Patent ID: 12196287

DETAILED DESCRIPTION OF EMBODIMENTS

In order to clarify the present invention more specifically, practical embodiments of the present invention will be described in detail below in reference to the drawings.

First,FIG.1shows an electromagnetic actuator10according to a first practical embodiment of the present invention. In the present practical embodiment, by being mounted onto a target member12whose vibration is to be damped, such as a vehicle body, the electromagnetic actuator10constitutes an active vibration damper that demonstrates an active vibration damping effect with respect to the target member12. The electromagnetic actuator10includes a mover16serving as a mass member that is oscillated with respect to a stator14in the axial direction. In the following description, the vertical direction and the axial direction refer to the vertical direction inFIG.1, which coincides with the center axial direction of the electromagnetic actuator10.

Described more specifically, the electromagnetic actuator10includes a hollow housing18. The housing18includes an outer tube member20and a bottom member22, each of which has an inverted, generally round tubular shape with a bottom that opens downward. The housing18including a housing area26inside is constituted by a tube part of the bottom member22being press-fitted or inserted into the lower opening of the outer tube member20and being subjected to welding or the like as necessary.

In addition, upper base walls of the outer tube member20and the bottom member22are each penetrated by a circular through hole at its center portion in the vertical direction. As a result, the upper base walls of the outer tube member20and the bottom member22respectively define flanged parts27a,27bin the form of an annular disk.

In the present practical embodiment, in a part of the circumference of the flanged part27aof the outer tube member20(the left side inFIG.1), there is provided a generally rectangular insertion hole28that penetrates in the vertical direction. In addition, the bottom member22is provided with an annular rib that extends outward from the peripheral edge of the lower opening thereof, and a pair of attachments30,30that protrude further outward are integrally formed with the outer peripheral edge of the annular rib. At the attachments30,30, the housing18is configured to be attached to the target member12with fixing bolts or the like.

Inside the housing area26, provided are the mover16disposed on the center axis of the outer tube member20, and the stator14located on the outer peripheral side of the mover16. These mover16and stator14are elastically connected to each other on both the upper and lower sides by leaf springs36,36in the shape of a roughly annular disk. As shown inFIG.2, in the present practical embodiment, according to the required spring characteristics, etc., there is formed a slit38that penetrates the leaf spring36in the vertical direction and extends in the circumferential direction in the form of, for example, a rough spiral.

The mover16serving as a mass member includes a generally rod-shaped inner shaft member40extending in the vertical direction in its center. The inner shaft member40includes a large-diameter head part42at its upper end, and a male screw part at its lower end.

Around the inner shaft member40, an upper mass44and a lower mass46are externally fitted, and a permanent magnet48is externally fitted vertically between the upper and lower masses44,46. The permanent magnet48has a circular disk shape with a predetermined thickness, while the upper and lower masses44,46are identical in shape but are vertically inverted with respect to each other, and have a roughly circular block shape protruding axially outward as it goes from the outer periphery toward the center. The opposed faces of the upper and lower masses44,46having planar shapes are overlapped in contact with the corresponding upper and lower faces of the permanent magnet48.

The upper and lower masses44,46are made of ferromagnetic material such as iron with high magnetic permeability and form a magnetic path. The permanent magnet48is magnetized in the axial direction, and the axially upper and lower surfaces thereof are provided with the respective one of N and S magnetic poles. In addition, the lower end of the upper mass44and the upper end of the lower mass46both have an outer peripheral surface of round tubular shape protruding outward in the radial direction with an outside diameter dimension larger than that of the permanent magnet48. With this configuration, the upper and lower masses44,46constitute a yoke of the permanent magnet48, and the outer peripheral surfaces of the upper and lower masses44,46protruding outward in the radial direction above and below the permanent magnet48comprise external magnetic pole faces each having the same magnetic pole as the respective one of the upper and lower surfaces of the permanent magnet48.

