Abstract:
A switch is provided, which is stable in operating characteristics and can be operated with a small operating force, and which is long in life and easy to manufacture. The switch comprises a base, a moving contact piece having one end thereof, which is supported pivotally on the base, coming into pressure contact with a common stationary contact, an operating lever having one end thereof supported pivotally on the base and having a drive part, which extends from the one end, pushing a coil portion of the moving contact piece, and a cover fixed to the base to compress the coil portion. The operating lever pushes the coil portion of the moving contact piece whereby the moving contact piece turns about an end thereof, the coil portion slides on a bottom surface of the base, and the other end of the moving contact piece slides on a stationary contact exposed from an inner surface of the base.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a switch, and more particular, to a thin-type switch mountable on a printed board. 
   2. Background Art 
   Conventionally, a thin-type switch mountable on a printed board comprises, for example, a housing having a space therein, a first stationary terminal having an end provided outside the housing and the other end provided inside the housing and provided with a contact portion having a contact groove, a second stationary terminal having an end provided outside the housing and the other end provided inside the housing and provided with a contact portion, a contact piece provided in the housing, provided at an end thereof with a stationary portion, which is latched in the contact groove of the first stationary terminal to contact with the contact portion of the first stationary terminal, and at the other end thereof with a moving portion capable of contacting with the contact portion of the second stationary terminal, the contact piece being biased by a coil spring formed at an intermediate portion thereof in a direction of twist and in a direction of compression, and an operating body provided at a base end thereof with a support portion, which is provided in the housing and defines a center of swinging, the remaining portion thereof being capable of swinging about the support portion as the center of swinging, and formed with a push surface, which abuts against the contact piece, the operating body swinging to enable pushing the contact piece in the direction of twist (see JP-A-2004-327115). 
   With the switch described above, however, the operating body  60  directly pushes the moving portion  50   e  being one end of the contact piece  50  made of a coil spring, and the contact portion  50   g  of the operating body slides on the contact portion  40   c  of the second stationary terminal while twisting the contact piece  50 . Therefore, when the operating body  60 , the contact piece  50 , etc. involve dispersion in outside dimension and assembly accuracy, unexpected elastic deformation such as warping of the moving portion  50   e , or the like is liable to occur. Consequently, dispersion is liable to generate in contact pressure, at which the contact portion  50   g  of the operating body contacts with the contact portion  40   c , and so the operating characteristics are liable to become unstable. Accordingly, when it is tried to ensure a desired operating characteristics, the switch described above needs high part accuracy and assembly accuracy, so that manufacture is not easy. 
   Also, in order to perform contact switchover in the switch described above, it is necessary to increase a twist angle of the moving portion  50   e . Therefore, there is caused a problem that a large operating force is necessary and a torsional moment acting on the contact piece  50  becomes large to make the switch susceptible to fatigue and short in life. 
   SUMMARY OF THE INVENTION 
   In view of the problem described above, the invention has its object to provide a switch, which can be operated with a small operating force and is long in life and easy in manufacture. 
   In order to solve the problem, a switch according to the invention has a construction comprising a base, a moving contact piece made of a coil spring and having one end thereof, which is supported pivotally on the base, coming into pressure contact with a common stationary contact, an operating lever having one end thereof supported pivotally on the base and having a drive part, which extends from the one end, pushing a coil portion of the moving contact piece, and a cover having a planar shape capable of covering the base and fixed to the base to compress the coil portion, and in which the operating lever pushes the coil portion of the moving contact piece to give thereto a torsional moment whereby the moving contact piece turns about an end thereof, the coil portion of the moving contact piece slides on a bottom surface of the base, and the other end of the moving contact piece slides on at least one stationary contact exposed from an inner surface of the base. 
   According to the invention, the operating lever pushes the coil portion of the moving contact piece, which is made of a coil spring, so that the other end of the moving contact piece is not subjected to unexpected elastic deformation and a switch is obtained, which can ensure a predetermined contact pressure and is stable in operating characteristics. 
   Also, even when the base, the operating lever, etc. involve dispersion in dimensional accuracy and assembly accuracy, the moving contact piece is elastically deformed to absorb an error, so that high part accuracy and assembly accuracy are not needed and manufacture is easy. 
   Further, since the moving contact piece turns about an end thereof and the other end thereof slides on the inner surface of the base, a twist angle of the whole moving contact piece is smaller than that in the related art. Therefore, since a torsional moment acting on the moving contact piece is small, there is produced an effect that a large operating force is not necessary and a switch is obtained, which is hardly susceptible to fatigue and long in life. 
