US2579723A - Magnetic device - Google Patents

Description

S. G. BEST MAGNETIC DEVICE Dec. 25, 1951 2 SHEETS-SHEET 1 Fixed Oct. 28, 1947 NTOR I e3 6113952 ATTORNEY Dec. 25, 195] s BEST 2,579,723

MAGNETIC DEVICE Filed 00%.. 28, 1947 2 SHEETSSHEET 2 Patented Dec. ,25, 1951 2,519,723 MAGNETIC DEVICE Stanley G. Best, Manchester, Conn., assignor to United Aircraft Corporation, East Hartford, Coma, a corporation of Delaware Application October 28, 1947, Serial No. 782.535

17 Claims. 1

This invention relates to a magnetic device and particularly to a magnetic device having an armature whose movements are substantially proportional to the voltage impressed on, or the amperage flowing through, the electromagnetic coils or solenoid.

An object of this invention is a magnetic device having a linearly movable armature which is moved, as a result of an electric current signal impressed on the electromagnetic coils or sole noid, a distance substantially proportional to the strength of the signal impressed on the coils.

Another object of this invention is a magnetic device combined with a control valve for moving said valve in accordance with, the strength of a signal impressed on the device.

Other objects and advantages will be apparent from the specification and claims, and from the accompanying drawings which illustrate what is now considered to be a preferred embodiment of the invention.

Fig. 1 is a vertical cross-section taken along the lines l-l of Fig. 4 of the proportional magnetic device connected to a control valve.

Fig. 2 is a section taken along the line 2--2 of Fig. 1. i

Fig. 9 is a section taken along the line 1-3 of Fig. 1.

Fig. 4 is a section taken along the line 4-40! Fig. l.

Fig. 5 is a force-displacement diagram for constant' current in a conventional elec'tromagnet.

Fig. 6 is a displacement-current curve for a conventional .electromagnet showing the nonlinear relation between the current and displacement.

Fig. 7 is a diagram showing the flux paths in applicant's proportional magnetic device.

Fig. 8 is a force displacement diagram for constant current in the proportional magnetic device.

Fig. 9 is a theoretical displacement-current curve for the proportional magnetic device.

Fig. 10 is a displacement-current curve showing'the type of control which has been obtained in practice.

.pymagnetic device which will have a displacement substantially proportional to the applied idl tage or current is desirable for many types di -controls, and finds particular utility in a propeller pitch control in which the input voltage or current may be proportional to a speed variation from a predetermined standard or reference speed. As the speed variations may be above or below, or both above and below, the standard,

such a solenoid should be double-acting to correct all such speed variations.

In the magnetic device shown in Fig. 1, a linearly movable armature I2 is centered between end plates 22 and 24 by means of opposed springs l8 and 20 having a linear spring rate. A cylindrical casing or yoke 26 surrounds and is concentric with the armature l2 and springs l8 and 20 and encloses a pair or concentrically arranged, annular, axially spaced electromagnets or coils Ill and I4 located concentric with and between the armature I2 and the shell 26 with their magnetic axes parallel to the armature axis. Midway between end plates 22 and 24, is a permanently magnetized washer 28 forming an. annular permanent magnet with its magnetic axes extending radial or normal to the armature axis and located between and concentric with electro magnetic coils or solenoids I0, l4 and snugly fitting within a depending flange 21 of the easing 26 and closely surrounding armature l2. Armature i2 is guided linearly along the central axis of the magnetic device by means of corrugated discs 30 and 32 which serve to support armature 12 in its axial position at all times. Disc 30 is held in position by a cap 34 and disc 32 is held in position by a washer 36. The discs are slotted as shown in Fig. 4 and a vent passage 31 connects the areas under the discs. The above assembled magnetic device is mounted on a casing 38 which is shown as the governor casing now usually provided on the nose oi airplane engines and enclosing. well known propeller pitch governor mechanism. Such a governor casing including the governor mechanism is shown in Woodward Patent 2,204,640. This patent also shows schematically how the governor mechanism is driven by the engine and hydraulically connected to the propeller. The governor shown in Fig. 1 of this application, while similar to the governor of Woodward Patent 2,204,640 discloses a double-acting valve 40 having a valve opening linearly proportional to the valve movement from the centered position shown, in place of the single-acting valve shown in the Woodward patent. Armature l2 and linearly movable valve member 40 are arranged in axial alignment and directly secured together so that each movement of the armature results in a corresponding and equal movement of valve member 40 and. a change in the valve opening linearly proportional to, the valve movement. In the device shown in Fig. l the sleeve 42 is driven by the engine in a manner similar to that shown in the Woodward patent, but the fiy-weights oi the Woodward patent are omitted and their functions are replaced by the above described magnetic device. The gear 44 is a part of the gear pump supplying oil under pressure in the well known manner to pressure line 46 from which it may be distributed by valve 40 to either line 48 or line 50. When one of lines 48 or 50 is connected with the pressure line 46, the otherline is connected by valve 40 with a drain 52. Lines 48 and 50 connect to opposite sides of a double-acting propeller pitch changing motor such as shown in Patent No. 2,402,065. Continuous rotation of sleeve 42 not only drives the gear 44, but provides rotating or sliding friction at all times between sleeve 42 and valve 40, thus reducing the friction between these two elements and rendering the governor valve more sensitive to impulses of the magnetic device.

