EP0444027B1 - Device for scavenging the cylinder of a two-stroke engine, supercharging by the effect of post-filling, and engine related thereto - Google Patents

Abstract

Process and device for scavenging the cylinder of a two-stroke internal combustion engine, with supercharging by the effect of post-filling. Said device is characterized in that the intake set (12a, 12b; 14a, 14b) is arranged in relation to the cylinder (10) so that the scavenging air flows from the intake ports (12a, 12b) join at an impact point located on the upper wall (10a) of the cylinder (10) above the exhausted ports (16), in order to effect a so-called reverse loop. The altitude (A) of the lower edge of the e exhaust ports (12a, 12b) is arranged sufficiently high in the cylinder (10) in relation to the altitude (B) of the upper edge of the exhaust ports (16) to avoid essentially every possibility of a crossing of air flows entering the cylinder (10) with the burnt gases emerging from the cylinder (10) during passage between the intake point of the scavenging air flows and their point of impact. In this way a substantial improvement in scavenging is obtained, thereby improving engine operation.

Description

The present invention relates to a device for scanning a two-stroke internal combustion engine cylinder, with piston driven by a reciprocating rectilinear movement, of the self-supercharging type by post-filling effect, in which the distribution of each cylinder is exclusively provided by the piston in cooperation with the intake lights-intake ducts group and with the exhaust lights-exhaust ducts group, the intake lights group being discovered longer by the piston than the group exhaust lights, and two-stroke engine provided with such a sweep.

More particularly, the invention essentially relates to a device for managing the flow for the temporary counter-sweeping of the burnt gases in the intake ducts during the pre-exhaust phase preceding the opening of the exhaust lights. , then for their reintroduction followed by the introduction of the purge air proper inside the cylinder to improve the efficiency of such an engine. Consequently, all of the air arriving at the cylinder, either for sweeping or for post-filling, enters through the intake duct. This type of self-supercharging engine by post-filling effect uses the direct action of gases leaving a cylinder on an air reserve in order to compress it and introduce it into a cylinder at an appropriate time in the cycle to overeating him. The cylinder-air reserve-cylinder pressure transfer phases take place in an essentially closed environment so as to avoid any loss of energy to the outside.

Post-filling is therefore understood to mean the introduction of an additional air charge into the cylinder, after sweeping and closing the exhaust orifices.

In general, it will be appropriate to hereinafter refer to as purging air the purging agent intended for the renewal of the burnt gases from the cylinder, whether it be pure air or any other oxidant-fuel mixture.

Engines of the aforementioned type are already known, in particular such a two-stroke engine, consisting of at least one group of two cylinders, the operating cycles of which are set relative to one another at an angle of 180 ° crankshaft, in which the energy of the pre-exhaust gases from one cylinder is used to carry out the post-filling of the other cylinder, is described in FR-A-2 346 558 or its equivalent CH-A-593 420 of this applicant, and shown in Figures 1 to 5 of this publication.

Another process described in the French patent application ^No. 87 04757 of the present applicant, also discloses an aforementioned type motor producing a self-supercharging of each cylinder by itself by a post-charging effect, thanks to the use of a reserve of air pressurized by the action of the energy of the pre-exhaust gases.

A preferred version of the device for implementing this method is the subject of co-deposition of a request form PCT inventor under the ^No. PCT / FR 88/00155 published under ^No. WO 88/08073 and based on French priority 87 04757.

To facilitate the continuation of the description, it will be advisable to call "twin-cylinder solution" that which is the subject of FR-A-2 346 558 or CH-A-593 420, it being understood that it can also be applied to a multiple a group of two cylinders, and "solution drum" that used for implementing the process according to french patent application ^No. 87 04757, it being understood that it can be universally applied irrespective of the number and the arrangement of the cylinders.

