GB2158648A - Electromagnetic devices - Google Patents

Abstract

An electromagnetic device includes members 31, 34 relatively movable along one direction under the force of a magnetic field from windings 33, 36. The members are separable and assembled by relative movement other than along said one direction. As shown, member 34 rotates relative to member 31 and the members are assembled by inserting member 34 into member 31. Alternatively, linear displacement of an armature may be provided and the stator may be arranged in two parts for ease of assembly. The device may be used in an electro-fluid control valve (Figure 8). <IMAGE>

Description

SPECIFICATION Electromagnetic devices This invention relates to electromagnetic devices having two relatively movable magnetisable members and a winding through which electric current can be passed to produce a magnetic field to effect the relative movement. More particularly the invention relates to such devices in which the magnetisable members are shaped to engage one another when an attempt is made to separate them.

UK Patent Specification 1504873 describes an electromagnetic device, illustrated for example in Figure 1 of the Specification and reproduced here as Figure 1, in which the magnetisable members are a core 10 and an annulus 13 provided with interengagable screw threads allowing appreciable relative movement in an axial direction. The screw thread produces a turning force in addition to the desired axial force. Furthermore the only waay of producing such devices is to "screw" the core into the annulus.

No technique has been described to avoid this problem.

It is an object of the present invention to provide a constructional technique for such devices which overcomes these problems.

According to the invention there is provided an electromagnetic device in which magnetisable members relatively movable along one direction by a magnetic field on energisation of the device engage one another on extreme movement in the one direction which members are assembled into the device by relative movement other than that of said one relative movement.

Conveniently one of the members is constructed in two or more parts so that these can be separated from each other, and the other member, by said other movement.

A winding may be provided on that member which is constructed in two or more parts and the winding may also be in two or more parts. Advantageously the magnetic flux of the magnetic field does not link the parts of the one member.

In one form the device may be of a rotor and a stator providing the relatively movable members with lengthwise ribs on both rotor and stator providing the engagement, with the one direction of relative movement being rotational and the other direction of movement being axial to separate the members.

Embodiments of the invention will now be described with reference to the accompanying drawings in which: Figure 1 is the above-mentioned prior art of Figure 1 of UK Patent Specification 1504873, and Figure 2 illustrates one form of the magnetic field of this device, Figure 3 is a view of an embodiment of the invention to provide a rotary action.

Figures 4, 5, 6 and 7 are views of embodiments of the invention to provide a displacement action, and Figure 8 is a further embodiment, shown in section, for electro-fluid control.

Considering the prior art shown in Figures 1 and 2 the core 10 is held ina cup 12to a mounting 11 so that an annulus 13 can move axially in cup 12 under the action of a magnetic field, between faces 21 and 22 (Figure 2), produced by energising windings 18, 19 with currents in the directions shown conventionally. Projections 16 and 17 and recesses 14 and 15 are respectiveiy formed by a two-start screw thread on the core 10 and annulus 13. The core is assembled to the annulus, after the windings 18, 19 are applied, by "screwing" the core into the annulus along the direction of movement when a magnetic field acts.

Figure 3 shows an embodiment of the invention in which a stator31 is provided with ribs 32 and windings, some of which are indicated at 33,36 and an armature 34 with ribs 35 is supported for a small angular rotation in the stator 31. The rib and coil configuration is similar to that shown in Figure 2 for the screw-threads of the prior art in its operation but the important advantage of the embodiment according to the invention is that the construction is much simpler than that of the prior art as the armature is simply pushed into the stator to assemble the device. Also the stator and rotor are both elongate forms of uniform cross-section and can be produced by extrusion or other simple and economic techniques whereas the two members of the prior art devices are complex in form.Furthermore windings 33 can easiiy be produced by conventional means as they form simple rectangular coils which can be pushed on to the ribs 32. Conveniently the stator is fixed, to simplify electrical connection, and the armature moves. The armature may be supported in a simple bush bearing or by a simple flexure spring, not shown. The working air gap is indicated at AG and the working face at WF.

Figures 4a and 4b show another embodiment of the invention with a simple constructional form. This is the inverse of that in Figure 3 having the wound, fixed stator 41 inside the movable armature 44, with respective ribs 42,45 and windings on stator 41, some of which are indicated at 43,46, as before. A further advantage of this construction, as in the previous embodiment (Figure 3), is that prewound simple coils, as shown in Figure 4b, can be placed over ribs 42 to form the windings 43,46.

