This application is claims priority to European Patent Application No. 17 203 737.6 filed on Nov. 27, 2018, the entire disclosure of which is incorporated herein by reference.
The present invention relates to a system and a method for actuating an engine valve of an internal combustion engine.
The invention relates, in particular, to a known type of actuating system comprising a movable member directly or indirectly controlled by a cam of a camshaft of the internal combustion engine, and mechanically or hydraulically connected to the engine valve, and at least one return spring biassing the engine valve to the closed position.
A particularly advantageous application of the invention is directed to hydraulic actuating systems, of the type comprising a master piston directly or indirectly controlled by the cam of the camshaft of the internal combustion engine, and a slave piston that drives the engine valve and that is hydraulically controlled by the master piston, by means of a volume of pressurized fluid interposed between the master piston and the slave piston.
However, application of the invention is not excluded to mechanical actuating systems wherein the aforesaid movable member controlled by the cam is a tappet connected directly or indirectly to the engine valve.
A preferred embodiment of the invention is directed to variable hydraulic actuating systems of engine valves, of the type that also includes:
in such a way that:
For a long time, the Applicant has developed internal combustion engines equipped with a variable actuating system of the engine valves of the type indicated above (see, for example, EP 1 674 673 B1).
It should be noted, however, that the present invention is of general application and can also be directed to mechanical or hydraulic actuating systems of an engine valve that do not provide variable actuation of the engine valve.
Furthermore, although the exemplary embodiments illustrated herein all relate to the actuation of intake valves of the engine, the invention is likewise applicable to the control of exhaust valves.
In all known systems involving hydraulic actuation of an engine valve, the transmission of the cam movement to the engine valve may not be immediate, and can result in a loss of movement due to the need to overcome the action of the spring or springs that push the engine valve to its closed position. The return spring must be designed and arranged to exert a relatively high force or, in any case, a force sufficient to ensure that the engine valve remains closed during the part of the rotation cycle of the cam in which the engine valve must remain closed, whatever the operating conditions of the engine are, as well as the running conditions of the vehicle using said engine. Therefore, it is not possible to facilitate the opening stage of the engine valve by adopting a reduced stiffness and/or a reduced load of the return spring or springs below a certain limit.
Therefore, in hydraulic actuating systems, a relatively high pressure level in the volume of fluid that transmits movement from the cam to the engine valve is required, resulting in greater energy consumption. In addition, the risk of a loss of movement in the transmission between the cam and the engine valve is particularly damaging in a variable actuating system, which must respond accurately and promptly to varying engine operating conditions (for example, rotational speed and load of the engine) by correspondingly varying the lift and the opening and closing times of the engine valves.
In more conventional actuating systems with a cam-driven tappet that mechanically drives the engine valve, there is still the problem of attenuating vibrations and noise due to the high load of the return spring or springs of the engine valve.
The object of the present invention is to overcome the problem discussed above by providing an actuating system for an engine valve that, on the one hand, reduces the energy consumption of the system and, on the other hand, still ensures a precise and immediate response of the engine valve at the command provided by the actuating cam.
In view of achieving the aforesaid object, the invention relates to an actuating system of an engine valve of an internal combustion engine having the characteristics that have been indicated at the beginning of the present description, and also characterized in that it comprises an auxiliary device for applying an additional force to the engine valve, tending to keep the engine valve in a closed position, said auxiliary device being configured or controlled in such a way that the total force tending to keep the engine valve in its closed position varies during each rotation cycle of the actuating cam of the engine valve, said total force being higher at least in a part of the rotation cycle of the cam in which the engine valve must remain in its closed position and being, however, reduced at least in a part of the rotation cycle of the cam in which the engine valve is not in its closed position.
