Abstract: A first cooling water circuit is configured such that the cooling water that has come out from the engine passes through the first intake-air cooling device and returns to the engine again. A second cooling water circuit is configured such that the cooling water that has come out from the engine passes through the second intake-air cooling device and returns to the engine again. A heat exchanger is configured to perform heat exchange between the cooling water that has come out from the engine and flowing to the first intake-air cooling device and the cooling water that has come out from the second intake-air cooling device and that is flowing to the engine.

Abstract: An EGR gas cooling system of the present invention includes a main cooling water circuit which circulates cooling water between an engine, a main radiator that radiates heat of the cooling water of the engine and a primary EGR cooler that cools EGR gas by the cooling water and a low temperature cooling water circuit which circulates the cooling water between the engine, a sub-radiator provided integrally with or separately from the main radiator to radiate heat in the cooling water and a secondary EGR cooler that cools the EGR gas by the cooling water. A flow rate controller which controls a flow rate of the cooling water is provided between the engine and the sub-radiator of the low temperature cooling water circuit.