Abstract:
An overload-protection push-button switch with automatic resetting mechanism is disclosed. The switch is characterized in that a pressing stem actuates a conducting leaf via an enabled rocking lever, and that a wrecking bar is provided to dislocate the position of a positioning unit so that the pressing stem will automatically return back to its reset position in case the rocking lever is disabled due to overload. By means of the above structure, a push-button switch which is capable of exactly functioning and has a simple structure to easily assemble is available.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     Not Applicable 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a push-button switch and, in particular, to an overload-protection push-button switch with a simple structure capable of actually tripping and automatically going to a reset position in case of overload. 
     2. Description of the Related Art 
     There are many types of push-button switches for various applications, such as one having a turn-on indicating lamp and one providing an overload protection function. In terms of one having an overload protection function, there are also several kinds of protection principles or mechanisms being adopted. For example, both the blow-out of a fuse wire and the thermal deformation of a bimetal blade have ever been adopted as a trigger source for an overload protection. However, the fuse wire is not repetitive and thus its utility rate gradually decreases. As for the thermal bimetal blade. there are many kinds of mechanism, such as those disclosed in U.S. Pat. Nos. 5,786,742, 5,223,813, 4,937,548, 4,661,667, 4,931,762, 5,451,729, and 4,704,594. 
     For example, in the U.S. Pat. No. 5,786,742, a so-called power-cutting member ( 72 ) used to alternatively set a set and a reset position of a switch is disclosed. In that case, a bimetallic blade ( 75 ) is used to push a shaft seat ( 71 ) to trip and automatically reset a switch. However, the contacts in such a switch are directly depressed by a button. Thus, if the button has jammed or pushed down by an external force, they would be kept in its conducting position even if overload occurs. Moreover, such a switch is not economical because of a use of up to four contacts to construct a conducting circuit. It also increases the possibility of generating an arc. Furthermore, it is troublesome in assembly due to a need for connecting a wire between the bimetallic blade ( 75 ) and the conducting plate ( 74 ). 
     In U.S. Pat. No. 5,223,813, a bimetal sheet ( 13 ), a common trip ( 17 ) actuated by the bimetal sheet, and a cam member ( 27 ) are incorporated with a rocker actuator ( 33 ) to make contact members ( 7 ,  1 ) contact together or separate from each other. In such a patent, the common trip ( 17 ) will be displaced in response to a deformation of the bimetal sheet so that the cam member ( 27 ) is released and the switch trips. However, even though the common trip is indirectly actuated by a rocker actuator so that a jamming of the rocker actuator or a contact of the contact members by a neglectful re-push after overload can be avoided, such a switch is rather complicated. Moreover, since it needs a wire to connect its cantilever spring ( 5 ) and its bimetal sheet ( 13 ), its assembly is also troublesome. Furthermore, a fail-action is possible in case of overload since the bimetal sheet may be unable to simultaneously actuate both of the rocker actuator ( 33 ) and the common trip ( 17 ). 
     In a circuit breaker disclosed in U.S. Pat. No. 4,937,548, a thermal actuator ( 76 ) is used to displace a lock lever ( 62 ) upon deformation so as to release a bell crank lever operator ( 52 ). In this case, even a jamming of the actuator and a connection between the contacts upon a neglectful re-push on the switch after overload can be avoided, such an arrangement has not an automatic resetting function and is difficult to install an indicator therein. Moreover, since two thermal actuators are forced against one biasing spring, a tilt of the two thermal actuators may happen. 
     In U.S. Pat. No. 4,661,667, a double-heart-shaped cam locking mechanism is used to obtain two locking-positions. However, such a switch has not an overload protection function and a status-indicating function. 
     BRIEF SUMMARY OF THE INVENTION 
     A main object of the present invention is to provide an overload-protection push-button switch with an automatic resetting mechanism which has a simple structure and a low manufacturing cost and is easy to assemble. 
     Another object of this invention is to provide an overload-protection push-button switch with an automatic resetting mechanism in which a reset function will be exactly performed in case of meeting a trip condition. 
