Ford Uses Hybrid Simulation to Accelerate Powertrain NVH EngineeringFord and LMS Partner to Implement Hybrid Test-Analysis Simulation Process

Ford Motor Company has validated a new simulation approach to extend its capability to

accurately and efficiently predict the Noise, Vibration & Harshness (NVH) performance of its

complete powertrain assemblies. Current Finite-Element (FE) methodologies used for full-

powertrain NVH simulations often do not deliver sufficient accuracy or require extensive modeling

efforts and unrealistic processing power. The new hybrid simulation methodology, implemented by

Ford and LMS, combines dynamic test-derived models and full-size FE component models to form

a larger hybrid model of a complete powertrain. Experimental modeling significantly increases

the speed of the simulation process and allows an easier integration of more complicated or re-

used components already available in hardware. Simulations with hybrid powertrain models yield

much more accurate NVH predictions early in the design phase and has the potential to set new

capability and performance standards across Ford’s entire powertrain development process.

Ford powertrain engineers typically optimized the NVH characteristics of powertrain components using either FE analysis or physical prototype testing. On one hand, FE analysis has the obvious advantage of not requiring a physical prototype, which is frequently unavailable in the early design phases. In addition, the model can easily be changed to evaluate the effect of design modifications. On the other hand, to provide accurate results, FE analysis usually requires modeling the complete powertrain assembly. But quite often, it is impossible to produce such a large model with significant degree of detail required to capture the NVH characteristics of the complete powertrain. Simplified models are often created but their accuracy can be affected because of the assumptions involved.The alternative to FE analysis for evaluating NVH performance is experimental modal analysis, in which a structure is excited and its response measured to determine its dynamic performance. Test-based modeling avoids the often-lengthy FE modeling process and provides more reliable results than FE analysis because it directly reflects physical reality. It is most suitable for components that may be used with little or no modification from earlier designs. Others components are usually not available as prototypes until much later.

Offering experimental modal analysis expertise

Ford’s initiative was to obtain the best of both worlds by combining FE models and test results into a single hybrid model that would predict the NVH performance of a powertrain assembly. They selected LMS International, Troy, Michigan, as a partner because of the company’s unique experience in setting up experimentally defined models and tying them together with traditional FE models to simulate complex assemblies. Mario Felice, Supervisor, Ford’s Powertrain NVH Research & Advanced Engineering, explained, “Ford engineers felt that the flexibility to pick and choose between analytical models and physical testing offered the potential for dramatic improvements in the accuracy and speed of NVH predictions at the early design stages. This in turn would provide an enormous payback by avoiding the need for additional prototyping and testing work in the later stages of the development process. In order to validate the new approach, we asked LMS Engineering Services to create a hybrid assembly model consisting of an existing engine block FE model and test-derived models of its cylinder heads. The success of this pilot engineering project would be determined by how accurately the hybrid model could predict the dynamics performance of this actual engine-related assembly.” LMS also supports Ford’s engine-related benchmarking tests, by directing a test plan that introduces data quality enablers specifically developed for hybrid model data acquisition and dedicated techniques for additional efficiency improvements.

Accurately coupling Test and FE models

At the start of this pilot project, Ford engineers provided the LMS consultants with the FE model of the engine block of Ford’s 4.6L V8 engine and the physical prototypes of two cylinder heads. The creation of a hybrid assembly model requires characterizing each of the components in the assembly. Deriving the test-based model of the cylinder heads begins by measuring a set of FRFs on the free-free suspended items. To generate accurate models for hybrid system synthesis, the rigid-body modes as well as the local behavior in connection points needs to be captured, along with the overall dynamics in the frequency band of interest. From the measured FRF sets, the consultants produced complete modal models of the cylinder heads, including rigid body/low frequency, flexible modes and high frequency residual modes, to describe the local behavior in the connection points.

To couple the test-based modal models of the cylinder heads and the FE-derived model of the engine block, LMS Virtual.Lab offers three coupling methods that are capable of establishing rigid, flexible and frequency-dependent connections. The FRF Based Substructuring (FBS) coupling technique attaches the components based on their FRFs, and the technique of modal coupling is based on the individual modes of the different involved components. The third method is called FE-FE coupling; couplings of this type are executed by the FE solver, after LMS Virtual.Lab automatically transformed test-based modal models

into dynamically equivalent FE models. Through its integrated environment and strong coupling features, LMS Virtual.Lab is capable of independently executing FBS and modal couplings and automatically driving FE-FE couplings. LMS consultants evaluated all three methods but, for this project, they focused on modal coupling. The spring elements of the couplings were originally modeled by using spring rates derived from previous hybrid models. At this point, the model already showed an acceptable match with the physical testing results for the complete assembly. As the spring rates and the validated FE models were further optimized, the correlation levels continued to increase.

Extending the hybrid simulation model

With the success of the initial pilot project, LMS consultants are now extending the model to include all of the other static engine parts not included in the original model, including the oil sump, camshaft cover and transmission. The next step will be to further extend the model by integrating force input locations for forced response assessments representing the operation of the dynamic engine parts. Then acoustic radiation calculations will be added by using the Acoustic Transfer Vector (ATV) method, which allows fast predictions of noise levels over the full rpm range of the engine. “This study demonstrates the feasibility of reaching our ultimate goal, which is accurately and efficiently predicting the NVH performance of the complete engine and transmission at a very early stage in the design process,” Felice said. “The components in this model will be based on test results when they are available and on FE models when prototypes do not exist or when iterations are required. The combined use of Test data and CAE modeling is much faster and more accurate than the traditional approach of using FE models alone. Gaining early insights in the NVH performance of our powertrain systems will make it possible to determine how we need to optimize component designs in order to meet our system targets. As a result, we will be able to evaluate and improve the design early on and reduce the process time required to meet our objectives.”

To develop a new approach for powertrain NVH simulations, Ford and LMS started from the FE model of a cilinder block.

Engineers coupled an experimental cylinder head model with the cilinder block FE model to form a hybrid simulation model.

The vibration simulation results of the hybrid test-analysis model show an acceptable match with the results of physical tests.

LMS INTERNATIONALResearchpark Z1, Interleuvenlaan 68 B-3001 Leuven [Belgium]T +32 16 384 200 | F +32 16 384 350info@lmsintl.com | www.lmsintl.com

Worldwide For the address of your local representative, please visit www.lmsintl.com/lmsworldwide

LMS is an engineering innovation partner for companies in the automotive, aerospace and other advanced manufacturing industries. LMS enables its customers to get better products faster to market, and to turn superior process efficiency to their strategic competitive advantage. LMS offers a unique combination of virtual simulation software, testing systems and engineering services.

LMS is focused on the mission critical performance attributes in key manufacturing industries, including structural integrity, system dynamics, handling, safety, reliability, comfort and sound quality. Through our technology, people and over 25 years of experience, LMS has become the partner of choice for most of the leading discrete manufacturing companies worldwide.

LMS is certified to ISO9001:2000 quality standards and operates through a network of subsidiaries and representatives in key locations around the world.