Patent Publication Number: US-6659713-B1

Title: Fluid pumps

Description:
FIELD OF THE INVENTION 
     The present invention relates to fluid pumps for supplying a fluid, and more particularly, to fluid pumps that are used as fuel pumps for supplying fuel from a fuel tank to an engine. 
     BACKGROUND OF THE INVENTION 
     An example of a fuel pump is disclosed in Japanese Laid-Open Patent Publication No. 8-14184, which is an in-tank fuel pump disposed within a fuel tank. 
     In this known fuel pump, an impeller is mounted on a shaft of a motor and is rotatably disposed within a pump housing. Blades are formed within both axial end surfaces of the impeller and are disposed at a predetermined pitch along the perimeter of the impeller. A blade groove is formed between each of the blades. The pump housing has an inlet port through which fuel flows in, an outlet port through which fuel is discharged, a pump channel and a partition. The inlet port is formed on one axial side of the impeller. The outlet port is formed on the other axial side of the impeller. The pump channel extends from the inlet port to the outlet port along a travelling path of the impeller blades. The partition is formed between the inlet port and the outlet port. The pump channel includes a first pump channel and a second pump channel. The first pump channel faces one end surface of the impeller on the side of the inlet port. The second pump channel faces the other end surface of the impeller on the side of the outlet port. In this known fuel pump, a terminal end of the outlet port is located at a position displaced by one-half of the pitch of the blades from a terminal end of the first pump channel downstream in the direction of rotation of the impeller. Further, a starting end of the second pump channel is located at a position displaced by one-half of the pitch of the blades from a starting end of the inlet port downstream in the direction of rotation of the impeller. 
     In fuel pumps that are typically used, one-half of the pitch of the blades is about 10° or less. Specifically, in this case, the terminal end of the outlet port is located at a position displaced at a maximum of about 10° from the terminal end of the first pump channel downstream in the direction of rotation of the impeller. The starting end of the second pump channel is located at a position displaced at a maximum of about 10° from the starting end of the inlet port downstream in the direction of rotation of the impeller. 
     Fuel that flows through the second pump channel is directly discharged through the outlet port. Further, fuel flowing through the first pump channel is drawn from near the terminal end of the first pump channel to the second pump channel and then discharged through the outlet port. In the known fuel pump, if the rotational speed (peripheral velocity) of the impeller is high, fuel flowing through the first pump channel will pass a position corresponding to the outlet port before flowing from near the terminal end of the first pump channel to the second pump channel. Therefore, the known fuel pump cannot increase fuel discharge, thus preventing an increase in the pump efficiency. 
     Further, some of the fuel within the blade grooves is not discharged through the outlet port. Such fuel is drawn toward the inlet port while being confined within the blade grooves by the partitions. The fuel that is confined within the blade grooves by the partitions is highly pressurized. Therefore, after having passed along the partitions, such fuel is ejected into the second pump channel and the inlet port at the starting end of the second pump channel and the starting end of the inlet port. In the known fuel pump, the high-pressure fuel that has been confined within the blade grooves flows back into the inlet port and collides with fuel that flows in through the inlet port. Therefore, the known fuel pump cannot increase the amount of fuel that flows in through the inlet port, thus preventing an increase in the pump efficiency. 
     DISCLOSURE OF THE INVENTION 
     It is, accordingly, an object of the present invention to provide a fluid pump having increased pump efficiency. 
     One means for attaining this object is to adjust the distance between a terminal end of the outlet port and a terminal end of the first pump channel provided on the side of the inlet port. Preferably, the terminal end of the outlet port is located at a position displaced about 25° to 60° from the terminal end of the first pump channel in the direction of rotation of the impeller. With this construction, the fluid that flows through the first pump channel can be reliably discharged through the outlet port even when the rotational speed of the impeller is high. Thus, the pump efficiency can be increased. 
