US1235132A - Electrical motive apparatus. - Google Patents

Description

RJH. GAYLORD & G. B. CAPPS.

ELECTRICAL MOTIVE APPARATUS. APPLICATION FILED JULY 23.1914.

Patented July 31, 1917.

3 SHEETSSHEET 1.

R. H. GAYLORD & G. B. CAPPS.

ELECTRICAL MOTIVE APPARATUS.

APPLICATION HLED JULY 23. 191.4.

1,235, 1 32. Patented July 31, 1917.

3 SHEETSSHEET 2.

L/Z Cap v6,

R. H. GAYLORD & G. B. CAPPS. ELECTRICAL MOTIVE APPARATUS. APPLICATION FILED JULY 23.1914.

1 ,235, 1 32. Patented July 31, 1917.

'3 SHEETS-SHEET 3.

2 b526 W I jfoer 2 W W UNITED STATES PATENT oFrIcE.

ROBERT H. GAYLORD, OF PASADENA, AND GUY B. CAPPS, 0F LOS ANGELES, CALIFORNIA.

ELECTRICAL MOTIVE APPARATUS;

Specification of Letters Patent.

Patented July 31, 191 "0.

Application filed July 23, 1914. Serial No. 852,531.

.Angeles and State of California, and GUY B. CArPs, residing at Los Angeles, in the county of Los Angeles and State of California, both citizens of the United States,- have invented a new and useful Electrical Motive Apparatus, of which the following is a specification.

This invention relates to electrical motive apparatus for operation of elevators, or hoists, or other apparatus presenting considerable momentum when in operation, and the main object of the invention is to provide for increasing theeffective speed of the motive means relatively to the speed of the elevator or other apparatus, in starting and stopping the same, so as, on the one hand, to facilitate starting of the motive means under load, and, on the other hand, to enable the said motive means to run above the normal speed when the apparatus is being brought to rest, and to thereby enable the said motive means to deliver electrical energy to the operating line or circuit at the same time producing an efiicient dynamic brake.

Our invention is especially advantageous in the operation of apparatus such as above described by alternating current, an important object of the invention being to enable elevators and other apparatus to be driven by alternating current, at higher speed than is practicable with the usual motive arrangements, while permitting of effective control in starting and stopping.

A further object of the invention is to provide, in an apparatus driven by induction motors, means of control for variation of the speed, without undue complication. of the control apparatus, and. particularly without the use of shift gears.

Our invention, as hereinafter described, is particularly designed for the operation of electric elevators by alternating current, in such manner as to provide for such operation under the conditions ofspeed generally obtained in practice. Electric elevators, particularly passenger elevators, are in common practice, operated at a rate of speed as high as six hundred feet per minute, and for such high speeds the alternating current motor drive has not been found practicable, for the reasons hereinafter stated.

It has not been possible to obtain with an induction motor, the high starting torque required with high speed elevators, without excessive current flow in starting, which seriously affects the circuit and the source of supply.

It has not been practicable to obtain efficiently with an induction motor, the variable speeds and gradual acceleration necessary for high speed elevator operation, without making the control apparatus too complicated. An induction motor of the variable speed type is wasteful of energy at any speed other than its normal speed, and at any other than normal speed, will vary with the load, so that with the controlling lever in a given position, the motor will run slower under 'a heavy load than under a light load, making it diflicult for the operator to accurately judge the speed of his car and thereby make an accurate stop.

Another and most serious dificulty in connection with the use of the induction motor in high speed elevator" work is the incapability of such motors of producing dynamic braking action, by working either in a closed braking circuit or in connection with the supply circuit. For this reason, elevators driven by an induction motor must depend wholly on a mechanical brake for deceleration and stopping. While the mechanical brake is suitable for low speed elevators, where the speed does not exceed two hundred feet perminute, it is'not suitable for high speed service, for-the reason that the brake must be adjusted .so that it will bring a fully loaded car to a positive stop and when it is so adjusted, a lightly loaded carwill be stoppedtoo abruptly. Moreover,

