FR3074228A1 - ELECTROMAGNETIC DEVICE - Google Patents

Abstract

The invention relates to an electromechanical device, in particular a solenoid valve (1), comprising: - a coil (20), - an element (40) movable under the effect of the magnetic field generated by the coil, - an electrical resistance (2) of CTN type electrically connected in series with the coil and thermally coupled thereto so as to at least partially compensate for the variation of the resistivity of the coil with the temperature.

Description

ELECTROMAGNETIC DEVICE

The present invention relates to electromechanical devices comprising a coil and a movable element under the effect of the magnetic field of the coil, and more particularly but not exclusively the so-called canister bleed solenoid valves used in the automotive field.

The tank of vehicles with internal combustion engines is equipped with an activated carbon filter called a canister which absorbs and retains the fuel vapors coming from the tank.

The canister is connected to the engine intake via a purge solenoid valve which is closed when the engine is stopped and which opens to allow the filter to be purged when the engine is running.

EP 1 181 442 discloses an example of a purge solenoid valve. Conventionally, the solenoid valve comprises a hollow fixed core made of a ferromagnetic material extending along an axis, a coil mounted around the fixed core and a closure element, movable along the axis of the fixed core under the effect of the magnetic field. generated by the coil.

The coil of this solenoid valve undergoes during engine operation a significant temperature variation which causes a variation in its electrical resistivity, and modifies its response time.

There is an advantage in reducing the amplitude of variation of the solenoid valve response time in order to improve the operation of the purge circuit.

More generally, for electromechanical devices comprising a coil and a movable element under the effect of the magnetic field of the coil, there is an advantage in benefiting from the most homogeneous operating conditions possible despite the temperature variations to which these devices are exposed in their environment of use.

There is a need to further improve the electromechanical devices and in particular the solenoid valves, in particular with a view to obtaining performances varying relatively little with temperature.

The invention aims to meet this need and it achieves this by means of an electromechanical device, in particular a solenoid valve, comprising:

A coil, a movable element under the effect of the magnetic field generated by the coil, a CTN type electrical resistance electrically connected in series with the coil and thermally coupled to it so as to at least partially compensate for the variation in resistivity of the coil with temperature.

The presence of the CTN resistor makes it possible to at least partially compensate for the change in the conductivity of the electrical conductor of the coil with the temperature; thus, the resistance of the assembly constituted by the coil and the NTC resistance varies less than if the coil were alone.

The electrical performance of the device then varies to a lesser extent with temperature, which makes it possible to control the device more precisely, and improves the management of fuel vapors in the case where this device is a purge solenoid valve.

Preferably, the device includes an electrical resistance mounted in parallel with the CTN type resistance.

The benefit is twofold. First, the presence of this resistance reduces the compensation error due to the non-linearity of the CTN. Then, the resistor ensures continuity of supply to the coil in the event of failure of the CTN type resistor.

The resistor can be a power resistor, for example in the form of a discrete component with a power between 1 and 5W.

Preferably, in order to improve the thermal coupling between the coil and the resistor of the CTN type, and to decrease the temperature gradient between the two, the device comprises at least one thermal conductive element, for example made of copper, of higher thermal conductivity or equal to 100, better to 200 Wnf'lC ¹ , better greater than or equal to 300 Wnf'lC ¹ , placed between the coil and the CTN type resistor.

This thermal conductive element can be in the form of a ring or produced otherwise.

The thermal conductive element may comprise a first portion in contact with the coil and a second portion in contact with the resistor of the CTN type. The first portion is preferably in the form of a cylinder portion, of the same axis as the coil, and surrounds the latter for example over 180 °, or even over 270 ° or more.

In the absence of such a thermal conductive element, and in particular when the device comprises a plastic body in which the coil is received, it is possible to ensure that said body has a resistance between the coil and the resistor of the CTN type. relatively low thermal, preferably less than or equal to 50 KW ' ¹ . One way to do this is to make sure you have a thin wall between these two elements. Thus, the body advantageously has a wall which is thinned in an area between the coil and the resistor of the CTN type. The body may in particular have, between the CTN type resistance and the coil, a thickness of material less than or equal to 1.5 mm, better still at 1 or 0.75 mm, and preferably greater than 0.5 mm. Preferably, the plastic material of said body has, in particular between the coil and the electrical resistance of the CTN type, an electrical conductivity greater than or equal to 0.25 W / m / K, better still to 1 W / m / K.

