EP0435730B1 - Two-stroke engine with controlled pneumatic injection - Google Patents

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 housing. When the corresponding cylinder openings are released by the piston, fresh gases are introduced into the cylinder through the transfer conduits and openings and produce a sweeping of fresh gases intended to replace the burnt gases which are generally evacuated by exhaust openings. arranged 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 a multi-cylinder engine, to ensure a pneumatic injection of fuel into a first cylinder by using the pressure of the fresh gases inside the pump housing of a second cylinder whose piston moves with an angular offset with respect to the piston of the first cylinder, if we consider the rotation of the crankshaft crossing in the axial direction all of the engine crankcases.

Generally, the pressurized air used for injection into a cylinder comes from the pump housing of a second cylinder whose delay with respect to the rotation of the crankshaft can be 120 °, in the case of an engine with three, six, ... three n cylinders or 90 °, in the case of an engine with four, eight, ... four n cylinders relative to the cylinder in which the injection is carried out.

Devices for controlling the injection of the fuel mixture have also been proposed, and in particular devices for controlling the start of introduction of this fuel mixture at the end of the sweeping by the fresh air of the engine cylinder.

These devices can be constituted by an automatic valve, a controlled valve, a rotating plug or by an opening in the second cylinder from which the injection is carried out, cooperating with the skirt of the corresponding piston.

Generally, no injection control or command is carried out directly at the outlet of the pump housing, at an opening of this pump housing to which the connecting pipe is connected to the first cylinder.

It has already been proposed, for example in document EP-A1-0,296,969, a two-stroke engine comprising at least a first cylinder in which a piston moves and a second cylinder, one of the ends of which communicates with a casing -pump crossed by the crankshaft of the engine in an axial direction comprising an air intake means in the pump housing, at least one connecting pipe between the pump housing of the second cylinder and the combustion chamber of the first cylinder, means for supplying fuel to at least one of the connecting pipes and injection control means for isolating or connecting the pump casing of the second cylinder and the combustion chamber of the first cylinder , and means of connection between the movable pistons in the first and second cylinders linked to the crankshafts, so that there is an angular offset between the cycles of the first and second cylinders.

The prior art has also already proposed, for example in document FR-1,165,071, to place a rotary distributor in the pump housing of a two-stroke engine. This element is intended to control the admission of carburetted air into the pump housing.

The invention relates to an engine of the aforementioned type, this engine further comprising injection control means, at the pump housing of the second cylinder ensuring an injection perfectly adjusted with respect to the engine operating cycle.

To this end, the injection control means according to the invention comprise at least one substantially cylindrical flange rigidly fixed on the axis of the crankshaft, inside the pump housing of the second cylinder having at least one recess in its peripheral part so as to achieve the insulation and / or the communication between the combustion chamber of the first cylinder and the crankcase of the second cylinder at determined times of the engine operating cycle under the effect of rotation of the crankshaft. The injection control means provide in particular a discharge of the pressurized air present in the pump housing of the second cylinder.

Without departing from the scope of the invention, the injection control means further comprise an automatic assisted valve, the rod of which is connected to a flexible membrane separating two chambers in leaktight manner, at least one of which is connected by a conduit to a closable opening communicating with the interior volume of one of the pump casings of the first or second cylinder.

In order to clearly understand the invention, we will now describe, by way of nonlimiting examples, with reference to the appended 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 of the piston corresponding.

FIG. 2 is a sectional view along II of FIG. 1.

Figures 3, 4, 5 and 6 are schematic views of two cylinders of a two-stroke engine according to the invention and according to a first embodiment, during four successive phases of the engine operating cycle.

Figure 7 is a schematic view of two cylinders of a two-stroke engine according to the invention and according to a second embodiment.

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

Figures 8A, 8B, 8C, 8D and 8E 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 11 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.

Figure 14 is a diagram showing the control pressures of the power assisted valve shown in Figure 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 implementing an automatic assisted valve according to FIG. 11, during two successive phases of the engine operating cycle.

In Figure 1, we see a part of the wall of the housing 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 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 6 and 7. The chamber 5 constituting the pump casing associated with the cylinder communicates with the lower part of the cylinder combustion chamber.

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 (or 5') into which opens the lower part of the cylinder itself.

The pump housing 5 (or 5 ′) has an air inlet opening or adjustment 9 on which is interposed a valve 10 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 is likely to 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 5 of each of the cylinders communicates via at least one external conduit and an opening such as 11 with the chamber of the cylinder. An exhaust pipe 12 makes it possible to evacuate burnt gases before their replacement by fresh air coming 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 a pressurized air injection pipe 14 into which a fuel injector 13 opens.

