Patent Publication Number: US-6702546-B2

Title: Turbine fuel pump

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is based upon, claims the benefit of priority of, and incorporates by reference, the contents of Japanese Patent Applications No. 2001-232749 filed Jul. 31, 2001 and No. 2002-124745 filed Apr. 25, 2002. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a turbine fuel pump for pressure-feeding fuel from a fuel tank to a fuel injection apparatus on a vehicle. 
     2. Description of the Related Art 
     A turbine fuel pump may be used for pressure-feeding fuel in a fuel tank to a fuel injection apparatus on a vehicle such as an automobile. The turbine fuel pump (also referred to as a “Westco pump”) generally includes a disk-shaped impeller having multiple blades and blade grooves alternately formed along the circumference on an outer peripheral surface of the impeller, a motor housing that has C-shaped pump flow passages communicating to the blade grooves and that also stores the rotating impeller, and a motor for driving the impeller. 
     There have been needs for increasing the efficiency of a fuel supply apparatus including a fuel pump in view of decreasing fuel consumption of vehicles and atomizing fuel for low emissions. For these purposes, the shape of the blades and the blade grooves of the impeller, and the shape of a fuel outlet opening to which a terminal end of a pump flow passage of the motor housing communicates, have been improved. 
     However, a smooth flow of fuel at a fuel inlet opening, with which a start end of the pump passage of the motor housing communicates, has not been sufficiently studied. For example, in a turbine fuel pump in FIG.  12  and FIG. 13 (see Japanese Patent Laid-Open Publication No. Hei. 11-117890), a motor housing  120  is attached to a pump housing  135 , and comprises a pump cover  122  on one side (a bottom side)  131  of the impeller  130 , and a pump casing  126  on the other side (a top side)  132  of the impeller  130 . 
     The pump cover  122  and the pump casing  126  form a circular impeller storage space, and a C-shaped pump flow passage  125 . A fuel inlet opening  123  is formed on the pump cover  122  for communicating to a start end  125   a . A fuel outlet opening  127  is formed on the pump casing  126  for communicating to a terminal end  125   b  of the pump flow passage  125 . The impeller  130  has multiple blades  133  and blade grooves  134  alternately formed on an outer periphery, and is stored in the impeller storage space. The blade grooves  134  communicate to the pump flow passage  125 . 
     The fuel inlet opening  123  passes through the pump cover  122  in the axial direction (in the vertical direction in FIG.  12 ). Thus, the flow direction of the fuel drawn from the fuel inlet opening  123  into the start end  125   a  is orthogonal to the rotational direction of the impeller  130 , and is orthogonal to the flow direction of the fuel in the pump flow passage  125 . The direction of the fuel flow changes by almost a right angle at the start end  125   a.    
     As a result, the flow rate of the fuel decreases at the start end  125   a , and a loss of pressure (a pressure loss) is generated in the fuel. Consequently, a local negative pressure is generated in the fuel pressure at the start end  125   a , a part of the fuel is vaporized, and the flow quantity decreases accordingly in the pump flow passage  125 . Especially when the temperature of the fuel is high, the local negative pressure increases the effect of vaporizing the fuel, and the flow quantity of the fuel markedly decreases. 
     Then, the flow quantity of the pressure-fed fuel from the start end  125   a  to the terminal end  125   b  decreases, and the outlet quantity from the fuel outlet opening  127  decreases. Thus, problems such as the pump efficiency scarcely increases, and the pump performance decreases when the fuel temperature is high. 
     SUMMARY OF THE INVENTION 
     The present invention was devised in view of the above problems, and an object is to provide a turbine fuel pump for preventing a pressure loss at the start end of the pump flow passage and for preventing the accompanying resultant local negative pressure. Additionally, increasing pump efficiency and overall operating performance while at a high temperature is a goal. 
     The present inventor studied a constitution of a first housing where a direction of drawing the fuel at the start end of the side groove on the inlet side is not orthogonal to the rotational direction of the impeller, and is not orthogonal to the fuel flow direction in the side groove on the inlet side. As a result, such an idea as the fuel inlet opening not being made as a port (an opening) but as a fuel inlet passage having a predetermined length was devised resulting in completion of the present invention. 
     A turbine fuel pump of a first aspect of the present invention includes a disk-shaped impeller provided with multiple blades and multiple blade grooves formed alternately around a circumference on a first surface and on an outer periphery of the second surface, and a pump housing for storing the impeller during rotation. 
