Internal combustion engine with two intake valves per cylinder controlled by a mechanical actuation system and an electronically controlled hydraulic actuation system respectively

Abstract

An internal combustion engine comprises a first intake valve (V1) and a second intake valve (V2) associated with each engine cylinder. The first intake valve (V1) is controlled by the respective tappet (15) with a lift profile as a function of the crank angle that is invariable and bound to the profile of a respective actuation cam (14), while the second intake valve (V2) of each cylinder is controlled by the respective tappet (15), through the interposition of an electronically controlled hydraulic circuit. The cam (14) that operates the first intake valve (V1) has a profile with two lobes (14A, 14B) that determine, at each operating cycle of the cylinder, a first opening period that begins when the respective piston is near TDC and ends when the respective piston is at an intermediate position between TDC and BDC, and a second opening period that begins when the respective piston is near BDC and ends when the piston is at an intermediate point between BDC and TDC. The first intake valve (V1) is therefore fully closed during an intermediate period in which the respective piston is still descending towards its BDC, so as to create a vacuum in the respective cylinder that generates a jet of air entering the cylinder during the second opening period. The electronic controller (25) associated with the hydraulic system that operates the second intake valve (V2) is configured to cause an opening period of the second intake valve (V2) that begins during the second opening period of the first intake valve (V1) and ends substantially when the second opening period of the first intake valve (V1) ends.

Description

[0001] Internal combustion engine with two intake valves per cylinder controlled by a mechanical actuation system and an electronically controlled hydraulic actuation system respectively

[0002] TEXT OF THE DESCRIPTION

[0003] Field of the invention

[0004] The present invention relates to internal combustion engines of the type comprising:

[0005] - one or more cylinders and a piston movable in each cylinder between a Top Dead Center (hereinafter “TDC”) and a Bottom Dead Center (hereinafter “BDC”) and operatively associated with a crankshaft, wherein each engine cylinder has respective operating cycles including an intake stage, a compression stage, an expansion stage and an exhaust stage,

[0006] - a first intake valve and a second intake valve associated with each engine cylinder, to control a flow of intake air from a first intake port and a second intake port respectively, in each operating cycle of the cylinder,

[0007] - each of said first intake valve and second intake valve being controlled, through a tappet, by a cam of a camshaft driven by the crankshaft.

[0008] Prior art

[0009] Since long, the Applicant has developed internal combustion engines including a variable intake valve actuation system, marketed under the “MULTIAIR” brand. In such a known system, each intake valve is controlled by its respective tappet, against the action of a return spring, with the interposition of an electronically controlled hydraulic circuit that includes:

[0010] - a pumping plunger actuated by the tappet and configured to transfer pressurized fluid, through a pressure chamber, to a hydraulic actuator associated with the intake valve,

[0011] - an electrically actuated control valve adapted to connect the pressurized fluid chamber with a low-pressure discharge channel communicating with a pressurized fluid accumulator, so that when such control valve is opened, pressurized fluid discharges from the pressure chamber into said low-pressure channel, whereby the intake valve closes by the effect of its respective return spring, regardless of the action of its respective cam, and wherein an electronic controller is configured to control the electrically actuated control valve associated with the hydraulic circuit, depending upon a plurality of engine operating parameters, including engine load and engine rotation speed.

[0012] The same Applicant is the owner of various patents and patent applications relating to engines equipped with a system of the type specified above (see, for example, EP 0 803 642 B1 , EP 1 555 398, EP 1 508 676 B1 , EP 1 674 673 B1 and EP 2 261 471 A1 ).

[0013] Figure 1 of the attached drawings shows a sectional view of an engine equipped with the “MULTIAIR” system, as described in the European patent EP 0 803642 B1.

[0014] With reference to this figure 1 , the engine illustrated therein is a multicylinder engine, for example a four-cylinder in-line engine, comprising a cylinder head 1. The head 1 includes, for each cylinder, a cavity 2 formed by the base surface 3 of the head 1 , defining the combustion chamber, into which two intake ducts 4, 5 and two exhaust ducts 6 lead. The connection of the two intake ducts 4, 5 with the combustion chamber 2 is controlled by two intake valves 7, of the traditional mushroom type, each comprising a stem 8 mounted for sliding in the body of the head 1 .

[0015] Each valve 7 is returned to the closed position by springs 9 placed between an internal surface of the head 1 and an end cup 10 of the valve. The connection of the two exhaust ducts 6 with the combustion chamber is controlled by two valves 70, also of the traditional type, which are associated with return springs 9 for returning to the closed position.

[0016] The opening of each intake valve 7 is controlled, in the way that will be described below, by a camshaft 11 mounted rotatable around an axis 12 within supports of the head 1 , and comprising a plurality of cams 14 for actuating the intake valves 7.

