US2653284A - Motor-protection during dynamic braking - Google Patents

Description

Sept. 22, 1953 G. R. PURlFOY ETAL ,6

MOTOR-PROTECTION DURING DYNAMIC BRAKING Filed June 26, 1952 PROGRESS WITNESSES: INVENTORS George R. Purifoy '4 William L. Borcloy,ur.

BY mm ATTORNEY Patented Sept. 22, 1953 2,653,284 I C E MOTOR-PROTECTION DURING DYNAMIC BRAKING George R. Purifoy, Pittsburgh, Pa., and William L. Barclay, Jr., Scarsdale, N. Y., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application June 26, 1952, Serial No. 295,794

22 Claims.

Our invention relates to direct-current electrically propelled railway-vehicles, and it has particular relation to electrical control-systems therefor, in which provision is made for dynamic braking. The principal object of our invention is to provide a new means or instrumentality for reducing the high buildup-rate and overshooting of the motor-current and the motor-voltage when the dynamic-braking circuits are established while the motors are operated at high speeds. Excessive motor-current and excessive motorvoltage result not only in a rough brake-application, but also in motor-flashing. Our invention is an improvement over the control-equipment which is shown in an application of G. R. Purifoy and R. E. Burkhart, Serial No. 269,752, filed February 4, 1952, in which other means were provided in order to mitigate overshooting when dynamic braking is applied.

We have provided two novel means for reducing overshooting during dynamic braking. One of these means is an impulse-coil or kick-coil or transformer, for responding to excessive rates of increase of the motor-current, with means associated therewith for temporarily recalibrating the limit-relay which controls the rate of application or progression of dynamic braking. A second novel means, which we have provided, relates to the use of an auxiliary switching-segment on the field-controller, for taking care of an objectionable condition which sometimes occurs when the motorman elects to operate the car or train, for a while, on the switching position of the master controller, with the train running at speeds much higher than switching-speeds, and subsequently going into dynamic brake from said switching position.

With the foregoing and other objects in view, our invention consists in the circuits, systems, apparatus, combinations, parts, and methods of design and operation, hereinafter described, and illustrated in the accompanying drawing, the single figure of which is a simplified circuit-diaram of the parts of one car, which are necessary to illustrate our present invention, omitting many parts which are known to be needed in a successful railway-control equipment of the type to which our invention is applied, but which are not necessary to be discussed in setting forth the nature and operation of our present improvement.

The drawing represents some of the equipment which is carried by a single electrically propelled railway-car embodying our invention. Directcurrent power is supplied to the car from a third rail I95, or a trolley wire, which is engaged by thirdrail shoe I96, or a trolley pole, pantograph, or other current-collecting equipment, carried by the car. The third-rail shoe I96 energizes a line I9! which constitutes a supply-circuit for the car. The traction-motors for the car are series motors, which are indicated, by way of a simple example, in the drawing, as comprising two motor-armatures AI and A2, each being associated with its own series field winding SFI and SP2, respectively, the ordinary reversing-switches being omitted for the sake of simplicity. Two series-motor means, or circuits, are shown. The first series-motor means comprises, in series, an armature-terminal ATi, a motor-armature or armatures AI, an intermediate connection-point AX I, a series field winding or windings SFI, for supplying the field-excitation for said armature or armatures, and a field-terminal FI I. The corresponding parts for the second series-motor means are indicated at ATZ, A2, AX2, SF2, and FT.

A series-parallel motor-control arrangement is shown in the drawing, in which a line-switch or relay LSI and a ground-switch GI are used as power-switch means for establishing a power-circuit for energizing the motors, by connecting the first armature-terminal ATI to the supply-circuit I91, and connecting the second armature-terminal ATZ to ground. For completing the seriescircuit connections, a switch JR is closed in addition to the power-switches LSI and GI. For parallel-motor operation, two switches M and G are closed in addition to the power-switches LSI and GI. The parallel-motor switch M provides a circuit-connection between the armatureterminal A'II of one series-motor means and the field-terminal FT of the other series-motor means; while the other parallel-motor switch G provides a circuit-connection between the other armature-terminal AT2 and the other field-terminal Fl I. During an intermediate transitionperiod, a switch J is closed. These motor-controlling connections are all in accordance with a well-known switching-system.

Dynamic-braking circuits are established by opening the two power-switches LSI and GI and closing a braking-switch BI in addition to the two parallel-connection switches M and G, also inv accordance with a Well-known system or arrangement. The braking-switch BI provides a common dynamic-bral ing circuit-connection I98 between the respective intermediate connectionpoints AXI and AXZ of the two series-motor means, thus providing two dynamic-braking circuits wherein the motor-armature or armatures of each of said series-motor means are loaded by the field winding or windings of the other one of said series-motor means, respectively.

A suitable number of series-connected accelerating resistances are used, as indicated at RI, R2, R3 and R4. The resistance RI is disposed between the supply-line I91 and the first armature-terminal ATI, and is shorted out by means of a second line-switch LS2. The resistance R2 is in series with the first field-terminal Fl I, and is progressively shorted out by means of switchcontacts SI, S3 and S9. The resistance R3 is in series with the second field-terminal FT, and is progressively shorted out by switch-contacts S2,

S4 and SIG. The resistance R4 is in the seriesmotor connection which is made by the switch JR, and this resistance is finally shorted out by the transition-switch J, for. obtaining the full series power-circuit connectionof the motors;

During parallel motor operation, the switch contacts S3, S4 and S9, Sill are successively or progressively closed, during the acceleration of the motor, and after all of the accelerating-resistances R2 and R3 have been cut out, the fieldstrengths of the motors are progressively reduced, to provide short-field operatingcondi-- tions.

In accordance with a usual arrangement, the motor-fields are reduced. by equipping each of the series field windings SFI and SF2 with a field-shunt, comprising an inductive reactor Xi of X2, as the case may be, and. a variable resistor RSI or RS2, respectively. The field-shunts XI- RSI and X2-RS2 are first connected in parallel relation to their respective field-windings SFI and SFZ, by means of contact-terminals II and I2, respectively, of a progressively or sequentially operating field-controlling means, which is herein illustrated as an electrically operated drumtype field-controller FC. After the respective field-shunts have been connected into operation, the field-shunt resistances RSI and RS2 are then progressively shorted out by successive controller-points I3, [5, l1 and I9, for RSI, and I4, I6, l8 and 20, for RS2, as the field-controller F is moved from its initial full-field position FF, through its intermediate positions Fl, F2, F3 and F4 to its short-field position SF, at which point the field-winding currents are reduced to about fifty per cent of their unshunted values.

