US 3329247 A
Description (OCR text may contain errors)
July 4, 1967 V R. JAESCHKE 3,329,247
ELECTROMAGNETIC COUPLING APPARATUS FIG],
VOLTAGE MULTIPLIER k CONTROL 30 Filed 0ct 6, 1965 U CH I c B l D47 0F 05 09 ll 01 cm United States Patent 3,329,247 ELECTROMAGNETIC COUPLING APPARATUS Ralph L. Jaeschke, Kenosha, Wis., assignor to Eaton, Yale & Towne, Inc., a corporation of Ohio Filed Oct. 6, 1965, Ser. No. 493,396 11 Claims. (Cl. 192-84) The present invention relates to electromagnetic coupling apparatus and more particularly to such apparatus which provides a rapid buildup of torque transmitted between relatively rotatable members of a coupling.
It has previously been proposed to obtain rapid buildup of a given transmitted torque in electromagnetic coupling apparatus by initially energizing the coupling at a higher voltage than that which is subsequently applied to maintain the transmission of the given torque. The arrangements proposed, however, include complicated switching circuits for applying power from two different sources during the different phases of energization of the coupling, or employing series resistors to effect a voltage drop after an initial energization of the coupling. The provision of the switching components and the second supply considerably increases the expense of the apparatus. The use of resistors has the disadvantage of power loss and dissipating the heat thereby produced.
Among the several objects of the invention may be noted the provision of electromagnetic coupling apparatus which provides exceptionally rapid initial energization Without complicated switching arrangements; the provision of such apparatus which does not incur substantial power losses; the provision of such apparatus which does not require the use of separate power supplies for initial and for sustained energization of a coupling; the provision of such apparatus in which a clutch and a brake may be alternately energized to effect accelerated rates of actuation; the provision of a method for energizing the field coil of such apparatus to provide accelerated actuation of the apparatus; and the provision of such apparatus which is simple, reliable and inexpensive. Other objects and features will be in part apparent and in part pointed out hereinafter.
Briefly, the invention is applicable to electromagnetic coupling apparatus having a pair of relatively rotatable members and a field coil, the energization of which controls the transmission of torque between the two members. The coil is energized to obtain a rapid buildup of a given torque between said members by a control including a voltage multiplier which develops a voltage of a first level under no-load conditions and which under the sustained load of said coil drops to a second level of voltage substantially lower than this first level. The second voltage level is one which is sufiicient to maintain the coil energized for the steady state transmission of the given torque. The coil is selectively connected by a switching device or means to a voltage multiplier. The multiplier includes means for storing energy at said first voltage level when disconnected from the coil. Upon connection of the coil to said multiplier, the coil is initially overexcited by being energized at the first voltage level and thereby rapidly builds up said given torque and, after discharging of stored energy, the coil continues to be energized at this second voltage level to maintain. the transmission of said given torque. The term electromagnetic coupling apparatus as used herein includes apparatus wherein torque is controllably transmitted between a pair of relatively rotatable members whether it is either or both of the members which rotate. Examples of such apparatus are clutches, brakes and dynamometers.
The invention accordingly comprises the apparatus and methods hereinafter described, the scope of the invention being indicated in the following claims.
In the accompanying drawingsin which several of various possible embodiments of the invention are illustrated,
FIG. 1 is a diagrammatic illustration of an electromagnetic coupling apparatus of the present invention;
FIG. 2 is a schematic diagram of circuitry for controlling the operation of the apparatus of FIG. 1 including means for providing accelerated actuation of the clutch and brake;
FIG. 3 is a schematic diagram of modified control circuitry providing accelerated actuation of the brake alone;
FIG. 4 is a schematic diagram of a modification wherein the clutch is energized at a lower voltage level than either the initial or sustained energization level of the brake;
FIG. 5 is a schematic diagram of a circuit for controlling operation of an electromagnetic brake to provide extreme decelerations; and
FIG. 6 is a schematic diagram of another embodiment of this invention.
Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.
