US2625661A - Electrical apparatus - Google Patents

Description

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ATTORNEYS Patented Jan. 13,A 1,953

ELECTRICAL APPARATUS Arthur W. Hayden, Cheshire, Conn., assigner to Philips Laboratories, Inc., Irvington-on-Hudson, N. Y., a corporation of Delaware Application May 23, 1950, Serial No. 163,649

Claims. (Cl. 307-41) 1 This invention relates to electrical switching apparatus for successively supplying current from a common source to a plurality of electric circuits. It is more particularly concerned with, and therefore Will be ydescribed in connection with, such an Y apparatus for successively causing the energization of the propeller de-icing circuits of an airplane.

For de-icing the blades of airplane propellers, it has been established that it is much more satisfactory to supply current to heating elements built into the leading edge of the propeller blades at regular intervals for relatively short periods of time, rather than to supply continuous current thereto. In addition it has been found that ice does not accumulate near the tips of the blades, possibly due to higher centrifugal forces and air velocity. It has also been found that due to the characteristics of the air stream passing over the propeller blades, ice is ydeposited only on the leading edges of the blades. Thus, ice actually accumulates only on about two-thirds of the leading edge of each of the blades, By allowing it to accumulate there, it is only necessary to heat the propeller blade along two-thirds of its leading edge, until the adhesion of the undersurface of the ice coating is broken, in order to throw it off by the centrifugal force produced by rotation of the blades. This avoids the necessity of heating the entire blade, or of melting all of the accumulated ice, or of keeping all the blades continuously above the freezing point. The ice acts as an insulating blanket reducing the heat loss as the blade rotates in the cold atmosphere, and thus reduces the amount of current required to bring the blade up above the melting point of the ice. Continuous heating of the leading edge of the blade would cause the ice to melt and run back on the trailing edge, where it would freeze unless the entire blade were heated.

In airplanes having multiple engines, a further advantage is gained in that the on time of the various heaters may be arranged in small groups in consecutive non-overlapping relation, whereby only two or three blades of the airplanes propellers are de-iced at one time. In order that a state of unbalance will not exist as de-icing takes place, two opposing blades of a four-bladed propeller are de-iced simultaneously. In the case of an airplane provided with three-bladed prO- pellers, it will be clear, of course, that in order to avoid unbalance and the resultant detrimental vibration caused thereby the heaters in all three blades must be energized at the same time.

It will readily be appreciated that a considerable reduction in current requirements is thereby effected, resulting in an appreciable saving in size, weight, and cost of the necessary current generating equipment and a corresponding increase in the airplanes load carrying capacity. The importance of this will be easily appreciated when it is realized that larger generators mean larger engines to drive the combined load o propeller and generator and more gasoline to supply the added horsepower. Pay load is thus reduced by increased weight of generator, engine, and gasoline all combined.

It is among the primary objects of this invention to provide apparatus by which the heating elements in the propellers of an airplane may be supplied with current in succession and at regular intervals. The apparatus must be simple, reliable and remain in accurately timed condition indenitely so that there will be negligible pause and no overlap between the breaking of the current flow to one heating element circuit and the initiation of current flow to the next successive circuit.

Another object of this invention is to provide an apparatus for the above described purpose which constitutes an improvement over the apparatus disclosed in the R. G. Hoof, U. S. Patent 2,466,238. The apparatus disclosed in that patent employs a combination of commutator type switches and a cam actuated switch, the commutator type switches successively preparing paths to the different heating element control circuits in overlapping relation and the circuits being completed by cam actuation of a double throw switch which simultaneously breaks one of the paths created by the commutator switches and completes another path. When the cam actuated double throw switch is next actuated the commutator type switches have prepared a new circuit to be completed thereby. In Hoofs apparatus the double throw switch is actuated once each time one circuit is broken and a new one completed. Therefore, in an apparatus adapted to handle the making and breaking of, for instance, eight circuits the double throw switch will of necessity be actuated eight times per cycle.

The apparatus of the present invention is designed to be relatively much simpler and less costly than that disclosed in the Hoof patent and to eliminate the necessity of closing any single switch every time the common source of current is connected to a different heating element control circuit. Hence, the lives of the switches involved are considerably increased and replacevelectric circuits.

ment thereof and the costs incident thereto are less frequently necessary.