     The pump housing includes a disk-like first housing provided on a first side of the impeller, and a disk-like second housing provided on a second side of the impeller. The first housing includes a side groove on an inlet side, and a fuel inlet passage. The side groove on the inlet side is formed on an inner side surface of the first housing, and extends from a start end to a terminal end in approximately a C-shape. 
     The fuel inlet passage extends from the start end of the side groove on the inlet side toward the inside in the radial direction, and simultaneously toward the terminal end, and has an opening on an outer side surface of the first housing. The second housing includes a side groove on an outlet side, and a fuel outlet opening. The side groove on an outlet side is formed on an inner side surface of the second housing, and extends from a start end to a terminal end in approximately a C-shape. The fuel outlet opening communicates to the terminal end of the side groove on the outlet side. The impeller rotates to increase the pressure of fuel while the fuel drawn from the fuel inlet passage is being transported to the fuel outlet opening. 
     In this fuel pump, the fuel inlet passage extends from the start end toward the terminal end of the side groove on the inlet side, and has the opening on the outer side surface. Thus, the fuel flowing from the fuel inlet passage to the start end is not orthogonal to the fuel flow in the side groove on the inlet side, and is not orthogonal to the rotational direction of the impeller. As a result, the decrease of the flow rate when the inlet fuel merges is small, the loss of the pressure is prevented at the start end, and the inlet fuel smoothly merges with the fuel in the side groove on the inlet side. Additionally, since a centrifugal force is applied to the fuel in the fuel inlet passage, the fuel flow rate increases. 
     A turbine fuel pump of an eleventh aspect of the present invention includes a disk-shaped impeller provided with multiple blades and multiple blade grooves formed alternately in the circumferential direction on a first surface and on a second surface around an outer periphery. Additionally, a pump housing is provided for storing said rotating impeller. The pump housing includes a disk-like first housing provided on one side of the impeller, and a disk-like second housing provided on the other side of the impeller. 
     The first housing includes a side groove on an inlet side, and a fuel inlet passage. The side groove on the inlet side is formed on an inner side surface of the first housing, and extends from a start end to a terminal end in approximately a C-shape. The fuel inlet passage extends from the start end of the side groove on the inlet side to an opening on an outer side surface of the first housing. The opening is positioned on the inside of the start end in the radial direction, and simultaneously on a side close to the terminal end in the circumferential direction. 
     The second housing includes a side groove on an outlet side in approximately a C-shape formed on an inner side surface thereof, and a fuel outlet opening communicating to a terminal end of the side groove on the outlet side. The impeller rotates to increase a fuel pressure while the fuel drawn from the fuel inlet passage is being transported to the fuel outlet opening. 
     In this fuel pump, the opening on the outer side surface of the first housing is placed on the inside of the start end in the radial direction, and on a side close to the terminal end in the circumferential direction. Thus, the fuel flowing from the fuel inlet passage to the start end is not orthogonal to the fuel flow in the side groove on the inlet side and the rotational direction of the impeller. As a result, the decrease of the flow rate when the inlet fuel merges is small, the loss of the pressure is prevented at the start end, and the inlet fuel smoothly merges with the fuel in the side groove on the inlet side. Additionally, because a centrifugal force is applied to the fuel in the fuel inlet passage, its flow rate increases. 
     In turbine fuel pumps of second and twelfth aspects, the fuel inlet passage extends linearly in the turbine fuel pumps as in the first and eleventh aspects. With these fuel pumps, the fuel flows smoothly in the fuel inlet passage. 
     In turbine fuel pumps of third and thirteenth aspects, the fuel inlet passage is tilted or angled with respect to a tangent of the start end in a plan view of the inner side surface of the first housing in the turbine fuel pumps of the second and twelfth aspects. With these fuel pumps, the fuel inlet direction is not orthogonal to the fuel flow in the side groove on the inlet side. Thus, the flow rate does not sharply decrease at the start end, and the loss of pressure is prevented. 
     In turbine fuel pumps of the fourth and fourteenth aspects, the fuel inlet passage is tilted with respect to a bottom surface of the side groove on the inlet side in a section in the axial direction of the turbine fuel pump as in the turbine fuel pumps of the second and twelfth aspects. With these fuel pumps, the inlet direction of the fuel is not orthogonal to the rotational direction of the impeller. Thus the flow rate does not sharply decrease at the start end, and the fuel smoothly flows into the blade grooves. 