the distance that the car will travel after throwing off the current and putting on the brake, will, with a mechanical brake, vary greatly with the load and speed, since the braking resistance is constant and the energy to be absorbed varies directly as the mass and as the square of the velocity of the car. Therefore the operator has to judge his stopping distance according to the load and speed of the car, and often overruns or ,falls short, bymisjudgment. The dynamic "brake, where it can be used, largely overcomes this difliculty, as thebraking resistance increases with the velocity, so that the greater the momentum of the car the greater will be the braking action, and the braking or stopping distance will vary relatively little under variations of load and speed,

the speed of the car may be varied while permitting the motor operating the same to be run at its normal and most efiicient speed.

By, providing for increase in the ratio of 'motor speed to car speed, in starting, we

are enabled to reduce the starting torque required, so that a low starting torque motor may be used, and the motor will start under load without drawing an excessive current from the line, and at the same time give a rapid and gradual acceleration to the car.

By providing for temporarily speeding up the motor relatively to the car speed, in stopping or deceleration, the motor may be caused to run faster than synchronous speed, and to deliver electrical energy to the line,

so as to exert a braking efi'ect on the car.

While our invention is applicable generally in connection with electrical motor driven apparatus, we have for the purpose o of.illustration, shown it in the accompany.-

ing drawings as applied to operation of an elevator driven by induction motors.

Referring to the drawings: Figure 1 is a side elevation partly in section, showing one form of the invention.

Fig. 2 is a view similar to ing a modified form. I

-Fig. 3 is a cross section through the differential gearing, showing another form of Fig. 1, showgearing.

Fig. 4 1s aview similar to Fig. -1, showinga form used for traction or high speed elevators. i 0

Fig. 5' is a side'elevation in detail of a brake.

Fig. 6 is a cross section through a modified form of differential gearing.

Fig.7 is a diagrammatic view showing the connections. e

In the form shown in Fig. 1, 2 designates the shaft of the driven apparatus, said shaft carrying, for example, drum l'for an elevator cable, and said shaft carrying a gear 3, which is driven from a worm 4, the latter being mounted in suitable bearings 5. 6,

and -7 designate two alternating current induction motors, which are arranged'axially in line, motor 6 havinga shaft 8 which extends freely through the motor 7 with its end 9 journaled in the shaft 10 of the worm v 4. The motor 7 has a hollow shaft 11, through which the shaft 9. freely passes, and

carried rigidly on shaft 11 is a beveled gear;

, 12, while rigidly mounted on the shaft .9 is

a beveled gear 1'3, thegears 12 and 13 formmovement or to engage wit switch 9 having contacts g g lwire 35 with contact ing the two members of a differential gear ing, beveled pinions 14 meshing between the gears 12 and 13 and being carried by a casing 15, the latter being rigidly secured to a '-flange 16 on the shaft 10. Brakes 17, 18

and 19 are respectivelyemployed for shaft 8 of motor 6, shaft 11 of motor 7, and the differential case 15, these brakes being similar in construction, and illustrated in detail in Fig. 5. 2O designates an electromagnetic device formed in this instance by a solenoid with armature 21 having a wedge 22, which is adapted to act between rollers 23 on brake members 24 pivoted at 25 to a block 26, and

' having friction segments 27 adapted to bear against a friction drum 28.- A rod 29 extends through both members 24, and com-' pression springs 30 act to force the members 24 toward each other and cause the friction segments 27 to bear against the drum 28 and apply the brake. Release of the brake is effected by energization of the solenoid 20, which raises its armature 21, causing the wedge 22 to force apart the members 24 and thus release the drum 28.

With this construction it is obvious that if motors 6 and 7revolve .at the same speed and in the same direction as one another they'will rotate gears 12 and 13 at the. same speed, thereby rotating the differential gear case 15 at the same speed, and with it the worm 4 thus driving the shaft 2, drum 1 and car, not shown, at the maximum speed. If one of the motors is held stationary, the other motor will through its connected gear 12 or 13 and pinions-14, drive the difi'erential gear case 15 at a slower speed, giving a corresponding slow speed of the drum and car.

