Tracking Down Irritating Vibrations and Noises

NVH behavior of hybrid powertrains and lightweight components is particularly complex

Powertrain acoustics has a major influence on ride comfort. Besides combustion engine and transmission, electric drives and lightweight components are playing an increasingly important part in this context. IAV is focusing much attention on the subject of NVH (noise, vibration, harshness) and assists its customers throughout the V model process. Experienced NVH engineers use modern simulation methods and provide valuable input for the virtual release of development steps.

In recent years, the classic sources of noise and vibration, i.e. combustion engine and transmission, have been joined by electric motors and lightweight components. “They all have their own particular acoustic characteristics and, in some cases, lead to new effects”, explains Dr. Bernd Findeisen, head of the NVH and Mechanics / Dynamics Simulation department at IAV. “Under load, for example, electric motors produce a typical whine not familiar from the combustion engine.” For this reason, IAV is currently extending its database by adding the scatter bands of electric drives to provide benchmarks for new drive systems as a basis for assessing their ability to compete in terms of NVH.

The challenges become particularly complex when combustion engines and electric motors are used side by side in hybrid powertrains. Wherever possible, occupants must not be allowed to notice when the combustion engine cuts in or shuts down. And during particularly quiet, all-electric operation, hitherto inaudible noises must be kept out of the passenger compartment – such as air, wind, rolling or transmission-related noises.

Lightweight components made of plastic also have an influence on acoustics. Although they reduce vehicle weight, they demand special know-how in relation to NVH rating. “Current projects are showing that these materials harbor huge potential”, Findeisen says.

Assistance from design to start of production

IAV assists its customers with matters of NVH throughout the development process. At the design stage, the experts use modern simulation and optimization methods as well tools developed in-house. “We use our methodology of modular powertrain simulation in an early concept definition phase. It is a modular system that allows us to evaluate and mathematically optimize torsional vibration behavior in a very short time. This gives us information, for example, in relation to decoupling rotational irregularities as well as for assessing rattle and jerk”, Findeisen says. Complex control structures and calibration models are also integrated into the simulation process.

In subsequent development phases, the models are refined in ever greater detail. This provides the basis for computing and analyzing acoustic phenomena, such as transmission whine, propshaft boom and rearaxle differential hum, but also the sound radiated from the oil sump or e-motor.

Tailpipe noise in particular has a significant impact on a vehicle’s sound characteristics. Using simulations, the intake and exhaust system is designed to generate the sound that is wanted. “Computations of this type are becoming increasingly important in our work because the trend is moving towards simulationbased virtual release”, Findeisen says.

To evaluate NVH behavior in the vehicle interior, IAV’s specialists use the noise-transfer path method, a combination of measurement and simulation. “Understanding the physical interaction of all components and systems is particularly important in terms of optimizing the NVH behavior of a powertrain or entire vehicle. Optimizing individual components does not automatically result in enhancing a vehicle’s NVH behavior”, Findeisen says.

However, it is not yet possible to do without measurements on component or full powertrains. For testing, IAV’s developers benefit from high-performance test benches – e.g. for combustion engines, hybrid drives, transmissions and e-motors. “We conduct vibration and acoustics measurements. We can use these to validate our models in tests and further enhance prediction quality”, Findeisen explains.

Transmission noise level reduced by ten decibels

IAV’s profound expertise in NVH is directly reflected in measurable improvements. In close collaboration with the company’s transmission specialists, it has been possible to reduce the noise level of a transmission by ten decibels as a result of correcting gear toothing. And with a latest-generation centrifugal pendulum IAV experts have been successful in more or less halving the vibration of a propshaft in the lower speed range.

“Psycho-acoustics is also an important aspect for us”, Findeisen says. “For this reason, we have developed our own gage for assessing harshness. Using it, we can better replicate the way people perceive it and enhance the sense of vehicle occupant well-being.”

NVH Service Portfolio

Simulating and testing the NVH behavior of the powertrain, its components and functional systems from concept design to manufacturing readiness using state-of-the-art simulation, measurement and testing methods.

  • Optimization of combustion engine, hybrid and electric drive systems
  • Many years of expertise in NVH development
  • High-performance computers, test benches and measuring equipment
  • Simulation and testing on a “one-stop shop” basis
  • Modal analysis, operational vibration and time domain analysis
  • Structure-borne sound, airborne sound, sound design, psycho-acoustics
  • Transfer path analysis, mounting design
  • Evaluation of passenger compartment comfort
  • Transmission rattle, whine, micro and macro-geometry optimization
  • Layout and optimization of decoupling elements
  • Knock sensor positioning
  • Integration of mathematical optimization methods into the development process
  • Combining methods (FEM, MBS, EHD, CFD), calibration and control technology
  • NVH benchmarking
  • NVH consulting