Volvo is one of the most well-known and respected car brands in the world, with sales in about 100 countries. The Volvo Car Group (Volvo Cars) is owned by Zhejiang Geely Holding (Geely Holding) of China. Volvo Cars was part of the Swedish Volvo Group until 1999, when Ford Motor Company bought the company. In 2010, Geely Holding acquired Volvo Cars.
As with many other environmental regulations, limits on pass-by noise emissions have become a key factor in any vehicle development cycle. Standards and legal frameworks are constantly evolving, requiring engineers to adapt quickly to new challenges. To make sure all Volvo cars can easily meet future pass-by noise regulations, the Volvo Car Group (Volvo Cars) recently teamed up with Siemens PLM Software. Relying on their longstanding relationship, the acoustics engineers chose Simcenter Testlab™ software from Siemens PLM Software to support their design processes.
High customer expectations and a stringent legal framework have made noise emission a defining competitive asset for any type of new road vehicle on the market. Pass-by noise legislation provides car builders with a framework and maximum noise emissions limits, requiring them to prove that their cars, trucks, buses and motorcycles comply with noise regulations. All the noise-testing procedures are governed by international standards. The International Standards Organization (ISO) 362 pass-by noise testing standard has become the generally accepted standard in many regions, occasionally being slightly adapted to regional or local needs.
ISO 362 describes how pass-by noise tests should be performed based on environmental and operational conditions, what instruments should be used and the minimal requirements for measurement quality. While the standard defines testing requirements, it does not impose maximum noise emission levels. Governmental bodies, such as the European Council, use legislation to define regional limits.
Both increasing traffic and continuous developments in noise emission have led to several revisions to the ISO 362 standard. For instance, the wide open throttle (WOT) acceleration test, as described in the 1998 revision, no longer reflects noise emission in a contemporary urban environment.
Always an innovation frontrunner, Volvo Cars invests extensively in analyzing the acoustic performance of every car component, a process that puts high demands on the amount and quality of test data available to engineers. With the current European Union (EU) pass-by noise regulations being revised and bearing in mind the prospect of emission levels being reduced by at least three to four A-weighted decibels, or dBA, Volvo Cars decided to try the pass-by noise testing module included with Simcenter Testlab in a pilot project to fine-tune its existing testing methods.
A major change in the new approach is the testing location. Although the ISO 362 standard still requires testing on an outdoor test track, new standards are under discussion that would allow certification testing to be performed indoors in a chassis dynamometer (dyno) facility. The advantage of indoor tests is that they are not dependent on weather conditions so productivity can increase and time-to-market can be reduced. A controlled lab environment facilitates easy, reproducible and reliable run and re-run processes for vehicle component modifications.
Volvo Cars’ latest acoustic laboratory, at the very heart of its production complex in Torslanda, Sweden, is fully equipped for indoor pass-by noise testing. Using a roller bench in a semi-anechoic chamber, outdoor pass-by noise measurement conditions are replicated with a fixed car and a ”sweeping window” of microphones simulated by Simcenter Testlab.
The number of microphones used is impressive: twenty array microphones are installed on each side of the car, while 35 separate microphones (covering 7 sources) record powertrain noise levels. The exhaust is represented by 3 sources, which are registered by 13 microphones, and 8 more microphones cover the right-hand side tires. In total, 75 microphones, 2 speed channels (vehicle and engine), 1 kick-down channel (triggering the start of tests) and 1 engine reference accelerometer all feed into the testing system.
The overall pass-by noise level produced by a car is the sum of the noise contribution from different sound sources, mainly the powertrain and tires. As indoor measurements are usually performed with slick tires, indoor pass-by levels mainly consist of powertrain noise. Volvo Cars measures tire noise on an outdoor track by equipping a vehicle with regular tires and having it coast with its engine shut off. This coast-down measurement is then repeated indoors with slicks to improve the overall tire model. The indoor noise testing allows researchers to separate powertrain and tire noise and conduct an in-depth analysis so they can rank individual components.
For Volvo Cars, initial conclusions from this new measurement method have produced interesting insights into the noise contribution of separate components under various testing conditions. The imminent introduction of constant speed testing, as prescribed in ISO 362:2007, makes these findings particularly relevant.
Tests were conducted using a 2.5l, 5-cylinder diesel engine with both slick tires and regular tires.
Using slick tires, the dominant sources in order of importance were the front tires, powertrain, rear tires, tailpipe and muffler. In higher gears and at a constant speed, the rear tires proved more important than the powertrain. The tailpipe contribution remained below that of the powertrain in all tests.
Using regular tires, the dominant sources of noise in order of importance were the front tires, powertrain, rear tires, tailpipe and muffler. The importance of the rear tires depends on how they are positioned and the gear used in the tests. The contribution of the tailpipe becomes greater than the powertrain in constant speed tests and in higher gears, but the powertrain dominated in all acceleration tests.
Engineers at Volvo Cars are particularly impressed with the transfer path analysis-based source contribution provided by Simcenter Testlab In-room Pass-by Noise Testing. Sources and paths can be modified so the effect can be seen on the receiver microphones.
As a test case, the contribution from all 6 powertrain sources was reduced by 6 dB(A) between 300 and 3,000 hertz (Hz). Source editing revealed that this led to an overall noise reduction of only about 1.25 dB(A). The experiment illustrates the difficulty in achieving even the slightest change in the overall pass-by noise level. Simcenter Testlab In-room Pass-by Noise Testing gives immediate feedback on the magnitude of modifications when adjusting individual component designs.
In anticipation of having to meet future measurement standards and maximum noise levels, Simcenter Testlab In-room Pass-by Noise Testing has become a valuable and highly appreciated tool for Volvo Cars’ acoustic engineers. The possibility of quickly adapting to test setups for these built-in standards, including room size and microphone positions, offers substantial time savings.
Automation enables technicians to easily set up dedicated measurements. Tests at Volvo Cars are conducted by two people with the direct support of Simcenter™ Engineering services. The Simcenter Testlab channel setup makes it possible to trigger the start of a test run using an acceleration kick-down. Using the software solution enables a recommended approach speed and engine revolutions per minute (RPMs) according to the chosen gear and selected testing standards. Moreover, it offers the possibility of developing a gearbox database based on collected test data. Test results are directly reported according to testing conditions for specific standards after each pass-by noise measurement, thus allowing the test engineer to get immediate validation.
Although this is the first collaboration in pass-by noise measurement, Volvo Cars and Siemens PLM Software can already look back on a solid common history. Previous joint efforts included transfer path analysis (TPA) and modal analysis and road noise TPA. The Volvo Cars’ engineering teams have come to appreciate the ongoing efforts of Simcenter Engineering to support their development processes. The Siemens PLM Software combination of top-of-the line products and an unmatched know-how plays a vital part in Volvo Cars’ continuous efforts to be the world’s most progressive and desired luxury car brand.