[0017] Each cam 14 which controls an intake valve 7 cooperates with the plate 15 of a tappet 16 mounted to slide along an axis 17 which, in the case of the example illustrated in the cited previous document, is directed substantially at 90° with respect to the valve axis 7. The plate 15 is returned against the cam 14 by a spring associated with it. The tappet 16 constitutes a pumping plunger slidably mounted within a bushing 18 carried by a body 19 of a pre-assembled group 20, incorporating all the electrical and hydraulic devices associated with the actuation of the intake valves, as described in detail below.

[0018] The pumping plunger 16 is able to transmit a thrust to the stem 8 of the valve 7, so as to cause the opening of the latter against the action of the elastic means 9, by means of pressure fluid (preferably oil coming from the lubrication circuit of the engine) present in a pressure chamber C which the pumping plunger 16 faces, and by means of a piston 21 mounted to slide in a cylindrical body consisting of a bushing 22 which is also carried by the body 19 of the pre-assembled group 20.

[0019] Still in the known solution illustrated in figure 1 , the pressure fluid chamber C associated with each intake valve 7 can be connected with an exhaust channel 23 by means of a solenoid valve 24. The solenoid valve 24, which can be of any known type, suitable for the function illustrated here, is controlled by electronic control means, indicated schematically with 25, as a function of signals S indicative of engine operating parameters, such as the accelerator position and the number of engine revolutions.

[0020] When the solenoid valve 24 is opened, the chamber C is connected with the channel 23, whereby the pressure fluid present in the chamber C flows into this channel and a decoupling of the cam 14 and the respective tappet 16 from the intake valve is obtained 7, which then quickly returns to its closed position by the action of the return springs 9. By controlling the connection between the chamber C and the discharge channel 23, it is therefore possible to vary, as desired, the opening time and stroke of each intake valve 7.

[0021] The exhaust channels 23 of the various solenoid valves 24 all flow into the same longitudinal channel 26 connected with pressure accumulators 27, only one of which is visible in figure 1 .

[0022] All the tappets 16 with the associated bushings 18, the pistons 21 with the associated bushings 22, the solenoid valves 24 and the relative channels 23, 26 are carried and obtained from the aforementioned body 19 of the pre-assembled group 20, to the advantage of speed and ease of assembly of the engine.

[0023] The exhaust valves 70 associated with each cylinder are controlled, in the embodiment illustrated in figure 1 , in a traditional way, by a respective camshaft 28, by means of respective tappets 29, although in principle it is not excluded, in the case of the document mentioned above, an application of the hydraulic actuation system also to the control of the exhaust valves.

[0024] Again with reference to figure 1 , the variable volume chamber defined inside the bushing 22 and facing the piston 21 (which in figure 1 is illustrated in its minimum volume condition, the piston 21 being in its stroke end upper position) is connected with the pressure fluid chamber C by means of an opening 30 obtained in an end wall of the bushing 22. This opening 30 is engaged by an end nose 31 of the piston 21 in such a way as to achieve hydraulic braking of the movement of the valve 7 in the closing phase, when the valve is near the closed position, as the oil present in the variable volume chamber is forced to flow into the pressure fluid chamber C passing through the gap existing between the end nose 31 and the wall of the opening 30 engaged by it. In addition to the connection constituted by the opening 30, the pressure fluid chamber C and the variable volume chamber of the piston 21 are connected with each other by means of internal passages obtained in the body of the piston 21 and controlled by a non-return valve 32 which allows the passage of fluid only from the pressure chamber C to the variable volume chamber of the piston 21 .

[0025] During the normal operation of the known engine illustrated in figure 1 , when the solenoid valve 24 excludes the connection of the pressure fluid chamber C with the discharge channel 23, the oil present in this chamber transmits the movement of the pumping plunger 16, imparted by the cam 14, to the piston 21 which controls the opening of the valve 7. In the initial phase of the valve opening movement, the fluid coming from the chamber C reaches the variable volume chamber of the piston 21 passing through the non-return valve 32 and further passages which connect the internal cavity of the piston 21 , which has a tubular shape, with the variable volume chamber. After an initial movement of the piston 21 , the nose 31 comes out of the opening 30, so that the fluid coming from the chamber C can pass directly into the variable volume chamber through the opening 30, now free.

[0026] In the reverse closing movement of the valve, as already mentioned, during the final phase the nose 31 enters the opening 30 causing the hydraulic braking of the valve, so as to avoid impacts of the valve body against its seat, for example following an opening of the solenoid valve 24 which causes the immediate return of the valve 7 to the closed position.

