WO1994001663A1 - Two-stroke internal combustion engine cylinder feeding device and method - Google Patents

Abstract

A two-stroke internal combustion engine cylinder feeding device and method, wherein said cylinder comprises a fresh gas feed duct acting as a seat for counter-scavenging by the exhaust gas. Penetration of counter-scavenging exhaust gas into the feed duct (40) is restricted to a portion thereof which is defined by the related port (41), and by a buffer volume (42) of fresh gas forming a pressure reserve in constant communication with said duct and in interruptible communication with the pump housing (14), whereby the infeed of fresh gas into the cylinder (13) through said duct is subsequently delayed then extended substantially until the exhaust port (17) closes, by means of the above-mentioned pressure reserve.

Description

 Method and device for feeding a two-stroke internal combustion engine cylinder.

The invention relates to the supply of a two-stroke internal combustion engine cylinder, comprising at least one port associated with a supply line for fresh mixture and an exhaust port for the burnt gases.

Two-stroke engines are commonly encountered fitted with conduits which open out through lights in the cylinder, to ensure the admission of fresh gas (generally an air-fuel mixture) and the exhaust of burnt gases. Distribution is then ensured by the piston which closes or discovers these lights during its travel. The exhaust light is generally décc ^ erte before the supply light or lights, and it is closed after the obtura¬ tion of this or these latter. The engine casing, often called the pump casing because of the function it provides, thus makes it possible to carry out a sweeping of the gases burned by the fresh gases introduced under pressure into the cylinder. We then obtain a fluid "piston", which is in fact all the less perfect as the loads are important: indeed, a significant amount of fresh gas can pass directly to the exhaust, and the late closing of the light exhaust further accentuates the phenomenon. Therefore, when these fresh gases consist of air and fuel, a significant amount of fuel is lost to the exhaust, which results in a sharp deterioration in engine performance and significant pollution of the atmosphere by the hydrocarbons that are present in the exhaust gases. Specialists have therefore sought solutions to prevent the fuel present in the fresh mixture from reaching the exhaust port before it closes. This problem is difficult to solve because, with this type of engine, the transfer of fresh gases is almost complete when the piston comes to bottom dead center: therefore, during the remaining opening time, fresh gases can (under the effect of their kinetic energy) reach the exhaust light and thus be lost.

It has been proposed to lengthen the path of the fresh mixture by organizing a loop or bell sweep, but this solution is not very effective insofar as there are still short-circuits of fresh mixture originating from the trans¬ ferts concerned (channels d 'admission to the cylinder in communication with the pump housing), which are close to the exhaust port, towards this exhaust.

For the past twenty years, it has been proposed to stratify the supply of fresh mixture by arranging the corresponding pipe or pipes far from the exhaust, other channels being able to supply non-carbide gases. The carburetion can thus be done by semi-direct injection, at low pressure, in a pipe opening facing the exhaust. However, this injection is carried out when the piston is close to the bottom dead center in air which is no longer driven by a very high speed, which is unfavorable for spraying and mixing. In addition, this solution is relatively expensive. As a variant, it has also been proposed to provide separate inlets in the pump housing, with an inlet for fresh air which then feeds lateral transfers, and at least one other inlet for producing the air-fuel mixture, then feeding rear pipes (solutions of this type are illustrated in documents FR-A-2 609 498 and US-A-4 253 433).

These solutions, which use fresh air to constitute a buffer between the burnt gases and the fresh mixture, make it possible to avoid direct losses of fresh mixture from transfer pipes opening near the exhaust, but losses from other pipelines still exist.

More recently, it has been proposed to constitute a burnt gas buffer in front of the fresh mixture, by arranging the pipe concerned for supplying fresh mixture of such that it is the seat of a counter-sweep by the burnt gases during the opening of the associated supply light: the objective is then to create in the cylinder a "barrier" of gas burnt in front of the fresh gases heading towards the exhaust. Such a solution is for example described in document EP-A-202216. After the start of this counter-sweep, the pressure in the cylinder decreases and becomes lower than that which prevails in the pump casing, and the burnt gases concerned emerge from this pipeline when the fresh gases from the associated transfers begin to exit. Unlike the previous solutions, a buffer of fresh air is no longer created between the burnt gases and the fresh mixture, but a buffer of burnt gases which tends to oppose the transit of fresh gases. The counter-sweep is therefore used to "regurgitate" in the remainder of the sweeping phase, the burnt gases which then constitute a "barrier" between the exhaust light and the fresh gases coming from conventional transfers, fresh gases leaving only at the end of scanning of these high light transfers. However, as before, the pressure in the pump housing drops quickly after the back-sweeping, so that the transfer of fresh gas to the cylinder is almost complete at bottom dead center. The counter-sweep / discharge phase is therefore short, and it is impossible to avoid the loss of fresh gas leaving these transfers in the vicinity of the exhaust, as well as those coming from other transfers and reaching the exhaust port. In addition, the counter-sweeping transfers shown are highly dimensioned, so that there can be a mixture of fresh gas - burnt gas.

