Trimming wiring harnesses becomes design focus
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FlexRay and Ethernet are being considered by Delphi as the need for bandwidth and determinism grows.

Trimming wiring harnesses becomes design focus

Wires and cables help design teams add electronic features and functions, but networks and wiring harnesses add a fair amount of weight while their connections can be the cause of failures. That’s prompting developers to examine ways to reduce the size and weight of wires and cables.

TechNavio market researchers expect global automotive wiring harness market revenue to see an average of about 7% compound annual growth through the almost completed 2011-2015 time frame. Design teams struggling to meet fuel efficiency and cost requirements want to rein in expansion in wiring, which continues to grow as more electronic modules are added.

“OEMs are trying to drive down cost and weight by reducing the size of the wiring harness and the number of electrical connections,” said Anil Sondur, Vice President of Tata Elxsi. “As the value and volume of electronics goes up, there’s a huge drive to consolidate devices and bus systems.”

However, it’s challenging to reduce wiring. For example, engine and transmission controllers must communicate with each other as powertrain designers strive to keep engines running in their sweet spot. That sometimes requires specialized wiring.

“When separate, data sharing between the engine and transmission is essential; a dedicated serial data bus is becoming a requirement when handling the critical communications that must occur,” said Donna Haiderer, Global Chief Engineer for Engine Controls at General Motors.

Next-generation powertrains and advanced safety systems will probably use a range of buses and networks to handle the many pieces of data collected from sensors and related systems. That means that centralized controllers will have to handle a range of communication protocols.

“It is expected that there will be a growth in gateway modules that can translate data into a variety of formats and mediums while protecting the integrity and priority of the data,” said Brian Daugherty, Visteon’s Associate Director of Advanced Development and Intellectual Property.

While network selection is a major factor in wiring, it’s far from the only consideration. Design teams are turning to secondary 48-V battery systems as vehicles employ electric motors for steering and braking while also using more high-power electronic features and functions such as stop-start. Cabling could be a factor in this trend since connections to these higher-powered architectures can be made with lighter wiring harnesses.

“Cable sizes are dramatically smaller with 48-V systems,” said Pat Hunter, Automotive Systems Marketing at Texas Instruments.

Wireless communications are also getting some attention for applications that aren’t mission critical. It’s being considered for simple systems, marking a change from years past when wireless was generally viewed with disdain.

“Wireless sensors are being looked at in areas that aren’t safety related like door locks and mirror adjustments,” Hunter said. “They also fit well in high vibration areas because cables can disconnect. Wireless lets you get rid of connectors and reduce the size and weight of the wiring harness.”

Many of the biggest cabling changes will occur in networks, where product developers are trying to stem the growth in the number of CAN (controller area network) buses used in vehicles. Some vendors are moving to Ethernet and FlexRay. Others are focused on CAN FD, a new version that provides an enhanced data link layer protocol that allows data frames up to 64 bytes compared instead of the current maximum of 8 bytes.

“CAN-FD is the next step evolution of conventional CAN where NXP expects to quadruple the data exchange rate up to 2 Mbit/s,” said Klaus Reinmuth, Senior Director Segment Marketing Automotive & Transportation at NXP Semiconductors. “In addition, there is a significant improvement in message length with a 64-byte frame, which will benefit especially the streaming of data like software updates and downloads. Extended sensor data (vectors with a time relation) coming from gasoline direct injection and hybrid-electric vehicle requirements will find a perfect landing place in these longer frames.”

While CAN will maintain a role in many areas, many suppliers envision a central backbone that sends data to and from the many systems and sensors that share data. That technique is expected to see more use as vehicles offer more autonomy, which requires many systems to work together to avoid accidents.

“People are talking about using Ethernet or FlexRay as a backbone that is used with a domain controller,” Sondur said. “Domain controllers centralize things into one main controller and a number of smaller controllers.”

Some suppliers feel a singular architecture may serve better than a multiplicity of networks. Ethernet Audio Video Bridging (AVB) will work well for cameras, radar, and other sensors. It may also be used to connect controllers.

“FlexRay may play a role, but most sensors seem to be converting to Ethernet AVB,” said Andy Gryc, Senior Automotive Product Marketing Manager for QNX Software Systems. “CAN has served admirably, but I kind of hope it will fade away.”

In powertrains and many system functions, determinism is at least as important as raw performance. Determinism can help ensure that data arrives on time and that engineers can meet functional safety requirements set by standards like ISO 26262.

“FlexRay and Ethernet have significant increased bandwidth over current networks and bandwidth is expected to increase over time,” said Jeff Owens, Delphi’s Chief Technology Officer. “The elements for deterministic data or time stamping can be included. As an example, see the development of Ethernet AVB standards. As functional safety, ISO 26262, continues to be deployed, combinations of traditional networks and these newer high speeds will be implemented to provide the necessary safety and redundancy.”

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