US3654578A

US3654578A - Condition responsive switch mechanism

Info

Publication number: US3654578A
Application number: US36624A
Authority: US
Inventors: Paige W Thompson
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1970-05-12
Filing date: 1970-05-12
Publication date: 1972-04-04
Anticipated expiration: 1989-04-04

Abstract

A condition responsive electric switch mechanism includes a switch having open and closed positions. A switch actuator is connected to the switch for moving it between its open and closed positions and a spring assembly is connected to the actuator for moving it between the switch open and closed positions. A thermally responsive mechanism, including a sealed expansible chamber assembly, is connected to the switch actuator for controlling movement between the switch open and closed positions. The sealed expansible chamber assembly is partially filled with liquid and partially filled with vapor so that the change in vapor volume between the switch open and closed positions is relatively large as compared to the total vapor volume. The mechanism may include two sets of spring contacts, each with its own actuator. A toggle mechanism is provided to operate one actuator. There is an operator to engage the toggle mechanism for movement of the toggle mechanism between open and closed positions of one set of contacts. There is a manually adjustable support and a spring mounted between the support and the operator. The thermally responsive expansible chamber assembly also engages the operator. The manually adjustable support has a position engaging both actuators for manually opening both sets of contacts.

Description

United States Patent Thompson [4 Apr. 4, 1972 [54] CONDITION RESPONSIVE SWITCH 57 ABSTRACT MECHANISM A condition responsive electric switch mechanism includes a 72 Inventor; Paige w Thompson, Morrison, 1 switch having open and closed positions. A switch actuator is I connected to the switch for moving it between its open and Asslgnee: General Elecmc Company closed positions and a spring assembly is connected to the ac- [22] Filed: May 12 1970 tuator for moving it between the switch open and closed positions. A thermally responsive mechanism, including a sealed PP 36,624 expansible chamber assembly, is connected to the switch actuator for controlling movement between the switch open and closed positions. The sealed expansible chamber assembly is g "337/317" 2355: partially filled with liquid and partially filled with vapor so that [58] Fleid 326 327 the change in vapor volume between the switch open and closed positions is relatively large as compared to the total vapor volume. The mechanism may include two sets of spring [56] Relerences cued contacts, each with its own actuator. A toggle mechanism is UNITED STATES p provided to operate one actuator. There is an operator to engage the toggle mechanism for movement of the toggle 3,065,323 ll/l962 Grnnshaw ..337/327 mechanism between open and closed positions of one Set of 13; 3 2 contacts. There is a manually adjustable support and a spring onneger mounted between the support and the operator. The thermally responsive expansible chamber assembly also engages the operator. The manually adjustable support has a position engaging both actuators for manually opening both sets of contacts.

PATENTEDAFR 4 1912 3. 654, 578

sum 2 OF 2 FIG/1- INVENTOR.

Page 14 7' hompsarz.

A t t0 rwey.

BACKGROUND OF THE INVENTION This invention relates generally to an improved condition responsive electric switch mechanism such as thermostat units for use in connection with heating and cooling apparatus.

Some conventional thermostats for heating and cooling applications incorporate a temperature responsive sealed vaporfilled bellows assembly and a spring, acting in opposite directions on an operating member which actuates the switch contacts, the operating member being moved first and second positions in response to expansion and contraction of the bellows in response to temperature changes. In order to provide a differential between the temperatures at which the switch contacts are respectively opened and closed, a spring mechanism is conventionally provided which acts upon the operating member and produces a snap action movement of the member between its two extreme positions.

One long-standing problem with such mechanisms has been the high level of noise produced during operation. US Pat. No. 3,354,280 issued to John L. Slonneger on Nov. 21, 1967, and assigned to General Electric Company, assignee of the present invention, shows and describes a condition responsive switch mechanism which provides the desired quick action coupled with quiet operation. The aforesaid US. Pat. No. 3,354,280 is incorporated herein by reference.

