FR3032241A1 - HYDRAULIC MECHANISM WITH MEANS FOR GUIDING PISTON TRANSLATION - Google Patents

Abstract

Hydraulic mechanism, motor or pump, comprising a cam; a cylinder block rotatably mounted relative to the cam; at least one cylinder (110i, 110e) formed in this cylinder block; at least one piston assembly adapted to cooperate with a cylinder (110i, 110e), said piston assembly comprising a piston (111i, 111e) slidably mounted inside said cylinder (110i, 110e); a roller (123) rotatably mounted on the piston (111i, 111e) and configured to cooperate with the cam, the roller (123) being delimited by two transverse end faces; first and second wedging pieces (129) each disposed between an end face of the roll (123) and the inner face of the roll (110i, 110e) on which said wedge piece (129) bears so as to maintain the axial position of the roll (123); the cylinder (110i, 110e) has a groove (131) formed in its inner face, and the piston assembly has a projection (136) configured to cooperate with the groove (131) of the cylinder (110i, 110e) so as to maintain the orientation of the roller (123).

Description

FIELD OF THE INVENTION This presentation concerns the field of hydraulic machines with radial pistons, and more specifically the means for guiding in translation the pistons of such hydraulic machines.

STATE OF THE PRIOR ART Hydraulic machines are known comprising a cylinder block having a plurality of housings in which pistons slide, comprising means for guiding the pistons in their housings. The document FR 2 727 471 in the name of the applicant presents for example a hydraulic machine structure in which the pistons are guided in translation by a U-shaped clip, inserted firstly in a recess of the cylinder block, and on the other hand part in a radial groove arranged on a wedge piece ensuring the maintenance of the piston roller. However, such a U-shaped staple that spans a portion of the cylinder block is fragile and poorly withstands significant mechanical forces, including shearing, which can occur under certain circumstances, for example in case of cavitation or hydraulic shock.

In particular, some hydraulic machines, such as tree cutting machines, experience violent power surges during which the machine brakes and reboots suddenly and frequently: such jolts cause pressure inversions in the block. cylinders, so that the pistons can suddenly take off from the cam against which they are normally in contact. On such occasions, the piston may have a tendency to pivot in its housing, thus generating high bending / shearing forces in the staple, resulting in fatigue and subsequent breakage of the staple. In addition, such sudden and repeated forces can wear the groove of the wedge, thereby reducing the effectiveness of the rotational locking of the piston even if the staple is not damaged. There is therefore a need for a hydraulic mechanism provided with translation guiding means which are devoid, at least in part, of the drawbacks inherent in the aforementioned known systems. PRESENTATION OF THE INVENTION The present disclosure relates to a hydraulic mechanism, motor or pump comprising a cam; a cylinder block rotatably mounted relative to the cam; at least one cylinder formed in this cylinder block; at least one piston assembly adapted to cooperate with a cylinder, this piston assembly comprising a piston slidably mounted inside said cylinder; a roller rotatably mounted on the piston and configured to cooperate with the cam, the roller being delimited by two transverse end faces; first and second wedging members each disposed between an end face of the roll and the inner face of the cylinder on which said chock member bears so as to maintain the axial position of the roll. The cylinder has a groove in its inner face, and the piston assembly has a projection configured to cooperate with the groove of the cylinder to maintain the orientation of the roll, the projection having a tapered inner end. In the present description, the terms "axial", "radial", "tangential", "interior", "exterior" and their derivatives are defined with respect to the main axis of the hydraulic mechanism.

With such a configuration, the translational guidance is more robust: it is able in particular to withstand power surges of the hydraulic mechanism and abrupt movements of the piston that they can generate. Indeed, the guide is here in the cylinder itself through the cooperation of the projection of the piston assembly with the groove of the cylinder. Thus, this projection can be shorter and this cooperation can be done more closely to the axis of the piston, which reduces the lever arm and therefore the importance of shear forces when the piston seeks to rotate in the cylinder . In addition, thanks to this configuration, there is greater freedom of design to provide the projection of sufficient size to ensure its strength and a significant interface of cooperation with the groove, which allows to better distribute the mechanical forces undergone by the projection. Similarly, in this configuration, the wedging pieces can be devoid of groove, which makes them more massive and therefore stronger.

These locking means are also easier to manufacture and assemble: in particular, the projection can be an integral part of an existing part of the piston assembly, which reduces the number of parts used.

