Abstract:
A temperature responsive switch includes a housing, an actuator arm for movement in response to temperature conditions, a movable contact, and an adjustable contact connected to a auxiliary terminal for completing an auxiliary circuit. The movable contact engages and disengages the auxiliary contact to cycle a first element on and off in response to exceedingly large temperature swings a specified location, and also engages a stationary contact to complete a main circuit and cycle a different electrical element on and off in response to relatively modest changes in temperature changes at the same specified location.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to condition-responsive switches and, more particularly, to a switch for controlling more than one circuit in response to a specified temperature reference point. 
     Switches that are responsive to temperature changes, commonly known as thermostats or cold controls, are widely used in refrigeration systems, and typically regulate the switching cycle of a compressor in response to the temperature of the air contained at a remote location. When the temperature exceeds a certain “turn-on” point, the switch contacts are closed and the compressor is switched on to cool the air. When the temperature drops below a certain “turn-off” point, the switch contacts are opened and the compressor is switched off. Thus, the thermostat opens and closes a main electrical circuit in response to temperature changes at a specified location. 
     Sometimes, however, it is desirable to also control an auxiliary circuit in response to changes in temperature at the same location that stimulates the main circuit. Thus, extreme temperature conditions, or fault conditions in the main circuit, may be corrected by or identified by auxiliary elements connected to the auxiliary circuit. 
     Accordingly, it would be desirable to provide a condition responsive switch capable of providing temperature control of both a main circuit and an auxiliary circuit. 
     BRIEF SUMMARY OF THE INVENTION 
     In an exemplary embodiment of the invention, a condition responsive electric switch includes a housing, an actuator arm, a movable electrical contact, and an adjustable electrical contact for completing an auxiliary circuit. The actuator arm is mounted within the housing for pivotal movement that moves the movable contact and opens and closes the movable and adjustable electrical contacts to complete or break an auxiliary circuit through the switch in response to environmental conditions outside of the housing, such as the temperature of a specified reference point. 
     When the reference temperature falls, refrigerant inside a bellows and in fluid communication with the temperature reference point contracts and moves the actuator arm, which causes the movable contact to engage the adjustable contact and complete an auxiliary circuit. As the temperature of the reference point rises, the refrigerant expands in the bellows and causes the actuator arm to move and disengage the movable contact from the adjustable contact. Thus, the auxiliary circuit can be used to avoid excessively cold temperatures at the temperature reference point, by, for example, switching on a heating element through the auxiliary circuit. 
     The position of the adjustable contact relative to the movable contact is adjustable to calibrate the sensitivity of the auxiliary circuit to movement of the actuator arm. Thus, the auxiliary contact may be moved closer to or farther away from the movable contact to vary the required temperature change, or differential in the reference point temperature that cause the movable contact and the auxiliary contact to engage, thereby closing the auxiliary circuit. The smaller the separation of the movable contact and the auxiliary contact, the smaller the temperature differential at the reference point that will close the contacts. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view of a refrigerator thermostat; 
     FIG. 2 is a cross-sectional view with parts removed along line  2 — 2  of FIG. 1; 
     FIG. 3 is a cross sectional view with parts removed along line  3 — 3  of FIG. 2; 
     FIG. 4 is a front view of the auxiliary terminal shown in FIG. 1; 
     FIG. 5 is a bottom view of the auxiliary terminal shown in FIG. 1; 
     FIG. 6 is a side view of the auxiliary terminal shown in FIG. 1; and 
     FIG. 7 is a cross sectional view along line  8 — 8  of FIG.  7 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 is a partial cross sectional view of a condition responsive electric switch, or thermostat  10 . Thermostat  10  includes a housing  12 , an actuator arm  14 , a movable electrical contact (not shown in FIG.  1 ), and an adjustable auxiliary contact  16  for completing an auxiliary circuit (not shown) through an auxiliary terminal  18  extending through housing  12 . 
     Housing  12  includes an insulated housing portion  20 , a first terminal (not shown in FIG.  1 ), a second terminal (not shown in FIG.  1 ), and a pair of ground terminals  22  for plug-in connection to a main electric circuit, such as, for example, a power circuit for a refrigeration compressor (not shown). The power circuit is broken and completed through the first and second terminals by the operation of a bistable spring switch (not shown in FIG.  1 ). 
     Actuator arm  14  is pivotally mounted within housing  12  for a rocking movement that manipulates the bistable spring switch to engage or disengage the electrical contacts in response to environmental conditions outside housing  12 , such as, for example, a temperature at a designated location or temperature reference point. A bellows  26  and capillary tube  24  are charged with an operating fluid, such as a refrigerant gas, that expands and contracts due to temperature changes at the reference point. As the operating fluid expands and contracts, bellows  26  move actuator arm  14 , which transmits the movement of bellows  26  to the bistable spring switch to actuate the switch between circuit open and circuit closed positions. 
