EP1577508B1 - Valve return device motor provided with such a device - Google Patents

Description

The invention relates to the control of valves in internal combustion engines.

It relates to a valve return device and an internal combustion engine equipped with such a device.

Remember that the opening and closing of the intake and exhaust valves of internal combustion engines is controlled by a camshaft coupled in rotation to the motor shaft.

In order to ensure opening and closing of the valve at the chosen moment, it is essential that it be kept in contact with the corresponding cam of the camshaft.

This is why the motors are equipped with return devices which comprise, for each valve, a spring which urges it permanently in the direction of its closure (that is to say in the direction of the cam corresponding).

Most of these return devices include mechanical springs which, when the engine speed is moderate, constantly maintain the valve resting on the corresponding cam.

However, the main disadvantage of the mechanical springs is resonance when the engine speed is high enough, this phenomenon, known as the "panic of the valves", resulting in the translational movement of the valve being located. dissociated from the rotational movement of the camshaft.

This results in a notorious loss of power.

Various solutions have been proposed to remedy this problem.

It is thus known to equip each valve with several springs of different stiffness, in order to increase the resonant frequency of the elastic system thus formed.

This solution is suitable for large-scale engines, whose operating speeds are relatively moderate (that is to say that their maximum speed does not generally exceed 8000 revolutions per minute).

This solution, however, finds its limits in engines of motorcycles and racing cars, whose maximum speed often exceeds 15,000 revolutions per minute.

In fact, it has already been found in this type of engine the appearance of the phenomenon of panic valves, even when they are equipped with multiple spring return devices.

To remedy this problem, it has been proposed to replace, in certain high-speed engines, the mechanical springs by pneumatic springs, less likely to resonate at high engine speed.

Thus, a pneumatic valve return system for internal combustion engines is known from document FR-2 529 616, published some time ago.

The proposed system comprises a piston integral with a valve stem and sliding in a cylinder, the piston, the valve stem and the cylinder forming a sealed chamber which encloses a compressible fluid at a predetermined minimum setting pressure corresponding to the fully closed position of the valve.

If this system has already been satisfactory, it does not allow a control of the return force to which the valve is subjected.

The document US Pat. No. 5,233,950 provides for it to equip the return device with means for regulating the pneumatic pressure prevailing in the cylinder in which the valve slides.

If the valve control system so proposed is an advance over the system of the document FR-2 529 616, the structure used to provide pressure control is however relatively complex, while its reactivity, insufficient, is detrimental to sudden changes in engine speed.

The invention aims in particular to overcome the aforementioned drawbacks, by proposing a return device for precise regulation of the return force to which the valve is subjected and which, while having increased reactivity (in other words a reduced response time, especially during sudden changes in engine speed), can further reduce the risk of panic valves.

• un piston solidaire de ladite soupape, monté coulissant dans un cylindre,
• une alimentation en fluide sous pression raccordée audit cylindre par un canal d'alimentation, et
• un clapet de surpression, raccordé audit cylindre par un canal d'évacuation, et agencé pour limiter la pression régnant dans le cylindre à une pression maximale prédéterminée,

ce dispositif comportant en outre des moyens pour réguler la pression maximale en fonction de la pression d'alimentation suivant une loi de type affine.For this purpose, the invention proposes a device for returning a valve of an internal combustion engine comprising:

• a piston secured to said valve, slidably mounted in a cylinder,
• a supply of pressurized fluid connected to said cylinder by a supply channel, and
• a pressure relief valve, connected to said cylinder by an evacuation channel, and arranged to limit the pressure prevailing in the cylinder to a predetermined maximum pressure,

this device further comprising means for regulating the maximum pressure as a function of the feed pressure according to an affine law.

It is thus possible to vary linearly the stiffness of the pneumatic spring constituted by the fluid under pressure contained in the cylinder, according to predetermined parameters, such as the engine speed.

This results in a better regulation of the return force to which the valve is subjected, which reduces the risk of panic.

où :

• P_M est la pression maximale,
• λ est une constante,
• P_A est la pression d'alimentation, et
• P₂ est une constante.

