US2283075A - Thermostat - Google Patents

Description

May 12, 1942. H. D. MATTHEWS THERMOSTAT Filed April 11, 1940 1 WW mo. h 1 D m M o. H

wa /5 W M Pinned May UNITED STATES PATENT OFFICE THERMOSTAT Howard D. Matthews, Minneapolis, Minn., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware I Application April 11, 1940, Serial No. 329,125

' 2 Claims. (c1. 297-16) The present invention relates to motion comof minor convolutions A, B, etc. to Y and Z. The

pensating means for a condition responsive demlnor helix is then wound Into a majorv helix. vice, and more particularly to the structure of Asshown in the drawing, the minor helix is rightsuch a device. hand wound the the major helix is left-hand Condition responsive devices, and more partic- 5 wound. It will also be noted that the two arcuularly bimetallic temperature responsive eleate ends II and I2 are also left-hand wound.

ments, which are subjected to mediums which A motion takeoiT arm 13 is provided onthe end contain impurities, quite frequently become sticky I 2, and a suitable mounting arm I4 is formed due to deposits of these impurities which impede from the other compensating end H.

, the operation thereof. Particularly when the el- In winding the'compound coiled member there ements are confined upon sliding guides does this are three factors to be considered: The first faccondition prevail. With present condition retor concerns the side of the minor convolutionssponsive elements of the compound coiled type, which is the high expansion metal. If the high as shown in United States Patent No. 2,121,259, expansion metal is on the inside of the minor and French Patent No. 710,481, and utilized-to l5 convolutions, these convolutions will expand sticky because of continued exposure to impurihelixis wound, If the minor helix is right-hand ties, but in many adaptations appreciably reduce Wound, d the interior metal of e me al s the eificien'cy of the element, even when perfectly the high expansion metal, the helix will rotate clean, because of sliding friction. angularly in a counter-clockwise direction when It is an object of this invention to obtain optiheated; and if left-hand wound, the rotation will mum efiiciency in a compound coiled, axially be clockwise. Obviously, if the'high expansion movable condition responsive element, by commetal Were placed 1 the t d of the m nor the appended claims, tor concerns the direction in which the major I th drawing; 3O helix is wound and, in combination with the 01:11- Figure l is an elevational view of any device, er two factors, determines the angular direction Figure 2 is an end view looking atthe left d of movement of the entire portion ll] of the'temof Figure 1, and

Figure '3 is a diagrammatic view to illustrate fu y de ed later. that w n ny one of these the method of'computing linear movement of a three factors is reversed, the axial movement of compound helix.

Referring now more particularly to the drawthat if two factors are changed, the axial moveing. Thecondition responsive element is shown ment W not b C an d. as comprising a compound coiled helix generally Assume r p that t interier'metal indicated by the reference character I0. Ends 40 0f the himetal s the high exp s n e a a d "H and [2 are provided and are adapted to comhe xt ri r m tal is the low expansion metal, pensate the center portion In for angular movethe minor helix being right hand wound and the ment upon changes in the condition'to which the J helix being. e ha Wound, as Show element responds. The entire element is com- Upon an increase in at e e vo u nsAto posed of two metals having difierent coefflicients Z Will tend t p P- It s a We nown of expansion which are suitably secured together. phenomenon i a fi i l bimetallic helix h t e I made of brass and mvar 1101'1 suitably welded toa d t X nds t e o ate axially 'I 'heregether. The brass is the high expansion metal 0 fore, upon an increase in temperature the first and the mvar iron is the low expansion metal convolution A of the minor helix will expand and However, many other metals may be used without this expansion will move the second minor helix departing from the spirit of the present inven- B toward the right as viewed in Figure 1. In tion.

