Multi-cylinder internal combustion engine, with cylinders equipped with intake valve variable actuation systems having hydraulic circuits which cross each other

Abstract

An internal-combustion engine has a plurality of cylinders each with two intake valves driven by respective pumping pistons operatively associated to cams of a camshaft, by respective hydraulic circuits. The hydraulic has its pressure chamber communicating with hydraulic actuators of the two intake valves, so that the two intake valves of each cylinder are controlled, via two different hydraulic circuits, by cams associated to two different cylinders. Each cam is configured to give rise to a cycle of opening and closing of each of the intake valves in an angular range of rotation of the crankshaft less than 180 such that, in each operating cycle of a cylinder, only the first intake valve initially opens and closes while the second intake valve remains closed, and then the second intake valve opens and closes while the first intake valve remains closed.

Claims

1. An internal combustion engine, comprising: a crankshaft; a plurality of cylinders configured to execute respective operating cycles in a predetermined firing order, each cylinder including: a piston operatively connected to the crankshaft so as to reciprocate within the cylinder, a first intake valve controlling a flow of intake air from a first intake duct, the first intake valve including a first hydraulic actuator and a first return spring, and a second intake valve controlling a flow of intake air from a second intake duct, the second intake valve including a second hydraulic actuator and a second return spring; a camshaft driven via the crankshaft, the camshaft including a plurality of cams respectively associated with each cylinder; a plurality of hydraulic circuits respectively associated with each cam, each hydraulic circuit including: a tappet configured to engage the associated cam of the associated cylinder, a pressure chamber, a pumping piston driven by the associated cam via the tappet, the pumping piston configured to act on the pressure chamber so as to transfer pressurized fluid towards (i) the first hydraulic actuator of the first intake valve of the associated cylinder, and (ii) the second hydraulic actuator of the second intake valve of a preceding cylinder, the preceding cylinder being a cylinder of the plurality of cylinders which immediately precedes the associated cylinder in the predetermined firing order, such that the first and second intake valves of the associated cylinder are respectively controlled via two different cams of the plurality of cams, a pressurized-fluid accumulator, and an electrically actuated control valve configured to selectively communicate said pressure chamber with the pressurized-fluid accumulator via a low-pressure exhaust channel such that, when said electrically actuated control valve is open, the pressurized fluid is discharged from the pressure chamber into said low-pressure exhaust channel so as to deactivate the first intake valve of the associated cylinder and/or the second intake valve of the preceding cylinder; and an electronic controller configured to control each electrically actuated control valve as a function of engine load and engine speed, wherein each electrically actuated control valve is further configured to be switched to at least one of: a full-lift mode in which both intake valves of the hydraulic circuit operate in accordance with a lift profile of the associated cam, an early-closing mode in which both intake valves of the hydraulic circuit operate in accordance with a lift profile that is reduced with respect to the lift profile of the associated cam, and a partial deactivation mode in which only one intake valve of the hydraulic circuit is deactivated, and wherein, during an intake stage of each cylinder, an opening and closing timing of the second intake valve occurs subsequent to an opening and closing timing of the first intake valve.

2. The internal-combustion engine according to claim 1, wherein each electrically actuated control valve is a two-way, two-position solenoid valve.

3. The internal-combustion engine according to claim 1, wherein each electrically actuated control valve is a three-way, three-position solenoid valve.

4. The internal combustion engine according to claim 1, wherein, in each cylinder, a diameter of the first hydraulic actuator is different from a diameter of the second hydraulic actuator such that the first intake valve and the second intake valve exhibit different lifts.

5. The internal combustion engine according to claim 1, wherein, in each cylinder, the first and second return springs include different spring loads and/or spring constants such that the first intake valve and the second intake valve exhibit different lifts.