The maximum pressure is for example a function of the supply pressure according to a law of the type: $${\mathrm{P}}_{\mathrm{M}}\mathrm{=}{\mathrm{\lambda P}}_{\mathrm{AT}}\mathrm{+}{\mathrm{<figure-callout\; id="2"\; label="P"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">P</figure-callout>}}_{\mathrm{2}}$$

or :

• P _M is the maximum pressure,
• λ is a constant,
• P _A is the supply pressure, and
• P ₂ is a constant.

According to a preferred embodiment, the pressure relief valve is provided with a return spring, in which case the constant P ₂ is the set pressure of said pressure relief valve provided by said return spring.

In order to achieve the pressure law presented above, the pressure relief valve is for example connected to the supply by a bypass channel.

Furthermore, it can be provided a non-return valve placed on the supply channel, the bypass channel being connected to the supply upstream of the non-return valve.

The power supply can be controlled to regulate the supply pressure according to one or more determined parameters, such as the engine speed.

Thus, the power supply is preferably controlled to increase the supply pressure as the engine speed increases.

According to another object, the invention proposes an internal combustion engine equipped with a return device as presented above.

• les figures 1 à 6 sont des vues schématiques du dispositif de rappel d'une soupape, illustrant de manière successive un cycle complet d'ouverture/fermeture de la soupape ;
• la figure 7 est un diagramme illustrant les variations de la pression P à l'intérieur du cylindre, en fonction du déplacement h du piston, au cours d'un cycle complet d'ouverture/fermeture de la soupape ;
• les figures 8 et 9 sont des diagrammes analogues à celui de la figure 7, illustrant des cycles d'ouverture/fermeture de la soupape, avec régulation de la pression d'alimentation.

Other objects and advantages of the invention will become apparent in the light of the description given hereinafter with reference to the appended drawings in which:

• Figures 1 to 6 are schematic views of the valve return device, illustrating successively a complete cycle of opening / closing of the valve. valve ;
• FIG. 7 is a diagram illustrating the variations of the pressure P inside the cylinder, as a function of the displacement h of the piston, during a complete cycle of opening / closing of the valve;
• Figures 8 and 9 are diagrams similar to that of Figure 7, illustrating cycles of opening / closing the valve, with regulation of the supply pressure.

FIG. 1 shows a return device 1 of a valve 2 of an internal combustion engine of which only the intake (or exhaust) pipe 3 has been shown, the valve 2 of which controls the opening and the closing.

As can be seen in FIG. 1, the valve 2 comprises a rod 4 which ends, at one of its ends, with a head 5 able to bear against a seat 6 which forms the mouth of the tubing of admission 3.

The rod 4 ends, at its opposite end, with a tail 7 shaped as a cam follower which is held in abutment by a pneumatic spring 8 (described below) against a cam 9 of a camshaft whose rotation controls the opening and closing of the valve 2.

The valve 2 is provided with a piston 10 which, secured to the valve stem 4, is slidably mounted in a cylinder 11.

The device 1 also comprises a supply 12 of fluid under pressure, fluidly connected to the cylinder 11 by a supply channel 13 on which is placed a check valve 14.

The device 1 further comprises a pressure relief valve 15 fluidly connected, on the one hand to the cylinder 11 by a discharge channel 16 and, on the other hand, to the supply 12 by a bypass channel 17 which, as can be seen in FIGS. 1 to 6, is connected to the supply 12 upstream of the non-return valve 14.

The pressure relief valve 15 comprises a cylinder 18 in which slides a piston 19 which is integral with a valve 20. The piston 19 divides the cylinder 18 into two sealed chambers, namely a so-called overpressure chamber 21, into which the bypass channel 17, and an expansion chamber 22 in which the discharge channel 16 opens and a venting channel 23 through which the pressure in the expansion chamber 22 is constantly equal to atmospheric pressure.

The piston 19 is movably mounted between a so-called closing position, illustrated in FIG. 1, in which the valve 20 closes off the evacuation channel 16, and a so-called opening position, illustrated in FIG. 3, in which the valve 20 is separated from the evacuation channel 16 that it thus communicates with the expansion chamber 22.

