Abstract:
In a case for a small-sized motor, there are provided projections and convex portions in the cylindrical portion of the case for holding permanent magnets in the case without using any binding agent, springs or screws.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to construction of a case for a small-sized electric motor. 
     In a conventional case for a small-sized electric motor arched magnets are fixed to the case for a small-sized electric motor either by means of binding agent, springs or screws. However, fixing by the binding agent causes a problem in that the arched magnets are not fixed stably enough to withstand vibration. And fixing by the springs or the screws required more elements and assembling steps. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an useful and economical case for a small-sized electric motor, in which said case is provided with projections and convex portions for readily holding permanent magnets. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 shows a partial cross section of the motor case of the present invention. 
     FIG. 2 shows a front view of the case illustrated in FIG. 1, and 
     FIG. 3 shows an enlarged partial view of the motor case illustrated in FIG. 2. 
     FIG. 4 shows a partial cross section of another motor case of the present invention. 
     FIG. 5 shows a front view of the case illustrated in FIG. 4, and 
     FIG. 6 shows an enlarged partial view of the motor case illustrated in FIG. 5. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Now referring to FIG. 1, FIG. 2 and FIG. 3, showing the first embodiment of the invention, a numeral number 1 designates a case for a small-sized electric motor. Two arched permanent magnets 2 are disposed on an inner periphery of a cylindrical portion 1a of the case 1. A symbol a designates a shoulder portion provided at the end of the inner periphery of the cylindrical portion 1a. The shoulder a abuts the magnets at one of their axial ends. A symbol d designates a convex portion which is protruded between the two magnets 2 from the cylindrical portion 1a in the radial direction. A symbol c designates a projection which is provided on the convex portion d by cutting and pressing in a circular direction of the cylindrical portion 1a. The projection c urges the ends of magnets in the circular direction. Another projection b is provided on the cylindrical portion 1a by cutting and pressing, and this projection b urges the magnet 2 to the shoulder a. In a construction as aforementioned, the shoulder a, the first projection c, the second projection b and the convex portion d are easily formed unitary with the cylindrical portion by a pressing process. The magnet 2 is disposed on the inner periphery of the cylindrical portion 1a of the case 1 and between the shoulder a and the second projection b. 
     The magnet 2 is put into the case 1 until it abuts the shoulder a provided in the cylindrical portion 1a. The spring action of the projection b urges the magnet 2 to the shoulder a, whereby the magnet 2 is secured in its correct axial position. At the same time the magnet 2 is held between the first projection c and the side of another convex portion d, whereby the magnet 2 is secured stably in the inner periphery of the cylindrical portion 1a by the spring action of the first projection c. 
     The first projection c may be substituted for a projection c&#39; shown in FIGS. 4, 5 and 6. As shown in these figures, the projection c&#39; is formed by cutting both sides of the projection c&#39;, while the projection c is formed by cutting three sides thereof. The projection c&#39; and the convex portion d hold the magnet 2 stably therebetween and against the inner periphery of the cylindrical portion 1a in the same manner as described in FIGS. 1, 2, and 3. Though the second projection b serves to restrict movement of the magnet 2 in the axial direction, the magnet 2 can be restricted in the axial direction by the first projection c or c&#39; and the convex portion d alone without using the second projection b. Therefore, in this case the second projection b can be eliminated.