Abstract:
A fluid fuel pump and its electrically driven brushless motor are located at opposite ends of a common housing.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is based on and incorporates herein by reference Japanese Patent Applications No. 2005-257416 filed on Sep. 6, 2005, and No. 2006-171173 filed on Jun. 21, 2006. 
     FIELD OF THE INVENTION 
     The present invention relates to a fluid pump having a housing. 
     BACKGROUND OF THE INVENTION 
     For example, according to US 2005/0074343 A1 (JP-A-2005-110478), a fuel pump includes a brushless motor. In general, a motor (brush-type motor) having contact brushes causes losses such as slide resistance between a commutator and a brush, electric resistance between the commutator and the brush, and fluid resistance caused by grooves, via which the commutator is divided into segments. By contrast, a brushless motor may not cause the above losses arising in the brush-type motor. Therefore, a brushless motor is higher than a brush-type motor in motor efficiency, so that a fuel pump having a brushless motor is enhanced in pump efficiency. Here, the pump efficiency is a ratio of an amount of work produced by the fuel pump relative to electricity supplied to the fuel pump. The amount of work produced by the fuel pump can be calculated by multiplying fuel discharge pressure by a fuel discharge amount. 
     When the amount of work is constant, as the efficiency of the fuel pump increases, a motor portion can be downsized, so that the fuel pump can be downsized. A fuel pump including a brushless motor may be applied to a small vehicle such as a motor cycle. 
     A fuel pump including a brush-type motor has a stator core that is located radially outside a rotator. The outer circumferential periphery of the stator core is surrounded by a housing for restricting fuel from leaking. The housing is not necessary to form a magnetic circuit in a brushless motor. According to US 2005/0074343 A1, the thickness of the housing is larger in a portion surrounding the outer circumferential periphery of the stator core. Accordingly, in this structure, the outer diameter of the housing surrounding the stator core is relatively large. Consequently, it is difficult to reduce the outer diameter of the fuel pump. 
     SUMMARY 
     In view of the foregoing and other problems, it is an object of the present exemplary embodiment to produce a fluid pump that includes a downsized housing. 
     According to one aspect of the present exemplary embodiment, a fluid pump includes a stator core having an inner circumferential periphery. The fluid pump further includes a plurality of coils that are wound around the stator core. The plurality of coils circumferentially generate magnetic poles in the inner circumferential periphery of the stator core when being supplied with electricity. The magnetic poles are switched by controlling electricity supplied to the plurality of coils. The fluid pump further includes a rotor that is rotatable within the inner circumferential periphery of the stator core. The rotor has an outer circumferential periphery opposed to the inner circumferential periphery of the stator core. The outer circumferential periphery defines magnetic poles different from each other with respect to a rotational direction of the rotor. The fluid pump further includes a pump portion that has a rotor member. The rotor of the motor is adapted to rotate the rotor member of the pump for pumping fuel. 
     According to one aspect of the present exemplary embodiment, the fluid pump further includes a housing that has a pump housing portion and a motor housing portion. The pump housing portion surrounds the outer circumferential periphery of the pump portion. The motor housing portion defines an accommodating portion that surrounds an outer circumferential periphery of the stator core. The motor housing portion is dented radially inwardly with respect to the pump housing portion. The motor housing portion may have an outer diameter that is less than an outer diameter of the pump housing portion. 
     Alternatively, according to another aspect of the present exemplary embodiment, the fluid pump further includes a housing that has an inner circumferential periphery defining a recession, which accommodates the stator core. 
