EP0786045B1 - Two-stroke engine comprising an enhanced injection device and associated injection method - Google Patents

Abstract

PCT No. PCT/FR95/00866 Sec. 371 Date Mar. 10, 1997 Sec. 102(e) Date Mar. 10, 1997 PCT Filed Jun. 28, 1995 PCT Pub. No. WO96/07817 PCT Pub. Date Mar. 14, 1996The present invention relates to a two-stroke engine comprising at least: a cylinder (111) in which a piston (112) moves and one end of which communicates with a pump crankcase (115) crossed through by the crankshaft (114) of the engine, a capacity under pressure (87) opening at one end into the combustion chamber (113) of the cylinder (111), at least one valve (86) ensuring an intermittent sealing between the chamber (113) and the capacity (87), a means (88) intended for carburetting the gas passing in said capacity (87), a means for controlling the opening of said valve (86) comprising a supple membrane (89) separating two chambers (95a, 95b) and connected to the rod of the valve. The engine according to the invention further comprises a liking means (92) between one (95b) of said chambers and the pump crankcase (115) of said cylinder, allowing notably the opening of the valve (86) to be activated as soon as possible when the pressure PB in the chamber (95b) becomes lower than the pressure PS in said capacity (87).

Description

The present invention relates to the field of motors with two-stroke pneumatic injection controlled.

More specifically, the present invention relates to the pneumatic injection command and control fuel, in single-cylinder two-stroke engines or multi-cylinder.

A conventional way to order the injection pneumatic consists of connecting the valves to a camshaft. This purely mechanical solution turns out to be of little use flexible since each cam imposes a precise movement of a valve and in addition, the camshaft supporting several cams, it is a given general movement which is imposed from the origin of all the cams. This technology therefore generates general control common to all valves on the shaft to cam. Adjustment is difficult and a problem with one of the cams and / or valves can have repercussions on the whole other pieces put into play.

More flexible control systems are known, based especially on pressure variations between different chambers cooperating with the movement of the valve.

Thus, the French patents FR 2 656 653 and FR 2 656 656 describe multi-cylinder two-stroke engines in which pneumatic fuel injection is carried out using pressure differences between different chambers. This art previous relates specifically to engines having multiple cylinders since the pressure differences are created thanks to the angular offset existing between the cycles of the different cylinders.

The objective of the present invention is to simplify this technology and especially to be able to apply it to motors single cylinder, which the above-mentioned prior art in no way allows.

The present invention can however be applied to multi-cylinder engines but unlike the prior art, in this case the injection works independently in each cylinder. In other words according to the present invention, each cylinder works, with regard to its injection pneumatic, independently, autonomously, without special connections between cylinders. A motor multicylinder according to the invention must therefore be considered as an engine having juxtaposed autonomous cylinders.

Generally stated, the subject of the invention is to use the different pressure variations inherent in the cylinder operation to actuate so automatic pneumatic fuel injection device in this cylinder. In other words it is, according to the invention, control the opening and closing of a valve so automatic at each engine revolution, at specific times and determined, without resorting to a control means mechanical such as a camshaft.

It follows from the above that the adjustment and control of the injection according to the invention is individual, at the level of each cylinder, which simplifies the conventional solution multicylinder.

• un cylindre dans lequel se déplace un piston et dont l'une des extrémités communique avec un carter-pompe traversé par le vilebrequin du moteur,
• une capacité sous pression débouchant à une extrémité dans la chambre de combustion du cylindre, au moins une soupape assurant l'obturation intermittente entre la chambre de combustion et la capacité,
• un moyen destiné à carburer le gaz passant dans ladite capacité,
• un moyen de commande de l'ouverture de ladite soupape comprenant une membrane souple séparant deux chambres et reliée à la tige de la soupape,

Thus the present invention relates to a two-stroke engine comprising at least:

• a cylinder in which a piston moves and one end of which communicates with a pump housing through which the engine crankshaft passes,
• a pressurized capacity opening at one end into the combustion chamber of the cylinder, at least one valve ensuring intermittent closure between the combustion chamber and the capacity,
• means for carburizing the gas passing through said capacity,
• a means for controlling the opening of said valve comprising a flexible membrane separating two chambers and connected to the valve stem,

• un moyen de liaison entre l'une desdites chambres et le carter-pompe dudit cylindre, permettant notamment de déclencher l'ouverture de la soupape au plus tôt quand la pression P_B dans ladite chambre devient inférieure à la pression P_S dans ladite capacité.

