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Circuit protection solutions target new vehicle trends

Posted: 11 Aug 2011 ?? ?Print Version ?Bookmark and Share

Keywords:hybrid? electric vehicles? fuel economy?

Global initiatives to improve fuel economy and reduce CO2emissions present great challenges for the automotive industry, and reducing vehicle mass is one of the most common strategies being pursued by manufacturers today. With electric vehicles (EVs) and hybrid electric vehicles (HEVs) also addressing the world's energy and emissions crises, automakers and battery manufacturers are rapidly developing new materials and solutions to advance those technologies.

The connected lifestyle has also found its way into the automobile and has dramatically affected new vehicle designs. Consumer demands and competitive pressures have led automakers to add a growing number of functions and features to their vehicles, which in turn affects electrical/electronic architecture and components.

In this report
??Greener, lighter designs
??Alternative power systems
?? Migration to power electronic functions
??The connected car
??Down the road

Greener, lighter designs
Improving fuel economy and reducing greenhouse gas (GHG) emissions are important design criteria for today's automotive engineers. EVs and HEVs are obvious solutions to both of these challenges, but vehicle weight reduction technology also provides some clear benefits; as the reduction in vehicle mass and rolling resistance translates to reduced energy requirements and effectively helps reduce CO2emissions.

In addition to the greater degree of component integration and the use of advanced materials that are helping automakers reduce weight, wire harness weight is an area of particular interest and has led design engineers to revisit their approach to protecting automobile power functions against damage from high-current fault conditions.

A challenge for designers is to retain and/or add circuit protection devices that help protect against damage from potential overload conditions in the vehicle's electrical system, while simultaneously reducing total cost and weight. Since a typical vehicle may contain hundreds of electrical circuits and more than a kilometer of wire, the complexity of the wiring system can make conventional circuit design techniques difficult to use and may lead to unnecessary overdesign.

Many manufacturers have found that employing a decentralized architecture combined with resettable polymeric positive temperature coefficient (PPTC) overcurrent protection devices can significantly reduce vehicle weight. Figures 1 and 2 illustrate the difference between a traditional centralized architecture and a decentralized architecture. A centralized approach requires each module to be protected by a separate fuse in the junction box, as illustrated in yellow. In this type of "star" architecture, each function also requires a separate wire, which adds weight and cost. In contrast, a decentralized architecture, where several junction boxes are supplied by power busses, the wires exiting the junction boxes can each be protected by a resettable circuit protection device.

Centralized architecture

Figure 1: Typical centralized architecture.

Decentralized architecture

Figure 2: Typical decentralized architecture.

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