Although conventional round wire harnesses continue to evolve to support
additional electronic content in vehicles, the technology has remained much
the same over the last 50 years. Going forward with steer-by-wire and brake-by-wire
technologies looming, can the current wiring harnesses technology cope? Has
the traditional wire harness loom had its day? What are the alternatives?
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Car electrics have become extremely complex. In 1960 the wiring loom of an
upmarket car contained about 200 connectors. Today the figure is nearer 1,800.
In 1960, the same car contained about 200 metres of wiring – now it is more
like 2.5 kilometres with over 800 wires. Many vehicle functions that had previously
been hydraulically or mechanically activated are being replaced by electrical/electronic
activation. For example, a top-of-the-range 1993 model year Ford Explorer had
963 electrical circuits while a comparable 2000 model year model had more than
1,800 circuits.
Wiring looms are heavy, too. The average loom per vehicle carries around 80
pounds of copper wire and insulation. And that could double over the next five
years as the avalanche of multimedia and safety devices descend on tomorrow’s
car.
For manufacturers, the increase in the content and complexity of electrical
and electronic components requires a broader overall design perspective. This
shift in design philosophy is, as Lear Corp describes it, ‘moving from the wire
itself to the wire ends’, reflecting a view that design should include both
the wiring and the electromechanical and electronic devices to which they are
connected.
Further challenges confront the electrical circuit designer as a result of
the growing number of sensors carried by vehicles, particularly since the data
produced by the sensors may be required by several systems operating in real
time, e.g. safety and emission control. Other challenges include higher power
and current requirements and electro-magnetic and radio frequency interference.
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By GlobalDataBut there are alternative solutions to the traditional wire harness loom emerging,
such as multiplexing, fibre optics and flexible printed circuit boards.
Multiplexing?
Multiplexing is one solution, separating power and signal requirements,
and the simplification of the signal wiring. In other words, multiplexed systems
need fewer wires, thereby reducing bulk and weight. Manufacturers claim that
multiplexing cuts the amount of wiring by 20% over conventional wire harness
designs. Information is shared rather than duplicated, improving service repair,
diagnostics and the flexibility to change options.
Given that fewer cables and connections are needed in a multiplexed car, this
saves both space and weight resulting in reduced fuel consumption and improved
reliability. For example, the wiring inside Citroën’s Picasso multi-purpose
vehicle has been reduced by around 20%. In fact, multiplexed wiring allowed
Citroën to offer a number of high-tech refinements on its C5 model, including
tyre pressure sensors, light and rain sensitive headlamps, sunlight sensitive
air conditioning and an auto-find facility for locating the car in a car park.
Volvo’s S80 is another example of a highly multiplexed vehicle. Also, Mitsubishi
Motors’ Airtrek SUV features a so-called smart wiring (multiplexing) system
that is used to control all functions of electrical equipment related to the
body. The system links the steering column switch, power window main switch,
front ECU, electronic time and alarm control system, sunroof motor assembly
and the security system. The BMW 7 Series uses both multiplexing and networking
technologies incorporating come 1,000 copper circuits, 20 optical fibre circuits
and several wireless modules, the latter for keyless entry and mobile phones.
Without multiplexing, BMW’s flagship vehicle would require about 4,000 circuits
for the equivalent features and controls.
By 1998, around half of all new vehicles in North America had some level of
multiplexing. Today, nearly all new vehicles have some level of multiplexing,
but widespread integration of mixed plastic fibre and copper systems is more
prevalent in Europe than in North America.
fibre optics?
The traditional method of assembling a wire harness is in the form of a
single component that is then threaded into the car as it moves down the assembly
line. The main reason for this one-piece approach was the cost of the connectors
and concerns over product reliability. It is now rare to find harnesses built
conventionally, i.e. individual wires bundled and wrapped. A ribbon configuration
is more suitable for floor or roof mounting and flat multi-pin connectors are
easier to manufacture and assemble. The distinction between power and signalling
is now established allowing cable runs to be optimised. Dual voltage systems
will provide fresh challenges as the industry adopts a 36-volt standard alongside
old 12-volt components. A signalling revolution may be imminent, as conductive
circuits are abandoned in favour of optical fibre.