     Alternatively, according to another aspect of the present exemplary embodiment, the fluid pump further includes a housing that includes a pump housing portion, an intermediate housing portion, and a motor housing portion. The pump housing portion circumferentially surrounds the outer circumferential periphery of the pump portion. The motor housing portion circumferentially surrounds the outer circumferential periphery of the stator core. The intermediate housing portion is interposed axially between the pump housing portion and the motor housing portion. The intermediate housing portion has an inner diameter that is less than an inner diameter of the pump housing portion. The inner diameter of the intermediate housing portion is less than an inner diameter of the motor housing portion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the present exemplary embodiment will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings: 
         FIG. 1  is a longitudinal partially sectional view showing a fuel pump according to a first embodiment; 
         FIG. 2  is a longitudinal partially sectional view showing a fuel pump according to a second embodiment; 
         FIG. 3  is a longitudinal partially sectional view showing a fuel pump according to a third embodiment; 
         FIG. 4  is a longitudinal partially sectional view showing a fuel pump according to a fourth embodiment; 
         FIG. 5  is a sectional view taken along the line V-V in  FIG. 4 ; 
         FIG. 6  is a sectional view showing a molding die accommodating components of the fuel pump; and 
         FIG. 7  is a cross sectional view showing a fuel pump according to a fifth embodiment. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     First Embodiment 
     As shown in  FIG. 1 , a fuel pump  10  may be an in-tank turbine pump that is provided in a fuel tank of a motorcycle with an engine size of 150 cc, for example. 
     The fuel pump  10  includes a pump portion  12  and a motor portion  13 . The motor portion  13  rotates the pump portion  12 . A housing  14  is shaped by press-forming a metallic thin plate to be in a cylindrical shape. The thickness of the metallic thin plate may be around 0.5 mm. The housing  14  at least partially accommodates the pump portion  12  and the motor portion  13 . The housing  14  formed of the thin plate has an inwardly directed protrusion  16 . The protrusion  16  is formed by radially inwardly denting the circumferential periphery of the housing  14  between the pump portion  12  and the motor portion  13 . The housing  14  has an inner circumferential periphery  14   a  that defines axially extending recesses  18 ,  19  on both sides of protrusion  16 . The protrusion  16  is axially interposed between the recesses  18 ,  19 . 
     The pump portion  12  serves as a turbine pump. The pump portion  12  includes pump cases  20 ,  22 , and an impeller  24 , for example. The pump case  22  is press-inserted into the recession  18  of the housing  14 , and axially abutted against the protrusion  16  of the housing  14 . Thus, the pump case  22  is axially aligned. The pump case  20  is fixed by crimping one end of the housing  14 . When the pump case  20  is fixed by crimping the one end of the housing  14 , the housing  14  is applied with axial force by a crimping jig attached to the outer circumferential periphery of the protrusion  16  of the housing  14 . 
     The pump cases  20 ,  22  rotatably accommodate the impeller  24  as a rotor member. The pump cases  20 ,  22  and the impeller  24  define pump passages  200  thereamong. The pump passages  200  are in substantially C-shapes. Fuel is drawn through an unillustrated inlet port provided to the pump case  20 , and is pressurized through the pump passages  200  by rotation of the impeller  24 , thereby being press-fed toward the motor portion  13 . The fuel press-fed toward the motor portion  13  is supplied toward an engine through an outlet port  204  after passing through a fuel passage  202 . The fuel passage  202  is defined between the stator core  30  and the rotator  50 . 
     The motor portion  13  is a brushless motor that includes the stator core  30 , bobbins  40 , coils  42 , and the rotator  50 . The stator core  30 , the bobbins  40 , and the coils  42  are accommodated in the recession  19  of the housing  14 . The stator core  30  is formed by crimping axially stacked magnetic steel plates to each other. The stator core  30  is provided with six teeth protruding toward the center of the motor portion  13 . The six teeth are circumferentially arranged at substantially regular intervals. Each of the coils  42  is wound around each of the bobbins  40  of each of the teeth  32 . 
     Each of the coils  42  electrically connects with each of terminals  44 . Supplying electricity to each of the coils  42  is controlled in accordance with a rotational position of the rotator  50 . An end cover  46  is integrally molded of electrically insulative resin when the stator core  30  and the coils  42  are molded of the electrically insulative resin. The end cover  46  has an outer circumferential periphery  47  that is press-inserted into an end  15  of the housing  14 . In  FIG. 1 , the winding of each of the coils  42  is not illustrated. 
