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Title:
THERMOSTAT CONTROL MECHANISM
United States Patent 3573698
Abstract:
A thermostat control includes a return-bent bimetal member having a pair of longitudinally extending arms. One of the arms carries a yoke or armature for actuating an associated magnetic switch. The other arm is mounted to a pivotable member for setting the operating temperature of the thermostat. An anticipation heater is mounted on the bimetal member, between the arms and adjacent the return bend so as to efficiently transfer heat to a large portion of the bimetal element. The magnetic switch includes a pair of spaced stationary contacts and a movable contact structure, which is pivotable between extreme positions respectively engaging each of the stationary contacts. The movable contact structure includes a magnet, which moves in response to the relative positioning of an armature for pivoting the movable contact structure. The movable contact structure tends to rebound from its extreme positions. A damper of nonmagnetic material is loosely mounted about the magnet for movement therewith. There is sufficient lost motion between the magnet and damper that they collide approximately as the movable contact structure begins to rebound.


Inventors:
MITICK STANLEY R
Application Number:
04/795876
Publication Date:
04/06/1971
Filing Date:
02/03/1969
Assignee:
GENERAL ELECTRIC CO.
Primary Class:
Other Classes:
337/107, 337/377
International Classes:
H01H36/00; H01H37/52; H05B1/02; (IPC1-7): H01H37/14; H01H37/18; H01H37/52
Field of Search:
335/145,205 337
View Patent Images:
US Patent References:
3339043Thermostat with heat anticipator1967-08-29Baak
3316374Thermostat with an improved heat anticipation means1967-04-25Nelson
3168804Heater construction and method of making same1965-02-09Quinn
3064103Variable thermostat anticipator1962-11-13Biermann et al.
2905790Space thermostat with adjustable anticipator1959-09-22Markham
2493294Control device1950-01-03Kronmiller
2240847Magnetic switch1941-05-06Hildebrecht
2145722Condition responsive control1939-01-31Hall
Primary Examiner:
Gilheany, Bernard A.
Assistant Examiner:
Morgan, Dewitt M.
Claims:
I claim

1. A control device including a movable member; means for manually adjusting the position of said movable member, a bimetal including a pair of longitudinally extending arms joined by a return bent portion; one of said arms being connected to said movable member for movement therewith; means for limiting movement of the other of said arms between first and second extreme positions; a heater for said bimetal to cause said other arm to move between its extreme positions, said heater being mounted between said arms adjacent said return-bent portion; a switch including a sealed container of nonmagnetic material, said container being mounted adjacent said other bimetal arm; at least one stationary contact mounted in said container; a movable contact structure mounted in said container for selective engagement with said stationary contact; said movable contact structure including an elevated distal section; said other bimetal arm carrying a bifurcated yoke positioned to approach opposite sides of said distal section as said other bimetal arm moves to its extreme positions; one of said distal section and said yoke including magnet means to provide a magnetic attraction between said yoke and said distal section for causing said distal section to move to its extreme positions for moving said movable contact structure into and out of engagement with said stationary contact; and a damper of nonmagnetic material loosely mounted about said distal section for movement with said distal section with lost motion therebetween.

Description:
BACKGROUND OF THE INVENTION

This invention relates generally to control devices, such as room thermostats used for controlling domestic heating and air-conditioning systems.

Room thermostats commonly employ a bimetal member for operating a control switch. The room temperature rise and fall, in response to a temperature-controlled heating system is relatively sluggish. This inertia effect tn tends to produce an objectionable temperature lag or overshoot when the heating of the room is allowed to depend entirely upon the effect of room temperature on the thermostat. Therefore, it has become common practice to provide an anticipation heater as a part of the thermostat. The anticipation heater causes the thermostat temperature to rise faster than the room temperature. This causes the heating system to be given an off signal before the room reaches the desired temperature. The inertia effect will then carry the the room temperature to that set on the thermostat. Prior art anticipation heater arrangements have generally required the use of more than the optimum wattage input to raise the bimetal member to its operating temperature. An excessive wattage input to the anticipation heater results in excessive room-temperature control-point droop. Control-point droop is the lowering of the temperatures in the room at which the heating system is turned on and off. This droop varies directly with anticipator heater wattage, as well as the percent of on time of the system.

