Patent Abstract:
An electric transfer switch unit for selective connection to different power supplies is provided with moveable contacts, associated stationary contacts connected to said power supplies, a turnable drive handle and a toggle mechanism for connecting the drive handle to the moveable contacts. The toggle mechanism includes a spring system adapted for storing and releasing mechanical energy upon turning of the drive handle. Use of the spring system assures swift and stable turning of the drive handle for shifting between the different power supplies.

Full Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an electric transfer switch unit, and more particularly relates to an electric transfer switch unit provided with a two-position toggle mechanism for selective connection to different power supplies. 
     STATE OF THE ART 
     An electric transfer switch is used for selective connection between different power supplies. For example, an electric load is connected, via a transfer switch unit, to a normal power supply under normal conditions but connected to an emergency power supply in case of blackout due to earthquakes or floods, etc. On recovery of the normal power supply, the electric load is connected back to the normal power supply through shifting in position of the transfer switch. 
     In one type of the conventional electric transfer switch unit, a moveable contact is employed for selective contact with a plurality of stationary contacts and an energy storage mechanism such as a toggle mechanism is used for swift shifting of the moveable contact. After the moveable contact has performed shifting in position, the toggle mechanism locks the moveable contact for maintenance of contact with a selected stationary contact. 
     One example of such a transfer switch unit is disclosed in U.S. Pat. No. 4,590,387. All of the conventional transfer switch units of this type are, however, accompanied with lots of problems. First, the transfer switch units are in general much complicated in construction necessitating use of many mechanical elements. Second, due to use of many mechanical elements, they are relatively large in construction. Third, large distances between stationary contacts necessitate use of a circuit interrupter. 
     SUMMARY OF THE INVENTION 
     It is the primary object of the present invention to provide an electric transfer switch unit simple and compact in construction. 
     It is another object of the present invention to provide an electric transfer switch unit which assures reliable operation without need of a circuit interrupter. 
     It is the other object of the present invention to provide an electric transfer switch unit of low cost and adapted for easy assemblage. 
     In accordance with the present invention, an electric transfer switch unit is provided with a toggle mechanism for swift selective shifting between two different power supplies such as a normal power supply and an emergency power supply. 
     The toggle mechanism is used for a transfer switch unit including a moveable contact mounted to a rotatable crossbar. The moveable contact is able to shift between the first and second stationary contacts which are respectively connected to different power supplies such as a normal power supply and an emergency power supply. The toggle mechanism includes link arms for forming a pair of toggle linkages for driving the crossbar, extensible links and coil springs encircling respective extensible links. Mechanical energy for swift shifting operation is stored in the coil springs. 
     The toggle mechanism further includes a handle mounted to the crossbar. As the handle turns about the longitudinal axis of the crossbar, the crossbar and the toggle linkages are also driven for rotation for intended shifting in position of the transfer switch unit. The handle may be driven for turning by manual operation or by operation of a proper drive unit such as solenoids. 
     Turning of the handle causes compression of the pair of extensible links and the associated coil springs. Upon turning of the handle over a prescribed angle, the moveable contact is made to shift by rotation of the crossbar from a closed position with one stationary contact to a neutral open position. Thereafter, as one pivot of the extensible link traverses a straight line connecting both pivots of the extensible link to the longitudinal axis of the crossbar, the extensible links and the coil sprigs are extended and release stored energy for swift rotation of the crossbar. Next, the moveable contact carried by the crossbar shifts to the neutral open position to a closed position with the other stationary contact so that the moveable contact is brought into electric connection with the other stationary contact. Since a large distance is reserved between the moveable contact and the stationary contact for reliable insulation, no use of current interrupter is necessitated. 
     The coil springs store energy until one pivot of the extensible ling traverses the straight line connecting the both pivots of the extensible link and the longitudinal axis of the crossbar. Consequently, the handle is locked by the toggle linkages in order to inhibit separation of the moveable contact from the stationary contact. Thus, the toggle mechanism inhibits accidental separation for the moveable contact from the stationary contact due to possible application of mechanical or electric external forces. 