     The rotator  50  includes a shaft  52 , a rotational core  54 , and a permanent magnet  56 . The rotator  50  is rotatable within the inner circumferential periphery of the stator core  30 . The shaft  52  is rotatably supported by bearings  26  at both ends. The permanent magnet  56  is a resin magnet that is produced by mixing magnetic powder with thermoplastic resin such as polyphenylene sulfide (PPS). The permanent magnet  56  is in a substantially cylindrical shape. The permanent magnet  56  is located around the outer circumferential periphery of the rotational core  54 . The permanent magnet  56  has eight magnetic poles  57  arranged with respect to the rotative direction. The eight magnetic poles  57  are magnetized to define magnetic poles toward the outer circumferential periphery of the permanent magnet  56 . The outer circumferential periphery of the permanent magnet  56  is opposed to the inner circumferential periphery of the stator core  30 . The magnetic poles are different from each other with respect to the rotative direction. 
     The end cover  46  has the outlet port  204  that accommodates a valve member  60 , a stopper  62 , and a spring  64 . The valve member  60  is lifted against bias force of the spring  64  when pressure of fuel pressurized in the pump portion  12  becomes equal to or greater than a predetermined pressure, so that fuel is discharged toward the engine through the outlet port  204 . 
     In the first embodiment, the protrusion  16  is formed by circumferentially inwardly denting the housing  14 , which is constructed of the thin plate substantially uniform in thickness, for example. The inner circumferential periphery  14   a  of the housing  14  defines the protrusion  16  and the recessions  18 ,  19 . Components of the pump portion  12  and the motor portion  13  are accommodated in the recessions  18 ,  19  without partially increasing the thickness of the housing  14 . Thus, the outer diameters of the pump portion  12  and the motor portion  13  are reduced. 
     In the first embodiment, the housing can be readily shaped such that the portion of the housing between the stator core and the pump portion is radially and inwardly dented, by such as press forming or die forming a thin plate in dependence on a material of the housing. Therefore, the recession can be readily formed in the inner circumferential periphery of the housing for accommodating the stator core. 
     Second Embodiment 
     As shown in  FIG. 2 , in the second embodiment, a fuel pump  70  includes a metallic housing  72  that has a thick portion  74 . The thick portion  74  radially protrudes inwardly between the pump portion  12  and the motor portion  13  in the metallic housing  72 . The housing  72  has an inner circumferential periphery  72   a  that is thinner than the thick portion  74 . The inner circumferential periphery  72   a  defines recessions  75 ,  76  that are located on axially both sides of the thick portion  74  serving as a protrusion. The recessions  75 ,  76  respectively accommodate components of the pump portion  12  and the motor portion  13 . The inner circumferential periphery  72   a  of the housing  72  defines the thick portion  74  and the recessions  75 ,  76 . The inner circumferential periphery  72   a  is accurately shaped by machining work after forging the housing  72 , for example. Therefore, the center of the stator core  30 , which is accommodated in the recession  76 , and the center of a rotator  80 , which is accommodated in the stator core  30 , can be accurately aligned. Furthermore, the stator core  30  can be axially accurately aligned. 
     The pump case  20  and the end cover  46  are fixed by crimping both axial ends of the housing  72 . The stator core  30  and the pump case  22  are abutted against the axial ends of the thick portion  74 , so that the stator core  30  and the pump case  22  can be axially aligned. 
     The rotator  80  includes a shaft  82  and a permanent magnet  84 . The permanent magnet  84  is directly fitted to the outer circumferential periphery of the shaft  82 . The outer circumferential periphery of the shaft  82  is knurled. The permanent magnet  84  has eight magnetic poles  85  arranged with respect to the rotative direction. The eight magnetic poles  85  are magnetized to define magnetic poles toward the outer circumferential periphery of the rotator  80 . The outer circumferential periphery of the rotator  80  is opposed to the inner circumferential periphery of the stator core  30 . The magnetic poles are different from each other with respect to the rotative direction of the rotator  80 . 
