WO2022029510A1

WO2022029510A1 - Two-stroke internal combustion engine

Info

Publication number: WO2022029510A1
Application number: PCT/IB2021/052698
Authority: WO
Inventors: Vincenzo MATTIA; Roland HOLZNER; Alessandro LUNARDON
Original assignee: Gimax S.R.L. Con Unico Socio
Priority date: 2020-08-06
Filing date: 2021-03-31
Publication date: 2022-02-10

Abstract

A two-stroke internal combustion engine (1) with fuel injection and having: at least one cylinder (2), which has, on the inside, a combustion chamber (6) provided with an exhaust port (8); a piston (7); a cylinder head (37); a crankcase (3); a crankshaft (5); an intake duct (21); an exhaust duct (9), which originates from the exhaust port (8) and is provided with a main catalytic converter (10); an alternative duct (11), which originates in the area of the exhaust port (8), ends in the exhaust duct (9) upstream of the main catalytic converter (10) and houses a secondary catalytic converter (12); and an exhaust valve (13), which is arranged in the area of the exhaust port (8) and has a shutter (14), which is movable between a minimum resistance position, in which the shutter (14) closes the inlet of the alternative duct (11), thus forcing the exhaust gases to flow through the sole exhaust duct (9), and a maximum resistance position, in which the shutter (14) closes the inlet of the exhaust duct (9), thus forcing the exhaust gases to flow through the sole alternative duct (11).

Description

"TWO-STROKE INTERNAL COMBUSTION ENGINE"

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application claims priority from Italian patent application no . 102020000019471 filed on 06/ 08 /2020 , the entire disclosure of which i s incorporated herein by reference .

TECHNICAL FIELD

The invention relates to a two- stroke internal combustion engine . PRIOR ART

The two-stroke internal combustion engine was invented by Dugald Clerk in 1879 and mainly di f fers from the more common four-stroke internal combustion heat engine because of the di fferent alternation of the active stokes (power strokes ) in relation to the revolutions of the crankshaft ; indeed, whereas in the four-stroke engine there is one active stroke (namely, the expansion stroke , during which chemical energy is trans formed into thermal energy and, hence , into kinetic energy) for every two revolutions o f the shaft , in the two-stroke engine there is an active stroke for each complete revolution of the shaft . From a structural point of view, a two-stroke internal combustion engine usually does not have the traditional intake and exhaust valves , which are replaced by the "ports" , namely non-circular slits , which are directly obtained on the cylinder and are opened and closed by the reciprocating motion of the pi ston .

The two-stroke internal combustion engine is an extremely simple engine , is compact , light and economic and, for this reason, in the past it was almost always used in mopeds with small displacements (usually of no more than 5- 150 cc ) and in all small-si zed applications ( small generator sets , chainsaws , lawn mowers , small outboard motor for boats ) . However, current two-stroke internal combustion engines are not capable of complying ( i f not with anti-economic complications ) with the most recent standards enforced in terms of emissions of internal combustion engines .

Patent application EP0396262A2 describes a two-stroke internal combustion engine with fuel inj ection and spark ignition; in particular, an exhaust emission control apparatus is provided, which separately treats hot exhaust gases and uses hot-treated gases to heat scavenging gases . DESCRIPTION OF THE INVENTION

The obj ect of the invention is to provide a two-stroke internal combustion engine , which complies with the most recent standards enforced in terms of emissions of internal combustion engines and, at the same time , can be manufactured in a simple and low-cost manner . According to the invention, there is provided a two- stroke internal combustion engine according to the appended claims .

The appended claims describe preferred embodiments of the invention and form an integral part of the description . BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to the accompanying drawings , showing a non-limiting embodiment thereof , wherein :

• figure 1 is a schematic side view, with a partial longitudinal section and with parts removed for greater clarity, of a two-stroke internal combustion engine according to the invention;

• figure 2 is a schematic perspective view, with a partial longitudinal section and with parts removed for greater clarity, of the internal combustion engine of figure 1 ;

• figure 3 is a schematic front view, with a partial longitudinal section and with parts removed for greater clarity, of the internal combustion engine of figure 1 ;

• figures 4 and 5 are two schematic views of an exhaust valve of the internal combustion engine of figure 1 in two di f ferent positions ; figure 6 is a perspective view of a reed valve of the internal combustion engine of figure 1 ;

• figure 7 is a diagram showing, in the plane defined by the rotation speed and by the load, the areas in which the internal combustion engine of figure 1 operates with spontaneous ignition ( sel f-ignition) of the mixture and the areas in which the internal combustion engine of figure 1 operates with controlled ignition of the mixture ;

• figure 8 is a variant of the diagram of figure 7 ; and

• figures 9 and 10 are two schematic variant views of the exhaust valve of figures 4 and 5 in two di f ferent positions .

PREFERRED EMBODIMENTS OF THE INVENTION

In figures 1 , 2 and 3 , number 1 indicates , as a whole , a two-stroke internal combustion engine with fuel inj ection .

In the (non-limiting) embodiment shown in the accompanying figures , the engine 1 is a one-cylinder engine , namely it comprises one single cylinder 2 , which proj ects from a crankcase 3 ( according to other embodiments , which are not shown herein, the heat engine 1 could be a two-cylinder engine or even have more than two cylinders 2 ) . Inside the crankcase 3 there is obtained a crank chamber 4 , which houses a crankshaft 5 ( schematically shown in figure 1 ) . The cylinder 2 comprises , on the inside , a combustion chamber 6 , which has a cylindrical symmetry around a longitudinal axis and where a piston 7 (which is schematically shown in figure 1 ) slides in a reciprocating manner .