The Slonneger mechanism utilizes thermal damping to control the velocity of the snapping mechanism and thus the noise. The exemplification mechanism shown in the Slonneger patent includes a sealed expansible chamber, such as a bellows, and an attached tube. The bellows and tube are connected by a section of tubing of low thermal conductivity. The entire assembly is filled with an expansible fluid which is part liquid and part vapor, with the liquid being in the tube. In addition to the usual preheater, adjacent the tube, there is a separate bias heater to insure the bellows temperature remains above the tube temperature. While the arrangement shown in the Slonneger patent provides excellent noise control through the use of thermal damping," it is somewhat complicated in construction and operation. This construction adds to the cost of such devices and requires care in manufacture, shipping, installation and operation to insure the liquid remains in the tube.

SUMMARY OF THE INVENTION Accordingly, it is an object of this invention to provide an improved condition responsive electric switch mechanism.

Another object of this invention is to provide an improved condition responsive switch mechanism which controls the noise of operation by thermal damping."

Still another object of this invention is to provide such an improved switch mechanism which is simple in construction and operation. 1

In carrying out the invention, in one form thereof, I provide a condition responsive electric switch mechanism including a switch means having open and closed positions. Switch actuating means is connected to the switch means and is movable between first and second positions for operating the switch means between its open and closed positions. Spring means is connected to the switch actuating means for transferring the switch means between open and closed switch positions. Thermally responsive means, including a sealed expansible chamber assembly, is connected to the switch actuation means for controlling movement of the switch actuation means between its first and second positions in response to first and second predetermined temperatures. The sealed expansible chamber assembly is partly filled with liquid and partly filled with vapor such that the change in the volume of vapor as the switch actuating means moves between its first and second positions is relatively large as compared to the total vapor volume for producing thermal damping to control the velocity of the switch actuating means as it travels between its first and second positions.

2 BRIEF DESCRIPTION OF THE DRAWINGS The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be better understood by reference to the following description taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a side elevational view of a condition responsive switch mechanism illustrating one form of the present inven tion, with the cover and operating knob removed;

FIG. 2 is a plan view of the switch portion of the mechanism, generally as seen along line 22 in FIG. 1 and with the switch housing cover removed;

FIG. 3 is an enlarged, cross-sectional view of the bellows assembly included in the switch mechanism of FIG. 1; and

FIG. 4 is a cross-sectional view of the exemplification condition responsive switch mechanism generally as seen along line 4-4 of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings there is shown an exemplification thermally responsive switch mechanism in the form of a thermostat generally indicated at 10. Such an exemplification thermostat normally would be used for purposes such as controlling the heating and cooling of a house, for example. These thermostats normally include elements such as cover plates and control knobs which have been omitted from the drawings for ease of illustrating various operating components of the switch mechanism.

The thermostat 10 includes a base 11 having a cavity 12 formed in its upper surface. A switch housing cover 13 is removably attached to the bottom surface of the base 11 and, with the base 1 1, forms a cavity 14. Two sets of stationary and

movable contacts

15, 16 and 17, 18 respectively are positioned in the cavity 14. Stationary contact 15 is mounted to a bus bar element 19 to which a first terminal 20 is connected. Movable contact 16 is mounted on a resilient or spring contact strip 21 which is secured to a bus bar element 22. A second terminal 23 is connected to the bus bar element 22. Similarly, stationary contact 17 is connected to a bus bar element 24 to which is connected a terminal 25; and movable contact 18 is mounted on a resilient contact strip 26 which is secured to a bus bar element 27, to which a tenninal 28 is connected. The set of stationary movable contacts 15, 1 6 are utilized to provide a temperature responsive cycling control while the contacts 17, 18 are used in conjunction with the

contacts

15, 16 to provide a manual off position.

A generally U-shaped frame 29 is attached to the base 11 by some suitable means such as rivets 29a and forms a support for other components of the switch mechanism. A manually adjustable support in the form of a cam follower 30 is positioned within the frame 29 with one end pivotally seated on a pair of ears 31, provided in the frame 29, and its other end 32 cooperatively engaging a cam 33. The cam 33 includes a sloped cam surface 34 for selectively varying the position of the cam follower 30 and a notch 35 for positioning the cam follower somewhat removed from the range provided by the cam surface 34. The cam is fixedly attached to a shaft 33a so that as the shaft is rotated by a control knob (not shown) different portions of the sloped surface 34 or the notch 35 are selectively brought into engagement with the end 32 of cam follower 31).

