Not only are tram drivers exposed to noise from surrounding traffic, but also to the noise made by their own vehicles.
The monotonous hum from the compressor in an air-conditioning unit above the driver’s seat, for example, is always clearly audible. While it is running, it produces vibrations that travel along the roof of the tram and reverberate inside the vehicle.
Until now, that is.
Because as part of the so-called InMAR project (Intelligent Materials for Noise Reduction), engineers at the Fraunhofer Institute for Structural Durability and System Reliability (LBF) in Darmstadt, Germany, have developed an active mounting that isolates the vibrations from the compressor and prevents them from being propagated to the tram roof.
Christoph Axt, a member of LBF’s mechatronics/adaptronics team, said: 'Three active mountings are used to reduce vibrations from the compressor by up to 15 decibels, both over a wide frequency spectrum and at individually selectable frequencies.'
The original prototype, which was created for the InMAR project, has since been further developed in co-operation with ISYS Adaptive Solutions, and was shown at the 2009 Hannover Messe event.
With an eye to volume production, the engineers are now attempting to simplify the design.
More information on the InMAR research can be found here.