EP2809895B1 - Device for the variable control of at least one valve, for example for a reciprocating engine - Google Patents

Description

The present invention generally relates to a device for controlling at least one valve, for example for an alternating motor and, more particularly, a device for variable control of at least one valve actuated by at least two cams carried by shafts. synchronous and dephasable angularly relative to each other. The invention applies in particular to the variable distribution in operation of an alternating motor whose head carries two coaxial camshafts connected by a phase shifter, for example hydraulic.

By distribution means, in a conventional manner, all the opening and closing sequences of the engine valves.

It is known that the performance of the reciprocating engines is very dependent on the angular positions of the crankshaft for which the valves open and close in the cycle of the engine, and that the optimal distribution diagram changes with the operating conditions, and in particular with the diet and the load. This distribution influences the effective compression and expansion rates (Miller cycles), the amount of flue gases possibly recycled, the energy available in the exhaust gas, the volumetric efficiency, the mechanical friction, etc. It is therefore desirable to be able to independently modify, during the operation of the engine, the angular positions of the crankshaft for which the opening and closing of the intake and exhaust valves take place.

In addition, the lift of the intake valves largely determines the level of turbulence in the combustion chamber and it may be advantageous to adjust the power of a spark-ignition engine by rolling the intake flow at the seat of the valves. rather than at the level of a butterfly disposed upstream of an intake manifold.

Finally, it may be advantageous to disable some engine cylinders by keeping their intake valves and / or their exhaust valves closed during certain phases of engine operation.

In the case where the valves are actuated by camshafts, said valves are supported, via mechanisms oscillating or sliding by return springs, on rotating cams whose profile imposes the kinematics of reciprocating translational movements of said valves. To avoid shocks, the contacts between the elements of the mechanical chain connecting the cams and the valves must not be broken, and the valves must land on their seat with a speed almost zero.

Most of the variable devices used to date generate the movement of a valve from the profile of a single cam that is deformed mechanically or hydraulically.

The complexity of the known devices for mechanically varying the duration and the lifting of the valves (such as the device "Valvetronic" including the subject of the patent EP 1 039 103 in the name of BMW) imposes high machining precision which makes these devices relatively expensive.

Electro-hydraulic devices (such as the device "Uniair" described in particular in patents EP 0 803 642 and EP 1 344 900 in the name of CRF) have the disadvantage of losing all or part of the energy accumulated in the return springs and depend largely on the viscosity of the lubricating oil.

Other devices generate the movement of a valve from the profiles of two cams dephasable, usually carried by two coaxial shafts, one of which ensures the opening of the valve and the other closing.

The patent application WO 02/48510 , on behalf of the applicant, teaches to hydraulically mix the profiles of two cams out of phase to modulate the duration of opening, with the disadvantage of having a minimum threshold of the valve lift prohibiting gradually reduce the permeability of the orifice controlled by the valve until it is completely closed.

The present invention, which is based on the same principle aims to offer the same functionality as the best known devices, from a simple rotary phase shifter connecting two synchronous camshafts.

The main object of the present invention is therefore to be able to adjust in operation the angular duration of opening of at least one valve and its lifting until its total closure, without losing, by rolling a hydraulic fluid, the energy accumulated in the return means of the device.

For this purpose, the invention proposes a device for controlling at least one valve, for example for an alternating motor, driven by reciprocating rectilinear movement intended to open or close an orifice provided with a sealing seat. , said valve comprising an elastic return means to a closed position, the device comprising a body comprising a non-deformable cavity communicating exclusively with the outside by at least four straight cylinders respectively closed by four reciprocable pistons in reciprocating motion between a bottom dead center remote from the interior of the cavity and a top dead center close to the inside of the cavity, characterized in that said pistons are a piston mechanically connected to the valve and antagonistic to its return means, an actuated opening piston by an opening cam driven in rotation by a first shaft, a closing piston actuated by a closing cam e driven in rotation by a second shaft rotating in synchronism with the first shaft and displaceable relative to the first shaft by an adjustable angle in operation, a shuttle piston moving between a first fixed stop defining the bottom dead center and a second fixed stop defining the top dead center towards which the shuttle piston is returned by a means elastic, in that the portion of the cavity delimited by the pistons is filled by a constant reference volume of substantially incompressible hydraulic fluid defined when the valve rests on its seat, that the opening and closing pistons are in their neutral position bottom and that the shuttle piston is at its top dead center, in that the opening piston, the closing piston and the shuttle piston have a common displacement and move the same volume of fluid between their bottom dead point and their neutral position high, and in that the elastic return means of the shuttle piston and the valve are such that the pressure of the fluid required to move the shuttle piston to its bottom dead point is less than the pressure required to open the valve.

In the device according to the invention, a working cycle corresponding to an opening-closing of the valve is performed on a complete rotation of the synchronous shafts which drive the cams opening and closing the valve. The cycle begins and ends in a rest configuration of the device that defines the reference volume of hydraulic fluid present in the cavity. In the rest configuration, the valve is returned to its seat by elastic means, the piston Ps of the valve is at its top dead point, the shuttle piston Pa is returned to its second stop by the corresponding elastic means and is at its top dead center, and the opening piston P1 and closing P2 are at their bottom dead point, the latter being defined by the base circles of the opening cams C1 and closure C2.

During the rotation of the shafts, the stroke of the opening pistons P1 and closing P2 depends solely on the angular position of the cams C1 and C2 according to their respective profiles. A crankshaft driving the cams can thus control the flow of positive or negative instantaneous fluid discharged into the cavity by the pistons P1 and P2 and, consequently, the instantaneous total flow rate that supplies the cavity, equal to the algebraic sum of the instantaneous flow rates discharged by P1 and P2. The pistons P1 and P2 being simultaneously at their bottom dead point at the beginning of a cycle, the overall volume discharged into the cavity by the pistons P1 and P2 from the beginning of the cycle is at any time between zero and twice the common cylinder capacity of the pistons P1, P2 and Pa for the duration of the cycle. Since the reference volume of hydraulic fluid present in the cavity remains constant, the global flow delivered by the pistons P1 and P2 from their bottom dead point must be absorbed by the pistons Pa and Ps which were at their top dead center at the beginning of the cycle. . Given the calibration of their respective biasing means, the total flow discharged is exclusively absorbed by the shuttle piston Pa as said flow rate remains lower than the aforementioned common displacement. The piston Ps can therefore absorb only the discharged flow exceeding said common displacement, which can no longer be absorbed by the shuttle piston Pa, since the piston has reached its first stop at its bottom dead point. The piston Ps of the valve can therefore absorb a volume between zero and said common cylinder. It can be seen that the displacement phase of the shuttle piston Pa, from its top dead center to its bottom dead point, constitutes an arming phase of the device prior to any displacement of the valve.

