EP0704017B1 - Fuel-air mixture feed device for a two-stroke internal combustion engine - Google Patents

Abstract

PCT No. PCT/FR94/00972 Sec. 371 Date Jan. 17, 1996 Sec. 102(e) Date Jan. 17, 1996 PCT Filed Aug. 2, 1994 PCT Pub. No. WO95/04212 PCT Pub. Date Feb. 9, 1995Air/fuel mixture supply device for a two-stroke internal-combustion engine, of the type with scavenging by compressed air in the casing, comprising at least one cylinder, a piston capable of reciprocating motion in the cylinder, and a scavenging-air compression casing, the cylinder comprising at least one exhaust port, at least one transfer port and a port for introduction of an air/fuel mixture. A rotary closure member (19) driven in synchronism with the rotation of the engine is associated with the port (16) for introduction of the air/fuel mixture into the combustion chamber, this closure member being placed in an air reservoir (14) fed with air under a pressure greater than the pressure in the combustion chamber (10) after opening of the exhaust port (11).

Description

The present invention relates to a device for supplying the air-fuel mixture to a two-stroke internal combustion engine of the type swept by compressed air in the casing, comprising at least one cylinder, a piston moving in back and forth in said cylinder to delimit a combustion chamber and a purge air compression housing provided with an air intake orifice, the cylinder comprising at least one exhaust port, at least one port transfer communicating through a transfer channel with the housing, and a light for introducing an air-fuel mixture into the combustion chamber, towards the end of the sweep.

Internal combustion engines operating on a two-stroke cycle have been found to have relatively high consumption and pollution. This double problem is due to the sweeping of the combustion chamber, which sweeping is carried out using an air-fuel mixture and, to be effective in order to achieve a good filling of the combustion chamber with air-fuel mixture and to evacuate the burnt gases as much as possible from the combustion chamber, results in a direct passage of part of the air-fuel mixture through the exhaust port, that is to say an exhaust of unburnt gases.

This is the reason why he has already proposed to sweep the combustion chamber with clean air rather than by an air-fuel mixture, the fuel being introduced into the combustion chamber only towards the end. of the sweep. For this, it is possible to inject the fuel either directly into the combustion chamber (see patent application FR-2 582 349), or indirectly (patent application FR-2 609 504), or even to introduce it pneumatically (patent application FR-2 496 757). To introduce fuel by injection, it is necessary to have a relatively high injection pressure and the injectors used are often electronically controlled for reasons of flexibility of adjustment. On the other hand, the pneumatic fuel introduction systems are produced by a valve controlled for example electronically or by cam as a function of the rotation of the engine, which limits the operating speed due to the risks of panic of the valve or the time for actuation of the electronic control.

In addition, document WO-A-91 02 144 describes a two-stroke internal combustion engine in which the air flow from the compression housing to the combustion chamber takes place through two passages. A first passage controlled by the piston is traversed by the major part of the air flow. A second passage traversed by a reduced part of the air flow contains a rotary shutter driven in synchronism with the rotation of the engine, a fuel introduction taking place in said reduced part of the air flow, downstream of the rotary shutter, in such a way that an air-fuel mixture is admitted into the combustion chamber through an air-fuel mixture introduction port, during a limited angle of rotation of the engine.

All these known solutions reduce the intrinsic advantages of the two-stroke engine, namely a relatively simple construction and a reduced cost price, advantages which are particularly advantageous for small engines used for example on two-wheeled vehicles.

The present invention aims to eliminate or at least reduce to a large extent the drawbacks of the solutions already proposed with a view to reducing the consumption and pollution of two-stroke engines.

The subject of the invention is a device for supplying the air-fuel mixture to a two-stroke internal combustion engine of the type swept by compressed air in the casing, this engine comprising at least one cylinder, a movable piston. back and forth in the cylinder to define a combustion chamber and a purge air compression housing provided with an air intake orifice. The cylinder comprises at least one exhaust port, at least one transfer port communicating via a transfer channel with the casing, and a port for introducing an air-fuel mixture into the combustion chamber towards the end of the sweep. . The supply device comprises an air reservoir supplied with air at a pressure higher than the pressure prevailing in the combustion chamber after opening of the exhaust port, and a rotary shutter member driven in synchronism with the rotation of the engine, associated with the light for introducing the air-fuel mixture into the combustion chamber. According to the invention, a venturi is placed between said tank and the rotary shutter and a fuel inlet from a constant level tank opens into the divergent portion of said venturi

In this case, the rotary shutter is preferably placed inside said tank.

The rotary obturator can preferably be a cylindrical plug obturator whose axis is parallel to the axis of the cylinder and which has in its cylindrical wall a window controlling the communication of the tank by the introduction light with the combustion chamber .

