WO1993018572A1

WO1993018572A1 - Reluctance machine

Info

Publication number: WO1993018572A1
Application number: PCT/GB1993/000300
Authority: WO
Inventors: Wilfred Morris
Original assignee: Wilfred Morris
Priority date: 1992-03-04
Filing date: 1993-02-12
Publication date: 1993-09-16
Also published as: GB9204667D0; CN1076807A

Abstract

The device of the present invention comprises a ferromagnetic support member (10, 20) supporting a coil or coils (11) for generating an electromagnetic field. A central sleeve (12/22) of non-ferrous material extends through aligned bores of said support frame and coils and accommodates a ferromagnetic core (13, 23), which is actually displaceable within the non-ferrous sleeve upon application of a current to the coil/s. The actual displacement of the ferromagnetic core may then be utilised as a solenoid device or alternatively in a twin coil double ended arrangement as a reciprocating electric motor.

Description

RELUCTANCE MACHINE

The present invention relates to a reluctance machine which may be employed in a variety of applications, but which is particularly suitable for converting electrical energy into a reciprocating mechanical action which may be used to drive a variety of machines, such as pumps, compressors, or to control valves.

A variety of electric machines are presently in existence ranging from the simple solenoid to various types of electric motors or generators, all of which can convert electrical energy into mechanical energy or vice versa. All types of such electrical machines use the principles of electromagnetism, in which either electric currents flowing in wires situated in the magnetic field experience mechanical force, or in which electromagnets supply force to a ferromagnetic material. Electric motors usually produce rotational motion, although such can be converted to reciprocating motion by simple mechanical means.

The various types of motor can be classified into two groups, namely "electromagnetic" machines and "magnetic" machines. The electromagnetic group includes induction, synchronous, DC, AC polyphase commutator, single phase AC commutator and repulsion motors, whilst magnetic machines include reluctance and hysteresis motors and solenoids and relays. The classification into "magnetic" and "electromagnetic" machines is a comparatively recent concept and may seem inaccurate, since machines in both classes make use of electromagnets. However, the difference between the two classes is of fundamental importance in appreciating the different uses to which motors of each class are put. Generally speaking, electromagnetic machines have a performance which improves naturally as they are made bigger, whilst magnetic machines, on the other hand, generally improve as they are scaled down to smaller sizes.

The present invention relates primarily to magnetic machines and in particular to reluctance machines. Known types of reluctance machines are utilised for example in mains driven electric clocks, in which the reluctance motor is simply a synchronous motor with the magnetised rotor replaced by a unmagnetised piece of steel so shaped that it has a number of preferred positions into which it will settle for any primary field configuration. A "preferred position" is one in which the resistance of the magnetic circuit (the reluctance) is a minimum, hence the name of this type of motor. Another type of device which utilises an unmagnetised ferromagnetic core surrounded by electromagnetic is the humble solenoid, the core being magnetically drawn into the coil when the solenoid is energised. Solenoids are widely used in a variety of applications, however, there has been little development of the basic design of solenoids nor of reluctance motors in recent years, the design of such having changed little since they were originally developed.

It is the object of the present invention to seek to provide an improved solenoid and also to develop such for the purpose of producing a reluctance motor of improved performance which, in particular, is capable of producing a direct reciprocating action.

According to the present invention there is provided an improved solenoid in which a magnetic path is provided by means of a ferromagnetic material supporting an electrically energisable coil, a bore being provided through said ferromagnetic material and being lined with a non-ferrous sleeve, within which is located a ferromagnetic core, said core having a tapered end portion.

The provision of the non-ferrous sleeve enables precise control of the "air" gap so that the magnetic flux can be concentrated with minimum leakage, the air gap being precisely controlled by careful dimensioning of the core and the non-ferrous sleeve. The non-ferrous sleeve may be of any suitable material such as copper tubing or plastics material, or the like. The tapering end of the ferromagnetic core member is preferably conical and the angle of the cone can be varied according to the desired length of stroke of the core member, when the core is energised. The conical angling of the cone, apart from enabling a greater stroke length to be achieved, also provides a braking effect on the core member to prevent such emerging fully from the supporting bore. For a 2" (5cm) bore, the stroke length is approximately 10" (25.4cm), although optimally the stroke length can be six times the bore diameter. Such a design of solenoid avoids many of the disadvantages of the prior art arrangements, in that it avoids metal-to- metal contact at the end of the stroke of the core and thereby reduces the noise of operation to a minimum, it effectively lengthens the stroke of the solenoid, and provides an even force throughout and maximises the power-to-weight ratio of the solenoid.

