Patent Application
20140318484
The present invention relates to internal-combustion engines of the type comprising, for each cylinder:
a combustion chamber;
at least two intake ducts and at least one exhaust duct which give out into said combustion chamber;
at least two intake valves and at least one exhaust valve associated to said intake and exhaust ducts and provided with respective return springs that push them towards a closed position;
a camshaft for actuating the intake valves, by means of respective tappets;
wherein each intake valve is controlled by the respective tappet against the action of the aforesaid return spring by interposition of hydraulic means including a pressurized-fluid chamber facing which is a pumping plunger connected to the valve tappet, said pressurized-fluid chamber being designed to communicate with the chamber of a hydraulic actuator associated to each intake valve;
a single electrically actuated valve for each cylinder, designed to set said pressurized-fluid chamber in communication with an exhaust channel in order to decouple each intake valve from the respective tappet and cause fast closing of the intake valves as a result of the respective return springs; and
electronic control means, for controlling said electrically actuated valve so as to vary the instant of opening and/or the instant of closing and the lift of each intake valve as a function of one or more operating parameters of the engine.
An engine of the above type is described, for example, in any one of the 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, all filed in the name of the present applicant.
The present applicant has been developing for some time internal-combustion engines comprising a system for variable actuation of the intake valves of the type indicated above, marketed under the trade name “Multiair”. The present applicant is the holder of numerous patents and patent applications regarding engines provided with a system of the type specified above.
With reference to said
Each valve 7 is recalled into the closing position by springs 9 set between an internal surface of the cylinder head 1 and an end valve retainer 10. Communication of the two exhaust ducts 6 with the combustion chamber is controlled by two valves 70, which are also of a traditional type, associated to which are springs 9 for return towards the closed position.
Opening of each intake valve 7 is controlled, in the way that will be described in what follows, by a camshaft 11 rotatably mounted about an axis 12 within supports of the cylinder head 1, and comprises a plurality of cams 14 for actuation of the intake valves 7.
Each cam 14 that controls an intake valve 7 co-operates with the plate 15 of a tappet 16 slidably mounted along an axis 17, which, in the case of the example illustrated in the prior document cited, is set substantially at 90° with respect to the axis of the valve 7. The plate 15 is recalled against the cam 14 by a spring associated thereto. The tappet 16 constitutes a pumping plunger slidably mounted within a bushing 18 carried by a body 19 of a pre-assembled unit 20, which incorporates all the electrical and hydraulic devices associated to actuation of the intake valves, according to what is described in detail in what follows.
The pumping plunger 16 is able to transmit a thrust to the stem 8 of the valve 7 so as to cause opening of the latter against the action of the elastic means 9, by means of pressurized fluid (preferably oil coming from the engine-lubrication circuit) present in a pressure chamber C facing which is the pumping plunger 16, and by means of a plunger 21 slidably mounted in a cylindrical body constituted by a bushing 22, which is also carried by the body 19 of the subassembly 20.
Once again in the known solution illustrated in
When the solenoid valve 24 is open, the chamber C enters into communication with the channel 23 so that the pressurized fluid present in the chamber C flows in said channel, and a decoupling is obtained of the cam 14 and of the respective tappet 16 from the intake valve 7, which thus returns rapidly into its closing position under the action of the return springs 9. By controlling the communication between the chamber C and the exhaust channel 23, it is consequently possible to vary as desired the time and stroke of opening of each intake valve 7.
The exhaust channels 23 of the various solenoid valves 24 all give out into one and the same longitudinal channel 26 communicating with pressure accumulators 27, only one of which is visible in
All the tappets 16 with the associated bushings 18, the plungers 21 with the associated bushings 22, the solenoid valves 24 and the corresponding channels 23, 26 are carried and constituted by the aforesaid body 19 of the pre-assembled unit 20, to the advantage of rapidity and ease of assembly of the engine.
The exhaust valves 70 associated to each cylinder are controlled, in the embodiment illustrated in
Once again with reference to
During normal operation of the known engine illustrated in
In the opposite movement of closing of the valve, as has already been said, during the final step the nose 31 enters the opening 30 causing hydraulic braking of the valve so as to prevent impact of the body of the valve against its seat, for example following upon an opening of the solenoid valve 24, which causes immediate return of the valve 7 into the closing position.
In the system described, when the solenoid valve 24 is activated, the valve of the engine follows the movement of the cam (full lift). An anticipated closing of the valve can be obtained by deactivating (opening) the solenoid valve 24 so as to empty out the hydraulic chamber and obtain closing of the valve of the engine under the action of the respective return springs. Likewise, a delayed opening of the valve can be obtained by delaying activation of the solenoid valve, whereas the combination of a delayed opening and an anticipated closing of the valve can be obtained by activation and deactivation of the solenoid valve during the thrust of the corresponding cam. According to an alternative strategy, in line with the teachings of the patent application No. EP 1 726 790 A1 filed in the name of the present applicant, each intake valve can be controlled in “multi-lift” mode, i.e., according to two or more repeated “subcycles” of opening and closing. In each subcycle, the intake valve opens and then closes completely. The electronic control unit is consequently able to obtain a variation of the instant of opening and/or of the instant of closing and/or of the lift of the intake valve, as a function of one or more operating parameters of the engine. This enables the maximum engine efficiency to be obtained, and the lowest fuel consumption, in every operating condition.
