US1947828A

US1947828A - Variable resistance device

Info

Publication number: US1947828A
Application number: US583016A
Authority: US
Inventors: Arthur O Codney; Heights Cleveland; David J Somerville
Original assignee: Willard Storage Battery Co
Current assignee: Willard Storage Battery Co
Priority date: 1931-12-24
Filing date: 1931-12-24
Publication date: 1934-02-20
Anticipated expiration: 1951-02-20

Description

7 Feb. 20, 1934.

. A. O. CODNEY El AL VARIABLE RESISTANCE DEVICE Filed Dec. 24. 1931 .1110 671607". ARTHUR 0. Canuev 1.2-4. 4- 0A WD J. SOMERVILLE Patented Feb. 20, 1 934 UNITED STATES PATENT OFFICE VARIABLE RESISTANCE DEVICE Application December 24, 1931 Serial No. 583,016

7 Claims.

This invention relates to variable resistance devices for use in electric circuits, and more particularly to improved contact means for such devices.

An object of our invention is to provide a contact device of the type mentioned, which is of improved and simplied construction, easily operated and very durable.

Another object of our invention is to provide a novel construction for a rheostat contact of the type embodying a spring, wherein the arrangement is such that the spring operates at a relatively cool temperature and remains serviceable for a long period of time.

Other objects and advantages of our invention will be apparent from the following description, when taken in conjunction with the accompanying sheet of drawings, wherein Fig. 1 is a side elevational view of a variable resistance device embodying our invention.

Fig. 2 is a sectional plan view thereof, taken substantially on line 2--2 of Fig. 1.

Fig. 3 is a sectional view taken on line 33 of Fig. 1.

Fig. 4 is a detail elevational view of the contact element, and

Fig. 5 is an end elevation thereof.

In the accompanying drawing to which detailed reference will now be made, we have illustrated electrical resistance apparatus embodying the contact means of our invention; and although we have shown but one structural embodiment ofour device, it will be understood, of course, that our invention may assume various other forms.

As indicated in the drawing, our contact device, which may also be referred to as a terminal device, is of the sliding type and is intended for use principally with rheostats of the wire wound type. Rheostats of this kind are commonly used for changing the resistance value of various electrical circuits, such as battery charging circuits and the like. We are aware that sliding contacts have been used with rheostats of this kind, but in the constructions heretofore proposed the contact devices have been short lived and generally unsatisfactory, principally by reason of the fact that the spring, which presses the contact element against the resistance element, is positioned relatively close to the latter element and is subjected to destructive heating thereby.

In Figs. 1 and 2 of the drawing we have shown a wire wound rheostat with which our contact device 11 cooperates. The rheostat may be of any suitable construction, and as herein shown, may comprise a tubular insulating body 12, having resistance wire 13 wound thereon. Any suitable mount or frame may be provided for the rheostat, such as the spaced frame members 14.

For slidably supporting the contact device 11 in operative relation to the resistance element, we provide a guide bar 15, which is preferably round in cross-sectional shape, and which is formed of suitable conducting material. This guide is arranged with its axis substantially parallel to the axis of the insulating body 12, and may be supported in any appropriate manner, such as by being mounted in the frame members which support the resistance element 13. Suitable means may be provided for connecting the device in an electric circuit, such as the terminals 16 and 17 mounted on one of the frame members 14. One end of the resistance wire of the rheostat is connected to'terminal 16 and the other terminal is connected to the guide bar 15, by a suitable conductor 18, so that the rheostat may be connected in the desired relation in an electric circuit by attaching conductors 19 and 20 to the terminals 16 and 17.

The contact device itself comprises a tubular body 22 formed of conducting material and having pivotal and sliding connection intermediate its ends with the guide bar 15. This connection may be formed by providing aligned openings through the wall of the body in which opening the guide bar 15 slidably engages. As shown in this instance, we prefer to form these aligned openings as axially extending slots 23. We mount the tubular body on the guide bar with the latter extending through the aligned openings and so that the body is disposed to extend substantially radially outwardly from the resistance element 90 13, or, in other words, with its axis normal to the axis of the guide bar 15, as shown in Figs. 1 and 2. When disposed in this position, it will be noted that the slotted end 24 of the tubular body extends outwardly from the guide bar in a direction away from the resistance element 13, while the unslotted end 25 of the tubular body extends inwardly of the guide bar and towards the resistance element.

A contact element 26, formed of suitable COR-r ducting material, is provided for engagement with the resistance element 13, and is arranged for movement relative to the tubular body. This contact element is preferably formed with a stem 1 or plunger portion 27 which is slidable in the inner or unslotted end 25 of the tubular body, and a head or shoe portion 28 which engages the re sistance element 13. This shoe portion is of such shape and size as to afford the desired area of no contact, the particular shape of this portion being dependent upon the shape of the resistance element with which it cooperates. In this instance, the shoe portion is shown as having a concave contact face 29 of substantially the same radius of curvature as the outer surface of the resistance element.

In accordance with our invention the stem portion of the contact element is slotted for a portion of its length, as shown in Figs. 4 and 5, and is so proportioned that when slidably mounted in the end 25 of the tubular body, this slotted portion straddles the guide bar 15, and its outer end 30 extends outwardly into the slotted end 24 of the tubular body for a short distance, as indicated in Figs. 1 and 2. For pressing the shoe portion of the contact element against the resistance element 13, we arrange a coil spring 31 within the tubular body; As shown in Figs. 1 and 2 this coil spring is housed and guided in the outer or slotted end 24 of the tubular body, and cooperates with the stem portion of the contact element. One end of this spring engages a metallic bearing disc 32 provided at the forked end of the stem portion, and the other end of the spring engages abutment means provided on the body. This abutment means may be of any desired form, and may comprise a bearing disc 33 retained in the opening of the tubular member by a transversely extending pin 34.

