FR3103216A1 - Control system for a piston-operated intake valve of a two-stroke engine - Google Patents

Abstract

Control system for a piston-operated intake valve of a two-stroke engine Control system (3) comprising a main tappet (9) configured to move the intake valve relative to the piston (7) according to a lift law between a closed position and a maximum lift position, the main pusher (9) being configured to be movable along a displacement axis (13) of the intake valve relative to the piston; a drive device (15) configured to drive the main pusher (9) along the axis of movement (13) as a function of a crankshaft angle (17) of the two-stroke engine (1), the drive device (15) comprising an intermediate actuating mechanism (19) and a lifting cam (21) having a cooperation profile, the intermediate actuating mechanism (19) comprising a first element (25) arranged to cooperate with the cam. lift (21) and a second element (27) arranged to cooperate with the first element (25), the lifting law being defined by the cooperation profile and by the cooperation between the first element (25) and the second element (27 ). Figure 3

Description

Control system for a piston intake valve of a two-stroke engine

Field of invention

The present invention relates to a control system for an intake valve of a two-stroke engine and also to a method of operating the two-stroke engine. In particular, the two-stroke engine is a heat engine operating according to the Miller cycle.

Prior art

It is known to use a two-stroke engine comprising an intake valve formed in a piston. The piston delimits two chambers of variable sizes in a cylinder of the two-stroke engine: a main chamber or upper chamber (upper engine) in which combustion takes place and a pre-compression chamber or lower intake chamber (lower engine).

The transfer of fresh gases from the pre-compression chamber to the main chamber is carried out through the intake valve which is housed in the piston.

This arrangement is interesting in the sense that the absence of openings (orifices opening into the cylinder) makes it possible to obtain a closed lubrication circuit, which avoids having to use a mixture (fuel and oil) to ensure the lubrication of the mechanical parts of the two-stroke engine. This therefore avoids the combustion of this same lubricant.

Thus, the two-stroke engine is no longer dependent on the problems of lubrication posed by the intake and exhaust ports in the cylinder and the pollution inherent in the conventional architecture of two-stroke engines with ports.

The use of the inlet valve makes it possible to have both a dry metal/metal contact to ensure sealing and a fresh gas passage section, unlike the ports in the cylinder involving lubrication of the parts participating in the opening/closing of these (cylinder/piston/segments).

Furthermore, an advantage of this arrangement is that it no longer makes the intake and exhaust times dependent on the fixed geometry of the ports arranged in the cylinder: they depend on the cam profiles which control the intake valve.

The control of the opening and closing of the intake valve can be achieved in various ways, for example by coupling the control of the lift of the intake valve directly to the rotation of the crankshaft of the engine thanks to a cam housed in the crankshaft pin.

It is a relatively simple design because it involves a minimum of mechanical components for this function. However, such an intake valve control system makes the intake valve lift law particularly dependent on the amplitude of the stroke thereof, thus exposing the design of the cam profile to the angles of attack. which promote shocks, rebounds and wear of mechanical parts due to contact forces normal to the cam profile and significant resulting friction.

Indeed, the rotational displacement speed of the crank pin (supporting the cam) of the crankshaft relative to the cam tappet is too slow with regard to the opening and closing time of the piston valve on the scale of a cycle. (360° in total for the two-stroke engine) to allow a significant valve stroke amplitude and at the same time allow great flexibility in the choice of the opening time of this valve.

In this context, the choices in the very definition of the cam profile (angle limit between the profile of the cam and the axis of the tappet to limit in particular the contact forces, the opening force and the rebound) are restricted. However, it is this flexibility which offers a high degree of conceptual freedom in the search for compromise on the one hand to control the movement of this control (kinematics, mechanical constraints), but also on the other hand to obtain the lifting law desired (start of opening, end of opening, amplitude).

In other words, in this context, the intake valve lift law (particularly if the desired opening time is low) and its amplitude (particularly if it must be high) are technically limited by reaching too sharp a profile for the crankshaft pin cam.

The present invention aims to solve all or part of the drawbacks mentioned above. It also aims at the application of a control system for an intake valve involving, over the entire engine cycle, continuous contact between the parts ensuring the valve lift so as to avoid shocks between the parts in contact.

