FR2656653A1 - Two-stroke engine with pneumatic injection controlled by an assisted valve - Google Patents

Abstract

The means (82) for controlling the injection into a first cylinder of the engine (111) includes a valve, the stem of which is secured to a membrane separating, in leaktight fashion, two chambers (95a and 95b) from the means (82). At least one of the chambers (95a, 95b) is connected by a pipe to a closable opening (125, 126') communicating with the internal volume of one of the pump cases (115, 115'). A flange (116, 116') fixed onto the crankshaft (114) of the engine, level with the pump case (115, 115') constitutes a means for selectively closing the opening by virtue of a cutout (131, 132) in its peripheral part.

Description

 The invention relates to a two-stroke engine with controlled pneumatic injection.

 Two-stroke engines with several cylinders generally comprise, associated with each of the cylinders, a casing called pump housing communicating with one of the ends of the combustion chamber of the cylinder and ensuring the introduction of fresh gas into the cylinder, by through at least one conduit and a 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 placed 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 crankcase. When the corresponding cylinder openings are released by the piston, fresh gases are introduced into the cylinder through the transfer ducts and openings and produce a sweep of fresh gases intended to replace the burnt gases which are evacuated by exhaust openings generally disposed offset from the transfer openings. The piston moves away from the housing so as to compress the gases contained in the cylinder. The ignition and combustion of a mixture of air and fuel then produces the engine displacement of the piston towards the crankcase.

 It has been proposed in the case of two-stroke engines to ensure a pneumatic injection of a mixture of air and fuel into each of the cylinders by means of an injection control device ensuring the control of the start and possibly the end the introduction of the fuel mixture into the cylinder.

 The injectlon control device can advantageously consist of an automatic valve assisted by the opening and closing of an orifice opening into the combustion chamber of the cylinder. ba valve stem is connected to a flexible membrane constituting a sealed separation wall between two chambers of the injection control device.

spring allows the valve to be returned to the closed position
Such a valve is controlled or assisted, at the opening and possibly at the closing by an introduction of gas under pressure in at least one of the chambers separated by the flexible membrane.

 ne difficulty encountered when using such assisted valve devices lies in achieving perfect synchronization of the opening or closing of the valve with the different phases of the engine operating cycle.

 The object of the invention is therefore to propose a two-stroke engine comprising at least first and second cylinders in each of which moves a piston and one of the ends of which communicates with a crankcase crossed by the engine crankshaft in an axial direction, connecting means between the movable pistons in the first and second cylinders connected to the crankshaft so that there is an angular offset between the cycles of the first and second cylinders, a fuel air supply pipe connected to each of the cylinders by means of an injection control means comprising a valve for closing a cylinder supply orifice, the rod of which is connected to a flexible membrane constituting a sealed partition wall between two chambers injection control means and a return spring of the valve in the closed position, this injection control means ensuring, in a simple manner, a help to synchronize the opening and closing of the valve with the phases of the engine operating cycle.

 For this purpose, at least one of the two chambers of the injection control means of at least one of the two cylinders is connected by a pipe to a closable opening communicating with the internal volume of one of the pump casings. of one of the two cylinders and at least one flange of generally cylindrical shape fixed on the crankshaft at the pump casing constitutes a means of selectively closing the opening thanks to a cut in its peripheral part.

 In order to clearly understand the invention, we will now describe, by way of nonlimiting examples, with reference to the attached figures, several embodiments of a two-stroke engine according to the invention.

 Figure 1 is an exploded perspective view of the pump housing of a cylinder of an engine according to the invention and the corresponding piston.

 FIG. 2 is a view in section along II of FIG. 1.

 FIGS. 3, 4, 5 and 6 are schematic views of two cylinders of a two-stroke engine in which direct pneumatic injection is carried out without assisted valve, during four successive phases of the engine operating cycle.

 FIG. 7 is a schematic view of two cylinders of a two-stroke engine according to an alternative embodiment of the embodiment of FIGS. 3 to 6.

 Figure 8 is a schematic view of two cylinders of a two-stroke engine in which the injection control means in the cylinders comprise valves controlled by cams.

 Figures 8A, 8B, 8C, BD and sE are diagrams corresponding to different types of engine operation shown in Figure 8, with regard to the control of the start and end of injection of the fuel mixture into a cylinder.

 Figure 9 is a sectional view of an automatic assisted valve constituting a means for controlling injection into a cylinder of a two-stroke engine according to the invention.

 FIG. 10 is a diagram showing the variations of the pressure in a cylinder and in the associated crankcase of an engine according to the invention, as well as in the crankcase of a second cylinder of the engine, as a function of l 'angle of rotation of the crankshaft.

 Figure II is a sectional view of a first alternative embodiment of an automatic assisted valve constituting an injection control means of a two-stroke engine according to the invention.

 FIG. 12 is a diagram showing the different control pressures of the assisted valve shown in FIG. 11, as a function of the angle of rotation of the crankshaft.

 Figure 13 is a sectional view of an automatic assisted valve according to a second embodiment constituting the injection means into a cylinder of a two-stroke engine according to the invention.

 FIG. 14 is a diagram showing the control pressures of the assisted automatic valve shown in FIG. 13, as a function of the angle of rotation of the crankshaft.

 Figures 15 and 16 are schematic views of two cylinders of a two-stroke engine according to the invention using an automatic assisted valve according to Figure 11. during two successive phases of the engine operating cycle.

 In Figure 1 we see a part of the wall of the casing 1 of a cylinder of an engine according to the invention comprising, at its upper part, the combustion chamber of the cylinder in which the piston 2 moves connected by a connecting rod articulated 3 to the crankshaft 4 of the engine passing in an axial direction a lower chamber 5 delimited in the lower part of the casing 1 and by two lateral flanges e and 7. The chamber 5 constituting the pump crankcase associated with the cylinder communicates with the lower part of the combustion chamber of the cylinder.

