Two-stroke internal combustion engine

Abstract

A two-stroke internal combustion engine (1) presenting: a cylinder (2), which presents, on the inside, a combustion chamber (5) provided with an exhaust port (8) and an intake port (10); an exhaust chamber (9) originating from the exhaust port (8); an exhaust valve (14), which is arranged in the exhaust chamber (9) on the outside of the combustion chamber (5); a piston (6), which is mounted inside the cylinder (2) so as to slide in a reciprocating manner; a drive shaft (4), which is mounted so as to rotate around a rotation axis (A1); a connecting rod (7), which connects the piston (6) to the drive shaft (4); and a control system (15) for the exhaust valve (14), which is designed to control the opening and the closing of the exhaust valve (14) and presents: at least one cam (16), which is integral to the drive shaft (4) so as to rotate around the rotation axis (A) together with the drive shaft (4); and a cam-follower roller (17), which engages the cam (16) and is connected to the exhaust valve (14) so as to move the exhaust valve (14) between a closing position and an opening position.

Description

[0001] “TWO-STROKE INTERNAL COMBUSTION ENGINE”

[0002] Cross-Reference to Related Applications

[0003] This Patent Applications claims priority from Italian Patent Applications No. 102024000007297 and No. 102024000007300 both filed on April 3, 2024, the entire disclosure of which is incorporated herein by reference.

[0004] Field of Technology

[0005] The present invention relates to a two-stroke internal combustion engine.

[0006] State of the Art

[0007] The two-stroke internal combustion engine was invented by Dugald Clerk in 1879 and differs from the more widespread four-stroke internal combustion engine mainly due to the different alternation of the active phases (useful or power phases) in relation to the crankshaft revolutions: in fact, if in the four-stroke engine there is an active phase (i.e. the expansion phase in which the transformation of chemical energy into thermal energy and therefore into kinetic energy occurs) for every two complete revolutions of the shaft, in the two-stroke engine there is an active phase for every complete revolution of the shaft. Structurally, a two-stroke internal combustion engine does not normally have the classic intake and exhaust valves, which are replaced by "ports", i.e. slits that are made directly on the cylinder and are opened and closed by the up and down motion of the piston.

[0008] The two-stroke internal combustion engine is an extremely simple, compact, lightweight, and economical engine and for this reason it has almost always been used in the past in smalldisplacement mopeds and in small-scale applications (small generators, chainsaws, lawnmowers, small outboard marine engines).

[0009] Patent application US2004127295A1 discloses a torsional vibration damping device to be mounted on the drive shaft of an internal combustion engine.

[0010] Patent application US2015184574A1 discloses a two-stroke internal combustion engine equipped with a fuel injection device.

[0011] Patent application US2012222658A1 discloses an internal combustion engine equipped with a cylinder having a double chamber. Description of the Invention

[0012] The purpose of this invention is to create a two-stroke internal combustion engine that can deliver high power, is particularly light and compact, and, at the same time, is easy and economical to produce.

[0013] According to the present invention, a two-stroke internal combustion engine is provided, as claimed in the appended claims.

[0014] The claims describe preferred embodiments of the present invention and form an integral part of this specification.

[0015] Brief Description of the Drawings

[0016] The present invention will now be described with reference to the attached drawings, which illustrate a non-limiting example of its implementation, in which:

[0017] - Figure 1 is a perspective view schematic with parts removed for clarity, of a two-stroke internal combustion engine made in accordance with the present invention;

[0018] - Figure 2 is a sectional view schematic with parts removed for clarity of the internal combustion engine of Figure 1 ;

[0019] - Figure 3 is a perspective and exploded view of two cams of the internal combustion engine of Figure 1 ;

[0020] - Figure 4 is a perspective and exploded view of a crankshaft balancing system of the internal combustion engine of Figure 1 ; and

[0021] - Figure 5 is a perspective view of a component of the balancing system of Figure 4.

[0022] Preferred Embodiments of the Invention

[0023] In figures 1 and 2, number 1 indicates a complete two-stroke internal combustion engine with fuel injection.

