First acoustic tests of the conspicuousness of an electric car with the THOR AVAS system carried out in Russia

931 days ago

5 minutes

Electric transport does not have a motor, making it is practically inaudible when driving, and it is hardly noticeable, which increases the likelihood of collisions with other road users.

According to European 138 UN Regulations, such vehicles must be equipped with a special sound warning system – AVAS, the task of which is to increase the visibility of silent electric vehicles.

Since the law was passed back in 2016, and the electric transport industry is developing rapidly, the solution in the form of AVAS (Acoustic Vehicle Alerting System), which provides for the inclusion of warning sounds at speeds from 0 to 20 km / h, is also not entirely relevant. The latest Tesla accelerates from 0 to 100 km / h in 3 seconds. Which can lead to serious consequences on the roads.

Car Systems company (THOR), a resident of Skolkovo that produces the unique THOR AVAS sound notification system is also scrupulously studying all aspects, conducting its research with electric vehicles, taking into account various data on loudness and sounds created by the company’s sound engineers, taking into account various scenarios.

In October 2021, the THOR AVAS division conducted the first open road tests in Russia at the Skolkovo innovation center with the support of WATTS BATTERY, which provided portable power supplies for connecting acoustic equipment. And of course, the Dewesoft Base Station, a mixed-signal acquisition system and multichannel data logger in one device, helped the engineering team make such accurate measurements.

The essence of the study was to assess the conspicuousness of an electric car with the THOR AVAS system: the test participants (experts) took a specially designated place near the roadway, the car began to move 500 meters away from them and, at the moment when the experts began to hear the car, they pressed a button on the remote control. t the same time, the equipment recorded the distance from the car to the experts (according to GPS coordinates), the acoustic conditions next to the experts, and the speed of the car.

The work of acoustic engineers at THOR presents the results of an experiment evaluating the subjective indicators of a car’s conspicuousness by pedestrians (listeners), which were determined through the distance to the car at the moment the expert fixed its approach, and the time from the moment of fixation to the car’s approach to the expert.

These subjective indicators of conspicuousness were compared with the objective parameters of the noise from the car measured according to UN Regulation No. 138 – the level of sound pressure, its frequency response, as well as the sound level.

The electric Tesla Model 3 with the THOR AVAS system drove at five speed modes of 10, 20, 30, 40, and 50 km / h with three positions of the AVAS volume control – 60% (corresponds to the maximum permissible sound level according to UN Regulation No. 138), volume 30% and with the AVAS system turned off. For comparison, 2 cars with an internal combustion engine (ICE) were taken.   

At low speeds of 10 and 20 km / h, the noise from a car with an internal combustion engine is greater than from an electric car, which can be seen from the results of measurements of the maximum sound pressure level LZmax (Pic. 1.b). The Tesla is with turned off of AVAS system.

The qualitative fact that electric cars are less noticeable to pedestrians than conventional cars with internal combustion engines (ICE) is well known from our everyday experience.

According to the results of our experiment, we were able to express this visibility already quantitatively – we determined the time of fixation by pedestrians of an electric car and a car with an ICE (i.e. the time that passes from the moment when the pedestrian noticed the car to the moment when the car drove up to the pedestrian). For an electric car, this time is approximately 10 seconds, and for a car with an internal combustion engine – 15 seconds. The results of acoustic measurements showed that this is due to the noise of the ICE  in the low-frequency region, which is determined by the second harmonic of the fundamental tone of the engine operation.

An experiment to estimate the fixation time for an electric car with an AVAS system operating at maximum volume (according to UN Regulation No. 138) showed that an electric car is noticed by a pedestrian in a suburban environment for too long a time – 25-45 seconds. Moreover, with an increase in speed, this time decreases.

An ideal AVAS system should work in such a way that the fixation time does not depend on the speed of the electric vehicle (at least at speeds up to 40 km / h), or on the level of environmental noise, and at the same time does not exceed the fixation time of cars with ICE. That is, the AVAS system should be intelligent and be able to adapt to the environment, which is not provided for by the existing international regulatory documents, and more flexibly adjust to the speed of movement.

A scientific approach to the development of the sounds of the AVAS system will make it more noticeable at a lower volume, which will have a beneficial effect on the acoustic ecology and reduce the noise level of cities.

The problem of low conspicuousness applies not only to electric cars but also to lighter vehicles with electric propulsion: scooters, mopeds, motor scooters, and the rest of the so-called micro-transport, which is not defined as a vehicle at all in regulatory documents.


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