• 1) avec la plus petite quantité d'air de balayage possible,
• 2) le plus complètement possible,
• 3) avec le moins de perte d'air de balayage possible,
• 4) avec la plus petite dépense d'énergie possible, mise en oeuvre à cet effet,
• 5) dans le temps imparti, imposé par le régime de fermement du moteur,
• 6) avec un refroidissement aussi intense que possible du cylindre et de la tête de piston,
• 7) en profitant, si possible, du mouvement naturel descendant puis ascendant du piston pour soutenir l'aérodynamique du balayage.
  Le balayage d'un moteur, du type particulier décrit précédemment et faisant l'objet de l'invention tout en satisfaisant le mieux possible aux contraintes générales 1) à 7) qui viennent d'être rappelées, doit en plus résoudre simultanément un ensemble de contraintes particulières énoncées ci-dessous. Ces contraintes particulières supplémentaires sont inhérentes au principe de fonctionnement commun à la solution bicylindre et à la solution monocylindre et sont les suivantes :
• 8) organiser le contre-balayage temporaire des gaz brûlés dans les conduits de balayage, puis leur retour en direction du cylindre, de telle façon qu'ils se mélangent aussi peu que possible avec l'air de balayage, ce qui exclut la possibilité d'imposer aux conduits de balayage une forme utilisant des rayons de courbure trop faibles,
• 9) mettre en oeuvre une forme de balayage, à l'intérieur du cylindre, à l'aide des gaz d'échappement ressortant des conduits de balayage, puis du front de l'air de balayage proprement dit réalisant les critères 1) à 7) ci-dessus de façon équivalente à ce que l'on obtient avec les formes de balayage connues dans les moteurs du type classique où les lumières d'échappement sont découvertes plus longtemps par le piston que les lumières de balayage, c'est-à-dire en créant un front d'air de balayage aussi uni et concentré que possible de façon à éviter la création d'îlots de gaz brûlés à l'intérieur de la zone de balayage (difficulté de synchroniser le retour de plusieurs fronts d'air de balayage issus de différents conduits de longueur et/ou de volumes individuels différents),
• 10) un entraxe des cylindres aussi réduit que possible pour la solution bicylindre ou pour la solution monocylindre appliquée à un moteur multicylindre,
• 11) impartir aux conduits de balayage, dans lesquels va se dérouler le phénomène d'échange de pression en milieu clos pour le système cylindre-conduit de balayage-volume suralimenté (cylindre associé calé à 180° pour la solution bicylindre, et réserve d'air interne au piston pour la solution monocylindre) un volume optimal pour atteindre l'effet de post-remplissage maximal. Le volume optimal théorique (les gaz de pré-échappement occupent alors un volume égal à celui des conduits de balayage) est en effet fonction de l'importance de l'effet de post-remplissage envisagé, lui-même dépendant de l'état thermodynamique des gaz en cours de détente (objectif très dépendant en particulier du rapport air-combustible et du taux de gaz résiduels avec lesquels la combustion s'est déroulée). Le volume optimal réel des conduits de balayage doit naturellement être supérieur au volume optimal théorique pour éviter tout risque de post-remplissage par des gaz brûlés mais aussi peu que possible, sous peine de voir se dégrader d'une part le potentiel d'autosuralimentation (diminution du niveau de pression atteint dans lesdits conduits, si l'énergie apportée par les gaz de pré-échappement est répartie sur un volume trop important) et d'autre part le rendement du moteur (perte de détente dans le cylindre accrue sans effet bénéfique sur l'augmentation du post-remplissage ainsi obtenu),
• 12) impartir aux dits conduits de balayage une longueur nécessaire à la création du volume optimal, tel qu'expliqué en 11) ci-dessus, mais aussi faible que possible de façon à rendre maximal le régime du moteur, auquel un effet de post-remplissage sera encore tout juste atteint (l'augmentation du régime entraîne une augmentation quasi-proportionnelle du temps de parcours, exprimé en degré de vilebrequin, de l'onde de pression engendrée par la détente des gaz de pré-échappement.

