US2725439A - Magnetic coupling device - Google Patents

Description

H. G. NEWBOULT MAGNETIC COUPLING DEVICE Nov. 29, 1955 2 Sheets-Sheet 1 Filed June 29, 1951 Attorney Nov. 29, 1955 H. G. NEWBOULT MAGNETIC COUPLING DEVICE 2 Sheets-Sheet 2 Filed June 29, 1951 Attorney United States Patent MAGNETIC COUPLING DEVICE Henry Grattan Newboult, Slough, England, assignor to Ronald Trist & Co. Limited, Slough, England Application June 29, 1951, Serial No. 234,274

Claims priority, application Great Britain June 30, 1950 7 Claims. (Cl. 20087) Magnetic coupling devices can be used with advantage in the control of steam boilers and other containers of liquid because one magnet can be mounted on one side of a wall of a non-magnetic container connected to the steam and water spaces of the boiler or the like and another can be mounted outside the wall. If the first magnet is connected to a float or the equivalent so that it is moved (usually by rocking about a horizontal axis), the second magnet will also be moved, either with snap action as a result of magnetic repulsion or in step with the first magnet as a result of magnetic attraction. To make the most efiicient use of the available magnetic forces the gap between the two magnets should be as small as possible, and so the outer or driven magnet is commonly mounted in a casing fixed to the wall of the liquid container in which the inner or driving magnet is mounted. Now it the container wall is hot, and particularly if the device is used in the control of. a high-pressure steam boiler, the heat is conducted to the casing of the driven magnet, which often contains a heatsensitive device operated by the driven magnet. For instance, if this casing encloses an electricswitch actuated by the driven magnet the contact elements of the switch, and some kinds of electrical insulation, may be damaged or destroyed by the high temperature, and if the casing encloses a valve controlling, say, the flow of compressed air to some device or instrument, the lubricant necessarily present in the valve may likewise be adversely affected.

If the container within which the driving magnet is mounted is at a very low temperature, the conductance of heat away from the driven magnet may also be deleterious by producing condensation on the contacts of a switch operated by the driving magnet or by damaging the oil of a lubricated valve so operated. Again, in some installations it may be necessary for physical reasons to space the driven magnet and the device it operates away from the container wall.

It is an object of this invention to provide a magnetic coupling device which can be used in conjunction with a hot or cold wall without risk of damage to any device operated thereby.

It is another object of this invention to provide an improved construction of coupling device comprising a plurality of magnetic members.

A further object of the invention is to construct a device capable of transmitting energy magnetically at a distance.

With these and other objects in view a device according to this invention includes not only driving and driven magnetic members but also one or more relay magnetic members interposed between the driving and driven members in such a way that the driving magnet acts on and moves a relay magnetic member, which in turn acts on and moves the driven magnet or, if there is more than one relay member, the next relay magnetic member and so on until the last relay member acts on and moves the driving magnet. Since there is some loss of 2,725,439 Patented Nov. 29, 1955 power at each air gap, it is preferred to employ simply one relay member.

I prefer to use a device comprising three bar magnets mounted end to end, though each such magnet may be composite in that it consists of two or more magnets placed end to end in contact with one another and mounted to rock as a unit.

The preferred construction according to the invention will now be described by way of example with reference to the accompanying drawings in which Figure l is a plan of the device, and Figure 2 is a side view of it, mainly in section on the line 11-11 in Figure l.

The device shown serves to control an electric switch 1 in accordance with the rise and fall of a float 2 inside a container 3 in the form or" a chamber connected to the steam and water spaces of a boiler. The device includes a fitting 4 which is let into a hole in and bolted to a wall 5 of the chamber 3, so as to make a fluid-tight joint with the edge of the hole. The fitting 4 carries two arms 6 extending into the chamber 3 and carrying a pin 7 which constitutes a horizontal pivot for the float 2. The float has a tail 3 in which a driving bar magnet 9 is housed so that one pole of this magnet moves in an are close to the inner wall of the fitting i.

The switch 1 is mounted in a casing ltd which also contains a driven bar magnet 11 carried by a housing 12 which is mounted on pivot pins 13. When the magnet rocks, one end of the magnet 11 moves in a recess 14 in the casing 10, the end positions of the magnet being determined by the sides of the recess, and two blade contacts 15 make and break contacts 16 and 17 forming part of the switch. The casing ill is secured by tie rods 18 to the fitting 4, and it has a forked extension 19 carrying a pin 20. This pin serves as a pivot for a third bar magnet 21, one end of which rocks in a recess 22 in the fitting 4 between end positions determined by the sides of the recess and the other end of which rocks close to the wall of the recess 14.

The magnet 21 is composite, consisting of two bar magnets end to end with a short soft-iron cylinder 23 between them, all surrounded by a sleeve 2 The pin 20 actually passes through the soft-iron 23, thus avoiding the need for piercing the magnet. In addition, this arrangement lengthens the magnet 21 and so leads to the driven magnet being further away from the hot wall.

The provision of the relay magnet 21 eliminates all risk of damage by heat from the hot wall to any heatsensitive device operated by the driven magnet ii.

