Abstract:
A snap switch with a self-cleaning function having a switch body with a fixed contact and a movable contact for performing make-break operations. A knob, mounted on the switch body, operates a contact operation member causing the movable contact to abut the fixed contact when the knob is rotated by a predetermined rotational angle and further causing the movable contact to slide on the fixed contact when the knob is further rotated.

Description:
BACKGROUND OF THE INVENTION 
     1. Field Of The Invention 
     The present invention generally relates to snap switches, and particularly relates to a snap switch having a self-cleaning function. 
     2. Description Of The Prior Art 
     A snap switch is known in which a knob is swingably provided on a switch body provided with a fixed contact and a pair of movable contacts, and in which the movable contacts are alternately caused to come into contact with the fixed contact. 
     In such a snap switch as described above, the movable contact moved by a knob so that the movable contact contacts a perpendicularly disposed fixed contact. A faulty contact will result if dust or the like adheres to the contact surface between the movable and fixed contacts, or if carbide is generated by an arc in a contact switching operation. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to eliminate the foregoing disadvantage in the prior art. 
     Another object of the present invention is a snap switch in which during a contact switching operation, contacts are caused to come into contact with each other while removing dust, oxides, or the like, to ensure that it is always possible to maintain a good contact condition. 
     In order to attain the above objects, the snap switch according to the present invention comprises a switch body provided with a fixed contact and a movable contact for performing make-break operations therebetween, a knob swingably mounted on the switch body, a contact operation member operable by the knob to cause the movable contact to abut the fixed contact when the knob is rotated by a predetermined rotational angle, and to further cause the movable contact to slide on the fixed contact when the knob is further rotated. 
     The movable and fixed contacts may be provided in a first and second set with first and second contact operation members so that when the knob is rotated in a first direction, the first contact operation member causes the movable contact in the first set to come into contact with the fixed contact in the first set and then causes the same movable contact to slide on the same fixed contact under the condition that the former is kept in contact with the latter. When the knob is rotated in a second direction, the second contact operation member causes the movable contact in the second set to come into contact with the fixed contact in the second set and then causes the same movable contact to slide on the same fixed contact under the condition that the former is kept in contact with the latter. 
     The manner by which the above objects and other objects, features, and advantages of the present invention are attained will be fully apparent from the following detailed description taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view showing a first embodiment of the snap switch according to the present invention; 
     FIG. 2 is a diagram for explaining the operation of the snap switch of FIG. 1; 
     FIG. 3(a) is an enlarged perspective view showing the movable contact portion of the snap switch of FIG. 1; 
     FIG. 3(b) is an enlarged cross-sectional view showing the movable contact portion of the snap switch of FIG. 1; 
     FIG. 4(a) is a partial cross-sectional view showing a second embodiment of the snap switch according to the present invention; 
     FIG. 4(b) is a diagram for explaining the operation of the snap switch of FIG. 4(a); 
     FIG. 5 is a partial enlarged diagram showing another embodiment of the reception portion of the snap switch of FIG. 4(a); and 
     FIG. 6 is a partial cross-sectional view showing a third embodiment of the snap switch according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the accompanying drawings, embodiments of the snap switch according to the present invention will now be described. 
     FIG. 1 shows a first embodiment of the snap switch according to the present invention. In FIG. 1, a switch body 1 is provided with a knob 2, fixed contacts 4 and 4&#39;, movable contacts 5 and 5&#39;, and contact operation members 6 and 6&#39;. The knob 2 is swingably mounted on the switch body 1 through a pin 3. The fixed contacts 4 and 4&#39; are disposed in the vicinity of the longitudinally opposite ends of a bottom surface of the switch body 1. The movable contacts 5 and 5&#39; are disposed opposite the fixed contacts 4 and 4&#39;, respectively, with a predetermined gap therebetween. 
     As shown in FIG. 3(a), the movable contact 5 is constituted by an arm portion 5a of an elastic material having a free end portion shaped into a dome-like portion 5b, a contact piece 5c fixed at the center of the dome-like portion 5b for performing the make-break operation with the corresponding fixed contact 4, and legs 5d formed integrally with the dome-like portion 5b at its circumference so as to abut on the circumference of a through hole 7a of a holder 7 which will be described later. As shown in FIG. 3(b), the dome-like portion 5b is arranged so that it is reversed (shown by a two-dot chain line in the drawing) when a predetermined urging force acts on the contact piece 5c and it returns to its original state when the urging force is removed. 