[0024] In the (non-limiting) embodiment illustrated in the attached figures, the engine 1 is singlecylinder, that is, it comprises a single cylinder 2 (illustrated in figure 2); according to other embodiments not illustrated, the engine 1 could be twin-cylinder or could even have more than two cylinders 2. Inside a crankcase 3, a crank chamber (not illustrated) is obtained in which a crankshaft 4 is housed, mounted so as to rotate around a rotation axis A1 .

[0025] Cylinder 2 internally comprises a combustion chamber 5 (illustrated in figure 2) which has a cylindrical symmetry around a longitudinal axis; inside cylinder 2 a piston 6 (illustrated in figure 2) slides alternately, the seat of which is obtained in cylinder 2. The piston 6 is connected to the crankshaft 4 by means of a connecting rod 7, the lower part of which is located inside the crank chamber.

[0026] In the side wall of the combustion chamber 5, (at least) one exhaust port 8 opens which expels the exhaust gases towards an exhaust chamber 9 and is cyclically opened and closed by the rotary movement of the crankshaft 4, in synchrony with the reciprocating movement of the piston 6. The exhaust chamber 9 is different and separate from the combustion chamber 5, it is located next to the combustion chamber 5, and is connected to the combustion chamber 5 through the exhaust port 8, i.e. the exhaust chamber 9 originates from the exhaust port 8. In other words, next to the combustion chamber 5 there is another confined volume that constitutes the exhaust chamber 9, is separated from combustion chamber 5, and communicates with combustion chamber 5 only through exhaust port 8.

[0027] Similarly, in the cylinder 3, (at least) one intake port 10 opens (schematically illustrated in figure 2) which is arranged in a different position from the exhaust port 8, receives a mixture of air (combustible) and fuel from an intake duct 11 (schematically illustrated in figure 2), and is cyclically opened and closed by the reciprocating movement of the piston 6. The intake duct 11 originates from a filter box (not illustrated) which houses an air filter inside it and ends in the intake port 10 (possibly passing through the crank chamber).

[0028] According to a possible embodiment, a reed valve configured to regulate the opening and closing of the intake duct 11 and a fuel injector preferably located upstream of the reed valve are provided along the intake duct 11. In other words, the reed valve opens (i.e. allows the flow of fresh air towards the combustion chamber 5) when the pressure present upstream of the reed valve is higher than the pressure present downstream of the reed valve and the reed valve closes (i.e. prevents the flow of fresh air towards the combustion chamber 5) when the pressure present upstream of the reed valve is lower than the pressure present downstream of the reed valve. Therefore, the reed valve is a passive device for regulating the flow rate of fresh air into the combustion chamber 5.

[0029] According to a possible embodiment, a butterfly valve can be arranged along the intake duct 11 and upstream of the reed valve pack and the injector, which regulates the flow of air that flows along the intake duct 11.

[0030] The internal combustion engine 1 comprises a cylinder head 12 that closes the combustion chamber 5 at the top; that is, the cylinder head 12 is a sort of cover that delimits the combustion chamber 5 at the top. A spark plug 13 is arranged (screwed) through the cylinder head 12 and has a pair of electrodes arranged at the bottom inside the combustion chamber 5; cyclically (that is, at the end of the compression phase) a spark is struck between the electrodes which determines the ignition of the air and fuel mixture present in the combustion chamber 5. In the embodiment illustrated in the attached figures, the spark plug 13 is arranged at the center of the cylinder head 12 (and therefore at the center of the combustion chamber 5) and is coaxial with the longitudinal axis of the combustion chamber 5; according to other embodiments not illustrated, the spark plug 13 has a different position (that is, no longer central) and / or a different inclination with respect to the longitudinal axis of the combustion chamber 5.

[0031] The internal combustion engine 1 described above can operate both with spontaneous ignition (self-ignition) of the mixture (therefore keeping the spark plug 13 off), and with controlled ignition of the mixture thanks to the intervention of the spark plug 13. Spontaneous ignition of the mixture allows for particularly high energy efficiency to be obtained and also allows for a reduction in the generation of pollutants; however, to obtain spontaneous ignition of the mixture in a stable manner, it is necessary that the engine point (defined in the rotation speed / load plane) is not too high, that is, it is possible to obtain spontaneous ignition of the mixture 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 very high (that is, when the rotation speed and the load are high) then it is not possible to obtain spontaneous ignition of the mixture in a stable manner and it is necessary to resort to controlled ignition of the mixture which allows for maximum performance to be obtained.

