Effect of turbo compressor outlet hose used in heavy commercial vehicles upon turbo compressor originated whistle noise propagation

Diesel engined heavy commercial vehicles that is having turbocharging are being used in lots of different areas for cargo transportation. Heavy commercial vehicles that are classified according to carried load such as tractor, construction series and road truck, are designed considering tough road conditions. Design process is changed according to scope of the program. In case of totally new design, duration is exceed standart process which is 4 years. Design phase includes lots of input parameter such as cost, performance, visuality, functionality and comfort in its structure. Expectation from the issue criterias which are visuality and comfort having long term verification and validation processes are jumped to automobile level in recent years. For this purpose, one of the comfort criteria called as vehicle interior noise's being low, was become selective factor and transformed to open course which was required to be researched. In order to respond this requirement, one of the noise generated by turbo compressor, which was used in heavy commercial vehicles, and mentioned noise's diffused section called as hot side high pressure hoses were investigated and started to work on designs to reduce the noise within the scope of thesis. Since the design change on turbo compressor was not feasible considering the phase of the project, study was focused and restricted on air induction system. Spesific to study, the progression being follewed are; identification of the current situation, investigation of the root cause of the problem, design and manufacturing, testing of the last situation with validation. In the first step, vehicle test was performed in order to actualise designated manoeuvres with experts in their field and the vehicle, which was called to has noise subjectively, was selected. It should be pointed that, manoeuvres were special to company. Following this, tests were re-performed to actualise identical manoeuvres by setting microphones into the several points of vehicle. At the end of test, gained data was processed and the frequency band having noise was determined on colormap. After that, root cause research was done upon the components which could make noise on designated frequency band and at the end of the investigation, it was seen that noise was originated from turbo compressor after eliminating background sounds on colormap and implementing A filter which was simulated human hearing behaviours and suitable for automotive industry. Since the improvements, which could be done on noise source, were not feasible on the basis of time and cost, study was focused on compressor outlet pipe and while at the same time hot side high pressure hose that was the component diffusing the noise. Due to fact that there was no opportunity to work on noice source, redesign process of the air induction system part was forced relevant engineers to make the changes on time respectively. In the second step, the design parameters of hot side high pressure hose were reviewed in order to increase quietness. Damping and isolation parameters were investigated within the scope of quietness study. Wall thickness change from 5 mm to 9mm on glass fibered PA based commercial polymer was invastigated spesific to damping parameter. Secondly, raw material change from glass fibered PA based commercial polymer to aluminium casting alloy was investigated spesific to isolation parameter. Instead of using currently used plastic material having 5mm wall thickness, that was reinforced with glass fiber, identical reinforced plastic material usage but having 9mm wall thickness was done for the sake of damping and wall thickness criteria was investigated. In the direction of criteria, thick part was manufactured in the same plastic blow molding tool and part was assembled into the vehicle that performed previous tests. It was seen that, there was improvement on the noise level subjectively after the repeated test for the problematic frequency band while there was worsening for the upper frequency band which was close to upper hearing limit that was associated with high pitched sound. Improvement on the problematic frequency band was verified after the data, that was got from the vehicle, was processed on colormap by implementing A filter and eliminating background sounds as well. Again on the basis of damping, aluminium alloy casting material usage instead of glass fiber reinforced plastic material, that had same wall thickness and routing, and different material effect were investigated. In this direction, new casting tool was manufactured and new part coming from production was assembled into the vehicle that performed previous tests. It was seen that, there was an important level of progress regarding noise subjectively after the tests that were re-done. Processed situation of the test data with added A filter without background noises on colormap was a qualification which was verified the reduction of noise level. Finally, on the basis of another quietness parameter, which was isolation, applicability of material that has insulant attribute was investigated. In this content, a commercial isolation material, that has insulant attribute, was assembled onto the plastic hot side hose which was not in serial production line, and measurements was taken from the same test vehicle by applying identical manoeuvres with same drivers and auditors. It was seen that, there was reduction on noise level according to reference level in both cases: subjective assessment as well as measurement results which had same dB filter without background noises. Change on the subjective assessment was presented as the biggest subjective improvement by drivers and auditors compared to other tried options which were material wall thickness change and raw material change. On the other hand, due to fact that the materials, which showed insulant attribute, used on hot side high pressure hoses was not feasible on the basis of process time and cost and was not widely distributed in industry at least based on heavy truck sector in Turkey for serial production, improvement was not offered a solution. At the end of investigated parameters, it was seen that, different material usage provided a significant improvement, which was considered with all positive and negative effects, compared to other investigated parameters which were wall thickness change and insulated material usage on hot side high pressure hoses and material change from glass fiber reinforced polymers to aluminium casting alloys was offered as the most effective solution. For this purpose, investigation of the different glass fiber used reinforced polymers' and aluminium casting materials' damping coefficients were offered related with different material usage.