Vehicle acoustics are considered to be more and more important for development engineers of automotive manufacturers and of automotive suppliers. The goal of acoustic vehicle development is no longer simply a quiet product. It is rather a suitable acoustic atmosphere in the vehicle. To achieve this goal, detailed studies of the noise generated by engines, auxiliary units and power transmission are necessary, as well as of tire-road noise, wind noise, and components such as HVAC systems. In addition to acoustic optimization, creating the best possible vibrational comfort is very important.
To cope with these needs, FKFS has set up its own acoustics department, right back at the start of the 1970s. Research and development projects on acoustics and vibrations in engines as well as acoustics and vibration of vehicles are currently ongoing in two closely-linked departments, both with excellent equipment and outstanding staff.
- Tire-Road and Rolling Noise
- Drivetrain Acoustics
- Squeak and Rattle, Operational Sounds
- Vibrational Comfort
Whereas starting and acceleration maneuvers at lower speeds are dominated by the drivetrain noise, at least for conventional drives, at other operating points up to around 120 km/h the tire-road noise dominates the noise level. At higher speeds, aerodynamic noise – and therefore aeroacoustics – come to the fore. In addition, flow noise caused by components such as air conditioning systems and cooling fans has to be taken into account regardless of the driving speed.
Regarding the interior noise, aerodynamic noise has a detrimental effect on comfort, in certain frequency bands even at significantly lower speeds than the above mentioned 120 km/h. This fact particularly applies to electric vehicles, where the aerodynamic noise is not masked by the noise of a internal combustion engine. In order to optimize the acoustics, it is therefore necessary to be able to isolate the aerodynamic noise for detailed investigations. FKFS operates a full-scale aeroacoustic wind tunnel for this purpose.
Due to the airflow around the measured object, the use of conventional acoustic measurement techniques to record exterior noise is problematic in wind tunnels. Microphones in the flow are affected by extraneous noise by the flow around the microphones. Therefore surface Microphones or the large microphone array system out of the flow are used for exterior noise measurements.
Aeroacoustic investigations in wind tunnels are usually carried out under steady flow conditions. On-road driving, however, is affected by natural wind or other vehicles which cause turbulent flow. This turbulent flow in turn causes unsteady, modulated noise which may lead to a subjective impression of a lower quality product. The active turbulence and side wind generator FKFS swing® enables the simulation of unsteady flow conditions with corresponding wind noise in the aeroacoustic wind tunnel in a reproducible manner. The system consists of eight vertically mounted wing profiles in the nozzle exit plane which can change dynamically the yaw of the flow based on specified signals.
Tire-road noise affects both the exterior as well as the interior noise of a vehicle. The exterior noise in particular has become increasingly important since the 1970s, as it has been possible to significantly reduce the equally-relevant drivetrain noise during this period. With the electrification of the drivetrain and the associated further reduction of the powertrain noise, optimization in the field of tire-road noise becomes even more important.
The exterior noise component can be determined from far-field measurements on test tracks, however, also by using a tire-road noise trailer. Its contribution to the interior noise can be determined by means of a test bench, developed at FKFS, separately.
For the determination of the rolling noise in the vehicle interior, the servo-hydraulic 4-post test bench at FKFS is suitable.
This field is concerned with inner-engine operations regarding the noise and vibration behavior of combustion engines and electric motors, including the associated drivetrain components.
This is based on the use of the very latest test facilities as well as problem-focused analysis and calculation procedures.
- Investigation and optimization of noise excitation due to combustion and mechanisms e.g. valve train, pistons, crankshaft bearing
- Combustion noise optimization based on engine-specific structural insulation, taking into consideration conflicts arising from consumption and emissions targets
- Excitation and guidance of structure-borne noise
- Modal and operational vibration analysis
- Quantification (level, psychoacoustic parameters) and subjective evaluation of engine noise emissions
Instrumentation and Analytic Technology
- Air and structure-borne noise instrumentation
(microphones, artificial head, accelerometer, scanning laser vibrometer)
- High and low-pressure indication
- Contactless measurement (eddy current principle) of small distances
(crankshaft displacement, piston transverse motion, flywheel wobble, movements in the valve train)
- Rotational irregularity measurement and torsional vibration analysis
- Simultaneous, digital measurement signal recording, time and crank angle-dependent,
> 60 channels
- Conventional and special procedures for digital signal analysis
It is not only in premium class vehicles that squeak and rattle noise quickly leads to the customer rating the vehicle negatively. Customers expect an adequate acoustic atmosphere in the vehicle and are increasingly discerning in this regard.
Therefore, it is essential to avoid clattering windscreen wipers as well as components which rattle, creak or squeak. Also, operational and functional sounds have to be designed in such a way that they match customer wishes as closely as possible.
Squeak and rattle noise can be measured in a clearly defined environment. For example, FKFS can use its own servo-hydraulic 4-post test bench to excite the vehicle for this purpose. FKFS`s anechoic acoustic test chamber is particularly suited to investigating operational and functional sounds.
Besides the noise comfort the vibrational comfort plays a critical role in vehicle development. Both, noise as well as vibrational comfort have a significant influence on the customer's decision to purchase the vehicle or not. Vibrations in the lower frequency range and low-frequency noise (which can have a particular influence on the perception of comfort) are therefore an important issue in vehicle development.
FKFS mainly uses its servo-hydraulic 4-post test bench to investigate the phenomena arising in this field. This test bench enables FKFS to study components such as the engine mounting or suspension struts as well as entire vehicles. Additionally, different shakers can be used to excite parts of the vehicle or components in a defined way for investigations of vibrational characteristics