The piston 7 is connected to the crankshaft 5 by means of a connecting rod, whose lower part is arranged inside the crank chamber 4 .

In the side wall of the combustion 6 chamber there is at least one exhaust port 8 , which expels the exhaust gases towards an exhaust duct 9 and is cyclically opened and closed by the reciprocating movement of the piston 7 . The exhaust duct 9 houses , among other things , a main catalytic converter 10 . In parallel to an initial portion the exhaust duct 9 there is arranged an alternative duct 11 , which originates in the area of the exhaust port 8 and ends in the exhaust duct 9 ( largely) upstream of the main catalytic converter 10 . The alternative duct 11 houses a secondary catalytic converter 12 , which has a ( signi ficantly) smaller si ze than a si ze of the main catalytic converter 10 . Furthermore , the secondary catalytic converter 12 has a greater density compared to a dens ity of the main catalytic converter 10 ; namely, starting from the same si zes , the secondary catalytic converter 12 would turn out to be heavier and have greater load losses than the main catalytic converter 10; in other words, the secondary catalytic converter 12 is smaller and more "concentrated" than the main catalytic converter 10.

The internal combustion engine 1 comprises an exhaust valve 13, which is arranged in the area of the exhaust port 8 and comprises a shutter 14, which is hinged so as to rotate (move) between two limit positions: a minimum resistance position (shown in figure 5) , in which the shutter 14 closes the inlet of the alternative duct 11, thus forcing the exhaust gases to flow through the sole exhaust duct 9, and a maximum resistance position (shown in figure 4) , in which the shutter 14 closes the inlet of the exhaust duct 9, thus forcing the exhaust gases to flow through the sole alternative duct 11. In particular, the shutter 14 is operated (rotated) by an electric actuator 15, which moves (rotates) the shutter 14 between the minimum resistance position (shown in figure 5) and the maximum resistance position (shown in figure 4) .

According to a preferred embodiment, which is better shown in figures 4 and 5, the shutter 14 has a wall 16, which closes the inlet of the alternative duct 11 in the minimum resistance position (shown in figure 5) and closes the inlet of the exhaust duct 9 in the maximum resistance position (shown in figure 4) . According to a possible embodiment shown in the accompanying figures, the shutter 14 has a further wall 17, which is connected to the wall 16, is arranged approximately perpendicularly to the wall 16, is crossed by at least one through hole 18 and partially closes the inlet of the alternative duct 11 in the maximum resistance position (shown in figure 4) ; namely, in the maximum resistance position (shown in figure 4) the exhaust gases, from the exhaust port 8, cannot access the exhaust duct 9 at all and can flow into the alternative duct 11 only through the through hole 18 of the wall 17. The function of the wall 17 provided with the through hole 18 is that of increasing the resistance to which the exhaust gases are subjected in to order to flow into the alternative duct 11 when the shutter 14 is in the maximum resistance position (shown in figure 4) .

According to a possible (though non-binding) embodiment, a further exhaust port 19a is provided, which is separate from and independent of the exhaust port 8, has a smaller size than a size of the exhaust port 8, is not affected by the shutter 14 in any way and directly leads to the alternative duct 11 through a suitable duct, which leads into (ends in) an inlet opening 19b (shown in figures 4 and 5) . In other words, through the exhaust port 19a, a (limited) part of the exhaust gases can reach the alternative duct 11 regardless of the position assumed by the shutter 14 and, hence, thanks to the exhaust port 19a, a (limited) part of the exhaust gases reaches the alternative duct 11 and flows through the secondary catalytic converter 12 even when the shutter 14 is in the minimum resistance position (shown in figure 5) , in which the shutter 14 closes the inlet of the alternative duct 11. In this way, the secondary catalytic converter 12 is always kept properly hot (and, hence, active) even when the shutter 14 is in the minimum resistance position (shown in figure 5) .

According to a possible embodiment shown in the accompanying figures, the shutter 14 does not interfere in any way with the inlet opening 19b in both its positions; according to a different embodiment which is not shown herein, the shutter 14 could interfere with the inlet opening 19b (namely, the shutter 14 could at least partially close the inlet opening 19b) when it is in the minimum resistance position (shown in figure 5) and, as a consequence, the shutter 14 has a suitable through hole, which, when the shutter 14 is in the minimum resistance position (shown in figure 5) , overlaps the inlet opening 19b so as to leave the inlet opening 19b completely free.

The internal combustion engine 1 has the intake in the crankcase 3, i.e. fresh air (containing approximately 20% of oxygen and coming from the outside) and fuel (usually petrol) are fed to the crank chamber 4 under the piston 7 and are sucked into the combustion chamber 6 through (at least) one transfer duct 20 obtained through the cylinder 2. In particular, fresh air is sucked into the crank chamber 4 due to the depression generated in the crank chamber 4 by the upward movement of the piston 7 from the BDC (bottom dead centre) to the TDC (top dead centre) ; on the other hand, fresh air is sent to the combustion chamber 6 through the transfer duct 20 due to the overpressure generated in the crank chamber 4 by the downward movement of the piston 7 from the TDC (top dead centre) to the BDC (bottom dead centre) .

