Stepping motor

A stepping motor includes a stator, a rotor rotatably supported by the stator, and an auxiliary magnetic member. The auxiliary magnetic member has a body, side edge parts at both circumferential ends of the body, and an opening between the side edge parts. The auxiliary magnetic member is elastically mounted around a flange of the stator. The auxiliary magnetic member includes, at one of the side edge parts, a projecting part protruding radially inward from a projected inner circumferential surface of the body across the opening.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese patent application serial number 2018-108261, filed Jun. 6, 2018, and entitled “Stepping Motor,” which is hereby incorporated herein by reference in its entirety for all purposes.

Not applicable.

BACKGROUND

This disclosure relates generally to stepping motors, more specifically, stepping motors with an auxiliary magnetic member.

One type of stepping motor is a claw pole type stepping motor. A claw pole type stepping motor has a stator and a rotor. The stator includes a bobbin. The bobbin is provided with yokes and is wound by coils. The rotor has a rotor shaft and magnets. The rotor shaft is rotatably supported by the stator. The magnets are attached to the rotor shaft and arranged such that N-poles and S-poles of the magnets are alternately aligned in a circumferential direction of the rotor. The stator has ring-shaped flanges, each having an outer diameter larger than those of the coils. The stator has an auxiliary magnetic member formed in a substantially hollow cylindrical shape. The flanges of the stator are fitted into the auxiliary magnetic member.

One kind of the auxiliary magnetic member is made of a magnetic plate rolled to have a C-shaped cross-section so as to be elastically mounted around the flanges of the stator. The auxiliary magnetic member having the C-shaped cross-section has an opening between a pair of side edge parts. The opening extends in an axial direction of the auxiliary magnetic member. The side edge parts face each other across the opening.

BRIEF SUMMARY

In one aspect of this disclosure, a stepping motor includes a stator, a rotor, and an auxiliary magnetic member. The stator includes a bobbin, a coil winding around the bobbin, and a flange formed in a ring shape having the outer diameter larger than that of the coil. The bobbin is provided with a yoke. The rotor includes a rotor shaft rotatably supported by the stator and magnets arranged around the rotor shaft. N-poles and S-poles of the magnets are alternately aligned in a circumferential direction of the rotor. The auxiliary magnetic member is made of a magnetic plate and has a body, side edge parts at both circumferential ends of the body, and an opening between the side edge parts. The side edge parts face each other across the opening. The auxiliary magnetic member is elastically mounted around the flange of the stator. The auxiliary magnetic member includes, at one of the side edge parts, a projecting part protruding radially inward from a projected inner circumferential surface extended along an inner circumferential surface of the body across the opening.

According to this aspect, the projecting part of the auxiliary magnetic member elastically abuts on the flange of the stator in a state where the auxiliary magnetic member is elastically mounted around the flange of the stator. Therefore, the noise caused by the auxiliary magnetic member when intermittently supplying the power to the coil is decreased.

In another aspect of this disclosure, a stepping motor includes a stator, a rotor, an auxiliary magnetic member, and an intervening member. The stator includes a bobbin, a coil winding around the bobbin, and a flange formed in a ring shape having the outer diameter larger than that of the coil. The bobbin is provided with a yoke. The rotor includes a rotor shaft rotatably supported by the stator and magnets arranged around the rotor shaft. The auxiliary magnetic member is made of a magnetic plate and has a body, opening edge parts at both circumferential ends of the body, and an opening between the opening edge parts. The opening edge parts face each other across the opening. The auxiliary magnetic member is elastically mounted around the flange of the stator. The intervening member is interposed between one of the opening edge parts and the flange of the stator.

According to this aspect, the intervening member can inhibit the corresponding opening edge part from coming into direct contact with the flange of the stator. Thus, noise caused by the auxiliary magnetic member when intermittently supplying the power to the coil is decreased.

According to another aspect of the disclosure, a stepping motor comprises a stator having a first flange, an auxiliary magnetic member mounted around the first flange, and a projection. The auxiliary magnetic member has a body with a projected inner circumferential surface. The projection is connected to the body of the auxiliary magnetic member. At least a portion of the projection is positioned radially inward from the projected inner circumferential surface of the body.