' The control of the motors is indicated in the diagram in Fig. 7 and referring thereto: 31 designates a controlling switch having lever 32 adapted to be moved into engagement with contacts a, b, or c, to ve a forward the contacts, a, b or 0 for a reverse movement. of, e, f, g and it designate controlling switches, switch at. having contacts d d d d d 01 and switch e having contacts e 6, e", e, 6

6, switch f, having contacts f F, f,

9 .9mm, switch 72. having contacts k 12. h, h, If, h 33, 34 and 35 designate the three leads of the motor circuit; Wire 33 is connected by a wire 36 with contact d A wire 37 connects,

Wire 38' connects wire 34 with contact d wire 35 with contact d wire 33 with contact e. wire 35 with contact e 3. wire 34 with contact e wire 34 with contact f wire35 with contact 7. wire 33 with contact g. wire 34 with contact 9 Wire 39 -connects Wire 40 connects Wire 41 connects Wire 42 connects Wire 43 connects Wire 44 connects Wire 45 connects Wire 46 connects Wire 47 connects wire 34 with contact 71.

provided for switch a solenoid 51 for switch 6, a solenoid 52 for switch a sole-' noid 53 for switch 9, and a solenold 54- for switch it. A wire 55 connects contact a with one pole of solenoid 52. A wire 56 connects contact 6 with one pole of solenoid 50. A wire 57 connects contact 0 with one pole of solenoid 53. A wire 58 connects contact a with wire 55. Wire 59 connects contact b with one pole of solenoid 51. A wire. '60 connects contact 0 with one pole of solenoid 54. A wire 61 connects contacts 03 and a I A wire 62 connects contacts d and e. A wire 63 connects contacts (2 and e. A wire 64 connects contacts 9 and h s A I wire 65 connects contacts 9 and h A wire 66 connects contacts 9 and it. A wire 67 is connected with solenoid 50, and is connected by a wire 68 with solenoid 51, and by a wire 69 with solenoid 52, and by a wire 70 with solenoid 53, and by a wire 71 with solenoid 54. A wire 72 leads from wire 69 to wire 4 A lead 73 from motor 6 connects with wire 62. A lead 74 from motor 6 connects with wire 61. Alead 75 from motor 6 connects with wire 63. A wire 76 connects lead 74 with one pole of'solenoid of brake 17, and a wire 77 connects lead 75 with the other pole of solenoid of brake 17. A wire 78 connects I 4 contact f with one pole of solenoid of differential gear brake 19, and a wire 7 9 conthat brake. The controlling lever 32 is next nects contact y with the other pole of the solenoid of differential gear brake 19. One lead 80 from motor 7 connects with wire 65. Another lead 81 from motor 7 connects with wire 64. Another lead 82 from motor 7 connects with wire 66. A wire 83 connects lead 81 with one pole of the solenoid of switch 18, and a wire 84 connects the lead- 82 with the other pole ofthe solenoid of switch 18. Wire 85 connects lever 32 with wire 33. D, E, F, G, H designate the respective armatures for the respective solenoids 03, e, f, g and h.

The operation is as follows: For starting at slow speed, lever 32 is moved onto contact a, hereby closing a circuit as follows:

from line wire 33 through lever switch 32 to contact a, through wire 55, through solenoid 52 and wire 86 to wire 72 and wire 35, energizing solenoid 52, and lifting its armature F, which tacts f f and between contacts f f thereby establishing the following circuit: from wire 35 through wire 43 to contact 7 to contact f to wire 78, solenoid of brake 19,

through wire 79 to contact f to contact f to wire 34. Solenoid of differential gear brake 19 is thus energized, which releases moved to contact 5, which establishes a circloses circuit between con- D, closing contact d and (Z 03 and d (5 and d whereupon the circuits are established as follows: from wire 35 through wire 38 to contact d to .contact 03 wire 62 ,wire 73 to motor 6,.also from wire 34 to contact d to contact d through wire 61 to wire 74 and motor 6, and also from wire 33 through wire 36 to contact d to contact 01 and through wire 63 to lead 75 and motor 6, and also establishes a circuit from wire 74 through wire 76 to solenoid of brake 17 and from this solenoid through wire 77 to wire 75, thereby releasing brake 17 of motor 6, and also closing the circuit through motor 6, whereupon as motor 7 is still stationary andunder its brake 18, motor 6 operates through its shaft 8 to drive gear 13, and through the pinions 14 operates the differential gear casing 15 around the stationary gear 12, the latter being held stationary with shaft 11 of motor 7, and thereby driving the differential gear casing 15 and shaft 10 attached thereto together with worm 4, gear 3 and drum 1 at a reduced speed.