The technology presented also makes it possible not to involve a hydraulic, pneumatic or electromagnetic circuit for the piston valve control: this is a guarantee of precision and consistency of the valve lift movements, because a cam system is less sensitive. accelerations and oscillation speeds of the piston at high engine speed.

This invention avoids having to resort to a gear system of the planetary gear type with a cam connected to a cascade of gears on a connecting rod, which are more expensive to produce and more restrictive when it comes to multi-cylinder engine blocks.

To this end, the present invention relates to a control system for an intake valve of a two-stroke engine, said intake valve being formed in a piston of the two-stroke engine, the two-stroke engine further comprising a connecting rod configured to drive the piston, the control system comprising:

- a main pusher configured to move the intake valve relative to the piston according to a lift law between a closed position and a maximum lift position, the main pusher being configured to be movable or to comprise at least one movable portion along an axis displacement of the intake valve relative to the piston,

- a drive device configured to drive the main tappet along the axis of movement as a function of a crankshaft angle of the two-stroke engine, the drive device comprising an intermediate actuation mechanism and an intermediate lifting cam having a cooperation profile, the intermediate actuation mechanism comprising a first element arranged to cooperate with the lifting cam and a second element arranged to cooperate with the first element, the lifting law being defined by the cooperation profile and by the cooperation between the first item and the second item.

The fact that the control system or the timing control of the intake valve is composed of a cooperating profile acting on the opening and of a second element acting on the closing of the intake valve makes it possible to dissociate the lift function and distribute it over several sub-assemblies.

The first sub-assembly being the connecting rods and the components attached to it: this assembly is responsible for opening the intake valve. The second sub-assembly being the crankshaft, in particular its crankpin, which is responsible for closing the intake valve.

This separation allows intake valve lift to be performed from sub-assemblies having different relative velocities with respect to intake valve opening point and time. Connecting rod swing is a fast motion relative to the intake valve opening point and time while crankpin rotation on its axis is a slow motion relative to the intake valve opening time .

The exploitation of the movement of sub-assemblies having different relative speeds (swinging of the connecting rods/rotation of the crank pin) gives a greater degree of conceptual freedom for the definition of the lift law of the intake valve.

It is for this reason in particular that with equal diagrams, the cam profiles have smaller angles than if there was only one active cam profile on the crankshaft pin. This distribution of the valve lift function on different components allows greater flexibility in the definition of asymmetrical valve lifts between the up and down travel and having a short total opening time (90°) with regard to the overall cycle of the two-stroke engine (360°).

The simultaneous effect of the slope of the cooperation profile and the relative displacements of the intermediate elements in contact allows during the angular displacement of the connecting rod a rapid closing of the intake valve at the end of the admission of fresh air into the cylinder.

Limiting the slope of the cooperation profile also allows permanent contact between the cooperation profile and a part of the main pusher or of the first element cooperating with the cooperation profile. This avoids mechanical shocks which are sources of vibration, wear, destruction and noise.

In the present text, the two-stroke engine is described as comprising a cylinder, a piston and a corresponding connecting rod. However, the control system is also applicable to an engine comprising several cylinders, each cylinder corresponding to a control system.

This control system eliminates the need for intake and exhaust ports (orifices opening directly into the cylinder wall). This arrangement makes it possible to have a piston lubrication circuit which is closed by a set of scraper rings housed in the piston. Segmentation (sealing and scrapers) never passing in front of the lubricant supply holes drilled in the cylinder wall.

As a result, it is not necessary to resort to oil mist in the high engine to lubricate the mechanical parts, so there is no need to burn off lubricant during the combustion process.

According to one aspect of the invention, the lifting cam is configured to be fixed on the crankshaft so as to be fixed with respect to an extension axis of a crank pin of the crankshaft, the cooperation profile having a contour evolving between a high point and a low point with respect to the axis of extension of the crankpin, and the second element has an actuation surface configured to cooperate with a roller of the main pusher.

In other words, the cooperation profile is arranged to move the first element according to the angle of the crankshaft. The shape of the actuation surface as well as the force exerted on the second element by the first element define the lifting law.

This arrangement therefore allows precise control of the lift of the intake valve using a reliable mechanical system comprising a reduced number of parts. This arrangement also makes it possible to define a fixed lifting law with respect to the crankshaft angle.