[0027] In the system described, when the solenoid valve 24 is activated, the engine valve follows the movement of the cam (full lift). An earlier closing of the valve can be achieved by deactivating (opening) the solenoid valve 24, so as to empty the hydraulic chamber and obtain the closing of the engine valve by the action of the respective return springs. Similarly, a delayed opening of the valve can be achieved by delaying the actuation of the solenoid valve, while the combination of a delayed opening with an earlier closing of the valve can be achieved by activating and deactivating the solenoid valve while pushing the relevant cam. According to an alternative strategy, according to the teachings of the patent application EP 1 726 790 A1 of the same applicant, each intake valve can be controlled in “multi-lift” mode, i.e. according to two or more repeated “sub-cycles” of opening and closing. In each sub-cycle, the intake valve opens and then closes completely. The electronic control unit is therefore able to obtain a variation of the opening time and / or the closing time and / or the lift of the intake valve, depending on one or more engine operating parameters. This allows maximum engine efficiency and the lowest fuel consumption to be achieved in all operating conditions.

[0028] In the known system described above, it is possible provide that the two intake valves 7 associated with the same engine cylinder are controlled by a single pumping plunger 16 in turn controlled by a single cam of the engine camshaft. Or it may be provided that each intake valve of each engine cylinder is controlled by a respective cam of the camshaft and by a respective hydraulic circuit including a respective pumping plunger, in which case it is possible to benefit from total flexibility in differentiating the openings of the two intake valves of each cylinder.

[0029] In the Italian patent applications IT 102022000025410, IT 102023000003450 and 102023000013266 (still secret at the priority date of the present invention), the Applicant has presented progressions of the known system described above wherein the intake valves are operated by cams having a profile with two lobes arranged and configured such that, if the respective hydraulic circuits are kept under pressure, in each cycle of each cylinder the intake valves have a first opening period and a second opening period interspersed with an intermediate period in which the valves are closed. The first opening period begins when the respective piston is near its TDC and ends when the respective piston is still descending toward its BDC. The second opening period begins when the respective piston is near its BDC and ends when the piston is already rising toward its BDC. Thus, each intake valve is fully closed during an intermediate period when the respective piston is still descending toward its BDC, so as to create a vacuum in the respective cylinder that generates a jet of air entering the cylinder during the subsequent second opening period of the intake valve.

[0030] The “air jet” operation, i.e. obtaining a jet of air entering the cylinder with the second opening period of the intake valves, increases combustion efficiency, even at low engine loads, as the jet of air gives rise to a high Turbulence Kinetic Energy or TKE.

[0031] The availability of high TKE, not obtainable with known intake cycles, also allows to increase the quantity of internal EGR that can be aspirated, even at the lowest loads; as already indicated, the introduction of internal EGR allows to increase the mass of gases to be compressed as well as the temperature at TDC, with a reduction in pumping losses; the difficult combustion of the internal EGR is compensated by the higher turbulence.

[0032] In practice, the piston of each cylinder behaves like an air spring that first creates a vacuum in the cylinder and then, during the ascent, pushes the piston towards the TDC thanks to the vacuum generated, so that the compression work in the cylinder begins only when the pressure returns to being greater than 1 barA: this means that the later the second opening period begins, the greater pumping work will be recovered.

[0033] Further studies and experiences of the Applicant on the engine according to this new proposal have shown that there may be problems in creating cams with two lobes capable of operating correctly in all operating conditions, in particular also at high engine rotations, and such as to generate lifts of the intake valves high enough to guarantee adequate filling of the cylinder. In particular, the main problems are due to pressure oscillations that are induced in the hydraulic circuit immediately after the first opening period of the intake valves.

[0034] Therefore, the need for further improvements in this field is felt.

[0035] Object of the invention The main object of the invention is to provide an internal combustion engine of the type indicated at the beginning of this description that is characterized by high combustion efficiency in all engine operating conditions and specifically in conditions of low engine loads.

[0036] In particular, the invention aims to retain all the advantages of the previously proposed “air jet” solution, while at the same time making it easier to create intake valve actuation cams capable of operating correctly in all operating conditions, in particular even at high rotation speeds.

[0037] A further important purpose of the invention is to reduce the construction complexity and size of the intake valve actuation system.

[0038] Summary of the invention

[0039] In order to achieve the aforementioned purposes, the invention has as its object an internal combustion engine having the features of claim 1 and a control method according to claim 5.

[0040] Preferred and advantageous features of the invention are indicated in the dependent claims.

[0041] Detailed description of the invention

[0042] Further features and advantages of the invention will emerge from the following description with reference to the attached drawings, provided purely by way of non-limiting example, in which:

[0043] - figure 1 is a sectional view of the cylinder head of an internal combustion engine equipped with an electronically controlled hydraulic system for operating the engine intake valves, according to the prior art illustrated in document EP 0 803 642 B1 and discussed above,

[0044] - figure 2 is a schematic view of a variable actuation system for the engine intake valves, according to a solution proposed in Italian patent application IT 102022000025410 (still secret at the priority date of the present invention), in which the two intake valves of each cylinder are controlled by two separate cams, through respective tappets, respective pumping plungers and respective hydraulic circuits, and in which each cam is shaped with two lobes,

[0045] - figure 3 is a schematic view of an exemplary embodiment of an intake valve actuation system according to the present invention, and - figures 4-7 are diagrams illustrating the operating principle and advantages of the present invention.

