The present application is based on and claims priority from Japanese Patent Application 2001-312453, filed Oct. 10, 2001, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an impeller type fuel pump for pumping fuel up from a fuel tank.
2. Description of the Related Art
A fuel pump that has an impeller is well known, as disclosed in U.S. Pat. Nos. 5,765,992 and 5,011,369.
U.S. Pat. No. 5,765,992 discloses a pump having an impeller in which fuel flows along an arc-shaped passage and is discharged from a fuel discharge port that is located radially outward from the arc-shaped passage. Because an end of the arc-shaped passage is formed near the discharge port, the fuel collides with a wall of the housing when the fuel flows toward the discharge port. This collision generates a considerable flow resistance and a noise.
U.S. Pat. No. 5,011,369 discloses another pump having an impeller. This fuel pump has an arc-shaped fuel passage whose cross section increases as it nears the end of the arc-shaped fuel passage. Therefore, flow speed of the fuel decreases and flow energy decreases as the fuel nears the discharge port. This decreases the pump efficiency.
Therefore, the present invention has been made in view of the above problems.
According to a feature of the invention, a pump passage includes an arc-shaped fuel passage connected to a suction port and a terminal fuel passage connected to a discharge port. The discharge port is located outside the pump passage in the radial direction. The terminal fuel passage extends so that a portion thereof is located radially more outside as the portion moves in the rotation direction. The sectional area of the terminal fuel passage except spaces occupied by the impeller is approximately constant between the arc-shaped passage and the fuel discharge port. Therefore, the fuel flowing into the base of the blade ditches immediately flows out from the outer edge of the blade ditches so that formation of circulating flow can be suppressed. Therefore, the fuel flow is converged into a flow flowing along the circumference of the impeller. Because fuel flows from the arc-shaped fuel passage to the terminal fuel passage smoothly, flow energy loss can be suppressed so that pump efficiency can be improved.
According to another feature of the invention, the terminal fuel passage has a radially outside surface inclining so that a space between the outside surface and the outer circumference of the impeller increases as the outside surface nears the discharge port.
According to another feature of the invention, an angle formed between the outside surface and a tangential line of the outer circumference of the impeller is approximately the same as an angle between fuel flow discharged from the blade ditches and the tangential line. Therefore, the fuel flowing out of the blade ditches of the impeller does not change the flow direction thereof and flows in the terminal fuel passage along the outer passage surface without pealing off, so that flow energy loss can be minimized.