Thus, the upper leaf spring36, the upper mass44, the permanent magnet48, the lower mass46, and the lower leaf spring36are externally fitted onto the inner shaft member40in that order from the top, and a nut50is screwed to the male screw part at the lower end of the inner shaft member40. With this arrangement, the central portions of the upper and lower leaf springs36,36, upper and lower masses44,46and the permanent magnet48are securely supported to the inner shaft member40by being sandwiched vertically between the head part42of the inner shaft member40and the nut50.

The stator14has a generally round tubular shape overall. The stator14includes a first coil52and a second coil54serving as coils arranged so as to be overlapped with each other in an upper-lower two-stage manner in the axial direction. The first coil52and the second coil54are each constituted by a conductive coil wire58being wound around a rigid resin bobbin56that opens to the radially outer side. A first yoke member60and a second yoke member62serving as yoke members are respectively arranged around the first coil52and the second coil54. For example, a general magnet wire having a resin insulating film can be used as a coil wire.

The first yoke member60and the second yoke member62are made of a ferromagnetic material such as iron, and each have a split structure constituted by a plurality of yoke segments. That is, by being split into multiple parts, the yoke member can be attached to the coil later to form a magnetic path that surrounds the coil.

The first yoke member60includes an upper yoke segment64serving as a yoke segment that covers the first coil52from above, and a first middle yoke segment66serving as a yoke segment that covers the first coil52from below. The upper yoke segment64covers the outer peripheral surface and the upper surface of the first coil52roughly entirely, and covers a part of the radially inner surface (the upper end portion) of the first coil52from above. The first middle yoke segment66covers the lower surface of the first coil52roughly entirely, and covers a part of the radially inner surface (the lower end portion) of the first coil52from below.

The second yoke member62includes a lower yoke segment68serving as a yoke segment that covers the second coil54from below, and a second middle yoke segment70serving as a yoke segment that covers the second coil54from above. The lower yoke segment68covers the outer peripheral surface and the lower surface of the second coil54roughly entirely, and covers a part of the radially inner surface of the second coil54from below. The second middle yoke segment70covers the upper surface of the second coil54roughly entirely, and covers a part of the radially inner surface of the second coil54from above.

Around the first and second coils52,54, a magnetic path to guide a magnetic flux generated through energization to the coil wire58is formed by the first and second yoke members60,62. On the radial insides of the first coil52and the second coil54, the radially inner edges of the upper yoke segment64and the first middle yoke segment66, and the radially inner edges of the lower yoke segment68and the second middle yoke segment70, are opposed to each other at a predetermined distance in the axial direction. Accordingly, on the aforementioned magnetic path, there are formed magnetic gaps72,72respectively between axially opposed faces of the upper yoke segment64and the first middle yoke segment66, and between axially opposed faces of the lower yoke segment68and the second middle yoke segment70. Each magnetic gap72extends about the entire circumference in the circumferential direction with an approximately constant vertical distance.

Then, the magnetic flux is generated around the first and second coils52,54owing to power feed from the outside to the first and second coils52,54through a power feed terminal74that is conductive with respect to the coil wire58that constitutes the first coil52. In addition, the generated magnetic flux is guided by the magnetic path constituted by the first and second yoke members60,62, so as to form the magnetic poles on vertically both sides of the magnetic gaps72,72.

In the present practical embodiment, the coil wire58of the first coil52and the coil wire58of the second coil54are wound around the resin bobbins56,56in the adverse directions relative to each other, thereby generating magnetic fluxes in the adverse directions through the energization. It should be noted that the coil wires58,58of the first and second coils52,54may be wired continuously in series with each other.

The outer peripheral portions of the leaf springs36,36are secured on vertically both sides of such stator14. Specifically, the outer peripheral portion of the upper leaf spring36is sandwiched and supported vertically between the upper yoke segment64and the upper base wall (the flanged part27a) of the outer tube member20. Meanwhile, the outer peripheral portion of the lower leaf spring36is sandwiched and supported vertically between the lower yoke segment68and the upper base wall (the flanged part27b) of the bottom member22.