     In turbine fuel pumps of the fifth and fifteenth aspects, the length of the inlet passage is twice to four times the thickness of the first housing in the turbine fuel pumps of the first and eleventh aspects. With these fuel pumps, since the fuel inlet passage is not too long, the pressure loss is small while the fuel is flowing through the fuel inlet passage. 
     In a turbine fuel pump of a sixth aspect, the fuel inlet passage includes a tilted groove that is tilted with respect to the bottom surface of the side groove on the inlet side, which gradually increases its depth, and a through hole tilted with respect to the tilted groove, and having an opening on the outer side surface of the first housing in the turbine fuel pump of the fourth aspect. With this fuel pump, the fuel smoothly flows through the fuel inlet passage. 
     In a turbine fuel pump of a seventh aspect, a boundary between the fuel inlet passage and the side groove on the inlet side is rounded as in the turbine fuel pumps of the fourth aspect. With this fuel pump, the fuel flows even more smoothly through the fuel inlet passage. 
     In a turbine fuel pump of an eighth aspect, the side groove on the inlet side includes an inner side groove and an outer side groove concentrically formed as in the turbine fuel pump of the first aspect. A start end of the inner side groove and a start end of the outer side groove are formed in the fuel inlet passage. With this fuel pump, the flow quantity of the pressure-fed fuel is doubled to increase the pump efficiency, and simultaneously, the one fuel inlet passage is shared by the two side grooves on the inlet side. 
     In a turbine fuel pump of a ninth aspect, the impeller includes multiple communication holes passing from one surface to another surface inside the multiple blades and the multiple blade grooves in the radial direction on one surface and on the other surface as in the turbine fuel pump of the first aspect. With this fuel pump, since the fuel flows through the communication holes at the start end and the terminal end of the pump flow passage, it is not necessary to form communication parts in the first housing and the second housing. 
     In a turbine fuel pump of a tenth aspect, a first communication part is formed on the outer peripheral side of the start end of the side groove on the inlet side in the turbine fuel pump of the first aspect. A second communication part is formed on the outer peripheral side of the terminal end of the side groove on the inlet side. A third communication part is formed on the outer peripheral side of the start end of the side groove on the outlet side. A fourth communication part is formed on the outer peripheral side of the terminal end of the side groove on the outlet side. The first communication part communicates to the third communication part, and the second communication part communicates to the fourth communication part. With this fuel pump, since the fuel flows through the first to fourth communication parts of the pump housing on the start end and the terminal end of the pump flow passage, it is not necessary to form communication holes on the impeller. 
     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front sectional view showing a turbine fuel pump of a first embodiment of the present invention; 
     FIG. 2 is an enlarged view of a principal part of FIG. 1; 
     FIG. 3A is a plan view of the pump cover of the first embodiment as seen from the inside; 
     FIG. 3B is a plan view of the pump cover as seen from the outside; 
     FIG. 4 is a sectional view taken along the line  4 — 4  in FIG. 3A; 
     FIG. 5A is a plan view of a pump casing of the first embodiment as seen from the inside, 
     FIG. 5B is a plan view of the pump casing as seen from the outside; 
     FIG. 6 is a vertical cross-sectional view of a principal part showing a turbine fuel pump of a second embodiment of the present invention; 
     FIG. 7 is a vertical cross-sectional view taken along the line  7 — 7  in FIG. 6; 
     FIG. 8A is a plan view of a pump cover of the second embodiment as seen from the inside; 
     FIG. 8B is a cross-sectional view taken along line  8 — 8  in FIG. 8A; 
     FIG. 9 is a plan view of a pump casing of the second embodiment as seen from the outside; 
     FIG. 10 is a descriptive plan view showing a relationship between the pump cover and an impeller of the second embodiment; 
     FIG. 11 is a plan view of a principal part showing a modification of the first embodiment; 
     FIG. 12 is a front cross-sectional view of a principal part showing a conventional turbine fuel pump; and 
     FIG. 13 is a plan view of a pump cover of the conventional turbine fuel pump as seen from the inside. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
     Impeller 
     The drawings show an impeller that has a disk-like shape. The first and second housings guide both side surfaces of the impeller at the center. On its outer periphery, partitions extending in the radial direction and the circumferential direction are formed. On a first side surface and on a second side surface, multiple blades and multiple blade grooves are alternately formed in the circumferential direction. 