According to this aspect, the portion of the projection positioned radially inward from the projected inner circumferential surface of the body reduces noise caused by the auxiliary magnetic member when intermittently supplying the power to the stepping motor.

Other objects, features and advantage of the present teaching will be readily understood after reading the following detailed description together with the accompanying drawings and the claims.

DETAILED DESCRIPTION

Each of the additional features and teachings disclosed above and below may be utilized separately or in conjunction with other features and teachings to provide improved stepping motors. Representative examples of the present teachings, which examples utilized many of these additional features and teachings both separately and in conjunction with one another, will now be described in detail with reference to the attached drawings. This detailed description is merely intended to teach a person skilled in the art further details for practicing preferred aspects of the present teachings and is not intended to limit the scope of the claimed subject-matter. Only the claims define the scope of the claimed subject-matter. Therefore, combinations of features and steps disclosed in the following detailed description may not be necessary to practice the claimed subject-matter in the broadest sense, and are instead taught merely to particularly describe representative examples of the present teachings. Moreover, various features of the representative examples and the dependent claims may be combined in ways that are not specifically enumerated in order to provide additional useful embodiments of the present teachings.

As previously described, one kind of the auxiliary magnetic member has a C-shaped cross-section and is elastically mounted about the flanges of the stator. Sometimes, a space may arise between the side edge parts and the flanges of the stator due to manufacture tolerances, manufacturing errors, or the like. In such cases, when supplying power to the coils, the side edge parts may come into contact with the flanges of the stator in response to electromagnetic attracting forces, and when the power supply to the coils is stopped, the side edge parts move away from the flanges due to elastic restoring forces. Thus, when repeatedly turning on/off the supply of power to the coils, the side edge parts may slightly vibrate and generate noise due to contact with the flanges. Accordingly, embodiments described herein are directed to devices and methods for reducing noise resulting from contact between the side edge parts of auxiliary magnetic members and the flanges.

Referring now toFIG. 1, a first embodiment of a stepping motor10is shown. In this embodiment, the stepping motor10is configured for use as an actuator of a flow control valve. For the purposes of clarity and further explanation, upper, lower, right, and left directions are based on the orientation of the stepping motor10shown inFIG. 1. However, these directions are not intended to limit the installation orientation or direction of the stepping motor10.

As shown inFIG. 1, the stepping motor10includes a stator12, a rotor14, and a cover15. The stator12is fitted into an auxiliary magnetic member. In this embodiment, the auxiliary magnetic member comprises a stator plate16that is rolled to have a generally C-shaped cross-section. The stator12and the stator plate16form a stator assembly18.

As shown inFIGS. 1 and 4, the stator12has a bobbin20and coils22. The bobbin20is made from a resin material and is formed by integrating four yokes24and four terminals25with each other by insert molding. The bobbin20includes a bobbin body26, an upper support27, and a lower support28. The bobbin body26has a cylindrical part30, an upper flange32, a middle flange33, and a lower flange34. The cylindrical part30has a substantial hollow cylindrical shape. Each of the upper flange32, the middle flange33, and the lower flange34is formed in an annular, ring shape extending radially outward from the cylindrical part30.

As shown inFIG. 4, the upper flange32includes a guide projection32a, which is formed in an arc shape protruding radially outward. Plural (e.g., two) guide grooves32b, which are configured to guide the coil wires of the coils22, are formed in parallel with each other at an upper surface of the upper flange32and a side surface of the guide projection32a. The upper flange32includes a pair of stoppers32cat an upper end of the upper flange32. The stoppers32cproject radially outward. The stoppers32care disposed on opposite circumferential sides of the guide projection32a, such that there is a predetermined interval between each of the stoppers32cand the guide projection32a.

The middle flange33has a guide projection33a, which is formed in an arc shape protruding radially outward. Plural (e.g., two) guide grooves33b, which are configured to guide the coil wire of the coils22, are formed in parallel with each other at a side surface of the guide projection33a. The lower flange34has a guide projection34aformed in an arc shape protruding radially outward. The guide projections32a,33a,34aare formed to have substantially the same outer diameter as each other in the plan view.