     To achieve the above objects of this invention, this invention provides an overload-protection push-button switch with an automatic resetting mechanism comprising: 
     a housing; 
     a switching circuit installed in the housing and including a first terminal, a second terminal, a first conducting leaf, and a bimetal sheet; the bimetal sheet having a movable closed end, being able to move to an overload position from a normal position in case of overload, and an open end formed with a first and a second legs for respectively connecting the first terminal and the first conducting leaf; the first conducting leaf being movable between a conduction position in which the second leg of the bimetal sheet is electrically connected to the second terminal and a broken position in which the second leg is disconnected from the second terminal; and 
     an actuating unit installed in the housing and including: 
     a slidable pressing stem to be actuated to one of a set and a reset positions; 
     a positioning unit including a cantilever and a heart-shaped stepping recess and being able to position the pressing stem in the set position when the pressing stem is pressed downward; 
     an enabling supporter being alternatively located in a supporting position and a tripping position in response to the normal position and the overload position of the bimetal sheet respectively; 
     a rocking lever pivotally supported on the pressing stem along a pivoting axle and formed with a nose for abutting against the first conducting leaf, a toe portion to be supported by the enabling supporter, and a pivoting hole located between the nose and the toe portion so as to be actuated by the pressing stem; 
     a wrecking bar for departing the cantilever from the heart-shaped stepping recess in case of being actuated by the rocking lever; and 
     a lever-reseating member for abutting against the rocking lever during the returning course of the pressing stem back to its reset position so that the toe portion can be supported by the enabling supporter. 
     Whereby the toe portion could be enabled by the enabling supporter and the nose can make the first conducting leaf be alternatively located in its conduction position and its broken position in response to the location of the pressing stem in the set position and in the reset position respectively when the bimetal sheet is located in its normal position, and whereby the toe portion could trip and be disabled so as to release the abutment of the nose against the first conducting leaf and to make the wrecking bar depart the cantilever from the heart-shaped stepping recess and thus make the pressing stem automatically return back to its reset position and the first conducting leaf be in a broken position. 
     By means of the above structure, since the rocking lever is indirectly actuated, the switch can still exactly and transiently trip at the time overload occurs even if the stem jams. Moreover, by virtue of the wrecking bar being actuated by the rocking lever, the switch could automatically return to its reset position after overload. Furthermore, by means of the reseating member, in the stroke of the pressing stem returning to its reset position the toe portion of the rocking lever will return to a position able to be enabled by the enabling supporter once the bimetal sheet is deformed into its normal position. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     In the following, preferred embodiments of the present invention will be described in detail in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is an exploded schematic perspective view of an overload-protection push-button switch with automatic reset mechanism in accordance with a first embodiment of this invention; 
     FIG. 2 is an assembled elevation view partly in section of the push-button switch of FIG. 1 in an OFF status; 
     FIG. 3 is a view similar to FIG. 2 but in an ON status; 
     FIG. 4 is a view similar to FIG. 2 but in a trip status before the pressing stem returns to its reset position. 
     FIG. 5 is an exploded schematic perspective view showing a part of the elements in a switch according to a second embodiment of this invention, which is a modification of the first embodiment. 
     FIG. 6 is an assembled elevation view partly in section of the push-button switch of FIG. 5 in a trip status before the pressing stem returns to its reset position; 
     FIG. 7 is an exploded schematic perspective view of an overload-protection push-button switch with automatic reset mechanism in accordance with a third embodiment of this invention; 
     FIG. 8 is an assembled elevation view partly in section of the push-button switch of FIG. 7 in an OFF and an ON status respectively drawn by dotted lines and solid lines; and 
     FIG. 9 is an assembled elevation view partly in section of the push-button switch of FIG. 7 in a trip status before the pressing stem returns to its reset position. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following, an overload-protection push-button switch with an automatic resetting mechanism according to a first preferred embodiment of this invention will be described in reference to drawings. 