The mixture of pressurized air and fuel is injected at a specific time inside the cylinder, mixed with the fresh air introduced into the cylinder and then compressed, as shown in the right part of Figure 3. A candle 15 fixed in the cylinder head attached to the casing 1 at its upper part ensures the ignition and combustion of the mixture which causes the descent of the piston in the direction of the pump casing.

According to the invention, as shown in FIGS. 1 and 2, the flanges 6 and 7 have recesses or cutouts respectively 16 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 20 and 21 respectively of sheet metal, so as to have a cylindrical shape and to constitute a disc ensuring the closing of the pump casing 5 on one of its lateral sides, inside the casing 1. The fairing can be replaced by an insert of low density.

Beveled recesses 16 and 17 are 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 parts machined at a bevel 16 and 17 to make cuts in the lateral surface of the flanges 6 and 7 intended to put the interior volume of the pump casings 5 into communication with one or more openings opening out 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 lining 26, 27 in the form of a portion of 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 comprising the bevelled parts 16 and 17 is placed facing the openings of the linings 26 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 housing 5 is placed in communication with the openings 24 and 25 and through them, with a pipe 30 connected outside the wall of the housing 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 casing 5 with the pipe 30.

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

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 '(prime).

The injection is implemented 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 injection line of pressurized carburetted air 14 of the first cylinder, by means of a connecting pipe.

The lateral flanges such as 6 ′ of the pump housing 5 ′ of the second cylinder include 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 communication of the interior volume of the pump housing 5 ′ with the line 30 ′ 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 FIG. 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' rotates so as to come and 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 is strongly compressed. This pressurized air is discharged into the line 14 in which it is mixed with pulverized fuel coming from the injector 13. The mixture of pressurized air and pulverized fuel is injected into the chamber of the first cylinder which has been previously drained of the combustion gases which it contained and filled with fresh air from the pump housing 5 through the openings such as 11.

According to the invention, 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 recesses have been machined. such as 16 ', the position of which ensures injection of the fuel mixture into the cylinder at the desired time in 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 zone where the pipe 30' is located connected to the pump housing 5 '. The fuel injection line remains under pressure insofar as 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 120 °, in as regards the rotation of the crankshaft, relative to the cylinder in which the injection is carried out. In the same way, injection into line 14 ′ can be carried out and controlled from the pump housing of a cylinder whose cycle of operation has a delay of 120 ° with respect to the second cylinder 1 '.

In FIG. 6, a phase has been represented 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 housing of the second cylinder is then in its high position, in the extension of 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 according to the invention, with regard to the supply of crankcases with atmospheric air via the nozzles 9 and 9 'of the valves 10 and 10', is identical to the operation of the classic two-stroke engines.

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

In Figure 7, there is shown a first alternative embodiment of an engine according to the invention 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 'communicating with the lower part of the chamber and 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 housing 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 Figures 1 and 2, by machining or beveling the surface peripheral of the flange 46 ′ constituted 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 angles of the flange 46 'and of the cutout 56'.

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

The fuel air injection pipe 54 is connected via connecting 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 Figure 7, the air contained in the pump housing 45 'is under high pressure, the piston 42' going to its low position.

The cutout 56 'of the flange 46' is placed opposite 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 cutout 56 'of the flange 46' comes to be placed opposite the pipe 48 'so to create a vacuum in the pipe 59, and through it, in the pipe 54, which causes the opening of the valve 58 and the introduction into the pipe 54, of fuel coming from the carburetor 55. The vacuum caused in the line 54 by passing the cutout 56 ′ at the level of line 48 ′, for a time t makes it possible to ensure the introduction of fuel into line 54.

It would also be possible to produce the vacuum in the pipe 54 by cutting in one of the lateral flanges of the pump housing 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 casing 45 ', the cutouts of the flanges of the pump crank 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 placing a cut in a side flange coincident with 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.

Similarly, 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 'to pistons 62 and 62'.

The pump casings 65 and 65 ′ have an atmospheric air inlet nozzle 69 (or 69 ′) on which a valve 70 (or 70 ′) is placed.

In addition, the pump housings 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 comprises, in a position slightly offset with respect 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 65 '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 housing 65 'has an opening into which a conduit 68 opens, the position of which relative to the flange 66' allows the interior volume of the housing 65 'to be brought into communication with the conduit 68, when the cutout 76 'of the flange 66' coincides with the opening of the pump housing 65 '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 in 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 to the upper part of the chamber of the first cylinder delimited by the engine cylinder head.

