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This paper focuses on the design and test technique of an auxiliary power unit (APU) for a range-extended electric vehicle (RE-EV). The APU system is designed to improve RE-EV power and economy; it integrates the power system, generator system, battery system, and APU controller. The parameters of the APU parts are computed and optimized considering the vehicle power demand and the matching characteristic of the engine and generator. The hardware and software systems are developed for the APU-integrated control system. The APU test bench, combined with the displaying part, the control part, and the bench with its accessory, is constructed. Communication connection in the APU system is established by controller area network (CAN) bus. The APU controller outputs a corresponding signal to the engine control unit (ECU) and motor controller. To verify the rationality of the control strategy and the validity of the control logic, the engine speed control and integrated control experiment of the APU system are completed on the test bench. The test results showed that the test control system is reliable and the relevant control logic is in agreement with simulation analysis. The APU-integrated system could be well suited for application in RE-EVs.

In this study, the ductile iron ingots are cast using a metal mold, and the riser neck diameter is changed to control the micro-shrinkage porosity, which can affect the ultra-low temperature toughness of ferritic ductile iron. The metallographic structure and micro-shrinkage porosity were observed by an Axiovert200 MAT measurer metallographic microscope and an MLA 250 (FEI quanta) scanning electron microscope, and the number and diameter of graphite nodules and micro-shrinkage porosity size were measured by Nano Measurer 1.2 software. The effect of micro-shrinkage porosity on the ultra-low temperature toughness of ferritic ductile iron was studied. It is found that the impact energy of ductile iron decreases with the increase of micro-shrinkage porosity size, and the influence of micro-shrinkage porosity is more obvious with the decrease of temperature. The results point out that the micro-shrinkage porosity becomes the key factor affecting the ultra-low temperature impact toughness of ductile iron when the spheroidization rate of ferritic ductile iron is greater than 98% and the number of graphite nodules is more than 810 mm−2. The impact energy of ferritic ductile iron can still reach more than 12 J at −70°C when the length of micro-shrinkage porosity is less than 3.7 μm.

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