Three-way three-position control valve having a piezoelectric or magnetostrictive actuator, and fuel-injection system comprising the aforesaid valve

An electrically actuated control valve has three mouths and three operating positions, in which the three mouths includes a first mouth for inlet of a working fluid, and a second mouth and a third mouth for outlet of the working fluid. The three operating positions include a first operating position in which a passage of fluid from the first mouth to the second mouth and the third mouth is enabled, a second operating position in which a passage of fluid from the first mouth to only one of said second and third mouths is enabled, and a third operating position in which the passage of fluid from the first to the second mouth and the third mouth is disabled. The control valve includes an electric or electromagnetic actuator for controlling the passage of fluid from the first mouth to the second and third mouths providing the aforesaid three operating positions.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority from European patent application No. 13168666.9 filed on May 22, 2013, the entire disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present disclosure relates to an electrically or electromagnetically actuated control valve, in particular of the type comprising three mouths and three operating positions, wherein the three mouths comprise:

a first mouth for inlet of a fluid, for example fuel for an internal-combustion engine, and

a second mouth and a third mouth for outlet of the working fluid,

and wherein the three operating positions comprise:

a first operating position in which a passage of fluid from the first mouth to the second and third mouths is enabled,

a second operating position in which a passage of fluid from the first mouth to just one of the second and third mouths is enabled, and the passage of fluid between the second and third mouths is simultaneously disabled, and

a third operating position in which the passage of fluid from the first mouth to the second and third mouths is disabled,

wherein the solenoid valve further comprises an electromagnet that can be controlled for causing a switching of the operating position.

GENERAL TECHNICAL PROBLEM

Numerous examples of valves with three mouths and three operating positions are known whereby a fluid communication between an inlet mouth and two outlet mouths is selectively set up in order to direct alternatively the fluid towards one of the aforesaid outlet mouths or to both of them.

In the present disclosure, the term “operating position” is intended to indicate a condition of operation of the solenoid valve in which assigned to one or more moving elements of the solenoid valve itself is a position that results, amongst other things, in a particular mode of connection of the operating mouths of the valve.

In general, the environments giving out into which are the inlet and outlet mouths have pressure values different from one another, where the maximum value of pressure impinges on the inlet mouth, whereas impinging on the outlet mouths are two different levels of pressure, which are both lower than the pressure that impinges on the inlet mouth. Switching of the solenoid valve can be exploited to modulate the level of pressure in a load connected to the inlet mouth.

However, the fact that the valve comes to work facing environments at different pressures and sometimes with marked pressure swings between them and markedly variable even in each environment, renders the dynamic behaviour of the valve difficult to control in so far as the moving elements present inside it are perturbed significantly by the pressure of the environments giving out into which are the operating mouths, and consequently their actuation will prove to be markedly conditioned by the levels of operating pressure.

In greater detail, the different levels of pressure of the environments connected to the mouths of the solenoid valve determine the modulus of the resultant of the pressure forces acting on the moving elements of the valve itself, in particular in the axial direction.

The electrical or electromagnetic actuator of the valve must consequently be sized in such a way as to be able to actuate the moving elements even when the resultant of the pressure forces assumes a maximum value. This represents the main design constraint since, as the maximum force required by the electromagnet for actuation of the moving elements increases, both the costs and the overall dimensions of the actuator increase. Nevertheless, this is accompanied with an increase of the switching times between the different operating positions of the solenoid valve, which can become at this point so long as to jeopardize the possibility of use of the valve in contexts where a high speed of response is required.

In fact, in various oleodynamic applications, it is necessary for an electrically or electromagnetically actuated control valve to guarantee not only processing of a certain flow of fluid, but also a response to the commands in extremely short times: today increasingly numerous are the applications in which response times in the region of milliseconds are required as against operating pressures in the region of several hundreds of bar.

In the European patent application No. EP 11 190 645.9 of Nov. 24, 2011, still secret at the date of the present invention, the present applicant proposed a solenoid control valve having all the characteristics listed at the start of the present description and further characterized in that it comprises a first open/close element and a second open/close element, co-operating with a first contrast seat and a second contrast seat, respectively, wherein the first open/close element and the first contrast seat are provided for regulation of the passage of fluid from the first mouth to the third mouth, wherein the second open/close element and the second contrast seat are provided for controlling the passage of fluid from the first mouth to the second mouth, the solenoid valve being moreover characterized in that the electromagnet can be actuated for impressing on the second open/close element:

a first movement whereby the second open/close element is brought into contact with the second contrast seat disabling the passage of fluid from the first mouth to the second mouth and providing a passage from the first operating position to the second operating position, and

a second movement, subsequent to the first movement, whereby the second open/close element moves the first open/close element into contact against the first contrast seat, disabling the passage of fluid from the first mouth to the third mouth, hence enabling a passage from the second operating position to the third operating position, where, during the second movement, the second open/close element is in contact with the second contrast surface,

and wherein moreover the first and second open/close elements are coaxial to one another and hydraulically balanced.

The solenoid valve of said prior proposal is consequently able to operate facing three environments at pressures that differ from one another and with marked pressure swings between them, where actuation of moving elements of the valve will be substantially irrespective of the levels of pressure in the environments connected to the mouths of the valve itself. Moreover, the valve is able to process high flows of fluid and will be characterized by extremely contained switching times.

OBJECT OF THE INVENTION

The object of the present invention is to improve further the valve proposed in the prior European patent application No. EP 11 190 645.9, by providing a three-way and three-position electrically or electromagnetically actuated control valve that will be suited for being advantageously used in a wide range of applications and in which in particular it is also possible to vary the law of motion of the mobile elements of the valve as desired.

SUMMARY OF THE INVENTION

The object of the present invention is achieved by a valve having the characteristics forming the subject of the ensuing claims, which form an integral part of the technical teaching provided herein in relation to the invention.

DETAILED DESCRIPTION OF THE INVENTION

As indicated above, the embodiments ofFIGS. 1-7have already been illustrated in the European patent application No. EP 11 190 645.9 (still secret at the date of the present invention). The variants ofFIGS. 8, 9 and 10have already been illustrated in the European patent application No. EP 12 178 720.4 (still secret at the date of the present invention). The variant ofFIG. 11has been illustrated in the European patent application No. EP 13 165 631.6 (still secret at the date of the present invention).

The description of the aforesaid embodiments is useful for an understanding of the present invention, in so far as the valve according to the invention can be obtained with an identical structure, except for the fact that the electromagnetic actuator of the valves proposed previously is replaced by an actuator of the piezoelectric type or of magnetostrictive type, as will be illustrated in detail in what follows.

With reference toFIGS. 1A-1D, the reference number1designates as a whole a solenoid valve according to a preferred embodiment.

With reference to the schematic representation ofFIG. 1B, the solenoid valve1comprises a first mouth2for inlet of a working fluid, and a second mouth4and a third mouth6for outlet of said working fluid. In a preferred embodiment, the working fluid is oil, but the solenoid valve1can work in the same way with other liquids or with gaseous fluids, such as for example fuel, as described in the practical application schematically represented inFIGS. 12 and 13.

Once again with reference toFIG. 1B, the solenoid valve1comprises three operating positions designated by the references P1, P2, P3. An electromagnet8comprising a solenoid8acan be controlled for causing a switching of the operating positions P1, P2, P3 of the solenoid valve1, as will be described in detail hereinafter.

In the position P1 a passage of fluid from the first mouth2to the second mouth4and the third mouth6is enabled, in the position P2 a passage of fluid from the first mouth2to the third mouth6is enabled, whilst the passage of fluid from the mouth2to the mouth4is disabled (it should be noted that the opposite connection, i.e., the hydraulic connection from the first mouth2to the second mouth4without there being a hydraulic connection between the first mouth2and the third mouth6cannot be provided by the solenoid valve according to the invention), whereas finally in the position P3 the passage of fluid from the mouth2to the mouths4and6is completely disabled.

Once again with reference toFIG. 1B, the dashed segments connecting the mouths2,4and6indicate schematically the leakages of liquid through the dynamic seals provided between the moving components: said leakages (hydraulic consumption of the valve) come out of the mouth that is at a lower pressure.