In this presentation, the term "tapered", a shape that tapers towards its end; this end being for example frustoconical with possibly a rounded tip. This shape can be assessed in a radial plane (orthogonal to the main axis of the mechanism) and / or in the axial plane (containing the main axis of the mechanism and the axis of the piston). This allows, in cases where the projection can exit the groove, facilitate its reinsertion into the groove and automatically refocus the piston. The assembly of the mechanism is also facilitated. In some embodiments, the projection is integral with the piston. The guide of the piston in translation and its locking in rotation is therefore provided directly. In some embodiments, the projection is an end portion of a pin inserted into a bore of the piston. Such a configuration is very easy to achieve since it suffices to provide the piston with such a bore and then to engage the pin. This pin can be fixed in the bore, for example by tight fitting, or slide freely in the bore. In some embodiments, the pin is metallic. In other embodiments, the projection is a protrusion forming an integral part of the piston. Such a one-piece piece can be obtained by removing material from a precursor piece to form this protrusion; it can also be obtained by molding or other techniques. In certain embodiments, the lateral surface of the piston has a flat surface, the projection projecting from this flat surface. Such a flat facilitates the introduction of the projection: when the projection is a pin inserted into a bore of the piston, the bore is easier to drill on the flat surface of the flat; when the projection is an outgrowth of the piston made by removal of material, this flat may be the surface remaining after removal of material. In addition, such a flat allows the passage of hydraulic fluid along this portion of the piston, which is particularly useful in the case of a stepped piston. In some embodiments, the projection is integral with the first wedging piece. In such a case, the piston can be left intact, the function of translational guiding and rotational locking being integrated with the wedging function in the wedging piece. It is thus possible to use existing pistons in new cylinder blocks according to the invention by equipping them with this type of wedging piece. In some embodiments, the projection is a boss integral with the first wedging member. The wedging piece can thus be obtained integrally, for example by molding. We thus obtain a more massive piece and therefore more solid. In some embodiments, the first wedging piece is plastic.

In some embodiments, the groove extends to the outer end of said cylinder and opens into the outer face of the cylinder block. In certain configurations, the projection can therefore possibly leave the groove for a short time when the piston follows the cam: in this way, the piston is not blocked in translation, which offers a large amplitude to the piston and thus improves performance hydraulic mechanism. In some embodiments, said cylinder has an outer portion, having a first diameter, defining an outer chamber, and an inner portion, having a second diameter smaller than the first diameter, defining an inner chamber; the piston has an outer portion, having a first diameter, and an inner portion, having a second diameter smaller than the first diameter; the groove is formed in the inner portion of the cylinder and the projection projects on the inner portion of the piston. This configuration is adapted to stepped pistons which have a narrower inner section, thus allowing to have a greater number of pistons around the axis of the cylinder block. In some embodiments, the groove extends to the outer end of the inner portion of the barrel and opens into the outer barrel chamber. This facilitates the mounting of the stepped piston and increases the section of passage of the hydraulic fluid.

In some embodiments, the projection extends perpendicularly to the axis of the piston. In some embodiments, the projection height of the projection decreases toward its inner end. In the present description, the term "height of projection" the height of an element, at a given point, measured from the surface on which this element protrudes and perpendicular to this surface. This also makes it easier to insert the projection into the groove and to prevent it from catching on the edge of the cylinder.

In some embodiments, the hydraulic mechanism is devoid of any fastener mounted in an outer or lateral face of the cylinder block and overlapping the periphery of a cylinder. The manufacture of the cylinder block is thus facilitated and the risk of stall and loss of an element in the housing of the mechanism is reduced.

In some embodiments, the groove of the cylinder is formed in the thickness of the cylinder block. In some embodiments, the groove extends in a direction parallel to the cylinder axis. In some embodiments, the piston is provided with a seal ensuring the seal between the piston and the inner face of the cylinder. In some embodiments, the groove of the cylinder is provided to never be overlapped by the piston seal when the piston is guided by the cam. This prevents hydraulic fluid can escape from the piston chamber bypassing the seal by the groove. The above-mentioned characteristics and advantages, as well as others, will appear on reading the following detailed description of embodiments of the proposed hydraulic mechanism. This detailed description refers to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings are schematic and are intended primarily to illustrate the principles of the invention. In these drawings, from one figure (FIG) to the other, identical elements (or element parts) are identified by the same reference signs. In addition, elements (or parts of elements) belonging to different exemplary embodiments but having an analogous function are indicated in the figures by incremented numerical references of 100, 200, etc. FIG 1 is a general view in axial section of a hydraulic mechanism. FIG 2A is a cross-sectional view of a cylinder block according to a first embodiment. FIG 2B is a sectional view along the IIB-IIB plane of FIG 2A. FIG 3A is a front view of a wedging piece according to the first embodiment. FIG 3B is a sectional view along the plane IIIB-IIIB of FIG 3A. FIG 4 is a partial cross-sectional view of the piston assembly engaged in the cylinder block of FIG2A.

