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Water pump

The conventional water pump of the above type has a pump impeller fixed to the end of a rotation shaft rotated by the engine, said pump impeller being constructed of a boss fix to the rotation shaft, a flange extending outward in a radial direction, and a vane formed on the flange. Consequently, such conventional water pump operates always with full capacity regardless of whether the engine is warmed up or cooled, and as the result, the power-loss of water pump becomes high and the operation efficiency becomes low.

A water pump for solving the above problem is disclosed in the Japanese Laid-open Utility Model Bulletin Jitsu-kai-sho No. 59-97295 (97295/1984). This water pump employs a structure such as shown in FIG. 11. In the figure, a rotation shaft 61 rotated by an engine (not illustrated) has pump impeller 62 fixed thereto and wax type thermostat 64 installed on the end of the rotation shaft 61. Also disk 65 is fixed to thrust shaft 64' which is axially movable by said thermostat 64. Compression spring 66 is installed between the base of the pump impeller 62 and the base of the disk 65. The pump impeller 62 is constructed of cylindrical boss section 62a, a flange section 62b which extends outwardly in the radial direction from said boss section 62a, a vane section 62c formed on said flange section 62b. The disk 65 has a cuplike recession formed at the center and has nearly the same cross sectional shape and radius as those of flange section 62b of the pump impeller 62. There are formed notches, to which vane section 62c of pump impeller 62 is fitted, in the circular portion of the disk 65 corresponding to the number of vanes.

When the temperature of the engine cooling water is relatively high, the thermostat 64 detects the temperature and moves the disk 65 fixed to the thrust shaft 64' leftward in the figure against spring 66. Consequently, the working area of vane section 62c of pump impeller 62 (area of the portion of the vane protruding from the notch of disk 65) increases and the working range of pump impeller 62 widens, resulting in increased flow rate of the pump. Conversely, when the temperature of the engine cooling water is relatively low, disk 65 moves rightward, the working area of the vane becomes smaller, and working range of pump impeller 62 narrows, resulting in decreased flow rate of the pump.

By the above-mentioned construction and operation, the water pump proposed in the Jitsu-kai-sho No. 59-97295 can make it possible to reduce the power-loss, increase the operation efficiency and reduce the fuel expense, as compared with the conventional water pump in which the pump impeller is only fixed to the rotation shaft, because it controls the water flow rate from the pump so as to make it correspond to the temperature variation by detecting the temperature of engine-cooling water. Still, this water pump has a problem to be solved, too. Namely, when it is necessary to lower the water flow rate of the water pump, the capability of pump impeller 62 should be reduced by moving the disk 65 rightward to narrow the working area of the vane. But, in the above situation, the cooling water flows in the direction to the flange 62b of pump impeller 62 through a gap between the cut portion of disk 65 and the pump impeller 62 and is disturbed in between the pump impeller 62 and the disk 65. Consequently, the water flow rate of the pump and the power loss are not reduced to such extent as expected.