Title of Invention

A FUEL PUMP

Abstract

A fuel pump having an impeller driven by an electric motor is submerged in fuel contained in a fuel tank of an automotive vehicle. When the impeller is rotated, the fuel is sucked into the fuel pump and supplied to an engine through the fuel pump. A rotor of the electric motor is rotatably supported by a pair of bearings disposed at both axial ends of the rotor. Each bearing is composed of a cylindrical body and a protecting film covering the surface of the cylindrical body. The >protecting film is made of a material having an acid- resistant property in order to protect the bearing body from erosion. It is preferable to provide the protecting film with an anti-sulfuratiion property in addition to the acid-resistant property. >

Full Text

FUEL PUMP HAVING BEARING COVERED WITH ACID-RESISTANT FILM BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel pump for pumping up fuel from a fuel tank. 2. Description of Related Art A fuel pump having an impeller driven by an electric motor has been known hitherto. Fuel in a fuel tank is pumped up by the impeller and supplied to an internal combustion engine, for example. When a fuel pump of this type is used for pumping up insufficiently refined fuel that includes a considerable amount of sulfuric components, bearings supporting a rotor shaft of the electric motor are sulfurated and eroded. It is required, therefore, to provide the bearings with an anti-sulfuration property to prevent its erosion. Further, organic acid may be' contained in the fuel. Accordingly, it is also required to provide the bearings with an acid-resistant property. SUMMARY OF THE INVENTION The present invention has been made to provide a durable fuel pump even if it is used for pumping up insufficiently refined fuel containing sulfuric components and/or organic acid. An object of the present invention is to provide a fuel pump that has bearings having an acid-resistant property. Another object of the present invention is to provide a fuel pump that has bearings having both of the acid-resistant and anti-sulfuration properties. The fuel pump includes an electric motor and an impeller driven by the electric motor, both contained in a housing. A rotor of the electric motor is rotatably supported in the housing by a pair of bearings disposed at both axial ends of the rotor. The fuel pump is submerged in « fuel contained in a fuel tank. When the impeller is,rotated by the electric motor, the fuel is sucked into the fuel pump and supplied to an internal combustion engine through a fuel passage formed in the fuel pump. Each of the pair of bearings is composed of a cylindrical bearing body and a protecting film covering the surface of the bearing body. The protecting film is formed by coating a material having an acid-resistant property. Since the protecting film prevents the bearing from being eroded by acid contained in the fuel, the durability of the fuel pump is improved. It is preferable to form the protecting film from a material that is superb in both acid-resistant and anti- sulfuration properties. In this case, the bearings are not eroded by the fuel if the fuel pump is used in insufficiently refined fuel including sulfuric and/or acid components. It is further preferable to form the bearing body from a material having the anti-sulfuration property, so that the bearing is prevented from erosion even if the protecting film is removed by abrasion. The cylindrical bearing body is sufficiently protected from erosion if its surface exposed to the fuel is covered with the protecting film. It is, however, preferable to cover an entire surface of the bearing to simplify the process of coating the protecting film. Preferably, the thickness of the protecting film is set to a range from 1 μm to 50 μm. According to the present invention, a sufficient durability of the fuel pump is secured even if it is used in the fuel containing sulfuric and/or acid components. Other objects and features of the present invention will become more readily apparent from a better understanding of the preferred embodiment described below with reference to the following drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIG. lA is a cross-sectional view showing a bearing used in a fuel pump according to the present invention; FIG. IB is a cross-sectional view showing a portion of the bearing (a portion IB designated in FIG. lA) in an enlarged scale; and FIG. 2 is a cross-sectional view showing a fuel pump. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described with reference to accompanying drawings. A fuel pump 10 shown in FIG. 2 is used, e. g., in an electronically controlled fuel injection system for an internal combustion engine. The fuel pump 10 is submerged in a fuel tank of an automotive vehicle to pump up fuel and to supply the fuel to the fuel injection system. The fuel pump 10 is composed of a pump assembly 20 and an electric motor 50, both contained in a cylindrical housing 11. The electric motor 50 is a direct current motor having an annular permanent magnet disposed inside the housing 11 and a rotor 52 rotatably disposed in the annular permanent magnet. Electric current is supplied to the electric motor 50 through brushes (not shown)- The pump assembly 20 is composed of a casing 21, casing cover 22 and an impeller 23. A fuel passage 61 is formed in the casing 21 and the casing cover 22, and the impeller 23 is rotatably disposed in the fuel passage 61. The impeller 23 is disc-shaped and has plural blades and ditches alternately formed on the outer periphery of the disc-shaped impeller. The casing 21 and the casing cover 22 are made of aluminum by die-casting, for example. The casing 21 is firmly connected to one end of the cylindrical housing 11, and a bearing 30 for supporting a rotor shaft 55 is fixed to the center of the casing 21. The casing cover 22 is abutted with the casing 21 thereby forming the fuel passage 61 between the casing 21 and the casing cover 22. The casing cover 22 is also firmly connected to the end of the cylindrical housing 11. One end of the rotor shaft 55 is rotatably supported by the bearing 30, and the other end of the rotor shaft 55 is rotatably supported by another bearing 40. Both bearings 30, 40 are formed in a similar shape as shown in FIGS. lA and IB. The bearing 30 (40) is composed of a cylindrical bearing body 32 (42) and a. protecting film 34 (44) covering an entire surface of the bearing body 32 (42). Since the structure of both bearings 30, 40 is similar, only the bearing 30 will be explained below as a representative. The bearing body 32 is made by sintering copper-nickel-zinc (Cu-Ni-Zn) alloy powder into a cylindrical shape. The protecting film 34 is made of polytetrafluoroethylene (referred to as PTFE). It is formed on the surface of the bearing body 32 by spraying, for example. The thickness of the protecting film 34 is set in a range from 1 μm to 50 μm. The Cu-Ni-Zn alloy forming the bearing body 32 has a high anti-sulfuration property, and the PTFE forming the protecting film 34 is superb in both of the acid-resistance property and the anti-sulfuration property. As shown in FIG. 2, the rotor 52 includes an armature coil wound on a magnetic core 52a and a disc-type commutator 54 for supplying electric current to the armature coil. A terminal 68 is disposed in a connector 67. The electric current is supplied from an outside power source to the armature coil of the rotor 52 through the terminal 68, brushes (not shown) and the commutator 54. Operation of the fuel pump 10 will be briefly described with reference to FIG, 2. When the electric motor 50 is energized, the impeller 23 is rotated in the fuel passage 61. Fuel in the fuel tank is sucked from an inlet port 60 into the fuel passage 61. The fuel is pressurized in the fuel passage 61 and delivered to a fuel chamber 51 in the electric motor 50 through an opening (not shown) formed in the casing 21. The fuel in the fuel chamber 51 is further sent to an outlet port 65 through an air gap between the outer periphery of the rotor 52 and the annular permanent magnet disposed on the inner periphery of the housing 11. The fuel is supplied to the internal combustion engine from the outlet port 65. An one-way valve 66 is disposed in a passage to the outlet port 65 to prevent a reversal flow of the fuel. As described above, an entire surface of the bearing 30 (40) is covered with a protecting film 34 that is superb in both the acid-resistant property and the anti-sulfuration property. Therefore, the bearings are prevented from being eroded even if the fuel pump 10 is used in insufficiently refined fuel containing sulfuric components and/or organic acid. Accordingly, the rotor 52 supported by the bearings smoothly rotates- Since the protecting film 34 made of PTFE reduces a rotational resistance between the rotor shaft 55 and the bearings 30, 40, an efficiency of the fuel pump 10 is improved. Further, since PTFE is strong against abrasion, a life of the bearings can be prolonged. The bearing body 32 is made of Cu-Ni-Zn alloy that has a. superb anti-sulfuration property. Therefore, the bearing 30 is not eroded by the sulfuric components, even if the protecting