The body may include a tubular wall defining a housing for the coil, this wall entirely surrounding the coil in at least one section plane perpendicular to the axis thereof. This tubular wall may have come from injection molding with the body.

Preferably, the device is a solenoid valve, in particular for purging the fuel vapor management circuit of a motor vehicle, but the invention is applicable to other types of electromechanical devices where compensation for the variation in the electrical conductivity of the coil must be achieved.

Conventionally, when the device is a solenoid valve, this can then include:

a hollow fixed core made of a ferromagnetic material, extending along an axis,

- the coil, mounted around the fixed core,

- a plunger core, movable along the axis of the fixed core under the effect of the magnetic field generated by the coil.

Preferably, the fixed core has a thinned zone, positioned axially between the axial ends of the plunger core. This makes it easier to reach saturation of the magnetic material of the fixed core in the thinned area and thus to increase the attraction force of the plunger to the position it takes when the coil is electrically supplied.

This particular feature makes it possible to increase the performance of the solenoid valve, for example to make it faster during its passage from the shutter state to the open state, or allows, with constant characteristics, to reduce the cross-section. copper and / or the current in the coil.

The thinned zone can thus advantageously be produced so that when the coil is traversed by its nominal current, it is more than 95% saturated by magnetic induction, or even 100%.

The thinned area can be achieved in various ways. Preferably, the thinned zone has a progressive decrease in its section to a minimum of section, then a progressive increase in its section from this minimum of section. This makes it possible to limit magnetic field leaks, by avoiding very angular zones, which create strong field gradients.

The thinned zone can be defined at least partially by at least one recess open radially outward, formed on the fixed core. This hollow is for example formed by machining with the rest of the fixed core.

The thinned area can be delimited externally by an annular groove of general V shape, open radially outwards. This groove is preferably biconical in shape. It can be symmetrical with respect to a median plane of symmetry, perpendicular to the longitudinal axis of the fixed core. Preferably, the thinned zone is delimited at least partially by at least one cone whose angle relative to the axis of the fixed core is between 15 and 35 °.

The fixed core may have a thickness of material e _n outside the thinned zone and a minimum thickness e _m i _n in the thinned zone, with e _m in <e _n / 2. We can have e _n > 2 mm, better 2 <e _n <4 mm. Preferably, we have _m j _n <1.5 mm, better 0.75 mm <e _min <1.25 mm.

The distance measured along the axis of the fixed core, between the thinnest zone of thickness e _m i _n and the axial end closest to the plunger core, can be between 1 and 2 times e _m j _n .

The fixed core may have, along at least part of the thinned area, a cylindrical surface of revolution, of the same axis as the fixed core. Preferably, this cylindrical surface extends axially along at least part of the groove.

The fixed core may have a shoulder and an extra thickness extending between the cylindrical surface and the shoulder. This extra thickness can be used to adjust the intensity of the pulling force of the plunger. The shoulder can serve as a driving stop for an insert made of a non-magnetic material, introduced into the fixed core, serving as a guide for a return spring of the plunger core in the closed position.

The plunger core can carry a valve seal and be returned to a closed position by a coil spring.

The invention will be better understood on reading the detailed description which follows, examples of non-limiting implementation thereof, and on examining the appended drawing, in which:

FIG. 1 represents, schematically, in perspective, an example of a solenoid valve according to the invention,

- Figure 2 shows in axial section the solenoid valve of Figure 1,

FIG. 3 is an electrical diagram illustrating a possibility of connection of the NTC resistor,

- Figure 4 illustrates the effect of the temperature variation on the electrical resistance of different components of the solenoid valve,

- Figure 5 shows in cross section the solenoid valve,

FIG. 6 represents the electromagnetic system of the solenoid valve of FIG. 1 in isolation,

FIG. 7 is an axial section of the system of FIG. 6,

FIG. 8 represents the fixed core in isolation,

FIG. 9 is a detail of FIG. 7,

FIG. 10 represents the fixed core in axial section in isolation,

FIG. 11 is a result of simulation of the intensity of the magnetic induction in the fixed core and the plunger core during the operation of the solenoid valve, and

- Figure 12 is a view similar to Figure 5 of an alternative embodiment of the solenoid valve.

