US3582719A

US3582719A - Forcing circuit for inductors

Info

Publication number: US3582719A
Application number: US835408A
Authority: US
Inventors: Leo L Stuckens
Original assignee: Stearns Electric Corp
Current assignee: PT Components Inc; Stearns Electric Corp
Priority date: 1969-06-23
Filing date: 1969-06-23
Publication date: 1971-06-01
Anticipated expiration: 1988-06-01

Abstract

For developing forcing current in a circuit in which prompt electrical response in inductive loads is desirable, a plurality of capacitances are charged in parallel at the working voltage of the source. When forcing voltage is required, the capacitances are disconnected from their parallel charging lines and connected in series for forcing purposes to supply the resulting high voltage into the circuit which exhibits the inductive property of opposing change in current. When two such circuits are to be forced in alternation, means is provided for dissipating the energy in one circuit concurrently with delivery of forcing voltage into the other. Versatility is enhanced by connecting the respective coils to separate sockets into which various capacitances, potentiometers and/or suppression units are interchangeably plugged.

Description

United States Patent [72] Inventor Leo L. Stuckens Milwaukee, Wis.

[21] Appl. No. 835,408

[22] Filed June 23, I969 [45] Patented June 1, 1971 [73] Assignee Stearns Electric Corporation Milwaukee, Wis.

[54] FORCING CIRCUIT FOR INDUCTORS Primary Examiner-Robert K. Schaefer Assistant Examiner-William J. Smith Attorney-Wheeler, Wheeler, House and Clemency ABSTRACT: For developing forcing current in a circuit in which prompt electrical response in inductive loads is desirable, a plurality of capacitances are charged in parallel at the working voltage of the source. When forcing voltage is required, the capacitances are disconnected from their parallel charging lines and connected in series for forcing purposes to supply the resulting high voltage into the circuit which exhibits the inductive property of opposing change in current. When two such circuits are to be forced in alternation, means is provided for-dissipating the energy in one circuit concurrently with delivery of forcing voltage into the other. Versatility is enhanced by connecting the respective coils to separate sockets into which various capacitances, potentiometers and/or suppression units are interchangeably plugged.

FORCING CIRCUIT FOR INDUCTORS BACKGROUND OF INVENTION The need for forcing circuits has long been recognized but heretofore such need has been satisfied by charging the forcing capacitance to high voltage from a source which is separate from the source which supplies the working current. An example is U.S. Pat. 3,379,292 ofApr. 23, 1968.

SUMMARY OF INVENTION The present invention has many advantages. A major factor is the use of a single current source which supplies the working current while the circuit is in use, and at the same time, and with the same voltage, charges forcing capacitances. In the device selected to exemplify the invention, there are clutch and brake actuating windings which are energized alternately and which desirably are immediately effective when energized. The forcing circuit substantially eliminates delay which would otherwise be attributable to inductance. A single source supplies the windings in first and second circuits alternately with their working current while in use and at the same time charges in parallel a plurality of capacitances in one circuit. In practice, there is a pair of capacitances serving each winding. When switching is done to energize the brake and render the clutch inactive, or vice versa, the coil which is deenergized has its energy dissipated and, at the same time, the capacitances which were charged in parallel are connected in series with the winding of the other circuit, thereby providing the required forcing voltage.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a general schematic drawing of a circuit exemplifying the invention.

FIG. 2 is a diagrammatic plan view of a preferred mechanical organization of the components of the above circuit permitting parts to be interchanged readily as desired.

DETAILED DESCRIPTION Particulars of the components are given hereafter only by way of example and not by way of limitation.

Terminals 2 and 4 of a conventional l 15 volts 60 cycle circuit are respectively connected to the terminals 6 and 8 of rectifier 10, preferably of a bridge type. In addition, a transient voltage-suppressing device 12, comprising diodes back to back in symmetrical arrangement, is connected across the line. It protects the rectifying bridge 10 against high voltage spikes. Connected between the positive output terminal 14 and the negative output terminal 16 of the bridge 10 is a relay 18 controlled by switch 20. This relay mechanism may be single or multiple. If there is a single relay, it would normally be a four-pole double-throw device. Alternatively, it may consist of two instruments in parallel, each being doublepole double-throw.

The positive terminal 14 of the rectifier is connected by lead 22 to a pair of diodes 24 and 26 which pass current only in a direction away from the bridge circuit terminal.

