The real “golden age” of electronic suspension can be probably located in the 1980s; during that decade the exceptional potential of replacing a traditional spring-damper system with a fully fledged electronically controllable fast-reacting hydraulic actuator was demonstrated. High costs, significant power absorption, bulky and unreliable hydraulic systems, and uncertain management of the safety issues: the fatal attraction for fully active electronic suspensions lasted only a few years. In the second half of the 1990s, a new trend emerged: it became increasingly clear that the best compromise of cost (component cost, weight, electronics and sensors, power consumption, etc.) and performance (comfort, handling, safety) was to be found in the technology of electronically controllable suspensions: the variable-damping suspension or, in brief, the semi-active suspension. After a decade this technology is still highly promising and attractive: it has been introduced in the mass-market production of cars; it is entering the motorcycle market; a lot of special vehicles or niche applications are considering this technology; many new variable-damping technologies are being developed. Semi-active suspensions are expected to play an even more important role in the emerging trend of electric vehicles with in-wheel motors: in such a vehicle architecture the role of suspension damping is more crucial, and semi-active suspensions can significantly contribute to reduce the negative effects of the large unsprung mass. As in many other electronically controlled systems, the actuator is not “smart itself”: it simply inherits the smartness (or dumbness) of its control algorithm designer. The key of semi-active suspensions is in the algorithm. For the discussed reasons, this paper briefly reviews the basic theoretical concepts for variable-damping shock absorber technologies and the available control algorithms.
A leaf spring is a simple form of spring commonly used for the suspension in wheeled vehicles. Weight reduction is the major problem faced by many automobile industries. Weight reduction can be achieved by designing new materials and sophisticated manufacturing processes. Due to increasing competition and innovation in recent decades, automobile industries show interest in replacing conventional steel leaf spring with fiber-reinforced composite leaf spring which has advantages such as higher strength to weight ratio, higher stiffness, high impact energy absorption, and lesser stresses. Selection of constituents for the composites is based on the type of application, availability, strength required, and cost of material. This paper gives an overview about the research carried out for the part of two decades on selection of material, different fabrication processes, experimental investigation, design and analysis using CAD tools.
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