US1275817A - Electromagnetic switch. - Google Patents

Description

J. l. WOOD.

ELECTROMAGNETIC SWITCH.

APPLICATION FILED NOV. 20. 1914.

Patented Aug. 13, 1918.

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ELECTROMAGNETIC SWITCH.

APPLICATION FILED NOV. 20. 1914.

' Patented Aug. 13, 1918.

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JAMES J. woon, orron'r WAY E, INDIANA, ASSIGNOR TO, GENERAL ELECTRIC COMPANY, .A CORPORATION on NEW YORK.

ELECTROMAGNETIC SWITCH.

'Speqificationof Letters Patent.

Patented; Aug. 13, 1918,

Application filed November 20, 1914. Serial No. 873,212.

To all whom it concern:

Be it known that I, James J. WOOD, a citizen of the United States, residing at Fort Kayne, county of Allen, State of Indiana, have invented certain new and useful Imp cm n sin ec oma n Sw t h of which thejfollowing is a specification.

This invention relates to electromagnetic switches for the. control, of electric circuits and has forits object the. provision of improved means whereby an electric circuit may be controlled in a reliable, simple and effi ient manner. f i

My invention relates more specifically to electromagnetic switches for controlling electric motor circuits, one of the objects being to provide a device of this character which will efi'ect the automatic starting of the motor under the control of the motor current. In the operation of electric motors it is common to" both start the motor and control its speed. by means of a resistance which is cut in and out of circuit. Every time a section of resistance is cut out the current temporarily rises above normal value. The increase in speed which is caused by the cutting'out of the section of resistance immediately reduces the current. During the starting of the motor, therefore, there is, a temporary rush of current for each section of resistance which is cut out. These sections are frequently cut out of circuit by electromagnetic switches which operate auitomaticall'y in succession. In order to prevent the switche's from operatingtoo rapidly and. increasing the current beyond 'a safe value,variousmeans have been devised. Ail ideal switch forthispurpose is one containing a winding which'carries the motor current and a switch member controlled thereby for cutting out the resistance, the arrangement being such that the switch member-win not be operated to cut out the resistance until the current has fallen to. a predetermined value and-twill assnme an open position when the. winding is deenergiz'ed.) A switch of this character was invented by Walter O. Lum and forms the subject matter of an application, Serial, No. 611,151, filed February 27, 1911, assigned to the same assignce as this application.

lVhile the broad features of my device aredescribed and claimed in the, said Lum application, the morejspecific features thereof constitute important improvements which lend themselves to eiiiciency of operation and also make the device more accurate and positive in operation. Likewise, the improved mechanical construction of the switch renders it more rugged and comact and likewise decreases th'e cost of production.

In the accompanying drawings illustrating one form of my invention, Figure 1 is a side elevation. of a. complete electromagnetic switch embodying my improvements; Fig. 2 is a front elevation of the same; and Figs. 3, 4.- and' 5 show in outline the variouspositions which the switch assumes; and Figs. 6 to 10 are similar views of a modified form of my invention.

