Abstract:
A two position switch of an electric motor has an actuator that is biased by a resilient terminal arm into sliding engagement with an annular collar of a centrifugal actuator. The centrifugal actuator collar controls movement of the switch actuator which closes and opens electrical contacts to energize start and run winding circuits of the motor. The resilient terminal arm that closes the star circuit is slotted to reduce its biasing force exerted on the actuator of the switch.

Description:
BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The present invention pertains to a switch for an electric motor. More specifically, the present invention pertains to a switch having a resilient terminal arm that is slotted to reduce its biasing force exerted on an actuator of the switch. 
     (2) Description of the Related Art 
     Common capacitor start and split phase induction motors have a run winding and a start winding wrapped around poles of a stator of the motor. An example of this type of motor is disclosed in the U.S. Patent of Hildebrandt et al. U.S. Pat. No. 4,296,366. The start winding of the motor stator is energized during start up of the motor, or when the operating speed of the motor falls below a specified operating speed. Energizing the start winding of the stator creates a rotating magnetic field in the stator that applies a sufficient torque to the rotor of the motor to begin rotation of the rotor. However, once the rotor has begun its rotation and has reached a desired operating speed, it is able to follow the alternations of the magnetic field created by the run windings of the stator and energizing the start windings is no longer needed. Commonly, in motors of this type, the start winding is not intended for continuous use and may fail if not de-energized during normal run operation of the motor. Therefore, motors of this type are typically operated by a two position switch having an actuator that is moveable between first and second positions. In the first position of the actuator it closes a first set of electrical contacts that establishes a circuit through the start windings of the motor, and in the second position of the actuator it closes a second set of electrical contacts that establishes a circuit through the run windings of the motor while opening the first circuit of the start windings. 
     Two position switches of this type are typically moved between their two positions by a centrifugal actuator assembly mounted on the rotor shaft of the motor. FIGS. 1 and 2 show a two position switch  12  of the prior art and a centrifugal actuator assembly  14  mounted on the rotor shaft  16  of a motor (not shown). The centrifugal actuator assembly  14  rotates with the motor shaft and is responsive to the speed of rotation of the shaft for moving the switch actuator  18  from its first or start position to its second or run position in response to the rotation of the motor shaft attaining a predetermined operating speed. Some centrifugal actuator assemblies  14  include an annular collar  22  that is mounted on the rotor shaft for axially shifting movement between two positions, a start position of the collar on the shaft shown in FIG. 1, and a run position of the collar on the shaft shown in FIG.  2 . 
     The co-assigned U.S. Patents of Hildebrandt et al. U.S. Pat. No. 4,296,366 and Lewis et al. U.S. Pat. No. 5,744,883 each disclose a two position motor switch that is acted on by a centrifugal actuator assembly. These patents are incorporated herein by reference. The same type of switch  12  is shown in FIG.  3  and includes a switch actuator  18  that resembles a bell crank. The switch actuator  18  is mounted by a pivot connection  24  to the housing  26  of the switch. The switch actuator has an exterior arm  28  that extends from the pivot connection  24  to the exterior of the switch housing and an interior arm  32  that extends from the pivot connection  24  to the interior of the switch housing. The exterior arm  28  is provided with a follower surface  34  on a distal end of the arm that engages with the annular collar  22  of the centrifugal actuator assembly mounted on the motor shaft. The interior arm  32  engages with two resilient terminal arms in the interior of the switch housing. The first or start terminal arm  36  is fixed to the switch housing at its proximal end and has an electrical contact  38  at its distal end. The start terminal arm contact  38  engages a first or start winding electrical contact  42  in the switch housing to close the circuit through the start winding of the motor. The second or run terminal arm  44  also is fixed to the switch housing  26  at its proximal end and has an electrical contact  46  at its distal end. The run terminal arm contact  46  engages a second or run winding electrical contact  48  in the switch housing to close the circuit through the run winding of the stator. Thus, the switch actuator  18 , with its exterior arm  28  in sliding engagement with the cam surface of the centrifugal actuator collar  22 , moves between two positions in response to the axial movement of the collar between its two positions on the rotor shaft  16 . In the first position of the collar shown in FIG. 1, it positions the switch actuator  18  in its start position relative to the switch housing  26 . This closes the circuit through the first, start winding terminal arm  36  of the switch, energizing the start winding of the motor. The start position of the actuator  18  is shown in solid lines in FIG.  3 . When the collar moves to its second, run position on the rotor shaft shown in FIG. 2, the exterior arm  22  of the switch actuator slides over the exterior cam surface of the collar  22  allowing the exterior arm to move radially inwardly relative to the rotor shaft  16 . This movement of the exterior arm is caused by the resiliency of both the first and second terminal arms. The first  13  and second  14  terminal arms exert a biasing force on the interior arm  32  of the switch actuator. The biasing force causes the interior arm to pivot about the pivot connection  24  in the switch housing. As the interior arm is moved, the resiliency of the first terminal arm moves its electrical contact  38  out of engagement with the start winding electrical contact  42  of the start circuit, opening the start circuit. Also as the interior arm is moved, the resiliency of the second terminal arm moves its electrical contact  46  into engagement with the electrical contact  48  of the run winding, establishing a circuit through the run winding of the stator. The run position of the actuator  18  is shown in dashed lines in FIG.  3 . 