The mover16, the stator14, and the leaf spring36,36are accommodated inside the outer tube member20, and then accommodated within the housing area26of the housing18by the bottom member22being secured to the lower opening part of the outer tube member20. By so doing, the outer peripheral portions of the leaf springs36,36and the first and second yoke members60,62having the first and second coils52,54inside are sandwiched and supported vertically between the upper base wall (the flanged part27a) of the outer tube member20and the upper base wall (the flanged part27b) of the bottom member22. As a result, the stator14is secured in a vertically positioned state with respect to the housing18, and the attachments30to the target member12is indirectly provided with respect to the stator14via the housing18(the bottom member22).

In such an assembly state, the magnetic pole faces provided on the outer peripheral surfaces of the upper and lower masses44,46are radially opposed to the respective magnetic gaps72,72provided on the radial insides of the first and second coils52,54.

With this configuration, when a magnetic field is generated in the upper and lower magnetic gaps72,72through energization to the first and second coils52,54of the stator14, an axial magnetic attractive force is exerted on the outer peripheral portion of one of the upper and lower masses44(46), while an axial magnetic repulsive force is exerted on the outer peripheral portion of the other of the upper and lower masses46(44). Based on the action of these magnetic forces, the mover16is subjected to a driving force in one of the axial directions depending on the direction of energization to the first and second coils52,54. That is, by controlling the interval and direction of energization to the first and second coils52,54, it is possible to exert an axial oscillation force on the mover16and hence the inner shaft member40by prescribed periods.

In the present practical embodiment, the mover16is held in the initial axial position relative to the stator14by the elasticity of the upper and lower leaf springs36,36, and the mover16quickly returns to the initial position when the driving force by the power supply from the outside is cancelled.

Also, in the present practical embodiment, the electromagnetic actuator10is configured as an active vibration damper by being secured to the target member12, such as a vehicle body, by bolting or the like via the attachment30provided on the outer peripheral surface of the outer tube member20. That is, the housing18and the stator14are securely attached to the target member12such as a vehicle body, which is the primary vibration system, and the mover16is elastically connected to the housing18and the stator14via the leaf springs36,36, so as to constitute a mass-spring system, which is the secondary vibration system.

Then, with the active vibration damper (the electromagnetic actuator10) mounted onto the target member12, by controlling the power supply to the first and second coils52,54depending on the axial vibration to be damped, it is possible to oscillate the mover16and inner shaft member40constituting the secondary vibration system thereby obtaining the desired vibration damping effect.

Here, the first and second middle yoke segments66,70of the present practical embodiment are mutually identical in the shape of generally annular disk. The first and second middle yoke segments66,70have a generally flat-plate shape overall, and their radially inner edges are bent in the axial direction to form the magnetic gaps72,72in cooperation with the radially inner edges of the upper yoke segment64and the lower yoke segment68.

In each outer peripheral edge of the first and second middle yoke segments66,70, there is formed a notch80in a part of its circumference (the right side inFIG.1) so as to penetrate in the vertical direction and open to the radially outer side. That is, at the formation positions of the notches80,80, the outside diameter dimensions of the first and second middle yoke segments66,70are reduced. The first and second middle yoke segments66,70are vertically inverted with respect to each other and overlapped, and the upper and lower notches80,80are aligned in the circumferential direction and communicate with each other in the vertical direction. Note that the first and second middle yoke segments66,70may be temporarily secured to each other by adhesion, welding, or the like.

The resin bobbins56,56are overlapped on the axially outer side of these first and second middle yoke segments66,70. In the present practical embodiment, as shown inFIG.3, the resin bobbins56,56and the first and second middle yoke segments66,70are integrally formed with one another. That is, by setting the first and second middle yoke segments66,70in a mutually overlapped state in a cavity, and performing molding by injecting a resin material into the cavity, the resin bobbins56,56are formed as a primary molded component82including the first and second middle yoke segments66,70.