As may be seen, in the conventional system of
The above solution presents evident advantages of smaller overall dimensions on the cylinder head, and of lower cost and lower complexity of the system, as compared to a solution that envisages a cam and a solenoid valve for each intake valve of each cylinder.
The system of
The solution illustrated in
On the other hand, the solution with a single solenoid valve per cylinder rules out the possibility of differentiating the control of the intake valves of each cylinder. Said differentiation is instead desirable, in the case of diesel engines in which each cylinder is provided with two intake valves associated to respective intake ducts having conformations different from one another, in order to generate different movements of the flow of air introduced into the cylinder (see, for example, FIG. 5 of EP 1 508 676 B1). Typically, in said engines the two intake ducts of each cylinder are shaped for optimizing, respectively, the flows of the “tumble” type and of the “swirl” type inside the cylinder, said forms of motion being fundamental for optimal distribution of the charge of air inside the cylinder, from which there depends in a substantial way the possibility of reducing the pollutant emissions at the exhaust.
In controlled-ignition engines, instead, said differentiation is desired at low engine loads both for optimizing the coefficients of air outflow through the intake valves, consequently reducing the pumping cycle, and for optimizing the range of motion of the air within the cylinder during the intake stroke
As has been said, in Multiair systems with a single solenoid valve per cylinder, it is not possible to control in an independent way the two intake valves of each cylinder. It would, instead, be desirable to be able increase each time the fraction of charge of air introduced with the tumble motion and the fraction of charge of air introduced with the swirl motion as a function of the engine operating conditions (r.p.m., load, cold start, etc.).
Likewise, in an engine with controlled ignition, in particular when this works at partial loads or in idling conditions, there is posed the problem of having to introduce a small charge of air with a sufficient kinetic energy that will favour setting-up of a range of motion optimal for combustion inside the cylinder. In these operating conditions, it would consequently be preferable for the entire mass of air to be introduced by just one of the two intake valves to reduce the dissipative losses during traversal of the valve itself. In other words, once the mass of air that must be introduced into the combustion chamber has been fixed, and the pressure in the intake manifold has been fixed, and given the same evolution of the negative pressure generated by the motion of the piston in the combustion chamber, there are lower dissipation losses (and hence a higher kinetic energy) for the mass of air introduced by a single intake valve opened with a lift of approximately 2 h as compared to the case of the same mass of air introduced by two intake valves with a lift h.
In the European patent application No. EP 11 190 639.2 filed on Nov. 24, 2011 and still secret at the date of filing of the present patent application, the present applicant has proposed an internal-combustion engine of the type referred to at the start of the present description and further characterized in that the solenoid valve associated to each cylinder is a three-way, three-position solenoid valve, comprising an inlet permanently communicating with said pressurized fluid chamber and with the actuator of a first intake valve, and two outlets, which communicate, respectively, with the actuator of the second intake valve and with said exhaust channel. In this solution, the solenoid valve has the following three operating positions:
a first position, in which the inlet communicates with both of the outlets, so that the actuators of both of the intake valves are set in the discharge condition, and the intake valves are both kept closed by their return springs;
a second position, in which the inlet communicates only with the outlet connected to the actuator of the second intake valve and does not communicate instead with the outlet connected to the exhaust channel so that the pressure chamber is isolated from the exhaust channel, the actuators of both of the intake valves communicate with the pressure chamber, and the intake valves are thus both active; and
a third position, in which the inlet does not communicate with any of the two outlets so that the aforesaid pressure chamber is isolated from the exhaust channel and the aforesaid first intake valve is active, whilst the second intake valve is isolated from the pressure chamber.
The electrically actuated valve associated to each cylinder of the engine can have a solenoid electric actuator or any other type of electric or electromagnetic actuator.
The object of the present invention is to propose an engine of the type indicated at the start of the present description that will be able to solve the problems indicated above and to meet the requirement of a differentiated control of the two intake valves of each cylinder, albeit using a single electrically actuated or electromagnetically actuated control valve in association with each cylinder.
A further object of the invention is to provide operating modes of the engine intake valves that are not possible with known systems.
With a view to achieving the aforesaid object, the subject of the invention is an internal-combustion engine having the characteristics of Claim 1.
The subject of the invention is also a method for controlling an internal-combustion engine according to Claim 11.
For the purposes of the invention, any electrically actuated or electromagnetically actuated control valve that presents the characteristics indicated above can be used.
However, preferably, the engine according to the invention uses an electrically actuated valve specifically provided for the aforesaid purposes. The main characteristics of this electrically actuated valve are indicated in the annexed Claim 2.
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:
With reference to the schematic illustrations of
Hence, as has been seen, in the engine according to the invention it is possible to render the two intake valves 7A, 7B associated to each cylinder of the engine both sensitive to the movement of the respective tappet, or else again decouple them both from the respective tappet, causing them to be kept closed by the respective return springs, or else again it is possible to decouple from the tappet only the intake valve 7A, and leave only the intake valve 7B active.
When a command for opening of the valves 7A, 7B ceases, the solenoid valve is brought back into the position P1 for enabling the pumping element 16 to draw in a flow of oil from the volume 270 towards the volume C.