Also according to the present invention there is provided a reluctance machine comprising a support frame of ferromagnetic material providing a magnetic path and supporting a pair of electrically energisable magnetic field generating elements mounted back-to-back, each of said elements and the support frame having aligned central through bores through which extends a support tube of non-ferrous material within which is located a displaceable ferromagnetic core, said ferromagnetic core having a cylindrical central portion and correspondingly tapered end portions.

The present invention will now be described with reference to the accompanying drawings, in which:-

Fig. 1 illustrates an improved solenoid according to the present invention;

Fig. 2 illustrates the components of a reluctance machine according to the present invention configured for use as a reciprocating pump;

Fig. 3 illustrates the assembled form of the pump shown in Fig. 2, with the addition of cooling fins for the coils;

Fig. 4 illustrates various graphs demonstrating the force produced with respect to the position of the core for a flat-end core and for tapered-end cores for different power supplies; and

Figures 5a, b, c and d illustrate various applications of the reluctance machine of the present invention.

Referring to firstly Fig. 1, the basic concept of the present invention can be explained. A frame 10 of ferromagnetic material is provided having coil 11 mounted thereon and accommodates in a through bore provided therein, a tubular support sleeve 12 of non- ferrous material, such as copper or plastics material. Within the sleeve 12 a displaceable ferromagnetic core member 13 is located. The core member 13 has a conical end portion 14, which preferably is provided with grooves or fluting and may also be provided with an extension member 15, of non-ferrous material, as a thrust rod or the like.

When the coil 11 is energised, a field is produced causing the core member 13 to be drawn along the tube 12 so that the conical end portion 14 protrudes from the end face of the frame 10 at the opening of the sleeve 12 and the activating rod 15 may operate whatever device may be appropriate for the purpose for which it is to be utilised. The shaping of the end 14 determines the force acting upon the core 13 in accordance with the principles of Maxwells Stress Concept and the Reluctance formula:

^{R =} /μA

where μ is the permeability of the material, L is the length of the magnetic circuit, and A is the cross sectional area of the magnetic circuit. Maxwells Stress Concept states that for every degree you bend a line of magnetic force its tangential force is doubled. Thus, the tapering end portion serves to bend the lines of magnetic force to increase the tangential force applied to the core by the magnetic field. Further, since the reluctance of a magnetic circuit is the ratio of the magnetomotive force (mmf) applied to a magnetic circuit to the flux produced by the this mmf, for work to be done the reluctance must continuously reduce as the mmf is applied, so that as the diameter of the cone increases as it passes through the flux in the air gap at the opening of the bore in the frame 10, the reluctance reduces and the mmf increases to a maximum. Thus, by a combination of these two effects, effective work may be efficiently produced in a smooth and controllable manner. As can be appreciated from Figure 1, in contrast to conventional solenoid designs, the magnetic pole comprised by the displaceable ferromagnetic core member 13 actually passes through its opposite magnetic pole comprised by the portion of the frame member 10 surrounding the opening therein in contrast to conventional solenoids and as well as providing the advantages referred to above in connection with the physics of such arrangement, provides a substantially silently operating solenoid device, which is particularly advantageous when compared with existing designs, which can be very noisy.

Referring now to the arrangement shown in Figs. 2 and 3, these show respectively the components of a pump and an assembled pump employing the principles of the solenoid arrangement shown in Fig. 1. In this device, a frame member 20 effectively doubles up on the frame member 10 of Fig. 1 and accommodates a sleeve 22 in bores 25 therethrough. The core 23 has two conical end portions 24 and 24* of a similar configuration to that disclosed in Fig. 1, the sleeve 23 accommodating the core in use. To the ends of the core may be attached an appropriate flexible coupling, or alternatively, piston heads, or actuating rods accommodating piston heads for pumping fluids through pipes attached thereto. A schematic of the pump configuration is also shown in Fig. 3. The arrangement effectively combines a pair of solenoid type devices as disclosed in connection with Fig. 1 mounted back-to- back, each half of the device being alternately energised to cause the core member 23 to reciprocate within the sleeve 22. Actuating rods connected to the ends of the core 23 extend to appropriate pistons or pump members in attached pipework which may be of conventional design and not relevant for discussion here .

With regard to the shaping of the conical end portions 24 and 24' of the core 23, these may be smooth cones but preferably incorporate flutings for improved performance.

