US2327809A - Motor control system - Google Patents

Description

Aug. 24, 1943- c. M DONALD ET AL MOTOR CONTROL SYSTEM Filed Aug. 22, 1941 2 Sheets-Sheet 1 Inventors John F. Trible,

Jacob W. McNah" Char-lea MacDohald,

by Their Attorney.

Aug. 24, 1943. c MacDONALD ET AL 2,327,809

MOTOR CONTROL SYSTEM Filed Au 22, 1941 I 2 Sheets-Sheet 2 Pig. 2. 's? 6 5 Fig. 5. a y 5 A5! a I E a E I, l 35 I i I BRAKE gg; g g E g E $19 [Eb r Q f 1 g I I I 5/53 I5 Am i I CZP L am :flll

l 'T. J I37 1' 9 I l 3 I 1 A47 l zzrqzb IF- 2 A98 I I I I I I (BI/3' 46 A86 I i i g l I [4/ :I

I m I I I I I47 Aw I I 1 I I I BRAKING I48 ACCELERATION CONTROLLER 7 J7 CONTROLLER "Pig. 5.

MASTER CONTROLLER STEPS CON TA CTORS ACCELERAT/NG BRAKING lnventors John F: Trible, Jacob W. MoNair'g, Charles MacDonald,

Th eir' Attorney Patented Aug. 24, 1943 MOTOR CONTROL SYSTEM Charles MacDonald, Evanston, 111., Jacob W. McNairy, Bridgeport, Conn, and John F. Tritle, Erie, Pa., assignors to General Electric Company, a. corporation of New York Application August 22, 1941, Serial No. 407,872

24 Claims.

This invention relates to motor control systems, more particularly to systems of control for electric motor driven trolley busses or coaches utilizing a series motor, and has for its object a simple and reliable acceleration and dynamic braking control system providing for a predetermined limiting rate of acceleration and dynamic braking and preadjustment of the dynamic braking resistance in accordance with speed when power is taken off the driving motor thereby to provide a quick dynamic braking response.

Our invention has a special application to trolley bus controlsystems of the type described and claimed in United States Patent No. 2,198,- 4.81, issued on April 23, 1940, to Jacob W, McNairy and Charles MacDonald, wherein the controls for acceleration and dynamic braking are operated by separate pedals, thereby to simulate the operation of the conventional mechanically driven automobile.

A further object of our invention is a control system wherein the return of the acceleration controller to its oil position initiates the operation of control means to adjust the starting resistance for the motor in accordance with the speed or" the vehicle so that the resistance is preselected at a suitable value to give efiective dynamic braking quickly upon depression of the braking pedal.

Another object of the invention is means for establishing dynamic braking immediately by depression of the brake pedal without the prior application of power to the motor, for example, in the event that the vehicle starts rolling from standstill down a steep grade.

.Still another object of the invention is the utilization for dynamic braking of the same resistor short-circuiting contactors that are used during acceleration with the addition of one or more steps as required by control of the field of the motor.

In carrying out our invention in one form, we provide contactors for controlling the resistance during both acceleration and deceleration together with a relay which is responsive to the current in the motor circuit for automatically controlling these contactors and also for controlling the'field of the motor during dynamic braking.

We also provide a dynamic braking relay which is picked up and locked in by operation of the acceleration controller to start the motor, which relay remains picked up when the controller is returned to'its off position and thereby effects the preadjustment oi the resistance for dynamic braking during coasting operation of the vehicle. Another feature is switching means incorporated in the braking controller for picking up this dynamic braking control relay immediately upon depression of the braking pedal thereby to start dynamic braking without first applying energy to the motor by operation of the acceleration controller.

For a more complete understanding of our invention, reference should be had to the accompanying drawings, Fig. 1 of which is a diagrammatic representation of a system of control for a trolley bus embodying our invention; Fig. 2 is a layout diagram of the acceleration controller; Fig. 3 is a layout diagram of the braking controller; Fig. 5 is a sequence chart of the principal contactors and relays shown in Fig. 1; Fig. 6 is a layout diagram of the reversing controller; while Fig. 4 is a diagrammatic representation of the operating mechanism for the braking controller.

Referring to the drawings, we have shown our invention in one form as applied to a system of control for a trolley bus or coach driven by a series direct current motor provided with an armature H3 and a series field winding H. The motor may be connected for operation to the direct current supply mains l2 and l 3, which may be energized from suitable trolleys bearing on overhead trolley wires, an accelerating resistance 14 being provided which is cut out in sections by the short-circuiting switches or contactors Rl to R8 inclusive.

The acceleration of the motor ill is effected by means of a rotatable controller 22 (Fig. 2) which may be moved forward step by step or which may be turned immediately to a full speed position. In the latter case, the acceleration of the motor is controlled by means of a relay AER having a current coil 24 connected in series with the armature ill, and a current responsive coil 25 utilized during dynamic braking.

The connections of the motor for dynamic braking are control'ed by a braking controller 26 (Fig. 3) which when turned to a braking position causes the short-circuiting of the braking resistance to be controlled by the coil 25 of the AER relay to maintain a predetermined braking cur rent and torque.

As shown, the control circuits are supplied from separate supply mains 21 and 28 which are connected to a suitable supply source, for example, to a 36-volt storage battery (not shown). The mains i2 and i3 supplying the motor may, for example, be supplied from a GOO-volt trolley. circuit. One advantage of this separate storage battery source of supply for the control circuits is that dynamic braking of the motor can be obtained even in the event of a failure of the supply source to the high voltage mains l2 and l 3.

Acceleration It will be assumed that the acceleration controller 22, which is manually operated by a handle or preferably by a foot pedal (not shown), is turned from the off or coast position shown in Fig. 2 immediately to its sixth and full speed running position so that all of its acceleration controlling switches are closed. The first acceleration controller switch A to be closed energizes the LB (line breaker) coil 3| which closes the LB switch in the motor circuit and also the LB interlock switch 33. This circuit for the coil 3| is from the supply main l2 through the switch A30, coil 3|, B (braking) interlock switch 34, and

OLR (overload relay) switch to the supply '42 to the supply main 28. Thereupon the coil 36 picks up its armature, closing the R! switch for completion of the motor circuit, opening its interlock switch 36, and closing its interlock switch 66 before the opening-of switch 30 to establish a holding circuit for the coil 36 independent of the contact 62 on the relay ABR.

At this time, the motor circuit is closed by the closing ofthe LB switch and the R! switch with all of the resistance I l i'n'circuit with the motor.