     As shown in the exploded perspective view of FIG. 1, the overload-protection push-button switch with an automatic resetting mechanism according to a first preferred embodiment of this invention generally comprises a switching circuit  10 , an actuating unit  20 , and a housing  1  for receiving the switching circuit  10  and the actuating unit  20 . The housing  1  comprises a main body la and a cover lb. The switching circuit  10  comprises a first terminal  11 , a second terminal  12 , a third terminal  13 , a thermal-deformed bimetal sheet  14 , a first conducting leaf  15 , a second conducting leaf  16 , an indicating lamp  17 , and a resistor  18 . The actuating unit  20  comprises a pressing stem  21 , a positioning unit mainly composed of a cantilever  22   a  and a heart-shaped stepping recess  22   b,  a biasing spring  23  for biasing the pressing stem, a rocking lever  24 , an enabling supporter  25 , a biasing spring  26  for biasing the enabling supporter  25 , a wrecking bar  27 , a biasing spring  28  for biasing the wrecking bar  27 , a lever-reseating member  29 , and a key  30 . 
     The main body  1   a  is provided with a top wall, a bottom wall and three sidewalls, and is formed with a key opening (not indicated with numeral) on the top wall and a number of terminal holes (not indicated with numeral) on the bottom wall. Moreover, a lot of members for guiding or fixing the elements mentioned above are formed integrally with the main body  1   a.  For example, a guiding rod  1   c  for guiding the pressing stem  21  is formed. The cover  1   b  can be installed on the main body  1   a  so as to close the main body  1   a.    
     As for the switching circuit  10 , each terminal  11 ,  12 , or  13  passes through respective terminal hole from inside of the housing to outside of the housing. The second terminal  12  is provided with a lower contact pad  12   c  inside the housing  1 . The thermal-deformed bimetal sheet  14  is of a reversed-U shape having a closed end and an open end. The open end of the bimetal sheet  14  is constructed with two legs respectively being connected to the first terminal  11  and one end of the first conducting leaf  15  (as shown in FIG.  1 ). 
     The thermal-deformed bimetal sheet  14  is in a normal position as shown in FIG. 2 if the current pass therethrough is not overloaded, while the said sheet  14  is in an overload position as shown in FIG. 4 if the current pass therethrough is overloaded. Once overload disappears, the bimetal sheet  14  will automatically return to its normal position from its overload position. 
     The first conducting leaf  15  is fixed and electrically connected to the bimetal sheet  14  (as shown in FIG. 1) at one end thereof, and is provided with an upper contact pad  15   c  at its free end so as to contact a lower contact pad  12   c  of the second terminal  12 . Moreover, the first conducting leaf  15  is further provided with a dome  15   d  at its substantially middle portion so as to be abutted by the actuating unit  20 . 
     As shown in FIGS. 1 and 2, the second conducting leaf  16  has a fixed end electrically connected to the third terminal  13  and a free end to be contacted by the resistor  18  (as shown in FIG.  3 ). The resistor  18  is connected with the indicating lamp  17  and the indicating lamp  17  is electrically connected to the second terminal  12  via the biasing spring  23  by passing through a hole formed in the pressing stem  21 . 
     By means of the above, when the first conducting leaf  15  is actuated by the actuating unit  20  and moves into a conduction position as shown in FIG. 3, an electrical contact is built between the upper and lower contact pads  15   c  and  12   c.  Thus, the power from the first terminal  11  will be transmitted to the second terminal  12  and to the third terminal  13  via the indicating lamp  17  so as to light up the indicating lamp  17 . 
     As shown in FIGS. 1 and 2, the main body la is formed with a hole  1   e  on a side wall in the neighborhood of the first terminal  11 . The first terminal  11  is provided with a screw hole  11   a  in an extending fin substantially parallel to the bimetal sheet  14 . By means of engaging an adjusting screw  19  into the screw hole  11   a,  the inner end of the screw  19  could push against one leg of the bimetal sheet  14  so as to adjust the position of the bimetal sheet  14 . 
