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A New Cpx Drum Test to Obtain Equivalent Sound Pressure Levels of Tyre Noise for Type Approval
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Air, road, and tire temperatures substantially affect tire/road noise emission. For measuring purposes, one would like to normalize measurements to a reference temperature by means of a reliable correction procedure. Current studies show that temperature effects remain an important source of uncertainty in tire/road noise measurements and tire testing, even after applying the correction terms provided in the various standards. This seems to be the case for the measurement methods used in OBSI, CPX, SPB, and various regulations or directives based on ECE R117. This paper examines a new dataset consisting of 7.5 million temperature measurements aimed at contributing to a better understanding of temperature effects and the ways they relate to air, road, and tire temperatures. It is assumed that tire temperatures are the most relevant for noise corrections; therefore, special studies are made for how tire temperatures relate to air and road (test surface) temperatures. A profound analysis is provided on how these relationships vary over different day times, seasons, and climatic regions. Based on this analysis, the authors provide suggestions for improvement of temperature normalization in current tire/road noise and tire testing standards. Special considerations are devoted to measurements on test tracks having ISO 10844 reference surfaces.
Tyre/road noise is one of the major environmental problems related to road traffic. There are several measuring methods of tyre/road noise that may be carried out on the road (for example Coast-down and Close Proximity Method) or in the laboratory (Drum Method). Road measurements are preferred for evaluations of pavement properties while laboratory methods are mostly used to evaluate tyres. One of the biggest problems associated with laboratory methods is to ascertain that tyre interfaces with pavement that has texture, porosity and mechanical impedance the same as with the real road surface. The paper presents results of tests performed by the Close Proximity Method (with test trailer Tiresonic Mk.4) and drum method where very similar or exactly the same surfaces are used. The reported measuring program includes tests performed on an innovative poroelastic road surface called PERS.
Tyre/road noise is the dominant component of overall vehicle noise at medium and high speeds and for cars even at low speeds. Consequently, road traffic noise can be reduced with the proliferation of quieter tyres. One way to achieve this is to give the tyre noise label greater attention among tyre and transportation consumers. Hence, the STEER project has evaluated the relevance and performance of the noise part of the European tyre label, looking at how it works in practice, analyzing its uncertainties and suggesting how it can be improved. Its main finding is that the uncertainties in the measurement of noise level for the label are too high to be acceptable. This paper focusses on the solutions offered by STEER for an improved tyre label. With four main improvements, the overall uncertainty of the current procedure can be halved. A few possible future strategies to increase the market share of quieter tyres have been analyzed and their effects quantified. If the tyre noise label is improved and the market share of quieter tyres can be increased as project STEER proposes, area-wide reductions of up to 3 dB in road traffic noise emissions compared to the present situation are possible.
Traffic noise is one of the most predominant noise sources that affect citizens’ quality of life in urban areas. The increasing presence of alternative powered vehicles, such as electric or hybrid vehicles, could provide an improvement of such a situation due to the absence of internal combustion engines. However, tyre/road noise is independent of the vehicle type and still exists in alternative powered vehicles. Hence, efforts should focus also on reducing noise emission by means of new tyre designs. The tyre/road noise emission of newly produced tyres is currently evaluated by the Coast-By method, and as a result the rolling sound pressure level at the measuring distance, located 7.5 m away from the test vehicle is obtained. Such an acoustic index provides a very representative data of the annoyance that a pedestrian located at such distance could suffer. However, this value could be affected by external factors, such as environmental conditions. For that reason, this paper presents a methodology for extrapolating the sound pressure levels that are obtained in a Coast-By test, by means of the sound power level emitted by the specific tyre/road combination evaluated. This methodology could serve as the basis for defining a universal model to evaluate a tyre when rolling on a road, by using its sound power emission and predicting the Coast-By sound pressure level.
