WO2021198572A1

WO2021198572A1 - Hydraulic piston with a depressurised recess

Info

Publication number: WO2021198572A1
Application number: PCT/FR2021/000028
Authority: WO
Inventors: Vianney Rabhi
Original assignee: Vianney Rabhi
Priority date: 2020-03-30
Filing date: 2021-03-18
Publication date: 2021-10-07
Also published as: FR3108690A1; KR20220160002A; JP2023519595A; FR3108690B1; CN115315576A; CA3171713A1; EP4127452A1; AU2021249497A1

Abstract

The hydraulic piston with a depressurised recess (1) may translate in a cylinder (2) and comprises a fixed skirt (3), an axial compression face (4) which forms a fluid chamber (5) with the cylinder (2), and an axial working face (6) which cooperates with the transmission means (7), the piston (1) also comprises sealing means (8), a depressurised radial recess (9) opening at the surface of the fixed skirt (3), an axial decompression duct (11) arranged inside the skirt (3) and which opens near the axial working face (6), and a radial decompression duct (12) which puts the depressurised radial recess (9) in communication with the axial decompression duct (11).

Description

Title of the invention: hydraulic piston with depressurized groove

[1] The present invention relates to a hydraulic piston with a depressurized groove in particular intended to receive the sealing device for a piston described in patent No. FR 3 009 037 published on January 29, 2016 and belonging to the applicant.

[2] The depressurized groove hydraulic piston according to the invention applies primarily to axial piston hydraulic pumps and motors, regardless of their maximum operating pressure. However, this does not exclude the application of said invention to any other type of pump or hydraulic motor comprising one or more pistons.

[3] It is known that the sealing device according to patent FR 3 009 037 is intended for a piston which moves in a cylinder, one of the ends of which is closed by a fluid chamber.

[4] In patent FR 3 009 037, it is noted that the piston which receives the sealing device has a piston head which comprises a fixed skirt. Said piston also comprises on the one hand, a piston bearing face to exert a force on the transmission means and on the other hand, a compression face which opens into the fluid chamber to receive the pressure of a fluid. .

[5] The sealing device according to patent FR 3 009 037 comprises in particular a sliding skirt of cylindrical shape which is housed with low clearance in the cylinder and which is placed in the extension of the piston head, on the side of the face. compression of said piston, and in the axis of said head.

[6] Still according to patent FR 3 009 037, the sliding skirt is connected to the piston head by a mechanical inter-skirt connection which allows said sliding skirt to move in longitudinal translation relative to said head.

[7] It is noted that the sealing device according to patent FR 3 009 037 also comprises a pressure transmission channel arranged inside the sliding skirt and passing through the latter right through in the axial direction.

[8] The sealing device according to patent FR 3 009 037 also comprises an extendable continuous segment of continuous annular shape, interposed between the fixed skirt and the sliding skirt, and comprising an internal cylindrical face of the segment subjected to the pressure of the fluid via the pressure transmission channel, an external cylindrical face of the segment able to come into contact with the cylinder, an axial face of the segment on the fixed skirt side maintained in sealed contact with the fixed skirt, and an axial face of a segment on the sliding skirt side maintained in sealed contact with the sliding skirt.

[9] Finally, the sealing device according to patent FR 3009037 comprises a sliding skirt spring which tends to bring the sliding skirt closer to the fixed skirt, and to axially compress the continuous extensible segment.

[10] The sealing device according to patent FR 3009037 makes it possible to ensure lasting tightness between the piston and the cylinder with which it cooperates. In fact, by inflating under the effect of the pressure, the expandable continuous segment comes into contact with the cylinder and prevents the hydraulic fluid contained in the fluid chamber from escaping from the latter, without said segment exerting any pressure. excessive pressure on said cylinder.

[11] The result of this particular configuration is excellent sealing of the hydraulic piston which receives said device without excessive friction losses and this, even if the hydraulic pump which receives said piston operates under high pressures of several hundred or even several thousand bars. .

[12] In practice, the sealing device according to patent FR 3 009 037 proves to be very effective, especially when it is implemented on guided hydraulic pistons such as those included in the hydraulic motor-pump. with fixed or variable displacement, the subject of patent WO2014 / 118477 published on August 04, 2015 and belonging to the applicant.

[13] However, for the continuous extendable segment of the sealing device according to patent FR 3 009 037 to function correctly it is necessary that, on the one hand, the sliding skirt forms a sufficient seal with the cylinder in which it is housed and that, on the other hand, the fixed skirt of the hydraulic piston which receives said device is sufficiently leaky.

[14] For indeed, to inflate and achieve the desired seal with the cylinder, the continuous extensible segment must be subjected to a sufficient radial pressure difference between its internal cylindrical face of the segment subjected to the pressure of fluid via the pressure transmission channel, and its segment outer cylindrical face which can come into contact with the cylinder. However, said difference arises from the gap in sealing between that produced by the sliding skirt, which must be high, and that produced by the fixed skirt, which must be low.

[15] If the sealing device according to patent FR 3009037 is implemented on the axial pistons of a conventional hydraulic pump or motor, unlike the fixed or variable displacement hydraulic pump motor object of patent WO2014 / 118477 which provides a guided hydraulic piston pusher, the fixed skirt of said axial pistons is responsible for orienting the latter in their cylinder while said skirt is subjected to significant radial forces.

[16] Indeed, in a pump or a conventional axial piston motor, the pistons are most often housed in a rotating barrel and are terminated by an articulated shoe which slides on an inclined or tilting plate depending on whether said pump or said motor is fixed or variable displacement.

[17] It follows from this particular configuration that each piston is subjected to high radial forces. Indeed, when the tilting plate is strongly inclined and a high pressure prevails in the fluid chamber, the articulated shoe that each said piston has exerts a high radial force on said plate. Said force in return produces equally high radial forces which are exerted by each said piston on the cylinder in which it moves.

[18] A first radial force appears between said piston and said cylinder at the end of said piston which is positioned opposite the articulated shoe, while a second radial force appears at the end of the cylinder which emerges in the direction of the inclined plateau.

