Patent Publication Number: US-9841018-B2

Title: Fluid pump

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is based on and incorporates herein by reference Japanese Patent Application No. 2015-81915 filed on Apr. 13, 2015. 
     TECHNICAL FIELD 
     The present disclosure relates to a fluid pump that draws and discharges fluid by changing a volume of respective pump chambers formed between external teeth of an inner rotor and internal teeth of an outer rotor. 
     BACKGROUND 
     A previously proposed fluid pump has an inner rotor, an outer rotor and a pump housing. The inner rotor includes external teeth, and the outer rotor includes internal teeth for meshing with the external teeth. The pump housing receives the inner rotor and the outer rotor. When the inner rotor is rotated, a rotational force of the inner rotor is transmitted from the external teeth to the internal teeth. Thereby, the outer rotor is also rotated. When the inner rotor and the outer rotor are rotated, the volume of the respective pump chambers, which are formed between the external teeth and the internal teeth, changes. In response to increasing of the volume of the pump chamber, the fluid is drawn into the pump chamber through a suction passage formed in the pump housing. Thereafter, in response to decreasing of the volume of the pump chamber, the fluid is compressed in the pump chamber and is discharged from the pump chamber. 
     A suction groove, which is communicated with the suction passage, is formed in an inside wall surface of the pump housing. The suction groove is shaped to extend along a rotational path of the external teeth and a rotational path of the internal teeth, and the suction groove increases a radial extent of a fluid passage, through which the fluid is supplied from the suction passage into the pump chamber (see, for example, JP2013-60901A). 
     Various developments have been made to improve the pump efficiency of the fluid pump through elaborations on, for example, configurations of the suction groove and the suction passage. Lately, demand for energy saving has been progressively increased, and thereby a further improvement of the pump efficiency has been demanded. 
     SUMMARY 
     The present disclosure is made in view of the above point. According to the present disclosure, there is provided a fluid pump that includes an inner rotor, an outer rotor, a pump housing, a suction passage, and a suction groove. The inner rotor has a plurality of external teeth. The outer rotor has a plurality of internal teeth for meshing with the plurality of external teeth. The pump housing receives the outer rotor and the inner rotor and forms a plurality of pump chambers, each of which has a variable volume, between the plurality of internal teeth and the plurality of external teeth. The suction passage is formed in the pump housing and conducts the fluid to be drawn into at least one of the plurality of pump chambers. The suction groove is formed in an inside wall surface of the pump housing and is communicated with the suction passage while the suction groove is shaped to extend along a rotational path of the plurality of external teeth and a rotational path of the plurality of internal teeth. An edge of the suction groove has both of a chamfered edge part, which is chamfered, and an unchamfered edge part, which is not chamfered and is not rounded. The unchamfered edge part is located in a direct-inflow region of the suction groove, which overlaps with the suction passage in a view taken in a direction of a rotational axis. The chamfered edge part is located in a peripheral region of the suction groove, which is other than the direct-inflow region. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
         FIG. 1  is a partial cross-sectional view indicating a fuel pump according to an embodiment of the present disclosure; 
         FIG. 2  is a cross-sectional view taken along line II-II in  FIG. 1 ; 
         FIG. 3  is a cross-sectional view taken along line III-III in  FIG. 1 ; 
         FIG. 4  is a cross-sectional view taken along line IV-IV in  FIG. 1 ; 
         FIG. 5  is a view taken in a direction of an arrow V in  FIG. 1 ; 
         FIG. 6  is a partial enlarged view of  FIG. 5 ; and 
         FIG. 7  is an enlarged cross-sectional view of a pump cover shown in  FIG. 1   
     
    
    
     DETAILED DESCRIPTION 
     An embodiment of a fluid pump according to the present disclosure will be described with reference to the accompanying drawings. The fluid pump of the present embodiment is installed in a vehicle. A subject fluid to be pumped with the fluid pump is liquid fuel used for combustion in an internal combustion engine. Specifically, in the present embodiment, light oil (diesel fuel), which is used for combustion in a compression self-ignition internal combustion engine, is used as the subject fluid to be pumped. The fluid pump is received in an inside of a fuel tank. 
     As shown in  FIG. 1 , the fluid pump  101  of the present embodiment is a rotary internal gear pump of a positive displacement type. The fluid pump  101  includes a pump body  102 , a pump main body  103 , an electric motor  104  and a side cover  105 . The pump main body  103  and the electric motor  104  are received in an inside of the pump body  102 , which is shaped into a cylindrical tubular form, such that the pump main body  103  and the electric motor  104  are arranged one after another in an axial direction. The side cover  105  is installed to an opening of one of two axially opposite end parts of the pump body  102 , which is located on the electric motor  104  side. 
