US1881919A - Thermostat - Google Patents

Description

Patented Oct. 11, 1932 UNITED STATES ARTHUR L. PATTON, OF DENVER, COLORADO THERMOS'IAT Application filed May 29,

This invention relates to electrical contacts for thermostatic controls. The greatest source of trouble with a thermostat which handles a relatively heavy electric current results from the electrical contacts therein. A

thermostat is, by its very nature, a slowly operating device. Therefore, the circuit breaking points slowly withdraw from each other causing arcing and burning of the contact surfaces. This soon results in corrosion and oxidization which either prevents the contacts from again closing the circuit or causes them to stick together so as to prevent breaking at the proper time. Another cause of trouble is the relatively small distance separating the open contacts which may in some cases allow a continuous arc. It is diffieult to increase this distance owing to the small amount of movement of the thermostatic blade and the relatively weak power developed.

The principal object of this invention is to provide a contact construction for thermostats which will avoid the above troubles and be a novel arrangement of a plurality of contact points arranged in series with each other with the contact pressure equalized among all the points.

Another object of the invention is to arrange the points upon a series of pivoted members so as to allow the circuit to be broken at one or more points while the remaining points are simultaneously and automatically wiped or cleaned.

A still further object of the invention is to construct a thermostatic blade in such a way that it may have a relatively wide width without lateral curvature. This enables the blade to have a greater actuating power at relatively low temperature variations.

The invention has been found to work satisfactorily under the heavy loads carried by lar e electrical heating devices, such as tire casing vulcanizers, water heaters, incubators, etc., where single or double contact points did not give satisfaction.

It is well known that each contact point will introduce resistance in the series depending upon the pressure exerted between the points in contact. In this invention a series 1930. Serial No. 456,946.

of points are provided and arranged so that the contact pressure at all points is identical. As the thermostatic blades lessen the pressure on all of these points, the resistance to the flow of the current greatly increases so that at the instant of breaking, a relatively small current is flowing so that arcing or burning is reduced to a minimum.

A series of contact points could not be employed without an equalizing device since the point having the least pressure would naturally, owing to its greater resistance, become heated so as to destroy the efficiency of the entire device. This is eliminated in the present invention by a construction which insures a uniform and identical pressure at all of the contact points.

Other objects and advantages reside in the detail construction of the invention which is designed for simplicity, economy, and efliciency. These will become more apparent from the following description.

In the following detailed description of the invention. reference is had to the accompanying drawing which forms a part hereof. Like numerals refer to like parts in all views of the drawing.

In the drawing:

Fig. 1 illustrates an adaptation of the in vention as it might be applied to any heating unit, such as an electrically heated, tire casing vulcanizer.

Fig. 2 is a bottom View, looking upward, at the thermostat of Fig. 1.

Fig. 3 is a detail perspective View of the contact portion of the thermostat.

Fig. 4 is a cross section through izing plate taken on the line 44, Fig. 3.

Fig. 5 is a detail side elevation of the contact portion of the thermostat of Fig. 1.

Fig. 6 is a longitudinal section through a second adaptation of the invention, taken on the line 66, Fig. 7.

Fig. 7 is a fragmentary plan View of the form of Fig. 6.

The first adaptation illustrated of the invention, illustrated in Figs. 1, 2, 3, 4, and 5, comprises a pair of thermostatic blades 10 and 11, formed of metallic material. The blades 10 and 11. in the present instanceare the equalillustrated as secured to the bottom of an electrically heated tire casing vuicanizer, indicated at 12. The blades 10 and 11 are secured to the vulcanizer 12 at their outer extremities by means of suitable clamp screws 13.

The inner extremity of each of the blades 10 and 11 carries an angle clip 1%, insulated therefrom by means of suitable insulation 15. A bridging member 16 is pivoted to each angle clip 14 upon pivot pins 17. The bridging members 16 carry spaced apart contact points 18.

Immediately below the bridging members 16 is an equalizing plate 19, preferably formed of insulating material. Two binding posts 20 pass through the plate 19 and terminate in contact plates 21 on the upper face thereof.