After this starting, to obtain full speed, the lever 32 is moved tact 0, thereby establishing circuits as follows: from contact 0 through wire 57 through'solenoid 53 through wire 70 to wire 71 to wire 35, thereby energizing solenoid switch 9 and attracting its armature G thereby closin contacts g g g 9 g and 9 which esta lishes the from wire 35 through wire 46 to contact 9 to contact 9 through wire 65 to wire 80 and motor 7, and from wire 34 through wire 45 to contact 9 to contact 9 through wire 64 to wire 81 and motor 7, and from wire 33 through wire 44 to contact 9 to contact 9 through wire 66 to wire 82 and motor 7 and following clrcuits still farther onto conalso from wire 81 through wire 83 and solei is running, it operates through its shaft 11 j and gear-12' to coact with gear 13 driven from motor 6 to drive the differential gear casing 15 at the same speed as the motor shaft, thereby driving worm 4, gear 3 and drum 1 at maximum speed.

When it is desired to slow down, the'lever l 32 is movedofi' from contact 0, thereby cutting off the current through the before described connections from motor 7, and deenergizing the solenoid of brake 18 and peri mitting brake 18 to hold shaft of motor 7 stationary, thereby tending to reduce the speed of the difierential housing and the 'car connected thereto. ,The momentum of the drum and car tends to maintain'the motor 6 through the befored'escribed connections and deenergizes solenoid "of'brake 17 causing the latter to set, and then the lever 32 is moved off from contact a, which deenergizes the solenoid of brake 19, which causes the latter to set tight on the diiferential gear casing 15, and thus act as a further brake, although it will be apparent that the brake on the dilferential gear casing 15 is not an essential feature, but is an added safeguard.

In running in the opposite direction, the

lever 32 is first moved onto. contact a through wire 58 to wire through solenoid 52 wire 86 and wire 72 to wire 35, thereby energizing solenoid 52 and raising its armature F and closing contacts 7, f f f whereupon a,circuit is established as follows: from Wire 35 through wire 43 to contact f to contact and wire 78 to solenoid of differential gear brake 19 through wire 7 9 to contact to contact f to wire 34, thus releasing brake 19 of the differential-gear. The lever 32 is next moved onto contact 5 whereupon circuits are established as fol lows: from contact 5 through wire 59 to solenoid 51 through wire 68 to wire 69 and wire 35, thereby energizing solenoid 51 and attracting armature E, thereby establishing a circuit through motor 6 and solenoid of brake 17, thereby releasing brake 17 the circuits through motor 6 being as follows:

' from wire 33 through wire 39 to contact 6 to contact 6 to wire 63 to wire 75 and motor 6 from wire 34 through wire 41 to contact" e to contact 6 and wire 62 to wire 7 3' and motor 6; and from wire 35through wire 40 to contact a to contact e to wire 61 to, wire 74 and motor 6, these circuitsgiving a reverse rotation of the motor6, by reason of the wires 41 and 46 of solenoid switch e being connected respectively to wires 34 and 35, while .in forward running, the concircuits are established as follows: from contact 0 through wire 60 to solenoid 54 and wire 71 to wire 69 wire 72 and wire 35, thereby energizingsolenoid 54 and attracting armature'H;,whereupon circuits are established as follows: from wire 33 through wire 47 to contact h to contact 72, to wire 66 to wire 82 to motor 7; also from wire 34 through wire 49 to contact 71? to contact 71. wire 87 to wire 80 and motor 7, and also from wire 35 through wire 48 to contact 71. to contact h to wire 86 and wire 81 and motor 7. Circuit is also established from wire 81 through wire 83 solenoid of brake 18 and wire 84 to wire 82. This energizes the solenoid of brake 18 and releases brake 18 and supplies current to motor 7, which now operates in unison with motor 6 and drives the worm 4, gear 3, and drum 1 at full speed. When'thus moving reversely to come to a reduced speed, the lever 32 is moved off from contact 0 thereby through the before described connections stopping motor 7 and setting brake 18. The momentum of the drum and car will have a tendency to revolve the worm 4' ahead of the normal speed of motor 6, which will be retarded by motor 6, which will act as a brake. In coming to a stop, the lever 32 is moved off from contact 5 which stops motor 6 and sets brake 17 and by moving lever 32 011' from contact a the solenoid, of the differential gear brake is deenergized, setting that brake also.