     The side cover  105  includes an electric connector  105   a , which supplies an electric power to the electric motor  104 , and a discharge port  105   b , through which fuel is discharged from the fluid pump  101 . In the fluid pump  101 , a rotatable shaft  104   a  of the electric motor  104  is rotated when the electric power is supplied from an external circuit through the electric connector  105   a . Thus, an outer rotor  130  and an inner rotor  120  of the pump main body  103  are rotated by a drive force of the rotatable shaft  104   a  of the electric motor  104 , and thereby fuel is drawn into and compressed in the fluid pump  101  and is then discharged from the fluid pump  101  through the discharge port  105   b . The fluid pump  101  pumps the light oil, which has the higher viscosity in comparison to gasoline, as the fuel. 
     In the present embodiment, the electric motor  104  is an inner rotor brushless motor and includes magnets  104   b , which form four magnetic poles, and coils  104   c , which are installed in six slots. For example, at a start preparation time (e.g., a time of turning on of an ignition switch of the vehicle), a positioning control operation of the electric motor  104  is executed to rotate the rotatable shaft  104   a  toward a drive rotation side or a counter-drive rotation side (the counter-drive rotation side being opposite from the drive rotation side). Thereafter, the electric motor  104  executes a drive control operation, which rotates the rotatable shaft  104   a  from the position, at which the rotatable shaft  104   a  is positioned in the positioning control operation, toward the drive rotation side. 
     Here, the drive rotation side is a positive direction side of a rotational direction Ri of the inner rotor  120  in a circumferential direction of the inner rotor  120 . The counter-drive rotation side is a negative direction side of the rotational direction Ri of the inner rotor  120 , which is opposite from the positive direction side. 
     Hereinafter, the pump main body  103  will be described in detail. The pump main body  103  includes a pump housing  110 , the inner rotor  120 , the outer rotor  130  and a joint member  160 . The pump housing  110  includes a pump cover  112  and a pump casing  116 , which are placed one after another in the axial direction. 
     The pump cover  112  is made of metal and is shaped into a circular disk form. The pump cover  112  axially projects outward from the end part of the pump body  102 , which is located on the side of the electric motor  104  that is opposite from the side cover  105 . 
     In order to draw the fuel from an outside of the fluid pump  101 , the pump cover  112  shown in  FIGS. 1 and 2  has a suction passage  112   a , which is formed as a cylindrical hole, and a suction groove  113 , which is shaped into an arcuate form. In the pump cover  112 , the suction passage  112   a  is communicated with the suction groove  113  at a predetermined opening location Ss, which is eccentric from a central axis (hereinafter referred to as an inner central axis) Ci of the inner rotor  120 . The suction groove  113  is axially grooved, i.e., formed in an inside wall surface of the pump cover  112  and opens on the pump casing  116  side of the pump cover  112 . A communicating portion of the suction groove  113 , which is communicated with the suction passage  112   a , extends through the pump cover  112  in the axial direction. A non-communicating portion of the suction groove  113 , which is not directly communicated with the suction passage  112   a , is shaped into a cup form having a bottom. As shown in  FIG. 2 , the suction groove  113  has a circumferential extent, which is less than one half (less than 180 degrees) of an entire circumference of the inner rotor  120  in the rotational direction Ri (also see  FIG. 4 ). Shaded areas, which are indicated by reference signs B 1 , B 2  in  FIG. 2 , do not represent a cross-section but represent extents of peripheral portions  1132 , respectively, which will be described later. 
     The suction groove  113  extends from a start end part  113   c  to a terminal end part  113   d  in the rotational direction Ri, Ro such that a radial extent (hereinafter referred to as a width) of the suction groove  113 , which is measured in a radial direction of the rotational axis, progressively increases in the rotational direction Ri, Ro from the start end part  113   c  to the terminal end part  113   d . The suction passage  112   a  opens in a groove bottom portion  113   e  of the suction groove  113  at the opening area Ss, so that the suction groove  113  is communicated with the suction passage  112   a . As shown particularly in  FIG. 2 , in an entire range of the opening area Ss, in which the suction passage  112   a  opens, the width of the suction groove  113  is smaller than a width (diameter) of the suction passage  112   a.    