Description

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(1) Further characteristics and advantages of the invention will emerge from the ensuing description with reference to the annexed drawings, which are provided purely by way of non-limiting example and in which:

(2) FIG. 1 is a cross-sectional view of a cylinder head of an internal-combustion engine equipped with a MULTIAIR system according to the prior art described, for example, in the document EP 0 803 642 B1;

(3) FIG. 2 is a scheme of the MULTIAIR system according to the prior art, as illustrated in the document EP 1 674 673 B1;

(4) FIG. 3 is a further schematic view of the known system of FIG. 2;

(5) FIG. 4 is a further schematic view of a system known from the document EP 2 801 706 B1;

(6) FIG. 5 is a further schematic view that again illustrates the MULTIAIR system according to the prior art, where the four hydraulic circuits associated with the four cylinders of a four-cylinder internal-combustion engine are illustrated;

(7) FIG. 6 is a schematic illustration of a first embodiment of the invention similar to that of FIG. 5;

(8) FIG. 6A shows a lift diagram of the intake valves of a cylinder in early-closing mode implemented by the system of FIG. 6;

(9) FIG. 7 is once again a schematic illustration of a second embodiment of the invention;

(10) FIG. 7A shows a lift diagram of the intake valves of a cylinder in a mode implemented by the system of FIG. 7, where a first intake valve remains substantially closed, while the second intake valve is in an early-closing mode; and

(11) FIG. 7B shows a detail of FIG. 7 in the operating condition that gives rise to the mode of actuation of the intake valves that is illustrated in FIG. 7A.

(12) FIGS. 1-4, which regard the systems of the prior art, have already been discussed above.

(13) FIG. 5 also regards the prior art and illustrates the four hydraulic circuits associated with the four cylinders of a four-cylinder internal-combustion engine, equipped with the MULTIAIR system mentioned above. With reference to FIG. 5, associated with each of the four engine cylinders CYL 1, CYL 2, CYL 3, and CYL 4 are two intake valves V1, V2.

(14) Associated with the four engine cylinders are, respectively, four cams CAM 1, CAM 2, CAM 3, and CAM 4 for actuation of the engine intake valves.

(15) Associated with each of the four cams is a respective tappet 15 with the respective pumping piston 16 (see FIGS. 1 and 2). In FIG. 5 the pumping piston 16 associated with each cam is illustrated schematically (as in FIGS. 3 and 4).

(16) In the known solution illustrated in FIG. 5, the electrically actuated control valve 24 associated with the hydraulic circuit of each cylinder is a two-way, two-position solenoid valve, as in the case of FIG. 3. When each solenoid valve 24 is in the open position (illustrated in FIG. 5) the pressure chamber C of each hydraulic circuit is in communication with the low-pressure environment and with the respective fluid accumulator 270, so that the valves V1, V2 are insensitive to the movement of the respective cam and remain constantly closed. When each solenoid valve 24 is in its closed position, the pressure chamber C of each hydraulic circuit is isolated from the low-pressure environment and with respect to the accumulator 270 so that the movement of each cam causes, following upon transfer of fluid from the pumping piston 16 to the hydraulic actuators 21, opening of the two intake valves V1, V2 of each cylinder.

(17) In the schematic illustration of FIG. 5, represented in the block corresponding to each cylinder is the diagram of the lift L of both of the intake valves V1, V2 as a function of the crank angle CA.

(18) In the aforesaid known solution, both of the intake valves V1, V2 of each engine cylinder open and close simultaneously in the condition where the solenoid valve 24 closes following a conventional lift profile that starts in the proximity of top dead centre (TDC) and ends in the proximity of bottom dead centre (BDC). The cam of each cylinder consequently presents a conventional profile such as to generate the aforesaid lift profile.

