US1306555A - Electromagnetic switch - Google Patents

Description

E.;J.'MURPHY. ELEQTRQMAGNETIC SWITCH. "APPLICATION man APR. 29. p16.

Patented J une li), 1919.

2 SHEETS-SHEET 1.

Inventor":

Edwin JM rphg, y His N; ornegr E. J. MURPHY.-

ELECTROMAGNETIC SWITCH.

APPHCATION FILED APR.29. ma.

Patenmd June 10, 19 19.

' 2 SHEETSSHEET 2- Inventor";

Edwin J. r-phg, b5

v His a cltorneg.

N i T T ED STATES Enwm J. mourns,

OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL COMPANY, A CORPORATION OF NEW YORK.

PATENT OFFICE.

ELECTROMAGNETIC SWITCH.

. To all whom it may concern Be it known that I, EDWIN J MURPHY, a

. citizen of the United States, residing at and useful Improvements in Electromag- "Schenectady, c'ounty of Schenectady, State of New York, have invented certain new netic Switches, of which the following is aspecification.

My invention relates to means for controlling the circuits of electric motors and more particularly to improved means whereup to speed. Various means havebeen de- .vised for controlling the operationiof the switches so that they will only close when the current is at a proper value, that is, after a switch has operated to cut out a section of resistance ,the next. switch will not operfate'until the current has dropped to a safe value due to the speeding up of the motor.

A formof switch which has frequently beenv proposed for'this purpose is one in which a shunt coil closes the'switch and a series coil, instead of controlling the circuit of the shunt coil, positively prevents the switch from. closing by actually holding it open, that is, the shunt coil pulls against the series or holding out coil. A switch of this general character, is disclosed in" patent to Fraser #655,335. The difl iculty with the device shown in this patent is that the value of current in the holding out winding at which the switch will close de pends upon the pull of the-shunt coil, which of course will vary with thevoltage and also with the temperature of the coil. In

other words, the setting of the switch, '11. a.

the motor current value at which it closes, changes with change of voltage. It also closes at one value of current in the series coil when the shunt coil is cold and another when it is at its operating temperature,

which is ordinarily about (30 degrees C.

Attempts have been made to overcome this difficulty by having an auxiliary memher, which is operated by the shunt coil,

place a spring under: tension which tends to move the switch member to closed position. This tendency is opposed by the series Specification of Letters Patent.

Patented June 10, 1919 Application filed April 29, 1916. Serial No. 94,465.

coil when the current is high and when the current drops to a predetermined value, the spring overcomes the pull of the-series coil and closes the switch. .Such' an arrangement is unsatisfactory forithe reason'that the switch is closed by a spr ng instead of by electromagnetic pull, and it is impossible to obtain the required pressure between the contacts. The spring weakens as the switch member moves toward closed position, and the pressing together of the' 'c'ontacts is accomplished when the spring is weakest. As the parts wear, the pressure between the contacts decreases.

' One of the objects of my invention is to improve the electroma etic switch of the type above described g providin means whereby the switch member will be operated so as to be positively closed and-wiped home by the electromagnetic pull of the shunt coil when the current in the series coil drops to a predetermined value, the arrangement being such that the value of current in nnnc'mxc the series coil at which the switch closes will be independent of the variations in pull of the shunt coil due to variations in voltage and other causes.

In the accompanying drawing illustrating my invention embodied in concrete form, Figure 1 is a side elevation of an electromagnetic switch embodying my invention; Fig. 2 is a front elevation of the same; Figs. 3 and 4 are diagrannnatic views of the switch showing the parts in difierent positions; Fig. 5 is a diagrammatic view showing my switches connected to start a motor, and Figs. 6-10 are similar views of a modified form of my invention.

Referring to the drawing, 10 represents the slate base upon which the parts are mounted. These parts comprise, a stationary contact 11, a switch member 12 operated byshaped magnet frame 15 having a pole piece 16 cooperating with the switch member and The ma etic structure a leg 17 to which the switch-member is pivoted at 18.. The switch member is provided. with the usual contact 19 supported by spring 20 so that the contactsll and 19 may wipe upon each other as the spring 20 yields in a well understood manner.

In order to prevent the switch member from closing when the current in the series coil 14 is above a predetenmined value I provide means whereby the series coil is opposed by a spring instead of by the shunt coil, although it is not this spring but the shunt coil which closes the switch.