     In the second embodiment, the thick portion  74  inwardly protrudes circumferentially between the pump portion  12  and the motor portion  13 , so that the inner circumferential periphery  72   a  of the housing  72  defines the recessions  75 ,  76  respectively accommodating the components of the pump portion  12  and the motor portion  13 . The housing  72  is thin around the recessions  75 ,  76 . Thus, the outer diameter of the fuel pump  70  is reduced. 
     In the second embodiment, the thick portion  74  defines the recessions  75 ,  76 , so that the outer circumferential periphery of the housing  72  does not define a recession. Therefore, the outer circumferential periphery of the housing  72  can be readily plated uniformly for protecting the housing  72  from corrosion. 
     Third Embodiment 
     As shown in  FIG. 3 , in the third embodiment, a fuel pump  90  includes an outer circumferential housing  94  and an inner circumferential housing  96 . The outer circumferential housing  94  and the inner circumferential housing  96  are shaped by press-forming metallic thin plates to be in substantially cylindrical shapes, for example. The inner circumferential housing  96  serving as a protrusion is press-inserted into the inner circumferential periphery of the outer circumferential housing  94 , for example. The inner circumferential housing  96  is located between the pump portion  12  and the motor portion  13 . The inner circumferential periphery  92   a  of the housing  92  defines recessions  98 ,  99  on axially both sides of the inner circumferential housing  96 . The recessions  98 ,  99  respectively accommodate components of the pump portion  12  and the motor portion  13 . The pump case  20  and the stator core  30  are fixed by crimping axially both ends of the outer circumferential housing  94 . The pump case  22  and the stator core  30  are abutted against the axial ends of the inner circumferential housing  96 , so that the pump case  22  and the stator core  30  can be axially aligned. 
     The rotator  100  is constructed of a shaft  102  and the permanent magnet  84 . The permanent magnet  84  is fitted directly to the outer circumferential periphery of the shaft  102 . The outer circumferential periphery of the shaft  102  has a chamfer  103 . 
     In the third embodiment, the inner circumferential housing  96  is press-inserted into the inner circumferential periphery of the outer circumferential housing  94 , for example. The inner circumferential housing  96  is located between the pump portion  12  and the motor portion  13 , so that the recessions  98 ,  99  are defined. The recessions  98 ,  99  respectively accommodate components of the pump portion  12  and the motor portion  13 . The housing  94  is thin around the recessions  98 ,  99 . Thus, the outer diameter of the fuel pump  90  can be reduced. 
     In the third embodiment, the recession  99  can be readily formed for accommodating the stator core  30  in a simple structure, in which the inner circumferential housing  96  is press-inserted into the inner circumferential periphery of the outer circumferential housing  94 , without increasing the thickness of the outer circumferential housing  94 . The inner circumferential housing  96  may be welded and fixed to the inner circumferential periphery of the outer circumferential housing  94 . 
     In the third embodiment, the inner circumferential housing  96  is press-inserted into the inner circumferential periphery of the cylindrical outer circumferential housing  94 , so that the recessions  98 ,  99  are defined. The outer circumferential periphery of the outer circumferential housing  94  need not define a recession. Therefore, the outer circumferential periphery of the outer circumferential housing  94  can be readily plated uniformly for protecting the outer circumferential housing  94  from corrosion. 
