Future-ready Wire Harness
Upcoming regulations on greenhouse gas emissions and safety are driving a technological leap in the automotive industry. Electrical powertrains and their complement of 48-volt architecture, along with all the functions required for different levels of autonomous driving, contain a plethora of innovations aimed towards the stringent new requirements. Further electrification of the powertrain and surrounding systems requires a communication architecture to control the actuation and sensing. Electromagnetic noise is a key issue in any electrical power train, in either full electrical or hybrid architectures , since it affects the operation of the electronic circuits within the car. Countermeasures have to be taken at early stages of the design. Otherwise, projects face unacceptable risks of high engineering costs, wasted resources or project delays.
New 48-volt Electrical Architecture
The new 48-volt electrical architecture in cars pushes the envelope in terms of electromagnetic compatibility and safety requirements. New safety precautions are needed, since even a single malfunction between the 48-volt and the 12-volt electrical system, such as a short circuit, may damage the entire 12-volt system due to overvoltage. 1000BASE-RH, the Ethernet specification for a Gigabit capable, Plastic Optical Fiber-based (POF) communication protocol is optimal for the new architectures, as it provides intrinsic Electromagnetic Compatibility (EMC). Powertrains that are either fully electrical or hybrid profit from the natural galvanic isolation between communicating modules and radiation-free harness. With excellent performance in Electromagnetic Interference (EMI) and in Electromagnetic Susceptibility (EMS), these optical Ethernet links are ideal for communications between the 48-volt and the 12-volt domain. They provide 100 Mbps and 1 Gbps Ethernet compatible solutions today, and multi-gig in the future, with enough margin to withstand the harsh automotive environment. Its native galvanic isolation and mechanical robustness make optical Ethernet technology ideally suited for current and future in-vehicle network infrastructure. Applications such as Battery Management Systems (BMS) and Integrated Smart Antenna (ISA) modules profit from the inherent electromagnetic compatibility of POF.
Smart Antenna Modules
Integrated Smart Antenna (ISA) Modules consist of several antennas for signal reception, an Antenna Hub, and an Ethernet connection to the consumers of the antenna signals such as a radio device. If each of the several antennas in a car is routed to its respective ECU with its own cable, the complexity soon becomes unacceptable. The Antenna Hub routes all signals from each antenna to an Ethernet network connected to all receptors of the signals. Gigabit Ethernet over POF is ideally suited for an Ethernet connection due to its natural EMC-free property and supports the rates required by technologies such as LTE-A. In conventional systems, if the roof is not metallic, or has openings, an immense amount of energy is radiated by the coaxial cable that is coupled back into the ISA. This seriously degrades the ISA performance. Replacing the coaxial cable with POF completely solves this issue.
Battery Management Systems
Propulsion batteries in EV or HEVs are grouped into clusters that need to be controlled. Responsible for this control is the so-called Battery Management System (BMS). The BMS communicates with each battery cluster in order to gather information relevant for control, such as state of charge or cell temperature. The BMS in turn sends control commands to the local ECUs inside each cluster.
Although the amount of data moving back and forth between the clusters and the control module is not very high (typically below 100 Mbps), the communication between the BMS control module and the individual clusters is crucial and needs to be very reliable. These BMS links are critical to avoid battery damage, and must be suitable in emergency situations like crashes or fires.
Optical links between the BMS control module and the battery clusters are the best means to ensure the high reliability needed. Copper-based communications create parasitic loops, which, in the case of emergency events, may translate into dangerous conditions for the driver and occupants. A dielectric medium such as plastic optical fiber reduces to zero the contribution of the data cables to the conducted emissions and conducted immunity. Radiated emissions and radiated immunity can be optimized to pass with ample margin all the OEM specs with high-quality reference designs from the optical PHY vendor.
Noise Propagation in HEV/EV Powertrains
The powertrains of hybrid electrical (HEV) and electrical vehicles (EV) require multiple electronic units placed all around the car. These Electronic Control Units (ECUs) regulate and control the electrical flow of the energy between the batteries, converters, and motors/generators. The energy flow and conversion generate electrical noise which will affect other areas of the car like the infotainment or navigation systems today and the autonomous control systems tomorrow.
Connecting the ECUs optically isolates all noise within the ECU that originates it, avoiding its propagation to all the other ECUs dispersed all over the car. It is very difficult and expensive to try to achieve a similar isolation with a copper-based network. This translates into a longer engineering development cycle and a more expensive and complex ECU, which may then again turn out in lower reliability.
Fault Protection in 48-/12-volt Systems
Mixed 48-/12-volt energy systems will be the mainstream in next generation HEVs and PHEVs (Plug-in HEVs). 48 volts are reserved for “hungry” electrical modules like starters, alternators or battery modules, while 12 volts are dedicated for the more “delicate” electronic modules like Infotainment or ADAS processing units. Both domains share the same ground system, the car chassis. The ECU in the 48-volt domain is designed with electronic components sized for such voltages. These components are typically rated to withstand more than 70 volts. The 12-volt ECUs are designed with electronic components that typically support up to 60 volts. In case of an event like a loss of ground in a 48-volt ECU, and if there are non-galvanic isolated links between the 48-volt and the 12-volt domains, there will be an electrical path between both domains. This will expose the 12-volt ECUs and their components to voltages higher than the ones they were rated to support, causing failures or a reduction of their service life. Since galvanic isolation is native in optical networks, there is no need to include protections to prevent such events or design the 12-volt ECU to withstand potential events at 48 volts or higher.
Optical Automotive Networks
POF cables are the most reliable solution: they can withstand harsh environments, vibrations, misalignments, dirtiness, humidity, wide temperature range, etc. In addition, POF allows fast dynamic bending, tight static bending, and immersion in liquid. Additionally, optical Ethernet generates very low noise and can operate in noisy environments, such as in RF electronic boards. As a plastic fiber with a large diameter, POF is more cost-effective to manufacture and install: installation is just easy plug and play; winding and clamping is similar to copper cables. Moreover, during the car assembly, the optical harness can be installed in the same process as the copper harness. POF has been present in vehicles for more than 10 years and is installed in millions of cars. With the first automotive Gigabit Ethernet POF (GEPOF) transceiver KD1053, Spanish Startup KDPOF provides high connectivity with a flexible digital host interface, low latency, low jitter, and low linking time. The transceiver complies with the standard amendment IEEE Std 802.3bv and thus fully meets the requirements of carmakers.
About the author: Óscar Ciordia is Marketing Director of KDPOF