     Alternatively, the movable contact 5 may be arranged such that, for example, the free end of the arm portion 5a of the movable contact 5 is formed into a flat portion and the contact piece 5c is fixed to the flat portion. 
     Each of the contact operation members 6 and 6&#39; is constituted by the holder 7 movably provided on the switch body 1 for holding the corresponding movable contact 5, a pushing member 8 for urging the contact piece 5c as the knob 2 is rotated, and lever 2a formed integrally with the knob 2 and engaged with the through hole 7a of the holder 7 for actuating the holder 7 in response to the rotation of the knob 2. 
     The pushing member 8 is constituted by a pushing piece 9 movably provided in a cylindrical portion 2b formed integrally with the knob 2, and a spring 10 for urging the pushing piece 9 toward the outside of the cylindrical portion 2b, so that the contact piece 5c is urged by the pushing piece 9 as the knob 2 is rotated to reverse the dome-like portion 5b. 
     In the first embodiment of the present invention, when one end portion of the knob 2 is pushed to rotate the knob 2, the pushing portion 9 comes into contact with the contact piece 5c due to the rotation of the knob 2. Then, the pushing portion 9 is urged against the contact piece 5c to thereby reverse the dome-like portion 5b so that the contact piece 5c is caused to come into contact with the fixed contact 4. Next, when the pushing portion 9 is further urged against the contact piece 5c, the contact piece 5c is urged against the fixed contact 4 (at this time, the pushing portion 9 slightly retreats in the cylindrical portion 2b against the spring force of the spring 10), while the lever 2a pushes against the side of the through hole 7a of the holder 7 to thereby cause the holder 7 to move in the direction of the arrow of FIG. 2. As a result, the contact piece 5c slides on the fixed contact 4 under the condition that the former is being urged against the latter. 
     Therefore, even if dust, a carbide, or the like, adheres to the respective contact surfaces of the fixed contact 4 and the contact piece 5c, the dust or the like will be scraped off before the fixed contact 4 and the contact piece 5c come into contact with each other so that a good contact condition can be obtained therebetween. 
     FIGS. 4(a) and 4(b) show a second embodiment of the snap switch according to the present invention. This embodiment is different from the first embodiment in arrangement of the contact operation member 6. That is, the contact piece 5c is provided with a reception portion 11 that is L-shaped in cross section so that the pushing portion 9 engages the reception portion 11. When the knob 2 is rotated, the dome-like portion 5b is reversed by a vertical component P v  of the urging force P of the pushing portion 9 acting on the reception portion 11 to cause the contact piece 5c to come into contact with the fixed contact 4. When the knob 2 is further rotated, a horizontal component P h  of the urging force P of the pushing portion 9 acting on the reception portion 11 is increased so that the movable contact 5 is caused to move in the direction of the arrow shown in FIG. 4(a) by the horizontal component P h . That is, the contact piece 5c is caused to slide on the fixed contact 4. 
     In this second embodiment, the contact piece 5c is caused to come into contact with, and to slide on, the fixed contact 4 by the vertical and horizontal components, respectively, of the urging force P of the pushing portion 9 acting on the reception portion 11. Therefore, the holder 7 and the lever 2a used in the first embodiment can be omitted. 
     Alternatively, the reception portion 11 may be arranged such that, for example, as shown in FIG. 5, the end surface of the contact piece 5c is curved inwardly to create a semi-cylindrical surface to engage the pushing portion 9. 
     FIG. 6 shows a third embodiment of the snap switch according to the present invention. In this embodiment, a member 12, corresponding to the cylindrical portion 2b in the first embodiment, is vertically movably provided on the switch body 1, so that the pushing portion 9 and the spring 10 are disposed in the member 12. 
     As the knob 2 is rotated, a protrusion 2c formed on the knob 2 integrally therewith urges the member 12 down to carry out the same operation as in the first embodiment. At this time, however, the pushing direction by the pushing portion 9 coincides with the reversing direction of the dome-like portion 5b, so that the reversing and urging operations can be easily performed in comparison with the first embodiment. 
     As described above, according to the present invention, as the knob is rotated, the movable contact is urged against the fixed contact and caused to slide thereon, so that a good contact condition can be obtained even if dust, a carbide, or the like, adheres to the respective contact surfaces of the movable and fixed contacts.