Referring first to Figs. 1 and 2, 10 represents an energizing winding for magnetizing the magnetic structure composed of a core 11 j oined. at its inner end to a U-shaped magnet frame 12, the ends of which form poleifaces l3 and 14. These parts constituting an electromagnet are secured to an insulating base 15 and. a stationary contact16 is suitably supported above the electromagnot so as to cocperate with the movable contact in a manner hereinafter described. Supported by lugs 17 projecting from the end of the magnet is a switch member 18 of magnetic material. The lugs 17 are on a bracket, preferably of brass, which is secured to the end of the core by being fitted over its reduced end. This switch member is pivoted intermediate its ends in the lugs 17 so asto cooperate with the two polepieces 13 and 151. T o the upper end of the switch member is pivoted the contact 19 and a spring 20 is interposed between the member and the contact support so as to give a yielding pressure between contacts 16 and 1 9, which are shaped so as to close with a wiping or rolling action. Pivoted on the same pivot 17 as'that of the switch member is a pressure element 21 of magnetic material arranged to cooperate with the polepiece 14 and be attracted thereby when the winding is energized. The end of this element is turnedto form a lip 21' to improve the magnetic circuit at that point. The purpose of this element is to place a spring pressure upon the switch member to give it a tendency to close while the switch member is being held in the open position by the polepiece 13. The particular form of this switch member and of the pressure element 21 form no part of my present invention, but for purposes of illustration I have shown the upper part of the switch member as being composed of two curved arms united at their outer ends by a strut 22.. The pressure'ele ment 21 fits in between these two arms and has two wing portions which are as wide as the arms so as to make the maximum width the same as that of the switch member, and are curved to conform to the shape "of the arms. The outer ends of these arms cooperate with the pole face 14, which is provided with projections 14 to give a pole area at these points equal to that of the ends of the arm, and the pressure element locatedbetween these two ends also cooperates with the main portion of the polepiece. A tension device is interposed between the pressure element 21 and the switch member 18. This consists of a spring'24 having a bearing upon the switch member, which spring is compressed by means of a rod which is pivoted in the pressure element and extends between the two arms of the switch member.

The spring 24 surrounds the rod 25 and a nut 26 is screwed on the endof the rod to act as a stop bearing for the outer end of the spring. When the pressure element is pulled in and the switch member is held out by the magnetic pull at the pole piece 13 due to a high current (see Fig. 4) the spring will be compressed a certain amount. When the switch member follows the pressure element in response to the spring pressure which overcomes the decreased pull of the pole piece due to a lower magnetizing current (see Fig. 5) the spring would be relaxed by substantially the amount which it has been compressed, and the effective pressure on the contacts will not be as great as would be desirable. In order to overcome this disadvantage and offset the effect of the relaxation of the spring, the tension device is arranged so as to increase its eifect upon the switch member by increasing its effective leverage upon the member as the latter moves inward to closed position. To this end, the inner end of the spring is mounted upon a washer 27 which is pivoted between the two arms of the switch member on a pin 28 so as to have the effect of a rocker bearing. As shown in the drawing, (Figs. 4 and 5) it will be obvious that as the switch member moves inward in response to the pressure of the-spring 24 supplemented by the pull at the pole face 14, the rod 25 will 7 be rocked slightly outward around its pivot toward a position perpendicular to the pressure member, that is, the center of the spring will move toward substantially a position of maximum effect. As shown in Fig. 5, the

spring has moved substantially to this maximum position. 7 This increases the pressure between the contacts over what it would be if the line of action of the spring did not stantially up to what it would be if the 7 spring had not been relaxed by the inward movement of the switch member, which condition would exist if the switch member were released, but instead of moving toward the stationary member, the stationary Qmember would move toward it. By adjusting the screw 26 the pressure on the spring and consequently the value of current at which the switch will close will be adjusted.

V In the operation of my device, when the. winding 10 is energized above a predetermined value, the flux across the gap at the pole facelS will hold the switch member in open position; At the sametime the member 23 will bedrawn inward and the spring compressed. The parts will now be inthe position shown in Fig. 4. There will nowbe two forces controlling the switch, one due to the pressure of the spring and the other, which may be negligible, due to the pull of the polepiece 14. Opposed to these closing forces is the holding out force due to. the magnetic pull of the polepiece 13. The switch will therefore remain in open position until the'current has fallen to the predetermined value. As the current decreases the magnetic flux at the polepieces 13 and 14 will be decreased, and hence both the clos- 111g magnetic force and the holding out magnetic force will be decreased. The closing closed, position, the holding out gap is greatly increased and the closing gapdecreased, so that the magnetic pulltoward closing position increases rapidly until the switcharm comes in contact with the polepiece 14 and is pulled strongly so as to press the contacts firmly together. As the switch member moves inward toward closed position, the arm 25 moves outward toward the tangential or position of maximum effort. This increases the leverage of the spring upon the switch member and offsets to a large degree the effect of the decreased tension on-the'spring. The contacts will therefore be held together .with a maximum' spring pressure. By adjusting the screw 26 the value of current at which the switch closes may be adjusted, the screw 26 may be left stationary and the adjustment be made by ad usting the 'air gap at the polepiece 13 by turning the'screw 29. V r

