GB2155242A - Electromagnetic actuator - Google Patents

Abstract

An electromagnetic actuator includes an annular armature 15 which is located about a stator structure 11, the armature and stator structure being of tapering form and defining complementary circumferentially extending radial pole faces 14. The stator structure carries electrical windings 13 which when energised cause relative axial movement of the armature and stator structure. The interconnecting portions 23 of the armature which connect the pole faces 16 thereof are provided with apertures 24 to allow displacement of liquid during relative movement of the armature and stator structure. <IMAGE>

Description

SPECIFICATION Electromagnetic actuator This invention relates to electrotnagnetic actuators of the kind comprising a stator structure and an axially movable armature mounted about the stator structure, the stator structure defining a plurality of circumferentially extending axially spaced magnetisable pole pieces which define radial pole faces respectively, the diameters of the pole faces increasing from one end of the structure to the other, winding means carried by the stator structure and which when supplied with electric current causes adjacent pole pieces to assume opposite magnetic polarity, said armature being of hollow cylindrical form and defining radial pole faces complementary to those of the stator structure, the armature being moved axially upon energisation of the winding means towards the other end of the stator structure.

An actuator of the kind specified is described in SAE paper 810462 published by the Society of Automotive Engineers Incorporated and is described and claimed in British patent specification 2036453B. The actuator is fast acting particularly when it is operated in a gaseous fluid. However, if it is operated in a liquid such for example as fuel, the relative movement of the armature and stator structure is impaired by the fact that during such relative movement, liquid must be displaced from between the armature and the stator structure upon energising the stator structure and liquid must be allowed to flow into said space when the windings are de-energised.

The object of the present invention is to provide an electromagnetic actuator of the kind specified in a simple and convenient form.

According to the invention in an actuator of the kind specified the interconnecting portions between adjacent pole faces of the armature are apertured to allow escape and ingress of liquid to the space between the armature and stator structure as relative movement occurs therebetween.

An example of an actuator in accordance with the invention will now be described with reference to the accompanying drawings in which; Figure 1 is a sectional side elevation of the actuator, and Figure 2 is a similar view to a smaller scale, of part of the actuator seen in Figure 1 but separated therefrom.

Referring to the drawings the actuator comprises a hollow casing 10 in which is located a stator structure 11. The stator structure defines a plurality of circumferentially extending, axially spaced, magnetisable pole pieces 12 which are integrally formed with the main body of the stator structure.

The diameters of the pole pieces reduce towards one end of the stator structure and intermediate the pole pieces are defined slots which accommodate windings 13 respectively. The windings are conveniently connected in series, the pole pieces conveniently being slotted to accommodate the interconnections between the windings, and are wound in opposite directions so that when electric current is passed through the windings adjacent pole pieces 12 will assume opposite magnetic polarity. The sides of the pole pieces which face the narrower end of the stator structure define pole faces 14 respectively and the opposite sides of the pole pieces are shaped so that magnetic leakage is kept to a minimum and also efficient use is made of the material forming the pole pieces.

Mounted about the stator structure is an armature generally indicated at 15 and which is of hollow cylindrical form being formed from magnetisable material. The general shape of the armature is complementary to that of the stator structure and it is machined to define pole faces 16 which are complementary to the pole faces 14. At one end the armature defines a right cylindrical portion 17 which forms a bearing with the housing 10 and at its narrower end, the armature defines a further right cylindrical portion 18 which has an inturned lip 19 which defines an abutment surface for a plate member 20 which is connected to an output member 21. The latter in use is connected to whatever is to be moved by the actuator for example a valve member.

When the windings 13 are energised the pole pieces 12, as previously explained, assume opposite magnetic polarity and an attraction force is created between the pole faces 14 on the stator structure and the pole faces 16 on the armature.

Axial movement of the armature therefore takes place until the pole faces abut as is shown in Figure 1 of the drawings. Such movement of course is imparted to the output member 21. During the movement, the volume of the space between the armature 15 and the stator structure 11 decreases which means that the fluid in the space has to be displaced. If the fluid is a gas then there is practically no hinderance to the movement. However, if the fluid is a liquid such for example as fuel, the movement of the armature is impaired. A similar problem exists when the windings are de-energised and the armature returns to its initial position as determined by the abutment of the armature with an end stop 22, however in this case liquid has to flow into the aforesaid space.

In order to minimise the restriction offered to movement of the armature, the interconnecting portions 23 between the portions of the armature defining the pole faces 16, are provided with apertures 24 as seen in Figure 2. In the particular example each interconnecting portion is provided with four equiangularly spaced apertures and conveniently the apertures in adjacent ones of the interconnecting portions 23 are angularly displaced.

Apertures may also be provided in the right cylindrical portion 18 and as shown, a central drilling is provided in the core structure although this is mainly intended to carry an end connection to the windings. If desired the member 20 can also be provided with apertures which not only allow rapid displacement of the liquid but also reduce the mass of the moving parts.

It will also be noted that the interconnecting portions 23 of the armature incline inwardly towards the wider end of the armature. The effect of this inclination is to reduce the effective total projected area of the armature and thereby the displacement of liquid is kept to a minimum.

Tests have shown that as compared with an armature without the apertures 24 and with interconnecting portions disposed parallel to the axis of the armature an improvement of about 20% can be obtained in the speed of operation of the armature by incorporating the modifications described.

Claims (5)

1. An electromagnetic actuator comprising a stator structure and an axially movable armature mounted about the stator structure, the stator structure defining a plurality of circumferentially extending axially spaced magnetisable pole pieces which define radial pole faces respectively, the diameters of the pole faces increasing from one end of the structure to the other, winding means carried by the stator structure and which when supplied with electric current causes adjacent pole pieces to assume opposite magnetic polarity, said armature being of hollow cylindrical form and defining radial pole faces complementary to those of the stator structure, the armature being moved axially upon energisation of the winding means towards the other end of the stator structure, the interconnecting portions between adjacent pole faces of the armature being apertured to allow escape and ingress of liquid to the space between the armature and stator structure as relative movement occurs therebetween.

2. An actuator according to Claim 1 including a drilling formed in the stator structure, said drilling communicating with said space.

3. An actuator according to Claim 1 or Claim 2 in which the end portion of the armature at said one end of the stator structure defines a right cylindrical portion which has an inturned lip defining an abutment surface for a plate member connected to an output member, said right cylindrical portion being apertured.

4. An actuator according to Claim 3 in which said plate member is provided with apertures.

5. An electromagnetic actuator comprising the combination and arrangement of parts substantially as hereinbefore described with reference to the accompanying drawings.