US1217413A - Apparatus for the control of electric motors. - Google Patents

Description

E. R. COE.

APPARATUS FOR THE CONTROL OF ELECTRIC MOTORS.

APPLICATION FILED SEPT. 25, 1915. 1,217,413. Patented Feb. 27,1917.

2 SHEETS-SHEET 1.

WITNESSES INVENTOR E. R. COE.

APPARATUS FOR THE CONTROL OF ELECTRIOMOTORS.

APPLICATION HLE'D sEPT.25, 1915.

,2 1 7 ,41 3 Patented Feb. 27 1917.

UNITED STATES PATENT OFFICE.

ELMER R. ODE, OF WILKINSBURG, PENNSYLVANIA, ASSIGNOR TO THE UNION &

SIGNAL COMPANY, OF SWISSVALE, PENNSYLVANIA, A CORPORATION OF PENNSYL- VANIA.

} Specification of Letters Patent.

Patented Feb. 27, 1917.

Application filed September 25, 1915. Serial No. 52,691.

To all whom it may concern:

Be it known that I, ELMER R. Con, a citizen of the United States, residing at \Vilkinsburg, in the county of Allegheny and State of Pennsylvania, have invented certain new and useful Improvements in Apparatus for the Control of Electric Motors, of which the following is a specification.

My invention relates to apparatus for the control of electric motors.

One object of my invention is to provide means for preventing the operation of an alternating current motor by current of any but a predetermined frequency.

I shall describe two forms of apparatus embodying my invention, and shall then point out the novel features thereof in claims.

In the accompanying drawings Figure l is a perspective view,'partly diagrammatic, showing one form of apparatus embodying my invention applied to the motor of a relay, which as here shown forms part of an alternating current signaling system for railroads. Fig. 2 is a diagrammatic view showing a modification of the apparatus shown' in Fig. 1 embodying my invention.

Referring to the drawing, reference character M designates an electric motor comprising a rotor 1 and a stator which is diagran'unatically represented by field windings f and 7. The shaft 2 on which rotor 1 is mounted is vertical and terminates at its upper end in arms 3. Bell cranks 61 of a centrifugal governor G are pivotally mounted in the slotted ends of arms 3 by means of pins 62, so that the bell cranks are free to swing in a vertical plane. A fly ball is attached to one arm of each bell crank and causes it to depend vertically from its point of suspension when the motor is standing still. The end of the other arm of each bell crank is ball shaped and is inserted in a hole 63 through a sleeve 64 fitting loosely over a rod 4. The lower end of rod 4 is inserted into a vertical hole 67 in shaft 2 and fits loosely therein so that shaftQ can rotate with respect to the rod. Theupper end of rod 4 is bifurcated and pin-connected to an arm 6 riveted to a bracket 7 mounted on pivots 8. -A plurality of contacts are usually mounted on the bracket, but to simplify'the drawing, I have shown only one contact 0 comprising a flexible contact finger 1.0 fixed at one end to the bracket 7 by means of insulated studs 9. The other end of finger 12-44 is held closed by means of a weight W adjustably mounted on a screw 15 riveted to bracket 7 When the relay is energized by current in field windings f f, rotor 1 is rotated so that the balls of the governor fly apart. By means of the bell cranks fil, sleeve 64 is moved downwardly, so that it engages a collar integral with rod 4. The rotor is prevented by suitable means from moving vertically upward; consequently, rod 4 is pulled downwardb means of governor G with a force depending upon the speed of rotation of the rotor. Since the rotor speed varies with the frequency of the current supplied to the motor, it follows that the downward force on rod t depends on the frequency of the motor current. The weight IV is so adjusted that its biasing force on bracket 7 is not overcome by the downward force on rod 4 until the rotor has accelerated to a speed corresponding to a predetermined frequency, say, 60 cycles. Then bracket 7 is turned counter-clockwise until contact tip 11 engages contact point 13.

The motor is provided with a brake B by means of which the rotor can be quickly retarded, so that when the motor .is denen gized and the brake is applied, the upper or front contacts are opened immediately.