To modify the distribution, it has a maximum phase shift angle allowed by the phase shifter to, for example, advance the second shaft in operation relative to the first shaft, the opening and closing cams each having a circular arc of base and a single lobe whose profile is constituted by a rising ramp for moving the corresponding piston from its bottom dead center to its top dead center, followed by a second circular arc concentric to the base circle and larger diameter that it, to immobilize the opening and closing pistons to their top dead center, followed by a downward ramp to bring the opening and closing pistons to their bottom dead center, the opening angularly of the base arc of the opening cam being at least equal to the angular aperture of the rising ramp of the closing cam, increased by the maximum phase shift angle, the angular aperture of the basic circle arc of the closing cam being at least equal to the angular aperture of the down ramp of the aperture cam increased by the maximum phase shift angle.

According to one characteristic of the invention, over the entire range of phase shift, the relative angular setting of the first and second shafts is such that the opening piston leaves its bottom dead point under the action of the rising ramp of the cam opening, after the shuttle piston has reached its top dead point under the action of the rising ramp of the closing cam, and that the closing piston reaches its bottom dead point under the action of the downward ramp of the closing cam before the opening piston leaves its top dead center under the action of the downward ramp of the opening cam.

Under these conditions, from the rest position, the rising ramp of the closure cam C2 starts the work cycle by moving the closing piston P2 from its bottom dead point to its top dead center by driving a displacement in the cavity. common fluid to repel, without shock, the shuttle piston Pa from its top dead center to its lowest dead point and thus arm the device. During this phase, the piston P1 remains at its bottom dead point defined by the base circle of the cam C1 and the piston Ps remains at its top dead center. The piston P2 then remains immobilized at its top dead point, defined by the second arc of the cam C2, when the rising ramp of the cam C1 ensures the next phase by moving the piston P1 from its bottom dead center to its neutral position high to discharge into the cavity a second common cylinder of hydraulic fluid required to open the valve.

According to one embodiment of the invention, the relative angular setting of the shafts is defined in such a way that, for a zero phase angle between the first and second shafts, which corresponds to the maximum opening time of the valve, the closing piston leaves its top dead center after the opening piston has reached its, so as to create an initial range of phase shift for which the valve parks for a while at maximum lift between its opening and closing phases.

For this configuration of the invention, the piston P1 reaches its top dead center before the piston P2 leaves its own, with the result that the entire common fluid cylinder is sucked by the single piston Ps which opens the valve until at the greatest lift allowed by the device, which it keeps until the piston P2 leaves its top dead center, by the effect of the downward ramp of the cam C2, absorbing the flow rate discharged by Ps during the closing the valve.

According to another embodiment of the invention, the relative setting of the shafts is defined in such a way that, for a zero phase shift angle between the first and second shafts, the closing piston leaves its top dead center before the piston of opening reaches his.

Under these conditions, before the end of the discharge stroke of the piston P1, the piston P2 begins to suck up an increasing fraction of the flow delivered by the piston P1 thereby decreasing the overall flow sucked by the piston Ps and thus the maximum lift of the valve, the latter being reached only for a single angle of rotation of the trees and not for a certain angular period of rotation of the shafts.

According to one embodiment of the invention allowing the valve to close completely, the maximum phase angle of the closing cam relative to the opening cam is sufficient for the closing piston to leave its top dead center. that the opening piston leaves its low dead point and that, at any time during the opening phase of the valve, the volume of fluid sucked by the closing piston from its top dead center is greater than the volume of fluid discharged by the opening piston from its bottom dead point, so that, the total discharged flow remaining lower than or equal to the common cylinder capacity, the valve remains closed for the duration of the cycle and that the shuttle piston leaves and reaches its point death down to maintain the volume of the cavity at its reference value.

In this way, it is possible to phase shift the cams C1 and C2 so that the total flow delivered by the pistons P1 and P2 remains lower than the common cylinder capacity and the device is disarmed throughout the cycle, without being able to move the valve to which the piston Pa replaces which leaves and rejoins its bottom dead stop to maintain the volume of the cavity at its reference value.

The angular duration of opening of the valve and its lifting can be adjusted during operation, by modifying the phase shift angle of the second shaft and by holding the first shaft fixed, or conversely, or by simultaneously modifying the phase angle each of the shafts relative to a crankshaft driving said shafts.

Between the zero phase shift where the valve reaches its maximum opening time and its maximum lift and the maximum phase shift where the valve does not open, the opening angular duration is a continuous decreasing function of the phase angle between the shafts. . The lift is also a decreasing function of said phase shift angle, the maximum lift possibly being maintained during an initial angular period of rotation of the shafts as indicated above. The invention thus makes it possible to adjust the angular duration of opening and also makes it possible to adjust the corresponding lift of the valve between a zero value and a maximum value.

If we have a single phase shifter, we can choose between a fixed opening start and a variable end of closure, or vice versa. If two phase shifters are available, the start of opening and the end of closing of the valve can be adjusted simultaneously.

In all embodiments of the invention, the profiles of the opening and closing cams may be such that there is a rest period during which the valve is in the closed position, the shuttle piston is in its neutral position high and the opening and closing pistons are at their bottom dead points, making it possible to compensate for leaks in the cavity in order to recalibrate the fluid reference volume via a unidirectional communication with a source of fluid at a pressure insufficient to move the shuttle piston.

Such a characteristic makes it possible to cancel the operating games of the device. The restoration, at the beginning of each cycle, of a minimum pressure in the cavity guarantees the support (direct or indirect) of the pistons on their cam. In addition, the arming phase of the device is accompanied by an increase in pressure in the cavity proportional to the elastic return force of the shuttle piston Pa which strengthens the mechanical attachment between the cams C1, C2 and the valve, thus acting the role of the classic ramp of silence.

Modern engines generally have four valves per cylinder, including two identical twin intake valves operating in synchronism controlled by two cams of an intake shaft and two identical twin exhaust valves also operating in synchronism controlled by two cams. an exhaust shaft. To respect this architecture, the conventional camshaft can be replaced in the invention by a tubular shaft carrying fixed cams and dephasable cams, the latter being keyed on a coaxial shaft inside the tubular shaft and driven by the latter via a phase shifter. The complexity of this out-of-phase camshaft increases with the number of cams per cylinder.

On the other hand, a perfect synchronism of the twin valves assumes a symmetrical hydraulic path between each valve piston and pistons P1 and P2. This symmetry involves regrouping at a central point the fluid flow rates displaced by the pistons P1 and P2 and then separating them towards the two valve pistons Ps with a detrimental increase of the reference volume and changes of direction of the fluid flows. A hydraulically advantageous configuration with two fixed opening cams framing a single phase-out closing cam will be described later. Moreover, besides the hydraulic symmetry, the synchronism of the twin valves presupposes two perfectly identical return springs and the same friction between the two valve stems and their guides. A more desirable configuration with only one opening cam and one closing cam arranged side by side nevertheless makes it possible to guarantee the synchronism of two twin valves. A first solution is characterized in that the two valves are controlled by two independent devices whose two opening pistons are actuated in synchronism by a single opening cam and the two closing pistons are actuated in synchronism by a single cam of closing. Another solution is characterized in that the two valves are actuated by a single device according to the invention via a synchronizer.

