Abstract:
A fuel pump includes an impeller having a plurality of front and rear blades and a plurality of front and rear blade ditches, a pump passage around the impeller, a fuel suction port and a fuel discharge port. Each of the front and rear blade ditches has a concave surface. Each of the front blade ditches has a tip depth at the tip of the front blade and a bottom depth at a portion adjacent to the tip. The fuel discharged from the front ditches is turned by the concave surface inwardly, thereby forming circulating flow effectively.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
         [0001]    The present application is based on and claims priority from Japanese Patent Application 2001-340394, filed Nov. 6, 2001, the contents of which are incorporated herein by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a fuel pump for pumping fuel up from a tank.  
           [0004]    2. Description of the Related Art  
           [0005]    A fuel pump that has an impeller is well known, as disclosed in JP-A-9-14173. Such an impeller has a plurality of blades and blade ditches between the adjacent blades. The blade ditches are partitioned from each other by partition walls. When the impeller rotates, fuel in the blade ditches is driven radially outward under centrifugal force. The fuel in one of the blade ditches circulates along the partition walls and flows into the next one of the blade ditches. While the fuel continues to circulate, the fuel is pressurized until it is discharged from a fuel discharge port. Therefore, the pump pressure and pump efficiency can be improved if the blade ditch accepts more fuel and the fuel flows out from the ditch at a higher speed.  
           [0006]    A fuel pump disclosed in JP-A-9-14173 has an impeller whose axial width of a blade ditch is larger than a half the axial width of the impeller, thereby preventing stagnation of the fuel in the fuel passage formed around the impeller. The blade ditch, which is formed at the intermediate portion between a blade and a partition wall, has a curved surface projecting from one axial end of the impeller toward the other axial end. The curved surface is like a parabolic surface that has a tangential line at the tip of the blade extending axially outward. Although the fuel flows from a blade ditch on one end of the impeller into one of the blade ditch on the other end, such fuel may not turn to flow to the next ditches on the opposite end of the impeller again. It is difficult to form an effective circulation flow. Because the partition wall of the impeller disclosed in JP-A-9-14173 has a zigzag surface in the circumferential direction, the impeller has blades of different sizes. Therefore, the smaller front surface of the impeller can not give fuel sufficient energy.  
         SUMMARY OF THE INVENTION  
         [0007]    Therefore, the present invention has been made in view of the above problems.  
           [0008]    An object of the invention is to provide an improved fuel pump that can increase fuel flow speed and give fuel more kinetic energy by preventing stagnation of fuel.  
           [0009]    According to a main feature of the invention, a fuel pump includes an impeller having a plurality of front and rear blades with a plurality of front and rear blade ditches between the respective blades, a pump passage around the impeller, a fuel suction port and a fuel discharge port. Each of the front blade ditches has a front concave surface that has a first tip depth at the tip of the blade and a bottom depth that is deeper than the tip depth at a portion adjacent to the tip of the blade. Preferably, the front concave surface is a partially cylindrical surface.  
           [0010]    Therefore, the concave surface turns fuel inward, so that a circulating fuel flow can be formed effectively.  
           [0011]    In addition, each of the rear blade ditches has a rear concave surface that has a second tip depth at the tip of the blade and a bottom depth that is deeper than the second tip depth at a portion adjacent to the tip of the rear blade. This further increases the effect of circulating flow.  
           [0012]    According to another feature of the invention, the first tip depth is formed to be larger than a half of a thickness of said impeller. As a result, the fuel is given kinetic energy by the blade at the front surface thereof in the rotation direction, thereby preventing stagnation of the circulating flow otherwise formed in the pump passage.  
           [0013]    According to another feature of the invention, the front concave surface has a tangential line inclining toward the front end of said impeller at the portion that crosses the blade tip. Therefore, the shape of the circulating flow becomes approximately circular.  
           [0014]    According to another feature of the invention, the cylindrical surface has its center inside the front blade ditch. Therefore, the fuel speed outside the blade ditches can be increased.  
           [0015]    According to another feature of the invention, each of the front and rear blades inclines forward in the rotation direction of said impeller. Therefore, the fuel flow speed can be increased.  
           [0016]    According to another feature of the invention, the front and rear blades are a half-pitch shifted from each other. Preferably, the second tip depth is smaller than a half the thickness of the impeller. As a result, the impeller can provides the front and rear blades without increasing the thickness. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    Other objects, features and characteristics of the present invention as well as the functions of related parts of the present invention will become clear from a study of the following detailed description, the appended claims and the drawings. In the drawings:  
         [0018]    [0018]FIG. 1 is a schematic diagram illustrating a main portion of an impeller of a fuel pump according to a preferred embodiment of the invention;  
         [0019]    [0019]FIG. 2 is a cross-sectional side view of the fuel pump according to the preferred embodiment;  
         [0020]    [0020]FIG. 3 is a perspective view of the impeller of the fuel pump according to the preferred embodiment;  
         [0021]    [0021]FIG. 4 is an enlarged fragmentary perspective view of the impeller shown in FIG. 3;  
         [0022]    [0022]FIG. 5 is an enlarged fragmentary perspective view of the impeller shown in FIG. 3;  
         [0023]    [0023]FIG. 6 is an enlarged fragmentary side view of the impeller shown in FIGS. 1 and 3;  
         [0024]    [0024]FIG. 7 is a schematic diagram illustrating a main portion of the impeller shown in FIG. 6 cut along line VII-VII; and  
         [0025]    [0025]FIG. 8 is a schematic diagram illustrating a main portion of the impeller and a fuel passage. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0026]    A fuel pump according to a preferred embodiment of the invention will be described with reference to the appended drawings.  