The air tank can be supplied with pressurized air by a system external to the engine, or by a system internal to the engine. In the latter case, the reservoir is advantageously supplied with air from the casing by a conduit also controlled by a rotary shutter driven in synchronism with the rotation of the engine.

The upper edge of the light for introducing the air-fuel mixture into the combustion chamber may be at the same level as the upper edge of the exhaust light, but according to a preferred embodiment, the upper edge of the introduction light is located closer to the cylinder head than the upper edge of the exhaust light, so that when the piston rises, the combustion chamber still communicates with the air tank and the increasing the pressure in the combustion chamber leads to an increase in the air pressure in the tank for the introduction of the air-fuel mixture during the next cycle.

Preferably, the air-fuel jet of the air-fuel mixture supply device is oriented towards the cylinder head so that said jet does not meet the exhaust lumen.

Referring to the single figure of the accompanying drawing, an illustrative and nonlimiting embodiment of a device according to the invention will be described below in more detail.

The engine as illustrated in the drawing is an internal combustion engine operating on a two-stroke cycle, of the type scanned by compressed air in the casing. We recognize on the drawing a cylinder 1 defined in a cylinder block 2 surmounted by a cylinder head 3 carrying a spark plug 4. The cylinder block 2 is attached to a casing 5 provided with an air intake opening 6 and a non-flap valve represented. In the casing 5 rotates a crankshaft 7 to which is coupled by a connecting rod 8 a piston 9 which is movable back and forth in the cylinder 1 and delimits in the latter a combustion chamber 10 with the cylinder head 3.

The cylinder 1 also comprises an exhaust light 11 as well as a transfer light 12 communicating via a transfer channel not shown with the casing 5, the two lights 11 and 12 being formed in the cylinder 1 so as to open into the combustion chamber 10 at a height such that they are completely cleared only when the piston 9 is in bottom dead center, as shown.

According to the invention, the engine as described above also comprises a device 13 for supplying the air-fuel mixture to the combustion chamber 10. This device 13 comprises an air reservoir 14 communicating through a passage 15 with the casing 5 as well as by a light 16 with the cylinder 1, the light 16 being substantially at the same height as the exhaust light 11. A venturi 17 into the divergence of which opens a fuel inlet 18 connected to a tank constant level, not shown, is mounted in the chamber 13 at the point where the latter exits towards the lumen 16. A rotary shutter 19 rotating around an axis parallel to the axis of the cylinder 1 is rotatably mounted at the inside the chamber 14 so as to control the communication between the inside of the chamber 14 and the cylinder 1. In the example shown, the shutter 19 is a plug valve with a cylindrical wall located between the ve nturi 17 and the light 16 has a window 21. The shaft 20 of the shutter 19 also carries another rotary shutter 22 whose light 23 controls the communication between the chamber 14 and the casing 5 via the conduit 15, as well as 'a drive pinion 24 consisting of a bevel gear engaged with a not shown bevel gear of a shaft which is parallel to the crankshaft 7 and is driven by the latter.

It should be noted in the example shown, the insertion light 16 is arranged in such a way that its lower edge is located at the height of the top of the piston 9 when the latter is in bottom dead center and that its upper edge is located at a level slightly above the upper edge of the exhaust lumen 11. Furthermore, the introductory lumen 16 is opposite the exhaust lumen 11 and the venturi 17 is oriented obliquely upwards towards the cylinder head 3 so as to produce a jet which crosses the axis of the cylinder 1 and passes over the exhaust port 11.

The mode of operation of the engine as defined above will be described below.

From the bottom dead center position according to the drawing, the piston 9 moves towards the cylinder head 3 in the direction of the top dead center. During this piston rise stroke, the volume of the casing 5 increases and air is drawn into the casing 5 through the inlet port 6 and the valve not shown.

When the piston 9 has reached top dead center, the spark plug 4 triggers the combustion of the air-fuel mixture contained in the combustion chamber 10 and under the thrust of the gases resulting from this combustion, the piston 9 moves away from cylinder head 3 towards bottom dead center. During this descent of the piston 9, the air previously sucked into the casing 5 is compressed, the valve not shown preventing any discharge of air through the intake orifice 6.

During this downward movement, the piston 9 successively discovers the introduction light 16, the exhaust light 11 and the transfer light 12. The introduction light 16 is still closed by the shutter 19, the gases of exhaust are evacuated by the exhaust port 11, this movement being assisted by the introduction, via the transfer orifice 12, of fresh air previously compressed in the casing 5.

During this time, although the insertion light 16 is discovered by the piston 9, the communication between the air reservoir 14 and the cylinder 1 remains interrupted by the plug 19.