According to one aspect of the invention, the intermediate actuation mechanism comprises a third element configured to be fixed on the connecting rod of the two-stroke engine, the second element comprising a rocker arm mounted so as to be able to rotate about a pivot of the third element, the actuation surface being provided on the balance.

The positioning of the third element on the connecting rod is defined by the relative displacement of the first element and the second element according to the crankshaft angle.

According to one aspect of the invention, the second element is movable relative to the first element, the lift law being defined by the cooperation profile and by a relative displacement of the first element relative to the second element.

This arrangement makes it possible to define a lifting law in a more flexible way than if only the lifting cam and an intermediate part were used that did not include two elements that move relative to each other.

Indeed, to achieve an opening or closing of the intake valve on a low crankshaft angle, the cooperation profile must have a significant slope. However, this significant slope can cause rebounds and/or friction losses.

The fact that the intermediate actuation mechanism comprises a first element and a second element that are movable relative to each other makes it possible to amplify the effect of the cooperation profile on the lifting law.

According to one aspect of the invention, the first element is fixed relative to the second element.

According to one aspect of the invention, the first element is attached to the second element. Preferably, the first element and the second element are included in the same part.

This arrangement makes it possible to simplify the design of the control system by limiting the number of parts.

According to one aspect of the invention, the control system comprises a return spring arranged to exert a force in a closing direction of the intake valve, the cooperation profile having a downward slope oriented towards the axis of extension of the crankpin, an intermediate pusher of the first element being configured to cooperate with the downward slope so as to cause rotation of the balance around the pivot in the direction of the closing direction.

This arrangement allows rapid closing since the balance and its cam profile move in the direction of the closing direction under the effect of the return spring.

According to one aspect of the invention, the intermediate pusher is mounted to move in translation on the third element.

Thus, the intake valve lift law can describe gradual opening and rapid closing. From a mechanical point of view, this results in the design of parts avoiding premature wear of the parts in contact.

According to one aspect of the invention, the actuating surface has a deflection slope configured to cooperate with the roller so as to move the intake valve from the closed position to the maximum lift position when the cooperation profile has a rising slope away from the axis of extension of the crank pin.

This arrangement makes it possible to reduce the inclination of the rising slope of the cooperation profile, which limits the forces normal to the actuation surface and therefore the friction between the first element and the lifting cam.

According to one aspect of the invention, the movement of the intake valve from the closed position to the maximum lift position is defined on an angular portion of the opening of the crankshaft.

According to an exemplary embodiment, the angular opening portion is between 180° and 270°, a top dead center being defined as the angular origin.

According to one aspect of the invention, the actuation surface has a holding slope adjoining the deflection slope, the holding slope being arranged to cooperate with the roller so as to hold the intake valve in the maximum lift position .

This arrangement allows good air intake since the intake valve does not begin to close immediately after reaching the maximum lift position.

According to one aspect of the invention, the holding of the intake valve in the maximum lift position is defined on an angular holding portion of the crankshaft.

According to an exemplary embodiment, the angular holding portion is between 240° and 260° approximately.

According to one aspect of the invention, the main pusher is configured to be movable along the axis of movement so as to move the intake valve relative to the connecting rod.

In this configuration, the main tappet has a translational movement and moves the intake valve towards the inside of the combustion chamber when the intake valve opens.

According to one aspect of the invention, the at least one movable portion of the main tappet comprises a support configured to cooperate with a valve seat integral with the movement of the piston so as to move the valve seat along the axis of movement with respect to at the inlet valve.

This arrangement allows the intake valve to open towards the inside of the piston. In this way, it is possible to use only one intake valve to ensure a sufficient air supply allowing a sweep in the form of a column of fresh air in the center of the cylinder.

This arrangement also makes it possible to generate a concentrated scanning front with a current having different orientations. For example, it is possible to configure the geometry of the piston head and the intake valve to generate a swirl.

According to one aspect of the invention, the main tappet comprises a central portion integral with the intake valve. Preferably, the central portion is rotatably mounted on the connecting rod or on a connecting element to the connecting rod. In particular, the central portion is arranged to move together with the valve relative to the connecting rod so that the valve remains oriented in the direction of movement.