     As stated above, movement of the switch actuator  18  that causes the exterior arm  28  to move radially inwardly toward the rotor shaft  16  of the motor is caused by a biasing force exerted on the interior arm  32  of the switch actuator by both the first, start terminal arm  36  and the second, run terminal arm  44 . The resiliency of the two terminal arms results in the arms functioning as leaf springs that each exert a biasing force on the interior arm of the switch actuator. As shown in FIG. 3, first  52  an second  54  abutments on the interior arm  32  of the switch actuator engage the respective first  36  and second  44  terminal arms when the actuator is in the start position, causing the terminal arms to bow upwardly between their opposite ends. The biasing force exerted by the terminal arms holds the exterior arm follower surface  34  in sliding engagement with the collar  22  of the centrifugal actuator. The biasing force also causes the exterior arm of the switch actuator to move radially inward toward the rotor shaft in response to the axial movement of the centrifugal actuator assembly to its run position on the shaft. 
     Although the two position switch functions well for its intended purpose, it has been observed that the biasing force exerted by the first  36  and second  44  terminal arms on the interior arm  32  of the switch actuator causes the follower surface  34  on the exterior arm of the switch actuator to engage in sliding contact with the collar  22  of the centrifugal actuator assembly with a force that increases the wear rate of the follower surface. In addition, the wear rate problem of the follower surface cannot be overcome by simply reducing the biasing force of the terminal arms because the biasing force of the start terminal arm  36  must be sufficient to break a weld that often forms between the contact  36  of the start terminal arm and the start winding electric contact  42  of the switch. 
     When the start terminal arm contact  38  engages with the start winding electrical contact  42  of the switch, the amount of current that passes through the engaging contacts causes the contacts to go through a molten stage producing a weld between the contacts. The resiliency of the start terminal arm  36  must exert a sufficiently large biasing force on the interior arm  32  of the switch actuator to assist in biasing the switch actuator from its start position to its run position, but it must also be sufficiently large to cause the contact  38  of the start terminal arm to break the weld with the start winding electrical contact  42  of the switch and separate from the contact, opening the start winding circuit as the switch actuator moves from its start position to its run position. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the disadvantages of the prior art two position switch by providing a two position switch with a start terminal arm that exerts a reduced biasing force on the interior arm of the switch actuator while still being capable of exerting a sufficient force on the contact of the terminal arm to break a weld between the arm contact and the start winding electrical contact of the switch. The terminal arm of the invention is constructed in much the same manner as prior art terminal arms. The terminal arm has a generally rectangular configuration with longitudinally opposite proximal and distal ends. The proximal end is secured to the switch housing and the distal end has an electrical contact. Laterally spaced longitudinal edges extend along opposite sides of the arm between the proximal and distal ends. 
     The start terminal arm differs from the prior art terminal arm in that it is provided with at least one gap in the terminal arm between its proximal and distal ends. In the preferred embodiment, the gap is in the form of an oblong slot that passes through the terminal arm between the longitudinal edges of the arm. Alternatively, the gap could be provided by one or more holes through the arm, or by one or more notches in one or both of the longitudinal edges of the arm. 
     In the preferred embodiment, the slot opening extends longitudinally along the length of the terminal arm and has radiuses at its opposite ends. The slot is positioned in the terminal arm between the distal end of the arm and the area of the arm that comes into contact with the interior arm of the switch actuator. 
