Fault Tolerant Drive By Wire Systems: Impact on Vehicle Safety and Reliability

A brief overview of fault tolerant drive-by-wire technology is presented in this chapter. A review of drive by wire system benefits in performance enhancements and vehicle active safety is then discussed. Challenges in relation to the fault tolerant design of drive by wire system are then presented. This is followed by in-depth coverage of fault tolerant design of a steer by wire system. Future trends in the design of fault tolerant drive by wire systems are presented at the conclusion of the chapter.

Drive-by-wire systems in automobiles and fly-by-wire systems in aircrafts have made these vehicles versatile with added features and benefits, along with ease of reconfiguration, in particular during graceful degradation. However, there are certain consequences of such by-wire systems in terms of overall system reliability. The issue has not been quantitatively discussed in the literature in a systematic manner, to the best of the knowledge of the author. The chapter discusses details of the drive-by-wire system architectures from a system viewpoint, analyzes the reliability with quantitative metric, and indicates methods of enhancing reliability by using both hardware and software redundancies.

The chapter deals with the dependability and the functional safety of a system by illustrating the key points of the theoretical corpuses formulated on the two subjects: the dependability theory and the functional safety standards. Dependability is concerned with the ability of a system to deliver the intended service, including the ability to cope with a fault. Functional safety is concerned with the safety-critical systems and focuses on the characteristics of the extra systems added to a system with the purpose of making its operation safe. The chapter starts by providing the definitions of system and service. Then it passes to the illustration of the key concepts of the dependability theory, which are the threats, the attributes, and the techniques used to enforce the dependability. Particular attention is given to the fault-tolerance techniques and the architectures of the faulttolerant systems. Afterwards, the chapter presents the key issues of the functional safety standards, which are the analyses of hazard and risk of a safety-critical system, and the safety requirements for the extra systems. At last, a case of study is examined from the standpoints of both the dependability and the functional safety.

Global positioning system (GPS) and embedded computing technology offer new automation opportunities in mobile equipment applications. GPS signals are widely used in direction guidance of cars, ships and airplanes. Construction, mining and agricultural equipment industries stand to benefit from the application of GPS in various control functions. Using GPS and digital embedded control technology, many motion control functions such as motion planning and motion execution can be automated. Automated control of various machine functions without operator (human) involvement brings the embedded control technology closer to autonomous operation capability. Many of these machines require an expert operator who must deal with steering, throttle, and multi-axis tool motion control tasks at the same time, while being very careful in the rather hazardous work environment. It is, therefore, desirable to be able to operate these machines without the operator, that is autonomously, and remove the operator from the dangerous work environment. Autonomous steering of a motor grader is studied in this paper. The system automates the process of generating the desired motion path for a given field operation, and then using GPS signals for its position measurement, it controls the steering system to follow the planned path. This concept can then be integrated with automatic throttle, transmission, brake and tool control sub-systems to achieve completely autonomous mobile machine operation. The system design details of the by-wire-steering system are discussed in hardware and software components. Simulation and tests results on a motor grader are presented. Path tracking accuracy of the by-wire steering system using carrier phase differential GPS (CP-DGPS) position signal was less than 10 cm consistently in our tests using a motor grader.

Developing new construction equipment or modifying an old model requires large investment in reengineering and testing. This paper presents a virtual operator model that can be used to (1) control, test and evaluate virtual construction equipment before building the prototype, (2) autonomously control the construction equipment after being built. Furthermore, the virtual operator model is adaptive to properly control different models of the same machine. The operator model is useful in evaluating a new machine design and predicting its performance in applications under realistic conditions as a real human operator would operate it. Using this model, potential problems can be identified in early design stage, hence reducing the costly prototype testing stage of the machine development.