The internal combustion engine 1 comprises an intake duct 21, through which fresh air needed for the combustion (namely, air containing approximately 20% of oxygen and coming from the outside) is taken in. The intake duct 21 originates from a filter box 22 (schematically shown in figure 1) , which houses, on the inside, an air filter (not shown) and leads into the crank chamber 4 through an intake opening 23 made in a wall of the crankcase 3.

The intake duct 21 ends with a reed valve 24, which is arranged in the area of the intake opening 23 so as to regulate the opening and the closing of the intake duct 21. In other words, the reed valve 24 opens (i.e. allows fresh air to get into the crank chamber 4) when the pressure inside the intake duct 21 is (properly) greater than the pressure present in the crank chamber 4 , and the reed valve

24 closes ( i . e . prevents fresh air from getting into the crank chamber 4 ) when the pressure inside the intake duct 21 is smaller than the pressure present in the crank chamber 4 . Therefore, the reed valve 24 is a passive device designed to adj ust the flow rate used to introduce fresh air into the crank chamber 4 by opening and closing the intake duct 21 depending on the pressure di f ferential between the crank chamber 4 and the intake duct 21 .

According to figure 6 , the reed valve 24 is of the type disclosed in patent application WO2019073448A1 (which is included herein through reference ) and comprises a support body 25 , which is wedge-shaped and in which the base is completely open and makes up the inlet area on the intake side (namely, the area through which fresh air flows in) . The support body 25 has two inclined outer walls , which are opposite one another and have a contrary inclination relative to one another ; in each outer wall there is obtained a pair of through openings , each engaged by a corresponding flexible petal 26 . Between the two outer walls of the support body 25 there is a groove 27 , which has two inner walls , which are parallel to and face one another ; in each inner wall there is obtained a pair of through openings , each engaged by a corresponding flexible petal 26 . Each flexible petal 17 is fixed to the support body 25 on one single side, so that it is free to deform by lifting from the corresponding opening, thus allowing fresh air to flow through the opening.

The reed valve 24 further comprises an injector 28, which is mounted on the support body 25 and directly injects into the crank chamber 4; in other words, the injection nozzle 24 sprays fuel towards the crank chamber 4 (hence, towards the combustion chamber 6) , namely it sprays fuel downstream of the reed valve 24 relative to the fresh air feeding direction along the intake duct 21.

Thanks to its position, the injector 28 is capable of spraying fuel into the crank chamber 4 in any moment, regardless of the inflow of air through the intake opening 23, namely regardless of the opening/closing of the petals 26; therefore, the injection of fuel into the crank chamber 4 carried out by the injector 28 is completely independent of the air intake due to the movement of the petals 26, thus ensuring greater simplicity and freedom in the management of injection times and ensuring an efficiency increase, with a consequent saving of fuel without affecting performances.

The intake duct 21 comprises a throttle valve 29, which adjusts the flow rate of the air flowing along the intake duct 21 up to the intake opening 23 regulated by the reed valve 24. As already mentioned above , the engine 1 is a two- stroke engine and, therefore , it requires a constant supply of lubricant ( oil ) to lubricate , among other things , the main bearings , the bearings of the connecting rod, the crankshaft 5 , the piston pin and the cylinder 2 . In order to do so , the internal combustion engine 1 is provided with a lubricant feeding system 30 ( schematically shown in figure 1 ) , which is of the type disclosed in patent application WO2019073448A1 ( included herein through reference ) and comprises a lubricant tank 31 (which is separate from and independent of the fuel tank) and an electronically-controlled lubrication pump 32 , which gets the lubricant from the tank 31 and feeds the lubricant under pressure towards the intake duct 21 through a feeding duct 33 .

The feeding duct 33 (which, in its end part , branches of f ) leads into two lubrication ori fices , which are obtained through the inner wall o f the support body 25 of the reed valve 24 close to respective openings , so that each lubrication ori fice is closed by a corresponding petal 26 when the petal 26 rests against the inner wall (namely, when the petal closes the respective opening) . In this way, the lubricant under pressure is fed ( getting mixed with the air take in) only when air is actually taken in (hence , only when the engine 1 has been started) , namely only when the petals 26 open, thus simultaneously freeing both the openings through which the air taken in flows and the lubrication orifices through which the lubricant flows .

According to figure 1 , the internal combustion engine 1 comprises a further intake duct 34 , which is arranged in parallel to the intake duct 21 and through which fresh air needed for the combustion is taken in . The intake duct 34 originates from a filter box 22 and leads into the combustion chamber 6 through an intake opening 35 (namely, an intake port ) , which is obtained in a wall of the cylinder 2 and is closer to the exhaust port 8 than the trans fer duct 20 ; the intake opening 35 is cyclically closed by the piston 7 during its reciprocating movement along the cylinder 2 . Furthermore , the intake duct 34 comprises a throttle valve 36 , which adj usts the flow rate of air flowing along the intake duct 34 up to the intake opening 35 regulated by the movement of the piston 7 . It should be pointed out that the two throttle valves 29 and 36 are functionally independent of one another ( even though they could be integrated in one single body) and, hence , can be controlled in a di f ferent manner . Furthermore , it should be pointed out that the intake duct 21 is a main intake duct , through which a larger quantity of air is taken in, whereas the intake duct 34 is a secondary intake duct , through which a smaller quantity of air is taken in; as a consequence , the intake duct 21 has a greater si ze compared to a si ze of the intake duct 34 and the throttle valve 29 is larger than the throttle valve 36 .

