Title:
Fuel pump
Kind Code:
A1


Abstract:
A fuel pump may have an armature 16 and a pump section 10. The armature 16 may include a shaft 17, a core 21 fixed to the shaft 17, and coils 29 that is wound around the core 21. The pump section 10 is rotatably driven by the shaft 17. Preferably, the armature 16 includes a guide 34 that guides the coils 29 on the outside of the outer surface of the shaft 17 on at least at one axial end of the core 21. The coils 29 are wound around opposing slots. On the end where the guide 34 is provided, the coils 29 are preferably guided by the guide 34, and thereby are wound to detour around the region in proximity to the shaft 17.



Inventors:
Honda, Yoshihiko (Obu-shi, JP)
Takeda, Sumito (Obu-shi, JP)
Application Number:
11/178392
Publication Date:
01/19/2006
Filing Date:
07/12/2005
Assignee:
Aisan Kogyo Kabushiki Kaisha
Primary Class:
Other Classes:
417/423.3
International Classes:
F04B17/00; F04B35/04
View Patent Images:
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Primary Examiner:
KASTURE, DNYANESH G
Attorney, Agent or Firm:
Arlington/LADAS & PARRY LLP (ALEXANDRIA, VA, US)
Claims:
1. A fuel pump comprising: an armature having a shaft, a core fixed to the shaft, and a coils wound around the core; and a pump section to be rotated by the shaft, wherein the coils are wound around opposing slots, and the coils are wound to detour around the region in proximity to the shaft on at least at one axial end of the core.

2. A fuel pump as in claim 1, wherein the armature further comprises a guide for guiding the coils on the outside of the outer surface of the shaft on at least at one axial end of the core, and wherein the coils are wound to detour around the region in proximity to the shaft by being guided by the guide.

3. A fuel pump as in claim 2, wherein the guide is made of resin material.

4. A fuel pump as in claim 3, wherein an insulating coating is formed on the core and the insulating coating and the guide are integrally formed.

5. A fuel pump as in claim 1, wherein guides are provided on both ends of the core.

6. A fuel pump comprising: an armature having a shaft, a core fixed to the shaft, and a coil wound around the core; and a pump section to be rotated by the shaft, wherein the coils are wound around opposing slots, and wherein the armature further comprises a guide to restrict further protrusion of the coils toward the end of the shaft on at least at one axial end of the core.

7. A fuel pump comprising: an armature having a shaft, a core fixed to the shaft, and a coil wound around the core; and a pump section to be rotated by the shaft, wherein the armature further comprises a guide on at least at one axial end of the core, the guide having a first surface, which guides the coils on the outside of the outer surface of the shaft, and a second surface which restricts further protrusion of the coils toward the end of the shaft, the coils are wound around opposing slots, and the coils are wound so as to detour around the region in proximity to the shaft by being guided by the guide.

Description:

CROSS REFERENCE

This application claims priority to Japanese Patent application numbers 2004-205453 and 2005-41863, the contents of which are hereby incorporated by reference as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fuel pump for drawing a fuel such as gasoline etc., increasing the pressure thereof, and discharging this pressurized fuel.

2. Description of the Related Art

FIG. 9 shows a conventional fuel pump. In this fuel pump, a cylindrical housing 104 encloses a pump section 101 and a motor section 102. The motor section 102 comprises an armature 106 and magnets 105. FIG. 10 schematically shows a cross-section of the armature 106. The armature 106 includes a shaft 107, a core 111 fixed to the shaft 107, coils 119 wound around the core 111, and a commutator 108 for supplying current to the coils 119. A pair of bearings 110, 113 is disposed in the vicinity of both ends of the shaft 107. The shaft 107 is rotatably supported by the bearings 110, 113. The bottom end of the shaft 107 engages with the pump section 101. When the shaft 107 rotates, the pump section 101 also rotates.