During dynamic braking, the two motors are connected by the common dynamic-braking circuit-connection I98, which contains the brakingswitch BI and a braking-resistance R5. This resistance R5 is used, in addition to the previously mentioned accelerating-resistances R2 and R3, in establishing, the complete dynamic-braking circuit. The braking-resistance R5 is progressively shorted out by means of brakingswitches B2, B5 and B6, during dynamic-braking operations, after which the acceleration resistances R2 and R3, or portions thereof, are progressively shorted out, as by the switch-contacts S3, S4, and S9, SH]. (The switch contacts SI and S2 are permanently closed during the dynamic-braking operations, in the illustrated system.)

The'progressive operation of the various resistance-shorting switches, during both motoring operation and dynamic braking, is under the automatic control of a suitable limit-relay or relays, which are. energized to be responsive to conditions which accompany excessive torque in the motors. Such a limit-relay is illustrated in the form of a current-relay CR, having an actuating-coil CR which is connected in series-circuit relation with the series field winding SF2. This current-relay CR also has a back-contact I99 (also marked CR), which is normally closed, that is, which is closed in the non-actuated or lowcurrent position of the relay.

The current-relay OR is also provided with certain recalibrating-means. In accordance with previous practice, this relay is provided with a cumulatively operating rate-coil RC, which is energized through a weight-responsive rheostat 200, during accelerating operations, and which is energized through a braking-responsive rheostat during dynamic-braking conditions.

The weight-responsive .2 positions.

rheostat 200 is automatically adjusted according to the variable weight or live load carried by the car, so that the ratecoil RC is the most strongly excited during lightload conditions, thus reducing the minimumcurrent setting at which the limit-relay CR, picks up and opens its back-contact I99. The brakingresponsive rheostat 20l is automatically changed in response to the position of a brake-handle 202, which will be subsequently described, so that the rate-coil RC has its maximum excitation when a low braking-rate is called for, thus providing a low minimum-current setting at which the limit-relay CR picks up andv opens its back contact I99, and also providing limit-relay calibration which is different for braking and power-operating conditions.

All of the electrically controlled relays and switches which are shown in the drawing are diagrammatically indicated as having vertical switch-stems (indicated by dotted lines), which are biased by gravity toward their lowermost positions, and all of these switches and relays are shown in their deenergized or non-actuated All of the relays and switches are electrically controlled, and they are illustrated as being electrically or magnetically operated, by means of an appropriately numbered or lettered coil or solenoid, represented by a circle, acting magnetically to lift an armature which is represented diagrammatically by a smaller circle inside of the coil-circle. In general, the same switch-designation is applied to any particular switch, its coil, and its contacts, by way of iden tification of the parts belonging to a given switch or relay.

The various electrical control-circuits for a train are under the control of a number of trainline wires, which extend from car to car, throughout the entire length of the train (not shown). In the simplified circuit-diagram of the drawing, eight of these train-line wires are used, being given their usual designations, namely (+),3, 4, 5, 6, I, I2 and GS.

Energy for the various relay-circuits or switchcircuits' is provided by means of a battery B on each car. The negative terminal of each battery is permanently grounded, while the positive terminal of each battery is connected, through a switch 203, to the positive train-line wire Each end of each car is provided with a mo tormans master controller MC, only one of which is indicated in the drawing. The illustrated master controller MC is indicated as being an accelerating-controller having an off-position and three on- positions 1, 2 and 3. In each of the three on-positions of the master-controller, MC, the positive control-wire is connected to the train-line wires I2, GS and 6. The train-line wire I2 is the energizing-wire for the operatingcoil LSI of the line-switch LSI; while the train line wire GS is the energizing-wire for the operating-coil GI of the ground-switch GI, as will be subsequently described.

In the second and third on-positions of the accelerating-drum of the master controller MC, the train-line wire 4 is energized from the positive bus while in the third on-position of this controller, the train-line wire I is energized from the positive bus In the ofi-position of the accelerating drum or master controller MC, a connection is made from the positive control-wire to the trainline wire 3. In the master controller MC, in accordance with a known practice, there is an overlap between the off-position contact which energizes this conductor 3, and the on-position contacts which energize the conductors I2 and GS, so that, during the notching-oif of the mastercontroller MC, the contact at 3 is made before the contacts at I2 and GS are broken. This overlapping construction is particularly neces sary in properly controlling a braking-operation protective-relay BP which will be subsequently described, and which also constitutes the subject matter of a Riley application, Serial No. 95,904, filed May 28, 1949, patented May 20, 1952, No. 2,597,183.

The first on-position of the accelerating-controller MC, in Fig. 1, is a switching position, in which the control-wires I2, GS, and 6 are all energized. The control-wire I2 energizes a control-circuit wire I0, through interlocks which are provided, by the braking-switches BI and B5, in the form of back- contacts 204 and 205, respectively; and the control-circuit wire I0 is used to energize the operating-coil LSI of the lineswitch LS I In accordance with a usual practice, the exciting-circuit for the line-switch operating-coil LSI also contains a make-contact 205 of a line-relay LR, which is a voltage-responsive relay which drops out upon a voltage-failure of the supplyline I91. This line-relay LR is shown as an undervoltage relay which has an operating-coil LR which is connected between the supply-line I9"! and ground, through a back-contact 201 of the line-switch LS2, said back-contact being paralleled by a make-contact 208 of the linerelay LR.

As set forth in the previously mentioned Purifoy-Burkhart application, the control-wire I0 energizes a control-wire I20 through a back-contact 209 of the line-relay LR. This line-relay back-contact 209 thus closes in the event of a power-line voltage-failure, which might result from either a third-rail gap or from any other cause; and if the master-controller MC is, at the time, on any on-position, the conductors I2 and I0 will be energized, and hence the line-relay back-contact 209 will energize the control wire I20, which we use as an auxiliary holding-circuit for the protective relay or brake-power relay BP, which we will subsequently describe in more detail.

The train-line wire GS energizes the operating-coil GI of the ground-switch GI, through interlocks which are provided by back-contacts 2 I0, 2H and 2I2, which are carried by the braking-switches BI and B5, and by the paralleloperation switch G, respectively. The back-contact 2I2 is paralleled by a make-contact 2I4 of the ground-switch GI. v p

The train-line wire 6 is connected, through an LSI make-contact 2E5, to a relay-circuit til, which is connected, through a GI make-contact 2I6, to a circuit 62 which constitutes a holdcircuit for the switch-progression for the accc1- crating-resistance short-circuiting switches SI to SW and J. This hold-circuit B2 is used to energize the operating coil J R of the series-motor circuit switch JR, through interlocks on the switches J and G, in the form of back-contacts 2I'I and 2I8, respectively. The said hold-circuit 62 is also used to directly energize the close-coil or actuating-coil BP-Close of the braking-operation protective-relay BP.

