Optical measurements that drive progress

Optimizing tire acoustics by model validation

Designing the optimal tire is always a trade-off between mileage, longitudinal and lateral dynamics, wear as well as acoustics. Here, laser vibrometers help building the bridge between FE simulation and real test, as the model validation on rolling tires are the fundament for optimizing the tire as a system.  

The most important issues about tire acoustics is the influence of the rolling tire on the interior acoustics of the passenger car in order to comply with the increasing official regulations regarding noise emission all over the world. Full-field vibration analysis reveals not only the operational deflection shapes of the tire side walls including chassis parts, but also help determining the transfer paths. Laser Doppler Vibrometry provides the unique properties to measure right on the rolling tire on the acoustic test bench. Introducing Polytec’s Xtra laser technology, the optical vibration sensor gathers enough backscattered light even from dark rubber to scan the entire side walls plus the original source of noise: the tire tread. The PSV-3D Xtra Scanning Vibrometer captures the surface vibrations of the tire in 3D without contact, offering detailed information about structure-born noise from the complete tire tread. This allows engineers to visualize and describe the vibrational behavior quantitatively and qualitatively. Why measure tire acoustics Xtra laser technology? This advanced method of laser vibration measurement together with a powerful evaluation electronics enables capturing also high vibration velocities which even works at an angle on the tire tread. Before, the angle of incidence of the laser beam has been a challenging condition for such measurements. The Xtra laser technology successfully overcomes this limitation making the Polytec Laser-Doppler vibrometry the ideal tool for analyzing and optimizing tire acoustics.

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Minimizing noise and wear

As the drivetrain is the initial source of noise, wear and even driving discomfort, understanding its dynamics is vital if a vehicle is to be a success. Polytec’s optical measuring technology lends your production facilities a helping hand with tasks where they need it most: from inspecting the stroke of the injection valve needle, over characterizing the valve elevation curves, to measuring torsional vibration at the downforce transmission paths. You can also establish the design of cardan and constant velocity drive shafts and characterize dual-mass flywheels for better driving comfort.

Polytec’s laser vibrometers have next to no frequency limitations, so, working together with you, they cover the entire scope of use for any acoustic and structural dynamic phenomena. This is precisely why they are so well-suited to analyzing high-frequency phenomena such as rattling and whining sounds in the gearbox. Scanning measurements, on the other hand, use detailed operational deflection shapes to illustrate solution processes, with a view to preventing acoustic radiation through the enclosure.

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All the measurement data in next to no time

In-vehicle noise is very much dominated by wind noises of more than 80 km/h. A reliable check is carried out in an aeroacoustic wind tunnel with extensive force, flow and sound pressure measurements. The excitation of outer surfaces – particularly the windshield, rear window and undercarriage – caused by turbulences on the vehicle’s body shell is extensively recorded by a scanning vibrometer. The excited deflection shapes have to be recorded without influencing the flow.

The Scanning Vibrometers from Polytec allow you to capture the necessary measurement data, without having to go through the time-consuming process of vehicle instrumentation, with short measuring times all around – even if you’re trying to capture data from below through a glass base.

Durability testing, high cycle fatigue and noise identification on electronics

It is impossible to imagine modern vehicles without electronics. Not only do electronics control vehicles; they are increasingly powering them too. This is precisely why reliable electronics are critical for market success. Vibration and impact loads are therefore extensively tested prior to SOP.

The non-contact vibration sensors from Polytec are ideal for dealing with these problems. The high-sensitivity laser technology reliably detects vibration-related weak points on printed circuit boards or individual components, right down to individual bond wires. Modal tests and order analyses quickly provide the right data for component, PCB, enclosure and attachment optimization.

The additional noises produced by pumps, adjusting drives and fans can be heard much more clearly if the combustion engine is not being used as a masking noise factor in electric or hybrid vehicles running in electric mode. There is also the high-performance electronics, which add a new source of high acoustic sharpness to the vehicle acoustics. Laser vibrometers from Polytec enable clear 3D visualization and quantification of transfer paths into vehicle interiors and efficiently identify source of noise on electronics boards. Polytec laser Doppler vibrometers are the testing instruments of choice worldwide of OEM and tier 1 suppliers.

 

 

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Accelerate your modal testing and time-to-market

Experimental modal analysis (EMA) is the powerful method in automotive development to confirm, validate and correct (model updating) simulation results of a finite element calculation (FE model, FEM). Designing components based on a finite element model is an efficient way of shortening development times. But the feasibility of the resulting structural dynamic models needs to be assessed. Consequently, it is essential to perform the experimental modal test on prototypes so as to validate the models.

Design right the first time - here Scanning Vibrometers from Polytec speed up the process significantly. Non-contact measurement means zero mass-loading, so they do not influence the vibrational characteristics. The FE-like spatial data resolution or point density allows for performing modal analysis for higher modes and meaningful MAC analyses. Simply import the measurement grid from your FE model into the PSV software to use the identical coordinate system instead of interpolation. The virtually unlimited measurement points on your structure result in high spatial resolution, unlike conventional tactile methods like with accelerometers. Achieve high data quality even overnight – with the fully automatic RoboVib® Structural Test Station.

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Making vehicles quieter

Droning, humming, squeaking and rattling are typical acoustic problems found in vehicles – and particularly in lightweight construction. They are a source of irritation to end customers and consequently need to be eliminated. The term NVH (noise, vibration and harshness) is an umbrella term used to refer to all those measures that enhance acoustic comfort for drivers and passengers alike.

Developing quiet, low-vibration products is a joint simulation and testing task. Polytec’s Scanning Vibrometers allow you to unveil sources of sound radiation quantitatively and with high spatial resolution. Inverse panel contribution measurements and qualification of damping materials (sound package) are made a great deal easier with the automatic scanning process.

You can use a scanning vibrometer to examine the source of sound excitation in detail and, in so doing, identify the structure-borne sound transmission paths and the causative deflection shape. The 3D visualization of the operational deflection shapes helps the NVH engineer to quickly come up with ideas to solve the problem – even just before production starts.

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Optimize lightweight construction with laser precision

Lightweight construction forms the basis for better construction. The body shell offers the best potential in this regard. High tensile steels, aluminum and composite materials made from carbon fiber-reinforced plastic are being used instead of conventiopmal car body steel. Joining methods such as bonding and riveting are entering production processes, making simulation calculations susceptible to faults since joint attenuation cannot be determined with any real degree of certainty. Consequently, proof from an experimental modal analysis is more important than ever before during FE model validation.

Since fewer prototypes are used nowadays, each optimization step needs to be faster and more reliable. Even lightweight bodies tend to drone, which is precisely why high-frequency mode validation is a topic for the future too as regards the acoustic calculation. A well-validated inventory model is normally used as a basis for the next generation. The better the model, the earlier a new vehicle’s properties can be calculated.

Lightweight bodies long for lightweight measuring technology, the non-contacting method per laser light is the ideal sensor technology. In offering you the 3D Scanning Vibrometers and the automated RoboVib® solution, Polytec is providing you with a highly productive tool that is extremely beneficial to you:

• Avoid impact on the sample thanks to zero mass loading
• Directly transfer the geometries data from FE models
• Automated measurement even overnight saves time
• High spatial resolution allows validating acoustic simulations

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