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EP-4735741-A1 - INTERNAL COMBUSTION ENGINE WITH VARIABLE INTAKE VALVE ACTUATION, BOOT PROFILE CAMS, AND ENGINE CONTROL METHOD

EP4735741A1EP 4735741 A1EP4735741 A1EP 4735741A1EP-4735741-A1

Abstract

An internal combustion engine has at least one intake valve (V1, V2) for each cylinder actuated by a cam (14) shaped to create a lift profile having a boot conformation. The intake valve is actuated by a respective cam by means a hydraulic circuit which can be pressurized or discharged by means of an electrically actuated control valve (24), governed by an electronic controller. The electronic controller is configured to actuate the intake valve (V1, V2), under given engine operating conditions, so that during a final part of the descent of the respective piston towards the BDC at least one intake valve (V1, V2) is kept completely closed or is kept open to an extent sufficiently small to generate a pressure drop of at least 0.4 bar (40,000 Pa) in the cylinder due to the simultaneous descent of the piston towards the BDC. During a subsequent ascent phase of the respective piston towards the TDC, substantially from the BDC, the intake valve is opened, to generate a jet of air entering the cylinder, due to the depression created in the cylinder during the previous descent phase of the piston towards the BDC.

Inventors

  • RICCO, RAFFAELE
  • GARGANO, MARCELLO

Assignees

  • C.R.F. Società Consortile per Azioni

Dates

Publication Date
20260506
Application Date
20240606

Claims (11)