It should be noted that the RI switches 66 and 46 are of a walking beam floating contact bar type, these two switches having a single straight movable contact arm to which the reference numerals 40 and 46 are applied. This arm is pivotally mounted centrally'on a pivot 65 carried by the operating armature of the RI coil 36 or a member actuated by the armature. As shown, with the coil 36 deenergized, the lefthand end of this contact arm constituting the movable arm of the switch 46 is biased downward into engagement with the left-hand contact by means of a spring 46, while the other end of the arm is disengaged from the right-hand contact.

When the coil 36 is energized, the pivot is lifted by the armature of the coil 36 thereby first to raise the right-hand end of the contact arm constituting the movable arm of switch 46 into engagement with the right-hand stationary contact which is above the arm as seen in the drawings. Further upward movement of the pivot 45 lifts the left-hand end of the contact arm against the force applied by the spring 46 to disengage the left-hand contact which is below the arm. The spring now holds the right-hand end of the contact arm against the right-hand contact. This constitutes a simple and reliable switching means for first closing a holding circuit for the coil 36 and thereafter opening the pick-up circuit of the coil. During this movement it will be observed that the contact arm first pivots on the left-hand contact until the right-hand contact is engaged, and then pivots on the righthand contact to disengage theleft-hand contact.

interlock tarily prevented. When the motor current drops upon acceleration of the motor, the switch 42 closes at the drop out current value for which the relay is set and closes the circuit for the R2 coil 52. This circuit leads from the R1 switch 39 through Fl interlock switch 53, which is now closed, the A41 switch, coil 52, R2 switch 54, RI

' interlock switch 55, which is now closed, R1 interlock switch 4| and the switch 42 to the supply main 28.

Upon its energization, the R2 coil 52 first closes an interlock holding switch 56 and then opens its switch 54. It will be understood that vthese switches 56 and 56, and others which are shown in the drawings in the same manner as the switches 46 and 34, are of the walking beam type and operate in the manner described in connection with the latter switches.

The coil 52 also closes the R2 switch to shortcircuit the first section of the resistance id and closes an interlock switch 61 to provide for the energization of the R3 coil 58 under the control of the ABR relay.

As the motoraccelerates and the ABR switch 62 recloses, the R3 coil 58 is energized, the circuit leading from the Fl switch 53 through the A66 switch, the coil 58, its interlock switch 56, the switch 5? which is'closed and thence through the R7 switch ll and the switch 32 to the main 28. The coil 56 then closes the next resistance shortcircuiting switch" R3 and closes its interlock switch 66 for the next coil R6 6!, the coil 66 establishing a holding circuit for itself, as will be understood from the description of the coils 36 and 52.

Assuming that the acceleration controller 21 remains in its full on or sixth position, the acceleration continues automatically under the control of the ABR. relay, and the coils R6 6!, R5 62, R6 63 and R? 66 are successively energized in the order mentioned in a manner which will be understood with reference to the preceding description.

It will be noted that the coils for the an to R6 switches are all energized through the RJ 39 switch, which is normally closed. Therefore, when the R! switch closes, opening the R'l 39 switch, these coils are all deenergized and the R! to R6 switches drop open.

Also, it will be noted that the RI coil 36 is energized independently of the acceleration controller switches. The remaining coils, however, are energized through various acceleration controller switches and, consequently, if the acceleration controller is turned only part way to its full running position, the acceleration stopsat the point determined by the controller position.

, Thus, if the acceleration controller is moved to ascasco switch closed in the fourth position of the acceleration controller sets up a circuit for the R coil 52 and the R8 coil 63. In the fifth position of the acceleration controller, the A50 switch is closed for energization through the conductor Silo of the R1 64 and R8 65 coils. Finally, in the sixth position, the ASI switch is closed and sets up a control circuit for the Fl 14 coil and the F2 coil.

It will also be noted that the coils 6| to 65 inclusive are initially energized through the conductor 66, leading directly to the ABR switch 42 without going through the R1 4| switch.

As previously noted, when the R? switch closes and thereby short-circuits all of the resistance except the left-hand section No, the R1 interlock switch 39 opens the circuits of the coils for the Rl to R6 switches and these switches there:

fore open for subsequent sequencing operation as indicated clearly on the sequence chart Fig. 5, whereby various control combinations of the sections of the resistance l4 are made thereby gradually to reduce the resistance in the motor circuit for further acceleration. This is described below.

When the R8 switch closes, connecting the remaining sections of the resistance l4 in series with each other and in parallel with the left-hand section, its interlock switch 6'! closes and establishes again a pick-up circuit for the coils of the switches Rl to R6, the R? 39 switch being open. Also, a second R8 switch 68 is closed, whereby the R4 E! coil is next energized for closure of the R4 switch under the control of the AER relay. The E4 switch short-circuits the three left-hand sections of the resistance The coils of the R1, R2 and R3 switches are not energized at this time and these switches are therefore not closed because of the fact that the R1 switch 4| is now open. The coils of the R5 and R6 switches, however, are energized in succession to cut out additional sections of the resistance l4.

With the R6, R1 and R8 switches closed and the Hi switch open, thetwo left-hand sections of the resistance l4 only are connected in parallel with each other in the motor circuit.

In closing the R8 switch closes its switch 69 in the circuit of the RI coil 36, whereby the RI switch is next closed under the control of the ABR relay as before. With the R! and R8 switches now closed, the entire resistance l4 is short-circuited. The circuit for the El coil may be traced from the supply main 2i through the switch 3'1, wire 38, switch 33, R8 switch S1,

Ri coil'36, RI switch 40, conductor "Ell, RB switch 69, R8 switch 68, conductor 66 and AER switch 472 to the supply main 28.

Two additional points of acceleration are obtained by successively closing the Ft switch and the F2 switch to shunt and thereby weaken the motor field. The Fl switch in closing connects a resistance 72 and a reactance 73 in series with each other across the field winding ll, while the F2 switch in closing short-circuits the resistance l2. The coils l4 and 15 of these field shunting switches are controlled successively by the ABR relay after the closing of the R8 interlock switch 76 and the closing of the El switch 78. The circuit for the coil 14 is traced from the supply main 21 through switch 37, wire 33, switch 33, acceleration switch A which is now closed, acceleration switch A5l which is closed, R8 switch 76, coil 14, Fl switch l'i, Rl switch '58 which is now closed, LB switch 19 which is closed to the conductor 68 and through the AER switch 2 to the main 28.

The closing of the Fl interlock switch 80 sets up a circuit for the F2 coil 15, this circuit leading through the ASI switch as previously traced and then through the coil 15, the F2 switch 3|, switch 80, LB switch 32 to the conductor 66 and through the ABR switch 42 to the main 28.

The motor is now running at full speed with the resistance 14 short-circuited and the field ll weakened by field shunting, the Fl and F2 switches being both closed.