A conventional double-acting 'electromagnet has a very non-linear displacement vs. current characteristics. Such a magnet might be similar to the one shown in Fig. 1, except that the permanent magnet shown in the center of the solenoid in Fig. 1 would be replaced by an unmagnetized shell portion of good magnetic flux conducting material. In such a conventional electromagnet, when coil II] is energized the armature I2 would move upwardly as seen in Fig. 1, regardless of the polarity of the applied voltage. When coil [4 is energized, the armature 12 would move downwardly regardless of the polarity of the applied voltage. Hence if this conventional electromagnet were utilized to control a valve such as a propeller governor valve, the speed responsive mechanism would have to apply voltage to one coil or the other coil depending upon the direction of motion desired. When coil It is energized, the magnetic flux travels across gap I5 emerging from the armature near its midpoint to complete the circle around coil Ill. The flux in traveling across gap it would pull the armature upward. For a given gap the force is proportional to the square of the current. As the armature moves upward and diminshes the gap, the fiux, and the force produced by this flux, increases. The relationship between the current, the force produced by this current, and the displacement of the armature may be shown in a curve. Typical force displacement characteristics of the conventional double-acting electromagnet for constant current are shown in solid lines in Fig. 5. From this diagram it will be noted that when coil I is energized by a current of one unit, a force of about one quarter unit is exerted which increases as the displacement increases. As a current of three units is impressed, the force varies in accordance with a curved line from about 2.25 units to about 4.5 units. Opposed springs l8 and 20 acting to center the armature I2 are linear springs, that is they have a substantially linear spring rate so that their characteristics can be represented by a straight line showing that the force exerted by the spring increases substantially proportional to the displacement. If the curve, representing the spring characteristics, is superimposed on the force-displacement curves of the electromagnet as shown by the dotted line in Fig. 5, the points of intersection will indicate the points of equilibrium between the forces exerted by the electromagnet and the forces exerted by the springs. It will be noted from Fig. that these equilibriums are very unequally spaced for equal increments of current. This feature may be shown 4 shows that equal increments of current produce very unequal increments of displacement.

A non-linear spring such as a Belleville washer, which stiiIens up as it is displaced, might theoretically be used to obtain a linear displacement-current curve. This, however, would be impractical for two reasons. First, it would be diflicult to align the Belleville spring so that its non-linearity matches that of the electromagnet and secondly, at the same time that the nonlinear functions are aligned, to additionally align the control valve in its center position. The spring should be adjusted to center the pilot valve at zero current in the electromagnet.

Ithas been found possible, by utilizing a polarized magnetic device shown'in Fig. 1, to provide a magnetic device having linear or substantially linear characteristics. In such a polarized magnetic device, current applied to either coil l0 or l4 or both coils simultaneously will displace the armature 12. The direction of displacement depends, not on which coil is energized, but on the polarity of the energized coil.