Mention may also be made of document OA-91/02144 which proposes using a rotary valve arranged to periodically close a short transfer which is the seat of a counter-scan, so as to periodically organize the communication of this transfer with the fresh mix inlet passage. This solution is however complex and complicates the production of the engine; in addition, the presence of the rotary valve makes it considerably more difficult to adjust the distribution of this motor. The state of the art can finally be supplemented by mentioning various counter-scanning systems, illustrated in documents DE-C-551.375, GB-A-2.083.550, AT-A-138.547, GB-A-111.162, US -A-3,797,467, or without counter-scanning, illustrated in documents US-A-4,242.993, FR-A- 2,166,420, GB-A-904,670, GB-A-2,115,485, EP-A -0.060.184.

The object of the present invention is to propose another more efficient solution, not presenting the drawbacks and / or the limitations of the abovementioned feeding techniques. The subject of the invention is therefore a method and a supply device which make it possible to greatly reduce the direct losses of fresh air-fuel mixture to the exhaust, and without having to use a dedicated mechanical distribution system with positive control. The invention also relates to a method and a supply device which promote the stratification of burnt gases / fresh air / fresh mixture in the cylinder.

It is more particularly a process for supplying a two-stroke internal combustion engine cylinder, this cylinder comprising at least one lumen associated with a fresh gas supply pipe which is the seat of a counter-sweeping by the burnt gases during the opening of said light, and a burnt-out exhaust light, characterized in that the penetration of burnt gases, during the counter-sweep, into the or each pipe of supply is limited to a portion thereof delimited by the associated lumen, and by a buffer volume of fresh gas forming a pressure reserve, which is in permanent communication with said pipeline and in closable communication with the pump housing associated with cylinder, and by the fact that the introduction of fresh gas into the cylinder via this pipe is subsequently delayed, then extended substantially until the exhaust port closes, thanks to the aforementioned pressure reserve.

In the particular case of a process in which the supply pipe is equipped with a carburetion device, it will be advantageous to provide that the penetration of the burnt gases is limited to a portion of this pipe which is delimited by the associated light and by the carburetion device, when said device is arranged between said lumen and the buffer volume.

Furthermore, when the cylinder concerned is equipped with sweeping transfers making it possible to inject fresh air from the pump housing into said cylinder, it is advantageous for the sweeping to be organized so as to form a separating layer between the light d exhaust and the supply port (s) of fresh gas from which the burnt gases emerge from the counter-sweep, then the fresh gases, when the pressure in the buffer volume becomes greater than that of the cylinder.

The invention also relates to a device for supplying a cylinder of a two-stroke internal combustion engine, this cylinder comprising at least one lumen associated with a supply pipe for fresh gas, which is the seat of a counter scanning by the burnt gases during the opening of said light, and a burnt gas exhaust light, characterized in that the or each fresh gas supply line is in communication with a buffer volume of fresh gas forming a pressure reserve, this buffer volume also being in communication with the pump housing associated with the cylinder, the communication with said pipe being direct and permanent, while the communication with said pump housing is closable by an associated closure means , and said pipeline the supply of fresh gas is also sufficiently long and narrow to prevent the penetration of the burnt gases into said buffer volume during the backwashing and to limit their mixing with the fresh gases being in this pipeline, and by the fact that the or each fresh gas supply light is arranged to have an opening period close to or longer than that of the exhaust light.

In the case of a supply device in which the supply line is equipped with a carburetion device, it may prove advantageous for this carburetion device to be arranged between the buffer volume of fresh gas and the cylinder, in which case said pipe is then dimensioned so as to avoid the penetration of the burnt gases into said carbura¬ tion device during the back sweep.

The carburetion device used can be mounted in series with the buffer volume on the associated supply pipe. As a variant, the buffer volume is mounted as a bypass on the associated supply pipe which is equipped with the carburetion device.

The associated closure means can be a non-return valve controlled by the pressure variations generated by the movement of the piston which slides in the cylinder. As a variant, this sealing means is a disc or a controlled rotary distributor, making it possible to have an asymmetrical opening.

According to another variant, the associated obtura¬ tion means is constituted by the skirt of the piston which slides in the cylinder, said skirt having a traver¬ health light whose axial path passes at the level of the supply light of the pipe. associated with said through light.

In this case, the fresh gas supply line may consist of a single branch, or may alternatively comprise several branches, including at least one branch comprising a light which cooperates with the through-hole of the skirt of the piston, and at least one other branch which opens into the cylinder at a height close to or greater than that of the light d 'exhaust.

It is also advantageous for the lengthening of the opening period of the or each fresh gas supply light to be obtained by placing said supply light (s) at a height close to or greater than that of the exhaust light, or by notching, at the level of said supply light (s), the piston which slides in the cylinder.

Furthermore, in the case where the cylinder is equipped with tr ~ nsferts scanning for injecting into said cylinc fresh air from the pump housing, it is advantageous qx. the sweep transfers are arranged laterally, while the supply line (s) in fresh mixture open into the cylinder at the level of lights which are arranged opposite the exhaust light, and these transfers open into the cylinder by a light which has a height less than that of the light of said one or more pipes.