The cam follower 30 is provided with a recessed seat 36 in which is mounted one end of a range spring 37. The other end of the range spring 37 bears against a collar 38 which is threadily received about an operator 39, in the form of an altitude rod. One end 41 of the operator 39 is received in a cupshaped recess 42 in a bellows 43. The other end of the bellows is sealed to a mounting cup 44 by some suitable means such as solder 45, and the mounting cup 44 is attached to the frame 29. The bellows is provided with a short fill tube 46 which is pinched off, or otherwise suitably sealed, as at 47 once the bellows has been provided with a suitable charge of fluid. A fluid tight seal is provided between the tube 46 and cup by crimping over the tube and the use of an additional body 48 of solder.

With this arrangement a force is exerted on the operator 39 which is, in efi'ect, the net force of the spring 37 and the bellows 43, which act on the operator 39 in opposite directions. The effective net force for any particular condition of the fluid within the bellows may be varied for calibration by adjusting the position of the collar 38 on the altitude rod or operator 39. This calibration is done by rotating the altitude rod relative to the collar 39. For this purpose, the end of the altitude rod removed from the bellows is provided with a slot 49 by which the rod may be rotated by some suitable means such as a screwdriver.

The thermostat also includes a toggle mechanism generally indicated at 50. The toggle mechanism includes an arm 51 having one end 52 pivotally mounted on a finger 53 connected to the frame 29 and the other end 54 pivotally connected to a return bent toggle spring 55. The other end of the toggle spring 55 is pivotally connected to a follower 56 which is slideably mounted in a recess 57 formed between the base 11 and frame 29. The follower 56 is threadily engaged by an adjustment screw 58 which, in turn, is captured in a slot 59 in the frame 29. Thus, as the screw 58 is rotated, the follower 56 is moved axially through the slot 57 to adjust the tension in the toggle spring 55. The toggle spring biases the end 54 of the arm 51 to the left (as seen in FIG. 1) with a negative gradient force. That is, the force in the direction of movement at the end of the arm 51 becomes greater the farther to the left (as seen in FIG. 1) the end 54 moves.

The operator or altitude rod 39 is formed with a shoulder 60 which engages the arm 51 intermediate its end to transfer the net effective force of the bellows 43 and range spring 37 to the pivoted arm 51. In fact the shoulder 60 engages a very weak centering spring 61 which is attached to the arm 51 which prevents the edge of the altitude rod passing through the pivoted arm 51 from engaging the edge of the opening 62, which would be detrimental to proper operation of the device.

With this arrangement of parts the toggle spring 55 biases the arm 51 to the left as seen in FIG. 1 until such time as the net effective force of the range spring 37 and bellows 53 is sufficient to overcome this force and pivot the arm 51 to the right (as seen in FIG. 1) to the full line position of FIG. 1. It will be understood that once the net effective force exerted by the operator 39 becomes sufficiently large to overcome the toggle mechanism and begins to pivot the arm 51 in the clockwise direction the decreasing force exerted by the toggle spring will tend to cause the arm 51 to snap through to the position shown in FIG. 1. On the other hand when the net effective force exerted through the operator 39 becomes insufficient to hold the arm 51 in the position shown in FIG. 1 the toggle spring 55 will tend to snap the arm 51 in a counterclockwise pivoted movement.

This movement of the pivoted arm 51 is utilized to control the opening and closing of contacts and 16. To this end an actuator 65 includes a shoulder 66 bearing against the resilient contact strip 21, with a small extension 67 extending through the strip for insuring constant engagement of the actuator 65 with the resilient contact strip 21. The actuator 65 includes a second shoulder 68 which engages the pivoted arm 51 and a reduced diameter extension 69 which slideably projects through an opening (not shown) in the arm 51 into proximity with the cam follower 30. The resiliency of the contact strip 21 maintains the shoulders 66 and 68 in engagement with the strip 21 and arm 51 respectively. As the arm 51 is pivoted in a clockwise direction to the position shown in FIG. 1, the actuator 65 moves the resilient contact strip 21 so as to separate the

contacts

15, 16. As the pivoted arm 51 is pivoted in a counterclockwise direction away from its position shown in FIG. 1, the actuator 65 allows the resilient contact strip to return to a position in which the

contacts

15, 16 are closed.