     Furthermore, the pump cover  112  forms an installation space  158  at an area that is opposed to the inner rotor  120  along the inner central axis Ci. The installation space  158  is shaped into a recessed hole. A main body  162  of the joint member  160  is rotatably installed in the installation space  158 . 
     The pump casing  116  shown in  FIGS. 1, 3, 4 and 5  is made of metal and is shaped into a cylindrical tubular form having a bottom. An opening portion  116   a  of the pump casing  116  is covered with the pump cover  112  such that an entire circumferential extent of the opening portion  116   a  is tightly closed by the pump cover  112 . As shown particularly in  FIGS. 1 and 4 , an inner peripheral portion  116   b  of the pump casing  116  is formed as a cylindrical hole that is eccentric relative to the inner central axis Ci of the inner rotor  120 . 
     The pump casing  116  forms a discharge passage  117 , which is formed as an arcuate hole, to discharge the fuel from the discharge port  105   b  through a high pressure passage  106  defined between the pump body  102  and the electric motor  104 . The discharge passage  117  axially extends through a recessed bottom portion  116   c  of the pump casing  116 . Particularly, as shown in  FIG. 3 , the discharge passage  117  has a circumferential extent, which is less than one half (i.e., less than 180 degrees) of the entire circumference of the inner rotor  120  in the rotational direction Ri. A radial extent (hereinafter referred to as a width) of the discharge passage  117 , which is measured in the radial direction, progressively decreases in the rotational direction Ri, Ro from a start end part  117   c  to a terminal end part  117   d.    
     Furthermore, the pump casing  116  includes a reinforcing rib  116   d  in the discharge passage  117 . The reinforcing rib  116   d  is formed integrally with the pump casing  116  such that the reinforcing rib  116   d  extends across the discharge passage  117  in a crossing direction, which crosses the rotational direction Ri of the inner rotor  120 , and thereby the reinforcing rib  116   d  reinforces the pump casing  116 . 
     An opposing suction groove  118  shown in  FIG. 3  is formed in the recessed bottom portion  116   c  of the pump casing  116  at a corresponding area that is opposed to the suction groove  113  in the axial direction while pump chambers  140  (described later in detail) are interposed between the opposing suction groove  118  and the suction groove  113  in the axial direction. The opposing suction groove  118  is an arcuate groove that corresponds to a shape, which is produced by projecting the suction groove  113  onto the pump casing  116  in the axial direction. In this way, in the pump casing  116 , the discharge passage  117  is formed to be symmetric to the opposing suction groove  118  with respect to the symmetry axis located between the discharge passage  117  and the opposing suction groove  118 . As shown particularly in  FIG. 2 , an opposing discharge groove  114  is formed in the pump cover  112  at a corresponding area that is opposed to the discharge passage  117  in the axial direction while the pump chambers  140  are interposed between the opposing discharge groove  114  and the discharge passage  117  in the axial direction. The opposing discharge groove  114  is formed as an arcuate groove that is shaped to correspond with a shape, which is produced by projecting the discharge passage  117  onto the pump cover  112  in the axial direction. In this way, in the pump cover  112 , the suction groove  113  is formed to be symmetric to the opposing discharge groove  114  with respect to the symmetry axis located between the suction groove  113  and the opposing discharge groove  114 . 
     As shown in  FIG. 1 , a radial bearing  150  is securely fitted to the recessed bottom portion  116   c  of the pump casing  116  along the inner central axis Ci to radially support the rotatable shaft  104   a  of the electric motor  104  in a manner that enables rotation of the rotatable shaft  104   a . Furthermore, a thrust bearing  152  is securely fitted to the pump cover  112  along the inner central axis Ci to axially support the rotatable shaft  104   a  in a manner that enables the rotation of the rotatable shaft  104   a.    
     As shown in  FIGS. 1 and 4 , a receiving space  156 , which receives the inner rotor  120  and the outer rotor  130 , is formed by the recessed bottom portion  116   c  and the inner peripheral portion  116   b  of the pump casing  116  and the pump cover  112 . 
     The inner rotor  120 , which is indicated in  FIGS. 1 and 4 to 6 , is centered at the inner central axis Ci and is thereby coaxial with the rotatable shaft  104   a  (i.e., coaxial with a rotational axis of the rotatable shaft  104   a ), so that the inner rotor  120  is eccentrically placed in the receiving space  156 . An inner peripheral portion  122  of the inner rotor  120  is radially supported by the radial bearing  150 , and two slide surfaces  125  of the inner rotor  120 , which are respectively formed at two opposed axial ends of the inner rotor  120 , are supported by the recessed bottom portion  116   c  of the pump casing  116  and the pump cover  112 , respectively, in a manner that enables rotation of the inner rotor  120 . 