     A shaft  28  extends partially through housing  12  and is rotatable for adjustment of the temperature conditions that cause actuator arm  14  to cycle the completion of the main circuit, thereby turning elements connected to the circuit on and off. 
     In a particular embodiment for use in a refrigeration system, shaft  28  has an OFF position, a WARM position, and a COLD position. In the OFF position, the electrical contacts of the switch are forced apart and the switch is unresponsive to temperature changes in the evaporator tube. In an ON position, i.e., not in the OFF position, shaft  28  may be rotated to any desired setting between the WARM position and the COLD position to vary the temperature of the air in, for example, a refrigerator compartment, i.e., the reference point, by cycling a refrigeration compressor connected to the main circuit on and off. 
     A cam assembly  30  includes a cam  32  within housing  12  and connected to shaft  28 , and a spring loaded cam follower  34  connected to actuator arm  14 . Hence, a primary bias spring  36  connects cam follower  34  to actuator arm  14  and serves both to bias actuator arm  14  against movement and to keep cam follower  34  in contact with cam  32 . A screw  38  allows primary bias spring  36  to be calibrated to preset factory specifications during manufacture of thermostat  10  so that actuator arm  14  will pivot appropriately at desired temperature ranges. A secondary spring  40  also biases actuator arm against movement. 
     FIG. 2 is a cross-sectional view of FIG. 1 including actuator arm  14  communicating with a bistable spring switch element  42 . A movable contact  44  engages and disengages a stationary contact  46  to complete an electrical connection between a first terminal  48  and a second terminal  50 . Movable contact  44  also engages and disengages auxiliary contact  16  located on auxiliary terminal  18  to complete an electrical connection through first terminal  48  and auxiliary terminal  18 . A tongue  54  of bistable spring switch element  42  interfaces with actuator arm  14  and causes snap action movement, further explained below, of movable contact  44  as actuator arm  14  pivots in response to temperature changes at the temperature reference point. 
     The position of auxiliary contact  16  relative to stationary contact  46 , and also relative to movable contact  44 , is adjustable with an adjust screw  56  extending through housing  12 . Adjust screw  56  contacts auxiliary terminal  18  and deflects auxiliary terminal  52  to vary the separation of auxiliary contact  16  and stationary contact  46 . As the separation of contacts  16 ,  46  decreases, a lesser movement of actuator arm  14  is required to engage movable contact  44  and auxiliary contact  16 , which corresponds to a lesser temperature change, or temperature differential, in the evaporator tube. In other words, the auxiliary circuit through thermostat  10  becomes more sensitive to changes in temperature of the temperature reference point as the separation between contacts  16 ,  46  becomes smaller. 
     In alternative embodiments, a round or polygonal adjustment member (not shown) is press fit into an aperture (not shown) through thermostat housing  12  and engages auxiliary terminal  18  for adjustment of the position of auxiliary contact  16  by pushing on the adjust member. In another alternative embodiment, the position of auxiliary contact  16  is adjustable by mechanically bending auxiliary terminal  18 . 
     FIG. 3 illustrates bistable spring switch element  42  operated by actuator arm  14  (shown in FIGS.  1  and  2 ). Bistable spring switch element  42  selectively opens and closes an electrical circuit between first terminal  48  and second terminal  50 . Bistable spring switch element  42  is fixedly connected to first terminal  48  and carries moveable contact  44  that is selectively engageable with stationary contact  46  (shown in FIG. 2) that is located on second terminal  50 . Auxiliary terminal  18  is positioned between first terminal  48  and second terminal  50 , and includes auxiliary contact  16  (shown in FIG. 2) for engagement with movable contact  44 . 
     Bistable spring switch element  42  includes a head  60  on which movable contact  44  is mounted, and a pair of arms  62  extending outwardly from head  60 . Tongue  54  extends outwardly from head  60  and is positioned between arms  62 . As bellows  26  (shown in FIG. 1) expand and contract, actuator arm  14  (shown in FIGS. 1 and 2) engages and moves tongue  54  upward and downward. As the evaporator tube temperature rises, bellows  26  expand and cause actuator arm  14  to push tongue  54  upward so that bistable spring switch element  42  snaps into a convex configuration that engages movable contact  44  and stationary contact  46 , completing an electrical circuit through first and second terminals  48 ,  50 , respectively. As the evaporator tube temperature falls, tongue  54  is moved downward, and bistable spring switch element  42  snaps into a concave configuration that separates contacts  44 ,  46  and opens the circuit between first and second terminals  48 ,  50 . When first and second terminals  48 ,  50  are connected to a main circuit (not shown) including, for example, a compressor (not shown), bistable spring switch element  42  therefore cycles the compressor on and off in response to the temperature of the evaporator tube. 
