EP1236869A1 - Arrangement for introducing air-fuel mixture in a combustion chamber, in particular for a two-stroke engine - Google Patents

Abstract

The present invention relates to a device for introducing under pressure a fuel mixture into a combustion chamber of a cylinder of an internal combustion engine, in particular of a two-stroke engine, comprising a valve (38) for shutting off '' a pipe (40) for introducing the fuel mixture, an assistance member linked to said valve and comprising a movable separation element (50) delimiting an upper chamber (54) as well as a lower chamber (56), means for supplying pressurized air (62) to one of the chambers and means for fluid communication (64) between the chambers (54, 56). According to the invention, the communication means comprise braking means (70, 72) for the movement of the pressurized air leaving one of the chambers (54, 56). <IMAGE>

Description

The present invention relates to a device for introducing under pressure a fuel mixture in a combustion chamber of a cylinder of a internal combustion engine, in particular a two-stroke engine.

It is already known, in particular by document FR-A-2 641 336 published in the name of the applicant, to use such a device which includes a valve for closing a pressure introduction pipe of a fuel mixture in a combustion chamber and an organ travel assistance related to this valve.

This assistance unit includes a movable separation element, such as a flexible membrane, connected to the valve stem and delimiting two rooms in a closed housing, a superior room connected to a pressurized air tubing notably from the pump housing that comprises the engine and a lower chamber connected to a pipe in which circulates a fluid at constant pressure, such as pressure atmospheric, or variable pressure.

In operation, during the injection phase of the fuel mixture, the pressure of the pump housing acts both on the face of the diaphragm opposite of the upper chamber of the assistance member by the air tubing under pressure and on the face of the valve opposite the pipeline of introducing the fuel mixture and produces a force tending to open the valve.

Thus, depending on the variations of the forces applying on either side of the membrane, we will get variations of opening or closing of the valve for controlling the fuel mixture supply to the engine combustion chamber.

The Applicant has found that this device has drawbacks non negligable.

Indeed, when the lower chamber is connected to fluid under pressure variable, it is necessary to provide specific and complicated devices not only to get this variable pressure but also to determine the precise moment when the valve will be closed.

In the case where this lower chamber is connected to the pressure atmospheric, the pressurized fluid circulating in the air tubing under pressure enters the upper chamber and the resulting force of this pressure is applied to the membrane, generating a movement in opening of the valve then, after the passage of this air and disappearance of the force, this same valve will suddenly close by hitting its seat and under the effect of the accumulated energy will rebound creating a so-called rebound phenomenon, i.e. successive sequences opening and closing, the amplitude of which will decrease depending on the time.

This rebound phenomenon generates undesirable noise during operation of the engine as well as parasitic valve openings, openings that are detrimental to the proper functioning of the engine.

The invention proposes to remedy the drawbacks mentioned above by proposing a device for introducing a fuel mixture under pressure in a chamber of a cylinder of an internal combustion engine, in particular a two-stroke engine, comprising a valve for the obturation of a pipe for introducing the fuel mixture, an organ assistance linked to said valve and comprising a movable element of separation delimiting a superior room as well as a room lower, means for supplying pressurized air to one of the chambers and means of fluid communication between the chambers, characterized in that the means of communication include means for braking the movement of pressurized air leaving one of the bedrooms.

According to another characteristic, the means of communication can be a conduit.

The braking means may include a means for reducing the communication section.

The reduction means may include a calibrated orifice.

The diameter of the calibrated orifice can be substantially equal to a third of the diameter of the duct.

The length of the conduit between the calibrated orifice and the lower chamber can be substantially equal to twice the length of the conduit between the chamber upper and said calibrated orifice.

In a first variant, the braking means may consist of a hinged flap.

In another variant, the braking means may consist of a diaphragm with controlled opening.

• la figure 1 est une vue représentant l'agencement d'un moteur à deux temps comportant le dispositif selon l'invention ;
• la figure 2 est une vue à plus grande échelle montrant le dispositif selon l'invention.

The present invention will be better understood on reading the description which follows with reference to the appended drawings, given by way of example and in which:

• Figure 1 is a view showing the arrangement of a two-stroke engine comprising the device according to the invention;
• Figure 2 is an enlarged view showing the device according to the invention.

In FIG. 1, the internal combustion engine, here a two-stroke engine, comprises a cylinder 10 closed at the top by a cylinder head 12, a piston 14 subjected to an alternative translational movement in the cylinder under the effect of a connecting rod 16 and crank 18 assembly housed in a pump housing 20 closing the lower part of the cylinder.

