EP0060184A1 - Charging of two-stroke engines - Google Patents

Abstract

According to the invention, fuel injection is controlled by a regulating chamber 29, 32 as a function of the variations in the dynamic pressure prevailing at two distant points 17, 22 of an auxiliary storage chamber 13 for engine precompression, opening into the combustion chamber 2 via an aperture 16 located lower than the outlets 7 of the main transfers. The invention makes it possible to improve the efficiency and reduce the pollution of two-stroke engines. <IMAGE>

Description

The present invention relates to improvements to an internal combustion engine of the two-stroke type making it possible to obtain better efficiency and better operating performance by improving the combustion and by reducing the losses of fresh gas at the exhaust.

It is well known that the two-stroke engine has advantages over the four-stroke engine for simplicity and greater specific power, in particular for small displacements. On the other hand, the very principle of supplying and sweeping the engine cylinder by the fresh fuel gas, open exhaust lights, leads to losses of fresh gas at the exhaust. These losses are detrimental to the operation of the engine both in terms of efficiency (consumption) and pollution.

Many and various attempts have been made to improve these conditions.

One solution is to perform a pre-sweep of the engine cylinder with clean air and to inject the fuel gas in a rich mixture only when the exhaust port is closed. This a priori satisfactory solution presents difficulties of execution, in particular at the level of the injection under pressure of the rich fuel mixture after the closing of the exhaust and at the level of the problems of distribution. In practice, the two-stroke engine then loses its advantages of simplicity compared to the four-stroke engine and is no longer competitive.

An intermediate solution recommended is to provide separate transfers for the purge air and for the fuel gas mixture and to draw the combustion chamber and the piston, so as to trap the fuel rich mixture in the room behind a cushion of purge air, so as to limit exhaust losses to the lowest possible quantity of carbureted air. In practice, one is limited in this way by the questions of injection pressure and homogeneous mixture in the combustion chamber of the fuel mixture, too strong stratification of the fuel mixture in the combustion chamber affecting the operating efficiency of the engine.

The object of the invention is to solve the above-mentioned problems, that is to say to limit the pollution of two-stroke engines and to increase their operating efficiency by using the principle of separate transfers for the main air of sweeping and combustion, and for the rich fuel mixture injected into the combustion chamber, and this without using a complicated mechanical distribution device and injection pump.

It has also been recommended to use to inject the combustion chamber of the engine with a fuel mixture an injector supplied with fuel by a gasoline pump of the membrane type actuated by the pressure variations appearing in the crankcase; it is however difficult to modulate such a supply as a function of the variable engine speed.

In accordance with the invention, and in order to resolve the difficulties mentioned, a two-stroke engine of the type is used comprising, for its supply of fuel mixture, an injector supplied with fuel by a membrane type petrol pump, actuated (directly or indirectly) by pressure variations appearing in the engine crankcase during engine operation, said engine being characterized in that said injector opens into an auxiliary chamber for storing the crankcase pre-compression connected to it by a non-return valve or any equivalent means, and said injector is located and / or directed in said auxiliary chamber so that it creates at its outlet a pressure differential favoring a fuel injection when means, such as a light or equivalent means, discover an outlet orifice from said auxiliary chamber towards said combustion chamber of the engine. It appears that the use of such an arrangement allows efficient injection of the fuel mixture into the combustion chamber, at the most opportune time and under a modular pressure that is most appropriate for the proper functioning of the engine. In addition, this arrangement avoids the use of any complicated mechanical system, the regulation being done automatically by virtue of the laws of fluid dynamics and allowing all the possible adjustments and adjustments. According to another characteristic of the invention, the auxiliary chamber opens into the combustion chamber of the engine through a transfer orifice located lower (relative to the top dead center of the engine) (PHM) than the sweeping and filling transfers of air from said combustion chamber. This is extremely favorable because it reduces, or even eliminates, the losses of fresh exhaust gases, and this is possible due to the provision of the aforementioned auxiliary pressure storage chamber and the particular configuration and / or positioning of the injector in this auxiliary chamber.

According to an advantageous construction characteristic, said injector is situated substantially at the level of a narrowed intermediate section of the auxiliary chamber, forming Venturi.

