EP1481406B1 - Electromagnetic actuator with controlled attraction force - Google Patents

Description

The invention relates to an electromagnetic actuator, in particular a DC electromagnetic actuator for actuating a motor valve.

BACKGROUND OF THE INVENTION

Electromagnetic actuators are known comprising an actuating rod connected to a pallet to form a mobile assembly associated with a motor unit which propels the mobile assembly from one extreme position to another, the extreme positions corresponding to the open and closed positions of the valve.

The motor member comprises at least one coil equipped with a core, a face of the pallet being adapted to come into contact with a face of the core of the coil when the valve is in one of the open or closed positions. The coil is used to move the pallet and retain it to keep the moving assembly in the corresponding extreme position. For this purpose the coil is connected to a DC power supply device.

During operation of the actuator, the coil is supplied with current, which has the effect of creating a magnetic flux that closes in the pallet. The coil thus exerts an attraction force on the pallet.

When the pallet is still far from the core of the coil, the total gap that must cross the flow between the pallet and the core is important. The coil must then be fed with a current of high intensity so that the attraction force it develops overcomes the resistant force experienced by the moving assembly.

But when the pallet arrives in the vicinity of the core, the total gap between the pallet and the core decreases very rapidly, and the power supply electronics is generally not fast enough to lower the current intensity. proportional feeding the decrease of the gap.

The attraction force exerted by the coil on the end-of-stroke pallet greatly exceeds the resisting force exerted on the moving assembly. The pallet thus comes against the core with a high speed, which produces an undesirable snap noise, and prevents good control of the speed of docking of the valve against its seat in the closed position.

It was thought to reduce the attraction force at the end of the race by limiting the intensity of the flow that can be established in the pallet.

However, the pallet is generally sized to operate at the magnetic saturation limit for the maximum flux developable by the coil which is established when the pallet is away from the core. A flow limitation would certainly reduce the attraction force at the end of the race, but degrade the performance of the actuator when the pallet is away from the core. An electromagnetic actuator according to the preamble of claim 1 is known from the document JP-A-10332027 .

OBJECT OF THE INVENTION

The invention aims to provide a means for adapting the attraction force of the coil on the pallet end of stroke, without degrading the performance of the actuator when the pallet is away from the core.

BRIEF DESCRIPTION OF THE INVENTION

For this purpose, there is provided an electromagnetic actuator comprising an actuating member connected to a pallet which is movable under the effect of a motor member comprising at least one coil for generating a magnetic flux in a core having a face extending facing one side of the pallet, at least one facing face having at least one recessed portion characterized in that the pallet and the core are arranged to define in a first zone of the pallet and the encompassing core the recessed portion, a first magnetic path which is interrupted by an air gap at least equal to the withdrawal of the recessed portion when the pallet bears on the core, and, in a second zone of the pallet and the core excluding the recessed portion, a second magnetic path which is interrupted only by a residual gap when the pallet is supported on the core, the recessed portion having a total area at most equal to an area bringing the saturation magnetic flux in the second zone of the pallet.

Thus, when the face of the pallet is away from the face of the core by a distance that is large in front of the withdrawal of the recessed portion, the value of the flux in the core is determined primarily by the distance between the pallet and the core. , so that the recessed portion has only a negligible influence on the performance of the actuator. When the pallet reaches the vicinity of the core, the withdrawal of the recessed portion becomes significant relative to the residual space remaining between the facing faces. The total gap that the flow must cross in the first zone is therefore increased. For a given current, the attraction force exerted by the coil on the pallet is reduced.

Thus, the invention makes it possible, for the same dynamics of the power supply electronics, to lower the attraction force at the end of the stroke, so that the pallet arrives less quickly against the core and the slamming noise found to be diminished. The invention therefore makes it possible to increase the variation of the attraction force for a given current variation.

It will be noted that the presence of the recessed portions causes a correlative increase in the holding current of the pallet against the core. By playing on the relative surfaces of the first and second zones, it is possible to make a compromise between the reduction of effort sought at the end of the race and the increase correlative of the current holding the pallet against the nucleus.

It is important in this regard to ensure that the magnetic flux in the second zone does not exceed a saturation value, which would cause a degradation of the performance of the actuator.

For an actuator whose core comprises a central branch and two lateral branches having ends which define the face of the core, the recessed portion advantageously extends on the face of the pallet facing at least one of the branches of the core.

According to a first embodiment of the invention, the pallet comprises recessed portions which each extend opposite one of the lateral branches of the core, preferably symmetrically with respect to the actuating member.

Preferably, the recessed portion extends transversely of the arm opposite a distance at least equal to the withdrawal of the withdrawal portion relative to the face of the pallet.

According to a second embodiment of the invention, the recessed portion extends transversely to the three branches, opposite each of them.

