M Tirovic

Analysis of automotive disc brake cooling characteristics

Abstract The aim of this investigation was to study automotive disc brake cooling characteristics experimentally using a specially developed spin rig and numerically using finite element (FE) and computational fluid dynamics (CFD) methods. All three modes of heat transfer (conduction, convection and radiation) have been analysed along with the design features of the brake assembly and their interfaces. The spin rig proved to be very valuable equipment; experiments enabled the determination of the thermal contact resistance between the disc and wheel carrier. The analyses demonstrated the sensitivity of this mode of heat transfer to clamping pressure. For convective cooling, heat transfer coefficients were measured and very similar results were obtained from spin rig experiments and CFD analyses. The nature of radiative heat dissipation implies substantial e ects at high temperatures. The results indicate substantial change of emissivity throughout the brake application. The influence of brake cooling parameters on the disc temperature has been investigated by FE modelling of a long drag brake application. The thermal power dissipated during the drag brake application has been analysed to reveal the contribution of each mode of heat transfer.

Interface pressure distributions and thermal contact resistance of a bolted joint

The paper studies interface pressure distributions and thermal contact resistance (TCR) of a large automotive bolted joint. The research was initiated by the need to determine accurately conductive heat dissipation from a commercial vehicle disc brake. The main area of interest was the conduction between the grey cast iron disc and the spheroidal graphite cast iron wheel carrier. The bolt clamp forces and interface pressure distributions were investigated theoretically and experimentally. Finite-element analyses and pressure-sensitive paper experiments provided very similar interface pressure distributions. TCR change with interface pressure was studied experimentally, by conducting numerous temperature measurements. The derived linear relationship is of generic nature, enabling the calculation of the TCR for a variety of engineering bolted joints, over a wide range of interface pressures.

Design and development of an elastomer-based pneumatic seal using finite element analysis:

Abstract To create a dynamic seal where sealing action takes place between surfaces in sliding contact, a variety of different shaped seals can be used. One such example is the lobed ‘O’ ring. This paper presents details of the experimental and analytical procedures used in order to develop a lobed seal design. To develop adequate and productive procedures, finite element models were created and non-linear analysis of an existing seal design was conducted in order to build further knowledge and understanding of the seals performance characteristics. Experimental procedures have been developed to confirm these findings. Results obtained from the finite element analyses (FEAs) provided a very favourable comparison with empirical data and procedures developed were used to devise a new higher-performance seal. Key areas of improvement were reduced frictional forces, increased seal stability and higher operating pressures and temperatures. An irradiated polymer was used for the existing and new seal designs. This meant that manufacturing methods, valve body and spool dimensions were unchanged (making both seal designs interchangeable), but the potential of extending the temperature range was limited. The new seal design achieved all design objectives and procedures developed demonstrated that FEA is a very powerful tool in designing high-performance seals in a short time and at low cost.

Understanding and improving the convective cooling of brake discs with radial vanes

Abstract Detailed computational fluid dynamics (CFD) analyses of airflow and convective heat dissipation from a standard disc with radial vanes gave vital information regarding its weak points. Heat transfer from vanes is found to be particularly non-uniform, offering the largest scope for increasing local and average values of the coefficient of convective heat dissipation. A relatively simple modification — installation of an additional small vane (per channel, between the existing vanes) — demonstrated the ability to increase convective cooling from the ventilation channels. The radial position of these additional vanes was altered from disc ID towards OD, and best results were obtained with the vanes placed at the channel outlets (OD). An improvement in the total convective cooling (product of the average convective heat transfer coefficient and the entire disc wetted area) of nearly 14 per cent was achieved. In spite of better cooling, the new design has lower mass (air) flow when compared with the baseline design. The results are also presented in the form of Nusselt numbers, enabling their wider use. Conducted validation provided strong confidence in the accuracy of the results when searching for new solutions.

A low cost, accurate instrument to measure the moisture content of building envelopes in situ: a modelling study

This paper argues that there is a pressing need for a suitable instrument capable of insitu moisture measurements in building envelopes. Techniques do exist for such moisture measurement but all exhibit deficiencies in at least one critical area. A thermal dual-probe is investigated as a candidate for an appropriate instrument. As part of an ongoing study, two modelling approaches to investigate this issue are described. Firstly, the use of a one-dimensional heat and moisture transfer model to investigate the impact of the instrument on any moisture movement within a sample is described. Secondly, the development and testing of two and three-dimensional finite element (FE) models is detailed and initial evidence provided that there are no major barriers to the design of a successful dual-probe instrument for use in a range of building fabrics. It appears that the dual probe approach is indeed applicable to moisture measurements in typical building fabrics. A proven FE model is now available and this model will be used to optimize the design of the probe. Future papers will report on the optimization, building and testing of the instrument.

