Friction Braking in a Changing Vehicular World

ON THE ROLE OF FRICTION WITHIN THE CURRENT PARADIGM SHIFT

Transportation is one of the most societally important and growing sectors ongoing through considerable developments and changes. The not-so-distant future is envisioned as an era of autonomous transportation (SAE Brake Colloquium 21 Panel). Also, the role of vehicles changed significantly as they are becoming embedded systems “connected” to the internet and using different applications improving functionality and safety. Combined with “electrification”, Artificial Intelligence (AI), including Machine Learning (MI), their performance is being continuously improved (SAE Brake Colloquium 22 Panel).

There is also ongoing intense discussion addressing braking of the future vehicles. Some groups predict a total absence of the friction brake, believing that “job could be done” solely by the regenerative braking, converting the kinetic energy of vehicle into electric current. And there are opinions supporting “the necessity to have a friction brake (foundation brake)” combined with the regenerative braking capacity to be able not only warrant efficiency and safety, but also because the objective arguments that the currently designed regenerative braking systems are not able to operate (be functional) at high and low speeds, energy conditions, or required high and low decelerations. In these scenarios, the “regen” and “friction” brake, respectively, must “communicate” to deliver an optimal performance required by driver, autonomous system, or combination of both.

Current vehicles mostly use numerous electronic devices, able to sense, provide information to controlling computer/internet, which will then provide the necessary instructions to actuate and deliver a proper response, or, in short, to optimize the braking (and whole vehicle) operation/performance. These “electrification processes” are in focus of current “exponentially grooving development effort” and are also being used to correct or at least mitigate the “old challenges” related to braking (e. g. vibration and noise, corrosion, pollution). Some designers believe that “electrification” can resolve all of them. This however seems to be too optimistic. In addition, they are delivered at some costs, reflected particularly by the increasing costs and mass of vehicles. It is not only the “heavy batteries” responsible for the trend.

While the electrification is in focus today, and the newest technologies are being rapidly employed, not entirely surprisingly, the development of new friction materials, representing an older technology, is addressed to a lesser extent. Vice versa, the importance of brake materials optimization was diminished.  Today, the most manufacturing processes of friction materials are still at the level corresponding to the end of the 19th century. The new friction materials could “do better”, however, and this blog aims to argue that it will be the case. Today, there are numerous new materials bringing the development of advanced newly emerging technologies. They are often called responsive metamaterials with programable and tunable perceptual elements with 2D response as sensor and 2D/3D/4D response as actuators. The perceptual single elements or the integrated perceptual systems with microscopic regulation and macroscopic response could sense (=find the need) and actuate (= deliver a proper response) without the necessity to “add additional mass” related to mentioned added electronic devices.

When combined with the regenerative braking, the friction brake is used to a lesser extent (5 to 20%). By utilizing a smarter designs and materials selections, allowing sensing and reaction, rotors and brake pads/linings can be considerably smaller (not larger as many current design scenarios suggest, as the mass and speed of vehicles increases) when compared to the currently adopted systems. Utilization of these tunable response materials could also lower wear/pollution, mitigate or eliminate vibration, corrosion, and other aspects relevant to brakes. And they could still be providing means for communication with e. g. radar, lidar, cameras, driver and internet if needed. These materials are equally rapidly being developed and numerous are readily available and used in other than braking (e. g. human-machine interactions, augmented/virtual reality, wearable devices, and others) designs. Their use in brakes, not tomorrow, but certainly in the predictable future, will change as the really “optimal performance could be further optimized” by employing a combined effort of “electrification” and adoption of new friction materials. The earlier the manufacturer of friction materials will be able to adopt this, the larger market advantage they will get.

Professor Peter Filip works and teaches at the Department of Mechanical Engineering and Energy Progresses, Southern Illinois University at Carbondale. His areas of activities are in friction science, nanotechnology, materials engineering, and biomaterials at several institutions in the US, Europe, and Asia. He served as Director of the NSF sponsored Center for Advanced Friction Studies, consultant, and expert witness, co-authored more than 500 scientific publications. Peter holds a DSc in Material Science and Engineering, MS and PhD in Physical Metallurgy from Ostrava, Czech Republic. He is a member of and an instructor in Brake Academy.