(19) As already described above, in the system of FIG. 5, both of the intake valves of each cylinder may have lift profiles that are always identical to one another, but both modified with respect to the full-lift profile by controlling opening of the solenoid valves 24, for example in such a way as to cause a late opening (late-opening mode) or an early closing (early-closing mode) or multiple cycles of opening and closing (multi-lift mode) of both of the intake valves, the different modes being implemented by the electronic controller as a function of the operating conditions of the engine

(20) FIG. 6 shows how the scheme of FIG. 5 changes in the case of a first embodiment of the invention, which once again regards a four-stroke, four-cylinder internal-combustion engine. In FIG. 6, the parts in common with those of FIG. 5 are designated by the same references. However, for reasons that will emerge clearly from what follows, in FIG. 6 the blocks corresponding to the four cylinders have been represented from left to right in the succession 1-3-4-2, which corresponds to the conventional succession of the operating cycles in the cylinders of an engine with four cylinders in line (in a conventional representation, where the cylinders are numbered from 1 to 4, from one end to the other of the engine). Consequently, in FIG. 6, also the cams that are associated with the four cylinders are illustrated in the aforesaid succession 1-3-4-2.

(21) Apart from the different order in which the cylinders are illustrated in FIG. 6 with respect to the order illustrated in FIG. 5 (which, as will be seen, is due to the need for a greater ease of representation of the solution according to the invention), the main difference in the solution of FIG. 6 from that of FIG. 5 lies in the fact that in the case of FIG. 6 the pressure chamber C associated with each pumping piston 16 communicates with the hydraulic actuators 21 of two intake valves V1, V2 associated with two different engine cylinders. Consequently, the two intake valves V1, V2 of each engine cylinder are controlled, via two different hydraulic cylinders, by pumping pistons 16 associated with two different cams of the engine camshaft.

(22) With reference in particular to FIG. 6, the pressure chamber C associated with the cam CAM 2 communicates with the hydraulic actuators of the intake valve V1 of the cylinder CYL 3 and with the intake valve V2 of the cylinder CYL 1.

(23) The pressure chamber C associated with the cam CAM 3 communicates with the hydraulic actuators 21 of the intake valve V1 of the cylinder CYL 4 and of the intake valve V2 of the cylinder CYL 3.

(24) The pressure chamber C associated with the cam CAM 4 communicates with the hydraulic actuators 21 of the intake valve V1 of the cylinder CYL 2 and of the intake valve V2 of the cylinder CYL 4.

(25) Finally, the pressure chamber C associated with the cam CAM 1 communicates with the hydraulic actuators 21 of the intake valve V1 of the cylinder CYL 1 and of the intake valve V2 of the cylinder CYL 2.

(26) Hence, as may be seen, the cam associated with a given engine cylinder controls, by means of the respective hydraulic circuit, a first intake valve associated with said given engine cylinder and a second intake valve that, instead, is associated with the cylinder that immediately precedes said given engine cylinder in the succession of the operating cycles of the engine cylinders. It is for this reason that in FIG. 6 the cylinders have been illustrated in the order in which their operating cycles follow one another so as to be able to represent easily the connection of each hydraulic circuit to the hydraulic actuators of the intake valves of different cylinders.

(27) As a consequence of the arrangement described above, the two intake valves V1, V2 of one and the same engine cylinder are designed to have, during a conventional intake stage in each operating cycle of the cylinder, respective opening and closing cycles in different angular ranges of the rotation of the crankshaft.

(28) The above situation emerges clearly from the diagrams in the lower part of FIG. 6. In each of these diagrams, there appears the lift L of the first intake valve V1 and of the second intake valve V2 as a function of the crank angle CA. Each diagram also shows the conventional lift diagram of the known system illustrated in FIG. 5 (with a dashed line).

(29) The diagrams illustrated in FIG. 6 refer to the case where the solenoid valves 24 are all in a closed condition in such a way that the pressure chamber C of each of the four hydraulic circuits will be isolated from the low-pressure environment. In this condition, each of the two intake valves V1, V2 of each cylinder has a lift diagram that extends for a small angular range of the rotation of the crankshaft, of much less than 180. This result is obtained in so far as the cam associated with each cylinder has a corresponding configuration, reduced with respect to the conventional configuration.

