ANTI-SIPHON VALVE AND HYDRAULIC SYSTEM COMPRISING A CYLINDER ASSOCIATED WITH SUCH A VALVE

Abstract

The invention relates to a bidirectional anti-siphon valve (11) comprising a main conduit (12) equipped with a movable obturator within a range of motion (PD) which consecutively includes a first opening range (P1), a closing range (P0), and a second opening range (P2), for allowing fluid to pass in a first direction when the obturator is in the first opening range (P1) and in a second direction when the obturator is in the second opening range (P2), and return means (16) continuously tending to return the obturator to a median position located within the closing range (P0) so as to allow opening only when the obturator is subjected to a pressure difference greater than a threshold value. Figure 3

Description

Description Title of the invention: ANTI-SIPHON VALVE AND HYDRAULIC SYSTEM COMPRISING A CYLINDER ASSOCIATED WITH SUCH A SYSTEM FLAP Technical field

[0001] = The invention relates to an arrangement for reducing or even eliminating static leaks in a hydraulic system controlling a double-acting cylinder. It applies in particular to hydraulic control systems of aircraft engines such as turbojets, turboprops or other turbomachines, such as for example hydraulic control systems for variable pitch vanes, in which the fluid hydraulic used can be oil or fuel. STATE OF THE PRIOR ART

[0002] — As shown schematically in [Fig.1], a double-acting cylinder 1 comprises a body 2 in which a piston 3 slides separating this body 2 into a first chamber 4 and a second chamber 6, with a rod 7 passing through a end of body 2.

[0003] — The first chamber 4 is hydraulically supplied by a first conduit 8, and the second chamber 6 is supplied by a second conduit 9, which allows, to move the rod in one direction or the other by controlling the hy- pressures hydraulics in these conduits.

[0004] — As visible in [Fig.1], in operation, the crossing of the body 2 by the rod 7 necessarily having an imperfect seal, it includes a gap It sus- likely to cause leaks from the second chamber to the environment exterior. The seal between the piston and the body, which is also necessarily im- perfect, is symbolized in the figures by a gap I2 crossing the piston 3, and which represents the leaks flowing from the first chamber 4 to the second chamber 6 or vice versa.

[0005] …— On the other hand, the hydraulic circuit supplying conduits 8 and 9 also comprises leaks, particularly in its lower duct sections, i.e. located in lower part of the circuit.

[0006] Given the high pressures prevailing in the chambers, these leaks are compensated in operation by the hydraulic supply circuit: the oil leaking out of the cylinder is collected and / or drained out of the motor, and it is replaced and / or reinjected into the supply circuit.

