GB2447769A

GB2447769A - A latching solenoid

Info

Publication number: GB2447769A
Application number: GB0805097A
Authority: GB
Inventors: Richard Alexander Burke; Robert Graham Harris
Original assignee: BiFold Fluidpower Ltd
Current assignee: BiFold Fluidpower Ltd
Priority date: 2007-03-22
Filing date: 2008-03-19
Publication date: 2008-09-24
Anticipated expiration: 2028-03-19
Also published as: GB2447769B8; GB0705487D0; GB0805097D0; GB2447769B

Abstract

An electromagnetic actuator comprises an armature 21 and first and second coils 30, 31 formed around a common axis, which are spaced apart along the said axis. Each of the coils 30, 31 has respective pole pieces. The actuator is arranged such that on activation of the first and/or second coils 30, 31 the armature 21 will move between separate first and second axial positions. A permanent magnet 36 is arranged to latch the armature 21 in one of the first and/or second axial positions. The armature 21 may be a disc of ferromagnetic material and the coils 30,31 may be supported in respective coil holders 18, 19 which may be received in an outer housing. Each coil holder 18, 19 may be cylindrical in shape with an annular recess to receive a coil and a bore 37 within the coil recess which may support a permanent magnet 36 at a surface facing the armature 21. The coil holders 18, 19 may be made or ferromagnetic material. Threaded axial armature-position adjustment means and spring biasing means are also described. The actuator may be used to operate a valve 50.

Description

A LATCHING SOLENOID

The present invention relates to a latching solenoid in which the solenoid armature is maintained in an energised position once a respective energising coil has been de-energised.

Solenoid controlled actuators are used to convert an electrical signal into linear mechanical movement and have many applications. For example, many pneumatic or hydraulic directional flow control valves are operated by a solenoid operator. In a typical arrangement, the armature is in the form of a reciprocal plunger disposed concentrically within the coil and connected in some way to the valve member. When the solenoid is de-ene.rgised no current flows in the coil and the plunger is biased by a spring or other resilient member to maintain the valve member in a closed position.

When the coil is energised by an electrical current flowing through it the magnetic field induced in the coil serves to move the plunger against the opposing force of the spring to open the valve member.

In many applications it is undesirable to maintain a holding current in the coil in order to keep a valve member in an open position. It is known to eliminate the requirement for a holding current by adopting a latching mechanism. This is typically achieved by using a permanent magnet to hold the armature in a latched condition against the spring force thereby allowing the energising current to be removed without releasing the plunger. This type of solenoid must be mechanically reset once latched.

It is an object of the present invention to provide for an improved latching solenoid mechanism.

According a first aspect of the present invention there is provided a latching solenoid having an axis and comprising first and second coil windings disposed around and spaced apart along said axis, each coil winding being independently energisable by application of an electric current, an armature associated with said coils and arranged to travel in an axial direction, first and second pole pieces associated with the respective coil windings and arranged on opposite sides of the armature, wherein energisation of a first coil winding serves to generate a magnetic field such that the first pole piece attracts or repels said armature so as to move it to a first axial position and energisation of the second coil winding serves to generate a magnetic field such that the second pole piece attracts or repels said armature so as to move it to a second axial position, a permanent magnet having a polarity arranged to hold the armature in one of the first or second axial positions.

In one embodiment there may be one or more permanent magnets arranged to hold the armature in the second position only. A spring or other biasing means may be used to hold the armature in the first axial position against the attractive/repulsive force of the magnet. In an alternative embodiment of the present invention two sets of permanent magnets may be provided: at least one first permanent magnet that serves to latch the armature in the first axial position and at least one second permanent magnet that serves to latch the armature in the second axial position.

The armature may be disposed in a clearance between the coil windings. The first and second coil windings may supported within respective first and second coil holders in which case the armature may be disposed in a clearance between the respective holders. The first and second coil holders may be received in an outer housing along with the armature.

In one embodiment the pole pieces are configured to attract the armature to the respective first and second axial positions when the respective coil is energised.

Similarly the first and second permanent magnets have polarities that are arranged to attract the armature.

The coil holders may each define a respective pole piece and may be substantially cylindrical. In one embodiment of the invention the coil windings are each received in a respective annular recess defined in the respective coil holder.

