US2750473A - Sensitive snap-acting room thermostat - Google Patents

Description

June E, i956 M. c. KILEY 7%473 SENSITIVE SNAP-ACTING ROOM THERMOSTAT Filed May 17, 1954 2 Sheets-Sheet l June 1956 M. c. KILEY 2,750,473

SENSITIVE SNAP-ACTING ROOM THERMOSTAT Filed May 17, 1954 2 Sheets-Sheet 2 l Zy\ Z4? 2g i i g 's l l 'f .5@ g 32 5 g jm gg ,l In" 35 t u Tg() l 50 lgg Z0 United States Patent SENSITIVE SNAP-ACTING RUOM THERMOSTAT Martin C. Kiley, Evanston, lli.

Application May 17, 1954, Serial No. 430,089

7 Claims. (Cl. 269-138) 'Ihe present invention relates to the art of thermostatic switches of the type commonly termed room thermostats.

One of the objects of the present invention is to provide a novel room-type thermostat in which the electrical contacts have a snap action and in which the differential between the snap-on and snap-oi temperatures is small and easily adjustable.

An additional object is-to provide an improved room thermostat of the above character in which no magnets nor anticipation heaters are needed.

Yet another object is to provide a novel precision snapacting room temperature sensing thermostat having the above characteristics which operates upon a new principle that makes it unnecessary to fabricate the elements of the thermostat within the precise limits ordinarily required.

Other objects and advantages will become apparent from the following description of a preferred embodiment of myY invention which is illustrated in the accompanying drawings.

In the drawings, in which similar characters of reference refer to` similar parts throughout the several views:

Fig. l is a vertical sectional View taken just inside the case of the thermostatic unit so as to show the operating elements in elevation;

Fig. 2 is a Vertical sectional View which may be considered as taken in the direction of the arrows substantially along the line 2 2 of Fig. l;

Fig. 3 is a horizontal sectional View taken along the line 3 3 of Fig. 1 looking upwardly as indicated by the arrows;

Fig. 4 is a fractional sectional View taken in a vertical plane substantially along the line 4 4 of Fig. 1 in the direction indicated by the arrows;

Fig. S is a horizontal' sectional view taken in an upwardly direction as indicated by the arrows, along the line 5 5 of Fig. 1;

Fig. 6 is a fractional sectional View which may be considered as taken in the direction of the arrows substantially along the line 6 6 of Fig. 1; y

Fig. 7 is a horizontal sectional view of a detail and is taken in the direction of the arrows along the line 7 7 of Fig. l;

Fig. 8 is a vertical sectional View on a much enlarged scale, showing a detail of the construction. This ligure may be considered as taken along the l-ine 8 8 of Fig. 3 in the direction indicated by the arrows;

Fig. 9 is a fractional sectional view on a greatly enlarged scale which may be considered as takenvin the direction of the arrows substantially along the line 9 9 ofFig., 8; and l Fig. 10` is a greatly enlarged fractional sectional view of the electrical contacts and snap-acting mechanism and may be considered as taken in the direction of the arrows along the line 10 10 of Fig. 1.

Room thermostatsY are ordinarily providedto control heating systems in many applications. Essentially they comprise a bimetal element which operates one or more sets of contacts such that these contacts open or close as the temperature of the space varies with reference to some selected temperature. Usually also some arrangement, such as permanent magnets for instance, is used so as to insure that the contacts positively open or close even though this expedient has the disadvantage of usually introducing a considerable differential between the temperature at which the contacts open and the` temperature at which they reclose. This disadvantage is frequently overcome, to some extent at least, by using anticipation heaters which apply some heat to the bimetal actuator in addition to that supplied by the ambient air. The result is that conventional thermostatic units of this general character are comparatively expensive.

The present invention is illustrated in an embodiment which has a single set of contacts which are either opened or closed, depending upon the ambient temperature as compared with some selected setting. It will be appreciated, of course, that additional contacts can be arranged to be operated by the actuating element if desired.