     The inner rotor  120  has a plurality of insertion holes  127  that extend in the axial direction at a corresponding area of the inner rotor  120 , which is opposed to the installation space  158 . In the present embodiment, the number of the insertion holes  127  is five, and these insertion holes  127  are arranged one after another at equal intervals in the circumferential direction along the rotational direction Ri. The insertion holes  127  extend through the inner rotor  120  from the installation space  158  side to the recessed bottom portion  116   c  side in the axial direction. Legs (projections)  164  of the joint member  160  are inserted into the insertion holes  127 , respectively, so that the drive force of the rotatable shaft  104   a  is transmitted to the inner rotor  120  through the joint member  160 . Thereby, the inner rotor  120  is rotated in the circumferential direction about the inner central axis Ci in response to the rotation of the rotatable shaft  104   a  of the electric motor  104  while the slide surfaces  125  of the inner rotor  120  are slid along the recessed bottom portion  116   c  and the pump cover  112 , respectively. 
     The inner rotor  120  includes a plurality of external teeth  124   a , which are formed in an outer peripheral portion  124  of the inner rotor  120  and are arranged one after another at equal intervals in the circumferential direction along the rotational direction Ri. Each of the external teeth  124   a  can axially oppose the suction groove  113 , the discharge passage  117 , the opposing discharge groove  114  and the opposing suction groove  118  in response to the rotation of the inner rotor  120 . Thereby, it is possible to limit sticking of the inner rotor  120  to the recessed bottom portion  116   c  and the pump cover  112 . 
     As shown in  FIGS. 1 and 4 , the outer rotor  130  is eccentric to the inner central axis Ci of the inner rotor  120 , so that the outer rotor  130  is coaxially received in the receiving space  156 . In this way, the inner rotor  120  is eccentric to, i.e., is decentered from the outer rotor  130  in an eccentric direction De, which is the radial direction. An outer peripheral portion  134  of the outer rotor  130  is radially supported by the inner peripheral portion  116   b  of the pump casing  116  in a manner that enables rotation of the outer rotor  130 . Furthermore, the outer peripheral portion  134  of the outer rotor  130  is axially supported by the recessed bottom portion  116   c  of the pump casing  116  and the pump cover  112  in a manner that enables the rotation of the outer rotor  130 . The outer rotor  130  is rotatable in the rotational direction (certain rotational direction) Ro about an outer central axis Co, which is eccentric to the inner central axis Ci. 
     The outer rotor  130  has a plurality of internal teeth  132   a  for meshing with the external teeth  124   a  of the inner rotor  120 . The internal teeth  132   a  are formed in an inner peripheral portion  132  of the outer rotor  130  and are arranged one after another at equal intervals in the rotational direction Ro. Each of the internal teeth  132   a  can axially oppose the suction groove  113 , the discharge passage  117 , the opposing discharge groove  114  and the opposing suction groove  118  in response to the rotation of the outer rotor  130 . Thereby, it is possible to limit sticking of the outer rotor  130  to the recessed bottom portion  116   c  and the pump cover  112 . 
     A fuel pressure (discharge pressure) in an inside of the discharge passage  117  is axially exerted against the inner rotor  120  and the outer rotor  130  toward the suction passage  112   a . A fuel pressure in the opposing discharge groove  114  is also the discharge pressure and is axially exerted against the inner rotor  120  and the outer rotor  130  toward the electric motor  104  side. Since the opposing discharge groove  114  is axially opposed to the discharge passage  117 , the fuel pressure of the opposing discharge groove  114  and the fuel pressure of the discharge passage  117  are balanced with each other. Therefore, it is possible to limit tilting of the inner rotor  120  and the outer rotor  130 , which would be otherwise caused by the discharge pressure. 
     Similarly, since the opposing suction groove  118  is axially opposed to the suction groove  113 , the fuel pressure (the suction pressure) of the opposing suction groove  118  and the fuel pressure (the suction pressure) of the suction groove  113  are balanced with each other. Therefore, it is possible to limit tilting of the inner rotor  120  and the outer rotor  130 , which would be otherwise caused by the suction pressure. 
