The MANN+HUMMEL Group is one of the world leaders in development, production and distribution of liquid and air filter systems, intake systems and cabin filters. Additional products include cylinder head covers made of plastic with many integrated functions for the automotive industry, and filter elements for the maintenance and repair of motor vehicles.
The light turns from red to green. A sports car starts off with a roar. You can feel the envious glares from nearby pedestrians as they cannot resist the temptation to look. That powerful sound of a sports engine is a carefully engineered mix of tunes and tones, bass and booms. Even the familiar engine sound of a luxury limousine or a sedan is thoughtfully designed by acoustic engineers. That distinctive engine sound mirrors the brand identity of a vehicle or manufacturer.
Creating the right sound has long been the task of engineers who specialize in engine acoustics and exhaust acoustics, but not anymore. The air flow tubes and ducts as well as the air inlet of a car are sound media that cannot be neglected. Engine noise originating from the combustion process can radiate into the ducts and up to the inlet, producing undesirable sounds.
Not only should a car’s engine sound right, it should also be fairly quiet. Noise emission regulations are becoming more stringent. In order to reach demanding target levels, car manufacturers and parts suppliers (from air intake to exhaust suppliers) need to work hand-in-hand to get the sound right.
The MANN+HUMMEL Group (MANN+HUMMEL) is one of the original equipment suppliers that has always taken the acoustics challenge seriously. The company’s product portfolio includes air filter systems, intake manifold systems, liquid filter systems, cabin filters and cylinder head covers. MANN+HUMMEL designs and manufactures complete air intake systems, from air inlets to air manifolds.
The shared objective of all car manufacturers is to generate more engine power with less fuel consumption. The air intake system functions as the lungs of a car by supplying and filtering ambient air to the engine. It delivers the right amount of clean air to the engine to ensure the most efficient combustion process, filtering and separating oxygen from humidity or dust particles. What remains is pure air that enters the combustion chamber.
It is not only engine performance, but also engine reliability that requires flawless air intake. Clean air is essential for smooth, long-term engine operation. Pollutants, such as dust or soot, can enter the combustion chamber and cause premature wear on the engine. Air intakes are designed to ensure maximum performance and durability of the engine under any operating conditions.
The acoustics of the air intake system also need to be considered. MANN+HUMMEL has a global team that is dedicated to relentlessly improving the acoustics of air intake systems, which have critical acoustical behaviors by nature. Air cleaning systems are typically considered troublemakers. The acoustics engineering team performs full acoustical analyses on air cleaners, from concept to validation and troubleshooting.
The task is always difficult because the engineers have to adjust a design that has already been optimized for maximum engine performance and reliability. They cannot significantly modify the design for the purpose of acoustics optimization. While acoustic optimization comes last in the process, it is not the least of engineering challenges. In a competitive world, a perfect air cleaner acoustics are a strong asset that enhances the value of a brand.
Recently, MANN+HUMMEL has taken acoustic engineering to the next level by introducing the Symposer, a sound quality optimizer. The Symposer is an additional component that is placed at the heart of the engine with a membrane that resonates at a fixed frequency. It transmits a desired sound into the car’s interior. With the Symposer, the intake system is now used as an instrument to emphasize the acoustic character of the car.
Due to local constraints, regional teams in France, Korea, the United States, Japan and China have also adapted sound characteristics. In some Asian countries, air intakes need to be fitted with an extra valve to prevent water from entering the air duct. This influences the overall acoustic behavior and necessitates additional analyses to ensure that the target sound pressure level is met. Temperature variations, from extremely hot in equatorial regions and extremely cold around the polar circle to humid air conditions in tropical latitudes also influence the air intake acoustical design. When taking up the challenge of optimizing sound design around the world, MANN+HUMMEL acoustical engineers need easy-to-use, reliable tools that let them understand, compare and share the acoustical behavior of numerous designs with the core German team as well as with other engineers worldwide.
In the engineering world, prototypes are scarce valuables. Engineers at MANN+HUMMEL seldom have access to full vehicle or parts prototypes. Under these circumstances, they need to rely on methods that allow them to optimize the product without the need for a prototype. In the product development process, simulation is essential to delivering a final product that meets customer requirements.
In low frequencies, simulation engineers consider the system’s acoustical behavior to be uniform on any section of the air duct with unidirectional sound pressure waves. However, when frequencies jump over 500 hertz (Hz), transversal acoustic effects distort the analysis. Neglecting the rising transversal effects at higher frequencies leads to huge assessment errors.
The trend towards turbochargers that boost engine performance has made frequencies up to seven kilohertz (kHz) a common phenomenon. With this turbocharging trend, acoustic engineers at MANN+HUMMEL needed a fast, efficient and reliable acoustic simulation tool that would allow them to understand multidirectional sound effects and precisely fine-tune parameters at any stage of the development cycle. The tool needed to be easy-to-use, so that both experts and beginners worldwide could work with it consistently.
To efficiently solve its acoustic issues, MANN+HUMMEL has relied on LMS Virtual.Lab™ Acoustics software since 1995. Julia Schempp, noise, vibration and harshness (NVH) acoustic engineer at MANN+HUMMEL, is an expert user and advocate of the software.
“LMS Virtual.Lab Acoustics is very reliable and when we compare test to simulation results, we see a good match,” says Schempp.”
Matthias Alex, head of the company’s Center of Competence and Schempp’s manager, acknowledges that the software efficiently supports his global team when fulfilling the difficult task of accurate acoustics prediction: “Thanks to an easy-to-use and dependable tool like LMS Virtual.Lab Acoustics, our local acoustic experts are able to respond quickly to any customer’s request.”