 Referring to any one of FIGS. 3 to 6, it can be seen that the casing 1 of the first cylinder shown on the left of the figure or the casing 1 'of the second cylinder shown on the right of the figure constitute, in their part upper, the cylinder chamber in which moves a piston 2 (or 2 ') and, in their lower part, the pump housing 5 tou 5') into which opens the lower part of the cylinder itself.

 The pump housing 5 (or 5 ′) has an air inlet opening or nozzle 9 on which a valve 10 is interposed allowing the entry of atmospheric air into the pump housing 5 when the latter is in depression. The nozzle 9 is fixed to the wall of the casing 1 at the pump casing, between the flanges 6 and 7.

 Atmospheric air may be drawn inside the pump housing when the piston 2 moves upwards and compressed inside the pump housing 5, when the piston moves to reach its low position as shown on the left side of Figure 3, for example.

 The pump housing side of each of the cylinders communicates via i: at least one external conduit and an opening such as 11 with the cylinder chamber. an exhaust line 12 allows these burnt gases to be evacuated before they are replaced by fresh air from the pump housing 5.

 In the case of a pneumatic injection engine, the combustion chamber of the cylinder in which the piston 2 moves is connected to an in-pressurized air section pipe 14 into which a fuel injector 13 opens.

 The mixture of pressurized air and fuel is injected at a determined instant inside the cylinder, mixed with the air Irais introduced into the cylinder then compressed, as shown on the right part of Figure 3. A candle 15 fixed in the cylinder head attached to the casing l at its upper part makes it possible to ensure the ignition and ia combustion of the mixture which causes the piston to descend directly from the pump crankcase.

 According to the invention as i is represented in FIGS. 1 and 2, the flanges o and 7 have recesses or cutouts respectively 1 and 17 of bevelled shape, on a part of the periphery of the flange corresponding to a certain angular zone around the crankshaft axis 4.

 Each of the flanges 5 and 6 comprises a balancing unbalance 18, 19 which is constituted by a massive metallic piece and a fairing respectively 20 and 21 made of metal sheet, so as to have a cylindrical shape and to constitute a disc ensuring the closing of the pump housing 5 on one of its lateral sides, inside the housing 1. The fairing can be replaced by a low density insert.

 Bevelled recesses 16 and 17 are preferably machined in the massive part of the corresponding flange constituting the unbalance 18 or 19. It is however possible to imagine other embodiments in which the fairings 20 and 21 have a profiled shape so as to replace the machined bevelled parts 16 and 17 to make cuts in the lateral surface of the flanges 6 and 7 intended to bring the interior volume of the pump casings 5 into communication with one or more openings opening to the outside of the casing.

 In the case of the embodiment shown in FIGS. 1 and 2, the wall of the casing 1 has two openings 24, 25 opening towards the inside of the pump casing 5 each in a lumen passing through a portion-shaped lining 26, 27 crown housed inside the wall of the motor casing 1. The linings 26 and 27 have C-shaped cross sections visible in particular in Figure 2 to ensure the closure of the lights passing through the linings 26 and 27 and the isolation of the internal volume of the pump housing 5 of the openings 24 and 25, when the lateral part of the flanges 6 and 7 not including the bevelled parts 16 and 17 is placed facing the openings of the linings z6 and 27.

 On the other hand, as can be seen in FIG. 2, when the bevelled parts 16 and 17 constituting the lateral cutouts of the flanges 6 and 7 are located opposite the openings of the linings 26 and 27 and the openings 24 and 25 of the wall 1, the interior volume of the pump casing 5 is placed in communication with the openings 24 and 25 and through them, with a pipe 30 connected outside the wall of the casing 1 to the openings 24 and 25 by a part flared end.

 During the operation of the engine, the flanges 6 and 7 integral with the crankshaft 4 are caused to rotate about the axis of rotation of the crankshaft so that the cutouts 16 and 17 located on their lateral surface are placed during certain phases of the cycle of operation of the motor opposite the linings 26 and 27 and the openings 24 and 25 so as to ensure the communication of the interior volume of the pump housing 5 with the pipe 30.

 Referring to Figures 3, 4, 5 and 6, we will now describe the operation of an engine whose flanges laterally delimiting the pump housing of a cylinder have peripheral cutouts of shape and dimensions such that they allow control pneumatic injection into another engine cylinder.

 In FIGS. 3, 4, 5 and 6 on the one hand and in FIGS. 1 and 2 on the other hand, the corresponding elements bear the same references.

 However, the elements of the cylinder shown in the right-hand part of FIGS. 3, 4, 5 and 6 have corresponding marks presenting the exponent I (prime).

 The injection is carried out by connecting the channel 30 'of the second cylinder capable of being placed in communication with the interior volume of the pump housing 5' of this second cylinder, during the rotation of the flanges such as 6 ', with the pressurized fuel air injection pipe 14 of the first cylinder, via a connecting pipe.

 The lateral flanges such as 6 ′ of the pump casing 5 of the second cylinder have a cutout such as 16 ′ having a certain circumferential extension and a position such on the periphery of the flange 6 ′, depending on the arrangement of the connecting rod 3, that this cutout 16 'ensures the putting into ccmmunicatlon of the interior votume of the pump housing 5' with known, te .z1; and the fuel mixture injection pipe 14, at well-defined instants of the engine operating cycle.