[0032] In the embodiment illustrated in the attached figures, the electrodes of the spark plug 13 are arranged directly in the ceiling of the combustion chamber 5; according to a different embodiment not illustrated, a pre-chamber is obtained in the cylinder head 12 which communicates with the ceiling of the combustion chamber 5 through one or more connecting openings and houses the electrodes of the spark plug 13 inside it. When the pre-chamber is present which houses the electrodes of the spark plug 13 inside it, the internal combustion engine 1 is more easily adaptable to operate with fuels other than pure petrol (such as, for example, a mixture of petrol and ethanol or hydrogen).

[0033] According to a possible embodiment not illustrated, when the pre-chamber is present which houses the electrodes of the spark plug 13, the injector could be positioned in correspondence with the cylinder head 12 and could end inside the pre-chamber (i.e. the injector injects the fuel inside the pre-chamber).

[0034] According to a further embodiment not illustrated, when the pre-chamber is present which houses the electrodes of the spark plug 13 inside it, two separate and distinct injectors are present (and which are generally used alternatively): an injector which is arranged along the intake duct 11 upstream of the reed valve pack which is used when the spark plug 13 is not activated and spontaneous ignition of the mixture occurs, and a further injector which ends inside the pre-chamber (i.e. injects the fuel directly into the pre-chamber) and is used when the spark plug 13 is activated and controlled ignition of the mixture occurs.

[0035] According to a further embodiment not illustrated, the pre-chamber obtained in the cylinder head 12 contains only one injector (which may be the only injector of the internal combustion engine 1 or an additional injector with respect to the injector arranged along the intake duct 11); that is, in this embodiment, the pre-chamber obtained in the cylinder head 12 does not contain the electrodes of the spark plug 13.

[0036] To summarize, a pre-chamber can be obtained in the cylinder head 12 which communicates with the top of the combustion chamber 5 through one or more connecting openings and houses inside it the electrodes of the spark plug 13 and / or the nozzle of an injector (which can be the only injector of the internal combustion engine 1 or an additional injector with respect to the injector 28 arranged along the intake duct 11).

[0037] As illustrated in Figure 2, the internal combustion engine 1 comprises an exhaust valve 14 which is arranged in the exhaust chamber 9 outside the combustion chamber 5 (i.e., it is arranged laterally to the exhaust port 8 and at a certain distance from the exhaust port 8) and is movable between a closed position (in which it prevents the flow of exhaust gas from the exhaust chamber 9 to an exhaust duct arranged downstream of the exhaust chamber 9) and an open position (in which it allows the flow of exhaust gas from the exhaust chamber 9 to the exhaust duct). Furthermore, the internal combustion engine 1 comprises an exhaust valve 14 control system 15 adapted to control the opening and closing of the exhaust valve 14, i.e. adapted to move the exhaust valve 14 between the closed position and the open position.

[0038] The exhaust valve 14 is mounted outside the combustion chamber 5 so as never to interfere with the reciprocating movement of the piston 6 and therefore safeguarding the internal combustion engine 1 from catastrophic valve / piston interference caused by momentary over- revving or breakages of the components involved in the kinematic chain of the motion of the exhaust valve 14.

[0039] The control system 15 comprises two cams 16, each of which is integral with the drive shaft 4 to rotate together with the drive shaft 4 around the rotation axis A1 ; furthermore, the control system 15 comprises two cam-follower rollers 17 (better illustrated in figure 3), each of which engages a respective cam 16 and is connected to the exhaust valve 14 so as to move the exhaust valve 14 between the closed position and the open position. In the preferred embodiment illustrated in the attached figures, two twin cams 16 are provided, placed side by side (each coupled to a respective cam-follower roller 17) to operate in parallel, while according to a different embodiment not illustrated, a single cam 16 and therefore a single cam-follower roller 17 is provided.

