THE ISSUES OF MEASURING THE EXTERIOR AND INTERIOR NOISE OF ROAD VEHICLES THE ISSUES OF MEASURING THE EXTERIOR AND INTERIOR NOISE OF ROAD VEHICLES

(different vehicle speeds, acceleration). The reason for measuring the road vehicle noise [3 and 5]: (1) road vehicles approval; (2) tests in operation; (3) other (research-development testing, etc.). The basic legislative frameworks contain various combinations of these types of tests. For example, during the type-approval of road vehicles, the exterior noise of the standing vehicle as well as the vehicle in motion is measured. On the contrary, during the technical control of road vehicle in its operation, technician, in the technical inspection station (TIS), only measures the vehicle exterior noise standing at increased engine speed (revolutions per minute). Nowadays, within the issues of road vehicles operation, we place great emphasis especially on the most important operating characteristics such as fuel consumption, exhaust emissions as well as performance indicators. However, in the field of driving comfort, a noise inside the vehicle, affecting its crew, represents an important aspect as well. The paper analyzes the interior and exterior vehicle noise, methods of its detection and practical research measurement indicating the rate of interior vehicle noise during various traffic conditions.


Introduction
Noise represents a special position among several negative environmental factors and unfavorable, even damaging, human effects. Nowadays, risk evaluation of noise exposure represents extremely urgent issue due to the enormous increase in acoustic energy in the environment. Road transport has the largest share in generating the traffic noise. Thus, road traffic noise is one of the fundamental reasons considered within the contact human -transport [1 and 2].
Below mentioned basic terms define and directly specify the noise as an objectionable environmental sound causing even annoying feeling that has generally an unfavorable effect [2 -4]: (1) Noise -every unwanted, intrusive, annoying or harmful sound that causes the biological reaction of humans and animals; (2) The Noise Level (LA) in dB -the level of acoustic pressure weighted using the weighting filter A; (3) The Percentage Noise Level -the sound level with A weighting obtained during the weighing time function F (fast), exceeded in percentage of the total evaluation period. Denotation -LN (e.g. L1,10,50,90,99); (4) The Equivalent Noise Level (LA eq ) in dB -is consistent data that is used to describe the sound course with a varying sound level which includes the road traffic noise as well. It is calculated as an acoustic pressure which is energetically equivalent to the long-term effect of intermittent noise or noise with a varying sound level.

Legislation relating to the field of measuring the road vehicles noise
In the beginning of the legislative framework analysis relating to the issue of road vehicles noise, it is important to mention the basic divisions of road vehicles noise which are regulated by different legislative rules either in the field of road vehicles approval, or the operation itself [5].
The field of road vehicles noise [4 and 5]: (1) inside the vehicle -interior noise; (2) noise outside the vehicle -exterior noise.
In terms of the road vehicle operation, it is possible to measure the interior and exterior noise [5]: (1) standing vehicle (idle engine speed or increased engine speed); (2) vehicle in motion (different vehicle speeds, acceleration).
The basic legislative frameworks contain various combinations of these types of tests. For example, during the type-approval of road vehicles, the exterior noise of the standing vehicle as well as the vehicle in motion is measured. On the contrary, during the technical control of road vehicle in its operation, technician, in the technical inspection station (TIS), only measures the vehicle exterior noise standing at increased engine speed (revolutions per minute).

Practical measurements
Practical measurements were carried out on a selected group of road passenger vehicles with the parameters defined in Table 1

Exterior noise of the vehicle in motion
For a selected group of vehicles, exterior noise level was measured according to the "Methodology" defined in the Council Directive 70/157/EEC. 3 measurements for each

Council Directive 70/157/EEC
Council Directive 70/157/EEC of 6 February 1970 on the approximation of the laws of the Member States relating to the permissible sound level and the exhaust system of motor vehicles. Since its adoption, this Directive was repeatedly substantially amended. The latest reduction in sound level limits for motor vehicles in 1995 did not bring the desired effect. Studies have shown that a test method used by the Directive, did not reflect the true nature of driving in urban traffic any longer. As pointed out in the Green Paper on a future policy on noise since November 4, 1996, in the test method, the contribution of a tire rolling noise to the total noise emission was underestimated. This directive refers to the Regulation of the United Nations Economic Commission for Europe (UNECE) no. 51 on noise emissions, setting out a test method for noise emissions, and the Regulation of the UNECE no. 59 on provisions concerning the approval of replacement silencing systems [6 -8].
According to this directive, the following vehicles are controlled [6 -8]: • standing vehicle -measurement is carried out according to this directive requirements (noise meter microphone placement) at different engine speeds. The result is logged to the vehicle registration certificate and is the basis for the vehicle test in operation. • vehicle in motion -measurement is carried out according to this directive specific requirements. The result of this test must meet the prescribed limits defined by this directive for specific categories of road vehicles. According to this directive, the measured noise values of the standing vehicle and vehicle in motion are logged into the vehicle registration certificate as well.
Used vehicles during the practical measurement Table 1 Vehicle brand