Whilst this arrangement is configured as a pump, which may pump either fluids or gases, such may be employed for any other suitable purpose where reciprocating action is required and may, for example, operate a mechanical linkage. Due to the continuously variable power requirements of this device, this will be particularly suitable for areas where mains power may not be available, since such will preferably operate as a DC device and may be powered by batteries or could be directly powered by solar cells, or by a combination of such, so that such device could be readily utilised in third world countries to drive irrigation pumps and the like. Due to the relevantly simple form of construction of the device and due to its substantially frictionless operation, the device is particularly reliable and low maintenance and is therefore particularly suitable for low technology environments, again as found in the third world.

With reference to the arrangement of Fig. 3, which shows an assembled pump incorporating the features of the present invention, in order to dissipate heat produced by the energising coils, a plurality of fins are preferably provided, which fins may be air or water cooled according to requirements. In the case of water cooling, the energy collected from the fins may be usefully used elsewhere.

The arrangement of the present invention comprises a DC pulsed, variable voltage, continuously variable speed device having a variety of potential uses.

Examples of the output of a solenoid/pump made according to such design, compared to a standard solenoid arrangement with a flat-end core, are shown in Fig. 4, for a variety of conical end portions, the area under each curve indicating the available work which may be done by the device.

Figures 5a to d illustrate various examples of the application of a reluctance machine of the present invention according to already identified proposals.

Firstly, referring to Figure 5a, this illustrates the use of the reluctance machine as a gas compressor in which through-bored pistons incorporating flap valves are connected to opposite ends of the ferromagnetic core, the pipework and valve arrangements being conventional in the art, a primary advantage of such arrangement being that such is virtually silent in operation.

Figure 5b illustrates the reluctance machine of the present invention for closed-loop fluid flow control which can be utilised to precisely control fluid flow by maintaining the position of a variable cross sectional valve member, a flow sensor device and a differential controller incorporating, for example, a microprocessor. The arrangement in Figure 5b is shown in the fully closed position, but by precisely controlling the electromagnetic field, the position of the ferromagnetic core can be precisely adjusted to control the flow rate.

Referring now to Figure 5c, this illustrates the application of the reluctance machine as a two-way needle valve in which the needle valves are provided connected to connecting rods attached to each end of the ferromagnetic core to enable switching of fluid flow under the control of a electrically controlled means. The design of the reluctance machine utilising a non- ferrous sleeve within which the ferromagnetic core is axially displaceable provides a glandless, non-leak capability and accurate "air gap" for long life.

Referring now to Figure 5d, this illustrates the application of the reluctance machine as a stamping machine in which a counterweight is connected to one end of the ferromagnetic core and a stamp is connected to the opposite end thereof, the reciprocating action of the reluctance machine enabling a highly controllable stamping operation. The control of such machine utilises a simple thyristor control circuit.

Claims

1. An improved solenoid in which a magnetic path is provided by means of a ferromagnetic material supporting an electrically energisable coil, a bore being provided through said ferromagnetic material and being lined with a non-ferrous sleeve, within which is located a displaceable ferromagnetic core, said core having a tapered end portion.

2. A solenoid as claimed in claim 1 in which the magnetic path is provided by a generally rectangular frame of ferromagnetic material within which is supported said coil.

3. An improved solenoid as claimed in claim 2 in which said non-ferrous sleeve extends through openings in opposite sides of said rectangular ferromagnetic frame member said openings being aligned with an axial opening in said coil.

4. An improved solenoid as claimed in any preceding claim in which said ferromagnetic core comprises a substantially cylindrical member having a substantially conical end portion.

5. A solenoid as claimed in any preceding claim in which the end portion of the ferromagnetic core incorporates grooves or fluting.

6. A reluctance machine comprising a support frame of a ferromagnetic material providing a magnetic path and supporting a pair of electrically energisable magnetic fields generating elements mounted back to back, each of said elements and the support frame having aligned central through bores through which extends a support tube of non-ferrous material, within which is located a displaceable ferromagnetic core, said ferromagnetic core having a cylindrical central portion and correspondingly tapered end portions.

7. A reluctance machine as claimed in claim 6 in which the support frame is of an E and I bar construction, so that electrically energisable magnetic field generating elements comprising a pair of coils mounted back to back in said support frame.

8. A reluctance machine as claimed in claim 6 or 7 in which said variable magnetic core comprises a substantially cylindrical member having substantially conical end portions and being generally symmetrical.

9. A reluctance machine as claimed in any of claims 6 to 8 in which the support tube comprises a copper or plastics material tube.

10. A reluctance machine as claimed in any of claims 6 to 9 in which cooling fans are provided for the coils.