The pump housing has an air intake 22 provided with a non-return valve 24 and an air introduction channel 26 leading to the lights of transfer 28 provided in the lower part of the cylinder 10.

At the same level as the transfer lights 28 is a light exhaust 30 communicating with an exhaust pipe 32.

The cylinder head 12 carries a spark plug 34, a device for introducing under pressure a fuel mixture through an inlet 36 and an assistance unit linked to a valve 38.

The orifice 36 is capable of being controlled in closing and in opening by the valve 38 and communicates with a pressurized air line 40 in which is disposed a fuel injection device 42 which can be associated with a Venturi type nozzle 44 placed in this pipe in upstream of the orifice 36 and downstream of the fuel injection device 42.

The pressurized air in line 40 can come either from the pump housing 20, or from the pump housing of another cylinder in the case of an engine multi-cylinder.

The valve 38 has a head 46 which comes to bear in the position of closure, in the orifice 36 forming a valve seat and a rod 48 connected to an assistance member comprising a flexible membrane 50 which is fixed sealingly between the two parts of a closed casing 52 so as to form an upper half-casing defining an upper sealed chamber 54 and a lower half-casing defining a lower sealed chamber 56.

Preferably, the casing is fixed on the cylinder head 12 above the orifice 36 and a return spring 58 is arranged in line with the valve, surrounding the rod 48 while being interposed between the flexible membrane 50 (or the end of the rod 48) and the upper surface 60 of the cylinder head 12.

Thus, the valve 38 is subjected to an opening / closing movement of the orifice 36 as a function of the pressure difference existing between the rooms 54 and 56.

Referring now in addition to Figure 2, the upper chamber 54 communicates via a tube 62, connected to an air inlet orifice under pressure 63 disposed on the peripheral wall of the upper half-casing, with a pressurized air generator means which, for example, consists by the pump housing 20 and this by connecting this tubing, either with the pressurized air duct 40, either with the air introduction channel 26, either directly with said pump housing.

As best seen in this figure, means of communication fluidics are provided between the upper chamber 54 and the lower chamber 56, these means of communication comprising a conduit 64 outside the housing 52.

This conduit includes a first end which is connected to a pressure air outlet opening 66 which is provided on the wall horizontal of the upper crankcase and away from the inlet 63, this opening 66 allowing pressurized air admitted into the chamber upper 54 by the inlet 63 to come out, and a second end which is connected to a pressure air inlet opening 68 provided on the wall peripheral of the lower half-casing so as to put in communication the two chambers 54 and 56.

This duct carries a means of braking the movement of the air under pressure which runs through it and preferably comprises a means of reduction of the passage section of the duct, such as a restriction member 70 with a calibrated orifice 72, but any other member, such as a valve pivoting around an axis or a diaphragm with controlled opening type with iris making it possible to reduce the passage section in the conduit, can be used.

Advantageously, this calibrated orifice is of circular section with a diameter D1 which is substantially equal to one third of the internal diameter D2 of the conduit 64, which is also of circular section, and is part of an organ restriction 70 of circular tubular shape whose internal diameter corresponds to the diameter of the orifice 72, the external diameter of which is close to the diameter D2 of the conduit 64.

Preferably, this calibrated orifice is located in the conduit 64 of such that the length L1 of the conduit between the calibrated orifice and the opening 68 of the lower chamber 56 is substantially equal to two times the length L2 of the conduit between this calibrated orifice and the opening 66 of the upper room 54.

For example, the length L2 of the conduit is 5 cm and the length L1 of 10 cm while the diameter D1 of the calibrated orifice 72 is 2 mm for a pipe diameter D2 of 6 mm.

Thus in operation, during the injection phase of the fuel mixture as as illustrated in FIG. 1, the pressurized air coming from the tubing 62 enters through the inlet port 63 in the upper chamber 54 of the housing 52.

This pressurized air will create a pressure front or pressure wave which is materialized by a separation surface between two fluids at different pressures.

In a practical manner and with reference to FIG. 2, it is agreed to connect the tubing 62 to the conduit 26 as shown in dotted lines in this figure.

Thus, after the compression / explosion phase in the cylinder 10, the piston 14 will move from its top dead center to its bottom dead center to compress the air that was admitted to the pump housing 20 during the phase previous by the air intake 22 and which is at a corresponding pressure substantially to that of atmospheric pressure.

