Patent Publication Number: US-2016238016-A1

Title: Fuel pump

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application is based on and incorporates herein by reference Japanese Patent Application No. 2013-196615 filed on Sep. 24, 2013 and Japanese Patent Application No. 2014-095859 filed on May 7, 2014. 
     TECHNICAL FIELD 
     The present disclosure relates to a fuel pump. 
     BACKGROUND ART 
     There is known a fuel pump that includes an impeller, which is rotatable in a pump chamber, and a motor, which generates a drive force to rotate the impeller. The fuel pump pumps fuel of a fuel tank to an internal combustion engine through rotation of the impeller. The patent literature  1  recites a fuel pump that includes an impeller. The impeller includes an engaging hole, which has a cross section of a D-shape and receives a shaft of an electric motor, and a hole, which receives a weight that corrects weight distribution of the impeller. 
     In a case of the fuel pump, which uses a brushless motor as the motor, the shaft is rotatable in two opposite directions, i.e., a normal direction, which is a rotational direction at the time of pressurizing the fuel with the impeller, and a reverse direction, which is a rotational direction at the time of sensing a rotational position of the rotor relative to the stator. A manufacturing tolerance exists in a size of the engaging hole of the impeller. Therefore, a gap is formed between an inner wall of the impeller, which forms the engaging hole, and a side wall of one end portion of the shaft, which is received in the engaging hole. When the operational state of the brushless motor is changed from one state, in which the one end portion of the shaft is rotatable in one of the normal direction and the reverse direction, to another state, in which the one end portion of the shaft is rotatable in the other one of the normal direction and the reverse direction, the shaft is rotated in the engaging hole, so that a rotational torque of the shaft, which is rotated with an accelerating force of a some degree, is applied to a contact surface of the engaging hole. Therefore, a damage of the impeller may possibly occur. 
     Furthermore, there is known another type of fuel pump, in which both of the cross section of the engaging hole and the cross-section of the one end portion of the shaft have an I-shape, so that two contact surfaces of the one end portion of the shaft simultaneously contact two contact surfaces of an inner wall of the engaging hole of the impeller. However, in the case of the impeller, which is molded through the injection molding, it is difficult to form the impeller such that the two contact surfaces of the impeller can simultaneously contact the two contact surfaces of the shaft. Therefore, at the time of contacting the shaft against the impeller, only one of the two contact surfaces of the shaft may possibly contact the impeller to possibly cause the damage of the impeller. 
     CITATION LIST 
     Patent Literature(s) 
     Patent Literature 1: JPH11-082208A 
     SUMMARY OF THE INVENTION 
     It is an objective of the present disclosure to provide a fuel pump, which can effectively limit a damage of an impeller. 
     According to the present disclosure, there is provided a fuel pump, which includes a pump case, a stator, a rotor, a shaft and an impeller. The pump case includes a suction port, through which fuel is drawn into the pump case, and a discharge port, through which the fuel is discharged from the pump case. A plurality of windings is wound around the stator, which is configured into a tubular form, and the stator is received in the pump case. The rotor is rotatably placed on a radially inner side of the stator. The shaft is coaxial with the rotor and rotates integrally with the rotor. The impeller includes an engaging hole, which receives one end portion of the shaft. When the impeller is rotated integrally with the shaft, the impeller pressurizes the fuel drawn through the suction port and discharges the pressurized fuel through the discharge port. The one end portion of the shaft includes at least one shaft side contact surface that is contactable with the impeller. The engaging hole includes at least one impeller side contact surface, which opposes the at least one shaft side contact surface and is contactable with the at least one shaft side contact surface. The impeller includes at least one deformation enabling space that is deformed when the at least one shaft side contact surface and the at least one impeller side contact surface contact with each other. 
     In the fuel pump of the present disclosure, the shaft and the impeller are formed such that the shaft and the impeller integrally rotate while the shaft side contact surface and the impeller side contact surface contact with each other. When the impeller is rotated integrally with the shaft, the shaft side contact surface and the impeller side contact surface may possibly contact with each other in an incorrect state depending on the processing accuracy of the engaging hole and/or the position of the shaft relative to the engaging hole. In the impeller of the fuel pump of the present disclosure, when the shaft side contact surface and the impeller side contact surface contact with each other, the deformable space is deformed by a force, which is applied from the shaft to the impeller. When the deformable space is deformed, the resiliently deformable amount of the impeller is increased. Therefore, the shape of the engaging hole is changed, and the shaft side contact surface correctly contacts the impeller side contact surface. As discussed above, in the fuel pump of the present disclosure, the shaft side contact surface and the impeller side contact surface can correctly contact with each other through the deformation of the deformation enabling space without being influenced by the processing accuracy of the engaging hole and/or the position of the shaft relative to the engaging hole. Thus, the surface pressure, which is applied to the impeller at the time of rotating the shaft, becomes small, and the damage of the impeller can be effectively limited. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a cross-sectional view of a fuel pump according to a first embodiment of the present disclosure. 
         FIG. 2  is a top view of an impeller of the fuel pump of the first embodiment. 
         FIGS. 3( a ) to 3( d )  are schematic diagrams for describing an operation of the fuel pump according to the first embodiment. 
         FIG. 4  is a top view of an impeller of a fuel pump according to a second embodiment of the present disclosure. 
