PURPOSE: To prolong the service life of a heat exchanger to a great extent, by switching the high-temperature side of the heat exchanger to the low-temperature side through operation of a plurality of valves when performance of the heat exchanger at its low-temperature side is lowered, and thereby restoring the initial performance of the heat exchanger.
CONSTITUTION: A first and a second exhaust gas passages 7, 8 are provided for communicating a first and a second high-temperature exhaust gas passages 5a, 5d with each other, and a first and a second valves 9, 10 are connected respectively in the passages 5a, 5b between the positions thereof where the passages 7, 8 are connected to the passages 5a, 5b, respectively. Further, a third and a fourth valves 11, 12 are connected respectively in the passages 7, 8. Similarly, a first and a second air passages 13, 14 are provided for communicating a first and a second low-temperature air passages 6a, 6b with each other, and a fifth and a sixth valves 15, 16 are connected respectively in the passages 6a, 6b between the positions thereof where the passages 13, 14 are connected to the passages 6a, 6b. Further, a seventh and an eighth valves 17, 18 are connected to the passages 13, 14, respectively.
KUROHORI HIDESABUROU
YAMAUCHI MASAO