It is contemplated that the ABR current coil 24 will regulate its switch 42 so as to maintain the motor current below a, predetermined maximum value during starting. Since holding circuits for the various contactors when they close are set up independently of the switch 42, this switch has no control over the motor during running conditions after the acceleration period is over. In the event of an overload under running conditions and also during acceleration, the OLR (overload relay) coil 83 opens its switch 35 and thereby deenergizes the LB coil 3 l, whereupon the LB switch opens to disconnect the motor from the supply circuit. Also, the OLR switch 84 closes to close a circuit for the OLR holding coil 35. This switch 84 is arranged to close before the switch 35 opens. It connects the coil 35 momentarily in parallel circuit with the LB coil 3i, and the coil 85 holds the switch '35 open and the LB coil 3| deenergized after the motor circuit is opened by the opening of the LB switch. In order to reenergize the. motor, it is necessary to return the acceleration controller to its off position so as to open its switch shit and deenergize the coil 85 for reclosure of the *OLR switch 35.

Coasting Dynamic braking circuits are set up upon the return of the acceleration controller 22 to its off or coasting position for automatic adjustment of the resistance id in the braking circuit r in accordance with the speed of the motor, but

dynamic braking becomes effective only when the braking controller 28 is moved to a braking position. With the controller 22 operated by means of a pedal (not shown), it is biased by a suitable spring (not shown) to this off or coast position and returns to that position when the pedal is released. In that position, it will be observed from Fig. 2 that the switches A41, A48, A43, and A59 after being opened are again closed when the controller 22 reaches its full off or coasting position. The opening of the acceleration controller switch A30 deenergizes the coil 3i whereby the LB switch opens. Also, the LB switch 33 opens and deenergizes the operating coils of the contactor or switches Rl to R3 and Fl and FZ'Whereup-On these contactors drop open.

During acceleration the BR (braking relay) coil 8? is energized in preparation for braking through the -B interlock switch 88 which is then closed. This circuit is from main 2'! through switch 3?, switch 38, BR coil 87, OLR switch 89 to the main 28. The BB interlock switch 90 then closes and establishes a holding circuit for the coil 81 leading from wire 38, wire 82, through the B switch 3i which is closed, B R. switch 90, coil 8? and switch 89 to the main 28. Therefore, the BR, coil 87 remains energized after the acceleration switch 22 is returned-to its off or coast position.

The BR interlock switch 93 is closed partially to close circuits to the supply main 28 for the B coil 94 and the FF (field flashing) coil 95 in preparation for dynamic braking when the line breaker LB drops out. Also, the BR switch 93 partially closes a circuit for the AR coil 96 whereupon this relay picks upwhen the A98 switch is closed. The circuit for the AR coil 96 .is from main 2'! through switches 31, 91, A98, R4 switch 99, B switch I00, coil 96, BR switch 93 and OLR switch 89 to the main 28. A holding circuit in parallel with the B switch I is established by the closing of the AR switch IOI.

When the line breaker LB opens, its interlock switch 91 closes a circuit for the E coil 94 and the FF coil 95 in parallel with each other. This circuit leads through the acceleration switch A98 which is closed, the coils 94 and 95 in parallel with each other, BR switch 93 which is closed and OLR switch 89 to the main 28. This closes the B switches 99a and IBM and opens the B switch IOIa, the FF switch I02 being also closed.

A circuit to maintain the BR coll 8'I energized is established by the B interlock switch I09 before the B switch 9| opens, this circuit having an RI holding switch I04 and an R8 holding switch I05 connected in it in parallel with each other and leading through the FF switch I66. It may be traced from the conductor 39 through conductor 92, switch I03, through either one or both of the switches I00 and I05 and then through the FF switch I96, the BR coil Bl and OLR switch 89 to the main 28. This provides for the pickup of either the RI switch I09 or the R8 switch I05 without deenergizing the BR coil 87. When both of these switches are picked up, however, at the same time the BR coil 8'? is deenergized. It should be noted that the B switches BI and I09 constitute a walking beam switch as hereinbefore described in connection with the RI switches 90 and 04. Also, the B switch I03 when closed provides for a supply of energy from the conductor 92 to the conductor 38a for the operation of the RI switch, and the resistance controller contactor switches R2 to R8 underthe control of the ABR relay switch 42.

During coasting the RI switch is first closed,

the circuit for the RI coil 36 now being through the conductor 92, B switch I03 which is closed, R'I switch 39 which is closed, the coil 36, the RI switch 90, R1 switch ll and ABR switch 92 to the main 28. The closure ,of the RI switch completes the dynamic braking circuit from the righthand side of the armature I0 through the resistance I0, the RI switch, conductor I08, perinanent braking resistance I09, B switch I08a, field winding II which is then reversed, OLR coils 83 and H0 and the B switch 9911 back to the lefthand side of the armature I0. At this time, current is supplied for field forcing from the main I2 through the FF switch I02, resistance III, OLR coils H0 and 83, field winding II, B switch I00a, resistance I09, conductor I08, and the ABR coil 24 to the main I3. This field forcing circuit, it will be observed, is established by the closing of the switches FFI02 and BI00a independently of the RI switch, which completes the dynamic braking circuit. 7

The motor now builds up as a generator with full field excitation and the ABR coil 25 now controls the successive closing of the resistance switches R2 to R8 in response to the voltage drop across the resistance I09 and therefore in response to the current in the braking circuit and the speed of the motor. It should be noted that reduced field excitation.

the switches BIII and A86 are now closed and connect the coil 25 directly across the resistance I09 for the most sensitive response of the coil, whereby the braking control coil 25 operates to maintain a predetermined low coasting current in the braking circuit, such as 25 amperes, which is so low that no appreciable dynamicbraking effort is produced.

The function of the auxiliary relay AR is to control the field shunting switch FI so as to provide a weakened motor field for the coasting follow-up, and also to' provide the required number of control steps for braking without resorting to additional resistor steps and contactors over those required for acceleration,

The B switch I I2 is now closed during coasting and the switch BI I3 is also closed during coasting and these two switches establish a circuit for the AR coil 96 in parallel with the R4 switch 99 and the AR switch IOI. Consequently, during coasting the R4 switch 99 can open without opening the circuit of the AR coil 96 and the AR relay remains in its picked up position throughout coasting. If the braking controller is turned to a braking position, whereby the BI I3 switch is opened, while the vehicle is still operating at a high speed, the AR relay is deenergized when the R9 switch closes. The AR relay in dropping out opens the FI switch to reestablish full field excitation and also causes the R2 and R3 switches to drop out. The switches R2 and R9 are now closed in sequence with full field excitation under the control of the ABR relay. Thisoperation will be described more in detail under dynamic braking operation.