The result of the master-control energization in the No. 1 on-position of the master-controller MO, is thus to close the main-circuit or powercircuit contacts of the traction-motor switches LSI, GI and JR, thereby completing a seriesconnection motor-circuit for causing a slow movement of the train, for so-called switching purposes, with all of the accelerating-resistances in series with the motors. This circuit can be traced from the supply-circuit iSl, through the main LSI contact, the resistor R1, the armature AI, the series field SFI, the resistance R2, the resistance R5, the main JR contact, the resistanee R3, the series field SP2, the current-relay coil CR, the motor armature A2, and the main GI contact, to ground.

At the same time, the energization of the braking-operation protective-relay BP paves the way for the subsequent energization of the dynamicbraking circuits of the motors, and also for the automatic progression-control, under the control of the limit-relay or current-relay CR, both for the motoring progression during acceleration, and for the dynamic-braking progression during an application of the brake-lever 202, as will be subsequently described.

The hold-circuit $52, which is energized in the No. 1 on-position of the master-controller, is also connected, through an LSI make-contact 222, to a hold-circuit M, which is used in the subsequent progression-control.

The No. 2 position of the accelerating-controller MC is the first of two running- positions 2 and 3. It initiates the accelerating progression of the series-meter connections, by energizing the trainline wire 5, which is connected, through an LSi make-contact 22 3, to a conductor 40. The conductor as is connected, through an LS2 backcontact 225, and a JR make-contact 225, to a conductor 52, which energizes the operating-coil LS2 of the second line-switch LS2, which acts as the first acceleration-progression switch, by short-circuiting the first accelerating-resistor RI. This LS2 switch has a maize-contact 221 which picks up and serves as a holding-circuit contact between the circuits 5% and d2.

This second line-switch LS2 also has a makecontact 228 which connects the. circuit ii] to a circuit 25. The circuit is connected, through the CR limit-relay back-contact W0, and through 2. BP make-contact 2350, to a circuit 0-5, which constitutes the main limit-relay progressioncircuit of the control-equipment. This limitrelay progression-circuit 48 is thus not only under the control of the limit-relay or current-relay CR, which is responsive to excessive motor-currents, but it is also under the control of the braking-operation protective-relay BP, which must be closed (with the protective relay in its actuated position), before there can be any progression during either the motoring operation or the braking operation.

This limit-relay progression-circuit it is connected, through an LSi make-contact 23L to a progression-wire M, which is connected through an LS2 make-contact to a control-wire 50. The control-wire 5 3 energizes the operating-coil 1-2 of a second resistor-shorting progressionswitch I-2, which carries the two main contacts Si and this energization being effected through a back-contact 233 of this same switch -2. Thus, this energizing-circuit from the conductor {it includes the switch-out interlock 233, a conductor 55, and the coil I--2. This second progression-switch I2 picks up and closes a holding-circuit make-contact 236;, which energizes the circuit from the hold-circuit B'I.

The actuation ofwthe second resistance-shorting switch l2 also closes a make-contact 235, which energizes a circuit 53 from the progression-circuit 41, through a back-contact 2350f a third resistance-shorting switch 3-4, which. is the switch Which'carries the main switching-contacts S3 and S4. The energizing-circuit for this switch extends from the conductor 53, through the operating-coil 3-4 and a back-contact 231 of a: fourth resistance-shorting switch 9l0, thence through a control-circuit conductor I09, and a J-switch back-contact 238, to the ground negative battery-terminal The actuation of the third resistance-shorting switch 34 closes a make-contact 239 which establishes a holding-circuit for the conductor 53 from the hold-wire 61.

The actuation of the third progression-switch 3--4 also closes a make-contact 24l, whichcompletesa circuit from the progression-wire 41 to a conductor 59, which energizes the actuating coil 9--I0 of the fourth resistance-shorting switch 9-40, which carries the main switch-contacts S9 and SH], the negative terminal of said coil 9| being connected to the previously described wire M9. The actuation of this fourth switch 9-I0 also closes a make-contact 242 which establishes a holding-circuit for the conductor 59 from the hold-wire 31.

The'actuation of the fourth resistance-shorting switch 9-) also closes a. make-contact 243, which is connected between the progression-wire 4'! and a. circuit 65, through a back-contact 244 of the third resistance-shorting switch 34. This circuit 65 energizes the operating-coil J of the transition-switch J, through a G-switch back contact 246. The transition-switch J then closes its main or power-circuit contact J, which constitutes the last step in series motor-connection for the traction-motors, cutting out the last accelerating-resistance R4. This transition-switch J has a make-contact 241 which establishes a holding-circuit from the conductor 65 back to the hold-line 62. The previously described J- switch back-contacts 2li and 238 are opened,

upon the energization of the transition-switch J thus dropping out the initial series-connection switch JR, and the third and fourth acceleratingswitches 3-4 and 9-H).

The next step in the acceleration of the traction-motors is accomplished by a movement of cOntact. 250 of the transition-switch J, so as to energize a control-circuit 3|, which is in turn connected, through a JR, back-contact 25!, to a control-circuit 66 which energizes the operatingcoils M and G of the parallel-motor-connection switches M and G, These switches M and G thereupon connect the traction-motors in parallel. between the supply-circuit I91 and ground, with only the first two of the resistance-shorting switches .energized, in the illustrated form of embodiment of our invention, namely the second line-switch (or first progression-switch) LS2, and the second progression-switch l-2 which carries the main switching-contacts SI and S2. The energization of the parallel-connection switch G opens the previously described back-contact 246, which drops out the transition-switch J. The energization of the parallel-connection switch M closes a, make-contact 252, which establishes a holding-circuit for the@ conductor 66 from the line 60.

Responsive to'theydropping-out of "the transition-switch J, the back contact 238 of this switch recloses, and. re-initiates the switch progression of the resistance-shorting contacts S3 to Sill, under the control of the switches 3-4 and 9.l0, through the circuits which have beenpreviously described. This establishes the maximum armature-voltage conditions onthe motors, and it completes the connections for the full-field parallel-connection operation. of the traction-motors.

