Electromagnetic Thrusters

Abstract

Solenoid devices intended primarily to exert a force closely proportional to energizing current and particularly adapted for use in fluid pressure and flow controlling systems. The device includes an annular housing of magnetic material enclosing a nonmagnetic bobbin on which a coil is wound. An armature reciprocable within the bobbin in proximity to a pole piece of the housing exerts a force on a plunger extending through the pole piece. The controlled fluid may communicate with the interior of the bobbin; one end of the bobbin is closed and the other end is sealed to the housing so that the fluid may not escape from the device.

Description

My invention is directed to electromagnetic thrusters; that is, to devices which are intended to exert a force which is a function, preferably a linear function, of the energization of a coil or solenoid which is a part of the device. The thrusters according to my invention are particularly adapted for use in engine controlling systems and in general in systems in which the force exerted may be a means for providing an interface between an electrical control system and a fluid flow or pressure regulating system. The solenoid devices according to my invention are of structure which is particularly adapted to leakproof operation, to linearity of response, and to economical fabrication and compact dimensions.

Generally speaking, in its preferred embodiment, the thruster comprises a cup-shaped housing, having an annular pole piece closing one end of the housing, and having a bobbin mounted within the housing defining a guide for an armature reciprocable within the bobbin. The armature is attracted to the pole piece upon energization of a solenoid wound around the bobbin. The fluid may be displaced past the armature in case of its movement, and the bobbin is sealed to the pole piece to contain fluid within the enclosure defined by the bobbin. Force is transmitted from the armature by a push rod or plunger extending through the pole piece.

The nature of my invention and its advantages will be more fully apparent from the succeeding detailed description of preferred embodiments of the invention and the accompanying drawings.

FIG. 1 is a longitudinal sectional view of an electromagnetic device embodying the invention.

FIG. 2 is a similar view of a modified device.

FIG. 3 is a fragmentary view of the application of the device of FIG. 2 to valve operation.

FIG. 4 is a graph illustrating the force characteristics of the device as a function of current.

Referring first to FIG. 1, the electromagnetic force exerting device comprises a cup-shaped housing 2 defining a generally cylindrical internal chamber 3 recessed as indicated at 4 at the open end of the housing. An annular pole piece 6 fitted in the recess 4 substantially closes the open end of the housing. The pole piece includes an external boss 7 and an internal boss or pole 8 extending into the housing along its axis. The housing and pole piece are made of a suitable magnetic material such as soft silicon core iron such as is used for transformer cores. The solenoid or coil 10 which generates the magnetic force is wound on a bobbin or spool 11 made of a suitable nonmagnetic material. The preferred material is a glass fiber reinforced acetal resin derived by polymerization of formaldehyde sold by du Pont under the trademark Delrin 570. The bobbin includes a flange 12 which abuts the inner surface of the pole piece 6 and is impinged between it and a shoulder 14 at the bottom of recess 4. It includes a central hollow cylindrical portion 15 and a second flange 16.

The cylindrical portion defines internally a guideway for a magnetic reciprocable armature 18, also of soft iron. The end of the bobbin remote from pole piece 6 extends into and is located radially by a bore 19 in the closed end of the housing. This end of the bobbin is closed by an integral wall 20. The portion of the bobbin adjacent the pole piece 6 fits over the pole 8 so that the bobbin is located radially by its piloted fit over this pole and with the interior of bore 19 and is located axially between the pole piece 6 and the housing 2.

The armature 18 is approximately of cylindrical shape with a conical forward end 22 which is disposed adjacent to a corresponding conical recess 23 in the pole, the device defining an air gap between the surfaces 22 and 23. There is also an air gap between the armature and the housing at the bore 19. Armature 18 is tapped to receive the threaded end 24 of an actuating rod 26, the latter being reciprocable in a suitable bore 27 along the axis of the pole piece. Preferably, the armature has two shallow flanges 28 and 29 which bear against the interior of the bobbin cylinder 15. These flanges are partially cut away as indicated at 31 and 32 to permit fluid to flow freely past the armature when it moves. Assuming that the actuating rod 26 is exposed to fluid, the fluid may enter the device through the bore 27 and fill the space around the armature. It is prevented from leaking by an O-ring 34 disposed between the forward face of the bobbin and the pole piece. It is essential to fast transient response that no significant fluid pressure differential is generated by shifts of the armature. If slow response is acceptable, some fluid damping of armature movement by fluid in the cylinder 15 may be desirable.

The boss 7 of the pole piece may be mounted in a suitable recess in a device which is to be controlled and the actuator may be held in place by suitable clamping means engaging a flange 35 on the housing. Electrical lead-in wires 36 extend through an opening in the housing.

As will be understood, if magnetizing current is passed through leads 36 to the solenoid 10, the resulting magnetic flux flows through the housing 2, armature 18, and pole piece 6, and intends to draw the armature to the right, as illustrated, into contact with the pole piece. For any given position of the armature, the force thus exerted is substantially proportional to the magnetomotive force, which again is substantially proportional to current as long as the saturation of the iron does not significantly vary the reluctance of the magnetic circuit. If the armature moves, the force increases as the surfaces 22 and 23 approach each other.

The device is intended primarily, however, for use in a substantially stationary condition in which force is modulated rather than position. This modulation may be accomplished by varying the magnitude of a constant current or by varying the average current as, for example, by duty cycle control of current flowing through the solenoid.

Actuating rod 26 should be of a nonmagnetic material such, for example, as stainless steel type 302 or 303, in order to minimize any tendency of the flux to pass through the actuating rod into the pole piece 6 which would tend to cause binding or friction in the actuator.

