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Many decisions need to be made when test track data is used to set up Squeak & Rattle evaluations of subsystems or components. These decisions are judgment-based so different people with different backgrounds and experience levels will make different decisions - few of which can be called right or wrong - but they are different which causes problems. Squeak & Rattle evaluation has become more scientific in recent years as subjective evaluation has been replaced by quantitative methods like N10 Loudness and shakers have become quiet. It is the authors' contention that the variations caused by different judgment calls can no longer be tolerated. Therefore a methodical process was developed which assures that different people will get the same results from the same set of test track data.

Many car companies use rumble strips to evaluate Buzz, Squeak & Rattle (BSR) performance of vehicles. Some call these surfaces by other names such as chatter bumps or wake-up strips. But regardless of what they're called, these surfaces are characterized by a uniform spacing of bumps or strips which are driven over at a particular speed(s). This is a relatively easy way to generate relatively high vibration levels so these surfaces are often favorites of the team doing total vehicle evaluation for BSR. If this is the case, then it is essential that a rumble strip evaluation be performed at the subsystem or component level when certifying that a particular item will not generate BSR problems in the vehicle. One of Siemens' customers uses Rumble Strips to evaluate the Radio/CD player that Siemens supplies. Carefully defined test track tests showed that the particular dynamic characteristics of the Rumble Strip surface made it very challenging to have a repeatable, realistic test.

The pressure to shorten vehicle product development time-to-launch means more in-lab tests must be performed earlier, and before vehicle prototypes are available for road or test track evaluations. Squeak and Rattle (S&R) evaluations of subsystems/modules and components must be performed using realistic road excitation conditions. How S&R performance degrades as the vehicle, module or component accumulates customer miles or kilometers must be assessed before the design is frozen. Durability tests must be performed earlier in the design/development timeline as well. All these pressures point to having a systematic, disciplined and streamlined methodology or protocol for acquiring and processing road vibration data useful for S&R and durability tests.

In order to engineer Squeak & Rattle (S&R) free vehicles it is essential to develop an objective measurement method to compare and correlate with customer satisfaction and subjective S&R assessments. Three methods for exciting S&Rs -type surfaces. Excitation methods evaluated were road tests over S&R surfaces, road simulators, and direct body excitation (DBE). The principle of DBE involves using electromagnetic shakers to induce controlled, road-measured vibration into the body, bypassing the tire patch and suspension. DBE is a promising technology for making objective measurements because it is extremely quiet (test equipment noise does not mask S&Rs), while meeting other project goals. While DBE is limited in exposing S&Rs caused by body twist and suspension noises, advantages include higher frequency energy owing to electro-dynamic shakers, continuous random excitation, lower capital cost, mobility, and safety.

Engineers doing squeak and rattle testing of instrument panels (IP's) have successfully used large electrodynamic vibration systems to identify sources of squeaks and rattles (S&R's). Their successes led to demands to test more IP's, i.e., to increase throughput of IP's to reflect the many design, material, and/or manufacturing process changes that occur, and to do so at any stage of the development, production, or QA process. What is needed is a radically different and portable way to find S&R's in a fraction of the time and at lower capital cost without compromising S&R detection results.

The laboratory test method commonly known as “random vibration” is almost always used for Squeak & Rattle testing in today's automotive applications due to its obvious advantages: the convenience in simulating the real road input, the relatively low cost, and efficiency in obtaining the desired test results. Typically, Loudness N10 is used to evaluate the Squeak & Rattle (S&R) performance. However, due to the nature of random distribution of the excitation input, the repeatability of the loudness N10 measurements may vary significantly. This variation imposes a significant challenge when one is searching for a fine design improvement solution in minimizing S&R noise, such as a six-sigma study. This study intends to investigate (1) the range of the variations of random vibration control method as an excitation input with a given PSD, (2) the possibility of using an alternate control method (“time-history replication”) to produce the vibration of a given PSD for a S&R evaluation.

The traditional role of the test lab has been to subject prototype products or components to carefully defined programs and evaluate acceptability from the viewpoint of vibration, stress, durability, life, noise, safety, reliability, performance, etc. If a product or component fails prescribed test criteria, it is sent back for rework by an appropriate designer. The test engineer seldom works with or meets the designer, except when “crisis” type problems are encountered. Computer Aided Engineering (CAE) already has had a dramatic effect on drafting, design analysis, and testing groups. Mini-computer based testing systems, using modal analysis and animated mode shape test capabilities were introduced into the test lab in the early 1970's. Many new tools and techniques have become available since then. These later tools have a revolutionary impact on mechanical product development and the role of mechanical test engineers in the development process.

Many engineers today use large, powerful multi-purpose test systems to do squeak & rattle testing of modules and subsystems such as Instrument Panels, Consoles and Seat Assemblies. Such test systems include Multi-Axis Hydraulic Shaker Tables and Electrodynamic Vibration Systems with large head expanders and rigid (or at least stiff) fixtures. These test systems have been successful when used for squeak & rattle test programs, have been validated as approved test methods, and have become the standards of comparison in many labs today. They are, however, expensive and throughput can be limited due to the time needed to unbolt, unload, handle, load, and re-bolt a test item at its many attachment points on the rigid fixture. Furthermore, the capital cost of these Legacy systems can be prohibitive, especially for the smaller supplier, who is being compelled to perform squeak & rattle testing on the products they supply to their customers, the vehicle manufacturers and Tier 1 suppliers.