[0046] As will be apparent from the following description, starting from the known solution described above with reference to figure 1 , the invention allows to obtain a fast combustion, due to the generation of a high turbulence in the charge introduced into the cylinder, which leads to a more efficient combustion, in particular at medium-low engine loads. The invention allows in particular to obtain a diluted combustion, with recirculated air and exhaust gas (EGR) and / or with an ultra-lean mixture. The invention is also applicable in the case in which the engine operates with a fuel having a lower vapor pressure than that of gasoline, such as methanol. The invention also allows to achieve a stratified combustion, characterized by high efficiency, as will be illustrated below. Finally, the invention is also suitable to support the combustion of gaseous fuels (for example hydrogen) characterized both by the absence of latent heat of evaporation (which entails a risk of detonation) and by ease of ignition (which entails a risk of unwanted ignition).

[0047] Figure 2 shows a schematic view of a variable actuation system of the engine intake valves, according to a solution proposed in the Italian patent application IT 102022000025410 (still secret at the priority date of the present invention). In the solution of figure 2, each engine cylinder has two intake valves V1 , V2. Each of the two intake valves V1 , V2 is controlled by a respective cam 14 with a respective hydraulic circuit, including a respective pumping plunger 16, a respective pressure chamber C, a respective hydraulic actuator 21 of the intake valve, a respective two- position solenoid valve 24 capable of controlling the communication between the pressure chamber C and a pressure accumulator 270 which is also in communication with a low-pressure circuit of the engine lubrication oil.

[0048] In this solution, furthermore, each of the two cams 14 that control the two intake valves V1 , V2 of each engine cylinder is provided with two lobes 14A, 14B, configured to tend to cause two opening periods of the respective valve V1 or V2 for each rotation of the cam 14.

[0049] The two lobes 14A, 14B can be part of a single cam body or be part of two separate bodies, coupled onto the camshaft in such a way as to be integral in rotation with each other and with the camshaft. Preferably, the two lobes 14A, 14B are offset from each other in the direction of the camshaft axis and the tappet plate 15 (figure 1 ) is sufficiently extended to be able to cooperate with both lobes

[0050] Thanks to the provision of a cam 14 with two lobes 14A, 14B for each intake valve of each engine cylinder, and thanks to the provision of a respective hydraulic circuit interposed between each cam and each intake valve, both intake valves of the engine can have a first opening period and a second opening period, spaced apart, corresponding to a conventional opening phase of an intake valve.

[0051] In an application example of the solution of figure 2, the electronic controller 25 is configured for the detection, when the engine load is relatively low, i.e., below a predetermined threshold value and / or when the engine rotational speed is below a predetermined threshold value (e.g., 3.000 rpm), and in this condition, the electronic controller 25 is configured to control the electrically actuated control valve 24 so as to cause, at each engine cycle, a first opening period and a second opening period of each intake valve, with an intermediate phase in which the intake valve is fully closed while the respective piston is descending towards its BDC, so as to create a depression in the respective cylinder which generates a jet of air entering the cylinder during the subsequent second opening period of the intake valve.

[0052] In an example application of the solution in figure 2, the first opening period of each intake valve of each cylinder begins substantially when the respective piston is at its Top Dead Center (TDC) and ends when the piston is substantially midway between its TDC and its Bottom Dead Center (BDC). The second opening period of each intake valve begins when the piston has passed the BDC and is ascending towards TDC.

[0053] As a result of the above features, during a first part of said second opening period, while the piston is ascending towards the TDC, the above jet of air is created entering the cylinder due to the depression created in the cylinder between the first opening period and the second opening period, while during a second part of the second opening period the depression in the cylinder is progressively reduced until it is eliminated and a portion of air is pushed back into the intake duct by the piston continuing to ascend towards the TDC.

[0054] In practice, the piston behaves like an air spring that first creates depression in the cylinder and then, during the ascent, the piston is pushed upwards by the depression generated, so the compression work begins only when the pressure in the cylinder returns to being greater than 1 barA: this means that the later the second suction phase begins, the greater the pumping work will be recovered.

[0055] In the case of the embodiment of figure 2, where the cams have double-lobe profiles, with zero lift between one lobe and the other, said result is obtained by always keeping the control valve 24 closed.