With reference toFIG. 1A, the solenoid valve1comprises a plurality of components coaxial to one another and sharing a main axis H. In particular, the solenoid valve1comprises a jacket10, housed in which are a first open/close element12and a second open/close element14and the electromagnet8containing the solenoid8a. Moreover provided on the jacket10are the mouths2,6, whereas, as will emerge more clearly from the ensuing description, the mouth4is provided by means of the open/close element14itself.

The jacket10is traversed by a through hole sharing the axis H and comprising a first stretch16having a first diameter D16 and a second stretch18comprising a diameter D18, where the diameter D18 is greater than the diameter D16. At the interface between the two holes there is thus created a shoulder19.

The mouths2,6are provided by means of through holes with radial orientation provided, respectively, in a position corresponding to the stretch16and to the stretch18and in communication therewith.

Moreover provided on an outer surface of the jacket10are a first annular groove20, a second annular groove22, and a third annular groove24, each of which are designed to receive a gasket of an O-ring type, arranged on opposite sides with respect to the radial holes that define the mouth2and to the radial holes that define the mouth6.

In particular, the mouth6is comprised between the grooves20and22, whereas the mouth2is comprised between the grooves22and24.

Preferably, the three annular grooves20,22,24are provided with the same seal diameter so as to minimize the unbalancing induced by the resultant of the pressure forces acting on the outer surface of the jacket10, 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 element12is basically configured as a hollow tubular element comprising a stem26—which is hollow and provided in which is a first cylindrical recess27—, a neck28, and a head30, which has a conical contrast surface32and a collar34. The neck28has a diameter smaller than that of the stem26.

Moreover, preferably provided in the collar34is a ring of axial holes34A, whilst a second cylindrical recess35having a diameter D35 is provided in the head30.

The stem26of the valve element12is slidably mounted within the stretch16in such a way that the latter will function as guide element and as dynamic-sealing element for the valve element12itself: the dynamic seal is thus provided between the environment giving out into which is the first mouth2and the environment giving out into which is the second mouth4. This, however, gives rise to slight leakages of fluid through the gaps existing between the valve element12and the stretch16: 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 stem26, and the diametral clearance) and, not least, by the temperature of the fluid, which as is known determines the viscosity thereof.

The axial length of the stem26is chosen in such a way that it will extend along the stretch16as far as the holes that define the mouth2, which thus occupy a position corresponding to the neck28that provides substantially an annular fluid chamber.

The head30is positioned practically entirely within the stretch18, except for a small surface portion32that projects within the stretch16beyond the shoulder19. In fact, the head30has a diameter greater than the diameter D16 but smaller than the diameter D18, so that provided in a position corresponding to the shoulder19is a first contrast seat A1 for the valve element12, in particular for the conical surface32.

In a variant of the solenoid valve ofFIG. 1A, in a region corresponding to the shoulder19an annular chamfer is made that increases the area of contact with the conical surface32at the same time reducing the specific pressure developed at the contact therewith, hence minimizing the risks of damage to the surface32. It in any case important for the seal diameter between the valve element12and the shoulder19to be substantially the same as the diameter D16.

Provided at a first end of the jacket10is a first threaded recess36engaged in which is a bushing38having a through guide hole40sharing the axis H. The diameter of the hole40is equal to the diameter D35 for reasons that will emerge more clearly from the ensuing description.

The bushing38comprises a castellated end portion42, which functions as contrast element for a spacer ring44.

The spacer ring44offers in turn a contrast surface to the head30of the valve element12, in particular to the collar34. In addition, the choice of the thickness of the spacer ring44enables adjustment of the stroke of the valve element12and hence of the area of passage between the mouth2and the mouth6.

Provided at a second end of the jacket10, opposite to the first end, is a second threaded recess46, engaged in which is a ringnut48. The ringnut48functions as contrast for a ring50, which in turn offers a contrast surface for a first elastic-return element52housed in the cylindrical recess27.

The ringnut48is screwed within the threaded recess46until it comes to bear upon the shoulder between the latter and the jacket10: in this way, the adjustment of the pre-load applied to the elastic-return element52is determined by the thickness (i.e., by the band width) of the ring50.

The second valve element14is set inside the stem26and is slidable and coaxial with respect to the first valve element12.

The valve element14comprises:

a terminal shank54at a first end thereof,

a stem56, and

a head58, set at a second end thereof, having a conical contrast surface60and a cup-shaped end portion64, in which the head58and the shank54are connected by the stem56.

It should moreover be noted that the geometry of the castellated end42contributes to providing, by co-operating with the holes34a, a passageway for the flow of fluid that is sent on through the section of passage defined between the conical surface60and the contrast seat A2 towards the second mouth4.

The cup-shaped end portion64has an outer diameter D64 equal to the diameter of the hole40and comprises a recess that constitutes the outlet of a central blind hole66provided in the stem56. The hole66intersects a first set of radial holes and a second set of radial holes, designated, respectively, by the reference numbers68,70. In this embodiment the two sets each comprise four radial holes68,70set at the same angular distance apart.

The position of the aforesaid sets of radial holes is such that the holes68are located substantially in a position corresponding to the cylindrical recess35, whilst the holes70are located substantially in a position corresponding to the cylindrical recess27.

Coupling between the cup-shaped end portion64(having a diameter D64) and the hole40(having a diameter substantially equal to the diameter D64) provides a dynamic seal between the valve element14and the bushing38: this seal separates the environment giving out into which is the third mouth6from the environment giving out into which is the second mouth4. In a way similar to what has been described for the dynamic seal provided between the mouths2and6, the hydraulic consumption depends not only upon the temperature and the type of fluid, but also upon the difference in pressure existing between the environments giving out into which are the mouths2and4, upon the diametral clearance, upon the length of the coupling between the cup-shaped end portion64and the bushing38, and upon other parameters such as the geometrical tolerances and the surface finish of the various components. The hydraulic consumptions of the two dynamic seals add up and define the total hydraulic consumption of the solenoid valve1.

Fitted on the terminal shank54is an anchor71provided for co-operating with the solenoid8, which has a reference position defined by a half-ring72housed in an annular groove on the shank54; advantageously, the anchor71can be provided as a disk comprising notches with the dual function of lightening the overall weight thereof and of reducing onset of parasitic currents.

Provided at a second end of the jacket10, opposite to the one where the bushing38is located, is a collar73inserted within which is a cup74, blocked on the collar73by means of a threaded ringnut76that engages an outer threading made on the collar73.

Set in the cup74is a toroid78housing the solenoid8, which is wound on a reel80housed in an annular recess of the toroid78itself. The toroid78is traversed by a through hole79sharing the axis H and is surmounted by a plug82bearing thereon and blocked on the cup74by means of a cap84bearing a seat for an electrical connector85and electrical connections (not visible) that connect the electrical connector to the solenoid8.

The toroid78comprises a first base surface, giving out on which is the annular recess79, which offers a contrast to the anchor71, determining the maximum axial travel thereof (i.e., the stroke), designated by c. The maximum axial travel of the anchor71is hence determined by subtracting the thickness of the anchor71itself (i.e., the band width thereof) from the distance between the first base surface of the toroid78and the ringnut48. In order to adjust the stroke c of the anchor71a first adjustment shim R1 is provided, preferably provided as a ring having a calibrated thickness; alternatively, it is possible to replace the anchor71with an anchor of a different thickness. The stroke c of the anchor71is hence constituted by three components:a first component cv, which represents the loadless stroke, which terminates when the top surface of the anchor engages the half-ring72;a second component Δh14, which corresponds to the displacement of just the second valve element14; anda third component Δ12, which corresponds to the simultaneous displacement of both of the valve elements.

It should moreover be noted that the pressure of the fluid in the environment giving out into which is the mouth4exerts its own action also on the anchor71, on the toroid78, on the elastic element90, on the ringnut48, and on the shank54of the valve element14this entailing adoption, for protecting the electromagnet8, of static-sealing elements.

The plug82comprises a through hole84sharing the axis H and comprising a first stretch and a second stretch with widened diameter86,88at opposite ends thereof. It should be noted that the through hole84enables, by means of introduction of a measuring instrument, verification of the displacements of the valve element14during assemblage of the solenoid valve1.

The stretch86communicates with the hole79and defines therewith a single cavity set inside which is a second elastic-return element90, co-operating with the second valve element14. The elastic-return element90bears at one end upon a shoulder made on the shank54and at another end upon a second adjustment shim R2 bearing upon a shoulder created by the widening of diameter of the stretch86. The adjustment shim R2 has the function of adjustment of the pre-load of the elastic element90.