As soon as the resistance-shorting switch 9- -l 0 closes, it closes an. additional contact 254, which energizes a field-controller actuating-circuit. from the progress-wire ",said circuit extending from the wire-41 through the previously mentioned make-contact 1 254 of the resistance-shorting switch 9l0, a back-contact 256 of the third progression-switch. 37-4, a make-contact 251 of the parallel-connection switch M, and a makecontact 253 of the line-switch LS2, and thence to the short-field wire 39 of the field-controller FC.

The-short-field wire 39 of the field-controller FC energizes the short-field coil FC--SF, or other means which may be used to move the fieldcontroller from its full-field position FF to. its short-field position SF. Thisstartsthe progressive operation of the field-controller, and-it. may be brought about in any one of several ways. In the illustrated form of. embodiment, since the powerfor the short-field wire139 is obtained from the progressewirejl, which. is under the control of the limit-relay CR, the field weakening braking-protective relay 'BP is used, as shown,

the brake-wire 3 is also used to directly energize a hold-coil BP-hold of the brakingprotective relay BP, and this hold-coil may be regarded as representative of any holding-means which is eilective only after the protective relay HP has previouslybeen moved to itsactuated position. When a separate-holding-coil, BP-hold, is used as-such a holding-means for the BP relay, said coil will be made so as to be-too weak to pick up the BP relay if the relay is in. its non-actuated position when the hold-coil is energized, but the hold-coil BP-hold has enough energy to hold the relay actuated or closed, once it has been. actuated.

As set forth in the previously mentioned. Purifoy-Burkhart application, the BP-hold coil is also provided with a second energizing-circuit, which is independent of the-brake-wire 3, and thus operative in any of the three on-positions of the master-controller MC. This second holdcoil energizing-circuitincludes a make-contact 259 of this brake-protective relay 3?, and this make-contact 259 is used to energize the brake- Wire 3 from the previouslydescribed controlcircuit I20, which is under the control of the line-relay LR, so that the control-circuit [20 is energized whenever there is a failure of the linevoltage, at a time when the train-iine wire 52 is energized, that is, at a time when the mastercontroller is on any one of its three on-positions, as previously described. In this way, we not only maintain the energization of the BP-hold coil under the no-voltage conditions just described, thus making sure that the brake-protective relay 13]? remains in its actuated condition, but we also immediately energize the brake-line 3, without waiting for the master-controller M to be returned to its off-position, which establishes the coasting braking-circuit connections, as will now be described.

The brake-wire 3 is connected, through an LS! back-contact 256 and a BP make-contact 26!, to a control-circuit MB. This control-circuit 3 IB is connected, through a GI back-contact 252, to the previously described control-circuit wire 3|, which energizes the previously described parallel-motoring switches M and G- through the JR back-contact 255 and the control wire 66. The control-conductor tlB is also connected, through a G! back-contact 263, to a control-wire 31C, and thence to the positive terminal of the braking-switch coil Bi, the negative terminal of which is connected in a circuit which includes a B5 back-contact 265, a conductor I02, another B5 back-contact 265, a conductor IM, and a JR back-contact 261, and thence to the grounded negative battery-terminal The closure of the switches M, G and Bi completes the establishment of a weak coasting-operation dynamicbraking circuit-connection for the traction-motors, with all of the available dynamic-braking resistances R5, R2 and R3 in circuit, this dynamic-braking resistance being large enough so that the braking tractive-eiiort is usually quite weak, at moderate motor-speeds, thus permitting the train to coast, with little or no sensible or perceptible braking-effect, as long as the fieldcontroller PC remains in its short-field position.

A connection is also provided, for controlling the fiel -controller FC during the coasting-operation. Ll accordance with a known practice, we provide a circuit extending from the controlwire tlC, through a back-contact 258 of a brakerelay BR, to a control-circuit 32, and thence through the back-contact 269 of a spotting-relay SR, to the full-field wire 33 of the fieldcontroller FC. The brake-relay BR was shown and described in a Riley-Purifoy Patent 2,523,143, granted September 19, 1950. The spotting relay SR is a previously used relay, having an operating-coil SR which is included in the common brake-circuit connection I88, so that this relay is responsive to the braking-circuit current. This spottin -relay SR is adjusted to have a low-current pickup-value, so that it can hold the braking-circuit current to a small value suitable for spotting purposes, during the coasting operation of the traction-motors, as is well understood in the art.

The full-field wire 33 of the field-controller FC energizes a full-field coil FC-FF, or other means for causing the field controller FC to the spotting-relay SR. has a make-contact 219 which connects the circuit 32 to a circuit 35, which goes to a field-controller contact-segment 21!, which is closed only certain early points in the progressive movement of the fieldcontroller F0 from its full field position toward its short-field position SE. This field-controller segment 2'5: is preferably opened at a certain point near the short-field position 53F, preferably before the field-controller reaches this short-field position SF. As shown, we prefer to have this field-controller segment Zil closed at the positions FF through F3 of the field-con troller FC. This field-controller segment 21! is used to connect the wire 36 to the short-field wire 39 of the field-controller FC. In this way, when the spotting current is too large, that is, large enough to pick up the spotting-relay SR, the spotting current is reduced by adjusting the motor-fields toward a Weaker condition, by making the field-controller FC progress in the direction towards its short-field position, but this progression is usually arrested before the field-controller returns all of the way back to its original short-field position SF, which it occupied before the spotting-control commenced to operate.

A service braking-application is made by the closure of the brake-lever 202, which energizes the fu1l-brake wire 5 from the brake-wire 3. This full-brake Wire -5 is connected directly to the coil BR of the brake-relay BR. The brakerelay BR has a make-contact 272, which connects the full-brake line 5 to the conductor 45 which leads up to the limit-relay progressioncircuit :16, thus putting the braking progression under the control of the back-contact IQ?) of the limit-relay 0r current-relay CR, as well as under the control of the BP make-contact 23%, both of which are in circuit between the conductor t5 and the limit-relay progression-circuit it. At the same time the opening of the back-contact 268 of the now-actuated brake-relay BR takes the braking progression out of the control of the spotting relay SR.

Whenever a braking-application is called for, the energization of the brake-relay BR closes a BB. make-contact 213, which is used in the initiation of the dynamic-braking progression. Thus, the BR make-contact 213 is used to make a connection from the limit-relay progressioncircuit 46 to the full-field wire 33 of the fieldcontroller PC. This causes a progression of the field-controller FC until it reaches its full-field gosition FF, under the control of the limit-relay The closure of the brake-relay BR also closes a make-contact 214 which makes a connection from the control-wire 3| C to a braking-operation hold-wire il, in readiness for use in the subsequent brake-progression operations.

