Challenges in Automotive Wire Harness Assembly

Automotive manufacturing witnesses the highest deployment of robotic automation. Welding, assembly, machine tending, material removal, part transfer etc. are the assembly operations best suited to robotic automation. However, when it comes to tasks that need judgement and decision making, there is still scope for improvement in the performance of robots. Wire harness is the nervous system of automobiles, consisting of wire and connector assemblies of multiple sizes and shapes. The harness carries various control and power signals between the main control unit, battery and various parts of the automobile. Assembling such cables with connectors requires high levels of skill and is most time -consuming. It involves pairing the cables with appropriate connectors and fixing the complex wiring structure inside the automobile. The task of installing wire harnesses in car bodies has traditionally been difficult for robots. Therefore, multiple approaches such as simplifying the harness architecture and improving the robot’s capabilities are being adopted to solve the complex problems associated with wire harness.

Simplification of the harness architecture

A recent patent publication (US20190217794) on modular wiring harness attracted global attention. The patent application from Tesla claims ease of assembling the wiring harness during vehicle manufacture. The patent also discloses reduction in the total length of wires.

The patent application identifies problems in wire harness and provides solutions as listed below:

Tesla’s innovative wiring architecture presented in the patent application is reproduced below.

Top view of an automobile with its wiring system connecting multiple devices to a backbone structure

Some interesting technologies identified by SciTech Patent Art include:

• Flexible Printed Circuit Boards
• In-Vehicle Network
• Optimization of circuit body, and
• Single line for power and data transmission

Flexible Printed Circuit Boards

Flexible printed circuit (FPC) boards are mostly used in high power applications, but could be considered as an alternative to wire harnesses. A single FPC may include bus bars, power distribution cables, back panels, etc.

Benefits of FPC:

• Decreased assembly time
• Reduction in materials and number of parts
• Increased reliability – reduction of assembly errors
• Decreased space, increased air flow
• Improved thermal characteristics
• Increase in interconnect options

Trackwise, a UK-based manufacturer specializing in products related to printed circuit technology, has employed its technology for temperature and voltage monitoring circuits in EV battery packs. Use of Flexible Printed Circuit Boards can contribute to approximately 75% weight reduction as compared to conventional wiring harnesses.

Trackwise has developed the Improved Harness Technology (IHT) which facilitates manufacturing of flexible printed circuits of any length. Recently, the company manufactured the world’s first and longest FPC of 26 meters which supports control and transmission of power and communication signals without the need for an additional wire harness. Currently, this technology is being employed in space vehicles due to its lightweight benefits, and may be adopted in automotive to attain equivalent benefits.

In-Vehicle Networks

While it is not easy to totally eliminate wiring harness in automobile and aerospace technology, with the advancements in wireless technology, it is possible to wirelessly transmit control signals within an automobile.

Yazaki Corporation, whose core product is automotive wire harness assembly, is working on wirelessly transmitting control signals from the vehicle’s electronic control unit (ECU) to the electronic devices in the extension system. The company was recently awarded a patent (US10122125B2) in which it claimed a vehicle wire harness structure designed to interconnect multiple main devices with communication lines and signal lines. Each system consists of a main device ECU and an auxiliary device wire-connected to the main power line, wherein both the devices communicate wirelessly, thereby reducing additional wiring for communication signals.

In the accompanying figure, each of the electronic devices in the extension system consists of a wireless communication interface. The ECU ensures a wireless communication channel with each of the electronic devices in the extension system enabling bidirectional data communication for the purpose of control.

Optimization Of Circuit Body

Sinble Line For Power And Date Transmission

Power-Over-Data-Line (PoDL)

Automobiles have multiple wirings for transmitting data and power separately. The additional cables make the harness heavier and more complex, making it difficult to feed parts of the harness through narrow passageways within vehicles. The technology of Power-over-Data-Line (PoDL) uses the 100Base-T1 and 1000Base-T1 interfaces to supply power parallel to signal on a single unshielded twisted pair.

TE Connectivity, a Switzerland-based designer and manufacturer of connectivity and sensor products is testing PoDL in combination with MATEnet (modular and scalable connectors), and will validate this option within the MATEnet interconnection system. The results so far have been very positive, indicating a beneficial use with up to 48 VDC.

Data over Power Lines

In contrast to the above concept, there is enough evidence of data transmission over power lines. “Broadband over Power Lines (BPL)”, a power line communication technology (PLC) in which relatively high speed digital data is transmitted over public electric power distributing wires is already known. There are challenges in implementing the architecture for long-distance transmissions. However, for short distance communications, this technology may be used for reducing complex cabling structures.

YamarElectronics, an Israel-based SME, specializes in technology for communication over noisy DC power lines. It is targeted towards reduction of wires, thereby resulting in reduced cost and weight. Yamar introduced “Automotive Power Line Communication” using the DC- BUS technology, merging data over the power lines using existing CAN and LIN protocols, thus eliminating extra harness. This proposed solution may reduce the length of total harness from 2km to 200 meters.

Yamar’s patent application US20180302187A1 claims a transceiver as well as a method for asynchronous data transfer through noise channels (AC/DC lines). This solution can be employed in vehicles and commercial trucks to reduce additional wiring requirements.