     In the closed position, the moveable contact is urged for reliable contact with the stationary contact thanks to operation of the coil springs. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view of the electric transfer switch unit provided with a toggle mechanism in accordance with the present invention, 
     FIG. 2 is a side view of the electric transfer switch unit provided with a toggle mechanism in accordance with the present invention, 
     FIG. 3 is a section taken along a line III—III in FIG. 1, 
     FIG. 4 is a side view of the transfer switch unit partly taken away for clear illustration, 
     FIG. 5 is a perspective view of the toggle mechanism associated with a crossbar, 
     FIG. 6 is a front view of the crossbar associated with moveable contacts, 
     FIG. 7 is a plan view of the crossbar associated with the toggle mechanism and the moveable contacts, 
     FIG. 8 is a side view of the crossbar associated with the moveable contacts, 
     FIG. 9A is a schematic side view of the toggle mechanism registered at the first position, 
     FIG. 9B is a schematic side view of the moveable contact and a stationary contact when the toggle mechanism is at the position shown in FIG. 9A, 
     FIGS. 10A is a schematic side view of the toggle mechanisms on a way from the first to third position, 
     FIG. 10B is a schematic side view of the moveable contact and a stationary contact when the toggle mechanism is at the position shown in FIG. 10A, 
     FIG. 11A is a schematic side view of the toggle mechanism registered at the third position, 
     FIG. 11B is a schematic side view of the moveable contact and a stationary contact when the toggle mechanism is at the position shown in FIG. 11A, 
     FIG. 12A is a schematic side view of the toggle mechanisms on a way from the third to second position, 
     FIG. 12B is a schematic side view of the moveable contact and a stationary contact when the toggle mechanism is at the position shown in FIG. 12A, 
     FIG. 13A is a schematic side view of the toggle mechanism registered at the second position, and 
     FIG. 13B is a schematic side view of the moveable contact and a stationary contact when the toggle mechanism is at the position shown in FIG.  13 A. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention shall be described in more detail in reference to the accompanying drawings. In FIGS. 1 to  4 , the electric transfer switch unit  1  of the present invention includes a frame  2 , a toggle mechanism  3  and a crossbar  4 . The crossbar  4  is mounted to the frame  2  in a rotatable arrangement around its own longitudinal axis A—A. 
     As shown in FIGS. 2 and 4, the toggle mechanism  3  includes a drive handle  5  and a pair of toggle linkages  6 . As shown in FIGS. 4 and 5, each toggle linkage  6  is provided with a link arm  7 , an extensible link  8  and a coil spring  9 . The drive handle  5  and the link arm  7  of the toggle linkage  6  are both secured to one end of the crossbar  4  in an arrangement rotatable about the longitudinal axis A—A of the crossbar  4 . 
     The drive handle  5  is driven for turning by manual operation or by operation of a proper drive mechanism such as solenoids  10  shown in FIG.  2 . 
     In FIG. 2, a pair of solenoids  10  is secured to the frame  2  in a symmetric arrangement with respect to the longitudinal axis A—A. A plunger  10   a  of each solenoid  10  is coupled to the drive handle  5  via a connector  32  and a rod  5   a.    
     As shown in FIG. 3, a plurality of moveable contacts  11  are carried by the crossbar  4 . Each moveable contact  11  is provided with a contact bar  12  and contacts  13  attached to opposite surfaces  12   a  and  12   b  both parallel to the longitudinal axis A—A. As the crossbar  4  rotates, each moveable contact  11  shifts from the first position (shown with solid lines) for contact with the first stationary contact  14  to the second position (shown with imaginary lines) for contact with the second stationary contact  15 . The first and second positions are arranged symmetrically with respect to the longitudinal axis A—A and the first and second stationary contacts  14  and  15  are also arranged symmetrically with respect to the longitudinal axis A—A. 
     In the condition shown in FIG. 9B, the moveable contact  11  is registered at the first closed position so that its contact  13  is placed in contact with the associated stationary contact  14 . In the condition shown in FIG. 13B, the moveable contact  11  is registered at the second closed position so that its contact  13  is placed in contact with the stationary contact  15 . 
     As shown in FIG. 3, the stationary contacts  14  and  15  are connected, via terminals  26  and  27 , to different power supplies, e.g. one to a normal power supply and the other to an emergency power supply. In the condition shown in FIG. 11B, the moveable contact  11  is registered at a neutral position. 
     As shown in FIGS. 3,  5  and  7 , the base portion of the contact bar  12  of the moveable contact  11  is accommodated within a receptive recess  16  formed in the crossbar  4  and, as shown in FIG. 3, connected to various electric loads via conductors  28 ,  29  and  30  and a terminal  31 . The receptive recess  16  is defined by opposite first and second side walls  17  and  18  extending in parallel to the longitudinal axis A—A and opposite third and fourth side walls  19  and  20  extending normal to the longitudinal axis A—A. 
     The contact bar  12  is accommodated within the receptive recess  16  with its one side surface  12   a  extending in parallel to the first side wall  17 . A contact spring  21  is inserted into the receptive recess  16  with its one end in engagement with the side wall  18  and its the other end in engagement with the side surface  12   b  of the contact bar  12 . 
     When the contact bar  12  is closed on the side of the first stationary contact  14  as shown in FIG. 9B, the contact bar  12  tilts about a contact point with the upper end  17   a  of the first side wall  17  so as to lift from the lower end  17   b  of the side wall  17 . By this tilting, the contact bar  12  compresses the contact spring  21 . As a result, spring force presses the moveable contact  11  against the stationary contact  14 . 