[19] For the same pressure prevailing in the fluid chamber, the more the plate is inclined and the more the piston comes out of the rotating barrel, and the higher the two radial forces which have just been described are high.

[20] It is noted that the radial force exerted by the piston on the outlet of the cylinder is equal to the radial force exerted by the articulated shoe on the inclined plate increased by the radial force exerted on the cylinder l end of the piston opposite to said pad. [21] The forces which have just been described are the source of the difficulties encountered during the implementation of the sealing device according to patent No. FR 3009037 on conventional axial piston pumps and motors.

[22] In fact, in this particular context of application of said device, the fixed skirt of the hydraulic piston must firstly be sufficiently elusive to allow the extendable continuous segment to operate, and secondly, capable of ensuring contact. little energy dissipative between the piston and its cylinder despite the high radial forces produced between these two members, and more particularly, despite the high radial forces occurring at the outlet of the cylinder oriented towards the inclined plate.

[23] Because in fact, to make the fixed skirt sufficiently elusive, it is possible either to provide a large clearance between said skirt and the cylinder, or to provide axial decompression grooves on the surface of said skirt to cancel it. sealing as provided for in patent WO2017109329 entitled “cooling and lubrication system for a sealing device for a piston”, the application of which was published on June 29, 2017.

[24] But the arrangements which have just been described are not satisfactory, because whether it is one or the other, these two solutions increase the friction losses generated at the interface of the skirt. fixed and cylinder.

[25] Indeed, an increased clearance between the fixed skirt and the cylinder reduces the bearing surface of said skirt on said cylinder. As the contact between these parts is more punctual, more pressure is exerted on the oil film which becomes less bearing, less thick, and more viscous. The coefficient of friction between the fixed skirt and the cylinder is increased, as are the resulting energy losses.

[26] If, as an alternative, axial decompression grooves are provided on the surface of the fixed skirt, said grooves locally break the bearing capacity of the oil film. This also tends to increase the friction losses generated at the interface of said fixed skirt and the cylinder.

[27] The two strategies which have just been described therefore increase the friction losses and correspondingly reduce the total efficiency of any conventional hydraulic pump which receives the sealing device according to patent FR 3009037. This is particularly evident when said pump operates at high power, that is to say under high pressure and displacement.

[28] It is indeed noted that at low displacement, that is to say when the plate of said pump is slightly inclined and that the radial forces between the piston and the cylinder are low, the total energy efficiency of a hydraulic pump conventional equipped with the sealing device according to patent FR 3 009 037 is much higher than that of the same said pump not equipped with said device.

[29] However, if the displacement of said pump is close to its maximum, which implies that its plate is also inclined close to the maximum, the friction losses of said pump are increased to such an extent that the energy benefit provided by the device d sealing according to patent FR 3009037 is found to be greatly reduced, or even destroyed to the point of leaving room for a loss.

[30] It therefore emerges from tests and experience feedback that when the sealing device according to patent FR 3 009 037 equips the axial pistons of conventional hydraulic pumps and motors, the additional energy losses by friction that it induces at the The level of contact between said pistons and their cylinder are high at high displacement to the point of being able to annihilate the significant gains in efficiency provided at low displacement by said device.

[31] It is to eliminate the drawbacks which have just been described that the hydraulic piston with depressurized groove is provided according to the invention.

[32] Indeed, said piston according to the invention makes it possible to implement the sealing device according to patent FR 3 009 037 on the hydraulic pistons of any axial piston pump or motor on the one hand, by bringing together all the conditions necessary for the proper functioning of the extendable continuous segment, and on the other hand, by bringing back to a normal level the energy losses by friction of said pumps or motors when the latter operate at high displacement and high power.

[33] Thus, the hydraulic piston with depressurized groove according to the invention allows in particular:

• To produce hydraulic pumps and motors whose axial or radial pistons receive the sealing device according to patent FR 3009037 and the efficiency of which always remains at least greater than or equal to that of the same said pumps and motors not fitted with said device;

• To open up the sealing device market according to patent FR 3 009 037 to pumps and hydraulic motors with axial or radial pistons which would otherwise remain confined to devices whose pistons are not subjected to radial forces.

[34] In addition, the hydraulic piston with a depressurized groove according to the invention also allows, according to a particular embodiment:

• To simplify the manufacture, assembly, and adjustment of the sealing device according to patent FR 3009037 when the latter applies to pumps and hydraulic motors with conventional axial or radial pistons;

• To reduce the cost of manufacturing the sealing device according to patent FR 3009037 when the latter applies to pumps and hydraulic motors with conventional axial or radial pistons.

[35] The depressurized groove hydraulic piston according to the invention according to the invention is provided inexpensive to mass-produce, this to remain compatible with the economic constraints of most of the applications for which it is intended.

[36] It is understood that the hydraulic piston with a depressurized groove according to the invention can be applied, in addition to hydraulic pumps and motors with axial or radial pistons, to any piston of any hydraulic or pneumatic device which can advantageously receive the device. 'sealing according to patent FR 3009037, or which can receive, as an alternative to said device, one or more cutting segments or any other sealing means which only works correctly on the condition of being mounted on a piston whose skirt fixed is sufficiently elusive.

[37] The depressurized groove hydraulic piston according to the present invention can translate in a cylinder, the external cylindrical surface of said piston constituting a fixed skirt while one of the ends of said piston has an axial compression face which forms with the cylinder a fluid chamber of variable volume filled with a working fluid, while the other end of said piston has an axial working face which cooperates with transmission means, said piston comprising:

• Sealing means positioned in the vicinity of the axial compression face, on the fixed skirt or at the end of the latter, said means being able to come into contact with the cylinder;

• At least one depressurized radial groove opening out at the surface of the fixed skirt, said groove possibly being continuous or non-continuous;

• At least one axial decompression duct arranged inside the fixed skirt and opening out in the vicinity of the axial working face;

• At least one radial decompression duct which places the depressurized radial groove in communication with the axial decompression duct.

