US2068270A - Thermostatic switch construction - Google Patents

Description

Jan. 19, 1937.

G. E. HuLsE THERMOSTATIC SWITCH CONSTRUCTION Filed Jan. -26, 1935 I INVENTOR 610/9'65 f flags:

- ATTORNEYS Patented Jan. 19, 1937 UNITED STATES PATENT OFFICE THERMO STATIC SWITCH CONSTRUCTION Application January 26, 1935, Serial No. 3,610

2 Claims.

This invention relates to a thermostatic switch construction and more particularly to a thermostatic switch for use in refrigerator cars or the like.

One of the objects of this invention is to provide a construction of the above nature which is simple in construction and thoroughly practical. Another object is to provide a construction of the above nature which is amply strong to withstand rigorous use under difficult conditions. Another object is to provide a construction of the above nature which is inexpensive to manufacture, easy to install and when installed takes up but a small amount of space. Another object is to provide a construction of the above nature which is thoroughly efficient in operation and is accurately responsive to temperature variations. Another object is to provide a construction of the above nature which is able to withstand continued vibration induced by motion of a refrigerator car or the like without damage to any of the parts or without a change of the critical temperature setting. Another object is to provide a construction of the above nature the temperature responsive parts of which are in a condition of static balance. Other objects will be in part apparent and in part pointed out hereinafter.

The invention accordingly consists in the features of construction, combinations of elements, and arrangements of parts as will be exemplified in the structure to be hereinafter described and the scope of the application of which will be indicated in the following claims.

In the accompanying drawing in which is shown one of the various possible embodiments of my invention,

Figure 1 is a front elevation of the thermostatic switch, certain portions thereof being broken away;

Figure 2 is a sectional elevation of the switch taken along the line 22 of Figure l; and

Figure 3 is a horizontal section of the switch taken along the line 33 of Figure 2.

Similar reference characters refer to similar parts throughout the several views of the draw- As conducive to a clearer understanding of certain features of this invention, it might be well to consider some of the difficulties encountered in the use of temperature control apparatus such as a thermostatic switch in refrigerator cars or the like. Many of these switches when used in refrigerator cars operate inaccurately, this being due in most instances to the vibration of the car while in motion. Such vibration usually induces a sympathetic vibration of such magnitude in the temperature responsive coil that the making and breaking of circuits at certain temperature is not assured and often a circuit is not maintained continuously when desired. Also the critical temperature setting is often changed from the desired value and, in many instances, the thermostatic coil itself is damaged. This vibration, which may be induced by the vibration of the car when in motion or by the operation of refrigeration machinery, for example, is often accentuated because the coil assembly or other temperature responsive elements is not only in a condition of static unbalance but is characterized by a small moment of inertia. Often the localities of a car least affected by vibration are undesirable locations for this apparatus and it is therefore most desirable to have controlling apparatus which will operate effectively and accurately regardless of the vibrating condition which it may be subjected to. Another object of this invention is to obviate the above difiiculties in addition to many others.

Referring now to Figure 1 of the drawing, a thermostatic switch generally indicated at comprises a frame I I to which is secured a casing I2 provided with the usual knock-outs l3. Casing 12 contains suitable terminals or the like (not shown) for connection to the main circuit in which the thermostatic switch is to be installed. A face plate I4 is secured to the front of frame H and has attached thereto a pair of stationary contacts generally indicated at l5 and a temperature responsive coil assembly generally indicated at Hi, all as will be more fully described hereinafter.

As is more clearly shown in Figure 3, a bracket member generally indicated at I! is secured to face plate I 4 by a suitable screw l8 or the like. Bracket I! has outwardly extending arms Ila and I'll) the ends of which pivotally support a pin IS. A bimetallic thermally responsive coil generally indicated at 2B is secured to pin l9 so as to rotate or pivot therewith. The convolutions of coil 20 are formed preferably by. a pair of metallic strips 200 and 28d each having different coefiicients of expansion. Thus the coil preferably expands in response to a rise in temperature and contracts upon a decrease in temperature.

As is more clearly shown in Figure 1, coil 20 has an inner end 20a, this end being secured to pin [9; an outer end Zlib of the coil is secured in any suitable manner to an insulating block 2|. Block 2| also acts as a carrier for a contact arm 22 preferably of steel which is secured to the block by a screw 23. Screw 23 also secures a lead 24 to contact arm 22, contact arm 22 being provided with contacts 25 and 26, the purpose of which will be described hereinafter. Contact 26 is preferably mounted on a leaf spring 32 which is secured to arm 22 as by a rivet 22a, contact 26 extending through a hole 221) (Figure 2) in arm 22. A carrying block 21 or the like preferably formed of dielectric material is suitably secured to face plate I4 and has extending therefrom two poles 28 and 29 of a horse-shoe magnet generally indicated at 60 which is secured to block 21 in a manner to be described hereinafter.

