US2505712A - Resistance contact apparatus - Google Patents

Description

April 25, 1950 R. L. JAEscHKE ET Al. 2,505,712

RESISTANCE CONTACT APPARATUS Filed June 25, 1948 aimlmm n 2. Af, n f f fa.. G E .I H

Patented Apr. 195o 2,505,712

RESISTANCE CONTACT APPARATUS Ralph L. Jaeschke, Kenosha, Wis., and Martin P. Winther, Waukegan, Ill.; said Jaeschke assignor to Dynamatic Corporation, Kenosha,

Wis.,

a corporation of Delaware, and said Winther assignor to himself as trustee Application June 25, 1948, Serial No. 35,144

2 Claims.

This invention relates to resistance contact apparatus, and with regard to certain more specific features, to shunt-contact banks, and constitutes an improvement over constructions such as shown in United States Patent 2,050,479.

Among the several objects of the invention may be noted the provision of shunt-contact apparatus such as shown in said patent but simpliiied so as to reduce the size, number of parts and manufacturing cost; the provision of a bank of the class described which will eliminate insulating spacers between contacts, resistances external to the bank per se, and jumper Wires and the like between respective contacts and resistances; and the provision of compact apparatus of the class described having reduced vulnerability to shock and reduced maintenance cost. Other objects will be in part apparent and in part pointed out hereinafter.

The invention accordingly comprises the elements and combinations of elements, features of construction, and arrangements of parts which will be exemplified in the structures hereinafter described, and the scope of the application of which will be indicated in the following claims.

In the accompanying drawings, in which one of various possible embodiments of the invention is illustrated,

Fig. 1 is a diagrammatic view of an exemplary embodiment of the apparatus;

Fig. 2 is a vertical section taken on line 2 2 of Fig. 1;

Fig. 3 is an enlarged axial section showing certain contact and resistor elements; and,

Fig. 4 is a plan view of one of said elements.

Similar reference characters indicate corresponding parts-throughout the several views of the drawings.

In said patent is shown a so-called caterpillar type of shunt-contact resistance bank which, in response to a control element, is adapted to cut sectional resistances into and out of a circuit. The resistance sections, being external to the contact bank, need to be connected by jumper wires. Insulators are also required between adjacent shunt contacts. This involves a, substantial number of small parts that need to be assembled, requiring time-consuming soldering and other operations not needed in the case of the present invention. The resulting prior structure is more vulnerable to shock and requires more maintenance than the present construction, notwithstanding that the prior construction is as simple and satisfactory a device as could be made until now.

Referring now more particularly to the drawings, numerals I indicate conducting shunt leaf springs, each of which includes at one end a supporting and contact area or eye 3 including a hole 5. Each spring includes a silver contact button 'I at its other end. Certain of these springs, which are in the present example used at the ends of a bank, carry conductive tabs 9 for making connections with a circuit II. The circuit includes a suitable source of voltage V and a load section L, the current to which it is desired to control by changing the resistance in the circuit.

In order to mount the leaf springs I in spaced, banked relationship, a backing plate I3 is used, forming a backstop for the last leaf spring I to the left. An insulator 2 is interposed between plate I3 and this spring. Through the sides of the plate I3 pass tension bolts I 5. These also pass through openings in a holding plate I1. Members I3 and I1 are forced toward one another by the bolts I 5 which act as compressing means. An insulator 4 is interposed between plate I1 and the last spring to the right. The plate I1 is formed with a clevis I9 carrying a pivot 2| for a bell crank control arm 23. Together the plate I1 and clevis I9 form a bracket. One limb oi this bell crank carries a roller 25 which, when the eye 21 of the other limb is positionally adjusted, will press upon one or more of the leaves I so as successively to bring the contact buttons 1 into and out of engagement.

To provide the desired resistance between each pair of springs I, a resistance washer element 29 is sandwiched between each pair (see Figs. 3 and 4). Each resistance element has in it a hole 3I corresponding to the holes 5 in the contact areas 3 of the springs I. This permits the springs and resistance washer elements to be alternately sandwiched and stacked or strung on an insulating support 33. In this case the support 33 is in the form oi' an insulating post which may be threaded into the plate I1 and which extends into a guide opening 35 in the plate I3. This allows assembly movement between members I3 and I9. Then by threading up nuts 31 of the bolts I5, assembly such as shown in Figs. 1 and 2 may be brought about. The endwise springs I used are of the type having the stated connecting tabs 9. Tabs 9 need not be at the end of the bank, as for example when it is desired to connect that circuit across less than all of the contacts. Thus several different circuits might be controlled from one bank. It will also be understood that the elements I and 29 may be supported otherwise than on a pin such as 33. For

il example, they may rest on an insulating V-shaped member support. There are other obvious equivalents in these respects.