When running in either direction at full speed, upon slowing down to reduce speed by moving lever 32 off from contacts a or 0 the motor 'which continues; in operation speeds up inexcess of synchron ism, due to the car momentum driving same and acts as a dynamic brake, causing the motor to act as a generator, and the current 'thusproducedjs returned to the line. Thus, the energy which is employed to bring the car to a stop is in part turned back into'the line, whereas in other systems where a direct I current motor is employed and the dynamic brakin efiect made use of, resistance is utilize and the energy is wholly dissipated. When the motor, acting as a generator, gradually overcomes the car momentum and the motor has slowed down to .synchronism with the alternating supply circuit, its

'dynamic braking action ceases, and the nections are through solenoid switch (2, in generator automatically becomes a motor which Wires 38 and'37 are respectively con- 1 nected to wires 35 and 34.

The motor 6 thus operates through the beforedescribed gearing to revolve the drum 1 in the opposite direction atjythe reduced speed, as at this time the motor 7 is sta- "tionary and its brake 18 holds shaft 11- and gear 12 stationary.

To run reversely at full speed the lever 32 is next moved onto contact 0 whereupon and maintains the reduced speed. The

motor is then brought to rest by moving speed. By suitably proportioning the gears tion of its full speed before the dynamic braking effect is exhausted. Thus, as shown in Fig. 3, the gear 12*, may be smaller than the gear 13, so as to increase the.

speed reduction of the car relatively to the motor, in starting or at slow speed, and to increase the speeding up of the motor in stopping, so as to extend the dynamic braking action. I

By the above described means the car may be run at either low or high speed without the use of shift gears and with the induction motive means running at normal speed. As such means also provides for reducing the starting torque on thestarting motor, it enables a motor with low starting torque to be used and also eliminates the overdraft on the supply circuit and source of current by rush of current to the induction motor, in starting under excessive load.

Fig. 2 shows a modified form in which the motors 6 and 7 are on opposite sides of the worm 4". In this form it is necessary to carry the shaft 9 of motor 6 completely through the worm 4: to connect withthe differential gear. In this form, the operation is precisely the same except for the relative arrangement of the motors and their brakes.

. The form shown in Fig. 4is adapted for traction elevators in which 1 designates the drum, which constitutes the casing of the differential gear consisting of gears 12" and 13, which are respectively carried on shafts 8 and 11 of motors 6 and '2' respectively, pinions 149 being mounted directly on the drum; The brake 28 of solenoid 19 is directly mounted on the drum 1*, and the brake 28 of motor 7 is operated by solenoid 18 while brake 28 of motor 6" is operated by solenoid 17 r Fig. 6 shows differential gearing adapted to be used in the traction type of Fig. 4, to give a different gear reduction in which the gear 12 is smaller than the gear 13 and pinions 14 are set at a corresponding angle.

What we claim is:

l. A driven element, two induction motors, braking means for the motors respectively, and means connecting said motors to the driven element whereby when the motors are operated at synchronous speed in the same direction as one.another the driving element is driven and when one motor is held against rotating the other motor will be operated by the driven element at a greater speed than synchronous s eed so that said operating motor will pro uce dynamic braking action.