Forced in the stretch88is a ball92that isolates the hole84with 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 valve1is described in what follows.

In a preferred application, the solenoid valve1is inserted in an oleodynamic circuit in such a way that each of the mouths2,4,6is hydraulically connected to a corresponding environment, each having its own level of pressure—respectively p2, p4, p6—and being such that p2>p6>p4.

FIG. 1Cshows a single-line diagram that illustrates the solenoid valve1in a generic operating position: it should be noted how arranged between the first mouth2and the second mouth4are two flow restrictors with variable cross section A1 and A2, which represent schematically the passage ports provided by the first and second valve elements.

In the node between the mouths2,4and6, designated by6′, the value of the pressure is equal to that at the third mouth6but for the pressure drops along the branch6-6′. Set between the mouth4and the node6′ is the flow restrictor A2, which represents schematically the action of the second valve element14. Likewise, set between the mouth2and the node6′ is the flow restrictor with variable cross section A1, which represents schematically the action of the first valve element12.

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 elements12,14, 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.

FIG. 1Aillustrates the first operating position P1 of the solenoid valve1, in which the first and second valve elements12,14are in the resting position. This means that no current traverses the solenoid8and no action is exerted on the anchor71, so that the valve elements12,14are kept in position by the respective elastic-return elements52,90.

In particular, the first valve element12is kept bearing upon the ring44by the first elastic-return element52, whilst the second valve element14is kept in position thanks to the anchor71: the second elastic-return element90develops its own action on the shank54, and said action is transmitted to the anchor71by the half ring72, bringing the anchor71to bear upon the ringnut48.

In this way, with reference toFIG. 1A(without neglecting the corresponding schematic representation ofFIGS. 1B and 1C), the passage of fluid from the inlet mouth2to the first outlet mouth4and to the second outlet mouth6is enabled. In fact, the fluid entering the radial holes that define the mouth2invades the annular volume around the neck28of the first valve element12and traverses a first gap existing between the conical surface32and the first valve seat A1.

In said annular volume there is set up, on account of the head losses due to traversal of the radial holes that define the mouth2, a pressure p6′>p4. In this way, the fluid proceeds spontaneously along its path towards the mouth4traversing the second gap set between the conical surface60and the second valve seat A2.

In this way, the fluid can invade the cylindrical recess35and pass through the holes68, invading the cup-shaped end portion64and coming out through the hole40; it should be noted that the pressure that is set up in the volume of the cylindrical recess35is slightly higher than the value p4by virtue of the head losses due to traversal of the holes68. Finally, it should be noted that the valve element12itself and the guide bushing38define the second mouth4.

The diagrams ofFIGS. 4A, 4B and 4Crepresent the time plots of various operating quantities of the solenoid valve1, observed in particular during a time interval in which two events of switching of the operating position of the solenoid valve1occur.

The diagram ofFIG. 4Aillustrates the time plot of a current of energization of the solenoid8, the diagram ofFIG. 4Billustrates the time plot of the area of passage for the fluid offered by the sections of passage created by the valve elements12,14co-operating with the respective valve seats A1, A2, and the diagram ofFIG. 4Cillustrates the plot of the (partial) absolute displacements h12, h14of the valve elements12,14, having assumed as reference (zero displacement) the resting position of each of them. The reference hTOTindicates the overall displacement of the valve element14, equal to the sum of the displacement h12and of the partial displacement h14(the anchor will, instead, shift by hTOT+cv).

Corresponding to the operating position P1 illustrated inFIG. 1is a current of energization of the solenoid8having intensity L with zero value (FIG. 4A).

At the same time, with reference toFIG. 4B, in the operating position P1 the second valve element14defines with the valve seat A2 a gap having area of passage S2, whereas the first valve element12defines with the valve seat A1 a gap having area of passage S1, which in this embodiment is smaller than the area S2. The function of dividing the total stroke htotinto the two fractions Δh12and Δh14is entrusted to the shim44.

In addition, with reference toFIG. 4C, in the operating position P1 the displacements of the valve elements12,14with respect to the respective resting positions are zero.

With reference toFIGS. 2A, 2B, the enlargements illustrate in detail the configuration of the valve elements in the operating position P2.

The operating position P2 is activated following upon a first event of switching of the solenoid valve1that occurs at an instant t1in which an energization current of intensity I1is supplied to the solenoid8.

The intensity I1is chosen in such a way that the action of attraction exerted by the solenoid8on the anchor71will be such as to overcome the force developed by the elastic-return element90alone. In other words, the solenoid8is actuated for impressing on the second valve element a first movement Δh14in an axial direction H having a sense indicated by C inFIG. 2whereby the second valve element, in particular the conical surface60, is brought into contact with the second valve seat A2 disabling the passage of fluid from the first mouth2to the second mouth4, and hence providing a transition from the first operating position P1 to the second operating position P2.

With reference to the diagrams ofFIG. 4, the above is equivalent to a substantial annulment of the area of passage S2 and to a displacement Δh14of the valve element14in an axial direction and with sense C. The anchor71is detached from the ringnut48and substantially occupies an intermediate position between this and the toroid78.

It should be noted that the movement of the valve element14stops in contact with the valve seat A2 since, in order to proceed, it would be necessary to overcome also the action of the elastic element52, which is impossible with the energization current of intensity I1that traverses the solenoid8.

The valve element14(as likewise the valve element12, see the ensuing description) is moreover hydraulically balanced; consequently, it is substantially insensitive to the values of pressure with which the solenoid valve1operates.

By “hydraulically balanced” referred to each of the valve elements12,14is meant 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 element14is the diameter D64, which is identical to the diameter D35 of the cylindrical recess35, which determines the seal surface of the valve element14in a region corresponding to the valve seat A2 provided on the valve element12.

The same applies to the valve element12, where the dynamic-seal diameter is the diameter D16, which is equal to the diameter of the stem26(but for the necessary radial plays) and coincides with the diameter of the valve seat A1, provided on the jacket10, which determines the surface of influence of the valve element12.

In a particular variant, it is possible to design the solenoid valve1in such a way that the diameters D64 and D35 associated to the valve element14are substantially equal to the diameter D16 and to the diameter of the seat A1 of the valve element12.

The configuration of the valve elements12,14in the third operating position P3 is illustrated inFIGS. 3A-3B. With reference moreover toFIGS. 4A to 4C, at an instant t2, a command is issued for an increase in the energization current that traverses the solenoid8, which brings the intensity thereof from the value I1(kept throughout the time that elapses between t1and t2) to a value I2>I1.

This causes an increase of the force of attraction exerted by the solenoid8on the anchor71, whereby impressed on the second valve element14is a second movement, subsequent to the first movement, thanks to which the second valve element14draws the first valve element12into contact against the first contrast surface A1, hence disabling the passage of fluid from the mouth2to the mouth6. In fact, there is no longer any gap through which the fluid that enters the mouth2can flow towards the mouth6. The diagram ofFIG. 4Bis a graphic illustration of the annulment of the section of passage S1 at the instant t2.

It should be noted that—on account of what has been described previously—during the aforesaid second movement, in which the valve element12is guided by the bushing38, the second valve element14remains in contact with the first valve element12maintaining the passage of fluid from the mouth2to the mouth4disabled. The corresponding displacement of the valve element14, which is the same as the one that the valve element12undergoes (both of them in the sense C and in the axial direction), is designated by Δh12inFIG. 4C.

There is thus obtained a transition from the second operating position P2 to the third operating position P3, in which, in effect, the environments connected to each of the mouths of the solenoid valve1are 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 mouth4. In the design stage, the dynamic seals are conceived in such a way that any leakage of fluid is in any case negligible with respect to the one 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 solenoid8is necessary to overcome the combined action of the elastic-return elements90and52, which tend to bring the respective valve elements14,12back into the resting position.

It should be noted that also in this circumstance, given that the valve element12is hydraulically balanced, the action of attraction developed on the anchor71must overcome only the return force of the springs90,52, in so far as the dynamic equilibrium of the valve elements12,14is indifferent to the action of the pressure of the fluid, given that said valve elements are hydraulically balanced.

It is in this way possible to choose a solenoid8of contained dimensions and it is thus 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, with a pressure p2, for example, in the region of 400 bar. Other typical pressures for the environment connected to the mouth for inlet of the fluid are 200 and 300 bar (according to the type of system).