[0056] The introduction of an air jet into the cylinder during the second opening period of the intake valves generates a TKE sufficient to support both an efficient mixing of the air with the fuel and with an eventual quantity of recirculated exhaust gas (EGR), and the propagation of the flame during combustion.

[0057] The present invention starts from the desire to retain all the advantages of the “air jet” solution previously proposed and illustrated in figure 2, while at the same time making it easier to create intake valve actuation cams capable of operating correctly in all operating conditions, in particular also at high rotation speeds, and reducing the construction complexity and size of the entire system.

[0058] Figure 3 shows a diagram of a first exemplary embodiment of the intake valve actuation system in the engine according to the invention.

[0059] Even in the engine according to the invention, each cylinder is associated with a first intake valve V1 and a second intake valve V2, each controlled by a cam 14 of a camshaft. According to the invention, however, unlike the solution previously proposed and illustrated in figure 2, only the intake valve V2 (with reference to figure 3) is operated by an electronically controlled hydraulic system of the type described above with reference to figure 2. The intake valve V1 is instead controlled by the respective tappet 15, against the action of a return spring 9, in a conventional manner, by means of a mechanical transmission, so that the intake valve V1 has a lift profile as a function of the crank angle that is invariable and bound to the profile of the respective cam 14.

[0060] It is understood that in this description, and in the claims that follow, the term “mechanical transmission” means any transmission that determines a fixed and invariable relationship between the profile of the cam and the lift profile of the respective intake valve, including the case in which such transmission includes a hydraulic chamber.

[0061] Compared to a conventional solution, the mechanical actuation system of the intake valve V1 of the system of figure 3 differs in that the cam 14 that actuates the valve V1 has two lobes 14A, 14B arranged and configured to cause, at each cycle in each cylinder, two successive opening periods separated by an intermediate period in which the intake valve V1 is kept closed.

[0062] Figure 4 of the attached drawings shows an example of the lift profile of the intake valve V1 as a function of the crank angle. In this description, and in the attached drawings, the convention has been adopted whereby the crank angle is considered equal to 360° and 540° respectively when the piston is at TDC and BDC, at the beginning and the end of a conventional intake stroke.

[0063] As shown in figure 4, due to the two-lobe profile of cam 14 that operates intake valve V1 , in each cycle of each cylinder, the intake valve has a first opening period that begins when the respective piston is close to TDC and ends when the respective piston is at an intermediate position between TDC and BDC (for example, approximately halfway between TDC and BDC). The intake valve V1 also has a second opening period that begins when the respective piston is close to BDC (for example, immediately before BDC) and ends when the piston is at an intermediate point between BDC and BDC, i.e. when the piston is rising towards BDC (for example, after a rotation of approximately 100° of the crankshaft).

[0064] Therefore, at each cylinder cycle, the intake valve V1 is fully closed during an intermediate period in which the respective piston is still descending towards its BDC, so as to create a vacuum in the respective cylinder that generates a jet of air entering the cylinder during the subsequent second opening period of the intake valve V1 . As indicated, always with reference to figure 3, the intake valve V2 of each cylinder is instead controlled by the respective tappet, against the action of the respective return spring, with the interposition of an electronically controlled hydraulic circuit that includes the pumping plunger 16, the pressure chamber C, the hydraulic actuator 21 associated with the intake valve V2, the electrically actuated control valve 24 adapted for putting the pressurized fluid chamber C in communication with the pressurized fluid accumulator 270, and the electronic controller 25, in a way completely analogous to what has been described above with reference to figures 1 and 2.

[0065] In the example illustrated in figure 3, the cam 14 that operates the intake valve V2 also has two lobes 14A, 14B, configured and arranged in such a way as to tend to cause two opening periods as in the solution of figure 2. As will be seen below, it is however possible that the cam 14 associated with the valve V2 has only one lobe, configured and arranged to cause only one opening period of valve V2 that begins together with the second opening period of valve V1 .

[0066] In the example illustrated in figure 4, the lift profile of valve V2, corresponding to the profile of the two-lobe cam, has a first opening period that begins after the TDC and ends substantially together with the end of the first opening period of valve V1 . Again with reference to figure 4, the second valve V2 then has a second opening period that, if the hydraulic circuit is always kept under pressure, begins together with the second opening period of valve V1 and ends approximately at 30° before the TDC.

[0067] At high rotation speeds, the hydraulic circuit can be discharged in the phase in which the first lobe of cam 14 would tend to produce the first opening period of valve V2, so as to eliminate the first opening period of valve V2, so as not to incur problems of pressure oscillation in the hydraulic circuit.

[0068] At lower rotation speeds (e.g. below 3000 rpm), it is possible to implement both opening periods of the valve V2, thus maximizing filling and reducing pumping losses.

