EP0406079A2 - Two-stroke engine with pneumatic injection and flow throttle in at least one transfer passage - Google Patents

Abstract

The engine comprises a cylinder (1), a housing (3) connecting with one of the ends of the cylinder (1), at least one transfer pipe (10) joining the housing (3) to the cylinder (1), a fuel injector (15) fed with air under pressure by a capacitor (18) connected to the housing (3) and an exhaust pipe (8). A means (22) of restricting the passage of the gases is arranged in the transfer pipe. The opening and closing of this means is controlled and regulated as a function of at least one operating parameter of the engine. This arrangement allows the quality of fuel injection to be improved. <IMAGE>

Description

The invention relates to a two-stroke engine with pneumatic fuel injection and flow restriction in at least one transfer duct.

Two-stroke engines with one or more cylinders generally comprise, associated with each of the cylinders, a casing called a pump casing communicating with one of the ends of the cylinder and ensuring the introduction of fresh gas into the cylinder, via '' at least one conduit and one transfer opening. The piston which moves alternately in the cylinder also ensures the suction and compression of the fresh gases in the pump housing. An intake valve disposed on the pump housing allows the introduction of fresh gases into the housing, when the piston moves in the direction opposite to the housing, these fresh gases being then compressed and ensuring the closure of the valve, when the piston moves towards the housing. When the corresponding cylinder openings are cleared by the piston, fresh gases are introduced into the cylinder through the transfer conduits and openings and produce a sweeping of fresh gases intended to replace the burnt gases which are evacuated by exhaust openings generally arranged slightly offset from the transfer openings. The piston moves away from the housing, so as to compress the gases contained in the cylinder. Ignition and combustion of the mixture then produces the engine displacement of the piston towards the crankcase.

It has been proposed, in French patent 2,496,757 of the French Petroleum Institute, to ensure a pneumatic injection of fuel into the cylinder by using the pressure of the fresh gases inside the pump housing. For this, a liquid fuel metering means is connected directly to the pipe coming from the pump casing. The compressed air in the pump casing sent to the metering device via the conduit ensures the atomization and injection of the fuel inside the cylinder.

Some improvements have been made to this device; it has been proposed for example to place a capacity on the duct connecting the pump casing to the injector and a valve at the end of the duct connected to the pump casing. A reserve of compressed air is thus formed at a pressure close to the maximum pressure in the pump casing during the cycle, this reserve of compressed air then serving to spray the fuel and to introduce it into the cylinder in the form of carburetted air, when the injector is triggered.

One of the drawbacks of two-stroke engines is the loss of efficiency due to the fact that the fresh carburetted gases are not sufficiently separated from the gases burnt inside the cylinder and are consequently responsible for the creation of unfavorable conditions for the initiation of combustion.

To remedy this drawback, it has been proposed to place a flow restriction member on the engine transfer conduits, in the vicinity of the cylinder, to slow the emptying of the burnt gases. A stratification of the fresh gases and the burnt gases is thus obtained, the fresh gases being pushed back into the region of the cylinder where the injection and ignition take place. However, such a technique of restricting the air flow coming from the casing has never been used, in the case of a two-stroke engine comprising a pneumatic injection device using the compressed air from the pump casing.

On the other hand, in the case of a pneumatic injection using the compressed air from the pump housing, the pressure difference between the air used for injection and the gases filling the cylinder at the time of injection may generally be too low to ensure good spraying of fuel and very high efficiency of injection. This defect remains significant in the case where a capacity connected to the injector and a conduit separated by a valve of the pump casing are used. Indeed, the pressure in the capacity which is at most equal to the maximum pressure in the pump casing is sometimes insufficiently higher than the pressure in the cylinder at the time of injection when the cylinder pressure undergoes an increase due to effects of waves in the exhaust pipe.

The object of the invention is therefore to propose a two-stroke engine comprising at least one cylinder in which a piston moves, a casing communicating with one of the ends of the cylinder and comprising a means for admitting air into the casing, at least one non-carburetted air intake duct into the cylinder joining the casing to a cylinder transfer opening, a pneumatic fuel injection device in the cylinder constituted by a pneumatic injector, a supply means and metering of this pneumatic fuel injector and a supply line of the injector with pressurized air for spraying the fuel, connected to the casing by means of a valve and constituting a connected pressurized air capacity to the pneumatic injector, as well as an exhaust duct situated in a position offset in the direction of the stroke of the piston relative to the transfer opening of the cylinder, this two-speed engine s with increased efficiency and improved operation, thanks to improved spraying and injection of fuel into the cylinder.