With reference toFIG. 5, an application of the solenoid valve1to an anti-lock braking system (ABS) of a motor vehicle is illustrated by way purely of example.

With reference toFIG. 5A, the solenoid valve1, which in the embodiment described is of the so-called “cartridge” type, is inserted into a body100—which functions as connection element—communicating with a first environment, a second environment, and a third environment designated by the references VC, V1, V2. The environments VC, V1, V2 are, respectively, at a level of pressure pMAX(or control pressure), PINT(intermediate pressure), and pSC(exhaust pressure), lower than the intermediate pressure PINT.

It should moreover be noted that the solenoid valve1is inserted in the body100in a seat102in 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 housed, respectively, in the annular grooves20,22and24and designated, respectively, by the reference numbers104,106,108.

In particular, the O-ring104guarantees an action of seal in regard to the body across the environments V2 V1, whilst the O-ring106guarantees an action of seal in regard to the body across the environments V1 and VC. The last O-ring, designated by the reference number108, exerts an action of seal that prevents any possible leakage of fluid on the outside of the body.

With reference toFIG. 5B, in the specific application considered, the environment VC at pressure pMAXis a control volume of a braking system set on a hydraulic power line that hydraulically connects a braking-liquid pump110to a cylinder112of a brake calliper114, here represented as being of a floating type but the same applies to callipers of a fixed type.

The calliper114exerts its own action on a disk116, connected in rotation to the wheel of a vehicle.

The control volume VC is hydraulically connected to the inlet mouth2of the solenoid valve1, whilst connected to the second and third mouths4,6of the solenoid valve1are the environments V2 and V1, respectively, where the environment V1 is functionally a further control volume kept at a level of pressure lower than the pressure pMAXthat obtains in the control volume VC during braking, whilst the environment V2 coincides with an exhaust environment, in which the relative pressure is substantially zero.

In normal operating conditions of the vehicle, in which the ABS does not intervene, the control volume VC is pressurized—during a braking action—by the action of the user, who via the hydraulic pump110sends pressurized fluid to the cylinder112causing gripping of the calliper114on the disk116. The solenoid valve1is kept in the operating position P3, which is equivalent to a completely traditional operation of the braking system of the vehicle.

The pressure that is set up in the control volume VC is equal to the pressure of the fluid in the cylinder112during braking, whereas the value of intermediate pressure pintis modulated by means of an electronic control unit operatively connected to a regulation device (neither of which are illustrated inFIG. 5B), as a function of the boundary conditions detected by sensors in themselves known, such as, for example, icy, wet, or damp, road surface, the type of asphalt or else again the temperature of the disks116.

In the case where the sensors of the ABS, in themselves known, detect locking of the wheels of the vehicle during braking, the system intervenes and performs its own function by exploiting the switching of the operating positions of the solenoid valve1to modulate the braking action.

In particular, the solenoid valve1is switched into the position P1 in the case where a control unit of the ABS determines the need for a practically total release of the braking action on the disk116or when the braking action impressed by the user ceases.

In this case, in fact, the control volume VC, and consequently the cylinder112, would be hydraulically connected to the environment V2, thus setting it in the discharging condition.

In the case where the aforesaid control unit of the ABS determines that there is the need for a partial restoring (or, if there has not been a total release of the braking action, it determines that there is the need for a partial release) of the braking action on the disk116, the electromagnet8is controlled so as to switch the solenoid valve into the operating position P2, in which the control volume VC is hydraulically connected to the volume at intermediate pressure V1 and is isolated from the exhaust environment V2.

In this case, the control volume VC is depressurized, causing a partial release of the action on the disk116. Finally, should the electronic control unit of the ABS determine that it is necessary to restore the maximum braking action on the disk116, the solenoid8is governed so as to switch the solenoid valve again into the position P3.

Of course, it is possible to exploit the potentialities of modern electronic control units so as to impart high-frequency signals to the solenoid valve1obtaining switchings that are very fast, i.e., with frequencies typical of ABSs.

Moreover, the application of the solenoid valve1to a braking system entails a second advantage: in fact, for what has been described previously, it is not possible to make a direct switching from the operating position P3 to the operating position P1, which imposes on the solenoid valve to assume, albeit for an extremely short time interval, the operating position P2. This results in a more gradual deceleration during release of the brake.

It should be noted that in said perspective, it is extremely important for the valve elements12and14to be hydraulically balanced, in so far as, if it were not so, there would be the need for forces of actuation that would be too high to guarantee the required dynamics, which in turn would entail an oversizing of the components (primarily, the solenoid8) 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.

For example, the seals between the valve elements12,14and the respective valve seats A1, A2 can be provided by means of the contact of two conical surfaces, where the second conical surface replaces the sharp edges of the shoulders on which the valve seats are provided.

Moreover, in the case where the working fluid is of a gaseous type or in the case where the application for which the solenoid valve is designed does not admit of any hydraulic consumption (or, likewise, in the case where a total lack of hydraulic communication between the various environments giving out into which are the various mouths of the solenoid valve is required), 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, in themselves known and specific for use with gaseous fluids.

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.

FIG. 6illustrates, by way of example, an embodiment of the solenoid valve1that envisages use of dynamic-seal rings designated by the reference number130.

In the example of application described here, there is assumed the hydraulic connection of the second mouth4with an environment with minimum pressure (typically an exhaust environment) and the hydraulic connection of the third mouth6with an environment with a pressure intermediate between the value of the pressure p2and the value of the pressure P4.

If the connection of the mouths4and6to the respective environments is reversed, i.e., if the mouth4is connected to an environment at intermediate pressure and the mouth6to an environment at minimum pressure, the behaviour of the solenoid valve1varies.

In particular, in the operating position P1 of the solenoid valve, as previously defined, the environment connected to the first mouth2and the environment connected to the second mouth4will be set in the discharging condition towards the environment connected to the third mouth6and the leakages of fluid will have a direction such as to flow from the environment connected to the mouth4to the environment connected to the mouth6.

By switching the solenoid valve1from the operating position P1 to the operating position P2, the environment connected to the second mouth4is excluded, while there remains only the hydraulic connection of the inlet environment connected to the first mouth2with the mouth6, i.e., with the exhaust: as compared to the previous operating position, the flowrate measured at outlet from the mouth6will be lower than in the previous case, since the contribution of the flow from the mouth4to the mouth6ceases.

Finally, by switching the solenoid valve1from the operating position P2 to the operating position P3, also the hydraulic connection between the environment connected to the mouth2and the environment connected to the mouth6will be disabled.

The inventors have moreover noted that it is particularly advantageous to connect the mouths2,4,6of the solenoid valve1between environments with pressure levels that are different again from the cases described. In particular, it is possible to connect the mouth6to an environment with pressure p6with p6>p4and p6>p2, irrespective of the values of the pressures p4and p2, in the environments connected, respectively, to the mouths4and2(this means that we may indifferently have p4>p2or p2>p4). It should be noted that in this situation it is the mouth6that performs the function of inlet mouth for the fluid, whereas the mouths2and4function as outlet mouths for the fluid. Consequently, according to the convention so far adopted in this case the mouth6is the first mouth and the mouths4,2are the second and third mouths, respectively. At times the correspondence will be explicitly indicated in brackets in the text, where necessary.

With this mode of connection, in the operating position P1 there hence will be a flow of fluid both from the mouth6to the mouth4and from the mouth6to the mouth2; consequently, both of the environments at pressure p4and at pressure p2will be supplied.

By switching the solenoid valve1from the operating position P1 to the operating position P2, connection of the environment at pressure p4to the other two environments will be disabled and consequently there will be only a flow of fluid from the mouth6to the mouth2. Finally, by switching the solenoid valve from the operating position P2 to the operating position P3, also the hydraulic connection between the environment at pressure p6and the environment at pressure p2(i.e., between the mouth6and the mouth2) will be disabled.