The reason for this is that the permanent magnet 28 midway between the ends of the magnetic device has low permeability for the electromagnetic flux induced by the energized coils l8, l4. The permanent magnet, therefore, acts like a large air gap with respect to the electromagnetic flux so that the electromagnetic flux travels the entire length of casing 26 and across the end plates 22 and 24 and through the entire length of the armature l2. Thus the electromagnetic flux passes through both gap l6 and gap 54. The path of the electromagnetic flux is shown by the dotted lines 56 in Fig. 7. Since the sum of these gaps remains constant when the armature is displaced, the permeance of the flux path is constant and the flux is therefore independent of the displacement of the armature.

The flux from the permanent magnet passes in both directions through the casing 26. One branch'of the flux crossing gap [6 travels back through the upper portion Fig. 1 (left-hand portion Fig. 7) of the armature to the permanent magnet. The other branch of the flux passes through gap 54 and the lower part Fig. 1 (righthand portion Fig. '7) of the armature back to the electromagnet as shown by the full lines 51 in Fig. '7. The flux 51 from the permanent magnet thus aids the electromagnetic flux in one gap, gap 54, as shown in Fig. 7 and opposes the electromagnetic fiux in the other gap, l6, asshown in Fig. '7. Since the permanent magnetic flux increases onone side and decreases onthe other side when the armature is displaced, the total flux through the permanent magnet tends to remain constant. The permeance of the permanent magnet being low compared with the remainder of the permanent magnet flux path'including the gap, renders slight any tendency of an increase of the gap in one flux path and a corresponding decrease of thegap in the parallel flux path to vary the total flux and thus accentutes the tendency of the total flux of the permanent magnet to remain constant.

It can be shown mathematically that the force exerted by the armature varies linearly with the electromagetic flux andwith the gap at one end of the armature.

If we denote the total flux through the permanent magnet @0," and assume it to be constant, and call the permanent magnet flux in gap I6 @m" and that in gap 54 em, then The force on the armature is the difference between the forces at the two ends, proportional to the squares of the fluxes. Assuming an electromagnetic flux as shown in Fig. 7 and denoting the electromagnetic flux @r,"

From the above equation it will be noted that as the permanent magnetic flux is constant and the total gap G is constant, the force exerted on the armature varies as a straight line function of the electromagnetic flux Iu and the gap 9 at one end ,of the armature. This may be represented by a series of parallel lines for the different currents as shown in Fig. 8, thus the constant current curves which also represent a constant electromagnetic flux are parallel equally spaced straight lines. Now drawing the spring characteristic curve as shown by the dotted line in Fig. 8 on top of the constant current curve to obtain the equilibrium points, it will be noted that the equilibrium points are equally spaced. Reversing the current and electromagnetic polarity only reverses the direction of displacement.

I have thus provided a magnetic device in which the displacement of the armature is proportional to the current impressed on the electromagnets. Although the coils may be connected in series, in order to provide a safety factor the two solenoids or electromagetic coils ar connected in parallel so that the burning out of either coil will not render the device inoperative. As shown in Fig. 1, the current supplied to the electromagnets may be regulated by means of a potentiometer having a contactor 58. Movement of the contactor 58 to one side of the midpoint of the potentiometer will direct current in one direction through coils I II and I4 and movement of contactor 58 to the other side of the midpoint will direct current in the opposite direction to those coils.

This device shown in Fig. 1 may be used in any of various types of control. It is particularly useful in controlling the pitch of a propeller to control the speed of an engine driving a controllable pitch propeller. By actuating the contactor 58 by. a speed responsive device the propeller pitch may be varied to maintain constant engine speed or the device may be used to maintain the speed of an engine in accordance with that of a preselected standard speed in the manner shown in Fig. 4 of Patent 2,258,462 in which one of the alternators may be driven either by an engine with which it is desired to compare the speed of the controlled engine or it may be driven by a reference device such as a constant speed motor with which it is desired to match the speed of the controlled engine.

The electrical signal imparted to the electromagnet coils can be imparted by any other suitable device such as an electronic control which will impress a voltage on the coils proportional to the variation in speed from a reference speed.