Referring to the drawings, the device there shown comprises a generally rectangular sheet metal base plate 20 having the operating elements attached thereto, these operating elements being enclosed within a sheet metal cover 22 which is attached to the base plate at the sides thereof. Near its center line and toward the upper end of the base, a spiral bimetal element 24 is shown with its inner loop 26 embracing the outer end of a threaded stem 2S. lt is secured rigidly to the system by outer and inner clamping nuts 3) and 32 respectively.

Beyond the inner nut 32, the stem 28 passes through a hole in a LZ-shaped sheet metal bearing forming member 34 which is attached to the base by means of rivets 36, and thence through a rectangular arm 3S to which the stem 28 is secured by a setscrew 40. The inner face of this arm 38 lies at against the outer surface of the base plate 20 and the stern 28 extends therethrough and has its end provided with a washer and head as indicated at 42.

The arrangement therefore is such that the stern 23 is free to rotate relative to the base 2i) and bearing forming bracket member 34 and that as this stem rotates it carries with it the arm 38 and the inner turn 26 of the bimetal spiral element 24.

The arm 38 extends generally upwardly from the stem 28 and is arranged so that near its upper end its left-hand face, as seen in Fig. l, bears against the end of a coil spring 44, the opposite end of which is fixed to a spring base 46. This spring base is comprised of a tab of the sheet metal of which the base is formed being bent outwardly so that it extends at right angles to the main portion of the base. In order to keep the spring 4d in alignment, its ends embrace short cylindrical plugs 48 and 50 which are secured, respectively, to the spring base 46 and to the pivotal arm 38.

The characteristics of the spring 44 should be such that it has a strongftendency to rotate the upper end of the arm 38 toward the right so as to cause the stem 28 to turn in a clockwise direction. This torque exerted by the spring 44 should be considered greater than any counter torque that can be developed by the spring action of the spiral element 24.

Near the righthand upper portion of Fig. 1 it will be seen that there is a block S2 which is secured to the base 2@ so as to project outwardly therefrom, and that this block is internally threaded to take a threaded stern 54 the right hand end of which projects out through a slot in the cover 22. Outwardly of the cover this stern is secured to a dial 56 graduated around its circumference with numerals indicating temperatures to be selected. The left hand end of the threaded member 54 bears against the flat head of a screw 58 which is threaded through the arm 38. The opposite end of this screw is provided with a screw driver slot 60 by means of which the screw 58 can be moved toward the right or left. In order to keep it in any certain position, a comparatively short stiff coil spring 62 is arranged to surround the screw 58 and to bear with one end against the left hand face of the screw head, while its other end bears against the right hand face of the arm 38.

By adjusting the position of the screw 68 by means of a screw driver inserted into the slot 60, the position of the arm 38 and hence of the stem 28 can be predetermined, since the spring 44 will always keep the head of the screw 58 against the left hand end of the threaded member 54. Similarly, turning the dial 56 will also move the arm 38 in a clockwise or counterclockwise direction. Thus, the dial 56 can be set to a certain reading and the screw 58 can then be adjusted so as to give a correct starting position for the spiral bimetal element 24. Thereafter, ordinarily the screw 58 needs no further adjustment and the position of the arm 38 will be determined entirely by the setting of the knob 56. The clamping of the arm 38 between the end of the threaded stem 54 and the rather stiff spring 44 at a higher position tends to swing the stern 28 toward the left and these elements thus serve to hold the arm 38 and stern 28 rigidly so that there is no wobble in the mechanism even though the lit of the stem 28 in the base plate and bracket 34 is not precise.

The outside end 64 of the bimetal element 24 is secured, for instance by means of rivets 66, to a downwardly extending insulating strip 68 so that as the temperature of the bimetal element 24 changes, or as the position of the dial 56 is changed, the lower end of the strip 68 will be moved toward the right or left as seerr in Fig. l.

An electrical contact 70 is secured to the lower end of a comparatively soft acting spring metal strip 72, the upper end of which is connected by means of rivets 74 to the right hand face of the strip 68 in a position somewhat below the outer end 64 of the bimetal element 24. The rivets 74 also form an electrical connection between the contact carrying strip 72 and a pigtail lead 76, the opposite end of which is secured to a pin '78 which is attached to a metal terminal block 80. This block is mounted upon an insulating strip 82 secured to the base 20 by means of screws 84. An electrical connection is made to the terminal block 80 by means of a terminal screw 86 which extends through a clearance hole in the base 20, there being an insulating strip 88 between the back of the base 20 and the head of the screw 86.