When the braking-controlling progression has proceeded to the point at which full-field conditions are restored in the traction-motors, the field-controller FC closes a full-field contact member 216, which closes a circuit from the fullfield wire 33 to a conductor 49, and thence through a BR make-contact 27? to a brakingprogression circuit 48.

The energization of the braking-circuit progression-wire 48 immediately serves, through a BI make-contact 218, which is already closed, to energize a circuit 12, which is connected, through a B2 back-contact 219, to a circuit 82 which is connected to the positive terminal of the B2 actuating-coil, the negative terminal of which is connected to the previously described conductor I02. The B2 switch thus picks up and closes its main contact B2 which shorts out a part of the braking-resistance R5 in the common dynamic-braking circuit I98 of the traction-motors. The actuation of the B2 switch also closes a make-contact 280 which establishes a holding-circuit for the wire 82 from the hold-wire I I.

A circuit is next established from the lower end of the progression-wire 40, through a B6 back-contact 28I, to a conductor 15, and thence through a B2 make-contact 282, which has just been closed, to a conductor 85 which is connected to the positive terminal of the B5 actuating-coil, the negative terminal of which is connected to the previously mentioned wire I04. The B5 switch closes its main-circuit contact B5, which shorts out more of the braking-resistance R5 in the common dynamic-braking circuit I98 of thetraction-motors. At the same time, the B5 switch closes a make-contact 283 which establishes a holding-circuit from the conductor 85 back to the hold-wire I I.

The energization of the braking-progression switch B5 opens its previously mentioned backcontacts 265 and. 266, thus dropping out the switches BI and B2, the main contacts of which are both short-circuited, now, by the main contact B5. The dropping-out of the BI switch closes its lowermost back-contact 284, which completes a circuit from the conductor I5 to a B5 make-contact 295,and thence to a wire 86, which is connected to the positive terminal of the B6 coil, the negative terminal of which is connected to the wire I04. The B6 switch thus closes, and closes its main contact B6 which further shorts outsome of the braking-resistor R5, thus still further reducing the eifective braking-resistance in the dynamic-braking circuits. At the same time, the actuation of the B6 switch closes its make-contact 286, which establishes a holding-circuit for the wire 86 from the wire II.

The actuation of the B6 switch also closes a make-contact 281, which connects the progression-wire 48 to the previously described conductor I2, thereby reenergizing the B2 switch, the negative circuit of which is now completed from the wire I02, through a B6 make-contact 298, to the wire I04.

"It will be understood that all of these brakingprogression operations are'under the control of the limit-relay progression-circuit 46, which interrupts the progression whenever an excessive motor-current causes an opening of the currentrelay back-contact I99, which is connected in the energizing circuit for said wire 46, thus interrupting the progression until the motor-current subsides to a desirable value.

The braking-circuit progression-wire 48 is also connected, through a GI out-contact or back-contact 289, to the accelerating-resistance progression-wire 41. a

After the second closure or actuation of the B2 switch, so that the B2 and B6 switches are now both closed, a circuit is made, from the accelerating resistance progression wire 41, through a B2 make-contact 290 and a B6 makecontact 29 I, to the previously described conductor 50, thus re-initiating the progression of the switches I--2, 3-4, and 9I 0, which progressively close the accelerating-resistor switches SI to SIII, thereby cutting out the accelerating resistors R2 and R3 which are in the individual portions of the respective dynamic-braking circuits of the traction-motors, this progression being also under the same limit-relay control.

Ever since the actuation of the B5 switch, a B5 make-contact 292 has been energizing the accelerating-resistance hold-circuit 61 from the wire II, in readiness for this progression of the accelerating-resistor switches SI to SIB. The braking-progression thus continues until substantially all of the braking-resistance is removed from the dynamic-braking circuit, thus resulting in the completion of the dynamic-braking operation, during which the speed of the car or train has been reduced from the initial speed at which the dynamic brake was applied, down to a low speed at which the dynamic brake fades out.

If a braking-operation is to be discontinued, after once having been started, the braking-circuit switches are released by an opening of the brake-handle 202, without requiring the establishment of a (perhaps momentary) power-circuit (or MC on-position), in order to deenergize the braking hold-wire II. This is accomplished by the BR-contact 214, which is in series with the hold-wire I I. The opening of the brake-handle 202 deenergizes the brake-relay BR and opens its contact 214, without requiring an onposition of the master controller MC to release the brake-wire 3, in order to deenergize the conductor 3IC and hence the hold-wire II.

It has long been customary to automatically adjust the calibration or setting of the limit-relay CR, in order to cause this relay to drop out in response to various accurately controlled desirable minimum motor-current values, during both the acceleration-progression and the dynamicbraking progression. This is conveniently done by various controls for the energization of the rate-coil RC of the limit-relay CR. In the drawing, we have shown three circuits for the ratecoil control or calibration. Two of these ratecoil energizing-circuits are known. One such rate-coil circuit involves the weight-responsive rheostat 200, and is traceable from the positive control-power line through an LS2 makecontact 293, the aforesaid weight-responsive rheostat 200, a resistance 294, a conductor 92, a resistance 295, and the rate-coil wire 95. A second old or known rate-coil energizing-circuit involves the braking-responsive resistance MI, and is'traceable from the positive bus through a BR make-contact 296, and the aforesaid brakingresponsive rheostat 20I to the conductor 92.

In accordance with one feature of our present invention, we provide a suitable means for responding to an excessive rate of increase of the motor-current. Ordinarily, objectionably high rates of current-increase are not obtained during the accelerating-operation, but only during the first second and a half (or the like) of the dynamic-braking operation, and then only if the dynamic-braking operation is established while the carer train is operating at a rather high rate of speed, near its maximum speed, when dynamic braking is applied.

In the illustrated form of embodiment of our invention, we provide, in the motor-circuit, say in series with the series-field windings SF2, an impulse or kick-coil induction-means, in the form of a transformer which preferably has more turns in its secondary winding 30I than in its primary winding 302, for example 500 secondary-turns, to 164 primary-turns. It is important, for our purposes, in general, that this impulse or kick-coil induction-means or transformer 302-30I shall have a magnetizable flux-circuit 303 of its own,

which is separate from the motor-field. In other words, the series field winding SFI or SFZ cannot be used as an induction-means for responding to the rate of change of the motorcurrent, because the field-windings are subject to wider current-variations as a result of fieldshunting (which takes place during the dynamicbraking build-up period), than the variations in the armature-current. A field-winding induction-means, for limit-relay recalibration, would respond each time a notch is taken, during both acceleration and braking, instead of responding only to the current-increments which occur during very high armature-current conditions, such as prevail during the establishment of highspeed dynamic-braking conditions.