SUMMARY OF THE INVENTION

Therefore it is an object of the present invention to provide an improved control of the room thermostat type.

It is another object of this invention to provide an improved bimetal and anticipation heater, particularly suitable for use in a thermostat, in which a minimum heater wattage will raise the bimetal to its operating temperature.

It is a further object of this invention to provide such a bimetal and anticipation heater wherein heat from the heater is transferred to the bimetal member in an expeditious and uniform manner.

The invention, in one aspect thereof, provides a control device such as a there thermostat which includes a movable member with means for manually adjusting the position of the movable man member. A bimetal element is provided with a pair of longitudinally extending arms joined by a return-bent portion. One of the arms is connected to the movable member for movement therewith and means are provided for limiting movement of the other of the arms between first and second extreme positions. A bimetal heater is mounted between the arms, adjacent the return-bent portion for causing the other of the arms to move between its extreme positions. A magnet is provided and includes a sealed container of nonmagnetic material mounted adjacent the other bimetal arm. At least one stationary contact is mounted in the container and a movable contact structure is mounted in the container for selective engagement with the stationary contact. The movable contact structure includes a distal section, and the other bimetal arm carries a bifurcated yoke or armature positioned to approach opposite sides of the distal section of the movable contact structure as the other bimetal arm moves between its extreme positions. There is a magnetic attraction between the yoke and the distal section for causing the distal section to move to extreme positions for moving the movable contact structure into and out of engagement with the stationary contact in response to the yoke approaching opposite sides of the switch.

The above mentioned and other features and objects of this invention and them the manner of obtaining 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:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of a thermostat with the front cover and temperature indicator removed;

FIG. 2 is a fragmentary 1 of a portion of the thermostat of FIG. 1 showing the heater assembly, with the calibration indication sheet removed for purposes of illustration;

FIG. 3 is a view similar to FIG. 2 but showing the heater assembly from its underside;

FIG. 4 is a schematic diagram of the thermostat and an associated electric cu circuit;

FIG. 5 is a slightly enlarged perspective view of the magnetic switch incorporated in the thermostat of FIG. 1;

FIG. 6 is an enlarged plan view of the switch of FIG. 5 with a portion of the housing broken away for purposes of illustration;

FIG. 7 is an enlarged side elevational view of the switch of FIG. 5, with certain parts broken away and certain parts in section for purposes of illustration;

FIG. 8 is a view taken along line 8-8 of FIG. 7;

FIG. 9 is a view taken along the line 9-9 of FIG. 7;

FIGS. 10a, 10b, 10c, 10d and 10e are diagrammatic presentations showing some of the relative positions of the magnet and damper of the switch of FIG. 5, as the magnet moves in one direction between its extreme positions; and

FIGS. 11a, 11b, 11c, 11d and 11e are diagrammatic presentations similar to FIGS. 10a--10e, showing the relative positions of the magnet and damper as the magnet moves in the other direction between its extreme positions.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, particularly to FIGS. 1--3 there is shown an improved control such as a room thermostat 1. The thermostat is the general type shown and described in applicant's U.S. Pat. No. 2,953,664, which is assigned to General Electric Co., assignee of the present invention. Such thermostats are designed to control either or both a house heating system and a house cooling or air-conditioning system.

The thermostat 1 includes a base 2 upon which various operating components of the thermostat are mounted or attached. A post structure 3 is provided adjacent each corner of the base for mounting a cover structure, which has been omitted for the sake of simplicity. A projecting portion 4 of the base houses a switch structure generally indicated at 5 for adjusting the thermostat and associated circuitry between a heating operation and a cooling operation.