As shown inFIG. 1, the upper support27is formed in a stepped cylindrical shape above the cylindrical part30such that the upper support27closes an upper end of the cylindrical part30. The upper support27has a counterbore or receptacle27aat a central portion of the lower surface thereof. The lower support28is formed in an annular, ring shape at a lower end of the bobbin body26. The lower support28has an outer diameter larger than that of the stator plate16. The lower support28has an attachment flange28aextending radially outward from a lower end thereof. The lower support28includes a sleeve28bformed in a hollow cylindrical shape. The sleeve28bextends from an inner circumferential edge of the lower surface of the lower support28in the axial direction (downward inFIG. 1).

As the four yokes24have substantially the same shape, the structure of only one of the yokes24will be described it being understood the other yokes24have the same shape. In this embodiment, the yoke24is made of a metal plate, such as an iron plate, and is shaped by press-molding. The yoke24includes a basal plate24aand a plurality (e.g. six) of magnetic pole teeth24bextending radially from the basal plate24a. The basal plate24ais formed in a substantially annular plate shape. Each of the magnetic pole teeth24bhas a substantially annular plate shape. The magnetic pole teeth24bare formed by press-molding such that the magnetic pole teeth24bextend from an inner circumferential edge of the basal plate24aat approximately right angles. As shown inFIG. 4, the basal plate24aincludes a plurality of circumferentially-spaced concave recesses24cextending radially inward from an outer circumferential portion thereof.

The four yokes24are divided into two pairs. Each pair of yokes24are arranged such that the magnetic pole teeth24bmesh with each other. Further, the two pairs of yokes24are concentrically stacked in the vertical direction. As shown inFIG. 1, the basal plate24aof the yoke24disposed at the highest position is disposed in the upper flange32. The basal plate24aof the yoke24disposed at the lowest position is disposed in the lower flange34. The basal plates24aof the two yokes24adjacent to each other and disposed in the middle between the uppermost basal plate24aand the lowermost basal plate24aare buried in the middle flange33. As shown inFIG. 4, the outer circumferential portions of the basal plates24aof the yokes24and some of the concave recesses24care exposed from the flanges32,33,34, except at positions where the guide projections32a,33a,34aare provided.

Each flange32,33,34includes a flange portion. The flange portions of the flanges32,33,34are concentrically formed in a substantial circle shape so as to basically have the same outer diameter, referred to as “flange outer diameter.” The flanges32,33,34have a flange outer diameter that is larger than the outer diameter of the coils22.

As the four terminals25have substantially the same shape, the structure of only one of the terminals25will be described it being understood the other terminals25have the same shape. In this embodiment, the terminal25is made of a metal plate, such as an iron plate, and is shaped by press-molding. The terminal25has a basal end (lower end inFIG. 1) disposed in the upper support27. As shown inFIG. 4, the terminal25includes a pin part25aand a coil connection part25b. The pin part25aprojects upward from the top surface of the upper cylindrical part of the upper support27. The coil connection part25bis exposed from the upper surface of the bobbin body26. The four terminals25are divided into two pairs. Each pair of terminals25is arranged parallel to each other and symmetrically aligned in left/right direction. Further, the two pairs of terminals25are disposed symmetrically in the front/rear direction. As shown inFIG. 3, the pin parts25aare uniformly circumferentially-spaced on the upper cylindrical part of the upper support27.

The coils22wind around the cylindrical part30in spaces between the upper flange32and the middle flange33and between the middle flange33and the lower flange34. The coil wires (not shown) of the coils22are engaged with the guide grooves32bof the upper flange32and the guide grooves33bof the middle flange33. Ends of the coil wires are connected to corresponding coil connection parts25bof the terminals25.

