News Release

Furukawa Automotive Systems Inc. (Headquarters: Inukami-gun, Shiga Prefecture; President: Shigenobu Abe), a member of the Furukawa Electric Group, has delivered modules for use in the fuel cell (FC) systems of new Toyota MIRAI model vehicles. Based on technologies developed by Furukawa Automotive Systems in the auto power distribution components business, these high-voltage power distribution component modules^{(note 1)} are highly efficient and compact.

Global warming caused by increased emission of carbon dioxide and other greenhouse gases has caused various climatic anomalies and has become a major ecological issue throughout the world. In response, the Japanese government announced its intention to become carbon neutral by 2050 and has formulated its “Green Growth Strategy Through Achieving Carbon Neutrality.” Among other objectives, the strategy calls on the automotive industry to ensure that all new vehicles sold are electric vehicles by the mid 2030s. This is forecast to accelerate the adoption and use of electric vehicles and hydrogen fuel cell vehicles. Hydrogen fuel cell vehicles in particular have attracted attention as the ultimate ecologically friendly car, as these vehicles use hydrogen as fuel and are capable of completely eliminating the emission of harmful gas.

The high-voltage power distribution component modules that were recently delivered connect components electrically in the FC stack^{(note 2)} and boost converter, allowing for high-voltage and high-current power to be distributed. An FC stack is a type of power generator used in fuel cell vehicles. The power it generates is boosted up to a maximum of 650 V by an FC boost converter and then distributed to devices such as the PCU.

Although FC system components are connected together electrically in multiple locations, they are generally bolted or welded together and use bus bars^{(note 3)} as the transmission media. Components installed in the system must be connected together in multiple locations, and a high degree of positional accuracy is required when assembling these components to each bus bar. There is also only limited space for bus bar routing^{(note 4)}. Routing must therefore be efficient while also ensuring sufficient insulation from other components. In order to ensure workability during the assembly process, it is also important that products remain free-standing after they are temporarily retained in place and that the bus bar position does not shift. Furukawa Automotive Systems has leveraged the operations management engineering technologies it has developed over many years to optimize its manufacturing management and inspection processes during the stamping, insert molding^{(note 5)}, and assembly processes, resulting in superior positioning accuracy.
In order to meet this requirement, this product makes use of the bus bar module method in which bus bars are insert molded. Standard copper is used for the conductors, and the product was designed with recyclability in mind. Engineering plastic was chosen as the resin material in order to withstand high-temperature environments, due to its high heat resistance and low thermal stress near the linear coefficient of expansion for copper. Materials were carefully selected and the structural design was optimized, resulting in a highly efficient routing structure and excellent workability during assembly.

Although the FC system of the new model has a higher maximum output and loaded current compared with the previous model, the module structure allows bus bars to be routed at minimum pitch, resulting in an approximately 23% reduction in overall size—even considering the increase in size due to the higher loaded current. This has helped result in an FC system with an output density (output per unit capacity) that is among the best in the world.
When using insert molding, differences in the linear coefficient of expansion for each component can cause issues with thermal stress due to the heat generated from nearby components and the increase in internal temperature during current loading. In order to prevent resin from cracking due to thermal stress, a thermal stress analysis simulator was used to predict internal stress prior to setting the optimal bus bar layout and resin thickness at each location. A resin flow analysis was also conducted in order to take resin orientation and welding areas into consideration during molding, in an attempt to reduce thermal stress.

The Furukawa Electric Group will continue to develop products in order to help promote the adoption and use of electric vehicles and contribute toward achieving carbon neutrality by 2050.