EP1174595A1 - Valve actuator for internal combustion engine - Google Patents

Abstract

The valve activator comprises two electromagnets (1,2) each comprising a supply reel (5,6) and a magnetic armature (8), located between the electromagnets, connected to a valve driving part (9) against the action of a commutation energy storage spring (13,14). A permanent magnet (22,23) interposed in the body of each electromagnet has its magnetization parallel to the field generated in the body by the corresponding supply reel.

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 provided an air gap.

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

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

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

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

In the saturation phase, this force is constant and cannot be controlled by the current.

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

This double non-linearity makes it very difficult to control the valve by 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 low, which reduces the range of use and poses a problem regarding initialization of the actuator.

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

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

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

Therefore, you cannot slow the valve down if you notice a speed too important.

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

In order to remedy these drawbacks, we have been obliged so far, to make the valve control device more complex, using sensors high-performance valve position, electronic control precise and fast, a sophisticated software strategy and possibly having use of a mechanical shock absorber.

Despite these increases in the complexity of control means and control, the expected performance in terms of impact speed may remain insufficient forcing additional resources to be implemented sound insulation.

On admission, the actuator must be able to provide the necessary energy at switching. This is to compensate for friction losses which rise at about 0.2 J for an 8 mm stroke or lift of the valve, and by therefore from the range of electromagnets.

The energy provided by an electromagnet throughout the race above, is equal to the integral of the force.

This energy is relatively low due to the strong decrease strength for the great air gap values.

For example, at an engine speed 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 unit displacement, one can be satisfied with such dimensions although they remain a handicap.

However, these dimensions are not compatible with displacements weaker units.

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

It was found during tests that the current actuators are insufficient exhaust and do not allow the engine to run at full load.

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

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

An engine revolution has a duration of 60 ms at 1000 rpm, while a valve transition takes approximately 3.5 ms. We can see that at low speed, the system statistically very often in a stable position, either open or closed.

To keep the valve in the open or closed position, apply a current in the coil on the side concerned, in order to fight against the force of the spring which tends to return the valve to the intermediate position.

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

However, the consumption of electric current weighs heavily in the calculation of the consumption of the vehicle which is done at an average speed of 1600 RPM approximately, representative of the actual use of vehicles which contains a lot driving at low engine speeds.

For example, 100 W electrical requires approximately 200 W for the internal combustion engine, approximately 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 large height due to stacking of springs, two electromagnets and a plate actuator or pallet.

When parked, on the engines of current vehicles, there is always a cylinder in compression.

The engine thus provides an additional parking brake that some users use as an additional brake to the handbrake, in particular in the ribs.

When using electromagnetic actuators, the valves are in an equilibrium position in the middle, so that all the engine chambers are at atmospheric pressure and there is no more additional braking possible.

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

The invention aims to remedy the drawbacks of electromagnetic actuators of conventional valves by creating an actuator, which while being of a relatively low cost price, presents performances improved in all the areas mentioned above.

It therefore relates to an electromagnetic valve actuator internal combustion engine comprising two electromagnets each comprising a supply coil, a magnetic pallet placed between the two electromagnets, linked to a valve drive member against the action of at least one switching energy storage spring of said valve, characterized in that in the magnetic body of at least one electromagnet is interposed a permanent magnet whose magnetization combines with field generated in said body by the supply coil.

• les corps magnétiques des deux électroaimants définissant entre eux un entrefer dans lequel ladite palette est montée déplaçable à l'encontre d'au moins un ressort antagoniste de stockage d'énergie de commutation, un aimant permanent est interposé dans le corps magnétique de chaque électroaimant ;
• l'aimant permanent est interposé dans le corps magnétique de l'électroaimant du haut ;
• le corps de chaque électroaimant comporte deux pièces polaires, un aimant permanent étant interposé entre les deux pièces polaires du corps de chaque électroaimant ;
• l'aimant permanent est disposé dans le corps de l'électroaimant de manière que l'aimantation de l'aimant permanent soit parallèle au champ engendré dans ledit corps par la bobine d'alimentation correspondante ;
• l'aimant permanent est disposé dans le corps de l'électroaimant de manière que l'aimantation de l'aimant permanent soit incliné par rapport au champ engendré dans ledit corps par la bobine d'alimentation correspondante.