A relatively long contact plate 22 extends across the upper surface of the equalizing plate 19. The contact points 18 of the bridging members 16 normally rest against the plates 21 and 22 so that a closed circuit is formed from one binding post 20 through one bridging member across the plate 22 to the other bridging member and thence the other binding post 20.

The equalizing plate is carried upon ful crum points 23 extending from a supporting bar 24 so that it is free to rock in either direct-ion as shown in Fig. 5. It is prevented from falling from the supporting bar 24 bv means of a screw 25 wh1ch passes loose- 1y through a slotted opening in the center of the plate 19.

In the particular adaptation illustrated the supporting bar 2% extends from an adjusting able upon a supporting standard 27 bymeans of a temperature adjusting screw 28. Thus, by rotating the adjusting screw 28 the equalizing plate can be raised or lowered to regulate the tension in the blades 10 and 11 and the temperature at which the circuit will be broken.

The principal feature of the invention is a plurality of breaking points in series with each other combined with means for insuring a uniform contact pressure at all of the points.

Another method of embodying this principle is illustrated in Figs. 6 and 7 in which a thermostat frame is illustrated at 29, carrying at its bottom a blade of thermostatic metal 30. Immediately above the blade 30 is an operating bar 31 hinged upon a flexible metal hinge 32. The movements of the blade 30 are communicated to the operating bar 31 by means of a temperature adjusting screw 33. The resistance to movement can also be adjusted by means of asecond adjusting screw 34 which forces a leaf spring 35 against the operating bar 31.

A bridging member 36 is pivoted on an upwardly turned extremity of the operating block 26 which is vertically movbar 31. This bridging member is somewhat similar to the bridging members 16 of the previously described form, and is preferably formed of insulating material, such as pressed fiber, with a conducting band or bridge across the bottom carrying contact points 37. The contact points 37 contact with similar points on the extremities of two levers 38 which are independently hinged upon a hinge pin 39. The levers are suitably insulated from the pin 39.

The rearward extremities of the two levers 38 carry contact points which rest against similar points upon contact plates 40. The plates 40 are carried upon an insulating block 11, formed of porcelain or similar material. The plates 40 connect with suitable binding posts 412 to which the electrical conductors are attached.

It will be noted that the pressure of the leaf spring 35- causes the bridgingmember 36 to force the forward extremities of the levers 38 downwardly causing their rear ward extremities to be forced upwardly and, since the levers are independently pivoted on the pin 39, the pressure at all of the four contact points will be uniform and identical as in the previously described form.

Upon a relatively long surface such as encountered in electrically heated tire casing vulcanizers, the portion nearest the thermostatic blade might become chilled. This would keep the contacts closed and allow the remainder of the surface to become overheated. To prevent this two thermostat blades are employed as at 10 and 11.

Let us suppose one of these plates moves faster than the other. This will first result in tilting the equalizing plate 19, causing the contact points to wipe along the plates 21 and 22 so as to brighten and clean them and still maintain the circuit closed. Finally one or both of the blades will have moved upward sufficiently far to break the contact at 1, 2, 3, or 4 points. Should a single contact point be stuck its bridge will rock or tilt to break the contact at the opposite extremity of the bridging member. Should both contacts of a bridging member be stuck, the equalizing plate will rock to break the contact at one or both contacts of the opposite bridging member. This tilting or rocking of the bridging members and the equalizing plate will con stantly act to wipe the contacts so as to maintain them clean and bright and insure a break at from 1 to 4 points.

It will be noted that as the pressure lessens upon all the points identically, that the resistance of the separating points is multiplied. This results in greatly reduced current flow at the time of breaking so that arc ing and sparking is reduced to a minimum.

For low temperature operation it is desirable to employ relatively wide blades of thermostatic material. This has been impractical heretofor because of the lateral curvature or twist imparted by the temperature changes. In this invention this has been eliminated by forming a split 34: almost throughout the entire length of the blade. This reduces the lateral curvature and still allows the blade to be handled and assembled as a single unit.

