Andrew J. Day

Drum brake interface pressure distributions

A review of recent research work predicting contact and pressure distributions at the friction interface of drum brakes is presented. Previously published results are summarized and used, together with new results, to illustrate the effects of friction coefficient, lining compressibility and brake shoe stiffness, actuation force, lining/drum conformity, and wear, on brake performance. The results are discussed in the context of geometry and bulk deformation effects, and of macroscopic interface pressure distribution effects, and confirm the importance of interface pressure distribution in the performance and continued operation of drum brakes to required design levels.

The Dissipation of Frictional Energy from the Interface of an Annular Disc Brake

The performance of resin bonded composite friction materials in a particular brake design is strongly dependent upon the dissipation of frictional heat from the interface. This energy transformation has been studied using finite element techniques for a simulation of the braking friction process in an annular disc brake, which combines both brake performance and brake temperature analysis and avoids many of the assumptions necessary in conventional analyses. Negligible amounts of energy interchange, compared with the total kinetic energy dissipated, arise from chemical reactions within the friction material, but the formation of surface layers and interfacial wear products do have a significant effect upon heat transfer from the interface. Calculated temperature distributions over individual brake applications indicate that interface contact resistance leads to different temperatures at the surfaces of disc and lining so that heat partition between the two mating bodies cannot realistically be assumed constant under braking conditions. The distribution of frictional heat generation over the interface is dependent upon interface pressure distribution and is therefore also affected by material wear and thermal expansion. These effects are incorporated in the analysis, and calculated temperature, interface contact and pressure, and wear distributions are compared with observed and measured experimental results from an annular brake rig.

Sensor-fusion of hydraulic data for burst detection and location in a treated water distribution system

Abstract This paper presents research into analysis and data fusion for sensors measuring hydraulic parameters (flow and pressure) of the pipeline water flow in treated water distribution systems. An artificial neural network (ANN) based system is used on time series data produced by sensors to construct an empirical model for the prediction and classification of leaks. A rules based system performs a fusion on the ANNs’ outputs to produce an overall state classification for a set of zones. Results are presented using data from an experimental site in a distribution system of a UK water company in which bursts were simulated by hydrant flushing. The ANN system successfully detected events and a study of the pressure gradient across the zone provided a more precise location within the zone.

Thermal Effects and Pressure Distributions in Brakes

Heat generated at the sliding interface between the friction material and the mating surface of a friction brake is not uniformly distributed over the sliding surfaces but depends upon the local interface pressure. Many thermal problems associated with brake friction pairs, including performance variation (fade, speed sensitivity) and rotor damage (heat spotting and thermal cracking) can be analysed in terms of localized frictional heat generation as discussed here. This paper describes how the thermal effects of interface pressure distribution may be divided into bulk temperature effects, such as brake drum expansion and brake disc coning, and its macroscopic thermal effects, such as heat spotting, and suggests how the two are related through the process of thermoelastic instability. The results of analyses, using finite element methods, indicate that uniform friction interface pressure is very important in minimizing brake thermal problems. However, more basic research in the area of interface contact and pressure distribution, and frictional heat generation and dissipation, still remains to be done in order to understand fully the role played by each part of the friction pair in thermally related braking problems.

A knowledge based design methodology for manufacturing assembly lines

In assembly line design, the problem of balancing has received most attention from past researchers, and a number of algorithms have been devised for the analysis of single, multi- and mixed-product assembly lines [Int. J. Prod. Res. 27 (1989)637]. In many cases, such algorithms seek a solution for the particular situation, which is under consideration and therefore have very little flexibility for generic application to assembly line design. Real life practical design issues include stochastic operation times, parallel workstation requirements, feasibility for workstation combining, and parallel line implementations, all of which are features which are ignored in many analyses. This paper presents a Knowledge Based Design Methodology (KBDM) for automated and manual assembly lines, which can be applied equally well to single, multi- and mixed-product assembly lines with either deterministic operation times or stochastic operation times. The methodology starts from a suitable assembly system selection and thereafter decides suitable cycle times, parallel workstation requirements, and parallel line implementation for the type of assembly system being selected. An economical number of workstations are decided with the aid of workstation combining options depending upon the factual information provided. The end result is the detailed design of a manufacturing assembly line. A case study from a practical assembly line is presented to illustrate how the KBDM works.