In FigsQG to 10 I have shown a modified" form of my invention, in which two windings are employed instead of one. I have shown these windings as being in series with each other so that the current between the two windings will decrease proportionately although, of course, this particular arrangement of winding is not an essential feature of my invention. By referring to Figs. 6 and 7 it will be seen that the two windings and 31 are mounted respectively on cores 32 and 33 which are connected together at their inner end by a plate of magnetic material 34. Supported between the two windings is a standard 35 of magnetic material, which is connected with the plate 34, and forms a pivotal support for the movable parts. The switch member 36 which in this case is substantially the same in shape as that shown in Fig. 5, is pivoted at 37 and its lower end 38 is provided with an adjusting screw 39. An auxiliary pole piece 40 is secured to the upper core and bent outward, as shown, to coiiperate with the end of the switch member. The member 41 pivoted concentrically with the switch member, opcrates between the auxiliary polepiece 40 and the switch member. The tension device between the pressure element and the switch member is the same as that shown in Fig. 5, and further description is therefore unnec essary. One advantage of a construction of this character is that it is possible to concentrate the flux so as to apply a greater holding out force because of the presence of the coil 31. On the other hand, it has the disadvantage of having an extra coil and not being so rugged and compact.

The operation of this form of my device is substantially the same as that described with reference to Figs. 1 to 5, the difi'erence in the acting forces being chiefly one of degree. Figs. 8 to 10 show the parts in the various conditions, and correspond to Figs. 3, f and 5.

While I have described my invention in concrete form and as operating in a specific manner in accordance with the patent statutes, it should be understood that I do not limit my invention thereto as various modifications thereof will suggest themselves to those skilled in the art without de parting from the spirit of my invention, the scope of which is set forth in the annexed claims.

What I claim as new and desire to secure by Letters Patent of the United States, is

1. An electromagnetic switch comprising an electromagnet, a movable switch member normally in open position, an element movable by said magnet, and a tension device interposed between said element and said switch member to force them together,

said device comprising a spring having a rocker bearing upon the switch member causing the spring to shift as the member moves under the influence of the spring and increase the leverage at which it acts upon the switch member to close it, and means for holding the member against said closing tendency when the magnet is energized above a predetermined value.

2. An electromagnetic switch comprising an electromagnet, a switch normally in open position, an element movable by said magnet, a tension device interposed between said element and said switch comprising a rod provided with a stop pivoted to the element, and extending through the switch member, a spring surrounding said rod between the stop and the switch member, and having a rocker bearing upon the latter, and means for holding the member in open position against the tension of the spring when the magnet is energized by a current above a predetermined value.

3. An electromagnetic switch comprising an electromagnet having two polepieces, a switch member cotiperating with said pole pieces and pivoted between them, an element pivoted concentrically with said switch member and movable into contact with one of said pole pieces when the winding is energized, a rod provided with a stop pivoted to said element and extending through the switch member, a spring surrounding the said rod between the stop and the switch member and having a rocker bearing upon the latter, said switch member being held by the opposite polepiece against the tension of the spring when the magnet is energized by a current above a predetermined value.

4. An electromagnetic switch comprising an electromagnet, a movable switch member normally in open position, an element movable by said magnet, a spring interposed between said element and said switch member to give the latter a tendency to close when the magnet is energized, means whereby the spring is caused to act upon the switch member as it closes so as to increase the leverage,

means for holding the member in open position against said closing tendency when the magnet is energized by a current above a predetermined value, and a pole piece for pulling the member into closed position when released.

In witness whereof, I have hereunto set my hand this 14th day of November 191%. JAMES J. WVOOD. Witnesses:

N. E. CRANE, L. M. GURMAN.

Copies of this patent may be obtained for five cents each, by addressing the Commissioner of Patents,

Washington, D. G.

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