US3185950A

US3185950A - Adjustable resistance device

Info

Publication number: US3185950A
Application number: US146904A
Authority: US
Inventors: Lionel E Weyenberg
Original assignee: Individual
Current assignee: Individual
Priority date: 1961-10-23
Filing date: 1961-10-23
Publication date: 1965-05-25
Anticipated expiration: 1982-05-25

Description

May 25, 1965 L. E. wEYENBl-:RG 3,185,950

ADJUSTABLE RESISTANCE DEVICE Filed Oct. 23. 1961 IN VEN TOR.

Lionel E. Weyenberg /ndr'us Sfar/ye Mge@ United States Patent O 3,155,950 ADJUSTABLE RESSTANCE DEVICE Lionel E. Weyenherg, 3845 N. 169th St., Brookfield, Wis. Filed (let. 23, 1961, Ser. No. 146,964 8 Claims. (Cl. SSS-JVM) This invention relates to an Iadjustable resistance device, particularly power rheostats, high temperature rheostats and the like, and to the method of making the same.

In electrical circuits, variable resistance devices such las a power rheostat may be connected in the circuit tor varying the voltage, cur-rent, or other characteristic thereof. A power rheostat generally includes a resistance coil wound on .a suitable core or support. One end of the coil is connected in a circuit and :a -contact `or wiper is slidab'ly mounted on the coil `and connected in the circuit to provide 'a means of adju-sting the portion of the lrheostat coil which is inserted into the circuit. Power rheostats lare normally designed to carry substantial current and must be oi a high temperature variety. Current in a conductor `generates heat in :accordance with the lsquare of the current and the resistance of the wire and as a result, substantial amounts of heat are generated within a rheostat coil. The amount of current or power that the rheostat can carry is directly dependent upon the dissipation of the heat generated within the rheo-st-at. Consequently, power rheostats are normally not enclosed in protective housings but rather tare mount-ed for free circulation of the air or the like to establish rapid dissipation of the heat. Power rheostats 4are consequently `subject to the deteriorating eti-ect of the foreign elements in the :surrounding atmosphere.

As the proportion of the resistance coil connected in the circuit decreases, the current through the coil normally increases. ln order to carry normal full load current, power rheostats have heretofore required that a substantial portion of the rheostat be connected in the circuit.

Totally enclosed rheostats and the like have been provided ter very small ratings wherein heat dissipation is not a severe restriction. For example, Unite-d States Patent No. 2,870,304 to OBrian discloses a helically wound resistor coil mounted within an insulating protective housing. A ring contact is secured to a threaded follower in sliding `engagement with the coil. In response to rotation of the shaft, the ring -contact is selectively positioned yupon the resistance coil. Rheostats as shown in 'OBrian, are satisfactory for relatively smell wattages; for

example, in the range of 5 watts or the like.

In power rheostats which normally vare rated in terms of 100 watts or more, totally enclosed rheostats have not been satisfactory because of the resulting heat concentrations.

T he present invention provides `an 'adjustable resistance device having an enclosing hou-sing and adapted for high power ratings. The presentinvention further provides `an improved method of forming a t-otally enclosed power rheostat as well ras other rheostats and similar devices in an inexpensive and rapid manner.

In accordance with the present invention a high heat dissipating housing of suitable metal or the like is provided. A resistance coil is `bonded .to the inner wall of the housing by an electrically insulating and high temperature compound which `also has good heat transfer characteristics. The compound .intimately bonds the coil 3,185,950 Patented May 25, 1965 ICC to the housing and creates a rapid transfer of the heat to the housing. The generated heat is rapidly distributed throughout the housing `and then dissipated -to the surrounding atmosphere. Applicant has found that the coil can be totally enclosed within a suitable -dustp-roof enc'losurefwithout .requiring abnormal large cooling surfaces while maintaining power ratings of wattages of one hundred watts and the like. T he construction of the present invention permits carrying full load with .as much as 75 percent of resistance coil removed from the circuit.

