US2792475A - Condition responsive switch apparatus - Google Patents

Description

May 14, 1957 R. P. SWEGER 2,792,475

CONDITION RESPONSIVE SWITCH APPARATUS Filed Oct. 21, 1954 2 Sheets-Sheet l INVENTOR. fiusse?! fijn gger Cit/1m ATTORNEYS May 14, 1957 R. P. SWEGER 2,792,475

CONDITION RESPONSIVE SWITCH APPARATUS Filed Oct. 21, 1954 2 Sheets-Sheet 2 L 2o I IN V EN TOR.

[Passe]? Swqger BY a t 3 (Law/(M 42 ATTURNE Y5 United States Patent This invention relates to a switch responsive to a change in condition such as temperature and, more particularly, to a snap act-ion switch in which a movable contact is supported by an over-center spring.

in a switch of this type, a lesser force is' required to hold the spring in the over-center position than is needed to snap the spring HCEOSS center.

The general object of the invention is to provide a new and improved apparatus of the above character in which the switch operates in one direction at a predetermined valueofthe condition as the latter increases and at a diflerent'value as the condition decreases and in which -the differential between the two operating values is maintained precisely.

A more detailed object is to obtain the diiferential by taking advantage of the difierent forces required to move and to hold the switch through the use t a two-way lost motion connectionv formed by a switch actuating element moving between spac d abutments and supported by a second spring which exerts a force of a magnitude between the forces of the switch spring so that the element may yield without actuating the switch until. engaged by one or the other of the abutments.

Another object is to support the actuating element on a lever which is rocked about its fulcrum in response to changes in the condition being sensed and to adjust the position of the fulcrum to vary the magnitudes of the condition at which the switch is actuated.

A.- further object is to utilize the movable fulcrum in providing a means which permits the lever to move beyond its normal range without damaging connected or adjacent parts.

The invention also resides in the novel construction and arrangement of the various parts of the apparatus and especially of the actuating element, abutments, lever and fulcrum.

Other objects and advantages of the invention will become apparent from the following detailed description taken in connection with the accompanying drawings, in which Figure l isa front view of thermostat embodying the novel features of the present invention, parts being broken away. and shown in section.

Fig. 2 is a sectional view taken along the line 22 in Fig. 1.

Fig. 3 is a sectional view taken along the line 3--3 in Fig. l.

Fig. 4 is a perspective view of the lever supporting the actuating element.

'Fig. 5 is a fragmentary vertical sectional view of the lever and the switch with the latter shown schematically.

The invention is directed to a switch apparatus responsive to changes in a condition and, as shown in the drawings for purposes of illustration, is particularly adapted for use in a thermostat. For this purpose, the movable contact of aswitch 11 is moved back and forth from one stationary contact 12 to another contact 13 in response to'the movement of a resilient metallic bellows pin and acts between the head 34 of the pin 2,792,475 Patented May 14, 1957 l t-which is connected through a tube 15 to a remote temperature sensitive bulb 16. Thus, changes in the temperature surrounding the bulb expands or contracts the bellows and this is transmitted to the switch 11 through a movable member 17. The latter preferably is a lever formed from a sheet metal strip with downturned side flanges 18 and is fuicrumed at one end on a pin 1; projecting through the flanges. At its other end, the lever carries an actuating element 20 which engages anddepresses the actuator 21 of the switch.

Enclosing the switch 11 and the. lever 17 is a casing 22 composed of a flanged mounting plate 23 and an L-shaped cover 24 (Fig. 2). The switch is disposed within a housing .25 of insulating material and the contacts lull; and 13 are connected to terminals 26 which, in turn, are connected by rigid right angle leads 27 to the terminalsZS of a terminal plate 29. The latter is disposed against the side of the housing 25 and is held in place by the ieads 27, the housing and the plate being; secured tothe mounting plate by screws The .beilows i4 is su ported within a on the lower flange "*2 of the plate 2-3 by a cap 2 -3 bo'ted the boss.