Brake B comprises a lever arm 21 pivotally mounted near its middle on a shaft 22. One end of lever 21 is provided with a shoe 2;;

of leather or other frictional material, which nated core comprising two vertical legs 16 and 16 and two horizontal cross bars 31 ably mounted (by supports not shown onthe drawing) adjacent the lower end of core G for purposes which I shall point out below. The upper ends of legs 16 and 16 terminate in pole pieces 19 and 19. An armature 20 adapted to bridge these pole pieces is mounted on lever arm 21, so that when the armature is attracted to the pole pieces, asl shall describe hereinafter, lever 21 is turned about shaft 22 so that shoe 23 is.

raised from disk 24 in opposition to the biasing weight W. Thus rotor 1 is free to rotate until brake B is again applied by the release of armature 20.

Cross bar 32 of core G is wound with a primary coil 17. connected to a suitable source of alternating current. Gross bar 31 is provided with a secondary coil 18 which is connected in circuit with a con denser 30 and one phase f of the stator winding. This circuit I shall call the secondary circuit. When alternating current is sent through. primary coil 17, an alternating flux is set up through core C, the greatest part of which flows in the low reluctance path comprising cross bar 32,

the lower half of leg 16, crossbar 31, and the lower half of leg 16 The flux in cross bar 31 induces an alternating electromotive force in secondary coil 18 so that current is caused to flow in the secondary circuit. If both and 25 cycle currents are impressed on the primary 17, currents of both frequencies are induced in the secondary circuit. lBy proper relative adjustment of the various parts as hereinafter explained, it is possible to make the secondary circuit of high impedance to, say, the 25 cycle current, and resonant to the 60 cycle current. Thus the 25 cycle current is choked down to a negligible value whereas the 60 cycle current is but slightly resisted and therefore is of considerable strength.

To make the secondary circuit resonant to the 60 cycle current I provide the bridge 35 adjacent the core C as shown on the drawing, so that not all of the primary flux passes/through the secondary winding 18,

but part thereof leaks through the bridge 35. It is well known that a transformer in which part of the primary flux leaksaround the secondary coil has a characteristic similar to the characteristic of a transformer having an inductive secondary circuit.

1 Bridge 35 has, therefore, the same efl'ect as an additional inductance connected in the .secondary circuit, and may for purpose of discussion be regarded as such. The value of this additionalinductance varies accord- If bridge 35 is moved very close to cross bar 32, the leakage is high and the additional inductance is large, and vice versa. With 60 cycle current in the primary coil the air gap between bridge 35 and core 0 is adjusted until a condition of resonance is reached, 2'. 6., a condition in which the inductive effect of the leakage flux counterbalances the capacity of reactance of the condenser in the secondary circuit. When this is the case the impedanceacross the terminals of coil 18 is equal to the comparatively small effective resistance of the secondary circuit, so that for a given voltage across the primary a heavy secondary current is set up. A large'current in winding .18 sets up a high counter magneto-motive force, so that'part of the primary flux is forced to flow through the upper part of core C. This flux attracts armature 20 to the core 0 and so raises brake shoe 23 from disk 24. Winding f is supplied, as described hereinafter, from a source of 60 cycle current having proper phase relation to the current in winding 7, so that the rotor begins to turn and operates the relay contacts after it has been sufiiciently accelerated.

It is evident that the secondary circuit is not resonant to current of any frequency other than 60 cycles; consequently, when 25 cycle current is supplied to primary 17 the secondary impedance is very high and but a negligible amount of current can flow in winding 7. At the same time, only a small counter magneto-motive force is set up in cross bar 31, which is not sufiicient to force enough flux through armature 20 to attract it to the pole pieces 19. Asa result, rotor 1 is not freed by brake B and the relay contacts cannot be operated.