According to this invention, apparatus for successively supplying current from a common source to a plurality of electric circuits comprises rst and second double throw switches the switch contacts of which are electrically connected, respectively, to one each of the terminals of the A third double throw switch is provided and has its switch contacts electrically connected, respectively, to the switch arms of the first and second double throw switches. The switch arm of the third double throw switch is adapted to be electrically .connected to the common source. The apparatus also includes a constant speed electric motor and means for mechanically connecting the motor to the switches to cause the switches to be operated in sequence when the motor is operated and to cause each switch to perform at least one electrical transfer during a complete cycle of operation of the apparatus. Each electric circuit is thereby successively supplied with current from the common source during the cycle of operation.

It is contemplated, though the invention should not necessarily be sovlimited, that the means for mechanically connecting the motor to the double throw switches be either a cam shaft driven by the electric-motor and having xedly secured to it a single cam adapted to operate in sequence all of the switches, or a cam shaft driven by the electric motor having aplurality of substantially identical cams (one for each switch) fixedly secured thereto and so positioned circumferentially with respectto one another that each of the switches is operated in sequence.

For a more detailed description'of several speciiic forms of the apparatus of this invention, reference may be made to the accompanying drawings in which:

Fig. 1 is a schematic diagram of one form of the apparatus which may be used in the distribution of heating current to four 4bladed propellers;

Fig. 2 is a perspective View showing the arrangement of the cams, double throw switches and cam shaft;

Fig. 3 is a schematic diagram ofa modified form of apparatus for use in the distribution of heating current to four 3-bladed propellers; and

Fig. 4 is a schematic diagram of another modified form of apparatus for use in the distribution of heating current to four 3-bladed propellers.

In Fig. 1 there are shown four 4-b1aded propellers It, II, I2 and I3, each being of the same design. In each blade I4 of eachpropeller there is mounted a heating element I5. As pointed out previously, reduction in cost of the airplanes generating equipment and increase in theairplanes load carrying capacity may be accomplished and more effective de-icing obtained by arranging the heater circuits so that a minimum number of heaters are connected at the same instant, care being taken not to cause mechanical unbalance as the blades are de-iced. In order that an unbalance does not result in any of the four-bladed propellers, two elements are supplied with current simultaneously, each in an opposite blade of one propeller. Thus, in each propeller the heating elements I5 in a pair of opposite blades I4 are connected together in one heating element circuit. Hence, in a four-i-bladed propeller airplane there are eight heating circuits that must be energized in sequence, with negligible pause and no overlap for greatest eirlciency.

The means by which current is provided to the heating elements of one propeller is identical to the means provided for supplying current to the heating elements of another, and therefore a description of this means for one propeller will suince to describe the means for all of the propellers. In propeller It the two heating circuits may be designated as IE5 and I6'. One terminal of each of the heating circuits is connected by conductor I7 to a slip ring I8 mounted on a shaft ifi rotating with the propeller. A brush 2li is provided to ground slip ring I8 at all times and thus it will be understood that one terminal of each of the heating circuits I6 and I5 is always grounded. Current may be provided to heating circuit I5 through a conductor 2! connected to the ungrounded terminal of this heating circuit and to a slip ring 22 also mounted on shaft I. A brush 23 is provided to supply current to the slip ring 22. The ungrounded terminal of heating circuit I6 is connected by a conductor 24 to a slip ring 25 also mounted on shaft I9, and adapted to be provided with current through brush 26. Brushes 23 and E6 are connected, respectively, by conductors 2l and 28 to switch contacts 2s of a pair of relays St.

`Armatures 3i of the relays are normally maintained by springs 32 out of contact with relay contacts 29. These armatures are connected through conductors 33 to a common source of current capable of supplying the desirable heavy current to one heating circuit (composed of two heating elements).

Each of the relays has one terminal grounded at 313. The other terminals of the eight relays 3S are connected, respectively, by conductors 3B, 3l, 3S, 39, lit, 11,152 and d3 to terminals 45, 45, lil, 48, 139, 5G, 5l and 52 of a terminal board 53.

My apparatus is designed to successively supply current to the terminals S- so that the eight relays 3Q may be successively energized to close their relay switches 2S and thereby successively provide a heavy current rom the common source tothe heating element circuits.

