Patent Publication Number: US-6710271-B2

Title: Centrifugal operated switch

Description:
CROSS-REFERENCE TO RELATED APPLICATAION 
     This application claims benefit to U.S. provisional application Ser. No. 60/340,049, filed on Oct. 19, 2001. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to electrical switches, and more particularly, to switches operated by centrifugal forces imparted through the rotation thereof. 
     BACKGROUND OF THE INVENTION 
     It is known to provide electric motors with starter windings in addition to the normal run windings. The starter windings, as the name implies, are used upon startup of the motor to achieve higher levels of starting torque. As the motor reaches operating speeds, the circuit to the starter windings is interrupted. Various switching devices are known for interrupting the starter winding circuits. 
     Devices can be attached to the motor shaft or rotor, and include components moved by centrifugal force when the motor achieves a desired operating speed. Movement of the components by centrifugal force is used to operate circuit control switches. Such centrifugal switches can have wide application and use, including the control of starter winding circuitry. 
     In some centrifugal switches, metallic contact slip rings and brushes run in substantially continuous contact during motor operation, which can result in excessive wear to the parts. Magnetically attracted contacts also have been used, to keep the circuit closed. As the motor achieves the desired operating speed, centrifugal forces are used to overcome the magnetic attraction and open the starter winding circuit. Accumulation of dirt and grime on the magnetic contacts adversely affects this type of switch by affecting the strength of the attractive force. Other centrifugal switches are complex in construction, with several linkages and mechanism. Complex switches can be expensive to manufacture, and can be prone to failures. 
     The target speed of rotation at which the starter windings are deactivated can vary significantly from one motor to another. It is desirable to have a more or less standardized basic structure for a centrifugal operated switch, which can be customized for specific uses. Many structures known heretofore for centrifugal switches are customized to specific motor applications and target speeds, requiring substantial redesign for use on another motor and for another target speed. This requires manufacturers to stock completely different switches for the different uses to which the switches will be put. 
     The present invention is directed to overcoming one or more of the problems set forth above. 
     SUMMARY OF THE INVENTION 
     The present invention provides a centrifugal operated switch mechanism that is reliable and customizable for specific applications. 
     In one aspect thereof, the present invention provides a centrifugal switch with a first electrical terminal, a second electrical terminal, and an electrical contactor for establishing an electric circuit connection between the terminals. The contactor has an end movable relative to one of the terminals. A spindle is mounted for rotation. A plunger engages the contactor, and at least one swing arm is rotated by the spindle and pivotally mounted for movement by centrifugal force. The swing arm is connected to the plunger for movement thereof upon movement of the swing arm. 
     In another aspect thereof, the invention provides a centrifugally operated switch, with a housing; a spindle vertically mounted in the housing for rotation and having an upper end in the housing; and a plunger at the upper end of the spindle. The plunger is configured for vertical movement in the housing. Opposed swing arms are connected to the spindle for rotation by the spindle. The swing arms each are connected about a substantially horizontal pivot and have a lever below the pivot. The lever has a distal end engaging the plunger for pushing downwardly on the plunger as a rotational speed of the spindle increases. An electrically conductive contactor extends between first and second terminals, the contactor being connected to the plunger and having an end movable relative to one of the terminals upon vertical movement of the plunger. 
     In yet another aspect thereof, the present invention provides a method for operating a centrifugal switch, having steps of providing a housing with electrical terminals therein, a movable contactor between the terminals, a spring engaged with the contactor under tension, a spindle mounted for rotation in the housing and a plunger disposed between the spindle and the contactor; providing swing arms rotated by the spindle and responsive to changes in centrifugal force to cause movement of the plunger; moving the plunger by changing centrifugal force on the swing arms; deflecting a portion of the spring to urge the contactor into engagement with one of the terminals; and removing deflection of the spring to urge the contactor away from the one of the terminals. 
     In still another aspect thereof, the invention provides a centrifugally operated switch with a housing and a spindle vertically mounted in the housing for rotation. A plunger at an upper end of the spindle is configured for vertical movement in the housing. A first spring biases the plunger upwardly. Opposed swing arms are connected to the spindle, for rotation by the spindle. The swing arms are each connected about a substantially horizontal pivot and have a lever below the pivot. The levers have distal ends engaging the plunger for pushing downwardly on the plunger as a rotational speed of the spindle increases. First and second spaced electrical terminals are provided in the housing, with an electrically conductive contactor having a first end engaged with the first terminal and a second end movable between contacting and non-contacting position with the second terminal. A second spring is disposed under tension between the first terminal and the contactor. The second spring is adapted and arranged to urge the second end of the contactor away from the second terminal in a non-deflected position of the second spring, and to urge the second end of the contactor into engagement with the second terminal in a deflected position of the second spring. A coupling engages a portion of the second spring and the plunger, to transfer movement of the plunger to cause deflection of the second spring. 