Figure 5 shows another embodiment of the invention providing simple construction of a device to produce linear displacement of an armature, rather than rotational movement as in the two previous embodiments. Two similar stators 51,56 are provided with ribs such as 52 which carry windings such as 53 and can be supported in such a way as to position the two stators at a predetermined separation. These windings can be preformed coils as mentioned above and shown in Figure 4b. The armature 54 is a plate or sheet with ribs 55 on both sides. The armature is assembled as in a sandwich, between the two stators with the ribs engaged to produce the magnetic circuit shown in Figure 2 and to allow a longitudinal freedom of movement relative to the stator. This movement is the same as that of the prior art device in operation.Current direc tions are shown conventionally in Figure 5 for the windings. The windings are preferably formed so that they fill the space available between the ribs, but not all are shown, to avoid confusion in the drawing.

An important feature of the device shown in Figure 5 and following embodiments is that the magnetic circuit does not link the parts of the stator being effective when confined to the respective parts. Also any small air gap due to slight mis-match of the parts does not matter as the flux does not pass through the gap.

Figure 6a shows a sectional scrap-view and Figure 6b a part-sectional elevation and an end view of an embodiment of the invention as a generally cylin dricai device to produce axial displacement The stator is in two halves 61 and 66 shaped to fit together and each carrying windings, 63, 67. Again the magnetic circuit is confined to respective stator halves. The armature 64, is a tube carrying rib rings 65. The stator halves are assembled around the armature and clamped together, not shown, to produce the assembly shown in Figure 6. Simple prewound coils as shown in Figure 6b can be used.

Figure 7 shows an embodiment which is a variant of Figure 6 in that the stator is of cylindrical form again spiit along line A-Ainto two halves 71,76 for easy assembly around an armature 74. Coils in this case are simple prewound ring-shaped windings.

They can also be used alternatively in the embodimenu shown in Figure 6a.

The embodiments illustrated in Figures 3,4,5,6 and 7 can all have the armature supported on simple flexure springs or supported in bearing bushes to permit the required displacement.

Figure 8 shows an electro-fluid control valve for pneumatic or hydraulic fluids, with particularly effective use of the magnetic material in the armature. A disc-shaped armature 84 is placed between circular stators 81 and 86, the stators being confined and positioned by external parts (not shown). The stators have ring-shaped grooves leaving ring ribs such as 82,88. The simple sandwich construction and winding arrangement permits a thin armature since each winding has a respective part of the armature and the armature carries the total flux in separate parts.

Afluid-pressure supply to ports 96,97 is controlled in a generally known manner at orifices 93,94 by the action of the armature 84 and holding gap HG to connect either supply to drain port 95 and block the flow from the other supply to produce appropriate flows at utilisation outlets 91,92, all in known manner. Pressure or suction, of gas or liquid, may be used, in known manner.

Alternatively an arrangement of similar electromagnetic construction to that shown in Figure 7 can be effected. In this aiternative arrangement the disc-shaped armature 84 is attached to or drives a rod or rods positioned along the axis of the device thereby providing an external mechanical displacement In certain applications only one stator such as 81 together with its windings 83 need be provided to cause a unidirectional displacement of the armature 84 with the reverse or contrary displacement displacement being provided by external means or by an internal spring arrangement.

The above arrangements provide simple constructions to achieve compact efficient electromagnetic devices with relatively movable members. In particular the windings are generally on the outer parts and therefore more easily cooled permitting larger currents to be used in a given winding. Afurther important advantage is that as the construction avoids the need to have parts of screw thread form the turning torque arising from the inclined position of the thread is avoided and this reduces the waste of the limited winding energy in unwanted effects and unwanted directions of movement, improving the efficiency of the device. This is very important for relays and like devices to avoid overheating of the winding.

Claims (6)

1. An electromagnetic device in which magnetisable members relatively movable along one direction by a magnetic field on energisation of the device engage one another on extreme movement in the one direction which members are assembled into the device by relative movement other than that of said one relative movement.

2. A device according to Claim 1 in which one of the members is constructed in two or more parts so that these can be separated from each other, and the other member, by said other movement.

3. Adevice according to Claim 2 in which a winding is provided on that member which is constructed in two or more parts and the winding also is in two or more parts.

4. A device according to Claim 1 or Claim 2 in which the magnetic flux of the magnetic field does not link the parts of the one member.

5. A device according to Claim 1 including a rotor and a stator providing the relatively movable members with lengthwise ribs on both rotor and stator providing the engagement, with the one direction of relative movement being rotational and the other movement being axial to separate the members.

6. An electromagnetic device substantially as herein described with reference to Figures 3 to 8 of the accompanying drawings.