According to a particular embodiment, the buffer volume of fresh gas has a large capacity, in particular of the order of two to ten times the displacement.

The invention also applies to cases where the engine comprises a plurality of cylinders.

It is then possible to provide that the buffer volume of fresh gas is pooled between several cylinders, while being supplied by the pump casings of - JS cylinders. Alternatively, the buffer volume of a cylinder is constituted by the casing of the neighboring cylinder, the delayed introduction of fresh gas into these cylinders being further organized with a certain phase shift from one cylinder to another. This other variant will be particularly applicable to the cases of star motors and oscillating barrel motors.

Other characteristics and advantages of the invention will appear more clearly in the light of the description which follows and of the appended drawings, relating to a particular embodiment, with reference to the figures in which:

- Figure 1 illustrates in section a two-stroke engine cylinder equipped with a supply system according to the invention (the crankshaft and the associated connecting rod have not been shown to simplify the representation), with a volume- buffer which is here mounted in derivation of a supply pipe equipped with a carburetion device, and a shutter by non-return valve controlled by the pressure variations generated by the movement of the piston;

FIGS. 2 and 3 are two diagrams showing the evolution of the different masses transferred as a function of the position of the piston, respectively with a supply organized in accordance with a conventional design and with a supply organized in accordance with the invention with • a arrangement according to Figure 1;

- Figures 4a, 4b, 4c and 4d are schematic views of an engine, the power supply of which is organized in accordance with the invention, for different angular positions of the crankshaft, aiming in particular to illustrate the limited counter-scanning (Figure 4b ) and the stratification in the cylinder (Figure 4c);

- Figure 5 illustrates in section a variant of the previous arrangement, with a closure produced by the skirt of the piston fitted with a through-hole, the fresh gas supply pipe illustrated here being arranged in two branches;

- Figure 6 is a diagram of the masses transferred as a function of the position of the piston, and Figure 7 the associated distribution diagram, for a food organized in accordance with the arrangement of Figure 5;

- Figure 8 illustrates in section another variant incorporating the closing principle of Figure 5, but with a supply line constituted by a single branch;

FIGS. 9 and 10 are two diagrammatic views illustrating two neighboring cylinders of a multi-cylinder engine, each cylinder of which can be supplied in accordance with the invention, respectively with a buffer volume common to two cylinders, and with a buffer volume of a cylinder which is constituted by the casing of the neighboring cylinder.

FIG. 1 illustrates a two-stroke engine 10, the cylinder of which is equipped with a supply system according to the invention. There is a motor housing, the upper part 11.1 of which carries a cylinder head 12 in order to define a cylinder 13, and the lower part 11.2 of which defines a pump housing 14 through which the crankshaft passes (not shown here). The upper part 11.1 comprises an exhaust channel 16 opening out through an escape light 17 into the cylinder 13. The engine illustrated also includes sweeping transfers making it possible to inject fresh air from the cylinder into the cylinder 13. pump housing 14, with in this case a rear transfer (the qualifier "rear" given in relation to the arrangement of the exhaust light 17) which opens out through a light 21, and two lateral transfers 18 (only one is visible in the section of FIG. 1) which open out through an associated light 19 in the cylinder 13. The cylinder head 12 is equipped with a conventional type ignition means, which in this case is a spark plug 27. The engine comprises also an air intake pipe 22, fitted with a throttle valve 23, this fresh air intake pipe opening out through an admission opening 24 in the pump housing 14; the discharge of air from the pump housing 14 into the pipe 22 is prohibited by a valve non-return valve 25 controlled by the pressure variations generated by the movement of the piston 15 of the engine, which valve rests on its reed 33 at the time of air intake. The seal during closing is ensured by a seal 26.

A fresh gas supply pipe 40 is also provided, which opens out through a light 41 in the cylinder 13. This fresh gas supply pipe is the seat of a counter-sweep by the gases burned during the 'opening of this light 41 at the redes¬ cente of the piston, as will be explained in more detail with reference to the schematic views of Figures 4a to 4d.

According to a characteristic of the invention, the penetration of the burnt gases, during the backwashing, into the supply line 40 is limited to a portion of the latter delimited by the associated lumen 41, and by a buffer volume 42 of fresh gas forming a pressure reserve, which is in permanent communication with this pipe 40 and in closable communication with the pump housing 14, and the introduction of fresh gas into the cylinder 13 by this pipe is subsequently delayed and then substantially extended until the exhaust port 17 closes thanks to the aforementioned pressure reserve. The assembly constituted by the buffer volume 42 and the supply pipe 40 thus constitutes a delay circuit.

In this case, the supply line 40 is equipped with a carburetion device 43 of conventional type: the penetration of the burnt gases is then limited to a portion of the supply line 40 which is delimited by the associated light 41 and by this carburetion device 43. In this case, there is, during feeding, fresh mixture downstream of the carburetion device 43. As will be explained below, it is however possible to arrange such a device of carburation not between the cylinder and the buffer volume as shown in Figure 1, but between the pump housing and the buffer volume. In such a case, the penetration of the burnt gases during the counter-sweep will then be limited to a portion of the supply line which is delimited by the lumen 41 and by the buffer volume 42 of fresh gas.