By reference to Figs. l and 2, my apparatus may be seen to comprise a constant speed electric motor. Ell which Vdrives a cam shaft d5 through suitable reduction gearing 55 (Fig. 2). Cams A, B, C, D, E, F, .and G are ixedly mounted on cam shaft 55 and are adapted to be rotated thereby to operate, respectively, double throw switches A', B', C', D', E', and G. These cams are identical to one another and have dwells of approximately degrees. Cain followers 55, through which the cams operate their respective double throw switches, may be best seen in Fig. 2 although they are shown schematically in Fig. 1. Each of the double throw switches comprises,

as the name implies, a switch arm and two switch contacts 58 and 59 (Fig. l). Normally the switch arm is maintained in contact with switch contact 5S, as by spring means (not shown), and must be positively urged by its associated cam into contact with switch Contact 555.

The switch contacts of double throw switches D', E', F and G (eight in number) are respectively connected to terminals i5-52 of the terminal board E3. For instance, in the case of double throw switch D', its switch contact 5a is electrically connected to terminal i5 of the terminal board and its switch contact 58 is electrically connected to terminal 4t of the terminal board. The switch contacts of double throw switches B', and C' (four in number) are electrically connected, respectively, to the switch arms 51 of double throw switches D'-G. For instance, in the case of double throw switch B', its switch contact 59 is electrically connected to switch arm 5i of double throw switch D and its switch contact 58 is electrically connected to the switch arm of the double throw switch E. The switch contacts 59 and 58 of double throw switch A' are in turn respectively connected to the switch arms 51 of double throw switches B' and C'.

Current for the operation of constant speed motor 5t is provided to one terminal of the motor through a conductor 55, a fixed resistance 6i, a variable resistance 52, and conductor 63 connected to terminal 5d of the terminal board 53, terminal i3d in turn being connected to a source of current through conductor 55. The other terminal of motor 55 is grounded through a conductor 55. A filter condenser 51 is preferably provided to minimize radio interference in the operaticn of the motor. Current for the energization of relays 35 is also provided from the same source of current through conductor 55, terminal 64, conductor 53, and conductor 68, the latter conductor connecting the switch arm of double throw switch A to conductor 53. The housing for the timer (not shown) is internally grounded through a conductor 59 connected to terminal it. This arrangement of electrically connected double throw switches between the terminals i5- 52 and the common source may be termed `a Tanning-out circuit arrangement.

The operation of my apparatus to successively supply current to terminals 45-52 of the terminal board, and thereby successively to the relays 35, depends upon the relative circumferential positioning cf cams A-G on the cam. shaft 55. With the cams positioned as shown in Figs. l and 2, current is being supplied to terminal 52 and therefore to the rightmost relay 35 (as seen in Fig. i) of propeller I3, through double throw switches A', C', and G'. Upon further revolution of the cam shaft, in a clockwise direction as seen in Fig. l (remembering that all cams are xedly, and therefore non-rotatably, mounted on the cam shaft), the double throw switch that will be first operated is A'. When this occurs the supply of current to terminal 52 of the terminal board will be cut off and current will be supplied to terminal d5 through double throw switches A', B' and D'. The supplying of current to terminal i5 will continue until the cam shaft has rotated through approximately 45 degrees, at which time the switch arm of double throw switch D will be permitted by cam D to move from its contact with its switch contact 59 into contact with its switch contact 58. Thus, terminal 55 will be supplied with current through double throw switches A', B', and D. Upon a further revolution of the cam shaft through approximately 45 degrees the switch arm 51 of double throw switch B' will be permitted by cam B to move from contact with its switch contact SQ into contact with its switch contact 53. By this means, terminal 41 will be supplied with current through double throw switches A', B' and E'. Further rotation of the cam shaft will successively cause the supply of current to terminal 48 through double throw switches A', B and E', to terminals d@ and 5i), successively, through double throw switches A', C' and F', and to terminals 5| and 52, successively, through double throw switches A', C and G. Thus, in one revolution of the cam shaft each of the terminals 45-52 is successively and individually supplied with current, each double throw switch being operated twice during the revolution and each of the terminals being supplied for the same portion of the revolution.

The length of time any one pair of heating elements, or any one heating circuit, is supplied with current is thus dependent upon the speed with which motor 54 drives the cam shaft 55. The speed of the motor may be varied by adjustment of the variable resistance B2. In most cases this adjustment is made during installation of the de-icing equipment and depends upon the type of propeller blades and heaters. In other cases two or more taps (not shown) may be taken off resistor B2 and run through suitable terminals and connections to the pilots compartment of the airplane to make it possible for the pilot to select different cam shaft speeds depending upon icing conditions, outside temperature, etc. as will be readily understood by anyone familiar with the art. The control switch for turning on and ofi of the complete de-icing system may of course also be located in the pilot's compartment.