     An advantage of the present invention is providing a centrifugal switch useful for switching the starter windings of a motor, and which can be adjusted or modified easily and quickly for use at different target speeds for switch activation, thereby reducing the number of parts required for motor manufacturers to stock. 
     Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims and drawings in which like numerals are used to designate like features. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view of a centrifugal operated switch mechanism in accordance with the present invention; 
     FIG. 2 is a cross-sectional view similar to that shown in FIG. 1, but illustrating the switch mechanism in another state of operation; and 
     FIG. 3 is a cross-sectional view similar to that shown in FIG. 1, but illustrating a second embodiment of the switch mechanism. 
    
    
     Before the embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use of “including” and “comprising” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items and equivalents thereof. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now more specifically to the drawings, and to FIG. 1 in particular, numeral  10  designates a centrifugal operated switch mechanism in accordance with the present invention. Switch mechanism  10  is particularly suitable for controlling the operation of a start winding circuit (not shown) in an electric motor (not shown). 
     Switch mechanism  10  includes a housing  12 , which may be of plastic or the like. Housing  12  essentially defines a substantially closed electric components chamber  14 , and a substantially closed mechanical components chamber  16 . Chambers  14  and  16  are separated by an internal wall  18 , and need not be completely sealed one from the other. 
     Within electrical components chamber  14  are a first electric terminal  20  and a second electric terminal  22 , which, in known fashion are electrically connected to a start winding circuit (not shown) in a motor (not shown). An electrically conductive, movable contactor  24  is positioned between terminals  20  and  22 , to selectively complete or interrupt an electric circuit path between terminals  20  and  22 . In this regard, contactor  24  has a first end  26  in continuous electrical connection to first terminal  20 , and a free second end  28  that can be moved into and out of electrical connection to second terminal  22 . A spring  30  is connected to contactor  24  and to a bracket  32  extending downwardly from first terminal  20 . To enable the desired movement of contactor  24 , first end  26  thereof is lodged in a notch  34  formed in first terminal  20 , and spring  30  is under tension between bracket  32  and contactor  24 . When a central portion  36  of spring  30  is deflected upwardly, as shown in FIG. 1, free second end  28  of contactor  24  is urged upwardly into electrical contact with second terminal  22 . When spring  30  is in a non-deflected state, as shown in FIG. 2, free second end  28  of contactor  24  is biased away from second terminal  22 . 
     A spindle  40  is rotatably disposed in housing  12 , and includes an outer end  42  which extends through an opening  44  defined by housing  12 . Outer end  42  is connected to a shaft (not shown) of the motor (not shown) such that spindle  40  is rotated as the motor shaft is rotated. A bearing, low friction bushing or low friction surface  46  is provided on spindle  40 , in opening  44 , to facilitate long term rotation of spindle  40  in opening  44 . Housing  12  can be constructed as two or more components, with opening  44  defined by two or more of such components, so that, during assembly, surface  46  can be captured in opening  44 . 
     An inner end  48  of spindle  40  is disposed in mechanical components chamber  16 , and is adapted for engagement with a plunger  50 . Inner end  48  defines a cavity  52  at the end thereof. A spring  54  is disposed in cavity  52 . 
     Plunger  50  has a reduced end  56  adapted to be received in cavity  52 , and plunger  50  is biased outwardly of cavity  52  by spring  54 . Alternatively, although not shown, the plunger  50  can be configured to include a cavity to surround the spring  54 . Other configurations are suitable in accordance with the principles of the present invention. Plunger  50  can move upwardly and downwardly in housing  12 , with reduced end  56  moving essentially axially in cavity  52 . The inward movement of plunger  50  is restricted by a collar  58  that is larger than the diameter of cavity  52 . 
     A coupling  60  mechanically links an end  62  of plunger  50  with central portion  36  of spring  30 , such that axial movement of plunger  50  is transmitted through coupling  60  to spring  30 . In an uppermost position of plunger  50 , biased thereto by spring  54 , central portion  36  of spring  30  is deflected upwardly, and contactor  26  is urged upwardly such that free second end  28  thereof is in electrical contact with second terminal  22 . 
     Spindle  40  further includes a yoke  64  and opposed swing arms  70  and  90 . Swing arm  70  is connected to yoke  64  via a horizontal pivotal axis  72  such that swing arm  70  can swing upwardly and downwardly in chamber  16  about axis  72 . 
     Inward of, and below axis  72 , a lever  74  extends inwardly toward plunger  50 . Lever  74  extends above and engages collar  58 . Depending downwardly from lever  74 , a holder  76  extends outwardly beyond axis  72 , and is adapted to receive and retain one or more weight blocks  78 . Holder  76  receives and holds weight blocks  78  of different physical weight. Swing arm  70  is arranged such that upward movement of holder  76  is accompanied with downward movement of lever  74 . 
     Swing arm  90  is connected to yoke  64  via a horizontal pivotal axis  92  such that swing arm  90  can swing upwardly and downwardly in chamber  16  about axis  92 . 
