An electric oil pump system is provided to allow the cooling of an electric oil pump (EOP) and an oil pump controller (OPU) to be performed efficiently in the vehicle equipped with the electric oil pump. The system includes an electric oil pump in which a pumping part is operated by power of a motor to suction and direct pressurized oil. and an oil pump controller operates the electric oil pump. A water-cooled cooling apparatus cools the oil pump controller using coolant and an oil-cooled cooling apparatus cools the electric oil pump using oil. The coolant of the water-cooled cooling apparatus and the oil of the oil-cooled cooling apparatus pass through a heat exchanger and as the coolant and oil pass therethrough, heat exchange is achieved.

In a water-cooled inner combustion engine (1), in particular for equipping scooters and motorcycles, the arrangement of the outer cooling tubes connected to a radiator is simplified by arranging a by-pass valve (27), arranged directly on the engine block (2) at a discharge opening (18) obtained therein, which, when the cooling water is lower than a reference temperature, prevents the water circulation in the radiator (18) and it addresses it through a by-pass line (26) by implementing a cooling circuit wholly included in the engine block (2).

In a water-cooled inner combustion engine (1), in particular for equipping scooters and motorcycles, the arrangement of the outer cooling tubes connected to a radiator is simplified by arranging a by-pass valve (27), arranged directly on the engine block (2) at a discharge opening (18) obtained therein, which, when the cooling water is lower than a reference temperature, prevents the water circulation in the radiator (18) and it addresses it through a by-pass line (26) by implementing a cooling circuit wholly included in the engine block (2).

In a water-cooled inner combustion engine (1), in particular for equipping scooters and motorcycles, the arrangement of the outer cooling tubes connected to a radiator is simplified by arranging a by-pass valve (27), arranged directly on the engine block (2) at a discharge opening (18) obtained therein, which, when the cooling water is lower than a reference temperature, prevents the water circulation in the radiator (18) and it addresses it through a by-pass line (26) by implementing a cooling circuit wholly included in the engine block (2).

In a water-cooled inner combustion engine (1), in particular for equipping scooters and motorcycles, the arrangement of the outer cooling tubes connected to a radiator is simplified by arranging a by-pass valve (27), arranged directly on the engine block (2) at a discharge opening (18) obtained therein, which, when the cooling water is lower than a reference temperature, prevents the water circulation in the radiator (18) and it addresses it through a by-pass line (26) by implementing a cooling circuit wholly included in the engine block (2).

A cooling water passage structure includes a cooling water passage in an internal combustion engine, a water pump, and a communication member. The communication member has a cooling water communication passage to supply cooling water from the water pump to the cooling water passage. The cooling water communication passage includes a water pump housing, a first cooling water passage, and a second cooling water passage. The water pump housing contains the water pump. The first cooling water passage has a substantially triangular shape that widens from a vertex on an upstream side. The second cooling water passage includes a cylindrical passage extending in a direction orthogonal to an operating axis of the water pump. The second cooling water passage is displaced from an operating plane of the water pump.