Abstract:
An improved actuator assembly is disclosed. The actuator has a rotor assembly rotatably mounted in a stator frame formed of a synthetic resin material. The stator frame has a borehole therein that receives a rotor assembly, a pair of mounting recesses, and a pair of bobbins portions. Each bobbin portion includes a slot. Induction magnets are mounted in each mounting recess of the stator frame such that they face the rotor assembly. A coils is would about each bobbin portion of the stator frame. The coils and induction magnets are angularly spaced about the rotor assembly. A core having a plurality of poles and holding portions, is also provided. Each core pole extends through an associated one of the bobbin slots and faces the rotor magnet. The holding portions are arranged to hold the induction magnets in place.

Description:
This application is a continuation of application Ser. No. 07/842,928, filed Feb. 27, 1992, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     This application claims the priority of Japanese Patent Application No. 3-129949 filed on May 31, 1991 which is incorporated herein by reference. 
     1. Field of the Invention 
     The present invention relates to an actuator, and more particularly, to an actuator which drives, for example, an intake valve in an internal combustion engine. 
     2. Description of the Related Art 
     A conventional actuator of this type is disclosed in Japanese Unexamined Patent Publication No. 2-140419. As shown in FIG. 5, such an actuator 30 comprises a four-pole stepping motor 31 whose core 32 is shaped into a square barrel. The core 32 includes a peripheral wall 32a which forms magnetic paths and four poles 33a to 33d which protrude inward from the peripheral wall 32a. The core 32 is formed of a plurality of laminated metal plates. Each of the metal plates is made through a pressing process and has four side edges linked to one another and four projections which extend inward from the respective side edges of the plate in association with the poles 33a to 33d, respectively. The core 32 has coils 34a to 34d wound around the poles 33a to 33d, respectively. A rotor 36 with a magnet 36a is held rotatable in the center of the core 32. The rotor 36 will be intermittently rotated every 90 degrees by properly changing the direction of conduction to one coil pair 34b and 34d while keeping the direction of conduction to the other coil pair 34a and 34c the same. 
     The prior art described above is designed to have the poles 33a to 33d projecting inward from the inner surface of the peripheral wall 32a. With this structure, to wind the coils 34a through 34d around the respective poles 33a-33d is relatively difficult because the adjacent poles, which have their coils already wound thereabout, and the peripheral wall 32a interfere with this work. 
     Since the coils 34a to 34d should be arranged so that they do not interfere with one another, clearances have to be provided between the coils. The internal space of the core 32 cannot therefore be effectively used. 
     The opposing pair of poles 33a and 33c in FIG. 5 may be replaced respectively with magnets 35a and 35b shown in FIG. 6. This provides another type of actuator in which the rotor 36 may be rotated in 90 degree intervals. This actuator has its core 31 provided with a pair of poles 33b and 33d. It is therefore easier to wind the coils 34b and 34d around the poles 33b and 33d in this case than in the above described prior art. 
     This modified actuator does not differ from the conventional case in that the peripheral wall 32a is still an obstruction when the coils 34b and 34d are to be wound around the poles 33b and 33d. Further, this modification gives rise to a new shortcoming where the magnets 35a and 35b have to be incorporated at the determined positions of the metallic core against their magnetic force. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide an actuator which can be made compact by accomplishing the effective use of its internal space, and is designed to facilitate the winding of coils around poles and to easily support magnets on the stator side at determined positions. 
     To achieve the above object, an actuator is provided that has a rotor assembly rotatably mounted in a stator frame formed of a synthetic resin material. The stator frame has a borehole therein that receives a rotor assembly, a pair of mounting recesses, and a pair of bobbins portions. Each bobbin portion includes a slot. Induction magnets are mounted in each mounting recess of the stator frame such that they face the rotor assembly. A coil is wound about each bobbin portion of the stator frame. The coils and induction magnets are angularly spaced about the rotor assembly. A core having a plurality of poles and holding portions, is also provided. Each core pole extends through an associated one of the bobbin slots and faces the rotor magnet. Each holding portion is arranged to hold an associated induction magnet in place. 