If coasting is initiated by turning the acceleration controller to its ofi position while the vehicle is operating at a speed above 30 miles per hour, the low coasting or spotting current is established very quickly and the ABR coil- 25 picks up its switches, the ABR switch I I0 closing a circuit for the F! coil I9. This circuit leads from the conductor 92 through the BI03 switch, conductors 38a and 50a, A50 switch which is now closed, AR switch II5, coil I4, FI switch "I1, AR switch H6, conductor III'and the ABR switch M9 to main 28. The Fl switch now closes for field shunting through the resistance 12 and inductance '13 for A holding circuit for the FI coil "I9 is established by the closing of the FI switch II8 through the conductor II9 directly to the main 28.

If coasting is initiated at a low speed, the ABR .relay may not pick up and, in that case, the field during coasting, the BIII switch being closed,

and has a very sensitive response to braking current, the coil I22 holds the BR relay in its 'picked-up position during coasting down to a low speed such as 5 miles an hour when the BR relay opens and deenergizes all of the control circuits.

Dynamic braking When the braking controller 26 is turned to a braking position thereby to establish efiective dynamic braking, the acceleration controller 22 being in its oil position, the BI! I switch is opened, whereby a resistance I 23 is inserted in series with the ABR coil 25 and the BR coil I22. These two coils are now connected in parallel with each other through the A86 switch and in series with the resistance I23 across the resistance I09. This decreases the braking current response of the coil 25, i. e., raises its current setting. Also, the resistance I23 reduces the current in the coil I22, which coil is not effective in the control at this time because the BR8'I coil is energized through the BI32 switch. The AER relay then operates to maintain a predetermined greater current in the braking circuit which gives efiective dynamic braking.

In the event that the braking controller is turned to a braking position when the vehicle is moving at a speed of more than 30 miles per hour, the ABR relay picks up immediately and energizes the Fl coil 14 as previously described. This closes the Fl switch and establishes field shunting and weak field excitation. The R2 and R3 switches now close under the control of the ABR relay as the vehicle speed decreases, thereby to maintain the predetermined braking current.

When the R4 switch is picked up, however, it opens its switch 99, But movement of the braking controller to a braking position has opened the switch Bl l3 and, consequently, the AR coil 96 is deenergized by the opening of the R4 switch 99. The AR switches [l5 and H6 in circuit with the FI coil I4 now open and open the F5 switch to reestablish full field excitation. the AR switch l2$ opens and thereby opens the circuit of the R2 and R3 coils, whereby these switches open.

It will be noted that during braking the coils of the R2 and R6 switches inclusive are fed through either the normally closed Fl switch 53 or through the normally open AR switch I26. Therefore, when either of these switches closed, the resistance switches can be picked u; in normal sequence. With the Ft switch 53 no closed, the switches R2 to R6 close in sequence with full field excitation.

switches under the control of the AER relay will be understood from the description in comiection with the acceleration. In view of the fact that the AR relay has been dropped out, its switches H5 and H6 are open and therefore the Fl field shunting switch cannot be closed. The F2 field shunting switch cannot be closed during dynamic braking because of the fact that the ASI switch is open at that time.

The Fl coil I4 is provided with suitable timing means to provide a time interval in the dropout of its armature or core after the circuit or the coil has been opened, such as a dash pot it??? or a short-circuited copper sleeve (not shown) between the coil and the core. This time interval is suilicient to provide for opening of the switches R2, R3 and RA before the switch 53 closes during braking'at high speeds.

As the deceleration of the vehicle proceeds, the RI and R8 switches or contactors are both closed when the resistance I i has been out out of the braking circuit and, consequently, the RE switch Hid and the R8 switch WE are both open at that time. Also, at this-time the contactors R2 to R7 are all closed as indicated in the last braking step, N0. 15, on the sequence chart, Fig.

The opening of the switches Rl-lut and RO-IOS transfers the control of the circuit of the BR coil 81 to the braking controller switch BI32 which is closed as long as the braking controller 26 is held in a braking position. Therefore, as'long as the braking controller 26 is held in a braking position, the BR coil 81 remains energized and the dynamic braking connections are maintained. If the braking controller is held in its braking position until the vehicle comes to rest, or even longer, the braking connections are maintained,

This feature of positively maintaining the dynamic braking connections by means of the switch BI32 is important when the vehicle is operated in very hilly regions or where the grades are severe enough to warrant this extra protection from the standpoint of safety. Thus if the vehicle starts to roll down a grade, dynamic braking can be established immediately by depressing the braking controller pedal I28, without the necessity of first applying power to the vehicle to set up the braking circuits.

If the braking controller 26 is released and allowed to move to its off position by mean of its biasing spring when th vehicle is moving at a substantial'speed, the BI32 switch being opened, the BR coil 81 is deenergized if or when the switches I02 and I05 both are opened. The BB relay is then held in its pickedup position by the BR coil I22, the BIII switch being closed for maximum energization of the coil I22, until the vehicle speed is reduced to some low speed such as 5 miles an hour at which the enerzgiation of the BR coll i22 will have decreased to a low value such that the BR relay drops open and its switch 93 opens to open the circuits of the B coil 94 and the FF coil 95 thereby to open the dynamic braking circuit. It will be observed that the B interlock switch I03 now opens and deenergizes the operating coils of all of the switches or contactors RI to R1 inclusive.

During dynamic braking, the current setting of the AER relay can b raised to call for greater dynamic braking by further depression of the braking controller pedal I28 (Fig. 4) whereby a spring l29 connected between the pedal and the AER relay is stretched, thereby to apply a force tending to hold the relay in its deenergized position.

When the braking controller 26 is operated to a braking position, its switches BI30, Bl3l and user are closed and its switch BI33 is opened.

The Bi3ll switch in closing sets up the circuit for the OLR holding coil 35 so that the coil can be energized independently of the switch A30 which is open. The opening of the Bi33 switch prevents the connection of the coil 85 in parallel with the coil 3i, which coil is deenergizcd during braking. If the OLE. relay picks up in response to an excessive current, however, it switch 84 closes a circuit for the coil 85 between the mains l2 and I3, and this coil then holds the OLR relay picked up. The OLR switch 89, then being open, opens the circuit for the E coil 94, the AR coil as and the BR coil 81, thereby to interrupt the dynamic braking connections. To again apply dynamic braking, the braking controller must be returned to its off position, thereby to open the switch BI 36 and deenergize the OLR coil 85.

The OLR braking coil i IE applies a force which is in the same direction as the forc applied by the coil 83 to their common armature. In other words, these two coils are additive in their effects and consequently the OLR relay is picked up by a lower current during braking than during motoring operation. This is because the electric braking rate is normally less than the accelerating rate on account of reverse torque limitations of the rear axle drive, i. e., 2 mphps. as compared with 3 to a mphps.