The direction of rotation of the crankshaft 4 and the flanges 6 and 6 'has been represented by the arrows 31 and 31
In Figure 3. the piston 2 of the left cylinder or first cylinder is in its lowest position, after the expansion of the combustion gases in the cylinder chamber. The piston 2 'of the right cylinder or second cylinder begins to move downward, under the effect of the combustion and the expansion of the gases in the second cylinder. The flange 6' of the corresponding pump housing 5 ' moves in rotation so as to place the recess 16 'opposite the pipe 30'
In the next phase shown in FIG. 4, the piston 2 begins to rise inside the chamber of the first cylinder and the opening 16 ′ has reached opposite the line 30 ′ of the second pump housing. 5 '. The piston 2 'of the second cylinder is close to its lowest position, so that the air drawn into the pump housing 5' via the nozzle 9 'and the valve 10' is strongly compressed. This pressurized air is discharged into line 14 in which it is mixed with atomized fuel from injector 13.The mixture of pressurized air and atomized fuel is injected into the chamber of the first cylinder which has been previously drained combustion gases which it contained and filled with fresh air coming from the pump casing 5 via the openings such as 11.

 The means for controlling the injection of carburetted air into the cylinder therefore consists of the flange (s) such as 6 ′ of the pump housing 5 ′ of the second cylinder on the periphery of which have been provided recesses such as 16 ′ of which the position ensures an injection of the fuel mixture into the cylinder at the desired time of the engine operating cycle.

 In FIG. 5, a subsequent phase of the engine operating cycle has been shown, the piston 2 of the first cylinder having moved upwards so as to compress the mixture of fresh air and fuel air injected previously. in the cylinder. Simultaneously, the cutout 16 'has moved, so as to be outside the area where the line 30' is connected to the pump housing 5'.The fuel injection line remains under pressure to the extent that the internal volume of the pump housing 5 'was under pressure when the cutout 16' left the peripheral zone of the pump housing in which the pipe 30 'is located. The piston 2 ′ has started to move upwards so as to ensure the sweeping and filling with fresh air of the second cylinder into which a fuel mixture can be introduced via the line 14 ′ connected to the pump housing of a cylinder of the motor delimited by lateral flanges having cutouts such as the flange 6 '.

 In the embodiment shown in FIGS. 3, 4, 5 and 6, the cylinder 1 is supplied with a fuel mixture from the pump housing of a cylinder 1 ′ whose operating cycle has a delay of 1200, in that which concerns the rotation of the crankshaft, relative to the cylinder in which the injection is carried out.

In the same way, the injection into the line 14 ′ can be carried out and controlled from the pump housing of a cylinder whose operating cycle has a delay of 1200 with respect to the second cylinder 1 ′
FIG. 6 shows a phase corresponding to the end of the downward movement of the piston 2 inside the first cylinder, under the effect of the combustion and the expansion of the gases previously compressed in the phase represented on Figure 5 and whose ignition was provided by the spark plug 15.

 The cutout 16 ′ of the flange 6 ′ of the pump casing of the second cylinder is then in its high position, in line with the chamber of the second cylinder. The piston 2 'is in its high position and ensures the compression of the gases formed by the mixture of fresh air and carburetted air. The ignition of the fuel mixture by the spark plug 15 'ensures the downward movement of the piston 2' and the rotation of the flange 6 'so as to rotate the cutout 16' to return to its position corresponding to the phase shown in figure 3.

 It is obvious that the operation of the engine, with regard to the supply of crankcase pumps to atmospheric air via the nozzles 9 and 9 'of the valves 10 and 10', is identical to the operation of two-stroke engines of the conventional type. .

 Likewise, the supply of fresh air to the cylinders and the evacuation of the burnt gases are carried out in a manner equivalent to that for engines according to the prior art.

 In Figure 7, there is shown a first alternative embodiment of an engine comprising a first cylinder whose housing 41 defines a chamber in which moves a piston 42 and a pump housing 45 whose internal volume communicates with the lower part of the chamber in which the piston 42 moves. The engine comprises a second cylinder whose casing 41 'delimits a chamber in which a piston 42' and a pump casing 45 'communicates with the lower part of the chamber and is delimited laterally by flanges such as 46 'fixed on the crankshaft 44 of the engine so as to rotate inside the pump housing 45', in the direction of the arrow 51 '.

 The pump casings of the cylinders comprise, in a known manner, a nozzle 49 and a valve 50 (49 ′ and 50 ′ for the second cylinder) making it possible to supply the corresponding pump crankcase 45 or 45 ′ with atmospheric air.

 The flange 46 'of the pump housing 45' of the second cylinder has a cutout 56 'which can be produced, in the same way as the cutouts 16 and 17 shown in FIGS. 1 and 2 by machining or bevel forming the peripheral surface of the flange 46 'formed in the form of a disc or a cylinder of low height.

 The pump housing 45 'further comprises two pipes 47' and 48 'arranged in a similar manner to the pipe 30 shown in Figure 2 so as to be placed in communication with the interior volume of the pump housing 45', in certain positions of the flange 46 'and of the cutout 56'.

 The first cylinder has a fuel injection pipe 54 opening out through the wall of the casing 41 into the chamber of the cylinder proper and on which is placed bypass a carburetor 55 provided with a valve 58 making it possible to isolate or put in communication the carburetor 55 with the fuel air injection pipe 54.

 The fuel air injection pipe 54 is connected via connection pipes 59 and 60, both to the pipes 47 'and 48' capable of being placed in communication with the internal volume of the pump housing. 45 '. during certain phases of engine operation.

 Shortly before the phase shown in FIG. 7, the air contained in the pump housing 45 'is under high pressure, the piston 42' going towards its low position.

 The cutout 56 'of the flange dd' is placed in front of the line 47 'so that pressurized air is sent into the line 54 and injects fuel previously introduced into the line 54 by the carburetor 55 .

 Conversely, when the piston 42 'arrives in the vicinity of its high position, the pressure in the pump housing 45' being low, the cutting 56 'of the flange 46' comes to be placed opposite the pipe 48 'so re to create a depression in the pipe 59.. and through it, in line 54, which causes the opening of valve 58 and the introduction into line 54, of fuel coming from carburetor 55.

