US2209368A - Eddy current relay - Google Patents

Description

July 30, 1940. c. c. wHrrTAKER EDDY CURRENT RELAY Filed` March 25, 1958 2 Sheets-Sheet l July 30, 1940. c. c. wHlTTAKER EDDY CURRENT RELAY Filed March 25, 1938 2 Sheets-Sheet 2 wlTNEssEs: 907.6%

Patented July 30, 1940 UNITED STATES 'PATENT OFFICE EDDY CUBREN T RELAY Pennsylvania Application March 25, 1938, Serial N0. 198,087

6 Claims.

My invention relates, generally, to speed-responsive relays and, more particularly, to relays of the eddy current Aor magnetic drag type.

While numerous devices which operate on the well-known magnetic drag principle have been utilized as speedometers for automobiles and other vehicles, none of the foregoing devices develop suiiicient torque to make them suitable for use as speed-responsive relays having contact members which must carry a relatively high current.

An object of my invention, generally stated, is to provide a speed-responsive relay of the magnetic drag type which shall be simple and eilicient in operation and which may be economically manufactured and installed.

A more specific object of my invention is to provide a relay of the magnetic drag type which shall be capable of' developing a relatively high torque.

Another object of my invention is to provide a magnetic drag relay having substantially constant operating characteristics.

A further Object of my invention is to provide a magnetic drag relay having relatively low eddy current losses.

A still further object of my invention is to provide a relay of the magnetic drag type which is readily adaptable to a wide variety of applica- Other objects of the invention will be explained fully hereinafter or will be apparent to those skilled in the art. v

In a relay-constructed in accordance with the invention, eddy currents are set up in a rotatable disc by a rotating magnet of special construction, thereby causing a magnetic drag on the disc. The magnet is composed of an alloy having desirable magnetic properties, and is reinforced mechanically by a non-magnetic casting which encircles the magnet and is mounted on the driving shaft.- A contact member is carried by the shaft of the disc and is biased to a predetermined position by a spring, the force of which is overcome by the torque of the disc when the magnet is driven at a predetermined speed.

For a fuller understanding of the nature and objects of the invention, reference may be had to the following detailed description, taken in conjunction with the accompanying drawings, in

which:

Figure 1 is a view, partially in elevation and partially in section, of a relay embodying my invention, the sectional view being taken along the line I-I of Fig. 2;

(Cl. 20o- 92) Y Fig. 2 is a View, insection, taken along the line II-II of Fig. 3; and

Fig. 3 is a view, in end elevation, of the relay structure, a. portion of the cover being broken away to show the arrangement of the contact i members of the relay.

Referring now to the drawings, and particularly to Fig. 2, the speed-responsive relay shown therein is of the magnetic drag type and comprises a rotatable disc III, which may be com- 10 posed of copper, aluminum or other suitable nonmagnetic material, a' rotating magnet having two sections I I and I2, which are disposed on opposite sides of the disc I0 to rotate in planes parallel to the disc, and a contact member I3 (see ll Fig. 3) actuated` by the disc I0.

The disc I0 is mounted on one end of a shaft I4 carried by ball bearings I5 which are enclosed in a housing I6 supported by a partition member II of the relay structure. The wall I1- is zo preferably composed of brass or other non-magnetic material to prevent leakage of the flux established by the magnets II and I2.

The contact member I3 is carried by an arm I8 secured to the other end of the shaft I4 and 25 a spring I9 is disposed to bias the arm I8 to a position in which the contact member I3 engages a contact member 2I mounted on a bracket 22 that is secured to the wall I'I. When the torque of the disc I0 is suilicient to overcome the bias- $0 ing force of the spring I9, the contact member I3 is disengaged from the contact 2l and actuated into engagement with a contact member 23 that is mounted on a bracket 24 also secured to the wall II. The tension of the spring I 9 may 35 be adjusted by means of a screw 25 to vary the speed setting of the relay.