   According to the embodiment of the invention, the stationary contact exposed from the inner surface of the base may comprise a normally opened stationary contact, or a normally closed stationary contact, or a normally opened stationary contact and a normally closed stationary contact. 
   According to the embodiment, there is obtained a switch, for which freedom in selecting a product is increased and which is wide in usage. 
   A switch according to another invention has a construction comprising a base, a moving contact piece made of a coil spring and having one end thereof, which is supported pivotally on the base, coming into pressure contact with a common stationary contact, an operating lever having one end thereof supported pivotally on the base and having a drive part, which extends from the one end, pushing a coil portion of the moving contact piece, and a cover having a planar shape capable of covering the base and fixed to the base to compress the coil portion, and in which the operating lever pushes the coil portion of the moving contact piece to give thereto a torsional moment whereby the moving contact piece turns about an end thereof, the coil portion of the moving contact piece slides on at least one stationary contact exposed from a bottom surface of the base, and the other end of the moving contact piece slides on an inner surface of the base. 
   According to the invention, the operating lever pushes the coil portion of the moving contact piece, which is made of a coil spring, whereby the coil portion compressed by the cover comes into pressure contact with the stationary contact to enable ensuring a predetermined contact pressure, so that a switch is obtained, which is stable in operating characteristics. 
   Also, even when the base, the operating lever, etc. involve dispersion in dimensional accuracy and assembly accuracy, the moving contact piece is elastically deformed to absorb an error, so that high part accuracy and assembly accuracy are not needed and manufacture is easy. 
   Further, since the moving contact piece turns about an end thereof and the other end thereof slides, a twist angle of the whole moving contact piece is smaller than that in the related art. Therefore, since a torsional moment acting on the moving contact piece is small, a large operating force is not necessary and a switch is obtained, which is hardly susceptible to fatigue and long in life. 
   According to the embodiment of the invention, the stationary contact exposed from the bottom surface of the base may comprise a normally opened stationary contact and a normally closed stationary contact. 
   The embodiment produces an effect that there is obtained a switch, for which freedom in selecting a product is increased and which is wide in usage. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view showing the whole of a first embodiment of a switch according to the invention; 
       FIG. 2  is an exploded, perspective view showing the switch shown in  FIG. 1 ; 
       FIG. 3A  is a perspective view showing a base of the switch shown in  FIG. 2 , and  FIG. 3B  is a perspective view showing contact terminals shown in  FIG. 2 ; 
       FIGS. 4A and 4B  are perspective views showing the switch shown in  FIG. 1  before and after operation; 
       FIGS. 5A ,  5 B, and  5 C are horizontal, cross sectional views showing the switch shown in  FIG. 1  before, during, and after operation; 
       FIGS. 6A and 6B  are perspective views showing a base and contact terminals according to a second embodiment of the invention; 
       FIGS. 7A and 7B  are perspective views showing a switch according to the second embodiment shown in  FIG. 6  before and after operation; 
       FIGS. 8A ,  8 B, and  8 C are plan views showing the switch shown in  FIG. 6  before, during, and after operation; 
       FIGS. 9A ,  9 B, and  9 C are horizontal, cross sectional views illustrating different methods of using the first, second, and third embodiments according to the invention; 
       FIGS. 10A ,  10 B, and  10 C are horizontal, cross sectional views showing fourth, fifth, and sixth embodiments according to the invention; and 
       FIGS. 11A and 11B  are a plan view and a cross sectional view illustrating different methods of using the fourth embodiment. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Embodiments of the invention will be described below with reference to the accompanying drawings of  FIGS. 1 to 11 . 
   A first embodiment comprises, as shown in  FIGS. 1 to 5 , a base  10 , into which stationary contact terminals  20 ,  21  are insert-molded, and which is square in plan, a moving contact piece  30  made of a coil spring, an operating lever  40  supported pivotally on the base  10 , and a cover  50  that covers the base  10 . In addition, an exemplary product as actually assembled has an outside dimension of a total height 0.9 mm, a base width of 3.0 mm, and a length of 3.5 mm. 