In the present invention, however, on one hand, it is ensured that in the step in which the engine valve must remain closed, it remains effectively closed, at every operating condition of the engine and in every driving condition of the motor-vehicle using said engine and, on the other hand, it reduces the effort required to cause the opening of the engine valve, at least in a part of the opening step. Thanks to this arrangement, it is therefore possible to provide reliable and accurate operation of the actuating system, without the need to establish a very high pressure level in the volume of high pressure of the system.
In one embodiment, said auxiliary device comprises a solenoid carried by the engine structure and a ferromagnetic anchor associated with the engine valve, and configured to cooperate with the solenoid to tend to keep the engine valve in its closed position when the solenoid is energized. The aforesaid auxiliary device also comprises a control circuit of the solenoid configured to supply current to the solenoid, at least in a part of the rotation cycle of the cam in which the engine valve must remain in its closed position, and not to supply current to the solenoid, instead, at least in one part of the rotation cycle of the cam in which the engine valve is not in its closed position.
In a second embodiment, the auxiliary device comprises an auxiliary elastic element carried by a supporting structure that is fixed with respect to said engine valve during the movement of the engine valve, and configured to cooperate with an engagement element associated with said engine valve in such a way that in a first step of opening the engine valve, a cam surface of said engagement element associated with the engine valve deforms said auxiliary elastic element, generating an additional force tending to close the engine valve, while in a second step of the opening of the engine valve, said auxiliary elastic element is in sliding engagement against a cylindrical surface of said engagement element, so that said auxiliary elastic element remains in a deformed condition, but substantially no longer exerts any additional return force of the engine valve towards its closed position.
In a third embodiment, the auxiliary device comprises a hydraulic cylinder including two cylinder elements slidably mounted with each other, and defining a cylinder chamber between them, and a spring tending to keep said cylinder elements in a position corresponding to a maximum elongation configuration of said cylinder chamber. The aforesaid hydraulic cylinder is operatively interposed between said engine valve and the engine structure, and is configured to have a first operative condition in which the chamber of said hydraulic cylinder is isolated, so that said hydraulic cylinder constitutes an uncompressible member that blocks the engine valve in its closed position, and a second operative condition, in which the chamber of said hydraulic cylinder communicates with a discharge environment, so that said hydraulic cylinder does not prevent opening of the engine valve.
Preferably, the invention is applied to a hydraulic actuating system, comprising a master piston directly or indirectly controlled by the cam of the camshaft of the internal combustion engine, and a slave piston that drives the engine valve and that is hydraulically controlled by the master piston, by means of a volume of pressurized fluid interposed between the master piston and the slave piston.
In the particular case of application of the invention to a variable hydraulic actuating system of the engine valve of the type mentioned above, the system can be configured in such a way that the force tending to keep the engine valve in its closed condition is greater in any condition in which the engine valve must remain closed, that is, both in the part of the actuating chamber rotation cycle, in which the cam does not cause movement of the master piston, and also in all conditions in which the variable actuating system excludes the coupling between the cam and engine valve by discharging the volume of pressurized fluid.
Further characteristics and advantages of the invention will become apparent from the description that follows with reference to the attached drawings, provided purely by way of non-limiting example, wherein:
Each valve 7 is recalled towards the closed position by springs 9 interposed between an inner surface of the head 1 and an end spring plate 10 of the valve. Communication of the two exhaust ducts 6 with the combustion chamber is controlled by two valves 70 (one of which is visible in the Figure), of a traditional type, which also have associated return springs towards the closed position.
The opening of each intake valve 7 is controlled, as described below, by a camshaft 11 rotatably mounted about an axis 12 within the head supports 1 and comprising a plurality of cams 14 for actuating the intake valves 7 of the internal combustion engine.
Each cam 14 that controls an intake valve 7 cooperates with the plate 15 of a tappet 16 slidably mounted along an axis 17 which, in the case of the example illustrated in the aforementioned document, is substantially directed at 90° with respect to the axis of the valve 7. The plate 15 is recalled against the cam 14 by a spring associated therewith. The tappet 16 constitutes a pumping piston, or master piston, slidably mounted within a bushing 18 carried by a body 19 of a preassembled assembly 20 incorporating all the electrical and hydraulic devices associated with the actuation of the intake valves, according to that described in detail below. A separate assembly 20 can be provided for each cylinder of the engine.