FIG. 11 shows a cross section view along the line XI-XI of FIG. 10. The core 111 has a plurality of slots 114 (eight slots in this case). Each coil 119 is wound around four slots 114. In this specification, when one coil 119 which has passed a first slot returns to a (1+Y)-th slot, this will be referred to as the coil 119 having been wound around the Y slots. The coil 119 is wound around opposing slots on both sides of the shaft 107. This is to increase the magnetic flux of the magnets 105 which pass through the coil 119 so that the magnetic energy of the magnets 105 will be effectively utilized. If the coil 119 is wound around opposing slots, the coil 119 will pass through the vicinity of the shaft 107, and will overlap in an axial direction of the core 111 (in an axial direction of the shaft 107). Therefore, the coils 119 will project in the axial direction from both ends 111a, 111b of the core 111. The coil 119 which projects from both core ends 111a, 111b will be in close contact with the shaft 107 which has an insulating coating on the surface.

SUMMARY OF THE INVENTION

This type of fuel pump is utilized within a fuel tank, and therefore the axial length of the fuel pump is restricted by the shape (dimension) of the fuel tank. In recent years, fuel tanks have tended to become flatter. Therefore, there is need for the axial length of the fuel pump to be shorter as well. As shown in FIG. 10, the conventional fuel pump has a configuration wherein the shaft 107 is provided with (listing from the top) the upper bearing 113, the commutator 108, the coils 119 which extend further than the core 111 in the axial direction, and the lower bearing 110, these being provided in series. Therefore, the length L3 between the upper bearings 113 and the lower bearing 110 must be at least equal to [the length of the upper bearing 113+the length of the commutator 108+the upwardly projecting length of the coils 119+the length of the core 111+the downwardly projecting length of the coils 119+the length of the lower bearing 110].

The length of the fuel pump in the axial direction is affected by the length of the armature, and the length of the armature is determined by the length between the bearings 113 and 110 of the shaft 107. For example, if it is assumed that the axial length of the bearings 113, 110, the commutator 108, and the core 111 cannot be shortened, there is no way to shorten the axial length of the fuel pump other than to shorten (the upwardly projecting length of the coils 119) and/or (the downwardly length of the coils 119). As shown in FIG. 11, the upwardly (or downeardly) projecting length of the coils 119 is determined by the number of windings of the coil 119 which overlap in the axial direction at the end of the core 111. Therefore, in order to shorten the upwardly (or downwardly) projecting length of the coils 119, the number of windings of the coils 119 must be reduced, but if the number of windings of the coils 119 is reduced, the lamination factor of the winding will drop and the pump efficiency will also be reduced.

Japanese Laid-Open Patent Publication No. 2002-272047 discloses technology to compress the coil ends that projects from the core using a special jig in order to shorten the projecting length of the coil in the axial direction. However, this technology is not very effective when the number of windings of the coil is low or when the diameter of the wire in the winding is small, and this technology does not fundamentally resolve the aforementioned problem. Furthermore, there is a possibility of damaging the insulating coating of the coil during compression because the coil ends are compressed by the jig.

It is, accordingly, one object of the present teachings to provide a fuel pump which can shorten the projecting length of the coils without reducing the number of windings of the coils, and thereby can reduce the axial length of the fuel pump.

In one aspect of the present teachings, fuel pump may comprise a pump section and a motor section. The motor section may include an armature having a shaft, a core fixed to the shaft, and a coils wound around the core. When the armature (i.e., the shaft) rotates, the pump section is also rotationally driven. A guide which guides the coils on the outside of the shaft is preferably provided on at least at one axial end of the core. The coils are wound between opposing slots. The coils are guided by the guide and wound so as to detour away from the region in proximity to the shaft at the end where the guide is provided. Therefore, the coils overlap in a broad area in the radial direction of the core at the end where the guide is provided. Thus, the projecting length of the coils from the end of the core can be shortened. Thereby, the length of the fuel pump in the axial direction can be shortened without reducing the number of windings of the coils (winding lamination factor). Furthermore, there is no concern of damaging the various components of the armature because operations such as compressing the part of the coils which protrudes from the end of the core will not be performed.