The solenoid valve 1 shown in Figure 1 is intended to be mounted within a fuel vapor evacuation circuit of a motor vehicle, but the invention is not limited to this application, nor to a solenoid valve . The solenoid valve can be connected to inlet and outlet conduits, not shown, by means of respective end pieces 81 and 82. The end piece 82 can be molded with the body 84 of the solenoid valve, made of plastic, and the end piece 81 with a part 83 which is attached to the body 84 and closes it. The solenoid valve 1 has a connector for its electrical connection, of which the base 85 can be seen in FIG. 1.

The solenoid valve 1 is, in the example considered, closed at rest, and opens when electrically supplied, for example at a DC voltage between 10 and 15V. The materials of the solenoid valve are chosen to resist hydrocarbon vapors, especially gasoline.

The body 84 of the solenoid valve 1 internally houses an electromagnetic system, shown in isolation in FIG. 6. The latter comprises, as can be seen in particular in FIGS. 2 and 7, a fixed core 10, tubular of axis X, carried at one end by a plate 13 extending perpendicular to the axis X, the core 10 and the plate 13 being made of a soft ferromagnetic material such as for example iron or ferromagnetic steel. The core 10 and the plate 13 can be made in a single piece in a monolithic manner, as illustrated in FIG. 8, in particular by machining.

The solenoid valve 1 comprises a coil 20 mounted on a support 21, for example of plastic material, of axis X, this coil 20 extending around the fixed core 10 to generate within it a magnetic field when electrically powered. The coil 20 is for example made of insulated copper wire, in particular enameled.

An external yoke 30 made of a ferromagnetic material makes it possible to loop back the magnetic flux between the end 11 of the fixed core 10 opposite the plate 13 and the latter. The plate 13 has diametrically opposite reliefs 14 at its lateral ends, for the attachment of fixing lugs 31 of the cylinder head 30.

The solenoid valve 1 also comprises an element movable along the axis X under the effect of the magnetic field generated by the coil 20, this movable element being in the form of a plunger core 40, made of a ferromagnetic material, movable axially according to the X axis inside the fixed core 10.

The plunger core 40 is inside the fixed core, in the example considered, and the flow controlled by the solenoid valve, which is preferably gaseous (fuel vapors in this case), takes place in contact with it when the solenoid valve is open.

Preferably, the plunger core 40 is made of a soft magnetic material, which loses its magnetization when the magnetic field of the coil ceases, as does the fixed core 10.

The plunger core 40 comprises, as can be seen in FIG. 7, a tubular part 41 and a head 42 formed by an annular return towards the inside. The head 42 is crossed at its center by an orifice for mounting a valve seal 50. The latter has an annular groove in which the return 42 engages and bears against a seat 80, visible in FIG. 2 , when the solenoid valve is at rest, to close the associated duct 81.

A return spring 60 ensures the return of the plunger core 40 to its rest position, closing the above-mentioned conduit 81, in the absence of electrical supply to the solenoid valve. This spring 60 is interposed between a stop 61 formed by an insert 62 fixedly housed in the core 10, and the inner face of the head 42 of the plunger core 40. The spring 60 is for example of helical shape, being guided by Γinsert 62 The latter may have a shoulder which defines the stop 61. This shoulder may be formed by an enlarged middle part 63 of 62 insert 62, situated between end parts 66 of truncated ogival shape, to facilitate flow within the solenoid valve when it is open. In the open configuration, the seal 50 is detached from its seat 80.

The insert 62 is made of a non-magnetic material, for example a thermoplastic material, and comes to bear, as can be seen in particular in FIG. 5, by a shoulder 63 against a corresponding shoulder 15 of the fixed core 10.

The fixed core 10 advantageously has a thinned zone 70 which makes it possible to concentrate the magnetic induction therein to the point of almost saturating the magnetic material which constitutes this fixed core, as will be detailed below.

The electrical resistance of the coil 20 increases linearly with temperature, as illustrated in FIG. 4.

In order to compensate for this increase, the solenoid valve includes a resistor 2 of the CTN type, the resistance of which decreases when the temperature increases, electrically connected in series with the coil 20, as illustrated in FIG. 3.

An example of a decrease in the electrical resistance of resistance 2 of the CTN type with temperature is illustrated in FIG. 4.

A power resistor 3 can be mounted in parallel with the resistor 2 to adjust the way in which the total resistance between the power point 4 and the mass 5 changes as a function of the temperature. The variation of the electrical resistance of the circuit formed by the resistors 2 and 3 in parallel is illustrated in FIG. 4.