This invention has been described as applied to thermostats. It will be found proportionately useful, however, in all types of automatic switches.

While a specific form of the improvement has been described and illustrated herein, it is desired to be understood that the same may be varied, within the scope of the appended claims, without departing from the spirit of the invention.

Having thus described the invention, what is claimed and desired secured by Letters Patent is 1. A contact construction for automatic switches having an actuating member, comprising: a bridging member operatively connected to said actuating member; a first pair of interconnected contacts on said bridging member; a second pair of contacts spaced from, and parallel to said first pair; and tilting means hinged between said two pairs of contacts so as to transmit the pressure of one pair to the opposite pair.

2. A contact construction for automatic switches having an actuating member, comprising: a bridging member operatively connected to said actuating member; a first pair of interconnected contacts on said bridging); member; a second pair of contacts spaced from, and parallel to said first pair; and tilt ing means hinged between said two pairs of contacts so as to transmit the pressure of one pair to the opposite pair; and contact members carried by said tilting means so as to complete a circuit between all four of said contact points.

3. A thermostat comprising: a first blade of thermostatic metal; a second blade of thermostatic metal, said two blades being secured at their one extremity and positioned adjacent each other at their other extremities; rocking bridge members carried on said latter extremities, interconnected contacts on each of said bridge members; an equalizing plate; a fulcrum for said equalizing plate positioned at an angle to the axis of said bridge members so that it will equalize the pressure between said two bridge members and contact members carried by said equalizing plate and adapted to complete a series circuit between all of said contact points.

4. A thermostat comprising: a first blade of thermostatic metal; a second blade of thermostatic metal, said two blades being secured at their one extremity and positioned adjacent each other at their other extremities; rocking bridge members carried on said latter extremities;intercmniect-ed contacts on each of said bridge members; an equalizing plate; a fulcrum for said equalizing'plate positioned at an angle to the axis of said bridge members so that it will equalize the pressure between said two bridge members; and contact members carried by said equalizing plate and adapted to complete a series circuit between all of said contactpoints, said-contact-meim bers comprising: relatively flat plates carried upon one face of said equaliz ng plate and adapted to wipe across said contact points upon the tilting of either or both said bridging members or said equalizing plate.

5. A contact construction for automatic switches having an actuating member, comprising: a bridging member operatively connected to said actuating member; a first pair of interconnected contacts on said bridging member; a second pair of contacts spaced from, and parallel to, said first pair; tilting means hinged between said two pairs of contacts so as to transmit the pressure of one pair to the opposite pair; and manual means for moving said tilting means toward or away from said contacts.

6. A contact construction for automatic switches comprising: a bridging member arranged to rock upon a pivot; contacts carried by said bridging member each side of said pivot; and a second bridging member arranged to rock upon a pivot in a plane at right angles to the plane of movement of said first bridging member, said second member having contacts at each side of its pivot adapted to contact with the contacts of said first bridging member.

7. A thermostat comprising: a first thermostatic blade; a second thermostatic blade arranged substantially in alignment with said first blade; means for securing the outer extremities of each of said blades; a clip carried by the inner extremity of each of said blades; a rocking contact member pivoted on each of said clips and arranged to swing in planes parallel to each other; an equalizing plate; contact members carried by said equal izing plate so as to form a series circuit with said rocking contact members; and means for supporting said equalizing plate for rocking movement along a line parallel to the planes of movement 01" said bridging members so as to equalize the pressure between the latter.

8. A thermostat comprising: a first thermostatic blade; a second thermostatic blade arranged substantially in alignment with said first blade; means for securing the outer extremities of each of said blades; a clip carried by the inner extremity of each of said blades; a rocking contact member pivoted on each of said clips and arranged to swing in planes parallel to each other; an equalizing plate; contact members carried by said equalizing plate so as to form a series circuit with said rocking contact members; means for supporting said equalizing plate for rocking movement along a line parallel to the planes of movement of said bridging members so as to equalize the pressure between the latter; and manually operated means for moving said equalizing plate toward or away from said bridging members.

In testimony whereof I aflix my signature.

ARTHUR L. PATTON.

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