[0007] These leaks are thus validly managed when the engine is in service, but it turns out that when the engine is stopped, they can cause the circuit to drain according to a phenomenon called siphoning. More particularly, and as illustrated in [Fig.2] where the cylinder extends vertically with its rod protruding from its upper part, when the engine is stopped, the pressure in the conduits and in the chambers gradually drops towards the ambient static pressure when the engine is stopped. Under these conditions, due to the hydraulic column constituted by the cylinder 1 whose chambers contain oil, the pressure is higher in the lower part of the hydraulic system than in its upper part. This situation thus allows the admission of air through gap I] then through gap I2, together with the leakage of oil via leakage portions of the lower part of the system, such as for example its lower pipes. In practice, this can lead, as illustrated schematically in [Fig.2], to emptying cylinder 1 of the oil it contains, which requires a checking and / or filling procedure prior to putting the engine back into service. The aim of the invention is to provide an anti-siphon valve arrangement to cancel or at least significantly limit static leaks, i.e. the siphoning phenomenon, in a system comprising a hydraulic circuit. Description of the invention To this end, the invention relates to a two-way anti-siphon valve comprising a main conduit equipped with a closure member movable in a displacement range which consecutively comprises a first opening range, a closing range and a second opening range, this valve being closed when the closure member is in the closing range, this valve being open for a first direction of fluid circulation when the closure member is in the first opening range and open for a second direction of fluid circulation when the closure member is in the second opening range, and return means tending continuously to return the closure member to a middle position situated in the closing range. With this arrangement, the valve provides a two-way anti-siphon function to prevent gravity siphoning of a hydraulic circuit when the circuit is stopped, while allowing hydraulic fluid to flow in both directions through this valve when the hydraulic system is in operation. The invention also relates to a valve thus defined, comprising a cylindrical sleeve surrounded by the main conduit, a piston sliding in this sleeve to form the movable closure member, means for guiding the piston to keep it in the axis of the cylindrical sleeve, and in which the return means are formed by an elastic element tending continuously to bring the piston back into the sleeve. The invention also relates to a valve thus defined, equipped with means for guiding the piston comprising an openwork tube extending an internal face of the sleeve on each side of this sleeve. The invention also relates to a valve thus defined, comprising a rod rigidly secured to the piston, and in which the guide means comprise a fixed sheath in which the rod slides. The invention also relates to a valve thus defined, comprising fixed stops limiting the extent of movement of the piston outside the sleeve. The invention also relates to a valve thus defined, in which the main duct comprises a bulge locally increasing its passage section, a flap extending into the main duct at the level of the bulge, this flap pivoting around an axis normal to the axis of the main duct to form the movable closure member, this flap closing the duct when it extends entirely into the bulge, and elastic return means tending continuously to bring the flap back into the middle range. The invention also relates to a valve thus defined, comprising return means comprising at least one elastic element having a fixed end connected to the main duct and its other end connected to the flap. The invention also relates to a hydraulic system comprising a double-acting cylinder supplied by conduits and comprising a valve thus defined equipping a conduit located in the lower part of this system. The invention also relates to an aircraft engine comprising variable-pitch blades powered by a hydraulic system thus defined. Brief description of the drawings [Fig.1] already described is a schematic representation of a double-acting cylinder control hydraulic system in operation; [Fig.2] already described is a schematic representation of a double-acting cylinder control hydraulic system at a standstill which is being emptied; [Fig.3] is a schematic view in longitudinal section of the valve according to the invention when its piston occupies a central closing position; [Fig.4] is a schematic view in longitudinal section of the valve according to the invention when its piston occupies a closing position offset towards the first opening range and resulting from a pressure difference below a threshold; [Fig.5] is a schematic view in longitudinal section of the valve according to the invention when its piston is located in the first opening range due to a pressure difference greater than the threshold; [Fig.6] is a schematic view in longitudinal section of the valve according to the invention when its piston occupies another closing position offset towards the second opening range and resulting from a pressure difference below a threshold; [Fig.7] is a schematic view in longitudinal section of the valve according to the invention when its piston is located in the second opening range due to a pressure difference greater than the predetermined threshold; [Fig.8] is a schematic view in longitudinal section of a first variant of the valve according to the invention when its piston occupies a median closing position; [Fig.9] is a schematic view in longitudinal section