Herein, “opposing slots” does not only mean that the two slots have a positional relationship on completely opposite sides of the shaft, but may also mean that a pair of the slots are considered to be “opposing slots” even if the positional relationship is such that the inside edge of the coil is guided by a guide when the coil is wound around the pair of slots.

In another aspect of the present teachings, fuel pump may include a guide which is provided at a position separated only a predetermined distance toward the end of the shaft from the core. The guide restricts further protrusion of the coils toward the end of the shaft. Therefore, on the end where the guide is provided, the coils cannot be overlapped past the guide in the axial direction of the core, and thus the coils will be overlapped in the radial direction of the core. Therefore, the protrusion length of the coils from the end of the core can be shortened without reducing the number of windings (winding lamination factor) of the coils, and thereby the axial length of the fuel pump can be made shorter. Furthermore, an operation of compressing or the like of the coils which protrudes from the end of the core by a jig is not performed, so damage to the various components of the armature is not a concern.

In another aspect of the present teachings, fuel pump may have a guide on at lease one end of the core. The guide may include a first surface and a second surface. The first surface guides the coils on the outside of the outer surface of the shaft. The second surface is located a predetermined distance away from the core toward the end of the shaft, and restricts further protrusion of the coils toward the end of the shaft. Therefore, the coils are guided by the first surface of the guide and are wound so as to detour around the region in proximity to the shaft. Furthermore, the coils are restricted from further protruding toward the end of the shaft by the second surface of the guide. Thus, the protrusion length of the coils past the end of the core can be shortened without reducing the number of windings of the coils. Thereby, the axial length of the fuel pump can be shortened.

In each aspect of the aforementioned teachings, the guide are preferably formed from resin material (e.g., plastic). By forming the guides from resin material, the coils and the shaft can be insulated.

Furthermore, if the guide are formed from resin material, the guide and the insulating coating formed on the core are preferably integrally formed. By integrally forming the guide and the insulating coating on the shaft, the number of components can be reduced and the assembly of the fuel pump can be simplified.

Furthermore, with the aforementioned fuel pumps, guides are preferably provided on both ends of the core. By providing the guides on both ends the core, the fuel pump can be further shortened in the axial direction.

In another aspect of the present teachings, coils are wound around opposing slots. On at least one end in the axial direction of the core, the coils are preferably wound so as to detour around the region in proximity to the shaft. By winding the coils so as to detour around the region in proximity to the shaft, the winding of the coils will be broadly overlapped in the radial direction of the core. Thereby the axial length of the fuel pump can be shortened without reducing the number of windings of the coil.

These aspects and features may be utilized singularly or, in combination, in order to make improved fuel pump. In addition, other objects, features and advantages of the present teachings will be readily understood after reading the following detailed description together with the accompanying drawings and claims. Of course, the additional features and aspects disclosed herein also may be utilized singularly or, in combination with the above-described aspect and features.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a fuel pump of a first representative embodiment of the present teachings.

FIG. 2 schematically shows a cross-sectional view of an armature of the first representative embodiment.

FIG. 3 is a cross-sectional view along the line III-III of FIG. 2.

FIG. 4 shows a routing of coil windings and tensile forces acting on the windings.

FIG. 5 schematically shows a cross-sectional view of an armature of a second representative embodiment of the present teachings.

FIG. 6 is a side view of an armature of a third representative embodiment of the present teachings (prior to coil winding).

FIG. 7 is a side view of the armature of the third representative embodiment (after coil winding).

FIG. 8 schematically shows the structure of the armature of another representative embodiment of the present teachings.

FIG. 9 is a cross-sectional view of a conventional fuel pump.

FIG. 10 schematically shows a cross-sectional view of a armature of the fuel pump shown in FIG. 9.

