Pump with shaftless impeller

#The present invention relates to a pump including an impeller having a magnet or a second conductor therein, which is adapted to be directly rotated by virtue of magnetic fields of stator coils, and more particularly to a pump including an impeller which is rotated within a casing in close proximity thereto via ceramic bearing members, one bearing member having spiral grooves on its slide surface.

#In a conventional pump, an impeller having a magnet or a secondary conductor therein is directly driven by stator coils, as disclosed in the Japanese Patent Laid-Open Specification No. 49-129106.

#FIG. 1 is a longitudinal cross sectional view of such a conventional pump. In the drawing, an impeller 13 arranged within a pump casing 6 is provided with an annular permanent magnet 16 in its outer rear end perpendicular to a rotary axle 12 of the impeller 13, and the surface of the annular permanent magnet 16 is coated with a synthetic resin (not shown) for preventing it from contacting with liquid in the casing 6. The rear end of the casing 6 is closed by a rear plate 20 on which stator coils 23 and a rear bearing 24 for supporting the impeller 13 are mounted. A- front bearing 25 for supporting the impeller 13 is mounted to the casing 6. The stator coils 23 are covered by a plastic film 27 for preventing them from contacting with the liquid.

#FIG. 1 is a longitudinal cross sectional view of a conventional pump;

#FIG. 2 is a longitudinal cross sectional view of another conventional pump;

#FIG. 3 is a longitudinal cross sectional view of one embodiment of a pump according to the present invention;

#Referring now to the drawings, wherein like reference numerals designate similar or corresponding components throughout the different figures, there is shown in FIG. 3 one embodiment of a pump according to the present invention.

#In the drawing, an impeller 113 is arranged in a pump casing 106, and an annular permanent magnet 128 is embedded in an outer rear end portion of the impeller 113 perpendicular skew to a rotary axis thereof. An annular ceramic protecting thin plate 126 is adhered to the outer surface of the magnet 128 for protecting the magnet 128. In the annular permanent magnet 128, different magnetic polarities are alternately spaced at equal distances in its peripheral direction. Reference numerals 129 and 130 denote blades of the impeller 113 and flow paths, respectively.

#The impeller 113 is provided with a ceramic flat disk plate 131 in its central rear end constituting a bearing portion, and the disk plate 131 made of a silicon carbide sintered body by an atmospheric sintering process, defines a rotary slide surface. The rotary slide surface of the ceramic disk plate 131 is finished smooth, for instance, Rmax.ltoreq.3 .mu.m or so by a lapping process, and then spiral grooves 138 having a depth of about 3-50 .mu.m are formed therein by a shot-blasting process.