According to one aspect of the invention, the at least one movable portion comprises a movement transmission mechanism arranged to transmit a translation movement of the roller to the support so that a movement of the roller along the axis of movement generates a translational movement in the same direction of the support along the axis of displacement. Preferably, the roller is movably mounted on a part of the movement transmission mechanism.

The present invention also relates to a two-stroke engine comprising a control system as described above.

According to one aspect of the invention, the connecting rod comprises a head configured to cooperate with the crankpin, the crankpin being rotatable around the axis of extension of the crankpin, the connecting rod comprising two parts arranged on either side of the lifting cam.

By arranged on either side of the lifting cam, it is understood arranged in relation to the axis of extension of the crankpin. Thus, the two-stroke engine comprising the control system is compact since the lifting cam is integrated in the big end.

According to one aspect of the invention, the two parts of the connecting rod are arranged on either side of the drive device.

This arrangement also contributes to the compactness of the two-stroke engine equipped with the control system.

The present invention also relates to a method of operating a two-stroke engine comprising a control system as described above comprising the following steps:

- explosion of a gas mixture contained in a main chamber of the cylinder of the two-stroke engine at top dead center at a crankshaft angle of 0°,

- expansion of the combustion gas mixture to bottom dead center at a crankshaft angle of 170°,

- exhaust of the burnt gas mixture from a crankshaft angle of 170°, the exhaust being produced by opening at least one exhaust valve of the two-stroke engine housed in a cylinder head of the two-stroke engine,

- admission of a mixture of fresh gases into the cylinder through an intake opening of the intake valve generated by the main tappet and the drive device, the intake opening occurring after an exhaust opening and an intake closure occurring after an exhaust closure,

- compression of the fresh gas mixture admitted, the fresh gas mixture coming from a pre-compression stage carried out in a pre-compression chamber of the cylinder configured to be supplied by an inlet channel of the two-stroke engine, the main chamber and the pre-compression chamber being separated by the piston.

The expansion of the combustion gas mixture occurs over the entire expansion stroke of the piston, that is to say from top dead center to practically bottom dead center, ie at 170°. This arrangement maximizes the efficiency of the two-stroke engine. The yield could approach 0.5.

The rate of expansion, ie the driving phase over the complete cycle of the two-stroke engine is therefore greater than conventional two-stroke engines whose efficiency is approximately 0.3.

The pre-compression stage allows definition and control of the amount of fresh gas mixture. According to one aspect of the invention, the two-stroke engine comprises intake valves made in the inlet channel.

The intake valves are configured to open when the pressure in the pre-compression chamber is lower than the pressure in the inlet channel on the opposite side of the pre-compression chamber relative to the intake valves .

According to one aspect of the invention, this pressure differential can also be increased by adding an air compressor.

Thus, the pre-compression chamber is supplied with a mixture of fresh air when the piston rises in the cylinder and when the pressure difference allows it.

During expansion, the fresh gases admitted under the piston are pre-compressed because the inlet valves are closed.

The inlet valve opens when the rise of the piston begins around 180°, this is when the mixture of fresh gases pre-compressed in the pre-compression chamber crosses the piston to pass into the main chamber.

It is at this stage that the sweeping of the burnt gases by the fresh gases takes place, in other words that the fresh gases drive the burnt gases out of the cylinder. The cylinder gradually fills with fresh gas until the inlet valve closes on the piston at around 270°.

The exhaust valve closes almost at the same time, a little ahead of the intake valve to prevent the fresh gases from ending up in the exhaust.

From 270° the piston compresses the admitted gases to top dead center. It is also during this phase that the pre-compression chamber fills again with fresh gas. And the cycle begins again.

During this last phase, the lifting cam, which has a cooperation profile which cooperates with the actuating surface of the second element to create a combined movement between the inlet closing point and the top dead center so that the control system regains its initial position without varying the operating clearances between the contacting parts while the intake valve remains closed. This arrangement avoids shocks between the parts in contact which are sources of vibrations, destruction and noise.

The various non-incompatible aspects defined above can be combined.