An elongated member 6 is mounted for pivotal movement on the base 2 by means of a rivet 7 which passes through the base 2 and the member 6. The base is provided with three angularly spaced arcuate bosses such as that shown at 8. They are positioned around the rivet 7 and engage the underside of member 6 to provide stability to member 6 even if it is not even. Also a spring washer, not shown, may be connected between rivet 7 and the underside of base 2 to insure the proper force between member 6 and bosses 8. The end 9 of the member 6 is provided with a U-shaped bracket 10 which threadily receives adjusting and operating screw 11. The inner end of the screw 11 bears against a cam 12, which is rotatably mounted to the base and includes a manual adjusting knob 13. The other end 14 of the member 6 rides on an arcuate ridge 15 formed in the base 2 and is provided with an upstanding tab 16. A spring 17 is connected to the tab 16 and to a post 18. With this arrangement the spring 17 biases the end 14 of member 6 in a clockwise direction, as seen in FIG. 1. This insures that the screw 11 remains in contact with the cam 12 so that the position of the member 6 is determined by the position of the cam. As the cam 12 is rotated by the manual adjusting knob 13 it bears against the screw 11 so as to move the member 6 against the biasing force of spring 17. This causes the end 14 to accurately move along the ridge 15 in a clockwise or counterclockwise direction, depending upon the direction in which the knob 13 is rotated.

A bimetal element 19 is provided and includes a pair of longitudinally extending arms 20 and 21, joined by a return-bent portion 22. The distal end of arm 20 is securely attached to the tab 16 of member 6. A bifurcated yoke or armature 23 is attached to the distal end of arm 21 and has a pair of spaced generally parallel fingers 24 and 25. The fingers 24 and 25 are positioned to engage a pair of spaced stops 26 and 27, which are formed to extend outwardly from the base 2.

The arms 20 and 21 are generally parallel although, in certain circumstances, they may either converge or diverge slightly, depending on the prestressing of the bimetal and its temperature. As the cam 12 is rotated so that end 14 of member 6 moves in an arcuately clockwise direction, the tab 16 carries the entire bimetal assembly with it until the finger 24 engages the stop 26. Further clockwise movement of the member 6 will cause the distal ends of the bimetal arms 20 and 21 to become divergent as the tab 16 continues to carry the end of arm 20 downwardly while the stop 26 restrains any further movement of the armature 23 end of the arm 21. This further movement builds up stresses within the bimetal 19 which must be overcome by a temperature change of the bimetal in order to cause it to move from the stop 26 to the stop 27.

In a similar manner counterclockwise movement of the elongated member 6 (as seen in FIG. 1) will move the entire bimetal assembly as a unit until the finger 25 comes into engagement with the stop 27. Additional counterclockwise or upward movement of the tab 16 and bimetal arm 20 causes the arms 20 and 21 to converge, as the end of arm 21 is restrained from further counterclockwise movement. This again creates stresses in the bimetal which must be overcome by a change in temperature of the bimetal in order to cause the bimetal to move to its other position, that is with finger 24 in contact with stop 26. Thus the stops 26 and 27, in conjunction with the fingers 24 and 25 of the armature 23, function to provide predetermined extreme positions for the fingers 24 and 25 and enable the bimetal to be prestressed so as to change the operating temperature of the control. In fact, the cover structure (not shown) normally would have a scale marked in degrees, for use with the cam 12 so that the user can know at what operating temperature the thermostat is set. The screw 11 serves as an adjusting means to precalibrate the thermostat so that it does in fact operate at the control temperature to which it is set. Thus the cam 12 sets the control temperature or control point for the bimetal 19.

During operation, the bimetal will be in the position shown in FIG. 1 until the temperature of the bimetal varies a predetermined amount away from the control temperature. At that time it will snap to its other extreme position; that is to the position in which the arm 21 carries the armature finger 25 into engagement with stop 27. The bimetal will stay in that position until the bimetal temperature varies from the control temperature in to the other direction a predetermined amount. Then the bimetal will snap so that the arm 21 quickly moves armature finger 24 into engagement with stop 26. With the particular thermostat shown, the bimetal is in its position for the room temperature to be getting warmer. It will stay in this position until the temperature of the bimetal rises above the control temperature or control point a predetermined amount.