A modified form of apparatus according to my invention is illustrated in Fig. 3 as applied to four 3-bladed propellers. As previously pointed out, in the case of 3-bladed propellers the heating elements in all of the blades of one propeller must be energized at the same time if a condition of unbalance is to be avoided. Therefore, each of 3-bladed propellers I0', H', I2' and I3' is provided with but one heating circuit, all of the heating elements of the particular propeller being connected in the one heating circuit. One terminal of each is again connected to a slip ring I8 which is grounded through a brush 20'. The other terminal of the circuit is connected to a slip ring 22 through which current may be supplied to it from brush 23', conductor 21', and relay armature 3 I from a common source of current for the heating circuits of all of the propellers, when the armature is in contact with relay contact 29'. It will be clear that but one relay 3Q' need be provided for each propeller and that therefore only four circuits must be successively supplied with current by my modied apparatus. As was the case with respect to the control of the heating elements of Fig. 1, each of the relays 3U has one terminal grounded at 34 and the other connected to a terminal on a terminal board 53' by a suitable conductor. The four terminals on the terminal board 53 to which the relays are connected by conductors 35', 31', 38', and 39' may be designated, respectively, 45', 4B', 41 and 48'.

My apparatus for successively supplying current to each of terminals i5-138' again comprises a constant speed electric motor 54 supplied with current at one terminal through conductor 50', fixed resistance 6I', variable resistance 52', conductor E3', terminal 64 on the terminal board 53', and a conductor 65' connecting this terminal to a source of current. The other terminal of the motor is grounded through conductor 66 and the housing (not shown) internally grounded through conductor 69'. In this modified form, only three cams H, J, and K are required. These cams are all iixedly mounted on a single cam shaft driven by motor 54' and serve to operate double throw switches H', J and K.

As indicated in Fig. 3, my apparatus is in position to supply current to terminal 48' through double throw switches I-I and K', the switch arm cam; shaft has rotated another 90. degrees.

:to operate all ofthe double throwswitches.

of double throwV switch H' 'being electrically :con-

:nected to'conductor. .63. by conductor 68. .Upon

revolution of the` cam shaft .in a clockwise direction, as indicated, the switch arm `of double throw switch H' will be moved upwardlybreaking the. circuit to terminal 48' and completing one to terminal d' through double throw .switch J As the cam shaft continues to rotate,.and..after it has rotated approximately 90 degreesin this form of apparatus, the switch arm of double throw .switch J will be permitted to fall, whereby vthe supply of current toY terminal d5 will .be discontinued'anda supply of current to fli.;initiated. The. next switch to be operated lupon the further vrevolution of the cam shaft will .be H,;the;switch arm of which will be permitted toV fall .afterV the r:This will discontinue the supply of .current to terminal 46' .and initiate the supply of current to terminal 41. because, by this time, the switch arm of double .throw switch K will have been moved upwardly,

as viewed in the drawing, by cam K.

Another modilied forni of apparatus according Y.to my inventionis illustrated in Fig. 4 and is comparable to that illustrated in Fig. 3 in that itis adapted to be used for the energization of the heating elements in four B-bladed propellers through terminals 45" to d8" and conductors 36" to 39". Additionally, it comprises, -asdoes the form illustrated in Fig. 3, a constant speed electric motor 54" supplied with current at one terminal through conductor G", nxed resistance. 6 l vari- .able resistance 62", conductor c3", terminalt" on the terminal boardtll", and a conductor 55" connecting this terminal to a source of. current.

The other terminal of the motor is grounded through conductor E6" and the housing (not shown) internally grounded through conductor 69". .Three double throwswitches L, M, and N, respectively, .are electrically connected to one another in a tanning-out circuit arrangement between conductor 68, .which is continuously supplied with current from the commonsource, and terminals 45 to d8 in the same .way aswere double throw switchesH', J and K intheimodi .cation of Fig. 3.

scribed forms of my invention,y but they are so arranged in this form that in each .theV switch `arm is normally urged toward the. cam. AThis results in double throw switchi N being` in an inverted position as compared .tothe Yposition of the comparable double throw switch K in 3. However, to .maintain for descr-iptivepurposes the sequential'supplying of current to terminals-d to 48 respectively the electrical conductors from .the switch contacts of double throw switch N are criss-crossed. As will be noted from Fig. 4, cam P has a dwell or approximately 1.30 degrees.