The polar arrangement of the magnets is such that the third magnet 21 is moved by magnetic attraction and the driven magnet 11 by magnetic repulsion. The reason is that if, as is most convenient, the three magnets are of substantially the same magnetic power the torque exerted by the driving magnet 9 on the third magnet 22 should be greater than the counteracting torque produced by the driven magnet 11, and therefore the distance be tween the re-acting poles should be smaller at the driving-magnet end than at the driven-magnet end of the magnet 21. If the magnet 21 is attracted by the driving magnet, the adjacent poles of the two magnets will always be as close together as the structural features of the device and container wall will permit, whereas at the other end of the magnet 21 the distance between the adjacent poles will be larger until the critical position is reached at which the driven magnet moves with snap action. Other polar arrangements may be used, however, provided that the driven magnet will always respond to the movements of the driving magnet.

The invention is not limited to the use of magnets as described above and shown. The essential advantage of reducing the action of heat from the hot wall on the driven magnet 11 can be obtained if instead of using a permanent magnet 21 a bar of magnetic material is used. Moreover, in an arrangement of the kind shown with the relay magnet 21 a permanent magnet, either or both of the driving and driven magnets may be made of magnetic material without being permanent magnets.

Yet again, other arrangements may be used. For instance, the driving magnet may rise and fall in a verti cal path, causing the relay magnet either to rock, as in the arrangement illustrated, or to slide in a horizontal path towards and away from the vertical path in accord ance with the proximity of the one or other pole of the driving magnet to the end of the third magnet close to the vertical path.

Moreover, bar magnets arranged end to end need not be in a straight line. For instance, a relay magnet may be arranged in the Way illustrated in relation to a driving magnet but the driven magnet may be mounted to reel; about a horizontal axis at 90 to that illustrated.

I claim:

1. in a magnetic coupling device for transmitting motion from a heated location to a second location Without any accompanying transfer of heat, a first magnetic member mounted for rocking motion, a second magnetic member also mounted for rocking motion spaced from said first member by an air gap and magnetically coupled to said first magnetic member, and a third magnetic member also mounted for rocking motion spaced from said second member by an air gap and magnetically coupled to said second magnetic member, said second member responding to movements of said first member by way of said first magnetic couple and said third member responding to movements of said second member by way of said second magnetic couple, said third member being effectively isolated by means of an intervening air space from the heat emanating from said heated location.

2. in a magnetic coupling device of the kind in which a magnetic member mounted outside a wall of a container which is heated in use is driven as a result of magnetic action by a driving magnetic member mounted inside the container wall, the improvement comprising a movable magnetic relay member mounted outside the container wall and interposed and magnetically coupled between the other two members with air gaps formed between the relay member and the other two members so that the driven member is spaced away from the hot wall and thermally isolated therefrom by means of an intervening air gap.

3. In a magnetic coupling device comprising a driving magnet mounted inside and a driven magnet mounted outside a wall of a container which is heated in use and heat-sensitive device operated by the driven magnet. the improvement comprising a relay magnet mounted outside the container wall between the driving and driven magnets with air gaps formed between the relay magnet and the driving and driven magnets respectively and the relay magnet forming magnetic couplings with said driving and driven magnets so that the relay magnet is moved by the driving magnet, as a result of magnetic coupling, and in turn the driven magnet is moved by the relay magnet as a result of magnetic coupling, whereby said driven magnet is effectively thermally isolated from said heated container.

4. A device according to claim 3 in which all the magnets are bar magnets arranged end to end and mounted to rock about parallel axes transverse to the bars; said relay magnet and said driven magnet being separated by an air space.

5. A device according claim 4 in which the driven magnet is mounted in a casing secured to but spaced away from the container wall and the relay magnet is mounted in an extension of this casing; an electric switch in said casing operated by said driven magnet; said electric switch being thermally isolated from said heated container Wall by virtue of the air space therebetween.

6. In a magnetic coupling device, three bar magnets arranged end to end each for rocking motion about an axis transverse to the length of the bar, the adjacent poles of the first and second of said magnets spaced by an air gap and attracting one another magnetically to form a first magnetic couple and the adjacent poles of said second and third magnets spaced by an air gap and repelling one another magnetically to form a second magnetic couple.

7. In a magnetic coupling device in which a driving magnet is located inside a container that is heated in use; a driven magnet, and an electric switch operated thereby, said driven magnet and said electric switch being located in a casing remote from said container, so as to be thermally isolated therefrom; a relay magnet, operatively located between said driving magnet and said driven magnet so as to provide a means for transmitting motion therebetween said relay magnet being separated from said driving and driven magnets by first and second air gaps respectively, whereby said electric switch is operated as a result of the motion of said driving magnet, while being protected from the heat emanating from said heated container.

References Cited in the file of this patent UNITED STATES PATENTS 246,718 Cable Sept. 6, 1881 2,012,153 Bates Aug. 20, 1935 2,204,161 Shephard June 11, 1940 2,371,511 Faus Mar. 13, 1945 2,475,684 Weckerly July 12, 1949 2,520,935 Hubbell Sept. 5, 1950 2,522,815 Early Sept. 19, 1950 2,577,165 Thorsheim Dec. 4, 1951 FOREIGN PATENTS 476,114 Great Britain Dec. 2, 1937 553,168 Great Britain May 11, 1943

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