The contact '70 faces toward the right as seen in Fig. l and is positioned to engage a contact at the end 90 of a screw 92 which is threaded through an L-shaped sheet metal bracket 94 secured to the insulating strip 82 by means of rivets. The bracket 94 also acts as an electrical terminal block and is provided with a terminal screw 98 in a manner substantially identical to that used for the terminal screw 86.

From the above it is apparent that when the bimetal element moves the insulating strip 68 so that its lower end is urged toward the right a sufficient distance, the contact 70 will come against the contact 90 thereby closing an electrical circuit between the terminal screws 98 and 86. Conversely, a change in temperature of the bimetal element 24, which causes the lower end of the insulating strip 68 to move toward the left, will separate the contacts 70 and 90 thereby opening an electrical circuit between the terminal screws 86 and 98. Because of the considerable length of the bimetal element, this action can be accomplished with a minor change in temperature.

Near its lower end the insulating strip 68 is secured to a post or knob 100 which projects toward the left for a short distance. This knob is threaded to receive a screw 102 which extends transversely therethrough in a direction at right angles to the plane of the base 20. The screw 102, therefore, can be adjusted so that its inner end 104 is moved toward or away from the base 20 and in a selected positionV it can be locked by means of a setscrew 105 which extends into the post 100 at right angles to the screw 102.

As is best seen in Fig. l0, the inner end of the screw 102 is formed to provide a truncated cone having a socket in the end thereof to receive a small steel ball 106. This ball may be considered as being identical with those which are commonly used in ball point pens, and preferably is similarly secured so that it is free to rotate within its socket.

The lower end portion of a comparatively stiff spring leaf 108 is situated directly behind the ball 106. From this position the leaf 108 extends upwardly as seen in Fig. l, and has its upper end anchored to a block 110 which is secured to the base 20. The leaf 108, therefore, lies substantially parallel to the base 20, but in a position somewhat outwardly therefrom. At about the midpoint of the spring leaf 108, its inner face rests against the end of a screw 112 which is provided with a knurled adjusting knob 114 near its center. This screw 112 has its inner end passed through a guide hole in the block 110, the block being slotted to provide clearance for the adjusting knob 114. The outer end of the screw 112 is threaded through a removable strip 116 which forms a portion of the base 110, this strip being secured thereto by the same screws 118 and 120 which attach the spring metal member 108 to the base 110. By rotation of the knurled knob 114, the upper end of the screw will act to move the free end of the spring metal blade 108 outwardly or inwardly with respect to the ball 106 at the end of the screw 102.

Conveniently, one of the screws, the one indicated at 120 in the drawings for instance, which attach the blade 108 to the base 110, can have an outward extension surrounded by an insulating plastic sleeve 122 which acts as a stop to limit motion of the insulating strip 68 toward the left to a reasonable range.

The Elower end of the blade 108 is encased in a molded plastic covering forming a generally at shoe indicated at 124. Although several plastics are suitable for this purpose, I have found that those having a high order of wear resistance together with a slight resiliency are highly satisfactory. For the purpose, such polyamide resins as nylon, for instance, have been found to be very well qualified. The plastic coating 124 has its outer surface formed, during the moulding operation, to provide very ne grained corrugations as indicated at 126. These corrugations or ridges extend vertically, as seen in Fig. l, and need cover only the outer surface, that is, the surface directly beneath the ball 106. The positioning of the lower end of the strip 108 is such that the ball 106 rests against the corrugated surface 126 so that as the strip 68 is moved from right to left to close and open the contacts 70 and 90, the ball 106 will roll across the corrugations 126.

