Abstract:
A contact structure for a sliding switch includes a conductive stationary contact disposed on a base and a conductive movable contact for electrically contacting the stationary contact. The movable contact is movable along a path between a non-contact position and a make-contact position with respect to the stationary contact, and at least one of the contacts has a protruding portion that provides an electrical interface for discharge of arcing as the movable contact breaks from the stationary contact. As a result, the invention prevents or substantially reduces degradation in switch performance which might otherwise be caused by debris accumulation associated with arcing.

Description:
TECHNICAL FIELD 
   The present invention relates generally to the structure of contacts of a sliding switch and, in particular, to the structure and configuration of stationary and movable contacts. 
   BACKGROUND OF THE INVENTION 
   There is a growing demand for sliding switches that use printed circuit boards, wire frames, and the like as stationary contacts. Such switches are used in vehicles (e.g., to control lights, turn signals, etc.), in household devices (e.g., as program switches for washers and dryers, etc.), and many other applications. 
   A conventional arrangement and structure of contacts of a sliding step switch is shown in  FIGS. 12–14 . The arrangement depicts a three function configuration  510  for a sliding switch. A circuit board substrate  512  is formed of a synthetic resin made of an insulating material. A first conductive stationary contact pad  514  connected to a positive terminal of a power source is disposed on substrate  512 . Second, third, and fourth conductive stationary contact pads  516 ,  518 ,  520  connected to a negative terminal of a power source through an electrical load via a ground connection are disposed on substrate  512 . An insulating material  522  such as a solder mask is disposed between contact pads  514 ,  516 ,  518 ,  520 . 
   A movable contact assembly  524  is mounted to an unillustrated holder which permits movement in the directions indicated by arrows A and B. Movable contact  524  includes first and second cylindrically shaped movable conductive contact heads  526 ,  528 , mounted to respective conductive contact springs  530 ,  532 . Contact springs  530 ,  532  are connected together by a conductive metal strip  534 . 
   As shown on  FIG. 12 , movable contact assembly  524  is in a first steady state position enabling current to flow from first contact pad  514  through movable contact  524  into second contact pad  516  to activate the function controlled by second contact pad  516 . As movable contact assembly  524  moves along a path in parallel with the direction of arrow B movable contact heads  526 ,  528  moves to other positions where various functions are activated or deactivated. Likewise, movable contact assembly  524  can also move along a path in parallel with arrow A. 
   Electrical contact is made between a cylindrically shaped movable contact head and a flat stationary contact pad by pressing the contact head onto the stationary contact pad creating a line of electrical contact points. Upon operation of the switch, contact is broken by movement of the movable contact head past the edge of the stationary contact pad, a line of electrical contact points being maintained until just before breaking the contact. 
   Under specific voltage and current conditions, an arc is initiated at the last point of electrical contact as the electrical contacts are moved apart from each other. The current flowing through the gap between contacts generates heat, resulting in temperatures high enough to cause arc erosion; some of the nearby insulation may be burned away. 
     FIG. 13  illustrates an electrical schematic of the switch configuration shown on  FIG. 12 .  FIG. 14  shows a sectional view of the switch configuration shown on  FIG. 12 . 
     FIG. 15  illustrates the area  546  on a conventional contact pad where arcing occurs. This area is known as an arcing zone. During the life of the switch, debris fields  548  including both conductive and insulating material build up on the stationary contact pads and insulating regions as a result of arc erosion. 
   Sliding movement of the contact head through the debris field also causes debris particles to be dragged into a main or steady state area of contact, known as a contacting zone  542 , on the stationary contact pad  520  resulting in increased contact resistance when the contact head electrically contacts the contacting zone on the stationary contact pad during steady state use of the switch. The switch fails when debris causes the resistance between contacts to increase to a level whereby the contacts can no longer effectively complete a circuit or resistance becomes unacceptably high.  FIG. 16  illustrates a graph showing voltage drop across contacts as a function of switching cycles of a conventional switch. In the illustrated example, voltage begins to increase and become unstable after about 25 arcing cycles. 
   During switch operation, debris particles are also dragged onto insulating material disposed between stationary contact pads as the contact head is moved from one contact pad to another. Debris on the insulation material reduces the dielectric strength of the insulation. The switch fails when the isolation resistance between the contact pads is reduced to a point where a circuit is established between contact pads. Lubrication of the contacts generally increases the rate at which debris is deposited onto the insulation. 
   As electrical performance requirements for sliding switches continue to increase, improvement in sliding switch performance is needed to satisfy increasingly stringent requirements. 