of a second variant of the valve according to the invention when its piston occupies a central closing position; [Fig.10] is a schematic view in longitudinal section of a third variant of the valve according to the invention when its piston occupies a central closing position; [Fig.11] is a schematic view in longitudinal section of a fourth variant of the valve according to the invention in the form of an angled conduit having improved compactness: [Fig.12] is a schematic view in longitudinal section of a second embodiment of the valve according to the invention when its flap occupies a central closing position; [Fig.13] is a schematic view in longitudinal section of a second embodiment of the valve according to the invention when its flap occupies a first closed position; [Fig.14] is a schematic view in longitudinal section of a second embodiment of the valve according to the invention when its flap occupies a median closing position; [Fig.15] is a schematic representation of a hydraulic system equipped with an anti-siphon valve according to the invention. DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS In [Fig. 3], the valve 11 according to the invention comprises a generally cylindrical main duct 12, in which is housed a cylindrical sleeve 13, the external diameter of which corresponds to the internal diameter of the duct 12, and the internal diameter of which is significantly smaller than that of the duct 12. This cylindrical sleeve 13 receives a piston 14 whose external diameter coincides with the internal diameter of the sleeve, and which is movable in translation along the axis of the sleeve 13 to be movable inside this sleeve 13 and outside this sleeve, on either side of it. More particularly, the piston 14 is movable in translation along an axis AX coinciding with the axis of the cylindrical main conduit 12 and of the sleeve 13 over a displacement range PD whose length is greater than that of the sleeve 13. This displacement range PD is broken down into a median closing range PO, a first opening range P1, and a second opening range P2, the first range P1 and the second range P2 extending on either side of the median range PO, along the axis AX, When the piston 14 occupies a position located in the middle range PO, as in [Fig.3], 4 or 6, it closes the sleeve 13, to close the valve 11 by preventing the passage of fluid through it, that is to say through the conduit 12. When the piston 14 occupies a position located in the first opening range PI or in the second opening range P2 as in the case of [Fig.5] or 7, it is located outside the sleeve 13, so that it allows the passage of hydraulic fluid in this sleeve, that is to say through the conduit 12. As visible in [Fig. 3], the valve comprises return means, here in the form of a spring 16 which continually tend to return the piston 14 to a median position located halfway along the length of the sleeve 13, i.e. halfway along the median range PO, to keep the valve closed. When the pressure is the same on both sides of the conduit 12, the piston 14 occupies the middle position, as in [Fig. 3]. When the valve 11 is subjected to a pressure difference, for example a higher pressure on the right side of the figures than the pressure on the left side, the piston 14 shifts to the left against the spring 16. If this pressure difference is less than a threshold value, the piston 14 is shifted to the left side while remaining within the middle range PO, i.e. in the sleeve 13 to keep it closed in order to keep the valve closed, which corresponds to the situation in [Fig.4]. If this difference is greater than a threshold value, the piston 14 shifts beyond the sleeve 13 to place itself in the first opening range P1, as in [Fig. 5]. In this case, the sleeve 13 is no longer closed by the piston, to allow the passage of fluid, so that the valve 11 is open to allow the circulation of hydraulic fluid in a first direction, namely right to left in the example of [Fig. 5]. Similarly, when the valve 11 is subjected to a pressure higher on the left side in the figures than the pressure on the right side, the piston 14 shifts to the right against the return spring 16. If this pressure difference is lower than a threshold value, the piston 14 remains in the middle range PO to close the sleeve 13 in order to keep the valve closed, as in [Fig.6]. If this pressure difference is greater than a threshold, the piston 14 moves beyond the sleeve 13 to place itself in the second opening range P2, as in [Fig.7]. The sleeve 13 is then no longer closed, so that the valve 11 is open to allow the passage of hydraulic fluid in a second direction, namely from left to right in the example of [Fig.7]. Thus, the valve according to the invention is bidirectional, but it only opens when the closure member is subjected to a pressure difference greater than a threshold value, thus allowing the piston to be placed outside the sleeve. The spring 16 has a stiffness chosen to allow the piston 14 to move outside the middle range PO when it experiences a pressure difference greater than a threshold value which is much lower than the pressure differences it experiences when the motor is in service, that is to say when the cylinder is hydraulically controlled. Under these conditions, the valve according to the invention allows normal operation when the cylinder is controlled, since the pressure differences it undergoes are then sufficient to open it by moving its piston 14 outside the closing range PO. When the engine is stopped, the pressures decrease sharply in the system to approach the surrounding atmospheric pressure, and the pressure differences that the piston can undergo are then limited to the hydrostatic pressure of the system, that