In accordance with another aspect of this invention, a pair of opposed sliding contacts are secured toen axially moving positioning shaft. The opposed sliding contacts allow adjustment in half turns of the coil for relatively fine control. If either one of the sliding contacts burns out, or is otherwise destroyed, the other contact maintains operati-on, until the `defective contact brush can lbe replaced or repaired.

lt is important that the rheostat winding be firmly and intimately bonded to the heat dissipating and enclosing housing. A particularly highly satisfactory and novel method oi securing a winding such as the rheostat winding of the present invention in a housing includes the steps of winding a coil on a mandrel preferably having resilient facings adjacent the areas with which the sliding contacts engage. A layer of the bonding compound is applied over the outer circumference of the coil and the mandrel and allowed to set. The compound actually iows between the adjacent convolutions of the coil and securely embeds the coil within the compound, except adjacent the resilient facing which maintains the adjacent face of the coil free from the compound. The coil supported by the outer layer of compound is properly located within the housing and an additional or second layer of compound is filled between the housing and the back side of the iirst layer. The second layer is allowed to set and securely and intimately bond the coil to the housing.

rl`he present invention provides a lightweight, compact rheostat or other similar electrical device and is particularly adapted for forming of totally enclosed resistance devices having power or high temperature ratings. The device introduces a minimum amount of reactance into the circuit and can carry full wattage ratings with only small portions of the resistance coil or the like connected in the circuit. 'K

The drawing furnished herewith illustrates the best mode presently contemplated for carrying out the invention.

In the drawing: j

FIG. l'is a side elevational view of a totally enclosed rheostat;

FIG. 2 is a vertical longitudinal section of the rheostat shown in FIG. l;

FIG. 3 is a fragmentary View taken on lines 3-3 of FG. 2;

FIG. 4 is a radial section taken on lines 4 4 of FIG. 2;

FIG. 5 is a diagrammatic illustration showing the initial winding of a rheostat coil such as shown in FIGS. 2 and 3;

FIG. 6 is a diagrammatic illustration showing the application of an initial layer of compoundupon a wound coil; and

FIG. 7 is a diagrammatic illustration showing the assembly of a wound coil within a housing and the application of the final bonding compound to secure the coil within the housing as shown in FIGS. 1 4.

Referring to the drawing and particularly to FGS. 1 4, a power rheostat l of general cylindrical shape is shown having a pair of input terminals 2 and a pair of output terminals 3 secured to one end and an input shaft or rod 4 slidably mounted in the opposite end thereof. A resistance coil 5 of relatively tine wire is secured within the rheostat l and connected at its opposite ends to the terminals 2. A pair of opposed brushes 6 and .7 slidably engage coil 5 and are mounted on opposite ends et a tubular brush holder 8 which is connected to the inner end of input shaft or rod 4 for selective positioning of the brushes 6 and 7 on the coil 5 by axial movement of the rod li. The brushes 6 and 7 are connected to the terminals 3, as hereinafter described, to vary the proportion of the coil 5 connected between the respective terminals 2 and the brushes 6 and 7 for insertion into a suitable electrical circuit, not shown.

Referring particularly to FIGS. 2 and 4, the illustrated rheostat ll includes a cylindrical housing or casing 9 formed of a suitable metal having good heat dissipating characteristics. Aluminum, magnesium and other similar lightweight metals have been found particularly satisfactory. End walls lit and 11 are removably secured to the corresponding ends of the casing 9 to provide an airtight enclosure for coil 5. The end walls il@ and il project into the casing 9 and are Secured in place by a plurality of circumferentially distributed set screws i2 which extend through suitably located openings in the ends of casing 9 and thread into suitably tapped openings in the end walls and il.

The resistance coil 5 includes a single layer of helicaily wound closely spaced convolutions which are bonded to the inner wall of the casing 9 by a suitable layer of cement 13. rThe coil 5 is formed of a suitable resistance wire for carrying selected currents with suitable dissipation of heat from the coil.

The cement 13 is any suitable cement having goed electrical insulating and heat transfer characteristics in order to both insulate the coil 5 from the metal casing 9 and to rapidly transfer the heat from the coil 5 to the casing 9 from which the heat is dissipated to the surounding atmosphere. The cement ll3 is spaced inwardly at the ends of the casing 9 and at 14 and i5 to allow attachment of the end walls 10 and 11.

The cement 13 extends between the convolutions of the coil 5 and over the inner face of portions of coil 5 as at 16 to physically lock the individual convolutions of the coil 5 together and to firmly support the coil within the casing 9.