     Fourth Embodiment 
     As shown in  FIG. 4 , the end cover  46  has a bearing hole  112  that directly supports one axial end of the shaft  82  in a fuel pump  110 . The bearing hole  112  partially communicates with a fuel passage through which fuel is introduced from the motor portion  13  toward the outlet port  204 . The end cover  46  has an outer circumferential periphery  114  that makes contact with the inner circumferential periphery  72   a  of the housing  72 . The axial end of the housing  72  is crimped onto the end cover  46 , so that the inner circumferential periphery  72   a  of the housing  72  and the outer circumferential periphery  114  of the end cover  46  define a fuel seal therebetween. Fuel may leak from the side of the inner circumferential periphery of the stator core  30  to the side of the outer circumferential periphery of the stator core  30 . The fuel seal restricts the fuel from further leaking to the outside of the fuel pump  110 . Thus, pressure of fuel increased in the fuel pump can be maintained. 
     The stator core  30  has an axial end  34  on the side of the pump portion  12 . The axial end  34  has an outer circumferential end  35  on the side of the outer circumferential periphery of the bobbin  40 . The circumferential periphery of the outer circumferential end  35  is at least partially or entirely not exposed to an electrically insulative resin, which is charged around the stator core  30  and the coils  42 , and is formed to be the end cover  46 . The outer circumferential end  35  is abutted against one axial end  76   a  of the recession  76  by crimping the housing  72  onto the end cover  46 . Thus, the stator core  30  can be readily aligned axially with respect to the housing  72 . 
     The outer circumferential periphery of the stator core  30  and the inner circumferential periphery  72   a  of the housing  72  define a fuel seal therebetween. The outer circumferential periphery  114  of the end cover  46  and the inner circumferential periphery  72   a  of the housing  72  define a fuel seal therebetween. The fuel seals and the portion of the outer circumferential end  35  of the stator core  30 , which is abutted against the one axial end  76   a  of the recession  76 , define a space  208  thereamong on the side of the outer circumferential periphery of the stator core  30 . 
     As shown in  FIG. 5 , the outer circumferential periphery of each of the teeth  32  of the stator core  30  defines a groove  36  that axially extends. The electrically insulative resin, which is formed to be the end cover  46 , is charged into the groove  36 . 
     As shown in  FIG. 4 , a slant restriction member  120  is in an annular shape. The slant restriction member  120  defines a through hole at the center thereof. The slant restriction member  120  makes contact with the end of the bobbin  40  on the opposite side of the pump portion  12 . The slant restriction member  120  has fitting holes with which terminals  44  fit. 
     As shown in  FIG. 6 , a molding die  300  is used for molding the end cover  46  of the electrically insulative resin, which is charged around the stator core  30  and the coils  42 . The molding die  300  includes an outer die  302  and an inner die  304 . The stator core  30  having the bobbins  40  is located between the outer die  302  and the inner die  304 . Each of the coils  42  is wound around each of the bobbins  40 . The side of the inner die  304  opposed to the stator core  30  has protrusions  306 . The teeth  32 , which are circumferentially adjacent to each other, define a clearance therebetween. Each of the protrusions  306  engages with the clearance between the teeth  32  from the radially inward circumferential periphery of the inner die  304 , thereby circumferentially aligning the teeth  32 . The outer circumferential end  35  ( FIG. 4 ) of the stator core  30  on the side of the pump portion  12  makes contact with a bottom portion of the molding die  300  on the side of the outer circumferential periphery of the bobbin  40 . The slant restriction member  120  makes contact with the end of the bobbin  40 . The terminals  44  fit to the fitting holes of the slant restriction member  120 . 
     Thus, the electrically insulative resin is charged from the side of the slant restriction member  120  into the molding die  300  in a condition where inserted components are located in the molding die  300 , so that the end cover  46  is injection molded. The inserted components include the stator core  30 , the bobbin  40 , the coils  42 , the terminals  44 , the slant restriction member  120 , and the like. In this condition, the outer circumferential end  35  of the stator core  30  on the side of the pump portion  12  makes contact with the bottom portion of the molding die  300 . Therefore, the inserted components can be readily aligned with respect of the molding die  300 . In addition, the stator core  30  can be restricted from being axially misaligned with respect to the molding die  300  even when the stator core  30  is applied with molding pressure axially from the slant restriction member  120 . 