A field-winding induction-means would also be affected by the long time-constant of the motor-circuits, which causes the field windings to have an increased voltage thereacross, long after the termination of the transient period during which there is a high rate-of-increase in the motor-current, as a result of the progressive notching or advancement of the dynamic-braking control. We want our rate-of-change response to provide a control-voltage kick or impulse of relatively short duration, which will only momentarily recalibrate the limit-relay CR, so as to slightly delay, the next notch in the braking-progression, without becoming involved in the long time-constants of the motorcircuits. We are thinking about delaying the successive notching-points of the dynamicbraking progression, so that they will take from 0.5 second to as much as 1 or 2 seconds, during the critical time when excessive motor-current increments are encountered, as distinguished from the previously obtained notching-intervals of the order of from 0.1 second, or less, to something like 0.2 or 0.4 second.

A convenient means for making use of the impulse-voltages in the secondary transformerwinding 301, so as to temporarily or transiently recalibrate the limit-relay CR which controls the braking-progression, is to apply this secondary transformer-voltage directly across the terminals of the rate-coil RC of the limit-relay CR, as shown in the drawing, wherein one secondary terminal is connected to the conductor 95, while the other is connected to the grounded r negative bus In one embodiment of our invention, the resistance of the secondary winding 30! was about equal to the resistance of the rate-coil RC, so that, when there was no sensible rate of increase of the motor-current, the rate-coil excitation would be cut approximately in half by the parallel connection of the transformersecondary 30!, thus necessitating a readjustment of the values of the resistances 200, 2!, 294 and 295 in series with the rate-coil energizingcircuit 95. Other than this, the parallelconnected transformer-winding 3M had no discernible efiect upon the rate-coil operation, except when there occurred a high rate of change in the magnitude of the motor-current which traversed the primary winding 302, in which case the secondary winding 30| applied a momentary recalibrating voltage-impulse to the rate-coil RC, which strengthened the rate-coil excitation, and thus reduced the amount of current necessary to flow in the operating-coil CR in order to produce a pick-up response or the limit-relay CR.

In accordance with another feature of our present invention, we provide our field-controlling means FC with a contact-segment 306 which is closed at all controller-positions except those positions which are close to the full-field position FF. As illustrated, the contact-segment 306 of the field-controller PC is closed in the controller-positions between the intermediate position F3 and the short-field position SF, inclusive. In accordance with our invention, we use this PC contact-segment 306 to make a connection from the train-line wire 6, which controls the switching-operation of the tractionmotors, to the train-line wire 4, which controls the progressive series-motor running-connections.

The operation of the simplified illustrated apparatus will be clear from the running comments which have been made during the progress of the description, as well as from the prior art. A few words of added explanation, as to the features which are more particularly related to our novel control-circuit parts, may, however, be helpful.

One of the novel features of our present invention relates to the use of the impulse or kickcoil induction-means 30230l. In the broader aspects of our invention, we are not limited to the particular turn-ratios which have been suggested as being preferable. Neither are we limited to the particular point of connection of the primary winding 36?, in a, portion of the motorcircuit which is in use during motoring or powercircuit operation, as well as during the dynamicbraking operation. Usually, during the progression or acceleration during the motoring-operation, the motor-current does not reach excessive rates of increase, between successive accelerating-notches, such as would require the use of transient or temporary limit-relay recalibration in accordance with our present invention. Our impulse or kick-coil induction-means 3U230l automatically takes care of this situation by developing only negligibly small voltage-impulses in its secondary Winding 30! during the motoring operations. If desired, all motoring-operation responses of the induction-means 302-30| could obviously be avoided by including the primary winding 302 in the dynamic-braking motor-circult-portion IE8, between the intermediate armature-connections AXI and AX2, as is done in the case of the operating-coil SR of the spottingrelay SR. We wish it to be understood, therefore, that the really essential thing in regard to the kick-coil connection, is that the kick-coil 3fi23lll shall be at least responsive during the dynamic-braking operations, which is the important field of operation of this kick-coil means.

Even in the dynamic-braking operations, our new kick-coil induction-means or transformer 3532-46! is not needed at low motor-speeds, because excessive rnotor-current increments are not obtained, during the progression of the dynamicbraking control, except when a dynamic-braking operation is initiated at a time when the traction-motors are operating at a high rate of speed, usually a rate of speed which is close to the maximum motor-speed. At such times, the successive motor-current increments, during successive notchings or progressions of the dynamic-braking control, become sufficiently severe to make the motor-current overshoot to values in excess of the highest desired value, if some such means as our present invention were not applied. The motors are operating as series generators, during these dynamic-braking operations, so that an excessive motor-current, during such an operation, means the production of an excessive motor-flux in the series field-windings SF! and SF2. And an excessive motor-flux, coupled with a high motor-speed, means an excessive motor-voltage The combination of an excessive motor-current and an excessive motor armature-voltage, during dynamic braking spells a rough or excessive brake-application. The excessive motor-voltage also results in motor-flashing at its commutator.

'The foregoing difiiculties are avoided by our induction-means 302-30l, which develops enough secondaryvoltage, during the dynamicbraking notching-progression, at high motorspeeds, to produce a sensible and efiective recalibrating-voltage which transiently or momentarily recalibrates the limit-relay CR which controls' the motor-current values at which successive steps are taken in the progressive application of successive notches of dynamic-braking control.

The second novel feature of our invention, namely the field-controller contact-segment 306, has to. do with the prevention of rough-brake conditions which have sometimes been encountered as a result of the motormans misuse of his master-controller MC. Sometimes, when the car or train is running at high speed, with the motors in their short-field condition, that is,

with the field-controller FC in its short-field position SF, the motorman momentarily throws oil" the power, establishing a momentary coastingoperation, by moving his master controller M to the off-position, and then immediately again moves the master controller MC to its switchingposition, or No. 1 position, which is not a running-position, and not intended to be used except for slow-speed operations while the car or train is being switched from track to track.

Nevertheless, motormen sometimes leave the master controller MC in this switching-position while the car or train is running at a high speed. and while the motorman is making up his mind whether he wants to resume full running conditions, with a full-power application, or whether he is going to have to initiate a dynamic-braking operation. Meanwhile, in previous motor-control systems, the traction-motors are connected across the power-supply line in their series motor-connections, and the motor-fields are very weak.

