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A dual-loop waste heat recovery system with Rankine steam cycles for improving the fuel efficiency of gasoline automobiles has been investigated. A high-temperature (HT) loop recovers waste heat only from the exhaust gas. A low-temperature (LT) loop recovers heat dissipation from the HT loop, and waste heat from the engine coolant. The two separate loops are coupled with a heat exchanger. This paper has dealt with the layout of the dual loop system, a review of working fluids, and the design of the cycle. The design points and the target heat recoveries of the HT boiler and LT boiler, which are core parts of their loops respectively, have been presented. The prototype of the HT boiler was evaluated by an experiment. For the performance evaluation of the HT boiler, the inlet temperature condition of the HT boiler working fluid was set to a degree of subcool of 5°C. The exit condition was the degree of superheat, which was set at 5°C.

Recently, as part of the effort to enhance fuel efficiency and reduce costs for eco-friendly vehicles, the R-gearless system has been implemented in the TMED (P)HEV system. Due to the removal of the reverse gear, a distinct backward driving method needs to be developed, allowing the Electronic Motor (e-Motor) system to facilitate backward movement in the TMED (P)HEV system. However, the capability of backward driving with the e-Motor is limited because of partial failure in the high-voltage system of an R-gearless system. Thus, we demonstrate that it is possible to improve backward driving problems by applying a new fail-safe strategy. In the event of a high-voltage battery system failure, backward driving can be achieved using the e-Motor with constant voltage control by the Hybrid Starter Generator (HSG), as proposed in this study.