     Another means for attaining this object is to provide an enlarged channel portion that is defined between a partition and a channel communicating portion at which the first pump channel communicates with the inlet port. The enlarged channel portion has a larger flow passage area than a flow passage area decreased by the partition. In this case, the distance between a starting end of the second pump channel and a starting end of the enlarged channel portion is preferably adjusted. Thus, the starting end of the second pump channel is preferably located at a position displaced about 8° to 30° from the starting end of the enlarged channel portion in the direction of rotation of the impeller. With this construction, the high-pressure fuel that has been confined within the blade grooves can be prevented from flowing back into the inlet port. Further, negative pressure can be increased in the channel communicating portion on the side of the inlet port. Thus, the amount of fluid that flows in through the inlet port can be increased, thereby improving the pump efficiency. 
     A further means for attaining this object is to adjust the length of the partition formed on the side of the second pump channel. Preferably, the angular length of the partition formed on the side of the second pump channel is chosen to be between about 25° to 45°. With this construction, the relationship between the length (sealing width) of the partition and the flow passage length of the second pump channel can be optimized, so that the pump efficiency can be increased. 
     A still further means for attaining this object is to adjust the length of the partition formed on the side of the first pump channel. Preferably, the angular length of the partition formed on the side of the first pump channel is chosen to be between about 60° to 80°. With this construction, the relationship between the length (sealing width) of the partition and the flow passage length of the first pump channel can be optimized, so that the pump efficiency can be increased. 
     Additional objects, features and advantages of the present invention will be readily understood after reading the following detailed description together with the accompanying drawings and the claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view of a fluid pump according to a preferred embodiment of the present invention; 
     FIG. 2 is a sectional view taken along line II—II shown in FIG. 1; 
     FIG. 3 is a sectional view taken along line III—III shown in FIG. 1; 
     FIG. 4 is a plan view as viewed from one side of an impeller; 
     FIG. 5 is a plan view as viewed from the other side of the impeller; 
     FIG. 6 is a sectional view taken along line VI—VI shown in FIG. 1; 
     FIG. 7 is a sectional view taken along line VII—VII shown in FIG. 6; 
     FIG. 8 is a sectional view taken along line VIII—VIII shown in FIG. 4; 
     FIG. 9 is a plan view of an opening of the impeller; 
     FIG. 10 is a graph showing the relationship between the pump efficiency and the distance from the terminal end of the first pump channel to the terminal end of the outlet port; 
     FIG. 11 is a graph showing the relationship between the pump efficiency and the distance from the starting end of the enlarged channel portion to the starting end of the second pump channel; 
     FIG. 12 is a graph showing the relationship between the pump efficiency and the cover seal angle; and 
     FIG. 13 is a graph showing the relationship between the pump efficiency and the body seal angle. 
    
    
     BEST MODES FOR PERFORMING THE INVENTION 
     Typically, fluid pumps include an impeller having blade grooves formed along a perimeter of the impeller and a pump housing covering the impeller. The pump housing has an inlet port formed on one axial side of the impeller, an outlet port formed on the other axial side of the impeller, a pump channel extending between the inlet port and the outlet port along a travelling path of the blade grooves, and a partition formed between the inlet port and the outlet port. Further, the pump channel has a first pump channel that faces one end surface of the impeller on the side of the inlet port and a second pump channel that faces the other end surface of the impeller on the side of the outlet port. 
     Fluid is drawn into the inlet port and flows toward the outlet port along the first pump channel or the second pump channel via the impeller. Fluid within the second pump channel is directly discharged through the outlet port. Further, fluid within the first pump channel is drawn into the second pump channel and is then discharged through the outlet port. At this time, if the peripheral velocity of the impeller is higher than the flow velocity at which the fuel within the first pump channel flows toward the second pump channel, the fuel within the first pump channel will not be drawn into the second pump channel. Such fuel will pass along the partitions while being confined within the blade grooves. In one aspect of the present invention, the distance between the terminal end of the first pump channel and the terminal end of the outlet port is adjusted. Preferably, the distance between the terminal end of the first pump channel and the terminal end of the outlet port is chosen to be between about 25° to 60° . 
