Stefan Stölzl

Fault-tolerant drive-by-wire systems

The article begins with a review of electronic driver assisting systems such as ABS, traction control, electronic stability control, and brake assistant. We then review drive-by-wire systems with and without mechanical backup. Drive-by-wire systems consist of an operating unit with an electrical output, haptic feedback to the driver, bus systems, microcomputers, power electronics, and electrical actuators. For their design safety, integrity methods such as reliability, fault tree and hazard analysis, and risk classification are required. Different fault-tolerance principles with various forms of redundancy are considered, resulting in fail-operational, fail-silent, and fail-safe systems. Fault-detection methods are discussed for use in low-cost components, followed by a review of principles for fault-tolerant design of sensors, actuators, and communication. We evaluate these methods and principles and show how they can be applied to low-cost automotive components and drive-by-wire systems. A brake-by-wire system with electronic pedal and electric brakes is then considered in more detail, showing the design of the components and the overall architecture. Finally, we present conclusions and an outlook for further development of drive-by-wire systems.

FAULT-TOLERANT DRIVE-BY-WIRE SYSTEMS : CONCEPTS AND REALIZATIONS

Abstract The development of automotive systems shows an increasing integration of electronic sensors, microcomputers and actuators for single components, engine, drive-chain, suspensions and brakes. After considering electronic driver assisting systems such as ABS, TCS, ASR, ESP, BA the developments towards drive-by-wire systems with and without mechanical or hydraulic backup are considered. Drive-by-wire systems consist of an operating unit (steering wheel, braking pedal) with an electrical output, a haptic feedback to the driver, bus systems, microcomputers, power electronics, and electrical actuators. For their design safety integrity methods like reliability, fault tree, hazard analysis and risk classification are required. Different fault tolerance principles with various forms of redundancy are considered resulting in fail-operational, fail-silent and fail-safe systems. Fault-detection methods are discussed for use in low-cost components. This is followed by some principles for fault-tolerant design of sensors, actuators and communication. A brake-by-wire system with electronic pedal and electrical brakes is then considered in more detail showing the design of the components and the overall architecture. An outlook then shows the further development of drive-by-wire systems.