For this purpose, the engine according to the invention further comprises, inside the transfer duct or conduits in the vicinity of the cylinder, one or more organs for restricting the passage of fresh gases admitted into the cylinder controlled and adjusted for its opening. and its closure, as a function of at least one operating parameter of the engine.

Thus, a member for restricting the passage of the transfer conduit controlled and adjusted for its opening and its use is used. closing as a function of at least one operating parameter of the engine, in order to increase the pressure of the air compressed by the piston in the crankcase, when the pneumatic injection of fuel is carried out in the internal combustion chamber.

We know two-stroke engines of the cross-scanning type (in English cross-scavenging) in which all of the transfer openings through which fresh air is admitted into the combustion chamber of the cylinder, is grouped on one side of the cylinder, all the exhaust openings being grouped on the other side of the cylinder, these openings being arranged on either side of an axial plane of symmetry of the cylinder, in substantially symmetrical positions.

The flushing gas consisting of compressed air from the pump housing is introduced into the combustion chamber of the cylinder through the transfer openings and scans the combustion chamber containing the burnt gases, in a unidirectional direction transverse.

The purging gases can also be deflected by the upper part of the piston constituted in the form of a deflecting piston, to carry out the purging of the upper part of the combustion chamber before emerging through the exhaust openings.

One of the advantages of engines of the transverse scanning type is their low cost as regards the machining of the cylinder block, the transfer lights and the exhaust lights being able to be machined from the outside of the cylinder block.

Another advantage of this type of engine, in the case of engines with several cylinders, is to allow a reduction in the length of the cylinder block, the different cylinders arranged in line being able to be juxtaposed with a very small spacing, insofar as the transfer conduits are not arranged between the successive cylinders. The spacing between the cylinders can therefore be maintained at a value close to the bore of the cylinders.

However, we have never proposed so far, in the case of two-stroke multi-cylinder engines of the cross-sweeping and pneumatic injection type, to use members restricting the passage of the transfer conduits. In addition, it has not been proposed to have restricting members so as to facilitate the construction of the engine and to improve its operating conditions.

The object of one of the variants of the invention is therefore to propose a two-stroke engine comprising at least two cylinders of the transverse scanning type arranged in line, this engine comprising members for restricting the passage of the transfer conduits arranged so to facilitate the construction of the engine and to simplify and improve its operation

For this purpose, the ends of the transfer conduits connected to the chambers of the corresponding cylinders are substantially aligned in a direction parallel to the axis of the line of cylinders and the members restricting the passage of the transfer conduits are aligned along the same axis d actuation arranged in the direction parallel to the axis of the line of cylinders.

• La figure 1 représente les diagrammmes de pression relevés pendant le fonctionnement d'un moteur à deux temps à injection pneumatique suivant l'art antérieur.
• La figure 2 représente les diagrammes de pression relevés pendant le fonctionnement correspondant d'un moteur à injection pneumatique et à restriction de débit admis par le ou les conduits de transfert.
• La figure 3 est une vue schématique en élévation et en coupe d'un moteur à deux temps suivant l'invention.
• La figure 4 est une vue en coupe par un plan vertical de symétrie d'un cylindre d'un moteur à deux temps à balayage transversal.
• La figure 5 est une vue en coupe transversale suivant 5-5 de la figure 4
• La figure 6 est une vue en coupe transversale, suivant 6-6 de la figure 7, d'un moteur à plusieurs cylindres suivant l'invention et suivant un premier mode de réalisation.
• La figure 7 est une vue en coupe suivant 7-7 de la figure 6.
• La figure 8 est une vue en coupe transversale d'un cylindre d'un moteur suivant une variante du premier mode de réalisation représenté sur la figure 6.
• La figure 9 est une vue en coupe transversale, suivant 9-9 de la figure 10, d'un moteur suivant l'invention et suivant un second mode de réalisation.
• La figure 10 est une vue en coupe suivant 10-10 de la figure 9.
• La figure 11 est une vue en coupe transversale d'un cylindre d'un moteur suivant une variante du second mode de réalisation représenté sur la figure 9.
• Les figures 12A et 12B sont des vues en perspective de deux variantes de réalisation d'un boisseau rotatif utilisé dans un moteur suivant l'invention et suivant le second mode de réalisation.

In order to clearly understand the invention, a description will now be given, by way of nonlimiting example, with reference to the attached figures, of a two-stroke engine with exhaust flow restriction according to the invention and its operating mode compared to the operating mode of a two-stroke engine according to the prior art.