     There is no restriction on the specific shape and the number of rows of the blades and blade grooves. For example, the blade grooves on the first side surface may be formed opposite the same positions of the blade grooves on the second side surface in the circumferential direction. Or the blade grooves on the one side surface may be displaced (formed staggeredly) with respect to the blade grooves on the other side surface. The blades on the one side surface and the other side surface may extend parallel to the axis of the impeller, or they may be angled with respect to the axis. 
     The impeller may have multiple communication holes passing in the axial direction through a part inside in the radial direction of the blades and the blade grooves on the one side surface and on the other side surface. These communication holes serve as communication passages from the start end of the side groove on the inlet side to the start end of the side groove on the outlet side. They also serve as communication passages from the terminal end of the side groove on the inlet side to the terminal end of the side groove on the outlet side. 
     Pump Housing 
     (1) The following section describes a pump housing that has an overall disk shape. The pump housing includes a disk-shaped first housing (a pump cover) on the one side of the impeller, and a disk-shaped second housing (a pump casing) on the other side of the impeller. The pump cover and the pump casing may have approximately symmetric storage shapes, or the pump cover may be a disk shape and the pump casing may be a storage shape. In either case, the first housing and the second housing define an impeller storage space in a flat disk shape and the pump flow passage in approximately a C-shape extending from a start end to a terminal end. 
     The “approximately C-shape” means a shape which curves from the start end to the terminal end, and the start end and the terminal end are slightly separated in the circumferential direction. The curvature of the “approximately C-shape” may be constant or may not be constant. When the curvature of the pump flow passage is constant, it may continue almost half way around or almost completely around. 
     (2) First Housing 
     The following section describes the first housing. A side groove on an inlet side extends from a start end to a terminal end in the approximately C-shape, and is formed on the inner side surface along the outer periphery of the first housing. There is no specific restriction on the sectional shape and the number of the side groove on the inlet side. 
     In the first housing, a fuel inlet passage extends from the start end of the side groove on the inlet side to an opening on the outer side surface, and this passage is directed toward the inside in the radial direction, and simultaneously toward the terminal end. More specifically, the fuel flow passage is formed in a region enclosed by an extension in the tangential direction at the start end, and a line connecting the start end of the side groove on the inlet side and the center of the first housing in a plan view of the inner side surface of the first housing. The relative position of the opening with respect to the start end determines the tilt direction of the fuel inlet passage in the plan view, and the tilt angle and length of the fuel inlet passage in the sectional view in the axial direction of the fuel pump. 
     In terms of the tilt direction, for example, when the opening is placed inside the start end in the radial direction, and simultaneously on the terminal end side on the extension, the passage bends at the start end toward the center, and forms acute angles with respect to the extension and the connection line. When the opening is too close to the extension, the direction of the fuel flow greatly changes. When the opening is too close to the connection line, the distance to the terminal end is too short, and seal capability between the start end and the terminal end decreases. 
     The tilt angle of the fuel inlet passage with respect to the bottom surface of the side groove on the inlet side has a close relationship with the length of the fuel inlet passage in the first housing as shown in the axial cross section. When the tilt angle is large, the length becomes small. When the tilt angle is small, the length becomes large. The tilt angle can be an acute angle, and the length can be twice to four times of the thickness of the first housing. 
     The fuel inlet passage may extend linearly, may curve, or may bend between the start end and the opening. For example, the fuel inlet passage may comprise a through hole and a tilted groove. The through hole has a predetermined first acute angle with respect to the inner side surface of the first housing or an extension of the side groove on the inlet side, and passes through the pump cover. The tilted groove has a predetermined second acute angle smaller than the first acute angle with respect to the inner side surface of the first housing (the pump cover), and connects the side groove and the through hole with each other. 
     The sectional area of the fuel flow passage may be constant or may change gradually between the start end and the opening. Further, it is preferred that a boundary between the fuel flow passage and the side groove on the inlet side be rounded. 
     A first communication part may be formed on the outer peripheral side of the start end of the side groove on the inlet side, and a second communication part may be formed on the outer peripheral side of the terminal end of the side groove on the inlet side. 
