THOR acoustic tests of the conspicuousness of an electric car with the THOR AVAS
As you know, electric transport does not have a motor, which means that it is practically inaudible when driving, and it is hardly noticeable, which increases the likelihood of collisions with other road users.
According to European laws, namely 138 UN Regulations, such vehicles must be equipped with a special sound warning system - AVAS (Acoustic Vehicle Alerting System), the task of which is to increase the conspicuousness of silent electric vehicles.
Car Systems Company (THOR) not only produces the unique THOR AVAS sound notification system but also scrupulously studies all aspects, conducting its research with electric vehicles. Tests take into account different loudness and sound data for different scenarios.
In October 2021, the THOR AVAS division conducted the first open pass tests 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.
Since the law on AVAS was adopted back in 2016, and the electric transport industry is developing rapidly, the solution in the form of the AVAS sound warning 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.
The essence of the THOR team's research was to assess the conspicuousness of an electric vehicle with the THOR AVAS system.
Considering that modern electric cars began to accelerate very quickly; it was necessary to understand how long it would take to hear an approaching vehicle safely.
During the street tests, the experts (listeners) took a specially designated place near the roadway. The electric car started moving 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. At the same moment, the distance from the car to the experts (according to GPS coordinates), the acoustic conditions near the experts, and the speed of the car were recorded.
The Tesla Model 3 electric car 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.
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 in terms of 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 indices of conspicuousness were compared with objective parameters of noise from a car measured according to UN Regulation No. 138 - sound pressure level, its frequency response, as well as sound level.
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.
Pic 1. The results of measuring the sound level (a) and sound pressure level (b) from vehicles according to UN Regulation No. 138 when driving at different speeds
The qualitative fact that electric cars are less noticeable to pedestrians than conventional cars with internal combustion engines is well known from our everyday experience.
According to the results of our experiment, we were able to express this conspicuousness already quantitatively - we determined the time of fixation by pedestrians of an electric car and a car with an internal combustion engine (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 internal combustion engine 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 (in accordance with UN Regulation No. 138) showed that an electric car is noticed by a pedestrian in suburban conditions for too long a time - 25-45 seconds. Moreover, with an increase in speed, this time decreases.
On the comparative graph of the measurement results of an electric car with an AVAS system and two cars with an internal combustion engine, it can be seen that the current AVAS system, operating according to UN Regulation No. 138 (silent vehicles), is excessively manifested up to 28 km / h, and it is not enough at speeds up to 40 km / h. Green shows how a modern system such as THOR AVAS should work adaptively.
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 visibility applies not only to electric cars, but also to lighter vehicles with electric propulsion: scooters, mopeds, motor scooters, electric bicycles and electric motorcycles - all micro-transport, which is not defined as a vehicle at all in regulatory documents.