EP1229560B1 - Electromagnetic valve actuator with electromagnet for an internal combustion engine - Google Patents

Abstract

The electromagnetic driver has a body with a feed coil (3) and a magnetic plate (16) connected to the valve (18) drive unit (17). The drive unit has a spring return (20,21). There is a permanent magnet (6) in the electromagnet body with a field perpendicular to the feed coil field.

Description

The present invention relates to valve actuators of internal combustion engines.

A valve actuator of the aforementioned type generally comprises two electromagnets between which is formed a gap.

In the air gap is mounted a magnetic pallet connected to the valve to be actuated, movable by the electromagnets against energy storage springs.

The arrangement thus formed forms a harmonic oscillator in which the storage of the energy required for rapid switching is ensured by the springs and the change of position is controlled by means of the electromagnets.

This system is simple in appearance, but it has technical limitations.

The control of the position of the valve is ensured by means of the two coils of the electromagnets by application of current which generates a magnetic field producing a force F.

In the saturation phase, this force is constant and uncontrollable by the current.

Excluding saturation, this force is proportional to the square of the current injected into the coils and inversely proportional to the square of the gap.

This double non-linearity makes very difficult the control of the valve by the electromagnets.

Indeed, at a great distance, that is to say at a distance equal to 3 to 4 mm, the force applied to the pallet is very small, which decreases the range of use and poses a problem with regard to the initialization of the actuator.

At the intermediate distance between 1 and 3 mm, the force is difficult to control by the current because of the aforementioned quadratic dependence.

At a short distance, when the valve approaches its seat for example, the force increases very rapidly, practically without any control by the current. There is a runaway effect responsible for impact noise. This phenomenon is quite comparable to the slam produced by the electromagnet of a closet door.

The force exerted on the pallet is always positive because of its proportionality to the square of the supply current of the coils.

Therefore, the valve can not be slowed down if too much speed is detected.

To this problem relating to the force is added the important presence of eddy currents, which attenuate and delay the effect of the coils.

In order to overcome these drawbacks, up to now it was necessary to make the valve control device more complex, by means of high-performance sensors for position of the valve, of a precise and fast control electronics, a sophisticated software strategy and possibly using a mechanical damper.

Despite these increases in the complexity of the control and control means, the expected performance in terms of impact speed may remain insufficient requiring the implementation of additional means of sound insulation.

At the intake, the actuator must be able to provide the necessary energy for switching. This is to compensate for friction losses that amount to about 0.2 J for a stroke or 8 mm lift of the valve, and therefore the range of electromagnets.

The energy provided by an electromagnet over the whole of the aforementioned race is equal to the integral of the force.

This energy is relatively weak because of the strong decrease of the force for the great values of gap.

For example, at a speed of rotation of the engine of 6000 rpm, on a two-stroke cycle, which would optimize the use of the actuator, the useful power would be 20 W, which is low compared to its mass. , of the order of 1 kg and its large volume.

For an engine of 500 cm ³ , of cubic capacity, one can be satisfied with such dimensions although they remain a handicap.

On the other hand, these dimensions are not compatible with smaller unit displacements.

At the exhaust, the energy to be supplied is of the order of 1.4 J to fight against the pressure in the cylinder chamber during the opening of the valve.

It has been found during tests that current actuators are insufficient in the exhaust and do not allow to operate the engine at full load.

In conclusion, the current actuator has a low power density which limits its use for controlling engine intake valves with a cubic capacity greater than or equal to 500 cm ³ .

The efficiency of an actuator is the ratio between the mechanical energy returned (useful) and the electrical energy consumed. It is of the order of 30%, the losses being due mainly to induced currents and Joule losses.

One engine revolution has a duration of 60 ms at 1000 rpm, while a valve transition lasts about 3.5 ms. It can be seen that at low revs, the system is statistically very often in a stable position, either open or closed.

To maintain the valve in the open or closed position, a current is applied in the coil of the concerned side, in order to combat the force of the spring which tends to bring the valve to the intermediate position.

The actuator lends itself well to this operation, since the force produced by the electromagnet is naturally high at zero air gap.

However, the consumption of electric current weighs heavily in the calculation of the vehicle consumption which is at an average speed of about 1600 rpm, representative of the actual use of vehicles that contains a lot of urban driving at low engine speed. .

For example, 100 W electric require about 200 W for the engine, or about 1.5% of fuel consumption per cycle.

However, maintenance consumption could be theoretically zero since it produces no work.

In conclusion, the consumption of the current actuator is high and can be reduced.

Current actuators have a relatively high height due to the stacking of springs, two electromagnets and an actuating plate or pallet.

In parking, on the engines of current vehicles, there is always a cylinder in compression.