     As the temperature reference point temperature continues to fall, the concave curvature of bistable spring switch element  42  becomes more pronounced and movable contact  44  moves toward auxiliary contact  16 . Eventually, movable contact  44  engages auxiliary contact  16  and completes a circuit through first terminal  48  and auxiliary terminal  18 . When first terminal  48  and auxiliary terminal  18  are connected to an auxiliary circuit (not shown), including, for example, a heater element (not shown), bistable spring switch element  42  therefore cycles the heater element on and off to counteract unacceptably cool temperatures. 
     Of course, thermostat  10  may be used for temperature responsive control of elements other than compressors and heaters by electrically connecting alternative elements to first and second terminals  48 ,  50  and to the first and auxiliary terminals  48 ,  16  respectively. Also, bellows  26  (shown in FIG. 1) could be attached to actuator arm  14  in such a manner as to reverse the movement of the actuator arm in response to temperature changes at the temperature reference point, thereby cycling the connection of the auxiliary circuit on and off in response to designated temperature increases at the temperature reference point. 
     FIG. 4 is a front view of auxiliary terminal  18  including a blade portion  70 , a connecting portion  72 , and auxiliary contact  16  positioned above blade portion  70 . Blade portion  70  extends along a first longitudinal axis  74  and includes a tapered leading edge  76  and an aperture  78 . Planar connector portion  72  includes a first portion  80  that is substantially perpendicular to and extends away from first longitudinal axis  74 , a second portion  82  that is substantially parallel to first longitudinal axis  74 , and a third portion  84  substantially perpendicular to second portion  82  and extending toward first longitudinal axis  74 . A bifurcated stake  86  extends from second portion  82  for connection to switch housing  12  (FIG.  1 ). Stake  86  is inserted through a housing aperture and forks  88  are separated from one another to hold auxiliary terminal  18  in position relative to housing  12  as shown in FIG. 1. A ledge  90  extends from and perpendicular to second portion  82  and supports said auxiliary terminal  18  inside housing  12 , as also illustrated in FIG.  1 . 
     Auxiliary terminal  18  is fabricated from brass and is integrally formed according to known methods. Alternatively, auxiliary terminal  18  could be made from other electrically conducting materials known in the art. In alternative embodiments, other connection mechanisms known in the art are used in lieu of stake  86  to connect auxiliary terminal to switch housing. 
     FIG. 5 is a bottom view of auxiliary terminal  18  illustrating coplanar blade portion  70  and connector portion first portion  80 , second portion  82 , and third portion  84 , together with an arm portion  100  extending from connector second portion  82  and distancing auxiliary contact  16  from connector portion  72  along a second longitudinal axis  102 . Second longitudinal axis  102  is substantially perpendicular to first longitudinal axis  74  that extends through blade portion  70  and blade portion beveled leading edge  76 . Ledge  90  extends from connector portion  72 , and includes a leading edge  104  that is generally parallel to first longitudinal axis  74 . 
     FIG. 6 is a side view of auxiliary terminal  18  including beveled blade portion leading edge  76 , arm portion  100  extending transversely from connector portion  72 , ledge  90  extending generally parallel to arm portion  100 , and auxiliary contact  16  located on a distal end  106  of arm portion  100 . Arm portion  100  extends as a cantilever beam from connector portion  72  and spans approximately the distance between first terminal  48  and second terminal  50  so that arm portion  100  generally extends above bimetal spring switch element tongue  54  (see FIG. 3) and positions auxiliary contact  16  in proximity with movable contact  44 . When auxiliary contact  16  receives adjust screw  56  (shown in FIG.  2 ), arm portion  100  deflects to facilitate adjustment of auxiliary contact  16  position relative to stationary contact  46 . 
     FIG. 7 is a cross sectional view taken through auxiliary contact  16 , and illustrating auxiliary contact first end  110  and second end  112 . First end  110  includes a conical depressed surface  114  to accommodate a head (not shown in FIG. 7) of adjust screw  56  (see FIG. 2) and ensures engagement of adjust screw  56  (shown in FIG. 2) and auxiliary contact  16 . 
     Thus, dual circuit temperature controlled switch is provided for automatic, temperature responsive control of both a main and an auxiliary circuit to cooperatively operate more than one electrical element to control the temperature of a desired reference point. 
     While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.