1n the particular arrangement shown in the drawing, I provide a locking member 21 pivoted at 22 so that when the current in the winding 14 is above a predetermined value (or for that matter, even when the windings are de'einergized), it will prevent the closing of the switch member. As shown a stop finger 23 engages the locking member 21 to prevent the closing movement of the switch member 12 when the locking member is in the position shown in the draw ing. This locking member 21 is controlled by a member 24 pivoted at 25 which acts as an armature for the winding 14. This armature member is provided with a projection 26 which engages the locking member 21. The switch member 12 and the armature member 24 are connected by a resilient connection such that when the switch member starts to move, it compresses the sprin 27 which tends to force the armature mem er 2t away from the magnet and trip the locking member. The armature member is normally in the position shown in the drawing, that is, it rests against the pole piece of the magnet 14, it being held in this position by the weight of the switch member acting through the rod 28 extending through the spring 27 having nuts 29 at its lower end as shown which bear against the lug 30 on the armature member. The latch 21 is held in the position shown in Figs. 1 and 3 of the'drawing by the pin 31.

As thus constructed and arranged, the operationof my device will be as follows: Normally the parts will be in the position shown in Fig. l of the drawing. Assuming that the two windings of the switch are' energized simultmieously and the winding l-l energized by a current above the value at.

which it is desired that the switch should close, the parts will assume the posit'on shown in Fig. 3. Referring to this figure it will be seen that the switch member 12 has been moved slightly until the stop finger 23 engages the locking member 21. This causes a certain amount of compression of the spring 27 tending to move the armature member 21 on its pivot but this tenden y is resisted by the magnet winding 14. The shunt-coil is now pulling the switch nrmbcr against the locking member or latch and the switch member can not close until the latch is tripped. It will also he observed that the tripping of the latch, and therefore the release of the switch member depends operated line switch for closing the arma- 'ture circuit and is provided with interlockdetermined value, the armature member will be released and deliver a hammer blow to the latch 21. The parts-[will now assume the position shown in Fig.4 in which it 'will be seen that the latch has been tripped and i the switch member is positively closed and .75 the contacts wiped home by the shunt coil. The switch member is therefore positively held open under the control of the current in the series'coil and the variations of ull, in the shunt coil will have no effect w atso ever upon the value of current at which the switch member will close.

In Fig. 5, I have shown a diagram of con- .nections for starting an electric motor in which a plurality of switches of the type above described are used as resistance switches. Referring to this figure, A re resents the armature and F the shunt fie d of an electric motor. B is an electrically ing contacts C which connect the shunt coils 13 of the various resistance switches D, E and F in circuit. In order to effect automatic progression of these switches, I divide the series coils 14 of all but the first one to operate into two parts. The arrangement is such that when the first switch F closes, a portion of the series winding of the next switch is cut out to reduce the num ber of :unpere turns so as to enable the switch to close when the current drops to a predetermined value. Likewise when the econd switch closes, it cuts out a portion of the series winding of the next switch.

The operation of this system will now be understood from an ins ection of Fig. 5. When the line switch B'c oses. the armature circuit is completed from the positive side of the line through starting resistances R, R, R and through the series windings 11 to the negative side of the line. The iuterlocking contact C on the line switch places all of the shunt coils 14 in circuit across the line. When the current drops to the )roper value, the first switch F will close tiereby short circuiting resistance R its own series coil 14, and a portion of the series winding 14 of switch It. When the current again drops to a proper value, due to the speeding up of the motor, the switch E will close. shortcircuiting resistance R, its own series winding, and a ortion of the series winding of switch D. en the current again drops to the proper value the switchD will close, thereby connectingthe motor directly across the line.

Referring to Figs. 6 to 10, it will be seen that I have shown a modified arrangement for holding the switch member in open posi- 13!) tion. In this case the series coil 14 is pro-- shown is slight,eonipresses.a spring 38 surroundingfr rod 39, one'end of which bears against. jection on the armature 32-and at'right e link. The rod 39 slides in a proangles thereto. I The spring 38 is interposed between a shoulder 41 on the rod and the projection 40. When the parts are in their normal positions, the pivot points 33 and 37 are in line with pivot point 42 connecting the link with the switch arm extension 36.