Referring now to the drawings, there is shown diagrammatically in FIG. 1 electromagnetic coupling apparatus of a type with which the control of the present invention is particularly useful. The electromagnetic coupling apparatus comprises both a clutch 11 and a brake 13 which are preferably of the friction type and are arranged for controlling the speed of rotation of a driven shaft 15, taking rotational energy from a motor 17.
The shaft of motor 17 is connected to a clutch driving 7 member which in the present case is illustrated as a rotating electromagnet assembly 19 including a field coil or winding 21. Current is supplied to the coil 21 through suitable slip rings (not shown). A disc-like armature 23 is mounted on the output or driven shaft 15 for rotation therewith. Armature 23 is positioned within the field of electromagnet assembly 19 so that when the coil 21 is energized armature 23 will be drawn into frictional engagement with driving member 19. Thus torque may be selectively transmitted between the members 19 and 23 by controlling the energization of coil 21.
The brake 13 is similar in construction to clutch 11 and includes an armature 24 and an electromagnet 25 wound with a field coil or winding 27. However, in the case of the :brake, the electromagnetic structure is stationary and does not rotate, being attached to the frame or other stationary reference point as at 29. When winding 27 is energized, the armature 24 is drawn into frictional engagement with the electromagnet 25' so that a braking torque is exerted between electromagnet 25 and the shaft 15.
Due to the inductance of the windings 21 and 27 and also to the production of eddy currents in the typically unlaminated magnetic members of the clutch and brake, neither of these devices operates immediately upon the application of a voltage across the respective coil. Rather, a significant period of time elapses before the current flowing in the coil and the torque transmitted through the coupling reach their steady state levels. To obtain a more rapid buildup of current and torque, the coils 21 and 27 are energized by a voltage multiplier control 30. As described in greater detail hereinafter, this control overexcites a coil by initially energizing it with a voltage higher than that which is required to maintain the energization of the coil for steady state transmission of the desired torque. This initial overexcitation is provided without the use of a plurality of power supplies and without timed switching means for effecting the changeover.
FIG. 2 illustrates a control circuit according to the invention which provides accelerated energization of both the clutch and the brake coils 21 and 27, respectively. The clutch and brake coils are energized by separate power supplies each of which includes a voltage multiplier constituted by a voltage-doubling rectifier circuit drawing power from an A.C. power source represented by a pair of A.C. supply lines L1 and L2. The brake power supply includes a pair of rectifiers or diodes D1 and D2 which are connected to supply line L1 and are oppositely poled or oriented so that each provides half-wave rectified or pulsating D.C. to one of a pair of filter and storage capacitors C1 and C2. One terminal of each capacitor is commonly connected to line L2. Due to the opposed polarities of the diodes D1 and D2 the capacitors C1 and C2 are charged to opposite D.C. potentials with respect to supply line L2 during alternate half cycles of the applied A.C. power. Thus, this circuit functions as a voltage doubler, the voltage produced under no-load conditions across capacitors Cl and C2 together, or in series, being approximately double the peak supply voltage. The brake coil 27 is selectively connected across capacitors C1 and C2 by a set of contacts 81A of a switch S1 which may, for example, be an electromagnetically operated relay.
The clutch coil power supply includes a similar voltage doubler wherein a pair of capacitors C3 and C4 are alternately charged to opposite potentials with respect to supply line L2 through a pair of oppositely poled diodes D3 and D4 connected to line L1. The clutch coil 21 is selectively connected across the series-connected capacitors C3 and C4 by means of a pair of contacts 81B of switch S1.
The voltage regulation characteristics of voltage multiplier circuits are typically quite poor in the sense that the voltage provided under loading is significantly lower than that provided under no-load conditions. The regulation characteristics depend to a large extent on the value of the capacitors used. In the apparatus illustrated in FIG. 2, the ratings of the clutch and brake coils 21 and 27 are chosen so that the voltage required for full, steady state energization thereof is substantially below the peak voltage provided by the respective voltage-doubling power supplies. For example, in apparatus supplied from A.C. mains providing A.C. at 110 volts R.M.S., or approximately 150 Volts peak value, the voltagedoubling power supply for the clutch coil 21 will, under no-load conditions, charge the capacitance constituted by series-connected capacitors C3 and C4 to a total voltage of substantially 300 volts. The clutch coil 21 may, for example, have a continuous energization rating of about 50 volts. The values of the capacitors C3 and C4 are then chosen so that the voltage supplied by the doubler circuit to the clutch coil under conditions of continuous energization is approximately 5.0 volts, a level which will permit the clutch coupling to continuously maintain the rated torque transfer between the relatively rotatable components thereof.
