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The Evolution of Automotive Brake Emission: Part 2 of 3

Written by: Carlos Agudelo

An image depicting a cityscape with smog and another with no smog.
Automotive Brake Emission also contribute to Air Pollution

Image Credit: Tomskyhaha, CC BY-SA 4.0, via Wikimedia Commons


Ten things the industry did to reduce brake emissions — a view from 2032

Ten is a particular number in Western culture. We split our history and lives into decades. We reference how Chicago owned the 1920s and the Bauhaus prominence in the 1930s. I grew up with English rock from the 1970s and moved to the United States in the early 2000s. And probably, the 2020s will be marked by the Covid-19 pandemic. Ten is also how to handle data with significant differences using logarithms and orders of magnitude, including brake particle emissions. Jane McGonigal — world-renowned future forecaster and game designer who predicted in 2008 a pandemic of a fictional virus in the fall of 2019, using social simulation tools; https://janemcgonigal.com/, indicates ten years as a relevant and manageable timeframe to ‘imagine’ the future. According to Jane and others, imagining the future is not about soothsaying or being accurate in our predictions. It is about using the collective imagination to envision what our lives, business, and society could look like ten years from today. Future thinking also gives us the courage to develop creative solutions and take actions to shape our future and avert or minimize risks.

“The future is whatever time feels far enough away for things to really change.” Jane McGonigal – Imaginable, 2022

Imagining the future of brake emissions is a relevant platform to exercise this future-building mindset. We already know that brake emissions will continue as a significant source of non-exhaust particulate matter (PM) unless we do something about it. We know that to emit less, brakes need to wear less. Brake emissions represent a percent of fine particle air pollution. The actual percentage remains elusive due to the complexities and dependency of location, traffic, weather patterns and seasons, day-to-day variation, and fleet composition. The correct answer will probably be that “it depends…”. Of particular interest are particles with an average diameter of 2.5 μm or smaller (PM2.5). The figure below illustrates the total PM2.5 concentrations (including transportation) and the annual averages of the population-averaged values for 2019; Home | State of Global Air. Visit the website to learn more about how COVID-19 affected air quality and for more in-depth analysis. The HEI website for insights and extensive research efforts on the health effects of transportation systems.


As of June 1st, 2022, Covid-19 has caused 6.3 million deaths. In the same period, ambient particulate matter caused 7 to 9.6 million deaths

The list

Over the next decade, what we do (or don’t) to lessen or minimize air pollution from friction brakes will influence our future. If we attempt a ten-year future simulation, these could be ten things we see in retrospect the industry and society doing, most of them as collaborative efforts. The list is in no particular order of importance of probability of happening or succeeding. Some may occur at different times, at different scales, in other regions, and some may merge to leverage the benefits further. The actual list of potential measures is much longer than this. You can play yourself a simulation or collaborate with your colleagues and peers to develop at least three more.


The achievements enumerated in this blog are from my ten-year future simulation and do not reflect the policies or plans of individual companies, entities, or regulatory bodies. The list includes some possible futures without any qualification on their likelihood or impact on reducing braking systems’ environmental or health effects.


1. Complete migration to Non-Asbestos Organic formulations

Upon multiple independent studies and developments, the automotive industry migrated to new formulations without relying on a metallic matrix, with significant reductions in particle mass and particle number emitted per vehicle-kilometer driven on new vehicles. The developments involved brake sizing and brake control technologies limiting the amount of temperature increase during routine and emergency braking. A side benefit of these formulas was reducing corrosion effects, enabling special coatings, extending the service life of the brake discs and pads, and reducing the scrap from used parts. Low- or semi-metallic formulations are limited to special applications without significant representation in the vehicle population.


2. Smart driving technologies

With low-cost mechatronics and vehicle connectivity with 6G technologies in most countries, navigation systems integrate personal scheduling and travel planning to recommend routes and travel times that leverage low-traffic and light acceleration and light braking driving into AACC (Advanced Automated Cruise Controls). Google and Apple now offer default friend and family pool programs with incentive programs for ride sharing and low pollution driving star ratings.


3. X-prize for zero corrosion

SAE and FISITA (sponsored by several industry consortia) implemented an X-Prize competition among young engineers and scientists to develop market-ready technologies to eliminate corrosion on foundation brake systems. The X-Prize winners include teams from regions as diverse as Vietnam, Brazil, Egypt, and Estonia. Some examples of winning initiatives include, among others:

  • New alloys with recycled materials

  • Carbon-neutral coatings for brake calipers, brake hardware, and brake discs

  • Open-source software for the brake controls manager modules detects corrosion-inducing conditions (integrating weather data) and activates the brake to reduce corrosion build-up

4. Smart brake work distribution

For the past five years, the Electromechanical Brakes (EMB) fitted in all four wheels in over 90% of new vehicles integrate with a Centralized Brake Optimizing System (CBOS). This mechatronic integration distributes the braking forces in real time to limit the brake temperatures below the threshold limits for particle number (typically starting at about 170 °C). The CBOS incorporates sensors and inputs from driving intended deceleration, traffic and vehicle speed data, axle loading, vehicle steering, and brake output to predict brake temperatures in real time and adjust the brake balance accordingly. The AutoMotor Sports Magazine developed a new ranking system for brake optimization and has replaced the former method to rank vehicles based on stopping distance at high speed and elevated temperatures as the primary metric for vehicle braking performance.


5. Low-wear materials

Less wear generates fewer emissions. The correlation between brake wear and particulate matter is evident. The Recent Interlaboratory Study (led by the Joint Research Centre within the Particulate Measurement Program of the UNECE) with 15 test facilities demonstrates such a relationship. The graph shows the relationship between the total wear of the friction couple (during six WLRP-Brake cycles) and the emission factors for PM2.5 and PM10.



Data  graph courtesy of Dr. Theodoros Grigoratos – European Commission – Joint Research Centre
Data courtesy of Dr. Theodoros Grigoratos – European Commission – Joint Research Centre

The industry was able (in collaboration with the UNECE/GRPE/PMP, ISO, JSAE, and SAE) to develop new or adapt laboratory methods to allow individual companies to perform simple wear testing methods to reduce wear rates. Direct brake emissions measurements remain part of mandatory homologation programs. Several vehicle manufacturers (to meet the PM limits for internal combustion engine powertrains still in production) have adopted devices to capture particles to reduce the particulate matter from the brakes that become airborne. The devices have become widely available for the aftermarket as well.

What can be the role of accelerated automotive electrification and artificial intelligence in reducing wear? I will discuss that in my next blog.

Carlos Agudelo is Director of Applications Engineering for LINK Group, developing new features and systems based on data and experimentation, emphasizing non-exhaust brake emissions and Hardware-in-the-Loop. Carlos obtained his bachelor’s degree in Production Engineering from EAFIT University-Colombia (in association with Aachen University and Ruhr University Bochum) and a Six Sigma Black Belt certification. He is Chairman of the SAE Brake Dynamometer and the Vehicle Dynamics Standards Committees, Vice-Chairman of the SAE Brake Lining Standards Committee, and the Truck & Bus Hydraulic Brake Committee. He is active on SAE, ISO, and PMP Committees and task forces. Carlos is a member of and an instructor in Brake Academy.

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