The engine thus provides a complementary parking brake that some users use as an additional brake to the parking brake, especially in the ribs.

When the electromagnetic actuators are used, the valves are in equilibrium position in the middle, so that all the chambers of the engine are at atmospheric pressure and there is no longer any additional braking possible.

Finally, the actuator itself is relatively inexpensive because of its simplicity, but the associated control electronics as well as the valve position sensor, are complex and therefore expensive.

The invention aims to overcome the disadvantages of conventional solenoid valve actuators by creating an actuator, which while at a relatively low cost, has improved performance in all of the areas mentioned above.

It therefore relates to an electromagnetic valve actuator of an internal combustion engine comprising at least one electromagnet comprising a body, at least one supply coil, a magnetic paddle connected to a valve driving member against the action of at least one switching energy storage spring of said valve, characterized in that in the magnetic body of the electromagnet is interposed a permanent magnet whose field is perpendicular to the field generated in said body by said at least one feed reel.

• le corps magnétique dudit électroaimant comprend deux pièces polaires entre lesquelles est disposé ledit aimant permanent, chaque pièce polaire comprenant transversalement à la direction de polarisation de l'aimant, une branche courte et une branche longue, les branches courte et longue d'une pièce polaire définissant des entrefers respectifs avec les branches longue et courte de l'autre pièce polaire, ladite armature étant montée déplaçable dans lesdits entrefers ;
• les branches courte et longue de chaque pièce polaire sont en forme de L, les extrémités libres des branches courte et longue d'une pièce polaire définissant lesdits entrefers avec les extrémités libres des branches longue et courte de l'autre pièce polaire ;
• les extrémités libres des branches des pièces polaires sont parallèles entre elles ;
• lesdites pièces polaires sont en ferrite, ou en matériau à base de poudre de fer agglomérée, ou en tout autre matériau ferromagnétique ;
• l'aimant permanent est disposé entre des parties centrales des pièces polaires et l'actionneur comporte une bobine d'alimentation enroulée autour desdites parties centrales des pièces polaires et de l'aimant ;
• l'aimant permanent est disposé entre les parties centrales desdites pièces polaires et l'actionneur comporte deux bobines d'alimentation portées chacune par une branche d'une pièce polaire correspondante, les branches des deux pièces polaires étant situées du même côté de ladite palette.

According to other characteristics:

• the magnetic body of said electromagnet comprises two pole pieces between which is disposed said permanent magnet, each pole piece comprising transversely to the polarization direction of the magnet, a short branch and a long branch, the short and long branches of a pole piece defining respective air gaps with the long and short legs of the other pole piece, said armature being movably mounted in said air gaps;
• the short and long branches of each pole piece are L-shaped, the free ends of the short and long branches of a pole piece defining said air gaps with the free ends of the long and short branches of the other pole piece;
• the free ends of the branches of the pole pieces are parallel to each other;
• said pole pieces are made of ferrite, or material based on agglomerated iron powder, or any other ferromagnetic material;
• the permanent magnet is disposed between central parts of the pole pieces and the actuator comprises a supply coil wound around said central parts of the pole pieces and the magnet;
• the permanent magnet is disposed between the central parts of said pole pieces and the actuator comprises two supply coils each carried by a branch of a corresponding pole piece, the branches of the two pole pieces being located on the same side of said pallet.

• la Fig.1 est une vue schématique en perspective d'un actionneur électromagnétique de soupape suivant l'invention en position de soupape ouverte;
• la Fig.2 est une vue analogue à celle de la figure 1 montrant l'actionneur en position de soupape fermée ; et
• la Fig.3 est une vue schématique en perspective d'un actionneur électromagnétique de soupape suivant un autre mode de réalisation de l'invention.

The invention will be better understood with the aid of the description which follows, given solely by way of example and with reference to the appended drawings, in which:

• the Fig.1 is a schematic perspective view of an electromagnetic valve actuator according to the invention in open valve position;
• the Fig.2 is a view similar to that of the figure 1 showing the actuator in the closed valve position; and
• the Fig.3 is a schematic perspective view of an electromagnetic valve actuator according to another embodiment of the invention.

The electromagnetic valve actuator shown in FIG. figure 1 comprises an electromagnet 1 comprising a body of magnetic material 2 carrying a supply reel 3.

The body 2 essentially comprises two pole pieces 4,5 between which is disposed a permanent magnet 6 whose direction of polarization indicated by the arrow 7 is perpendicular to the direction of the magnetic field generated by the supply reel 3.

Each of the pole pieces 4,5 advantageously made of ferrite, or of agglomerated iron powder-based material comprises a central portion 8, 9 around which the turns of the supply coil 3 which also surrounds the permanent magnet 6 pass. .