According to other characteristics:

• the magnetic bodies of the two electromagnets defining between them an air gap in which said pallet is mounted displaceable against at least one opposing switching energy storage spring, a permanent magnet is interposed in the magnetic body of each electromagnet;
• the permanent magnet is interposed in the magnetic body of the upper electromagnet;
• the body of each electromagnet comprises two pole pieces, a permanent magnet being interposed between the two pole pieces of the body of each electromagnet;
• the permanent magnet is arranged in the body of the electromagnet so that the magnetization of the permanent magnet is parallel to the field generated in said body by the corresponding supply coil;
• the permanent magnet is arranged in the body of the electromagnet so that the magnetization of the permanent magnet is inclined relative to the field generated in said body by the corresponding supply coil.

• la Fig.1 est une vue schématique d'un premier mode de réalisation d'un actionneur électromagnétique à deux électroaimants suivant l'invention ;
• la Fig.1a est une vue schématique partielle d'une variante de l'actionneur de la Fig. 1 ;
• la Fig.2 est une vue schématique en coupe d'un autre mode de réalisation de l'actionneur électromagnétique de soupape à deux électroaimants suivant l'invention ;
• la Fig.3 est une vue schématique en coupe d'encore un autre mode de réalisation de l'actionneur électromagnétique de soupape suivant l'invention; et
• la Fig.4 est un graphique comparatif de la force exercée sur la palette d'un actionneur pourvu ou non d'un aimant permanent.

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

• Fig.1 is a schematic view of a first embodiment of an electromagnetic actuator with two electromagnets according to the invention;
• Fig.1a is a partial schematic view of a variant of the actuator of Fig. 1;
• Fig.2 is a schematic sectional view of another embodiment of the electromagnetic valve actuator with two electromagnets according to the invention;
• Fig.3 is a schematic sectional view of yet another embodiment of the electromagnetic valve actuator according to the invention; and
• Fig.4 is a comparative graph of the force exerted on the pallet of an actuator with or without a permanent magnet.

The electromagnetic valve actuator shown in Figure 1, comprises two electromagnets 1,2 each comprising a body 3,4 made of magnetic sheet laminated film carrying a respective supply coil 5.6. The faces electromagnets 1,2 turned towards each other, define an air gap between them 7 of a value corresponding to the lifting of a pallet 8 made of magnetic material attached to one end of a rod 9 for actuating a valve 10 of internal combustion engine.

The rod 9 passes through the body 4 of one of the electromagnets 2 between which and a housing 12 formed in the cylinder head wall C of an engine, are arranged two opposing springs 13,14 of energy storage surrounding the rod 9 and the tail 15 of the valve to be actuated.

The spring 13 bears on the one hand on the body 4 of the electromagnet 2 and on the other hand, on a connecting piece 16 of the rod 9 with the tail 15 of the valve 10. The spring 14 bears between said connecting piece 16 and the bottom of the housing 12 formed in the wall of the cylinder head C.

According to the invention, the bodies 3 and 4 of the electromagnets 1 and 2 comprise each two pole pieces 18,19,20,21 between which are inserted respective permanent magnets 22.23.

The power coils 5,6 are wound around the branches pole pieces 18,19,20,21 between which the respective magnets are interposed 22.23.

The pole pieces 18 to 21 respectively have branches 24,25,26,27 which define two by two, the air gap 7 in which is movably mounted pallet 8 of the actuator.

The addition of a magnet in series in the magnetic circuit of each coil 5,6, allows, when the valve is in closed or open position, to have a significant permanent holding force without consuming current.

Sa being the section of a magnet and Se being the section of the air gap, the use with a section Sa greater than Se amplifies the field created by the permanent magnet. We can use a ferrite magnet if desired relatively inexpensive.

The thickness of the magnet measured in the direction of its magnetization is in principle fairly reduced so that the coils 5 and 6 remain effective for the steering of the system.

According to a variant not shown, a magnet is only placed in the most used closing solenoid.

During the approach phase of a stop, we also benefit of the strength of the corresponding magnet.

For takeoff, it is the opposite, because you have to apply a current negative to reduce or cancel the field created by the corresponding magnet.

FIG. 4 shows a graph of the force F _{1 which} it is possible to obtain as a function of the air gap e1 between an electromagnet and the movable pallet for a non-polarized electromagnet and a polarized electromagnet according to the invention .