As shown inFIG. 1, the rotor14includes a rotor shaft35and magnets36mounted to the rotor shaft35. The rotor shaft35is made from metal, such as stainless steel. The rotor shaft35has a small diameter shaft part35aat an upper end thereof and a threaded shaft part35bat a lower end thereof. The magnets36are attached to the upper portion of the rotor shaft35. Each of the magnets36may be a permanent magnet. The magnets36are magnetized such that their N-poles and S-poles alternately arranged on the outer circumferential surface of the rotor14. That is, the magnets36are arranged around the rotor shaft35such that N-poles and S-poles of the magnets36are alternately aligned in the circumferential direction of the rotor14. The number of the N-poles and the number of S-poles corresponds to the number of the magnetic pole teeth24bof each yoke24of the stator12.

A central portion of the rotor shaft35is rotatably supported by a retainer40via a bearing38. In this embodiment, the bearing38is a ball bearing. The retainer40is made from a resin material. The retainer40has an outer cylindrical part40aand an inner cylindrical part40b. Each of the outer cylindrical part40aand the inner cylindrical part40bis formed in a hollow cylindrical shape. The inner cylindrical part40bis positioned in the outer cylindrical part40ato form a double cylinder structure. The bearing38is disposed in an upper portion of the outer cylindrical part40a.

The rotor14is disposed in the stator12. The small diameter shaft part35aof the rotor shaft35is rotatably supported in the receptacle27aof the stator12. The outer cylindrical part40ais fitted into the lower support28of the stator12by press fitting from below. As a result, the rotor14is rotatably housed in the stator12.

The threaded shaft part35bof the rotor shaft35is coupled to a movable member. In this embodiment, the movable member is a valve member46. The valve member46is made from a resin material. The valve member46includes a connection cylindrical part46aformed in a hollow cylindrical shape. The connection cylindrical part46ais threadedly engaged with the threaded shaft part35b. The connection cylindrical part46ais fitted into the inner cylindrical part40bof the retainer40, such that the connection cylindrical part46acan move in the axial direction, i.e., the vertical direction inFIG. 1, and is prevented from rotating about its axis.

The cover15is made from a resin material. The cover15is formed in a hollow stepped cylindrical shape. The cover15has an upper wall part15aand a fitting hole15bextending vertically through a central portion of the upper wall part15a. The upper wall part15ais provided with a connector42that is formed in a hollow cylindrical shape extending upward from the upper wall part15a. The cover15houses the stator assembly18therein. The upper cylindrical part of the upper support27of the stator12is fitted into the fitting hole15b. An O-ring43is disposed between the cover15and the upper cylindrical part of the upper support27. The lower support28of the stator12is fitted into an opening in the lower end of the cover15. An O-ring44is provided between the cover15and the lower support28. A lower end surface of the cover15abuts the attachment flange28aof the stator12.

The stepping motor10is installed in a passage forming member (not shown). The connector42is connected with an external connector linked to a controller that is configured to control the stepping motor10. Thus, the stepping motor10is controlled by the controller to rotate the rotor shaft35in the forward and reverse directions. When the rotor shaft35is rotated in the forward or reverse direction, the valve member46moves upward or downward in the axial direction, depending on the rotational direction of the rotor shaft35. Consequently, the valve member46opens and closes a flow passage formed by the passage forming member to control the amount of fluid flowing through the flow passage.

FIG. 5schematically shows a positional relationship between the stator plate16and each of the flanges32,33,34of the stator12. As shown inFIG. 5, each flange32,33,34of the stator12has the same predetermined flange outer diameter Db.

As shown inFIG. 6, the auxiliary magnetic member may include a body and one or more projections attached to the body. In this embodiment, the stator plate16is formed in a shape substantially having a C-shaped cross-section. The stator plate16may be shaped by rolling a magnetic plate by press-molding or the like. The stator plate16has a plate body16a, side edge parts16b, and an opening48. The plate body16acorresponds to a main body of the stator plate16. The side edge parts16bare formed at both circumferential ends of the plate body16aand are formed as projections attached to the main body in this embodiment. The opening48extends linearly in the axial direction of the stator plate16. The opening48is positioned between the side edge parts16bsuch that the side edge parts16bessentially face each other across the opening48. The plate body16ais formed to have a circular arc shaped (e.g., C-shaped) cross-section when the stator plate16is disassembled. The plate body16ahas an inner diameter Ds. The inner diameter Ds in the disassembled state may be slightly smaller than the flange outer diameter Db (seeFIG. 5) of each flange32,33,34of the stator12. As noted above, in this embodiment, the stator plate16corresponds to the auxiliary magnetic member. In this embodiment, the plate body16acorresponds to the body of the auxiliary magnetic member.