It can also be seen in this figure that the evolution of the electrical resistance of the overall circuit between terminals 4 and 5 is relatively constant, which gives the solenoid valve performances that are substantially constant with temperature, in a range ranging for example from -25 °. C at + 120 ° C.

Preferably, the resistor 2 is disposed within the solenoid valve so as to have a good thermal coupling between the coil 20 and the resistor 2, so that any variation in resistivity of the coil 20 linked to a variation in its temperature is compensated as quickly as possible by a corresponding change in the temperature of the resistor 2.

A first way of ensuring this thermal coupling is to reduce the thermal resistance between the coil 20 and the resistor 2, for example by varying the thickness of material separating the coil 20 from the resistor 2.

It is thus possible, as illustrated in FIG. 5, to make the resistor 2 as close as possible to the coil 20 by virtue of a thinning of the wall 8 surrounding the coil 20, in a zone 7 separating the coil 20 from the resistance 2 The wall 8 can be cylindrical outside the thinned zone 7, at least in the portion separating the housing receiving the coil and the compartment receiving the resistors 2 and 3, and having a thickness / between outside the thinned zone 7 1.5 mm and 2.5 mm, preferably greater than 1.5 mm, for example 2 mm.

Preferably, the wall thickness r in the thinned zone 7 is less than 1.5 mm, for example of the order of 1 mm, so as to have a thermal resistance less than 50 K / W between the resistance 2 and the coil 20. This thickness may depend on the plastic material used, and on its conductivity, for example due to the presence of fillers.

Preferably, the thermal conductivity of the material of the wall 8 is better than 0.25 W / m / K.

A good synchronization of the temperature of the resistor 2 is thus obtained with respect to the coil 20 and the error of correction of the temperature by the resistor 2 is reduced.

It is still possible to thermally couple the resistor 2 and the coil 20 using a coupling element made of a material which is a good conductor of heat. In this case, the wall 8 may not have a thinned zone 7.

FIG. 12 shows an example of such a thermal coupling element 100, for example made of copper or aluminum, and more generally in any good thermal conductor with thermal conductivity better than 200, or even 300 Wnf'lC ¹ . We see in this figure that the wall 8 which defines the housing receiving the coil can be cylindrical with the same axis as the coil 20, at least on its portion separating the coil 20 from the resistor 2.

The element 100 may be in the form of an aluminum or copper ring, which has a portion 100a engaged on at least part of the coil 20 at its periphery, as illustrated, and an opposite portion 100b which extends to resistance 2 and on contact. The portion 100a comes into contact with the coil 20 at its periphery, for example over 180 ° around the axis of the coil, as illustrated. The portion 100b extends for example outside the wall 8, in contact with the latter and the resistor 2.

Thus, any variation in temperature of the coil 20 is rapidly transmitted to the resistor 2.

The presence of a thermal coupling element 100 makes it possible, if desired, to avoid the presence of a thinning of the wall 8 surrounding the coil 20, in the zone extending between the coil 20 and the resistor 2.

Returning to FIGS. 8 to 11, it is possible to give the thinned zone 70 present on the fixed core 10 various shapes. However, as illustrated in FIG. 10 in particular, it is preferred to produce the thinned zone 70 with a hollow biconical shape. The thinned zone 70 is delimited, on the radially outer side, by a groove 71 having two conical surfaces 72 and 73 of axis X, respectively convergent and downward and diverging upward. The angle that each conical surface 72 or 73 makes with the axis X is for example between 15 and 35 °.

The presence of the saturated thinned zone 70 ensures strong magnetic coupling with the plunger core. There is preferably a 100% saturation of the material by magnetic induction in the thinned zone 70.

FIG. 11 shows the result of a simulation showing the intensity of the magnetic induction in the material of the fixed core 10, the saturation occurring where the wall of the fixed core 10 is the thinnest. In this figure, the light areas correspond to the areas where the magnetic induction is strongest.

The taper of surfaces 72 and 73 tends to ensure homogenization of the magnetic induction in the zone where the reduction in section is greatest.

The tilt value a above makes it possible to ensure a coupling without too much magnetic leakage, but strong enough to ensure a discontinuity in magnetic induction due to the saturation in the thinned zone 70.