The cylinder 2 comprises a cylinder head 37 , which closes the combustion chamber 6 at the top ; namely, the cylinder head 37 is a sort of lid, which delimits the combustion chamber 6 at the top . Through the cylinder head 37 there is arranged ( screwed) a spark plug 38 , which has , at the bottom, a pair of electrodes arranged inside the combustion chamber 6 ; a spark cyclically goes of f between the electrodes (namely, at the end of the compression stroke ) , thus determining the ignition of the air and fuel mixture present in the combustion chamber 6 . In the embodiment shown in the accompanying figures , the spark plug 38 is arranged at the centre of the cylinder head 37 ( and, hence , at the centre of the combustion chamber 6 ) and is coaxial to the longitudinal axis of the combustion chamber 6 ; according to other embodiments which are not shown herein, the spark plug 38 has a di f ferent position (namely, it is no longer central ) and/or a di f ferent inclination relative to the longitudinal axis of the combustion chamber 6 .

In the embodiment shown in the accompanying figures , the electrodes of the spark plug 38 are directly arranged in the ceiling of the combustion chamber 6 ; according to a different embodiment which is not shown herein, in the cylinder head 37 there is obtained a pre-chamber, which communicates with the ceiling of the combustion chamber 6 through one or more connection openings and houses, on the inside, the electrodes of the spark plug 38. When there is the pre-chamber, which houses, on the inside, the electrodes of the spark plug 38, the internal combustion engine 1 can more easily be adapted to also operate with fuels other than pure petrol (such as, for example, a mixture of petrol and ethanol or hydrogen) .

According to a possible embodiment which is not shown herein, when there is the pre-chamber, which houses, on the inside, the electrodes of the spark plug 38, the injector 28 could be arranged in the area of the cylinder head 37 and could end inside the pre-chamber (namely, the injector 28 directly injects fuel into the pre-chamber) .

According to a further embodiment which is not shown herein, when there is the pre-chamber, which houses, on the inside, the electrodes of the spark plug 38, there are two separate and distinct injectors 28 (which are usually used alternatively) ; an injector 28, which is coupled to the reed valve 24 (as shown in the accompanying figures) and is used when the spark plug 38 is not activated and a spontaneous ignition of the mixture takes place (as better described below) , and a further injector 28, which ends inside the pre-chamber (namely, directly inj ects fuel into the pre-chamber ) and is used when the spark plug 38 is activated and a controlled ignition of the mixture takes place ( as better described below) .

According to a further embodiment which is not shown herein, the pre-chamber obtained in the cylinder head 37 contains one single inj ector 28 (which can be the sole inj ector 28 of the internal combustion engine 1 or an additional inj ector 28 in addition to the inj ector 28 coupled to the reed valve 24 ) ; namely, in this embodiment , the pre-chamber obtained in the cylinder head 37 does not contain the electrodes of the spark plug 38 .

To sum up, in the cylinder head 37 there can be a prechamber, which communicates with the ceiling of the combustion chamber 6 through one or more connection openings and houses , on the inside , the electrodes of the spark plug 38 and/or the noz zle of an inj ector 28 (which can be the sole inj ector 28 of the internal combustion engine 1 or an additional inj ector 28 in addition to the inj ector 28 coupled to the reed valve 24 ) .

According to an alternative embodiment shown with a broken line in figure 1 , there could be an isolation valve 39 , which is arranged along the alternative duct 11 (very) close to the confluence with the exhaust duct 9 . The isolation valve 39 is necessarily ( completely) opened when the shutter 14 is in the maximum resistance position ( shown in figure 4 ) , in which the shutter 14 closes the inlet of the exhaust duct 9 , thus forcing the exhaust gases to flow through the sole alternative duct 11 ; indeed, in this configuration, the exhaust gases must flow through the alternative duct 11 and, hence , must be capable of flowing from the alternative duct 11 to the exhaust duct 9 flowing through the isolation valve 39 . On the other hand, the isolation valve 39 is generally ( completely) closed when the shutter 14 is in the minimum resistance position ( shown in figure 5 ) , in which the shutter 14 closes the inlet of the alternative duct 11 , thus forcing the exhaust gases to flow through the sole exhaust duct 9 ; in this case , the function of the isolation valve 39 is that of preventing the exhaust gases from expanding, when flowing through the alternative duct 11 , along the alternative duct 11 downstream of the secondary catalytic converter 12 , hence creating potential negative interferences with the regular flow of the exhaust gases along the exhaust duct 9 .

It should be pointed out that , when the shutter 14 is in the minimum resistance position ( shown in figure 5 ) , the isolation valve 39 could be opened or closed depending on the engine point (namely, depending on the rotation speed and on the load) so as to prevent the exhaust gases flowing through the exhaust duct 9 from expanding along the alternative duct 11 , when this expansion negatively af fects performances , and so as to allow the exhaust gases flowing through the exhaust duct 9 to expand along the alternative duct 11 , when this expansion positively af fects performances .

Generally speaking, the isolation valve 39 is an ON/OFF valve, namely it can only assume a complete open position and a complete close position .

According to an alternative embodiment shown with a broken line in figure 1 , there could be a reed valve 40 , which is arranged at the end of the intake duct 34 close to the intake opening 35 . The function of the reed valve 40 is that of ensuring that the air flow along the intake duct 34 always flows in one single direction, namely always flows into the combustion chamber 6 ; in this way, the gases present in the combustion chamber 6 are prevented from flowing into the intake duct 34 , reaching the throttle valve 36 and even flowing past it .