The master piston 16 is able to transmit a thrust to the stem 8 of the valve 7, in order to cause the valve to open against the action of the elastic means 9, by pressurized fluid (preferably oil coming from the lubrication circuit of the engine) present in a volume of pressurized fluid C to which the master piston 16 faces, and by means of a slave piston 21 slidably mounted within a cylindrical body formed by a bushing 22, which is also carried by the body 19 of the preassembled assembly 20.
Still with reference to
The solenoid valve 24 can be of any known type suitable for the function illustrated herein, and is controlled by electronic control means 25, according to signals S indicative of operating parameters of the engine and/or of the variable actuating system of the engine valves, such as the accelerator position and engine speed, or the oil temperature or viscosity in the variable actuating system of the valves.
When the solenoid of the solenoid valve 24 is energized, the solenoid valve is closed, so as to keep the volume of fluid C under pressure, and to enable the actuation of each intake valve 7 by the respective cam 14, by means of the master piston 16, the slave piston 21 and the volume of oil contained therein.
When the solenoid of the solenoid valve 24 is de-energized, the solenoid valve opens, so that the volume C enters into communication with the channel 23, and the pressurized fluid present in the volume C flows into that channel. Consequently, decoupling of the cam 14 and the master piston 16 from the intake valve 7 is obtained, which then returns quickly to its closed position under the action of the return springs 9.
By controlling the communication between the volume C and the exhaust channel 23, it is therefore possible to vary the opening moment and/or the closing moment, and the opening stroke of each intake valve 7.
The exhaust channels 23 of the various solenoid valves 24 all lead into the same longitudinal channel 26 communicating with pressure accumulators 270, one of which is visible in
The master piston 16 with the associated bushing 18, the slave piston 21 with the associated bushing 22, the solenoid valve 24 and the channels 23, 26 are carried or formed in the aforesaid body 19 of the preassembled assembly 20, for the sake of speed and ease of assembly of the engine.
In the illustrated example, the exhaust valves 70 associated with each cylinder are traditionally controlled by a respective camshaft 28 through respective tappets 29, although in principle, the application of the variable actuating system to the exhaust valves is not excluded. This also applies to the present invention.
Still with reference to
During normal operation of the known engine illustrated in
In the described system, when the solenoid valve 24 is activated, the valve of the engine follows the movement of the cam (full lift). An early closure of the engine valve can be obtained by opening the solenoid valve 24, so as to empty the volume of pressurized fluid C and to obtain closure of the valve 7 under the action of the respective return springs 9. Likewise, a delayed opening of the valve 7 can be obtained by delaying the closing of the solenoid valve 24, while the combination of a delayed opening with an early closing of the valve can be obtained by controlling the closing and opening of the solenoid valve during the thrust of the relative cam. According to an alternative strategy, in accordance with the disclosures of EP 1 726 790 A1 by the same Applicant, each intake valve can be controlled in a “multi-lift” mode, that is, according to two or more repeated opening and closing “sub-cycles”. In each sub-cycle, the intake valve opens and then closes completely. The electronic control unit is, therefore, able to obtain a change in the time of opening and/or the time of closing and/or the lift of the intake valve, as a function of one or more operative parameters of the engine. This allows maximum efficiency of the engine to be obtained, and the lowest fuel consumption, in all operating conditions.
The system of
In the case of the embodiment of
Still with reference to the characteristics of the known system already implemented by the Applicant, which are also usable within the scope of the present invention, it should be noted that a hydraulic clearance compensation device 400 (“lash adjuster”) can be interposed between the slave piston 21 and the stem of the engine valve 7. This solution is, for example, described in the document EP-A-1 635 045 by the same Applicant.
