FR2812025A1 - ELECTROMAGNETIC VALVE ACTUATOR OF INTERNAL COMBUSTION ENGINE - Google Patents

Abstract

The valve activator comprises an electromagnet (1) comprising a supply reel (2) and a magnetic armature (15) connected to a valve (17) driving part (16) against the action of a commutation energy storage spring (18,19). A permanent magnet (5) interposed in the electromagnet body has its magnetization combined with the field generated in the body by the 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 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 necessary for rapid switching is ensured

  by the springs and the change of position is controlled using the electroai-

  mants. This system is apparently simple, but it has technical limitations. The control of the valve position 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 not controlled

ble by the current.

  Excluding saturation, this force is proportional to the square of the current

  thrown into 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.

  For small air gap values between the paddle and the electromagnet, the

  force produced by the electromagnets varies very strongly with the air gap.

  This force is also very sensitive to the current injected into the coils. When approaching the contact between the paddle and the electromagnet, it occurs

  a runaway effect which generates a breakdown responsible for the noise of the action-

  neurs. To overcome this drawback, sophisticated and costly solutions using in particular closed-loop control of the position of the

palette were considered.

  The electromagnet can only attract the pallet or plate because the reversal of the direction of the current in the supply coils does not change the direction of the

  force exerted on the pallet, since this force is a function of the square 12 of the

rant in the coils.

  This constitutes an additional difficulty in controlling the ac-

  costage, because if you bring too much energy to the pallet, it is no longer possible to slow it down and shock with the body of the electromagnet is inevitable.

  For air gaps greater than 1 mm, the force developed by the electric

the magnet becomes weak.

  The force curve of a conventional actuator is therefore well suited to

  holding the valve in the closed or open position, but it is not suitable

  ted to performing work over the entire stroke of the valve.

  This insufficiency is noted when it is desired to actuate exhaust valves because, for a hot engine, the actuator must then supply mechanical energy greater than 1 Joule at each transition, against 0.2 Joule at intake. In addition, it is always difficult to initialize valves because when stopped, the gap between the actuating paddle and the body of the electromagnet is 4 mm. To this problem relating to force is added the significant presence of

  Eddy currents which attenuate and delay the effect of the coils.

  On admission, the actuator must be able to supply the necessary energy

  to switch. This is to compensate for friction losses which

  wind at approximately 0.2 J for a stroke or lift of 8 mm from 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 a motor rotation 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 , around 1 kg and

its large volume.

  For an internal combustion engine with 500 cc of cubic capacity, we can

  satisfy such dimensions although they remain a handicap.

  However, these dimensions are not compatible with cylinders.

weaker unit feeds.

  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 has been observed during tests that the current actuators are insufficient for the exhaust and do not allow the engine to be operated at

full load.

  In conclusion, the current actuator has a low power density which limits its use to the control of the intake valves of engine of

  unit displacement greater than or equal to 500 cm3.

  The efficiency of an actuator is the ratio between the mechanical energy returned (useful) and the electrical energy consumed. It is around 30%, the losses being mainly due to induced currents and losses by the Joule effect. An engine revolution has a duration of 60 ms at 1000 rpm, while a

  valve transition takes approximately 3.5 ms. It is clear that at low speed, the system

  teme is statistically very often in a stable position, either open or closed.

  To keep the valve in the open or closed position,

  plique 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 pro-

  duite 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

  blow of urban driving at low engine speed.

  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.

  Current actuators have a relatively large height.

  aunt 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 forms an additional parking brake which some

  Some users operate as an additional brake to the handbrake, especially on hills. When using electromagnetic actuators, the valves

  are in an equilibrium position in the middle, so that all the chambers of the mo-

  tor are at atmospheric pressure and there is no longer any 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 electric actuators

  tromagnetics by creating an actuator, which while being relatively low cost, has improved performance in

areas mentioned above.

  It therefore relates to an electromagnetic valve actuator

  internal combustion engine comprising an electromagnet comprising a bo-

  power supply, a magnetic pallet 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 body magnetic

  of the electromagnet is interposed a permanent magnet whose magnetization is

  bine to the field generated in said body by said supply coil.

According to other characteristics:

  - the magnetic body of the electromagnet comprising two parts for

  laires each comprising a first and a second branch defining

  between them, air gaps, said pallet being mounted movable in the

  irons defined by the first and second branches of two pole pieces, said permanent magnet is disposed between said pole pieces;

  - the permanent magnet is placed in the body of the electromagnet

  negates that its magnetization is parallel to the field generated in said body by said supply coil

  - the permanent magnet is placed in the body of the electromagnet

  denies that its magnetization is inclined with respect to the field generated in said

  body by said supply coil.

  The invention will be better understood using the description which follows,

  given only by way of example and made with reference to the accompanying drawings, in which:

  - Fig.1 is a schematic sectional view of an electro- actuator

  magnetic valve to an electromagnet according to the invention; and - Fig. 2 is a partial schematic sectional view of a variant

  electromagnetic valve actuator according to the invention.