         FIG. 5  is a top view of an impeller of a fuel pump according to a third embodiment of the present disclosure. 
         FIG. 6  is a top view of an impeller of a fuel pump according to a fourth embodiment of the present disclosure. 
         FIG. 7  is a top view of an impeller of a fuel pump according to a fifth embodiment of the present disclosure. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Various embodiments of the present disclosure will be described with reference to the accompanying drawings. 
     First Embodiment 
     A fuel pump according to a first embodiment of the present disclosure will be described with reference to  FIGS. 1 to 3 ( d ). 
     The fuel pump  1  includes a motor device  3 , a pump device  4 , a housing  20 , a pump cover  60  and a cover end  40 . In the fuel pump  1 , the motor device  3  and the pump device  4  are received in a space, which is formed by the housing  20 , the pump cover  60  and the cover end  40 . The fuel pump  1  draws fuel from a fuel tank (not shown) through a suction port  61 , which is indicated in a lower side of  FIG. 1 , and discharges the fuel toward an internal combustion engine through a discharge port  41 , which is indicated in an upper side in  FIG. 1 . In  FIG. 1 , the upper side will be referred to as “the upside”, and the lower side will be referred to as “the downside.” The housing  20 , the pump cover  60  and the cover end  40  serve as a pump case of the present disclosure. 
     The housing  20  is configured into a cylindrical tubular form and is made of metal (e.g., iron). The pump cover  60  and the cover end  40  are installed to two end portions  201 ,  202 , respectively, of the housing  20 . 
     The pump cover  60  closes the end portion  201  of the housing  20 , at which the suction port  61  is located. A peripheral edge part of the end portion  201  of the housing  20  is inwardly swaged, so that the pump cover  60  is fixed at the inside of the housing  20 . Thereby, removal of the pump cover  60  from the housing  20  in the axial direction of the fuel pump  1  is limited. The pump cover  60  includes the suction port  61 , which opens toward the downside. An intake passage  62  is formed in an inside of the suction port  61  to extend through the pump cover  60  in a direction (axial direction) of a rotational axis CA 52  of a shaft  52 . A groove  63 , which is connected to the intake passage  62 , is formed in a surface of the pump cover  60 , which is located on a side where the pump device  4  is placed. 
     The cover end  40  is made of resin and closes the end portion  202  of the housing  20 , at which the discharge port  41  is located. A peripheral edge part of the end portion  202  of the housing  20  is swaged, so that the cover end  40  is fixed in the inside of the housing  20 . Therefore, the removal of the cover end  40  from the housing  20  in the axial direction of the fuel pump  1  is limited. The cover end  40  includes the discharge port  41 , which opens toward the upside. A discharge passage  42  is formed in an inside of the discharge port  41  to extend through the cover end  40  in the direction of the rotational axis CA 52  of the shaft  52 . An electric connector portion  43 , which receives three connecting terminals  38  to receive an electric power from an outside, is formed in an end portion of the cover end  40 , which is located on a side that is opposite from the side where the discharge passage  42  is formed. 
     A bearing receiving portion  44 , which is configured into a generally tubular form, is formed in an inside of the cover end  40 , which is placed in the inside of the housing  20 . The bearing receiving portion  44  includes a receiving space  440  that is formed in an inside of the bearing receiving portion  44  to receive an end portion  521  of the shaft  52  and a bearing  55 . The bearing  55  rotatably supports the end portion  521  of the shaft  52 . 
     The motor device  3  generates a rotational torque through use of a magnetic field that is generated when the electric power is supplied to the motor device  3 . The motor device  3  includes a stator  10 , a rotor  50  and the shaft  52 . The motor device  3  of the fuel pump  1  of the first embodiment is a brushless motor that senses a position of the rotor  50  relative to the stator  10  through sensing of rotation of the shaft  52 . 
     The stator  10  is configured into a cylindrical tubular form and is received at a radially outer side location in the inside of housing  20 . The stator  10  includes six cores  12 , six bobbins, six windings and the three connecting terminals. The stator  10  is integrally formed through resin molding of these components. 
     Each core  12  is formed by stacking a plurality of plates, which are made of a magnetic material (e.g., iron). The cores  12  are arranged one after another in a circumferential direction to radially oppose a magnet  54  of the rotor  50 . 
     The bobbins  14  are made of a resin material. At the time of manufacturing, the cores  12  are inserted into and integrated with the bobbins  14 , respectively. Each bobbin  14  includes an upper end portion  141 , an insert portion  142  and a lower end portion  143 . The upper end portion  141  is formed on the discharge port  41  side. Each core  12  is inserted into the insert portion  142  of the corresponding bobbin  14 . The lower end portion  143  is formed on the suction port  61  side. 
     Each of the windings is, for example, a copper wire that has an outer surface coated with a dielectric film. Each winding is wound around the corresponding bobbin  14 , into which the core  12  is inserted, to form one coil. Each winding includes an upper end winding portion  161 , an insert winding portion (not shown) and a lower end winding portion  163 . The upper end winding portion  161  is wound around the upper end portion  141  of the corresponding bobbin  14 . The insert winding portion is wound around the insert portion  142  of the bobbin  14 . The lower end winding portion  163  is wound around the lower end portion  143  of the bobbin  14 . The windings are electrically connected to the connecting terminals  38  received in the electric connector portion  43 . 