     The electrically insulative resin charged into the molding die  300  is also filled into the groove  36  defined in the outer circumferential periphery of each of the teeth  32 . Thus, each of the teeth  32  is urged onto the inner die  304  by molding pressure. Consequently, the inner circumferential periphery of each of the teeth  32  on the side of the rotator  80  is circumferentially aligned along the outer circumferential periphery of the inner die  304 . Therefore, the gap, which is defined between the stator core  30  and the permanent magnet  84  after molding the end cover  46 , can be uniformized with respect to the rotative direction. 
     As described above, the inert-molding process of the stator core  30  has been described with reference to  FIG. 6 . The molded stator core  30  is removed from the molding die  300 . Subsequently, the molded stator core  30  is assembled with the rotator  80  and the housing  72  to be in the condition shown in  FIG. 5 . Specifically, in  FIG. 5 , when the molded stator core  30  is inserted into the housing  72 , the molded stator core  30  and the housing  72  therebetween define the space  208  around the outer circumferential periphery of the stator core  30 . 
     In the molding process of  FIG. 6 , the electrically insulative resin material filled into each groove  36  and the electrically insulative resin material filled between the teeth  32  may cause a flash and such a flash may be detached after molding the end cover  46 . Even when the flash is detached to the circumferentially outer side of the stator core  30  after or when the molded stator core  30  is inserted into the housing  72 , the detached flash is retained in the space  208  ( FIG. 4 ) defined around the outer circumferential periphery of the stator core  30 . Therefore, the flash can be restricted from being stuck in a sliding member of the fuel pump  110 , so that pressure of the fuel pump  110  can be maintained. 
     The injection molding is conducted in the condition where the terminals  44  fit to the fitting holes of the slant restriction member  120 , so that the terminals  44  can be restricted from being inclined by molding pressure, thereby being restricted from causing interference with peripheral components of the terminals  44 . 
     In the fourth embodiment, the terminals and the stator core are insert-molded of electrically insulative resin material, so that the coils can be insulated from fuel. Thus, the coil can be protected from corrosion. 
     In the fourth embodiment, the outer circumferential end of the one axial end of the stator core is at least partially not exposed to the electrically insulative resin. The outer circumferential end of the stator core is abutted against the axial end of the recession. Therefore, the stator core can be readily aligned axially with respect to the housing when the stator core charged with the electrically insulative resin is assembled into the housing. 
     In the above first to fourth embodiments, the recession defined by the inner circumferential periphery of the metallic housing accommodates the stator core  30 , so that the thickness of the housing surrounding the outer circumference of the stator core  30  can be reduced, and the outer diameter of the brushless motor can be reduced. Consequently, the fuel pump downsized using the brushless motor, which is excellent in motor efficiency, can be further reduced in size. Therefore, the fuel pump can be provided in a fuel tank, even in a small fuel tank for a motorcycle, for example. Furthermore, even a fuel tank for a motorcycle has a saddle shape, the fuel pump can be provided to a limited space in the fuel tank. 
     In the second to fourth embodiments, the recession can be defined in the inner circumferential periphery of the housing for accommodating the stator core without denting the outer periphery of the housing. Therefore, when a treatment such as plating is applied to the outer circumferential periphery of the housing, the treatment can be readily and uniformly applied. 
     In the first to fourth embodiments, the housing includes a pump housing portion, an intermediate housing portion, and a motor housing portion. The pump housing portion circumferentially surrounds the outer circumferential periphery of the pump portion  12 . The motor housing portion circumferentially surrounds the outer circumferential periphery of the stator core  30 . The intermediate housing portion is interposed axially between the pump housing portion and the motor housing portion. The intermediate housing portion may be defined by one of the protrusion  16  in the first embodiment, the thick portion  74  in the second and fourth embodiments, and the inner circumferential housing  96  in the third embodiment. The intermediate housing portion has the inner diameter that is less than the inner diameter of the pump housing portion. The intermediate housing portion has the inner diameter that is less than the inner diameter of the motor housing portion. 