The coil 5 is provided with a pair of diametricaliy opposed

coil facings

17 and 18 which are free of all cement 13 and suiiciently wide to accommodate the brushes 6 and 7.

Suitable leads 19 and Ztl connect the opposite ends of the coil 5 to the terminals 2 for connection into a circuit.

The terminals 2 are diametrically spaced from each other, as most clearly shown in FIG. 4, and formed by a threaded screw which passes through a suitable opening in the end wall 19. A hex nut 21 is threaded onto each of the screw terminals 2 and locks the corresponding terminal to the end wall it). Suitable insulation 22 is disposed between the terminals 2 and the wall l() to electrically isolate the terminals from the casing 9. When an input is connected to either one of the terminals 2, the current path is through the connected end portion of the coil 5 to and through the brushes 6 and 7 to the terminals which are connected to brushes 6 and 7, as hereinafter described.

The illustrated brushes 6 and 7 are generally conventional rectangular carbon blocks which are slidably disposed within the opposite ends of the tubular brush holder 8 and slidably engage the diametrically opposite portions v17 and 18 of the coil 5.

The tubular brush holder 8 is somewhat shorter than the inner diameter of the coil 5 to allow free movement ot the brush holder 8 through the coil and includes open ends corresponding to the cross-sectional configuration of the brushes 6 and 7. The brush holder 8 includes a central opening accommodating a reduced threaded end 23 of the rod 4. A hex nut 24 is threaded onto the rod 4 and locks the holder to the rod d. Insulation 25 is dis posed between the connection of rod d and holder 8 to electrically isolate the rod from the holder.

The rod i is slidably journaled in a tubular bearing member which is secured within a suitable opening in the end wall l. Lock nuts 27 and 28 are threaded on the hearing member 26 on opposite sides of the end wall ill to rigidly lock the bearing member 26 in place. The tubular bearing member 26 preferably extends axially outwardly out of the end wall 11 and serves as a mounting means for the rheostat.

The holder 8 is guided within the casing 9 for rectilinear movement by the

guide rods

29 and 3@ which project axially of the casing 9 and pass through correspondingly spaced guide openings in holder 8 on opposite sides of the rod 4. Each of the

guide rods

29 and 30 is secured as an extension of one of the output terminals 3 on the end wall i0.

The terminals 3 are generally threaded members from the wall l@ similar to terminals 2 and extend through suitable openings in the end wall ril with a locking hex nut 31 threaded on the outer ends. insulation 32 is disposed betwcen the end wall lil and the terminals 3 to electrically isolate the terminals and the guide rods Z9 and Sil from the end wall lil and casing 9.

Referring particularly to FIG. 4, the terminals 3 and therefore guide

rods

29 and 3@ are located in a plane perpendicular to the plane including the terminals 2 and generally bisecting the exposed cement-free tacings of the coil 5. The holder 3 and brushes 6 and 7 are consequently aligned with the cement-free coil acings 17 and 1S.

The brushes 6 and 7 are continuously biased from the holder 8 into engagement with the facings t7 and i3 by coil springs 33 and 34 which are provided within the holder S. Contact blocks 35 and 3d are disposed between the inner end of the coil springs 33 and 34 respectively and the

adjacent guide rods

29 and 30. In the assembled position, the springs 33 and 34 are compressed between the brushes 6 and 7 and the corresponding Contact blocks 35 and 36 to resiliently hold brushes 6 and '7 in firm sliding engagement with coil 5 and blocks 35 and 36 in iirm sliding engagement with rods 29 and 3l).

Similar jumper leads 37 and 38 connect the respective contact blocks 35 and 36 to the brushes 6 and 7 and establish a low resistance path therebetween. Current from the brushes 6 and 7 is connected through the jumper leads 39 and 4d and contact blocks 35 and 36 to the

guide rods

29 and 30 and then to the terminals 3.

The axial positioning or the rod 4 within the casing 9 determines the position of the brushes 6 and 7 with re spect to the coil 5 and consequently the portion of the resistance coil 5 connected in the circuit.