Thus as the temperature of the fluid within the bellows changes about a predetermined operating point, which has been calibrated by the positioning of the altitude rod 39 and set by positioning cam 33, the net effective force exerted on the pivoted arm 51 causes the

contacts

15, 16 to be cycled between their opened and closed position.

Many household temperature controls have a thermal lag, that is, the room temperature precedes the control temperature. For this reason, when such a thermostat is set to respond between two predetermined temperatures, the temperature of the air in the house will overshoot and undershoot the predetermined temperatures. For this reason it is common for such thermostats to include a preheater, such as 71, mounted adjacent the bellows 43. The preheater 71 is connected by a pair of

leads

72 and 73 to connectors 74 and '75 respectively. The connector 74 is connected to bus bar 19 while the connector 75 is connected to the bus bar 24 so that when

contacts

15, 16 are closed to energize the heating system for the house the preheater 71 is also energized. This causes the fluid within the thermostat to sense a temperature somewhat higher than the actual air temperature within the house. The thermostat then will operate to de-energize the heating system before or coincidentally as the air temperature within the house reaches the desired operating temperature, of the thermostat, and thus eliminate the thermal lag of the control. It will be understood that, as the household temperature cools with the heating system off, the thermostat responds substantially directly to the air temperature within the house.

A second actuator 76 is provided with a shoulder 77 engaging the resilient contact strip 26 for contact 18. The other end 78 of the actuator 76 extends through appropriate openings in the arm 51 and the frame 29 and is disposed in proximity to the cam follower 31). Thus, the movement of the pivoted arm 51 controls opening and closing of the

contacts

15, 16 but does not affect the opening and closing of contacts 17, 18. When the cam 33 is rotated so that the end 32 of the cam follower 30 drops in the notch 35, the cam follower will engage the

ends

69 and 78 of the actuators 65 and 76 and move them downwardly (as seen in FIG. 4) so as to cause both sets of

contacts

15, 16 and 17, 18 to be opened in order to completely de-energize the system, regardless of the temperature sensed by the fluid within the bellows 43.

With such condition responsive switch mechanisms or thermostats it is necessary to have more force available than is necessary for moving contact 16 between its opened and closed position with respect to contact 15 to insure positive operation of the device. This excess force is absorbed by engagement between various components such as between the arm 51 and the base 11 or frame 29 at the limits of movement of the arm 51. These engagements cause noise which is undesirable, particularly in room heating and cooling controls. The aforementioned Slonneger patent discloses a thermostat mechanism which uses thermal damping to control the instantaneous available force so as to provide sure but quiet operation. I have found that I can provide this thermal damping without including the sensing tube and bias heater arrangement of the exemplification thermostat shown in Slonneger and without'the necessity for the care needed with the Slonneger exemplification to insure that the liquid portion of the fluid was confined to the sensing bulb.

Viewing particularly FIG. 3 it will be seen that the bellows 43 and cup 44 provide a sealed thermally responsive expansible chamber. That is, the thermally responsive fluid is contained within an expansible chamber which does not have attached thereto any significant length of tubing or sensing bulb, the fill tube being pinched off very close to the bellows so as to form, in effect, a portion of the bellows. It will be also noted from FIG. 3 that the thermally responsive fluid within the chamber is partially a liquid as indicated at 80 and partially a vapor as indicated at 81.

It will be understood that as the fluid comprised of the liquid 80 and vapor 81 changes temperature in response to changes in the sensed temperature the vapor pressure of the fluid will change. This causes expansion and contraction of a bellows and exerts a varying force on the operator 39 for causing the

contacts

15, 16 to be moved between their opened and closed positions. I have found that by filling the expansible chamber with a fluid, which is partially liquid and partially vapor, to the extent that the change in vapor volume, as the bellows moves between its positions corresponding to contact open and contact closed, is relatively large in comparison to the volume of the vapor at the beginning of the movement in either direction there will be thermal damping.