  1. 1. An internal combustion engine, comprising: - 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, - at least one intake valve (V1 , V2) associated with each engine cylinder, to control a flow of intake air from a respective intake duct (5) during the intake stage into the cylinder in each cylinder operating cycle, - a camshaft (11 ) driven by the crankshaft, carrying a cam, to drive said at least one intake valve of each engine cylinder, via a tappet (15), - wherein said at least one intake valve (V) of each cylinder is actuated by said tappet (15), against the action of a return spring (9), by interposition of a hydraulic circuit including: - 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 at least one intake valve (V) of each engine cylinder, - an electrically actuated control valve (24) adapted to connect said pressurized fluid chamber (C) with a low-pressure drain channel (23) communicating with a pressurized fluid accumulator (270), so that when said control valve (24) is open, pressurized fluid drains from the pressure chamber (C) into said low-pressure drain channel and said at least one intake valve (V) closes by the effect of the respective return spring (9), regardless of the action of the respective cam, said engine further comprising an electronic controller (25) for controlling the electrically actuated control valve (24) associated with said hydraulic circuit, depending on a plurality of engine operating parameters, including engine load and engine rotational speed, the engine being characterized in that: - said cam (14) associated with said at least one intake valve (V1 , V2) of each engine cylinder is so shaped as to generate, when the pressure chamber (C) is always kept under pressure, a lift profile of said at least one intake valve, as a function of the crank angle, having a boot conformation, with a first part defining a substantially constant first level of lift, followed by a second bell-shaped part, which substantially starts from the BDC and has a maximum point defining a second level of lift equal to at least 2.5 times said first level of lift, said electronic controller is configured to govern the electrically actuated control valve (24) associated with said hydraulic circuit of each cylinder, under given engine operating conditions, so that: - during the intake stage, in each operating cycle of each cylinder, during a final part of the descent of the respective piston towards the BDC said at least one intake valve (V1 , V2) is kept completely closed or is kept open to an extent sufficiently small to generate in the cylinder, due to the simultaneous descent of the piston towards the BDC, a pressure drop of at least 0.4 bar (40,000 Pa), - during a subsequent ascent phase of the respective piston towards the TDC, substantially from the BDC, said at least one intake valve is opened, to generate a jet of air entering the cylinder, due to the depression created in the cylinder during the previous descent phase of the piston towards the BDC.
  2. 2. The engine according to claim 1 , characterized in that said electronic controller (25) is configured to govern the electrically actuated control valve (24) so that said at least one intake valve is actuated with a first opening period and a second opening period, respectively at said first part and said second bell-shaped part of said boot profile, with an intermediate phase in which said at least one intake valve is kept closed, while the respective piston is descending towards its BDC, so as to create said depression in the respective cylinder generating said jet of air entering the cylinder during the subsequent second opening period of said at least one intake valve, wherein said first opening period of said at least one intake valve of each cylinder begins substantially when the respective piston is at its TDC and ends when the piston is substantially midway between its TDC and its BDC, and wherein said second opening period of said at least one intake valve of each cylinder is of a first type (2A) or a second type (2B), wherein said second opening period of the first type (2A) begins when the piston has passed 4/5 of its path from the TDC to the BDC and has not yet reached its BDC, preferably at not more than 30° crank angle before the BDC, and at not less than 20° crank angle before the BDC, wherein said second opening period of the first type (2A) ends when the piston has passed the BDC and is in the process of rising to the TDC, preferably at least 20° crank angle after the BDC, and at not more than 30° crank angle after the BDC, wherein the second opening period of the second type (2B) begins when the piston has passed the BDC and is in the process of rising to the TDC, preferably at least 20° crank angle after the BDC, and at not more than 30° crank angle after the BDC, and wherein said second opening period of the second type (2B) ends at least 80° crank angle after the BDC, and at not more than 100° crank angle after the BDC.
  3. 3. The engine according to claim 1 , characterized in that said electronic controller (25) is configured to maintain the pressure chamber (C) always under pressure, so that said at least one intake valve (V1 , V2) remains constantly open during the intake stage in each operating cycle of each cylinder, and in that the boot profile of the cam has said first level that is low enough so that during the descent of the respective piston towards its BDC inside the cylinder the pressure drops by at least 0.4 bar (40,000 Pa), while, at the second bell-shaped part of the boot profile, starting when the piston reaches the BDC and begins to ascend towards the TDC, said at least one intake valve opens further, allowing said jet of air to enter the cylinder.
  4. 4. The engine according to claim 3, characterized in that the cam is configured to generate a lift profile having the maximum point of the second bell-shaped part corresponding to a lift equal to about 5-6 times the first lift level defined from said first part at substantially constant lift.
  5. 5. The engine according to claim 1 , characterized in that it comprises a first intake valve (V1 ) and a second intake valve (V2) for each cylinder, and in that the two intake valves (V1 , V2) of each cylinder are driven by a single cam and a single pumping plunger (16) through a pressure chamber (C) in communication with both hydraulic actuators (21 ) of the two intake valves, the ration of the surface area of the pumping plunger facing the pressure chamber to the sum of the corresponding areas of the two hydraulic actuators is greater than 2 and preferably is not less than 2.4
  6. 6. The engine according to claim 5, characterized in that said boot profile has a first part at substantially constant lift from a crank angle of about 240°, where a crank angle of 360° corresponds to the BDC, and an intermediate part at substantially constant lift between said first part and said second bell-shaped part, said intermediate part defining a lift level greater than the lift level of said first part.
  7. 7. The engine according to claim 2, characterized in that said camshaft (11 ) is associated with a timing shifting device configured to vary the angular position of said camshaft with respect to said crankshaft.