According to figure 1 , the internal combustion engine 1 comprises a liquid cooling system 41 , which is provided with a circulation circuit 41 (provided with a radiator ) and with a cooling pump 43 . The circulation circuit 41 comprises , among other things , a feeding duct 44 , which leads a cooling liquid ( typically water mixed with anti- freeze and anti-corrosion additives ) in the area of ( close to ) the electric actuator 15 controlling the shutter 14 in order to prevent the electric actuator 15 from reaching temperatures that are too high .

According to a possible embodiment , the bearings supporting the crankshaft 5 could be sel f-lubricating bearings (namely, could have a lubricant tank of their own isolated from the outside instead of using a total-loss lubricating system shared with the rest of the internal combustion engine 1 ) and could feature a liquid cooling, which uses the cooling liquid of the internal combustion engine 1 ; as a consequence , the circulation circuit 41 could comprise a feeding duct 45 , which also leads the cooling liquid of the internal combustion engine 1 towards the main bearings where the bearings supporting the crankshaft 5 are housed . For example , the main bearings could define chambers that are hydraulically isolated by means of suitable gaskets , surround the bearings and allow the cooling liquid of the internal combustion engine 1 to flow inside them . In this way, the lubricant introduced by the lubricant feeding system 30 does not need to reach the bearings supporting the crankshaft 5 and, therefore , can be introduced with a smaller flow rate compared to a standard internal combustion engine (with a signi ficant reduction in the consumption of oil and, hence , in the generation of polluting emissions ) ; in other words , the lubricant introduced by the lubricant feeding system 30 only has to lubricate the connecting rod and the piston 7 , but does not have to lubricate the bearings supporting the crankshaft 5 with a saving of lubricant .

According to a di f ferent embodiment which is not shown herein, the crankshaft 5 has a series of through holes/channels , which are designed to let through part of the lubricant caused to circulate by the lubrication pump 32 ; namely, the crankshaft 5 has a series of through holes/channels , which are part of the lubricant feeding system 30 and, in use , are flown through by the lubricant caused to circulate by the lubrication pump 32 . These through holes/channels of the crankshaft 5 lead in the area of the main bearings in order to properly lubricate the bearings supporting the crankshaft 5 . In this way, the lubricant directly gets close to the bearings supporting the crankshaft 5 and does not need to reach the bearings supporting the crankshaft 5 from the lubrication ori fices obtained through the inner wall o f the support body 25 of the reed valve 24 (with an overall lubricant saving) .

According to a preferred embodiment , the exhaust valve 13 , the alternative duct 11 and the secondary catalytic converter 12 are housed in a decomposable support body ( a lid) , which is fixed on the outside of the cylinder 2 ; in this way, these components can be added to an existing internal combustion engine 1 in a relatively simple manner .

The internal combustion engine 1 described above can operate both with a spontaneous ignition ( sel f-ignition) of the mixture (hence , keeping the spark plug 38 turned of f ) and with a controlled ignition of the mixture thanks to the intervention of the spark plug 38 . The spontaneous ignition of the mixture allows for a particularly high energy ef ficiency and also reduces the generation of pollutants ; however, in order to obtain the spontaneous ignition of the mixture in a stable manner, the engine point ( defined in the rotation speed / load plane ) cannot be too forced, namely the spontaneous ignition of the mixture can be obtained in a stable manner only when the rotation speed and the load are not too high . When the engine point ( defined in the rotation speed / load plane ) is highly forced ( i . e . when the rotation speed and the load are high) , the spontaneous ignition of the mixture cannot be obtained in a stable manner and the controlled ignition of the mixture needs to be used, which allows for maximum performances .

According to figure 7 , in the plane defined by the rotation speed ( on the abscissa in figure 7 ) and by the load ( on the ordinate in figure 7 ) it is possible to identi fy an area ( indicated with letter "S" ) , in which a control unit 46 ( schematically shown in figure 1 ) causes the internal combustion engine 1 to operate with the spontaneous ignition of the mixture , and another complementary area ( indicated with letter "P" ) , in which the control unit 46 ( schematically shown in figure 1 ) causes the internal combustion engine 1 to operate with the controlled ignition of the mixture (namely, with the traditional ignition by means of a spark generated by the spark plug 38 ) .

In order to increase ( expand) the area ( indicated with letter "S" ) , in which a control unit 46 ( schematically shown in figure 1 ) causes the internal combustion engine 1 to operate with the spontaneous ignition of the mixture , the shutter 14 is placed in the maximum resistance position ( shown in figure 4 ) , in which the shutter 14 closes the inlet of the exhaust duct 9 , thus forcing the exhaust gases to flow through the sole alternative duct 11 and, hence , to also flow through the secondary catalytic converter 12 . Indeed, when the shutter 14 is in the maximum resistance position, the exhaust gases are faced with a high pneumatic resistance while flowing out of the combustion chamber 6 and this causes a signi ficant increase in the pressure inside the combustion chamber 6 , thus encouraging the spontaneous ignition of the mixture . In other words , thanks to the fact that the shutter 14 can be placed in the a maximum resistance position, in which the exhaust gases are forced to follow a path with a high pneumatic resistance (namely, a path with high load los ses ) , the pressure inside the combustion chamber 6 can be increased and, hence , a spontaneous ignition of the mixture can be obtained in an area ( indicated with letter "P" ) which is very large (namely, almost for the entire normal use of the internal combustion engine 1 ) .