Most residential house heating systems have such a temperature lag that, if the bimetal of the thermostat is allowed to respond totally to the room temperature, there will be an overshoot. In other words, if the bimetal turns off the house heating system when the room temperature reaches 72°, by way of example, the temperature in the room will actually rise somewhat above 72°. To overcome this problem it has become the practice to incorporate an anticipation heater in the thermostat, which heats the bimetal at a faster rate than the room or house temperature rises. Thus the bimetal will reach its control temperature before the room temperature reaches the control temperature and the heating system will be deactivated. Thus the overshoot inherent in the heating system will merely bring the room temperature up to the desired point.

An important aspect of this invention is to provide an improved bimetal and anticipation heater arrangement for a control such as a thermostat. Viewing FIGS. 1, 2 and 3 it will be seen that the anticipation heating assembly 28 is mounted upon and connected to the bimetal 19 by means of a strap 29 which is firmly connected to the arm 20 of bimetal 19 adjacent the return bent portion 22. The strap 29 includes a T-shaped section 30 which extends away from the arm 20 and has an elongated arm or portion 31 which extends generally parallel to the arm 20. A heater support 32 of suitable insulating material is attached to the elongated portion 31 adjacent its ends by rivets 33 and 34. A resistance heater 35 of a suitable uninsulated wire is wound about the support 32. One end 36 of the wire is secured to the support 32 by use of an opening 37 adjacent one end of the support 32 while the other end of the wire is wound about a stub shaft 38, forming a strain relief, and then is electrically joined to the end 39 of a supply conductor 40 by some suitable method such as soldering at an opening 41 in the heater support. In order to prevent the elongated portion 31 of strap 29 from shorting the heater, a strip of insulating material 42, such as a suitable insulating tape, is placed between the portion 31 and the heater 35.

A member 43 is pivotally connected to the strap section adjacent the bimetal 19 and extends outwardly under the heater 35. The member 43 is formed with a rider 44 which engages the wire forming the heater 35, so ta that, as the member 43 is pivoted the rider 44 moves across the wire and effectively connects a predetermined portion of the heater 35 between the bimetal 19 and the conductor 40. Member 43 also includes a pointer 45 which is return bent over the top of the heater assembly. This pointer cooperates with an indicator sheet 46 to show how much of the heater 35 is effectively connected into the circuit. To this end the sheet 46 may have indicia such as that indicated at 47 to assist in properly positioning the member 43. Since, as the portion of the heater connected is increased the instantaneous heating effect is increased, the member 43 may be used to calibrate the heating effect. This is desirable since the same basic thermostat may be used with a number of heating systems, and it is necessary to modify the effect of the anticipation heater from system to system. The present arrangement provides an adjustment for the installer which is easily made and sure in its effect.

It will be noted that the heater assembly 28 is mounted adjacent the return bent portion 22 of the bimetal and extends longitudinally between and generally parallel to the arms 20 and 21. With this arrangement the heat given off by the heater 35 is transferred to and through the bimetal 19 all the way around the return bent portion 22 and substantially out along both of the arms 20 and 21. This causes the bimetal to be quickly and evenly heated, as the heat given off by the heater is expeditiously and uniformly transferred to the bimetal. Because of the enhanced tan transfer of heat to the bimetal, the wattage input to the heater necessary to cause bimetal operation is greatly reduced. This greatly alleviates operating point droop of the thermostat. Also the expeditious and uniform heat transfer to the bimetal causes it to be heated more uniformly from operation to operation so that its reaction is more certain.

The uniform heating of the bimetal is also assisted by making the bimetal 19 a three layer element in which the center layer is a good conductor, such as copper, and is sandwiched between outside layers of typical bimetal materials. The copper, being a very good heat conductor, assists in quickly and uniformly transferring the heat throughout the bimetal structure. Also, as will be understood the bimetal 19 is an electrical current carrying member, conducting current from the tab 16 to the strap 29. Thus all three layers of the bimetal, in the embodiment illustrated, must be electrical conductors. However it will be understood that other bimetal constructions may be utilized in this control and the term bimetal is used in its broad sense, indicating a device which bends or deforms in response to a temperature change.