Each of the side edge parts16bof the stator plate16is bent radially inward relative to the plate body16a, for example by press-molding, along a corresponding linear bending line L that extends in the axial direction. Thus, as shown inFIG. 7, each of the side edge parts16bhas a radially inward portion that is positioned radially inward from a projected inner circumferential surface16F of the plate body16a. The projected inner circumferential surface16F is drawn by extending the inner circumferential surface of the plate body16aof the stator plate16across the opening48. In this embodiment, the radially inward portion of the side edge part16bis depicted as the projecting part16bppositioned radially inward (upward inFIG. 7) of the projected inner circumferential surface16F. The projecting parts16bpof the side edge parts16blinearly extend in the axial direction of the stator plate16. The projecting parts16bpalso extend in essentially a circumferential direction from the linear bending line L towards the opening48. Based on a bending angle about the linear bending line L and the relative length of the portion of the stator plate16that comprises the side edge part16b, the thickness of the projecting part16bpin a radial direction (upward in FIG.7) may gradually increase from the linear bending line L to the opening48.

The flanges32,33,34of the stator12are fitted into the stator plate16due to elastic deformation of the stator plate16. As shown inFIG. 2, the stator plate16is positioned such that the guide projections32a,33a,34aof the flanges32,33,34are between the side edge parts16band in the opening48of the stator plate16.

As shown inFIG. 5, in a state where the flanges32,33,34of the stator12are fitted in the stator plate16, the radially inward portion of the side edge part16babut the outer circumferential surface of the flanges32,33,34. In this state, there are gaps or spaces C between the flanges32,33,34of the stator12and portions of the stator plate16.

For example, when the stator plate16is fitted around the stator12, the stator plate16elastically deforms to accommodate the size the flange outer diameter Db. As the projecting part inner diameter Dp is smaller than the flange outer diameter Db in the disassembled state, the stator plate16is elastically deformed when mating with the flanges32,33,34. More specifically, the diameter (e.g., cross-sectional length) of the stator plate16between the projecting part16bpand a portion of the body16adirectly across the projecting part16bin the disassembled state is the projecting part inner diameter Dp. When mating, the stator plate16is elastically deformed such that diameter (e.g., cross-sectional length) between projecting end part16bpand the body16ais increased to a size corresponding to a mated projecting part inner diameter Dpm. In the mated state, the mated projecting part inner diameter Dpm of the stator plate16has essentially the same diameter as the flange outer diameter Db and a larger diameter than the projecting part inner diameter Dp (which is the diameter in the disassembled state).

In some versions of the first embodiment, the space C between the stator12and the flanges32,33,34in the mated state may be the largest at the linear bending line L. For example, the stator plate16may abut the stator12at a portion corresponding to each of the projecting end parts16bpand a portion of the body plate16opposite the opening48. From the portion of the stator plate16opposite the opening48towards the linear bending line L in the circumferential direction, the size of the space C in the radial direction may gradually increase. From the linear bending line L towards the projecting end part16bpin the circumferential direction, the radial size of the space C may decrease. In some versions, the rate of size increase of the space C per unit length between the portion of the stator plate16opposite the opening48and the linear bending line L in the circumferential direction may be less than the rate of size decrease of the space C per unit length between the linear bending line L and the projecting end part16bpin the circumferential direction.