Before setting out the specific constraints specific to this particular type of two-stroke engine, it is useful to recall the purpose of scanning in the two-stroke engine in general; its purpose is to be able to expel from the cylinder the gases burned from the previous cycle:

• 1) with the smallest amount of purge air possible,
• 2) as completely as possible,
• 3) with the least loss of sweeping air possible,
• 4) with the smallest possible energy expenditure, implemented for this purpose,
• 5) within the time limit imposed by the engine speed,
• 6) with as intense cooling as possible of the cylinder and of the piston head,
• 7) by taking advantage, if possible, of the natural downward and then upward movement of the piston to support the aerodynamics of the sweep.
  The scanning of an engine, of the particular type described above and forming the subject of the invention while satisfying as well as possible the general constraints 1) to 7) which have just been mentioned, must in addition simultaneously resolve a set of specific constraints set out below. These additional particular constraints are inherent in the operating principle common to the twin-cylinder solution and to the single-cylinder solution and are the following:
• 8) organize the temporary counter-sweeping of the burnt gases in the sweeping conduits, then their return towards the cylinder, so that they mix as little as possible with the sweeping air, which excludes the possibility of '' impose on the scanning conduits a shape using too small radii of curvature,
• 9) implementing a form of sweeping, inside the cylinder, using the exhaust gases emerging from the sweeping conduits, then from the front of the sweeping air proper, fulfilling criteria 1) to 7 ) above in an equivalent manner to that obtained with the known sweeping forms in engines of the conventional type where the exhaust lights are discovered longer by the piston than the sweeping lights, i.e. - say by creating a sweeping air front as united and concentrated as possible so as to avoid the creation of burnt gas islands inside the sweeping area (difficulty in synchronizing the return of several air fronts of sweep from different ducts of different length and / or individual volumes),
• 10) a cylinder center distance as small as possible for the twin-cylinder solution or for the single-cylinder solution applied to a multi-cylinder engine,
• 11) impart to the scanning conduits, in which the phenomenon of pressure exchange in a closed environment will take place for the cylinder-scanning duct-supercharged volume system (associated cylinder set at 180 ° for the two-cylinder solution, and reserve of internal air in the piston for the single-cylinder solution) an optimal volume to achieve the maximum post-filling effect. The theoretical optimal volume (the pre-exhaust gases then occupy a volume equal to that of the sweeping conduits) is in fact a function of the importance of the envisaged post-filling effect, itself dependent on the thermodynamic state gases in the course of expansion (objective very dependent in particular on the air-fuel ratio and the rate of residual gases with which the combustion took place). The actual optimal volume of the sweeping conduits must naturally be greater than the theoretical optimal volume to avoid any risk of post-filling with burnt gases, but as little as possible, otherwise the potential for self-supercharging will deteriorate ( reduction in the pressure level reached in said conduits, if the energy provided by the pre-exhaust gases is distributed over an excessively large volume) and on the other hand the efficiency of the engine (loss of expansion in the cylinder increased without beneficial effect on the increase in post-filling thus obtained),
• 12) allocate to the said scanning conduits a length necessary for the creation of the optimal volume, as explained in 11) above, but as low as possible so as to maximize the engine speed, to which a post-effect filling will still be just reached (the increase in speed results in a quasi-proportional increase in the travel time, expressed in degree of crankshaft, of the pressure wave generated by the expansion of the pre-exhaust gases.

The difficulty of simultaneously meeting all of these requirements has considerably slowed down the development of this type of engine.

The aforementioned document CH-A-593,420 reveals only a schematic arrangement, from which it is impossible to collect lessons capable of providing a global technical solution satisfying all the requirements mentioned. Indeed it does not take into account the architectural constraints specific to a grouping of two cylinders with parallel axes mentioned in 10). The constraint 8) is only partially taken into account and does not otherwise make it possible to propose a satisfactory solution to the constraints 9) to 12). In particular, the scanning system disclosed is of the transverse type with a piston head in the form of a deflector. This scanning system, known per se, leads to a relatively poor scanning efficiency.

Other forms of scanning of the loop type, also known as "Schnürle" scanning, have been tried. They made it possible to better take into account, although imperfectly, the constraint mentioned in 9), but without satisfying the other requirements, in particular 8), 11) and 12).

The evolution of the sweeping technique of engines of the conventional type with distribution exclusively ensured by the piston in cooperation with exhaust lights and intake lights did not ultimately retain, despite the very large number of devices offered, that the aforementioned Schnürle loop solution which consists in making the sweeping air penetrate into the cylinder by making it bear initially on the piston head, then on the lower part of the cylinder in the immediate vicinity of the piston head diametrically opposite to the exhaust lights, then on the bottom of the cylinder head and finally on the cylinder wall located above the exhaust lights before undergoing an inflection in the opposite direction towards the exhaust lights.