We see in Figure 9 that there is, at rest, a gap 88 of length e along the axis X between the lower end of the plunger core 40 and the shoulder 15 of the fixed core 10; this air gap 88 allows the plunger core 40 to move axially downward when the electric coil is supplied, under the effect of the magnetic field created by it.

The fixed core 10 may have on its radially inner surface, facing the plunger core 40, in particular in the area at the level of the groove 71, a cylindrical surface of revolution 75 around the axis X, as illustrated in FIG. 10.

An additional thickness 76 can be formed below the zone where the wall thickness of the fixed core 10 is minimal, as seen in FIG. 10.

Such additional thickness 76 allows, by choosing its axial extension and its thickness, to precisely adjust the force exerted on the plunger core 40 when the coil 20 is electrically supplied.

The bottom of the groove 71 may have, on the radially outer side, in axial section, a radius, for example of the order of 0.2 mm.

The overlapping distance l between the bottom of the groove 71 and the lower end of the plunger core 40, measured along the axis X, is for example between 0.1 and 0.4 mm, being for example of the order 0.3mm. This distance l is for example between 1 and 2 times e _m in.

The thickness e _n of the fixed core 10 outside the thinned zone verifies for example the relation e _m j _n <e _n / 2 where e _m j _n is the minimum thickness in the thinned zone, as can be seen on FIG. 6. We have for example e _n > 2 mm, better 2 <e _n <4 mm, and e _m j _n <1.5 mm, better 0.75 mm <e _m in <1.25 mm.

Of course, the invention is not limited to the examples which have just been described. One can in particular modify the shape of the thinned zone as a function of the desired result and in particular of the position that one seeks to give to the plunger core 40 when the solenoid valve is electrically supplied.

The thermal coupling between the resistor 2 and the coil 20 can also be carried out otherwise. In particular, it is possible to combine both the coupling using a good thermal conductive element 100 and a reduction in the thickness of the wall 8 between the coil 20 and the resistor 2.

The invention can be applied to linear actuators.

Claims (15)

1. Electromechanical device, in particular solenoid valve (1), comprising: A coil (20), an element (40) movable under the effect of the magnetic field generated by the coil, an electrical resistor (2) of the CTN type electrically connected in series with the coil and thermally coupled to the latter so as to at least partially compensate for the variation in the resistivity of the coil with temperature. 2. An electromechanical device according to claim 1, comprising an electrical resistor (3) mounted in parallel with the resistor (2) of the CTN type. 3. Device according to one of the preceding claims, comprising at least one thermal conductive element (100) of thermal conductivity greater than or equal to 100, better 200 Wnf'K ' ^1, disposed between the coil (20) and the resistor (2 ) of CTN type. 4. Device according to claim 3, the thermal conductive element (100) being of thermal conductivity greater than or equal to 300 WnT ¹ K ' ¹ 5. Device according to one of claims 3 and 4, the thermal conductive element (100) being in the form of a ring. 6. Device according to any one of claims 3 to 5, the thermal conductive element comprising a first portion (100a) in contact with the coil (20) and a second portion (100b) in contact with the resistor (2) of type CTN. 7. Device according to claim 6, the first portion (100a) being in the form of a cylinder portion of the same axis as the coil (20) 8. Device according to any one of claims 3 to 7, the thermal conductive element (100) being made of copper. 9. Device according to any one of the preceding claims, comprising a body (84) of plastic material in which is received the coil (20). 10. Device according to claim 9, said body having between the coil (20) and the resistor (2) of the CTN type a thermal resistance less than or equal to 50 KW ′ ¹ 11. Device according to claim 9 or 10, said body having a wall (8) which is thinned in a zone (7) between the coil (20) and the resistor (2) of the CTN type. 12. Device according to any one of claims 9 to 11, the body having between the resistor (2) of the CTN type and the coil (20) a thickness of material less than or equal to 1.5 mm, and preferably greater than 0 , 5 mm. 13. Device according to any one of claims 9 to 12, the plastic material 5 of said body (84) having an electrical conductivity greater than or equal to 0.25 W / m / K. 14. Device according to any one of claims 9 to 13, said body (84) comprising a tubular wall (8) defining a housing for the coil (20), this wall (8) completely surrounding the coil (20) in au minus a cutting plane 10 perpendicular to the axis thereof. 15. Device according to any one of the preceding claims, being a solenoid valve (1), in particular for purging the fuel vapor management circuit of a motor vehicle.