We have also provided a manually operated double throw switch I36 which is normally maintained closedas by a spring as shown in the circuit oi the ABI switch. When this switch is moved to its other position, it energizes an auxiliary ABR coil I35, and opens the circuit leading from the ASI switch. This coil I35 opposes the coil 24. It serves to raise the current setting of v the AER relay to provid sufficient acceleration when climbing steep grades. The opening of the circuit leading from the AEI switch prevents progression of the control to shunt the field and thereby prevents excessive current with weakened field under extreme conditions.

A reversing switch I36 (Fig. 6) which is manually operated is provided for the motor field winding l I. This switch, which is of th drum type, is shown in the forward position. In addition to the usual central ofi position and a for-' ward and a reverse position on opposite sides of the on position, two emergency positions are provided which are reached respectively by continued movement of the reversing switch in the reverse or the forward direction.

In the emergency position of the reversing switch, a long segment I3I- electrically connects together the points I38, I39 and I 40, and a shorter segment I electrically connects together the points I42 and I43, whereby the motor field I I is connected for forward rotation of the motor, its connection thereby being reversed. Also, the connectionof the point I38 with the point I39 closes a low resistance dynamic braking circuit through the conductor I44 and containing the left-hand section I4a only of the resistance. This circuit can be traced from the point I39 through circuit, but with the motor field reversed with respect to the first mentioned emergency position. The reversing switch 3! is maintained closed by an operating cam I48 on the reversing switch when the switch is in its reverse, off, and forward positions. When the switch is thrown to either of its emergency positions, however, th switch 31 opens and deenergizes all of the low voltage control circuits from the supply main 21..

This emergency braking with the reversing switchis for use in the event that all other braking systems fail. If the vehicle is moving forward, the emergency switch is rotated by means i of its handle (not shown) beyond the forward position to the right hand emergency position shown in Fig, 6, whereby the field is reversed with respect to the forward position and the braking circuit established by the segments I45,

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

1. The combination, in a propulsion system for a vehicle, of a traction motor, an acceleration controller movable from a predetermined position to a running position to establish a supply circuit for said motor, a braking relay for controlling dynamic braking of said motor having a coil energized to pick up said relay in response to movement of said acceleration controller to a running position thereby partially to complete dynamic braking connections for said motor, means for holding said relay in its energized position, and means operated by said acceleration controller for completing said dynamic braking connections when said acceleration controller is returned to said predetermined position.

2. The combination in a propulsion system for a vehicle, of a traction motor, a braking resistance for said motor, an acceleration controller movable from a predetermined position to a running position to establish a supply circuit for said motor, a braking relay for controlling dynamic braking having a coil energized to pick up said relay in response to movement of said acceleration controller to a running position thereby partially to complete dynamic brakin connections for said motor, means operated by said coil for establishing a holding circuit for said coil so that said coil remains energized when said acceleration controller is returned to said predetermined position, and means operated by said acceleration controller for completing said dynamic braking connections when said acceleration controller is returned to said prede termined position whereby a dynamic braking circuit for said motor is established including said resistance.

3. The combination in a propulsion system for a vehicle, of a traction motor, a braking resistance for said motor, an acceleration controller movable from a predetermined position to a running position to establish a supply circuit for said motor, a braking relay for controlling dynamic braking having a coil energized to pick .up said relay in response to movement of said acceleration controller to a running position therebypartially to complete dynamic braking connections for-said motor, means operated by said coil for establishing a holding circuit for said coil so that said coil remains energized when said acceleration controller is returned to said predetermined position, means operated by said acceleration controller for completing said dynamic braking connections when said acceleration controller is returned to said predetermined position whereby a dynamic braking circuit for said motor is established including said resistance, a braking coil responsive to the current in said braking circuit for controlling said braking resistance to maintain a'predetermined low coasting current in said braking circuit, and a braking controller movable to decreasethe current response of said braking coil thereby to initiate dynamic braking.

4. The combination, with a traction motor provided with a field winding, means for controlling the acceleration of said motor, a manually operated reversing switch for said field winding provided with forward and reverse running positions and with a braking position beyond one of said running positions, and switching means in said reversing switch in said braking position for refor controlling said resistance to accelerate said motor, a manually operated reversing switch for said motor provided with forward and reverse running positions and with two emergency braking positions respectively beyond the said forward and reverse positions, and switching means in said reversing switch in each of said emergency positions for establishing a low resistance dynamic braking circuit for said motor.

6. The combination, with a traction motor provided with a field winding, of an acceleration and braking resistance for said motor, means forestablishing a supply circuit for said motor for acceleration of said motor and a dynamic braking circuit for said motor, means responsive to the current in said motor for controlling said resistance during acceleration and dynamic braking of said motor, a manually operated reversing switch for said field .winding provided with forward and reverse operating positions and with two emer-' gency dynamic braking positions respectively beyond the said forward and reverse positions, and switching means in said reversing switch in each of said emergency positions for'reversing said field Winding with respect to said adjacent forward or reverse position respectively and for establishing a dynamic braking circuit for said motor.

7. The combination with a traction motor provided with a field winding, of an acceleration and braking resistance for said motor, switching means for controlling said resistance to control the acceleration and braking of said motor, a running operating coil responsive to the current in the circuit of said motor and operating to control said switching means so as to maintain a predetermined current in said motor during acceleration, a manually operated acceleration controller movable from a predetermined position to a running position to establish a supply circuit for said motor through said resistance, means operated by said acceleration controller upon the return of saidcontroller to said predetermined position to connect said motor in a dynamic braking circuit with said resistance but excluding said running operating coil, a braking operating coil having an armature responsive to the current in said braking circuit thereby to control said switching means to maintain a predetermined low coasting current in said braking circuit which does not give any appreciable dynamic braking effort, a braking controller. an

operating pedal connected to move said braking controller to a dynamic braking position, means responsiveto movement of said braking controller to said braking operating coil thereby to initiate dynamic braking, whereupon said braking operating coil controls said switching means to maintain 'a predetermined dynamic braking current, a resilient connection between said pedal and said armature of said braking operating coil for applying an increasing biasing force to said armature upon further movement of said pedal thereby to decrease the current response of said braking operating coil, means operated by said braking operating coil for partially disabling said field winding, and means operated by movement of said acceleration controller to a running position for disabling said last named means.