Structural analysis of a commercial vehicle disc brake caliper

Disc brake calipers are subjected to significant mechanical loading, with design requirements being particularly stringent with respect to the stresses, the deflections, the installation envelope, the noise, vibration, and harshness, and the thermal aspects. Modern finite element (FE) techniques can successfully model caliper assemblies; however, the limitations in predicting the caliper behaviour are primarily related to accurate definition of the boundary conditions, because of complex interactions between the individual components. Traditionally, strain gauges and displacement transducers have been used for measuring the caliper strains and deflections. This approach is expensive and time consuming, requiring installation of numerous transducers and complex data processing, and has limited accuracy. The application of digital image correlation (DIC) to a commercial vehicle disc brake caliper provided valuable strain results. In comparison with strain gauges, DIC proved to be exceptionally easy to use and enables straightforward comparison of measured strains with FE predicted values. Initial work dealt with the static actuating forces, and excellent correlation between the predicted and the measured strain values was achieved throughout the operating range of clamp forces. The present authors are confident that the addition of the dynamic frictional forces will give even more interesting results, providing insight into the interaction of different components within the brake assembly.

Convective Heat Dissipation From a Wheel-hub-mounted Railway Brake Disc

Abstract Air flow and convective heat dissipation from a wheel-hub-mounted railway brake disc were studied using computational fluid dynamics (CFD). The analyses enabled detailed insight into air flow, temperature, speed, pressure, and convective heat transfer coefficient distributions, never before available to a brake designer. Such results are practically impossible to experimentally obtain at reasonable cost. Particularly interesting finding is the existence of relatively considerable secondary flow — circumferential flow behind the vanes. Although this effect may reduce air pumping, and therefore radial air speed, it increases turbulence by promoting airflow between channels. Average values of the convective heat transfer coefficients obtained using CFD are practically identical to the experimental values derived from cooling tests performed on dynamometer and spin rig. Compared with other railway disc designs, this disc demonstrates exceptionally good convective cooling characteristics, in particular considering its size and investigated operating condition (rotation in still air). The computational studies of air flow and heat dissipation characteristics are an excellent base for development work in improving existing and generating new disc designs with high heat dissipation characteristics. Future work is concentrated on conducting additional analyses of the current disc design, in order to investigate the most effective ways of maximizing convective cooling.

Design optimization of an opposed piston brake caliper

Successful brake caliper designs must be light and stiff, preventing excessive deformation and extended brake pedal travel. These conflicting requirements are difficult to optimize owing to complex caliper geometry, loading and interaction of individual brake components (pads, disc and caliper). The article studies a fixed, four-pot (piston) caliper, and describes in detail the computer-based topology optimization methodology applied to obtain two optimized designs. At first sight, relatively different designs (named ‘Z’ and ‘W’) were obtained by minor changes to the designable volume and boundary conditions. However, on closer inspection, the same main bridge design features could be recognized. Both designs offered considerable reduction of caliper mass, by 19% and 28%, respectively. Further finite element analyses conducted on one of the optimized designs (Z caliper) showed which individual bridge features and their combinations are the most important in maintaining caliper stiffness.

Maximising heat dissipation from ventilated wheel-hub-mounted railway brake discs

Improvement of convective heat dissipation from wheel-mounted discs presents a unique challenge due to the existence of a secondary air flow (in the circumferential direction), between the vanes and wheel web. Although this flow reduces pumping efficiency (air mass flow), it promotes air mixing between different channels and increases turbulence. Beginning with the existing design, a procedure was developed to maximise convective heat dissipation based on specific post-processing procedures and monitored parameters. These included the secondary flow (behind the vanes), air speed in the channels at specific planes and points, global air flow pattern and the distribution of the convective heat transfer coefficient. By analysing these plots and graphs it was possible to identify areas where flow and heat transfer characteristics could be improved. Ultimately, the specific power dissipation (the product of the average convective heat transfer coefficient and the disc wetted area), provided a single quantitative measure of disc design effectiveness in convective cooling. The newly developed design showed an increase in convective heat dissipation of over 10% when compared with the existing disc.

Modular Battery Cell Model for Thermal Management Modelling

Internal policies of the major car markets are urging for a cut in oil imports, leading to powertrain electrification. Due to their high weight-to-power ratio, Lithium-ion batteries, especially Lithium-Nickel-Manganese-Cobalt Oxide 21700 cylindrical cells, are rapidly becoming the most diffused electric powertrain energy storage devices. These devices need to be operated in a tight temperature range to prevent major power drops and also for safety reasons. It is therefore essential to provide an accurate but computationally inexpensive battery model. Current models are either too simplistic and not applicable for thermal management design purposes or too computationally expensive and impractical for heat exchange modelling purposes. This work was focused on a computationally convenient system-level-modelling-oriented battery cell model. Starting from a 1D model obtained from manufacturer’s data, experiments were carried out on real cells, a more sophisticated 3D model for cell characterization was implemented and then a lighter 1D model obtained from it was proposed. The outcome is a novel thermal model of batteries, with a reasonable computational cost, developed on the purpose of thermal management design. This represents an advancement in battery thermal management design, as no such model is currently available in literature.