[0040] The exhaust valve 14 is mushroom-shaped and comprises a stem 18 which at one end supports the head (shutter) of the exhaust valve 14 and at the opposite end is connected to the two cam-following rollers 17. That is, the two cam-following rollers 17 are hinged at one end of the stem 18 and are arranged on opposite sides of the stem 18. Therefore, each cam-following roller 17 engages the respective cam 16 by rolling on one side and on an opposite side is carried by a terminal portion of the stem 18 of the exhaust valve 14 arranged on the opposite side with respect to a head (shutter) of the exhaust valve 14.

[0041] According to a preferred embodiment illustrated in the attached figures, each cam 16 has a groove 19 closed on itself and the corresponding cam follower roller 17 is inserted in the groove 19 of the cam 16 to roll-engage the groove 19 so as to move the exhaust valve 14 both from the closed position to the open position and from the open position to the closed position. That is, the control system 15 is desmodromic since the movement of the cam follower rollers 17 generated by the cams 16 controls both the opening stroke and the closing stroke of the exhaust valve 14 (therefore without the use of any return spring that generates the movement of the exhaust valve 14).

[0042] As better illustrated in figure 3, the two cams 16 are arranged as mirror images of each other and face each other and the two cam follower rollers 17 are arranged between the two cams 16 in an opposite position with respect to the stem 18 of the exhaust valve 14. In other words, two opposing shells are provided, in each of which a corresponding cam 16 is obtained. According to a preferred embodiment illustrated in Figures 1 and 2, the control system 15 also comprises a deformable compensation member 20 mounted on the stem 18 of the exhaust valve 14 to recover its clearances. In particular, the compensation member 20 comprises a spring 21 which is coaxial with the stem 18 of the valve, is abutted with one end against the cylinder 2 of the internal combustion engine 1 and with the other end against a stop body 22 integral with the stem 18 of the exhaust valve 14.

[0043] According to a preferred embodiment, the crankshaft 4 comprises two coaxial half-shafts

[0044] 23 which are separate and independent and are arranged coaxially (i.e. coaxial to the same main rotation axis A1) at a certain distance from each other on opposite sides with respect to the connecting rod 7; in this embodiment, the cams 16 are integral with one of the two halfshafts 23. Furthermore, in this embodiment, two connecting discs 24 are provided (better illustrated in figures 4 and 5), each of which is integral with a respective half-shaft 23 and connects the respective half-shaft 23 to the connecting rod 7. That is, the connecting rod 7 is arranged in an empty space between the two connecting discs 24 (i.e. between the two halfshafts 23).

[0045] According to a preferred embodiment illustrated in figures 4 and 5, each connecting disc

[0046] 24 has a central seat 25 of cylindrical shape which is coaxial to the main rotation axis A1 and houses one end of a respective half-shaft and a peripheral seat 26 of cylindrical shape which is coaxial to a secondary rotation axis A2 parallel and spaced from the main rotation axis A1 (therefore the peripheral seat 26 is arranged eccentrically with respect to the central seat 25) and houses one end of a connecting rod pin 27 on which one end of the connecting rod 7 is hinged (i.e. the crank pin or connecting rod big end). In each connecting disc 24, the central seat 25 faces outwards (i.e. on the opposite side to the other connecting disc 24) while the peripheral seat 26 faces inwards (i.e. on the same side to the other connecting disc 24); in fact, the two half-shafts 23 are arranged outside the space delimited by the two connecting discs 24 while the connecting rod pin 27 is arranged between the two connecting discs 24.

[0047] According to a preferred embodiment, a compressor 28 is provided (schematically illustrated in figure 2) which is arranged along the intake duct 11 (which ends in the intake port 10) and is driven by the drive shaft 4; in particular, the compressor 28 is driven by one of the two half-shafts 23 which make up the drive shaft 4. According to a possible embodiment, the compressor 28 is coaxial with the drive shaft 4 (i.e. it is coaxial with the main rotation axis A1) and comprises an impeller directly driven by the drive shaft 4 and in particular by one of the two half-shafts 23 which make up the drive shaft 4; according to a different embodiment, the compressor 28 is not coaxial with the drive shaft 4. Preferably, the compressor 28 has a radial intake (inlet) and an axial delivery (outlet). Preferably, a transmission is interposed between the drive shaft 4 and the compressor 28 which increases (for example with a transmission ratio of 1 :8) the rotation speed of the compressor 28 with respect to the rotation speed of the drive shaft 4; for example, the transmission may be of the epicyclic type.