The engine according to the invention further comprises:

• a connection means between one of said chambers and the pump casing of said cylinder, making it possible in particular to trigger the opening of the valve as soon as possible when the pressure P _B in said chamber becomes lower than the pressure P _S in said capacity.

Preferably, the capacity leads by its other end in an opening of the pump housing, a means of control of said opening being also provided.

In particular, the engine according to the invention can further include means for sealing so as to intermittently said connecting means in order to delay the fall of pressure in the connecting means, i.e. the opening of the valve.

More precisely, said intermittent shutter means may include a flange placed in the pump housing, linked in rotation at the engine crankshaft and comprising at least one peripheral recess.

According to one of its characteristics, the engine may further include control means related to the closing the valve.

Advantageously, said control means include a means of connection between the other of said chambers and said pump housing, said means being arranged such that it is intermittently closed on the pump housing side, said means alternately to amplify the opening of the valve and help close it.

According to one embodiment of the invention, said means of connection opens through an opening in the lower part of the cylinder so as to be alternately covered and discovered by the piston.

According to the other embodiment of the invention, the obturation intermittent connection means is realized by a flange specific linked to the crankshaft.

Without departing from the scope of the invention, the engine can further include an elastic return member of the valve on its seat, which cooperates with said flexible membrane.

The present invention relates to a method of controlling the opening of a fuel mixture injection valve in an engine as defined above, which consists in controlling the opening of said valve as soon as possible when the pressure P _B in a chamber-pump housing connection becomes lower than the pressure P _S in a capacity.

• La figure 1 est en vue en coupe d'une soupape assistée pouvant fonctionner selon l'invention;
• La figure 2 est une coupe longitudinale simplifiée d'un cylindre d'un moteur à deux temps selon un mode de réalisation de l'invention;
• La figure 3 est un diagramme montrant les différentes pressions de commande d'une soupape selon un premier mode de réalisation de l'invention, en fonction de l'angle de rotation du vilebrequin;
• La figure 4 est un diagramme montrant les différentes pressions de commande d'une soupape selon un autre mode de fonctionnement de l'invention, en fonction de l'angle de rotation du vilebrequin;
• La figure 5 est une coupe longitudinale simplifiée d'un cylindre d'un moteur à deux temps selon encore un autre mode de réalisation de l'invention;
• La figure 6 est un diagramme montrant les différentes pressions de commande d'une soupape dans un moteur selon la figure 5, en fonction de l'angle de rotation du vilebrequin.

The present invention will be better understood, its characteristics, advantages and embodiments will be better understood on reading the description which follows, given by way of illustration and in no way limiting with reference to the appended figures according to which:

• Figure 1 is a sectional view of an assisted valve operable according to the invention;
• FIG. 2 is a simplified longitudinal section of a cylinder of a two-stroke engine according to an embodiment of the invention;
• FIG. 3 is a diagram showing the different control pressures of a valve according to a first embodiment of the invention, as a function of the angle of rotation of the crankshaft;
• FIG. 4 is a diagram showing the different control pressures of a valve according to another operating mode of the invention, as a function of the angle of rotation of the crankshaft;
• Figure 5 is a simplified longitudinal section of a cylinder of a two-stroke engine according to yet another embodiment of the invention;
• FIG. 6 is a diagram showing the different control pressures of a valve in an engine according to FIG. 5, as a function of the angle of rotation of the crankshaft.

In Figure 1 is shown a control device injection into a cylinder of a two-stroke engine, designated generally by the reference 82.

Such an injection device of the automatic valve type assisted can in particular be associated with each of the cylinders of a two-stroke engine as shown in Figures 2 and 4.

In FIGS. 2 and 4, it can be seen that the injection device at assisted automatic valve 82 is fixed on the cylinder head of the engine at the corresponding cylinder.

As can be seen in Figure 1, the injection device 82 has a fuel air (or gas) supply channel 84 machined in the cylinder head 83 and emerging, through an opening 85, in the interior volume of the cylinder. Channel 84 is connected to a line 87 into which the end of a means of metering and / or fuel injection 88.