Brief description of figures

The invention will be better understood with the aid of the detailed description which is given below with regard to the appended drawings.

is a schematic sectional view of part of a two-stroke engine.

is a theoretical valve opening and closing diagram of the two-stroke engine.

is a sectional view of a detail of the two-stroke engine crank assembly including a control system for a bottom dead center intake valve at a crank angle of 180° of the cycle.

is a sectional view of a detail of the two-stroke engine crankshaft at a 190° crankshaft angle of the cycle.

is a sectional view of a detail of the two-stroke engine crankshaft at a crankshaft angle of 200° of the cycle.

is a sectional view of a detail of the two-stroke engine crankshaft at a crankshaft angle of 240° of the cycle.

is a sectional view of a detail of the two-stroke engine crankshaft at a 260° crankshaft angle of the cycle.

is a sectional view of a detail of the two-stroke engine crankshaft at a crankshaft angle of 300° of the cycle.

is a sectional view of an engine detail from the two-stroke crankshaft to a crankshaft angle of 330° of the cycle.

is a sectional view of a detail of the two-stroke engine crankshaft at top dead center at a 360° crankshaft angle of the cycle.

is a sectional view of a detail of the two-stroke engine crankshaft at a 70° crankshaft angle of the cycle.

is a sectional view of a detail of the crank assembly of the two-stroke engine according to a variant embodiment.

Description with reference to figures

In the detailed description which will follow of the figures defined above, the same elements or the elements performing identical functions may retain the same references so as to simplify the understanding of the invention.

As shown in Figure 1, a two-stroke engine1 includes a control system3 for an intake valve5 of said two-stroke engine1. The intake valve5 is housed in a piston7 of the two-stroke engine1.

As illustrated in Figures 3 to 11, the control system3 comprises a main pusher9 configured to move the intake valve5 relative to the piston7 according to a lift law between a closed position and a maximum lift position.

As soon as the intake valve5 opens, fresh air is admitted into a cylinder11 of the two-stroke engine1, the main pushrod9 being configured to be movable in translation along an axis of displacement13 of the intake valve with respect to the plunger7.

The control system3 comprises a drive device15 configured to drive the main pusher9 along the axis of displacement13 as a function of a crankshaft angle17 of the two-stroke engine1.

The drive device15 comprises an intermediate actuation mechanism19 and a lifting cam21 having a cooperation profile23.

The intermediate actuation mechanism 19 comprises a first element 25 arranged to cooperate with the lifting cam 21 and a second element 27 movable with respect to the first element 25. The lifting law is defined by the cooperation profile23 and by a relative displacement of the first element25 with respect to the second element27.

In this intermediate actuation mechanism19, the first element25 is housed in the body of the linkage. This first element25 follows the cooperation profile23 of the lifting cam21 and it serves as a support on its other end for the second element27 which is pivoted relative to the body of the connecting rod. The translation movement of the first element25 induced by the lifting cam21 is therefore transmitted to the second element27. The translational movement of the first element25 characterizes the angular position of the second element27 with respect to the connecting rod body.

The intake valve lift law5 is defined both by the second element27 and by the cooperation profile23 of the lift cam21. There is a chain of contacts between the first element25, the second element27, the connecting rod body and the lifting cam21. It is the relative displacements of these components and their respective profiles that define the lift law of the intake valve5. The respective displacements of these components depend not only on the angular position of the connecting rod with respect to the axis of displacement13 but also on the angular position of the crankshaft31 (and therefore of the lifting cam21 which is fixed to the crankshaft31).

The two-stroke engine1 is described as comprising a cylinder11, a piston7 and a corresponding connecting rod29. However, the control system 3 is also applicable to a two-stroke engine 1 comprising several cylinders 11, each cylinder 11 corresponding to a control system 3 .

The lifting cam21 is configured to be fixed on a crankshaft31 of the two-stroke engine1 so as to be fixed with respect to an extension axis33 of a crankpin35 of the crankshaft31.

The cooperation profile23 presents a contour evolving between a high point37 and a low point39 with respect to the axis of extension33 of the crank pin35.

The first element25 and the second element27 are arranged to cooperate, the second element27 having an actuation surface41 configured to cooperate with a roller43 of the main pusher9.

In other words, the cooperation profile23 is defined to act on the first element25 according to the crankshaft angle31 (in a complete cycle of 360°): it is responsible for the axial position of the first element25 with respect to the body connecting rod29.

