Coil device
BACKGROUND OF THE INVENTION 
     The present invention relates to a coil device used as a solenoid. 
     In a conventional coil device such as disclosed in Japanese utility model publication No. Hei3(1991)-33046 published after examination, each of the ends of a wire wound around a resin bobbin is connected to a terminal corresponding thereto, and a resin protective layer is provided on parts of the wire and the terminals. When such a coil device is incorporated in a specific apparatus such as a solenoid, those parts are subjected to a concentration of stress if there is a big change in the ambient temperature because of the shrinkage force acting between the ends of the wire and the respective terminals. In this case, there will be no problem if the size of the wire is large enough. However, it is sometimes inevitable that a wire having a small diameter is used in view of the rating of the coil device. In such a case, since there is a possibility of wire disconnection due to the concentration of stress, it is necessary to wind wire with a tension which is somewhat small. 
     Such approach, however, can result in improper winding, creating a problem that the inductance of the coil can derive from the design value. 
     SUMMARY OF THE INVENTION 
     It is, therefore, a primary object of the present invention to provide a coil device without the foregoing drawbacks. 
     Another object of the present invention is to provide a coil device in which the concentration of stress produced Between the ends of the wire and the respective terminals can be properly handled without making a tension during the winding of the wire somewhat small. 
     In order to attain the foregoing objects, a coil device comprises a bobbin provided at one end thereof with a flange, a wire wound around the bobbin, a pair of terminals provided on the flange and connected to both ends of the wire, and means for reducing the concentration of stress to the ends of the wire during shrinkage and expansion of the bobbin associated with changes in temperature. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will be more apparent and more readily appreciated from the following detailed description of a preferred exemplarily embodiment of the present invention, taken in connection with the accompanying drawings, in which; 
     FIG. 1 is a perspective view of a coil device according to the present invention taken during the process of manufacturing the same; 
     FIG. 2 is a view in the direction of the arrow &#34;A&#34; in FIG. 1; 
     FIG. 3 is a view showing a slack state of a coil device according to the present invention; and 
     FIG. 4 is a sectional view of a solenoid valve as which a coil device according to the present invention is mounted. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A preferred embodiment of the present invention will be described hereinafter with reference to the attached drawings. 
     Referring now to FIGS. 1 to 3 inclusive, a coil device 1 includes a bobbin 10. The bobbin 10 has a cylindrical portion 10c having at its both ends a pair of flanges 10a and 10b, respectively. A wire 13 is wound around the cylindrical portion 10c of the bobbin 10 in a well-known manner, though the wound condition of the wire 13 is not shown. Ends 13a and 13b of the wire 13 extends along grooves 15 and 16, respectively, which are obtained by cutting the flange portion 10a, and are connected to terminals 11a and 12a, respectively. As will be described later, each of the ends 13a and 13b of the wire 13 are adapted to form slack 40 in the vicinity of the respective ends 13a and 13b when the coil device 1 is completed. 
     The connection of the end 13a (13b) of the wire 13 to the terminal 11 (12) is accomplished by fusing. Specifically, a gap is formed or defined between a main body portion 11x (12x) of the terminal 11 (12) and a retaining portion 11a (12a) which is integrally formed with the main body portion 11x (12x) and is bent so that it is substantially parallel with the main body portion 11x (12x), and the end 13a (13b) of the wire 13 is placed in the gap. In this state, a current is applied from the retaining portion 11a (12a) to the main body portion 11x (12x), and the heat produced thereby melts the coating on the end 13a (13b) of the wire 13. Then, the retaining portion 11a (12a) is pushed toward the main body portion 11x (12x), and the end 13a (13b) of the wire 13 is thereby electrically connected to the terminal 11 (12). 
     The connection of the end 13a (13b) of the wire 13 to the terminal 11 (12) as described above is carried out with the terminal 11 (12) incompletely inserted in a groove 30 (31) formed in the flange 10a. Specifically, the connection is made with the terminal 11 (12) inserted in the groove 30 (31) so that a gap X is left between it and a bottom wall 30a (31a) of the groove 30 (31) instead of being completely inserted. When the connection of the end 13a (13b) of the wire 13 to the terminal 11 (12) is completed, further insertion is made until the tip 11y (12y) of the terminal 11 (12) abuts against the bottom wall 30a (31a) of the groove 30 (31), and the ends 13a and 13b of the wire 13 will have the respective slacks 40 formed in the vicinity of the respective ends 13a and 13b of the wire 13 as shown in FIG. 4. Thereafter, a connector 3 which is in the form of a molding 33 as shown in FIG. 4 is formed around the wire 13 after molding thereof. A resin hardened by ultraviolet rays which has high plastically is provided in each groove 15 (16) for the connection of the ends 13a (13b) to the flange 10a. The terminals 11 and 12 are not buried in the molding 33. The presence of the slack 40 allows the ends 13a and 13b to absorb expansion and shrinkage of the bobbin 10 due to change in temperature, thereby preventing disconnection of the wire 13. 
     The process for manufacturing this coil device 1 is summarized as follows; The manufacturing process for the coil device 1 comprises a first step for preparing the bobbin 10 having, on one end thereof, the flange portion 10a in which a pair of grooves 30 and 31 are formed, a second step for inserting a pair of terminals 11 and 12 in the grooves 30 and 31 in the flange portion 10a so that the terminals are spaced from the bottom walls 30a and 31a of the grooves by a predetermined quantity, a third step for connecting the ends 13a and 13b of the wire 13 to the respective terminals 11 and 12, a fourth step for further inserting the terminals 11 and 12 to which the ends 13a and 13b of the wire 13 are connected in the respective grooves 30 and 31, and a fifth step for molding the wire 13. 
     FIG. 4 shows a solenoid valve 2 in which a coil device 1 according to the present invention is used. The solenoid valve 2 has a core 5, and the coil device 1 is mounted on the core 5. The coil device 1 is coupled together with a connector 3 from which the terminal 11 is exposed in a state in which it is bent by approximately 90 degrees. A small diameter portion 5a and a large diameter portion 5b are formed in the core 5. The core 5 is connected, at the large diameter portion 5b thereof, to a base member 4 on which an orifice 4a and a drain port 4b are formed. A sleeve is disposed at the large diameter portion 5b of the core 5, and a plunger 7 which axially slides when the coil device 1 is excited is disposed in the sleeve 6. A valve ball 8 which controls communication between the orifice 4a and the drain port 4b is disposed between the plunger 7 and the base member 4, and the plunger 7 is continually urged against the valve ball 8 by a spring 9. When the solenoid 2 which is of the foregoing structure is mounted on a motor vehicle, since the motor vehicle is used in an environment in which big changes in temperature take place, there is a great advantage that the disconnection of the wire 13 of the coil device 1 is avoided and reliability of the mechanisms or devices associated therewith is guaranteed. 
     As described above, according to the present invention, the slack 40 in the vicinity of the ends 13a and 13b of the wire 13 absorbs expansion and shrinkage of the bobbin 10 due to change in the ambient temperature. This results in a great advantage that the wire 13 is not disconnected and the reliability of not only the coil device 1 but also of the mechanisms or devices associated therewith is guaranteed. 
     Obviously, many modifications and variations of the present invention are possible in the light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practised otherwise than as specifically described.