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Moving From Round to Flat in Automotive Wire Harnesses

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Multiplexing of electrical signals in automobiles is beginning to be used as vehicles are continually being designed with more electronics and options. Multiplexing is essentially putting a digitally encoded signal on a wire and decoding that signal at the other end. This allows merging multiple communication paths into a single serial signal path.

The advantages of multiplexing include reducing the number of wires needed in a vehicle, increased functionality, increased flexibility, integration of system functions and improved systems diagnostics.

Flat Flex

Coming hand-in-hand with multiplexing is the use of flex circuits and flat flexible cable (FFC) to replace wiring harnesses. Flat flexible cables are typically used in applications that require repeated flexing.

Examples of applications include:

-Office equipment
-Industrial controls
-Laptop computers
-Disk drives
-Printers
-Avionics
-Appliances
-Cellular phones

The drivers pushing auto manufacturers to use FFC are reduced weight, less connectors, package efficiency, improved EMI/RFI performance, the move towards multiplexing and the trend toward infotainment systems in automobiles.

Multiplexing and FFC/flex circuits will see their first use in instrument panels as the real estate in this area becomes more crowded and the demand for plug and play infotainment systems continues.

The instrument panel is being designed to integrate remote electronic devices into fewer, smaller, and faster packages. This includes the radio, driver information, climate control, wire harnesses, pigtails, and connectors – all packaged into an integrated architecture.

Overall, the result of replacing wire harnesses with FFC and/or flat flex circuits throughout a vehicle (except for headlights and in the engine compartment) will result in a connector reduction of 75%; wire harness reduction of 50%; space reduction of 70% (about one cubic foot of space for the instrument panel); and simplified troubleshooting.

Major Players

The automotive OEM goals are to offer more options and reduce weight at lower cost. Conventional wire harnesses are bulky and offer less electrical integrity. The use of FFC and/or flex circuits allows auto manufacturers to achieve both goals.

The technology is currently being used or investigated for instrument panel, headliner, floor, door, and tailgate applications and it currently specifies in-body electrical applications for Ford, Chrysler, and GM vehicles.

All the major instrument panel producers such as Visteon and Delphi, are developing these multiplexed, integrated instrument panels. Hence, all of the wire harness producers are developing FFC and/or flex circuits for use in the instrument panel.

This has the potential for major growth as FFC and flex circuits replace wire harnesses in the instrument panel. Use of FFC in other areas will occur as its advantages are realized as they are now being realized for the instrument panel.