• FIG. 1 represents the pressure diagrams recorded during the operation of a two-stroke engine with pneumatic injection according to the prior art.
• FIG. 2 represents the pressure diagrams recorded during the corresponding operation of an engine with pneumatic injection and with restriction of flow admitted by the transfer duct or ducts.
• Figure 3 is a schematic elevational view in section of a two-stroke engine according to the invention.
• Figure 4 is a sectional view through a vertical plane of symmetry of a cylinder of a two-stroke scanning engine transverse.
• Figure 5 is a cross-sectional view along 5-5 of Figure 4
• Figure 6 is a cross-sectional view, along 6-6 of Figure 7, of a multi-cylinder engine according to the invention and according to a first embodiment.
• FIG. 7 is a sectional view along 7-7 of FIG. 6.
• FIG. 8 is a cross-sectional view of a cylinder of an engine according to a variant of the first embodiment shown in FIG. 6.
• Figure 9 is a cross-sectional view, along 9-9 of Figure 10, of an engine according to the invention and according to a second embodiment.
• FIG. 10 is a sectional view along 10-10 of FIG. 9.
• FIG. 11 is a cross-sectional view of a cylinder of an engine according to a variant of the second embodiment shown in FIG. 9.
• Figures 12A and 12B are perspective views of two alternative embodiments of a rotary plug used in an engine according to the invention and according to the second embodiment.

FIG. 1 and FIG. 2 show the variations in the pressure in the cylinder (curve P1), in the capacity of the pneumatic injection device (curve P2) and in the transfer duct (curve P3), as a function of the angle of rotation of the crankshaft, in the case of an engine according to the prior art with pneumatic injection and in the case of an engine according to the invention, respectively

In Figure 3, there is shown schematically an engine according to the invention with pneumatic injection and flow restriction in the transfer duct (s).

An engine according to the prior art, the operating diagram of which is shown in FIG. 1, can be described at from the same elements, with the exception of the regulated set of flow restrictions admitted by transfers.

The engine comprises a cylinder 1 closed at its upper part by a cylinder head 2 and communicating at its lower part with a pump casing 3, the chamber of the cylinder 1 and the internal capacity of the pump casing 3 being arranged on either side of the piston. 4 alternately moving inside the cylinder 1. The piston 4 is connected by a connecting rod 5 to the crankshaft 6. The wall of the cylinder 1 is pierced by exhaust openings or openings 7 communicating with an exhaust duct 8.

Lights or transfer openings 9 placed in a position slightly offset downward relative to the lights 7 communicate with a transfer duct 10 connected to the interior volume of the pump housing 3.

The pump casing 3 is pierced with an orifice 11 fitted with a valve 11a and communicating with an air intake pipe 12 in which is placed a butterfly 13 capable of more or less closing the passage section of the pipe 12.

A pneumatic injector 15 fixed on the cylinder head 2 opens into the upper part of the cylinder 1. The pneumatic injector 15 which may be of the type described and shown in FIG. 7 of French patent 2,496,757 is supplied with liquid fuel via a line 16 and in compressed air by a duct 17 on which is placed a compressed air storage capacity 18. The compressed air capacity 18 is itself connected by a duct 17 ′ extending the duct 17 to the pump housing 3. The orifice placing the casing 3 and the duct 17 ′ in communication carries a valve 20 which is distant from its seat to ensure communication between the casing 3 and the duct 17 ′, when the pressure is greater than a certain limit in the casing 3. When the valve 20 is lifted from its seat, the compressed air from the casing 3 can fill the capacity 18 which it recharges.

The pneumatic injector 15 may comprise a rod controlled by a cam ensuring the start of the injection at a determined time in the engine operating cycle. The pressurized air the capacity 18 then ensures the spraying of the fuel brought to the pneumatic injector via the line 16 which may include a fuel metering means and the introduction of the sprayed fuel suspended in air under pressure, inside the cylinder 1.

A spark plug 21 is fixed on the cylinder head 2.

A flow restriction member 22 constituted for example by a butterfly is disposed inside the transfer duct near the cylinder 1. The member 22 can be connected to the butterfly 13 of the air intake pipe 12 in the pump casing 3 by a link and articulated control assembly 24 ensuring the opening and closing of the member 22 depending on the opening and closing of the butterfly valve 13.

The flow restriction member 22 and its connecting means 24 to the throttle 13 ensuring a proportional action to these two flow restriction members constitutes the essential characteristic element of the device making it possible to substantially improve the performance of the pneumatic injection, as will be explained later with reference to FIGS. 1 and 2.

A two-stroke pneumatic injection engine as shown in Figure 3 operates as will be explained below.