The current through the coil 5 results in generation of heat in proportion to the square of the current and the resistance of the coil 5. As previously noted, the rate of dissipation of the heat constitutes one limiting factor on the rating of the rheostat. In accordance with the illustrated embodiment of the invention, the heat generated within the coil 5 is rapidly transferred by the cement t3 to the casing 9 from which the heat is rapidly dissipated to the surrounding atmosphere. Applicant has found that a rheostat constructed in accordance with the above teachings can carry full load with percent of the winding disconnected from the circuit. The present invention provides a light and compact power rated rheostat having an outer dustproof housing.

The brushes 6 and 7 result in a two point contact, individually connected into the circuit through the separate 5

guide rods

29 and 30. If either one of the brushes 6 and 7 malfunctions or is destroyed, the opposite brush maintains the connection into the circuit.

Referring to FIGS. 5-7, a preferred method of forming the illustrated embodiment of the invention of FIGS. 1-4 is illustrated.

Referring particularly to FIG. 5, a winding mandrel 39 is provided having an outer diameter substantially corresponding to the inner diameter lof the coil 5. Resilient strips 40 and 41, corresponding in width to the exposed

facings

17 and 18 of the coil S in FIGS. l-4, are secured on diametrically opposite sides of thekmandrel 39. A wire 42 is wound on the mandrel 39 and strips 40 and 4l to form the coil 5. k

After the wire 42 has been completely wound on the winding mandrel 39 to form coil 5, a layer of cement 43 is applied over the back side of the coil, as shown in FG. 6. The layer of cement 43 may be applied directly inany suitable manner, with or without a forming container.

Theinner layer of cement 43 moves between and at least partially around the convolutions of coil 5 throughout the circumference of coil 5 except at the area of the resilient strips 40 and 41 which establish the cement-free facings 17 and 1S without additional operations. The convolutions are tightly locked in place by the cement to provide excellent support during operation of the rheostat. The cement 43 adjacent the

facings

17 and 18 bonds to the outer surfaces of the convolutions of coil 5 to support those portions of coil S.

The cement 43 is allowed to harden and the mandrel 39 may then be removed. The mandrel 39 may be of break-away, collapsible construction or other suitable removable variety.

rfhe coil 5 and the hardened cement layer 43 thereon is then properly located within a casing 9 to coaxially align the coil 5 within the casing 9 of greater diameter than the cement 43. A cement 44 is introduced to fill the space 45 between the back side of the cement layer 43 and the casing 9. The cement 44 is allowed to harden and in so doing bonds to the inner wall ofthe casing 9 and to the cement layer 43 to form a continuous layer of cement adhesively bonding the coil 5 to the casing 9.

The end walls 1t) and 1l and other properly located elements are attached to form the totally enclosed rheostat 1. The cement 43 and 44 in addition to physically supporting the coil 5 provides rapid and effective heat transfer of the generated heat to the casing 9 from which it can be dissipated to the surrounding atmosphere.

The present invention provides a totally enclosed rheostat tor similar device which is compact and relatively inexpensive which can be readily produced employing modern mass production techniques.

Various modes fof carrying out the present invention are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention.

I claim:

l. In an adjustable electrical resistance device, a tubular metallic casing, a resistance wire coil within the casing, a bonding and insulating material securing the coil to the casing, said coil including at least diametrically opposed facings free of said material, a brush holder slidably mounted within the casing and movable axially therein, and a pair of contacts resiliently secured in the brush holder in individual engagement with the opposed facings.

2. The construction of claim l having separate output connections for said brushes.

3. In an adjustable electrical resistance device, a tubular metallic casing, a resistance wire coil within the casing, an electrically insulating bonding cement securing the coil to the inner wall of the casing, said coil having a cement-free facing extending generally axially thereof,

a rod-like brush holder slidably mounted to the casing and movable axially therein, a guide member disposed within the housing and connected to the brush holder, means coupled to the brush holder and cooperating with said guide member to prevent rotation of the brush holder, and a brush resiliently secured in the brush holder in engagement with the cement-free facing.

4. In an adjustable electrical resistance device, a tubular metallic casing, removable metallic end walls to form a substantially closed enclosure, a resistance wire coil of spaced convolutions disposed within the casing, a layer of a bonding and insulating cement securing the coil to the inner wall of the casing and extending between and about the convolutions except in a selected contact path, a brush holder slidably disposed within the casing and movable axially therein, and a pair of brushes resiliently secured in the brush holder in individual engagement with the opposed cement-free facing.

