Squeak and Rattle - State of the Art and Beyond

Modern trends in noise control engineering have subjected the automobile to the “drained swamp” syndrome. Squeaks and rattles (S&R) have surfaced as major concerns. Customers increasingly perceive S&R as direct indicators of vehicle build quality and durability. The high profile nature of S&R has led manufacturers to formulate numerous specifications for assemblies and components. Even so, a large majority of buzz, squeak and rattle (BSR) issues are identified very late in the production cycle, some often after the vehicle is launched. Traditionally, the find-and-fix approach is widely adopted, leading to extensive BSR warranty bills. The designright-the-first-time approach must replace the find-and-fix approach. Due to the vast breadth and depth of S&R issues, a comprehensive summary of the present state of the art is essential. This article includes a literature survey of the current state of the art of S&R and discusses the methods available to further advance it. Dedicated and focused attempts to advance the state of the art require the formulation of an integrated design strategy that attacks S&R during the earliest stages of design and development, leading to substantial savings in fix and warranty bills. The sound inside a passenger cabin is composed of many elements, a fundamental element of which is irritating noises comprised of buzzes, squeaks and rattles. Customer perception of buzz, squeak and rattle (BSR) is measured by Things Gone Wrong (TGW), warranty claims and JD Power surveys.1 A market survey as early as 1983 reported squeaks and rattles as the third most important customer concern in cars after 3 months of ownership.2 The absence of S&R provides direct positive feedback to the customer of the perceived vehicle build quality. In the highly competitive automotive market, a superior S&R strategy can easily poise manufacturers for market leadership through customer perceived initial build quality and published JD Power survey rankings. The battle against S&R is not an easy one. Modern advances regularly reduce the general level of other major sound sources such as the powertrain, wind, road and tire, both actively at the source and passively at the receiver end. The trend towards lightweight body construction and lightweight materials combined with the increase in general content in the subsystems keeps growing. Controlling S&R is thus an even bigger challenge. Vehicle owners of the new millennium will demand a tremendous increase in the instrument panel (IP), seat and door subsystem content. Electric cars of the future will highlight even the most subtle of S&R issues because of the general low level of powertrain noise and the use of lightweight components inherent to their design. Currently, manufacturer warranty bills from S&R issues are estimated to be about 10% of total things-gone-wrong costs.1 Instrument panels (IP), seats and doors are responsible for over 50% of the total S&R problems, with IP being the main offender.3 The traditionally applied “find-and-fix” approach methodology used to obtain quality improvements has resulted in a tremendous increase in product costs with little proven durability. The ‘band-aid’ corrective actions often depend on operator installation accuracy. The best resolution, generally onetime tooling revisions, occurs late in the production cycle and is prohibitively expensive. Because of the high profile nature of S&R, manufacturers have formulated numerous specifications for S&R performance of assemblies and subcomponents. These efforts have naturally focussed on long term durability, considering the effects of multiple and simultaneous environments. Over the years, manufacturers have borne the high cost of maintaining large shakers, four post simulators, drive-in environment chambers and semi-anechoic chambers. These high cost ‘legacy’ systems have helped to reduce S&R, but only in the form of find-and-fix solutions that are slow and costly. Hence, the need exists for a design approach that targets S&R. Significant gains can be achieved by approaching S&R from a design perspective upstream in the design and development cycle. A comprehensive survey reveals a scarcity of published literature aimed towards attaining such a goal. Due to the relatively recent importance that S&R has garnered, it is hardly surprising that all the applicable published literature spans only the past decade. It is important to be aware that the proprietary nature of a company’s S&R know-how only adds to this void. Nevertheless, the vast breadth and depth of S&R issues require the formulation of an extensive design-intensive strategy to combat BSR and hence advance the state of the art. Squeak & Rattle – Background and Theory