According to a particular aspect of the invention, the first zone and the second zone are magnetically isolated.

This arrangement avoids the migration of the flow to the second zone where it could more easily be established, which would weaken the effectiveness of the recessed portions.

Preferably, the core is composed of a stack of sheets, at least one magnetic barrier being inserted into the stack of sheets to separate the sheets making up the first zone and the second zone of the core.

BRIEF DESCRIPTION OF THE DRAWINGS

• la figure 1A est une vue en coupe schématique selon le plan 1A de la figure 2A d'un actionneur selon l'invention sur laquelle la palette est illustrée éloignée du noyau;
• la figure 1B est une vue en coupe schématique selon le plan IB de la figure 2B sur laquelle la palette est illustrée en contact avec le noyau ;
• la figure 2A est une vue en perspective partielle d'un premier mode de réalisation de l'invention sur laquelle la palette est illustrée éloignée du noyau, le conducteur de la bobine ayant été omis ;
• la figure 2B est une vue partielle analogue à la figure 2A sur laquelle la palette est illustrée en contact avec le noyau ;
• la figure 3A est une vue en perspective partielle d'un deuxième mode de réalisation de l'invention sur laquelle la palette est illustrée éloignée du noyau, le conducteur de la bobine ayant été omis ;
• la figure 3B est une vue analogue à la figure 3A sur laquelle la palette est illustrée en contact avec le noyau ;
• la figure 4 est une vue en perspective partielle d'un actionneur selon une variante du deuxième mode de réalisation de l'invention ;
• la figure 5 est une vue de côté schématique de l'actionneur des figures 3A et 3B ;
• la figure 6 est une vue de côté schématique de l'actionneur de la figure 4.

Other features and benefits of the invention will appear more clearly in the light of the following description of particular non-limiting embodiments of the invention. Reference will be made to the appended figures among which:

• Figure 1A is a schematic sectional view along the plane 1A of Figure 2A of an actuator according to the invention on which the pallet is illustrated remote from the core;
• Figure 1B is a schematic sectional view along the plane IB of Figure 2B on which the pallet is illustrated in contact with the core;
• Fig. 2A is a partial perspective view of a first embodiment of the invention on which the pallet is shown remote from the core, the coil conductor having been omitted;
• Figure 2B is a partial view similar to Figure 2A in which the pallet is illustrated in contact with the core;
• Fig. 3A is a partial perspective view of a second embodiment of the invention on which the pallet is shown remote from the core, the coil lead having been omitted;
• Figure 3B is a view similar to Figure 3A in which the pallet is illustrated in contact with the core;
• Figure 4 is a partial perspective view of an actuator according to a variant of the second embodiment of the invention;
• Figure 5 is a schematic side view of the actuator of Figures 3A and 3B;
• FIG. 6 is a schematic side view of the actuator of FIG. 4.

In the figures the scales have not been respected, to better understand the invention.

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIGS. 1A and 1B, the illustrated actuator comprises, in a manner known per se, two coils arranged facing one another. A single coil 1 has been shown to lighten the drawing. The coil 1 comprises a core 2 having a central branch 3 and two lateral branches 4. A conductor 5, whose turns are seen in section, is wound around the central branch 3 of the core 2. An actuating rod 6 is mounted sliding in a bore of the central branch 3 in a direction perpendicular to a face 7 of the core 2 defined by the end of the central branch 3 and side branches 4. The actuating rod 6 is secured to a pallet 8 which has a face 9 parallel to the face 7 of the core 2, and which is constrained to move between the coils.

DC power supply electronics, not shown, feeds the DC conductor 5 to establish a flow 11 between the core 2 and the pallet 8 in order to exert on the pallet 8 an attraction force. The magnetic flux 11 flows in the core 2 through the central branch 3 and each of the lateral branches 4. The magnetic flux 11 is closed in the pallet 8 by crossing a total gap equal to the space separating the pallet 8 from the core 2 to the level the central branch 3 increased the space between the pallet 8 and the core 2 at each lateral branch 4.

According to the first embodiment of the invention, the faces of the pallet 8 each have four adaptation portions 10 set back a withdrawal distance r relative to the face carrying the recessed portion 10 considered. The recessed portions 10 each extend opposite one of the lateral branches 4 of the core 2 and are arranged symmetrically with respect to the actuating rod 6.

In the figures, the recessed portions 10 are illustrated on each of the faces of the pallet 8 because the pallet 8 also cooperates with another not shown reel which extends opposite the other face of the pallet 8. For the purposes of the description, only the recessed portions 10 made in the face 9 facing the nucleus will be taken into consideration.

