Transient analysis of tyre friction generation using a brush model with interconnected viscoelastic bristles

An analysis of the mechanism of tyre contact force generation under transient conditions is presented. For this purpose, two different versions of a brush model are used, both with inertial and viscoelastic properties. The first model consists of independent bristles, while the second, with a more realistic scenario, introduces viscoelastic circumferential connections between the sequential bristles, which affect the lateral degrees of freedom. Friction between the tyre and the ground follows an experimentally verified stick-slip law. For the model with independent bristles, the state of each bristle at any instant of time depends only on the state of the same bristle at a previous time step. In the second model, the instantaneous state depends on the state of the same bristle at the preceding time step, as well as on the state of the two adjacent bristles at the same time. Simulation results reveal the differences between the two models and most importantly show how transient friction force generation may differ substantially from steady state predictions. The findings suggest that transient tyre behaviour should not be attributed solely to the contributions of the flexible belt and carcass. On the contrary, the observed transience in the neighbourhood of the contact patch should also be taken into account

Tribology of the ring–bore conjunction subject to a mixed regime of lubrication

This paper provides a detailed analysis of the compression ring–bore/liner conjunction. The analysis includes ring–bore conformability and global in-plane deformation of ring fitted in situ. The analysis for fitted ring in an out-of-round bore shows very good agreement with precise measurements, using a coordinate measuring machine. The analysis also includes the lubricated conjunction under a transient regime of lubrication, taking into account combined elastohydrodynamics and asperity interactions. The transient nature of the tribological conjunction has been demonstrated, particularly the prevalent mixed/boundary regime of lubrication at the top and bottom dead centres. The analysis is applied to a high performance motorbike engine subjected to very high impact loads and engine speeds of the order of 13 000 r/min. Furthermore, the predictions of the model show good conformance to the measurements of friction reported by other research workers

Investigation of steady-state tyre force and moment generation under combined longitudinal and lateral slip conditions

The paper provides an insight into the contact mechanical behaviour of pneumatic tyres in a wide range of steady-state operating conditions. Tyre forces and self-aligning moment generation during steady-state manoeuvres are studied in some depth. For this purpose, two different versions of a dynamic model of a tyre are developed. The simplest version consists of a one-dimensional series of bristles distributed on the tyre periphery. The bristles incorporate anisotropic stiffness and damping in the lateral and longitudinal directions, while the distributed tread mass is also taken into account. The vertical pressure distribution along the contact patch is assumed to be parabolic and the length of the contact area is assumed to be known apriori. The friction forces developed on the contact patch follow a stick-slip friction law. The second version of the tyre model improves the potential of the simple model by introducing radial and tangential stiffness and damping, as well as a Kelvin element for rubber behaviour in the simulation of the impact on the leading edge of the contact area. The Kelvin model closely conforms to the semi-infinite incompressible nature of rubber. The tyre models show effective reproduction of measured longitudinal and lateral forces, as well as the self-aligning moment, under pure side-slip, pure longitudinal slip and combined slip situations. The generated curves show qualitative concordance with the results obtained experimentally, or by semi-empirical models such as the Pacejka’s Magic Formula. In addition, the tyre models seem to be capable of reproducing the generated contact pressure profiles and the shape of the observed variations in tyre forces between side-slipping, braking and traction diagrams. An investigation of these three situations reveals the different mechanisms that result in the different shapes of the diagrams. Finally, a study is carried out for tyre behaviour at very high speeds, which indicates deviations from the results of traditional investigations

Combined bounce, pitch, and roll dynamics of vehicles negotiating single speed bump events

This paper investigates vehicle dynamic response for the increasingly common manoeuvre over single speed bumps, which is a non-trivial complex motion. One major aim of the study is to investigate the effect of the anti-roll bar upon vehicle body dynamics, while negotiating such traffic calming features. Numerical predictions are made with an intermediate vehicle model, whose results conform well to the actual vehicle tests. These results seem to suggest that events caused by truncated speed bumps can have implications for design of anti-roll bars from a ride comfort viewpoint, over and above the usual requirements dictated by safe vehicle handling

A framework for the characterization of the transient handling responses of non-linear vehicles

The paper attempts to provide an integrated framework for the objective assessment of the transient handling responses of non-linear vehicles. The ultimate aim of the proposed framework is the characterization of such responses as neutral or under/over-steering. A new methodology is employed, which has previously been applied for the classification of the transient response of linear vehicles. The success of the proposed method is judged based on its robustness, the consistency of the results, and their practical implications. Furthermore, the results are compared with the findings of traditional approaches for the characterization of the steady-state and transient handling behaviour. The corresponding discussion reveals the agreement between the approaches, but also highlights the slightly different definition of the neutrally steering vehicle, as perceived by the proposed method