From the ends of the central portions 8 and 9 extend branches 10, 11, 12 and 13 perpendicular to said central portions 8, 9 and to the permanent magnet 6.

A branch 10,12 of each pole piece 4,5 is a short branch and a branch 11,13 of each pole piece is a long branch.

The short branch 10 of the pole piece 4 and the long branch 13 of the pole piece 5, extend from the ends of the central zones 8 and 9 located opposite one another.

The long branch 11 of the pole piece 4 and the short branch 12 of the pole piece 5 extend from the other ends of the central zones 8 and 9 located opposite one another.

Each of the branches 10 to 13 of the pole pieces 4,5 has a respective end 10a to 13a perpendicular to the corresponding branch, so that each of these branches has an L shape.

The short branches 10 and 12 form with the respective long branches 11, 13, air gaps 14,15 whose value corresponds to the lifting of a valve to actuate.

In these gaps is mounted movable in translation, a magnetic pallet or plate 16 to which is connected an actuating rod 17 of a valve 18.

The actuating rod 17 and the tail 19 of the valve 18 are surrounded by two return springs 20, 21 whose ends facing each other bear against a connecting piece 22 of the stem. actuation 17 and tail 19 of the valve 18.

The head 23 of the valve 18 cooperates with a not shown valve seat of a motor yoke 24.

The short branches 10 and 12 of the pole pieces 4 and 5 define with the plate 16, a high magnetic circuit. The long branches 11 and 13 form with the magnetic plate 16, a low magnetic circuit.

Between the magnetic plate 16 and the branches of the pole pieces 4 and 5 defining between them the air gaps 14 and 15, the plate 16 and the short and long branches in turn define air gaps e1, e2 whose sum is equal to the lifting L of the valve, this lift being equal to the difference between the gap 14,15 between each short branch and each respective long branch of the pole pieces 4 and 5 and the thickness of the plate 16.

• Bih : induction magnétique créée par la bobine d'alimentation 3 dans l'entrefer e1 entre le circuit magnétique haut défini par les branches courtes 10,12 des pièces polaires 4 et 5 et la palette 16 ;
• Bib : induction magnétique créée par la bobine d'alimentation 3 dans l'entrefer e2 entre le circuit magnétique bas défini par les branches longues 11,13 des pièces polaires 4 et 5 et la palette 16.

For the following explanation, we will adopt the following notations:

• Bih: magnetic induction created by the supply coil 3 in the gap e1 between the high magnetic circuit defined by the short branches 10,12 of the pole pieces 4 and 5 and the pallet 16;
• Bib: magnetic induction created by the supply coil 3 in the gap e2 between the low magnetic circuit defined by the long branches 11,13 of the pole pieces 4 and 5 and the pallet 16.

When the magnet 6 is long enough in the direction of its magnetization, the flow of the coil passes successively in the branch 12, the air gap e1, the pallet 16, the air gap e2 and goes up in the branch 13. It also passes in the branch 11, the gap e2, the pallet 16, the gap e1 and the rise in the branch 10. In this case Bih = Bib = Bi.

• Ba : induction magnétique créée par l'aimant permanent 6.

When the magnet 6 is shorter, which corresponds to the actual case, the flow of the coil flow also passes between the parts 4 and 5 of the magnetic circuit, and more precisely between the two central parts 8 and 9, which constitute a circuit parallel with that of air gaps. This parallel circuit is particularly interesting at low air gap because it increases the efficiency of the coil when the gap is very small (pallet high or low position).

• Ba: magnetic induction created by the permanent magnet 6.

S étant la surface équivalente d'attraction de la palette.During the opening phase, the total force exerted on the plate 16 is directed downwards. It is given by the relation: $$\mathrm{F}=\frac{{\left(\mathit{Bih}-\mathit{<figure-callout\; id="2"\; label="Ba"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">Ba</figure-callout>}\right)}^2}{2{\mu }_0}\mathrm{S}-\frac{{\left(\mathit{<figure-callout\; id="2"\; label="Bib"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">Bib</figure-callout>}\right)}^2}{2{\mu }_0}\mathrm{S}$$

S being the equivalent area of attraction of the pallet.

The application of a negative current to the supply coil 3 makes it possible to increase the force, that is to say the phase of attraction in opening.

The application of a zero current makes it possible to maintain the magnetic plate 16 and consequently the valve 18 in position without consumption of electric current.

The application of a positive current equal to or greater than Ba / 2 makes it possible to cancel and even to reverse the total force applied on the board and in particular in the starting phase.

