Brake By Wire Functional Safety Concept Design for ISO/DIS 26262 2011-01-2357

The importance of functional safety design has recently grown with the increasing widespread application of electric/electronic (E/E) systems in today's automotive industry. Such E/E systems, usually composed of mechatronic actuators, various sensors, and electronic control units (ECU), have become too complex to be handled in the conventional quality management manner that was used for most predominantly mechanical applications.

ISO/DIS 26262, an adaptation of the pre-existing IEC 61508 requirements specifically for the automotive industry, has been prepared as the global standard to meet such demands for a more structured and systematic approach to functional safety design. The functional safety concept design includes a hazard analysis and risk assessment phase that is based on ASIL (Automotive Safety Integrity Level) categorization. ASIL has four levels, A, B, C, and D, where A has the lowest risk and D has the highest.

In this study, the concept phase of this ISO26262 standard for application to the Brake-by-Wire (BBW) system will be investigated. A BBW system is one in which the existing hydraulic system is replaced by motor driven electro-mechanical calipers. In this system a pedal simulator is used to provide pedal feel and recognize the driver brake demand. This demand signal is sent to the main controller which controls the independent actuators at each wheel. The target system structure of the current study is composed of conventional electro-mechanical brakes (EMB) on the rear axle and electric wedge brakes (EWB), which use self-reinforcement through the vehicle kinetic energy, on the front. Development of BBW began in the late 1990s but has yet to successfully be introduced in series production mainly due to cost, reliability, and safety concerns. The current investigation is an attempt to take a step forward in tackling the safety concerns.