S _{P is} the area of the surface of the piston 19 turned on the side of the pressure chamber 21, and S _S the area of the surface of the valve 20 turned towards the side of the discharge channel 16.

As shown in Figures 1 to 6, the pressure relief valve 15 is equipped with a return spring 24 which constantly urges the piston 19 to its closed position.

According to an embodiment illustrated in FIGS. 1 to 6, the supply 12 comprises a pressure regulator connected via a channel 26 to a source of pressurized fluid (not shown), this regulator being arranged to vary the pressure in the feed channel 13 as a function of one or more determined parameters such as the engine speed, which is characterized by the rotational speed - denoted V _R - of the motor shaft.

• P_A la pression d'alimentation, qui règne dans le canal d'alimentation 13 en amont du clapet anti-retour 14 et dans le canal de dérivation 17 ;
• P₁ la pression de tarage du clapet anti-retour 14 ;
• P₂ la pression de tarage du clapet de surpression 15, résultant de la force de rappel exercée sur le piston par le ressort 24 ;
• P la pression qui règne dans le cylindre 11, dans le canal d'alimentation 13 en aval du clapet anti-retour 14 et dans le canal d'évacuation 16 ;
• P_m la valeur minimale de la pression P, cette valeur minimale vérifiant la relation suivante : $${\mathrm{P}}_{\mathrm{A}}\mathrm{=}{\mathrm{P}}_{\mathrm{m}}\mathrm{+}{\mathrm{P}}_{\mathrm{1}}\mathrm{;}$$
  
• λ le rapport (constant) des superficies S_P et S_S : $$\mathit{\lambda }=\frac{S_P}{S_S};$$
  
• P_M la valeur maximale de la pression P. Cette valeur correspond à la pression qui règne dans la chambre de surpression 21, et vérifie par conséquent la relation suivante : $${\mathrm{P}}_{\mathrm{M}}\mathrm{=}{\mathrm{\lambda P}}_{\mathrm{A}}\mathrm{+}{\mathrm{<figure-callout\; id="2"\; label="P"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">P</figure-callout>}}_{\mathrm{2}}\mathrm{;}$$
  
• et enfin P₀ la pression atmosphérique.

We note:

• P _A the supply pressure, prevailing in the feed channel 13 upstream of the check valve 14 and into the bypass channel 17;
• P ₁ the calibration pressure of the non-return valve 14;
• P ₂ the calibration pressure of the pressure relief valve 15, resulting from the restoring force exerted on the piston by the spring 24;
• P the pressure in the cylinder 11, in the feed channel 13 downstream of the non-return valve 14 and in the discharge channel 16;
• P _m the minimum value of the pressure P, this minimum value satisfying the following relation: $${\mathrm{P}}_{\mathrm{AT}}\mathrm{=}{\mathrm{P}}_{\mathrm{m}}\mathrm{+}{\mathrm{P}}_{\mathrm{1}}\mathrm{;}$$
  
• λ the ratio (constant) of areas S _P and S _S : $$\mathit{\lambda }=\frac{S_P}{S_S};$$
  
• P _M the maximum value of the pressure P. This value corresponds to the pressure that prevails in the booster chamber 21, and therefore verifies the following relation: $${\mathrm{P}}_{\mathrm{M}}\mathrm{=}{\mathrm{\lambda P}}_{\mathrm{AT}}\mathrm{+}{\mathrm{<figure-callout\; id="2"\; label="P"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">P</figure-callout>}}_{\mathrm{2}}\mathrm{;}$$
  
• and finally P ₀ the atmospheric pressure.

The pressure relief valve 15 is designed to limit the pressure P prevailing in the cylinder 11 to the maximum pressure P _M : indeed, when the pressure P reaches or exceeds this maximum pressure P _M , the fluid of the discharge channel 16, in from the cylinder 11, exerts on the valve 20 a pressure which compensates the pressure P _M prevailing in the pressure chamber 21, which tends to move the piston 19, initially in its closed position, to its open position, putting thus the evacuation channel 16 in communication with the chamber of relaxation 22.

