How tire development can tackle a safety issue: noiseless electric vehicles
Electric vehicles are becoming increasingly common on our roads; however, one aspect continues to generate discussion: their quietness. This aspect is of special interest as it affects pedestrian’s and vulnerable road user’s (VRU) safety. Through the EU-funded PBNv2 project, Applus+ IDIADA has been working in collaboration with several partners to improve this issue with regard to tires.
Vehicle tires are much more complex structures than they are often perceived to be, and generally consumers give more importance to aspects such as the engine, colour, interiors, etc. forgetting that the tire has many functions on a vehicle: enabling the vehicle to roll smoothly over the road surface, helping prevent the vehicle from skidding on water/snow/ice, etc. and also importantly, acting as an alert system; since the noise generated by the vehicle’s tires alerts nearby pedestrians and VRU’s to its presence.
Although making vehicles more environmentally-friendly is a good thing, making them silent comes at the cost of safety. In the case of vehicle noise, a major contribution comes from the engine (with powertrain) and the tire, but not equally. For a vehicle travelling at higher speeds, the noise from the tire dominates the other noises and at lower speeds the opposite occurs. The use of components and the noise they emit has been constantly scrutinized by governments. The EU has a very ambitious plan to make society greener and safer in the future. To this end, the EU has boosted its advocacy towards electric vehicles. Since these vehicles do not have internal-combustion engines, their noise is near to zero, especially at low speeds. While good for the environment, this may be fatal for pedestrians and VRU’s, since they may not detect a vehicle moving slowly (up to 50 km/h). Thus, the EU is now drafting a standard to make sure that every vehicle emits minimum noise so that it remains detectable, but not annoying.
This is a challenging task for vehicle manufacturers. One solution is to add artificial sources of noise, but their directivity is an important factor and they involve additional costs for the manufacturer and hence for the customer. However, as vehicle tires are also a source of noise, their design can be studied to make a vehicle detectable without adding any extra financial burden to the buyer. To tackle these issues, Applus+ IDIADA is collaborating with the EU and the Marie Curie innovative training network (ITN) program and hosting a research activity – c. PBNv2 is a consortium of various automotive manufacturers and research giants that have committed themselves to studying the contribution of noise from the perspective of automotive safety.
At Applus+ IDIADA, our researchers have been investigating tire construction, its behaviour, materials and noise generation mechanisms. As mentioned before, tires are complex components: tire behaviour is dependent on various constructional factors like rubber hardness, plies used, and their orientation; and external factors like tire pressure or temperature of operation. A small variation in these leads to different results in the test. The outcome of this research is a simulation tool that models tire noise generation, propagation and its perception or psychoacoustics. Applus+ IDIADA is working in collaboration with INSA Lyon, France where tire noise is analysed for psychoacoustics, i.e. for its detection and annoyance.
IDIADA’s collaboration in the project will help provide solutions for “silent” vehicles to achieve the objectives of both safer and more environmentally-friendly vehicles for present and future generations.