     Second Housing 
     The following section describes the second housing. An approximately C-shaped side groove on an outlet side is formed along the outer peripheral edge of the inner side surface of the second housing. There is no restriction on the sectional shape and the number of the side groove on the outlet side. However, the number is the same as that of the side groove on the inlet side. There is no restriction on the constitution of a fuel outlet opening. 
     A third communication part communicating to the first communication part may be formed on the outer peripheral side of the start end of the side groove on the outlet side. A fourth communication part communicating to the second communication part may be formed on the outer peripheral side of the terminal end of the side groove on the outlet side. When the impeller does not have the communication holes for the fuel, the fuel flows from the side groove on the inlet side to the side groove on the outlet side through the first communication part and the third communication part at the start end of the pump flow passage. Also, the fuel flows from the side groove on the inlet side to the side groove on the outlet side through the second communication part and the fourth communication part at the terminal end of the pump flow passage. 
     First Embodiment 
     The following describes a first embodiment of the present invention while referring to FIG. 1 to FIG.  5 . 
     In FIG. 1, a turbine fuel pump is roughly separated into an upper motor part  10  and a lower pump part  35 . 
     Constitution 
     (1) Motor Part 
     The motor part  10  includes a motor housing  11  and an armature  16 . A motor cover  12  is attached to the upper end of the cylindrical motor housing  11  with openings on both ends. Brushes (not shown) are integrated into the motor cover  12 , and slidingly contact with a commutator  14  of the armature  16 . An outlet opening  18  is provided on the motor cover  12 . A pump casing  40  and a pump cover  26  described later are attached to the bottom end of the motor housing  11 . 
     A motor room  13  is formed between the motor cover  12  and the pump casing  40 . The armature  16 , including the commutator  14 , is placed in the motor room  13 . The motor cover  12  rotatingly supports a top end part  17   a  of a shaft  17  of the armature  16 . The pump cover  26  rotatingly supports a bottom end part  17   b  thereof. A pair of magnets  19  are fixed to an inner side surface of the motor housing  11 . 
     (2) Pump Part 
     The pump part  35  includes a pump housing  38  and an impeller  50 . The pump housing  38  has a pump casing  40  and a pump cover  26 . 
     As shown in FIG.  2  and FIG. 3, the overall pump cover  26  has a disk shape. A C-shaped side groove  27  is formed along the outer peripheral edge on an inner side surface  26   a  of the pump cover  26 . The side groove  27  extends from a start end  28  to a terminal end  29 . A first communication groove  31  is formed on the outer peripheral side of the start end  28 . A second communication groove  32  is formed on the outer peripheral side of the terminal end  29 . The first and second communication grooves  31  and  32  have a predetermined length in the circumferential direction and the axial direction, and a predetermined depth in the radial direction. 
     A fuel inlet passage  33  communicates with the start end  28 . The fuel inlet passage  33  extends from the start end  28  to an opening  36  on an outer side surface  26   c . The opening  36  is positioned on the inside with respect to the start end  28  in the radial direction, and on the opposite side with respect to the start end  28  in the circumferential direction. The opening  36  is separated from the start end  28  by about three times the thickness of the pump cover  26 . As a result, in a plan view of the inner side surface  26   a  of the pump cover  26 , the fuel inlet passage  33  has an acute angle θ 1  (about 50°) with respect to a tangent (t) passing through the start end  28  (more specifically, an extension line in the tangential direction at the start end  28 ). The fuel inlet passage  33  has an acute angle (90°-θ 1 ) with respect to a normal (n) passing through the start end  28  (more specifically, a line connecting the start end  28  and a center  26   b  with each other). Thus, the fuel inlet passage  33  extends from the start end  28 , and bends toward the center  26   b  of the pump cover  26 . 
     The fuel inlet passage  33  has a predetermined acute angle (about 20° to 25°) with respect to the inner side surface  26   a  of the pump cover  26  in a section in the axial direction (the thickness direction) of the pump cover  26 . Namely, the fuel inlet passage  33  obliquely passes through the pump cover  26  at an angle of about 70° with respect to the axial direction. More specifically, as shown in FIG.  3 A and FIG. 4, the fuel inlet passage  33  has a through hole  36  and a tilted groove  34 . The through hole  36  has a first predetermined acute angle θ 2  (about 25°) with respect to the inner side surface  26   a  of the pump cover  26 , passes from the inner side surface  26   a  to the outer side surface  26   c , and has an opening on the outer side surface  26   c . The tilted groove  34  has a second predetermined acute angle θ 3  (about 20°) with respect to the bottom surface of the side groove  27 , and gradually increases its depth from the inner side surface  26   a , where the acute angle θ 3  is smaller than the acute angle θ 2 . The tilted groove  34  smoothly connects the side groove  27  and the through hole  36  with each other. The side groove  27  and the tilted groove  34  form a C-shaped pump passage. 
