US2749404A

US2749404A - Electrical timing apparatus

Info

Publication number: US2749404A
Application number: US303297A
Authority: US
Inventors: Charles H Flubacker
Original assignee: Cook Electric Co
Current assignee: Cook Electric Co
Priority date: 1952-08-08
Filing date: 1952-08-08
Publication date: 1956-06-05
Anticipated expiration: 1973-06-05

Description

June 5, 1956 c. H. FLUBACKER 2,749,404

ELECTRICAL TIMING APPARATUS Filed Aug. 8, 1952 INVENTOR.

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JZA ZyzM A United rates ELECTRICAL TIMING APPARATUS Charles H. Flubacker, Chicago, lllL, assignor to Cook Electric Company, Chicago, Ill., a corporation of llliuois A Application August 3, 1952, Serial No. 303,297

4 Claims. (ill. 200-413) This invention relates to electrical timing apparatus and more particularly to thermally actuated timing apparatus designed to control various extrinsic electrical circuits.

it is a principal object of this invention to provide new and improved timing apparatus for intermittently completing various electrical circuits.

it is a further object of this invention to provide such improved apparatus which is extremely rapid in operation and requires minute operating currents.

The apparatus heretofore employed in intermittently making and breaking electrical circuits in response to changes in current in a control circuit have generally incorporated either a magnetic coil and contacts mounted on a movable armature or contacts actuated by the deformation of a bimetallic strip. The electromagnetic type of device is not well suited for use where severe shocks are encountered, or where extremes of humidity and other atmospheric conditions may exist. The bimetallic element is relatively immune to shocks and vibration and is not adversely affected by high humidity but has a relatively large power requirement and a substantial thermal delay.

in aircraft operations, it is extremely important that a switching mechanism of this type utilize extremely small currents for actuation and also be immune to the deleterious effects of motion, vibration, and various other shocks. it is further desirable that such switching apparatus be extremely light in weight, as many such devices may be necessary in an airplane and weight conservation is one of the fundamental concerns in the design of aircraft ap paratus.

Therefore it is a further object or" this invention to provide extremely stable intermittent switch which is not subject to faulty operation due to vibration or shock.

It is an additional object of this invention to provide such improved apparatus which will not be subject to atmospheric conditions but will operate satisfactory at high altitudes and with extreme temperature and humidity variations.

it is another object of this invention to provide improved timing apparatus which is of extremely light weight and occupies relatively little space.

It is a further object of this invention to provide timing apparatus in which the actuating and deactuating currents .are substantially adjustable whereby the periodicity ot' intermittent pulsing is established.

Additional objects of this invention will be manifest from the description, accompanying drawings, and appcnded claims.

In carrying out this invention in one form, a switch mechanism is provided which is actuated by the elongation of a pretensioned thermally expandable wire. More particularly, one form of this invention comprises a normally closed heating circuit which will cause the extension of said thermally expandable wire to open the circuit whereby cooling will be effected to once again complete .said circuit, causing continuous intermittent operation of :the associated electrical contacts.

For a more complete understanding of the invention tion.

v arsenal Patented June 5, 1956} ice reference should be made to the accompanying drawings, wherein Figure 1 is an isometric view of one embodiment of this invention;

Fig. 2 is a plan view of said embodiment;

Fig. 3 is a partial view in elevation showing the wire in its unheated state and the heating circuit closed;

Figure 4 illustrates the same portions of the structure as Fig. 3, but in the actuated position; and

Fig. 5 illustrates the apparatus after the wire has substantially cooled, creating a tension tending to complete the heating circuit through the contacts.

Referring now to the drawings, and more particularly to Fig. 1, one apparatus ll, illustrative of this invention, is shown. The apparatus includes a base member 12 which is adapted to be fastened to chassis or other frame for electrical equipment. Base member 12 is of an L- shape and is adapted to receive a pair of mounting screws 1;? which will support the remainder of the structure in a vertical position. While the apparatus is here shown vertically mounted, this device does not rely on gravitational forces for its operation and may therefore be operated in any desired position with equally satisfactory results.