     Each connecting terminal  38  extends through the cover end  40  and is fixed to the upper end portion  141  of the corresponding bobbin  14 . In the fuel pump  1  of the first embodiment, the number of the connecting terminals  38  is three, and these connecting terminals  38  receive the three-phase electric power from an electric power source device (not shown). 
     The rotor  50  is rotatably received on the inner side of the stator  10 . The rotor  50  includes the magnet  54 , which is placed to surround an iron core  53 . The magnet  54  is magnetized to have N-poles and S-poles, which are alternately arranged one after another in the circumferential direction. In the first embodiment, the number of pole pairs of the N-pole and the S-pole is two, so that the total number of the poles is four. 
     The shaft  52  is securely press fitted into a shaft hole  51  of the rotor  50 , which extends along a central axis of the rotor  50 , and the shaft  52  is rotated integrally with the rotor  50 . An end portion  522  of the shaft  52 , which serves as one end portion of the shaft  52  of the present disclosure and is located on the suction port  61  side, is connected to the pump device  4 . 
     The end portion  522  of the shaft  52  includes a shaft first planar surface (serving as a shaft side first contact surface or a shaft side contact surface)  523 , which extends in the vertical direction and is formed as a planar surface, and a shaft second planar surface (serving as a shaft side second contact surface or a shaft side contact surface)  524 , which is formed as a planar surface and is generally parallel to the shaft first planar surface  523 . The end portion  522  of the shaft  52  includes a shaft first curved surface  525  and a shaft second curved surface  526 . The shaft first curved surface  525  connects between one side of the shaft first planar surface  523  and one side of the shaft second planar surface  524  and is formed as a curved surface. The shaft second curved surface  526  connects between another side of the shaft first planar surface  523  and another side of the shaft second planar surface  524  and is formed as a curved surface. In this way, a cross section of the end portion  522  of the shaft  52 , which is taken in a direction perpendicular to the rotational axis CA 52  of the shaft  52 , has a generally I-shape. 
     The pump device  4  pressurizes the fuel drawn through the suction port  61  and discharges the pressurized fuel into the inside of the housing  20  through use of the rotational torque generated by the motor device  3 . The pump device  4  includes a pump casing  70  and an impeller  65 . 
     The pump casing  70  is configured into a generally circular disk form and is placed between the pump cover  60  and the stator  10 . A through-hole  71  is formed in a center portion of the pump casing  70  to extend through the pump casing  70  in a plate thickness direction of the pump casing  70 . A bearing  56  is fitted into the through-hole  71 . The bearing  56  rotatably supports the end portion  522  of the shaft  52 . In this way, the rotor  50  and the shaft  52  are rotatable relative to the cover end  40  and the pump casing  70 . 
     In a surface of the pump casing  70 , which is axially placed on the impeller  65  side, a groove  73  is formed at a location that is opposed to the groove  63  of the pump cover  60 . A fuel passage  74 , which extends through the pump casing  70  in the direction of the rotational axis CA 52  of the shaft  52 , is communicated with the groove  73 . 
     The impeller  65  is made of resin and is configured into a generally circular disk form. The impeller  65  is received in a pump chamber  72 , which is formed between the pump cover  60  and the pump casing  70 . 
     An engaging hole  66  is formed generally in a center of the impeller  65 . A cross section of the engaging hole  66  is configured to have a generally I-shape to correspond with the cross section of the end portion  522  of the shaft  52 . The end portion  522  of the shaft  52  is received in the engaging hole  66 . In this way, the impeller  65  is rotated in the pump chamber  72  by the rotation of the shaft  52 . The details of the shape of the impeller  65  will be described later. 
     The impeller  65  includes a plurality of tilt surfaces  64 , which are placed at a location that corresponds to the grooves  63 ,  73 . As shown in  FIG. 2 , the tilt surfaces  64  are arranged one after another at generally equal intervals in the circumferential direction in a radially outer end part of the impeller  65 . 
     In the fuel pump  1  of the first embodiment, when the electric power is supplied to the windings of the motor device  3  through the terminals  38 , the impeller  65  is rotated together with the rotor  50  and the shaft  52 . When the impeller  65  is rotated, the fuel in the fuel tank, which receives the fuel pump  1 , is guided to the groove  63  through the suction port  61 . The fuel, which is guided to the groove  63 , is pressurized through the rotation of the impeller  65  and is guided to the groove  73 . The pressurized fuel is guided to an intermediate chamber  75 , which is formed between the pump casing  70  and the motor device  3 , through the fuel passage  74 . The fuel, which is guided to the intermediate chamber  75 , is conducted through a fuel passage  77 , which is formed between the rotor  50  and the stator  10 , a fuel passage  78 , which is formed between an outer wall of the shaft  52  and inner walls  144  of the bobbins  14 , and a fuel passage  79 , which is formed on a radially outer side of the bearing receiving portion  44 . Furthermore, the fuel, which is guided to the intermediate chamber  75 , is conducted through a fuel passage  76  that is formed between an inner wall of the housing  20  and an outer wall of the stator  10 . The fuel, which flows through the fuel passages  76 ,  77 ,  78 ,  79 , is discharged to the outside of the fuel pump  1  through the discharge passage  42  and the discharge port  41 . 