If, now, the motorman should go into a dynamic-braking operation, with the motor-fields in an excessively weakened condition for that particular motor-speed, then the dynamic-braking operation would start with the motors having a very low field-flux. This low-flux condition would be doubly aggravated, not only on account of the presence of the field-shunts Xl-RSI and X2-RS2,. which divert a considerable part of what little motor-current there had been, immediately prior to the establishment of the dynamic-braking connections, but the motoringcurrents themselves had been excessively small, because the motorman had been erroneously op erating, at a high speed, on his No. 1 switching-- position, which means that all of the accelerating-resistances RI, R2, R3 and R4 had been in the motor-circuits, so that very little motor-current could be flowing, that is prior to our introduction of the new field-controller contact-segment 306.

Thus, when dynamic-braking connections are established, while the motor-flux was so extremely weak, and remembering that the motors have a rather slow time-constant; so that theirmotor-flux cannot be built up anything like, as rapidly as the progression-rate during the bulidup of dynamic-braking conditions, then the. dynamic-braking currents will at firstbeextremly low, causing the dynamic-braking progression to proceed at its maximum rate, without interruption by the picking-up of the limit relay CR, so that, when the motor-flux finally builds up to its increased value, too much resistancewill have been cut out of the dynamic-braking circuits, and excessive dynamic-braking currents willube. obtained.

We avoid these diflicultiescby, in effect, preventing the motorman from operating ,a fastmoving car or train withthe switching-connections of the motors. Whenever the accelerationprogression of the traction-motor control has advanced far enough to cause the field-controller FC to adjust itself to any of its positions F3 to SF, if the motorman should then move his master-controller MC to its off-position, and should then immediately notch it up again to its No. 1 switching-position, while the trainis still running fast, our new field controller contact 305 connects the switching-controlling wire 6 to the progression-controlling circuit 4-40- 45-46-41, which rapidly and uninterruptedly cuts out all motor-resistance during these seriesmotor-connection operating-conditions, thus materially increasing the field-strength of the mo tors, even though the motorman should improperly leave his master-controller on its No. 1 switching-position while the car or train is operating so fast.

It will be understood, of'course, that if the motorman had left his master controller in the offposition, for even a very briefmoment, before going into dynamic braking, the coasting or spotting conditions would have been established, wherein the motors would be connected in parallel, and the motor field-strengths would have been properly maintained and adjusted by the mild dynamic-braking currents which flow during coasting or spotting. The trouble came, in previous motor-control systems, when the motorman went into the maximum-resistance series-motor switching-connection while the car was running fast, and then immediately changed into the dynamic-braking connection for a brake-- operation.

While we have described our invention, and explained its manner of operation, inconnection with a particular simplified illustrative form of embodiment, we wish it to be understood that the efficacy of the invention would not be affected by the addition of desired additional features or safeguards, or by the omission of undesired or unnecessary features, or by the substitution of equivalent or alternative forms of various means Or elements for performing the essential elementfunctions which have been described and explained.

We claim as our invention:

1. A motor-controlling assembly, including the combination, with a series-motor means to be controlled, said series-motor means including a motor-armature and a series fieldwwinding connested in series therewith, of: (a) a supply-circuit for the series-motor means; (b) a powerswitch means, for establishing a power-circuit for energizing the series-motor'means from the supply-circuit; (c) a braking-switch means, for establishing a dynamic-braking circuit for the series-motor. means; (11) a progressively operating braking-controlling means, for controlling the braking-adjustment of the dynamic-braking circuit during dynamic-braking conditions, said braking-controlling means including a brakingcontrolling limit-relay means having an operating-coil which is energized to be responsive to conditions which accompany a lower-than-desired braking-current in the dynamic-braking circuit, and means for progressively operating said braking-controlling means under the control of said braking-controlling limit-relay means; and (e) an induction-means for recalibrating the response of said braking-controlling limit-relay means in response to transient braking-current conditions in the dynamic-braking circuit, said induction-means having a magnetizable fluxcircuit which is separate from the motor-field.

2. The invention as defined in claim 1, characterized by said induction-means including a transformer having more secondary turns than primary turns.

3. The invention as defined in claim 1, characterized by said braking-controlling limit-relay means being a current-responsive relay having an operating-coil in series with a motor-armature.

4. The invention as defined in claim 3, characterized by said induction-means including a transformer having more secondary turns than primary turns, an auxiliary rate-controlling coil on said braking-controlling limit-relay means, and connection-means for connecting the secondary terminals of said transformer across the terminals of said auxiliary rate-controlling coil.

5. A motor-controlling assembly, including the combination, with a series-motor means to be controlled, said series-motor means including a motor-armature and a series field winding connected in series therewith, of: (a) a supply-circuit for the series-motor means; (b) a powerswitch means, for establishing a power-circuit for energizing the'series-motor means from the supply-circuit; (c) a braking-switch means, for establishing a dynamic-braking circuit which uses said series-motor means as an entirely selfexcited series-generator means, said dynamicbraking circuit including a controllable braking circuit resistance; (d) an accelerating controlmeans, for controlling the closure of said powerswitch means and, contingent upon such closure, progressively controlling the acceleration of said series-motor means during power-circuit operating-conditions, said accelerating control-means comprising an acceleration-controlling limit-relay means having an operating-coil which is energized to be responsive to conditions which accompany a lower-than-desired motor-current during acceleration, and means for progressively operating said accelerating control-means under the control of said acceleration-controlling limitrelay means; (e) a spotting-current controlmeans, operating to close said braking-switch means in response to an opening of said powerswitch means; (I) a dynamic-braking controlmeans, operative to convert said spotting-current conditions into dynamic-braking conditions, said dynamic-braking control-means comprising a braking-controlling limit-relay means having an operating-coil which is energized to be responsive to conditions which accompany a lower-than-desired motor-current during dynamic braking, and means for progressively operating said dynamicbraking control-means under the control of said braking-controlling limit-relay means; and (g) an induction means for recalibrating the response of said braking-controlling limit-relay means in response to transient motor-current conditions during dynamic braking, said induction-means having a magnetizable flux-circuit which is separate from the motor-field.

6. The invention as defined in claim 5, characterized by said inductive-means being energized in series with a portion of the motor-armature circuit which is in both the power-circuit and the dynamic-braking circuit.

'7'. The invention as defined in claim 5, characterized by said induction-mean including a transformer having more secondary turns than primary turns.

8. The invention as defined in claim 5, characterized by said braking-controlling limit-relay means being a current-responsive relay having an operating-coil in series with a motor-armature.

