Automobile purchasers are continually demanding better driving comfort, improved driving dynamics, and safety.

Vibracoustic, the vibration control business of Freudenberg, answers this call by closely cooperating with its customers in order to prevent annoying vibration and noise in vehicles. Through LMS Test.Lab, Vibracoustic has implemented a comprehensive and productive testing environment that makes it possible to quickly configure and run a wide range of tests, evaluate results, determine root causes, and assess potential solutions.

Freudenberg Vibracoustic designs and produces a variety of modules and components for vibro-acoustic control in chassis and suspension, engine mounts, dynamic dampers, torsional vibration dampers, drive train components, and air spring modules.

Vibracoustic can analyse any noise vibration and harshness (NVH) problem and to develop optimal vibro-acoustic control solutions from a full-vehicle perspective. Airspring modules for example are designed to reduce harshness and support maximum comfort under all loading conditions. In the subsidiary’s lab at Weinheim, Germany, vibration and acoustic evaluations of product variants are extensively tested while integrated into the total vehicle.

To assess the NVH performance of the vibration control component and to optimise their functioning in each vehicle variant, Freudenberg Vibracoustic requires a broad variety of tools and techniques. The broad functionally of LMS Test.Lab for rotating machinery as well as structural dynamics in one software suite, allows the Vibracoustic engineers to make in depth NVH analysis and drill down to the root cause of a problem.

Mr Wojts-Saary, Engineer, System Development & Technologies Business Area at the Weinheim facility, comments: “For our troubleshooting and validation activities, LMS Test.Lab delivers a huge productivity increase through its intuitive user interface and the template-based testing and analysis approach. The Test.lab systems offer extensive and accurate measurement and analysis capabilities, which allow us to profoundly test and optimize our products, and to respond very quickly to OEM requirements.”

Leaving no angle unexplored

Vibracoustic covers a broad range of physical prototype tests with LMS Test.Lab: from a simple impact testing with modal analysis on a motor, to spectral analysis on brackets, to complete signature testing of a car on a roller bench. “The fact that our testing team can run this wide variety of tests offers the tremendous benefit of not having to learn and maintain different systems and software tools. In addition, we gained the flexibility to apply different testing techniques to solve more complex NVH problems,” commented Mr Wojts-Saary. “The LMS Test.Lab workbook concept, guides the user through a sequence of well-defined process steps eg documentation, channel setup, calibration, acquisition etc. This adds to lowering the threshold for operators, enables broad analysis and reduces training requirements.”

Vibracoustic's test lab in Weinheim uses roller benches, multi-axle test rigs, impact testing, and road testing to analyse NVH problems and optimise designs. The challenge for the Freudenberg engineers is to assess the noise, vibration and harshness impact of any modification either in the vibro-acoustic control component or in the vehicle design.

A typical example of the Vibracoustic whole-vehicle approach to optimize NVH is a case where the OEM modified the differential of the gearbox. The vehicle is tested on the roller bench, the 4-poster test rig, on the street or a test track. On the roller bench, a 70-channel measurement setup with charge accelerometers on the vehicle, microphones inside and outside the car, and tachometer tracking is used. The high channel setup allows fast and in depth evaluation of the differences in NVH performance, especially on the chassis, axle, engine, and inside the passenger cavity of the car for interior noise.

Typically measurements are done in run up, start/stop, idle, and shift conditions. During the test runs, LMS Test.Lab offers online visualization of the acquired data through multiple graphical displays that are defined during setup and modifiable during the measurement. “Real-time viewing of all the signals in the time or frequency domain provides immediate validation of the measurement. The user configurable displays deliver immediate feedback on the progression of the test and the quality of the acquired data for vibration or acoustic channels. They allow the testing teams to make a first assessment on the spot and perform additional testing if needed,“ said Mr. Wojts-Saary. “During measurements on the test track, the on-line processing combined with the use of references allows our operators to immediately check, how the dynamic characteristics of the current modification is different from a reference test or a former test. At the same time, we can record the raw data to a throughput file for later detailed analysis.”

The Freudenberg engineers also make extensive use of Operational Deflection Shapes to validate test runs. Immediately after the test run, the deflection shapes of a structure in operational conditions can be analyzed starting from either the time or frequency domain. This functionality enables full flexibility for the engineer in choosing the appropriate offline analysis to further explore a specific problem.

Mr. Wojts-Saary adds: “The online processing and visualization formats provide full visibility, which allows us to be very efficient in the field and come back within a short period loaded with an abundance of information and a good sense of where the problem is located. In a post-processing we zoom in on the issue by comparing the actual measurements with historical data. ”

The post-processing phase may include the calculation of additional orders or maximum order contribution, and allows further exploring the NVH issues at hand. In the post-processing phase LMS Test.Lab enables retrieval of earlier projects with web-based navigation tools, making it possible to analyse the physical process in greater detail.

TheVibracoustic engineering team faces the continuous challenge of testing prototypes in ever-shorter time frames and assessing a wide variety of design changes to optimize the NVH performance of their vibro-acoustic control components, in the full-vehicle context. Mr. Wojts-Saary comments: “In addition to the broad application coverage and functionality of the LMS products, there is LMS’ very responsive technical support that helps us get even more out of our measurements. The people at the other end of the line know the software very well. The reactiontime is very fast and they always come back with helpfull answers to our questions.”

LMS Test.Lab offers the productivity that Vibracoustic requires, as it contains all the features required to drill to the root causes of NVH vibration issues in one integrated solution. During measurement as well as in the post-processing phase, LMS Test.Lab provides the engineers with the comprehensive array of tools for in depth investigation and comparisons of the vast amounts of data generated during the testing.

Bruno Massa is with LMS International nv, Leuven, Belgium. www.lmsintl.com