     The fuel pump  1  of the first embodiment has a characteristic feature with respect to a shape of the impeller  65 . Now, the details of the shape of the impeller  65  will be described with reference to  FIGS. 2 to 3 ( d ).  FIG. 2  is a top view of the impeller  65 .  FIGS. 3( a ) to 3( d )  are schematic diagrams showing a positional relationship between the engaging hole  66  and the shaft  52  at the time of driving the fuel pump  1 . Here, it should be noted that the shape of the engaging hole  66  of  FIGS. 3( b ) to 3( d )  is exaggerated in comparison to the actual shape of the engaging hole  66  for the descriptive purpose. 
     The engaging hole  66  of the impeller  65  is formed by an impeller first planar surface (serving as an impeller side first contact surface or an impeller side contact surface)  661 , an impeller second planar surface (serving as an impeller side second contact surface or an impeller side contact surface)  662 , an impeller first curved surface (serving as an engaging hole first forming surface or an engaging hole forming surface)  663  and an impeller second curved surface (serving as an engaging hole second forming surface or an engaging hole forming surface)  664 . 
     The impeller first planar surface  661  is a planar surface that is formed to extend in a direction (axial direction) of a central axis CA 66  of the engaging hole  66 . The central axis CA 66  also serves as a central axis of the impeller  65 . The impeller first planar surface  661  is formed at a corresponding location, at which the impeller first planar surface  661  opposes the shaft first planar surface  523 . When the shaft  52  is rotated, the impeller first planar surface  661  is contactable with the shaft first planar surface  523 . 
     The impeller second planar surface  662  is a planar surface that is formed to extend in the direction of the central axis CA 66 . The impeller second planar surface  662  is generally parallel to the impeller first planar surface  661 . The impeller second planar surface  662  is formed at a corresponding location, at which the impeller second planar surface  662  opposes the shaft second planar surface  524 . When the shaft  52  is rotated, the impeller second planar surface  662  is contactable with the shaft second planar surface  524 . 
     The impeller first curved surface  663  connects between one side of the impeller first planar surface  661 , which is parallel to the central axis CA 66 , and one side of the impeller second planar surface  662 , which is parallel to the central axis CA 66 . A cross section of the impeller first curved surface  663  is generally configured into a shape of an arc, which is centered at the central axis CA 66  and is radially outwardly bulged. A first groove (serving as a deformation enabling space)  665  is formed generally in a center (circumferential center) of the impeller first curved surface  663 . 
     The impeller second curved surface  664  connects between another side of the impeller first planar surface  661 , which is parallel to the central axis CA 66 , and another side of the impeller second planar surface  662 , which is parallel to the central axis CA 66 . A cross section of the impeller second curved surface  664  is generally configured into a shape of an arc, which is centered at the central axis CA 66  and is radially outwardly bulged. A second groove (serving as a deformation enabling space)  666  is formed generally in a center (circumferential center) of the impeller second curved surface  664 . 
     The first groove  665  is configured into a form of a slit and extends from the impeller first curved surface  663  in the radially outward direction. The first groove  665  is formed to communicate with the engaging hole  66  and extends through the impeller  65  in the direction of the central axis CA 66 . 
     The second groove  666  is configured into a form of a slit and extends from the impeller second curved surface  664  in the radially outward direction. The second groove  666  is formed to communicate with the engaging hole  66  and extends through the impeller  65  in the direction of the central axis CA 66 . 
     The first groove  665  and the second groove  666  extend in opposite directions, respectively, which are opposite to each other when the first groove  665  and the second groove  666  are viewed from the central axis CA 66 . Furthermore, a radial length of the first groove  665  and a radial length of the second groove  666  are equal to each other. 
     Now, the operation and advantages of the fuel pump  1  of the first embodiment will be described with reference to  FIGS. 3( a ) to 3( d ) . 
     In the fuel pump  1  of the first embodiment, as shown in  FIG. 3( a ) , it is desirable to satisfy the relationship of that when the shaft first planar surface  523  of the shaft  52  and the impeller first planar surface  661  of the engaging hole  66  are placed parallel to each other, the shaft second planar surface  524  of the shaft  52  and the impeller second planar surface  662  of the engaging hole  66  are placed parallel to each other. 
     However, in the case of the impeller  65 , which is made of resin and is formed through injection molding, it is difficult to form the impeller  65  in a manner that satisfies the above relationship. Therefore, in some cases, for example, in a state where the shaft first planar surface  523  and the impeller first planar surface  661  are placed parallel to each other, the shaft second planar surface  524  and the impeller second planar surface  662  may not be parallel to each other. 
     For instance, in some cases, as shown in  FIG. 3( b ) , the engaging hole  66  may be formed such that although the shaft first planar surface  523  and the impeller first planar surface  661  are held parallel to each other, the shaft second planar surface  524  and the impeller second planar surface  662  are not parallel to each other, and an intersection line  667  between the impeller second planar surface  662  and the impeller second curved surface  664  is held further away from the point along the central axis CA 66  of the engaging hole  66 . 