For instance, as the sensed temperature rises and the fluid rises in temperature, the liquid 80 tends to evaporate and form more vapor. This exerts a greater force on the operator 39 until the net force of the bellows 43 and range spring 37 is sufficient to cause arm 51 to pivot against the force of toggle spring 55 and contact strip 21 for opening contacts l5, 16. As the contacts move open, the operator 39 moves to the right (as seen in FIG. 1) and the bellows expands. This expansion of the bellows increases the volume available for vapor within the expansible chamber, which increase is relatively large compared to the beginning vapor volume. Temporarily the force exerted by the bellows decreases until enough liquid has evaporated to provide sufficient vapor pressure to cause the bellows force to return to the necessary level. This increased vapor pressure is available at the sensed temperature; however, it takes a significant period of time to develop. Thus, there is thermal damping in the sense that the necessary force for moving the

contacts

15, 16 from their closed to their open position is available with time but is not instantaneously available and there is no build-up of excess force which would cause excess speed and attendant impact noises.

A similar situation occurs as the sensing fluid cools and the contacts close. As the contacts close, the bellows must contract. This contraction of the bellows decreases the volume available for vapor within the expansible chamber, which decrease is relatively large compared to the beginning vapor volume. Temporarily the force exerted by the bellows increases until sufficient vapor has condensed to provide the desired reduced pressure. This decreased vapor pressure is available at the sensed temperature; however, it takes a significant period of time to develop. Thus thermal damping is provided both in the contact opening and the contact closing directions of operation of the thermostat.

By way of example, with a thermostat constructed generally as shown in the drawings and including an expansible chamber having a volume of about 0.98 c.c. when depressed to a mechanical stop, a volume of about 1.11 c.c. when contacts l5, 16 are closed and about 1.19 c.c. when the contacts l5, 16 are open; and which mechanism includes the following characteristics, as measured at the end of operator 39 having slot 49: contact gap between 0.004 and 0.007 inches, total travel between 0.014 and 0.021 inches, a force differential of between 180 and 200 grams, a contact force between contacts l5, 16 of between 17 and 23 grams, friction in the mechanism of about 75 grams maximum and an excessive available force of about grams; 1 found that the fill volume of the expansible chamber, that is the bellows, should be greater than 0.55 c.c. and less than 0.7 c.c. with best results being obtained with a fill of about 0.60 c.c. plus or minus 2 percent. Too small a fill produces a control with excessive noise and too large a fill produces a control with insufficient operating speed to insure proper action.

While in accordance with the Patent Statutes, I have described what at present is considered to be the preferred embodiment of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is therefore aimed in the appended claims to cover all such equivalent variations as fall within the true spirit and scope of the invention.

I claim:

1. A condition responsive electric switch mechanism includm a. switch means having open and closed position;

b. switch actuating means connected to said switch means movable between first and second positions for operating said switch means between said open and closed positions;

c. spring means connected to said for transferring said switch closed switch positions;

d. thermally responsive meansincluding a sealed expansible chamber assembly, connected to said switch actuating means for controlling movement of said switch actuating means between said first and second positions in response to first and second predetermined temperatures; and

. said sealed expansible chamber assembly being partly filled with liquid and partly filled with vapor such that at least a 14 percent change in the volume of vapor occurs as said switch actuating means moves between said first and second positions for producing thermal damping to control the velocity of said switch actuating means as it travels between said first and second positions.

2. A switch mechanism as set forth in claim 1 wherein: said switch actuating means includes a toggle mechanism exerting a force tending to transfer said switch means to one of its open and closed positions; said spring means includes a range spring exerting a force tending to transfer said switch means to the other of its open and closed positions; and means interconnects said toggle mechanism, said range spring and said sealed expansible chamber assembly whereby a thermally damped net effective force is provided to transfer said switch means between its open and closed positions.

3. A switch mechanism as set forth in claim 2 wherein: said switch means includes a first set of contacts having open and closed positions; a first actuator interconnects said toggle mechanism and said first set of contacts for transferring said first set of contacts between their open and closed positions; said switch means also includes a second set of contacts having open and closed positions; a second actuator is provided for said second set of contacts; and manually actuatable means is provided for selectively engaging both of said first and second actuators for transferring both of said first and second set of contacts to their respective open positions.