The above described relay is adapted for many uses, for example, as a track relay in an alternating current signalingvsystem for an electrical railroad using alternating propulsion current. Such an application of the relay is shown on the drawing. Reference character It denotes the track rails of a railroad, which rails are divided into blocks by means of insulated joints 50. Only one such block is shown on the drawing. Impedance bonds I are provided to connect electrically current is furnished by a 60 cycle alternator A, which is connected through a transformer T to the track rails at one end of the block. Coil 17 of the relay is connected to the other end of the block. The signaling current flows from transformer '1 through the track rails to coil 17 provided there is no train in the block. Flow of current from one rail across to the other through the impedance bonds is negligible, for the bonds offer a high impedance to current flowing through the two halves of the winding in one direction, because such current magnetizes the core. Thecurrent in coil 17 eventually energizes the winding f of the relay as hereinbefore explained. WVinding f is energized by current from alternator A. Thus current from alternator A' reaches both windings f and f of the relay, provided there is no train in the block. To make these currents of proper phase relation, an adjustable resistance r is connected between generator G and winding 7' and a variable impedance 1' is connected between the transformer T and the track rails. The resistance and inductance are adjusted until the signal currents in windings j" and f are displaced from each other, so that motor M is caused to rotate and hold front contact 11-13 closed. This contact controls a signal or other apparatus not shown on the drawing. When a train enters the block its wheels and axles form a low resistance shunt across the track rails so that the signaling current is shunted from coil 17 and therefore from motor winding f. Then, as explained hereinbefore, brake B is applied so that the rotor speed is immediately lowered and contact 1113 is 'opened. When the train leaves the block, potential is again restored to coil 17 so that current is set up in winding f and brake B is lifted from the rotor. Motor M is thus free to rotate and close contact 11-13 after it has sufiiciently accelerated.

It is easily conceived that the 25 cycle current may'create a difference of potential across the terminals of coil 17 due to certain causes; such for instance, as unequal bondingv of the two lines of rails. This causes a flow of 25 cycle current through coil 17 As explained hereinbefore, this current is choked down to a very small value in winding f and is unable to operate the. brake. Thus the 25 cycle current is prevented from interfering with the normal operation of the relay.

Refezring now to Fig. 2, I have here shown the rotor 1 of motor M provided with a brake B, which differs from brake B dey scribed for Fig. 1 in the following particulars. Shoe 23 of the brake is mounted in an arm 80 fixed to one end of a shaft 81. The other end of this shaft is secured in a central hole through a Z armature b2. The

.setup in core G.

weight of arm 80 biases brake B to an operative position, 0., a position wherein the brake shoe engages disk 24. To raise the brake shoe from the disk I provide means for turning the'Z armature clockwise. As here shown this means is a closed laminated core C comprising legs 32 and 31 wound with a primary coil 17 and a secondary coil 18" respectively. The secondary coil is connected, as in Fig. 1, in series with a condenser 30 and one stator winding f of motor M. Midway between legs 32 and 31 are pole. pieces P P between which the Z armature 82 is adapted to turn. l

The operation of this form of device is similar to the operation explained for the form shown in Fig. 1, and may be briefly de scribed as follows: Coil 17 is connected to sources of alternating currents of a plural ity of frequencies, say, 25 and 0 cycle currents. It is desired to make the motor responsive only to the 60 cycle current. The 60 cycle current flowing through coil 17' sets up flux which flows partly through coil 18 and partly through the Z armature 82. The leakage of flux through the Z armature has the same effect as an inductance in the secondary circuit and may be regarded as such for reasons hereinbefore explained. The condenser 30 is of such capacity that at 60 cycles its capacity reactanee neutralizes the inductive reactance caused by the leakage flux through the Z armature and the inductive reactance of winding f. Hence, the secondary circuit is resonant to the (30 cycle current, so that for a. given voltage impressed on coil 17' a comparatively heavy current is caused to flow through stator winding f and secondary coil 18'. The current in coil 18 creates a high counter magneto-motive force in leg 31 of core C so that a great deal of the flux in the core flows through the path including the Z armature. This causes the armature to turn clockwise so thatbrake B is raised off rotor 1. If 60 cycle current of proper phase relation to the current in winding f is furnished to winding F from a suitable source, the motor will rotate and operate the relay contact (not shown) by turning shaft 2.

