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Compared to conventional hybrid electric vehicles, plug-in hybrid vehicles have a larger-capacity battery and an onboard charger. These devices are mounted in functionally optimal locations, so it is a challenge to provide a thermal management system that achieves a good balance between high cooling performance and low cost. The battery should be operated at required temperature to secure safety and durability at high temperatures, and to mitigate the decrease in output power and capacity. However, setting separate cooling systems suited for each device leads to both an increased cost and weight. Therefore, an integrated water cooling system was devised for the battery, charger, and DC-DC converter, and the cooling performance was verified through simulations and tests. A valve installed before the battery in the cooling circuit allows it to be bypassed when coolant temperature rises due the charger or low-speed engine operation, helping to preserve battery life.

Research was conducted on a method for the simulation of the diffusion of pressurized hydrogen leaking at high speed from a small opening into the complexly shaped space of a fuel cell electric vehicle with a practicable calculation time. The fact that the scale of the calculations was large and the calculation time was therefore extended represented issues in relation to this simulation method. The reduction of calculation time through the use of a three part partitioning method was proposed in order to resolve this issue. In this method, the calculation region is divided into three: In the first part, steady-state compressible flow calculations are conducted for the region close to the hydrogen outlet where the Mach number is higher than 0.5.