4. A condition responsive electric switch mechanism including:

a. switch means having open and closed positions;

c. spring means connected to said switch actuating means for transferring said switch means between open and closed switch positions;

d. thermally responsive means, including a sealed expansible chamber assembly, connected to said switch actuating means for controlling movement of said switch actuating means between said first and second positions in response to first and second predetermined temperatures;

. said sealed expansible chamber assembly including a sealed expansible chamber having a first internal spacial volume when said switch actuating means is in said first position and a second internal spacial volume when said switch actuating means is in said second position; and

f. said sealed expansible chamber assembly being partly filled with liquid and partly filled with vapor with said vapor occupying a first vapor volume within said first internal spacial volume and a second vapor volume within said second internal spacial volume, said first vapor volume being at least 14 percent greater than said second vapor volume whereby thermal damping may be produced to control the velocity of said switch actuating means as it travels between said first and second positions. 1

5. A switch mechanism as set forth in claim 4 wherein: said switch means includes a toggle mechanism exerting a force tending to transfer said switch means to one of its open and closed positions; said spring means includes a range spring exerting a force tending to transfer said switch means to the other of its open and closed positions; and means intercon nects said toggle mechanism, said range spring and said sealed switch actuating means means between open and expansible chamber assembly whereby a thermally damped net effective force is provided to transfer said switch means between its open and closed positions.

6. A switch mechanism as set forth in claim wherein: said switch means includes a first set of contacts having open and closed positions; a first actuator interconnects said toggle mechanism and said first set of contacts for transferring said first set of contacts between their open and closed position;

Claims

1. A condition responsive electric switch mechanism including: a. switch means having open and closed position; b. switch actuating means connected to said switch means movable between first and second positions for operating said switch means between said open and closed positions; c. spring means connected to said switch actuating means for transferring said switch means between open and closed switch positions; d. thermally responsive means- including a sealed expansible chamber assembly, connected to said switch actuating means for controlling movement of said switch actuating means between said first and second positions in response to first and second predetermined temperatures; and e. said sealed expansible chamber assembly being partly filled with liquid and partly filled with vapor such that at least a 14 percent change in the volume of vapor occurs as said switch actuating means moves between said first and second positions for producing thermal damping to control the velocity of said switch actuating means as it travels between said first and second positions.

4. A condition responsive electric switch mechanism including: a. switch means having open and closed positions; b. switch actuating means connected to said switch means movable between first and second positions for operating said switch means between said open and closed positions; c. spring means connected to said switch actuating means for transferring said switch means between open and closed switch positions; d. thermally responsive means, including a sealed expansible chamber assembly, connected to said switch actuating means for controlling movement of said switch actuating means between said first and second positions in response to first and second predetermined temperatures; e. said sealed expansible chamber assembly including a sealed expansible chamber having a first internal spacial volume when said switch actuating means is in said first position and a second internal spacial volume when said switch actuating means is in said second position; and f. said sealed expansible chamber assembly being partly filled with liquid and partly filled with vapor with said vapor occupying a first vapor volume within said first internal spacial volume and a second vapor volume within said second internal spacial volume, said first vapor volume being at least 14 percent greater than said second vapor volume whereby thermal damping may be produced to control the velocity of said switch actuating means as it travels between said first and second positions.

5. A switch mechanism as set forth in claim 4 wherein: said switch means includes a toggle mechanism exerting a force tending to transfer said switch means to one of its open and closed positions; said spring means includes a range spring exerting a force tending to transfer said switch means to the other of its open and closed positions; and means interconnects said toggle mechanism, said range spring and said sealed expansible chamber assembly whereby a thermally damped net effective force is provided to transfer said switch means between its open and closed positions.

6. A switch mechanism as set forth in claim 5 wherein: said switch means includes a first set of contacts having open and closed positions; a first actuator interconnects said toggle mechanism and said first set of contacts for transferring said first set of contacts between their open and closed position; said switch means also includes a second set of contacts having open and closed positions; a second actuator is provided for said second set of contacts; and manually actuatable means is provided for selectivity engaging both of said first and second actuators for transferring both of said first and second set of contacts to their respective open positions.