Block 21 carries an adjustable stationary contact 30 suitably positioned to engage contact 25 on contact arm 22 when coil 20 expands under the influence of a rise in temperature. A contact 3| is mounted on a pin 3|a or the like which extends into block 21. Thus contact 3| is in the path of contact 26 on arm 22 contact 26 abutting against contact 3| upon the expansion of coil 20.

Contacts 26 and 3| rapidly engage before and disengage after contacts 25 and 30 in order to take the sparks at the making or breaking of the circuit and in this way protect main contacts 25 and 36 from injury by sparking. The rapid closing of contacts 26 is effected by the magnetic attraction of poles 26 and 29 on arm 22 when the arm comes Within the field of the magnet. Rapid disengagement is effected by the snap action of arm 22 breaking away from poles 28 and 29 when the tension of coil 26 resulting from a decrease in temperature overcomes the magnetic attraction of magnet 66. Leaf spring 32 allows contact 26 to move individually with respect to arm 22 to further insure that contacts 26 and 3| make or break before the main contacts 25 and 30 make or break.

A pin 34 (Figures 1 and 2) extends into block 21 and connects with contact 3|]. The end of pin 34 is threaded and receives a pair of nuts 35 (Figure 2) which clamps a bus bar 36 against the side of block 21. The other end of bus bar 36 fits over a pin or screw 36 which extends into block 21 and is held in that position by a nut 39 threaded on pin 38. Pin 38 holds magnet 5|] in position on block 21 and is connected to pin 3|a of contact 3|. Pin 38 also serves to carry the end of a lead 40 which is clamped between nut 39 and nut 39a. Thus one lead of the circult is established by way of contact 36 (Figure 1), pin 34, bus bar 36, pin 38, and lead 40. The other side of the circuit is established by way of lead 24 which has an electrical connection with a pin 4| which extends into block 21, a pair of nuts 42 and 42a (Figure 2) being suitably threaded on the end of pin 4| to clamp the end of a lead 43 therebetween. Thus, the other side of the circuit comprises lead 24, pin 4|, and lead 43. Leads 40 and 43 preferably extend through face plate l4 and frame II by way of a hole |4a into casing l2 and are connected to the main terminals therein.

It may now be seen that upon a rise in temperature bimetallic coil 20 expands to swing contact arm 22 to the right as viewed in Figure 1. Contact point 26 on arm 22 first engages contact 3| due to the magnetic attraction of magnet 60 when arm 22 enters its field thus to take the sparks which usually occur at the making or breaking of a circuit. Thereafter, main contacts 25 and 30 engage to establish the circuit. Until the temperature falls below a predetermined critical point, the above-mentioned contacts remain in engagement. Upon the car being cooled to the critical temperature, coil 26 contracts and the contacts are broken when the tension in coil 20 overcomes the magnetic attraction of magnet 60, main contacts 25 and 36 separating first and secondary contacts 26 and 3| separating thereafter as pointed out above. Thus, upon the breaking of the circuit, as upon the making thereof, any sparking which might ocour will occur between cont- acts 26 and 3|, accordingly protecting main contacts 25 and 36.

In order to set the thermo-responsive coil in a predetermined position and thus to establish the critical temperature at which the circuit is made or broken by the contacts, I provide a lever 44 (Figure 1) which is pivotally mounted on screw |8 (Figure 3). As is more clearly shown in Figure 2, the lower end of face plate I4 is preferably circular and has suitably imprinted thereon graduations to indicate different temperature settings for lever 44. Lever 44 preferably swings in a counter-clockwise manner, as seen in Figures 2, to determine higher critical temperatures and has extending from the end thereof, a boss Me which supports an outwardly extending pin 45 (Figures 1 and 3). As pin 45 is spaced from the pivotal point of lever 44, it swings in an arc thereabout and abuts against an end 46a of a lever 46.

The other end 451) of lever 46 (Figure 3) is secured to end 26a of coil 26. Accordingly, when lever 44 is swung in a counterclockwise direction as viewed in Figure 2, pin 45 swings upwardly against end 46a of lever 45 and accordingly changes the pivotal position of coil 20 and contact arm 22 is swung farther away from con tacts 36 and 3|, the result being that the critical temperature at which the circuit is made is increased. Conversely, when lever 44 is substantially in the position shown in Figure 2, coil 20 is free to pivot in a clockwise direction thus to position contact arm 22 closer to contacts 30 and 3! in which position only a slight rise in tempera.- ture will result in the making of the circuit. Thus, if the temperature is to be maintained at a low temperature, lever 44 is moved in a clock wise direction. Conversely, if a high critical temperature is desired, lever 44 is swung in a counterclockwise direction to the desired point.