In the primary molded component82, the upper and lower resin bobbins56,56are linked and formed as an integral unit by a linking resin83that wraps around the bottom face of the upper and lower notches80,80. In the primary molded component82, in the resin bobbin56that constitutes the first coil52, a terminal part84to which the power feed terminal74is fixed is integrally formed and protrudes upward.

In this primary molded component82, the outer peripheral ends of the first and second middle yoke segments66,70, except for the formation position of the notches80,80, protrude to the radially outer side of the resin bobbin56,56. The coil wires58,58are wound around the resin bobbins56,56of the primary molded component82, and the upper yoke segment64and the lower yoke segment68are arranged from the vertically outside of the coil wires58,58. Incidentally, inFIG.3, the coil wires58,58in the wound state are shown separately from the primary molded component82. However, the coil wires58,58can be wound simultaneously with the formation of the first and second coils52,54by, for example, winding the coil wires58,58around the respective resin bobbins56,56of the primary molded component82.

The upper yoke segment64and the lower yoke segment68include respective tube parts86,86located on the outer peripheral side of the first and second coils52,54and extending about the entire circumference in the circumferential direction. The tube parts86,86include respective annular parts88,88protruding radially inward from the vertically outer ends thereof. In the radially middle portions of the annular parts88,88, respective stepped parts are provided, so that the outer peripheral portions of the leaf spring36,36are overlapped on the respective stepped parts. Besides, the radially inner edges of the annular parts88,88are bent inward in the vertical direction to form the magnetic gaps72,72in cooperation with the radially inner edges of the first and second middle yoke segments66,70.

The tube parts86,86of the upper yoke segment64and the lower yoke segment68each have through holes90penetrating the vertically middle portion thereof in the thickness direction (the radial direction of the tube part86). In the present practical embodiment, a plurality of through holes90are formed at approximately equal intervals in the circumferential direction. In the tube part86and the annular part88that constitute the upper yoke segment64, a notch92that penetrates the upper yoke segment64in the radial and vertical directions is formed at the position corresponding to the insertion hole28of the outer tube member20in the circumferential direction.

Then, the upper yoke segment64and the lower yoke segment68are externally placed from the vertically outside around the primary molded component82around which the coil wires58,58are wound. In this state, except for the formation position of the notches80,80, the vertically inner ends of the tube part86,86are in contact with the outer peripheral ends of the first and second middle yoke segments66,70that protrude from the resin bobbins56,56to the radially outer side. In addition, at the formation position of the notches80,80, the linking resin83located on the bottom faces of the notches80,80does not reach the upper and lower tube parts86,86in the radial direction. With this configuration, a gap93ais formed between the vertically opposed ends of the tube parts86,86, while gaps93b,93bare formed radially between the linking resin83and the tube parts86,86.

In addition, the tube parts86,86are located on the outer peripheral side of the first and second coils52,54at a predetermined distance therefrom. Furthermore, the annular parts88,88are located vertically outside of the first and second coils52,54at a predetermined distance therefrom. Accordingly, annular spaces are formed radially between the tube parts86,86and the first and second coils52,54, and vertically between the annular parts88,88and the first and second coils52,54.

A synthetic resin fills such a space between the first coil52and the upper yoke segment64and a space between the second coil54and the lower yoke segment68. Then, the upper yoke segment64and the first middle yoke segment66, as well as the lower yoke segment68and the second middle yoke segment70, are fixed to each other by the synthetic resin to form the first and second yoke members60,62.

In the present practical embodiment, the primary molded component82around which the coil wires58,58are wound, the upper yoke segment64, and the lower yoke segment68are set in the cavity, and in that state, the resin material is injected into the cavity and molding is performed, thereby filling the insides of the first and second yoke members60,62with the synthetic resin. That is, the synthetic resin that fills the space between the first coil52and the upper yoke segment64as well as the space between the second coil54and the lower yoke segment68, and the synthetic resin that mutually fixes the upper yoke segment64and the first middle yoke segment66as well as the lower yoke segment68and the second middle yoke segment70, serve as a mold resin94. With this configuration, in the present practical embodiment, inside resin layers96,96filling the first and second yoke members60,62are constituted by the mold resin94. While a rigid synthetic resin is preferably adopted as the mold resin94, it need not be the same as the synthetic resin that constitutes the primary molded component82(the resin bobbins56,56).

