US2031784A - Electrical apparatus - Google Patents

Description

Feb. 25, 1936. c l, MCNEIL ELECTRICAL APPARATUS Filed Jan. 51," 1954 INVENTOR. C/mr/es Mc/Vefl BY ORNE.

I Pdtented Feb. 25, 1936 UNITED STATES PATENT OFFICE Eclipse Aviation Corporation,

East Orange,

N. J., a corporation of New Jersey ApplicationJanuary 31, 1934, Serial No. 709,210

3 Claims.

This invention relates to electric current generating and battery charging systems such as are employed on motor vehicles, and particularly to certain improvements to be associated 5 with the reverse current cut-outcommonly employed in such systems to open the battery-generator circuit and prevent the discharging of the battery when the voltage of the generator becomes less than that of the battery.

1 In conventional compound generators the characteristics are frequently such that a reverse current of insumcient value to cause an immediate opening oi the contacts of the reverse current cut-out may at the same time be sufliciently 15' strong to produce a reversal of polarity in the generator itself, due to the'relationship or relative strengths of, the series and shunt fields of the generator. That is, when the reversal of current occurs, such reversal produces a buck- 2 ing effect in the series field of the generator,

which bucking effect reduces the effective voltage across the terminals of the shunt field to such an extent that the polarity of the machine may be reversed before the reverse current cutout function. More specifically, an object of the invention is to provide means for maintaining the shunt field of the generator comparatively free of the influence of such series field bucking tendency, whereby the strength of the shunt field may be held at a sufficient value to prevent reversal of the polarity of the generator.

A feature of the invention, therefore, is the provision of a system having two safeguards 35 against reverse current tendencies, instead of the usual single safeguard; the first safeguard functioning during the initial stage of current reversal, and continuing to function until the usual safe- 'guard-the opening of theconventional cut-out' 40 has had sumcient time to become effective.\

In the embodiment of the invention herein illustrated and described, the shunt field controlling means operates to establish an alternate pat after the initial excitation, or building up 45 of he generator has taken place. By reason of this alternate path, any reversal of current which would ordinarily be sufficiently strong to create a danger of reversal inpolarity in the generator, will have no efiect upon the strength of the shunt 50 field, which will be energized at full battery voltage, and danger of reversal, thereby nullified;

It is to be understood however, that the method and means employed for this purpose in the preierred embodiment as shown are merely illus- 55 trative and do not define the limits of the invention, reference being had for the latter purpose to the appended claims In the drawing, the single figure is a diagrammatic representation of the electrical circuits and parts involved in the preferred embodiment of the invention, ,such parts including the generator armature 5 with the usual shunt and series windings 8 and 1 respectively, the former being in series with a variable resistance 8 and in shunt across the out-put feeds 9 and III. 'Feed 9 preferably includes the usual series winding ll of the reverse current relay and the usual shunt or voltage winding l2, the former being connected with the battery through the normally closed armature switch [4 and the latter having connection with the second feed I0 through the instrumentality of the lead I5.

The battery adapted to be charged by the generator is indicated at It with one terminal connected to feed I0 by way of lead H and its other terminal to the second section 9a of the line 9 by way oi lead IS. The lighting or other power consuming load l9 adapted to be supplied by the generator and/or battery is supplied by the ex-., tensions of lines So and I0 indicated at 20 and 2|.

The novel means of the present invention for maintaining full strength in the shunt field 6 even on those occasions when there is a reversal in the direction 01' current flow in the windings of the reverse current device, takes the form of a second relay including a winding 25 connected across the main lines 9 and ID as indicated at 28 and 21 and having associated therewith an armature 28 movable into contact with either of two conducting plates 29 and 30, the former being in connection with main feed 9 and the latter being inconnection with the second section of the feed 90. through the provision of a connecting lead 32, suitable means such as the tension spring 33 being provided to maintain the 40 said armature 28 in the upper position during starting of the generator, the setting of the spring and the design of the coil 25 being preferably such that the electro-magnetic fieldproduced by the flow of current through said coil is insufficient to draw the armature 28 downwar so into contact with the plate 30 during the starting or building up period of the generator but becomes sumcient to produce such downward movement at the completion of the building up 0 period. -Or in other words, when the voltage across the lines 9 and I0 (and hence the voltage across the coil l2 oi the reverse current cut-out) becomes sufiicient to insure closing of the switch I4. When both these switch movementsthat is, of the armatures 28 and ll-occur, the excitation of the shunt field will thereafter proceed through the conductors 9, ll, I4, 32, 30, 28 and 36 and will continue in this manner during the entire period of operation of the generator, ex-

- cept on occasions when there is a tendency for a reversal in the direction of current fiow--that is, a tendency for the current to flow from the battery into the generator. The operation on such occasions will be as follows: 7

As the current begins to flow in a reversed direction through the series winding M oi. the reverse current cut-out, there is of course a certain time lag in the opening of the switch 5,,

during which time the above described bucking efiect will occur in the series field winding 7. The shunt field winding, however, will be maintained at full strength by reason of the direct connection with the battery constituted by the lead 32 and including the contact 30 with which the armature 28 is engaged. This battery excitation through this direct path between the battery and the shunt field 5 will continue to constitute the means for maintaining the shunt field at full battery strength until after actual opening of the switch M. When such opening occurs, the above described bucking efiect ceases and there is then no further necessity of main taining full strength of current flow in the shunt field.

So long as the voltage across the generator terminals remains at or above the predetermined value, the coil 25 holds the strength of the magnetic field acting upon the armature 28 at such a value that the spring 33 is unable to return the armature 28 to a position of engagement with the contact plate 29, and such return .will be delayed until just prior to the return of the generator rotor to a condition of rest, at which time the return of the armature 28 to contact with conductor 29 will serve to place the parts in condition for self-excitation of the generator on the occasion of the next starting thereof, on which occasion the cycle of operation above described will of course be repeated.

There is thus disclosed a system in which the reversal effects of the operating current of reverse current cut-out devices are nullified by maintaining the shunt field excitation at a value equivalent to operating conditions until after complete opening of the reverse current relay or cut-out and the effect of the reverse current has expired.

What is claimed is:

1. In a system of the class described, a battery and generator connected for energization of the 5 former upon rotation of the latter, a reverse current cut-out between the generator and battery, a shunt field constituting part of the generator, means for energizing said field by current taken from the generator, means for energizing 10 said field by current taken from the battery, and selective means for rendering said energizing means successively efiective, said lective means comprising a switch connecting said shunt field with the generator during the initial excitation 15 period and movable substantially simultaneously with the closing of said reversed current cut-out to a position insuring excitation of said shunt field directly from the battery.

2. In a system of the class described, a battery 20 and generator connected for energization of the former upon rotation of the latter, a. reverse current cut-out between the generator and battery, a, shunt field constituting part of the generator, and meansior preventing a reversal in 25 polarity of the generator regardless of the strength of the current passing through said reverse current cut-out, said means including a switch movable to connect said shunt field with the battery side of the reverse current cut-out as 30 soon as the generator voltage has built up to the normal running value.

3. In a system of the class described, a battery and generator connected for energization of the shunt field with the battery independently of said'reverse current cut-out as soon as the said. terminal voltage reaches the normal running value.

CHARLES I. MCNEIL.

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