     In the case of the engaging hole  66 , which is configured into the shape shown in  FIG. 3( b ) , when the shaft  52  is rotated in a direction R 1  indicated by a solid arrow, the shaft first planar surface  523  and the impeller first planar surface  661  contact with each other, and the shaft second planar surface  524  and the impeller second planar surface  662  are spaced away from each other. The shaft  52  and the impeller  65  are further rotated in the direction R 1  in this state. At this time, a force F 1  is applied between the shaft first planar surface  523  and the impeller first planar surface  661  in a direction that is from the shaft first planar surface  523  to the impeller first planar surface  661 . Because of the applied force F 1 , the impeller  65  is deformed such that the first groove  665  is expanded, as shown in  FIG. 3( d ) . Due to the deformation of the first groove  665 , the shape of the engaging hole  66  is changed such that the shaft second planar surface  524  and the impeller second planar surface  662 , which were previously spaced from each other, now contact with each other. In  FIG. 3( d ) , a dotted line indicates the shape of the engaging hole  66  and the shape of the first groove  665  before the occurrence of the deformation of the first groove  665 . 
     Here, it is described that the two planar surfaces of the shaft  52  contact the two planar surfaces of the impeller  65  due to the expansion of the first groove  665 . This phenomenon may also occur in the second groove  666 . 
     Now, advantages of the first embodiment will be described. 
     (a) In the fuel pump  1  of the first embodiment, when the shaft  52  contacts one of the impeller first planar surface  661  and the impeller second planar surface  662  upon rotation of the shaft  52  in the engaging hole  66 , the first groove  665  or the second groove  666  is deformed to cause the change in the shape of the engaging hole  66 . When the shape of the engaging hole  66  is changed, the other one of the shaft first planar surface  523  and the shaft second planar surface  524 , which does not contact the one of the impeller first planar surface  661  and the impeller second planar surface  662 , contacts the other one of the impeller first planar surface  661  and the impeller second planar surface  662 . Thereby, the two planar surfaces of the shaft  52  contact the inner wall of the engaging hole  66 . In this way, the rotational torque of the shaft  52  is applied to both of the impeller first planar surface  661  and the impeller second planar surface  662 , and thereby the surface pressure of the rotational torque applied to the impeller  65  is reduced. Therefore, the surface pressure, which is applied to the impeller  65 , becomes relatively small, and thereby it is possible to effectively limit the damage of the impeller  65  caused by the rotational torque of the shaft  52 . 
     (b) Furthermore, in the fuel pump  1  of the first embodiment, at the time of molding the impeller  65  through the injection molding, it is no longer required to precisely control the parallelism of the impeller first planar surface  661  relative to the shaft first planar surface  523  and the parallelism of the impeller second planar surface  662  relative to the shaft second planar surface  524 . Thereby, the two planar surfaces of the shaft  52  can contact the two planar surfaces of the engaging hole  66  while the number of the manufacturing steps of the fuel pump  1  is reduced. Therefore, the manufacturing costs of the fuel pump  1  can be reduced. 
     (c) The first groove  665  and the second groove  666  are formed in the center of the impeller first curved surface  663  and the center of the impeller second curved surface  664 , respectively, which are opposed to each other. The first groove  665  and the second groove  666  extend for the same length in the two opposite directions, respectively, which are opposite to each other when the two opposite directions are viewed from the central axis CA 66 . In this way, when the rotational torque of the shaft  52  is applied to the impeller first planar surface  661  or the impeller second planar surface  662 , the impeller  65  is deformed to the similar shape. Thereby, the concentration of the stress on any particular portion of the impeller  65  can be limited. Thus, it is possible to limit the damage of the impeller  65  caused by the rotational torque of the shaft  52 . 
     Second Embodiment 
     Next, a fuel pump according to a second embodiment of the present disclosure will be described with reference to  FIG. 4 . The second embodiment differs from the first embodiment with respect to the shape of the impeller. In the following description, components, which are similar to those of the first embodiment, will be indicated by the same reference numerals and will not be described further. 
       FIG. 4  is a top view of an impeller  67  of a fuel pump according to the second embodiment. An engaging hole  68  is formed generally in a center of the impeller  67 . The end portion  522  of the shaft  52  is received in the engaging hole  66 . 
     A cross section of the engaging hole  68  is configured to have a generally I-shape to correspond with the cross section of the end portion  522  of the shaft  52 . The engaging hole  68  is formed by an impeller first planar surface (serving as an impeller side first contact surface or an impeller side contact surface)  681 , an impeller second planar surface (serving as an impeller side second contact surface or an impeller side contact surface)  682 , an impeller first curved surface (serving as an engaging hole first forming surface or an engaging hole forming surface)  683  and an impeller second curved surface (serving as an engaging hole second forming surface or an engaging hole forming surface)  684 . 
     The impeller first planar surface  681  is formed to extend in a direction of a central axis CA 67  of the engaging hole  68 . The impeller first planar surface  681  is formed at a corresponding location, at which the impeller first planar surface  681  opposes the shaft first planar surface  523 . When the shaft  52  is rotated, the impeller first planar surface  681  is contactable with the shaft first planar surface  523 . 
     The impeller second planar surface  682  is a planar surface that is formed to extend in the direction of the central axis CA 67 . The impeller second planar surface  682  is generally parallel to the impeller first planar surface  681 . The impeller second planar surface  682  is formed at a corresponding location, at which the impeller second planar surface  662  opposes the shaft second planar surface  524 . When the shaft  52  is rotated, the impeller second planar surface  682  is contactable with the shaft second planar surface  524 . 