It should be noted that the embodiment illustrated in FIG. 1 has only one fresh gas supply pipe 40, but this is only an example. The engine can in fact be equipped with a plurality of such fresh gas supply pipes, in which case each pipe will be in communication with a buffer volume of fresh gas forming a reserve of pressure. As can be seen in FIG. 1, the pipe 40 for supplying fresh gas is in direct communication with the buffer volume 42 of fresh gas forming a pressure reserve. This buffer volume 42 is also in communication with the pump casing 14 associated with the cylinder, but this communication can be closed by an associated closure means, here produced in the form of a non-return valve 29. The part lower part of the casing 11.2 in fact has a lumen 28 opening into the interior of the pump casing 14, and a connection block 31 is fixed on this part 11.2 of the casing at the level of said lumen 28, the seal being ensured by a gasket associated 30. The block 31 carries a support reed 32 associated with the valve 29, which valve is only controlled by the pressure variations generated by the movement of the piston 15 which slides in the cylinder, without the need to do so. use of any positive-controlled mechanical means.

According to another characteristic of the supply system according to the invention, the supply line for fresh mixture is also sufficiently long and narrow, on the one hand to prevent the penetration of the burnt gases. in the buffer volume 42 during the counter-sweep, or in the carburetion device 43 when this device is arranged between the buffer volume and the cylinder (which is the case in the embodiment illustrated in FIG. 1), and on the other hand to avoid mixing of the burnt gases with the fresh gases. In addition, the light 41 for supplying fresh gas is here arranged at a height close to or greater than that of the exhaust light 17, so as to have an open period close to or longer. Thanks to the buffer volume 42 and the associated shutter valve 29, the supply of fresh gas to the pipe or pipes 40 for admission to the cylinder is carried out with a relatively constant pressure and of a level close to that of the pressure in the cylinder when the lights close. This then makes it possible to extend the introduction of fresh gases into the cylinder, while moderating their rate of introduction at the start of the sweep. The closable communication, thanks to the presence of the non-return valve 29, between the buffer volume and the pump housing makes it possible to prevent the backflow of fresh gases between the buffer volume and the pump housing. In addition, by arranging the light 41 of supply in fresh mixture at a height close to or greater than that of the exhaust light 17, it is possible, by using the counter-scanning, to create a significant delay in the introduction. of the air and fuel mixture in the cylinder. The same result would be obtained by notching the piston 15 at the level of this supply lumen 41 (variant not shown).

In order to better understand the organization of the aforementioned delay, we have presented in FIGS. 2 and 3 diagrams giving the evolution of the different masses transferred as a function of the position of the piston, with respectively a supply organized in accordance with a classi¬ as (diagram of FIG. 2), and a supply organized in accordance with the invention, with an arrangement according to the figure 1 (diagram of figure 3).

In FIG. 2, three curves are thus distinguished giving the evolution of the masses (cumulative) transferred from a top dead center position (TDC) to another top dead center position. In a conventional engine, the succession of openings and closings of the lights is carried out as follows: after the top dead center TDC, there is successively the opening of the exhaust light (OE), the opening of the conventional type transfer light (OT), the bottom dead center (PMB), the closing of the conventional type transfer light (FT), the closing of the exhaust light (FE), and finally a new point dead high TDC. The abscissa line of the diagram thus corresponds to the angle of the crankshaft. The three curves illustrated here represent the variations of the masses transferred (accumulated masses) respectively at the admission of the pump housing (curve MC), in the transfers of conventional type (curve MTC), and in the exhaust pipe (curve ME ). The MTC curve shows a portion of counter-scanning CB which is extremely reduced, up to the point denoted A, and above all shows that the maximum of transferred mass, at the point denoted B, can occur after the bottom dead center PMB. The gap t. at this point B and the closing of the exhaust light FE, shows that there is a significant period of time during which the fresh gases can reach this exhaust light, with the harmful consequences already mentioned in the introduction of the description.

FIG. 3 illustrates a similar diagram, with a supply organized in accordance with the invention. A distinction has been made on this curve for transfers of the conventional type denoted T or TC (these transfers in FIG. 1 are referenced 20 for the rear transfer and 18 for the two lateral transfers), and the delay transfer denoted TR (which corresponds on the Figure 1 at line 40). In this case, on the abscissa line which corresponds to the angle of crankshaft, we then successively find, after a TDC top dead center, the opening of the OE exhaust and the OTR delay transfer (these two openings being here simultaneous due to an ad hoc arrangement of the corresponding lights ), the opening of the conventional OT type transfer light, the bottom dead center PMB, the closing of the conventional FT type lights, the closing of the FE exhaust light and the FTR delay transfer light (these closures being carried out simultaneously here), and finally the new top dead center TDC. The curves illustrated in the diagram in FIG. 3 indicate the masses transferred (accumulated) to the exhaust (curve ME), to the admission of the pump housing (curve MC), to transfers of the conventional type (TCM), and finally to the delay transfer (MTR curve). We find, on the curve MTR, a counter-scanning portion CB (up to point A '), but which is clearly more important than in the case of a conventional type motor. This diagram illustrates above all the existence of a delay RI in the introduction of fresh gas, and a delay R2 in the delivery of the delay transfer (point B 'on the MTR curve) compared to the delivery of conventional transfers. (point B on the MTC curve).