According to yet another characteristic of the invention, the injector is connected to a regulation chamber which comprises a membrane actuating a shutter member (such as a valve) of the fuel supply duct supplied by said fuel pump , and said membrane is permanently subjected to two opposing pressures taken in said auxiliary chamber at distant points, subjected to different dynamic pressures, in particular at the time of opening of said outlet orifice of said auxiliary chamber towards said combustion chamber. Thus is obtained, automatically and according to modular laws, the injection of the exactly desired quantity of fuel into the auxiliary chamber to be transferred into the combustion chamber at the times of actual transfer from the fuel mixture to the combustion chamber, the quantities of injected fuel which can be adjusted automatically according to the instantaneous engine operating speed.

The invention will appear more clearly with the aid of the description which follows, given with reference to the appended drawings, giving only by way of examples and schematically some embodiments.

• La figure 1 est une vue en coupe montrant schématiquement un moteur deux temps équipé des moyens de l'invention.
• Les figures 2 et 3 sont des vues semblables à celle de la figure 1, et sont relatives à deux variantes.
• La figure 4 montre une modification de la variante de la figure 3.
• La figure 5 est un diagramme de distribution facilitant la compréhension du fonctionnement.

In these drawings:

• Figure 1 is a sectional view schematically showing a two-stroke engine equipped with the means of the invention.
• Figures 2 and 3 are views similar to that of Figure 1, and relate to two variants.
• FIG. 4 shows a modification of the variant of FIG. 3.
• FIG. 5 is a distribution diagram facilitating the understanding of the operation.

We will first refer to FIG. 1, in which we see a two-stroke engine 1, comprising a combustion chamber 2, formed between the cylinder 3 and the piston 4 of the engine. In 5, one diagrammatically illustrates one of the two lateral transfers allowing the main sweeping and combustion air, pre-compressed in the casing 6 during the downward movement of the piston 4 towards its bottom dead center, to pass through the combustion chamber when the outlet lights 7 destranferts5 are released by the piston. At 8, we can see the exhaust pipe opening through the light 9 in the chamber 2. The air is pre-compressed in the casing 6, being supplied by a duct 10, controlled by the throttle valve 11. At 12, there is shown a non-return valve allowing pre-compression in the casing 6. All that has been described so far is all that is most conventional.

According to the invention, an auxiliary chamber 13 is provided for the engine for storing the pre-compression of air dans.le crankcase 6 during descent to the bottom dead center of the piston 4. In the example illustrated, the chamber auxiliary 13 has been shown separated from the engine as an appendix which has been added to it and which communicates with the casing by an orifice 14 closed by a non-return valve 15 allowing the passage of air from the casing 6 to the auxiliary chamber 13 and forbidding it in the other. It is understood, however, that the auxiliary chamber 13 could be provided in the body of the engine, the illustrated example showing the auxiliary chamber 13 separated for clarity, and further corresponding to the test prototype carried out.

The auxiliary storage chamber 13 also opens into the combustion chamber 2 through a light 16. Advantageously, and as will be explained more clearly below, the light 16 is located in the chamber 2 a little lower than the lights 7 of the outlets of the main transfers 5, and its section can be reduced compared to the section of the lights 7 of the main transfers. The ratio of the sections will advantageously be between 1/5 to 1/20.

The injection of fuel is done at the appropriate time, by an injector 17, in the auxiliary chamber 13. In the example illustrated, the injector 17 is placed in a narrowed section 18 of the chamber 13 forming Venturi.

The injector 17 is supplied with fuel by a pump membrane 19, connected by a fuel supply conduit 20 coming from a tank (not shown). The diaphragm pump 19 is actuated under the effect of the pressure variations prevailing in the auxiliary chamber 13 during the different engine operating times. The pressure tap is made by a conduit 21, opening at 22 into the auxiliary chamber 13, and acting on the diaphragm 23 of the pump 19 on one side of it in opposition to the action of a spring 24. The pressure pulses appearing in the chamber 13 cause a pumping action of the pump 19, allowing, thanks to the provision of non-return valves 25, 26, to bring fuel under pressure to the level of an orifice 27 controlled by a member shutter such as a valve or needle 28.1 orifice 27 opening into a balancing chamber 29. A small spring 30 normally maintains the orifice 27 closed by application of the needle 28 against said orifice, and this as long as the pressures on either side of a membrane 31 closing the bottom of the balancing chamber 29 and separating it from an adjacent chamber 32 communicating with the conduit 21 are substantially equal. Under these conditions, there can therefore be no fuel injection.