When the clutch coil 21 is not connected to its power supply, however, the capacitors C3 and C4 become charged so that the total voltage across them reaches approximately 300 volts and a significant quantity of energy will thus be capacitively stored at this voltage level. Accordingly, when the clutch coil 21 is initially connected across its power supply by the closing of contacts SIB, the stored energy will overexcite the clutch coil 21 at this higher voltage level so that it becomes fully energized and capable of transmitting its rated torque much more rapidly than it would if a voltage only equal to its sustained energization rating were applied. The stored energy will provide overexcitation for only a relatively short time and thus, after a predictable delay interval, the voltage provided by the doubler circuit will drop or sag to the level which the doubler is capable of supplying under steady state load conditions. This level is, as noted previously, selected by choice of value for capacitors C3 and C4 to be substantially equal to the rated voltage of the clutch winding 21.
A similar situation exists with respect to the brake coil 27. That is, the capacitors C1 and C2 are chosen to provide a steady state voltage which is equal to the sustained energization rating of brake winding 27. However, when the brake winding is disconnected from its power supply these capacitors will be charged to a voltage which is substantially double the peak voltage supplied by the lines L1 and L2. Thus, upon initial connection of brake coil 27 to its power supply by the closing of switch contacts S1A, the brake coil will be initially overexcited, thereby providing an accelerated braking operation. After discharging of capacitively stored energy, coil 27 will subsequently be maintained energized by a voltage substantially equal to its sustained energization rating.
While the clutch and brake power supplies exhibit socalled soft voltage regulation characteristics, it should be noted that the drop in voltage upon loading is not due to resistive dissipation which would cause substantial power losses and create heat dissipation problems. Rather, the difierence in voltage arises because of reactive voltage drops developed across capacitive elements, which voltage drops do not entail significant power loss.
Under certain circumstances only one of the two coupling coils needs to be initially overexcited or electrically forced to obtain accelerated energization while the other coil need be energized only at its rated voltage. In FIG. 3 the brake coil 27 is again connectable across the output of the voltage doubler comprising diodes D1 and D2 and capacitors C1 and C2. The clutch coil 21, however, is not provided with a separate voltage doubler power supply but rather is connectable, through contacts SIB, across one (C2) of the two capacitors used in the brake coil power supply. Thus clutch winding 21 is provided only with half-wave rectified power and does not draw from any voltage doubler or multiplier circuit. Accordingly, clutch coil 21 is chosen to have a sustained voltage rating approximately equal to the value of the half-wave rectified A.C. provided by lines L1 and L2 and rectifier D2. In operation, the control of FIG. 3 thus provides essentially normal operation of clutch coil 21 but will, due to the voltage drop characteristics of the doubler power supply, pro vide an initial overexcitation of brake winding 27 so that rapid decelerations of shaft 15 may be obtained. However, due to the fact that half of the doubler circuit is never under no-load conditions, the ratio of peak to full-load voltages will not be as great as that obtained using the circuitry of FIG. 2.
Another arrangement wherein only one of the coupling coils is initially overexcited is illustrated in FIG. 4. In this embodiment, the brake winding 27 is selectively connectable by means of contacts 81A to the voltage doubler power supply comprising diodes D1 and D2 and capacitors C1 and C2, the doubler power supply again being supplied from lines L1 and L2 with line L1 providing A.C. power at a first voltage level with respect to line L2.