     Further, some of the fuel within the blade grooves is not discharged through the outlet port, but is instead confined within the blade grooves. In this state, the fuel is highly pressurized and passes along the partitions. The high-pressure fuel is then ejected into the channel communicating portion at which the first pump channel communicates with the inlet port. If the high-pressure fuel that has been ejected into the channel communicating portion flows back into the inlet port, the high-pressure fuel will collide with fuel that flows in through the inlet port. This collision will cause a reduction of the amount of fuel that flows in through the inlet port. In another aspect of the invention, the enlarged channel portion is formed in the partition that is formed on the side of the inlet port and located in the wall surface adjacent to the inlet port. Further, if the distance between the starting end of the enlarged channel portion and the starting end of the second pump channel is close, the high-pressure fuel that has been confined within the blade grooves will be ejected substantially at the same time into the enlarged channel portion and the second pump channel. In this case, negative pressure will be reduced in the channel communicating portion on the side of the inlet port, which reduces the amount of fuel that flows in through the inlet port. Therefore, in a further aspect of the invention, the distance between the starting end of the enlarged channel portion and the starting end of the second pump channel is adjusted. Preferably, the distance between the starting end of the enlarged channel portion and the starting end of the second pump channel is chosen to be between about 8° to 30°. 
     Further, if the flow passage lengths of the pump channels are increased, the pump efficiency will be increased. On the other hand, if the length (sealing width) of the partition is shortened, a greater amount of fuel will leak from the outlet port side to the inlet port side via the partition. As a result, the pump efficiency will be reduced. Therefore, in a still further aspect of the invention, the length of the partition formed on the side of the first pump channel or the length of the partition formed on the side of the second pump channel is adjusted. Preferably, the length of the partition formed on the side of the first pump channel is chosen to be between about 60° to 80°. Further, the length of the partition formed on the side of the second pump channel is chosen to be between about 25° to 45°. 
     Representative examples of the present invention will now be described in detail with reference to the attached drawings. This detailed description is merely intended to teach a person of skill in the art further details for practicing preferred aspects of the present teachings and is not intended to limit the scope of the invention. 
     FIG. 1 is a view of a representative embodiment, showing an in-tank fuel pump for a vehicle that comprises a fluid pump according to the present invention. FIG. 2 is a sectional view taken along line II—II shown in FIG.  1 . FIG. 3 is a sectional view taken along line III—III shown in FIG.  1 . FIG. 4 is a plan view as viewed from one axial side of an impeller. FIG. 5 is a plan view as viewed from the other axial side of the impeller. FIG. 6 is a sectional view taken along line VI—VI shown in FIG.  1 . FIG. 7 is a sectional view taken along line VII—VII shown in FIG.  6 . FIG. 8 is a sectional view taken along line VIII—VIII shown in FIG. 4 (a sectional view taken along the radial direction of the impeller). FIG. 9 is a plan view of an opening of the impeller. 
     As shown in FIG. 1, the fuel pump includes a motor section  1  and a pump section  2  that are disposed within a cylindrical housing  3 . A motor cover  4  and a pump cover  5  are fixedly attached to the upper end (the upper portion in FIG. 1) and the lower end (the lower portion in FIG. 1) of the housing  3 , respectively. 
     Bearings  9  and  10  support an upper end portion and a lower end portion of a shaft  8  of an armature  7  of the motor section  1 , which are disposed within the motor cover  4  and the pump cover  5 , respectively. Thus, the armature  7  is rotatably disposed within a motor receiving portion  6 . A plurality of commutator segments  12  are disposed in the armature  7  and are insulated from each other. The commutator segments  12  are primarily formed of copper or silver and are connected to the coil of the armature  7 . A magnet  11  is disposed on the inner peripheral surface of the housing  3 . 
     A brush  13  and a spring  14  are disposed within the motor cover  4 . The brush  13  contacts and slides along the commutator segments  12  of the armature  7 . The spring  14  urges the brush  13  toward the commutator segments  12 . The brush  13  is connected to an outside connecting terminal via a choke coil  15 . A check valve  17  is disposed within a discharge port  16  that is formed in the motor cover  4 . A fuel supply pipe (not shown) is connected to the discharge port  16 . 
     A pump body  18  is secured to the lower end of the housing  3  below the pump cover  5  by caulking. The pump cover  5  and the pump body  18  form a pump housing. The pump cover  5  and the pump body  18  may be formed, for example, of die-cast aluminum. 