The cooperation profile23 is responsible for closing the intake valve5. It is the shape of the second element27 exerting a stress normal to its surface on the roller43 according to the angular displacement of the body of the connecting rod29 which is responsible for the opening of the intake valve5. Thus, the axial position of the first element25 with respect to the body of the connecting rod29, which keeps the second element27 in contact, is directly linked to the lift law of the intake valve5.

The intermediate actuation mechanism19 comprises a third element45 configured to be fixed on the connecting rod29 of the two-stroke engine1. The first element25 comprises an intermediate pusher47 mounted to move in translation on the third element45 and the second element27 comprises a rocker arm49 mounted to move in rotation on a pivot50 of the third element45. The actuation surface41 is provided on the balance wheel49.

The control system3 comprises a return spring arranged to exert a force in a closing direction51 of the intake valve5. The cooperation profile23 has a downward slope53 oriented towards the axis of extension33 of the crankpin35, the intermediate pusher47 being configured to cooperate with the downward slope53 so as to cause the rotation of the balance wheel49 in the direction of the closing direction51.

The actuation surface41 has a deflection slope55 configured to cooperate with the roller43 so as to move the intake valve5 from the closed position to the maximum lift position.

This movement of the roller43 is made possible because the second element27 is held angularly relative to the connecting rod29 around the pivot50, i.e. thanks to the intermediate pusher47 and the cooperation profile23 presenting a rising slope57 moving away from the axis of extension33 crankpin35.

The displacement of the intake valve5 from the closed position to the maximum lift position is defined on an angular portion of the crankshaft opening31.

The angular opening portion is between 180° and 270° as shown in Figures 4 to 6 and in the diagram of Figure 2, a top dead center being defined as the angular origin as shown in Figure 10.

The actuation surface 41 has a holding slope 59 adjacent to the deflection slope 55, the holding slope 59 being arranged to cooperate with the roller 43 so as to maintain the intake valve 5 in the maximum lift position.

Maintaining the inlet valve5 in the maximum lift position is defined on an angular holding portion of the crankshaft. The angular holding portion is between 240° and 270° as shown in Figures 6 and 7.

The connecting rod 29 comprises a head 61 configured to cooperate with the crank pin 35, the crank pin 35 being rotatable relative to the connecting rod head around the axis of extension 33 of the crank pin 35, the connecting rod 29 comprising two parts arranged on either side of the lifting cam21.

“Arranged on either side of the lifting cam21” means arranged in relation to the axis of extension33 of the crankpin35. The two parts of the connecting rod29 are arranged on either side of the drive device15.

As also illustrated in Figure 2, a method of operating the two-stroke engine1 comprises a step of explosionE1 of a mixture of gases included in a main chamber63 of the cylinder of the two-stroke engine1 at top dead center at a crankshaft angle of 0°.

Then, the operating method includes a step of expansionE2 of the combustion gas mixture to a bottom dead center at a crankshaft angle of 180° as shown in Figure 3.

This motor phase of the E2 expansion stage is maximized compared to conventional two-stroke engines thanks to the absence of intake and exhaust ports. In addition, the lift of the intake valve5 which is asymmetrical between the top dead center to bottom dead center (rebound) and bottom dead center to top dead center (intake-compression) paths allows the application of the Miller cycle.

The operating method includes an exhaust stage E3 of the burnt gas mixture from a crankshaft angle of approximately 170°. The exhaust (OE) is produced by an exhaust openingOE of at least one exhaust valve65 housed in a cylinder head of the two-stroke engine1.

The method of operation includes a step of admissionE4 of a mixture of fresh gases into the cylinder11 through an admission openingOA of the intake valve5 generated by the main pusher9 and the drive device15.

Intake opening OA occurs after exhaust opening OE and intake closing FA occurs after exhaust closing FE.

It is at this stage that the sweeping of the burnt gases by the fresh gases takes place, in other words that the fresh gases drive the burnt gases out of the cylinder11. Cylinder11 gradually fills with fresh gas until the inlet valve closes on piston7 at around 270°.

The exhaust valve65 closes almost at the same time but a little ahead of the intake valve5 to prevent fresh gases from ending up in the exhaust.

The method of operation finally comprises a step of compressionE5 of the mixture of fresh gases admitted.

The fresh gas mixture comes from a pre-compression stageE0 carried out in a pre-compression chamber67 of the cylinder11 configured to be supplied by an inlet channel69 of the two-stroke engine1, the main chamber63 and the pre-compression chamber69 being separated by the piston7.