is to say the weight of a column of hydraulic fluid of height corresponding to that of the hydraulic system. The spring 16 is sized to allow the displacement of the piston 14 outside the closing range PO when the pressure difference it experiences is greater than a threshold value which is expected to be greater than the hydrostatic pressure (and lower than the system operating pressures). In this respect, it should be noted that in practice one meter of oil column generates a hydrostatic pressure of one tenth of a bar, whereas the hydraulic supply pressure of a cylinder, for example in the aeronautical field, is a few tens of bars, or even a few hundred bars. Thus, when the engine is stopped, the valve is necessarily closed because the pressure difference experienced by the piston is necessarily less than the pressure difference at which the valve opens. It is therefore not possible for oil to circulate in the valve to flow towards a leak located downstream of it, so that this valve prevents the hydraulic system from being able to siphon itself during an engine shutdown phase. In the example of figures 3 to 7, the piston 14 slides in an openwork tube 17 which extends the cylindrical internal face of the sleeve 13, on each side of this sleeve 13. Thus, when the piston 14 leaves the middle range PO to be located in the first range P1 or in the second range P2, the hydraulic fluid passes through the valve 11 by circulating radially through the openings of this tube 17 after having passed through the sleeve 13. This tube 17 which extends the sleeve 13 on either side of the latter can be made up of two half-tubes each rigidly secured to one side of the sleeve. It may also be a tube inserted into the sleeve 13 protruding from its ends and the central portion of which is free of holes. The sleeve 13 and the tube 17 protruding from its ends may also be manufactured in a single piece. The openings of this perforated tube 17 may be holes, perforations, or bores, regularly distributed and having sufficient dimensions to allow circulation of the hydraulic fluid while introducing minimal pressure losses. The tube 17 may be made of a single piece enclosed externally by the sleeve 13, and protruding on either side of the latter. As can be seen in the example of [Fig.3], one of the ends of this tube 17 is terminated by a base 18 carrying a fixed sheath 19 which guides a rod 21 rigidly secured to the piston 14. This sheath 19 ensures guidance of the piston 14 along the axis AX of the sleeve 13, the rod 21 being able to pass through the base 18 when the piston is moved towards the base 18. Additionally, the valve 11 is equipped with fixed stops 22, 23 which delimit the displacement range PD to limit the stresses on the spring 16. In the example of Figures 3 to 7, these stops have the shape of flat crowns carried by the tube 17 while extending inside it. The stop 22 is located at the free end of the range P1 so that the piston 14 comes to bear on it when it is moved by a flow circulating from right to left in the figures. The stop 23 is located symmetrically, at the free end of the range P2 to receive the piston 14 when it is moved by a hydraulic flow circulating from left to right in the figures. In the example of figures 3 to 7, the piston 14 is guided by its rod 21 sliding in the sheath 19, but this guidance can also be ensured solely by the guidance provided by the tube 17 with the sleeve 13, as illustrated in the example of [Fig.8], which thus presents a simpler general structure than that of figures 3 to 7. Furthermore, in the examples of Figures 3 to 8, the stops 22 and 23 are carried by the tube 17, but these stops can also be carried by the rod 21 of the piston as in the example of [Fig.9]. In this case, when the piston 14 reaches one end of its displacement range PD, one or other of the stops 22 or 23 comes to bear against one or other of the ends of the sleeve 19. In another variant based on the embodiment of [Fig. 3], the valve 11 is devoid of an openwork tube 17, the piston 14 being guided solely by the sheath 19 which is then carried by a [bottom 18 in the form of an openwork wall carried directly by the main conduit 12, this other variant being shown in [Fig. 10]. In the examples of Figures 3 to 10, the main duct 12 of the valve 11 is a cylindrical duct which is rectilinear. To reduce the size, the duct 12 can also be a cylindrical duct in the form of a double elbow comprising a parallel inlet and outlet offset from each other and constituting a chicane between these two entrances. In this case, the constituent elements of the valve itself are located in the baffle portion of the duct, as illustrated in [Fig. 11], which itself constitutes a cylindrical duct which is oriented perpendicular to the parallel inlet and outlet of the valve. According to another embodiment illustrated in Figures 12 to 14, instead of being a piston, the closure member is a flap 24 movable in rotation around an axis AY normal to the axis AX of the main conduit 12 and offset relative to the latter. The axis AY of rotation of the flap 24 is then relatively close to the wall of the conduit 12. The flap 24 comprises, relative to its axis of rotation AY, a distal end 26 and a proximal end 28, the distance between the axis AY and the distal end 26 being preferably greater than twice the distance between the axis AY and the proximal end 28. The higher the ratio between these two distances, the greater the difference in hydrostatic pressure experienced by the flap 24 exerts a significant rotational torque on the flap. As illustrated in the figures, a return spring 16 having a movable end connected to the distal end 26, and a fixed end secured to an internal face of the conduit 12, and