The relay 18 includes a normally closed switch 28 which is a part of the relay as indicated by the broken line 30. Also included as a part of relay 18 is a normally open switch 32, its connection with the relay coil being indicated by the broken line 34. Further included in the relay organization are the normally open switch 36 and the normally closed switch 38, relay actuation being indicated by the broken lines 40 and 42 respectively. The four switches 28, 32, 36 and 38 are all in the circuit switch controls of the winding 46. In the selected exarnple, this winding is the winding of an electromagnetically operated clutch.-

Included in the clutch winding controls are circuits of the capacitances 50 and 52 which, when the switches 28 and 38 are closed, are charged in parallel through the resistor 54 and through the

diodes

56 and 58, return connection being made via lead 60 and switch 38 to the negative terminal 16 of the bridge rectifier 10.

For one particular installation, the resistor 54 is rated at 250 ohms and 50 Watts in order to give the desired time constant of the resistor and capacitance assembly. In this assembly, the capacitors 50 and 52 are at 250 mfd. When connected in circuit, they are in parallel with each other and in series with a resistor 54.

The same considerations apply to the resistor and capacitors 68 and 70.

However, for other installations, perhaps providing a more powerful forcing circuit or involving other variables, the values would be modified. Those given are merely by way of example of a particular installation.

When current is first supplied to the terminals 2 and 4, the first circuit and its capacitors 50 and 52, then connected in parallel, both receive current from the rectifier source 10. Concurrently, the coil 67 in the second circuit is energized but without forcing current, since its capacitors 68 and 70 will not be charged until the switch 20 has been closed.

The closing of switch 20 energizes relay 18 and supplies forcing current from capacitors 50 and 52, then connected in series, to the clutch winding 46. At the same time, the circuit completed by the closing of normally open switch 84 charges capacitances 68 and 70, then being in parallel and disconnected from brake coil 67.

The brake coil 67 will have dissipated its energy. It has been disconnected from the supply circuit by the opening of normally closed switch 65. Dissipation of its energy is assisted by the varistor 86. In practice, this varistor is a General Electric rod type THYRITE one-fourth inch in diameter (their number 6611-2100). A varistor has resistance which varies according to voltage. It begins to conduct at about 150 volts and its conductance increases exponentially with voltage. As shown, the resistor 88 (10 ohms; 1 Watt) is connected across varistor 86 in series with capacitance 90 (0.22 mfd. 600 V; DC).

The opening of switch 20 as shown in FIG. 1 deenergizes relay 18. The various switches controlled by the relay assume the positions illustrated in the drawing. The capacitances 50 and 52 previously connected in series with each other and with clutch coil 46 in the first circuit are now connected in parallel with each other to receive current from the rectifier l0. Capacitances 70 and 68, on the other hand, are now connected in the second circuit in series with each other and with the brake coil 67. These will now supply high voltage forcing current to the brake coil 67. Supply of normal current and forcing current occurs through the normally closed switch 65, with return through lead 60.

It will be understood that the alternatively energized coils 46 and 67 are designated only for exemplification purposes as a clutch coil and a brake coil, respectively. Whatever the purpose for which they are used, the arrangement is such that repetitive opening and closing of the master switch 20 will altemately apply normal current and forcing current to the coils 46 and 67 in turn. One opening and closing sequence of the switch is required before both of the forcing circuit capacitances have been charged in readiness for connection in series to supply forcing voltage to the respective circuit.

It is very important to note that the functioning of the apparatus as described is dependent on the fact that alternate discharge paths from the capacitances are blocked by diodes as shown. Thus, in the circuit which includes coil 46, the

diodes

56 and 58 and 92 and 26 cooperate with the functioning of the switches as described, to require the current to flow in parallel to the capacitances when these are being charged and preclude current flow from the series connected capacitances in any direction other than through the forced coil 46.

The primary function of diodes 24 and 26 is to prevent discharge of series-connected capacitors in a first circuit into the capacitors of the other circuit wen the latter are at low voltage. At the end of the relay contact transfer, i.e., when charged capacitors 50 and 52 are series-connected, they must not be able to discharge into the relatively uncharged capacitors 68 and 70. The diode 26 prevents this. Similarly, when capacitors 68 and 70 in the second circuit are charged and connected in series, the diode 24 prevents discharge into the then uncharged capacitors 50 and 52 in the first circuit.

A secondary function of diodes 24 and 26 is to protect the bridge 10, which is the source of current for the two circuits. The bridge might be destroyed in the event that its peak reverse voltage rating is below the voltage of the series charge of the forcing capacitors. The bridge would be required to block this high voltage and might not have a rating adequate for the purpose.

Similarly,

diodes

24, 78 and 80 require movement of the rectified current in the correct direction for charging capacitances 68 and 70 when these are connected in parallel and preclude discharge of the series-connected capacitors 68 and 70 in any direction except through diode 74 and coil 67.

