US2039073A - Elevator signal and control system - Google Patents

Description

W. F. EAMES ELEVATOR SIGNAL AND CONTROL SYSTEM April 28 1936.

Filed July 16, 1935 INVENTOR 9- William 1754/7265.

WETNESSES:

ATT

Patented Apr. 28, 1936 UNITED STATES Ai'ET QFFEQE ELEVATOR SIGNAL AND CONTROL SYSTEM Application July 16,

13 Claims.

My invention relates to signal and control systems for elevators and more particularly to systems for supplying operating current to the signal and control circuits of elevators.

In a large number of elevator systems embodying a plurality of cars, the cars are usually operated by means of what is known as the Ward- Leonard system, in which each car is provided with a drive including a motor generator set and an exciter. In many systems of this character, the electrical energy for operating the control circuit for the cars is obtained by connecting such circuits to the exciter associated with any one of the cars that is in operation. However, 15 when that car is taken out of operation, it is necessary to disconnect the control circuit from its exciter and connect it to the exciter of another car which is in operation.

In some instances of this nature, the transfer of the control circuits from one eXciter to another has caused difficulties by reason of the fact that the control circuits usually have energized stop call relays or other energized relays in their system, because some operation is being performed at the time, and, when the circuits are disconnected from the one exciter and connected to the other exciter, the supply circuit for such relays is temporarily opened. Of course, the circuit is opened only momentarily when the transfor is made, but the energized relays drop out by reason of this opening and are not reenergized automatically to resume their operated condition when the transfer is completed. The deenergization of the relays before they complete the work for which they were energized causes trouble.

For instance, if a passenger has registered a stop call and the registering relay is deenergized before the call is completed, the passenger is unaware of the fact and is irritated when no car answers his call. This has given rise to complaints that cars pass floor calls without answering them. On the other hand, if the signal and control circuits are connected to a second exciter before being disconnected from the first exciter, the difference in the voltage of the exciters may cause trouble. Also, if an arc holds on momentarily during a transfer, it may result in a high current flowing between the machines by reason of a difference in voltage of the machines which may cause the burning of fuses and injury to the relays.

Therefore, one object of my invention is to provide for transferring the control circuits of a bank of elevator cars from one operating exciter 1935, Serial No. 31,616

to another operating exciter without deenergizing any of the energized relays in such circuits and without causing any reversal of polarity of short circuits or operation of the exciters in series.

A further object is to provide a transfer system which will be responsive to the shutting down of one of a group of exciters for automatically transferring the control circuits associated therewith to another one of such exciters.

It is also an object of my invention to provide a system for transferring elevator control circuits from one exciter to another exciter which shall be simple and inexpensive in construction, installation and operation.

For a better understanding of the invention, reference may be had to the accompanying drawing, in which Figure l is a diagrammatic representation of the individual exciter generators for three elevator cars and a means for connecting the control circuit for such cars to the exciter generators in accordance with my invention; and

Fig. 2 is a diagrammatic representation of a modified form of the system represented in Fig. 1 for connecting the control circuit of three elevator cars to the exciter generators associated with such cars.

Referring more particularly to the drawing, I have illustrated an elevator system embodying three exciter generators to be individually associated with three elevator cars (not shown). These generators are of the type provided for supplying current for the circuits and the field Windings of generators individual to the cars such as are employed in the elevator art and, for convenfence, will be hereinafter referred to as exciters.

The exciter for the first car is designated by the letters AEX, for the second car by BEX, and for the third car by CEX. Throughout the following explanation of the diagram, the letters A, B and C associated with the various parts of this system indicate the corresponding cars with which such parts are associated.

The exciter AEX comprises an armature All) and a self-excited shunt field winding ASF. The eXciter may be operated by any suitable means as by a squirrel cage motor All such as may be employed for driving a Ward-Leonard set (not shown) for operating the hoisting, motor of car A (not shown). Inasmuch as systems of this character are old and well known, no further description or illustration thereof will be given. However, if desired, further detailed information regarding such a system may be obtained from Patent No. 1,921,679, issued August 8, 1933, to

Westinghouse Electric Elevator Company on an improvement in elevator control systems by Luther J. Kinnard.