   SUMMARY OF THE INVENTION 
   The present invention provides contact structures for a sliding switch capable of extending the service life of the switch while maintaining voltage stability as compared with a conventional contact structure. 
   In accordance with a first aspect of the present invention, an improved contact structure is provided for a sliding switch having a stationary contact pad and a movable contact that is capable of directing accumulation of arcing debris away from a portion of a steady state contacting zone on the stationary contact pad. Consequently, a portion of the contacting area between stationary and movable contacts remains generally free of arcing erosion debris for an extended portion of the service life of the switch, thus extending the service life and improving voltage stability as compared to a conventional configuration. 
   In accordance with the first aspect of the present invention, a contact structure for a sliding switch includes a stationary contact pad and a movable contact which moves along a path extending between a non-contact position where the movable contact is electrically isolated from the stationary contact pad and a make-contact position where the movable contact maintains a primary electrical interface with the stationary contact pad, the stationary contact pad including a contacting zone that electrically makes contact with the movable contact when the movable contact is in the make-contact position, the stationary contact including an arcing zone that electrically breaks from or makes the movable contact when the movable contact moves from the make-contact position to the non-contact position and vice versa, the arcing zone providing an area where arcing occurs between the stationary contact and the movable contact, the stationary contact and the movable contact are shaped and configured such that when the contacting zone is projected in parallel with respect to the path onto the arcing zone, at least a portion of a projection of the contacting zone lies outside the arcing zone to provide a region within the contacting zone which is generally outside of an arcing erosion debris path created by the movable contact as it slides across the stationary contact. 
   In a preferred embodiment of a sliding switch including a movable contact and a flat stationary contact pad, a contact edge defined on the stationary contact pad such that the contact edge electrically contacts the movable contact as the movable contact moves between a non-contact position and a steady state contact position, the movable contact has a cylindrically shaped contact head and the flat stationary contact pad has a V-shaped contact edge configured to partially define a concave region on the stationary contact pad. Consequently, two arcing zones are provided and a substantially arc free region is provided in between. Thus a portion of a contacting zone projected along a path of movement of the movable contact head falls on the substantially arc free region. A portion of the contacting zone, therefore, lies generally outside of an arcing erosion debris path created by the movable contact as it slides across the stationary contact. Other contact configurations may be used so that at least a portion of a projection of the contacting zone lies outside the arcing zone to provide a region within the contacting zone which is generally outside of an arcing erosion debris path created by the movable contact as it slides across the stationary contact. 
   In accordance with a second aspect of the present invention, a contact configuration is provided which is capable of directing arcing toward the contact pad connected to the positive terminal of a power source and away from contact pads connected to a negative terminal. This configuration is advantageous because accumulation of conductive arcing debris between adjacent stationary contact pads is reduced compared with configurations known in the art. Thus, dielectric strength between adjacent contact pads is maintained over an extended portion of the service life of a switch. 
   Further in accordance with the second aspect of the present invention, a contact configuration for a sliding switch includes a first stationary contact pad connected to a positive terminal of a power source, a second stationary contact pad connected to a negative terminal, and a movable contact, an insulating region electrically isolating each of the contact pads, the movable contact is configured to be movable between a contact position where the movable contact electrically connects the first and second stationary contact pads and a non-contact position where movable contact is electrically isolated from the second stationary contact pad, the first stationary contact pad and movable contact being configured so that as the movable contact moves from the contact position to the non-contact position the movable contact breaks from second stationary contact pad before it breaks from the first stationary contact pad and as the movable contact moves from the non-contact position to the make contact position, the movable contact makes contact with the first stationary contact pad before it makes contact with the second stationary contact pad. 
   In accordance with a third aspect of the present invention, a contact configuration is provided which is capable of directing arcing to occur simultaneously at a contact pad connected to a negative terminal and a contact pad connected to a positive terminal. Consequently, arcing energy is split between each contact pad. This configuration results in a decreased formation of arcing erosion debris at the contact pad connected to the negative terminal as compared to the amount generated by configurations known in the prior art. 
   Further in accordance with the third aspect of the present invention, a contact configuration for a sliding switch includes a first stationary contact pad connected to a positive terminal of a power source, a second stationary contact pad connected to a negative terminal, and a movable contact, an insulating region electrically isolating each of the contact pads, the movable contact is configured to be movable between a contact position where the movable contact electrically connects the first and second stationary contact pads and a non-contact position where movable contact is electrically isolated from the second stationary contact pad, the first stationary contact pad and movable contact being configured so that as the movable contact moves from the contact position to the non-contact position the movable contact breaks from second stationary contact pad at the same time that it breaks from the first stationary contact pad and as the movable contact moves from the non-contact position to the make contact position, the movable contact makes contact with the first stationary contact pad at the same time that it makes contact with the second stationary contact pad. 