In the aforesaid known systems, the electronic control unit 25 is programmed to implement different actuating modes of an engine valve (in the example illustrated in
The valve mode “EVC” (“early valve closing”) envisages that the solenoid valve 24 keeps the communication passage closed between the volume of pressurized fluid C and the lower pressure environment 23 at the beginning of the lift cycle of the cam 14, so that a first part of the lift profile of the engine valve corresponds to the first part of the lift profile of the cam 14. However, in this mode, the valve 24 opens the aforesaid communication before the lift cycle of the cam 14 is terminated. When the communication opens, pressurized fluid flows from the chamber C to the lower pressure environment 23 and the valve 7 rapidly closes, under the action of the return spring 9, even if the cam 14 is still in a position in which it would tend to keep the valve open. Therefore, the lift profile of the valve 7, in the EVC mode, follows the line indicated with a continuous line, in place of the dashed line profile, corresponding to the profile of the cam. With this operation mode, the engine valve 7 then reaches the closed condition in advance with respect to the closing time in the FL mode.
Again, with reference to
An additional valve mode “ML” (“multi-lift”) enables the control valve 24 to close and open the aforesaid communication several times within the same lift cycle of the cam 14, in such a way that the valve 7 opens and closes completely two or more times within the same lifting cycle of the cam. Also in this mode, as in the LVO mode, it can be verified that the valve 7 closes before the closing of the conventional cycle corresponding to the cam profile, even if the control valve 24 keeps the communication closed between the volume C and the lower pressure environment 23.
In
The upper end of the slave piston 21 faces a variable volume chamber C1, which, in turn is intended to communicate with the volume of pressurized fluid C. At the top of the guide bushing 20, a hydraulic braking device 30 is provided, which reduces the communication passage between the chamber C1 and the chamber C in the final closing step of the engine valve, in order to brake the movement of the engine valve, so as to avoid an impact of the engine valve against its seat 7A upon reaching the closed position.
All the characteristics described above with reference to
In the embodiment of
According to the invention, the electronic unit E is configured to supply current to the solenoid S during each rotation cycle of the actuating cam 14 (
Incidentally, in the example of
However, application of the invention is general. In particular, the invention is applicable both to variable actuation systems of different types of valves, for example, with a more traditional cam profile, without a boot profile, as well as to conventional systems that do not provide a variable actuation of the engine valves.
With reference again to
In the prior art resolutions, where the force tending to keep the engine valve closed is generated solely by the spring 9, this spring must be designed and arranged to generate a relatively high return force, in order to ensure that the engine valve remains closed in the conditions in which it must be closed. In the case of the present invention, instead, during the phases in which the engine valve must remain closed, the necessary force is obtained thanks to the auxiliary device (whatever its embodiment). This makes it possible to design and arrange the spring 9 with a significantly lower rigidity and/or load. Consequently, in the phase in which the slave piston 21 must cause the engine valve to open, the force that it has to overcome is considerably reduced compared to the prior art solutions described above. Consequently, the pressure level that must be maintained in the high pressure volume C can also be lower than that which is necessary in the known solutions.
The main advantage deriving from the aforesaid device lies in the fact that the system is able to actuate the engine valve easily and immediately, without the risk of a loss of movement in the transmission of motion from the cam to the valve; moreover, as the pressure level is lower, this results in a reduction in the compression work of the aforesaid oil, with obvious benefits on the organic performance of the engine
Naturally, in the case of application to a variable actuation system of the valves, to which the example of
According to the conventional technique, the element 401 is slidably mounted on the lower end of the piston 21 and defines within it the hydraulic chamber 402 of the tappet 400. The chamber 400 contains a non-return valve that controls the communication between the chamber 402 and a chamber 210 formed within the slave piston 21. This non-return valve comprises a valve element 403 pushed by a spring 404 towards a position in which it closes a communication hole 211 between the chamber 402 and the chamber 210. All the aforesaid elements of the hydrated tappet 400 are known per se and are only illustrated here to allow a complete understanding of the device illustrated in
In any case, what is important is that the end portion 920 of the bushing 92, defined by the two semi-cones 92A, has a cylindrical outer surface with a flush arrangement and placed on the extension of the outer surface of the element 401 with which it is in contact. Furthermore, this outer cylindrical surface of the end portion 920 is joined to the lower portion of the outer surface of the bushing 92, defined by the two semi-cones, by means of a tapered surface 922, which acts as a cam, configured to cooperate with the ends 804 of the elastic wings. 803.
