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Customer Case Study

“NVH is such an important issue in the industry today because of the rise inelectric motor developments and the production of complex gearboxes. Weuse Romax DESIGNER so that we can perform accurate simulation of thesenew gearbox designs, and assess the NVH performance.” 

Carsten Schmitt, Volkswagen

Client

Europe’s biggest carmaker,Volkswagen Group deliversover 10 million cars tocustomers each year and hasannual group sales revenue(2015) of €202.5 billion.Almost one in four new cars(24.8%) in Western Europeare made by Volkswagen,a group which comprises12 leading brands fromseven European countries:Volkswagen Passenger Cars,Audi, SEAT, ŠKODA, Bentley,Bugatti, Lamborghini,Porsche, Ducati, VolkswagenCommercial Vehicles, Scaniaand MAN.

Challenge

Developing a reliablevalidation strategy forgearbox noise, vibrationand harshness (NVH) toallow design changes to bemade with condence, andsatisfying the demandingneeds of the market-leadingbrands.

Solution

Romax DESIGNER softwarefor gearbox simulation, fastand accurate NVH analysis,at each stage of design andvalidation.

Benefts

Time-saving and condent

developments through thecreation of a reliable andaccurate validation strategy,which can be reused forfuture projects.

NVH Simulation and Testing:Correlation Studies to Establish Integrated Validation Strategies

Employing over 15,000 people, Volkswagen’s primary transmission site at Kassel,Germany, supplies about four million manual and automatic transmissions every year.Volkswagen engineers at Kassel have used Romax DESIGNER software for more thanve years, to support the effective production of gearboxes and to ensure the requiredNVH quality is achieved. Kassel’s Acoustics and System Simulation department focuseson NVH correlation and simulation: “Our main challenge is gear whine, and the need tosupport our high acoustic standards,” says Carsten Schmitt, PhD student of Volkswagen’spostgraduate program. “NVH is such an important issue in the industry today becauseof the rise in electric motor developments, and the simultaneous increase in theproduction of complex gearboxes. We use Romax DESIGNER so that we can perform

accurate simulation of these new gearbox designs, and assess the NVH performance.”

From trial and error to simulation for development

Previously, sporadic correlation studies on the main parts of a gearbox would beconducted based on eigenfrequencies, which allowed for little correlation guarantee.“We have a requirement to develop simulation models that are representative of thereal world, so that our design changes can be made with condence,” says Schmitt.“This gave rise to the need for an integral validation strategy, which we investigated inRomax DESIGNER. We have already used the software for over ve years on multipleprojects. The speed and unique system-level simulation which Romax DESIGNER offersstand it apart from other products currently available on the market.”

“Only with Romax DESIGNER can we quickly andaccurately investigate gear whine phenomenaon a system level – looking deeper into modelsto work out where the problems are. This iswhat allows us to meet high expectations forNVH within even the most cutting-edge systemdesigns... The speed and unique system-levelsimulation which Romax DESIGNER offers stand it

apart from other products currently available onthe market.” 

Carsten Schmitt, VolkswagenGear contact pattern testing

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• Meet increasing demands forNVH which satisfy cutting-edge

 gearbox designs, e.g. for electricmotors or complex gearboxes

• Resolve validation errorsquickly and easily through anunderstanding of exactly wherethey occurred, removing the needfor time-consuming investigatorywork

• Obtain and maintain customertrust – deliver exactly what they

require, with confdence

• Know that design changes aremade not relying on trial anderror, but based on proven,trustworthy simulation

An integral validation strategy

The strategy developed by Volkswagen focuses on a step-by-step

process, allowing correlation between measurement and simulationalong the acoustic transfer path at each of the following stages:gear excitation, shaft systems, bearings, gearbox housing, and wholevehicle testing. “If test and simulation are compared only at the endof the system development, then it is not possible to work out wherediscrepancies may arise, hence the need to perform correlation at eachlevel. This gives us an understanding of exactly where problems areoccurring, so that we can resolve validation errors quickly and easily,and avoid time-consuming investigatory work,” Schmitt explains.“And Romax software plays a big part in this investigation. Only withRomax DESIGNER can we quickly and accurately investigate gear whinephenomena on a system level – looking deeper into models to work outwhere the problems are. This is what allows us to meet high expectations

for NVH within even the most cutting-edge system designs. Romax’sunique system level view is a huge benet to us, as well as its easy-to-use bearing catalogues, which make it easy to model gearboxes even ifyou are not a bearing expert, and its reliable and accurate transmissionerror calculations.”

A step-by-step process

The gears are validated rst, with testing and simulationperformed across a range of loads. The gear contact patternis checked; poor correlation indicates either incorrect micro-geometry in the simulation, or deviations in the manufacturing

process. The next stage is shaft system validation, whichconsists of modelling single parts and assemblies, thenperforming nite element analysis (including pretest analysisand experimental modal analysis, if necessary). This is againvalidated against test data, and if this is unsuccessful themodel must be updated in Romax DESIGNER. Whenevercorrelation is not successful, changes can be made whichwill improve the process for the future, as Schmitt explains:“In the rst run we did, we found that the model did needupdating. The updates that we performed, includingaccounting for Young’s modulus and part-to-part stiffnessconnections, improved the correlation signicantly.”

The third stage is correlating the bearing stiffness, and thenal step is the correlation for the gearbox housing, for which there are twooptions, as Schmitt explains: “The validation can be performed by building upthe components separately using different tools and testing each individually, and then adding together to make the nalmodel. Alternatively a single model can be created in Romax DESIGNER, which means just one experimental modal analysis,one correlation analysis, and only one model to update. We found that there was little difference between the methods, sothe full housing assembly was done in order to save time and effort – this is a very useful way of doing the correlation.”

“Now we have developed the framework, we are condent that the work that we have put into this implementation willenable time and cost savings for future projects, as well as maintaining our customer’s trust in our ability to deliver theirrequirements,” Schmitt concludes. “We have developed a clear strategy to perform straightforward model updatingprocedures, and extended the validity and trust of our Romax gear whine models. Our design changes are not reliant ontrial and error, but are based on proven, trustworthy simulation.”

or www.volkswagen.co.uk

CS-VW2-R1

“We have developed a clear strategy to perform straightforward model updating procedures, andextended the validity and trust of our Romax gear whine models. Our design changes are notreliant on trial and error, but are based on proven, trustworthy simulation.”

Carsten Schmitt, Volkswagen

Laservibrometer measurement and Romax DESIGNERsimulation of rear wheel drive and drive shaft