     The external teeth  124   a  and the internal teeth  132   a  are shaped to have a trochoid tooth profile. The number of the internal teeth  132   a  is set to be larger than the number of the external teeth  124   a  by one. The inner rotor  120  is meshed with the outer rotor  130  due to the eccentricity in the eccentric direction De. In this way, the pump chambers  140  are radially formed between the internal teeth  132   a  and the external teeth  124   a  in the receiving space  156 . A volume of each pump chamber  140  is increased and decreased through the rotation of the outer rotor  130  and the rotation of the inner rotor  120 . 
     The volume of each of opposing ones of the pump chambers  140 , which are axially opposed to and communicated with the suction groove  113  and the opposing suction groove  118 , is increased in response to the rotation of the inner rotor  120  and the rotation of the outer rotor  130 . Thereby, the fuel is drawn from the suction passage  112   a  into the corresponding pump chambers  140  through the suction groove  113 . At this time, since the width (radial extent) of the suction groove  113  progressively increases from the start end part  113   c  to the terminal end part  113   d  in the rotational direction Ri, Ro (also see  FIG. 2 ), the amount of fuel drawn into the pump chamber  140  through the suction groove  113  corresponds to the amount of increase in the volume of the pump chamber  140 . 
     The volume of each of opposing ones of the pump chambers  140 , which are axially opposed to and communicated with the discharge passage  117  and the opposing discharge groove  114 , is decreased in response to the rotation of the inner rotor  120  and the rotation of the outer rotor  130 . Therefore, simultaneously with the suctioning function discussed above, the fuel is discharged from the corresponding pump chamber  140  into the high pressure passage  106  through the discharge passage  117 . At this time, since the width (radial extent) of the discharge passage  117  progressively decreases from the start end part  117   c  to the terminal end part  117   d  in the rotational direction Ri, Ro (also see  FIG. 3 ), the amount of fuel discharged from the pump chamber  140  through the discharge passage  117  corresponds to the amount of decrease in the volume of the pump chamber  140 . 
     The joint member  160  is made of synthetic resin, such as poly phenylene sulfide (PPS). The joint member  160  relays the rotatable shaft  104   a  to the inner rotor  120  to rotate the inner rotor  120  in the circumferential direction. The joint member  160  includes the main body  162  and the legs  164 . 
     The main body  162  is installed in the installation space  158 , which is formed in the pump cover  112 . A fitting hole  162   a  is formed in a center of the main body  162 , and thereby the main body  162  is shaped into a circular ring form. When the rotatable shaft  104   a  is fitted into the fitting hole  162   a , the main body  162  is securely fitted to the rotatable shaft  104   a  to rotate integrally with the rotatable shaft  104   a.    
     The number of the legs  164  corresponds to the number of the insertion holes  127  of the inner rotor  120 . Specifically, in order to reduce or minimize the influence of the torque ripple of the electric motor  104 , the number of the legs  164  is different from the number of the magnetic poles and the number of the slots of the electric motor  104  and is thereby set to five (5), which is a prime number, in the present embodiment. The legs  164  axially extend from a plurality of locations (five locations in the present embodiment), respectively, on a radially outer side of the fitting hole  162   a , which is a fitting location of the main body  162 . The legs  164  are arranged one after another at equal intervals in the circumferential direction. Each leg  164  is resiliently deformable because of the resilient material and the axially elongated shape of the leg  164 . When the rotatable shaft  104   a  is rotated, each leg  164  is flexed through the resilient deformation thereof in conformity with the corresponding insertion hole  127 . Thereby, the leg  164  contacts an inner wall of the insertion hole  127  while absorbing circumferential dimensional errors of the insertion hole  127  and the leg  164  generated at the manufacturing. In this way, the joint member  160  transmits the drive force of the rotatable shaft  104   a  to the inner rotor  120  through the legs  164 . 
     Next, the shape of the suction groove  113  will be described with reference to  FIGS. 2 and 5 to 7 . 
     As shown in  FIGS. 2 and 5 to 7 , an edge E of a portion of the pump housing  110 , which forms the suction groove  113  (hereinafter referred to as an edge E of the suction groove  113 ), includes chamfered edge parts E 3 , E 4 , E 5 , which are chamfered, and unchamfered edge parts E 1 , E 2 , which are not chamfered and are not rounded. As shown in  FIGS. 2 and 3 , each of the opposing suction groove  118 , the opposing discharge groove  114  and the discharge passage  117  is chamfered along its entire peripheral edge, so that an unchamfered edge part is not formed in each of the opposing suction groove  118 , the opposing discharge groove  114  and the discharge passage  117 . 