The cone shaped gap I6 (or 54) provides a decreased length of gap and an increased surface area over that which would be provided by a fiat ended armature and thus decreases the reluctance of the flux path between the armature and the end plate. The above described magnetic device provides an armature whose movements are proportional to the impressed voltage or current in the electromagnet and whose movement is linear through the center of the device. By such a construction a direct connection between the armature and the linearly movable control valve is attained so that each movement of the armature results in a corresponding and equal movement of the control valve with no opportunity for lost motion. a

While the results shown in Fig. 9 might be theoretically possible under ideal conditions, leakage effects and variations in the permanent magnet flux as the armature is displaced will cause slight departures from a perfect straight line. In the practical results obtained, it has been found, however, that magnetic devices which have been made will produce curves similar to that shown in Fig. 10 by means of which an entirely satisfactory governor control for propeller pitch can be obtained. It should be noted that in the curve in Fig. 10 the displacement is along astraight line substantially proportional to the current for a considerable displacement from the zero position. The deflection which occurs in'this curve at the higher currents and shows a larger proportional displacement for the increase in current at the high currents occurs so far out on the curve as to not interfere with the operation in practice.

What I claim as new and desire to secure by Letters Patent is:

1. A magnetic device comprising a cylindrical casing having end plates and enclosing an an nular permanent magnet, an annular electromagnetic coil or solenoid, and an axially movable armature all arranged substantially co-axial with said casing, means urging said rmature into an intermediate position between said end plates. said armature, casing and end plates completing a circuit of magnetic material, except for gaps between opposite ends of said armature and said end plates, for the magnetic flux of said electroao'ia'las magnet, said permanent magnet having one of its poles adjacent said armature and the other adjacent said casing and extending between intermediate portions of said casin and armature, said casing and armature/completing two magnetic flux flow paths for the permanent magnet flux from an intermediate portion of said armature in opposite directions through said armature, said gaps and said casing.

2. A magnetic device comprising a hollow cylindrical casing, having an axis, end plates on said casing, a pair of concentrically arranged axially spaced annular electromagnetic coils supported coaxial with, and within, said casing and having their magnetic axes substantially parallel to said axis, an annular permanent magnet arranged concentric with, and between, said electromagnetic coils, and having magnetic axes substantially normal to said casing axis, an axially movable armature located within, and substantially eo-axial with, said annuli, and between said end plates, means for urging said armature into an intermediate position between said end plates.

3. A magnetic device comprising a hollow cylindrical casing having an axis, end plates on said casing, an annular electromagnetic coil supported co-axial with, and within, said casing and having its magnetic axis substantially parallel to said casing axis, an annular permanent magnet arranged concentric with said electromagnetic coil and having magnetic axes substantially normal to said casing axis, an axially movable armature located within, and substantially co-axial with, said annuli, and between said end plates, means for centering said armature between said end plates, means outside of said casing for guiding said armature along the casing axis.

4. A magnetic device comprising a hollow cylindrical casing, end plates on said casing, a pair of concentrically arranged axially spaced annular electromagnetic coils supported co-axial with, and within, said casing, an annular permanent mag' net arranged concentric with, and between, said electromagnetic cells, an axially movable armature located within, and co-axial with, said annull, means for centering said armature between said end plates, said electromagnets being connected in parallel so as to cooperate to produce a common magnetic field, said armature, casing and end plates completing a circuit of magnetic material, except for gaps between opposite ends of said armature and said end plates, for the magnetic flux of said electromagnets, said permanent magnet having one of its poles adjacent said armature and the other adjacent said casing and extending between intermediate portions of said casing and armature, said casin and armature completing two magnetic flux flow paths for the permanent magnet flux from an intermediate portion of said armature in opposite directions through said armature, said gaps and said casing.

5. A magnetic device comprisin a hollow cylindrical casing, end plates on'said casing, an'annular electromagnetic coil whose magnetic axis extends along its coil axis supported co-axial with, and within, said casing, an annular permanent magnet located between said end plates and having one pole adjacent its inner periphery and the other pole adjacent its outer periphery and arranged concentric with said electromagnetic coil, an axially movable armature located within, and co-axial with, said annuli, and between said end plates, means includin a pair of opposed springs for centering said armature between said end plates, said centering means having a rate of increase of force with armature displacement greater than the rate of increase of pull of the permanent magnet with armature displacement.