COMBINED THERMAL AND MECHANICAL ANALYSIS OF DRUM BRAKES

The frictional heat generated during braking is included in the full analysis of a commercial vehicle drum brake, avoiding artificial heat partitioning by the use of a novel technique for the dynamic simulation of heat transfer at the friction interface. The effects of lining wear, empirically related to local values of surface temperature and pressure, together with thermo-elastic effects, are taken account of in the calculation of interface pressure distributions and consequent brake performance. Analyses have been completed using two-dimensional finite element meshes which model the combined assembly of brake shoes, linings and drum. These have been validated by comparisons between measured and calculated brake performance, and by observations of rubbing contact pattern.

A Finite Element Approach to Drum Brake Analysis

Although conventional methods of brake analysis are adequate for general design purposes they ignore shoe and drum distortion and so give inaccurate prediction of brake torque. Advanced designs require a more accurate technique such as the finite element method described. The method is adapted to deal with the case of a friction interface and uses a model of shoe and brake lining to determine drum distortion and also thermal effects. Material properties used in the model to represent the steel shoe and friction material are detailed. The work carried out also shows that different types of pressure distribution are compatible with each other. The sinusoidal pressure curve, the uniform distribution, the cubic and u-shaped pressure curves are all design aspects of the drum brake. Which form applies at any instant depends on flexural and thermal deflections as well as the nature of the interface contact. (TRRL)

Steering drift and wheel movement during braking: static and dynamic measurements

Abstract This paper reports on an experimental investigation into braking-related steering drift in motor vehicles, and follows on from a previous paper by the authors in which it was concluded that braking can cause changes in wheel alignment that in turn affect the toe-steer characteristics of each wheel and therefore the straight-line stability of the vehicle during braking. Changes in suspension geometry during braking, their magnitude and the relationships between the braking forces and the suspension geometry and compliance are further investigated in an experimental study of wheel movement arising from compliance in the front suspension and the steering system of a passenger car during braking. Using a kinematic and compliance (K&C) test rig, movement of the front wheels and the suspension subframe, together with corresponding changes in suspension and steering geometry under simulated braking conditions, have been measured and compared with dynamic measurements of the centre points of the front wheels. The results have enabled the causes and effects of steering drift during braking to be better understood in the design of front suspension systems for vehicle stability during braking.

Steering drift and wheel movement during braking: parameter sensitivity studies

Abstract In spite of the many significant improvements in car chassis design over the past two decades, steering drift during braking where the driver must apply a corrective steering torque in order to maintain course can still be experienced under certain conditions while driving. In the past, such drift, or ‘pull’, would have been attributed to side-to-side braking torque variation [1], but modern automotive friction brakes and friction materials are now able to provide braking torque with such high levels of consistency that side-to-side braking torque variation is no longer regarded as a cause of steering drift during braking. Consequently, other influences must be considered. This paper is the first of two papers to report on an experimental investigation into braking-related steering drift in motor vehicles. Parameters that might influence steering drift during braking include suspension compliance and steering offset, and these have been investigated to establish the sensitivity of steering drift to such parameters. The results indicate how wheel movement arising from compliance in the front suspension and steering system of a passenger car during braking can be responsible for steering drift during braking. Braking causes changes in wheel alignment which in turn affect the toe steer characteristics of each wheel and therefore the straight-line stability during braking. It is concluded that a robust design of suspension is possible in which side-to-side variation in toe steer is not affected by changes in suspension geometry during braking, and that the magnitude of these changes and the relationships between the braking forces and the suspension geometry and compliance require further investigation, which will be presented in the second paper of the two.

Noise and Vibration Analysis of an S-Cam Drum Brake

Modal analyses of an S-cam drum brake assembly, using finite element analysis, are presented. A friction interface contact pressure-dependent model for the coupling between the lined brake shoe assembly and the brake drum is described. Using this model, natural modes and frequencies are predicted which compare well with measured data for the brake assembly. A parametric study of brake design and performance variables is presented which predicts the noise propensity of the brake design based on the binary flutter model. Good agreement with measured brake noise and trends, experience and other published work on S-cam brake noise is shown.