Methoden der in-situ Visualisierung der Reibzonendynamik trockenlaufender Reibpaarungen unter Ergänzung physikalischer und chemischer Charakterisierungen der Reibpartner

Die vorliegende Arbeit charakterisiert die Wirkmechanismen der Reibschicht trockenlaufender Reibpaarungen. Mittels in-situ Visualisierungsmethoden wird die Dynamik der Patchlebenszyklen über eine Bremsungsdauer ermittelt. Zudem werden die Bewegungsgeschwindigkeiten und –bahnen sowie die Verweildauern der Abriebpartikel in der Reibzone charakterisiert. Der Charakterisierungsansatz, der zudem lokal aufgelöste Belagtopographie-, Kompressibilitäts- und Porositätsanalysen sowie chemische Analysen vorsieht, offenbart ebenfalls Zusammenhänge zwischen der Patchdynamik und der Reibbelagphysik und –chemie in Bezug auf das tribologische und thermische Verhalten. Letzteres erlaubt es, Hitzeflecken in der Reibzone zu beschreiben, indem ihre Anzahl und Flächen dynamisch bestimmt werden. Mittels der vorgestellten Methode ist es möglich, die Dynamik und Wirkmechanismen vom einzelnen Patch über verschiedene Patchzonen bis hin zur kompletten Reibzone (inklusive Reibringverlagerungen) zu charakterisieren.The tribological behaviour of dry-running friction couples is till today not entirely describable. The need of the knowledge of that what happens inside the friction zone during a brake application is enormous. Hence it is an essential objective of the present work to overcome existing limits of in-situ investigations of the friction processes on a multi scale level (nano, micro, macro) to characterize the mechanisms of the friction layer. Therefore enhanced in-situ visualisation investigations were undertaken by the use of especially developed brake discs and original brake linings of passenger cars. The latter include the consideration of different compositions such as ECE, NAO and copper-free ECE formulations. As a result the comparability of the knowledge obtained from the in-situ test concept to conventional friction couples (cast iron disc – organic brake lining) can be stated what underlines the capability and significance of the novel method. Direct analogies regarding the number, size and shape of patches can be observed by the appeared patch behaviour. Using the visualisation and complementary analysis methods it is for the first time feasible to characterize the dynamic of the patch life cycles as a function of the surface area over the braking time. Moreover the force transmitting friction zone surfaces between brake applications were determined and allow conclusions regarding the onset of residual torques. Beside patch analyses the wear particle velocities, traces and dwell times inside the friction zone could be determined for the first time. It was shown that the particles not only move much slower compared to the rotor speed but also that the lining composition has a crucial influence on the development of particle traces and the mutual interaction of the particle motion behaviour. The characterization approach which also includes additional local resolved brake pad topography, compressibility and porosity analyses (by the use of three dimensional computer tomography) as well as chemical analyses (using an EDX analyser) reveals moreover important relationships between the established patch dynamic and the pad physics and chemistry regarding the tribological (dry and wet friction processes) and thermal (thermoelastic instabilities) behaviour. The latter allows for the first time to describe hot spots inside the friction zone by the dynamic determination of their number and surface areas. By means of the presented investigation method it is now feasible to characterize the dynamics and mechanisms from the single patch over certain patch zones finally to the entire friction zone (inclusive friction ring shifts)

Analysis of TRWP particle distribution in urban and suburban landscapes, connecting real road measurements with particle distribution simulation

This article deals with methods and measurements related to environmental pollution and analysis of particle distribution in urban and suburban landscapes. Therefore, an already-invented sampling method for tyre road wear particles (TRWP) was used to capture online emission factors from the road. The collected particles were analysed according to their size distribution, for use as an input for particle distribution simulations. The simulation model was a main traffic intersection, because of the high vehicle dynamic related to the high density of start–stop manoeuvres. To compare the simulation results (particle mass (PM) and particle number (PN)) with real-world emissions, measuring points were defined and analysed over a measuring time of 8 h during the day. Afterwards, the collected particles were analysed in terms of particle shape, appearance and chemical composition, to identify the distribution and their place of origin. As a result of the investigation, the appearance of the particles showed a good correlation to the vehicle dynamics, even though there were a lot of background influences, e.g., resuspension of dust. Air humidity also showed a great influence on the recorded particle measurements. In areas of high vehicle dynamics, such as heavy braking or accelerating, more tyre and brake particles could be found

