EP1481406A1

EP1481406A1 - Electromagnetic actuator with controlled attraction force

Info

Publication number: EP1481406A1
Application number: EP03720653A
Authority: EP
Inventors: David Walraet
Original assignee: Johnson Controls Technology Co
Current assignee: Valeo Systemes de Controle Moteur SAS
Priority date: 2002-03-01
Filing date: 2003-02-28
Publication date: 2004-12-01
Anticipated expiration: 2023-02-28
Also published as: DE60317777D1; JP2005519465A; AU2003224230A1; ES2299696T3; WO2003075293A1; FR2836755B1; EP1481406B1; US20050083159A1; FR2836755A1; DE60317777T2; JP4473582B2; US7042321B2

Abstract

The invention concerns an electromagnetic actuator comprising an actuating member (6) connected to a relay armature (8) which is mobile under the effect of a drive member including at least a coil (1) for generating a magnetic flux in the core (2) having a surface extending opposite one surface of the relay armature (8), one at least of the opposite surfaces comprising at least one recessed portion (10), the relay armature (8) and the core (2) being arranged to define, in a first zone (12) of the relay armature (8) and of the core (2) including the recessed portion, a first magnetic path which is interrupted by an air gap at least equal to the recess of the recessed portion (10) when the relay armature (8) is pressed on the core (2), and in a second zone (13) of the relay armature (8) and of the core (2) excluding the recessed portion (10) a second magnetic path which is interrupted only by a residual air gap when the relay armature (8) is pressed on the core (2), the recessed portion having a total area not greater than the area bringing the magnetic flux to saturation in the second zone of the relay armature.

Description

Electromagnetic actuator with controlled attraction force

The invention relates to an electromagnetic actuator, in particular an electromagnetic direct current 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 member 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 drive member comprises at least one coil fitted with a core, one face of the pallet being adapted to come into contact with one face of the core of the coil when the valve is in one of the open or closed positions. The spool is used to move the pallet and to hold it to keep the mobile 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 which 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 air gap which the flow between the pallet and the core must cross. The coil must then be supplied with a current of high intensity so that the attraction force which it develops overcomes the resistant force which the mobile assembly undergoes.

But, when the pallet arrives in the vicinity of the core, the total air gap between the pallet and the core decreases very quickly, and the supply electronics are generally not fast enough to reduce the intensity of the current. proportionate feeding of the reduction in the air gap.

The attraction force exerted by the reel on the pallet at the end of the travel greatly exceeds the resistant force exerted on the mobile assembly. The pallet therefore arrives against the core with a high speed, which produces an undesirable clicking noise, and prevents good control of the speed of approach of the valve against its seat in the closed position.

We 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 palette.

However, the pallet is generally sized to operate at the limit of magnetic saturation for the maximum flux developable by the coil which is established when the pallet is distant from the core. Limiting the flow would certainly reduce the attraction force at the end of the stroke, but would degrade the performance of the actuator when the paddle is far from the core. OBJECT OF THE INVENTION

The invention aims to propose a means for adapting the force of attraction of the coil on the pallet at the end of the stroke, without degrading the performance of the actuator when the pallet is distant from the core. BRIEF DESCRIPTION OF THE INVENTION

To this end, an electromagnetic actuator is provided comprising an actuating member connected to a pallet which is movable under the effect of a motor member comprising at least one coil to generate a magnetic flux in a core having a face extending opposite a face of the pallet, at least one of the opposite faces comprising at least one recessed portion, the pallet and the core being according to the invention arranged to define in a first zone of the pallet and from the nucleus encompassing the recessed portion, a first magnetic path tick which is interrupted by an air gap at least equal to the withdrawal of the recessed portion when the pallet is in contact with the core, and, in a second zone of the pallet and of the core excluding the recessed portion, a second magnetic path which is interrupted only by a residual air gap when the pallet is supported on the core, the recessed portion having a total area at most equal to an area bringing the magnetic flux to saturation in the second area of the pallet. Thus, when the face of the pallet is distant from the face of the core by a distance which is large before the withdrawal of the recessed portion, the value of the flux in the core is determined mainly 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 arrives in the vicinity of the core, the withdrawal of the recessed portion becomes significant with respect to the residual space remaining between the facing faces. The total air 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 therefore reduced.

Thus, the invention makes it possible, for the same dynamics of the supply electronics, to reduce the attraction force at the end of the stroke, so that the pallet arrives less quickly against the core and the clicking noise is finds it diminished. The invention therefore makes it possible to increase the variation in 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 current for holding the pallet against the core. By playing on the relative areas of the first and second zones, it is possible to achieve a compromise between the reduction in effort sought at the end of the race and the increase correlative of the pallet holding current against the core.