The depression caused in the pipe 54 by the passage of a cutout 56 'at the pipe 48', for a time t makes it possible to ensure the introduction of fuel into the pipe 54.

I1 would also be possible to produce the vacuum in the pipe 54 by cutting in one of the lateral flanges of the pump crankcase 45 'and the injection of pressurized air ensuring the control of the introduction of fuel into the cylinder. , by a cut in the second flange of the pump crankcase 45 ', the cutouts of the flanges of the pump crankcase 45' cooperating with pipes placed in angular positions similar to those of pipes 47 'and 48'
FIG. 8 shows two cylinders of a two-stroke engine in which the control of the injection of the fuel mixture into a cylinder of the engine can be ensured either by coinciding a cut in a lateral flange of the pump housing of another cylinder placed in coincidence with an opening in the wall of this pump housing, either by a valve controlled by a cam, or even by these two means simultaneously.

 Likewise, the injection can be stopped, in the case of the device shown in FIG. 8, either by the first means described, that is to say a cutout made on the lateral surface of a flange of the pump housing cooperating with an opening, either by a valve controlled by a cam, or by these two means simultaneously.

 FIG. 8 schematically represents two cylinders of a two-stroke engine according to the invention and according to a second variant embodiment.

 The two cylinders have casings 61 and 61 'delimiting in their upper part a combustion chamber in which a piston 62 (or 62') moves.

The lower part of the cylinder chamber communicates with a pump housing 65 (or 65 ′), the pump casings of the engine cylinders being traversed, in their axial direction, by the crankshaft 64 of the engine connected by means of connecting rods respectively 63 and 63 'with pistons 62 and 62'
The pump housings 65 and 65 'have an atmospheric air inlet nozzle 69 (or 6D') on which a valve 70 (or 70 ') is placed.

 In addition, the pump casings 65 and 65 'are connected to the chamber of the corresponding cylinder by means of conduits such as 67 and 67' opening into the cylinder by lateral openings such as the opening 71.

Each of the cylinders also includes in a slightly offset position relative to the fresh air intake openings such as the openings 71, exhaust pipes for the burnt gases 72 (or 72 ′).
The internal volume of the pump housing 6Os is delimited laterally by flanges such as 66 ′ secured to the crankshaft 64 ensuring the rotation of these flanges in the direction of arrow 73.

 At least one of the flanges 66 'in the form of a disc or of a flattened cylinder has a lateral cutout such as 76'. On the other hand, the wall of the pump casing 65 'includes the opening for crossing a duct 68 whose position relative to the flange 66' allows the interior volume of the casing 65 'to be brought into communication with the duct 68, when the cutout 76 'of the flange 66' coincides with the opening of the pump housing 5 'into which the pipe 68 opens, during the rotation of the crankshaft 64 and of the flange 66' in the direction of the arrow 73.

 The pipe 68 opening into the pump housing 65 'is connected by a pipe to an injection pipe 74 into which opens an injector 75 ensuring the spraying of fuel at determined times, the injection pipe 74 being itself connected by means of an intake device 76 at the upper part of the chamber of the first cylinder delimited by the cylinder head of the engine.

 The intake device 76 consists of a chamber into which the pipe 74 opens and which is in communication with the interior volume of the combustion chamber of the first cylinder, through an opening which can be closed by a valve 77, the stem of which is integral with a bearing surface 78 at its end situated opposite the closure element of the opening putting the intake device 78 into communication with the cylinder chamber .

 A return spring 73 is interposed between the bearing surface 78 and the outer wall of the intake device 76.

 A cam 80 secured to a camshaft rotating in the direction indicated by the arrow 81 is also in contact with the bearing surface 78 of the valve 77 so as to ensure the opening of this valve 77 at a determined instant of the engine operating cycle.

 In FIGS. BA to 8E, the time intervals during which the opening of the pipe 68 opening into the pump housing 65 ′ is shown in line with the cutout 7 ′, the time intervals injection 74 of the first cylinder then being in communication with the interior volume of the pump housing 65 'of the second cylinder and the time intervals during which the valve 77 of the intake device 76 is open.

In Figures aA to 8E, there have been associated with the ends of the different line segments representing these time intervals, indications the meaning of which is given below
DI: start of injection,
FI: end of injection, 0E: opening of recess 68,
FE: closing of the recess 68,
OS: opening of valve 77, FS: closing of valve 77.

 In the case of FIG. BA, the opening of the valve 77 precedes the opening of the recess putting the duct 68 into communication with the pump housing 65 ′ and the closing of the valve is subsequent to the closing of the recess in the duct 68.

 In this case, the start of injection is controlled by the opening of the recess in the casing into which the conduit 68 opens and the end of injection is controlled by the closing of this recess.

 In the case of FIG. 3B, the opening of the recess and the opening of the valve are simultaneous and correspond to the start of injection.

 On the other hand, the closing of the valve is subsequent to the closing of the recess and the end of injection is controlled by the closing of the recess.

In the case of FIG. 8C, the opening of the valve 77 precedes the opening of the recess and the closing of the recess and of the valve are simultaneous
In this case, the start of injection is controlled by opening the recess and the end of injection by simultaneously closing the recess and the valve.

 In the case of FIG. BD, the opening of the valve precedes the opening of the recess and the closing of the recess is subsequent to the closing of the valve.

 In this case, the start of injection is controlled by the opening of the recess and the end of injection by the closure of the valve.

 In the case of FIG. BE, the opening of the recess precedes the opening of the valve and the closing of the valve is subsequent to the closing of the recess.

 In this case, the start of injection is controlled by opening the valve and the end of injection by closing the recess.