   The base  10  comprises substantially U-shaped side walls  11 ,  12 ,  13  provided continuously and protrusively along a peripheral edge of an upper surface thereof, and the stationary contact terminals  20 ,  21 , respectively, are insert-molded on the opposite side walls  11 ,  13 . Positioning steps  11   a ,  13   a , respectively, are provided on outer side surfaces of the side walls  11 ,  13 , on which the stationary contact terminals  20 ,  21  are insert-molded, while a positioning recess  12   a  is formed on an outer side surface of the side wall  12  positioned between the side walls  11 ,  13 . Further, a low step  13   b  is formed on an inside edge of the upper surface of the side wall  13 , on which the stationary contact terminal  21  is insert-molded, and a latch hole  14  is provided on the step  13   b  to have an end  32  of the moving contact piece  30  latched thereon. A common stationary contact  21   a  is exposed from an inner peripheral surface of the latch hole  14 . Also, a normally opened stationary contact  20   a  of the stationary contact terminal  20  is exposed from an inner surface of the side wall  11 , on which the stationary contact terminal  20  is insert-molded. Further, the base  10  comprises spindles  16 ,  17  protrusively provided at adjacent corners on that outer peripheral edge of the upper surface, which is not provided with any side wall, to support an operating lever  40  described later, and a coming-off preventive projection  18  protrusively provided between the spindles  16 ,  17  to prevent coming-off of the operating lever  40 . 
   An end  32  of the moving contact piece  30  made of a coil spring, which extends from an upper end of a coil portion  31  to be bent, is inserted into the latch hole  14  of the base  10  and pivotally supported and is press-contact with the common stationary contact  21   a . On the other hand, the other bent end  33  functioning as a moving contact can slide on the inner surface of the side wall  11  of the base  10  and contact with the normally opened stationary contact  20   a . The moving contact piece  30  is arranged so that the coil portion  31  slides on a bottom surface of the base  10 . 
   The operating lever  40  comprises an axial hole  41  positioned in a central position of a substantially sector shape in plan view and fitted rotatably onto the spindles  16 ,  17  of the base  10 . An operating part  42  and a drive part  43  extend at a predetermined angle about the axial hole  41 , and an arcuate groove  45  about the axial hole  41  is formed by connecting the operating part  42  and the drive part  43  to each other by means of a reinforcement rib  44 . In addition, the axial hole  41  of the operating lever  40  can be fitted on either of the spindles  16 ,  17  of the base  10 , and the drive part  43  is shaped to be able to appropriately drive the moving contact piece  30  even in the case where the operating lever  40  is supported by either of the spindles  16 ,  17 . 
   The cover  50  has a planar shape to enable covering the base  10 . However, an insulating sheet (not shown) may be stuck integrally to a roof surface of the cover at need. The cover  50  is bent vertically from three adjacent outer peripheral edges to form engagement tongue pieces  51  (not shown),  52 ,  53 , and bendable pawls  51   a  (not shown),  52   a ,  53   a , respectively, are extended from lower end edges of the tongue pieces  51 ,  52 ,  53 . 
   Subsequently, an explanation will be given to a method of assembling the switch according to the embodiment. 
   First, the end  32  of the moving contact piece  30  is latched and supported pivotally on the latch hole  14  of the base  10 , into which stationary contact terminals  20 ,  21  are insert-molded, to be accommodated on the upper surface of the base  10 . Thereby, the end  32  of the moving contact piece  30  is brought into contact with the common stationary contact  21   a  and the other end  33  can contact with the normally opened stationary contact  20   a , while the coil portion  31  is placed slidably on the upper surface of the ridge  15 . The axial hole  41  of the operating lever  40  is fitted on, for example, the spindle  17  of the base  10  to be supported pivotally thereon Then, the cover  50  is put on the base  10  to be pushed thereagainst whereby the tongue pieces  51 ,  53  and the tongue piece  52 , respectively, are engaged by the positioning steps  11   a ,  13   a  and the recess  12   a  to be positioned. Thereby, the coil portion  31  is compressed, so that a lowermost end surface of the coil portion  31  can contact with the bottom surface of the base  10  at a predetermined contact pressure. When the operating lever  40  is pushed inward against the spring force of the moving contact piece  30  in this state, the drive part  43  gets over the coming-off preventive projection  18  and the projection  18  is latched in the arcuate groove  45 . Therefore, even when the operating lever  40  is biased outward by the moving contact piece  30 , it is prevented from coming off and the end  32  of the moving contact piece  30  is brought into pressure contact with the common stationary contact  21   a  at a predetermined contact pressure. Thereafter, the assembling work is completed by inward by bending the engagement pawls  51   a ,  52   a ,  53   a  of the tongue pieces  51 ,  52 ,  53  and fixing the cover  50  to the base  10 . 
   Subsequently, an explanation will be given to a method of operating the switch. 
   In the case where any operating force is not exerted on the operating lever  40 , a spring force generated on the moving contact piece  30  by an action of beforehand loaded torsion causes the end  32  to be brought into pressure contact with the common stationary contact  21   a  and the other end  33  to be brought into pressure contact with the inner surface of the side wall  11  at a predetermined contact pressure. 