This mold resin94is injected from the radially outer side of the first and second yoke members60,62, so as to fill the radial insides of the tube parts86,86via the through holes90,90provided in the tube parts86,86, the gap93abetween the tube parts86,86and the gaps93b,93bbetween the tube parts86,86and the linking resin83. With this configuration, within the first and second yoke members60,62, the mold resin94(the inside resin layers96,96) is fixed to the resin bobbins56,56so as to cover their openings to the radially outer side. In addition, the inside resin layers96,96filling the first and second yoke members60,62are linked with each other by a connecting resin97comprising the mold resin94at the formation position of the notches80,80, and the connecting resin97is fixed to the outer peripheral surface of the linking resin83integrally formed with the resin bobbins56,56.

Moreover, the mold resin94extends to the outer peripheral surface of the first and second yoke members60,62, so that an outside resin layer98is formed and fixed to cover the outer peripheral surfaces of the first and second yoke members60,62. That is, the inside resin layers96,96filling the insides of the first and second yoke members60,62and the outside resin layer98covering the outer peripheral surfaces of the first and second yoke members60,62are linked and integrally formed with each other by filling resins100,100filling the insides of the through holes90,90. Furthermore, the inside resin layers96,96and the outside resin layer98are also linked with each other by the connecting resin97connecting the inside resin layers96,96, and by a filling resin101filling the inside of the gap93a.

In the present practical embodiment, the outside resin layer98covers the entirety of the outer peripheral surfaces of the first and second yoke members60,62. Accordingly, the upper and first middle yoke segments64,66, which constitute the outer peripheral surface of the first yoke member60, and the lower and second middle yoke segments68,70, which constitute the outer peripheral surface of the second yoke member62, are fixed to one another by the mold resin94(the outside resin layer98). Besides, the inside resin layers96,96filling the insides of the first and second yoke members60,62are connected with each other by the connecting resin97. Thus, the upper and first middle yoke segments64,66, which constitute the first yoke member60, and the lower and second middle yoke segments68,70, which constitute the second yoke member62are fixed to one another by the mold resin94(the inside resin layer96and the connecting resin97). Then, the first and second middle yoke segments66,70, which respectively constitute the first and second yoke members60,62, can be secured to each other by these inside resin layers96,96and outside resin layer98. However, in the present practical embodiment, since the linking resin83straddling the first and second middle yoke segments66,70is provided, the first and second middle yoke segments66,70may be secured to each other by the linking resin83.

Then, the mold resin94is formed as an integral unit including the first and second coils52,54and the first and second yoke members60,62, thereby providing the stator14serving as a secondary molded component. Since the secondary molded component (the stator14) is integrally formed, the mold resin94does not exist by itself as shown inFIG.3, but is shown by itself inFIG.3to show the shape of the mold resin94in an easy-to-understand way.

In the present practical embodiment, a connector102for external connection, in which the power feed terminal74is arranged, is integrally formed at the upper end of the mold resin94. The connector102is formed so as to cover the terminal part84that protrudes upward through the notch92of the upper yoke segment64, and is inserted into the insertion hole28of the outer tube member20so as to protrude to the outside of the electromagnetic actuator10.

The outside diameter dimension of the secondary molded component (the stator14) as described above is slightly smaller than the inside diameter dimension of the outer tube member20, and the stator14is inserted without being press-fitted into the outer tube member20in the state of being elastically connected with the mover16.