The valve 86 for closing the end of the channel 84 opening into the cylinder has a bearing head, in the valve closed position as shown in FIG. 1, in the opening 85 constituting a seat for valve. The stem (not referenced) of the valve 86 is connected to its other end to a flexible membrane 89 fixed according to its entire periphery and sealingly, between two parts of the wall of a casing 90 of the injection means 82.

Preferably, the housing 90 consists of a upper hollow half-shell 90a and half-shell lower 90b interconnected and at the periphery of the membrane 89 by means of external flanges constituting housing flanges 90.

The upper part 90a of the casing 90 has a pipe 91 opening into its internal volume and the part lower 90b of the housing 90 which is tightly fixed on the cylinder head 83 above the opening 85 of the channel 84 comprises a pipe 92 opening into its interior volume.

A return spring 93 is preferably inserted between the flexible membrane 89 or the end of the rod of the valve 86 and the upper surface of the cylinder head 83.

An assisted valve injection device such as that shown in Figure 1 is known from the prior art and ensures the opening and closing control of the valve determining the start and end of injection into the cylinder, by adjusting the differential pressure between the chambers 95a and 95b delimited in the casing 90 by the membrane 89.

For this, the pipes 91 and 92 can be connected to pressure-regulated gas supply devices allowing to ensure the opening or closing of the valve 86 by differential pressure in chambers 95a and 95b as well as by differential pressure between chamber 84 and the cylinder.

According to the invention, in the case of a two-stroke engine having one or more cylinders and with pneumatic injection, the control pressure in at least one of chambers 95a and 95b is produced by connecting this room with the interior volume of the pump housing of the same cylinder of the engine.

Figure 2 shows an embodiment of the invention that the injection device 82 is part of an engine including a cylinder 111 is shown in longitudinal section.

Conventionally, the cylinder 111 has a chamber combustion unit 113 in which a piston 112 moves communicating at its lower part with a pump casing 115.

The pump casing 115 conventionally includes a air intake nozzle 119 on which a valve 120 is placed.

The fresh air introduced into the casing 115 and compressed by the piston 112 is injected into the combustion chamber 113 of the cylinder 111, via transfer conduits such as 121 opening into the cylinder chamber through openings 122. The burnt gases are evacuated from chamber 113 by a driving 123.

According to the invention, the conduit 87 is pressurized either by an external source either by the fact that this conduit opens by its end 127 opposite to that opening into the injection device 82, directly in the pump housing 115.

The opening 127 is preferably controlled by a non-return valve or any other means capable of closing this opening as soon as the pressure in the pump casing 115 becomes lower than the pressure in conduit 87 which is therefore used as pressure storage capacity.

Furthermore, the pipe 92, which communicates by one of its ends with the chamber 95b of the injection device 82, opens out according to the invention into the pump housing 115 by its other end. Therefore, the pressure P _B in the chamber 95b follows the pressure variations in the pump housing 115 of the cylinder 111.

According to a first embodiment of the invention, the pressure P _A in chamber 95a can be atmospheric pressure or another rather constant pressure.

• de la pression P1 dans le cylindre 111, pression représentée en trait plein,
• de la pression P_S dans la capacité 87 et la chambre 84, pression représentée en traits mixtes,
• de la pression P_B dans le carter-pompe 115, la conduite 92 et la chambre 95b pression représentée en traits pointillés.

The operation of the injection device according to the invention will now be explained in relation to FIG. 3 in which the variations appear as a function of the angle of rotation of the crankshaft:

• the pressure P1 in the cylinder 111, pressure shown in solid lines,
• of the pressure P _S in the capacity 87 and the chamber 84, pressure shown in dashed lines,
• of the pressure P _B in the pump casing 115, the pipe 92 and the pressure chamber 95b shown in dotted lines.

Thus, according to this embodiment of the invention, from top dead center (TDC zero crankshaft angle) to the vicinity (OT) of the opening of the transfer lights, the cylinder pressure P1 is always greater than the pressure P _S in capacity 87. The valve 86 therefore does not open.

From the moment when the cylinder pressure P ₁ becomes lower than the pressure P _S , the valve 86 should open if the engine was not in accordance with the invention. This would therefore involve opening the valve and starting injection as soon as the transfers open, that is to say very early in the cycle.

