inputs. The parameterization process of four tyre models or contact models are discussed in detail. The parameterized models are then validated against test results on various hard but rough off-road terrain and the results are discussed.http://www.elsevier.com/locate/jterrahb201

The dynamic rolling radius of a pneumatic tyre on hard terrains

Extensive research was done on the rolling radius of a tyre from the 1960s to the 1980s, specifically looking at the tractive performance of tractors and agricultural vehicles. The research was limited to investigating slip conditions at low vehicle speed where it was safe to assume that the rolling radius is static or quasi-static. This paper revisits some of these investigations, and looks at the validity of the static or quasi-static rolling radius assumption on hard, high friction and uneven surfaces at higher speeds. The aim is to establish whether the rolling radius defined under static conditions can be used to estimate tyre contact patch velocity, a state needed to determine longitudinal tyre slip. Longitudinal tyre slip plays a crucial role in the performance of advanced driver assist systems. It is known that these systems' performance decreases on rough roads when the static rolling radius assumption may become inaccurate.http://www.inderscience.com/jhome.php?jcode=IJVSMTMechanical and Aeronautical Engineerin

Longitudinal vehicle dynamics control for improved vehicle safety

The aim is to investigate the improvements in vehicle safety that can be achieved by limiting the vehicle speed based on GPS path information. The control strategy is aimed at reducing vehicle speed before a potentially dangerous situation is reached, in contrast with widely used stability control systems that only react once loss of control by the driver is imminent. An MSC.ADAMS/View simulation model of an off-road test vehicle was developed and validated experimentally. A longitudinal speed control system was developed by generating a reference speed based on the path information. This reference speed was formulated by taking into account the vehicle’s limits due to lateral acceleration, combined lateral and longitudinal acceleration and the vehicle’s performance capabilities. The model was used to evaluate the performance of the control system on various tracks. The control system was implemented on the test vehicle and the performance was evaluated by conducting field tests. Results of the field tests indicated that the control system limited the acceleration vector of the vehicle’s centre of gravity to prescribed limits, as predicted by the simulations, thereby decreasing the possibility of accidents caused by rollover or loss of directional control due to entering curves at inappropriately high speeds.http://www.elsevier.com/locate/jterrahb201

Tire Lateral Vibration Considerations in Vehicle-Based Tire Testing

Vehicle-based tire testing can potentially make it easier to reparametrize tire models for different road surfaces. A passenger car equipped with external sensors was used to measure all input and output signals of the standard tire interface during a ramp steer maneuver at constant velocity. In these measurements, large lateral force vibrations are observed for slip angles above the lateral peak force with clear peaks in the frequency spectrum of the signal at 50 Hz and at multiples of this frequency. These vibrations can lower the average lateral force generated by the tires, and it is therefore important to understand which external factors influence these vibrations. Hence, when using tire models that do not capture these effects, the operating conditions during the testing are important for the accuracy of the tire model in a given maneuver. An Ftire model parameterization of tires used in vehicle-based tire testing is used to investigate these vibrations. A simple suspension model is used together with the tire model to conceptually model the effects of the suspension on the vibrations. The sensitivity of these vibrations to different operating conditions is also investigated together with the influence of the testing procedure and testing equipment (i.e., vehicle and sensors) on the lateral tire force vibrations. Note that the study does not attempt to explain the root cause of these vibrations. The simulation results show that these vibrations can lower the average lateral force generated by the tire for the same operating conditions. The results imply that it is important to consider the lateral tire force vibrations when parameterizing tire models, which does not model these vibrations. Furthermore, the vehicle suspension and operating conditions will change the amplitude of these vibrations and must therefore also be considered in maneuvers in which these vibrations occur

Parameterisation and modelling of large off-road tyres for on-road handling analyses

Very few off-road vehicles are used exclusively under off-road conditions. Good off-road mobility does however dictate large high aspect ratio tyres, with aggressive tread, soft suspension for good ride comfort as well as other vehicle parameters including large ground clearance and the related high centre of mass. This often results in less-than-satisfactory handling and high rollover propensity when operating on hard terrains. In order to simulate vehicle handling and roll over propensities, tyre characteristics in the form of side-force versus slip-angle curves, as well as suitable tyre models are required. For large offroad tyres these characteristics are not readily available. Tyre manufacturers either do not have these characteristics, or do not openly publish them. Similarly, the majority of tyre models have been developed and validated for passenger car tyres and their applicability to large tyres are unknown. The purpose of this study is to measure side-force versus slip-angle characteristics for a Michelin 16.00R20 XZL tyre - typically used on off-road trucks. The data is used to parameterise a Fiala, UA (University of Arizona), Pacejka89 (ADAMS View implementation) and FTire model. Simulation results are compared to both steady state and dynamic handling test results to determine the accuracy of these models.http://www.elsevier.com/locate/jterra2016-10-31hb201

Improving the braking performance of a vehicle with ABS and a semi-active suspension system on a rough road

Rapid advances have been made in the field of vehicle dynamics in terms of improving the ride, handling and safety using actuators and control systems. Optimising a vehicle’s ride comfort or handling has led to the development of semi-active suspension systems. Anti-lock braking systems (ABS) have resulted in significant improvements in vehicle braking whilst maintaining directional control over the vehicle. These advances have improved vehicle and occupant safety in general, but there are often some trade-offs. For example, the stopping distance of a vehicle fitted with ABS on an undulating road is significantly increased compared to braking without ABS. This has severe implications, especially in the off-road vehicle industry. The effects of spring and damper characteristics on the braking performance of a sports-utility-vehicle (SUV) on hard rough terrain are investigated. The approach is simulation based, using an experimentally validated full vehicle model of the SUV, built in Adams in co-simulation with MATLAB and Simulink. The simulations were performed on measured road profiles of a Belgian paving and parallel corrugations (or a washboard road). The results indicate that the suspension system has a significant impact on the braking performance, resulting in differences in stopping distances of up to 9 m.The National Research Foundation (DAAD-NRF)http://www.elsevier.com/locate/jterrahj201

Parameterization and modelling of large off-road tyres for ride analyses: Part 1 – Obtaining parameterization data

Multi-body vehicle dynamic simulations play a significant role in the design and development process of off-road vehicles. These simulations require tyre models to describe the forces and moments, which are generated in the tyre-road contact patch. All external forces acting on the vehicle are either generated in the tyre–road interface or are due to aerodynamic effects, which can be neglected at typical off-road driving speeds. The accuracy of the tyre model describing the forces in the tyre–road interface is thus of exceptional importance. The parameterization of most tyre models relies on some experimental test data that is used to extract the necessary information to fit model parameters. Acquiring the test data, with sufficient accuracy, is often the biggest challenge in the parameterization process. Published data for large off-road tyres is virtually non-existent. This paper describes different methods to acquire the required parameterization data. Experimental measurements are conducted on a 16.00R20 Michelin XZL tyre. Laboratory tests, as well as field tests, over discrete obstacles and uneven hard surfaces were conducted. The paper presents an extensive set of parameterization and validation test data on a large off-road tyre that can be used by researchers to develop and validate tyre models.http://www.elsevier.com/locate/jterrahb201