Projecting siidably into the boss 31 and abutting against upper end of bellows i l is the head 34 of a vertical .pin 35. At its upper end, the pin bears against the lower pointed end of a screw 36 threaded through the lever 17. Acoiled compression spring 37 encircies the a stationaryccllar 38 encirclin the pin and rigid with the plate 23 so that the spring opposes the resiliency or" the bellows l4 and loads the latter. A contractile spring 3; is anchored at one end to a lug 49 on the bottom flange 32 and at the other end to an car 41 struck down from the lever 17 between the fulcrum pin 19 and the screw 36. The spring 39 thus biases the lever toward the pin 35 and the lever swings back and forth about its fulcrum upon expansion and contraction of the bellows 14 and hence in response to temperature changes.

In the present instance, the switch 11 is of the snap action type, such as those commonly-sold under the trade name Micro Switch," and, for this purpose, the movable contact 10 is supported on one end of a cantilever spring 42. At the other end, the spring is secured to the housinga25cand, between its ends, the spring is engaged by the. innerend of the actuator 21 which is a pin projecting through the housing. The spring 42 normally holds the movable contact 10 against the contacti2 but, when the actuator 21 is depressed, the spring moves over center and snaps the movable Contact across to the contact 13.

In a switch of the above type, a greater force is required to move the spring 42 across center than is needed to .hold the. spring in the over-center position. For ex ample, :a force as high as 11 ounces may be required to snap the movable contact 10 over against the contact 13 while a force of 7 ounces will hold the movable contact in this position. According to the present invention, advantage is taken of this diiference in forces to obtain a differential in magnitudes of the condition at which the apparatus responds as the condition changes in opposite directions. Thus, in the thermostat shown, the contact 10 moves over center at a predetermined temperature upon afall in temperature but does not move back upon a rise until'a higher temperature is reached.

To obtain the differential in the temperatures at which the switchll operates, the actuating element 20 is part of a two-Way lost motion connection and is resiliently mounted on the lever 17 by means of a spring 43 which exerts a force less than that required to move the switch spring 42 across center but sufficient to hold the spring in the over-center position. In the illustration given above, for example, the spring'43 might exert a force of 9 ounces. By virtue of this mounting, the'spring'43 urges 3 the actuating element 20 down against the actuator 21 but the element yields as the lever 17 swings down. Movement of the element relative to the lever is limited in the downward direction by an abutment 44 (Fig. 5) and in the opposite direction by an abutment 45, both abutments being rigid with the lever. 7

With the foregoingarrangement, a temperature drop contacts the bellows 14 which, through medium of the pin 35, permits the lever 17 to swing down under the action of the spring 39, the latter being stronger than either of the springs 42 and 43. During this turning of the lever, the element 20 engages the actuator 21 and, since the spring 43 is weaker than the switch spring, it yields until engaged by the abutment 45. Thereupon, further downward swinging of the lever depresses the actuator 21 snapping the switch spring 42 across center and moving the contact against the contact 13. With a rise in temperature, the bellows expands turning the lever back up. Because the spring 43 now is stronger than the switch spring 42, the element holds the actuator pin 21 depressed. As a result, the elements remain stationary during upward swinging of the lever until it is picked up by the abutment 44 and raised away from the actuator pin permitting the switch spring 42 to snap the contact 10 back against the contact 12. Thus a higher temperature is required to release the switch actuator than has been needed to depress it.

Herein, the actuating element 20 and the spring 43 are formed integrally as an elongated fiat leaf spring with one end 46 (Fig. 5) inserted in a slot 47 in the lever 17 near the screw 36 and hooked over a lug 48 to anchor this end to the lever. From the anchored end 46, the spring projects down from the lever, through a slot 49 in an ear 5! struck down from the lever and then is flexed to extend generally parallel to the lever. The free end of the leaf spring projects through a hole 51 in another ear 52 struck down from the lever near the outer end thereof and constitutes the actuating element 20. The

hole 51 is comparatively wide in the vertical dimension to permit the spring end 29 to flex up away from the lower edge of the hole which edge thus forms the abutment 44. The upper abutment 45 is formed by a screw 53 threaded through the outer end of the lever. By threading this screw in or out the amount the end 20 may flex relative to the lever may be varied thus setting the difierential between the operating values of the switch 11.

In order to adjust the control point of the apparatus, that is, the position of the operating differential on the temperature scale, the fulcrum pin 19 is arranged to be moved up and down to raise or lower the temperature value at which the switch 11 is actuated. For this purpose, the pin 19 is fixed to and extends ttransversely through the lower end of a vertical rod 54 which slides up and down through a circular boss 55 upstanding from the upper flange 56 of the support plate 23. The rod is guided additionally in its vertical movement by the pin 19 whose ends are received in elongated vertical parallel guideways 57 and 58, the former being a recess in a boss 59 (Fig. 2) on the plate 23 while the latter is a slot in a small plate 60 bolted to the boss.

