Donaldson Company, Inc. is a leading worldwide provider of filtration systems and replacement parts. Founded in 1915, Donaldson serves customers in the industrial and engine markets, including dust collection, power generation, specialty filtration, compressed air purification, off-road equipment, industrial compressors, heavy trucks and light vehicles.
Business is changing at Donaldson Company, Inc. (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 coming in for designing and building complete air intake systems for long-haul trucks. There’s definitely a sense of urgency since truck engines are being redesigned to meet looming deadlines for strict Euro 6 emission standards.
This shift in research and development (R&D) from the original equipment manufacturers (OEMs) to the suppliers follows a trend in the segments in which responsibility for system development is increasingly being delegated to subcontractors. The result is a win-win situation in which OEMs are better able to focus on total vehicle design while capable suppliers gain new business due to their system-level knowledge.
Procuring these major contracts is no simple matter, as Donaldson engineers can attest. Although filter orders are based mostly on specified sizes 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 the intake nozzle, air-handling ducts, support brackets, filter housings and rubber bellows.
There are a number of packaging constraints that complicate the task because the ducts must snake their way around parts mandated by Euro 6, including the selective catalytic reduction (SCR) and exhaust gas recirculation (EGR) units, which take 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 affecting air quality and temperature and, therefore, engine efficiency.
One of the most challenging aspects is to keep the air intake system from contributing excessively to either the cab noise or pass-by noise levels of the vehicle. In practice, this means keeping its contribution of 10 decibels (dB) lower than the vehicle target sound pressure level. For example, if a vehicle has a target of 70 dB for the total cab sound pressure level at cruising speed (100 kilometers/hour), the target contribution sound pressure level of the air intake system should be below 60 dB.
“Cab acoustics impact 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,” says 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 mockups and trial-and-error testing is just too expensive, timeconsuming and uncertain given the huge number of interacting variables.”
According to Proost, the answer is using acoustic simulation that enables engineers to evaluate sound levels and possible noise reduction fixes quickly and easily using computer models. Rather than outsourcing such simulation 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,” says Proost. “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.”
Donaldson selected the acoustics simulation from the Simcenter Portfolio from Siemens Digital Industries Software as its acoustics simulation tool of choice. The decision to select Siemens Digital Industries Software technology was based on the company’s reputation; the widespread use of the software in the automotive industry; the quality of the PLM vendor’s delivery of technical assistance 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, with the aim of having 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, ongoing 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,” says Proost. “Simcenter Engineering services have been with us every step of the way with technical assistance to validate models and fine-tune our overall approach.”
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 it 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 so 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 Simcenter SCADAS™ Mobile hardware with its easy portability, speed in gathering data and seamless compatibility with the simulation solution from the Simcenter Portfolio. This measurement enables engineers to back-calculate the noise transfer function (NTF), the ability of the air to transfer sound energy from 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 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 Simcenter SCADAS Mobile hardware for vibration control for accelerated fatigue-life shaker tests. This demonstrates in just a day or two the ability of the air intake to withstand the vibrations it will likely experience over a lifetime on the road.
“Using a predictive process based on the acoustics simulation solution from the Simcenter Portfolio, 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 mockups,” says Proost. “This approach gives us the capabilities that 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 from vehicle manufacturers around the world.”