[38] The hydraulic piston with depressurized groove according to the present invention comprises at least one axial decompression groove which opens onto the surface of the fixed skirt and which places the sealing means in communication with the depressurized radial groove, said axial groove possibly being continuous or non-continuous.

[39] The hydraulic piston with depressurized groove according to the present invention comprises an axial decompression groove which is helical.

[40] The depressurized groove hydraulic piston according to the present invention comprises a fixed skirt which is hollow and which permanently and tightly accommodates a decompression sleeve, a radial space left between the interior of said skirt and the exterior of said skirt. sleeve forming at least part of the axial decompression duct.

[41] The depressurized groove hydraulic piston according to the present invention comprises a decompression sleeve which accommodates an internal sleeve lubrication duct which cooperates with an internal piston lubrication duct, the latter opening at the level of the axial working face or in the vicinity of the latter, this to convey part of the working fluid from the fluid chamber to the transmission means.

[42] The hydraulic piston with depressurized groove according to the present invention comprises sealing means which consist of: • At least one sliding skirt of cylindrical shape, housed with low clearance in the cylinder and placed in the extension and in the axis of the fixed skirt on the side of the axial compression face, said sliding skirt being connected to the fixed skirt by a mechanical inter-skirt connection which allows a displacement in longitudinal translation of said sliding skirt relative to the fixed skirt, the amplitude of said displacement being limited by a sliding skirt stop which is directly or indirectly secured to the mechanical inter-skirt connection ;

• At least one pressure transmission channel arranged inside the sliding skirt and passing right through the latter in the axial direction;

• At least one extensible continuous segment of continuous annular shape, interposed between the fixed skirt and the sliding skirt, and having an internal cylindrical face of the segment subjected to the pressure of the working fluid via the pressure transmission channel, an external cylindrical face of segment that can come into contact with the cylinder, an axial face of a segment on the fixed skirt side maintained directly or indirectly in sealed contact with the fixed skirt and an axial face of a segment on the sliding skirt side maintained directly or indirectly in sealed contact with the sliding skirt.

[43] The depressurized groove hydraulic piston according to the present invention comprises at least one sliding skirt spring which tends to bring the sliding skirt closer to the fixed skirt, and to axially compress the continuous extensible segment.

[44] The hydraulic piston with depressurized groove according to the present invention comprises a mechanical inter-skirt connection which consists of a double-threaded screw which has a first thread which is screwed into an internal thread made inside the fixed skirt. and which axially plates the decompression sleeve in said skirt by means of a screw shoulder, and a second thread onto which the sliding skirt stopper is screwed.

[45] The depressurized groove hydraulic piston according to the present invention comprises a sliding skirt spring which is housed in a spring basket which passes through all or part of the sliding skirt, the radial thickness of the latter being provided sufficiently small so that said skirt can accommodate said basket in its center, said basket having, on the one hand, an outer basket flap which bears on the sliding skirt, and on the other hand, an inner basket flap on which rests on one of the ends of the sliding skirt spring, the other end of the latter resting on a spring bearing shoulder arranged or attached to the mechanical inter-skirt connection.

[46] The depressurized groove hydraulic piston according to the present invention comprises an outer surface of the spring basket which has centering means which radially center said basket in the sliding skirt, while the axial orientation of said basket with respect to said skirt is ensured by the contact between the outer basket flap and said skirt.

[47] The depressurized groove hydraulic piston according to the present invention comprises a sliding skirt stop which can be supported either on the outer basket flap or on the inner basket flap.

[48] The hydraulic piston with depressurized groove according to the present invention comprises a mechanical inter-skirt connection which accommodates an internal lubricating connection duct which cooperates with an internal piston lubrication duct, the latter opening at the level of the axial face of the piston. work or in the vicinity of the latter, this to convey a part of the working fluid from the fluid chamber to the transmission means.

[49] The depressurized groove hydraulic piston according to the present invention comprises an axial length of the depressurized radial groove which is greater than the diameter of the radial decompression duct, so that said groove constitutes a reservoir of working fluid.

[50] The description which will follow with regard to the accompanying drawings and given by way of non-limiting examples will make it possible to better understand the invention, the characteristics that it has, and the advantages that it is likely to provide:

[51] [Fig. 1] is Figure 1 is a schematic sectional view of a variable displacement hydraulic pump equipped with depressurized groove hydraulic pistons according to the invention, said pistons being oriented axially.

[52] [Fig. 2] is a schematic sectional view of the hydraulic piston with a depressurized groove according to the invention, the sealing means of which consist of a segment with a section. [53] [Fig. 3] is a schematic sectional view of the hydraulic piston with depressurized groove according to the invention, a decompression sleeve being screwed directly into the fixed skirt to form with the latter part of the axial decompression duct, while the sealing means consist of a cut segment.

[54] [Fig. 4] is a schematic sectional view of the hydraulic piston with depressurized groove according to the invention, a decompression sleeve being fixed in the fixed skirt by means of a screw to form with said skirt part of the axial decompression duct, while the sealing means consist of a sectional segment.

[55] [Fig. 5] is a schematic sectional view of the hydraulic piston with depressurized groove according to the invention, a decompression sleeve being fixed in the fixed skirt by means of a double-threaded screw to form part of the axial duct with said skirt. decompression, while the sealing means consist of a continuous extensible segment held clamped between a sliding skirt and the fixed skirt by a sliding skirt spring.

[56] [Fig. 6] is a close schematic sectional view of the depressurized groove hydraulic piston according to the invention and according to its variant shown in Figure 5, which illustrates the operation of said piston when the working fluid is admitted into the fluid chamber.

[57] [Fig. 7] is a close schematic sectional view of the hydraulic piston with depressurized groove according to the invention and according to its variant shown in Figure 5, which illustrates the operation of said piston when the working fluid is forced out of the fluid chamber.

[58] [Fig. 8] is a three-dimensional view of the depressurized groove hydraulic piston according to the invention, the sealing means of which consist of an expandable continuous segment held clamped between a sliding skirt and the fixed skirt by a sliding skirt spring.

