Miracle Wires

Data-intensive automated vehicles will benefit from new technology that delivers Gigabit data and power through the same wires.

Automated and connected vehicles require ultra-fast data-transfer capability — both onboard and when connecting to the cloud. Sharing wiring previously dedicated only to power will help reduce weight and complexity.

With data-transmission rates ranging from 10Mbps to 10Gbps being standardized or already in place, Ethernet technology has a promising future for automotive applications. To reduce the level of cabling, a technology known as Power over Data Line (PoDL) has been developed that enables the data and power to share the same pair of wires.

We believe this technology will see expanded consideration by automated vehicle engineering teams as they seek efficiencies in their cabling - architecture strategies. This is likely given the immense volume of data shared between a phalanx of onboard processors—as well as between the vehicle and the “cloud.”

It’s also likely that this dual-function “hybrid” cabling—one single unshielded twisted pair (UTP) carrying data and power — will be attractive to manage the sum total of cabling links necessary in future automated vehicles.

Examples for calculating creepage and clearance distances.

Finally, the potential for much stronger encryption of vehicle network data will be hard for engineers to ignore, as onboard algorithms increasingly are responsible for driver, passenger and pedestrian safety decisions.

TE Connectivity’s Automotive group is studying the connector requirements needed to insure safe power transmission for these PoDL voltages and is developing a design that meets these requirements.

Documents such as IEC60664-1 have been used as a reference to calculate the required creepage and clearance distances for electrical connectors. In the automotive sector, many OEM requirements for high-voltage connectors are based on this document. These connectors are usually designed for high voltage and current applications where larger wire and higher pitch connectors are required. In these instances, the required creepage and clearance distances can usually be met without much difficulty.

PoDL changes the game

Recommended design changes (left) and PoDL compliant plastic housing (right).

However, with PoDL technology, data and power now are being transmitted over considerably smaller-gauge wire. Smaller pitch connectors are advantageous for the signal integrity of the high-speed data, but this begins to pose design issues for meeting the required creepage and clearance distances. This is especially true in the automotive environment, where higher pollution degree ratings need to be met.

Clearance and creepage paths.

The requirements are highly dependent on the selected insulating material for use between conductors, as well as environmental conditions such as pollution degree and altitude. Clearance — the shortest measured distance in air between two conductive surfaces — of a connector should be dimensioned to withstand the expected steady-state voltages, temporary overvoltages or recurring peak voltages of the system to prevent possible arcing.

Consideration of these factors led to TE Connectivity’s MATEnet connection system: a modular and scalable connector designed specifically for automotive Ethernet. It is based on the miniaturized NanoMQS standard automotive terminal and is designed to withstand the harsh automotive environment. While these connectors were designed to meet the signal integrity requirements of the data path, they were not designed for PoDL requirements.

When measuring the clearance and creepage distances on the MATEnet connector system, the PTC CREO Spark Analysis Extension (SAX) tool allowed for rapid calculations using an accurate 3D representation of the electromechanical system and a spreadsheet specifying a parameter known as “groove width,” as well as the clearance and creepage target requirements. The tool output is an array of values and visual representations that allows the user to clearly identify the areas of concern and quickly proceed to the optimization phase of the process.

The groove width (x) is defined as the largest gap that the creepage can jump across. This value is dependent on pollution degree and it is only used to measure creepage; for clearance distances less than 3mm, the minimum dimension is reduced to one-third of this clearance. If the thickness of a gap, groove or protrusion between the terminals is greater than x, the creepage is measured along the contours of the groove. However, if the thickness of a gap, groove or protrusion is smaller than or equal to x, it is understood that the voltage “jumps” or shorts from one wall to another.

For the MATEnet connector, the nominal terminal pitch is 1.8mm. Provided there is no insulation between the terminals, once the thickness of the terminals is considered, the maximum clearance of the system at a nominal pitch is 1.2 for the male terminals and 0.8 for the female terminals. It was discovered that while the PCB header side (male) met the clearance requirements for pollution degree 3, the plug side (female) did not and thus had to be optimized to meet the clearance requirements.

The creepage of the system, like the clearance, was measured using the CREO SAX tool. Unlike clearance, creepage calculations required the input of the groove width x value. Since in this case the overall clearance cannot be greater than the pitch, the groove width is taken as one-third of the required clearance for each pollution degree and the analysis is performed using x values equal to 0.086mm for pollution degree 2 and 0.344mm for pollution degree 3.

While the MATEnet system met the clearance and creepage requirements for pollution degree 2, some modifications were required for the system to meet pollution degree 3 requirements at the different voltage levels. Since the output of the tool includes both values and a visual representation of both the clearance and creepage paths in the form of a red line across the zone of interest, the critical zones were easily identified.

Eric DiBiaso is an R&D staff engineer in TE Connectivity’s Automotive group. He holds an Electrical Engineering undergraduate degree from Penn State University and an Electrical and Computer Engineering master’s degree from the Georgia Institute of Technology.
Guadalupe Chalas is a product development engineer in TE Connectivity’s Automotive group. A mechanical engineer, she is a 2014 graduate of Penn State University. Both work in TE’s Middletown, PA, offices.

An additional step was performed to confirm the terminal’s tolerance of the true position (TP) was considered. With a 0.1mm tolerance requirement, the three cases analyzed involved a nominal pitch of 1.8mm, a lower value of 1.7mm and an upper value of 1.9mm. This was done to confirm the part would meet clearance and creepage requirements regardless of TP variation given by the tolerance zone.

Optimizing the design

Once the zones were identified, the optimization process began. Lengths and thicknesses were changed to increase the clearance and creepage paths until the part met the requirements for pollution degree at the nominal pitch as well as the upper and lower values of the tolerance spectrum. The optimization was done in small increments to avoid adding too much material to the plastic housing.

When this optimization was completed, recommendations for design changes were sent to the design team, which utilized these recommendations and made the necessary changes to the plastic parts, while considering the manufacturing processes already in place as well as moldability of the housings.

The result was validated creepage and clearance requirements for automotive Ethernet PoDL-compatible connectors that will help enable a new level of automotive wiring and data-transmission flexibility. The new PoDL technology should improve the efficiency and capability of the wiring architectures for autonomous vehicles.

The authors thank the following colleagues for their assistance with this article: Zachary Lyon for his support with the CREO SAX tool, Robert Wuerker for the MATEnet connector implementation support and Marjorie Myers for reviewing the paper.