If it is assumed that at the initial instant the piston 4 is at its top dead center of the fuel mixture being compressed in the upper part of the cylinder 1, the ignition of this mixture by the spark plug 21 produces a combustion which repels the piston 4 down. During its downward movement, the cylinder 4 discovers the exhaust openings 7, then slightly delayed in time, the transfer openings 9. The exhaust gases are expelled in the conduits 8 and the air compressed by the piston in the pump casing 3 is sent into the cylinder by the transfer conduits 10.

The air pressure in the pump housing 3 increases to the maximum, the valve 11a being closed. When the air pressure in the pump housing 3 exceeds that of the capacity, the valve 20 opens and the capacity 18 is recharged with air at a pressure close to the maximum pressure in the pump housing 3.

The valve 20 closes again and the piston 4 reaches its bottom dead center then begins to move up again. The fuel injection is carried out at the top of the cylinder by the injector 15, under the effect of the compressed air from the chamber 18. In its upward movement, the piston 4 masks the openings 9 and 7 and ensures compression of the fuel mixture. The valve 11a opens and air is admitted into the pump housing 3.

Figures 1 and 2 show the variation of pressures in the cylinder, in the capacity of the pneumatic injection device and in the transfer duct as a function of the angle of the crankshaft for a complete cycle, in the case of a two-stroke engine with pneumatic injection according to the prior art and in the case of a two-stroke engine according to the invention, respectively.

In FIGS. 1 and 2, the position of the bottom dead center and the top dead center (PMB and TDC respectively) has been plotted on the abscissa. The positions corresponding to the opening and closing of the transfer lights 9 and the positions corresponding to the opening and closing of the exhaust lights 7 have also been indicated.

In the case of an engine according to the prior art (FIG. 1), the pressure P1 in the cylinder rapidly decreases when the piston moves towards its bottom dead center, this displacement being accompanied by the opening of the exhaust ( OE) and transfer (OT). There is simultaneously an exit of the exhaust gases in the duct 8 and a sweeping of the cylinder by the compressed air in the pump housing 3.

The pressure P2 in the capacity is established at the start of the scanning at a maximum value corresponding substantially to the maximum value of the pressure in the pump casing 3 which also corresponds to the maximum pressure given by the curve P3.

The injection (I) is triggered at the end of the sweep, this period being favorable because of the relatively low pressure in the cylinder and the lower risk of entrainment of the fuel by the exhaust with the burnt gases.

The injection is ensured by the pressurized air P2 filling the capacity 18. The quality of the fuel atomization and of the injection, at the time of the opening of the injector rod 15 depends on the pressure difference between capacity 18 and the cylinder.

In the diagram in FIG. 1, this variable pressure difference during the injection corresponds to the vertical distance between the curves P2 and P1. The extent of the hatched area between these curves during injection I gives an image of the energy usable for injection. The pressure difference ΔP = P2 - P1 decreases during the injection and vanishes in the vicinity of the closing of the FE exhaust. In fact, the pressure P1 first increases slowly and then rapidly at the end of the scanning, while the pressure P2 decreases during injection, the capacity 18 emptying part of its compressed air.

In Figure 2, there is shown the operating diagram of a two-stroke engine according to the invention comprising a restriction member 22 in the transfer conduits.

The pressure P3 in the transfer duct upstream of the restriction member 22 undergoes a greater increase during the compression of the crankcase because of the difficulty that the crankcase has in emptying into the cylinder.

The air contained in the casing which undergoes compression during the downward movement of the piston 1 therefore reaches a maximum pressure, during the initial scanning phase, higher than in the case where there is no flow restriction in the duct. transfer. The capacity 18 is charged with compressed air at a pressure close to the maximum pressure of the curve P2 Fig. 2 and is at a higher level than in the case of an engine according to the prior art.

It follows that the pressure difference ΔP = P2 - P1 is greater during the entire injection phase I, in the case of an engine according to the invention (FIG. 2) than in the case of an engine according to l prior art (Figure 1). This favorable effect is obtained thanks to a higher pressure P2, at least at the start injection.

In the case of the engine according to the prior art on the same operating point, the pressure in the cylinder has a minimum value during injection of the order of 1.05 bar.

The loading pressure P2 of the capacity at the start of injection is 1.18 bar in the case of the engine according to the prior art (FIG. 1) and 1.25 bar in the case of the engine according to the invention.

It follows that in the case of the engine according to the prior art ΔP = 1.18 - 1.05 = 0.13 bar and in the case of an engine according to the invention ΔP = 1.25 - 1.05 = 0.20 bar, at the start of injection.

There is therefore obtained a very significant gain in the pressure difference, which results in a significant increase in the amount of air reaching the injector and used to spray the fuel and likewise, a significant increase in speed. of this air performing the spraying and injection.