Comparison of methods for sampling particulate emissions from tires under different test environments

Traffic-related emissions are strongly criticised by the public because they contribute to climate change and are classified as hazardous to health. Combustion engine emissions have been regulated by limit values for almost three decades. There is currently no legal limit for non-exhaust emissions, which include tire wear particle emissions and resuspension. As a result, the percentage of total vehicle emissions has risen continuously. Some of the particles emitted can be assigned to the size classes of particulate matter (≤10 µm) and are therefore of particular relevance to human health. The literature describes a wide range of concepts for sampling and measuring tire wear particle emissions. Because of the limited number of studies, the mechanisms involved in on-road tests and their influence on the particle formation process, particle transport and the measuring ability can only be described incompletely. The aim of this study is to compare test bench and on-road tests and to assess the influence of selected parameters. The first part describes the processes of particle injection and particle distribution. Based on this, novel concepts for sampling and measurement in the laboratory and in the field are presented. The functionality and the mechanisms acting in each test environment are evaluated on the basis of selected test scenarios. For example, emissions from external sources, the condition of the road surface and the influence of the driver are identified as influencing factors. These analyzes are used to illustrate the complexity and limited reproducibility of on-road measurements, which must be taken into account for future regulations

Survey on modelling and techniques for friction estimation in automotive brakes

The increased use of disc brakes in passenger cars has led the research world to focus on the prediction of brake performance and wear under different working conditions. A proper model of the brake linings’ coefficient of friction (BLCF) is important to monitor the brake operation and increase the performance of control systems such as ABS, TC and ESP by supplying an accurate estimate of the brake torque. The literature of the last decades is replete with semi-empirical and analytical friction models whose derivation comes from significant research that has been conducted into the direction of friction modelling of pin-disc couplings. On the contrary, just a few models have been developed and used for the prediction of the automotive BLCF without obtaining satisfactory results. The present work aims at collecting the current state of art of the estimation techniques for the BLCF, with special attention to the models for automotive brakes. Moreover, the work proposes a classification of the several existing approaches and discusses the relative pro and cons. Finally, based on evidence of the limitations of the model-based approach and the potentialities of the neural networks, the authors propose a new state observer for BLCF estimation as a promising solution among the supporting tools of the control engineering

Maschinendiagnose mit erweitertem Frequenzbereich

Mit der Verbesserung der Sensorik erweitern sich die Möglichkeiten der Anwendungen von Verfahren der Schallemission auch für die Bereiche der Maschinendiagnose, der Technischen Akustik und für Instandhaltungsaufgaben. Mit breitbandig ausgelegter Sensorik kann ein hybrider Zugang erreicht werden, der simultan Bewertungen vom traditionellen niederfrequenten Bereich (Struktur- und Betriebsschwingungen) bis hin zu hochfrequenten transienten Vorgängen auch quantitativ möglich macht. Flexible Algorithmen für die Signalverarbeitung bilden dafür das Gerüst

Advanced electric vehicle components for long-distance daily trips

This paper introduces a holistic engineering approach for the design of an electric sport utility vehicle focused on the reliable capability of long-distance daily trips. This approach is targeting integration of advanced powertrain and chassis components to achieve energy-efficient driving dynamics through manifold contribution of their improved functions. The powertrain layout of the electric vehicle under discussion is designed for an e-traction axle system including in-wheel motors and the dual inverter. The main elements of the chassis layout are the electro-magnetic suspension and the hybrid brake-by-wire system with electro-hydraulic actuators on the front axle and the electro-mechanical actuators on the rear axle. All the listed powertrain and chassis components are united under an integrated vehicle dynamics and energy management control strategy that is also outlined in the paper. The study is illustrated with the experimental results confirming the achieved high performance on the electric vehicle systems level

Connected and shared X-in-the-loop technologies for electric vehicle design

The presented paper introduces a new methodology of experimental testing procedures required by the complex systems of electric vehicles (EV). This methodology is based on real-time connection of test setups and platforms, which may be situated in different geographical locations, belong to various cyber-physical domains, and are united in a global X-in-the-loop (XIL) experimental environment. The proposed concept, called XILforEV, allows exploring interdependencies between various physical processes that can be identified or investigated in the process of EV development. The paper discusses the following relevant topics: global XILforEV architecture; realization of required high-confidence models using dynamic data driven application systems (DDDAS) and multi fidelity models (MFM) approaches; and formulation of case studies to illustrate XILforEV application