Preferably, the system according to the invention is provided with one or more of the solutions illustrated in
When the system is in the position P3, given that the volume of fluid pumped by the pumping element 16 is fixed, and given that the volume between the outlet u1 and the chamber of the hydraulic actuator of the valve 7A vanishes, there is posed the problem of disposing of the volume of fluid in excess that in the position P2 is pumped into the delivery branch of the aforesaid valve 7A. This volume of fluid, in the absence of countermeasures, gives rise in the position P3 to a supplementary stroke of the valve 7B. In practice, if the valves 7A and 7B are the same as one another, then in the position P2 they both undergo a lift by a stroke h, whereas in the position P3 the valve 7A would remain closed whilst the valve 7B would present a stroke 2h. Said characteristic may be altogether acceptable, but if, instead, it is preferred to avoid it, the following countermeasure, illustrated in
With reference to
As indicated above, the system of the invention can envisage one or both of the solutions illustrated with reference to
Of course, the system according to the invention is unable to reproduce the same operating flexibility that it is possible to obtain in a system that envisages two separate solenoid valves for control of the two intake valves of each cylinder of the engine, but enables in any case a sufficient operating flexibility, as against a drastic reduction in complexity, cost, and dimensions of a solution with two solenoid valves.
As has already been clarified above, the system according to the invention can be implemented by resorting to a three-way, three-position solenoid valve having any structure and arrangement, provided that it responds to the general characteristics that have been described above.
Preferably, however, the solenoid valve used presents the further characteristics that are specified in the annexed Claim 2. Said characteristics have been implemented in some preferred embodiments of a solenoid valve that has been specifically developed by the present applicant.
Said preferred embodiments of the solenoid valve that can be used in the system according to the invention are described in what follows with reference to
With reference to
With reference also to the diagram of
With reference to
The jacket 10 is traversed by a through hole sharing the axis H and comprising a first stretch 16 having a first diameter D16 and a second stretch 18 comprising a diameter D18, where the diameter D18 is greater than the diameter D16. In a position corresponding to the interface between the two holes a shoulder 19 is thus created.
The mouths 2, 6 are provided by means of through holes with radial orientation made, respectively, in a position corresponding to the stretch 16 and in a position corresponding to the stretch 18 and in communication with said stretches.
Moreover provided on an outer surface of the jacket 10 are a first annular groove 20, a second annular groove 22, and a third annular groove 24, each designed to receive a gasket of an O-ring type, arranged on opposite sides with respect to the radial holes that define the mouth 2 and to the radial holes that define the mouth 6.
In particular, the mouth 6 is comprised between the grooves 20 and 22 whilst the mouth 2 is comprised between the grooves 22 and 24.
Preferably, the three annular grooves 20, 22, 24 are provided with the same seal diameter so as to minimize the unbalancing induced by the resultant of the forces of pressure acting on the outer surface of the jacket 10, which otherwise would be such as to jeopardize fixing of the jacket of the solenoid valve in the corresponding seat provided on a component or in an oleodynamic circuit where it is installed.
The first valve element 12 is substantially configured as a hollow tubular element comprising a stem 26—which is hollow and provided in which is a first cylindrical recess 27—, a neck 28, and a head 30, which has a conical contrast surface 32 and a collar 34. The neck 28 has a diameter smaller than that of the stem 26.
Moreover, preferably provided in the collar 34 is a ring of axial holes 34A, whilst a second cylindrical recess 35 having diameter D35 is provided in the head 30.
The stem 26 of the valve element 12 is slidably mounted within the stretch 16 in such a way that the latter functions as guide element and as dynamic-seal element for the valve element 12 itself, the dynamic seal is thus provided between the environment giving out into which is the first mouth 2 and the environment giving out into which is the second mouth 4. This, however, gives rise to slight leakages of fluid through the gaps existing between the valve element 12 and the stretch 16; the phenomenon is typically described as “hydraulic consumption” of the solenoid valve, and depends upon the difference in pressure between the environments straddling the dynamic seal itself, upon geometrical parameters of the gaps (in particular the axial length, linked to the length of the stem 26, and the diametral clearance) and, not least, upon the temperature of the fluid, which as is known determines the viscosity thereof.
The axial length of the stem 26 is chosen in such a way that it will extend along the stretch 16 as far as the holes that define the mouth 2, which thus occupy a position corresponding to the neck 28 that substantially forms an annular fluid chamber.
The head 30 is positioned practically entirely within the stretch 18, except for a small surface portion 32 that projects within the stretch 16 beyond the shoulder 19. In fact, the head 30 has a diameter greater than the diameter D16 but smaller than the diameter D18, so that in a position corresponding to the shoulder 19 a first valve seat A1 is provided for the valve element 12, in particular for the conical surface 32.
In a variant of the solenoid valve of
Provided at a first end of the jacket 10 is a first threaded recess 36 in which a bushing 38 having a through guide hole 40 sharing the axis H is engaged. The diameter of the hole 40 is equal to the diameter D35 for reasons that will emerge more clearly from the ensuing description.
The bushing 38 comprises a castellated end portion 42 that functions as contrast element for a spacer ring 44.
The spacer ring 44 offers in turn a contrast surface to the head 30 of the valve element 12, in particular to the collar 34. Moreover, the choice of the thickness of the spacer ring 44 enables adjustment of the stroke of the valve element 12 and hence the area of passage between the mouth 2 and the mouth 6.
At a second end of the jacket 10, opposite to the first end, a second threaded recess 46 is provided in which a ringnut 48 is engaged. The ringnut 48 functions as contrast for a ring 50, which in turn offers a contrast surface for a first elastic-return element 52 housed in the cylindrical recess 27.