   These and other features and advantages of the present invention will become apparent from the following brief description of the drawings, detailed description, and appended drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above-mentioned features of the present invention can be more clearly understood from the following detailed description considered in conjunction with the following drawings, in which like numerals represent like elements and in which: 
       FIG. 1  is a plan view of a first exemplary embodiment of a contact structure in accordance with the present invention; 
       FIG. 2  is a sectional view of the contact structure shown on  FIG. 2 ; 
       FIG. 3  is a plan view of a second exemplary embodiment of a contact structure in accordance with the present invention; 
       FIG. 4  is a plan view of a third exemplary embodiment of a contact structure in accordance with the present invention; 
       FIG. 5  is a plan view illustrating an aspect of the present invention; 
       FIG. 6  is a graph depicting contact voltage between a movable contact head and stationary contact as a function of switching cycles for an exemplary embodiment of a contact configuration of the present invention; 
       FIG. 7  is a plan view illustrating an aspect of an alternate embodiment of the present invention; 
       FIG. 8  is a plan view illustrating an aspect of a second alternate embodiment of the present invention; 
       FIG. 9  is a plan view illustrating an aspect of a third alternate embodiment of the present invention; 
       FIG. 10  is a plan view illustrating an aspect of a fourth alternate embodiment of the present invention; 
       FIG. 11  is a section view of the an aspect of the fourth alternate embodiment of the present invention; and 
       FIG. 12  is a plan view of a contact structure known in the prior art; 
       FIG. 13  is an electrical schematic of the contact structure shown on  FIG. 12 ; 
       FIG. 14  is a sectional view of a prior art contact structure; 
       FIG. 15  is a plan view illustrating an aspect of a prior art contact structure; and 
       FIG. 16  is a graph depicting an aspect of a prior art contact structure. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   As discussed above, contact configurations in accordance with the present invention are capable of providing an increased number of switching cycles while providing a more stable resistance across contacts than achieved by known contact configurations. 
   Referring to the figures,  FIGS. 1–2  illustrate a first exemplary embodiment of a contact configuration  110  for a sliding switch. 
   A circuit board substrate  112  is formed of a synthetic resin made of an insulating material. A first conductive stationary contact pad  114  connected to a positive terminal of a power source is disposed on substrate  112 . Second, third, and fourth conductive stationary contact pads  116 ,  118 ,  120  connected to a negative terminal of a power source via a ground connection are disposed on substrate  112 . An insulating material  122  such as a solder mask is disposed between contact pads  114 ,  116 ,  118 ,  120 . 
   A conductive movable contact assembly  124  is mounted to an unillustrated holder which permits movement in the directions indicated by arrows A and B. Movable contact assembly  124  includes first and second cylindrically shaped conductive movable contacts  126 ,  128 , mounted to respective conductive contact springs  130 ,  132 . Contact springs  130 ,  132  are connected together by a conductive metal strip  134 . As shown on  FIG. 1 , second movable contact  128  maintains electrical contact with respective stationary contact pads  116 ,  118 ,  120  generally at a contact line  128   a  where the cylindrically shaped second movable contact  128  contacts a respective contact pad  116 ,  118 ,  120 . 
   As shown on  FIG. 1 , movable contact assembly  124  is in a first steady state position enabling current to flow from first contact pad  114  through movable contact assembly  124  into second contact pad  116  to activate the function controlled by second contact pad  116 . As movable contact assembly  124  moves along a path in parallel with the direction of arrow B movable contacts  126 ,  128  move to a second steady state position illustrated in phantom at  136   a ,  136   b , respectively that represents a first OFF position. Movable contact assembly  124  can continue to move in the direction of arrow B to a third steady position illustrated by contacting zones shown in phantom at  138   a ,  138   b  where the function controlled by third contact pad  118  is activated, to a fourth steady position illustrated in phantom at  140   a ,  140   b  respectively, that represents a second OFF position, and to a fifth steady state position illustrated by contacting zones shown in phantom at  142   a ,  142   b  respectively, where the function controlled by fourth contact pad  120  is activated. Likewise, movable contact assembly  124  can move from fifth steady position illustrated by contacting zones shown in phantom at  142   a ,  142   b  respectively along a path in parallel with arrow A to other steady state positions. 