From the arrangement described it will be seen that when the device is assembled on the guide bar, the arcuate bottom portion of the slots 23 of the tubular body provides bearing surfaces 35 which engage the outer surface of the guide bar 15. The coil spring interposed between the stem portion of the contact element and. the abutment means of the tubular body, tends to cause relative sliding movement between these elements, whereby the bearing surfaces 35 are frictionally pressed against the surface of the guide bar and the concave surface of the shoe portion 28 is frictionally pressed against the outer surface of the resistance element 13. This biasing action of the spring results in proper electri cal contact being made between the element 26 and the resistance element 13, and also results in sufiicient friction being created between the tubular body and the guide bar, and between the contact element and the resistance element, to retain the contact device in any desired position of adjustment along the axis of the rheostat. The concavity of the shoe portion of the contact element aifords an interengagement between the latter and the resistance element, which, under the influence of the spring 31, tends to cause a self-centering of the contact element on the resistance element, and prevents the contact element from being easily jarred out of engagement with the resistance element.

In our contact device, as herein illustrated and described, it will be noted that the coil spring 31 is positioned outwardly of the guide bar 15 and is relatively remote from the resistance element 13, so that only a small portion of the heat generated in the latter will be transmitted to the spring. Consequently the operating temperature of the spring can be maintained at a relatively low value which will not destroy the temper of the spring or impair its efficiency. It will also be noted that the outwardly projected portion of the tubular body affords a protective housing for the spring and also serves as a convenient handle portion by means of which the contact device may be slid along the guide bar.

Although in illustrating our invention we have shown the rheostat 10 arranged with its axis in a vertical position, it should be understood, however, that the position of the rheostat is unimportant, and that our contact device will operate efficiently regardless of the particular manner or position in which the rheostat may be supported. Likewise, it is immaterial to our invention whether the guide bar be supported on the frame of the rheostat, as shown in the drawing, or whether it be provided with an independent support.

While we have illustrated and described the apparatus of our invention in a detailed manner, it should be understood, however, that we do not intend to limit ourserves to the precise details of construction and arrangement of parts illustrated and described, but regard our invention as including such changes and modifications as do not involve a departure from the spirit of the invention and the scope of the appended claims.

Having thus described our invention what we claim is:

1. In a contact device for a resistance element, the combination of an elongated guide bar adjacent said element, a body mounted on said guide bar for sliding movement along the latter, said body being elongated and arranged to extend transversely of the guide bar with the ends of the body extending in opposite directions from said guide bar, movable contact means associated with one of the ends of said body including an actuating portion extending transversely of said guide bar, and a spring associated with the other end of said body and engaging said actuating portion, said spring being effective for irictionally pressing said body against said guide and for yieldingly pressing said contact means against said resistance element.

2. In apparatus of the character described the combination of a resistance element, a guide member adjacent thereto, a tubular body slidably mounted on said guide member with its axis extending transversely of the axis of the latter, a contact engaging said element and having a stem slidable in one end of said body, said stem having a slotted portion extending transversely of said guide member, and a spring mounted in the other end of said body and engaging said stem.

3. The combination with a resistance element having a guide member adjacent thereto, oi a contact device adapted to be moved along said guide member and comprising an elongated body disposed with its axis substantially normal to the axis of said guide member, said body being provided with an opening through which said guide member extends, a contact engaging said element and having a portion slidable relative to said body, said portion having a slot in registration with the opening of said body, abutment means on said body, and a spring interposed between said slidable portion and said abutment means, said spring being efiective for frictionally pressing said body against said guide member and for yieldingly pressing said contact against said resistance element.

4. The combination with a. resistance element having an elongated member adjacent thereto, of a contact device slidable along said guide member and comprising a tubular body extending transversely of the guide member and having a slotted portion through which said guide member extends, said body being disposed with the slotted portion thereof extending outwardly from said guide member in a direction away from said element, a contact engaging said element and having a stem portion slidable in said tubular body, and a spring disposed in the outwardly extending portion of said body, said spring having portions cooperating respectively with said stem portion and with said outwardly extending portion of the body whereby said contact is biased against said element and said body is biased against said guide member.

5. The combination with a resistance element having an elongated guide member adjacent thereto, of a terminal device slidable along said guide member and comprising a body, a contact movable relative to said body, said body and contact being arranged to extend transversely of said guide member with corresponding ends thereof extending outwardly for different distances from said guide member and in a direction away from said element, and resilient means cooperating with said ends and tending to cause relative axial movement therebetween whereby said body is held in engagement with said guide member and said contact is yieldingly pressed against said element.

6. The combination with a resistance element having a guide member adjacent thereto, of a contact device adapted to be moved along said guide member and comprising a body, a contact slidably mounted on said body, said contact and said body being provided with forked ends and arranged with said forked ends straddling said guide member and extending outwardly therefrom for different distances and in a direction away from said element, and resilient means cooperating with said forked ends and tending to cause relative separating movement therebetween whereby said body is held in engagement with said guide member and said contact is yieldingly pressed against said element.

7. In a device of the character described the combination of a resistance element, an elongated support adjacent said element, a hollow body having pivotal connection with said support, said pivotal connection being such as to permit sliding movement of said body along said support, a contact slidable in said hollow body between said pivot and said element, and a spring disposed in said hollow body for biasing said contact toward said element, said contact having means thereon shaped for cooperation with said element to normally prevent rotation of said body relative to said support.

ARTHUR O. CODNEY. DAVID J. SOMERVILLE.