The motor AH comprises a rotor M2 and a stator A13. The rotor Al2 is mounted on a shaft AM on which the armature All] of the exciter AEX is also mounted to be driven thereby. The stator Al3 of the squirrel cage motor All is provided with phase windings AIS, AH and A|8 which may be connected by a starting switch Al 9 to any suitable source of energy, such as that indicated by the supply conductors I, II and III. Hence, when the switch AIS is closed, the motor All and the exciter AEX (the only parts of the WardLeonard set shown in the drawing) are started in operation.

An accelerating relay AM controlled by the voltage of the motor All, is provided for short circuiting a plurality of resistors R2l, R22 and R23 in the circuit through the switch A19, after the motor All starts in operation, for the purpose of accelerating it to its normal high speed. The exciters for the other cars are constructed and operated in the same manner.

The exciter AEX is provided with a pair of brushes A-28 and A+28 to which a pair of supply conductors +25 and +25 are attached for the purpose of distributing to the individual circuits of car A the energy generated by the exciter. Similarly, the exciter BEX is provided with supply conductors +26 and +25 and the exciter CEX with supply conductors 2'l and +21. A plurality of fuses A29, A30, B29, B31], C29 and C30 are disposed in the supply circuits to prevent damage by reason of sudden excessive overloads. The circuits individual to the cars are designated by the arrows A-25 and A+25 for car A, B26 and B+26 for car B, and C2'! and C+21 for car C.

In addition to the individual circuits, the installation is provided with a control circuit which is common to all the cars. It is necessary to provide the common control circuit with suitable energy and, instead of providing a separate source of energy for that circuit, I have provided for connecting it to one of the operating exciters and, if that exciter shuts down, to transfer it to another operating exciter so that it is always attached to some one of the operating exciters.

The common control circuit for the cars is designated by the characters L+ and L. By the term control circuit I mean the various circuits in an elevator installation such as signal circuits, lamp circuits, control relay circuits, etc., which are common to all the cars in that installation and which it is desired to connect to a suitable source of energy.

In practicing my invention I provide for connecting the control circuit L+ and L- to the exciters by a plurality of transfer relays and means for controlling the passage of energy from the exciters. The transfer relay associated with the exciter AEX is designated as AT and that for the exciter BEX as BT. No transfer relay is provided for the exciter CEX because the connection of its supply circuit to the control circuit will be automatically controlled by the operation of the transfer relays AT and ET.

A first auxiliary transfer relay AD and a secand auxiliary transfer relay AE are associated with the transfer relay AT, and a first auxiliary transfer relay BD and a second auxiliary transfer relay BE are associated with the transfer relay ET, for connecting and disconnecting the control circuit L+ and L to the exciters in accordance with certain predetermined conditions.

In addition to the transfer relays for controlling the passage of energy from the exciters, I have provided current limiting means disposed to be connected in the circuits from the exciters to the control circuit in accordance with the operation of the transfer relays. Although any suitable current limiting means may be utilized, I have indicated as one such suitable means a plurality of resistors RI, R2, R3 and R4.

It is believed that the invention will be understood best by an assumed operation.

It will be assumed that the cars have been out of service but that car B is now placed in condition for operation, by closing the starting switch BIS to start the motor Bl I. The closing of the switch Bl9 energizes the windings of the stator BIS by a circuit in which one branch extends from the supply conductor I through conductor 35, the contact members 0 of switch Bl9, resistor R5, conductor 3| and phase winding BIB to the junction point 32; another branch extends from supply conductor II through conductor 33,

relay to close its contact members a, b and c. The

closing of the contact members a, b and 0 short circuits the resistors R7, R6 and R5 and thereby causes the motor Bll to operate at its normal high speed.

The operation of the motor BII rotates the shaft BM thereby operating the armature BIB of the self-excited generator or exciter BEX, thereby causing the exciter to supply its conductors 26 and +26 with energy as its field BSF builds up.