[0048] According to a preferred embodiment, a fuel pump is provided which is operated by a cam integral with the crankshaft 4.

[0049] As illustrated in figures 4 and 5, the internal combustion engine 1 comprises two twin balancing masses 29, each of which is hinged to the crankshaft 4 and can rotate with respect to the crankshaft 4 about the secondary rotation axis A2 so as to balance the rotational inertia of the rotating masses acting on the connecting rod pin 27. In the preferred embodiment illustrated in the attached figures, two twin balancing masses 29 are provided, arranged symmetrically on opposite sides of the connecting rod pin 27 or arranged symmetrically on the opposite side with respect to the connecting rod 7; according to a different embodiment not illustrated, a single balancing mass 29 is provided.

[0050] Each balancing mass 29 is coupled with a respective system 30 for controlling the movements of the balancing mass 29 which comprises a counter-thrust group which pushes the balancing mass 29 towards a central position with a predetermined force. The function of the control systems 30 is to make the movements of the balancing masses 29 gradual during the transient regimes for balancing the imbalance induced by the rotating masses acting on the connecting rod pin 27. Preferably, for each balancing mass 29 a respective system 30 for controlling the movements is provided which is independent from the system 30 for controlling the movements of the other balancing mass 29; therefore, the two balancing masses 29 are independent of each other and can rotate autonomously from each other around the secondary rotation axisA2.

[0051] In the embodiment illustrated in the attached figures, each balancing mass 29 can rotate in both directions by approximately 10° around the central position. Preferably, the central position of each balancing mass 29 is 180° from the seat 26 of the connecting rod pin 27 and is therefore opposite to the TDC (Top Dead Center) and internal to the BDC (Bottom Dead Center).

[0052] In the embodiment illustrated in the attached figures, each counter-thrust group is of the mechanical type and comprises at least one elastic body 31 (in particular a compression spring) that generates an elastic force that pushes the balancing mass 29 towards the central position; preferably, each counter-thrust group comprises two elastic bodies 31 (in particular two compression springs) that generate two opposite elastic forces that push the balancing mass 29 towards the central position. The two elastic bodies 31 (i.e. the two compression springs) of each counter-thrust group are arranged on diametrically opposite sides with respect to the balancing mass 29 to push the balancing mass 29 towards the central position. As illustrated in figures 4 and 5, each counter-thrust group comprises two abutment elements 32 integral with the drive shaft 4 and each elastic body 31 is compressed between a respective abutment element 32 and one end of the balancing mass 29; in particular, the two striking elements 32 are obtained in a respective connecting disk 24 (which is integral with a half-shaft 23) inside which the balancing mass 29 is housed.

[0053] According to a preferred embodiment, each balancing mass 29 has an anchor shape and comprises a main body shaped like a circular arc and a connecting element which is arranged radially with respect to the main body and at an end opposite the main body is hinged to the connecting rod pin 27 next to the connecting rod 7 (i.e. each balancing mass 29 is hinged to the connecting rod pin 27 next to the connecting rod 7).

[0054] According to a different embodiment not illustrated, each counter-thrust group is of the hydraulic type and comprises at least one labyrinth inside which a fluid flows. More specifically, in the case of a hydraulic-type counter-thrust unit, the balancing mass 29 is connected to at least one piston that pushes on a fluid (which is substantially incompressible) that, in order to move, is forced through a labyrinth with a system of narrow and tortuous passages that regulate the flow of the fluid, generating a controlled hydraulic resistance to the movement of the fluid.

[0055] According to a different embodiment not illustrated, the exhaust valve 14 control system 15 does not use cams but uses, for example, an electro-hydraulic actuation, as these systems are more versatile and suitable for managing the Sabathe cycle with the advantage of eliminating the expensive and complicated throttle body. Summarizing the above, the internal combustion engine 1 has a semi-open cycle, has supercharging in the intake by means of the compressor 28, has fuel injection preferably in an active pre-chamber, and has mechanically managed fresh / burnt gas exchange.