To allow all the configurations, the device according to the invention can control in synchronism a number N of identical valves, and can comprise a number P of synchronous opening pistons between them actuated by Q identical opening cams, a number R of synchronous closing pistons between them actuated by S identical locking cams and at least one shuttle piston, the overall volume displaced by the P pistons of openings between their bottom dead point and their top dead point being identical to the overall volume displaced by the R's. closing pistons between their bottom dead point and top dead center, and also being identical to the overall volume displaced by the shuttle piston (s) between its bottom dead center and its dead point (s) high.

The invention also relates to a set of two devices of the aforementioned type, each intended to actuate a single valve, characterized in that they share a single opening cam and a single closing cam, so as to ensure the synchronism of the opening and closing of said valves.

Alternatively, a single device according to the invention actuates at least two identical valves, via a rudder or a rocker arm synchronization.

According to another embodiment, the body may comprise an additional non-deformable cavity, communicating with the other body cavity via a first cylinder, and communicating with the outside via a second straight cylinder of smaller section than the first cylinder, parallel and facing the first cylinder, as well as via a third straight cylinder, the additional cavity communicating unidirectionally with a source of fluid under pressure. In this case, a first piston slides in the first cylinder, a second piston slides in the second cylinder, the second piston being connected to the first piston and to a first valve, of axis parallel to the first and second pistons, a third piston slides in the third cylinder, the third piston being connected to a second valve, of axis parallel to the third piston. Furthermore, the additional cavity contains a substantially incompressible fluid volume which is equal to the volume of said additional cavity when the first and second valves rest on their seats in the closed position of said valves.

The device according to the invention may further comprise means for erasing the first bottom dead stop of the shuttle piston, so that said piston can suck the algebraic sum of the volumes of fluid discharged by the opening piston. and the closing piston, to prevent the opening of the valve regardless of the phase angle between the opening shaft and the closing shaft.

It is thus possible to disable and / or reactivate easily one or more cylinders of a motor.

• déplacer le piston de fermeture de son point mort bas à son point mort haut, par l'intermédiaire de la rampe montante de la came de fermeture, de façon à repousser le piston navette de son point mort haut à son point mort bas afin d'armer le dispositif de commande, le piston d'ouverture restant à son point mort bas, par l'intermédiaire de l'arc de cercle de base de la came d'ouverture,
• déplacer le piston d'ouverture par l'intermédiaire de la rampe montante de la came d'ouverture, de façon à ouvrir la soupape, le piston de fermeture restant à son point mort haut, par l'intermédiaire du second arc de cercle de la came de fermeture,
• régler la levée et la durée d'ouverture de la soupape en déphasant la came de fermeture par rapport à la came d'ouverture pour déplacer le piston de fermeture à partir de son point mort haut, par l'intermédiaire de la rampe descendante de la came de fermeture, à un moment quelconque de la course de refoulement du piston d'ouverture, par l'intermédiaire de la rampe montante de la came d'ouverture avant qu'il rejoigne son point mort haut,
• poursuivre le déplacement du piston de fermeture jusqu'à à son point mort bas, par l'intermédiaire de la rampe descendante de la came de fermeture, de façon à fermer la soupape, le piston d'ouverture restant à sont point mort haut, par l'intermédiaire du second arc de cercle de la came d'ouverture,
• déplacer le piston d'ouverture de son point mort haut vers son point mort bas, par l'intermédiaire de la rampe descendante de la came d'ouverture, de manière à déplacer le piston navette de son point mort bas à son point mort haut et à désarmer le dispositif.

Finally, the invention also relates to a method of operating a control device of the aforementioned type, characterized in that each revolution of the shafts it performs a cycle of opening and closing the valve comprising the successive steps of from a rest position of the control device in which the valve rests on its seat, in which the opening and closing pistons are at their bottom dead point and in which the shuttle piston is at its top dead point:

• move the closing piston from its bottom dead center to its top dead center, via the rising ramp of the closing cam, so as to push the shuttle piston from its top dead center to its bottom dead point in order to cocking the control device, the opening piston remaining at its bottom dead point, through the basic arc of the opening cam,
• moving the opening piston through the rising ramp of the opening cam, so as to open the valve, the closing piston remaining at its top dead center, via the second arc of the closing cam,
• adjust the lift and the opening time of the valve by displacing the closing cam relative to the opening cam to move the closing piston from its top dead center, via the downward ramp of the closing cam, at any moment of the discharge stroke of the opening piston, via the rising ramp of the opening cam before it reaches its top dead center,
• continue moving the closing piston to its bottom dead point, via the downward ramp of the closing cam, so as to close the valve, the opening piston remaining at the top dead center, by through the second arc of the opening cam,
• move the opening piston from its top dead center to its bottom dead center, via the downward ramp of the opening cam, so as to move the shuttle piston from its bottom dead center to its top dead center and to disarm the device.

• la figure 1 est une vue schématique d'un dispositif de commande d'une seule soupape, selon une première forme de réalisation de l'invention, dans laquelle la soupape est actionnée par deux arbres à cames parallèles portant des cames d'ouverture et de fermeture identiques inversées,
• les figures 2A à 2E sont des vues illustrant schématiquement les différentes étapes d'un cycle de fonctionnement du dispositif de commande de la figure 1,
• la figure 3 est un diagramme illustrant les volumes refoulés par les pistons d'ouverture et de fermeture, le volume absorbé par le piston de la soupape, et par le piston navette, en fonction de la position angulaire des cames, pour plusieurs décalages angulaires des cames d'ouverture et de fermeture,
• les figures 4A et 4B sont des vues en coupe, respectivement selon les lignes BB' et AA' des figures 4B et 4A, d'une seconde forme de réalisation de l'invention, dans laquelle deux arbres coaxiaux portent trois cames par cylindre destinées à actionner en synchronisme deux soupapes identiques ou jumelles,
• les figures 5A et 5B sont des vues en coupe, respectivement selon les lignes BB' et AA' des figures 5B et 5A, d'une troisième forme de réalisation de l'invention, dans laquelle deux arbres coaxiaux portent deux cames par cylindre destinées à actionner en synchronisme deux soupapes identiques ou jumelles, par l'intermédiaire d'un palonnier,
• la figure 6 est une vue en coupe d'une quatrième forme de réalisation de l'invention.