(30) As a result of the crosswise arrangement of the hydraulic circuits of the various cylinders, and as a result of the aforesaid conformation of the cams, in each cylinder the first intake valve opens in the proximity of top dead centre TDC and closes substantially after a rotation of 90 of the crankshaft, hence long before bottom dead centre BDC. The second intake valve V2 openswith reference to this example of embodimentlong after closing of the first intake valve and closes with a certain delay with respect to bottom dead centre BDC. As has been mentioned, the diagrams of FIG. 6 refer to the case where both of the intake valves have a full lift in so far as the solenoid valves 24 remain closed during the entire active phase of each cam that brings about opening of the intake valves.

(31) Of course, by exploiting the possibilities afforded by the variable-actuation system, it is possible to obtain that each of the intake valves of each engine cylinder has a reduced lift diagram as compared to the full-lift diagram, as illustrated in FIG. 6A. This figure regards the case where, during the active phase of each cam of the engine, where the cam would cause opening of the respective intake valves, the solenoid valve 24 associated with said cam will be brought into an open condition so as to set the respective pressure chamber C in communication with the low-pressure environment and cause closing of the intake valves controlled by said cam in advance with respect to the full-lift profile (early-closing mode).

(32) FIG. 7 illustrates a second embodiment of the invention that differs from the first embodiment merely in that the electrically actuated control valves that are associated with the hydraulic circuits of the engine cylinders are three-way, three-position solenoid valves of the type in itself known illustrated in FIG. 4.

(33) In the schematic illustration of FIG. 7, the three-position solenoid valves 24 are illustrated in their intermediate operating condition where the pressure chamber C associated with each cam is in communication with both of the intake valves controlled thereby and is instead isolated from the low-pressure environment. In this condition, operation of the system is altogether similar to what has been described with reference to FIG. 6.

(34) In the case where the three-position solenoid valves 24 are brought into the operating condition corresponding to the left-hand section of each solenoid valve (with reference to FIG. 7), the pressure chamber C associated with each cam is always in communication with both of the hydraulic actuators of the two intake valves controlled thereby, but at the same time is also in communication with the low-pressure environment and with the respective fluid accumulator 270. In this situation, both of the intake valves controlled by said cam remain closed, even when the cam would tend to bring about opening thereof.

(35) Finally, when each three-position solenoid valve 24 is in the operating condition corresponding to the right-hand section (with reference to FIG. 7) of the solenoid valve, the intake valve V2 controlled by said cam is driven positively by the fluid into the respective pressure chamber C given that said chamber is isolated from the low-pressure environment. At the same time, however, the intake valve V1 controlled by said cam is isolated both from the pressure chamber C and from the low-pressure environment so that it remains blocked in the condition in which it is. This mode of actuation of the intake valves is illustrated in FIG. 7A, and the operating condition of each three-position solenoid valve corresponding to this actuation mode is illustrated in FIG. 7B.

(36) As may be seen, in the case of the embodiment of FIG. 7, it is possible to exclude completely actuation of one of the two intake valves of each cylinder, as it is also possible to adopt an early-closing mode, with partial lift, of the other intake valve of the cylinder (see FIG. 7A).

(37) In a variant, the hydraulic actuators 21 associated with the intake valves V1, V2 of each cylinder have different diameters, so as to give rise to different lifts of the respective intake valves V1, V2 for the same displacement of the respective pumping pistons 16. Additionally or alternatively, the return springs 9 associated with the two intake valves V1, V2 of each cylinder can be provided so as to have loads and/or flexibilities different from each other, so as to give rise to different lifts of the intake valves V1, V2 for the same displacement of the respective pumping pistons (16).

(38) As indicated, the invention may be applied in general to four-cylinder, four-stroke engines, or else also to two-cylinder, two-stroke engines. In theory, the invention could be applied also to an engine with a different number of cylinders (for example, three cylinders) maintaining for one or more cylinders a system of actuation of the intake valves of a conventional type and adopting for the remaining part of the cylinders an actuation system according to the present invention.

(39) Naturally, without prejudice to the principle of the invention, the details of construction and the embodiments may vary widely with respect to what has been described and illustrated herein, without thereby departing from the scope of the present invention.