We also know, from the German patent DE-C-477 041 KRUPP, cited in a book on scanning written by VENEDIGER, printed by FRANCKHISCHE VERLAGSHANDLUNG, Abt. Technik. Stuttgart, 1947, taken up by French patent FR-A-769,039, a so-called reverse loop scanning system consisting in making the scanning air penetrate while trying to make it bear on the wall of the cylinder liner located at the - above the exhaust lights.

This reverse loop system has not succeeded in imposing itself, since it has in particular the disadvantage of causing a crossover of the upward flows of sweeping air in the direction of the wall of the targeted jacket and the flow of burnt gases. leaving in the direction of the exhaust lights, with a large contact surface and insufficient support of the sweeping air as it enters the cylinder, thus realizing two characteristics which must be carefully avoided if one wishes to guarantee stability sufficient for scanning (see page 73, first paragraph, of VENEDIGER's book).

As a result, there was a bias in the art for the use of reverse direction loop scanning.

In all the solutions proposed in the context of reverse loop scanning, as in almost all of the other known solutions, the lower edge of the intake ports coincides with the position of the piston head at bottom dead center. (see in particular figure 1 of FR-A-769 037 or FR-E-45284).

A main aim of the invention is to propose a global technical solution to the problems posed by simultaneously satisfying all of the requirements mentioned above.

Another objective of the invention is to keep the advantages described in the two above-mentioned patents CH-A-593 420 (twin-cylinder) and patent application FR-87 04757 (single-cylinder) to the maximum.

The main object of the invention is also to solve the new technical problem consisting in providing a solution allowing, in the context of self-supercharging by post-filling, to use an inverted loop while eliminating the drawbacks inherent in this. boils the reverse cited by VENEDIGER.

The present invention solves this technical problem by overcoming the prejudices thereof relating to the use of a reverse loop and to the positioning of the lower edge of the intake lumen at the bottom dead center.

An additional objective is to organize a large turbulence field ensuring a good mixture of air and fuel, with a view to the combustion phase, at all loads and all engine operating speeds, while also avoiding the particular case of the spark ignition engine any loss of fuel from the exhaust.

The invention relates to a device for scanning a two-stroke internal combustion engine cylinder, with self-supercharging by post-filling effect in which the distribution of each cylinder is exclusively ensured by a piston driven by a reciprocating rectilinear movement, in cooperation with a group of intake lights-intake ducts, hereinafter referred to as intake group, and with a group of exhaust lights-intake ducts, hereinafter referred to as exhaust group, including the intake lights intake are discovered longer by the piston than the exhaust ports, comprising post-filling means in an essentially closed environment, the intake group serving as the sole air intake path for the cylinder, characterized in that the intake group is arranged relative to the cylinder so that the purge air flows from the intake lights meet in a impact point located on the upper wall of the cylinder above the exhaust lights, to perform a so-called reverse loop; and the altitude of the lower edge of the intake lights is located near or above the altitude of the Upper edge of the exhaust lights to substantially completely eliminate any possibility of intersection of the air flows entering the cylinder with the burnt gases leaving the cylinder during the path between the entry points of the purge air flows and their point of impact, and the intake ducts are inclined at an angle of elevation relative to the cylinder so as to produce during the pre-exhaust a separation front of the burnt gases with the sweeping air substantially perpendicular to the line of the centers of the intake ducts.

Other alternative embodiments are set out in the subclaims and are incorporated here by reference.

The invention also relates to an engine equipped with such a device.

Other objects, characteristics and advantages of the invention will appear in the light of the explanatory description given with reference to the appended drawings given simply by way of illustration and which therefore cannot in any way limit the scope of the invention.