According to the variant shown in figure 8 , in the plane defined by the rotation speed ( on the abscissa in figure 8 ) and by the load ( on the ordinate in figure 8 ) it is possible to identi fy a further transition area ( indicated with letter "T" ) arranged between the area S , in which the control unit 46 causes the internal combustion engine 1 to operate with the spontaneous ignition of the mixture , and the area P, in which the control unit 46 causes the internal combustion engine 1 to operate with the controlled ignition of the mixture (namely, with the traditional ignition by means of a spark generated by the spark plug 38 ) . In the transition area T, the operation of the internal combustion engine 1 can be uncertain, since , in the transition area, the control unit 46 activates the spark plug 38 in any case , even if there can previously be (namely before the spark goes of f between the electrodes of the spark plug 38 ) a spontaneous ignition of the mixture .

In other words , in the transition area T a spontaneous ignition of the mixture should take place, but , to be on the safe side , the control unit 46 activates anyway the spark plug 38 in order to avoid mis fires should the spontaneous ignition of the mixture fail to take place . The presence of the transition area T makes the operation of the internal combustion engine 1 more regular when shi fting from the area A to the area P .

Besides , when the internal combustion engine 1 is started from cold, the shutter 14 is placed in the maximum resistance position ( shown in figure 4 ) , in which the shutter 14 closes the inlet of the exhaust duct 9 , thus forcing the exhaust gases to flow through the sole alternative duct 11 and, hence , to also flow through the secondary catalytic converter 12 ; in this way, the exhaust gases can very quickly heat the secondary catalytic converter 12 (which has a much smaller volume than the main catalytic converter 10 and is also arranged in contact with the cylinder 2 , thus also receiving heat from the cylinder 2 through conduction) in order to quickly reach an ef fective catalytic treatment of the exhaust gases (which is what the most recent standards enforced in terms of internal combustion engine type approval require ) .

During the first instants of a cold start , the feeding duct 34 (which only feeds fresh air into the combustion chamber 6 ) can be used to increase the quantity of fresh air present in the combustion chamber 6 (namely, to have excess fresh air, hence oxygen, relative to the stoichiometric ratio ) , which allows the temperature of the catalytic converter 12 to increase more quickly .

Obviously, the control mode described above and schematically shown in figure 7 applies to an internal combustion engine 1 used within a wide range (which is , for example , what happens in motorcycle applications ) ; i f the internal combustion engine 1 is used at a constant speed and with a relatively scarcely variable load (which is , for example , what happens in case of an electric motor generator ) , a control mode would be possible , which entails an operation always ( or almost always ) featuring a spontaneous ignition of the mixture , which allows for a greater energy ef ficiency and for a smaller production of polluting substances .

The map shown in figure 7 and stored in the control unit 46 obviously also depends on other factors (namely, is corrected/compensated based on other factors ) such as , for example , the temperature of the cooling liquid .

As mentioned above and according to a preferred embodiment , the exhaust port 19a is provided, which allows a ( limited) part of the exhaust gases to reach the alternative duct 11 and flow through the secondary catalytic converter 12 even when the shutter 14 is in the minimum resistance position (shown in figure 5) ; in this way, even when the shutter 14 is in the minimum resistance position (shown in figure 5) , the secondary catalytic converter 12 carries out the catalysis and remains properly hot and, therefore, if the shutter 14 is moved to the maximum resistance position (shown in figure 4) , the secondary catalytic converter 12 immediately is active and effective .

It should be pointed out that, regardless of the position of the shutter 14, the main catalytic converter 10 is always flown through by the exhaust gases and, hence, is constantly heated by the exhaust gases, since the alternative duct 11 where the second catalytic converter 12 is housed leads into the exhaust duct 6 upstream of the main catalytic converter 10.

According to figures 9 and 10, the shutter 14 of the exhaust valve 13 has a side wall (whose presence is necessary to ensure the shutter 14 a sufficient rigidity) , which, when the shutter 14 is in the minimum resistance position (shown in figure 10) , in which the shutter 14 closes the inlet of the alternative duct 11, covers the inlet opening 19b; in order to prevent the side wall of the shutter 14 from closing the inlet opening 19b when the shutter 14 is in the minimum resistance position (shown in figure 10) , hence nullifying the function of the inlet opening 19b, the side wall of the shutter 14 has a through hole 47 , which, when the shutter 14 is in the minimum resistance position, is centred on the inlet opening 19b .

The embodiments described herein can be combined with one another, without for this reason going beyond the scope of protection of the invention .

It should be pointed out that the internal combustion engine 1 described above can find advantageous application in multiple application fields : terrestrial mobility ( as single engine for motorcycles , mopeds and snowmobiles , but also as "range-extender" for electric drive vehicles when connected to an electric generator ) , boating, aeronautics , work tools ( rotary tillers , string trimmers , lawn mowers , electric saws ) , electric motor generators and others .

The internal combustion engine 1 described above has numerous advantages .

First of all , the internal combustion engine 1 described above ensures a high energy efficiency and, especially, a particularly small pollutant emis sion, to such an extent that it can be granted type approval according to the most recent anti-pollution standards ( for example , in case of motorcycles and mopeds , the so-called "Euro5" standards ) ; this result is obtained ( also ) thanks to the presence of the exhaust valve 13 , which deflects the exhaust gases towards the alternative duct 11 provided with the secondary catalytic converter 12 , so as to remarkably extend the operation points of the internal combustion engine 1 in which the spontaneous ignition of the mixture can be obtained in a stable manner .