In the electromagnetic actuator10according to the present practical embodiment with the structure as described above, in the first and second yoke members60,62which have a split structure, the upper yoke segment64and the first middle yoke segment66are fixed by the mold resin94, and the lower yoke segment68and the second middle yoke segment70are fixed by the mold resin94. Therefore, when the first and second yoke members60,62are placed around the first and second coils52,54respectively, there is no need to perform press-fitting or cutting for the press-fitting, thereby reducing the labor and cost. In particular, since the upper yoke segment64and the first middle yoke segment66, and the lower yoke segment68and the second middle yoke segment70are fixed from both inside and outside by the inside resin layer96and the outside resin layer98, respectively, stable fixing force can be obtained.

In addition, the gap between the first yoke member60and the first coil52and the gap between the second yoke member62and the second coil54are filled with the mold resin94. Thus, during vibration input from the outside or the like, contact between the first and second yoke members60,62and the respective coil wires58,58is prevented, thereby avoiding an electrical short circuit. In particular, in the present practical embodiment, the mold resin94is fixed to the resin bobbin56from the outside of the coil wire58so as to cover the opening to the radially outer side of the resin bobbin56around which the coil wire58is wound. This makes it possible to more reliably prevent the contact between the coil wires58and the first and second yoke members60,62.

Furthermore, since the outer peripheral surfaces of the first and second yoke members60,62are covered by the outside resin layer98, a gap between the outer peripheral surfaces of the first and second yoke members60,62and the outer tube member20can be stably set, thereby preventing the two members from excessively approaching or directly contacting each other. Therefore, leakage of the magnetic flux generated around the first and second coils52,54to the outside through the first and second yoke members60,62and the outer tube member20can be avoided, or an amount of the leakage can be minimized. In particular, in the present practical embodiment, since the outer peripheral surfaces of the first and second yoke member60,62are covered by the outside resin layer98roughly entirely, the leakage flux can be reduced more reliably.

Furthermore, the inside and outside resin layers96,98are fixed to the first and second yoke members60,62. Thus, the upper and first middle yoke segments64,66that constitute the first yoke member60and the lower and second middle yoke segments68,70that constitute the second yoke member62are fixed to one another by the inside and outside resin layers96,98. Therefore, the positioning of the first and second yoke members60,62can be easily achieved, and the misalignment of each segment64,66,68,70which constitute the first and second yoke members60,62can also be prevented.

In addition, filling of the mold resin94into the insides of the first and second yoke members60,62is achieved via the through holes90provided in the tube parts86,86on the radially outer side of the first and second coils52,54and via the gap93abetween the tube parts86,86. Note that the through holes90for filling the mold resin94are provided in the outer peripheral portions of the first and second yoke members60,62. Accordingly, in comparison with the case where, for example, the through holes are provided in the upper parts of the first and second yoke members60,62(the annular part88and the second middle yoke segment70), filling of the mold resin94can be performed more quickly, and it is possible to prevent the outside resin layer98that covers the outer surfaces of the first and second yoke members60,62from becoming unnecessarily large.

Moreover, in the present practical embodiment, the connector102in which the power feed terminal74is arranged is integrally formed with the mold resin94. Thus, the labor and cost can be reduced in comparison with the case where the connector is separately formed.

Although the practical embodiment of the present invention has been described above, the present invention is not limitedly interpreted based on the specific or restrictive description in the practical embodiment and in the summary section, but may be embodied with various changes, modifications and improvements which may occur to those skilled in the art.

For example, in the preceding practical embodiment, securing of the upper yoke segment64and the first middle yoke segment66, as well as the lower yoke segment68and the second middle yoke segment70, which are the yoke segments, is achieved only by fixing with the mold resin94. However, it would also be acceptable to adopt not only the fixing with mold resin94, but also fixing force, detaining force or the like of each segment concomitantly.

Also, in the preceding practical embodiment, the outside resin layer98is fixed by covering the outer peripheral surface of the yoke member (the first and second yoke members60,62) roughly entirely, but may adopt an embodiment that partially covers the outer peripheral surface of the yoke member.