The first and second permanent magnets may be supported respectively by said first and second coil holders and to this end there may be bores defined in a surface of the respective coil holders for receipt of said magnets. This surface of each holder may face the armature.

The armature may take any suitable form but may conveniently be a disc, which may have an outer diameter that is substantially similar to an outer diameter of the coil holders. The armature, whether or not in the form of a disc, may not have any part that extends into the area circumscribed by the coil windings.

The armature may be substantially coaxial with said coil windings.

The first and second permanent magnets may be disposed radially inboard respectively of said first and second coil windings and may be positioned between the respective first and second coil and the axis. Two or more such first permanent magnets and two such second permanent magnets may be provided.

The armature may be made of a ferromagnetic material, as may the coil holders.

The first and second coil windings may be supported on first and second bobbins, which in turn are received in the respective coil holders.

The armature may have an adjustment screw threadedly engaged in a threaded bore for linear adjustment. The threaded bore is disposed about said axis. In an embodiment where the armature is a disc the screw is thus centrally disposed. The screw may be adjustable along the axis and may be adapted for abutment or engagement with a plunger.

The second coil holder may have a bore for receipt of said plunger and that bore may be aligned with the threaded bore in the armature.

According to a second aspect of the present invention there is provided a solenoid-operated actuator comprising a plunger and a latching solenoid as defined above, the plunger being connectable directly or indirectly to said armature. It is to be appreciated that "connectable" is used in this context to include being brought into engagement or abutment with.

According to a third aspect of the present invention there is provided a solenoid-operated valve comprising a valve body with a valve member movable between at least first and second positions and being connectable directly or indirectly to a plunger of said solenoid operated plunger as defined in the second aspect.

A specific embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a first sectioned view of an embodiment of the latching solenoid in accordance with the present invention; Figure 2 is a second sectioned view of the solenoid of figure 1, in a plane at right angles to that of figure 1, along line AA of figure 3; Figure 3 is a side view of the outside of the solenoid of figures 1 and 2; Figure 4 is a sectioned view of the solenoid of figures 1 to 3 connected to a valve assembly; and Figure 5 is a sectioned view of an alternative embodiment of a solenoid in accordance with the present invention and connected to a valve assembly.

Referring now to the drawings, the exemplary solenoid has an outer housing that receives an internal solenoid assembly II. The housing 10 is generally cylindrical with an open end 12 that is closable by a removable end cap 13, an opposite end wall 14 with an axial port 15 therethrough and a side wall 16 penetrated by a radially extending side port 17.

The solenoid assembly 11 comprises first and second coil holders 18, 19 of cylindrical configuration that are spaced apart to define a clearance 20 between the respective front faces of the holders, and an intermediate armature disc 21 disposed in the clearance 20. A pair of screws 22 holds the assembly 11 together, as can be seen in figure 1, whilst maintaining the clearance 20 in which the disc 21 can move axially between the holders 18,19. The outer diameters of the coil holders 18, 19 and the disc 21 are all substantially identical and slightly less than the inner diameter of the outer housing 10 so that they are received and supported therein.

The coil holders 18, 19 and the armature disc 21 are all made from ferromagnetic material and are penetrated by central coaxial bores 23-25, with the central bore 24 in the disc 21 being threaded for engagement with a short adjusting screw 26. When the solenoid is connected to a valve assembly 50, a plunger rod 51 of the assembly extends into the bore 25 of the second coil holder 19 and abuts one end of the adjusting screw 26 as illustrated in figure 4. This is described in more detail below.

Each coil holder 18, 19 contains a coil winding 30, 31 that is supported on a bobbin 32, 33 (see figures 1 and 2) in an annular recess 34 of each holder such that the coil 30, 31 surrounds the central axis. The two free ends of each coil 30, 31 are connected to a terminal block 35 disposed between the first coil holder 18 and the end cap 13. An electrical power source (not shown) is connectable to the coils 30,31 via the terminal block 35 and electrical conducting wires (not shown) that pass through the side port 1 7.

The coil windings 30, 3lare connected into a circuit that allows only one of them, or neither, to be energised at any given point in time. When a given coil 30, 31 is energised by an electrical current it generates a magnetic field in the holder 18, 19 whose front face serves as a pole piece to attract the ferromagnetic armature disc 21 towards the respective coil holder. The armature disc 21 is thus arranged to reciprocate between a first position where it is in abutment with the front face of the first coil holder 18 and a second position where it is in abutment with the front face of the second coil holder 19 in response to energisation of the appropriate coil 30, 31.