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, by means of an opening which can be closed by a valve. 77, the rod of which is integral with a bearing surface 78 at its end situated opposite the closure element of the opening putting the intake device 76 into communication with the cylinder chamber.

A return spring 79 is interposed between the bearing surface 78 and the outer wall of the intake device 76.

A cam 80 integral with 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. 8A and 8B, the time intervals during which the opening of the pipe 68 opening into the pump casing 65 ′ is shown in line with the cutout 76 ′, 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 FIGS. 8A 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,
OE: opening of the recess 68,
FE: closing of the recess 68,
OS: opening of valve 77,
FS: valve 77 closed.

In the case of FIG. 8A, the opening of the valve 77 precedes the opening of the recess putting the conduit 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 housing into which the conduit 68 opens and the end of injection is controlled by the closing of this recess.

In the case of FIG. 8B, 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. 8D, 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. 8E, 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 the recess.

We see 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 adjustment of the cam 81, 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 shown 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.

FIG. 9 shows a device for controlling injection into a cylinder of a two-stroke engine generally designated by reference numeral 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 assisted valve injection devices which are identical in terms of their structure, but different in functional terms, as will be explained below, the device injection 82 comprises an injection channel 84 machined in the cylinder head 83 and opening, through an opening 85, into 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 sealingly, 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 pipe 92 opening into 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 makes it possible to control the opening and closing of the valve determining the start and end of the injection into the cylinder, by adjusting the differential pressure between the chambers 95a and 95b delimited in the casing 90 by the membrane 89. For this, the pipes 91 and 92 can be connected to gas supply devices with regulated pressure making it possible to ensure opening or closing of the valve 86 by differential pressure in the chambers 95a and 95b, as well as by differential pressure between the channel 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 Figure 10, there is shown, depending on the angle of rotation of the crankshaft of a two-stroke three-cylinder engine, the variations of the pressure in the chamber of a first cylinder of the engine (curve 100 in solid lines), the variations of the pressure PC1 in the crankcase of the first cylinder (curve 101 in dashed lines), the variations in pressure PC2 in the pump housing of a second cylinder of the engine whose operating cycle is offset by 120 ° of rotation of the crankshaft relative to the first cylinder (curve 102 in dashed lines) and the control pressure P1 of the assisted automatic valve ensuring injection into the first cylinder (curve 103 in dotted lines).

The control pressure of the valve is applied in the chamber 95a, this chamber being connected via the pipe 91 to a conduit which can be placed in communication or, on the contrary, isolated from the interior volume of the pump housing of the second cylinder, in using one or more flanges fixed on the engine crankshaft at the pump housing 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 190 °, 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 segment in two parts 104 represented in FIG. 10. The origin of the segment 104 is located at a point 105 corresponding to a rotation of 190 ° of the crankshaft and the end of the segment 104 at a point 106 corresponding to a rotation of 40 ° 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 including the communication or insulation with respect to the internal volume of this pump housing is provided by one or two flanges having a lateral cutout.

As can be seen in FIG. 10, between 40 ° and 190 ° 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 crankcase -pump of the second cylinder during the cycle. This pressure is applied in the chamber 95a and in the pipe 87, insofar as the opening of the pipe opening into the pump casing has been closed by the flange or flanges of this pump casing 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 chamber 95a via line 91, the control pressure P1 therefore passes from its constant and low value to the value PC2 in the pump housing of the second cylinder at an instant corresponding to the 190 ° rotation of the crankshaft (see FIG. 10 ).

The pressure in the pump housing PC2 is then higher than the pressure in the chamber of the first cylinder (curve 100).

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 86 and the injection of air fuel in the chamber of the first cylinder. The line 87 is also 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 into 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), until the moment when this pressure in the pump casing 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 FIG. 10. This injection period begins at 190 ° crankshaft (opening of the conduit opening into the pump housing 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 references) 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) whereas 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. 9, on the upper part of the cylinder head 83 of the corresponding cylinder in which the injection channel 84 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 casing 115 delimited laterally by flanges such as 116 fixed on the crankshaft 114 axially passing through the pump casing 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 122. The burnt gases are evacuated from chamber 113 through 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 the cylinder 111 and has similar elements which have been designated by the same reference mark assigned by the exhibitor'.

On the pump crankcase 115 are on the other hand fixed conduits 125, 126 and 127 comprising an opening opening into the internal volume of the pump crankcase 115. The conduits 125 and 126 are placed so that their opening opening into the crankcase pump is located opposite one of the flanges delimiting the pump housing 115, such as the flange 116.