[59] [Fig. 9] is a cut-away three-dimensional view of the hydraulic piston with depressurized groove according to the invention and according to its variant shown in FIG. 8, which makes it possible in particular to distinguish a decompression sleeve fixed in the fixed skirt by means of a double screw net. [60] [Fig. 10] is an exploded three-dimensional view of the hydraulic piston with depressurized groove according to the invention and according to the variant shown in Figures 8 and 9, the different components which form said variant can be clearly distinguished.

[61] DESCRIPTION OF THE INVENTION:

[62] Figures 1 to 10 show the depressurized groove hydraulic piston 1 according to the invention, various details of its components, its variants, and its accessories.

[63] It can be seen, particularly in FIGS. 1 to 5, that the hydraulic piston with depressurized groove 1 according to the invention can translate in a cylinder 2, the external cylindrical surface of said piston 1 constituting a fixed skirt 3 while one of the ends of said piston 1 has an axial compression face 4 which forms with cylinder 2 a fluid chamber 5 of variable volume filled with a working fluid 23, while the other end of said piston 1 has an axial working face 6 which cooperates with transmission means 7.

[64] It is noted in Figures 1 to 10 that the hydraulic piston with depressurized groove 1 according to the invention comprises sealing means 8 positioned in the vicinity of the axial compression face 4. Said means 8 are arranged or housed either on the fixed skirt 3, or at the end of the latter.

[65] Note in Figures 1 to 7 that the sealing means 8 can come into contact with the cylinder 2 and be, for example and as shown in Figures 2 to 4, consist of a segment 38 housed in a throat known per se.

[66] Said means 8 can also consist of any other sealing device whose operation requires that the fixed skirt 3 is preferably leaky and non-sealed.

[67] It will be noted in Figures 1 to 10 that in Figures 1 to 10 that the hydraulic piston with depressurized groove 1 according to the invention comprises at least one radial depressurized groove 9 opening out at the surface of the fixed skirt 3, said groove 9 being able to be continuous or non-continuous. [68] It will also be noted that the depressurized radial groove 9 is positioned axially on the fixed skirt 3 so as to never be able to exit from the cylinder 2 whatever the axial position of said skirt 3 with respect to said cylinder 2.

[69] Particularly visible in Figures 1 to 7 and in Figure 9, it has been shown that the hydraulic piston with depressurized groove 1 according to the invention comprises at least one axial decompression duct 11 arranged inside the fixed skirt 3 and emerging in the vicinity of the axial working face 6.

[70] By way of example shown in FIG. 1, the axial decompression duct 11 can open out inside the pump casing 49 of a variable-displacement axial piston hydraulic pump 37, the pressure prevailing in said casing 49 being low compared to that reached inside the fluid chamber 5.

[71] Finally and as can be seen clearly in Figures 2 to 10, the hydraulic piston with depressurized groove 1 according to the invention comprises at least one radial decompression duct 12 which places the radial depressurized groove 9 in communication with the axial duct of decompression 11.

[72] In Figures 5 to 10, it has been shown that the hydraulic piston with depressurized groove 1 according to the invention can comprise at least one axial decompression groove 10 which opens onto the surface of the fixed skirt 3 and which places the means in communication. sealing 8 with the depressurized radial groove 9, said axial groove 10 possibly being continuous or non-continuous.

[73] It will also be noted that according to this variant of the hydraulic piston with depressurized groove 1 according to the invention, the axial decompression groove 10 can be helical to prevent the local lift defect that it produces does not remain oriented on a only angular position with respect to the hydraulic piston with depressurized groove 1 during the displacement stroke of the latter in the cylinder 2.

[74] Note that according to another embodiment of the hydraulic piston with depressurized groove 1 according to the invention shown in Figure 1, Figures 3 to 7 and Figures 9 and 10, the fixed skirt 3 can be hollow and can accommodate in a fixed and sealed manner a decompression sleeve 13, a radial space left between the inside of said skirt 3 and the outside of said sleeve 13 forming at least part of the axial decompression duct 11. [75] Note that the decompression sleeve 13 can be held in place inside the skirt 3 by means of at least one sleeve screw 51 as shown in Figure 4, by a clip or by a rivet, or more directly by screwing as shown in Figure 3, by welding, by crimping, or by any fixing means known to those skilled in the art.

[76] It is also noted that one or more elastomer seals, annealed copper or any material whatsoever can be inserted between the inside of the fixed skirt 3 and the decompression sleeve 13 to perfect the seal between these two organs 3, 13.

[77] Advantageously, the end of the decompression sleeve 13 which is closest to the axial working face 6 can be planar, conical, spherical, or of any geometry whatsoever, this to form a sealed contact with a additional span fitted inside the fixed skirt 3.

[78] Note in Figure 3 that advantageously, the decompression sleeve 13 can accommodate an internal sleeve lubrication duct 14 which cooperates with an internal lubrication duct of piston 15, the latter opening at the level of the axial working face 6 or in the vicinity of the latter.

[79] This particular configuration allows part of the working fluid 23 to be conveyed from the fluid chamber 5 to the transmission means 7 to lubricate the latter which may for example take the form of an articulated shoe 16 sliding on a tray 17 tiltable or not.

[80] In Figure 1 then in Figures 5 to 10, it has been shown that according to a particular embodiment of the hydraulic piston with depressurized groove 1 according to the invention, the sealing means 8 may consist of at least one sliding skirt. 18 of cylindrical shape, housed with small clearance in the cylinder 2 and placed in the extension and in the axis of the fixed skirt 3 on the side of the axial compression face 4.

[81] According to this particular configuration of the sealing means 8, the sliding skirt 18 is connected to the fixed skirt 3 by a mechanical inter-skirt connection 19 which allows displacement in longitudinal translation of said sliding skirt 18 relative to the skirt. fixed 3, the amplitude of said displacement being limited by a stop sliding skirt 29 which is directly or indirectly integral with the mechanical inter-skirt connection 19.

[82] It should also be noted that the sliding skirt stop 29 can be attached to the inter-skirt mechanical connection 19 by screwing with locking by a lock nut 40 or not, by welding, by crimping, or by any other means of fixing known to those skilled in the art.