The accelerating relay BM is provided with an additional pair of contact members at and the closing of these contact members connects the winding of relay BT across the conductors 2E and +26 when that voltage rises to a predeter mined value the relay ET is operated through a circuit extending from the brush B-".8 of the exciter BEX through the conductor -26, fuse B29, conductor 39, the contact member (1 of relay BM the coil of relay BI", fuse B36 and conductor +26 to the brush B+2i3 of the exciter.

The energization of the transfer relay ET closes its contact members a, b and c. Closure of contacts a and b energizes the first auxiliary transfer relay BD by a circuit extending from the supply conductor +25 through conductor 42, the coil of relay BD, conductor 53, the contact members a of relay BT, conductor 44, and the contact memhers I) of relay BT to the supply conductor +25.

The energization of the relay BD closes its contact members a, b and c and opens its contact members of.

The closing of the contact members a completes a self-holding circuit for relay BD, as should be apparent.

The opening of the contact members (2 of relay BD opens the circuit extending to the exciter The closing of the contact members 0 of relay BD connects the supply conductor +25 of the exciter BEX to the supply conductor L+ of the control circuit by a circuit extending from conductor +26 throughiconductors 48 and 49, the contact members c of relay BD, resistor R4 and conductors 50 junction point 69, contact members d of relay AD, and conductors 61 and 5| to the supply conductor L+. The control circuit L+ and L- is now energized through the resistor R4.

However, the simultaneous closing of the contact members b of the relay BD energizes the second auxiliary transfer relay BE by a circuit extending from the supply conductor 26 through conductor 53, the coil of relay BE, conductor 54, the contact members I) of relay BD, junction point and the contact members 0 of relay BT to the supply conductor +26. The energization of the relay BE closes its contact members a, b and c and opens its Contact members (1. The closing of the contact members a of relay BE completes a self holding circuit for that relay extending from the supply conductor 54 through the contact members a of relay BE, conductor 56 to junction point 55 and thence through the contact members 0 of relay BT to the supply conductor +26. The closing of the contact members 12 of relay BE provides an additional holding circuit for the relay BD extending from the junction point 46 through conductor 51, the contact members b of relay BE and conductor 48 to the supply conductor +26. This second holding circuit for relay ED is provided to insure the deenergization of the relay BE before that of the relay BD when the exciter BE is shut down.

The closing of the contact members 0 of the relay BE connects the supply conductor L+ to the exciter BEX by a circuit extending from the supply conductor +26 through conductors 48 and 49, the contact members 0 of relay BE and conductors 59 and 50, junction point 69, contact members d of relay AD and conductors 51 and 5| to the supply conductor L+, thereby short circuiting the resistor R4. Inasmuch as the supply conductor L of the control circuit is connected to the supply conductor 26 of the exciter BEX by conductors 60 and 5!, the control circuit is now connected directly to the supply conductors +26 and +26 leading from the brushes B28 and B+28 of the exciter and will remain supplied with current from that exciter until some other change takes place in the operation of the cars.

It may be stated here that ordinarily, in the system shown, the control circuit is supplied with energy from the exciter AEX when all of the three cars are. in operation. However, as shown by the preceding operation, the starting of any one of the cars, when they are all out of operation, automatically causes the control circuit to be directly supplied with current by the exciter of that car.

If car C is now placed in operation by closing the switch CIS, its exciter CEX will not be connected to the control circuit supply conductors L+ an L- because of the open contact members (1 of relay BD of car B and as long as car B remains in operation and car A remains out of operation, the exciter CEX for car C cannot be connected to the control circuit conductors L+ and L.

It will be assumed now that car A is placed in operation along with car B by the closing of the starting switch Al9 for car A. The closin of the starting switch Al 9 energizes the phase windings Al6, All and AIS through the resistors R2 l, R22 and R23 in a manner sirmlar to the starting of the motor Bll for car B. After the motor All starts and the voltage across the motor windings has risen to a predetermined value, the accelerating relay AM is operated to close its contact members a, b and 0, thereby short circuiting the resistors R2l, R22 and R23 to cause the motor All to operate at normal high speed. The operation of the motor All operates the exciter AEX and causes its brush A-28 and A+28 to energize its supply conductors 25 and +25.