Testing of alternative disc brakes and friction materials regarding brake wear particle emissions and temperature behavior

In this study, different disc brakes and friction materials are evaluated with respect to particle emission output and characteristic features are derived. The measurements take place on an inertia dynamometer using a constant volume sampling system. Brake wear particle emission factors of different disc concepts in different sizes are determined and compared, using a grey cast iron disc, a tungsten carbide-coated disc and a carbon ceramic disc. The brakes were tested over a section (trip #10) novel test cycle developed from the database of the worldwide harmonized Light-Duty vehicles Test Procedure (WLTP). First, brake emission factors were determined along the bedding process using a series of trip-10 tests. The tests were performed starting from unconditioned pads, to characterize the evolution of emissions until their stabilization. In addition to number- and mass-related emission factors (PM2.5-PM10), the particle size distribution was determined. Another focus was the evaluation of temperature ranges and the associated challenges in the use of temperature readings in a potential regulation of brake wear particle emissions. The results illustrate the challenges associated with establishing a universal bedding procedure and using disc temperature measurements for the control of a representative braking procedure. Using tungsten carbide coated discs and carbon ceramic discs, emission reduction potentials of up to 70% (PM10) could be demonstrated along the WLTP brake cycle. The reduction potential is primarily the result of the high wear resistance of the disc, but is additionally influenced by the pad composition and the temperature in the friction contact area

Impacts on Brake Particle Emission Testing

The presented article picks out brake particle emission testing as a central theme. Those emissions are part of the so-called non-exhaust emissions, which play an increasing role for particle emissions from transportation. The authors propose a laboratory test setup by using a brake dynamometer and a constant volume sampling approach to determine the emissions in regard to the particle number concentration. Several impacts were investigated while the same test cycle (novel worldwide harmonized light vehicles test procedure (novel-WLTP)) was applied. In a first item, the importance of the bedding process was investigated and it is shown that friction couples without bedding emit much more particles. Furthermore, the efforts for reaching a bedded friction state are discussed. Additionally, the impact of brake lining compositions is investigated and shows that NAO concepts own crucial advantages in terms of brake particle emissions. Another impact, the vehicle weight and inertia, respectively, shows how important lightweight measures and brake cooling improvements are. Finally, the role of the load profile is discussed, which shows the importance of driving parameters like vehicle speed and reservoir dynamics. The authors show that, under urban driving conditions, extreme low particle emissions are detected. Furthermore, it is explained that off-brake emissions can play a relevant role in regard to brake particle emissions

Comparative Study on the Friction Behaviour and the Particle Formation Process between a Laser Cladded Brake Disc and a Conventional Grey Cast Iron Disc

Brake-wear particle emissions are the result of the components of a friction brake being in tribological contact, and they are classified as non-exhaust emissions. Since most of the emitted particles belong to the size classes of particulate matter (≤10 μm) and differ significantly in terms of their physico-chemical properties from automotive exhaust emissions, this source is of particular relevance to human health and, therefore, the focus of scientific studies. Previous studies have shown that coated brake discs offer significant wear and emission reduction potential. Nevertheless, no studies are available that describe the specific particle formation process, the contact conditions, the structure of the friction layer and the differences compared to conventional grey cast iron discs. The aim of this study is to describe those differences. For this purpose, the tribological behaviour, the structure of the friction layer and the associated particle dynamics within the friction contact between a laser cladding coated disc and a conventional grey cast iron disc are compared. The required investigations are carried out both ex situ (stationary) and in situ (dynamic). Parallel to the tribological investigations, the particle emission behaviour is determined on an inertia dynamometer using a constant volume sampling system (CVS) and equipment for particle number and particle size distribution measurement. The results show that, for two different brake pads, the laser cladding brake disc has lower wear and less particulate emissions than the grey cast iron brake disc. The wear behaviour of the coating varies significantly for the two brake pads. By contrast, the grey cast iron brake disc shows a significantly lower influence