In addition to verifying exhaust emissions, investigations also include verifying vehicle noise emissions. The Kraftfahrt-Bundesamt (KBA) takes samples from the field under selection criteria depending on field abnormalities. The noise measurements are carried out on a separate comparison measuring section. In addition, measurements are carried out on an ISO measuring section. The UN regulation number 51 serves as the basis for the test.
Test set-up according to UN regulation number 51 AES. 02:
The vehicle to be tested shall be tested in accordance to UN Regulation No. 51 AES. 02. The vehicle shall approach line A-A` at a speed of 50 km/h (see Figure for a measurement setup of the pass measurement) and then experiences maximum acceleration without causing a so-called "kickdown" (in automatic transmissions). At least two measurements must be taken on each side of the vehicle. The highest A-weighted sound level in decibels (dB (A)) is to be measured while the vehicle is traveling between lines AA ’and BB’. This value is the measurement result.
In order to be able to examine a vehicle in detail, the vehicle is equipped with a high-resolution GPS system. Using the GPS coordinates, the current positions, the vehicle speed and the distance travelled can be recorded. In addition, this system can simultane-ously record further measurement data such as throttle valve position, accelerator pedal position, engine speed and the gears engaged via the CAN bus of the vehicle.
The sound pressure level emitted by the vehicle while accelerating past is recorded with the help of a sound pressure level measuring device at the edge of the test track. The entry into the measuring section is defined by a light barrier. The recorded measurement data from the GPS system and the sound pressure level measuring device are subsequently evaluated and coordinated with one another in time.
In addition to the UN regulation number 51 AES. 02, KBA also checks vehicles that are approved with the new UN Regulation number 51 AES. 03.