  8. 8. The engine according to claim 2, characterized in that the cam (14) associated with each intake valve (V1 ; V2) of each engine cylinder is of a type with multiple profiles that can be rendered active selectively.
  9. 9. A method for controlling an internal combustion engine, wherein the engine comprises: - at least one intake valve (V1 , V2) associated with each engine cylinder, to control a flow of intake air from a respective intake duct (5) during the intake stage into the cylinder in each cylinder operating cycle, - a camshaft (11 ) driven by the crankshaft, carrying a cam, to drive said at least one intake valve of each engine cylinder, via a tappet (15), - wherein said at least one intake valve (V) of each cylinder is actuated by said tappet (15), against the action of a return spring (9), by interposition of a hydraulic circuit including: - 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 at least one intake valve (V) of each engine cylinder, - an electrically actuated control valve (24) adapted to connect said pressurized fluid chamber (C) with a low-pressure drain channel (23) communicating with a pressurized fluid accumulator (270), so that when said control valve (24) is open, pressurized fluid drains from the pressure chamber (C) into said low-pressure drain channel and said at least one intake valve (V) closes by the effect of the respective return spring (9), regardless of the action of the respective cam, said engine further comprising an electronic controller (25) for controlling the electrically actuated control valve (24) associated with said hydraulic circuit, depending on a plurality of engine operating parameters, including engine load and engine rotational speed, said method being characterized in that: - said cam (14) associated with said at least one intake valve (V1 , V2) of each engine cylinder is so shaped as to generate, when the pressure chamber (C) is always kept under pressure, a lift profile of said at least one intake valve, as a function of the crank angle, having a boot conformation, with a first part defining a substantially constant first level of lift, followed by a second bell-shaped part, which substantially starts from the BDC and has a maximum point defining a second level of lift equal to at least 2.5 times said first level of lift, said process comprising governing, by means of said electronic controller, the electrically actuated control valve (24) associated with said hydraulic circuit of each cylinder, under given engine operating conditions, so that: - during the intake stage, in each operating cycle of each cylinder, during a final part of the descent of the respective piston towards the BDC said at least one intake valve (V1 , V2) is kept completely closed or is kept open to an extent sufficiently small to generate in the cylinder, due to the simultaneous descent of the piston towards the BDC, a pressure drop of at least 0.4 bar (40,000 Pa), - during a subsequent ascent phase of the respective piston towards the TDC, substantially from the BDC, said at least one intake valve is opened, to generate a jet of air entering the cylinder, due to the depression created in the cylinder during the previous descent phase of the piston towards the BDC.
  10. 10. The method according to claim 9, characterized in that said electronic controller (25) is configured to govern the electrically actuated control valve (24) so that said at least one intake valve is actuated with a first opening period and a second opening period, respectively at said first part and said second bell-shaped part of said boot profile, with an intermediate phase in which said at least one intake valve is kept closed, while the respective piston is descending towards its BDC, so as to create said depression in the respective cylinder generating said jet of air entering the cylinder during the subsequent second opening period of said at least one intake valve, wherein said first opening period of said at least one intake valve of each cylinder begins substantially when the respective piston is at its TDC and ends when the piston is substantially midway between its TDC and its BDC, and wherein said second opening period of said at least one intake valve of each cylinder is of a first type (2A) or a second type (2B), wherein said second opening period of the first type (2A) begins when the piston has passed 4/5 of its path from the TDC to the BDC and has not yet reached its BDC, preferably at not more than 30° crank angle before the BDC, and at not less than 20° crank angle before the BDC, wherein said second opening period of the first type (2A) ends when the piston has passed the BDC and is in the process of rising to the TDC, preferably at least 20° crank angle after the BDC, and at not more than 30° crank angle after the BDC, wherein the second opening period of the second type (2B) begins when the piston has passed the BDC and is in the process of rising to the TDC, preferably at least 20° crank angle after the BDC, and at not more than 30° crank angle after the BDC, and wherein said second opening period of the second type (2B) ends at least 80° crank angle after the BDC, and at not more than 100° crank angle after the BDC.
  11. 11. The method according to claim 9, characterized in that, by means of said electronic controller (25), the pressure chamber (C) is always kept under pressure, so that said at least one intake valve (V1 , V2) remains constantly open during the intake stage in each operating cycle of each cylinder, and in that the boot profile of the cam has said first level that is low enough so that during the descent of the respective piston towards its BDC inside the cylinder the pressure drops by at least 0.4 bar (40,000 Pa), while, at the second bell-shaped part of the boot profile, starting when the piston reaches the BDC and begins to ascend towards the TDC, said at least one intake valve opens further, allowing said jet of air to enter the cylinder.

Description

“Internal combustion engine with variable intake valve actuation, boot profile cams, and engine control method” **** Field of the invention The present invention refers to internal combustion engines of the type indicated in the preamble of claim 1 . Engines of this type are described for example in documents 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 of the same Applicant. Prior art The Applicant has long developed internal combustion engines including a variable intake valve drive system of the type indicated above, marketed under the “MULTIAIR” brand. The same Applicant is the owner of various patents and patent applications relating to engines equipped with a system of the type specified above. 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. 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, and two exhaust ducts 6 lead. The connection of the two intake ducts 4 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 . 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. 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. 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. 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. 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. 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. 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 . 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. 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 ment