[0056] The embodiments described herein may be combined with each other.

[0057] It is important to note that the internal combustion engine 1 described above can find advantageous application in many fields of application: land mobility (as the sole engine for motorcycles, mopeds and snowmobiles, but also as a “range-extender” for electric-powered vehicles when connected to an electric generator), boating, aeronautics, work tools (motor hoes, brush cutters, lawnmowers, electric saws, etc.), electric motor generators, and others.

[0058] The internal combustion engine 1 described above has several advantages.

[0059] First of all, the internal combustion engine 1 described above is particularly light and compact when compared to a similar two- or four-stroke internal combustion engine of equal performance. This result is also achieved thanks to the exhaust valve 14 control system 15 which is extremely simple, compact and light and uses the lubrication already present in the crank chamber for lubrication. Furthermore, this result is also achieved thanks to the balancing masses 29 which allow the rotational inertia of the rotating masses acting on the connecting rod pin 27 to be balanced extremely effectively while using components of modest overall mass.

[0060] The control system 15 of the supply valve 14 does not use a spring to return the supply valve 14 to the closed position; in this way, the fluttering of the supply valve 14 and the consequent losses of cycle efficiency are avoided, especially at high rotation speeds. In other words, the valve return springs, at high operating frequencies and due to physical limitations, are unable to follow the alternating movement of the valves in real time, causing detachments from the control element and detachments from the sealing seat. In the control system 15 of the supply valve 14, the problem is solved at the root by eliminating the use of a spring to return the supply valve 14 to the closed position.

[0061] That is, the crankshaft 4 is rigid and light while still having a correct balance. In fact, the two eccentric balancing masses 29 inserted inside the connecting discs 24 in the area adjacent to the connecting rod big end and centered on the connecting rod big end axis (i.e. the secondary rotation axis A2) have a controlled rotation of a few degrees but such as to balance the inertia of the rotating masses in transient regimes (acceleration or release), so as to lighten the crankshaft 4 as much as possible with advantages in the readiness of acceleration and without unbalancing the system.

[0062] The internal combustion engine 1 described above can generate extremely high power and torque in relation to its displacement and size.

[0063] The internal combustion engine 1 described above has excellent running smoothness at all operating speeds.

[0064] Finally, the internal combustion engine 1 described above is particularly economical when compared to a similar two- or four-stroke internal combustion engine of equal performance.