The yoke or armature 23 cooperates with a switch 47 for controlling the associated heating or cooling system. When the armature 23 is in the position shown it causes the switch to assume one setting or configuration and, when the armature is in its other position, that is with the finger 24 adjacent the switch 47 and the finger 25 against stop 27, the switch is caused to have another setting or configuration. The switch in turn provides a signal to the associated heating or cooling system dependent upon its configuration or setting.

Referring now particularly to FIGS. 5 through 11 there is shown, in greater detail an exemplification magnetic switch 47 used in the new and improved thermostat of FIGS. 1--4. The switch 47 includes a sealed housing 48 of suitable nonmagnetic material such as glass. Three leads 49, 50 and 51 extend through the housing at one an end and are sealed therein. Within the housing a body of suitable insulation material 52 is formed around all three leads, giving them further structural stability and insuring that they are spaced apart so as to be electrically insulated. Leads 49 and 50 terminate in stationary contacts 53 and 54 respectively. Lead 51 extends axially beyond the contacts 53 and 54 and then is bent so as to have a termination 55 which is in axial alignment with the space between the stationary contacts 53 and 54. A U-shaped conductor 56 is mounted about the lead 51 and includes a lanced tongue 57 which is attached to the termination 55 so that the conductor 56 may pivot about the termination 55. One distal end of the conductor 56 extends between the stationary contacts 53 and 54 and is formed with a double contact structure 58, disposed selectively to engage the stationary contacts 53 and 54. The other distal end of the conductor 56 has its top portion cutaway to form a pair of opposed side arms 59 and 60. These arms firmly engage a generally cylindrical permanent magnet 61. Thus the lead 51, conductor 56, double contact 58 and permanent magnet 61 form a movable contact structure 62 with the permanent magnet 61 forming a distal portion thereof. In order to make the termination 55 and lances tongue 57 a stable pivot and to prevent excess vibration of the movable contact structure 62, a stabilizing member in the form of a leaf spring 63 is provided. A central bight portion 64 of the spring is attached to the termination 55 on the opposite side from tn tongue 57. A pair of arm portions 65 and 66 angle outwardly away from the central bite 64, with the arm portion 66 passing through an opening 67 in the conductor 56. As best seen in FIG. 9, the distal ends of the arms 65 and 66 each engage the inner surface of the housing 48. This arrangement serves to center the termination 55 and tongue 57 for proper pivoting movement of the movable contact structure 62 during switch operations. At the same time it provides a fairly stiff yet somewhat resilient securing means preventing damage to the movable structure at such times as during shipping.

The magnet 61 moves, as a result of magnetic attraction, between the extreme position shown in FIG. 7, in which contact 58 engages stationary contact 54, and its other extreme position, in which contact 58 engages contact 53. In the thermostat shown in FIG. 1 the magnet attraction is provided by the yoke or armature 23 which is of ferromagnetic material. Thus, when finger 25 is moved adjacent the edge of the housing 48, the magnet 61 is attracted to the position shown in FIGS. 1 and 7. By the same ta token, when the finger 24 is moved adjacent the housing 48, the magnet is attracted to its other position. It will be understood that it is not necessary to have the magnet 61 and armature 23 as shown in order to provide a switch which is selectively operated. For instance, the magnet 61 could be replaced by a cylindrical or flat armature of ferromagnetic material and the fingers 24 and 25 could be replaced by small permanent magnets.

With any of these general forms of magnetic switch constructions the movable contact structure tends to rebound or bounce. In the switch illustrated the contact 58 will tend to bounce from or rebound from the contacts 53 or 54 upon initial engagement as the magnet 61 is attracted between its extreme positions.