2. The method of electric drive, which method comprises operating induction motors in the same direction as one another at normal speed to drive a driven element, and then reducing the speed of one motor to cause the driven element to drive the other motor at a higher rate of speed than said normal speed so as to produce dynamic braking action of said other motor.

3. A driven element, two motors, gearing between the two motors for driving the driven element, a brake for each motor, solenoids for controlling said brakes, controlling means, a supply circuit, means operated by said controlling means in one position for connecting one motor and the associated brake solenoid with the supply cir cuit, and when in another position to also connect the other motor and its brake solenoid to the supply circuit.

4. The combination of two electric induction motors, electric supply connections therefor, bevel gears connected respectively with said motors, an intermediate member carrying bevel gears engaging the aforesaid bevel gears to form a differential gearing adapted to permit turning of the motois in the same direction as one another, a load device connected to be driven by and to drive said intermediate member, and means for arresting one of said motors to cause the other motor to run at an increased speed by operation of said load device.

5. A driven element, two motors, a hollow shaft 011 one motor, a shaft on the other motor extending through the hollow shaft, a gear on each shaft, pinions between said gears, a casing carrying said pinions and driving the drlven element, a brake for the hollow shaft, and a brake for the other shaft.

6. A driven element, two motors, a hollow shaft on one motor, a shaft on the other motor extending through the hollow shaft, a gear on each shaft, pinions between said gears, a casing carrying said pinions and driving the driven element, a brake for the hollow shaft, a brake for the other shaft, and a brake for the casing.

7. A driven element, two motors, a hollow shaft on one motor, a shaft on the other motor extending through the hollow shaft, a gear on each shaft, pinions between said gears, a casing carrying said pinions and driving the driven element, a brake for the hollow shaft, a brake for the other shaft, and a solenoid for releasing such brake, each solenoid being in circuit with the associated motor.

' 8. In elevator operating mechanism, two electric induction motors, electric supply connections therefor, a differential gearing comprising two ear members connected respectively to sai motors and an intermediate member provided with gears engaging the aforesaid gear'members to permit of turning of the motors in the same direction as one another, said intermediate member i being connected to the elevator car to drive the same and to be driven thereby, and

means for arresting one of said motors tocause the other motor to be driven at an increased speed so as to act as a dynamic brake. V

9. In combination a differential gear comprising two opposite gear members, an intermediate member provided with gears rotatablymounted thereon and engaging the aforesaid gear members, two electric induction motors adapted to turnin the same direction as one another and connected respectivelyto said opposite gear members to drive said opposite gear members and theintermediate member at the same rotative speed, and means for arresting one of said normal speed so as to produce connected to said motors motors to enable the intermediate member to drive the other motor at an increased speed, so that said other motor w1ll act as a dynamic brake.

current supply circuit,'tw'o induction motors connected thereto, a driven element, a differential gearing having opposite members an having an intermediate member connected to said driven element to allow turning of the motors in the same direction as one another, and means for arresting one of'said motors to causethe other motor to operate at a high speed relatively to the driven member.

11.-In combination with an alternating current supply circuit, an induction motor connected thereto, a driven element, means connecting said driven element to said motor to drive said driven element at a definite speed when the motor is running at normal speed, and means for changing the connection between the motor and driven element to cause the motor to run above normal'and above synchronous speed, while the driven element isrunning at or below normal speed,

whereby the motor is caused to act as agenerator, and as a dynamic brake.

12. The method of electric drive, which method com rises operating difierentially connected in uction motors at normal speed to move a load, and then mechanically arresting one motor to cause the load to drive the other motor at a higher speed than said dynamic braking action of said other motor.

13. The method of electric drive, which method comprises energizing differentially connected motors to cause operation thereof at synchronous speed in the same direction as one another to move a load, and then producing braking action on one of said motors and deenergization thereof so-that' the inertia of the moving load will run the other motor above. synchronous s eed.