At the same time, the energization of the ac celerating relay AM causes its contact members d to close, thereby effecting the subsequent operation of the transfer relay AT for car A (as explained with exciter BEX) to close its contact members a, b and c, by a circuit extending from the conductor 25 through contact members cl of relay AM and the coil of relay AT to conductor +25.

The closing of the contact members a of relay AT energizes the first auxiliary transfer relay AD to effect the first stage of the transfer of the control circuit from exciter BEX to exciter AEX.

The circuit for relay AD extends from the supply conductor -25 through conductor 63, the coil of relay AD, junction point 66, the contact members a of relay AT, conductor 64, junction point and the contact members b of relay AT to the supply conductor +25. The operation of the relay AD will effect the first stage of transferring the control circuit from the exciter BEX of car B to the exciter AEX of car A by closing its contact members b and c and opening its contact 65 and the contact members b of relay AT to the supply conductor +25. The opening of the contact members d opens the direct connection between the supply conductor L+ and the conductor 50 leading to the supply conductor +26 of exciter BEX, thereby throwing the circuit connection between conductor L+ and conductor +26 from the contact members d of relay AD to the normally closed contact members at of relay AE. The current supplied by the conductor +26 to the supply conductor L+ now flows from the conductor 56 through the junction point 66, the contact members (1 of relay AE, the resistor RI and the conductor 5| to the supply conductor L+. Thus, the opening of the contact members (1 of relay AD now throwsthe circuit for the supply conductor L+ through the resistor RI. However at the same time that the contact members a, of relay AD are opened, its contact members c are closed. This operation closes the gap between the supply conductor +25 and the supply conductor L+ so that we now have a circuit extending from the supply conductor +25 through conductors l0 and "H, the contact members 0 of relay AD, the resistor R2 and conductors 61 and 5| to conductor L+.

Under these conditions, the resistor RI is connected in the circuit to exciter BEX and the resistor R2 in the circuit to the exciter AEX. Hence it will be seen that although the control circuit conductor L+ is momentarily connected at the same time to the exciter BEX and to the exciter AEX, the circuit to each exciter includes a current limiting resistor which prevents an excessive interchange of energy between the exciters. At the same time, the control circuitwill be constantly connected to a source of supply of current which will prevent any energized relay in the control circuit from being deenergized before it should be deenergized in it's normal operation.

The closing of the contact members b of relay AD energizes the relay AE to complete the transfer of the control circuit from exciter BEX to exciter AEX, by a circuit extending from the supply conductor -25 through conductor 68, the coil of relay AE, junction point 12, contact members b of relay AD, junction point 13, and the contact members 0 of relay AT to the supply conductor +25. The energization of the relay AE closes its contact members a, b and c and opens its contacts members d. The closing of the contact members a completes a self-holding circuit for the relay AE extending from the junction point 12 through the contact members a of relay AE, conductor 14, junction point 13, and the contact member a of relay AT to the supply conductor +25.

The closing of the contact members b of relay AE completes a branch self-holding circuit for the relay AD extending from the junction point 65 through conductor 15, the contact members 17 of relay AE, and conductor 10 to the supply conductor +25. By reason of this circuit, it will be seen that the second auxiliary relay AE must be deenergized before the first auxiliary relay AD can be energized, that is, these relays will be energized in the order AD and AE and be deenergized in the order AE and AD.