Each resistance element 29 is of special form. comprising a plate or washer 39 (in this case a washer) of compressed carbon such as is used in carbon pile resistors. The opposite faces of these washer plates are spray coated and thus impregnated with a conducting medium such as copper 4I. For example, a metal spray gun may be used for applying the coatings 4i which may be in a thin film several thousandths of an inch thick. This is sometimes referred to as metallizing. Plating methods may also be used. Thus the coating becomes integral and firmly attached or bonded and allows no relative movement between it and the carbon under a Wide range of pressure variations that may be applied to the plate as a whole. The coatings should not extend across any rim portion of the plate. For example, inthe washer type of plate shown, it-should not extend across the outer rim or across the inner opening 3l. Any desired variation in resistance of a given plate is accomplished in the same manner as is used by manufacturers in making the usual non-coated discs and the like for carbon pile resistances, that is, the factors of the carbon mixture and pressure used during manufacture are controlled to give the desired resistance per plate. It is preferable in the present case that each plate be of the same thickness so that the clearances between contact button 1 can be maintained constant. This, however, is not absolutely necessary since structural compensation can be made at the contacts 1 for differences in plate thicknesses. The plates may vary in resistance from a fractional to a multiple number of ohms. Plates made as specified with the firmly attached (relatively immovable) conducting surfaces 4i, have a special property unlike ordinary uncoated carbon plates. They are capable of being clamped into a solid stack under reasonable variations in pressures, without their individual resistances being changed. In an ordinary carbon pile, the variation in resistance due to small changes in pressure on the carbon pile is an effect obtained at the carbon contact surfaces of the plates. In such cases the over-all resistance of a pile when closed is a function of the pressure at the surfaces of the discs. In the present case this functionality is eliminated by the attached copper on the disc surfaces, so that a substantial variation in the clamping pressures does not affect the resistance of any plate unit nor the over-all resistance. Hence it is possible to employ the resistance of each plate as the step value desired between adjacent contacts l, despite pressure variations that may occur during assembly when the nuts 31 are pulled up.

In the condition of the parts shown in Fig. 1, all of the current in the circuit il is subjected to the total resistance of all of the Washers 39. By moving the bell crank 23 counterclockwise, successive contacts are brought about between adjacent contact buttons 1. When contact occurs between any pair, the resistance plate between that pair is short-circuited, thereby reducing the resistance in the circuit Il by the resistance of the corresponding plate. By suflicient movement of the bell crank 23, the entire row of contacts 1 will sequentially be brought into contact, thus shorting out all of the resistance plates.

While I have shown carbon resistance plates coated with conductive copper for the separators clamped between the conductors i, it is to be understood that other resistance materlalscoated with other conductors may be used. The carbon is particularly desirable for a range of resistance steps of the order of say, 116 to 2 ohms. If it is desired to have the resistance change per step inthe bank very high, it might be desirable to use a higher resistance material such as nichrome in the body of the plate with an integral low-resistance contact surface such as copper. Or, if it were desired to have very low resistance steps, a'plate might be used having a resistance lower than carbon such as iron. for example, having an integral contact surface of still lower resistance such as silver. 'I'his would produce smaller resistance steps. However, it is in general true that, for controlling a large majority of ordinary power circuits, the carboncopper inegral combination is the best and most economical.

Relative to the resistance elements, the term integral is used herein in the sense that the contact surfaces of said elements are bonded to the remainders of the elements, so as to prevent relative motions between the contact surfaces and the main bodies of the elements where they are in contact, thereby eliminating resistance changes caused by a substantial range of pressures that may be applied to the elements across said contact surfaces.

It is clear from the above that an assembly of parts for making a resistance bank may be accomplished much more economically than the assembly shown in said Patent 2,050,479. Furthermore, it is much more economical to make because the number of costly parts is reduced. The assembly is less vulnerable to shock and may be more readily maintained.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

Asmany changes could be made in the above constructions 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.

We claim:

1. Electrical shunting apparatus comprising spaced pressure members, compressing means for forcing said members toward one another, an insulating supporting pin mounted between said pressure members permitting assembly movement therebetween, conducting leaf springs each carrying a contact at one end aligned with the contacts of the others and each carrying an eye strung on the pin for self-support thereon, resistance washers strung on said pin alternately with said eyes for self-support on the pin along with said -eyes to form a stack, said pressure members clamping together the stack of springs and washers in their self-supported positions upon the pin, each resistance washer being composed of a carbon disc the opposite faces of which, where contacted by the eyes, have integrally bonded low-resistance copper facings,

having a portion at the opposite end of said line o! contacts.

2. Electrical shunting apparatus comprising spaced pressure members, tension rods forming compressing members for forcing said members toward one another, one of said members constituting a backing plate and the other a bracket, an insulating supporting pin mounted between said pressure members permitting assembly movement therebetween, conducting leaf springs each carrying a contact at one end aligned with the contacts of the others and each carrying an eye strung on the pin for self-support thereon, resistance washers strung on said pin alternately with the eyes for self-support; on the pin along with said eyes to form a stack, said pressure members clamping together the stack of springs and washers, each resistance washer being composed of a carbon disc the opposite faces of which,

,where contacted by the eyes, have integrally bonded low-resistance copper facings, whereby the resistance of said string of eyes and washers is independent of pressure applied thereto by the compressing members, and a control lever pivoted on the bracket and having a part cooperating with one end of said line of contacts to engage and disengage them sequentially.

RALPH L. JAESCHKE. MARTIN P. WINTHER.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS

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