14. In combination, two induction motors, a differential connection for said motors, a

10. In combination with an alternating .ber to rest.

rotative member connected to and driven by the differential when the motors are running at synchronous speed in the same d rection asione another and driving the differential when one of the motors is cut out,

there being means to reduce the speed of said motor, so that the speed of the other tarding the same, braking means for each motor shaft, and gearing connecting each motor shaft with the driven member to cause the driven member to operate at the same speed as the motor shafts when both motors are operating and to cause the-driven member to operate at a reduced speed relative to one of the motors when the othermotor is retarded by its brake, whereby the load device may be operated at a reduced speed in starting and may operate one of the motors at an increased speed in stopping toproduce a dynamic braking action of said motor.

16. The combination of a driven member,

two motors, each provided with driving con- -nections .and with a shaft, braking means for each shaft, differential gearing connecting both of said shafts 'to said driven member to operate" the driven member by the joint action of said motorsand to cause the driven member to operate one of the motors at an increased speed when the other motor is retarded by its braking means.

17. A driven element, differential gearing connected to drive the same, two motors connectedto opposite members of said differential gearing for joint operation of said driven element, braking means for one of said motors to cause the driven member to operate at a reduced speed relative" to the other motor so as to reduce the speed of the driven member in starting and to increase the speed of said other motor for producing a dynamic braking action of said other motor in stopping, and braking means for sald other motor to bring the driven mem- 18.. A load deviceya diflerential gear conload device and to be operated thereby,'two motors provided with operating connections and having shafts connected to opposite members of said. differential gear to operate the load device by the joint action of said necteil to said load device to operate said motors, means for braking one of said motors to cause the load to. operate at a reduced I speed relative to the other motor, whereby the load device may be operated at a reduced speed in starting and may operate the said other motor at an increased speed in stopping to produce a dynamic brake action, and means for braking said other motor to bring the load device to rest.

19. In combination, induction motors, a driven element difierentially connected to the induction motors, brakes for the induction motors, and means to establish an electric circuit for release of one brake andenergization of its associated motor and to then establish an electric circuit for release of the other brake and energization of its associated motor to drive said last named motor in the same direction and at the same speed as the first named motor.

20. In combination, induction motors, a driven element diflerentially connected to the induction motors, brakes for the induction motors, and means to establish electric circuits for release of the brakes and energization of their associated motors and to then break one of said circuits to deenergize one of said motors and to set the associated brake to allow the driven element to drive the other motor at a higher speed than synchronous speed so as to produce dynamic braking action of said other motor.

21. The method of electric drive, which method comprises operating induction motors at normal speed to drive a driven element, and then bringing one motor to a stop to cause the driven element to drive the other motor at a higher rate of speed than said normal speed so as to produce dynamic braking action of said other motor.

22. The combination of two induction motors, electric supply connections therefor, bevel gears connected respectively with said motors, an intermediate member carrying bevel gears engaging the aforesaid beve gears to form a differential gearing, a load device connected to be driven by and to drive said intermediate member, and means for stopping one of said motors to cause the other motor to run at an increased speed by operation of said load device.

23. In elevator operating mechanism two induction motors, electric supply connections therefor, a diflerential gearing comprising two gear members connected respectively to said motors, and an intermediate member provided with gears engaging the aforesaid gear members, said intermediate member being connected to the elevator car to drive the same and to be driven thereby, and means for stopping one of said motors to cause the other motor to be driven at an increased speed so as to act as a dynamic brake. 1

24:- In combination, a differential gear comprising two opposite gear members and an intermediate member provided with gears rotatively mounted thereon and engaging the aforesaid gear members, two induction motors connected respectively to said opposite gear members to drive said opposite gear members and the intermediate member at the same rotative speed, and means for stopping one of said motors to enable the intermediate member to drive the other motor at an increased speed so that said other motor will act as a dynamic brake.

25.- In combination with an alternating current supply circuit, two induction motors connected thereto, a driven element, a differential gearing having opposite members connected to said motors and having an intermediate member connected to said driven element, and means for stopping oneof said motors to cause the other motor to operate at higher speed relative to the driven member.

In testimony whereof, we have hereunto set our hands at Los Angeles, California,

this 16th day ofJuly, 191

ROBERT H. GAYLORD. GUY B. CAPPS.

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