Murata, T., Nakagawa, T., Nishino, H., and Matsuura, K., "Efficiency Improvement in Exhaust Heat Recirculation System," SAE Technical Paper 2016-01-0184, 2016, doi:10.4271/2016-01-0184.
In order to speed up engine coolant warm-up, the exhaust heat recirculation system collects and reuses the heat from exhaust gases by utilizing the heat exchanger. The conventional system improves actual fuel economy at the scene of the engine restart in winter season only. The heat recirculation system becomes more effective at the low outside temperature because it takes longer time to warm up engine coolant. However, the heat recirculation system becomes less effective at the high outside temperature because it takes shorter time to warm up engine coolant. Therefore, the new exhaust heat recirculation system is developed, which adopted as follows: 1) a fin-type heat exchanger in order to enhance exhaust recirculation efficiency 2) a thinner heat exchanger component and smaller amount of engine coolant capacity in the heat exchanger in order to reduce the heat mass As a result, the actual fuel economy is more improved in winter season. In addition, even at the high outside temperature seasons, the actual fuel economy is improved. Due to the change mentioned above, the weight of the heat exchanger is reduced by 20% compared to the heat exchanger in the conventional system. The new exhaust heat recirculation system has been adopted to the 4th generation PRIUS.