In the position illustrated in FIG. 1A, the pallet 8 is remote from the core 2 and the withdrawal r of the recessed portions 10 is negligible compared with the distance d measured between the face 9 of the pallet 8 and the face 7 of the core 2. The total air gap that the flux must cross is thus substantially equal to twice the distance d, the presence of the recessed portions having a negligible influence.

For example, the withdrawal r is of the order of 0.2 millimeters for a maximum distance d of the order of eight millimeters.

The attraction force exerted by the coil 1 is not disturbed by the presence of the recessed portions 10 when the pallet 8 is still distant from the core 2.

In the position illustrated in Figure 1B, the face 9 of the pallet 8 and the face 7 of the core 2 are in contact. Due to the surface defects of the core and the pallet there remains between the two faces in contact a residual space ε much less than the withdrawal of the recessed portions 10. The total gap that must cross the flow is therefore substantially equal to the distance withdrawing r opposite the recessed portions 10, whereas it would have been equal to twice the residual space ε in the absence of the recessed portions 10.

At a given current, the attraction force exerted by the coil 1 on the pallet 8 varies inversely with the square of the gap. When the pallet reaches the vicinity of the core 2, the attraction force is therefore decreased significantly compared to the recessed portions so that for a given current reduction dynamics the invention makes it possible to reduce more quickly the speed of the pallet during its docking on the core. In addition the additional gap of the recessed portions decreases the inductive effect of the pallet on the coil 1 and thus improves the dynamic reduction of the current in the coil.

In the first embodiment of the invention illustrated in FIGS. 2A and 2B, the recessed portions 10 do not extend over the entire length of the lateral branches 4, but only over part of it.

The recessed portions 10 delimit longitudinally a first zone 12 of the pallet 8 and the core 2 for which the total gap that must cross the flow is substantially equal to the withdrawal r of the recessed portions 10, and a second zone 13 of the pallet 8 and the core 2 for which the total air gap is equal to twice the residual space ε between the faces 7 and 9.

Note that after contacting the pallet on the core, maintaining the pallet against the core then requires powering the coil with a holding current which is all the more important that the withdrawal r and the surface of the shrinkage portions are large. The surface of the recessed portions therefore results from a compromise between the desired force reduction in order to increase the variation of the attraction force and a reasonable increase in the holding current. In practice it has been determined that for a shrinkage distance of 0.2 mm a surface of the recessed portions equal to one third of the surface of the lateral branches of the core constitutes a satisfactory compromise.

By modifying the relative length of the zones 12 and 13 it is possible to modulate the attenuation at the end of stroke of attraction effort. However, this modulation is limited by the fact that an excessive increase in the areas of the recessed portions could cause saturation of the second zone 13.

Such saturation would cause a degradation of the performance of the actuator.

In practice, it will limit the total area of the recessed portions to 50% of the total area of the faces opposite the pallet and the core.

According to a particular aspect of the invention, the recessed portions protrude transversely from the side branch facing a distance 1 at least equal to the withdrawal r of the recessed portion. In the illustrated example, the recessed portions 10 are delimited transversely by a fillet 14 equal to the withdrawal r of the recessed portions 10, the center of the fillet 14 being substantially at the internal edge 15 of the side branch 4 when the pallet 8 is in contact with the core 2.

This arrangement minimizes the passage of the flow to the zone 13 in the vicinity of the inner edge 15 in which the distance to be crossed would be less than the withdrawal distance of the recessed portions, which would reduce the effectiveness of the recessed portions 10.

Moreover, the core 2 is advantageously composed of a stack of cut sheets which limit the longitudinal migration of the flow. This arrangement contradicts the tendency of the flow normally to be established in the zone 12 to migrate to the zone 13 where the total air gap is lower. To further limit this migration, a magnetic barrier 16, for example a piece of non-magnetic material of the same shape as the sheets forming the core may be inserted into the stack of sheets to magnetically isolate the core portion corresponding to the zone 12 the corresponding core part at zone 13.

According to a second embodiment of the invention illustrated in FIGS. 3A and 3B, the recessed portions are formed by steps 17 which extend transversely facing the central branch 3 and the lateral branches 4 of the core 2. In this case , the withdrawal of the recessed portion affects the flow not only in its passage between a lateral branch and the pallet but also in its passage between the central branch and the pallet.

The step 17 is easier to machine than the recessed portions 10 illustrated in FIGS. 2A and 2B and eliminates any risk of magnetic flux passing through the internal edge 15 of the side branches 4.

The step 17 delimits two zones 12 and 13 in the same way as in the preceding embodiment. In the zone 12 corresponding to the step 17, the flow must cross once the withdrawal r of the step 17 in the gap with the central branch 3 and once the same distance in the air gap with the lateral branches to be able establish. For the same attenuation as in the first embodiment, it is sufficient that the withdrawal r of the step 17 is equal to half the withdrawal distance of the recessed portions 10.

