Read an Excerpt
Automotive Buzz, Squeak and Rattle
Mechanisms, Analysis, Evaluation and Prevention
By Martin Trapp Fang Chen
Butterworth-Heinemann
Copyright © 2012 Elsevier Ltd.
All right reserved.
ISBN: 978-0-08-055911-7
Chapter One
Overview on Vehicle Buzz, Squeak and Rattle Frank Chen, Martin Trapp Ford Motor Company
Chapter Outline
1.1. Customer Expectation and Vehicle Quality 1 1.2. Buzz, Squeak and Rattle Mechanism 5 1.3. Vehicle BSR Phenomena and Examples 11 Body Interior – IP 11 Example one: Tacoma IP/cross-car beam squeak 12 Example two: 1997 Probe IP rattle/buzz (TSB/article #: 98-2-9) 12 Body Closure – Doors and Liftgates 13 Example one: 2004 Scion xB liftgate rattle (TSB #: NV008-03) 13 Example two: Expedition window regulator squeak (TSB/article #: 98-17-21) 14 Underbody BSR 15 Transmission/Gear Rattle 15 Example – 2001 Jeep wrangler gear rattle 15 Seat Squeak and Seat Belt/Retractor Rattle 16 1.4. Design Process 16 1.5. Design Parameters and BSR Prevention 17 Force Isolation 18 Modal Separation 18 Structural Rigidity 18 Material Pair Compatibility 19 1.6. Computer Aided Engineering (CAE) 19 Manufacturing Process 20 1.7. Conclusion 20 References 22
1.1. Customer Expectation and Vehicle Quality
Vehicle noise may be roughly divided into two categories: the persistent type and the transient or come-and-go style. Persistent noise such as engine or road boom noise or wind noise will occur constantly during certain regular and wide-ranging operation conditions, and is often more annoying and discomforting to customers, and should be the first to be eliminated. With recent significant reductions in the persistent type of noise, the come-and-go kind of noise, including buzz, squeak and rattle (BSR), becomes more apparent and further needs to be eliminated to continuously improve vehicle quality.
As discussed in reference 1, even as early as 1983 a market survey showed that squeak and rattle were already ranked the third highest customer concern for the three months in service (3MIS) period. In recent quality surveys, BSR was rated as the top quality issue including all original equipment manufacturers (OEMs – automobile makers). As Chance Parker, executive director of product and research analysis at JD Power and Associates, commented: "While the Initial Quality Study (IQS), which measures problems experienced in the first 90 days (3MIS) of ownership, can be an indicator of how models will perform over time, our studies consistently show that long term durability is a tremendously important factor to consumers. As the number of the problems owners experience with their vehicles increases, repurchase intent and the number of recommendations owners will make to others decreases." The brands that perform better than the industry average vehicle dependability study (VDS) typically have $1000 more residual value than others that are below the average, according to JD Power and Associates. VDS is surveyed every year for three-year-old models. An example is Ford, which made a significant improvement (on average, rectified nine faults) in its IQS from 2006 to 2008, as shown in Figure 1.1, which is modified to include most nameplates/ brands and exclude luxury vehicles. Ford's vehicle quality improvement in recent years has also been recognized by JD Power and Associates' leading index and other leading vehicle quality research firms such as Consumer Reports, Strategic Vision, and Auto-Pacific. The 2008 JD Power and Associates' Automotive Performance, Execution and Layout (APEAL) study showed that the Focus gained 88 index points over the last year. The Ford Escape also earned a spot among the top 10 most improved vehicles in the industry. In addition, five Ford Motor Company vehicles received second- or third-place honors in their segments. Strategic Vision put Ford neck-and-neck with Toyota for total quality, and ahead of everyone else. Ford has improved to 64% recommended vehicles from 54% in 2007 and 93% of Ford vehicles have average or better predicted reliability compared to last year's 63% according to Consumer Reports. Part of Ford's quality improvement is due to the reduction of BSR.
Prospective customers may first consult various quality reports including Consumer Reports and JD Power and Associates' quality study, and decide which vehicle they may want to evaluate before buying. If there is an indication that some nameplate vehicle has a low quality ranking, it may not be even on the consideration lists of prospective customers. Every year JD Power and Associates will issue the rankings in their vehicle Initial Quality Study (IQS).
When a prospective customer test drives a vehicle, if there is a BSR the customer will perceive the vehicle as low quality. If this can go wrong, then something else might go wrong later. It will not only affect the customer's decision to buy this vehicle but may also project a negative image for the nameplate, brand or even for the manufacturer. The same effect holds or is even worse when a customer finds a BSR after purchasing. Since it is a come-and-go type noise, it usually takes several trips to a dealer to fix. One often hears people say "this is my first and last 'nameplate'", and "I cannot wait to trade this one in and get my 'previous nameplate' back".