The fuel is therefore sprayed more finely and introduced under better conditions inside the cylinder.

The adjustment of the opening or closing position of the restriction member 22 as a function of the corresponding position of the intake throttle 13 must make it possible to obtain a maximum pressure difference P during the entire injection phase, leading to an injection energy represented by the shaded area in FIG. 2, as large as possible.

In the embodiment shown in FIG. 3, the position of the throttle valve 13 varies with the load of the engine so that the connection assembly 24 makes it possible to adjust the position of the restriction member 22 also according to the load of the engine.

Generally, the transfer flow restriction member may be constituted by any butterfly, flap or plug arranged inside the exhaust duct or in the vicinity of the exhaust ports passing through the wall of the cylinder.

It is also possible to use an element with lights rotating around the axis of the cylinder.

These shutter members may be mechanically connected by any means such as rods hinged to the butterflies or bushels for admitting air into the casing, the position of which depends on the load of the engine.

It is also possible to use motorized shutter members, the opening and closing control of which is ensured by electronic means taking into account, as input data, parameters reflecting the engine speed and load. These parameters can be of various kinds and the corresponding data obtained by means of sensors can relate for example to the degree of opening of the throttle valve or bushel of the intake pipe or even to the value of the vacuum at the intake.

Other parameters of the engine reflecting its speed and its load can also be taken into account and among these the air temperature at the intake, the temperature of the engine cooling water or various pressures in the engine whose value will be compared to atmospheric pressure.

It is obvious that the engine according to the invention may include any type of transfer flow restriction member controlled upon opening and closing by any means of mechanical, electronic or other type.

Finally, the engine according to the invention may include any number of cylinders placed according to any arrangement.

The pneumatic injector 15 may include a mechanically, electronically, electromechanically controlled valve, an automatic valve, a rotating plug or any other equivalent means.

FIGS. 4 and 5 show a cylinder 30 of a two-stroke engine with transverse scanning of the conventional type.

The cylinder 30 comprises a cylinder block 31 closed at its upper part by a cylinder head 32 and machined to constitute a bore in which a piston 33 moves. The combustion chamber 34 of the cylinder is delimited by the upper surface of the piston 33 and by the internal surface of the cylinder head 32.

The cylinder 30 comprises, in the extension of its bore in which the piston 33 moves, a pump housing 35 which is crossed by the crankshaft 36 of the engine secured to a flywheel 38.

The piston 33 is connected to the crankshaft 36 by means of a connecting rod 37.

Transfer wall 39 passes through the wall of the cylinder through a transfer duct 40 to the pump housing 35.

Exhaust openings 41 also pass through the wall of the cylinder 30, in positions slightly offset from the transfer openings, in the axial direction of the cylinder 30.

During its movements in the bore of the cylinder, the piston 33 is caused to mask or to uncover the openings 39 and 41.

The wall of the cylinder 30 is also crossed by an opening 42 at the level of which is fixed an air intake duct in the pump housing 35, provided with a valve not shown.

When the piston 33 moves towards its top dead center, a certain vacuum is produced in the pump housing 35 and atmospheric air is admitted through the opening 42, after opening the valve.

When the piston 33 moves towards its bottom dead center, it achieves a certain compression of the air contained in the pump casing, at the outlet of which a part of this compressed air is forced back into the transfer duct 40 and introduced in the combustion chamber 34 through the openings 39 (arrows 44).

In the case of a cylinder of a two-stroke engine with transverse scanning, as shown in FIGS. 4 and 5, the transfer openings 39 are all arranged on the same side of an axial plane of symmetry of the cylinder and the exhaust openings 41 are placed opposite, on the other side of the axial plane of symmetry of the cylinder 30;

In addition, the piston 33 has, at its upper part, an extension of profiled shape 45 machined along curved and inclined surfaces, so as to constitute a deflector of the air flow admitted into the chamber 34 through the transfer openings 39.

The sweeping air from the chamber 34 is directed upwards (arrow 46), so as to sweep the upper part of the combustion chamber 34.

The burnt gases contained in the combustion chamber are evacuated through the exhaust openings 41 arranged opposite the transfer openings 39 (arrows 47).

This arrangement of the transfer openings and the exhaust openings as well as the use of a deflector 45 therefore make it possible to carry out an effective transverse sweep of the combustion chamber and in particular of its upper part.

In the case of a pneumatic injection engine, when the combustion chamber has been swept and filled with fresh air, atomized fuel is introduced into a stream of compressed air by an injector arranged at the top of the cylinder. The compressed air used generally comes from the pump housing 35 or from a capacity supplied with compressed air from the pump housing.