The invention will be better understood and other details, features and advantages of the invention will become apparent on reading the following description given by way of non-limiting example with reference to the accompanying drawings in which:

• the figure 1 is a schematic view of a single valve control device, according to a first embodiment of the invention, in which the valve is actuated by two parallel camshafts carrying identical inverted opening and closing cams. ,
• the Figures 2A to 2E are views schematically illustrating the various steps of an operating cycle of the control device of the figure 1 ,
• the figure 3 is a diagram illustrating the volumes discharged by the opening and closing pistons, the volume absorbed by the piston of the valve, and by the shuttle piston, as a function of the angular position of the cams, for several angular offsets of the cams. opening and closing,
• the Figures 4A and 4B are cross-sectional views respectively along lines BB 'and AA' of Figures 4B and 4A a second embodiment of the invention in which two coaxial shafts carry three cams per cylinder for synchronously actuating two identical or twin valves,
• the Figures 5A and 5B are cross-sectional views respectively along lines BB 'and AA' of Figures 5B and 5A of a third embodiment of the invention, in which two coaxial shafts bear two cams per cylinder intended to synchronously actuate two identical or twin valves, via a spreader,
• the figure 6 is a sectional view of a fourth embodiment of the invention.

We now refer to the figure 1 which represents a first embodiment of a control device according to the invention, mounted on the cylinder head 1 of an internal combustion engine.

The cylinder head 1 is conventionally equipped with at least one valve 2, for example an intake valve, comprising a head 3 held in abutment on a sealing seat 4 of the cylinder head 1, by a return spring 5. The valve 2 further comprises a rod 6 opposite to the head 3, supporting a cup 7 of support of one end of the return spring 5. The other end of the return spring is for example directly on the yoke 1.

The device according to the invention comprises a body 8 fixed on the yoke 1, for example by screwing, and surrounding a cavity 9 communicating with the outside through four orthogonal cylinders 10, 11, 12, 13.

A piston Ps is fixed to the free end of the rod 6 of the valve 2 and is slidably mounted in the first cylinder 10 of the body 8.

The piston Ps is movable between a top dead center ( figure 1 ) for which the valve 2 is closed, that is to say rests on its seat 4, and a bottom dead point, for which the valve 2 is open at its maximum adjustable lift, that is to say is peeled of the seat 4.

The pistons P1, P2 and Pa, respectively called the opening piston, the closing piston and the shuttle piston, are slidably mounted respectively in the cylinders 11, 12 and 13 of the cavity 9.

The pistons P1, P2, Pa and Ps delimit a portion of the cavity 9, filled with a substantially constant volume of incompressible fluid, such as oil, and whose sealing is ensured by the pistons P1, P2, Pa and Ps. The volume of fluid in the cavity 9 is the reference volume defined above, which does not evolve in operation, with the exception of possible leaks that can be compensated, as will be better described later.

In this example, the pistons P1 and P2 are coaxial, as are the pistons Pa and Ps. The pistons P1 and P2 are furthermore oriented perpendicular to the pistons Pa and Ps.

The piston Pa has an outer end 14, that is to say opposite to the cavity 9, comprising a flange 15 adapted to abut against an outer face 16 of the body 8 (internal abutment). The outer end 14 of the piston Pa is also able to bear against an external fixed stop 17 (external stop). The piston Pa is thus movable between its internal and external stops, a return spring 18 tending to push the shuttle piston Pa towards its internal stop.

The shuttle piston Pa is movable between a top dead center, defined by the internal stop, and a bottom dead point, defined by the outer stop.

The piston P1 is actuated by an opening cam C1, driven in rotation about an axis 19, by a first shaft (not shown).

The piston P2 is actuated by a closure cam C2, driven in rotation about an axis 20, by a second shaft (not shown), synchronous and parallel to the first shaft and perpendicular to the section plane of the figure 1 . The axes 19, 20 intersect the common axis of the pistons P1 and P2. The direction of rotation of the cams C1, C2 is represented by arrows at the figure 1 and corresponds to the counterclockwise direction in this figure.

The device according to the invention further comprises phase shift means (not shown) of the second shaft relative to the first shaft, or vice versa.

In this way, it is possible to adjust in operation the angular position of the closure cam C2 relative to the opening cam C1, or vice versa.

In the embodiment of the Figures 1 to 3 , the second shaft (and thus the closure cam C2) can be advanced in operation relative to the first shaft (and therefore with respect to the opening cam C1) up to a maximum phase shift angle.

The outer ends of the pistons P1 and P2 comprise flanges 21, 22 cooperating with torsion springs 23, 24 mounted around fixed pins 25, 26 and tending to move the pistons P1 and P2 towards the outside of the cavity, c ' that is, towards their bottom dead center, so that the outer ends of the pistons P1 and P2 respectively bear on the opening cam C1 and closure C2, by means of rockers 27, 28 pivoting about fixed axes 29, 30 to avoid radial forces on the pistons P1 and P2.

The opening C1 and closure C2 cams each comprise a base circle arc C11, C21 centered on the axis of rotation 19, 20 of each cam C1, C2 and a single lobe whose profile is constituted by a rising ramp C12, C22 making it possible to move the corresponding piston P1, P2 from its bottom dead center to its top dead center, followed by a second circular arc C13, C23 concentric with the base circle C11, C21 and of larger diameter than this one, to immobilize the opening pistons P1 and closing P2 at their top dead center, followed by a downward ramp C14, C24 to bring the opening pistons P1 and closing P2 to their neutral position low. The angular aperture α11 of the basic circular arc C11 of the opening cam C1 is at least equal to the angular aperture α22 of the rising ramp C22 of the closing cam C2, increased by the phase angle maximum between the first and second trees. In addition, the angular aperture α21 of the basic circular arc C21 of the closing cam C2 is at least equal to the angular aperture α14 of the descending ramp C14 of the aperture cam C1 increased by the angle maximum phase shift. The profile of each of the cams C1, C2 is continuous.

The rising ramp C12 of the opening cam C1 and the downward ramp C24 of the closing cam C2 are so-called fast ramps. The rising ramp C22 of the closing cam C2 and the descending ramp C14 of the opening cam C1 are so-called slow ramps.

The angular aperture α12, α24 of the fast ramps C12, C24 is smaller than the angular aperture α14, α22 of the slow ramps C14, C22

The opening C1 and closure C2 cams are reversed in that the fast ramp C24 of the closing cam C2 is descending when the fast ramp C12 of the opening cam C1 is rising, and that the slow ramp C22 of the closure cam C2 is rising when the slow ramp C14 of the opening cam C1 is descending.

The angular aperture α13, α23 of the second circular arcs C13, C23 is equal to that α12, α24 of the fast ramps C12, C24, in order to be able to reach the maximum lifting of the valve 2 of which the device is capable.