[0069] As already indicated, the second lobe 14B of the cam 14 that actuates the intake valve V2 is shaped and arranged to cause a second opening period of the intake valve V2 that begins substantially together with the beginning of the second opening period of the intake valve V1 .

[0070] To achieve this effect, the electronic controller 25 associated with the hydraulic system that actuates the intake valve V2 of each engine cylinder is configured to govern the electrically actuated control valve 24 in such a way as to maintain pressure in the chamber C of the hydraulic actuation circuit when the second lobe 14B of the cam 14 tends to cause the second opening period of the intake valve V2.

[0071] As already indicated, at the highest rotation speeds the electronic controller 25 can deactivate the first opening period of the valve V2, so that the valve V2 opens only together with the second opening period of the valve V1 .

[0072] Furthermore, still in the case of the example illustrated in figure 4, the electronic controller 25 can be configured to open the electrically actuated control valve 24 when the intake valve V2 reaches a determined lift, so as to cause an earlier closing of the intake valve V2 with respect to what would be the closing determined by the respective cam profile. This operating mode is made clear in figure 4, where both the actual lift profile of the intake valve V2 (“earlier closing V2”) and the lift profile that would be determined by the cam 14 (“hydraulic cam full lift V2”) are illustrated.

[0073] Furthermore, the controller 25 can be configured to delay the start of the second (or only) opening period of the valve V2, for example to generate a desired swirl motion in the cylinder. In fact, if the controller does not control the first opening period of the valve V2, the effect is that the opening of the valve V1 alone during the first part of the intake stage generates a swirl motion. If it is desired to have said swirl motion also in correspondence with combustion, it is sufficient to delay the opening of the valve V2 (in fact the valve V1 , opening before the V2 also at the BDC will further strengthen the swirl motion previously generated).

[0074] In this way, the maximum lifts of the intake valve V1 can be relatively reduced, so as to facilitate the provision of a cam 14, for the intake valve V1 , capable of operating properly even at high speeds, while the lift of the intake valve V2 can be relatively shorter and higher (as made evident by figure 4), so as to ensure a suitable filling of the cylinder.

[0075] In a variant, the cam 14 that controls the intake valve V2 has a single lobe, configured and arranged to cause only the second opening period of the intake valve V2 that is illustrated in figure 4.

[0076] Figure 5 of the attached drawings shows the lift profiles of the intake valve V1 and the intake valve V2, for the exemplary embodiment of the invention that is illustrated in figure 3, compared to a known solution according to the so-called “Atkinson cycle” that provides a single lift for both intake valves.

[0077] Figure 6 is a diagram showing the mass of air introduced into the cylinder as the crank angle varies, in the case of the invention and the known Atkinson cycle.

[0078] Figure 7 is a diagram showing the TKE in the cylinder as the crank angle varies, in the case of the invention and the known Atkinson cycle. The diagram makes clear the drastic increase in TKE that occurs in the case of the invention, with the advantages that have been discussed above.

[0079] At very low loads, the controller 25 can be controlled to significantly delay, even beyond 680° of crank angle, the closing angle of the second opening period, so as to generate a backflow into the intake manifold according to a feature which in itself has already been proposed by the Applicant in a previous patent application (still secret at the date of the present invention).

[0080] Of course, notwithstanding the principle of the invention, the construction details and the embodiments may vary widely from what is described and illustrated purely by way of example, without thereby departing from the scope of the invention, as defined in the attached claims.

[0081] For example, the valve V1 , although controlled by a double-lobe cam, may also be actuated by a known collapsible tappet-type device, capable of reducing or completely suppressing the opening of the valve V1 , for example to reduce the filling of the cylinder with air at extremely low loads.

[0082] Alternatively, the valve V1 may be actuated by any known device capable of varying the opening profile discretely (in practice, the valve may be actuated with two different profiles depending on the operating conditions).

[0083] Furthermore, the invention is also applicable to compression ignition engines, or to SPCCI (“Spark Plug Controlled Compression Ignition”) engines as the invention allows the swirl to be modulated and stratified combustion to be generated.

[0084] Even for conventional compression ignition engines, according to the Diesel cycle, the invention offers important advantages because it allows the swirl to be generated and modulated, without compromising the filling of the cylinder because it does not use a “swirling” intake port (i.e. configured to generate swirl) which would produce a low filling coefficient..