     A disc-like impeller  21  is rotatably disposed within the pump housing. The impeller  21  has a plurality of blade grooves  23  that are formed within both axial end surfaces of the impeller  21  and along the perimeter of the impeller  21 . The impeller  21  is fitted around and connected to the shaft  8  of the armature  7 . The impeller  21  may be formed, for example, of phenol resin. 
     Fuel flows in through an inlet port  19  that is formed on one axial side of the impeller  21  (in the pump body  18  under the impeller  21  in FIG. 1) in the pump housing. Further, fuel flows out through an outlet port  20  that is formed on the other axial side of the impeller  21  (in the pump cover  5  on the impeller  21  in FIG.  1 ). As shown in FIGS. 2 and 3, the inlet port  19  and the outlet port  20  are disposed in a position separated from each other in the circumferential direction of the impeller  21 . A body groove  31  is formed on one axial side of the impeller  21  (in the pump body  18  under the impeller  21  in FIG.  1 ). The body groove  31  extends between the inlet port  19  and the outlet port  20  along the travelling path of the blade grooves of the impeller  21 . In addition, a cover groove  32  is formed on the other axial side of the impeller  21  (in the pump cover  5  on the impeller  21  in FIG.  1 ). The cover groove  32  extends between the inlet port  19  and the outlet port  20  along the travelling path of the blade grooves of the impeller  21 . Further, as shown in FIG. 7, a partition  33  is formed on one axial side of the impeller  21  (on the side of the body groove  31 ), and a partition  34  is formed on the other axial side of the impeller  21  (on the side of the cover groove  32 ). The body groove  31  and the cover groove  32  define a first pump channel  35  and a second pump channel  36 . The first pump channel  35  and the second pump channel  36  extend between the inlet port  19  and the outlet port  20  along the travelling path of the blade grooves that are formed along the perimeter of the impeller  21 . The partitions  33  and  34  partition the body groove  31  and the cover groove  32 , respectively, between the outlet port  20  and the inlet port  19 . 
     The pump channels  35  and  36  correspond to a first pump channel and a second pump channel of the present invention, respectively. 
     A blocking wall  37  extends from the wall surface of the partition  33  formed on the side of the inlet port  19  of the pump body  18  and protrudes in the direction of rotation of the impeller  21  (to the right as viewed in FIG.  7 ). The first pump channel  35  communicates with the inlet port  19  at a channel communicating portion  39 . The blocking wall  37  extends from the partition  33  into the channel communicating portion  39  in the direction of rotation of the impeller  21 . The blocking wall  37  is contiguous with the entire peripheral wall surface of the inlet port  19  except a wall portion defining the channel communicating portion  39 . The blocking wall  37  may be integrally formed with the pump body  18 . Alternatively, the blocking wall  37  may be separately formed in advance and fixedly attached to the pump body  18 . Further, the blocking wall  37  defines a enlarged channel portion  38  between the partition  33  and the channel communicating portion  39 . The enlarged channel portion  38  has a larger flow passage area than the flow passage area that is by the partitions  33  and  34 . 
     The construction of the impeller  21  will now be explained. As shown in FIGS. 4 and 5, blades  22  are formed within both axial end surfaces of the impeller and are disposed along the perimeter of the impeller. Blade grooves  23  are formed between each of the blades  22 . 
     As shown in FIG. 8, each of the blade grooves  23  may have a curved section with respect to the radial direction of the impeller  21 . Further, as shown in FIG. 7, the blade groove  23  has a curved section with respect to the circumferential direction of the impeller  21 , which curved section is inclined rearward in the direction of rotation of the impeller  21 . For example, it has an inclined circular or elliptical shape. 
