Passengers and drivers of electric buses expect “silent” vehicles, and this market expectation can be a challenging one to overcome.
In recent years substantial progress in capability and affordability of electric vehicles has seen their popularity rise while demand for traditional diesel-powered vehicles declines. The global transition to a low carbon economy has accelerated the need for alternatively powered vehicles; consequently, the entry performance level of electric vehicle designs and advancements with each subsequent evolution are key to capturing meaningful market share. In 2017, there was 386,000 electric buses in service worldwide. This number is expected to grow to 1.2 million by 2025, which will constitute nearly 50% of the global city bus fleet.
Launched in Brussels on 13th July, 2017, the European Clean Bus deployment Initiative came into effect when 40 cities and regions and 11 bus manufacturers came together and signed a declaration to accelerate the roll-out of clean buses. As stated on the European Commission website “clean (alternatively fueled) buses in urban areas can offer considerable advantages. Reductions in emissions of greenhouse gases, air pollutants and noise bring about considerable public health benefits. Moreover, moving on quietly and smoothly means greater passenger comfort.”
Electric vehicles certainly have their advantages, but they also bring with them a range of new technical challenges within the field of noise control and thermal comfort. An integrated approach to new solution design and product development is needed to solve these challenges.
While the main drivers behind the move to electrification are clean technologies and the environment, passenger comfort is also a key competitive advantage used by electric bus OEMs, with an increasing number of people now opting to take public transport over long congested commutes by car.
Passengers and drivers of electric buses expect “silent” vehicles, but even the more realistic market expectations for “quiet” electric buses is challenging to deliver when the forces at play are considered. While overall noise levels in electric buses are often (but not always) reduced at low vehicle speeds, the challenge of road and wind noise persist at elevated cruise speeds in conjunction with the new, non-trivial challenge of providing a subjectively quiet environment at low speeds.
Reduced overall noise levels alone do not deliver upon this expectation as the quality of sound present significantly contributes to the subjective impression of the occupant; indeed, at low speeds electric buses often present a plurality of annoying tonal noise sources previously unheard beneath a rounded combustion engine sound signature.
Large electric motors capable of moving such heavy vehicles emit piercingly audible tones, the axle and transmission whine is apparent and various ancillary pumps, power electronics whistle and buzz, and low-level cabin trim creaks and rattles abound.
Previously a lot of these noises would have been inaudible, because they were masked by a diesel engine that produced noise across a broad range of the acoustic frequency spectrum; but now their irritating sound signatures are audible at low level and are often not continuous but turn on and off with demand. This means that they are less likely to be filtered out by the brain and are an annoying distraction each time they turn on. People are distracted and irritated by the tonal noises, and importantly reference their experience against their expectation of a quiet or silent vehicle.
The fact remains that these electric powered vehicles are relatively new on the market and industry knowledge of noise and thermal control is limited. As such, manufacturers often seek Ventac’s long-standing acoustic experience and technical expertise in this specific area. We have developed a solution which, in conjunction with our noise control solution also delivers thermal efficiency.
The electric bus market has presented new technical and acoustic challenges to the market and these problems need new and innovative solutions to overcome.
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