There is no unique process for the acoustical optimization of an air intake system. It starts with the customer requirements. Some automotive original equipment manufacturers (OEMs) may ask for a relative sound transmission loss (delta decibels) on parts of the system, while others will deliver a target curve, showing the sound pressure level against revolutions per minute (RPM), which the developed part has to comply with. The constraints, however, remain the same in all cases.
Acoustic engineers perform improvements on a draft design that has been computed and optimized by the computational fluid dynamics (CFD) department. Tangible data such as the shapes, lengths and diameters of ducts and other elements can only be modified in exceptional situations. The air intake package size is also fixed. The final design needs to fit in a prearranged box, approximately the size of a shoe box, for the air cleaner.
Following the motto “any size, any shape,” engineers adjust all parameters to create a design that will fill the often tiny space under the hood. Finally, there are the absolute laws of physics that engineers have to deal with. A long neck (total length of tubes connecting the intake to the engine) will induce low frequency resonances.
A flat air cleaner box amplifies sounds like a loudspeaker. Therefore, there seems to be little freedom left for the engineers to tune the parameters. In order to trap unwanted noise, the engineers add a rectangular piece, called a resonator, to the design. The engineers will place a resonator to target each annoying frequency peak, voiding the disturbing sound waves. The resonator achieves the desired acoustical effect without obstructing the air flow. It is only when troubling noise occurs on a large frequency range that a redesign of the system, such as an increase of duct diameter, is considered in order to optimize both air flow and acoustics.
Because design optimization should happen as early as possible in the development process, the integration of turbochargers in the engine brings a new challenge. Turbochargers require calibration, which takes place toward the end of the development cycle, and often modifies existing frequency peaks. It can also create a shift of the resonance in the frequency range. The size, shape or position of the resonator needs to be adapted. Acoustic engineers have to solve this issue at a development stage where they have even less freedom to adjust parameters.
LMS Virtual.Lab Acoustics is an integrated solution to minimize noise and optimize sound quality in air intake designs. It can be used to simulate both internal and external acoustic radiation. LMS Virtual.Lab Acoustics for air intake and exhaust systems addresses the myriad noise issues that acoustic engineers typically face. Standard transmission loss analyses based on finite element (FE) acoustics technology provide fast and clear insights into potential noise problems.
Engineers also rapidly obtain dimensions of countermeasures, such as resonators or quarter wavelength tubes, using parameterized computer-aided design (CAD) for geometry-based optimization. In addition, LMS Virtual.Lab users can customize the software for their specific applications. The software perfectly fits the internal development processes and fully integrates into the computer-aided engineering (CAE) environment.
Beyond standard applications, LMS Virtual.Lab Acoustics enables you to tackle the most complex noise problems. For example, flow-induced noise, which results from acoustic leaks in the air intake system, can be analyzed with LMS Virtual.Lab Aero-Acoustics based on the input from CFD analyses. Internal pressure fluctuations or engine vibration can also excite the shell of the intake manifold.
To address this issue, engineers need a vibro-acoustics solver, such as the integrated LMS Virtual.Lab structural finite element method (FEM) solver that resolves the fully-coupled problem instantly and accurately. The effects of temperature and air flow on the acoustic performance are captured with high fidelity. Coupling these sophisticated acoustic technologies with the LMS FEM automatically matched layer (AML) technology results in accurate, fast and efficient noise simulations.
Time is always a constraint. MANN+HUMMEL engineers sometimes have less than three weeks to optimize a design. A complete system model takes up to 100,000 degrees of freedom (DOF) into account.
“Fast solvers are essential to deliver results on schedule,” says Schempp. “The speed of the LMS Virtual.Lab Acoustics solver is a great advantage in that regard. But we need to go some steps further and find new ways to optimize our simulation processes. Automated tools are required.
“To predict sound pressure levels on the air cleaner, we have developed an automated process and implemented this in LMS Virtual.Lab Acoustics. It lets us immediately compute a transmission loss curve, with all the correct boundary conditions. This saves significant development time.”
Another automation tool provides orifice noise analyses based on the absolute sound power level emitted by the engine. On top of saving time, automation standardizes processes. MANN+HUMMEL engineers will introduce more automated tools in the future.
“We are currently in the deployment phase of a new library of standard components in LMS Virtual.Lab Acoustics that will especially help us to get faster through the quotation phase,” says Schempp.
Designing a filter right the first time can have a big impact on profitability. Size, position and a total number of resonators may vary from one design to the other. Adding or deleting a resonator respectively increases or decreases the complete part’s price. If a few cents are multiplied by the total number of produced parts and price incorrectly, estimations might be way off. A quick and accurate price estimation based on fast and accurate simulation is a must. The engineering team often has to provide a price estimate on a design overnight.
There are other cost constraints that even the manager of an acoustics department has to consider. On the manufacturing side, huge economies of scale can be realized when reducing the number of design variants. The number of engine variants has dramatically increased in the past years. Manufacturers no longer focus on the traditional 1.2 or 2.0 liter engines, but instead have introduced many variants, such as the 1.8-, 2.2- or 2.4-liter engines.
Meeting the customers’ requirements becomes more difficult from a technical point of view, but also raises the issues of manufacturing costs. In some cases, it might be beneficial to over-engineer a system that will be used with both downsized and high-performance engines. A single design will fulfill the performance, durability and noise requirements of multiple engine variants, and can bring manufacturing costs down.
Engineers at MANN+HUMMEL tackle daily challenges when optimizing the acoustics of air intake systems. Extreme precision is required to fine-tune parameters within strict boundary conditions. LMS Virtual.Lab Acoustics is the trusted tool to perform accurate prediction on tough deadlines.