another return spring 16' is connected to the distal end 26 and to the internal face of the conduit 12, these two return springs being arranged symmetrically with respect to a plane normal to the axis AX and passing through the axis AY. These two return springs 16 and 16° continually tend to bring the shutter back into a plane normal to the axis AX so that it closes the conduit 12 so as to close the valve 11. Just as in the embodiment of figures 3 to 11, the closure member that constitutes the shutter 24 is movable according to a displacement range PD which comprises a central closing range PO and two opening ranges PI and P2 which extend on either side of the range PO. The flap 24 has a general shape of a flat wall with a circular outline of diameter substantially greater than the nominal diameter of the conduit 12 which is generally cylindrical. Additionally, the conduit 12 comprises, at the level of the flap 24, a bulge 27 which coincides with the central closing range PO, and the shape of which coincides with the surface swept by the edge of the flap 24 when the latter pivots around its axis AY in the range PO. Under these conditions, for any position of the flap 24 in the range PO, its outer edge is contiguous with the entire internal circumference of the bulge 27 of the duct 12, so as to close this duct so that the valve is closed. In other words, the valve is closed when the flap extends entirely into the region of the bulge 27. When the inclination of the shutter 24 places it in the first opening range PI, as in the situation of [Fig.13], the distal end 26 is then spaced from the internal face of the conduit to, on the contrary, open the valve 11 so as to allow a hydraulic fluid to pass, circulating from right to left in the situation of [Fig.13]. Symmetrically, when the inclination of the shutter places it in the second opening range P2, it allows the passage of fluid through the conduit 12, but in the opposite direction, that is to say from left to right in the figures. Thus, the valve 11 is open when its flap 24 extends partly outside the bulge 27, that is to say when its distal end 26 is located outside the bulge 27, while being inside the conduit 12. As will be understood, the operation of the valve of figures 12 to 14 is of the same type as that of the valve of figures 3 to 11, that is to say that its closure member is continually returned to a median closing position located in the PO range, and that it only opens the valve 11 when it leaves this PO range. It may be noted that in either of the two opening ranges P1 and P2, as the inclination of the flap approaches the direction of the axis AX of the duct 12, that is to say substantially the direction of flow, the rotational torque exerted on the flap by the effect of the flow of the fluid decreases. The flap stabilizes in the inclined position when this torque balances with that exerted by the elastic return system, in this case the system with two return springs 16 and 16'. Consequently, it is possible to dispense with stops limiting the movement of the flap. Advantageously, the sealing of the edge of the proximal end 28 of the flap can be improved, as illustrated in [Fig. 14], by providing on the internal face of the conduit 12 a curved wall 29 corresponding to the surface swept by the edge of the proximal end 28 when the flap is moved in the closing range PO. In the example which has been described in relation to figures 11 to 13, the conduit 12 is essentially cylindrical, but the invention applies by analogy to a conduit having a square, rectangular, ovoid, or other section. As regards the return springs 16 and 16°' shown schematically in the form of helical springs in figures 11 to 13, they can be replaced by one or more spiral springs centered on the axis AY, by leaf type springs, or by any type of elastic return means. Furthermore, it is possible to provide for a pivoting rod materially forming the axis AY of rotation of the shutter to pass through the wall of the duct 12 in a sealed manner, to allow a lever arm secured to this rod to be arranged outside the duct 12. It is then possible to provide an elastic return system entirely located outside the duct 12 and comprising at least one return spring connecting the lever arm to at least one fixed point relative to the duct. Such an arrangement can facilitate the assembly and calibration of this elastic return system, as well as its replacement if necessary. As will be understood, in the examples of figures 3 to 11, the valve comprises a single spring 16 which is stressed in tension or compression depending on the direction of movement of the piston 14. Just as in the embodiment of figures 12 to 14, it is possible to provide two return springs in the examples of figures 3 to 11, these two springs then being arranged symmetrically with respect to the piston 14. In the same way, the helical springs of figures 3 to 11 can be replaced by any other elastic return means adapted to return the piston 14 to its middle position. More generally, the invention makes it possible to constitute a two-way anti-siphon valve having a small footprint and a low mass, intended to equip a pipe located for example in the lower part of a hydraulic system. Such a hydraulic system is for example of the type of that of [Fig. 15], comprising a double-acting cylinder having two chambers 4 and 6 supplied via two conduits 8 and 9, and in which the valve 11 equips a conduit located in the lower part of the system, namely here the conduit 8 supplying the lower chamber of the cylinder. The invention thus applies advantageously to an aircraft engine equipped with a variable-pitch blade control system controlled hydraulically by means of a double-acting cylinder.