Exterior noise of the standing vehicle
A microphone is placed at a distance of 0.5 m ± 0.01 from a reference point of the exhaust pipe and at angle of 45° (± 5°) to the vertical level in which the exhaust flow axis at the exhaust pipe outlet is placed. A microphone must be placed at a reference point, however, no less than 0.2 m from the ground surface. The microphone reference axis must be placed in a level parallel to the ground surface and must be directed to the reference point at the exhaust pipe outlet [11, 14 and 15].
Noise emission limits during the test of the standing vehicle are listed in following Table 3.
According to the Council Directive 70/157/EEC, it is necessary to measure the noise emissions of the standing vehicle for the selected vehicles at engine speed equal to ¾ of vehicle were carried out with a requirement of the noise measuring on the vehicle left and the right side [6, 8 and 10].
A microphone must be placed at a distance of 7.5 m +/-0.2 m from a reference line of the roadway and 1.2 m +/-0.1 m above the ground. Its axis of maximum sensitivity must be horizontal and perpendicular to the vehicle roadway. When the vehicle front reaches the specific line, the accelerator fully opens as quickly as possible and is held in the fully opened position, until the rear vehicle intersects another specific line. Then, the accelerator closes as quickly as possible [11 -13].T he measured values are compared with the "Methodology" and listed in following Table 2.
Noise emission limits during the test of the standing vehicle Table 3 Vehicle Individual values from the comparison of exterior and interior noise of the vehicle in motion are summarized in Table 3.

Comparison of exterior and interior noise of the standing vehicle
The comparison of the standing vehicle exterior and interior noise at various levels of engine speed (idle engine speed, 1000 rpm, 2000 rpm and ¾ of rated engine speed) can be considered as a test with a greater degree of explanatory value.
The measured noise level data can be assessed in two ways [12 and 19]: • by evaluation of the absolute values, • by evaluation of the exterior noise reduction (difference, ratio, etc.).
The comparison of exterior and interior noise of the standing vehicle is shown in Table 5.
From the detected noise values summarized in Table  5, the increase rate of the exterior and interior noise of the standing vehicle can be calculated as well. Evidently, Peugeot 206 is the noisiest vehicle in terms of the interior as well as exterior noise. An enormous noise increase, when increasing rated engine speed. In this case, the test is extended to noise emission values at idle engine speed and engine speed of 1000 rpm and 2000 rpm. The highest noise value exceeding the limit specified by this directive is achieved by Peugeot 206 [11, 14 and 15].

Comparison of exterior and interior noise of the vehicle in motion
A vehicle comfort level with respect to its noise on the passengers could be evaluated not only through the interior vehicle noise at a point of the driver's right organ of hearing, but also determining the "reduction rate of exterior noise into the vehicle passenger cab" [3, 9 and 16].
The individual measured and recorded values are summarized in Table 4.

Conclusions
The issues of measuring the noise of road vehicles can be considered broadly comprehensive and highly topical. A lot of experts at international level deal with this field of study. The group known as "GBR" (Working Group on Noise from Road Vehicles), which is part of the World Forum for the Harmonization of Vehicle Regulations (WP.29) -part of the inland transport committee in the European Economic Community, represents an illustrative example [2, 8 and 25].
The processed article reports, inter alia, an overview of the exterior noise of road transport vehicles evaluation which is considered to be a part of the vehicle approval tests. A special attention is paid to the noise inside the vehicle. When purchasing the vehicle, its common a future user has available an amount of data about the required vehicle (performance, fuel consumption, parameters, etc.), however, an important detail regarding the comfort inside the vehicle is not available for him. This parameter is represented by the interior noise affecting the vehicle crew, especially the vehicle driver [26 and 27].
Authors of this paper predict that this issue of measurement and evaluation of vehicle interior noise will be readily available and important criterion concerning the vehicle selection in the future.

Acknowledgement
This paper has been developed under the support of: National Natural Science Foundation of China (No. 71503011) and Beijing Social Science Foundation of China (No. 16GLC041).
the engine speed, can be seen as well. On the contrary, Opel Zafira is considered to be the least noisy vehicle based on the performed measurements. At the rated engine speed, it is able to reduce the vehicle interior noise by 12.9 dB compared to the exterior noise.

Noise measurements in the technical inspection station
In normal operation of road vehicles, their noise level can be controlled in the technical inspection stations. Exterior noise level of the standing vehicle is measured according to the Methodical instruction No. 77/2011 [20].
Exterior noise level of the standing vehicle is assessed by the inspection technician subjectively, without using a sound level meter. If inspection technician, on the basis of his subjective judgment, cannot clearly assess whether the exterior noise level is not higher than the permissible value, he carries out the particular measurement [6, 21 and 22].
The resulting measured data is compared with a reference value. The reference value is determined from the data on the standing vehicle exterior noise level indicated in a given vehicle registration certificate plus a tolerance of + 5 dB (A) [22 -24].
From the analyzed road vehicle group, Peugeot 206 does not meet a prescribed procedure of the inspection. It exceeds the value indicated in a vehicle registration certificate by 7.3 dB. In this case, if the measured exterior noise level value of the standing vehicle is higher than the permissible value, the vehicle is evaluated as "B" (temporarily fit for traffic) during the technical inspection. This means that the vehicle must be returned for performing the technical inspection within 30 days.