The ringnut 48 is screwed within the threaded recess 46 until it comes to bear upon the shoulder between the latter and the jacket 10: in this way, the adjustment of the pre-load applied to the elastic-return element 52 is determined by the thickness (i.e., by the band width) of the ring 50.
The second valve element 14 is set inside the stem 26 and is slidable and coaxial with respect to the first valve element 12.
The valve element 14 comprises:
a terminal shank 54 at a first end thereof;
a stem 56; and
a head 58, located at a second end thereof, having a conical contrast surface 60 and a cup-shaped end portion 64, where the head 58 and the shank 54 are connected by the stem 56.
It should moreover be noted that the geometry of the castellated end 42 contributes to providing, by co-operating with the holes 34a, a passageway for the flow of fluid that is sent on through the section of passage defined between the conical surface 60 and the valve seat A2 towards the second mouth 4.
The cup-shaped end portion 64 has an outer diameter D64 equal to the diameter of the hole 40 and comprises a recess that constitutes the outlet of a central blind hole 66 provided in the stem 56. The hole 66 intersects a first set and a second set of radial holes, designated, respectively, by the reference numbers 68, 70. In this embodiment the two sets each comprise four radial holes 68, 70 set at the same angular distance apart.
The position of the aforesaid sets of radial holes is such that the holes 68 substantially occupy a position corresponding to the cylindrical recess 35, whilst the holes 70 substantially occupy a position corresponding to the cylindrical recess 27.
The coupling between the cup-shaped end portion 64 (having diameter D64) and the hole 40 (having a diameter substantially equal to the diameter D64) provides a dynamic seal between the valve element 14 and the bushing 38: this seal separates the environment giving out into which is the third mouth 6 from the environment giving out into which is the second mouth 4. In a way similar to what has been described for the dynamic seal provided between the mouths 2 and 6, the hydraulic consumption depends not only upon the temperature and upon the type of fluid, but also upon the difference in pressure existing between the environments giving out into which are the mouths 2 and 4, upon the diametral clearance, upon the length of the coupling between the cup-shaped end portion 64 and the bushing 38, and upon other parameters such as the geometrical tolerances and the surface finish of the various components. The values of hydraulic consumption of the two dynamic seals are added together and define the total hydraulic consumption of the solenoid valve 1.
Fitted on the terminal shank 54 is an anchor 71 provided for co-operating with the solenoid 8, which has a position reference defined by a half-ring 72 housed in an annular groove on the shank 54. Advantageously, the anchor 71 can be provided as a disk comprising notches with the dual function of reducing the overall weight thereof and reducing onset of parasitic currents.
Provided at a second end of the jacket 10, opposite to the one where the bushing 38 is situated, is a collar 73, inserted within which is a cup 74, blocked on the collar 73 by means of a threaded ringnut 76, which engages an outer threading made on the collar 73.
Set in the cup 74 is a toroid 78 housing the solenoid 8, which is wound on a reel 80 housed in an annular recess of the toroid 78 itself. The toroid 78 is traversed by a through hole 79 sharing the axis H and is surmounted by a plug 82 bearing thereon and blocked on the cup 74 by means of a cap 84 bearing a seat for an electrical connector 85 and electrical connections (not visible) that connect the electrical connector to the solenoid 8.
The toroid 78 comprises a first base surface, giving out onto which is the annular recess 79, which offers a contrast to the anchor 71, determining the maximum axial travel (i.e., the stroke) thereof, designated by c. The maximum axial travel of the anchor 71 is hence determined by subtracting the thickness of the anchor 71 itself (i.e., the band width thereof) from the distance between the first base surface of the toroid 78 and the ringnut 48. In order to adjust the stroke c of the anchor 71 a first adjustment shim R1 is provided preferably made as a ring having a calibrated thickness; alternatively, it is possible to replace the anchor 71 with an anchor of a different thickness. The stroke c of the anchor 71 is hence constituted by three components:
It should moreover be noted that the pressure of the fluid in the environment giving out into which is the mouth 4 exerts its own action also on the anchor 71, on the toroid 78, on the elastic element 90, on the ringnut 48, and on the shank 54 of the valve element 14. This calls for adoption, in order to protect the electromagnet 8, of static-seal elements.
The plug 82 comprises a through hole 84 sharing the axis H and comprising a first stretch with widened diameter 86 and a second stretch with widened diameter 88 at opposite ends thereof. It should be noted that the through hole 84 enables, by introducing a measuring instrument, verification of the displacements of the valve element 14 during assemblage of the solenoid valve 1.
The stretch 86 communicates with the hole 79 and defines a single cavity therewith, set inside which is a second elastic-return element 90, co-operating with the second valve element 14. The elastic-return element 90 bears at one end upon a shoulder made on the shank 54 and at another end upon a second adjustment shim R2 bearing upon a shoulder created by the widening of diameter of the stretch 86. The adjustment shim R2 has the function adjustment of the pre-load of the elastic element 90.
Forced in the stretch 88 is a ball 92 that isolates the hole 84 with respect to the environment preventing accidental exit of liquid.
All the components so far described are coaxial to one another and share the axis H.
Operation of the solenoid valve 1 is described in what follows.
In the first example described here, the solenoid valve 1 is inserted in the circuit illustrated schematically in
In the node between the mouths 2, 4 and 6, designated by 6′, the value of the pressure is equal to the value in the region of the third mouth 6 but for the pressure drops along the branch 6-6′. Set between the mouth 4 and the node 6′ is the flow restrictor A2, which schematically represents the action of the second valve element 14. Likewise, set between the mouth 2 and the node 6′ is the flow restrictor with variable cross section A1, which schematically represents the action of the first valve element 12.