It should moreover be noted that, unlike the mode of connection previously described in which the mouth2functions as inlet mouth for the fluid, in this case the solenoid valve1induces lower head losses in the current fluid that traverses it and proceeds from the mouth6to the mouths2and4. This is represented schematically in the single-line diagram ofFIG. 1D: by reversing the functions of the mouths2and6, the gaps defined by the valve elements12,14are arranged in parallel with respect to one another, i.e., the fluid that from the inlet mouth6(first mouth) proceeds towards the outlet mouths2(third mouth) and4(second mouth) must traverse a single gap, in particular the gap between the valve element14and the valve seat A2 for the fluid that from the mouth6proceeds towards the mouth4, and the gap between the valve element12and the valve seat A1 for the fluid that from the mouth6proceeds towards the mouth2(the node6′ hence has substantially the same pressure as the one that impinges on the mouth6). In the case of the connection where the mouth2functions as inlet mouth for the fluid (FIG. 1C), the fluid that flows towards the mouth4must traverse both of the gaps, with consequent higher head losses.

FIG. 7illustrates a second embodiment of a solenoid valve according to the invention, which is designated by the reference number200.

In a way similar to the solenoid valve1, the solenoid valve200comprises a first mouth202for inlet of a working fluid, and a second mouth204and a third mouth206for outlet of said working fluid.

Once again with reference toFIG. 1B, the solenoid valve200can assume the three operating positions P1, P2, P3 previously described, establishing the hydraulic connection between the mouths202,204and206as has been described previously. This means that in the position P1 a passage of fluid from the first mouth202to the second mouth204and the third mouth206is enabled, in the position P2 a passage of fluid from the first mouth202to the third mouth206is enabled, whilst the passage of fluid from the mouth202to the mouth204is disabled; finally, in the position P3 the passage of fluid from the mouth202to the mouths204and206is completely disabled.

An electromagnet208comprising a solenoid208acan be driven for causing a switching of the operating positions P1, P2, P3 of the solenoid valve200, as will be described in detail hereinafter.

With reference toFIG. 7, the solenoid valve200comprises a plurality of components coaxial with one another and sharing a main axis H′. In particular, the solenoid valve200comprises a jacket210housed in which are a first valve element212and a second valve element214and fixed on which is the solenoid208a, carried by a supporting bushing209.

Moreover provided on the jacket210are the mouths2,6, whilst, as will emerge more clearly from the ensuing description, the mouth4is provided by means of the valve element212.

The jacket210is traversed by a through hole sharing the axis H′ and comprising a first stretch216having a diameter D216 and a second stretch218comprising a diameter D218, where the diameter D218 is greater than the diameter D216. In an area corresponding to the interface between the two holes a shoulder219is thus created.

The mouths202,206are provided by means of through holes with radial orientation made, respectively, in a position corresponding to the stretch216and to the stretch218and in communication therewith.

Moreover provided on an outer surface of the jacket10are a first annular groove220, a second annular groove222, and a third annular groove224, each designed to receive a gasket of the O-ring type, arranged on opposite sides with respect to the radial holes that define the mouth202and the radial holes that define the mouth206.

In particular, the mouth206is comprised between the grooves222and224whilst the mouth2is comprised between the grooves220and222.

Preferably, the three annular grooves220,222,224are 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 jacket210, 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 element212is basically configured as a hollow tubular element comprising a stem226—which is hollow and provided in which is a first cylindrical recess227—, a neck228, and a head230, which has a conical contrast surface232and a collar234. The neck228has a diameter smaller than the stem226.

Moreover, preferably provided in the collar234is a ring of axial holes234A, whilst a second cylindrical recess235having a diameter D235 is provided in the head230.

The stem226of the valve element212is slidably mounted within the stretch216, in such a way that the latter will function as guide element and as dynamic-sealing element for the valve element212itself: the dynamic seal is thus provided between the environment giving out into which is the first mouth202and the environment giving out into which is the second mouth4. As has been described previously, this, however, gives rise to slight leakages of fluid through the gaps existing between the valve element212and the stretch216, contributing to defining the hydraulic consumption of the solenoid valve200.

The axial length of the stem226is chosen in such a way that it will extend along the stretch216as far as the holes that define the mouth202, which are thus in a position corresponding to the neck228that provides substantially an annular fluid chamber.

The head230is positioned practically entirely within the stretch218, except for a small surface portion232that projects inside the stretch216beyond the shoulder219. In fact, the head230has a diameter greater than the diameter D216 but smaller than the diameter D218 so that provided in a position corresponding to the shoulder19is a first valve seat A1′ for the valve element212, in particular for the conical surface232.

In a variant of the solenoid valve ofFIG. 7, made in a position corresponding to the shoulder219is an annular chamfer that increases the area of contact with the conical surface232at the same time reducing the specific pressure developed at the contact therewith, hence minimizing the risks of damage to the surface232. It is in any case important for the seal diameter between the valve element212and the shoulder219to be substantially equal to the diameter D216.

Provided at a first end of the jacket210is a first threaded recess236engaged in which is a bushing238comprising a plurality of holes that define the mouth204. Some of said holes have a radial orientation, whilst one of them is set sharing the axis H′.

The bushing238houses a spacer ring240, fixed with respect to the first valve element212, bearing upon which is a first elastic-return element242housed within the recess227. The choice of the band width of the spacer ring240enables adjustment of the pre-load of the elastic element242. Fixed at the opposite end of the jacket210is a second bushing244having a neck246fitted on which is the supporting bushing209. The bushing244constitutes a portion of the magnetic core of the electromagnet8and offers a contrast surface to a spacer ring248that enables adjustment of the stroke of the first valve element212and functions as contrast surface for the latter against the action of the elastic element242. In effect, also the bushing238functions as contrast for the elastic element242in so far as the elastic forces resulting from the deformation of the elastic element are discharged thereon.

The second valve element214is set practically entirely within the bushing244. In particular, the latter comprises a central through hole250that gives out into a cylindrical recess252, facing the valve element212. The valve element214comprises a stem254that bears upon a head256, both of which are coaxial to one another and are set sharing the axis H′, where the stem254is slidably mounted within the hole250, whilst the head256is slidably mounted within the recess252. It should be noted that in the embodiment described here the stem254simply bears upon the head256since—as will emerge more clearly—during operation it exerts an action of thrust (and not of pull) on the head256, but in other embodiments a rigid connection between the stem254and the head256is envisaged. The stem254is, instead, rigidly connected to the anchor264.

The head256further comprises a conical contrast surface258designed to co-operate with a second valve seat A2′ defined by the internal edge of the recess235.

Set between the head256and the bottom of the recess252is a spacer ring260, the band width of which determines the stroke of the second valve element214. In addition, the spacer ring260offers a contrast surface to the valve element214, in particular to the head256, in regard to the return action developed by a second elastic-return element262, bearing at one end upon the head256and at another end upon the bushing238. The elastic element262is set sharing the axis H′ and inside the elastic element242.

At the opposite end, the stem254is rigidly connected to an anchor264of the electromagnet208that bears upon a spring266used as positioning element. The maximum travel of the anchor266is designated by c′.

Preferably, the stroke of the anchor266is chosen so as to be equal to or greater than the maximum displacement allowed for the valve element214.

Operation of the solenoid valve200is described in what follows. In the position illustrated inFIG. 7, corresponding to the position P1, the fluid that enters through the holes that define the mouth202traverses a first gap existing between the surface232and the seat A1′ and a second gap existing between the seat A2′ and the surface258, flowing within the first valve element212and coming out from the bushing238through the mouth204. In fact, in the position P1 the valve elements212,214are kept detached from the respective valve seats and in contact, respectively, with the bushing244and the spacer ring260, thanks to the action of the respective elastic elements242,262.

In traversing the first gap, part of the fluid can come out through the holes that define the third mouth206, whereas another part of the fluid traverses the holes234aand proceeds towards the second gap.

To switch the solenoid valve200from the position P1 to the position P2, it is sufficient to control the electromagnet208so that it impresses on the second valve element214a first movement that brings the latter, in particular the conical surface258, to bear upon the second valve seat A2′, disabling fluid communication between the first mouth202and the second mouth204. In a way similar to the valve element14, the valve element214is 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 recess252.

This means that the force of actuation that must be developed by the electromagnet must overcome substantially just the action of the elastic element242, remaining practically indifferent to the actions of the pressurized fluid inside the solenoid valve200.

The aforesaid first movement is imparted to the valve element214by means of circulation, in the solenoid208a, of a current having an intensity I1sufficient to displace the anchor264of just the distance necessary to bring the valve element to bear upon the seat A2′ and to overcome the resistance of just the elastic element262.