• les figures 1a, 1b représentent de manière schématique, en coupe axiale verticale, un cylindre d'un moteur à deux temps dont les lumières d'admission et d'échappement sont disposées symétriquement par rapport au plan de symétrie de balayage de manière à réaliser la boucle Schnürle classique de l'art antérieur ;
• la figure 2 représente de façon schématique une vue similaire à la figure 1, mais d'un dispositif conforme à l'invention permettant de mettre en oeuvre le procédé selon l'invention ;
• la figure 3 représente une vue en coupe transversale du dispositif selon l'invention de la figure 2, qui comporte un seul groupe de deux lumières d'admission et un seul groupe d'une seule lumière d'échappement, selon un mode de réalisation actuellement préféré ;
• la figure 4 représente une vue en demi-coupe rabattue du plan vertical parallèle à l'axe du cylindre contenant le vecteur de direction principale du flux de gaz issu du conduit d'admission représenté à la figure 3 par la flèche 30 ;
• la figure 5 représente une autre vue en coupe verticale passant par les flèches 30 de la figure 3, permettant de voir les deux conduits d'admission disposés symétriquement par rapport aux conduits d'échappement, faisant l'objet de la figure 3 et représente le début du pré-échappement en montrant le front de séparation des gaz ;
• la figure 6 représente un mode de réalisation d'un moteur équipé de deux cylindres calés à 180° ;
• les figures 7a, 7b représentent une variante de réalisation du piston avec un abattement local au droit d'une des deux lumières d'admission.

In the drawings:

• Figures 1a, 1b schematically represent, in vertical axial section, a cylinder of a two-stroke engine whose intake and exhaust ports are arranged symmetrically with respect to the plane of symmetry of scanning so as to achieve the classic Schnürle loop of the prior art;
• Figure 2 shows schematically a view similar to Figure 1, but of a device according to the invention for implementing the method according to the invention;
• Figure 3 shows a cross-sectional view of the device according to the invention of Figure 2, which comprises a single group of two intake ports and a single group of a single exhaust port, according to an embodiment currently prefer ;
• FIG. 4 shows a folded half-section view of the vertical plane parallel to the axis of the cylinder containing the main direction vector for the flow of gas coming from the intake duct shown in FIG. 3 by the arrow 30;
• FIG. 5 represents another view in vertical section passing through the arrows 30 in FIG. 3, making it possible to see the two intake ducts arranged symmetrically with respect to the exhaust ducts, forming the subject of FIG. 3 and start of pre-exhaust by showing the gas separation front;
• FIG. 6 represents an embodiment of an engine equipped with two cylinders set at 180 °;
• Figures 7a, 7b show an alternative embodiment of the piston with a local reduction to the right of one of the two intake ports.

With reference to FIG. 1, it can be observed that according to the Schnürle device, the cylinder 1 comprises at least two intake ports 2 and at least one exhaust port 3, the lower edge of the intake port is located conventionally at the bottom dead center (PMB), which also coincides with the lower edge of the exhaust port. In addition, in a decisive manner, the exhaust port is arranged in a wall of the cylinder substantially opposite to the wall of the cylinder towards which the purge air flows coming from the intake conduits 2 converge.

According to this Schnürle device, a scavenging of the burnt gases is therefore obtained according to a loop 5 shown in FIG. 1, called the Schnürle loop.

Referring to Figures 2 to 5, there is shown a scanning device according to the invention according to which the cylinder 10 comprises a group of intake lights 12a, 12b and intake ducts 14a, 14b (intake group) that can be seen in Figures 2 to 5, and a group of exhaust ports 16 and exhaust ducts 18 (exhaust group). The intake ports 12a, 12b are arranged laterally in the cylinder 10 relative to the exhaust ports 16 so that the intake ports 12a, 12b are exposed by the piston 22 longer than the exhaust ports 16.

According to the invention, the intake group (12a, 12b; 14a, 14b) is arranged relative to the cylinder (10) so that the flows of purge air coming from the intake lights (12a, 12b) meet at a point impact located on the upper wall (10a) of the cylinder (10) above the exhaust ports (16), to perform a so-called inverted loop; and the altitude (A) of the lower edge of the intake ports (12a, 12b) is arranged high enough in the cylinder (10) relative to the altitude (B) of the upper edge of the exhaust ports (16) to substantially completely eliminate any possibility of intersection of the air flows entering the cylinder (10) with the burnt gases leaving the cylinder (10) during the path between the entry points of the purge air flows and their point d 'impact.