Little previous research results have been reported from laboratory tire-pavement noise test methods, especially on small laboratory specimens. This research aims to introduce and explore the feasibility of a new test method used with laboratory specimens. The proposed method measured the tire-pavement noise when a rolling tire from a sloping track hit a horizontal slab specimen of a given pavement mixture. A high speed camera and a weighing sensor were utilized to identify the tire-pavement contact time and distance. The contact time was found to be 30.72ms. The exact start time of contact was determined by analyzing the recorded sound signal. Altogether, five data analysis methods were employed. The analysis results were evaluated using Sound Pressure Level (SPL) and 1/3 octave band spectrum. They were compared with the corresponding reference pavements from past research, and on site results. Finally, two methods were recommended. They may potentially characterize laboratory tire-pavement noise.
Tyre/road sound emissions have been proved to be the main source of noise caused by road traffic when traveling at medium and high speeds (Sandberg and Ejsmont, 2002). Tyre/road noise has been widely studied among the last decades. However, an important part of this research has been focused, mainly, on track tests. Different track or road methods have been developed for measurement of tyre/road sound emissions. The most important ones are the Coast-By, the Close-Proximity, the Statistical Pass-By or the Controlled Pass-By methods. Among all of them, the Coast-By method has been raised in Europe as standard method concerning the approval of tyres with regard to tyre/road sound emissions as preconized in UNECE Regulation 117 (2007)[2]. However, all the above mentioned methods have several disadvantages such as the influence of environmental factors, the different results that can be obtained depending on the test track or the vehicle upon which the tests are carried out, the lack of repeatability or, the most important aspect, which is the limitation of the measured magnitude, the sound pressure level. A new methodology (Clar-Garcia et al., 2016) based on drum tests and the ISO 3744 (1994), which was developed in order to avoid these limitations, has been proved to be comparable to the Coast-By (CB) method. This paper describes how different tyres have been tested according to both the CB and the new Alternative Drum test method (A-DR) while their results have been compared. In order to be able to carry out this comparison, as the measured magnitudes and test conditions differ widely from one test to another, the standardised ISO 9613 sound propagation method (ISO 9613-2, 1996) has been applied to obtain the sound pressure value at 7.5 m from the sound power level of a tyre measured under laboratory-controlled conditions when rolling against a drum. Results have shown that both methods are not only comparable but also have remarkably similar sound spectra and, for that reason, the new methodology based on drum tests can be used in order to obtain tyre/road noise emission approved values.
Abstract
The usage of low-noise road surface can be an important and effective noise mitigation action and, in many cases, it might represent the only viable solution. After the laying of a low-noise road surface, it is necessary to verify if the planned objectives have been actually obtained: the Close Proximity Method (CPX) could be a possible method to achieve this result.
The current release of the ISO 11819 draft regarding CPX redirects to a future third part for all details about the reference tyre to be used, while the previous one gave indications on dimensions, kind of tread pattern and maintenance conditions. As well known, tyre dimensions and tread pattern are the main sources of variability of rolling noise. Even though many tyres available on the market comply with all ISO requirements, the choice of a brand or a model rather than another one could nevertheless influence results of measurements.
In this work, results obtained in several measurement sessions, repeated using different tyres, are compared, aiming to analyse the influence of the tyre choice in assessing the acoustic performance of a low-noise road surface. Limitations and advantages of the CPX method in regards to the evaluation of the effectiveness of a noise mitigation action are reported, and new perspectives are suggested, in order to improve the relationship with the noise level reduction at the receiver.
The electric vehicle is the best-positioned alternative to the ICE conventional vehicle become of, among other reasons, its environment friendly properties. One of its most significant properties is its quiet electric engine which can be a good tool for decreasing noise pollution in cities. In this respect, the electric vehicle can be acoustically assessed from different points of view; on the one hand, as a moving point source, its detectability or annoyance for pedestrians can be studied, and, on the other hand, as part of the traffic flow in a road its effect on the whole noise map. In this paper the effect of introducing a flow of electric vehicles into real urban traffic has been studied and quantified. For this purpose, experimental procedures were used to add to the NMPB ROUTES noise prediction model of the electric vehicle as a potential noise source in the traffic flow. Several conditions have been analysed and was evaluated the change in the number of citizens exposed to diverse ranges of noise levels.