Thus, with a supply organized in accordance with the invention, there is then, at the start of opening, a back-sweeping of the supply pipe by the burnt gases. The pressure in the buffer volume being at this time lower than that prevailing in the pump casing, the quantity of burnt gas which enters this supply line is greater than that which would have entered if this line had been in direct contact with the pump housing, as provided in certain prior devices (for example that described in document EP-A-202 216). The pump housing still supplies the buffer volume during this start of opening, and, when transfers of conventional type open, the pressure in the pump housing drops rapidly and the supply of the buffer volume through the pump housing stops. Almost simultaneously, the pressure in the cylinder becomes lower than that of the buffer volume, the flow in the supply line is reversed, and the burnt gases which had entered it exit towards the cylinder then, after them, exit the fresh gases which had hitherto been contained by the burnt back-flushing gases. These fresh gases therefore penetrate later into the cylinder than if they had passed through conventional transfers, which represents the delay in the supply organized for the supply in accordance with the invention. The supply line associated with this counter-sweep is arranged with a dimension sufficient to prevent the penetration of the burnt gases into the buffer volume during the counter-sweep (or in the carburetion device when such a device is arranged between the buffer volume and the outlet of this pipe), and to avoid their mixing with the fresh gases. A long and narrow supply line will therefore be chosen, as well as a buffer volume of fresh gas having a large capacity, in particular of the order of two to ten times the engine displacement. Thanks to this large capacity of the buffer volume, its pressure varies little during filling or emptying, and this pressure is greater the greater the maximum pressure of the pump housing. By having a pressure in the buffer volume of sufficient size, the admission of fresh gases into the cylinder can then be extended until the closing lights of the delay transfers are closed (point B 'is located practically at the level from the instant of closing FTR) and therefore until the closing of the exhaust light (FE) or slightly beyond.

When a carburetion device is placed between the buffer volume and the cylinder, as illustrated in FIG. 1, it will be preferable to arrange this carburetion device substantially equidistant from the light 41 for admission to the cylinder and the orifice for communication with the buffer volume 42, in order to prevent the burnt gases from reaching the carburetor during the counter-sweep fresh gas carbides at the buffer volume.

Due to the delay in introducing the fresh charge into the cylinder and the spreading of this introduction during the scanning phase (thanks to the pressure reserve of the buffer volume), the fresh charge arrives late in the light d 'exhaust, thus resulting in a significant reduction in losses of fresh mixture and a very noticeable improvement in consumption and a reduction in pollution by hydrocarbons. In addition, the fuel of this fresh charge, which travels through the delay transfers previously heated by the counter-sweeping of the burnt gases, is vaporized by this supply of heat, and the air-fuel mixture is all the better homogenized, this which results in better combustion, and greater regularity of engine speed, as well as better idling. In addition, as will be illustrated in FIG. 4c, the delay transfer (s) allow, by being associated with conventional transfers ensuring the delivery of fresh air to the cylinder, a stratification of fresh mixture / fresh air / gas burned in the cylinder, which results in generally poor combustion and limits the production of pollutants, while giving the engine a good tolerance for differences in richness and differences in fuel quality. The sweeping can thus be organized so as to form a separating layer between the exhaust lumen and the lumen (s) supplying fresh mixture from which the burnt gases emerge from the counter-sweep, then the fresh mixture, when the in the buffer volume 42 becomes greater than that of the cylinder.

In FIG. 1, the buffer volume 42 is mounted as a bypass on the supply line associated 40 which is equipped with the carburetion device 43. However it is also possible to provide that the carburetion device is mounted in series with the buffer volume on the associated supply pipe, as illustrated in the schematic figures 4a to 4d which will be described below in more detail.

It should also be observed that, when the cylinder is equipped with sweeping transfers making it possible to inject fresh air coming from the pump housing into said cylinder, these sweeping transfers 18 are advantageously arranged laterally, while the or the pipes 40 supplying fresh mixture open into the cylinder at the level of lights which are arranged opposite the exhaust port 17, these transfers 18 opening into the cylinder through a port 19 which has a height less than that of the lumen 41 of the supply line for fresh mixture.

In the schematic Figures 4a to 4d, there is shown a two-stroke engine whose power is arranged according to the invention, for different angular posi¬ tions ^• the crankshaft, in particular so as to illustrate the limited-scan against (Figure 4b) and the stratification in the cylinder (Figure 4c).

