Development of Intelligent Power Unit for 2018 Model Year Accord Hybrid

A compact intelligent power unit capable of being installed under the rear seating was developed for the 2018 model year Accord Hybrid that is to be equipped with the SPORT HYBRID Intelligent Multi Mode Drive (i-MMD) system. The space under the rear seat features multiple constraints on dimensions. In the longitudinal direction, it is necessary to attempt to help ensure occupant leg room and to position the fuel tank; in the vertical direction, it is necessary to attempt to help ensure occupants comfort and a minimum ground clearance; and in the lateral direction, it is necessary to avoid the position of the body side frames and the penetrating section of the exhaust pipe. The technologies described below were applied in order to reduce the size of components, making it possible to position the IPU amid these constraint conditions. The number of series-connected cells in each lithium-ion battery module was increased from 18 to 36, making it possible to reduce the number of modules from four to two, reducing the size of the battery pack against the previous model. In the case of the junction board, reduction of the size of the contactor that shuts off the high-voltage circuits made it possible to reduce the thickness of the board and employ a direct connection to the battery modules. In addition, integration of the body components and the components holding the battery in place under the rear seat and optimization of the battery cooling structures in the IPU made it possible to do away with the battery exhaust duct employed in the previous model, contributing to reduced size. In addition, the integration of the 12 V DC-DC converter which had been built into the IPU until the previous model with the power control unit in the engine compartment ultimately made IPU compact enough to install under the rear seat. As a result, the vehicle gained trunk room equal to gasoline-powered automobiles and realized a structure allowing continuous open space from the trunk through to the rear passenger compartment. The increased compactness also achieved a 10% reduction in weight.