[83] Still according to said particular configuration of the sealing means 8, it is noted, particularly in Figures 6 and 7, that at least one pressure transmission channel 20 is arranged inside the sliding skirt 18 and passes through this last through in the axial direction.

[84] Figure 1 and Figures 5 to 10 further show that according to said particular configuration of the sealing means 8 of the hydraulic piston with depressurized groove 1 according to the invention, at least one extendable continuous segment 21 of continuous annular shape is interposed between the fixed skirt 3 and the sliding skirt 18, and has an internal cylindrical face of segment 22 subjected to the pressure of the working fluid 23 via the pressure transmission channel 20, an external cylindrical face of segment 24 being able to come into contact with the cylinder 2, an axial face of a segment on the fixed skirt side 25 maintained directly or indirectly in sealed contact with the fixed skirt 3 and an axial face of a segment on the sliding skirt side 26 maintained directly or indirectly in sealed contact with the sliding skirt 18.

[85] As a variant of said particular configuration of the sealing means 8 of the hydraulic piston with depressurized groove 1 according to the invention, it has been clearly shown in FIGS. 5 to 7 and in FIGS. 9 and 10 that at least a sliding skirt spring 27 may be provided which tends to bring the sliding skirt 18 closer to the fixed skirt 3, and to axially compress the extendable continuous segment 21.

[86] It is noted that the sliding skirt spring 27 can be for example helical, or else consist of a multi-turn wave spring as shown in Figure 1, Figures 5 to 7 and Figures 9 and 10, the latter type of spring having the advantage of an angularly uniform support. These examples being given only by way of nonlimiting, the sliding skirt spring 27 can also be of any type known to those skilled in the art. [87] Insofar as the sealing means 8 consist in particular of an extendable continuous segment 21 interposed between a sliding skirt 18 and the fixed skirt 3 as has just been described, it is noted that the mechanical connection between skirts 19 may consist of a double-threaded screw 30 shown in figure 1, in figures 5 to 7 and in figures 9 and 10.

[88] In this case, the double-threaded screw 30 has a first thread which is screwed into an internal thread formed inside the fixed skirt 3 and which axially plates the decompression sleeve 13 in said skirt 3 via a screw shoulder 31, and a second thread onto which the sliding skirt stop 29 is screwed.

[89] It is noted that as a particular embodiment of the hydraulic piston with depressurized groove 1 according to the invention, the screw shoulder 31 can provide a shoulder key socket 41 allowing the tightening of the double screw. thread 30 in the fixed skirt 3. As an alternative and for the same purpose, a wrench or screwdriver socket can be fitted at the end of the second thread.

[90] It is also noted that the double-thread screw 30 may have a narrowing of diameter 42 over part of its length as shown in Figures 9 and 10, this to locally reduce the section and give it more elasticity, and in order to prevent any loosening of said screw 30.

[91] As shown in Figures 5 to 10, a stop key socket 43 can be provided on the sliding skirt stop 29 which makes it possible to immobilize the latter when it is locked in position by a lock nut 40.

[92] According to a variant of the hydraulic piston with depressurized groove 1 according to the invention shown in Figures 5 to 10, the sliding skirt spring 27 can be housed in a spring basket 32 which passes through all or part of the sliding skirt 18, the radial thickness of the latter being provided sufficiently small so that said skirt 18 can accommodate said basket 32 at its center.

[93] In this case, the spring basket 32 may have, on the one hand, an outer basket flap 33 which bears on the sliding skirt 18, and on the other hand, an inner basket flap 34 on which rests one of the ends of the sliding skirt spring 27, the other end of the latter resting on a spring bearing shoulder 44 fitted or attached to the inter-skirt mechanical connection 19. [94] We see in Figures 5 to 7 and Figures 9 and 10 that the spring bearing shoulder 44 can be arranged on the sliding skirt stop 29, the latter being screwed onto the second thread with a screw. double thread 30.

[95] As can be seen clearly in FIG. 10, the spring basket 32 can advantageously be perforated to allow the working fluid 23 to circulate.

[96] In Figures 6, 7 and 10, it is noted that the outer surface of the spring basket 32 may have centering means 39 which radially center said basket.

32 in the sliding skirt 18, while the axial orientation of said basket 32 with respect to said skirt 18 is ensured by the contact between the outer basket flap

33 and said skirt 18.

[97] As illustrated in a particularly visible manner in Figures 6, 7 and 10, the centering means 39 may for example consist of an elastic ring 28 which encloses a groove arranged on the periphery of the body of the spring basket 32, or else consist of a boss arranged on the periphery of said body.

[98] Note that the sliding skirt stop 29 can be supported either on the outer basket flap 33 or on the inner basket flap as illustrated in Figures 6 and 7.

[99] As shown in Figures 5 to 7 and Figures 9 and 10, the mechanical inter-skirt connection 19 can accommodate an internal lubrication duct 35 which cooperates with an internal lubrication duct of piston 15, the latter opening at the level of the axial working face 6 or in the vicinity of the latter, in order to convey a part of the working fluid 23 from the fluid chamber 5 to the transmission means 7 in order to lubricate the latter.

[100] Like what has been previously presented, it is noted that the transmission means 7 may for example consist of an articulated shoe 16 sliding on a tilting plate 17 or not.

[101] Note that, as clearly shown in Figures 5 to 7, the internal lubrication link 35 may be formed of an axial duct and one or more radial ducts.

[102] In Figures 5 to 10, there has been shown a particular embodiment of the hydraulic piston with depressurized groove 1 according to the invention according to which the length axial of the depressurized radial groove 9 may be greater than the diameter of the radial decompression duct 12.

[103] According to this advantageous variant, the depressurized radial groove 9 constitutes a working fluid reservoir 36 which never empties entirely via the radial decompression duct 12 during the movement of the depressurized groove hydraulic piston 1 according to the invention in the cylinder 2, and under the effect of the acceleration which results from said displacement.