     The impeller first curved surface  683  connects between one side of the impeller first planar surface  681 , which is parallel to the central axis CA 67 , and one side of the impeller second planar surface  682 , which is parallel to the central axis CA 67 . A cross section of the impeller first curved surface  683  is configured into a shape of an arc, which is centered at the point along the central axis CA 67  and is radially outwardly bulged. A first groove (serving as a deformation enabling space)  685  is formed generally in a center (circumferential center) of the impeller first curved surface  683 . 
     The impeller second curved surface  684  connects between another side of the impeller first planar surface  681 , which is parallel to the central axis CA 67 , and another side of the impeller second planar surface  682 , which is parallel to the central axis CA 67 . A cross section of the impeller second curved surface  684  is configured into a shape of an arc, which is centered at the point along the central axis CA 67  and is radially outwardly bulged. A second groove (serving as a deformation enabling space)  686  is formed generally in a center (circumferential center) of the impeller second curved surface  684 . 
     The first groove  685  is configured into a form of a slit and extends from the impeller first curved surface  683  in the radially outward direction. The first groove  685  is formed to communicate with the engaging hole  68  and extends through the impeller  67  in the direction of the central axis CA 67 . The second groove  686  is configured into a form of a slit and extends from the impeller second curved surface  684  in the radially outward direction. The second groove  686  is formed to communicate with the engaging hole  68  and extends through the impeller  67  in the direction of the central axis CA 67 . 
     The first groove  685  and the second groove  686  extend in two opposite directions, respectively, which are opposite to each other when the two directions are viewed from the central axis CA 67 . Furthermore, a radial length of the first groove  685  and a radial length of the second groove  686  are equal to each other. Here, it is assumed that an imaginary circle, which is centered at the central axis CA 67  and circumferentially connects radially inner side parts of the tilt surfaces  64  of the impeller  67 , is an imaginary circle VL 64 , and an imaginary circle, which is centered at the central axis CA 67  and extends along the impeller first curved surface  683  and the impeller second curved surface  684 , is an imaginary circular VL 68 . In such a case, a radially outer side wall surface  687  of the first groove  685 , and a radially outer side wall surface  688  of the second groove  686 , are formed on a radially inner side of an intermediate imaginary circle VL 67  that is radially equally spaced (by a distance D2 in  FIG. 4 ) from both of the imaginary circle VL 64  and the imaginary circle VL 68 , as shown in  FIG. 4 . 
     In the fuel pump of the second embodiment, the first groove  685  and the second groove  686  are formed on the radially inner side of the intermediate imaginary circle VL 67 . In this way, the impeller  67  can be appropriately deformed by the action of the shaft  52 . Therefore, the fuel pump of the second embodiment achieves the advantages, which are similar to those of the first embodiment. Also, in the fuel pump of the second embodiment, the tolerable amount of deformation is increased in comparison to that of the first embodiment. Thereby, the damage of the impeller  67  caused by the rotational torque of the shaft  52  can be further effectively limited. 
     Third Embodiment 
     Next, a fuel pump according to a third embodiment of the present disclosure will be described with reference to  FIG. 5 . The third embodiment differs from the first embodiment with respect to the shape of the impeller. In the following description, components, which are similar to those of the first embodiment, will be indicated by the same reference numerals and will not be described further. 
     In the fuel pump of the third embodiment, the impeller  85  includes a plurality of tilt surfaces  84 , an engaging hole  86  and a plurality of through-holes (serving as deformation enabling spaces)  87 . 
     Similar to the tilt surfaces  64  of the first embodiment, the tilt surfaces  84  are formed at the location that corresponds to the grooves  63 ,  73 . 
     Similar to the engaging hole  66  of the first embodiment, a cross section of the engaging hole  86  is configured to have a generally I-shape to correspond with the cross section of the end portion  522  of the shaft  52 . The engaging hole  86  is formed by an impeller first planar surface (serving as an impeller side first contact surface or an impeller side contact surface)  861 , which is contactable with the shaft first planar surface  523 , and an impeller second planar surface (serving as an impeller side second contact surface or an impeller side contact surface)  862 , which is contactable with the shaft second planar surface  524 . 
     The through-holes  87  extend through the impeller  85  in a direction of a central axis CA 85 . In the fuel pump of the second embodiment, the total number of the through-holes  87  is six, and these through-holes  87  are arranged one after another at equal intervals along an imaginary circle, which is located on a radially outer side of the engaging hole  86  and is centered at a point along the central axis CA 85  of the engaging hole  86 . Each of the through-holes  87  is formed at a corresponding location which is point symmetric to another one of the through-holes  87  about a symmetric point that is a point along the central axis CA 85 . 
