As hydraulic hoses are replaced with electric wires, more harnesses will probably be required in vehicles.

Automotive engineers are eager to replace traditional mechanical linkages and hydraulic actuators with by-wire technology, such as brake-by-wire, suspension-by-wire and steer-by-wire. Drive-by-wire technology uses a highly organized network of wires, sensors, controllers and actuators to control “mechanical” functions.

As hydraulic hoses are replaced with electric wires, more wire harnesses will probably be required in vehicles. But, it depends on the application.

“I believe the trend will be toward fewer traditional wiring harnesses,” notes Todd Hubing, Michelin professor of vehicular electronics at the Clemson University International Center for Automotive Research. “This is not directly due to X-by-wire, but due to the improving cost advantage associated with sending data digitally, which will allow more sensors to share wires in a harness.

“Digital data transmission requires more expensive electronics, but it reduces the amount of wiring,” Hubing points out. “As the cost of wire continues to rise and the cost of electronics continues to fall, we’ll see more and more data exchanged digitally.”

“There are competing trends at work here, and the future is highly complex,” adds Ian Riches, director of the global automotive practice at Strategy Analytics Inc. “One certainty is that vehicles will continue to have more and more electronic features. However, at the same time, [automakers] and suppliers are working hard to ensure that E/E architecture complexity is reduced.

“We have already come a long way with the now near-ubiquitous use of CAN multiplexing in vehicles,” says Riches. “More recently, initiatives such as AUTOSAR [AUTomotive Open System ARchitecture] hold out the possibility of decentralizing vehicle software, breaking the paradigm of one function equals one ECU. Although there will be vehicles that buck the trend, it is likely that established markets have reached the high water mark for vehicle wiring.”

Many of today’s vehicles use a serial databus communication protocol, such as CANbus ,which enables multiple signals to be carried on a single pair of wires and reduces the number of wires and harnesses required.

“Harnesses [were] greatly simplified with the introduction of multiplexing in the 1990s,” notes Krishnasami Rajagopalan, global program manager for automotive chassis and safety systems at Frost & Sullivan Inc. “Today’s distributed architecture ensures that most body electrical functions are handled locally. Control Area Network (CAN) architecture is specifically designed to integrate a large number of local area networks seamlessly. Additional electronic functions directly translate into a higher number of modules.”

With distributed control architecture, vehicles typically have a large number of control modules. “But, the wiring required will be lesser as modules increase,” Rajagopalan predicts. [For example], power windows and central locking control modules are present in [many car doors] today. Though the number of modules has increased, the wiring required compared to a single central control module is drastically reduced.

“[Use of] multiplexing means that the signal side is physically decoupled from the load side,” explains Rajagopalan. “The switch is not directly connected to the output. Instead, communication occurs through microprocessors. So, wiring on the switch side can be made thinner with no side effects. Wiring on the output side, though, will still be a consequence of the output load.”