[104] This particular configuration of the hydraulic piston with depressurized groove 1 according to the invention forces the working fluid 23 to interfere between the fixed skirt 3 and the cylinder 2, to ensure its lubrication during said movement.

[105] HOW THE INVENTION WORKS:

[106] The operation of the depressurized groove hydraulic piston 1 according to the invention is easily understood in view of Figures 1 to 10 which show non-limiting embodiments of said invention.

[107] Figure 1 shows the depressurized groove hydraulic piston 1 according to the invention applied to a variable displacement axial piston hydraulic pump 37 known per se, said pump 37 having a pump casing 49 in which its main components are housed .

[108] In Figure 1 and Figures 5 to 10, it has been shown that the sealing means 8 can advantageously consist of an extendable continuous segment 21 held clamped between a sliding skirt 18 and the fixed skirt 3 by a spring. sliding skirt 27. It can therefore be seen that said means 8 are here and by way of non-limiting example those provided by the sealing device for a piston described in patent No. FR 3009037 belonging to the applicant.

[109] When the transmission shaft 45 of the variable displacement axial piston hydraulic pump 37 is rotated by a power source (not shown), it in turn drives a barrel 46 to which it is integral.

[110] When the tilting plate 17 that comprises said pump 37 is tilted, the hydraulic pistons with depressurized throat 1 which hosts said pump 37 perform back and forth movements in the cylinder 2 with which they cooperate. [111] In doing so, initially and as illustrated in Figure 6, said pistons 1 suck working fluid 23 in an intake duct 47 that comprises the variable displacement axial piston hydraulic pump 37 shown in Figure 1.

[112] For example, the inlet duct 47 is supplied with working fluid 23 at a pressure of ten bars, while the interior of the pump housing 49 is subjected to atmospheric pressure. This pressure difference makes it possible in particular to always maintain the hydraulic pistons with depressurized groove 1 pressed against the tilting plate 17, by means of an articulated shoe 16

[113] Secondly and as shown in Figure 7, the depressurized groove hydraulic pistons 1 which equip the variable displacement axial piston hydraulic pump 37 shown in Figure 1 expel into a delivery duct 48 that comprises said pump 37 the working fluid 23 which they previously admitted, this under a pressure of for example four hundred bars.

[114] The usual operation of the variable displacement axial piston hydraulic pump 37 having been recalled, we will here focus our attention on the operation of the depressurized groove hydraulic piston 1 when the sealing means 8 that it comprises are formed from the sealing device for piston subject of patent FR 3009037.

[115] We recalled in the preamble of the present patent application that to function effectively, the device of patent FR 3 009 037 must cooperate with a fixed skirt 3 sufficiently elusive to allow the continuous extensible segment 21 that comprises said device to inflate under the effect of the pressure in the fluid chamber 5.

[116] In addition to this first condition necessary for the correct functioning of the device of patent FR 3 009 037, we have also recalled that if the latter equips a variable displacement axial piston hydraulic pump 37 like that shown in FIG. 1, the fixed skirt 3 must remain properly carried by the lubricating film of the working fluid 23 thanks to which it slides with low friction on the cylinder 2. This is particularly true at the level of the outlet of the cylinder 2 which opens onto the inside of the pump housing 49 and on which the fixed skirt 3 exerts significant radial forces. [117] As such, any groove made on the surface of the fixed skirt 3 and passing at the level of the said outlet of the cylinder 2 significantly increases the energy loss by friction generated at the interface of the said skirt 3 and of the said cylinder 2, at the level of the said cylinder. outlet.

[118] This loss is particularly high when the displacement of the variable displacement axial piston hydraulic pump 37 is close to its maximum, that is to say when the inclination of the tilting plate 17 of said pump 37 is also close to its maximum. maximum.

[119] Because indeed, at full displacement of said pump 37, the pistons of the latter butt in the cylinders 2 with which they cooperate. This generates a large radial load between said pistons and said cylinders 2, particularly at the outlet of said cylinders 2 into the pump casing 49.

[120] This is the reason why the hydraulic piston with depressurized groove 1 according to the invention allows the axial portion of the fixed skirt 3 which slides in contact with the outlet of the cylinder 2 to expose a smooth surface free from any decompression groove, this while allowing the continuous extensible segment 21 to function correctly thanks to a sufficiently elusive fixed skirt 3.

[121] In addition to avoiding the use of any decompression groove whatsoever to make the fixed skirt 3 sufficiently leaky, the hydraulic piston with depressurized groove 1 also avoids having to resort to an increased clearance between the fixed skirt 3 and the cylinder 2 to depressurize said skirt 3. A normal clearance between the fixed skirt 3 and the cylinder 2 can thus be preserved, so that the bearing surface of said skirt 3 on said cylinder 2 remains normally extended and that the pressure exerted on the film of working fluid 23 interposed between said skirt 3 and said cylinder 2 remains sufficiently low.

[122] In fact, the higher the said pressure, the lower the thickness of the working fluid film 23, the higher the viscosity of said film, and the greater the energy losses by friction generated at the bearing surface of the fixed skirt 3 on cylinder 2 are elevated.

[123] To avoid any decompression groove and any increase in clearance as has just been described, the depressurized groove hydraulic piston 1 according to the invention comprises a depressurized radial groove 9 which opens onto the surface of the fixed skirt 3. This is clearly visible in Figures 1 to 10,

[124] The depressurized radial groove 9 is axially positioned on the fixed skirt 3 so as to never be able to exit from the cylinder 2 whatever the axial position of said skirt 3 with respect to said cylinder 2. As positioned, the depressurized radial groove 9 does not occupy the place of any bearing surface whatsoever.

[125] As can be seen in Figures 1 to 10, the depressurized radial groove 9 considerably reduces the leakage length between the sealing means 8 and the outlet of the cylinder 2 in the pump casing 49.

[126] Indeed, the depressurization which according to the state of the art had to be carried out from the sealing means 8 to the outlet of the cylinder 2 in the pump casing 49, that is to say over the entire length. of the fixed skirt, should only be provided between said means 8 and the depressurized radial groove 9.