The clutch winding 21 is connected to receive halfwave rectified power through a diode D5 and switch contacts S1B from a supply line L1A which provides A.C. power at a second preselected level with respect to line L2. The peak voltage present at line L1A with respect to line L2 is chosen to the less than either the initial voltage at which the coil 27 is overexcited or the lower voltage level at which its energization is maintained. Thus, in operation the brake winding will be initially overexcited to provide rapid stops of the shaft 15 as in the previous examples but energization of the clutch coil 21 will take place at one voltage level only, which voltage level is lower than both the initial and sustained voltage levels applied to winding 27. It will be understood that the potential difference between L1A and L2 may be selected to be equal to or greater than the L1-L2 voltage.
Voltage multipliers which treble, quadruple, etc. the supply voltage typically have even poorer voltage regulation characteristics than doublers. In other words, larger ratios of no-load voltage to full-load voltage are en counted. Accordingly, by employing circuits using even higher degrees of voltage multiplication in controls according to the present invention, even more rapid accelerations may be obtained. In the control illustrated in FIG. the brake winding 27 is energized from a voltage quadrupler power supply which comprises a series string of diodes D6-D9. A plurality of capacitors C6-C9 couple A.C. to each of the rectifiers in the string from the lines L1 and L2. Under no-load conditions, this supply will develop a voltage which is substantially equal to four times the peak voltage appearing across the supply lines L1 and L2. The capacitors C6 C9 will be charged and will thus represent a quantity of stored energy avialable for intially overexciting winding 27 at the higher voltage upon its initial connection to the supply. Upon continued connection of coil 27 to this multiplier power supply, however, the voltage applied to the winding will drop to a much lower value, the level of which is in large part determined by the individual capacity values of the capacitors C6-C9. By proper choice of these capacitance values the steady state voltage provided by the supply may be made approximately equal to the rated voltage of the coil 27 even though this value is very small in relation to the peak voltage initially provided by the quadrupler supply. Accordingly, it can be seen that the control of FIG. 5 is capable of providing a very high degree of initial overexcitation for extremely rapid operation of the brake. It should be understood that a clutch coil could be similarly operated and that both a clutch and brake may be alternately operated in this manner from separate voltage multiplier supplies in the manner illustrated in FIG. 2.
FIG. 6 illustrates a control which is similar to that shown in FIG. 5. The voltage multiplier which supplies power to winding 27 is again a quadrupler which includes diodes D6-D9 connected in a series string. A set of capacitors C11C14 couples A.C. to each of the rectifiers. However, A.C. is coupled to the higher voltage rectifier stages by capacitors which draw power from the lower voltage stages rather than directly from the lines L1 and L2. Accordingly, under load, the series-connected capacitors act as A.C. voltage dividers which cause an even greater drop in the output voltage. Thus, when used in a control according to the present invention this multiplier circuit permits an increased ratio of initial excitation voltage to sustained energization voltage.
While various particular voltage multipliers are shown by way of illustration, it is to be understood that there are other such circuits which provide substantially different levels of voltage under no-load and full-load conditions and do not involve substantial dissipation of power within the supply under loaded conditions, and such circuits may be used in the practice of the present invention. Similarly, while electromagnetically controlled friction clutches and brakes have been shown, other types of electromagnetic couplings which normally respond only after a delay following energization, such as eddycurrent couplings, may advantageously employ the present invention. Also, two or more clutches may be alternate- 1y employed to drive a load from shafts rotating at different speeds or in opposite directions.
In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.
As various changes could be made in the above constructions and methods without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.
What is claimed is:
1. In electromagnetic coupling apparatus having a pair of relatively rotatable members and a field coil the energization of which controls the transmission of torque between the two members; a control for obtaining rapid buildup of a given torque between said members, said control comprising:
a voltage multiplier which develops a voltage of a first level under no-load conditions and which under the sustained load of said coil drops to a second level of voltage substantially lower than said first level, said second voltage level being sufiicient to maintain said coil energized for the steady state transmission of said given torque; and
switching means for selectively connecting said coil to said voltage multiplier, said multiplier including means for storing energy at said first voltage level when said coil is disconnected therefrom whereby, upon connection of the coil to said multiplier, said coil is initially overexcited by being energized at said first voltage level thereby to rapidly build up said given torque and, after discharging of stored energy, said coil continues to be energized at said second voltage level to maintain the transmission of said given torque.