Furthermore , the internal combustion engine 1 described above has an excellent operating regularity, at all speeds .

Finally, the internal combustion engine 1 described above is particularly light , compact and economic compared to a similar four-stroke internal combustion engines with the same performances and the same type approval class .

LIST OF THE REFERENCE NUMBERS OF THE FIGURES

1 internal combustion engine

2 cylinder

3 crankcase

4 crank chamber

5 crankshaft

6 combustion chamber

7 piston

8 exhaust port

9 exhaust duct

10 main catalytic converter

11 alternative duct

12 secondary catalytic converter

13 exhaust valve shutter electric actuator wall wall hole a exhaust port b inlet opening trans fer ducts intake duct filter box intake opening reed valve support body petal groove inj ector throttle valve feeding system tank lubrication pump feeding duct intake duct intake opening throttle valve cylinder head 38 spark plug

39 isolation valve

40 reed valve

41 cooling system

42 circulation circuit

43 cooling pump

44 feeding duct

45 feeding duct

46 control unit 47 hole

Claims

1) A two-stroke internal combustion engine (1) with fuel injection; the internal combustion engine (1) comprises : at least one cylinder (2) , which comprises, on the inside, a combustion chamber (6) provided with a first exhaust port (8) ; an exhaust duct (9) , which originates from the exhaust port ( 8 ) ; a main catalytic converter (10) , which is arranged along the exhaust duct (9) ; a piston (7) , which is mounted inside the cylinder (2) so as to slide in a reciprocating manner; a cylinder head (37) , which closes the combustion chamber (6) at the top; a spark plug (38) , which is arranged in the cylinder head (37) ; a crankcase (3) , from which the cylinder projects (2) and in which a crank chamber (4) is obtained; a crankshaft (5) , which is housed in the crank chamber (4) ; a main intake duct (21) , which feeds fresh air towards the combustion chamber (6) ; an alternative duct (11) , which is arranged in parallel to the exhaust duct (9) , originates in the area of the first exhaust port (8) and ends in the exhaust duct (9) upstream of the main catalytic converter (10) ; a secondary catalytic converter (12) , which is arranged along the alternative duct (11) and has a smaller size than a size of the main catalytic converter (10) ; and an exhaust valve (13) , which is arranged in the area of the exhaust port (8) and comprises a shutter (14) , which is movable between a minimum resistance position, in which the shutter (14) allows the exhaust gases to flow through the exhaust duct (9) , and a maximum resistance position, in which the shutter (14) closes the inlet of the exhaust duct (9) , thus forcing the exhaust gases to flow through the sole alternative duct (11) ; and a control unit (46) ; the internal combustion engine (1) is characterized in that the control unit (46) is configured to cause the internal combustion engine (1) to operate both with the spontaneous ignition of the mixture without activating the spark plug (38) and with the controlled ignition of the mixture activating the spark plug (38) .

2) The internal combustion engine (1) according to claim 1, wherein: the control unit (46) is configured to use a map in the plane defined by the rotation speed and by the load, in which there are defined a first operation area (S) , in which the internal combustion engine (1) operates with the spontaneous ignition of the mixture, and a second operation area (P) with the controlled ignition of the mixture, in which the internal combustion engine (1) operates with the controlled ignition of the mixture; and the first operation area (S) with the spontaneous ignition of the mixture has a smaller load compared to the second operation area (P) with the controlled ignition of the mixture .

3) The internal combustion engine (1) according to claim 2, wherein in the plane defined by the rotation speed and by the load there is identified a third transition area (T) , which is arranged between the first area (S) and the second area (P) and in which the spontaneous ignition of the mixture is expected, but the control unit (46) activates anyway the spark plug (38) in order to avoid misfires should the spontaneous ignition of the mixture fail to take place.

4) The internal combustion engine (1) according to claim 1, 2 or 3, wherein the control unit (46) is configured to place the shutter (14) in the maximum resistance position in order to cause the internal combustion engine (1) to operate with the spontaneous ignition of the mixture.

5) The internal combustion engine (1) according to one of the claims from 1 to 4, wherein the control unit (46) is configured to place the shutter (14) in the maximum resistance position and to hold it there when the internal combustion engine (1) is started from cold.

6) The internal combustion engine (1) according to one of the claims from 1 to 5, wherein: in the minimum resistance position, the shutter (14) closes the inlet of the alternative duct (11) , thus forcing the exhaust gases to flow through the sole exhaust duct ( 9 ) ; and the shutter (14) comprises: a first wall (16) , which closes the inlet of the alternative duct (11) in the minimum resistance position and closes the inlet of the exhaust duct (9) in the maximum resistance position; and a second wall (17) , which is connected to the first wall (16) , is crossed by at least one through hole (18) and partially closes the inlet of the alternative duct (11) in the maximum resistance position.