The solid curve represents the variation of the force as a function of the air gap for a polarized electromagnet, that is to say provided with a permanent magnet while the dotted curve represents the variation of the force in function of the air gap for a non-polarized electromagnet.

avec J = aimantation de l'aimant

Sa = Section de l'aimant

Se = Section de l'entrefer

la = largeur de l'aimant / épaisseur

S = Section du plateau sur laquelle s'applique la force

e = entrefer

The force exerted on the plate by the electromagnet is given by the relation: F S = S 2μ o Jla + μ o or 2 e + the himself Her 2

with J = magnetization of the magnet

Sa = Magnet section

Se = Air gap section

the = width of the magnet / thickness

S = Section of the plate on which the force is applied

e = air gap

To attract the tray or pallet, the force at a long distance, that is to say for a large air gap, is greater. The control area is therefore the himself Her more extensive.

For air gaps smaller than one millimeter, the polarized actuator is less sensitive to saturation and therefore easier to control.

The control of the force by the current is much easier because it varies in (Bala + µ ₀ .nl) ² .

• Ba = champ créé par l'aimant permanent,
• la = largeur de l'aimant,
• n = nombre de spires de la bobine d'alimentation.

In this relationship:

• Ba = field created by the permanent magnet,
• the = width of the magnet,
• n = number of turns of the supply coil.

When I is not too large, a variation dl results in a linear variation of the force in 2.Ba.la.µ ₀ .n.dl.

Similarly, instead of being proportional to 1 / e ² , e being the air gap, the force varies in 1 ( e + the himself 2Sa ) 2 Se = section of the air gap, Sa = section of the magnet.

The sensitivity to the air gap is therefore very low.

The polarized actuator is much more easily controllable and must allow reach very low impact speeds much more easily.

The useful power of a polarized actuator compared to its volume can be multiplied by a factor equal to at least 2 with respect to that of an actuator not polarized.

Regarding power consumption, actuator efficiency polarized is greatly improved compared to that of a non actuator polarized.

Consumption is easily reduced from 30% to 6000 rpm and from 60% to 1500 rpm due to the lack of maintenance consumption.

The polarized actuator has a footprint roughly close to that of an actuator without a permanent magnet in its magnetic circuit.

The actuator partially shown in FIG. 1a, has two electromagnets such as the electromagnet 1a respectively having bodies such as 2a in magnetic sheet, turned towards each other each carrying a coil supply such as the coil 3a. A magnetic pallet 8a is mounted movable between the magnetic sheet bodies of the electromagnets.

The supply coil such as the coil 3a is carried by a central branch 9a of the body 2a which further comprises two lateral branches 10a, 11a. In the central branch 9a is placed a permanent magnet 12a. The second electromagnet of this actuator variant is similar to that described in reference to FIG. 1a and the rest of the actuator is similar to that of FIG. 1.

The electromagnetic actuator shown in FIG. 2 is of the type also comprising two electromagnets 30,31 whose respective bodies 32,33 made of magnetic material, for example laminated sheet, are each provided a supply coil 34.35.

The electromagnets 30,31 each mounted on holding pieces end 36,37 in non-magnetic material, define between them an air gap 38 whose value corresponds to the lifting of a pallet or magnetic plate 39 carried by a rod 40 for driving a valve 41. The rod 40 passes through the body 32.33 of the electromagnets 30.31 as well as the end retaining parts 36.37 which each have a blind sleeve 42.43 externally threaded and containing a corresponding 44.45 energy storage spring.

Each spring 44.45 bears on the one hand, against the bottom of the sleeve blind 42.43 corresponding and on the other hand, on a disc 46.47 in contact by its face opposite the spring with a corresponding end of the rod 40 valve 41.

The valve 41 has a stem 49 which bears on the face of the disc 47 opposite the rod 40, which is surrounded by the spring 45 and which passes through the bottom of the blind sleeve 43, the head 50 of said valve cooperating with a valve seat of an engine cylinder head (not shown).

As in the embodiment of FIG. 1, each of the bodies magnetic 32.33 electromagnets 30.31, has two pole pieces 51.52.53.54 respectively, between which are placed permanent magnets 55.56 whose function is similar to that of permanent magnets 22.23 of the embodiment of FIG. 1.

We can see that the magnetization directions of the permanent magnets 55.56 are parallel to the fields generated by the actuating coils 34.35 carried by the bodies 32.33 of the electromagnets 30.31.

The electromagnetic actuator shown schematically in the figure 3 comprises two electromagnets 60, 61 of which the bodies made of magnetic material for example in laminated sheets, each carry a supply coil 63.64.

The body of each electromagnet has two pole pieces 65.66 and 67.68 joined together by a respective permanent magnet 69.70 surrounded by the corresponding supply coil 63.64.