Moreover, in the preceding practical embodiment, the through holes90for filling the mold resin94inside the yoke member (the first and second yoke members60,62) are provided in the respective tube parts86,86on the outer peripheral side of the coil (the first and second coils52,54). However, the present invention is not limited to such embodiment. Specifically, the through hole may be provided in the upper or lower wall of the yoke member (for example, the annular parts88,88of the upper yoke segment64and the lower yoke segment68). Besides, in the preceding practical embodiment, filling of the mold resin94into the inside of the yoke member is also achieved by the gap93abetween the tube parts86,86, but it would also be possible to only provide either of the through holes90and the gap93a.

Furthermore, in the preceding practical embodiment, the coil comprises the first coil52and the second coil54, but may alternatively comprise a single coil or three or more coils. Also, in the preceding practical embodiment, an active vibration damper is constituted by using the electromagnetic actuator10. However, the present invention may also be implemented in an active actuator used for an active vibration damping device such as the one described in, for example, U.S. Publication No. US 2005/218734. Additionally, it is acceptable as long as the present invention has an actuator structure that utilize an electromagnetic force, and the present invention may also be implemented in an electromagnet-type active actuator that includes a mover made of a ferromagnetic material and drives the mover by exerting a magnetic attractive force thereon by utilizing a magnetic force generated due to energization to the coil, for example.

Also, in the preceding practical embodiment, the yoke member (the first and second yoke members60,62) is split into two yoke segments (the upper and first middle yoke segments64,66, the lower and second middle yoke segments68,70), but may alternatively be split into three or more yoke segments. Moreover, even in the case of being split into two, the split position is not limited to the mode of the preceding practical embodiment.

In the preceding practical embodiment, both the first yoke member60and the second yoke member62have a split structure, but it is acceptable as long as at least one of them has a split structure. Also, even when both the first yoke member and the second yoke member have a split structure, it is not necessary that the plurality of yoke segments that constitute both of the yoke members are all fixed by the mold resin. That is, the yoke segments that constitute one of the yoke members may be secured in a way of press-fitting as in the conventional structure, for example.

In addition, in the preceding practical embodiment, the first and second yoke members60,62are mutually independent of each other, but are not limited to this embodiment. Specifically, a component that is common to the yoke segment constituting the first yoke member and the yoke segment constituting the second yoke member may be adopted, for example, by adopting a tubular yoke segment extending on the outer periphery of the first and second coils in the axial direction, or by forming the first middle yoke segment and the second middle yoke segment as an integral unit, or the like. When a tubular yoke segment extending on the outer periphery of the first and second coils in the axial direction is adopted, a through hole can be provided at a position corresponding to the gap93abetween the tube parts86,86in the preceding practical embodiment, for example, and it is also possible to fill the inside of the yoke member with the mold resin via the through hole.

Besides, in the preceding practical embodiment, the resin bobbins56,56and the first and second middle yoke segments66,70are integrally formed as the primary molded component82. However, the resin bobbins and the first and second middle yoke segments may be formed separately and then fixed later or attached later. Indeed, the resin bobbin is not essential, but an air-core coil may be adopted. In this case, for example, the entire periphery of the coil may be covered with the mold resin.

In the preceding practical embodiment, the upper and lower resin bobbins56,56are linked by the linking resin83located in the notches80,80provided in the outer peripheral edges of the first and second middle yoke segments66,70. However, instead of or in addition to this embodiment, for example, a through hole may be provided so as to vertically penetrate the radially middle portion of the first and second middle yoke segments, so that the upper and lower resin bobbins are mutually linked by the resin filling the through hole.

Furthermore, in the preceding practical embodiment, the mold resin94(the inside resin layer96) filling the insides of the first and second yoke members60,62is fixed to the resin bobbins56, but it need not be fixed. That is, a gap may be provided between the coil wire and the mold resin (the inside resin layer).

In the preceding practical embodiment, a vehicle body is exemplified as the target member12whose vibration is to be damped. However, the electromagnetic actuator may be attached to a body other than the vehicle body, and an active vibration damper or an active vibration damping device for use in other than a vehicle may be constituted.