The presence of the pipe 92 according to the invention allows the chamber 95b to remain at a pressure P _B greater than the pressure P _S for another approximately 30 ° crankshaft.

The effect of the pressure P _B will then be predominant compared to that of the pressure P _S (if we consider the sections of the membrane 89 and of the valve 86 as equivalent).

Thus, with such a dimensioning, the opening of the valve 86 will be delayed at least until the time when the casing pressure P _B becomes lower than the capacity pressure P _S.

If the membrane 89 has an upper section, the opening of the valve will be further delayed.

The injection I therefore begins, according to this configuration and under the operating conditions of the engine of FIG. 3, around 165 ° crankshaft, to finish when the cylinder pressure P ₁ becomes greater than the capacity pressure P _S , that is to say - say about 270 ° crankshaft.

The invention therefore makes it possible to significantly delay the start of the injection of fuel mixture, and this in a way simple and reliable. Engine operation is improved since said delay makes it possible to limit the unburned fuel directly exhausted.

In Figure 2 also appears a flange 116 linked to crankshaft. This element, which is not necessarily present in the pump housing 115, however, makes it possible to obtain the following additional feature: selective filling of connection 92.

Indeed, the flange 116 is cut at the periphery of such so that only a given angular sector closes the orifice 92a of connection 92, so during a certain angular range given to an engine cycle.

As can be seen in FIG. 4, the pressure P _B in the conduit 92 and the chamber 95b is stored at a given value taken before the pressure drop in the pump housing, that is to say taken for example at opening of OT transfers. The flange 116 makes it possible here to close the orifice 92a until the desired moment to trigger the opening of the valve, that is to say for example up to the PMB according to FIG. 4.

Selective sealing of the conduit 92 therefore makes it possible to store the casing pressure P _B for a period of time determined by the value of the angular sector of the flange 116.

The delay in opening the valve is greater here than in the previous case since the opening begins at around 180 ° crankshaft, whereas in the previous case (without flange) this opening was around 165 ° crankshaft; remember that without the invention the opening of the valve takes place when the pressure in the cylinder becomes lower than the pressure in conduit 87, i.e. for the case of figure envisaged, around 130 ° crankshaft.

Furthermore, the flange 116 according to the invention makes it possible to better control the opening of valve 86 since as it appears in particular in Figure 4 the opening of the conduit 92 being frank, the pressure drop is just as much so that the opening is also better controlled since it no longer depends decrease in pressure in the pump housing, decrease which is not always as fast depending on the conditions of engine load and speed, According to this embodiment of the invention, the opening of the valve simply depends on the opening of the conduit 92 by the flange 116.

Another improvement of the present invention can consist in communicating, intermittently, the chamber 95a with the pump housing 115.

As will be explained in more detail below, in relation to FIGS. 5 and 6, such an embodiment of the invention makes it possible in particular to obtain a more open rapid by amplifying the valve movement, thus that an improvement in the closing of the valve. In indeed, in the previous embodiments, some inertia of the automatic valve has sometimes been observed, this which slows down its opening.

Thus, Figure 5 shows a similar embodiment to the previous ones but according to which the engine further comprises a connection 91 between the chamber 95a and the pump housing 115.

Preferably, connection 91 leads through a light 91a located in the lower part of the cylinder, just above of the pump housing. So connection 91 is set up communication with the pump housing when the piston 112 passes above said light 91a, that is to say so intermittent.

Thus the connection 91 which is therefore controlled by the skirt of piston can be closed from the opening of the lights of transfer 122 until the closing of these same lights, that is to say symmetrically with respect to bottom dead center.

Without departing from the scope of the invention, another phasing can be obtained, for example an opening and closing not symmetrical with respect to bottom dead center, thanks to a linked flange to the crankshaft. This flange may or may not be the same as that which controls connection 92.

FIG. 6 illustrates the operation of this mode of realization of the invention.

The pressure P _A in the chamber 95a, the pressure P _B in the chamber 95b both remain equal to the pressure in the pump housing until the transfers OT open. The valve 86 is then held in its seat by the difference between the pressure P1 in the cylinder 113 and the pressure P _S in the capacity 87, possibly assisted by a return spring.

Then the light 91a is closed by the piston.