The pistons P1 and P2 are identical and each move the same volume as the piston Pa between their bottom dead point and their top dead center. This volume is called common cylinder capacity. The stroke and the diameter of the piston Pa may be different from those of the pistons P1 and P2 to optimize the return spring 18 which generates in the cavity 9 a much lower pressure than that generated by the spring 5 of the valve 2, taking into account the the low inertia of the piston Pa and the slowness of the ramps C14 and C22.

The return springs 18, 5 of the shuttle piston Pa and the valve 2 are such that the pressure of the fluid necessary for the displacement of the shuttle piston Pa to its bottom dead point is less than the pressure required to open the valve 2.

The device according to the invention also comprises means of recalibration of the fluid reference volume in the cavity 9, comprising a supply conduit 32 in incompressible fluid equipped with a nonreturn valve 33 and connecting a source 34 of fluid under pressure at the cavity 9 (see Figures 4A and 5A ). The fluid pressure from the supply duct 32 is insufficient to move the piston Pa. Such recalibration means are known from the document WO 02/48510 , in the name of the Applicant.

We now refer to Figures 2A to 2E which represent the different stages of the operation of the control device of the figure 1 during the duration of a cycle performed by a complete rotation of the cams C1 and C2. The cycle is represented for an intermediate phase shift cams C1 and C2, corresponding to an intermediate maximum lift of the valve 2 (see for example the curve 5 at the figure 3 ).

The Figure 2A represents the device at the end of the recalibration phase of the fluid reference volume in the cavity 9, via the aforementioned recalibration means. In this position, the pistons P1 and P2 are at the bottom dead center on the base circle C11, C21 of the cams C1 and C2, the pistons Ps and Pa being at high dead point under the action of the return springs 5 and 18. During this rest phase, the rotation of the cams C1, C2 thus produces no movement of the pistons and the hydraulic fluid in the cavity 9.

The Figure 2B represents the device during the second phase of the cycle, called the arming phase, where the piston P1 remains stationary at its bottom dead point on the base circle C11 of the cam C1 when the piston P2, on the slow rising ramp C22 of the C2 cam drives into the cavity 9 a first common cylinder of fluid that pushes the shuttle piston Pa, the latter passing from its top dead center to its bottom dead stop by raising the pressure in the cavity 9 to compress the return spring 18 Pa piston.

The Figure 2C represents the device at the end of the third phase of the cycle, said opening of the valve 2, where the valve 2 reaches its maximum lift, when the piston P1, on the fast ramp C12 of the cam C1, pushes in the cavity 9 a second common cylinder of fluid and that the piston P2 on the rapid descending ramp C24 of the cam C2 sucks a fraction of the volume discharged by P1 to limit the volume of fluid that pushes the piston Ps and to reduce the maximum lift of the valve 2 reached when the remaining volume to be discharged by the piston P1 is equal to the volume already sucked by the piston P2.

The 2D figure represents the device at the end of the fourth phase of the so-called closing cycle of the valve 2, where the piston P1 is immobilized at its top dead center on the second circular arc C13 of the cam C1 when the piston P2, on the C24 fast descending ramp of the C2 cam sucks the fluid discharged by the piston Ps under the action of the return spring 5 which closes the valve 2.

The figure 2E represents the device during the fifth phase of the disarming cycle, where the valve 2 has fallen back on its seat 4 and the piston Ps has found its top dead center, where the piston P2 has found its low dead point and where the piston P1 on the slow descending ramp C14 of the cam C1 sucks the common cylinder discharged by the piston Pa under the action of its return spring 18 to disarm the device and return to the position of the Figure 2A from which a new cycle can be approached.

We now refer to the figure 3 which shows an operating diagram of the device of the figure 1 whose abscissae represent the angle of rotation of the cams C1, C2 between the beginning and the end of a cycle, whose positive ordinates represent the volume of fluid discharged by the piston P1 (bold line), the volume of fluid discharged by the piston P2 (thin line) and the volume of fluid absorbed by the piston Ps of the valve 2 (dotted), and whose negative ordinate represents the volume of fluid absorbed by the shuttle piston Pa. The curves numbered 1 to 7 correspond to seven successive phase shifts between the shafts, the first curve 1 corresponding to a zero angle where the valve 2 is wide open and the last curve 7 corresponds to a phase shift of 50 degrees, for which the valve 2 no longer opens.

The dotted curves thus also illustrate the lifting laws of the valve 2 for the seven phase shifts. It is recalled that the lifting of a valve 2 is the distance between the range of its head 3 and the seat 4 of the cylinder head 1.

Note that the aforementioned control device allows, in operation and by adjusting the phase shift between the two shafts, to adjust the maximum lift of the valve 2 and, simultaneously, to shift the closing angle of the valve 2 so as to adjust the duration angular opening of the valve 2 and, if necessary, to keep the valve 2 closed for the duration of a cycle.

In the case of figure 3 , the relative angular setting of the shafts is defined in such a way that, for a zero phase shift angle (curve 1), the closure piston P2 leaves its top dead center at the same time that the opening piston P1 reaches its own, so that the maximum lifting of the valve 2 which is capable of the device is reached for a single angle of the cycle.

In a variant not shown, it is possible to define the relative angular setting of the shafts such that, for a zero phase angle between the first and second shafts, the closing piston P2 leaves its top dead center after the piston opening P1 has reached its own, so as to create an adjustable angular period of the cycle when the valve 2 is stationary at its maximum lift between its opening and closing phases.

In another variant, the device may comprise means for erasing the abutment 17 of the bottom dead center of the shuttle piston Pa (shown schematically in FIG. figure 1 by an arrow 56), so that the piston Pa can suck the algebraic sum of the volumes of fluid discharged by the opening piston P1 and the closing piston P2, in order to prevent the arming of the device whatsoever the phase shift angle between the opening shaft and the closing shaft.

The Figures 4A and 4B illustrate a control device according to a second embodiment of the invention, for the synchronous actuation of two identical or twin valves 2a, 2b, via three cams C1a, C1b and C2, so as to ensure a hydraulic symmetry of the device.

In this embodiment, the twin valves 2a, 2b have parallel axes and are actuated by two coaxial shafts 35, 36, whose axis is in the plane of the axes of the valves 2a, 2b and perpendicular to said axes, respectively carrying two cams of openings C1a, C1b a closure cam C2.

The cams of openings C1a, C1b are arranged symmetrically on either side of the closure cam C2. The identical profiles of the cams C1 a, C1b and that of the cam C2 are similar to those described above.

The body 8 has a cavity 9 and a plane of symmetry BB '. The cavity 9 opens outwards by six cylinders, respectively two parallel symmetrical cylinders 10a, 10b parallel to which slide two pistons Psa, Psb fixed on the free ends of the stems of the valves 2a, 2b, two other symmetrical cylinders 11a, 11b parallel to each other , where two opening pistons P1a, P1b slide, a first central cylinder 12 in which slides a closing piston P2, and a second perpendicular central cylinder 13 in which a shuttle piston Pa slides.