Supported by the mounting screws 13 are a plurality of insulating

spacers

28, 29, Ell, a pretensioned spring member 15, a magnet support 14, and a contact support 19. The spring member 15 at its lower extremity forms an electrical terminal in adapted to receive one or more conductors connected to associated equipment which are to be energized intermittently. Attached to the upper portion of spring member is is an electrically conductive thermally expandable wire 17. Wire 17 will normally be tensioned to support spring member 3.5 in an actuated posi- This wire may be secured to the spring member 15 by any convenient means but is here shown attached by brazing. The wire 17 should be chosen of some material which will expand when heated so that the tension exerted by wire 17 will be'relieved, allowing spring member 15 to assume its normal position. Wire 3? is secured at its other end to a threaded terminal 318 which is retained in a bracket 19 whichis also held in place against the insulating members 29 by the mounting screws 13. The threaded terminal 18 is movable in'a bushing 21 of an insulating material so that bracket 19 is electrically isolated from terminal 13. The magnet support 14 extends upwardly to support a permanent magnet 22; which is mounted in such a position that spring ltd, which has a soft iron bar 23 mounted thereon, will be attracted to said magnet against the tension of wire 17. Vertical support lid is secured to bracket 19 by any convenient means and is adapted to support an adjustable contact 25 which is threadedly mounted in a metallic bushing 21) to form an electrical terminal. This terminal bushing 243 is, in turn, mounted in an insulating bushing 27 whereby terminal 25 is electrically isolated from support as. Terminal 25 is adapted to engage a Contact 26 which is secured to spring member 315, and when these contacts are engaged two circuits are completed, one for heating the wire 17 and a second for completing any desired external circuits connected to terminal to, as will be explained in greater detail hereinafter.

Figs. 3, 4 and 5 illustrate the sequential steps in a single operation of this apparatus. in Fig. 3 the apparatus is shown in its actuated position with spring 15 moved to its extreme position under the tension of wire 17 so that contact 26 is in engagement with the adjustable terminal 25. in this position there will normally be a predetermined voltage applied between bushing 24? and terminal 13 which will cause a heating current to flow. The path of this current will be from bushing 2% through adjustable contact 25 and contact 26, spring member 15, wire 17, to terminal 18. This heating current will raise the temperature of Wire 17 an amount determined by the character of the wire. Wire 17 will generally be of a fine gauge and composed of some material, such as Nichrome, which has a high thermal coefiicient of expansion and can withstand high temperatures without mechanical failure. Therefore, a very small current flowing in wire 17 for an extremely short time will cause it to expand sufiiciently so that the spring under its own tension will cause contact 26 to move to the right, leaving contact 25, at which time the heating circuit just described will be opened. However, in such a wire there is a suificient thermal delay that it will continue to expand for a limited time after the circuit is broken and will thus allow spring 15 to continue to move to the right. To augment this motion, permanent magnet 22 and the associated iron shorting bar 23 are provided. As the spring 15 moves to the right, magnet 22 will attract shorting bar 23, as best shown in Fig. 4, and will cause the heating circuit to remain open for a substantial period of time determined by the relative magnitudes of the tension of wire 17, the tension of spring 15, and the strength of permanent magnet 22. The particular embodiment herein shown has an adjustable repetition rate of between three and fifteen cycles per second.

As the wire 17 begins to cool it will once again contract, applying a lateral force to spring member 15 tending to return it to its position whereby engagement of contact 26 with terminal 25 is effected. However, the force of magnet 22 on the shorting bar 23 will oppose the motion and will cause spring 15 to assume the tortuous shape illustrated in Fig. 5. Ultimately the construction of wire 17 will create sufiicient force to break the magnetic circuit and allow spring 15 to once again move to the left, thus causing contact 26 to engage terminal 25 and complete the heating circuit. When this heating circuit is completed once again, the cycle of events just described will recur, causing an intermittent reciprocating motion in spring member 15.

Terminal 18 is mounted for vertical adjustment so that the tension which is applied by wire 17 to spring member 15 can be critically adjusted. This will determine the precise current necessary to break the heating circuit and will also affect the period of time necessary for one complete cycle of operation. Additionally, terminal 25 is provided with a threaded adjustment so that a pre-tension can be applied to the spring member 15 which will result in continued engagement for small rises of temperature for wire 17 but a rather sudden action of spring member 15 when the wire 17 reaches a predetermined temperature. This quick action, in combination with the snap action provided by permanent magnet 22 upon remaking the heating circuit, is very desirable in that it decreases arcing and burning on the switch contacts, thus greatly prolonging the life of the switch mechanism.

In addition to completing and breaking the heating circuit above described, this device is also adapted to make and break any desired circuits which are connected to terminal 16. Terminal 16 is an extension of the spring member 15, as shown best in Fig. 1, and is adapted to receive a plurality of conductors. In aircraft operation it is often desirable to have various intermittent alarms, such as flashing lights, whereby a pilot or crew member is apprised of various dangerous circumstances aifecting the operation of the aircraft. Such circuits would be completed through terminal bushing 20, adjustable contact 25, contact 26, and spring member 15, to terminal 16.