     Thus, with the material of the arm removed by the slot between the distal end of the arm and the portion of the arm engaged by the switch actuator, the section of the arm between the distal end and the switch actuator exerts a reduced biasing force on the switch actuator. This results in reduced wear of the follower surface on the exterior arm of the switch actuator. However, with the material of the terminal arm between the proximal end of the arm and the portion of the arm engaged by the actuator intact, the resiliency of the arm still exerts a sufficient force to break any weld that forms between the contact of the terminal arm and the electrical contact of the start winding of the switch. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further objects and features of the invention are revealed in the following detailed description of the referred embodiment of the invention and in the drawing figures wherein: 
     FIG. 1 is a schematic representation of a side elevation view of the prior art two position motor starting switch with the exterior arm of the switch actuator in sliding engagement with a peripheral surface of an annular collar of a centrifugal actuator assembly mounted on a rotor shaft; 
     FIG. 2 is a view similar to FIG. 1, but showing the position of the exterior arm of the actuator in sliding engagement with the annular collar when the arm has moved to its second, run position relative to the collar; 
     FIG. 3 is a schematic representation of the prior art two position switch including the switch actuator and the start terminal arm and the run terminal arm of the switch, as well as a portion of the centrifugal actuator collar; 
     FIG. 4 is a view of a switch housing containing the start terminal arm of the invention with the switch actuator in its first, start position; 
     FIG. 5 is a view of the switch housing of FIG. 4 with the switch actuator in its second, run position; 
     FIG. 6 is a side view of the terminal arm of the invention removed from the switch housing; 
     FIG. 7 is a plan view of the terminal arm of the FIG. 6; and 
     FIGS. 8-10 are plan views of variant embodiments of the terminal arm of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 4 shows an actuator switch  18  employing the first or start terminal arm  62  of the invention. The actuator switch  18  is basically the same as the prior art actuator switch discussed earlier except for the substitution of the start terminal arm  62  of the invention for the start terminal arm  36  of the prior art. Thus, prior art component parts of the switch actuator  18  shown in FIG. 4 as well as in FIG. 5 are given the same reference numbers employed earlier in describing these component parts of the prior art actuator switch and their functioning. FIG. 4 shows the relative positions of the switch actuator  18  and the start terminal arm  62  of the invention in the start position of the switch actuator  18  and FIG. 5 shows the relative positions of the switch actuator and the start terminal arm  62  of the invention in the run position of the actuator. 
     The first or start terminal arm  62  of the invention is constructed in much the same manner as the prior art terminal arms. The terminal arm  62  is constructed of a thin, resilient strip of metal having a generally rectangular configuration. The terminal arm  62  is shown removed from the switch housing  26  in FIGS. 6 and 7. In these figures, it can be seen that the rectangular configuration of the terminal arm has opposite proximal  64  and distal  66  ends. A pair of laterally spaced, longitudinal edges  68 ,  72  extend along the opposite sides of the arm between the proximal end  64  and the distal end  66  of the arm. The proximal end  64  of the arm is secured to a base portion  74  of an electrical plug  76  that is mounted in the switch housing. The electrical plug  76  is the same electrical plug employed with the prior start terminal arm. The proximal end  64  of the arm is secured to the base  74  of the plug by riveting, spot welding, or any other method conventionally employed in securing the terminal arm to the electrical plug. Adjacent the distal end  66  of the arm is the electrical contact  78  that engages with the start winding electrical contact  42  of the two position switch to establish a current through the start winding of the motor as described earlier. The electrical contact  78  is the same as that employed on the prior art terminal arm and is secured to the terminal arm by riveting, spot welding, or any other method commonly employed in securing the electrical contact to the terminal arm. 
     The start terminal arm  62  of the invention differs from the prior art terminal arm in that it is provided with at least one gap  82  in the terminal arm between its proximal and distal ends. In the preferred embodiment, the gap  82  has the form of an oblong slot that passes through the terminal arm between the longitudinal edges  68 ,  72  of the arm such as that shown in FIG.  7 . Alternatively, the gap  82  could be provided by one or more holes  86  through the arm as shown in FIG. 8, by a single notch  88  in one of the longitudinal edges  68  of the arm as shown in FIG. 9, or by a pair of notches  92  formed in the opposite longitudinal edges  68 ,  72  of the arm as shown in FIG.  10 . The preferred oblong slot  84  of FIG.  7  and the alternative holes  86  and notches  88 ,  92  of FIGS. 8-10 all remove material from a specific area of the arm and thereby increase the resiliency in this area of the arm while decreasing the biasing force of this area of the arm, as will be further explained. 
     As stated earlier, the preferred embodiment of the gap  82  is in the form of an oblong slot  84  shown in FIG.  7 . The oblong slot  84  extends along a portion of the length of the arm adjacent its distal end  66 . Preferably, the slot  84  is formed with radiuses at its opposite ends. Alternative embodiments could have angled or laterally extending edges at the ends of the slot. With the terminal arm  62  having a longitudinal length of 1.437″ between its opposite proximal  64  and distal  66  ends, the longitudinal length of the slot  84  ranges from 0.30 to 0.50 of an inch, and the lateral width of the slot  84  ranges from 0.06 to 0.15 of an inch. In the preferred embodiment of the terminal arm, the slot  84  has a longitudinal length of 0.40 of an inch and a lateral width of 0.11 of an inch. 