The pistons Psa, Psb of the valves 2a, 2b, the opening pistons P1a, P1b and the closing piston P2 are parallel to each other. The shuttle piston Pa is orthogonal to the aforementioned pistons Psa, Psb, P1a, P1b, P2.

The axis of the closing piston P2 and the axis of the shuttle piston Pa are located in the plane of symmetry BB 'of the body 8.

As before, the shuttle piston Pa is movable between inner and outer stops 16 and 17 respectively defining its top and bottom dead spots, a return spring 18 tending to push it towards its internal abutment 16.

The return springs 18, 5a, 5b of the shuttle piston Pa and the valves 2a, 2b are such that the pressure of the fluid necessary for the displacement of the shuttle piston Pa to its bottom dead point is less than the pressure required to open the any of the valves 2a, 2b.

The two opening cams C1a, C1b are identical, as are the two opening pistons P1a, P1b, that the two valve pistons Psa, Psb, that the two valves 2a, 2b and that the springs of recall 5a, 5b. The control device is thus symmetrical with respect to the plane BB '.

As before, each valve 2a, 2b comprises a head 3a, 3b intended to rest on a seat 4a, 4b of a yoke 4 on which is fixed the body 8, for example by screwing.

Each cam C1a, C1b, C2 actuates the corresponding piston P1a, P1b, P2 via a pawl 27a, 27b, 28, pivoting about an axis 29a, 29b 30. The opening pistons P1 a, P1 b and P2 closing are maintained in contact with the latches 27a, 27b, 28, and the latches 27a, 27b, 28 are maintained in contact with the cams C1a, C1b, C2, through the springs of recall 23a, 23b, 24 tending to move the pistons P1a, P1b, P2 to their bottom dead center.

The closing cam C2 is integral with the internal shaft 36, the latter being coupled to the coaxial outer shaft 35 carrying the opening cams C1a, C1b, via a not shown phase shifter. Such a phase-shifter is well known from the state of the art and will not be detailed here.

The closing cam C2 is secured to the internal shaft 36 by a pin 37 which passes through the outer shaft 35 by two oblong slots 38 allowing the desired phase variation.

The volume displaced by the closing piston P2 and the shuttle piston Pa is equal to twice the volume displaced by each opening piston P1a, P1b.

As before, the cavity 9 also communicates with a fluid source 34 under pressure via a duct 32 equipped with a unidirectional valve 33 oriented in the plane of symmetry BB '.

Since the device is rigorously symmetrical relative to the plane BB ', the opening and closing flows of the twin valves 2a, 2b run on identical hydraulic paths, which guarantees the synchronism of the valves 2a, 2b provided that their return springs 5a , 5b are perfectly identical.

The control device is housed inside a camshaft support 50 fixed on the yoke 1, for example by screwing.

The operation of such a control device is similar to that described with reference to Figures 1 to 3 .

A control device according to a third embodiment is shown in FIGS. Figures 5A and 5B . This aims to mechanically ensure the synchronism of two twin valves 2a, 2b whose return springs 5a, 5b are not perfectly identical, from an asymmetrical hydraulic circuit activated by two cams only.

In this embodiment, the twin valves 2a, 2b have parallel axes and are actuated, via a spreader 39, by two coaxial shafts, respectively external 35 and internal 36, respectively carrying an opening cam C1 and a closing cam C2. The profiles of the cams C1, C2 are similar or identical to those described above.

The body 8 has a cavity 9 and a plane of symmetry BB '. The cavity 9 opens outwards by four cylinders, respectively a cylinder 10 which slides a piston Ps formed by a part of the spreader bar 39 ( Figure 5B ), a cylinder 11 in which slides an opening piston P1, a cylinder 12 in which a closing piston P2 slides, and a cylinder 13 in which a shuttle piston Pa slides. The opening piston P1, the closing piston P2 are parallel. between them. The shuttle piston Pa is, for example, orthogonal to the aforementioned pistons P1, P2, Ps.

The shuttle piston Pa and the piston Ps of the spreader bar 39 have their axes in the plane of symmetry BB 'of the body 8. The opening pistons P1 and P2 closing pistons are identical and are arranged on either side of the plane of symmetry BB 'of the body 8.

As before, the shuttle piston Pa is movable between two stops, respectively defining its top and bottom dead spots, a return spring 18 tending to push it towards its top dead center.

More particularly, the shuttle piston Pa is formed of two parts 40, 41 assembled to each other, for example by screwing, a first part 40 comprising a flange 42 intended to abut against an internal sealing seat 43 of the cylinder 13, so as to define the bottom dead stop and limit leakage, a second portion 41 having a flange 44 intended to abut against an outer wall 45 of the body 8, so as to define the stop point dead high.

The return springs 18, 5a, 5b of the shuttle piston Pa and the valves 2a, 2b are such that the pressure of the fluid necessary for the displacement of the shuttle piston Pa to its bottom dead point is less than the pressure required to open the valves 2a, 2b.

As before, each valve 2a, 2b comprises a head 3a, 3b intended to rest on a seat 4a 4b of a yoke 1 on which is fixed the body 8, for example by screwing.

The free ends of the rods of the valves 2a, 2b each bear on a flange 46a, 46b of the spreader 39. More particularly, the spreader 39 has a central portion intended to form the piston Ps mounted in the cylinder 10 of the body 8, and two symmetrical wings 46a, 46b extending laterally on either side of the central portion. The movement of the spreader 39 thus causes the synchronous movement of the twin valves 2a, 2b, even if the return springs 5a, 5b of said valves 2a, 2b are not perfectly identical.

Each cam C1, C2 actuates the corresponding piston P1, P2 through an articulated roller rocker arm. Each rocker arm has an arm 47 pivoting about a fixed axis 49 and carrying the axis 51 of a roller 48 in contact with the cam.

Each rocker arm further comprises a clevis articulated on the axis 51 of the roller 48, comprising two lateral branches 52 extending on either side of the roller 48 and traversed by the shaft 51, and a central branch 53, solidarizing the lateral branches 52, and carrying a rod the end comprises a sphere 54 trapped in a complementary spherical housing 55 formed in the corresponding piston P1, P2, so as to form a ball joint connection between the yoke and the corresponding piston P1, P2.

The rollers 48 are held in contact with the cams C1, C2, by means of return springs, not shown.

The inner shaft 36 is coupled to the coaxial outer shaft via a not shown phase shifter.

The closure cam C2 is secured to the internal shaft 36 by a pin 37 which passes through the outer tube 35 by two oblong slots allowing the desired phase variation.

The volumes displaced by the opening piston P1, the closing piston P2 and the shuttle piston Pa are equal to each other.

As previously, the cavity 9 also communicates with a source of fluid 34 under pressure, via a duct 32 equipped with a unidirectional valve 33.