     In the fuel pump of the third embodiment, when the shaft  52  is rotated in the engaging hole  86  of the impeller  85 , only one of the shaft first planar surface  523  and the shaft second planar surface  524  of the shaft  52  may contact the inner wall of the engaging hole  86  in some cases. In such a case, the shape of the engaging hole  86  is changed due to the deformation of the through-holes  87 , and the other one of the shaft first planar surface  523  and the shaft second planar surface  524  of the shaft  52 , which was not previously in contact with the inner wall of the engaging hole  86 , now contacts the inner wall of the engaging hole  86 . In this way, the fuel pump of the third embodiment can achieve the advantages, which are similar to the advantages discussed in the sections (a) and (b) of the first embodiment, can be achieved. Furthermore, the through-holes  87  are arranged one after another at equal intervals along the imaginary circle, which is centered at the point along the central axis CA 85 , and each of the through-holes  87  is formed at the corresponding location which is point symmetric to another one of the through-holes  87  about the symmetric point that is the point along the central axis CA 85 . In this way, when the rotational torque of the shaft  52  is applied to the impeller first planar surface  861  or the impeller second planar surface  862 , the impeller  85  is deformed to the similar shape. Thereby, the concentration of the stress (force) on any particular portion of the impeller  85  can be limited. Thus, it is possible to limit the damage of the impeller  85  caused by the rotational torque of the shaft  52 . 
     Fourth Embodiment 
     Next, a fuel pump according to a fourth embodiment of the present disclosure will be described with reference to  FIG. 6 . The fourth embodiment differs from the third embodiment with respect to the shape of the impeller. In the following description, components, which are similar to those of the third embodiment, will be indicated by the same reference numerals and will not be described further. 
       FIG. 6  is a top view of an impeller  88  of a fuel pump according to the fourth embodiment. The impeller  88  includes the tilt surfaces  84 , the engaging hole  86  and a plurality of through-holes (serving as deformation enabling spaces)  89 . 
     The through-holes  89  extend through the impeller  88  in the direction of the central axis CA 88 . In the fuel pump of the fourth embodiment, the total number of the through-holes  89  is six, and these through-holes  89  are arranged one after another at equal intervals along an imaginary circle, which is located on a radially outer side of the engaging hole  86  and is centered at a point along the central axis CA 88  of the engaging hole  86 . 
     Here, it is assumed that an imaginary circle, which is centered at the central axis CA 88  and circumferentially connects radially inner side parts of the tilt surfaces  84  located at the radially outer side in the impeller  88 , is an imaginary circle VL 84 , and an imaginary circle, which is centered at the central axis CA 88  and extends along the impeller first curved surface (serving as the engaging hole forming surface)  863  and the impeller second curved surface (serving as the engaging hole forming surface)  864  of the engaging hole  86 , is an imaginary circular VL 88 . In such a case, the through-holes  89  are formed on a radially inner side of an intermediate imaginary circle VL 88  that is radially equally spaced (by a distance D4 in  FIG. 6 ) from both of the imaginary circle VL 84  and the imaginary circle VL 86 , as shown in  FIG. 6 . 
     In the fuel pump of the fourth embodiment, the through-holes  89  are formed on the radially inner side of the intermediate imaginary circle VL 88 . In this way, the impeller  88  can be appropriately deformed by the action of the shaft  52 . Therefore, the fuel pump of the fourth embodiment achieves the advantages, which are similar to those of the third embodiment. Also, according to the fourth embodiment, the tolerable amount of deformation is increased in comparison to that of the third embodiment. Thereby, the damage of the impeller  88  caused by the rotational torque of the shaft  52  can be further effectively limited. 
     Fifth Embodiment 
     Next, a fuel pump according to a fifth embodiment of the present disclosure will be described with reference to  FIG. 7 . In the fifth embodiment, the shape of the end portion of the shaft and the shape of the impeller are different from those of the third embodiment. In the following description, components, which are similar to those of the third embodiment, will be indicated by the same reference numerals and will not be described further. 
       FIG. 7  is a top view of an impeller  95  of a fuel pump according to the fifth embodiment. The impeller  95  includes a plurality of tilt surfaces  94 , an engaging hole  96  and a plurality of through-holes (serving as deformation enabling spaces)  991 - 995 . 
     The tilt surfaces  94  are formed at a location, which corresponds to the groove  63  formed in the pump cover  60  and the groove  73  formed in the pump casing  70 . 
     The cross section of the engaging hole  96  is configured into a generally D-shape to correspond with a cross section of the one end portion  922  of the shaft  92 . The engaging hole  96  is formed by an impeller third planar surface (serving as an impeller side third contact surface or an impeller side contact surface)  961  and an impeller curved surface (serving as an engaging hole forming surface)  963 . The impeller third planar surface  961  is contactable with a shaft third planar surface (serving as a shaft side third contact surface or a shaft side contact surface)  923  formed in the one end portion  922  of the shaft  92 . The impeller curved surface  963  is formed to extend along a shaft third curved surface (serving as a shaft third curved surface or a shaft curved surface)  925 . The shaft third curved surface  925  is an arcuately curved surface and connects between two ends of the shaft third planar surface  923 , which are generally parallel to a central axis CA 95 . 
     The through-holes  991 - 995  extend through the impeller  95  in the direction of the central axis CA 95 . In the fuel pump of the fifth embodiment, the impeller  95  includes the five through-holes  991 - 995 . The through-holes  991 - 995  are arranged one after another at equal intervals along an imaginary circle, which is located on the radially outer side of the engaging hole  96  and is centered at the point along the central axis CA 95  of the engaging hole  96 . Furthermore, among the through-holes  991 - 995  of the impeller  95 , two of them, i.e., the through-holes  992 ,  995  are placed adjacent to two points  962 ,  964 , respectively, at each of which the impeller third planar surface  961  and the impeller curved surface  963  are connected with each other. 