 It is thus seen that the device is very flexible and allows, depending on the amplitude of the cutout 76 'of the flange 66' of the second cylinder and according to the design and the adjustment of the cam eî, to control the start and the end of injection of the carburetted air into the first cylinder by means which can be chosen to obtain the best possible precision and optimal operation.

 In particular, the combination of the injection control means described and represented in FIG. 8 makes it possible to ensure satisfactory operation with much less severe conditions as regards the design and adjustment of the cams and cutouts, in the measure where either of the two control means can be used to determine the instant corresponding to the start or end of the injection into the cylinder.

 All the embodiments described so far, although using one or more flanges rotating in a pump housing, do not form part of the field of the invention which will be described below.

 FIG. 9 shows a device for controlling injection into a cylinder of a two-stroke engine generally designated by the reference 82.

 Such an injection device of the assisted automatic valve type can be associated with each of the cylinders of a two-stroke engine as shown in FIGS. 15 and 16.

 In FIGS. 15 and 16, it can be seen that the assisted automatic valve injection device 82 (or 82 ′) is fixed to the cylinder head of the engine at the level of the corresponding cylinder.

 As can be seen in FIG. 9 as well as in FIGS. 11 and 13 which represent injection devices with assisted valve identical in terms of their structure but different in functional terms, as will be explained below, the injection device 82 comprises an injection channel 84 machined in the cylinder head 83 and opening through an opening 85, in the interior volume of the cylinder. The channel 84 is connected to a pipe 87 into which the end of a fuel injector 88 opens.

 The valve 86 for closing the end of the channel 84 opening into the cylinder has a head coming to bear, in the valve closed position as shown in the figures, in the opening 85 constituting a valve seat. The stem of the valve 86 is connected at its end to a flexible membrane 89 fixed along its entire periphery and in leaktight manner, between two parts of the wall of a casing 90 of the injection means 82.

 Preferably, the casing 90 consists of an upper hollow half-casing 90a and a lower half-casing 90b connected together and at the periphery of the membrane 89 by means of external flanges constituting flanges of housing assembly 90.

 The upper part 90a of the casing 90 comprises a pipe 91 opening into its internal volume and the lower part 90b of the casing 90 which is tightly fixed on the cylinder head 83 above the opening 85 of the channel 84 has a duct 92 opening in its interior volume.

 A return spring 93 is interposed between the flexible membrane 89 or the end of the valve stem 86 and the surface of the cylinder head 83.

 An assisted control valve injection device as shown in FIG. 9 is known from the prior art and makes it possible to ensure the opening and closing control of the valve determining the start and the end of the injection. in the cylinder, by adjusting the differential pressure between the chambers 95a and 95b delimited in the casing 90 by the membrane 89.

 or ceià the pipes 91 and 92 can be connected to pressure-regulated gas supply devices making it possible to ensure the opening or closing of the valve 86 by differential pressure in the chambers 95a and 95b. As well as by differential pressure between the chamber 84 and the cylinder.

 According to the invention, in the case of a two-stroke engine with several cylinders and with pneumatic injection, the control pressure in at least one of the chambers 95a and 95b is produced by placing this chamber in communication with the volume inside the pump housing of one of the engine cylinders.

In FIG. 10, as a function of the angle of rotation of the crankshaft of a two-stroke three-cylinder engine, the variations in the pressure in the chamber of a first cylinder of the engine 100 are shown in solid lines3 , the variations of the pressure PC1 in the pump housing of the first cylinder (curve 101 in dashed lines), the variations of the pressure PC2 in the pump housing of a second cylinder of the engine whose operating cycle is offset by 1200 by rotation of the crankshaft relative to the first curved cylinder 102 in phantom) and the control pressure P1 of the assisted automatic valve ensuring injection into the first turbo cylinder 10 ;; with dots}
The control pressure <ie the valve is applied in the chamber 95a, this chamber being connected via the pipe 91 to a duct which can be placed in communication or, on the contrary, isolated from the interior volume of the pump housing of the second cylinder, using one or more flanges fixed on the engine crankshaft at the pump casing and having a peripheral cutout, for example as shown in FIGS. 1 and 2.

 The peripheral cutting in the side flange (s) of the pump housing is such that the communication with the pump housing is interrupted between 40 and 1900, if we consider the rotation of the crankshaft and that, on the contrary, this communication is ensured , during the rest of the cycle, this part of the cycle during which the communication with the pump casing of the second cylinder is ensured being shown diagrammatically by the straight line segment in two parts 104 represented in FIG. 10.

The origin of segment 104 is located at a point 105 corresponding to a rotation of 190 of the crankshaft and the end of segment 104 at a point 106 corresponding to a rotation of 400 of the crankshaft.

 In order to inject fuel air into the first cylinder at the desired time, the pipe 87 connected to the channel 84 at one of its ends is connected, at its other end, to the pipe opening into the casing -pump of the second cylinder whose communication or isolation from the internal volume of this pump housing is ensured by one or two flanges comprising a lateral cutout.

 As can be seen in FIG. 1t, between 40 and 1900 of the rotation of the crankshaft, the control pressure P1 in the chamber 95a (curve 103) is maintained at a constant and low level corresponding to the minimum pressure in the pump casing of the second cylinder during the cycle. This pressure is applied in the chamber 95a and in the line 87, insofar as the opening of the pipe opening into the pump housing has been closed by the flange (s) of this pump housing at the time when the pressure in the pump housing was at its minimum value.

When the initial part of the cutout provided in the flange (s) of the pump housing of the second cylinder reaches the level of the opening of the pump housing into which the pipe opens, the pressure
PC2 prevailing in the pump housing is transmitted to the chamber 95a by ia pipe 1, the control pressure P1 therefore changes from its constant and low value to the value PC2 in the pump housing t second cylinder at an instant corresponding to the rotation 190 of the crankshaft washhouse figure 10)
The pressure in the pump housing PC2 is then greater than the pressure in the chamber of the first curved cylinder 100i.