FIG. 11 is a cross-sectional view along the line XI-XI of FIG. 10.

FIG. 12 shows a routing of coil windings and tensile forces acting on the windings for a conventional fuel pump.

DETAILED DESCRIPTION OF THE INVENTION

A fuel pump according to a first representative embodiment of the present teachings will be explained while referring to the drawings. The fuel pump of the present embodiment is used in a motor vehicle, the fuel pump being utilized within a fuel tank and being utilized for supplying fuel to the engine of the motor vehicle. As shown in FIG. 1, the fuel pump comprises a pump section 10, and a motor section 12.

The pump section 10 comprises a pump cover 19, a pump body 25, and an impeller 26. The pump cover 19 and the pump body 25 are formed, for instance, die casting aluminum. The pump cover 19 and the pump body 25 are fitted together to form a casing 27 wherein the impeller 26 is housed.

The impeller 26 is formed in substantially a disc shape by means of resin molding. Concavities 26a are formed at both upper and lower faces of the impeller 26. A bottom portion of each of the upper and lower concavities 26a communicates via a through hole 26c. The concavities 26a form groups of concavities which extend along a circumferential direction at a position inwardly offset by a pre-determined distance from an impeller outer circumference face 26d. The outer circumference face 26d is a circular face without irregularities.

A fitting shaft portion 17a—this being D-shaped in cross-section—at a lower end portion of the shaft 17 fits into a cross-sectionally D-shaped fitting hole formed in the center of the impeller 26. Thereby, the impeller 26 is connected with the shaft 17 in a manner allowing follow-up rotation whereby slight movement in the axial direction is allowed.

As shown in FIG. 1, a groove 31 is formed in a lower face of the pump cover 19 in an are opposite the concavities 26a in the upper face of the impeller 26. The groove 31 continuously extends in the direction of rotation of the impeller 26 from an upstream end to a downstream end. A discharge hole 24 is formed in the pump cover 19, this discharge hole 24 extending from the downstream end of the groove 31 to an upper face of the pump cover 19. The discharge hole 24 passes through from the interior to the exterior (an inner space 12a of the motor section 12) of the casing 27.

An inner circumference face 19c of a circumference wall 19b of the pump cover 19 faces, along the entire circumference of this pump cover 19, the impeller outer circumference face 26d, with a minute clearance therebetween. For the sake of clarity, the clearance is represented as larger in the figure than it is in reality.

As shown in FIG. 1, a groove 30 is formed in an upper face of the pump body 25 in an area thereof opposite the concavities 26a in the lower face of the impeller 26. The groove 30 extends continuously along the direction of rotation of the impeller 26 from an upstream end to a upstream end. An intake hole 32 is formed in the pump body 25, this intake hole extending from a lower face of the pump body 25 to the upstream end of the groove 30. The intake hole 32 communicates with the groove 30. The intake hole 32 communicates between the interior and the exterior of the casing 27.

The pump body 25, this being in a superposed state with the pump cover 19, is attached by means of caulking to a lower end portion of the housing 14. A thrust bearing 28 is fixed to a center region of the pump body 25. Thrust loads of the shaft 17 are received by the thrust bearing 28.

In FIG. 1, for the sake of clarity, each clearance is represented as larger than it is in reality. The groove 30 of the pump body 25 is not directly communicated with the discharge hole 24 of the pump cover 19. The circumference wall 19b of the pump cover 19 is in proximity to the outer circumference face 26d of the impeller 26 even at the position of the discharge hole 24, and the groove 30 and the discharge hole 24 are essentially not connected on the outward side of the outer circumference face 26d of the impeller 26. The groove 30 and the discharge hole 24 are connected by through holes 26c of the impeller 26.