Preferably, the altitude (A) of the lower edge of the intake lights (12, 12b) is located in the vicinity or above the altitude (B) of the upper edge of the exhaust lights (16).

According to another characteristic of the device according to the invention, the intake ducts 14a, 14b of each pair are arranged laterally symmetrically with respect to a scanning plane of symmetry which substantially coincides with the longitudinal plane of symmetry of the cylinder passing through the slots exhaust.

In addition, the intake ports 12a, 12b and the exhaust ports 16 are arranged symmetrically with respect to the abovementioned scanning plane of symmetry which here coincides substantially with the longitudinal plane of symmetry passing through the exhaust port 16.

According to another characteristic of the device according to the invention, the intake ducts 14a, 14b are arranged laterally inclined relative to the cylinder, at an elevation angle β mentioned in FIG. 4, so that the front separating the burnt gases with the air of scanning is substantially perpendicular to the line of the centers of each intake duct 14a, 14b, as shown in FIG. 5.

According to a particular embodiment, groups of intake ducts 14a, 14b are provided, arranged in pairs, each pair being able to have a different inclination, so that the meeting point of the flows of all the pairs is at an altitude. substantially identical. Preferably, the arrow half-angle α defined by the angle between the trace of the plane parallel to the axis of the cylinder 10 containing the main direction vector of the gas flow from each of the intake ducts 14a, 14b and the trace of the scanning plane of symmetry S clearly visible in FIG. 3 is provided in cooperation with the aforementioned angle β so that the meeting point M of the respective intake air flows symbolized by the arrow 30 of each pair if killed substantially in an area between the upper edge of the intake ports 12a, 12b and the top 11 of the cylinder 10. Advantageously, the angle ϑ associated with each pair of intake ports 12a, 12b, defined by the angle between the plane of symmetry S and the radius CL, L being the point of intersection of the arrow 30 with the cylinder 10, is between approximately 45 ° and approximately 135 °. In the case of the presence of a single pair of intake ports, as shown, the angle ϑ is advantageously between approximately 70 ° C. and 110 ° C.

According to a currently preferred embodiment, as shown, this device comprises a single group of two intake ports 12a, 12b and a single group of a single exhaust port 16, or two exhaust ports 16.

It is thus conceivable that with such a device according to the invention, the best possible scanning is obtained in a reverse loop compared to the conventional Schnürle loop, thereby improving the operation of a two-stroke engine with self-supercharging by post-filling.

Likewise, the front of separation of the burnt gases and the purging air is substantially straight or perpendicular with respect to the line of the centers of the intake ducts.

In FIG. 2, a distinction has been made between the different fluids present by representing the burnt pre-exhaust or exhaust gases by solid circles, and the purge intake air by bubbles. In addition, the intermediate positions of the gas separation front are shown in dashed lines and in front the front F of the position actually represented. In addition, the arrow 13 represents the movement of circulation of the sweeping air in the chamber according to the so-called reverse loop.

Various modifications can be made to the device according to the invention described above, without however departing from the scope of the invention.

It will be understood that the angles of elevation β and of half-arrow α of the main vectors (30) of the intake ducts relative to the cylinder can vary within certain limits as a function of the circumferential position of the intake ports 12a, 12b, defined by the aforementioned angle,, but also of the upper edges respectively of the intake ports 12a, 12b and the exhaust ports 16 and of the stroke-bore ratio of the cylinder 10 considered.

By way of example, for the circumferential position shown of the variant comprising a single pair of intake ports 12a, 12b; the deflection angle (2α) of the pair of intake ducts 14a, 14b of the embodiment of FIGS. 2 to 5, corresponding to an angle ϑ of approximately 110 °, has a value of approximately 135 ° and l elevation angle β of the main direction vector of the gas coming from each intake duct has a value of approximately 45 ° and the meeting point M visible in FIG. 3 of the two planes containing the main direction 30 is located at a distance = about 0.7 of the radius (R) of the cylinder from the center C.