In a variant of this embodiment, illustrated in FIG. 4, the step 17 is replaced by a bevel 18. The distance between the face 7 of the core 2 and the bevel 18 is not constant but increases with the distance relative to in the center of the pallet 8. The bevel 18 has the same effect as the step 17, but it avoids undesirable edge effects that could occur along the edge of the step 17.

Moreover, in FIG. 5, the position that the walking pallet 8 is capable of presenting with respect to the core 2 is exaggeratedly illustrated. mounting games of the actuator. It is found that the distance between the face 7 of the core 2 and the bottom of the step 17 decreases toward the end of the blade 8, and the magnetic flux tends to focus at the end edge 19 of the pallet 8, which decreases the performance of the actuator.

In Figure 6, there is illustrated a palette 8 to bevel 18 in the same configuration as before. It is found that the distance between the face 7 of the core 2 and the bevel 18 remains increasing toward the end of the pallet, the risk of concentrating the magnetic flux on the terminal edge 20 of the pallet 8 is then avoided.

This risk of imbalance of positioning of the pallet is further minimized by a symmetrical arrangement of the recessed portions with respect to the actuating member 6.

The invention is not limited to the particular embodiment that has just been described, but on the contrary intends to cover any variant that falls within the scope of the invention as defined by the claims.

Although recessed portions have been illustrated in the form of a step or bevel, the recessed portions may more generally take any shape that is capable of ensuring a space between the recessed portions and the face opposite when the two faces are in contact, for example a series of grooves.

Although the invention has been illustrated with recessed portions made on the pallet, the recessed portions may also be made on the face of the core or simultaneously on the pallet and the core although this solution appears a priori more complex to realize that the recessed portions on the pallet.

Although we have illustrated the faces of the pallet and the core being planar, the faces can take any complementary forms able to allow their contact outside the recessed portions.

Although it has been indicated that the recessed portions are delimited transversely by a fillet, the recessed portions may be delimited by any other form provided that the recessed portions project transversely of the side branch with respect to a distance of at least equal to the withdrawal distance.

Although it has been indicated that the recessed portions extend opposite the lateral branches, or straddling the central branch and the lateral branches, it will also be possible to provide recessed portions which extend only opposite the central branch.

Although the invention has been described in relation to a two-coil actuator, it also applies to a single-spindle actuator whose core has active ends facing both faces of the pallet.

Claims (10)

1. An electromagnetic actuator comprising an actuator member (6) connected to an armature (8) which is movable under drive from a drive member comprising at least one coil (1) for generating magnetic flux in a core (2) having a face facing a face of the armature (8), at least one of the facing faces including at least one set-back portion (10; 17; 18), the actuator being characterized in that the armature (8) and the core (2) are arranged, in a first zone (12) of the armature (8) and of the core (2) including the set-back portion, to define a first magnetic path which is interrupted by an air gap that is not less than the setback of the set-back portion (10; 17; 18) when the armature (8) bears against the core (2), and in a second zone (13) of the armature (8) and of the core (2) excluding the set-back portion, to define a second magnetic path which is interrupted solely by a residual air gap when the armature (8) bears against the core (2), the total area of the set-back portion being no greater than an area that would bring the magnetic flux to saturation in the second zone of the armature.
2. An electromagnetic actuator according to claim 1, characterized in that the total area of the set-back portion is less than 50% of the total area of the facing faces.
3. An electromagnetic actuator according to claim 1, characterized in that the core (2) comprises a central branch (3) and two side branches (4) having ends which define the face (7) of the core (2), and in that the set-back portion (10; 17; 18) extends over the face of the armature (9) facing at least one of the branches of the core.
4. An electromagnetic actuator according to claim 3, characterized in that the armature (8) has set-back portions (10) which extend facing the side branches (4) of the core.
5. An electromagnetic actuator according to claim 3, characterized in that the set-back portions are symmetrical relative to the actuator member.
6. An electromagnetic actuator according to claim 3, characterized in that the set-back portion (10) extends transversely beyond the facing branch over a distance (ℓ) that is less than the setback (r) of the set-back portion (10) relative to the actuator member.
7. An electromagnetic actuator according to claim 3, characterized in that the set-back portion (17, 18) extends transversely relative to all three branches (4, 3, 4), facing each of them.
8. An electromagnetic actuator according to claim 7, characterized in that the set-back portion (17) is in the form of a chamfer.
9. An electromagnetic actuator according to claim 1, characterized in that the first zone (12) and the second zone (13) of the core (2) are magnetically isolated from each other.
10. An electromagnetic actuator according to claim 9, characterized in that the core is made up of a stack of laminations, at least one magnetic barrier (16) being inserted in the stack of laminations, to separate the laminations making up the first and second zones (12 and 13) of the core (2).

Images