On the other hand, 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 housing 115 'of the second cylinder 111' has three conduits 125 ', 126' and 127 'opening into the interior volume of the pump housing 115' and arranged in the same manner as the conduits 125, 126 and 127, respectively.

To carry out 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 84 from the cylinder head 111 to the duct 127 'of the pump housing 115'.

In addition, the flange 116 of the pump housing 115 includes 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 120 ° behind the rotation of the crankshaft over 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 PC1 and PC2 in pump casings 115 and 115 '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 housing. During this time interval, the pressure PC1 of the air in the pump casing 115 is transmitted to the chamber 95a of the injection device 82, by the corresponding connection pipe.

The interval of time or of rotation of the crankshaft during which the line 126 ′ of the pump housing 115 ′ is put in communication with the internal volume of this pump housing, is shown in the form of a straight line 141 'recess 131 of the flange 116' being in coincidence with the opening 126 '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 PC2 of the air contained in the pump housing 115 '.

The injection channel 84 of the device 82 is constantly in communication with the interior volume of the casing 115 '.

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 rotation of the crankshaft and 150 ° of this rotation during the next cycle (segment 140).

When the duct 125 is closed (for 150 ° crankshaft), the pressure PC1 in the pump housing 115 is close to its maximum, the piston 112 being in its low position. Pressure air P1 in the chamber 95a (upper part of the curve 138) is therefore maintained at a high level between 150 ° and 270 ° 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 270 °.

The cycle of the cylinder 111 ′ being 120 ° behind the cycle of the cylinder 111, the pressure PC2 in the pump housing 115 ′ is at its maximum when the duct 126 ′ 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 PC1, of 270 ° crankshaft, until the opening of the conduit 126 'through the recess 131, for 190 ° crankshaft of the following cycle (upper part of curve 139).

From 190 ° to 270 ° crankshaft, the pressure in the chamber 95b corresponds to the pressure PC2 (interval represented by the segment 141).

It follows that the curves 138 and 139 representative of P1 and P2 respectively have parts merged with the curves 136 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 95b, when the conduits 125 and 126 'open 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 ′ at 190 ° crankshaft, by setting coincidence of the recess 131 with the opening of the conduit 126 ', the pressure in the chamber 95b 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 value of the pressure 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 carbureted 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 137) is constantly equal to the pressure PC2 in the casing 115 '.

It should be noted that before the start of 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 the injection, the difference in pressures in chambers 95a and 95b, that is to say the difference between pressures PA and PB or P1 and P2 decreases constantly to become zero for 270 ° crankshaft, at the time of opening the conduit 125 and closing the conduit 126 '.

The end of the injection is controlled by the opening of the conduit 125 which produces a drop in the pressure P1 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 at 270 ° 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 position closing by the spring 93 on the one hand and by the high cylindrical pressure due to the compression of the gases on the other hand.

In FIG. 16, the cylinders 111 and 111 ′ have been 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 the closing of conduit 126 '.

It is obvious that the conduits 126 and 127 of the first cylinder 111 are respectively connected to the chamber 95a of an injection device similar to the device 82 or 82 'of a cylinder in advance of 120 ° crankshaft on the cylinder 111 and to the injection channel of this cylinder respectively.

The conduit 126 has an opening opening into the pump housing 115, opposite the second flange of this pump housing (not 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 it is visible on the curve 137 ′ in FIG. 14 representing the pressure PS in the injection channel 84, this pressure PS is no longer constantly identical to the pressure PC2 in the pump housing of a cylinder in delay of 120 ° crankshaft relative to the cylinder in which the injection is carried out.

This pressure PS has variations identical to the control pressure P1 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 which is 120 ° crankshaft behind the cylinder into which the injection is carried out, by means of a pipe situated at a level flange having a recess ensuring the opening of the conduit opening into the pump housing, between 190 ° and 40 ° crankshaft.

Between 40 ° and 190 ° crankshaft, the pressure PS 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 pressure is extremely low 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 at 190 ° 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 87 and the air channel 84 of the pump crankcase at pressure PC2. Simultaneously, the pressure P1 drops and becomes much lower than the pressure P2, which causes the opening of the valve 86.

In all cases, the injection device with assisted automatic control valve makes it possible to carry out a perfectly controlled injection, at an instant in the perfectly determined engine cylinder cycle.

It is obvious that the invention is not limited to the embodiments which have been described.

