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Working with Telent Technology Services, Loughborough University and Birmingham University we were contracted to develop a set of brackets to enable sensor attachment to trains on the Southern Rail network.
The brackets would mount directly to the axlebox of a Bombardier Class 377 Electrostar bogie and enable the associated sensors to record an array of data relating to wheelset kinematics.
The only snags with what initially sounded like a fairly simple plan was that everything had to weigh less than 2kg, withstand 100G and transmit these forces with extremely low deflection, and have a minimum frequency response over 2khz.
The kinematic envelope was tight and complex, and no 3D models were available to assist with the design process. We did manage to obtain a set of axlebox and bogie engineering drawings, from which we reverse-modelled the necessary parts to enable visualisation of the system as our designs progressed. A latter benefit of modelling these off-the-shelf parts was the ability to include them in our FEA and bolt calculation modelling.
The rail operator specified that our sensors must be removeable from the bogie without disturbing the axlebox bolts. These would be set to a specific torque upon installation and if touched it would cause the carriage to be out of service while technicians reset the torque again, whereas removal of a secondary bracket would not affect passenger safety.
We set about designing a two-piece bracketry system that could be reversed and flipped to work with all four wheels. Fundamental parameters were set, such as the bolt circle diameter of the axlebox inner cover, to which the bracket would locate. The secondary, sensor housing bracket was largely constrained by sensor size and the kinematic envelope in which it would live.
The remaining design time saw many iterations, all driven by finite element analysis an each becoming slightly closer to achieving the desired specifications. It was impossible to move away from a shape largely resembling a drum purely due to the available space, so this was mitigated with a tuned ridge around the perimeter of the main bracket together with additional tuned holes across the surface. The creation of a stiff joint between the two brackets gave further resilience to shock loadings and pushed the lowest frequency response beyond 2.2khz.
In order to satisfy the safety documentation we produced numerous sets of bolted joint calculations along with engineering drawings and FEA results. Ordinarily one set of bolted joint calculations are created, however with this system we needed to provide the torque settings for assembly using an old sealing gasket and a new gasket, each of two different materials to cover all eventualities.
We conducted the manufacturing tender for Telent and worked closely with the selected precision engineering companies to produce a quality set of brackets. We transported the parts to site and assisted in fitment and initial testing, where Telent and their partner institutions were able to gather data as hoped.