     As shown in FIG.  2  and FIGS. 5A and 5B, the pump casing  40  takes a storage shape which includes a bottom wall  41  and a circumferential wall  42  around the bottom wall  41 . A side groove  43  is formed along the outer peripheral edge of the bottom wall  41 , and has the same C-shape as the side groove  27 . The side groove  43  extends from a start end  46  to a terminal end  47 . A third communication groove  48  is formed on the outer peripheral side of the start end  46 . A fourth communication groove  49  is formed on the outer peripheral side of the terminal end  47 . The third and fourth communication grooves  48  and  49  have a predetermined length in the circumferential direction and the axial direction, and a predetermined depth in the radial direction. The third communication groove  48  communicates to the first communication groove  31 . The fourth communication groove  49  communicates to the second communication groove  32 . 
     A fuel outlet opening (not shown) communicates to the terminal end  47 , passes through the pump casing  40  parallel with the axis, and has an opening on an outer side surface  40   b . The fuel outlet opening communicates to the pump room  13  (See FIG.  1 ). 
     (3) Impeller 
     The following describes the impeller  50 . As shown in FIG. 2, the impeller  50  is disk-shaped. Multiple blades and blade grooves  52  are alternately formed in the circumferential direction at the outer periphery on one side and the other side of a partition wall  51 . An annular part  54  is provided on the outer peripheral surface of the partition wall  51 . The impeller  50  is stored in a storage space of the pump housing  38  for rotation. The blade grooves  52  communicate to the side grooves  27  and  43 . 
     Action and Effect 
     The following describes the action and effects of the first embodiment. When electrical power is supplied for the motor part  10 , and the armature  16  rotates, the impeller  50  attached to the bottom end part  17   b  of the shaft  17  rotates counterclockwise in FIG.  3 A. As a result, the fuel is drawn through the fuel inlet passage  33 , and circulates through the side grooves  27  and  43  from the start ends  28  and  46  to the terminal ends  29  and  47  in a spiral manner. The pressure of the fuel increases accordingly. 
     Namely, the fuel flows into the blade grooves  53  from the inner peripheral side, and flows through the blade groove  53  outward in the radial direction under a centrifugal force generated by the rotation. Then, the fuel collides with the outer peripheral wall  42 , and is separated into left and right flows. The left and right flows flow through the left and right side grooves  27  and  43  inward in the radial direction, and flow into the blade groove  53  following in the rotation direction. The fuel repeats this action, and the pressure of the fuel increases. The fuel flows into the motor room  13  from the fuel outlet opening in this pressurized state, and is discharged into a fuel supply line through the outlet opening  18 . 
     The following section details the flow of the fuel in the fuel inlet passage  33 . The fuel flows into the start end  28  of the side groove  27  through the through hole  36  and the tilted groove  34 . The through hole  36  and the tilted groove  34  form an acute angle (about 25°) with respect to the inner side surface  26   a  of the pump cover  26 , and this acute angle is much smaller than a right angle. The fuel flows inside the blade grooves  52  at this acute angle with respect to a side surface  50   a  of the impeller  50 . Then, the fuel is guided by a side surface of the partition wall  51 , and flows through the blade groove  52  outward in the radial direction. 
     The fuel inlet passage  33  forms an acute angle with respect to the extension in the tangential direction at the start end  28 , and has an acute angle with respect to the line connecting the start end  28  and the center  26   b  with each other in a plan view of the inner side surface  26   a  of the pump cover  26 . The fuel inlet passage  33  is separated from the center  26   b  by a predetermined distance. The angled directions of the through hole  36  and the angled groove  34  are close to the direction of the side surface  51   a  of the partition wall  51 . The change in the direction of the fuel flow decreases compared with that of the conventional fuel flow when the fuel flows into the side groove  27 . As a result, the pressure loss at the start ends  28  and  46  decreases, and the generation of local negative pressure is prevented. The flow rate of the fuel is increased by the centrifugal force when the fuel flows through the fuel inlet passage  33 . As a result, a decrease of the flow rate at the start end  28  is prevented. 