Threaded on the end of the rod 54 beyond the boss 55 is a knob 61 which is formed with a depending annular flange 62 to provide an internal shoulder 63. The latter abuts against the upper end of the boss 55 and is held in this position by the spring 39. By threading the knob 61 up and down on the rod 54, the vertical position of the fulcrum pin 19 is varied. This changesthe amount of expansion or contraction of the bellows 14 required to actuate the switch thereby adjusting the control point of the apparatus. The knob 61 may be marked with indicia cooperating wim a mark on the flange 56 to indicate the adjusted position of the fulcrum.

The foregoing arrangement of the fulcrum pin 19 may also be utilized to limit the amount of upward movement I of the outer end of the lever 17 in the event of abnormal conditions without damage to any of the parts so as to protect any other equipment which may be located above this end. T 0 this end, a limit stop 64 rigid with the support plate 23 is disposed above the lever 17 between the screw 36 and the free end of the lever. When temperatures substantially exceeding the normal range are encountered, the lever engages the stop 64 and further expansion of the bellows 14 causes the lever to fulcrum about the stop. This raises the shoulder 63 ofi the boss 55 lifting the pivot pin 19 against the action of the spring 39 without raising the outer end of the lever.

It will be observed that an apparatus constructed in accordance with the invention produces an accurate differential between the temperature at which the switch operates upon a temperature rise and the value at which it operates on a fall. This is maintained precisely because, in each direction of temperature change, the actuating element 20 is moved by the positive action of one or the other of the abutments 44 and 45. In addition, the movable fulcrum pin 19 provides a simple but effective means for adjusting the control point of the switch and, at the same time, is adapted for use in preventing over-travel of the outer end of the lever 17. By using a separate spring 37 to load the bellows 14, the spring 39 biasing the lever against the bellows pin 35 need only be sufficient to overcome the elfects of the springs 42 and 43. Thus, the spring 39 may be comparatively weak so as to prevent the pivot pin 19 from being subjected to excessive pressure. Further, the spring 39 is connected to the lever near the operating point of the bellows, that is, near the screw 36 and, as a result, the force of this spring is not increased substantially during normal operation and does not materially increase the force on the bellows. In this way, the possibility of deforming the bellows is minimized. With the spring 39 between the fulcrum 19 and the bellows, the fulcrum, although movable, remains in place during normal operation.

I claim as my invention:

1. A condition responsive switch comprising a support, a member movably mounted on said support to move in response to changes in the condition being sensed and having a forwardly projecting part formed with an aperture therein, an elongated spring anchored to said member with its free end projecting through said aperture, said spring urging said end against the outer edge of said aperture with a force of predetermined magnitude, an over center switch stationarily mounted on said support in the path of said end and having a movable contact and a spring biasing the contact toward one side of center, said switch requiring a force greater than said first force tc move said contact across center against the action of said spring and a force lesser than said first force to hold the contact in the over center position, an actuator for moving said contact across center and engaged by said free end, said elongated spring yielding and said end moving away from the outer edge of said aperture as said member moves toward said switch, and a stop spaced behind said outer edge to limit the yielding movement of said free end and adjustably supported on said member to be spaced different distances behind the edge thereby to vary the range of movement of said end.

2. A condition responsive switch comprising a support, an over center switch stationarily mounted on said support and having a movable contact and a spring biasing the contact toward one side of center, said switch requiring a first predetermined force to move said contact across center against the action of said spring and a second and lesser force to hold the contact in the over center position, an actuator for moving said contact across center, a member mounted on said support for,

able with said actuator, a second spring resiliently supporting said element on said member to yield and move relative to the member when the'element engages said actuator and the member moves toward the actuator, and spaced abutments on said member disposed on opposite sides of said element to limit movement of the same relative to the member in bothdirections, said abutments being selectively movable relative to each other to vary the range of movement of said element, said second spring exerting a force of a magnitude between said first and second forces whereby said contact is moved across center in both directions after said element engages one or the other of said abutments.