The groove 31 extending in the circumference direction of the pump cover 19, and the groove 30 extending in the circumferential direction of the pump body 25, extend along the direction of rotation of the impeller 26, and extend from the intake hole 32 to the discharge hole 24. When the impeller 26 rotates, the fuel within the fuel tank is drawn into the casing 27 via the intake hole 32. The fuel drawn into the casing 27 flows into the groove 30, the concavities 26a of the impeller 26, and the groove. The rotation of the impeller 26 causes a revolving current of the fuel between the lower concavities 26a and the groove 30 and the upper concavities 26a and the groove. The pressure of the fuel rises as it flows along the grooves 30 and 31 from intake hole 32 to the discharge hole 24.

The pressurized fuel that has flowed along the groove 31 passes through the through hole 26c and merges with the pressurized fuel that has flowed along the groove 31. The fuel that has been pressurized is delivered to the motor section 12 through the discharge hole 24. The highly pressurized fuel delivered to the motor section is further delivered to the exterior of the fuel pump from a discharge port 38.

The motor section 12 is composed of a direct current motor provided with an armature 16, a brush 13, and permanent magnets 15 fixed within the cylindrical housing 14. The armature 16 is provided concentrically with the magnets 15. The brush 13 is pushed by a spring load so as to make contact with a commutator 18. The brush 13 is connected to an external power source (not shown).

A lower portion of the shaft 17 of the armature 16 is rotatably supported by the bearing 20 in the pump cover 19. An upper end of the shaft 17 is rotatably supported by the bearing 23 in the motor cover 22 which is attached to the upper end portion of the housing 14.

When voltage is applied from an external power source to the brush 13, current flows from the brush 13 to the coils 29 via the commutator 18, causing the armature 16 to rotate. When the armature 16 rotates, the impeller 26 also rotates and fuel is drawn into the fuel pump via the intake hole 32. The fuel which has been drawn in is pressurized by the pump section 10 as described above, and is discharged to the exterior from the discharge port 38.

FIG. 2 schematically shows a cross-sectional view of the armature 16, and FIG. 3 shows a cross-sectional view along the line III-III of FIG. 2. As shown in FIGS. 2 and 3, the armature 16 comprises a core 21 which consists of laminated magnetic plates, guides 34 positioned on both ends of the core 21, the coils 29 wound around slots 24 of the core 21, the commutator 18 which supplies current to the coils 29, and a shaft 17 which supports the core 21, the guides 34, and the commutator 18. The core 21 is surrounded by the magnets 15.

As shown in FIG. 3, the guides 34 are substantially cylindrical shaped members formed separate from the shaft 17, and have an outside diameter larger than the shaft 17. A through hole 34a is formed in the center of the guide 34. The shaft 17 is inserted through the through hole 34a. The guide 34 may be formed integrally to the insulating coating when an insulating coating is formed on the shaft 17.

The coils 29 are wound around opposing slots 24 (i.e., around 4 slots in the representative embodiment). As is clear from the drawings, the coils 29 make contact with an outside surface of the guide 34 in the region around the shaft 17. Therefore, the coils 29 are guided to the guide 34 and wound so as to detour around the region in proximity to the shaft 17.

As shown in FIG. 2, the lower guide 34 is also positioned on the bottom side of the core 21. Therefore, when the coils 29 are wound around on the bottom end of the core 21 as well, the coils 29 are guided by the guide 34 and wound so as to detour around the region in proximity to the shaft 17.

FIG. 4 shows a route S for the coil 29 (specifically the windings 29a which make up the coil 29) to wrap around the core 21 and the direction of tensile force T which acts on the windings 29a. FIG. 12 shows a route S′ for a coil 119 (windings 119a) to wrap around the core 111 of a conventional fuel pump, and the direction of tensile force T′ which acts on the windings 119a.