Light 92a can optionally be closed simultaneously by the flange 116 as shown in FIG. 6, but this is not compulsory.

The start of the valve opening control occurs as soon as the pressure P _B falls below the pressure P _S in the capacity. The pressure drop P _B can occur either naturally, that is to say without the flange 116, or when the lumen 92a is opened by the flange 116.

At this time, the pressure P _A which becomes greater than the pressure P _B makes it possible to amplify the force necessary for the opening of the valve by means of an adequate ratio between the surface of the membrane 89 and that of the valve 86. The opening of the valve 86 is therefore faster and its amplitude can also be increased thanks to this effect.

Furthermore, when the light 91a is found by the piston (in the vicinity of the closing of the transfers FT according to FIG. 6), then the pressure P _A in the chamber 91a drops suddenly which initiates the closing of the valve 86, seen pressure differences P ₁ , P _A , P _B. P _A and P _{B therefore} follow the variations in the pressure in the pump housing, a pressure much lower than the pressure P ₁ in the cylinder.

As already mentioned, a calibrated return spring 93 can equip the valve stem. This spring will be chosen stiffer in the last configuration because the force required to the valve opening is then higher than in the cases previous.

The strong stiffness of the spring 93 will assist in closing, which is thereby facilitated.

It is possible, according to this embodiment of the invention, limit the valve stroke by appropriate means such as only stops (not shown).

Claims (11)

1. Two-stroke engine comprising at least

   a cylinder (111) in which a piston (112) moves and one of the ends of which communicates with a pump-crankcase (115) through which the crankshaft (114) of the engine passes,

   a capacity under pressure (87) debouching at one end into the combustion chamber (113) of the cylinder (111), at least one valve (86) effecting intermittent blockage between the combustion chamber (113) and the capacity (87),

   a means (88) designed for carburetting the gas passing through said capacity (87),

   a means of controlling the opening of said valve (86) comprising a flexible diaphragm (89) separating two chambers (95a, 95b) and connected to the stem of the valve,
   characterised in that it additionally comprises

   a connection means (92) between one (95b) of said chambers and the pump-crankcase (115) of said cylinder permitting notably triggering of the opening of the valve (86) at the earliest when the pressure P_B in said chamber (95b) becomes less than the pressure P_S in said capacity (87).
2. Engine according to claim 1, characterised in that said capacity (87) debouches at its other end into an opening (127) of the pump-crankcase (115) and in that it additionally comprises a means of controlling said opening (127) of said capacity (87) at the pump-crankcase (115) of the cylinder (111).
3. Engine according to any one of claims 1 or 2, characterised in that it additionally comprises a means designed for intermittent blockage of said connection means (92) in order to retard the drop in pressure in the connection means (92), i.e. the opening of the valve (86).
4. Engine according to claim 3, characterised in that said means for intermittent blockage comprises a flange (116) placed in the pump-crankcase (115), connected in rotation to the crankshaft of the engine and comprising at least one peripheral recess.
5. Engine according to any one of the preceding claims, characterised in that it additionally comprises means of control connected to the closure of the valve.
6. Engine according to claim 5, characterised in that said means of control comprise a means of connection (91) between the other of said chambers (95a) and said pump-crankcase (115), said means being arranged such that it is blocked intermittently on the side of the pump-crankcase (115), said means permitting alternative amplification of the opening of the valve and assistance in its closure.
7. Engine according to any one of the preceding claims, characterised in that it additionally comprises an elastic element (93) for returning the valve (86) to its seat (85), which co-operates with said flexible diaphragm (89).
8. Engine according to claim 6, characterised in that said means of connection (91) debouches through an opening (91a) into the lower part of the cylinder so as to be alternatively covered and uncovered by the piston (112).
9. Engine according to claim 6, characterised in that the intermittent blockage of the means of connection (91) is effected by a specific flange connected to the crankshaft.
10. Engine according to any one of the preceding claims, characterised in that it additionally comprises a stop limiting the amplitude of opening of the valve (86).
11. Process for controlling the opening of a valve for injecting carburetted mixture into an internal combustion engine according to any one of the preceding claims, characterised in that it consists in effecting said opening at the earliest when the pressure P_B in the connection becomes less than the pressure P_S in the capacity (87).

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