The natural depression created when the inlet valve closes5 draws the gases into this chamber: the gases enter the pre-compression chamber67 from the inlet channel69. It is possible to add a compressor to increase the fresh gas filling of this pre-compression chamber67.

To prevent the backflow of fresh gases, the two-stroke engine1 includes inlet valves71 arranged in the inlet channel69. The intake valves71 are configured to be open when the pressure in the pre-compression chamber67 is lower than the pressure in the inlet channel69, and this, on the opposite side to that of the pre-compression chamber67 with respect to the intake valves71.

Thus, the pre-compression chamber67 is supplied with a mixture of fresh air when the piston rises in the cylinder11 and when the pressure difference allows it.

During expansion, the fresh gases admitted under the piston7 are pre-compressed because the admission valves are closed. Thus, the pre-compression stage E0 takes place during the relaxation stage E2.

The inlet valve5 opens when the rise of the piston7 begins towards 180°, it is then that the mixture of fresh gases pre-compressed in the pre-compression chamber67 crosses the piston to pass into the main chamber.

The method of operation can also be carried out with a control system3 produced according to the embodiment variant of FIG. 12.

The lifting law is defined by the cooperation profile23 and by the cooperation between the first element25 and the second element27. The first element25 is fixed relative to the second element27.

In particular, the first element25 is attached to the second element27 so that the first element25 and the second element27 are included in the same part.

The main pusher9 comprises at least one movable portion provided with a support73 configured to cooperate with a valve seat75 integral in movement with the piston7 so as to move the valve seat75 along the axis of movement13 with respect to the inlet valve5.

The main tappet9 includes a central portion77 integral with the inlet valve5. The central portion77 is rotatably mounted on the connecting rod29 or on a connecting element to the connecting rod29.

The central portion77 is arranged to move together with the inlet valve5 relative to the connecting rod29 so that the inlet valve5 remains oriented in the direction of movement13.

The at least one movable portion of the main pusher9 comprises a movement transmission mechanism79 arranged to transmit a translational movement of the roller43 to the support73 so that a movement of the roller43 along the axis of movement13 generates a translational movement of same direction of the support73 along the axis of displacement13. The roller43 is movably mounted on a part of the motion transmission mechanism79.

The variant in figure 12 thus has the effect of reversing the movement of the inlet valve5 which opens on entering the interior of the piston7. The benefit of this system is to have a column of fresh gas sweeping the cylinder along its axis and through its center, like a two-stroke engine fitted with transfers.

It therefore appears that, thanks to the method of operation, the expansion of the combustion gas mixture occurs over the entire expansion stroke of the piston7, that is to say from top dead center to bottom dead center. This arrangement maximizes the efficiency of the two-stroke engine1. The yield could approach 0.5.

The efficiency would therefore be higher than that of conventional two-stroke engines. Indeed, the rate of expansion, that is to say the driving phase with respect to the complete cycle of the two-stroke engine1 is higher than the conventional two-stroke engine (with lights) for which the efficiency is approximately 0.3, and higher to the expansion rate of four-stroke engines.

The rate of expansion, ie the driving phase over the complete cycle of the two-stroke engine1 is therefore greater than conventional two-stroke engines whose efficiency is approximately 0.3.

The efficiency of this two-stroke engine being the best at constant speed and load, this technology could be used in an on-board generator or as a current generator to recharge a hybrid vehicle battery.

From a mechanical point of view, the lift law can be controlled more flexibly than if only the lift cam and an intermediate part were used that did not include two elements that move relative to each other.

This arrangement therefore allows precise control of the lift of the intake valve using a reliable mechanical system (because less shocks and thanks to the constancy of the valve lift whatever the engine speed) and comprising a reduced number of pieces.

It goes without saying that the invention is not limited to the single embodiment described above by way of example, on the contrary it embraces all variant embodiments.