To damp such rebound or bounce, a generally cylindrical damper 68, of nonmagnetic material, is mounted loosely about the magnet 61 so that there is some space therebetween, as illustrated at 69. In the exemplification the damper 68 includes a cylindrical sidewall 68a which fits along the magnet 61 and an end wall 68b which extends across the free end of the magnet. This cup shape of the damper prevents the damper moving the left along the magnet. Also the sidewall 68a is longer than the distance from the end of the magnet 61 to the end of the housing 48. This prevents the damper coming off the end of the magnet during shipping or other handling. For operation, the switch preferably is mounted with the distal end of the magnet 61 elevated at least slightly relative to its pivot. It may even be mounted so that the movable contact structure 62 pivots about a vertical axis. With this arrangement gravity assures proper contact between the magnet and the damper. As the magnet moves between its extreme position, it will positions, it will cause the damper to move with it; however, there will be lost motion between the magnet and the damper. This lost motion results in an operation such that, after the movable contact structure reaches its extreme position, with contact 58 engaging either contact 53 or contact 54, and is rebounding or bouncing, the damper 68 will collide with the magnet. The best damping results are obtained by sizing the magnet and damper to provide the degree of lost motion between them that the collision between them occurs approximately as the movable contact structure begins to rebound.

Viewing FIGS. 10a--10e and 11a--11e there is illustrated diagrammatically certain of the relative positions between the magnet and the damper of the switch illustrated in FIGS. 1 and 5 through 9, when it is mounted as illustrated in FIG. 1. FIG. 10a shows the magnet and damper at rest with the armature finger 25 closely adjacent to the switch. When the armature moves from the position shown in FIG. 10a to that sown in FIG. 10e the magnet is drawn downwardly and moves through the damper to engage its lower portion, as viewed in FIG. 10b. FIG. 10c shows the situation at some time when contact 58 is in midposition (that is not engaging either of the fixed contacts 53 and 54). At this time the magnet is driving the damper. In the view of FIG. 10d the contact 58 has engaged the contact 53 and the magnet is decelerating. While it still has some velocity that velocity is small compared to the velocity of the damper, which has not encountered any decelerating force up to this point. FIG. 10e shows the situation at the point where, due to the resiliency of the movable contact structure, the magnet is moving up as a result of the energy stored during deceleration. The damper is still moving down so that the magnet and the damper collide or engage. This collision dissipates at least a large portion of the energy of the movable contact structure. There may be a small number of collisions as the magnet and damper tend to vibrate about the collision point, however most of the energy is dissipated by the first collision.

It will be understood that, with an ideal design of elements the motion of the magnet and thus the movable contact structure would be stopped completely on the first impact. However due to various structural and material limitations this may not always be possible. However, in any event, the damper may be made much more efficient than prior art devices which relied upon some resistance or friction for keeping the speed of the movable contact slow. It is quite important to provide correct differences in diameter between the damper and the corresponding distal portion of the moving contact structure so that collision takes place approximately as the corresponding portion of the movable contact structure, in this case the magnet, begins rebounding. Also maximum damping will be obtained by making the damper as heavy as possible within the available space and energy limitations of the switch.

FIG. 11a through FIG. 11e show the corresponding positions and relationship of the armature, magnet and damper as the magnet is moved in the opposite direction, that is to have the contact 58 from the contact 53 to the contact 54.

Referring now to FIG. 5 and completing the description of the switch 47, three conductors, such as those illustrated at 70, 71 and 72 may be attached to the leads 49, 50 and 51 respectively by some suitable means such as welding and then the connections enclosed within a protection covering or cap such as that shown at 73.