Because of the flexibility of the spiral bimetal element 24 in the fore and aft direction, the ball 106 will always be positioned in one of the troughs in the corrugated surface 126. It will be understood that each ridge of the corrugated surface 126 rises between two adjacent trough portions of the corrugated surface formed by support surfaces merging with the base of the ridge at opposite longitudinal sides thereof. As shown in Figs. l and 3, each ridge of the corrugated surface 126 is generally parallel to the medial plane of the spiral element 24 and generally symmetrical to a plane extending into proximity to the radially inner end of the element. As the temperature of the bimetal element 24 is changed so as to cause the lower end of the insulating strip 68 to tend to move toward the left for instance, the contact 70 and strip 68 will not be permitted to move until suicient force has been developed in the bimetal element 24 to cause the ball 106 to roll over the hump formed by one of the corrugations 126 into the next trough. As

this rolling motion takes place, the ball 106 will move outwardly with respect to the comparatively stiff spring blade 108 and this motion is possible because of the inherent high order of fiexibility of the spiral bimetal element 24.

The amount of force which must be stored in the bimetal element 24 before the ball 106 is snapped from one of the troughs to the next trough, is determined by the position of the lower end of the spring metal blade 108 and therefore this can be adjusted by turning the adjusting knob 114 inwardly or outwardly. Thus the angular position of the knob 114 will determine the temperature differential between the point at which the contacts 70 and 90 snap open and snap closed. Conveniently, therefore, the outer face of this knob can -carry indicia such as the numerals shown near the rim thereof in Fig. l, so that the instrument can be preset to give a desired differential between its opening point and its closing point. These numerals indicate on the device shown that a temperature differential of one, two, three, or four degrees Fahrenheit can be obtained by properly positioning the knob, and of course intermediate differentials can be obtained by interpolation.

The adjustable knob 114 may be pre-set to any desired indicated differential, after which adjustment of the screw 102 can be made until the differential between the opening and closing points for the contacts 70 and 90 is the same as that indicated. Thereafter, no further adjustment of the screw 102 is necessary.

Arcing is reduced and it is not necessary that the spacing between the contacts 70 and l90 be precisely adjusted because of the flexibility of the strip 72 which carries the contact 70. Referring to Fig. 10, it will be seen that as the ball 106 rolls from the trough where it reposes to the next trough to the right thereof, the distance thus traveled by the contact 70 would be greater than the spacing between the contact 70 and the contact 90. Therefore, the contact 70 is brought against the -contact 90 before the ball 106 reaches the next trough. Additional movement of the ball 106 beyond the point Where the contacts first touch acts to compress the spring strip 72 thereby holding Contact 70 against contact 90 under the Vspring pressure developed in the member 72. Conversely, when the ball 106 snaps toward the left by an amount equivalent to the spacing between `successive troughs in the corrugated covering 124, .some motion of the insulating strip 68 will take place before the contact 70 is snapped away from the contact 90. The contacts, therefore, make and Ibreak at high speed after the carrier for -contact 70 is already in motion, thereby greatly reducing the problem of arcing which is a commonly encountered di'iculty in room thermostats.

From the above description of a preferred embodiment which is illustrative of my invention it will be appreciated that changes can be made without departing from the scope or spirit thereof. The scope of the invention therefore is to be measured by the scope of the following claims.

Having described my invention, what I claim as new and useful and desire to secure by Letters Patent of the United States is:

l. A room thermostat comprising a fixed contact, a movable contact, a spiral bimetal element, means fixing one end of said bimetal element, spring means secured to the free end of said bimetal element and to said movable contact, said spring means being more readily deformable than said bimetal element, a ball, means securing said ball rotatably to said bimetal element at the free end thereof for movement therewith, means forming a -corrugated surface, means to support said corrugated surface in contact with said ball so that said ball rolls over the corrugations on said surface as the free end of said bimetal element moves, and the lspacing between adjacent corrugations on said surface being greater than the spacing between said contacts after said bimetal element has moved said ball from one corrugation to the next corrugation in contact opening direction under conditions where such degree of movement is suicient to separate lsaid contacts.

2. A room thermostat comprising a fixed contact, a movable contact, a spiral bimetal element, means fixing one end of said bimetal element, means securing said movable contact to said bimetal element for movement thereby, a rotatable ball, means securing said rotatable ball to said bimetal element for movement therewith, means forming a corrugated surface, and means to support said corrugated surface in contact with said ball so that said ball rolls over the corrugations on said surface as the free end of said bimetal element moves.