     In referring to FIG. 4, it can be seen that the longitudinal positioning of the slot  84  in the terminal arm  62  (designated by the bracket  94 ) positions the slot between the distal end  66  of the arm and an area  96  of the arm that will come into engagement with the first abutment  52  of the interior arm  32  of the switch actuator  18 . 
     FIG. 4 shows the position of the switch actuator  18  relative to the start terminal arm  62  of the invention in the start position of the switch actuator. As seen in FIG. 4, the first abutment  52  of the switch actuator interior arm engages an area  96  of the start terminal arm  62  that is intermediate the distal  66  and proximal  64  ends of the arm. In addition, the gap  82  in the arm  62  is positioned entirely between the electrical contact  78  on the distal end of the arm and the area of the arm  96  engaged by the switch actuator abutment. It can be seen in FIG. 4 that the engagement of the first abutment  52  of the actuator interior arm  32  with the terminal arm  62  causes the arm to bow upwardly between its proximal and distal ends when the switch actuator  18  is in the start position. The biasing force exerted by the first or start terminal arm  62  on the abutment  52  of the switch actuator  18  is the combination of the biasing force of that portion of the terminal arm between its proximal end  64  secured to the electrical plug base  74  and the area of the arm  96  engaging the first abutment, and that portion of the arm between the distal end  66  of the terminal arm engaging the start winding contact  42  and the area of the arm  96  engaging the first abutment  52  of the actuator switch. By the presence of the gap  82  in the terminal arm eliminating material of the terminal arm between the distal end  66  of the arm and the area of the arm  96  engaging the first abutment  52 , the biasing force of this portion of the terminal arm is reduced from that of the prior art terminal arm that does not have a gap and does not have material removed from this portion of the arm. Thus, the terminal arm of the invention exerts a reduced biasing force on the switch actuator  18  from that of the prior art start terminal arm. This results in the follower surface  34  of the switch actuator exterior arm  28  engaging in sliding contact with the centrifugal actuator collar  22  at a reduced force, thus reducing the wear rate of the follower surface against the collar. 
     When the annular collar  22  of the centrifugal actuator moves from its start position shown in FIG. 1 to its run position shown in FIG. 2, the follower surface  34  of the switch actuator  18  begins to move radially toward the rotor shaft  16  of the motor and the switch actuator  18  begins to move from its start position shown in FIG. 4 to its run position shown in FIG.  5 . The movement of the switch actuator is caused by the biasing force of the start terminal arm  62  exerted on the first abutment  52  of the switch actuator interior arm and by the biasing force of the run terminal arm  44  on the second abutment  54  of the switch actuator interior arm. As the switch actuator moves toward the run position, the biasing force exerted by the start terminal arm  62  on the first abutment  52  of the switch actuator is lessened until eventually the first abutment  52  of the interior arm disengages from the area of engagement  96  on the start terminal arm  62  and the switch actuator is biased solely by the run terminal arm  44 . At this point, the start terminal arm  62  no longer exerts a biasing force against the switch actuator  18  and all of the resilient biasing force of the start terminal arm  62  is directed toward breaking the weld contact between the electrical contact  78  of the arm and the start winding contact  42  of the switch. Because the start terminal arm  62  cantilevers from its connection to the base  74  of the switch electrical plug  76 , the resilient force of the arm needed to break the weld between the arm electrical contact  78  and the switch start winding contact  42  is primarily provided by that portion of the arm between the arm proximal end  64  and the area of the arm  96  that was previously in engagement with the first abutment  52  of the switch actuator. Thus, the removal of the material of the terminal arm  62  by the gap  82  does not appreciably affect its resilient force devoted to breaking the weld between the arm electrical contact  78  and the start winding contact  42  of the switch. Because the portion of the terminal arm between the proximal end  64  and the area of the arm  96  that engages with the switch abutment is unaffected by the removal of material from the terminal arm by the gap  82 , the start terminal arm  62  of the invention maintains a minimum of 60 grams of force to break the weld between the arm electrical contact  68  and the start winding contact  42  of the switch. 
     Thus, with the material of the arm removed by the gap between the distal end of the arm and the portion of the arm engaged by the switch actuator abutment, the section of the arm between the arm distal end and the switch actuator exerts a reduced biasing force on the switch actuator. This results in reduced wear of the follower surface on the exterior arm of the switch actuator. However, with the material of the terminal arm between the proximal end of the arm and the portion of the arm engaged by the switch actuator intact, the resiliency of the arm still exerts a sufficient force to break any weld that forms between the electrical contact of the terminal arm and the start winding contact of the switch. 
     While the present invention has been described by reference to a specific embodiment, it should be understood that modifications and variations of the invention may be constructed without departing from the scope of the invention defined in the following claims.