On the other hand, when a pressure imbalance occurs between the chambers 29 and 32, and more precisely a pressure drop in the chamber 29 relative to that prevailing in the chamber 32, the membrane 31 controls against the spring 30, the release of the needle 28 allowing the introduction of fuel into the chamber 29 in the direction of the injector 17. Such an imbalance occurs when, the light 16 comes to be released by the piston.4 which approaches from its bottom dead center, an effective dynamic injection of the air stored under pressure in the auxiliary chamber 13 occurs towards the combustion chamber 2, the pressure at the level of the injector 17 placed at the neck of the Venturi 18 of the auxiliary chamber 13 then suddenly drops below that prevailing higher in the chamber 13, at the pressure tap 22. As has therefore been understood, this arrangement allows the automatic injection of fuel into the auxiliary chamber 13 at the precise moment where opens re the third trans fert, when the light 16 is released by the descending piston 4.

The operating cycle is understandable, further referring to the distribution diagram in the figure. 5.

In this diagram, the angular coordinates corresponding to the have been identified in PMH and PMB. moment when the piston reaches the top dead center then the bottom dead center. The arrow indicates the direction of rotation of the motor.

According to the example shown, the opening of the exhaust, indicated by the letters O.E., occurs a little before the piston is halfway.

Continuing its descent, the piston discovers a little later at the point marked OT, the main transfers 5 ensuring a first filling and sweeping of the combustion chamber 2 by the main air compressed in the casing 6, under the piston which continues its descent . It will be noted that as long as this opening has not occurred, the pressure in the casing 6 has risen, and part of the compressed air has been stored in the auxiliary chamber 13, the lumen 16 of which is closed. When the transfers open, the pressure drops in the casing and the non-return valve 15 isolates the auxiliary chamber 13 from the casing, maintaining in the auxiliary chamber the overpressure which will be necessary to ensure the injection of the mixture. later.

Indeed, the piston continuing its course, releases a little later light 16 at the point indicated O.T ', a little before the bottom dead center. The injection of rich fuel mixture then occurs in the combustion chamber thanks to the pressure stored in the auxiliary chamber 13 and thanks to the pressure differential appearing between points 17 and 22 during the dynamic flow of air fuel from chamber 13 to chamber 2, as explained above,

The injection by the light 16 of the rich fuel mixture being made substantially opposite to the exhaust light 9, it will be noted that between the rich fuel mixture and the exhaust interposes a cushion of purge air beforehand injected and which continues to be injected by the main transfers 5. We therefore further reduce,. risk of loss to the exhaust fresh gas.

The piston then passes through the bottom dead center, and there is successively the closing of the light 16 stopping the injection at the point marked F.T ', the closing of the main transfers at the point marked FT, then the closing of the exhaust at point marked FE Ignition can then occur a little before top dead center at the point marked Al.

The variant embodiment illustrated in FIG. 2 will now be described.

This variant differs from the embodiment described in FIG. 1 in that the fuel pump 19 directly receives the pressure fluctuations necessary for its operation from the crankcase by a conduit 40 which makes it possible to apply the instantaneous pressure prevailing in the crankcase 6 to the diaphragm 23 of the pump 19.

So as to allow the injection of fuel into the auxiliary chamber 13, under the pressure which prevails there at the time of injection, a pressure which will be greater than that prevailing at this time in the casing 6, due to the opening of the main transfers 5, a small pressure accumulator 42 has also been provided on the conduit 41 connecting the outlet of the pump 19 to the injector 17.

On the other hand, so as to allow, as in the embodiment of FIG. 1, the release of the valve 28 revealing the orifice 27 for supplying fuel to the injector 17 when the light 16 is discovered by the piston 4, the chamber 32 is subjected to the pressure prevailing in the auxiliary chamber 13, taken at a point 43, distant from the injector 17 and which can be positioned substantially like point 22 of the outlet of the conduit 21 of the example illustrated in Figure 1. Note that in the example of Figure 2, there is no communication between the chamber 32 and the volume 44 of the pump 19, located above the membrane 23 relative to the spring 24, which of the rest can be omitted in this embodiment.

Obviously, the operation of the device illustrated in FIG. 2 is identical to that of the device illustrated in FIG. 1.

We will now describe the illustrated embodiment in Figure 3, which is very similar to that illustrated in Figure 1.