As before, the control device is housed inside a camshaft support 50 fixed on the yoke 1, for example by screwing.

The operation of such a control device is similar to that described with reference to Figures 1 to 3 .

• les soupapes jumelles 2a, 2b ont forcément des axes parallèles et des courses identiques;
• une seule des deux soupapes 2a, 2b bénéficie de l'annulation hydraulique du jeu de fonctionnement, l'autre ne venant pas au contact de son siège si la géométrie n'est pas parfaite.

This simple embodiment where the twin valves 2a, 2b are actuated by a mechanical lifter 39 nevertheless has the following drawbacks:

• the twin valves 2a, 2b necessarily have parallel axes and identical strokes;
• only one of the two valves 2a, 2b benefits from the hydraulic cancellation of the operating clearance, the other not coming into contact with its seat if the geometry is not perfect.

• d'annuler le jeu de fonctionnement des deux soupapes jumelles 2a, 2b, d'actionner des soupapes jumelles 2a, 2b dont les axes ne sont pas parallèles,
• d'actionner des soupapes jumelles 2a, 2b dont les levées ne sont pas égales.

To overcome these drawbacks, the mechanical lifter 39 can be advantageously replaced by a hydraulic lifter whose principle is schematized on the figure 6 . The hydraulic lifter aims at:

• to cancel the operating clearance of the two twin valves 2a, 2b, to actuate twin valves 2a, 2b whose axes are not parallel,
• to operate twin valves 2a, 2b whose lifts are not equal.

To simplify the presentation, figure 6 represents two parallel twin valves 2a, 2b whose lifts are equal.

A control device according to this fourth embodiment shown in FIG. figure 6 is identical to the previous one to the cylinder 10 where the piston Ps slides. In this new embodiment, the body 8 comprises an additional non-deformable hydraulic cavity 57 communicating with the cavity 9 via the cylinder 10 and communicating with the outside via a cylinder 58a, of axis parallel to the cylinder 10, and preferably coaxial with the cylinder 10, and via a cylinder 58b which is not necessarily parallel to the cylinder 58a. A piston Ps slides in the cylinder 10 and is integral with a piston Psa, of smaller diameter (half section in the figure), which slides in the cylinder 58a and is integral and parallel to the valve stem 2a. A piston Psb of any section (half section of Ps on the figure 6 ) integral and parallel to the valve stem 2b slides in the cylinder 58b. The cavity 57 closed by the pistons Ps, Psa, Psb contains a constant volume of hydraulic fluid equal to its volume when the valves 2a and 2b rest on their seats in the closed position. To compensate for leaks, the cavity 57 communicates with the pressure source 34 via a nonreturn valve 33a. In this embodiment, the piston Ps activates the valve 2a via the piston Psa, the assembly being mechanically secured and therefore having the same stroke. The operating clearance of the valve 2a is canceled by the valve 33. At the same time, the piston Ps delivers a volume of oil proportional to the difference in section between the pistons Ps in the cavity 57. and Psa which is absorbed by the displacement of the piston Psb which actuates the valve 2b. The operating clearance of the valve 2b is canceled by the valve 33a. This embodiment allows the piston Ps to move the valves 2a and 2b in synchronism with different lifts and non-parallel axes of movement. The lifting of the valve 2b is equal to that of the valve 2a multiplied by the ratio between the section difference Ps-Psa and the section Psb.

Claims (15)