Claims (10)

Control system (3) for an intake valve (5) of a two-stroke engine (1), said intake valve (5) being arranged in a piston (7) of the two-stroke engine (1), the two-stroke engine (1) further comprising a connecting rod (29) configured to drive the piston (7), the control system (3) comprising:

• a main tappet (9) configured to move the intake valve (5) relative to the piston (7) according to a lift law between a closed position and a maximum lift position, the main tappet (9) being configured to be movable or include at least one movable portion along an axis of movement (13) of the intake valve (5) relative to the piston (7),
• a drive device (15) configured to drive the main tappet (9) along the displacement axis (13) as a function of a crankshaft angle (17) of the two-stroke engine (1), the drive device (15) comprising an intermediate actuation mechanism (19) and a lifting cam (21) having a cooperation profile (23), the intermediate actuation mechanism (19) comprising a first element (25) arranged to cooperate with the lifting cam (21) and a second element (27) arranged to cooperate with the first element (25), the lifting law being defined by the cooperation profile (23) and by the cooperation between the first element (25) and the second element (27).

A control system (3) according to claim 1, wherein:

• the lifting cam (21) is configured to be fixed on the crankshaft (31) so as to be fixed with respect to an extension axis (33) of a pin (35) of the crankshaft (31), the profile of cooperation (23) having a contour evolving between a high point (37) and a low point (39) with respect to the axis of extension (33) of the crank pin (35),
• the second element (27) has an actuation surface (41) configured to cooperate with a roller (43) of the main pusher (9).

Control system (3) according to Claim 2, in which the intermediate actuating mechanism (19) comprises a third element (45) configured to be fixed to the connecting rod (29) of the two-stroke engine (1), the second element (27) comprising a rocker (49) rotatably mounted around a pivot (50) of the third element (45), the actuating surface (41) being formed on the rocker (49). Control system (3) according to one of Claims 1 to 3, in which the second element (27) is movable relative to the first element (25), the lift law being defined by the cooperation profile (23) and by a relative displacement of the first element (25) with respect to the second element (27). Control system (3) according to one of Claims 1 to 3, in which the first element (25) is fixed relative to the second element (27). Control system (3) according to claim 3, comprising a return spring arranged to exert a force in a closing direction (51) of the intake valve (5), the cooperation profile (23) having a downward slope (53) oriented towards the extension axis (33) of the crankpin (35), an intermediate pusher (47) of the first element (25) being configured to cooperate with the downward slope (53) so as to cause rotation of the pendulum (49) around the pivot (50) in the direction of the closing direction (51). Control system (3) according to one of Claims 2 or 3, in which the actuating surface (41) has a deflection slope (55) configured to cooperate with the roller (43) so as to move the valve admission (5) from the closed position to the maximum lift position when the cooperation profile (23) has a rising slope (57) moving away from the axis of extension (33) of the crank pin (35). Control system (3) according to one of Claims 1 to 7, in which the main tappet (9) is configured to be movable along the displacement axis (13) so as to move the intake valve (5) relative to the connecting rod (29). Control system (3) according to one of Claims 1 to 7, in which the at least one movable portion of the main tappet (9) comprises a support (73) configured to cooperate with a valve seat (75) integral in movement of the piston (7) so as to move the valve seat (75) along the axis of movement (13) relative to the inlet valve (5). Method of operating a two-stroke engine (1) comprising a control system (3) according to one of Claims 1 to 9, comprising the following steps:

• explosion (E1) of a gas mixture contained in a main chamber (63) of the cylinder (11) of the two-stroke engine (1) at top dead center at a crankshaft angle (17) of 0°,
• expansion (E2) of the combustion gas mixture to bottom dead center at a crankshaft angle (17) of 170°,
• exhaust (E3) of the burnt gas mixture from a crankshaft angle (17) of 170°, the exhaust being produced by opening at least one exhaust valve (65) of the two-stroke engine (1 ) housed in a cylinder head of the two-stroke engine(1),
• inlet (E4) of a mixture of fresh gases into the cylinder (11) through an inlet opening (OA) of the inlet valve (5) generated by the main pusher (9) and the drive device ( 15), the intake opening (OA) occurring after an exhaust opening (OE) and an intake closing (FA) occurring after an exhaust closing (FE),
• compression (E5) of the fresh gas mixture admitted, the fresh gas mixture coming from a pre-compression stage (E0) carried out in a pre-compression chamber (67) of the cylinder (11) configured to be supplied by an inlet channel (69) of the two-stroke engine (1), the main chamber (63) and the pre-compression chamber (67) being separated by the piston (7).