While in the illustrations herewith this apparatus is shown having rather large dimensions to best illustrate the principles involved, it should be understood that any size and dimensions could be assumed, and it is usually desirable that the dimensions be extremely minute. By making all of the parts of small size and providing spring member 15 with a small mass and relatively high elasticity, a wire 17 of extremely fine diameter can be utilized. By way of example, in one embodiment of this invention a Nichrome wire with a diameter of .005 inch is utilized for controlling the switch member and thereby a current of the order of .l ampere is sufiicient to heat wire 17 and effect an opening of

contacts

25 and 26.

Thus it can be seen that circuit control apparatus is here taught which can control various apparatus intermittently at any desired time interval with extremely small actuating currents. Apparatus is further provided which is not subject to faulty operation under adverse weather and atmospheric conditions and is not subject to damage resulting from severe shocks and vibrations.

Without further elaboration, the foregoing will so fully explain the gist of my invention that others may, by applying current knowledge, readily adapt the same for use under varying conditions of service, without eliminating certain features, which may properly be said to constitute the essential items of novelty involved, which items are intended to be defined and secured to me by the following claims.

1 claim:

1. In electrical timing apparatus, an elongated longitudinally deformable resilient member fixed at one end,

the free end having an actuated position and a normal unactuated position, an electrical contact mounted in spaced relation to the free end of said resilient member to be engaged thereby, magnetic means disposed adjacent said free end to maintain said resilient member in the unactuated position, and a flexible conductor having a substantial thermal ex ansion and having one end thereof secured to a point on said resilient member intermediate said fixed end and said free end and the other end fixed in spaced relationship to said resilient member, said flexible conductor being normally tensioned to maintain said resilient member in the actuated position under longitudinal tension whereby the thermal expansion of said conductor will cause said resilient member to move to the unactuated position to be maintained there by said mag netic means.

2. In electrical timing apparatus, an elongated longitudinally deformable resilient member having a free end movable between an actuated position and an unactuated position and having one end fixed to form an electrical terminal, an electrical contact mounted in spaced relation to the free end of said resilient member to be engaged thereby, magnetic means disposed adjacent said free end to maintain said resilient member in the unactuated position, and a flexible conductor having a sub stantial thermal coefficient of expansion and having one end thereof secured to a point on said resilient member intermediate the free end and said fixed end and the other end fixed in spaced relation to said resilient member to normally maintain said resilient member under longitudinal tension and to form a conductor terminal, whereby an electric current flowing from said contact member to said conductor terminal will cause the thermal expansion of said conductor and a motion of the resilient member to the unactuated position.

3. In electrical timing apparatus, an elongated longitudinally deformable resilient member having a free end movable between an actuated position and an unactuated position and having one end fixed to form an electrical terminal, an electrical contact mounted in spaced relation to the free end of said resilient member to be engaged thereby, magnetic means mounted in spaced relationship to the free end of said resilient member to maintain said resilient member in the unactuated position, a movable terminal adjustably mounted in spaced relation to the fixed end of said resilient member, and a flexible conductor having a substantial thermal coefficient of expansion and having one end thereof secured to a point on said resilient member intermediate said free end and said fixed end and the other end thereof secured to said movable terminal whereby said resilient member is normally maintained under tension and a predetermined magnitude of electric current flowing from said contact member to said movable terminal will cause the thermal expansion of said conductor and a motion of said resilient member to the unactuated position.

4. In electrical timing apparatus, an elongated longitudinally deformable resilient member having a free end movable between an actuated position and an unactuated position and having one end fixed to form an electrical terminal, an electrical contact mounted in spaced relation to the free end of said resilient member and adjustable with respect thereto to determine the actuated position of said resilient member, magnetic means mounted in spaced relationship to the free end of said resilient member to maintain said resilient member in the unactuated position, a movable terminal adjustably mounted in spaced relation to the fixed end of said resilient member, and a flexible conductor having a substantial thermal coeflicient of expansion and having one end thereof secured to a point on said resilient member intermediate said free end and said fixed end and the other end thereof secured to said movable terminal whereby said resilient member is normally maintained under tension and a predetermined magnitude of electrical current flowing from said contact member to said movable terminal will cause the thermal expansion of said conductor and a motion of said resilient member to the unactuated position.

References Cited in the file of this patent UNITED STATES PATENTS 1,946,894 Brogger Feb. 13, 1934 1,979,349 Schmidinger Nov. 6, 1934 2,243,563 Hottenroth May 27, 1941 2,299,767 Schmidinger Oct. 27, 1942 2,302,399 Stimson Nov. 7, 1942 2,312,974 Owens Mar. 2, 1943 2,319,241 Leuthold May 18, 1943 2,512,268 Eros et a1. June 20, 1950 2,659,787 Prickett Nov. 17, 1953