Brake-by-wire technology was often well on the way to large-scale production. So far, it has not been launched on the market. But that is set to change: The first brake-by-wire systems could be available by 2025.
Comparison of the brake pedal stroke of a conventional braking system with the potential of brake-by-wire technology. Figure 2 from: Brake-by-wire – The Braking System of the Future, ATZworldwide 10-2022, page 42.
Bosch
Until now, there has always been a direct mechanical connection between the brake pedal and the service brake. Soon, that could be a thing of the past. In the foreseeable future, brakes and steering systems will be moved only by electronic control pulses plus actuators, i.e. "by wire". The brake pedal will then be a control unit with which the driver merely triggers the electronic impulses. Springer author Ferit Küçükay describes it in the chapter Abbremsung und Bremssysteme (page 866f) des Buchs Grundlagen der Fahrzeugtechnik as follows: "In the electromechanical braking system (EMB), the hydraulic units are dispensed with. Instead, the deceleration request is detected via pedal travel sensors and transmitted to an actuator on the brake caliper via signal lines (brake-by-wire)."
Brake-by-wire systems have several advantages over conventional braking systems. For example, a "major advantage of the electromechanical brake [...] is the reduction of residual braking torque and thus also of brake dust emissions due to the electrical control of the wheel brake," explains Ralf Stroph from BMW in the guest commentary Ist die Zeit reif für eine elektromechanische Bremse? (page 50) from ATZextra Bremsen – Funktionen, Systeme, Komponenten. Another advantage is the freedom of design space, since there is no longer a rigid mechanical or hydraulic connection between the brake pedal and the brake force actuator. There are also advantages in production with regard to assembly, parts supply and the elimination of the need to fill the brake system. A disadvantage, according to Stroph, is the increased complexity: on the one hand, due to the brake actuator itself and, on the other, due to the entire connection to the safe energy supply and vehicle communication.
E-mobility and autonomous driving revive by-wire solutions
The fact that brake-by-wire, but also steer-by-wire, are now gaining ground is primarily due to two developments: electromobility and autonomous driving. "In addition to their traditional tasks of decelerating and stabilizing the vehicle, braking systems are gaining more and more functions and features", Bosch explains in the article Brake-by-wire – The Braking System of the Future (page 40) from ATZ worldwide 10-2022. For example, emergency brake assistants would place increasing dynamic demands on the brake system, and with the emerging electrification of the powertrain, vacuum-free braking and recuperation efficiency would come to the fore. The highly automated driving functions also required redundantly designed braking systems.
Today, a large number of systems in the vehicle rely on a redundant electrical system, for example to enable highly automated driving according to SAE level 3 or higher. "That's why brake-by-wire technology is becoming increasingly economical in the medium term. Furthermore, we have electronic components available today that significantly simplify redundancy, such as microcontrollers with multiple processing cores and independent monitoring," says Alexander Gaedke of Bosch in the interview "Wir werden Brake-by-Wire-Systeme ab 2025 im Markt sehen" (page 8f) from ATZextra Bremsen – Funktionen, Systeme, Komponenten.
Ensuring reliability
A decisive prerequisite for all by-wire systems is functional safety: brakes or even the steering in the vehicle must never fail; the car must remain controllable even in the event of a partial failure of the electronics. But how do you ensure redundancy? "To avoid a complete system failure caused by a single fault, both the sensors used to detect the driving brake request and the transmission of the signals must be designed accordingly," explains brake specialist Gaedke (page 9f). Different and thus independent measuring principles are needed to create redundancy in the sensors, for example. In data transmission, he says, redundant and separate paths are absolutely necessary in order to be able to compensate for any breakage or tearing of a cable. "A sophisticated monitoring concept to safeguard all paths is the basic prerequisite for operating a by-wire system safely," Gaedke says. In addition, security architectures for by-wire technologies must cover everything from the supplier structure for vendor components to the issue of cybersecurity.
Series production at Hella and Bosch expected in 2025
Gaedke predicts that by-wire technology will be seen in initial applications on the market starting in 2025. "We further assume that there will be a shift from classic brake systems to by-wire systems and that the shares in the market will increase by the end of the decade," Gaedke said. Bosch plans to have a hydraulic brake-by-wire concept available ready for series production in 2025. Hella (Forvia) has also announced its first large-volume series production for probably 2025.
The basic prerequisite for the introduction of brake-by-wire technology is the economic viability of the system. Ralf Stroph from BMW also draws attention to this: "In my opinion, there is no question that the electromechanical by-wire braking system will become established in the automotive industry. Clarifying under which boundary conditions this also makes economic sense is a central task of further development work."