Brake-by-wire

Brake-by-wire technology in the automotive industry is the ability to control brakes through electronic means, without a mechanical connection that transfers force to the physical braking system from a driver input apparatus such as a pedal or lever. The three main types of brake-by-wire systems are: electronic parking brakes which have, since the turn of the 21st century, become more common; electro-hydraulic brakes (EHB) which can be implemented alongside legacy hydraulic brakes and as of 2020 have found small-scale usage in the automotive industry; and electro-mechanical brakes (EMB) that use no hydraulic fluid, which as of 2020 have yet to be successfully introduced in production vehicles. Electro-hydraulic braking systems control or boost the pressure applied to the hydraulic pumps through the brake pedal. Safety requires that the system remains fail-operational in the event of a power failure or an electronic software or hardware fault. Traditionally this has been achieved by means of a mechanical linkage between the brake pedal and the brake master cylinder. With a mechanical linkage, the braking system still operates hydraulically via the pedal, whether or not electrical control is present. EHBs can be implemented by-wire, without legacy hydraulic systems and mechanical connections. In such a case, fail-operational redundancy is implemented, allowing the vehicle to brake even if some of the brake systems fail. Electro-mechanical brakes offer the advantage of reduced braking system volume and weight, less maintenance, easier compatibility with active safety control systems, and absence of toxic braking fluid. Their novel actuation methods such as wedge brakes have kept them, as of 2020, from successfully being introduced in production vehicles. Since by-wire systems have no mechanical linkages that would provide manual control over the brakes, they require fail-operational redundancy as specified by the ISO 26262 standard level D. Redundant power supplies, sensors, and communication networks are required.