 The chamber 95b of the injection device being vented via the line 92, the establishment of the pressure PC2 in the chamber 95a participates in the opening of the valve ae and the injection of air carburetted in the chamber of the first cylinder, the line 87 also being connected to the conduit opening into the pump housing of the second cylinder and being supplied with air at the pressure PC2. Fuel is injected by the injector 88 into the stream of pressurized air sent to the cylinder.

 The control pressure P1 in the chamber 95a is maintained at the value PC2 throughout the duration of the rotation of the crankshaft between the points 105 and 106 delimiting the segment 104 corresponding to the time interval during which the conduit opening into the casing- second cylinder pump is open.

 The pressure PC2 remains higher than the pressure in the chamber of the first cylinder (curve 100 Y, until the pressure in the pump housing reaches its maximum, the corresponding piston being in its low position inside the chamber of the second cylinder. From this position corresponding substantially to a rotation of the crankshaft of 270, the pressure PC2 decreases very quickly and becomes lower than the pressure in the chamber of the first cylinder. The curves 102 and 103 representative of the pressure PC2 and therefore of the control pressure P1 intersect the curve 100 and pass below this curve. The valve 86 closes, which corresponds to the end of the injection period I indicated in the figure lij. This injection period begins at 1900 crankshaft (opening of the conduit opening into the pump casing of the second cylinder) and ends when the pressure PC2 becomes lower than the pressure in the chamber of the first cylinder.

 According to the invention, by using one or more flanges rotating inside the pump housing and comprising a peripheral cutout, an injection of carburetted air is thus perfectly adjusted inside the cylinder.

 However, in the embodiment shown in FIGS. 9 and 10, only the start of the injection is assisted and controlled by the flange or flanges rotating in the pump housing of the second cylinder.

 Referring to Figures 11 and 12 and Figures 15 and 16, we will now describe an embodiment of an assisted valve injection device in which the assistance of the valve is carried out both at the start and '' at the end of the injection, by the rotation of the flange in the pump housing of the second cylinder.

 In general, the injection device 82 shown in FIG. 11 has the same elements (designated by the same reperdes) as the assisted automatic valve injection device shown in FIG. 9. However, the chambers 95a and 95b receive each a control pressure (respectively P1 and P2) while in the case of the device shown in FIG. 9, the chamber 95b was vented through the conduit 92.

 The device 82 shown in FIG. 11 and also visible in FIGS. 15 and 16 is fixed, like the device shown in FIG. I, on the upper part of the cylinder head 83 of the corresponding cylinder in which the injection channel r is machined. emerging through an opening 85 in the cylinder chamber.

 Referring to FIGS. 15 and 16, it can be seen that the assisted valve injection device 82 is fixed to the upper part of the cylinder head of a first cylinder 111 comprising a combustion chamber 113 in which a communicating piston 112 moves at its lower part with a pump housing 115 delimited laterally by flanges such as 116 fixed on the crankshaft 114 axially passing through the pump housing 115.

 The pump housing 115 comprises, in a conventional manner, an air intake nozzle 119 on which a valve 120 is placed.

 The fresh air introduced into the casing 115 and compressed by the piston 112 is injected into the combustion chamber 113 of the cylinder 111, by means of transfer conduits such as 121 opening into the cylinder chamber through openings 12t2. The burnt gases are evacuated from the chamber 113 by a pipe 123.

The second cylinder 111 ′ which is shown on the right-hand side of FIGS. 15 and 16 has a structure identical to cylinder 111 and has similar elements which have been designated by the same reference mark assigned by the exhibitor
On the other hand, the pump casing 115 is fixed conduits 125, 126 and 127 comprising an opening opening into the internal volume of the pump casing 115. The conduits 125 and 126 are placed so that their opening opening into the casing pump is located opposite one of the flanges delimiting the pump casing 115, such as the flange LI.

 revenge. the conduit 127 opens through its opening in the internal volume of the pump housing 115, between the flanges laterally delimiting this pump housing.

 the pump casing 115 ′ of the second cylinder 111 ′ has three conduits 125 ′, 126 ′ and 107 ′ opening into the interior volume of the pump crankcase 115 ′ and arranged in the same manner as the conduits 125, 126 and 127, respectively.

 To implement an assisted pneumatic injection both at the start of the injection and at the end of the injection, as will be explained with reference to FIG. 12, the chamber 95a of the injection device 82 of the cylinder 111 is connected by a connecting pipe to the pipe 125. The chamber 95b is connected to the pipe 126 'of the pump housing 115' of the second cylinder 111 'and the injection pipe 87 of the device 82 opening into the injection channel o4 from the cylinder head 111 to the duct 127 'of the pump housing 115'.

 In addition, the flange 115 of the pump housing 115 has a recess 130 of large angular amplitude on its periphery. The flange 116 'of the pump housing 115' has a recess 131 whose angular amplitude is substantially less than that of the recess 130.

FIGS. 15 and 16 also show the direction of rotation of the crankshaft 114, by the arrows 132,
FIG. 15 represents the position of the elements of the two cylinders 111 and 111 ′ at the start of injection and FIG. 16 represents the position of these elements at the end of injection, this as regards the cylinder 111.

 We will now refer to FIG. 12 to explain the operation of the injection device shown in FIG. 11 and in FIGS. 15 and 16.

 The second cylinder 111 'has an operating cycle which is 1200 by the rotation of the crankshaft behind the operating cycle of cylinder 111.

 In Figure 12, there is shown in the form of a curve in solid lines 135, the pressure in the combustion chamber 113 of the first cylinder 111 and in the form of curves 136 and 137 constituted by dashes, the pressures PCl and PC2 in pump housings 115 and 11S 'respectively depending on the angle of rotation of the crankshaft.

