Automotive Buzz, Squeak and Rattle: Mechanisms, Analysis, Evaluation and Prevention

By Martin Trapp and Fang Chen

Buzz, squeak, and rattle (BSR) is the automotive industry term for the audible engineering challenges faced by all vehicle and component engineers. Minimizing BSR is of paramount importance when designing vehicle components and whole vehicle assemblies. This is the only book dedicated to the subject. It provides a self-contained reference to the background theory, testing, analysis, and elimination of BSR. Written for practicing engineers and industry researchers, the book has a strong focus on real-world applications making it an ideal handbook for those working in this important area. Chapters from leading experts from across the motor industry—with input from the design and research labs of Ford, Toyota, Daimler-Chrysler and GM—review the techniques available and provide readers with the appropriate physics, structural dynamics and materials science to address their own BSR issues.

• The only book available on automotive BSR (buzz, squeak and rattle)—the number one cause of complaint on new cars
• Comprehensive and authoritative, with contributions from leading figures in the field and companies such as Ford, Toyota and Daimler-Chrysler
• Enables readers to understand and utilize the complex tools used to assess, identify and rectify BSR in vehicle design and testing

• Language: English
• Publisher: Elsevier Science
• Release date: Nov 25, 2011
• ISBN: 9780080559117

Book preview

Table of Contents

Cover image

Front Matter

Copyright

Chapter 1. Overview on Vehicle Buzz, Squeak and Rattle

1.1. Customer Expectation and Vehicle Quality

1.2. Buzz, Squeak and Rattle Mechanism

1.3. Vehicle BSR Phenomena and Examples

1.4. Design Process

1.5. Design Parameters and BSR Prevention

1.6. Computer Aided Engineering (CAE)

1.7. Conclusion

Chapter 2. Friction Sliding and Rattle Impact Analysis

2.1. Introduction

2.2. Experimental Set up

2.3. Results

2.4. Conclusions

Chapter 3. Stick-Slip Characteristics of Leather/Artificial Leather

3.1. Introduction

3.2. Measuring Methods for Determining Stick-Slip Properties

3.3. Leather Tests

3.4. Artificial Leather Tests

Chapter 4. Material Pair Testing and Instrumentation

4.1. Introduction

4.2. Material Properties of Sliding Pairs

4.3. Challenges for Accurate Measurements

4.4. Equipment Design

4.5. Functional Principle?

4.6. Application Examples

4.7. Discussion, Conclusion and Outlook

Chapter 5. Full Vehicle Testing

5.1. Introduction

5.2. Road Testing

5.3. Road Simulators

5.4. Finding and Fixing

Chapter 6. Buzz, Squeak and Rattle Detection for Modules, Subsystems and Components

6.1. Introduction

6.2. Major Issues Involved with the Physical Test Setup

6.3. Vibration Test Methods

6.4. Evaluation of BSR Noises in the Lab

6.5. Application Example (Including Test Methods and Lessons Learned)

6.6. Conclusion and Outlook

Chapter 7. Universal Graining to Prevent Creaking Noises with Plastic and Elastic Contact Partners

Chapter 8. Squeak and Rattle CAE Simulation Using FEA

8.1. Introduction

8.2. Nonlinear Method – Rattle Simulation Using Rattle Factor

8.3. Quasi-Linear Method – Rattle HotSpot Check

8.4. Summary and Outlook

Chapter 9. Squeak and Rattle Prevention in the Design Phase Using a Pragmatic Approach

9.1. Motivation for Prevention: Warranty Cost, Afterworks Cost and Image Loss

9.2. S&R Elimination Starts in the Design Phase

9.3. Solutions in Prevention of Squeak

9.4. Solutions in Prevention of Rattle

9.5. How to Proceed

Chapter 10. Experimental Friction Behavior of Elastomers on Glass

10.1. The Problem

10.2. Experimental Setup

10.3. Results

10.4. Test Method

10.5. Summary

Chapter 11. Development of Squeak and Rattle Countermeasures Through Up-Front Designs