The separation of the coil holders thus determines the stroke length of the armature. In order to latch the armature disc 21 in each position a pair of permanent magnets 36 are associated with each holder so that the disc is maintained in position after the current in the coil 30, 31 stops flowing. The magnets 36 are retained in blind bores 37 in the front face of the holder 18, 19, those bores being positioned between the axis and the coils, and provide sufficient magnetic attractive force to hold the ferromagnetic disc 21 in abutment with the respective holder 18, 19 but insufficient to prevent the disc 21 being attracted to the opposite holder 18, 19 when the opposite coil is energised.

The armature disc 21 is supported for axial movement on cylindrical support pillars 38 through the centre of which the screws 22 pass. The pillars 38 extend between the coil holders and thus set the length of the clearance 20 and therefore the stroke length of the armature.

An application of the solenoid assembly is illustrated, by way of example only, in figure 4 in which the solenoid is used to operate a valve assembly 50 of conventional design. The assembly comprises a valve body 52 penetrated by a bore 53 that has a central valve chamber 54 in which resides a reciprocal valve member 55 that is movable between open and closed positions in a valve chamber 54 by a valve stem 56. The valve member 55 is biased upwards towards a predetermined position (i.e. open or closed) by a return spring 57 mounted in the bore 53 at one end of the body 52. The solenoid is joined to the valve assembly 50 via an intermediate cylindrical adaptor bush 58 that interconnects the axial port in the end wall and the bore 53 in the valve body 52. The actuating plunger rod 51 extends through the interface where it is supported for reciprocal movement. A first end of the rod 51 engages with the valve stem 56 and the other end projects through the bore 24 in the second coil housing 19 into abutment with the adjusting screw 26 in the armature disc 21. In figure 4, the armature 21 is shown latched by the permanent magnets 36 in a first position in which it is in abutment with the first coil holder 18. When it is desired to change the status of the valve a current is supplied to energise the second coil winding 31 whereupon the armature disc 21 is pulled towards the second coil holder 19, the attractive force overcoming that of the permanent magnets 36 in the first coil holder 18. After the current to the second coil 31 is removed the permanent magnets 36 in the second coil holder 19 serve to latch the armature 21 in place.

The second embodiment of the solenoid assembly in figure 5 is connected to a valve assembly in the same manner as the arrangement shown in figure 4.

Components that are in common with those shown in figure 4 are given the same reference number but increased by 100 and are not described further except in so far as they differ from their counterparts in figure 4. The only significant difference is that there are only two permanent magnets 137 both of which are associated with the armature 121. These are arranged within the lower second coil 131 and serve to latch the armature 121 when it is in the second position (i.e. attracted into abutment with the second coil holder 119). In this position the valve member 155 is held in a position against the bias of the spring 157. Ordinarily, and as in the embodiment of figure 4, the valve member 155 is biased upwards towards a predetermined position (i.e. open or closed) by the return spring 157 mounted in the bore 153. There are no permanent magnets in the first (upper) coil holder 130 and the spring 157 is designed to have sufficient stiffness to hold the armature disc 121 away from the second (lower) coil 131 and against the attractive force applied by the permanent magnets 137 after the first coil 130 after its windings have been de-energised. In this arrangement, a coil 130, 131 has to be energised to change the position of the armature 121 (and therefore the valve member 1 55) but when the coil 130, 131 is de-energised the armature 121 remains latched in position, either by the permanent magnets 137 or by the spring 157.

This arrangement provides for lower power consumption in the coils. The solenoid assembly may include a spring to hold the armature in said first position rather than relying on a spring that is part of an assembly to which it is connected.

It will be appreciated that numerous modifications to the above described design may be made without departing from the scope of the invention as defined in the appended claims. For example, the number and shape of the permanent magnets may vary depending on the application.

