Texte remanié de: Diss.--Hannover, 2000. / Bibliogr. p. 567-575. Notes bibliogr. Index.

Automotive brake lining materials are complex composites consisting of numerous ingredients allowing for their optimal performance. Different types of carbons have been used in all types of brake pad formulations for more than century. The role of carbon, however, does not seem to be completely understood, since carbon materials possess a wide variety of characteristics and properties and they interact with other ingredients present in the friction process. Carbons/graphites are commonly considered to be solid lubricants but this role is only available at relatively low temperatures and at a sufficient humidity. Since regulations are increasingly limiting Cu content in brake pads and Cu exhibits extremely high thermal conductivity, graphites, being excellent heat conducting materials themselves, are often considered for use when potential Cu replacement options in the low-metallic, non-asbestos organic, hybrid, and ceramic pads are explored. This paper surveys the role of two types of graphites with high thermal conductivity but different mechanical properties and morphology: the so-called i) purified flake graphite (PFG) and the ii) resilient graphitic carbon (RGC). A successful “high-end” commercial low-metallic brake pad was re-formulated (SIU Carbondale) by removing of over 20 wt. % of Cu and replacing it with a cocktail of ingredients including 15 wt. % of these two graphite types. OEM Crown Victoria 1999 mold was used to prepare the pads and they were subjected to the SAE J2430 test and BEEP evaluation using the full-scale automotive brake dynamometer (Link Engineering) and original hardware (rotor and caliper). After friction tests, the surfaces of pads were explored using scanning electron microscopy equipped with the energy dispersive X-ray microanalysis (FEG450 and Inca System) and X-ray diffraction (Rigaku Max-Flash-B). Although the brake pad formulations were otherwise identical and were prepared at the same conditions, the performance of two different low-metallic pads was different. The effectiveness of PFG sample reached value 0.5 and wear of pad was 5.3 g, while the effectiveness was 0.4 and wear detected was 5.9 g in the case of RGC containing sample. Both formulations exhibited extremely good stability of friction during fade section and only low sensitivity to speed variations between 50 and 160 km/h. Surfaces of both pads were covered by a discontinuous (patchy) friction layer which was formed as a consequence of a gentle abrasive mechanisms involved. The different friction levels and different wear of samples were related to the specific character/differences in detected different friction layers. Importantly, the capacity of the PFG to reduce surface oxides is considerably higher when compared to the RGC. It was concluded that the proper understanding of role of individual graphitic forms in particular formulations can be very beneficial when optimizing the performance of brake pads.

The main objective of this research is to address the relationship between formulation of friction lining materials and their propensity to friction induced noise generation. The basic idea was formulated earlier by Dr. Filip, who showed that the friction layer plays the relevant role when noise is observed during braking. It was shown that when newly formed patches (parts of the friction layer) exhibit a large difference in the coefficient of friction, brake lining is stretched and released repeatedly, which leads to significant vibrations and corresponding noise when coupled with the vibration mode of the system. Farhang ,on the other hand, demonstrated that noise can be related to specific surface roughness parameters and when properties of friction lining and friction layer (such as compressibility, stiffness and modulus of elasticity) fit into certain specific value ranges, noisy behavior occurs. This research will address the braking related to friction induced noise in relation to the properties of the bulk lining material and the character and properties of the friction layer. The friction tests will be performed using the CAFS-developed (Szary and Lee) real time noise measurement system compatible with the major part of SAEJ2521 standard (note that the system does not allow for reliable measurement of frequencies lower than 900 Hz). The mechanical properties of fourteen samples will be investigated. Of the fourteen samples, friction layer of three of the samples will be investigated by several analytical techniques developed by Dr. Filip [1]. They include polarized light microscopy, scanning and transmission electron microscopy equipped with energy dispersive microanalysis, and X-ray diffraction. This research summarizes data from the J2521 dynamometer test of the Dodge Caravan samples exhibiting specific compressibility, porosity and hardness. Also, this research provides the results of friction surface analysis by SEM with energy dispersive microanalysis, light microscopy, surface roughness, and X ray diffraction. Of the fourteen samples, Bendix has the largest occurrence of noisy braking. Based on techniques developed by Dr. Filip, the characteristics of the friction layer strongly influence brake noise propensity. The friction layer characteristics are dependent on brake formulation. As predicted, "noisy stop" and "quiet stop" samples exhibit completely different friction surfaces.

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This thesis describes the modelling and control of an electromechanical brake (EMB) for a drive-by-wire vehicle. The investigation comprised two components on the development, identification and assessment of an EMB model, and the development of an improved control algorithm for an EMB. / The first component of the study began with the examination of a simplified model for an electromechanical disk brake without the positive feedback of brake self-energisation. A methodology was proposed for practical identification of the model parameters on an assembled actuator. Experiments were conducted on a prototype EMB, and for the first time the model fidelity was tested in isolation without a feedback controller acting to reject disturbances. Laboratory tests of the model fidelity were complemented with closed-loop simulations against field data from a brake-by-wire test vehicle. It was determined that the EMB model reasonably predicted the key behaviours of the brake apply, force modulations and lockup due to load-dependent stick-slip friction. The limitations of the model were then identified and extensions were considered to describe secondary effects. / The second component of the study utilised the model to develop an improved control algorithm for an EMB, particularly considering the problem of tracking a brake force command from the driver, or from another vehicle control. Existing EMB controllers were seen to have a limited effectiveness; with a suboptimal handling of actuator nonlinearity, they suffered from problems of the load dependent mechanism friction, and they could not maintain performance throughout the operational envelope. These shortcomings were overcome sequentially by the development of a friction compensation algorithm and a modified control architecture to better manage actuator nonlinearity. To address model uncertainty the modified architecture was incorporated within a robust control design, but this gave an overly conservative brake performance. In a more successful approach, the modified architecture was extended with a model predictive control to optimise the EMB performance and a method for updating the control algorithm was proposed to handle uncertainty and adapt to actuator variation. At each stage experimental tests were conducted on a prototype EMB to demonstrate performance and the incremental improvements achieved. The control improvement was found to be most pronounced for fine manoeuvres whereas large manoeuvres were typically limited by the actuator constraints. / The study outcomes regarding EMB modelling, identification and control are a significant incremental advancement on prior work, and may help to facilitate the development of improved brake-by-wire platforms, anti-lock brake systems and advanced driver assist functions.

München, Techn. University, Diss., 2003.

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