According to another alternative embodiment, each group of intake ducts 14a, 14b leads to a group of lights located below the bottom dead center (PMB) as described and shown with particular reference to Figures 1b; 5a, 5b; 6a, 6b of the PCT application WO 88/08073 of the applicant incorporated here by reference. These lights are placed in intermittent communication either with the intake source, or with a storage chamber provided inside the piston, this solution being called single cylinder.

In summary, according to the invention there is obtained an excellent scanning efficiency, including for large values of the stroke / bore ratio, greater than what can commonly be obtained with the conventional loop scanning system of the Schnürle type.

Maximum simplicity is obtained of the scanning device, and therefore of the engine, while having sufficient permeability generated by the favorable section-time diagram of the distribution of the particular type of engine described above, two-stroke, self-supercharging by effect. post-filling, which generally allows to start the scanning phase of the scanning ducts substantially concomitantly with the opening of the exhaust ports.

FIG. 6 represents an alternative embodiment of an engine equipped with the twin-cylinder solution of the type described in CH-593 420, with the device according to the invention which is the subject of the preceding figures 2 to 5, limited here by simplification to a module of two cylinders 10A, 10B, set at 180 °, equipped with two intake pipes 14a, 14b and two exhaust pipes 30a, 30b each leading to the light 16a, 16b. The cutting of this engine is carried out perpendicular to the axis of each cylinder. The scanning symmetry planes of the two cylinders are merged and pass, as mentioned previously, through the two axes 32a, 32b of the cylinders 10A, 10B.

It can thus be seen that the invention makes it possible to satisfy all of the aims referred to in points 1 to 12 at the start of the description and in particular in point 10, concerning the minimum center distance enabling a maximum displacement to be achieved in a given size.

According to an alternative embodiment, it has been provided that each pair of intake lights has a light (12a) on one side of the aforementioned scanning plane of symmetry which is discovered longer by the piston than the light (12b) located on the other side of this plane of symmetry.

As a result, it is possible to create at the end of the post-filling period, in each cylinder, a vortex with an axis parallel to that of the cylinder.

It is easy to adjust the intensity so as to make optimal, in a manner known per se, the preparation of the air-fuel mixture and the course of combustion which will succeed in only about a quarter of rotation of the crankshaft at the phase post-filling, which in itself has an additional advantage.

It is important to note in this regard that the early opening of one of the conduits of a pair of intake conduits 14a, 14b will not cause significant asymmetry (and even no asymmetry if the anticipated opening is not carried out not by a height different from the upper leading edge of the intake lumen but by a local depression 40 in the piston head with respect to the extent of said lumen) of the purge air stream inside of the cylinder because the intake lights used for scanning are completely uncovered when the scanning air front reaches the cylinder. It is also possible to compensate for the greater penetration of the burnt gases in this duct by bringing it into communication with the inlet of sweeping air before that of the other duct.

Figures 7a, 7b show an alternative embodiment of a piston 22 with a local reduction 40 of the edge 38 to the right of one of the two intake ports to cause a delayed closure of this light relative to the other light in order to create the vortex represented by the arrow T.

Furthermore, according to an advantageous alternative embodiment of the method of the invention, the engine is not cooled at low loads by interrupting the engine cooling circuit and in particular the supply paths including the intake ducts, while we refrigerate since intermediate loads up to the maximum load by opening the refrigeration circuit. The absence of refrigeration at low loads makes it possible to raise the temperature of the intake air by virtue of its heating by the walls of the intake ducts 14a, 14b themselves heated by the pre-exhaust gases. The rise in temperature of the intake gases increases their volume and produces a decrease in the volume of residual exhaust gases in the cylinder, which favorably influences the minimum flammability threshold of the purge air-residual gases mixture mainly in the case of spark ignition engines.

Advantageously, the part of the intake conduits 12a, 12b opening into the cylinder 10 is provided to be substantially perfectly cylindrical, which greatly facilitates the production of the shapes and the precision of their geometry.