As indicated in Fig. 4 the apparatus isfinaposition to supply current to terminal 35' through double throw switches L and M, the switch-arm of double throw switch L being electrically connected to conductor 83" by conductor S8". 'Upon revolution of cam shaft", and therefore cani P, through about 90 degrees in a clockwise direction, as indicated, the switch arm of "double throw switch M will be permitted Ato/move down- -wardlybreaking the circuit Yto terminal y45" and completing one to terminal 46". During this rotation of the cam shaft and cam the switch arm of double lthrow switch'N will` be moved downwardly in preparation forthe supplying of current to terminal` 4'1". As the cam shaft continues to rotate and after it has rotated through another degrees the switch arm of double throw switch L will be moved to the left, as seen in the drawing, and current will be supplied to terminal lll" through switch L and .switch N. After another 90 degrees of rotation of the cam shaft and cam the switch arm of double throw switch N will be permitted to move upwardly whereby current is then supplied to terminal 43 through switches L and N. During this last 90 degrees of rotation of the cam shaft'and cam the switch arm of double throw switch M will be moved upwardly to prepare the circuit for the supply of current to terminal 45". This last-mentioned circuit will be completed when the cam shaft and cam have been rotated through yet another 90 degrees to their position as shown in the drawing at which time the switch arm of double throw switch L is permitted to move to the right as seen in the drawing. This completes one cycle of operation of the vapparatus.

In all forms of my apparatus it will be noted that the primary double throw switches (A, H and L) perform two electrical transfers in one cycle while the secondary double throw switches (B', C', D', E', F', G', J', K', M and N) perform one electrical transfer during a complete cycle.

In the interest of simpliiication, I have shown, for instance in Fig. 1, all switches as having simple movable arms 57 operated by cam followers 56. However, in order to avoid any appreciable interval between the breaking of one circuit, when an arm 5l leaves a contact and the making of the succeeding circuit, when the arm touches the corresponding contact 59, caused by the gradual rise of follower 5t on the cam as shaft 55 slowly rotates,.I prefer to use any of the several commercially available single pole double thrown lsnap action switches, whereby, the circuit transfer occurs rapidly and independently of the rate of motion of the cam shaft 55. Thus, the utilization of current from the common source is almost continuous, providing uniform loading of `thegenerator and most eiiicient use of the generating equipment.

As was the case with the apparatus used for successively supplying current to eight circuits, the ones shown in Fig. 3 and 4 for supplying current to but four circuits will require the operation of each double throw switch twice per cycle or revolution of the cam shaft. Thus, in no form of my invention must any switch be operated more than twice in one complete cycle. This provides a very definite advantage over the apparatus disclosed in the Hoof Patent 2,466,238, wherein a double throw switch is operated eight times for eight circuit operation and four times for four circuit operation. The switch life in an apparatus designed to control eight circuits is thus increased by 300%, or four times, while that of apparatus designed to control four circuits is increased by or doubled. Comparable increases in switch life for apparatus designed, according to my invention, to control diiierent numbers of circuitsV may be achieved. For instance, in a six circuit apparatus switch life will be increased by 209% or three times.

Among the advantages of my apparatus are its simplicity, its consequent low cost, and its longer life in use before requirement for replacement of any of its parts. It will, of course, be understood that various minor changes and modifications may be made in the apparatus without departing from the invention as set forth in the appended claims.

I claim:

1. Apparatus for successively supplying current from a common source to a plurality of electric circuits which comprises a plurality of double throw switches electrically connected in a fanning-out circuit arrangement between the common source and the plurality of electric circuits; a constant speed electric motor; and means mechanically connecting the motor to the double throw switches to cause the double throw switches to be operated in seouence when the motor is operated, said mechanical connecting means being so constructed and arranged that each double throw switch performs at least one electrical transfer during a complete cycle of o-peration of the apparatus and each electric circuit is successively supplied with current from the common source 4during the cycle of operation.