[0065] LIST OF FIGURE REFERENCE NUMBERS

[0066] 1 Internal Combustion Engine

[0067] 2 Cylinder

[0068] 3 Crankcase

[0069] 4 Crankshaft

[0070] 5 Combustion Chamber

[0071] 6 Piston

[0072] 7 Connecting Rod

[0073] 8 Exhaust Port

[0074] 9 Exhaust Chamber

[0075] 10 Intake Port

[0076] 11 Intake Manifold

[0077] 12 Cylinder Head

[0078] 13 Spark Plug

[0079] 14 Exhaust Valve

[0080] 15 Control System

[0081] 16 Cam

[0082] 17 Cam Follower Roller

[0083] 18 Rod

[0084] 19 Groove

[0085] 20 Compensation Member

[0086] 21 Spring 22 Stop Body

[0087] 23 Half Shafts

[0088] 24 Connecting Discs

[0089] 25 Central Seat 26 Peripheral Seat

[0090] 27 Connecting Rod Pin

[0091] 28 Compressor

[0092] 29 Balancing Mass

[0093] 30 Control System 31 Elastic Body

[0094] 32 Strike Elements

[0095] A1 Main Rotation Axis

[0096] A2 Secondary Rotation Axis

Claims

CLAIMS1 . A two-stroke internal combustion engine (1) comprising: a cylinder (2), which comprises, on the inside, a combustion chamber (5) provided with an exhaust port (8) and an intake port (10); an exhaust chamber (9) that is different and separate from the combustion chamber (5) and is connected to the combustion chamber (5) through the exhaust port (8), i.e. , the exhaust chamber (9) originates from the exhaust port (8); an exhaust valve (14), which is arranged in the exhaust chamber (9) on the outside of the combustion chamber (5); a piston (6), which is mounted inside the cylinder (2) so as to slide in a reciprocating manner; a drive shaft (4), which is mounted so as to rotate around a rotation axis (A1); a connecting rod (7), which connects the piston (6) to the drive shaft (4); and a control system (15) for the exhaust valve (14), which is designed to control the opening and the closing of the exhaust valve (14) and comprises: at least one cam (16), which is integral to the drive shaft (4) so as to rotate around the rotation axis (A) together with the drive shaft (4); and a cam-follower roller (17), which engages the cam (16) and is connected to the exhaust valve (14) so as to move the exhaust valve (14) between a closing position and an opening position; the internal combustion engine (1) is characterized in that: the cam (16) has a groove (19) closed on itself; and the cam-follower roller (17) is inserted in the groove (19) of the cam (16) to engage the groove (19) in a rolling manner so as to move the exhaust valve (14) both from the closing position to the opening position and from the opening position to the closing position.

2. The internal combustion engine (1) according to claim 1 , wherein the control system (15) comprises two cams (16) and two cam-follower rollers (17), each engaging the groove (19) of a respective cam (16).

3. The internal combustion engine (1) according to claim 2, wherein the two cams (16) are arranged in a mirror-like manner and face one another and the two cam-follower rollers (17) are arranged between the two cams (16) in an opposite position relative to a stem (18) of the exhaust valve (14).

4. The internal combustion engine (1) according to one of the claims from 1 to 3, wherein the cam-follower roller (17) engages the cam (16) in a rolling manner on one side and, on the opposite side, is carried by an end portion of a stem (18) of the exhaust valve (14) arranged on the opposite side relative to a head of the exhaust valve (14).

5. The internal combustion engine (1) according to one of the claims from 1 to 4, wherein the exhaust valve (14) is arranged on the side of the exhaust port (8).

6. The internal combustion engine (1) according to one of the claims from 1 to 5, wherein the control system (15) comprises a deformable compensation member (20) mounted on a stem (18) of the exhaust valve (14) to compensate for the clearances thereof.

7. The internal combustion engine (1) according to claim 6, wherein the compensation member (20) comprises a spring (21 ), which is coaxial to the stem (18) of the exhaust valve (14), abuts, with an end, on a cylinder (2) of the internal combustion engine (1) and, with the other end, on a stop body (22) integral to the stem (18) of the exhaust valve (14).

8. The internal combustion engine (1 ) according to one of the claims from 1 to 7, wherein: the drive shaft (4) comprises two coaxial half-shafts (23) arranged on opposite sides of the connecting rod (7); and the cam (16) is integral to one of the two half-shafts (23).

9. The internal combustion engine (1) according to claim 8 and comprising two connection discs (24), each integral to a respective half-shaft (23) and connecting the respective half-shaft (23) to the connecting rod (7).

10. The internal combustion engine (1) according to one of the claims from 1 to 9 and comprising: an intake duct (11), which ends in the intake port (10); and a compressor (28), which is arranged along the intake duct (11) and is operated by the drive shaft (4).

11. The internal combustion engine (1) according to claim 10, wherein the compressor (28) is coaxial to the drive shaft (4).

12. A two-stroke internal combustion engine (1) comprising: a cylinder (2), which comprises, on the inside, a combustion chamber (5) provided with an exhaust port (8) and an intake port (10);an exhaust chamber (9) that is different and separate from the combustion chamber (5) and is connected to the combustion chamber (5) through the exhaust port (8), i.e. , the exhaust chamber (9) originates from the exhaust port (8); an exhaust valve (14), which is arranged in the exhaust chamber (9) on the outside of the combustion chamber (5); a piston (6), which is mounted inside the cylinder (2) so as to slide in a reciprocating manner; a drive shaft (4), which is mounted so as to rotate around a rotation axis (A1); a connecting rod (7), which connects the piston (6) to the drive shaft (4); and a control system (15) for the exhaust valve (14), which is designed to control the opening and the closing of the exhaust valve (14) and comprises: at least one cam (16), which is integral to the drive shaft (4) so as to rotate around the rotation axis (A) together with the drive shaft (4); and a cam-follower roller (17), which engages the cam (16) and is connected to the exhaust valve (14) so as to move the exhaust valve (14) between a closing position and an opening position; the internal combustion engine (1) is characterized in that: the drive shaft (4) comprises two coaxial half-shafts (23) arranged on opposite sides of the connecting rod (7); and the cam (16) is integral to one of the two half-shafts (23).

