Patent ID: 7497669

Claim:
A fuel pump comprising: a pump chamber which is formed of a pump housing and a pump cover covering the pump housing; an impeller which is rotatably arranged within the pump chamber, is rotated by an electric motor within a motor chamber, and is provided with a plurality of blade grooves communicating the top and back sides in an outer periphery thereof; and a discharge hole which has a fuel flow passage provided in a depressed shape in a peripheral direction along the blade grooves of the impeller on a lower surface facing the pump chamber of the pump housing, and is formed in a terminal end portion in a rotational direction of the impeller so as to communicate the pump chamber with the motor chamber, wherein an opening area of said discharge hole is made smaller toward a front side in a rotational direction of the impeller, said discharge hole is open to a lower surface of the pump housing via a step portion facing the pump chamber, the step portion surrounds said discharge hole and has an outer boundary or perimeter formed in a shape geometrically similar to the shape of the discharge hole so that the step portion has a substantially uniform width all around said discharge hole, and the flow of air from the pump chamber to the motor chamber is inhibited by formation of a fuel film due to surface tension of fuel at a lower end of the discharge hole, at a time when the fuel pump is stopped.