We recognize the cylinder 13 and the pump crankcase 14, and we distinguish here the crankshaft 35 and the associated connecting rod 36 which ensures the reciprocating movement of the piston 15. The lateral transfer 18 shown here (we can distinguish only one of the two lateral transfers) ends at the top with an essentially circumferential lumen 19, which is lower in level than that of the exhaust lumen 17 of the associated channel *, and of the intake lumen 41 associated with the supply line. supply 40. We find the passage opening 28 allowing the exit of the fresh air contained in the pump housing 14, this fresh air being admitted by a pipe 22 equipped in a known manner in itself, an intake check valve 25. It will also be noted the presence, on this portion of pipe 22, of a device for lubricating the fresh air 34. The fresh air leaving the pump housing arrives here directly in a carburetor 43, before entering, via a non-return valve 29, into the buffer volume 42 of fresh mixture forming a pressure reserve.

In FIG. 4a, the crankshaft has a position which is close to top dead center, and the piston begins to descend. During and after the combustion of the fresh gases in the cylinder 13, these fresh gases repel the piston 15 while relaxing. In the pump housing 14, the fresh air contained is compressed and part of it is transferred to the buffer volume 42, via the carburetor 43 which makes it possible to load this fresh air with fuel, and then via the check valve. -back 29 which then opens for this purpose. Fresh mixture is then found in the supply pipe 40 going from the carburetor 43 to the light 41 of this pipe which is long and narrow. In FIG. 4b, the situation corresponds to the counter-sweep and to the exhaust. In fact, the piston 15 discovers the transfer and exhaust ports in the cylinder, and, as the pressure is higher than that which prevails in the buffer volume 42, the burnt gases pass thereto through the pipeline transfer 40 in accordance with a counter-scanning process, but this penetration is limited thanks to the length of the pipe, and their mixing with the fresh gases is prevented thanks to the narrowness of this pipe: reference 45 is volume of burnt gas concerned which has entered the pipe 40, up to a zone 46 which is located in front of the volume-buffer of fresh mixture.

In FIG. 4c, the piston 15 has uncovered the lateral sweeping transfers (light 19), and the fresh air coming from these sweep the cylinder 13, and constitutes a separating layer 50 between on the one hand the exhaust, and on the other hand the supply transfer from which the burnt gases emerge from the counter-sweep, then finally the fresh mixture, when the pressure in the buffer volume 42 becomes greater than that of the cylinder. One has thus illustrated such a stratification with a lower layer of fresh air 50 and an upper layer of burnt gases 52, and between these layers a layer 51 of rich mixture whose passage to the exhaust is still blocked by the gases. burns escaping. Thus the fresh air and, a little later, the fresh mixture expels a good part of the burnt gases from the cylinder. A large part of the air passes through the exhaust with the burnt gases, while little fresh mixture reaches it due to the delay in the introduction of fresh mixture and the discharge of the burnt gases, before this fresh mixture can emerge. . Fresh air is transferred from the pump housing 14 to the cylinder 13 through the scanning channels 18. The pressure drop in the pump housing 14 does not, however, affect the pressure of the buffer volume 42 thanks to the check valve. - associated return 29. In FIG. 4d, which corresponds to the admission of fresh air into the casing (with an opening of the intake valve 25), the volume increases in the pump casing, the pressure decreasing in this crankcase, so that the filling with fresh air outside. In the cylinder 13, after the late extension of the supply of fresh mixture (thanks to the arrangement of the supply port 41 at a height close to that of the exhaust port 17), the gases which are stratified are then tablets. We will now describe another variant of the previous arrangement, in which the means for shutting off the communication between the buffer volume of fresh gas and the pump housing is no longer ensured by a valve controlled by the pressure variations. generated by the movement of the piston, but by the skirt of this piston. The engine illustrated in FIG. 5 comprises a large number of members identical to that of FIG. 1, and the same references have been kept for these members, without these being the subject of a new description. The essential difference lies in the fact that the skirt 44 of the piston 15 which slides in the cylinder has a through hole 45, the axial path of which passes at the level of the supply lumen of the associated pipe. In this case, the fresh gas supply line comprises two branches 40.1 and 40.2 which both open into the fresh gas buffer volume 42. There is thus a branch 40.2 which opens into the pump housing 14 at level d a supply light 28, in front of which the aforementioned through-light 45 passes when the piston is at the corresponding height, which corresponds to an instant of communication between the buffer volume 42 and the pump housing 14. The other branch 40.1 opens for its part at a light 41 in the cylinder 13, which light is close to or greater than that of the exhaust light 17. The counter-scanning (illustrated by the double arrow) is effected by this light 41 when the latter is discovered on the descent of the piston 15. In practice, provision may be made for a branch 40.2, which is a rear branch, and two lateral branches 40.1, so that the delay circuit thus produced comprises three c anal. The light 45 formed in the skirt 44 of the piston must be positioned precisely, so that the arrangement of the operating cycle is optimal.

Illustrated in FIG. 6 is a diagram of the (accumulated) masses transferred as a function of the position of the piston, for a supply organized in accordance with the arrangement of FIG. 5. The notations used for this diagram are the same as those used for Figure 3 previously described in connection with the arrangement of Figure 1. We thus find a first delay RI 1 intro duction of fresh gas in the cylinder, and a second delay R2 concerning the offset between the maximum delivery at the delay transfer (point B 'on the MTR curve) compared to conventional type transfers (point B on the MTC curve). The delay R2 is in this case a little lower than with the arrangement of FIG. 1, insofar as the point B 'precedes the moment of closing of the exhaust lights and of delay transfer FE and FTR. These delays can be optimized by a judicious choice of the dimensioning of the supply line with two branches. However, they retain characteristics which remain advantageous compared to those of the power supply produced with a conventional two-stroke engine.

