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Brake Noise, Vibration and Harshness: Technology Driving Customer Satisfaction

As vehicles continue to move upscale in amenities and pricing,motorists have become increasingly more demanding in regard to smooth, quiet braking performance over the life of their vehicles. The entire automotive industry can attest to this, with brake noise, vibration and harshness (NVH) repairs often dominating OE warranty claims at dealerships and aftermarket service center workloads. More than $100 million is spent annually on brake NVH warranty work in North America alone. To reduce such warranty and brake repair costs, more attention is being placed on optimizing NVH performance to eliminate brake squeals, groans and other related issues at the OE level. This is especially true considering new vehicle quality perceptions are often driven in part by brake performance and warranty repairs. The aftermarket parts and service industry, likewise, has placed greater focus on brake NVH issues. Consumers are beginning to expect OE level performance over the life of their vehicles. Aftermarket friction material suppliers have introduced a multitude of friction products during the past few years to restore OE brake NVH performance with varying degrees of success. Technology-based aftermarket suppliers with comprehensive engineering capabilities have done well. Others without access to such resources have struggled to produce viable friction products that live up to their NVH performance claims.

To reduce warranty and brake repair costs, more attention is being placed on optimizing NVH performance to eliminate brake squeals, groans and other related issues at the OE level.

Japanese Technology Credited with Original Brake NVH Breakthroughs

The focus on brake NVH performance is a relatively recent trend. Up until the 1980s, most motorists accepted a certain level of brake noise and roughness, even in some luxury and near-luxury models imported from Europe. The first breakthroughs in brake NVH technology coincided with the industry push to develop non-asbestos organic (NAO) brake pads. Much of this work was led by Japanese brake suppliers Akebono Corp., Nisshinbo (NBK) and Sumitomo. Their efforts focused on low metallic and other NAO friction formulations. Akebono introduced the automobile industry's first NAO brake pads for mass production featuring proprietary ceramic formulations in the 1980s. They were specifically engineered for the popular Honda Accord and Toyota Camry models sold in North America.

akebonobrakes.com

A variety of factors contribute to brake NVH performance issues. The challenge to Akebono and other brake suppliers is to successfully identify the root cause(s), which often vary from one model to the next.

AKEBONO BRAKING TECHNOLOGY

These friction technology advances forever helped to change consumer expectations in North America and, not surprisingly, sales of these Japanese vehicles exploded. The Japanese OEMs set new performance and quality benchmarks for quiet, smooth braking that were admired by the entire industry.

The first breakthroughs in brake NVH technology coincided with the industry push to develop non-asbestos organic (NAO) brake pads.

During this time, North American OEMs were losing longtime customers to the Japanese automakers and facing a rising amount of costly brake noise warranty work. In response, the domestic auto

Ford Motor Co. led the charge during this time to make quiet, smooth braking the OE standard in North America. The best-selling Ford Taurus was one of the first North American passenger cars to feature ceramic brake pads. GM, concerned with brake noise on its growing lineup of lightduty trucks and SUVs, also began using ceramic friction products during the 1990s. DaimlerChysler began to focus more resources on brake NVH performance and advanced ceramic friction materials as well, particularly in North America.

Akebono engineers have access to more than 20 brake and chassis noise dynamometers at the company's North American technical center. The $2-million corner noise dynamometer (above) measures corner suspension assembly for noise over a wide frequency spectrum.

Akebono System Approach to Solving Brake NVH Issues Most Effective

Vehicle program launch delays are not easily tolerated in today's increasingly competitive automotive marketplace. Unfortunately, brake NVH issues can stop a vehicle launch in its tracks or cause irreparable harm to consumer impressions during this time. Consequently, automakers try to pinpoint brake NVH issues as early as possible in a vehicle's development. Brake NVH expertise is a key factor when selecting suppliers for vehicle programs.

industry began devoting increasingly more resources toward benchmarking Japanese vehicles to identify the attributes which lead them to steady market gains in the early 1990s.

Akebono measures brake system noise and vibration on complete vehicles in its Chassis Noise Dynamometer room, found at the company's North American R&D technical center in Farmington Hills, Mich.

All brake technology suppliers are concerned with eliminating noise and vibration. Their levels of commitment to optimizing brake NVH and approaches taken vary, however. In its simplest terms, brake NVH performance is determined by

akebonobrakes.com

AKEBONO BRAKING TECHNOLOGY

engineers also direct their efforts on eliminating low frequency groans and pulsations. In many cases, the brakes work fine from a performance perspective and these noises are simply annoying.