     In a preferred embodiment, the core is divided into a pair of core sections each of which has a core pole, a pair of holding arms that extend substantially in parallel with the core pole, and a linking portion for linking the core pole to the holding arms. The holding arms constitute the holding portions and are arranged to abut against outer walls of an associated induction magnet to hold the associated induction magnet in place. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention, together with the objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiment together with the accompanying drawings in which: 
     FIG. 1 is a cross section of an actuator according to one embodiment of the present invention; 
     FIG. 2 is an exploded perspective view of the stator for the actuator shown in FIG. 1; 
     FIG. 3 is a perspective view of the stator shown in FIG. 2 in an assembled state; 
     FIG. 4 is an exploded perspective view showing the whole actuator; 
     FIG. 5 is a plan view of a conventional actuator; and 
     FIG. 6 is a plan view of another conventional actuator. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A preferred embodiment of the present invention as applied to an actuator for opening and closing an intake valve in an internal combustion engine for a vehicle will now be described referring to FIGS. 1 to 4. 
     As shown in FIG. 4, an actuator 1 comprises a casing 2, a stator 3, a rotor 4, a cover 5 and a valve 6. The casing 2 is formed almost cylindrical, and has a bottom and a top opening. The stator 3 is retained in the casing 2. The cover 5 is attached to the opening of the casing 2 to prevent foreign substances from entering the casing 2. The rotor 4 includes a rotary shaft 7 and a magnet 8 fitted around the periphery of the rotary shaft 7. 
     The ends of the rotary shaft 7 are rotatably supported by the bottom of the casing 2 and the cover 5 respectively. The magnet 8 is inserted rotatable in the stator 3. The distal end of the rotary shaft 7 projects from the cover 5. A valve 6 is securely fitted over the distal end of the rotary shaft 7, so that the valve 6 and the rotary shaft 7 will integrally rotate. 
     The structure of the stator 3 will now be described in detail. The stator 3 is made of a synthetic resin and has a frame 9 that generally takes the shape of a rectangular parallelepiped, as shown in FIGS. 1 to 3. In the center of the frame 9, a vertically extending borehole 11 is provided, as seen in FIG. 2. The magnet 8 of the rotor 4 is inserted through the borehole 11. A pair of bobbins 10a and 10b are formed integrally with the frame 9, such that they extend to opposite sides of the frame 9. The bobbins 10a and 10b respectively include sleeves 12a and 12b, and flanges 13a and 13b projecting sideward from the respective sleeves 12a and 12b. 
     Stator coils 14a and 14b are wound around the sleeves 12a and 12b between the frame 9 and the flanges 13a and 13b, respectively. Further, rectangular slots 15a and 15b are formed in the bobbins 10a and 10b. The slots extend through the sleeves 12 from the flanges 13 to the borehole 11. 
     In a plane perpendicular to a plane where the bobbins 10a and 10b are formed and the axis of the borehole 11 lies, the frame 9 has a pair of magnet openings 16a and 16b each having a rectangular cross section, which are positioned on the respective sides (left and right sides in FIG. 1) of the borehole 11. The magnet openings 16a and 16b communicate with the borehole 11. First and second induction magnets 17a and 17b are inserted into the magnet openings 16a and 16b, facing the magnet 8 of the rotor 4. In this embodiment, that side of the first induction magnet 17a which faces the rotor 4 is set to the &#34;N&#34; pole, while that side of the second induction magnet 17b which faces the rotor 4 is set to the &#34;S&#34; pole. The outside portions of the induction magnets 17a and 17b are thus set to the &#34;S&#34; and &#34;N&#34; poles, respectively. 
     A core 18 includes two substantially E-shaped sections 18a and 18b respectively corresponding to the bobbins 10a and 10b. The E-shaped sections 18a and 18b are formed by a plurality of laminated metal plates which have been pressed into an almost E shape. The E-shaped sections 18a and 18b respectively include bases 20a and 20b to be joined to the flanges 13a and 13b, pairs of side walls 21a and 21b extending almost in parallel to each other along the sides of the bobbins 10a and 10b, and poles 19a and 19b to be inserted into the slots 15a and 15b. The free ends of the side walls 21a and 21b are joined to one another, as well as to the respective induction magnets 17a and 17b. The attraction forces of the magnet 8 of the rotor 4 and the induction magnets 17a and 17b securely hold the E-shaped sections 18a and 18b, and keep the induction magnets 17a and 17b in the magnet openings 16a and 16b. 