thismaimer each of the convolutions in the en- The compound helix I0 is composed of a series tire compound helical member ID will move an I incrementtoward the poses the degree of stance corresponding right until the convolutions Y and Z of the minor helix are moved a substantial distance in this direction. For practical puraxial movement may be computed by considering the expansion of only one of the convolutions of the minor helix as it would be plotted from a projection of a cross section of one convolution taken perpendicular to the longitudinal axis thereof. lt has been found that the opposite convolution of the major helix will be moved a distance corresponding to the distance which it would have been moved by the minor convolution if the connecting convolutions were considered asbeing a link. To more clearly disclose this principle of computation a diagrammatic Figure 3 is shown in the drawing. In this figure a convolution c may, for practical purposes, be considered as mounted upon a fixed support d. The free end of the: minor convolution c carries a link e which is connected to an upperv convolution f and separates the two convolutions a distance equal to the diameter of the major helix. In the position shown in full lines for the link e the bimetallic members are in their cold position. When the convolutions of the temperature responsive element heat up the link e might be assumed to move through an angle a: for a given temperature change and will assume the dotted line position e. Therefore it is seen that the upper convolution f is moved through an angle which a single bimetal would impart to the convolution f it the convolution 0 were considered as a simple bimetal loop and the connection e were a solid link. The upper convolution f for the same temperature change will expand an amount substantially equal to the amount of expansion of the convolution 0, hence a lower convolution connected to the convolution I would be moved in a straight line substantially perpendicular to the link e. It will be seen that the expansion of a complete convolution of 'the major helix of the temperature responsive element may be computed by plotting the movement which would be imparted by a single minor convolution in moving an upper convolution a disto a distance that the upper convolution would be moved it the two convolutions were rigidly connected by means of a link.

When the temperature responsive element l0 is subjected to a rising temperature the convolution A will axially elongate, hence moving the convolution B a slight distance away from the convolution A. Likewise each of the convolutions in the minor helixfrom A to Z will separate from each other, and the entire minor helix will be substantially elongated. This elongation will result in a wrapping up movement in the convolutions Y and Z assuming that the mounting arm M is securely fixed. In addition to the angular movement caused by the minor helix there is also a substantial angular movementinherent in the major helix.

To compensate for the angular movement of the compound helix In the arcuately shaped bimetallic pieces II and 12 are disposed at either end thereof and have the high expansion metal also on the inside of the convolution to impart an unwrapping movement to the entire element upon an increase in temperature. It will be understood that although ends II and i2 are both so adapted, that only one portion of the bimetal to be used to compensate the would actually need compound coil l0.

Upon cooling of verse of the above the bimetallic element the redescribed action will occur.

As has been previously'pointed out, the minor helix A to Z is right-hand wound. As a result of its being right hand wound the movement of each of the convolutions A to Z upon being heated was toward the right in respect to each other. It will be obvious, then, that if the convolutions are left hand wound the movement with respect to each other would be toward the left and the entire element [0 will contract axially. Whether the convolutions are either right or left hand wound the angular or rotative movement of the element H) as a result of temperature changes will be identical. If the high expansion metal is placed on the outside of the minor helix the action of the element In will also be reversed. The rotation of the element will likewise be in the opposite angular direction. However, if the minor helix is so wound, then the compensating ends will also have the high expansion metal on the outside and the element In will be compensated for rotative movement. Hence it is seen that the compensating ends H and I2 can compensate for angular movement helix whether it is adapted to expand or contract axially upon a given temperature change. If the major helix is right hand wound instead of left hand wound, as shown, the angular movement of the compound coil ID will be reversed. However, the compensating ends will also be reversed in the direction of wind and, hence, will compensate for angular movement of the temperature responsive element.

For the purpose of enabling others to practice my invention the accompanying chart is presented to show various forms which my temperature responsive element may take:

Thermostatic bimetal double helixes Movement with M h 1 M h l tincreaseto' mor our 2 01' out empera ure slde winding winding It will be noted that when different elements of the bimetal are reversed that the axial movement of the element is reversed and that also the winding or unwinding of the major helix is also effected. Where a very active element is desired either of the types shown in 1 or 2 of the accompanying chart may be used. These" bimetals will bevery sensitive to temperature changes inasmuch as the high expansion metal is on the outside of the minor helix and hence more exposed to the current of heated air or other medium to which the entire element is subjected. It will be noted that the type 1 opens when heated and type 2 closes when heated. If slow responsive elements are desired either of the types5 or 6 might be used where the high expansion metal is located on the inside or the minor helix, therefore making the helix respond more slowly to temperature changes. Other types may be selected as desirable for the uses to which they-are to be put. In all of the types charted there is an angular rotation of the double helix, the direction of which is'shown so that proper compensation may be provided.

of the compound While I have shown and described one form which my invention may take 'it will be apparent that many changes will occur to -those skilled in the art. Therefore it is to be clearly understood that I am to be limited only by the scope of the appended claims.

I claim as my invention:

1. A device of the HOWARD D. MATTHEWS.

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