When a force is applied to the switch arm,

therefore tendingto move it 'to closed position, there is no tendency for the armature to move away from the magnet due to the pull of the shunt coil. .Thereis a small initial movement however of the link by reason of the sliding connection with the armature which compresses the spring 38. The reaction of the spring 38 against the projection 40 tends to force the armature 32 away from its magnet. When the current in the winding 14 drops to a predetermined value, the spring will overcome the magnet1c pull. The armature will turn on its pivot and throw the pivot points out of line so that the shunt coil will close 'the switch, the parts assuming the position shown in Fig. 10. This form of switch may be used in the system shownfin Fig. 5.

It will be seen that I have provided an electromagnetic switch which is closed by a shunt coil but is held open while the current in the series coil is above the predetermined value, the closing point of the switch always 45 being the same regardless of the variations in pull of the shunt coil.

While I have described my invention as embodying a concrete structure and as operating in a specific manner in accordance with the provisions of the patent statutes,

it should be understood that I do not limit my invention thereto, sincevarious modifications thereof will suggest themselves to those skilled in the art without departing from the spirit of my invention, the scope of which isset forth in the annexed claims.

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

1. An elcctromagnetic s tch comprising a switch member, an act|lati:;; winding connected to a source of substantially constant potential, and a magnetic structun. lhcrefor for moving the switch member to closed position, a winding carrying a variable current and means whereby the switch member is held in open position when the current in the latter windin is above a predetermined value and is c osed byfthe potential coil when the current drops to said value regardless of variations in the pull of the potential coil.

a switch member, a shunt coil for closing the same, a Winding carrying a variable current,

means for preventing the closure of the switch member whenthe current in said c 2. An electromagnetic switch comprising winding is high and means for releasing the switch member to permit it to be closed by the shunt coil when the current in the winding drops to a definite value, regardless of variation in the pull of the shunt coil.

3. An electromagnetic switch comprising a switch member, a shunt coil for closing the same, an electromagnet energized by a variable current, a spring placed under strain by the shunt coil in opposition to the pull of the electromagnet and means including said spring for preventing the closure of the .switch member when the current in said winding is high and releasing the switch member to permit it to be closed by'the- 'mitting it to be closed when the current drops to a definite value which is independent of the pull of the shunt coil.

5. An electromagnetic switch comprising a switch member, a shunt coil for closing the same, electromagnetic means controlled by a variable current for preventlng closure of the switch member when the current is high and a spring opposingthe electromagnetic means and acting to release the switch member when the current drops to a, definite value sothat it will be closed by the shunt coil.

6. An electromagnetic switch comprising a. switch member, a shunt coil for closing the same, electromagnetic means controlled by a variable current for preventing the closure of the switch member when the current is high, a spring, said means including a movable element which places said spring under strain to oppose the electromagnetic means and acts to release the switch member when the current drops to a definite value so that it will be eloscd by the shunt coil.

7. An electromagnetic switch comprising sure of the switch member when the current is high, a spring held under tension by the magnet and means controlled by said spring whereby when the current drops to a definite value a hammer blow 1s delivered which releases the switch member and permits it to be closed by the shunt coil.

8. An electromagnetic switch comprising a switch member, a shunt coil for closing the same, electromagnetic means controlled by a variable current for preventing closure of the switch member when the current is high, and a spring placed under strain by the shunt coil to oppose the electromagnetic means and acting to release the switch member when the current drops to a definite value and permit it to be closed by the shunt coil.

9. An electromagnetic switch comprising a switch member, a shunt coil for closing the same, a spring placed under strain by said coil, and means controlled by a variable current for preventing the closure of the switch member when the current is high comprising a magnetic winding carrying the variable current, a movable mechanism held against the spring strain, said mechanism operating in response to the spring tension when the current drops to a definite value, and per mi-tting said switch member to be closed by the shunt coil.

10. An electromagnetic switch comprising a switch member, an actuating winding connected to a source of substantially constant potential, a magnetic structure therefor for moving the switch member to closed position, a winding carrying a variable current and means whereby the switch member is normally locked in open position and is held in said position when the currentin the latter winding is above a predetermined value and is closed by the potential coil when the current drops to said value regardless of variations in the pull of the potential coil.

It witness whereof, I have hereunto set my hand this 28th day of April, 1916.

- EDXVIN J.- MURPHY.

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