         [0027]    The fuel pump  1  is usually located in a fuel tank of a vehicle as a component of an electrically controlled fuel injection system for pumping up and supplying fuel to an engine.  
         [0028]    The fuel pump  1  includes a pump section  10  and a motor section  20 . The motor section  20  is a DC motor that has a cylindrical housing  21  with a plurality of permanent magnets on the inside surface, an armature  22  that is coaxially disposed in the housing  21  opposite the permanent magnets and a brush unit. The pump section  10  includes a main casing  11 , a casing cover  12  and an impeller  30 . The main casing  11  and the casing cover  12  form a fuel passage member, in which the impeller  30  is rotatably supported. The impeller  30  has a front blade group  41  (left in FIG. 3) and a rear blade group  42  (right in FIG. 3). The front blade group  41  includes a plurality of front blades  32   f  and a plurality front blade ditches  33   f  formed between partition walls  31  and the front blade  32   f.  The rear blade group  42  includes a plurality of rear blades  32   r  and a plurality rear blade ditches  33   r  formed between the partition walls  31  and the rear blades  32   r.  The main casing  11  and the casing cover  12  are made of aluminum die-casting. The main casing  11  has a bearing  13  at the center thereof and the outer periphery force-fitted deep into an end of the housing  11 . The casing cover  12  is also inserted into the same end of the housing  21  so as to cover the main casing  11  and is clamped by the edge portion of the housing  21 . A thrust bearing  14  is force-fitted to a center hole of the casing cover  12  to support an end of the rotary shaft  23  in the axial direction. The rotary shaft  23  is also supported by a bearing  13  at the other end thereof.  
         [0029]    A fuel inlet port  16  is formed at the casing cover  12 , from which fuel is pumped up and supplied to a pump passage  17  when the impeller  30  rotates. The fuel supplied to the pump passage  17  is pressured while the impeller  30  is rotating and discharged to a fuel chamber  24  of the motor section  20  from a fuel discharge port (not shown) of the main casing  11 . A pump groove  11   a  is formed at a portion of the main casing  11  around the tips of the blades  32 . Another pump groove  12   a  is also formed at a portion of the casing cover  12  opposite the pump groove  11   a.  The pump grooves  11   a  and  12   a  form a pump passage  17 .  
         [0030]    The pump groove  11   a  has an end at a portion past the fuel discharge port in the rotation direction of the impeller  30 . A suitable gap is formed between the circumference of the pump groove  11   a  and the blade tips  32   c  at the end of the pump groove  11   a  past the discharge port in the rotation direction of the impeller  30 . Fuel held in the blade ditches  33   f,    33   r  of the impeller  30  is discharged from the pump passage  17  through the gap and the fuel discharge port.  
         [0031]    The armature  22  of the motor section  20  has an armature core  25 . A disk shaped commutator  26  is disposed at the upper end of the armature  22 . Electric power is supplied via a terminal  28  of a connector  27  and the brush unit (not shown) to the commutator  26 . When electric power is supplied to the armature  22 , the armature  22  rotates the impeller  30 . The impeller  30  pumps up fuel from the fuel inlet port  16  and supplies the fuel to the pump passage  17 . Then, the fuel is given kinetic energy by the impeller and discharged to the fuel chamber  24 . The fuel flowing into the fuel chamber  24  passes around the armature  22  and flows outside the fuel pump  1  from the discharge port  29 .  
         [0032]    The front blades  32   f  of the front blade group  41  are ½ pitch shifted in the circumferential direction from the rear blades  32   r  of the rear blade group  42 . Therefore, the partition walls  31  are formed between the front blades  32   f  on the front end of the impeller  30  and the rear blade ditches  33   r  on the rear end of the impeller  30 . As shown in FIG. 6, each of the blade ditches  33   f,    33   r  is surrounded by the partition walls  31  and the blades  32 . When fuel is discharged from the pump passage  17 , a fuel-pressure wave caused by the front blades  32   f  and a fuel-pressure wave caused by the rear blades are a half cycle shifted from each other. Therefore, noise when the fuel is discharged is reduced.  