     Each of the unchamfered edge parts E 1 , E 2  is formed as a right-angled edge part. That is, one of two intersecting surfaces, which intersect with each other at a right angle to form the unchamfered edge part E 1 , E 2 , extends continuously from and is in parallel with a slide surface of the pump cover  112 , along which the inner rotor  120  or the outer rotor  130  slides. The other one of the two intersecting surfaces, which form the unchamfered edge part E 1 , E 2 , extends continuously from and is in parallel with an inside wall surface of the suction groove  113 , i.e., an inner-side wall surface  1121   a  and an outer-side wall surface  1122   a , which will be described later with reference to  FIG. 7 . The unchamfered edge parts E 1 , E 2  are located in a direct-inflow region A of the suction groove  113 , which overlaps with the suction passage  112   a  in a view taken in a direction of the rotational axis, such that the unchamfered edge part E 1  is located at a radially outer-side part of the edge E, and the unchamfered edge part E 2  is located at a radially inner-side part of the edge E that is opposed to the radially outer-side part of the edge E in the radial direction. 
     A portion of the suction groove  113 , which is located in the direct-inflow region, will be referred to as a direct-inflow portion  1131 . Other portions of the suction groove  113 , which are located in other regions (peripheral regions B 1 , B 2 ) that are other than the direct-inflow region A, will be referred to as the peripheral portions  1132 . The diagonal lines in the peripheral regions B 1 , B 2  of  FIG. 2  indicate the extents of the peripheral portions  1132 . 
     Each of the unchamfered edge parts E 1 , E 2  is angled at 90 degrees (the right angle). In contrast, each of the chamfered edge parts E 3 , E 4 , E 5  is shaped to tilt at 45 degrees, i.e., is pitched at 45 degrees (see  FIG. 7 ). That is, the tilt surface of each chamfered edge part E 3 , E 4 , E 5  is tilted at 45 degrees relative to the slide surface of the pump cover  112  and is tilted at 45 degrees relative to the inside wall surface of the suction groove  113  (relative to the corresponding one of the inner-side wall surface  1121   a  and the outer-side wall surface  1122   a  described later). Each of the chamfered edge parts E 3 , E 4 , E 5  is located in a corresponding one of the peripheral regions B 1 , B 2 , which are other than the direct-inflow region A. Furthermore, each of the chamfered edge parts E 3  is located at a radially outer side of the corresponding one of the peripheral edge regions B 1 , B 2  in the radial direction of the rotational axis. Each of the chamfered edge parts E 4  is located at a radially inner side of the corresponding one of the peripheral edge regions B 1 , B 2  in the radial direction of the rotational axis. The edge parts E 5  are located at the start end part  113   c  and the terminal end part  113   d , respectively. 
     As discussed above, the unchamfered edge parts E 1 , E 2  are located in the direct-inflow region A. Furthermore, connections Er (see  FIG. 6 ), each of which directly connects between a corresponding one of the chamfered edge parts E 3 , E 4 , E 5  and a corresponding one of the unchamfered edge parts E 1 , E 2 , are also located in the direct-inflow region A. Each of the connections Er is shaped into a curved form, which is recessed in an enlarging direction of the width of the suction groove  113 , in the view taken in the direction of the rotational axis. A radial extent (a width w 1 ) of the direct-inflow portion  1131  is larger than a radial extent (a width w 2 ) of the peripheral portion  1132 . That is, an outline (contour) of the suction groove  113  is shaped to extend in parallel with a rotational path of the external teeth  124   a  and a rotational path of the internal teeth  132   a . The chamfered edge parts E 3 , E 4  are located on an inner side of the outline of the suction groove  113 . Therefore, the width w 2  of the peripheral portion  1132  is smaller than a width (a radial extent) of the outline of the suction groove  113 , and the width w 1  of the direct-inflow portion  1131  coincides with the width of the outline of the suction groove  113 . 
     Next, the manufacturing procedure of the unchamfered edge parts E 1 , E 2 , the chamfered edge parts E 3 , E 4 , E 5  and the connections Er will be described. First of all, the chamfered edge parts E 3 , E 4 , E 5  are formed from the pump casing  116  side of the pump cover  112  through a cutting process (first step). Thereafter, the groove bottom portion  113   e  is drilled with a drill in a cutting process to communicate the suction groove  113  to the suction passage  112   a . At the time of executing the cutting process to form the hole (the direct-inflow portion  1131 ) through the groove bottom portion  113   e , the unchamfered edge parts E 1 , E 2  and the connections Er are formed (second step). 