3. A condition responsiveswitch having, in combination, a support, first and second members mounted on said support for movement relative to each other, means responsive to thecondition to be sensed and operable to move said members relative to each other according to the changes in condition, an over center switch mounted on said first member and having a movable contact and a spring biasing the contact toward one side of center, said switch requiring a firstpredetermined force to move said contact across center against the action of said spring and a second and lesser force to hold the contact in the over center position, an actuator for moving said contact across center, first and second abutments rigid with said second member and spaced apart with the first abutment near said actuator, an actuating element mounted on said second member to engage said actuator and supported for movement back and forth between a position against said first abutment and a position against said second abutment, means for selectively moving one of said abutments relative to the other to adjust the range of movement of said element, and a spring yieldably urging said element against said first abutment with a force of a magnitude between said first and second forces whereby said element moves against said second abutment before said contact moves across center and the contact remains over center until the element is engaged by said first abutment.

4. A condition responsive switch comprising a support, amember movably mounted on said support to move in response to changes in the condition being sensed and having a forwardly projecting part formed with an aperture therein, an elongated spring anchored to said member with its free end projecting through said aperture, said spring urging said end against the outer edge of said aperture with a force of predetermined magnitude, an over center switch stationarily mounted on said support in the path of said end and having a movable contact and a spring biasing the contact toward one side of center, said switch requiring a force greater than said first force to move said contact across center against the action of said spring and a force lesser than said first force to hold the contact in the over center position, an actuator for moving said contact across center and engaged by said free end, said elongated spring yielding and said end moving away from the outer edge of said aperture as said member moves toward said switch, and a stop spaced behind said outer edge and limiting the yielding movement of said free end.

5. A condition responsive switch comprising a support, an over center switch stationarily mounted on said support and having a movable contact and a spring biasing the contact toward one side of center, said switch requiring a first predetermined force to move said contact across center against the action of said spring and a second and lesser force to hold the contact in the over center position, an actuator for moving said contact across center, a member mounted on said support for movement toward and away from said actuator in response to changes in the condition being sensed, an actuating element carried by said member and engageable with said actuator, a second spring resiliently supporting said element on said member to yield and move relative to the member when the element engages said actuator and the member moves toward the actuator, and spaced abutments on said member disposed on opposite sides of said element to limit movement of the same relative to the member in both directions, said second spring exerting a force of a magnitude between said first and second forces whereby said contact is moved across center in both directions after said element engages one or the other of said abutments.

6. A condition responsive switch having, in combination, a support, first and second members mounted on said support for movement relative to each other, means responsive to the conditions to be sensed and operable to move said members relative to each other according to the changes in condition, an over center switch mounted on said first member and having a movable contact and a spring biasing the contact toward one side of center, said switch requiring a first predetermined force to move said contact across center against the action of said spring and a second and lesser force to hold the contact in the over center position, an actuator for moving said contact across center, first and second abutments rigid with said second member and spaced apart with the first abutment near said actuator, an actuating element mounted on said second member to engage said actuator and supported for movementback and forth between a position against said first abutment and a position against said second abutment, and a spring yieldably urging said element against said first abutment with a force of a magnitude between said first and second forces whereby said element moves against said second abutment before said contact moves across center and the contact remains over center until the element is engaged by said first abutment.

7. A condition responsive switch apparatus comprising a support, a member mounted on said support to move back and forth along a PIBClElfil'llllI'lfidPflfil, .a lever fulcrumed on said member, a switch mounted on said support and having an actuator engageable with a part on said lever whereby swinging of the lever about its fulcrum actuates the switch, a bellows operable to expand and contract in response to changes in the condition to be sensed and having a part abutting against said lever to swing the same in one direction, an abutment on said support engaging said member to limit the movement of the member in one'direction, and a spring acting on said lever to hold the lever against said bellows part and simultaneously biasing said member against said abutment to hold said fulcrum yieldably in a normal position, said spring acting on said lever between said fulcrum and said bellows part and near the latter to prevent movement of the fulcrum when in said normal position and to permit yielding of said fulcrum without substantially increasing the pressure on said bellows.

8. A condition responsive switch apparatus having, in combination, a support, a member mounted on said support to move relative to the same back and forth along a predetermined path, an abutment disposed in said path and operable to engage a part on said member to limit movement of the member in one direction, a lever fulcrumed on said member and carrying an actuating element, a switch mounted on said support and having an actuator engaged by said element whereby the switch is actuated upon swinging of said lever, means responsive to changes in the condition to be sensed to turn said lever about its fulcrum, and a spring acting on said lever to urge the same toward said switch and simultaneously biasing said part against said abutment to hold said fulcrum yieldably in a normal position.