In addition, repair of vehicles with BSR problems at dealers costs the industry hundreds of millions of dollars per year in warranty. BSR warranty costs were reported to be as high as 10% of the total warranty. As will be described in later sections, BSR is an issue involving various components and systems from bumper to bumper in a vehicle. Collectively, it will be the very top warranty item if not the number one, as remarked by a quality manager of an OEM: "Buzz, squeak and rattle will be the #1 warranty concern of automotive companies in the next 10 years". In turn, the industry spends significant resources to reduce and prevent BSR.
Although it is desired and imperative, reducing and preventing BSR is a monumental task since it involves multiple disciplines, cross functions and robust processes from upfront innovative design, complete verification, and manufacturing quality control to effective customer feedback. Each of these processes already constitutes a sufficient challenge itself.
As noted, although vehicle BSR is a very important topic both in research and application, there are not so many technical articles on this subject. The main body of the literature resides in SAE technical papers and transactions. With higher customer expectation and intensified competition among OEMs, the research and application SAE papers on reduction and elimination of BSR have significantly increased after the mid 1990s as shown in Figure 1.2. The papers selected in Figure 1.2 are such that they includes all papers in which BSR is the main topic as well as those papers that study other subjects with BSR as one of the related attributes to discuss. The following overview largely depends on SAE papers. Some of the recent published SAE papers can be found in the references 8–15.
1.2. Buzz, Squeak and Rattle Mechanism
Squeak is a friction induced noise from two solid surfaces in contact sliding in the opposite direction against each other. To generate squeak, there must be relative motion between the two surfaces. However, not every relative motion produces squeak. One of the fundamental squeak generation mechanisms is unstable vibration that has stick-slip motion characteristics.
When stick-slip occurs at the two surfaces, one of the surfaces may have impulsive deformation that stores energy, which will be impulsively released when it snaps back to generate squeak. The occurrence of stick-slip may depend on loading conditions such as contact pressure, sliding speed, surface profiles, material properties, and most importantly the characteristics of the coefficient of friction. The properties of the materials may also be affected by temperature and humidity. Friction coefficients can be used to characterize and analyze stick-slip motion, which is as one of the factors determining friction force.
There are quite a few friction models that have been developed although there is no universal one that can fit any situation. The models can be divided into two groups: one is from the microscopic perspective (details can be found in various literature listed in the references) and the other is from the macroscopic view and will be briefly described in the following. The most well-known friction model is the Coulomb model. It describes friction with two values at zero velocity in which one is the static friction coefficient due to stiction and the other represents the dynamic or kinetic friction coefficient. There are two major limitations of the Coulomb model: one is the multiple values at zero or discontinuity and the other is it cannot account for the Stribeck phenomenon. To overcome these limitations and represent various real situations, a variety of models have been developed. The Karnopp model defines one value to use at zero velocity. The Dahl model describes friction as a function of displacement. Armstrong's integration model has all four regions together – static friction, boundary lubrication, partial fluid lubrication and full lubrication. There are also other models such as Tan and Rogers' model, the Antunes model, and the Oden and Martin model, and exponential models. A general and schematic description of typical combined friction characteristic models is illustrated in Figure 1.3, in which the first region (close to time zero) is the Coulomb type, the second region close to the origin is the so-called Stribeck phenomenon and negative damping, and the third region is usually a viscous damping zone. The first and second regions are responsible for the generation of unstable vibration since as velocity increases, damping decreases.
When a vehicle exhibits a periodic excitation or vibration caused by resonance, there may be a condition that the non-smooth relative motion, stick-slip motion, will occur. The following classic and simple model in Figure 1.4 can be used to illustrate it. If the excitation force gradually increases and overcomes friction and restoration forces, there will be a sudden relative motion between the two contact surfaces – slip. When the excitation force becomes smaller than the friction and restoration forces during the sliding process, the slide or the relative motion will cease for a short period – the two contact surfaces will stick together. This loop of stick-slip motion can be repeated under this periodic excitation or vibration, and so that results in squeaks. During this stick-slip motion, there is a stick period and then a sudden slide, which is the characteristic of non-smooth motion.
(Continues...)
Excerpted from Automotive Buzz, Squeak and Rattle by Martin Trapp Fang Chen Copyright © 2012 by Elsevier Ltd.. Excerpted by permission of Butterworth-Heinemann. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.