     As shown in FIGS. 1 and 2, the pressing stem  21  of the actuating unit  20  is of a square hollow shape in which a biasing spring  23  is received and thus the pressing stem  21  is biased upward to a reset position (as shown in FIG. 2) by the biasing spring  23 . The top end of the pressing stem  21  is provided with a tray  21   a  for receiving the indicating lamp  17  and the resistor  18 . The tray  21   a  is formed with two holes (not indicated with numeral) for the pass of the pins of the lamp  17  and the resistor  18 . The pressing stem  21  is provided with a snap shaft  21   b  on its front side surface for pivoting the rocking lever  24  and with a heart-shaped stepping recess  22   b  on its right side surface. The heart-shaped stepping recess  22   b  is formed with an upper locating point. 
     The cantilever  22   a  of the positioning unit is constructed by a steel wire having proper flexibility and rigidity. A fixed end of the cantilever  22   a  is fixed on the main body  1   a  and a moving end thereof is inserted into the heart-shaped stepping recess  22   b.  The detailed description of the heart-shaped stepping recess  22   b  is disclosed in the U.S. Pat. No. 5,786,742 and thus is omitted herein. The content of the U.S. Pat. No. 5,786,742 is incorporated herein for reference. The moving end of the cantilever  22   a  will move into the upper locating point when the pressing stem  21  is pressed-downward and thus retain the pressing stem  21  in a set position. However, if the pressing stem  21  is pushed again, the moving end of the cantilever  22   a  will escape the upper locating point and release the pressing stem  21  back to the reset position. 
     The rocking lever  24  is formed with a pivoting hole  24   e  so as to pivot on the snap shaft  21   b.  The rocking lever  24  is further formed at its one end with a toe portion  24   a  and an arch portion  24   c,  and formed at the other end with a nose  24   b  and a reseating shoulder  24   d.  The arch portion  24   c  is constructed by a rim of the rocking lever  24  which is located between the toe portion  24   a  and the pivoting hole  24   e,  and is used to push the wrecking bar  27 . The nose  24   b  is used to abut against the first conducting leaf  15  when the pressing stem  21  is moved to the reset position in case the toe portion  24   a  is supported by the enabling supporter  25 . The reseating shoulder  24   d  is constructed by a rim of the rocking lever  24  which is located upper than the nose  24   b.    
     The enabling supporter  25  is provided with an abutting surface  25   a  and a supporting portion  25   b  respectively located at two ends thereof. The enabling supporter  25  is pivoted on the housing  1  along an axis parallel to the pivoting axis of the rocking lever  24 , and is biased by a biasing spring  26  to a supporting position as shown in FIG.  2 . At such a supporting position, the abutting surface  25   a  abuts against the closed end of the bimetal sheet  14  and the supporting portion  25   b  supports the toe portion  24   a.  Thus, the rocking lever  24  is enabled to actuate the first conducting leaf  15 . 
     The wrecking bar  27  is pivoted on the housing  1  along an axis parallel to the pivoting axis of the rocking lever  24  and is provided with a wrecking portion  27   a  and a handle portion  27   b  respectively located at two ends thereof The wrecking bar  27  is biased by a biasing spring  28  toward a suspending position in which the moving end of the cantilever  22   a  is inserted into the heart-shaped stepping recess  22   b.  The wrecking portion  27   a  extends in a direction parallel to the axis of the wrecking bar  27  and substantially vertical to the cantilever  22   a,  and is formed with an opening. The cantilever  22   a  is received in the opening and thus can be moved by the wrecking portion  27   a.  The handle portion  27   b  extends to a position in which the arch portion  24   c  of the rocking lever  24  will pass in the stroke the switch trips due to overload. 
     The lever-reseating member  29  as shown in FIGS. 2 and 3 is fixedly provided on the main body  1   a  and extends at a direction parallel to the pivoting axis of the rocking lever  24 . The lever-reseating member  29  is located in a position in which the reseating shoulder  24   d  will be stopped when the pressing stem  21  is returning to its reset position until the toe portion  24   a  of the rocking lever  24  moves into a position to be supported by the supporting portion  25   b  of the enabling supporter  25 . 