Figure 7 is a distribution diagram corresponding to a supply organized according to the arrangement of Figure 5. The notations used on this diagram are the same as those used for the diagram of Figure 6 above. Again, it was considered that the opening of the delay transfer line and the opening of the exhaust were simultaneous, but it goes without saying that this opening may occur slightly after or before the opening of the light d 'exhaust. It should be noted that the diagram in FIG. 7 also includes the indication of the opening and closing of the lumen between the pump housing and the buffer volume, respectively denoted OVT and FVT. The direction of rotation of the crankshaft, determining the direction of the operating cycle, is identified by the arrow 100.

A variant of the arrangement of FIG. 5 has been illustrated in FIG. 8, which differs therefrom by the arrangement of the delay pipeline. This delay line 40 is in this case single branch, and there is shown the carburetion device 43 which the team. Lights 28 and 41 are then the same. The closable communication is carried out as before by the skirt of the piston which has a through light.

There are of course still other possible embodiments for achieving the closed communication, as a variant of the non-return valve and of the piston skirt with through light: for example, a disc or a controlled rotary distributor can be provided ( variant not shown here) with a control by the rotation of the crankshaft, which allows in particular to have an asymmetrical opening more advantageous than the symmetrical opening obtained with the piston skirt, this disc or this distributor being able to be the one which used to distribute the housing.

The embodiments which have just been described concerned a two-stroke engine with a single cylinder and an exhaust port. It is however naturally possible to apply the supply system according to one invention to an engine whose cylinder is equipped with exhaust valve (s).

More generally, the invention also applies to the case where the engine comprises a plurality of cylinders. In this case, the multiplicity of cylinders can lead to a judicious choice of the associated buffer volume.

Figures 9 and 10 are schematic views thus illustrating two neighboring cylinders of a multi-cylinder engine, with two different arrangements of the associated buffer volume. These tick diagrams have kept the same references as those already used previously.

In FIG. 9, the buffer volume 42 of fresh gas is pooled between several cylinders, in this case two adjacent cylinders, while being supplied by the pump casings 14 of these cylinders. Two delay pipes 40 then leave this buffer volume 42, and emerge at a light 41 in the two cylinders concerned. It should be noted that the view of the figure 9 is very schematic: in particular, this view does not show the valves which are necessarily provided between the casings 14 of the cylinders and the common buffer volume 42 (at the level of the curved links not referenced). In FIG. 10, the buffer volume 42 of a cylinder is constituted by the casing of the neighboring cylinder, and the delayed introduction of fresh gas into these cylinders is organized with a certain phase shift from one cylinder to the other. In this case, the adjacent casing serves as a buffer volume, which simplifies the production with respect to the pre-dent structure shown diagrammatically in FIG. 9.

Such arrangements could thus be used for engines with several adjacent cylinders such as star, barrel, or in-line engines. We have thus managed to organize in a simple manner the supply of a two-stroke engine cylinder, with not only an extension of the path of the mixture of air and fuel in the cylinder, but also with a later introduction during the scanning, which is an important advantage over conventional systems.

The precise dimensioning of the supply line (s) of the delay circuit will in practice be chosen as a function of the engine displacement considered, so as in all cases to limit the penetration of the burnt gases during the back-sweeping and to avoid mixing them with the fresh gases, as explained above. As an indication, with a displacement of 50 cm, it is possible to use a buffer volume of fresh gas of 300 cm, and at least one delay transfer line whose length is of the order of 20 to 30 cm, and of which the diameter and of the order of 0.6 to 0.8 cm. In all cases, the buffer volume enables fresh gas to be supplied at a pressure greater than or equal to that prevailing in the crankcase at the same time. Furthermore, in the case of dome sweeping motors, it is possible to arrange the lights of the delay transfers above those of the sweep transfers, which provides a particularly clear barrier between the fresh gases and the burnt gases of the made of the direct proximity of the scanning and supply flows.

This has resulted in a method and a supply device that greatly reduce direct losses of fresh air-fuel mixture to the exhaust, without having to use any mechanical distribution system with positive control. In addition, the method and the device according to the invention favorite¬ also feels the stratification of burnt gases / fresh air / fresh mixture in the cylinder. The invention is not limited to the embodiments which have just been described, but on the contrary encompasses any variant, incorporating, with slow means, the essential characteristics set out above.