Claims

Claims

1. A two-way anti-siphon valve (11) comprising a main conduit (12) equipped with a movable closure member in a range of de- placement (PD) which consecutively includes a first range opening range (P1), a closing range (PO) and a second range opening (P2), this valve (11) being closed when the member shutter is in the closing range (PO), this valve being open for a first direction of fluid circulation when the organ shutter is in the first aperture range (P1) and open for a second direction of fluid circulation when the closure member is in the second opening range (P2), and return means (16,16') continually tending to bring the closure member back to a middle position located in the closing range (PO).

2. A valve according to claim 1, comprising a cylindrical sleeve (13) surrounded by the main conduit (12), a piston (14) sliding in this sleeve (13) to form the movable closure member, means piston guide (14) to keep it in the axis (AX) of the cylindrical sleeve (13), and in which the return means are formed by an elastic element (16) continually tending to bring back the piston (14) in the sleeve (13).

3. Valve according to claim 2, equipped with piston guiding means (14) comprising an openwork tube (17) extending an internal face of the sleeve (13) on each side of this sleeve (13).

4. Valve according to claim 2, comprising a rod (21) rigidly secured to the piston (14), and in which the guide means comprise a fixed sheath (19) in which the rod (21) slides.

5. Valve according to claim 2, comprising fixed stops (22, 23) limiting the extent of movement of the piston (14) out of the sleeve (13).

6. A valve according to claim 1, wherein the main conduit (12) has a bulge (27) locally increasing its section of passage, a flap (24) extending into the main duct (12) at the level of the bulge (27), this flap (24) pivoting around an axis (AY) normal to the axis (AX) of the main duct (12) to form the organ movable shutter, this shutter (24) closing the conduit (12) when it extends entirely into the bulge (27), and elastic means of reminder (16, 16°) continually tending to bring the shutter (24) back into the mid-range (PO).

7. Valve according to claim 6, comprising return means (16, 16') comprising at least one elastic element having a fixed end connected to the main duct (12) and its other end connected to the shutter (24).

8. 8. Hydraulic system comprising a double-acting cylinder (1) supplied by conduits (8, 9) and comprising a valve according to one of the res- previous indications equipping a conduit located in the lower part of this system.

9. Aircraft engine comprising powered variable pitch blades by a hydraulic system according to claim 8.