The air present in the tubing 62, the chambers 54, 56 and the duct 64 is also at atmospheric pressure by the fact that before the piston compresses the air from the pump housing, it is in communication with the tubing 62, itself in communication with the chamber 54 which is in communication with chamber 56 via conduit 64.

The air contained in this pump casing will be compressed by this piston, during its displacement from top dead center to substantially towards its point dead low and then be injected in a compressed state at least into the tubing 62.

During this injection, a pressure front or pressure wave is created between the compressed air and the air present in this tubing and moves, at a determined speed, generally that corresponding substantially to the speed of sound, in the tubing by pushing back the air at pressure atmospheric throughout this tubing and replacing it with air compressed, then enters through the inlet 63 into the upper chamber 54 in filling this chamber with compressed air.

Under the effect of the pressure prevailing in the chamber 54, the flexible membrane 50 is subjected to a force going against the spring 58 and tends to open the valve 38 so that the fuel mixture from the line 40 is introduced under pressure into the combustion chamber cylinder 10 through port 36.

Once this action has been produced for a determined period of time, the air compressed spring through the opening 66 of the chamber 54 and another front of pressure will be created between this compressed air and air at atmospheric pressure present in the conduit 64 connected to the opening 66.

This pressure front, with a propagation speed substantially equal to that of the previous pressure front, travels the length L2 of the conduit 64 until reaching the restriction member 70 provided with the calibrated orifice 72 then crosses this orifice.

By this passage through the orifice 72, this front and the compressed air which the accompanying are braked and come out of this orifice calibrated with a propagation speed much lower than the speed in the conduit of length L2.

This pressure front and this compressed air then flow, with a movement speed slowed down, the length L1 of the conduit 64 up to enter the lower chamber 56 through the opening 68. The compressed air which accompanies this forehead fills this chamber and the resulting force of this pressure acts on the membrane 50 so as to close the valve 38, which was made possible by replacing the compressed air in the chamber 54 by air at atmospheric pressure, as it takes place in the usual way during the engine operating cycle by putting to the atmosphere of the pump housing.

Thanks to this device, possible valve bounces are avoided since a force will be exerted on the face of the membrane 50 facing the lower chamber and thus maintain this valve in the closed position.

Advantageously and in the event that a spring is provided valve 38 back, the force resulting from the air pressure on the membrane will add to that of the spring and thus provide a closure much faster from this valve.

Thus, thanks to the conduit 64 possibly provided with the calibrated orifice 72, the pressure applied to the face of the membrane 50 of the lower chamber 56 is out of phase with a time delay relative to the pressure applied to the face of the membrane of the chamber 54 which allows avoid simultaneous application of the same pressure on both sides of this membrane.

Of course, the present invention is not limited to the example described, but encompasses any variant.

In particular, the diameters D1 and D2 as well as the lengths L1 and L2 above are only given as an example and all other values may be calculated so as to obtain the desired settings for the lifting laws of valve 38.

In addition, it can be envisaged to dispense with a restriction organ and use only a conduit of appropriate length and diameter in such a way the pressure front can be braked from one end to the other end of the duct so that it reaches the lower chamber with a time lag from its theoretically expected arrival.

Claims (8)

Device for pressurizing a fuel mixture into a chamber of a cylinder (10) of an internal combustion engine, in particular of a two-stroke engine, comprising a valve (38) for closing a pipe ( 40) for introducing the fuel mixture, an assistance member linked to said valve and comprising a movable separation element (50) delimiting an upper chamber (54) as well as a lower chamber (56), supply means in pressurized air (62) from one of the chambers and fluid communication means (64) between the chambers (54, 56), characterized in that said communication means comprise braking means (70, 72) of the displacement of the pressurized air leaving one of the chambers (54, 56). Device according to claim 1, characterized in that the communication means are a conduit (64). Device according to one of the preceding claims, characterized in that the braking means comprise means for reducing (70, 72) the cross-section of the communication means (64). Device according to claim 3, characterized in that the reduction means comprises a calibrated orifice (72). Device according to claim 4, characterized in that the diameter (D1) of the calibrated orifice orifice (72) is substantially equal to one third of the diameter (D2) of the conduit (64). Device according to one of claims 2 to 5, characterized in that the length (L1) of the conduit (64) between the calibrated orifice (72) and the lower chamber (56) is substantially equal to twice the length (L2 ) between the upper chamber (54) and said calibrated orifice. Device according to one of the preceding claims, characterized in that the braking means consist of an articulated flap. Device according to one of claims 1 to 6, characterized in that the braking means consist of a diaphragm with controlled opening.

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