In the closing phase of the valve, the total force F exerted on the plate is directed upwards is given by the relation: $$\mathrm{F}=\frac{{\left(\mathit{BiB}\mathit{+}\mathit{<figure-callout\; id="2"\; label="Ba"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">Ba</figure-callout>}\right)}^2}{2{\mu }_0}\mathrm{S}-\frac{{\left(\mathit{<figure-callout\; id="2"\; label="Bih"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">Bih</figure-callout>}\right)}^2}{2{\mu }_0}\mathrm{S}$$

The application of a positive current makes it possible to increase the force in order to achieve the closing attraction phase.

The application of a zero current keeps the valve in position without consumption of electrical energy.

The application of a negative current less than or equal to -Ba / 2 makes it possible to cancel and even to reverse the total force in the starting phase.

The valve being closed, it is kept closed by the sole force of the permanent magnet 6.

A negative current is applied to the coil 3.

The plate 16 comes off and is pushed back by the lower spring 21 which gives it speed and compresses the upper spring 20.

The plate describes a typical sinusoidal trajectory of a harmonic system in free oscillation.

Maintaining the negative current throughout the travel of the plate 16 compensates for energy lost by friction. The valve 18 then arrives in the open position shown in FIG. figure 1 with a very low speed.

It is then possible to cancel the current in the coil, the plate 16 being held by the force of the permanent magnet 6.

When the valve is open, the same process is applied, this time with a positive current.

On the figure 3 , there is shown in perspective a variant of the electromagnetic valve actuator according to the invention.

The construction of this actuator is similar to that of the actuator shown in FIG. figure 1 .

The same elements of the actuators figures 1 and 3 are designated by the same reference numbers.

The actuator of the figure 3 differs from that of the figure 1 in that it comprises two supply coils 30, 31 each wound around a branch of a pole piece 4.5.

In the present example, the supply coils 30, 31 are wound around the respective short branches 10, 12 of the pole pieces 4,5.

Said short branches 10, 12 are situated on the same side of the magnetic pallet 16.

The coils 30, 31 are fed so as to generate a flow of the same direction as the flux generated by the coil 3 of the actuator of the figure 1 they replace.

The winding directions of the two coils 30, 31 as well as the supply currents of these coils are such that the effects of the fields generated by them add up.

Thus, the operation of the two-coil actuator of the figure 3 is in all respects similar to that of the actuator of the figure 1 .

It can therefore be seen that, thanks to the arrangement just described, it is possible to control the movements of a valve with the aid of an electromagnetic actuator with considerably greater precision than that which can be obtained with the electromagnetic actuators. conventional electromagnetic actuators.

Claims (7)

1. Electromagnetic actuator for an internal combustion engine valve, comprising at least one electromagnet comprising a body, of at least one supply coil (3; 30, 31), a magnetic vane (16) connected to a member (17) for driving the valve (18) against the action of at least one spring (20, 21) that stores the energy of switching of the said valve, characterized in that interposed within the magnetic body of the electromagnet is a permanent magnet (6) the field of which is perpendicular to the field generated within the said body by the said at least one supply coil (3; 30, 31).
2. Electromagnetic actuator according to Claim 1, characterized in that the magnetic body (2) of the said electromagnet comprises two pole pieces (4, 5) between which the said permanent magnets (6) is positioned, each pole piece comprising, transverse to the direction of polarization of the magnet (6), a short branch (10, 12) and a long branch (11, 13), the short and long branches (10, 11) of one pole piece (4) defining respective air gaps (14, 15) with the long and short branches (13, 12) of the other pole piece (5), the said vane (16) being mounted such that it can move in the said air gaps.
3. Electromagnetic actuator according to Claim 2, characterized in that the short and long branches (10, 12, 11, 13) of each pole piece are L-shaped, the free ends (10a, 11a) of the short and long branches (10, 11) of one pole piece (4) defining the said air gaps (14, 15) with the free ends (13a, 12a) of the long and short branches (13, 12) of the other pole piece (5).
4. Actuator according to one of Claims 2 and 3, characterized in that the free ends (10a, 11a, 12a, 13a) of the branches of the pole pieces (4, 5) are mutually parallel.
5. Actuator according to one of Claims 2 to 4, characterized in that the said pole pieces (4, 5) are made of ferrite or of a material based on an agglomerated iron powder.
6. Actuator according to one of Claims 1 to 5, characterized in that the permanent magnet (6) is positioned between central parts (8, 9) of the pole pieces (4, 5), and in that it comprises a supply coil (3) wound around the said central parts (8, 9) of the pole pieces (4, 5) and of the magnet (6).
7. Actuator according to one of Claims 2 to 5, characterized in that the permanent magnet (6) is positioned between central parts (8, 9) of the said pole pieces (4, 5), and in that it comprises two supply coils (30, 31) each borne by one branch (10, 12) of a corresponding pole piece (4, 5), the branches (10, 12) of the two pole pieces (4, 5) lying on the same side of the said vane (16).

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