  The actuator shown in FIG. 1 comprises an electromagnet 1 of which

  the body made of magnetic material, for example made of laminated sheets, carries a box

power supply 2.

  The body comprises two pole pieces 3,4 joined together by a permanent magnet 5 surrounded by the supply coil 2

  In the present example, the magnetization of the permanent magnet 5 is

  parallel to the field generated by the supply coil 2 in the magnet body

than electromagnet.

  Each pole piece 3,4 of the magnetic body has a portion 6,7 perpendicular to the permanent magnet 5. Each of the portions 6,7 has a first short branch 8,9, straight and a second longer branch, in L , 10,11 whose free end is aligned with the free end

  correspondent of the respective branch 8.9.

  Between the branches 8,10 on the one hand, and 9,11 on the other hand, air gaps 13,14 are defined in which a magnetic pallet is movably mounted

  or plate 15 fixed to a rod 16 for driving a valve 17.

  The stem 16 and the stem of the valve 17 are surrounded by res-

  helical spells 18,19 arranged on either side of the magnetic plate 15, and bearing respectively between the corresponding face of said plate and the magnetic body of the electromagnet 1 as regards the spring 18 and the wall

  of cylinder head C with regard to spring 19.

  According to the variant shown in partial schematic section at the end

  gure 2, the actuator comprises an inclined permanent magnet 20, disposed between two pole pieces 21, 22 having inclined ends in contact with

  the side faces of the magnet 20, the magnet 20 and the ends of the pole pieces

  res 21,22 being surrounded by a supply coil 23.

  Thus, the direction of the magnetization is inclined relative to the field

  generated by the supply coil 23.

  Furthermore, the actuator of FIG. 2 is in all respects similar to

  that of FIG. 1 and will therefore not be described.

  The operation of the electromagnetic actuator which has just been

  described with reference to Figure 1 is as follows.

  The supply of the coil 2 causes the creation in the body of

  the electromagnet of an electromagnetic field parallel to the direction of the magnet

  tation of the permanent magnet and which combines with said magnetization.

  Depending on whether the pallet is located near the short branches 8,9 or long branches 10,11 of the pole pieces of the electromagnet body, it is moved up or down, which causes closing or opening

  of the valve 17 and the compression of the corresponding spring 18 or 19.

  The pallet 15 is held in position by the permanent magnet.

  5 only, that is to say without current consumption.

  Thus, thanks to the particular construction of the actuator, a single elect

  troaimant provides in combination with the two energy storage springs

  18,19, the movement of the valve 17 in the direction of opening and closing

meture.

  To move the pallet from one position to another, we feed again

  calf the reel which generates a force of release of the pallet.

  The associated spring 18.19 causes the displacement of the pallet 15 from its points of contact with the branches 8.9 towards its points of contact

  with the branches 10,11 of the magnetic circuit of the electromagnet or vice versa.

  The arrangement which has just been described allows an electrical consumption.

  than keeping the valve in a zero or very limited position.

  The power consumption required for switching is equal to

  reduced by the reduction of losses by the Joule effect.

  It also allows better control of the valve thanks to the li-

  relative nearity of the force as a function of the air gap, which makes it possible to obtain a

gain in noise.

  The use of a single electromagnet considerably reduces the space

actuator.

  The oblique arrangement of the magnet further reduces the space

  BREMENT. Finally, the fact of being able to leave the valves closed without consuming any current further improves the possibility of using the actuator of the invention

as a parking brake.

  It has an increased power density allowing an applica-

  tion at the exhaust and on engines with a smaller unit displacement.

Claims (4)

  1. Electromagnetic actuator of an internal combustion engine valve comprising an electromagnet comprising a supply coil (2; 23), a magnetic pallet (15) linked to a drive member (16) from the valve (17) to the 'against the action of at least one switching energy storage spring (18,19) of said valve, characterized in that in the magnetic body of the electromagnet is interposed a permanent magnet (5; 20) whose magnetization combines with the field generated in said body by said coil supply (2; 23).   2. Electromagnetic actuator according to claim 1, characterized   in that the magnetic body of the electromagnet comprising two pole pieces   res (3,4), each comprising a first and a second branch (8,9, 10,11) defining between them air gaps (13,14), said pallet (15) being   movable climb in the air gaps defined by the first and second branches   ches (8,9,10,11) of two pole pieces, said permanent magnet (5) is arranged   between said pole pieces (3,4).   3. Actuator according to one of claims 1 and 2, characterized in   that the permanent magnet (5) is placed in the body of the electromagnet so that its magnetization is parallel to the field generated in said body by said supply coil (2).   4. Actuator according to one of claims 1 and 2, characterized in that   that the permanent magnet (20) is placed in the body of the electromagnet   denies that its magnetization is inclined with respect to the field generated in said   body by said supply coil (23).