Research and /or Engineering Questions/Objective:
In the field of brake discs, an ongoing development over the past decades brought new concepts into the market, with a focus on lightweight design. One representative of a mounted disc is the pin disc, where a cast-iron friction ring and an aluminium disc hat are connected via stainless steel pins that can float inside the friction ring. The interfacial conditions between pin and friction ring may however vary (e.g. over lifetime), with possible impacts on the modal and acoustic behaviour. So far, no technique is available to evaluate these conditions for individual pins in a fully mounted disc.
The article introduces different approaches to evaluate the pin to friction ring interface together with sample measurements on two boundary samples (disc with ideally floating pins vs. disc with press fit at the pins). The methods are compared in terms of their ability to reproducibly show the contrast between the two boundary samples on the level of individual pins. As most promising concept, propagation measurements for the first shock wave (transfer path analysis from disc hat via the pin to the friction ring) are described in detail and are correlated with a simple theoretical model.
In terms of feasibility, measurement approaches that only give integral information on the component level (e.g. tight fit at all pins vs. all pins able to float) are discussed in contrast to those that are able to evaluate individual pins by discarding any information on the adjacent pins. The high potential of shock wave propagation time measurements is underlined and a good correlation between theoretical model and sample measurements is shown. Subsequently, conditions for an ideal test setup are formulated, giving the basis to transfer the developed strategies into a quality control procedure.
Limitations of this study:
So far, studies are limited to pin discs. However, the results indicate potential to transfer the proposed measurement approach to other types of mounted discs, where interfacial conditions between parts can vary.
What does the paper offer that is new in the field in comparison to other works of the author:
The work offers a methodology for an evaluation of interfacial conditions and forces in mounted brake discs. A high relevance of the work for practical use is given by the fact that the state of individual pins can be assessed in a non-destructive manner. So far, this was only possible by destructive methods (e.g. pin pull-out force measurements).
With the methodology proposed here, it is possible to better understand pin disc variations over lifetime, e.g. caused by corrosion, wear or dust. Due to the non-destructive approach, interface conditions at individual pins can be monitored, e.g. over an endurance run. This allows to better detect critical states that might occur, e.g. situations where the pin to friction ring conditions might become non-symmetric along the disc’s circumference, therewith affecting disc mode shapes and, thus, the system’s NVH behaviour. To further increase the noise robustness of brakes with pin discs, the proposed strategies can be transferred into new quality control methods.
Sebastian Gramstat, Kai Bode Jan Münchhoff - Audi AG; Arved Eßer - Technische Universität Darmstadt