     By thus forming the blade groove  23  having a curved section with respect to the circumferential direction of the impeller  21 , the pump efficiency can be increased. Specifically, as shown by arrows in FIG. 8, when fuel flows from the inlet port  19  to the outlet port  20 , the fuel flows outward in the radial direction along the blade grooves  23  of the impeller  21  and collides with the radially outwardly protrusions of the wall surfaces of the body groove  31  and the cover groove  32 . Then, the fuel flows inward in the radial direction along the wall surfaces of the body groove  31  and the cover groove  32  and again flows outward in the radial direction along the blade grooves  23 . Thus, an eddy flow is generated. The velocity of the eddy flow in the circumferential direction is less than the peripheral velocity of the impeller  21 . Therefore, after the fuel has moved inward in the radial direction along the body groove  31  and the cover groove  32 , the fuel flows into blade grooves  23  located rearward in the direction of rotation of the impeller  21 . In this embodiment, because each of the blade grooves  23  has a curved section with respect to the circumferential direction of the impeller  21 , fluid resistance in the blade grooves  23  is reduced in the circumferential direction, thereby enhancing the pump efficiency. 
     As shown in FIG. 9, an opening of each of the blade grooves  23  includes four opening edge portions  61 ,  62 ,  63  and  64 . The opening edge portion  61  is located forward in the direction of rotation of the impeller (on the right side as viewed in FIG. 9) and extends in the radial direction. The opening edge portion  62  is located rearward in the direction of rotation of the impeller (on the left side as viewed in FIG. 9) and extends in the radial direction. The opening edge portion  63  is located inward in the radial direction of the impeller (on the lower side as viewed in FIG. 9) and extends in the circumferential direction. The opening edge portion  64  is located outward in the radial direction of the impeller (on the upper side as viewed in FIG. 9) and extends in the circumferential direction. A meeting portion  65  between the opening edge portions  62  and  63 , a meeting portion  66  between the opening edge portions  62  and  64 , a meeting portion  67  between the opening edge portions  61  and  63 , meeting portions  68  and  69  between the opening edge portions  61  and  64 , and the opening edge portion  62  each have a curved shape. In this embodiment, the meeting portion  66  has a circular shape having a radius R in the direction of rotation of the impeller. The meeting portion  69  has a circular shape having a radius r in the direction of rotation of the impeller. By thus forming the opening edge portion of the opening of the blade groove  23  and the meeting portions of the opening edge portions with a curved shape, the pump efficiency can be increased. Specifically, because the meeting portion  65  between the opening edge portions  62  and  63  has a curved shape, fuel smoothly flows into the blade groove  23  and thus can be prevented from flowing backward. Further, because the opening edge portion  62  has a curved shape, the eddy flow discharged from the blade grooves  23  can smoothly change its direction, so that the velocity vector in the circumferential direction can be readily generated. Further, because the meeting portion  67  between the opening edge portions  61  and  63  and the meeting portions  68  and  69  between the opening edge portions  61  and  64  have a curved shape, fluid resistance can be reduced, which increases the pump efficiency. 
     In addition, the opening of the blade groove  23  may be tilted in the radial direction of the impeller. For example, as shown by dotted line  70  in FIG. 9, the opening may be formed in a position rotated forward in the direction of rotation of the impeller by an angle of θ with respect to a radial line P. Also in this case, fluid resistance can be reduced. 
     Communicating holes  24  may each extend between the rear portions (the left portions as viewed in FIGS.  7  and  9 ), which are located rearward in the direction of rotation of the impeller, of each back-to-back pair of the blade grooves  23  that are formed within both axial end surfaces of the impeller  21 . The shape and size of the communicating holes  24  can be determined appropriately. By thus forming the communicating holes  24  between the rear portions of the back-to-back pairs of the blade grooves  23  formed in the both end surfaces, the pump efficiency can be increased. Specifically, because the eddy flow is generated within the blade grooves  23  in the rear in the direction of rotation, the pressure increases within the blade grooves  23  in the rear in the direction of rotation. Therefore, as shown by arrow G in FIG. 7, when the blade grooves  23  reach a position that faces the outlet port  20 , the fuel can be more easily and smoothly drawn out of the blade grooves  23  formed on the side opposite to the side of the outlet port  20  into communicating holes  24  and the fuel is discharged from the outlet port  20  through the communicating holes  24 . As a result, the pump efficiency can be increased. Vapor is generated when the temperature of the fuel rises. If the vapor is drawn into the first pump channel  35  or the second pump channel  36  through the inlet port  19  and enters the blade grooves  23 , the pump efficiency will be reduced. Therefore, a vapor discharge port is typically provided in the body groove  31  or the cover groove  32  so that vapor within the blade grooves  23  is discharged through the vapor discharge port. In this embodiment, because the communicating holes  24  extend between the blade grooves  23  that are formed within both axial end surfaces of the impeller  21 , the vapor within the blade grooves  23  can be discharged more efficiently. Specifically, vapor within the blade grooves  23  formed on the side opposite to the side of the vapor discharge port is directed into the blade grooves  23  formed on the side of the vapor discharge port through the communicating holes  24 . As a result, vapor can be more efficiently discharged from the blade grooves  23  formed on the side opposite to the side of the vapor discharge port, which improves the pump efficiency. 