11.1. Introduction

11.2. Root Causes of Squeak and Rattle Problems

11.3. Squeak and Rattle Sensitivity Areas

11.4. Development of Squeak and Rattle Countermeasures Through Up-Front Designs

Chapter 12. Coatings for Low-Noise Body Seals

12.1. Coatings

12.2. Mechanism of Function

12.3. Materials

12.4. Troubleshooting Anti-Noise Coating Problems

Index

Front Matter

Automotive Buzz, Squeak and Rattle

Mechanisms, Analysis, Evaluation and Prevention

Martin Trapp

Fang Chen

In cooperation with Ziegler-Instruments FILK

AMSTERDAM • BOSTON • HEIDELBERG • LONDON NEW YORK • OXFORD • PARIS • SAN DIEGO SAN FRANCISCO • SINGAPORE • SYDNEY • TOKYO

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Copyright

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ISBN: 978-0-7506-8496-5

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11 12 13 14 1510 9 8 7 6 5 4 3 2 1

Chapter 1. Overview on Vehicle Buzz, Squeak and Rattle

Frank Chen and Martin Trapp

Ford Motor Company

Chapter Outline

1.1. Customer Expectation and Vehicle Quality1

1.2. Buzz, Squeak and Rattle Mechanism5

1.3. Vehicle BSR Phenomena and Examples11

Body Interior – IP11

Example one: Tacoma IP/cross-car beam squeak12

Example two: 1997 Probe IP rattle/buzz (TSB/article #: 98-2-9)12

Body Closure – Doors and Liftgates13

Example one: 2004 Scion xB liftgate rattle (TSB #: NV008-03)13

Example two: Expedition window regulator squeak (TSB/article #: 98-17-21)14

Underbody BSR15

Transmission/Gear Rattle15

Example – 2001 Jeep wrangler gear rattle15

Seat Squeak and Seat Belt/Retractor Rattle16

1.4. Design Process16

1.5. Design Parameters and BSR Prevention17

Force Isolation18

Modal Separation18

Structural Rigidity18

Material Pair Compatibility19

1.6. Computer Aided Engineering (CAE)19

Manufacturing Process20

1.7. Conclusion20

References22

BSR may be the single largest factor that affects customers' perception of both vehicle initial quality and dependability. Vehicle dependability drives vehicle market share and residual value. Squeak generation requires that two contact surfaces have unstable and relative motion such as stick-slip motion. Buzz or rattle is produced by impact between two surfaces, either originally in contact or not. Most of the BSRs come from three major areas: IP, body closures, and underbody. BSR prevention is a system engineering process; the art is to achieve it with total cost effectiveness and durability. CAE may not render an absolute prediction if a design is subjected to yield BSR; however, it will provide the trend. It has become an indispensable tool for reducing product development time and cost. BSR prevention verification may be performed at the component, system or vehicle level. At the component or system level, usually a bench test can be performed with simulated load cases. At the vehicle level, it can be either a road test or using a hydraulic ride simulator with simulated road cases. Many BSR issues stem from the manufacturing process; SPC is often used to control assembly quality. Examples of the main technical papers and references are selected to illustrate BSR issues, which might shed some light on the state of the art.

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 [1], [2], [3], [4], [5], [6], [7], [8], [9], [10] and [11].

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) [2] and [3]. 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 [4] and [5]. 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 [6]. 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[2]. 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 [7] 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], [9], [10], [11], [12], [13], [14] and [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 [16], [17], [18], [19], [20], [21], [22] and [23]. 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 [24], [25], [26], [27], [28], [29], [30], [31], [32], [33] and [34]. 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.

To put it into mathematical form, assume that there is a sinusoidal excitation force applied on to a block that has a contact surface with the other object: the governing equation of motion in the horizontal direction for the model in Figure 1.4 can be written as

(1.1)

In (1.1), Ff denotes the friction force, which is usually described by the classic Coulomb friction model with both μs and μk being constants.