3. A room thermostat including a spiral bimetal element, means fixing one end of said bimetal element, a rotatable ball, means securing said rotatable ball to said bimetal element for movement therewith, means forming a corrugated surface, means to support said corrugated surface in contact with said ball so that said ball rolls over the corrugations on said surface as the free end of said bimetal element moves, and means to vary the mutual pressure between said ball and said surface.

4. A room thermostat comprising a base, a contact fixed with respect to said base, a movable contact, a spiral bimetal element, adjustable means fixing the center of said bimetal element to said base, spring means secured to the free end of said bimetal element and to said movable contact, said spring means being more readily deformable than said bimetal element to permit limited displacement of said movable contact Without producing appreciable movement of said free end, a ball, means securing said ball rotatably to said bimetal element at the free end thereof for movement therewith, means forming a corrugated surface of a polyamide resin, means secured to said base to support said corrugated surface in contact with said ball so that said ball rolls over the corrugations on said surface as the free end of said bimetal element moves, and the spacing between adjacent corrugations on said surface being greater than the spacing between said contacts after said bimetal element has moved said ball from one corrugation to the next corrugation in contact opening direction under conditions where such degree of movement is sufficient to separate said contacts.

5. A room thermostat comprising, in combination, a base contact, a movable contact, a spiral bimetal element, means xing one end of said bimetal element, means securing said movable contact to said bimetal element for movement thereby, a rotatable member, means securing said rotatable member on said bimetal element for rotation thereon and movement therewith, means forming a corrugated surface, and means to support said corrugated surface in contact with said rotatable member so that the latter rolls over the corrugations on said surface as the free end of said bimetal element moves.

6. An adjustable thermostatic control device comprising, in combination, a bimetal control element having a spiral shape with reference to a medial plane thereof, a mount supporting the radially inner end of said bimetal element, means supporting said mount for rotary adjustment to precondition the control device to respond to a change in temperature at various temperature levels as determined by the rotary position of the mount, a rst contact mounted on the radially outer end of said bimetal element for movement thereby as an incident to changes lin temperature thereof, a second contact mounted in opposing relation to said first contact, a shoe defining a substantially straight ridge generally parallel to said medial plane of said element and generally symmetrical to a plane extending into proximity of said radially inner end of said bimetal element, said shoe defining support surfaces on opposite longitudinal sides of said ridge merging with the base thereof, a rotatable member, and support means rotatably mounting said rotatable member on the free radially outer end of said spiral element for engagement with said shoe ridge or either of said shoe surfaces merging with opposite sides of the base of said ridge, said shoe being positioned with respect to said medial plane of said spiral element to apply a light force to said spiral element through said rotary member and supporting means therefor perpendicularly to said last mentioned plane.

7. A thermostatic control device comprising, in combination, a bimetal control element having a spiral shape with reference to a medial plane thereof, a mount supporting the radially inner end of said spiral element, a rst contact mounted on the radially outer end of said spiral element for movement thereby as an incident to changes in temperature thereof, a second Contact mounted in opposing relation to said irst'contact, a shoe dening a substantially straight ridge generally parallel to said medial plane of said element and oriented generally perpendicularly to the direction in which the outer end of said spiral element moves as an incident to changes in temperature thereof, said shoe defining support surfaces on opposite longitudinal sides of said ridge merging with the base of the ridge, a rotatable member, and support means rotatably mounting said rotatable member on the free radially outer end of said spiral element for engagement with said shoe ridge or either of said shoe surfaces merging with opposite sides of the base of said ridge, said shoe being positioned with respect to said medial plane of said spiral element to apply a light force to said spiral element through said rotatable member and said support means therefor perpendicularly to said last mentioned plane.

References Cited in the le of this patent UNITED STATES PATENTS 1,612,114 Hall Dec. 28, 1926 2,020,538 Denison Nov. 12, 1935 2,602,129 Valverde July 1, 1952

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