Fibre optic systems transmit information and data throughout the vehicle for
signalling and communication. Optical fibre would have a higher information
rate than a conductive medium of comparable size, and would not be affected
by electromagnetic interference. The optical fibre technology is engineered
to support large and rapid data transmission requirements such as mobile multimedia
applications. These innovations accommodate large bandwidth, provide electromagnetic
compatibility, reduce weight and provide speed, signal clarity and cost improvements
over copper-based technologies. The benefits of optical fibre are ideally suited
to integrated safety systems.
Claimed advantages of using fibre optics over copper wires include weight
saving and higher data quality, reliability and integrity. Not only is it possible
to send large volumes of data through the network at the speed of light, it
also guarantees excellent electromagnetic compatibility.
On the downside, however, fibre optics are more expensive than traditional
wire harness technology as they need more parts to convert electrical signals
to light pulses and back again.
and flexible printed circuit boards
Another novel departure in wiring materials is the flexible printed circuit
(FPC). FPCs enable larger sections of the wiring harness to be made in a flat
printed circuit board (PCB) configuration. Because of its PCB construction,
FPCs can integrate switches and LEDs.
Benefits of FPCs include weight and space saving, increased automation of
production, improved consistency of performance and added value through mounting
components on the harness. Flexible circuits are said to be more expensive than
the wire harnesses they replace, although they can save cost elsewhere in the
vehicle’s electrical system. They can also reduce the number of connectors required.
However, given that FPC connectors have current capacity of a few amps, applications
are limited. Most applications have been confined to instrument clusters and,
more recently, headliners in some vehicles. Other applications include door
wiring, seat wiring, HVAC, antenna and mirror systems. Given that flexible circuits
cannot tolerate high temperatures, their use in the engine compartment is ruled
out altogether. Molex’s director of automotive marketing, Bob Fuerst, told just-auto:
“One reason why existing harness makers have not embraced flat wiring is
because it impacts all facets of their operations from design to manufacturing,
thereby obsoleting huge amounts of installed capital.”
Market pressures
The migration from electrical distribution systems to electronic and electrical
distribution systems is facilitating the integration of wiring, electronics
and switch/control products within the overall electrical architecture of a
vehicle. This migration will reduce the overall system cost and weight and will
also improve reliability and packaging.
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The demands on wire harness makers by their OEM customers are many and varied,
as David Wright, director of advanced engineering and research and development
for Delphi Packard Electric, told just-auto: “The complexity of today’s
wiring harnesses is staggering, with countless opportunity for error. Only the
most capable suppliers are able to design, manufacture and deliver these products
to the quality levels expected by our customers. They are demanding more design
and release support, flawless quality and responsiveness all around the globe.
The depth of technical understanding in the application of wiring systems and
the design and development of connection systems continues to develop.”
As the complexity of wire harness design moves into uncharted territory, that
inevitably impacts on manufacturers’ design and development capabilities, as
David Wright said: “We need to support each of our customers in their own
CAD/CAE environments. They are also asking for simulation capabilities and architectural
proposals at the design concept stage.”
Like most component suppliers, wire harness manufacturers have long since felt
acute pressure to reduce their prices offered to the vehicle makers. Most have
remained profitable by enhancing operational efficiency, redesigning products
to reduce the amount of material needed as well as relocate manufacturing to
low-wage countries.
Taking advantage of low labour rates, most major wire harness manufacturers
have established manufacturing operations in central Europe, Mexico and parts
of Asia such as the Philippines. The labour content of a wire harness is said
to be amongst the highest of any component system. Supplying both local carmakers
and other manufacturers in Western Europe, it is estimated that about $1 billion
worth of harnesses was manufactured in the region in 2002.