     By means of the above construction, as shown in FIG. 2, when the bimetal sheet  14  is in a normal position, the enabling supporter  25  is biased by the biasing spring  26  into a supporting position and the toe portion  24   a  is to be supported by the supporting portion  25   b  in an enabling position. Moreover, since the cantilever  22   a  is not pulled out of the heart-shaped stepping recess  22   b,  the rocking lever  24  will move downward counterclockwise rotates around the toe portion  24   a  when the pressing stem  21  is pushed downward so that the nose  24   b  will force the first conducting leaf  15  to move downward until the upper and the lower contact pads  15   c  and  12   c  contact together. On the other side, when the pressing stem  21  is pushed again and thus biased upward by the biasing spring  23  into the reset position, the rocking lever  24  will move upward and rotate around the toe portion  24   a.  The nose  24   b  in turn releases the abutment against the first conducting leaf  15  and thus the upper contact pad  15   c  separates from the lower contact pad  12   c  due to the resilience of the first conducting leaf  15 . Therefore, the nose  24   b  will alternatively make the first conducing leaf  15  move into a conduction position as shown in FIG. 3 and a broken position as shown in FIG. 2 in response to the movement of the pressing stem  21  into its set position and its reset position. 
     However, when the bimetal sheet  14  is deformed to an overload position as shown in FIG. 4 due to overload, the enabling supporter  25  will rotate to a trip position upon the push of the closed end of the bimetal sheet  14  at the abutting surface  25   a,  and thus the supporting portion  25   b  departs from the toe portion  24   a.  Consequently, upon the resilience of the first conducting leaf  15 , the nose  24   b  is pushed upward and the toe portion  24   a  rotates clockwise to a disabling position around the snap shaft  21   b,  in which the first conducting leaf  15  is at a broken position and the upper contact pad  15   c  separates from the lower contact pad  12   c.  On the other side, during the rotation of the rocking lever  24 , the handle portion  27   b  of the wrecking bar  27  will be pushed by the arch portion  24   c.  Thus, the wrecking bar  27  rotates into a pulling position in which the moving end of the cantilever  22   a  is pulled out of the heart-shaped stepping recess  22   b.  Such situation is shown in FIG.  4 . 
     By means of the movement of the moving end of the cantilever  22   a  out of the heart-shaped stepping recess  22   b,  the pressing stem  21  is dislocated from set position and returns to its reset position upon the action of the biasing spring  23 . In the meanwhile, the rocking lever  24  is moved upward and the shoulder  24   d  abuts against the lever-reseating member  29  so that the toe portion  24   a  rotates counterclockwise into a position to be supported and enabled by the supporting portion  25   b.  Once the bimetal sheet  14  is deformed back to its normal position, the toe portion  24   a  is supported again. Thus, the described switch has a function of automatic reset. 
     As shown in FIGS. 1 and 4, before the bimetal sheet  14  returns back to its normal position, the upper contact pad  15   c  will not come into contact with the lower contact pad  12   c  even if the key  30  and the pressing stem  21  are pushed downward. This is because the toe portion  24   a  is not supported by the supporting portion  25   b  of the enabling supporter  25  yet and thus the nose  24   b  fails to force the first conducting leaf  15  downward. Thus, a reliable overload protection is available. 
     As for the second conducting leaf  16 , furthermore, the free end thereof will depart from the resistor  18 , as shown in FIG. 2, when the pressing stem  21  returns back to its reset position upon the biasing of the biasing spring  23 . Thus, the second conducting leaf  16  is also in a broken position. 
     Therefore, the push-button switch according to this invention is provided with an overload-protection function as well as an automatic resetting function in case of overload. And, since the whole motion is transmitted via the rocking lever  24 , the trip action and the automatic resetting action in the switch are assured. 
     FIGS. 5 and 6 show an actuating unit of the overload-protection push-button switch according to a second embodiment of this invention. However, since there are a lot of members identical to those in the first embodiment and thus only the different parts are shown in FIG.  5  and described herein. Moreover, the element corresponding to that in the first embodiment is signified with the same numeral adding of a sign of ′. The main difference between the first and the second embodiments resides in the substitution of a cross bar  27 ′ for the previous wrecking bar  27 . 