     Inward of, and below axis  92 , a lever  94  extends inwardly toward plunger  50 . Lever  94  extends above and engages collar  58 . Depending downwardly from lever  94 , a holder  96  extends outwardly beyond axis  92 , and is adapted to receive and retain one or more weight blocks  98 . Holder  96  receives and holds weight blocks  98  of different physical weight. Swing arm  90  is arranged such that upward movement of holder  96  is accompanied with downward movement of lever  94 . 
     Weight blocks  78  and  98  are provided in corresponding pairs of one weight block  78  and one weight block  98  of equal weight. The various pairs thereof can be provided in different weights, for the use and application as will be described. 
     In the use of switch mechanism  10 , for switching a starter winding of a motor, spindle  40  is mounted on a shaft of the motor for rotation of spindle  40  in direct response to the rotation of the motor shaft. First and second terminals  20  and  22  are electrically connected to the starter winding circuit in known fashion, to interrupt the starter winding circuit and disable the starter winding circuit in response to disconnect of the circuit between first and second terminals  20  and  22 , as will be described more fully hereinafter. 
     In a non-rotating state of spindle  40 , or if spindle  40  is being rotated sufficiently slow, swing arms  70  and  90  are in the lower most positions of each, as shown in FIG.  1 . The resultant effect is that levers  74  and  94  are in the upper most positions. Plunger  50  is thereby urged upwardly by spring  54 , and central portion  36  of spring  30  is deflected upwardly, placing second end  28  of contactor  24  into electrically conductive contact with second terminal  22 . The circuit through terminals  20  and  22  is complete, and the starter windings connected thereto are operational. 
     As spindle  40  is rotated as indicated by arrow  100  in FIG. 2, and as the speed thereof increases, centrifugal force results in the outward movement and rise of swing arms  70  and  90 , indicated by arrows  102  and  104 , and the rotation thereof about axis  72  and axis  92 , respectively. As swing arms  70  and  90  move outwardly and rise, levers  74  and  94  are urged downwardly against collar  58 . The downward force applied by levers  74  and  94  against collar  58  forces plunger  50  to compress spring  54 . In the orientation shown in FIGS. 1 and 2, plunger  50  and coupling  60  are moved downwardly. The deflection in central portion  36  of spring  30  is relaxed, and second end  28  of contactor  24  is moved away from second terminal  22 , thereby interrupting the circuit between first and second terminals  20  and  22 . Thus, the starter winding circuit electrically connected to terminals  20  and  22  is disabled. 
     The tension in spring  30  and pivotal engagement of contactor  24  with first terminal  20  cause an abrupt change of position for contactor  24  as spring  30  is moved between deflected and non-deflected positions. Only slight deflection of central portion  36  is required to move end  28  into contact with second terminal  22 . Thus, changes between the switch open and switch closed positions shown in FIGS. 1 and 2 occur as rapid, snap-like changes. 
     In some situations, micro-welds can occur between second end  28  of contactor  24  and second terminal  22 . The mere relaxing of the deflection in spring  30  may not apply sufficient force to break the micro-welds and open the circuit. FIG. 3 illustrates a modified embodiment of switch mechanism  10  that overcomes this situation. A modified plunger  120  has a cavity  122  for a spring  124  operatively associated with spindle  40  as described previously for plunger  50 , cavity  52  and spring  54 . A shoulder  128  of plunger  120  is in operative arrangement with levers  74  and  94  as described previously with respect to collar  58  of plunger  50 . A coupling  130  is mechanically connected to an enlarged end  132  of plunger  120 , such as by a snap fit of end  132  in a cavity  134  having a reduced width access opening  136  thereto. Alternatively, end  132  could be assembled by sliding through a side access to cavity  134 . Coupling  130  defines a hook  138  that hooks over spring  30 , to provide a direct mechanical connection between spring  30  and plunger  120 . Thus, as plunger  120  is moved downward, hook  138  pulls downwardly on central portion  36  of spring  30 , adding additional force to move spring  30  from a deflected position thereof, and to break any micro-welds that may have been formed. 
     By changing weight blocks  78  and  98 , the rotational speed of spindle  40  sufficient to generate the centrifugal force necessary to operate switch mechanism  10  can be varied. Thus, in assembly of motors, costs can be reduced by not having to provide substantially different mechanisms for switch mechanism  10 . All that is necessary for adjusting switch mechanism  10  for different motor operational characteristics is to select and install the correct pair of weight blocks  78  and  98  for the rotational speed at which disconnect of the starter winding circuit is to occur. 
     Variations and modifications of the foregoing are within the scope of the present invention. It is understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text and/or drawings. All of these different combinations constitute various alternative aspects of the present invention. The embodiments described herein explain the best modes known for practicing the invention and will enable others skilled in the art to utilize the invention. The claims are to be construed to include alternative embodiments to the extent permitted by the prior art. 
     Various features of the invention are set forth in the following claims.