2. Electromagnetic coupling apparatus providing rapid buildup of a given transmitted torque, said apparatus comprising:
an electrically controllable coupling including a pair of relatively rotatable members and a field coil the energization of which controls the transmission of torque between the two members;
a voltage multiplying rectifier circuit for providing DC. power for energizing said coil from an A.C. power source, said rectifier circuit including a capacitance and being operative when said coil is disconnected therefrom to charge said capacitance to a first voltage which is substantially higher than the steady state voltage which said circuit can maintain across said coil, said steady state voltage bein-g sufiicient to maintain said coil energized for the transmission of said given torque; and
switching means for selectively connecting said coil to said rectifier circuit whereby, upon connection of the coil to said circuit, said coil is initially overexcited by being energized at said first voltage level thereby to rapidly build up torque and, after discharging of energy stored in said capacitance, said coil continues to be energized at said steady state voltage to maintain the transmission of said given torque.
3. Apparatus as set forth in claim 2 wherein said relatively rotatable members are frictionally engageable and are magnetically drawn into engagement by energization of said field coil.
4. Apparatus as set forth in claim 2 wherein said capacitance comprises at least two capacitors and said rectifier circuit includes at least two rectifiers through which said capacitors are alternately charged.
5. Apparatus as set forth in claim 2 wherein said volt-, age multiplying rectifier circuit comprises:
first and second capacitors constituting said capacitance, one terminal of each of said capacitors being commonly connected to one side of said A.C. source;
first and second rectifiers each of which connects the other terminal of a respective one of said capacitors to the other side of said A.C. source, said rectifiers being oppositely oriented whereby said capacitors are charged to voltages of opposing polarities with respect to said oneside of said source, said switching means being operative to connect said coil across said two capacitors in series.
6. Apparatus as set forth in claim 5 wherein said electrically controllable coupling includes a third relatively rotatable member and a second field coil the energization of which controls the transmission of torque between said third member and one of the other members and wherein said switching means includes means for selectively connecting said second coil across one of said two capacitors.
7. Apparatus as set forth in claim 2 wherein said electrically controllable coupling includes a third relatively rotatable member and a second field coil the energization of which controls the transmission of torque between said third member and one of the other said members, and wherein said apparatus includes a second voltage multiplying rectifier circuit for energizing said second coil, and wherein said switching means includes means for selectively connecting said second coil to said second rectifier circuit for energization alternately with the first said coil.
8. Apparatus as set forth in claim 2 wherein said electrically controllable coupling includes a third relatively rotatable member and a second field coil the energization of which controls the transmission of torque between said third member and one of the other members and wherein said apparatus includes means for selectively energizing said second field coil at a voltage which differs from said first voltage.
9. Apparatus as set forth in claim 8 wherein said differing voltage is lower than said steady state voltage.
10. Apparatus as set forth in claim 2 wherein said voltage multiplying rectifier circuit includes a plurality 25 of rectifiers poled in the same direction and connected in a series string and a plurality of capacitors for coupling A.C. along said string.
11. The method of energizing the field coil of an electromagnetically controllable coupling from an AC. source to obtain a rapid buildup of a given torque between two relatively rotatable members thereof, said method comprising:
rectifying the supplied AC. power in a voltage multiplying circuit; charging a capacitance to the voltage supplied by said rectifying circuit, said rectifying circuit being operative under no-load conditions to charge said capacitance to a first voltage which is substantially higher than the steady state voltage which said circuit can maintain across said coil, said steady state voltage being suflicient to maintain said coil energized for the transmission of said given torque; and selectively connecting said coil across said capacitance thereby to initially overexcite said coil at said first voltage to rapidly build up torque and, after discharging of energy stored in said capacitance, continuing to energize said coil at said steady state voltage to maintain the transmission of said given torque.
References Cited UNITED STATES PATENTS 2,811,686 10/1957 Hill 321-l5 X 2,888,629 5/1959 Everhart et al. 321--15 3,254,746 6/1966 Myers 19284 3,268,045 8/1966 Poumakis 192-84 MARK NEWMAN, Primary Examiner.
ARTHUR T. MCKEON, Examiner.