Firstly, the brake-by-wire system is designed to resemble, feel and operate exactly as a conventional vacuum booster or electrohydraulic system would to a driver today. The driver applies pressure to a brake pedal that is linked to a simulator, which in turn provides the feedback it would deliver in a standard system – i.e. the driver will feel that they have applied the brake through the pedal. As it is linked to a Human Machine Interface (HMI), it also has the ability to be designed, adapted and adjusted in many different ways, for example to suit a variety of driving styles, such as comfort, sport, or economy, depending on the customers’ unique specifications.
This pedal / simulator combination has a dedicated sensor that, once the pedal is depressed, is able to gauge the position of the pedal and then feed that information back to the vehicle’s brake control unit (BCU). Once received, the BCU then processes the information and determines the correct level of torque required by each braking corner, which in turn is relayed to dedicated electrohydraulic actuators.
Up to this stage, all systems on the market work the same. The ultimate goal for all is the real dry brake, where no hydraulic fluid is necessary. This means that all four calipers are electrically controlled and actuated by electric actuators. Since the market, the OEM and particularly the end customer still lack confidence in such a completely decoupled system, "hybrid systems" are being promoted in parallel today, where a certain intervention or redundancy is still provided by a partial hydraulic circuit, for example on the front axle, in the event of failure of an electric module. The actuation in such "dry-wet" systems is identical. However, here the electronic signal is passed on to the electrohydraulic actuators and thus the brake calipers are operated hydraulically. These actuators then convert electrical energy sourced from the vehicle’s battery to hydraulic pressure, which is then applied at the determined level. In general, all variants of brake-by-wire enable far more efficient braking and shorten both the system's reaction time and the braking distance.
All four brake discs are standard components, as are the front calipers, however the rear calipers are pure electrical and are therefore controlled by the BCU. Again, the electrical energy from the battery is converted into what is known as clamping force, which is applied in relation to the force target identified by the BCU. This pure electric caliper can also be used where an electronic parking brake function is required, adding additional functionality.