As shown in FIG. 4, the windings 29a are guided by the guide 34 and therefore have a route S which bulges toward the outside from the shaft 17 without passing through the region in proximity to the shaft 17. Therefore, the tensile forces T which acts on the winding 29a will have a large component in the circumferential direction of the core 21. Thereby the winding 29a will overlap in the radial direction of the core 21 along the wall surface 24b away from the center 24a of the slot 24. When the winding 29a overlaps in the radial direction of the core 21, the winding 29a is wound across a broad area of the end surface of the core 21. Therefore, the rate of increase of the projecting length of the coils29 with regards to the increase in the number of windings of the coils29 can reduced.

On the other hand, as shown in FIG. 12, if the shaft 107 does not have a guide, the winding 119a will pass by in proximity to the shaft 107 (or in other words the route of the winding 119a will be route S′ in the drawing). Therefore, the tensile forces T′ which act on the winding 11 9a will have a large component toward the center of the core 21 (i.e., a large radial component). Therefore, the winding 119a will overlap from the center 114a of the slots 114. If the winding 119a overlaps from the center 114a of the slots 114, the winding 119a will be wound to accumulate in the area around the shaft 107 (in other words, the winding 119a will overlap in the axial direction of the shaft 107). Therefore, the rate of increase of the projecting length of the coils 119 with regards to the number of windings of the coils 119 will be large.

With the fuel pump of the first representative embodiment, the increase in the projecting length of the coils from the end surface of the core with regards to the increase in the number of windings of the coils 29 can be reduced by winding the coils 29 using the guides 34 attached to the shaft 17. Therefore, the axial length of the armature 16 can be shortened without reducing the number of windings (winding lamination factor) of the coils 29. Therefore, the axial length of the fuel pump can be shortened and the fuel pump can be made smaller and lighter.

Furthermore, because the fuel pump is shorter in the axial direction without reducing the number of windings of the coils 29, the motor efficiency of the fuel pump can be maintained at a high level. That is, the rotational torque generated on the shaft 17 is determined by the current (amps) flowing to the coils 29 multiplied by the number of windings. Therefore, if the number of windings of the coils 29 is equal, the rotational torque generated by the motor section 12 will also be equal.

The preferred representative embodiment of the present teachings have been described above, the explanation was given using, as an example, the present teachings is not limited to this type of configuration.

For instance, in the above embodiment, disc shaped guides 34 were engaged to the shaft 17, and the coil 29 was guided by the guides 34. However, the present teachings is not restricted to this configuration, and for instance, a second representative embodiment shown in FIG. 5 is also possible. In the second representative embodiment shown in FIG. 5, a wall 36 is provided around the shaft 17 on both end surfaces (21a, 21b) of the core 21, and the coils 29 are guided by the walls 36. The wall 36 may be formed around the whole circumference of the shaft 17 (in other words in a cylinder around the outside of shaft 17), or the wall 36 may be partially formed in specific areas along the circumferential direction of the shaft 17. By guiding the coils 29 using the walls 36, the weight of the armature 46 can be reduced.

Furthermore, in the aforementioned embodiment, the coils are guided by a guide or a wall attached to the shaft, but the present teachings can be implemented without attaching a guide or wall to the shaft. For instance, a jig may be used when winding the coils around the core of the armature, and the jig removed after the coils are wound. The jig may use a cylindrical member with an inside diameter which is slightly larger than the outside diameter of the shaft, and the outside diameter of the jig may be any desired dimension. When the coils are wound, the shaft is inserted through a through hole in the jig, one end of the jig is made to contact with the end surface of the core, and the coils are wound in this condition. After winding of the coils is complete, the jig is removed. Note, after the jig is removed, the coils and the core are preferably integrated together by a plastic resin or the like in order to prevent deforming of the coils.

Next, a third representative embodiment of the present teachings will be described referring FIGS. 6 and 7. As shown in FIGS. 6 and 7, an armature 50 of the third representative embodiment, similar to the armature 16 of the first representative embodiment, comprises a core 56 which overlaps magnetic plates, coils 60 which is wound around slots in the core 56, a commutator 54 which supplies current to the coils 60, and a shaft 52 which supports the core 56 and the commutator 54. However, the armature 50 of the third representative embodiment differs from the armature 16 of the first representative embodiment in that a disc shaped guide 58 is provided at a position a predetermined distance from an end surface 56b of the core 56 at an end 52b opposite to the commutator 54 side of the shaft 52.