Vhen 25 cycle current flows through primary coil 17' it causes 25 cycle flux to be By far the greater part of this flux flows through leg 31', but it causes only a small 25 cycle current to flow in the secondary circuit, because this circuit offers high impedance to the 25 cycle current. Consequently, coil 18 creates only a small counter magneto-motive force in core 31, so that the 25 cycle flux is not forced to flow through the Z armature in more than negligible quantity. Thus brake B is not raised oil the motor and but-little 25 cyclc current can reach winding f. As a result, the motor cannot be operated by the 25 cycle current and the relay contacts remain unaffected.

Although I have herein shown and described only two forms of apparatus embodying my invention it is understood that var1ous changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1 1. In combination, an alternating current motor, and means controlled by the frequency of the current supplied to said motor for braking the motor.

2. In combination, analternating current motor comprising a member adapted to rotate, and means controlled by the frequency of the current supplied to said motor for braking said member.

3. In combination, an alternatingcurrent motor, braking means for said motor, and means responsive to a predetermined frequency of current supplied said motor for controlling said braking means.

4:. In combination, an alternating current motor, braking means for said motor, and means responsive to the frequency of current supplied'said motor for controlling said braking means.

5. In combination, an alternating current motor, braking means for said motor adapted normally to oppose the motor, and means responsive to the frequency of the current supplied to said motor for rendering said braking means ineffective to oppose the motor.

.6. In combination, an alternating currentmotor, braking means for said motor, a circuit for energizing said motor, means for rendering said circuit resonant to alternating current of one frequency, and means controlled by the value of thecurrent in said circuit'for governing the braking means.

7. In combination, an alternating current motor, a transformer whose secondary supplies current to a Winding of said motor, means for rendering said transformer resonant to current of a predetermined frequency and of high impedance to currents of other frequencies whereby all current but that of said predetermined frequency is choked down to a negligible value, a brake for said motor, and means controlled by current of said predetermined frequency for governing said brake.

8. In combination, an alternating current motor, normally active mechanical braking means tending to oppose operation of said motor, and means responsive to current of a predetermined frequency supplied to said and a transformer having a secondary conwhich currents of different frequencies are present at times, a secondary coil on said core, a circuit includin said secondary coil for energizing a win mg of said motor, means for rendering said circuit resonant to current of a predetermined frequency,'said core comprising also an open magnetic path for shunting part of the flux set up by current in the primary coil when current of the predetermined frequency is flowing in the secondary circuit, an armature in said open magnetic path and controlled by the flux in said latter path, and a brake for the motor controlled by said armature.

11. In combination, an alternating current motor, a magnetizable core comprising a closed path, a primarycoil on said core in which currents of different frequencies are present at times, a secondary coil on said core, a circuit including said secondary coil for energizing a winding of said motor,

means for rendering said circuit resonant to current of a predetermined frequency so that said secondary coil creates a high opposing magneto-motive force with current of said predetermined frequency, a shunt magnetic path around that portion of said core which is enveloped by said secondary coil and through which a portion of the flux passes when said high opposing magneto-motive force is created, an armature in said shunt path and controlled by the flux in-said lat ter path, and a brake for the motor controlled by said armature.

12. In combination, an alternating current motor, a magnetizable core comprising a closed path, a primary coil on said core in which currents .of different frequencies are present at times, a secondary coil on said core, a circuit including said secondary coil for energlzmg a winding of sald motor,

means for rendering said circuit resonant to current of a predetermined frequency so that said secondary coil creates a high opposing magneto-motive force with current of said predetermined frequency, a shunt magnetic path around that portion of said core which controlled by flux in said shunt path.

13. In combination, an alternating current motor, a magnetizable core comprising a closed path, a primary c011 on said core in which currents of different frequencies are present at times, a secondary coil on said core, a circuit including said secondary coil forenergizing a winding of said motor, means for rendering said circuit resonant to current of a predetermined frequency so that said secondary coil creates a high opposing magneto-motive force with current of said predetermined frequency, a shunt magnetic path around that portion of said core which is enveloped by said secondary coil and through which a portion of the flux passes When said high opposing magneto-motive force is created, and a 2 armature in said shunt magnetic path and a brake for the 15 motor controlled by said 2 armature.

In testimony whereof I afiix my signature in presence of two witnesses.

ELMER R. COE. Witnesses:

A, C. NOLTE, C. O. HERRINGTON, Jr.

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