February 24, 2014 -- Instead of having an outside facility analyze cabin noise, Italian truck manufacturer Iveco predicts sound levels using LMS Virtual.Lab Acoustics to streamline the development process and improve designs through deeper insight into vehicle behavior.
During the past few years, the commercial truck industry has been on a bumpy road. The global economic slowdown reduced orders dramatically and a long-term sales recovery is still far from certain. Moreover, manufacturers must make significant nose-to-tail redesigns for vehicles to meet tough new government fuel efficiency and emissions regulations. All this drains the limited resources of beleaguered truck producers as they try to hang on in an evolving market while an economic recovery slowly gains traction.
Process changes underway
In the face of these challenges, process changes are underway to bolster profitability and market share at Iveco, a leader in the global commercial highway transportation industry. Based in Turin, Italy, this subsidiary of the Fiat Group has five R&D centers and 28 factories in 16 countries around the world producing light, medium and heavy-duty trucks as well as buses and vehicles for defense, firefighting and other specialty applications.
A corporate-wide initiative focuses on improving product design – including vehicle cost optimization and higher cabin interior quality standards – and on streamlining product development processes through the use of virtual prototyping and simulation. In light of this initiative, Iveco managers across all vehicle platforms and business units were directed to evaluate their operations and implement appropriate changes.
One area receiving close scrutiny was the prediction of truck cabin noise levels. Cabin acoustics is one of the critical elements in vehicle development and a key selection criterion for truck fleet managers, especially in over-the-road trucks making long-haul trips of a week or more. In this premium vehicle segment, quietness reduces driver fatigue for increased safety, comfort and productivity.
Diminishing sound levels is often difficult, however, because noise sources such as the engine, exhaust, air intake and transmission all interact within short distances from the cabin – sometimes less than a meter away. As a result, acoustics must be exhaustively studied in minute detail to accurately predict excessive cabin noise early in development.
“Previously, Iveco used a separate research facility to build analysis models, perform simulations, correlate results and identify sound-level hotspots,” explained Massimo Martini, who is responsible for vibro-acoustic and NVH evaluation at Iveco. “Data was exchanged via Ethernet and disks. Lots of emails, telephone calls and visits between sites were needed to discuss briefings, interpret results and resolve issues. Outsourcing the analysis was cumbersome and time-consuming. Difficulties were compounded when we had to convey engineering change requests to analysts and transfer the massive amounts of test data required to validate and refine analysis models.”
Faster and better simulation
To eliminate these bottlenecks, Iveco brought their main acoustic simulation activities in-house with a license for LMS Virtual.Lab Acoustics software. “The LMS solution was selected based on its reputation and widespread use in the automotive industry, and on the versatility of the technology in handling complex acoustic simulation applications,” noted Mr. Martini. “By enabling engineers to perform their own analyses, acoustic simulations that used to take up to four weeks are now completed in a week or less. This speed helps engineers perform a greater number of simulations early in development so that fewer prototype test cycles are needed and vehicle development time is reduced. Most importantly, LMS Virtual.Lab Acoustics provides engineers with greater insight into sound sources, noise paths and overall vehicle acoustic behavior. This resolves issues faster, better evaluates performance trade-offs and optimizes designs faster than ever.”
Seamless link to LMS Test.Lab
Efficiency is also gained in importing data seamlessly from the LMS Test.Lab system used in the Iveco measurement group. This tight integration between the LMS test and simulation solutions helps the engineering and test groups work closely together in an efficient, coordinated manner.
According to Mr. Martini, one exceptional advantage of LMS Virtual.Lab Acoustics is that it supports both finite element method (FEM) and boundary element method (BEM). This gives Iveco the flexibility of using either of these methods depending on the type of sound propagation being studied.
Using these simulation tools, Iveco engineers use a highly disciplined approach to acoustic studies and sound abatement prescribed by the Centro Richerche Fiat S.C.p.a. (CRF), the Fiat Group’s major R&D center where LMS technologies are also used extensively. Indeed, Mr. Martini explained that LMS Engineering Services was instrumental in quickly enabling Iveco to deploy LMS Virtual.Lab Acoustics, train engineers and establish a smooth workflow for the new solution with minimal disruption to normal operations.
Smooth sounding interiors
The approach implemented at Iveco for truck acoustics is an adaptation of typical methods used throughout the automotive industry for passenger cars. The process begins with acoustic requirements provided by the marketing and quality group, basically a list of preferred sound levels taken at the driver’s ear at given vehicle speeds and loads. Engineers focus on reducing loudness, of course, but also focus on acoustic subtleties, such as sharpness, frequency, transitions between different gears and any sounds that drivers might consider unfamiliar or objectionable. From these requirements, engineers compile a set of vehicle technical specifications (VTS) that serve as global vibro-acoustic targets that are then cascaded down to secondary targets for major subsystems and components, such as the engine, transmission, exhaust, air intake, chassis, and suspension.
Next, engineers create FE or BEM models of the various components and subsystems to determine natural frequencies, bending moments, vibration amplitudes and operational deflection shapes. Analysis results are then correlated with supplier data and tests of actual parts on predecessor vehicles and the simulation models are adjusted accordingly.
Hitting acoustic targets
Confident in the models’ accuracy, engineers can then iteratively modify the designs and run further simulations until acoustic targets are met for components and subsystems. These optimized models are combined into an overall global vehicle model, including a cavity model complete with various panels – the dashboard, doors, overhead area and floor – that vibrate to produce interior noise. Simulations are then performed on this global vehicle model to predict cabin noise and optimize the overall acoustic performance.
In this process, LMS Virtual.Lab Acoustics has a range of tools aimed at identifying and reducing noise problems. Frequency response functions (FRF) are used to evaluate the behavior of the structure at various noise-producing vibration frequencies. Transfer path analysis (TPA) traces vibration paths back through the structure to determine noise sources. Noise transfer functions (NTF) represent stiffness properties in the structural transmission path.
Contribution analysis helps identify which interior panels are the greatest noise producers. This gives engineers insight into where to add damping materials, stiffen parts, insert ribs, modify component geometries, thicken walls or shift part locations to prevent vibrations from entering the cabin and also reduce material costs by determining which parts are not so useful in sound abatement. Operational deflection shapes of the frame are also studied to understand how the full structure deforms at particular frequencies that may cause the most interior cabin noise. During this optimization process, engineers make adjustments throughout the structure, re-run the acoustic simulation and quickly see the result in color-coded sound-pressure maps.
“Once the vehicle acoustic model is created, engineers quickly evaluate alternative designs and explore acoustic modifications instead of building and reconfiguring a physical mock-up. Ten years ago, all acoustic work was done at Iveco through hardware testing. Now, simulation has cut the number of test cycles in half. In the next five years, plans are to start trimming the number of test cycles down to two: one set at the beginning of design to adjust the simulation models and another near the end of development to verify the acoustic performance of the final product. This level of reliable acoustic prediction lower costs of testing and materials while continuing to improve the acoustic performance of our vehicles – both powerful competitive advantages in a tough global market.”
For more information, visit http://www.lmsintl.com/ or contact:
Peter De Clerck
Tel +32 16 384 200
LMS North America
Tel +1 248 502 2380