The positions P1, P2, P3 correspond to particular values of the section of passage of the flow restrictors A1, A2, in turn corresponding to different positions of the valve elements 12, 14, as will emerge more clearly from the ensuing description. In particular:
position P1: A1, A2 have a maximum area of passage;
position P2: A1 has a maximum area of passage, A2 has a zero area of passage;
position P3: A1, A2 have a zero area of passage.
In particular, the first valve element 12 is kept bearing upon the ring 44 by the first elastic-return element 52, whilst the second valve element 14 is kept in position thanks to the anchor 71; the second elastic-return element 90 develops its own action on the shank 54, and said action is transmitted to the anchor 71 by the half ring 72, bringing the anchor 71 to bear upon the ringnut 48.
In this way, with reference to
In said annular volume there is set up, on account of the head losses due to traversal of the radial holes that define the mouth 2, a pressure p6′>p4, In this way, the fluid proceeds spontaneously along its path towards the mouth 4 traversing the second gap set between the conical surface 60 and the second valve seat A2.
In this way, the fluid can invade the cylindrical recess 35 and pass through the holes 68, invading the cup-shaped end portion 64 and coming out through the hole 40. It should be noted that the pressure that is set up in the volume of the cylindrical recess 35 is slightly higher than the value p4 by virtue of the head losses due to traversal of the holes 68. Finally, it should be noted that the valve element 12 itself and the guide bushing 38 define the second mouth 4.
The graphs of
The graph of
Corresponding to the operating position P1 illustrated in
At the same time, with reference to
In addition, with reference to
With reference to
The operating position P2 is activated following upon a first event of switching of the solenoid valve 1, which occurs at an instant t1 in which an energization current of intensity I1 is supplied to the solenoid 8.
The intensity I1 is chosen in such a way that the action of attraction exerted by the solenoid 8 on the anchor 71 will be such as to overcome just the force developed by the elastic-return element 90. In other words, the solenoid 8 is actuated for impressing on the second valve element a first movement Δh14 in an axial direction H having a sense indicated by C in
With reference to the graphs of
It should be noted that the movement of the valve element 14 stops in contact with the valve seat A2 since, in order to proceed, it would be necessary to overcome also the action of the elastic element 52, which is impossible with the energization current of intensity I1 that traverses the solenoid 8.
The valve element 14 (like the valve element 12, see the ensuing description) is moreover hydraulically balanced. Consequently, it is substantially insensitive to the values of pressure with which the solenoid valve 1 is operating.
The term “hydraulically balanced” referred to each of the valve elements 12, 14 is meant to indicate that the resultant in the axial direction (i.e., along the axis H) of the forces of pressure acting on the valve element is zero. This is due to the choice of the surfaces of influence on which the action of the pressurized fluid is exerted and of the dynamic-seal diameters (in this case also guide diameters) of the valve elements. In particular, the dynamic-seal diameter of the valve element 14 is the diameter D64, which is identical to the diameter D35 of the cylindrical recess D35, which determines the seal surface of the valve element 14 at the valve seat A2 provided on the valve element 12.
The same applies to the valve element 12, where the dynamic-seal diameter is the diameter D16, which is equal to the diameter of the stem 26 (but for the necessary radial plays) and coincides with the diameter of the valve seat A1, provided on the jacket 10, which determines the surface of influence of the valve element 12.
In a particular variant, it is possible to design the solenoid valve 1 in such a way that the diameters D64 and D35 associated to the valve element 14 are substantially equal to the diameter D16 and to the diameter of the seat A1 of the valve element 12.
The configuration of the valve elements 12, 14 in the third operating position P3 is illustrated in
This causes an increase of the force of attraction exerted by the solenoid 8 on the anchor 71, whereby a second movement is impressed on the second valve element 14, subsequent to the first movement, thanks to which the second valve element 14 draws the first valve element 12 into contact against the first contrast surface A1, hence disabling the passage of fluid from the mouth 2 to the mouth 6. In fact, there is no longer any gap through which the fluid that enters the mouth 2 can flow towards the mouth 6. The diagram of
It should be noted that, for the reasons described previously, during the aforesaid second movement, in which the valve element 12 is guided by the bushing 38, the second valve element 14 remains in contact with the first valve element 12 keeping passage of fluid from the mouth 2 to the mouth 4 disabled. The corresponding displacement of the valve element 14, which is the same that the valve element 12 undergoes (both of which in the axial direction and with sense C), is designated by Δh12 in
There is thus obtained a transition from the second operating position P2 to the third operating position P3, in which, in actual fact, the environments connected to each of the mouths of the solenoid valve 1 are isolated from one another, except for the flows of fluid that leak through the dynamic seals towards the environment with lower pressure, i.e., towards the second mouth 4. In the design stage, the dynamic seals are conceived in such a way that any leakage of fluid will in any case be negligible as compared to the leaks that can be measured when the solenoid valve is in the operating positions P1 and/or P2.
The higher intensity of current that circulates in the solenoid 8 is necessary to overcome the combined action of the elastic-return elements 90 and 52, which tend to bring the respective valve elements 14, 12 back into the resting position.
It should be noted that also in this circumstance, given that the valve element 12 is hydraulically balanced, the action of attraction developed on the anchor 71 must overcome only the return force of the springs 90, 52, in so far as the dynamic equilibrium of the valve elements 12, 14 is irrespective of the action of the pressure of the fluid, given that said valve elements are hydraulically balanced.