8. The combination with a traction motor, of an acceleration and braking resistance for said motor, a plurality of electromagnetically operated switches for short-circuiting said resistance to control the acceleration and braking of said motor, a control relay for controlling said switches, a running operating coil for said relay responsive to the current in the circuit of said motor and operating said relay to control said switches so as to maintain a predetermined current in said motor during acceleration, a man ually operated acceleration controller movable from a predetermined position through a plurality of running positions to establish a supply circuit for said motor through said resistance and for limiting the operation of said switches in accordance with the running position of said acceleration controller, thereby to limit the speed to which said motor accelerates, switching means operated by said acceleration controller upon the return of said controller to said predetermined position to connect said motor in a dynamic braking circuit with said resistance but excluding said running operating coil, a braking operating coil for said control relay connected so as to be responsive to the current in said braking circuit and thereby control said switches to maintain a predetermined low coasting current in said braking circuit which does not give any appreciable dynamic braking efiort, a braking controller, an operating pedal connected to said braking controller so as to move said braking controller when said pedal is depressed to a dynamic braking position, means responsive to movement of said braking controller to said braking position for decreasing the current response of said. braking operating coil thereby to initiate dynamic braking, whereupon said braking operating coil controls said switching means to maintain a predetermined dynamic braking current, and a resilient connection between said braking controller and said relay'for applying an increasing biasing force to said relay upon further depression of said pedal therebyto decrease the current response of said braking coil and increase the dynamic braking current maintained by said relay.

9. The combination with a traction motor, of a braking resistance for said motor, saidmotor being provided with a field winding, switching means for controlling said resistance, a braking control coil responsive to the current in-said motor during dynamic braking of said motor for controlling said resistance switching means, means for disabling said field winding controlled by said braking coil, a normally open auxiliary relay switch for controlling said field disabling means provided with an operating coil, connections for energizing the operating coil of said auxiliary relay, whereby said auxiliary relay switch is closed to set up a circuit for the opera- .tion by said braking coil of said field disabling braking for said motor, means operated by said resistance switching means after exclusion of part or said resistance from the dynamic braking circuit for deenergizing' said auxiliary relay operat ing coil thereby to establish full excitation of said I in said dynamic braking circuit when said auxiliary relay is deenergized, and a normally closed switch which is closed by the operation of said field disabling means to establish full excitation of said field winding thereby to set up a circuit for operation of said resistance switching means under the control of said braking coil.

10. The combination with a traction motor, a braking resistance for said motor, said motor being provided with a field winding, switching means for controlling said resistance, a braking control coil responsive to the current in said motor during dynamic braking of said motor for controlling said resistance switching means, a normally open switch movable to closed position to shunt said field winding providedwith an operating coil, a normally open' switch in circuit with the operating coil of said field winding switch operated by said braking coil, a normally open auxiliary relay switch provided with an operating coil, connections for energizing the operating coil of said auxiliary relay whereby said auxiliary relay switch is closed partially to set up a circuit for the operating coil of said field shunting switch for closure of said field shunting switch by said braking coil in response to a predetermined dynamic braking current, a braking controller movable from a, predetermined position to another position to initiate dynamic braking for said motor, means operated by said resistance switching means to deenergize said auxiliary relay operating coil thereby to open the operating coil circuit of said field shunting switch and establish full excitation of said field windin means operated by said auxiliary relay when deenergized for controlling said resistance switch-' ing means to insert said resistance in said dynamic braking circuit when said auxiliary relay is deenergized, and a normally closed switch which is closed when said field shunting switch opens thereby to set up a circuit foroperation of said resistance switching means under the control of ,said braking coil with full excitation of said field winding.

11. The combination with a traction motor, of an acceleration resistance for said motor, said motor being provided with a field winding, a plurality of normally open electromagnetieally operated resistance switches for short-circuiting said resistance in steps, a control relay having a normally closed switch, connections for sequentially closing said resistance switches through said normally closed relay switch, a normally open switch for said control relay, an operating coil for said control relay responsive to the current in said motor during dynamic braking oi said motor for opening said normally closed relay switch in responseto a predetermined current and closing said normally open relay switch, a normally open switch movable to closed position to shunt said field winding provided with an operating coil controlled by said normally open relay switch, a nor-,

mally open auxiliary relay switch provided with an operating coil, connections for energizing the operating coil of said auxiliary relay, whereby said auxiliary relay switch is closed to set up a circuit for the operating coil of said field shuntingswitch for closure of said field shun-ting switch when said control relay closes its normally open switch in response to a predetermined dynamic braking controller is in said predetermined position, but

opened to give the control of said auxiliary relay operating coil to saidfirst holding switch when said braking controller is moved to initiate dynamic braking, whereby when said intermediate resistance switch closes, said first holding switch is opened to deenergize said auxiliary relay operating coil thereby to open the'operating coil circuit of said field shunting switch and establish full excitation of said field winding, a normally open third holding switch on said auxiliary relay for deenergizing said intermediate resistance switch and all preceding closed resistance switches when said auxiliary relay opens, and a normally closed holding switch on said field shunting s itch which is closed when said field shunting s itch opens thereby to set up a circuit for reclosure of said short-circuiting switches under the control of said control relay.

12. The combination with a traction motor, of an acceleration resistance for said motor, said motor being provided with a field winding, a plurality of normally open electromagnetieally operated resistance switches for short-circuiting said resistance in steps, a control relay having a normally closed switch, connections for sequentially closing said resistance switches through said normally closed relay switch, a normally open switch for said control relay, an operating coil for said control relay responsive to the current in said motor during dynamic braking of said motor for opening said normally closed relay switch in response to a predetermined current and closing said normally open relay switch,

a normally open switch movable to closed position 'to shunt -said field winding provided with an operating coil controlled by said normally open relay switch, a manually operated acceleration 4 controller normally in a predetermined position to establish a dynamic braking circuit for said motor including said resistance and movable from said predetermined position to establish a supply circuit for said motor through said resistance, a normally open auxiliary relay switch provided with an operating coil, switching means closed in response to the return of said acceleration controller to said predetermined position for energizing the coil of said auxiliary relay, whereby said auxiliary relay is operated to set up a circuit for the operating coil of said field shunting switch for closure of said field shunting switch switch, said second holding switch being closed when said braking controller is in said predetermined position, but opened to give the control of said auxiliary relay operating coil to said first holding switch when said braking controller is moved to initiate dynamic braking, whereby when said intermediate resistance switch closes said first holding switch is opened to'deenergize said auxiliary relay thereby to open the operating coil circuit of said field shunting switch and estab lish full excitation of said field shunting switch, a normally open third holding switch on said auxiliary relay for deenergizing said intermediate resistance'switch and all preceding closed resistance switches when said auxiliary relay opens, and a normalily closed holding switch on said field shunting switch which is closed when said field, shunting switch opens thereby to set up a circuit for reclosure of said short-circuiting switches under the control of said control relay.