   When the operating part  42  of the operating lever  40  is pushed in, the drive part  43  pushes the coil portion  31  as shown in  FIGS. 4 and 5 . Therefore, a torsional moment acting on the coil portion  31  increases, so that the operating lever  40  turns about the spindle  17  against the spring force of the moving contact piece  30  and the other end  33  slides on the inner surface of the side wall  11  to contact with the normally opened stationary contact  20   a.    
   When a load on the operating lever  40  is released, the operating lever  40  is pushed back outward by the spring force of the moving contact piece  30 . Therefore, the moving contact piece  30  turns about the end  32  of the moving contact piece  30  in a reverse direction to the direction described above, and the other end  33  thereof slides on the stationary contact  20   a  to effect opening. 
   According to the embodiment, the moving contact piece  30  turns deforming elastically to open and close the contact whereby a switch is obtained, which does not need as high part accuracy and assembly accuracy as those in the related art, and which is high in productivity and stable in operating characteristics. 
   In particular, since the other end  33  of the moving contact piece  30  moves sliding on the stationary contact  20   a , an angle of torsion generated on the moving contact piece  30  is small as compared with the case where the other end does not move. Therefore, an internal stress generated on the moving contact piece  30  is small and fatigue failure is hard to occur. 
   Further, according to the embodiment, not only an operation in a counterclockwise direction but also an operation in a clockwise direction can be accommodated by fitting the operating lever  40  onto the spindle  16 . Therefore, since parts can be used in common, a single metallic mold can serve, thus enabling reduction in production cost. Consequently, according to the embodiment, there is an advantage that a switch capable of accommodating operation in three directions can be manufactured by a single kind of metallic mold. 
   A second embodiment provides a normally closed contact type, in which a normally closed stationary contact  20   b  is arranged on an inner surface  11  of a base  10  as shown in FIGS.  6  and  8 . 
   That is, as shown in  FIG. 6 , a normally closed stationary contact  20   b  is exposed to the inner surface  11  of the base  10 . As shown in  FIGS. 7 and 8 , when an operating lever  40  is pushed in, a torsional moment acting on a coil portion  31  increases, so that the other end  33  slides on the normally closed stationary contact  20   b . When a load on the operating lever  40  is released, the operating lever  40  is pushed back outward by the spring force of the moving contact piece  30  to return to an original position. Since the rest is the same as that in the embodiment described above, the same parts as those in the latter are denoted by the same reference numerals as those in the latter, and an explanation therefor is omitted. 
   In addition, as shown in  FIGS. 9A and 9B  the first embodiment and the second embodiment may be made clockwise by mounting the operating lever  40  on the spindle  16 . 
   According to a third embodiment, a normally closed stationary contact  20   a  and a normally opened stationary contact  22   a  are exposed to an inner surface of a side wall  11 . 
   Accordingly, when an operating lever  40  is pushed in, a torsional moment acting on a coil portion  31  of a moving contact piece  30  increases, so that the moving contact piece  30  turns about an end  32 . Therefore, after the other end  33  slides on the normally closed stationary contact  20   a , it contacts with the normally opened stationary contact  21   b  to switch over the contact. Since the rest is the same as that in the embodiment described above, the same parts as those in the latter are denoted by the same reference numerals as those in the latter, and an explanation therefor is omitted. 
   According to a fourth embodiment, a normally opened stationary contact  21   b  is arranged on a bottom surface of a base  10  as shown in  FIG. 10A . 
   According to the embodiment, since the normally opened stationary contact  21   b  is arranged on the bottom surface of the base  10 , a coil portion  31  of a moving contact piece  30  contacts with the stationary contact  21   b  at a constant contact pressure, so that there is an advantage that dispersion is hard to generate in operating characteristics. 
   The embodiment may be of course made counterclockwise by mounting the operating lever  40  on the spindle  17  as shown in  FIG. 11 . 
   Also, a normally closed stationary contact  21   c  may be arranged on a bottom surface of the base  10  as shown in  FIG. 10B  (a fifth embodiment). Also, as shown in  FIG. 10C , a normally closed stationary contact  20   d  and a normally opened stationary contact  21   b  may be arranged on a bottom surface of the base  10  (a sixth embodiment). 
   Like the fourth embodiment described above, the fifth and sixth embodiments have an advantage that a switch can be obtained, in which dispersion in contact pressure is hard to generate and which has a stable operating characteristics. 
   In addition, according to the embodiments, both an operation in a clockwise direction and an operation in a counterclockwise direction can be accommodated by changing a position, in which the operating lever  40  is mounted to the base  10 . 
   Also, while according to the embodiments, an end of the moving contact piece extending from above is supported pivotally on the base, the other end thereof extending from under may be supported pivotally on the base. 
   The switch according to the invention is of course applicable to a switch other than ones according to the embodiments.