1. A control device for actuating at least one valve (2), e.g. for a reciprocating engine, the valve being driven with reciprocating motion in rectilinear translation to open or close an orifice having a sealing seat (4), said valve (2) including resilient return means (5) urging it towards a closed position, said device comprising a body (8) including a non-deformable cavity (9) communicating exclusively with the outside via at least four rectilinear cylinders (10, 11, 12, 13) that are closed respectively by four pistons (P1, P2, Pa, Ps), each of which is movable in reciprocating motion between a respective bottom dead-center remote from the inside of the cavity (9) and a top dead-center close to the inside of the cavity (9), the device being characterized in that said pistons comprise a piston (Ps) mechanically connected to the valve (2) and opposing its return means (5), an opening piston (P1) actuated by an opening cam (C1) that is driven in rotation by a first shaft, a closing piston (P2) actuated by a closing cam (C2) that is driven in rotation by a second shaft that rotates synchronously with the first shaft and that may be offset in operation relative to the first shaft through an adjustable angle, and a shuttle piston (Pa) movable between a first stationary abutment (17) defining its bottom dead-center and a second stationary abutment (16) defining its top dead-center, the shuttle piston (Pa) being urged towards its top dead-center by resilient means (18), in that the portion of the cavity (9) that extends between the pistons (P1, P2, Pa, Ps) is filled with a constant reference volume of substantially incompressible hydraulic fluid that is defined when the valve (2) rests against its seat (4), when the opening and closing pistons (P1, P2) are at their bottom dead-centers, and when the shuttle piston (Pa) is at its top dead-center, in that the opening piston (P1), the closing piston (P2), and the shuttle piston (Pa) have a common cylinder capacity and move the same volume of fluid between their bottom and top dead-centers and in that the resilient return means (18, 5) of the shuttle piston (Pa) and of the valve (2) are such that the fluid pressure needed for moving the shuttle piston (Pa) to its bottom dead-center is less than the pressure needed for opening the valve (2).
2. A control device according to claim 1, characterized in that the second shaft may be advanced in operation relative to the first shaft up to a maximum phase-shift angle, the opening and closing cams (C1, C2) each comprising a base circular arc (C11, C21) and a single lobe of profile that is constituted by a rising ramp (C12, C22) enabling the corresponding piston (P1, P2) to be moved from its bottom dead-center to its top dead-center, followed by a second circular arc (C13, C23) concentric with the base circle (C11, C21) and of greater diameter, enabling the opening and closing pistons (P1, P2) to be held stationary in their top dead-centers, followed by a descending ramp (C14, C24) enabling the opening and closing pistons (P1, P2) to be returned towards their bottom dead-centers, the central angle (α11) of the base circular arc (C11) of the opening cam (C1) being not less than the central angle (α22) of the rising ramp (C22) of the closing cam (C2) plus the maximum phase-shift angle, the central angle (α21) of the base circular arc (C21) of the closing cam (C2) being not less than the central angle (α14) of the descending ramp (C14) of the opening cam (C1) plus the maximum phase-shift angle.
3. A control device according to claim 2, characterized in that, over the entire phase-shift range, the relative angular setting of the first and second shafts is such that the opening piston (P1) leaves its bottom dead-center under the action of the rising ramp (C12) of the opening cam (C1) after the shuttle piston (Pa) has reached its top dead-center under the action of the rising ramp (C22) of the closing cam (C2), and such that the closing piston (P2) reaches its bottom dead-center under the action of the descending ramp (C24) of the closing cam (C2) before the opening piston (P1) leaves its top dead-center under the action of the descending ramp (C14) of the opening cam (C1).
4. A control device according to claim 3, characterized in that the relative angular setting of the shafts is defined in such a manner that, for a zero phase-shift angle between the first and second shafts, which angle corresponds to the maximum duration of valve opening, the closing piston (P2) leaves its top dead-center after the opening piston (P1) has reached its top dead-center, thereby creating an initial phase-shift range in which the valve (2) remains stationary for a certain length of time at its maximum lift between its opening and closing stages.
5. A control device according to claim 3, characterized in that the relative setting of the shafts is defined in such a manner that, for a zero phase-shift angle between the first and second shafts, the closing piston (P2) leaves its top dead-center before the opening piston (P1) reaches its top dead-center.
6. A control device according to any one of claims 2 to 5, characterized in that the maximum phase-shift angle of the closing cam (C2) relative to the opening cam (C1) is sufficient for the closing piston (P2) to leave its top dead-center before the opening piston (P1) leaves its bottom dead-center, and, at all times during the opening stage of the valve, for the volume of fluid sucked in by the closing piston (P2) from its top dead-center to be greater than the volume of fluid delivered by the opening piston (P1) from its bottom dead-center, such that the total flow delivered remains less than or equal to the common cylinder capacity, the valve (2) remaining closed throughout the duration of the cycle and the shuttle piston (Pa) leaving and returning to its bottom dead-center so as to keep the volume of the cavity at its reference value.
7. A control device according to any one of claims 1 to 6, characterized in that the angular duration of the opening of the valve (2) and its lift are adjusted in operation by modifying the phase-shift angle of the second shaft while not shifting the first shaft, or vice versa, or indeed while simultaneously modifying the phase-shift angle of each of the shafts relative to a crank shaft driving said shafts.
8. A control device according to any one of claims 1 to 7, characterized in that the profiles of the opening and closing cams (C1, C2) are such that a rest period exists during which the valve (2) is in its closed position, the shuttle piston (Pa) is at its top dead-center, and the opening and closing pistons (P1, P2) are at their bottom dead-centers, thereby enabling leaks from the cavity (9) to be compensated in order to recalibrate the reference volume of fluid via one-way communication (32, 33) with a source (34) of fluid at a pressure that is not sufficient to move the shuttle piston (Pa).
9. A control device according to any one of claims 1 to 8, characterized in that it controls a number N of identical valves (2) synchronously and has a number P of mutually synchronous opening pistons (P1) that are actuated by Q identical opening cams (C1), a number R of mutually synchronous closing pistons (P2) that are actuated by S identical closing cams (C2), and at least one shuttle piston (Pa), the total volume moved by the P opening pistons (P1) between their bottom dead-centers and their top dead-centers being identical to the total volume moved by the R closing pistons (P2) between their bottom dead-centers and their top dead-centers, and also being identical to the total volume moved by the shuttle piston(s) (Pa) between its(their) bottom and top dead-centers.
10. A set of two devices according to any one of claims 1 to 8, each for actuating a single valve (2), the set being characterized in that the devices share a single opening cam (C1) and a single closing cam (C2) in common, so as to ensure that said valves (2) are open and closed synchronously.
11. A device according to any one of claims 1 to 8, characterized in that it actuates at least two identical valves (2a, 2b) via a T-bar (39) or a synchronization rocker.
12. A control device according to any one of claims 1 to 8, characterized in that the body (8) includes an additional undeformable cavity (57) communicating with the cavity (9) via a first cylinder (10) and communicating with the outside via a second cylinder (58a) that is straight and of section smaller than the section of the first cylinder (10), being parallel thereto and facing the first cylinder (10), and via a third cylinder (58b) that is straight, the additional cavity (57) communicating in unidirectional manner with a source of fluid under pressure (34), and in that a first piston (Ps) slides in the first cylinder (10), a second piston (Psa) slides in the second cylinder (58a), the second piston (Psa) being connected to the first piston (Ps) and to a first valve (2a) of axis parallel to the first and second pistons (Ps, Psa), a third piston (Psb) slides in the third cylinder (58b), the third piston (Psb) being connected to a second valve (2b) of axis parallel to the third piston (Psb), and in that the additional cavity (57) contains a volume of substantially incompressible fluid that is equal to the volume of said additional cavity (57) when the first and second valves (2a, 2b) are resting on their seats in the closed positions of said valves (2a, 2b).
13. A control device according to any one of claims 1 to 12, characterized in that the first and second shafts (35, 36) are coaxial.
14. A control device according to any one of claims 1 to 12, characterized in that it includes means for retracting the first abutment (17) for the bottom dead-center of the shuttle piston (Pa) so that said piston (Pa) can suck in the algebraic sum of the volumes of fluid delivered by the opening piston (P1) and the closing piston (P2) so as to prevent the valve (2) from opening regardless of the phase-shift angle between the opening shaft and the closing shaft.
15. A method of operating a control device according to any one of claims 2 to 14, characterized in that at each revolution of the shafts it executes an opening and closing cycle of the valve (2), which cycle comprises successive steps starting from a rest position of the control device in which the valve (2) rests against its seat (4), in which the opening and closing pistons (P1, P2) are at their bottom dead-centers, and in which the shuttle piston (Pa) is at its top dead-center, the steps consisting in:

    moving the closing piston (P2) from its bottom dead-center to its top dead-center by means of the rising ramp (C22) of the closing cam (C2) so as to push the shuttle piston (Pa) from its top dead-center to its
    bottom dead-center in order to load the control device, the opening piston (P1) remaining at its bottom dead-center by means of the base circular arc (C11) of the opening cam (C1);

    • moving the opening piston (P1) by means of the rising ramp (C12) of the opening cam (C1) so as to begin to open the valve (2), the closing piston (P2) remaining at its top dead-center by means of the second circular arc (C23) of the closing cam (C2);

    • adjusting the lift and the duration of the opening of the valve (2) by shifting the phase of the closing cam (C2) relative to the opening cam (C1) so as to move the closing piston (P2) from its top dead-center by means of the descending ramp (C24) of the closing cam (C2) at any moment during the delivery stroke of the opening piston (P1) by means of the rising ramp (C12) of the opening cam (C1), before it reaches its top dead-center;

    • continuing to move the closing piston (P2) to its bottom dead-center by means of the descending ramp (C24) of the closing cam (C2) so as to close the valve (2), the opening piston (P1) remaining at its top dead-center by means of the second circular arc (C13) of the opening cam (C1) ; and

    • moving the opening piston (P1) towards its bottom dead-center by means of the descending ramp (C14) of the opening cam (C1), so as to move the shuttle piston (Pa) from its bottom dead-center to its top dead-center and unload the control device.

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