Claims

CLAIMS1. An internal combustion engine, comprising:- one or more cylinders and a piston movable in each cylinder between a TDC and a BDC and operatively associated with a crankshaft, wherein each engine cylinder has respective operating cycles including an intake stage, a compression stage, an expansion stage and an exhaust stage,- a first intake valve (V1 ) and a second intake valve (V2) associated with each engine cylinder, to control a flow of intake air from a first intake port (4) and a second intake port (4) respectively, in each operating cycle of the cylinder,- each of said first intake valve (V1 ) and second intake valve (V2) being controlled, through a tappet (15), by a cam (14) of a camshaft (11 ) driven by the crankshaft, said engine being characterized in that:- said first intake valve (V1 ) of each cylinder is controlled by the respective tappet (15), against the action of a return spring (9) by means of a mechanical transmission, so that the first intake valve (V1 ) has a lift profile as a function of the crank angle that is invariable and bound to the profile of the respective cam (14),- said second intake valve (V2) of each cylinder is controlled by the respective tappet (15), against the action of a return spring (9), with the interposition of an electronically controlled hydraulic circuit that includes:- a pumping plunger (16) actuated by the tappet (15) and configured to transfer pressurized fluid, through a pressure chamber (C), to a hydraulic actuator (21 ) associated with said second intake valve (V2) of each engine cylinder,- an electrically actuated control valve (24) adapted to connect said pressurized fluid chamber (C) with a low-pressure discharge channel (23) communicating with a pressurized fluid accumulator (270), so that when said control valve (24) is opened, pressurized fluid discharges from the pressure chamber (C) into said low-pressure channel and said second intake valve (V2) closes by the effect of the respective return spring (9), regardless of the action of the respective cam (14),said engine further comprising an electronic controller (25) for controlling the electrically actuated control valve (24) associated with said hydraulic circuit, depending upon a plurality of engine operating parameters, including engine load and engine rotation speed, further wherein: the cam (14) that actuates the first intake valve (V1 ) in an invariable manner has a profile with two lobes (14A, 14B) arranged and configured to cause, in each operating cycle of the cylinder:- a first opening period of the first intake valve (V1 ) that begins when the respective piston is near TDC and ends when the respective piston is at an intermediate position between TDC and BDC,- a second opening period of the first intake valve (V1 ), that begins when the respective piston is near BDC and ends when the piston is at an intermediate point between BDC and TDC, so that in each operating cycle of the cylinder said first intake valve (V1 ) is fully closed during an intermediate period in which the respective piston is still descending towards its BDC, so as to create a vacuum in the respective cylinder that generates a jet of air entering the cylinder during the subsequent second opening period of said first intake valve (V1 ), and further wherein:- the electronic controller (25) associated with the hydraulic system that operates the second intake valve (V2) of each engine cylinder is configured to govern the electrically actuated control valve (24) in such a way as to cause, at each cycle in each cylinder, at least one opening period of said second intake valve (V2) of each cylinder beginning during the second opening period of the first intake valve (V1 ) and ends when the piston is at an intermediate point between BDC and TDC.

2. The engine according to claim 1 , characterized in that the electronic controller (25) associated with the hydraulic system that operates the second intake valve (V2) of each engine cylinder is configured such that the opening period of said second intake valve (V2) of each cylinder beginning during the second opening period of the first intake valve (V1 ) is achieved by keeping the electrically actuated control valve (24) closed at a stage when the respective cam (14) causes the second intake valve (V2) toopen and by opening the electrically actuated control valve (24) after a determined lift is reached, so as to cause an earlier closing of the second intake valve (V2) with respect to what would be the closing determined by the respective cam profile, so that the opening period of said second intake valve (V2) of each cylinder beginning during the second opening period of the first intake valve (V1 ) corresponds to a lift profile of the second intake valve which is higher and shorter than the lift profile of the second opening period of the first intake valve (V1 ).

3. The engine according to claim 1 or 2, characterized in that the cam (14) controlling the second intake valve (V2) has a single lobe, configured to cause said opening period of said second intake valve (V2) that begins during the second opening period of the first intake valve (V1 ).

4. The engine according to claim 1 or 2, characterized in that the cam (14) controlling the second intake valve (V2) has two lobes, configured and arranged to cause both said opening period of said second intake valve (V2) that begins during the second opening period of the first intake valve (V1 ), and, in chronological order, a first opening period of the second intake valve (V2), substantially simultaneous with the first opening period of the first intake valve (V1 ), said electronic controller (25) being configured to either enable or eliminate the first opening period of the second intake valve (V2) depending on the operating conditions of the engine, and in particular depending on the engine load and engine rotation speed.