5. An adjustable rheostat, comprising a tubular metallic casing having removable metallic end walls, a coil of resistance Wire within the casing, a layer of electrically insulating and heat transmitting cement bonding the coil to the casing and supporting the coil, said cement extending between the convolutions of the coil and overlying the face of the coil, a pair of diametrically opposed cementfree coil facings, a pair of brush terminals secured to the end wall in the plane of the cement-free coil facings and projecting axially inwardly of the casing, a tubular brush holder, an axially movable rod journaled in an end wall and secured to the brush holder for selective positioning of the holder, a pair of guide rods secured one each to said brush terminals and projecting axially to the opposite end of the casing, said brush holder having guide rod openings accommodating said guide rods to slidably support the brush holder with the ends thereof aligned with said coil facings and to prevent rotation thereof, contact brushes slidably disposed within the ends of the brush holder, and resilient means disposed within the tubular member and resiliently holding the contact brushes in engagement with the exposed facings.

6. An adjustable rheostat, comprising a tubular metallic casing having removable metallic end walls, a coil of resistance wire within the casing, a layer of electrically insulating and heat transmitting cement bonding the coil to the casing and supporting the coil, said cement extending between the convolutions of the coil and overlying the face -of the coil, a pair of diametrically opposed cement-free coil facings, a pair of coil terminals secured to one end Wall in a plane normal to the longitudinal plane through the cement-free coil facings and connected one each to opposite ends of the coil, a pair of brush terminals secured to the end wall in the plane of the cement-free coil facings, a tubular brush holder, an axially movable positioning rod journaled in the end wall opposite said terminals and centrally secured to and in electrically insulated position from the brush holder for selective positioning of the holder, a pair of guide rods secured one each to said brush termials and projecting axially to the opposite end of the casing, said brush holder having guide rod openings on opposite sides of the positioning rod accommodating said guide rods to slidably support the brush holder with the ends thereof aligned with said coil facings and to prevent rotation thereof, Contact brushes slidably disposed Within the ends of the brush holder, contact blocks within the outer ends of the brush holder, coil springs disposed between the contact blocks and the contact brushes resiliently biasing the contact blocks into engagement with the guide rods and the contact brushes into engagement with the exposed facings, and jumper leads connecting the corresponding contact blocks and contact brushes.

7. An adjustable rheostat, comprising a coil of resistance wire, a support for the coil, a tubular brush holder, an axially movable positioning rod mounted for axial susana@ movement through the coil, means securing the brush holder to the rod for selective positioning or" the holder, a pair of combination terminal and guide rods projecting through the coil on opposite sides of the positioning rod, said brush holder having guide rod openings accommodating said guide rods to slidably support the brush holder with the ends thereof aligned with selected portions of said coil and to prevent rotation thereof, and Contact brushes slidably disposed within the ends of the brush holder and slidably engaging the adjacent portions ofthe coil.

8. The construction of an adjustable rheostat according to claim 7 having contact blocks within the brush holder slidably engaging the guide rods, spring means disposed between the contact blocks and the contact brushes rel siliently biasing the Contact blocks into engagement with the guide rods and the Contact brushes into engagement with the exposed facings, and jumper leads connecting the corresponding Contact blocks and contact brushes.

Reorences Cited by the Examiner UNHED STATES PATENTS RICHARD M. WOOD, Primary Examiner.

Claims

1. IN AN ADJUSTABLE ELECTRICAL RESISTANCE DEVICE, A TUBULAR METALLIC CASING, A RESISTANCE WIRE COIL WITHIN THE CASING, A BONDING AND INSULATING MATERIAL SECURING THE COIL TO THE CASING, SAID COIL INCLUDING AT LEAST DIAMETRICALLY OPPOSED FACINGS FREE OF SAID MATERIAL, A BRUSH HOLDER SLIDABLY MOUNTED WITHIN THE CASING AND MOVABLE AXIALLY THEREIN, AND A PAIR OF CONTACTS RESILIENTLY SECURED IN THE BRUSH