9. A condition responsive switch apparatus comprising a support, a member mounted on said support to move back and forth along a predetermined path, a lever fulcrumed on said member, a switch mounted on said support and having an actuator engageable with a part on said lever whereby swinging of the lever about its fulcrum actuates the switch, a bellows operable to expand and contract in response to changes in the condition to be sensed and having a part abutting against said lever to swing the same in one direction, an abutment on said support engaging said member to limit the movement of the member in one direction, and a spring acting on said lever to hold the lever against said bellows part and simultaneously biasing said member against said abutment to hold said fulcrum yieldably in a normal position, said spring acting on said lever near said bellows part to permit yielding of said fulcrum without substantially increasing the pressure on said bellows.

10. A condition responsive switch apparatus comprising a support having an elongated guideway, a member having a part projecting into said guideway to permit the member to move back and forth along a path paralleling the guideway, a lever fulcrumed on said member and carrying an actuating element, a switch mounted on said support and having an actuator engaging said element to actuate the switch upon swinging of said lever, means responsive to the condition to be sensed and operable to turn said lever about its fulcrum, an abutment engaged by said member and limiting the movement of the member in one direction, and a spring biasing said member against said abutment to hold said fulcrum in a normal position but permitting the fulcrum to yield.

11. A condition responsive switch apparatus having, in combination, a support, a member mounted on said support to move relative to the same back and forth along a predetermined path, an abutment disposed in said path and operable to engage a part on said member to limit movement of the member in one direction, a lever fulcrumed on said member and carrying an actuating element, a switch mounted on said support and having an actuator engaged by said element whereby the switch is actuated upon swinging of said lever, means responsive to changes in the condition to be sensed to turn said lever about its fulcrum, and a spring biasing said part against said abutment to hold said fulcrum in a normal position but permitting the fulcrum to yield.

127 A condition responsive switch apparatus having, in combination, a support, a member mounted on said support to move relative to the same back and forth along a predetermined path, an abutment disposed in said path and operable to engage a part on said member to limit movement of the member in one direction, a lever fulcrumed on said member and carrying an actuating element, a switch mounted on said support and having an actuator'cngaged by said element whereby the switch is actuated upon swinging of said lever, means responsive to changes in the condition to be sensed to turn said lever about its fulcrum, a spring biasing said part against said abutment to hold said fulcrum in a normal position but permitting the fulcrum to yield, and means selectively operable to move said abutment relative to said part to change the normal position of said fulcrum and thereby change the effective point of operation of said switch.

13. A condition responsive switch apparatus comprising a support, a lever fulcrumed on said support and carrying an actuating element, a switch mounted on said support and having a movable contact and a spring urging said contact in one direction, an actuator engaged by said lever and operable upon swinging of the lever to move said contact against the action of said spring, a resilient bellows responsive to the condition to be sensed and having a part abutting said lever, a spring acting between said support and said bellows and operable to load the bellows, and a separate spring acting on said lever and operating to hold the lever in engagement with said part as the lever is turned by the part upon expansion and contraction of said bellows.

14. In a condition responsive switch, the combination of, a support, an overcenter switch mounted on said support and having a movable contact and a spring biasing the contact toward one side of center, said switch having an actuator for moving said contact across center requiring a first predetermined force to move the contact across center against the action of said spring and a second and lesser force to hold the contact in the overcenter position, an elongated lever fulcrumed on said support for movement toward and away from said actuator and having two abutments thereon facing toward each other and spaced apart transversely of the lever and longitudinally of the direction of movement thereof toward and away from the actuator, and an elongated spring anchored to and extending longitudinally of said lever with one end portion projecting and movable back and forth between said abutments and engageable with said actuator, said spring being flexed laterally of its length to urge said end portion against the one of said abutments nearest said actuator with a force intermediate said first and second forces.

References Cited in the file of this patent UNITED STATES PATENTS 2,092,085 Riley Sept. 7, 1937 2,150,203 Bondurant Mar. 14, 1939 2,314,211 Hausler Mar. 16, 1943 2,691,084 Miller Oct. 5, 1954

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