The closing of the contact members 0 of the energized relay AE connects the supply conductor +25 directly to the supply conductor L+ by a circuit extending through the conductors iii and II, the contact members 0 of relay AE and the conductor 5|. At the same time, the opening of the contact members d of relay AE opens the circuit between the supply conductor L+ and the supply conductor +26. Hence, we now find that the supply conductors L+ and L are directly connected to the supply conductors +25 and +25 of the exciter AEX for car A and that the exciters for the other two cars are disconnected from the control circuit because of the open-contact members d of relay AE and the open contact members d of relay AD. Therefore, although the exciter BEX is still in operation and its transfer relay BT and its auxiliary transfer relays BD and BE are still energized, it is not connected to the control circuit because of the open contact members d on the relays AE and AD of car A.

It will now be assumed that car B is taken out of service and that car C is placed in service thus leaving cars A and C in service. The shutting down of car B is effected by opening the starting switch BIS thereby deenergizing the motor Bil and stopping the exciter BEX and also deenergizing the accelerating relay BM.

The deenergization of the relay BM opens its contact members d thereby deenergizing the transfer relay ET. The opening of the contact members 0 of relay BT opens the self-holding circuit of the second auxiliary relay BE thereby deenergizing that relay which, in turn, opens its contact members d, thus deenergizing the relay BD, because the first self-holding circuit for relay BD that was established through the contact members I) of relay BT was broken by the deenergization of the relay BT. With the relays BE and BD deenergized, their contact members 0 are opened and their contact members d are closed to again prepare a connecting circuit for the supply conductors leading from the exciters BEX and CEX. However, that connecting circuit cannot be again completed until the exciter AEX is shut down because of the open contact members (1 on relay AD.

It will be assumed now that car C is started in operation and that the switch C19 is closed to energize the motor Cil which places the exciter CEX in operation. However, the supply conductors +21 and +21 for car C cannot be connected with the control circuit now because, while car A is running, the contact members at of its relays AE and AD are open.

It will be assumed now that car A is shut down leaving only car C in operation. Under these conditions, the switch AIS is opened, thus deenergizing the motor Al! to stop the exciter AEX. The opening of the switch Al9 also deenergizes the accelerating relay AM which opens its contact members d thereby deenergizing the transfer relay AT.

The deenergized relay AT opens its contact members a, b and c. The opening of the contact members a and 1) opens the pick-up and preliminary self holding circuit of the relay AD and is without efiect at this time. The opening of the contact members 0 opens the self-holding circuit for the relay AE and deenergizes that relay to open its contact members a, b and c and close its contact members d. The opening of the contact members b of relay AE opens the secondary selfholding circuit of relay AD thereby deenergizing that relay to open its contact members a, b and c and close its contact members d.

Inasmuch as relay AE opened its contact members c and closed its contact members d before the contact members d of relay AD were closed, we again have the condition where the exciters oi the cars A and C are both momentarily connected to the control circuits through the resistors RI f and R2. However, the relay AD opens promptly, thereby opening its contact members c and closing its contact members d. The opening of the contact members 0 of relay AD disconnects the supply conductor +25 from the supply conductor L+ and the closing of the contact members d of relay AD connects the exciter CEX directly to the control circuit L+ by a circuit ex tending from the supply conductor +21 through conductor 41, junction point 16, the contact members cl of relay BD, conductor 50, junction point 69, the contact members (1 of relay AD and conductors Bl and 51 to the supply conductor L+.

By reason of the foregoing, it is seen that my invention provides for the automatic connection of the control circuit for all the cars to one of the exciters for operating the cars and that it also provides for automatically changing the connection between the exciters and the control circuit as the cars are placed in and taken out of service. At the same time, it is apparent that the manner in which the connection is automatically made will prevent any damage to the apparatus or to the control circuit and will also maintain in operation while the transfer is being made such energized relays as exist in the control circuit. It will be apparent that this is correct even though there may be some difference in the voltages in the various circuits as the con nections are made.

Referring now to Fig. 2 of the drawing in the diagram therein given, the control circuit is connectcd to the exciter of each car as that car is started into operation and the connection remains while the cars are in operation. Hence, if three cars are in operation, the control circuits are connected to the exciters for the three cars. However, in order to avoid injury to the control circuit and the exciters, the dropping out of relays, reversal of polarity, etc., I have provided in this modification for the insertion of suitable current limiting devices in the circuits connecting the control circuit to the exciters in such manner that the control circuit is connected directly to one of the exciters and indirectly to the other exciters.