     The fuel pump thus constructed operates as follows. 
     When the motor section  1  is energized, the shaft  8  rotates and thus the impeller  21  rotates. Thus, fuel is drawn from a fuel tank (not shown) into the inlet port  19  and flows toward the outlet port  20  along the first pump channel  35  or the second pump channel  36  via the blade grooves  23  of the impeller  21 . When the fuel reaches the outlet port  20 , the fuel is discharged into the motor receiving portion  6  through the outlet port  20 . At this time, fuel within the second pump channel  36  is directly discharged through the outlet port  20 . Further, fuel within the first pump channel  35  is drawn into the second pump channel  36  by pressing against the wall of the terminal end of the body groove  31 . Then, the fuel is discharged through the outlet port  20 . 
     If the peripheral velocity of the impeller  21  is higher than the flow velocity at which the fuel within the first pump channel  35  flows toward the outlet port  20 , the fuel within the first pump channel  35  will not be discharged through the outlet port  20 . Such fuel will be confined within the blade grooves  23  and will flow toward the inlet port  19 . As a result, the pump efficiency will be reduced. 
     In this respect, the distance between the terminal end of the outlet port  20  and the terminal end of the first pump channel  35  may be adjusted, so that the fuel within the first pump channel  35  can be reliably discharged through the outlet port  20  even when the peripheral velocity of the impeller  21  is higher. Therefore, in the present embodiment, the pump efficiency is increased by adjusting the distance between the terminal end of the outlet port  20  and the terminal end of the first pump channel  35 . 
     FIG. 10 shows the relationship between the pump efficiency and the distance {circle around ( 1 )} (see FIGS. 6 and 7) between the terminal end of the first pump channel  35  and the terminal end of the outlet port  20 . The terminal end of the outlet port  20  is located forward (downstream) of the terminal end of the first pump channel  35  in the direction of rotation of the impeller  21 . The data shown in FIG. 10 was obtained by conducting an experiment using a fuel pump that has an impeller  21  having a thickness of 3.8 mm and an outer diameter of 33 mm. In the experiment, the fuel pump was operated at a motor supply voltage of 12 V, a fuel pressure of 324 kPa, a fuel discharge rate of 100 liters/hr, and a rotational speed of 7000 rpm. The pump efficiency was obtained from the following equation: 
     
       
         pump efficiency= g ×( P×Q )/( T×N ), 
       
     
     wherein g represents acceleration, T represents the motor torque, N represents the rotational speed, P represents the fuel pressure, and Q represents the fuel discharge rate. 
     As shown in FIG. 10, improved pump efficiency can be obtained when the distance (angle in FIG. 10) {circle around ( 1 )} between the terminal end of the first pump channel  35  and the terminal end of the outlet port  20  is chosen to be between about 25° to 60°. With the above-noted specifications, the best pump efficiency can be obtained when the angle {circle around ( 1 )} between the terminal end of the first pump channel  35  and the terminal end of the outlet port  20  is about 42°. In this embodiment, the pump efficiency can be increased by a maximum of about 1%. 
     Further, some of the fuel within the blade grooves  23  is not discharged through the outlet port  20 . The fuel is confined within the blade grooves  23  by the partitions  33  and  34 . In this state, the fuel is highly pressurized and passes along the partitions  33  and  34 . When the blade grooves  23  confining the high-pressure fuel reaches the channel communicating portion  39  at which the first pump channel  35  communicates with the inlet port  19 , or the starting end of the second pump channel  36 , the high-pressure fuel within the blade grooves  23  is ejected into the channel communicating portion  39  or the second pump channel  36 . If the high-pressure fuel that has been ejected into the channel communicating portion  39  flows back into the inlet port  19 , the high-pressure fuel will collide with fuel flowing in through the inlet port  19 . This collision will cause a reduction of the amount of fuel that flows in through the inlet port  19 , which reduces the pump efficiency. 