The actuating rod 26 may be coupled to any device. For example, it might actuate a valve or oppose the flyweights in a governor for variable speed setting.

FIG. 2 illustrates a thruster which may be essentially the same as or identical to that in FIG. 1 except for the structure of the armature and the actuating rod or tappet which transmits the movement or force of the armature to the exterior of the thruster. This device comprises a housing 2, pole piece 6, solenoid 10, bobbin 11, and O-ring 34 as described above. The armature 42 may be essentially the same as that described above except that it has no interior bore and the conical tip 22 terminates in a flat end 43.

The actuating rod 44 in this case is a tappet having a rounded inner end 46 engageable by the end surface 43 of the armature and having a flat head 47 at the exterior of the pole piece. This head 47 when biased by the armature may press against any desired device.

FIG. 3 illustrates the application of the device of FIG. 2 to the closing of a valve providing controllable resistance to flow of fluid from a source or cavity. As shown there, the housing 2 is mounted so that the pole piece 6 abuts a body or valve block 54 which defines a recess 55 into which the external boss 7 of the pole piece is piloted. An O-ring 56 prevents leakage around the boss 7. The recess 55 defines a valve chamber having an entrance 58 and containing a spherical valve member 59 which may engage a seat 60 at the end of the entrance passage 58. The head 47 of the actuating rod 44 may bear against the sphere to urge it with varying degrees of force against the seat 60. Fluid which passes through the valve may exhaust through a drain or other exit passage 62. The solenoid may be held in place by a suitably attached retaining ring 64. As will be apparent, if fluid is introduced through the passage 58, the resistance to its escape will be a function of the force exerted by the armature 42 and, therefore, the average current going through the solenoid 10 of the valve device may maintain the pressure communicating with the inlet 58 at a particular desired value as a function of this current. If the supply of fluid through passage 58 is limited, this regulation may be accomplished with slight travel of valve member 59. The valve is thus well-adapted to regulate a pressure to control further hydraulic devices as a function of solenoid current.

FIG. 4 is a graph illustrating current force characteristics of a device as illustrated. With a sufficiently wide air gap, as illustrated in the curve labeled A, the relationship of force exerted to current in a particular example is essentially linear. As illustrated in curve B, with a much narrower air gap, the curve is less linear because of the effect of saturation. However, above the point C on the curve, the increment of force as a function of current is substantially constant. There are two air gaps in series, one at each end of the armature.

Among the advantages of the thruster device as illustrated herein are the substantially constant or consistent relation of force to current, a fast response to transients, and negligible hysteresis; that is, variation of the force exerted between increasing and decreasing current flows.

The particular thrusters illustrated are shown to scale and have a housing about 11/2 inches in diameter and a solenoid of 600 turns.

The detailed description of the preferred embodiment of the invention for the purpose of explaining the principles thereof is not to be considered as limiting or restricting the invention, since many modifications may be made by the exercise of skill in the art.

Claims

1. An electromagnetic force-exerting device comprising, in combination, a housing; a pole piece abutting the housing including a hollow boss extending into the housing; an annular bobbin in the housing piloted at one end of the bobbin on the said boss, the bobbin including a portion providing a pilot connection between the other end of the bobbin and the housing and locating with the boss the axis of the bobbin; a solenoid on the bobbin; an armature reciprocable within the bobbin, the armature and boss having confronting portions defining an air gap; an actuating rod slidable within the said boss actuatable by the armature; means closing the said other end of the bobbin against escape of fluid; and means providing a fluid seal between the bobbin and the pole piece; the actuating rod and armature having sufficient clearance from the pole piece and bobbin for flow of fluid upon reciprocation thereof; the housing, pole piece, and armature being of a magnetic material and the bobbin and

2. An electromagnetic force-exerting device comprising, in combination, a generally cylindrical housing; a pole piece abutting the housing at one end including a hollow boss extending into the housing; an annular bobbin in the housing including a cylindrical portion piloted at one end of the bobbin on the said boss, the cylindrical portion providing a pilot connection between the other end of the bobbin and the housing and locating with the boss the axis of the bobbin; a solenoid on the bobbin; an armature reciprocable within the cylindrical portion of the bobbin, the armature and boss having confronting portions defining a radial air gap; an actuating rod slidable within the said boss actuatable by the armature; means closing the said other end of the cylindrical portion against escape of fluid; and means providing a fluid seal between the cylindrical portion and the pole piece; the actuating rod and armature having sufficient clearance from the pole piece and bobbin for flow of fluid upon reciprocation thereof; the housing, pole piece, and armature being of a

3. An electromagnetic force-exerting device comprising, in combination, a generally cylindrical housing; a pole piece abutting the housing at one end including a hollow boss extending into the housing; an annular bobbin in the housing piloted at one end of the bobbin on the said boss, the bobbin including a portion extending into an opening in the housing providing a pilot connection between the other end of the bobbin and the housing and locating with the boss the axis of the bobbin; a solenoid on the bobbin; an armature reciprocable within the bobbin and spaced radially from the housing by the bobbin, the armature and boss having confronting portions defining an air gap; an actuating rod slidable within the said boss actuatable by the armature; means forming part of the bobbin closing the said other end of the bobbin against escape of fluid; and means providing a fluid seal between the bobbin and the pole piece; the actuating rod and armature having sufficient clearance from the pole piece and bobbin for flow of fluid upon reciprocation thereof; the housing, pole piece, and armature being of a magnetic material and the bobbin and actuating rod being nonmagnetic.