To switch the solenoid valve200into the position P3 from the position P2, it is necessary to increase the intensity of the current circulating in the solenoid208aup to a value I2, higher than the value I1, such as to impart on the valve element214a second movement overcoming the resistance of both of the elastic elements242,262. 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 valve1) of the first valve element212in conjunction with the second valve element214up to the position in which the first valve element (thanks to the conical surface232) comes to bear upon the seat A1′, disabling the hydraulic connection between the mouths2and4.

Also the valve element214is hydraulically balanced since the seal diameter, i.e., the diameter of the valve seat A2′, is equal to the diameter of the recess252in which the head256is guided and slidably mounted.

During the second movement, the second valve element214remains in contact against the first valve element212keeping the hydraulic connection between the mouths202and206closed.

There moreover apply the considerations on the various alternatives for connection of the mouths202,204, and206to environments with different levels of pressure, and the considerations set forth for the solenoid valve1apply in the case where also the solenoid valve200is used in an ABS. Nevertheless, it is also possible to use dynamic-seal rings in the case where the solenoid valve200is used with gaseous fluids.

FIGS. 8 and 9illustrate further embodiments of the solenoid valve, conceptually similar to that ofFIG. 1A. In these figures, the parts corresponding to those ofFIG. 1Aare designated by the same reference numbers. As may be seen, the solenoid valves illustrated inFIGS. 8 and 9differ in some constructional details from that ofFIG. 1A, for example for the different arrangements of the openings68associated to the valve element14.

FIG. 10illustrates a further embodiment, which likewise entails a different arrangement of the openings68made in the valve element14and a different arrangement of the electromagnet, which in this case envisages an anchor71constituted by the top part of the body of the valve element14that penetrates axially within the central opening of the solenoid8a. A further difference of the valve ofFIG. 10lies in the fact that, in this case, the spring52that recalls the valve element12to the resting position is set on the outside of the above element instead of on its inside.

FIG. 11shows a further variant, which is characterized by a series of additional arrangements (which, on the other hand, may be adopted also in the other embodiments illustrated above). InFIG. 1the parts common to those illustrated inFIGS. 1A, 5A, 6 and 7are designated by the same reference numbers.

A first important characteristic of the solenoid valve ofFIG. 11lies in the fact that both of the springs86,52that recall the two valve elements14and12are set outside of the solenoid8a. Consequently, within the solenoid8athere may be provided a solid fixed body800, which enables a greater magnetic flux to be obtained that attracts, towards the aforesaid body800, a head71aof an anchor, the stem71of which carries at the bottom end the valve body14.

Moreover, the head71ahas channels71b,71cthat enable communication of the pressure of the fluid that circulates in the valve on both sides of the head71aso as to prevent any unbalancing.

A further preferred characteristic consists in providing a tubular insert801made of non-magnetic material (for example, AISI 400 steel) within which the head71ais guided. In this way, the lines of magnetic flux are forced to follow the path designated by F, passing around the insert801and rendering the magnetic force that attracts the head71ato the body800maximum.

Finally, in a way similar to the solutions ofFIGS. 8,10, an elastic ring (circlip)900is provided, which withholds the set of the two valve elements within the body10.

FIG. 12illustrates a schematic cross-sectional view of a first embodiment of the control valve according to the present invention. The valve ofFIG. 12differs from the valves illustrated inFIGS. 1-11in that it is provided with an electric actuator8that is not a solenoid actuator, but rather a piezoelectric actuator, comprising a stack of piezoelectric elements PZ set on top of one another. The opposite ends of each piezoelectric element PZ are connected to terminals501,502, in parallel to the opposite ends of the other piezoelectric elements. Across the terminals501,502a voltage may be applied via electrical-supply means (not illustrated), which preferably are of a type that is such as to enable adjustment of the applied voltage.

Each of the piezoelectric elements PZ is typically constituted by a piezoelectric crystal. Piezoelectric crystals have been studied and used for some time. By applying a voltage to the opposite ends of a piezoelectric crystal there is obtained lengthening of the crystal that is proportional to the voltage applied. Normally, the linear lengthening of an individual crystal is in the region of a few microns. Consequently, by providing a stack of piezoelectric crystals set on top of one another and applying a voltage at the ends of each piezoelectric element, it is possible to obtain an overall displacement for example in the region of hundredths or tenths of a millimeter.

A piezoelectric actuator is able to generate considerable forces, of the order of hundreds of newtons. Another advantage of piezoelectric actuators is that they are characterized by an extremely fast response; finally, the property of piezoelectric elements of undergoing lengthening in a way proportional to the voltage applied enables the valve elements60and32to occupy intermediate positions with respect to the case of the solenoid actuator.

In the case of the embodiment illustrated schematically inFIG. 12, the actuator member, designated as a whole by AM, is constituted by the stack of piezoelectric elements PZ. Said actuator member AM is connected to the second valve element14with interposition of a transmission that generates a length of movement of the second valve element14greater than the length of movement corresponding to lengthening of the actuator member AM. This transmission could be, for example, a mechanical transmission, in particular a lever transmission, designed to enable multiplication of the displacement generated by the actuator member AM. Preferably, however, as illustrated schematically inFIG. 12, the transmission is a hydraulic transmission, comprising a hydraulic cylinder T with a fluid chamber having a section of smaller diameter C1 and a section of larger diameter C2. In the wall of the cylinder T at least one hole F is provided connected to a pressurized-fluid environment (as will emerge clearly in what follows) in such a way as to guarantee automatic restoration within the chamber C1, C2 of pressurized fluid following upon possible losses due to leakage. The fluid in the cylinder T is the same fluid that traverses the valve1.

Thanks to the arrangement described above, lengthening of the actuator member AM constituted by the stack of piezoelectric elements PZ determines a displacement of the fluid from the chamber C2 to the chamber C1, with consequent multiplied linear displacement of a driven member D that is slidable within the section of smaller diameter of the cylinder T and that is operatively connected to the second valve element14.

In the embodiment illustrated schematically inFIG. 12, in the cylinder T elastic means are provided constituted, in the specific example illustrated, by a helical spring SP, which induce a state of precompressive stress in the stack of piezoelectric elements PZ in order to improve operation thereof, according to a technique in itself known. Use of said precompressive elastic means is of course possible also in the case where a transmission T for multiplication of the displacement is not adopted.

For the rest, the structure of the control valve1is substantially similar to the one already described above with reference toFIGS. 1-11. Consequently, inFIG. 12the parts common to those ofFIGS. 1-11are designated by the same reference numbers.

The valve1comprises a body10slidably guided within which are the first valve element12and the second valve element14. The first valve element12has a conical surface32co-operating with a valve seat A1. It is pushed by a spring52into an opening position, in which the bottom end (with reference to the figure) of the valve element12bears upon a ring44rigidly connected to the body10of the valve. In this opening position, the conical surface32is spaced apart from the valve seat A1.

The second valve element14has an end head with conical surface60co-operating with a valve seat A2 and pushed by a spring86(which in this case is set between the two valve elements12,14) into an opening position, in which the head of the second valve element14bears upon a surface S of the body of the valve. In this opening position, the conical surface60of the second valve element14is spaced apart from the valve seat A2. InFIG. 12, the second valve element14is illustrated in an intermediate position between its opening position and its closing position.

In a similar way to the embodiments ofFIGS. 1-11, the control valve1comprises an inlet mouth2and two outlet mouths4,6. In the resting condition, when both of the valve elements12,14are pushed by the respective springs52,86into their opening positions, in contact respectively with the ring44and with the surface S, the pressurized fluid at inlet through the mouth2can flow both as far as the outlet mouth4and as far as the outlet mouth6. In order to reach the mouth4, the fluid entering through the mouth2flows within a chamber503and from this into a chamber504through holes505made in the body of the first valve element12. From the chamber504the fluid passes through the passage left open between the valve seat A2 and the conical surface60of the second valve element14. The fluid then flows through holes506made in the body of the second valve element14as far as a chamber507provided within the body of the second valve element14and within the body10. The chamber507communicates with the outlet mouth4. In a similar way, the pressurized fluid entering through the mouth2is able to flow as far as the outlet mouth6passing through the chamber503and through the passage defined between the valve seat A1 and the conical surface32of the first valve element12.

The condition described above corresponds to the position P1 of the control valve1.

When the control valve1is in its second operative position P2, i.e., when the actuator member AM has caused closing of the second valve element14against the valve seat A2, with the first valve element12still in the opening position, communication between the inlet mouth2and the outlet mouth4is interrupted, whereas communication of the inlet mouth2with the outlet mouth6continues to exist.

