By Martha Uniacke Breen
Despite the astonishing advances made in brake technology in recent years, one problem continues to plague aftermarket manufacturers, techs and consumers alike: noise, vibration and harshness (NVH).
Just why is NVH such a thorny problem for engineers to address? Brian Kowalski, VP branded sales with Brake Parts Inc., explains that modern formulations, for all their advances in other aspects, may have exacerbated this ongoing issue. “Typically in the past, noise was primarily associated with semi-met friction materials because of their higher metallic content. Today, due to legislation that has been passed in several states, manufacturers are working to remove copper from ceramic friction formulations and replace it with alternative materials. With this mandated change has come an increase in noise-related concerns from customers.
“Brake noise, even for vehicle manufacturers, continues to be the single largest brake warranty item, even after many hundreds of hours are spent on both brake dynamometer and vehicle to eliminate brake noises for each new vehicle platform,” observes Bob Peters, chief engineer, friction material engineering with Akebono Brake Corporation. “The fact is that brake noise is nearly impossible to simulate on the computer and, consequently, most noise mitigation work is done on actual parts, using both special noise dynamometers and on the vehicle. This is expensive and time-consuming.”
“Another issue causing excessive brake noise is the escalating effect of rust and contaminants that have entered the brake system. This involves more than friction. Rust on friction, rotors, calipers, caliper brackets and hardware is a growing concern and is due in part to increasing amounts of chemicals used on the roads for snow and ice removal and, in turn, eroding the brake components,” adds Dean Weber of ProForce Automotive Inc.
In recent years, manufacturers have continued to develop innovative technologies and design improvements geared to helping the technician address what is, according to Weber, the number-one complaint among brake service customers.
As BPI’s director, friction product development Jerry Forystek explains, “Brake Parts Inc. has introduced proprietary hybrid friction formulations (EHT, or enhanced hybrid technology) to give customers the characteristics of ceramic, with low dusting on rims and quiet operation, coupled with the stopping performance of a semi-metallic brake friction. To best combat noise, installing top-quality rotors to mate with premium quality pads designed specifically for the vehicle application will bring the brake system as close as possible to its original, quiet operation.”
“Most brake pads come with stainless steel hardware now, which ProForce recommends for replacement with every brake job,” says Weber. “Improved material used in shims (multi-layered Nitrile) has also been a key factor in reducing noise complaints.” Weber also recommends Geomet Coated rotors, which contain anti-rust characteristics in the coating to reduce noise.
According to Akebono’s Peters, “The company has an industry-leading number of conventional and special noise dynamometers and also has two dedicated chassis noise dynamometers capable of accepting complete vehicles in full climate controlled hemi-anechoic chambers. We are leaders in the industry in the use of 3D vibrometry, CAE-based modelling capability, plus full in-house prototype friction material capability. Our understanding of brake noise and its myriad of contributing factors are constantly being fed back into our brake design and friction formulation programs.”
Down the road, new technologies continue to appear, especially those that address the unique problems of new types of powertrains such as hybrid and electric.
“The EV and hybrid vehicles add another significant challenge to brakes,” says BPI’s Brian Kowalski. “Most of these vehicles utilize some type of regenerative braking that will handle a significant amount of the braking as compared to conventional braking. Therefore, due to limited use, the pads may wear longer, but the lack of use will cause challenges when it comes to rust, noise and proper braking actuation. Typically, the brake components will have to have even stronger corrosion protection and greater NVH characteristics.”
According to Bob Peters, “Because noise is so sensitive to boundary conditions, and given the extreme set of conditions the brake must operate in, it is no small wonder that in some cases the energy that is normally converted to heat, occasionally escapes as brake noise. Brake service featuring a high quality ceramic friction material, a quality brake rotor, and attention to detail and cleanliness offer the best chances to avoid brake noise.”