Browse Publications Technical Papers 2002-01-2600

Mojacar and Los Angeles City Traffic Vehicle Testing: A Comparison & Analysis of Subjective Ratings and Objective Measurements 2002-01-2600

For several decades now, OEM's, brake systems and other tier-2 suppliers have been running extended mileage vehicle tests for noise and wear. In North America (NA), these have more or less converged toward the Los Angeles City Traffic (LACT) test and, in Europe, toward the Mojacar/Spain circuit. Today, results from these two test sites are almost always an integral part of the project sign-off process. Additionally, as OEM's based in one of these two key markets seek to grow sales in the other, it has become increasingly necessary to know if good results at one test site (e.g., Mojacar) will be a reliable indicator for performance in the other market (e.g., NA). Full brake system (FBS) suppliers who have to be in a position to ensure good global performance for a specific platform have to be particularly savvy about similarities and differences between these two very widely used test circuits.
The first part of this paper provides an overview of the Mojacar and LACT vehicle test routes. Comparative vehicle test data / information is presented for a variety of test attributes that allow overall conclusions to be drawn in terms of the extendibility or relevance of results from one test route to vehicle usage in the other market.
In the second part of this paper, delving into further analysis, the correlation of subjective driver ratings to measured parameters such as sound pressure levels (SPL) and noise duration is investigated. Ideas on how to improve the correlation by combinations and further calculations from the measurements are also presented.
The need for this work was driven by the fact that while most sign-off requirements are still based on subjective driver noise ratings that depend highly on trained drivers, the alternative -- use of objectively measured values -- can only be accepted for brake noise evaluations if it reflects the ‘average’ perception of the drivers.
The analysis of subjective and objective data is divided into two parts. Firstly, data acquired from a brake noise measurement system from two-week long vehicle tests at Mojacar is analyzed. Brake noise data like sound pressure level (SPL), frequency and noise duration is compared to driver evaluations. The correlation of subjective noise ratings to data such as the max. SPL, the percentage of noisy stops, and combinations from SPL and noise duration, is examined. Secondly, for a more detailed investigation, single-stop subjective ratings are compared to noise data measured by binaural head measurement equipment. In this case as well, the relationship of driver ratings to measured data such as SPL and noise duration is investigated; these driver ratings are then also compared to psycho-acoustic factors calculated from time-domain noise data.
From an overall standpoint, the output of this work is expected to facilitate the potential incorporation of meaningful objective measurements into future customer evaluations and sign-off processes.


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