9. The invention as defined in claim 8, characterized by said induction-means including a transformer having more secondary turns than primary turns, an auxiliary rate-controlling coil on said braking-controlling limit-relay means, and connection-means for connecting the secondary terminals of said transformer across the terminals of said auxiliary rate-controlling coil.

10. The invention as defined in claim 5, characterized by said acceleration-controlling limitrelay means and said braking-controlling limitrelay means being one and the same relay, having different calibrations during acceleration and braking, respectively.

11. The invention as defined in claim 10, characterized by said induction-means including a transformer having more secondary turns than primary turns.

12. The invention as defined in claim 11, characterized by said transformer being energized in series with a portion of the motor-armature circuit which is in both the power-circuit and the dynamic-braking circuit.

13. The invention as defined in claim 10, characterized by said one and the same relay being a current-responsive limit-relay having an operating-coil in series with a portion of the motorarmature circuit which is in both the power-circuit and the dynamic-braking circuit.

14. The invention as defined in claim 13, characterized by said induction-means including a transformer having more secondary turns than primary turns, an auxiliary rate-controlling coil on said current-responsive limit-relay, and connection-means for connecting the secondary terminals of said transformer across the terminals of said auxiliary rate-controlling coil.

15. The invention as defined in claim 14, characterized by said transformer being energized in series with a portion of the motor-armature circuit which is in both the power-circuit and the company a lower-than-desired braking-current; (c) a progressively operating braking-control means, operativeonly whenever a low-current condition exists in said limit-relay means, for progressively controlling the braking-adjustments of both of said dynamic-braking circuits during dynamic-braking conditions; and (d) an induction-means for recalibrating the response of said braking-controlling limit-relay means in response to transient braking-current conditions in the dynamic-braking circuit, said inductionme'aiis having a magnetizable flux-circuit which is separate from the motor-field.

17. The invention as defined in claim 16, characterized by said induction-means including a transformer having more secondary turns than primary turns.

18. The invention as defined in claim 16, char acterized by said braking-controlling limit-relay means being a current-responsive relay having an operating-coil in series with a motor-armature.

19. The invention as defined in claim 18, characterized by said induction-means including a transformer having more secondary turns than primary turns, an auxiliary rate-controlling coil on said bralting-controlling limit relay means, and connection-means for connecting the secondary terminals of said transformer across the terminals of said auxiliary rate c'ontrolling coil.

20. A motor-controlling assembly, including the combination, with a plurality of series motors to be controlled, each series motor including a motor-armature and a series field winding connected in series therewith, of: (a) a supply-circuit for the series motors: (b) a power-switch means, for establishing a power-circuit for energizin the series motors, first in a series-motor connection, and then in a parallel-motor connection, from the supply-circuit; (c) a braking-switch means, for establishing a dynamic-braking circuit for the series motors; (d) a variable fieldcontrolling means, for progressively adjusting said series field winding toward full-field con dition and toward a short-held condition, respec tively; (e) a progressively operating acceleration-controlling means, for controlling the acceleration of the series-motor means during each of the power-circuit operating-conditions, said acceleration-controlling means including a finallyoperating means for causing said field-controi ling means to progressively adjust said series field winding toward its shoft-iield condition in the parallel-motor power-circuit connection; (f) a progressively operating spotting controlling means, for controlling the spotting-adjustment of thedynamic-braking circuit during coasting conditions, said spotting-controlling means including a means for causing said field-controlling means to progressively adjust said series field winding toward its full-field. condition; (9) a progressively operating braking controlling means, for controlling the braking-adjustment of the dynamic-braking circuit during dynamicbraliing conditions, said braking-controlling means including a first-operating means for causing said field-controlling means to adjust said series field winding to its full-field condition; (h) an accelerating-control1er, having an off-position, a switching-position, a series-motorconnection running-position, and a parallelmotor-connection running-position; (i) a braking-controller, having an off-position and an onposition or positions; (7') a starting-circuit means, for closing the power-switch means in a seriesmotor connection, while maintaining said progressively operating acceleration controlling means in its lowest-speed condition, in response to a switching-position of the accelerating-controller; (it) an accelerating-circuit means, responsive to a closed condition of the power-switch means, and each of the running-positions of the accelerating-contro1ler, for causing a progressing operation of the progressively operating acceleration-controlling means; (Z) a spotting-circuit means, responsive to an off-position of the accelcrating-controller and an off-position of the braking-controller, for closing the brakingswitch means and causing a progressing operation of the spotting-controlling means; (m) a braking-circuit means, responsive to an off-position of the accelerating-controller and an onposition or positions of the braking-controller, for causing said field-controlling means to adjust said series field winding toward a fuller field; and a means, operative after full-field conditions have been established during dynamic braking conditions, for causing a continuing progressive operation of the progressively operating brakingcontrolling means; and (n) a means, responsive to a shortened field condition of said field controlling means, for establishing a temporary tiir cuit-connection between the switch-position and a running-position of the accelerating controller.

21. The invention as defined in claim 20, char acterized by said progressively operating brakingcontrolling means (9') including a, progressioncontrolling limit-relay, having an operating-coil in series with the braking-circuit, and an induc nonmieans, also in series wlththe braking-circuit, for recalibrating the response of said limit relay in'responseto transient braking-current conditions in the braking-circuit, said inductionmeans having a magnetizable flux circuit which is separate fromthe motor -field.

22; A motor-controlling assembly, including the combination, with a series-motor means to be controlled, saidseries-motor' means including a motor armature and a series field winding connected in series therewith, of z (a) a supply circuit for the series-motor means; (b) a power-switch means, for establishing a power-circuit for ener gizing the series-motor means from the supply= circuit; (0) a braking-switch means, for establish= ing a. dynamic-braking circuit tor the seriesmotor means; (it) a progressively operating brak ing-contrclling means, for controlling the brak ing-adjustment of the dynamic braki'ng circuit during dynamic-braking conditions, said braking controlling means including a braking-controlling limit relay means having an operating-coil which is energized to be responsive to conditions which accompany a lower than-desired braking-current in the dynamic-braking circuit, and means for progressively operating said braking-controlling means under the control of said braking-control ling limit-relay means; and (e) an inductioh means, responsive to a predeterminedly high rate of increase in the braking-current in the dy namic-Joraking circuit, for transiently altering the motor-controlling assembly in correction or said high rate of increase in the braking-current, said induction-means having a magnetizable fluxcircuit which is separate from the motor-field.

GEORGE R. PURIFOY. WILLIAM L. BARCLAY, JR.

No references cited.

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