Additionally, the diameter (e.g. cross-sectional length) of the stator plate16between the linear bending line L and a portion of the body16aopposite the linear bending line L may be the largest diameter of the stator plate16when the stator plate16is mated with the flanges32,33,34. That is, the largest diameter of the stator plate16in the mated state may be the mated linear bending line inner diameter Dlm. Accordingly, the mated linear bending line inner diameter Dlm may be larger than both the flange outer diameter Db and the mated projecting end part inner diameter Dpm. However, in the disassembled state, the diameter (e.g., cross-sectional length) of the stator plate16abetween the linear bending line L and a portion of the body16aopposite the linear bending line L, depicted as the linear bending line inner diameter Dl inFIG. 6, is approximately the same as the inner diameter Ds of the body16a. Accordingly, the linear bending line inner diameter Dl may be slightly smaller than flange outer diameter Db.

As shown inFIG. 2, the guide projections32a,33a,34aare positioned between the side edge parts16bof the stator plate16in the circumferential direction. A lower end surface of the stator plate16abuts an upper surface of the lower support28of the stator12. Upper end surfaces of the side edge parts16babut or are adjacent to lower surfaces of a pair of stopper32cof the upper flange32. Thus, the stator plate16is generally positioned in the axial direction, i.e., the vertical direction.

According to the stepping motor10described above, in the state where the flanges32,33,34of the stator12are fitted in the stator plate16, the side edge parts16bof the stator plate16elastically abut the flanges32,33,34of the stator12. Thus, the stator plate16is prevented from generating noise when cycling the supply of the power to the coils22. Further, potential dimensional errors due to manufacturing tolerances, or the like, between the flanges32,33,34of the stator12and the stator plate16do not cause any problems. Accordingly, the dimensional accuracy required for manufacturing the flanges32,33,34and the stator plate16can be decreased. Thus, dimensional control of the flanges32,33,34and the stator plate16can be simplified and costs reduced.

The side edge parts16bcan be easily formed by obliquely bending end portions of the stator plate16radially inward along the bending lines L.

The minimum value of the bending amount of the side edge parts16b, e.g., the inward projection amount of projecting parts16bpfrom the projected inner circumferential surface16F of the plate body16aof the stator plate16, is set as the variable A. The maximum value of the difference between the largest flange outer diameter Db and the smallest flange outer diameter Db of the flanges32,33,34, which may be caused by manufacturing error or the like, is set as the variable B. The minimum value of A is set to be equal to or larger than the maximum value of B. Due to this configuration, the volume of the spaces C between the stator plate16and the flanges32,33,34of the stator12can be decreased, while still accommodating the manufacturing errors or the like. Thus, a decrease in the thrust of motor caused by the spaces C is decreased.

A second embodiment will be described. The second embodiment corresponds to the first embodiment with some changes. Thus, while the differences will be described in greater detail below, similar configurations will not be described in the interest of conciseness. As shown inFIG. 8, the stator plate16has opening edge parts16c, which are portions of the stator plate16adjacent the opening. In contrast to the side edge parts16bof the first embodiments, the opening edge parts16cof the plate body16ado not protrude radially inward about a projected inner circumferential surface of the body16a. Instead, when the stator plate16is in a disassembled state, the inner diameter (e.g., cross-sectional length) from each of the opening edge parts16cto an opposite portion of the body16ahas approximately the same the inner diameter as another portion of the plate body16a. In some cases, the inner diameter from the opening edge part16cto the body16ais approximately the same as the flange outer diameter Db, or may be slightly smaller. However, due to manufacturing errors or the like, the inner diameter from the opening edge part16cto the body16amay in fact be larger than the flange outer diameter Db.

To help mitigate the issues caused by the manufacturing errors or the like, the body of the auxiliary magnetic member may be structure with an attached projection. For example, if spaces S are formed between the opening edge parts16cand the flanges32,33,34of the stator12(for example between the flanges32,33,34and the projected inner circumferential surface of the stator plate16), a projection may be attached to the body of the auxiliary magnetic member, the projection being configured to at least partially fill the space S. For example, an intervening member may be provided in each of the spaces S. In this embodiment, the intervening member is structured in the form of fillers52. The fillers52may be made from an adhesive, curable filler, vibration dampening material, or the like. Each of the fillers52is placed between the corresponding opening edge part16cand the flanges32,33,34so as to partially or fully fill the spaces S.