In this way, it is possible to choose a solenoid 8 of contained dimensions and it is hence possible to work with contained energization currents and with times of switching between the various operating positions of the solenoid valve contained within a few milliseconds, for example, operating with a pressure p2 in the region of 400 bar. Other typical values of pressure for the environment connected to the fluid-inlet mouth are 200 and 300 bar (according to the type of system).
With reference to
It should moreover be noted that the solenoid valve 1 is inserted in the body 100 in a seat 102 in which there is a separation of the levels of pressure associated to the individual environments by means of three gaskets of an O-ring type designated by the reference numbers 104, 106, 108 and housed, respectively, in the annular grooves 20, 22, and 24.
In particular, the O-ring 104 guarantees an action of seal in regard to the body across the environments that are at pSC and pINT, whereas the O-ring 106 guarantees an action of seal in regard to the body across the environments that are at pINT and pMAX. The last O-ring, designated by the reference number 108, exerts an action of seal that prevents any possible leakage of fluid on the outside of the body.
Of course, it is possible to exploit the potentialities of modern electronic control units so as to impart high-frequency signals to the solenoid valve 1 obtaining very fast switching. This is advantageous in so far as it is not possible to provide a direct switching from the operating position P3 to the operating position P1.
It should be noted that in this perspective it is extremely important for the valve elements 12 and 14 to be hydraulically balanced, in so far as if it were not so, excessively high forces of actuation would be necessary to guarantee the required dynamics, which in turn would call for an oversizing of the components (primarily the solenoid 8) in addition to a dilation of the switching times, which might not be compatible with constraints of space and with the operating specifications typical of the systems discussed herein.
Of course, the details of construction and the embodiments may vary widely with respect to what is described and illustrated herein, without thereby departing from the sphere of protection of the present invention, as defined by the annexed claims.
For example, the seals between the valve elements 12, 14 and the respective valve seats A1, A2 can be provided by means of the contact of two conical surfaces, in which the second conical surface replaces the sharp edges of the shoulders on which the valve seats are provided.
In addition, as an alternative to the dynamic seals provided by means of radial clearance between the moving elements described previously, it is possible to adopt dynamic-seal rings, specific for the use of interest.
For example, the rings can be of a self-lubricating type, hence with a low coefficient of friction, so as not to introduce high forces of friction and not to preclude operation of the valve itself.
In the example described so far, there has been assumed the hydraulic connection of the mouth 4 with the exhaust environment and the hydraulic connection of the mouth 6 with the actuator of the valve 7A, at a pressure intermediate between the pressure p2 and the pressure p4.
By reversing the connection of the mouths 4 and 6 to the respective environments, i.e., by connecting the mouth 4 to the actuator of the valve 7A and the mouth 6 to the exhaust environment, the behaviour of the solenoid valve 1 varies.
In particular, in the operating position P1 of the solenoid valve, as has been defined previously, the pressure chamber C connected to the mouth 2 and the actuator of the intake valve 7A connected to the mouth 4 will be set in the discharging condition and the leaks of fluid will have a direction going from the environment connected to the mouth 4 to the environment connected to the mouth 6.
By switching the solenoid valve 1 from the operating position P1 to the operating position P2 the environment connected to the second mouth 4 is excluded, whereas only the hydraulic connection remains of the inlet environment connected to the first mouth 2 with the mouth 6, i.e., with the exhaust: as compared to the previous operating position, the flowrate measured at outlet from the mouth 6 will be lower than in the previous case, the contribution of the flow from the mouth 4 to the mouth 6 thus vanishing.
Finally, by switching the solenoid valve 1 from the operating position P2 to the operating position P3, also the hydraulic connection between the environment connected to the mouth 2 and the environment connected to the mouth 6 will be disabled.
The inventors have moreover noted that it is particularly advantageous to use the mouths 2, 4, 6 of the solenoid valve 1 respectively as the outlet “u1”, the outlet “u2”, and the inlet “i” of
It should be noted that, unlike the modes of connection described previously in which the mouth 2 functions as inlet mouth for the fluid, in this case the solenoid valve 1 induces lower head losses in the fluid current that traverses it and proceeds from the mouth 6 towards the mouths 2 and 4. This is represented schematically in the single-line diagram of
In a way similar to the solenoid valve 1, the solenoid valve 200 comprises a first mouth 202 for inlet of a working fluid, and a second mouth 204 and a third mouth 206 for outlet of said working fluid.
The solenoid valve 200 can assume the three operating positions P1, P2, P3 described previously, establishing the hydraulic connection between the mouths 202, 204 and 206 as described previously. This means that in the position P1 a passage of fluid from the first mouth 202 to the second mouth 204 and the third mouth 206 is enabled, in the position P2 a passage of fluid from the first mouth 202 to the third mouth 206 is enabled, whereas the passage of fluid from the mouth 202 to the mouth 204 is disabled; finally, in the position P3 the passage of fluid from the mouth 202 tow the mouths 204 and 206 is completely disabled.
An electromagnet 208 comprising a solenoid 208a can be controlled for causing a switching of the operating positions P1, P2, P3 of the solenoid valve 200, as will be described in detail hereinafter.
With reference to
Moreover provided on the jacket 210 are the mouths 2, 6, whilst, as will emerge more clearly from the ensuing description, the mouth 4 is provided by means of the valve element 212.