Claims (11)

1. Scavenging device for a cylinder of a two-stroke internal combustion engine, with self-supercharging by post-filling effect in which the distribution of each cylinder is effected exclusively by a piston driven with an alternating rectilinear movement, in cooperation with a group of inlet ports-inlet manifolds comprising at least one pair of inlet manifolds, referred to hereinafter as inlet group, and with a group of exhaust ports-exhaust manifolds, referred to hereinafter as exhaust group, the inlet ports of which are arranged in the cylinder so as to be uncovered by the piston for a longer time than the exhaust ports, comprising means for post-filling in an essentially closed environment,the inlet group serving as the only way by which air reaches the cylinder, characterised in that the inlet group (12a, 12b; 14a, 14b) is arranged relative to the cylinder (10) so that the scavenging air flows from the inlet ports (12a, 12b) join one another at a point of impact situated on the upper wall (10a) of the cylinder (10) above the exhaust ports (16), to produce a loop termed reversed; the height (A) of the lower edge of the inlet ports (12a, 12b) is located in the vicinity of or above the height (B) of the upper edge of the exhaust ports (16) to eliminate substantially completely any possibility of crossing of the air flows entering the cylinder (10) and the burnt gases leaving the cylinder (10) on the path between the points of entry of the scavenging air flows and their point of impact, and the inlet manifolds (14a, 14b) are inclined at an angle of elevation (β) with respect to the cylinder (10) so as to produce during the pre-exhaust a separation front between the burnt gases and the scavenging air substantially perpendicular to the centre line of the inlet manifolds (14a, 14b).
2. Device according to Claim 1, characterised in that the inlet manifolds (14a, 14b) are arranged in pairs, each pair being able to have a different inclination, so that the meeting point (M) of the flows of all the pairs is located at a substantially identical height, the whole cooperating to create a combined rising stream of scavenging air having, particularly in immediate proximity to the cylinder head before undergoing its first change of direction, a maximum velocity along the wall of the cylinder (10) and decreasing progressively until it is substantially completely cancelled out in the vicinity of the longitudinal plane of the cylinder separating the rising current and the falling current.
3. Device according to Claim 2, characterised in that the inlet manifolds (14a, 14b) of each pair are arranged laterally symmetrically with respect to a scavenging plane of symmetry which coincides substantially with the longitudinal plane of symmetry of the cylinder passing through the exhaust ports.
4. Device according to one of Claims 1 to 3, characterised in that the circumferential position (angle ϑ) of the inlet ports (12a, 12b), the angle of elevation (β) and the half-angle of the arrow (α) of the inlet manifolds (14a, 14b) or of the pairs of inlet manifolds (14a, 14b) are selected such that the meeting point (M) of the principal vectors (30) of the respective inlet air flows is located substantially at a distance (d) from the centre (C) of the cylinder (10) between approximately 0.5 R and 0.9 R and at a height between the upper edge of the inlet ports (12a, 12b) and the apex (11) of the cylinder (10).
5. Device according to Claim 4, characterised in that the aforesaid angle ϑ of each pair of inlet ports, defined by the angle enclosed between the plane of symmetry (S) and the radius CL, L being the point of intersection of the arrow (30) with the cylinder (10), ranges between approximately 45° and approximately 135°.
6. Device according to one of Claims 1 to 5, characterised in that it comprises a single group of two inlet ports (12a, 12b) and a single group of one or two exhaust ports (16); advantageously the aforesaid angle ϑ ranges between approximately 70° and approximately 110°.
7. Device according to one of Claims 2 to 6, characterised in that each group of inlet manifolds (14a, 14b) ends at the same inlet ports (12a, 12b) of an associated cylinder (10) fixed at 180° of crankshaft.
8. Device according to one of Claims 2 to 6, characterised in that each group of inlet manifolds (14a, 14b) ends at a group of ports located below bottom dead centre (PMB), the said ports being able to be placed in communication intermittently either with the inlet air source or with a storage chamber provided inside the piston.
9. Device according to one of Claims 3 to 8, characterised in that each pair of inlet ports (12a, 12b) has a port located on the same side of the scavenging plane of symmetry which is uncovered by the piston for a longer time than that located on the other side of the same plane.
10. Device according to Claim 9, characterised in that the piston has a local cut-away (40) on the head opposite one (12a) of the inlet ports (12a, 12b) of the pair of inlet ports under consideration.
11. Engine equipped with a scavenging device as defined by one of Claims 1 to 10.

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