In this regard, it is important to ensure that the magnetic flux in the second zone does not exceed a saturation value, which would cause a deterioration in 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 over the face of the pallet opposite at least one of the branches of the core.

According to a first embodiment of the invention, the pallet has 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 projects transversely from the branch 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 towards the second zone where it could more easily be established, which would weaken the efficiency of the recessed portions. Preferably, the core is composed of a stack of sheets, at least one magnetic barrier being inserted in 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 Other characteristics and advantages 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 IA of Figure 2A of an actuator according to the invention in which the pallet is illustrated remote from the core;

- Figure 1B is a schematic sectional view along the plane IB of Figure 2B in which the pallet is illustrated in contact with the core;

- Figure 2A is a partial perspective view of a first embodiment of the invention in which the pallet is illustrated remote from the core, the conductor of the coil 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 in which the pallet is illustrated remote from the core, the conductor of the coil 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;

- Figure 6. is a schematic side view of the actuator of Figure 4.

In the figures, the scales have not been respected, in order to better understand the invention. DETAILED DESCRIPTION OF THE INVENTION With reference to FIGS. 1A and 1B, the actuator illustrated comprises in a manner known per se two coils arranged opposite 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, the turns of which can be 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 the lateral branches 4. The actuating rod 6 is integral with a pallet 8 which has a face 9 parallel to the face 7 of the core 2, and which is forced to move between the coils.

An electronic DC power supply, not shown, supplies the conductor 5 with direct current 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 circulates in the core 2 through the central branch 3 and each of the lateral branches 4. The magnetic flux 11 closes in the pallet 8 by crossing a total air gap equal to the space separating the pallet 8 from the core 2 at the level of the central branch 3 increased by the space separating the pallet 8 from the core 2 at the level of 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 from 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 coil, not shown, which extends opposite the other face of the pallet 8. For the purposes of the description, only the recessed portions 10 taken in face 9 opposite the core will be taken into account.

In the position illustrated in FIG. 1A, the pallet 8 is distant from the core 2 and the withdrawal r of the recessed portions 10 is negligible compared to the distance d measured between the face 9 of the pallet 8 and the face 7 of the core 2. L 'total air gap that must cross the flow is therefore substantially equal to twice the distance d, the presence of the recessed portions 10 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 therefore not disturbed by the presence of the recessed portions 10 when the pallet 8 is still far from the core 2.

In the position illustrated in FIG. 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 of 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 air gap which the flux must cross is therefore substantially equal to the distance of shrinkage 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 attractive force exerted by the coil 1 on the pallet 8 varies in inverse function to the square of the air gap. When the pallet arrives in the vicinity of the core 2 the force of attraction is therefore very significantly reduced with respect to the recessed portions so that, for a given current reduction dynamic, the invention makes it possible to reduce the speed of the pallet more rapidly when it comes into contact with the core. In addition, the additional air gap of the recessed portions reduces the inductive effect of the pallet on the coil 1 and therefore makes it possible to improve the dynamics of 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 longitudinally delimit a first zone 12 of the pallet 8 and of the core 2 for which the total air gap to be crossed by the flow is substantially equal to the withdrawal r of the recessed portions 10, and a second zone 13 of the pallet 8 and of the core 2 for which the total air gap is equal to twice the residual space • ε between the faces 7 and 9.

It will be noted that after bringing the pallet into contact with the core, maintaining the pallet against the core then requires supplying the coil with a holding current which is all the more important as the withdrawal r and the surface of the withdrawal portions are large. The surface of the recessed portions therefore results from a compromise between the reduction in force sought in order to increase the variation in attraction force and a reasonable increase in the holding current. In practice, it has been determined that for a withdrawal 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 zones 12 and 13 it is possible to modulate the attenuation at the end of race of the effort of attraction. However, this modulation is limited by the fact that an excessively large increase in the areas of the recessed portions would risk causing saturation of the second zone 13. Such saturation would cause degradation of the performance of the actuator.