(1.2)

If the friction coefficient or the pressure/weight is zero, which means no friction force, then the motion/displacement or vibration will just be the sinusoidal and is smooth. However, if the pressure or the friction coefficient is not zero, then there will be stick-slip motion as shown in Figure 1.5, in which it is plotted against the multiple of static friction coefficient μs and pressure/weight mg. It can be seen that there is a stick period of time, and if FFT is applied, then there will be not only the fundamental frequency with a shape the same as the excitation force (smooth sinusoidal curve) but also the higher frequencies.

If there is one direction force or movement (this could happen during one movement of a periodic excitation), due to the difference of static and dynamic friction coefficients, stick-slip may also commence. Assume that a small mass (latch catch), of which one end is connected to a spring attached to a fixed end, which rests on another and there is a translating mass (striker) that moves in one direction as, shown in Figure 1.6. At the beginning, the static friction force is larger than the spring force (the spring is at its neutral position), and the small mass will move with the large mass, which the two contact surfaces stick together. During this period, the spring will start to be stretched and the spring/restoration force will increase. When the spring force increases to a value that is larger than the static friction force, the mass will start to slide. When the mass slides, the friction force is a dynamic friction force that is smaller than the static one. The spring will start to de-stretch due to the smaller dynamic friction force so that the spring force will gradually decrease until it reaches the value of the dynamic friction force. This causes the mass to gradually cease moving. Once it stops sliding, the static friction force governs the situation again. This will form the limit cycle of stick slide-slip as shown in the phase map in Figure 1.7. The horizontal line represents the stick period in which mass one’s velocity is equal to the base velocity V. The two masses move together. Trajectory A, except the horizontal line, depicts the sliding period under one constant coefficient of kinetic friction, since usually the kinetic friction coefficient is velocity dependent. Trajectory B just represents another stick-slip vibration under a different constant coefficient of kinetic friction and velocity, and it also shows that if the kinetic friction coefficient keeps changing, the curve may become spiral-like and vibration grows from a small to a large limit cycle.

It should be noted that in the above two examples damping has not been considered, which either can help to suppress the unstable stick-slip motion or actually to cause it. The following example will show how negative damping will make a vibration system unstable, thus resulting in squeak. Below is the vibration-governing equation that includes the two damping terms, of which one is positive damping and the other is negative damping. The positive damping c1 is associated with viscous damping while negative damping c2 is the term associated with the negative friction-velocity curve of the Stribeck region in Figure 1.3. The term c1 dissipates vibration energy while c2 supplies energy into the system, which will make the system vibration grow.

(1.3)

If the value of c2 is larger than c1, then the system will become unstable. Friction-induced stick-slip motion or instability is a very complex problem since friction models are often not as simple as the classic Coulomb friction model. They are often nonlinear, and speed and material property-dependent. In addition the squeak system has multiple degrees of freedom, and the modes will interact with each other, which may make the system more prone to instability. More detailed studies and surveys can be found in some recent review papers [35] and [36]. There is also another type of stick-slip motion called geometric constraint-induced sprag-slip. It was first investigated in reference 37. Sprag-slip can commence under a constant friction coefficient. It is essentially a dig-in and release process. The excitation is mainly due to geometric constraints from the configuration viewpoint and kinematical constraints in terms of motions and forces.

Stick-slip motion in a vehicle is usually low frequency. However, the sound or squeak noise generated has significant high frequencies due to the impulsive nature of stick-slip. As mentioned above, it can be seen from Figure 1.5 that if a Fourier transform is applied to the stick-slip curve, it will contain both the fundamental frequency as well as as the excitation frequency and the other higher frequencies. In addition, sound with frequencies below 20 Hz or even 50 Hz cannot be heard well by human beings. A typical squeak usually happens at vehicle instrument panel contact surfaces or door seal locations when driven on a rough road, door hinges when opened/closed, and window glass when raised or lowered. Frequencies of squeak usually range from 200 Hz to 8 kHz. It should be noted that squeak prevention is a system optimization process and a trade-off among different attributes. Although by going to extremes one can eliminate squeak, a well-balanced system with minimum squeak propensity and optimal costs and functions in high mileage conditions would be the