5. A method for controlling an internal combustion engine, wherein the engine comprises:- one or more cylinders and a piston movable in each cylinder and operatively associated with a crankshaft, wherein each engine cylinder has respective operating cycles including an intake stage, a compression stage, an expansion stage and an exhaust stage,- a first intake valve (V1 ) and a second intake valve (V2) associated with each engine cylinder, to control a flow of intake air from a first intake port (4) and a second intake port (4) respectively, in each operating cycle of the cylinder,- each of said first intake valve (V1 ) and second intake valve (V2)being controlled, through a tappet (15), by a cam (14) of a camshaft (11 ) driven by the crankshaft, said method being characterized in that:- said first intake valve (V1 ) of each cylinder is controlled by the respective tappet (15), against the action of a return spring (9) by means of a mechanical transmission, so that the first intake valve (V1 ) has a lift profile as a function of the crank angle that is invariable and bound to the profile of the respective cam (14),- said second intake valve (V2) of each cylinder is controlled by the respective tappet (15), against the action of a return spring (9), with the interposition of an electronically controlled hydraulic circuit that includes:- a pumping plunger (16) actuated by the tappet (15) and configured to transfer pressurized fluid, through a pressure chamber (C), to a hydraulic actuator (21 ) associated with said second intake valve (V2) of each engine cylinder,- an electrically actuated control valve (24) adapted to connect said pressurized fluid chamber (C) with a low-pressure discharge channel (23) communicating with a pressurized fluid accumulator (270), so that when said control valve (24) is opened, pressurized fluid discharges from the pressure chamber (C) into said low-pressure channel and said second intake valve (V2) closes by the effect of the respective return spring (9), regardless of the action of the respective cam (14), further wherein: the cam (14) that actuates the first intake valve (V1 ) in an invariable manner has a profile with two lobes (14A, 14B) arranged and configured to cause, at each engine cycle:- a first opening period of the first intake valve (V1 ) that begins when the respective piston is near TDC and ends when the respective piston is at an intermediate position between TDC and BDC,- a second opening period of the first intake valve (V1 ), that begins when the respective piston is near BDC and ends when the piston is at an intermediate point between BDC and TDC, so that in each operating cycle of the cylinder said first intake valve (V1 ) is fully closed during an intermediate period in which the respective piston is still descending towards its BDC, so as to create a vacuum in therespective cylinder that generates a jet of air entering the cylinder during the subsequent second opening period of said first intake valve (V1 ), and wherein the method further comprises governing, by means of the electronic controller (25) associated with the hydraulic system that operates the second intake valve (V2), said electrically actuated control valve (24) in such a way as to cause, at each cycle of each cylinder, at least one opening period of said second intake valve (V2) that begins during the second opening period of the first intake valve (V1 ) and ends when the piston is at an intermediate point between BDC and TDC.

6. The method according to claim 5, characterized in that, by means of the electronic controller (25) associated with the hydraulic system that operates the second intake valve (V2) of each engine cylinder, the opening period of said second intake valve (V2) of each cylinder beginning during the second opening period of the first intake valve (V1 ) is achieved by keeping the electrically actuated control valve (24) closed at a stage when the respective cam (14) causes the second intake valve (V2) to open ,and by opening the electrically actuated control valve (24) after a determined lift of the second intake valve (V2) is reached, so as to cause an earlier closing of the second intake valve (V2) with respect to what would be the closing determined by the respective cam profile, so that the opening period of said second intake valve (V2) of each cylinder beginning during the second opening period of the first intake valve (V1 ) corresponds to a lift profile of the second intake valve that is higher and shorter than the lift profile of the second opening period of the first intake valve (V1 ).

7. The method according to claim 5 or 6, characterized in that the cam (14) controlling the second intake valve (V2) has a single lobe, configured to cause said opening period of said second intake valve (V2) that begins during the second opening period of the first intake valve (V1 ).

8. The method according to claim 5 or 6, characterized in that the cam (14) controlling the second intake valve (V2) has two lobes, configured and arranged to cause both said opening period of said second intake valve (V2) that begins during the second opening period of the first intake valve (V1 ), and, in chronological order, a first opening period of the second intake valve (V2), substantially simultaneous with the first opening period of thefirst intake valve (V1 ), and in that, by means of said electronic controller (25), the first opening period of the second intake valve (V2) is either enabled or eliminated, depending on the operating conditions of the engine, and in particular depending on the engine load and engine rotation speed.

9. The method according to claim 5, wherein, at engine loads below a minimum determined threshold, the opening period of the second intake valve (V2) that begins during the second opening period of the first intake valve (V1 ) ends in the second half of the stroke of the piston from BDC to TDC, so as to generate a backflow into the intake manifold.

10. The method according to claim 5, wherein the second intake valve (V2) is controlled so as to favor the swirl motion generated by the first intake valve (V1 ), by having said opening period of the second intake valve (V2) beginning after the start of the second opening period of the first intake valve V1 .

11. The method according to claim 5, wherein the first intake valve (V1 ) is actuated by means of a tappet of a collapsible type, so that at engine loads below a determined threshold, the first intake valve (V1 ) can be kept closed, or can be opened only partially.

12. The method according to claim 5, wherein, by means of a phase variator device that varies the angular position of the camshaft relative to the crankshaft, the opening profile of at least the first intake valve (V1) is modified such that an internal EGR is obtained by anticipating the start of the first opening period of the first intake valve (V1 ).

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