Today’s cars represent a complex compromise between contradictory requirements with regard to safety, exhaust emissions, noise, performance and price. However, since it is widely recognised that the quality of life, particularly in the urban environment, is heavily influenced by air and noise pollution resulting from road traffic, one of the top priorities for car manufacturers is the reduction of noise and emissions from vehicles, with particular attention currently being focused on CO2.
Today engine downsizing represents the most direct and cost effective approach to improving fuel efficiency in road vehicles. However this new generation of engines, while being ideally suited to city vehicle applications, can result in a perceivable degree of deterioration in terms of noise and vibration when compared with the vehicles currently on the market.
Similarly, the mass reduction required to lower CO2 emission and fuel consumption can lead to considerable augmented noise levels, which should be adequately compensated by integrated, light noise abatement means. Although current vehicles have already a structure optimised to have low weight without reducing the required performances, some components of the structure can be further reduced in weight still matching the resistance, crash and fatigue performances. But these weight reductions results in a poor performance in terms of noise and vibrations increasing both the structure-borne and airborne sound transmission.
Within a vehicle many components contribute to the overall emitted noise of a vehicle individually radiating noise between 60 – 70 dB(A). But the problem of multiple noise sources and transfer paths will become more and more challenging with the upcoming multi-material design of the vehicle body and envisioned flexibility and modularity of the vehicle power train. In order to achieve an overall noise reduction for vehicles, all noise sources and their transfer paths to radiating components have to be treated simultaneously and in a holistic approach. The scope of Green City Car is therefore to develop flexible, integrated passive and active solutions which will not only permit noise and vibration to be attenuated in new vehicles equipped with the next generation of highly fuel-efficient power trains but enable vehicle design guidelines to be defined in order to reduce weight without compromising on comfort and safety. Frequently, new technologies in the fields of smart materials and active control provide potential solutions but have only been proved in the laboratory. Within Green City Car such advanced laboratory-level technologies will be combined with conventional solutions with direct application to next generation city-car in order to assess practical feasibility, promote industrial development and determine cost-benefit evaluations.
Description of work
During the project, city car prototypes will be realised featuring pioneering technology aiming to push its environmental-friendly characteristics to a new level. The starting point will be a next-generation city car equipped with a newly developed twin-cylinder engine which will provide very significant gains in terms of reducing fuel consumption and, as a consequence, CO2 emissions. Furthermore, the vehicle will be provided with the latest technology in terms of safety aspects related to pedestrian’s impact and car-to-car compatibility, which are of major importance in an urban environment. The noise reduction technology to be developed and implemented on such a city car will be oriented to decrease the mass of the complete sound packages, using new materials, passive or active piezoelectric or electro-magnetic patches on vehicle and engine panels, smart Helmholtz resonators, broadband active noise cancellation. Further improvements will be pursued through the development of new tyres aiming at the reduction of noise and rolling resistance. The innovation lies in the novel design process rather than in the tyre itself. In this project the design process will be shifted towards rolling resistance, airborne noise and reduced structure borne sound transfer towards the passenger compartment in view of lightweight vehicle and suspension structures.