     The following description of this embodiment will be given of the case where the valve 6 is located at the closing position indicated by the alternate long and two short dash line shown in FIG. 1, i.e., a position where the valve 6 closes the intake path (not shown) of the internal combustion engine. In this case, a current flows through the coils 14a and 14b in one direction. The distal end of the first pole 19a is then magnetized to the &#34;N&#34; pole, and the distal end of the second pole 19b is magnetized to the &#34;S&#34; pole. At this time, in accordance with the magnetic forces of the induction magnets 17a and 17b and the poles 19a and 19b, the rotor 4 is kept stationary at the position shown in FIG. 1. In other words, the &#34;S&#34; pole of the rotor 4 is located between the first induction magnet 17a and the first pole 19a, while the &#34;N&#34; pole is set between the second induction magnet 17b  and the second pole 19b. 
     To change the valve 6 to the opening position indicated by the alternate long and short dash line in FIG. 1, i.e., a position where the valve 6 opens the intake path of the internal combustion engine, the direction of conduction to the coils 14a and 14b should be reversed from the one in the previous case. The poles 19a and 19b are then inverted, so that the distal end of the first pole 19a may be &#34;S&#34;, and that of the second pole 19b &#34;N&#34;. 
     The &#34;S&#34; pole of the rotor 4 repels the first pole 19a, and is attracted by the first induction magnet 17a and the second pole 19b to be rotated to the middle point between the first induction magnet 17a and second pole 19b. At the same time, the &#34;N&#34; pole of the rotor 4 repels the second pole 19b and is attracted by the second induction magnet 17b and the first pole 19a to be rotated to the middle point between the second induction magnet 17b and the first pole 19a. In other words, the rotor 4 rotates 90 degrees counterclockwise in FIG. 1, thereby moving the valve 6 to the opening position indicated by the alternate long and short line in FIG. 1. 
     Reversing the direction of conduction to the coils 14a and 14b again can rotate the rotor 4 clockwise in FIG. 1 to return the valve 6 to the closing position. 
     In assembling the above-described actuator, the stator portion should be assembled first. That is, the coils 14a and 14b are wound around the bobbins 10a and 10b of the frame 9. Since there is no obstruction around the sleeves 12a and 12b, the winding can be done easily. The induction magnets 17a and 17b are inserted in the magnet openings 16a and 16b, respectively. As the casing 2 is made of a synthetic resin, the magnetic forces of the induction magnets 17a and 17b will not interfere with this assemblage, unlike in the prior art. 
     The poles 19a and 19b of the E-shaped sections 18a and 18b of the core 18 are retained in the associated slots 15a and 15b. At the same time, the free ends of the side walls 21a and 21b are joined to each other, and further to the corresponding induction magnets 17a and 17b. By the attraction forces of the induction magnets 17a and 17b, the E-shaped sections 18a and 18b are securely held to the frame 9, and the induction magnets 17a and 17b are retained in the magnet openings 16a and 16b. The assemblage of the stator is then complete. 
     After the stator portion is accommodated in the casing 2, the rotor 4 will be inserted into the borehole 11 of the frame 9. The opening of the casing 2 is then closed with the cover 5, and the valve 6 is fitted over the rotor 4, completing the assemblage of the actuator. 
     In this embodiment as described above, the core 18 is separated into E-shaped sections which will be assembled after the coils 14a and 14b have been wound around the frame 9. Unlike the case of winding coils directly around the respective poles of an integral core, this embodiment does not require that clearances for winding the coils be previously provided around the poles. It is therefore possible to design the actuator compact and also to facilitate the coil winding. 
     In this embodiment, the induction magnets 17a and 17b are retained in the frame 9 of a synthetic resin. As a result, the induction magnets 17a and 17b can be easily assembled without any influence of magnetic force. Further, the E-shaped sections 18a and 18b partially abut on the outer surfaces of the induction magnets 17a and 17b. In this way, the induction magnets 17a and 17b can be prevented from coming off the magnet openings 16a and 16b and can always be held at predetermined positions. 
     Although only an embodiment of the present invention has been described herein, it should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Therefore, the present example and embodiment are to be considered as illustrative and not restrictive and the invention is not to be limited to the details given herein, but may be modified within the scope of the appended claims.