13. The internal combustion engine (1) according to claim 12 and comprising two connection discs (24), each integral to a respective half-shaft (23) and connecting the respective half-shaft (23) to the connecting rod (7).

14. A two-stroke internal combustion engine (1) comprising: a cylinder (2), which comprises, on the inside, a combustion chamber (5) provided with an exhaust port (8) and an intake port (10); a piston (6), which is mounted inside the cylinder (2) so as to slide in a reciprocating manner; a drive shaft (4), which is mounted so as to rotate around a main rotation axis (A1); and a connecting rod (7), which connects the piston (6) to the drive shaft (4), is hinged to the drive shaft (4) on a connecting-rod pin (27) and can rotate, relative to the drive shaft (4), around a secondary rotation axis (A2) eccentric relative to the main rotation axis (A1);the internal combustion engine (1) is characterized in that it comprises at least one balancing mass (29), which is hinged to the drive shaft (4) and can rotate, relative to the drive shaft (4), around the secondary rotation axis (A2) so as to balance the rotational inertia of the rotating masses acting upon the connecting-rod pin (27).

15. The internal combustion engine (1) according to claim 14 and comprising a control system (30) controlling the movements of the balancing mass (29) and comprising a counterthrust assembly, which pushes, with a predetermined force, the balancing mass (29) towards a central position.

16. The internal combustion engine (1) according to claim 15, wherein the counter-thrust assembly is of the mechanical kind and comprises at least one elastic body (31), which generates an elastic force pushing the balancing mass (29) towards the central position.

17. The internal combustion engine (1) according to claim 16, wherein the counter-thrust assembly comprises two elastic bodies (31), which generate two opposite elastic forces pushing the balancing mass (29) towards the central position.

18. The internal combustion engine (1) according to claim 17, wherein the counter-thrust assembly comprises two compression springs arranged on diametrically opposite sides relative to the balancing mass (29).

19. The internal combustion engine (1) according to claim 17 or 18, wherein: the counter-thrust assembly comprises two striker elements (32) integral to the drive shaft (4); and each elastic body (31 ) is compressed between a respective striker element (32) and an end of the balancing mass (29).

20. The internal combustion engine (1) according to claim 19, wherein the balancing mass (29) has an anchor-like shape and comprises a main body shaped like an arc of a circle and a connection element, which is arranged radially relative to the main body and, at an end opposite the main body, is hinged to the connecting-rod pin (27) beside the connecting rod (7).

21. The internal combustion engine (1) according to one of the claims from 14 to 20 and comprising two balancing masses (29) arranged on opposite sides of the connecting rod (7).

22. The internal combustion engine (1) according to claim 21 and comprising, for each balancing mass (29), a respective movement control system (30) independent of the movement control system (30) of the other balancing mass (29).

23. The internal combustion engine (1) according to claim 21 or 22, wherein the two balancing masses (29) are independent of one another and can rotate around the secondary rotation axis (A2) independently of one another.

24. The internal combustion engine (1) according to one of the claims from 14 to 23, wherein the balancing mass (29) is hinged to the connecting-rod pin (27) beside the connecting rod (7).

25. The internal combustion engine (1) according to one of the claims from 14 to 24, wherein the drive shaft (4) comprises two coaxial half-shafts (23) arranged at a given distance from one another on opposite sides of the connecting rod (7).

26. The internal combustion engine (1) according to claim 25 and comprising two connection discs (24), each integral to a respective half-shaft (23) and supporting an end of the connecting-rod pin (27).

27. The internal combustion engine (1) according to claim 26, wherein the two connection discs (24) are axially spaced apart from one another and define, between them, a space, which accommodates the connecting-rod pin (27).

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