The operation of the embodiment illustrated in
Starting from the closed condition of the valve 7 (illustrated in
As soon as the engine valve 7 has moved away from its closed position by a distance sufficient to bring the ends 804 of the elastic wings 803 into contact with the cylindrical portion 921 of the outer surface of the bushing 92 defined by the two semi-cone 92A, further movement of the engine valve takes place with the ends 804 that slide on the aforesaid cylindrical surface 921 and then on the cylindrical surface of the element 401, remaining in their enlarged deformed condition, but without contributing to the force that tends to return the valve back into the closed position. In this condition, if friction is ignored between the ends 804 and the cylindrical surface that slides between them, the force opposing the opening of the engine valve is substantially only that generated by the spring 9.
Therefore, the solution of
In the case of the embodiment illustrated in
Within the cylindrical stem 912, a chamber 913 is defined, which is capable of communicating with the low pressure fluid environment through an axial duct 914, and with an axial duct 915, formed in the stem 912 on opposite sides with respect to the chamber 913. Communication of the chamber 913 with the ducts 914, 915 is controlled by two non-return valves, comprising two spheres 916 between which a spring 917 is interposed. A spring 918 inside the bushing 911 is interposed axially between the head 910 of the bushing 911 and a striking surface formed on the cylindrical stem 912. The spring 918 tends to maintain the hydraulic cylinder 900 defined by the bushing 911 and the stem 912 in a configuration of maximum extension, corresponding to the maximum extension of the spring 918. Communication of the chamber 913 with the low pressure environment can be established by a pin actuator 919 carried by a small piston 920, which is slidably mounted within a cylindrical body 921, rigidly connected to the cylinder head structure. The small piston 920 faces a chamber 930 that is in communication with the high pressure environment of the variable actuating system of the engine intake valves. Therefore, when the volume C (
As is clear from the above description, the system according to the present invention is based on the principle of varying the force that tends to keep the engine valve (for example, an intake valve) in the closed position during each rotation cycle of the actuating cam, in such a way that this force is greater in the part of the rotation cycle of the cam corresponding to the closed position of the engine valve, and is reduced in the part of the rotation cycle of the cam that causes a movement of the engine valve.
In an embodiment of the invention, not illustrated and described, the auxiliary device is designed for inserting and disengaging a constraint, or rather an almost infinite force, upon axial translation of the valve: said constraint remains inserted during the angular interval during which the valve must remain closed.
In general, the invention is applicable to any hydraulic actuating system of an engine valve, both for the intake valves and for the engine exhaust valves. It has been shown that the application of the invention to a variable actuating system of an engine valve is particularly advantageous.
As indicated, the invention can also be applied to a mechanical actuating system, of the type in which a tappet controlled by the cam mechanically actuates the engine valve.
Of course, without prejudice to the principle of the invention, the details of construction and the embodiments may vary widely with respect to those described and illustrated purely by way of example, without departing from the scope of the present invention.
Number | Date | Country | Kind |
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17203737 | Nov 2017 | EP | regional |
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Entry |
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Search Report for European Application No. 17203737.6 completed on May 29, 2018. |
Number | Date | Country | |
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20190162085 A1 | May 2019 | US |