In the position P3 of the control valve1, both of the valve elements12,14are in their closing position, in contact with the respective valve seats A1, A2 so that the communication of both of the outlet mouths4,6with the inlet mouth2is interrupted.

The main advantage of a piezoelectric actuator of the type illustrated schematically inFIG. 12as compared to a solenoid actuator lies in the possibility of varying as desired the law of motion of the valve elements12,14, by regulating the supply voltage of the piezoelectric actuator. In the case of the solenoid actuator, the movements of the valve between the positions P1, P2, P3 are substantially instantaneous. In the case of the piezoelectric actuator ofFIG. 12, instead, the speed of displacement of the second valve element14during passage from the position P1 to the position P2, and the speed of displacement of the set of the two valve elements12,14during passage from the position P2 to the position P3, as well as finally the speed of the displacement of return of the two valve elements12,14into the resting position corresponding once again to the position P1, depend upon the supply voltage of the piezoelectric actuator; moreover, since the piezoelectric actuator is of a linear type, the valve1can work, no longer in just three operating positions, but in infinite operating positions, since intermediate operating positions are now allowed between P1 and P2 or between P2 and P3, it being necessary to respect just the constraint whereby the intermediate positions between P2 and P3 can be obtained only after the second valve element14has come to bear upon the first element12. In practice, it is possible to have infinite working positions of the valve1between the position P1 and the position P2, progressively reducing the section of passage A2 whereas the section of passage A1 remains completely open; thus, it is possible to have infinite intermediate positions between the position P2 and the position P3 of the valve1, maintaining the section A2 closed and reducing the section of passage A1.

Thanks to the above characteristic, the valve ofFIG. 12is suited to being used advantageously in a wide range of applications.

A particularly advantageous application consists in the use of the valve ofFIG. 12as control valve for driving a fuel-injection valve in an internal-combustion engine. This application is illustrated schematically inFIG. 13, with reference, by way of example, to an injection system designed for a direct-injection diesel engine.

With reference toFIG. 13, designated by IV is an injection valve comprising a body600mobile within which is a pulverizer plug601, the tip of which co-operates with pulverization holes602formed in the body600. The plug601is connected to a plunger603slidable in the body600of the valve IV between a head chamber604and an injection chamber605. A spring606is set in the head chamber604between the plunger603and the top end of the internal cavity of the body600for pushing the plunger603and the plug601into the position of obstruction of the pulverization holes602.

Obstruction of the holes602takes place when the edge T on the tip of the plug601, defined for example between two conical portions with different angle of conicity, bears upon the bottom surface of the body600providing a seal covering the diameter Dt (the holes602are hence not occluded directly by the plug601); it should be noted that the seal diameter Dt is much smaller than the diameter Dsp of the plunger603.

The arrangement of the valve IV described above is such that the mobile element comprising the plunger603and the plug of the pulverizer601is hydraulically semi-balanced, in the sense that it remains in its closing position, which obstructs the sump650for delivery to the pulverization holes602as long as the first chamber606and the second chamber605are at the same pressure. The term “semi-balanced”, referred to the mobile element, is due to the fact that, in the closing position, i.e., when there is sealing of the edge T at the bottom surface of the body600, acting on the surface defined by the diameter Dt of the mobile element is the pressure of the combustion chamber into which the valve IV gives out, which is much lower than the pressure of the injection chamber605and the pressure of the head chamber604: this generates a force FHythat contributes to maintaining the mobile element in the closing position, and hence the risk is prevented of even microscopic amounts of fuel flowing from the injection chamber605into the sump650at undesired instants (in practice, outside the time interval during which injection takes place).

In addition to being hydraulically semi-balanced, in the way just described, the mobile element is recalled into the position of obstruction of the sump650also by a spring606that exerts a force FM.

The mobile element603shifts into a position of opening of the pulverization holes602only when the pressure in the injection chamber605exceeds the pressure in the head chamber606by a pre-determined value Δp depending upon the forces FHyand FM. From a practical standpoint, in the design step, once Dsp, Dtand the pre-load of the spring FMchosen have been defined, the desired Δp is determined, and the valve1is configured accordingly: in particular, Δp will depend upon the section of passage A1 defined within the valve1and hence upon the position of the first valve element12.

In the application illustrated inFIG. 13, the injection valve IV is driven by a control valve1of the type described with reference toFIG. 12. The inlet mouth2of the valve1is connected to the delivery of a pump607, which takes in the fuel from a tank R generally at atmospheric pressure. The delivery of the pump607is also connected via a line608to the injection chamber605of the valve IV. The outlet mouth4is connected to the discharge tank R, whilst the outlet mouth6is connected to the head chamber604. Associated to the injection chamber605is a pressure-limiting valve609, which sets the chamber605in discharge once a pre-determined maximum value of pressure is exceeded.

The system illustrated by way of example inFIG. 13regards the case in which a closed-loop control of the motion of the plug of the pulverizer is provided. In this case, pressure sensors610,611are thus provided associated to the line608(or to the injection chamber605) and to the head chamber604, these signals being sent to an electronic control unit612, which controls the value of the supply voltage of the piezoelectric actuator8accordingly.

FIGS. 14A, 14B, 14Ccorrespond toFIGS. 4A, 4B, 4Calready discussed above for the case where the electric actuator of the valve1is a piezoelectric actuator instead of a solenoid actuator.FIG. 14Ashows the variation in time of the supply voltage of the piezoelectric actuator, which enables shifting of the valve from the position P1 to the position P2 and from the position P2 to the position P3. The diagrams ofFIGS. 14B and 14Cshow the corresponding variations of the area of passage S1, S2 in a region corresponding to the valve seats A1, A2, as the valve elements12,14move into the closing position.FIG. 14Cshows the corresponding axial displacements of the valve elements.

As is evident from a comparison ofFIGS. 14A, 14B, 14CwithFIGS. 4A, 4B, 4C, the piezoelectric actuator provides a non-instantaneous displacement of each valve element12,14from its opening position to its closing position. The speed with which this displacement takes place depends both upon the law with which the supply voltage of the piezoelectric actuator is applied and upon the intensity thereof. Consequently, as already indicated above, a variation of the supply voltage enables adjustment as desired of the law of motion of the valve elements12,14. It should be recalled that, for what has been said previously, also intermediate positions of the valve elements are possible between those that correspond to the maximum openings S1 and S2 and appearing inFIGS. 14A, 14B, 14C.

With reference now again toFIG. 13, as well as toFIG. 15, operation of the control system ofFIG. 13will be described.

As already indicated, the plug601of the pulverizer can rise into its opening position only when the pressure in the injection chamber605reaches a value Pth that exceeds the value of pressure P0 in the head chamber604by a pre-determined ΔP.

With reference to the diagram ofFIG. 15, prior to the instant in time A the supply voltage of the piezoelectric actuator8is zero (V0inFIG. 15). In this condition, the springs52,86maintain the two valve elements12,14in their opening positions. As has already been illustrated above, in this condition the inlet mouth2of the control valve1communicates with both of the outlet mouths4,6. Consequently, in this condition, corresponding to the position P1 of the control valve1, the pressurized fuel coming from the pump607reaches the inlet mouth2of the valve1and from here passes to the discharge R through the outlet mouth4. In this condition, the pressure in the chambers604,605of the injection valve IV does not increase, notwithstanding the fact that both of the above chambers are in communication with the delivery of the pump607.

With reference toFIG. 15, at the instant A a voltage V=V(t) is applied (V0-V1inFIG. 14A) across the piezoelectric actuator8. The actuator member AM constituted by the stack of piezoelectric elements PZ hence starts to lengthen at a rate that is a function of the value of voltage applied in time. Lengthening of the piezoelectric actuator is transmitted to the driven member D by the fluid present in the cylinder T so that the second valve element14starts to move away from its opening position and to approach the valve seat A2, against the action of the spring86.

The instant B inFIG. 15is the one at which the second valve element14comes to bear upon the valve seat A2. In this way, the control valve1is brought into the position P1 in which communication between the inlet mouth2and the outlet mouth4is interrupted, so that the delivery of the pump607is no longer connected to the discharge R.

