In the braking system – out of sight for the driver – a revolution is taking place: the classic vacuum brake booster makes way for an electric variant, and the days of the familiar master brake cylinder seem to be counted. With ABS first and later ESP we thought that the braking system was pretty much ready for the future. Nothing could be further from the truth! With the advent of regeneratively braking cars and the first steps towards autonomous driving, there has to be a decoupling between the brake pedal and the brake discs or drums. Maarrr … if the electronics fail, there is still a fixed connection between the pedal and the disks. That sounds complicated, but is it?
To allow cars to brake independently or to smooth the transition between regenerative and mechanical braking on EVs and cars with a hybrid powertrain, the classic vacuum-assisted braking system is no longer sufficient. That vacuum system has never been useful for diesels and EVs anyway, because it is not possible to use an underpressure in the inlet channel and therefore a separate vacuum pump is required.
At parts suppliers such as Bosch and Continental we see systems in which the function of the vacuum booster is taken over by a lightning-fast electric motor that ensures that brake pressure can be built up via a gear or spindle transmission. Analogue becomes digital. In combination with adaptive cruise control (the first steps to autonomous driving) or active safety systems, the braking system with these electric motors is also able to brake the car without driver input. Furthermore, for regenerative braking, a decoupling is possible between the brake pedal and the disc brakes. The electronics in the ESP control block ensure that no pressure is built up in the calipers, but the fluid is diverted back towards the fluid reservoir
Incidentally, these new braking systems not only have an effect on EVs, hybrids and self-braking cars, they also make sense for conventional cars. The electric braking systems are able to press the brake pads against the discs faster than with a conventional vacuum-assisted system. As a result, it is now possible (without affecting the speed of attack) to keep the brake pads just a little further away from the discs, so that less friction takes place (which saves fuel and therefore CO2 emissions) and the service life of the brake pads is extended.
In the unlikely event that the electricity fails or the computer gets confused, it must still be possible to brake. And that is possible, for those unexpected situations, it turns out that there is still a hydraulic connection between the brake pedal and the brake pads, but without power.
We saw the first car with the Bosch system (the iBooster) with the plug-in hybrid Porsche 918 Spyder, quickly followed by Tesla for the simple reason that the Autopilot cannot handle a conventional braking system. At Alfa Romeo, we see systems without Continental brake master cylinders in the Giulia and Stelvio, as in the Audi E-tron, the new A3 and the new Volkswagen Golf, for example.