   As shown on  FIG. 1 , fourth contact pad  120  has first and second protruding portions  144   a ,  144   b  that provide an electrical interface for discharge of arcing as second movable contact  128  moves between fourth and fifth positions in a direction parallel with respect to arrows A and B thereby making contact with or breaking contact from fourth contact pad  120 . Protruding portions  144   a ,  144   b  are each at least partially defined by a peripheral edge  146  that is in non-parallel relation with respect to contact line  128   a.  As shown on  FIG. 1 , first and second protruding portions  144   a ,  144   b  in combination form a “V” shape. The top of the “V” functioning as first and second arcing zones  148   a ,  148   b , respectively, which provide an electrical interface for discharge of arcing. 
   As illustrated on  FIG. 1 , when contacting zone  142   b  is projected along movement path (indicated by arrows A and B) onto first and second arcing zones  148   a ,  148   b,  at least a portion of a projection  150  of contacting zone  142   b  lies outside arcing zones  148   a ,  148   b  thereby providing a region  152  within contacting zone  142   b  which is generally outside of an arcing erosion debris path ( 648   a ,  648   b  as shown on  FIG. 5 ) created by second movable contact  128  as it slides across fourth contact pad  120 . 
   Likewise, second and third contact pads  116 ,  118  have protruding portions that provide an electrical interface for discharge of arcing. 
     FIG. 5  shows a movable contact  628  and a stationary contact pad  620  similar to second movable contact  128  and fourth stationary contact pad  120  as shown on  FIGS. 1 and 2 .  FIG. 5  illustrates two areas, known as arcing zones  646   a ,  646   b , that provide an electrical interface where arcing occurs on stationary contact pad  620  as movable contact head  628  moves between fourth and fifth steady state positions  640   a ,  642   a  as depicted on  FIG. 1 . Arcing erosion debris fields including both conductive and insulating material that build up on stationary contact pad  620  and insulating material  622  during the service life of switch are generally shown at  648   a ,  648   b.  Debris fields  648   a ,  648   b  generally spread from arcing zones  646   a ,  646   b  in parallel with respect to a path of movement of contact head  628  in the direction of arrows A and B. Consequently, there is a portion  650  of contacting zone  642   a  that generally remains outside of arcing erosion debris fields  648   a ,  648   b  over an extended portion of the service life of switch. As a result, as shown on  FIG. 6 , contact voltage between movable contact  628  and stationary contact pad  620  remains low and stable over an extended portion of the service life of switch. This is a significant improvement over the performance, as shown by graph  702  on  FIG. 16 , of contact configurations of switches known in the prior art. 
     FIG. 3  illustrates a second contact arrangement  310  for a sliding switch. Second contact arrangement  310  is similar to arrangement  110  depicted in  FIG. 1  in that it includes second, third, and fourth conductive stationary contact pads  316 ,  318 ,  320  connected to a negative terminal of a power source via a ground connection are disposed on substrate  312 . Second contact arrangement  310  further includes a conductive movable contact assembly  324  including first and second cylindrically shaped conductive movable contacts  326 ,  328 . Second contact arrangement  310  varies from first contact arrangement  110  in that a first stationary contact pad  314  which is connected to a positive terminal of a power source includes first, second, and third conductive pad portions  360 ,  362 ,  364  with a first insulating region  366  being disposed between first and second pad portions  360 ,  362  and a second insulation region  368  being disposed between second and third pad portions  362 ,  364 . 
   Second contact arrangement  310  is configured such that as the switch moves from an ON position to an OFF position, first movable contact  326  breaks contact first from first stationary contact pad  314  before breaking from one of second, third, or fourth contact pads  316 ,  318 ,  320 . Second contact arrangement  310  is also configured such that as the switch moves from an OFF position to an ON position, second movable contact  328  makes contact with one of second, third, or fourth contact pads  316 ,  318 ,  320  before first movable contact  326  makes contact with first stationary contact pad  314 . Consequently, arcing occurs between first movable contact  326  and first stationary contact pad  314  and does not occur for a significant portion of the service life of switch between second movable contact  328  and second, third, and fourth stationary contacts pads  316 ,  318 ,  320 . This is advantageous in that conductive arc debris does not form between second, third, and fourth stationary contact pads  316 ,  318 ,  320  that reduces the dielectric strength between adjacent pads or which could cause a conductive circuit to form between pads. Protruding portions  344   a ,  344   b  are illustrated on second portion  362  of first stationary contact pad  314 . Arcing generally occurs at the protruding portions  344   a ,  344   b  generally within path  370 . 