     Second Embodiment 
     Constitution 
     A second embodiment of the present invention will be described with reference to FIG. 6 to FIG.  10 . The first section describes the constitution of the second embodiment. The second embodiment is mainly different from the first embodiment in the constitution of an impeller  60  and the constitution of a pump cover  80  (especially a fuel inlet passage  85 ). The other constitutions of the first and the second embodiments are the same, and the following section mainly describes the different parts. 
     As FIG. 6, FIG. 7, and FIG. 10 show, blades  62  and blade grooves  63  are alternately formed in the circumferential direction on one side  61   a  of the impeller  60 . Blades  65  and blade grooves  66  are formed in the circumferential direction on the other side  61   b  of the impeller  60  in the same way. As a result, an outer peripheral annular part  68  is formed. 
     The blade grooves  63  are shifted with respect to the blade grooves  66  in the circumferential direction by a distance corresponding to half of the pitch at which these blades are formed. As shown in FIG. 7, the blade grooves  63  and  66  are angled such that an innermost side is backward with respect to an entrance side in the rotational direction X of the impeller  60 . In other words, the entrance side is forward with respect to the innermost side. The tilt angle of front wall surfaces  64   a  and  67   a  is larger than the tilt angle of the rear wall surfaces  64   b  and  67   b . As a result, the dimensions of the blade grooves  63  and  66  in the circumferential direction gradually decrease from the entrance side to the innermost side on a section which is parallel with the axis, and passes through a middle of the blade grooves  63  and  66  in the radial direction. 
     Further, the blade grooves  63  extend toward the opposite side surface  61   b  beyond the center of the impeller  60  in the axial direction. In the same way, the blade grooves  66  extend toward the opposite side surface  61   a  beyond the center of the impeller  60  in the axial direction. As a result, as shown in FIG. 6, the innermost part of the blade groove  63  and the inner most part of the blade groove  66  overlap each other in the axial direction in a section of the impeller. 
     As shown in FIG.  6  and FIG. 10, communication holes  71 , as many as there are blade grooves  63  and  66 , are formed inside the blade grooves  63  and  66  in the radial direction. The individual communication holes  71  pass through from the first side surface  61   a  to the second side surface  61   b , and have a rectangular section longer in the radial direction. 
     Shallow grooves  73  and  75  are respectively formed inside the blade grooves  63  and  66  in the radial direction on the first side surface  61   a  and the second side surface  61   b . The shallow grooves  73  and  75  are displaced by a distance corresponding to ¼ of the forming pitch of the blade grooves  63  and  66  with respect to the blade grooves  63  and  66  in the circumferential direction. With this structure, the blade grooves  63  on the first side surface  61   a  communicate to the blade grooves  66  on the second side surface  61   b  through the shallow grooves  73 , the communication holes  71 , and the shallow grooves  75 . 
     As shown in FIG.  8 A and FIG. 9, a side groove  85  extending from a start end  82  to a terminal end  83  in approximately a C-shape (see FIG.  6 ), and a fuel inlet passage  88  extending from the start end  82  to an opening  87  on an outer side surface  81   b  are formed on an inner side surface  81   a  of a pump cover  80 . As shown in FIGS. 6-7, the length in the radial direction (the width) of the side groove  85  is approximately equal to the sum of the lengths of the blade grooves  63  and  66  of the impeller  60  in the radial direction, and the length of the communication hole  71  in the radial direction. 
     As shown in FIGS. 8A and 8B, the fuel inlet passage  88  has the same acute angle θ 1  with respect to an extension in the tangential direction at the start end  82 , and the line connecting the start end  82  and the center of the pump cover  80  with each other in the plan view of the inner side surface  81   a  of the pump cover  80  as the fuel inlet passage  33  of the first embodiment (FIG.  3 A). The fuel inlet passage  88  is angled in the same direction as the fuel inlet passage  33 . In the present embodiment, the distance between the start end  82  and the opening  87  is shorter than that in the first embodiment (about a half). As a result, as shown in FIG. 8B, the length of the fuel inlet passage  88  is shorter than the fuel inlet passage  33 . 