     In this respect, the high-pressure fuel may be prevented from flowing back into the inlet port  19 , thereby preventing the high-pressure fuel from colliding with fuel flowing in through the inlet port  19 . Therefore, in the present embodiment, the enlarged channel portion  38  is provided in the partition  33  of the pump body  18  on the side of the inlet port  19  in order to prevent the high-pressure fuel from flowing back into the inlet port  19 . Thus, the amount of fuel that flows in through the inlet port  19  is not reduced. 
     As shown in FIG. 7, in the present embodiment, a blocking wall  37  extends from the wall surface of the partition  33  of the pump body  18  on the side of the inlet port  19  (forward in the direction of rotation of the impeller). The blocking wall  37  has a stepped shape with respect to the partition  33 . Thus, the enlarged channel portion  38  is defined between the partition  33  and the channel communicating portion  39 . The enlarged channel portion  38  has a larger flow passage area than the flow passage area that is reduced by the partitions  33  and  34 . The configuration of the blocking wall  37  may be varied, and the flow passage area of the enlarged channel portion  38  also may be varied. For example, the blocking wall  37  may have a plate-like shape, or may have an inclined wall surface that is formed along the inlet port  19  and inclined in the direction of rotation of the impeller  21  from the side of the inlet port  19  toward the channel communicating portion  39 . Further, a wall surface of the channel communicating portion  39  that faces the blocking wall  37  may preferably comprise an inclined surface that is inclined in the direction of rotation of the impeller  21  from the side of the inlet port  19  toward the first pump channel  35 . 
     When the high-pressure fuel that has been confined within the blade grooves  23  passes along the partition  33  and reaches the enlarged channel portion  38 , the fuel is ejected into the enlarged channel portion  38 . Then, the fuel is directed to the channel communicating portion  39  along the blocking wall  37  that defines the enlarged channel portion  38 . Thus, the high-pressure fuel that has been confined within the blade grooves  23  can be prevented from flowing back into the inlet port  19 , thereby preventing a reduction of the amount of fuel that flows in through the inlet port  19 . As a result, the pump efficiency is increased. 
     Further, if the distance between the starting end of the enlarged channel portion  38  and the starting end of the second pump channel  36  is close, the high-pressure fuel that has been confined within the blade grooves  23  will pass along the partitions  33  and  34  and then will be ejected substantially at the same time into the enlarged channel portion  38  and the second pump channel  36 . In this case, the ejecting pressures of the high-pressure fuel that is ejected into the enlarged channel portion  38  and thus into the channel communicating portion  39  will be reduced. If the ejecting pressure of the high-pressure fuel that is ejected into the channel communicating portion  39  is reduced, negative pressure will be reduced in the channel communicating portion  39  on the side of the inlet port  19 , thereby reducing the amount of fuel that flows in through the inlet port  19 . 
     In this respect, the ejecting pressures of the high-pressure fuel that is ejected into the enlarged channel portion  38  and thus into the channel communicating portion  39  can be increased by adjusting the distance between the starting end of the enlarged channel portion  38  and the starting end of the second pump channel  36 . Therefore, in the present embodiment, the distance between the starting end of the enlarged channel portion  38  and the starting end of the second pump channel  36  is adjusted in order to prevent a reduction of the negative pressure in the channel communicating portion  39  on the side of the inlet port  19 . 
     FIG. 11 shows the relationship between the pump efficiency and the distance {circle around ( 2 )} (see FIGS. 6 and 7) from the starting end of the enlarged channel portion  38  to the starting end of the second pump channel  36 . The starting end of the second pump channel  36  is located forward of the starting end of the enlarged channel portion  38  in the direction of rotation of the impeller  21 . The data shown in FIG. 11 was obtained by using a fuel pump having the same specifications as the above-mentioned fuel pump used in the experiment of FIG.  10 . 