Claims

A latching solenoid having an axis and comprising first and second coil winclings disposed around and spaced apart along said axis, each coil winding being independently energisable by application of an electric current, an armature associated with said coils and arranged to travel in an axial direction, first and second pole pieces associated with the respective coil windings and arranged on opposite sides of the armature, wherein energisation of a first coil winding serves to generate a magnetic field such that the first pole piece attracts or repels said armature so as to move it to a first axial position and energisation of the second coil winding serves to generate a magnetic field such that the second pole piece attracts or repels said armature so as to move it to a second axial position, a permanent magnet having a polarity arranged to hold the armature in one of the first or second axial positions.
2. A latching solenoid according to claim 1, wherein there is provided a first permanent magnet having a polarity arranged to hold the armature in the second first axial position and a second permanent magnet having a polarity arranged to hold the armature in the second position.
3. A latching solenoid according to claim I or 2, wherein the armature is disposed in a clearance between the coil windings.
4. A latching solenoid according to claim 1, 2 or 3, wherein the first and second coil windings are supported within respective first and second coil holders.
5. A latching solenoid according to claim 4, wherein the first and second coil holders are received in an outer housing.
6. A latching solenoid according to claim 4 or 5, wherein the parts of the coil holders define said pole pieces.
7. A latching solenoid according to claim 4, 5 or 6, wherein the coil holders are substantially cylindrical.
8. A latching solenoid according to claim 7, wherein the coil windings are received in annular recesses in the respective coil holders.
9. A latching solenoid according to any one of claims 4 to 8, wherein the permanent magnet is supported in one of said coil holders.
10. A latching solenoid according to claim 9, wherein the permanent magnet is supported in a bore defined in a surface of one of the coil holders, said surface facing the armature.
II. A latching solenoid according to claim 2, wherein the first permanent magnet is supported by the first coil holder and the second permanent magnet is supported by said second coil holder.
12. A latching solenoid according to claim 11, wherein the first permanent magnet is supported in a bore defined in a surface of the first coil holder and the second permanent magnet is supported in a bore defined in a surface of the second coil holder, said surface facing the armature.
13. A latching solenoid according to any preceding claim, wherein said armature is a disc.
14. A latching solenoid according to claim 13, wherein the disc has an outer diameter that is substantially similar to an outer diameter of the coil holders.
15. A latching solenoid according to claim 13 or 14, wherein the armature does not extend into an area between the coil windings and said axis.
16. A latching solenoid according to any preceding claim where said armature is coaxial with said coil windings.
17. A latching solenoid according to any preceding claim, wherein the permanent magnet is disposed radially inboard of one of the coil windings.
18. A latching solenoid according to any preceding claim, wherein the permanent magnet is positioned between one of the coil windings and the axis.
19. A latching solenoid according to claim 2, wherein the first permanent magnet is disposed radially inboard of the first coil winding and the second permanent magnet is disposed radially inboard of the second coil winding.
20. A latching solenoid according to claim 2 or 19, wherein the first permanent magnet is positioned between the first coil winding and the axis and the second permanent magnet is positioned between the second coil winding and the axis.
21. A latching solenoid according to any preceding claim, wherein the armature is made of a ferromagnetic material.
22. A latching solenoid according to any one of claims 4 to 11, wherein said coil holders are made of a ferromagnetic material.
23. A latching solenoid according to any preceding claim, wherein the first and second coil windings are supported on first and second bobbins.
24. A latching solenoid according to any preceding claim wherein the armature has an adjustment screw threadedly engaged in a threaded bore for linear adjustment.
25. A latching solenoid according to claim 24, wherein said threaded bore is disposed on said axis.
26. A latching solenoid according to claim 25, wherein said adjustment screw is adapted for abutment or engagement with a plunger.
27. A latching solenoid according to claim 26, wherein said second coil holder has a bore for receipt of said plunger.
28. A latching solenoid according to any preceding claim wherein there is provided a biasing element for biasing the armature towards said first coil holder.
29. A latching solenoid according to any preceding claim, where the biasing element is a spring.
30. A latching solenoid substantially as hereinbefore described with reference to the accompanying drawings.
31. A solenoid-operated actuator comprising a plunger and a latching solenoid according to any preceding claim, the plunger being connectable directly or indirectly to said armature.
32. A solenoid-operated actuator according to claim 31, wherein a biasing element is connected to said plunger so as to bias the armature toward the first coil holder.
33. A solenoid-operated valve comprising a valve body with a valve member movable between at least first and second positions and being connectable directly or indirectly to a plunger of said solenoid operated plunger of claim 31 or 32.