6. A magnetic device comprising a hollow cylindrical casing, end plates on said casing, an annular electromagnetic coil supported co-axial with, and within, said casing, an annular permanent magnet arranged concentric with said electromagnetic coil, an axially movable armature located within, and co-axial with, said annuli and between said end plates, means for centerin said armature between said end plates, said armature and casing and end plates completing a circuit of magnetic material, except for gaps between opposite ends of said armature and said end plates, for the magnetic fiux of said electromagnets, said permanent magnet having one of its poles adjacent said armature and the other adjacent said casing and extending between intermediate portions of said casing and armature, said casing and armature completing two magnetic flux flow paths for the permanent magnet fiux from an intermediate portion of said armature in opposite directions through said armature, said gaps and said casing, said centering means having a rate of increase of force with armature displacement greater than the rate of increase of pull of the permanent magnet with armature displacement.

7. A magnetic device comprisin an annular electromagnetic coil, an annular permanent magnet arranged concentric with said electromagnetic coil, a metal shell including end plates, arranged concentric with, and surrounding said magnet and coil, an armature linearly movable through, and along the axis of, said magnet and coil, means at each end of said armature for decreasing the reluctance of the fiux path between said armature and end plates, said shell and armature acting as a flux path for both the permanent and electromagnets, said permanent magnet having one of its poles adjacent said armature and the other adjacent said shell and extending between intermediate portions of said shell and armature, said shell and armature completing two magnetic flux flow paths for the permanent magnet flux from an intermediate portion of said armature in opposite directions through said armature, said gaps and said shell.

8. A magnetic device comprising a casing, end plates on said casing, a movable armature guided for longitudinal movement within said casing and having its ends adjacent said end plates, an electromagnetic coil within said casing and surrounding said armature, a permanent magnet within said casing around said armature and located between the ends of said casing, between the ends of said coil, and between the ends of said armature, said permanent magnet havin one of its poles adjacent said casing and the other pole adjacent said armature.

9. Means for creating magnetic flux and a flux circuit comprising a casing, end plates on said casing, an armature within said casing and having its ends adjacent said end plates, an electromagnetic coil within said casing and surrounding said armature, a permanent magnet fixed within said casing, around said armature and located between the ends of said'casing, said coil and said armature, said permanent magnet having one of its poles adjacent said casing and the other pole adjacent said armature, said casing, end plates and armature providin two separate main flux paths for the permanent magnet flux from the permanent magnet, one path from the permanent magnet including the casing, armature and casing, one end plate, the armature, and the other end plate back to the casing,

10. .A control mechanism comprising a casing having end plates, a control armature arranged for longitudinal controlling movement between the end plates and, with the casing, completing a circuit of magnetic material except for the gaps between opposite ends of said armature and said end pieces, a permanent magnet arranged with one of its poles adjacent said armature and located between and connecting intermediate portions of said casing and armature and, with the casing and armature, completing two separate magnetic flux circuits of magnetic material except for the gap, each circuit including a portion of the armature, the gap between the end of the armature and the respective end piece, the end piece, a portion of the casing and the permanent magnet, an electromagnetic coil arranged to produce magnetic flux in said first mentioned circuit and resilient means for centering said armature.

11, A magnetic device comprising a casing, having end plates, an armature spaced from and movable between said end plates to inversely vary the spacing at each end but maintain the total spacing constant, resilient means having a substantially uniform spring rate centering said armature between said end plates, means creating a steady non-reversing magnetic flux and directing said flux into two fiow paths through said casing, armature, and end plates, each path including the space at a respective end of said armature, a portion of said flux flow paths utilizing a common path, an electro magnet for creating a flux flow through a single path including said armature, said casing and said end plates, variable in quantity and direction for moving said armature in accordance with the extent and direction of said electromagnetic flux, said common path having a lower permeance for said electromagnetic flux than said casing.