The combination in a propulsion system for vehicle, of a traction motor, a braking resistance for said motor, an acceleration controller movable from a predetermined position to a runposition to establish a supply circuit for said motor, a braking relay for controlling dynamic braking having a coil energized to pick up said relay in response to movement of said acceleration controller to a running position thereby partially to completedynamic braking connections for said motor, means operated by said coil for establishing a holding circuit for said coil so that said coil remains energized when said. acceleration controller is returned to said predetermined position, means operated-by said acceleration controller for completing said dynamic braking connections when said accelera tion controller is returned to said predetermined position whereby a dynamic braking circuit for said motor is established including said resistance, a braking coil responsive to the current in said braking circuit for controlling said resistance to maintain a predetermined low coasting current in said braking circuit and for deenergizing said braking relay coil, a, braking controller movable to decrease the current response of said braking coil thereby to initiate dynamic braking, and a second coil for said braking relay connected to said braking circuit for holding said braking relay picked up until the speed of the vehicle has decreased to a predetermined low value whereupon said braking relay opens.

14. The combination in a propulsion system for a vehicle, of a traction motor, a braking resistance for said motor, an acceleration controller movable from a predetermined position to a running position to establish a supply circuit for said motor, a braking relay for controlling dynamic braking having a coil energized to pick up said relay in response to movement of said acceleration controller to a running position thereby partially to complete dynamic braking connections for said motor, means operated by said coil for establishing a holding circuit for said coil so that said coil remain energized when said acceleration controller is returned to said predetermined position, and means operated by said acceleration controller for completing said dynamic braking connections when said acceleration controller is returned to said predetermined lishing a control means means to maintain a predetermined low coasting current in said braking circuit, a braking controller movable to decrease the current response of said braking operating coil thereby to initiate dynamic braking, means operated by said resistance switching means when said resistance is substantially short-clrcuited for opening the circuit 01' said braking relay coil, and a second coil for said braking relay connected to said braking circuit for holding said braking relay picked up until the speed of the vehicle has decreased to a predetermined low value whereupon said braking relay opens.

15. The combination in a propulsion system for a vehicle of a traction motor, a braking resistance for said motor, an acceleration controller movable from a predetermined position to a running position to establish a supply circuit for said motor, a braking relay having a coii energized to pick up said reiay in response to movement of said acceleration controller to a running position, means operated by said coil for estabhoiding circuit ior'said coil so that said coil remains energized when said acceleration controller is returned to said predetermined position, a switch on said braking the energiaation of said braking relay for partially completing connections for dynamic braking', means operated by said acceleration controller for completing said dynamic braking connections when said acceleration controller is returned to predetermined position whereby a dynamic braking circuit for said motor is established including said resistance, braking control means responsive to the current in said braking circuit for controlling said resistance to maintain a predetermined low coasting current in said braking circuit, a braking controller movable to decrease the current response of said braking control means thereby to initiate dynamic braking, means operated by said braking for opening the circuit of said braking relay coil, and a second coil for said braking relay connected to said braking circuit for holding said braking relay picked up until the speed of the vehicle has decreased to a predetermined low value whereupon said braking relay moves to its unattracted position to discontinue dynamic braking.

16. The combination in a propulsion system for a vehicle of a traction motor, an acceleration and braking resistance for said motor, resistance switching means for controlling said resistance to control the acceleration and braking of said motor, a manually operated acceleration controller movable from a predetermined position to a running position to establish a supply circuit for said motor through said resistance for acceleration of said motor, means responsive to the current in the circuit of said motor for controlling said switching means to maintain a predetermined current in said motor during acceleration, a braking relay having a coil energized to pick up aid relay in response to movement of said acceleration controller to a running position, means operated by said coil for establishing a holding circuit for said coil so that said coil remains energized when said acceleration controller is returned to said predetermined position, a switch on said braking relay closed by the energization of said braking relay for partially completing connections for dynamic braking, means operated by said acceleration controller for completing said dynamic braking connecrelay closed by tions when said acceleration controller is returned to its predetermined position whereby a dynamic braking circuit for said motor is established including said resistance, braking control means responsive to the current in said braking circuit for controlling said resistance switching means tormaintain a predetermined low coasting current in said braking circuit, a braking controller movable to decrease the current response of said braking control means thereby to initiate dynamic braking, means operated by at least one of said resistance switching means when said resistance is substantially short-circuited for opening the circuit of said braking relay coil, and a second coil for said braking relay connected to said braking circuit for holding said braking relay picked up until the speed of the vehicle has decreased to a predetermined low value whereupon said braking relay moves to its unattracted position to discontinue dynamic braking.

17. The combination in a propulsion system of said motor, a manually operated acceleration controller movable from a predetermined position to a running position to establish a supply circuit for said motor through said resistance for acceleration of said motor, means responsive to the current in the circuit of said motor for controlling said switching means to maintain a predetermined current in said motor during acceleration, a braking relay having a coil energized to pick up said relay in response to movement of said acceleration controller to a running position, means operated by said coil for establishing a holding circuit for said coil so that said coil remains energized when said acceleration controller is returned to said predetermined position, a switch on said braking relay closed by the energization of said brakingrelay for partially completing connections for dynamic braking, means operated by said acceleration controllepfor completing said dynamic braking connections when saidacceleration controller is returned to its predetermined position whereby a dynamic braking circuit for said motor is established including said resistance, said partially completed connections including an auxiliary relay, shunting switching means for said field winding controlled by said auxiliary relay, braking control means responsive to the current n said braking circuit for controlling said resistance switching means and said field shunting switching means to maintain a predeternuned low coasting current in said braking circuit, a braking controller movable to decrease the current response of said braking control means thereby to initiate dynamic braking, means operated by at least one of said resistance switching means I when said resistance is substantially excluded for opening the circuit of said braking relay C011, and a second coil for said braking relay connected to said braking circuit for holding said braking relay picked up until the speed of the vehicle has decreased to a predetermined low value whereupon said braking relay moves to its unattracted position to discontinue dynamic braking.

18. The combination in a motor control system, of a resistance for inclusion in the circuit of a motor, anv electromagnetically operated switch for controlling said resistance provided with an armature and an operating coil, a member connected to said armature. a contact arm pivotally mounted on said member at a point intermediate the ends of said arm, a pair of con-, tacts on opposite sides of said arm adjacent the ends of said arm, a spring connected to said arm so as to bias a first end of said arm when said operating coil is deenergized into engagement with a first one of said contacts with the other end of said arm disengaged from the other contact, a normally open relay responsive to the current in the circuit of said motor, an energizing circuit for said operating coil including" said arm and said first contact and said relay, whereby when said relay is closed said operating coil is energized to pick up said armature whereupon said arm first pivots on said iirst contact into engagement with said other contact thereby to close a holding circuit for said coil and then pivots on said other contact against the force applied by said spring to disengage said first contact thereby to open said energizing circuit.