     Fifth Embodiment 
     As shown in  FIG. 7 , in a fuel pump  130  of the fifth embodiment, a housing  132  is shaped by press-forming a metallic thin plate to be in a substantially cylindrical shape. The housing  132  has an accommodating portion  134  that accommodates components of the pump portion  12 . The housing  132  has an accommodating portion  135  that is radially dented inwardly with respect to the accommodating portion  134 . The accommodating portion  135  accommodates components of the motor portion  13  including the stator core  30 . That is, the outer diameter of the accommodating portion  135  is less than the outer diameter of the accommodating portion  134 . The accommodating portion  134  and the accommodating portion  135  define a step  136  therebetween. In the step  136 , the outer diameters of the accommodating portions  134 ,  135  are different from each other. 
     The housing  132  has an end  138  on the opposite side of the pump portion  12 . The end  138  is press-fitted to an outer circumferential periphery  140  of the end cover  46 . The end  138  is axially abutted against a step  142  defined by the outer circumferential periphery  140 , so that the end cover  46 , the stator core  30 , and the housing  132  are axially aligned. 
     The pump case  22  is press-inserted into the accommodating portion  134  of the housing  132 , thereby being axially abutted against the step  136  of the housing  132 . 
     In the fifth embodiment, the accommodating portion  135 , which accommodates the component of the motor portion  13 , is radially dented inwardly with respect to the accommodating portion  134 , which accommodates the components of the pump portion  12 . Therefore, the accommodating portion  135  accommodating the stator core  30  can be readily formed without increasing the thickness of the housing  132 . In addition, the outer diameter of the motor portion  13  is reduced. Thus, the outer diameter of the motor portion  13  is reduced. Therefore, the fuel pump can be provided in a fuel tank, even if the fuel tank is small (in a motorcycle, for example). 
     The outer circumferential periphery of the housing  132  defines only the step  136 , in which the outer diameter of the housing  132  changes. Therefore, the outer circumferential periphery of the housing  132  can be readily plated uniformly for protecting the housing  132  from corrosion. 
     Other Embodiment 
     In the above embodiments, the pump portion  12  is constructed of the turbine pump including the impeller  24 . Alternatively, the pump portion may be constructed of a pump having another structure such as a gear pump. 
     In the above embodiments, the housing  14 ,  72 , the outer circumferential housing  94 , the inner circumferential housing  96 , and the housing  132  are formed of metal. Alternatively, the housings may be formed of a material other than metal such as resin. 
     In the fourth embodiment, the entire circumferential periphery of the outer circumferential end  35  of the axial end  34  of the stator core  30  on the side of the pump portion  12  is not exposed to the electrically insulative resin. Alternatively, the circumferential periphery of the outer circumferential end  35  may be partially exposed to the electrically insulative resin by only partially abutting the outer circumferential end  35  against the molding die, and charging electrically insulative resin. 
     The above structures of the embodiments can be combined as appropriate. For example, the structure of the housing  132  in the fifth embodiment can be combined with the housings  72 ,  94 ,  96 , in the above second to fourth embodiments, in dependence upon design of the stator core and the pump portion. The outer diameter of the fuel pump can be effectively reduced by applying and combining the above structures. 
     In the above embodiments, the structures of the housings are applied to fuel pumps. However, the structures of the housings are not limited to the application of the fuel pumps. The structures of the housings can be applied to any other fluid pumps. 
     It should be appreciated that while the processes of the embodiments have been described herein as including a specific sequence of steps, further alternative embodiments including various other sequences of these steps and/or additional steps not disclosed herein are intended to be within the steps of the present invention. 
     Various modifications and alternations may be diversely made to the above embodiments without departing from the spirit of the present invention.