     FIG. 4  illustrates a third contact arrangement  410  for a sliding switch. Third contact arrangement  410  is similar to arrangement  310  depicted in  FIG. 3  and includes a first stationary contact power pad  414  which is connected to a positive terminal of a power source. First stationary contact power pad  414  includes first, second, and third conductive pad portions  460 ,  462 ,  464  with a first insulating region  466  being disposed between first and second pad portions  460 ,  462  and a second insulation region  468  being disposed between second and third pad portions  462 ,  464 . A third insulating region  480  exists between first and second stationary contact pads  416 ,  418  and a fourth insulation arrangement  482  exists between second and third stationary contact pads  418 ,  420 . 
   Third contact arrangement  410  is configured such that as the switch moves from an ON position to an OFF position, a first movable contact  426  breaks contact from first stationary contact pad  414  simultaneously with second movable contact  428  breaking contact with one of second, third, or fourth contact pads  416 ,  418 ,  420 . Second contact arrangement  410  is also configured such that as the switch moves from an OFF position to an ON position, second movable contact  428  makes contact with one of second, third, or fourth contact pads  416 ,  418 ,  420  at the same time first movable contact  426  makes contact with first stationary contact pad  414 . Consequently, arcing occurs with both the first and second movable contacts  426 ,  428 . This configuration is capable decreasing formation of arcing erosion debris at the contact pads connected to the negative terminal as compared to the amount generated by configurations known in the prior art. 
     FIG. 7  depicts a first alternate contact pad configuration  710  of many possible configurations in accordance with the present invention where a stationary contact pad  720  and a movable contact  728  are mutually shaped and configured such that at least a portion  750  of a contacting zone  742   a  lies outside an arcing zone  746   a  when contacting zone  742   a  is projected along a path of movement of contact head  728  as depicted by arrows A and B. Therefore, a region  750  is provided within contacting zone  742   a  which is generally outside arcing erosion debris path  748   a  created by movable contact  728  as it slides across stationary contact pad  720 .  FIG. 7  illustrates a protruding portion  744   a , a receiving edge  760 , and a line of contact  762  of movable contact  728 . The line of contact  762  and the receiving edge  760  are in nonparallel relation with respect to each other. 
     FIG. 8  depicts a second alternate contact pad configuration  810  of many possible configurations in accordance with the present invention where a stationary contact pad  820  and a movable contact  828  are mutually shaped and configured such that at least a portion  850  of a contacting zone  842   a  lies outside an arcing zone  846   a  when contacting zone  842   a  is projected along a path of movement of contact head  828  as depicted by arrows A and B. Therefore, a region  850  is provided within contacting zone  842   a  which is generally outside arcing erosion debris path  848   a  created by movable contact  828  as it slides across stationary contact pad  820 . A receiving edge  860  is shown in nonparallel relation to movable contact  862 . 
     FIG. 9  depicts a third alternate contact configuration  910  of many possible configurations in accordance with the present invention. A conventional stationary contact pad  920  is rectangular shaped and movable contact  928  has first and second projecting portions  928   a ,  928   b.  Stationary contact pad  920  and movable contact  928  are mutually shaped and configured such that at least a portion  950  a contacting zone  942   a  lies outside an arcing zone  946   a ,  946   b  when contacting zone  942   a  is projected along a path of movement of movable contact  928  as depicted by arrows A and B. Therefore, a region  950  is provided within contacting zone  942   a  which is generally outside arcing erosion debris path  948   a ,  948   b  created by movable contact  928  as it slides across stationary contact pad  920 . 
     FIGS. 10 and 11  depict a fourth alternate contact configuration  1010  of many possible configurations in accordance with the present invention. A stationary contact pad  1020  is rectangular shaped and movable contact  1028  includes first, second, and third furcations  1028   a,b,c . Stationary contact pad  1020  and movable contact head  1028  are mutually shaped and configured such that at least a portion  1052   b,c  of contacting zone  1052   a,b,c  lies outside an arcing zone  1048  when contacting zone  1052   a,b,c  is projected along a path of movement of movable contact  1028  as depicted by arrows A and B. 
   The preferred embodiments shown and described herein are provided merely by way of example and are not intended to limit the scope of the invention in any way. Preferred dimensions, ratios, materials and construction techniques are illustrative only and are not necessarily required to practice the invention. It is intended that the scope of the present invention herein disclosed should not be limited by the particular disclosed embodiments herein. Further modifications and alterations may occur to others upon reading and understanding the specification.