As shown in FIG. 6, the guide 58 is a disc shaped member, and is fixed to the shaft 52. The guide 58 can be formed from plastic resin. By forming the guide 58 from plastic resin, the guide 58 will also function as an insulating coating to insulate the coils 60 and the shaft 52. The guide 58 include an inner side portion 58a (or in other words, the region in proximity to the shaft 52) and outside portion 58b. The thickness of the inner side portion 58a is thicker than that of the outside portion 58b. When the guide 58 is fixed to the shaft 52, the end surface 56b of the core 56 and a guide surface (i.e., surface contacting the coils 60) of the guide 58 will be facing each other. The distance from the end surface 56b of the core 56 to the guide surface of the guide 58 may be designed based upon the number of windings of the coils 60. The guide 58 may be integrally formed with the insulating coating of the core 56. If the guide 58 and the insulating coating of the core 56 are integrally formed, the number of components can be reduced.

When the coils 60 are wound around opposing slots of the core 56, first the coil 60 is wrapped around in proximity to the shaft 52 and overlaps in the axial direction of the core 56 even on the end 56b where the guide 58 is provided. When the coils 60 overlaps in the axial direction of the core 56 and contacts the guide 58, the coils 60 will not be able to further overlap in the axial direction of the core 56. Therefore, after the coils 60 contacts the guide 58, the coils 60 will overlap in the radial direction of the core 56. With this embodiment, the coils 60 will efficiently overlap in the radial direction because of the thicker thickness of the inner side portion 58a of the guide 58, and thereby the coils 60 will be balanced around the core 56.

With the third representative embodiment, the coils 60 broadly overlap in the radial direction of the core 56. Therefore, the projecting length that the coils 60 projects from the end surface 56b of the core 56 can be reduced without reducing the number of windings of the coils 60. Thereby the axial length of the fuel pump can be shortened without reducing the motor efficiency.

In the third representative embodiment, the guide 58 is provided only on the end of the shaft 56 opposite to the commutator 54, but a guide can also be provided on the commutator side of the shaft. Furthermore, the shape of the guide is not restricted to a disc shape, and any shape which restricts protrusion of the coils in the axial direction is acceptable. For instance, a guide which has a plurality of rod shaped members in a radial pattern from the shaft may be used in suitable circumferential locations to restrict protrusion of the coils in the axial direction. Furthermore, with the third representative embodiment, after winding the coils 60 around the core 56 using the guide 58, the guide 58 may be removed. In this case, the coils 60 and the core 56 are preferably integrated using a plastic resin in order to prevent the coils from deforming after the guide 58 is removed.

Furthermore, a guide which provides both the function of the guide 34 of the first representative embodiments and the function of the guide 58 of the third representative embodiment may be used. For instance, as shown in FIG. 8, a guide 72, which is positioned at the end of a core 80, comprises a ring shaped portion 76 which mates with the shaft 70 and a flange portion 74 formed on the bottom end of the ring shaped portion 76. The outer side wall of the ring shaped portion 76 guides the coils 78, and thereby the coils 78 are wound so as to detour away from the region around the shaft 70. Furthermore, the coils 78 contacts with the upper face of the flange portion 74, so that overlapping of the coils 78 in the radial direction past the flange portion 74 can be restricted. Thereby, the projecting length of the coils 78 from the end of the core 80 can be shortened.

Finally, although the preferred representative embodiments have been described in detail, the present embodiments are for illustrative purpose only and not restrictive. It is to be understood that various changes and modifications may be made without departing from the spirit or scope of the appended claims. In addition, the additional features and aspects disclosed herein also may be utilized singularly or in combination with the above aspects and features.