The jacket 210 is traversed by a through hole sharing the axis H′ and comprising a first stretch 216 having a diameter D216 and a second stretch 218 comprising a diameter D218, where the diameter D218 is greater than the diameter D216. At the interface between the two holes there is thus created a shoulder 219.
The mouths 202, 206 are provided by means of through holes with radial orientation made, respectively, in positions corresponding to the stretch 216 and to the stretch 218 and in communication therewith.
Moreover provided on an outer surface of the jacket 10 are a first annular groove 220, a second annular groove 222, and a third annular groove 224, each designed to receive a gasket of an O-ring type, set on opposite sides with respect to the radial holes that define the mouth 202 and the radial holes that define the mouth 206.
In particular, the mouth 206 is comprised between the grooves 222 and 224, while the mouth 2 is comprised between the grooves 220 and 222.
Preferably, the three annular grooves 220, 222, 224 are provided with the same seal diameter so as to minimize the unbalancing induced by the resultant of the forces of pressure acting on the outer surface of the jacket 210, which otherwise would be such as to jeopardize fixing of the jacket of the solenoid valve in the corresponding seat provided on a component or in an oleodynamic circuit where it is installed.
The first valve element 212 is substantially configured as a hollow tubular element comprising a stem 226—which is hollow and provided in which is a first cylindrical recess 227—, a neck 228, and a head 230, which has a conical contrast surface 232 and a collar 234. The neck 228 has a diameter smaller than that of the stem 226.
In addition, preferably provided in the collar 234 is a ring of axial holes 234A, while a second cylindrical recess 235 having diameter D235 is provided in the head 230.
The stem 226 of the valve element 212 is slidably mounted within the stretch 216 in such a way that the latter functions as guide element and as dynamic-seal element for the valve element 212 itself the dynamic seal is thus provided between the environment giving out into which is the first mouth 202 and the environment giving out into which is the second mouth 204. As has been described previously, this, however, gives rise to slight leakages of fluid through the gaps existing between the valve element 212 and the stretch 216, contributing to defining the hydraulic consumption of the solenoid valve 200.
The axial length of the stem 226 is chosen in such a way that it will extend along the stretch 216 as far as the holes that define the mouth 202, which thus occupy a position corresponding to the neck 228, which provides substantially an annular fluid chamber.
The head 230 is positioned practically entirely within the stretch 218, except for a small surface portion 232 that projects within the stretch 216 beyond the shoulder 219. In fact, the head 230 has a diameter greater than the diameter D216 but smaller than the diameter D218, so that provided in a position corresponding to the shoulder 19 is a first valve seat A1′ for the valve element 212, in particular for the conical surface 232.
In a variant of the solenoid valve of
Provided at a first end of the jacket 210 is a first threaded recess 236, engaged in which is a bushing 238 comprising a plurality of holes that define the mouth 204. Some of said holes have a radial orientation, whereas one of them is set sharing the axis H′.
The bushing 238 houses a spacer ring 240, fixed with respect to the first valve element 212, bearing upon which is a first elastic-return element 242 housed within the recess 227. The choice of the band width of the spacer ring 240 enables adjustment of the pre-load of the elastic element 242. Fixed at the opposite end of the jacket 210 is a second bushing 244 having a neck 246 fitted on which is the supporting bushing 209. The bushing 244 constitutes a portion of the magnetic core of the electromagnet 8 and offers a contrast surface to a spacer ring 248 that enables adjustment of the stroke of the first valve element 212 and functions as contrast surface for the latter against the action of the elastic element 242. In effect, also the bushing 238 functions as contrast for the elastic element 242 in so far as the elastic forces resulting from the deformation of the elastic element are discharged thereon.
The second valve element 214 is set practically entirely within the bushing 244. In particular, the latter comprises a central through hole 250 that gives out into a cylindrical recess 252, facing the valve element 212. The valve element 214 comprises a stem 254 that bears upon a head 256, both of which are coaxial to one another and are arranged sharing the axis H′, where the stem 254 is slidably mounted within the hole 250, whereas the head 256 is slidably mounted within the recess 252. It should be noted that, in the embodiment described herein, the stem 254 simply bears upon the head 256 since—as will emerge more clearly—during operation it exerts an action of thrust (and not of pull) on the head 256, but in other embodiments a rigid connection between the stem 254 and the head 256 may be envisaged. The stem 254 is, instead, rigidly connected to the anchor 264.
The head 256 further comprises a conical contrast surface 258 designed to co-operate with a second valve seat A2′ defined by the internal edge of the recess 235.
Set between the head 256 and the bottom of the recess 252 is a spacer ring 260, the band width of which determines the stroke of the second valve element 214. In addition, the spacer ring 260 offers a contrast surface to the valve element 214, in particular to the head 256, in regard to the return action developed by a second elastic-return element 262, bearing at one end on the head 256 and at another end on the bushing 238. The elastic element 262 is set sharing the axis H′ and inside the elastic element 242.
At the opposite end, the stem 254 is rigidly connected to an anchor 264 of the electromagnet 208, which bears upon a spring 266 used as positioning element. The maximum travel of the anchor 266 is designated by c′.
Preferably, the stroke of the anchor 266 is chosen so as to be equal to or greater than the maximum displacement allowed for the valve element 214.
Operation of the solenoid valve 200 is described in what follows. In the position illustrated in
In traversing the first gap, part of the fluid can come out through the holes that define the third mouth 206, whilst another part of the fluid traverses the holes 234a and proceeds towards the second gap.