         [0033]    Each of the blades  32   f,    32   r  inclines toward the direction of rotation of the impeller  30 , as shown in FIG. 5, so that kinetic energy can be applied to the fuel held in the blades ditches  33   f,    33   r.  The back side  32   a  of each of the blade ditches  33   f,    33   r  in the rotation direction of the impeller  30  is larger than the fore side  32   b  thereof, as shown in FIG. 6. Because the fore side  32   b  of the blade ditches  33   f,    33   r  in the rotation direction is located just at the back of the blades  32   f,    32   r,  it does not give kinetic energy to the fuel.  
         [0034]    As shown in FIG. 1, each of the front blade ditches  33   f  has the following features:  
         [0035]    (1) A concave cylindrical surface extends from the front end  30   a  of the impeller toward the rear end  30   b  of the impeller  30 . Each of the front blade ditches  33   f  has a bottom or maximum depth a, a tip depth b at the blade tip  32   c  of the blade  32 . The bottom depth a of the front blade ditch  33   f  is larger than tip depth b (or a&gt;b), so that the surface of the front blade ditches  33   f  are introverted at the blade tips  32   c.    
         [0036]    (2) If the impeller  30  has an axial thickness t, the tip depth b is larger than t/2 (or b&gt;t/2).  
         [0037]    (3) Each of the front blade ditches  33   f  has a partially cylindrical front surface C that has a tangential line L at the portion that crosses the blade tip  32   c.  The tangential line L inclines to the front end  30   a,  so that an angle θ formed between the tangential line L and the blade tip  32   c  is smaller than 90° (or θ&lt;90°). That is, the front concave cylindrical surface C of the front blade ditches  33   f  extends toward the front end  30   a  of the impeller  30 . Accordingly, the fuel driven into the front blade ditches  33   f  of the front blade group  41  is discharged from the blade tip  32   c  toward the front end  30   a  of the impeller  30 .  
         [0038]    Therefore, fuel flows into the front blade ditches  33   f  from the front end  30   a  of the impeller  30  is discharged to the pump passage  17  from a portion of the impeller  30  rear from the axial center thereof without stagnation, as shown in FIG. 8.  
         [0039]    (4) The front concave cylindrical surface C of the front blade ditches  33   f  has the center O located inside the blade ditch  33 . Because the center O of the concave cylindrical surface C where the speed of the circulating fuel flow is the lowest, the speed of the fuel flow can be effectively increased. This effectively prevents stagnation of the fuel flow in the pump passage  17 .  
         [0040]    The rear blade ditches  33   r  have substantially the same feature except for the following features, as shown in FIG. 7.  
         [0041]    (5) Each of the rear blade ditches has tip depth b′ that is smaller than a half of the axial thickness t of the impeller  30  (that is, b′&lt;t/2). Therefore, the front and rear blades  33   f,    33   r  can be formed without increasing the axial thickness of the impeller.  
         [0042]    (6) Each of the rear blade ditches  33   r  has a rear concave cylindrical surface C′ that has a tangential line at the portion that crosses the blade tip  32   c.  The tangential line inclines to the rear end  30   b  of the impeller  30  in the same manner as the front concave cylindrical surface C. Accordingly, the fuel driven into the rear blade ditches  33   r  of the rear blade group  42  is discharged from the blade tip  32   c  toward the rear end  30   b  of the impeller  30 .  
         [0043]    When the front blades  32   f  of the front blade group  41  form circulating fuel flow along the front concave cylindrical surface C, the rear blades  32   r  of the rear blade group  42  form another circulating fuel flow along the rear concave cylindrical surface C′. Accordingly, the front and rear blade groups  41 ,  42  alternately and jointly form the circulating fuel flow.  
         [0044]    As indicated by arrows shown in FIG. 8, the fuel in the fuel passage  17  flows into the blade ditches  33   f,    33   r  when the impeller  30  rotates. Because each of the front blades  32   f  inclines toward the direction of rotation of the impeller  30 , as shown in FIG. 5, the fuel is mainly gathered at the base portion  32   d  of the front blades  32   f,  so that the fuel flows along the concave cylindrical surface C and given kinetic energy by the front blades  32   f.  As the fuel flows along the front concave cylindrical surface C toward the blade tip  32   c,  the fuel is gradually pressed to the left or forward, so that the flow speed is increased. The fuel discharged from the front blade ditches  33   f  is guided by the concave cylindrical surface C and forms circulating flow, and flows into the rear blade ditches  33   f  at the base portion of the rear blade  32   r.  Then the fuel flows along the rear concave cylindrical surface C′ toward the blade tip  32   c  in the same manner as described above. Thus, the fuel is repeatedly pressured by the impeller  30 .  
         [0045]    All the front blades  32   f  have a cross-sectional area in the rotation direction that is the same to each other, and all the rear blades  32   r  also have a cross-sectional area in the rotation direction that is the same to each other. Therefore, the impeller according to the invention can form smooth circulating flow.  
         [0046]    In the foregoing description of the present invention, the invention has been disclosed with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes may be made to the specific embodiments of the present invention without departing from the scope of the invention as set forth in the appended claims. Accordingly, the description of the present invention is to be regarded in an illustrative, rather than a restrictive, sense.