     Next, the shape of the suction passage  112   a  will be described with reference to  FIG. 7 . Although an upstream portion of the suction passage  112   a  has a circular cross section in an axial view, a downstream portion of the suction passage  112   a  is shaped to have a radially inner-side step and a radially outer-side step, which are different from each other. Specifically, in the pump cover  112 , a radially inner side of the suction passage  112   a  is formed by an inner-side wall portion  1121 , and a radially outer side of the suction passage  112   a  is formed by an outer-side wall portion  1122 . The inner-side wall portion  1121  and the outer-side wall portion  1122  have steps  1121   b ,  1122   b , respectively, which reduce a passage cross-sectional area of the downstream side portion of the suction passage  112   a  in comparison to a passage cross-sectional area of the upstream side portion of the suction passage  112   a.    
     A wall surface of the inner-side wall portion  1121 , which is located on the downstream side of the step  1121   b , is referred to as the inner-side wall surface  1121   a , and a wall surface of the outer-side wall portion  1122 , which is located on the downstream side of the step  1122   b , is referred to as the outer-side wall surface  1122   a . The inner-side wall surface  1121   a  and the outer-side wall surface  1122   a  extend in parallel with a suction center line Cs of the upstream portion of the suction passage  112   a . The suction center line Cs is parallel with the inner center line Ci and the outer center line Co. An axial length of the inner-side wall surface  1121   a  is set to be larger than an axial length of the outer-side wall surface  1122   a . For example, the axial length of the inner-side wall surface  1121   a  is set to be at least five times larger than the axial length of the outer-side wall surface  1122   a.    
     Thereby, a flow velocity of the fuel, which flows along the inner-side wall surface  1121   a , is increased in comparison to a flow velocity of the fuel, which flows along the outer-side wall surface  1122   a . That is, there is formed a flow velocity distribution in the direct-inflow portion  1131  of the suction groove  113  such that the flow velocity of the fuel at the radially inner-side part of the direct-inflow portion  1131  is higher than the flow velocity of the fuel at the radially outer-side part of the direct-inflow portion  1131 . 
     Advantages of the present embodiment will now be described. 
     In the present embodiment, the edge E of the portion of the pump housing  110 , which forms the suction groove  113 , includes the chamfered edge parts E 3 , E 4 , E 5 , which are chamfered, and the unchamfered edge parts E 1 , E 2 , which are not chamfered and are not rounded. Each of the unchamfered edge parts E 1 , E 2  is located in the direct-inflow region A, and each of the chamfered edge parts E 3 , E 4 , E 5  is located in the corresponding one of the peripheral regions B 1 , B 2 , which are other than the direct-inflow region A. 
     A suction velocity of the fuel in the direct-inflow region A of the suction groove  113  is higher than a suction velocity of the fuel in the peripheral regions B 1 , B 2 . Therefore, in comparison to the fuel, which flows from the peripheral region B 1  into the pump chamber  140 , the fuel, which flows from the direct-inflow region A into the pump chamber  140 , is more likely to generate cavitation. Therefore, it is advantageous to form the unchamfered edge part(s) in the edge E of the direct-inflow region A for the purpose of limiting or reducing the cavitation to improve the pump efficiency. 
     In contrast, it is advantageous to chamber the part(s) of the edge E, which is located in the peripheral region B 1 , to reduce the pump loss at the time of distributing the fuel (fluid) from the suction groove  113  to the pump chamber  140  and thereby to improve the pump efficiency. A main flow direction of the fuel (direct-inflow fuel), which flows from the direct-inflow region A into the pump chamber  140 , is the direction of the rotational axis (axial direction). In contrast, a flow direction of the fuel (peripheral fuel), which flows from the peripheral region B 1 , B 2  into the pump chamber  140 , is spread into the radially outer direction, the radially inner direction, the rotational direction and the direction of the rotational axis. 
     That is, it is effective to limit or reduce the cavitation of the direct-inflow fuel at the direct-inflow region A in terms of the pump efficiency improvement. In contrast, in terms of the pump efficiency improvement, it is effective to prioritize the limiting or reducing of the pressure loss of the peripheral fuel at the peripheral region B 1 , B 2  at the time of distributing the fuel from the peripheral region B 1 , B 2  to the pump chamber  140  over the limiting or reducing of the cavitation. 
     In view of the above points, according to the present embodiment, the unchamfered edge part E 1 , which is not chamfered and is not rounded, is located in the direct-inflow region A, and the chamfered edge parts E 3  are located in the peripheral regions B 1 , B 2 . Therefore, the generation of the cavitation in the direct-inflow fuel can be limited or reduced, and the pressure loss of the peripheral fuel can be limited or reduced. Thus, the pump efficiency can be improved. That is, the flow velocity energy of the discharge fuel can be obtained with the relatively small electric power consumption. 