The operation of the device 1 is described below.

In Figure 1, the valve is shown at its top dead center (TDC see Figure 7) where, pressed against the seat 6, it closes the intake manifold 3.

In this position, the sum P + P ₁ of the pressures inside the cylinder 11 and the calibration of the nonreturn valve 14 is less than or equal to the supply pressure P _A , which causes the valve to open. non-return 14 until the pressure equalization, which occurs when P = P _m .

When this balancing occurs, the check valve 14 closes (Figure 2), which corresponds to point A in the diagram of Figure 7.

The rotation of the cam 9 (FIG. 3) then causes the valve 2 to move towards its open position, which compresses the fluid contained in the cylinder 11.

There is an increase in the pressure P until the value thereof reaches the maximum pressure P _M , which corresponds to point B of the diagram of FIG. 7.

At this moment, there is a balancing of the pressures in the pressure relief valve 15: the piston 19 is pushed towards its open position, the discharge channel 16 is thus placed in communication with the expansion chamber 22. The pressure P is thus maintained equal to the maximum pressure P _M.

This situation, which corresponds to the line joining the points B and C in the diagram of FIG. 7, continues as long as the movement of the cam 9 tends to compress the fluid that is in the cylinder 11 (FIG. 4).

When the valve 2 reaches its bottom dead center (PMB), the fluid present in the cylinder 11 no longer tends to be compressed, so that the pressure P _M prevailing in the pressure chamber 21 is sufficient to push the piston 19 towards its closed position, the valve 20 thus closing again the discharge channel 16 (Figure 5), which corresponds to the point C in the diagram of Figure 7 .

The rotation of the cam 9 then allows the valve 2, under the effect of the air spring 8 constituted by the pressurized fluid present in the cylinder 11, which keeps the cam follower 7 in permanent contact with the cam 9, back up to its closed position, as shown in Figure 6. There is then an expansion of the fluid in the cylinder 11, which corresponds to the line joining the points C and D in the diagram of Figure 7.

This expansion continues until the pressure P of the fluid present in the cylinder 11 reaches its minimum value P _m (point D in the diagram of FIG. 7), which causes the non-return valve 14 to open ( Figure 6).

This situation (corresponding to the line joining the points D and A in the diagram of FIG. 7) continues as long as the valve 2 has not reached its top dead center again, the pressure P of the fluid present in the cylinder 11 being thus kept constant and equal to the minimum value P _m despite the movement of the valve 2 which, according to the cam 9, tends to relax the fluid.

As soon as the valve 2 reaches its top dead point (FIG. 1), the cycle just described is repeated.

It will be understood that the presence of check valves 14 and of overpressure 15 makes it possible to limit between two extreme values (corresponding, respectively, to the minimum pressure P _m and to the maximum pressure P _M , the restoring force exerted on the valve 2 by the air spring 8 constituted by the fluid present in the cylinder 11.

In order to optimize the movement of the valve (and in particular to avoid its panic), it is desired to vary the stiffness of the air spring 8 as a function of one or more determined parameters.

In practice, it is desired to vary this stiffness as a function of the engine speed, and, more specifically, it is desired to increase the stiffness of the air spring 8 when the rotation speed V _R of the driving shaft increases, which makes it possible to increase the reactivity of the valve and push back its panic limit.

FIG. 8 shows a diagram illustrating the pressure P of the fluid contained in the cylinder 11 as a function of the displacement h of the piston 10, illustrating three successive cycles of opening / closing of the valve 2, between which it has been controlled, first an increase in the supply pressure P _A consecutive to the increase in the engine speed, then a decrease in the supply pressure P _A following a decrease in engine speed.

Initially (point A), the pressure P is equal to the minimum pressure P _m1 corresponding to the initial supply pressure P _A. At this initial supply pressure P _A also corresponds to a maximum pressure P _M1 , which reigns in the overpressure chamber 21.

The opening phase of the valve 2 is as previously described (between the points A and B, curve in solid lines), the pressure relief valve 15 intervening (between points B and C) when the pressure P reaches the maximum pressure. P _M1 .