In this manner, the contact members of the relay may be utilized to perform switching operations in response tothe speed at which the 40 rotating magnets II and I2 are driven. In accordance with a principle well known in the art, eddy currents are set up in the disc I0 by the flux produced by the magnets and the rotation of the magnets causes a magnetic drag or torque on the 45 disc which is proportional to the speed of rotation of the magnets.

Either one or two magnets may be utilized, depending upon the amount of torque required for a particularv application of the relay. As 50 shown, the magnet II comprises a circular plate 26 having a hole 21 at its center, and four equally spaced shoulders 28 at its periphery which constitute four magnetic poles. The magnet I2 is similar to the magnet II, and has four poles 29 5;

disposed on the opposite side of the disc I from poles of opposite polarity of the magnet II.

The magnets II and I2 are composed of a special aluminum and nickel alloy which has desirable magnetic properties, but is weak mechanically, making it unsafeto rotate at high speeds. In order to overcome this diiculty, the magnet II is mounted in a circular casting 3|, which is shrunk on the magnet, and also secured on the end of a driving shaft 32, which is coaxial with the shaft I4, thereby supporting the magnet I I and rotating it in a plane parallel to the disc I0 at the speed of the shaft 32. The casting 3| may be composed of bronze or any other nonmagnetic material having the desired mechanical strength.

When two magnets are utilized, as shown in the drawings, the second magnet I2 also has a bronze ring 33 shrunk on it. The two bronze rings are then bolted together by means of stud bolts 34 with non-magnetic spacing members 35 and 36 placed between them to determine the air gap between the two' magnets. If the drag of one magnet is sumcient, the magnet I2 'is replaced by a piece of soft steel which functions as an armature for the magnet- I I.

In this manner, whether one or two magnets are utilized, there is no eddy current loss except that which occurs in the conductor disc I0, which is necessary and desired. In other speed-responsive devices of the magnetic drag type having a rotating magnet and a xed armature for the return path of the magnetic flux, undesirable eddy current losses occur in the xed armature.

'Ihe conducting disc I0 is made as a at plate, which is the most simple structure, thereby permitting the material of which the disc is composed to be varied to provide relay characteristics suitable for various applications. In general, the material having the lowest resistance provides maximum torque on the disc shaft and copper or aluminum are suitable for most applicatio'ns.

However, the heat generated in the device while in continued operation causes the resistance of the disc to change when it is composed of copper or aluminum. The change in resistance changes the operating characteristics of the relay which is undesirable in certain cases.

When it is necessary to provide a -relay having constant characteristics, the disc may be composed of an alloy having a zero temperature coeflicient of resistance. 'Ihere are numerous alloys on the market which have a fine temperature.

characteristic and a relatively low specic resistance. The at disc structure makes it possible to utilize these alloys which, because of. their toughness, are diicult to shape into other forms of drag members, such as the cup members usually provided in speed-responsive devices ofthe magnetic drag type.

'I'he rotating magnets and the disc are enclosed by a housing 31 and the partition I1 which is bolted to the housing 31 by bolts 38. The housing 31 is also provided with an integral bearing bracket 39 which supports the shaft 32 for the rotating magnets, VThe shaft 32 is mounted on ball bearings 4I enclosed by the cylindrical bearing bracket 39 which is provided with a removable cap 42. One end of the shaft 32 extends through the cap 42 and may be connected directly to a rotating machine or it may be geared or belted to the machine. Provision is made for lubricating the bearings 4| and felt washers 43 and 44 are provided for retaining the lubricant in the housing 39. A threaded collar 45 is provided for adjusting the shaft 32 in the bearings 4I,

On account of the very strong magnets and small air gaps, it is necessary to'have the operating parts completely enclosed to prevent iron particles, such as brake shoe dust, being attracted to the magnets. For this reason, a breather hole 46 covered by a felt filter 41 is provided in the housing 31. 'I'he filter 41 issecured to the housing 31 by a plate 48 and rivets 49. 'I'he plate 48 is provided with a hole 5I to permit air to pass through the lter 41. 'I'he breather hole, 46 prevents air being forced out or sucked in through the ball bearings with each change in temperature of the imprisoned air; The form of the magnets is such that the pole pieces 28 and 29 function as paddle-wheel fans and circulate the air within the-case to cause maximum radiation during the operation of the device.