In practice, the total area of the recessed portions will be limited 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 10 project transversely from the side branch opposite over a distance 1 ^at least equal to the withdrawal r of the recessed portion. In the example illustrated, the recessed portions 10 are delimited transversely by a leave 14 of radius equal to the withdrawal r of the recessed portions 10, the center of the leave 14 being situated substantially at the level of the internal edge 15 of the lateral branch. 4 when the pallet 8 is in contact with the core 2. This arrangement minimizes the passage of the flux towards the zone 13 in the vicinity of the internal edge 15 in which the distance to be crossed would be less than the distance for withdrawing the recessed portions, which would reduce the efficiency of the recessed portions 10. Furthermore, the core 2 is advantageously composed of a stack of cut sheets which limit the longitudinal migration of the flow. This arrangement counteracts the tendency of the flow normally expected to be established in zone 12 to migrate towards zone 13 where the total air gap is weaker. In order 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 in the stack of sheets to magnetically isolate the part of the core corresponding to the zone 12 of the corresponding core part in 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 opposite 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 parasitic passage of magnetic flux through the internal edge 15 of the lateral branches 4. The step 17 delimits two zones 12 and 13 in the same way as in the previous embodiment. In the zone 12 corresponding to the step 17, the flow must cross once the withdrawal r of the step 17 in the air gap with the central branch 3 and once the same distance in the air gap with the side branches to be able to establish. For the same weakening as in the first embodiment, it therefore suffices that the withdrawal r of the step 17 is equal to half the distance of withdrawal of the recessed portions 10. In a variant of this embodiment, illustrated in Figure 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 from the center of the pallet 8. The bevel 18 has the same effect as step 17, but it avoids unwanted side effects that could occur along the edge of step 17.

Furthermore in Figure 5, there is illustrated, in an exaggerated manner, the position that the pallet 8 step 17 is likely to present vis-à-vis the core 2 because actuator mounting clearances. It can be seen that the distance between the face 7 of the core 2 and the bottom of the step 17 decreases towards the end of the pallet 8, and the magnetic flux tends to be concentrated at the level of the terminal edge 19 of the pallet 8, which reduces the performance of the actuator.

In FIG. 6, a pallet 8 with bevel 18 has been illustrated in the same configuration as above. It can be seen that the distance between the face 7 of the core 2 and the bevel 18 remains increasing in the direction of the end of the pallet, the risk of concentration of the magnetic flux on the terminal edge 20 of the pallet 8 being then avoided.

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

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

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

Although the invention has been illustrated with recessed portions produced on the pallet, the recessed portions may also be produced 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 the sides of the paper have been illustrated lette and the core as being flat, the faces may take any complementary shape capable of allowing their contact outside the recessed portions.

Although it has been indicated that the retracted portions are delimited transversely by a leave, the recessed portions may be delimited by any other form provided that the recessed portions project transversely from the lateral branch opposite a distance 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, provision may also be made for recessed portions which extend only opposite the central branch. Although the invention has been described in relation to an actuator with two coils, it also applies to a single-coil actuator whose core has active ends facing the two faces of the pallet.

Claims

1. Electromagnetic actuator comprising an actuating member (6) connected to a pallet (8) which is movable under the effect of a motor member comprising at least one coil (1) to generate a magnetic flux in a core (2 ) having a face extending opposite a face of the pallet (8), at least one of the facing faces comprising at least one recessed portion (10; 17 ^' ; 18), characterized in that the pallet (8) and the core (2) are arranged to define, in a first zone (12) of the pallet (8) and of the core (2) encompassing the recessed portion, a first magnetic path which is interrupted by an air gap at least equal to the withdrawal of the recessed portion (10; 17; 18) when the pallet (8) is in contact with the core (2), and in a second zone (13) of the pallet (8) and of the core (2) excluding the portion in. withdrawal, a second magnetic path which is interrupted only by a residual air gap when the pallet (8) is in contact with the core (2), the recessed portion having a total area at most equal to an area bringing the magnetic flux to saturation in the second palette area.

2. Electromagnetic actuator according to claim 1, characterized in that the recessed portion has a total area less than 50% of the total area of the facing faces.

3. electromagnetic actuator according to claim 1, characterized in that the core (2) comprises a central branch (3) and two lateral branches (4) having ends which define the face (7) of the core (2), and in that the recessed portion (10; 17; 18) extends over the face of the pallet (9) opposite at least one of the branches of the core.

4. Electromagnetic actuator according to claim 3, characterized in that the pallet (8) comprises recessed portions (10) which extend opposite the lateral branches (4) of the core.

5. Electromagnetic actuator according to claim 3, characterized in that the recessed portions are symmetrical relative to the actuating member

6. Electromagnetic actuator according to claim 3, characterized in that the recessed portion (10) projects transversely from the opposite branch over a distance (1) at least equal to the withdrawal (r) of the recessed portion (10 ) in relation to the actuator.

7. Electromagnetic actuator according to claim 3, characterized in that the recessed portion (17,18) extends transversely to the three branches (4,3,4) opposite each of them.

8. Electromagnetic actuator according to claim 7, characterized in that the recessed portion (17) is in the form of a bevel.

9. 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.

10. Electromagnetic actuator according to claim 9, characterized in that the core is composed of a stack of sheets, at least one magnetic barrier (16) being inserted in the stack of sheets to separate the sheets making up the first (12) and second (13) zones of the core (2).