Claims

CLAIMS 1. Method for supplying a two-stroke internal combustion engine cylinder, this cylinder comprising at least one lumen associated with a supply line for fresh gas which is the seat of a counter-sweep by gases burnt during the opening of said light, and an exhaust light for the burnt gases, characterized in that the penetration of burnt gases, during the counter-sweep, into the or each supply line (40) is limited to a portion thereof delimited by the associated lumen (41), and by a buffer volume (42) of fresh gas forming a pressure reserve, which is in permanent communication with said pipe and in closable communication with the pump casing (14) associated with the cylinder, and by the fact that the introduction of fresh gas into the cylinder (13) by this pipe is subsequently delayed, then extended substantially until the exhaust port (17) closes thanks to the aforementioned pressure reserve. 2. Method according to claim 1, in which the supply line (40) is equipped with a carburetion device (43), characterized in that the penetration of the burnt gases is limited to a portion of this line which is delimited by the associated light (41) and by the carburetion device (43), when said device is arranged between said light and the buffer volume (42). 3. Method according to claim 1 or 2, wherein the cylinder is equipped with sweeping transfers (18) making it possible to inject into said cylinder fresh air coming from the pump housing (14), characterized in that the scanning is organized so as to form a separa¬ tric layer (50) between the exhaust port (17) and the port or ports (41) for supplying fresh gas from which the burnt gases emerge from the counter-scanning, then the fresh gases, when the pressure in the buffer volume (42) becomes greater than that of the cylinder. 4. Device for supplying a two-stroke internal combustion engine cylinder, this cylinder comprising at least one lumen (41) associated with a pipe (40) for supplying fresh gas, which is the seat of '' a counter-sweep by the burnt gases during the opening of said lumi-era, and a light (17) for exhausting the burnt gases, characterized in that the or each pipe (40) for supplying gas fresh is in communication with a buffer volume (42) of fresh gas forming a pressure reserve, this buffer volume also being in communication with the pump housing (14) associated with the cylinder, the communication with said pipe being direct and permanent, while the communication with said pump housing is closable by an associated closure means (29, 44), and said fresh gas supply pipe is also sufficiently long and narrow to prevent the penetration of burnt gases into said volume - stamp during against sweeping, and to limit their mixing with the fresh gases being in this pipeline, and by the fact that the or each light (41) for supplying fresh gas is arranged to have an adjacent or longer opening period than that of the exhaust light (17). 5. Device according to claim 4, in which the supply line (40) is equipped with a carburetion device (43), characterized in that the carburetion device (43) is arranged between the buffer volume ( 42) of fresh gas and the cylinder (13), said channeling then being dimensioned so as to avoid the penetration of the burnt gases into said carburetion device during the back-sweep. 6. Device according to claim 4 or 5, characterized in that a carburetion device (43) is mounted in series with the buffer volume (42) on the canali- associated power station (40). 7. Device according to claim 4 or 5, characterized in that the buffer volume (42) is mounted in bypass on the associated supply pipe (40) which is equipped with the carburetion device (43). 8. Device according to one of claims 4 to 7, characterized in that the associated closure means is a non-return valve (29) controlled by the pressure variations generated by the movement of the piston (15) which slides in the cylinder. 9. Device according to one of claims 4 to 7, characterized in that the associated sealing means is a disc or a controlled rotary distributor, allowing to have an asymmetrical opening. 10. Device according to one of claims 4 to 7, characterized in that the associated closure means is constituted by the skirt (44) of the piston (15) which slides in the cylinder, said skirt having a through-hole "5) whose axial path passes at the level lumiè-β of slowdown (28) of the pipe (40; 40.2) associated with said through light. 11. Device according to claim 10, characterized in that the fresh gas supply line is constituted by a single branch (40). 12. Device according to claim 10, characterized in that the fresh gas supply line comprises several branches (40.1, 40.2), at least one branch (40.2) comprising a light (28) which cooperates with the through light (45) of the skirt of the piston, and at least one other branch (40.1) which opens into the cylinder at a height close to or greater than that of the exhaust port (17). 13. Device according to one of claims 4 to 12, characterized in that the lengthening of the opening period of the or each light (41) for supplying fresh gas is obtained by placing said supply port (s) at a height close to or greater than that of the exhaust port (17), or by notching, at said supply port (s), the piston ( 15) which slides in the cylinder. 14. Device according to one of claims 4 to 13, in which the cylinder is equipped with sweeping transfers (18) making it possible to inject into said cylinder fresh air coming from the pump housing (14), characterized by the the fact that the sweep transfers (18) are arranged laterally, while the pipe or pipes (40) for supplying fresh mixture open into the cylinder at the level of lights which are arranged opposite to the light exhaust (17), and these transfers (18) open into the cylinder by a light (19) which has a height less than that of the light of said one or more pipes. 15. Device according to one of claims 4 to 14, characterized in that the buffer volume (42) of fresh gas has a large capacity, in particular of the order of two to ten times the displacement. 16. Device according to one of claims 4 to 15, in which the engine comprises a plurality of cylinders, characterized in that the buffer volume (42) of fresh gas is shared between several cylinders, being supplied by the crankcases of these cylinders. 17. Device according to one of claims 4 to 15, wherein the engine comprises a plurality of cylinders, characterized in that the buffer volume (42) of a cylinder is constituted by the housing of the neighboring cylinder, the delayed introduction of fresh gas into these cylinders being further organized with a certain phase shift from one cylinder to another.