As described herelnbefor'e, the shaft I4, which carries the disc Ill, is supported by ball bearings I mounted in a -housing I6. In order that the disc I0 may be centered between the magnets II and I2, the housing I6 is threaded into a sleeve 52 which is pressed into the Wall I1. A hole at the bottom of the housing 31, normally closed by a. pipe plug 53, permits a view of the position of the disc I 0 in the air gap during assembly. The housing I6 is shifted axially until the disc is in the correct position and then locked by means of screw 54. This adjustment may be made by removing a cover 55 which protects the relay contact members. As shown in Fig. 2, the cover 55 is attached to a flanged ring A56 by bolts 51, the ring 56 being secured tothe housing 3.1 by the bolts 38.

It will be understood that the contact arrangement can be varied greatly to suit different conditions, and that additional contacts may be readily provided, if desired. Furthermore, the relay may be designed to operate at various speeds or a's a speed governor. It may also be utilized as a rotation .detector relay by so arranging the contact members that one contact makes for either direction of rotation as soon as rotation occurs.

I do not desire to be restricted to the specific embodiment of my invention herein -shown and described, since it is evidentA that it may be changed and modified without departingvfrom the spirit and scope of my invention as dened in the appended claims. Y y

I claim as my invention:

1. A speed-responsive relay comprising a rotatable metal disc, a shaft for supporting said disc, a rotating non-magnetic member, a shaft for supporting said-rotating member independy ently of said disc, said shafts being disposed coaxially, a magnet disposed within the non-magnetic member and rotating therewith to cause a magnetic drag on the disc, said magnet being mechanically supported by said non-magnetic member, and switching means carried by the shaftof said disc.

2. A speed-responsive relay comprising' a rotatable metal disc, a shaft for supporting said disc, a rotating non-magnetic member, a shaft -for supporting said rotating member independently of said disc, said shafts being disposed c0- axially, a magnet disposed within the non-magnetic member and rotating therewith to cause a magnetic drag on the disc, said magnet being mechanically supported by vsaid non-magnetic member, means lfor-moving one of said shafts axially to adjus't the position of said disc relative to the magnet, and a contact member actuated by the disc.

3. A speed-responsive relay comprising a rotatable metal disc, a shaft for supporting said disc, a rotating non-magnetic member, a shaft for supporting said rotating member independently of said disc, said shafts being disposed coaxially, a magnet disposed within the non-magnetic member and rotating therewith to cause a magnetic drag on the disc, said magnet being mechanically supported by said non-magnetic member, a contact member actuated by the disc, and means for biasing said contact member to a predetermined position.

4. A speed-responsive relay comprising a rotatable non-magnetic disc, a magnet disposed at one side of the disc to rotate in a plane parallel to the disc, a similar magnet disposed at the other side of the disc and rotating with the first magnet to cause a magnetic drag on the disc, a non-magnetic member encircling the magnets and rotating therewith, both of said magnets being mechanically supported by said non-magnetic member, and switching means actuated by the disc 5. A speed-responsive relay comprising a rotatable metal disc, a rotating non-magnetic member disposed co-axially with the disc, a magnet disposed within the non-magnetic member and rotating therewith at one side of the disc, a similar magnet disposed at the other side of the disc, a non-magnetic ring encircling the second magnet, means for securing the ring to the rotating non-magnetic member, thereby causing the magnets to produce a magnetic drag on the disc, and switching means actuated by the disc.

6. A speed-responsive relay comprising a rotatable metal disc, a rotating non-magnetic member disposed co-axially with the disc, a magnet disposed within the non-magnetic member and rotating therewith at one side of the disc, a similar magnet disposed at the other side of the disc, a non-magnetic ring encircling the second magnet, means for securing the ring to the rotating non-magnetic member, thereby causing the magnets to produce a magnetic drag on the disc, a housing for enclosing the rotating members, means for adjusting the position of the disc between the magnets from the outside of the housing, and switching means actuated by the disc.

CHARLES C. W'HITI'AKER.

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