FIG 5A is a cross-sectional view of a cylinder block according to a second embodiment. FIG 5B is a view along the arrow VB of FIG. 5A. FIG 6 is a perspective view of a piston according to the second embodiment.

FIG 7 is a perspective view in section of the piston assembly engaged in the cylinder block of FIG 5A. DETAILED DESCRIPTION OF THE EMBODIMENT (S) In order to make the invention more concrete, examples of hydraulic mechanisms are described in detail below, with reference to the appended drawings. It is recalled that the invention is not limited to these examples. The engine 1 of FIG 1 comprises: - a housing in two parts la, lb, assembled by screws 2; a corrugated cam 3, integral with the casing 1a, 1b; - An output shaft 4, rotatably mounted in the housing, about an axis 5, by means of two roller bearings 6, and whose inner end is provided with grooves 7; a cylinder block 8, which comprises a central recess provided with splines 9, associated with the splines 7 of the shaft for securing the shaft 4 in rotation with the cylinder block 8 and for centering the cylinder block with respect to this tree; - A plurality of cylinders 10 arranged radially in a star with respect to the axis 5, each containing a piston 11, which is slidably mounted therein; - A flat face 12, which is provided with the cylinder block 8, which is perpendicular to the axis of rotation 5, and in which open conduits 13 connected to the different cylinders 10; a fluid distributor 14 to the various cylinders 10, which is provided with a planar distribution face 15, perpendicular to the axis of rotation 5 and disposed facing and in abutment with the communication face 12 of the cylinder block, and an axial face which comprises two circular grooves 16, 17 communicating, respectively, selectively with a supply of pressurized fluid 18 and with a fluid outlet 19, while a driving device 20 makes this distributor integral in rotation. fluid 14 with the portion of the casing, and that ducts 21, 22, connect the grooves 16, 17 respectively, to the flat face 15 and are capable of being placed in communication, successively, during the relative rotation of the block cylinders 8 relative to the distributor 14, with the ducts 13 of the cylinder block 8. In this case, the axial face of the distributor has a third circular groove 16 '. This is indeed a two-cylinder engine operation, the groove 16 'can be connected to the groove 16 or the groove 17 by a displacement selector (not shown) to operate the engine in large or in small displacement. It goes without saying that the invention applies equally to engines with one or more displacements. A cylindrical roller 23 is housed in a bearing 24 formed at the end of each piston 11, is rotatably mounted about a roller axis 25 orthogonal to the piston pin 26, coinciding with the axis of the cylinder 10, and is pressed against the cam 3. This roller 23 is capable of penetrating at least partially inside the cylinder, so that, on the side of each transverse face 27 delimiting the roller, a recess 28 is formed in the part of the piston 11 which supports this roll, which allows to form, on either side of said roll, spaces. Each recess corresponds at least to the space between at least the surface of the cylinder 10, the cylindrical surface of the roller 23 and the corresponding transverse face 27 of the roller, said space being moreover open to the outside of the piston, at least in the area where the roller is protruding out of the piston. In this example, the plane perpendicular to the axis 25 of the roller 23 and containing the axis 26 of the piston, is a plane of symmetry for the piston 11, the bearing 24, the roller 23, and the two spaces. It would also be possible, and in accordance with the invention, to have an asymmetric arrangement in which the spaces would not be symmetrical to each other with respect to a plane perpendicular to the axis 25 of the roll.