[127] This particular configuration, specific to the hydraulic piston with depressurized groove 1 according to the invention, makes it possible to leave free of any decompression groove and any abnormal increase in play the axial portion of the fixed skirt 3 which slides in contact with the cylinder outlet 2.

[128] The fact remains that the remaining portion of the fixed skirt 3 which is between the sealing means 8 and the depressurized radial groove 9 must be depressurized, or by a sufficient clearance left between said skirt 3 and cylinder 2, or, as shown in FIGS. 5 to 10, by providing axial decompression grooves 10 which can advantageously be helical and which open out on the surface of the fixed skirt 3 to put the sealing means 8 in communication with the depressurized radial groove 9.

[129] The portion of the fixed skirt 3 provided with axial decompression grooves 10 being slightly radially loaded, the reduction in the total efficiency of the variable-displacement axial piston hydraulic pump 37 which results from a lower lift of the fluid film of work 23 at said grooves 10 is low, or even zero. [130] It will be noted in Figures 6 to 10 that advantageously, the junction between the fixed skirt 3 and the axial compression face 4 of the hydraulic piston with depressurized groove 1 according to the invention forms a pressure distribution chamfer 50 which allows the continuous stretch segment 21 to operate optimally over its entire circumference.

[131] Incidentally, the pressure distribution chamfer 50 allows the working fluid 23 coming from the fluid chamber 5 and passing between the extendable continuous segment 21 and the cylinder 2 to lubricate the outer surface of the fixed skirt 3 lying between said chamfer 50 and the depressurized radial groove 9. This occurs in particular during the phase of suction of the working fluid 23 in the fluid chamber 5 by the hydraulic piston with depressurized groove 1.

[132] Figure 6 shows said suction phase. Note in said Figure 6 that the continuous extendable segment 21 is parked during said phase, as illustrated by the dotted arrows. Indeed, the pressure prevailing in the fluid chamber 5 is insufficient for the pressure difference between the internal cylindrical face of segment 22 and the external cylindrical face of segment 24 to significantly inflate said continuous segment 21.

[133] During said suction phase, the working fluid 23 coming from the fluid chamber 5 can therefore pass between the expandable continuous segment 21 and the cylinder 2. This done, said working fluid 23 continues its path from the chamfer. pressure distribution 50 up to the depressurized radial groove 9, passing partly via the clearance left between the external surface of the fixed skirt 3 and the cylinder 2, and for the other part via the axial decompression grooves 10 which open on the surface of the fixed skirt 3. The path of the working fluid 23 which has just been described is symbolized in FIG. 6 by wavy arrows.

[134] On its path, the working fluid 23 lubricates the outer surface of the fixed skirt 3 between the pressure distribution chamfer 50 and the depressurized radial groove 9. Then, said fluid 23 fills the depressurized radial groove 9 for example halfway, and possibly up to overflowing through the radial decompression duct 12 to escape successively via said radial duct 12 then via the axial decompression duct 11, and to finally emerge into the pump casing 39 at the level of the face working axial 6. [135] Figure 7 shows the discharge phase during which a pressure of four hundred bars prevails in the fluid chamber 5.

[136] During said phase, the pressure difference between the internal cylindrical face of segment 22 and the external cylindrical face of segment 24 is sufficient to inflate the expandable continuous segment 21 to the point that the latter comes into contact with cylinder 2 and forms with the latter a seal. The swelling of said segment 21 is symbolized by dotted arrows.

[137] The arrows in solid lines in FIG. 7 symbolize the communication of the pressure of the working fluid 23 contained in the fluid chamber 5 to the internal cylindrical face of segment 22 of the expandable continuous segment 21 via the flow channel. pressure transmission 20.

[138] We also note in Figure 7 that advantageously, the spring basket 32 is perforated to better allow the working fluid 23 to circulate not only to communicate the pressure of the fluid chamber 5 to the internal cylindrical face of the segment. 22, but also to ensure the lubrication of the transmission means 7 which we have seen in Figure 1 that they are constituted, according to the non-limiting example of implementation of the hydraulic piston with depressurized groove 1 according to the invention taken here to illustrate its operation, articulated pads 16 cooperating with a tilting plate 17.

[139] Indeed, after having passed through the pressure transmission channel 20 and then through the spring basket 32, a majority of the working fluid 23 enters the internal lubrication duct 35 formed by an axial duct. and three radial ducts housed by the inter-skirt mechanical connection 19 here consisting of a double-thread screw 30.

[140] Then and as can easily be understood from the view of FIG. 5 which gives an overview of the hydraulic piston with depressurized groove 1 according to the invention, the working fluid 23 passes through the internal piston lubrication duct 15 to reach the articulated shoe 16 and lubricate the contact interface formed by the latter with the tilting plate 17.

[141] As has just been demonstrated, the hydraulic piston with depressurized groove 1 according to the invention makes it possible, on the one hand, to ensure the correct operation of the sealing device for a piston which is the subject of patent FR 3 009 037 and on the other hand, to avoid any arrangement or arrangement of the fixed skirt 3 which is likely to increase the friction losses generated by said skirt 3 at the level of its contact with the outlet of the cylinder 2.

[142] However, the sealing means 8 from patent FR 3 009 037 have been given here only by way of example. The hydraulic piston with depressurized groove 1 according to the invention can produce its advantages for the benefit of other said means 8, the operation of which requires that the fixed skirt 3 is preferably leaky and non-sealed, while said skirt 3 remains subjected to forces. important radials. For example, the depressurized groove hydraulic piston 1 can deliver all of its advantages if the sealing means 8 are cut segments 38 such as those shown in Figures 2 to 4.

[143] It is also understood in view of Figures 1 to 10 that the depressurized groove hydraulic piston 1 according to the invention is simple to produce and to assemble, and does not require any expensive or complex manufacturing process to implement.

[144] It will be noted that the exemplary embodiment of the hydraulic piston with depressurized groove 1 according to the invention which has just been described is nonlimiting. As such, said piston 1 can advantageously be applied to any hydraulic or pneumatic machine provided with pistons, regardless of the field of application of said machine.

