Ideal solution for design changes to meet Euro 6 emission standards and tougher OEM requirements
Jul 18, 2014 -- Business is changing at Donaldson, one of the world’s largest manufacturers of filters for trucks, buses, construction equipment and industrial machinery. In addition to orders for standard and custom air filters, a growing number of requests are for designing and building complete air intake systems for long-haul trucks that will meet current Euro 6 emission standards.
This shift in research and development work from the OEM to the supplier follows the trend in other segments where responsibility for system development is delegated more and more to subcontractors. The result is a win-win situation with OEMs better able to focus on total vehicle design while capable suppliers gain new business from their system-level know-how.
As Donaldson engineers can attest, landing these major contracts is no simple matter. Whereas filter orders are based mostly on specified size and materials, the air intake system must be developed around broad system requirements, such as filtered air quality and temperature, air handling volume capacity and cab noise. Teams must design and piece together a whole assembly of parts including intake nozzle, air-handling ducts, support brackets, filter housings and rubber bellows.
Complicating the task are mind-boggling packaging constraints in which the ducts must snake their way around parts mandated by Euro 6 including the Selective Catalytic Reduction (SCR) and Exhaust Gas Recirculation (EGR) units that hog up available space. Teams must also determine the best position for the intake nozzle – at the top or rear of the cab, or near the nose of the truck – a critical factor impacting air quality and temperature, and therefore engine efficiency.
Truck cabs as quiet as cars
One of the most challenging aspects is to ensure that the air intake system will not contribute excessively to either the cab noise or pass-by noise levels of the vehicle, in practice this means keeping its contribution 10dB lower than the vehicle target sound pressure level. For example if a vehicle has a target of 70dB for the total cab sound pressure level at cruising speed (100km/h), the target contribution sound pressure level of the air intake system should be below 60dB.
“Cab acoustics impacts driver fatigue, safety and productivity – especially on long-haul trips of a week or more – so truck manufacturers put noise reduction high on their list of design requirements,” explained Gert Proost, Engineering Manager for On-Road Vehicle Filtration at Donaldson’s European development center in Leuven, Belgium. “Meeting interior and pass-by noise targets using physical mock-ups and trial-and-error testing is just too expensive, time-consuming and uncertain, given the huge number of interacting variables.”
Gaining acoustic simulation expertise
The answer, according to Mr. Proost, is acoustic simulation that enables engineers to evaluate sound levels and possible noise reduction fixes quickly and easily using computer models. Rather than outsourcing such simulations work to other facilities and putting up with long waits in shuffling project iterations back and forth, the Leuven group decided to bring acoustic simulation in-house. “Doing acoustic simulation ourselves is highly efficient. We can see how sound characteristics vary with slight changes in components, materials and geometries. This gives our engineers tremendous insight into the acoustic behavior of the entire system,” said Mr. Proost.
Donaldson selected LMS Virtual.Lab Acoustics as the acoustics simulation software of choice. The decision was based on reputation and widespread use of the software in the automotive industry, the technical assistance available from Siemens PLM Software, and the modeling capabilities of the software in handling airborne as well as structure-born noise and vibrations. Donaldson is currently using the simulation software to develop an air intake system for a major European truck manufacturer aiming to have one of the quietest long-range truck cabs on the market. Donaldson has also been approached by other vehicle manufacturers requesting quotes for system-level designs. “Clearly, on-going work with the initial truck project will enable us to employ the same approach for future contracts in developing complete air intake systems that produce minimal cab noise,” Mr. Proost noted. “Siemens has been with us every step of the way with technical assistance to validate models and fine-tune our overall approach.”
Finding and fixing unacceptable noises
As the first simulation step, Donaldson engineers represent the air intake system with a boundary element method (BEM) model, a technology particularly well suited to studying airborne noise since the method does not require engineers to go through the tedious task of modeling interior air volumes. This BEM model is used to determine standing-wave frequencies produced in various duct sections. Structure-born vibrations are studied using a coupled finite-element method (FEM) analysis to ensure that standing waves do not excite ducts and other parts of the system to vibrate at resonance.
Next, engineers compute the transfer function of audible noise transmitted from the nozzle to the driver’s ear. For this computation, they set up a low-frequency sound source in the cab and measure the corresponding frequency response at the nozzle with a LMS Test.Lab SCADAS Mobile signal data acquisition and analysis system – used for its easy portability, speed in gathering data and seamless compatibility with LMS Virtual.Lab. This measurement enables engineers to back-calculate the noise transfer function (NTF) – the ability of the air to transfer sound energy from the nozzle to the cab. Finally, the NTF is multiplied by the combined airborne and structure born vibration energy to determine total interior cab noise. The result is a color-coded 3D plot of sound energy distribution in the cab interior to identify any hot spots of sound power density. Engineers can then quickly modify the intake design with resonators, stiffeners and other modifications to eliminate resonances. They almost immediately see the results of these modifications. A few rounds of these changes are generally all it takes to optimize cab noise levels.
Near the end of development, the Donaldson engineers use a LMS SCADAS Vibco vibration control system for accelerated fatigue-life shaker tests. This demonstrates in just a day or two the ability of the air intake to withstand the vibration it will likely experience over a lifetime on the road.
Business value of predictive processes
“Using a predictive process based on LMS Virtual.Lab Acoustics, our engineering teams can perform studies in a few hours that would take months or even years and cost tens of thousands of Euros in physical mock-ups,” noted Mr. Proost. “This approach gives us the capabilities we need to develop complete air intake systems optimized to meet rigorous noise limits. Our cutting-edge acoustics know-how has certainly become a critical competitive advantage and helps us gain research and development contracts up the supply chain for vehicle manufacturers around the world.”
For more information, visit http://www.plm.automation.siemens.com/en_us/ or contact:
United States :
LMS North America , a Siemens business
Peter De Clerck
LMS International, a Siemens business
Tel: +32 16 384 200