WO2000016357A1

WO2000016357A1 - Electromagnetic actuator

Info

Publication number: WO2000016357A1
Application number: PCT/IB1999/001579
Authority: WO
Inventors: Philip Edward Fugate; James Clifford Irwin
Original assignee: Kelsey Hayes Co
Current assignee: ZF Active Safety US Inc
Priority date: 1998-09-12
Filing date: 1999-09-13
Publication date: 2000-03-23
Anticipated expiration: 2001-03-12
Also published as: GB9819844D0; AU5878599A

Abstract

An electromagnetic actuator comprising a body (11), a plunger (12) received by the body for movement relative thereto, an electromagnet (13, 16, 19) energisable to displace the plunger (12) axially relative to the body (11) from an axial rest position to an actuated position, and first and second abutment components (33, 35) on said plunger and said body respectively, said abutment components being aligned in an angular rest position of the plunger relative to the body so as to abut to prevent axial displacement of the plunger towards said actuated position, said plunger and said electromagnet being so arranged that energisation of the electromagnet with the plunger in its angular rest position generates a torque moving the plunger angularly relative to the body from said angular rest position to displace said abutment components relative to one another and generating an axial loading on the plunger to move the plunger axially from its axial rest position to its actuated position.

Description

ELECTROMAGNETIC ACTUATOR

This invention relates to an electromagnetic actuator of the kind including a plunger movable between a rest position and an actuated position by energisation of an electromagnet winding associated with the plunger.

It is known to oppose inadvertent movement of the plunger of such an actuator from the rest position to the actuated position by means of a spring or other resilient biasing device the loading of which is overcome by the electromagnetic force acting on the plunger whan the electromagnet winding is energised. There are however situations in which resiliency biasing the plunger to its rest position is inadequate reliably to prevent inadvertent movement of the plunger to its actuated position, for example if vibration or sudden shock loading is applied to the actuator, and it is an object of the present invention to provide an actuator wherein this problem is obviated in a simple and convenient manner.

In accordance with the present invention there is provided an electromagnetic actuator comprising a body, a plunger received by said body for movement relative thereto, an electromagnet energisable to displace the plunger axially relative to the body from an axial rest position to an actuated position, first and second abutment components on said plunger and said body respectively, said abutment components being aligned in an angular rest position of the plunger relative to the body so as to abut to prevent axial displacement of the plunger towards said actuated position, said plunger and said electromagnet being so arranged that energisation of the electromagnet with the plunger in its angular rest position generates a torque moving the plunger angularly relative to the body from said angular rest position to displace said abutment components relative to one another, and generating an axial loading on the plunger to move the plunger axially from its axial rest position to its actuated position.

Preferably said plunger includes at least one axially extending spline and said electromagnet includes a flux plate having an aperture through which said plunger extends, said aperture including at least one radially inwardly projecting tooth, said tooth defining, when the electromagnet is energised, a magnetic pole to which said spline is attracted thus generating torque displacing the plunger angularly relative to the electromagnet body.

Desirably said plunger includes a plurality of equiangularly spaced axially extending splines , and said aperture includes a plurality of equiangularly spaced radially inwardly projecting teeth.

Preferably said plunger extends axially within a central bore of a bobbin on which the winding of said electromagnet is wound, one of said abutment components being an end face of said spline, or one of said splines, and the other of said abutment components being a protrusion on the wall of the bore of the bobbin

Conveniently said protrusion includes a circumferentially extending shoulder defining said other abutment component, and an axially extending wall against which the spline abuts when its end face abuts the shoulder. Desirably the actuator includes resilient means urging said plunger angularly and axially to a rest position relative to said body.

One example of the invention is illustrated in the accompanying drawings wherein:-

Figure 1 is a diagrammatic perspective view of an actuator,

Figure 2 is an exploded perspective view of the actuator of Figure 1 ,

Figure 3 is a cross-sectional view of the bobbin of the electromagnet of the actuator of Figures 1 and 2, and

Figures 4 and 5 are diagrammatic representations illustrating co-action between the bobbin wall and the plunger of the actuator of Figures 1 and 2.

Referring to the drawings the actuator comprises a body 1 1 incorporating an electromagnet, and a plunger 12 movable by energisation of the electromagnet.