[145] The possibilities of the depressurized groove hydraulic piston 1 according to the invention are not limited to the applications which have just been described and it should also be understood that the above description has only been given. by way of example and that it in no way limits the field of said invention, which would not be departed from by replacing the details of execution described by any other equivalent.!

Claims

[Claim 1] jHydraulic piston with depressurized groove (1) translatable in a cylinder (2), the outer cylindrical surface of said piston (1) constituting a fixed skirt (3) while one end of said piston (1) has an axial compression face (4) which forms with the cylinder (2) a fluid chamber (5) of variable volume filled with a working fluid (23), while the other end of said piston (1) has a axial working face (6) which cooperates with transmission means (7) characterized in that it comprises:

Sealing means (8) positioned in the vicinity of the axial compression face (4), on the fixed skirt (3) or at the end of the latter, said means (8) being able to come into contact with the cylinder ( 2);

At least one depressurized radial groove (9) opening out at the surface of the fixed skirt (3), said groove (9) possibly being continuous or non-continuous;

At least one axial decompression duct (11) arranged inside the fixed skirt (3) and opening out in the vicinity of the axial working face (6); At least one radial decompression duct (12) which places the radial depressurized groove (9) in communication with the axial decompression duct (11).

[Claim 2] A hydraulic piston with a depressurized groove according to claim 1, characterized in that it comprises at least one axial decompression groove (10) which opens onto the surface of the fixed skirt (3) and which places the means of communication in communication. 'sealing (8) with the depressurized radial groove (9), said axial groove (10) being able to be continuous or non-continuous.

[Claim 3] Hydraulic piston with a depressurized groove according to Claim 2, characterized in that the axial decompression groove (10) is helical.

[Claim 4] Hydraulic piston with depressurized groove according to claim 1, characterized in that the fixed skirt (3) is hollow and fixedly and tightly accommodates a decompression sleeve (13), a radial space left between the interior of said skirt (3) and the outside of said sleeve (13) forming at least part of the axial decompression duct (11). [Claim 5] A depressurized groove hydraulic piston according to Claim 4, characterized in that the decompression sleeve (13) accommodates a sleeve internal lubrication duct (14) which cooperates with an internal piston lubrication duct (15), the latter opening at the level of the axial working face (6) or in the vicinity of the latter, in order to convey part of the working fluid (23) from the fluid chamber

(5) to the means of transmission (7).

[Claim 6] Hydraulic piston with depressurized groove according to Claim 1, characterized in that the sealing means (8) consist of:

• At least one sliding skirt (18) of cylindrical shape, housed with low clearance in the cylinder (2) and placed in the extension and in the axis of the fixed skirt (3) on the side of the axial compression face (4) ), said sliding skirt (18) being connected to the fixed skirt (3) by a mechanical inter-skirt connection (19) which allows a displacement in longitudinal translation of said sliding skirt (18) relative to the fixed skirt (3) , the amplitude of said displacement being limited by a sliding skirt stop (29) which is directly or indirectly integral with the inter-skirt mechanical connection (19);

• At least one pressure transmission channel (20) arranged inside the sliding skirt (18) and passing right through the latter in the axial direction;

• At least one extendable continuous segment (21) of continuous annular shape, interposed between the fixed skirt (3) and the sliding skirt (18), and having an internal cylindrical face of the segment (22) subjected to the pressure of the working fluid (23) via the pressure transmission channel (20), an outer cylindrical face of the segment (24) able to come into contact with the cylinder (2), an axial face of the segment on the fixed skirt side (25) held directly or indirectly in sealed contact with the fixed skirt (3) and an axial face of a segment on the sliding skirt side (26) maintained directly or indirectly in sealed contact with the sliding skirt (18).

[Claim 7] Hydraulic piston with depressurized groove according to Claim 6, characterized in that at least one sliding skirt spring (27) tends to bring the sliding skirt (18) closer to the fixed skirt (3), and to axially compress the continuous extensible segment (21).

[Claim 8] Hydraulic piston with depressurized groove according to claims 4 and 6, characterized in that the mechanical inter-skirt connection (19) consists of a double-thread screw (30) which has a first thread which is screwed into an internal thread formed inside the fixed skirt (3) and which axially plates the decompression sleeve (13) in said skirt (3) by means of a screw shoulder (31), and a second thread on which is screwed the sliding skirt stop (29).

[Claim 9] Hydraulic piston with depressurized groove according to Claim 7, characterized in that the sliding skirt spring (27) is housed in a spring basket (32) which passes wholly or partly through the sliding skirt (18), l 'radial thickness of the latter being provided sufficiently small so that said skirt (18) can accommodate said basket (32) at its center, said basket (32) having, on the one hand, an outer basket flap (33) which rests on the sliding skirt (18), and on the other hand, an inner basket flap (34) on which rests one end of the sliding skirt spring (27), the other end of the latter resting on a spring bearing shoulder (44) fitted or attached to the mechanical inter-skirt connection (19).

[Claim 10] A depressurized groove hydraulic piston according to claim 9, characterized in that the outer surface of the spring basket (32) has centering means (39) which radially center said basket (32) in the sliding skirt (18). ), while the axial orientation of said basket (32) relative to said skirt (18) is ensured by the contact between the outer basket flap (33) and said skirt (18).

[Claim 11] Hydraulic piston with depressurized groove according to Claim 9, characterized in that the sliding skirt stop (29) can bear either on the outer basket flap (33) or on the inner basket flap.

[Claim 12] A hydraulic piston with a depressurized groove according to claim 6, characterized in that the inter-skirts mechanical connection (19) accommodates an internal lubricating connection duct (35) which cooperates with a internal piston lubrication duct (15), the latter opening at the level of the axial working face (6) or in the vicinity of the latter, in order to convey part of the working fluid (23) from the fluid chamber (5) ) to the transmission means (7).

[Claim 13] A depressurized groove hydraulic piston according to claim 1, characterized in that the axial length of the depressurized radial groove (9) is greater than the diameter of the radial decompression duct (12), so that said groove ( 9) constitutes a working fluid reservoir (36). |