     As shown in FIG. 11, improved pump efficiency can be obtained when the distance (angle in FIG. 11) {circle around ( 2 )} between the starting end of the enlarged channel portion  38  and the starting end of the second pump channel  36  is chosen to be between about 8° to 30°. With the above-noted specifications, the best pump efficiency can be obtained when the angle {circle around ( 2 )} between the starting end of the enlarged channel portion  38  and the starting end of the second pump channel  36  is about 17°. In this embodiment, the pump efficiency can be increased by a maximum of about 0.5%. 
     Further, if the flow passage lengths of the pump channels  35  and  36  are increased, the pump efficiency will be increased. On the other hand, when the flow passage lengths of the pump channels  35  and  36  are increased, the lengths (sealing widths) of the partitions  33  and  34  are shortened if the circumferential length of the impeller  21  is not changed. If the lengths of the partitions  33  and  34  are shortened, an increased amount of fuel will leak from the outlet port side to the inlet port side via the partitions  33  and  34  due to the fuel pressure difference between the outlet port side and the inlet port side of the partitions  33  and  34 . As a result, the pump efficiency will be reduced. In this respect, the pump efficiency can be changed by varying the lengths (sealing widths) of the partitions  33  and  34  or the relationship between the lengths (sealing widths) of the partitions  33  and  34  and the flow passage lengths of the pump channels  35  and  36 . 
     Therefore, in the present embodiment, the flow passage length of the second pump channel  36  and the length (sealing width) of the partition  34  are adjusted in order to increase the pump efficiency. FIG. 12 shows the relationship between the pump efficiency and the length {circle around ( 3 )} (see FIGS. 6 and 7) of the partition  34  formed on the side of the pump cover  5 . The data shown in FIG. 12 was obtained by using a fuel pump having the same specifications as the above-mentioned fuel pump used in the experiment of FIG.  10 . 
     As shown in FIG. 12, when the length of the partition  34  (cover seal angle of the partition  34  in FIG. 12) {circle around ( 3 )} is chosen to be between about 25° to 45°, the relationship between the length (sealing width) of the partition  34  and the flow passage length of the second pump channel  36  can be optimized, so that the pump efficiency can be increased. 
     Further, in this embodiment, the flow passage length of the first pump channel  36  and the length (sealing width) of the partition  33  are adjusted so that the pump efficiency can be increased. FIG. 13 shows a relationship between the pump efficiency and the length {circle around ( 4 )} (see FIGS. 6 and 7) of the partition  33  formed on the side of the pump body  18 . The data shown in FIG. 13 was obtained by using a fuel pump having the same specifications as the abovementioned fuel pump used in the experiment of FIG.  10 . In this case, the pressure difference between the outlet port side and the inlet port side of the partition  33  is larger than the pressure difference between the outlet port side and the inlet port side of the partition  34 , due to negative pressure developed by the existence of the inlet port  19 . Therefore, the length of the partition  33  is required to be longer than the length of the partition  34 . 
     As shown in FIG. 13, when the length of the partition  33  (body seal angle of the partition  33  in FIG. 13) {circle around ( 4 )} is chosen to be between about 60° to 80°, the relationship between the length (sealing width) of the partition  33  and the flow passage length of the first pump channel  35  can be optimized, so that the pump efficiency can be increased. 
     In the above-mentioned embodiment, the pump efficiency was described as being increased by adjusting the distance {circle around ( 1 )} between the terminal end of the first pump channel  35  and the terminal end of the outlet port  20 , the distance {circle around ( 2 )} between the starting end of the enlarged channel portion  38  and the starting end of the second pump channel  36 , the cover seal angle {circle around ( 3 )} and the body seal angle {circle around ( 4 )}. However, the pump efficiency can be also increased by adjusting only one or some of {circle around ( 1 )} to {circle around ( 4 )}. 
     Further, although a fuel pump for supplying fuel was described in this specification, the present invention may be applied to a fluid pump for supplying various kinds of fluids other than fuel. 
     The present invention is not limited to the constructions that have been described as the representative embodiment, but rather, may be added to, changed, replaced with alternatives or otherwise modified without departing from the spirit and scope of the invention.