The spraying of the fuel and the injection of the fuel mixture into the combustion chamber are carried out under conditions which are all the more satisfactory the higher the pressure of the compressed air available in the pump housing at the time of the pneumatic injection. .

In order to increase this injection pressure, a member for restricting the passage of compressed air in the transfer duct 40 is used to reduce the passage of air prior to pneumatic injection and thus increase the pressure of the air available for pneumatic injection into the pump housing.

In the case of a two-stroke engine with several cylinders and with transverse scanning, as shown in FIG. 6, the successive cylinders 50a, 50b, 50c can be arranged in line and juxtaposed with a reduced center distance, insofar as the transfer conduits of the successive cylinders which are all placed in one same side of a vertical plane passing through the axis 51 of the line of cylinders lie entirely outside the zones situated between the successive cylinders 50a, 50b and 50c. A multi-cylinder engine is thus obtained with a perfectly compact structure.

Such an arrangement of the successive cylinders of multi-cylinder engines makes it possible to obtain a center-to-center ratio between the cylinders / cylinder bore less than 1.15.

Furthermore, according to the invention, the ends of the transfer conduits 52a, 52b and 52c communicating with the combustion chambers 54a, 54b, 54c of the cylinders, via the corresponding transfer openings 55, can be aligned in a direction. 56 parallel to the axis of the line of cylinders 51 and placed in a lateral position with respect to the line of cylinders.

Restrictors 57a, 57b, 57c of the passage of the transfer conduits can be arranged in each of the end portions 52a, 52b, 52c of these transfer conduits and aligned in the direction 56 parallel to the axis of the line of cylinders 51.

In a first embodiment, as shown in FIG. 6, each of the restriction members 57a, 57b, 57c consists of a shaft end aligned in the direction 56, mounted to rotate around its geometric axis in the cylinder block and carrying a throttle valve 58 for restricting the passage of compressed air, at the end 52a, 52b or 52c of the corresponding transfer duct.

Preferably, the ends of the shaft 57a, 57b, 57c each carrying a butterfly valve 58 for restricting the passage of compressed air are integral with a single actuation shaft or constituted by successive parts of this single shaft arranged according to the direction 56.

The single actuation shaft can be placed in an angular position determined as a function of an engine operating parameter; for example, the actuation shaft carrying out the adjustment of all the butterflies 58 can be connected to a member for adjusting the air intake in the pump casings of the cylinders.

As can be seen in FIG. 7, when the air admitted into the pump housing is compressed by the piston 53a in order to sweep the chamber 54a of the cylinder 50a, the butterfly valve 58 of the means for restricting the passage of compressed air 57a being in the partially closed position during sweeping, the restriction of the compressed air flow in the transfer duct makes it possible to increase the pressure of the compressed air in the pump housing and available to carry out pneumatic fuel injection into the combustion chamber 54a after filling with fresh air.

The same advantages are obtained during the corresponding operating phases of the cylinders 52b and 52c.

FIG. 8 shows a variant embodiment of a cylinder 50 ′ of a two-stroke engine with transverse scanning comprising means for restricting the passage of compressed air in the cylinder chamber, by its transfer openings 55 ′.

In its end part communicating with the transfer openings 55 ′, the transfer duct 52 ′ is separated into several parts by partitions 59, each of the parts of the duct 52 ′ being placed opposite an opening transfer 55 ′.

In this case, the restriction means 57 ′ of the passage of compressed air in the end part of the duct 52 ′ consists of a shaft end rotatably mounted in the cylinder block and in the partitions 59 and carrying a butterfly 58 ′ on each of its successive sections situated in a part of the end of the duct 52 ′, opposite a transfer opening 55 ′.

The operation of a multi-cylinder engine comprising several cylinders such as the cylinder 50 ′ arranged in line is identical to the operation of the multi-cylinder engine as shown in FIGS. 6 and 7.

In Figure 9, there is shown a second embodiment of a multi-cylinder engine with transverse scanning according to the invention, comprising means for restricting the passage of compressed air in the end parts of the transfer conduits of each of its cylinders.

The engine comprises successive cylinders 60a, 60b, 60c aligned along a line of cylinders with axis 61, so that the end portions 62 of the transfer conduits of each of the cylinders are aligned in a direction 66 parallel to the axis 61 of the line of cylinders and placed in a lateral arrangement with respect to this line of cylinders.

The means for restricting the passage of compressed air in the direction of the transfer openings 65 of each of the cylinders are constituted by cylindrical plugs 67a, 67b, 67c mounted to rotate around the axis 66 each inside a end part of the transfer duct 62 of the corresponding cylinder.