Preferably there is no positive connection be tween pin 45 and end 45a of lever 46 (Figure 1). Hence to effect a clockwise pivot of coil 20 upon the setting of lever 44 at a low critical temperature, I provide an arm 41 or the like suitably secured to end 26a of coil 26. A spring 48 is attached to the free end of lever 41 and at the other end to arm l'lb of bracket l1. Spring 48 thus constantly urges arm 41 in a clockwise clirection, as viewed in Figure 1, which in turn tends to swing the entire coil assembly IS in a clock- Wise direction to move contact arm toward contacts 36 and 3|. Accordingly, spring 48 acting through arm 41 (Figure 1) maintains the engagement between pin 45 and lever 46, thus causing the desired movement of the coil assembly when arm 44 is swung in a clockwise direction (Figure 2).

I have found that when the above-described thermostat is installed in a vehicle such as a refrigerator car or the like the vibration of the car when in motion induces a sympathetic vibration in coil assembly 16 (Figure 1). This vibration results from the fact that coil 2|], block 2|, and contact arm 22 form a statically unbalanced assembly which renders the operation of the thermostat quite unsatisfactory. Considering coil 20, block 2| and contact arm 22 as a unit, the center of mass of this unit is spaced considerably above the pivotal axis of pin l9. Furthermore, the moment of inertia of this unit is so small as to permit immediate and excessive vibration thereof. Accordingly, I have provided a weight 49 or the like (Figures 1 and 2) which is preferably secured by a pin 50 to the outermost convolution of coil 29. Weight 49 is also preferably centered with respect to the pivotal axis of the coil and its mass is so proportioned as to bring the unit comprising coil 20', block 2!, and contact arm 22 substantially into a condition of static balance. By the addition of weight 49 the center of mass of the unit is brought substantially into coincidence with the pivotal axis thereof, that is, the axis of pin l9. Under certain conditions, however, it might not be desirable to bring the system into a condition of static balance or to lower the center of mass thereof to the point already indicated. Under these conditions, weight 49 is proportioned accordingly and in this instance has the efiect of increasing the moment of inertia of the unit. By increasing the moment of inertia, the tendency of the unit to vibrate decreases proportionately.

Thus weight 49 acts in several ways: first, to bring the system into a condition of static balance; second, to lower the center of mass thereof; and third, to increase the moment of inertia of the unit or system. All or any one of these functions of operation counteracts the tendency of the unit to vibrate. By dampening the vibration of the coil assembly, thermostat l0 may be positioned in any desirable location in a refrigerator car or other vehicle requiring temperature controlling apparatus. Efficiency of operation and accessibility for adjustment may determine such location without any fear of harmful vibration.

It will thus be seen that I have provided a thoroughly practical and efiicient construction in which the several objects hereinabove referred to as well as many others are successfully and practically accomplished.

As many possible embodiments may be made of the above invention and as many changes might be made in the embodiment above set forth, it is to be understood that all matter hereinbefore set forth or shown in the accompanying drawing is to be interpreted as illustrative and not in a limiting sense.

I claim 1. In a thermostatic switch, in combination, a base adapted to be suspended in a vertical position, a bracket member secured to said base and extending from the lower portion thereof, means forming a contact member secured to said base and extending from the upper portion thereof, a

bimetallic member comprising a fiat strip spirally shaped with the several convolutions thereof in substantial alignment, means forming a pivotal connection between the end of said bracket member and the inner end of said bimetallic member, a bar connected to said last-mentioned end of said bimetallic member and extending away therefrom radially with respect to said covolutions to a point spaced above said bracket member, spring means connecting the outer end of said bar member to said bracket member, the other end of said bimetallic member being bent upwardly into a substantially vertical position, a block of electrical insulating material secured to said last-mentioned end of said bimetallic member, a contact arm secured to said block and extending upwardly substantially parallel to said base to a point substantially adjacent said contact member so that expansion and contraction of said bimetallic member moves said contact arm into and out of engagement with said contact member, and a weight element secured to the outermost convolution of said bimetallic member at a portion thereof below said bracket member.

2. In a thermostatic switch, in combination, a base adapted to be suspended in a vertical position, a bracket member secured to said base and extending from the lower portion thereof, means forming a contact member secured to said base and extending from the upper portion thereof, a bimetallic member comprising a flat strip spirally shaped with the several convolutions thereof in substantial alignment, means forming a pivotal connection between the end of said bracket member and the inner end of said bimetallic member, a bar connected to said last-mentioned end of said bimetallic member and extending away therefrom radially with respect to said convolutions to a point spaced above said bracket member, spring means connecting the outer end of said bar member to said bracket member, the other end of said bimetallic member being bent upwardly into a substantially vertical position, a block of electrical insulating material secured to said last-mentioned end of said bimetallic member, a contact arm secured to said block and extending upwardly substantially parallel to said base to a point substantially adjacent said contact member so that expansion and contraction of said bimetallic member moves said contact arm into and out of engagement with said contact member, said bimetallic member, said insulating block and said contact arm forming a unit which independently has a center of mass above said pivotal connection, and an arcuate shaped weight element se-

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