In Fig. 2 the exciter AEX may be connected to the control circuits L+1 and L-l by a transfer relay ATS; the exciter BEX may be connected by a transfer relay BTS and the exciter CEX may be connected by a transfer relay CTS.

It will be assumed that car C is placed in operation by operation of the switch Ci9 in Fig. 2 to start the motor CH which, in turn, operates the exciter CEX. The starting of the motor CH also causes the accelerating relay CM to be energized for the purpose of short circuiting the resistors R9, RIG and RH to accelerate the motor to its normal high speed. In the system shown in Fig. 2, the relay CM is modified to the extent that it has an additional pair of contact members (1. Therefore, the energized relay CM closes its contact members :1 thereby energizing the transfer relay CTS by a circuit extending from the supply conductors 27 through the contact members d of relay CM and the coil of relay CTS to the supply conductor +21. The energization of the relay CTS closes its contact members a and b. The closing of the contact members a of relay CTS connects the control circuit L+1 to the supply conductor +21 of the exciter CEX by a circuit extending from conductor +21 through contact members a of relay CTS, conductor 80, the contact members of relay BTS, conductor 8| the contact members 0 of relay ATS and conductor 82 to the control circuit conductor L+l. The closing of the contact members I) of the relay CTS completes a circuit for connecting the control circuit conductor L-l to the supply conductor 21 by a circuit extending from the supply conductor Z1 through the contact members I) of relay CTS, conductor 83, contact members at of relay BTS, conductor 84, the contact members at of relay ATS, and conductors 85 and 86 to the supply conductor L-I. Thus it is seen that the starting of one of the cars of a group causes the control circuit for the system to be immediately connected to the exciter for that car.

It will be assumed now that car A is placed in operation along with car C by closing the starting switch Al 9. This energizes the motor Al I and consequently operates it as heretofore described. The operation of the motor Al I also energizes the relay AM to close its contact members a, b, c and d. The closing of the contact members it of relay AM energizes the relay ATS, causing it to close its contact members a and b and open its contact members 0 and d.

The closing of the contact members a of relay ATS directly connects the control circuit conductor L-l-l to the exciter AEX by a circuit extending from conductor L+l through conductor 82, junction point 81, conductor 88 and the contact members a of relay ATS to the supply conductor +25. The closing of the contact members b of relay ATS connects the control circuit conductor L| to the exciter AEX by a circuit extending from conductor L-I through conductor 86 and the contact members I) of relay ATS to the supply conductor 25. At the same time, the opening of the contact members 0 and d of the relay ATS opens the short circuit around the resistors RH and R15 and restores them to operation in the circuit connecting the exciter CEX and the supply circuit conductors L+| and L- I.

In this operation it will be seen that, although both cars A and C are now in operation, the control circuit is directly connected to the exciter AEX and through the resistors Hi3 and RI5 to the exciter CEX. The resistors prevent an excessive interchange of energy between the exciters.

It may be stated in connection with the system shown in Fig. 2 that with all the cars in operation, the control circuit Will usually be connected directly to one particular exciter at all times and through the resistors to the other cars. However if that particular car is shut down, the control circuit will be automatically transferred to direct connection with another exciter and through resistors to the exciter of any additional operating car.

Assuming that car A is shut down and that car 13 is placed in operation, then the relay ATS is deenergized and the relay BTS is energized. The deenergization of the relay ATS opens its contact members a and b thereby disconnecting the supply conductors -25 and +25 from the control circuit L+I and LI The closing of the contact members 0 and d of relay ATS restores the shunt circuits around the resistors Rl3 and R15. At the same time, the energization of the relay BTS closes its contact members a and b and opens its contact members 0 and d. The closing of the contact members a and b of relay BTS directly connects the supply conductors L-l-i and L! to the supply conductors 26 and +25 of the exciter BEX, the one circuit extending from the supply conductor L+l through conductor 82, junction point 81, contact members 0 of relay ATS, conductor 8|, junction point 89, conductor 95 and the contact members a of relay BTS to supply conductor +26 and the other circuit extending from the supply conductor L-I through conductors 86 and 85, the contact members at of relay ATS, conductors 84 and 9| and contact members b of relay BTS to the supply conductor -26.