It is possible to envisage any embodiment of the flanges rotatably mounted in the pump casings, these flanges being able to comprise 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 lagging 120 ° crankshaft on the cylinder in which the injection is carried out opening at a point on the cylinder covered during the cycle by the piston skirt in which an opening is provided, as described in the European patent application of the FRENCH PETROLEUM INSTITUTE N. 406 083, published on 02.01.91. 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 comprising a cutout on its peripheral edge.

In the case where the injection is controlled both by a cutout provided in a flange and by a valve (case of Figure 8), it is possible to avoid the use of a cam for controlling the valve using a spring having a moderate restoring force, the valve can then be controlled by the pressure difference between the injection pipe and the combustion chamber of the cylinder.

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 (10)

1. A two-stroke engine having at least a first cylinder (1; 41; 61; 111) in which a piston (2; 42; 62; 112) moves and a second cylinder (1'; 41'; 61'; 111'), one of the ends of which communicates with a pump crankcase (5'; 45'; 65'; 115'), crossed in an axial direction by the engine crankshaft and having an air intake means (9'; 49'; 69') in the pump crankcase, at least one connection duct (14,; 54; 74; 87) between the pump crankcase (5'; 45'; 65'; 115') of the second cylinder and the combustion chamber of the first cylinder, means for supplying fuel (13; 75; 88) to at least one of the connecting ducts, injection control means for isolating or providing communication between the pump crankcase of the second cylinder and the combustion chamber of the first cylinder and means for connecting the moving pistons in the first and second cylinder connected to the crankshaft so that there is an angular delay between the cycles of the first and second cylinders, characterised in that the injection control means has at least one flange (6'; 46'; 66'; 116') of an essentially cylindrical form rigidly fixed to the axis of the crankshaft (4; 44; 64; 114) inside the pump crankcase (5'; 45'; 65'; 115') of the second cylinder and having at least one recess (16'; 56'; 76'; 131) on its peripheral edge so as to provide intermittent communication as a result of rotation of the crankshaft at given instants of the operating cycle between the combustion chamber of the first cylinder and the pump crankcase of the second cylinder and a discharge of pressurised air from the pump crankcase (5'; 45'; 65'; 115').
2. An engine in accordance with claims 1, characterised in that the recess (16, 17) of the flange (6, 7) is formed by a bevelled section on the peripheral surface of the flange (6, 7) so as to co-operate with an aperture (24, 25) through the wall (1) of the pump crankcase (5) and opening into a duct (30) fixed to the outside of the pump crankcase (5).
3. An engine in accordance with claim 2, characterised in that the sealed segments (26, 27) through which the apertures are formed are arranged in the wall (1) of the pump crankcase (5) at the level of the apertures (24, 25) through this wall so as to co-operate with the peripheral section of the flange (6, 7) to isolate or place in communication with each other the duct (30) and the interior volume of the pump crankcase (5).
4. An engine in accordance with any of claims 1, 2 and 3, characterised in that the injection control means also has a valve (77, 86) for opening and closing off a passage of communication between an injection duct (74, 84) connected to the pump crankcase of the second cylinder via one of the connecting ducts and the combustion chamber of the first cylinder (61, 111).
5. An engine in accordance with claim 4, characterised in that the valve (77) is controlled by a cam (80) and a return spring (79).
6. An engine in accordance with claim 4, characterised in that the valve (86) is an assisted automatic valve, the shank of which is connected to a flexible membrane (89) providing a tight seal between two chambers (95a, 95b), at least one of which is connected to a duct (91, 92) at a closable aperture communicating with the interior volume of one of the pump crankcases (115, 115') of the first or second cylinder.
7. An engine in accordance with claim 6, characterised in that one of the chambers (95a) of the injection control means (86) is connected to the pump crankcase of the second cylinder and the other chamber (95b) is vented to the atmosphere.
8. An engine in accordance with claim 6, characterised in that one-of the chambers (95a) of the injection control means is connected to the pump crankcase (115) of the first cylinder whilst the second chamber (95b) is connected to the pump crankcase (115') of the second cylinder.
9. An engine in accordance with one of claims 7 or 8, characterised in that the duct (87) providing the supply of carburetted air is placed in communication with the pump crankcase (115') of the second cylinder permanently by an aperture that may not be closed off.
10. An engine in accordance with claim 1, characterised in that the connecting duct (54) between the chamber of the first cylinder and the pump crankcase (45') is connected to the pump crankcase (45') via at least two apertures (47', 48') that may be closed off by means of the flange (46') with a recess (56') so as to cause, a depression in the duct (54) via one of the closable apertures (47', 48') and an injection of pressurised air into the duct (54) by means of the other closable aperture (47', 48').

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