film 34 is removed by abrasion or peeled off for any reason. Since the protecting film 34 is formed with the thickness of at least 1 μm, both of its acid-resistant property and the anti-sulfuration property are secured. On the other hand, the thickness of the protecting film 34 is controlled not to exceed 50 μm. Therefore, a proper clearance between the rotor. shaft 55 and the bearing 30 is secured, and the protecting film 34 does not adversely affect a smooth rotation of the rotor 52, The protecting film 34 may be formed by plating gold (Au), nickel (Ni) or tin (Sn), in place of PTFE, on the surface of the bearing body 32. Alternatively, a compound plating of nickel and PTFE may be used. The Cu-Ni-Zn alloy may be replaced with a similar material such as Cu-based Ni or Zn, or Cu-based Ni and Zn. Further, the Cu-Ni-Zn alloy may be replaced with other materials that do not have the anti-sulfuration property in certain applications. The PTFE used for forming the protecting film 34 may be replaced with materials that have only the acid-resistant property in case where the anti-sulfuration property is not required. Though an entire surface of the bearing body 32 is covered with the protecting film 34 in the foregoing embodiment, it may be possible to cover only such portions that are exposed to the fuel. In the bearing structure shown in FIG. 2, at least both axial ends and the inner surface of the bearing 30 must be covered with the protecting film 34. It may not be necessary to cover the outer surface of the bearing body 32 with the protecting film 34, because the outer surface is inserted into a bore of the casing 21 and is not exposed to the fuel. However, the process of forming the protecting film 34 is simplified if the entire surface of the bearing body 32 is covered with the protecting film 34. While the present invention has been shown and described with reference to the foregoing preferred embodiment, it will be apparent to those skilled in the art that changes in form and detail may be made therein without departing from the scope of the invention as defined in the appended claims. WHAT IS CLAIMED IS: 1. A fuel pump for pumping up fuel contained in a fuel tank, the fuel pump comprising: a housing; an electric motor including a rotor disposed in the housing; and a bearing for rotatably supporting the rotor in the housing, wherein: the bearing comprises a bearing body and a protecting film covering at least such portions of the bearing that are exposed to the fuel; and the protecting film has an acid-resistant property. 2. The fuel pump as in claim 1, wherein: the protecting film further has an anti-sulfuration property. 3. The fuel pump as in claim 1 or 2, wherein: the bearing body is formed in a cylindrical shape; and the protecting film covers at least both axial ends and an inner surface of the cylindrical bearing body. 4. The fuel pump as in claim 1 or 2, wherein: the protecting film covers an entire surface of the bearing body. 5. The fuel pump as in any one of claims 1-4, wherein: the bearing body is made of a material having an anti-sulfuration property. 6. The fuel pump as in any one of claims 1-5, wherein: the thickness of the protecting film is in a range from 1 pm to 50 |im. 7. A fuel pump for pumping up fuel contained in a fuel tank, the fuel pump comprising: a housing; an electric motor including a rotor disposed in the housing; and* a pair of bearings for rotatably supporting the rotor in the housing, wherein: each of the bearings comprises a cylindrical bearing body and a protecting film covering an entire surface of the cylindrical bearing body; the cylindrical bearing body is made of a material having an anti-sulfuration property; and the protecting film is made of a material having an acid-resistant property and an anti-sulfuration property. 8. The fuel pump as in claim 7, wherein: the cylindrical bearing body is made of a copper-nickel-zinc alloy- 9. The fuel pump as in claim 7, wherein: the protecting film is made of polytetrafluoroethylene• 10. A fuel pump substantially as herein described with reference to the accompanying drawings.

Documents:

684-che-2003 abstract granted.pdf

684-che-2003 claims granted.pdf

684-che-2003 description (complete) granted.pdf

684-che-2003 drawings granted.pdf

684-che-2003-abstract.pdf

684-che-2003-claims.pdf

684-che-2003-correspondnece-others.pdf

684-che-2003-correspondnece-po.pdf

684-che-2003-description(complete).pdf

684-che-2003-drawings.pdf

684-che-2003-form 1.pdf

684-che-2003-form 26.pdf

684-che-2003-form 3.pdf

684-che-2003-form 5.pdf

684-che-2003-other document.pdf