12. A magnetic device comprising an armature of magnetic material, and a yoke of magnetic material overlapping the ends of the armature, and establishing two gaps, one at each end of the armature, between said armature and said yoke, said armature, yoke and both gaps. defining a closed flux path, said armature being longitudinally movable toward said yoke to increase one gap and equally decrease the other gap, means having a substantially uniform rate of change of force for each unit of displacement centering said armature within said yoke, means creating a steady flux flow in two paths, said paths extending from an intermediate portion of said armature in opposite directions through said armature, said gaps and said yoke to an intermediate portion of said yoke, and back through the flux creating means to said intermediate portion of said armature, and means for creating an independent variable flux flow through said closed path.

13. A magnetic device as claimed in claim 12 in which varying the flux flow through said closed path will move said armature from said central position a distance linearly proportional to said variable flux flow, in combination with a control valve havin an axially movable valve element and having a valve opening linearly proportional to the movement of said element from a central position, and means connecting said armature and said valve element to render said valve element axially movable by said armature a distance linearly proportional to the movement 01' said armature.

14. A device as claimed in claim 12 in which the means for creating the independent variable flux flow is an electromagnet and in. which the armature is movable in opposite directions from a centered position by reversal of current in said electromagnet, the variable flux assisting the steady flux through one gap and opposing the steady flux through the other gap to move said armature in one direction and upon said reversal of current, opposing the steady flux through said one gap and assisting the steady flux through the other gap to move said armature in the opposite direction.-

15. An electrically operated control valve movable from a central position a distance linearly proportional to the electrical inputthereto comprising a cylindrical casing having end plates and enclosing an annular permanent magnet having one pole adjacent its inner periphery and the other adjacent its outer periphery, an annular electromagnetic coil having an axially extending magnetic axis, and an axially movable armature extending between said end plates and movable axially to increase the gap between the armature and one end plate and equally decrease the gap between the armature and the other plate, all arranged substantially coaxial with said casing, said permanent magnet extending between an intermediate portion of said armature and an intermediate portion of said casing, means having a uniform spring rate urging said armature into a central position, whereby selectively electrically energizin said electromagnet will move said armature from said central position a distance linearly proportional to the electrical input, an axially movable valve element, having a valve opening linearly proportional to its movement from a central position, arranged substantially coaxial with said armature and means connecting said armature and valve element to render said valve element axially movable by said armature a distance linearly proportional to the movement of said armature,

16. A valve as claimed in claim 15 in which said valve element and said armature are mov able in opposite directions from said central position and are moved in one direction. from said central position by flow of current in one direction in said electromagnetic coil and are movable in the opposite direction from said central position by reversal oi. current in said electromagnetic coil, the magnetic flux of said coil assisting the magnetic flux of said magnet through said armature adjacent one end plate and opposing the magnetic flux of said magnet through said armature adjacent the other end plate to move said armature in one direction and upon said reversal of current, opposing the flux of said magnet adjacent one end and assisting the flux 01' said magnet adjacent said other end to move said armature in the opposite direction.

17. A magnetic device comprising an armature of magnetic material, and a yoke of magnetic material overlapping the ends of the armature and establishing two gaps, one at each end 01 the armature, between said armature and said yoke, said armature, yoke and both gaps, defining a closed flux path, said armature being longitudinally movable toward said yoke to increase one gap and equally decrease the other gap, means having a substantially uniform rate of change of force for each unit of displacement centering said armature with said yoke, a permanent magnet, located between said armature and said yoke and intermediate the ends of said armature with one pole adjacent said armature and the other adjacent said yoke, said armature and yoke providing two magnetic fluxdlovy paths for said permanent magnet flux froifan intermediate portion of said armature in opposite directions through said armature, said gaps and said yoke, and means for creating an independent variable flux flow through said closed path.

STANLEY G. BEST.

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

Number Number 15 398,331 1 ,184

12 UNITED STATES PATENTS Name Date Haines Jul 19, 1898 Simon Oct. 24, 1911 Bliss May 7, 1912 White July 2, 1918 Campbell June 21, 192i Lederer July 5, 1927 West May 23, 1939 Lakates July 25, 1939 Kennedy -1 July 1, 1947 FOREIGN PATENTS Country Date France of 1909 Great Britain of 1883

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