It controls (arbitrarily) an increase in the engine speed in the closing phase of the valve 2, corresponding to the expansion of the fluid (between the points C and D of the diagram of FIG. 8): the regulator 25 then controls the increase of the supply pressure P _A.

This results in an increase of the minimum pressure which is established at a new value - noted P _m2 -, while the maximum pressure is established simultaneously, through the diversion channel 17, to a new value - noted P _M2 -, these new values P _m2 and P _M2 being respectively greater than the previous values P _m1 and P _M1 .

When the pressure P reaches the minimum pressure P _m2 , the non-return valve 14 comes into action, the pressure P then remaining constant and equal to the value P _m2 until the valve reaches its top dead center again (point A 'in the diagram of Figure 8).

The air spring 8 is thus modified with respect to the previous cycle, its stiffness being greater.

The opening phase of the valve is as described above (points B 'and C', dotted line). During the closing phase of the valve 2 (between the points C 'and D'), a reduction of the engine speed is controlled (arbitrarily): the regulator 25 then controls a decrease in the supply pressure P _A , the the minimum pressure is then established at a new value P _m3 while the maximum pressure prevailing in the booster chamber 21 is set at a new value P _M3 , these new values P _m3 and P _M3 being, respectively, less than initial values P _m1 and P _M1 .

When the pressure P reaches, during the expansion, the value P _m3 (point D '), the pressure relief valve 14 comes into action to keep constant at this value the pressure P (between points D' and A '') , as long as valve 2 has not reached its top dead center (point A ").

The opening phase of the valve 2 is then repeated as before (between the points A "and B", then between the points B "and C", curve in phantom), the air spring 8 however having a stiffness less than the stiffness that it presented during the two previous cycles;

During the relaxation (between the points C "and D"), it is assumed that an increase in the engine speed occurs again, which returns to its initial value.

The regulator 25 then controls an increase in the supply pressure P _A , the minimum and maximum pressures then returning to their respective initial values P _m1 and P _M1 .

When the pressure P reaches the minimum value P _m1 (point D "), the valve 14 then comes into action to keep constant at this value the pressure P (between points D" and A).

• pendant la phase d'ouverture, une baisse du régime moteur avant que la pression P n'ait atteint la pression maximale initiale P_M1 mais après qu'elle a dépassé la nouvelle valeur P_M2 résultant de la régulation de la pression d'alimentation P_A, et
• au cours de la détente, une augmentation subite du régime moteur avant que la pression P n'ait atteint la valeur minimale P_m2 correspondant à cette régulation, mais après que la pression P soit passée sous la valeur P_m3 issue de la nouvelle régulation de la pression d'alimentation P_A.

FIG. 9 illustrates an opening / closing cycle of the valve 2 during which successively:

• during the opening phase, a decrease in the engine speed before the pressure P has reached the initial maximum pressure P _M1 but after it has exceeded the new value P _M2 resulting from the regulation of the supply pressure P _A , and
• during the expansion, a sudden increase in the engine speed before the pressure P has reached the minimum value P _m2 corresponding to this regulation, but after the pressure P has passed below the value P _m3 resulting from the new regulation of the supply pressure P _A.

Initially (point A), the minimum pressure is at a value P _m1 , the valve 2 is at its top dead center.

The rotation of the cam 9 causes, as previously described, the compression of the fluid present in the cylinder 11. However, it occurs at a given moment (point B ₁ in the diagram of FIG. 9) where the pressure P n ' has not yet reached the maximum value P _M1 , a sudden drop in engine speed resulting in the control by the regulator 25, of the decrease of the supply pressure P _A , the minimum and maximum pressures then being set to values P _m2 and P _M2 lower, respectively, to the initial values P _m1 and P _M1 .

The overpressure immediately causes the valve 15 to open, the pressure P falling until reaching the new value of the maximum pressure P _M2 (point B ₂ ).

It should be noted that, in the diagram of FIG. 9, the inertia of the system has not been taken into account, so that the segment connecting the points B ₁ and B ₂ appears both rectilinear and vertical.

