Abstract
In the last years exchange of goods among different countries has increased dramatically and consequently the number of commercial vehicles running through roads and cities. Recent studies have shown that heavy trucks are one of the main sources of traffic noise: brakes, the engine and tyres. To deal with this issue, trucks and caliper manufacturers have raised their noise acceptance threshold. The aim of this work is to study and develop a dynamometric bench noise test program, devoted to simulate standard road conditions of heavy trucks and to analyze the relative noise behavior in laboratory without vehicle tests. The first step was the collection of the essential parameters to reproduce vehicle conditions during the noise test: brake pad and disc temperatures, brake pressures and vehicle speed. All these data were recorded with data logger equipment and also caliper vibrations were recorded installing accelerometers and a microphone in the cabin of the truck in order to analyze them and set up the dynamometric noise test program. Referring to the bench hardware, it was not possible to use the entire vehicle suspension because of the bench size, so we designed a new equipment using caliper, hub and rotor only. Thermocouple and accelerometer were placed in the same position of the vehicle and recorded the noise with a microphone. To test the reliability of the model, we performed several reference tests and we compared the results with the road truck tests. Results showed an adequate level of reliability. This allows to reduce the vehicle tests during the screening of different material performance and also the time to select friction material before the truck test. Running these tests in laboratory gives the researcher the opportunity to collect more data about friction material characteristics especially those that are difficult to record during vehicle tests. The main limit to this work was the bench size. It was not possible to experiment with a complete axle to refine the laboratory results. Another issue was that the presence of the accelerometer on the caliper limited the maximum reachable temperature to 350°C. This could be solved using a laser system to record vibrations. It is easy to figure out the saving of time and money that a reliable laboratory test could assure but we would like to point out that a noise dynamometric standard procedure for heavy trucks is still missing, while it is already set for passenger cars. This work could be a starting point to reflect on, introducing rules and procedures on the evaluation of this dynamometric noise test.
KEYWORDS: Noise, Heavy trucks; dynamometric bench, laboratory test; procedure