It is furthermore necessary to provide a means of maintaining in axial position in its bearing 24 the roller 23 mounted on a piston 11 and of keeping its angular orientation constant with respect to the axis 26 of the piston, in order to make this roller 23 is disposed opposite the cam 3 and correctly oriented relative to this cam to roll on the cam. To this end, each space defined between a recess 28 of the piston 11 and the inner wall of the cylinder 10 contains a wedging piece 29a, 29b, of a shape corresponding to that of the recess and of cross section shaped substantially in a lunula. These wedging pieces 29a, 29b each have a flat face disposed facing one of the end faces 27 of the roll 23 and a cylindrical face bearing on the inner face of the cylinder 10. These parts thus perform the axial wedging of the roll. each transverse face 27 is in contact with the opposite face of the piece 29a, 29b.

In this first exemplary embodiment, as shown in FIGS. 2A and 2B, the inner wall of the cylinder 10 has a groove 31 extending radially inwards from the outer edge of the cylinder 10 in the axial plane containing the cylinder. axis 26 of the piston 11 and the axis 25 of the roller 23: this groove 31 thus opens within one of the recesses 28. The groove 31 extends over a length such that the seal 11 'of the piston It never reaches it when the piston moves back and forth in the cylinder 10, guided by the cam 3; in other words, the position of the seal at the upper dead point of the piston is more internal than the inner end 32 of the groove 31. Thus, the length of the groove 31 may be less than half, or third, of the length of the cylinder 10, depending on the magnitude of the piston stroke 11.

The groove 31 has a tapered shape. More specifically, it has the shape of a truncated cone cut in a longitudinal plane with an inner end 32 rounded: thus, both its tangential dimension and its axial dimension decrease when one approaches its inner end 32. As this 3a and 3b, the wedging piece 29a intended to fill the recess 28 in which the groove 31 is provided comprises in turn a boss 35 of shape substantially complementary to the groove 31. This boss 35 extends radially inwardly from the outer edge of the wedging piece 29a over a substantially identical length, or shorter, than that of the groove 31. It also has a tapered shape, more precisely the shape of a truncated cone cut in a longitudinal plane with a rounded inner end 36; the angle of the cone may be for example about 50. As shown in FIG 4, such a boss 35 is configured to engage in the groove 31 of the cylinder 10 to block the roller 25 and therefore the piston 11 in its entirety in rotation about its axis 26. In this example, the bottom dead center of the piston, the inner end 36 of the boss 35 rests at the inner end 32 of the groove 31; on the other hand, at the top dead center, the inner end 36 of the boss 35 protrudes beyond the outer edge of the cylinder 10 and thus leaves the groove 31. Therefore, when the cam 3 again guides the piston 11 inwards, the Tapered shapes of the boss 35 and the groove 31 allow the reengagement and the automatic refocusing of the boss 35 in the groove 31, so the realignment of the roll 25 on its nominal axial direction. Such guidance and refocusing is ensured even in case of jerk of the hydraulic machine and detachment of the roller 25 of the cam 3. In this example, the cylinder 10 has a single groove 31 and only the first wedging piece 29a is provided with such a boss 35. However, it goes without saying that two diametrically opposed grooves 31 may be provided in the cylinder 10; in this case, the second wedging piece 29b may also be provided with a boss 35. FIGS. 5 to 7 illustrate a second example of a hydraulic mechanism generally similar to the first example, except that the block cylinders 108 here comprise stepped cylinders 110 configured to receive stepped pistons 111. These stepped cylinders 110 comprise an outer section 110e, of a certain diameter, defining an outer chamber, and an inner section 110i, having a smaller diameter, defining an interior chamber. The stepped pistons 111 have in turn an outer portion 111e, having a diameter substantially equal, within one set, to the diameter of the outer portion 100e of the cylinder 110, and an inner portion 111i, also known as a piston foot, having a diameter at least less than the diameter of the inner section 110i of the cylinder 110. In such a stepped configuration, the sealing of the cylinder is effected by a seal provided at the outer portion 111e of the piston which bears against the surface of the outer section. 110e of the cylinder 110. The hydraulic fluid can thus be distributed in the inner chamber bypassing the inner portion 111i of the piston to apply its hydraulic pressure both against the inner surface of the outer portion 111e of the piston 111 and against the inner surface of its inner portion 111i. The outer portion 111e of the piston also supports, in a similar manner to the preceding example, a roll 123 and wedging pieces 129. The inner portion 111i has two diametrically opposite flats 137, preferably arranged orthogonal to the axis. 5 of the engine. A bore 138 is further pierced in the flat 137 opposite the fluid supply conduit 113. A metal pin 135 is inserted and retained in this bore 138 so that its distal end 136 protrudes orthogonally on the flat portion 117. This distal end 136 of the pin 135 is thus configured to engage in a groove 131 formed in the surface of the inner section 110i of the cylinder 110. This groove 131 thus extends radially inwardly from the outer edge of the inner section. 110i of the cylinder 110 over substantially the entire length of this inner portion 1101. It thus opens all along the inner chamber and opens at its outer end into the outer chamber of the cylinder 110. This groove preferably extends in the axial plane containing the axis 26 of the piston 11 and the axis 25 of the roller 23, opposite the conduit 113 for supplying fluid.