The rest of the cycle is (momentarily) as previously described. The pressure P is kept constant and equal to the value P _M2 to the bottom dead point (point C) where the closure of the pressure relief valve 15 occurs, the cycle then initiating its opening phase of the valve 2.

During the expansion, it occurs, before the pressure P has reached the current minimum value P _m2 (point D ₁ ), a sudden rise in the engine speed that the regulator 25 reflects by an increase in pressure. feeding, the minimum pressure then establishing a new value P _m3 greater in the example described, to the previous values P _m1 and P _m2 .

The non-return valve 14 then enters into action, the pressure P then rising abruptly to the new minimum value P _m3 (point D ₂ ), which value it conserves up to the top dead point (point A ').

As before, the inertia of the system has been neglected, so that the segment which connects in the diagram of FIG. 9 the points D ₁ and D ₂ appears both rectilinear and vertical.

As we have just seen, the return device 1 makes it possible to regulate, not only the minimum pressure P _m required in the cylinder 11, but also the pressure maximum P _M, depending on the supply pressure P _A.

This regulation responds to a law of the affine type, which makes it possible to precisely regulate the stiffness of the air spring 8 in particular as a function of the engine speed, as shown above.

As we have seen, this regulation operates simply and quickly, since the pressure relief valve 15 is directly connected to the supply 12.

The structure described above (in particular the presence of the bypass channel 17 and the return spring 24) makes it possible to establish in a simple manner the affine pressure law P _M = λP _A + P ₂ at which the maximum pressure P obeys. _M.

Simultaneously, the minimum pressure P _m also obeys an affine type law, since it verifies the relation P _m = P _A -P ₁ , which results from the presence on the supply channel 13 of the nonreturn valve 14.

It is thus possible to control a linear variation of the stiffness of the air spring 8 as a function (as we have seen) of the engine speed, so that this stiffness is both sufficiently high (which results from the regulation of the pressure minimum P _m ) to avoid the panic of the valves, but sufficiently measured to prevent premature wear of the parts in contact, namely the valve stem 7 and the corresponding cam 9.

Claims (10)

1. A return device (1) for a valve (2) of an internal-combustion engine, including:

   - a piston (10) integral with said valve (2), mounted to slide in a cylinder (11),

   - a pressurised fluid feed (12) connected to said cylinder by a feed line (13), and

   - an overpressure valve (15) connected to said cylinder (11) by an evacuation line (16), arranged to limit the pressure (P) in the cylinder (11) to a maximum predetermined pressure (P_M),

   this device being characterised in having means (25, 17, 24) to control the maximum pressure (P_M) as a function of the feed pressure according to a law of the affine type.
2. A device (1) according to Claim 1, in which the maximum pressure (P_M) is a function of the feed pressure according to a law of the type: $${\mathrm{P}}_{\mathrm{M}}={\mathrm{\lambda P}}_{\mathrm{A}}+{\mathrm{P}}_2$$

   

   
   where:

   P_M is the maximum pressure,

   λ is a constant,

   P_A is the feed pressure, and

   P₂ is a constant.
3. A device (1) according to Claim 2, in which the overpressure valve (15) is equipped with a return spring (24), the constant P₂ is the set pressure of said overpressure valve (15) provided by said return spring (24).
4. A device (1) according to one of Claims 1 through 3, in which the overpressure valve (15) is connected to the feed (12) by a bypass line (17).
5. A device (1) according to one of Claims 1 through 4, which includes a check valve (14) positioned on the feed line (13).
6. A device (1) according to Claims 4 and 5, taken together, in which the bypass line (17) is connected to the feed (12) upstream of the check valve (14).
7. A device (1) according to one of Claims 1 through 6, in which the feed (12) is controlled by regulating the feed pressure (P_A) as a function of one or more determined parameters.
8. A device (1) according to Claim 7, in which the feed (12) is controlled to regulate the feed pressure (P_A) as a function of the engine speed (V_R).
9. A device (1) according to Claim 8, in which the feed (12) is controlled to increase the feed pressure (P_A) when the engine speed (V_R) increases.
10. An internal-combustion engine equipped with a return device (1) according to one of Claims 1 through 9.

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