Consequently, in the time that elapses from the instant A to the instant B the valve has moved from its position P1 to its position P2. The length of said time interval is a function of the law of application of the supply voltage of the piezoelectric actuator, as well as of the geometries of the sections of passage of the valve1and of the capacity of the pump607. As has already been mentioned above, this constitutes an important difference with respect to the case of a solenoid actuator, for which switching from the position P1 to the position P2 is substantially instantaneous. Consequently, with the control valve ofFIG. 12it is possible to adjust the supply voltage of the piezoelectric actuator8in order to obtain a desired law of motion of the second valve element14during passage of the valve from the position P1 to the position P2.

When the valve is in the position P2, the supply pump607, no longer connected to the discharge R, is able to cause the pressure to rise both in the injection chamber605, which is directly connected to the delivery of the pump607via the line608, and in the head chamber606, which receives the pressurized fluid through the outlet mouth6of the control valve1. In this position P2 of the valve, consequently, the plug601of the pulverizer continues to remain in its closed position, in so far as, as has already been said, the plug601cannot be opened as long as the pressure in the chambers604,605has substantially the same value.

Passage from the position P2 to the position P3 takes place by applying across the piezoelectric actuator8a higher value V2of voltage (seeFIG. 14A) in such a way as to push the first valve element12, via the second valve element14, into its position of closing on the valve seat A1, against the action of the spring52. As mentioned above, also this passage takes place at a rate that depends upon the law of application of the voltage. Consequently, the position P3 of the valve is reached at an instant C (FIG. 15) subsequent to the instant B. At the instant C, the value of the pressure in the injection chamber605has reached the pre-determined value Pth and hence the plug601has the possibility of starting to open.

The rate at which the plug601of the pulverizer opens, and consequently the instantaneous flow injected in the very first instants, depends upon the speed of the movement of closing of the first valve element12(as well as upon the capacity of the pump607and upon the sections of passage A1 and upon the geometry of the hydraulic connections). Once in the design step the ΔP of intervention has been pre-determined, the instant in which the valve element12closes defines the level of pressure Pth, which corresponds to the value of the injection pressure. Consequently, via the control valve according to the invention, it is possible to obtain an adjustment of the injection pressure as a function of the engine operating points.

What has been mentioned above applies in a similar way also for the end of the injection event, i.e., for the passage from the instant D to the instant E inFIG. 15(passage of the valve from the position P3 to the position P2) and the subsequent passage from the instant E to the instant F, corresponding to passage of the valve from the position P2 to the position P1.

In the position P1 the pump607performs the minimum work, because its delivery is set directly in discharge.

As is evident from the foregoing description, the valve ofFIG. 12consequently enables correlation of the law of motion of the plug601of the pulverizer to the laws of motion of the valve elements12,14, which can be controlled by means of the supply voltage of the piezoelectric actuator.

Of course, the injection system ofFIG. 13can be used also without a closed-loop control. Moreover, the system can be adopted in any type of engine, for example a diesel engine, or a petrol engine, or a gas-supplied engine. As has been said, the main advantage of the system consists in the possibility of assigning any desired law of motion to the plug601of the pulverizer.

In the specific case of a diesel engine, control of the law of motion of the plug601of the pulverizer enables control of the instantaneous flowrate of fuel through the pulverizer (injection rate). The law of injection (injection rate) affects the combustion and consequently the products of combustion (in particular, HC and NOx).

FIG. 16shows a schematic diagram of the injection rate as a function of time, according to three different particular modes: “rectangular”, “ramp”, “boot”. According to the engine operating point, each of the three laws presents optimal characteristics with respect to the others. In particular, injection of a “boot” type enables reduction of the NOx emissions as compared to the others.FIG. 17is a real diagram that shows the three different injection modes, corresponding to the theoretical diagram ofFIG. 16.FIG. 18shows the advantage in terms of reduction of NOx that is obtained with the “boot” mode.

The majority of diesel-injection systems known and currently available on the market, in which a two-way and two-position control valve is used, does not enable actuation of the plug of the pulverizer with a law for example of the “boot” type or of the “ramp” type.

Instead, the three-way and three-position valve according to the invention, with piezoelectric actuator, enables actuation of the plug of the pulverizer with multiple laws of motion. In practice, the possibility of controlling the valve elements12,14with any law of motion enables control of the law of motion of the plug of the pulverizer and hence the injection rate of the injection valve.

In the system illustrated above, the aforesaid source of pressurized fluid may comprise, according to a technique in itself known, a high-pressure pump comprising pumping elements operated by a rotary cam or by a rotary eccentric member. Moreover, downstream of the high-pressure pump there may be provided a rail, in turn connected to the control valve1and to the first fluid chamber605of the injection valve.

FIG. 19shows a variant ofFIG. 13that differs in that opening of the valve is obtained with lowering of the plug601with respect to the body600. In this case, the spring606tends to recall the plug601upwards (as viewed in the drawing), into a position of closing of the valve. The plug601remains in its closing position as long as the pressure in the chambers604,605remains the same. The plug drops, thus opening the valve, when the pressure in the head chamber604exceeds the pressure in the injection chamber605by a pre-determined ΔP. In this case, the injection chamber605is connected to the outlet mouth6of the control valve1, whereas the head chamber604is connected, via the line608, to the delivery of the supply pump607. The outlet mouth4is always connected to the discharge tank R. The pressure-limiting valve609is associated to the head chamber604and connects this chamber to the discharge tank R above a pre-set maximum pressure. In this case, when the control valve1is brought into the position P3, communication of the injection chamber605with the outlet mouth6is interrupted so that the pressure in the head chamber604increases with respect to the value of pressure in the injection chamber605up to a pre-determined value at which the plug601opens.

FIG. 20illustrates a second embodiment of the valve according to the invention in which the actuator8is constituted by an actuator of a magnetostrictive type, instead of by a piezoelectric actuator. In this case, the actuator8consequently comprises a bar800made of magnetostrictive material, set inside a solenoid801. Supply of the solenoid801induces a magnetic flux through the bar800that causes lengthening thereof (the path of the lines of magnetic flux is represented schematically with a dashed line).

The magnetostrictive materials have been known and used for some time. They present the characteristic of undergoing pre-determined lengthening when they are subjected to a magnetic field generated by a solenoid. By varying the supply current of the solenoid801it is possible to vary the rate of lengthening of the bar800of magnetostrictive material. In the case of the example illustrated inFIG. 20the fluid cylinder T is likewise provided for multiplying the displacement of the actuator, shaped and functioning in a way identical to what has been described with reference toFIG. 12. For the rest, the constructional details of the valve1may be identical. Also in this case, elastic means SP are provided designed to induce a precompressive state of stress in the bar800of magnetostrictive material.

Also the actuator of a magnetostrictive type presents the advantages that have been described above with reference to the piezoelectric actuator. Consequently, also in this case, it is possible to vary the law of motion of the valve elements12,14as desired, by appropriately regulating the electric current (instead of the voltage) for supply of the solenoid801. Consequently, all the advantages set forth above with reference to the embodiment ofFIG. 12apply also in the case of the embodiment ofFIG. 20. In addition, also the embodiment ofFIG. 20is suited to being used in an injection system of the type illustrated inFIG. 13or inFIG. 19.

Once again in a way similar to what has been indicated above, the transmission designed to multiply the displacement determined by the actuator member800may be of any type and in particular may be also a mechanical transmission, for example with levers, instead of a fluid transmission.

Moreover, as in the embodiment ofFIG. 12, also in this case a spring SP is provided that recalls the actuator member800into the condition of minimum length.

Moreover, both for the embodiment ofFIG. 12and for the embodiment ofFIG. 20there is in any case envisaged the possibility of using an actuator of a piezoelectric type or of a magnetostrictive type, without using a transmission for multiplication of the displacement.

As has already been mentioned above, all the constructional details regarding the body of the valve1, the valve elements12,14, the springs52,86, the arrangement of the sealing elements and any further constructional details may be provided in a way identical or similar to what has been illustrated inFIGS. 1-11for the valves with solenoid actuator.

Moreover, in the annexed drawings the constructional details of the piezoelectric actuator and of the magnetostrictive actuator are not illustrated both in so far as they can be provided in any known way and in order to render the drawings simpler and more readily understandable, as well as also in so far as the above actuators, taken in themselves, do not fall within the scope of the present invention.

Of course, without prejudice the principle of the invention, the details of construction and the embodiments may vary widely with respect to what has been described and illustrated by way of example, without thereby departing from the scope of the present invention.