2. Apparatus for successively supplying current from a common source to a plurality of electric circuits which comprises a primary double throw switch electrically connected to the common source; a plurality of secondary double throw 'switches electrically connected in a tanning-out circuit arrangement Ibetween the primary double throw switch and the plurality of electric circuits; a constant speed electric motor; and means rnechanically connecting the motor to all of the double throw switches, said mechanical connect ing means being so constructed and arranged that each of the double throw switches is operated twice during a complete cycle of operation of the apparatus, the primary double throw switch performs two electrical transfers during the complete cycle of operation of the apparatus and the secondary double throw switches perform one electrical transfer each during the complete cycle of operation, each electric circuit thereby being successively supplied with current from the common source during the cycle of operation.

3. Apparatus for successively supplying current from a common source to a lplurality of electric circuits which comprises iirst and second double throw switches the switch contacts of which are electrically connected respectively to the terminals of the electric circuits, each double throw switch controlling two circuits, a third double throw switch, the switch contacts of which are electrically connected to the switch arms of the first and second Adouble throw switches and the switch arm of which is adapted to be electrically connected to the common source; a constant speed electric motor; a cam shaft driven by said motor; a plurality of substantially identical cams fixedly and non-rotatably mounted on the cam shaft, each of the cams being adapted to operate one of the double throw switches, the cams being circumferentially positioned relative to one another so that during the first half of one revolution of the cam shaft the iirst double throw switch is operated, the third double throw switch being positioned to supply current to said iirst double throw switch, and during the second half of the revolution of the cam shaft the second double throw switch is operated, the third double throw switch being now positioned to supply current to the second double throw switch, whereby during one revolution of the cam shaft each electric 10 circuit will be successively supplied with current from the common source.

4. Apparatus for successively supplying current from a common source to a plurality of electric circuits which comprises rst and second double throw switches each having two switch contacts and a switch arm adapted to be moved into engagement with either of its switch contacts, raid switch contacts each being electrically connected to one terminal of one of said electric circuits; a third double throw switch having a switch arm adapted to be electrically connected to said common source and having two switch contacts one of which is electrically connected to the switch arm of said first double throw switch and the other of which is electrically connected to the switch arm of said second double throw switch; a constant speed electric motor; a cam shaft driven by said motor; a cam for each double throw switch fiXedly mounted on said cam shaft, said cams being operable to move the switch arms of their respective dou-ble throw switches into contact with the switch contacts of the respective double throw switches, each cam being substantially identical to the other cams and being shaped to move its respective switch arm into engagement with one switch contact during approximately degrees of its revolution and into engagement with the other switch contact during the remaining approximately 180 degrees, said cams being circumferentially positioned on the cam shaft relative to one another so that during approximately the first half of one revolution of the cam shaft the switch arm of said third double throw switch will be in contact with that one of its switch contacts which is electrically connected to the switch arm of said first double throw switch and during the second half of the revolution will be in contact with that one of its switch contactsl electrically connected to the switch arm of said second double throw switch and so that during said first half of the revolution of the cam shaft the switch arm of the first double throw switch will be in contact first with one of its switch contacts and then with the other of its switch contacts and during the second half of the revolution of the cam shaft the switch arm of said second double throw switch will be in contact first with one of its switch contacts and then with the other of its switch contacts, whereby during one revolution of the cam shaft each electric circuit will be successively supplied with current from the common source.

5r. Apparatus for successively supplying current from a common source to a plurality of electric circuits which comprises first and second double throw switches the switch contacts of which are electrically connected respectively to the terminals of the electric circuits, each double throw switch controlling two circuits, a third double throw switch, the switch contacts of which are electrically connected to the switch arms of the first and second double throw switches and the switch arm of which is adapted to be electrically connected to the common source; a constant speed electric motor; a cam shaft driven by said motor; a cam having a dwell of approximately 180 degrees fixedly mounted on said cam shaft and adapted to operate each double throw switch twice during a complete cycle of operation of the apparatus, the three double throw switches being so positioned and arranged about said cam that the third double throw switch performs two electrical transfers during the complete cycle of op- 1 (algemener u 1 I f 1 2l eration andeach of the rst 'and the second double'` v r Y throw switches performs oneelectricalttransfer- REFERENCES CITED during the cycle of operation;eachl electric circuit thereby beingsuccessively supplied. with. current r le: 0f thlsvpatenff from the common source during the. cyclezfofi: 5 UNITED STATESfpAfI'ENTS operation. e e e o HUH Number Name Date ART W' HAYDON' 2,466,238 Hoof Apr. 5, 1949 The) following -references'are of record in thel

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