In some instances of the second embodiment, the filler52may be inserted into the spaces S after the stator plate16has been mated with the flanges32,33,34. By applying the filler52after the mating, the amount of filler52may be adjusted to accommodate the various sized spaces S that may be formed due to manufacturing errors of the like. Additionally, the amount of filler52may be adjusted if pressuring bonding is used, thereby avoiding unnecessary overflow and material wastage.

In some other instances, the filler52positioned on either the stator plate16or the flanges32,33,34before mating. More specifically, the filler52may be positioned in a location so as to at least partially fill spaces S that may be formed due to manufacturing errors or the like when the stator plate16and the flanges32,33,34are mated. In some instances, the filler52will be positioned so as to be most effective in reducing the amount of noise generated by vibrations, while reducing the amount of filler52required. For instance, the filler52may be positioned towards an opening side of the opening edge part16c. However, if the filler52is made of a curable material and pressure bonding is to be used when curing the filler52, the filler52may be positioned so as to reduce the amount of material that would exit (overflow from) the space S when pressure bonding. Alternatively, the filler52may be formed or cured before the stator plate16and the flanges32,33,34are mated.

In some further instances, the intervening member may be formed as a projection attached to one or both opening edge parts16c. For example, projections may be attached to each of the opening edge parts16c. These projections are structured and attached to the opening edge parts16cso that at least a portion of the projection is positioned radially inward from a projected inner circumferential surface of the body16a. When the stator plate16is mated with the flanges32,33,34, the projection abuts the flanges32,33,34.

According to the second embodiment, the fillers52prevent the opening edge parts16cof the stator plate16from coming into direct contact with the flanges32,33,34. Thus, noise generated when cycling the supply of the power to the coils22can be reduced or prevented. Further, dimensional errors between the flanges32,33,34of the stator12and the stator plate16due to manufacturing errors or the like do not cause any problems. The necessary dimensional accuracy required when manufacturing the flanges32,33,34and the stator plate16can be reduced. Thus, the dimensional control of the flanges32,33,34and the stator plate16can be simplified. Further, new manufacturing equipment, additional manufacturing steps, or new designs may not be needed for producing the stator plate16.

Additionally, it is easy from a manufacturing standpoint to fill the spaces S between the opening edge parts16bof the stator plate16and the flanges32,33,34of the stator12with the fillers52.

A third embodiment will be described. The third embodiment corresponds to the first embodiment, with some exemplary changes to the side edge parts16bof the stator plate16. Thus, while the changes will be described, same configurations will not be described in the interest of conciseness. As shown inFIG. 9, each of the side edge parts16b(one of which is shown inFIG. 9) includes a chamfer part16b3having a straight or rounded shape between an inward facing surface16b1and circumferentially facing end surface16b2of the side edge part16b. Each chamfer part16b3may be shaped by press-molding or the like.

According to the third embodiment, collision of the outer circumferential surfaces of the flanges32,33,34of the stator12with a pointed corner of the side edge parts16bof the stator plate16is reduced, thereby reducing possible damage to the flanges32,33,34.

While preferred embodiments have been shown and described, modifications thereof can be made by one skilled in the art without departing from the scope or teachings herein. The embodiments described herein are exemplary only and are not limiting. Many variations and modifications of the systems, apparatus, and processes described herein are possible and are within the scope of the disclosure.

For example, the stepping motor10may be used for driving sources of various devices other than the above described flow control valve. That is, the movable member coupled with the rotor shaft35is not limited to the valve body46, and may be another reciprocating member moving in the axial direction of the rotor shaft35or a rotation member integrally fixed on the rotor shaft35, such as gear, arm, cam, or the like.

The filler52may be provided between at least one of the opening edge parts16cof the stator plate16and at least one of the flanges32,33,34of the stator12. The intervening member may be made from elastic member, such as rubber or sponge-like foamed resin, or non-elastic member having high rigidity, such as metal or cured resin. The non-elastic member as the intervening member may be attached to the opening edge parts16cof the stator plate16by adhesion or the like. Each of the chamfer parts16b3may have a chamfer plane instead of the round surface. The chamfer parts16b3may be formed by bending the side edge parts16bby press-molding or the like.