7) The internal combustion engine (1) according to one of the claims from 1 to 6, wherein a second exhaust port (19a) is provided, which is separate from and independent of the first exhaust port (8) , has a smaller size than a size of the first exhaust port (8) , is not affected by the shutter (14) in any way and directly leads to the alternative duct (11) . 8) The internal combustion engine (1) according to claim 7, wherein: the second port (19a) directly leads to the alternative duct (11) through a suitable duct leading into an inlet opening (19b) ; the shutter (14) of the exhaust valve (13) has a side wall, which, when the shutter (14) is in the minimum resistance position, covers the inlet opening (9b) ; and the side wall of the shutter (14) has a through hole (47) , which is centred, when the shutter (14) is in the minimum resistance position, on the inlet opening (19b) .

9) The internal combustion engine (1) according to one of the claims from 1 to 8, wherein: the main intake duct (21) leads to the crank chamber (4) through a first intake opening (23) obtained in a wall of the crankcase (3) ; a first reed valve (24) is provided, which is arranged inside the main intake duct (21) close to the first intake opening (23) and is provided with a support body (25) ; and a fuel injector (28) is provided, which is mounted through the support body (25) of the first reed valve (24) so that the injection nozzle (24) is on the outside of the support body (25) and sprays fuel downstream of the first reed valve (24) relative to the direction in which fresh air is fed along the main intake duct (21) . 10) The internal combustion engine (1) according to one of the claims from 1 to 9, wherein: the main intake duct (21) originates from a filter box

(22) and leads to the crank chamber (4) through a first intake opening (23) obtained in a wall of the crankcase ( 3 ) ; and a secondary intake duct (34) , which is arranged in parallel to the main intake duct (21) , originates from the filter box (22) and leads to the combustion chamber (6) through a second intake opening (35) obtained in a wall of the cylinder (2) .

11) The internal combustion engine (1) according to claim 10, wherein: the main intake duct (21) comprises a first throttle valve (29) , which adjusts the flow rate of the air flowing along the intake duct (21) up to the first intake opening

(23) regulated by the first reed valve (24) ; and the secondary intake duct (34) comprises a second throttle valve (36) , which adjusts the flow rate of the air flowing along the secondary intake duct (34) up to the second intake opening (35) regulated by the movement of the piston ( 7 ) .

12) The internal combustion engine (1) according to claim 11, wherein the two throttle valves (29, 36) are functionally independent of one another and, hence, can be controlled in a different manner.

13) The internal combustion engine (1) according to claim 10, 11 or 12, wherein a second reed valve (40) is provided, which is arranged at the end of the secondary intake duct (34) close to the second intake opening (35) .

14) The internal combustion engine (1) according to one of the claims from 1 to 13, wherein the spark plug (38) is arranged in a pre-chamber, which communicates with a ceiling of the combustion chamber (6) through one or more connection openings.

15) The internal combustion engine (1) according to one of the claims from 1 to 14, wherein an isolation valve (39) is provided, which is arranged along the alternative duct (11) downstream of the secondary catalytic converter (12) .

16) The internal combustion engine (1) according to claim 15, wherein the control unit (46) is configured to always open the isolation valve (39) when the shutter (14) is arranged in the maximum resistance position.

17) The internal combustion engine (1) according to one of the claims from 1 to 16 and comprising: a lubricant feeding system (30) ; a liquid cooling system (41) ; and two bearings, which support the crankshaft (5) and are self-lubricating, since they are provided with their own lubricant tank, which is isolated from the lubricant feeding system (30) .

18) The internal combustion engine (1) according to claim 17, wherein: the bearings feature a liquid cooling, which uses the cooling liquid of the liquid cooling system (41) ; and the liquid cooling system (41) comprises a feeding duct (45) , which leads the cooling liquid of the internal combustion engine (1) towards main bearings, which house the bearings supporting the crankshaft (5) .

19) The internal combustion engine (1) according to one of the claims from 1 to 18, wherein: the shutter (14) is operated by an electric actuator (15) , which moves the shutter (14) between the minimum resistance position and the maximum resistance position; and a liquid cooling system (41) is provided, which leads a cooling liquid close to the electric actuator (15) .

20) A two-stroke internal combustion engine (1) with fuel injection; the internal combustion engine (1) comprises : at least one cylinder (2) , which comprises, on the inside, a combustion chamber (6) provided with a first exhaust port (8) ; an exhaust duct (9) , which originates from the exhaust port ( 8 ) ; a main catalytic converter (10) , which is arranged along the exhaust duct (9) ; a piston (7) , which is mounted inside the cylinder (2) so as to slide in a reciprocating manner; a cylinder head (37) , which closes the combustion chamber (6) at the top; a spark plug (38) , which is arranged in the cylinder head (37) ; a crankcase (3) , from which the cylinder projects (2) and in which a crank chamber (4) is obtained; a crankshaft (5) , which is housed in the crank chamber (4) ; a main intake duct (21) , which feeds fresh air towards the combustion chamber (6) ; an alternative duct (11) , which is arranged in parallel to the exhaust duct (9) , originates in the area of the first exhaust port (8) and ends in the exhaust duct (9) upstream of the main catalytic converter (10) ; a secondary catalytic converter (12) , which is arranged along the alternative duct (11) and has a smaller size than a size of the main catalytic converter (10) ; and an exhaust valve (13) , which is arranged in the area of the exhaust port (8) and comprises a shutter (14) , which is movable between a minimum resistance position, in which 40 the shutter (14) allows the exhaust gases to flow through the exhaust duct (9) , and a maximum resistance position, in which the shutter (14) closes the inlet of the exhaust duct (9) , thus forcing the exhaust gases to flow through the sole alternative duct (11) ; and a control unit (46) .