19. The combination, in a propulsion system for a vehicle, of a'traction motor, a braking resistance for said motor, an acceleration controller movable from a predetermined position to a running position to establish a supply circuit for said motor, means operated by said acceleration controller for establishing a coasting circuit for said motor including said resistance when said acceleration controller is returned to said predetermined position, an electromagnetically operated switch for controlling said resistance provided with an armature member and an operating coil, a contact arm pivotally mounted on said member at a point intermediate the ends of said arm, a pair of contacts on opposite sides of said arm adjacent the ends of said arm, means for biasing a first end of said arm into engagement with a first one of said contacts with the other end of said arm disengaged from the other contact, a relay responsive to the current in said coasting circuit for closing an energizing circuit for said operating coil to control said resistance whereupon said armiirst pivots on said first contact into engagement with said other contact thereby to close a holding circuit for said operating coil and then pivots on said other contact to disengage said first contact thereby to open said energizing circuit, and a braking controller movable to decrease the current response of said relay thereby to initiate dynamic braking.

20, The combination in a propulsion system for a vehicle of a traction motor, an acceleration controller movable from a predetermined position to a running position to establish a supply circuit for said motor, a braking relay for controlling dynamic braking of said motor having a coil energized to pick it up in response to movement of said acceleration controller to said running position thereby partially to complete dynamic braking connections for said motor, means for holding said relay in its energized position when said acceleration controller is returned to said predetermined position, switching means operated by the return of said acceleration controller to said predetermined position for com pleting. said dynamic braking connections, a dynamic braking controller movable from one position to a second position to initiate efiective dynamic braking of said motor, and switching means operated by movement of said braking controller to said second position before operae' tion of said acceleration controller to a running position for energizing said coil to pick up said braking relay and initiate dynamic braking.

21. The combination in a propulsion system for a vehicle of a traction motor, a supply switch for said motor, an acceleration controller movable from a predetermined position to a running position to close said supply switch for operation of said motor, a braking relay for controlling dynamic braking of said motor having a coil energized to a pick it up in response to movement ofsaid acceleration controller to said running position thereby partially to complete dynamic braking connections for said motor, switching means for establishing dynamic braking connections for said motor, means for holding said relay in its energized position when said acceleration controller is returned to said predetermined position to open said supply switch, means operated by the opening of said supply switch for operating said switching means to establish said dynamic braking connections, a dynamic braking controller movable from one position to a second position to initiate effective dynamic braking of said motor, and switching means operated by movement of said braking controller to said sec-' and position before operation of said acceleration controller to a running position for energizing said coil to pick up said braking relay and initiate dynamic braking.

22. The combination with a traction motor of a braking resistance for said motor, said motor being provided with a field winding, a plurality of normally open electromagnetically operated resistance switches for short-circuiting sections of said resistance, a control relay having a normally closed switch, connections for sequentially closing said resistance switches through said normally closed switch thereby to short-circuit said resistance, a normally open switch forming a part ofsaid control relay, an operating coil for said control relay responsive to the current in said motor during dynamic braking of said motor so as to open said normally closed switch in response to a predetermined maximum dynamic braking current and at the same time close said normally open switch, and switching means responsive to closure of said normally open switch for disabling at least a part of said field winding.

23. The combination with a traction motor of a braking resistance for said motor, said motor being provided with a field winding, a plurality of separately operable normally open electromagnetic resistance switches for short-circuiting said resistance in sections, braking switching means for establishing a braking circuit for said motor including said resistance, a normally closed switching means operated by said braking control coil in response to said predetermined braking current for at least partially disabling said field winding.

24. The combination ,with a traction motor of a braking resistance for said motor, said motor being provided with a field winding, a plurality of separately operable normally open electromagnetic resistance switches for short-circuiting said resistance in sections, braking switching means for establishing a braking circuit for said motor including said resistance, a normally closed resistance control switch, connections leading through said resistance control switch for efiecting the closing of said resistance-switches in sequence, a braking control coil responsive to the current in said braking circuit for opening said control switch to interrupt the closing 015 said resistance switches in response to a predeter- 'mined braking current, additional switching means operated by said braking control coil in response to said predetermined braking current for at least partially disabling said field winding, and switching means operated by the closing of an intermediate one of said resistance switches for establishing full excitation of said field winding and for opening said previously closed resistance switches whereupon said braking control coil operates to close said resistance switches with full field excitation.

CHARLES MACDONALD. JACOB W. McNAIRY. JOHN F. TRI'I'LE,

v cmmncm: or 001mm1101;; Patent 110. 2,327,309. lu ustzh, 1915.

, cums HacDOKALD, ET AL.

It is hereby certified that error appears in the, printed specification of the above numbered potent requiring correction as follows: Page 2, secsecond column, line 55, for "enerzgiation' read -energizstion; line hl,

for R1 to R7 read --Rl to R8"; page 7, first colnmn, line 70, claim 7,

ondcol'mnn, line hi for controller 27" read -controller 22"" page 5,

after "braking insert the words -position for decreasing the current response of said braking"; page 9, first column, line 16, claim 12, for "normalily' read --normelly--; page ll, second colxmm, line 12, claim 25, strike out *u'se" and that the said Letters Patent shouldbe readwith this correction therein that the same may conform to the record of the case in the Yatent Officet- Signed end sealed. this 19th day of October, 'AQD. 1911.}.

Henry Ian Arsdale,

(3681) Acting Commissioner of. Patents.

Potent 110. 2,327

cnamxcms or connncnoi izn 9 9- CHARLES HBcDONALD, ET AL.

It is hereby certified, that error appears in the. printed ap'eczu filcationof the above mambered pitent requiring correction up follows: Page 2, secondlcolumn, 11ne M, for "controller 27" read --controller 22"; page 5, second column, line 33, for "enerzgzlation' read -epergization; line 11.1, for R1 to R? reed -31 110118; page 7, first column, line 70., claim 'I,

after, 'brakihg' .in'sert the words "position fordecreasing the current response of saidbrakin page 9, first column, line 16, claim 12, for

'normalily' read --normh11y--; page 11., second column; line 12, claim 25,

strike out "ube' and that the said Letters Patent shouldbe read with this correctionthereih that the aamemey conform to the reeord of the case in the Patent Office.

Signed end sealed this 19th duty of October, AQD. 19L

' Henry Ian Arsdale', -Y 1 Acting commissioner of, Patents.

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