Preferably, the plugs 67a, 67b and 67c consist of the three successive parts of a cylindrical rod 69 in each of which is provided an opening or lumen 70 over a length corresponding substantially to the length of the end part 62 of the transfer duct.

In FIGS. 12A and 12B, two alternative embodiments of the opening 70 through the rod 69 have been shown.

In the case of FIG. 12A, the opening 70 is a passage opening of diametral direction passing through the cylindrical rod 69 at its central part.

In the case of FIG. 12B, the opening 70 ′ is a lumen obtained by milling a lateral part of the rod 694.

The cylindrical rod 69, as can be seen in FIG. 9, is rotatably mounted in the cylinder block of the engine and arranged, in the direction 66, so as to pass, along their entire length, the ends of the transfer conduits 62 of each of the cylinders 60a, 60b and 60c. The successive parts 67a, 67b, 67c of the rod 69 constituting the rotary plugs crossed by the openings 70 are each arranged in the end part of a transfer duct 62.

The adjustment in position of the rod 69 around its axis 66, as a function of an engine operating parameter, makes it possible to simultaneously place the rotary plugs each associated with a cylinder of the engine in the desired position.

As can be seen in FIG. 10, during its rotation, the plug 67a can ensure complete opening of the transfer duct 62 or, on the contrary, a more or less complete closure of this duct, resulting in a restriction or elimination of the compressed air flow towards transfer openings 65.

Restricting the passage of compressed air in the direction of the transfer openings 65 makes it possible to improve the pneumatic injection of fuel into the combustion chamber 64a.

In Figure 11, there is shown an alternative embodiment of a cylinder 60 ′ of an engine according to the invention with transverse scanning and flow restriction by means constituted by a rotary plug.

In this alternative embodiment, the end 62 ′ of the transfer duct is separated into several successive parts separated by partitions 73, each of the parts of the duct 62 ′ communicating with a transfer opening 65 ′ of the cylinder 60 ′.

In this case, the rotary plug 67 ′ for reducing the passage of the end of the transfer duct 62 ′ of the cylinder 60 ′ is constituted by a section of rod 69 ′ rotatably mounted in the cylinder block 60 ′ and in the partitions 73 , comprising an opening 71, at each of the parts of the end of the transfer duct 62 ′ situated opposite a transfer opening 65 ′.

The operation of a multi-cylinder engine comprising juxtaposed cylinders such as the cylinder 60 ′ is identical to the operation of the multi-cylinder engine shown in FIGS. 9 and 10.

In all cases, the multi-cylinder two-stroke engine according to the invention makes it possible to improve the pneumatic injection into each of the cylinders, by restricting the passage of compressed air at the end of the transfer duct communicating with the transfer openings opening into the combustion chamber.

This result is obtained in a simple manner, for all of the engine cylinders arranged in line, using means for restricting the passage of compressed air aligned in a direction parallel to the axis of the line of cylinders and arranged laterally. with respect to this line of cylinders.

These flow restriction means can be assembled or added or machined on a single actuation shaft rotatably mounted in the cylinder block of the engine.

The machining of the engine cylinder block is facilitated, insofar as the end portions of the transfer conduits of the various cylinders are aligned in a direction parallel to the axis of the line of cylinders.

In addition, the adjustment of the means for restricting the air passage of the transfer conduits can be carried out in a simple manner, insofar as this adjustment can be ensured by the timing of a single actuation shaft.

Finally, the multi-cylinder engine according to the invention has a compact structure, the different cylinders being juxtaposed to form a line of cylinders, with a center distance of a length little greater than the bore of the cylinders.

The invention is not limited to the embodiments which have been described.

Thus, one can imagine other modes of realization of the means for restricting the passage of compressed air at the outlet of the transfer conduits, depending on the shape of the end part of these conduits communicating with the openings. transfer.

One can also imagine devices for adjusting these means as a function of an engine operating parameter, of any type.

In the case where the flow restriction means are constituted in the form of distributors with drawers movable in translation, the drive shaft is moved in translation by means which can be mechanical, hydraulic or pneumatic.

Finally, the invention applies to any two-stroke multi-cylinder engine with transverse scanning and pneumatic injection.