It is only after the piston 9 has reached the bottom dead center and then started its upward movement in the direction of the cylinder head 3 that the window 21 of the shutter 19 comes opposite the introduction light 16 and thus establishes the communication between the reservoir 14 and the cylinder 1. Under the air pressure in the reservoir 14, a pressure which is higher than the pressure in the cylinder 1, the exhaust port 12 still not being closed , the air passes from the reservoir 14 through the venturi 17 carrying with it the fuel coming from the fuel inlet 18, this flow of air and fuel being directed towards the top of the combustion chamber 10, au- above the exhaust port 11, so that the minimum amount of fuel reaches this port before it is closed by the piston 9.

After the consecutive closing of the exhaust light 11, the window 21 and the light 16 still allow, for a short time, a communication of the combustion chamber 10 with the tank 14, so that the pressure which increases in the chamber combustion 10 due to the upward movement of the piston 9 increases the pressure of the air contained in the tank 14, for the introduction of fuel during the next cycle.

The piston 9 then continues its upward movement in the direction of the cylinder head 3, compressing the air-fuel mixture in the combustion chamber 10 and sucking air into the casing 5 through the intake port 6 and the valve not shown.

When the piston 9 reaches the top dead center, the described steps of the cycle are repeated in the same order.

It should be noted that the embodiment shown and described has been given only by way of illustrative and nonlimiting example and that numerous modifications and variants are possible within the scope of the invention.

Thus, the introduction of pressurized air into the reservoir 14, instead of being done by a system internal to the engine (transfer in the reservoir 14 of part of the compressed air in the casing 5), could also be done by a system external to the engine.

Instead of locating the upper edge of the entry light 16 above the upper edge of the exhaust light 11, it would be also possible to place the upper edges of these two openings at the same height, which would suppress the increase in air pressure in the reservoir 14 when the piston 9 rises.

Furthermore, the shutter 19 could be a rotary shutter other than in the form of a plug, rotating around an axis other than parallel to the axis of the cylinder 1, although the arrangement described and shown is particularly favorable in the measurement. where it makes it possible to place the shutter as close as possible to the insertion lumen 16 and to produce the insertion device 13 as a whole in a particularly compact form.

Claims (9)

1. Air/fuel mixture supply device for a two-stroke internal-combustion engine , of the type with scavenging by compressed air in the casing, comprising at least one cylinder, a piston capable of reciprocating motion in the said cylinder for defining a combustion chamber and a scavenging-air compression casing provided with an air inlet orifice, the cylinder comprising at least one exhaust port , at least one transfer port communicating via a transfer duct with the casing, a port for introduction of an air/fuel mixture into the combustion chamber, towards the end of the scavenging , a rotary closure member (19) driven in synchronism with the rotation of the engine and associated with the port (16) for introduction of the air/fuel mixture into the combustion chamber (10) and an air reservoir (14) supplied with air under a pressure greater than the pressure prevailing in the combustion chamber after opening of the exhaust port (11), characterized in that it furthermore comprises a ventury (17) placed between the said reservoir (14) and the rotary closure member (19), and a fuel feed (18) coming from a constant-level tank and emerging in the divergent cone of the venturi.
2. Device according to Claim 1, characterized in that the rotary closure member (19) is placed inside the reservoir (14).
3. Device according to Claim 2, characterized in that the rotary closure member (19) is a cylindrical slide valve closure member whose axis is parallel to the axis of the cylinder (1) and which includes in its cylindrycal wall a window (21) controlling the communication of the reservoir (14) via the introduction port (16) with the combustion chamber (10).
4. Device according to any one of the preceding claims, characterized in that the air reservoir (14) is supplied with pressurized air by a system external to the engine.
5. Device according to any one of Claims 1 to 3, characterized in that the air reservoir (14) is supplied with pressurized air by a system internal to the engine.
6. Device according to Claim 5, characterized in that the reservoir (14) is supplied with pressurized air from the casing (5) via a conduit (15) controlled by a turning closure member (22) driven in synchronism with the rotation of the engine.
7. Device according to any one of the preceding claims, characterized in that the upper edge of the port (16) for introduction of the air/fuel mixture into the combustion chamber (10) lies at the same level as the upper edge of the exhaust port (11).
8. Device according to any one of claims 1 to 6, characterized in that the upper edge of the port (16) for introduction of the air/fuel mixture into the combustion chamber (10) lies at a level closer to the cylinder head (3) than the upper edge of the exhaust port (11).
9. Device according to any one of the preceding claims, characterized in that the air/fuel jet of the air/fuel mixture supply device (13) is directed towards the cylinder head (3) so that the said jet does not meet the exhaust port (11).

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