The opening of the contact members 0 and d of relay BTS opens the short circuit heretofore existing around the resistors RI6 and R11 so that these resistors are now reinserted in the circuit connecting the control circuit conductors L+l and L-l to the supply conductors +21 and 21 of the exciter CEX. Therefore, it is apparent that, although car A is shut down and cars B and C are both running, the control circuit represented by the conductors L+l and L-l is directly connected to the supply conductors of the exciter BEX and that they are also connected to the supply conductors of the exciter CEX, but that the resistors RIG and RI! have been inserted in the circuit to the latter exciter so that the control circuit now takes its supply of energy from the exciter BEX.

Although I have illustrated and described only one embodiment of my invention and one modification thereof, it is to be understood that many other modifications and changes may be made in the invention without departing from the spirit and scope thereof.

I claim as my invention:

1. In a switching circuit for connecting a control circuit and a plurality of generators, means for connecting the control circuit to one of the generators when it is the only one in operation, means responsive to the operation of a second generator for transferring said control circuit from said one generator to said second generator, and means responsive to operation of the transfer means for preventing an excessive exchange of energy between said generators regardless of a difference in voltage of said generators.

2. In a switching circuit for connecting a control circuit and a plurality of generators, means for connecting the control circuit to one of the generators when it is the only one in operation, means responsive to the operation of a second generator for transferring said control circuit from said one generator to said second generator without deenergizing the control circuit, and means responsive to operation of the transfer means for preventing an excessive exchange of energy between said generators regardless of a difference in voltage of said generators.

3. In a switching circuit for connecting a control circuit and a plurality of generators, a plurality of supply circuits, one for each generator, means for connecting the control circuit to the supply circuit of one of the generators when it is the only one in operation, means responsive to the operation of a second generator for transferring said control circuit from the supply circuit of said one generator to the supply circuit of the second generator without deenergizing the control circuit, a current limiting means, and means responsive to operation of the transfer means for connecting said current limiting means between the control circuit and the supply circuit of said one generator to prevent an excessive exchange of energy between the circuits.

4. In a switching circuit for connecting a control circuit and a plurality of generators, a plurality of supply circuits, one for each generator, means for connecting the control circuit to the supply circuit of one of the generators when it is the only one in operation, means responsive to the operation of a second generator for transferring said control circuit from the supply circuit of said one generator to the supply circuit of the second generator without deenergizing the control circuit, a current limiting means associated with the supply circuit of the second generator, means responsive to operation of the transfer means for connecting said current limiting means between the control circuit and the supply circuit of said one generator to prevent an excessive exchange of energy between the circuits, means responsive to the operation of a third generator for transferring the control circuit from the supply circuit of said second generator to the supply circuit of the third generator without deenergizing the control circuit, a current-limiting means associated with the supply circuit of the third generator, and means responsive to operation of the transfer means associated with the third generator for connecting the current limiting means associated therewith between the control circuit and the supply circuits of the second generator and said one generator.

5. In a switching circuit for connecting a control circuit and a plurality of generators, a plurality of supply circuits, one for each generator, means for connecting the control circuit to the supply circuit of one of the generators when it is the only one in operation, electromagnetic means responsive to the operation of a second generator for transferring the control circuit from the supply circuit of said one generator to the supply circuit of the second generator without deenergizing the control circuit, a resistor associated with the supply circuit of the second generator, and means responsive to operation of the transfer means for inserting the resistor between the control circuit and the supply circuit of said one generator.

