By: Prof. Marko Tirovic
Friction brakes and associated actuation and control systems are safety critical systems which provide unparalleled combination of high performance, high reliability, low mass and low cost. In addition to braking, they are used in traction control systems and most critically in Electronic Stability control systems. In such a way, they offer not only exceptional vehicle deceleration in all conditions, maintaining vehicle stability and steer-ability but they also vastly increase vehicle safety by improving steering/handling and propulsion in non-braking driving conditions.
Friction brakes are here to stay for many reasons. I have seen many proposals, even coming for automotive engineers about the demise or downsizing of friction brakes. They really do not know what they are talking about. The best laugh was when one delegate on a conference said that even parking brakes are not needed as electric motors can keep vehicle on a gradient (20%). There was a very loud and long laugh and even electric engineers said that they would not like the motors to be energized for prolong times in the same rotor/stator position as that will deform the magnets/poles. Not to mention that the torque can only be provided until the batteries go flat.... etc.
Not that I need to re-iterate to you but cannot resist!
Many of my colleagues do not understand brakes or braking and still think something can be ‘downsized’. At best, probably thickness I say but not the diameters, as the torque is crucial. The truth is that more powerful electric motors require more powerful brakes in terms of brake thermal capacity (due to speed increase) and cooling due to more frequent brake applications. And this is shown for road and race vehicles...many times in practice.
There are many reasons for friction brakes to stay for many years to come, they will no doubt develop and evolve, particularly the control systems, but still the hydraulics for cars and pneumatics for trucks will not fundamentally change any time soon. Simplicity and ‘primitivism’ of friction brakes is unmatched. That makes them light, cheap and above all very reliable. Although friction level is relatively ‘unpredictable’, it is way more reliable than regen braking. No electric motor/controller can provide maximum deceleration at Vmax, as the power would need to be in MW, the batteries could not take the current even if ‘optimally empty’ and at lowest possible temperature. Not to mention the reliability aspects, ABS, ESP etc...