The body 1 1 includes a U-shaped ferromagnetic frame 13 the parallel limbs 14, 15 of which are bridged at their free ends by a ferromagnetic flux plate 16. Positioned within the frame 13 with its axis parallel to the limbs 14, 15, is a moulded synthetic resin bobbin 1 7 having a cylindrical bore 18 extending therethrough. An electromagnet winding 19 is wound on the bobbin 1 7 in conventional manner, the winding 19 being wound between the opposite end flanges 21 , 22 of the bobbin 17. The base wall of the frame 13 is formed with a centrally disposed aperture

23 which serves to locate one axial end of a cylindrical ferromagnetic core

24 received within one axial end of the bore 18 of the bobbin 17. The flux plate 16 is formed with a centrally disposed generally circular aperture 25 of larger diameter than the diameter of the bore 18 of the bobbin 1 7. The wall of the aperture 25 includes a plurality of equiangularly spaced, radially inwardly extending teeth 26 the tips of which define parts of a cylindrical surface generally co-extensive with the wall of the bore 18 in use. The outer face of the end flange 22 of the bobbin 1 7 is formed with a plurality of axially extending, integral pegs 27 which protrude upwardly through the gaps between the teeth 26 of the flux plate 16 to locate the bobbin 1 7 angularly relative to the flux plate. In Figure 1 , a clearance is present between the teeth 26 and the pegs 27. The size of the clearance in Figure 1 has been exaggerated for clarity, and in practise the pegs 27 may be a tight fit within the gaps between the teeth 26.

The plunger 12 comprises an elongate rod of ferromagnetic material having a frusto-conical end region 28 at one axial end for co-operation with a frusto-conical recess 29 in the core 24. At its opposite axial end the plunger 12 includes an integral head formation 31 designed for cooperation with the mechanism to be actuated by the actuator in use. Intermediate the head formation 31 and the end region 28 the outer cylindrical surface of the plunger 12 is formed with a plurality of integral, equi-angularly spaced, axially extending splines 32 equal in number to the number of teeth 26 on the periphery of the aperture 25 of the flux plate 16. At their ends adjacent the frusto-conical end region 28 of the plunger, the splines 32 define radially inwardly extending shoulders 33 (Figures 4 and 5).

The outer faces of the splines 32 define parts of a cylindrical surface concentric with, and of slightly smaller diameter than, the cylindrical surface of the bore 18. Thus in the absence of any other interaction between the bore 18 and the plunger 12 the plunger is slidable and rotatable freely within the bore 18. However, the wall of the bore 18 is formed with an axially elongate projection 34 which is integral with the bobbin 17 and projects radially inwardly into the bore 18. The width of the projection 34 measured circumferentially of the bore 18 is such that the projection 34 can be received between an adjacent pair of splines 32 of the plunger 12. Thus when the projection 34 lies between a pair of splines the plunger can still slide freely in an axial direction but is held against rotation relative to the body 1 1 by engagement of the projection 34 between adjacent splines 32 (Figure 4). Intermediate its ends the projection 34 is formed with a transverse step defining a shoulder 35 presented towards the end of the bobbin 17 formed with the flange 22. It will be recognised that the plunger 12 can be moved outwardly of the bore 18 to a position at which the shoulders 33 of the splines align with the level of the shoulder 35 of the projection 34 and at this point in the movement of the plunger 12 the plunger can be rotated relative to the bore 18 so that a shoulder 33 at the end of the spline seats on the shoulder 35 of the projection 34 and the wall of the spline engages the wall of the narrower region 36 of the projection 34 (Figure 5). In this position any attempt to move the plunger axially into the bore 18 is resisted by abutment of the shoulder 33 at the end of the spline with the shoulder 35 of the projection 34. In use the plunger 12 is urged to an angular and an axial rest position relative to the body in which the narrow region 36 of the projection 34 is engaged between a pair of adjacent splines, and one of the splines has its shoulder 33 seated on the shoulder 35 of the projection. The plunger 12 is conveniently urged towards the rest position by spring action which applies axial and angular loading to the plunger relative to the body 1 1. The spring may form part of the actuator assembly, but it is to be understood that in some instances the plunger may be urged to its rest position by a spring or other device within the mechanism actuated by the actuator.

It will be understood that in the rest position of the plunger should any attempt be made to move the plunger axially into the body 1 1 , towards its actuated position, then such movement will be resisted by abutment of the shoulder 33 at the end of the relevant spline 32 and the shoulder 35 of the projection 34. Furthermore, in this position the narrower region 36 of the projection 34 forms an angular abutment resisting further movement angularly of the plunger relative to the body 1 1 under the action of the means urging the plunger to its rest position.