     An angle θ 4  of the fuel inlet passage  88  with respect to the inner side surface  81   a  of the pump cover  80 , namely the bottom surface of the side groove  85  on the inlet side, is larger than the tilt angles θ 2  and θ 3  in the first embodiment. Further, a gentle slope  89  smaller in tilt angle than the other parts is formed on a boundary between the fuel inlet passage  88  and the start end  82  of the side groove  85 . 
     The first communication groove  31  and the second communication groove  32  (see FIG. 3A) in the first embodiment are not formed on the outer peripheral side of the start end  82  and the terminal end  83  of the side groove  85 . 
     A pump casing  90  has a constitution similar to that of the pump casing  40  of the first embodiment. However, the third communication groove  48  and the fourth communication groove  49  in the first embodiment are not formed on the outer peripheral side of a start end (not shown) and a terminal end  93  of a side groove. 
     Action and Effect 
     The following section describes the action and effects of the second embodiment. In the second embodiment, the tilt angle θ 4  of the fuel inlet passage  88  in the pump cover  80  is larger than that in the first embodiment, and the length of the fuel inlet passage  88  is shorter. As a result, the time and the distance of the fuel flow in the fuel inlet passage  88  are shorter, and the pressure loss decreases accordingly. 
     Also the blade grooves  63  and  66  extend beyond the center in the axial direction, and overlap in the axial direction. As a result, an effective volume is secured for increasing the momentum of the fuel flowing through the blade grooves  63  and  66 , and the pump efficiency increases. 
     Further, a part of the fuel flowing into the start end  82  of the side groove  85  from the fuel inlet passage  88  of the pump cover  80  flows to the start end of the side groove of the pump casing  90  through the shallow groove  73 , the communication hole  71  and the shallow groove  75  of the impeller  60 . Then, the fuel is transported to the terminal end  93  of the side groove by the blade groove  66  of the impeller  60 , and is pressurized. The fuel flows to the terminal end  83  of the side groove (fuel inlet passage)  85  through the shallow groove  75 , the communication hole  71 , and the shallow groove  73 . 
     Because the communication holes  71 , and the shallow grooves  73  and  75  for communicating the blade grooves  63  and  66  to each other are formed on the impeller  60 , the fuel flowing through the communication holes  71  is prevented from moving the impeller  60  in either direction in the radial direction. 
     Modified Embodiment 
     The following describes a modification of the embodiment. Two concentric side grooves  101  and  103  in a C-shape are formed on an inner side surface of a pump cover  100  in a modified embodiment shown in FIG. 11. A start end  102  of the inner side groove  101  and a start end  104  of the outer side groove  103  communicate with a fuel inlet passage  105 . The fuel inlet passage  105  bends by a predetermined acute angle with respect to the tangent at the start end  102  of the inner side groove  101 , and extends toward the center  100   b  of the pump cover  100 . 
     The terminal end  106  of the inner side groove  101 , and the terminal end  107  of the outer side groove  103  respectively communicate to a fuel outlet opening (not shown). Two side grooves are formed on a pump casing (not shown). Blades and blade grooves on an inner peripheral side, and blades and blade grooves on an outer peripheral side are formed on an impeller (not shown). 
     In this modified embodiment, the fuel flows into the start end  102  of the inner side groove  101 , and the start end  104  of the outer side groove  103  through the fuel inlet passage  105  having a small acute angle with respect to an inner side surface  100   a  of the pump cover  100 . Then, the fuel flows into the blade grooves at this angle with respect to a surface on one side of the impeller  50  (see FIG.  2 ). 
     In this modified embodiment, the fuel inlet passage  105  communicates to, namely is shared by, both the start end  102  of the inner side groove  101 , and the start end  104  of the outer side groove  103 . Since the two side grooves  101  and  103  for the outside and the inside are formed on the pump cover  100 , the pump efficiency increases. 
     As described above with the turbine fuel pumps of the first and second embodiments, the fuel flowing from the fuel inlet passage to the start end is not orthogonal to the rotational direction of the impeller, and is not orthogonal to the fuel flow direction in the blade grooves on the inlet opening side. As a result, the decrease of the flow rate is small when the fuel is merged, and the pressure loss at the start end is prevented. Consequently, a local negative pressure is not generated. Thus, such effects as the pump efficiency and high temperature performance increases are provided. In addition, the flow rate of the fuel in the fuel inlet passage increases due to the centrifugal force, and simultaneously, the fuel from the fuel inlet passage smoothly merges with the fuel in the blade grooves on the inlet side. 
     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.