6. In a switching circuit for connecting a control circuit and a plurality of generators, means responsive to operation of one of the generators when it is the only one in operation for connecting the control circuit to that generator, means responsive to the operation of a second generator for transferring said control circuit from said one generator to the second generator without deenergizing the control circuit, and means responsive to operation of the transfer means for preventing an excessive exchange of energy between said generators while the transfer is being eifected regardless of a difference in voltage of the generators.

7. In an elevator system a pair of operating generators, a control circuit connected to one of said operating generators, means responsive to the stopping of the generator to which the control circuit is connected for transferring the control circuit to the other operating generator without deenergizing the control circuit, and means responsive to operation of the transfer means for preventing an excessive exchange of energy be tween said generators when the transfer is effected.

8. In an elevator system for operating a plural ity of cars, a control circuit for the cars, a plurality of generators, one for each car, a plurality of supply circuits, one for each generator, a plurality of circuits for connecting the control circuit to the supply circuits of the generators, a plurality of current-limiting devices associated with the connecting circuits, a plurality of switches disposed in the connecting circuits, and

a plurality of transfer devices responsive to operation of the generators for operating the switches to connect the control circuit to only one operating generator, to transfer the control circuit to another operating generator when said one generator is shut down without deenergizing the control circuit, and for inserting a currentlimiting device between the control circuit and the generator from which the control circuit is being transferred while the transfer is being effected to prevent injurious exchange of energy between the circuits.

9. In a switching circuit for connecting a con trol circuit and a plurality of generators, means for connecting the control circuit to one of the generators when it is the only one in operation, a plurality of current-limiting devices, means responsive to operation of a second generator for first simultaneously connecting the control cir cuit through the current-limiting devices to said one generator and to said second generator and for then eliminating the current-limiting device between the control circuit and said second generator, whereby the transfer is effected without deenergizing the control circuit and without permitting an excessive exchange of energy between the control circuit and the generators.

10. In a switching circuit for connecting a control circuit and a plurality of generators, means for connecting the control circuit to one of the generators when it is the only one operating, a plurality of current-limiting devices, a transfer relay, means responsive to operation of a second generator for operating the transfer relay, a first auxiliary relay responsive to operation of the transfer relay for simultaneously connecting the control circuit through one of the current-limiting devices to said one generator and through another current-limiting device to the second generator, and a second auxiliary transfer relay responsive to operation of the first auxiliary transfer relay for disconnecting the control circuit from said one generator and for rendering ineffective the current-limiting device disposed between the control circuit and the second generator.

11. In an elevator system for operating a plurality of cars, a control circuit for the cars, a plurality of generators, one for each car, a plurality of electromagnetic devices for connecting the control circuit to the operating generators, a plurality of current-limiting devices responsive to operation of the electromagnetic devices for preventing an excessive interchange of energy between the generators through said connecting means, and a plurality of accelerating relays responsive to operation of the operating generators for effecting operation of the electromagnetic means in accordance with the operation of the generators.

12. In an elevator control system for operating a plurality of cars, a control circuit for the cars, a plurality of generators, one for each car, a plurality of accelerating relays, one for each generator, a plurality of resistors, a plurality of connecting circuits, and a plurality of transfer relays operably responsive to operation of the accelerating relays for operating the connecting circuits to connect the control circuit directly to one of the operating generators, to transfer the control circuit to another operating generator when said one generator is shut down without deenergizing the control circuit, and to insert the resistors in the connecting circuits to prevent an excessive exchange of energy between the generators.

13. In an elevator system for operating a plurality of cars, a control circuit for the cars, a

plurality of generators one for each car, a plurality of supply circuits one for each generator, a plurality of individual car circuits one connected to each supply circuit, means responsive to operation of one of the generators when it is the only one in operation for connecting the control circuit to the supply circuit of that generator, means responsive to the operation of a second generator for transferring said control circuit from the supply circuit of said one generator to the supply circuit of the second generator without deenergizing the control system, and means responsive to operation of the transfer means for preventing an excessive exchange of energy between the supply circuits of said generators while the transfer is being effected regardless of a difference in voltage of the generators.

WILLIAM F. EAM'ES.

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