It differs from this in that the chamber 44 of the pump 19, above the membrane 23, is in communication with the volume of the auxiliary chamber 13 by a conduit 45 which is different from the calibrated conduit 46 joining said chamber 13 to the capacity 32 ensuring the regulation of the fuel injection when the lumen 16 for injecting the rich fuel mixture is discovered. This arrangement allows a simpler adjustment of the regulation, in particular by adjusting the calibration of the conduit 46. Of course, in this example, it is the outlet 47 of the conduit 46 in the auxiliary chamber 13, which plays the role of the outlet 22 of the pipe 21 (FIG. 1) or of the outlet 43 (FIG. 2) allowing the injection of rich carburetted air at the time of the opening of the light 16, thanks to the birth of a pressure differential between this point and that or opens the injector 17, in the Venturi 18 of the chamber 13, at the time of injection.

The adjustment of the fuel flow can also be modulated, as illustrated in FIG. 3, by providing a bypass 48 on the pipe 46, forming an air leak controlled by a needle 49 whose engagement is linked to the position of the butterfly gases 11, for example by a linkage, the conduit 48 being able to open upstream and downstream of the butterfly valve 11 on the main air intake pipe 10.

Alternatively, and as illustrated in Figure 4, the needle 49 can be omitted.

It will be noted that, in accordance with the invention, it is very easy to adjust and modulate the flow rate and the richness of the rich fuel mixture injected into the combustion chamber from the auxiliary chamber. Indeed, the modulation can be done not only at the level of the calibration of the injectors and the pressure conduits, but especially at the level of the location and / or the orientation of the differential pressure taps in the auxiliary chamber 13, such as 'indicated in 17 and 22 in Figure 1, in 17 and 43 in Figure 2, in 17 and 47 in Figure 3. Depending on the location and direction of these sockets, one can modulate.la carburation and arrive to optimize the operating efficiency of an engine.

Of course, the invention is in no way limited to the illustrated and described embodiments which have been given only by way of examples, the invention on the contrary comprising all the technical equivalents of the means described as well as their combinations if these are carried out according to its spirit and implemented within the framework of the claims which follow.

Claims (10)

1. Two-stroke engine of the type comprising for its supply of fuel mixture an injector supplied with fuel by a gasoline pump of the diaphragm type, actuated (directly or indirectly) by the pressure variations appearing in the crankcase during engine operation , said engine being characterized in that said injector 17 opens into an auxiliary chamber 13 for storing the pre-compression taking place in the casing 6 and connected to it by a non-return valve 15 or any equivalent means, and said injector is located and / or directed in said auxiliary chamber so that it creates at its outlet a pressure differential favoring a fuel injection when means, such as a light 16 or equivalent means, discover an outlet orifice of said auxiliary chamber 13 in the direction of the combustion chamber 2 of the engine. 2. Engine according to claim 1, characterized in that the auxiliary chamber 13 opens into the combustion chamber 2 of the engine through a transfer orifice 16 located lower (relative to the top dead center of the engine) than the outlets 7 of the transfers sweeping and air filling 5 of said combustion chamber. 3. Engine according to claim 1 or claim 2, characterized in that said injector 17 is situated substantially at the level of a narrowed intermediate section 18 forming a Venturi of the auxiliary chamber 13. 4. Engine according to one of the preceding claims, characterized in that the injector 17 is connected to a regulation chamber 29, comprising a membrane 31 actuating a closure member 28 (such as a valve) of the conduit fuel supply 27, supplied by said fuel pump 19, and said diaphragm 31 is permanently subjected to two opposing pressures taken in said auxiliary chamber 13 at distant points (17,22; 17,43; 17,47) subjected at different dynamic pressures, in particular when opening said outlet orifice 16 from said auxiliary chamber towards said combustion chamber. 5. Motor according to claims 3 and 4, characterized in that the two aforementioned opposing pressures are taken respectively at the level of said narrowed section 18 and at another level. 6. Engine according to one of the preceding claims, characterized in that the fuel pump 19 is actuated by the pressure variations appearing in said auxiliary chamber 13 as a result of pressure variations appearing in the engine casing. 7. Engine according to one of claims 1 to 5, characterized in that the fuel pump 19 is actuated by the pressure variations appearing in the casing 6, and there is provided a pressure accumulator 42 on the supply circuit in fuel from the injector 17 after said pump. 8. Engine according to one of claims 4 to 7, characterized in that at the level of at least one of the opposing pressure taps 47 acting in the regulation chamber 29,32 a controlled leak 48. 9. Engine according to claim 8, characterized in that the magnitude of the leak is controlled as a function of the position of the throttle valve 11, for example by means of a linkage actuating a needle needle 49. 10. Engine according to claim 8, characterized in that the magnitude of the leak is controlled as a function of the pressure prevailing in the leak channel 48, connected to the air intake pipe 10 of the engine.

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