Claims (13)

1. - Two-stroke engine comprising at least one cylinder (1) in which a piston (4) moves, a casing (3) communicating with one of the ends of the cylinder (1) and comprising an inlet means d in the casing (3), at least one non-carburetted air intake duct (10) in the cylinder (1) joining the casing (3) to a transfer opening (9) of the cylinder, a device for pneumatic injection of fuel into the cylinder consisting of a pneumatic injector (15), a means of supply and metering (16) of this pneumatic fuel injector and a conduit (17) for supplying the injector (15) in pressurized air for spraying fuel, connected to the casing (3) by means of a valve (20) and constituting a capacity (18) of pressurized air connected to the pneumatic injector (15), thus that an exhaust duct (8) connected to the cylinder (1), by an exhaust opening located in a position offset in the direction of the stroke of the piston (4) relative to the transfer opening (9) of the cylinder (1), a member (22) for restricting the passage of the transfer duct (4) controlled and adjusted for its opening and closing, based on at least one engine operating parameter. 2 - Two-stroke engine according to claim 1, characterized in that the restriction member (22) is a butterfly disposed inside the transfer duct (4), near the cylinder (1). 3. - two-stroke engine according to any one of claims 1 and 2, characterized in that the restriction member (22) is connected by an articulated mechanical assembly (24) to an element (13) of restriction flow arranged in an air intake duct (12) in the casing (3). 4. - Two-stroke engine according to any one of claims 1 to 2, characterized in that the restriction member (22) is motorized and controlled for its opening or its closing by an electronic device taking into account at least one parameter translating the speed or the load of the engine. 5. - two-stroke engine according to claim 1, comprising at least two cylinders (50a, 50b, 50c, 50 ′, 60a, 60b, 60c, 60 ′) of the transverse scanning type arranged in line, characterized in that the ends (52a, 52b, 52c, 52 ′, 62, 62 ′) of the transfer conduits connected to the chambers of the corresponding cylinders (50a, 50b, 50c, 50 ′, 60a, 60b, 60c, 60 ′) are substantially aligned along a direction (56, 66) parallel to the axis of the line of cylinders (51, 61) and that the members (57a, 57b, 57c, 57 ′, 67a, 67b, 67c) restrict the passage of the transfer conduits are aligned along the same actuation axis (56, 66) disposed in the direction parallel to the axis of the line of cylinders (51, 61). 6. - Motor according to claim 5, characterized in that the members (57a, 57b, 57c, 57 ′, 67a, 67b, 67c, 67 ′) restricting the passage of the transfer conduits (52a, 52b, 52c, 52 ′, 62, 62 ′) are integral with a single actuation shaft rotatably mounted about an axis (56, 66) parallel to the axis of the line of cylinders (51, 61), in the block engine cylinders. 7. - Motor according to claim 6, characterized in that the flow restriction means (57a, 57b, 57c) are constituted by ends of the shaft aligned on which are fixed butterflies (58) for adjusting the passage d compressed air in the end parts of the transfer conduits (52a, 52b, 52c, 52 ′). 8. - Motor according to claim 7, characterized in that a single butterfly (58) is fixed on each of the shaft ends disposed in an end part (52a, 52b, 52c) of a transfer duct of a cylinder (50a, 50b, 50c) of the engine. 9. - Motor according to claim 7, in the case where the end part (52 ′) of each of the transfer conduits of a cylinder (50 ′) is separated into several parts by partitions (59), each part the end of the transfer duct (52 ′) being located opposite a transfer opening (55 ′) of the cylinder, characterized in that each of the shaft ends carries a plurality of butterflies (58 ′) each disposed in a part of the end (52 ′) of the transfer duct of a cylinder (50 ′), disposed opposite a transfer opening (55 ′) . 10. - Motor according to any one of claims 5 and 6, characterized in that the means (67a, 67b, 67c) for restricting the passage of the transfer conduits (62) are produced in the form of rotary plugs and made up by a cylindrical rod (69) rotatably mounted in the cylinder block of the engine, about an axis (66) parallel to the axis of the line of cylinders (61) and having through openings (70) in corresponding positions at the positions of the end portions (62) of the transfer conduits of each of the cylinders (60a, 60b, 60c) of the engine. 11. - Motor according to claim 10, characterized in that the openings (70) are machined in the central part of the rod (69), in a diametrical direction. 12. - Motor according to claim 10, characterized in that the openings (70 ′) are formed by countersunk holes in the lateral surface of the rod (69 ′). 13. - Motor according to any one of claims 10, 11 and 12, in the case where the ends (62 ′) of the transfer conduits of each of the cylinders (60 ′) are separated into several parts by partitions (73) , each part of the end of a transfer duct communicating with a transfer opening (65 ′), characterized in that the means for restricting the passage of the transfer ducts consist of a rod (69 ′) comprising sets of openings (71) at each end of a cylinder transfer conduit (60 ′), each of the openings (71) being disposed in a portion of the end of the transfer conduit (62 ′) Communicating with a transfer opening (65 ′).

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