Energisation of the winding 19 of the electromagnet of the body generates a flux path, an air gap of which extends angularly between one or more of the splines 32 and one or more of the teeth 26 of the plate 16, so that upon energisation of the winding 19 the teeth 26 act as magnetic poles attracting the splines 32. The magnetic attraction results in a torque being applied to the plunger 12 to rotate the plunger relative to the body in a direction to move the shoulder 33 of the spline 32 angularly off the shoulder 35 of the projection 34, aligning the gap between the adjacent splines 32 with the projection 34 so that the plunger can move axially into the body. The flux path of the electromagnet arrangement also includes an air gap between the frusto-conical end region 29 of the plunger and the core 24 and thus an axial loading is applied to the plunger to draw the plunger into the body 1 1 to its actuated position.

It will be understood therefore that energisation of the electromagnet removes the latching of the plunger and the body and draws the plunger into the body.

It will be recognised that in a simplistic arrangement the plunger could have a single spline, and the aperture 25 of the plate 16 could have a single tooth 26, but such an arrangement would necessitate specific angular location of the plunger, the plate 16, and the bobbin 1 7 relative to one another during assembly of the actuator. The provision of equiangularly spaced teeth 26 and equi-angularly spaced splines 32 reduces the need for specific angular location of the plunger relative to the plate 16 and bobbin 17 during assembly.

The actuator described above may find use in a number of different applications, but one particular application is the locking mechanism of the disc drive for a portable computer. Energisation of the electromagnet winding 19 withdraws the plunger 12 into the body thus freeing the head for operation. When the computer is switched off the electromagnet of the actuator is de-energised and the plunger 12 returns to its rest position physically locking the head of the computer disc drive against movement thereby greatly minimising the risk of damage to the drive through careless handling of the portable computer. The latching arrangement which prevents the plunger being moved inwardly inadvertently from its rest position, unless energisation of the electromagnet takes place, provides a much more robust locking arrangement for the hard-drive than is the case with, for example, an actuator which relies solely on spring balance to hold the plunger in its rest position.

Claims

1. An electromagnetic actuator comprising a body (11 ), a plunger (12) received by the body for movement relative thereto, an electromagnet (13, 16, 19) energisable to displace the plunger (12) axially relative to the body (11) from an axial rest position to an actuated position, and characterised by first and second abutment components (33, 35) on said plunger and said body respectively, said abutment components being aligned in an angular rest position of the plunger relative to the body so as to abut tc prevent axial displacement of the plunger towards said actuated position, said plunger and said electromagnet being so arranged that energisation of the electromagnet with the plunger in its angular rest position generates a torque moving the plunger angularly relative to the body from said angular rest position to displace said abutment components relative to one another and generating an axial loading on the plunger to move the plunger axially from its axial rest position to its actuated position.

2. An electromagnetic actuator as claimed in claim 1 characterised in that said plunger (12) includes at least one axially extending spline (33) and said electromagnet includes a flux plate (16) having an aperture (25) through which said plunger extends, said aperture including at least one radially inwardly projecting tooth (26), said tooth defining, when the electromagnet is energised, a magnetic pole to which said spline (33) is attracted thus generating torque displacing the plunger angularly relative to the actuator body (1 1 ).

3. An electromagnetic actuator as claimed in claim 2 characterised in that said plunger (12) includes a plurality of equiangularly spaced axially extending splines (33), and said aperture (25) includes a plurality of equiangularly spaced radially inwardly projecting teeth (26).

4. An electromagnetic actuator as claimed in claim 2 or claim 3 characterised in that said plunger (12) extends axially within a central bore (18) of a bobbin (17) on which the winding (19) of said electromagnet is wound, one (34) of said abutment components being an end face of said spline (33), or one of said splines (33), and the other (35) of said abutment components being a protrusion on the wall of the bore (18) of the bobbin (17).

5. An electromagnetic actuator as claimed in claim 4 characterised in that said protrusion includes a circumferentially extending shoulder (35) defining said other abutment component, and an axially extending wall against which the spline (33) abuts when its end face (34) abuts the shoulder (35).

6. An electromagnetic actuator as claimed in any one of the preceding claims, characterised by resilient means urging said plunger angularly and axially to a rest position relative to said body.