     Here, it is assumed that an imaginary circle, which is centered at the central axis CA 95  and circumferentially connects radially inner side parts of the tilt surfaces  94 , is an imaginary circle VL 94 , and an imaginary circle, which is centered at the central axis CA 95  and extends along the impeller curved surface  963 , is an imaginary circular VL 96 . In such a case, the through-holes  991 - 995  are formed on a radially inner side of an intermediate imaginary circle VL 98  that is radially equally spaced (by a distance D5 in  FIG. 7 ) from both of the imaginary circle VL 94  and the imaginary circle VL 96 , as shown in  FIG. 7 . 
     In the fuel pump of the fifth embodiment, the cross section of the end portion  922  of the shaft  92  has the D-shape, and the cross section of the engaging hole  96  has the D-shape. Here, the total number of the through-holes  991 - 995  is five, which is the odd number and corresponds to the shape of the engaging hole  96 . In this way, unlike the I-shape of the cross section of the engaging hole, which receives the end portion of the shaft and contacts the end portion of the shaft at the two opposed sides of the engaging hole, even in the case of the engaging hole, which has the cross section that has the D-shape to contact with the end portion of the shaft only at the one side of the engaging hole, the impeller  95  can be deformed such that the shaft third planar surface  923  contacts the impeller third planar surface  961 . Therefore, in the fifth embodiment, the advantages, which are similar to those of the third embodiment, are achieved. 
     Furthermore, in the fuel pump of the fifth embodiment, the through-holes  991 - 995  are formed on the radially inner side of the intermediate imaginary circle VL 98 . In this way, the impeller  95  can be appropriately deformed by the action of the shaft  52 . As a result, the fuel pump of the fifth embodiment can further effectively limit the damage of the impeller  95  caused by the rotational torque of the shaft  92 . 
     Furthermore, in the impeller  95 , the number of the through-holes  991 - 995  is five, which corresponds to the shape of the engaging hole  96 . In this way, the weight balance of the impeller  95  is kept uniform throughout the impeller  95 , so that occurrence of defects, such as vibrations, at the time of rotation of the impeller  95  can be limited. 
     Other Embodiments 
     (A) In the first and second embodiments, the first groove and the second groove are formed as deformation enabling spaces, respectively. In the third to fifth embodiments, the through-holes are formed as deformation enabling spaces, respectively. However, the shape of the deformation enabling space(s) is not limited to any of these shapes. Specifically, the shape of each deformation enabling space can be any other suitable shape as long as the deformation enabling space is formed in the impeller and can be deformed to increase the resiliently deformable amount of the impeller at the time of occurrence of the contact between the shaft and the impeller. 
     (B) In the above embodiments, the shaft first planar surface (serving as the shaft side first contact surface), the shaft second planar surface (serving as the shaft side second contact surface), the impeller first planar surface (serving as the impeller side first contact surface), and the impeller second planar surface (serving as the impeller side second contact surface) are formed as the planar surfaces, respectively. However, it is not necessarily to form these surfaces as the planar surfaces, respectively. Specifically, any one or more of these surfaces may be formed as, for example, a curved surface or any other suitable form as long as the shaft side first contact surface and the impeller side first contact surface are contactable with each other, and the shaft side second contact surface and the impeller side second contact surface are contactable with each other. 
     (C) In the above embodiments, the shaft first planar surface (serving as the shaft side first contact surface) and the shaft second planar surface (serving as the shaft side second contact surface) are formed to be generally parallel to each other. Alternatively, the shaft first planar surface and the shaft second planar surface may be formed to be non-parallel to each other. 
     (D) In the first and second embodiments, the plurality of deformation enabling spaces is formed in the first and second embodiments. Alternatively, it is possible to provide a single deformation enabling space. 
     (E) In the first and second embodiments, the first groove and the second groove are formed in the center of the impeller first curved surface and the center of the impeller second curved surface, respectively. However, the location of the first groove and the location of the second groove should not be limited to these locations. 
     (F) In the first and second embodiments, the radial length of the first groove and the radial length of the second groove are equal to each other, and the first groove and the second groove extend to the opposite directions, respectively. However, the relationship between the first groove and the second groove should not be limited to this relationship. 
     (G) In the third to fifth embodiments, the through-holes are arranged one after another at equal intervals along the imaginary circle, which is centered at the point along the central axis of the impeller, in the impeller, and each of these through-holes is point-symmetric to another one of these through-holes. However, the locations of the through-holes should not be limited to these locations. 
     (H) In the third and fourth embodiments, the total number of the through-holes of the impeller is six. Furthermore, in the fifth embodiment, the total number of the through-holes of the impeller is five. In the case where the cross section of the engaging hole of the impeller is the I-shape, it is desirable that the total number of the through-holes is even number. Furthermore, in the case where the cross section of the engaging hole of the impeller is the D-shape, it is desirable that the total number of the through-holes is odd number. However, the total number of the through-holes is not limited to any of these. 
     (I) In the above embodiments, the motor device of the fuel pump is the brushless motor. However, as long as the motor can rotate the shaft in the two directions, i.e., the normal direction and the reverse direction, any other suitable motor, which is other than the brushless motor, may be used. 
     The present disclosure is not limited to the above embodiments, and the above embodiments may be modified in various ways within the principle of the present disclosure.