     When the contact bar  12  is brought into contact with the second stationary contact  15  as shown in FIG. 13B, the contact bar  12  tilts about a contact point with the lower end  17   b  of the side wall  17  so as to lift from the upper end  17   a  of the side wall  17 . By this tilting, the contact bar  12  compresses the contact spring  21 . As a result, the spring force presses the moveable contact  11  with the stationary contact  15 . 
     Two sets of moveable contacts  11 , stationary contacts  14  and  15  are employed in the embodiment shown in FIGS. 1 and 5 to  7 . It should be, however, understood that the number of contacts may vary depending on the number of phase of the power supply. A single-phase power supply employs two sets of contacts and a three-phase power supply employs three sets of contacts. Although adjacent two moveable contacts  11  form one set in the case of the illustrated embodiment, only one moveable contact  11  may be used when current-carrying capacity is small. 
     As shown in FIGS. 4,  5  and  9  to  13 , each toggle linkage  6  of the toggle mechanism  3  includes the link-arm  7 , the extensible link  8  and the coil spring  9 . The pair of link arms  7  extends from one end of the crossbar  4  in a direction traverse the longitudinal axis A—A with symmetry with respect to the longitudinal axis A—A. 
     Each of the pair of extensible links  8  extends through the associated coil spring  9  and pivoted at one end to the front end of the associated link arm  7  and pivoted at the other end to the frame  2 . The pivots to the frame  2  are located symmetric to the longitudinal axis A—A of the crossbar  4 . Arrangement of the extensible link  8  within the coil spring  9  enables compactification of the entire switch unit. 
     Each extensible link  8  includes two link bars  22  and  23  which are coupled to each other in a longitudinally extensible fashion. One link bar  22  is pivoted at one end to the link arm  7  and provided, at the other end, with a slot  24  extending in the longitudinal direction. The other link bar  23  is pivoted, at one end, to the frame  2  and provided, at the other end, with a slot  24  extending in the longitudinal direction. The two link bars  22  and  23  are coupled to each other in a longitudinally extensible fashion through engagement of the slots  24  and  25 . Each coil spring  9  urges the associated link bars  22  and  23  in the direction of extension. 
     As the drive handle  5  is turned clockwise from the closed position shown in FIG. 9A, the extensible link  8  is compressed and the coil spring  9  is also compressed to start to sore mechanical energy. Once the drive handle  5  assumes the neutral closed position shown in FIG. 11A past the position shown in FIG. 10A, the pivots on both ends of the extensible link  8  and the longitudinal axis A—A are located on a common straight line. Concurrently with this process, the link arm  7 , the extensible link  8  and the coil spring  9  are also located on the common straight line and the coil spring  9  arrives at its dead center of compression. 
     When the drive handle  5  is further turned and pivot between the extensible link  8  and the link arm  7  traverses a straight line connecting the pivot on the frame  2  and the longitudinal axis A—A, the mechanical energy stored by the coil spring  9  is released. This release of mechanical energy causes concurrent extension of the extensible link  8  and the drive handle  5  swiftly returns to the closed position shown in FIG. 13A past the position shown in FIG.  12 A. 
     During this process, the moveable contact  11  shifts to the closed position shown in FIG. 13B for contact with the other stationary contact  15  past the positions shown in FIGS. 10B,  11 B and  12 B. At this closed position, the upper portion of the contact bar  12  of the moveable contact  11  lifts about its lower end from the side wall  17  of the crossbar  4 . As a consequence, the spring force of the contact spring  21  operates to keep constant pressure contact of the contact  13  of the moveable contact  11  with the stationary contact  15 . 
     When the drive handle  5  is turned counter-clockwise together with the crossbar  4  from the closed position shown in FIG. 13A, the toggle mechanism  3  operates in a mode opposite to the foregoing case of clockwise turning. That is, the drive handle  5  shifts swiftly to the closed position shown in FIG. 9A past the positions shown in FIGS. 12A,  11 A and  10 A. 
     During this process, the moveable contact  11  shifts from the closed position for contact with the stationary contact  15  to the closed position for contact with the stationary contact  14  past the positions shown in FIG. 12B,  11 B and  10 B. 
     At the closed position shown in FIG. 9B for contact with the stationary contact  14 , the contact bar  12  of the moveable contact  11  lifts about its middle portion from the side wall  17  of the crossbar  4 . As a consequence, the spring force of the contact spring  21  operates on the contact bar  12  so that the contact  13  of the moveable contact  11  is kept in constant pressure contact with the stationary contact  14 . In this way, the moveable contact  11  is brought into pressure contact with respective stationary contact  14  or  15  at the first and second closed positions by the spring force of the single contact spring  21 . 
     In accordance with the present invention, use of a toggle mechanism able to store mechanical energy assures swift and stable shift from one power supply to the other power supply. The transfer switch unit of the present invention is very simple in construction and compact in size with use of reduced number of elements.

Technology Classification (CPC): 7