In order to switch the solenoid valve 200 from the position P1 to the position P2, it is sufficient to govern the electromagnet 208 so as to impress on the second valve element 214 a first movement that brings the latter, in particular the conical surface 258, to bear upon the second valve seat A2′, thus disabling fluid communication between the first mouth 202 and the second mouth 204. In a way similar to the valve element 14, the valve element 214 is hydraulically balanced because the seal diameter, coinciding with the diameter D235 of the valve seat A2′, is substantially equal to the guide diameter, i.e., the diameter of the recess 252.
This means that the force of actuation that must be developed by the electromagnet must overcome substantially just the action of the elastic element 242, remaining practically indifferent to the actions of the pressurized fluid inside the solenoid valve 200.
The aforesaid first movement is imparted on the valve element 214 by means of circulation, in the solenoid 208a, of a current having an intensity I1 sufficient to displace the anchor 264 by just the distance necessary to bring the valve element to bear upon the seat A2′ and to overcome the resistance of just the elastic element 262.
In order to switch the solenoid valve 200 into the position P3 from the position P2, it is necessary to increase the intensity of the current circulating in the solenoid 208a up to a value I2, higher than the value I1, such as to impart on the valve element 214 a second movement overcoming the resistance of both of the elastic elements 242, 262. Said second movement results in the movement (in this case with an action of thrust and not of pull as in the case of the solenoid valve 1) of the first valve element 212 in conjunction with the second valve element 214 as far as the position in which the first valve element (thanks to the conical surface 232) comes to bear upon the seat A1′, thus disabling the hydraulic connection between the mouths 2 and 4.
Also the valve element 214 is hydraulically balanced since the seal diameter, i.e., the diameter of the valve seat A2′, is equal to the diameter of the recess 252 in which the head 256 is guided and slidably mounted.
During the second movement the second valve element 214 remains in contact against the first valve element 212 maintaining the hydraulic connection between the mouths 202 and 206 closed.
There remain moreover valid the considerations on the various alternatives for the connection of the mouths 202, 204, and 206 to environments with different levels of pressure.
The diagram at the top left in
The top right-hand part of
In greater detail, the cam is characterized by a profile 14 such as to move the plunger 17 of the pumping element 16 rigidly connected thereto, with a law h=h(∂), where h is the axial displacement of the plunger 17 and ∂ the angular rotation of the shaft on which the cam 11 is fixed. According to the angular velocity of the cam, the plunger will consequently move with a law h=(∂, t).
Irrespective of the angular velocity of the cam, at each turn of the camshaft the plunger 17 will displace always the same volume of oil Vstmax=hmax·areast, where hmax is the maximum stroke of the plunger imposed by the cam profile (the losses due to filling of the pumping chamber, leakages, or non-perfect coupling between cam and plunger will be neglected; the oil is assumed as being incompressible).
The maximum displacement of the intake valves depends upon the amount of the volume of oil pumped into the element 21: the case of full lift of both of the intake valves corresponds to the case where the entire volume Vstmax is used to move the aforesaid valves, which will consequently reach their maximum lift Smax. If the solenoid valve 24, intervening when the plunger is moving, sets a certain volume of oil in discharge, the stroke S of the intake valves will be less than Smax, and the difference Smax−S will be proportional to the volume by-passed by the solenoid valve 24: it is now understandable why in the left-hand diagram of
Also in the case of
The top right-hand part of
The operating modes illustrated in
The diagrams of
In the top part of
The left-hand section of
Once again with reference to the part at the top left of
Once again with reference to the bottom part of
The right-hand section of the top part of
Consequently, in the operating mode described in the right-hand sections of
The top left-hand part of
The right-hand part of
In the case of the present invention, the operating modes described with reference to
In the case of the diagrams on the left in
In the system according to the invention, the electronic control unit for control of the solenoid valves is programmed for executing one or more of the aforesaid modes for controlling the intake valves as a function of the operating conditions of the engine. According to a technique in itself known, the control unit receives the signals coming from means for detecting or determining one or more parameters indicating the operating conditions of the engine, amongst which, for example, the engine load (position of the accelerator), the engine r.p.m., the engine temperature, the temperature of the engine coolant, the temperature of the engine lubricating oil, the temperature of the fluid used in the system for variable actuation of the engine valves, the temperature of the actuators of the intake valves, or other parameters still.
A first important characteristic of the solenoid valve of
Moreover, the head 71a has channels 71b, 71c that enable communication of the pressure of the fluid that circulates in the valve on both sides of the head 71a so as to prevent any unbalancing.
A further preferred characteristic consists in providing a tubular insert 801 made of non-magnetic material (for example, AISI 400 steel) guided within which is the head 71a. In this way, the lines of magnetic flux are forced to follow the path indicated by F, passing around the insert 801 and rendering the magnetic force that attracts the head 71a towards the body 800 maximum.
Finally, as in the case of the solutions of
Of course, without prejudice to the principle of the invention, the details of construction and the embodiments may vary widely with respect to what is described purely by way of example herein, without thereby departing from the scope of the claims.
It should in particular be noted that the electrically actuated control valve, in all the embodiments, can be obtained with any other type of electric or electromagnetic actuator instead of the solenoid.
| Number | Date | Country | Kind |
|---|---|---|---|
| 13165631.6 | Apr 2013 | EP | regional |