The functions of

diodes

74 and 92 is also very important. The output of the bridge rectifier has an average DC voltage and is actually only 0.637 of its peak magnitude voltage. Thus if the design is such as to yield an average voltage of 100 volts, as contemplated by the foregoing discussion, then the peak voltage would run to 157 volts. The

diodes

74 and 92 function to hold the voltage applied to the load (46 or 67) to a value such as to be within the design-rated voltage.

It will be apparent from the foregoing description that each of the two controlled windings in which forcing is desirable during use has a set of capacitances which are charged in parallel from the same source which energizes the winding during use, and are discharged in series whenever the bridge circuit is connected to the respective windings for the energization thereof. The initially high forcing current soon dissipates, leaving the forced coil to be served with normal operating voltage from the rectifying bridge.

As suggested in FIG. 2, there are

separate sockets

96 and 98 mounted on a carrier 100 and to which are connected through barrier block 99 the respective coils 46 and 67 shown in FIG. 1. The remaining components of the forcing circuits of FIG. I or, alternatively, conventional arc suppression or potentiometer units may be plugged into these sockets in alternation with the forcing units above described.

For example, it may be desired to obtain a sharp response from one of the coils 46 or 67 and a soft response from the other. Alternatively, it may be desired to substitute a potentiometer or an arc suppression unit or either or both for the forcing unit. This is readily possible in the FIG. 2 constmction since it is only necessary to replace a forcing unit 102 with an arc suppression unit 104 or a potentiometer unit 106, according to the effect desired.

The plug-in forcing unit 102 may include the

diodes

26, 92, 56 and 58 (or 24, 74, 80 and 78); the capacitance 66 (or 90); the resistor 64 (or 88) and the varistor 62 (or 86); and the capacitances 50 and 52 (or 68 and 70).

The are suppression plug-in unit 104 contains the capacitance 66 (or 90); the resistor 64 (or 88); and the varistor 62 (or 86).

The potentiometer and suppression unit 106 contains a potentiometer 108; and the capacitance 66 (or in series with the resistor 64 (or 88); these being coupled across the varistor 62 (or 86).

lclaim:

1. In a circuit having inductance, forcing means comprising a plurality of capacitances, a source of working voltage for said circuit, switching means for connecting said source to the circuit and to the capacitances in parallel, and switching means for selectively breaking the connection in parallel and connecting said capacitances in series to said circuit, said circuit including a rectifier, a relay coil, a plurality of electromagnetic windings, means for dissipating energy from a winding, said switching means being controlled by the relay coil and including means for alternately connecting energy dissipating means to respective windings, there being a plurality of capacitances for each of said electromagnetic windings, said switching means including means for connecting the source to the capacitances for one such winding and for connectmg said last capacitances in parallel at a time when the energy dissipating means is connected to another winding, and means for connecting the capacitances in series to a respective winding which is connected to said source and is disconnected from the energy dissipating means.

2. A circuit comprising the combination with a clutch winding and a brake winding, of a rectifier, a relay including a coil and a control switch, a pair of capacitances for each said winding, current control means for directing current from said rectifier in parallel through one pair of said capacitances, control means for directing current in series through the other pair of capacitances and through the other said winding, and means for interchanging the connections of said capacitances for directing current from said rectifier in parallel through the second set of capacitances while connecting the first set of capacitances in series with each other and with the first said winding.

3. A circuit according to claim 2 in further combination with means for selectively dissipating energy from the winding to which the capacitances are not connected in series, and during the parallel connection to the rectifier of the pair of capacitances for the last mentioned winding.

4. The combination with a current source, of two circuits each having an inductance and each having forcing means comprising a plurality of capacitances, switching means for connecting said source and the said capacitances of one of said circuits in parallel and for connecting the capacitances of the other of said circuits in series to the inductance thereof, said switching means including means for reversing the connections to connect said source to the capacitances of said last mentioned circuit in parallel and for connecting the capacitances of the first mentioned circuit in series to its respective inductance, said switching means further including diodes for isolating parallel-connected capacitances from the voltage of series-connected capacitances.

Claims

1. In a circuit having inductance, forcing means comprising a plurality of capacitances, a source of working voltage for said circuit, switching means for connecting said source to the circuit and to the capacitances in parallel, and switching means for selectively breaking the connection in parallel and connecting said capacitances in series to said circuit, said circuit including a rectifier, a relay coil, a plurality of electromagnetic windings, means for dissipating energy from a winding, said switching means being controlled by the relay coil and including means for alternately connecting energy dissipating means to respective windings, there being a plurality of capacitances for each of said electromagnetic windings, said switching means including means for connecting the source to the capacitances for one such winding and for connecting said last capacitances in parallel at a time when the energy dissipating means is connected to another winding, and means for connecting the capacitances in series to a respective winding which is connected to said source and is disconnected from the energy dissipating means.