 FIG. 12 also shows in the form of a dotted curve 138, the control pressure P1 in the chamber 95a of the injection device 82 and in the form of a curve 139 in dashed lines, the pressure of P2 command in the chamber 95b of the injection device 82.

 Also shown, in the form of a line segment 140 in two parts, the time interval or rotation of the crankshaft during which the pipe 125 of the pump housing 115 is in communication with the internal volume of the pump housing , the recess 130 being, during this interval, in accordance with the opening of the conduit 125 opening into the pump casing. During this time interval, the pressure PCl of the air in the pump casing 115 is transmitted to the chamber 95a of the injection device a2, by the corresponding connection pipe.

 The time interval or rotation of the crankshaft during which the line 126 of the pump casing 115 ′ is placed in communication with the internal volume of this pump casing, the recess 131 has been represented in the form of a straight line segment 141 of the flange 116 'being in coincidence with the opening 12d' opening into the internal volume of the pump housing 115 '.

During this time interval, the chamber 95b of the injection device 82 is subjected to the pressure PCG of the air contained in the pump housing 1L5 "
The injection channel 84 of the device 82 is constantly in communication with the interior volume of the casing 11S '.

 The angular amplitude of the recess 130 and the arrangement of the flange 116 relative to the crankshaft 114 are such that the opening of the conduit 125 via the recess 130 occurs between 270 of the rotation of the crankshaft and 1500 of this rotation during the next cycle (segment 140).

 When the duct 125 is closed (for 1500 crankshaft), the pressure PCl in the pump housing 115 is close to its maximum, the piston 112 being in its low position. The air pressure P1 in the chamber 95a (upper part of the curve 138) is therefore maintained at a high level between 1500 and 2700 crankshaft.

 The recess 131 and the position of the flange 116 'are such that the closing of the line 126' occurs for a value of the angle of rotation of the crankshaft of 2700.

 The cycle of the cylinder 111 'being lagging behind 1200 on the cycle of the cylinder 111, the pressure PC2 in the pump housing 115' is at its maximum when the duct lys6 'is closed. The pressure P2 in the chamber 95b of the device 82 is therefore maintained at a constant and high value equal to the maximum value of the pressure PCl, of 270 crankshaft, until the opening of the conduit 126 'through the recess 131, for 1900 crankshaft of the following cycle (upper part of curve 139).

 From 1900 to '' 7t) crankshaft, the pressure in your chamber 95b corresponds to the pressure Pt interval represented by the segment l4l.

 It follows that the curves 138 and 139 representative of P1 and P respectively have parts merged with the curves 186 and 137 respectively, the horizontal segments corresponding to the upper level of pressure in the pump casings and the vertical junction parts corresponding to the pressure drop in the control chambers 95a and at the time of opening of the conduits 125 and 126 'respectively.

As can be seen in FIG. 12 in which the injection interval I has been shown, the start of injection is controlled by opening the duct 126 ′ of the pump housing 115 ′ to 1900 crankshaft, by coincidence of the recess 131 with the opening of the conduit 126 ', the pressure in the chamber 9b then passing to the value PC2 of the pressure in the pump housing 115'. This pressure is then significantly lower than the maximum pressure in the pump housing, the piston 112 'being in an intermediate position between the top dead center and the bottom dead center, as can be seen in FIG. 15. The pressure in the chamber 95a is maintained at the maximum pressure value
PC1 in the casing 115, the conduit 125 being closed at the start of the injection, as shown in FIG. 15.

 As a result, the pressure PA in the chamber 95a is much higher than the pressure PB in the chamber 95b, which assists the opening of the valve 86 by differential pressure at the start of injection.

The injection of carburetted air via the channel 84 is ensured by the fact that the channel 84 is connected to the interior volume of the pump housing 115 ′ and that the pressure PS in the injection channel 84 (curve L37) is constantly balanced with the PC pressure in the casing ilj
It should be noted that before the start of the injection, the pressures PA and PB in the chambers 95a and 95b are identical. The valve 86 is then held in the closed position by the spring 93, the pressure
PS in the injection pipe 84 then being slightly higher than the pressure in the cylinder 111 (curve 137 above the curve 135).

 During 1 injection. the difference of the pressures in the chambers 95a and 95b, that is to say the difference between the pressures PA and PB or P1 and P2 decreases constantly to become zero for 2700 crankshaft, at the time of the opening of the conduit 125 and the closing of the conduit 126 '.

 The end of the injection is controlled by the opening of the conduit 125 which produces a drop in the pressure PI from its maximum value to a low value.

The pressure PB then becomes much higher than the pressure PA, which causes rapid and assisted closing of the valve 86 to 270V crankshaft.

 FIG. 12 shows the zone in which the pressure PA is greater than the pressure PB, this zone corresponding to the injection and the zone (in two parts) in which the pressure PB is greater than the pressure PA, the valve 86 being maintained in the closed position by differential pressure.

 Between these two zones, the pressures PA and PB are identical and, as indicated, the valve 86 is maintained in the closed position by the spring 93 on the one hand and by the high cylindrical pressure due to the compression of the gases on the other go.

 In FIG. 16, the cylinders 111 and 11 ′ are shown at the end of injection, that is to say at the time of opening of the duct 125 thanks to the recess 130. This phase also corresponds to closing the conduit 126 '.

 It is quite obvious that the ducts 1S 'and 127 of the first cylinder 111 are connected respectively to the chamber 35a of an injection device similar to the device 82 or 8S' of a cylinder in advance of 1200 crankshaft on the cylinder 111 and to the injection channel of this cylinder respectively.