Thus, when the piston 111 goes back and forth in the cylinder 110, the pin 135 slides in the groove 131 and thus blocks the piston 111 in rotation about its axis 26. The embodiments or examples of embodiment described in this presentation are given in FIG. illustrative and non-limiting, a person skilled in the art can easily, in view of this presentation, modify these modes or embodiments, or consider others, while remaining within the scope of the invention. In addition, the various features of these modes or embodiments can be used alone or be combined with each other.

When combined, these features may be as described above or differently, the invention not being limited to the specific combinations described herein. In particular, unless otherwise specified, a characteristic described in connection with a mode or example of embodiment may be applied in a similar manner to another embodiment or embodiment. In particular, in the context of the second example described, the length of the groove 131 is such that the pin can never leave the groove during operation of the engine 1. However, in the opposite case, or in any case it would be possible to provide the pin 135 and / or the groove 131 of a tapered shape similar to that described with reference to the first embodiment. In addition, in addition to these guide means using a pin 135 and a groove 131, or as a replacement, it would be possible to provide a wedging piece 129 of this stepped piston 111 of a boss similar to that of the first example configured to engage a groove in the outer portion 110e of the barrel 110.

Claims (11)

REVENDICATIONS1. Hydraulic mechanism, motor or pump, comprising a cam (3); a cylinder block (8) rotatably mounted relative to the cam (3); at least one cylinder (10) in said cylinder block (8); at least one piston assembly adapted to cooperate with a cylinder (10), said piston assembly comprising - a piston (11) slidably mounted inside said cylinder (10); - a roller (23) rotatably mounted on the piston (11) and configured to cooperate with the cam (3), the roller (23) being delimited by two transverse end faces (27); first and second wedging pieces (29a, 29b) each disposed between an end face (27) of the roll (23) and the inner face of the roll (10) on which said wedging piece (29a, 29b) takes support in order to maintain the axial position of the roller (23), characterized in that the cylinder (10) has a groove (31) formed in its inner face, and in that the piston assembly comprises a projection (35) configured for cooperating with the groove (31) of the cylinder (10) so as to maintain the orientation of the roller (23), this projection (35) having a tapered inner end (36). 2. Mechanism according to claim 1, wherein the projection (135) is integral with the piston (111). 3. Mechanism according to claim 2, wherein the projection is an end portion (136) of a pin (135) inserted into a bore (138) of the piston (111). 4. Mechanism according to claim 2, wherein the projection is a protrusion forming an integral part of the piston. 30322 4 1 13 5. Mechanism according to any one of claims 2 to 4, wherein the side surface of the piston (111) has a flat (137), the projection (136) projecting on the flat (137). 5 6. Mechanism according to claim 1, wherein the projection (35) is integral with the first wedging piece (29a). 7. Mechanism according to claim 6, wherein the projection is a boss (35) forming an integral part of the first wedging piece (29a). 8. Mechanism according to any one of claims 1 to 7, wherein the groove (31) extends to the outer end of said cylinder (10) and opens into the outer face of the cylinder block (8). ). 15 9. Mechanism according to any one of claims 2 to 5, wherein said cylinder (110) comprises an outer section (110e), having a first diameter, defining an outer chamber, and an inner section (110i), having a second diameter smaller than the first diameter, defining an inner chamber, wherein the piston (111) has an outer portion (111e) having a first diameter, and an inner portion (111i) having a second diameter smaller than the first diameter, and wherein the groove (131) is formed in the inner section (110i) of the cylinder (110) and the projection (135) projects on the inner portion (111i) of the piston (111). The mechanism of claim 9, wherein the groove (131) extends to the outer end of the inner section (110i) of the cylinder (110) and opens into the outer chamber of the cylinder (110). 11. Mechanism according to any one of claims 1 to 10, wherein the projection height of the projection (35) decreases towards its inner end (36).