Each of the permanent magnets 69.70 is mounted in a branch corresponding central unit 71.72 formed by corresponding portions of the parts polar 65.66 and 67.68. It is placed in the central branch of its circuit inclined magnetic, so that its magnetization is inclined relative to to the electromagnetic field generated by the supply coil 63.64 corresponding and thus combines with the latter.

The angle of inclination of the magnetic field of each permanent magnet 69.70 relative to the field generated by the corresponding 63.64 coil, is advantageously chosen so that the end of its longitudinal side interior furthest away from side branches of pole pieces 65,66,67,68 is at a distance d from these branches equal to the width of these.

The mounting of each permanent magnet 69.70 in the body of the corresponding electromagnet is produced by cutting the sheets of the pole pieces 65.66 and 67.68 so as to form between the pole pieces 65.66 on the one hand and 67.68 on the other hand, housings receiving the respective magnets 69.70.

The faces of the electromagnets 60,61 facing one another define between them an air gap 74 of a value corresponding to the lifting of a pallet 75 made of a magnetic material fixed to one end of an actuating rod 76 a valve 77 of the internal combustion engine.

As in the embodiment shown in Figure 1, the rod 76 passes through the body of the electromagnet 61 between which and a housing 78 formed in the wall of the cylinder head C of an engine, are arranged two springs 79.80 of energy storage surrounding the drive rod 76 and the stem 81 of the valve to operate.

The function of a magnet in series in the magnetic circuit of each coil 63,64, ensures in the embodiment of Figure 3, the same effect than in the previous embodiments.

In addition, tilting the magnets 69.70 relative to the direction fields generated by the power coils 63,64, reduces considerably the height of the magnetic circuits of the electromagnets 60,61.

We can thus reduce the overall size of the actuator by particularly with regard to its overall height, which facilitates its installation on the cylinder head of an internal combustion engine.

The arrangement which has just been described presents with respect to the state of the technical, the following advantages.

It allows better control of the valve thanks to the relative linearity force as a function of the air gap, which makes it possible to obtain a gain in noise.

The power consumption of holding the valve in position is none or very limited.

Switching power consumption is reduced by reduction losses by the Joule effect.

The polarized actuator is overall more powerful and therefore better suitable for use on exhaust valves or on an engine lower unit displacement.

Claims (7)

Electromagnetic actuator of an internal combustion engine valve comprising two electromagnets (1,2; 30,31; 60,61) each comprising a supply coil (5,6; 34,35; 63,64), a magnetic paddle ( 8; 39; 75) disposed between the two electromagnets, linked to a drive member (9; 40; 76) of the valve against the action of at least one spring (13,14; 44, 45; 79,80) for storing switching energy of said valve (10; 41: 77), characterized in that in the magnetic body of at least one electromagnet is interposed a permanent magnet (22,23; 55, 56; 69.70) whose magnetization combines with the field generated in said body by the supply coil (5.6; 34.35; 63.64). Electromagnetic actuator according to claim 1, in which the magnetic bodies of the two electromagnets (1,2; 30,31) define between them a gap (7; 38; 74) in which said pallet (8; 39; 75) is mounted displaceable at against at least one opposing spring (13,14; 44,45; 79,80) for storing switching energy, characterized in that a permanent magnet (22,23; 55,56) is interposed in the magnetic body of each electromagnet (1,2; 30,31; 60,61). Electromagnetic actuator according to claim 2, characterized in that the permanent magnet is interposed in the magnetic body of the closing electromagnet. Electromagnetic actuator according to one of claims 1 to 3, characterized in that the body of each electromagnet (1,2; 30,31; 60,61) comprises two pole pieces (18,19,20,21; 51,52 , 53.54; 65.67.67.67), a permanent magnet (22.23; 55.56; 69.70) being interposed between the two pole pieces of the body of each electromagnet. Actuator according to one of Claims 1 to 4, characterized in that the permanent magnet is arranged in the body of the electromagnet so that the magnetization of the permanent magnet (22,23; 34,35) is parallel to the field generated in said body by the corresponding supply coil (5,6; 34,35). Actuator according to one of Claims 1 to 4, characterized in that the permanent magnet is arranged in the body of the electromagnet so that the magnetization of the permanent magnet (69,70) is inclined relative to the field generated in said body by the corresponding supply coil (63,64). Actuator according to one of Claims 1 to 3, characterized in that the body (2a) of each electromagnet has a central branch (9a) and two lateral branches (10a, 11a), the supply coil (3a) is disposed around the central branch and the permanent magnet (12a) is placed in said central branch of the body (2a).

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