 The duct 126 has an opening opening into the pump casing 115, opposite the second flange of this tenon pump casing visible in FIGS. 15 and 16) comprising a recess having an appropriate amplitude and arrangement.

 In Figures 13 and 14, there is shown an alternative embodiment of an injection device with assisted valve opening and closing.

 The corresponding device is substantially identical to the device described with reference to Figures 11, 12, 15 and 16 and its operation is substantially identical.

 However. as can be seen on curve 137 ′ in FIG. 14 representing the pressure PS in the injection channel 84, this pressure PS nwest more constantly identical to the pressure PCS in the crankcase of a cylinder lagging behind 1200 crankshaft relative to the cylinder into which the injection is carried out.

 This pressure PS has variations identical to the control pressure PI of the embodiment shown in FIG. 10 (curve 103), during the engine operating cycle. The injection pipe 87 and the channel 84 are connected to the pump housing of the cylinder lagging 1,200 crankshaft relative to the cylinder in which the injection is carried out by means of a pipe located at the level of a flange having an obviously ensuring the opening of the conduit opening into the pump housing, between 1900 and 40 crankshaft.

 Between 40 and 1900 crankshaft, the pressure ES is maintained at a low value which corresponds to the pressure PC2 in the pump housing of the second cylinder, at the time of closing of the pipe connected to the injection pipe 87. This extremely low pressure is generally lower than atmospheric pressure, so that this pressure helps to keep the valve in the closed position before the start of injection, while the control pressures in chambers 95a and 95b are equal.

The opening of the pipe of the second pump housing connected to the injection pipe 87 to 1900 crankshaft, by coinciding a recess of a flange with the opening of the pipe of the pump housing makes it possible to supply the pipe d injection 87 and the air channel 84 of the pump crankcase at pressure PC2. At the same time, the pressure Pi drops and becomes much lower than the pressure
P2, which causes the valve 86 to open.

 In all cases, the injection device with assisted automatic control valve enables perfectly controlled injection to be carried out at a perfectly determined instant in the engine cylinder cycle.

It is obvious that the invention is not limited to the embodiments which have been described.
We can consider any embodiment of the flanges rotatably mounted in the pump casings, these flanges may include recesses or cutouts made in the peripheral part of the flange, by machining or forming or by other methods.
In the case of the use of an assisted automatic valve injection device, the control pressure can be established in at least one of the chambers of the device, by connecting this chamber to an opening in the casing of a cylinder overdue by 1200 crankshaft on the cylinder in which the injection is carried out opening out at a point on the cylinder covered during the cycle by the piston skirt in which an opening is provided, as described in the French patent application for FRENCH INSTITUTE OF PETROLEUM 8908855. This arrangement makes it possible to adjust the pressure in the control chamber to a desirable value, during engine operation, without having to use a flange rotatably mounted in a pump housing and having a cutout on its peripheral edge.

 In the case of the use of an automatic assisted valve, the fuel air supply pipe can be connected to a source of air under pressure different from the pump housing of one of the cylinders.

 Finally, the invention can be applied advantageously, for the design of any two-stroke engine with several cylinders in which a pneumatic fuel injection is carried out.

Claims (7)

 1.- Two-stroke engine comprising at least first and second cylinders (111, lll'i in each of which a piston moves and one end of which communicates with a pump housing (115, 115 'ì crossed by the engine crankshaft (114) in an axial direction, connecting means between the movable pistons in the first and second cylinders connected to the crankshaft so that there is an angular offset between the cycles of the first and second cylinders, a fuel air supply line (87) connected to each of the cylinders (111, 111 ') via an injection control means (82, 82') comprising a shut-off valve (86) of a cylinder supply orifice, the rod of which is connected to a flexible membrane (89) constituting a sealed separation wall between two chambers (95a, 95b> of the injection control means and a return spring (93) of the valve in closed position, characterized by the fact that at least one of the two chambers (95a, 95b) of the injection control means of at least one of the two cylinders (111, 111 ') is connected by a pipe (91, 92) to a closable opening communicating with the internal volume of one of the pump casings t11, 115 ') of one of the two cylinders (111, 111') and that at least one flange (116, 116 ') of generally cylindrical shape fixed on the crankshaft (11) at the pump casing (115, 115 ') constitutes a means for selectively closing the opening by means of a cutout (131, 1325 in its peri-risk part  2.- Engine according to claim 1, characterized in that a first chamber (95a) of the injection control means is connected to the pump housing (115 ') of the second cylinder and that the second chamber (95b} is vented, the fuel air supply line l87l of the first cylinder being connected to the pump housing 11l ') of the second cylinder.  3.- Motor according to claim 2 characterized in that the fuel air supply pipe (87j is connected to the pump housing 115'3 of the second cylinder by a non-closable opening.  4.- Engine according to claim 2, characterized in that the pipe (87) for supplying carburetted air is connected to the pump housing (115 ') of the second cylinder, by means of an opening which can be closed by a flange (116 ') integral with the crankshaft (114) of the engine.  5.- Engine according to claim 1, characterized in that a first chamber i95a) of the injection control device (82) is connected to the pump housing (115) of the first cylinder by a closable opening at determined times by a flange (116), that the second chamber (95b) of the inspection device (82) is connected to the pump housing (115 ') of the second cylinder (111') via an opening closable by a flange i116'1 and that the fuel air injection pipe (87) is placed in communication with the interior volume of the pump housing (115 ') of the second cylinder.  6.- Motor according to claim 5. characterized in that the pipe (87) for supplying carburetted air is placed in communication with the pump housing (115 ') of the second cylinder, permanently, by a non-opening closable.  7.- Motor according to claim 5, characterized in that the pipe (87) for supplying carburetted air to the first cylinder is placed in communication with the internal volume of the pump housing (115 ') of the second cylinder by an opening closable at determined times, by a flange (116