A multi-body dynamics approach for the study of critical handling manoeuvres on surfaces with uneven friction

The study of the dynamic behaviour of vehicles using computer simulation has been one of the major areas of research for many years. Based on the application area, the models used for performing these studies vary greatly in their capability, complexity and amount of data required. The multi-body approach is most preferred when it comes to iterative design optimization, whereas relatively simple models are mostly used for studying basic handling characteristics and vehicle stability. However, for studies involving critical handling manoeuvres, it is imperative to include certain amount of detail in the vehicle model, which accounts for the influence of suspension geometry and tyre characteristics on handling behaviour. The aim of the present research is to develop a vehicle model, based on Newton-Euler formulation of equations, incorporating sufficient degrees of freedom and adequate non linear characteristics for the realistic simulation of severe handling manoeuvres. The model is verified against experimental vehicle data and is finally used for the investigation of critical handling manoeuvres on surfaces with uneven friction. During this procedure, the tendency of the vehicle to rollover is assessed, together with other dynamic outputs such as yaw velocity and lateral acceleration

Influence of anti-dive and anti-squat geometry in combined vehicle bounce and pitch dynamics

The paper presents a six-degree-of-freedom (6-DOF) multi-body vehicle model, including realistic representation of suspension kinematics. The suspension system comprises anti-squat and anti-dive element. The vehicle model is employed to study the effect of these features upon combined bounce and pitch plane dynamics of the vehicle, when subjected to bump riding events. The investigations are concerned with a real vehicle and the numerical predictions show reasonable agreement with measurements obtained on an instrumented vehicle under the same manoeurves

Assessment of friction from compression ring conjunction of a high-performance internal combustion engine: a combined numerical and experimental study

The paper presents direct measurement of in-cylinder friction from a single cylinder motocross race engine under motored conditions and compares the same with a new analytical predictive method. These conditions are encountered in piston-cylinder system with the application of cylinder deactivation (CDA) technology, which is a growing trend. The analytical method takes into account the various regions within instantaneous contact of compression ring-cylinder liner, including lubricant film rupture, cavitation zone and the subsequent lubricant film reformation. The analysis also includes the effect of boundary friction and lubricant rheology. The predictions and direct measurements of cyclic friction show good agreement and indicate dominance of viscous friction under the investigated engine running conditions. In particular, it is shown that the compression ring contribution to in-cycle friction is most pronounced in the region of high cylinder pressures because of combined Poiseuille friction and some boundary solid interactions. The combined experimental-analytical approach has not hitherto been reported in literatur

Influence of tyre transience on anti-lock braking

Transient tyre characteristics can have significant influence in vehicle handling, particularly in anti-lock braking system (ABS), which involves wheel speed oscillations as a result of rapid changes in wheel brake pressure. Hitherto, ABS studies have been conducted mostly with straight-line motion. Relatively simple vehicle models have been used which cannot capture the interactions between non-linear handling dynamics and tyre behaviour. This article takes such interactions into account, using a non-linear 14-degrees-of-freedom vehicle model in combination with three different single-point contact tyre models with transient characteristics. They include a stretched-string-based model, a modified stretched-string model, and a contact mass model. The particularly demanding situation of combined cornering/ABS braking is investigated. It is shown that although all tyre models are of similar bandwidth (maximum frequency ≈ 15 Hz), the simple string tyre model fails to cope with the non-linearities involved in combined braking/cornering and predicts greater braking distances than the two more enhanced tyre models

In-cylinder friction reduction using a surface finish optimization technique

The paper describes the importance of reducing frictional losses in internal combustion (IC) engines, thereby improving engine efficiency. One of the main sources contributing significantly to engine friction is the interaction between the piston compression and oil rings and the cylinder bore/liner. Improving the tribological performance in these conjunctions has the greatest potential for performance improvement in the IC engine. Traditionally, the approaches used to tackle this problem have relied heavily on empirical engineering judgement. These have resulted in many inconclusive studies, involving a large number of alternatives, including the introduction of cylinder liners with surface modification work and/or with special coatings. This paper highlights a fundamental investigation of surface modification and coating and its impact on frictional performance. The study combines numerical and experimental approaches. Very good agreement is found between the conclusions of numerical predictions and those of engine test bed work