     As shown in FIGS. 5 and 6, the cross bar  27 ′ vertically extends from one side surface of the rocking lever  24 ′ to and over the cantilever  22   a ′ along an axis parallel to the snap shaft  21   b.  Moreover, the cantilever  22   a ′ is formed with an oblique portion  221 ′ located in a position the cross bar  27 ′ will pass. The oblique portion  221 ′ tilts far way from the heart-shaped stepping recess  22   b  from a lower portion to an upper portion. And, the cantilever  22   a ′ is biased by a biasing spring  31  to an inserting position. By means of such an arrangement, the moving end of the cantilever  22   a ′ will depart from the heart-shaped stepping recess  22   b  when the cross bar  27 ′ rotates downward in case the toe portion  24   a  is not supported. Consequently, the pressing stem  21  will automatically return back to its reset position. The structure in this embodiment is simpler than that in the first embodiment. 
     FIGS. 7 to  9  show a switch according to a third embodiment of this invention. The element identical to that in the first embodiment is signified with the same numeral and its description is omitted while the element corresponding to that in the first embodiment is signified with the same numeral adding of a sign of ″. 
     As shown in FIGS. 7 and 8, the main difference between the third embodiment and the first embodiment resides in the substitution of a cylindrical pressing stem  21 ″ for the pressing stem  21  and the provision of the heart-shaped stepping recess  22   b ″ on a pillar  1   d ″ in lieu of the pressing stem  21 . The pillar  1   d ″ extends from the main body  1   a ″ and is used for guiding the movement of the cylindrical pressing stem  21 ″. The pressing stem  21 ″ is formed with a hole  21   c ″for the pass of a moving end of a cantilever  22   a ″ and a pin hole  21   d ″ for sustaining a fixed end of the cantilever  22   a ″. As a result, the cantilever  22   a ″ is mounted on the pressing stem  21 ″ and the heart-shaped stepping recess  22   b ″ is provided on the main body  1   a ″. Moreover, the indicating lamp  17  and the resistor  18  are serially connected and mounted on the second terminal  12  and the third terminal  13  and thus the second conducting leaf  16  in the first embodiment is omitted. Furthermore, a wrecking bar  27 ″ substitutes for the wrecking bar  27  in the first embodiment. However, the wrecking bar  27 ″ is not provided with an opening at its wrecking portion  27   a ″. Moreover, the biasing spring  28  in the first embodiment is omitted in this embodiment. Such an arrangement is available due to the fact that the moving end of the cantilever  22   a ″ will be normally sustained in a position inserting into the heart-shaped stepping recess  22   b″.    
     FIG. 8 shows an ON status and an OFF status of the first conducting leaf  15  and the rocking lever  24 , which are drown respectively by solid lines and by dotted lines. FIG. 9 shows a situation the switch tripped due to overload. Since the operation and details of the third embodiment are substantially identical to those in the first embodiment, they are omitted herein. 
     According to the above third embodiment, it is understood that the concept of this invention is adapted to a changed positioning mechanism. Moreover, it is expected that the enabling supporter  25  is omissible if the toe portion  24   a  of the rocking lever  24  can be actuated in response to the deformation of the bimetal sheet  14 . For example, the toe portion can extend over the rim of the closed end of the bimetal sheet  14 . In such a case, the rim of the closed end would act as the supporting portion so as to enable the rocking lever  24  to function. Once the bimetal sheet  14  is deformed, the rim, i.e., the supporting portion, will depart from the toe portion  24   a  so as to disable the rocking lever  24  from function. 
     While the present invention is described by way of preferred embodiments, it is understood that the embodiments are used only to illustrate the technical concept of the present invention without limiting the scope thereof. It is therefore intended to show that all modifications and alterations that are readily apparent to those skilled in the art are within the scope as defined in the appended claims.