Referring now to FIG. 4, there is shown a schematic diagram for a circuit for use with the thermostat of FIG. 1, including the switch of FIG. 5, to provide control for both heating and cooling. Three terminals 74, 75 and 76 are provided. Terminal 74 is the common terminal while 75 is used for heat control and 76 is used for cooling or air-conditioning control. Conductor 72 extends from the terminal 74 to the lead 51, conductor 72 71 connects the lead 50 to the bimetal 19, and conductor 70 connects lead 49 to a terminal 77. The bimetal heater 35 is connected by conductor 4 40 to a terminal 78. A terminal 79 is connected to the cooling terminal 76 and a terminal 80 is connected to the heating terminal 75. The selector switch 5 is of a the double-pole type so that, in the position shown in solid line in FIG. 4, it interconnects terminals 78 and 80 to complete the heating circuit, while in the dashed line position, the terminals 78 and 80 are open and switch 5 connects the terminals 77 and 79 to complete the cooling circuit. Assuming the switch 47 is in the position shown, that is with contacts 54 and 58 closed, a circuit is completed from the common terminal through the conductor 72, the movable contact 58, the stationary contact 54 and the conductor 71 to the bimetal 19. The electrical circuit then extends through the arm portion 20 of the bimetal 19 to the anticipation heater 35 and then through the conductor 40, contact 78, switch 5 and contact 80 to the heating terminal 75. Thus, as long as the contacts 58 and 54 are closed, the circuit is completed to provide a heat-on signal to the heating system and to energize the anticipation heater 35. When the anticipation heater 35 has caused the temperature of the bimetal 19 to rise above the operating point set by the cam 12, the bimetal arm 21 moves so that the finger 24 is brought adjacent the switch 47 and finger 25 is moved away from the switch. This causes the movable contact structure 62 of the switch to move to its other position, disengaging contact 58 from contact 54 and engaging it with contact 53. This effectively turns off the anticipation heater and also provides a heat-off signal to the heating system. The closing of contacts 58 and 53 have not effect on the cooling circuit because the terminals 77 and 79 are open.

The thermostat then begins to cool and when it has cooled sufficiently, it will move back to the position shown in FIG. 4, again closing contacts 54 and 58. The them thermostat continues to cycle in this manner so that that the heating system maintains the room temperature at that set by cam 12 and adjusting knob 13.

The control circuit extends through the arm 20 of the bimetal 19; however, the good conductivity of the coop copper inner layer causes it to have very little heating effect on the bimetal and the heating of the bimetal remains essentially uniform even though no current flows through arm 21. Also, the schematic of FIG. 4 shows conductor 71 being connected directly to bimetal 19. While this is suitable connection, in the thermostat of FIG. 1 conductor 71 is connected to arm 6. Arm 6 is made from a conductive material and effectively carries the current to the bimetal.

When a cooling control is desired, the switch 5 is moved to the dotted line position so that terminals 78 and 80 are open and terminals 77 and 79 are closed. Then the circuit extends from the common terminal 74 through the conductor 72 and lead 51 to movable contact 58 and stationary contact 53. From stationary contact 53 the circuit extends through the lead 49, conductor 70 to the terminal 77, switch 5 and terminal 79 to the cooling terminal 76. A second circuit extends from common terminal 74 through a cooling anticipation heater to terminal 77. When the contacts 53 and 58 are engaged, the cooling anticipation heater 81 is effectively shorted from the circuit, and an on signal is provided to the associated cooling or air conditioning system. When the contacts 53 and 58 are open, an off signal is provided to the air conditioning system. Also the anticipation heater 81 is energized. It normally is desired that the anticipation heating of the bimetal in cooling operations be much slower than during heating control. Therefore the heater 81 normally is located somewhat more remotely from the bimetal. In the thermostat of FIG. 1 for instance it could be located on the underside of base 2 and connected to the rivet 7 so that the heat is transferred from the resistance 81 through the rivet 7 and elongated member 6 to the bimetal 19.

Also during cooling operations the closing of contacts 54 and 58 has no effect on either the heating system or the anticipation heater 35 since they are both effectively disconnected from circuit by the open terminals 78 and 80.

It will be understood that the control illustrated is a simplified version which has been shown to illustrate the construction and operation of the present invention. Various components having no relation to the invention have been omitted. For instance, thermostats for controlling both a heating and a cooling operation quite often have a separate selector switch for selectively causing the associated fan to operate either automatically only in conjunction with the heating or cooling system or to operate continuously. Also the thermostat has been illustrated as the type providing a heating and a cooling operation and the switch 47 has been illustrated as a single-pole double-throw switch so as to more completely describe the various aspects of the present invention. If it is desired to provide a thermostat for controlling a single operation, such as heating, a single-pole single-throw switch provided in conjunction with the other components of the thermostat would be sufficient. The switch best illustrated in FIGS. 5 through 9 may be modified to have a single-pole single-throw operation merely by eliminating one of the stationary contact structures and substituting a dummy structure therefor.