Tyre/road interaction is the main source of noise emission caused by road traffic when cruising at speeds over 30 km/h. Several methods such as the Coast-By, the Close-Proximity, the Statistical Pass-By or the Controlled Pass-By have been used over recent decades to measure noise emission. However, since Regulation (EC) No. 1222/2009 on the labelling of tyres was published, only the method described in UNECE Regulation 117 concerning the approval of tyres with regard to rolling sound emissions, can be used in order to obtain tyre/road noise emission approved values. All these conventional methods have several disadvantages such as the lack of repeatibility, the influence of environmental factors or the different results that can be obtained depending on the test track or the vehicle upon which the tests are carried out. A new methodology based on drum tests and the ISO 3744:1994 has been developed in order to avoid these limitations. This paper describes the new method including the positioning of microphones, calculating correction factors, characterising the background noise caused by the drum and obtaining the sound power level of a tyre when rolling against a drum.
Tyre/road noise is becoming a more and more significant source of road traffic noise as engines become quieter. To reduce the traffic noise nuisance, low noise road surfaces and tyres have been adopted in noise sensitive areas. The durability and persistency of these low noise road surfaces and tyres are of great concerns. This study aims to quantify the effects of road and tyre deterioration on tyre/road noise. The results show that the tyre/road noise measured on five types of low noise surface material increased by 1.2–1.5 dB(A) per year. The tyre rubber hardness increased by 0.6 shore-A value per month. The tyre/road noise level increased by 0.08–0.48 dB(A) for every unit of shore-A value increase, depending on the road surface material. It is evident that the minimum effect of the test tyre aging on tyre/road noise measurement is 0.6 dB(A) per year.
The rolling noise from tyre–pavement interaction represents the greatest sound contribution from a vehicle when cruising at a high speed. To evaluate the sound levels from this source, existing standardized methods that establish different measurement procedures in both the immediate tyre surroundings, for example the Close-Proximity method, as well as at greater distances, as the Coast-By method. A fundamental parameter that can quantify the sound generation of a source is its sound power level. The standardized methods establish procedures to measure the sound pressure level but not the power level of a tyre as a noise source. For this reason, this paper presents a novel methodology based on sound pressure measurements to obtain the sound power level that a vehicle emits in Coast-By conditions, where noise is generated at tyre/road interaction. The paper describes the testing procedure used to obtain the sound power level, and it is accompanied by a mathematical simulation that studies the feasibility of the proposal. Finally, the proposed methodology is further validated through a field study.
The sound field of a point source near the boundary of two media cannot be obtained by an acoustic‐ray approach. In fact, such an approach which utilizes the reflection coefficient for plane waves leads to completely contradictory results at grazing incidence. A more rigorous solution is obtained, the procedure followed being exactly similar to that initiated by Sommerfeld to derive the electromagnetic field of a vertical dipole situated near a conducting plane. The results of such an analysis as applied to an acoustic point source are presented. As pointed out by Van Der Pol, the resultant solution may be regarded as that due to the point source and a diffuse image. The discussion of the solution is restricted to cases in which the sound source is at the boundary although it is given for all source heights. The solution shows that when the boundary medium has a high real specific acoustic impedance, non‐zero fields are obtained at all points along the boundary. For bounding media adequately described by simple porosity theory, the acoustic pressure at the boundary is inversely proportional to the square of the distance and the square of the frequency, at reasonably large distances and low frequencies. Also there appears to be decreased phase velocities along the boundary. Some calculations of the sound pressure as a function of height above Quietone show, among other things, the presence of a minimum occurring some distance above the boundary. At large distances from the source there are very large decreases in amplitude as the receiver height is increased in the region above this minimum.
Reference is made to the large number of papers over the last 10 years
on point source propagation over thin screens located on finite
impedance ground. Of late, attention has also been given to sound
propagation over flat ground having regions of differing impedance. The
goal of the study presented here is to highlight the similarities
between some of the theoretical approaches to the screen problem and the
impedance jump problem. It is shown that the procedure described here
for predicting sound propagation over impedance discontinuities may be
calculated much more efficiently than hitherto supposed. A plane screen
located on an impedance boundary is considered, with use made of the
theoretical ideas employed by Thomasson (1978). An equation that can be
used for estimating sound propagation over two-impedance surfaces as
well as infinitely long screens is derived.
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