Akebono carefully selects fine ceramic ingredients (20 microns or less) for its friction formulations to optimize brake NVH performance and control rotor wear. The use of common ceramic particles may improve braking power, but results in poorer NVH performance, greater rotor wear and increased brake dusting.

the interaction of friction material, caliper and rotor. Since many brake systems are multi-sourced, most suppliers still evaluate NVH issues on a component level. Akebono is one of the few suppliers that uses a more comprehensive system approach to evaluate and optimize brake NVH performance.The goal is to find the root cause of an NVH performance issue, which is not always easy. In addition to evaluating friction material, caliper and

rotor on both an individual and three-set system level, other braking and suspension components are examined closely to optimize their compatibility during the design process. When engineers first began concentrating on NVH performance during the early 1990s, they focused much of their attention on eliminating high-frequency squeals and brake judder (roughness), often the result of mechanical brake issues.Today, however,

The essence of brake NVH technology has evolved little in recent years, with the focus remaining on optimizing component compatibility and eliminating vibration. But, the analytical and measurement tools used today are much more advanced.

Squealing, for example, is sometimes the result of an abrasive friction material on a rotor surface. Nevertheless, current consumer braking performance expectations necessitate the development of solutions to eliminate these occurrences. In addition to evaluating the compatibility of pad, caliper and rotor, this system approach to evaluating NVH performance also involves making sure the brake system itself is robust and durable enough for the vehicle. This is a real challenge today as automakers are looking to reduce the weight of the vehicle and, in turn, component weight. Less robust brake systems are much more sensitive to excitations (friction forces) that generate noise and vibration.

Modern Analysis Tools Lead to New Brake NVH Standards

The essence of brake NVH technology has evolved little in recent years, with the focus remaining on optimizing component compatibility and eliminating vibration. But the analytical and measurement tools used today are much more advanced. The resources needed to effectively evaluate

akebonobrakes.com

Akebono has built one of the most advanced brake system testing labs in North America and uses a variety of analysis tools to evaluate and optimize NVH performance.

AKEBONO BRAKING TECHNOLOGY

brake NVH performance simply did not exist as recently as a decade ago, when the automotive industry could measure brake noise frequency, but not much else. Contrast this to the modern NVH labs at Akebono and other leading brake suppliers. In addition to sophisticated structural and thermal analysis tools, advanced dynamic motion studies are regularly conducted in real brake-stopping environments to see how components interact. The movement that causes vibration and noise is very subtle, almost always invisible to the human eye. Most people cannot appreciate the tolerances involved in refining brake NVH

CERAMICS vs. SEMI-METALLICS

Brake NVH Performance Comparison

Fade Low Temp

Squeal

Friction Material Akebono Ceramics Semi-Metallics

Excellent Good

Fair

Most people cannot appreciate the tolerances involved in refining brake NVH performance. Engineers today are measuring distances on the micron level ­ down to one millionth of a meter.

performance. Engineers today are measuring distances on the micron level ­ down to one millionth of a meter. Proximity sensors are used to measure how components move relative to each other when brakes are applied. In instances where it is not possible to attach sensors, laser measuring devices are employed. Another major improvement in brake NVH analysis is environmental control. NVH events, especially those noise related, are almost always linked to specific temperature and humidity ranges. Akebono's engineering center in North America is the only one in the world that has full environmental controls on all of its custom-built brake and chassis noise dynamometers. The world-class facility also features a

number of small-scale dynamometers with complete environmental controls. In addition to running performance and basic wear tests, the Akebono small-scale dynamometers were custom designed to evaluate noise and feature all of the necessary instrumentation. Most OE brake suppliers typically have such environmental capabilities on only 20 percent of their dynamometers, forcing them to often use a hit-and-miss approach to identifying NVH issues.Very few, if any, brake suppliers in the aftermarket have environmental capabilities whatsoever. Such technology is cost prohibitive to many companies, considering the typical cost of a full-size component dynamometer

with environmental controls is at least $1 million. This point alone illustrates Akebono's commitment to optimizing brake NVH performance.

Market Dynamics May Play Biggest Role in Future of Brake NVH Performance

As global automotive tastes continue to merge, customer demand for quiet, smooth braking is growing in North America and other key markets worldwide. To meet this requirement, Akebono and other leading suppliers are spearheading a technological revolution in brake system design and safety. The greatest challenge they face in this regard is finding a balance between optimizing brake NVH performance and minimizing engineering and manufacturing costs to provide the greatest value to motorists. Their expectations must be met, however, or automakers run the risk of turning them into dissatisfied customers. The price to win these customers back may be more than dedicating the technological resources and ongoing commitment needed to ensure optimal NVH performance and quiet, smooth braking.

Advanced thermography analysis of rotor surfaces helps Akebono identify causes of brake judder, often the result of heat spots.

AKEBONO BRAKING TECHNOLOGY

akebonobrakes.com

Groan

Friction Stability

Wear High Temp Roughness Low Temp

Noise

Cold Friction

Corrosion

Vibration

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