     Furthermore, the unchamfered edge parts E 1 , E 2  are located at the radially outer-side part and the radially inner-side part, respectively, of the direct-inflow region A. Therefore, the cavitation of the fuel, which flows along the inner-side wall surface  1121   a , is reduced, and the cavitation of the fuel, which flows along the outer-side wall surface  1122   a , is also reduced. 
     Furthermore, the unchamfered edge parts E 1 , E 2  are formed to increase the radial extent of the passage cross-sectional area of the suction groove  113  by the amount, which corresponds to the radial extent of the chambered edge parts E 3 , E 4 . Therefore, since the width w 1  of the direct-inflow portion  1131  becomes larger than the width w 2  of the peripheral portion  1132 , the flow quantity of the direct-inflow fuel can be increased by the amount, which corresponds to a difference between the width w 1  of the direct-inflow portion  1131  and the width w 2  of the peripheral portion  1132 . 
     Furthermore, in the present embodiment, the connections Er, each of which connects between the corresponding chamfered edge part E 3 , E 4  and the corresponding unchamfered-edge part E 1 , E 12 , are located in the direct-inflow region A. Therefore, at the time of forming the unchamfered edge parts E 1 , E 2  and the connections Er through the cutting process in the direct-inflow region A after chamfering of all of the direct-inflow region A and the peripheral regions B 1 , B 2 , the cutting process of forming the unchamfered edge parts E 1 , E 2  and the connections Er can be executed in the state where a drill bit of the drill is held in the suction passage  112   a . Therefore, the processability of the unchamfered edge parts E 1 , E 2  and the connections Er can be improved. 
     Other Embodiments 
     The present disclosure has been described with respect to the one embodiment. However, the present disclosure is not limited to the above embodiment, and the above embodiment may be modified in various ways within a principal of the present disclosure. 
     In the embodiment shown in  FIG. 6 , the unchamfered edge parts E 1 , E 2  are located at the radially outer-side part and the radially inner-side part, respectively, of the direct-inflow region A. Alternatively, the unchamfered edge part may be formed only at one of the radially outer-side part and the radially inner-side part of the direct-inflow region A, and the other one of the radially outer-side part and the radially inner-side part of the direct-inflow region A may be chamfered. 
     In the embodiment shown in  FIG. 6 , the connections Er and the unchamfered edge parts E 1 , E 2  are formed from the pump casing  116  side of the pump cover  112  through the cutting process. Alternatively, the connections Er and the unchamfered edge parts E 1 , E 2  may be formed from the opposite side of the pump cover  112 , which is opposite from the pump casing  116 . 
     In the embodiment shown in  FIG. 4 , the external teeth  124   a  and the internal teeth  132   a  are shaped to have the trochoid tooth profile. Alternatively, the external teeth  124   a  and the internal teeth  132   a  may be shaped to have any other suitable type of tooth profile, such as a cycloid tooth profile or a profile of a combination of various curved lines. 
     The subject fluid to be pumped with the fluid pump  101  is not limited to the light oil (diesel fuel) and may be any other liquid fuel, such as gasoline or alcohol. Furthermore, the subject fluid to be pumped with the fluid pump  101  is not limited to the fuel and may be liquid, such as hydraulic oil used in a hydraulic actuator or any of various lubricant oils. The fluid pump  101  is not limited to the fluid pump installed in the vehicle. 
     In the embodiment shown in  FIG. 1 , the present disclosure is implemented in the fluid pump  101  that has the pump main body  103  and the electric motor  104 , which are integrated together. However, the electric motor  104  may not be provided in the fluid pump  101  of the present disclosure, and the electric motor  104  may be formed separately from the rest of the fluid pump  101 . In the embodiment shown in  FIG. 1 , the inner rotor  120  is driven by the electric motor  104 . Alternatively, the inner rotor  120  may be driven to rotate by a portion of a drive force for driving the vehicle, such as a drive force of a crankshaft of an internal combustion engine of the vehicle. 
     In the embodiment shown in  FIG. 1 , the discharge passage  117  is located on the opposite side of the pump housing  110 , which is opposite from the suction passage  112   a  in the axial direction. Alternatively, the discharge passage  117  and the suction passage  112   a  may be placed on the same axial side of the pump housing  110 .